GB2400418A - Liner for a pump assembly - Google Patents

Abstract

A pump assembly for use in delivering fuel to a common rail of an internal combustion engine. The pump assembly includes a pumping plunger (28), a drive member (34) that is co-operable with the pumping plunger (28) and driven, in use, by an associated cam arrangement (12) to impart drive to the plunger (28), and thus to cause pressurisation of fuel within a pump chamber (30), and a pump head (22) provided with a plunger bore (26) within which the plunger (28) reciprocates as it is driven. A main pump housing (10) is provided with an opening (18a, 18b, 18c) and an insert member (32) is mounted within a first end of the opening. A second end of the opening receives the pump head (22). The insert member (32) is separate and distinct from both the main pump housing (10) and the pump head (22) and defines a guide path for the drive member (34) as it is driven by the cam arrangement (12), in use.

Description

240041 8

PUMP ASSEMBLY

The invention relates to a pump assembly suitable for use in a common rail fuel injection system for supplying high pressure fuel to a compression ignition s internal combustion engine. In particular, but not exclusively, the invention relates to a fuel pump assembly of the type having pumping plungers that are driven, in use, by means of an engine driven cam.

In a known common rail fuel pump of radial pump design, for example as lo described in EP 1 184 568A, three pumping plungers are arranged at equi angularly spaced locations around an engine driven cam. Each plunger is mounted within a respective plunger bore provided in a main pump housing and, as the cam is driven, each of the plungers is caused to reciprocate within its plunger bore. As the plungers reciprocate, each causes pressurization of fuel within a pump chamber defined at one end of the associated plunger bore. 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 so fuel system.

In one known fuel pump of the aforementioned type, each of the plungers is coupled to a respective drive member in the form of a tappet. The cam carries a ring or rider that travels over the surface of the cam as it is driven by the engine.

:5 Each tappet is located within a tappet bore provided in the main pump housing and is arranged so that as the cam is driven each tappet is caused to reciprocate within its respective bore. Motion of the tappets serves to impart drive to the plungers, and reciprocating motion of the plungers occurs in a phased, cyclical manner.

The eccentricity of the cam surface causes each tappet to be driven radially outward from the cam (i.e. inwardly within its tappet bore), which in turn causes each plunger to be driven radially outward from the cam, thereby to reduce the volume of the pump chamber. This part of the pumping cycle is referred to as the pumping stroke of the plunger, during which fuel within the associated pumping chamber is pressurised to a relatively high level.

The tappets may be urged radially inwards by means of fluid pressure within a working chamber that, in addition to a force of a plunger return spring, serves to urge the plunger in a radially inward direction to perform a plunger return stroke.

Alternatively, a plunger return spring force alone may be used to effect the Is plunger return stroke. During this part of the pumping cycle the pump chamber volume is increased and lower pressure fuel fills the pumping chamber, ready for the next pumping cycle.

The main pump housing for a pump assembly of this type typically has an axially no extending opening through which the cam shaft extends and has three radially extending lobes, each of which is provided with an opening to define a guide path for a respective one of the tappets. Each tappet is received within a radially inner end of an opening, and an associated pump head housing is received within a radially outer end. Each pump head is provided with a plunger bore to receive the associated plunger. Examples of pump assemblies generally of the aforementioned type can be found in our co-pending patent applications: EP 1 184 568 and EPO 972 936.

It is a recognised problem with fuel pump assemblies of the aforementioned type that as the cam rider rides over the cam surface to drive the tappets, a significant side load is exerted on the main pump housing by the reciprocating tappets. The s main pump housing, typically being formed from hardened steel, prevents premature wear but is an expensive component.

It is one object of the present invention to provide a fuel pump assembly for use in a common rail fuel injection system in which this wear problem is overcome or to alleviated.

