GB2366336A

GB2366336A - Fuel pump

Info

Publication number: GB2366336A
Application number: GB0021295A
Authority: GB
Inventors: Peter Alban George Collingborn; Ian Roy Thornthwaite
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2000-08-31
Filing date: 2000-08-31
Publication date: 2002-03-06
Also published as: GB0021295D0; EP1184568A2; EP1184568A3; DE60107169D1; EP1184568B1; DE60107169T2

Abstract

A fuel pump comprises three assemblies in a star-arrangement and each including a pumping plunger 20a reciprocable within a plunger bore (19a, Fig.2) via a cam 14 and tappet 24a. The reciprocable tappet 24a defines, in part, an auxiliary pumping chamber 40a from which, in use, fuel is displaced and supplied through a flow path 43, 34 to the plunger bore. Each assembly also comprises a working chamber 51 arranged to receive fuel via a return flow path 52 which generates a force on the tappet 24a in a return direction to increase the volume of the auxiliary pumping chamber. Fuel passes via passage 54 to lubricate and cool the cam surfaces, rollers 16 and the tappets, and fuel leaking from the working chambers 51 can flow to reservoir 35 via passage 60.

Description

2366336 FUEL PUMIP The invention relates to a fuel pump for use in

supplying fuel to a compression ignition internal combustion engine.

A known high pressure fuel pump for use in supplying fuel to a compression ignition internal combustion engine comprises a pumping plunger reciprocable within a plunger bore under the influence of a cam drive arrangement so as to pressurise fuel within a pumping chamber. During a forward, delivery stroke of the plunger, the plunger moves inwardly within the plunger bore to reduce the volume of the pumping chamber, thereby causing the pressure of fuel therein to be increased. During the forward stroke of the pumping plunger, fluid is delivered from the pumping chamber through a suitable valve arrangement. Following each delivery stroke, the plunger performs a return stroke in which the plunger moves in an outward direction within the plunger bore to increase the volume of the pumping chamber. During the return stroke, fuel is delivered to the pumping chamber through an inlet valve arrangement ready for pressurisation during the next forward stroke.

It is known to provide the pumping plunger with a spring for the purpose of driving the pumping plunger during the return stroke. However, in certain circumstances the use of a spring can be undesirable.

EP 0 972 936 describes a fuel pump in which the return stroke of the pumping plunger is performed by supplying fluid to a working chamber defined, in part, by a tappet assembly which acts to transmit a force from the cam arrangement to the pumping plunger during the forward stroke of the plunger. A force due to fuel pressure within the working chamber acts on the tappet assembly and serves to drive the plunger to perform the return stroke, the pumping plunger moving outwardly from the plunger bore to increase the volume of pump chamber.

It is also known to provide the fuel pump with a low pressure pump to permit charging of the pumping chamber of the high pressure pump within the time available. However, the provision of such a separate low pressure pump results in the fuel system being relatively complex, bulky and expensive.

It is an object of the present invention to provide an improved fuel pump which is suitable for use in supplying fuel to a compression ignition internal combustion engine and in which the disadvantages of known pump arrangements are alleviated or removed.

According to the present invention there is provided a fuel pump comprising; a pumping plunger reciprocable within a plunger bore formed in a pump housing under the influence of a drive arrangement, the drive arrangement including a reciprocable member, a surface associated with the member defining, in part, an auxiliary pumping chamber for fuel, a flow path providing communication between the auxiliary pumping chamber and the plunger bore such that fuel displaced from the auxiliary pumping chamber, in use, can be supplied through the flow path to the plunger bore, and a working chamber arranged to receive fluid which generates a force on the member which acts on the drive arrangement in a return direction to increase the volume of the pumping chamber.

Preferably, a pumping chamber is defined by the plunger bore and a surface of the pumping plunger.

In use, reciprocable movement of the pumping plunger within the plunger bore causes fuel within the pumping chamber to be pressurised, pressurised fuel being delivered from the pumping chamber to a delivery passage. The delivery passage may, for example, deliver fuel to a common rail of a common rail fuel system or an accumulator.

