Pump unit and method of operating the same

Abstract

The present application relates to a pump unit for a fuel injection system. The pump unit has a low pressure fuel supply line and a high pressure fuel outlet. A pumping chamber having a plunger is operable to perform a pumping cycle comprising a pumping stroke and a filling stroke. The pump unit also includes an inlet valve having an inlet valve member movable between an open position for permitting the supply of fuel to the pumping chamber from the low pressure fuel supply line and a closed position for inhibiting the supply of fuel from the pumping chamber to the low pressure supply line. An outlet valve is provided in the high pressure fuel outlet. The pump unit also includes a means for latching the inlet valve member in its open position. The present application also relates to a method of operating a pump unit.

Claims

1. A pump unit for a fuel injection system, the pump unit comprising: a low pressure fuel supply line; a pumping chamber having a plunger operable to perform a pumping cycle comprising a pumping stroke and a filling stroke; an inlet valve having a valve seat and an inlet valve member movable between an open position apart from the valve seat for permitting the supply of fuel to the pumping chamber from the low pressure fuel supply line and a closed position seated with the valve seat for inhibiting the supply of fuel from the pumping chamber to the low pressure supply line; a high pressure fuel outlet having an outlet valve; and means for latching the inlet valve member in said open position; wherein the inlet valve member comprises a bore for selectively establishing fluid communication between the pumping chamber and either the fuel supply line or the outlet valve, the inlet valve member also comprises an armature; wherein the means for latching comprises a solenoid which circumferentially surrounds the inlet valve member when the inlet valve member is in the closed position such that current applied to the solenoid establishes a magnetic field which magnetically attracts the armature and latches the inlet valve member in said open position and such that termination of current to the solenoid stops magnetic attraction of the armature and unlatches the inlet valve member.

2. A pump unit as claimed in claim 1, wherein the latching means is operable to latch the inlet valve member in said open position for at least part of said pumping stroke of the plunger.

3. A pump unit as claimed in claim 2, wherein the latching means is operable to unlatch the inlet valve member during the pumping stroke of the plunger to meter the volume of fuel in the pumping chamber.

4. A pump unit as claimed in claim 1, wherein, in use, the inlet valve member is displaced to said open position by a pressure differential across the inlet valve member; and/or by an opening force applied to the inlet valve member by said latching means.

5. A pump unit as claimed in claim 1, wherein the latching means is operable to latch the inlet valve member in said open position when the inlet valve member is in said open position or proximal to said open position.

6. A pump unit as claimed in claim 1, further comprising a spring member for biasing the inlet valve member towards said closed position.

7. A pump unit as claimed in claim 1, wherein said latching means comprises an electromagnet.

8. A pump unit as claimed in claim 7, wherein said latching means additionally comprises a permanent magnet.

9. A pump unit as claimed in claim 1, wherein the bore moves with the inlet valve member when the inlet valve member move between the open position and the closed position.

10. A pump unit as in claim 1 wherein the inlet valve member comprises a body which defines the bore, the body extending through with an aperture defined by the armature.

11. A pump unit as claimed in claim 1, wherein the pump unit further comprises a pump head which defines the pumping chamber, the solenoid being located within the pump head.

12. A pump unit as claimed in claim 11, wherein the pump head defines a pump head bore which circumferentially surrounds the inlet valve member, the solenoid being located within the pump head bore.

13. A pump unit as claimed in claim 1, wherein the outlet valve includes an outlet valve member that is distinct from the pumping plunger and is also distinct from the inlet valve member, the outlet valve also includes an outlet valve seat which is distinct from the valve seat of the inlet valve, the outlet valve member being moveable between 1) an outlet valve open position apart from the outlet valve seat which provides fluid communication from the plunger to the high pressure fuel outlet and 2) an outlet valve closed position seated with the outlet valve seat which prevents fluid communication from the plunger to the high pressure fuel outlet.