According to the present invention, there is provided a pump assembly for use in delivering fuel to a common rail of an internal combustion engine, the pump assembly comprising: a pumping plunger, a drive member that is co-operable with the pumping plunger and driven, in use, by an associated cam arrangement to impart drive to the plunger and thus to cause so pressurization of fuel within a pump chamber, a pump head provided with a plunger bore within which the plunger reciprocates as it is driven, and :5 a main pump housing provided with an opening, an insert member being mounted within a first end of the opening and a second end of the opening receiving the pump head, wherein the insert member is separate and distinct from the main pump housing and the pump head and defines a guide path for the drive member as it is driven by the cam arrangement, in use.

Preferably, the plunger bore and the insert member are substantially coaxial with one another.

In one preferred embodiment the pump assembly takes the form of a radial pump assembly, including first, second and third pumping plungers radially spaced around the cam arrangement, each having an associated insert member and an lo associated drive member, and in which the main pump housing is provided with at least first, second and third radial openings, each for receiving an associated one of the insert members at a first end thereof, so as to define a guide path for the associated drive member, and an associated pump head at a second end thereof, so as to define a plunger bore for the associated plunger.

The pump assembly may therefore be considered as having three pump units, radially spaced around the cam arrangement, each having a pump head, a plunger coupled to a drive member and an insert member for mounting within a radially extending opening in a main pump housing.

It will be appreciated that the pump assembly of this preferred embodiment of the invention is not limited, however, to having three pump units, and a greater or lesser number of pump units may be provided, if required.

2s The present invention provides the advantage that side loading due to motion of the drive member as it is co-operates with the cam ring imparts a side load to the insert member or sleeve, and not to the main pump housing. Wear of the main pump housing is therefore substantially avoided. If required, the insert member, being a smaller and cheaper component, may be adaptably mounted within the opening so as to be removable and replaceable or repairable, if worn.

s It is a further advantage that the requirement to form the main pump housing from hardened steel is removed, as only the insert member needs to withstand side loading by the drive member.

In a particularly preferred embodiment, therefore, the main pump housing may be lo formed from aluminium and only the insert member need be formed from steel, so that the overall cost and weight of the assembly is considerably reduced in comparison with known pump assemblies formed entirely from steel, for

example.

An internal surface of the insert member typically defines the guide path for the drive member, and in an alternative embodiment the internal surface may be anodised to increase hardness. In this case the insert member may also be formed from aluminium, thereby further reducing the overall cost and weight of the assembly.

Preferably, the insert member takes the form of a sleeve of cylindrical form within which the drive member is driven to reciprocate, in use, and wherein the internal cylindrical surface of the sleeve defines the guide path for the drive member.

The insert member may be press-fitted into the opening of the main pump housing to provide an interference fit within the opening. Alternatively, the pump assembly may include additional fixing means for retaining the insert member in a fixed position within the opening' for example in the form of an adhesive. As a further alternative the additional fixing means may be a brazing material, with the insert member being brazed into the opening.

Preferably, the insert member has a wall thickness and a thermal coefficient of expansion selected to ensure the insert member maintains an interference fit within the opening over a full range of operating temperatures of the pump assembly. If the main pump housing is formed from aluminium and the insert lo member is formed from steel, for example, then as the two materials have quite different thermal expansion properties the interference fit between the insert member and the opening in the housing may be affected over the full range of operating temperatures of the pump assembly. This may be avoided, however, by providing an insert member having a wall thickness that is typically less than a few millimetres, and preferably is around 1 mm in thickness.

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 view of an embodiment of the pump assembly of the present invention, and Figure 2 is a sectional view of a main pump housing forming part of the assembly in Figure 1.

Referring to Figures 1 and 2, a pump assembly includes a first housing part in the form of a main pump housing 10 provided with an axially extending opening through which a cam drive shaft extends when the assembly is installed within the engine. In the section shown in Figure 1, the central axis 13 of the drive shaft is identified, although the drive shaft itself is not visible. The drive shaft co- operates with a cam arrangement including an eccentrically mounted cam 12.

Although not visible in the accompanying figures, the main pump housing 10 projects, at its front end, to accommodate the near full length of the drive shaft.

The assembly is typically closed at its back end by a rear closure plate (not shown) and at its front end by a front closure plate having three ears or flanges 16, each provided with a respective opening 14 for receive a suitable fixing for lo mounting the pump assembly to the engine.

