Injection pump
1. 2. 3. 4. 5. 6. 7. 8. 9.
Control lever Stop arm Control rack Pump element Delivery valve Delivery valve holder Delivery pipe to engine cylinder Smoke limiter Control rack stop for full load, with and without pressure from turbocharger 10. Pump coupling of steel disc type 11. Pump drive shaft 12. Pump gear
13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.
Timing gears Crankshaft gear Crankshaft Camshaft Roller tappet Cam for feed pump Fuel line from tank Feed pump Fuel line to filter Fuel line from filter Governor weights
Schematic diagram of injection pump, 14-litre engine, with centrifugal governor and smoke limiter
9-litre, 11-litre and 12-litre engines have no pump drive shaft 11 or pump coupling 10. Pump gear 12 is mounted on camshaft 16 and the injection pump is connected directly to the timing gears. Smoke limiter 8 is mounted on the governor housing, see also page 17, Smoke limiter.
Production engines are fitted with injection pumps from three different serial number series. The last four digits of the pump designation denote which type it is. Examples: PES 6P 120A 1320/5 RS3380 = 3000-pump PE 8P 120A720 LS7189-10 = 7100-pump PES 6P 120A 320 RS8046 = 8000-pump 3000 and 8000 pumps are used on 9-litre, 11-litre and 12-litre engines, 7100 pumps on 14-litre engines. The designation is given on a plate on the injection pump. See also ”injection equipment”. In the following descriptions, reference is made primarily to these pump number series.
a ~amount of fuel
The injection pump is connected to the pump drive shaft, which is part of the engine’s timing gear. On 9-litre and 11-litre engines, the injection pump is mounted directly on the timing gear housing, on 14-litre engines the pump drive shaft and steel disc coupling are used. The pump drive shaft is geared so that the pump is driven at half engine speed. The injection pump’s bearings, camshaft and tappets are lubricated with oil from the engine’s lubricating system The pump elements are lubricated by the fuel. The injection pump has a pump element for each engine cylinder. The pump elements always have the same stroke. The quantity of fuel injected is determined by how much the piston in the pump element is turned. The pump piston is turned by the control rack which is controlled by the governor. All pistons are turned at the same time and by the same amount. Fuel injection starts when the pump piston closes the spill- and inlet ports in the pump element. The pump piston has a diagonal helix edge. Fuel injection ceases when this helix edge passes the spill port in the pump cylinder.
Pump element and control rack, Bosch P Pump piston A. 0-feed groove B. Helix edge C. Leak-off return groove
Delivery valve Above each pump element is a delivery valve consisting of a valve housing 5 and valve piston 4. The valve piston is held against its seat 3 by a spring 2. The delivery valve opens and releases fuel into the delivery pipe when opening pressure is attained in the pump element. When fuel pressure drops after injection, the valve piston is forced back against its seat by the spring. When the delivery valve piston has closed, the available volume for the fuel in the delivery pipe increases. This lowers the pressure in the delivery pipe and injectors, reducing the risk of fuel dripping from the injectors. The change in capacity is adapted to the length of the delivery pipe and this length must never be changed. The delivery valve is held in the pump housing by the delivery valve holder 1, which is bolted to the housing from above.
1. Delivery valve holder 2. Valve spring 3. Valve seat
4. Valve piston 5. Valve housing
A) Closed B) Injection Delivery valve holder with delivery valve
Single-speed engines have delivery valves of 0-hole type, i.e. without idling hole.
Certain types of engine have delivery valve holders with a relief brake to counteract delivery pipe cavitation. When injection starts, the spring-loaded valve plate 3 is lifted and the fuel flows freely to the injector. At the end of injection, when the injector closes, a pressure wave is generated in the opposite direction. The valve plate is then pressed against its seat by the return spring 2 and the fuel flowing back is forced through the valve plate’s restrictor hole.
A) Delivery valve with idling hole B) Delivery valve without idling hole
1. 2. 3. 4.
A
B
Delivery valve holder Compression spring Valve plate Valve housing
Delivery valve holder with return restrictor hole
Pump element and delivery valve, principle of operation First phase of piston stroke: inlet port is exposed and fuel flows in.
Lower dead centre, fuel supply
Second phase of piston stroke: from bottom dead centre until the top of the piston closes the inlet.
Prestroke
Third phase of piston stroke: from when the top of the piston has closed the inlet ports until the inlet ports are opened by the helix edge. When the inlet ports are opened, the delivery valve closes and injection ceases.
Delivery stroke
Fourth phase of piston stroke: from when the spill port is opened until top dead centre.
Idle stroke
The axial groove is aligned with the port. In this position there is no fuel delivery. The piston is turned to this position to stop the engine. Note Not applicable to 8000 pumps with fuel shut-off valve
Non-delivery
Smoke limiter
General The smoke limiter limits control rack travel, giving a variable full load volume which is dependent on the turbo pressure in the intake manifold. This limitation considerably reduces the smoke in the exhaust, both during acceleration and when driving at full throttle at low engine speed when the turbocharger provides low charge pressure. A line connects the smoke limiter to the intake manifold and a diaphragm in the smoke limiter is actuated by changing pressure in the intake manifold.
