Valve assembly

Abstract

An inlet valve assembly for a high-pressure fuel pump is disclosed. The inlet valve assembly comprises an inlet valve member moveable between open and closed positions to control the fuel flow from a source of low-pressure fuel to a pumping chamber of the fuel pump, a first biasing spring arranged to apply a first force to the valve member in an opening direction, a second biasing spring arranged to apply a second force to the valve member in a closing direction, and an actuator arrangement operable to remove the first force from the valve member, thereby to allow the valve member to move into its closed position.

Claims

1. An inlet valve assembly for a high-pressure fuel pump, comprising: an inlet valve member moveable between open and closed positions to control the fuel flow from a source of low-pressure fuel to a pumping chamber of the fuel pump; a first biasing spring arranged to apply a first force to the valve member in an opening direction; a second biasing spring arranged to apply a second force to the valve member in a closing direction; and an actuator arrangement operable to completely remove the first force from the valve member, thereby to allow the valve member to move into its closed position; wherein the actuator arrangement is an electromagnetic actuator comprising a core member, a solenoid coil, and an armature moveable towards the core member in response to energisation of the coil, wherein movement of the armature in response to energisation of the coil removes the first force from the valve member and wherein the armature is separated from the valve member by an annular clearance defined by the armature and the valve member.

2. An inlet valve assembly according to claim 1, wherein the actuator arrangement is operable to retract the first biasing spring towards the core member.

3. An inlet valve assembly according to claim 1, wherein the first spring biases the armature into engagement with the valve member.

4. An inlet valve assembly according to claim 3, wherein the armature engages with a collar of the valve member.

5. An inlet valve assembly according to claim 4, wherein the collar comprises a spring seat for the second spring.

6. An inlet valve assembly according to claim 4, wherein the collar comprises a lift stop for limiting the opening movement of the valve member.

7. An inlet valve assembly according to claim 4, wherein the collar is formed from a non-magnetic material.

8. An inlet valve assembly according to claim 3, wherein the armature disengages from the valve member when the valve member is in its closed position.

9. An inlet valve assembly according to claim 1, further comprising a non-magnetic spacer member disposed between the armature and the core member.

10. An inlet valve assembly according to claim 1, wherein the core member includes an extended portion that overlaps with the armature during at least a part of the range of movement of the armature.

11. An inlet valve assembly according to claim 10, wherein the extended portion comprises an annular projection that extends from a face of the core member.

12. An inlet valve assembly according to claim 10, wherein the extended portion defines a recess that receives, in part, the armature.

13. An inlet valve assembly according to claim 1, wherein the actuator arrangement comprises an outer pole, and wherein the outer pole includes an aperture for receiving the armature.

14. An inlet valve assembly according to claim 1, wherein the annular clearance allows the valve member to move within the armature and relative to the armature in the closing direction.

15. An inlet valve assembly according to claim 1, wherein the armature circumferentially surrounds the valve member.

16. An inlet valve assembly according to claim 1, wherein the valve member extends into the armature.

17. An inlet valve assembly according to claim 1, wherein the first biasing spring is arranged to compress the second biasing spring when the coil is de-energized, thereby to allow the valve member to move into its open position such that the second biasing spring is compressed more in the open position compared to the closed position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which like reference numerals are used for like features, and in which:

(2) FIG. 1 is a cross-sectional view of part of a pump head having an inlet valve assembly according to an embodiment of the present invention, with the inlet valve assembly in an open position;

(3) FIG. 2(a) is a cross-sectional view of the pump head of FIG. 1, with the inlet valve assembly in an intermediate position; and

(4) FIG. 2(b) is a cross-sectional view of the pump head of FIG. 1, with the inlet valve assembly in a closed position.

(5) Throughout this description, terms such as upper and lower will be used with reference to the position of the parts as shown in the accompanying drawings. It will be appreciated, however, that the parts could adopt different orientations in use.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(6) FIG. 1 shows, in part, a pump head 10 comprising a head housing 12 and an inlet valve assembly 14 mounted on the head housing 12. Although not shown in FIG. 1, the head housing 12 defines a plunger bore for receiving a plunger that reciprocates in use along a pumping axis A to cyclically increase and decrease the volume of a pumping chamber 16 (only the upper end of which can be seen in FIG. 1).

