Bosch VE Pumps - manual, Manuais, Projetos, Pesquisas de Engenharia de Manutenção

Baixe Bosch VE Pumps - manual e outras Manuais, Projetos, Pesquisas em PDF para Engenharia de Manutenção, somente na Docsity! Diesel distributor fuel-injection pumps Diesel-engine management Technical Instruction Published by: © Robert Bosch GmbH, 1999 Postfach 3002 20, D-70442 Stuttgart. Automotive Equipment Business Sector, Department for Automotive Services, Technical Publications (KH/PDI2). Editor-in-Chief: Dipl.-Ing. (FH) Horst Bauer. Editors: Dipl.-Ing. Karl-Heinz Dietsche, Dipl.-Ing. (BA) Jürgen Crepin, Dipl.-Holzw. Folkhart Dinkler, Dipl.-Ing. (FH) Anton Beer. Author: Dr.-Ing. Helmut Tschöke, assisted by the responsible technical departments of Robert Bosch GmbH. Presentation: Dipl.-Ing. (FH) Ulrich Adler, Berthold Gauder, Leinfelden-Echterdingen. Translation: Peter Girling. Photographs: Audi AG, Ingolstadt and Volkswagen AG, Wolfsburg. Technical graphics: Bauer & Partner, Stuttgart. Unless otherwise specified, the above persons are employees of Robert Bosch GmbH, Stuttgart. Reproduction, copying, or translation of this publication, wholly or in part, only with our previous written permission and with source credit. Illustrations, descriptions, schematic drawings, and other particulars only serve to explain and illustrate the text. They are not to be used as the basis for design, installation, or delivery conditions. We assume no responsibility for agreement of the contents with local laws and regulations. Robert Bosch GmbH is exempt from liability, and reserves the right to make changes at any time. Printed in Germany. Imprimé en Allemagne. 4th Edition, April 1999. English translation of the German edition dated: November 1998. (prechamber engines and direct-injec- tion engines respectively). Direct-injection (DI) engines are more ef- ficient and more economical than their prechamber counterparts. For this rea- son, DI engines are used in all commer- cial-vehicles and trucks. On the other hand, due to their lower noise level, prechamber engines are fitted in passen- ger cars where comfort plays a more im- portant role than it does in the commer- cial-vehicle sector. In addition, the prechamber diesel engine features con- siderably lower toxic emissions (HC and NOX), and is less costly to produce than the DI engine. The fact though that the prechamber engine uses slightly more fuel than the DI engine (10...15%) is leading to the DI engine coming more and more to the forefront. Compared to the gasoline engine, both diesel versions are more economical especially in the part-load range. Diesel engines are particularly suitable for use with exhaust-gas turbochargers or mechanical superchargers. Using an exhaust-gas turbocharger with the diesel engine increases not only the power yield, and with it the efficiency, but also reduces the combustion noise and the toxic content of the exhaust gas. Diesel-engine exhaust emissions A variety of different combustion deposits are formed when diesel fuel is burnt. These reaction products are dependent upon engine design, engine power out- put, and working load. The complete combustion of the fuel leads to major reductions in the forma- tion of toxic substances. Complete com- bustion is supported by the careful matching of the air-fuel mixture, abso- lute precision in the injection process, and optimum air-fuel mixture turbulence. In the first place, water (H2O) and carbon dioxide (CO2) are generated. And in rela- tively low concentrations, the following substances are also produced: – Carbon monoxide (CO), – Unburnt hydrocarbons (HC), – Nitrogen oxides (NOX), – Sulphur dioxide (SO2) and sulphuric acid (H2SO4), as well as – Soot particles. When the engine is cold, the exhaust-gas constituents which are immediately noticeable are the non-oxidized or only partly oxidized hydrocarbons which are directly visible in the form of white or blue smoke, and the strongly smelling alde- hydes. The diesel engine 3 4-stroke diesel engine 1 Induction stroke, 2 Compression stroke, 3 Power stroke, 4 Exhaust stroke. 1 2 3 4 Fig. 2 U M M 00 13 Y Fields of application Diesel engines are characterized by their high levels of economic efficiency. This is of particular importance in commercial applications. Diesel engines are em- ployed in a wide range of different ver- sions (Fig. 1 and Table 1), for example as: – The drive for mobile electric generators (up to approx. 10 kW/cylinder), – High-speed engines for passenger cars and light commercial vehicles (up to approx. 50 kW/cylinder), – Engines for construction, agricultural, and forestry machinery (up to approx. 50 kW/cylinder), – Engines for heavy trucks, buses, and tractors (up to approx. 80 kW/cylinder), – Stationary engines, for instance as used in emergency generating sets (up to approx. 160 kW/cylinder), – Engines for locomotives and ships (up to approx. 1,000 kW/cylinder). Technical requirements More and more demands are being made on the diesel engine’s injection system as a result of the severe regulations govern- ing exhaust and noise emissions, and the demand for lower fuel-consumption. Basically speaking, depending on the particular diesel combustion process (direct or indirect injection), in order to ensure efficient air/fuel mixture formation, the injection system must inject the fuel into the combustion chamber at a pres- sure between 350 and 2,050 bar, and the injected fuel quantity must be metered with extreme accuracy. With the diesel engine, load and speed control must take place using the injected fuel quantity with- out intake-air throttling taking place. The mechanical (flyweight) governing principle for diesel injection systems is in- Diesel fuel- injection systems: An overview 4 Diesel fuel-injection systems: An overview Overview of the Bosch diesel fuel-injection systems M, MW, A, P, ZWM, CW in-line injection pumps in order of increasing size; PF single-plunger injection pumps; VE axial-piston distributor injection pumps; VR radial-piston distributor injection pumps; UPS unit pump system; UIS unit injector system; CR Common Rail system. VE VR M MW CR UIS PF VE MW A P VE MW A P ZWM CW PF CR UPS ZWM CW PF CR UPS VE VR MW P CR UPS UIS Fig. 1 U M K 15 63 -1 Y creasingly being superseded by the Elec- tronic Diesel Control (EDC). In the pas- senger-car and commercial-vehicle sec- tor, new diesel fuel-injection systems are all EDC-controlled. According to the latest state-of-the-art, it is mainly the high-pressure injection systems listed below which are used for motor-vehicle diesel engines. Fields of application, Technical requirements 5 In je ct ed fu el qu an tit y pe r st ro ke M ax . n oz zl e pr es su re m M ec ha ni ca l e E le ct ro ni c em E le ct ro m ec ha ni ca l M V S ol en oi d va lv e D ire ct in je ct io n In di re ct in je ct io n D I ID I P ilo t i nj ec tio n P os t i nj ec tio n V E N E N o. o f c yl in de rs M ax . s pe ed M ax . p ow er pe r cy lin de r Fuel-injection Injection Engine-related data system Type mm3 bar min–1 kW In-line injection pumps M 111,60 1,550 m, e IDI – 4…6 5,000 1,120 A 11,120 1,750 m DI / IDI – 2…12 2,800 1,127 MW 11,150 1,100 m DI – 4…8 2,600 1,136 P 3000 11,250 1,950 m, e DI – 4…12 2,600 1,145 P 7100 11,250 1,200 m, e DI – 4…12 2,500 1,155 P 8000 11,250 1,300 m, e DI – 6…12 2,500 1,155 P 8500 11,250 1,300 m, e DI – 4…12 2,500 1,155 H 1 11,240 1,300 e DI – 6…8 2,400 1,155 H 1000 11,250 1,350 e DI – 5…8 2,200 1,170 Axial-piston distributor injection pumps VE 11,120 1,200/350 m DI / IDI – 4…6 4,500 1,125 VE…EDC 1) 11,170 1,200/350 e, em DI / IDI – 3…6 4,200 1,125 VE…MV 11,170 1,400/350 e, MV DI / IDI – 3…6 4,500 1,125 Radial-piston distributor injection pump VR…MV 1,1135 1,700 e, MV DI – 4.6 4,500 1,150 Single-plunger injection pumps PF(R)… 150… 800… m, em DI / IDI – arbitrary 300… 75… 18,000 1,500 2,000 1,000 UIS 30 2) 11,160 1,600 e, MV DI VE 8 3a) 3,000 1,145 UIS 31 2) 11,300 1,600 e, MV DI VE 8 3a) 3,000 1,175 UIS 32 2) 11,400 1,800 e, MV DI VE 8 3a) 3,000 1,180 UIS-P1 3) 111,62 2,050 e, MV DI VE 6 3a) 5,000 1,125 UPS 12 4) 11,150 1,600 e, MV DI VE 8 3a) 2,600 1,135 UPS 20 4) 11,400 1,800 e, MV DI VE 8 3a) 2,600 1,180 UPS (PF[R]) 13,000 1,400 e, MV DI – 6…20 1,500 1,500 Common Rail accumulator injection system CR 5) 1,100 1,350 e, MV DI VE 5a)/NE 3…8 5,000 5b) 30 CR 6) 1,400 1,400 e, MV DI VE 6a)/NE 6…16 2,800 200 Table 1 Diesel fuel-injection systems: Properties and characteristic data 1) EDC Electronic Diesel Control; 2) UIS unit injector system for comm. vehs. 3) UIS unit injector system for pass. cars; 3a) With two ECU’s large numbers of cylinders are possible; 4) UPS unit pump system for comm. vehs. and buses; 5) CR 1st generation for pass. cars and light comm. vehs.; 5a) Up to 90˚ crankshaft BTDC, freely selectable; 5b) Up to 5,500 min–1 during overrun; 6) CR for comm. vehs., buses, and diesel-powered locomotives; 6a) Up to 30˚ crankshaft BTDC. Fuel-injection systems Assignments The fuel-injection system is responsible for supplying the diesel engine with fuel. To do so, the injection pump generates the pressure required for fuel injection. The fuel under pressure is forced through the high-pressure fuel-injection tubing to the injection nozzle which then injects it into the combustion chamber. The fuel-injection system (Fig. 1) in- cludes the following components and assemblies: The fuel tank, the fuel filter, the fuel-supply pump, the injection nozzles, the high-pressure injection tubing, the governor, and the timing device (if required). The combustion processes in the diesel engine depend to a large degree upon the quantity of fuel which is injected and upon the method of introducing this fuel to the combustion chamber. The most important criteria in this re- spect are the fuel-injection timing and the duration of injection, the fuel’s distribution in the combustion chamber, the moment in time when combustion starts, the amount of fuel metered to the engine per degree crankshaft, and the total injected fuel quantity in accordance with the engine loading. The optimum interplay of all these parameters is decisive for the faultless functioning of the diesel engine and of the fuel-injection system. Axial-piston distributor pumps 8 Mechanically-controlled (governed) axial-piston distributor fuel-Injection pumps VE Fuel-injection system with mechanically-controlled (governed) distributor injection pump 1 Fuel tank, 2 Fuel filter, 3 Distributor fuel-injection pump, 4 Nozzle holder with nozzle, 5 Fuel return line, 6 Sheathed-element glow plug (GSK) 7 Battery, 8 Glow-plug and starter switch, 9 Glow control unit (GZS). 