Inlet valve arrangement for a fuel pump

An inlet valve arrangement for a pump head of a fuel pump for use in a common rail fuel injection system comprises an inlet valve member moveable between open and closed positions to control the flow from a source of low-pressure fuel to a pumping chamber of the fuel pump. The inlet valve member is arranged to open in response to the pressure difference between the fluid pressure of fuel on an inlet side of the inlet valve member and the fluid pressure in the pumping chamber exceeding a threshold value. The inlet valve arrangement comprises means for selectively applying a closing force on the inlet valve member to bias it toward the closed position, such that, in use, the application of the closing force by said means acts to increase the threshold value of the pressure difference at which the inlet valve member opens.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. 371 of PCT Application No. PCT/EP2012/061229 having an international filing date of 13 Jun. 2012, which designated the United States, which PCT application claimed the benefit of European Patent Application No. 11169958.3 filed 15 Jun. 2011, the entire disclosure of each of which are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an inlet valve arrangement and, in particular, an inlet valve arrangement for a pump head of a fuel pump for use in a common rail fuel injection system.

BACKGROUND ART

High-pressure fuel pumps for common rail fuel injection systems typically comprise one or more hydraulic pump heads where fuel is pressurised in a pumping chamber of the pump head by the reciprocating movement of a plunger. Typically, low-pressure fuel is fed to the pump heads by a low-pressure lift pump in the fuel tank, or alternatively by a transfer pump built into the high-pressure fuel pump. Once pressurised, the high-pressure fuel is fed from the pumping chamber to the common rail.

An inlet metering valve is used to limit the fuel that is fed to the high-pressure pump to be compressed and delivered to the common rail. A conventional inlet metering valve is effectively a controllable orifice, which acts to throttle the flow of fuel to the inlet valve of the high-pressure pump in order to control the pressure on the inlet side of the valve, which is typically spring-biased into a closed position. Accordingly, the pressure at the inlet side of the valve determines when the valve opens and the quantity of fuel delivered to the pumping chamber. In this way, only the amount of fuel required by the engine is delivered to the rail, thereby saving both fuel and energy compared to the situation where fuel is fed by the lift or transfer pump at constant full delivery.

However, there are a number of disadvantages to conventional inlet metering valves. In particular, such valves are expensive and add to the overall cost of the common rail injection system, which is undesirable. Secondly, inlet metering valves are relatively large and space consuming components. Thirdly, such valves are vulnerable to wear and to bad fuels, which has a detrimental effect upon the common rail injection system in which they are installed. Furthermore, the use of a conventional inlet metering valve means that the metering/rail pressure control mechanism is relatively far from the pumping chamber of the high-pressure fuel pump, which leads to undesirable delays in rail pressure control.

It is an object of the present invention to provide an inlet valve arrangement for the pump head of a high-pressure fuel pump which substantially overcomes or mitigates at least some of the above-mentioned problems.

For more information relating to an inlet valve arrangement for a high pressure fluid pump, the reader is directed to German patent application number 10-2008-018018 in the name of Continental Automotive GmbH.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided an inlet valve arrangement for use in a common rail fuel injection system, the inlet valve arrangement comprising;

an inlet valve member moveable between open and closed positions to control the flow from a source of fuel at a first pressure on an inlet side of the inlet valve member to a chamber on an outlet side of the inlet valve member, wherein the inlet valve member is arranged to open in response to the pressure difference between the fluid pressure of fuel on the inlet side and the fluid pressure in the chamber exceeding a threshold value;

the inlet valve arrangement comprising means for selectively applying a closing force on the inlet valve member to bias it toward the closed position, such that, in use, the application of the closing force by said means acts to increase the threshold value of the pressure difference at which the inlet valve member opens.

The inlet valve arrangement according to the first aspect of the present invention has a particular application in the pump head of a fuel pump for use in a common rail fuel injection system, wherein the inlet valve member is moveable between open and closed positions to control the flow from a source of low-pressure fuel to a pumping chamber of the fuel pump, and the inlet valve member is arranged to open in response to the pressure difference between the fluid pressure of fuel on an inlet side of the inlet valve member and the fluid pressure in the pumping chamber exceeding a threshold value.