For the purpose of this specification, inward movement of the pumping plunger within the plunger bore to cause pressurisation of fuel within the pumping chamber shall be referred to as "the forward stroke", and outward movement of the pumping plunger from the plunger bore to increase the volume of the pumping chamber shall be referred to as "the return stroke".

The invention provides the advantage that the auxiliary pumping chamber is defined within the pump housing, rather than being a separate pump attached to the main pump housing. The volume occupied by the pump is therefore reduced.

The invention also provides the advantage that the need for a return spring to effect the return stroke of the pumping plunger is also removed, as the return stroke of the pumping plunger is driven by means of fluid within the working chamber. Preferably, the fluid within the working chamber is fuel.

Preferably, the auxiliary pumping chamber is defined, in part, by an additional bore provided in the pump housing.

The reciprocal member may preferably be a tappet member forming part of a tappet assembly which acts to transmi t a force from the drive arrangement to the pumping plunger during the forward stroke thereof.

The tappet assembly may be provided with a spring arrangement which serves to urge the pumping plunger outwardly from the plunger bore.

The provision of the spring arrangement provides the advantage that, upon engine start up, the pumping plunger and the tappet member are caused to reciprocate, thereby drawing fuel into the auxiliary pumping chamber. Only fuel displaced from the auxiliary pumping chamber is therefore delivered to the pumping chamber.

Preferably, the tappet member is provided with a further bore, the working chamber conveniently being defined, in part, by the further bore provided in the tappet member. The working chamber is preferably arranged to communicate with a return path for fuel, the return path preferably being provided with a damping arrangement to minimise pressure variations within the flow path through the forward and return strokes of the pumping plunger.

Preferably, the tappet member is shaped to ensure the working chamber communicates with the return flow path throughout the forward stroke and throughout the return stroke of the pumping plunger.

For example, the outer surface of the tappet member is preferably provided with a groove, recess or aperture, the groove, recess or aperture communicating with a drilling provided in the tappet member which communicates with the working chamber.

The flow path may be provided with a metering valve arrangement which serves to regulate the rate of fuel flow into the pumping chamber. The flow path may also be provided with a pressure regulator to control the pressure of fuel at the inlet of the metering valve arrangement.

The auxiliary pumping chamber may be provided with an inlet valve arrangement and an outlet valve arrangement for controlling the flow of fuel between the auxiliary pumping chamber and the flow path. The auxiliary chamber may communicate with the flow path by means of a flow passage defined within the pump housing, the inlet and outlet valve arrangements controlling the flow of fuel between the flow passage and the auxiliary pumping chamber.

As fuel within the auxiliary pumping chamber is only pressurised to a relatively low level, the inlet and outlet valve arrangements associated with the auxiliary pumping chamber can be arranged to share a common flow passage through which fuel flows to and from the auxiliary pumping chamber.

In one embodiment of the invention, the fuel pump may comprise a plurality of radially spaced pumping plungers which are reciprocable within respective plunger bores under the influence of a cam arrangement.

Preferably, each of the pumping plungers has an associated working chamber, the working chambers communicating with a common return path.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure I is a sectional view illustrating a fuel pump in accordance with an embodiment of the invention; and Figure 2 is a sectional view of a part of the pump in Figure 1; Figure 3 is a longitudinal view of the part of the pump in Figure 2; and Figure 4 is a perspective view of a tappet member forming part of the fuel pump in Figures I to 3.

Referring to Figures 1 to 3, there is shown a high pressure fuel pump for use in a fuel injection system of an internal combustion engine. In particular, the high pressure fuel pump is suitable for use in delivering high pressure fuel to an accumulator or the common rail of a common rail fuel system.

