Intelligent transformation and design of a fuel injection system test bench

l Preface
The fuel injection system is an important part of the diesel engine, and its performance directly determines the power, economy and emissions of the diesel engine. The jet pump is the most important part of the system. The fuel injection system test bench is the main equipment for adjusting and testing the fuel injection pump. 6PSDl30-1 electronically controlled fuel injection system test bench is a product of the 80s. The electrical control circuit is composed of a large number of discrete components, which not only has low test sensitivity, inconvenient setting adjustment, high failure rate, and most of the circuit components are deteriorated and damaged. In order to meet the preset number of fuel injection, automatic stop after counting and counting, and display of various correlation coefficients, computer and automatic control technology are used to carry out technical transformation to realize spindle speed preset, speed measurement and speed regulation, etc. A variety of functions.

2 Technical transformation plan The existing 6PSDl30-1 electronically controlled fuel injection system test bench belongs to D series electronically controlled stepless speed regulation type. That is, the thyristor slip clutch speed test bench. The main motor power of the fuel injection system test bench is 130 kW, the spindle speed range is 120~1200 r/min, the base of the oil counting times is 100 times, and the counting times are selected from 100 to 500 times; its power and control part The discrete components are used, and there is no test oil temperature monitoring and control system; the oil measuring part is visually inspected by a conventional Glass measuring Cylinder, which is inconvenient to test and has low precision. Foreign fuel injection system test benches have begun to use microcomputer oil and digital display systems. Therefore, in order to improve the test accuracy, the traditional structure is improved according to the national standard requirements, and the system is required to achieve: 1 digital display pressure, temperature, speed and counting parameters; 2 fuel temperature control at 40 ° C; 3 automatic control oil pouring time; 4 number The amount of oil displayed and the amount of oil displayed on the screen.
The AT89C52 microcontroller is used as the core of the entire control system. Figure 1 shows a general block diagram of the system design. It is mainly composed of sensors, AT89C52 single-chip microcomputer, PC, memory and interface circuit.

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The system uses sensors to collect signals such as spindle speed, injection pressure and temperature, and converts the signal into a corresponding voltage output signal. The output signal is processed by the signal processing circuit and sent to the AT89C52 microcontroller, under the control of the internal program of the microcontroller and the processing circuit. The corresponding fuel injection amount is generated and displayed by the PC.

3 system hardware design The hardware design of the system is divided into two parts: the fuel injection counting module and the spindle speed module. The latter is divided into a speed measuring module and a speed regulating module.
3.1 Fuel injection counting module The fuel injection counting module consists of AT89C52 single-chip microcomputer, external data memory RAM6264, counting sensor, shaping amplifier, photoelectric isolation circuit, relay, electromagnet, oil deflector mechanism, PC, RS485 interface. Figure 2 shows the hardware design of the fuel injection counting module.

The preset number of injections is input from the PC keyboard, and transmitted to the data memory of the MCU through communication between the PC and the AT89C52 MCU. After pressing the oil collection button, the relay pulls in, the electromagnet connected to the oil baffle in the oil cut-off mechanism is energized, the oil baffle is pulled out, the test oil begins to flow into the measuring cylinder, and the test bench is in the oil state. When the spindle rotates once, the fuel injection pump sprays oil once, and the T0 of the AT89C52 single-chip microcomputer uses the pulse output from the counting sensor to count. When the number of injections is equal to the preset value, the relay is disconnected, the electromagnet is de-energized, the oil deflector is pushed back, the injection of fuel is prevented from entering the measuring cylinder, and the test bench is in an oil-cut state. At this time, the amount of oil in the cylinder is the total amount of fuel injected for a given number of injections. In the real-time process of the oil quantity, the number of injections starts from zero and is displayed until the preset number of injections.
3.2 Spindle Speed ​​Module Figure 3 shows the hardware design circuit of the spindle speed module. It consists of AT89C52 MCU, external data memory RAM6264, RS485 serial interface, PC, 8155 programmable parallel I/O device, frequency divider, speed sensor, amplification shaping circuit, trigger isolation drive circuit, thyristor and motor.

The speed is given by the PC keyboard. The T1 count of the AT89C52 MCU and the 8155 timing combine to count and calculate the pulse from the speed sensor to measure the actual speed. The difference between the preset speed and the actual speed is adjusted by the PID algorithm and output to the D/A converter. The trigger circuit is used to change the conduction angle of the thyristor, thereby adjusting the excitation current of the spindle motor to achieve the purpose of controlling the spindle speed. The PC displays the spindle motor speed in real time.


4 control algorithm design and parameter tuning
4.1 Control algorithm
Since the MCU control belongs to a kind of sampling control, it calculates the control amount according to the deviation of the sampling time. Therefore, the regular numerical expression adjusted by PID is:


It can be seen from equation (3) that the incremental algorithm only needs to maintain the deviation value of the first three moments. In order to improve the speed of the system and avoid computational overflow, the algorithm limits the maximum deviation and the maximum output to the deviation and control output.
4.2 In the parameter tuning speed control process, the object model is often described by a first-order inertia plus pure lag link. The transfer function is:


Where: K is the static gain of the object; T1 is the time constant of the object; T is the pure hysteresis constant of the object.
Using the Cohn-Coon method for parameter tuning, the formula for extracting the characteristic parameters of the object based on the flying test curve of the object is:


From the equation (5), K, T, and Ï„ are obtained to set the PID regulator parameters.


5 system software design system software design adopts modular design method, mainly including PC, AT89C52 MCU and data communication modules. Among them, the PC module is the control center, which determines the structure and flow of the whole system program, mainly used to complete the interaction function between the system and the operator, realize parameter setting, dynamic data monitoring display, query standard debugging data, print data report, etc. Features. Figure 4 shows the design of the system dynamic data display.

AT89C52 MCU module is written in MCS-51 series MCU assembly language. It includes main program design, fuel injection counting program design, speed program design, speed control program design and data acquisition program design. The AT89C52 MCU module samples regularly according to the sampling period, and receives the commands sent by the PC to automatically control the experimental station; the data communication module can realize the data transmission between the PC and the MCU. Figure 5 shows the flow chart of the AT89C52 microcontroller module speed measurement program.

6 System Test and Conclusion Figure 6 shows the spindle speed curve of the fuel injection system test bench. Studies have shown that the modified test bench can automatically control the fuel injection count and spindle speed. Compared with the original test bench, the unit link consisting of discrete components is eliminated, which improves the automation and efficiency of the test, and is not only reliable, but also convenient to use and maintain.

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