Thus, by selectively applying a closing force on the inlet valve member, it is possible to vary the threshold value of the pressure difference across the inlet valve member which is required to open the valve. This, in turn, varies the time at which the inlet valve member opens and closes during operation of a fuel pump to which the inlet valve arrangement is installed and, moreover, varies the amount of fuel delivered to pumping chamber of the fuel pump. Accordingly, the requirement for a conventional inlet metering valve is obviated. Preferably, the means for selectively applying the closing force is operable to apply a force which varies proportionally with a control signal, which may be a control current.

Preferably, said means comprises an electrical component in the form of a solenoid coil operable to exert a closing force on the inlet valve member which is proportional to an electric current flowing therein.

More preferably, the inlet valve arrangement comprises an armature of ferromagnetic material coupled to the inlet valve member, such that the solenoid coil exerts an electromagnetic force on the armature when an electric current flows within the solenoid coil.

Conveniently, the inlet valve arrangement comprises a spring arranged to bias the inlet valve member toward the closed position, wherein the threshold value of the pressure difference corresponds to an opening force on the inlet valve member which is greater than the closing force exerted by the spring.

According to a second aspect of the present invention, there is provided a pump head for a fuel pump for use in a common rail fuel injection system, the pump head comprising a pump head housing and an inlet valve arrangement according to the first aspect.

Preferably, the fluid pressure of fuel on the inlet side of the inlet valve member is defined by the fluid pressure within a gallery, wherein the gallery communicates with an external chamber defined in part by a closure member mounted externally to the pump head housing, such that, in use, the gallery communicates with the source of low-pressure fuel via the external chamber.

More preferably, the external chamber comprises an entry port, the entry port being adapted so as to restrict the flow from the source of low-pressure fuel into the external chamber such that, in use, the maximum fluid pressure in the external chamber is limited to a pressure which is less than the output pressure of the source of low-pressure fuel. Even more preferably, the entry port is provided in the closure member.

Preferably, the inlet valve member comprises an elongate neck which is guided within a valve bore in the pump head housing, the valve bore extending between an upper surface of the pump head housing and a valve seat.

More preferably, the external chamber is defined between the closure member and the upper surface of the pump head housing; and a distal end of the neck, disposed away from the valve seat, projects above the upper surface of the pump head housing into the external chamber.

Even more preferably, said means comprises a solenoid coil operable to exert a closing force on the inlet valve member which is proportional to an electric current flowing therein;

the inlet valve arrangement comprises an armature of ferromagnetic material coupled to the inlet valve member, such that the solenoid coil exerts an electromagnetic force on the armature when an electric current flows within the solenoid coil, and a spring arranged to bias the inlet valve member toward the closed position, wherein the threshold value of the pressure difference corresponds to an opening force on the inlet valve member which is greater than the closing force exerted by the spring;

and the armature projects radially outwards from the distal end of the neck and acts as a spring seat, the spring being disposed between the armature and the upper surface of the pump head housing.

Still more preferably, the solenoid coil is mounted in or on the closure member such that, when closure member is mounted on the pump head housing, the solenoid coil is disposed adjacent to, and coaxial with, the inlet valve member and, conveniently, the distal end of the neck of the inlet valve member.

According to a third aspect of the present invention, there is provided a fuel pump for use in a common rail fuel injection system, comprising at least one pump head according to the second aspect.

It will be appreciated that preferred and/or optional features of the first aspect of the invention may be incorporated alone or in appropriate combination in the pump head of the second aspect and/or the fuel pump of the third aspect.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, the pump head1comprises a pump head housing2. The pump head housing2has a plunger bore4in which a pumping plunger5is disposed for reciprocating movement therein. As described in, for example, International Patent Application WO-A1-2010-007409 (published as U.S. Patent Application Publication 2011/0120418A1) in the name of the Applicant, a lower end of the pumping plunger5includes a foot which is driven by a cam mounted on a drive shaft (not shown inFIG. 1). As the drive shaft rotates, the cam imparts an axial force on the plunger foot, causing the pumping plunger5to reciprocate within the plunger bore4. The pump head housing2defines a pumping chamber6at an upper end of the plunger bore4, such that fuel is pressurised within the pumping chamber6by the reciprocal motion of the pumping plunger5within the plunger bore4.

