Overhaul of Solenoid Valves for Electronically Controlled Diesel Engine Injectors

Overhaul of Solenoid Valves for Electronically Controlled Diesel Engine Injectors

I. Structure and Working Principle of Injector Solenoid Valves

Function of Injector Solenoid Valves: To accurately control the injection quantity, injection timing, and injection pattern.

1. Injector Solenoid Valves for Bosch Common Rail Systems

The Bosch common rail injector (including the solenoid valve) is shown in Figure 4-57.

Figure 4-57 Structure of a Bosch common rail injector

1-Solenoid valve coil power supply

2-Control valve spring

3-Electromagnet and coil

4-Pivot

4-Return spring;

6-Cavity

7-Ball valve

8-Return throttling oil passage

9-Valve control chamber

10-Common rail connection

11-Inlet throttling orifice

12-Control piston

13-Nose spring

14-Pressure rod

14-Pressure chamber

16-Nose pin

17-Injector

Currently, domestically produced China III diesel engines widely adopt a pre-injection plus main injection process to address emissions and reduce noise. The injection waveform of the Bosch second-generation common rail system used domestically is shown in Figure 4-58.

(1) Composition and Function of Main Injection Current Waveform. The main injection current waveform consists of peak current and holding current. The function and related explanation of each current segment are as follows: ① Peak current accelerates the rise response speed of the solenoid valve; ② Holding current follows the peak current to reduce system energy consumption.

This is a typical current-controlled injector drive. The internal structure of the current-controlled drive is more complex than that of the voltage-controlled type, as its name suggests. In addition to performing the basic on/off function, it also provides a current limiting function. When the drive circuit is working, the loop current is unrestricted for a period of time until the injector needle valve opens. This time period is pre-adjusted by the manufacturer. Once the solenoid injector needle valve opens, due to the small working air gap and low magnetic reluctance of the magnetic circuit, a small holding current is sufficient to generate a large enough electromagnetic attraction to maintain the opening state of the solenoid control valve. Thus, the drive control current quickly drops to a small value to protect the injector from overheating and damage due to the large current throughout the pulse cycle, saving energy and facilitating the rapid closing of the solenoid control valve.