The pump comprises three equi-angularly spaced pumping arrangements, 10a, 10b, 10c, which extend radially around a drive shaft 12 within a pump housing 18. The drive shaft 12 carries a cam arrangement 14 which defines a cam surface, the cam surface being cooperable with roller members 16a, 16b, 16c associated with the pumping arrangements 10a, 10b, 10c respectively. The pumping arrangements 10a, 10b, 10c are substantially the same as each other and therefore, for convenience, only one of the pumping arrangements 10a will be described in detail.

The pump housing 18 is provided with a first plunger bore 19a within which a pumping plunger 20a is reciprocable. The plunger bore 19a defines a pumping chamber 22a to which fuel is delivered, in use. The pumping plunger 20a engages a tappet member 24a forming part of a tappet assembly, referred to generally as 17a, the tappet member 24a being slidably mounted in a further bore 26 provided in the pump housing 18.

The tappet member 24a carries the roller member 16a associated with the pumping arrangement 10a such that, upon rotation of the drive shaft 12 about its axis, the roller member 16a and the tappet member 24a transmit reciprocating motion to the pumping plunger 20a. The reciprocating motion of the pumping plunger 20a is such that, during inward movement of the pumping plunger 20a within the plunger bore 19a (the forward stroke), the pumping plunger 20a is moved to reduce the volume of the pumping chamber 22a. The pumping chamber 22a has an associated outlet valve arrangement 28a (as shown in Figure 1) having an associated spring 29a which serves to urge an outlet valve member against a seating to prevent fuel flow from the pumping chamber 22a into a fuel delivery path 3 1. When fuel pressure within the pumping chamber 22a is increased beyond a predetermined amount, the outlet valve member is caused to lift away from the seating to permit pressurised fuel to flow into the delivery path 31 and to a common rail or accumulator 30 associated with the fuel system. It will be appreciated that high pressure fuel is also delivered from the pumping chambers 22b, 22c associated with the pumping arrangements 10b, 10c to the common rail 30 in a similar manner. Closure of the outlet valve arrangement 28a occurs under the action of the spring 29a when the pumping plunger 22a has reached topdead-centre and starts the return stroke.

The pumping chamber 22a also has an associated inlet valve arrangement 32a, the inlet valve arrangement 32a having an open position in which fuel is delivered to the pumping chamber 22a through a primary fuel supply path 34. The primary fuel supply path 34 receives fuel from a secondary fuel supply path 43 through a metering valve arrangement 36 which serves to regulate, by means of a variable restriction, the rate of flow of fuel to the pumping chamber 22a. The secondary fuel supply path 43 receives fuel at transfer pressure, as will be described in further detail hereinafter. A pressure regulator 38 serves to regulate fuel pressure at the inlet of the metering valve arrangement 36, to permit excess fuel to return from the secondary fuel supply path 43 to a feed path 33 in communication with a fuel reservoir 35.

It will be appreciated that the pumping arrangements 10b, 10c also have associated inlet valve arrangements 32b, 32c respectively through which fuel is delivered to the respective pumping chamber 22b, 22c from the primary fuel supply path 34 in a similar manner, the primary fuel supply path 34 being comnion to all three pump arrangements 10a, 10b, 10c.

The tappet member 24a forming part of the pumping arrangement 10a defines, together with the bore 26a within which the tappet member 24a is reciprocable, an annular auxiliary pumping chamber 40a for fuel. The auxiliary chamber 40a has an associated inlet valve arrangement 42a which serves to control the supply of fuel to the auxiliary chamber 40a from the feed path 33, fuel being delivered from the feed path 33, through the inlet valve arrangement 42a, to the auxiliary chamber 40a via a flow passage 46 (as shown in Figure 3) provided in the pump housing 18. The auxiliary chamber 40a also has an associated outlet valve arrangement 44b which serves to control the flow of fuel from the auxiliary chamber 40a, through the flow passage 46, into the secondary supply path 43.

The auxiliary pumping chambers 40b, 40c also have inlet and outlet valve arrangements 42b, 42c and 44b, 44c respectively associated therewith, fuel delivered through the outlet valve arrangements 44b, 44c from the associated auxiliary pumping chamber 40b, 40c also being delivered to the secondary supply path 43.

