EP4702233A1

EP4702233A1 - Fuel pump roller tappet assembly

Info

Publication number: EP4702233A1
Application number: EP24726153.0A
Authority: EP
Inventors: David Richard Jones
Original assignee: Phinia Delphi Luxembourg SARL
Current assignee: Phinia Delphi Luxembourg SARL
Priority date: 2023-04-28
Filing date: 2024-04-26
Publication date: 2026-03-04
Also published as: GB2629429B; WO2024223910A1; GB2629429A; GB202306304D0

Abstract

A roller tappet assembly for a fuel pump assembly of an internal combustion engine, the roller tappet assembly comprising a tappet body with a tappet body cavity. First and second bearings are mounted to the tappet body within the tappet body cavity. An annular roller assembly is arranged inside the tappet body cavity for rolling contact with a cam surface of a camshaft of the fuel pump assembly. A pin extends through the first bearing, the roller assembly, and the second bearing, the pin being supported by the first bearing and the second bearing. A first retaining feature is disposed on the pin outside the first bearing and a second retaining feature disposed on the pin outside the second bearing. Interaction between the first retaining feature and the first bearing, and between the second retaining feature and the second bearing, constrains axial movement of the pin relative to the tappet body.

Description

FUEL PUMP ROLLER TAPPET ASSEMBLY

FIELD OF THE INVENTION

This invention relates to a roller tappet assembly for a fuel pump assembly of an internal combustion engine. The invention further relates to a fuel pump assembly comprising such a roller tappet assembly. The invention further relates to a method of assembly of a roller tappet assembly.

BACKGROUND

Common rail direct fuel injection systems use a high-pressure fuel pump to inject fuel into the engine’s combustion chamber. The high-pressure fuel pump uses one or more reciprocating plungers to feed fuel into the common rail at a pressure of typically more than 200 MPa. Each plunger is driven by a respective cam of a common rotating camshaft. A roller tappet assembly is coupled to the plunger so as to cause the plunger to follow the cam movement.

Typically, the roller tappet assembly comprises a tappet body that is connected to the plunger. An annular roller assembly is provided in a cavity of the tappet body and rolls over an outer surface of the rotating cam. A spring force may be used to ensure that the tappet assembly keeps in constant contact with the camshaft. The roller assembly is mounted inside the tappet body cavity by a pin that extends through the roller assembly. As a result, the pin functions as an axle around which the roller assembly rotates.

For optimal functioning of the tappet assembly and to minimise wear, it is important that the pin is axially and radially constrained relative to the tappet body. This can be achieved by deforming the pin at one or both ends after installing the roller assembly in the tappet body cavity and inserting the pin into the centre of the roller assembly.

In addition, axial movement of the roller assembly within the tappet body cavity can cause undesirable wear on the axially inward facing surfaces of the tappet body cavity, due to rubbing of the axial end faces of the roller assembly, which may be an unmachined surface formed from, for example, forged steel. It is against this background that the invention has been devised.

SUMMARY OF THE INVENTION

According to a first aspect, there is provided a roller tappet assembly for a fuel pump assembly of an internal combustion engine, the roller tappet assembly comprising: a tappet body with a tappet body cavity; a first bearing mounted to the tappet body within the tappet body cavity; a second bearing mounted to the tappet body within the tappet body cavity; an annular roller assembly arranged inside the tappet body cavity for rolling contact with a cam surface of a camshaft of the fuel pump assembly; a pin extending through the first bearing, the roller assembly, and the second bearing, the pin being supported by the first bearing and the second bearing; a first retaining feature disposed on the pin outside the first bearing; and a second retaining feature disposed on the pin outside the second bearing; such that interaction between the first retaining feature and the first bearing, and between the second retaining feature and the second bearing, constrains axial movement of the pin relative to the tappet body.

The first bearing may define a radially extending surface for axially engaging a first axial end of the roller assembly and the second bearing may define a radially extending surface for axially engaging a second axial end of the roller assembly, the second axial end being opposite the first axial end.

The radially extending surfaces of the first and second bearings help to prevent axial ends of the roller assembly from coming into contact with internal surfaces of the tappet body cavity.

