In the previous series of articles on the design of the fuel system of a gasoline engine, the topic of a high-pressure fuel pump for a diesel engine and gasoline engines with direct fuel injection was touched upon more than once.
This article is a separate material that describes the design of a high-pressure diesel fuel pump, its purpose, potential malfunctions, diagram and principles of operation using the example of the design of such a fuel supply system for a given type of internal combustion engine. So let's get straight to the point.
What is fuel injection pump?
The high pressure fuel pump is abbreviated as injection pump. This device is one of the most complex in the design of a diesel engine. The main task of such a pump is to supply diesel fuel under high pressure.
Pumps ensure the supply of fuel to the cylinders of a diesel engine under a certain pressure, as well as strictly at a certain moment. Portions of supplied fuel are measured very precisely and correspond to the degree of load on the engine. Injection pumps are distinguished by injection method. There are direct acting pumps, as well as accumulator injection pumps.
Direct acting fuel pumps have a mechanical plunger drive. The processes of pumping and fuel injection occur at the same time. A certain section of the fuel injection pump supplies each individual cylinder of a diesel internal combustion engine with the required dose of fuel. The pressure required for effective atomization is created by the movement of the fuel pump plunger.
A fuel injection pump with accumulator injection differs in that the drive of the working plunger is affected by the pressure forces of compressed gases in the cylinder of the internal combustion engine itself or the influence is exerted by means of springs. There are fuel pumps with a hydraulic accumulator, which are used in powerful low-speed diesel internal combustion engines.
It is worth noting that systems with a hydraulic accumulator are characterized by separate pumping and injection processes. Fuel under high pressure is pumped into the battery by a fuel pump, and only then supplied to the fuel injectors. This approach ensures efficient atomization and optimal mixture formation, which is suitable for the entire range of loads on the diesel unit. The disadvantages of this system include the complexity of the design, which became the reason for the unpopularity of such a pump.
Modern diesel units use technology that is based on the control of injector solenoid valves from an electronic control unit with a microprocessor. This technology is called “Common Rail”.
In-line injection pump
Structurally, it consists of separate injection sections made in the form of plunger pairs (piston-bushing). The mating parts are made of high-strength wear-resistant chrome vanadium steel, nitrided and hardened to high hardness. After grinding, the inner surface of the bushings is subjected to double honing: first with a coarse abrasive paste, then with a fine one. The plunger is finished using superfinishing.
When assembling fuel injection pumps, a selective method for selecting plunger pairs is used. Parts are sorted into groups with a deviation of up to 2 microns from each other, so parts of different units are not interchangeable.
Fuel injection by a plunger occurs due to the cutting off of a certain volume of fuel and subsequent compression in the pressure line. The piston is moved by a roller pusher from the cam shaft of the pump, which receives rotation from the crankshaft. For two revolutions of the crankshaft, each plunger will make one working stroke.
The amount of fuel is regulated using a drive rack, which is mechanically driven by the gas pedal, or is moved by a stepper motor from the ECU signal. For this purpose, the plunger surface is equipped with a helical groove. The rack, using a gear transmission, rotates the guide sleeves in the housing, as a result of which the angular location of the helical groove changes, and, consequently, the volume of the fuel portion.
The start of injection is adjusted automatically according to engine speed. A centrifugal injection timing regulator serves this purpose. It is located in the drive coupling (black flywheel on the left in the first photo). Inside, this unit consists of 2 coupling halves, elastically separated from each other by tangentially located springs and weights. As the speed increases, due to the centrifugal force of the loads, the springs are compressed and the cam shaft rotates at a certain angle relative to the drive coupling, thereby creating an injection advance.
Despite the age of the design, in-line pumps are still used on diesel truck engines. This is due to their high reliability and unpretentiousness in terms of fuel quality. As an example, the fuel injection pump of an 8-cylinder engine of a KAMAZ vehicle is shown. To reduce axial dimensions, it is made V-shaped, although it is still in-line.
