Hydraulic Torque Converters

Guide on Hydraulic Torque Converters

The automobile industry is on the peek of inventions, by utilizing the power of hydraulics.  Brakes, power steering, vehicle lifts, hydraulic jack, etc… are a few commonly used applications in the automobile industry that uses hydraulics. Here, we can deal with one such application called hydraulic torque converter.

You might have knowledge of manual and automatic transmission in vehicles. The primary difference between both is manual transmission will require clutch and gear shift for completely stopping the car and the other uses hydraulic torque converter instead of a clutch and gear shift. Other than an automotive automatic transmission, hydraulic torque converters are also used in industrial power transmission systems like forklifts, construction equipment, and railway locomotives, and in the marine propulsion system.

Also, Read: Basics of Hydraulics

What is a hydraulic torque converter?

It is a hydraulic fluid coupling that converts the engine’s torque and transfers it to the transmission system. With the fluid coupling, the engine can spin independently of the fluid transmission. Similar to any other fluid coupling system, the torque converter also contains a pump/impeller driven by an engine, turbine connected to the output shaft and hydraulic fluid-filled within a sealed chamber. This hydraulic torque converter has different benefits like increasing output torque, reducing vibration, decreasing output speed, and smoother driving experience.

Hydraulic Torque Converter Working

A torque converter has the same function as a gearbox. In a car that uses a manual transmission system, the driver needs to shift the gears by applying a force on the clutch for increasing or decreasing the speed. But for a car that uses an automatic transmission system, it doesn’t use any clutch or gear shifts. Instead, a hydraulic torque converter is used for obtaining continuous variation in speed. 

In a stoplight, for reducing the speed or stopping a car, there is no need to stop your engine.  This section will give you a complete idea on hydraulic torque converter working principle.

Also, Read: Hydraulic Oil Viscosity

A hydraulic torque converter is a simple device containing components like impeller/pump, turbine and stator. The torque converter oil it uses will be highly viscous and incompressible, filled inside a sealed chamber. The housing of the torque converter is bolted to the engine. So, whatever the speed of the engine, the impeller/pump inside the torque converter also will start rotating at the same speed. This action will push the fluid inside the torque converter towards the turbine blades. The force of fluid at the turbine blades will rotate the turbine and the transmission system connected with it in the same direction. The stator is located in between the turbine and impeller/pump for directing the returning fluid from the turbine. When the vehicle stops, the turbine will stop rotating without disturbing the impeller connected with the system and prevents the killing of the engine.

There are three stages of operations in the workings of a hydraulic torque converter: stall, acceleration, and coupling.


Stall operation is the situation when the vehicle doesn’t move but does not stop the engine. During this operation, the engine will power the impeller, but as a result of applied brake, it doesn’t rotate. Maximum torque multiplication occurs during stall operation.


When the driver applies force on the accelerator pedal, the impeller will rotate faster. This will create a large difference in the rotating speed of impeller and turbine. During this operation torque, multiplication will occur for obtaining required acceleration. But, it will be comparatively low.


Coupling occurs when the car reaches a maximum speed. That is when the turbine achieves 90% of the speed of impeller(or about the same rate). At this point, a lock-up clutch will lock both the impeller and turbine and provide the same speed for both. During this operation, the torque multiplication will stop and the torque converter will simply act as a fluid coupling. 

By Web Desk : Jul 16 2019 12:40PM 0 470

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