U.S. patent application number 12/615467 was filed with the patent office on 2010-05-27 for fluid pump assembly.
This patent application is currently assigned to DELPHI TECHNOLOGIES, INC.. Invention is credited to DANIEL JEREMY HOPLEY.
Application Number | 20100129246 12/615467 |
Document ID | / |
Family ID | 40565047 |
Filed Date | 2010-05-27 |
United States Patent
Application |
20100129246 |
Kind Code |
A1 |
HOPLEY; DANIEL JEREMY |
May 27, 2010 |
FLUID PUMP ASSEMBLY
Abstract
A fluid pump assembly comprising a driven cam and a
reciprocating member reciprocal within a bore provided in a pump
housing as the cam is driven, in use, to cause pressurisation of
fluid within a pump chamber. The pump assembly further comprises an
interface between the cam and the reciprocating member, for example
in the form of bevelled surfaces of the cam and the reciprocating
member, which serve to drive the reciprocating member (i) to
translate in a first, axial direction within the bore and (ii) to
rotate within the bore in a second, rotational direction. An
optional feature of the fluid pump assembly is that the pump
housing defines a bearing for the cam which is provided with a
recess to define a region of weakness to allow the bearing to
deflect, in use, thereby to provide an increased lubrication volume
between the cam and the bearing. The reciprocating member may take
the form of a tappet which cooperates with a pumping plunger to
pressurise fluid within the pump chamber.
Inventors: |
HOPLEY; DANIEL JEREMY;
(CHISLEHURST, GB) |
Correspondence
Address: |
DELPHI TECHNOLOGIES, INC;LEGAL STAFF - M/C 483-400-402
5725 DELPHI DRIVE, PO BOX 5052
TROY
MI
48007
US
|
Assignee: |
DELPHI TECHNOLOGIES, INC.
TROY
MI
|
Family ID: |
40565047 |
Appl. No.: |
12/615467 |
Filed: |
November 10, 2009 |
Current U.S.
Class: |
417/437 |
Current CPC
Class: |
F04B 1/326 20130101;
F04B 1/12 20130101; F04B 1/0426 20130101; F02M 59/102 20130101;
F04B 9/042 20130101 |
Class at
Publication: |
417/437 |
International
Class: |
F04B 9/04 20060101
F04B009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 24, 2008 |
GB |
08169804.5 |
Claims
1. A fluid pump assembly comprising: a driven cam; a reciprocating
member reciprocal within a bore provided in a pump housing as the
cam is driven, in use, to cause pressurisation of fluid within a
pump chamber; and an interface between the cam and the
reciprocating member which cause the reciprocating member (i) to
translate in a first, axial direction within the bore and (ii) to
rotate within the bore in a second, rotational direction, as the
cam is driven.
2. A fluid pump assembly as claimed in claim 1, wherein the
reciprocating member is caused to rotate about its own axis.
3. A fluid pump assembly as claimed in claim 1, wherein the
reciprocating member is an intermediate drive member which is
cooperable with a pumping plunger to cause pressurisation of fluid
within the pump chamber as the pumping plunger is driven by the
intermediate drive member.
4. A fluid pump assembly as claimed in claim 1, wherein the
reciprocating member is a pumping plunger which interfaces directly
with the cam.
5. A fluid pump assembly as claimed in claim 1, wherein the
reciprocating member rotates at substantially the same angular
velocity as the cam.
6. A fluid pump assembly as claimed in claim 1, wherein the
interface includes a bevelled face of the reciprocating member and
a correspondingly bevelled face of the cam which cooperate so as to
impart axial and rotational motion to the reciprocating member as
the cam rotates.
7. A fluid pump assembly as claimed in claim 1, further comprising
(i) an axial bearing for the cam defined by an axially-facing
internal surface of the pump housing and/or (ii) a radial bearing
for the cam defined by a radially-facing internal surface of the
pump housing.
8. A fluid pump assembly as claimed in claim 7, further comprising
a coating applied to the surface of the cam which deforms, in use,
to the profile of the radial bearing.
9. A fluid pump assembly as claimed in claim 7, wherein the axial
bearing is provided with at least one recess to provide a volume
for receiving lubricating fluid.
