Car ABS/ASR Integrated Control System Based on MC9S12DP256

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Car ABS/ASR Integrated Control System Based on MC9S12DP256 [Copy link]

Abstract: This paper introduces the car ABS/ASR integrated control system based on Motorola's new generation HSC12 series 16-bit MCU - MC9S12DP256 microprocessor, and describes in detail the hardware circuit and software logic of the integrated control system. Through the actual vehicle test, it is proved that the control effect is good, which lays the foundation for the integration of active safety control devices of cars.

Keywords: MC9S12DP256 ABS ASR integrated control

The anti-slip regulation system (ASR) is developed on the basis of the anti-lock braking system (ABS). After adding the engine output torque adjustment function and the drive wheel brake pressure adjustment function to the car equipped with ABS, the wheel speed sensor and pressure regulator used by ABS can all be used by ASR [1] . ASR and ABS are very similar in algorithm, and many program modules can be used universally. Therefore, in practical applications, the two can be integrated into one controller to form an ABS/ASR integrated system. 1 Introduction to the ABS/ASR integrated control system for cars 　　By modifying the hydraulic brake system of the Jetta GTX test vehicle, an ABS/ASR integrated system hydraulic actuator that can independently adjust the pressure of four wheel cylinders was realized [2] . On this basis, a car ABS/ASR integrated control system was developed, which mainly includes three parts: control system ECU, sensor, and actuator. Figure 1 is a schematic diagram of the ABS/ASR integrated control system for cars. Figure 1 ABS/ASR integrated control system block diagram 　　When the car is driving normally, the ECU of the ABS/ASR integrated control system collects and processes sensor signals in real time, and selects different control methods to control the car according to the information provided. The control methods include the braking torque control mode of adjusting the wheel cylinder pressure and the throttle opening control mode of adjusting the engine output torque. The realization of the ABS and ASR subsystem functions is the result of the appropriate combination and reasonable control of the above two control methods. 2 ECU of ABS/ASR integrated control system 2.1 Selection of MCU 　　MCU is the core of the ABS/ASR integrated control system. It is responsible for data collection and processing, all logical operations and the realization of the final control. Considering the requirements of the integrated control system for its computing power, storage space, I/O interface and the purpose of subsequent integration of other systems, the powerful Motorola new generation HSC12 series 16-bit MCU - MC9S12DP256 was selected. 　　It has strong computing power, rich I/O interfaces and ample storage space. Using STAR12 CPU, the core computing power can reach 50MHz, the bus speed can reach 25MHz, and the optimized instruction set is used, so the computing speed of instructions has been greatly improved. The on-chip PLL function can conveniently select the core frequency of the MCU regardless of the external crystal frequency. The chip integrates 256K FLASH, 12K RAM and 4K EEPROM, which can fully meet the program's requirements for storage space. It has a rich I/O interface, including two asynchronous serial communication interfaces (SCI), three synchronous serial communication interfaces (SPI), eight-channel input capture/output comparison (IC/OC), sixteen 10-bit A/D interfaces, eight 8-bit PWM, twenty-nine independent digital I/O interfaces, twenty digital I/O interfaces with interrupt and wake-up functions, five CAN bus interfaces, one IIC bus interface, and one BDLC (J1850) interface [3] . 　　The MCU has four input captures (with a holding buffer), and can use an independent ECT capture clock to complete the period calculation between two pulses. It is very suitable for collecting the wheel speed of four wheels, greatly improving the working efficiency of the MCU. 2.2 ECU Hardware Circuit Design 　　The peripheral circuit of MCU adopts modular design concept, that is, the electronic control unit is divided into different modules, and the relatively mature and fixed modules are composed of a separate circuit board, and the modules that change greatly during the research process are composed of another separate circuit board. The boards communicate with each other through the I/O expansion slot. This design method is conducive to the maintenance and expansion of the system during the experiment. For example, when the circuit needs to be changed or the system needs to be expanded, there is no need to redesign the entire circuit, just change or add to the corresponding module; modular design also has better electrical characteristics. For example, the drive module is a relatively large interference source, which has a great impact on the A/D conversion and the work of the MCU. It can be placed on different circuit boards and isolation measures can be taken for the signal line. 　　According to the characteristics of the ABS/ASR integrated control system, the entire electronic control unit is divided into A board and B board, and the two circuit boards are connected through the I/O bus expansion slot. 　　The A board mainly includes the main control chip MC9S12DP256 and its minimum system peripheral circuit, communication interface circuit and data acquisition circuit, as shown in Figure 2. Figure 2 Schematic diagram of the circuit structure of board A 　　The peripheral circuits of the MC9S12DP256 minimum system include power modules, peripheral reset circuits, clock crystal circuits, and working mode selection. 　　The communication interface circuit includes a BDM interface. Two SCI serial communication interface circuits, one of which is connected to the fault diagnosis driver chip MC33199 through a hardware jumper, and two CAN communication nodes are derived using the PCA82C250 driver chip, which are reserved for the expansion of the integrated control system. 　　