GB2131493A - Fuel injection pumping apparatus - Google Patents

Abstract

A fuel injection pumping apparatus includes a throttle member 18 angularly adjustable by a governor mechanism 24 to control the fuel flow from a low pressure pump 13 to a high pressure pump 10. The throttle member is also axially movable by fuel under pressure in a direction to slightly increase the amount of fuel supplied when the engine speed is above a predetermined value and is movable in the opposite direction when the engine speed is below said value, the rate of movement of the valve member in said opposite direction being restricted by a dashpot. The arrangement has the effect of minimising the possibility of engine stall when decelerating the engine with the throttle closed. At the predetermined speed, pressure from the pump 13 is sufficient to lift a valve 22 off its rest and pressurise a chamber within cup member 26. The end of the throttle member 18 within the cup 26 is of increased area whereby the throttle member is caused to be moved downwardly. When pressure falls, the valve 22 closes and the pressure in the cup 26 bleeds away at a rate which restricts the throttle's return speed. <IMAGE>

Description

SPECIFICATION Fuel injection pumping apparatus This invention relates to fuel injection pumping apparatus of the kind comprising a high pressure injection pump operable in timed relationship with an associated compression ignition engine, a low pressure supply pump for supplying fuel to the injection pump, an adjustable throttle member for controlling the quantity of fuel supplied to the injection pump and governor means for determining the setting of the throttle member, said governor means controlling at least the maximum and idling speeds of the associated engine.

Such apparatus is well known in the art and the known problem is the tendency for the associated engine to stall when it is decelerated. This is a particular problem when the engine is disconnected from for example a vehicle transmission. If stalling does not occur then often the engine iurches on its mountings. The reason for this is that the governor means acts to prevent the supply of fuel to the engine during the period of deceleration and then cannot react sufficiently quickly when the engine reaches its idling speed to restore a level of fuel flow necessary to keep the engine idling. In this event the engine will stall. If it does react it is in general too late with the result that the engine suddenly receives a high flow of fuel causing the engine to lurch on its mountings as it accelerates towards its idling speed.

The object of the present invention is to provide an apparatus of the kind specified in a simple and convenient form.

According to the invention said throttle member is movable by said governor means in one direction to increase the fuel flow through a flow path in part defined by said throttle member and in the opposite direction to decrease the fuel flow, the throttle member being movable in another direction to vary to a limited extent the flow of fuel in the flow path, said throttle member being moved one way in said another direction when the speed of the associated engine rises above a predetermined value to slightly increase the fuel flow to the engine and dashpot means acting to control the movement of the throttle member the other way in said another direction, when the engine speed falls below said predetermined value.

An example of a fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying diagrammatic drawing.

Referring to the drawing the apparatus comprises a high pressure injection pump 10 which is driven in timed relationship with an associated engine and it has a plurality of outlets 11 which are connected to injection nozzles respectively of the associated engine. The injection pump also has a fuel inlet 12. The apparatus also includes a low pressure supply pump 1 3 which conveniently is driven by a shaft which drives the high pressure pump. The low pressure supply pump 13 has a fuel inlet 14 which is connected to a source of fuel supply such for example as a fuel tank and it has an outlet 1 5. The inlet and outlet are interconnected by a relief valve 1 6 whereby the pressure at the outlet 1 5 varies in accordance with the speed at which the associated engine is driven.

The outlet 1 5 is connected to the inlet 12 by a throttle arrangement which is generally indicated at 1 7 and which comprises an angularly adjustable throttle member 1 8 which is carried within a bore 1 9. The bore is conveniently formed in a housing which accommodates the high pressure pump 10 and also the supply pump 13.

One end of the bore is connected to the outlet 1 5 of the low pressure pump and formed in the wall of the bore is a port 20 which is connected to the inlet 12. The throttle member 18 is of cylindrical form and is provided with a drilling extending between the ends thereof. The drilling intermediate its ends, defines a seating 21 for a ball 22 which is biased by a spring 23 into contact with the seating. In addition, the throttle member is provided with a longitudinally extending groove 24 which for reasons to be described, is angled slightly relative to the longitudinal axis. The groove is in constant communication with the outlet 1 5 of the supply pump and the groove 24 and the port 20 constitute a flow path between the outlet 1 5 and the inlet 12.

The angular setting of the throttle member 1 8 and therefore the effective area of the flow path, is controlled by a governor means 24. The governor means may be of the centrifugal weight type, the weights being driven from the aforesaid shaft, and will incorporate a governor spring to oppose the movement of the weights with increasing speed.

The force exerted by the spring is adjustable by means of a manually operable member. The output member of the governor means is coupled to an arm 25 which is secured to the portion of the throttle member extending from the bore. The governor means whether it is of the so-called all speed type or the so-called two-speed type, will control the maximum speed of the associated engine and also the idling speed.

In use, when the engine is in operation and the operator requires increased power from the engine, the throttle member is moved angularly to increase the effective area of the flow path presented by the groove 24 and the port 20. In the event that the maximum engine speed is attained, the governor means will move the throttle member to reduce the effective area of the flow path and hence restrict the flow of fuel to the injection pump.

