喜歡就充值下載吧。。資源目錄里展示的文件全都有，，請(qǐng)放心下載，，有疑問(wèn)咨詢QQ:414951605或者1304139763 ======================== 喜歡就充值下載吧。。資源目錄里展示的文件全都有，，請(qǐng)放心下載，，有疑問(wèn)咨詢QQ:414951605或者1304139763 ======================== The Development of Control Unit in Automotive Electric Power Steering System Zeng Qun Department of Information Engineering University of Nanchang Nanchang, China e-mail: Huang Juhua Department of Mechanical & Electrical Engineering University of Nanchang Nanchang, China e-mail: Abstract Electric power steering system (EPS) uses an electric motor to provide essential control to the driver. The EPS system uses variable assist, that provides more assistance as the speed of a vehicle decreases, on the contrary, it provides less assistance. This functionality requires a delicate balance of power and control that has only been available in recent years. The EPS system has been used to replace traditional hydraulic power steering system (HPS), EPS systems are used in high-end and low-end vehicles widely, they are destined to become mainstream among automotive manufacturers soon. In this paper, the control unit of the column assist type EPS system with a DC motor is presented. The hardware circuit, coupled with the appropriate software development, can effectively meet the needs of the electric power steering system. Key words-electric power steering system; control unit; logical circuit; driving circuit; automotive I. INTRODUCTION Most modern vehicles have electric power steering systems to increase the handling performance of vehicles and reduce the input torque on the steering wheel, because the manual torque required to turn the wheels gets higher as the front axle load of the vehicle gets higher. Electric power steering systems are playing an important role in steering assistance on the market because of their higher assistant force, higher reliability and lower cost1. Figure 1. The structure of C-EPS The efficiency advantage of an EPS system is derived from the fact that it is activated only when needed. Thus reducing fuel consumption about 3-5% compared to the same vehicle equipped with conventional HPS system23.The inputs of the EPS are the steering wheel torque sensor and vehicle speed sensor signals; the outputs are the signals to the electric motor that drive the electrical power assist steering. The EPS electronic control unit (ECU) provides control over the vehicle steering using electrical power assist. EPS systems are particularly useful on small vehicles because they replace the power steering booster module. This results in weight and space savings as well as improved fuel economy. EPS is a sophisticated system that uses sensors to constantly measure the wheel torque applied by the driver to maintain the vehicles path; continually resetting to adapt to changing road conditions or the vehicle turning a corner. According to the arrangement of the assist DC motor, there are three forms of EPS: the column assist type EPS(C-EPS), the pinion assist type EPS(P-EPS), and the rack assist type EPS(R-EPS). The hardware structure of C-EPS is shown in Figure 1. The C-EPS systems for vehicles such as automobiles and trucks typically include a steering wheel , an electric motor, a controller, one or more sensors, a steering shaft, and a steering gear assembly. The steering gear assembly can be a rack and pinion gear assembly, a recirculating ball steering gear assembly or any other suitable steering gear assembly. The electric motor is typically coupled to the steering shaft through a worm that is connected to the motor and a worm gear that is connected to the steering shaft, a torque sensor that provides a feedback signal to the controller. The feedback signal represents driver effort that is required to turn the steering wheel. As the driver effort increases, the electric motor rotates the worm that engages and rotates the worm gear. The worm gear is connected to the steering shaft and reduces driver effort that is required to turn the steering wheel45. In this paper, according to Electric Power steering control system characteristics, we design the EPS hardware system using a single-chip microcomputer MC9S12DP256B. The purpose of the C-EPS system is to make steering safer and more convenient. II. THE OVERALL DESIGN OF THE CONTROL UNIT Before we design the electric control unit of the EPS, it is important to know the overall structure of the system. The ECU of the EPS includes two main modules: the logic circuit module and power driving circuit module, as shown in Figure 2. 