High pressure fuel pump

The high-pressure fuel pump (short name – TNVD) is one of the main structural elements of the diesel engine injection system. As a rule, a pump performs two main functions: pumping a certain amount of fuel under pressure; regulation of the necessary moment of the beginning of injection. With the advent of battery injection systems, the function of regulating the injection moment is assigned to electronically controlled nozzles.

The basis of the high-pressure fuel pump is a plunger pair, which combines a piston (aka plunger) and a small cylinder (aka bushing). The plunger pair is made of stainless steel with high precision. Between the plunger and the sleeve provides a minimum clearance – precision mating.

Depending on the design, the following types of high-pressure fuel pumps are distinguished: in-line, distribution and main. In the in-line pump, fuel injection into the cylinder is performed by a separate plunger pair. The distribution pump has one or more plungers that provide fuel injection and distribution throughout the cylinders. The main pumps only deliver fuel to the battery.

A high-pressure fuel pump is also used in the direct injection system of a gasoline engine, but its operating pressure is an order of magnitude lower than the similar characteristics of a diesel pump.

The leading manufacturers of high-pressure fuel pumps are mainly foreign companies: Bosch, Lucas, Delphi, Denso, Zexel.

High-Pressure Inline Fuel Pump

Inline injection pump has plunger pairs by the number of cylinders. Plunger pairs are installed in the pump housing, in which channels for supplying and removing fuel are made. The movement of the plunger is carried out from the camshaft, which in turn has a drive from the crankshaft of the engine. The plungers are constantly pressed against the cams by means of springs.

When the cam shaft rotates, the cam runs onto the plunger pusher. The plunger moves up the sleeve, while the outlet and inlet are sequentially closed. The pressure is created at which the discharge valve opens, and fuel flows through the fuel line to the corresponding nozzle.

The regulation of the amount of fuel supplied and the moment of its supply can be carried out mechanically or electronically. Mechanical control of the amount of fuel supplied is carried out by turning the plunger in the sleeve. For rotation, gear is made on the plunger, which is connected to the gear rack. The rail is connected to the gas pedal. The upper edge of the plunger has an inclined surface, so when you turn the fuel cutoff and, accordingly, its amount will change.

A change in the moment the fuel supply starts is required when the engine speed changes. Mechanical control of the moment of fuel supply is carried out using a centrifugal clutch located on the camshaft. Inside the clutch, there are weights, which, when the engine speed increases, diverge under the action of centrifugal forces and rotate the camshaft relative to the drive. With an increase in engine speed, early fuel injection is provided, with a decrease – late.

The design of inline fuel injection pump provides high reliability. The pumps are lubricated with engine oil of the engine lubrication system, so they can run on low-quality fuel. High-pressure in-line fuel pumps are used on engines with separate combustion chambers and direct injection of medium and heavy trucks. On passenger diesel, this type of pump was used until 2000.

High-Pressure Distribution Fuel Pump

High-pressure distribution fuel pumps, unlike in-line injection pumps, have one or two plungers serving all engine cylinders. Distribution pumps have a lower weight and overall dimensions, as well as provide greater uniformity of flow. On the other hand, they are distinguished by the relatively low durability of the mating parts. All this determines the scope of these pumps, mainly on the engines of cars.

Designs of high-pressure distribution fuel pumps can have a different plunger drive:

Preferred in terms of operation are the first two types of drive plungers because they lack power loads from fuel pressure on the drive shaft units and, accordingly, higher durability.

The main element of the distribution injection pump with an end cam drive of the plunger (Bosch VE) is a plunger-distributor, which performs a reciprocating and rotational movement, providing forcing and distribution of fuel in the cylinders.

The reciprocating movement of the plunger occurs when the cam washer rotates, which runs around the stationary ring on the rollers. The washer presses the plunger, thereby creating fuel pressure. The plunger returns to its original position using a spring.

The plunger is rotated from the drive shaft. In this case, the fuel is distributed over the cylinders.

The regulation of the fuel supply is carried out automatically using mechanical or electronic devices. The mechanical regulator includes a centrifugal clutch with loads, which, through a system of levers, acts on a dispenser that changes the amount of fuel supply. The electronic controller is an electromagnetic valve.

The timing of the fuel injection in the distribution pump is controlled by turning the fixed ring by a certain angle.

The workflow of the distribution pump includes the inlet of fuel into the above-plunger space, injection and distribution into the respective cylinders.

In a rotary type distribution pump, the injection and distribution of fuel into the cylinders is carried out by different devices with a plunger and a distribution head. Fuel injection is carried out using two opposite plungers located on the camshaft. The plungers through the rollers run around the cam profile and make a reciprocating motion.

When the plungers move towards each other, the fuel pressure increases, after which the fuel is delivered to the nozzles of the respective cylinders through the channels of the distribution head and pressure valves.

Fuel is supplied to the plunger (s) under a slight pressure, which creates a fuel priming pump. In distribution pumps, a fuel priming pump is mounted on the drive shaft in the pump housing. Structurally, this can be a rotary vane pump, a gear pump with external or internal gearing.

The high-pressure distribution pump is lubricated with diesel fuel, which fills the pump housing.

High-pressure main fuel pump

The high-pressure main fuel pump is used in the Common Rail accumulator fuel injection system, where it performs the function of injecting fuel into the fuel rail. Trunk high-pressure fuel pumps provide higher fuel pressure ( in modern injection systems, about 180 MPA or more ).

Structurally, the main pump can have one, two or three plungers. The plungers are driven by a camshaft or a cam washer.

When the camshaft (cam eccentric) rotates under the action of the return spring, the plunger moves down. The volume of the compression chamber increases and the pressure in it decreases. Under vacuum, the inlet valve opens and fuel enters the chamber.

The upward movement of the plunger is accompanied by an increase in pressure in the chamber, the intake valve closes. At a certain pressure, the exhaust valve opens and fuel is supplied to the ramp.

Fuel supply control is carried out depending on the needs of the engine using a fuel metering valve. In the normal position, the valve is open. At the signal of the electronic control unit, the valve closes by a certain amount, thereby regulating the amount of fuel entering the compression chamber.

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