[0001] The invention relates to a pump assembly for use in supplying high pressure fuel
to the fuel injection system of a compression ignition internal combustion engine.
[0002] In a known fuel pump for use in a compression ignition internal combustion engine,
a plurality of plungers are reciprocable within respective plunger bores so as to
pressurise fuel within respective pumping chambers for delivery to the fuel injection
system associated with the engine. It is common to provide three plungers which are
equi-angularly spaced around a drive shaft, the plungers being moveable under the
influence of a cam drive arrangement. The cam drive arrangement includes a common
eccentric cam surface, which is cooperable with all three of the plungers to cause
reciprocal movement of the plungers within their respective plunger bores in a phased,
cyclical manner.
[0003] In an alternative known arrangement, each of the plungers is in connection with a
cylindrical tappet member which serves to drive movement of the associated plunger
within its bore. The tappets are slidable within tappet bores under the influence
of respective roller members, driven by means of an eccentric cam surface. The eccentricity
of the cam surface causes the tappets, and hence the plungers, to be driven inwardly
within their respective bores, the plungers thereby performing a forward or pumping
stroke in which fuel within the associated pumping chamber is pressurised. The tappets
are urged outwardly from their associated tappet bores by means of fluid pressure
within a working chamber, thus causing the respective plunger to be urged in an outward
direction to perform the return stroke.
[0004] Pump arrangements of the aforementioned type can be difficult to assemble. Furthermore,
the tappets require a relatively large accommodation space and are relatively expensive
components. Parasitic pumping power losses are also an inherent feature of hydraulic
tappet operation.
[0005] Our co-pending European patent application, EP 1223334A, describes a multi-plunger
fuel pump in which three plungers are equi-angularly spaced around a drive shaft and
driven under the influence of a reciprocable shoe and roller arrangement (a "roller-shoe"
drive arrangement). The roller is cooperable with the cam surface of the cam arrangement
so as to impart reciprocal movement to the shoe upon rotation of the drive shaft.
[0006] The pump includes three pump assemblies housed within a unitary, main pump housing,
each of the pump assemblies including a plunger which is slidable within a respective
bore in the housing to pressurise fuel within an associated pumping chamber.
[0007] Inlet and outlet valves to control fuel flow to and from the pumping chambers, respectively,
are provided in flow passages defined within the main pump housing. A pump housing
part in the form of a tubular member is arranged coaxially with the drive shaft and
housed within the main pump housing. The tubular member is provided with a plurality
of apertures, each of which is shaped to guide reciprocal movement of an associated
shoe as the roller rides over the cam surface. The shoe associated with each plunger
is of rectangular or square cross section.
[0008] One disadvantage of this type of pump is that it is difficult to manufacture main
pump housings having shoe guide apertures which are other than cylindrical, and which
have the desired degree of precision. Mismatching between the shoe and its guide path
can lead to excessive wear of the shoe and/or the guide aperture.
[0009] It is an object of the present invention to provide an improved pump assembly for
use in supplying high pressure fuel which alleviates at least one of the aforementioned
problems.
[0010] According to a first aspect of the present invention, there is provided a fuel pump
assembly for use in an engine, the fuel pump assembly comprising a plurality of pump
heads mounted upon a main pump housing, each of the pump heads including a pumping
plunger which is reciprocable, in use, within a plunger bore under the influence of
an associated drive arrangement so as to cause pressurisation of fuel within a pumping
chamber defined within a pump head housing, the drive arrangement including a shoe
and a roller which is cooperable with a driven cam, common to each of the pump heads,
so as to impart reciprocal movement to the shoe as the cam is driven, in use, the
shoe being of square or rectangular cross section and each pump head further comprising
an associated insert, being formed as a separate part from the main pump housing but
being assembled permanently therewith, wherein the insert defines a guide path of
substantially rectangular or square cross section for guiding reciprocating movement
of the associated shoe.
[0011] The invention provides the advantage that the insert of each pump head which defines
the shoe guide path can be more accurately formed as a separate component, prior to
it being fixed permanently to the main pump housing. The problem encountered in known
roller-shoe pump designs, that the accurate forming of a rectangular section guide
path for the shoe is difficult to achieve, is therefore overcome by the present invention.
