Power supply system of modern engines

4.12.1 Power supply system of modern engines

Nothing stands still - everything is constantly developing, including car feed systems. It is necessary to achieve a more accurate metering of fuel depending on the operating mode in order to improve all the technical indicators of the engine. It is also necessary to mix gasoline with air much more thoroughly for more complete combustion, and this can only be achieved by atomizing fuel. This was achieved by installing, instead of the carburetor, first a throttle body injection, then a multipoint injection and, as an apogee, direct fuel injection. Let's consider all the stages of development of power systems in more detail.

4.12.2 Monoinjection

The first part of the word comes from the Greek "monos", which means "one". In this system, manufacturers simply installed a similar mechanism instead of the carburetor. It differed in that the fuel was not atomized due to vacuum, but was injected by a single nozzle (an example of a fuel system with throttle body injection is shown in Figure 4.51). The control of the injection process was entrusted to the electronics, having achieved accurate metering of fuel during its injection.

The simplicity of the throttle body injection system is the trump card in the game against the carburetor. Low injection pressure (0.5-1.0 bar) made it possible to use a conventional electric fuel pump. And the control with the help of an electronic control unit (ECU) made it possible to constantly monitor the amount of injected fuel for maintaining the stoichiometry of the fuel mixture.

4.12.2.a Stoichiometry

Note
Stoichiometry for a fuel-air mixture is a certain ratio of fuel and air at which complete combustion of a given fuel occurs. For gasoline, this ratio is 1:14.7. This means that for complete combustion of 1 kg of gasoline, almost 15 kg of air is required.

4.12.2.b System sensors

Several sensors are used for controlling the entire system:

• throttle blade position sensor (opening angle);
• crankshaft position and rotation speed sensor;
• camshaft position sensor (also called phase sensor);
• oxygen excess sensor (another name - lambda probe);
• pressure regulator (controls the fuel injection pressure).

Having received data from all these sensors, the ECU sends a signal to the fuel injector, which injects exactly as much fuel as needed at a given time.

Figure 4.51 Example of feed system for gasoline engine with throttle body injection.

Surplus fuel is drained through the return line back to the fuel tank.

Fuel injection is synchronized with the help of ignition distributor.

4.12.3 Distributed and direct injection

In order to implement this system, instead of one common injector manufacturers installed one injector for each cylinder (thereby improving the operation of the engine). The injection pressure was increased for better atomization of fuel, so that mixing with air was more thorough. Such requirements have arisen due to the fact that the injectors are installed in the intake manifold after the throttle blades and directed to intake valves. The multipoint fuel injection diagram is shown in Figure 4.52.

Figure 4.52 Diagram of multipoint fuel injection.

4.12.3.a "Main composition" of sensors

The "main composition" of the sensors remained the same (relative to throttle body injection):

• throttle blade position sensor (opening angle);
• crankshaft position and rotation speed sensor;
• camshaft position sensor (also called phase sensor);
• oxygen excess sensor (another name - lambda probe);
• a pressure regulator is also installed for controlling the fuel injection pressure.

Note
The regulator “moved” from the injector body to the fuel rail of the feed system.

In addition, new sensors have appeared that collect data on engine operation:

• mass airflow sensor;
• coolant temperature sensor;
• knock sensor;
• voltage sensor in the on-board electric system;
• vehicle speed sensor;
• intake air temperature sensor;
• pressure sensor in the intake manifold.

Figure 4.53 Control system diagram of the engine control system with multipoint fuel injection.

1. Diagnostic connector; 
2. Instrument panel; 
3. Immobilizer sensor; 
4. Electronic control unit of immobilizer; 
5. Electric fan relay; 
6. Cooling installation electric fan; 
7. Electric control unit of the engine; 
8. Air filter body assembly; 
9. Mass airflow sensor; 
10. Throttle blade assembly; 
11. Throttle blade position sensor; 
12. Idle run regulator; 
13. Fuel injector; 
14. Spark plug; 
15. Ignition module; 
16. Coolant temperature sensor; 
17. Knock sensor; 
18. Battery (battery pack); 
19. Ignition lock; 
20. Main relay; 
21. Oxygen excess sensor (lambda probe); 
22. Speed sensor;
23. Crankshaft position sensor; 
24. Fuel filter; 
25. Fuel pump relay; 
26. Fuel pump assembly with fuel level sensor; 
27. Fuel tank; 
28. Purifier; 
29. Safety valve; 
30. Roll over valve; 
31. Return valve; 
32. Adsorber; 
33. Adsorber blow down valve.

The driver, when pressing the accelerator pedal, opens the throttle blade, and more air starts flowing into the intake system. The electronic control unit, which collects data from all sensors, issues a command to the fuel injectors. Thereby it determines the amount of fuel injected, and in modern engines - even the intensity and number of cycles per fuel injection. This results in improved fuel consumption, power and torque.

Note
The throttle blade can be actuated either by a cable directly from the accelerator pedal or electronically. In this case, a sensor of position of the accelerator pedal is installed on it. A stepper motor, which rotates by an angle corresponding to the movement of the "gas" pedal at a certain distance, is also installed on the throttle blade.

4.12.3.b Inlet valve

However, on the way to the ideal improving of the operation of the internal combustion engine, the intake valve was still installed - additional resistance in the path of the air-fuel mixture. It was decided to inject fuel directly into the cylinder in order to obtain the desired characteristics of the internal combustion engine. The designers were faced with an acute question of how to implement this, since the fuel, which is injected onto the valves during multipoint injection, had time to thoroughly mix with air, which was not the case with direct injection. The solution of this situation was found in the complex shape of the piston, or rather its top. However, in recent years, engine developers have made great strides in the design of direct injection gasoline engines. At first, nothing good came of it. They managed to obtain low fuel consumption, high power and consistently high torque, but at the same time, the requirements for fuel quality increased. The last moment became a limiting factor in the development of this technology in the CIS countries.

The direct fuel injection system uses the same sensors as the multiport fuel injection system. The difference lies in the fuel injectors, which must withstand higher operating temperatures, pressures and shock loads. The fuel metering accuracy in these injectors is almost an order of magnitude higher than in distributed injection injectors.

Note
It is worth mentioning that attempts to create a gasoline engine with direct fuel injection have been made more than once. The most striking example of use of such an engine in history is the 1954 Mercedes 500 SL. Direct injection system provided excellent power and torque characteristics with acceptable fuel consumption. However, the injection was mechanical. All the engine parts had to be precisely machined. As a result of this they were very expensive due to the technological level that was 60 years ago.