(7) The upper end of the head housing 12 comprises a generally cylindrical turret portion 18. As will be explained in more detail below, parts of the inlet valve assembly 14 cooperate with the turret to connect the inlet valve assembly 14 to the head housing 12.

(8) The pumping chamber 16 is formed as a bore in the head housing 12. During a return stroke of the plunger, fuel can be drawn into the pumping chamber 16 by way of an inlet bore 20. The inlet bore 20 communicates, by way of a drilling 22, with an annular space 24 formed by an annular v-shaped groove 26 in the top of the turret portion 18. The annular space 24 receives fuel at low pressure by way of inlet passages (not shown).

(9) The flow of fuel between the inlet bore 20 and the pumping chamber 16 is regulated by a poppet valve member 28 of the inlet valve assembly 14. At its lowest end, the valve member 28 is formed into a valve head 30 with a relatively large diameter. The remainder of the valve member 28 forms a valve stem 32. A frustoconical seating surface 34 extends from the valve head 30 to the valve stem 32, and the seating surface 34 is engageable with a frustoconical valve seat 36 formed in the head housing 12 where the pumping chamber 16 meets the inlet bore 20. In FIG. 1, the valve member 28 is shown in its open position, with the seating surface 34 disengaged from the valve seat 36 to allow fuel to enter the pumping chamber 16.

(10) The stem 32 of the valve member 28 extends upwardly from the valve head 30 through a guide bore 38 formed in the head housing 12. A guide portion 40 of the stem 32 has a suitable diameter to form a sliding fit in the guide bore 38, so that movement of the valve member 28 is guided in an axial direction. The guide bore 38, and hence the direction of movement of the valve member 28, is coaxial with the pumping axis A.

(11) An upper portion of the stem 32 of the valve member 28 emerges from the head housing 12 and, as will now be described, engages with an actuator arrangement 50 of the valve assembly 14 that can be used to control movement of the valve member 28.

(12) The actuator arrangement 50 generally comprises a core member 52, a solenoid coil 54, an outer pole 56, and a moveable armature 58. The outer pole 56 is mounted to the head housing 12 and is arranged to retain the core member 52 in a position spaced from the head housing 12, and the coil 54 and the armature 58 are disposed between the core member 52 and the head housing 12.

(13) The outer pole 56 comprises a generally cup-shaped body having a base 56a and a generally cylindrical wall 56b extending upwardly from the base 56a. A mounting flange or lip 56c extends downwardly from the base 56a to embrace the turret portion 18 of the head housing 12. An o-ring 60 forms a seal between the turret portion 18 and a chamfered part of the lip 56c, to prevent fuel leakage from the valve assembly 14.

(14) The core member 52 comprises a generally tubular central portion 52a, surrounded by an annular flange 52b. The flange 52b extends outwardly from the central portion 52a to mate with an annular slot 56d formed in the inside surface of the wall 56b of the outer pole 56. The uppermost edge 56e of the wall 56b is crimped over the flange 52b to retain the flange 52b in the slot 56d.

(15) The coil 54 is wound around a coil former 62, preferably of plastics material. The coil former 62 is ring-shaped, and the central portion 52a of the core member 52 is received in the centre of the ring. The coil former 62 therefore surrounds the central portion 52a of the core member 52, and is disposed between the flange 52b of the core member 52 and the base 56a of the outer pole 56. The coil 54 is received within an annular channel 64 formed in the outer face of the coil former 62.

(16) The centre of the coil former 62 is in fluid communication with the annular space 24 through which low-pressure fuel is delivered to the pumping chamber 16. To prevent leakage of fuel, the coil former 62 forms a seal with the flange 52b of the core member 52 at its upper end and with the base 56a of the outer pole 56 at its lower end, with respective o-rings 66, 68 being provided to effect the seals. By virtue of these o-rings 66, 68, and the o-ring 60 that forms a seal between the outer pole 56 and the head housing 12, fuel cannot leak from the valve assembly 14.

