Torque Converters

Genesis and application.

The earliest designs of automatic transmissions used a hydrokinetic clutch, which was developed over time into the torque converter design we know today. The torque converter is part of the classic automatic transmission and some designs of continuously variable transmissions (CVT).

The hydrokinetic clutch is a simpler device that was used in some older automatic transmissions. Its main function is to allow the smooth transfer of power from the engine to the transmission by eliminating the rigid connection between the two. The hydrokinetic clutch consists of two main components: a pump (connected to the engine) and a turbine (connected to the transmission). Both components are enclosed in a housing filled with fluid (ATF oil). The pump, driven by the engine, produces a flow of oil that sets the turbine in motion, transmitting torque to the transmission. The hydrokinetic clutch works on the principle of energy transfer through the fluid, allowing for a smooth, if somewhat lossy, power transfer.

The torque converter is a more advanced device that has replaced the hydrokinetic clutch in modern automatic transmissions. In addition to its power transfer function, the torque converter has the ability to increase torque, which improves system efficiency and vehicle performance. The torque converter consists of three main components: pump, turbine and stator. The pump, connected to the engine, produces a flow of oil that drives the turbine, which is connected to the transmission. The stator, located between the pump and turbine, directs the oil flow, increasing the efficiency of power transmission. The stator has a one-way clutch that allows it to rotate in one direction while locking in the opposite direction, increasing torque under certain conditions, such as starting from a standstill. In addition, modern torque converters are equipped with a locking mechanism (so-called lock-up clutch), which eliminates slippage between the pump and the turbine, providing a direct connection between the engine and the transmission. This significantly reduces fuel consumption by reducing power flow losses.

Construction and principle of operation.

The torque converter consists of several basic components:

1. Housing – The torque converter is enclosed in a sealed metal housing that contains the internal components and ATF oil. The housing is connected by a flywheel to the engine and rotates with it.
2. Pump - is connected to the torque converter housing and rotates with it. It is the component that directly receives torque from the engine, driving the oil into a swirling motion by means of a series of vanes.
3. Turbine - is located inside the torque converter opposite the pump and is connected to the transmission input shaft. The turbine blades are positioned to intercept the oil flow produced by the pump, causing the turbine to rotate and transmit torque to the transmission.
4. Stator - is located between the pump and turbine on a fixed shaft. It is the key component that directs the flow of oil between the turbine and the pump. The stator has vanes that change the direction of oil flow, increasing the efficiency of torque transmission. It is fitted with a one-way clutch, which allows it to rotate in one direction only. When there is a large speed difference between the pump and turbine, the stator locks, allowing the oil to be directed back to the pump at a greater angle, increasing torque.
5. Lock-up clutch - a mechanism to reduce or eliminate the speed differential between the pump and turbine, which reduces fuel consumption.
6. Bearings and seals - components responsible for the smooth movement of the torque converter components rotating independently of each other and for maintaining the tightness of the connections.

When the engine is running, the pump rotates with it, putting the ATF oil in a swirling motion. The oil is pushed by the pump blades onto the turbine blades. The transmission oil jet hits the turbine blades, causing the turbine to rotate. The turbine is connected to the input shaft of the transmission, so its rotation transfers torque, which drives the vehicle. As the oil flows through the turbine, it changes direction and returns towards the pump. At this point, the stator, which is mounted on a fixed shaft with a one-way clutch, directs the oil flow back to the pump blades at a greater angle. This increases the torque and improves the efficiency of torque transmission. The greatest torque amplification effect is achieved when there is large slippage between the pump and turbine, i.e. mainly when starting from standstill. The one-way clutch in the stator allows it to lock in one direction to change the direction of the oil flow, but rotate freely in the other, minimising energy loss when the pump and turbine are rotating at almost equal speed. Modern torque converters incorporate a locking mechanism to eliminate internal slippage at higher speeds. When the vehicle reaches a certain speed, the locking mechanism activates, directly connecting the pump to the turbine. This creates a direct connection between the engine and transmission, improving fuel efficiency and reducing power loss.

Remanufacturing process.

The process starts with emptying the converter of any residual oil. The converter housing then needs to be cut open, which is done on a lathe. All internal components of the converter are thoroughly cleaned to remove dirt, deposits and residues of used gear oil. Special cleaners and equipment such as ultrasonic cleaners are used for this. After cleaning, all components are carefully inspected for wear, damage and cracks. The pump and turbine blades, the stator, the operation of the stator's one-way clutch, the condition and wear of bearings, vibration dampers and spline connections and others are assessed. Worn or damaged components are replaced with new remanufactured ones. Most commonly, bearings, friction lining or lock-up clutch discs, seals and other mechanical components that show signs of wear are replaced. Once all the necessary components have been replaced and repaired, the converter is reassembled. The components are precisely aligned and assembled, and the housing is welded again to ensure tightness. Welding is carried out on a special automatic station, ensuring that an even and tight weld is made around the entire circumference of the converter housing. However, in order to 100% be certain that the weld has been carried out correctly, a leak test of the torque converter is carried out in the next step. The balance is then checked and, if necessary, corrected. The final step is the marking and painting of the torque converter.

Causes and types of damage

Symptoms that may indicate a defective torque converter are:

1. Jerking during gear changes.
2. "Slipping" drive, acceleration problems.
3. Engine choking when starting from a standstill.
4. Noises and vibrations.
5. Transmission overheating.
6. Increased fuel consumption.

The most common failures of torque converters are:

1. Damage or wear to the friction lining or discs/plates of the lock-up clutch
2. Damage to pump and turbine blades
3. Bearing wear
4. Worn or damaged stator
5. Wear or damage to seals
6. Damage to connections (splines and others)