Abstract:
A machine tool, in particular to a hand-operated hammer drill, having a compartment containing lubricant and a device for compensation of the pressure in the compartment in the area of a bearing of a component able to be driven so as to allow rotation. It is proposed that the bearing form at least a part of a lubricant seal of the pressure-compensation device via which a pressure in the compartment as able to be compensated.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a machine tool having a compartment containing lubricant and a device for compensation of the pressure in the compartment. 
     BACKGROUND INFORMATION 
     A machine tool forming the species, in particular a hand-operated hammer drill, is known from German Published Patent Application No. 42 31 987. The hammer drill has a driver motor, arranged within a motor compartment of a housing, having a motor shaft that extends through a housing section into a gear compartment, where it engages, via an integral pinion, with a gear unit for driving a tool-holding fixture. The gear compartment is provided with a pressure-compensation device that reduces a pressure, resulting during operation within the gear compartment, down to that of the atmosphere or of the motor compartment. The pressure-compensation device has a bore hole leading from the gear compartment to the outside or to the motor compartment and a rotary element, driven so that it is constantly rotating, in the form of a cover into which a passage is introduced. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a machine tool, in particular to a hand-operated hammer drill, having a compartment containing lubricant and a pressure-compensation device of the compartment in the area of a bearing of a component able to be driven so as to allow rotation. 
     It is proposed that the bearing form at least a part of a lubricant seal of the pressure-compensation device via which a pressure in the compartment may be compensated. Additional components, space, weight, assembly effort and costs can be saved. This can be achieved in a particularly inexpensive and uncomplicated manner in terms of design by using a lubricant seal implemented as a groove seal, which is arranged between the bearing and a bearing seat, it being possible to arrange the groove seal between an outer ring and/or an inner ring of the bearing and a bearing seat. Furthermore, it is conceivable that the lubricant seal, which is simultaneously usable for pressure compensation, is formed by a channel through the bearing, for example, a channel through a cage of a roller bearing and/or through bearing sealing washers fastened appropriately to the bearing. 
     In another embodiment of the present invention, it is proposed that the bearing and the bearing seat be formed of different materials having different coefficients of thermal expansion and that these be used to create the lubricant seal; specifically, it is beneficial that the bearing seat is formed of aluminum or an aluminum alloy and the bearing is formed of steel. If an outer bearing seat is formed of a material having a greater coefficient of thermal expansion than the bearing, as is beneficially the case for an aluminum bearing seat and a steel bearing, the bearing seat expands more when heated up and a gap between the bearing and bearing seat is created that may beneficially be used as a groove seal. Other material combinations that appear suitable to one skilled in the art are also conceivable in place of an aluminum-steel combination. 
     In this context, to prevent an undesired rotary movement of the bearing within the bearing seat, it is beneficially fixed in position in the circumferential direction within the bearing seat. This may be accomplished using various non-positive fit, positive fit and/or integral connections, for example, via a pin connection, a spring/groove connection and/or a positive-fit connection, in that an outer ring of the bearing has an outer contour that deviates from a round outer contour, etc. If the bearing is implemented as a locating bearing, and a component fixing the bearing in position in an axial direction is used to fix the bearing in position in the circumferential direction, additional components, space and assembly effort may advantageously be saved. For example, this can be achieved using a clasping component that holds the bearing in position in an axial direction, is torsionally fixed and has a projection that engages in a recess of an outer ring of the bearing. 
     In another embodiment of the present invention, it is proposed that a pressure-compensation channel be introduced into a bearing surface of the bearing and/or into a bearing surface of the bearing seat. A beneficial cross-section for the pressure compensation may be achieved with simplicity of design, and simultaneously a groove seal and/or labyrinth seal may be realized. The pressure-compensation channel in this case may be implemented, for example, in the form of an axial groove in a shaft, in an inner ring of a roller bearing, in an outer ring of a roller bearing and/or in a component forming an outer bearing seat, etc. 
     If the pressure-compensation channel is at least partially formed by a threaded-type recess, a beneficial labyrinth effect or labyrinth seal and, in addition, a recirculating effect may be achieved, which is done by coordinating the direction of threading and direction of rotation with each other. The threaded-type recess may in turn be introduced into the bearing and/or into a bearing seat. If the pressure-compensation channel opens through into at least one annular groove, it may be produced especially simply and economically, for example in one lathe operation, starting from a first annular groove and opening through into a second annular groove. 