The main pump housing 10 is provided with first, second and third radially extending openings or through bores 18a, lab, 18c respectively, each of which communicates at a first end thereof with the axially extending opening for the Is drive shaft. A radially outer open end of each opening receives a respective one of first, second and third pump heads or blocks. The first, second and third pump heads are identified by reference numbers 20a, 20b, 20c respectively and, for the purpose of simplicity and as the three pump heads are substantially identical to one another, only the first pump head 20a will be described in detail below.

The first pump head 20a includes a head portion 22 and a downwardly extending extension 24 (in the orientation shown) which is received within the radially outer open end of the opening 18a in the main pump housing 10. The extension 24 is provided with a plunger bore 26 for a pumping plunger 28, with a blind end of :5 the plunger bore 26 being located within the head portion 22 of the first pump head 20a. The blind end of the plunger bore 26 defines, together with a radially outer end of the plunger 28, a pump chamber 30 to which fuel at relatively low pressure (referred to as "transfer pressure") is received and within which pressurization of fuel to a relatively high level suitable for injection takes place as the plunger 28 is driven to perform a pumping stroke, in use, upon rotation of the drive shaft.

As can be seen most clearly in Figure 2, a hollow insert member or sleeve 32 of substantially cylindrical form is also received within a radially inner end of the opening 18a so as to be substantially co-axially aligned with the plunger bore 26 and such that an end region of the extension 24 projects part way into the sleeve to 32. An internal surface of the sleeve 32 defines a guide path for a drive member for the plunger 28 in the form of a tappet 34, preferably a so-called "bucket tappet". The tappet 34 is coupled to the plunger 28 and is of generally U-shaped or channelled cross section, and includes a base portion and first and second side walls (not identified).

The upper surface of the tappet base portion is provided with recess for locating one end of a plunger return spring 36 mounted concentrically with the plunger 28 and the extension 24 and occupying a clearance region defined between the internal surface of the sleeve 32 and the extension 24. The other end of the no plunger return spring 36 abuts the head portion 22 of the first pump head 20a so that the spring 36 serves to apply a return biasing force to the plunger 28, and hence to the tappet 34, to drive a plunger return stroke.

In order to assemble the parts, the sleeve 32 is conveniently inserted into the :5 opening 18a and then deformed so as to secure the sleeve 32 in position within the opening 18a (or, in other words, the sleeve 32 is "interference pressed" into the opening 18a). Alternatively, the sleeve 32 may be fixed in position within the 9 1 opening by means of an additional fixing means, for example a suitable brazing material, and using a brazing technique. As a further alternative the additional fixing means may take the form of an adhesive provided between the sleeve 32 and the surface of the opening 18a to secure the sleeve 32 in a fixed position within the opening 18a. Depending on the method used to secure the sleeve 32 within the opening 18a, it may be necessary to finish machine the internal surface of the sleeve 32 defining the tappet guide path after it has been fixed within the opening 18a.

lo The drive shaft co-operates with the cam 12 which, in turn, carries a generally; circular cam rider 38. The cam rider 38 is provided with three flattened surfaces, each one of which co-operates with the tappet 34 of a respective pump head 20a, 20b, 20c. As the tappet 34 is coupled to the plunger 28, rotation of the shaft causes the cam rider 38 to ride over the surface of the cam 12, thereby imparting drive to both the tappet 34 and the plunger 28. The tappet 34 is therefore caused to reciprocate within the sleeve 32, and the plunger 28 is caused to reciprocate within the plunger bore 26. As the drive shaft rotates, the tappet 34 and the pumping plunger 28 are therefore driven together causing the plunger 28 to perform a pumping cycle including a pumping stroke, during which the tappet 34 so and the plunger 28 are driven radially outward from the shaft (i.e. for the first! pump head 20a, vertically upwards in Figures 1 and 2) to reduce the volume of the pump chamber 30. During this pumping stroke the pumping plunger 28 is driven inwardly within its plunger bore 26.

