Patent Application
20110120418
The invention relates to high-pressure fuel pumps for use in common rail fuel injection systems for supplying high-pressure fuel to an internal combustion engine, and in particular to an improved pump head for use in such fuel pumps. The invention has particular application in compression ignition (diesel) engines.
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.
A known pump head of a high-pressure fuel pump is shown in
An inlet valve arrangement 32 is located above the pumping chamber 24 (in the orientation shown on the page). The inlet valve arrangement 32 is shown more clearly in the enlarged view of
The inlet valve arrangement 32 shown in
Another known pump head design is shown in U.S. Pat. No. 7,363,913. The pump head removes the need for a high pressure seal between high and low regions of the pump head as the feeding annulus occupies a position external to the pump head housing, and receives fuel at low pressure directly from an entry drilling. However, despite this benefit, the pump head has other disadvantages. For example, the pump head housing has a large pocket machined in its upper surface to define the feeding chamber. A projection of the pump head housing body extends into the feeding chamber and radial drillings provided in this projection define flow paths for fuel past the valve seat and into the pumping chamber when the inlet valve arrangement is open. From a manufacturing perspective the housing is difficult to machine due to its complex formation, particularly due to the requirement for the pocket in the upper surface of the pump head housing and the projection that extends into this pocket. The provision of drillings in the projection also reduces the rigidity of the housing.
It is an aim of the present invention to provide a high performance pump head that overcomes the above problems associated with known designs.
According to a first aspect of the 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, a pumping chamber defined within the pump head housing, and an inlet valve arrangement for controlling fuel flow into the pumping chamber. The inlet valve arrangement includes a valve member moveable between open and closed positions in response to fuel pressure within a gallery. The gallery communicates with an external chamber defined by a closure member mounted externally to the pump head housing, such that, in use, the gallery communicates with a source of low-pressure fuel via the external chamber. The pump head housing includes a projection which is received within the closure member to locate the closure member on the pump head housing.
The provision of the projection on the pump head housing to locate the closure member provides several advantages. The radially outer surface of the projection may engage with a radially inner surface of the closure member to locate the closure member on the projection. This enables an O-ring seal to be located in a groove provided in the radially outer surface of the projection to provide a seal against fuel flow out of the external chamber. In addition, the projection provides a large volume of material in which to form drillings to define one or more flow paths between the external chamber and the gallery, without compromise to the rigidity of the structure. The projection is compatible with applications where a plurality of such flow paths are required to enable higher inlet flow rates. High flow rates are particularly desirable in the context of applications in which the pump head is required to operate at high speed and to pressurise the common rail to high pressures.
The external chamber acts in a similar way to the feeding annulus 54 of the pump head shown in
The valve member preferably engages with a valve seat defined by the valve bore to control fuel flow between the external chamber and the gallery/pumping chamber. The pump head housing may also define the gallery, and/or a fuel path between the external chamber and the gallery. The fuel path may be provided by at least one drilling in the pump head housing, which extends between the gallery and the external surface of the pump head housing, in communication with the external chamber. This arrangement negates the need for a separate valve body 36 such as that shown in
In a preferred embodiment of the invention, the inlet valve body feature of known pump heads is defined by the pump head housing itself, i.e. it is integrated into the pump head.
The pump head may further comprise a low-pressure supply passage for conveying low pressure fuel from the source to the external chamber, wherein the low-pressure supply passage is defined, in part, within the projection. Preferably, therefore, the low-pressure supply passage opens at an external surface of the pump head housing within the external chamber. This arrangement is particularly advantageous, because it eliminates potential leakage paths between high and low pressure regions, and hence negates the need for a high-pressure seal. By eliminating the high-pressure seal, a source of high structural stress is removed which allows for cheaper processing because there is less need for complex and costly stress-reduction geometries and surface finishes. Furthermore, the number of parts is reduced further, and manufacture and assembly consequently facilitated. In addition, higher flow rates and higher fuel pressures can be reliably achieved by the pump head, which provides improved performance.
Preferably, the valve member is guided within a valve bore defined in the pump head housing. The resulting guided valve provides high pump performance in terms of both flow and pressure.
The valve member may be biased into the closed position by a spring engaged between an end portion of the valve member and an upper surface of the projection.
In a particularly preferred embodiment, the at least one fuel path opens at the upper surface of the projection outside the diameter of the spring. This ensures the flow of fuel into the gallery (and hence the pumping chamber) from the source of low-pressure fuel does not flow through the spring, which guards against cavitation problems and results in a less restricted flow. The spring life may also be benefited by this configuration. The relatively large volume of the projection on the pump head housing facilitates this layout of the flow path(s).
