“Anti-skid control system (ASR) is an important active safety system, and its control needs to adjust the output torque of the engine. Since most of the car engines installed in our country currently do not have independent intellectual property rights and cannot complete the intervention of the engine control system, this paper adopts the ASR system scheme of installing Electronic throttle to adjust the torque. In order to realize the need of driving anti-skid control (ASR), the software and hardware of the ETC system ECU are designed and developed, and the function test is carried out on the test bench where the electronic throttle body is installed, and it is applied to the ASR control. Ring test.
Authors: Wang Weida, Yuan Lijuan, Zhou Rui, Wang Yingna
In the early days, the throttle valve was a throttle device set on the carburetor cavity to adjust the gas charge of the gasoline engine, which was connected to the accelerator pedal through a lever and a wire cable. Because it is commonly used as a butterfly valve, it is called a throttle valve. After the electronically controlled injection system replaces the carburetor, the oil circuit becomes a self-contained system for pressure injection; in terms of the intake system, a simple but very important component below the carburetor intake pipe throat is retained – the throttle valve. And additional electronic control unit (ECU), throttle position sensor, air flow meter and other monitoring conditions. Electronic Throttle Control System (ETC) is in the throttle mechanism of the EFI system, some auxiliary compensation devices are removed, and new electronic control units, DC motors, reduction gears, drive circuits, etc. are added. Different from the traditional throttle control method, the throttle valve in the electronic throttle valve system is directly driven by the motor under any working conditions; and the ECU can synthesize vehicle management information and changes in engine working conditions to prepare an optimal mixture at any time. . This optimal mixture composition is determined according to the power and economy of the engine, especially according to the requirements of reducing the emission of harmful substances, and has good transition performance such as idling, acceleration and deceleration.
The electronic throttle valve is equivalent to replacing the traditional mechanical connection (ie rigid connection) with a flexible connection. In a rigid connection, the engine throttle opening is completely controlled by the accelerator pedal opening, and the engine operating conditions depend on the driver’s operation of the accelerator pedal. In the flexible connection mode, the accelerator pedal is only equivalent to a sensor that reflects the driver’s manipulation intention. The actual opening of the throttle valve is determined by its controller according to the current driving conditions of the car, the requirements of other on-board electronic control systems, and considering the characteristics of the engine. .
Anti-skid control system (ASR) is an important active safety system, and its control needs to adjust the output torque of the engine. Since most of the car engines installed in our country currently do not have independent intellectual property rights and cannot complete the intervention of the engine control system, this paper adopts the ASR system scheme of installing electronic throttle to adjust the torque. In order to realize the needs of driving anti-skid control (ASR), the software and hardware of the ETC system ECU are designed and developed, and the function test is carried out on the test bench where the electronic throttle body is installed, and it is applied to the ASR control. Ring test.
1 ECU hardware circuit design
ECU hardware mainly realizes the functions of accelerator pedal signal acquisition and processing, storage and operation control software, driving DC motor, and communicating with other ECUs or computers. The hardware design framework is shown in Figure 1.
The design of ECU also needs to consider several factors:
(1) The real-time requirements of the control program require the controller to be able to run the program quickly and have a high calculation speed;
(2) The reliability of the controller is required to ensure that it has strong anti-interference performance in the automotive-grade harsh electromagnetic environment, and the control program can run reliably and stably;
(3) Considering the volume and cost of the controller, it has certain market competitiveness.
1.1 MCU type selection and MCU minimum system design
The single-chip microcomputer is the core of the electronic control system ECU, which is responsible for data acquisition and processing and all logical operations, and directly affects the reliability of the controller circuit operation, cost control and the size of the controller.
Considering various factors, the chip model used in this article is MC68HC908AZ32A, which is a powerful 8-bit microcontroller specially designed for automobiles produced by Freescale. It has rich functional modules, including 1-way SPI interface module, 1-way SCI interface module, 15-way A/D conversion module, 1-way CAN communication interface module, etc. In addition, the number of independent digital I/O interfaces of the chip also meets the design requirements, and there is room for functional expansion.
After the single-chip microcomputer is selected, the power supply circuit, clock circuit and reset circuit are designed to form the minimum system of the single-chip microcomputer.
