Simulation of hydraulic power assisted variable sp

The simulation of the hydraulic power assisted variable speed control system of a tracked vehicle

can form the forward and slow direction of the actuator: the AMESim software is used to establish the simulation model of the hydraulic power assisted variable speed system of a tracked vehicle, adjust some parameters of the system to inject fault information into the model, and the fault simulation of the system is carried out, which provides a reference basis for the fault diagnosis of the system. The results show that the simulation model can simulate the fault response of the actual system

key words: hydraulic power assisted transmission system; AMESim； Fault simulation

the mobility of tracked vehicles is not only related to the power plant, transmission device and moving part, but also closely related to the flexibility and lightness of its operation. In order to improve the mobility and reduce the working intensity of the driver, tracked vehicles often use hydraulic power assisted control system

the variable speed control system of a tracked vehicle adopts hydraulic power, which can easily and reliably realize the hydraulic control and hydraulic shift of the main clutch. However, the hydraulic system is a mechanical and hydraulic integrated system with complex structure, which has the characteristics of mechanical hydraulic coupling, time-varying structure and nonlinearity, which have become a problem of fault detection and diagnosis. The author uses AMESim software to model and simulate the fault of the hydraulic system, which provides a reference for the fault diagnosis of the hydraulic system

1 principle of hydraulic power assisted variable speed control system

1.1 composition of hydraulic power assisted variable speed control system

hydraulic power assisted variable speed control system is mainly composed of oil pump, overflow pressure reducing valve, main clutch control valve, main clutch release cylinder, constant pressure output piston at both ends to form a pressure difference, so that the piston moves with the shift valve core, live valve and shift cylinder. The simplified structure of the hydraulic power assisted variable speed control system studied by the author is shown in Figure 1

1.2 working process of hydraulic power assisted variable speed control system

the working process of hydraulic power assisted variable speed control system can be divided into three stages

1) main clutch disengages. Step down the main clutch pedal, the control valve core of the main clutch moves to the right, opens the oil inlet of the control valve, and the hydraulic oil enters the control valve, pushes the one-way valve to enter the main clutch oil cylinder, but at this time, the valve core has not completely closed the oil outlet connected with the oil tank, and the main clutch oil cylinder has no action. The valve core of the control valve of the main clutch continues to move to the right, closes the oil outlet connected with the oil tank, establishes pressure, and pushes the clutch release cylinder to act, so as to separate the friction plate of the main clutch and cut off the power output

2) hydraulic shift. Move the valve core of the main clutch control valve to the right again, open the oil outlet to the constant pressure output valve, and the hydraulic oil enters the shift cylinder through the constant pressure output valve. When in neutral, the valve core of the shift cylinder closes the left and right fluid flow holes, and the piston does not move; When the shift lever is operated, it drives the shift cylinder spool to move. The spool closes the flow hole on one side and opens the other first-class hole. The pressure difference between the two ends of the piston makes the piston move with the shift spool. The piston moves to drive the shift fork to shift. After the shift, the transmission lever is positioned by the marble

3) main clutch is engaged. After shifting, release the pedal of the main clutch, return the spring to return the shafts, pull rods, pull arms, valve cores of the main clutch control valves, etc., close the oil circuit to the constant pressure output valve and shift cylinder of EU regulation No. 10/2011, which has been revised for 2 degrees, and open the oil outlet connected to the oil tank at the same time, so that the pressure drop of the main clutch cylinder is zero; The pressing spring of the main clutch is stretched to push the piston of the clutch release cylinder back to its original position, and the passive friction plate is combined with the active friction plate under the action of the pressing spring to transmit power to the transmission to realize gear shifting

2 simulation analysis of hydraulic power assisted variable speed control system

amesim (the most typical data processing of advanced modeling environment is the following points for simulation of Engineering Systems) is a software package specially used for modeling, simulation and dynamic analysis of hydraulic/mechanical systems launched by imagine company in 1995, which provides users with a perfect modeling and simulation environment. AMESim software adopts the modeling method based on the power bond graph theory, and the data can be transferred between components in both directions. The specified variables generally have physical meaning and follow the causal relationship. Using AMESim, the author can establish the dynamic model of hydraulic power assisted transmission system intuitively, conveniently and accurately, and analyze its influence on the dynamic characteristics of the system when changing a certain parameter

2.1 system modeling and simulation

2.1.1 build the system simulation model from the working principle diagram of the hydraulic power transmission system

amesim software system has no sliding sleeve model. The author uses the moving piston with spring and the mass body that can move relatively and has relative displacement limit to form a sliding sleeve spring device

shift resistance occurs when the gear is in contact with the gear sleeve when shifting; When shifting out of gear, its resistance is negligible compared with that of shifting in gear. The author uses the methods of shift cylinder piston displacement, speed control and signal loading to produce shift resistance

the main clutch control valve, constant pressure output valve, shift cylinder and main clutch cylinder use the HCD (hydraulic component design module) of AMESim software to build a model according to its working principle

the clutch and shift synchronizer are controlled by the piston displacement signal of the main clutch and the piston displacement signal of the shift cylinder respectively

the main parameters of hydraulic power assisted transmission system are as follows:

flow source: 100 L/min, overflow pressure regulating valve: 11 bar, main clutch control valve spool diameter: 18 mm, main clutch control valve spool rod diameter: 11 mm, shift cylinder spool diameter: 20 mm, shift cylinder spool rod diameter: 15 mm, shift cylinder piston diameter: 65 mm, shift cylinder piston rod diameter: 35 mm, pressure reducing valve spring preload: 106 n, engine output torque: 1000 nm, Maximum displacement of clutch release cylinder: 0.1 M, displacement range of shift cylinder piston: -0 02～0. 02m。

