GB2327716A - A control trigger valve for a fuel pump - Google Patents

Abstract

A control trigger valve for controlling a spill valve of a fuel pump comprises a valve member 84 slidable within a bore 86. The valve member 84 and bore 86 together define an inlet chamber 90, an outlet chamber 94 and a drain chamber 108. The valve member also defines a passage 100, 106 between outlet chamber 94 and the drain chamber 108 and is movable to control communication between the inlet chamber 90 and the outlet chamber 94 and between the drain chamber 108 and the drain outlet 122, via chamber 116, passage 118 and chamber 120.

Description

FUEL PUMP This invention relates to a fuel pump incorporating a spill valve, and to a trigger valve suitable for use in such a fuel pump for controlling the spill valve.

In a known fuel pump, pumping plungers are reciprocable within respective bores under the influence of a cam ring. The bores communicate with inlet and outlet ports whereby fuel at relatively low pressure can be supplied to the bores, and whereby inward movement of the plungers causes fuel to be supplied at high pressure from the bores.

The bores also communicate with a spill valve which controls communication with a volume whereby, upon the spill valve opening, fuel is able to escape to the volume from the bores thus reducing the fuel pressure within the bores. The spill valve comprises a valve member engageable with a seat, the valve member being carried by a piston member which is slidable with a cylinder. A spring biases the piston towards a position in which the valve member engages the seat.

The piston and cylinder together define a chamber which communicates through a passage with the bores. A trigger valve is located in the passage, thus the trigger valve controls whether or not high pressure fuel is able to flow to the chamber. In use, when delivery of high pressure fuel is to be terminated, the trigger valve is opened to permit high pressure fuel to be supplied to the chamber. The high pressure fuel acts on the piston, moving the piston against the action of the spring to lift the valve member from the seat, opening the spill valve. Once the spill valve is open, fuel can escape from the bores to the volume at a high rate, thus the fuel pressure in the bores falls rapidly.

In order to achieve rapid actuation of the spill valve, fuel must be able to flow through the trigger valve at a high rate as the chamber is of relatively high volume, and in conventional electromagnetically actuated arrangements, the lift of the valve member of the trigger valve is limited, thus the flow rate through the trigger valve is also limited. It is an object of the invention to provide a trigger valve permitting rapid opening of a spill valve. It is another object to provide a fuel pump suitable for use with such a trigger valve.

According to the present invention there is provided a trigger valve comprising a valve member slidable within a bore and defining with the bore an inlet chamber, an outlet chamber, and a drain chamber, the valve member being engageable with a seating to control communication between the inlet chamber and the outlet chamber, the valve member defining a passage between the outlet chamber and the drain chamber, the valve member being moveable to control communication between the drain chamber and a drain outlet.

In such a three-way trigger valve, when the valve member engages its seating, communication is not permitted between the inlet and outlet chambers. In this position, the drain chamber communicates with the drain outlet, thus fuel flow from the outlet chamber to the drain chamber and drain outlet is permitted. Such flow is conveniently at a rate governed by the dimensions of the passage. Movement of the valve member away from its seating permits fuel flow from the inlet chamber to the outlet chamber. The movement of the valve member also breaks the communication between the outlet chamber and the drain outlet.

The invention also relates to a fuel pump incorporating a trigger valve, the pump comprising a pumping plunger reciprocable within a bore and defining with the bore a pumping chamber, an inlet chamber of the trigger valve communicating with the pumping chamber, the fuel pump further comprising a spill valve controlling communication between the pumping chamber and a low pressure volume, the spill valve comprising a valve member engageable with a seat, the valve member being carried by a piston slidable within a cylinder independent of the low pressure volume, the cylinder communicating with an outlet chamber of the trigger valve.

The low pressure volume conveniently communicates with a source of fuel at low pressure whereby fuel can be supplied through the low pressure volume and spill valve to the pumping chamber. The low pressure volume is conveniently provided with a vent valve arranged to open when the fuel pressure within the low pressure volume exceeds the fuel pressure at the source to permit hot fuel to escape from the low pressure volume, thus reducing the quantity of hot fuel subsequently returned to the pumping chamber.

As the low pressure volume is independent of the cylinder, the spill valve can be maintained in an open position even though the fuel pressure in the low pressure volume is low.

The trigger valve is conveniently of the type defined hereinbefore.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a fuel pump in accordance with an embodiment of the invention; and Figure 2 is an enlargement of part of the fuel pump of Figure 1.

