Technical Field
[0001] The invention relates to a fuel pump for use in a common rail fuel injection system
for supplying high pressure fuel to a compression ignition internal combustion engine.
Background Art
[0002] In a known common rail fuel pump of radial pump design, for example as described
in EP 1 184 568A, three pumping plungers are arranged at equi-angularly spaced locations
around an engine driven cam. The surface of the cam cooperates with all three of the
plungers, so that as the cam is driven each of the plungers is caused to reciprocate
within a plunger bore to cause pressurisation of fuel within a respective pump chamber.
The delivery of fuel from the pump chambers to a common high pressure supply line
is controlled by means of respective delivery valves associated with each of the pumps.
The high pressure line supplies fuel to a common rail, or other accumulator volume,
for delivery to the downstream injectors of the common rail fuel system.
[0003] In one known fuel pump of the aforementioned type, each of the plungers is in connection
with an associated tappet that serves to drive movement of the plunger within its
bore. The cam carries a ring or rider that travels over the surface of the cam as
it rotates to impart drive to the tappets, and hence to the plungers, causing the
plungers to reciprocate in a phased, cyclical manner. The eccentricity of the cam
surface causes each tappet, and its respective plunger, to be driven inwardly within
its bore to reduce the volume of the pump chamber. During this forward, pumping stroke,
fuel within the respective pumping chamber is pressurised to a relatively high level.
The tappets are urged outwardly from the tappet bores by means of fluid pressure within
a working chamber which, in addition to a force of a plunger return spring, serves
to urge the plunger in an outward direction to perform a return stroke during which
the pump chamber volume is increased.
[0004] The housing for pump arrangements of this type has three radially extending lobes,
each for housing one of the plungers and its associated components. Such arrangements
can be difficult to assemble and, in addition, require a relatively large accommodation
space due to the radial layout of the plungers. In addition, due to the large radial
separation between the three pump units, it is difficult to combine the high pressure
flows from each pump chamber to a common high pressure outlet.
[0005] It is one object of the present invention to provide a fuel pump for use in a common
rail fuel injection system, which alleviates or avoids at least one of the aforementioned
problems.
Summary of the Invention
[0006] According to the present invention, there is provided a fuel pump for use in delivering
fuel to a common rail of an internal combustion engine, comprising at least first
and second pump units that are axially spaced along a camshaft to form an in-line
pump assembly, wherein each pump unit includes a pumping plunger, a drive member that
is cooperable with the pumping plunger and driven, in use, by an associated cam arrangement
to impart drive to the plunger upon rotation of the camshaft, and a pump chamber within
which fuel is pressurised for delivery to the common rail, wherein the pump chambers
of the first and second pump units are arranged within a common pump head, which is
mounted upon a main pump housing having a main housing opening through which the camshaft
extends, and wherein the pump head defines a high pressure supply passage to which
pressurised fuel is delivered from each of the pump chambers and from where pressurised
fuel is supplied to the common rail, in use.
[0007] In a preferred embodiment of the invention the fuel pump includes first, second and
third pump units of substantially similar form.
[0008] It is one advantage of the present invention that the plungers are mounted axially
along a camshaft, and therefore the pump is relatively compact. The accommodation
space required for the assembled pump is much less than that required for pumps of
radial design, even when three pump units are provided, as the need for two radial
lobes to house two of the plungers is avoided. The high accuracy requirement for angular
spacing of the flats on the cam rider and the corresponding housing features, as in
known radial pump designs, is also avoided.
[0009] As the overall length of the pump is much less than for known in-line pump designs,
the pump has advantages of stability in the limited space available in current engine
designs. By virtue of the compact design it is also possible to mount the pump within
the engine such that the centre of mass of the pump is relatively close to the fixings
to the engine, thereby reducing dynamic forces acting on, and deflection of, the pump
due to engine vibration and road shocks.
[0010] It is a further advantage that the hydraulics required to connect the pump chambers
to a common outlet or high pressure supply passage are simplified as all three pump
chambers are closely spaced apart, preferably along an axis that is parallel to the
axis of the camshaft.
[0011] The present invention requires only one component (the pump head) to withstand high
fuel pressures, and the main pump housing is not exposed to highly pressurised fuel.
There is also no requirement to transfer high pressure fuel across mating housing
parts, as it is contained at all times within the pump head unit.
[0012] In a preferred embodiment, the pump head is provided with first, second and third
plunger bores within which the pumping plunger of a respective one of the first, second
and third pump units is movable. Preferably the first, second and third plunger bores
are formed integrally in the pump head and the pump housing. The main pump head preferably
includes an extension or projection that extends into the opening provided in the
main pump housing, thereby to provide an increased length for provision of the first,
second and third plunger bores. It is easy to form a projection on the pump head,
and it provides the benefit that the sealing lengths of the plungers are relatively
long so that leakage of high pressure fuel from the pump chambers is reduced.