1 2 6 5 4 9 7 3 8 Fig. 1 U M K 11 99 Y Types The increasing demands placed upon the diesel fuel-injection system made it necessary to continually develop and improve the fuel-injection pump. Following systems comply with the present state-of-the-art: – In-line fuel-injection pump (PE) with mechanical (flyweight) governor or Electronic Diesel Control (EDC) and, if required, attached timing device, – Control-sleeve in-line fuel-injection pump (PE), with Electronic Diesel Control (EDC) and infinitely variable start of delivery (without attached timing device), – Single-plunger fuel-injection pump (PF), – Distributor fuel-injection pump (VE) with mechanical (flyweight) governor or Electronic Diesel Control (EDC). With integral timing device, – Radial-piston distributor injection pump (VR), – Common Rail accumulator injection system (CRS), – Unit-injector system (UIS), – Unit-pump system (UPS). Fuel-injection techniques Fields of application Small high-speed diesel engines demand a lightweight and compact fuel- injection installation. The VE distributor fuel-injection pump (Fig. 2) fulfills these stipulations by combining – Fuel-supply pump, – High-pressure pump, – Governor, and – Timing device, in a small, compact unit. The diesel engine’s rated speed, its power output, and its configuration determine the parameters for the particular distributor pump. Distributor pumps are used in passenger cars, commercial vehicles, agricultural tractors and stationary engines. Fuel-injection techniques 9U M K 03 18 Y Fig. 2: VE distributor pump fitted to a 4-cylinder diesel engine Subassemblies In contrast to the in-line injection pump, the VE distributor pump has only one pump cylinder and one plunger, even for multi-cylinder engines. The fuel deliv- ered by the pump plunger is apportioned by a distributor groove to the outlet ports as determined by the engine’s number of cylinders. The distributor pump’s closed housing contains the following functional groups: – High-pressure pump with distributor, – Mechanical (flyweight) governor, – Hydraulic timing device, – Vane-type fuel-supply pump, – Shutoff device, and – Engine-specific add-on modules. Fig. 3 shows the functional groups and their assignments. The add-on modules facilitate adaptation to the specific requirements of the diesel engine in question. Design and construction The distributor pump’s drive shaft runs in bearings in the pump housing and drives the vane-type fuel-supply pump. The roller ring is located inside the pump at the end of the drive shaft al- though it is not connected to it. A rotat- ing-reciprocating movement is imparted to the distributor plunger by way of the cam plate which is driven by the input shaft and rides on the rollers of the roller ring. The plunger moves inside the distributor head which is bolted to the pump housing. Installed in the dis- tributor head are the electrical fuel shutoff device, the screw plug with vent screw, and the delivery valves with their Axial-piston distributor pumps 10 The subassemblies and their functions 1 Vane-type fuel-supply pump with pressure regulating valve: Draws in fuel and generates pressure inside the pump. 2 High-pressure pump with distributor: Generates injection pressure, delivers and distributes fuel. 3 Mechanical (flyweight) governor: Controls the pump speed and varies the delivery quantity within the control range. 4 Electromagnetic fuel shutoff valve: Interrupts the fuel supply. 5 Timing device: Adjusts the start of delivery (port closing) as a function of the pump speed and in part as a function of the load. 1 5 2 4 3 Fig. 3 U M K 03 17 Y interior pressure then increases in proportion to the speed (in other words, the higher the pump speed the higher the pump interior pressure). Some of the fuel flows through the pressure- regulating valve and returns to the suction side. Some fuel also flows through the overflow restriction and back to the fuel tank in order to pro- vide cooling and self-venting for the injection pump (Fig. 2). An overflow valve can be fitted instead of the overflow restriction. Fuel-line configuration For the injection pump to function ef- ficiently it is necessary that its high- pressure stage is continually provided with pressurized fuel which is free of vapor bubbles. Normally, in the case of passenger cars and light commercial vehicles, the difference in height between the fuel tank and the fuel-injection equipment is negligible. Furthermore, the fuel lines are not too long and they have adequate internal diameters. As a result, the vane-type supply pump in the injection pump is powerful enough to draw the fuel out of the fuel tank and to build up sufficient pressure in the interior of the in- jection pump. In those cases in which the difference in height between fuel tank and injection pump is excessive and (or) the fuel line between tank and pump is too long, a pre-supply pump must be installed. This overcomes the resistances in the fuel line and the fuel filter. Gravity-feed tanks are mainly used on stationary engines. Fuel tank The fuel tank must be of noncorroding material, and must remain free of leaks at double the operating pressure and in any case at 0.3 bar. Suitable openings or safety valves must be provided, or similar measures taken, in order to permit excess pressure to escape of its own accord. Fuel must not leak past the filler cap or through pressure- compensation devices. This applies when the vehicle is subjected to minor mechanical shocks, as well as when Fuel-injection techniques 13 Interaction of the fuel-supply pump, pressure-control valve, and overflow restriction 1 Drive shaft, 2 Pressure-control valve, 3 Eccentric ring, 4 Support ring, 5 Governor drive, 6 Drive-shaft dogs, 7 Overflow restriction, 8 Pump housing. 1 2 3 4 5 6 7 8 Fig. 2 U M K 03 21 Y cornering, and when standing or driving on an incline. The fuel tank and the engine must be so far apart from each other that in case of an accident there is no danger of fire. In addition, special regulations concerning the height of the fuel tank and its protective shielding apply to vehicles with open cabins, as well as to tractors and buses Fuel lines As an alternative to steel pipes, flame- inhibiting, steel-braid-armored flexible fuel lines can be used for the low- pressure stage. These must be routed to ensure that they cannot be damaged mechanically, and fuel which has dripped or evaporated must not be able to accumulate nor must it be able to ignite. Fuel filter The injection pump’s high-pressure stage and the injection nozzle are manufactured with accuracies of several thousandths of a millimeter. As a result, Axial-piston distributor pumps 14 Vane-type fuel-supply pump for low- pressure delivery 1 Inlet, 2 Outlet. 1 2 U M K 03 20 Y Fig. 4 U M K 03 24 Y Fig. 3: Vane-type fuel-supply pump with impeller on the drive shaft contaminants in the fuel can lead to malfunctions, and inefficient filtering can cause damage to the pump com- ponents, delivery valves, and injector nozzles. This means that a fuel filter specifically aligned to the requirements of the fuel-injection system is absolutely imperative if trouble-free operation and a long service life are to be achieved. Fuel can contain water in bound form (emulsion) or unbound form (e.g., condensation due to temperature changes). If this water gets into the injection pump, corrosion damage can be the result. Distributor pumps must therefore be equipped with a fuel filter incorporating a water accumulator from which the water must be drained off at regular intervals. The increasing popularity of the diesel engine in the passenger car has led to the development of an automatic water- warning device which indicates by means of a warning lamp when water must be drained. Vane-type fuel supply pump The vane-type pump (Figs. 3 and 4) is located around the injection pump’s drive shaft. Its impeller is concentric with the shaft and connected to it with a Woodruff key and runs inside an eccentric ring mounted in the pump housing. When the drive shaft rotates, centrifugal force pushes the impeller’s four vanes outward against the inside of the eccentric ring. The fuel between the vanes’ undersides and the impeller serves to support the outward movement of the vanes.The fuel enters through the inlet passage and a kidney-shaped recess in the pump’s housing, and fills the space formed by the impeller, the vane, and the inside of the eccentric ring. The rotary motion causes the fuel between adjacent vanes to be forced into the upper (outlet) kidney-shaped recess and through a passage into the interior of the pump. At the same time, some of the fuel flows through a second passage to the pressure-control valve. Pressure-control valve The pressure-control valve (Fig. 5) is connected through a passage to the upper (outlet) kidney-shaped recess, and is mounted in the immediate vicinity of the fuel-supply pump. It is a spring- loaded spool-type valve with which the pump’s internal pressure can be varied as a function of the quantity of fuel being delivered. If fuel pressure increases beyond a given value, the valve spool opens the return passage so that the fuel can flow back to the supply pump’s suction side. If the fuel pressure is too low, the return passage is closed by the spring. Fuel-injection techniques 15 Pressure-control valve Overflow restriction Fig. 5 U M K 03 22 Y Fig. 6 U M K 03 23 Y Distributor head The distributor plunger, the distributor- head bushing and the control collar are so precisely fitted (lapped) into the distributor head (Fig. 8), that they seal even at very high pressures. Small leakage losses are nevertheless un- avoidable, as well as being desirable for plunger lubrication. For this reason, the distributor head is only to be replaced as a complete assembly, and never the plunger, control collar, or distributor flange alone. Fuel metering The fuel delivery from a fuel-injection pump is a dynamic process comprising several stroke phases (Fig. 9). The pressure required for the actual fuel injection is generated by the high-pres- sure pump. The distributor plunger’s stroke and delivery phases (Fig. 10) show the metering of fuel to an engine cylinder. For a 4-cylinder engine the distributor plunger rotates through 90° for a stroke from BDC to TDC and back again. In the case of a 6-cylinder en- gine, the plunger must have completed these movements within 60° of plunger rotation. As the distributor plunger moves from TDC to BDC, fuel flows through the open inlet passage and into the high-pressure chamber above the plunger. At BDC, the plunger’s rotating movement then closes the inlet passage and opens the distribu- tor slot for a given outlet port (Fig. 10a). The plunger now reverses its direction of movement and moves upwards, the working stroke begins. The pressure that builds up in the high-pressure chamber above the plunger and in the outlet-port passage suffices to open the delivery valve in question and the fuel is forced through the high-pressure line to the injector nozzle (Fig. 10b). The working stroke is completed as soon as the plunger’s transverse cutoff bore reaches the control edge of the control collar and pressure collapses. From this point on, no more fuel is delivered to the injector and the delivery valve closes the high-pressure line. Axial-piston distributor pumps 18 U M K 03 28 Y Fig. 9: The cam plate rotates against the roller ring, whereby its cam track follows the rollers causing it to lift (for TDC) and drop back again (for BDC) Fuel-injection techniques 19 Distributor plunger with stroke and delivery phases a Inlet passage closes. At BDC, the metering slot (1) closes the inlet passage, and the distributor slot (2) opens the outlet port. b Fuel delivery. During the plunger stroke towards TDC (working stroke), the plunger pressurizes the fuel in the high- pressure chamber (3). The fuel travels through the outlet-port passage (4) to the injection nozzle. c End of delivery. Fuel delivery ceases as soon as the control collar (5) opens the transverse cutoff bore (6). d Entry of fuel. Shortly before TDC, the inlet passage is opened. During the plunger’s return stroke to BDC, the high-pressure chamber is filled with fuel and the transverse cutoff bore is closed again. The outlet-port passage is also closed at this point. 