Construction machinery needs to change the direction of movement of the entire car body during steering and operation, that is, steering. For a deflection wheel type vehicle, the driver manipulates the steering wheel and turns the wheels at an angle through the steering mechanism. In the case of a chariot-connected frame type vehicle, turning the part of the frame that guides at an angle can guide the vehicle to change direction. Take the deflection wheel type as an example to analyze the principle of hydraulic steering.
The steering mechanism has two methods: direct drive by human power and power amplification (power steering). Manpower direct drive is easy to operate, but it is only suitable for light vehicles. When the construction machinery is turning, the steering part is subjected to a large steering resistance torque, which requires the steering mechanism to generate a large driving torque, and at the same time, it must have a sufficient rotation speed, which cannot be satisfied by manpower. Therefore, power amplification must be applied. The hydraulic power amplification method has large steering power, light weight, and light and stable operation.
Figure 2-6 shows the hydraulic system of the steering mechanism. The driver operates the steering wheel 1, assuming to turn the angle a clockwise, and finally the wheel turns through the corresponding Q angle, the vehicle is steered accurately to the desired driving direction. In the hydraulic steering mechanism, the spool 2a of the regulating valve 2 is connected to the steering wheel and turns clockwise a through it. Since the valve body 2b does not rotate, the regulating valve 2 changes from the neutral position to the upper position, that is, the P port and. The ports are connected, the high-pressure liquid of the pump is pressed into the 3C cavity of the hydraulic motor 3, and the liquid discharged from the 3D cavity of the hydraulic motor flows to the B port through the D port of the regulating valve 2. Since there is almost no resistance torque on the output shaft of the hydraulic motor, the pressure at port B is very similar to the pressure at port C. The liquid of channel B is sent into the rod chamber of the hydraulic cylinder 4a and the rodless chamber of 4b, so that the rod 4a is pulled and the rod 4b pushes the lever mechanism 8, thereby turning the wheel clockwise by an angle. At the same time, the hydraulic cylinders 4a and 4b are discharged
Figure 2-6 Steering mechanism hydraulic system
1 one steering wheel; 2—regulating valve, 3—hydraulic motor, 4—hydraulic cylinder; 5—hydraulic pump, 6,7—buffer valve, 8—lever mechanism
The liquid is collected together, passes through the A port of the regulating valve 2, and passes. The port flows back to the main tank.
Since the steering mechanism also has a function that can realize position feedback, that is, the output shaft of the hydraulic motor is connected to the valve body 2b of the regulating valve 2, when the regulating valve starts to enter the upper position, the output shaft of the hydraulic motor starts to rotate, dragging The moving valve body follows the valve core to rotate clockwise, so there is a tendency to close the valve ports c, D, A, and B, that is, the tendency for the regulating valve to return to the neutral position. However, since the driver has not turned the steering wheel to the a angle, the steering wheel and the spool continue to rotate, and the valve body always follows the spool slightly behind, so the regulating valve will not return to the neutral position. Once the steering wheel and spool stop at angle a, the valve body will eventually be dragged to the position where the regulating valve is neutralized. At this time, the hydraulic motor and the hydraulic cylinder stop moving, and the wheel just reaches the driver's desired yaw angle.
From the above analysis, it can be seen that as long as the driver gently toggle the spool of the regulating valve with a small force, the hydraulic cylinder can generate a lot of power and turn the wheels. This is the role of hydraulic power amplification.
When the driver operates the steering wheel to turn counterclockwise to change the regulating valve from the neutral position to the lower position, similar to the above case, the wheels will turn in the opposite direction.
When the engine is turned off and the hydraulic pump 5 stops pressing out the liquid, the hydraulic steering mechanism can be manually driven.
The principle is as follows: In the actual device, the shaft of the steering wheel 1 and the hydraulic motor 3 are on the same axis, but in general, the two are not connected. When the engine and pump are working normally, the driver turns the steering wheel, and the hydraulic motor follows the rotation of the regulating valve 2 based on the hydraulic principle, so there is no angular difference between the steering wheel and the hydraulic motor (at steady state) or very small (dynamic Time). When the engine stops and the pump stops working, the hydraulic control system does not work. The driver dials the steering wheel, and the hydraulic motor no longer tracks. The angle difference between the two continues to increase. When the steering wheel turns to a certain angle 0, the steering The disc shaft can mechanically force the hydraulic motor 3 to rotate through the key pin (not shown in Figure 2-6), so that it works with the characteristics of a human-driven "pump" and presses the liquid into the same 4a and 4b cylinders. The chamber, at the same time, the other chamber of the two cylinders discharges the liquid, driving the lever mechanism 8 to realize the steering, which is called manual steering.
