Design of ABS driving circuit based on integrated chip

introduction

ABS is an essential safety electronic device in today's cars, and its function is increasingly valued by people. The ABS system uses solenoid valves and oil return pumps to finely adjust the wheel cylinder pressure in the brake to prevent excessive braking from locking the wheels. Since the working environment of ABS is very harsh, in order to ensure the efficiency and reliability of the solenoid valve and motor response, in addition to the parameters of the actuator itself, the design of the drive circuit also directly determines the quality of the drive.

Today's automotive electronics market is extremely hot and the competition is very fierce. Major integrated chip companies, such as ST, Freescale, and Infineon, have designed dedicated integrated chips for ABS and proposed their own ABS solutions. This chip is like a black box, which facilitates the circuit design process, and because of its high degree of integration, it makes the circuit more concise and more reliable, representing the direction of future circuit design.

1 Integrated solution for ABS drive circuit

The integrated solution of ABS drive circuit is shown in Figure 1. TLE6210 is selected as the high-end driver of DC motor and solenoid valve master switch, and L9349 is selected as the low-end driver of 8 solenoid valves (4 in and 4 out).

The ABS controller changes the current on-off and frequency on-off of the solenoid valve coil through PWM control to realize the wheel cylinder boost, pressure maintenance and pressure reduction operations of wheel braking; when the solenoid valve ABS pressure reducing valve is opened for pressure reduction, the return oil pump can return the brake fluid in the wheel cylinder to the brake master cylinder for use in the next control cycle; the high-side master switch of the solenoid valve is used to control the power supply circuit of the solenoid valve. If the ABS system fails, the power supply is disconnected so that the 8 solenoid valves below do not work, and the output pin of the high-side master switch of the solenoid valve is restored to the normal state. VR, when the ABS system is powered on and reset or the watchdog gives a control signal, the output pin is switched to the ON state, which conforms to the actual working logic of ABS and ensures that when the ABS system fails, the control of the solenoid valve can be quickly exited and restored to normal braking. The MRA pin of the chip is the control signal input terminal, and the output pin MR drives the DC motor. When the I/O port of the MCU gives a high level to the MRA pin, the external MOSFET is turned on and the DC motor realizes the oil return function. Since the solenoid valve and the motor are inductive loads, an external reverse freewheeling diode is also required. The driver part of the chip has over-temperature protection, over-current protection and short-circuit protection. When the above fault conditions occur, the chip can be automatically shut down, so it has strong self-protection characteristics.

The highly integrated solution based on the TLE6210 chip can not only greatly simplify the motor drive circuit and the solenoid valve pre-drive circuit, but also greatly reduce the number of discrete chips required for the entire controller, and the PCB board size is also smaller, which reduces the cost and enhances the reliability of the controller.

2 Solenoid valve drive based on L9349

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According to experimental measurements, the maximum starting current of the four normally open oil inlet solenoid valves of a general ABS pressure regulator is about 3.6 A; the maximum starting current of the four normally closed oil outlet solenoid valves is about 2.4 A. The working voltage of L9349 is 4.5~32 V, the internal resistance of two channels is 0.2 Ω, the maximum load current is 3 A; the internal resistance of the other two channels is 0.3 Ω, and the maximum load current is 5 A, which can just meet the driving current requirements of the ABS normally open and normally closed solenoid valves. In addition, the lower on-resistance can ensure low power consumption. Therefore, L9349 is very suitable for driving and controlling the ABS solenoid valves. The schematic diagram of the solenoid valve driving circuit is shown in Figure 3.

In Figure 3, each L9349 can drive 4 solenoid valves, which is a typical low-end driver. The chip is supplied with 12 V power supply voltage through the Vs port; when the input terminals IN1~IN4 are given PWM control signals, the output terminals can be easily controlled to drive 4 solenoid valves. The maximum driving capacity of the OUT1 and OUT2 ports is 5 A, and the normally closed solenoid valves of the ABS should be connected; the maximum driving capacity of the OUT3 and OUT4 ports is 3 A, and the normally open solenoid valves of the ABS should be connected, and they cannot be connected in reverse; the EN port is the enable terminal, which can quickly shut down the chip through the MCU; the digital ground and analog ground of the L9349 are separated, which improves the anti-interference ability of the drive module.

D1~D4 are fault diagnosis pins, which must be connected to pull-up resistors to be used. When the circuit is working normally, the pin is at a logic high level. If a fault occurs, it will automatically be set to a logic low level. By logically combining the input control terminal and the state feedback terminal of each independent channel, the working state of the output terminal can be identified in real time, and corresponding measures can be taken immediately, including exiting the ABS function, lighting the fault display lamp, and transmitting the fault code. The function truth table is shown in Table 1.

3 Conclusion

The solenoid valve drive circuit design currently used in ABS design is mainly based on power MOSFET, supplemented by protection circuits, isolation measures, etc. to ensure its reliability, and a special self-diagnosis circuit must be designed for fault detection. Although the discrete solution has certain flexibility in the design of specific circuits, the cost and PCB space consumption are high; this solution uses ABS-specific integrated chips TLE621O and L9349, which integrate drive and monitoring functions. When used in ABS systems, it can reduce power consumption, facilitate fault detection, improve reliability, and greatly improve the performance of the entire system.