Patent Description:
In combustion engine systems, a fuel pump is used to pressurise fuel before it is injected into the cylinders of the engine. Modern compression-ignition engine systems use a high-pressure fuel pump to feed a common rail fuel volume which acts as a reservoir to store the pressurised fuel and feed the individual fuel injectors. In compression-ignition internal engines the fuel is pressurised to very high levels, typically in excess of <NUM> bar. Such high pressures are difficult to manage and engine designers have to pay careful attention to controlling fuel leakages within the engine to guard against system inefficiency, as well as damage to parts.

<CIT> describes a piston compressor for compressing a working fluid, particularly a liquid or gaseous fuel, comprising a piston which can move back and forth in a cylinder bore of a housing. The piston has a one or multi-piece design and delimits a compression chamber within the cylinder bore, which can be filled with the working fluid. The piston forms a pressure chamber which is open towards the compression chamber and is delimited radially on the outside by a sleeve-shaped wall section of the piston, said wall section being elastically deformable as a function of the pressure in the pressure chamber.

An aspect of the invention provides a pump for a fuel delivery system, the pump comprising:.

Accordingly, embodiments of the invention advantageously provide a pump in which a projecting portion of the main housing projects into a plunger bore of the plunger housing, which necessarily limits the topmost position of a plunger within the plunger bore. Thus, the topmost position of the plunger within the plunger bore is necessarily spaced further away from the point at which the main housing and the plunger housing seal against one another. This is beneficial because it may reduce the likelihood of a plunger becoming stuck or seized within the plunger bore due to distortions of the plunger bore caused when the main housing and the plunger housing are sealed together. At the same time, the projecting portion may advantageously have a size and shape such that it occupies a dead volume within the compression chamber so as to preserve the volumetric efficiency of the pump.

The main housing comprises an inlet valve for controlling the flow of fuel into the compression chamber, the inlet valve comprising a valve member arranged for reciprocating movement within a valve bore defined by the main housing. The valve bore may be formed, at least in part, in the projecting portion. The projecting portion comprises a valve seat disposed at a distal end thereof, the valve member comprising a valve head arranged to close against the valve seat when the inlet valve is in a closed state.

The pump may comprise a plunger arranged for reciprocating movement within the plunger bore. The plunger may have a substantially cylindrical form and comprise a close clearance annular portion disposed toward an end of the plunger proximal to the second face of the plunger housing, wherein the close clearance annular portion serves to limit and/or substantially prevent fuel from leaking out of the compression chamber, in use. In one embodiment, the end of the plunger proximal to the second face of the plunger housing comprises a recess therein. The close clearance annular portion of the plunger may be disposed between said end of the plunger and a base of the recess.

The projecting portion may be a substantially cylindrical boss. The valve bore may be co-axial with the substantially cylindrical boss.

In an embodiment, the valve head projects away from the valve seat into the compression chamber.

In one embodiment, a surface of the projecting portion and an adjacent wall of the plunger bore define therebetween an outlet path for pressurised fuel from the compression chamber.

In use, at least a portion of the valve head may be received within the recess of the plunger during a pumping stroke of the plunger.

The first and/or the second face may comprise an annular seal which encircles the projecting portion. The first and second opposed faces may each extend substantially perpendicular to a main axis of the plunger bore.

The annular seal may be provided on the main housing and has a cross section which tapers towards contact with the plunger housing. For example, the annular seal may define a relatively narrow annular contact surface at its extremity which contacts the plunger housing.

The main housing and the plunger housing may be coupled to one another by threaded fastening means.

According to another aspect of the present invention, there is provided a fuel delivery system comprising a pump in accordance with any one of the preceding paragraphs.

It will be appreciated that preferred and/or optional features of each aspect of the invention may be incorporated alone or in appropriate combination in the other aspects of the invention also.

In the following description, directional or relative references such as 'upper', 'lower', 'above' and 'below', relate to the orientation of the features as illustrated in the drawings, but such references are not to be considered limiting. The skilled reader will appreciate that pumps in accordance with embodiments of the invention may be oriented differently to the manner depicted in the drawings in practice.