The first bearing may define a first flange extending radially from the pin and the second bearing may define a second flange extending radially from the pin, wherein the first flange defines a radially extending surface for axially engaging a first axial end of the roller assembly and the second flange defines a radially extending surface for engaging a second axial end of the roller assembly opposite the first axial end. The first and second flanges may prevent axial ends of the roller assembly from coming into contact with internal surfaces of the tappet body cavity.

Each of the first and second flanges may include an aperture for allowing passage of a lubricant from passageways to the roller assembly.

The first bearing may define a first sleeve extending away from the tappet body cavity along a first portion of the pin and the second bearing may define a second sleeve extending away from the tappet body cavity along a second portion of the pin.

The first and second sleeves may provide an extended internal surface for bearing the pin, and/or assist with locating the first and second bearings relative to the tappet body.

The first and/or second retaining feature may comprise a radially outwardly extending caulking feature.

The first bearing may be retained within a first aperture formed in the tappet body and the second bearing may be retained within a second aperture formed in the tappet body.

The first and second bearings may be formed from a material that is harder than the material from which the tappet body is formed.

According to a second aspect, there is provided a fuel pump assembly comprising at least one roller tappet assembly as defined in the first aspect.

According to a third aspect, there is provided a method of assembling a roller tappet assembly according to the first aspect, the method comprising: mounting the first and second bearings to the tappet body; positioning the roller assembly within the tappet body cavity between the first and second bearings; axially sliding the pin through the first bearing, the roller assembly, and the second bearing; forming or mounting the first retaining feature on the pin outside the first bearing; and forming or mounting the second retaining feature on the pin outside the second bearing.

It will be appreciated that preferred and/or optional features of the first aspect of the invention may be incorporated alone or in appropriate combination within the second or third aspects of the invention also.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood, preferred non-limiting embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a side view of a fuel pump assembly, which is known in the art;

Figure 2 is an enlarged sectional view of a part of the fuel pump assembly of Figure 1 ;

Figure 3 is an enlarged sectional view of the roller tappet assembly of the fuel pump assembly of Figures 1 and 2;

Figure 4 is an enlarged sectional view of a roller tappet assembly according to an embodiment of the invention;

Figure 5 is an enlarged sectional view of the roller tappet assembly of Figure 4 looking through the first bearing, with the pin removed;

Figure 6 is a perspective view of the first bearing of the roller tappet assembly of Figures 4 and 5;

Figure 7 is an enlarged sectional view of a roller tappet assembly according to a further embodiment of the invention; and Figure 8 is a flowchart showing a method of assembling a roller tappet assembly according to a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Throughout this description, terms such as 'top', 'bottom', 'upper' and 'lower', and other directional references, are used with reference to the orientation of the tappet as shown in the accompanying drawings. However, it will be appreciated that such references are not limiting and that tappets according to the invention can be used in any orientation.

Figures 1 to 3 show a known common rail fuel pump assembly 10 (hereinafter “the pump”) for use in a compression-ignition internal combustion engine. The pump 10 is an in-line pump arrangement comprising a main pump housing 12 and first and second pump elements, which are driven by means of a common, engine-driven driveshaft 18 that extends through the main pump housing 12 and rotates at a speed proportional to the speed of the engine.

A low-pressure suction pump 13 is mounted to the side of the main pump housing 12 to deliver relatively low-pressure fuel to the pump 10. The driveshaft 18 carries first and second cam drive arrangements 20, 22, which are either mounted on, or form an integral part of, the driveshaft 18.

The driveshaft 18 is reciprocally connected to each of the pump elements via respective intermediate drive assemblies in the form of a first or second roller tappet assembly, referred to generally as 19, 21 respectively.

Each roller tappet assembly 19, 21 includes a corresponding tappet body, 23, 25. As can be seen most clearly in Figures 2 and 3, and describing only the first tappet assembly 19, the tappet body 23 comprises a tappet body cavity 60. The roller assembly comprises a pair of annular rollers in the form of an outer roller 27 and an inner roller 29. An outer surface of the outer roller 27 is arranged to roll over the surface of the associated cam arrangement 20. A pin 24 secures the tappet body 23 to the associated roller assembly 27, 29, and the inner roller 29 slides relative to the pin 24 and the outer roller 27. It will be appreciated that this arrangement of the roller tappet assembly 19, 21 and the roller assembly 27, 29 is just one example of how the drive assembly for a plunger is driven by rotation of the driveshaft 18. For example, in an alternative embodiment, the inner roller 29 may be replaced by a roller bearing in the form of a ball bearing that has its inner race fixedly connected to the pin 24 and its outer race to the outer roller 27 of the roller assembly.

