Variable discharge pump

Abstract

A variable discharge pump is provided, the pump comprising a pumping chamber and a reciprocating plunger disposed within a plunger bore so as to reciprocate within the pumping chamber. The pump also has an electrically actuated spill control valve which opens or closes fluid communication between the pumping chamber and a low pressure area. The control valve is operated for a first period of time extending from a first time point occurring after the plunger passes bottom dead center to a second time point occurring before the plunger passes top dead center. The control valve is then operated for a second period of time extending from a third time point occurring between the second time point and the passing of the plunger through top dead center to a fourth time point occurring after the plunger has passed top dead center.

Description

TECHNICAL FIELD

The present invention relates to the field of variable discharge pumps. Particularly, though not exclusively, the invention relates to a variable discharge pump suitable for pumping fuel into the common rail of a common rail fuel injection system.

BACKGROUND

The present invention relates to the field of variable discharge pumps. Particularly, though not exclusively, the invention relates to a variable discharge pump suitable for pumping fuel into the common rail of a common rail fuel injection system.

Each downward stroke of the plungers feeds fuel from the fuel feed port into the pumping chamber. When the control valve member is open, the fuel passes through the valve and back to the feed port via the return passage when the plungers move upward. When pressurized fuel is to be fed into the common rail, a control pulse moves the control valve member into the closed position. At the same time, the plunger is undertaking an upward stroke. Because the control valve is closed, pressurization of the fuel takes place in the pumping chamber. When the fuel pressure reaches a certain level, the discharge valve opens and the pressurized fuel passes from the pumping chamber into the common rail. The consequent drop in fuel pressure in the pumping chamber allows the valve spring to push the control valve member into its open position, whereupon it comes into contact with a valve stop.

In order to maintain fuel pressure in the common rail, the control valves in the pump are required to very frequently pressurize fuel in the pumping chambers. For each rotation of the pump camshaft, each control valve will be required to pressurize fuel several times depending upon the number of lobes on the cam. This means that the control valve member is being energized and de-energized extremely frequently. Every time that the valve member is de-energized, it impacts the valve seat under the action of the spring. Over a long period of time, this impact between the valve member and valve seat may damage the valve member. This may lead to a shortening of valve life and deterioration of the seal effected by the valve member when closed. Such seal deterioration may lead to variation in fuel pressure in the pumping chamber and consequent variation in overall pump performance.

It is an aim of the present invention to obviate or mitigate one or more disadvantages associated with prior art devices and methods.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a pump comprising a first pumping chamber and a first reciprocating plunger disposed within a first plunger bore so as to reciprocate within the first pumping chamber. The pump includes a first electrically actuated spill control valve adapted to open or close fluid communication between the first pumping chamber and a low pressure area. The pump also includes a controller adapted to operate the first control valve for a first period of time extending from a first time point occurring after the first plunger passes bottom dead center to a second time point occurring before the first plunger passes top dead center. The controller may also be adapted to operate the control valve for a second period of time extending from a third time point occurring between the second time point and the passing of the first plunger through top dead center to a fourth time point occurring after the first plunger has passed top dead center.

According to a second aspect of the present invention, there is provided an internal combustion engine including a pump according to the first aspect of the present invention.

According to a third aspect of the present invention, there is provided a method of pressurizing fluid in a pump, the method comprising the steps of supplying low pressure fluid to a pumping chamber and reciprocating a plunger within the pumping chamber so as to force fluid from the pumping chamber. The fluid may be returned from the pumping chamber through an electrically actuated spill control valve. The control valve may be operated to pressurize the fuel in the pumping chamber during a forward stroke of the plunger. The pressurized fuel may be discharged through a discharge port in communication with the pumping chamber. The operating step may include operating the control valve for two separate periods of time, a first period of time extending from a first time point occurring after the plunger passes bottom dead center to a second time point occurring before the plunger passes top dead center, and a second period of time extending from a third time point occurring between the second time point and the passing of the plunger through top dead center to a fourth time point occurring after the plunger has passed top dead center.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a common rail fuel injection system;

FIG. 2 is a front sectioned view of a variable discharge pump suitable for use in the injection system of FIG. 1;

FIG. 3 is a side sectioned view of the pump of FIG. 2;

FIG. 4 is a detail view taken from the side view of FIG. 3 showing the control valve of the pump; and

FIG. 5 is a chart illustrating the operation of a spill control valve forming part of the pump of FIGS. 2-4.