As a result of being able to machine the shoe guide part with improved accuracy, wear
on the guide path and the shoe is reduced.
[0012] Preferably, the insert of each pump head has an external surface profile of substantially
cylindrical form.
[0013] As the shoes are components having a generally square or rectangular cross section,
each of the inserts is preferably shaped to include two pairs of substantially parallel
facing walls or internal surfaces (e.g. of substantially square or rectangular cross-sectional
form).
[0014] Preferably, the insert associated with each pump head housing is formed by sintering
or metal injection moulding (MIM).
[0015] Preferably, said main pump housing is provided with a plurality of openings in the
form of radially extending bores in the main pump housing, each of the bores being
adapted to receive one of the inserts having an outer surface of cylindrical form.
[0016] Preferably, the cylindrical insert of each pump head is an interference fit with
the corresponding radially extending opening. Thus, although the insert is formed
as a separate part from the main pump housing, when assembled within the housing it
forms a permanent and immovable feature of the pump assembly. It is because the insert
can be formed as a separate part, however, that their pairs of parallel facing walls
can be formed conveniently, and with improved accuracy, compared with pump designs
in which a main housing itself defines the guide path for the shoe.
[0017] Inward movement of a pumping plunger within its respective plunger bore causes the
pumping plunger to perform a forward stroke, in which pressurisation of fuel within
the pumping chamber occurs. Each pump head may be provided with a return spring which
acts on the shoe so as to ensure the roller remains in engagement with the cam surface
during a return stroke of the pumping plunger.
[0018] The roller may preferably take the form of a cylindrical roller.
[0019] In one preferred embodiment, the pump head housing has an integral plunger bore in
the form of a plunger support tube extending substantially perpendicularly from the
lower surface of the pump head housing so as to be located within the shoe guide path.
[0020] Preferably, a first end of the return spring, in the region of the pump head housing,
surrounds the plunger support tube so as to retain the return spring in position.
[0021] Preferably, a second end of the return spring, distal to the pump head housing, is
associated with positioning means to maintain the return spring in a fixed relationship
with the shoe.
[0022] In one preferred embodiment the positioning means includes an annular groove on the
radially outer surface of the shoe. In a further preferred embodiment the positioning
means further includes a spring seat located on the inner end of the plunger, wherein
the spring seat abuts the radially outer shoe surface.
[0023] In another preferred embodiment, the insert of each pump head is shaped to define,
together with the opening in the main pump housing, a vent means for permitting fuel
displaced by the shoe during reciprocating motion thereof to vent to low pressure.
For example, the outer surface of each insert may be provided with at least one groove
or recess which defines, together with the internal surface of the opening, a return
flow path for fuel.
[0024] As the shoe reciprocates between the facing walls of its associated insert, the fuel
volume radially inward of the shoe can escape relatively easily between the main bore,
through drillings in the main pump housing and through the recesses or grooves formed
in the external surface of the insert, which define the return flow path. The return
flow path presents a relatively large flow area to fuel displaced by reciprocating
motion of the shoes to ensure movement of the shoes is substantially unimpeded.
[0025] In one embodiment the fuel pump assembly has a pair of pump heads radially mounted
upon the main pump housing at diametrically opposed positions about the drive shaft,
and wherein the cam has a cam surface with a single cam lobe so as to impart phased,
alternate motion to the respective plungers of the pair upon rotation of the shaft.
[0026] In the most preferred embodiment, the fuel pump assembly has three pump heads, and
thus three associated inserts to define the shoe guide paths, the pump heads being
radially mounted upon the may pump housing at equi-angularly spaced locations about
a pump drive shaft.
[0027] According to a second aspect of the present invention there is provided fuel pump
assembly for use in an engine, the fuel pump assembly comprising at least one pair
of pump heads mounted upon a main pump housing, each of the pump heads including a
pumping plunger which is reciprocable, in use, within a plunger bore under the influence
of an associated drive arrangement so as to cause pressurisation of fuel within a
pumping chamber defined within a pump head housing, each of the drive arrangements
being co-operable with a surface of a cam which is driven, in use, by an associated
engine drive shaft, so as to impart reciprocal movement to the pumping plunger upon
rotation of the drive shaft, wherein the cam surface is common to each of the pump
heads and wherein one pump head of the or each pair is positioned at substantially
90° to the other pump head of the pair, the cam surface being shaped to result in
there being two pressurisation events for each pump head of said pair per cycle as
the drive shaft rotates.
