THE CASE FOR SEMI-AUTOMATIC TRANSMISSIONS

The article relates the history of semi-automatic transmissions for motor vehicles, and discusses their future prospects. Manual gear selection and declutching were originally so difficult to control that alternative approaches were sought. The first approach sought to make the whole process automatic, and culminated in fully automatic transmissions, produced from the early 1940s on. The apparently cheaper and simpler second approach was to relieve the driver of the need to operate the clutch when changing gear, and when the vehicle was at rest. In such semi-automatic systems, the driver is still responsible for gear selection. The only requirement for such a system to work is a reliable servo clutch unit, which operates as smoothly as a skilled drivers foot. It was remarkably difficult to design such a unit well. Although these units were introduced widely from the mid-1950s on, they continued to have drawbacks. In the 1980s, they were improved by using electronic controls. One of the most popular units has been Saab's Sensonic system, whose clutch servo operation is essentially electro-mechanical. Today, Europe is the only potential volume market for semi-automatic transmission, as only 10% of cars sold in Europe are fully automatic, compared with 88% in North America and 73% in Japan.