[0013] In one embodiment, the main pump housing is provided with an additional opening or
recess, preferably extending approximately laterally to the axis of the camshaft,
said additional opening being shaped for cooperation with an outer surface of each
of the drive members to guide axial movement of the drive members, but to substantially
prevent lateral (i.e. lateral relative to the drive member axis) and angular movement
thereof. In this case, the main pump housing is preferably formed from a material
having good wear resistant properties, for example cast iron.
[0014] Preferably, the outer surface of each drive member is of part-cylindrical form. Advantageously,
the main housing opening has a correspondingly shaped wall for cooperation with said
part-cylindrical outer surfaces. The pump head has an underside for abutment with
the main pump housing. Preferably, the inner surface of each drive member is also
of part-cylindrical form. Preferably the outer walls have a greater degree of curvature
than the inner walls, and the radius of the outer walls is preferably selected to
be less than half the overall width of the drive member.
[0015] In one embodiment, the pump head may be shaped for cooperation with the outer surfaces
of the drive members to guide axial movement of the drive members, throughout substantially
a complete forward stroke of each drive member, but to substantially prevent lateral
(i.e. lateral in a direction relative to the axis of the drive members) and angular
movement of the drive members.
[0016] In this embodiment, the pump head may be provided with a skirt extension that is
shaped for cooperation with the outer surfaces of the drive members to guide said
axial movement thereof. Again, preferably, the outer surfaces of the drive members
are of part-cylindrical form.
[0017] In a preferred embodiment, the drive member of each pump unit takes the form of a
tappet that is cooperable, in use, with a cam ring rider of the associated cam arrangement
to impart movement to the associated plunger upon rotation of the camshaft.
[0018] The pump head is preferably provided with first, second and third inlet supply passages
for delivering fuel to the pump chambers of the first, second and third pump units
respectively, wherein the inlet passages are arranged substantially parallel to each
other and substantially perpendicular to the high pressure supply passage.
[0019] The fuel pump of the present invention may, but need not, be manufactured to include
first, second and third cams arrangements for imparting drive to the pumping plungers.
[0020] If provided, the first and second cam arrangements preferably include first and second
cams respectively that are integrally formed with the camshaft, and wherein the third
cam arrangement includes a third cam that is a separate component, the first, second
and third cams being arranged at axially spaced locations along the camshaft.
[0021] It will be appreciated, therefore, that references in this document to the first,
second and cams being arranged on the camshaft, shall to taken to include the cams
being integral with the shaft, or separate parts mounted upon the shaft.
[0022] It may be preferable to provide front and rear bearing journals, for example bearing
tubes, on the camshaft to define first and second bearing surfaces respectively for
a respective end one of the cams. The bearing journals may be integrally formed with
the shaft, or may be separate parts forming an interference fit with the shaft.
[0023] The rear bearing journal preferably has a diameter greater than that of the front
bearing journal, said rear bearing journal diameter being equal to or greater than
the diameter of the main housing opening to permit direct mounting of the rear bearing
journal upon, or support of the rear bearing journal by, the main housing.
[0024] In a further preferred embodiment, each of the first, second and third cam arrangements
includes a cam rider member of tubular form that is driven, in use, by an associated
one of the cams and which serves to impart drive to the associated drive member as
it rides over the surface of the associated cam.
[0025] It will be appreciated that the fuel pump of the present invention is not limited
to having three pump units, and a greater or lesser number of pump units may be provided,
if required.
Brief Description of the Drawings
[0026] The present invention will now be described, by way of example only, with reference
to the accompanying drawings in which:
Figure 1 is a sectional side view of a first embodiment of the fuel pump of the present
invention;
Figure 2 is an end sectional view of the fuel pump shown in Figure 1;
Figure 3 is a perspective view of a main pump housing part of the fuel pump in Figures
1 and 2, with the pump head removed;
Figure 4a is a perspective view of a tappet forming part of the fuel pump in Figures
1 to 3;
Figure 4b is a plan view of the tappet shown in Figure 4a;
Figure 5 is a perspective view, shown from the underside, of the pump head for mounting
upon the main pump housing shown in Figure 3;
Figure 6 is a perspective view of the assembled fuel pump illustrated in Figures 1
to 5, with the pump head mounted on the main pump housing;
Figure 7 illustrates a pump head forming part of an alternative embodiment of the
fuel pump in which tappets of the pump are guided by the pump head, rather than by
the main pump housing;
Figure 8 is a perspective view of a first type of cam arrangement for use with the
fuel pump illustrated in Figures 1 to 7, in which two of the cams are formed integrally
with the cam drive shaft; and
Figure 9 is a perspective view of a second type of cam arrangement for use in the
fuel pump illustrated in Figures 1 to 7, in which the cams are separate from the cam
drive shaft.