[0028] Preferably, only a single pair of pump heads are provided on the fuel pump assembly.
[0029] Preferably, the cam is a twin lobed cam. More preferably the cam lobes are diametrically
opposed.
[0030] It will be apparent that in this preferred embodiment of the pump assembly according
to the second aspect, four equally spaced pressurisation events will occur per cycle.
[0031] Preferably, each drive arrangement is a shoe and roller arrangement, or alternatively
a slipper and tappet arrangement. It will be appreciated that, although it may be
advantageous to provide the pump heads of the second aspect of the invention with
an insert for guiding movement of the associated shoe, this is not essential.
[0032] The invention will now be described, by way of example only, with reference to the
accompanying drawings in which:
Figure 1 is a perspective view of a fuel pump assembly in accordance with an embodiment
of the present invention,
Figure 2 is a sectional view of the pump assembly in Figure 1,
Figure 3 is a sectional end view of the pump assembly in Figures 1 and 2,
Figure 4 is a perspective view of part of a main pump assembly housing,
Figure 5 is a sectional view of a part of a pump head of the pump assembly in Figures
1 to 4 to show inlet and outlet valves of the assembly, and
Figure 6 is a sectional view of the pump assembly of Figures 1 to 5 showing a high
pressure fuel delivery passage.
[0033] Referring to Figures 1 to 3, there is shown a high pressure fuel pump assembly suitable
for use in the fuel injection system of a compression ignition internal combustion
engine. In particular, the fuel pump assembly is suitable for use in delivering high
pressure fuel to the common rail of a common rail fuel injection system. The pump
assembly includes a main pump housing 10 through which a cam drive shaft 12 of the
engine extends along a drive shaft axis extending perpendicularly to the plane of
the page. A front housing plate 11 is positioned on the main pump housing 10 and located
by means of a boss 11 a. First, second and third pump heads 13a, 13b, 13c respectively
are mounted upon the main pump housing 10 at approximately equi-angularly spaced radial
locations around the drive shaft axis. The drive shaft 12 extends through a central
through bore 40 provided in the main pump housing 10, and is supported by a plain
bearing bush 41 and a front plate bearing 41a. Each pump head 13a, 13b, 13c includes
a respective pump head housing 18a, 18b, 18c. On each pump head 13a, 13b, 13c a seal
member 72 in the form of a gasket is located in a recess between the main pump housing
10 and the pump head housing 18a, 18b, 18c so as to form a fluid tight seal between
these parts when the pump heads 13a, 13b, 13c are secured to the housing 10 by means
if screws 92. The gasket seal 72 serves to seal low pressure regions of the pump from
the high pressure regions of the pump, as discussed further below.
[0034] As the pump heads 13a, 13b, 13c are substantially identical to one another, only
the first one of the pump heads 13a will be described in detail below. As can be seen
most clearly in Figures 2 and 3, the first pump head 13a includes a pumping plunger
14 which is reciprocal within a blind bore 16 to perform a pumping cycle having a
pumping stroke (or forward stroke) and a return stroke. The blind bore 16 is defined
partly within a pump head housing 18a and partly within a plunger support tube 20
which extends from a lower surface of the pump head housing 18a. The bore 16 defines,
at its blind end within the pump head housing 18a, a pumping chamber 22. Reciprocating
movement of the plunger 14 within the bore 16 causes pressurisation of fuel within
the pumping chamber 22 during the pumping stroke. The pumping plunger 14 is driven
axially within the bore 16, in use, under the influence of a drive arrangement including
a shoe 24 and an associated roller 26. The shoe is a component having a substantially
rectangular cross section, although square section shoes may also be used. The roller
26 is co-operable with a cam surface 27 of a cam member 28 which is carried by the
drive shaft 12. As the shaft 12 rotates in use, the roller 26 rides over the cam surface,
imparting movement to the shoe 24 and, hence, imparting axial movement (i.e. along
the main plunger axis) to the pumping plunger 14 within the bore 16 to drive the pumping
stroke.