It is helpful to consider the operation of the pump assembly in Figures 1 to 3 to understand the technical problem that the invention sets out to address. Two separate pump elements in the form of the first and second pumping plungers, 14 and 16, as shown in Figures 1 and 2, but for the purpose of the following description only one of the plungers 14 will be described in detail.

The first pumping plunger 14 extends through a substantially tubular turret 28 that forms part of a pump head housing 30 mounted to the main pump housing 12. The turrets 28 downwardly extends from the pump head housing 30 and defines a substantially cylindrical plunger bore 32, the turret 28 projecting into the body of the main pump housing 12 and terminating in a lower turret surface 34. The plunger bore 32 is configured to receive the plunger 14, the lower end of which extends from the turret 28.

At the uppermost end of the plunger 14 (in the illustration shown), the plunger 14 defines, together with the bore 32 in the pump at 30, a pump chamber 36 (as shown in Figurel) for receiving fuel to be pressurised by the plunger 14 when the pump assembly is in use. Likewise, the second plunger 16 has an associated pump chamber 38.

The pump chamber 36 of the first plunger 14 is fitted with an inlet valve 40 and an outlet valve (not shown) to control, respectively, fuel flow into and out of the pump chamber 36 through the pump cycle. The configurations of such valve assemblies are well known in the art and, given that they are not central to the invention, will not be described in detail here, except to say that they are used to control flow of the fuel from a pump inlet 42 through to the pump chamber 36, and from the pump chamber 36 through to a pump outlet 44 to the common rail (not shown) each other go to spring (not identified), which acts to close the valve to prevent the passage of fuel therethrough. The plunger is movable between a bottom-dead-centre position (hereinafter, “BDC position”) and a top-dead-centre position (hereinafter, “TDC position”), defining a pumping stroke, and between the TDC position and the BDC position, defining a return stroke. A pumping stroke followed by a return stroke defines a pumping cycle for the plunger 14 and pump assembly 10. Figure 2 shows the plunger 14 on the right-hand side of the assembly with the plunger at the BDC position, while the plunger 16 on the left-hand side of the assembly is moving towards TDC position.

A spring abutment member in the form of an annular spring plate 50 forms a collar around the plunger 14 in a lower region of the plunger and is attached thereto such that the respective motions are coupled together. The spring plate 50 defines an abutment surface 52 for one end of a plunger return spring 54 (hereinafter, “return spring”) in the form of a helical coil spring. Accordingly, the spring plate 50 acts as a seat member for the return spring 54. The other end of the return spring 54 engages a fixed abutment surface defined by the underside of the pump head housing 30. The return spring 54 is thus permanently engaged with both the spring plate 50 and the pump head housing 30.

When the plunger is in the TDC position (as for the left-hand plunger 16 in Figure 2), both the inlet valve 40 and the outlet valve to the respective pump chamber 36 are closed, thereby preventing fuel from flowing into or out of the pump chamber 36. As the driveshaft 18 rotates and the tappet assembly 19 rides over the cam 20, the return spring 54 acts on the plunger 14 to urge the plunger away from the TDC position, through the return stroke to the BDC position. This causes an increase in the volume of the pump chamber 36, decreasing the pressure within it and establishing a pressure drop across the inlet valve 40. This pressure drop allows the inlet valve 42 open against the force of the inlet valve spring and fuel enters the pump chamber 36 until the pressure across the inlet valve 40 equalises, causing it to close. This typically occurs just after the plunger 14 reaches the BDC position. During the return stroke the fuel is supplied to the pump chamber 36 at a pressure of around three bar (300 kPa). Throughout the return stroke the return spring 54 serves to ensure that contact is maintained between the various drivetrain components, including maintaining contact between the plunger 14 and the tappet assembly 19, and between the tappet assembly 19 and the cam 20. Once the plunger 14 reaches the BDC position, it begins the pumping stroke as the driveshaft 18 continues to rotate. During the pumping stroke fuel in the pump chamber 36 is pressurised as the volume of the pump chamber 36 is reduced with the advancing plunger 14. During this phase of operation, the inlet valve 40 of the pump chamber 36 is caused to close due to the pressure drop across it and the pressure in the pump chamber 36 is increased, typically to at least 200 bar (20 MPa) and sometimes as high as 2500 bar (250 MPa). A pressure drop is created across the outlet valve (not shown), allowing it to open against the force of the outlet valve spring. Fuel exits the pump chamber 36 and flows into the common rail fuel volume. As the plunger 14 reaches the TDC position, the pressure across the outlet valve (not shown) equalises, causing it to close.

