Fuel injection pump

The invention provides a fuel injection pump comprising a pump housing and a pumping arrangement associated therewith, wherein the pumping arrangement includes a pumping plunger and a plunger drive arrangement, the pumping plunger having a first end reciprocably received within a plunger bore provided in the pump housing and a second end coupled to the plunger drive arrangement. A biasing spring is provided having first and second spring ends, the first spring end coupled to a spring plate member associated with the pump housing and the second spring end coupled the plunger drive arrangement. The pump housing includes first and second portions aligned on a common axis, the upper portion including a further bore in which at least an upper portion of a locking pin is receivable and wherein the spring plate member defines support means for supporting a lower end portion of the locking pin.

TECHNICAL FIELD

This invention relates to a fuel injection pump, and particularly a fuel injection pump suitable for use with a compression-ignition internal combustion engine.

BACKGROUND TO THE INVENTION

FIGS. 1A and 1Bshow perspective and cross section views, respectively, of a known fuel injection pump, indicated generally as2, which is suitable for use as a means of supplying pressurised fuel to a fuel injector of an internal combustion engine. The fuel pump2includes a generally tubular pump housing4having an axially disposed bore6within which a pumping plunger8is slidable. The pumping plunger8has a lower end10(in the orientation shown inFIG. 1) that is coupled to a drive arrangement12for transmitting reciprocating motion to the plunger8. The drive arrangement12includes a tappet body14and an associated cam roller16on which a cam member acts, in use (the cam member itself is not shown). A biasing means in the form of a helical spring17is received over the plunger8such that the spring17is disposed between the pump housing4and the tappet body14. An upper end18of the biasing spring17abuts a spring plate20attached to a lower end of the pump housing4and a lower end22of the spring17abuts the tappet body14, the spring17thus serving to bias the plunger8downwards in the orientation shown.

As shown inFIG. 1B, an upper end of the pump housing24defines a cup-shaped recess26into which a lower end of an outlet valve28is received. The lower end of the outlet valve28closes off the plunger bore6and defines a pressurisation chamber30between it and the upper end of the plunger8.

In use, the cam member drives the plunger8via the drive arrangement12on a pumping stroke during which fuel within the chamber30is pressurised. When the pressure of fuel within the pumping chamber30reaches a predetermined pressure, the outlet valve28opens to permit pressurised fuel to flow through the outlet valve28. Although not shown inFIGS. 1A and 1B, a fuel conduit may be attached to the outlet valve28to convey fuel to a fuel injector, for example.

As the cam member rotates further, the pumping plunger8passes a top dead centre position and thus commences a return stroke under the force of the spring17. During the return stroke, fuel is permitted to fill the pumping chamber30through a fill/spill port32which is connected to a source of fuel at a relatively low pressure.

In order to vary the delivery volume of the fuel pump2, the pumping plunger8is provided with a control arm40which extends radially away from the approximate mid point of the plunger8. Angular movement of the control arm40varies the angular position of the pumping plunger8.

In use, the control arm40engages a fuel delivery rack (not shown) via a control pin42that depends downwardly from a radially outer end of the control arm40. The position of the fuel delivery rack is determined by the engine governor and the rack, in turn, acts on the control arm40to cause radial movement of the pumping plunger8about its longitudinal axis. The radial position of the pumping plunger8determines the point of the pumping stoke that a spill helix41(not shown onFIG. 1A) registers with the low pressure spill port32, thus terminating fuel pressurisation earlier, or later, in the pumping stroke depending on the degree and direction of rotation of the pumping plunger8. The radial position also controls the start of fuel pressurisation by registration of the upper surface of the pumping plunger8with the spill port32. The variation of the effective stroke between the upper surface of the plunger8and the spill helix varies the fuel delivery to the associated engine.

Typically, a plurality of such fuel pumps2are installed into the cylinder block of an engine, one per cylinder. In order for the engine to run smoothly, the pumps2must be installed with the control arms40located in exact positions corresponding to a predetermined delivery setting, hereafter referred to the “reference position”.

Due to production tolerances of the components of the fuel pump2, each fuel pump2provides a given delivery volume with the pumping plunger8in a slightly different relative angular position. Thus, each fuel pump2is subject to a calibration process during manufacture in which the control arm40of each pump2is set into the correct position to provide a desired delivery at a given speed defined by a customer, for example an engine manufacturer. Once calibrated, the control arm40is locked into its reference position by a locking pin44associated with the pump. The locking pin44is received within a longitudinally extending bore46provided in the pump housing4that is approximately parallel to the longitudinal axis of the fuel pump2.

