Internal-combustion engines – Poppet valve operating mechanism – Tappet
Reexamination Certificate
1999-09-20
2001-04-03
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Tappet
C123S090430, C123S090460
Reexamination Certificate
active
06209499
ABSTRACT:
TECHNICAL FIELD
This invention relates to piston retention, especially for engine valve train lash adjusters.
BACKGROUND OF THE INVENTION
It is known in the art to retain the piston or body of an engine valve train lash adjuster by means of a C-clip positioned in a groove of the piston and engaging an abutment in the periphery of the cylinder in which the lash adjuster is installed. For example, a hydraulic element assembly or lash adjuster may be retained in a cylinder baffle of a direct acting cam follower; or a hydraulic lash adjuster by having a swivel foot for engaging a valve or other component may be retained in a cylinder recess of an associated rocker arm.
Typically in such arrangements, the C-clip is formed of resilient spring wire biased to spring outward against a bore or abutment in which the piston is reciprocably retained. The C-clip is retained in a groove on the exterior of the piston The groove has a depth such that, when added to the diametral clearance be een the piston and cylinder, the total exceeds the diameter of the spring wire of the C-clip. This is necessary to allow installation of the piston into a closed end cylinder without scratching or otherwise damaging the associated cylinder wall. The retaining groove typically has a cylindrical er surface and opposed upper and lower end surfaces, which are generally radial but may be sloped slightly outward for tool clearance.
To allow installation of the piston or body in a cylinder, the entry opening of the cylind r is generally angled to provide a lead-in cone angle. The cone angle com resses the C-clip into the piston groove and allows the piston with clip installed to be slid into the closed end cylinder and past a retaining abutment into operating position. The retaining abutment may be, for example, the upper edge of a baffle tube of a direct acting cam follower and its configuration is important in determining the ability of the C-clip to retain the hydraulic element assembly (HEA) in the cam follower cylinder.
For example, if the upper edge of the baffle tube is formed with a surface normal to the axis of the cylinder, that is horizontal when the cylinder axis is vertical, the retention of the piston in the cylinder by the expanded C-clip will be at a maximum since the horizontal or normal surface will not provide a substantial radial force for compressing the C-clip into the groove. Thus, if removal of the HEA is desired, it may be necessary to shear off the retaining parts of the C-clip in order to disassemble the assembly.
Since disassembly is sometimes required for inspection or replacement, the inner edge or abutment of the cylinder or baffle tube is generally sloped or angled downward and inward to provide a conical surface that engages the C-clip when retention or removal is desired. This angle may be varied as desired in order to maintain a sufficient force to retain the piston in place under anticipated operating conditions, while having a sufficient slope to allow removal of the lash adjuster or HEA from the cylinder when desired, without damaging the cylinder or HEA surface. The selection of the installation and retention angles on the cylinder edges is determined in part by the actual configuration of the C-clip and the diameter of wire from which it is made, as well as the depth of the retaining groove in which it is installed. These factors then, as well as the resilient force applied in expansion of the C-clip, all have a bearing on the selection of angles for accomplishing the various desired purposes of retention and ability to remove the HEA or lash adjuster when desired.
SUMMARY OF THE INVENTION
The present invention provides an improved lash adjuster assembly in a retaining cylinder based upon a piston having an improved cross-sectional configuration of the retaining groove in which the C-clip retainer is installed.
In a first feature of the invention, the retaining groove is made axially longer than is conventional so that the retainer clip may be slid between spaced upper and lower positions along the groove. The inner diameter of the groove is angled with the desired slope, referred to as the clip diameter assembly angle, which may be ten degrees more or less within a suitable operating range as conditions may require. For example, angles of five to fifteen or twenty degrees may be found useful in particular operating environments. The clip diameter assembly angle allows the clip to be compressed further during assembly of the piston within its cylinder than is permitted in the retention or removal condition of the assembly.
During assembly of the piston, the clip is pushed axially downward in the groove to the smaller diameter or deeper end of the groove so that the clip may be compressed further into the groove and provide a reduced rubbing force on the associated cylinder, thereby reducing the possibility of damage to the parts during assembly. After the piston is installed, attempted removal of the piston, either by operating forces or by attempted disassembly with tools, the retaining clip is forced upwardly in the groove to the larger diameter or shallower end where the retaining clip is urged outwardly to increase its resistance to compression into the groove. This increases the retaining force of the clip so that the assembly does not come apart too easily during operations.
An additional feature of the invention is the provision at the upper or retaining end of the groove of a clip retention back angle having an outward or upward slope of a suitable amount such as, for example, twenty degrees. The back angle cooperates with the bore retention angle formed at the upper edge of the associated cylinder so that the two angles together control the compression force acting on the C-clip to retain or allow removal of the piston from the cylinder.
As the clip retention back angle is increased to approach the bore retention angle, the radial compression force exerted by the bore retention angle during attempted disassembly of the piston from the cylinder, is reduced toward zero. Thus, reducing the clip retention back angle provides more positive retention of the piston in the cylinder but also makes it harder to remove the piston without damaging the cylinder or clip. Accordingly, selection of the clip retention back angle and bore retention angle are important in accomplishing the desired amount of force retaining the piston within the cylinder at this connection. The spring force of the clip and the diameter of the clip also need to be taken into account in determining the proper angles for the assembly.
In some cases, the bore retention angle is fixed by prior manufacturing practices. In such cases, the clip retention back angle may be adjusted as desired to provide the proper degree of retaining force while allowing removal of the piston for inspection or replacement.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.
REFERENCES:
patent: 3358660 (1967-12-01), Cornell
patent: 5365897 (1994-11-01), Speil et al.
patent: 5606939 (1997-03-01), Spath
patent: 5704319 (1998-01-01), Engelhardt et al.
patent: 5979377 (1999-11-01), Barth et al.
patent: 6039018 (2000-03-01), Spath
Lichti Thomas Howard
O'Neill Daniel Patrick
Owen Nathan B.
Delphi Technologies Inc.
Lo Weilun
Van Ophem John A.
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