Throughout the pumping stroke the force from the return string 54 continues to act through the drivetrain components to ensure contact is maintained between the roller tappet assembly 19 and the cam 20, while importantly minimising slippage between the outer roller 27 and the cam 20.

For optimal functioning of the tappet assembly 19 and to minimise wear, it is important that the pin 24 is axially and radially constrained relative to the tappet body 23. In known roller tappet assemblies 19 such as the one shown in Figure 3, these constraints can be achieved by a caulking process, in which an axial force is applied to an outer region of the pin 24 so as to deform a small portion of the pin’s outer diameter. The radially outer edge of the deformed portion interferes with the bore within which the pin 24 is retained, thereby preventing movement of the pin 24.

Caulking is a complex manufacturing process that may, for example, involve case hardening of only the central portion of the pin 24, or hardening of the full pin 24 followed by localised tempering to provide deformable end portions. Moreover, the inventor has identified that the significant forces required to caulk the pin such that it firmly engages the inner surface of the bore can cause appreciable distortion of the assembly with a significant increase in the cylindricity of the tappet outer diameter. This increased cylindricity can lead to inconsistent lubricant flow around the tappet outer diameter. In addition, the caulking operation adds complexity to the tappet assembly process, and controlling the operation to ensure reliable results can be challenging. Turning to Figure 4, there is shown a roller tappet assembly 100 forming part of a fuel pump assembly, such as fuel pump assembly 10. Roller tappet assembly 100 shares several elements with the roller tappet assembly 19 described earlier, and such shared elements are indicated with like reference signs in the drawings.

A first bearing 106 is mounted to the tappet body 23 within the tappet body cavity 60. This is achieved by press-fitting the first bearing 106 axially into a corresponding first aperture 108 formed in the tappet body 23. Similarly, a second bearing 110 is mounted to the tappet body 23 within the tappet body cavity 60. This is achieved by press-fitting the second bearing 110 axially into a corresponding second aperture 112. First aperture 108 is axially aligned with second aperture 112. An example of the fitting of the first bearing 106 and the second bearing 110 into the respective first aperture 108 and second aperture 112 is described in more detail below with reference to Figure 9.

Optionally, the first and second bearings 106, 110 can be formed from a material that is harder than both the material from which the tappet body 23 is formed, and/or the material from which the pin 24 is formed. In this context, “harder” means the properties of the materials, which can include any optional treatments applied to them. For example, at least part of an outer surface of the bearings 106, 110 can be hardened or toughened by various processes, such as case hardening, shot peening, or nitriding. Alternatively, or in addition, a wear-resistant coating can be applied to an outer surface of the bearings 106, 110 where increased wear resistance is required. Alternatively, or in addition, the basic material of the first and second bearings 106, 110 can be inherently harder or tougher than the material used to form the tappet body 23 and/or the material from which the pin 24 is formed.

The roller assembly 27, 29 is arranged inside the tappet body cavity 60 for rolling contact with a cam surface of a camshaft of the fuel pump assembly 19, as described above in relation to Figure 3.