[0035] It will be appreciated that the shoe and roller arrangement of each pump head 13a,
13b, 13c co-operates with the cam surface 27, which is thus common to all three pump
heads. As the drive shaft 12 rotates, the rollers co-operate with the common cam surface
27 to cause reciprocating motion of the shoes in a phased, cyclic manner depending
on the cam surface profile.
[0036] Referring to Figure 4, a radially extending opening 32 in the form of a radially
extending bore is provided in the main pump housing 10. The opening 32 defines an
internal surface of substantially cylindrical form, and a first, hollow insert 30a,
which is associated with the first pump head 13a, is located within the cylindrical
opening 32 so as to be coaxial with the bore 16. The insert 30a has an outer surface
of substantially cylindrical form, which corresponds to the shaping of the internal
surface of the opening 32 in the main pump housing 10. The internal surface of the
insert 30a defines a substantially rectangular cross section (in a plane perpendicular
to the axis of movement of the plunger 14 and the shoe 24). The internal surface of
the insert 30a therefore defines first and second pairs of substantially parallel
facing walls 34, 36, which define a guide path of appropriate form for the rectangular
section shoe 24 as it reciprocates, in use. The facing internal surfaces 34 of the
first pair have a smaller length, along an axis perpendicular to the plunger axis,
than the facing internal surfaces 36 of the second pair. The insert 30a is also formed
so that the first pair of internal surfaces 34 have a longer length, along the direction
of the plunger axis, than the second pair of internal surfaces 36, and thus upper
end regions 130 of the insert 30a are of increased axial height.
[0037] It will be appreciated that although the cross section of the insert guide path is
not exactly rectangular (e.g. due to interconnecting corner regions 230 being of curved
form - as shown in Figure 4), a guide path of substantially rectangular cross section
is defined to provide an adequate guiding surface for the generally rectangular cross
section of the shoe 24.
[0038] The second and third pump heads 13b, 13c are also provided with similar inserts 30b,
30c, respectively, each of the inserts 30b, 30c being received within a correspondingly
shaped radial opening or bore (such as 32) in the main pump housing 10. Each of first,
second and third inserts 30a, 30b, 30c is arranged such that a radially inner end
thereof opens into a main axial bore 38 provided in the main pump housing 10 (as can
be seen in Figure 3).
[0039] The insert 30a also defines a spring space 74 located above the shoe 24 (in the orientation
shown), within which a return spring 84 is located. The return spring 84 serves to
urge the shoe 24 and the roller 26 in a radially inward direction such that the roller
26 maintains contact with the cam surface 27 throughout a complete rotation of the
drive shaft 12. The force due to the return spring 84 is aided by the force due to
fuel pressure within the pumping chamber 22 which acts on the pumping plunger 14 to
provide a return force which serves to urge the pumping plunger 14 outwardly from
the bore 16 to perform the return stroke. It will be appreciated that this only occurs
if the pump is operating at its maximum displacement and, hence, at maximum filling.
[0040] The outer surface of the insert 30a is provided with first and second recesses 82a,
82b. The recesses 82a, 82b are provided along those facing sides of the insert 30a
which define the longer of the facing internal wall surfaces 36. The recesses 82a,
82b are thus formed in the region of the insert 30a which would otherwise be formed
from the greatest amount of insert material. A plurality of drillings 80 are provided
in the main pump housing 10 which, together with the recesses 82a, 82b provided in
the outer surface of the insert 30a, define a vent passage means in the form of a
return flow path, as discussed further below.
[0041] As can be seen most clearly in Figure 5, the return spring 84 is of a diameter such
that a first end is located around, and retained in position by, the plunger support
tube 20. The second end of the return spring 84 abuts a spring seat 86 attached to
the pumping plunger 14 by a retention clip 88. The clip 88 acts to maintain the spring
seat 86 in position. The spring seat 86 is located in and spaced from an annular groove
90 provided on the radially outer surface of the shoe 24.