     A filter element is beneficially connected in series with the lubricant seal formed at least partially by the bearing. While simultaneously ensuring the pressure compensation function, the sealing effect can be improved. A felt gasket, which can be manufactured especially economically and has proven beneficial characteristics, is especially suitable as a filter element. The felt element may be formed by various fibrous materials deemed appropriate by one skilled in the art, in particular such as animal hairs, plant fibers and/or synthetic fibers, etc. In order to save on additional holding components, the filter element is beneficially held in position by a component that holds a bearing in place. 
     Furthermore, in a space-conserving design, a beneficially large filter volume can be achieved, in that at least two radial pressure-compensation channels branch off from the bearing, and in particular in that the bearing is surrounded by an annular filter element, and the pressure-compensation channels open out from the bearing radially outwardly at the filter element. 
     The design approach of the present invention may be used in all machine tools deemed suitable by one skilled in the art, in particular in hand-operated machine tools, for example, grinders, saws, milling cutters, planers, drills, chisel hammers, etc. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematically illustrated hammer drill from the side. 
     FIG. 2 shows a section of FIG. 1 marked “II”. 
     FIG. 3 shows a variant of FIG. 2 having pressure compensation channels running radially outwardly. 
     FIG. 4 shows a variation of FIG. 2 having a threaded-type pressure-compensation channel. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a schematically illustrated hammer drill having a housing  104  in which a drive motor  58  is supported within a motor compartment  56 . A tool holder  60  and a drill bit  62  secured in tool holder  62  are able to be driven by drive motor  58 , via a gear unit (not shown) arranged within a gear compartment  10 , in a manner allowing rotation and striking. The hammer drill may be guided using two hand grips  64 ,  66  that extend essentially perpendicular to an operating direction, one handgrip  64  on a side facing away from bit  62  being integrally molded onto housing  104 , and one handgrip  66  on a side facing drill bit  62  being fastened to housing  104 . 
     Drive motor  58  has a drive shaft  68  on which a fan impeller  80  is arranged in a torsionally fixed manner within motor compartment  56  (FIG.  2 ). Drive shaft  68  projects from motor compartment  56  through a partition wall  70  made of aluminum into gear compartment  10  and is mounted in partition wall  70  so that it is able to rotate within a ball bearing  48 . 
     An outer ring  72  of ball bearing  48  is connected by a press-fit to partition wall  70 , and its inner ring  74  is connected in a rotatably-fixed manner to drive shaft  68  by a press-fit. Ball bearing  48  is implemented as a locating bearing, and specifically it is supported axially in the direction of gear compartment  10  against a shoulder  78  in partition wall  70 , and is axially supported in the direction of motor compartment  56  against a retaining ring  32  affixed in partition wall  70 . Gear compartment  10 , filled with lubricant, is sealed airtight and lubricant-tight at ball bearing  48  via a sealing washer  76  in the direction of motor compartment  56 . 
     Integrally molded on one end of drive shaft  68  projecting into gear compartment  10  is a pinion  82  via which drive shaft  68  meshes with a gear wheel (not shown) arranged in a rotationally fixed manner on an intermediate shaft  20  of the gear unit. Intermediate shaft  20  is rotationally mounted via a ball bearing  16  in partition wall  70 . Ball bearing  16  is implemented as a locating bearing, and specifically is axially supported in the direction of motor compartment  56  against a shoulder  88  in partition wall  70 , and is axially supported in the direction of gear compartment  10  by a retaining element (not shown) that is fastened in partition wall  70 . 
     According to the present invention, ball bearing  16  forms a part of a lubricant seal  24  of a pressure-compensation device  12  via which the pressure in gear compartment  10  is able to be equalized, that is, a buildup of pressure in gear compartment  10  due to heating during operation of the hammer drill may reliably be prevented. Ball bearing  16 , with its inner ring  84 , is connected in a rotatably-fixed manner to intermediate shaft  20  by a press-fit. 
     Moreover, ball bearing  16  is mounted, with its steel outer ring  86 , via a sliding fit in a bearing seat  28  formed by partition wall  70 . Then the hammer drill is operated, ball bearing  16  and partition wall  70  heat up. Because of their differing coefficients of thermal expansion, partition wall  70  made of aluminum expands to a greater extent than ball bearing  16  made of steel. Between outer ring  86  of ball bearing  16  and partition wall  70  there arises a gap that functions as lubricant seal  24  or as a groove seal of pressure-compensation device  12 , via which a pressure is able to be equalized. A bearing gap between inner ring  84  and outer ring  86  of ball bearing  16  is sealed airtight and lubricant-tight by a sealing ring  90 . 
