Single-clutch automated manual transmissions
Guide to the different systems, showing how they operate and why they go wrong.
Robotising a manual transmission may have made smaller ‘automatics’ more efficient, but these misunderstood systems are far from robust, as Rob Marshall discovers.
The traditional automatic gearbox, equipped with a torque converter and planetary gear sets, has been a victim of its own success. Even today, many people, including the motor trade, think that there are only two types of transmission available: manual and automatic. This is not the case. Wellestablished problems with the autobox include high cost, hefty weight and low efficiency, compared with a traditional manual ’box. While these disadvantages are masked by high-power engines, they are highlighted when automatic gearboxes are fitted to lower-powered and less expensive vehicles. A solution that manufacturers have adopted is to use a manual gearbox that has both its clutch and gears activated via electronics, thus giving the driver the convenience of a traditional automatic gearbox without the cost and performance drawbacks.
A brief history
Over the years, car-makers have produced their own automated manual gearboxes, many of which have been short-lived. While Citroën’s BVH transmission from the D-series in the late 1960s used a complex system of hydraulic valves to replace conventional gear and clutch linkages, the company’s C-matic of the 1970s simplified the system, by fitting a torque converter clutch onto a manual gearbox. Moving the gear-lever activated a switch that cut hydraulic pressure momentarily from the converter, breaking drive between the engine and transmission to facilitate gear selection. Once Peugeot levelheadedness took over in the 1980s, more conventional automatic transmissions were being used on Citroëns, until the arrival of Sensodrive, introduced from the beginning of the 21st Century, which was followed by the more current EGS/ ETG6 automated manual gearboxes.
Other manufacturers developed their own solutions. Renault’s Dauphine could be specified with an optional Farlec semiautomatic system until the early 1960s, which disengaged the clutch upon sensing gear-lever movement. Simca employed a similar method shortly afterwards, while NSU of Germany produced its own version for the upmarket Ro80 saloon, as did Volkswagen for several of its models from 1968. Just when most people had forgotten about these systems, Saab introduced Sensonic in the mid-1990s. Fitted to the GM 900 Turbo model, Sensonic employed a traditional H-gate gear-lever that controlled a dry clutch but without the requirement for a clutch pedal. At around the same time, Ferrari employed a comparable operating principle for its Valeo transmission.