Low-pressure fuel is fed to the pumping chamber6by a low-pressure lift pump in a fuel tank (not shown inFIG. 1), or alternatively by a transfer pump built into the high-pressure fuel pump. The pump head housing2includes an exit drilling7in fluid communication with the pumping chamber6. In use, pressurised fuel is fed from the pumping chamber6, along the exit drilling7, and through an outlet valve8to downstream components of a fuel injection system, such as a common rail.

The fuel pump head1includes an inlet valve arrangement9which comprises a moveable inlet valve member10for controlling fuel flow into the pumping chamber6. The inlet valve member10has a conical body12and an elongate neck14and is moveable between open and closed positions in response to the fuel pressure in a gallery16, which is machined in the pump head housing2above the pumping chamber6, so as to surround a frustoconical lower end surface of the inlet valve member10.

The conical body12is housed within the pump head housing2, adjacent to the pumping chamber6, whilst the neck14extends from the conical body12, coaxially with the plunger bore4, away from the pumping chamber6. The neck14is slidable within a valve bore18defined by the pump head housing2. Consequently, the inlet valve member10is guided by the pump head housing2at the lower end of the neck14.

The neck14of the inlet valve member10extends beyond the valve bore18, and out from an upper surface20of the pump head housing2. The upper surface20of the pump head housing2is planar and substantially flat. A proximal end22of the neck14(adjacent to the conical body12) remains within the pump head housing2, whilst a distal end24of the neck14remains outside the pump head housing2and carries an armature26, which acts as a spring seat. The armature26is fixed to the inlet valve member10by press-fitting it onto the neck14. A valve return spring28is provided between the upper surface20of the pump head housing2and the armature26to urge the inlet valve member10closed against a valve seat30when fuel pressure within the gallery16drops below a threshold value. A slight recess32is provided in the otherwise flat upper surface20of the pump head housing2to locate the lower end of the spring28therein.

A closure member in the form of a valve cap34is mounted on top of and, thus, externally to, the upper surface20of the pump head housing2. The valve cap34is provided over the distal end24of the neck14of the inlet valve member10(i.e. the part of the inlet valve member10that is outside the pump head housing2). The valve cap34is a generally cylindrical member comprising a circular body portion36and an annular wall portion37which projects from the periphery of the body portion36. The pump head housing2includes a raised portion or projection40that is substantially circular, and projects into, and fits the footprint of, the annular wall portion37of the valve cap34. The valve cap34may be fitted over the raised portion40such that the raised portion40protrudes into the annular wall portion37in a manner similar to a plug and socket arrangement.

The valve cap34defines an external chamber42within which the distal end24of the inlet valve member10is housed. The radial outer surface of the projection40faces, and engages, a radial inner surface of the annular wall portion37. The external chamber42is therefore defined between the internal surface of the valve cap34, and the upper surface20of the raised portion40. A low-pressure seal is provided between the radial inner surface of the annular wall portion37and the radial outer surface of the raised portion40, for example by an O-ring (not shown inFIG. 1) surrounding the raised portion40. The O-ring may be located within an annular groove provided in the radial outer surface of the raised portion40and serves to minimise the loss of fuel from the external chamber42.

The body portion36of the valve cap34comprises an axial blind bore38, which houses a solenoid coil39. The solenoid coil39is arranged such that it is coaxial with the blind bore38. When the valve cap34is attached to the pump head housing2, the blind bore38of the body portion36is aligned such that it is coaxial with the valve bore18in the pump head housing2. Accordingly, the solenoid coil39in the valve cap34is aligned such that it is coaxial with the inlet valve member10and, in turn, the armature26. The armature26is made from a suitable ferromagnetic material such that energisation of the solenoid coil39causes an electromagnetic force to be exerted on the armature26, and thus the inlet valve member10as will be described in more detail later.

