GB2134668A - Fuel pumping apparatus - Google Patents

Abstract

A fuel pumping apparatus for supplying fuel to an internal combustion engine includes a high pressure pump to which fuel is supplied by way of a throttle, by a low pressure pump. A regulating means 25 is provided to generate a control pressure which varies as the square of the speed of the associated engine. The regulating means includes a centrifugal weight 33 which generates a force opposed by the force produced by the control pressure acting upon a pair of pistons 26, 27 of differing diameters. The pistons control fuel flow from the low pressure pump to the space at the inner ends of the bores containing the pistons and from the space to a drain respectively. The control pressure therefore varies with the square of the speed but is also made responsive to engine acceleration and deceleration by pivotally mounting the weight about a pivot 34 which is offset from the axis of rotation and also the centre of mass of the weight. <IMAGE>

Description

SPECIFICATION Fuel pumping apparatus This invention relates to a fuel pumping apparatus for supplying fuel to an internal combustion engine, the apparatus being of the kind comprising a low pressure fuel supply pump, a high pressure injection pump which receives fuel from the low pressure supply pump and delivers fuel at high pressure to an associated engine, fuel control means for controlling the amount of fuel supplied by the supply pump to the injection pump and regulator means for generating a control pressure for use in the fuel control means.

Such an apparatus is known from the specification of British Patent 1078402 in which a centrigual regulator provides a control pressure which varies in accordance with the square of the speed at which the apparatus is driven. The control pressure is applied to one end of a throttle member to move the throttle member in a direction to reduce the amount of fuel supplied to the engine against the action of a governor spring.

The control pressure in conjunction with the governor spring provides a speed governing function.

A problem with the type of apparatus described in the aforesaid specification occurs when the apparatus is fitted to certain types of engine which are capable of decelerating quickly. If for example the force exerted by the governor spring is suddenly reduced as for example occurs when the driver of a vehicle powered by the engine takes his foot off the throttle pedal, the throttle member will be moved by the control pressure to the minimum or zero fuel position and the engine will start to decelerate. Although the control pressure will fall as the engine speed falls it is found that the movement of the throttle member to increase or restore the fuel supply to the engine as the engine idling speed is approached, takes place too late and as a result the engine can stall. A similar problem can occur when the engine is accelerated mainly under no ioad conditions.In this case there is a tendency for the maximum engine speed to be exceeded before the governing action becomes effective.

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 in an apparatus of the kind specified said regulator means comprises valve means movable in one direction by a force proportional to said control pressure, a centrifugal weight driven in use about a rotary axis at a speed proportional to the speed of the associated engine, the force generated by said weight opposing movement of said valve means in said one direction, said valve means controlling port means to maintain a balance between said forces, said centrifugal weight being pivotally mounted about an axis parallel to said rotary axis whereby in use, said control pressure will also vary in accordance with the rate of acceleration and deceleration of the engine, said control pressure being increased during conditions of engine acceleration and decreased during conditions of engine deceleration.

An example of a pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a block diagram of the apparatus, Figure 2 is a representation of one part of one of the blocks seen in Figure 1, Figures 3 and 4 are side views showing two examples of another of the blocks shown in Figure 1, Figure 5 is a sectional side elevation of a fuel pump and valve assembly, and Figures 6 and 7 are sectional views on the lines 6-6 and 7-7 of Figure 5.

Referring to Figure 1 of the drawings the apparatus comprises a low pressure fuel supply pump 10 which has a fuel inlet 11 connected in use by way of a filter, to a source of fuel supply for example a fuel supply tank. The pump 10 has an outlet 12 which is connected by way of a fuel control means 13, to the fuel inlet of a high pressure pump 14. The pump 14 is provided with a plurality of outlets 1 5 which are connected in use, to the injection nozzles respectively of an associated engine.

The output pressure of the low pressure pump 10 is controlled by a valve 1 6 which is connected between the outlet 12 and the inlet 1 1. The valve conveniently comprises a spring-loaded relief valve.

An example of the fuel control means 13 is seen in Figure 2 and it comprises a throttle member 17 which is slidable within a bore 1 8. A port 1 9 is formed in the wall of the bore, the port 19 communicating with the inlet of the pump 14.