As can be observed inFIGS. 1A and 1B, the locking pin44is supported along substantially its entire length except for its tip48that protrudes from the open lower end of the bore46to engage a depression or pit (not shown) provided in the control arm40. It is desirable for the locking pin44to be supported close to the spring plate20in this way to avoid unwanted movement of the control arm40or bending of the locking pin44during the process of delivering the fuel pump2to a customer. Movement of the control arm40would affect the reference position of the control arm, thus negating the pump calibration exercise.

A problem with the above described arrangement is that due to assembly requirements, and the need to support the locking pin44along its length, the pump housing4is required to be manufactured with a lower portion50which is eccentric to an upper portion52of the pump housing4, i.e. axially offset. The process of machining the pump housing4to include eccentrically disposed upper and lower portions is complicated and, therefore, expensive. Consequently, it is desirable to provide a fuel injection pump that confers the same advantages and packaging profile as the fuel pump ofFIGS. 1A and 1B, but which may be manufactured more readily so as to reduce production effort and overall unit costs.

SUMMARY OF INVENTION

It is against the above background that the invention provides a fuel injection pump comprising a pump housing and a pumping arrangement associated with the pump housing wherein the pumping arrangement includes a plunger and a plunger drive arrangement, the plunger having a first end reciprocably received within a plunger bore provided in the pump housing and a second end coupled to the plunger drive arrangement. Further, the fuel injection pump is provided with a biasing spring having first and second spring ends, the first spring end coupled to a spring plate member associated with the pump housing and the second spring end coupled to the plunger drive arrangement. The pump housing includes first and second portions aligned on a common axis, the upper portion including a second bore in which at least an upper portion of a locking pin is received and wherein the spring plate member defines a support arrangement for supporting a lower end portion of the locking pin.

The invention confers a significant advantage in terms of manufacturing effort and the costs associated therewith. By virtue of the invention, the requirement to manufacture an eccentrically disposed lower end housing portion is avoided since an arrangement is provided to support the lower end of the locking pin on the spring plate.

An importance difference between the fuel injection pump of the invention and the prior art pump as described above with reference toFIG. 1is that, in the invention, the first and second housing portions are disposed along a common axis. In other words, the first and second portions are substantially concentric with one another. It should be understood that this is not the case with the fuel injection pump ofFIGS. 1A and 1Bin which the configuration of the pump housing is in the form of two cylinders, one disposed eccentrically relative to the other.

In order to permit control of the fuel delivery volume of the fuel injection pump, the pumping plunger preferably includes a radially extending control arm, which is moveable back and forth to cause the pumping plunger to move angularly within its bore. The control arm is set to a predetermined reference position to provide the required fuel pump delivery setting.

In the preferred embodiment of the invention, the spring plate member takes the form of first and second axially spaced concentric annular members, each of which defines a respective aperture. Preferably, each aperture is centrally disposed and of circular form.

One of said apertures preferably has substantially the same diameter as the second housing portion so as to define a press fit therewith. This feature thus enables the spring plate member to be attached to the pump housing. Conversely, the aperture of the other annular member is smaller, having substantially the same diameter as the pumping plunger, so as to allow the plunger to pass slidably therethrough.

Preferably, the spring plate member includes a lateral slot defined between the first and second annular members through which the control arm of the pumping plunger extends. The slot therefore serves to guide angular movement of the control arm.

Although the spring plate member may be manufactured as a multi-part assembly, preferably it is a one-piece cast, or milled, component such that the first and second annular members are joined by an integral semi-circular wall.

In the preferred embodiment, the support arrangement is a further aperture provided in the spring plate member. Preferably the further aperture is formed on a rim of one of the annular members, the dimension of the aperture being selected such that the lower end portion of the locking pin may be inserted and retracted. Preferably, the aperture is formed on a lobed region of one of the annular members.

From a second aspect, the invention provides a spring plate member for use with a fuel injection pump as described above. It will be appreciated that preferred and/or optional features of the fuel injection pump of the first aspect of the invention may also be incorporated within the spring plate member of the second aspect of the invention, alone or in appropriate combination.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 2A and 2Bshow a fuel injection pump100in accordance with the invention which comprises three main structural sections: a central pump housing102; an outlet valve arrangement106connected to an upper, head region104of the pump housing102; and a pumping arrangement110connected to a lower, neck region108of the pump housing102.

