From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Four-wheel braking and car control, discussing front axle rigidity and steering effects.
Identifier | ExFiles\Box 30\6\ Scan198 | |
Date | 7th September 1925 | |
R.R. 433a (50 HD{Mr Hayward/Mr Huddy}) (P.D. 31. 12-8-25) J.H.D. K1559 EXPERIMENTAL REPORT. Expl. No. REF: HsRm1/LG7.9.25. To DA.{Bernard Day - Chassis Design} from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} FOUR WHEEL BRAKING AND CAR CONTROL. From our experience the rigidity of the front axle in torsion has a much greater effect on steering safety than exact centre point. Even if the brakes are perfectly equalised, if they are applied on a lock with sufficient violence to cause the pivots to assume a forward lean, the steering will inevitably take charge. If they are reasonably well equalised the point of contact between the tyre and the road can be as much as 2+" out of centre point without there being the slightest effect on the steering when braking on full load. We have proved this on the Lambda Lancia car where the pivots are absolutely rigid in torsion owing to the construction of the car. There still remains a certain amount of doubt amongst a large number of people that the latter statement is true. Many cars fitted with centre point steering will exhibit a dangerous tendency to dive into the ditch if one front brake only is applied at speed. The following mathematical explanation was advanced to account for this :- Supposing the near-side front brake only to be in operation (this will give the same steering effect as if the back wheels also were braking but not locked). Then there is a couple tending to turn the car about the point of contact with the ground of the front wheel on which the braking is being done equivalent to - M.I./g * t/2 lbs. ft. This is resisted by the rear wheels which will not skid sideways. The frame, however, must tend to exert some force F along the axis of the stub axle due to this couple. Owing to the fact that the pivot has a slight backward lean to give a castoring or self-centering action, the force F.{Mr Friese} will have a moment Y about the point where the portion of weight of the car acting on this wheel cuts the pad of the tyre in contact with the ground. This moment we believe is sufficient to steer the wheel and cause the car to turn towards the side where the brake is applied. When values for a normal car are substituted, however, it will be seen that this moment is exceptionally small. contd :- | ||