Automatic control unit tested by busmen
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AN automatic control device for semi-automatic bus transmissions is being offered by Sevcon Ltd for 000. The device — described and evaluated in CM, July 4 — is said to take four or five man-hours to fit and is under evaluation by nearly 20 operators in the UK. Vehicles currently fitted with the device include Daimler FIeetline, Leyland Atlantean, Leyland National, Bristol VRT, Bristol RE and Ailsa.
Sevcon designed the control gear on the Chloride Silent Rider electric bus and it was during research for that project that a need for automatic control on existing semiautomatics was uncovered. At a London press conference last week Sevcon staff claimed that their device differed from the competition by emplyoing digital rather than analogue logic. This was said to give precise control of gear-change points in all conditions.
The number of buses in the UK fitted with pneumocyclic boxes suitable for automatic control fitment is estimated at 32,000. Operators now evaluating the Sevcon unit include some of Britain's largest, and representatives of two of these attended the press conference. Mr C. Curtis, a development engineer with London Transport, gave a background to LT's lengthy experience with automatic control systems. He admitted that a "colossal mistake" had been made in specifying automatic control for the Routemaster before undertaking considerable development work on the gearbox itself. "The application of automatic control to existing gearboxes only brings out faults and shortcomings in the transmission.," be said.
Moving on to present double-deckers in the fleet, Mr Curtis said that the switch from the 7f-ton RM to the 91/2-ton Fleetline had added to transmission problems and made 1st gear starts essential. Throttle dipping had been considered but, with one week's gearbox life costing only El, the additional stresses of fullthrottle changes did not add much to the cost. In his view an automatic control system needed to be reliable and simple. LT is currently trying a Sevcon-equipped bus.
Mr R. Hawkins, chief engineer of Eastern National, the other operator present, has a Sevcon vehicle on trial. He was enthusiastic about the system because it offers fourstage modulation of the gear changes compared with only two on competitive equipment. He 'revealed •that another National Bus Company operator had obtained a 2831it/ 100km (1mpg) improvement on the 421it/100km (6.7mpg) normally achieved by its Leyland Nationals by fitting the Sevcon,