Torque Converter Explained: How it Works and the Best Cars

A Torque Converter is the quintessential automatic transmission due to its abundant presence in cars. Torque Converter gearboxes have existed in cars since the 1940s, however, they have evolved over the years and today offer one of the best experiences among automatic transmissions.

Torque Converters are present not just in mass-market cars, but luxury and sports cars as well. However, as we climb up the price ladder, the technology behind a Torque Converter gets more sophisticated, offering a quicker and smoother shifting experience. Overall, the concept behind a torque converter and its functioning remains largely identical across all cars. Let’s take an indepth look at how a Torque Converter gearbox works, its advantages, disadvantages and more.
 

What is a Torque Converter?

Usually denoted with the abbreviation ‘AT’, a Torque Converter gearbox uses the concept of fluid dynamics to transmit power from the engine to the transmission. It consists of a Pump (Impeller) which is connected to the engine and constantly spins with it, pushing transmission fluid into the Turbine and spinning it, which in turn is connected to the transmission shaft. The oldest Torque Converters have used this concept, but modern units use more key components to deliver a more sophisticated experience.
 

How does a Torque Converter Work?

In a Torque Converter automatic transmission, the Pump has a set of blades that drive transmission fluid into the Turbine. The force of the fluid spins the Turbine, which then channels the power to the wheels. When starting from a stop or at slow speeds, the Pump and Turbine can spin at different speeds. This is called slip. It is crucial for smoothness. It also keeps the engine from stalling when the car comes to a stop.

Modern Torque Converters use additional hardware to further increase the efficiency. A Stator is positioned between the Pump and Turbine to optimise the flow of transmission fluid between the two. This helps in torque multiplication allowing for better acceleration at slower speeds. At higher speeds, the slip in the Torque Converter is no longer useful and instead reduces efficiency. To address this, a lock up clutch is used that locks the Pump and Turbine together.

Torque Converters use a planetary gear set for achieving the required gear ratio. It’s a complicated arrangement of gears that come together in different combinations, and can create multiple gear ratios. The gear selection process is controlled by the Transmission Control Unit or TCU. It uses data from an array of sensors to make the required gear changes and control the slip in the Torque Converter. They are:

1. Throttle Position Sensor - Used to measure the throttle position 
    
2. Vehicle Speed Sensor - Uses wheel speed to calculate car speed
    
3. Engine Speed Sensor - More commonly known as RPM or revolutions per minute
    
4. Input Shaft Sensor - Measures the engine speed and is helpful in engaging the lock up clutch
    
5. Output Shaft Sensor - Measures the transmission speed and helps in determining slip
    
6. Transmission Fluid Sensor - Used for measuring the temperature and pressure of transmission fluid

More sensors can be used by the TCU to determine when to make a more calculated decision.
 

Advantages of a Torque Converter

Torque Converters have been used in all types of cars for years and that is because they work well in a number of scenarios:

1. Smooth Operation: The slip created between the Pump and the Turbine in a Torque Converter helps smoothly overcome the interruption in power delivery during gear shifts. It is also useful when the driver demands a sudden burst of acceleration and the transmission quickly downshifts one or two gears.
    
2. Less wear: The use of a fluid coupling allows for less wear and tear, meaning Torque Converters are inherently robust. Torque Converters can also handle heavier amounts of torque compared to other types of automatic transmissions.
    
3. Torque Multiplication: The torque multiplication feature of a Torque Converter is ideal for slow speed driving.

Their smoothness and robustness make Torque Converters ideal for all types of cars.
 

Disadvantages of a Torque Converter

Torque Converters, though versatile, come at a cost:

1. Expensive: A modern day Torque Converter costs a premium over a manual transmission. A good way to overcome the price barrier is by looking at used automatic cars.
    
2. Complex Design: Modern Torque Converters have become complex. While maintenance isn’t a big issue, an unexpected malfunction can incur heavy maintenance bills.
    
3. Heavy weight: Torque Converters are heavier than manual transmissions. 
    

Top Cars with a Torque Converter in India

Torque Converters are found in many cars in India. Here are some of the best ones:

Conclusion

Torque Converters are the most versatile type of automatic transmission as they are inherently smooth and modern technology has also reduced their fuel efficiency losses. The lock up clutch has also reduced the lag in power that was sometimes felt at higher speeds. A testament to this is the fact that BMW’s M cars now use Torque Converter transmissions over the previously preferred DCTs.