Land Rover Diesel Distributor Pumps Bosch Bosch Manual
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Fuel-injection techniques 19Distributor 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. 56 1 2 3 2 4 UT OT OT = TDC UT = BDC UT OTUT UT Fig. 10 UMK0329Y
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 1Control collar, 2Distributor head, 3Distributor plunger, 4Delivery-valve holder, 5Delivery-valve. 1 2 3 4 5 Fig. 11 UMK0335Y
Delivery valve with return-flow restriction Precise pressure relief in the lines is necessary at the end of injection. This though generates pressure waves which are reflected at the delivery valve. These cause the delivery valve to open again, or cause vacuum phases in the high-pressure line. These pro- cesses result in post-injection of fuel with attendant increases in exhaust emis- sions or cavitation and wear in the injec- tion line or at the nozzle. To prevent such harmful reflections, the delivery valve is provided with a restriction bore which is only effective in the direction of return flow. This return-flow restriction com- prises a valve plate and a pressure spring so arranged that the restriction is ineffective in the delivery direction, whereas in the return direction damping comes into effect (Fig. 12). Constant-pressure valve With high-speed direct-injection (Dl) engines, it is often the case that the “retraction volume” resulting from the retraction piston on the delivery-valve plunger does not suffice to reliably prevent cavitation, secondary injection, and combustion-gas blowback into the nozzle-and-holder assembly. Here, constant-pressure valves are fitted which relieve the high-pressure system (injection line and nozzle-and-holder assembly) by means of a single-acting non-return valve which can be set to a given pressure, e.g., 60 bar (Fig. 13). High-pressure lines The pressure lines installed in the fuel- injection system have been matched precisely to the rate-of-discharge curve and must not be tampered with during service and repair work. The high-pres- sure lines connect the injection pump to the injection nozzles and are routed so that they have no sharp bends. In automotive applications, the high- pressure lines are normally secured with special clamps at specific intervals, and are made of seamless steel tubing.Fuel-injection techniques 21 Delivery valve with return-flow restriction 1Delivery-valve holder, 2Return-flow restriction, 3Delivery-valve spring, 4Valve holder, 5Piston shaft, 6Retraction piston.Constant-pressure valve 1Delivery-valve holder, 2Filler piece with spring locator, 3Delivery-valve spring, 4Delivery-valve plunger, 5Constant-pressure valve, 6Spring seat, 7Valve spring (constant-pressure valve), 8Setting sleeve, 9Valve holder, 10Shims. 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 10 Fig. 12 UMK1183Y Fig. 13 UMK1184Y
Mechanical engine- speed control (governing) Application The driveability of a diesel-powered vehicle can be said to be satisfactory when its engine immediately responds to driver inputs from the accelerator pedal. Apart from this, upon driving off the engine must not tend to stall. The engine must respond to accelerator- pedal changes by accelerating or decel- erating smoothly and without hesitation. On the flat, or on a constant gradient, with the accelerator pedal held in a given position, the vehicle speed should also remain constant. When the pedal is released the engine must brake the vehicle. On the diesel engine, it is the injection pump’s governor that ensures that these stipulations are complied with. The governor assembly comprises themechanical (flyweight) governor and the lever assembly. It is a sensitive control device which determines the position of the control collar, thereby defining the delivery stroke and with it the injected fuel quantity. It is possible to adapt the governor’s response to setpoint changes by varying the design of the lever assembly (Fig. 1). Governor functions The basic function of all governors is the limitation of the engine’s maximum speed. Depending upon type, the gov- ernor is also responsible for keeping certain engine speeds constant, such as idle speed, or the minimum and maximum engine speeds of a stipulated engine-speed range, or of the complete speed range, between idle and maxi- mum speed. The different governor types are a direct result of the variety of governor assignments (Fig. 2): – Low-idle-speed governing: The diesel engine’s low-idle speed is controlled by the injection-pump governor. Axial-piston distributor pumps 22 Distributor injection pump with governor assembly, comprising flyweight governor and lever assembly Fig. 1 UMK0343Y
– 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 nvaries 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 afunction 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. d=n lo– nvonvo or expressed in %: d=n lo– nvo .100%nvo where d= Speed droop n lo= High idle (maximum) speed n vo= 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 aMinimum-maximum-speed governor, bVariable-speed governor. 1Start quantity, 2 Full-load delivery, 3Torque control (positive), 4Full-load speed regulation, 5Idle. 23 4 1 5 23 4 1 5 a b 0 Engine speed min –1 mm Control-collar travel mm Control-collar travel Fig. 2 UMK0344E
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 thegovernor 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 M 2. 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 aStart position, bIdle position. 1Flyweights, 2Sliding sleeve, 3 Tensioning lever, 4Starting lever, 5Starting spring, 6Control collar, 7 Distributor-plunger cutoff port, 8Distributor plunger, 9Idle-speed adjusting screw, 10Engine-speed control lever, 11Control lever, 12Control-lever shaft, 13Governor spring, 14Retaining pin, 15Idle spring. aStarting-spring travel, cIdle-spring travel, h 1max. working stroke (start); h2min. working stroke (idle): M 2fulcrum for 4 and 5. 1 1 23 4 5 M 2 6 7 8h 1h2 12 13 14c 15 M 2 10 119 ab a Fig. 3 UMK0346Y
