Hydraulic tappet assembly

Abstract

 A hydraulic tappet assembly (10) comprises a tappet body (11) providing a being surface (13), a mounting member (15) within the tappet body (11), and a piston (17) mounted in the body (11) by the mounting member (15), the assembly further comprising an inside wall (26) of the body (11) which is provided with an interference formation (40) and the mounting member (15) is retained in the body (11) at least primarily as an interference fit with the interference formation (40).

Description

Description of Invention

[0001] This invention relates to a hydraulic tappet assembly of the kind comprising a tappet body providing a bearing surface, a mounting member within the tappet body, and a piston mounted in the body by the mounting member.

[0002] Conventionally the bodies of such hydraulic tappet assemblies are made from steel and the bearing surface is hardened by a suitable hardening process to withstand and give sufficient durability to bear on a cam lobe of a cam shaft of an internal combustion engine.

[0003] The mounting members too are conventionally made of steel and are fixed within a hollow of the body by welding or blazing or a similar technique.

[0004] Notwithstanding that the bearing surfaces of the tappet bodies are hardened, the steel does not give optimum wear properties and an inherently harder material for the tappet bodies would be preferred, such as for example, cast iron. However, steel is an ideal material for the mounting members, but the steel cannot be fixed to an iron body by conventional fixing techniques.

[0005] According to a first aspect of the invention we provide a hydraulic tappet assembly comprising a tappet body providing a bearing surface, a mounting member within the tappet body, and a piston mounted in the body by the mounting member characterised in that an inside wall of the body is provided with an interference formation and the mounting member is retained in the body at least primarily as an interference fit with the interference formation.

[0006] Thus in a hydraulic tappet assembly in accordance with the invention, there is no barrier to the tappet body being made of one material and the mounting member being made of a different material, so that the optimum materials for these two components may be used.

[0007] The bearing surface of even an iron tappet body may need some surface treatment but the material is inherently harder and gives improved wear characteristics.

[0008] Typically the body is generally cylindrical providing a generally cylindrical hollow therein in which the mounting member is retained, and the interference formation of the inside wall of the body may comprises a groove e.g. extending around the cylindrical inside wall of the body in which a peripheral portion of the mounting member is received.

[0009] The peripheral portion may comprise all or substantially all of the entire circular periphery of the mounting member in which case the groove may extend around the entire inside wall, or a part only of the circular periphery.

[0010] In each case the peripheral portion of the mounting member may be of curved configuration in cross section and the corresponding surface part of the groove may be shaped to correspond closely to the curved configuration of the peripheral portion so that there is a minimal gap or space between the mounting member and the inside wall of the body.

[0011] In the event there is any gap between the mounting member and the inside wall of the tappet body, this may be closed with a filling material, such as an anaerobic adhesive.

[0012] Further, where the entire circular periphery of the mounting member is not received in the groove, e.g. the periphery of the mounting member may comprises a plurality of separated segments, any gaps or spaces which could otherwise permit oil to leak therethrough, may be sealed with such adhesive.

[0013] Although the invention has been developed particularly to enable a hydraulic tappet assembly to be produced in which the tappet body is made of cast iron and the mounting member is made of steel, the invention may be utilised where one or both of these components are made of other materials or are both made of one of these materials.

[0014] In each case, the mounting member may comprise a generally central opening in which the piston is mounted, usually received in a cylinder which is retained by the mounting member such that the piston may move relative to the cylinder and the mounting member in use. Preferably a spring means is provided between the piston and the cylinder to bias the piston outwardly of the cylinder.

[0015] According to a second aspect of the invention we provide a method of retaining a mounting member for a piston in a body of a hydraulic tappet assembly comprising the steps of providing in an inside wall of the body, a retaining formation and inserting the mounting member into the tappet body so that the mounting member is an interference fit with the retaining formation.

[0016] The invention will now be described with reference to the accompanying drawings in which:-

FIGURE 1 is a cross sectional view through a prior art hydraulic tappet assembly;

FIGURE 1a is an enlarged fragmentary view of part of the assembly of figure 1;

FIGURE 2 is a view similar to that of figure 1 but showing a hydraulic tappet assembly in accordance with the invention;

FIGURE 2 is an enlarged fragmentary view of part of the assembly of figure 2;

FIGURES 3a, 3b and 3c are enlarged plan and side view of alternative forms of mounting member for use in the assembly of figure 2.

