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).
Technical explanation of a gyroscopic non-skid mechanism for motor cars, including diagrams and application examples.
| Identifier | ExFiles\Box 77\5\ scan0171 | |
| Date | 29th April 1911 guessed | |
| 2 that it is required, and before any momentum has been attained by the vehicle in a sideway direction. It is hardly to be expected, and in fact it is hardly necessary, that any non-skid mechanism should permit sharp turns to be taken at very high speeds over road-surfaces that can offer only a very slight adhesion to any type of tyre; and in this sense therefore it would be quite a mistake for anyone to go in for a gyroscopic non-skid equipment on their own cars with the intention of making a future practice of taking any such foolish risks. Elementary Features. Speaking generally, this gyroscopic non-skid mechanism consists of nothing more nor less than an additional flywheel which is fitted in the front of the car and is driven by the engine. It differs, however, radically from the ordinary fly-wheel, inasmuch as it is mounted upon a co-axial universal joint that is interposed between itself and its shaft, and inasmuch as its movement in relationship to this universal joint is restrained in a particular manner which will be referred to in greater detail in a moment. At this stage of our article it may advantageously be mentioned that the ordinary fixed fly-wheel upon the crank-shaft of every engine is subjected to exactly the same forces as this additional gyroscopic wheel, but that since it is rigidly fixed to its shaft, and that shaft is held down in well-fitted bearings, the actual strains that are set up by the wheel upon the frame of the chassis are quite slight, even when a very violent side-slip causes the tail of the car to swing round quite suddenly. What actually happens is that the ordinary fixed fly-wheel tends to tilt the shaft in one direction or the other, increasing the pressure on the lower half of any bearing there may be on one side of the wheel, and to exert an upward pressure on the cap of any other bearing on the other side of it. Thus it is just conceivable that a minute influence might be found increasing the weight on one axle and decreasing it on the other, if very delicate measuring devices were fitted for the purpose; but generally speaking the ordinary fly-wheel on an ordinary car plays no gyroscopic role that can be taken into account, and certainly does not tend to prevent side-slip by exerting a lateral restraining force as the result and final reaction of a sudden lateral movement at the rear of the chassis. The gyro fly-wheel is not held in rigid bearings, and is in fact permitted to tilt bodily upwards or downwards when a side-slip or any other sudden lateral movement of the rear portion of the chassis in relationship to the front portion of the chassis tends to make it do so. In technical phraseology a certain amount of precession is permitted, the result in the first place being that the amount of restraining force exerted by the gyro-wheel is very considerably greater than in the case of a fixed wheel; and that, in the second place, a lateral reaction is ensured that gives the desired steadying effect in a lateral direction. Without attempting to complicate matters by going at all deeply into the theoretical aspects of gyro-wheels in general, it may be said that the extent to which this restraining force attains depends upon (a) the rapidity with which the car slews round about the axis of the gyro-wheel, (b) the freedom with which the gyro-wheel is permitted to tip or dip upwards or downwards within its restraining lateral guides, (c) the diameter of the wheel itself, (d) its weight, and (e) the rate at which it is revolving. These are in fact the five variants which determine the degree of effectiveness of the device, though it does not follow that the net restraining force that is exerted is in direct proportion to each of them. For instance, it may be that increased diameter is more effective than a proportionate increase of weight, though the main fact holds good that an increase in either respect increases the effectiveness. Practical Application. Turning now to our first illustration, the top diagram represents a gyro-wheel mounted on its horizontal shaft and so fitted that it lies immediately above the centre of the front axle of the car. The dotted lines then represent the position which the car is apt suddenly to try to assume when a side-slip occurs, and the chief point initially to observe is that, roughly speaking, the fulcrum about which the chassis swings is the centre of the front axle. Hence it will be recognised why the gyroscope is fixed in the position there shown, particularly when it is remembered that the force used to restrain side-slip is that exerted by the gyro-wheel in endeavouring to swing round about its own central pivoting point in a transverse plane. In other words the rim of the wheel on one side tries to come forcibly forwards, while on the other side it endeavours to swing round in a rearward direction. “Auto,” (Yellow Cover) Copyright. Fig. 1.—Diagram showing alternative possible positions for the skid-preventing gyro-wheel, and also demonstrating the action of a car when side-slip occurs. 