Referring to Figure 4, the tappet member 24a is provided a bore 70a which extends a part of the way along the axis of the tappet member 24a and which communicates, via radially extending drillings 72, with axial slots or apertures 74 provided on the surface of the tappet member 24a. As can be seen in Figures 1 to 3, the bore 70a provided in the tappet member 24a and a region of the housing 18 together define a working chamber 51 a for fuel. The working chamber 5 1 a communicates, via the drillings 72 and the apertures 74 provided in the tappet member 24a, with a return flow path 52 for fuel, the return flow path 52 also being in communication with corresponding working chambers associated with the other pumping arrangements 10b, 10c. The working chamber 5 1 a is arranged such that the pressure of fuel within the working chamber 5 1 a serves to urge the plunger member 20a and the tappet member 24a in a radially inward direction (i.e. outwardly from their respective bores) to perform a return stroke, as will be described in further detail hereinafter.

The tappet members 24b, 24c are also provided with corresponding apertures and drillings to provide communication between the respective working chamber 5 1 b, 5 1 c and the return flow path 52, the apertures in the tappet members 24a, 24b, 24c being arranged to ensure the working chambers 5 1 a, 5 1 b, 5 1 c remain in communication with the return flow path 52 throughout the full range of movement of the tappet members 24a, 24b, 24c.

The return flow path 52 receives fuel from the secondary supply path 43 through an auxiliary flow path 56 provided with a top-up valve arrangement 5 8. Fuel leakage from the working chamber 5 1 a is able to flow, via a backleak flow passage 60, to the fuel reservoir 35 through a backleak valve arrangement 63. Fuel is also able to flow, through a restricted flow path 54, from the secondary supply path 43 into the central region of the housing 18 to provide lubrication and cooling of the cam surfaces, the rollers 16a, 16b, 16c and the tappet members 24a, 24b, 24c.

The pumping plunger 20a is retained in position within the tappet assembly 17a by means of a spring arrangement 48 arranged within the working chamber 5 1 a, the spring arrangement 48 acting on the pumping plunger 20a in a radially outward direction to ensure that the pumping plunger 20a maintains the required position within the bore 19a upon pump start-up to permit filling of the auxiliary chamber 40a, the working chamber 5 1 a and the return flow path 52 prior to commencement of the forward stroke. The pumping arrangements I Ob, 1 Oc are also provided with corresponding spring arrangements for the same purpose.

In use, starting from the position illustrated in which the tappet member 24a and the pumping plunger 20a occupy their retracted, outermost positions within the bores 26a, 19a respectively, the auxiliary chamber 40a and the pumping chamber 22a are charged with fuel at relatively low pressure. Rotation of the drive shaft 12 and the cam arrangement 14 causes movement of the roller member 16a and, hence, inward movement of the tappet member 24a and the pumping plunger 20a within their respective bores 26a, 19a, thereby causing fuel within the pumping chamber 22a to be compressed. The provision of the outlet valve arrangement 28a prevents fuel from flowing from the pumping chamber 22a to the delivery passage 31 until such time as fuel pressure within the pumping chamber 22a is increased to an amount which is sufficient to overcome the force due to the spring arrangement 29a, thereby causing the outlet valve arrangement 28a to open and permitting fuel to flow from the pumping chamber 22a into the delivery passage 3 1.

As the tappet member 24a reciprocates within the bore 26a, fuel within the auxiliary chamber 40a is pressurised, fuel being delivered through the outlet valve arrangement 44a into the secondary fuel supply path 43 when the pressure of fuel within the auxiliary chamber 40a is sufficient to cause the outlet valve arrangement 44a to open. Fuel within the secondary supply path 43 is delivered through the metering valve arrangement 36 to the primary supply path 34 and through the inlet valve arrangement 32a associated within the pumping arrangement 10a to the pumping chamber 22a. In addition, fuel is delivered from the secondary supply path 43 to the return flow path 52 through the top-up valve arrangement 58, as described previously.