Detailed Description of the Preferred Embodiments
[0027] Referring to Figures 1 to 3, there is shown a fuel pump of a first embodiment for
use in supplying high pressure fuel to a common rail, or accumulator volume, of a
fuel injection system. The fuel pump includes a first housing part in the form of
a main pump housing 10 having an axially extending main housing opening or bore 13
through which a cam drive shaft 12 extends. The main pump housing 10 projects, at
its front end 10a, to accommodate the near full length of the camshaft 12, and is
closed at its back end by a rear closure plate 29.
[0028] A second housing part in the form of a pump head or block 34 is a separate part from,
and is mounted upon, the main pump housing 10, and extending laterally from the main
housing opening 13 for the camshaft 12. The pump head 34 includes an extension or
projection 34a that projects into an additional opening or aperture 11 provided in
the main pump housing 10. The main pump housing 10 is provided with two ears 55 (visible
in Figures 2 and 3 only), which act to stiffen the housing 10 around the opening 11.
[0029] The camshaft 12 has a central drive axis 14 about which the shaft 12 is driven, in
use, to impart rotation to first, second and third cams, or cam forms, 16, 18, 20
of respective first, second and third cam arrangements. The cams 16, 18, 20 are arranged
on the shaft 12 at axially spaced locations and oriented about the drive axis 14 at
angularly offset locations. The first, second and third cams 16, 18, 20 are of substantially
identical form and each one is mounted or formed eccentrically upon the camshaft 12
such that it is offset relative to the other two cams by substantially 120 degrees.
[0030] As the camshaft 12 is rotated, in use, the cams 16, 18, 20 impart drive to a respective
one of first, second and third pumping plungers 22, 24, 26 so that motion of each
plunger is phased by 120 degrees relative to the other two plungers. Each plunger
22, 24, 26 forms a part of one of three pump units 2, 4, 6 respectively that are axially
spaced along the drive shaft 12 to form an "in-line" assembly. The three pump units
2,4, 6 are substantially identical in construction and, where possible for simplicity,
only a first one of the pump units 2 will be described in detail. The pumping plunger
22, 24, 26 of each unit 2, 4, 6 is driven by its respective cam 16, 18, 20 to perform
a pumping cycle. As the camshaft 12 rotates, each plunger 22, 24, 26 is caused to
reciprocate within a respective plunger bore 28, 30, 32 provided in the pump head
34 so as to cause pressurisation of fuel within a respective pump chamber 23, 25,
27 defined by the blind end of the associated bore 28, 30, 32.
[0031] Each of the first, second and third cams 16, 18, 20 is arranged to cooperate with
a respective cam rider 36, 38, 40 that, in turn, cooperates with a respective first,
second or third drive member 48, 50, 52. The cam riders 36, 38, 40 are of substantially
tubular form and are mounted relative to the shaft 12 with their axes parallel to
the shaft axis 14. The drive members take the form of tappets 48, 50, 52, each of
which is coupled to the associated plunger 22, 24, 26, such that as the shaft 12 rotates
the cam riders 36, 38, 40 ride over the surface of the associated cam 16, 18, 20,
imparting drive to the tappets 48, 50, 52, and hence to the plungers 22, 24, 26, to
cause the plungers to reciprocate within the plunger bores 28, 30, 32.
[0032] As the camshaft 12 rotates, the tappets 48, 50, 52 and the pumping plungers 22, 24,
26 are together driven to perform a pumping or forward stroke, during which the tappet
and its plunger are driven radially outward of the shaft 12 (i.e. vertically upwards
in Figures 1 and 2) to reduce the volume of the associated pump chamber, followed
by a return stroke during which the tappet and its plunger are urged in a radially
inward direction (i.e. vertically downwards in Figures 1 and 2) to increase the volume
of the pump chamber. During the return stroke of the plunger and its tappet, fuel
at relatively low pressure fills the associated pump chamber and during the pumping
stroke fuel within the pump chamber is pressurised to a relatively high level, as
discussed further below.
[0033] Figure 2 illustrates an end sectional view of the pump, and in which only one of
the plungers 22 and its associated tappet 48 are visible. It can be seen that the
tappet 48 is of substantially U-shaped or channelled cross section, and includes a
base portion 48a and first and second substantially vertical side portions or walls
48b. The lower surface (in the orientation shown) of the tappet base portion 48a engages
with a flat 42 on the associated cam rider 36. The second and third tappets 50, 52
associated with the second and third plungers 24, 26 are of substantially identical
form, having side walls 50b, 52b respectively (as shown in Figure 3), and for convenience
only the features of the first tappet 48 are shown and described in detail below.