[0042] A low pressure transfer pump 42 is mounted upon the housing 10 at an end face remote
from the front plate 11. The transfer pump 42 is arranged to supply fuel at a pressure
dependent upon the speed of rotation of the engine, the rate of flow of fuel from
the transfer pump being controlled by means of a metering valve arrangement 44 in
a conventional manner The transfer pump 42 also supplies fuel at a low pressure to
the main bore 38 and the spring space 74 through a drilling 76 in the main housing
10.A back leak connector 45 is mounrted upon the front plate 11 in a conventional
manner for use in the return of fuel from the pump assembly to a low pressure fuel
reservoir (not shown).
[0043] Referring also to Figure 5, it can be seen that the gasket seal 72 is a generally
square frame seal having a side-tab seal portion 72b. The metered flow of fuel from
the transfer pump 42 is supplied to an entry drilling 55 provided in the pump head
housing 18a, which extends through an aperture 72a in the side tab portion 72b of
the gasket seal 72. The entry drilling 55 communicates with the pump chamber 22 through
an inlet valve arrangement 46, and thus defines a flow path for relatively low pressure
fuel into the pumping chamber 22. The upper end region 130 of the insert 30a defines
a support or abutment for the gasket seal 72, which aids unwanted movement of the
seal 72 relative to the housing surface 10, and thus benefits the gasket sealing function.
[0044] The inlet valve arrangement 46 includes a disc-like valve member 58 which is operable
in response to fuel pressure within a further drilling 64 so as to control the flow
of fuel into the pumping chamber 22 from the drillings 55, 64. The further drilling
64 is defined within an inlet valve body 59 and communicates with an outlet end of
the entry drilling 55. The inlet valve body 59 is sealed within a bore in the pump
head housing 18a by means of an O-ring 57 and a deformable knife-edge seal 60. The
valve member 58 is biased closed by means of a first valve spring 56 and, if fuel
pressure within the further drilling 64 exceeds a predetermined amount, the valve
member 58 is caused to lift away from its seating, against the force of the spring
56, to permit a metered flow of fuel (at "metered fuel pressure") to be suppplied
through the further drilling 64 to the pumping chamber 22.
[0045] The pumping chamber 22 is also provided with an outlet valve arrangement 48 which
is arranged to open when fuel pressure within the pumping chamber 22 is pressurised
to a level greater than a predetermined amount. The outlet valve arrangement 48 takes
the form of a ball valve including a ball 66 which is urged against a valve seating
67 by means of fuel pressure in the high pressure drillings. The ball valve controls
communication between the pumping chamber 22 and a common delivery passage 50. A high
pressure sealing member 70 is located between the outlet valve 48 and the common delivery
passage 50. Conveniently, the sealing member 70 may be a metal sealing washer of double
knife-edged form which is trapped in an annular recess in the main pump housing 10.
If the ball valve is urged open, fuel is able to flow from the pumping chamber 22,
past the second valve seat 67 and into the first arm 50a of the common delivery passage
50. The high pressure sealing member 70 has first and second so called 'knife-edge"
sealing faces to ensure substantially no high pressure fuel leaks from the common
delivery passage 50.
[0046] As shown in further detail in Figure 6, the common delivery passage 50 is defined
within the main housing 10 and is common to all three of the pump heads 13a, 13b,
13c. The common delivery passage 50 includes first, second and third radially extending
arms 50a, 50b, 50c which define a flow passage of generally 'Y' shaped configuration
such that stress concentration between the arms is minimised. Fuel is delivered through
the first one of the arms 50a to a common outlet port 52, through which high pressure
fuel is delivered to the downstream parts of the fuel injection system, for example
a common rail. The high pressure delivery passage 50 also communicates with a high
pressure limiting valve assembly 54 which acts to control the fuel pressure level
within the housing 10.
[0047] In use, metered fuel is delivered from the transfer pump 42 to the further drilling
64. If inlet fuel pressure exceeds an amount which is sufficient to overcome the force
due to the first valve spring 56 and any pressure in the pumping chamber 22, the valve
member 58 will be urged away from its seating to permit fuel flow into the pumping
chamber 22. As the drive shaft 12 rotates, the rollers 26 of each of the pump heads
13a, 13b, 13c are caused to move in a radially outward direction, thereby imparting
movement to the associated shoe 24, such movement of the shoe 24 being guided by co-operation
between the shoe and the walls 34, 36 of the insert 30a. The pumping plunger 14 is
caused to move axially within its bore 16 to pressurise fuel within the pumping chamber
22. When fuel pressure within the pumping chamber 22 exceeds an amount which is sufficient
to overcome the force acting on the ball 66 due to any pressure within the common
rail connected to the common outlet port 52, the outlet valve arrangement 48 is caused
to open to permit high pressure fuel to flow from the pumping chamber 22, through
the passage into the delivery passage 50.