Reciprocal movement of the tappet member 24a within the bore 26a causes fuel within the auxiliary pumping chamber 40a to be pressurised to a first, relatively low level, referred to as "transfer pressure". Thus, fuel flowing through the outlet valve arrangement 44a into the secondary fuel supply path 43 is pressurised to transfer pressure prior to being delivered to the primary fuel supply path 34, and hence to the pumping chamber 22a, where further pressurisation to a relatively high pressure occurs.

By appropriate shaping of the cam surface of the cam arrangement, reciprocal movement of the pumping plungers and the tappet members within their respective bores is phased in a cyclical manner such that, when a particular pumping plunger, for example 20a, is driven from its bottorndead-centre position to its top-dead-centre position, the volume of the associated auxiliary chamber 40a will decrease, whereas the volume of the auxiliary chamber 40b, 40c associated with at least one of the other pumping arrangements 10b, 10c will increase. Accordingly, fuel will tend to be drawn into any auxiliary chamber, the volume of which is increasing, from the feed path 33, through the respective inlet valve arrangement 42a, 42b, 42c. Conveniently, the cam arrangement may. be of generally cylindrical form, the surface of the cam arrangement including a single lobe.

It will be appreciated that fuel is delivered to the primary fuel supply path 34 from all three of the auxiliary pumping chambers 40a, 40b, 40c, and is delivered, from the primary fuel supply path 34, to all three pumping chambers 22a, 22b, 22c. The pressurisation of fuel within the pumping chambers 22b, 22c occurs in a similar manner to that described previously for the pumping chamber 22a, such that fuel is delivered through the outlet valve arrangements 28b, 28c to the common delivery passage 31 for delivery to the common rail 30. Due to the phased reciprocal motion of the pumping plungers 20a, 20b, 20c, the rate of flow of fuel to the common rail 30 is substantially constant throughout the pumping cycle for a given speed of rotation of the drive shaft 12.

As fuel pressure within the working chamber 51a is increased during inward movement of the tappet member 24a and the pumping plunger 20a within their respective bores, the force acting on the other tappet members 24b, 24c in a radially inward direction is also increased. Once the pumping plunger 20a has reached its top-dead-centre position, the force acting on the tappet member 24a due to fuel pressure within the working chamber 5 1 a serves to urge the pumping plunger 20a in a radially inward direction, outwardly from the bore 19a, to increase the volume of the pumping chamber 20 and the volume of the auxiliary chamber 40a. Furthermore, the pressure of fuel acting on the tappet member 24a ensures the roller member 16a maintains contact with the cam surface of the cam arrangement 14 during the return stroke. The total volume of fuel within the working chamber 5 1 a associated with the pumping arrangement 10a, the corresponding working chambers 5 1 b, 5 1 c associated with the pumping arrangements I Ob, 1 Oc, and the common return path 52 is therefore substantially constant, allowing for a small amount of fuel leakage through clearances within the pump arrangement which is able to escape through the back leak passage 60. As the total volume of the working chamber 5 1 a, and the volumes of the associated working chambers 51b, 51.c of the pumping arrangements 1.0b, 10c, is relatively small, the magnitude of the flow between the working chambers is relatively low and parasitic pumping losses are therefore reduced.

In order to avoid any unwanted increases in fuel pressure within the return passage 52 (i.e. pressure "spikes") it may be preferable to include a damping arrangement or damper circuit 62 within the. fuel pump (as shown in Figure 1) to provide some volumetric resilience.

As pressurisation of fuel to transfer pressure occurs within the auxiliary pumping chambers 40a, 40b, 40c within the pump housing 18, the need for a separate auxiliary or transfer pump is removed. Hence, the complexity and size of the fuel pump is reduced. Additionally, as fuel within the auxiliary chamber 40a is only pressurised to a relatively low level, both the flow of fuel to the auxiliary chamber 40a and from the auxiliary chamber 40a can pass through a common flow passage 46, thereby providing a further benefit in terms of pump size and complexity.