5 6 1 2 324 UT OT OT = TDC UT = BDC UT OT UT UT Fig. 10 U M K 03 29 Y During the plunger’s continued move- ment to TDC, fuel returns through the cutoff bore to the pump interior. During this phase, the inlet passage is opened again for the plunger’s next working cycle (Fig. 10c). During the plunger’s return stroke, its transverse cutoff bore is closed by the plunger’s rotating stroke movement, and the high-pressure chamber above the plunger is again filled with fuel through the open inlet passage (Fig. 10d). Delivery valve The delivery valve closes off the high- pressure line from the pump. It has the job of relieving the pressure in the line by removing a defined volume of fuel upon completion of the delivery phase. This ensures precise closing of the in- jection nozzle at the end of the injection process. At the same time, stable pressure conditions between injection pulses are created in the high-pressure lines, regardless of the quantity of fuel being injected at a particular time. The delivery valve is a plunger-type valve. It is opened by the injection pres- sure and closed by its return spring. Between the plunger’s individual delivery strokes for a given cylinder, the delivery valve in question remains closed. This separates the high-pres- sure line and the distributor head’s outlet-port passage. During delivery, the pressure generated in the high- pressure chamber above the plunger causes the delivery valve to open. Fuel then flows via longitudinal slots, into a ring-shaped groove and through the delivery-valve holder, the high-pressure line and the nozzle holder to the injection nozzle. As soon as delivery ceases (transverse cutoff bore opened), the pressure in the high-pressure chamber above the plunger and in the highpressure lines drops to that of the pump interior, and the delivery-valve spring together with the static pressure in the line force the de- livery-valve plunger back onto its seat again (Fig. 11). Axial-piston distributor pumps 20 Distributor head with high-pressure chamber 1 Control collar, 2 Distributor head, 3 Distributor plunger, 4 Delivery-valve holder, 5 Delivery-valve. 1 2 3 4 5 Fig. 11 U M K 03 35 Y – Maximum-speed governing: With the accelerator pedal fully depressed, the maximum full-load speed must not increase to more than high idle speed (maximum speed) when the load is removed. Here, the governor responds by shifting the control collar back towards the “Stop” position, and the supply of fuel to the engine is reduced. – Intermediate-speed governing: Vari- able-speed governors incorporate in- termediate-speed governing. Within certain limits, these governors can also maintain the engine speeds between idle and maximum constant. This means that depending upon load, the engine speed n varies inside the en- gine’s power range only between nVT (a given speed on the full-load curve) and nLT (with no load on the engine). Other control functions are performed by the governor in addition to its gov- erning responsibilities: – Releasing or blocking of the extra fuel required for starting, – Changing the full-load delivery as a function of engine speed (torque control). In some cases, add-on modules are necessary for these extra assignments. Speed-control (governing) accuracy The parameter used as the measure for the governor’s accuracy in controlling engine speed when load is removed is the so-called speed droop (P-degree). This is the engine-speed increase, expressed as a percentage, that occurs when the diesel engine’s load is re- moved with the control-lever (accelera- tor) position unchanged. Within the speed-control range, the increase in engine speed is not to exceed a given figure. This is stipulated as the high idle speed. This is the engine speed which results when the diesel engine, starting at its maximum speed under full load, is relieved of all load. The speed increase is proportional to the change in load, and increases along with it. δ = nlo – nvonvo or expressed in %: δ = nlo – nvo .100%nvo where δ = Speed droop nlo = High idle (maximum) speed nvo = Maximum full-load speed The required speed droop depends on engine application. For instance, on an engine used to power an electrical gen- erator set, a small speed droop is re- quired so that load changes result in only minor speed changes and there- fore minimal frequency changes. On the other hand, for automotive applications large speed droops are preferable because these result in more stable control in case of only slight load changes (acceleration or deceleration) and lead to better driveability. A low-value speed droop would lead to rough, jerking operation when the load changes. Mechanical governing 23 Governor characteristics a Minimum-maximum-speed governor, b Variable-speed governor. 1 Start quantity, 2 Full-load delivery, 3 Torque control (positive), 4 Full-load speed regulation, 5 Idle. 2 3 4 1 5 2 3 4 1 5 a b 0 Engine speed min–1 mm C on tr ol -c ol la r tr av el mm C on tr ol -c ol la r tr av el Fig. 2 U M K 03 44 E Variable-speed governor The variable-speed governor controls all engine speeds between start and high idle (maximum). The variable-speed governor also controls the idle speed and the maximum full-load speed, as well as the engine-speed range in between. Here, any engine speed can be selected by the accelerator pedal and, depending upon the speed droop, maintained practically constant (Fig. 4). This is necessary for instance when ancillary units (winches, fire-fighting pumps, cranes etc.) are mounted on the vehicle. The variable-speed governor is also often fitted in commercial and agricultural vehicles (tractors and combine harvesters). Design and construction The governor assembly is driven by the drive shaft and comprises the flyweight housing complete with flyweights. The governor assembly is attached to the governor shaft which is fixed in the governor housing, and is free to rotate around it. When the flyweights rotate they pivot outwards due to centrifugal force and their radial movement is converted to an axial movement of the sliding sleeve. The sliding-sleeve travel and the force developed by the sleeve influence the governor lever assembly. This comprises the starting lever, ten- sioning lever, and adjusting lever (not shown). The interaction of spring forces and sliding-sleeve force defines the setting of the governor lever assembly, variations of which are transferred to the control collar and result in adjust- ments to the injected fuel quantity. Starting With the engine at standstill, the fly- weights and the sliding sleeve are in their initial position (Fig. 3a). The start- ing lever has been pushed to the start position by the starting spring and has pivoted around its fulcrum M2. At the same time the control collar on the dis- tributor plunger has been shifted to its Axial-piston distributor pumps 24 Variable-speed governor. Start and idle positions a Start position, b Idle position. 1 Flyweights, 2 Sliding sleeve, 3 Tensioning lever, 4 Starting lever, 5 Starting spring, 6 Control collar, 7 Distributor-plunger cutoff port, 8 Distributor plunger, 9 Idle-speed adjusting screw, 10 Engine-speed control lever, 11 Control lever, 12 Control-lever shaft, 13 Governor spring, 14 Retaining pin, 15 Idle spring. a Starting-spring travel, c Idle-spring travel, h1 max. working stroke (start); h2 min. working stroke (idle): M2 fulcrum for 4 and 5. 1 1 2 3 4 5 M2 6 7 8 h1 h2 12 13 14 c 15 M2 10 11 9 a b a Fig. 3 U M K 03 46 Y start-quantity position by the ball pin on the starting lever. This means that when the engine is cranked the distributor plunger must travel through a complete working stroke (= maximum delivery quantity) before the cutoff bore is opened and delivery ceases. Thus the start quantity (= maximum delivery quantity) is automatically made available when the engine is cranked. The adjusting lever is held in the pump housing so that it can rotate. It can be shifted by the fuel-delivery adjusting screw (not shown in Figure 3). Similarly, the start lever and tensioning lever are also able to rotate in the adjusting lever. A ball pin which engages in the control collar is attached to the underside of the start lever, and the start spring to its upper section. The idle spring is attached to a retaining pin at the top end of the tensioning lever. Also attached to this pin is the governor spring. The connection to the engine- speed control lever is through a lever and the control-lever shaft. It only needs a very low speed for the sliding sleeve to shift against the soft start spring by the amount a. In the process, the start lever pivots around fulcrum M2 and the start quantity is auto- matically reduced to the idle quantity. Low-idle-speed control With the engine running, and the accelerator pedal released, the engine- speed control lever shifts to the idle position (Figure 3b) up against the idle- speed adjusting screw. The idle speed is selected so that the engine still runs reliably and smoothly when unloaded or only slightly loaded. The actual control is by means of the idle spring on the retaining pin which counteracts the force generated by the flyweights. This balance of forces determines the sliding-sleeve’s position relative to the distributor plunger’s cutoff bore, and with it the working stroke. At speeds above idle, the spring has been compressed by the amount c and is no longer effective. Using the special idle spring attached to the governor housing, this means that idle speed can be adjusted independent of the accelerator- pedal setting, and can be increased or decreased as a function of temperature or load. Operation under load During actual operation, depending upon the required engine speed or vehicle speed, the engine-speed control lever is in a given position within its pivot range. This is stipulated by the driver through a given setting of the accelerator pedal. At engine speeds above idle, start spring and idle spring have been compressed completely and have no further effect on governor action. This is taken over by the governor spring. Mechanical governing 25 Characteristic curves of the variable- speed governor A: Start position of the control collar, S: Engine starts with start quantity, S–L: Start quantity reduces to idle quantity, L: Idle speed nLN following engine start-up (no-load), L–B: Engine acceleration phase after shifting the engine-speed control lever from idle to a given required speed nc, B–B': The control collar remains briefly in the full-load position and causes a rapid increase in engine speed, B'–C: Control collar moves back (less injected fuel quantity, higher engine speed). In accordance with the speed droop, the vehicle maintains the required speed or speed nc in the part-load range, E: Engine speed nLT, after removal of load from the engine with the position of the engine- speed control-lever remaining unchanged. S B B' Full load L E No-load 0 500 1,000 1,500 2,000 min–1 Engine speed n mm C on tr ol -c ol la r tr av el s nA nC nLT nVH nLO A C Fig. 4 U M K 03 48 E Operation under load If the driver