[0034] Referring also to Figure 4a, the upper surface of the tappet base portion 48a is
provided with first and second recesses 60, 62 for locating a respective one of a
first pair of plunger return springs 50a, 50b. The opposite end of each plunger return
spring 50a, 50b abuts the pump head 34a, as shown in Figure 2. In this embodiment,
the plunger 22 and the tappet 48 are not coupled together so as to permit relative
movement between these parts during the pumping cycle. The plunger return springs
50a, 50b apply a return biasing force to the tappet 48, and hence to its plunger,
to drive the plunger return stroke and to ensure contact is maintained between the
tappet 48 and the cam rider 36 at all times throughout the pumping cycle. The base
portion 48a of the tappet 48 is also provided with a centrally located boss 58 (also
just visible in Figure 2) to limit the area for precision machining required to set
the height of the plunger relative to the pump chamber 23.
[0035] Referring also to Figure 4b, the side walls 48b of the tappet 48 have outer surfaces
56 of part-cylindrical form of radius R1, and inner surfaces 59 also of part-cylindrical
form. The outer surfaces 56 of the tappet side walls 48b are shaped so as to have
a greater degree of curvature than the inner surfaces 59. More specifically, the radius,
R1, of the outer surfaces 56 is selected to be less than the width, W, of the tappet,
where W = 2 * R2, and R2 is the radius of the circle (shown by the dotted lines 51)
which has the same degree of curvature as the inner surfaces 59 of the side walls
48b. Thus, the tappet 48 is not merely a right-circular cylinder with cut-away sides,
but is specifically shaped and dimensioned so as to provide unwanted angular movement
of the tappet, in use, about an axis aligned with the plunger axis. Although not visible
in the sections shown, the second and third plungers 24, 26 are also provided with
associated pairs of plunger return springs in a similar manner.
[0036] In an alternative embodiment (not shown in the accompanying drawings), the plunger
22 and the tappet 48 may be coupled together by means of a plate in connection with
the lower end of the plunger 22. The plate may be secured to the plunger 22 by means
of a clip, through an interference fit or through another integral projection or part
thereof that co-operates with the plunger to provide a secure means of fixing. The
plate locates within the side walls 48b of the tappet (as identified in Figure 3,
for example) and provides a platform on either side of the plunger 22 to define an
abutment surface for a respective one of the plunger return springs 50a, 50b. One
side of the plate may be provided with appropriately shaped recesses, each for accommodating
one end of the associated spring 50a, 50b. On the opposite side of the plate, a boss,
for example, may be provided for cooperation with one of the recesses 60 or 62 on
the facing side of the tappet 48. Cooperation between the tappet 48 and the plate
in this way, and between the plunger and the tappet, serves to prevent unwanted rotation
of the plate, in use.
[0037] Figure 3 shows the main pump housing 10 with the pump head 34 removed to illustrate
the location of the tappets 48, 50, 52. The opening 11 in the pump housing 10 has
facing side walls, each of which is shaped to define three regions of part-cylindrical
form. Each of the total of six part-cylindrical wall regions is shaped to cooperate
with a correspondingly formed outer surface of an associated one of the tappet side
walls 48b, 50b, 52b. This cooperation of parts, and the shape and dimensions of the
outer surfaces 56 of the tappet walls 48b, 50b, 52b, serves to guide movement of the
tappets 48, 50, 52 in an axial direction (i.e. in the direction along the tappet axis,
extending radially from the camshaft 12) over its stroke, but substantially prevents
undesirable lateral and angular movement of the tappets 48, 50, 52. It can be seen
from the location of the third tappet 52 in the view shown in Figure 3 that, in use,
the tappets 48, 50, 52 are driven such that at the end of their forward strokes the
tappet side walls 48b, 50b, 52b are caused to extend through the upper, open end of
the opening 11 and into a clearance space 61 (visible in Figure 2) defined by a recess
in the underside of the pump head 34.
[0038] Figure 5 shows the pump head 34 for mounting upon the main pump housing 10 in Figure
3. The view of the pump head 34 is from the underside, which abuts the upper surface
of the main pump housing 10 when the pump is assembled. The surface of the underside
of the pump head 34 is provided with recesses 54 having inner walls defining three
regions of part-cylindrical form. Part way through the tappet forward stroke the tappets
48, 50, 52 project from the opening 11 in the main pump housing 10 (as shown in Figure
3), into the clearance space 61, although they do not contact the inner walls of the
recesses 54.
