Analyze the phenomenon of oil blow-by in gear pump oil seal and its control method

1. The impact of component manufacturing quality

　　 (1) The quality of the oil seal.

　　 If the geometry of the oil seal lip is unqualified, the tightening spring is too loose, etc., causing air leakage in the air tightness test, and the gear pump is installed in the main engine to blow oil. At this time, the oil seal should be replaced and the material and geometry should be inspected (the quality gap between domestic oil seals and foreign advanced oil seals is large).

　　 (2) Processing and assembly of gear pumps.

　　 If there is a problem with the gear pump processing and assembly, the rotation center of the gear shaft is not concentric with the front cover stop, which will cause uneven wear of the oil seal. At this time, check the symmetry and displacement of the front cover bearing hole to the pin hole, and the coaxiality of the skeleton oil seal to the bearing hole.

　　 (3) Seal ring material and processing quality.

　　 If this problem exists, the seal ring will be cracked and scratched, resulting in weak or even failure of the secondary seal. Pressure oil enters the skeleton oil seal (low pressure channel), and the oil seal blows away. At this time, the material and processing quality of the sealing ring should be checked.

　　 (4) Processing quality of variable speed pump.

　　 The feedback information obtained from the OEM shows that the oil leakage problem of the gear pump oil seal assembled with the variable speed pump is more serious, so the processing quality of the variable speed pump also has a greater impact on the oil leakage. The variable-speed pump is installed on the output shaft of the gearbox, and the gear pump is installed on the output shaft of the transmission through the positioning of the stop of the variable-speed pump. If the stop end of the variable-speed pump faces the out-of-tolerance (perpendicularity) of the gear rotation center, it will Make the center of rotation of the gear shaft and the center of the oil seal not coincide and affect the seal. In the process of variable speed pump processing and trial production, check the concentricity of the rotation center to the stop and the runout of the end face of the stop.

　　 (5) The front cover oil return passage between the skeleton oil seal and the seal ring of the CBG gear pump is not unblocked, causing the pressure here to rise, thereby puncturing the skeleton oil seal. After improving here, the oil blow-by phenomenon of the pump has been significantly improved.

　　2. The influence of gear pump and main engine installation quality

　　 (1) The coaxiality of the gear pump and the host is required to be less than 0.05.

　　Usually, the working pump is installed in the variable-speed pump, and the variable-speed pump is installed in the gearbox. If the end of the gearbox or variable speed pump faces the out-of-tolerance of the center of rotation of the spline shaft, a cumulative error will be formed, which will cause the gear pump to bear radial forces under high-speed rotation, causing oil seals to blow-by.

　　 (2) Whether the installation clearance between components is reasonable.

　　 Gear pump outer spigot and variable speed pump inner spline, gear pump outer spline and gearbox spline shaft inner spline, whether the clearance fit between the two is reasonable or not, all have an impact on the oil blow-by of the gear pump. Because the inner and outer splines belong to the positioning part, the matching clearance should not be too large; the inner and outer splines belong to the transmission part, and the matching clearance should not be too small to eliminate interference.

　　 (3) The oil blow-by of the gear pump is also related to its spline and rolling keys.

　　 Due to the short effective contact length between the spline of the gear pump shaft and the inner spline of the gearbox output shaft, and the torque transmitted by the gear pump is relatively large when the gear pump is working, the spline bears a large torque and it is crushed and worn or even rolled. It generates huge heat, which causes burns and aging of the rubber lip of the skeleton oil seal, and oil leakage occurs. It is recommended that the OEM should check the strength of the spline extension of the gear pump shaft when selecting the gear pump to ensure sufficient effective contact length.

　　3. The influence of hydraulic oil

　　 (1) The cleanliness of hydraulic oil is too poor, and the pollution particles are large. The sticky sand and welding slag in various hydraulic control valves and pipelines are also one of the causes of pollution.

　　Because the gap between the shaft diameter of the gear shaft and the inner hole of the seal ring is very small, the larger solid particles in the oil enter it, causing the inner hole of the seal ring to wear, scratch or rotate with the shaft, causing the pressure oil of the secondary seal to enter The low pressure area (the frame oil seal) causes the oil seal to break down. At this time, filter or replace with new anti-wear hydraulic oil.

　　 (2) After the viscosity of the hydraulic oil decreases and deteriorates, the oil becomes thinner. Under the high pressure state of the gear pump, the leakage through the secondary seal gap increases. Since it is too late to return the oil, the pressure in the low pressure area will increase, which will hit Wear oil seals. It is recommended to test the oil regularly and use anti-wear hydraulic oil.

　　 (3) When the main engine has been working under heavy load for too long and the oil level of the fuel tank is low, the oil temperature can rise to 100°C, causing the oil to become thinner and the skeleton oil seal lip to age, which will cause oil leakage; should be regular Check the liquid level of the oil tank to avoid excessive oil temperature.