Main causes of malfunctions
The injection pump is an expensive device that is very demanding on the quality of fuel and lubricants. If a car is operated on low-quality fuel, such fuel necessarily contains solid particles, dust, water molecules, etc. All this leads to failure of the plunger pairs, which are installed in the pump with a minimum tolerance, measured in microns.
Low-quality fuel easily damages the injectors, which are responsible for the process of atomizing and injecting fuel.
Common signs of malfunctions in the operation of fuel injection pumps and injectors are the following deviations from the norm:
- fuel consumption is noticeably increased;
- increased exhaust smoke is noted;
- during operation there are extraneous sounds and noise;
- power and output from the internal combustion engine drop noticeably;
- difficulty starting is observed;
Modern engines with fuel injection pumps are equipped with an electronic fuel injection system. The ECU doses the fuel supply to the cylinders, distributes this process over time, and determines the required amount of diesel fuel. If the owner notices the slightest interruptions in the operation of the engine, then this is an urgent reason to immediately contact the service. The power plant and fuel system are thoroughly examined using professional diagnostic equipment. During diagnosis, specialists determine numerous indicators, among which the most important are:
- degree of uniformity of fuel supply;
- pressure and its stability;
- shaft rotation speed;
Design and principle of operation
In-line injection pumps of the PE series have their own cam shaft 14, which is installed in an aluminum housing. It is connected to the engine either directly or through a connecting unit and an injection advance clutch. The number of cams on the injection pump cam shaft corresponds to the number of engine cylinders. Above each cam there is a roller pusher 13 with a plate 12 of the spring 11. The plate transmits the force from the pusher to the plunger 8, and the spring returns it to its original position. The plunger sleeve 4 is a guide in which the plunger makes a reciprocating movement. The combination of the sleeve and plunger forms a pumping element, or plunger pair.
- Discharge valve body
- Spacer
- Discharge valve spring
- Plunger sleeve
- Discharge valve cone
- Inlet and distribution ports
- Plunger adjusting edge
- Plunger
- Plunger adjusting sleeve
- Plunger driver
- Plunger spring
- Spring plate
- Roller pusher
Device evolution
Tightening environmental standards and requirements regarding emissions of harmful substances into the atmosphere has led to the fact that mechanical high-pressure fuel pumps for diesel cars have begun to be replaced by electronically controlled systems. The mechanical pump simply could not provide fuel dosing with the required high accuracy, and was also not able to respond as quickly as possible to dynamically changing engine operating conditions.
World-famous manufacturers Bosch, Nippon Denso and others have offered electronic fuel control systems. These developments were based on the VE fuel pump. Such systems made it possible to achieve increased accuracy of fuel dosing into each cylinder separately.
The introduction of electronic systems ensured a reduction in the instability of the combustion process of the fuel-air mixture between cycles, as well as a reduction in irregularities during the operation of a diesel engine at idle.
Some systems had a quick-acting valve in their design, which made it possible to divide the fuel injection process into two phases. Two-phase injection led to a final decrease in the severity of the mixture combustion process itself.
The resulting precision in the process of controlling the injection system ensured a reduction in toxic emissions due to more complete combustion of the fuel-air mixture, and the increased efficiency of such combustion increased the efficiency of the engine and increased the final power of the power plant.
Distribution-type fuel pumps received electronic systems. Such pumps are equipped with controlled devices that adjust the position of the dispenser. Additionally, there is a valve for advancing fuel injection.
Main malfunctions of high pressure pumps
The design of any high-pressure fuel pump is a complex structure, which means that this mechanism has a lot of potential malfunctions. The main cause of possible problems is poor fuel quality, which applies to both diesel and gasoline systems. The plungers are subject to the greatest wear, and if, during inspection of the pump, abrasions are found on their surface, then this is the first signal of incorrect operation.
