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).
Performance and testing of A.T. speedometers, including inertia effects and trip mechanism failures.
| Identifier | ExFiles\Box 165\2\ img094 | |
| Date | 11th June 1937 | |
| 6051 Rm.{William Robotham - Chief Engineer} BY.12/G.11.6.37. A.T. SPEEDOMETERS. WST Referring to Rm.{William Robotham - Chief Engineer}4/R.10.6.37. my note was not intended to convey the idea of concession to the A.T. speedometer people but rather as a criticism of the suggested time of 2 seconds being a workable factor in covering the total speedometer range. I cannot personally imagine any car speedometer covering a range of 0 to 100 miles per hour in 2 seconds without exhibiting marked inertia effects, which one would expect to be of such a magnitude as to inevitably preclude any accurate records for particular speeds being obtainable. If for instance a speed was raised from 0 to 20 in 2/5th secs. and the speed held, I should imagine the needle of the speedometer would swing 15 or 20° beyond the point one was attempting to indicate. If 5 seconds were occupied in covering a range from 0 to 100 miles per hour on the speedometer, records could be made and the accuracy of the instrument could be deduced and recorded. I have no doubt that the present A.T. speedometer will cover a range from 0 to 100 miles per hour on the indicator in 2 seconds. My contention is that no useful measurements could be made, and as far as I can see no useful purpose would be served by testing in this manner. In regard to the failure of the trip mechanism on the A.T. speedometer, this has been confined completely to a short period of approximately 6 months, which commenced when the A.T. people were told from these Works that they must increase the strength of the springs to give more positive location of the trip figures, which ended when we instructed the A.T. speedometer people to go back to the original strength of spring. In the meantime, we had asked them to incorporate brass wheels, but the reversion to the original strength of spring has proved a change of material to be unnecessary. By BY.{R.W. Bailey - Chief Engineer} | ||