2.0 High pressure fuel pump cutaway
1 - drive shaft
2 - fuel inlet
3 - safety valve
4 - accelerator cable fastening lever
5 - centrifugal regulator
6 - return hole
7 - fuel cut-off valve
8 - high pressure fuel line
9 - distribution piston 10 - cam disc
11 - fuel injection advance clutch (rotated 90°for better viewing)
12 - pusher roller
13 - vane pump (also rotated 90°)
TD engines have distributor-type injection pumps, which are also more durable (see illustration 2.0a).
Attention! Distribution injection pump is particularly sensitive to impurities and fuel contamination (water, dirt), which clog the pump hole. The subsequent repair of the injection pump is very expensive, because it needs to be checked at the stand. For this reason, we recommend changing the fuel filter regularly, as well as draining accumulated condensate in a timely manner.
A component of the distribution injection pump is a slide-type fuel pump that takes fuel from the pipeline from the fuel filter. The impeller of the vane pump, rotating with the engine running, squeezes the fuel into the housing of the injection pump itself to the control piston. The piston is the main part of the high pressure fuel pump and in its function resembles the ignition distributor of a gasoline engine.
The control piston has a large number of holes and recesses, which helps it to perform its function: to take fuel and inject it. During the fuel intake stroke, the piston window is installed opposite the supply hole (see illustration 2.0b).
The fuel injected by the vane pump enters the receiving chambers of the distribution piston. After that, the piston is rotated by a toothed belt from the crankshaft and the supply hole is closed. Now the following two elements of the high-pressure fuel pump come into play. The control piston is connected to a cam which starts moving towards the roller follower. As soon as the lobes of the cam reach the pusher rollers, the cam together with the control piston is pressed back. This happens at the moment when the distribution channel in the piston coincides with the outlet channel of the valve injector and the fuel goes to the cylinder, in the combustion chamber of which everything is ready to receive and ignite it. The control piston moves further back and refills. After that, the cycle is repeated, and fuel is injected into the next cylinder (see illustration 2.0c).
Before fuel reaches the supply port and enters the injection pump control piston chamber, it must pass through the fuel shut-off solenoid valve. The fuel cut-off valve is activated when the ignition key is turned to the first position and opens the way for fuel. When the ignition is turned off, the power supply to the valve is turned off and it closes the fuel supply channel.
Given that during the movement there is a frequent change in engine loads, then to take them into account and provide the engine with fuel according to its current load, the high-pressure fuel pump has a centrifugal regulator. The weights of the regulator, depending on the engine speed, are mixed to a greater or lesser extent outside and at the same time press on the regulating valve, which opens the outlet hole in the control piston and thus diverts part of the fuel.
At the time of starting, the outlet is closed and the engine receives the maximum amount of fuel. However, this position is maintained only until the idle speed reaches the nominal value. From now on, the fuel supply is regulated.
In a similar way, the injection pump behaves in full and partial load modes. The maximum engine speed is also limited by the centrifugal governor. As soon as the engine speed reaches over 5200+100 rpm, the vent is fully opened and the engine is not able to increase the speed.
As the engine speed increases, fuel injection must be advanced so that the ignition of the mixture occurs in a timely manner. Earlier injection is provided by the fuel injection advance clutch. With an increase in the engine speed, the speed of rotation of the vane pump increases and the fuel pressure increases. This was used to advance the injection. Under fuel pressure, the spring is compressed and the piston is pressed out, which displaces the roller pusher around its axis. The cam stops reach the pusher rollers faster and the fuel is injected earlier. With a decrease in the number of revolutions, the clutch piston moves back, and with it the roller pusher.
The start of pump flow varies depending on the load on the engine. The injection pump recognizes the load on the engine as follows:
- the accelerator pedal is depressed and the engine speed is low - high load;
- accelerator pedal released and engine speed high (downhill forced idle) = No engine load.
When the load on the engine increases, the high-pressure fuel pump starts the fuel supply ahead of time, and when the load is low, it slows down.
Starting from 2/92, the high-pressure fuel pump is equipped with an actuating valve for regulating the start of the fuel supply, which turns off the regulation of the fuel supply depending on the engine load when it reaches more than 3000 rpm. This helps to reduce the content of harmful substances in the OT, and also to some extent reduces fuel consumption (see illustration 2.0g). The control valve is controlled by the EGR control unit.
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