Land Rover Diesel Distributor Pumps Bosch Bosch Manual
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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) 1Governor spring, 2Sliding sleeve, 3Tensioning lever, 4Start lever, 5Control collar, 6Distributor plunger, 7Governor shaft, 8Flyweights. M 2Pivot point for 3 and 4. 3 4 M 2 5 1 2 6 87 Fig. 9 UMK0369Y
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 controlport 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 700 mbar (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) aStart position (initial position), b Full-load position shortly before the control port is opened, cControl port opened, pressure reduction in pump interior. 1Longitudinal bore in the governor shaft, 2Governor shaft, 3Sliding-sleeve control port, 4Sliding-sleeve, 5Governor-shaft transverse passage, 6Control edge of the groove in the governor shaft, 7Governor-shaft transverse passage. 57 6 4321 a b c Fig. 10 UMK0370Y
Cold-start compensation The diesel engine’s cold-start charac- teristics are improved by fitting a cold- start compensation module which shifts the start of injection in the “advance” direction. Operation is triggered either by the driver using a bowden cable in the cab, or automatically by means of a temperature-sensitive advance mech- anism (Fig. 11). Mechanical cold-start accelerator (KSB) on the roller ring Design and construction The KSB is attached to the pump housing, the stop lever being connected through a shaft to the inner lever on which a ball pin is eccentrically mounted. The ball pin’s head extends into the roller ring (a version is available in which the advance mechanism en- gages in the timing-device piston). The stop lever’s initial position is defined by the stop itself and by the helical coiled spring. Attached to the top of the stop lever is a bowden cable which serves as the connection to the manual or to the automatic advance mechanism. The automatic advance mechanism is mounted on the distributor pump, where- as the manual operating mechanism is in the driver’s cab (Fig. 12). Method of operation Automatically and manually operated cold-start accelerators (KSB) differ only with regard to their external advance mechanisms. The method of operation is identical. With the bowden cable not pulled, the coil spring pushes the stop lever up against the stop. Ball pin and roller ring are in their initial position. The force applied by the bowden cable Add-on modules and shutoff devices 41 Mechanical cold-start accelerator (KSB), advance mechanism with automatic operation (cold-start position) 1Clamp, 2Bowden cable, 3Stop lever, 4Coil spring, 5KSB advance lever, 6Control device sensitive to the temperature of the coolant and the surroundings. Mechanical cold-start accelerator (KSB) engaging in roller ring (cold-start position) 1Lever, 2Access window, 3Ball pin, 4Longitudinal slot, 5Pump housing, 6Roller ring, 7Roller in the roller ring, 8Timing-device piston, 9Torque-control pin, 10Sliding block. 11Timing- device spring, 12Shaft, 13 Coil spring. 12 345 6 1 5 6 7 8234 91011 1213 Fig. 11Fig. 12 UMK0373Y UMK0372Y
causes the stop lever, the shaft, the inner lever and the ball pin, to swivel and change the roller ring’s setting so that the start of delivery is advanced. The ball pin engages in a slot in the roller ring, which means that the timing-device piston cannot rotate the roller ring any further in the “advance” direction until a given engine speed has been exceeded. In those cases in which the KSB is triggered by the driver from the cab (timing-device KSB), independent of the advance defined by the timing device (a), an advance of approx. 2.5° camshaft is maintained (b), as shown in Fig. 13. With the automatically operated KSB, this advance depends upon the engine temperature or ambient temperature. The automatic advance mechanism uses a control device in which a temperature- sensitive expansion element converts the engine temperature into a stroke move- ment. The advantage of this method is that for a given temperature, the optimum start of delivery (or start of injection) is always selected. There are a number of different lever configurations and operating mecha- nisms in use depending upon the direction of rotation, and on which side the KSB is mounted.Temperature-controlled idle-speed increase (TLA) The TLA is also operated by the control device and is combined with the KSB. Here, when the engine is cold, the ball pin at the end of the elongated KSB advance lever presses against the en- gine-speed control lever and lifts it away from the idle-speed stop screw. The idle speed increases as a result, and rough running is avoided. When the engine has warmed up, the KSB advance lever abuts against its stop and, as a result, the engine-speed control lever is also up against its stop and the TLA is no longer effective (Fig. 14). Hydraulic cold-start accelerator Advancing the start of injection by shifting the timing-device piston has only limited applications. In the case of the hydraulic start-of-injection advance, the speed-dependent pump interior pressure is applied to the timing-device piston. In order to implement a start- of-injection advance, referred to the conventional timing-device curve, the pump interior pressure is increased automatically. To do so, the automatic control of pump interior pressure is modified through a bypass in the pressure-holding valve.Axial-piston distributor pumps 42 Mechanical cold-start accelerator (automatically controlled) with temperature- dependent idle-speed increase 1Engine-speed control lever, 2Ball pin, 3KSB advance lever, 4Stop.Effect of the mechanical cold-start accelerator (KSB) aTiming-device advance, b Minimum advance (approx. 2.5° camshaft). 0 0 Pump speed p 2.5° a b Injection-timing advance ¡cms min –1 1 2 3 4 Fig. 13 UMK0374E Fig. 14 UMK0377Y
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 43Effect of the hydraulic cold-start accelerator (KSB) 1Injection-timing advance. Hydraulic cold-start accelerator (KSB) 11Pressure-control valve, 12Valve plunger, 13Restriction passage, 14Internal pressure, 15Fuel-supply pump, 16Electrically heated expansion element, 17KSB ball valve, 18Pressureless fuel return, 19KSB control valve, adjustable, 10Timing device. 1 2 6 7 8 9 103 4 5 1 Pump speed p Injection-timing advance ¡cms min –1 Fig. 15 UMK1195Y Fig. 16 UMK0379E
