Analysis and Elimination of Common Faults in the Hydraulic System of Vibratory Rollers

The vibration of the front wheel of a vibratory roller is achieved by the hydraulic motor rotating to drive a vibrating rotor that has lost its static balance to rotate (similar to the common frog tamper we see), causing the front wheel to vibrate and enhancing the compaction capacity and influence depth. Its hydraulic system is mainly composed of hydraulic oil pumps, solenoid control valves, regulating valves, hydraulic motors, auxiliary components, etc.

The performance of the hydraulic system of a vibratory roller is mainly reflected in the vibration frequency and amplitude. If the vibrating wheel does not vibrate or the vibration frequency and amplitude are lower than the initial values, it indicates that there is a fault in the hydraulic system.

1. The vibrating wheel does not vibrate

1. Phenomenon

When the circuit of the solenoid valve is connected, the vibrating wheel does not vibrate.

2 Cause analysis

The oil circuit of the vibratory roller's hydraulic motor is generated by the electromagnetic coil of the solenoid valve being energized to produce magnetic force, which drives the iron core to move the slide valve of the control valve, thereby connecting the pressure oil circuit and return oil circuit between the hydraulic motor and the oil pump. The hydraulic motor rotates under the action of pressure oil and drives the vibrator to vibrate. If the vibrating wheel does not vibrate after the circuit switch is turned on, it might be because the pressure oil circuit of the hydraulic motor is not connected. The reason is:

Circuit fault

If the power circuit of the solenoid valve is open-circuited or the electromagnetic coil is damaged, it cannot drive the slide valve of the directional control valve to slide relatively with the valve body. Therefore, the pressure oil circuit of the hydraulic motor cannot be connected without vibration.

(2) Fault of the reversing valve

The slide valve is stuck in the closed position by mechanical impurities, making it difficult to drive the solenoid valve and causing the hydraulic motor to fail to connect the oil circuit. As a result, the roller does not vibrate.

3 Diagnosis and Exclusion

Check the circuit

Use another wire, connect one end to the power supply and touch the live wire terminal of the solenoid valve coil with the other end. If the solenoid valve operates or the vibrating wheel starts to vibrate, it indicates that the power circuit is interrupted. Check each section one by one. Once found, eliminate the problem.

If the vibration wheel does not vibrate after the above-mentioned lap connection, then remove the solenoid valve and push the slide valve by hand. If the vibration wheel starts to vibrate, it indicates that the solenoid valve coil is damaged. You can also use a live wire to connect to the live wire terminal of the solenoid valve to scrape off the spark. If there is no spark, it indicates that the solenoid coil is open-circuited or the ground wire of the coil is open-circuited. If a small blue spark appears, it indicates that the electromagnetic coil is normal but still does not vibrate. It might be caused by the slide valve being stuck by mechanical impurities. Further investigation should be conducted and the symptoms should be eliminated accordingly.

Second, the vibration intensity of the vibrating wheel is small

1. Phenomenon

When the vibratory roller vibrates, it feels that the vibration force is not as strong as at the beginning.

2 Cause analysis

According to the principle of vibration, a vibratory roller can cause vibration mainly because a hydraulic motor drives a rotating part that has lost its static balance to rotate. That is, the center of gravity of the part does not coincide with the center of rotation, generating eccentricity and resulting in jumping during rotation. When the eccentric moment is constant, its vibration amplitude and vibration frequency can only decrease as the rotational speed of the hydraulic motor decreases. The average torque of a hydraulic motor can be calculated theoretically. Since the input of the hydraulic motor is liquid pressure energy, with a value of pQ, and the output is mechanical energy, Mw(torque and angular velocity). According to the principle, the input and output energies should be equal (in the formula, the total efficiency η of the motor should be taken into account). The average torque M and rotational speed n output by the hydraulic motor can be calculated by the following formula:

M=(pQ)η / w n=Qη■ / q

In the formula: p - the pressure difference between the inlet and outlet of the hydraulic motor;

p - Flow rate of the hydraulic motor;

q - Displacement of the hydraulic motor;

w - Angular velocity of the hydraulic motor;

n - The rotational speed of the hydraulic motor;

η - The total efficiency of the hydraulic motor, η=η■η■;

η■ -- The volumetric efficiency of the hydraulic motor (generally above 95%).

