INTERNAL combustion engines used in motor vehicles are notoriously inefficient with less than 20 per cent of the energy contained in fuel actually converted to mobile power.

Despite this inefficiency, very little change has been made to the engine since they were first invented. The internal combustion engine is still essentially the same as it was 100 years ago, but not so with the transmission.

One of the poor characteristics of the engine is that it produces torque and power over a very narrow Revs Per Minute (RPM) range, or in other words they have a narrow power band.

A transmission with various gear ratios is used to match the torque and power of the engine with the driving speed.

For example, when a car is moving from stop it requires very high torque to move it and the engine rotates at high RPM. That must be matched with the slow speed of the car. As the car speeds up the ratio is changed to match the higher speeds.

Transmission systems have changed radically over the years, the manual gearbox (MT) which uses a driveroperated clutch has been around before the motor car and has been improved over time with the introduction of synchronising gears, and other mechanisms.

There are several forms of the gearbox; the popular ones are the H-pattern system found in most cars and the sequential system common in motorcycles and racecars.

Epicyclical Automatic transmissions (AT) change gears as the vehicle moves, freeing the driver of this task. These systems, which use a torque converter, have been known to be quite inefficient and with the push towards energy efficiency other automatic systems have been invented.

The Continuously Varying Transmission (CVT) came out of this thrust to improve efficiency. CVT systems use a series of belts and cones to vary gear ratios continuously from low to high speeds thus removing the stepping gear sound normally heard in traditional transmissions.

Some manufacturers have actually programmed steps into the CVT’s computer to make the car feel like the traditional AT to get drivers used to this new system. CVT are claimed to be just as efficient as manual gearboxes.

In the 1980s Porsche developed a transmission for racing which combined the strength and efficiency of the manual gearbox with the automatic features of the AT, and came up with the Direct Shift Gearbox (DSG).

It is an electronically controlled dual clutch, dualshaft manual gearbox, without a conventional clutch pedal and with full automatic or semi-manual control.

In simple terms, it is two separate manual gearboxes (and clutches), contained within one housing, and working as one unit. It was designed by BorgWarner and was initially licensed to the German automotive industry’s Volkswagen Group (which includes the Volkswagen Passenger Cars, Audi, SEAT, Skoda, Lamborghini, Bentley, Bugatti, Porsche and Volkswagen Commercial Vehicles). By using two independent clutches a DSG can achieve faster shift times and eliminates the torque converter of a conventional epicyclic automatic transmission.

How does DSGs work?

DSG transmission’s two gearbox arrangement uses two input shafts and two clutches — the first shaft controls gears 1, 3 and 5, shaft two controls gears 2, 4 and 6.

A computer is used to control all shifting and these cars can be driven in manual or automatic modes. When gear one is selected the computer also selects gear two, but only the clutch for the first shaft is engaged. When the driver or the computer changes to gear two the clutch packs simply switches shaft one off and shaft two on, at the same time gear three is engaged on shaft one in preparation for the next shift.

Because the gears are preselected, gear changes are really switching of clutches, the net result is that gear changes are lightning fast, faster than the fastest sequential gearboxes used in Formula 1 cars. This makes them ideally suited for racing, however their complexity has so far kept them out of the big league racing. Shifting down is not as fast as upshifts.

DSGs, which are now available on many VW cars, were used in the VW Jetta TdI series in the USA. Drivers absolutely loved these transmissions which featured steering mounted paddle shifters — no clutch pedals, shifting with your foot flat on the gas, and no loss of pace during shifting.

With the drive towards fuel efficiency, motorists will be seeing more DSGs, and CVTs and much less ATs.

Andrew Jackson is CEO of used car dealership JETCON Corporation and past president of the Jamaica Used Car dealer Association. The views expressed do not reflect those of the JUCDA Visit our Facebookpage https://www.facebook.com/jetconcars.