Patent Abstract:
A seal ( 2 ) for a bearing ( 6 ) that rotatably supports a shaft ( 14 ) extending through a housing opening ( 8 ) of a housing element ( 10 ) that limits, at least partially, a lubricant-receiving chamber ( 4 ), includes a sealing ring ( 26 ) retainable between the housing element ( 10 ) and the shaft ( 14 ) and forming together with a limiting element ( 28 ) an annular gap ( 30 ), and having aeration recesses ( 34 ) which connect the annular gap ( 30 ) with the grease-containing chamber ( 4 ).

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a seal for a bearing that rotatably supports a shaft. The shaft extends through a housing opening of a housing element that limits, at least partially, a chamber containing a lubricant in form of a lubricating grease or oil. Between the lubricant-containing chamber and the bearing, there is provided a sealing ring that surrounds the shaft and is retained between the shaft and the housing element for protecting the bearing from the lubricant. The sealing ring forms, together with a limiting element, an annular gap. 
     2. Description of the Prior Art 
     The seals of the type descried above, are provided, e.g., on lubricant-receiving chambers or receptacles for gear units of, e.g., hand-held power tools. The sealing ring prevents the lubricant, which is provided in the associated gear housing, from directly contacting the bearing and from flowing through the bearing from the gear housing outwardly, e.g., into a motor housing. 
     European Patent EP 0 202 702 B1 discloses a seal for a shaft bearing and which includes a swivel ring connected with the shaft for a joint rotation therewith. The swivel ring forms a hub which extends radially outwardly and forms, together with a hub fixedly connected with the housing and extending from the housing opening radially inwardly, an annular gap. This annular gap has a labyrinth-shaped cross-section. 
     U.S. Pat. No. 5,876,126 discloses a shaft bearing seal that has a sealing disc retained on an outer ring of the bearing which is fixedly secured to the housing. The sealing disc forms, together with a shaft and a bearing inner ring press-fitted on the shaft, a labyrinth-shaped annular gap. 
     The drawback of the known shaft bearing seals consists in that despite the labyrinth-shaped annular gap, in particular at a vertical orientation of the shaft, the lubricant reaches the bearing and can leave the lubricant-receiving chamber through the bearing. 
     Such seals are not suitable for hand-held power tools which, e.g., are often used in overhead works and have the shaft oriented vertically for an extended time period in an operational or shut-down condition of the power tool when no lubricant should flow through the shaft bearing. 
     Accordingly, an object of the present invention is to provide a shaft bearing seal suitable for hand-held power tools and in which the above-mentioned drawback of the known shaft bearing seals is eliminated, and the bearing is better protected from the lubricant such as grease. 
     SUMMARY OF THE INVENTION 
     This and other objects of the present invention, which will become apparent hereinafter, are achieved according to the present invention by providing a shaft bearing seal of the type discussed above and in which the sealing ring has aeration recesses which connect the annular gap with the lubricant containing chamber. The aeration recesses permit to remove the lubricant, which penetrated in the annular gap during the operation or shut-down of the power tool as a result of a vertical orientation of the bearing, from the annular gap. To this end, a dynamic effect is used which is produced by a rotation of the sealing ring that limits the annular gap on one side, relative to another limitation that limits the annular gap on the second side. The sealing ring can be fixedly connected, e.g., with the shaft for joint rotation therewith, and the limiting element can be fixedly secured to the housing element or vice versa. The aeration recesses aerate the annular gap. The aeration of the annular gap during operation prevents development of underpressure in the annular gap that can cause an aspiration of lubricant in the annular gap or its retention there. 
     According to a particular advantageous embodiment of the present invention, the sealing ring is formed by an impeller-like disc connectable with the shaft for a joint rotation therewith, and the limiting element is fixedly connected with the housing element. During an operation, the sealing ring rotates together with the shaft, accelerating the lubricant accumulated on the sealing ring. Thereby, in particular with a suitable shape of the sealing ring, the lubricant can be particularly effectively forced out of the annular gap. 
