The torque converter is the component used in the automatic transmission system to transmit the engine torque or power to the transmission. The torque converter allows the engine to keep running while the vehicle is stopped, and it provides a smooth and gradual transfer of power from the engine to the wheels. In this article, I will discuss the torque converter construction and working diagram.

Torque Converter Construction and Working Diagram

A torque converter is a device that performs a function similar to that of a gearbox. that is, to increase tilt torque while reducing the speed. But whereas the gearbox provides only a small number of fixed ratios, the torque converter provides a continuous variation of ratio from the lowest to the highest.

A torque converter is designed to obtain a mechanical advantage or gear ratio by hydraulic means in the same manner as gears do by mechanical means. It provides a maximum gear ratio starting from rest and gradually decreases that ratio as the vehicle gains speed. So here is the brief of the details of torque converter construction and operation.

Construction

The construction of a torque converter is similar to that of a fluid coupling, the only difference being that it has an additional stationary member called the reaction member. Thus, a torque converter consists of three principal members instead of two, these are :

1. The driving member or impeller or pump, is connected to the engine.
2. Driven member or rotor or turbine, which is connected to the propeller
3. Stationary member or reaction member or stator, which is fixed to the frame. It is the member which makes it possible to obtain a change of torque between input and output The fluid coupling does not have this member and cannot produce any change of torque. The stator is mounted on a free-wheeling one-way clutch so that it can turn in only one direction. A stationary shaft, called the reaction shaft, extends from the geared transmission in the back of the converter through the pump to support the stator.

The driven member (turbine) faces the stator and is splined to the input shaft which rotates inside the reaction shaft and connects curved blades to project most of the oil into a hollow cylinder parallel to the axis of rotation. The turbine is driven by the stream of oil sent to it by the pump. The oil enters the blade section near the rim and passes through the blades. The entire assembly is contained and linked to the engine flywheel.

Operation

When the engine is running idle, the pump produces a slow circulation of oil, as the engine drives it. This slow circulation of oil is not sufficient to move the turbine. When the throttle is opened wide, the engine speed increases, and the pump moves faster projecting the oil toward the turbine. But the oil still has less force which is insufficient to turn the turbine.

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Therefore, the oil returns to the pump, with almost no loss of velocity, except that due to friction. The net effect of the redirection of flow is to increase the pump output. The pump output under these conditions is the output velocity that it is creating because of the engine torque, plus the input velocity of the redirected oil.

A built-up output velocity of two to three times the output velocity due to the engine alone is achieved when the turbine is stationary. This makes the turning force of the turbine three times that of the engine. The increased torque of the turbine enables it to rotate and thus drives the input shaft, which in turn transmits the power to the geared section of the transmission.

Whereas the fluid coupling transmits the same torque as given to it by the engine, the torque converter increases the torque in a ratio of about 2:1 to 3:1. Thus, it serves the same purpose as that of a gearbox but in a better way. In a gearbox, the torque variation is only in a finite number of steps, but in a torque converter, the torque variation is continuous. However, the efficiency of a torque converter is high only within narrow limits of speed.

Torque Converter as a Fluid Coupling

A torque converter is a type of fluid coupling that uses a fluid to transmit torque from one shell to another. Because a torque convert has a starter, which is not in the fluid coupling, it increases the torque ratio. However, at higher speeds, the torque converter works as a fluid coupling giving the ratio 1:1.

When the vehicle speed increases from slow to high, the need for mechanical advantages decreases and the gear ratio of the torque converter gradually changes to that of a fluid coupling. It is so because the turbine speed gradually approaches the pump speed. This reduces the vortex flow so that less oil is sent back to the pump by the turbine and stator. When the turbine speed reaches a point where the oil flow to the stator is no longer reflected, the starter starts to move with the rotating oil. This is the fluid coupling stage where the gear ratio becomes 1:1.

The action depends upon the throttle opening and vehicle load. At light throttle and steady load, the gear ratio may approach 1:1 at low speed. The torque converter automatically provides the effect of gear ratio as the need arises. Such conditions as hill climbing or rapid acceleration produce the change. In descending steep grades, the torque converter is a fluid coupling in transmitting torque to produce engine braking.

Conclusion on Torque Converter Construction and Working Diagram

So in the automatic transmission system, the torque convert is the component that is used to transmit the power from the engine to the transmission. This is the component that helps the vehicle to drive in the automatic or fully automatic transmission system.

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