It is preferable for the gallery to be defined within the pump head housing.
The invention also relates to a fuel pump for use in a common rail fuel injection system, wherein the fuel pump includes at least one pump head as set out in the first aspect of the invention.
The fuel pump may further comprise a main pump housing through which a drive shaft for the fuel pump extends, the fuel pump further comprising means for fixing the pump head to the main pump housing, said means being adapted to fix the closure member to the pump head also.
By adapting a fixing means to serve the function of both attaching the pump head to the main pump housing, and attaching the closure member to the pump head housing, the closure member arrangement can be provided on the pump without the need for additional fixing parts.
Preferably, the closure member is provided with at least one aperture for receiving a fixing of the fixing means.
By way of example, the pump head housing may be provided with a passage for receiving the fixing, the fixing extending further into the main pump housing to affix the pump head thereto.
According to a second aspect of the 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, a pumping chamber defined within the pump head housing and an inlet valve arrangement for controlling fuel flow into the pumping chamber. The inlet valve arrangement includes a valve member moveable between open and closed positions in response to fuel pressure within a gallery. The gallery communicates with an external chamber defined by a closure member mounted externally to the pump head housing, such that, in use, the gallery communicates with a source of low-pressure fuel via the external chamber. A spring acts on the valve member to urge the valve member into the closed position in which fuel is unable to flow into the pumping chamber. At least one fuel path is provided between the external chamber and the gallery, wherein the at least one fuel path opens at a surface of the pump head housing outside the diameter of the spring.
As described above, this provides the advantage that the spring is not located in a direct flow path for low-pressure fuel into the pumping chamber.
According to a third aspect of the invention, there is provided a fuel pump for use in a common rail fuel injection system, the fuel pump comprising a main pump housing, a pump head having a pump head housing, a pumping chamber defined within the pump head housing and an inlet valve arrangement for controlling fuel flow into the pumping chamber. The inlet valve arrangement includes a valve member moveable between open and closed positions in response to fuel pressure within a gallery, wherein the gallery communicates with an external chamber. Closure means is mounted externally to the pump head housing to define the external chamber, whereby, in use, the gallery communicates with a source of low-pressure fuel via the external chamber. The fuel pump further comprises means for fixing the pump head to the main pump housing, said means being adapted to fix the closure means to the pump head also.
As described above, where the fixing means serves to attach the pump head to the main pump housing, and to attach the closure member to the pump head housing, the closure member arrangement can be provided on the pump without the need for additional fixing parts.
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 second and third aspects of the invention also.
For the avoidance of doubt, relative terms such as ‘upper’ and ‘lower’ in the above description have been used for convenience, in order to describe the pump head in the orientation shown on the page. It should be understood that the actual orientation of the pump head will depend upon the geometry of the fuel pump, and as such these relative terms should not be interpreted as limiting the scope of the invention.
Reference has already been made to
a is an enlarged view of an inlet valve arrangement of the pump head shown in
In order that the invention may be more readily understood, reference will now be made, by way of example only, to
a is an enlarged view of an inlet valve arrangement of the pump head shown in
Referring to
The pumping plunger 116 extends into a pumping chamber 124 defined by the upper portion 112 of the pump head housing 110, at an upper end 126 of the plunger bore 118. Fuel is pressurised within the pumping chamber 124 by the reciprocal motion of the plunger 116 within the plunger bore 118. Whilst not shown in
The fuel pump head includes an inlet valve arrangement 132, which is shown more clearly in the enlarged view of
The conical body 147 is housed within the pump head housing 110, adjacent to the pumping chamber 124, whilst the neck 151 extends from the conical body 147, coaxially with the plunger bore 118, away from the pumping chamber 124. The neck 151 is slidable within a valve bore 148 defined by the upper portion 112 of the pump head housing 110. Consequently, the inlet valve member 146 is guided by the pump head housing 112 itself at the lower end of the neck 151. In this configuration, therefore, the pump head housing 112 serves as the inlet valve body 36 of
The neck 151 of the inlet valve member 146 extends beyond the inlet valve bore 148, and out from an upper surface 153 of the pump head housing 110. The upper surface 153 of the pump head housing 153 is planar and substantially flat. In this configuration, a proximal end 155 of the neck 151 (adjacent to the conical body 147) remains within the pump head housing 110, whilst a distal end 157 of the neck 151 remains outside the pump head housing 110 and carries a spring seat 159. A valve return spring 163 is provided between the upper surface 153 of the pump head housing 110 and the spring seat 159 to urge the inlet valve member 151 closed against a valve seat 161 when fuel pressure within the gallery 150 drops below a predetermined level. Although not shown in
A closure member in the form of a valve cap 142 is mounted on top of and, thus, externally to, the upper surface 153 of the pump head housing 110. The valve cap 142 is provided over the distal end 157 of the neck 151 of the inlet valve member 146 (i.e. the part of the inlet valve member 146 that is outside the pump head housing 110). The valve cap 142 is generally top-hat-shaped, i.e. comprising a dome 162 with an annular flange 164 extending radially outwards from the dome 162. The dome 162 is located over the part of the inlet valve member 146 that is external to the pump head housing 110, whilst the annular flange 164 lies flush against the upper surface 153 of the pump head housing 110. The valve cap 142 is secured to the pump head housing 110 using suitable fixing means (not shown), for example screws or bolts, that extend through apertures 166 provided in the annular flange 164. The screws or bolts that pass through the apertures 166 into the pump head housing 110 are conveniently the same fixings that are used to attach the pump head housing to the main pump body (not shown). Beneficially, therefore, no separate fixing means is required to secure the valve cap 142 to the pump head housing 110.
