GB1430427A - Fuel-air ratio control for governor-controlled engines - Google Patents

Abstract

1430427 Controlling 1C engines CATTERPILLAR TRACTOR CO 11 May 1973 [19 May 1972] 22592/73 Heading F1B An engine having a governor controlled fuel adjusting member 17 movable in a first direction, to the right in Fig. 1, to increase fuel supply incorporates a fuel-air ratio control device adapted to selectively over-ride the governor, the control device comprising pressure responsive means 68, 76 responsive to intake manifold pressure, a servounit 46 connected with the pressure responsive means and engageable with the member 17 to restrain movement of the latter under certain engine operating conditions. Resilient biasing means are arranged on opposite sides of the pressure responsive means and hold it in a normally balanced condition so that the servo unit 46 does not restrain the fuel adjusting member 17 during normal engine operation or during cranking but does restrain it upon a reduction in manifold airpressure to a sufficiently low value during engine operation. Air is supplied to intake manifold 30 by an engine driven supercharger 31 and pressurized fluid, e.g. engine lubrication oil, is supplied to an inlet 40 to chamber 53 to the right of piston 47 of servo unit 46. Prior to starting, the piston 47 and diaphragm 76 to which a valve spool 63 with lands 64, 65 is attached, are held apart by springs 72, 73 as in Fig. 1. During and immediately after starting, this position is maintained and fluid supplied to chamber 53 drains off via passages 56, 57, 60. As engine speed rises, the air-pressure in the intake manifold pushes diaphragm 76 and spool 63 to the right covering passages 56 so that fluid-pressure in chamber 53 pushes piston 47 to the left so that the shoulder 49a engages a stop 20 and moves the member 17 to a decreased fuel position as in Fig. 2. Under normal operating conditions, fluid drain is metered from chamber 53 by land 64 of spool 53 and drains via passages 74a and 75. In the engines idle condition, the spool 63 and hence the piston 47 and the shoulder 49a are moved further to the left. Anti-clockwise rotation of lever 28 is therefore not effective to increase fuel supply. If a reduced pressure occurred momentarily in manifold 30 e.g. under acceleration from low speed at light load, diaphragm 76 and hence servo unit 46 would be moved leftwards causing shoulder 49a to engage stop 20 as the latter tended to move to the right to meet the demand for more fuel. Increase of engine speed would increase pressure in manifold 30 so that spool 63 would move to the right opening passages 56. The fuel adjusting member 17 could then pull the servo unit 46 to the right. Under normal operating conditions the shoulder 49a does not restrict movement of member 17, but if the load rises enough to decrease the engine speed the consequential reduction of pressure in the manifold leads to the shoulder 49a being moved to a position which restrains stop 20 to prevent a disproportionately large increase in the amount of fuel injected relative to the available air. In another embodiment, Fig. 3 (not shown), the springs 72 and 73 are replaced by springs (80), (84) and (86) with different rates to enable the diaphragm 76 to respond more accurately to pressure variations in manifold 30.