14. A pump unit as claimed in claim 13, wherein the outlet valve member moves between the outlet valve open position and the outlet valve closed position in response to pressure within the pumping chamber.

15. A method of operating a pump unit, the method comprising the following steps: (a) displacing an inlet valve member with an armature to an open position which is apart from a valve seat to establish fluid communication between a low pressure fuel supply line and a pumping chamber through a bore in the inlet valve member; (b) latching the inlet valve member in said open position using a means for latching the inlet valve member which comprises a solenoid which circumferentially surrounds the inlet valve member when the inlet valve member is in the closed position, wherein latching the inlet valve member includes applying current to the solenoid which magnetically attracts the armature and latches the inlet valve member in said open position; (c) initiating a plunger pumping stroke within the pumping chamber when the inlet valve member is latched in said open position; and (d) unlatching the inlet valve member during the plunger pumping stroke to displace the inlet valve member to a closed position which is seated with the valve seat to inhibit fluid communication between the low pressure fuel supply line and the pumping chamber and to establish fluid communication between the pumping chamber and an outlet valve through the bore in the inlet valve member, wherein unlatching the inlet valve member includes terminating current to the solenoid which stops magnetic attraction of the armature and unlatches the inlet valve member.

16. A method as claimed in claim 15, wherein the unlatching of the inlet valve member is controlled to meter the volume of fuel in the pumping chamber.

17. A method as claimed in claim 15, wherein the inlet valve member is latched throughout the plunger pumping stroke.

18. A method as claimed in claim 15, wherein the inlet valve member is biased towards said closed position.

19. A method as claimed in claim 15, wherein a latching means for latching the inlet valve member in said open position is activated before the inlet valve member reaches said open position.

20. A method as claimed in claim 15, wherein the bore moves with the inlet valve member when the inlet valve member is displaced between the open position and the closed position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

(2) a. FIG. 1 shows a schematic representation of a pump unit in accordance with the present invention; and

(3) b. FIG. 2 shows the pump unit of FIG. 1 in a series of positions alongside an operational chart.

DETAILED DESCRIPTION OF AN EMBODIMENT

(4) A pump unit 1 according to a first embodiment of the present invention is shown in FIG. 1. The pump unit 1 comprises a pump head 3, a pumping chamber 5, an inlet valve 7 and an outlet valve 9. The fuel is supplied to the pumping chamber 5 from a low pressure inlet gallery 11 and is expelled from the pumping chamber 5 to a high pressure manifold 13.

(5) A plunger 15 is provided in the pumping chamber 5 for pressurising fuel. A cam mounted to a rotatable camshaft cooperates with a lower end of the plunger 15 to reciprocate the plunger 15. In use, the plunger 15 performs a pumping cycle comprising a pumping stroke and a filling stroke. The plunger 15 is mounted in a bore 17 formed in the pump head 3 and a seal is formed between the plunger 15 and the bore 17 in known manner.

(6) The inlet valve 7 comprises an inlet valve member 19 for controlling the flow of fuel into the pumping chamber 5. As described in more detail herein, the inlet valve member 19 is also operable to meter the volume of fuel within the pumping chamber 5. The inlet valve member 19 is movable axially between an open position in which the pumping chamber 5 is in fluid communication with the low pressure inlet gallery 11; and a closed position in which fluid communication between the pump chamber 5 and the low pressure inlet gallery 11 is exhausted.

(7) The inlet valve member 19 comprises a cylindrical body 21 and a disc-shaped armature 23. The cylindrical body 21 comprises an axial bore 25; and an annular valve 27. The annular valve 27 is formed at the top of the cylindrical body 21 and cooperates with a first valve seat 29 formed in the pump head 3 to seal the pumping chamber 5 when the inlet valve member 19 is in its closed position. An inlet return spring 31 is provided to bias the inlet valve member 19 towards said closed position.