In this configuration, the valve cap 142 defines an external chamber 168 within which the distal end 157 of the valve member 146 is housed. The external chamber 168 communicates with the gallery 150 defined in the pump head housing 110, and acts as the feeding annulus 54 of the pump head of
An entry drilling 128 and a plurality of radial feed drillings 152 (only one of which is shown in
Although for some applications, in order to ensure adequate flow rate into the pumping chamber 124, several radial drillings 152 may be required to define a flow path between the external chamber 168 and the gallery 150, because the drillings 152 are formed in the bulk of the pump head housing 110 no loss of rigidity occurs. Because the drillings 152 are provided in the bulk of the pump head housing 110 this also enables a greater plurality of drillings to be provided, if required, without compromise to the rigidity of the structure. A further benefit of the invention, over that in the prior art U.S. Pat. No. 7,363,913, is that the spring 163 is not in the flow path for fuel between the external chamber 168 and the gallery 150 (and hence the pumping chamber 124) because the radial drillings 152 communicate with the external chamber 168 at a position outside the spring diameter, with the spring 163 being located entirely external to the pump head housing 110. In U.S. Pat. No. 7,363,913 the flow of fuel into the radial drillings that feed the pumping chamber passes through the spring, which can give rise to cavitation and erosion problems, as well as contributing a resistance to fuel flow.
A low-pressure seal 158, for example an O-ring or gasket, is provided between the valve cap 142 and the upper surface 153 of the pump head housing 110. However, the need for a high-pressure seal is eliminated in the invention because the low-pressure feed chamber 168 is provided by the valve cap 142, which is externally-mounted on the pump head housing, thereby eliminating any potential leakage paths between high and low pressure regions. This arrangement removes one source of potential leakage, and one source of high structural stress, which enables higher pressures to be achieved in the pump head. In addition, manufacturing is simplified and costs are reduced because there is no need to machine a low-pressure feed chamber within the pump head housing 110, and there is less need for complicated and expensive stress-reduction geometries and surface finishes. Furthermore, by integrating the inlet valve body with the pump head housing 110, the number of parts is reduced, and the possibility of leakage is reduced further. The pump head has high pump performance in terms of both fuel flow and pressure, because the valve member 146 is guided by the pump head housing 110.
It will be appreciated that many modifications can be made to the components described above without departing from the inventive concept. For example, the 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.
Furthermore, whilst the upper flat surface 153 shown in
The radially outer surface of the projection 112a faces, and engages, a radially inner surface of the valve cap 142. The external chamber 168 is therefore defined between the internal surface of the dome 162, and the upper surface of the raised portion 112a. In this configuration, the low pressure seal 158 is provided between the radial internal surface of the dome 162 and the radial outer surface of the raised portion 112a, for example by an O-ring 170 surrounding the raised portion 112a. The O-ring 170 is located within an annular groove 171 provided in the radially outer surface of the raised portion 112a and serves to minimise the loss of fuel from the external chamber 168.
Although the provision of the raised portion 112a slightly complicates the machining process for the pump head housing 110, it provides the additional benefit that the cap 142 is located on the pump head housing 110. The apertures 166 in the cap 142 can therefore be aligned more readily with passages 172 through the pump head housing which receive the fixing means for the main pump body also.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0812888.6 | Jul 2008 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2009/050834 | 7/13/2009 | WO | 00 | 1/14/2011 |