The fuel pump illustrated in Figure 1 comprises a distributor member 10 which is rotatable within a sleeve 12. The distributor member 10 includes a region 14 of enlarged diameter which is provided with radially extending bores within which pumping plungers 16 are reciprocable. The outer end of each pumping plunger 16 carries a shoe and roller arrangement the roller 18 of which is engageable with the cam surface of a cam ring 20. An advance arrangement 22 of conventional form is arranged to adjust the angular position of the cam ring 20 with respect to the housing 24 of the pump to control the timing of fuel delivery by the pump.

The end of the distributor member 10 remote from the enlarged region 14 thereof is connected to the rotatable part of a feed pump 26 whereby fuel is supplied at relatively low pressure to an inlet passage 28 provided in the housing 24. A pressure regulator 30 is connected between the inlet and outlet of the feed pump 26 in order to control the fuel pressure supplied to the inlet passage 28. The pressure regulator 30 conveniently includes a piston of relatively large diameter acting as an accumulator, and a pressure relief valve arranged to open upon the accumulator pressure exceeding a predetermined level. When the pressure relief valve opens, for example between the filling parts of the pumping cycle as described hereinafter, fuel from the feed pump outlet is returned to its inlet thus absorbing the temporary excess output of the feed pump.

The inlet passage 28 communicates through a spring biased non-return valve 32 with a supply port 34 provided in the sleeve 12. The nonreturn valve 32 conveniently includes a spherical member which is spring biased into engagement with a seating, the spherical member conveniently being of hollow form in order to reduce the inertia of the valve 32. The supply port 34 communicates with an annular recess 36 provided in the distributor member 10, the recess 36 communicating through a plurality of supply passages 38 (only one of which is illustrated) with an axially extending bore 40 provided in the enlarged region 14 of the distributor member 10.

The part of the bore 40 with which the supply passage 38 communicates is of enlarged diameter, the bore 40 including a region 40a of reduced diameter which communicates with the radially extending bores, the connection between the enlarged diameter region and reduced diameter region 40a forming a seating. A spill valve member 42 is engageable with the seating, the spill valve member 42 including a reduced diameter region 42a which extends within the reduced diameter region 40a of the bore 40 in a piston like manner. A spring 44 is arranged to bias the spill valve member 42 into engagement with its seating, the spring 44 engaging a cap 46 which is secured to the end of the enlarged region 14 of the distributor member 10 by means of bolts 48.

The reduced diameter region 40a of the bore 40 which communicates with the radially extending bores is shaped to define an annular pumping chamber 50 which communicates through a delivery passage 52 with an outlet 54 provided on the surface of the distributor member 10. The outlet 54 is arranged to register, in turn, with outlet ports 56 provided in the sleeve, the outlet ports 56 communicating with respective outlets of the pump. Axially aligned with the outlet 54, the distributor member 10 is provided with a groove 58 which communicates with an annulus 60, the annul us 60 communicating with the inlet passage 28 provided in the housing 10. The purpose of this communication is to connect each of the outlets of the pump other than the outlet which is in communication with the pumping chamber 50 with fuel at transfer pressure. The seating diameter of the spill valve is substantially equal to the diameter of the region 42a of the spill valve member 42, thus the high pressure generated in the pumping chamber 50, in use, does not tend to lift the spill valve member 42 from its seating until such movement is triggered by the trigger valve 66 (described hereinafter).

The groove 58 also communicates with a part annular groove 59 provided in the distributor member 10 which is registrable with a passage 61 provided in the sleeve 12. Fuel is thereby permitted to flow through the groove 58 from the feed pump to a low pressure drain. The flow of fuel through the groove 58 cools a cylindrical part of the sleeve 12 provided with the outlet ports 56, and cools a corresponding part of the distributor member 10 thus reducing thermal expansion and the risk of seizure.

The delivery passage 52 communicates with radially extending passages 62 which are arranged to register, in turn, with a port 64 provided in the sleeve 12 which communicates with the inlet of a spill trigger valve 66 through a passage denoted by dashed line 68. The spill trigger valve 66 also includes an outlet which communicates, through a passage denoted by dashed line 70, with a port 72 provided in the sleeve 12. The port 72 communicates with an annulus 74 provided on the distributor member 10 which communicates through a passage 76 with a control chamber 78 defined by an end part of the reduced diameter region 40a of the bore 40 and an end of the spill valve member 42.

As shown in Figure 1, one of the drillings forming the delivery passage 52 extends to the surface of the enlarged diameter region 14 of the distributor member 10 providing a fuel flow passage 80 between the enlarged diameter part of the bore 40 and the exterior of the distributor member 10. A resilient C-shaped clip 82 is located within an annular recess around the part of the distributor member 10 at which the flow passage 80 emerges from the distributor member 10, the clip 82 providing a substantially fluid tight seal when the fuel pressure within the bore 40 is relatively low, the clip 82 flexing upon the fuel pressure within the bore 40 and flow passage 80 exceeding a predetermined level to permit venting of fuel from the bore 40 through the flow passage 80.

