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POSSIBLE IMPROVEMENTS IN SUSPENSION.
Page 118
Page 119
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The Difficulty of Finding a Substitute for the Leaf Spring. A New Shock Damper and a New Leaf Spring.
ALTHouGH it is admitted on all sides that the modern means of suspension, namely, the leaf spring, is by no means perfect, it has, like many things that are not perfect, answered its purpose fairly well. Designers who cling to it do so for the reason that they know it will do its work, even if it does not do all that a spring might be made to do. It is 'simple, which fact, in a commercial motor, is ffesirable, and forms' a very convenient means of connecting an axle to a frame, and in some cases it can do this without the use of such wearing parts as shackles or sliding slipper plates. If properly designed this class of spring can be made to take all stresses such as brake and driving torque. It will be seen from a consideration of these facts that it is no easy matter to dismiss the leaf spring, imperfect as it may be.'
The fact of the leaf spring holding its own should not he attributed to apathy on the part of our designers: it is more probably due to the difficulty of finding a real improvenithit upon it. When we say real improvement, we mean a spring that will not only give better results under academical conditions, but one that will give better results and still stand up to the rough, conditions which usually prevail in the use of
commercial vehicles, Ph e general opinion of designers in this country is that until something comes along that proves to he really better than the leaf spring, they
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would rather suffer the ills they know than fly to those they know not of, So for the present it would seem that we must he content with the leaf spring.
In the design of the private car, where running conditions are always easier and where luxury is studied more than in the commercial vehicle, the recent Show at Olympia proved that practically nothing in the nature of an improved spring had been produced and thought worthy of adoption. Why, then, should we expect the designer of the commercial motor to have been able to solve the problem?
The growing use of pneumatic tyres has aided in this solution to an extent, but only to a limited extent, for whilst it has changed the nature af the vibration and jar and rattle are almost abolished, bouncing is, if anything, increased. There are still, and probably will always be, certain conditions in which matic tyres cannot be used, so the problem of better suspen sion is still with us. It is necessary, therefore, to consider what improved systems there are on the market, and what is in embryo.
Two very complete and exhaustive articles have appeared in this journal dealing. with the subject of suspension, one in the issue of August 31st, 1926, and the other in that of September 21st, 1926, and to the interested in the subject these articles may prove of interest.
The .spring adopted by the Bristol Tramway and Carriage Co., Ltd., is one of the few improvements that have gone beyond the experimental at-age.." In this arrangement the half elliptical spring, as it is depressed by weight, bears against a cam which has the effect of reducing the length of the spring and so increasing its stiffness.
The type of "rag." or fibre such as is used in the flexible couplings of universal joints, is being tried out on private cars in, place of the shackle, and may be adopted in the near future in commercial vehicles.
One of the most interesting of recent invention in Connection with suspension is the Cardiac Moderator. This device takes the form of an attachment which can be applied to existing models. The illustration shows it as applied to a Morris private car, but its application to heavier models would not differ to any appreciable extent. It merely consists of a ball joint, which is attached to the differential casing, and two similar balls fixed to brackets from the frame. The ordinary springs may be retained. The position of these halls is such that when the frame is at half-way between its highest and lowest positions, the balls are all in a straight line, as shown in the central diagram. The Moderator consists of two cylinders, each containing a plunger forced outward by means of a strong helical spring. The ends of the cylinders and their plungers are cupped to fit over the balls, and arc compressed so as to exert a strong force against the balls fixed to the frame. When in a straight line, as in the central. diagram, there is no tendency for the Moderator either to lift or to depress
the frame in relation to the axle, but when the balls on the frame are above that in the centre, the helical springs tend to lift the frame, and when the balls on the frame are below the central ball the tendency of the helical springs is to force the frame downwards!.
The principle on which this device depends is not easy to grasp, but the effect is to alter the periodicity of the springs when the wheel pass over a pothole or over an obstruction. auch as a brick, yet not to alter the strength of the springs while in the normal position, as when the balls are in a straight line. On passing over a depression the axle candrop from its normal position, as it is assisted in doing so by the helical springs, the periodicity of which is more rapid than that of the leaf springs, and, when the wheels pass over a projection from the road surface, the axle can rise rapidly, as it is helped in doing so by the helical springs. No damping effect such as that produced by friction or dash-pot action is employed ; the device entirely relies on the difference in the periodicity of the main springs and of those in the cylinders, and the curious way in which the latter are applied.
Another promising departure in spring design is that shown in our set of three illustrations, the idea having recently been protected. In this arrangement two quarter-elliptic springs lie parallel to each other and some distance apart. The ends of both springs are firmly gripped by clamps, doe end to the frame and the other end to the axle. Reinforcement springs are provided acting in the direction in which the springs flex. Each separate spring is flexed in two directions. The main objects of the arrangement are better to provide for resistance to brake and driving torque, and to do away with shackles and wearing parts.