Automatic Transmission Oil Pump for Lubrication

Function of transmission auxiliary oil pump

The transmission auxiliary oil pump is the heart of the transmission oil. When the transmission oil circulates to the bottom, it can pressurize the oil from the bottom through the filter screen to the top. The following is the role of the engine oil pump:

1. Send engine oil to various friction parts of the engine to circulate the oil on the lubrication channel to ensure good lubrication of the engine;

2. The oil pump is mostly a Gear Pump composed of a gear pump body. When the engine is working, the camshaft drives the driving gear of the pump body to rotate. The gear swings the oil along the inner wall of the pump from the oil inlet to the oil outlet, forming a low pressure and generating a suction force that sucks the oil in the oil tank into the oil inlet;

3. The more oil at the oil outlet, the greater the pressure, and the oil engine will be pressed to the friction part to achieve forced lubrication.

The oil pump in the transmission is used to provide hydraulic position at the operation control valve and clutch, while delivering transmission oil to the cooler.

The function of the oil pump is to provide a certain pressure and flow of hydraulic oil for the hydraulic torque converter and hydraulic control system, and to ensure the lubrication needs of the friction side such as the planetary gear mechanism.

Critical parameters:

Hypocycloidal gear pump with crescent shaped partition

As shown in Figure 2, the main and driven tooth profiles of an hypocycloidal gear pump with a crescent shaped partition are both hypocycloids. The characteristic of an hypocycloidal gear pump is that the working cavity between each tooth increases. With the same outer diameter and theoretical displacement, its tooth width is only 2/3 of that of a traditional involute gear pump. The number of teeth in an hypocycloidal gear pump is relatively small, and the number of teeth in both the driving and driven gears is approximately half that of an involute gear pump. Like the involute gear pump, because the number of teeth of the driving and driven gears is greater than 2, the cycloid gear pump also uses a crescent shaped separator plate.

Compared with the involute tooth profile, the curvature of the cycloid tooth profile is smaller and the teeth are tall, approximately twice as large as the involute tooth profile. The flat and narrow tooth profile has two advantages: the flat tooth profile increases the sealing surface, and the reduction in tooth width reduces the axial distance that liquid must flow through to fill the space between the teeth, thereby improving the oil filling ability.

Compared to other types of pumps, due to the strong oil filling ability of cycloidal gear pumps, the possibility of cavitation is low. When the local pressure of the oil in the tooth cavity is lower than the saturated vapor pressure of the oil, bubbles will form in the hydraulic oil. When the pressure rises, the bubbles will rupture. The high-speed liquid flow caused by the bubble rupture impacts the metal surface, causing metal particles to fall off the surface of the oil pump components, causing cavitation.