2009 Asia-Pacific Conference on Information Processing978-0-7695-3699-6/09 $25.00 2009 IEEEDOI 10.1109/APCIP.2009.682402009 Asia-Pacific Conference on Information Processing978-0-7695-3699-6/09 $25.00 2009 IEEEDOI 10.1109/APCIP.2009.68242 Figure 2. The ECU modules The logic circuit module is composed of three parts: the minimal system, the exterior signal processing circuit and the driving signal distribution electric circuit. The power driving module is composed of two parts: the DC motor and the H bridge driving circuit including the H bridge67. The exterior signal processing circuit receives the sensor signals, including steering signal, current signal and switch signal, then change these signals into suitable forms for the MCU through the A/D ports or other I/O ports. This circuit also plays an important role in noise suppression of the input signals. The minimal MCU system refers to the minimum configuration that the MCU can work properly. Here we mainly define it as the necessary I/O ports and chips of the hardware. Driving signal distribution circuit process the PWM signal from MCU and then send it to the motor driving chip. PWM or Pulse Width Modulation refers to the concept of rapidly pulsing the digital signal of a wire to simulate a varying voltage on the wire. This method is commonly used for driving motors, heaters, or lights in varying intensities or speeds. The H-bridge driving circuit realizes the on-off control of the MOSFET and some protection functions. And the H- bridge is composed of four N-channel MOSFET. The function of it is to control the rotation of the DC motor. The hardware structure of the EPS controller is shown as figure 3. Figure 3. The hardware logical diagram of EPS It shows the structure of EPS controller in typical vehicle. The MCU receives the torque sensor and speed sensor signals, calculate the current the motor needs through the driving circuit to drive the motor. The power of the motor is supplied by the external relay and motor driving circuit. All sensors and actuators that connected to the EPS are monitored by the MCU. Once the system is abnormal, the ECU warning lamp will be lighted to send out the alarm signal, and then cut off the power through the relay circuit to prevent the accidents. The input signals of MCU include the torque sensor, the angle sensor, the vehicle speed sensor, the engine speed, the voltage of the battery, and the feedback current through the DC motor. The output of the MCU is the PWM signal that the duty cycle is changed according to the actual need of the motor. In additional, there is a clutch control circuit of motor. It is used to disconnect the motor from the reducer agency in case of failure. III. THE CHOOSE OF THE MICRO PROCESSOR The Freescale MC9S12DP256B micro controller unit is a 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit (HCS12 CPU), 256K bytes of Flash EEPROM, 12.0K bytes of RAM, 4.0K bytes of EEPROM, 2 asynchronous serial communications interfaces (SCI), three serial peripheral interfaces (SPI), an 8 channel IC/OC enhanced capture timer, two 8-channel, 10-bit analog-to-digital converters (ADC), an 8-channel pulse-width modulator (PWM), 89 discrete digital I/O channels (Port A, Port B, Port K and Port E), 20 discrete digital I/O lines with interrupt and wakeup capability, five CAN 2.0 A, B software compatible modules (MSCAN12), and an Inter-IC Bus. This series Freescale chip is widely used in the automotive electric field. The functions and features of the MCU are suitable for the EPS system. Figure 3 shows a block diagram of the MC9S12DP256B device. Figure 4. The block diagram of the MC9S12DP256B device 241243The system resource mapping, clock generation, interrupt control and bus interfacing are managed by the System Integration Module(SIM). The MC9S12DP256B has full 16-bit data paths throughout. However, the external bus can operate in an 8-bit narrow mode so single 8-bit wide memory can be interfaced for lower cost systems. The inclusion of a PLL circuit allows power consumption and performance to be adjusted to suit operational requirements. IV. THE DRIVING CIRCUIT DESIGN OF THE DC MOTOR DC motor is the implementation component of EPS system, and the motor driving circuit is very important for the system design. In this system we use the pulse-width modulation technology to control the H bridge circuit, which is composed of four MOSFET89. When the EPS system works, it needs the positive and negative direction of motor operation, so we choose the H-bridge circuit to realize, the system of H bridge circuit is shown as figure 5. This circuit is composed of four MOSFE(V1V4) and four continuous current diodes(VD1VD4). When the motor turn left, the current from +Us flows through V1, motor and V4 into negative electrode. And when the motor turn right, the current go through the reverse direction. Figure 5. The H bridge For its maximum working voltage is 12 voltages, its maximum working current is 20 amperes, we select IRF3205, it is the high-speed N-channel MOS, its largest drain current is 110 amperes. The good performance MOSFET driving circuit allows it works at more satisfied switching status, it reduces the switching time, and the switching power consumption, improve power conversion circuits operating efficiency. The MOSFET gate driving method has three forms: transformer driving, direct driving and photo coupler isolation driving. Transformer driving can isolate the driving signals, and the loss of driving power is very small, but it restricts the frequency, and it is not conducive to PWM signal transmission. Direct driving method is suitable for small capacity and the MOSFET unprotected occasions. The photo coupler isolation driving method requires the photo coupler has higher