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 experiments to understand and cure brake judder by modifying axle stiffness, inertia, and damping.
| Identifier | ExFiles\Box 84\2\ scan0310 | |
| Date | 25th February 1935 | |
| -4- The amount of energy that can be fed in to the violent judder per cycle is extremely large, and rules out any practical possibility of damping it. The amount fed into the incipient judder is however very much less and if damping were applied in a suitable manner it would probably be possible to control it, and so prevent the violent judder from starting. This should be a 99% cure of wet brake judder complaints, the remaining 1% being when cars start from rest on a very steep hill, and when the wheels momentarily lock and then rotate again. Experiments were carried out to determine the effect of (1) Increased stiffness of the axle, (2) Increased inertia of the carrier plate. (1) Increased stiffness merely has the effect of increasing the frequency and lowering the amplitude. The judder starts and then dies out at slightly lower speeds. (2) Increasing the inertia considerably reduces the frequency and the speed at which the judder commences when decelerating, but not the speed at which it dies out when accelerating. The judder is, however, of greater amplitude when it does occur and is therefore more damaging. The effect of damping the carrier plate was also tried by attaching a 25 HP. torque reaction damper between the carrier plate and the frame of the rig. This showed great promise of being a cure when decelerating, but it was not completely successful. When accelerating from rest with the brakes on the judder occurred as before. The damping was not completely successful because the method of attachment to the frame was not sufficiently rigid. The very small amplitude, 0.100-0.250 at the radius of the drum, of the incipient judder, demands rigid anchorage of the damper and also necessitates high damping loads to absorb the energy. For this reason it is doubtful whether a practical scheme could be applied to the present axle layout on the car. Another cause is that, with high brake loads, the wrapping shoe occasionally grabbed, momentarily locking the wheel, and so starting the judder. | ||