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 innerstop lever pushes against the start lever of the governor-lever mechanism. This swivels around its pivot point M 2and 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 1Outer stop lever, 2Start lever, 3Control collar, 4Distributor plunger, 5Inner stop lever, 6Tensioning lever, 7Cutoff port. M 2Pivot point for 2 and 6. Electrical shutoff device (pull solenoid) 1Inlet passage, 2Distributor plunger, 3Distributor head, 4Push or pull solenoid, 5High-pressure chamber. 1 3 4 5 2 5 6 M 2 7 4 3 1 2 Fig. 17 Fig. 18 UMK0382Y UMK0380Y
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 andcoupling, 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 measur ing 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 1Calibrating-oil tank, 2Injection pump, 3Calibrating nozzle, 4Measuring cell, 5Pulse counter, 6Display monitor. M 1 4 5 2 36 Fig. 18 UWT0059Y
Nozzles and nozzle holders The injection nozzles and their respec- tive nozzle holders are vitally important components situated between the in-line injection pump and the diesel engine. Their assignments are as follows: – Metering the injection of fuel, – Management of the fuel, – Defining the rate-of-discharge curve, – Sealing-off against the combustion chamber. Considering the wide variety of com- bustion processes and the different forms of combustion chamber, it is necessary that the shape, “penetration force”, and atomization of the fuel spray injected by the nozzle are adapted to the prevailing conditions. This also applies to the injec- tion time, and the injected fuel quantity per degree camshaft. Since the design of the nozzle-holder combination makes maximum use of standardized components and assem- blies, this means that the required flexi- bility can be achieved with a minimum of components. The following nozzles and nozzle holders are used with in-line injec- tion pumps: – Pintle nozzles (DN..) for indirect-injec- tion (IDI) engines, and – Hole-type nozzles (DLL../DLSA..) for direct-injection (DI) engines, – 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. Pintle nozzles Application Pintle nozzles are used with in-line in- jection pumps on indirect-injection en- gines (pre-chamber and whirl-chamber engines). In this type of diesel engine, the air/fuel mixture is for the most part formed by the air’s vortex work. The injected fuel spray serves to support this mixture-formation process. The following types of pintle nozzle are available: – Standard pintle nozzles (Fig. 1), – Throttling pintle nozzles, and – Flat-cut pintle nozzles (Fig. 2). Design and construction All pintle nozzles are of practically identi- cal design, the only difference being in the pintle’s geometry: Standard pintle nozzle On the standard pintle nozzle, the nozzle needle is provided with a pintle which extends into the injection orifice of the nozzle body in which it is free to move with a minimum of play. The injection spray can be matched to the engine’s requirements by appropriate choice of dimensions and pintle designs. Axial-piston distributor pumps 46 Standard pintle nozzle 1Lift stop surface, 2Ring groove, 3Needle guide, 4Nozzle-body shaft, 5Pressure chamber, 6Pressure shoulder, 7Seat lead-in, 8Inlet port, 9Nozzle-body shoulder, 10Nozzle-body collar, 11Sealing surface, 12 Pressure shaft, 13Pressure-pin contact surface. 1 2 4 5 68 9 10 11 12 13 7 3 Fig. 1 UMK1390Y
Throttling pintle nozzle The throttling pintle nozzle is a pintle nozzle with special pintle dimensions. The special pintle design serves to define the shape of the rate-of-discharge curve. When the nozzle needle lifts it first of all opens a small annular gap so that only a small amount of fuel is injected (throttling effect). As needle lift increases (due to pressure rise), the spray orifice is opened increas- ingly until the major portion of the injec- tion (main injection) takes place towards the end of needle lift. Since the pressure in the combustion chamber rises less sharply, this shaping of the rate-of-injec- tion curve leads to “softer” combustion. This results in quieter combustion in the part-load range. In other words, it is possible to shape the required rate-of- discharge curve by means of the pintle shape, the characteristic of the nozzle needle’s spring, and the throttling gap.Flat-cut pintle nozzle This nozzle’s pintle has a ground surface which opens a flow cross-section in addi- tion to the annular gap when the pintle opens (only slight needle lift). The result- ing increased flow volume prevents de- posits forming in this flow channel. This is the reason why flat-cut pintle nozzles coke-up far less, and any coking which does take place is more uniform. The annular gap between spray orifice and throttling pintle is very small (less than 10 mm). Very often, the flat-cut pintle sur- face is parallel to the nozzle-needle axis. Referring to Fig. 3, with an additional inclined cut on the pintle, the gradient of the injected-fuel-quantity curve’s flat por- tion can be increased so that the tran- sition to full nozzle opening is less abrupt. Specially shaped pintles, such as the “radius” or “profile surface” types, can be applied to match the flow curve to engine-specific requirements. Part-load noise and vehicle driveability are both improved as a result. Nozzles and nozzle holders 47 Flat-cut pintle nozzle a Side view, bFront view. 1 Needle seat, 2Nozzle-body floor, 3Throttling pintle, 4Flat cut, 5Injection orifice, 6Profiled pintle, 7Total overlap, 8Cylindrical overlap, 9Nozzle-body seat. 1 a b2 69 7 8 3 4 5 Flow quantity as a function of needle lift and nozzle version 1Throttling pintle nozzle, 2Throttling pintle nozzle with inclined cut on pintle (flat-cut pintle nozzle) l/h 300 200 100 0 Flow quantity 0 0.221 0.4 Needle lift0.6 0.8 mm Fig. 2 UMK1391Y Fig. 3 UMK1397E
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: –T ype Pwith 4 mm needle diameter, and –T ype Swith 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 gSpray-cone offset angle, d Spray cone. g d Fig. 4 UMK1402Y