The pin 24 extends through the first bearing 106, the roller assembly 27, 29, and the second bearing 110, the pin 24 being supported by the first bearing 106 and the second bearing 110. A first retaining feature is disposed on the pin 24 outside the first bearing 106 and a second retaining feature is disposed on the pin 24 outside the second bearing. The first and second retaining features can take the form of first and second radially outwardly extending caulking features, respectively. For example, in the implementation of Figures 4 and 5, the caulking features take the form of ridges 114 and 116 formed by a caulking process. However, it will be appreciated that other forms of retaining feature may be used. One example of an alternative retaining feature is a circlip, which can be retained by a circumferential groove formed in an outer surface of the pin 24. Other forms of retaining feature will suggest themselves to the skilled person.

Interaction between the first ridge 114 and the first bearing 106, and between the second ridge 116 and the second bearing 110, constrains axial movement of the pin 24 relative to the tappet body 23. This is because the first and second ridges 114, 116 project radially outward further than the adjacent inner diameter of the first and second bearings 106, 110. As such, as the pin 24 moves right, for example, the first ridge 114 comes into contact with a left end edge 118 of the first bearing 106, which prevents further axial movement of the pin 24. A similar constraint happens when the pin 24 moves left and the second ridge 116 comes into contact with a right end edge 120 of second bearing 110.

In the implementation of Figures 4 and 5, the first bearing 106 defines a first flange 122 extending radially from the pin 24 and the second bearing 110 defines a second flange 124 extending radially from the pin 24. The first flange 122 defines a radially extending surface 126 for axially engaging a first axial end 128 of the roller assembly 27, 29 and the second flange 124 defines a radially extending surface 130 for engaging a second axial end 132 of the roller assembly 27, 29 opposite the first axial end 128.

The first flange 122 includes a first port 134 extending axially through it and the second flange 124 includes a second port 136 extending axially through it. The first and second ports 134, 136 allow passage of lubricant from passageways 138 (formed in the tappet body 23) to the roller assembly 27, 29. The first bearing 106 defines a first sleeve 140 extending away from the tappet body cavity 60 along a first portion of the pin 24. The second bearing 110 defines a second sleeve 142 extending away from the tappet body cavity 60 along a second portion of the pin 24. The first and second sleeves 140, 142 extend into, and are an interference fit with, the inner surfaces of the first aperture 108 and the second aperture 112, respectively, of the tappet body 23. As such, in the implementation of Figures 4 and 5, the first and second sleeves 140, 142 assist with locating the first and second bearings 106, 110 relative to the tappet body 23, and also provide an extended internal axial surface for bearing the pin 24.

Overall, the first and second bearings 106, 110 are generally top-hat shaped in cross section.

In use, the roller assembly 27, 29 rotates about the pin 24. Any tendency of the roller assembly 27, 29 to wander axially is constrained by interaction between the first and second axial ends 128, 132 of the roller assembly 27, 29 and the respective radially extending surfaces 126, 130 of the first and second flanges 122, 124, respectively. In this way, the first and second flanges 122, 124 prevent the first and second axial ends 128, 132 of the roller assembly 27, 29 from coming into contact with internal surfaces of the tappet body cavity 60.

In addition, axial movement of the pin 24 relative to the tappet body 23 is constrained by the interaction of the first ridge 114 and the left end edge 118 of the first bearing 106, and of the second ridge 116 and the right end edge 120 of the second bearing 110.

Turning to Figure 7, there is shown an alternative implementation of a roller tappet assembly 156. The roller tappet assembly 156 shares several elements with the roller tappet assembly 100 described earlier, and such shared elements are indicated with like reference signs in the drawings. Passageways 138 are omitted for clarity in Figure 7, and any necessary lubricant can be supplied in any suitable manner known in the art.

The roller tappet assembly 156 differs from the roller tappet assembly 100 due to the cross-sectional shape of the first and second bearings 106, 110. Instead of being top-hat shaped in section like those shown in Figures 4 to 7, the first and second bearings 106, 110 of the roller tappet assembly 156 do not have sleeves or flanges. Instead, they are rectangular in cross section. The skilled person will appreciate that other shapes, sizes, configurations, aspect ratios, and crosssections may be employed for the bearings, depending upon the needs of particular implementations.

As for the previous embodiment, the first and second bearings 106, 110 define radially extending surfaces, 126, 130 respectively, which cooperate with the axial ends 128, 132 of the roller assembly. This arrangement prevents the first and second axial ends 128, 132 of the roller assembly 27, 29 from coming into contact with internal surfaces of the tappet body cavity 60.

