Land Rover Diesel Distributor Pumps Bosch Bosch Manual
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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 9 UMK0318Y 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 modulesfacilitate 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 1Vane-type fuel-supply pump with pressure regulating valve: Draws in fuel and generates pressure inside the pump. 2High-pressure pump with distributor: Generates injection pressure, delivers and distributes fuel. 3Mechanical (flyweight) governor: Controls the pump speed and varies the delivery quantity within the control range. 4Electromagnetic fuel shutoff valve: Interrupts the fuel supply. 5Timing device: Adjusts the start of delivery (port closing) as a function of the pump speed and in part as a function of the load. 1 524 3 Fig. 3 UMK0317Y
holders. If the distributor pump is also equipped with a mechanical fuel shutoff device this is mounted in the governor cover. The governor assembly comprising the flyweights and the control sleeve is driven by the drive shaft (gear with rubber damper) via a gear pair. The governor linkage mechanism which consists of the control, starting, and tensioning levers, can pivot in the housing. The governor shifts the position of the control collar on the pump plunger. On the governor mechanism’s top side is the governor spring which engages with the external control lever through the control-lever shaft which is held in bearings in the governor cover. The control lever is used to control pump function. The governor cover forms the top of the distributor pump, andalso contains the full-load adjusting screw, the overflow restriction or the overflow valve, and the engine-speed adjusting screw. The hydraulic injection timing device is located at the bottom of the pump at right angles to the pump’s longitudinal axis. Its operation is in- fluenced by the pump’s internal pressure which in turn is defined by the vane-type fuel-supply pump and by the pres- sure-regulating valve. The timing device is closed off by a cover on each side of the pump (Fig. 4).Fuel-injection techniques 11 The subassemblies and their configuration 1Pressure-control valve, 2Governor assembly, 3Overflow restriction, 4Distributor head with high-pressure pump, 5Vane-type fuel-supply pump, 6Timing device, 7Cam plate, 8Electromagnetic shutoff valve. 5 67 4 8 3 1 2 Fig. 4 UMK0319Y
Pump drive The distributor injection pump is driven by the diesel engine through a special drive unit. For 4-stroke engines, the pump is driven at exactly half the engine crankshaft speed, in other words at camshaft speed. The VE pump must be positively driven so that it’s drive shaft is synchronized to the engine’s piston movement. This positive drive is implemented by means of either toothed belts, pinion, gear wheel or chain. Distributor pumps are available for clockwise and for counter-clockwise rotation, whereby the injection sequence differs depending upon the direction of rotation. The fuel outlets though are always supplied with fuel in their geometric sequence, and are identified with the letters A, B, C etc. to avoid confusion with the engine-cylinder numbering. Distributor pumps are suitable for en- gines with up to max. 6 cylinders. Fuel supply and delivery Considering an injection system with distributor injection pump, fuel supply and delivery is divided into low-pressure and high-pressure delivery (Fig. 1). Low-pressure stage Low-pressure delivery The low-pressure stage of a distributor- pump fuel-injection installation com- prises the fuel tank, fuel lines, fuel filter, vane-type fuel-supply pump, pressure- control valve, and overflow restriction. The vane-type fuel-supply pump draws fuel from the fuel tank. It delivers a virtually constant flow of fuel per revolution to the interior of the injection pump. A pressure-control valve is fitted to ensure that a defined injection-pump interior pressure is maintained as a function of supply-pump speed. Using this valve, it is possible to set a defined pressure for a given speed. The pump’s Axial-piston distributor pumps 12 Fuel supply and delivery in a distributor-pump fuel-injection system 1Fuel tank, 2Fuel line (suction pressure), 3Fuel filter, 4Distributor injection pump, 5High-pressure fuel-injection line, 6Injection nozzle, 7Fuel-return line (pressureless), 8Sheathed-element glow plug. 2 3 45 6 87 r s ‚ ƒ „ ‘ ’ “ ” ¡ ¢ £ ¯°± ² ¾ ¿ÀÁ Î ÏÐ ß 1 Fig. 1 UMK0316Y
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 theinjection 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 whenFuel-injection techniques 13 Interaction of the fuel-supply pump, pressure-control valve, and overflow restriction 1Drive shaft, 2Pressure-control valve, 3Eccentric ring, 4Support ring, 5Governor drive, 6Drive-shaft dogs, 7Overflow restriction, 8Pump housing. 12345678 Fig. 2 UMK0321Y
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 14Vane-type fuel-supply pump for low- pressure delivery 1Inlet, 2Outlet. 12 UMK0320Y Fig. 4 UMK0324YFig. 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, centrifugalforce 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 valveOverflow restriction Fig. 5 UMK0322Y Fig. 6 UMK0323Y
The spring’s initial tension can be adjusted to set the valve opening pressure. Overflow restriction The overflow restriction (Figure 6) is screwed into the injection pump’s governor cover and connected to the pump’s interior. It permits a variable amount of fuel to return to the fuel tank through a narrow passage. For this fuel, the restriction represents a flow resistance that assists in maintaining the pressure inside the injection pump. Being as inside the pump a precisely defined pressure is required as a function of pump speed, the overflow restriction and the flow-control valve are pre- cisely matched to each other.High-pressure stage The fuel pressure needed for fuel injection is generated in the injection pump’s high-pressure stage. The pressurized fuel then travels to the injection nozzles through the delivery valves and the fuel-injection tubing. Distributor-plunger drive The rotary movement of the drive shaft is transferred to the distributor plunger via a coupling unit (Fig. 7), whereby the dogs on cam plate and drive shaft engage with the recesses in the yoke, which is located between the end of the drive shaft and the cam plate. The cam plate is forced against the roller ring by a spring, and when it rotates the cam lobes riding on the ring’s rollers convert the purely rotational movement of the drive shaft into a rotating-reciprocating movement of the cam plate. The distributor plunger is held in the cam plate by its cylindrical fitting piece and is locked into position relative to the cam Axial-piston distributor pumps 16 Pump assembly for generation and delivery of high pressure in the distributor-pump interior Fig. 7 UMK0326Y
plate by a pin. The distributor plunger is forced upwards to its TDC position by the cams on the cam plate, and the two symmetrically arranged plunger- return springs force it back down again to its BDC position. The plunger-return springs abut at one end against the distributor head and at the other their force is directed to the plunger through a link element. These springs also prevent the cam plate jumping off the rollers during harsh acceleration. The lengths of the return springs are carefully matched to each other so that the plunger is not displaced from its centered position (Fig. 8).Cam plates and cam contours The cam plate and its cam contour in- fluence the fuel-injection pressure and the injection duration, whereby cam stroke and plunger-lift velocity are the decisive criteria. Considering the different combustion-chamber configurations and combustion systems used in the various engine types, it becomes imperative that the fuel-injection factors are individually tailored to each other. For this reason, a special cam-plate surface is generated for each engine type and machined into the cam-plate face. This defined cam plate is then assembled in the corresponding distributor pump. Since the cam-plate surface is specific to a given engine type, the cam plates are not interchangeable between the different VE-pump variants. Fuel-injection techniques 17Pump assembly with distributor head Generates the high pressure and distributes the fuel to the respective fuel injector. 1Yo k e , 2Roller ring, 3Cam plate, 4Distributor-plunger foot, 5Distributor plunger, 6Link element, 7Control collar, 8Distributor-head flange, 9Delivery-valve holder, 10Plunger-return spring, 4...8Distributor head. 4 5 6 7 10 8 91 2 3 Fig. 8 UMK0327Y
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 completedthese 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 UMK0328Y 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)