(8) An outer wall of the cylindrical body 21 forms a seal with an inside wall of the bore 17. The axial bore 25 extends through the cylindrical body 21 and forms the sole inlet/outlet for the pumping chamber 5. In use, when the inlet valve member 19 is in said closed position, high pressure fuel in the axial bore 25 causes the cylindrical body 21 to expand radially and provide an improved seal with the bore 17. When the inlet valve member 19 is in said open position, the inlet gallery 11 is in fluid communication with the pumping chamber 5 via the axial bore 25 to allow fuel to enter the pumping chamber 5. When the inlet valve member 19 is in said closed position (i.e. the annular valve 27 is seated in the first valve seat 29), the pumping chamber 5 is in fluid communication exclusively with the outlet valve 9 via the axial bore 25.

(9) The outlet valve 9 controls the supply of pressurised fuel from the pumping chamber 5 to the high pressure manifold 3. An axial communication channel 33 is formed in the pump head 3 to provide a fluid pathway from the pumping chamber 5 to the outlet valve 9. The outlet valve 9 comprises a movable outlet valve member 34, an outlet return spring 35, and a second valve seat 37. The outlet return spring 35 biases the outlet valve member 34 towards the second valve seat 31 to close the outlet valve 9. The biasing force of the outlet return spring 35 on the outlet valve member 34 and the hydraulic pressure of fuel in the high pressure manifold 13 must be overcome to open the outlet valve 9.

(10) A latch 39 is provided to latch the inlet valve member 19. The latch 39 comprises a solenoid 41 for establishing a magnetic field to engage the armature 23 and retain the inlet valve member 19 in its open position. The solenoid 41 has a circular plan form and extends around the inlet valve member 19. In the present embodiment, the magnetic field established by the solenoid 41 is insufficient to displace the inlet valve member 19 from said closed position to said open position. Rather, the inlet valve member 19 is displaced at least substantially to said open position by a negative pressure differential established across the inlet valve member 19 when the plunger 15 performs a filling stroke. The solenoid 41 is activated to latch the inlet valve member 19 when the inlet valve member 19 is positioned in said open position (or proximal to said open position). The magnetic field established by the solenoid 41 is sufficient to retain the inlet valve member 19 in said open position. Specifically, the solenoid 41 generates a latching force greater than the combination of the spring bias of the inlet return spring 31 and a positive pressure differential across the inlet valve member 19 established when the plunder 15 performs a pumping stroke. The latch 39 can thereby latch the inlet valve member 19 in said open position.

(11) The latch 39 can control the inlet valve member 19 to meter the volume of fuel in the pumping chamber 5. In particular, the inlet valve member 19 can be latched in said open position to delay or prevent closing of the inlet valve member 19. While the inlet valve member 19 is latched in said open position, fuel in the pumping chamber 5 can be returned to the inlet gallery 11 when the plunger 15 performs a pumping stroke. By controlling the unlatching (i.e. release) of the inlet metering valve 19, the volume of fuel returned to the inlet gallery 11 from the pumping chamber 5 can be controlled. The volume of high pressure fuel pressurised in the pumping chamber 5 and supplied to the manifold 13 via the outlet valve 9 can be metered. If the inlet valve member 19 is latched in said open position at least substantially for the duration of a pumping stroke of the plunger 15, the pumping chamber 5 is not sealed and the pumping cycle of the plunger 15 can be performed without introducing high pressure fuel to the manifold 13. The volume of high pressure fuel supplied to the manifold 13 can thereby be controlled.

(12) The latch 39 is controlled by an electronic control unit (not shown). The pump unit is provided with an electrical connector for connection to the electronic control unit. An array of the pump units 1 can be controlled by the electronic control unit.

(13) The operation of the pump unit 1 according to the present invention will now be described with reference to FIG. 2. The pump unit 1 is illustrated in five operating positions A-E in FIG. 2. An operational chart 100 is also shown illustrating the outlet valve lift (101); the pump pressure (103); the inlet valve lift (105); the solenoid current (107); and the plunger lift (109) in each of the five operating positions A-E. It will be appreciated that the plunger lift (109) is determined by an operating angle of the drive cam.