:5 During a subsequent plunger return stroke, the tappet 34 and the plunger 28 are urged in a radially inward direction (i.e. vertically downwards in Figures 1 and 2) to increase the volume of the pump chamber 30. During the return stroke of the plunger 28 and its tappet 34, the plunger 28 is urged outwardly from the plunger bore 26 and fuel at relatively low pressure fills the associated pump chamber 30.

During the pumping stroke fuel within the pump chamber 30 is then pressurised to a relatively high level in a manner which would be familiar to those skilled in

s this technology field.

The provision of the plunger return spring 36 serves to urge the plunger 28 to perform its return stroke and additionally ensures contact is maintained between the tappet 34 and the cam rider 38 at all times throughout the pumping cycle. The lo side walls of the tappet 34 have outer surfaces of generally cylindrical form, and this outer surface cooperates with a substantially cylindrical internal surface of the sleeve 32 such that the sleeve serves to guide motion of the tappet 34 as it reciprocates.

Is In pump assemblies of this type, the tappet 34 and the plunger 28 perform cyclical sinusoidal motion and are driven at a maximum frequency of about 120 Hz. The tappet 34 typically has a range of travel, between bottom-dead-centre and top-dead-centre, of around 10 millimetres.

So The pump assembly is provided with an appropriate inlet metering valve (not shown) with appropriate inlet and outlet valves (also not shown) being provided for each pump chamber 30 in a conventional manner. The inlet metering valve and the pump chamber inlet valve control the supply of low pressure fuel delivery into the pump chamber 30. Primarily, it is the inlet metering valve that controls as the quantity of fuel delivered during each filing stage. Delivery of pressurised fuel out of the pump chamber 30 to a delivery passage and, hence, to the downstream common rail or accumulator volume, is controlled by the pump chamber outlet valve.

The inlet and outlet valves are of known construction and further details may be s found, for example, in our co-pending European patent application EP 1184568A2 and British patent application GO 0201626.9. Pressurisation of fuel within the pump chamber 30 occurs during the pumping stroke of the associated plunger, during the period for which both the inlet and outlet valves are closed.

When fuel is pressurised to a level that is sufficient to open the outlet valve, lo pressurised fuel is supplied through the delivery passage to the common rail.

Typically, the pressure of fuel supplied through the outlet valve is in the range of between 1500 and 2000 bar.

During the return stroke of the plunger 28, fuel pressure downstream of the pump Is chamber 30 is higher than that within the pump chamber 30 and the outlet valve is urged closed. During the period of the return stroke for which the inlet valve is urged open, fuel at relatively low pressure is supplied to the pump chamber 30 ready for commencement of the following pumping stroke. This cycle of pumping is described in further detail in the aforementioned patent applications, no and in any case would be familiar to those skilled in this field.

The pump assembly of the present invention is intended for use with a low pressure fuel pump, such as a transfer pump, which supplies fuel through the inlet metering valve and the respective inlet valve to the pump chamber 30. Although :5 not illustrated in the accompanying drawings, it is convenient to mount the transfer pump upon a rear closure plate of the main pump housing 10, and to drive the transfer pump by means of a shaft extension in connection with the drive shaft.

It is a particular benefit of the pump assembly of the present invention that wear of the main pump housing 10, due to side loading by the tappet 34 as it reciprocates, is substantially avoided. The requirement to form the main pump housing 10 from a hard material (e.g. cast iron or steel) capable of withstanding such high loading is therefore avoided. Instead, only the insert member in the form of the sleeve 32 need be formed from a hard material, such as steel or cast lo iron. As the sleeve 32 is a relatively small component, the weight and cost of the pump assembly is therefore reduced and the service life is prolonged. The main pump housing 10 may therefore, for example, be formed from aluminium, which is lighter and cheaper than steel. Additionally, the sleeve 32 may be mounted within the opening 18a so as to be removable for repair or replacement quite conveniently, if required.

In high pressure pump assemblies in which the supply of pressurised fuel passes through passages defined within the main pump housing 10 itself, the present invention may be less useful as the high pressure flow can force the requirement for a steel housing regardless. The present invention is, however, particularly advantageous in pump assemblies of the type in which high pressure fuel does not flow through passages in the main pump housing 10, and thus in which there is no limitation on the material of the main pump housing 10 due to hydraulic flow considerations.