The throttle member is provided with a circumferential groove 20 which by way of a passage 21, is in constant communication with the outlet 12 of the low pressure pump. The throttle member is biased by a governor spring 22 in a direction to increase the degree of registration of the groove 20 with the port 19 and the force exerted by the spring can be adjusted by means of an operator adjustable cam 23. The movement of the throttle member under the action of the spring is opposed by the force exerted on the throttle member by a control pressure indicated by the arrow 24. The control pressure varies in accordance with the speed at which the apparatus is driven and the arrangement is such that as the pressure applied to the throttle member increases, the amount of fuel supplied to the high pressure pump 14 will decrease.Adjustment of the member 23 will vary the force exerted by the spring 22 and the spring 22 in conjunction with the control pressure and also the throttle member, constitutes a governor.

For various reasons it is convenient for the pressure 24 to vary in accordance with the square of the speed at which the engine and the apparatus are driven and regulating means 25 is provided to derive the control pressure from the pressure at the outlet 1 2 of the low pressure pump. The control pressure may also be applied to another adjustable component of the high pressure pump 14 for example a piston which controls the timing of delivery of fuel to the associated engine.

Referring now to Figure 3, there is shown one example of the regulating means 25 and this comprises a stepped valve member comprising a small piston 26 and a large piston 27. These two pistons are located in complementary co-axial bores defining between them a chamber 28, the bores extending diametrically within a rotating part 29 driven at a speed proportional to the speed of the associated engine. Adjacent the chamber 28 the smaller bore is provided with a port 30 which communicates with the outlet 12 of the low pressure pump. Moreover, adajacent the chamber 28 the larger bore is provided with a port 31 which communicates with a drain conveniently the inlet of the low pressure pump. A passage not shown connects the chamber 28 with the end of the bore, which contains the throttle member, and which is remote from the spring 22.The outer ends of the pistons 26, 27 bear against a cylindrical surface 32 of a generally annular weight 33. The external surface of the weight is eccentrically disposed relative to the internal surface 32. The weight carried in a rotary part which rotates about the axis of the part 29 and the eccentricity of the weight is such that the centre of mass of the weight is offset in the direction of the smaller piston, from the axis of rotation of the part carrying the weight. In addition, the weight is pivotally connected to the aforesaid part about a pivot 34 the axis of which is parallel to the axis of rotation of the part carrying the weight. The axis however is positioned in advance in terms of the direction of rotation, of the centre of mass of the weight and is offset relative to the axis of rotation of the weight.

In operation, and assuming a constant speed the centrifugal force generated by the weight is transmitted to the pistons in a direction to move them upwardly as shown in the drawing. The force opposing this movement is due to the pressure in the chamber 28 acting upon the differential areas of the two pistons and this force therefore acts downwardly. If the pressure in the chamber 28 decreases then the smaller piston will start to uncover the port 30 to allow fuel under pressure into the chamber 28 thereby restoring the pressure. If the speed of rotation is increased, then the same process will be repeated namely the port 30 will be uncovered slightly to increase the pressure in the chamber 28 to restore the various components to a position of quilibrium.If the speed decreases then the centrifugal force will decrease and the pressure in the chamber 28 will move the pistons in a direction so that the larger piston uncovers the port 31 thereby allowing the pressure in the chamber to decrease until equilibrium is again established. This explanation has ignored the effect of the pivot 34 and this has an effect during conditions of acceleration and deceleration. During conditions of acceleration, the centrifugal force will increase but in addition, the centre of mass of the governor weight being offset relative to the pivot will tend to cause pivotal movement of the weight about the pivot 34 in the clockwise direction. This has the effect of moving the pistons upwardly so as to increase the pressure in the chamber 28.Thus during conditions of acceleration at a given instantaneous speed, the actual pressure in the chamber 28 will be higher than the same pressure during steady conditions. During deceleration the opposite effect occurs so that the pressure in the chamber 28 is lower than it would be during steady state conditions. The practical effect therefore is that the pressure applied to the throttle member is increased during conditions of acceleration so that the throttle member will move earlier to control the maximum speed of the engine. Similarly during conditions of deceleration, the pressure applied to the throttle member is lower so that the throttle member starts to move to increase the supply of fuel to the engine before the engine idling speed is reached.

