Design of four-wheel lock anti-theft circuit based on vehicle brake system

I. Introduction

This article refers to the address: http://

At present, there are many products for automobile anti-theft on the market, but they are mostly used for car door, window and electronic key control. Although they have better alarm function, it is difficult to truly achieve the anti-theft function, so that criminals can take advantage of it. The design is based on the anti-theft control of the vehicle's brake system. Through the combination of mechanical, hydraulic and electrical, the four wheels are perfectly locked to ensure the safety of the vehicle.

Second, the system principle

The system principle is shown in Figure 1. According to the command of the remote controller, the controller controls the brake oil passage to lock or loosen the wheel through the forward and reverse rotation of the relay drive motor to realize the anti-theft function. When the motor rotates, it has a limit signal to prevent overcurrent due to excessive torque. When the remote controller controls the system, the system will automatically issue various voice prompts, especially when the vehicle is driving. The voice alarm will be carried out for a long time, and after a period of time, the vehicle will be gradually locked, the vehicle will be decelerated until it is locked, and the vehicle can be remotely controlled. In addition, the system can also close the hood during the running of the vehicle. The seat belt detects and issues a voice alarm.

Third, the system's hardware components

(1) Motor drive main circuit

The system realizes the function of locking and unlocking the wheel by controlling the forward and reverse rotation of the motor. The realization circuit is shown in Figure 2. According to the instruction of the controller, LOCK and OPEN respectively control the closing of relays K1 and K2 to realize the forward rotation and reverse rotation of the motor, thereby controlling the brake oil passage of the wheel, thereby achieving the purpose of four-wheel lock or release. Anti-theft function. In order to prevent the motor from rotating, the limit switches STB1 and STB2 are set to feed back the signal to the controller in real time, so that the system can work stably.

b) the control loop of the system

The principle of the control system is shown in Figure 3.

The controller selects the 89C52 single-chip microcomputer with 2 counters and 1 timer. The counter T0 is used to calculate the speed of the vehicle, which provides an important basis for the system to perform various control. The sinusoidal signal of the wheel speed sensor is transformed and shaped by the CD4013 and then collected and processed by the single chip microcomputer to determine the current speed of the vehicle.

The open and lock signals sent by the remote controller are amplified by the LM324. The MCU performs acquisition analysis and various protection processing to drive the FET to control the main control loop to realize the anti-theft function of the vehicle. At the same time, when the vehicle is anti-theft control, the system should issue various voice prompts and alarm functions. The voice chip API8108A is controlled by the single-chip microcomputer, and various voice signals required in advance are stored in the voice chip, and are directly driven by the API8108A when the output is needed. speaker.

In addition to the basic anti-theft function, the system also integrates other functions, such as collecting belts, hoods, starters and other signals. When various abnormal conditions occur, various alarms can be issued instantaneously until the vehicle stops.

In order to make the system work reliably, the control system uses a hardware watchdog to monitor the operating status of the microcontroller in real time using the MAX813. Since the system has a control loop and a main loop, various power supplies are required. The LM7805 provides a 5V power supply, and the three-terminal adjustable regulator LM317 provides power for the remote control circuit.

Fourth, the system software implementation

The system design adopts the single-chip C language, the program adopts modular design, and has strong expandability and convenient reading. After the system is powered on, after various initializations, the lock should be cyclically detected and various alarms should be issued to eliminate possible faults in time.

In the case that the system is not faulty, the controller controls according to the opening and closing signals of the remote controller and the current opening and locking states, and issues various alarm information and prompt information. During the control process, according to the current vehicle speed, starter status and other information, the driver is prompted to drive safely and safely. The specific control process is shown in Figure 4:

In the system work, the vehicle may be stolen and work in the locked state. The system must enable the vehicle to stop safely. The partial implementation code is as follows:

Fifth, the system's anti-jamming design

Due to the complex working environment of the vehicle, high requirements are placed on the stability and anti-interference of the system. The signal transmission uses shielded wires to ensure that the wheel speed signal is not disturbed; the pulse signal is shaped to eliminate clutter in signal reception; the electronic components are automotive grade standards and can be used in harsh environments; all boards use Dow Corning coatings, Moisture-proof, anti-corrosion and anti-shock functions, as well as good high-frequency and low-frequency dielectric properties, greatly improve the anti-jamming performance of the system.

This design not only has good anti-theft performance, but also has an alarm function, and can provide various safety tips to the driver during driving. It is a relatively advanced intelligent anti-theft system, which has been installed and used on some vehicles. Practice shows that the system is reasonable in design, strong in anti-interference and stable in operation, and it is a reliable and practical anti-theft product.