depresses the accelerator pedal, the engine-speed control lever is pivoted through a given angle. The starting and idle springs are no longer effective and the intermediate spring comes into effect. The intermediate spring on the minimum-maximum-speed governor provides a “soft” transition to the uncontrolled range. If the engine- speed control lever is pressed even further in the full-load direction, the intermediate spring is compressed until the tensioning lever abuts against the retaining pin (Fig. 7b). The intermediate spring is now ineffective and the uncontrolled range has been entered. This uncontrolled range is a function of the governor-spring pretension, and in this range the spring can be regarded as a solid element. The accelerator-pedal position (engine-speed control lever) is now transferred directly through the governor lever mechanism to the control collar, which means that the injected fuel quantity is directly determined by the accelerator pedal. To accelerate, or climb a hill, the driver must “give gas”, or ease off on the accelerator if less engine power is needed. If engine load is now reduced, with the engine-speed control lever position unchanged, engine speed increases without an increase in fuel delivery. The flyweights’ centrifugal force also in- creases and pushes the sliding sleeve even harder against the start and tensioning levers. Full-load speed control does not set in, at or near the engine’s rated speed, until the governor-spring pre-tension has been overcome by the effect of the sliding-sleeve force. If the engine is relieved of all load, speed increases to the high idle speed, and the engine is thus protected against over- revving. Passenger cars are usually equipped with a combination of variable-speed governor and minimum-maximum-speed governor. Axial-piston distributor pumps 28 Minimum-maximum-speed governor a Idle setting, b Full-load setting. 1 Flyweights, 2 Engine-speed control lever, 3 Idle-speed adjusting screw, 4 Governor spring, 5 Intermediate spring, 6 Retaining pin, 7 Idle spring, 8 Start lever, 9 Tensioning lever, 10 Tensioning-lever stop, 11 Starting spring, 12 Control collar, 13 Full-load speed control, 14 Sliding sleeve, 15 Distributor plunger cutoff bore, 16 Distributor plunger. a Start and idle-spring travel, b Intermediate-spring travel, h1 Idle working stroke, h2 Full-load working stroke, M2 fulcrum for 8 and 9. 1 1 M2 12 4 h1 a b 2 3 5 14 7 9 11 10 13 h2 b a 6 8 1516 M2 Fig. 7 U M K 03 52 Y Injection timing In order to compensate for the injection lag and the ignition lag, as engine speed increases the timing device advances the distributor pump’s start of delivery referred to the engine’s crankshaft. Example (Fig. 1): Start of delivery (FB) takes place after the inlet port is closed. The high pres- sure then builds up in the pump which, as soon as the nozzle-opening pres- sure has been reached leads to the start of injection (SB). The period between FB and SB is referred to as the injection lag (SV). The increasing compression of the air-fuel mixture in the combustion chamber then initiates the ignition (VB). The period between SB and VB is the ignition lag (ZV). As soon as the cutoff port is opened again the pump pressure collapses (end of pump delivery), and the nozzle needle closes again (end of injection, SE). This is followed by the end of combustion (VE). Assignment During the fuel-delivery process, the injection nozzle is opened by a pressure wave which propagates in the high- pressure line at the speed of sound. Basically speaking, the time required for this process is independent of engine speed, although with increasing engine speed the crankshaft angle between start of delivery and start of injection also increases. This must be compensated for by advancing the start of delivery. The pressure wave’s propagation time is determined by the length of the high-pressure line and the speed of sound which is approx. 1,500 m/s in diesel fuel. The interval represented by this propagation time is termed the injection lag. In other words, the start of injection lags behind the start of delivery. This phenomena is the reason for the injector opening later (referred to the engine’s piston position) at higher engine speeds than at low engine speeds. Following injection, the injected fuel needs a certain time in Injection timing 29 Curve of a working stroke at full load and at low speed (not drawn to scale). FB Start of delivery, SB Start of injection, SV Injection lag, VB Start of combustion, ZV Ignition lag, SE End of injection, VE End of combustion. 1 Combustion pressure, 2 Compression pressure, UT BDC, OT TDC. BDC TDC BDC TDC2 84 12 16-4-2-16 -12 -8 SV 0 100 200 300 400 bar TDC TDC ZV SV FB SB SE VE P um p hi gh p re ss ur e p N oz zl e- ne ed le li ft n D R at e of in je ct io n Q 0 0.1 0.2 0.3 mm 0 2 4 6 mm3 °cms °cms ATDC°cms BTDC Degrees camshaft C om bu st io n- ch am be r pr es su re bar 1 2 VB FB SB SE Plunger position h Fig. 1 U M K 03 57 E order to atomize and mix with the air to form an ignitable mixture. This is termed the air-fuel mixture preparation time and is independent of engine speed. In a diesel engine, the time required between start of injection and start of combustion is termed the ignition lag. The ignition lag is influenced by the diesel fuel’s ignition quality (defined by the Cetane Number), the compression ratio, the intake-air temperature, and the quality of fuel atomization. As a rule, the ignition lag is in the order of 1 millisecond. This means that pre- suming a constant start of injection, the crankshaft angle between start of injection and start of combustion increases along with increasing engine speed. The result is that combustion can no longer start at the correct point (referred to the engine-piston position). Being as the diesel engine’s most efficient combustion and power can only be developed at a given crankshaft or piston position, this means that the in- jection pump’s start of delivery must be advanced along with increasing engine speed in order to compensate for the overall delay caused by ignition lag and injection lag. This start-of-delivery advance is carried out by the engine- speed-dependent timing device. Timing device Design and construction The hydraulically controlled timing de- vice is located in the bottom of the distributor pump’s housing, at right angles to the pump’s longitudinal axis (Fig. 2), whereby its piston is free to move in the pump housing. The housing is closed with a cover on each side. There is a passage in one end of the timing device plunger through which the fuel can enter, while at the other end the plunger is held by a compression spring. The piston is connected to the roller ring Axial-piston distributor pumps 30 Distributor injection pump with timing device 1 Roller ring, 2 Roller-ring rollers, 3 Sliding block, 4 Pin, 5 Timing-device piston, 6 Cam plate, 7 Distributor plunger. 1 2 3 4 5 6 7 Fig. 2 U M K 03 54 Y Add-on modules and shutoff devices 33 Schematic of the VE distributor pump with mechanical/hydraulic full-load torque control LDA Manifold-pressure compensator. Controls the delivery quantity as a function of the charge-air pressure. HBA Hydraulically controlled torque control. Controls the delivery quantity as a function of the engine speed (not for pressure-charged engines with LDA). LFB Load-dependent start of delivery. Adaptation of pump delivery to load. For reduction of noise and exhaust-gas emissions. ADA Altitude-pressure compensator. Controls the delivery quantity as a function of atmospheric pressure. KSB Cold-start accelerator. Improves cold-start behavior by changing the start of delivery. GST Graded (or variable) start quantity. Prevents excessive start quantity during warm start. TLA Temperature-controlled idle-speed increase. Improves engine warm-up and smooth running when the engine is cold. ELAB Electrical shutoff device. A Cutoff port, nactual Actual engine speed (controlled variable), nsetpoint Desired engine speed (reference variable), QF Delivery quantity, tM Engine temperature, tLU Ambient-air temperature, pL Charge-air pressure, pA Atmospheric pressure, pi Pump interior pressure. 1 Full-load torque control with governor lever assembly, 2 Hydraulic full-load torque control. TLA GST Control of injected fuel quantity Engine-speed control LDA ADA ELAB HBA High-pressure pump with distributor Vane-type fuel- supply pump Delivery-valve assembly Timing device LFB 1 2 A KSB tLU /tM nsetpoint Uon /Uoff pL /pA ppi nactual Drive Fuel Injection nozzles QF Add-on module Basic pump tM Fig. 2 U M K 03 59 E to install torque control. In other words, the engine should receive precisely the amount of fuel it needs. The engine’s fuel requirement first of all climbs as a function of engine speed and then levels off somewhat at higher speeds. The fuel-delivery curve of an injection pump without torque control is shown in Fig. 3. As can be seen, with the same setting of the control collar on the distributor plunger, the injection pump delivers slightly more fuel at high speeds than it does at lower speeds. This is due to the throttling effect at the distributor plunger’s cutoff port. This means that if the injection pump’s delivery quantity is specified so that maximum-possible torque is developed at low engine speeds, this would lead to the engine being unable to completely combust the excess fuel injected at higher speeds and smoke would be the result together with engine overheat. On the other hand, if the maximum delivery quantity is specified so that it corresponds to the engine’s requirements at maximum speed and full-load, the engine will not be able to develop full power at low engine speeds due to the delivery quantity dropping along with reductions in engine speed. Performance would be below optimum. The injected fuel quantity must therefore be adjusted to the engine’s actual fuel requirements. This is known as “torque control”, and in the case of the distributor injection pump can be implemented using the delivery valve, the cutoff port, or an extended governor- lever assembly, or the hydraulically controlled torque control (HBA). Full-load torque control using the governor lever assembly is applied in those cases in which the positive full-load torque control with the delivery valve no longer suffices, or a negative full-load torque control has become necessary. Positive torque control Positive torque control is required on those injection pumps which deliver too much fuel at higher engine revs. The delivery quantity must be reduced as engine speed increases. Positive torque control using the delivery valve Within certain limits, positive torque control can be achieved by means of the delivery valve, for instance by fitting a softer delivery-valve spring. Positive torque control using the cutoff port Optimization of the cutoff port’s dimen- sions and shape permit its throttling effect to be utilized for reducing the delivery quantity at higher engine speeds. Positive torque control using the governor lever assembly (Fig. 4a) The decisive engine speed for start of torque control is set by preloading the torque-control springs. When this speed is reached, the sliding-sleeve force (FM) and the spring preload must be in equilibrium, whereby the torque-control lever (6) abuts against the stop lug (5) of the tensioning lever (4). The free end of the torque-control lever (6) abuts against the torque-control pin (7). If engine speed now increases, the sliding-sleeve force acting against the starting lever (1) increases and the common pivot point (M4) of starting lever and torque-control lever (6) changes its position. At the same time, Axial-piston distributor pumps 34 Fuel-delivery characteristics, with and without torque control a Negative, b Positive torque control. 