[0039] When the pump head 34 is mounted upon the main pump housing 10, the part-cylindrical
regions of the recesses 54 are generally in alignment with the part-cylindrical regions
of the wall of the opening 11. The extension 34a on the pump head 34 is clearly shown
in Figure 5 and, when the pump head 34 is mounted upon the main pump housing 10, the
extension 34a extends between the plungers 22, 24, 26 and their return spring pairs
50a, 50b so as to provide an increased length for the plunger bores 28, 30, 32. By
providing an increased length for the provision of the plunger bores 28, 30, 32, the
sealing length of each plunger is increased and, thus, losses due to fuel leakage
from the pump chambers 23, 25, 27 can be reduced. Figure 6 shows the fuel pump when
assembled with the pump head 34 in Figure 5 mounted upon the main pump housing 10
in Figure 3.
[0040] Referring again to Figure 1, the first pump chamber 23 associated with the first
plunger 22 communicates with an inlet supply passages 64 (also visible in Figure 6)
that is provided in the pump head 34. Three inlet supply passages 64 are provided
in total, one for each pump chamber 23, 25, 27, and each receives fuel from a relatively
low pressure fuel source, for example a transfer pump. The inlet passages 64 are provided
in the pump head 34 in a substantially parallel arrangement.
[0041] Each inlet passage 64 is provided with a respective inlet valve arrangement including
an inlet valve 66 that is operable in response to the pressure difference between
fuel in the inlet supply passage 64 and fuel within the respective pump chamber 23,
25, 27 to move between open and closed states. When an inlet valve 66 is in its open
state, fuel is supplied through the inlet supply passage 64 to the pump chamber and
when the inlet valve 66 is in its closed state the supply of fuel to the pump chamber
is prevented.
[0042] Each pump chamber 23, 25, 27 also communicates with a respective high pressure delivery
passage 68 provided in the pump head 34 for delivering fuel to the common rail. Each
delivery passage 68 is provided with a delivery valve arrangement including a delivery
valve 70 that is operable in response to the pressure difference between fuel in the
) associated pump chamber and fuel in the delivery passage 68 to move between open
and closed states. When a delivery valve 70 is in its open state, fuel is supplied
from the pump chamber to the delivery passage 68, and hence to the common rail. When
the delivery valve 70 is in its closed state the back flow of high pressure fuel from
the common rail into the pump chamber 23 is prevented.
[0043] As can be seen in Figures 5 and 6, the pump head 34 is provided with a common high
pressure supply passage 72, which is oriented substantially perpendicular to the inlet
passages 64 and which extends axially from the rear of the pump. The high pressure
supply passage 72 receives high pressure fuel from the delivery passages from each
pump chamber 23, 25, 27 and supplies fuel from the pump to a downstream common rail
or other accumulator volume for fuel.
[0044] The inlet and delivery valves 66, 70 are of known construction and further details
may be found, for example, in our co-pending European patent application EP 1184568A2
and British patent application GB 2,384,529A. Pressurisation of fuel within the pump
chambers occurs during the pumping stroke of the associated plunger, during the period
for which both the inlet and delivery valves are closed. When fuel is pressurised
to a level that is sufficient to open the delivery valve 70, pressurised fuel is supplied
through the delivery passage to the common supply passage 72 and, hence, to the common
rail.
[0045] During the return stroke of the plunger, fuel pressure downstream of the pump chamber
23 is higher than that within the pump chamber 23 and the delivery valve 70 is urged
closed. During the period of the return stroke for which the inlet valve 66 is urged
open, fuel at relatively low pressure is supplied to the pump chamber 23 through the
inlet supply passage 64 ready for commencement of the following pumping stroke. This
cycle of pumping is described in further detail in the aforementioned patent applications,
and in any case would be familiar to those skilled in this field and so will not be
described here in further detail.
[0046] The fuel pump shown in Figures 1 to 6 is intended for use with a low pressure fuel
pump, such as a transfer pump, which delivers fuel to the inlet supply passages 64
provided in the pump head 34 through a common inlet passage 57 (shown in dashed lines
in Figure 1). The common inlet passage 57 is provided with an inlet metering valve
arrangement (also not shown) and is located towards the front end 10a of the main
pump housing 10.