the system simulation model is built as shown in Figure 2

2.1.2 simulation of the action process of shifting from neutral to gear 2 and from gear 2 to gear 3

according to the actual operating procedures, the clutch should be quickly stepped down to make it separate quickly, and the gear operation should be carried out during the clutch separation, and the clutch should be combined at an appropriate speed after the gear is engaged. Therefore, the force applied to the main clutch control valve and shift cylinder spool is shown in Figure 3. That is, at 1 s, the control valve of the main clutch rapidly applies 40 n for 1 s (during which time it is engaged), and then the force slowly decreases from 40 n to 0 within 1 s. When the electrical switch on the panel is pulled, an 8N square wave signal is applied at the valve core of the shift cylinder at 1.1s to shift from neutral to gear 2. At the 13th s, step down the clutch for the second time to make the force continue to act for 1.2 s, and then slowly drop to 0 within 1 s

at 13.1s, a reverse 10 n square wave signal is applied at the valve core of the shift cylinder to shift from gear 2 to gear 3. At the 23rd s, an 8N square wave signal is applied at the valve core of the shift cylinder, that is, the simulation of the gear engaged state when the clutch is not stepped on

Figure 4 is the displacement diagram of the main clutch. It can be seen from Figure 4 that the piston of the main clutch cylinder can quickly move to the dead center position when the clutch is pressed, and can return to the original position smoothly when the clutch pedal is released, that is, the clutch can be quickly separated and smoothly combined. Figure 5 is a displacement diagram. It can be seen from Figure 5 that the shift cylinder spool can move to the specified position under the action of force, and the piston can also complete the servo movement following the spool under the action of hydraulic oil, so that the power is output by the corresponding speed change gear. However, when the shift cylinder is operated without depressing the clutch at the 23rd s, the hydraulic oil cannot enter the shift cylinder to establish oil pressure. At this time, the shift cylinder is operated, and the shift operation cannot be realized. The shift cylinder spool displacement changes due to the free gap between the spool and the piston. This is consistent with the design requirements. Figure 6 shows the torque curve. It can be seen from Figure 6 that when the clutch control valve is operated, the engine power can be cut off and transmitted immediately

2.2 fault state simulation

adjust the control pressure of the overflow valve to 11 bar, 10.5 bar and 10 bar respectively. Conduct simulation to check the influence of this parameter on the dynamic characteristics of the system

Figure 7 shows the piston displacement of the main clutch cylinder under different pressures. It can be seen from Figure 7 that when the pressure is lower than 11bar, the main clutch cylinder cannot act to the specified position, that is, the clutch cannot be completely separated or cannot be separated

adjust the spring preload of constant pressure output valve to 106 n, 96 N and 86 n respectively. Conduct simulation to check the influence of this parameter on the dynamic characteristics of the system. Figure 8 shows the piston displacement of the main clutch cylinder when the spring preload of the constant pressure output valve is different. Figure 9 shows the oil inlet pressure of the shift cylinder under different preloads of the constant pressure output valve spring. Figure 10 shows the displacement curve of valve core and piston of shift cylinder with different pre pressure of constant pressure output valve spring. Figure 11 shows the torque curve of the gearbox output shaft under different preloads of the output pressure reducing valve spring

it can be seen from figure 8 that the change of the spring preload of the constant pressure output valve has no effect on the clutch action. It can be seen from Figure 9 that the change of the spring preload of the constant pressure output valve directly affects the output pressure of the output valve. It can be seen from Figure 10 that the pressure reduction seriously affects the realization of the hydraulic power assistance function of the shift cylinder, and even loses the power assistance function, and the shift cannot be completed. It can be seen from Figure 11 that when the pre pressure is set to 96 n, the output shaft of the transmission has no power output, that is, gear shifting fails

adjust the free clearance between the shift cylinder spool and the piston to be (0.4 +0.4) mm, (0.8 +0.8) mm and (1 +1) mm respectively. Verify the influence of this parameter on the dynamic characteristics of the system

the figure shows the opening curve of the oil inlet of the left oil chamber of the shift cylinder, the pressure curve of the left oil chamber, the spool displacement and the piston displacement curve when the clearance between the shift cylinder and the piston is different. Figure 16 shows the torque curve of the output shaft of the transmission under different free clearances between the shift cylinder and the piston. It can be seen from Figure 12 that when the free clearance is (1 +1) mm, the opening of the oil inlet of the left piston cavity is> 0 at 1 ~ 2S, that is, the left piston cavity is filled with pressure oil. When the clearance is reduced, the oil inlet of hydraulic oil entering the piston chamber will not be opened. As can be seen from Figure 13, no hydraulic oil enters the piston oil chamber to establish pressure. It can be seen from figures 14 and 15 that when there is no hydraulic power, the movement of the valve core is only the result of the force on it, and the movement of the piston is the result of the action of the valve core through the compression spring. It can be seen from Figure 16 that when there is no assistance, only the original force will not be able to achieve the shift function, and the transmission output shaft has no power output

3 conclusion

AMESim software is used to establish the model of hydraulic power assisted variable speed control system with mechanical and hydraulic integration for simulation. It can easily and intuitively convert the mathematical physical model of the mechanical and hydraulic coupling system into a visual and modular simulation model, and inject fault information by modifying a parameter of the system model, establish the relationship between a parameter and the dynamic characteristics of the system, and realize the dynamic simulation of the fault of the hydraulic power transmission system

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