Turning to Figure 8, there is shown a method 144 of assembling a roller tappet assembly, such as roller tappet assembly 100 for example.

The method (144) comprises mounting (146) first and second bearings 106, 110 to the tappet body 23. This can be accomplished by press-fitting the first bearing 106 axially into the first aperture 108, and press-fitting the second bearing 108 axially into the second aperture 112. Such press-fitting operations can be performed as separate steps, or simultaneously. Optionally, the tappet body 23 can be heated to slightly enlarge the first and second apertures 108, 112, ensuring a tighter hold on first and second bearings 106, 110 upon cooling.

Next, the roller assembly 27, 29 is positioned (148) within the tappet body cavity 60 between the first and second bearings 106, 110.

The pin 24 is axially slid (150) through the first bearing 106, the roller assembly 27, 29, and the second bearing 110, such that the pin 24 is supported by the first and second bearings 106, 110 each side of the roller assembly 27, 29.

A first retaining feature is formed or mounted (152) on the pin 24 outside the first bearing 106. For example, the retaining feature can be formed by a caulking process, in which a die is pressed axially into the end of the pin 24, such that an outer edge of the pin 24 is deformed to form a caulking feature such as the first ridge 114. Alternatively, a circlip, collet, or other separate retainer can be attached to the pin 24 in a known manner. A second retaining feature is formed or mounted (154) on the pin 24 outside the second bearing 110. For example, the retaining feature can be formed by a caulking process, in which a die is pressed axially into the end of the pin 24, such that an outer edge of the pin 24 is deformed to form a caulking feature such as the second ridge 116. Alternatively, a circlip, collet, or other separate retainer can be attached to the pin 24 in a known manner.

Optionally, the caulking process can be performed simultaneously at both ends of the pin 24. In this way, it is not necessary to provide a counter force at the other end of the pin while forming each caulking feature separately.

By controlling the force applied during the caulking process, the magnitude of the pin end deformation can be constrained so that there is little (or ideally no) radial interference between the pin 24 and either the tappet body 23 or the inner surface of the first and second bearings 106, 110. When compared with the full radial deformation of the pin required to lock the pin in place in the prior art shown in Figures 1 to 3, the reduced forces required to perform the smaller amount of caulking required to axially retain the pin relative to the bearings results in reduced distortion of the pin.

Where the bearings 106, 110 include a flange (such as first and second flanges 122 and 124 in Figures 4 to 6), there is the additional benefit of optionally providing a more predictable engagement surface (e.g., radially extending surfaces 126 and 130) on the bearings for interacting with the axial ends of the roller assembly. This is particularly the case where the engagement surface is formed from a more wearresistant material, for example as described above.

Optionally, the pin 24 can be supported by the bearings 106, 110 in such a way that some rotation of the pin 24 relative to the bearings 106, 110 is allowed. This can help distribute wear across the pin, increasing longevity.

It will be appreciated by a person skilled in the art that the invention can be modified to take many alternative forms to those described herein, without departing from the scope of the appended claims.

References Used 10 - fuel pump assembly

12 - main pump housing

13 - low pressure suction pump

14 - plunger

16 - plunger

18 - drive shaft

19 - first roller tappet assembly

20 - first cam drive arrangement

21 - second roller tappet assembly

22 - second cam drive arrangement

23 - first tappet body

25 - second tappet body

24 - pin

27 - outer roller

28 - turret

29 - inner roller

30 - pump head housing

32 - plunger bore

34 - lower turret surface

36 - pump chamber

38 - pump chamber

40 - inlet valve

42 - pump inlet

44 - pump outlet

50 - spring plate

52 - abutment surface of spring abutment plate

54 - return spring

60 - tappet body cavity

100 - roller tappet assembly

106 - first bearing

108 - first aperture

110 - second bearing

112 - second aperture

114 - first ridge

116 - second ridge 118 - left end edge of first bearing

120 - right end edge of second bearing

122 - first flange

124 - second flange

126 - radially extending surface (first flange)

128 - first axial end of roller assembly

130 - radially extending surface (second flange)

