Realize the design of vehicle stability control system in two circuits of ABS and DYC

1 Introduction

When the vehicle is running, the DYC (Yaw Moment) circuit is in working condition. In case of an emergency, it is necessary to step on the brakes for control. At this time, the DYC circuit stops working and the ABS (Anti-lock Brake System) circuit is in working condition. How to realize the two The fast, efficient and reliable switching of a circuit system is the focus of this article.

2. Control system model

The vehicle stability control system model is shown in Figure 1:

Realize the design of vehicle stability control system in two circuits of ABS and DYC

When the vehicle encounters an emergency during driving, the driver steps on the brakes. At this time, in order to prevent the wheels from locking up and causing danger, the ABS (anti-lock brake system) circuit starts to work, and the DYC (yaw moment) circuit stops working; when Without stepping on the brakes, the DYC (Yaw Moment) circuit is working when the car is running, in order to prevent sideways and other dangers. This article needs to design a switching circuit to realize high-speed instantaneous switching between the ABS and DYC circuits and improve the safety of driving.

3. Design principle of interface system

3.1 Principle of switching circuit

The schematic diagram of the switching circuit is shown in Figure 2:

Realize the design of vehicle stability control system in two circuits of ABS and DYC

The circuit diagram uses two 8-way latches with 74LS373 three-state gates and a CD4069 inverter. When the pull-up resistor 10MΩ is not inputting the potential, the potential of the latch terminal automatically maintains the high potential, and the input signal changes with the output signal at this time.

74LS373 has 8 output D latches with three-state gates on-chip, and its structure diagram is shown in Figure 3. When the enable terminal G is at a high point, the content in the latch can be updated normally, and the latch is realized at the moment when it returns to a low level. At this time, the output control terminal of the chip is low, that is, the output three-state gate is opened, and the address information in the latch can be output through the three-state gate. In addition to 74LS373, 84LS273, 8282, 8212 and other chips can also be used as address latches, but the connection method is slightly different when used. Because the wiring is slightly more complicated, the hardware is more versatile, and the price is slightly more expensive, it is not as common as the 74LS373. Therefore, considering the cost and simplicity of the circuit, 74LS373 is used as the main chip for the circuit design of the interface system. 74LS373 function table as attached table. Figure 3 shows the principle of the structure.

Z: High impedance output signal level has been established before steady state input

3.2 The working principle of the circuit

When the vehicle is manoeuvring steadily, the DYC (yaw moment) circuit works. When the brake is stepped on, the signal becomes 1 (high level). At this time, the first 74LS373 chip with 8 input channels is selected, and the output signal makes the ABS circuit work. , To prevent the wheels from locking up. Realize the high-speed and high-reliability switching between DYC and ABS circuits.

4. Reliability design

4.1 Reliability of power supply

The vehicle power supply is 12V battery, and the voltage of 74LS373 needs 5V, so the DC-DC conversion is involved in the design process. Here, choose 7805, 7805 is a three-terminal regulator, which can be converted to a stable 5V voltage. As we all know, the DC output of a regulated power supply needs to be filtered. The output noise of a switching power supply is mainly divided into two categories: differential mode noise and common mode noise. The differential mode noise is mainly caused by the switching tube of the output part, and is typically caused by the switching diode. Adding LCR filtering or stringing saturated magnetic beads on the diode can significantly suppress this noise. A large amount of common mode noise exists in the isolated switching power supply, which is mainly generated by the switch tube at the input end. This noise is coupled to the output through the switching transformer. Adding LCR filtering has almost no effect. There are three ways to solve this noise: add a capacitor of several hundred to several thousand picofarads between the output and input ground; add tens of millihenries of power filter inductance before the input rectification; add a capacitor near the switching transistor. Here, a magnetic bead can be put on the wire or resistor, which is equivalent to the power Inductor to filter and suppress the high frequency, mainly the noise above 1MHz.

