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).
Article on the Oyston Comparator for investigating and measuring vehicle suspension and damping performance.
| Identifier | ExFiles\Box 154a\2\ scan0034 | |
| Date | 1st November 1938 | |
| Reprinted from THE AUTOMOBILE ENGINEER, NOVEMBER, 1938. EVALUATING SUSPENSIONS. The Oyston Comparator for Investigating Suspension and Damping. IF the results of efforts made during the past few years towards the improvement of road vehicles' suspensions are examined critically it is evident that achievement has not been commensurate with effort. Results certainly do not compare favourably with achievement in engine and transmission design. One reason for this is not far to seek. It is difficult enough to perfect mechanisms when functioning and performance can be readily and positively ascertained and related to some recognised and easily applied standard. Investigating the riding qualities of a motor car is most difficult because the functioning and performance cannot be positively ascertained and related to any recognised and easily applied standard. Thus the designer or investigator has to rely for much of his data upon the opinions of others, which at best are personal opinions and are complicated by the fact that the standard of excellence varies with the individual. The suspension designer may be a mechanical genius, an honest investigator, and also a production engineer, and still have little capacity for judging riding comfort. Even if he is a good judge, he has no terms in which to state his achievement, as has the engineer dealing with the propulsion equipment. He cannot produce anything analogous to a brake-horsepower curve, a record of miles to the gallon, of acceleration or of maximum speed in miles per hour. The Oyston Suspension Comparator is the result of practical experience of these very difficulties when working on improvements in suspension design. It was found that no two suspension engineers talk the same language, so to speak, in discussing the problem. It can be said, too, without fear of contradiction, that, if four suspension experts were sent out together to test the suspension of a particular car, their opinions would certainly not all coincide. Much might even depend upon the humour of each individual at the time he formed his opinion. Ideal suspension conditions could be said to obtain in a vehicle if its chassis frame maintained a constant ride level and angle with respect to the general plane of the road surface when traversing it. On this assumption instruments have been designed to measure variations, and to some extent the information they furnish is useful. But these measurements do not tell the whole story. Riding comfort is a function of pitch or change of angle in degrees and rate of change of angle in which both the fundamentals and harmonics are, so to speak, taken into account. What is meant here and its significance will be appreciated from the description and explanation of the functioning of the Oyston Suspension Comparator which follows. The instrument, when placed in a vehicle, makes a continuous record in ink which is not a true-to-scale chart of pitch angle in degrees, but is modified in accordance with accelerations, so that it represents a function of pitch and rate of change of pitch of the vehicle. The significance of this is that sharp pitching results in full deflection of the recording pen, whereas with slower pitching the amount of deflection is proportionately reduced. Thus the record, while constituting a compromise between pitch angle and rate of change of angle, can be more closely related to the riding qualities of the vehicle than a mere record of the pitch angles. Basically the instrument consists of a freely mounted gyroscope employed as a "spinning top" in conjunction with considerable inertia. The relative movement between gyro, mounting and instrument frame is not directly communicated to the recording pen, but through a form of dashpot which allows drift between its elements under slow pitching to reduce the amount of pen deflection, and no drift during sharp pitching to cause full deflection. Fig. I illustrates the instrument from Fig. 1. Rear side of instrument with case removed. Fig. 2. Front view showing recording paper. | ||