[0017] Referring first to Figure 1 and Figure 1a, there is shown a hydraulic tappet assembly 10 comprising a generally hollow tappet body 11 which in this example is generally cylindrical shape, having at one end thereof, an end wall 12 providing a bearing surface 13 which in use typically would bear on a lobe of a camshaft or the like of an internal combustion engine.

[0018] Within the hollow of the body 11 there is provided mounting member 15 for mounting a piston assembly 16 which comprises a hollow piston 17 received in a cylinder 18. Between the piston 17 and the cylinder 18 there is provided a spring 19, the piston 17 being able to move within the cylinder 18 against the biasing force of spring 19 away from the end wall 12 of the body 11, as hydraulic fluid, typically oil enters a working space 20 of the tappet body 11 through an opening 21 in the cylindrical wall 22 of the body 11. The oil is transmitted via a passageway 23 into the hollow of the piston 17 and acts against the piston to urge it inwardly of the cylinder 18 against the force of the spring. Oil is supplied to the opening 21 from an oil way of the internal combustion engine in which the tappet assembly 10 is provided.

[0019] The working space 20 of the body 11 is defined by the mounting member 15 which comprises a peripheral portion 25 of generally circular configuration, which conventionally is welded or braised to all inside surface 26 of the tappet body 11 both to fix the mounting member 15 in the hollow of the body 11, and the provide an oil seal around the mounting member 15 between the mounting member 15 and the inside wall 26 of the body 11.

[0020] The mounting member 15 is made from steel, usually as a pressing, and the piston assembly 16 is retained by the mounting member 15, by a circlip 30 received in a circumferential groove of the cylinder 18, which a circlip prevents the cylinder 18 from being withdrawn from the mounting member 18 in a direction away from the end wall 12. Nevertheless, it will be appreciated that the cylinder 18 can be moved towards the end wall 12 by deforming the spring 19, and that the pressure of oil in the working space 20 of the body 11 and in the hollow of the piston, will move the cylinder 18 away from the end wall 12 to the maximum extent permitted by the circlip 30 and by a value stem or connecting rod bearing on an end surface 27 of the piston 18.

[0021] In Figure 1a the detail of the connection between the mounting member 15 and the inside wall 26 of the body 11 is shown.

[0022] Referring now to Figure 2 and 2A similar parts of the hydraulic tappet assembly 10 to the conventional prior art assembly shown in Figures 1 and 1A are indicated by the same reference numerals.

[0023] In this arrangement, rather than fixing the mounting member 15 to the inside wall 26 of the tappet body by welding oil braising as shown in Figure 1A, the mounting member 15 is retained in the hollow of the body 11 and an interference fit, the peripheral portion 25 of the mounting member 15 engaging in a retaining formation 40 provided in the inside wall 26 of the body 11.

[0024] The retaining formation 40 comprises a very shallow groove to receive the peripheral portion 25 of the mounting member 15 and prevent the mounting member 15 from moving outwardly of the hollow of the body 11.

[0025] If the mounting member 15 is of the same configuration as the mounting member 15 shown in Figures 1 and 1A, it will be appreciated that a small gap G would be provided between the peripheral portion of the mounting member 15 and the inside wall 26 of the body 11, which gap may be exacerbated by the provision of the retaining groove 40. Any gap may be sealed by using an adhesive such as an anaerobic adhesive to prevent oil escaping from the working space 20 between the end wall 13 of the body and the mounting member 15. However the mounting member is primarily retain as an interference fit.

[0026] As indicated in Figure 2a however, the peripheral portion 25 of the mounting member 15 is modified slightly in configuration so that the peripheral portion 25 corresponds closely to the configuration of the retaining formation 40 provided in the inside wall 26 of the body, such that no or minimal gap occurs between the adjoining faces of the peripheral portion 25 of the mounting member 15 and the inside wall 26. Thus an aerobic or other adhesive to provide an oil seal may not be required.

[0027] In this embodiment, the tappet body 11 is not made of steel as with the prior art example as shown in figures 1 and 1A. Rather, the tappet body 11 is made from chilled grey cast iron so that the bearing surface 13 of the tappet body 11 is inherently much harder than steel, and more durable in use.