10. A fluid pump assembly as claimed in claim 7, wherein the axial
bearing includes an un-recessed area which defines a load bearing
surface for the cam.
11. A fluid pump assembly as claimed in claim 7, wherein the axial
bearing is provided with a region of weakness to allow the axial
bearing to deflect, in use, thereby to encourage lubricating fluid
to be drawn between the axial bearing and the cam as it
rotates.
12. A fluid pump assembly as claimed in claim 11, wherein the
region of weakness is defined by a recess formed in the axial
bearing.
13. A fluid pump assembly as claimed in claim 7, wherein the axial
bearing is provided with a cut-away section to define a lead-in
edge for lubricant drawn between the axial bearing and the cam as
it rotates.
14. A fluid pump assembly as claimed in claim 1, wherein either the
pump chambers are defined within the pump housing and are closed by
a plate mounted to the pump housing, or wherein the pump chambers
are defined entirely within the pump housing.
15. A fluid pump assembly as claimed in claim 1, wherein an output
end of the drive shaft extends rearward of the cam and acts against
a bearing defined by the pump housing so as to counter side loads
applied to an input end of the drive shaft.
16. A fluid pump assembly comprising: a driven cam; and a
reciprocating member reciprocal within a bore provided in a pump
housing as the cam is driven, in use, to cause pressurisation of
fluid within a pump chamber; wherein the reciprocating member
includes a bevelled face which cooperates with a correspondingly
bevelled face of the cam so as to impart drive to the reciprocating
member as the cam rotates.
17. A fluid pump assembly as claimed in claim 16, wherein the
reciprocating member is a tappet which is cooperable with a pumping
plunger.
18. A fluid pump assembly as claimed in claim 16, wherein the
reciprocating member is a pumping plunger which interfaces directly
with the cam.
19. A fluid pump assembly comprising: a driven cam; and a
reciprocating member reciprocal within a bore provided in a pump
housing as the cam is driven, in use, to cause pressurisation of
fluid within a pump chamber; wherein the pump housing defines a
bearing for the cam which is provided with a region of weakness to
allow the bearing to deflect, in use, thereby to provide an
increased lubrication volume between the cam and the bearing.
20. A fluid pump assembly as claimed in claim 19, wherein the
bearing is provided with a recess to define the region of weakness.
Description
TECHNICAL FIELD
[0001] The invention relates to a fluid pump assembly and, in
particular, but not exclusively, to a pump assembly for fuel. The
pump assembly is suitable for use in a common rail fuel injection
system for supplying high pressure fuel to a compression ignition
(diesel) internal combustion engine. In particular, the invention
has application in a pump assembly of the type in which an engine
driven cam imparts reciprocating, pumping motion to a drive
member.
BACKGROUND TO THE INVENTION
[0002] One known common rail fuel pump is of radial pump design and
includes three pumping plungers arranged at equi-angularly spaced
locations around an engine driven cam--such a pump is described in,
for example, WO 2004/104409. In this pump, each plunger is mounted
within a plunger bore provided in a pump head mounted to a main
pump housing. As the cam is driven in use, the plungers are caused
to reciprocate within their bores in a phased, cyclical manner. As
the plungers reciprocate, each causes pressurisation of fuel within
a pump chamber defined at one end of the associated plunger bore.
Fuel that is pressurised within the pump chambers is delivered to a
common high pressure supply line and, from there, is supplied to a
common rail or other accumulator volume, for delivery to the
downstream injectors of the common rail fuel system. The fuel pump
has an inlet valve for admitting fuel under low pressure and an
outlet valve for letting out the pressurised fuel.
[0003] In this pump assembly, the cam carries a cam rider that
extends co-axially with the drive shaft for the cam. The cam rider
is provided with a plurality of flat surfaces ("flats"), one for
each of the plungers. An intermediate drive member in the form of a
tappet co-operates with the flat on the cam rider and couples to
the plunger so that, as the tappet is driven upon rotation of the
cam, drive is imparted to the plunger.
[0004] A fuel pump of radial pump design necessarily occupies a
relatively high volume and, for some engine applications, this can
be a disadvantage. Furthermore, the tappets are prone to wear due
to the side loads experienced as they reciprocate, in use, and
there can be significant damage to the tappet face that cooperates
with the cam rider due to inadequate lubrication.
