Structure of Automatic Transmission Oil Pump

The function of the oil pump is to provide a certain pressure and flow of hydraulic oil for the torque converter and the hydraulic control system to ensure the lubrication needs of the friction pair such as the planetary gear mechanism. The oil pump is installed behind the torque converter and is driven by bushing at the rear end of the torque converter. In the oil supply system of the automatic transmission, commonly used oil pumps include an internal gear oil pump, rotor oil pump, and vane oil pump. The automatic transmission oil pump is usually mounted behind the torque converter and is driven by bushing at the rear end of the torque converter housing.

 

Type of oil pump

 

 

In the oil supply system of the automatic transmission, there are two kinds of oil pumps: fixed pumps and variable pumps.

 

In this blog, we mainly introduce the dosing pump.

 

Common quantitative pumps include internal gear pump, rotor pump, and vane pump, and the most widely used is still the internal gear pump.

 

The internal gear pump is mainly composed of external gears, internal gears, crescent-shaped partitions, pump casings, pump covers, etc. The gears are tightly installed in the inner cavity of the pump body, the external gears are driving gears, and the internal gears For the driven gear, a crescent-shaped spacer separates the external gear and the internal gear.

 

The inner and outer gears abut against the crescent-shaped partitions with tiny gaps. The pump body is cast, and after finishing, there are many oil passages in the pump body, with an oil inlet and oil outlet.

 

The pump cover is also a finished casting and also has many oil passages, and the pump cover and pump body are bolted together. The crescent-shaped partition of the internal gear pump divides the vacated volume between the internal gear and the external gear into two parts. When the gear rotates, the gear teeth of the gear enter the separated part from meshing, and its volume changes from small to large. It is called the oil suction chamber; the part where the gear enters the meshing from separation, its volume changes from large to small, is called the oil pressure chamber. Since the tooth tops of the inner and outer gears and the crescent-shaped partitions are closely matched, the oil suction chamber and the oil pressure chamber are sealed with each other.

 

When the engine is running, the shaft sleeve at the rear end of the torque converter housing drives the external gear and the internal gear to run together. At this time, in the oil suction chamber, as the external gear and the internal gear are continuously withdrawn from meshing, the volume continues to increase, so that a partial vacuum is formed. The hydraulic oil in the oil pan is sucked from the oil inlet, and as the gear rotates, the hydraulic oil between the teeth is brought to the pressure oil chamber and the volume is continuously increased, generating vacuum suction, and sucking the hydraulic oil from the oil pan through the filter screen. In the oil pump, the gear teeth enter the meshing end, the volume decreases continuously, the oil pressure rises, and the oil is forced out of the oil pump.

 

The oil pump rotates continuously to provide hydraulic oil with a certain pressure and flow for the hydraulic automatic control system. A cycloidal rotor pump is a kind of internal gear pump with a special tooth profile. It has the advantages of simple structure, compact size, low noise, stable operation, good high-speed performance, etc. The cycloid rotor pump is composed of a pump casing, a pump cover, and a pair of intermeshing rotors.

 

The inner rotor is an external gear, and its tooth profile curve is an epicycloid, and the outer rotor is an internal gear, and its tooth profile curve is an arc curve. The rotation centers of the inner and outer rotors are different, and there is an eccentric distance e between the two. Generally, the number of teeth of the inner rotor can be 4, 6, 8, 10, etc., and the outer rotor has one more tooth than the inner rotor.

 

The more teeth in the inner rotor, the smaller the oil pulsation. Usually, the inner rotor used in automatic transmissions has 10 teeth. When the engine is running, it drives the inner and outer rotors of the oil pump to rotate in the same direction. The inner rotor is the driving tooth, and the rotation speed of the outer rotor is one tooth per revolution slower than that of the inner rotor. With the rotation of the rotor, the volume of the working chamber changes continuously. When the rotor rotates clockwise, the volume of the working chamber on the right side of the center line of the inner and outer rotors changes from small to large, forming a partial vacuum, which sucks the hydraulic oil from the oil suction port. The volume of the working chamber on the left side of the center line of the inner and outer rotors changes from large to small, and the hydraulic oil is discharged from the oil outlet.

 

The vane pump is composed of a stator, rotor, vane, casing, and pump cover. The rotor is driven by the shaft sleeve at the rear end of the torque converter housing and rotates around its center (the stator is fixed, the rotor and the stator are not concentric, and there is a certain eccentricity between them.

 

The displacement of the vane pump depends on the diameter of the rotor, the width of the rotor, and the eccentric distance between the rotor and the stator. The larger the diameter of the rotor, the width of the rotor, and the eccentric distance between the rotor and the stator, the greater the displacement of the vane pump. The vane pump has the advantages of stable operation, low noise, uniform pump oil volume, and high volumetric efficiency, but it has a complex structure and is more sensitive to the pollution of hydraulic oil.

 

The vane pump is composed of a stator, rotor, vanes, casing, and pump cover. The rotor is driven by the shaft sleeve of the hydraulic torque converter casing and rotates around its center. The stator is fixed and the rotor is not concentric with the stator. There is an eccentricity between them. When the rotor rotates, under the action of centrifugal force, the blades open outwards, abut against the inner surface of the stator, and reciprocate in the rotor blade slot with the rotation of the rotor, so that a seal is formed between each adjacent blade working chamber.

 

If the rotor rotates clockwise, the volume of the working chamber on the right side of the center line of the rotor and the stator gradually increases, generating a certain degree of vacuum, and the hydraulic oil is sucked from the oil inlet, and the volume of the working chamber on the left side of the center line of the rotor and the stator gradually increases. When it decreases, the hydraulic oil pressure increases and is discharged from the oil outlet.

 

Conclusion

 

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