As previously explained in this form of apparatus there is a danger when the engine is decelerated, that the governor means will not be able to react sufficiently quickly when the engine approaches its idling speed, to move the throttle member to effect a supply of fuel to the pump 10 and hence to the associated engine. In order to overcome this difficulty the throttle member is movable in the axial direction and its end exposed beyond the bore 1 9 is slidable within a cup shaped member 26, the throttle member and the cup shaped member forming the equivalent of a dashpot. The drilling communicates with the dashpot and the arrangement is such that the ball 22 is lifted from the seating 21 when the engine speed attains a predetermined value.It will be noted that the diameter of the portion of the throttle member lying within the cup shaped member 26 is larger than that of the bore 19 and as a result when the ball 22 is lifted from its seating, there will be an increased force acting on the end of the throttle member lying within the cup shaped member 26. As a result, the throttle member will move towards the position in which it is shown in the drawing. The groove 24 is slightly inclined relative to the longitudinal axis of the throttle member so that when the throttle member moves as described, there will be a slight increase in the area of the flow path thereby resulting for a given angular setting of the throttle member, in a slightly increased flow of fuel to the injection pump and the associated engine.

The dashpot effect is obtained either by a small clearance 27 between the inner wall of the skirt of the member 26 and the throttle member or by a restricted passage 28 formed in the member 26.

The practicai effect therefore is that when the engine speed is above the aforesaid predetermined value the ball 22 will be lifted from its seating and fuel will flow from the chamber defined by the member 26 and the throttle member 18. As the engine speed falls below the aforesaid predetermined value the ball 22 will be forced into sealing engagement with the seat 21 by the spring 23 and the pressure in the dashpot chamber will start to fall as a result of leakage either along the clearance 27 or through the passage 28. A point will be reached at which the force exerted by the fuel under pressure acting on the portion of the throttle member within the bore 19 exceeds the force due to fluid pressure in the dashpot chamber.When this occurs the throttle member will move upwardly thereby reducing for a given angular setting of the throttle member the amount of fuel supplied to the engine.

The effect of the modification is to displace upwardly in terms of speed, the idling "pull-on" curve of the governor means when the engine speed is above the predetermined value. When the engine speed is below the predetermined value and the position of the throttle member has stabilised, the idling "pull-on" curve is restored to the ideal setting for controlling the idling speed of the engine. By virtue of the dashpot action the engine will start to receive fuel at a higher speed than in the conventional arrangement and the deceleration of the engine will gradually cease, the final idling speed being attained when the throttle member has moved upwardly its maximum extent, into contact with the base wall of the member 26.

It will be appreciated that the size of the clearance 27 or the degree of restriction provided by the passage 28 are important factors in determining the time required for the engine to attain its normal idling speed. In the case of the passage 28 the orifice therein can be of the sharp edged variety to avoid the speed at which the throttle member moves being dependent upon the viscosity of the fuel.

As shown in the drawing a coiled compression spring 29 is provided which is located between an abutment and the throttle member. The spring 29 opposes the movement of the throttle member under the action of fuel under pressure in the dashpot chamber. This spring allows the valve member to assume an axial position dependent upon the speed at which the engine is operating and can be used in the event that the level of fuelling increase required to give good idle speed recovery is found to be dependent upon the speed from which deceleration of the engine commences.

Claims (8)

1. A fuel injection pump apparatus comprising a high pressure injection pump operable in timed relationship with an associated compression ignition engine, a low pressure supply pump for supply fuel to the injection pump, an adjustable throttle member for controlling the quantity of fuel supplied to the injection pump, governor means for determining the setting of the throttle member, said governor means controlling at least the maximum and idling speeds of the associated engine, said throttle member being movable by said governor means in one direction to increase the fuel flow through a flow path in part defined by said throttle member and in the opposite direction to decrease the fuel flow, the throttle member being movable in another direction to vary to a limited extent the flow of fuel in the flow path, said throttle member being moved one way in said another direction when the speed of the associated engine rises above a predetermined value to slightly increase the fuel flow to the engine and dashpot means acting to control the movement of the throttle member the other way in said another direction, when the engine speed falls below said predetermined value.

2. An apparatus according to Claim 1 in which said throttle member is of cylindrical form and is located in a bore, the throttle member being angularly adjustable by said governor means, said throttle member being exposed at one end to the output pressure of said low pressure supply pump, the opposite end of said throttle member being of slightly larger diameter than said one end thereof and valve means operable at and above said predetermined speed to ailow fuel under pressure from said low pressure pump to act on the opposite end of the throttle member.

3. An apparatus according to Claim 2 in which said dashpot means is defined by the larger end portion of said throttle member and a cup-shaped member located thereabout, said valve means controlling the flow of fuel into the chamber defined by said cup-shaped member and restricted passage means through which fuel can escape from said chamber.

4. An apparatus according to Claim 3 in which said valve means comprises a spring loaded ball and a seating defined in a drilling extending between the ends of the valve member.

5. An apparatus according to Claim 4 including resilient means acting to assist the movement of the throttle member under the action of fuel under pressure acting upon said one end thereof.

6. An apparatus according to Claim 4 in which said restricted passage means comprises a clearance between the valve member and the wall of the cup-shaped member.

7. An apparatus according to Claim 4 in which said restricted passage means comprises a restricted passage formed in the cup-shaped member.

8. A fuel injection pumping apparatus for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.