1 Excess injected fuel, 2 Engine fuel requirement, 3 Full-load delivery with torque control, Shaded area: Full-load delivery without torque control. Engine speed n D el iv er y qu an tit y Q F min–1 mm3 stroke a b 1 2 3 Fig. 3 U M K 03 60 E the torque-control lever tilts around the stop pin (5) and forces the torque- control pin (7) in the direction of the stop, while the starting lever (1) swivels around the pivot point (M2) and forces the control collar (8) in the direction of re- duced fuel delivery. Torque control ceases as soon as the torque-control-pin collar (10) abuts against the starting lever (1). Negative torque control Negative torque control may be necessary in the case of engines which have black-smoke problems in the lower speed range, or which must generate specific torque characteristics. Similarly, turbocharged engines also need negative torque control when the manifold-pressure compensator (LDA) has ceased to be effective. In this case, the fuel delivery is increased along with engine speed (Fig. 3). Negative torque control using the governor lever assembly (Fig. 4b) Once the starting spring (9) has been compressed, the torque-control lever (6) applies pressure to the tensioning lever (4) through the stop lug (5). The torque-control pin (7) also abuts against the tensioning lever (4). If the sliding- sleeve force (FM) increases due to rising engine speed, the torque-control lever presses against the preloaded torque- control spring. As soon as the slid- ing-sleeve force exceeds the torque- control spring force, the torque-control lever (6) is forced in the direction of the torque-control-pin collar. As a result, the common pivot point (M4) of the starting lever and torque-control lever changes its position. At the same time the starting lever swivels around its pivot point (M2) and pushes the control collar (8) in the direction of increased delivery. Torque control ceases as soon as the torque-control lever abuts against the pin collar. Negative torque control using hydrauli- cally controlled torque control HBA In the case of naturally aspirated diesel engines, in order to give a special shape to the full-load delivery characteristic as a function of engine speed, a form of torque control can be applied which is similar to the LDA (manifold-pressure compensator). Here, the shift force developed by the hydraulic piston is generated by the pressure in the pump interior, which in turn depends upon pump speed. In contrast to spring-type torque control, within limits the shape of the full-load characteristic can be determined by a cam on a sliding pin. Add-on modules and shutoff devices 35 Torque control using the governor-lever assembly a Positive torque control, b Negative torque control. 1 Starting lever, 2 Torque-control spring, 3 Governor spring, 4 Tensioning lever, 5 Stop lug, 6 Torque-control lever, 7 Torque-control pin, 8 Control collar, 9 Starting spring, 10 Pin collar, 11 Stop point, M2 Pivot point for 1 and 4, M4 Pivot point for 1 and 6, FM Sliding-sleeve force, ∆ s Control-collar travel. 4 M4 2 6 7 b 3 4 2 5 9 11 10 1 M2 8 FM 1 M4 5 6 7 M2 8 a FM ∆ s ∆ s Fig. 4 U M K 03 62 Y jected fuel quantity must be adapted to the lower air mass. This is performed by the manifold-pressure compensator which, below a given (selectable) charge-air pressure, reduces the full-load quantity. Design and construction The LDA is mounted on the top of the distributor pump (Fig. 7). In turn, the top of the LDA incorporates the connection for the charge-air and the vent bore. The interior of the LDA is divided into two separate airtight chambers by a dia- phragm to which pressure is applied by a spring. At its opposite end, the spring is held by an adjusting nut with which the spring’s preload is set. This serves to match the LDA’s response point to the charge pressure of the exhaust turbocharger. The diaphragm is con- nected to the LDA’s sliding pin which has a taper in the form of a control cone. This is contacted by a guide pin which transfers the sliding-pin movements to the reverse lever which in turn changes the setting of the full-load stop. The initial setting of the diaphragm and the sliding pin is set by the adjusting screw in the top of the LDA. Method of operation In the lower engine-speed range the charge-air pressure generated by the exhaust turbocharger and applied to the diaphragm is insufficient to overcome the pressure of the spring. The diaphragm remains in its initial position. As soon as the charge-air pressure applied to the diaphragm becomes effective, the dia- phragm, and with it the sliding pin and control cone, shift against the force of the spring. The guide pin changes its position as a result of the control cone’s vertical movement and causes the reverse lever to swivel around its pivot point M1 (Fig. 7). Due to the force exerted by the governor spring, there is a non- positive connection between tensioning lever, reverse lever, guide pin, and sliding-pin control cone. As a result, the tensioning lever follows the reverse lever’s swivelling movement, causing the starting lever and tensioning lever to swivel around their common pivot point thus shifting the control collar in the direction of increased fuel delivery. Fuel delivery is adapted in response to the increased air mass in the combustion chamber (Fig. 8). On the other hand, when the charge-air pressure drops, the spring underneath the diaphragm pushes the diaphragm upwards, and with it the sliding pin. The compensation action of the governor lever mechanism now takes place in the reverse direction and the injected fuel quantity is adapted to the change in charge pressure. Should the turbocharger fail, the LDA reverts to its initial position and the engine operates normally without developing smoke. The full-load delivery with charge-air pressure is adjusted by the full-load stop screw fitted in the governor cover. Axial-piston distributor pumps 38 Charge-air pressure: Operative range a Turbocharger operation, b Normally aspirated operation. p1 Lower charge-air pressure, p2 Upper charge-air pressure. Charge-air pressure p p1 p2 mbar a b mm3/ stroke LDA operative range In je ct ed fu el qu an tit y Q e Fig. 8 U M K 03 68 E Load-dependent compensation Depending upon the diesel engine’s load, the injection timing (start of delivery) must be adjusted either in the “advance” or “retard” direction. Load-dependent start of delivery (LFB) Assignment Load-dependent start of delivery is de- signed so that with decreasing load (e.g., change from full-load to part- load), with the control-lever position un- changed, the start of delivery is shifted in the “retard” direction. And when en- gine load increases, the start of delivery (or start of injection) is shifted in the “advance” direction. These adjustments lead to “softer” engine operation, and cleaner exhaust gas at part- and full- load. Design and construction For load-dependent injection timing, modifications must be made to the gov- ernor shaft, sliding sleeve, and pump housing. The sliding sleeve is provided with an additional cutoff port, and the governor shaft with a ring-shaped groove, a longitudinal passage and two transverse passages (Fig. 9). The pump housing is provided with a bore so that a connection is established from the interior of the pump to the suction side of the vane-type supply pump. Method of operation As a result of the rise in the supply- pump pressure when the engine speed increases, the timing device adjusts the start of delivery in the “advance” direc- tion. On the other hand, with the drop in the pump’s interior pressure caused by the LFB it is possible to implement a (relative) shift in the “retard” direction. This is controlled by the ring-shaped groove in the governor shaft and the sliding-sleeve’s control port. The control Add-on modules and shutoff devices 39 Design and construction of the governor assembly with load-dependent start of delivery (LFB) 1 Governor spring, 2 Sliding sleeve, 3 Tensioning lever, 4 Start lever, 5 Control collar, 6 Distributor plunger, 7 Governor shaft, 8 Flyweights. M2 Pivot point for 3 and 4. 3 4 M2 5 1 2 6 87 Fig. 9 U M K 03 69 Y lever is used to input a given full-load speed. If this speed is reached and the load is less than full load, the speed increases even further, because with a rise in speed the flyweights swivel outwards and shift the sliding sleeve. On the one hand, this reduces the delivery quantity in line with the conventional governing process. On the other, the sliding sleeve’s control port is opened by the control edge of the governor-shaft groove. The result is that a portion of the fuel now flows to the suction side through the governor shaft’s longitudinal and transverse passages and causes a pressure drop in the pump’s interior. This pressure drop results in the timing- device piston moving to a new position. This leads to the roller ring being turned in the direction of pump rotation so that start of delivery is shifted in the “retard” direction. If the position of the control lever remains unchanged and the load increases again, the engine speed drops. The flyweights move inwards and the sliding sleeve is shifted so that its control port is closed again. The fuel in the pump interior can now no longer flow through the governor shaft to the suction side, and the pump interior pressure increases again. The timing-device piston shifts against the force of the timing- device spring and adjusts the roller ring so that start of delivery is shifted in the “advance” direction (Fig. 10). Atmospheric-pressure compensation At high altitudes, the lower air density reduces the mass of the inducted air, and the injected full-load fuel quantity cannot burn completely. Smoke results and engine temperature rises. To pre- vent this, an altitude-pressure compen- sator is used to adjust the full-load quantity as a function of atmospheric pressure. Altitude-pressure compensator (ADA) Design and construction The construction of the ADA is identical to that of the LDA. The only difference being that the ADA is equipped with an aneroid capsule which is connected to a vacuum system somewhere in the vehicle (e.g., the power-assisted brake system). The aneroid provides a con- stant reference pressure of 700mbar (absolute). Method of operation Atmospheric pressure is applied to the upper side of the ADA diaphragm. The reference pressure (held constant by the aneroid capsule) is applied to the diaphragm’s underside. If the atmo- spheric pressure drops (for instance when the vehicle is driven in the mountains), the sliding bolt shifts verti- cally away from the lower stop and, similar to the LDA, the reverse lever causes the injected fuel quantity to be reduced. Axial-piston distributor pumps 40 Sliding-sleeve positions in the load- dependent injection timing (LFB) a Start position (initial position), b Full-load position shortly before the control port is opened, c Control port opened, pressure reduction in pump interior. 