Design and Development of ECU for Electro-Hydraulic Power Steering System of Automobile

Design and Development of an ECU for an electro-hydraulic power steering system for automobiles 14:16:41 Source: Micro-Computer Information Author: Gao Ting

SYSTEM INTRODUCTION
Electricity
The Hydraulic Power Steering System (EHPS) is mainly composed of the following parts: the power steering control unit (ECU), power steering sensor, gear pump with electric pump, storage tank, steering transmission device,
CAN
Bus System. Our main task is to assist in the hardware and software research and development of the steering control unit (ECU. The power steering control unit is based on the signal sent from the power steering sensor, and CAN
The speed of the vehicle on the bus is used to control the speed of the electric pump, and the oil volume of the gear pump is controlled to control the power steering transmission device. In this way, we can choose
The previous driving speed is used to determine the steering power we need.
1. ECU design overview
1.1 ecu cpu Selection
The key to the design of the controller (ECU) is to select a single-chip microcomputer suitable for specific control objectives. For the vehicle electro-hydraulic power steering system, it has the following requirements for single-chip microcomputer:
① Anti-environmental interference, meeting the temperature range requirements of Automotive chips, that is,-40 ~ + 125 ℃.
② There are many I/O ports to achieve a variety of control functions; fast computing speed to meet real-time control requirements.
③ Use standard communication interfaces to Facilitate the Implementation of diagnostic functions, and have the ability to communicate with other CPUs on the vehicle.
④ There is a good price-performance ratio, which facilitates batch loading and makes it a popular product.
Based on the above features, the use of 16-bit single-chip microcomputer is a moderate choice for the electric hydraulic power steering system. In addition, the vast majority of foreign electro-hydraulic power steering system products currently use this grade of single chip microcomputer. Infineon XC 164CM is a moderate product, a 16-Bit Microcontroller designed by Infineon for the vehicle control system.
1.2 ECU Module Design

As shown in figure 1, the design is based on infineon XC 164CM single-chip microcomputer, which includes four modules: input, output, fault diagnosis, and vehicle information data transmission.
① Input module
Input
Each input channel corresponds to an independent Capcom channel. Capcom
The channel can interrupt each event after receiving it. It has a capture register CCX, that is, it can retain 1
Events. Because the interrupt address is independent, you do not need to identify the interrupt source when you enter the interrupt service program, which improves the processing efficiency of the interrupt service. CC16 and cc17 are also used in the system
As the input signal capturing channel of two Hall Device pulses, cc23 is used as the input signal capturing channel of the steering wheel corner pulse. Capcom
The channel greatly improves the quality of the collected signal and consumes less CPU time. The capture event resolution of Capcom is 400 ns at a 20 MHz clock speed.
② Output module
XC 164CM has 47 I/O ports. In this system, P1 port is used as the control output port. Each I/O port uses an independent controller to control the input/output.
③ Diagnosis module
Ehps
It is a high-reliability system that requires internal programs to monitor the system at any time. Once a fault occurs, it can be recorded in time and stored. This system uses the I2C bus E2
As the fault code storage device, the prom uses the synchronous serial function of XC 164CM to implement communication between the I2C bus and E2PROM. The XC 164CM serves as the host and E2PROM
As a slave. External diagnostic communication is achieved through the can1 port of XC 164CM, and communication with the PC is achieved through a USB data acquisition card.
④ Vehicle Information Data Transmission
Mcu xc 164CM comes with two CAN Bus controllers, can1 and can2. There is a 2 k-byte can register space inside to implement CAN communication. It has 32 information bodies, and each information body has 8 bytes of data that can be transmitted. The speed and engine speed required by the ehps system are designed through 2. ECU Software
The program structure adopts the popular multi-module structure in C language. Compared with the previous single-module structure, the program structure is clear and convenient for program transplantation and program maintenance.
2.1 main program of ehps ECU
The main ehps loop is a timed and cyclic calling program. The program diagram is shown in figure 2.

