Drive transmissions

摘要

An automatic transmission for a city bus and other highway vehicles comprises an engine-mounted gearbox with a laterally offset drive output to the rear wheels through a propeller shaft and differential drive unit. The gear box has four layshafts grouped round the drive input shaft. Multiplate pneumatic clutches, one on each layshaft, select transmission ratios under the control of a driver's selector switch acting through an electronic control unit and an electro-pneumatic valve supplied with air by a compressor. The control unit includes a retarder function provided by simultaneous partial engagement of the first and second gear clutches when the vehicle is in third or fourth gear. Access to the clutches for servicing is provided by end covers on the gearbox whereby the clutch elements can be replaced without stripping the gearbox.