Automatic gear shifting system for locomotive based on 8031 ​​single chip microcomputer

1 Overview

In the construction of subway projects, engineering diesel locomotives (referred to as engineering locomotives) play a very important role. Especially in the early stage of subway construction, due to the need to transport a large amount of construction materials and the relatively simple transportation conditions in the early stage, engineering locomotives became the main means of transportation. In the operation of the subway after completion, engineering locomotives can also undertake tasks such as shunting within the vehicle depot and transporting large engineering materials into tunnels. Since the subway uses a large amount of engineering locomotives, the labor intensity of engineering locomotive drivers is naturally very high. Therefore, how to apply automation technology to improve the performance of vehicles and reduce the labor intensity of drivers is an issue that must be considered in subway operations. The locomotive

automatic shifting system introduced in this article can automatically detect the real-time running speed of the locomotive, and compare the obtained locomotive speed signal with the speed of the diesel engine. Then the single-chip microcomputer outputs control instructions based on the comparison results to control the corresponding actuators to automatically shift gears. In addition, the single-chip microcomputer can also output instructions based on the current gear position of the locomotive to control the corresponding LED to display the running status of the locomotive. With the help of this system, the driver's labor intensity of frequent gear shifting can be reduced, and the locomotive can run in a more reasonable gear most of the time, which has a better effect on saving fuel and protecting the environment.

The hardware part of the locomotive automatic gear shifting system consists of a front-end input circuit, a single-chip microcomputer circuit, and an output amplifier circuit. The function of the front-end amplifier circuit is to convert the two speed parameter signals of the locomotive speed and the diesel engine speed into electrical signals and compare them, and then input the results into the single-chip microcomputer circuit. The function of the single-chip microcomputer circuit is to output the correct control instructions based on the comparison results to make the actuator shift gears, and at the same time display the current operating status of the locomotive. The function of the output amplifier circuit is to amplify the power of the control signal output by the single-chip microcomputer circuit so that it can drive the gear shift actuator.

2 Front-end input circuit

The front-end input circuit is mainly composed of a speed sensor, a pulse shaping circuit, a frequency-voltage conversion circuit, a voltage amplifier circuit, and a Schmidt voltage comparison circuit. The circuit block diagram is shown in Figure 1.

2.1 Composition of front-end input circuit

There are two speed parameter values ​​that need to be measured in this automatic shifting system, namely the locomotive speed and the diesel engine speed. Figure 1 is the input part of the locomotive speed in the front-end input circuit. The input circuit of the diesel engine speed is the same as that of the locomotive speed.

In Figure 1, the locomotive speed is first detected by a La Hall speed sensor. The characteristics of this sensor are stable operation and high frequency, which is more suitable for use in railway vehicles. The output of the La Hall sensor is a pulse signal, and the frequency of this signal is proportional to the speed of the locomotive. In order to improve the reliability of the circuit, the pulse output by the sensor needs to pass through a pulse shaping circuit. The pulse shaping circuit is composed of the integrated block 8751 as the core. 8751 is a switch tube integrated circuit. When the input is high level, the output is also high level, otherwise, the output is low level. Since 8751 has its own power amplifier and voltage stabilization circuit inside, and can self-correct the loss and defects in the input pulse waveform, a very stable and complete waveform pulse square wave frequency signal can be obtained at the output end of 8751. In order to compare the locomotive speed and the diesel engine speed, the frequency signals of both must be converted into voltage signals. Therefore, the frequency signal should be input into the frequency voltage conversion circuit. This circuit is based on the LM331 integrated circuit. Its output voltage value is 6~8V, and the output voltage is proportional to the frequency of the pulse signal. Since the converted voltage signal is obtained by a series of processing of the pulse output by the initial sensor, this signal represents the corresponding locomotive speed or diesel engine speed. In this way, by comparing these two voltages, the speed relationship between the locomotive and the diesel engine can be obtained. However, before the comparison, in order to improve the accuracy of the comparison, it is also necessary to input the voltage signal into a voltage amplifier circuit to generate a voltage value with a relatively large output resistance to improve the stability of the circuit.

2.2 Schmitt voltage comparison circuit

By comparing the locomotive speed and the diesel engine speed, it can be determined whether the locomotive needs to shift gears. When the locomotive speed is lower than the diesel engine speed, the locomotive runs in the first gear, and when the locomotive speed is greater than the diesel engine speed, the locomotive shifts to the second gear. The comparison of the voltages representing the two speeds is completed by the Schmidt voltage comparison circuit, which can not only compare the two voltage signals, but also generate a Schmidt hysteresis when switching from the second gear to the first gear.