The pump housing102has a generally tubular configuration and the two regions104,108are separated by a shoulder109. The pump housing102further includes a longitudinal through-bore112extending along its longitudinal axis ‘A’ which defines an opening at each end of the pump housing102. It should be mentioned at this point that the terms ‘upper’ and ‘lower’ are used with reference to the orientation of the fuel injection pump100as shown in the drawings and, as such, are not intended to limit the fuel injection pump100to a particular orientation.

At an upper face of the head region104, the bore112widens to define a cup shaped recess114that screw-threadingly receives a lower end of the outlet valve arrangement106. The outlet valve arrangement106includes a pump outlet116which is connectable to a fluid conduit for the purposes of conveying pressurised fuel to an associated fuel injector (neither the fluid conduit nor the fuel injector are shown inFIGS. 2A and 2B). The function of the outlet valve arrangement106is to provide the fuel pump100with a delivery output at a predetermined pressure, although its structural details will not be described in further detail here.

The pumping arrangement110includes a pumping plunger120, a portion of which is received within the pump housing bore112such that a pumping chamber122is defined within the bore112between an upper end of the pumping plunger120and a lower end of the outlet valve arrangement106. The pumping plunger120defines a sliding clearance with the bore112such that it is able to reciprocate back and forth.

The pumping arrangement110also includes pump drive means124for driving the pumping plunger120in a reciprocating manner. The pump drive means124includes a tappet body126which is coupled to the lower end of the pumping plunger120and which defines a downwardly depending arch128shaped to receive a cam roller130. Although not shown in the drawings, in use, the cam roller130is arranged to contact an engine-driven cam. As is known in the art, the engine driven cam provides a lobed cam surface that the cam roller130rides over as the cam rotates, to cause the pumping plunger120to reciprocate within the bore112.

In use, the pumping plunger120is driven on a pumping stroke during which fuel within the pumping chamber122is pressurised. When the pressure of fuel within the pumping chamber122reaches a predetermined pressure, the outlet valve106activates to permit pressurised fuel to flow through the pump outlet116. Control over the fuel delivery quantity is determined by means of the effective pumping stroke, as described previously with reference toFIGS. 1A and 1B. Following a pumping stroke, the pumping plunger120will commence a return stroke.

In order to assist the pumping plunger120to perform a return stroke following a pumping stroke, the pump drive means124includes a plunger biasing means in the form of a helical spring132received over the pumping plunger120such that it is disposed between the pump housing102and the tappet body126. An upper end132aof the spring132abuts a spring plate member140attached to a lower end of the neck region108of the pump housing102and a lower end132bof the spring132abuts the tappet body126. It should be appreciated that although the spring132is shown abutting the spring plate member140and the neck region108inFIGS. 2A and 2B, other coupling arrangements are possible: for example, a spring abutment member (e.g. a washer or shim) may be interposed between the spring132and the neck region108and/or the spring132and the spring plate member140. The spring132biases the pumping plunger120outwardly from the bore112. During the return stroke, fuel is permitted to fill the pumping chamber122through a spill/fill port142which is connected to a source of fuel at a relatively low pressure, for example a low pressure displacement pump (not shown).

In order to vary the delivery volume of the fuel pump100, the pumping plunger120is provided with a control arm143which extends radially away from an approximate mid-point of the plunger120. A control pin144extends downwardly from the control arm143and serves to engage with a fuel delivery rack (not shown inFIGS. 2A and 2B) when the fuel pump100is in situ in an engine. The position of the fuel delivery rack is determined indirectly by the engine governor. Movement of the rack causes angular movement of the pumping plunger120about its longitudinal axis. The angular position of the plunger120determines the point of the pumping stoke that a spill helix145registers with the low pressure port spill/fill port142, thus terminating fuel pressurisation.

Referring to the pump housing102in more detail, the head region104is provided with an outwardly projecting flange150at its uppermost end that serves to abut against a peripheral edge of a pocket formed in an engine cylinder block into which the head region104is received, in use (the engine cylinder block and the pocket are not shown inFIGS. 2A and 2B). The remaining length of the head region104is of substantially uniform diameter except for a radial recess152that constitutes a low pressure fuel gallery to which the spill/fill port142is connected. Two annular sealing rings154flank the radial recess152, one on either side, the function of which is to define a close fit with the pocket so as to prevent fuel leaking from the recess152when the fuel pump100is in operation.

