MMT TRANSMISSIONS
Multi mode transmissions
Automotive gear shift systems have undergone a revolution in the last couple of decades, the previous known quantities of manual or automatic transmission giving way to a number of brand defined shift systems such as Toyota`s MMT (Multimode Manual Transmission), Volkswagen`s Direct Shift Gearbox or Vauxhall`s Easytronic.
All work on the same basic principle of a manual transmission with the driver operated clutch replaced by an electronically controlled clutch with a sequential gearbox. While a true automatic transmission has a torque converter instead of a clutch, these sequential gearbox systems do still use a clutch, simply not in the form of a pedal on the floor. While gearshift is mostly electronically controlled with a lever/button gear selector mechanism, there is usually a manual over-ride feature.
Basic driving uses the same technique as a manual system. When you shift into first the sequential manual box will have a slight creep forward similar to an automatic. You accelerate and upon reaching peak engine performance, you press a paddle, button or similar device to shift up to the next gear. There is no provision for selecting gears out of sequence, you are obliged to follow second with third and so on. For a smoother shift you are advised to ease off the accelerator pedal a little, although gear change will still engage with the throttle depressed it will just feel somewhat bumpier. Downshifting follows a similar process. Most racecars and motorbikes use a manual sequential shift system as the response to controls is faster than an H-shaped manual gearbox and there is less room for error. Most of these transmissions can be also be driven in “Auto Mode”, which will appear to the driver to perform much like a fully automatic transmission.
This combination of the traditional manual and automatic transmissions is practical for city driving, making the constant stops and starts characteristic of poor traffic flow much easier on the left foot. Hand operated gear controls are usually located so that you don`t even have to take your hand off the wheel to effect a shift. It is convenient for less confident drivers or those with poor co-ordination or motor impairment issues, while fitting more easily into the engine bay of smaller cars than full automatics. Furthermore cars using the system are usually nippier and more fuel efficient than a true automatic.
While these transmission systems are popular and effective in performance cars, in lower end vehicles they have been criticised for jerky gearshift movements, slow response to manual over-ride and poor low-speed control. Furthermore, most do not feature the ability to move forward on an incline that so many find helpful in an automatic.
A further system called DSG (Direct Shift Gearbox) uses two clutches to control different gears, with electronic controls cleverly pre-selecting the next gear, allowing for lightning fast changes. However such mechanisms are heavy and expensive, making them less popular in mass production cars at this point, however, VAG Group have invested heavily in this technology and these transmissions can be found throughout their vehicle range.
Tiptronic is a similar idea, but not the same, while it has a gear selector lever, it uses a torque converter instead of a clutch, making it a true automatic gearbox at heart. Similarly to sequential manual boxes, gear shift is smooth and quick and can be performed with both hands on the wheel, but engines can suffer from a lower power output due to the torque converter. They are ideal for drivers who prefer the convenience of an automatic but with added manual control and are commonly found on higher performance vehicles as beloved by readers of torquecars.com or the likes of Porsche, BMW or Mercedes.