3 In the central diagram in Fig. 1 the gyroscopic wheel is shown where it has to be placed for constructional reasons on certain cars. Its fulcrum of action is then in front of that which is probably taken by the chassis as a fulcrum point when a side-slip occurs, and hence the position is not quite so ideal though clearly the difference is not greatly marked—and does indeed in practice seem almost inappreciable. In the lowest diagram are shown two gyro-wheels, these being mounted immediately above the two front road-wheels, and possibly from a theoretical point of view that constitutes the best arrangement of all, since one or other road-wheel or some point along the front axle between the two must actually be the fulcrum point when the rear part of the car swings round. The main moral, however, to be derived from Fig. 1 is that the gyroscope must essentially be mounted on a horizontal axis, and that it must be situated as near as possible centrally above the front axle. Another somewhat important detail to be observed from Fig. 1 is that when a back-wheel side-slip takes place the twisting motion of the chassis about the centre of the gyro-wheel is vastly greater in rapidity than could possibly be brought about by any manipulation of the steering-gear when turning a corner. If one thinks of the distance which the car would have to proceed forward in order to alter its line of direction from that shown by full lines to that shown by dotted lines in the top diagram in Fig. 1, it will at once be recognised that the slewing action is quite slow, whereas when a side-slip takes place it is very rapid indeed. This then is the reason why the gyro can have no perceptible restraining force that can interfere with the steering of the car, although that is a possible contingency which is bound at first to occur to the intelligent inquiring mind. Front and Rear Side-Slips. Before quite leaving Fig. 1 it should be made perfectly clear that the gyroscopic non-skid can only have a direct effect as regards side-slip of the rear wheels. The extent to which it restrains rear-wheel side-slipping is easily calculated with any given gyro-wheel if the force exerted by the wheel itself has been measured while undergoing an axial deviation of the same suddenness as that of the supposed attempted slip, for if we assume that the gyro-wheel has an effective radius of 6 ins., and that the direct force exerted by it has been found to be 300 lbs. under the exact conditions in question, then if the vehicle has a 10 ft. wheel-base, and the fulcrum-point for the skid is co-axial with the centre of the front axle and with the gyroscope, the restraining force as far as the back wheels are concerned would clearly be 15 lbs., since we only have to divide the 10 ft. radius by the 6 in. radius to obtain the 20 to 1 leverage ratio, and to then divide 300 lbs. by this figure 20. Although, however, no gyro-wheel so placed can possibly exert any perceptible influence tending to eliminate side-slip of the front wheels, yet for all that there is much to be said for the contention of the advocates of this new system that their apparatus does afford protection against the ordinary results of all side-slips. Side-slip with the front wheels is by no means as common as with the rear wheels, and when it occurs is usually rendered harmless by the application of the brakes and by their effect in steadying-up the car. What is really dangerous in connection with front-wheel side-slip is the subsequent tendency to rear-wheel side-slip directly the brakes are applied for this purpose. Thus it is argued with considerable reason that since the gyroscopic device eliminates side-slip at the rear, the brakes can safely be applied if side-slip occurs in front; and hence virtually—though admittedly indirectly—the gyro device is effective all round. Constructional Points. In Fig. 2 one of these special gyro-wheels is shown fitted in front of the radiator and in line with the crankshaft of the engine. Corresponding line drawings (elevation and plan) are given in Fig. 3 so that no difficulty will be experienced in following out the nature of the apparatus. The large universal-joint permits the heavy solid-steel gyro-ring to tip about its central point on the shaft in any direction that it pleases and at any angle. As a gyroscope it therefore differs in two very important respects from any other design hitherto used, for in the first place a very considerable amount of space indeed is saved by mounting the universal-joint inside it instead of by forming a universally-jointed cage arrangement outside it, and on the other hand the wheel itself tends normally (under the action of centrifugal force) to revolve at right angles to the shaft. In the design shown in Figs. 2 and 3 there is a supplementary lever device at the back of the rim which is not shown in those illustrations, but which assists in bringing the wheel back more quickly than it otherwise would to its normal position after it has tipped forward or backward (as the case may be) in a vertical plane as the direct outcome of an attempted back-wheel side-slip. In both those illustrations, however, will be Fig. 2.—View showing one form of gyroscopic non-skid fitted in front of the radiator and as a continuation of the crank-shaft. A.J.L. Fig. 3.—Front elevation and plan illustrating diagrammatically the arrangement shown in Fig. 2. “Auto,” Copyright. | ||