An Efficient Engine Governor
Page 59
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IT is well known that the racing of commercial-vehicle engines is damaging and that it frequently causes excessive wear. It is often advisable, therefore, to govern the engine speed, and the Pierce Governor Co., of Auderson, Ind., 'U.S.A., manufactures a device for the •attainment of this end. This governor, which may be obtained from the Rothermel Corporation, Ltd., the offices of which are at 24 and 26, Maddox Street, Regent Street, London, W.I., is fitted in its various forms to several of the leading makes of commercial vehicle.
The instrument is situated between the carburetter and the intake manifold, although the position depends largely upon the type of engine and the design of the intake manifold. To connect the governor to the driving unit either a flexible or a solid-steel shaft, enclosed in a suitable housing, should be utilized.
Normally, the butterfly valve in the governor valve box is situated in such a position as not to obstruct the flow of gas from the carburetter to the engine, . So soon as the motor reaches the predetermined speed at which the governor is set the valve closes slightly, thereby reducing the valve-port area, and the supply of petrol vapour.
The valve comprises two -weights mounted upon a revolving spider. As the velocity of the weights increases, centrifugal force swings the arms of the spider outwards and forces forward a plunger, which in turn operates the butterfly valve. The plunger is moved against a spring calibrated to a standard pressure, so that as the velocity of the weights is lessened they return to
their normal positions, thus permitting the butterfly valve to be fully opened.
It is possible to secure considerable latitude in adjustment, owing to the special construction of the Pierce governor, but experience shows that the standard type attains the highest efficiency at a speed of 900 r.p.m. to 1,000 r-p.m. By the use of reduction gearing in some part of the driving mechanism it is possible to govern the engine at a' speedlower or higher than that stipulated.'
Oiling . Oiling of. the governor may be easily
carried out, as an oil cup is mounted in the housing" The uremia for' adjustment of the-governor can be effectively sealed in order to prevent any unauthorized person from altering the maximum speed—a point which should prove helpful.
The use of solid-steel shafts for driving the governor is advocated whenever such an installation is possible, 'When
lengths of flexible tubing are employed a certain amount of backlash occurs, which it is impossible to eliminate, but instantaneous action of the governor characterizes the use of the solid shaft. There are some engines upon which the solid shafts cannot be used, however, due to interference with other necessary equipment ; but the rigid type will he found quite satisfactory for most purposes except when very long shafts are employed. It is seldom possible to connect the driving member with the governor by means of a straight shaft, owing to the location of the driving member of the engine and the difference between the height of this and of the intake manifold. In view of this special angle drives have been provided, these being supplied having various gear ratios, in order to give a satisfactory governor speed, regardless of the maximum engine speed required.