(17) The armature 58 is generally tubular, having an outer wall 58a and an inner bore 58b through which the stem 32 of the valve member 28 extends. One end of the armature 58, closest to the core member 52 (i.e. the upper end of the armature 58 in FIG. 1) is partially closed by an inwardly-directed flange 58c, defining a central aperture 58d through which the stem 32 of the valve member 28 extends. The diameter of the aperture 58d is larger than the diameter of the stem 32, so as to define an annular clearance 75 between the armature 58 and the valve member 28. The armature 58 is not fixedly connected to the valve member 28, but instead the flange 58c of the armature 58 cooperates with the valve member 28 to control movement of the valve member 28 as will be explained below.

(18) The base 56a of the outer pole 56 includes a central aperture 56f for receiving the armature 58. The outer wall 58a of the armature 58 is in sliding contact with the wall of the aperture 56f, so that the outer pole 56 guides axial movement of the armature 58 in use.

(19) The tubular central portion 52a of the core member 52 extends downwardly, towards the armature 58. At its upper end, the tube that forms the central portion 52a is closed, so that the core member 52 acts as a cap for the valve assembly 14, and defines a cavity 52c within the central portion 52a for receiving a first biasing spring 70 for the valve member 28.

(20) An upper end of the first spring 70 bears against the core member 52 at the closed end of the cavity 52c, whilst an opposite, lower end of the first spring 70 acts against the upper surface of the flange 58c of the armature 58. In turn, the lower surface of the flange 58c of the armature 58 bears upon a collar 72 mounted on the stem 32 of the valve member 28. In this way, the first spring 70 applies a first spring force to the valve member 28 that acts in the opening direction of the valve member 28.

(21) The collar 72 comprises a sleeve with a stepped outer diameter. The collar 72 is press-fitted onto the stem 32 of the valve member 28. At its lowermost end, a relatively small-diameter section 72a of the collar 72 acts as a stop member for the valve member 28. The lower surface of the small-diameter section 72a is arranged to abut a raised, central portion 76 of the turret 18 of the head housing 12 when the valve member 28 is in its open position, as shown in FIG. 1, thereby to limit the opening movement of the valve member 28.

(22) The uppermost end of the collar 72 is formed into a relatively large diameter seat section 72b. A second biasing spring 74 is received in the bore 58b of the armature 58. An upper end of the second spring 74 acts upwardly on the lower surface of the seat section 72b of the collar 72, and a lower end of the second spring locates on the raised portion 76 of the turret 18 and bears against the head housing 12. The second spring 74 therefore applies a second spring force to the valve member 28 that acts in the closing direction of the valve member 28.

(23) With the valve member 28 in its fully-open position, as shown in FIG. 1, the flange 58c of the armature 58 bears against the upper surface of the collar 72, which in turn abuts the raised portion 76 of the turret 18 of the head housing 12. Therefore the collar 72 also limits movement of the armature 58 away from the core member 52.

(24) The first and second biasing springs 70, 74 apply forces in opposite directions to the valve member 28. As will be explained in more detail below, the second spring 74 is arranged always to act on the valve member 28, providing a constant biasing force to the valve member 28 in the closing direction. However, the force applied to the valve member 28 by the first biasing spring 70, which acts in the opening direction, can be removed by operation of the actuator arrangement 50.

(25) The opening force applied to the valve member 28 by the first biasing spring 70 when the coil 54 is not energised is greater than the closing force applied to the valve member 28 by the second biasing spring 74. Therefore, when the coil 54 is not energised, the valve member 28 is biased into its open position as shown in FIG. 1, thereby to permit fuel to flow into the pumping chamber 16 from the inlet bore 20.

(26) As will be appreciated from FIG. 1, the internal diameter of the aperture 58d of the armature 58 is larger than the diameter of valve member stem 32. The flange 58c of the armature 58 does not therefore constrain the valve member 28 in the radial direction.

(27) To accommodate axial movement of the armature 58 towards the core member 52 (upwards in FIG. 1), the lowermost face of the central portion 52a of the core member 52 includes a recess 52d. The outer edge of the recess 52d is defined by a downwardly-extended portion 52e of the core member 52, in the form of an annular ridge or horn.

