Operation of the high-pressure fuel pump (HPFP) (Renault 19)

The picture on the left shows a Bosch fuel injection pump, on the right - a Roto fuel injection pump. The solenoid control shut-off device (2) interrupts the fuel supply to the pump when the ignition is off. If you want to turn the engine with the starter, you need to disconnect the electrical contact (1) so that the engine does not start. The following numbers indicate:

• 3 - cam disk "manual control rod of the accelerator" for switching on the microswitches of the exhaust gas recirculation and full load;
• 4 - exhaust gas recirculation microswitch;
• 5 - full load switch.

Vane fuel booster pump

The main element in the distribution fuel injection pump is the vane fuel pump. It sucks fuel from the pipeline coming from the filter. The pump wheel, into which the sliding sliders are inserted, is located in a round opening in the housing. When the pump sprocket turns, a certain volume always remains between the sliders, which then decreases towards the pump discharge, i.e. towards the outlet. The liquid in this volume is thus forcibly squeezed out.

The vane fuel pump supplies fuel under pressure to the high-pressure fuel pump housing. There, on the same shaft as the vane fuel pump, is the distribution plunger of the high-pressure fuel pump, from which the high-pressure distribution fuel pump got its name.

Fuel injection pump distributor plunger and cam disc

The secret of the injection pump distribution plunger is that it has many holes and recesses. Thus, it can perform its two main functions - filling and spraying.

Operating principle: during filling, the slotted slot of the distributor plunger is located opposite the filling hole. Fuel from the vane pump under pressure enters the free space in the piston and in front of the piston. The distributor plunger of the high-pressure fuel pump rotates further. The filling hole closes again. Filling is complete.

Now 2 other design elements come into play. The injection pump distributor plunger is connected to a pulley on which 4 projections are located. This is the cam disk; it moves against a counter-bearing which carries 4 rolls at the same interval as the projections on the cam disc to reduce friction. This is a roller ring. Then spraying occurs: the cam disc moves along the roller ring. If its projections have reached the rolls, the cam disc presses the distributor plunger of the high-pressure fuel pump forward. This happens when the next hole in the distributor plunger coincides with the channel of the outlet port to the injector. Fuel can only flow in the direction of the cylinder in which compression and ignition occur. Due to the forward movement of the distributor plunger of the high-pressure fuel pump, the volume of free space in front of it decreases. The fuel, already under pressure, goes to the injector. The injection process in the cylinder is complete. The crankshaft and high-pressure fuel pump (HPFP) rotate further. The injection pump distributor plunger slides back and fuel flows out of the filler hole.



The injection pump distributor plunger rotates toward the outlet port channel for the next cylinder. The cam disk lugs engage the rollers of the rolling ring again. The injection pump distributor plunger is pressed forward and fuel is injected under pressure.

Solenoid control cut-off device

Before diesel fuel enters the filling hole of the injection pump distributor plunger, it passes an electric valve with electromagnetic switching - a solenoid control cut-off device. It is activated when the ignition key is turned to the first position and frees the path for fuel. When the engine is turned off, the power supply is interrupted by the starting switch. The solenoid control cut-off device closes the fuel supply channel and the engine stops. There is no other way to turn off the diesel engine except by shutting it off or plugging the air filter snorkel or exhaust.

Centrifugal governor

In order to register the various operating modes of the engine and thus create the possibility of supplying the required amount of fuel for injection, a centrifugal regulator, which is sometimes also called an all-mode speed regulator, is installed in the high-pressure fuel pump. Its weights are pressed outward depending on the engine speed. The weights act through a lever mechanism on the regulating sleeve, which opens an opening in the distribution plunger of the high-pressure fuel pump to remove excess fuel. If the engine speed increases sharply in relation to the position of the gas pedal, the regulator opens the mentioned opening, and the speed decreases again. When the engine is started, this opening is completely closed. The engine receives the maximum amount of fuel, but only until the specified idle speed is reached. Then the regulator starts working again.



The same thing happens at idle and at partial load. The centrifugal governor balances the position of the accelerator pedal and the engine speed using the mechanics described above. If the relationship between the accelerator pedal position and the engine speed is achieved, then the removal of excess fuel begins. The maximum engine speed is also limited by the centrifugal governor. If the engine speed exceeds the maximum permissible limit, the centrifugal governor opens the hole to remove excess fuel. Thanks to this, the engine runs without exceeding the maximum permissible limit.

Electromagnetic fuel injection advance clutch

As the engine speed increases, the fuel must be injected earlier to ensure timely ignition. This advance of the ignition timing is accomplished by the fuel injection advance clutch. It is also installed in the high-pressure fuel pump.

If the engine speed increases, the vane fuel pump also rotates with the increase in speed in the high-pressure fuel pump. Due to this, the fuel pressure increases, and this is used by the fuel injection advance clutch. The fuel pressure acts on the plunger and moves it, compressing the spring. The roller ring is rigidly connected to this plunger. As the fuel pressure increases - at a higher speed - the plunger rotates the roller ring around its axis. As a result, the cams of the cam disk act on the rollers earlier; thus, the injection occurs earlier. When the rotation speed decreases, the plunger lags a little and, accordingly, the roller ring with it.

Cold engine starting device

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The hydraulic cold start accelerator on the Bosch high-pressure fuel pump consists of a limiting valve (1), a pressure-reducing valve (3) and an electrically heated thermoelement with expanding material (4). If the speed of the cold engine exceeds 2000 rpm, the ball valve (2) opens and normalizes the increased fuel pressure.

A cold engine starts better if the fuel is injected earlier into the hot compressed air. The car accelerates better in the first phase of operation of a cold engine, and thanks to this device, the annoying blue exhaust smoke during start-up is almost completely absent. The mentioned cold engine start accelerator works in the high-pressure fuel pump as a fuel injection advance clutch. It acts by means of fuel pressure on the plunger of the fuel injection advance clutch and presses it back. The roller ring rotates as a result of this by about 2.5° in the "advance" direction. The cold engine start device consists of a valve installed on the side of the high-pressure fuel pump, which is directly connected to a heating element screwed into the valve body, heated electrically. After starting the engine, the heating element increases in size and opens the valve. As a result, the injection pressure drops to the average norm, and the cold engine start accelerator no longer works. This happens depending on the ambient temperature within 30-180 seconds.



If the coolant temperature is more than 65°C and the fuel temperature is more than 45°C or 67°C, respectively (depending on the type of high-pressure fuel pump, the cold start accelerator remains switched off. If the speed increases more than 2000 rpm, then the valve opens without the participation of the cold engine start accelerator.

Fast Idle Speed Regulator

For comfort, the high-pressure fuel pump, in addition to the cold engine start accelerator, has a device for increasing the speed of revolutions. Thus, it is possible to avoid annoying beating and vibration at idle speed in a cold engine.

For this purpose, the idle speed limiter is equipped with a second lever, which is connected via a small Bowden cable to a wax thermostat screwed into the engine housing, heated by the coolant. When the engine is cold (coolant temperature below 15°C), this lever increases the idle speed to 1100-1200 rpm. As the engine heats up, the wax in the thermostat melts and expands. The cable tension weakens, and the idle speed lever approaches the normal idle speed limiter.