Board A also includes the digital, analog, and switch quantity acquisition and processing circuits in the ECU, mainly including four wheel speed signals, throttle opening signals, accelerator pedal opening signals, high-pressure accumulator pressure sensor signals, brake pedal switch signals, etc. 　　Board B mainly includes the actuator drive circuit and the switch quantity signal processing circuit, as shown in Figure 3. Figure 3 Schematic diagram of the circuit structure of board B 　　The actuators driven by the system mainly include four normally open oil inlet valves, four normally closed oil outlet solenoid valves, four ASR solenoid valves and an ABS motor of the ABS pressure regulator. 　　The enabling signals of the ABS and ASR subsystems and the related circuits of the working indicator lights are also placed on the circuit board. 2.3 ECU control software design 　　The ABS and ASR subsystems in the ABS/ASR integrated control system are complex control systems. The integration of the software system is not to simply superimpose the ABS and ASR control systems, but to organically integrate them, while also considering the real-time and reliability of the software operation. The 　　control software of the integrated control system is mainly composed of several parts, such as the system initialization module, the startup self-test module, the main control module, and the brake pedal interrupt service program module. The overall block diagram is shown in Figure 4. Figure 4 ABS/ASR integrated control system software block diagram 　　The system initialization module initializes the system when the system is powered on and reset. The initialization content includes the internal clock of the MCU, the settings of each port, the serial communication interface, the analog and digital channels, the watchdog timer, the system variables, etc., to ensure the normal operation of the MCU. In addition, it also includes resetting the actuator of the integrated system to ensure the safe driving of the vehicle. 　　The startup self-test module performs static detection on the key software and hardware parts after the system is initialized to determine whether the software and hardware of the system are working normally. If a fault is found in the integrated control system, the fault warning light will continue to light up. 　　The main control module is the main control program of the ABS/ASR integrated control system, as shown in the shaded dotted box in Figure 4. The main control module uses the real-time interrupt RTI to perform a fixed cycle of 20ms, continuously calling the fault diagnosis module, the data processing module, the reference speed calculation module, the road surface recognition module and the vehicle motion state recognition module to judge the vehicle motion state and the external environment in real time. Then, according to the current operating state of the vehicle, the control execution module controls the logical threshold value of ABS or ASR respectively. 　　Considering the need for emergency switching between the driver's braking action and the ASR braking intervention control, a brake pedal interrupt service program is designed. When the brake pedal-triggered interrupt is collected, the brake pedal interrupt service program is entered. If the integrated control system is in the ASR working mode, the current control is immediately exited, the actuator module is reset, and the normal braking mode is restored. The driver's braking action is not interfered with, ensuring the safety of vehicle driving. 3 Test results and analysis 　　Using the developed acquisition system [4] and the ABS/ASR integrated control system designed in this paper, typical ABS and ASR tests were carried out on the Jetta GTX test vehicle to verify its control effect. 　　The ABS test was carried out on a dry asphalt road with an initial braking speed of 50 km/h. Figure 5 shows the straight-line braking process with ABS control. The figure shows the process of the vehicle's left front wheel speed change. During the entire braking process, it can be relatively close to the vehicle speed, and the wheel slip rate is also controlled in a relatively ideal area, ensuring the directional stability of the vehicle during braking. Fig.5 Straight line braking with ABS control, dry road, initial speed 50km/hFig.6 Comparison of left and right driving wheel speeds on ASR split roadFig.7 Comparison of left and right driving wheel slip rates on ASR split road 　　The ASR test selected the first gear on the open road and the right wheel was on the low adhesion coefficient road. Figure 6 shows the comparison of the speed of the left and right driving wheels during the starting process, where curve 1 is the speed of the right driving wheel, curve 3 is the speed of the left driving wheel, and curve 2 is the speed of the non-driving wheel, which can be approximately regarded as the vehicle body speed. It can be seen that at the beginning of the start, the right driving wheel slipped significantly. At around 33.5 seconds, the ASR began to adjust and the wheel slip was significantly improved. Figure 7 shows the change curve of the slip rate of the left and right driving wheels during the starting process, which more clearly reflects that after the ASR control, the slip rate of the right slipping driving wheel is controlled within a relatively ideal range. At the same time, due to the influence of the brake intervention, the slip rate of the left driving wheel increased slightly. 　　Through the actual vehicle test, it is shown that the ABS and ASR functions in the ABS/ASR integrated control system have achieved relatively ideal control effects, creating conditions for the integration of other chassis active safety control systems.

小公举223

Thanks for sharing, old man.