From the above formula, it can be seen that the torque and rotational speed of the hydraulic motor are directly proportional to the input oil pressure, flow rate, volumetric efficiency and mechanical efficiency. If any one of them decreases, the rotational speed of the hydraulic motor will also decrease accordingly.

The main reasons for the reduction in the pressure or flow rate of the oil entering the hydraulic motor are mostly due to the decrease in the efficiency of the oil pump and the transmission efficiency.

3 Diagnosis and Exclusion

Check the leakage of the oil pump, the magnitude of mechanical friction, the leakage and blockage of the transmission pipeline, and whether the set pressure and flow rate of the regulating valve are correct. After identifying the issues, eliminate them accordingly.

In addition, check the volumetric efficiency, mechanical frictional resistance and back pressure of the hydraulic motor itself.

If the leakage of the hydraulic motor increases due to wear or poor sealing of the sealing parts, or if the mechanical frictional resistance is too large, it is mostly the reason for the low speed and small torque of the hydraulic motor. It is necessary to further identify and eliminate the symptoms accordingly.

Poor oil return in the hydraulic motor can cause an increase in back pressure. Since the torque of a hydraulic motor is directly proportional to the pressure difference between its inlet and outlet, when the inlet pressure is constant, an increase in back pressure will inevitably reduce the pressure difference between the inlet and outlet of the hydraulic motor. According to the formula M=(pQ)·η / w, the hydraulic motor rotates weakly. Therefore, the cause of the increase in back pressure should be identified and eliminated.

Iii. The hydraulic motor is out of control

1. Phenomenon

When starting the engine to work, if the solenoid valve circuit of the hydraulic motor is cut off, the vibrating wheel of the roller will still vibrate.

2 Cause analysis

From the composition and working principle of the vibrating part of the vibratory roller, it can be known that the vibration of the vibrating wheel is driven by the pressure energy of the working oil input into the hydraulic motor to excite the rotor. The hydraulic motor can drive the rotor to vibrate, which is controlled by the electromagnetic control valve. When the circuit is connected, the slide valve of the control valve moves under the action of electromagnetic force, connecting the oil circuit of the hydraulic motor, causing the hydraulic motor to rotate and vibrate. The current of the solenoid valve is cut off, and the slide valve returns to its original position under the action of the spring, cutting off the hydraulic oil circuit, and the hydraulic motor stops vibrating. When the engine is running, if the vibrating wheel still vibrates when the circuit of the control valve is cut off, it indicates that the slide valve of the control valve is in the position of connecting the oil circuit and cannot cut off the oil circuit. Furthermore, the reasons why the oil circuit leading to the hydraulic motor is not cut off are:

(1) The spool valve of the control valve moves by the magnetic force of the solenoid valve, while it returns to its original position by the elastic force of the spring. If the spool valve fails to return to its original position, it must be due to the spring force being less than the frictional resistance of the spool valve or the frictional resistance being greater than the spring force.

(2) When the solenoid valve encounters a short circuit, that is, when it is connected to another power circuit without a circuit switch, it is also possible for the spool valve to be in the position where the oil circuit is conducting.

(3) If mechanical impurities in the oil jam the spool valve at the position where the oil passage is open, the vibrating wheel will still be vibrating.

3 Diagnosis and Exclusion

(1) Remove the wires from the electromagnetic live wire terminal. If the spool valve returns to its original position, it indicates that there is a short circuit in the electromagnetic circuit. The short circuit should be identified section by section and eliminated.

(2) If the roller is still vibrating after the live wire of the solenoid valve coil is removed, or if the solenoid valve slide valve does not return to its original position after being removed, it indicates that the reset spring of the valve is broken or the slide valve is stuck at the connected circuit position by mechanical impurities. Further disassembly should be carried out to investigate and eliminate the symptoms.