- What is a high pressure fuel pump and what is it for?
- Development and improvement history
- High pressure pump design
- Principle of operation
- Types of injection pump
- Is there a fuel injection pump on a gasoline engine?
- Major malfunctions
- Repair of high pressure pumps
The vast majority of modern cars are equipped with fuel injection systems. There are modifications in which gasoline is sprayed with a nozzle in the intake manifold. There are also models in which fuel is sprayed directly into the engine cylinders.
Diesel engines work differently from gasoline engines. In them, the diesel is fed into the already compressed medium in the cylinder. In order for a portion of fuel to be atomized without hindrance, a mechanism such as a high-pressure fuel pump is needed.
Consider the features of such a mechanism, its modifications and signs of malfunction.
What is a high pressure fuel pump and what is it for?
The mechanism, which is abbreviated as a fuel pump, is part of the fuel system of a diesel engine, but there are also models for gasoline power units. The only difference between the fuel pump of a diesel engine is that the pressure it generates is much higher than its gasoline counterpart. The reason for this is the fundamental features of the unit's operation. In the cylinders of a diesel engine, air is first compressed to such an extent that it heats up to the ignition temperature of the fuel.
When the piston reaches top dead center, the nozzle sprays fuel and it ignites. The injector has to overcome enormous pressure. For the system to work properly, the pump must create a higher head than in the cylinders.
In addition to the mentioned function, the pump must also supply fuel in portions, depending on the operating mode of the power unit. This parameter is determined taking into account the rotation of the crankshaft. In a modern car, this process is controlled by an electronic control unit.
Development and improvement history
This device was first developed in the 1930s by Robert Bosch. In passenger cars, injection pumps began to be actively used in the second half of the same decade.
Since the first gasoline engines were equipped with carburetors, only diesel units needed such a mechanism. Nowadays, gasoline engines with a direct injection system also have a pump of this type (the carburetor is already extremely rare - only in older generation cars).
Although the principle of operation of the pump has remained practically unchanged, the mechanism itself has undergone multiple upgrades and improvements. The reason for this is an increase in the environmental standards and performance of the internal combustion engine. Initially, a mechanical injection pump was used, but it was not economical, which led to volumetric emissions of harmful substances. Modern electronic pumps show excellent efficiency, which allows transport to fit into the framework of environmental standards and satisfy modest drivers.
High pressure pump design
There is a wide variety of modifications of the fuel injection pump for a gasoline engine, as well as a diesel analogue. However, in most cases, the main elements of a mechanical pump are:
- A filter is installed at the inlet in front of the pump;
- A plunger piston located in a cylinder - the so-called. plunger pair;
- The body in which the recesses are made - through them fuel is supplied to the plunger pair;
- Shaft with cam and centrifugal clutch. This element is connected to the timing pulley using a belt drive;
- Plunger pair drive pushers;
- Springs that return the plunger piston back;
- Blower valves;
- Regulator of modes - associated with the gas pedal;
- Fuel pump return valve (through it, excess fuel is fed into the return);
- Low pressure pump (pumps fuel into the pump).
As already mentioned, mechanical pumps are gradually being replaced by electronic modifications due to their economy and efficiency. The mechanism itself is difficult to repair and adjust. Electronic pumps have their own control unit as well as several electronic valves and sensors.
Most electronic injection pumps have their own diagnostic system, due to which the device adapts to the malfunctions and errors encountered. This allows the device to work properly even if one of the sensors fails. Completely such a pump stops working only in the event of a breakdown of the microprocessor.
Principle of operation
The high pressure fuel pump operates on the principle of a two-stroke engine. Due to the rotation of the cam shaft, the plunger piston is driven. Diesel fuel enters the sub-plunger space, which goes further into the highway.
More details about the principle of operation of the plunger pair are described in the video:
Pressure is generated in the cavity, due to which the discharge valve opens. Diesel fuel flows through the fuel line to the nozzle and is atomized. The pump delivers only part of the fuel to the injector. The residue is returned to the fuel tank via the drain valve. To prevent fuel from returning from the system when the supercharger is opened, a check valve is installed in it.
The injection moment is determined by the centrifugal clutch. The mode regulator (or all-mode regulator) determines the quantity of the batch to be dispensed. This element is associated with the gas pedal. When the driver presses it, the regulator increases the portion volume, and when released, the amount decreases.
In electronic models, all processes are controlled by a control unit. The electronics distributes the moment of fuel supply, its amount based on the dynamics of the car. These fuel systems have fewer parts, which increases the stability and reliability of the mechanism.
Electronic injection pumps are able to divide the portion into two parts, thereby providing more efficient combustion and a smooth stroke of the piston group. As a result, there is less exhaust toxicity and increased engine performance. To ensure two-phase injection, the pump control unit records:
- Pressing the accelerator pedal;
- Timing camshaft revolutions;
- Temperature in the engine cooling system;
- The speed of the car itself;
- The pressure generated by the turbocharger;
- Work of injectors;
- Glow plug firing.