An end of the clip 82 is bent inwardly and received within a corresponding recess provided in the distributor member 10 to restrict angular movement of the clip 82 with respect to the distributor member 10, thus correctly locating the clip 82.

As most clearly illustrated in Figure 2, the trigger valve 66 comprises a valve member 84 which is slidable within a bore 86 of a valve body 88.

The valve member 84 includes a region of reduced diameter which defines with the bore 86 an annular inlet chamber 90 which communicates through a non-return valve 92 with the passage 68. The valve member 84 and bore 86 are also shaped to define an annular outlet chamber 94 which communicates with the passage 70.

Intermediate the inlet and outlet chambers 90, 94, the valve member 84 is engageable with a seating to control communication between the inlet chamber 90 and outlet chamber 94. An electromagnetic actuator 96 is arranged to maintain engagement between the valve member 84 and its seating, when energised, and a spring 98 is arranged to move the valve member 84 away from its seating when the electromagnetic actuator 96 is de-energised.

An axially extending blind drilling 100 is provided in the valve member 84, the open end of the drilling 100 being closed by a plug 102. A passage 104 communicates between the drilling 100 and the outlet chamber 94, and radially extending drillings 106 communicate with the blind end of the drilling 100 thus permitting fuel to flow from the outlet chamber 94 to a drain chamber 108 defined between the valve member 84 and the valve body 88.

The upper end of the valve member 84 is of reduced diameter, and is externally screw-threaded, an armature 110 being in screw-threaded engagement with the valve member 84. The armature 110 locates a shim 112 which is engageable with a lift stop 114 forming part of the valve body 88 to limit movement of the valve member 84 away from its seating. It will be appreciated that the engagement of the shim 112 with the lift stop 114 closes the drain chamber 108, and that when the valve member 84 is moved under the action of the electromagnetic actuator 96 into engagement with its seating, the shim 112 is lifted away from the lift stop 114 thus permitting communication between the drain chamber 108 and a chamber 116 within which the armature 110 is located. The chamber 116 communicates through a passage 118 provided in the valve body 88 with a chamber 120 into which the lower end of the valve member 84 extends, and the chamber 120 is vented to a suitable low pressure drain through an outlet 122.

In use, in the position illustrated in the accompanying drawings, the electromagnetic actuator 96 is energised thus the valve member 84 occupies a position in which it engages its seating thus fuel is unable to flow from the inlet chamber 90 to the outlet chamber 94. The chamber 78 communicates through the drilling 100 of the trigger valve 66 with the low pressure drain, thus is at low pressure. The spill valve member 42 is biased into engagement with its seating by the spring 44. The plungers 16 occupy their radially outer positions, and the pumping chamber 50 is charged with fuel at relatively low pressure. From this position, upon rotation of the distributor member 10 under the action of a drive shaft 124 which is keyed to the distributor member 10 and arranged to rotate at a speed associated with engine speed, the groove 54 moves into communication with one of the outlet passages 56. Once such communication has been achieved, the rollers 18 engage the leading flanks of cam lobes provided on the cam ring 20, such engagement causing the plungers 16 to commence inward movement.

The inward movement of the plungers 16 pressurizes the fuel in the pumping chamber 50 and displaces fuel at high pressure through the delivery passage 52 and groove 54 to the outlet port 56 with which the groove 54 is registered. Delivery of fuel in this manner continues until the electromagnetic actuator 96 of the trigger valve 66 is de-energized.

Deenergization of the electromagnetic actuator 96 results in the valve member 84 moving under the action of the spring 98 to lift the valve member 84 away from its seating. The movement of the valve member 84 results in communication being permitted between the inlet chamber 90 and outlet chamber 94. Such communication permits fuel at high pressure from the delivery passage 52 to flow through the trigger valve 66 to the chamber 78, the application of high pressure fuel to the chamber 78 causing the spill valve member 42 to move against the action of the spring 44 thus permitting fuel to flow directly from the pumping chamber 50 to the enlarged diameter part of the bore 40. The pressure within this part of the bore 40 rapidly increases to a level sufficient to lift the clip 82 away from the end of the flow passage 80 thus permitting fuel to be vented from the bore 40. Fuel is prevented from returning to the feed pump 26 through the supply passages 38 due to the non-return valve 32.