The symptoms of a fuel injection pump failure are in many ways similar to a malfunction of the engine and cooling system, and therefore for a more accurate diagnosis you should always contact a service center, where a test will be performed on a stand. In everyday conditions, possible pump malfunctions can be determined by the following manifestations:
- increased fuel consumption;
- Unstable engine operation at low speeds;
- difficulty starting;
- increased temperature of the unit and overheating of the engine;
- fuel leaks;
- reduction in power level;
- exhaust smoke;
- noises and extraneous sounds in the engine.
The high-pressure fuel pump can be called a unique unit, which does not yet have worthy alternative solutions. The evolution of this device over the past decades concerns exclusively the improvement of individual parts and increasing the accuracy of their manufacture without making fundamental changes to the general principle of operation.
Source
How the system works
The ECU receives corresponding signals from various sensors. The position of the gas pedal, engine speed, coolant temperature and the temperature of the fuel itself are taken into account. The electronic control unit receives data on the rise of the injector needle, vehicle speed, air boost pressure and intake temperature.
The ECU processes the information received from the sensors and then sends a signal to the injection pump. This ensures that the required and optimal amount of fuel is supplied to the injectors. Additionally, the best injection advance angle is ensured, taking into account the specific operating conditions of the engine. Any additional load is immediately noted by the ECU, a signal is sent to the injection pump and the fuel supply increases to compensate for the increased load.
The electronic control unit monitors the operation of the glow plugs. The ECU monitors the glow period, the operating mode of the glow plugs and the post-glow period. All this happens taking into account the temperature dependence.
Below is a diagram of the electronic control of a single plunger VE pump from Bosch for a diesel engine:
- injection start sensor;
- crankshaft speed and TDC sensor;
- air flow meter;
- coolant temperature sensor;
- gas pedal position sensor;
- Control block;
- accelerator device for starting and warming up the internal combustion engine;
- device for controlling the exhaust gas recirculation valve;
- device for controlling the fuel injection advance angle;
- device for controlling the drive of the metering clutch;
- dispenser stroke sensor;
- fuel temperature sensor;
- high pressure fuel pump;
The key element in this system is the device for moving the injection pump metering coupling (10). The control unit (6) controls the fuel supply processes. Information enters the block from sensors:
- injection start sensor, which is installed in one of the injectors (1);
- TDC and crankshaft speed sensor (2);
- air flow meter (3);
- coolant temperature sensor (4);
- accelerator pedal position sensor (5);
The control unit's memory stores the specified optimal characteristics. Based on information from the sensors, the ECU sends signals to the cyclic feed and injection timing control mechanisms. This is how the amount of cyclic fuel supply is adjusted in various operating modes of the power unit, as well as during a cold start of the engine.
The actuators have a potentiometer that sends a feedback signal to the computer, thereby determining the exact position of the metering clutch. Adjustment of the fuel injection advance angle follows a similar principle.
The ECU is responsible for creating signals that regulate numerous processes. The control unit stabilizes the rotation speed in idle mode, regulates exhaust gas recirculation, and determines the indicators from the signals of the mass air flow sensor. The block compares signals in real time from sensors with those values that are programmed into it as optimal. Next, the output signal from the computer is transmitted to the servo mechanism, which ensures the required position of the metering clutch. In this case, high control accuracy is achieved.
This system has a self-diagnosis program. This allows for the development of emergency modes to ensure the movement of the vehicle even in the presence of a number of specific malfunctions. Complete failure occurs only when the ECU microprocessor breaks down.
The most common solution for adjusting the cyclic flow for a distributor-type single-plunger high-pressure pump is the use of an electromagnet (6). Such a magnet has a rotating core, the end of which is connected by means of an eccentric to a metering coupling (5). An electric current passes in the winding of an electromagnet, and the angle of rotation of the core can be from 0 to 60°. This is how the dosing coupling (5) moves. This clutch ultimately regulates the cyclic flow of the injection pump.
Distribution type injection pump (VE pump). It's also an end pump
The scope of application of this type of pump is wide – passenger cars, trucks, commercial vehicles, tractors, agricultural machinery and others. Engines with this type of pump are available in 2, 3, 4 and 6 cylinders with a maximum power per working cylinder of 20 kW.
