Analyze the fault phenomenon of the final drive system and its causes.
The boring of the excavator may be the most common walking fault. It may be a single-sided fault or a fault on both sides. The cause of this fault is generally the following:
1. The central rotary joint leaks and leaks oil.
The central swivel joint of the excavator is an important hub for the hydraulic circuit of the upper body to connect the chassis. It ensures the smooth flow of the hydraulic circuit of the travel system when the excavator rotates. It consists of an inner cylinder and an outer casing. The inner cylinder is cast with annular groove oil. Each channel has an opening connected to the lower outlet, and at the same time, the cylinder of the central rotary joint is sealed with the casing and between each adjacent oil passage by a sealing rubber ring to ensure the central rotary joint. Different circuit hydraulic oils do not interfere with each other when the cylinder and the outer casing move relative to each other.
When the central rotary joint seals poorly, it will cause internal leakage or oil leakage. The hydraulic oil driving the hydraulic final drive motors cannot reach the hydraulic motor completely, and some hydraulic oil returns to the fuel tank through other circuits, causing pressure loss in the hydraulic circuit, resulting in hydraulic pressure. The motor is boring.
2, the travel motors leaks, fault
Before we talked about the walking system consists of a walking balance valve, a travel safety valve, a travel speed switching valve, a travel speed switching cylinder, a travel brake cylinder, a throttle valve and a final drives. When a certain valve group generates internal leakage, It will cause pressure loss in the hydraulic circuit of the walking system, resulting in a lack of walking.
3. Insufficient pressure of hydraulic pump and failure of pump control circuit
Insufficient pressure of the hydraulic main pump is also an important cause of boring walking. The cause of insufficient pressure of the hydraulic pump is mainly due to pump internal leakage and pump control system failure, resulting in pressure loss.
4, the main control valve is leaked
The main control valve is a multi-valve valve group. When the working time is long or the hydraulic oil contains impurities, the valve core will wear. When the hydraulic circuit spool of the control system is excessively worn, internal leakage will occur, resulting in hydraulic pressure. Loss of loop pressure causes walking to be weak.
5, the pilot system secondary pressure oil pressure is insufficient
The pilot system secondary pressure oil is output by the proportional control valve. When the running valve of the excavator cab is leaked or stuck, the pilot secondary pressure oil pressure is insufficient, and the main control valve spool cannot be pushed into position. This causes the hydraulic circuit flow of the traveling system to decrease.
6, the walking system high and low speed conversion failure
We know that the general excavator walking system has a rabbit file and a turtle file. When switching to the rabbit file, the hydraulic circuit of the walking system has a large flow, the pressure is low, the hydraulic motor speed is fast, but the torque is low. When switching to the turtle gear, the hydraulic circuit of the walking system has a small flow, high pressure, and the hydraulic motor is slow, but the torque is high.
When the walking system cannot switch to the turtle file, the excavator walking system will have symptoms of inactivity.
Engine brake while walking
Engine brakes are also a common fault on excavators. Today we will focus on the reasons for the brakes on the road.
1. Hydraulic motor reducer failure
The hydraulic motor is a high-speed, low-torque motor that cannot directly drive the excavator. Generally, the excavator will use the planetary gear set to decelerate the hydraulic motor and increase the torque.
When the reducer fails, the reducer's own resistance is too large, causing the hydraulic motor load to be too high, and the hydraulic circuit pressure to rise, causing the engine to brake.
2, the track is too tight
As we all know, the excavator's track tension is adjustable. By adjusting the stroke of the tightening cylinder, when the track is too tight, the hydraulic motor resistance is too large, which is easy to cause the brake.
3, winter crawlers are frozen
In the winter, the temperature in some areas is extremely low. The excavator is stained with water and mud on the track after the previous day's work. The water freeze on the next day will freeze the track, causing the hydraulic traveling motors to load too high and the hydraulic circuit pressure to rise. Causes the engine to brake.
1, the pilot valve stem is not in place
When the pilot valve stem is not in position, the pilot system cannot produce a stable secondary pilot pressure oil, resulting in the position of the main control valve spool not being fixed, resulting in walking and issuance.
2, reducer mechanical failure
When there is a mechanical failure in the internal gear set of the reducer, the reducer will work abnormally and cannot output stable speed and torque, resulting in walking and issuing.
3, walking system failure
When the components such as the travel balance valve, the travel safety valve, the travel speed switching valve, the travel speed switching cylinder, the travel brake cylinder, the throttle valve, and the travel motor are malfunctioning, the walking may be issued.
1, the main pump variable is unstable
The pump control system of the main pump of the excavator can collect the hydraulic pressure of the outlet of the main pump through the central controller. After the analysis and calculation, the electric signal is output, and the angle of the main pump swashplate is changed by the cooperation of the control valve, the pressure reducing valve and the adjusting cylinder. In order to achieve the purpose of adjusting the displacement of the main pump and the output flow.
When the pump control system fails, it is easy to cause the main pump output flow to be unstable, which causes a frustration when operating the excavator.
2. Safety relief valve main valve and secondary valve failure
Generally speaking, the maximum pressure of the excavator hydraulic system is determined by the relief valve. When the relief valve fails, such as the fatigue failure of the relief valve spring or the valve plug, it is easy to cause the overflow valve to overflow. The pressure set value changes, the pressure in the hydraulic circuit is unstable, and the operating excavator feels frustrated when walking.
1, the walking system high and low speed conversion failure
When the excavator's walking system has a high-low speed conversion failure, it may not be able to switch to the rabbit gear, causing the excavator to always walk in the turtle position and the walking speed is slow.
2. The pump control system is abnormal and the flow is insufficient.
The walking speed of the excavator is determined by the speed of the hydraulic motor. When the main pump control system is abnormal, the main pump output flow is unstable. When the main pump swash plate angle is too small, the output flow of the main pump is low, which will cause the excavator to travel slowly. .
3, the pilot system is abnormal
The pilot system secondary pressure oil is output by the proportional control valve. When the running valve of the excavator cab is leaked or stuck, the pilot secondary pressure oil pressure is insufficient, and the main control valve spool cannot be pushed into position. The flow rate of the hydraulic circuit of the walking system is reduced, resulting in a slow walking speed of the excavator.