Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
2000-12-27
2003-04-01
Schwartz, Christopher P. (Department: 3613)
Bearings
Rotary bearing
Plain bearing
Reexamination Certificate
active
06540403
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention concerns piston pin bushings.
2. Related Art
The present invention concerns a piston pin bushing in accordance with the introductory portion of patent claim
1
.
Piston pin bushings are known for example from U.S. Pat. No. 4,909,638 and DE-OS 28 18 378, both of which deal with the manufacture of bushings, in particular with notching. Such bushings are used for housing the connecting rod eye in combustion engines with pistons having an up and down motion. Both parallel bushings and trapezoid bushings are described that can feature oil ducts, as well as oil grooves appearing on the inner surface. These oil grooves, moreover, represent a material weakness; but they are simply inserted in the sleeve bearing material attached on the steel backing with the result that the material weakness of the entire bushing is so small that it has no impact on the radial pressure. The same applies to the oil ducts, whose diameter is so small that the elastic and plastic qualities of the bushing are not affected. Furthermore, the oil grooves extend over the entire interior circumference.
In
FIG. 1A
the installation position for a parallel bushing
20
,
20
a
is represented schematically which also applies to the bushing yet to be explained according to the present invention. Piston
2
executes an up and down motion in cylinder
1
that is transferred to connecting rod
5
and lifting pin
10
mounted in large connecting rod eye
7
of the crankshaft. Connecting rod
5
contains a push rod bushing in small connecting rod eye
6
, in which bushing the piston pin is housed that extends with both ends in both piston bores
3
.
In
FIG. 1B
piston pin bushings
20
b
,
20
c
are designed essentially trapezoidal in the longitudinal view for heavy-duty engines in order to be able to better receive larger forces occurring during the downward motion of the piston, whereby the axially longer section of the bushing lies in the area of maximum load during operation and the axially shorter part of the bushing faces the piston. In using bushings with such beveled ends, a bearing surface can be achieved in this application that is larger in the direction of main load and therefore more effective than those bushings whose ends run perpendicular to the bearing axis of the bushing. With such bushings, both end surfaces, as well as only one end surface, or even only one section of the end surface, can be beveled to the longitudinal axis of the bushing. In
FIG. 1B
, such half trapezoid piston bushings
20
c
are used in both piston bores
3
, in which the piston pins are no longer directly housed in the piston bores but in both piston pin bushings
20
c.
Piston pin bushing
20
,
20
b
is installed in the small end connecting rod eye
6
by press-seating so that, on the basis of contact, the piston pin bushing exerts a radial pressure on the connecting rod bore which runs a roughly parabolic course in the axial direction, as is shown in
FIG. 2
for the realms of both apex lines
23
and
24
by curves I and II.
The contact pressure diminishes at the edge where the piston pin bushing
20
is most loaded during downward motion of piston
2
under consideration of elastic deformation of the piston pin, as is shown for clarification in
FIG. 3
in exaggerated representation. Piston pin
4
is thus somewhat deflected by the pressure of the piston so that piston pin bushing
20
is most loaded at the edge, whereby both ends
8
and
9
of the small end connecting rod eye
6
are deflected downwards.
A relative motion between bushing body and connecting rod eye leads, hereby, to friction corrosion. If the load is removed, the bushing springs back to its original position and lifts from the connecting rod body so that in these places oil can penetrate under the bushing body. Both effects result in a diminished lifespan of the piston pin bushing.
Since the maximum cylinder pressure has been increased in automobile manufacture due to direct injection and turbo supercharging in diesel engines in order to reduce fuel consumption or to achieve the prescribed emission values, the load of the piston pin bushing and the connecting rod in the connecting rod eye has increased. The result is that friction corrosion has appeared on the edge of the axially longer section of the piston pin bushing in the rear while crack formations have appeared on the interior, which harm the life-span of the piston pin bushing.
Although it had been attempted in the past to improve conditions by special processing of the bore, precision installation, and optimization of the geometry of the connecting rod eye, problems have not yet been satisfactorily solved.
Proceeding from this knowledge, it is the task of the present invention to create a piston pin bushing that exhibits a sufficient lifespan even at higher piston pressures.
SUMMARY OF THE INVENTION
This task will be solved with a piston pin bushing in which the area of material reduction is limited to at least one transition region between the apex lines and that the bushing material is reduced in this transition region at least to the extent that a portion of the piston pin bushing's radial pressure in the area of the apex lines is shifted in its inserted position from the middle to the area of both bushing ends. that the bushing material is reduced in this transition region at least to the extent that a portion of the piston pin bushing's radial pressure in the area of the apex lines is shifted in its inserted position from the middle to the area of both bushing ends.
It has been shown that crack formation and friction corrosion are clearly diminished by these methods, which can be traced back to the fact that the contact pressure distribution in the area of the apex lines is changed by the material reduction in a such way that no motion occurs in the longitudinal direction of the bushing on the one hand and, on the other, that the bushing does not prematurely spring back during removal of the load. The bushing body clings to the connecting rod through the increased radial pressure in the end area of the bushing so that relative motions cannot occur.
In order not to impair the surface of the piston pin bushing, the material reduction is to be limited to a transition region between both vertical lines, in which, by reasons of symmetry, the methods in accordance with the present invention are implemented preferably in both possible transition regions between both vertical lines.
Preferably, the transition region on the interior side and/or the bushing exterior side can have at least one pocket. The two dimensional extension and form of the pocket as well as the depth of the pocket or pockets must be selected in such a way that the radial pressure increase according to the present invention occurs in the area of the bushing ends. Conventional pockets are simply put in the slide bearing material. According to the present invention, it is, however, an advantage if these pockets, which are provided on the bushing interior side, extend to the back of the bushings, because in this way the desired material attenuation can be achieved.
In manufacturing the pockets, the bushing material must be detached, by which is understood both the material of the bushing back and the slide bearing material. A pressing procedure for the manufacture of such pockets is not suitable because the material displaced from the pockets leads to a stiffening and thereby to an undesired impact on the elastic and plastic qualities of the bushing material, so that the radial pressure in the area of the bushing ends cannot be increased.
The material diminishment for the purpose of exceeding the flow limit in the inserted position of the bushing, i.e., with conventional press-seating in the connecting rod eye, can proceed until the bushing material is completely detached. The bushing can exhibit not only pockets, but also perforations, whereby pockets and perforations can be combined. These combinations include the possibility that the perforations ar
Federal-Mogul Wiesbaden GmbH
Reising Ethington Barnes Kisselle Learman & McCulloch PC
Schwartz Christopher P.
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