[0048] Fuel is also supplied by the transfer pump 42 to the pumping chambers of the second
and third pump heads 13b, 13c such that, as the drive shaft 12 rotates and the respective
rollers ride over the cam surface, the shoes reciprocate cyclically within their respective
bores to pressurise fuel within the pumping chambers of the second and third pump
heads 13b, 13c also.
[0049] The main pump housing 10 is filled with fuel at relatively low pressure (commonly
referred to as "housing pressure" and generally controlled by a housing pressurising
valve or an exit orifice) through a restricted feed (not shown) from the transfer
pump 42. Fuel pressure within this volume applies a force to the shoe 24, and hence
to the associated pumping plunger 14, which serves to oppose outward movement of the
pumping plunger 14 from the plunger bore 16. As the shoe 24 reciprocates between the
facing walls 34, 36 of the insert 30a, it is important that fuel within the volume
radially inward of the shoe 24 can escape relatively easily as, if this volume is
not vented, fuel pressure within the volume will tend to increase upon radially inward
movement of the shoe 24. Fuel passes between the main bore 38 and the spring space
74 through the drillings 80 in the main pump housing, and through the recesses 82a,
82b formed in the external surface of the insert 30a. The drillings 80 and the recesses
82a, 82b define a return flow path for fuel displaced by the shoe 24 between the spring
space 74 and the main axial bore 38, from where fuel flows to the low pressure return
45. The return flow path presents a relatively large flow area to fuel displaced by
reciprocating motion of the shoes to ensure movement of the shoes 24 is substantially
unimpeded, and thus fuel pressure in the space 74 remains similar to that in the main
bore 38.
[0050] It is a further benefit of the recesses 82a, 82b on the outer surface of the insert
30a that a more uniform contact pressure can be achieved between the outer diameter
of the cylindrical insert 30a and the opening 32 in the main pump housing 10.
[0051] In an alternative embodiment (not shown), the spring seat 86 for the return spring
84 and the retention clip 88 are removed, such that the return spring 84 acts directly
on the shoe 24. In this embodiment, pressure in the space 74 acts on the exposed end
of the plunger 14, and thus opposes to some extent (but does not prevent altogether)
the entry of fuel into the pumping chamber 22. The plunger 14 is maintained in contact
with fuel entering the chamber 22 during the filling stroke, and the formation of
vends or air bubbles in the filling circuit is prevented. In this case, a reduced
pressure difference is necessary to open the valve 58.
[0052] One advantage of the present invention is that the use of a separate insert 30a to
define a shoe guide path having a rectangular or square cross section to correspond
with that of the shoe can be produced more accurately and easily. Wear and manufacturing
difficulties are therefore reduced compared to existing roller-shoe pump designs.
A further advantage of the present invention is that the shoe and roller arrangements
24, 26 may be assembled within each individual insert in the main pump housing 10
before the pump head housings 18a,18b, 18c are mounted upon the main pump housing
10. Thus, manufacturing difficulties in assembling the shoe and roller arrangement
24, 26 from inside the main pump housing 10 are avoided. As the pump assembly is of
multi-part construction, access for machining precision is also greatly improved and
the assembly is readily adaptable for different user requirements.
[0053] In order to assemble the pump assembly, initially each of the pump heads 13a, 13b,
13c is assembled separately to include the respective pumping plunger 14, the inlet
and outlet valve arrangements 46, 48, and the spring 84. The insert 30a is introduced
into the passage 32 in the main pump housing 10 and is secured thereto in such a manner
that it forms an interference fit with the opening 32 in the main pump housing 10
to become a permanent feature of the housing 10 (i.e. assembled in a permanent manner
within the housing 10). By way of example, the insert 30a may be formed conveniently
by sintering or by means of metal injection moulding (MIM).
