Rocker tip roller hydrodynamic bearing oil slots

A hydrodynamic bearing for limited roller oscillation incorporates a pair of oil slots which clear debris from the roller/pin interface and provide oil to readily lubricate the entire load bearing surface of a pin. The preferred oil slots each extend lengthwise along the pin, and widthwise generally across respective chords of the pin circumference. The oil slots are positioned in spaced relationship such that their respective chords define an angle whose vertex is beyond the circumference of the pin, and their spacing defines an upper load bearing zone along a portion of the circumference of the pin, and opposite therefrom, a larger, lower load bearing zone defined along another portion of the circumference of the pin.

BACKGROUND OF THE INVENTION 
The present invention relates to the lubrication of a pin-mounted rocker 
tip roller, and in particular to bearing oil slots in the pin which supply 
lubricant to and clear debris from between the pin and roller. 
Rocker tip rollers have long been used in long-life combustion engines to 
transfer the rocking motion of a rocking member to a linear motion member, 
without imposing side loads, and with minimal wear between the members. 
Rocker tip rollers require lubrication at the roller/pin interface, to 
facilitate the rather limited roller rotation about the pin which is 
induced by relative motion between the rocking member and linear motion 
member. The limited roller rotation and point or line contact by the 
roller are what produce linear motion in the linear motion member, without 
side loading and with minimal friction wear. Longer life operation is 
thereby enjoyed in engines which use rocker tip rollers. 
In combustion engines, a rocker tip roller is typically incorporated into 
one end of a rocker arm and contacts the end of a valve stem to produce 
linear motion at the valve. Typically, the rocker tip roller is mounted on 
a pin and may include a bushing between the pin and roller. Lubrication is 
most often provided by lubricating oil applied at the roller/pin 
interface, and the oil penetrates into the interface. When pressure is 
applied to the rocker tip roller and causes the roller to roll relative to 
the pin, a squeeze film develops at the interface and oil squeezes out 
axially along the pin. Although oil again migrates into the interface when 
the pressure is reduced, it has been found that the center of the 
roller/pin interface is typically starved for oil so that a complete 
squeeze film does not form, increasing friction wear. The limited amount 
of oil available to penetrate to the center of the interface contributes 
to this problem. 
In addition, it has been found that debris manages to find its way into the 
roller/pin interface, causing damage to the pin and roller surfaces, and 
where used, to the bushing surfaces. The grooving, abrasion and increased 
friction at the roller/pin or bushing/pin interface can result in 
premature and sudden failure of the engine. 
Accordingly, the need exists for improved lubrication of rocker tip roller 
lubrication to prevent failure and improve the longevity of such elements 
in engines designed for long-life performance. 
SUMMARY OF THE INVENTION 
The present invention satisfies this need with a hydrodynamic bearing for 
limited roller oscillation which incorporates oil slots which clear debris 
from the roller/pin interface and provide oil to readily lubricate the 
entire load bearing surface of a pin. 
The hydrodynamic bearing of the present invention includes a generally 
cylindrical pin having first and second end portions for rigid connection 
to a supporting element, and first and second oil slots formed into the 
surface of the pin. More than simple grooves, the oil slots each extend 
lengthwise along respective portions of the pin between the end portions, 
and extend widthwise generally across respective chords of the pin 
circumference. The first and second oil slots are positioned in spaced 
relationship such that their respective chords define an angle whose 
vertex is preferably beyond the circumference of the pin. An upper load 
bearing zone is defined along the circumference of the pin lengthwise 
between the first and second oil slots, while a larger, lower load bearing 
zone is defined along the circumference of the pin lengthwise between the 
first and second oil slots. 
The cylindrical pin surface is finished for direct contact with the 
cylindrical bore of a roller which oscillates through an arc around the 
pin due to relative motion between the rocking member on which it is 
mounted via the pin and the linear motion member. When the pin is thus 
assembled with the roller, the first and second oil slots on the pin 
define therewith large oil reservoirs. Oil from the first and second oil 
slots is readily available over the entire load bearing zone, and as the 
roller oscillates through an arc, oil wipes across the roller surfaces and 
lubricates the roller/pin interface. The availability of large quantities 
of oil to the load bearing zones also serves to flush debris from the load 
bearing zones. 
These and other objects, features and advantages of the present invention 
will be apparent from the drawings and detailed description which follow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1-4, the hydrodynamic bearing 10 of the present 
invention includes a generally cylindrical pin 12 having first and second 
end portions 14, 16 for rigid connection to a supporting element 18, and 
first and second oil slots 20, 22 formed into the surface of the pin 12. 
