Abstract: Aiming at the problems of poor quality and low economy of gear shifing of electric vehicle, the new type of electronically control-ing AMT was proposed. The transmission was based on the structure and principle of normal AMT. The DC brush motor was used as a selectand shift gear motor of electronically controlling AMT. Therefore, MPC5634 microcontroller from Freescale was selected to design the hardware circuit of the transmission controller, and the main program and various sub-nodule programs of the controller were designed by relerrinto the basic control mode of nomal electronically controlling AT and the CAN communicating module and serial communicating modulesor achieving the data translering belyeen ECU and the controler of the electronically controlling AMT were added. The bench tests of geashifting of the controller indicates that the design of the controller can be an efficient shifting operation and a stable performance.
Key words: electric vehicle: automatic mechanical transmission(AMT): CAN communication: shift motor
At present, transmissions suitable for electric vehicles have also become one of the hot spots in electric vehicle research. Electronically controlled electric mechanical automatic transmission has been widely used in electric vehicles due to its advantages of simple structure and good reliability. At present, the international research on AMT shift control technology of electric vehicles mainly focuses on two aspects: gear shift process control and shift law research. Gear shift process control technology determines the shift quality and driving smoothness of electric vehicles during driving, and is one of the important research directions of mechanical automatic transmission control, and the shift motor is the B shift execution power source of AMT that affects the performance of AMT controller. In this study, an electronically controlled mechanical two-speed automatic transmission is proposed.
How the AMT controller works
AMT is a typical closed-loop control system, which consists of three parts: sensor, actuator and controller. The AMT controller is responsible for receiving the sensor signal and sending instructions to the actuator, while collecting the current of the shift motor as a feedback signal to control the output torque of the shift motor. The AMT system works as shown in Figure 1.
According to the driver's driving behavior, the AMT controller performs corresponding gear shifting operations according to the shift control strategy when it receives the accelerator signal, motor speed signal, brake pedal signal, vehicle speed signal and gear signal. The gear position signal is provided by the internal Hall sensor of the AMT system, the vehicle speed signal and the motor speed signal are obtained through CAN to reduce the occupation of the electrical resources of the whole vehicle, and the current feedback signal is obtained by the current sampling module.
2 AMT controller hardware implementation
2.1 MPC5634 features
MPC5634 is an automotive-grade 32-bit microprocessor chip produced by Freescale in the United States, with 1.5 MB Flash EEPROM storage space and 94 KB RAM running memory to meet the storage and operation requirements of AMT control programs; Built-in phase-locked loop hardware module, with internal overclocking function, speed up software running speed, reduce electromagnetic interference to other devices, and the overall operation is more stable.
2.2 Hardware architecture
The AMT controller's power module converts the on-board 12V voltage to 5V and 3.3V for the MCU and various sensors. The MCU receives digital signals, analog signals, pulse signals, vehicle speed signals from CAN bus networks, motor speed signals, etc. collected from various sensors to realize the MOSFET driver chip output two PWM signals to control the conduction of the control chip. The driver chip amplifies the weak electrical signal from the MCU to meet the current driving the MOSFET tube. Rectification and voltage regulation consist of an H-bridge circuit consisting of two four P-type MOSFETs to drive two brushed DC motors for gear shifting. The current detection mode is used to feedback the magnitude of the shift motor current, and the feedback signal is supplied to the driver chip for hardware protection and the other to the MCU for software protection, so as to meet the static and dynamic requirements of the entire system at the same time.
Starting from the functional requirements of the AMT controller, the controller hardware architecture designed in this article is shown in Figure 2.
2.3 AMT hardware module design
AMT controllers mainly include power supply module, main controller module, drive circuit module, CAN communication module, SCI communication module, current sampling module, JTAC debug module and overcurrent protection module. 2.3.1 CAN communication circuit
The MPC5634 microcontroller has a built-in MSCAN module and supports CAN20A/B protocol. The schematic of the CAN communication circuit of the AMT controller is shown in Figure 3.
2.3.2 Motor drive circuit design
The electronically controlled electric AMT system uses the DC brush motor as the power source of the shift actuator, and the MOSFET is used as the electronic switch, here the author chooses the AUIRFS8403 MOSFET of the international rectifier IR company as the electronic switch, which can fully meet the drive needs of the electronically controlled AMT optional column motor. In addition, considering that the electrical signal output at the pin end of the single-chip microcomputer cannot directly drive the chip to work, the author proposes to use IR's AWIRS2004S DC motor H-bridge special driver to amplify the driving current and then drive the on-off switching of the electronic switch. Two AUIRS2004S driver chips are used here to layout the drive circuit, send two PWM waves through the main control chip, realize the switching of four MOSFETs of the H-bridge drive circuit of the DC motor, realize the forward and reverse rotation and braking back of the motor, and also have overvoltage, undervoltage and overcurrent protection functions." In addition, the main control chip can realize the monitoring of the working condition of the driver chip. The schematic of the motor drive circuit is shown in Figure 4.