14-litre engines, smoke limiter on the injection pump The smoke limiter is mounted at the front end of the injection pump, see figure on page 4. Via pushrod 4, movements of diaphragm 2 actuate angle arm 5 which, at low charge pressure, restricts the movement of control rack 8.
1. From intake manifold 2. Diaphragm 3. Spring
4. 5. 6. 7.
Pushrod Angle arm Full load stop Control rack
Position of control rack at low charge pressure. At sufficiently high pressure the angle arm, and with it the control rack, are stopped by full load stop 6.
Position of control rack at high charge pressure
9-litre, 11-litre and 12-litre engines, smoke limiter on governor housing The smoke limiter is mounted on the governor housing at the rear end of the injection pump, see figure on page 3. Below is a simple description of how the different types work. Their operation is described more extensively in the booklet “Mechanical governor�.
Smoke limiter, RQ governor
1. 2. 3. 4.
The pressure in intake manifold 1 actuates diaphragm 2 and pushrod 4. Movement of control rack 6 is restricted by pressure-dependent full load stop 5.
Inlet Diaphragm Spring Pushrod
5. Pressure-dependent full load stop 6. Control rack
Smoke limiter, RQ governor
Smoke limiter, RQV-K governor The pressure in intake manifold 1 actuates diaphragm 2 and pushrod 4. It thus controls pressuredependent full load stop 5, the shoulder 6 of which restricts the movement of the control rack (not shown). 1. 2. 3. 4.
Inlet Diaphragm Spring Pushrod
5. Pressure-dependent full load stop 6. Shoulder
Smoke limiter, RQV-K governor
Smoke limiter, RSV governor The pressure in intake manifold 1 actuates diaphragm 2 and pushrod 4. Movement of control rack 6 is restricted by pressure-dependent full load stop 5.
1. 2. 3. 4. 5.
Inlet Diaphragm Spring Pushrod Pressure-dependent full load stop 6. Control rack
Smoke limiter, RSV governor
Pump setting and injection volumes In order for the engine to achieve its specified performance, the injection pump and governor must be correctly set. Setting of the regulator’s characteristics and the pump’s injection volume must be carried out using special test equipment. Reconditioning and testing should therefore only be carried out at workshops having experienced personnel and the requisite equipment. Pump and governor must be set in accordance with Scania’s test tables. These indicate the setting values and test equipment which are applicable to a certain type of pump. The test tables are included in ”Injection system”, a special version of the workshop manual. On completion of the work, the settings should be security sealed to prevent unauthorized persons from tampering with the pump.
Note An incorrectly adjusted injection pump leads to poorer combustion with increased black smoke and higher fuel consumption as a result. Incorrect adjustment can also cause damage to the engine.
Overflow valve The purpose of the overflow valve is to limit the pressure in the fuel system and continuously vent it. The overflow valve ensures that the fuel circulates round the system and that there is always fuel in the injection pump for cooling, lubrication and injection. The overflow valve is mounted either on the injection pump, see page 4, or on the shut-off valve, see page 3. Opening pressure is 0.6 - 0.8 bar. Working pressure is approx. 1 bar.
Diagram, closed and open overflow valve
Delivery pipes Delivery pipes are precision manufactured from steel tubing with cones and cap nuts at each end. They are attached with clamps in order to damp vibration and so reduce the risk of them fracturing. It is important to ensure that the delivery pipe is not bent or reshaped, that it is clamped in the right way and that the cap nut is tightened to the right torque. Otherwise, the delivery pipe could easily be damaged. Broken or otherwise damaged delivery pipes must not be repaired by soldering or welding, but should be changed. Delivery pipes must not be switched between different types or designs of engine as the delivery valve’s operation, see page 12, is dependent on the pipe being of the correct design.
1. 2. 3. 4. 5.
Delivery pipe Cap nut Washer Cone shaped end of pipe Connection Delivery pipe union
Double-wall delivery pipes Certain engines, usually marine engines, are equipped with double-wall delivery pipes, with or without level monitor. Double-wall delivery pipes consist of a regular delivery pipe which is fitted with an outer jacket which collects the fuel if the delivery pipe starts to leak. The danger of fire in the engine room is then reduced as no fuel is sprayed out onto the hot engine and warning of the leakage is given by the level monitor. Double-wall delivery pipes are changed as a complete assembly, inner and outer pipes, and are only available bent to shape as spare parts. In other respects, the same applies to double-wall delivery pipes as to standard delivery pipes.
Injectors Fuel is pumped through the delivery pipes to the injectors by the injection pump. The injectors atomize the fuel in the combustion chamber. Pressed into the connection on the injector is a rod-shaped filter. The fuel is pumped down to the nozzle through a passage in the rod filter. When fuel from the injection pump reaches a certain pressure (opening pressure), the nozzle needle lifts (start of injection). The fuel is then sprayed in atomized form into the engine’s combustion chamber through accurately calibrated holes. The fuel that leaks between the nozzle needle and nozzle housing is routed back to the fuel tank via the leak-off fuel line which is connected to the injectors. The opening pressure can be adjusted by means of washers.
1. Delivery pipe union 2. Rod filter 3. Connection for leak-off fuel pipe 4. Shim(s) 5. Spring 6. Nozzle needle
Injectors, function