FUEL PUMP

A fuel pump comprising a valve assembly. The valve assembly comprises a valve member defining a valve axis, and an electromagnetically controlled armature assembly configured to reciprocate linearly along the valve axis within an armature chamber of the fuel pump. The fuel pump further comprises a spring configured to engage a first side of the armature assembly to provide a spring force acting in a first direction along the valve axis. The fuel pump further comprises a lift stop provided on a floor surface of the armature chamber and configured to engage a second side of the armature assembly to limit movement of the armature assembly in the first direction. The armature assembly comprises an armature body fixed to an armature carrier. The armature carrier is fixed to the valve member.

FIELD OF THE INVENTION

This invention relates to a fuel pump, and in particular, but not exclusively, a fuel pump of a compression ignition internal combustion engine.

BACKGROUND

In an internal combustion engine, fuel is typically supplied to fuel injectors via a common rail. The fuel is typically stored at a high pressure in the common rail prior to delivery to the fuel injectors. In order to achieve the pressure in the common rail, an engine typically comprises a fuel pump. The fuel pump includes at least one pumping plunger which, through a pumping cycle, pressurizes the fuel within a pump chamber ready for delivery to the common rail. The pumping cycle may be effected by a cam arrangement configured to drive the pumping plunger, and various plunger layouts are known, including in-line arrangements and radial arrangements, for example.

A fuel pump may include a plurality of plungers to provide the pump capacity required for achieving high fuel pressure in the common rail. The fuel pump typically comprises a valve assembly associated with each plunger to control the supply of fuel into a respective pump chamber. In many examples, such a valve assembly may comprise an electromagnetically controlled/actuated valve, wherein a valve member is coupled to a magnetic armature located within a magnetic field produced by supplying an electric current to a solenoid winding. Energising the solenoid winding produces a magnetic force that motivates the armature in a given direction, thereby also moving the valve member that is coupled to the armature. The fuel pump may further include a spring configured to provide a spring force on the armature in an opposed direction to the magnetic force from the solenoid winding. The valve assembly may be an ‘energise-to-close’ assembly in which the spring force motivates the valve member away from a valve seat when the solenoid is not energised such that fuel is supplied into the pump chamber. In such a configuration, the valve member is motivated towards the valve seat by energising the solenoid winding to produce a magnetic force which overcomes the spring force, thereby closing the valve and blocking the supply of fuel to the pump chamber. The fuel pump may further comprise a lift stop configured to abut the armature during valve opening and thereby limit movement of the armature and the valve member in the opening direction to define the end of the valve stroke.

To enable electromagnetic control of the armature and thereby control the valve member, the armature must be influenced by the magnetic field produced by the solenoid winding. As such, the armature is formed of a material selected for its magnetic properties. However, materials with advantageous magnetic properties are typically relatively soft, typically having low wear resistance characteristics. Impacts between the armature and the lift stop during the reciprocating cycle of the valve can cause wear and damage to the magnetic armature, resulting in uneven loading of the valve member and/or potentially affecting the open and close timings of the valve.

It is against this background that the invention has been devised.

STATEMENTS OF INVENTION

In a first aspect of the invention there is provided a fuel pump comprising a valve assembly. The valve assembly comprises a valve member defining a valve axis, and an electromagnetically controlled armature assembly configured to reciprocate linearly along the valve axis within an armature chamber of the fuel pump. The fuel pump further comprises a spring configured to engage a first side of the armature assembly to provide a spring force acting in a first direction along the valve axis. The fuel pump further comprises a lift stop provided on a floor surface of the armature chamber and configured to engage a second side of the armature assembly to limit movement of the armature assembly in the first direction. The armature assembly comprises an armature body fixed to an armature carrier. The armature carrier is fixed to the valve member. In other words, the armature carrier and the valve member cannot move relative to one another.

The armature body may be fixed to the armature carrier by means of a press fit connection. Additionally or alternatively, the armature carrier may be fixed to the valve member by means of a press fit connection.

The armature carrier and armature body may each be formed of a different material. Preferably, the armature carrier may be formed of a material with a greater hardness than the material of the armature body.

The armature carrier and armature body may be arranged co-axially with the valve axis. The armature carrier may comprise a cylindrical central portion. The armature body may form an annular body around the armature carrier.

The first side of the armature assembly may comprise a spring-interfacing portion. The spring-interfacing portion may be defined by the armature carrier.

The spring may comprise a first dimension R1, and the spring-interfacing portion may extend radially from the valve axis over a second dimension R2. The second dimension R2may be greater than or equal to the first dimension R1.