DETAILED DESCRIPTION

Referring to FIG. 1, a fuel system, generally designated 10, is shown. The system 10 includes a number of fuel injectors 22, each of which is connected to a high pressure fuel rail 20 via a respective branch passage 21. The fuel rail 20 is supplied with high pressure fuel from a variable discharge pump 16 which receives low pressure fuel from a fuel tank 12 via a fuel transfer pump 14. The fuel tank 12 is also connected to the injectors 22 by way of a leak return passage 23. The system 10 is controlled via an electronic controller, or control unit (ECU), 18. The ECU 18 is connected to an electrical actuator 28 of the pump 16 via a control communication line 29 and also connected to each injector 22 via further communication lines (not shown). When in operation, control signals from the ECU 18 control when and how much fuel from the pump 16 is fed into the common rail 20, as well as when and for how long the injectors 22 inject fuel.

FIGS. 2 and 3 show that the pump 16 includes a high pressure outlet 30 fluidly connected to the high pressure rail 20 and an inlet 33 fluidly connected to the fuel transfer pump 14. A supply passage 43 connects the inlet 33 with first and second pumping chambers 46,56. The pump 16 also includes a first plunger 45 adapted for reciprocating movement in the first pumping chamber 46 in a first barrel 44. Furthermore, the pump 16 includes a second plunger 55 adapted for reciprocating movement in the second pumping chamber 56 in a second barrel 54. The first and second barrels are preferably formed in a common pump housing 40. A pair of cams 34 and 35 are operable to cause the plungers to reciprocate out of phase with one another. In the illustrated embodiment, the cams 34,35 each have three lobes such that one of the plungers 45,55 is undergoing a pumping stroke at about the time that one of the fuel injectors 22 is injecting fuel. Thus, the cams 34,35 are preferably driven to rotate directly by the engine at a rate that preferably synchronizes pumping activity to fuel injection activity in a conventional manner.

When the first plunger 45 is undergoing its retracting stroke, fresh low pressure fuel is drawn into pumping chamber 46 past a first inlet check valve 48 from a low pressure area, or gallery, 37 fluidly connected to the inlet 33. Similarly, when the second plunger 55 is undergoing its retracting stroke, fresh low pressure fuel is drawn into the second pumping chamber 56 past a second inlet check valve 58 from the gallery 37. When the first plunger 45 is undergoing its pumping stroke, fuel is displaced from the pumping chamber 46 either into the low pressure gallery 37 via a first portion 41 of a spill passage and spill control valve 38, or into a high pressure gallery 39 past a first outlet check valve 47. Similarly, when the second plunger 55 is undergoing its pumping stroke, fuel is displaced from the second pumping chamber 56 either into the low pressure gallery 37 via a second portion 51 of a spill passage and spill control valve 38, or into the high pressure gallery 39 past a second outlet check valve 57.

Referring in particular to FIG. 4, only one of the pumping chambers 46,56 is fluidly connected to spill control valve 38 at any one time. These fluid connections are controlled by a shuttle valve 80 which includes a ball valve member 81. The ball valve member 81 is exposed to fluid pressure in both the first and second pumping chambers 46,56. Because the plungers 45,55 are out of phase with one another, one pumping chamber will be at low pressure (retracting) when the other pumping chamber is at high pressure (advancing) and vice versa. This action is exploited to move the ball valve member 81 back and forth to connect either first spill passage 41 to the spill control valve 38, or the second spill passage 51 to the spill control valve 38. Dependent on its position, the ball valve 81 defines a portion of either the first or second spill passage 41,51 which allows the pumping chambers 46,56 to share a common control valve 38. When the first plunger 45 is undergoing its pumping stroke, the second pumping chamber 56 is refilled past the second inlet check valve 58. When the second plunger 55 is undergoing its pumping stroke, the first pumping chamber 46 is refilled past the first inlet check valve 48.