4.2 Reliability design of input and output ports

Optoelectronic isolation technology can be used. The main function is to isolate circuits with different electrical characteristics, such as analog circuits and digital circuits. The amplifying circuit is an analog circuit and the gain control is a digital circuit. The gain control signal transmits the control signal through the photoelectric coupling device to avoid the digital circuit. Coupling with analog circuits, photoelectric isolation switches are used in power Electronic systems to isolate high-voltage circuits, realize low-voltage circuits to control high-voltage circuits, and use photoelectric coupling devices to transmit control signals.

4.3 Anti-interference measures in PCB design

(1) Layout

Considering the size of the PCB, the PCB size is too large, the printed lines are long, the impedance increases, the anti-noise ability is reduced, and the cost increases; if the PCB size is too small, the heat dissipation is not good, and the adjacent lines are susceptible to interference. After determining the size, determine the location of the special component. Finally, according to the functional units of the circuit, all the components of the circuit are laid out. The following principles should be observed when determining the location of special components: try to shorten the connection between high-frequency components, try to reduce the distribution parameters and mutual electromagnetic interference, the susceptible components should not be too close, and the input and output components should be as far away as possible; There may be a high potential difference between these components or wires. The distance between them should be increased to avoid accidental short circuits caused by discharge. High-voltage components should be placed in places that are not easy to reach during debugging; components weighing more than 15g, Use brackets to fix and then weld. Those large, heavy, and heat-generating components should not be mounted on the printed board, but should be mounted on the chassis bottom plate of the whole machine, and the heat dissipation problem should be considered. The thermal components should be far away from the heating components. ; For the layout of adjustable components such as potentiometers, adjustable inductance coils, variable capacitors, micro switches, etc., the structural requirements of the whole machine should be considered. For external adjustment, its position should be adapted to the position of the adjustment knob on the chassis panel; the position occupied by the positioning hole of the printed board and the fixed bracket should be reserved.

(2) Component layout

According to the functional units of the circuit, when laying out all the components of the circuit, the following principles must be met:

Arrange the position of each functional circuit unit according to the circuit flow, so that the layout is convenient for signal circulation, and the signal is kept in the same direction as possible.

Take the core component of each functional circuit as the center and lay out around it. The components should be evenly, neatly and compactly arranged on the PCB, and the leads and connections between the components should be reduced and shortened as much as possible.

For circuits operating at high frequencies, the distributed parameters between components must be considered. Generally, the circuit should be arranged in parallel as much as possible. In this way, it is not only beautiful, but also easy to install and weld, and easy to mass produce.

The components located on the edge of the circuit board are generally not less than 2mm away from the edge of the circuit board. The best shape of the circuit board is rectangular, and the aspect ratio is 3:2 or 4:3. When the size of the circuit board is larger than 200×150mm, the mechanical strength should be considered.

(2) Wiring:

The wires used for the input and output terminals should be avoided as much as possible adjacent to parallel, and it is best to add ground wires between the wires to avoid feedback coupling.

When the thickness of the copper foil is 0.05mm and the width is 1 to 1.5mm, the temperature will not be higher than 3 degrees through a current of 2A. Therefore, a wire width of 1.5mm can meet the requirements. For integrated circuits, especially digital circuits, 0.2-0.3mm wire width is usually selected. For integrated circuits, especially digital circuits, as long as the process permits, the pitch can be as small as 5-8mm.

The corners of the printed conductors are generally arc-shaped, and the right angle or the included angle will affect the electrical performance in the high-frequency circuit. Try to avoid using a large area of ​​copper foil, otherwise, the copper foil will expand and fall off when exposed to heat for a long time. When a large-area feeder foil is required, the grid shape helps to eliminate the volatile gas generated by the heating of the adhesive between the copper foil and the substrate. According to the size of the printed circuit board current, try to increase the width of the power line to reduce the loop resistance. At the same time, make the direction of the power line and the ground line consistent with the direction of data transmission, which helps to enhance the anti-noise ability.

5. Concluding remarks

In summary, the switching between ABS and DYC circuits can be completed by an inverter CD4069 and two 74LS373. The circuit is simple and clear, high in efficiency, and inexpensive. After testing and running, it fully meets the functional requirements. The stability of vehicle operation is well controlled.

The Links:   1DI200Z-100 SKKT323-16E

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