The armature body may comprise an annular recess provided on the first side of the armature assembly and co-axial with the valve axis.

The armature carrier may comprise an outwardly extending annular lip. The annular lip may be located in the annular recess provided on the first side of the armature assembly.

The spring-interfacing portion may be defined by the annular lip of the armature carrier.

The second side of the armature assembly may comprise a lift stop-interfacing portion. The lift stop-interfacing portion may be defined by the armature carrier.

The lift stop may extend radially from the valve axis over a third dimension R3, and the lift stop-interfacing portion may extend radially from the valve axis over a fourth dimension R4The fourth dimension R4may be greater than or equal to the third dimension R3.

The armature body may comprise a second annular recess provided on the second side of the armature assembly and co-axial with the valve axis. The armature carrier may comprise a second outwardly extending annular lip. The second annular lip may be located in the annular recess provided on the second side of the armature assembly.

The lift stop-interfacing portion may be defined by the second annular lip of the armature carrier. The armature carrier may comprise a first carrier part and a second carrier part. The first carrier part may define the spring-interfacing portion. The second carrier part may define the lift stop-interfacing portion.

In a second aspect of the invention there is provided a fuel pump comprising a valve assembly. The valve assembly comprises a valve member defining a valve axis, and an electromagnetically controlled armature assembly configured to reciprocate linearly along the valve axis within an armature chamber of the fuel pump. The fuel pump further comprises a spring configured to engage a first side of the armature assembly to provide a spring force acting in a first direction along the valve axis. The fuel pump further comprises a lift stop provided on a floor surface of the armature chamber and configured to engage a second side of the armature assembly to limit movement of the armature assembly in the first direction. The armature assembly comprises an armature body formed of a magnetic material. The armature assembly further comprises a spring-interfacing portion formed of a different material to the armature body, and a lift stop-interfacing portion formed of a different material to the armature body.

The spring-interfacing portion may be formed of a material with a greater hardness than the material of the armature body. Additionally or alternatively, the lift stop-interfacing portion may be formed of a material with a greater hardness than the material of the armature body. The spring-interfacing portion and the lift stop-interfacing portion may be formed of the same material.

The armature assembly may comprise an armature carrier. The armature carrier may define both the spring-interfacing portion and the lift stop-interfacing portion. The armature body may be fixed to the armature carrier. The armature carrier may be fixed to the valve member.

The armature body may be fixed to the armature carrier by means of a press fit connection. Additionally or alternatively, the armature carrier may be fixed to the valve member by means of a press fit connection.

The armature carrier and armature body may be arranged co-axially with the valve axis. The armature carrier may comprise a cylindrical central portion. The armature body may form an annular body around the armature carrier.

The armature body may comprise an annular recess provided on the first side of the armature assembly and co-axial with the valve axis. The armature carrier may comprise an outwardly extending annular lip. The annular lip may be located in the annular recess in the armature body. The spring-interfacing portion may be defined by the annular lip of the armature carrier.

The armature body may comprise a second annular recess provided on the second side of the armature assembly and co-axial with the valve axis. The armature carrier may comprise a second outwardly extending annular lip. The second annular lip may be located in the annular recess in the armature body on the second side of the armature assembly.

The lift stop-interfacing portion may be defined by the second annular lip of the armature carrier.

The armature carrier may comprise a first carrier part and a second carrier part. The first carrier part may define the spring-interfacing portion. The second carrier part may define the lift stop-interfacing portion.

The spring may comprise a first dimension R1, and the spring-interfacing portion may extend radially from the valve axis over a second dimension R2. The second dimension R2may be greater than or equal to the first dimension R1.

The lift stop may extend radially from the valve axis over a third dimension R3, and the lift stop-interfacing portion may extend radially from the valve axis over a fourth dimension R4. The fourth dimension R4may be greater than or equal to the third dimension R3.

It will be appreciated that the various features of each aspect of the invention are equally applicable to, alone or in appropriate combination, with other aspects of the invention, even if the combination is not explicitly mentioned in the aforementioned statements.

SPECIFIC DESCRIPTION

The invention relates to a fuel pump1for use in an internal combustion engine, such as a compression ignition engine for example. With reference toFIG.1, the fuel pump1includes a plurality of pump units10(only one of which is shown). Each pump unit10is configured to pressurise fuel within a pump chamber12. As such, each pump unit10comprises a pumping plunger14, which may be driven by a cam arrangement (not shown). Whilst not shown in the accompanying figures, the fuel pump1may include a drive shaft extending through a main pump housing16and carrying a plurality of cams which are each arranged to drive an associated plunger14through a pumping cycle.

