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 the causes and characteristics of incipient and violent brake judder.
| Identifier | ExFiles\Box 84\2\ scan0309 | |
| Date | 25th February 1935 | |
| -3- Records of the incipient judder mentioned in paragraph 8 showed that in this case the forward velocity of the carrier plate at no time reached the velocity of the drum. Fig. 2 therefore fails to explain the incipient judder. Also if fig. 2 held good the violent judder would be very difficult to start and in the normal course of decelerating the car from higher speeds it would not occur. Some outside cause would have to reduce the relative speed of drum and shoe to zero, such as starting from rest with the brakes on or momentary locking of wheel. The recording apparatus was altered to give records lasting for one complete revolution of the wheel and records were obtained of the start of a violent judder. These showed that the judder always built itself up gradually, taking about 10-15 cycles or 1/10 sec. Actually, the building up process was an incipient judder. Immediately the incipient judder became of sufficient magnitude for the velocity of the forward swing of the carrier plate to equal the drum speed, the violent judder commenced. It was necessary to seek an explanation of the incipient judder so measurements of brake torque against speed were obtained. These are shown in Fig. 1. As can be seen, the curve of brake torque against speed falls as the speed increases. This is an unstable condition and must naturally lead to juddering of a mild nature. The speed at which the curve reaches a constant level increases as the brake load increases. This is in complete agreement with paragraph 1. The high static coefficient of friction does not enter into the incipient judder because the relative speed is never zero; this leads to the following important difference between the violent and the incipient judders. | ||