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).
Notes on the design and characteristics of a four-link coil spring rear axle.
| Identifier | ExFiles\Box 178\2\ img093 | |
| Date | 11th January 1940 | |
| Notes on Four Link Coil Spring Rear Axle. (1) The most important point is that, without the use of a Panhard rod with its attendant unsymmetrical action, the design gives a high pivot point for the rear axle. Consequently natural resonance frequency in tramp vibration can be around 1000 a minute, and thus "sculling" action is avoided. (2) The second point, discovered by R.{Sir Henry Royce} Schilling, is that the understeer line, or tramp-axis, must pass from the intersection A of the lower links to the intersection B of the upper links. Hence a downward-forward slope to this axis can be obtained without actually sloping the lower links downward-forward, by simply putting a slight Vee on the lower links as shewn. (Rear axles must have understeer geometry for safe handling. We know that, as a particular case of the fact that rear-steering of any sort on any vehicle - including aircraft - is essentially unstable. We don't know exactly what the limits are but say that line A-B should have a slope downward-forward from the horizontal of 3 to 10%). (3) All coil spring rear axles demand extra stabilizers because of eliminating the torsional stiffness of leaf springs. R.{Sir Henry Royce} Schilling obtains stabilizer effect by a slab between rear ends of the upper Vee rods. Cheap and light. (4) Point C. the intersection of the planes of upper and lower links in side view, is the "torque tube centre" for the axle. By bringing this approximately half way along the length of the propeller shaft, we can get the condition where U-joint angles are equal front and rear. (For uniform pinion speed). The need for this is not clear however and requires study on smooth drums on the bump rig, for each individual car. Engine mount affects U-joint roar to an important extent. (5) Harris rubbers are necessary at all eight joints, not only to allow necessary ball-joint action but to keep road noise down. (Much development work being done on these for correct "tuning" of the 6 degrees of freedom). (6) Harris rubbers are very satisfactory for life, but add to the spring rate without helping to carry the spring load. Hence a position of the spring forward of the axle such that the spring rate may be approximately double the suspension rate is desirable on the lines of wishbone front suspension. This makes a cheaper, shorter, spring, free from surge troubles, as shewn in last sketch. continued. | ||