For the purpose of explaining the present invention, only one of the pump units10will be described in detail with reference toFIG.1. However, it will be appreciated that the description applies equally to each of the respective pump units10in a fuel pump1.

The pump unit10includes a barrel18which is received within the main pump housing16and which is provided with a plunger bore20for receiving the pumping plunger14. The pump unit10further includes a pump head housing22(referred to hereinafter as the pump head) which is mounted on the barrel18. A turret portion24of the barrel18is received in a recess26in the pump head22. As shown inFIG.1, the pump chamber12may be defined in part by the pump head housing22and the turret portion24. The plunger14is driven within the plunger bore20, under the action of the driven cam (not shown), to perform a pump cycle in which fuel is drawn into the pump chamber12and pressurised before being delivered from the fuel pump1to the downstream parts of the system. A return spring28acts on the plunger14to effect a plunger return stroke, which forms part of the pump cycle.

A valve assembly30controls the supply of fuel to the pump chamber12when the fuel pump1is in use. The valve assembly30includes a valve member32defining a longitudinal valve axis A. In preferred examples, the valve member32may be aligned with the axis of the plunger14. The inlet valve member32includes an upper stem region32aand a lower head region32b. The head region32bdefines a seating surface which is engageable with a valve seat34defined within the recess26in the pump head22. Fuel is supplied to the pump chamber12at a relatively low pressure through a plurality of inlet channels36. The cross-sectional view inFIG.1shows two inlet channels36, though it will be appreciated that there may be more or less than two inlet channels36in some examples.

The head region32bof the valve member32is moveable towards and away from the valve seat34. When the head region32bof the valve member32is seated against the valve seat34, the flow route into the pump chamber12is blocked, and fuel is unable to enter the pump chamber12through the inlet channels36. Conversely, when the head region32bof the valve member32is moved away from the valve seat34(in a downwards direction inFIG.1), fuel is drawn into the pump chamber12through the inlet channels36and between the spaced-apart head region32band valve seat34. Fuel may be motivated into the pump chamber12by vacuum pressure in the pump chamber12as a result of the pump chamber volume expanding due to the plunger14being withdrawn from the pump chamber12under the force of the return spring28.

The fuel in the pump chamber12is pressurized by closing the valve head region32bagainst the valve seat34and driving the plunger14to reduce the volume in the pump chamber12. The pressurized fuel is supplied to downstream parts of the system via a conduit38in the pump head22and an outlet valve arrangement40. The outlet valve arrangement40is therefore in fluid communication with the pump chamber12via the conduit38. The outlet valve arrangement40includes an outlet valve42which is urged against an outlet valve seat44by a valve spring46. When the fuel pressure in the pump chamber12, and conduit38, exceeds a threshold sufficient to overcome the resistive force of the valve spring46(and other pressure in the downstream parts of the fuel system), the outlet valve42is lifted away from the outlet valve seat44and pressurized fuel flows from the pump chamber12to the downstream parts of the fuel system.

Referring now toFIG.2, a valve assembly130in accordance with an example of the prior art is shown in a schematic cross-sectional view. It will be appreciated that the prior art valve assembly130may be used in a fuel pump1such as that shown inFIG.1, and description of equal features will not be repeated here for conciseness. The valve assembly130includes a valve member132and an electromagnetically controlled armature148coupled to the valve member132. As explained by way of background above, the armature148is located within a magnetic field produced by supplying an electric current to a solenoid winding150. The prior art armature148is formed of a magnetic material so that when a magnetic field is created by providing an electric current through the solenoid winding150, the armature148, and therefore also the valve member132, are motivated in a specific direction.

In accordance with this example of the prior art, a spring152is also included to engage the armature148and provide a spring force in an opposing direction to the direction in which the magnetic field motivates the armature148. In the same way as described by way of background, the valve assembly130in this prior art example is a normally open, or ‘energise-to-close’, valve assembly. As such, the spring force acting on the armature148motivates the valve member132into an open position, and energising the solenoid winding150to produce a magnetic field attracts the armature148in an opposite sense to the spring force, thereby motivating the valve member132into a closed portion.

