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Show WHAT "HIGH SPEED" MEANS TO MODERN AUTO ENGINE Term Purely Relative in Its Application; How Modern Power Plants Are Assembled to Get Constant Torque, Rapid Motion and High Efficiency. There are many engineering . terms connected with the modern motor car which have gained currency among the general motoring public, but which are scarcely, if at all, understood by the very people who employ them. Such a term is "high speed" with reference to the engine and not to the vehicle's rate of progress. And yet the modern high speed engine Is ,so intimately connected with the future development 1 of the motor vehicle that any one really interested in this field cannot afford to be without some understanding of what the term actually means and how the condition benefits the operation of the car. To begin wi th, the term high speed Is relative- There is no hard and fast line on one side of which the engine is low cpeed and on the other high speed. For instance, a power plant having a maximum speed of 1000 revolutions per minute is certainly in the low speed class. On the other hand, when we find an engine en-gine with a maximum speed In the neighborhood of 3000 revolutions per minute, min-ute, we know that it is certainly a high speed power plant The actual comparison of the two types comes when we find that at a given car speed, say twenty miles per hour, one engine is turning over 1000 revolutions per minute and the other more than twice as many. At first blush the neophyte might be puzzled to know where an engine that revolves twice as many times as its rival to accomplish a given amount of work could possibly be considered the more efficient. The explanation lies in this fact, that tl high speed power plant with Its reduplicated revolutions is accomplishing ac-complishing its work through a series of light taps, so briefly spaced that they come almost in a continuous stream. On the other hand, the low speed engine is delivering its power in a series of thumps, with greater intervals between. The high speed delivery of power makes inevitably for smoother and easier operation, without with-out noticeable pau?e between the power delivery efforts. This characteristic is l obviously a very valuable one in a vehicle 1 intended for travel along a rather in-! in-! different surface, where jolts and jars i are certain to be encountered, at best. j i Evolution Explained- ! The present-day automobile power 1 plant is an evolution from the stationary 1 engine of yesterday. In this engine, de-I de-I liven' of power was practically the only j essential. It might come in a disjointed 1 series of terrific wallops: what did the j designers care. The engine, was located on a permanent base, it could be made I very heavy to witlistand heavy internal i blows. But when this engine came to be j transferred to the chassis of a vehicle , I intended for road travel, the case was ! I very different. There was a definite limit to the weight that could be car- ! ried and the delivery- of power had to be made in some tiling like a sready stream Instead of in a series of terrific hic-couchs. hic-couchs. So with the advent of the automobile auto-mobile the engineers at once began to study the problem of producing a !yr:o-)'h-running power plant. The modern rich speed engine is the latent prrviuct of the process of engineering evolution. One of the essentials io th production l of a high speed engine is the use of light, reciprocating parts. In the operation of all rotating parts there is a condition known as inertia. This means simply the dead weight of the part, which must be overcome by the propulsive medium. For instance, the piston each time it makes a revolution reaches what is known as dead center, top and bottom. At this point it ends its travel in one direction and is about to begin traveling in the opposite direction. In other words, for a fraction of time it is at rest. This is inertia and it takes an appreciable portion por-tion of the power generated to overcome this force. In order to assist the propulsive pro-pulsive force to overcome the inertia, the reciprocating parts must be made as light a possible, if high speed is to be obtained ob-tained within the power plant. Fuel Problem. 1 For this reason, high speed power j plants employ pistons made of steel, i aluminum or of very light cast iron sec-I sec-I tion. Aluminum is a very desirable I metal, which is being largely used in spite of its present high cost. In the same way, light rods and other similar parts must be employed in the high speed engine. Another factor to be considered in obtaining ob-taining high engiine speed is the ability of the power plant to use generous quantities quan-tities of fueL This means that an extra large quantity of fuel must be taken in, must be thoroughly burned and the burnt gases must be completely expelled. For this reason, the inlet valves of the high speed engine are made extra large and the inlet passages are so designed that the flow of gas from carbureter to combustion com-bustion chamber will be straight and free. There must be no sharp turns, nor any constriction to hinder the passage of the gas. In some htgh speed engines the flow of gas approaches 200 feet per second. It will also be obvious that in a high speed power plant the valves must be as light as possible to obtain tho sharp, snappy action needed in this system operating op-erating at extreme speed. The valve timing must be absolutely accurate. The design of the combustion chamber will also exert a considerable influence on the operation of the engine. It is necessary that combustion be as nearly instantaneous instan-taneous as possible. For this reason, the combustion chamber is usually made in the form of a perfect sphere. The L-head construction, with its offset chamber, is taboo for this reason, the valve-in-Lho-head being the accepted design. In the extremely high rate of revolution revolu-tion In the high speed engine, the crankshaft crank-shaft will be subject to unusual efforts at distortion. For this reason, it must be balanced to offset the forces that are trying try-ing to pull it out of shape. This method of balancing the crankshaft with counterweights coun-terweights is considered preferable to the other method of making- Jt extra heavy to withstand the pressure put upon it. The multiple cylinder engines, the eixes, eights and twelves, are simply one way of securing high engine speed, and many of them operate at as high as 3000 revolutions revo-lutions per minute. In this way they give what is practically an even arid uninterrupted un-interrupted flow of power strokes, which make for smoother operation. In considering the question of engine speed as it relates to efficiency, it must be remembered that there ie a peak point, up to which the power of the motor increases, in-creases, with its increasing revolutions, and beyond which the power curve sinks, even though the revolutions may continue con-tinue to increase. For instance, an engine en-gine may develop 20 horsepower at 1 f-00 revolutions per minute and yet develop only 26 horsepower when the engine is speeded up to 2W0. Therefore, to rr-.ach a positive conclusion as to the efficient speed of the engine we must dlacover the point at which both revolutions per minute min-ute and power reach their maximum. |
