During the walking and operation of construction machinery, it is necessary to change the moving direction of the whole vehicle body, that is, steering. For vehicles with deflection wheels, the driver manipulates the steering wheel to turn the wheels by an angle through the steering mechanism. For hairpin connected frame vehicles, turning the part of the frame that plays a guiding role by an angle can guide the whole vehicle to change direction. Taking the deflection wheel type as an example, the principle of hydraulic steering is analyzed.
The steering mechanism has two modes: direct human drive and power amplification (power steering). The manual direct drive mode is simple to operate, but it is only suitable for light vehicles. When engineering machinery turns, the guide part is subjected to a large steering resistance torque, which requires the steering mechanism to produce a large driving torque and sufficient rotation speed, which can not be met by manpower. Therefore, power amplification must be applied. The hydraulic power amplification mode has the advantages of large steering power, light weight, light and stable operation.
When the driver operates the steering wheel 1, it is assumed that the vehicle will be accurately turned to the desired driving direction if the wheel rotates angle a clockwise and finally the wheel rotates the corresponding angle Q. In the hydraulic steering mechanism, the spool 2a of the regulating valve 2 is connected with the steering wheel and is turned clockwise through the a. Since the valve body 2B does not rotate, the regulating valve 2 changes from the middle position to the upper path, that is, port P and port 2. The high-pressure liquid of the pump is pressed into the 3C chamber of the hydraulic motor 3, and the liquid discharged from the 3D chamber of the hydraulic motor flows to port B through port D 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 close to that at port C. Circuit B liquid is sent into the rod chamber of hydraulic cylinder 4A and the rod free chamber of 4B to pull the rod 4A and push the lever mechanism 8, so as to turn the wheel clockwise. At the same time, hydraulic cylinders 4A and 4B discharge
The liquid collects together and passes through port a of regulating valve 2. The outlet flows back to the main oil tank.
Since the steering mechanism also has a function of position feedback, that is, the output shaft of the hydraulic motor is connected with 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 valve body to track the valve core to rotate clockwise, so there is a trend to close the valve ports C, D, a and B, That is, the tendency to return the regulating valve to the middle position. However, since the driver has not turned the steering wheel to a full angle, the steering wheel and valve core continue to rotate, and the valve body always tracks the valve core slightly behind, so the regulating valve will not return to the middle position. Once the steering wheel and valve core stop at angle a, the valve body will eventually be dragged to the position where the regulating valve is centered. At this time, the hydraulic motor and hydraulic cylinder stop moving, and the wheel just reaches the angle of deflection desired by the driver.
Through the above analysis, it can be seen that as long as the driver gently moves the valve core of the regulating valve with a small force, the hydraulic cylinder can produce great power and turn the wheels, which is the role of hydraulic power amplification.
When the driver operates the steering wheel to rotate counterclockwise to change the regulating valve from the middle position to the lower position, similar to the above situation, the wheels will turn in the opposite direction.
When the engine stops and the hydraulic pump 5 stops pressing out liquid, the hydraulic steering mechanism can be driven manually.
The principle is as follows: in the actual device, the shaft of steering wheel 1 and hydraulic motor 3 are on the same axis, but in general, they are not connected. When the engine and pump work normally, the driver turns the steering wheel, and the hydraulic motor tracks the rotation of regulating valve 2 based on the hydraulic principle. Therefore, there is no angle difference between the steering wheel and the hydraulic motor (in steady state) or very small (in dynamic state). When the engine stalls and the pump stops working, the hydraulic control system does not work. The driver turns the steering wheel and the hydraulic motor no longer tracks, and the angle difference between the two increases continuously. When the steering wheel turns to an angle greater than 0, the steering wheel shaft can mechanically drive the hydraulic motor 3 to rotate through the key pin to make it work with the characteristics of human driven "pump", Press the liquid into the same cavity of cylinders 4A and 4B, and discharge the liquid from the other cavity of the two cylinders at the same time, driving the lever mechanism 8 to realize steering, which is called manual steering.
