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Automatic Pneumocyclic
Page 102
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• Leyland Motors Ltd. has announced that an SCG Pneumocyclic gearbox with electropneumatic control giving fully-automatic operation will be fitted to an Atlantean doubledecker bus to be shown at Earls Court. Only the barest information has been made available by Leyland; it is to be hoped that detailed technical information will be obtainable at the Show.
Used in conjunction with a two-speed type of governor the system is apparently responsive to changes of speed and torque and is claimed to obviate the jerkiness that was characteristic of earlier transmissions with the same type of automatic control. According to the press release, air-pressure modulating valves are associated with an electronic circuit and are used in conjunction with electropneumatic gear-selection valves. The circuit is connected to a driver's gear-selection
switch, an accelerator-pedal-controlled switch, a magnet valve (comprising the gear-selection, pressure-modulating and relaxing valves) and a speed signal generator. It is stated that the circuit energizes the gear-selection valves in sequence as the vehicle speed rises so that gear ratios appropriate to the speed of the vehicle are always in use and both -racing" and "labouring" of the engine are avoided. An "extremely consistent" level of torque is claimed that "falls smoothly from one gear to the next-.
In a reference to torque responsiveness, it is said that when the accelerator pedal is only partly depressed the switch associated with it eliminates the high-pressure stage so matching pressure to the lower torque demand; pressure is still further reduced by the response of the relaxing valve to the switch when the pedal is completely released and the engine is idling.