Design scheme of single chip microcomputer for automatic gear shifting system of locomotive

“The locomotive automatic shifting system introduced in this paper can automatically detect the real-time running speed of the locomotive, and compare the obtained locomotive speed signal with the rotational speed of the diesel engine. The actuator performs automatic shifting. In addition, the single-chip microcomputer can also control the corresponding LED to Display the running state of the locomotive according to the gear output command of the current locomotive running.

“

In the construction of subway engineering, the diesel locomotive for engineering (referred to as engineering vehicle) has played a very important role. Especially in the early stage of subway construction, construction vehicles became the main means of transportation due to the need to transport a large amount of building materials and the initial transportation conditions were relatively simple. In the operation after the subway is completed, the construction vehicle can also undertake tasks such as shunting in the depot and transporting large engineering materials to the tunnel. Since the subway uses a large amount of construction vehicles, the labor intensity of construction vehicle drivers is naturally very large. Therefore, how to apply automation technology to improve the performance of vehicles and reduce the labor intensity of drivers is a problem that must be considered in subway operations.

The locomotive automatic shifting system introduced in this paper can automatically detect the real-time running speed of the locomotive, and compare the obtained locomotive speed signal with the rotational speed of the diesel engine. The actuator performs automatic shifting. In addition, the single-chip microcomputer can also control the corresponding LED to display the running state of the locomotive according to the gear output command of the current locomotive running. This system can not only reduce the labor intensity of the driver to change gears frequently, but also make the locomotive 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 shifting system consists of front-end input circuit, single-chip circuit and output amplifier circuit. The function of the front-end amplifier circuit is to convert the two speed parameter signals of the speed of the locomotive and the speed of the diesel engine into electrical signals and compare them, and then input the results to the single-chip circuit. The function of the single-chip circuit is to output the correct control command according to the comparison result to make the actuator act to shift gears, and at the same time display the running state of the current locomotive. The function of the output amplifying circuit is to amplify the power of the control signal output by the single-chip microcomputer circuit, so that it can drive the 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-to-voltage conversion circuit, a voltage amplifier circuit, and a Schmitt voltage comparison circuit. Its circuit block diagram is shown in Figure 1.

2.1 The composition of the front-end input circuit

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

In Figure 1, the speed of the locomotive is first detected by the Lahaller speed sensor. This sensor is characterized by stable operation and high frequency, which is more suitable for railway vehicles. The output of the Lahaller sensor is a pulse signal whose frequency 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 go through a pulse shaping circuit. The pulse shaping circuit is composed of the integrated block 8751. 8751 is a switch tube, when the input is high, the output is also high, otherwise, the output is low. Because the 8751 has its own power amplification and voltage regulator circuit, and can repair the loss and defects in the input pulse waveform by itself, a very stable pulse square wave frequency signal with complete waveform can be obtained at the output end of the 8751. In order to compare the speed of the locomotive with the rotational speed of the diesel engine, the frequency signals of the two must be converted into voltage signals. Therefore, the frequency signal should be input to the frequency-voltage conversion circuit. The circuit is based on the LM331 integrated circuit. The output voltage 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 original sensor, this signal represents the corresponding locomotive speed or diesel engine speed. In this way, the speed relationship between the locomotive and the diesel engine can be obtained by comparing the two voltages. But 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, thereby generating 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 speed of the locomotive and the speed of the diesel engine, it can be determined whether the locomotive needs to be shifted. When the speed of the locomotive is lower than the speed of the diesel engine, the locomotive runs in the 1st gear, and when the locomotive speed is greater than the speed of the diesel engine, the locomotive shifts to the 2nd gear. The comparison of the voltages representing the two speeds is done by the Schmitt voltage comparison circuit, which can not only compare the two voltage signals, but also generate a Schmitt hysteresis during the transition from 2nd to 1st gear.

Figure 2 shows a specific circuit for converting locomotive speed and diesel engine speed voltage signals into shift signals. In the figure, Ua and Ub are voltage signals representing the speed of the locomotive and the speed of the diesel engine, respectively. Both 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 flip-flop, and the output of the monostable flip-flop can become a shift signal after being processed by a photoelectric isolation device. In Figure 2, the two input voltages of F1 and the input voltage of the inverting terminal of F2 are directly connected to Ua or Ub. The non-inverting input terminal of F2 is input after dividing the voltage of Ub by R1 and R2. 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 speed of the locomotive gradually increases, when the speed of the locomotive is greater than the speed of the diesel engine (ie Ua>Ub), F1 outputs a high level and is added to the S terminal of the monostable trigger. F2, from U2=0.95Ub, Ua>U2 can be obtained, so F2 outputs low level to the R end of the monostable flip-flop. In this way, the trigger will output a high level to control the circuit to output a 2-gear signal, so that the subsequent single-chip circuit can change gears. When the speed of the locomotive drops below the speed of the diesel engine, that is, Ua0.95Ub, F1 outputs a low level, but at this time, the non-inverting input terminal of F2 is U2=0. 95Ub, the output terminal of F2 is still low level, in this way, since the S and R terminals of the monostable flip-flop both input low level, its output terminal still maintains the original state and does not output the shift signal. When Ua

3 MCU circuit

The output of the Schmitt voltage comparator is the shift signal processed by the front-end input circuit, and the function of the subsequent single-chip circuit is to determine whether the locomotive shifts according to the shift signal combined with other parameters of the locomotive.

3.1 The composition of the single-chip microcomputer circuit

The single-chip microcomputer circuit is composed of 80C31 chip, 6264 read-only memory ROM, LED display lights (locomotive status indication circuit) driven by 74HC373, and 8155-based input and output circuits. Because the complete single-chip microcomputer circuit is more complicated, only the part involved in automatic shift control is given, and its circuit connection is shown in Figure 3.

When the circuit works, the locomotive shift signal is input to the P1.5 pin of the P1 port of the single-chip microcomputer through a photocoupler 4N26. The purpose of using the photocoupler is to avoid the interference signal transmitted 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 the 8155 is to output the working signal of the control shift valve, which can directly drive the shift actuator to realize automatic shifting after being amplified by the power of the output amplifying chip. The three pin signals of P2.5~P2.7 of the microcontroller can be used as read-only memory, 8155 input and output chip and chip select signal of 74HC373 after being decoded by 74HC138. These three pins constitute access to these three devices. The high-order three addresses of the time.

3.2 Software Design

After receiving the shift signal, according to the program instructions, the single-chip microcomputer 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 are no problems, the locomotive will shift gears.

Figure 4 shows the software flow chart of the locomotive shifting system. Its software initialization procedure is as follows:

START: mov A, #03H sets the status word to enable the 8155

4 Output amplifier circuit

The output amplifying circuit is mainly composed of some power amplifying 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 for shifting. The circuit is relatively simple and will not be described in detail here.