Fuel pump operation

Vane pump

The first link of the distribution fuel pump is a vane pump. It sucks fuel from the pipeline that comes from the filter. The pump rotor, in which movable sliding plates are installed, is housed in a specially shaped stator. The sliding plates always adjoin the walls of the stator, as the rotor rotates during engine operation, and under the action of centrifugal force and fuel pressure, they tend to get out of the grooves of the rotor. Thus sealing is achieved. When the rotor rotates, the cavity between the rotor, plates and stator decreases towards the discharge side of the pump, compressing the fuel.

Control piston and thrust washer

Thus, fuel under pressure moves in the fuel pump housing. There is a distribution piston. It is the most important part of the pump.

The principle of operation of the distribution piston is similar to the principle of operation of the ignition distributor of a carburetor engine. The distribution piston is pierced with holes and has grooves. During injection, the piston port is located opposite the intake port. Fuel supplied by a pressure vane pump enters through the channels in the piston to the nozzle, while the piston is moving forward (more on that below) and the fuel is compressed even more, injection is carried out.

The distributing piston turns further. The inlet is closed again. The injection stops.




Now let's talk about the other two parts. The distribution piston is connected to a washer, on which there are four bulges in the form of protrusions. This is a push washer that moves near the counter support, which has four rollers to reduce friction. The rollers are placed at the same distances from each other as the protrusions on the washer.




And again about the injection. The push washer moves near the roller ring. When the protrusions are pushed onto the rollers, the push washer moves forward along with the control piston. This happens just at the moment when the hole in the piston coincides with the channel that leads to the nozzle. Therefore, fuel can be supplied to the side of the cylinder where compression is carried out. Due to the forward movement of the distribution piston, the volume of the cavity in front of it decreases. The already pressurized fuel is further compressed and squeezed out to the nozzle.

The crankshaft continues to turn, the high pressure fuel pump is working. The control piston slides back. Additional fuel is supplied from the inlet. The control piston rotates towards the next cylinder's exhaust port. The protrusions of the pusher are again rolled onto the rollers of the ring. The control piston moves forward, fuel is injected under pressure into the next cylinder.

Electromagnetic switch

Before the diesel fuel enters the inlet at the control piston, it flows past the solenoid switch valve. When the ignition key is turned to the first position, voltage is applied to the electromagnetic switch and the fuel path is opened. When the engine is turned off, the key interrupts the electrical circuit. Then the switch closes the inlet, the engine stops. There is no other way to stop the diesel engine (except: close the air filter tube or exhaust pipe).

A vehicle with an automatic transmission additionally has a mechanical switch at the front of the pump. This switch can be used to stop the engine if the electromagnetic switch is defective.

Centrifugal regulator

The high pressure fuel pump has a centrifugal regulator in order to regulate the amount of fuel injected under various operating conditions of the engine. The counterweights of the centrifugal regulator, depending on the engine speed, more or less open and move the pusher. Through a lever mechanism, the counterweights press on the control valve, which allows excess fuel to flow out. To do this, the spool opens a hole in the control piston.

If the engine speed is too high for a certain position of the accelerator pedal, the regulator opens the hole in the camshaft piston and the speed is reduced.

At start-up, the control hole closes completely. The engine receives the full amount of fuel, but only until then. until the idle speed is reached.


The same happens at idle and partial load. Centrifugal governor by mechanical system "compares" accelerator pedal position and engine speed. When, according to the position of the pedal, a certain speed is reached, the action of the governor stops. The maximum engine speed is also limited by the centrifugal governor.

The control port opens when the engine speed exceeds the following values:

• 5550±50 min (for 1.5 l)
• 5350±50 min (for 1.6 l)
• 5100±50 min (for turbo diesel engine)

Injection advance controller

As the engine speed increases, the fuel must be injected earlier to ensure mixture formation. The injection advance controller performs this task: it regulates the injection moment depending on the position of the piston in the cylinder.

As the engine speed increases, the vane pump in the injection pump rotates faster. Therefore, the fuel pressure increases. This phenomenon is used in the operation of the regulator. Pressurized fuel acts on the regulator piston, shifting it against the force of the spring. The roller ring is rigidly connected to this piston. The illustration on shows this. With increasing fuel pressure (i.e. at higher rpm) the piston rotates the roller ring slightly around its axis. Therefore, the protrusions of the push puck run into the rollers earlier; thus injection occurs earlier. With a decrease in the number of revolutions, the piston and with it the roller ring return back, the injection advance decreases.

Cold start accelerator

Sometimes the cold start accelerator button (left at the steering wheel) compared to a button "Choke" some carbureted engines. But both buttons have little in common. The button is also pulled out when the engine is cold, but the air flow does not decrease because of this, but the injection moment shifts, it is carried out earlier. Then a cold engine starts better because the fuel is injected earlier and has more time to mix with the cold air. In addition, the engine then picks up speed better in the first phase of a cold start.

Annoying blue smoke from the exhaust (which, when started, gives rise to the suspicion that the engine is badly damaged) almost absent when the cold start accelerator button is pulled out.

The cold start accelerator button must be fully pulled out when starting off with a cold engine, regardless of outside temperature. After driving for about 1 minute, it must be pushed back in again. If you once forgot to press it back, it's still not a problem. The engine then runs a little harder and does not develop full power. What does a cold start accelerator do in a high pressure fuel pump? The answer is extremely simple. It performs the same function as the injection advance controller (read the previous section) The thrust of the cold start accelerator through the lever acts on the regulator piston and pushes it back (as at high speeds fuel pressure). This rotates the roller ring approximately 2.5 degrees for earlier injection.

Fuel regulator

Above, on the high pressure fuel pump, there is an additional device (at a car with a pipe diesel).

This is the fuel regulator. It performs the following function. The excess air that has been forced by the turbocharger requires additional fuel depending on the boost pressure present. The device works as follows.

The diaphragm at the top of the housing is actuated by the boost pressure from the suction tube through the hose. Due to this, the membrane bends down and transmits this movement through the pusher and angle to the same control spool, which is also affected by the centrifugal regulator. If the boost pressure rises, the spool takes longer than usual to close the bore of the control piston. Consequently, excess fuel cannot escape, but, on the contrary, is injected. Thus, with increased boost pressure, more fuel is supplied.