DCT Explained: How it Works and the Best Cars

A Dual Clutch Transmission, or DCT as we know it, was first used on the Hilman Minx in 1961. It was first used in racing by Porsche in their 962 C Le Mans race car in 1985 which won the World Sportscar Championship in 1986.  In mass-market cars in India, Volkswagen introduced the DCT as the DSG automatic with the Polo GT TSI in 2013. Now, more automakers like Hyundai, Kia and Tata have cars that use a dual-clutch automatic gearbox.  

It is safe to say that DCTs have a lot of fanfare attached to them compared to other types of automatic transmissions. In fact, their very presence in Indian cars is considered sporty, and while they are quick in their shifting, over the years they have grown to become better at being smooth as well. DCTs use two clutches which each control the odd or even set of gears in a transmission. To better understand how a Dual Clutch Transmission works in everyday cars, we have put together this article.
 

What is a DCT?

In cars which have DCT, the engine can send its power through two clutch packs. Clutch 1 operates gears 1,3,5 and 7. and Clutch 2 operates gears 2,4,6 and 8. Initial DCT cars had a total of six gears whereas newer cars with DCTs have a total of either 7 or 8 gears. 

How Does a DCT Work?

DCTs usually have two input shafts that connect to two separate clutches. With each clutch pack operating its own set of gears, the next gear is pre-selected by the clutch pack not in use. Instead of changing gears, DCTs directly change the clutch pack. This process can be completed quicker using electric and hydraulic actuators and the power delivery to the wheels is interrupted for a much lesser time than traditional automatic gearboxes.

Upshifts or  downshifts are managed by the Transmission Control Unit or the TCU. It is also referred to as Mechatronics. It controls all the actuators, hydraulic or electric, that are required for gear shifts. DCTs make use of many sensors to get the right information:

1. Throttle Position Sensor - Measures the throttle position 
    
2. Vehicle Speed Sensor - Used to calculate the speed of the car
    
3. Engine Speed Sensor - Speed of the engine or ‘RPM’
    
4. Input Shaft Sensors - Measures the speed of the input shafts and useful in synchronizing gears
    
5. Output Shaft Sensor - Measures the actual speed the vehicle is moving and useful for changing gears
    
6. Clutch Position Sensors - Used for measuring the position of the two clutches

A DCT can use more sensors, especially ones to warn itself of high temperatures or mechanical stress. DCT transmissions have a reputation for being largely complicated and unreliable. However, modern DCT gearboxes have improved in design and dependability.
 

Advantages of a DCT

Dual Clutch Transmissions are a rather modern kind of automatic gearbox and were invented in the pursuit of speedy gear shifts. Their advantages are:

1. Quick shifts: DCTs can upshift and downshift quickly. This is great for reducing the lag in power delivery and for better performance as well.
    
2. Smooth: Newer DCTs are smooth in their gear shifts, especially when accelerating gently, or coming to a gentle halt.
    
3. Fuel efficient: DCTs can be efficient if used right. The onboard TCU knows the best times to perform shifts and can optimise efficiency by minimising delays.
    
4. Can adapt to the driver: A DCT is known to adapt to driver habits and will optimise shifts for either being quicker or smoother shifts based on past driving patterns.

A DCT essentially uses data from sensors and uses it to maximise efficiency in real time.
 

Disadvantages of a DCT

Since their appearance in mass market cars, DCTs have demanded frequent repairs and services. Over the years, this has been their of of their biggest disadvantage:

1. Expensive: DCTs use complex parts in their construction and can lead to hefty repair bills in case of an unexpected malfunction.
    
2. Slow speed issues: DCTs aren’t always at their best at slow speeds. Gear changes can feel jerky but this has been ironed out to an extent in modern DCTs, like the ones in the Skoda Kushaq and Volkswagen Taigun. DCT cars can also be quite inefficient in their fuel consumption at slow speeds as well. 
    
3. Malfunctions: DCTs are also known for their malfunction issues such as overheating on hilly terrain in start/stop traffic. Buyers of older automatic transmission cars should avoid DCTs.

That said, brands like Skoda that have offered DCT cars in India for a decade are known to offer heavy discounts on gearbox malfunction bills for their older cars as they were quite widely known to have faults.
 

Best Cars with a DCT in India

DCTs are found on many mass market cars in all body types:

Is a DCT Right for you?

A DCT offers a cutting edge shifting experience that is often only found in high end cars. It is often the right kind of automatic transmission for those who prefer driving a manual transmission car, but shift over to an automatic transmission due to convenience.
 

Conclusion

Dual Clutch Transmissions offer quick shifting and feel great on winding roads, especially if the car is equipped with paddle shifters. In daily applications, they offer a smooth output in most scenarios, although some DCT cars offer a less than desirable experience at slow speeds.