[0054] The shoe 24 and the roller 26 are then positioned in the insert Each assembled pump
head 13a, 13b, 13c may then be presented to the main pump housing 10, such that the
pumping plunger 14 and the return spring 84 are positioned against the shoe and roller
arrangement 24, 26 of each pump head with the spring seat 86 received in the annular
groove 90.
[0055] For each pump head, the pump head housing 18a,18b, 18c is clamped against the main
pump housing 10, to compress the return spring 84 and the seals 70, 72 between the
pump head housing 18a, 18b, 18c and the main pump housing 10. The screws 92 (as shown
in Figure 1) are tightened into the screw-threaded drillings in the main pump housing
10 to secure the pump head housings 18a, 18b, 18c directly to the main pump housing
10.
[0056] In an alternative embodiment of the invention (not shown) a pair of pump heads, as
described previously, is mounted upon a main pump housing, with one pump head of each
pair being mounted upon the drive shaft at substantially 90° to the other pump head
of the pair. The cam arrangement takes the form of a twin-lobed cam having two cam
surfaces, shaped to result in there being two pressurisation events for each pump
head of said pair per cycle as the drive shaft rotates. Such an arrangement provides
particular advantage in smaller engines, where accommodation space is limited. It
will be appreciated that for this embodiment of the invention, the drive arrangement
for the pump head pair may be a roller/shoe or a slipper/tappet and need not be mounted
in inserts 30a, 30b but may be guided within a guide path defined by the respective
pump head housing 18a, 18b. Further pairs of pump heads may also be provided to enable
a higher number of pressurisation events per cycle, if required. In a further embodiment
(not shown) a pair of pump heads is mounted on the main housing diametrically opposite
one another, such that rotation of the drive shaft and the associated cam results
in the plungers pumping in an alternate, phased manner. In other words when a plunger
of one of the pump heads is at the top of its stroke, the plunger of the other pump
head is at substantially the bottom of its stroke. It is envisaged that such an embodiment
would be suitable for use in applications requiring a reduced rate of fuel delivery
to the common rail.
1. A fuel pump assembly for use in an engine, the fuel pump assembly comprising a plurality
of pump heads (13a, 13b, 13c) mounted upon a main pump housing (10), wherein each
of the pump heads (13a, 13b, 13c) includes:
a pumping plunger (14) which is reciprocable, in use, within a plunger bore (16) under
the influence of an associated drive arrangement (24, 26) so as to cause pressurisation
of fuel within a pumping chamber (22) defined within a pump head housing (18a),
the drive arrangement including a shoe (24) and a roller (26) which is cooperable
with a driven cam (28), common to each of the pump heads (13a, 13b, 13c), so as to
impart reciprocal movement to the shoe (24) as the cam (28) is driven, in use,
the shoe (24) being of substantially square or rectangular cross section, and
each pump head (13a, 13b, 13c) having an associated insert (30a) being formed as a
separate part from the main pump housing (10), but being assembled permanently therewith,
wherein the insert (30a) defines a guide path of substantially rectangular or square
cross section corresponding to that of the shoe (24), so that the guide path serves
to guide reciprocating movement of the shoe (24).
2. A fuel pump assembly as claimed in claim 1, wherein the insert (30a, 30b, 30c) associated
with each pump head (13a, 13b, 13c) is formed by sintering.
3. A fuel pump assembly as claimed in claim 1, wherein the insert (30a, 30b, 30c) associated
with each pump head (13a, 13b, 13c) is formed by metal injection moulding.
4. A fuel pump assembly as claimed in any one of the preceding claims, wherein the insert
(30a, 30b, 30c) associated with each pump head (13a, 13b, 13c) has an outer surface
of substantially cylindrical form.
5. A fuel pump assembly as claimed in any one of the preceding claims, wherein the insert
(30a, 30b, 30c) has an internal surface defining two pairs of substantially parallel
facing walls (34, 36).
6. A fuel pump assembly as claimed in any one of the preceding claims, wherein the main
pump housing (10) has a plurality of openings (32), each opening (32) defining an
internal surface of substantially cylindrical form, wherein each of the inserts (30a,
30b, 30c) is received permanently within a respective one of the openings (32) to
guide reciprocating movement of an associated shoe (24).