An entry port44is provided in the annular wall portion37of the valve cap34to allow fuel to flow into the external chamber42. The external chamber42communicates with the gallery16defined in the pump head housing2via a plurality of radial feed drillings46which are provided in the pump head housing2. The radial feed drillings46extend between the gallery16and the upper surface20of the pump head housing2, emerging at a position on the upper surface20of the pump head housing2which is outside the diameter of the spring28. The radial feed drillings46are equally spaced about the circumference of the gallery16.

The operation of the above-described inlet valve arrangement9will now be described.

In use, low-pressure fuel is pumped by a transfer or lift pump through the entry port44and into the external chamber42. Typically, in the context of a common rail fuel injection system, the low-pressure fuel is supplied at a pressure of about 5 bar. The low-pressure fuel is then fed from the external chamber42, through the radial feed drillings46in the pump head housing2, and into the gallery16. Movement of the inlet valve member10away from the valve seat30to allow fuel into the pumping chamber6is dependent on the balance of forces acting upon it. An opening force is provided by the difference in pressure between the inlet side of the inlet valve member10, i.e. the fluid pressure in the gallery16, and the fluid pressure in the pumping chamber6. The closing force acting on the inlet valve member10is provided by the spring28and any electromagnetic force exerted on the armature26by the solenoid coil39.

During a filling stroke of the high pressure pump, the pumping plunger5moves away from the inlet valve arrangement9and the volume of the pumping chamber6increases. This results in a negative pressure in the pumping chamber6of up to about −1 bar. As mentioned previously, the low pressure fuel may be supplied at a pressure of 5 bar. Accordingly, when the external chamber42, and thus the gallery16, are filled with fuel, the pressure on the inlet side of the valve arrangement will be 5 bar, which results in a total pressure difference, ΔP, between the inlet and outlet sides of the inlet valve member10of around 6 bar.

The spring28is selected such that the closing force it exerts on the inlet valve member10is less than opening force caused by the pressure difference, ΔP, across the inlet valve member10during a filling stroke. If the spring force were the only force acting to close the inlet valve member10, then it would always open when the opening force caused by ΔP exceeded the spring force and close again when ΔP fell below spring force. However, by virtue of the solenoid39, an additional force can be applied to the inlet valve member10. As mentioned previously, when a current is passed through the solenoid39this produces an electromagnetic force which attracts the armature26and thus provides an additional closing force to the spring force. The greater the current in the solenoid coil39, the greater the electromagnetic force on the armature26and, therefore, the greater the overall closing force acting on the inlet valve member10. Accordingly, by varying the current applied to the solenoid coil39, the pressure difference ΔP required to open the inlet valve member10varies, with higher current requiring a greater pressure difference ΔP and lower current requiring a lower pressure difference ΔP. Thus, by varying the current applied to the solenoid coil39, the time at which the inlet valve member10opens and closes during operation of the high pressure pump can be controlled. This, in turn, enables the quantity of fuel which is delivered to the pumping chamber6to be controlled.

For example, if a relatively small current is applied to the solenoid coil39, then the electromagnetic force on the armature26will be relatively small, resulting in a slightly larger closing force acting on the inlet valve member10than would be provided by the spring28alone. This means that the inlet valve member10will open slightly later during a filling stroke of the pumping plunger5and close slightly earlier when the pumping stroke commences. On the other hand, if a larger current is applied to the solenoid coil39, the additional closing force exerted on the inlet valve member10will be greater still. Accordingly, the inlet valve member10will open later still and close earlier, thereby reducing the quantity of fuel delivered to the pumping chamber6compared to the case where the applied current is lower, or not applied at all. In this way, the solenoid coil39can be used to provided a variable force on the inlet valve member10to match the pressure difference ΔP across it at the beginning of the plunger stroke, towards the end of the stroke, or at any other time, thereby determining the time at which the inlet valve member10opens and closes, and the quantity of fuel delivered.