In the arrangement shown in Figure 4, separate pistons 35, 36 are again utilised but in this example the positions of the two pistons are reversed. This is because the space 37 instead of being the source of the control pressure, is connected to the drain and the control pressure acts on the outer ends of the two pistons.

Moreover, the smaller piston 36 is constructed as a spool and controls two axially spaced ports 38, 39, the port 39 being the outer of the two and being connected to the outlet 12 of the low pressure pump. The other port 38 is connected to the space surrounding the pistons and performs the function of the port 31 of the example of Figure 3, the port 39 performing the function of the port 30 of the example of Figure 3.

Turning now to Figures 5, 6 and 7 of the drawings there is shown an assembly of the low pressure pump and a further example of the regulating means.

The assembly includes a cylindrical spindle 40 which is fixed in a supporting body 41 which conveniently forms part of the fuel injection pump 14. The body 41 defines a generally cylindrical chamber and the spindle extends axially through the chamber. Mounted about the spindle is a first rotor 42 a peripheral portion of which is provided with teeth 43 for engagement by a toothed driving belt 44 which conveniently is driven by the input shaft of the injection pump. The rotor is driven at any convenient speed proportional to the speed at which the injection pump is driven.

Formed in the rotor 42 are first and second radial bores 45, 46 respectively the bores being diametrically disposed in the rotor and located in the bores are first and second pistons 47, 48.

Formed in the wall of the bore 1 9 is a spill port 49 through which as will be described, fuel can be spilled from the inner ends of the bores. The effective size of the port is controlled by the inner end of the larger pistons 48. Formed in a similar position in the bore 45 is a supply port 50 and the effective size of this port is controlled by the inner end of the piston 47.

The outer ends of the pistons engaged the inner surface of a weight 33 as best seen in Figure 7. As with the weight of the examples of Figures 3 and 4 the weight is pivotally mounted about a pivot 34.

Formed on the spindle 40 is a circumferential groove 51 which is positioned to be in constant communication with the inner ends of the bores 45 and 46 and the groove communicates with a passage formed in the spindle which extends to the end of the spindle and is connected by a passage in the body 41 so that the control pressure therein can act upon the throttle member 17.

The pump portion of the assembly comprises a rotor 53 mounted for rotation about the spindle 40 and conveniently coupled to the rotor 43 by driving dogs 54 extending axially from the adjacent surfaces of the rotors. On opposite sides of the rotor are plates 55,56 and also located between the plates is a stator 57. Formed in the rotor 53 are a plurality of equiangularly spaced diverging slots 58. At their inner ends, the slots are connected to passages 59 which open onto the internal surface of the rotor and these can register in turn with a pair of outlet ports 60 formed in the spindle. The ports 60 communicate with an axially extending passage 61 in the spindle which intermediate its ends, is in communication with a circumferential groove on the spindle, this groove being in constant communication with the supply port 50.

Located in the slots 58 are rollers 62 respectively the rollers having their axes disposed parallel to the axis of rotation of the rotor and having their end faces in close proximity to the plates 55, 56.

The internal surface of the stator includes eccentrically disposed shapes which act to impart inward movement to the rollers twice per revolution of the rotor. The direction of rotation of the rotor is indicated by the arrow in Figure 6 and fuel inlet ports 63 are provided in the stator and which are connected to a source of fuel. During rotation of the rotor fuel is drawn into the enlarging volumes between the internal surfaces of the stator and the rotor and is expelled through the ports 60 as the spaces diminish in volume. The construction is in effect double acting so that the radial forces acting on the spindle 40 are substantially balanced.