The main manufacturers of pumps of this type are the following companies: Bosch (Bosch), Zexel (Zexel) and Denso (Denso), however, there is also the little-known Diesel Kiki (later known as Zexel) and the Korean Doowon, which at one time bought a license from Zexel for the production of these pumps.
The VE type distribution injection pump is divided into 2 modifications:
- With mechanical control;
- Electronically controlled.
First, I suggest you pay attention to the operating principle of a distribution-type fuel injection pump (VE) using the example of a Denso pump
- Fuel is pumped from the tank into the fuel filter by a booster pump (TNND), the filter removes water and dirt from the diesel fuel.
- Next, the fuel is pumped by the high-pressure pump into the high-pressure pump housing.
- The fuel located in the injection pump housing is forced by a plunger through the injection valves into the injectors and injected into the combustion chamber.
- Part of the fuel supplied to the injectors is used to lubricate them, then returns to the fuel tank.
- Part of the fuel entering the high pressure pump housing is used to lubricate the pump and cool its parts, then it is returned to the fuel tank through the drain bolt hole
Distribution injection pump VE Bosch, Zexel
Let's look at the most important components of a single-plunger high-pressure fuel pump of the distribution type (BE). I propose to consider the components according to the principle of operation of the pump, from the booster pump to the discharge valve.
Low pressure fuel pump (LPFP)
As the pump rotates, 4 plates (you can see them in the photo) pump fuel under pressure through the filter into the pump housing; by means of a control valve, the pressure changes in accordance with the engine speed.
Plunger pair (pump plunger)
During operation, the plunger combines rotation with back-and-forth movements, thereby distributing the supply of diesel fuel under high pressure to all nozzles in turn.
Design of the injection pump distribution plunger VE:
When the internal combustion engine rotates, the fuel injection pump drive shaft rotates the cam washer together with the plunger through the clutch at the same speed. The fuel pump shaft rotates twice as slow as the engine.
- the pump rollers are located on roller ring 2;
- cam washer 3 is constantly held pressed against the pressure rollers by the plunger spring;
- when the cam washer (wave washer) 3 rotates, the cams run into the rollers 2, forcing the plunger 4 to perform reciprocating movements;
- in the cam washer 3, the number of tubercles on it (cams) is a multiple of the number of engine cylinders;
- pump plunger 4 distributes fuel sequentially to the injectors in 1 revolution (the example shows a 4-cylinder internal combustion engine);
- the reciprocating movements of the pump plunger are used to take fuel (groove 6) and pump it to the injectors under high pressure through groove 8;
- The injection quantity and feed (cyclic) are adjusted by changing the position of the adjusting sleeve 5, under the control of a mechanical regulator.
To illustrate the operation of the plunger, please watch the video of the operation of the pump elements involved.
Discharge valves
They are located in the supply channels and are designed in such a way that they suck unused fuel back into the pump housing to keep the supply channels filled with fuel. The number of these valves depends on the number of engine cylinders.
Operating principle of the injection valve VE
- When fuel pressure increases, it opens the injection valves and holds them open;
- When fuel injection ends, the valves are pushed back by a spring;
- When the valves return to the lower position, the supply channels are closed and fuel is sucked back in;
- The pressure in the pipelines leading to the injectors drops quickly, by approximately 20 kg/cm2, to prevent fuel from leaking from the injectors;
- At the same time, the discharge valve fits tightly to the seat, blocking the high pressure line from the pump.
Video of the discharge valve working
In this article, we examined the most basic working parts of the VE distribution injection pump. There are many other important mechanisms in pumps of this type, which we will discuss in more detail in the following reviews.
To illustrate the number of elements involved inside a pump of this type, I will attach a clipping from the catalog using the example of pump 104746-1342, also known as 9460612334
A short list of BOSCH VE pumps (lateral designation R or L indicates the direction of rotation of the injection pump):
| 0460404091 VER 722 | Iveco-Aifo 8141 53 kw | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 0460403002 VE L 33/1 | Bukh |
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