[0005] It is an object of the present invention to provide a fluid
pump assembly which alleviates these problems when used to pump
fuel in a fuel injection system.
SUMMARY OF THE INVENTION
[0006] According to a first aspect of the present invention, there
is provided a fluid pump assembly comprising a driven cam and a
reciprocating member reciprocal within a bore provided in a pump
housing as the cam is driven, in use, to cause pressurisation of
fluid within a pump chamber. The fluid pump assembly further
includes interface means between the cam and the reciprocating
member which cause the reciprocating member (i) to translate in a
first, axial direction within the bore and (ii) to rotate within
the bore in a second, rotational direction, as the cam is driven.
The reciprocating member is arranged to rotate about its own axis
within the bore.
[0007] In one embodiment, the reciprocating member is an
intermediate drive member, typically in the form of a tappet, which
is cooperable with a pumping plunger to cause pressurisation of
fluid within the pump chamber as the pumping plunger is driven by
the intermediate drive member.
[0008] In another embodiment, the reciprocating member is a pumping
plunger which interfaces directly with the cam.
[0009] The invention is particularly applicable to fuel injection
systems for internal combustion engines in which a fuel pump
assembly pressurises fuel to a relatively high pressure suitable
for injection. Such a fuel pump assembly is particularly suitable
for use in a common rail fuel injection system. However, the
invention has wider application than fuel pumps for engines, and
may be used as a pump for any other type of fluid also.
[0010] In one embodiment, the interface means includes a bevelled
face of the reciprocating member and a correspondingly bevelled
face of the cam which cooperate so as to cause axial and rotational
motion of the reciprocating member as the cam rotates. As the
reciprocating member rotates about its own axis within its bore,
the constant relative velocity between the parts aids lubrication
so as to reduce the effects of wear due to friction.
[0011] The reciprocating member may be arranged to rotate at
substantially the same angular velocity as the cam.
[0012] The fluid pump assembly may comprise an axial bearing for
the cam which is defined by an axially-facing internal surface of
the pump housing. The fluid pump assembly may further comprise, in
addition or as an alternative, a radial bearing for the cam which
is defined by a radially-facing internal surface of the pump
housing.
[0013] The cam may be provided with a low friction coating, for
example a soft phosphate or PTFE coating, which deforms, in use, to
the profile of the radial bearing. The profile of the coating on
the cam being matched with the profile of the radial bearing
provides good conditions for promotion of a hydrodynamic film.
[0014] The axial bearing may be provided with at least one recess
to provide a volume for receiving lubricating fluid. The recess
therefore provides for a supply of lubricating fluid to the axial
bearing to aid lubrication between the rotating cam and the axial
bearing.
[0015] Furthermore, the axial bearing may include an un-recessed
area which defines a load bearing surface for the cam.
[0016] In one particular embodiment, the axial bearing is provided
with a region of weakness to allow the axial bearing to deflect, in
use, thereby to create an increased volume for lubricating fluid
between the axial bearing and the facing surface of the cam.
Deflection of the axial bearing in this way opens up an enlarged
gap between the cam and the axial bearing to encourage lubricating
fluid to be drawn between the parts. Optionally, the region of
weakness is defined by forming a recess in the bearing.
[0017] In another embodiment the axial bearing is further provided
with a cut-away section to define a lead-in edge for lubricant
drawn between the axial bearing and the facing surface of the
cam.
[0018] The fluid pump assembly may comprise at least two
intermediate drive members (e.g. tappets) and at least two pumping
plungers, each of the intermediate drive members being cooperable
with a respective one of the plungers and each of the intermediate
drive members being cooperable with a cam common to all
intermediate drive members. In one embodiment, for example, the
fluid pump assembly includes three intermediate drive members and
three pumping plungers, associated pairs of the drive members and
the pumping plungers being arranged at equi-angularly spaced
locations about a central pump axis. In an embodiment in which the
reciprocating members are pumping plungers which interface directly
with the cam, the pumping plungers are arranged at equi-angularly
spaced locations about the central pump axis.
[0019] In one embodiment, the pump chambers are defined within the
pump housing and are closed by a plate mounted to the pump housing.
