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A New . nuid-coupling Transmission
Page 85
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Combined in a Novel Manner with the Cotal Gearbox, the Coupling Provides Exceptional Ease of Control and Elimi nates the Clutch Pedal
ATRANSMISSION of particular interest to designers and users of commercial vehicles has been devised and patented by the Hydraulic Cotipling and Engineering Co., Ltd., Worton Road, Isleworth, Middlesex. It comprises a Vulcan-Sinclair Traction-type coupling and the Cotal electro-magnetic epicyclic gearbox—two components. familiar to most of our readers, which have already proved their reliability and merit.
The most ingenious feature of this transmission is the special method employed for gear changing which results in a remarkably • smooth and quiet action. It will be recalled that the epicyclic gearing in the Cotal box is selected by means ,of the braking effect of electro-magnets. the current to which is supplied through switches.. controlled by the gear lever.
The same method is used in the system under review, but a. new form of switch prevents any preselected circuit holm being completed until the accelerator is momentarily released. A lightning change then takes place at the very instant when the fluid coupling is " caught on the hop" between driving and overrunning.
When a coupling of this kind is revolving at speed, the oil which is circulated between the rotors provides an almost solid drive. So long as the engine is propelling the vehicle the motion of the oil follows what might be called a continuous helix through the cells in the rotors. Similar conditions apply during overrunning, but the direction of oil flow is then reversed.
There is a very brief interval, when changing over from one condition to the other, in which the oil is so disturbed that the.coupling becomes "soft." This instant is chosen for changes of gear--a fact which accounts for
the extreme smoothness of the change and which also obviates slip at the electro-magnets.
When getting away from a standstill the transmission naturally affords the normal advantages of the fluid coupling in that the vehicle will move off (after gear engagement) when the driver opens the throttle. No clutch pedal is needed. . The vehicle in which we tested this system was fitted with a normal accelerator for rightfoot operation and with a brake pedal for which the left foot was employed.
After a little practice this plan was found to afford an extremely safe means for control and the accuracy with which the vehicle could be rnanceuvred was very striking when driving in heavy London traffic.