Under influence of the opposing spring force and magnetic force, the armature148of the prior art valve assembly130reciprocates linearly along the valve axis A within an armature chamber154. A lift stop156is provided on a floor surface158of the armature chamber154. The lift stop156is configured to limit the extent of movement of the armature148in a given direction, for example to limit the extent of movement under influence of the spring152. The lift stop156engages the armature148to define a maximum stroke length of the valve member132, i.e. to define a maximum open position.

In order to accurately control the flow of fuel into the pump chamber12, the valve132must be opened and closed with considerable speed. As previously described, the valve132is moved by moving the armature148to which it is coupled. It follows that the armature148is similarly required to move at a considerable speed, and the spring force and magnetic forces acting on the armature148are therefore relatively high. As such, engagement between the armature148and lift stop156results in relatively high impact forces which can, over time, cause significant wear on the armature148, which is typically made from a relatively soft material selected for its advantageous magnetic properties. Wear on the armature148can affect the accuracy of open and close valve timings, can cause variations in the valve stroke length, and can cause uneven loading on, and subsequent fracture of, the valve stem132a.

As will now be described with reference to the examples in the remaining figures, the present invention overcomes at least some of the above-described challenges of valve assemblies130of the prior art.

FIG.3shows a schematic cross-sectional view of a valve assembly30in a fuel pump1such as that described previously with reference toFIG.1. Similar to aspects of the fuel pump1described in relation to the valve assembly130of the prior art, the fuel pump1in this example also comprises an armature chamber54and a lift stop56provided on a floor surface58of the armature chamber54. The fuel pump1further comprises a valve assembly30having a valve member32that defines the valve axis A.

In accordance with examples of the present invention, the valve assembly30further comprises an electromagnetically controlled armature assembly48configured to reciprocate linearly along the valve axis A within the armature chamber54. The armature assembly48comprises a magnetic armature body60coupled to an armature carrier62(i.e. a component62which carries the armature body60so that the body cannot move relative to it). Coupling the armature body60to the armature carrier62may comprise a threaded connection in some examples, or in other examples may comprise a press-fit connection, or even a crimped connection. As such, the invention is not limited to a specific method of coupling the armature body60to the armature carrier62. The armature carrier62is coupled to the valve member32. Coupling the armature carrier62to the valve member32may comprise a threaded connection in some examples, or in other examples may comprise a press-fit connection, or even a crimped connection. It follows that the invention is also not limited to a specific method of coupling the armature carrier62to the valve member32.

Providing the armature assembly48as a plurality of different components advantageously facilitates an optimized material selection for each component. As such, the armature carrier62and armature body60may be formed of different materials. For example, the armature body60is made of a material selected for its advantageous magnetic properties. A material with a greater hardness than the armature body60may be selected for the armature carrier62to increase the longevity of the armature assembly48and reduce wear.

The armature body60and armature carrier62are preferably arranged co-axially with the valve axis A. Such a configuration helps to ensure even loading of the valve member32in use, and thereby decreases wear on the valve member32during reciprocating valve strokes. For example, the armature carrier62may comprise a substantially cylindrical central portion64and the armature body60may form an annular body around the armature carrier62. Such a configuration facilitates both simplified manufacture of the armature body60and carrier62, and simple assembly of the armature assembly48.

In the same way as described previously with reference to the prior art valve assembly130, the fuel pump1in this example further comprises a spring52configured to engage a first side66, or first end, of the armature assembly48to provide a spring force acting in a first direction substantially along the valve axis A. The first side66of the armature assembly48therefore comprises a spring-interfacing portion68. As previously described, the lift stop56is configured to engage an opposing second side70, or second end, of the armature assembly48to limit movement of the armature assembly48in the first direction. It follows that the second side70of the armature assembly48comprises a lift stop-interfacing portion72. The spring-interfacing portion68is a separate part from the armature body60, which does not interface directly with the spring52.

To increase the longevity and wear resistance of the armature assembly48, the spring-interfacing portion68and the lift stop-interfacing portion72are each formed of a different material to the material selected for the armature body60. As such, the material of the spring-interfacing portion68, and the material of the lift stop-interfacing portion72, can be selected for hardness and wear resistance properties, whilst the armature body60may be formed of a material selected for its magnetic properties. The spring-interfacing portion68and the lift stop-interfacing portion72may be formed of the same material. For example, the spring-interfacing portion68and the lift stop-interfacing portion72may both be defined by the armature carrier62, as shown inFIG.3.

