Liquid fuel pumping apparatus

Claim 2

A liquid fuel pumping apparatus comprising in combination, an injection pump including a plunger operable by an adjustable cam, the injection pump being driven in timed relationship with the engine to which fuel is supplied, a fluid pressure operable piston for controlling the timing of injection of fuel by the injection pump, means connecting said piston and said cam whereby movement of the piston will effect adjustment of the cam, means for supplying fluid at a pressure which varies in accordance with the speed at which the pump is driven, a servo valve operable to control the application of liquid under pressure to one end of said piston, said servo valve being located within a bore defined in said piston, first and second resilient means of differing strengths acting upon said servo valve to urge the servo valve towards a closed end of the bore, said servo valve contacting the closed end of the bore to urge the piston towards a position in which the timing of injection is fully retarded, passage means through which fluid under pressure can flow to act on said servo valve in opposition to the force exerted by the resilient means and stop means operable firstly as the pressure of fluid increases, to limit the deflection of said first and weaker resilient means and secondly as the pressure of fluid further increases, to limit the deflection of said second and stronger resilient means.

Claim 3

A liquid fuel pumping apparatus comprising in combination, an injection pump including a plunger operable by an Adjustable cam, the injection pump being driven in timed relationship with the engine to which fuel is supplied, a fluid pressure operable piston for controlling the timing of injection of fuel by the injection pump, means connecting said piston and said cam whereby movement of the piston will effect adjustment of the cam, means for supplying fluid at a pressure which varies in accordance with the speed at which the pump is driven, a servo valve operable to control the application of liquid under pressure to one end of said piston, said servo valve being located within a bore defined in said piston, first and second resilient means of differing strengths acting upon said servo valve to urge the servo valve towards a closed end of the bore, said servo valve contacting the closed end of the bore to urge the piston towards a position in which the timing of injection is fully retarded, passage means through which fluid under pressure can flow to act on said servo valve in opposition to the force exerted by the resilient means and stop means operable firstly as the pressure of fluid increases, to limit the deflection of said first and weaker resilient means and secondly as the pressure of fluid further increases, to limit the deflection of said second and stronger resilient means, said stop means comprising an axially movable member which is loaded to a first position by the action of said second resilient means and which is movable to a second position against the action of said second resilient means, said first and second positions being determined by spaced stop surfaces engageable with a flange on said axially movable member.

Claim 4

A liquid fuel pumping apparatus comprising in combination, an injection pump including a plunger operable by an Adjustable cam, the injection pump being driven in timed relationship with the engine to which fuel is supplied, a fluid pressure operable piston for controlling the timing of injection of fuel by the injection pump, means connecting said piston and said cam whereby movement of the piston will effect adjustment of the cam, means for supplying fluid at a pressure which varies in accordance with the speed at which the pump is driven, a servo valve operable to control the application of liquid under pressure to one end of said piston, said servo valve being located within a bore defined in said piston, first and second resilient means of differing strengths acting upon said servo valve to urge the servo valve towards a closed end of the bore, said servo valve contacting the closed end of the bore to urge the piston towards a position in which the timing of injection is fully retarded, passage means through which fluid under pressure can flow to act on said servo valve in opposition to the force exerted by the resilient means and stop means operable firstly as the pressure of fluid increases, to limit the deflection of said first and weaker resilient means and secondly as the pressure of fluid further increases, to limit the deflection of said second and stronger resilient means, said stop means comprising an axially movable member which is loaded to a first position by the action of said second resilient means and which is movable to a second position against the action of said second resilient means, said first and second positions being determined by spaced stop surfaces engageable with a flange on said axially movable member.

Claim 5

An apparatus as claimed in claim 2 in which said axially movable member abuts said first resilient means, said first resilient means being interposed between the servo valve and said member.

Claim 6

An apparatus as claimed in claim 3 in which said axially movable member is of hollow form and partly accommodates said second resilient means.

Claim 7

An apparatus as claimed in claim 4 in which said servo valve includes a land for controlling flow of fluid through a port defined in the bore of the piston, said port communicating with one end of a cylinder in which the piston is located, the arrangement being such that when fluid under pressure flows through said port into the cylinder, the piston will move to close said port.

Claim 8

An apparatus as claimed in claim 5 in which the stop surface which defines said second position of the member is defined by a surface formed on a plug closing one end of said cylinder.

Claim 9

An apparatus as claimed in claim 6 in which the stop surface which defines said first position of the member is defined by a stop surface defined at the end of said cylinder adjacent the plug.

Claim 10

An apparatus as claimed in claim 6 in which the stop surface which defines said first postion of the member is defined by a further surface formed on said plug, said further surface being disposed intermediate said first mentioned surface and said cylinder.