Referring to <FIG> and <FIG>, an example of a pump <NUM> for use in a fuel delivery system generally comprises a main housing <NUM> and a plunger housing <NUM>. The plunger housing <NUM> is coupled to the main housing <NUM>, for example by threaded fastening means, so as to define a compression chamber <NUM> therebetween.

The main housing <NUM> comprises an inlet valve <NUM> and an outlet valve <NUM>. The inlet valve <NUM> controls the flow of fuel into the compression chamber <NUM>. The outlet valve <NUM> allows pressurised fuel to be conveyed from the compression chamber <NUM> to downstream components of the fuel delivery system, such as a common rail accumulator (not shown).

In more detail, the inlet valve <NUM> comprises a valve member <NUM> arranged for reciprocating movement within a valve bore <NUM> defined by the main housing <NUM>. The valve member <NUM> comprises a valve stem <NUM> and a valve head <NUM>. The valve head <NUM> projects into the compression chamber <NUM>. The diameter of the valve head <NUM> is sized so as to be larger than the diameter of the valve bore <NUM> at a lower end thereof where it opens into the compression chamber <NUM>. With this configuration, the lower opening of the valve bore <NUM> defines a valve seat <NUM>. When the inlet valve <NUM> is in a closed state, the valve head <NUM> closes against the valve seat <NUM> so as to prevent the flow of fuel therepast. Movement of the inlet valve <NUM> is effected by means of an actuator <NUM> (e.g. a solenoid actuator) and a valve spring <NUM>. The valve spring <NUM> is arranged so as to urge the valve head <NUM> away from the valve seat <NUM> toward an open position. When the pressure in the compression chamber <NUM> rises during a pumping stroke of the pump <NUM> this produces a force which acts against the valve spring <NUM>. Closing of the inlet valve <NUM> can then be effected by energizing the solenoid actuator <NUM> to exert an additional closing force on the valve stem <NUM> which is sufficient to overcome the force of the valve spring <NUM> such that the valve head <NUM> closes against the valve seat <NUM>.

The plunger housing <NUM> comprises an axial plunger bore <NUM> within which a plunger <NUM> is arranged for reciprocating movement therein. The plunger <NUM> is substantially cylindrical in shape. A lower end <NUM> of the plunger <NUM> is arranged, in use, to be in contact with an engine-driven cam (not shown). A plunger return spring <NUM> is disposed around the plunger housing <NUM>. The return spring <NUM> abuts a shoulder of the plunger housing <NUM> at one end thereof and abuts a cap <NUM> affixed to the lower end <NUM> of the plunger <NUM> at the opposite end thereof.

The upper end <NUM> of the plunger <NUM> comprises a close clearance annular portion <NUM> having a larger diameter relative to the portions of the plunger <NUM> disposed immediately above and below the close clearance annular portion <NUM> in the axial direction of the plunger <NUM>. The close clearance annular portion <NUM> is sized so as to be a close clearance fit with respect to the adjacent wall of the plunger bore <NUM>. The upper end <NUM> of the plunger <NUM> further comprises a recess or bowl <NUM> formed in an end face thereof. The base <NUM> of the bowl <NUM> extends below the close clearance annular portion <NUM>.

In use, the plunger <NUM> is driven upwards during a pumping stroke of the pump <NUM> so as to reduce the volume of the compression chamber <NUM> and thus to pressurise fuel disposed therein. When the pressure of the fuel in the compression chamber <NUM> reaches a threshold value it is sufficient to cause the outlet valve <NUM> to open such that the pressurised fuel can be conveyed to the common rail accumulator.

In order to achieve the desired pressure in the compression chamber <NUM> during a pumping stroke, the compression chamber <NUM> must be substantially sealed so as to prevent or substantially eliminate egress of fuel from the compression chamber <NUM> other than via the outlet valve <NUM>. To facilitate this, an annular seal <NUM> is provided on a lower face <NUM> of the main housing <NUM>. The annular seal <NUM> encircles both the valve head <NUM> of the inlet valve <NUM> and an outlet port <NUM> which is in fluid communication with the outlet valve <NUM>. The annular seal <NUM> has a cross section which tapers so as to define a relatively narrow annular contact surface at its extremity. Accordingly, when the plunger housing <NUM> is attached to the main housing <NUM>, an upper face <NUM> of the plunger housing <NUM> abuts the annular seal <NUM>. The tapered shape of the annular seal <NUM> serves to concentrate the contact force between the respective opposed faces of the main housing <NUM> and the plunger housing <NUM> over a small surface area to form a secure seal between them.