1 Longitudinal bore in the governor shaft, 2 Governor shaft, 3 Sliding-sleeve control port, 4 Sliding-sleeve, 5 Governor-shaft transverse passage, 6 Control edge of the groove in the governor shaft, 7 Governor-shaft transverse passage. 5 76 4321 a b c Fig. 10 U M K 03 70 Y Design and construction The hydraulic cold-start accelerator comprises a modified pressure-control valve, a KSB ball valve, a KSB control valve, and an electrically heated ex- pansion element. Method of operation The fuel delivered by the fuel-supply pump is applied to one of the timing device piston’s end faces via the injection pump’s interior. In accordance with the injection pump’s interior pressure, the piston is shifted against the force of its spring and changes the start- of-injection timing. Pump interior pressure is determined by a pressure- control valve which increases pump interior pressure along with increasing pump speed and the resulting rise in pump delivery (Fig. 15). There is a restriction passage in the pressure-control valve’s plunger in order to achieve the pressure increase needed for the KSB function, and the resulting advance curve shown as a dotted line in Fig. 16. This ensures that the same pressure is effective at the spring side of the pressure-control valve. The KSB ball-type valve has a correspondingly higher pressure level and is used in conjunction with the thermo-element both for switching-on and switching-off the KSB function, as well as for safety switchoff. Using an adjusting screw in the integrated KSB control valve, the KSB function can be set to a given engine speed. The fuel supply pump pressure shifts the KSB control valve’s plunger against the force of a spring. A damping restriction is used to reduce the pressure fluctu- ations at the control plunger. The KSB pressure characteristic is controlled by its plunger’s control edge and the section at the valve holder. The KSB function is adapted by correct selection of the KSB control valve’s spring rate and its control section. When the warm engine is started, the expansion element has already opened the ball valve due to the prevailing temperature. Add-on modules and shutoff devices 43 Effect of the hydraulic cold-start accelerator (KSB) 1 Injection-timing advance. Hydraulic cold-start accelerator (KSB) 11 Pressure-control valve, 12 Valve plunger, 13 Restriction passage, 14 Internal pressure, 15 Fuel-supply pump, 16 Electrically heated expansion element, 17 KSB ball valve, 18 Pressureless fuel return, 19 KSB control valve, adjustable, 10 Timing device.
  1 2 6 7 8 910 3 4 5 1 Pump speed p In je ct io n- tim in g ad va nc e °cms min–1 Fig. 15 U M K 11 95 Y Fig. 16 U M K 03 79 E Engine shutoff Assignment The principle of auto-ignition as applied to the diesel engine means that the engine can only be switched off by interrupting its supply of fuel. Normally, the mechanically governed distributor pump is switched off by a solenoid-operated shutoff (ELAB). Only in special cases is it equipped with a mechanical shutoff device. Electrical shutoff device (ELAB) The electrical shutoff (Fig. 17) using the vehicle’s key-operated starting switch is coming more and more to the forefront due to its convenience for the driver. On the distributor pump, the solenoid valve for interrupting the fuel supply is installed in the top of the distributor head. When the engine is running, the solenoid is energized and the valve keeps the passage into the injection pump’s high-pressure chamber open (armature with sealing cone has pulled in). When the driving switch is turned to “OFF”, the current to the solenoid winding is also cut, the magnetic field collapses, and the spring forces the armature and sealing cone back onto the valve seat again. This closes the inlet passage to the high-pressure chamber, the distributor-pump plunger ceases to deliver fuel, and the engine stops. From the circuitry point of view, there are a variety of different possi- bilities for implementing the electrical shutoff (pull or push solenoid). Mechanical shutoff device On the injection pump, the mechanical shutoff device is in the form of a lever assembly (Fig. 18). This is located in the governor cover and comprises an outer and an inner stop lever. The outer lever is operated by the driver from inside the vehicle (for instance by means of bowden cable). When the cable is pulled, both levers swivel around their common pivot point, whereby the inner stop lever pushes against the start lever of the governor-lever mechanism. This swivels around its pivot point M2 and shifts the control collar to the shutoff position. The distributor plunger’s cutoff port remains open and the plunger delivers no fuel. Axial-piston distributor pumps 44 Mechanical shutoff device 1 Outer stop lever, 2 Start lever, 3 Control collar, 4 Distributor plunger, 5 Inner stop lever, 6 Tensioning lever, 7 Cutoff port. M2 Pivot point for 2 and 6. Electrical shutoff device (pull solenoid) 1 Inlet passage, 2 Distributor plunger, 3 Distributor head, 4 Push or pull solenoid, 5 High-pressure chamber. 1 3 4 5 2 5 6 M2 7 4 3 1 2 Fig. 17 Fig. 18 U M K 03 82 Y U M K 03 80 Y Testing and calibration Injection-pump test benches Precisely tested and calibrated injection pumps and governors are the prerequisite for achieving the optimum fuel-con- sumption/performance ratio and compli- ance with the increasingly stringent exhaust-gas legislation. And it is at this point that the injection-pump test bench becomes imperative. The most important framework conditions for the test bench and for the testing itself are defined in ISO-Standards which, in particular, place very high demands upon the rigidity and uniformity of the pump drive. The injection pump under test is clamped to the test-bench bed and con- nected at its drive end to the test-bench coupling. Drive is through an electric motor (via hydrostatic or manually- switched transmission to flywheel and coupling, or with direct frequency control). The pump is connected to the bench’s calibrating-oil supply via oil inlet and outlet, and to its delivery measuring device via high-pressure lines. The measuring device comprises calibrating nozzles with precisely set opening pressures which inject into the bench’s measuring system via spray dampers. Oil temperature and pressure is adjusted in accordance with test specifications. There are two methods for fuel-delivery measurement. One is the so-called continuous method. Here, a precision gear pump delivers per cylinder and unit of time, the same quantity of calibrating-oil as the quantity of injected fuel. The gear pump’s delivery is therefore a measure of delivery quantity per unit of time. A com- puter then evaluates the measurement results and displays them as a bar chart on the screen. This measuring method is very accurate, and features good reproducibility (Fig. 1). The other method for fuel-delivery mea- surement uses glass measuring gradu- ates. The fuel to be measured is at first directed past the graduates and back to the tank with a slide. When the specified number of strokes has been set on the stroke-counting mechanism the mea- surement starts, and the slide opens and the graduates fill with oil. When the set number of strokes has been com- pleted, the slider cuts off the flow of oil again. The injected quantity can be read off directly from the graduates. Engine tester for diesel engines The diesel-engine tester is necessary for the precise timing of the injection pump to the engine. Without opening the high-pressure lines, this tester measures the start of pump delivery, injection timing, and engine speeds. A sensor is clamped over the high-pressure line to cylinder 1, and with the stroboscopic timing light or the TDC sensor for detect- ing crankshaft position, the tester calculates start of delivery and injection timing. Testing and calibration 45 Continuous injected-fuel-quantity measuring system 1 Calibrating-oil tank, 2 Injection pump, 3 Calibrating nozzle, 4 Measuring cell, 5 Pulse counter, 6 Display monitor.   M 1 4 5 2 3 6 Fig. 18 U W T 00 59 Y Hole-type nozzles Application Hole-type nozzles are used with in-line injection pumps on direct-injection en- gines. One differentiates between: – Sac-hole, and – Seat-hole nozzles. The hole-type nozzles also vary accord- ing to their size: – Type P with 4 mm needle diameter, and – Type S with 5 and 6 mm needle dia- meters. Design and construction The spray holes are located on the en- velope of a spray cone (Fig. 4). The num- ber of spray holes and their diameter de- pend upon: – The injected fuel quantity, – The combustion-chamber shape, and – The air swirl in the combustion cham- ber. The input edges of the spray holes can be rounded by hydro-erosive (HE) ma- chining. At those points where high flow rates occur (spray-hole entrance), the abrasive particles in the hydro-erosive (HE) me- dium cause material loss. This so-called HE-rounding process can be applied to both sac-hole and seat-hole nozzles, whereby the target is: – Prevent in advance the edge wear caused by abrasive particles in the fuel and/or – Reduce the flow tolerance. For low hydrocarbon emissions, it is highly important that the volume filled with fuel (residual volume) below the edge of the nozzle-needle seat is kept to a minimum. Seat-hole nozzles are there- fore used. Designs Sac-hole nozzle The spray holes of the sac-hole nozzle (Fig. 5) are arranged in the sac hole. In the case of a round nozzle tip (Fig. 6a), depending upon design the spray holes are drilled mechanically or by means of electrochemical machining (e.c.m.). Sac-hole nozzles with conical tip (Figs. 6b and 6c) are always drilled using e.c.m. Sac-hole nozzles are available – With cylindrical, and – Conical sac holes in a variety of different dimensions. Sac-hole nozzle with cylindrical sac hole and round tip (Fig. 6a): This nozzle’s sac hole has a cylindrical and a semispherical portion, and permits a high level of design freedom with respect to – Number of spray holes, – Spray-hole length, and – Injection angle. The nozzle tip is semispherical, and together with the shape of the sac hole, ensures that the spray holes are of identical length. Axial-piston distributor pumps 48 Spray cone γ Spray-cone offset angle, d Spray cone. γ δ Fig. 4 U M K 14 02 Y Sac-hole nozzle with cylindrical sac hole and conical tip (6b): This type of nozzle is used exclusively with spray-hole lengths of 0.6 mm. The tip’s conical shape enables the wall thickness to be increased between the throat radius and the nozzle-body seat with an attending improvement of nozzle- tip strength. Sac-hole nozzle with conical sac hole and conical tip (Fig. 6c): Due to the conical shape of this nozzle’s sac hole, its volume is less than that of a nozzle with cylindrical sac hole. The volume is between that for a seat-hole nozzle and a sac-hole nozzle with cylin- drical sac hole. In order to achieve uni- form tip-wall thickness, the tip’s conical design corresponds to that of the sac hole. Nozzles and nozzle holders 49 Sac-hole nozzle 1 Pressure shaft, 2 Needle-lift stop face, 3 Inlet passage, 4 Pressure shoulder, 5 Needle shaft, 6 Nozzle tip, 7 Nozzle-body shaft, 8 Nozzle-body shoulder, 