The spill control valve 38 includes a spill valve member 60 that includes a closing hydraulic surface 62. The spill valve member 60 is normally biased downward towards its open position via a biasing means, here represented by a biasing spring 64. The valve member 60 rests upon a valve stop 63 when in its open position. The spill valve member 60 can be moved upward to close by energizing an electrical actuator 28. In the illustrated embodiment, the actuator 28 is a solenoid having an armature 36 adapted to move the spill valve member 60. That said, those skilled in the art will appreciate that the actuator 28 could take a variety of forms, including piezo and/or piezo bender actuators.

FIG. 5 is a chart illustrating the operation and control of the spill control valve 38 over one complete rotation of the pump camshaft, i.e. the rotation of the camshaft over 360 degrees. The ECU 18 monitors the rotational position of the camshaft and also the angle of specific cams via sensors (not shown). The signals generated by the sensors allow the ECU to accurately determine when a specific plunger 45,55 is at its bottom dead center (BDC) position. Lines A and B in the FIG. 5 chart illustrate the movement of the first and second plungers, respectively, under the action of the first and second cams 34,35, over a single rotation of the camshaft. As the pump 16 has two plungers 45,55 and each of the cams 34,35 has three lobes, the pump 16 is able to pump fuel six times for each rotation of the camshaft. The lines C1 and C2 illustrate first and second control signals, respectively, fed to the spill control valve 38 via the actuator 28 during the operation of the pump. The first control signal C1 pulls the spill valve member into a closed position against the biasing force of the valve spring, while the second control signal C2 acts against the bias of the spring to decelerate the opening valve and reduce the impact of the valve member on the valve seat. The chart of FIG. 5 also shows the dwell D between the first and second signals C1,C2 and also the dwell d between the second signal C2 and the first signal C1 of the subsequent pumping event.

INDUSTRIAL APPLICABILITY

The present device and method may be used in any fluid system where there is a desire to control discharge using a pump having reduced valve wear and damage. In particular, the present device and method may be used with common rail fuel injection systems. However, those skilled in the art will appreciate that the present device and method may also be used in other hydraulic systems that may or may not be associated with an internal combustion engine.

Referring to FIG. 1, when the fuel system 10 is in operation, the first and second cams 34,35 rotate, causing the plungers 45,55 to reciprocate in their respective barrels 44,54 out of phase with one another. When the first plunger 45 is undergoing its pumping stroke, second plunger 55 will be undergoing its retracting stroke. This action is exploited via ball valve 80 to either connect the first pumping chamber 46 or the second pumping chamber 56 to the spill control valve 38. As one of the plungers begins its pumping stroke, fuel is initially displaced from the pumping chamber through spill control valve 38 to the low pressure gallery 37. When there is a desire to output high pressure from the pump, electrical actuator 28 is energized to close spill control valve 38. The first control signal C1 lasts for a first period of time extending from a first time point occurring after one of the plungers passes bottom dead center (BDC) to a second time point occurring before the plunger passes top dead center (TDC). During this first time period, the spill valve member is closed and then is stopped at the second time point as the increased pressure in the pumping chamber is sufficient to hold the valve member 60 closed against the bias of the valve spring 64. In the dwell D between the first and second control signals C1,C2, the advancing stroke of the plunger continues to compress the fuel in the pumping chamber until it reaches a sufficient pressure to be pushed past the respective check valve 47,57 into the high pressure gallery 39 and into the common rail 20.

As the pressurized fuel is discharged through one of the check valves 47,57, the pressure in the pumping chamber 46,56 rapidly drops. As a result, the forces on the valve member 60 are now unbalanced, with the force of the valve spring 64 outweighing the hydraulic forces on the lifting surface 62 of the valve member 60. The second control signal C2 is generated for a second period of time extending from a third time point occurring after the second time point (the end of first control signal C1) but before the passing of the plunger through TDC, to a fourth time point occurring after the plunger has passed TDC. In this way, the second control signal C2 is generated just as the pressurized fuel is discharged from the pumping chamber. The purpose of the second control signal C2 is to partially counter the force of the spring 64. In this way, the second control signal C2 decelerates the valve member as it returns towards the open position, ensuring that the impact of the valve member 60 on its valve stop 63 is significantly reduced compared with conventional arrangements in which the valve returns to the open position unchecked under the force of the spring 64.