Sealing of the compression chamber <NUM> during a pumping stroke of the plunger <NUM> is also achieved by means of dilation of the upper end <NUM> of the plunger <NUM>. During a pumping stroke of the plunger <NUM>, the pressure of fuel in the compression chamber <NUM> increases as the volume of the compression chamber <NUM> reduces. As mentioned previously, the close clearance annular portion <NUM> of the plunger <NUM> is a close clearance fit with the adjacent wall of the plunger bore <NUM>. The pressure in the plunger bore <NUM> below the close clearance annular portion <NUM> is maintained at substantially atmospheric pressure by means of a low pressure leak return path. Accordingly, there is a large pressure differential across the wall of the bowl <NUM> in the region below the close clearance annular portion <NUM>. This pressure differential causes the bowl <NUM> to dilate radially which, in turn, moves the close clearance annular portion <NUM> closer to the adjacent wall of the plunger bore <NUM>. Thus, although a small amount of fuel may escape past the close clearance annular portion <NUM> to the plunger bore <NUM> below, the dilation of the plunger <NUM> reduces any such leakage of fuel from the compression chamber <NUM>.

A potential disadvantage of the arrangement described with reference to <FIG> and <FIG> is that, when the plunger housing <NUM> is attached to the main housing <NUM>, for example by threaded fastening means, it is possible that the forces applied to the upper face <NUM> of the plunger housing <NUM> in the vicinity of the annular seal <NUM> cause distortions to the plunger bore <NUM>. Accordingly, this may lead to the plunger <NUM> sticking or seizing in the plunger bore <NUM> during operation of the pump. In particular, during normal operation, the upper end of the plunger bore <NUM> will typically dilate during a pumping stroke due to the high pressure in the compression chamber <NUM>. However, as the pressure in the compression chamber <NUM> decays after a pumping stroke, both the bowl <NUM> of the plunger <NUM> and the adjacent wall of the plunger bore <NUM> will return to their static dimensions. When this happens, distortions to the upper end of the plunger bore <NUM> may cause the close clearance annular portion <NUM> of the plunger to stick or seize within it, preventing or impeding the movement of the plunger <NUM> on its return stroke.

A further disadvantage of the above described arrangement is that, in order to maintain the volumetric efficiency of the pump <NUM>, it is necessary for the valve head <NUM> to be sized so as to occupy a substantial portion of the space within the bowl <NUM> of the plunger <NUM> when the plunger <NUM> is at the top of the pumping stroke. This is because the close clearance annular portion <NUM> of the plunger <NUM> must be disposed higher up the body of the plunger <NUM> than the base <NUM> of the bowl <NUM> in order to enable dilation of the bowl <NUM>. However, increasing the depth of the bowl <NUM> necessarily increases the volume of the compression chamber <NUM> which reduces volumetric efficiency. Thus, in order to compensate, the volume of the valve head <NUM> is correspondingly increased so as to occupy sufficient volume within the compression chamber <NUM> so that the volumetric efficiency is preserved. However, increasing the size of the valve head <NUM> is not desirable because it increases the inertia of the valve member <NUM> and the greater mass of the valve member <NUM> may lead to increased wear of the valve seat <NUM> and an increased likelihood of cracking or failure of the valve member <NUM>.

Referring to <FIG> and <FIG> an embodiment of a pump <NUM> in accordance with the present invention will now be described. The pump <NUM> generally comprises a main housing <NUM> and a plunger housing <NUM>. The plunger housing <NUM> is coupled to the main housing <NUM>, for example by threaded fastening means, so as to define a compression chamber <NUM> therebetween.

