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).
Letter discussing various suspension systems for commercial vehicles, including torsion-rod and pneumatic types.
| Identifier | ExFiles\Box 158\3\ scan0022 | |
| Date | 26th November 1939 | |
| ROLLS-ROYCE INC. ROOM 2-251 GENERAL MOTORS BUILDING DETROIT, MICHIGAN TELEPHONES TRINITY 2-1135 & 2-1136 Sunday, Nov. 26/39. Rolls Royce Limited Derby, England Rm{William Robotham - Chief Engineer}:- I notice in an earlier letter you suggest getting a 2-2½ ton truck. I have not worried about this yet, but shall be more or less in touch with such developments right along and will watch and wait. Latest interest in the line of suspension for commercial vehicles is the Hickman torsion-rod suspension (folder enclosed) on the Fageol bus, which is giving GMT at Pontiac a run for their money on the Greyhound long-distance bus business. This suspension has been seen by us from time to time for years, and it may be that it will prove an epoch-maker. You have doubtless been "au fait" with the Hickman developments for some years. At one time it was rumored as a likely development for the big Lincoln, saving Henry's face by retaining the front axle. On the Fageol it combines a close approximation to a "compound-interest" load deflection curve giving constant frequency at all loads, with a soft lateral control, like the Ford, which gives "low-frequency tuning" for the elimination of tramp and cross-shake. In passenger cars tried by us the soft lateral control of the Hickman Suspension has always resulted in a car with the sense of direction of a summer cloud or spherical balloon. But we are learning more and more that dimension changes demand complete changes in design, and a design which is intolerable on a passenger car may be acceptable on a huge bus. Compound interest springing increases the lift of the bus body as live-load is reduced, and therefore on trucks leads to increased difficulty at loading docks. This is being tackled in various ways, one of which is the use of Fire-stone pneumatic suspension with the reservoir pressure adjusted either manually or automatically by the load (now under consideration by G.M.T.). On a torsion rod suspension the same result can be achieved by winding-up or unwinding the "fixed" end of the torsion rod by means of a servo motor operated by a device sensitive to the average standing height of the vehicle. This combination, of compound-interest suspension (virtually the same as the Horstmann-Ainsworth Davis patent) with automatic standing-height adjustment, is undoubtedly on the way for commercial vehicles, but will take a year or two. The hope of the Firestone suspension is to get adequate damping from the flow of air to and fro between the air bag and the reservoir. This I think is a vain hope, and much bulkier and more expensive than | ||