Sealed bearing

Details Sealed bearing Sealed bearing

2001-07-27

2004-03-30

Footland, Lenard A. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

Reexamination Certificate

active

06712519

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a sealed bearing assembly for an internal combustion engine and, more particularly, to a sealed bearing assembly for supporting a crankshaft of a two-stroke engine.
BACKGROUND OF THE INVENTION
In a conventional internal combustion engine, the crankshaft is rotationally supported by bearings positioned in the crankcase. In a conventional four-stroke automotive engine, these bearings are usually of the sliding (bushing) type lubricated by a pressurized oil feed. In a conventional four-stroke engine as commonly used in motorcycles, ATV's, etc., the crankshaft is often supported by roller bearings that are lubricated by either a pressurized oil feed and/or oil spray from the crankcase. In either case, the crankcase is isolated from the combustion chamber, as is conventionally known, so the crankshaft bearing lubricating oil is kept isolated from the combustion chamber. Separate grease seals are often positioned outboard of the bearings to provide sealing between the crankshaft and an exterior of the crankcase. In recent years, environmental considerations have dictated that exhaust emissions be reduced in internal combustion engines. In a four-stroke engine, such efforts concentrate on the combustion process, since the crankcase lubrication is isolated from the combustion process and does not increase exhaust emissions in a well-maintained engine.
This is not the case for a two-stroke engine. In a conventional two-stroke engine, as used in motorcycles, snowmobiles, personal watercraft, etc., the crankshaft is usually supported by roller bearings with separate seals mounted outboard of the bearings to seal in both the lubrication and the intake charge present in a conventional two-stroke crankcase. The roller bearings can be lubricated by oil mixed in with the intake gas charge that enters the crankcase and/or by oil injection directly to the bearings. However, any oil entering the crankcase of a conventional two-stroke will enter the intake charge and be forced into the combustion chamber through the transfer ports, as is known. Thus, this oil will be burned in the combustion process, thereby increasing exhaust emissions. As a result, decreasing exhaust emissions in a two-stroke engine necessarily requires efforts with respect to both the combustion process and the crankcase lubricating oil.
Certain approaches to limiting the amount of lubricating oil entering the crankcase in a two-stroke engine have proven somewhat successful in reducing exhaust emissions. In one approach, the amount of lubricating oil supplied to the intake charge is merely reduced, thereby reducing the amount of oil which does not come into contact with any lubrication requiring surface but which is merely burned during the combustion process. The problem with this approach is that as the amount of lubricating oil is reduced, the probability of inadequate bearing lubrication increases, especially in engines having high power output, with predictable undesirable results.
Other efforts generally concentrate on reducing the amount of oil supplied to the intake charge, but separately supplying smaller additional quantities of oil directly where it is needed to compensate for the leaner concentration of oil in the intake charge. For instance, the amount of oil required by the crankshaft bearings can be directly injected to those bearings while simultaneously reducing the amount of lubricating oil supplied to the intake gas charge. Thus, the overall amount of lubricating oil used is reduced, along with the exhaust emissions from burning the oil. On the other hand, the lower limit of the amount of lubricating oil supplied to the crankcase (and thus, the combustion chamber) will depend on the lubrication requirements of the engine components, such as the crankshaft and rod bearings, pistons, etc. In any event, the oil supplied to the crankcase will either be burned during the combustion process or exit in the exhaust as unburned hydrocarbons. In recent years, as technical advances have resulted in increased power outputs from two-stroke engines, existing crankshaft bearings have been less able to withstand this increased loading over time, especially as lubricating oil has been reduced to lower exhaust emissions.
One proposal to limit the free lubricant supplied to the intake charge is given in U.S. Pat. No. 3,641,990 to Kinnersly, issued Feb. 15, 1972. Kinnersly discloses the use of a one-sided crankshaft supported by a pair of crankshaft roller bearings enclosed on either end by seals, with an annular chamber disposed between the two roller bearings filled with lubricant at the time of engine assembly. Kinnersly discloses that such an arrangement can be used with either a two-stroke or a four-stroke engine and that the roller bearings and seals can be separate or integral units. There is no disclosure as to what type of seal should be used or how such a seal would be integrated into the roller bearing. In a four-stroke engine, this is less significant because the crankcase pressures are generally not high enough to interfere with the seals. It is also clear that with the use of the one-sided crankshaft, that the Kinnersly engine is not intended for high performance and the severe loadings resulting therefrom.
Furthermore, conventional sealed bearings cannot be used to support the crankshaft in a two-stroke engine. Such bearings usually use a grease seal having a single sealing lip contacting the inner race of the bearing to provide the sealing engagement. While such sealed bearings are capable of sealing the lubricant in the bearing, they are not effective at withstanding the pressure pulses in the crankcase and preventing the intake charge from escaping the crankcase.
FIG. 4
shows such a sealed bearing
230
having an inner race
232
, an outer race
234
and a plurality of roller elements
236
separated by a cage
238
disposed between the inner and outer races. A seal
240
having a narrow outer edge
242
is mounted in a counterbore
244
in outer race
234
. The narrow outer edge
242
engages a groove
246
in the counterbore
244
to be retained in the bearing
230
. Since the outer diameter of the outer edge
242
of seal
240
is greater than the outer diameter of counterbore
244
, the seal
240
must be axially flexed to reduce the outer diameter of the seal so that the narrow outer edge
242
can engage the groove
246
. The seal
240
has a single lip
248
backed by a circumferential spring
250
for providing a sealing engagement with the inner race
232
. The axial flexibility of the seal
240
(necessary for installing the seal in the outer race), as well as the single lip
248
do not provide the desired effectiveness in preventing crankcase pressure loss.
While seals having two separate sealing lips for sealing the crankshaft/crankcase of a two-stroke engine are known, they have previously been used only as separate seals mounted outboard of the innermost crankshaft support bearings. See
FIG. 3
, which shows a partial section of a prior art two-stroke engine
10
of the assignee of the present invention where a separate seal
200
is mounted outboard of conventional crankshaft support bearing
202
, which is similar in design to conventional crankshaft support bearing
46
. The seal
200
has a narrow outer edge
204
that engages a groove
206
in the crankcase
16
to maintain the position of the seal. The seal includes a first circumferential sealing lip
208
and a spaced apart second circumferential sealing lip
210
, the sealing lips backed by circumferential springs
212
and
214
respectively.
SUMMARY OF THE INVENTION
Therefore, the present invention is a sealed bearing suitable for use in a crankcase of an engine and, more particularly, for supporting a crankshaft in a high output two-stroke engine. The sealed bearing assembly includes an inner race and an outer race with a plurality of roller elements (bearings) disposed between the inner and outer races. The outer race includes a counterbore to one side of the plurality of roll

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