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).
Analysis of a steering failure, discussing potential causes, forces involved, and considerations for design improvements.
| Identifier | ExFiles\Box 153\1\ scan0261 | |
| Date | 15th April 1939 | |
| - 2 - BY.7/G.15.4.39. sink right into it and set up the kind of heavy continuous blow which would produce the high loads on the steering connections necessary to cause such a failure. In this connection it is of interest that we have a Phantom lll. in the Works which hit a mound of small stones used for road surfacing, the car went through a hedge into a field as the result, but the steering gear was undamaged. In this case the mound was hard, and the wheel rode over it, it was the resulting deflection of the steering which caused the car to leave the road. There is an alternative explanation to the above, namely, that if there was a sharp step from the road to the verge the car going into this on a slight right hand inclination would cause a very heavy impact, turning the wheel to the left; the fact that the inclination of the car to the verge was slight, would prevent the wheel rising over the verge and could by the outward wedging action of the verge on the rim of the wheel set up forces on the steering which would produce forces in the neighbourhood of those necessary to shear the shaft. To indicate the magnitude of the forces necessary to shear the rocker shaft, I would like to point out that the force imposed on the ball end of the pendulum lever would be equal to suspending the chassis on a crane from this single point. It is quite clear that if there was no impact on the wheel, such as described in the above alternative suggestion, as to what caused failure, and assuming the rocker shaft had failed when going into the right hand gutter the car would have continued to turn to the right, so either :- (a). The car was turned to the left by Mr. Faroux. or (b). The car was turned left by impact of the right hand wheel with a step at the verge of the road. I think Mr. Faroux's statement as given by Sr. is fair and impartial, he has retained an open mind on the subject. It is a verg good judicial attitude on which I congratulate him. I am having the design reconsidered with the object of arranging a link in the transmission which will be collapsible under heavy road shocks without breaking, as it is very evident that the Marles steering is much less reversible under road shocks than our older form of worm and nut, mainly due to the former being able to break down the oil film between the steering cam and the follower roller. BY.{R.W. Bailey - Chief Engineer} | ||