9 Pressure chamber, 10 Needle guide, 11 Nozzle-body collar, 12 Locating hole, 13 Sealing surface, 14 Pressure-pin contact surface. Sac-hole shapes a Cylindrical sac hole with round tip, b Cylindrical sac hole with conical tip, c Conical sac hole with conical tip. 1 Shoulder, 2 Seat entrance, 3 Needle seat, 4 Needle tip, 5 Injection orifice, 6 Injection-orifice entrance, 7 Sac hole, 8 Throat radius, 9 Nozzle-tip cone, 10 Nozzle-body seat, 11 Damping cone. 5 6 7 8 9 10 11 4 2 3 1 a b c Fig. 5 U M K 14 03 Y Fig. 6 U M K 16 50 Y Seat-hole nozzle In order to minimise the residual volume – and therefore the HC emissions – the start of the spray hole is located in the seat taper, and with the nozzle closed it is covered almost completely by the nozzle needle. This means that there is no direct connection between the sac hole and the combustion chamber (Figs. 7 and 8). The sac-hole volume here is much lower than that of the sac-hole nozzle. Compared to sac-hole nozzles, seat-hole nozzles have a much lower loading limit and are there- fore only manufactured as Size P with a spray-hole length of 1 mm. For reasons of strength, the nozzle tip is conically shaped. The spray holes are always formed using e.c.m. methods. Standard nozzle holders Assignments and designs Nozzle holders with hole-type nozzles in combination with a radial-piston distrib- utor injection pump are used on DI engines. With regard to the nozzle holders, one differentiates between – Standard nozzle holders (single- spring nozzle holders) with and with- out needle-motion sensor, and – Two-spring nozzle holders, with and without needle-motion sensor. Application The nozzle holders described here have the following characteristics: – Cylindrical external shape with diame- ters between 17 and 21 mm, – Bottom-mounted springs (leads to low moving masses), – Pin-located nozzles for direct-injection engines, and – Standardised components (springs, pressure pin, nozzle-retaining nut) make combinations an easy matter. Design The nozzle-and-holder assembly is com- posed of the injection nozzle and the nozzle holder. The nozzle holder comprises the follow- ing components (Fig. 9): – Nozzle-holder body, – Intermediate element, – Nozzle-retaining nut, – Pressure pin, – Spring, – Shim, and – Locating pins. The nozzle is centered in the nozzle body and fastened using the nozzle-retaining nut. When nozzle body and retaining nut are screwed together, the intermediate element is forced up against the sealing surfaces of nozzle body and retaining nut. The intermediate element serves as the needle-lift stop and with its locating pins centers the nozzle in the nozzle- holder body. Axial-piston distributor pumps 50 Seat-hole nozzle Seat-hole nozzle: Tip shape Fig. 7 U M K 14 08 Y U M K 14 07 Y Fig. 8 This necessitates a nozzle holder with needle-motion sensor (Fig. 13) which outputs a signal as soon as the nozzle needle opens. Design When it moves, the extended pressure pin enters the current coil. The degree to which it enters the coil (overlap length “X” in Fig. 14) determines the strength of the magnetic flux. Method of operation The magnetic flux in the coil changes as a result of nozzle-needle movement and induces a signal voltage which is propor- tional to the needle’s speed of movement but not to the distance it has travelled. This signal is processed directly in an evaluation circuit (Fig. 12). When a given threshold voltage is ex- ceeded, this serves as the signal to the evaluation circuit for the start of injection. Nozzles and nozzle holders 53 Needle-motion sensor in a two-spring nozzle holder for direct-injection (DI) engines 1 Adjusting pin, 2 Terminal, 3 Current coil, 4 Pressure pin, 5 Spring seat. X Overlap length. 2 1 X 3 4 5 Two-spring nozzle holder with needle-motion sensor for direct-injection (DI) engines 1 Nozzle-holder body, 2 Needle-motion sensor, 3 Spring 1, 4 Guide element, 5 Spring 2, 6 Pressure pin, 7 Nozzle-retaining nut. 1 2 3 4 5 6 7 U M K 15 88 D Comparison between a needle-lift curve and the corresponding signal-voltage curve of the needle-motion sensor a Needle-lift- sensor signal Needle- motion- sensor signal Start-of-injection signal Theshold voltage N ee dl e lif t S ig na l v ol ta ge b °cks Fig. 12 U M K 14 27 E Fig. 14 U M K 15 29 Y Fig. 13 U M K 15 88 Y Mechanical diesel-engine speed control (mechanical governing) registers a wide variety of different operating statuses and permits high-quality A/F mixture formation. The Electronic Diesel Control (EDC) takes additional requirements into ac- count. By applying electronic measure- ment, highly-flexible electronic data pro- cessing, and closed control loops with electric actuators, it is able to process mechanical influencing variables which it was impossible to take into account with the previous purely mechanical control (governing) system. The EDC permits data to be exchanged with other electronic systems in the vehicle (for instance, traction control system (TCS), and electronic transmis- sion-shift control). In other words, it can be integrated completely into the overall vehicle system. System blocks The electronic control is divided into three system blocks (Fig. 1): 1. Sensors for registering operating conditions. A wide variety of physical quantities are converted into electrical signals. 2. Electronic control unit (ECU) with microprocessors which processes the in- Axial-piston distributor pumps, VE-EDC 54 Electronic Diesel Control (EDC): System blocks Needle-motion sensor Temperature sensors (water, air, fuel) Sensor for control-collar position Air-flow sensor Engine-speed sensor Vehicle-speed sensor Sensors Setpoint generators Glow control unit Transducer with EGR valve Fuel-injection pump ActuatorsECU Micro- pro- cessor Maps Start of injection Starting control EGR Engine shutoff Injected fuel quantity Atmospheric-pressure sensor Diagnosis Diagnosis displayAccelerator-pedal sensor Speed-selection lever Electronically-controlled axial-piston distributor fuel- injection pumps VE-EDC Fig. 1 U M K 04 67 E formation in accordance with specific control algorithms, and outputs corre- sponding electrical signals. 3. Actuators which convert the ECU’s electrical output signals into mechanical quantities. Components Sensors The positions of the accelerator and the control collar in the injection pump are registered by the angle sensors. These use contacting and non-contacting methods respectively. Engine speed and TDC are registered by inductive sensors. Sensors with high measuring accuracy and long-term stability are used for pres- sure and temperature measurements. The start of injection is registered by a sensor which is directly integrated in the nozzle holder and which detects the start of injection by sensing the needle move- ment (Figs. 2 and 3). Electronic control unit (ECU) The ECU employs digital technology. The microprocessors with their input and output interface circuits form the heart of the ECU. The circuitry is completed by the memory units and devices for the conversion of the sensor signals into computer-compatible quantities. The ECU is installed in the passenger com- partment to protect it from external in- fluences. There are a number of different maps stored in the ECU, and these come into effect as a function of such parameters as: Load, engine speed, coolant tem- perature, air quantity etc. Exacting de- mands are made upon interference immunity. Inputs and outputs are short- circuit-proof and protected against spu- rious pulses from the vehicle electrical system. Protective circuitry and me- chanical shielding provide a high level of EMC (Electro-Magnetic Compatibility) against outside interference. Electronic control for distributor pumps 55 Sensor signals 1 Untreated signal from the needle-motion sensor (NBF), 2 Signal derived from the NBF signal, 3 Untreated signal from the engine-speed signal, 4 Signal derived from untreated engine-speed signal, 5 Evaluated start-of-injection signal. Nozzle-and-holder assembly with needle-motion sensor (NBF) 1 Setting pin, 2 Sensor winding, 3 Pressure pin, 4 Cable, 5 Plug. 1 2 3 4 5 3 1 2 4 5 Fig. 2 Fig. 3 U M K 04 66 Y U M K 04 68 Y This clocked solenoid valve is used to modulate the positioning pressure at the timing-device piston, and this results in the dynamic behavior being comparable to that obtained with the mechanical start-of-injection timing. Because during engine overrun (with injection suppressed) and engine start- ing there are either no start-of-injection signals available, or they are inadequate, the controller is switched off and an open-loop-control mode is selected. The on/off ratio for controlling the solenoid valve is then taken from a control map in the ECU. Exhaust-gas recirculation (EGR) EGR is applied to reduce the engine’s toxic emissions. A defined portion of the exhaust gas is tapped-off and mixed with the fresh intake air. The engine’s intake-air quantity (which is proportional to the EGR rate) is measured by an air- flow sensor and compared in the ECU with the programmed value for the EGR map, whereby additional engine and injection data for every operating point are taken into account. In case of deviation, the ECU modifies the triggering signal applied to an electropneumatic transducer. This then adjusts the EGR valve to the correct EGR rate. Cruise control An evaluated vehicle-speed signal is compared with the setpoint signal input- ted by the driver at the cruise-control panel. The injected fuel quantity is then adjusted to maintain the speed selected by the driver. Supplementary functions The electronic diesel control (EDC) provides for supplementary functions which considerably improve the ve- hicle’s driveability compared to the mechanically governed injection pump. Active anti-buck damping With the active anti-buck damping (ARD) facility, the vehicle’s unpleasant longitudinal oscillations can be avoided. Idle-speed control The idle-speed control avoids engine “shake” at idle by metering the appro- priate amount of fuel to each individual cylinder. Safety measures Self-monitoring The safety concept comprises the ECU’s monitoring of sensors, actuators, and microprocessors, as well as of the limp-home and emergency functions provided in case a component fails. If malfunctions occur on important com- ponents, the diagnostic system not only warns the driver by means of a lamp in the instrument panel but also provides a facility for detailed trouble-shooting in the workshop. Limp-home and emergency functions There are a large number of sophisti- cated limp-home and emergency func- tions integrated in the system. For in- stance if the engine-speed sensor fails, a substitute engine-speed signal is generated using the interval between the start-of-injection signals from the needle-motion sensor (NBF). And if the injected-fuel quantity actuator fails, a separate electrical shutoff device (ELAB) switches off the engine. The warning lamp only lights up if important sensors fail. The Table below shows the ECU’s reaction should certain faults occur. Diagnostic output A diagnostic output can be made by means of diagnostic equipment, which can be used on all Bosch electronic automotive systems. By applying a special test sequence, it is possible to systematically check all the sensors and their connectors, as well as the correct