The movement of the valve member 84 also results in the shim 112 engaging the lift stop 114 thus the drain chamber 108 is closed and fuel is not able to flow to the low pressure drain through the trigger valve 66.

It will be appreciated that as the chamber 78 is of relatively low volume, only a small quantity of fuel is required to flow through the trigger valve 66 in order to move the valve member 42 away from its seating thus a relatively low rate of fuel flow to the chamber 78 is sufficient to cause spill in this arrangement.

Continued rotation of the distributor member 10 causes the rollers 18 to ride over the cam lobes thus permitting the plungers 16 to move radially outwardly. As, at this stage, the spill valve member 42 is still lifted from its seating, fuel is able to flow through the supply passages 38 and bore 40 to the pumping chamber 50, the supply of fuel being at a sufficiently high pressure to push the plungers 16 radially outwardly, but insufficient to cause the clip 82 to lift from the end of the flow passage 80. The spill valve member 42 is maintained out of engagement with its seating due to the pressure within the chamber 78 being sufficient to overcome the action of the spring 44. The pressure within the chamber 78 is maintained at a sufficiently high level due to the presence of the nonreturn valve 92 in the inlet of the trigger valve 66 and due to the engagement of the shim 112 with the lift stop 114 closing the drain chamber 108. Once a sufficient amount of fuel has flowed to the pumping chamber 50, the electromagnetic actuator 96 is energized lifting the valve member 84 against the action of the spring 98. The movement of the valve member 84 results in the shim 112 being lifted from the lift stop 114 thus fuel is able to flow from the drain chamber 108 to the low pressure drain. It will be appreciated, therefore, that fuel is able to flow from the chamber 78 through the passage 104, drilling 100 and radially extending drillings 106 to the drain chamber 108, thus the fuel pressure within the chamber 78 is allowed to fall. The reduction in pressure in the chamber 78 is sufficient to permit the spill valve member 42 to move under the action of the spring 44 into engagement with its seating. The movement of the valve member 84 also results in the valve member 84 moving into engagement with its seating, thus communication between the inlet chamber 90 and outlet chamber 94 is broken. The fuel pump is then ready for the next pumping cycle to commence, the movement of the distributor member 10 resulting in engagement between the groove 54 and another of the outlet ports 56.

The trigger valve 66 is of advantageous design in that the seating diameter is selected so that when the valve member 84 is in engagement with its seating, the valve member 84 is substantially pressure balanced.

The application of high pressure fuel to the inlet chamber 90 does not therefore apply a significant force to the valve member 84 tending to move the valve member away from its seating. The diameter of the passage 104 is selected so that the rate at which fuel is able to flow from the chamber 78 is sufficient to permit rapid movement of the spill valve member 42 under the action of the spring 44 thus the timing of the movement of the valve member 42 into engagement with its seating can be controlled relatively accurately.

When the electromagnetic actuator 96 is de-energized, it will be appreciated that after the initial movement of the valve member 84, the valve member 84 is no longer pressure balanced, thus the pressure of the fuel applied to the inlet of the trigger valve 66 results in a force being applied to the valve member 84 to assist the spring 98 in moving the valve member 84 to its lifted position. It will be appreciated that subsequently the action of the pressure of the fuel on the valve member 84 must be overcome to move the valve member 84 away from its lifted position. The pressure applied to the valve member 84 at this time is maintained at a high level due to the load of the spring 44, and in order to assist movement of the valve member 84 against the action of the fuel pressure, a spring 126 is located acting against the spring 98 and assisting the electromagnetic actuator.

The pump described hereinbefore is particularly suitable for use with an engine having more than four cylinders, for example a six cylinder engine. Conventional pumps for use in such applications suffer from limited filling duration and/or limited timing adjustment. As in the present arrangement filling occurs by way of an annul us provided on the distributor member, the supply passage is in constant communication with the feed pump other than when the non-return valve is closed. The filling duration is therefore less restricted than in prior, ported arrangements, and a greater degree of timing adjustment is permitted.

Claims (3)

1. A trigger valve comprising a valve member slidable within a bore and defining with the bore an inlet chamber, an outlet chamber, and a drain chamber, the valve member being engageable with a seating to control communication between the inlet chamber and the outlet chamber, the valve member defining a passage between the outlet chamber and the drain chamber, the valve member being moveable to control communication between the drain chamber and a drain outlet.

2. A trigger valve as claimed in Claim 1, wherein the passage is dimensioned to restrict the rate of flow between the outlet chamber and the drain chamber.

3. A trigger valve substantially as hereinbefore described with reference to the accompanying drawings.