Alternatively, the pump chambers may be defined entirely within the
pump housing.
[0020] Depending on the nature of the drive through which the
engine is coupled to the drive shaft, an output end of the drive
shaft may extend rearward of the cam and act against a bearing
defined by the pump housing so as to counter side loads applied to
an input end of the drive shaft. Such an arrangement is
particularly suitable for belt, chain or gear drive applications
where the nature of the input drive causes side loads to be
imparted to the drive shaft.
[0021] According to a second aspect of the invention, there is
provided a fluid pump assembly comprising a driven cam and a
reciprocating member reciprocal within a bore provided in a pump
housing as the cam is driven, in use, so as to cause pressurisation
of fluid within a pump chamber. The reciprocating member includes a
bevelled face which cooperates with a correspondingly bevelled face
of the cam so as to impart drive to the reciprocating member as the
cam rotates.
[0022] In the second aspect of the invention, the reciprocating
member may be driven both axially and rotationally within the
bore.
[0023] According to a third aspect of the invention, a fluid pump
assembly comprises a driven cam and a reciprocating member
reciprocal within a bore provided in a pump housing as the cam is
driven, in use, so as to cause pressurisation of fluid within a
pump chamber. The pump housing defines a bearing for the cam which
is provided with a region of weakness to allow the bearing to
deflect, in use, thereby to provide an increased lubrication volume
between the cam and the bearing. Optionally, it is an axial bearing
defined by the pump housing that is provided with the region of
weakness. Such an arrangement provides the aforementioned
advantages for lubrication between the rotating cam and the axial
bearing.
[0024] It will be appreciated that optional features of the first
aspect of the invention, as set out above and in the dependent
claims, may be included in the second or third aspects of the
invention also, alone or in appropriate combination.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The invention will now be described, by way of example only,
within reference to the following drawings in which:
[0026] FIG. 1 is a cross sectional view of a fuel pump assembly of
a first embodiment of the invention, having two pumping
plungers;
[0027] FIG. 2 is a cross sectional view of a part of the fuel pump
assembly in FIG. 1 to illustrate a spring seat for a return
spring;
[0028] FIG. 3a is a cross sectional view of a cam and a pump
housing of the fuel pump assembly in FIG. 1;
[0029] FIG. 3b is an end view of an axial bearing defined by the
pump housing in FIG. 3a;
[0030] FIG. 4a is a cross sectional view of the pump housing in
FIG. 3a to illustrate an area of weakness on the external
surface;
[0031] FIG. 4b is an end view of the internal surface of the pump
housing in FIG. 4a;
[0032] FIG. 5 is cross sectional view of a fuel pump assembly of a
second embodiment of the invention having two pumping plungers;
[0033] FIG. 6 is a cross sectional view of a fuel pump assembly of
a third embodiment of the invention having two pumping
plungers;
[0034] FIG. 7 is a cross sectional view of a fuel pump assembly of
a fourth embodiment of the invention having a single pumping
plunger;
[0035] FIG. 8 is a perspective view of a part of a fuel pump
assembly of a fourth embodiment of the invention having three
intermediate drive members for three pumping plungers; and
[0036] FIG. 9 is a cross sectional view of a fuel pump assembly of
a fifth embodiment of the invention in which the intermediate drive
members of previous embodiments are removed.
DETAILED DESCRIPTION OF EMBODIMENTS
[0037] Referring to FIG. 1, a first embodiment of the fuel pump
assembly 10 of the invention includes a pump housing having a first
housing part 12 which is provided with a central bore for receiving
a drive shaft 16 (only a part of which is shown). The first housing
part includes a front plate 12a of the pump housing and a
cylindrical body 12b towards the rear. The rear end of the drive
shaft 16 carries a cam 18 which rotates with the drive shaft 16, in
use. Typically, the front or input end of the drive shaft is driven
by the engine through an Oldham coupling, as would be familiar to a
person skilled in the art.
[0038] The cam 18 is wedge-shaped and so has a thin end 18a and a
thick end 18b with a bevelled contact surface 18c on its front
face. The back face of the cam 18 is planar and acts against an
axially-facing internal surface of the pump housing 12, which
therefore acts as an axial bearing 22 for the cam 18 as it rotates.
