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 vehicle suspension performance using a gyroscopic recording instrument and comparing results from different cars and adjustments.
Identifier | ExFiles\Box 154a\2\ scan0035 | |
Date | 6th February 1939 guessed | |
2 Evaluating Suspensions—contd. the rear with the case removed and shows the gyro. motor A directly coupled to the rotor B, the whole being pivotally mounted on the bearings D in the gimbal ring C, which in turn is pivoted at right angles on bearings E in the main frame. When operating, the gyro. assembly remains substantially at rest in space while the main frame of the instrument, resting on the floor of the vehicle, oscillates about the bearings E, relative motion between them being communicated to the recording pen G through a dashpot formed at the lower end of the tube F and connected to the gimbal ring C. The dashpot is filled with mercury and a “ paddle ” is suspended on bearings inside the upper end of the tube so as to dip into the mercury. The upper, external, end of this paddle is connected with the recording pen. It will be appreciated that this slow pitching allows the paddle to wade through the mercury, reducing the relative deflection of the pen G, whereas under sharp pitching this slipping effect will be reduced and thus fuller pen deflections recorded. A second stationary pen H draws a central datum line on the recording roll. Fig. 3 gives a view of the top of the instrument, showing particularly the pen mechanism which embodies a unique method of obtaining straight line motion of the pen. The pen arm L is attached to an arcuate-shaped part K which is rolled against a flat vertical surface by the upper end of the dashpot paddle to which it is attached from underneath. K being part of a disc having its centre at G, the motion of the pen describes a straight line along the top of the roller Q. Fig. 2 is a front view of the instrument and shows the roll of unused record paper P being unwound over the idler roller Q where the pens contact with it on to a detachable cardboard ferrule R which is driven at constant speed by the spring motor S mounted on the side of the main frame. Fig. 4 shows the instrument complete and ready for use. The battery lead T supplies current to the gyro. motor, the spring motor winding connection is at U, and the winding handle is shown in position on Fig. 1. The three press buttons V control the spring motor, the upper and lower respectively for starting and stopping, at the same time lowering or raising the pens, whilst the centre one is for “inching” the paper forward with the pens raised. An ink bottle W is provided and a place for spare cardboard ferrules at X. The instrument weighs 60 lb. and is completely self-contained, so that after placing it on the floor of a vehicle it only needs winding and connection to the vehicle’s battery to be ready for operation. The five records shown at Fig. 5 were taken from a 12 h.p. saloon car, fitted with double-piston type adjustable shock absorbers, which was driven over the same piece of road at the same speed (25 m.p.h.) in each case but with varying shock absorber adjustment. No. 1 record was taken with the shock absorbers purposely set on the “hard” side, No. 2 after reducing the resistances by two “clicks” of the adjusting screw, No. 3 four “clicks” and No. 4 six “clicks,” while No. 5 is a record taken from the same car when fitted with experimental shock absorbers. In examining these records one would immediately suppose No. 5 to be the most comfortable ride, and so it is, for in this record there are practically no sharp peaks, showing that the rate of change of pitch angle has been low. Even the maximum rate of change shown in this diagram is not appreciable to a passenger. No. 1 might not at first glance be thought to record the worst ride, but it undoubtedly does, for it shows the greatest number of peaks, and these are sharp, indicating sudden rates of change of pitch which are the cause of discomfort. No. 4 is not nearly such a bad ride as it looks ; it is obviously very soft, but the movement is excessive and would be dangerous on certain wavy road surfaces. The natural spring frequency is far too much in evidence. No. 3 combines the faults of Nos. 1 and 4 and indicates a lack of balanced adjustment between front and rear pairs of shock absorbers. No. 2 undoubtedly represents the best adjustment of the particular type of shock absorber and can be said to indicate a good ride, but still is obviously not so good as No. 5. A little experience of making records and comparing them with sensations during the ride soon enables the user to interpret them at sight, much as one does an “indicator card” or a B.H.P. curve, thus reducing to a minimum the road work entailed in designing suspension systems, and, of course, greatly facilitates the adjustment of control devices such as shock absorbers. Fig. 6 shows two records from each of three cars of 30 h.p., 12 h.p. and 10 h.p. respectively, all of which require shock absorber adjustments. It is interesting to note that the second record in each case is slightly better than the first, which is attributable to better weight distribution. In the first case both instrument and operator were in the front, whereas in the second they were in the back of the car. The 30 h.p. records indicate that the ride is too “hard” and would be diagnosed over-damping. The 12 h.p. records indicate over-damping in one set of shock absorbers and not enough in the other, and the 10 h.p. records indicate all-round lack of stabilising control, there being too much movement altogether and too much evidence of the natural frequency of the springs. 3 Evaluating Suspensions—contd. The high sensitivity of the instrument is apparent from the way it recorded immediately the effect of change in the distribution of the loading of the cars when the instrument and operator were moved from front to the rear. In the same way it will show immediately the effect of shock absorber adjustment. In the case of the three cars the records of which are shown, adjustments would be made based on interpretation of the records, and this procedure followed until the best settings were found for the control systems they employ. In making records it is best to select a definite piece of road for the purpose and carry out all trials on this piece of road at the different speeds desired. In this way a reference record is built up in the mind to which each subsequent record of any particular car is automatically referred and the actual ride and records definitely correlated. The Oyston Suspension Comparator is handled by the Cloudsley Engineering Company, Ltd., of 64, Queen Anne’s Gate, S.W.1, and is already employed by several automobile manufacturers’ and Government research departments. Application has been made for a Provisional Patent. Fig. 3. Top view showing pen mechanism. Fig. 4. The instrument complete in case. Fig. 5. Five records taken on 12 h.p. saloon car with double-piston type adjustable shock absorbers. Fig. 6. Comparative records of three cars. ‘F’—Passenger and instrument in front seat. ‘R’—Passenger and instrument in rear seat. Printed by The Cornwall Press Ltd., Paris Garden, S.E.1. | ||