The oil slots 20, 22 each extend lengthwise along respective portions of 
the pin 12 between the end portions 14, 16, as shown best in FIG. 1. The 
oil slots 20, 22 extend widthwise generally across respective chords 24, 
26 of the pin circumference, as shown best in FIG. 2. Referring still to 
FIG. 2, the first and second oil slots 20, 22 are positioned in spaced 
relationship such that their respective chords 24, 26 define an angle 
.alpha. whose vertex V is beyond the circumference of the pin 12. An upper 
load bearing zone 28 is defined widthwise along the circumference of the 
pin 12 and lengthwise between the first and second oil slots 20, 22. A 
larger, lower load bearing zone 30 is defined widthwise along the 
circumference of the pin 12 generally opposite from the first load bearing 
zone 28, and lengthwise between the first and second oil slots 20, 22. 
Being generally opposite from the first load bearing zone 28 means that 
the larger, lower load bearing zone 30 may be somewhat offset and 
positioned asymmetrically relative to the first and second oil slots 20, 
22. 
Referring still to FIG. 2, the cylindrical pin surface is finished for 
direct contact with the cylindrical bore 34 of a roller 32 which 
oscillates through an arc .beta. around the pin 12. As shown in the 
illustrative embodiment of FIG. 3, rotation of the roller 32 results from 
the relative motion between a rocking member 38 and a linear motion member 
40. Pin 12 is mounted (e.g. friction fit) on the tines 18a of a rocker arm 
38a and the roller 32 contacts the end 44 of a valve shaft 40a. In such an 
arrangement, a push rod 46 typically pushes upwards as indicated at P to 
rock the tines 18a of the rocker arm 38a downward. A spring 48 typically 
opposes the action of the push rod 46, and is mounted to return the valve 
stem 40a and the tines 18a upward as the push rod force abates. It is 
understood that the pin 12 and roller 32 could alternatively be mounted on 
the linear motion member 40 and contact a surface of the rocking member 38 
to transmit motion between the elements, however, some undesirable side 
loading of the valve stem 40a may result. Such undesirable side loading 
could be substantially avoided by curving the surface of the rocking 
member 38 at the point of contact with the roller 32 (e.g. at the rocker 
tip) when roller 32 is mounted in this alternative position. 
When the pin 12 is thus assembled with the roller 32, the first and second 
oil slots 20, 22 on the pin 12 define therewith large oil reservoirs. Oil 
from the first and second oil slots 20, 22 is readily available over the 
entire load bearing zone 28, 30. As the roller 32 oscillates through an 
arc .beta., oil wipes across the roller surfaces and lubricates the 
roller/pin interface. The availability of large quantities of oil to the 
load bearing zones 28, 30 also serves to flush debris from the load 
bearing zones. Thus, when pressure is applied to the rocker tip roller 32 
and causes the roller 32 to roll relative to the pin 12, a squeeze film 
more completely develops across the interface, and the ample quantity of 
oil available helps flush debris from the interface when the oil squeezes 
axially along the pin away from the interface. 
Referring to FIG. 2, it is preferred in accordance with the present 
invention that the first and second oil slots 20 and 22 have approximately 
the same dimensions, and that they be substantially planar. 
Alternately, the surfaces of the first and second oil slots 20, 22 may be 
slightly concave, as may be desirable for manufacturing purposes. It is 
preferred that such slightly concave oil slot surfaces have a radius R 
more than approximately five times the diameter of the cylindrical pin 12. 
This is desirable because too sharp a radius will cause the pin 12 to act 
as a scraper against the bore 34 of the roller 32 during rotation thereof. 
Thus, referring to FIG. 4, it may also be said that in the alterative 
embodiment where there are slightly concave oil slot surfaces, it is 
preferred that the angle .gamma. between a line l.sub.1 tangential to the 
concave surface and a line l.sub.2 tangential to the circumference of the 
pin 12 at the intersection thereof is less than 90 degrees. 
Referring again to FIG. 2, in accordance with the present invention, the 
oil slots 20, 22 are preferably cut into the pin below the horizontal 
centerline H of the pin 12 to facilitate oil flow from the large 
reservoirs of oil slots 20, 22 into the lower load bearing zone 30 for 
long-life performance. The lower load bearing zone 30 is where the 
hydrodynamic bearing 10 preferably experiences its highest loading, as 
typified by the illustrative application of FIG. 3. To further facilitate 
oil flow, to the load bearing zones 28, 30, it is also useful in some 
applications to remove (i.e. bevel) the edges of the oil slots where they 
intersect the circumference of the pin 12. The beveled edge 42 may be 
either curved (convex) or planar, as representatively shown in FIG. 4. 