Figure 2 shows a specific circuit for converting the locomotive speed and diesel engine speed voltage signals into shift signals. In the figure, Ua and Ub are voltage signals representing the locomotive speed and diesel engine speed respectively. The two operational amplifiers F1 and F2 are connected in the form of voltage comparators. The two output terminals are respectively input to the S and R terminals of a monostable trigger, and the output of the monostable trigger can be converted into a shift signal after being processed by a photoelectric isolation device. In Figure 2, the two input voltages of F1 and the inverting terminal input voltage of F2 are directly connected to Ua or Ub. The F2 common-mode input terminal is input after R1 and R2 divide the Ub voltage. Since R1 is 560Ω and R2 is 10kΩ, the actual input voltage is 0.95Ub. Usually the initial gear of the locomotive is 1st gear. As the locomotive speed gradually increases, when its speed is greater than the diesel engine speed (that is, Ua＞Ub), F1 outputs a high level and adds it to the S end of the monostable trigger. For F2, U2＝0.95Ub, it can be obtained that Ua＞U2, so F2 outputs a low level to the R end of the monostable trigger. In this way, the trigger will output a high level to control the circuit to output a 2nd gear shift signal, so that the subsequent single-chip microcomputer circuit shifts gears. When the locomotive speed drops to less than the diesel engine speed, that is, Ua＜Ub, but Ua＞0.95Ub, F1 outputs a low level, but because the common-mode input terminal U2＝0 at this time. 95Ub, the output of F2 is still at a low level. In this way, since both the S and R terminals of the monostable trigger input a low level, its output terminal still maintains the original state and does not output a shift signal. When Ua < 0. 95Ub, the output of F2 is converted to a high level. At this time, the input terminal S of the monostable trigger is at a low level and the R terminal is at a high level, so that the output of the trigger is at a low level, providing the locomotive with a shift signal from the 2nd gear to the 1st gear. From the circuit working process described above, it can be seen that when the locomotive changes gears from the 1st gear to the 2nd gear, once the speed reaches the shift point, the gear will be shifted immediately, and when the locomotive changes gears from the 2nd gear to the 1st gear, the gear will be shifted only when the speed reaches 95% of the shift point. This delay time can avoid frequent gear shifting and instability of the locomotive due to vibration or other factors.

3. MCU Circuit

The output of the Schmidt voltage comparator is the shift signal processed by the front-end input circuit, and the subsequent single-chip microcomputer circuit is used to determine whether the locomotive should shift gears based on the shift signal combined with other parameters of the locomotive.

3.1 Composition of the single-chip microcomputer circuit

The single-chip circuit is composed of 80C31 chip, ROM composed of 6264, LED display lamp driven by 74HC373 (locomotive status indication circuit) and input and output circuit based on 8155. Since the complete single-chip circuit is relatively complex, only the part involved in automatic shift control is given, and its circuit connection is shown in Figure 3.

When the circuit is working, the locomotive shift signal is input to the P1.5 pin of the P1 port of the single-chip through an optocoupler 4N26. The purpose of using the optocoupler is to avoid interference signals from the power supply. The 8 LEDs driven by the integrated block 74HC373 can display the gear position of the locomotive and the running program segment, so that the driver and technical maintenance personnel can understand the status of the locomotive. The function of 8155 is to output the control shift valve working signal. After the power amplification of the output amplifier chip, the signal can directly drive the shift actuator to realize automatic shifting. After being decoded by 74HC138, the signals of the three pins P2.5 to P2.7 of the microcontroller can be used as chip select signals for the read-only memory, the 8155 input and output chip, and the 74HC373 respectively. These three pins constitute the three high-order addresses when accessing these three devices.

3.2 Software Design

After receiving the shift signal, according to the program instructions, the microcontroller will combine several other locomotive parameters to decide whether to shift gears. These parameters include whether the shift permission signal is valid, whether any parameters exceed the locomotive alarm value, etc. If there is no problem, the locomotive will shift gears.

Figure 4 shows the software flow chart of the locomotive shift system. The software initialization program is as follows:
START: mov A, #03H sets the status word to enable the 8155

4 Output amplifier circuit

The output amplifier circuit is mainly composed of some power amplifier switch tubes, which can be used to further amplify the output signal of the single-chip microcomputer to directly drive the actuators such as the solenoid valve of the gear shift. This circuit is relatively simple and will not be described in detail here.