Adhesion between tyre and road RECENT STUDIES of anti-skid devices
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being currently developed, caused me to read an article (COMMERCIAL MOTOR, September 16) by Paul Brockington.
This article both interests and puzzles me. For instance, the account of the test of a Maxaret device fitted to a Jaguar. which prevented tail swing states that the brakes were applied fully on a slippery surface. Should this be taken to imply that cautious braking on a slippery surface will not necessarily invoke the action of the Maxaret and not necessarily avoid skidding?
Again, concerning the device fitted to a Leyland Beaver we are told that the sensing device operates at "a critical rate of wheel deceleration", but the device is driven by a propeller shaft connected to two wheels. The rate of angular deceleration of the propeller shaft is effectively the sum of the rates of angular deceleration of the two rear wheels. Does the de-braking occur when both wheels are decelerating in excess of g or only when the one wheel skids? In the former possibility one can visualize conditions where one wheel locks without causing a rapid enough rate of angular deceleration on the propeller shaft whereafter the other wheel would be required to decelerate at 2g in order to invoke de-braking.
Conversely, if the device acts when only the one wheel is decelerating at g what will be the required rate of deceleration on the other wheel?
Regarding inertially controlled anti-skid devices generally, I would draw your attention and that of your contributor, Mr. Brockington, to the Motor Industry Research Association's monthly summary of automobile engineering literature. A number of very detailed tests of inertially operated anti-skid devices are described in various papers available from there. The general conclusion is that even with a high frequency, low amplitude modulus these devices cannot be sufficiently sensitive, in order effectively to prevent wheel locking, without causing an increase in braking distance under good conditions. In other words a loss of adhesion between tyre and road does not necessarily have to be accompanied by a wheel or transmission angular deceleration equal to the magical value of g.
R. W. MASTERS. AMIMI Leeds.