The outer surface of the cam, at its thick end 18b, bears against a
radially-facing internal surface of the first housing part 12,
which therefore acts as a radial bearing 24 for the cam 18 as it
rotates.
[0039] The pump assembly includes first and second reciprocating
members, in the form of tappets 26, 28, each of which has a
bevelled surface 26a, 28a, respectively, for contact with the
correspondingly bevelled surface 18c of the cam 18. Each tappet 26,
28 is received within an associated tappet bore provided in a
second housing part 30 mounted to the first housing part 12, and is
coupled to an associated pumping plunger, 32, 34 respectively, in
axial alignment with its tappet 26, 28. The tappets 26, 28
therefore form an intermediate drive member between the cam 18 and
the associated plunger 32, 34.
[0040] Each pumping plunger 32, 34 is received within an associated
plunger bore provided in the second housing part 30. An end of the
pumping plunger 32, 34 remote from the tappet 26, 28 defines an
internal surface of a pump chamber 33, 35 which receives fuel to be
pressurised during a plunger pumping stroke, in use, as described
in further detail below.
[0041] Referring also to FIG. 2 (which shows only the first tappet
26), each tappet 26 takes the form of a bucket tappet of generally
U-shaped cross section having a base 26b, which defines the
bevelled contact surface 26a, and a cylindrical upper body 26c.
Within the internal volume of the tappet 26, on the side of the
base 26b opposed to the bevelled contact surface 26a, the tappet
includes a projection 26d which defines a contact surface for the
associated plunger 32. A spring seat assembly for a plunger return
spring 37 is received within the internal volume of the tappet 26
defined within the cylindrical upper body 26c. The return spring 37
serves to provide a return load to the plunger 30 and the tappet 26
to effect a return stroke of the plunger, as described in further
detail below.
[0042] The spring seat assembly has two parts. A first part 36 is
of top-hat construction and is located at the base of the plunger
32, the plunger 32 extending through a central bore of the first
part 36. The first part 36 defines an abutment surface for one end
of the return spring 37, the other end of the return spring 37
remote from the spring seat assembly 36, 38 abutting an internal
surface 41 of the second housing part 30. A second part 38 of the
spring seat assembly is an annular piece forms a push-fit on the
base end of the plunger 32 and serves to retain the first part 36
of the assembly in place.
[0043] In an alternative embodiment (not shown), the return spring
37 may be a smaller component located within the pump chamber 33,
35, rather than surrounding the plunger 32, 34.
[0044] Referring again to FIG. 1, the pump chambers 33, 35 are
closed by a plate 39 at the rear end of the pump assembly 10. The
closure plate 39 is provided with a plurality of drillings to allow
relatively low pressure fuel to be conveyed into the pump chambers
33, 35 and to allow pressurised fuel to be conveyed from the pump
chambers 33, 35 to a pump outlet (not shown). An inlet drilling is
provided for each of the pump chambers 33, 35, each inlet drilling
having a respective spring-biased inlet valve 40, 42 through which
relatively low pressure fuel passes to enter the associated pump
chamber 33, 35, prior to pressurisation. An outlet drilling is
provided for each of the pump chambers 33, 35, each outlet drilling
having a respective spring-biased outlet valve 44, 46 through which
pressurised fuel is delivered to the common outlet of the pump
assembly when the pressure level in the pump chambers 33, 55
reaches a predetermined amount. The common outlet is connected to a
common rail or accumulator volume of the fuel injection system,
from where fuel is delivered to the fuel injectors of the
engine.
[0045] Operation of the fuel pump assembly will now be described in
further detail.
[0046] Considering the first tappet 26 and its associated plunger
32, as the drive shaft 16 rotates, in use, cooperation between the
rotating bevelled surface 18c of the cam 18 and the bevelled
surface 26a of the tappet 26 results in the tappet 26 reciprocating
axially within its tappet bore and, thus, the plunger 32 is caused
to reciprocate within its plunger bore also. As the plunger 32 is
driven it performs the pumping stroke, in which fuel within the
associated pump chamber 33, 35 is pressurised to a high level
suitable for injection, followed by the return stroke which is
effected by means of the associated return spring 37.
