Troubleshooting methods for the heavy steering fault of XCMG ZL50G loader

The XCMG ZL50G loader adopts a flow amplification steering system, which is composed of a preferred flow amplification valve and a fully hydraulic steering gear. There are two situations where the steering wheel feels heavy when turning: one is that the steering wheel turns heavily; Another situation is that the steering wheel turns smoothly and lightly, while the entire machine turns weakly and heavily. The causes of these two situations are different. Sometimes, service personnel do not clearly distinguish between these two situations during the service process, which leads to inaccurate judgment of faults and even incorrect replacement of parts, causing unnecessary losses. To better understand the adjustment of the steering failure, the detailed situation of this system is described as follows.

I. Main Parameters of the Hydraulic System

1. Working hydraulic system pressure: 17.5 MPa

2 Steering hydraulic system pressure: 15.0 MPa

3 Pilot hydraulic system pressure: 2.2 -5MPa (no less than 2.2 MPa at idle speed; no more than 5MPa at high speed)

Ii. Cause Analysis

A heavy steering wheel is usually caused by a malfunction in the pilot system. You can check and analyze it from the following aspects:

1) Check whether the pressure of the measurement pilot system meets the requirements.

2) Check whether the pipeline connections are correct. (Mainly for vehicles that are being repaired or have just been repaired)

3) Check whether there is any blockage at the pipe joints.

2. If the steering wheel turns smoothly and lightly, but the overall steering is weak and heavy, it is usually caused by a fault in the steering system. You can check and analyze from the following aspects:

1) Check whether the pipeline connections are correct and whether there are any air intake or oil leakage points in the suction pipeline.

2) Check whether the pressure measured in the steering system meets the requirements.

3 Check whether there is any internal leakage in the oil cylinder

Iii. Solution

Before measuring and adjusting the system pressure, the entire machine should be parked on a flat ground, the boom lowered, the bucket leveled, and the engine turned off to ensure safety during operation.

Before measuring the pilot pressure, first lower the boom to the lowest position and bring the bucket to the maximum bucket Angle. The pressure measurement port of the pilot pressure is located on the joint block of the pressure selection valve. The oil from the double pump enters the pressure selection valve through this joint block, and the pressure measurement port is blocked with a screw plug of M14× 1.5 thread. (As shown in Figure 1

Before measuring the steering pressure, first remove the push rod used for the hydraulic limit (as shown in Figure 2). The function of this push rod is: when the vehicle turns to a certain Angle (not reaching the mechanical limit state), this push rod pushes the valve core of the limit valve to move, cutting off the steering oil circuit and stopping the vehicle from steering. The pressure measurement port for steering pressure is blocked on the joint block of the front frame with a 14× 1.5 threaded plug (as shown in Figure 3).

2. Measure whether the pressure of the system is normal.

Pilot pressure: Remove the pressure measuring port plug as shown in Figure 1, connect the (thread is M14× 1.5) connector, and measure the pressure of the pilot system with a pressure gauge with a range of 10MPa. The normal pressure is: the pilot pressure of the engine at idle throttle should not be less than 2.2 MPa, and the pilot pressure of the engine at high-speed throttle should not exceed 5MPa.

Steering pressure Remove the pressure gauge plug shown in Figure 3 below, connect it with a (thread of M14× 1.5) connector, and use a pressure gauge with a range of 25MPa to measure the pressure of the steering system. When measuring the pressure, the vehicle must be turned to the maximum Angle, be in the mechanical limit state, and keep the steering wheel in the steering state. When the engine is pressed at high speed, the pressure of the steering system reaches 15Mpa.

If the above two measured pressures do not meet the specified values, they need to be readjusted.

3. Adjust the pressure

The place to adjust the pilot pressure is at the relief valve A at the rear of the double pump (as shown in Figure 4). Loosen the lock nut of the relief valve and use a special tool to adjust the adjusting screw sleeve. Turning it clockwise increases the pressure, while turning it counterclockwise decreases the pressure.

2) The place to adjust the steering pressure is at the end B of the priority type flow amplification valve (as shown in Figure 5). Unscrew the cover at the A of the flow amplification valve and adjust the pressure regulating screw to adjust the pressure. Adjusting inward increases the pressure, and adjusting outward decreases the pressure.

4. Check whether the pipeline connections are correct. This situation mainly involves old cars, which have already had their pipes removed and repaired. At this point, it is necessary to focus on checking whether the connection of the return oil pipelines of the pilot pump and the limit valve is correct. Incorrect connection of pipelines usually leads to unexpected malfunctions. If the return oil pipeline is connected incorrectly, it is easy to cause problems such as increased back pressure and heavy operating force. In addition, it is necessary to check whether there are any air intake or oil leakage points in the oil suction pipeline.

5 Check whether there is any blockage at the pipe joints.

If the pipelines or joints are blocked by dirt, it is easy to cause problems such as increased back pressure and heavy operating force. This situation occurs from time to time.

6. Check whether there is any internal leakage in the oil cylinder. Pull the steering cylinder piston to the bottom, remove the oil pipe in the rodless cavity, and continue to fill the rod-filled cavity with oil. If there is a considerable amount of oil leaking from the oil port of the rodless cavity, it indicates that the piston sealing ring is damaged and should be replaced. If the oil cylinder leaks, the pressure in the steering system will generally be low, and at the same time, the steering will be weak.

Generally, heavy steering is caused by low pilot pressure. As the hydraulic system of the ZL50G wheel loader adopts a relatively advanced pilot hydraulic control system, higher requirements are put forward for use, maintenance and repair. Users should pay attention to maintenance in daily life, replace the oil and filter screen on time, and enhance their awareness in this regard to keep their machines in the best working condition at all times.