(28) When the armature 58 is in its lowest, fully-open position with the flange 58c resting on the collar 72, as shown in FIG. 1, the lowermost tip of the downwardly-extended portion 52e overlaps with the top of the armature 58 over a relatively short distance. When the coil 54 is energised to move the armature 58 upwards towards the core member 52, as will be explained in more detail below, the recess 52d receives the top end of the armature 58 and the extended portion 52e overlaps with the armature 58 over a longer distance.

(29) The inside diameter of the recess 52d is larger than the outside diameter of the armature 58, so that there is no radial contact between the armature 58 and the core member 52. Furthermore, a washer or spacer 78 of non-magnetic material is provided on the top face of the armature 58, to prevent direct contact between the armature 58 and the core member 52.

(30) The core member 52, the outer pole 56 and the armature 58 are preferably formed from a ferromagnetic material, such as mild steel. In this way, when the coil 54 is energised, the resulting magnetic flux is contained within a magnetic circuit defined by these ferromagnetic components. The collar 72 is made from a non-magnetic material, such as an austenitic stainless steel, which helps to stop the magnetic circuit from straying out of the armature 58 and into the valve member 28.

(31) Referring additionally to FIGS. 2(a) and 2(b), operation of the inlet valve assembly 14 will now be described.

(32) As explained above, when the coil 54 is de-energised, the first spring 70 applies an opening force to the valve member 28, by way of the armature 58 and the collar 72, which exceeds the closing force applied to the valve member 28 by the second spring 74. Therefore the net spring force acting on the valve member 28 acts in an opening direction to bias the valve member 28 into its open position, as shown in FIG. 1.

(33) When the coil 54 is energised, the armature 58 moves towards the core member 52, compressing the first spring 70. This has the effect of removing the first (opening) force, applied by the first spring 70, from the valve member 28. As movement of the armature 58 begins, the armature 58 may decouple from the collar 74, as shown in FIG. 2(a), to separate physically the first spring 70 from the valve member 28.

(34) Because the first spring 70 no longer applies a force to the valve member 28 in the opening direction, the net spring force applied to the valve member 28 becomes equal to the closing force applied by the second spring 74. In other words, the net force acting on the valve member 28 changes direction when the coil 54 is energised, causing the valve member 28 to move into its closed position.

(35) As shown in FIG. 2(b), closing movement of the valve member 28 stops when the seating surface 34 of the valve member 28 meets the valve seat 36. In the illustrated embodiment, further upward movement of the armature 58 is limited by the ability of the actuator arrangement 50 to compress the first spring 70, leaving a relatively small clearance between the top of the armature 58 and the core member 52 in the axial direction. Although not clearly shown in FIG. 2(b), when the valve member 28 is seated and the first spring 70 is retracted to its fullest extent, a small clearance is present between the armature 58 and the collar 72, so that the armature 58 remains disengaged from the valve member 28.

(36) Advantageously, because the armature 58 is decoupled from the valve member 28 during closing of the valve member 28, movement of the armature 58 can occur without being constrained by the valve member 28. Consequently, any variations in concentricity and/or alignment between the valve member 28 and the armature 58 can be accommodated without any adverse effect on the operation of the valve assembly 14. Said another way, because the armature 58 is decoupled from the valve member 28 during a first phase of operation of the valve assembly, additional axial and radial degrees of freedom of movement are present compared to conventional arrangements in which the armature is fixedly attached to the valve member. These additional degrees of freedom allow compensation for misalignment and dimensional variations due to manufacturing tolerances.

(37) Another advantage of the present invention is that the air gap between the armature 58 and the core member 52 is not directly linked to the range of movement of the valve member 28. In particular, wear of the seating surface 34 of the valve member 28 and/or the valve seat 36 of the head housing 12 does not change the distance over which the armature 58 must move to remove the force of the first spring 70 from the valve member 28. As a result, the inlet valve arrangement of the present invention is more controllable and less susceptible to performance degradation over its service life than arrangements in which an armature is directly attached to a valve member.

(38) Furthermore, because the extended portion 52e of the core member 52 (see FIG. 1), overlaps with the armature 58, the magnetic flux is guided into the armature 58 in a more efficient manner than would be the case if the extended portion 52e were not present (i.e. if the lower face of the central portion 52a of the core member 52 were planar). Therefore the actuator arrangement of the embodiment of FIG. 1 is effective even when the air gap between the armature 58 and the core member 52 is relatively large when the valve member 28 is fully open. Advantageously, this allows the clearance between the seating surface 34 of the valve member 28 and the valve seat 36 to be maximised, so as to provide a high flow rate of fuel into the pumping chamber 16 during the filling stroke of the pumping element.

