Maintenance and Repair of Damage to the Shifting Mechanism of a Loader Transmission

The loader power shift transmission uses a hydraulically pressed multi-plate wet clutch shift transmission mechanism to change speed. Each gear is composed of 2-5 friction plates and corresponding pressure plates, hydraulic cylinders, etc. When the shift lever is placed in a certain gear, the pressure oil flows into the corresponding hydraulic cylinder through the control valve, pushing the piston to compress the driving plate and the driven plate, thereby achieving the purpose of transmitting power. In actual use, maintenance is often carried out until the machine cannot work properly, resulting in the loss of the best maintenance opportunity and shortening the service life of the transmission. This article analyzes the causes of power shift transmission clutch damage, introduces a method for detecting clutch piston sealing and transmission failure prevention measures to increase the service life of the power shift transmission. 1． Causes of clutch damage: When the power shift transmission clutch is engaged, the pressure of the hydraulic oil overcomes the spring force and compresses the friction plate. As the hydraulic oil pressure increases, the friction plate contacts the metal plate and gradually tightens, allowing the clutch to smoothly transmit the flywheel power to the transmission input shaft. Every time you shift gears, the friction plate rubs against the steel plate, and the heat generated is dissipated by the coolant. When the friction plates and steel plates become thinner, more hydraulic oil is needed to fully engage them. The engine must be accelerated further, and the sliding time of the friction plates on the steel plates is also extended. The resulting friction heat will also be more, prompting the temperature of the hydraulic oil to increase. When the temperature reaches a temperature sufficient to change the performance of the seals in the transmission, the transmission will produce internal leakage. Internal leakage continues to cause an increase in heat from two aspects: high-pressure oil leaks through the damaged seal, causing the oil temperature to continue to rise; due to oil leakage, the hydraulic pump must deliver more oil to ensure the pressure required when engaging the clutch, so that the clutch is fully engaged, which also requires the engine to continue to accelerate, causing the hydraulic pump to generate greater flow. Such a vicious cycle will eventually lead to the clutch overheating or burning, until it completely fails. 2． Detection of clutch piston sealing When the loader is unable to move or the oil temperature is too high, it is necessary to determine whether the clutch piston is not tightly sealed or is caused by insufficient oil pressure. However, conventional detection methods are sometimes difficult to determine which cause is causing the failure, especially when there is no power. It is even more difficult to check the sealing rings of the assembled transmission assembly. At this time, the air pressure valve can be used for testing. First, remove the transmission control valve (for an assembled transmission, this should be done before installing the control valve), and then supply 0.6 to 0.8MPa gas to each oil hole of the transmission in turn. If a certain hole is connected to gas, a "bang" sound is heard and there is no sound. If the air leakage sound or the air leakage sound is very small, it means that the seal between the corresponding clutch piston and the cylinder barrel is good; if the sound of the piston pressing the friction plate cannot be heard and the air leakage sound is loud, it means that the seal between the clutch piston and the cylinder barrel has failed, and the seal should be replaced. 3． Prevention of transmission failure: The bearings and gear pairs of the power shift transmission are vulnerable parts, so the transmission should be inspected and maintained regularly. The typical maintenance interval of foreign transmissions is 5,000 to 10,000 hours. According to my country's national conditions, it is recommended that the clutch wear should be checked every 2500 to 5000 hours, and abnormal signals should be caught at any time. Since power shift transmissions are unlikely to fail quickly, they can usually continue to be used for 750-1000 hours after the friction plates first show signs of wear. If regular inspection and maintenance are performed during this period, and friction plates, seals and individual bearings are replaced in time, damage to undamaged parts (such as steel plates, gears, shafts, hydraulic cylinders and most bearings, etc.) can be avoided. The following abnormal conditions often occur before the clutch fails: (l) Although the machine can still work, the oil in the transmission has already deteriorated, the viscosity has dropped and contains metallic impurities. Therefore, the transmission oil samples should be analyzed more frequently before the recommended oil change interval. Because clutch wear is a sign of transmission failure, if metal impurities enter the gear pair or jam the gears so that they cannot be aligned, other components in the transmission will be crushed if the engine is not shut down. (2) Decreased shifting performance is a sign of clutch damage. When the clutch begins to slip, the machine will rush forward even if it is accelerated smoothly. At this time, the machine should be shut down for maintenance. The clutch control oil level in valve (3) drops. When the machine must be accelerated to engage the clutch, it means that the clutch has been excessively worn or the seal has failed. Therefore, clutch wear can be determined by measuring the oil pressure of the transmission and observing whether the oil temperature rises. At the same time, the oil quality should also be analyzed. If iron or chromium particles appear in the oil, it indicates that the gear pair has begun to wear. To sum up, if the seals and friction plates are replaced before the clutch fails, the maintenance cost will be 30% lower than repairing after the clutch fails. Similarly, if the planetary gearbox or gear pair is repaired before it fails, the cost will be 2/3 lower than repairing a completely damaged transmission.