Starting from the external features, in-depth analysis of the loader hydraulic transmission system failure

Jan 27th,2025 177 Views

When the hydraulic transmission system of the ZL40 loader is working, the gear pump sucks low-pressure oil from the oil pan through the filter, and then filters the high-pressure oil that passes through the filter into the speed distribution valve. When the system sets the pressure (pressure exceeds 1.1MPa), the pressure regulating valve is divided into two paths, one of which is at a pressure of 1.1-1.3MPa, reaches the holding distribution valve through the stop valve, and then enters different working states. The hydraulic cylinder realizes Ⅰ, Ⅱ or reverse gear according to work needs; the other is provided to the torque converter with a force of 0.57MPa through the safety valve. It turns out that after the torque converter dissipates heat, the oil pressure and flow in the torque converter will flow out of the low-pressure oil and lubricate the overspeed clutch and gear through the back pressure valve.

Generally speaking, the hydraulic transmission system of the ZL40 loader will have various faults after 3000 hours of use, and all have certain external performance. Starting from the external characteristics of the aircraft, the causes and troubleshooting methods of the system are analyzed.

1. Faults found on the hydraulic gauge

(1) Swinging of the pressure gauge pointer

The pressure gauge that swings under all gear pressures indicates that air has entered the oil circuit. At this time, the connection between the oil pump and the oil can be locked, and the oil pipe can be omitted.

(2) The pressure of each shift deviates from the normal value

(1) The pressure gauge is low (lower than 0.8MPa). Possible reasons are that the gear pump is severely burned and inefficient, the gear pump is severely burned and inefficient, the transmission valve pressure regulating spring loses its elasticity, the spring seat breaks, and the transmission device freezes. The valve stem or energy storage piston cannot compress the pressure regulating spring; the cut-off valve stem is stuck in the cutting position and is dead; the oil pan filter is severely blocked, resulting in insufficient oil supply; the sealing ring inside the seal of the speed distribution valve accumulator is damaged, and the high and low pressure chambers are connected to each other.

(2) The pressure of I and reverse gear is normal, and the pressure of the second gear is low

The possible reasons are that the sealing ring of the second fixed oil hole in the end cover and the box body combination is damaged or leaking (accompanied by oil leakage), and the rotating oil seal leaks at the joint between the middle part of the end cover and the hydraulic cylinder of the second gear, and the piston guide pin falls off, causing the high-pressure chamber to collude with each other.

(3) The pressure of the second and reverse gears is normal, and the pressure of the first gear is low

The possible reasons are as follows: the rectangular sealing ring at the connection between the hydraulic cylinder and the cylinder body is damaged or lost; the oil seal of the first gear piston is damaged or there are sand holes on the cylinder body.

(4) The pressure of the first and second gears is normal, and the pressure of the reverse gear is low

The possible reasons are as follows: the box wall is cracked in the reverse gear position, the reverse gear piston sealing ring is damaged, the shift valve sealing ring is damaged, and the shift valve sealing ring is damaged.

(I) The pressure of the first and reverse gears did not increase, and the pressure of the second gear was normal.

The possible reasons are as follows: the connecting bolts between the middle cover and the box are damaged; the gap between the middle cover and the hydraulic cylinder of the first cylinder body is not controlled between 0.3 and 0.4 mm.

2. Faults found in hydraulic oil

(1) A large amount of aluminum chips in the oil

The results show that the working wheels of the torque converter wear each other, which reduces the transmission efficiency and heats the working oil. Check the torque converter and find out the wearing parts. Replace the bearings if necessary and tighten the first-stage turbine cover.

(2) A large amount of copper chips in the engine oil

It indicates dry grinding or slipping between the main friction plate and the driven friction plate. Check whether the hydraulic oil injection is in place; Check whether the pressure of the hydraulic pump is normal. If the pressure is normal, it is improper assembly or deformation or deformation of the main and driven friction plates, which should be removed and replaced.

(3) A large amount of iron chips in the oil

It indicates that the overdrive clutch is slipping; At this time, the ground machine is loaded from high speed to low speed. At this time, there is a metal friction sound in the gearbox and the work is weak. Or the roller above the clutch is stuck in the wedge position and is dead; In this case, the work of the I gear is strong, and the speed of the second gear does not disappear.

3. Faults can be found from the changes in hydraulic oil and oil volume.

(1) The hydraulic oil in the gearbox increases and the hydraulic oil in the hydraulic tank decreases.

This is usually caused by the damage of the oil seal of the working gear pump or steering pump, which causes the hydraulic oil to be transmitted to the gearbox. After replacing the oil seal, if such a fault still exists, the sealing copper sleeve of the working gear pump should be checked, because the damage of the copper sleeve will cause the high-pressure oil to damage the frame oil seal. The clearance between the drive gear shaft and the copper sleeve of the working gear pump is controlled between 0.025 and 0.045 mm, and geometric deviation is not allowed.

(2) The hydraulic oil in the gearbox decreases and the hydraulic oil content in the hydraulic tank increases.

This situation is generally caused by the damage of the skeleton oil seal (PG45*62*12) of the transmission gear pump, and the hydraulic oil is sucked into the working gear pump.

(3) The oil in the gearbox is decreasing and the oil in the engine oil pan is increasing.

First, the seal ring and oil seal of the guide wheel are damaged, causing the hydraulic oil in the torque converter to leak into the flywheel housing.

2. The O-ring seal between the torque converter cover wheel and the pump wheel is damaged.

Third, the hydraulic oil return pipe of the torque converter is blocked, causing the torque converter to be slowly refueled or without oil return, resulting in the displacement of the torque converter seal.

4. The fault can be found from the hydraulic oil temperature gauge and the engine water temperature gauge.

(1) High oil temperature and high water temperature

In this case, the troubleshooting method of water temperature should be eliminated first. If the water temperature is normal, the oil temperature is high, which can be eliminated by following the steps below.

(2) High oil temperature and normal water temperature

(1) Check whether the working medium used is suitable. Usually 30# turbine oil or 6# hydraulic oil.

(2) Check the oil level in the oil tank. The oil level is too low or the coarse filter is blocked, which will reduce the oil supply and cause the oil temperature to be too high.

(3) The blockage of the hydraulic oil radiator and the excessive sludge between the radiator fins make the heat dissipation worse, resulting in an increase in oil temperature.

(4) Make the clutch overrun, slip and die.

(5) The 312 bearing of the gearbox II fixed cover is tightly assembled. The clearance between the shaft and the bearing should be controlled between 0.3-0.4mm.

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