(39) In use, the inlet valve assembly may be operated as follows. To fill the pumping chamber 16 during the filling stroke of the plunger, in which the plunger moves to increase the volume of the pumping chamber 16, the coil 54 is de-energised. As shown in FIG. 1, the valve member 28 is held in its open position by the first biasing spring 70, which overcomes the counteracting force of the second biasing spring 74. Fuel is drawn into the pumping chamber 16 past the open valve member 28 as a result of the increase in volume of the pumping chamber 16.

(40) An electronic control unit of the engine calculates the quantity of fuel that should be permitted to enter the pumping chamber 16 during each filling stroke, according to the current rail pressure and the demand for fuel based on the prevailing engine operating conditions. Once the valve member 28 has been in its open position for a sufficient portion of the filling stroke to admit the desired quantity of fuel, the coil 54 is energised in response to a signal from the electronic control unit. Movement of the armature 58 compresses the first spring 70, allowing the valve member 28 to close under the influence of the second spring 74 alone.

(41) Once the plunger has completed its filling stroke, the pumping stroke of the plunger begins to decrease the volume of the pumping chamber 16, thereby to increase the pressure of fuel in the pumping chamber 16. Flow of fuel out of the pumping chamber 16 through the inlet valve is prevented by the seated valve member 28. At this point, the coil 54 can be de-energised to save energy: the fuel pressure in the pumping chamber 16 applies a force to the valve member 28 in the closing direction, which, in combination with the closing force applied by the second spring 74, becomes sufficient to overcome the opening force applied to the valve member 28 by the first spring 70. The valve member 28 therefore remains in its closed position as a result of the fuel pressure in the pumping chamber 16.

(42) The high-pressure fuel in the pumping chamber 16 is expelled through an outlet valve (not shown) of the pump head, which opens at a pre-determined pressure. As the pumping stroke ends and the filling stroke begins, the fuel pressure acting on the valve member 28 drops and the first biasing spring 70 causes the valve member 28 to move back into its open position, as shown in FIG. 1, to admit fuel into the pumping chamber 16 once more.

(43) In the illustrated embodiment of the invention, the armature 58 becomes spaced apart from the collar 72 when the coil 54 is energised (see FIG. 2(a)). It will be appreciated, however, that the armature 58 may remain in contact with the collar 72 during part or all of the closing movement of the valve member 28. In such an arrangement, the benefit of the invention is still achieved because the armature 58 compresses the first spring 70, thereby relieving the valve member 28 of the force due to the first spring 70.

(44) Movement of the armature 58 towards the core member 52 may be limited by the ability of the actuator arrangement 50 to compress the first spring 70, as described above. In alternative arrangements, movement of the armature 58 towards the core member 52 may be halted when the coils of the first spring 70 touch one another, or when the spacer 78 contacts the core member 58. In the latter case, the non-magnetic nature of the spacer 78 helps to prevent the armature 58 from sticking to the core member 52 when the coil 54 is de-energised.

(45) Conceivably, alternative actuators could be provided to retract the first spring away from the valve member. For example, an hydraulic actuator or cam-driven actuator could be employed instead of an electromagnetic actuator.

(46) Whilst the inlet valve assemblies described above are of the normally-open type, it would also be conceivable to provide an inlet valve assembly of the normally-closed type, in which the actuator is arranged to remove the second force from the valve member to open the valve. In general terms, therefore, an inlet valve assembly for a high-pressure fuel pump may comprise an inlet valve member moveable between open and closed positions to control the fuel flow from a source of low-pressure fuel to a pumping chamber of the fuel pump, a first biasing spring arranged to apply a first force to the valve member in an opening direction, a second biasing spring arranged to apply a second force to the valve member in a closing direction, and an actuator arrangement operable to remove the either the first force or the second force from the valve member.

(47) It will be appreciated that further modifications and variations not explicitly described above are also possible without departing from the scope of the invention as defined in the appended claims.