An inlet valve arrangement having the above-described configuration has a number of advantages over the use of a conventional inlet metering valve. Firstly, it is much smaller when compared to a conventional inlet metering valve and has a simple construction, thereby reducing cost and space requirements. Furthermore, no moving parts are required to adjust the amount of fuel delivered to the pumping chamber6beyond those parts which are incorporated into the fuel pump head1already. Thus, the above-described arrangement has increased durability compared to a system employing a conventional inlet metering valve. Also, the above-described fuel pump head1is easy to assemble because attachment of the valve cap34to the pump head housing2ensures that the solenoid coil39is correctly positioned with respect to the armature26on the inlet valve member10.

The above-described inlet valve arrangement9is also convenient because, in the event of an electrical failure, it fails in the same way as a conventional inlet metering valve, meaning that it is compatible with the existing common rail system. More specifically, when the electrical supply to a conventional inlet metering valve is lost, the valve fails to an open state and results in 100% filling, i.e. the maximum amount of fuel is pumped by the transfer pump to the external chamber of the fuel pump head and onward to the pumping chamber when the inlet valve member opens. Any additional pressure in the system can be relieved by means of a pressure relief valve either on the common rail or on the valve. Likewise, with the inlet valve arrangement9described above, electrical failure would result in no additional closing force being provided by the solenoid coil39and, therefore, maximum filling, which would be relieved in the same way as in a system with a conventional inlet metering valve.

An inlet valve arrangement9having the above-described configuration is also advantageous when used in high-pressure pumps having multiple pumping plungers in order to balance the fuel delivered by each of the individual pumping elements. For example, a high-pressure pump may have two pumping plungers arranged on opposite sides of a cam mounted on a drive shaft, or three pumping plungers spaced equidistantly around the cam. Each pumping plunger is associated a separate fuel pump head1, and thus an individual inlet valve arrangement9. Accordingly, the solenoid coils39of the individual inlet valve arrangements9can be supplied with separate control signals, i.e. currents, from the Electronic Control Unit so that any variations between the various fuel pump heads (e.g. due to manufacturing tolerances) can be compensated for. This could be obtained by saving the electrical characteristics in for example a data matrix code or a learning function incorporated in the Electronic Control Unit.

In a variation of the above-described embodiment, the inlet port44of the valve cap34may be provided with a throttle which restricts the flow of fuel into the external chamber42. With this configuration, the rate at which the fuel in the external chamber42is replenished by the transfer pump after the pumping chamber6has been filled is reduced. This is advantageous in that, during operation of the high-pressure pump, the fluid pressure in the external chamber42will never reach the full 5 bar pressure of the transfer pump, because the external chamber42is not refilled quickly enough for this to happen. Accordingly, the maximum pressure difference ΔP across the inlet valve member10is less. This means that a spring28with a lower spring force can be used and, in turn, the electromagnetic force applied to the armature26by the solenoid coil39in order to control the timing of the opening and closing of the inlet valve member10can be less. The requirement for a lower electromagnetic force from the solenoid coil39means that a smaller control current can be supplied to it, thereby saving energy.

Moreover, the above-described inlet valve arrangement9is advantageous in that the control current supplied to the solenoid coil39is a closed loop control with respect to the rail pressure. This contrasts with, for example, a situation in which a solenoid coil is directly coupled to the inlet valve member so as to directly control switching, i.e. opening and closing, of the inlet valve member. Such a direct-acting arrangement would require an encoder and thus a more complicated control architecture than that required by the above-described inlet valve arrangement9.

In the embodiment described above with reference toFIG. 1, the inlet valve member10is integrated directly into the pump head housing2. However, it will be appreciated by those skilled in the art that the inlet valve member10need not be directly integrated into the pump head housing2. For example, the inlet valve arrangement9may be integrated with the valve cap34.

The inlet valve member does not necessarily require a conical body: in alternative embodiments of the invention, the body may be spherical or any other suitable shape with the corresponding valve seat being suitably shaped.