     Advantageously, the annular gap is formed between a radially outer rotational surface of the sealing ring and the limiting element. This insures a maximum acceleration of the lubricant that accumulated on the sealing ring during operation. This further optimizes removal of the lubricant from the annular gap. 
     Advantageously, the aeration recesses open into the rotational surface of the sealing ring, which insures a particularly good aeration of the annular gap and, thus, an unobstructed delivery of the lubricant out of the annular gap. 
     Preferably, the aeration recesses are substantially identical and are spaced from each other by a same angular distance. This insures a uniform removal of the lubricant over the sealing ring circumference. 
     Advantageously, there are provided at least three aeration recesses. This permits to achieve a particularly high delivery output of the sealing ring with respect to the lubricant in the annular gap. 
     Preferably, the aeration recesses extend from a lubricant containing chamber side end surface of the sealing ring to a bearing-side end surface of the sealing ring. Thereby, the aeration of the annular gap takes place over the entire width of the rotational surface. In addition, thereby, even the region of the annular gap, which is limited by the bearing-side end surface of the sealing ring remote from the lubricant-containing chamber, is aerated. 
     It is further particular advantageous when the aeration recesses extend radially inwardly up to a virtual cylinder a diameter (dZ) of which is smaller than an outer diameter of an inner ring of the bearing. Thereby, the side of the bearing adjacent to the lubricant-containing chamber can be completely aerated in the region between the shaft-side inner ring of the bearing and the outer ring of the bearing fixed to the housing. In this region, because of the insufficient sealing, the lubricant exits from the lubricant exits from the lubricant-containing chamber. Complement aeration prevents underpressure in this region. Therefore, with a suitable shape of the sealing ring, in this region also, a substantially complete removal of the lubricant is possible. 
     Advantageously, the aeration recesses extend over from 70% to 95% of a sealing ring circumference, and an acceleration element is formed between each two adjacent aeration recesses. With this propeller-shaped design of the sealing ring a particularly high delivery output with respect to the annular gap is achieved. 
     It is advantageous when the acceleration element has a side surface adjacent to a rotational direction and inclined toward a bearing axis at an angle. This likewise increases the delivery output. 
     Advantageously, the acceleration element alternatively or in addition is inclined toward the bearing axis at the rotational surface of the sealing element, at an angle. In this way, the sealing ring forms, during an operation, a conical rotational body, and an improved lubricant delivery takes place over the circumference of the sealing ring. 
     The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings show: 
         FIG. 1  a partially cross-sectional view of a shaft bearing seal according to the present invention; 
         FIG. 2  a plan view of the sealing disc of the shaft bearing seal according to  FIG. 1 ; 
         FIG. 3  a side view of the sealing disc according to  FIG. 2  in direction of arrow III; 
         FIG. 4  a plan view of another embodiment of the sealing disc of the shaft bearing seal according to the present invention; 
         FIG. 5  a side view of the sealing disc according to  FIG. 4  in direction of arrow V; 
         FIG. 6  a plan view of a further embodiment of the sealing disc of the shaft bearing seal according to the present invention; and 
         FIG. 7  a side view of the sealing disc according to  FIG. 6  in direction of arrow VII. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a shaft bearing seal  2  which is provided on a grease-containing chamber  4  of a gear housing, not shown in detail, of a hand-held power tool, e.g., in form of a hammer drill or a screw driving tool. The shaft bearing seal  2  is provided on a bearing  6  that is retained in the housing opening  8  of a wall-shaped housing element  10 . The housing element  10  separates the grease-containing chamber  4  from an outer chamber  12  of a motor housing, not shown in detail. 