[0047] Although not illustrated in the accompanying drawings, it is convenient to mount
the transfer pump upon the rear closure plate 29 of the main pump housing 10, and
to drive the transfer pump by means of a shaft extension in connection with the camshaft
12. The transfer pump supplies fuel at transfer pressure to the common inlet passage
57 for delivery to the inlet passages 64 and, hence, to the pump chambers 23, 25,
27. In order to pass fuel to and from the transfer pump, a communication hole may
be provided in each of the ears 55 of the main pump housing 10, one through which
fuel is drawn into the transfer pump at the rear of the main pump housing 10 and one
through which fuel is supplied from the transfer pump, to the inlet metering valve
arrangement and then to the common inlet passage 57.
[0048] It is a particular advantage of the fuel pump of this embodiment that it is convenient
to combine the high pressure fuel flow from each pump chamber 23, 25, 27 into the
common high pressure supply passage 72 as all three of the pump chambers 23, 25, 27,
and their corresponding delivery passages 68, are provided in the common pump head
34. This provides a benefit over known radial pump designs, where the pump chambers
are angularly spaced around the shaft and, hence, the combining of three high pressure
flows to a common supply passage is difficult to achieve. There is also a requirement
for only the pump head 34 to be capable of withstanding the high pressures of fuel
within the pump chambers 23, 25, 27, and the pump head component can be formed easily
with the extension 34a for increasing the sealing lengths of the plungers.
[0049] It is a further advantage of the "in-line" pump unit assembly that the plunger stroke
length is comparable to that achieved in known radial pump designs, but the height
of the assembled pump above the axis 14 of the camshaft 12 is moderate, and the overall
height of the pump is much less than in radial pump designs. Essentially, the reduced
height is achieved by avoiding the need for an extended protrusion of two pump units
beneath the camshaft axis 14, as in known radial pump designs. The requirement for
extremely accurate angular spacing of the flats on the cam rider, and the corresponding
housing features, in a radial pump design is also avoided.
[0050] In the embodiment of the fuel pump described previously, the main pump housing 10
is typically formed from cast iron. The use of a cast iron housing 10 is beneficial
in that it helps to limit wear of the tappets 48, 50, 52, in use, as their movement
is guided along the vertical tappet axis through cooperation with the part-cylindrical
regions in the wall of the opening 11. The wear resistant properties of cast iron
stem from the high carbon content, which acts as a solid lubricant.
[0051] In an alternative embodiment of the pump to that described with reference to Figures
1 to 6, the requirement to form the main pump housing 10 from cast iron can be avoided
by guiding movement of the tappets not by the wall of the opening 11 in the main pump
housing 10 but through cooperation with a part of the pump head. This alternative
embodiment is shown in Figure 7, and only the differences between this and the embodiment
of Figures 1 to 6 will be described in detail, with similar and identical parts numbered
with like reference numerals.
[0052] Referring to Figure 7, the pump head 134 is provided with a skirt extension 75 forming
an additional extension from the underside of the pump head 134 and enclosing the
extension 34a. In this embodiment, the opening 11 in the main pump housing 10 is formed
with substantially straight walls (not illustrated in Figure 7), rather than providing
the part-cylindrical wall regions. When the pump head 134 is mounted upon the main
pump housing 10, the skirt extension 75 and the extension 34a are received within
the opening 11, and the straight walls of the opening 11 in the main pump housing
10 align with outer straight walls 78 of the skirt 75 to locate the pump head 134.
The skirt extension 75 has an inwardly facing surface 80 that is provided with regions
of part-cylindrical form for cooperation with the correspondingly formed part-cylindrical
outer surfaces of the tappet side walls 48b, 50b, 52b. The skirt extension 75 therefore
serves to guide movement of the tappets 48, 50, 52 in an axial direction (i.e. in
the direction along the tappet axis, extending radially from the camshaft 12), but
prevents undesirable lateral and angular movement thereof.
[0053] The wear resistant properties of case hardened alloy steel, from which the pump head
134 is formed, are superior to those of cast iron. Furthermore, as the wear resistant
requirement for the main pump housing 10 is removed, the main pump housing 10 may
be formed from aluminium, for example, rather than cast iron. This provides a manufacturing
advantage as a cheaper and more accurate process can be used to form the housing 10,
for example die casting.
[0054] It will be appreciated that a difference between the pump head 34 in Figure 5 and
the pump head 134 in Figure 7 is that in the Figure 5 embodiment the pump head 34
plays no part in guiding the tappets 48, 50, 52 as the tappets, 48, 50, 52 project
from the main pump housing 10 into the clearance space 61 at the end of their forward
strokes and at the start of their return strokes. In contrast, in the embodiment of
Figure 7 movement of the tappets 48, 50, 52 is guided through cooperation with the
pump head skirt 75 throughout substantially the complete pumping stroke. The embodiment
of Figure 7 also provides all of the aforementioned advantages of the first embodiment
of the invention.