It will be appreciated that the timing of the control signals, and the first control signal C1 in particular, determines what fraction of fuel displaced by the plungers enters the high pressure gallery 39 and what fraction returns to the low pressure gallery 37. This operation ensures that the pressure can be maintained and controlled in the common rail. While one plunger is advancing (pumping), the other plunger is retracting and drawing low pressure fuel into its pumping chamber past one of the respective inlet check valves 48,58.

By generating a second control signal, the pump of the present invention ensures that wear and damage on the control valve member is reduced compared with previous proposals for variable discharge pumps. This will ensure that maintenance and replacement of pumps according to the present invention will be less than at present, with associated cost savings for users of such pumps. In addition, with less wear and damage on the valve member, the performance of the pump will be more consistent over its operating life than is the case at the moment.

It will be understood by those skilled in the art that the duration of the second control signal C2, i.e. the position of the fourth time point, and the dwell d between the end of the second control signal C2 and the beginning of the subsequent first control signal C1, can be varied by the ECU. The ECU can be provided with a receiving means which allows the ECU to receive data relating to fluid pressurization parameters from an external device, e.g. an engine speed sensor on an internal combustion engine. In addition, reference data relating to fluid pressurization parameters can be stored either by the ECU or by a data storage device connected to the ECU. This allows the ECU to vary the fourth time point for particular engine speeds (received data) and desired rail pressures (stored data). In addition, the ECU can vary the dwell d depending on data received for the external device.

Although the preferred embodiment of the pump described above comprises a pair of pumping chambers with associated plungers and plunger bores, it will be understood that the present invention could be provided with only a single pumping chamber with an associated plunger and plunger bore if desired.

Additionally, although the preferred embodiment of the present invention described above includes a single spill control valve opening and closing fluid communication between the pumping chambers and the low pressure area, the present invention may be modified to include a second spill control valve. In such an arrangement, the present invention includes first and second control valves opening and closing fluid communication between their respective first and second pumping chambers and the low pressure area. The controller is consequently adapted to operate each of the first and second control valves for first and second time periods dictated by the reciprocating movements of the respective first and second plungers, in the manner described above.

These and other modifications and improvements may be incorporated without departing from the scope of the present invention.

Claims

1. A pump comprising:

a first pumping chamber;

a first reciprocating plunger disposed within a first plunger bore so as to reciprocate within the first pumping chamber;

a first electrically actuated spill control valve adapted to open or close fluid communication between the first pumping chamber and a low pressure area; and

a controller adapted to operate the first control valve for a first period of time extending from a first time point occurring after the first plunger passes bottom dead center to a second time point occurring before the first plunger passes top dead center; and

the controller being adapted to operate the first control valve for a second period of time extending from a third time point occurring between the second time point and the passing of the first plunger through top dead center to a fourth time point occurring after the first plunger has passed top dead center.

2. The pump according to claim 1, wherein the first control valve is a solenoid valve.

3. The pump according to claim 1, wherein the controller comprises an electronic control unit.

4. The pump according to claim 3, wherein the electronic control unit includes a data storage device which stores one or more fluid pressure parameters, and wherein the control unit is adapted to vary the operating of the first control valve according to the stored parameters.

5. The pump according to claim 3, wherein the electronic control unit includes a receiver adapted to receive data relating to fluid pressure parameters from an external device, and wherein the control unit is adapted to vary the operating of the first control valve according to the received signals.

6. The pump according to claim 1 and including:

a second pumping chamber; and

a second reciprocating plunger disposed within a second plunger bore so as to reciprocate within the second pumping chamber;

wherein the first control valve is adapted to open or close fluid communication between the second pumping chamber and the low pressure area;

wherein the controller is adapted to operate the first control valve for a first period of time extending from the first time point occurring after one of the plungers passes bottom dead center to the second time point occurring before the one of the plungers moves through top dead center; and

wherein the controller is adapted to operate the first control valve for a second period of time extending from the third time point occurring between the second time point and the movement of the one of the plungers through top dead center to the fourth time point occurring after the one of the plungers has moved through top dead center.