2.3.3 Current sampling circuit design
The shift motor of the AMT system has a rated power of 60W, a rated voltage of 12V, a sampling resistor of 0.005Ω, a sampling resistance voltage drop of 0.025V, a magnification factor of 100 times, and a voltage signal corresponding to the maximum current is converted to the A/D conversion range of the single-chip microcomputer within 5V. LM358 is selected as an operational amplifier, the voltage signal is amplified and input to the AN16 port and AN17 port of the single-chip microcomputer, and the current sampling and releasing circuit is an analog circuit, and the analog ground and digital ground are isolated with a 0Ω resistor to improve the sampling accuracy and avoid phase interference. The schematic diagram of the current sampling circuit can be seen in Figure 5, the voltage amplification depends on the ratio of resistors R51 and R50, and capacitors C48~C50 are used to filter high-frequency noise signals and improve sampling accuracy.
2.3.4 Core system board circuit
The core system board is a relatively independent PCB board, which is mainly composed of power supply part, crystal oscillator circuit, reset circuit, JTAG circuit and other parts. The core system board circuit is shown in Figure 6.
AMT controller software implementation
Combined with the control objectives of the AMT controller, determine the control mode of the AMT controller.
3.1 Overall design of the AMT software part
The software part of the electronically controlled electric AMT control system adopts modular programming, and the main program of the electronically controlled AMT control system is shown in Figure 7.
The EV key is inserted, the ON gear switch is turned on, and the control system is activated. First, the interrupt is closed, and the main control chip I/0 port, A/D module, CAN bus module, PWM module, clock module EEPROM and serial communication module are initialized, and the interrupt is turned on after completion. The automatic transmission control unit performs to detect whether the subsystem of each module is in the normal flag position, report an error message if the system is abnormal, and wait for the START signal of the ignition switch if it is normal.
After the driver turns on the ignition switch, the TCU first reads the shift lever position signal, according to which the driver's operation intention is judged, and then obtains the speed, vehicle speed, throttle opening signal, etc. of the power motor through the CAN bus, and carries out gear shift control according to the pre-formulated shifting law. After completing the gear change and meeting the conditions for sending CAN messages, the current gear signal is sent to the vehicle control scraper through CAN communication.
3.2 Control algorithm design
The system adopts an electronically controlled electric shift actuator as the shift drive mode, so there is a situation where the positioning accuracy is low. In order to ensure the accurate realization of gear shifting and gear selection actions, smooth and fast gear shifting, the classic proportional-differential (PD) control algorithm is adopted for the shift motor to realize the closed-loop control cabinet of the shift position sensor and the position sensor feedback signal current
The control of the AMT actuator based on the PD algorithm is shown in Figure 8.
4. Analysis of experimental results
In this paper, the self-designed AMT controller is tested on a bench, and the operation of the shift motor under actual working conditions is shown in Figure (9~11).
Finally, when the PWM duty cycle is 90%, the working condition of the selected shift motor is the most ideal, and the current speed is measured by the motor speed tester to be 22rad/min. From the motor current characteristic curve in the figure, it can be found that there is a slight glitch phenomenon caused by the motor back EMF at the top of the drive signal waveform.
After the above-mentioned bench test, the author next conducted a vehicle road test. Due to the limitations of the test conditions, subjective judgment is used here to confirm the smoothness and comfort of the shifting process.
Through the vehicle road test, the test results of the AMT control system are obtained, as shown in Table 1.
In the case of no load, this study verifies that the AMT control system can drive the shift actuator to perform the shift operation according to the instructions issued. The shifting smoothness is better, and the shift impact is relatively small.
5. Conclusion
In this study, a two-speed mechanical automatic transmission controller for electric vehicles was designed based on Freescale's MPC5634 main control chip, and CAN communication function was added. After the bench test verifies, the results show that the controller software and hardware work normally, the shift motor runs forward and reverse, and can perform shift operation for the input signal in real time. In the vehicle test, the electric vehicle can quickly and accurately realize the shifting action during driving, which effectively reduces the shift impact of the AMT transmission and improves the riding comfort of the electric vehicle. The results of this research can realize the more efficient operation of the electric vehicle drive system, which has certain engineering practical value.