[0055] Referring in particular to Figure 2, and also to Figure 8, the outer surface of each
cam rider 36, 38, 40 is provided with a flat 42, 44, 46 respectively (only cam rider
38 is shown in Figure 8). By way of example, the flat 42 on the first cam rider 36
is engaged with the tappet 48 coupled to the first plunger 22. The cam riders 38,
40 for the second and third units 4, 6 are arranged in a similar manner.
[0056] The second and third cams 18, 20 are formed integrally with the shaft 12, but as
it is difficult to machine all three cams 16, 18, 20 to be integral with the shaft
12 the first cam 20 is a separate part. The first cam 16 forms an interference fit
with the shaft 12 and is of larger diameter than the third cam 20 so that, upon assembly,
the shaft is able to pass through it while retaining enough strength in the cam 16
to implement the required interference fit.
[0057] Front and rear bearing journals (the rear bearing journal 76 only being visible in
Figure 9) may be mounted on the shaft 12 so that the front bearing journal 74 abuts
against the first cam 16 and the rear bearing journal 76 abuts against the third cam
20. The bearing journals form an interference fit with the shaft 12 and serve to 'trap'
the first and third cam riders 36, 40 in position. The bearing journals are capable
of achieving high peripheral speeds and are selected to have a relatively large diameter
so as to provide extra area per unit length of the shaft and, thus, provide support
for high camshaft loads. The bearing journals thus provide plain bearing journal regions
of increased area (defined by their axial length and their diameter) and, hence, load-bearing
capability.
[0058] In an alternative embodiment, as shown in Figure 9, all three of the cams 16, 18,
20 are substantially identical components separate from the shaft 12 and mounted thereon
by means of an interference fit. The cam riders 36, 38, 40 are mounted upon their
respective cams 16, 18, 20 with the second, middle cam rider 38 being trapped between
the first and third cam riders 36, 40. In this embodiment both front and rear bearing
journals 74, 76 are visible, with the first bearing journal 74 abutting against the
first cam 16 and the second bearing journal 76 abutting against the third cam 20.
[0059] The axial length of the rear bearing journal 76 (i.e. the length of the journal 76
along the axis of the shaft 12) is less than that of the front bearing journal 74
so as to limit the overall axial length of the assembly. Although not illustrated
in the accompanying drawings, the diameter of the rear bearing journal 76 is selected
to be equal to or greater than the diameter of the main housing bore 13 to enable
the journal 76 to be supported by or mounted upon the housing 10 without a requirement
for an intermediate component or components.
[0060] It is an advantage of the embodiment in Figure 9 that the shaft 12 is of simple rod-like
construction, with appropriate end features in the form of bearing journals 74, 76,
thus facilitating convenient and economical manufacture. It is a further advantage
of the fuel pump of the present invention that the over all length of the assembly
is much less than is known for in-line pump designs. The pump therefore has advantages
of instability in the limited space available in current engine designs. By virtue
of its compact design it is possible to mount the pump within the engine such that
the pump centre of mass is relatively close to that part which fixes to the engine
(e.g. the ears 55 shown in Figure 1). The pump does not therefore suffer excessive
dynamic forces and deflection caused by engine vibration and road shocks.
[0061] To aid assembly of the cam, bearing journals and cam ring riders on the camshaft,
it is convenient to use a temporary tool, such as a rod, that extends through the
openings of these components. The rod is a close fit with the openings and serves
to locate the components in their correct angular and axial positions relative to
the shaft, prior to insertion of the camshaft, which when inserted forms an interference
fit in the openings and supports the aforementioned parts.
[0062] If a cast iron housing 10, first and second static bearing surfaces 79, 81 (identified
in Figure 1) for the front and rear bearing journals 74, 76 respectively may be cut
directly into the front end 10a of the main pump housing 10, therefore avoiding the
need to provide additional bearing support bushes for the journals. The pump head
34 is typically formed from case hardened alloy steel.
[0063] It will be appreciated that the use of the phrase "common rail" is not intended to
be in any way limiting, and that the fuel pump described in this document may be used
for delivering fuel to any form of accumulator volume or store for pressurised fuel,
from where fuel is subsequently supplied to injectors of an associated engine.
1. A fuel pump for use in delivering fuel to a common rail of an internal combustion
engine, the fuel pump comprising:
at least first and second pump units (2,4,6) that are axially spaced along a camshaft
(12) to form an in-line pump assembly, wherein each pump unit includes a pumping plunger
(22,24,26), a drive member (48,50,52) that is cooperable with the pumping plunger
and driven, in use, by an associated cam arrangement (16,18,20) to impart drive to
the plunger upon rotation of the camshaft, and a pump chamber (23,25,27) within which
fuel is pressurised for delivery to the common rail,
wherein the pump chambers (23,25) of the first and second pump units (2,4) are
arranged within a common pump head (34), which is mounted upon a main pump housing
(10) having a main housing opening (13) through which the camshaft extends (12), and
wherein the pump head defines a high pressure supply passage to which pressurised
fuel is delivered from each of the pump chambers and from where pressurised fuel is
supplied to the common rail, in use.