In more detail, the inlet valve <NUM> comprises a valve member <NUM> arranged for reciprocating movement within a valve bore <NUM> defined by the main housing <NUM>. The main housing <NUM> comprises a substantially cylindrical projecting portion or boss <NUM> on a lower face <NUM> thereof. The valve bore <NUM> extends though the projecting portion <NUM> and is co-axial therewith.

The valve member <NUM> comprises a valve stem <NUM> and a valve head <NUM>. The valve head <NUM> projects into the compression chamber <NUM>. The diameter of the valve head <NUM> is sized so as to be larger than the diameter of the valve bore <NUM> at a lower or distal end of the projecting portion <NUM> where it opens into the compression chamber <NUM>. With this configuration, the lower opening of the valve bore <NUM> in the projecting portion <NUM> defines a valve seat <NUM>. When the inlet valve <NUM> is in a closed state, the valve head <NUM> closes against the valve seat <NUM> so as to prevent the flow of fuel therepast. Movement of the inlet valve <NUM> is effected by means of an actuator <NUM> (e.g. a solenoid actuator) and a valve spring <NUM>. The valve spring <NUM> is arranged so as to urge the valve head <NUM> away from the valve seat <NUM> toward an open position. When the pressure in the compression chamber <NUM> rises during a pumping stroke of the pump <NUM> this produces a force which acts against the valve spring <NUM>. Closing of the inlet valve <NUM> can then be effected by energizing the solenoid actuator <NUM> to exert an additional closing force on the valve stem <NUM> which is sufficient to overcome the force of the valve spring <NUM> such that the valve head <NUM> closes against the valve seat <NUM>.

The upper end <NUM> of the plunger <NUM> comprises a close clearance annular portion <NUM> having a larger diameter relative to the portion of the plunger <NUM> disposed immediately below the close clearance annular portion <NUM> in the axial direction of the plunger <NUM>. The close clearance annular portion <NUM> is sized so as to be a close clearance fit with respect to the adjacent wall of the plunger bore <NUM>. The upper end <NUM> of the plunger <NUM> further comprises a recess or bowl <NUM> formed in an end face thereof. The base <NUM> of the bowl <NUM> extends below the close clearance annular portion <NUM>. Put another way, the close clearance annular portion <NUM> is disposed between the upper end <NUM> of the plunger <NUM> and the base <NUM> of the bowl <NUM> in the axial direction of the plunger <NUM>.

An annular seal <NUM> is provided on a lower face <NUM> of the main housing <NUM>. The annular seal <NUM> encircles both the projecting portion <NUM> of the main housing <NUM> and an outlet port <NUM> which is in fluid communication with the outlet valve <NUM>. The annular seal <NUM> has a tapering cross section towards its contact with the plunger housing <NUM>. Because the cross section tapers in this way, it defines a relatively narrow annular contact surface at its extremity. Accordingly, when the plunger housing <NUM> is attached to the main housing <NUM>, an upper face <NUM> of the plunger housing <NUM> abuts the annular seal <NUM> and the tapered cross-section of the annular seal <NUM> serves to concentrate the contact force between the respective opposed faces of the main housing <NUM> and the plunger housing <NUM> over a small surface area, thereby forming a secure seal between them.

When the plunger housing <NUM> is coupled to the main housing <NUM>, the projecting portion <NUM> of the main housing <NUM> and the valve head <NUM> of the inlet valve <NUM> are received within the upper end of the plunger bore <NUM>. Accordingly, the projecting portion <NUM> occupies part of the volume of the compression chamber <NUM>. The diameter of the projecting portion <NUM> is sized so as to be a clearance fit with the adjacent wall of the plunger bore <NUM> in order to provide a flow path for pressurised fuel out of the compression chamber <NUM> to the outlet port <NUM> during a pumping stroke of the pump <NUM>.

