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Development of Capacitive Energy Storage High-speed Solenoid Driver (1)
**Abstract:** This paper presents a capacitor-based high-speed solenoid valve drive circuit designed to enhance the performance and efficiency of fuel injection systems. By implementing high-end current feedback control combined with PWM output, the system achieves precise regulation of the solenoid valve's current. Compared to traditional drive circuits, this design simplifies the control logic, aligns better with the current response characteristics of the solenoid valve, and effectively reduces power consumption while preventing overload conditions. The proposed circuit is particularly suitable for applications requiring rapid and accurate control, such as in high-pressure common rail diesel engines.
**Keywords:** high-speed solenoid valve; drive circuit; capacitive energy storage; high-end current detection
**Introduction:**
The high-pressure common rail fuel injection system has become a key development direction in modern diesel engine technology. This system ensures precise fuel injection timing, accurate fuel quantity, and optimal injection rate by controlling the common rail pressure and enabling quick opening and closing of the fuel injectors. A critical component in this system is the high-speed solenoid valve, whose drive circuit must meet specific requirements to ensure efficient and reliable operation.
First, before the solenoid valve opens, the drive module should supply as much energy as possible to generate sufficient electromagnetic force, thereby reducing the turn-on response time. Once the valve is open, the magnetic circuit experiences low resistance due to the small air gap, allowing a smaller holding current to maintain the valve's position. This minimizes energy loss, reduces coil heating, and facilitates faster closure of the valve.
In summary, the drive circuit must provide an appropriate current profile throughout the solenoid valve’s operating cycle. Traditional drive circuits include adjustable resistance, dual voltage, pulse width modulation (PWM), and dual voltage PWM configurations. While these methods improve efficiency compared to simple resistive drives, they still face challenges, especially when multiple injection signals overlap in timing.
This issue arises because when two fuel injection signals occur simultaneously, the conduction of one solenoid valve can cause a voltage drop in the DC/DC boost circuit, which may prevent another valve from operating correctly. In the context of this paper, the dual-injector configuration in high-pressure common rail engines—featuring pilot and main injectors—often results in overlapping injection timings. Therefore, a new drive circuit is necessary to ensure reliable operation under these conditions, maintaining accurate injection timing and precise fuel delivery.
**Capacitor Energy-Saving High-Speed Solenoid Valve Drive Circuit:**
The main circuit of the capacitor energy-saving high-speed solenoid valve drive system is illustrated in Figure 1. The ignition pulse signal INJ1 from the front cylinder and the pilot injection signal INJ3 from the rear cylinder are fed into a high-side driver chip. After the DC/DC boost circuit, the 100V power supply charges capacitor C1 through MOSFET Q1 during the injection pulse period, and then Q1 is turned off. The PWM generator controls the duty cycle of the 12V power supply via MOSFET Q2. The sources of Q1 and Q2 are connected to the upper ends of solenoid valves L1 and L3 through diodes D11 and D12, which isolate the 100V and 12V voltages. Signals INJ1 and INJ3 are used to control the low-side MOSFETs Q4 and Q5, respectively. Diodes D13 and D14 serve as freewheeling diodes. A current sense amplifier and PWM generator are integrated for feedback control, ensuring stable and accurate current regulation.
**Figure 1:** Capacitive energy-saving high-speed solenoid valve drive circuit schematic diagram
**Figure 2:** Solenoid valve current waveform diagram
**Figure 3:** High-side current detection circuit diagram
This design not only improves energy efficiency but also enhances the reliability and responsiveness of the solenoid valve, making it well-suited for advanced fuel injection systems.