With the improvement of people’s requirement for vehicle comfort, AMT gearbox requires higher and higher acquisition accuracy, operation speed and stability of TCU. The design chooses Freescale 32-bit MCU K60DN512 with stable overfrequency up to 180MHz as the core, collects and processes the signals of speed and throttle opening in real time, and controls the clutch and shift actuator through peripheral driving circuit. Through the test of TCU, the TCU controller based on embedded system improves the system performance, and has practical significance for the design of AMT electronic control system. Without changing the original transmission structure of the manual mechanical transmission, an automatic control device is added to the electronic controlled mechanical automatic transmission. By collecting signals such as speed and throttle opening, the clutch separation/engagement, gear selection and other actions are automatically driven by the actuator after processing. AMT has high transmission efficiency and low cost. It has the advantages of easy manufacture [1]. AMT control unit (TCU) is the control core and key technology of AMT automatic transmission. This paper designs the hardware system of AMT controller based on 32-bit single-chip computer, and debugs the system on the basis of program design. The results show that the design basically meets the system requirements of AMT controller. In this design, 32-bit embedded system ARM-Cortex-M4 core Freescale MCU K60DN512ZVLQ10 is used as the core processor. Its main function is to use FTM timer, AD conversion module to collect real-time input signals of various sensors and action feedback signals of various executing agencies, and then calculate input signals and feedback signals. Processing, based on PWM pulse width modulation principle, through FTM timer output module to send instructions to the clutch actuator motor and shift mechanism solenoid valve control, automatic transmission automatic shift operation [2]. The TCU of AMT transmission is a multi-input and multi-output non-linear system. There are many signals to be processed and the circuit structure is relatively complex. However, each function of the circuit is relatively independent and can be clearly divided into different structural units. The framework of the control system is shown in Figure 1.
In this design, the 32-bit embedded system ARM-Cortex-M4 core MCU K60DN512ZVLQ10 is used as the core processor. The control strategy is combined with the embedded system to make the shift and clutch processing response faster, more reliable and more anti-jamming. In order to make the core processor work properly, it is necessary to construct the necessary reset circuit, filter circuit, crystal circuit, power circuit, writer circuit and other modules to constitute the minimum system of the core processor. Different modules in hardware system have different voltage requirements: K60DN512 minimum system module working voltage is 3.3V; STC89C52 signal generator module working voltage is 5V; motor drive module and solenoid valve drive module all need to provide 24V and 5V voltage for them; operational amplifier in analog signal amplifier circuit needs to provide 5V and – 5V voltage for them. Voltage. However, the input power supply is 24V, so the power management module must have the function of voltage conversion. The circuit of power management module includes three voltage conversion circuits: 24V to 5V, thermostatic element 5V to 3.3V and 24V to – 5V.
In this design, all three circuits adopt intelligent integrated circuit chips. The circuit principle is shown in Figure 3.
The LM2940 chip can realize the voltage conversion from 24V to 5V, and the 5V voltage is input, and the 3.3V voltage is obtained through LM1117. Voltage, because LM2940 not only provides voltage for the circuit of LM1117, but also provides voltage for other driving circuits, the output current of LM2940 has higher requirements, so two LM2940 divider chips are used simultaneously to reduce the current load of a single chip. The input terminal of LM1117 does not directly connect the 24V voltage of the vehicle power supply, but takes the output of LM2940 5V voltage as the input, which can reduce the voltage drop at both ends of the voltage divider chip and play the role of reducing heating and protecting the chip. Through LM2576-5, the voltage conversion from 24V to – 5V can be obtained. The capacitance added to the input and output terminals of the power supply can effectively filter out the noise of the power supply and keep the voltage stable. The stable and reliable demand voltage of the input power is obtained after the power management module. The input signal and its processing module include digital signals such as vehicle speed, engine speed and analog signals such as throttle opening and clutch position. For digital signals such as vehicle speed, this design not only verifies the feasibility of hardware system, but also brings a lot of convenience for detection by designing signal generator and sending out signals corresponding to actual signals. In order to obtain the digital signal which is similar to the actual sensor signal after filtering, amplification and shaping, STC89C52 programmable microcontroller is used in this design, and different speed signals are simulated through the square wave of different frequencies output by FTM timer module. The signal output by 52 single chip computer is an ideal square wave, which is convenient to test the hardware system. At the same time, the intensity of the signal output by 52 single chip computer can meet the requirements of the core processor, and the signal can be sent directly to the core processor. The schematic diagram of the signal generator is shown in Figure 2. The analog signals such as throttle opening and clutch position collected by the sensor are only voltage signals of millivolt level.