[0028] Referring Figures 3a, 3b and 3c, Figure 3a shows a mounting member 15 which has a generally circular peripherally 25 without there being any interruptions. If the retaining groove in the inside wall 26 of the body 11 is sufficiently shallow, it is envisaged that such a mounting member 15 with a circular periphery 25 may be used as minimum deflection of the periphery 25 is required in order for the mounting member 15 to be inserted in the position shown in Figure 2a.

[0029] Particularly but not exclusively in the event that a deeper retaining groove 40 is required than indicated in Figure 2a the periphery 25 may be divided into peripheral segments 25a, 25b, 25c and 25d for example shown in Figure 3b. In Figure 3b, the segment portions 25a to 25d are separated by small notches 41 which permit greater deflection of the peripheral portion segments to 25a to 25d as the mounting member 15 is inserted in position.

[0030] In figure 3c, similar notches 41 are shown, but of an alternative configuration.

[0031] If a mounting member 15 such as shown in Figure 3b or 3c is inserted into the body 11, the gaps provided by the notches 41 would need to be sealed by for example, an anaerobic adhesive, to prevent the escape of hydraulic oil from the working space 20 of the tappet body 11.

[0032] Various modifications may be made without departing from the scope of the invention.

[0033] For example, whereas it is preferred for the tappet body 11 to be made of a hard material such as iron, this may be made of alternative materials. In any event, the bearing surface 13 of the tappet body 11 may need to be treated by some hardening process to give desired wear characteristics. Thus essentially, other tappet body 11 need not be made of a similar material to the mounting member 15.

[0034] Although in the example described the mounting member 15 is conveniently made as a pressing in steel, it may be made in other materials, and by alternative manufacturing techniques as desired. Although preferred it is not essential for the body 11 of the tappet assembly 10 to be cylindrical in configuration although this is most useful.

[0035] The piston 17 need not have an internal recess as described in this example but other configurations are possible to both the piston assembly 16, and body 11 and mounting member 15 without departing from the scope of the invention.

Claims

1. A hydraulic tappet assembly (10) comprising a tappet body (11) providing a bearing surface (13), a mounting member (15) within the tappet body (11), and a piston (17) mounted in the body (11) by the mounting member (15) characterised in that an inside wall (26) of the body (11) is provided with an interference formation (40) and the mounting member (15) is retained in the body (11) at least primarily as an interference fit with the interference formation (40).

2. A hydraulic tappet assembly (10) according to claim 1 characterised in that the body (11) is generally cylindrical providing a generally cylindrical hollow therein in which the mounting member (15) is retained.

3. A hydraulic tappet assembly (10) according to claim 1 or claim 2 characterised in that the interference formation (40) of the inside wall (26) of the body (11) comprises a groove in which a peripheral portion (25) of the mounting member (15) is received.

4. A hydraulic tappet assembly (10) according to claim 3 characterised in that the peripheral portion (25) of the mounting member (15) is of curved configuration in cross section and the corresponding surface part of the groove (40) is shaped to correspond closely to the curved configuration of the peripheral portion (25).

5. A hydraulic tappet assembly (10) according to any one of the preceding claims characterised in that a filling material closes any residual gap between the mounting member (15) and the inside wall (26) of the tappet body (11).

6. A hydraulic tappet assembly (10) according to any one of claims 3 to 5 where appendant to claim 3 characterised in that all or substantially all of the entire periphery (25) of the mounting member (15) is received in the groove (40).

7. A hydraulic tappet assembly (10) according to any one of claims 3 to 6 where appendant to claim 3 characterised in that the periphery (25) of the mounting member comprises a plurality of separated segments (25a, 25b,25c and 25d).

8. A hydraulic tappet assembly (10) according to any one of the preceding claims characterised in that the mounting member (15) comprises a generally central opening in which the piston (17) is mounted.

9. A hydraulic tappet assembly (10) according to claim 8 characterised in that the piston (17) is received in a cylinder (18) which is retained by the mounting member (15) such that the piston (17) may move relative to the cylinder (18) and the mounting member (15) in use, and a spring means (19) is provided between the piston (17) and the cylinder (18) to bias the piston (17) outwardly of the cylinder (18).

10. A method of retaining a mounting member (15) for a piston (17) in a body (11) of a hydraulic tappet assembly (10) comprising the steps of providing in an inside wall (26) of the body (11), a retaining formation (40) and inserting the mounting member (15) into the tappet body (11) so that the mounting member (15) is an interference fit with the retaining formation (40).

Drawing