Even if high pressure fuel is required to flow through the main pump housing 10, however, it is possible that a cast iron main pump housing may be used, as opposed to steel, for fuel pressures as high as 1600 bar with the insert member suffering wear due to side loading by the tappet, as opposed to the main pump housing.

s In an alternative embodiment to that described previously, the sleeve 32 is similar structurally to that shown in the accompanying drawings but may be formed from aluminium, for example, with a hardened material coating applied to its internal surface. The hardening of the internal surface may be achieved by anodising the surface, for example.

It is important that the dimensions of the sleeve 32 and its material properties are selected to ensure the interference fitting of the sleeve 32 within the opening 18a in the main pump housing 10 is maintained throughout all pump operating conditions. In one particularly preferred embodiment of the invention, where the main pump housing 10 is formed from aluminium and the sleeve 32 is formed from steel, it is therefore important to take account of the different thermal expansion coefficients of aluminium and steel and the effect of this over the range of pump operating temperatures. Typically, for example, the pump assembly may reach a temperature in excess of 140 degrees during operation. It so is preferred, therefore, that the thickness of the wall of the sleeve 32 is between about 0.5 and 2 mm, and preferably is approximately 1 rnillimetre, so as to maintain the sleeve 32 in an interference fit within the opening 1 8a over substantially the full range of pump operating temperatures.

Claims (14)

1. A pump assembly for use in delivering fuel to a common rail of an internal combustion engine, the pump assembly comprising: s a pumping plunger, a drive member that is co-operable with the pumping plunger and driven, in use, by an associated cam arrangement to impart drive to the plunger and thus to cause lo pressurization of fuel within a pump chamber, a pump head provided with a plunger bore within which the plunger reciprocates as it is driven, and a main pump housing provided with an opening, an insert member being mounted within a first end of the opening and a second end of the opening receiving the pump head, wherein the insert member is separate and distinct from the main pump housing and the pump head and defines a guide path for the drive member as it is driven by the cam arrangement, in use.

2. The pump assembly as claimed in claim 1, wherein the plunger bore and the insert member are substantially co-axially aligned.

3. The pump assembly as claimed in claim 1 or claim 2, in the form of a as radial pump assembly including first, second and third pumping plungers, each having an associated insert member and an associated drive member, and in which the main pump housing is provided with at least first, second and third radial openings, each for receiving an associated one of the insert members at its first end, so as to define a guide path for the associated drive member, and an associated pump head at its second end, so as to define a plunger bore for the associated plunger.

4. The pump assembly as claimed in any one of claims 1 to 3, wherein the insert member takes the form of a sleeve of cylindrical form within which the drive member reciprocates, in use, and wherein the internal cylindrical surface of the sleeve defines the guide path for the drive member.

S. The pump assembly as claimed in any one of claims 1 to 4, wherein the insert member is formed from steel.

6. The pump assembly as claimed in any one of claims 1 to 5, wherein the Is main pump housing is formed from aluminium

7. The pump assembly as claimed in claim 4, wherein the internal surface of the sleeve is anodised to increase surface hardness.

so

8. The pump assembly as claimed in claim 7, wherein the insert member is formed from aluminium.

9. The pump assembly as claimed in any one of claims 1 to 8, wherein the insert member is secured within the opening by interference pressing.

10. The pump assembly as claimed in any one of claims 1 to 8, including additional fixing means for securing the insert member within the opening.

11. The pump assembly as claimed in any one of claims 1 to 10, wherein the insert member has a wall thickness and a thermal coefficient of expansion selected to ensure the insert member maintains an interference fit within the opening over a full range of operating temperatures of the pump assembly. s

12. The pump assembly as claimed in claim 11, wherein the wall thickness of the insert member is between 0.5 and 2.0 mm.

13. The pump assembly as claimed in any one of claims 1 to 12, wherein the lo insert member is adaptably mounted within the opening so as to be removable for replacement or repair, if worn.

14. A pump assembly substantially as herein described with reference to the accompanying drawings.