The transmission housing is a housing structure used to install the transmission transmission mechanism and its accessories. In order to reduce part wear and power loss caused by internal friction, lubricating oil must be injected into the housing, and splash lubrication is used to lubricate the working surfaces of gear pairs, shafts and bearings. Therefore, there is an oil filling port on one side of the casing and an oil drain plug at the bottom, and the oil level is controlled by the position of the oil filling port. Radial oil holes are drilled on the constant meshing gear of the first shaft and the third gear on the second shaft. The hub end faces of the reverse intermediate gear and the constant meshing transmission gear of the intermediate shaft are provided with radial oil grooves to lubricate the rollers at the positions. Needle bearings. In order to prevent lubricating oil from flowing into the clutch from the gap between the first shaft and the bearing cover and affecting its friction performance, an oil seal assembly is installed in the bearing cover, and there is an oil return groove in the inner hole of the bearing cover to prevent oil leakage. To prevent lubricating oil from flowing out from the rear end of the second shaft. An oil seal assembly is installed in the rear bearing cap of the transmission. Install sealing gaskets on the joint surfaces of each bearing cover, rear cover, upper cover, front and rear housing, etc., and apply sealant to prevent oil leakage. In order to prevent lubricating oil from leaking due to the increase of oil temperature and pressure when the transmission is working, a vent plug is installed on the transmission mechanism seat and the rear bearing cover of the transmission.According to the different structure of the transmission, the transmission housing is divided into three-shaft type and two-shaft type.