Types of injection pump
Fuel systems are of three types:
- Monoinjection. This is the very first modification. The representative was originally a carburetor. In its cavity, a fuel-air mixture was prepared and fed into the intake manifold. A little later, such systems, instead of a carburetor, received one nozzle that injects fuel into the intake manifold, where it is mixed with air;
- Multipoint injection. This is already a kind of injection system. An individual injector is installed for each cylinder on the intake manifold. The injection is also carried out into the intake manifold, only as close as possible to the intake valve;
- Direct injection. As the name suggests, fuel is sprayed directly into the cylinders when the air in them is already compressed by the piston.
In total, there are three types of such mechanisms that can be used in these types of fuel systems:
In-line injection pump
In-line injection pump consists of several pumps, enclosed in one casing. Each of them serves a separate nozzle. This modification was used in older diesel engines. The operation of the entire mechanism is strictly dependent on the timing drive.
The in-line modification has been used for a fairly long period. Even some modern cars (trucks) are equipped with such pumps. The reason is their high reliability and unpretentiousness to diesel quality.
The row system works as follows. The plunger pair is driven by the rotation of the crankshaft. One revolution of the pump camshaft corresponds to two revolutions of the engine crankshaft.
The plunger mechanism through the fuel cut-off valve of the high pressure pump separates part of the fuel from the common line and compresses it in the pressure section of the system. The portion volume is regulated by a toothed bar connected to the gas pedal. In cars with an ECU, it is controlled by a servo drive that reacts to signals from the control unit.
The injection timing is determined by the crankshaft speed. The mechanism has two half-couplings, which are separated by springs. When the engine speed increases, the springs are compressed, due to which the pump shaft turns slightly, which leads to a change in the injection timing.
Distribution type injection pump
Unlike the previous modification, this model is smaller. It also features stable performance. There are several modifications of the distribution pumps. There are plunger and rotary types. They also differ in the types of drive - internal, end or external location of the cams.
An external cam drive is not stable and reliable. Therefore, if possible, it is better to dwell on the other two types.
Such pumps wear out faster, since one plunger mechanism in them serves all the nozzles of the group. In this regard, in-line counterparts have advantages. Due to their small size, distribution injection pumps are installed in the fuel systems of cars and small trucks.
Main injection pump
In contrast to the two previous modifications, the main pump creates a pressure in a single line - the so-called fuel rail. It serves as an accumulator in which a constant fuel pressure is maintained.
Due to the smaller number of distribution mechanisms, this modification has established itself as the most reliable. The repair of main-type injection pumps is not particularly difficult. The dose volume is controlled by a solenoid dosing valve. Such pumps are installed in Common Rail fuel rail systems.
Is there a fuel injection pump on a gasoline engine?
Although the main application of fuel injection pumps is in diesel engines, many modern gasoline engines also operate by supplying fuel under high pressure. These mechanisms are used in internal combustion engines with direct injection.
GDI gasoline engines require the installation of such pumps. In fact, this system is a hybrid version that combines the design of a gasoline internal combustion engine with the principle of operation of a diesel unit. The only difference is that ignition is not due to the temperature of the compressed air, but due to the spark plugs. In such motors, an in-line modification is used.
Although fuel injection pumps differ in their design, there are several important rules that the car owner must follow in order for the pump to serve its allotted time:
- Most pumps are whimsical in terms of fuel quality, therefore, it is necessary to comply with the requirements set by the manufacturer for a particular pump;
- Due to the complexity of the design and the loads that are on the mechanisms, high-pressure pumps need regular maintenance;
- All rotating and rubbing parts must be well lubricated, therefore it is imperative to follow the manufacturer's recommendations for the selection of lubricants.
If you do not follow these rules, the device will become unusable faster, which will require its replacement or expensive repairs.
The following factors indicate a malfunction of the injection pump (with serviceable other systems, malfunctions in which may have similar manifestations):
- Black smoke in the exhaust and, as a result, more toxic emissions into the environment;
- Increased fuel consumption (due to fuel leaks);
- Drop in ICE power;
- During engine operation, noises from the pump are heard;
- Difficult starting of the motor;
- The timing belt often slips off;
- Unstable engine speed.
The most common malfunction in such elements of the fuel system is the failure of the plunger pair. Most often this is due to poor-quality fuel - plaque accumulates on the surfaces, which impedes the movement of parts. Also, the cause of failure of the mechanism is water, which often condenses in the fuel tank. For this reason, it is not recommended to leave a car with an empty tank overnight.
Repair of high pressure pumps
If it is not difficult to repair a conventional gasoline pump - it is enough to buy a repair kit and replace worn parts, then repairing and adjusting a fuel pump is a very complicated procedure. It is even impossible to determine what the cause of the malfunction is without additional equipment. Self-diagnostics of modern control units often do not help.
It often happens that the symptoms of a fuel pump breakdown are identical to malfunctions in the gas distribution mechanism or in the exhaust system. For these reasons, self-repair of the injection pump is not recommended. To do this, it is better to seek help from a specialized service center.
Additionally, watch the video on elimination of defects and repair of high pressure fuel pumps: