GB1462354A - Vacuum servo arrangements - Google Patents

Abstract

1462354 Regulating I C engine throttle valves; evacuating chambers BRITISH LEYLAND UK Ltd 6 Feb 1974 [9 Feb 1973] 6496/73 Headings F1B and F1N The level of vacuum in a vacuum reservoir 7, connected via a one-way valve 8 to the intake manifold 2 of a diesel engine 1 at a location between the engine and a butterfly throttle valve 9, is controlled by a pressure responsive unit 12. The unit senses when the degree of vacuum is insufficient and acts to close the valve so that the engine action can replenish the vacuum. The butterfly valve 9 is mounted upon a spindle 10 having a cam 15 at one end and a projection 22 at the other. The cam is engaged by pin 20 carried by a lever 16 which is connected by a cable 13 to the throttle pedal and to a lever 33 through a lost motion device. The lever 33 is connected by a cable 32 to the injection pump 31. The unit 12 comprises a casing 30 subdivided into upper and lower chambers by a diaphragm 27 biased downwardly by a spring 28, the diaphragm having an actuator 26 connected through a spring 25 to a lever 24 rotatably mounted about the spindle 10. A spring 21 acts between the lever 24 and the projection 22 to bias the valve to a closed position, this being aided by the unequal areas a 1 a 2 of the valve. The upper chamber 29 is connected to the vacuum reservoir and the lower is open to the atmosphere. In use, with the engine not switched on and the throttle pedal not depressed, the valve is closed by the spring 21, the pin 20 is out of contact with the cam, and the pin 23 is out of contact with the lever 22. When the engine is switched on a vacuum is produced by the engine in the reservoir, this vacuum being transmitted to the upper chamber of the unit 12. When the upward force on the diaphragm due to the atmosphere pressure in the lower chamber, overcomes the spring 28 the actuator 2 rises to cause the pin 23 to abut the projection 22 and partially open the valve, thereby stopping any further evacuation of the reservoir. Depression of the throttle pedal causes further opening of the valve with, after an initial lag due to the lost motion device, operation of the injection pump. In an idling or overrun situation where the valve is maintained open by the action of the unit 12 but the throttle pedal is undepressed, if there is loss of vacuum in the reservoir, perhaps caused by the application of the brake, then the pressure in the upper chamber of the unit 12 rises, this allowing the spring to push the actuator downwardly and remove the pin 23 from the projection 22. This in turn allows the spring 21 to bias the valve back to a closed position in which position the engine begins to apply vacuum to the reservoir. When the desired vacuum is reached the diaphragm once again moves up to cause pin 23 to abut the projection and re-open the valve to prevent further application of vacuum.