Automatic transmission training: analysis of working principle of hydraulic torque converter

Category:Brake system foundation - Date:2015-11-17

the working principle of the torque converter can be simply described as: the hydraulic torque converter is filled with automatic transmission oil, the engine drives the torque converter shell and the pump wheel to rotate through the drive disk, and the ATF oil flows out of the turbine from the pump wheel to realize the power transmission from the pump to the turbine.

Fig. 1 ATF oil impacting turbine blade from pump wheel.

Figure 2 ATF oil from turbine guide wheel flow back pump wheel

When the engine drives the torque converter shell and the pump wheel to rotate through the drive disk, the ATF oil flows from the inner side of the pump wheel to the outer edge of the pump wheel under the centrifugal force. The higher the engine speed, the greater the pressure in the outer edge of the impeller blade. The ATF oil impacted the outer edge of the turbine blade, and from the turbine blade side to the inside of the turbine blade, it flows back through the guide ring to the inner side of the impeller.

A careful analysis of the flow of ATF oil from the pump to the turbine. The necessary condition for the transmission of the torque converter is that the speed of the pump wheel must be higher than the turbine speed, because only the speed of the pump wheel is higher than the turbine speed, and the oil pressure at the outer edge of the blade of the pump wheel is larger than the oil pressure at the outer edge of the turbine blade. Under this pressure difference, the working fluid flows into the turbine from the pump wheel and drives the turbine to rotate.

the working principle of hydraulic torque converter is difficult to understand the action state of the guide wheel. When the ATF oil flows from the turbine through the guide wheel to the pump wheel, the flow direction of ATF oil has a great relationship with the turbine speed.

Figure 3 ATF flow through the guide wheel to the pump wheel

Analysis of the two working states of the figure 4 guide wheel

When the speed of the pump wheel is high and the speed of the turbine is low, the circulation speed of the working fluid in the turbine is small (the circulation is generated by the rotating of the working fluid around the axis of the turbine, the turbine speed is low so the circulation speed is low), and the swirl speed is large (the rotation speed of the pump is greater than the turbine speed, because the outer edge of the pump wheel is at the edge of the pump. " The pressure is greater than the pressure at the outer edge of the turbine, so the swirl speed is large. After the fluid is flowing out of the inner edge of the turbine blade, the direction of the synthetic liquid flow is impacted on the front (concave) blade of the guide wheel, trying to turn the guide wheel against the clockwise, because the unidirectional clutch is locked as the counterclockwise rotation of the guide wheel, that is, the guide wheel can not be relative to the guide wheel. The counterclockwise rotation of the fixed casing, the reverse action moment of the guide wheel to the working oil reacts on the turbine, and makes the output torque of the turbine increase, and the working fluid is directed to the impeller blade to enter the pump wheel after the guide blade is guided.

So the output torque of the turbine is equal to the torque of the pump wheel to the turbine (the torque of the pump wheel) plus the reacting force of the guide wheel against the oil, and the torque of the turbine (the torque of the guide wheel for short)

As the speed of turbine is increased, the direction of ATF liquid flow is further inclined to the circulation direction, the reverse torque of the guide wheel decreases and the output torque of the turbine is reduced, but the output torque is still larger than the input torque.

coupling state: when the turbine speed is 0.85 times of the speed of the pump wheel, the direction of the synthetic liquid is tangent with the guide wheel blade, and the guide wheel can not increase the torque. The output torque of turbine is the same as that of engine input, which is called the working state of coupling at the same time.

the free rotation state of the guide wheel: when the turbine speed is close to the speed of the pump wheel, the swirl speed of the working fluid in the turbine is small (because the difference between the outer edge of the turbine and the outer edge of the pump wheel is small), and the circulation velocity is large (because the turbine speed is large), the direction of the synthetic liquid flow is impacted on the back of the guide wheel (convex surface), trying to make the guide wheel go down the time. The needle rotates, as the one-way clutch does not lock clockwise to the guide wheel, that is, the guide wheel can rotate clockwise relative to the fixed sleeve, and the guide wheel becomes a free wheel. The output torque of turbine is the same as that of engine input.

the reason why torque converter is applied to automobiles is:

the output torque of the turbine varies continuously with the change of the turbine speed. When the car starts, the slope or the heavy resistance is encountered, the speed of the engine will decrease if the engine speed and load are constant, that is, the turbine speed is reduced. So the output torque of the turbine is increased accordingly to ensure that the car can overcome the increase of resistance and continue to drive, so the torque converter itself is a kind of stepless speed transmission which can change the output speed and torque automatically with the difference of the driving resistance of the car.

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