The fuel flowing through the ports 60 is conveyed along the passage 61 to a passage 64 in the body 41. Since the pump is in effect a constant displacement pump and the high pressure pump 14 will draw fuel intermittently, it is necessary to provide a relief valve which may be a simple spring loaded relief valve to ensure that excessive pressures are not generated. The supply port 50 receives fuel from the passage 61 and during rotation of the rotor the weight 33 tends to move in the direction to move the larger piston inwardly. This movement permits the smaller piston to move outwardly to further uncover the port 50 so that fuel under pressure is admitted to the inner ends of the bores. The fuel under pressure acts upon the inner differential area of the pistons and the result is a force acting on the piston 48 tending to oppose the centrifugal force generated by the weight. If for example the speed of rotation decreases the centrifugal force will also decrease and this will result in movement of the weight and the pistons in the direction of the larger piston the inner end of which will further uncover the port 49 to allow more fuel to escape from the inner ends of the bores. At the same time the smaller piston will tend to close the port 50.

The control pressure in the passage 52 will also depend on whether or not the associated engine is accelerating or decelerating in the same manner as the examples of Figures 3 and 4.

Claims (10)

1. A fuel pumping apparatus for supplying fuel to an internal combustion engine, the apparatus comprising a low pressure fuel supply pump, a high pressure injection pump which receives fuel from the low pressure supply pump and delivers fuel at high pressure to an associated engine, fuel control means for controlling the amount of fuel supplied by the supply pump to the injection pump and regulator means for generating a control pressure for use in the fuel control means, said regulator means comprising valve means movable in one direction by a force proportional to said control pressure, a centrifugal weight driven in use about a rotary axis at a speed proportional to the speed of the associated engine, the force generated by said weight opposing movement of said valve means in said one direction, said valve means controlling port means to maintain a balance between said forces, said centrifugal weight being pivotally mounted about an axis parallel to said rotary axis whereby in use, said control pressure will also vary in accordance with the rate of acceleration and deceleration of the engine, said control pressure being increased during conditions of engine acceleration and decreased during conditions of engine deceleration.

2. An apparatus according to Claim 1 in which said weight is of generally annular form, the outer peripheral surface of said weight being eccentrically disposed relative to the inner peripheral surface thereof.

3. An apparatus according to Claim 2 in which said valve means comprises a pair of pistons of differing diameters and located within respective co-axial bores the inner ends of which are connected, the outer ends of said pistons engaging the internal surface of said weight, a pair of ports opening into the bore respectively at positions to be controlled by the inner ends of the respective pistons, the port associated with the smaller pistons connected to the outlet of the low pressure pump and the port associated with the larger piston being connected to a drain said control pressure being produced at the inner ends of said bore.

4. An apparatus according to Claim 3 in which said bores are formed in a rotor which also carries said pivot.

5. An apparatus according to Claim 4 in which said rotor is rotatably mounted abut a central stem.

6. An apparatus according to Claim 5 including a further rotor carried by said stem, said further rotor forming the rotary part of the low pressure pump, means coupling the rotors and means for driving said rotors.

7. An apparatus according to Claim 6 in which said stem defines a circumferential groove which places the inner ends of said bores in communication with each other and a passage connected with said groove for supplying said control pressure, said stem defining a second circumferential groove which communicates with said supply port, and a further passage communicating with said second circumferential groove said further passage communicating with an outlet port opening onto the periphery of the stem at a position to register in turn with passages 59 in said further rotor and through which fuel is forced during rotation of said rotors.

8. An apparatus according to Claim 7 in which said further rotor defines a plurality of outwardly divering slots, the inner ends of the slots communicating with said passages respectively, rollers in said slots, said rollers having their axes disposed parallel to the axis of rotation of the rotors, stator surrounding the further rotor, said stator having an internal surface engageable by said rollers to effect inward movement thereof as the rotors rotate.

9. An apparatus according to Claim 2 in which said valve means comprises a pair of pistons of differing diameters and located within respective co-axial bores the inner ends of which are connected to a drain, a pair of ports opening into the smaller of the bores at axially spaced positions, the smaller pistons defining a land the ends of which control said ports respectively, the outer one of said ports being connected to the outlet of the low pressure pump and the inner one of said ports being connected to a surrounding space to which the outer ends of the pistons are exposed, said control pressure in use being derived from said space.

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