The head region104also includes a second through-bore156that is offset from the longitudinal axis A such that it extends approximately parallel thereto. A locking pin158is received by the bore156such that a lower portion of the locking pin158protrudes out of a lower bore opening defined in the shoulder109. The protruding locking pin158extends adjacent the neck region108to terminate substantially in line with the lower end thereof. An upper end of the locking pin158extends from an upper bore opening defined in the upper face of the head region104and permits access to the locking pin158for insertion and removal.

It should be appreciated that the neck region108of the pump housing102is in coaxial alignment with the head region104, along the longitudinal axis A. Put another way, the neck region108is concentrically disposed relative to the head region104, thus sharing a common axis. This is to be compared with the known fuel pump2inFIGS. 1A and 1Bin which the two housing portions are eccentrically disposed relative to one another. Arranging the head and neck regions104,108concentrically realises a significant manufacturing advantage, as will be explained in further detail later.

Due to the concentric alignment of the head and neck regions104,108, the lower portion of the locking pin158is not guided by the pump housing102itself. However, to compensate for this, the spring plate member140is provided with support means for supporting, or guiding, the lower end of the locking pin158.

Referring also toFIG. 3, which shows the spring plate member140in more detail, the spring plate member140comprises a generally cylindrical body160except for a lateral cut-out region or slot162, the depth of which is approximately half the diameter of the spring plate member140. The formation of the slot162divides the spring plate member140into upper and lower annular members160a,160bjoined by an integral semi-circular wall160c. The control arm143affixed to the pumping plunger120extends radially outwards through the lateral slot162of the spring plate member140. The shape of the slot permits the control arm143to move angularly about the axis A of the pumping plunger120by approximately 120 degrees, thus causing corresponding movement of the pumping plunger120. Typically, however, the control arm143only needs to move through approximately 90 degrees in order to control fuel delivery between minimum and maximum settings.

The upper annular member160ais provided with a central circular aperture164having a diameter that substantially corresponds to the diameter of the neck region108of the pump housing102such that the spring plate member140defines a press fit with the lower end of the neck region108. It should be noted that although the aperture164is circular in this embodiment, this is only so that the aperture164is able to accommodate the lower end of the neck region108, which is also circular. Accordingly, the aperture164could adopt another shape, if required, to accommodate a differently shaped neck region108.

The lower annular member160bis also provided with a central circular aperture166, but which is smaller than the aperture164, such that its diameter is a little larger than that of the pumping plunger120. As a result, when the spring plate member140is press fitted onto the neck region108of the pump housing102, the plunger120passes through the aperture166with a sliding clearance.

The lower surface of the lower annular member160bis provided with a downwardly depending annular projection168, concentric with the aperture166, which is received into the upper end132aof the biasing spring132. The projection168thus serves as a fixing point for the spring132to prevent lateral play between the spring132and the spring plate member140.

The upper annular member160aprovides the support means for the locking pin158in the form of a lobe170that extends slightly outward from the otherwise circular rim of the upper annular member160a. The lobe170is provided with an aperture172within which the lower end of the locking pin158is receivable such that the tip of the locking pin158can pass through the aperture172and engage the surface of the control arm143.

By virtue of this arrangement, the locking pin158is securely supported against lateral movement, or bending, which avoids loss of calibration accuracy. Furthermore, supporting the locking pin158in this way enables the neck region108of the pump housing102to be formed concentric with the head region104which significantly reduces manufacturing complexity and, therefore, unit costs of the fuel pump100.

It will be appreciated that various modifications may be made to the above described fuel pump without departing from the scope of the invention, as defined by the claims. For example, it is not essential for the spring plate member140to be press fit onto the neck region108of the pump housing102. Instead, it may be secured thereon by other means: for example, by welding or by a set screw. Furthermore, although the spring plate member140has been described as being a unitary cast component, it should be appreciated that this need not be the case and the spring plate member140could be an assembly of two or more parts: for example, a cast, or milled, component for mating with the neck region108, and for cooperating with the spring132, and a sheet metal flange for providing support to the locking pin158. In conclusion, this invention can be embodied in numerous forms. Reference should therefore be made to the appended claims, and not to the foregoing specific description, in determining the broadest scope of the invention.