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Torque Converter: Functions and Operating Principle of the Hydraulic Torque Converter
Release date:
2022-11-02 13:09
Source:
In vehicles equipped with an automatic transmission, there is no clutch between the engine and the transmission; instead, their connection is achieved via a hydraulic torque converter. According to Dana, a leading manufacturer of torque converters, the torque converter serves two primary functions: first, it transmits rotational speed and torque; second, it provides a rigid mechanical link between the engine and the automatic transmission, facilitating smooth gear shifts.
Some people claim that the torque converter in an automatic transmission (AT) functions like the clutch in a manual transmission (MT), serving to engage and disengage power. In fact, this analogy is incorrect. Unlike the MT’s clutch, which directly connects the engine crankshaft to the drivetrain, the AT’s torque converter operates differently: from the moment the engine starts, the torque converter begins to rotate. The actual engagement and disengagement of power are handled by internal clutches within the transmission—components that share certain similarities with the MT clutch, particularly in their “soft‑connect” characteristics, though they operate in a manner akin to the MT clutch’s “reverse‑connection” behavior.
The manufacturer of Dana torque converters points out that the operating principle of a hydraulic torque converter is akin to two fans facing each other—one running while the other remains stationary. This analogy vividly illustrates the working relationship between the pump impeller and the turbine within the torque converter. However, providing a detailed explanation of its operation would be rather complex.
After power is transmitted, the pump impeller—mounted on the torque converter housing—stirs the automatic transmission fluid (ATF) inside the converter and drives the turbine to rotate. The ATF undergoes a continuous circulation within the housing. Due to the centrifugal force generated by the rotating pump impeller, the ATF is flung outward, striking the front turbine before flowing along the shaft and returning to the side of the pump impeller. This cyclical motion transfers power to the turbine, which is connected to the gearbox.
However, only this component and the transmission mechanism can be referred to as a hydraulic coupling. To function as a torque converter, the shape of the turbine blades must be altered. Consequently, when the ATF passes through the turbine via the recirculation pump impeller, it rotates in the opposite direction to the pump impeller, generating an impact. Therefore, another component is required for it to serve as a torque converter. The stator is positioned between the pump impeller and the turbine; it regulates the ATF flow within the housing and is fixed to the housing by a one-way clutch.
It is precisely because of the stator that the torque converter possesses its “torque‑multiplying” capability. When there is a significant speed difference between the pump impeller and the turbine, the output torque increases. At this point, the torque converter functions as a continuously variable transmission, leveraging the speed differential to boost torque. During this phase, the stator remains stationary, regulating the flow of ATF. However, once the speed difference diminishes—when the turbine and impeller engage or lock up—the torques become roughly equal, eliminating the need for further torque multiplication. The stator rotates in the same direction as both the pump impeller and the turbine, actively recirculating the ATF to prevent power losses.
Dana torque converter
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