[0047] At the start of the return stroke, the outlet valve 44 is
closed under its spring force. As the plunger 32 moves outwardly
from its bore to expand the volume of the pump chamber 33, the pump
chamber 33 fills with fuel at relatively low pressure from a supply
pump (e.g. transfer pump) through the inlet valve 40 which is open.
As the cam 18 continues to rotate and the plunger 32 completes its
return stroke, cooperation between the bevelled surfaces 18c, 26a
of the cam and the tappet causes the tappet, and hence the plunger,
to move inwardly within their bores to reduce the volume of the
pump chamber 33. Soon after the volume of the pump chamber 33
starts to decrease, fuel pressure in the pump chamber 33 starts to
increase and the force due to fuel pressure acting on the inlet
valve 40 causes it to close. The pressure within the pump chamber
33 continues to rise as the plunger 32 continues through its
pumping stroke, until such time as the pressure in the pump chamber
33 is sufficient to overcome the closing force of the outlet valve
44, which is then urged open to allow pressurised fuel to be
delivered through the pump outlet.
[0048] As a result of the rotating bevelled surface 18c of the cam
18 interacting with the correspondingly bevelled surface 26a of the
tappet 26, the tappet is driven to move axially within its bore,
hence driving axial motion of the plunger. Importantly, cooperation
between the rotating bevelled surface 18c of the cam 18 and the
correspondingly bevelled surface 26a of tappet 26 also means that
the tappet is driven to rotate within its bore at the same angular
velocity at which the cam 18 is driven by the drive shaft 16. The
interface between the cam and the tappet therefore results in a
deliberately driven, continuous rotation of the tappet about its
axis.
[0049] Due to the nature of the two-part spring seat assembly,
rotation of the tappet 26 also causes the plunger 32 to rotate
within the plunger bore as it reciprocates. The spring seat
assembly is configured such that the frictional force between the
return spring 37 and the first part 36 of the spring seat assembly
is greater than the frictional force between the second and first
parts 38, 36 of the spring seat assembly. Hence, as the tappet 26
rotates, the plunger 32 may also rotate, whereas the first part 36
of the spring seat assembly and the return spring 37 remain static.
In this way relative movement between the end of the return spring
37 and the internal surface 41 of the second housing part 30 is
prevented, to avoid unwanted wear, whilst the plunger 32 is allowed
to rotate. Unwanted relative movement between the first part 36 of
the spring seat assembly and the return spring 37 is also
avoided.
[0050] The second tappet 28 and the second plunger 34 are driven in
a similar manner to operate in phased, cyclical motion with the
first tappet/plunger 26/32, with both pump chambers 33, 35 filling
a common rail with pressurised fuel through the respective outlet
valves 44, 46.
[0051] A clearance between each tappet and its tappet bore provides
a volume for lubricating fluid and so, due to the relative motion
between the rotating tappet and its bore, lubrication of parts is
promoted to reduce wear.
[0052] As illustrated in FIG. 3(a), the return load on the cam 18
due to pressurised fuel within the pump chamber 33 is exerted on
the cam 18 in a direction perpendicular to the bevel angle of the
cam surface 18c. The thick end 18b of the cam 18 bears against the
radially-facing internal surface of the first housing part 12,
which therefore acts as a radial bearing 24 for the cam 18 as it
rotates. The rear face 18d of the cam (i.e. the face opposed to the
bevelled surface 18c) bears against the axially-facing internal
surface of the pump housing 12, which therefore acts as an axial
bearing 22 for the cam 18 as it rotates.
[0053] FIG. 3(b) illustrates a coating that is applied to the
radially-facing surface of the cam 18. The surfaces of the cam 18
which bear against the axial and radial bearings 22, 24 may be
provided with a soft lubricating coating, for example phosphate or
PTFE. The dashed line illustrates the profile of the coating 25 on
the cam 18, in use. As the coating 25 is soft, the coating deforms
as the cam 18 rotates so as to conform to the profile of the
bearing surface 24, hence providing good conditions for promotion
of a hydrodynamic film. The soft phosphate coating is also applied
to the bevelled face 18c of the cam 18 which cooperates with the
bevelled surface 26a of the tappet.