132 - second axial end of the roller assembly

134 - first port

136 - second port

138 - passageways

140 - first sleeve

142 - second sleeve

144 - method

146 - mount bearings

148 - position roller assembly within tappet cavity body

150 - slide pin through bearings and roller assembly

152 - form/mount the first retaining feature

154 - form/mount the second retaining feature

156 - roller tappet assembly

Claims

CLAIMS:

1. A roller tappet assembly (100, 156) for a fuel pump assembly (10) of an internal combustion engine, the roller tappet assembly (100, 156) comprising: a tappet body (23) with a tappet body cavity (60); a first bearing (106) mounted to the tappet body (23) within the tappet body cavity (60); a second bearing (110) mounted to the tappet body (23) within the tappet body cavity (60); an annular roller assembly (27, 29) arranged inside the tappet body cavity (60) for rolling contact with a cam surface of a camshaft of the fuel pump assembly (10); a pin (24) extending through the first bearing (106), the roller assembly (27, 29), and the second bearing (110), the pin (24) being supported by the first bearing (106) and the second bearing (110); a first retaining feature (114) disposed on the pin (24) outside the first bearing (106); and a second retaining feature (116) disposed on the pin (24) outside the second bearing (110); such that interaction between the first retaining feature (114) and the first bearing (106), and between the second retaining feature (116) and the second bearing (110), constrains axial movement of the pin (24) relative to the tappet body (23).

2. The roller tappet assembly (100, 156) of claim 1 , wherein the first bearing (106, 108) defines a radially extending surface (126) for axially engaging a first axial end (128) of the roller assembly (27, 29) and wherein the second bearing (110, 112) defines a radially extending surface (130) for axially engaging a second axial end (132) of the roller assembly (27, 29) opposite the first axial end (128).

3. The roller tappet assembly (100, 156) of claim 2, wherein the first bearing (106) defines a first flange (122) extending radially from the pin (24) and the second bearing defines a second flange (124) extending radially from the pin (24), wherein the first flange (122) defines the radially extending surface (126) for axially engaging a first axial end (128) of the roller assembly (27, 29) and the second flange (124) defines the radially extending surface (130) for engaging a second axial end (132) of the roller assembly (27, 29) opposite the first axial end (128).

4. The roller tappet assembly (100, 156) of claim 3, wherein each of the first and second flanges (122, 124) includes a port (134, 136) for allowing passage of a lubricant from passageways (138) to the roller assembly (27, 29).

5. The roller tappet assembly (100, 156) of any preceding claim, wherein the first bearing (106) defines a first sleeve (140) extending away from the tappet body cavity (60) along a first portion of the pin (24) and the second bearing (110) defines a second sleeve (142) extending away from the tappet body cavity (60) along a second portion of the pin (24).

6. The roller tappet assembly (100, 156) of any preceding claim, wherein the first and/or second retaining feature comprises a radially outwardly extending caulking feature (114, 116).

7. The roller tappet assembly (100, 156) of any preceding claim, wherein the first bearing (106) is retained within a first aperture (108) formed in the tappet body (23) and the second bearing (110) is retained within a second aperture (112) formed in the tappet body (23).

8. The roller tappet assembly (100, 156) of any preceding claim, wherein the first and second bearings (106, 110) are formed from a material that is harder than the material from which the tappet body (23) is formed.

9. The roller tappet assembly (100, 156) of any preceding claim, wherein the first and second bearings (106, 110) are formed from a material that is harder than the material from which the pin (24) is formed.

10. A fuel pump assembly (10) comprising at least one roller tappet assembly (100, 156) as claimed in any of the preceding claims.

11. A method (144) of assembling a roller tappet assembly (100, 156) according to any of claims 1 to 9, the method (144) comprising: mounting (146) the first and second bearings to the tappet body; positioning (148) the roller assembly (27, 29) within the tappet body cavity between the first and second bearings; axially sliding (150) the pin (24) through the first bearing (106), the roller assembly (27, 29), and the second bearing (110); forming or mounting (152) the first retaining feature on the pin (24) outside the first bearing (106); and forming or mounting (154) the second retaining feature on the pin (24) outside the second bearing.