With this arrangement it will be appreciated that, when the plunger <NUM> is at the top of the pumping stroke, the enlarged annular portion <NUM> of the plunger <NUM> is disposed lower in the plunger bore, with respect to the upper face <NUM> of the plunger housing <NUM>, when compared to the arrangement described above with reference to <FIG> and <FIG>. This is because the uppermost portion of the plunger bore <NUM> is occupied by the projecting portion <NUM> of the main housing <NUM>. Accordingly, in the presently described embodiment, the likelihood that the plunger <NUM> will become stuck or seized in the plunger bore <NUM> due to distortion of the of the plunger housing <NUM> in the vicinity of the upper end of the plunger bore <NUM> is reduced. This is because, when the plunger housing <NUM> is attached to the main housing <NUM> and the upper face <NUM> of the plunger housing <NUM> is compressed against the annular seal <NUM> of the main housing <NUM>, any distortion caused to the upper end of the plunger bore <NUM> occurs in a region adjacent to the projecting portion <NUM> of the main housing <NUM>, and not in the region of the close clearance annular portion <NUM> of the plunger (when it is at or close to the top of the pumping stroke).

A further advantage of the presently described embodiment is that the size of the valve head <NUM> is reduced compared to the arrangement described with reference to <FIG> and <FIG>. As described previously, in order to maintain a suitable volumetric efficiency of the pump <NUM>, it is preferable for the compression chamber <NUM> to be sized so as to minimise the amount of fuel compressed in the compression chamber <NUM> over and above that which will be expelled at the desired pressure through the outlet valve <NUM>. To this end, in the arrangement of <FIG> and <FIG>, the valve head <NUM> is sized so as to occupy at least some of the dead volume which is created by having a plunger <NUM> with a bowl <NUM>.

In the presently described embodiment, the position of the close clearance annular portion <NUM> of the plunger <NUM> in the plunger bore <NUM> when the plunger <NUM> is at the top of the pumping stroke is lower with respect to the top of the plunger bore <NUM> than in the arrangement described with reference to <FIG> and <FIG>. This advantageously means that the close clearance annular portion <NUM> is further away from the part of the plunger bore <NUM> which is susceptible to distortions when the plunger <NUM> is at or close to the top of the pumping stroke. Moreover, with the presently described arrangement, because this displacement of the uppermost position of the close clearance annular portion <NUM> within the plunger bore <NUM> is achieved, in part, by virtue of the valve seat <NUM> being disposed within the plunger bore <NUM>, this permits the close clearance annular portion <NUM> to be located closer to the upper end <NUM> of the plunger <NUM> itself. In turn, this means that the depth of the bowl <NUM> in the plunger <NUM> can be reduced, while still allowing for the base <NUM> of the bowl <NUM> to be below the lower extremity of the close clearance annular portion <NUM>. By reducing the depth of the bowl <NUM>, this allows for a corresponding reduction in the size of the valve head <NUM>. Reduction of the volume of the valve head <NUM> may, advantageously, reduce wear of the valve seat <NUM> and reduce the likelihood of damage to components of the pump <NUM>, e.g. fracturing of the valve member <NUM>.

Claim 1:
A pump (<NUM>) for a fuel delivery system, the pump (<NUM>) comprising:
- a main housing (<NUM>) and a plunger housing (<NUM>) arranged to couple to the main housing (<NUM>) so as to define a compression chamber (<NUM>) therebetween,
- the main housing (<NUM>) and the plunger housing (<NUM>) comprising respective first and second opposed faces (<NUM>, <NUM>) which are arranged to form a seal therebetween;
- wherein the main housing (<NUM>) has a projecting portion (<NUM>) which projects from the first face (<NUM>) of the main housing (<NUM>) through an opening in the second face (<NUM>) of the plunger housing (<NUM>) into a plunger bore (<NUM>);
- wherein the main housing (<NUM>) comprises an inlet valve (<NUM>) for controlling the flow of fuel into the compression chamber (<NUM>), the inlet valve (<NUM>) comprising a valve member (<NUM>) arranged for reciprocating movement within a valve bore (<NUM>) defined by the main housing (<NUM>), wherein the valve bore (<NUM>) is formed, at least in part, in the projecting portion (<NUM>); and
- wherein the projecting portion (<NUM>) comprises a valve seat (<NUM>) disposed at a distal end thereof, the valve member (<NUM>) comprising a valve head (<NUM>) arranged to close against the valve seat (<NUM>) when the inlet valve (<NUM>) is in a closed state.