The present invention provides the further advantage that the plunger return stroke is driven by means of fuel pressure within the working chambers defmed, in part, by the bores 70a, 70b, 70c provided in the tappet members, thereby removing the need for a relatively large spring. Additionally, the arrangement of flow paths required to provide communication between the auxiliary pumping chambers 40a, 40b, 40c and the pumping chambers 22a, 22b, 22c is relatively simple.

The fuel pump of the present invention is particularly suitable for use in delivering high pressure fuel to the fuel injection system of an internal combustion engine. However, it will be appreciated that the pump may also be used in other applications. It will further be appreciated that the drive arrangement for the pump need not take the fort-ri of the cam arrangement illustrated, but may take an alternative form.

Claims

1. A fuel pump comprising; a pumping plunger reciprocable within a bore formed in a pump housing under the influence of a drive arrangement, the drive arrangement including a reciprocable member, a surface associated with the member defining, in part, an auxiliary pumping chamber for fuel, a flow path providing communication between the auxiliary pumping chamber and the plunger bore such that fuel displaced from the auxiliary pumping chamber, in use, can be supplied through the flow path to the plunger bore, and a working chamber arranged to receive fluid which generates a force on the reciprocable member which acts on the drive arrangement in a return direction so as to increase the volume of the pumping chamber.

2. The fuel pump as claimed in Claim 1, wherein a pumping chamber is defined by the plunger bore and a surface of the pumping plunger.

3. The fuel pump as claimed in Claim I or Claim 2, wherein the auxiliary pumping chamber is defined, in part, by a bore provided in the pump housing.

4. The fuel pump as claimed in any of Claims I to 3, wherein the reciprocal member is a tappet member forming part of a tappet assembly which acts to transmit a force from the drive arrangement to the pumping plunger during a forward stroke thereof.

5. The fuel pump as claimed in Claim 4, wherein the tappet assembly is provided with a spring arrangement which serves to urge the pumping plunger outwardly from the plunger bore.

6. The fuel pump as claimed in Claim 4 or Claim 5, wherein the tappet member is provided with a further bore, the working chamber being defined, in part, by the further bore.

7. The fuel pump as claimed in Claim 6, wherein the working chamber is arranged to communicate with a return flow path for fluid, and wherein the return flow path is provided with a damping arrangement which serves to minimise pressure variations within the return flow path.

8. The fuel pump as claimed in Claim 7, whereby, in use, the plunger member performs a forward stroke to cause pressurisation of fuel within the pumping chamber and a return stroke to increase the volume of the pumping chamber, the tappet member being shaped to ensure the working chamber communicates with the return flow path throughout the forward stroke and throughout the return stroke.

9. The fuel pump as claimed in any of Claims 1 to 8, wherein the flow path is provided with a metering valve arrangement which serves to regulate the rate of fuel flow into the pumping chamber.

10. The fuel pump as claimed in any of Claims 1 to 9, wherein the auxiliary pumping chamber is provided with an inlet valve arrangement and an outlet valve arrangement for controlling the flow of fuel between the auxiliary pumping chamber and the flow path.

11. The fuel pump as claimed in Claim 10, wherein the auxiliary chamber communicates with the flow path by means of a flow passage defined within the pump housing, the inlet and outlet valve arrangements controlling the flow of fuel between the flow passage and the auxiliary pumping chamber.

12. The fuel pump as claimed in any of Claims 1 to 11, wherein the plunger bore has, associated therewith, an additional inlet valve arrangement and an additional outlet valve arrangement which are arranged to control the flow of fuel between the plunger bore and the flow path.

13. The fuel pump as claimed in any of Claims 1 to 12, wherein the fuel pump comprises a plurality of radially spaced pumping plungers which are reciprocable within respective plunger bores under the influence of a cam arrangement.

14. The fuel pump as claimed in Claim 12, wherein each of the pumping plungers has an associated working chamber, the working chambers communicating with a common return path.

15. The fuel pump substantially as hereindescribed with reference to the accompanying drawings.