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Semi Automatic Transmission

Halfway to the comfort of an automatic

The forerunner of comfort, often initiated by the export of vehicles to the USA, where some people have never learnt the art of manual gear-changing. However, in this construction, one is only actually relieved of pressing the clutch. As can clearly be seen in the above drawing, the duties are shared, one clutch for pulling off, and on the right, and one clutch for changing gear, on the left.

Torque converter with a conventional gearbox

The torque converter provides for a smooth pulling off, which is also accompanied by the, almost as popular tendency of vehicles, to crawl. At the same time it substitutes for the first gear, whereby a semiautomatic gearbox mostly has one gear less than the same vehicle offered with clutch-pedal and gearbox.

The extra effort is not exhorbitant

The subsequent gearbox is preserved, it loses one gear and receives, in addition, a parking ratchet, because, through the torque converter, the direct contact of the driven wheels with the engine is lost. When the gear- shift lever is touched, a contact is triggered, which operates the substantially smaller clutch through a servo-unit which draws its energy from the inlet manifold vacuum.

Pulling off and driving through city traffic without gear-changing

The torque converter even allows the pulling off in the second gear of the semi-automatic, which would correspond to the third gear in the normal version. One can, in fact, travel through city traffic using only one gear- lever position. This construction appeared on the market around 1968 and has, in most vehicles, only three gears. Therefore only one gear-change operation is necessary, then when one leaves the built-up areas.

Gear-change laziness and converter increase the consumption

These are not of course, particularly economical for the consumption, and in addition, the torque converter makes the efficiency worse. However the operation of this construction is similar to that of a fully automatic gearbox with a distinctly lower purchase price and therefor, has its followers. The gearshift, of course, may not be touched during the journey...

If there is enough space, it can be used with all types of drive-chains

The above figure shows the semi-automatic made by Porsche, which is called the 'Sportomatic'. Because the Porsche 911 at that time, had five gears, four are now left. As usual, in the rear-engine-drive, the torque from the converter or shifting-clutch goes through the final drive to the non-coaxial gearbox up front and comes, with its drive shaft, then only, to the final drive. The semi-automatic is found in this form with all other drive-chain systems. Named after one manufacturer, it is also called the 'Saxomat'. 01/09