speed, higher insulation withstand voltage than the supply voltage, and larger common mode rejection ratio. We choose the IR2130 as a full-bridge driver. The IR2130 chip is a high voltage, high-speed power MOSFET and IGBT driver with three independent high and low side referenced output channels. It uses highly integrated level-shifting technology, it greatly simplifies the requirements of logic circuit for power device, as well as it improves the reliability of the driving circuit. It can be used to drive the MOSFET or IGBT that the bus voltage is not higher than 600 voltages, the largest positive peak output drive current is 250MA, while the reverse peak current is 500mA. The IR2130 is often used to drive BLDC motor, but it can be used to drive BDC motor too. When IR2130 works in normal condition, the 6-channel pulse input signals are divided into two groups. The signals L1 L3 go through the output driver amplifier directly to the power device to drive the low bridge. The signals H1 H3 signals first pass through IR2130 internal pulse processor and three-level shifter in the bootstrap circuit to transform into a 3-way potential of suspended driver pulse, then pass the 3-way output latch. Finally, after through the power amplifier, these signals are sent to the corresponding MOSFET. Once the load current is too large, the signal voltage from the current detection unit is higher than 0.5V, the IR2130 internal current comparator will be reversed quickly, thus makes the output of the fault logic processing unit low, block the 3-way pulse signal processor output, so the whole IR2130 outputs are low, thereby it can protect the power tube. On the other hand, at the same time the FAULT pin of IR2130 gives fault indication. If the power supply is low, the under-voltage detector of IR2130 will flip, it also carries out similar actions10. When IR2130 is protected, the output of the fault logic processing unit will remain the fault status. When the fault signals disappear and the input signals LIN1 LIN3 are set as high, we can clear the latch failure status. When the bootstrap power voltage that IR2130 driver supply to the bridge arm tube is low, the drive signal detector rapid action, blocking the path of output to avoid damage. When the H bridge arm of the same two-power devices receive high input signal at the same time, the output 2-way gate drive signals from IR2130 will be low, thereby avoid direct arm bridge situation happened reliably. The motor driving circuit with IR2130 is respectively shown in Figure 6. A PWM signal from MCU is sent to the port HO1 and LO2 in IR2130 chip to control the MOSFET V1 and V4 directly. The PWM signal through the anti-phase chip (74LS04) is also sent to the port HO2 and LO1 to control the MOSFET V2 and V3. The PWM signal controls the four MOSFET at the same time, here we use the bipolar PWM control mode. When the duty cycle ?is between 0 and 50%, the motor turns to left. When ?24224450%?the motor stop. When ?is larger than 50% , the motor turns to right1112. In the motor drive circuit?KF157 and IN4007 are fast recovery diode, the resistance R1R4 are used to restrict the driving current of the MOSFET, the value we choose here is 1030 ohm. The DC motor is connected to MOC+ and MOC-. Figure 6. The driving circuit The C4 is called the exterior bootstrap capacitor, and the value of it is about 0.1uf2uf?we recommend to use the tantalum capacitor. The exterior bootstrap capacitor value can be get by the following formula: (m ax)()2(2)ISccfISIqbsIcbs leakQ gQffCVVV+ Where: Qg: the gate charge of high-end device. F: operating frequency. IqbsS(max): the largest static current of high-end device. QIS: the charge request of the level conversion circuit in each cycle. IcbsS(leak): leakage current of the bootstrap capacitor. Vcc: the supply voltage. Vf: the forward voltage drop of bootstrap diode. VIS: the voltage of low-end device or high-end load. V. CONCLUSION Because of the many powerful features of the MC9S12DP256B, as well as its rich-chip resources, in general, we only need add some simple peripheral circuits for further application. The developed hardware circuit can meet the electric power steering system needs effectively. However, the electric power steering system design is not just dependent on the vehicle speed and torque signals, the steering angle, steering speed, lateral acceleration, gravity of front axle electric signals, these factors should be considered to improve the performance of the EPS system. In this paper, the design of electric power steering system hardware circuit and the design process of it are discussed. In order to obtain good control effect, appropriate software design is necessary. EPS systems have many advantages over traditional hydraulic power steering systems in engine efficiency, space efficiency, and environmental compatibility. The trend of technological development of automobile is the electrification of the automobile products. More and more electronic control devices will be used in the field of automobile. Steer by wire (SBW) is the development direction of EPS. 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