GB395700A - Improvements relating to valve operating mechanism for internal combustion engines - Google Patents

Abstract

395,700. Valve gear ; regulating. ATTWOOD, S. H., Chenies, Richmond Avenue, Wolverhampton, and SIMMS MOTOR UNITS, Ltd., Percy Buildings, Gresse Street, Rathbone Place, London. Jan. 18, 1932, No. 1430. [Class 7 (vi).] Valve gear, particularly for fuel-injection valves, comprises a pair of oscillating cams arranged so that the action of both is necessary to operate the valve, one cam determining the commencement; and the other the termination of the valve operation. Adjustment of the former cam mechanism varies the moment at which the valve opens, and means are provided whereby this is done without altering the duration of opening, which is governed by the adjustment of the other cam mechanism. Two cams 12, 13 are mounted loosely on shafts 7, 8 and oscillated by eccentric gears in opposite directions so as to act upon the opposite ends of a rocker 5, which is pivoted at its centre so that when only one cam is acting thereon, the rocker moves idly about its pivot, whereas while both cams are acting thereon, the rocker and valve 4 are raised bodily. The phases of the eccentrics operating the cams are so arranged that when the cams are moving in the direction of the arrows, Fig. 1, the arcs during which they are effective on the rocker overlap and cause opening of the valve, whereas when the cams return in the opposite direction their effective arcs do not overlap and the valve is closed by the spring 4a. The effective arcs are determined by the positions of rollers 14 carried between the cams and curved shoes 6 on the rocker by cages 15 fixed to the shafts 7, 8. Angular adjustment of the shaft 8 varies the moment at which the valve opens, and angular adjustment of the shaft 7 varies the duration of opening. In order that variations in the moment of opening shall not alter the duration of opening once this is set, the shafts 7, 8 are connected by helical gears 10, 11 so that both are rotatably adjusted. The setting of the duration may, however, be varied by axial movement of the gear 10, which causes a slight rotation of the shaft 7 without moving the shaft 8. This is effected by a toothec sector which is actuated bv the accelerator pedal and gears with a rack 39 connected to the gear 10. The angular adjustments of the shaft 8 are effected by an arm 35 connected to a speed governor, which advances the time o: injection as the speed increases. An adjustable stop may be provided to limit the slow-running position of the accelerator control. Since the actual duration of the fuel injection varies with engine speed, means are provided for reducing the effect of the accelerator control upon the gear 10 as the speed is reduced. Figs. 10 and 11 show an arm 40 which is actuated by the acelerator and connected by a link 41 and arm 43 to the sector 38 engaging the rack 39 for adjusting the gear 10. As the speed of the engine falls, the governor moves the lower end of the link 41 along a slot 41a so as to reduce the leverage acting on the sector 38. The cams 12, 13 are formed integrally with another pair of cams which respectively operate the air-inlet and exhaust valves 2, 3, Fig. 1. The fuel-injection valve is described in Specificatior 395,699.