It is mainly used to call various subprograms. The timing time depends on the complexity of the algorithm. When the algorithm is complex and time-consuming, the time of each loop can be defined for a long time. If the CPU
The function is strong and the algorithm is relatively simple. You can use a short cycle time. For example, 5 ms
Or even a shorter time. Some time-consuming programs, such as diagnostic programs, can be called outside the main ehps loop. Each time the program starts execution, the initialization program must be called. The hardware peripherals must be initialized first,
Such as serial port and timer. The initialization is defined only once upon each power-on, and the interruption must be enabled. Then, software initialization should be performed to set the ehps control threshold. Some of these thresholds change in the control process, and some
Is a constant. If it is a constant, you can use C
Macro-defined methods in the language are defined. Calling a diagnosis program is a comprehensive diagnosis of the system. This program takes a long time, so it is only outside the main ehps loop. Ehps
After the system completes the preparation, it enters the ehps loop. Ehps Loop
Generally, it can be defined as 4 ~ 50 ms
. To call various algorithms at this time, make sure that the total running time of each program is less than the ehps cycle time, so as to ensure that the ehps
. If the execution time of a program is greater than the ehps cycle time, the program will not work well, resulting in unstable system operation. Ehps
The cycle time is adjustable, that is, it must be adjusted according to the execution time of the program.
2.2 interrupt program for ehps ECU
The main cycle of the ehps is interrupted from time to time by the interrupted system. Once an interruption occurs, the CPU must respond to the interruption and exit the main cycle. Service programs that interrupt the system mainly deal with emergencies and random events. If there is no interruption, it will take a lot of time for the main program to query, so the interruption system is actually a parallel multi-task program.
The following interrupt types are used in the ehps software:
1) Steering Wheel Rotation interruption: it records the steering wheel rotation pulse signal to the register using the input capture interrupt to calculate the target rotation speed.
2) Motor Speed acquisition interrupt: it uses the input capture interrupt to record the pulse signal of the input speed to the Register at any time.
3) Interruption of serial communication: the serial communication is mainly used in the diagnosis system. When receiving the signal from the upper computer, the main cycle can be interrupted and the diagnosis program can be entered.
4) timer interruption: delay processing of the control system.
3. Design of ECU hardware circuit system
Electricity
The sub-control unit determines and controls the speed and current of the Motor Based on the steering speed and speed signal. The optimal steering power torque can be obtained at each speed. To protect the power drive circuit
The motor current must be sampled. In order to reduce the noise acquisition, the first-level sampling and holding circuit is used for the system current input. The differential input ends are all sampled and retained using the cc20 and cc21 ports of P9.
Sample the voltage of the sample signal. The principle of the motor current differential amplification circuit is shown in Figure 3. In order to improve the system's anti-interference capability, 5mV is added at the input end.
Bias voltage. In order to control the current phase change time of the motor, two Hall speed sensors are used to precisely control the phase change of the motor. Hall speed sensor can collect tle4905. To control the rotation of a motor
Speed: PWM chopper is used to control the motor voltage. Use p1l0 ~ of P1 port of XC 164CM ~ P1l3 controls the phase of the motor and uses the cc24 and cc25 ports of P1
For the voltage chopper, the waveform is superimposed by 74ls366 and sent to the power MOS.

4. Comparison of test results

Me
We use the MATLAB/Simulink control development and testing platform to simulate and test our EHPS system. Figure 4 and figure 5 are self-developed ECUs.
With the ECU of the original vehicle imported
The comparison shows that the control effects of the two controllers are consistent. At the same time, we performed a different driver driving experience, without notifying which controller we were driving.
The employee cannot tell whether the ECU on the original vehicle or the self-developed ECU is working.

Conclusion
During the last two years of research, we mainly used
Online debugging of the row Control Program, and repeated performance comparison with similar foreign products. This ensures the feasibility of product application in real-world vehicles. Based on the motor control curves of similar foreign products, we use EHPS ECU
The performance has basically reached the level of similar foreign products. However, the reliability should be further verified with the continuous loading of products.