1.2 Signal acquisition circuit design
The ETC system needs to collect and input analog signals such as accelerator pedal position signal and throttle position signal into the microcontroller. Because the analog signal may have more glitches or large voltage fluctuations due to interference, sudden failure, etc., in order to better collect the signal and protect the MCU, the analog signal input circuit is designed, as shown in Figure 2. This circuit is an active filter circuit that can greatly reduce glitches and reduce fluctuations.
The active low-pass filter circuit can filter out the interference signal on the transmission line on the one hand, and can improve the input impedance of the A/D on the other hand. The LM124 is an efficient integrated op amp. Capacitor C701 filters the analog signal output by the sensor to remove burrs. The role of the follower is to reduce the output impedance to a minimum level, because the A/D module of the MCU requires the smallest possible output impedance and a small sampling period to meet the requirements of rapidity and accuracy when dealing with rapidly changing analog signals. . In addition, the ECU also needs to input the braking signal in the form of switching quantity, which is realized by the interrupt function of the specific port of the microcontroller.
1.3 DC motor drive circuit design
Since the DC motor that controls the throttle opening is driven by the PWM signal output by the single-chip microcomputer, a power driver chip is required in the middle. This article selects TLE6209, which integrates H-bridge circuit inside. This chip is an intelligent power driver chip specially developed by Infineon to control the electronic throttle. Compared with other power driver chips, TLE6209 has high reliability and protection functions. It can communicate with the control unit through the SPI interface, send fault information and control commands, and provide conditions for the expansion of the control unit’s diagnostic function in the future; general The H-bridge drive signal requires two PWM signals to control the rotation of the motor. TLE6209 only needs one PWM signal and one direction signal, so hardware resources are saved, and the control is more flexible and reliable. Its main features are as follows:
(1) The maximum continuous output current is 6 A; the maximum operating voltage is 40 V; the maximum output frequency is 30 kHz.
(2) Separate power supply for logic voltage and driving voltage; internal integrated freewheeling diode; output short circuit protection.
(3) When IHN is low level, the chip stops working; when DIS is high level, the output terminal is in a high-impedance state.
(4) Two-way communication with the single-chip microcomputer can be carried out, and the programmable control word can be written to the TLE6209 through the SPI single-chip computer, and the TLE6209 can send the fault diagnosis information to the single-chip microcomputer.
(5) Only two signals are needed when working: DIR controls the direction of the output current; PWM controls the magnitude of the output current.
The circuit design of TLE6209 is shown in Figure 3.
1.4 CAN bus interface circuit design
Controller Area Network (CAN) is a serial communication protocol, which can effectively support distributed real-time control with high security level. CAN has a wide range of applications, from high-speed networks to low-cost multi-channel wiring can use CAN. In the automotive electronics industry, using CAN to connect engine control units, sensors, anti-skid systems, etc., the transmission speed can reach 1 Mb/s.
The ETC system needs to receive the opening demand signal of other on-board electronic control systems through the CAN bus.
MC68HC908AZ32A integrates a CAN controller on-chip. This article selects TJA1040 from Philips as a CAN transceiver. The specific CAN bus interface circuit is shown in Figure 4.
1.5 SCI communication circuit design
In order to monitor the control process, Display it in real time, perform data collection, analysis and processing, and in some cases replace CAN to realize the communication function between ECUs, the ECU reserves the SCI communication interface, and the SCI communication circuit is designed for this purpose, as shown in the figure 5 shown. Serial communication has the advantages of simple use and long transmission distance. Although its transmission rate is not high, it can meet the requirements of the system.
In addition, the ECU hardware also includes the BDM interface circuit and the fault diagnosis circuit, which will not be described in detail in this article.
2 ECU software design
The ECU software mainly includes: system initialization module, analog signal acquisition and processing module, data communication module, throttle opening control decision module, PWM signal generation module, etc. The overall flow of the program is shown in Figure 6.
The system initialization content mainly includes MCU internal clock, wheel speed input channel port settings, actuator output channel port settings, watchdog timer settings, communication port initialization, system variables, etc., to ensure the normal operation of the MCU.
The signal acquisition and processing module acquires two analog quantities of accelerator pedal position signal and throttle position signal and the switch quantity of brake signal. The data communication module receives the opening degree demand signal sent by other on-board electronic control systems, and uses it for the opening degree control decision.