The signal voltage recognized by the core processor is between 0 and 3.3V. Therefore, it must be amplified by the amplifier circuit to meet the signal strength requirements of the core processor. In addition, the analog signal is usually not a high-speed signal, so the interference of the high-frequency signal to the useful signal in the circuit can be reduced by the filter circuit. In this design, RC low-pass filter circuit and OP07 operational amplifier circuit are used to adjust the analog signal [5].
Clutch control is one of the important functions of TCU.
Two PWM signals are generated by K60DN512ZVLQ10 to control the DC drive motor of the clutch. The direction of the DC motor determines the separation/combination of the clutch and the speed of the clutch.
The speed of the motor is controlled by the duty cycle of the PWM module output of the core processor. The output current of the PWM signal from the core processor is only a few milliamperes, so the drive capability must be improved by building H bridge driver. The main chip of the circuit is BTS7970, which is a half-bridge driving integrated chip. The H-bridge driving circuit is built by two BTS7970 to drive the DC motor.
The driver chip interface circuit is shown in Figure 3. AMT shift selection is to control the actuator solenoid valve by using the PWM wave of different duty ratios output by the FTM timer module of the processor. The PWM signal output by the processor can not meet the requirement of directly driving the solenoid valve. Therefore, it is necessary to control the actuator solenoid valve through the driving circuit of the solenoid valve. 。 The driving circuit schematic diagram of solenoid valve is shown in Fig. 4. The signal processed by the core processor needs to be tracked and monitored. The most direct way is to connect with the host computer and detect it by the host computer. However, the core processor outputs TTL level signals, which need to be converted before they can be received by the host computer. RS232 communication circuit is used in this design. The main chip of this circuit uses MAX232 chip, which functions as USB signal to TTL signal. For AMT control, this design mainly collects the speed signal and throttle opening signal through the controller, and judges whether the shift critical point has been reached and carries on the shift operation. Through real-time acquisition of speed signal and throttle opening signal, the first step is to determine whether the throttle signal increases or remains unchanged. If it is satisfied, then to judge whether the speed measurement reaches the shift critical point of gear increasing law. Different critical points can be determined according to different throttle opening, and if they reach, they can be shifted. To the shift critical point of the gear reduction law, if it is reached, the shift processing will be carried out. In the process of shifting, clutch control directly affects the quality of shifting, so the treatment of clutch is particularly important. There are many control methods for clutch, among which the clutch speed control method is simple and easy to implement, so this study adopts speed control method. In the process of clutch combination, the non-torque transfer zone combines with a faster speed, the torque transfer zone combines with a slower speed, and the torque synchronous growth zone combines with a full combination state quickly, which can reduce the impact in the process of vehicle shift and achieve smooth shift. The shift process is shown in Figure 5. For the simulation of vehicle speed signal, the signal generator of STC89C52 is designed to output PWM wave of synchronous frequency to simulate vehicle speed signal.
At the same time, through the connection of core processor and host computer, the change of signal can be monitored in real time, so as to achieve more accurate control. Figure 6 shows the change of the speed signal on the upper computer. The controller receives signals and detects them with the host computer. The controller works steadily and successfully controls the actuators of the automatic transmission at the shift critical point, which verifies the feasibility and reliability of the designed controller. TCU with high performance and high reliability is the basic guarantee for AMT transmission to realize automatic shift. The hardware circuit system designed in this paper considers both functionality and engineering. Experiments show that the hardware design of the controller meets the design requirements. It can accurately collect input signals and output control signals in real time, and complete the set control. The strategy, with good reliability, is of great significance to the development and industrialization of China’s independent AMT technology.