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 M 2and 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 cand 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 25Characteristic 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 n LNfollowing engine start-up (no-load), L–B: Engine acceleration phase after shifting the engine-speed control lever from idle to a given required speed n c, 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 n cin the part-load range, E: Engine speed n LT, after removal of load from the engine with the position of the engine- speed control-lever remaining unchanged. S BB Full load L ENo-load 0 500 1,000 1,500 2,000 min– 1 Engine speed n mm Control-collar travel s nAnCnLTnVHnLO A C Fig. 4 UMK0348E
Example (Fig. 5): Using the accelerator pedal, the driver sets the engine-speed control lever to a specific position corresponding to a desired (higher) speed. As a result of this adjustment of the control-lever position, the governor spring is ten- sioned by a given amount, with the result that the governor-spring force exceeds the centrifugal force of the flyweights and causes the start lever and the tensioning lever to pivot around fulcrum M 2. Due to the mechanical transmission ratio designed into the system, the control collar shifts in the “Full-load” direction. As a result, the delivery quantity is increased and the engine speed rises. This causes the flyweights to generate more force which, through the sliding sleeve, opposes the governor-spring force. The control collar remains in the “Full- load” position until a torque balance occurs. If the engine speed continues to increase, the flyweights separate even further, the sliding-sleeve force prevails,and as a result the start and tensioning levers pivot around M 2and push the control collar in the “Stop” direction so that the control port is opened sooner. It is possible to reduce the delivery quantity to “zero” which ensures that engine-speed limitation takes place. This means that during operation, and as long as the engine is not overloaded, every position of the engine-speed control lever is allocated to a specific speed range between full-load and zero. The result is that within the limits set by its speed droop, the governor maintains the desired speed (Fig. 4). If the load increases to such an extent (for instance on a gradient) that even though the control collar is in the full- load position the engine speed con- tinues to drop, this indicates that it is impossible to increase fuel delivery any further. This means that the engine is overloaded and the driver must change down to a lower gear. Axial-piston distributor pumps 26 Fig. 5: Variable-speed governor, operation under load aGovernor function with increasing engine speed, bwith falling engine speed. 1Flyweights, 2Engine-speed control lever, 3Idle-speed adjusting screw, 4Governor spring, 5Idle spring, 6Start lever, 7Tensioning lever, 8Tensioning-lever stop, 9Starting spring, 10Control collar, 11Adjusting screw for high idle (maximum) speed, 12Sliding sleeve, 13Distributor-plunger cutoff bore, 14Distributor plunger. h 1Working stroke, idle, h2Working stroke, full-load, M2fulcrum for 6 and 7. 1 16 7 9 M 2 10 4 h 1h2 M2 ab 2 3 5 8 12 14 13 11 Fig. 5 UMK0349Y
Overrun (engine braking) During downhill operation the engine is “driven” by the vehicle, and engine speed tends to increase. This causes the flyweights to move outwards so that the sliding sleeve presses against the tensioning and start levers. Both levers change their position and push the control collar in the direction of less fuel delivery until a reduced fuel-delivery figure is reached which corresponds to the new loading level. At the extreme, the delivery figure is zero. Basically, with the variable-speed governor, this process applies for all settings of the engine-speed control lever, when the engine load or engine speed changes to such an extent that the control collar shifts to either its full-load or stop position.Minimum-maximum-speed governor The minimum-maximum-speed gover- nor controls (governs) only the idle (minimum) speed and the maximum speed. The speed range between these points is directly controlled by the ac- celerator pedal (Fig. 6). Design and construction The governor assembly with flyweights, and the lever configuration, are com- parable with those of the variable-speed governor already dealt with. The main difference lies in the governor spring and its installation. It is in the form of a compression spring and is held in a guide element. Tensioning lever and governor spring are connected by a retaining pin. Starting With the engine at standstill, the fly- weights are also stationary and the sliding sleeve is in its initial position. This enables the starting spring to push the flyweights to their inner position through the starting lever and the sliding sleeve. On the distributor plunger, the control collar is in the start-quantity position. Idle control Once the engine is running and the accelerator pedal has been released, the engine-speed control lever is pulled back to the idle position by its return spring. The centrifugal force generated by the flyweights increases along with engine speed (Fig. 7a) and the inner flyweight legs push the sliding sleeve up against the start lever. The idle spring on the tensioning lever is responsible for the controlling action. The control collar is shifted in the direction of “less delivery” by the pivoting action of the start lever, its position being determined by interaction between centrifugal force and spring force. Mechanical governing 27 Characteristic curves of the minimum- maximum-speed governor with idle spring and intermediate spring a Starting-spring range, b Range of starting and idle spring, d Intermediate-spring range, f Governor-spring range. Engine speed nmin–1 mm Control-collar travel s a b d Uncontrolled f Full load No-load Fig. 6 UMK0351E
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 aIdle setting, bFull-load setting. 1Flyweights, 2Engine-speed control lever, 3Idle-speed adjusting screw, 4Governor spring, 5Intermediate spring, 6Retaining pin, 7Idle spring, 8Start lever,9Tensioning lever, 10Tensioning-lever stop, 11 Starting spring, 12 Control collar, 13Full-load speed control, 14Sliding sleeve, 15Distributor plunger cutoff bore, 16Distributor plunger. aStart and idle-spring travel, bIntermediate-spring travel, h 1Idle working stroke, h2Full-load working stroke, M 2fulcrum for 8 and 9. 1 1 M 2 12 4 h 1 ab 2 3 5 14 7 9 11 10 13 h 2 b a6 8 15 16 M2 Fig. 7 UMK0352Y