Patent Application
20100000476
The present invention relates to tappets that are reciprocally slidable in bores in internal combustion engines; more particularly, to such tappets that must maintain rotational orientation in such bores during reciprocation; and most particularly, to a simple and inexpensive anti-rotation feature for attachment to a tappet during manufacture of an engine.
Tappets are well known in the engine arts for converting rotary motion of camshaft lobes into reciprocating linear motion that is useful in driving engine combustion valves or other engine devices, for example, fuel pumps for supplying high pressure fuel rails. As used herein, the generic term “tappet” should be taken to mean any such cam-actuated linear-acting device, including but not limited to hydraulic valve lifters for both valve-in-block and valve-in-head engines, and deactivation hydraulic valve lifters for use in engines having variable valve actuation (VVA).
In modern engines, a tappet typically includes a roller for rolling along the cam lobe surface to reduce friction and wear. While a roller is a significant technological improvement, it brings with it a requirement that the tappet be prevented from rotation during reciprocation, in order to maintain proper roller orientation to the camshaft lobe surface. Further, in VVA engines, typically the deactivation mechanism is fed by one or more oil galleries in the engine, which arrangement can benefit from fixed orientation of the lifter.
Because a cylindrical engine bore is the simplest and least expensive shape for receiving a tappet, it has not proved economical to provide a non-rotation flat in an engine bore for mating with a non-rotation flat on a tappet. Rather, it is known in the prior art to prevent rotation by forming a longitudinal channel in the side of a tappet bore, and providing a mating feature such as a pin extending outwards from the side of the tappet to ride in the channel. The channel may be rectilinear or cylindrical. In the prior art, the tappet pin is hardened to Rockwell C hardness of about 58 or higher, and is press-fit into the similarly-hardened tappet body. Because the tolerances between the two hardened parts is too tight for the parts to be machined to size cost-effectively, in practice suitable matching of pin to hole is achieved by the laborious process of sorting through the manufactured tolerances of tappet holes and pin diameters.
What is needed in the art is a simple, inexpensive, anti-rotation feature for easy attachment to a roller tappet that prevents rotation of the tappet in an engine bore having an anti-rotation channel, and that does not require close fit to the hole in the tappet body.
It is a principal object of the present invention to reduce the cost of manufacture of an internal combustion engine.
Briefly described, a hardened anti-rotation feature in accordance with the present invention comprises a first portion for extending outwards from the surface of a tappet and a second or pin portion for extending into a mounting hole in the tappet. Unlike somewhat similar prior art anti-rotation features, however, the first portion of the present improved feature extends longitudinally to either or both sides of the mounting hole such that when the feature and tappet are installed in an engine bore, the entire feature is prevented from rotation within the hole. Thus, the second portion extending orthogonally from the first portion into the mounting hole need not be particularly close-fitting to the hole. In a presently preferred embodiment, the first portion is substantially semi-cylindrical, having a convex cylindrical outer surface for fitting the walls of a semi-cylindrical channel in the engine bore and a concave cylindrical inner surface for fitting the outer wall of the tappet. The pin portion is preferably cylindrical for ease of fabrication of both the pin portion and the tappet hole. Obviously, other cross-sectional shapes, such as rectangular, oval, and the like as may be desired for any particular application are fully comprehended by the present invention. The anti-rotation feature may further be hardened for improved wear resistance.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
Referring to
The problems inherent in this prior art arrangement, which are eliminated by the present invention, are discussed above.
Referring now to
In one embodiment, feature 126 is not hardened after forming, resulting in an as-formed material hardness of around RC25. Optionally, feature 126 may be hardened for improved wear resistance. For example, feature 126 may be through-hardened to around RC50 using known hardening processes. In another example, feature 126 may be heat treated using a ferritic nitrocarborizing (FNC) process which provides a thin hardened layer having a thickness of about 0.1 mm. When an FNC process is used to harden the feature, since only a thin hardened layer is produced, a peening process may be used to deform pin portion 130 after the feature is assembled into tappet 10.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/134,133, filed Jul. 7, 2008, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61134133 | Jul 2008 | US |