functioning of the ECU’s. Axial-piston distributor pumps, VE-EDC 58 Advantages – Flexible adaptation enables optimi- zation of engine behavior and emission control. – Clear-cut delineation of individual func- tions: The curve of full-load injected fuel quantity is independent of governor characteristic and hydraulic configuration. – Processing of parameters which pre- viously could not be performed me- chanically (e.g., temperature-correction of the injected fuel quantity characteris- tic, load-independent idle control). – High degree of accuracy throughout complete service life due to closed con- trol loops which reduce the effects of tolerances. – Improved driveability: Map storage enables ideal control characteristics and control parameters to be established independent of hydraulic effects. These are then precisely adjusted during the optimisation of the complete engine/ vehicle system. Bucking and idle shake no longer occur. – Interlinking with other electronic sys- tems in the vehicle leads the way towards making the vehicle safer, more comfortable, and more economical, as well as increasing its level of environ- mental compatibility (e.g., glow systems or electronic transmission-shift control). The fact that mechanical add-on units no longer need to be accomodated, leads to marked reductions in the amount of space required for the fuel-injection pump. Engine shutoff As already stated on Page 40, the prin- ciple of auto-ignition as applied to the diesel engine means that the engine can only be switched off by interrupting its supply of fuel. When equipped with Electronic Diesel Control (EDC), the engine is switched off by the injected-fuel quantity actuator (Input from the ECU: Injected fuel quantity = Zero). As already dealt with, the separate electrical engine shutoff device serves as a standby shutoff in case the actuator should fail. Electrical shutoff device The electrical shutoff device is operated with the “ignition key” and is above all used to provide the driver with a higher level of sophistication and comfort. On the distributor fuel-injection pump, the solenoid valve for interrupting the supply of fuel is fitted in the top of the distributor head. With the diesel engine running, the inlet opening to the high- pressure chamber is held open by the en- ergized solenoid valve (the armature with sealing cone is pulled in). When the “igni- tion switch” is turned to “Off”, the power supply to the solenoid is interrupted and the solenoid de-energized. The spring can now push the armature with sealing cone onto the valve seat and close off the inlet opening to the high-pressure cham- ber so that the distributor plunger can no longer deliver fuel. Electronic control for distributor pumps 59 Failure Monitoring Reaction Warning Diagnostic of lamp output Correction Signal range Reduce injected ●sensors fuel quantity System- Signal range Limp-home sensors or emergency ● ● function (graded) Computer Program runtime Limp-home (self-test) or emergency ● ● function Fuel-quantity Permanent Engine shutoff ● ●actuator deviation Table 1. ECU reactions Prospects On the electronically-controlled distrib- utor pumps of the future, the electrical actuator mechanism with control collar for fuel metering will be superseded by a high-pressure solenoid valve. This will permit an even higher degree of flexibility in the fuel metering and in the variability of the start of injection. Design and construction This pump is of modular design. The field- proven distributor injection pump can thus be combined with a new electronically controlled fuel-metering system (Fig. 1). Basically speaking, the solenoid-valve- controlled distributor pump’s dimensions, installation conditions, and drivetrain in- cluding the pump’s cam drive, are identi- cal to those of the conventional distributor pump. The most important new compo- nents are: – Angle-of-rotation sensor (in the form of an incremental angle/time system [IWZ]) which is located in the injection pump on the driveshaft between the vane-type supply pump and the roller ring, – Electronic pump ECU, which is mount- ed as a compact unit on the top side of the pump and connected to the engine ECU, – High-pressure solenoid valve, installed in the center of the distributor head. With regard to its installation and hydrau- lic control, the timing device with pulse valve is identical to the one in the pre- vious electronically-controlled distributor pump. Components Angle-of-rotation sensor Angle-of-rotation detection uses the following components: Sensor, sensor retaining ring on the driveshaft, and the trigger wheel with a given tooth pitch. Detection is based upon the signals generated by the sensor. The pulses generated by the sensor are inputted to the ECU where they are pro- cessed by an evaluation circuit. The fact that the sensor is coupled to the pump’s roller ring ensures the correct assign- ment of the angular increment to the position of the cam when the roller ring is rotated by the timing device. Pump ECU The pump ECU is mounted on the upper side of the pump and uses hybrid tech- niques. In addition to the mechanical loading with which it is confronted in the vehicle's under-hood environment, the pump must also fulfill the following assignments: – Data exchange with the separately mounted engine ECU via the serial bus system, – Evaluation of the signal from the angle-of-rotation sensor (IWZ), – Triggering of the high-pressure sol- enoid valve, – Triggering of the timing device. Maps are stored in the pump ECU which not only take into account the setting points for the particular vehicle applica- tion and certain engine characteristics, but also permit the plausibility of the re- ceived signals to be checked. In addition, they form the basis for defining a number of different computational values. Axial-piston distributor pumps, VE-MV 60 Solenoid-valve-controlled axial-piston distributor fuel-injection pumps VE-MV Flame glow plug The flame glow plug burns fuel to heat the intake air. Normally, the injection system’s supply pump delivers fuel to the flame plug through a solenoid valve. The flame plug’s connection fitting is pro- vided with a filter, and a metering device which permits passage of precisely the correct amount of fuel appropriate to the particular engine. This fuel then evaporates in an evaporator tube sur- rounding the tubular heating element and mixes with the intake air. The resulting mixture ignites on the 1,000°C heating element at the flame-plug tip. Glow control unit For triggering the glow plugs, the glow control unit (GZS) is provided with a power relay and a number of electronic switching blocks. These, for instance, control the glow duration of the glow plugs, or have safety and monitoring functions. Using their diagnosis func- tions, more sophisticated glow control units are also able to recognise the failure of individual glow plugs and inform the driver accordingly. Multiple plugs are used as the control inputs to the ECU. In order to avoid voltage drops, the power supply to the glow plugs is through suitable threaded pins or plugs. Functional sequence The diesel engine’s glow plug and starter switch, which controls the preheat and starting sequence, functions in a similar manner to the ignition and starting switch on the spark-ignition (SI) engine. Switching to the “Ignition on” position starts the preheating process and the glow-plug indicator lamp lights up. This extinguishes to indicate that the glow plugs are hot enough for the engine to start, and cranking can begin. In the following starting phase, the drop- lets of injected fuel ignite in the hot, com- pressed air. The heat released as a result leads to the initiation of the combustion process (Fig. 3). In the warm-up phase following a suc- cessful start, post-heating contributes to faultless engine running (no misfiring) and therefore to practically smokeless engine run-up and idle. At the same time, when the engine is cold, pre- heating reduces combustion noise. A glow-plug safety switchoff prevents battery discharge in case the engine cannot be started. The glow-control unit can be coupled to the ECU of the Electronic Diesel Control (EDC) so that information available in the EDC control unit can be applied for optimum control of the glow plugs in accordance with the particular operating conditions. This is yet another possibility for reducing the levels of blue smoke and noise. Sheathed- element glow plugs, Flame glow plugs 63 Sheathed-element glow plugs: Temperature-time diagram 1 S-RSK, 2 GSK2. Typical preheating sequence 1 Glow-plug and starter switch, 2 Starter, 3 Glow-plug indicator lamp, 4 Load switch, 5 Glow plugs, 6 Self-sustained engine operation, tv Pre-heating time, tS Ready to start, tN Post-heating time. tV tS tN 1 2 3 4 5 6 Time t 0 10 20 30 40 50 650 750 850 950 1,050 1,150 s °C 1 2 Time t T em pe ra tu re Fig. 2 U M S 06 88 E Fig. 3 U M S 06 67 -1 E (4.0) 1 987 722 164 KH/PDI-04.99-En The Program Order Number Gasoline-engine management Emission Control (for Gasoline Engines) 1 987 722 102 Gasoline Fuel-Injection System K-Jetronic 1 987 722 159 Gasoline Fuel-Injection System KE-Jetronic 1 987 722 101 Gasoline Fuel-Injection System L-Jetronic 1 987 722 160 Gasoline Fuel-Injection System Mono-Jetronic 1 987 722 105 Ignition 1 987 722 154 Spark Plugs 1 987 722 155 M-Motronic Engine Management 1 987 722 161 ME-Motronic Engine Management 1 987 722 178 Diesel-engine management Diesel Fuel-Injection: An Overview 1 987 722 104 Diesel Accumulator Fuel-Injection System Common Rail CR 1 987 722 175 Diesel Fuel-Injection Systems Unit Injector System / Unit Pump System 1 987 722 179 Radial-Piston Distributor Fuel-Injection Pumps Type VR 1 987 722 174 Diesel Distributor Fuel-Injection Pumps VE 1 987 722 164 Diesel In-Line Fuel-Injection Pumps PE 1 987 722 162 Governors for Diesel In-Line Fuel-Injection Pumps 1 987 722 163 Automotive electrics/Automotive electronics Alternators 1 987 722 156 Batteries 1 987 722 153 Starting Systems 1 987 722 170 Electrical Symbols and Circuit Diagrams 1 987 722 169 Lighting Technology 1 987 722 176 Safety, Comfort and Convenience Systems 1 987 722 150 Driving and road-safety systems Compressed-Air Systems for Commercial Vehicles (1): Systems and Schematic Diagrams 1 987 722 165 Compressed-Air Systems for Commercial Vehicles (2): Equipment 1 987 722 166 Brake Systems for Passenger Cars 1 987 722 103 ESP Electronic Stability Program 1 987 722 177 Automotive electric/electronic systems Safety, Comfort and Convenience Systems Technical Instruction æ Æ Automotive Electric/Electronic Systems Lighting Technology Technical Instruction æ Æ Vehicle safety systems for passenger cars ESP Electronic Stability Program Technical Instruction æ Æ Engine management for diesel engines Radial-Piston Distributor Fuel-injection Pumps Type VR Technical Instruction æ Æ Electronic engine management for diesel engines Diesel Acumulator Fuel-Injection System Common Rail Technical Instruction æ Æ Engine management for spark-ignition engines Emission Control Technical Instruction æ Æ Gasoline-engine management ME-Motronic Engine Management Technical Instruction æ Æ Engine management for spark-ignition engines Spark Plugs Technical Instruction æ Æ Brake systems for passenger cars Brake Systems Technical Instruction æ Æ