     The bearing  6  serves for supporting a shaft  14  for rotation about an axis A. The shaft  14  projects from the outer chamber  12  into the grease-receiving chamber  4 . The bearing  6  has an inner ring  16  which, e.g., is press fit-mounted on the shaft  14  for joint rotation therewith. The inner ring  16  is rotated relative an outer ring  20  of the bearing  6  by a ball-shaped bearing body  18 . The outer-ring  20  is held fixedly in the housing element  10  and is axially secured with a circlip  22 . Between the inner ring  16  and the outer ring  20 , there are provided sealing elements  24 . 
     On the shaft  14 , there is further provided a sealing disc  26  in form of an impeller-like disc that, e.g., is connected with shaft  14  by a press fit for joint rotation therewith. The sealing disc  26  is held, with respect to the axis A, at an axial height of a limiting element  28  that is formed by a collar section of the housing element  10 , which projects radially inwardly in the housing opening  8 . A circumferential rotational surface  32 , which is defined by radially outer surfaces of the sealing disc  26 , and the limiting element  28  form an annular gap  30 . 
     As shown in  FIGS. 2-3 , the sealing disc  26  has three acceleration elements  33  which are separated from each other by aeration recesses  34 . The aeration recesses  34  extend over more than 90° of the rotational surface  32 . The acceleration elements  33  form radially outer circumferential surfaces  35  which define the rotational surface  32 . 
     Alternatively, the aeration recesses  34  can be formed by a multiplicity of smaller grooves which can be formed on the circumference of the sealing disc  26  (not shown). In each case, the rotational surface  32  is formed by the radially outer surfaces  36  of the sealing disc  26  which upon rotation of the sealing disc  26  in a direction D, form an outer cylindrical surface of the corresponding rotational body. 
     The aeration recesses  34  and thus, the acceleration elements  33  extend, as shown in  FIG. 1 , over an entire width of the sealing disc  26  from a chamber-side end surface  36  adjacent to the grease-receiving chamber  4  to a bearing-side end surface  28  adjacent to the bearing  6 . 
     As shown in  FIG. 1 , the aeration recesses  34  extend radially inwardly up to a common virtual cylinder Z having a diameter dZ. The diameter dZ is smaller than the outer diameter dR of the inner ring  16  of the bearing  6 . 
     When the respective hand-held power tool is operated or is shut down and the shaft  14  is so aligned that it extends, as shown in  FIG. 4 , vertically, the grease can flow from the grease-receiving chamber  4  into the annular gap  30  between the sealing disc  26  and the limiting element  28  and through the annular gap  30  into an intermediate chamber  40  between the sealing disc  26  and the bearing  6 . As a result, the grease directly contacts the sealing elements  24 . 
     As soon as the shaft  14  begins to rotate about the axis A, the grease would be accelerated in the annular gap  30  and in the intermediate chamber  40  by the sealing disc  26  and would be transported from the annular gap  30 . 
     The aeration recesses  34 , which connect the grease-receiving chamber  4  with the annular gap  30  and the intermediate chamber  40 , insure that both the annular recess  30  and at least a region of the intermediate chamber  40  that extends over the sealing elements  24 , is adequately aerated. In this way, the built-up of an underpressure is prevented, and almost complete removal of grease, which accumulated on the sealing elements, is insured. At that, a grease cone  42  is formed that permanently adjoins the annular gap  30  but cannot penetrate thereinto as long as the sealing disc rotates. 
       FIGS. 4 through 7  show alternative embodiments of the sealing disc  26 , with the elements, which perform the same functions, all having the same reference numerals as in  FIGS. 1-3 . 
     In the embodiment shown in  FIGS. 4-5 , the acceleration elements  33  form, with respect to the axis A, an angle (α) on both side surfaces  44  aligned in the rotational direction D. 
     In the embodiment of  FIGS. 6 and 7 , additionally, the radially outer circumferential surface  35  of the acceleration elements  33  forms, with respect to axis “A” an inclination angle (β), so that the sealing disc  26  forms, upon rotation in the rotational direction D, a conical rotational body, as shown with dash-dot lines. 
     Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.

Technology Classification (CPC): 5