The control decision-making module determines the target throttle valve opening degree according to a certain control algorithm according to the current driving conditions of the vehicle, the requirements of other on-board electronic control systems and considering the characteristics of the engine. The PWM signal generation module converts the throttle opening requirement into a corresponding PWM signal for controlling the DC motor, and drives the motor to rotate through the drive chip to make the throttle opening reach the target position.
3 ETC system function test
ETC system consists of electronic control unit, throttle body, DC drive motor, accelerator pedal module (including pedal position sensor), throttle position sensor, etc.
The throttle valve position sensor is used to collect the throttle valve opening degree in real time and perform position feedback for the closed-loop control. It is the only detection element of the throttle valve state. The electronic throttle valve requires a high degree of reliability, the position sensor adopts a redundant design, and the system adopts 2 throttle valve position sensors. In order to precisely control the opening of the electronic throttle valve, it is necessary to study the output voltage characteristics of the position sensor and find the corresponding relationship between the output voltage and the throttle valve position. The opening degree of the throttle valve ranges from 0° to 88°. Due to the idle speed opening, the working area above the static position of the throttle valve is actually 9°~88v°. The throttle position sensor has a good linear relationship. Therefore, according to the voltage signal provided by the throttle position sensor, the continuous rotation angle of the throttle valve can be accurately detected. Through the calibration test, the corresponding relationship between the output voltage and the throttle position is shown in Figure 7.
The motor output torque is proportional to the duty cycle of the drive signal. When the duty cycle increases, the motor driving torque is greater than the return spring resistance torque, and the throttle opening increases; when the duty cycle decreases, the motor driving torque is smaller than the return spring resistance torque, and the throttle opening decreases. In this paper, a PWM signal with a frequency of 10 kHz and an adjustable duty cycle output by the single-chip microcomputer is used to drive the DC motor after power amplification. Through the calibration test, the relationship between the throttle opening and the PWM signal duty cycle is shown in Figure 8. Due to the influence of nonlinear factors such as hysteresis of the return spring, the throttle opening and the duty cycle of the PWM control signal have an approximate linear relationship.
4 ETC applied to hardware-in-the-loop testing of ASR control
In the control of the developed ASR system, the control of the engine torque is achieved by adjusting the throttle valve opening. The ASR controller needs to send its throttle opening requirement to the ETC controller, and adjust the throttle opening through the ETC system. The developed electronic throttle valve system is used for ASR control, and a hardware-in-the-loop test platform with the advanced real-time simulation system dSPACE as the core is built. The overall structure is shown in Figure 9.
Among them, the hydraulic control unit is the actuator of the ASR controller; the vehicle system includes the vehicle model running in the dSPACE system and the actual components such as the accelerator pedal, its position sensor, and the brake pedal. The throttle valve opening of ETC controller and ASR controller is exchanged data through communication interface (CAN or SCI).
Using this test bench, the hardware-in-the-loop test based on adjusting the engine output torque to achieve the purpose of ASR control by adjusting the throttle opening can be carried out. A typical condition for testing ASR control is starting on a low-adhesion road, and the control results are shown in Figure 10 and Figure 11. The hardware-in-the-loop test was performed assuming an initial throttle opening of 100% and the two front wheels being the drive wheels.
The purpose of ASR control is to suppress excessive spin of the driving wheels and keep the wheel slip rate within a reasonable range. It can be seen from Figure 11 that the ETC system rapidly reduces the throttle opening from the initial 100% according to the ASR control requirements until the driving wheels no longer slip excessively, and then adjusts the throttle opening appropriately so that the wheel slip rate tends to Reasonable. The developed ETC system responds well to the control requirements of ASR. As can be seen from Figure 10, ASR achieved good control effect.
(1) The test results show that the ETC system ECU studied in this paper can complete the functions of signal acquisition and processing, data communication, and drive DC motor to adjust the throttle opening and other functions required by the design.
(2) Apply the developed throttle control system to ASR control, realize the opening adjustment required by ASR, and achieve the control purpose of ASR.
(3) The hardware-in-the-loop test method based on dSPACE can test the developed ECU on the bench under the condition that is closer to the actual working conditions, and can quickly and conveniently set various test conditions in the laboratory.