As well, in accordance with the present invention, it is preferred that the 
lower load bearing zone 30 include at least 120 degrees of the pin 
circumference. In combination with the upper load bearing zone 28, such a 
lower load bearing zone 30 provides, in effect, "three-point" contact 
between the pin 12 and roller 32, which provides stability, maintains 
control of the pin 12 in the roller 32, and promotes long-life operation. 
The upper load bearing zone 28 preferably has a width along the 
circumference of the pin 12 which is greater than approximately 10 percent 
of the pin diameter. Such width serves to spread the load imposed thereon, 
and thus prevents the upper load bearing zone 28 from acting as a scraper 
against the bore surface of roller 32. 
Thus, in accordance with the preferred cut of the oil slots 20, 22 below 
the horizontal centerline H of the pin 12 to enhance oil flow, and the 
preferred circumferential width greater than 120 degrees of the lower load 
bearing zone 30, it may be understood with reference to FIG. 4, that the 
angle .alpha. defined by the respective chords 24, 26 of the first and 
second oil slots 20 and 22 preferably is in the range of approximately 60 
degrees to approximately 90 degrees. 
Referring to FIG. 1, it is preferred that the first and second oil slots 
20, 22 extend lengthwise a distance greater than the width of a roller 32 
mounted on the pin 12. This facilitates the flow of lubricating oil into 
the oil slots 20, 22. Oil arrives at the pin 12 typically from mist or 
spray which is present in a mechanism. For example, in the engine 
embodiment shown in FIG. 3, oil mist or spray may result from forced 
lubrication of the bearing 50 on rocker arm 38a. It is further preferred 
that the first and second oil slots 20, 22 extend lengthwise into parts of 
the end portions 14, 16 one-quarter to one-third the width of the end 
portions 14, 16, so that exact lateral positioning of the pin 12, which is 
rigidly maintained in position in the tines 18a of rocker arm 38a by 
friction fit, is not critical. 
In an alternative embodiment, the hydrodynamic bearing 10 may further 
include a cylindrical bushing 52 (partially indicated by phantom line in 
FIG. 2a) having a cylindrical bore therethrough for contact with the pin 
12. Bushing 52 is positioned over the first and second oil slots 20, 22, 
and like the roller surface which it protects, is preferably narrower than 
the length of the first and second oil slots 20, 22. 
For purposes of illustration, and not limitation, a representative pin 12 
for use in a small combustion engine rocker arm 38a could have a diameter 
of approximately 0.22 inches, with oil slots 20, 22 positioned 60 degrees 
apart. The oil slots could thus be approximately 0.24 inches long by 0.16 
inches wide along the chords 24, 26, separated at the upper load bearing 
zone 28 by a straight line distance of 0.040 inches. The gap between the 
roller 32 and tines 18a on each side would be in the range of 10 to 15 
mils. In such an application, the pin 12 is preferably made of high carbon 
(e.g. 1%) or carburizing steel, hardened to HRC 60.+-.2, and is in contact 
with a roller 32 of similar material and hardness. 
Referring to FIGS. 1 and 4, in any application, it is preferred that the 
bisector B of the angle .alpha. is preferably directed towards the load 
(or center of the arc .beta.) at the lower load bearing zone 30, for 
balanced loading of the load bearing zones 28, 30. Further, it is 
understood that the pin 12 of the present invention may be used in any 
orientation, and is not limited to the orientations shown in the drawings. 
While upside-down orientation may cause less oil to remain in the oil 
slots 20, 22, capillary action and surface tension of the oil are 
sufficient to retain the relatively large volumes of oil in the oil slots 
20, 22 which provide the superior lubrication and flushing of debris made 
possible in accordance with the present invention. Even with only 15 to 
20% of the oil slots 20, 22 filled, the amount of oil available at the 
roller/pin interface greatly exceeds that available conventionally, and 
readily achieves the purposes of lubrication of the interface and flushing 
of debris therefrom. 
While certain representative embodiments have been shown for purposes of 
illustrating the invention, it will be apparent to those skilled in the 
art that various changes in the hydrodynamic bearing disclosed herein may 
be made without departing from the scope of the invention, which is 
defined in the appended claims.