The spring52comprises a first dimension R1, which may be a radius of the spring52for example. The spring-interfacing portion68extends radially from the valve axis A over a second dimension R2as shown inFIG.3. The second dimension R2is greater than or equal to the first dimension R1, thereby ensuring that the spring52only engages the spring-interfacing portion68of the armature assembly48, and not the armature body60.

With the valve member32assembled in the fuel pump1, the lift stop56on the floor surface58of the armature chamber54extends radially from the valve axis A over a third dimension R3. The lift stop-interfacing portion72of the armature assembly48extends radially from the valve axis A over a fourth dimension R4as shown inFIG.3. The fourth dimension R4is greater than or equal to the third dimension R3. This helps to ensure that the lift stop56only engages the lift stop-interfacing portion72of the armature assembly48, and not the armature body60.

Referring now toFIG.4, a further example of an armature assembly48in accordance with aspects of the invention is shown in a schematic cross section. In this example, the armature body60comprises an annular recess74provided on the first side66of the armature assembly48and co-axial with the valve axis A. The annular recess74further separates the armature body60from the spring52to ensure that the armature body60is not worn by contact with the spring52. The second side70of the armature assembly48may be configured in a similar manner, as shown inFIG.4, where an annular recess76is provided co-axially with the valve axis A. Similarly, the annular recess76on the second side70of the armature assembly48separates the armature body60from the lift stop56to further ensure the armature body60is not impacted by the lift stop56.

In preferred examples, such as that shown inFIG.4, the armature carrier62comprises an outwardly extending annular lip78. The spring-interfacing portion68is preferably defined by the annular lip78. The inclusion of a lip78facilitates an increased second dimension R2, i.e. increased radial dimension of the spring-interfacing portion68, without unduly increasing the radial dimension R5of the cylindrical central portion64. Accordingly, the volume of the armature body60and therefore the volume of magnetic material in the armature assembly48, can be increased without increasing the external dimensions of the armature body60.

The annular lip78is preferably located in the annular recess74provided on the first side66of the armature assembly48. The lip78abuts the recess74and the mechanical engagement of the lip78with the recess74helps to ensure that the inertial forces experienced by the carrier62do not result in any relative movement between the carrier62and the armature body60during armature energisation.

With reference toFIG.5, in a further example of an armature assembly48in accordance with aspects of the invention, the armature carrier62may comprise a second outwardly extending annular lip80on the second side70of the armature assembly48. The second outwardly extending annular lip80may be located in the annular recess76provided on the second side70of the armature assembly48and may define the lift stop-interfacing portion72of the armature assembly48. Such a configuration ensures that the inertial forces experienced by the carrier62during impacts with the lift stop56do not cause relative movement between the carrier62and the armature body60.

The second annular lip80may be included in addition to the previously described annular lip78on the first side66of the armature assembly48. As such, relative movement between the carrier62and armature body60is prevented in both directions throughout the reciprocating valve cycle.

For ease of manufacture, the armature carrier62in such an example may be formed of a first carrier part62aand a second carrier part62b. For example, the first carrier part62amay define the spring-interfacing portion68of the armature assembly48, and the second carrier part62bmay define the lift stop-interfacing portion72of the armature assembly48.

In some examples both the first and second carrier parts62a,62bmay be formed of the same material. However, it will be appreciated that in other examples it may be advantageous to form each of the carrier parts62a,62bof different materials. As such, this configuration further facilitates tailoring the material selection to the specific function of each component of the armature assembly48.

The annular lips78,80of the first and second carrier parts62a,62bmay be used to effectively clamp the armature body60relative to the valve member32. In such an example, the armature body60is again preferably fixed to the first and second parts62a,62bof the carrier62, with the first and second carrier parts62a,62bbeing fixed to the valve member32.

Whilst not shown in the accompanying figures, it will be appreciated than in some examples the armature carrier62may comprise an annular lip78as previously described, without requiring an annular recess74. In such an example it will be appreciated that the annular lip abuts a surface of the armature body60on the first side66of the armature assembly48. Further, the armature carrier62may comprise a second annular lip80as previously described, without requiring a second annular recess76. In such examples it will be appreciated that the second annular lip abuts a surface of the armature body60on the second side70of the armature assembly48. The provision of a carrier62comprising one or more annular lips78,80without requiring one or more annular recesses74,76is equally applicable in examples where the carrier62is formed of a first and second carrier part62a,62b.

It will be appreciated that various other examples of the invention are also envisaged without departing from the scope of the appended claims. Further, it will be appreciated that the above described examples are provided by way of example only, and that other examples of the invention may include any combination of the features described with reference to each of the examples above.