Why Is The Dual Clutch Transmission Not As Popular As The Normal Transmission?

Why Is The Dual Clutch Transmission Not As Popular As The Normal Transmission?

Despite The Genius Behind Dual-Clutch Transmissions, And While Dual-Clutch Transmissions Have Huge All-Around Advantages, Do We Long For Manual Transmissions?

Four decades ago, a technology that would ultimately significantly impact the drivability of today’s cars was born. The Dual Clutch Transmission (DCT), now a common feature in most cars and somewhat exclusive in some vehicles, was dreamed up by a small Porsche engineer.

By their admission, the success of the Porsche engineers at that time probably required more than they could, but they could do such a great job.

Dual Clutch Gearbox pedal

According to Autocar, Porsche’s dual-clutch gearbox (PDK gearbox) almost seemed overly ambitious and far-fetched in the early 1980s. The computing power was a fraction of what it is today, yet the engineers built it well enough to achieve great success in Group C races with the Porsche 962 and rally races with the Audi Quattro S1.

So now that the technology has not only been perfected but has evolved into something much better than first thought are drivers still inclined to go back to manual transmissions?

Porsche dual clutch gearbox

The idea behind DCT is that changing gear ratios in a few milliseconds should theoretically be possible without any torque interruption. By dividing the forward speeds of the transmission between two separate clutches, each forward gear (speed) can be pre-selected, and by opening and closing the clutches simultaneously, the ratio can change, taking one bag out of the equation and entering the other. Playing Shifting is done not by physically selecting the gear needed but by opening and closing clutches.

In the early days of the dual-clutch transmission, the lack of processing speed meant that gear changes were complex. Failure to fully synchronize the clutches resulted in nasty forward jumps during gear changes and, at the same time, put a lot of stress on the driveline.

 At the time, it lacked the refinement and robustness to meet the needs of everyday road cars.

how dual clutch transmission works

Twenty years later, high-speed machining and the development of motorcycle-style wet clutch technology (clutches immersed in oil rather than moving dry in the air) finally made the DCT a whole production reality.

So if such a technology exists, why do so many of us consider manual transmissions and, in some cases, have to reintroduce them to cars where the conventional message has been removed?

Porsche dual clutch gearbox

It may come back to psychology.

During the DCT’s transition from motorsport, single-clutch automatic transmissions such as Alfa Romeo’s Celspeed and BMW’s SMG were introduced. Both were criticized for being slow compared to conventional gearboxes. The average time for a smooth shift with an H-pattern gearbox is probably about half a second in vertical movements of the shift lever and much longer in transverse directions.

One of the engineers attributed the difference to perception, as the driver had nothing to do during the shift. It may have been confirmed and is probably why faster dual-clutch transmissions, despite their undeniable superiority, are not popular with some drivers.

Although dual-clutch transmissions are intelligent, they cannot keep the driver engaged and the challenge of shifting smoothly. It’s that driver involvement and sheer joy of getting the best out of a car that automation can never replace.

How does a double-clutch transmission work?

To explain the function of the double-clutch transmission or DCT, we must first look at the manual transmission. The driver must first press the clutch pedal in manual gearboxes to change to a higher, lower, or reverse gear.

By doing this, the connection between the engine and the gearbox and the power flow is interrupted. After pressing the clutch pedal, gear shifting is done using the gear lever; At this time, a toothed ring moves from a gear wheel to a gear wheel with different dimensions. Components known as synchronizers engage the gears in a coordinated manner before they are worn together.

After connecting the collar with the new gear, which moves the gear lever, the clutch pedal is released to re-establish the connection between the engine and the gearbox and transfer power to the wheels.

As it is known, in traditional manual gearboxes, the flow of power transmission is not permanent and is done in active, passive and active modes. This process causes a phenomenon known as torque disturbance and noticeable shaking of the car during gear shifting.

Dual Clutch Gearbox

In DCT transmissions, the two clutches in the system are operated by electronic and hydraulic tools and without the driver’s intervention. In this case, DCT is an automatic transmission, but unlike conventional automatic transmission, its clutches are independent.

For example, in a car equipped with a 6-speed dual-clutch gearbox, one clutch is engaged with gears 2, 4, and 6, and another is involved with gears 1, 3, 5, and reverse.

This design ensures no communication between the engine and the gearbox.

In double-clutch transmission, even odd gears are arranged on two axles with a concentric design. The more oversized clutch is connected to the even gears, and the smaller clutch is connected to the odd gears; For this reason, there is no disruption in power transmission, and gear shifting is done at high speed.

How Dual Clutch Gearbox works

The difference between DCT and automatic transmissions is the absence of a torque converter. DCT transmissions use wet multi-plate clutches or two dry single-plate clutches. In the wet type, the existing fluid prevents excessive heat and friction. In this design, the gearbox can manage torques higher than 350 Nm.

On the other hand, in the dry clutch, the maximum torque is limited to 250 Nm, but the fuel consumption will be much more optimal. The wet type is used in sports and powerful cars, and the dry type is used in urban and economic models.

 

Positive and negative features of double-clutch gearbox

One of the best advantages of dual-clutch transmission is the enjoyable driving experience. In addition to the quick and automatic gear change, it is possible to change it to semi-automatic mode so that, like in video games, the gear can easily change by pressing the pedals behind the steering wheel. The average gear change is about eight milliseconds, which is faster than any other type of gearbox.

Acceleration with cars equipped with a dual-clutch transmission is pleasant and without strong jolts, making the ride more comfortable for all passengers. But perhaps its most attractive advantage for car buyers is more efficient fuel consumption. Because the flow of power transmission is continuous in cars equipped with DCT, fuel consumption is significantly lower.

Dual Clutch Gearbox power transmission path

A 6-speed dual-clutch transmission consumes 10% less fuel than a 5-speed manual. The high speed of gear shifting, the possibility of choosing between fully automatic and semi-automatic modes, and better fuel consumption are the unique advantages of DCT transmissions.

The negative point of DCT can sum up in the higher price of manufacture and repair and more complexity.

Many car manufacturers such as Volkswagen, Lamborghini, Kia, BMW, BYD, Chery, Mercedes-Benz, Ferrari, Alfa Romeo, Chrysler, Honda, General Motors, Hyundai, Nissan, Mitsubishi, Renault, etc. use this type of double-clutch gearbox in their various products.

Dual Clutch Gearbox or DCT

Due to the higher cost of a dual-clutch transmission, many car manufacturers are looking for a cheaper type of automatic transmission. The most famous of them can be called Continuously Variable Transmission or CVT.

CVT transmissions enable optimal fuel consumption and a more comfortable ride, but they cannot manage high torques and engine braking; This is the reason why most family, economy and city cars use this type of gearbox, and off-road, sports and super sports models are equipped with other types of gearboxes.