[0054] Referring to FIGS. 4(a) and 4(b), the axial bearing 22 is
modified, on its front and rear faces, so as to aid lubrication
between the parts 12,18. Firstly, as shown in FIG. 4(b), the axial
bearing 22 includes first and second raised segments 46a, 46b, or
pads, separated by first and second recessed segments 48a, 48b. The
raised segments 46a, 46b are positioned so as to be axially aligned
with a respective one of the tappets 26, 28 so as to absorb the
tappet return load. The recesses 48a, 48b define an enlarged volume
for lubricating fluid to aid lubrication between the cam 18 and the
bearing 22 as the cam rotates.
[0055] In addition, and as can be seen in FIG. 4(a), the opposite
face 12c of the first housing part 12 to the axial bearing 22 is
provided with a further recess 50 to define a weakened region of
the first housing part 12. As the pump is driven and the cam 18 is
loaded by the tappet and bears on the axial bearing 22, the
weakened region of the pump housing 12 allows the housing to
deflect causing a wedge-shaped gap (not shown) to open between the
axial bearing 22 and the facing surface 18d of the cam 18. In
particular, the weakened region 50 allows approximately one half of
the pad to bend to provide a hydrodynamic wedge. This provides a
lead-in edge for lubricating fluid and allows fluid to be drawn
between the parts 12, 18, allowing a hydrodynamic bearing to be
generated between them as the cam 18 rotates.
[0056] In addition to the lead-in edge provided by deflection of
the pump housing 12, the axial bearing 22 may also be provided with
a chamfer, radius or bevel (not shown) at the lead-in edge to
further encourage lubricating fluid to be drawn between the parts
12, 18 as the cam rotates.
[0057] In FIG. 1, where an Oldham coupling is provided between the
engine and the drive shaft 16, there are only an insignificant side
loads on the drive shaft 16. However, where a belt, chain or gear
drive is used between the engine and the drive shaft 16, a
significant side load is exerted on the drive shaft which causes
unwanted tilt and translation forces to act on the cam 18. For
belt, chain or gear drive applications it is therefore necessary to
counter these side loads to prevent unwanted translation and/or
tilt of the cam 18 by providing a different bearing arrangement to
that shown in FIG. 1.
[0058] FIG. 5 shows an embodiment of the invention which is
appropriate for a belt, chain or gear drive coupling (not shown)
between the engine and the drive shaft 16. Similar parts to those
shown in FIGS. 1 to 4 are denoted with like reference numerals. In
this embodiment a rear or output end of the drive shaft 16 extends
further rearward into the pump assembly 10, and beyond the bevelled
contact face 18c of the cam 18, to be received within a central
bore provided in the second housing part 30. At the rearmost end of
the drive shaft 16 the internal surface of this central bore
defines a radial bearing 52 which counters the tilting force acting
on the front end of the drive shaft 16 and, hence, prevents
unwanted tilt of the cam 18 as it rotates. In addition, the thin
end 18a of the cam 18 is provided with an axially-extending flange
54, the outer surface of which bears on the radially-facing
internal surface 56 of the pump housing 12. The axially-extending
flange 54 bearing against the radially-facing internal surface 56
of the pump housing 12 counters the translation force acting on the
front end of the drive shaft 16 and, hence, prevents unwanted
translation of the cam 18 as it rotates. The bearing arrangement
52, 54, 56 of FIG. 5 therefore prevents unwanted tilting and
translation of the cam 18 due to side loading of the drive shaft 16
at its front end.
[0059] It will be appreciated that the pump assembly in FIG. 5 is
of greater width than that in FIG. 1 due to the need for the drive
shaft 16 to extend further rearward into the pump housing 12, 30,
and beyond the cam 18, to define the rear bearing 52, and hence the
need for separation between the tappets 26, 28 to be greater. The
width is also increased due to the provision of the flange 54 on
the cam 18.
[0060] In the FIG. 5 embodiment, the radially-facing internal
surface of the pump housing provides a bearing surface 24 for the
wide end 18b of the cam 18 and the axially-facing internal surface
22 of the pump housing 12 defines a bearing surface for the front
face of the cam 18, as in the FIG. 1 embodiment.
