Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2000-03-22
2001-10-02
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S564000, C384S568000
Reexamination Certificate
active
06296395
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The invention relates to a self-aligning roller bearing with two rows of symmetrical rollers, an outer ring with a curved outer track, an inner ring with two curved inner tracks, and a guide ring which is provided between the rollers and which is made as a circular ring disk
2. Description of the Related Art
Antifriction bearings which are used to transfer radial and/or axial loads to rotating parts are divided according to the shape of their roller bodies into ball bearings on the one hand, and roller bearings on the other. In roller bearings, it is distinguished between cylinder, barrel-shaped, needle, tapered and self-aligning roller bearings. Self-aligning roller bearings contain two rows of barrel-shaped rollers with roller axes which are tilted relative to the bearing axis. The outer track is hollow-spherical so that in case of alignment faults and when the assigned shaft sags, the rollers can be adjusted in an oscillating manner in the outer track. The profile of the tracks is generally rather narrowly matched to the profile of the rollers. The different embodiments of the self-aligning roller bearings differ both in size itself and also in the size and shape of the rollers. Thus, there are both embodiments with symmetrical rollers and also those with asymmetrical rollers. In addition, there are embodiments with and without rims.
Self-aligning roller bearings have been used for more than fifty years. Due to their high bearing capacity, they have proven effective and are used wherever high impact-like forces must be accommodated and alignment faults and greater sagging of the assigned shaft must be expected. The main applications are heavy rollers and supporting rolls, marine shafts and rudder posts, rock crushers, crankshafts, transmissions, vibrating screens, milk, grinding and crushing machines. Due to the numerous applications, during decades of use of self-aligning roller bearings, attempts have been made again and again to further increase bearing capacity and reduce production costs by structural modifications. Thus, there have been attempts to guide the rollers with a loose guide ring instead of a middle rim permanently connected to the inner ring, or to abandon special guides completely so that the roller are guided solely by a cage. Normally, one such cage is designed to keep the individual rollers of a row of rollers at a uniform distance to one another and thus, to prevent their mutual contact. In a self-aligning roller bearing however, the rollers of the two rows of rollers move under load onto one another so that wear of the cage occurs when the guidance of the rollers is not assumed additionally by a middle rim or a guide ring.
Whenever a fixed middle rim or a loose guide ring is used in a self-aligning roller bearing, in the prior art, this middle rim or this guide ring has a trapezoidal cross section. Thus, German patent 644 181,
FIGS. 2 and 3
, published in 1937, discloses a self-aligning roller bearing in which a loose guide ring is used to guide the rollers. Here, the width of the trapezoidal guide ring is so large that The rollers are pressed to the sides of the self-aligning roller bearing. U.S. Pat. No. 2,740,675 published in 1956 discloses a self-aligning roller bearing in which there is a loose trapezoidal guide ring located on the inner ring between the rollers of the two rows of rollers. To obtain optimum friction behavior under different radial loads, the width of the guide ring should correspond exactly to the distance between the rollers of the two rows of rollers. Both in the self-aligning roller bearing as patented in German patent 644 181 and also in the self-aligning roller bearing patented in U.S. Pat. No. 2,740,675, the guide ring is designed on the one hand to safeguard the distance between rollers of the two rows of rollers and on the other to prevent crossing of the rollers. U.S. Pat. No. 5,586,826 which just recently issued discloses a self-aligning roller bearing with a trapezoidal guide ring. Here, the friction will be reduced by a special configuration of the rollers.
SUMMARY OF THE INVENTION
The primary object of the invention is now to make available a self-aligning roller bearing with high bearing capacity which on the one hand, can be easily and economically produced, on the other, has low friction even under high load so that high rpms are possible and a long service life is ensured
The self-aligning roller bearing in accordance with the present invention in which the aforementioned object is achieved includes a guide ring that has a rectangular cross section and the cross sectional center line of the guide ring that runs parallel to the bearing axis. The advantage of a guide ring with a rectangular cross section compared to a guide ring which is made trapezoidal consists first of all in that this guide ring can be produced especially easily and consequently favorably. But mainly, the attained advantage is that a uniform distance between the rollers of the two rows of rollers is always ensured.
In conjunction with the above described measures one advantageous embodiment of the self-aligning roller bearing in accordance with the present invention acquires special importance; the guide ring is dimensioned such that the rollers are axially prestressed. Therefore, the guide ring exerts a force on the rollers at an acute angle to the roller axes, by which displacement of the contact points between the rollers and the outer track and the inner tracks is caused. Therefore, the pressure ellipses between the inner tracks and the rollers are shifted to the end face of the self-aligning roller bearing. Without this prestress, the rollers touch the outer track and the inner tracks at the location of their largest diameter so that the lines of force action of the inner ring and inner track - rollers and rollers - outer ring and outer track, cause crossing of the rollers. By displacement of the points of contact which is caused by the indicated prestress, the lines of force action of the inner ring and inner track - rollers and rollers - outer ring and outer track, are at an angle which reduces the crossing of the rollers.
In the self-aligning roller bearing in accordance with the present invention the guide ring, as is known, is preferably made as a loose guide ring. The guide ring is therefore guided on the inner ring, but is not joined to it. In this way, if necessary, a different material can be easily used for the guide ring than for the inner ring. But mainly, a loose guide ring has the advantage that the peripheral component of the guide ring speed is balanced by the co-rotation of the guide ring, i.e. approaches zero.
It is especially advantageous if in the self-aligning roller bearing, the end faces of the rollers facing the guide ring are made such that between the end faces of the rollers and the guide ring, there is only point contact, preferably the distance between the roller axes and the point contacts of the end faces of the rollers with the guide ring amounting to roughly 50 to 75% of the maximum roller diameter. The measure of executing the ends face of the rollers facing the guide ring such that between the end faces of the rollers and the guide ring there is only point contact can be accomplished in particular differently, specifically, either by the end faces of the rollers facing the guide ring being convexly curved, or by the rollers on the end faces which face the guide ring being provided with a bezel.
The above described measures ensure that with allowable crossing of the rollers, no contact of the edges of the end faces of the rollers with the guide rings occurs, so that “scoring” on the edges of the end faces of the rollers is precluded.
In particular, there are a host of possibilities for embodying the self-aligning roller bearing in accordance with the present invention
REFERENCES:
patent: 1498571 (1924-06-01), Palmgren
patent: 1528363 (1925-03-01), Bronander
patent: 1548821 (1925-08-01), Bronander
patent: 2740675 (1956-04-01), Palmgren
patent: 354750
Brand Armin
Ganss Werner
Grehn Martin
Weigand Michael
FAG OEM und Handel AG
Hannon Thomas R.
Nixon & Peabody LLP
Safran David S.
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