(14) The plunger 15 is illustrated performing a filling stroke in position A. The filling stroke reduces the pressure within the pumping chamber 5 and establishes a negative pressure differential across the inlet valve member 19 causing the inlet valve member 19 to be displaced towards said open position. A current is applied to the solenoid 41 to activate the latch 39 and establish a magnetic field. The magnetic field can attract the armature 23 thereby helping to displace the inlet valve member 19 to said open position.

(15) The current to the solenoid 41 is maintained to latch the inlet valve member 19 in the open position for the remainder of the filling stroke. The plunger 15 then initiates a pumping stroke and increases the pressure within the pumping chamber 5 establishing a positive pressure differential across the inlet valve member 19. However, the supply of current to the solenoid 41 is maintained to latch the inlet valve member 19 in said open position. The pumping stroke of the plunger 15 thereby expels fuel from the pumping chamber 5, as illustrated in position B of FIG. 2. By controlling the time period over which the inlet valve member 19 is latched in said open position, the volume of fuel in the pumping chamber 5 can be metered.

(16) In the present arrangement, the supply of current to the solenoid 41 is terminated during the pumping stroke of the plunger 15 to unlatch (release) the inlet valve member 19. The spring bias provided by the inlet return spring 31 and the positive pressure differential across the inlet valve member 19 displace the inlet valve member 19 to its closed position, as illustrated in position C of FIG. 2. The annular valve 27 seats in the first valve seat 29 to place the pumping chamber 5 in exclusive fluid communication with the outlet valve 9. The plunger 15 continues its pumping stroke and pressurises the fuel within the pumping chamber 5. When the pressure in the pumping chamber 5 is sufficient to overcome the spring bias of the outlet return spring 35 and the hydraulic pressure of the high pressure fuel in the manifold 13, the outlet valve member 34 lifts off the second valve seat 37 and high pressure fuel is expelled from the pumping chamber 5 into the manifold 13, as illustrated in position D of FIG. 2.

(17) The plunger 15 completes the pumping stroke and initiates another filling stroke. As illustrated in position E of FIG. 2, the pressure in the pumping chamber 15 decreases and the outlet valve member 34 is seated in the second valve seat 37. The reduction of pressure in the pumping chamber 15 establishes a negative pressure differential across the inlet valve member 19 and the inlet valve member 19 travels towards the open position. The current to the solenoid 39 is re-applied to latch the inlet valve member 19 in the open position.

(18) It will be appreciated that the latch 39 can control the latching and unlatching of the inlet valve member 19 to meter the volume of fuel pumped into the manifold 13 during each pump cycle. Moreover, if the latch 39 latches the inlet valve member 19 in said open position for the duration of the pumping stroke of the plunger 15, the pumping chamber 5 is not sealed and pressurised fuel is not delivered to the manifold 13.

(19) A modified arrangement of the latch 39 will now be described. A permanent magnet can be provided for establishing a first magnetic field to latch the inlet valve member 19 in its open position. An electromagnet is provided to establish a second magnetic field at least partially to counter or disrupt the first magnetic field and unlatch the inlet valve member 19. The inlet valve member 19 can then be displaced to said closed position by the inlet return spring 31 and the positive pressure differential established by the plunger 15 performing said pumping stroke. A pulse of current could be supplied to the electromagnet to unlatch the inlet valve member 19. The operation of the pump unit 1 using a modified latch 39 is unchanged from the embodiment described above. In particular, the latch 39 can meter the volume of fuel pumped during each pump cycle. This modified arrangement can reduce power consumption as the operation of the electromagnet is reduced.

(20) It will be appreciated that various changes and modifications can be made to the pump unit described herein without departing from the spirit and scope of the present invention.