[0061] Another alternative bearing arrangement suitable for use
with a belt, chain or gear drive is shown in FIG. 6. As in FIG. 5,
the drive shaft 16 extends further into the second housing part 30
and beyond the cam 18 so as to define a radial bearing 52 at the
rear end of the drive shaft 16 which counters the tilting force
applied to the cam 18 due to the side loads at the front end of the
drive shaft 16. In this case, however, the flange on the thin end
18a of the cam 18 is removed, and instead the cam 18 is made of
increased thickness in this region 18a' (i.e. the length of the cam
along the axis of the drive shaft is increased at its thinnest
end). The thin end 18a' of the cam 18 is therefore of greater
thickness than in FIG. 5 and bears against the radially-facing
internal surface 56 of the first housing part 12 to counter the
translation force acting on the cam 18 due to the side loading at
the front end of the drive shaft 16. This arrangement results in a
pump assembly of longer axial length than the FIG. 5 embodiment due
to the increased thickness of the cam 18 at region 18a', but one of
reduced width due to the removal of the flange 54 in the FIG. 5
embodiment.
[0062] A further alternative embodiment is shown in FIG. 7 which,
again, is appropriate for use with a belt, chain or gear drive.
Here, the drive shaft 16 does not extend rearward beyond the cam
18, but instead the wide end 18b of the cam is provided with a
radially-extending flange 58 which engages with a
radially-extending, axially-facing surface 60 of the second housing
part 30. The bearing provided by the radially-extending surface 60
of the second housing part 30 counters both the tilting and
translation forces exerted on the cam 18 due to the side loads at
the input end of the drive shaft 16.
[0063] Although the pump housing in FIG. 7 is still of two-part
construction, the first housing part 12 which defines the axial
bearing 22 is a much smaller component than in previous
embodiments, with the second housing part 30 extending further
towards the front end of the pump assembly 10 to define the bearing
surface 60. The radially-extending flange 58 bears against the
bearing surface 60 which counters the side loads on the input end
of the drive shaft. The bearing surface 60 therefore takes the
place of the bearing surfaces 52, 56 in FIGS. 1, 5 and 6.
[0064] Another difference between the embodiment in FIG. 7 and
those described previously is that in FIG. 7 there is only a single
pumping plunger 32 having a single associated tappet 26 cooperating
with the bevelled cam 18. In practice, the pump assembly may
include any number of plungers/tappets, depending on delivery
requirements. As shown in FIG. 8, for example, the pump assembly
may include three plungers (not shown), each having an associated
tappet 126, 226, 326 which cooperates with a common bevelled cam
18. In a tri-tappet assembly the tappets 126, 226, 326, and their
associated plungers, are arranged at equi-angularly spaced
locations around a central axis of the pump assembly which is
aligned with the drive shaft axis.
[0065] Another arrangement of the bearings (not shown) involves
removing the flange 58 in the FIG. 7 embodiment, and creating a
bearing between a flat portion 18e of the front face of the cam
(i.e. a portion that isn't bevelled) and the facing surface of the
second housing part 30. In this embodiment, the pump assembly has
two axial bearings (at 22 and 18e), facing in opposite directions,
to counter the side loads on the input end of the drive shaft
16.
[0066] In another example, as shown in FIG. 9, the tappets 26, 26,
126, 226, 326 of previous embodiments may be removed altogether and
the bevelled surface 18c of the cam 18 may act directly on a
correspondingly bevelled surface 32a, 34a of the reciprocating
plungers 32, 34. In other arrangements a single plunger, or more
than two plungers, may be provided to interface directly with the
bevelled cam 18, again avoiding the need for an intermediate drive
member.
[0067] Other embodiments of the invention are also envisaged
without departing from the scope of the invention as set out in the
claims. For example, the rear closure plate 39 in FIGS. 1, 5, 6, 7
and 9 may be replaced by a housing part (not shown) which includes
regions extending into the second housing part 30 so as to define
the plunger sealing lengths and the pump chambers 33, 35. In this
way the main pump housing 30 does not have to have the required
material strength to accommodate the high pressures of fuel within
the pump chambers 33, 35, and only the closure plate 39 needs to be
made from high-strength, expensive material. It is also envisaged
that an intermediate part may be provided between the cam and the
tappet e.g. to provide additional hardness.
* * * * *