7. The pump according to claim 6, wherein the one of the plungers is the second plunger.

8. The pump according to claim 6, wherein the first and second plungers are adapted so as to reciprocate out of phase with one another.

9. The pump according to claim 6 and including:

a spill passage fluidly connecting the first and second pumping chambers; and

a shuttle valve located in the spill passage and adapted to be exposed to fluid pressure in the first and second pumping chambers;

the shuttle valve including a shuttle valve member moveable between a first position in which the first pumping chamber is fluidly connected to the control valve and a second position in which the second pumping chamber is fluidly connected to the control valve.

10. The pump according to claim 9, wherein the shuttle valve is a ball valve and the shuttle valve member is a ball.

11. The pump according to claim 6, wherein the first control valve is a solenoid valve.

12. The pump according to claim 6, wherein the controller comprises an electronic control unit.

13. The pump according to claim 12, wherein the electronic control unit includes a data storage device which stores one or more fluid pressure parameters, wherein the control unit may vary the operation of the control valve according to the stored parameters.

14. The pump according to claim 13, wherein the electronic control unit includes a receiver adapted to receive data relating to fluid pressure parameters from an external device, wherein the control unit may vary the operation of the control valve according to the received signals.

15. The pump according to claim 1 and including:

a second pumping chamber;

a second reciprocating plunger disposed within a second plunger bore so as to reciprocate within the second pumping chamber; and

a second electrically actuated spill control valve adapted to open or close fluid communication between the second pumping chamber and the low pressure area;

wherein the controller is adapted to operate the second control valve for a first period of time extending from a first time point occurring after the second plunger passes bottom dead center a second time point occurring before the second plunger moves through top dead center; and

wherein the controller is adapted to operate the second control valve for a second period of time extending from a third time point occurring between the second time point and the movement of the second plunger through top dead center to a fourth time point occurring after the second plunger has moved through top dead center.

16. The pump according to claim 15, wherein the first and second plungers are adapted so as to reciprocate out of phase with one another.

17. The pump according to claim 15, wherein the first control valve is a solenoid valve.

18. The pump according to claim 15, wherein the second control valve is a solenoid valve.

19. The pump according to claim 15, wherein the controller comprises an electronic control unit.

20. The pump according to claim 19, wherein the electronic control unit includes a data storage device which stores one or more fluid pressure parameters, wherein the control unit may vary the operation of the control valve according to the stored parameters.

21. The pump according to claim 19, wherein the electronic control unit includes a receiver adapted to receive data relating to fluid pressure parameters from an external device, wherein the control unit may vary the operation of the control valve according to the received signals.

22. The pump according to claim 15, wherein the first and second control valves are actuatable towards a closed position when operated.

23. The pump according to claim 15 including first and second springs adapted to bias the first and second control valves, respectively, in the open position.

24. An internal combustion engine including a pump according to claim 1.

25. A method of pressurizing fluid in a pump, the method comprising the steps of:

supplying low pressure fluid to a pumping chamber;

reciprocating a plunger within the pumping chamber so as to force fluid from the pumping chamber;

returning a portion of the fluid from the pumping chamber through an electrically actuated spill control valve;

operating the electrically actuated spill control valve to pressurize the fuel in the pumping chamber during a forward stroke of the plunger; and

discharging the pressurized fuel through a discharge port in communication with the pumping chamber;

wherein the operating step includes operating the control valve for two separate periods of time, a first period of time extending from a first time point occurring after the plunger passes bottom dead center to a second time point occurring before the plunger passes top dead center, and a second period of time extending from a third time point occurring between the second time point and the passing of the plunger through top dead center to a fourth time point occurring after the plunger has passed top dead center.

26. The method according to claim 25 and including the step of receiving data relating to fluid pressure parameters from an external device, and varying one or both of the first and second periods of time of the operating step according to the received data.

27. The method according to claim 26, wherein a dwell time period between the fourth time point of the operating step and the first time point of a subsequent operating step is varied according to the received data.

28. The method according to claim 26 further comprising the step of storing data relating to one or more fluid pressure parameters, and varying one or both of the first and second periods of time of the operating step according to the stored data.

29. The method according to claim 28, wherein the fourth time point is varied according to the stored data and the received data.