7. A fuel pump assembly as claimed in claim 6, wherein the openings (32) take the form
of radially extending bores provided in the main pump housing (10).
8. A fuel pump assembly as claimed in claim 7, wherein the insert (30a, 30b, 30c) forms
an interference fit with the opening (32).
9. A fuel pump assembly as claimed in any of claims 6 to 8, wherein the insert (30a,
30b, 30c) defines, together with the associated opening (32) in the main pump housing
(10), a vent means for permitting fuel displaced by the shoe (24) during reciprocating
motion thereof to vent to low pressure.
10. A fuel pump assembly as claimed in claim 9, wherein the outer surface of the insert
(30a, 30b, 30c) is provided with at least one groove or recess (82a, 82b) which defines,
together with the internal surface of the associated opening (32), a return flow path
for fuel to low pressure.
11. A fuel pump assembly as claimed in any one of the preceding claims, wherein the cam
(28) defines a cam surface (27) over which the roller (26) rides, in use, wherein
each pump head (13a, 13b, 13b) is provided with a return spring (84) which acts on
the shoe (24) so as to ensure the roller (26) remains in engagement with the cam surface
(27).
12. A fuel pump assembly as claimed in claim 11, wherein a first end of the return spring
(84), in a region of the pump head housing (18a), surrounds the plunger support tube
(20) so as to retain the return spring (84) in position.
13. A fuel pump assembly as claimed in claim 11 or claim 12, wherein a second end of the
return spring (84), distal to the pump head housing (18a), is associated with positioning
means (86, 88, 90), which serves to maintain the return spring (84) in a fixed relationship
with the shoe (24).
14. A fuel pump assembly as claimed in claim 13, wherein the positioning means includes
an annular groove (90) on the radially outer surface of the shoe (24).
15. A fuel pump assembly as claimed in claim 14, wherein the positioning means includes
a spring seat (86) located on or otherwise attached to an end of the plunger (14),
and wherein the spring seat (86) locates within the annular groove (90).
16. A fuel pump assembly as claimed in any one of the preceding claims, wherein the roller
is a cylindrical roller (26).
17. A fuel pump assembly as claimed in any one of the preceding claims, wherein the pump
head housing (18a) has an integral plunger bore (16) defined in a plunger support
tube (20), the plunger support tube (20) extending substantially perpendicularly from
a lower surface of the pump head housing (18a) so as to be located at least partially
within the shoe guide path.
18. A fuel pump assembly as claimed in any one of the preceding claims, including a pair
of pump heads (13a, 13b) radially mounted upon the main pump housing (10) at diametrically
opposed positions about a pump drive shaft (12) carrying the cam (28), the cam (28)
having a cam surface (27) with a single cam lobe so as to impart phased, alternate
motion to respective plungers (14) of the pair of pump heads (13a, 13b) upon rotation
of the shaft (12).
19. A fuel pump assembly as claimed in any one of claims 1 to 17, including (10) at equi-angularly
spaced locations about a pump drive shaft (12) carrying the cam (28).
20. A fuel pump assembly for use in an engine, the fuel pump assembly comprising;
at least one pair of pump heads (13a, 13b) mounted upon a main pump housing (10),
each of the pump heads including a pumping plunger (14) which is reciprocable, in
use, within a plunger bore (16) under the influence of an associated drive arrangement
(24, 26) so as to cause pressurisation of fuel within a pumping chamber (22) defined
within a pump head housing (18a, 18b), each of the drive arrangements being co-operable
with a surface (27) of a cam (28) which is driven, in use, by an associated engine
drive shaft (12), so as to impart reciprocal movement to the pumping plunger (14)
upon rotation of the drive shaft,
wherein the cam (28) is common to each of the pump heads (13a, 13b) and wherein one
pump head of the or each pair is positioned at substantially 90° to the other pump
head of the pair, the cam (28) being shaped to result in there being two pressurisation
events for each pump head (13a, 13b) of said pair per pumping cycle as the drive shaft
rotates.
21. A fuel pump assembly as claimed in claim 20, including only a single pair of pump
heads.
22. A fuel pump assembly as claimed in claim 20 or claim 21, wherein the cam is a twin-lobed
cam, thereby to provide four equally spaced plunger pumping strokes per pumping cycle.