DIFFERENTIAL GEAR

Evening Star, Issue 24157, 30 March 1942, Page 7

DIFFERENTIAL GEAR

A NEW INVENTION Although the differential gear plays an important part in the running of an automobile, few motorists really understand how this intriguing device functions in the back axle. Strange to say, the differential gear was produced long before the coming of the motor era, it being invented by C. Peoquer, a Frenchman, as long ago as 1827. At that period, one of the difficulties attending the' construction of steam carriages was the connection between the driving wheels and the machinery, so as to obtain the full adhesion of the wheels and at the same time be able to turn sharp corners. Although few motorists understand how this wonderful mechanism works, most drivers appreciate the fact that the differential enables the outer rear wheel to make more revolutions than the inner wheel while cornering, thus obviating the drag and wear on the outer rear tyre that would otherwise occur when making a turn. The value of the differential is unquestioned, but it has an inherent fault with which most motorists are acquainted'—viz., when one of the driving wheels happens to ■ rest on slippery ground, it will fail to grip. This is because the differential gear is such a perfect balancing device that it can only transmit to the other wheel precisely the same force as is required to spin the slipping wheel. _ Therefore, practically no force at all is imparted to the wheel whiclrhas got a grip and the vehicle ■ remains stationary. It is now reported from London (states the ‘ Dunloip Bulletin’) that the problem of overcoming this differential fault has at last been solved by the Bendix people, 'who have developed a. device known as Ifield _ Restricted Ratio Differential. The device is based on the fact that to; negotiate any curve of which a particular automobile is capable, ‘ there is a' precise limit to the ratio that need he permitted between the respective speeds of the inrier'and outer driving wheels. , Most . motor. vehicles would be well served by a differential which permits one l driving- wheel, to turn no -more than 20 per cent, faster than the crown wheel, while the other wheel turns 20 per cent, slower. This would enable an outer wheel to make, say, 114 turns while the inner one makes 86. ■ • It is claimed for the new device that while doing all that an ordinary differential can do in balancing the load between the two driving wheels, it avoids its fault of permitting one wheel to let its mate down completely.