2. A fuel pump as claimed in Claim 1, including first, second and third pump units (2,4,6)
spaced axially along the camshaft (12).
3. A fuel pump as claimed in Claim 2, wherein the pump head (34) is provided with first,
second and third plunger bores (28,30,32) within which the pumping plunger (22,24,26)
of a respective one of the first, second and third pump units (2,4,6) is movable.
4. A fuel pump as claimed in Claim 3, wherein the main pump housing (10) is provided
with an additional opening (11) and the pump head includes a projection (34a) that
extends into the additional opening, thereby to provide an increased length for the
first, second and third plunger bores (28,30,32).
5. A fuel pump as claimed in Claim 3 or Claim 4, wherein the main housing opening (13)
is shaped for cooperation with an outer surface 56 of each of the drive members (48,50,52)
to guide axial movement of the drive members, but to substantially prevent lateral
and angular movement thereof.
6. A fuel pump as claimed in Claim 4 or Claim 5, wherein the outer surface 56 of each
drive member (48,50,52) is of part-cylindrical form, and wherein the additional opening
(11) in the main pump housing (34) has a correspondingly shaped wall for cooperation
with said part-cylindrical outer surfaces 56.
7. A fuel pump as claimed in any of Claims 1 to 4, wherein the pump head (34) is shaped
for cooperation with an outer surface 56 of each of the drive members (48,50,52) to
guide axial movement of the drive members throughout substantially a complete forward
stroke of each drive member, but to substantially prevent lateral and angular movement
of the drive members.
8. A fuel pump as claimed in Claim 7, wherein the pump head (34) is provided with a skirt
extension (75) that is shaped for cooperation with the outer surfaces 56 of the drive
members (48,50,52) to guide said axial movement thereof.
9. A fuel pump as claimed in Claim 7 or Claim 8, wherein the outer surfaces 56 of the
drive members (48,50,52) are of part-cylindrical form.
10. A fuel pump as claimed in any of Claims 5 to 9, wherein the outer surfaces 56 of the
drive members (48,50,52) are of part-cylindrical form of radius R1, where R1 is less
than half the width, W, of the drive member.
11. A fuel pump as claimed in any one of Claims 1 to 10, wherein the drive member (48,50,52)
of each pump unit takes the form of a tappet that is cooperable, in use, with a cam
ring rider (36,38,40) of the associated cam arrangement (16,18,20) to impart movement
to the associated plunger (22,24,26) upon rotation of the camshaft (12).
12. A fuel pump as claimed in any one of Claims 1 to 11, wherein the pump head (34) is
provided with at least first and second inlet supply passages (64) for delivering
fuel to the pump chambers (23,25) of the first and second pump units (2,4), wherein
the inlet passages are arranged substantially parallel to each other and substantially
perpendicular to the high pressure supply passage (68).
13. A fuel pump as claimed in any of Claims 1 to 12, including at least first and second
cam arrangements (16,18) for imparting drive to the pumping plunger (22,24) of the
associated first and second pump unit (2,4), the first and second cam arrangements
being axially spaced along the camshaft (12).
14. A fuel pump as claimed in Claim 13, including first, second and third cam arrangements
including first, second and third cams (16,18,20), wherein the first and second cams
(16,18) are integrally formed with the camshaft (12) and the third cam (20) is a separate
component, the first, second and third cams (16,18,20) being arranged axially along
the camshaft (12).
15. A fuel pump as claimed in Claim 14, wherein front (74) and rear (76) bearing journals
are provided on the camshaft (12) in an interference fit to define first and second
bearing surfaces respectively for a respective end one of the cams (16,18,20).
16. A fuel pump as claimed in Claim 15, wherein the rear bearing journal (76) has a diameter
greater than that of the front bearing journal (74), said rear bearing journal diameter
being equal to or greater than the diameter of the main housing opening (13) to permit
direct mounting of the rear bearing journal (76) upon, or support of the rear bearing
journal by, the main housing.
17. A fuel pump as claimed in any one of Claims 14 to 16, wherein each of the first, second
and third cam arrangements includes a cam rider member (36,38,40) of tubular form
that is driven, in use, by the associated one of the cams (16,18,20) and which serves
to impart drive to the associated drive member (48,50,52) as it rides over the surface
of the associated cam.