     To prevent an undesired rotary movement of outer ring  86  of ball bearing  16  within partition wall  70 , the outer ring is connected in the circumferential direction in a rotatably-fixed manner by a positive-fit connection to partition wall  70  via the retaining element axially holding ball bearing  16  in position in the direction of gear compartment  10 . 
     A filter element  46  formed by a felt ring is connected in series with the groove seal created between outer ring  86  and partition wall  70 . Filter element  46  is placed in a recess  94  in partition wall  70 , the recess surrounding ball bearing  48  in a ring shape, and is held in its place by retaining ring  32 . Introduced into partition wall  70 , coaxially with respect to intermediate shaft  20 , is a bore hole  92  that is covered in the direction of motor compartment  56  by filter element  46  and via which a pressure difference between gear compartment  10  and motor compartment  56  may be equalized. 
     FIG. 3 shows one variant of FIG. 2 having a pressure-compensation device  14 . Components that essentially remain the same are always numbered using the same reference numbers in the illustrated exemplary embodiments. Moreover, concerning features and functions that remain the same, refer to the description for the exemplary embodiment in FIGS. 1 and 2. The following description is essentially limited to the differences from the exemplary embodiment in FIGS. 1 and 2. 
     A drive shaft  22  of a drive motor  58  is supported via a ball bearing  18  in a partition wall  106 . Ball bearing  18 , according to the present invention, forms a part of a lubricant seal  26  of pressure-compensation device  14  via which the pressure in a gear compartment  10  is able to be compensated. Ball bearing  18 , with its inner ring  96 , is connected in a rotatably-fixed manner by a press fit to drive shaft  22 . Moreover, ball bearing  18 , with its steel outer ring  98 , is mounted via a sliding fit in a bearing seat  30  formed by partition wall  106 . When the hammer drill is operated, ball bearing  18  and partition wall  106  heat up. Because of their differing coefficients of thermal expansion, partition wall  106  made of aluminum expands to a greater extent than ball bearing  18  made of steel. Between outer ring  98  of ball bearing  18  and partition wall  106  there arises a gap that functions as a lubricant seal  26  or as a groove seal of pressure-compensation device  14  via which a pressure is able to be compensated. A bearing gap between inner ring  96  and outer ring  98  of ball bearing  18  is sealed airtight and lubricant-tight via a sealing ring  90 . 
     To prevent an undesired rotary movement of outer ring  98  of ball bearing  18  within partition wall  106 , the outer ring is connected in the circumferential direction in a rotatably-fixed manner by a form-fitting connection to partition wall  106  via a retaining ring  32  which axially holds ball bearing  18  in position in the direction of gear compartment  10 . 
     A filter element  46  formed by a felt ring is connected in series with the groove seal created between outer ring  98  and partition wall  106 . Filter element  46  is placed in a recess  94  in partition wall  106 , the recess surrounding ball bearing  18  in a ring shape, and is held in its place by retaining ring  32 . Extending from outer ring  98  of ball bearing  18  are four radial pressure-compensation channels  50 ,  52  which are distributed evenly over the periphery, are introduced into partition wall  106  and open out radially outwardly at filter element  46 . 
     An intermediate shaft  20  of a gear unit (not shown) in gear compartment  10  is supported via a ball bearing  100  in intermediate wall  106 . Partition wall  106  is sealed off, in the area of ball bearing  100 , from gear compartment  10  in the direction of motor compartment  56 . 
     In an exemplary embodiment in FIG. 4, an intermediate shaft  54  is rotationally mounted via a ball bearing  36  in a partition wall  70 . Ball bearing  36 , according to the present invention, forms a part of a lubricant seal  38  of a pressure-compensation device  34  via which the pressure in a gear compartment  10  is able to be compensated. Ball bearing  36 , with its inner ring  84 , is arranged in a rotatably-fixed manner on a bearing seat  40  of intermediate shaft  54  by a press fit. Moreover, ball bearing  36 , with its steel outer ring  86 , is mounted via press fit in a bearing seat  102  formed by partition wall  70 . 
     Introduced into a bearing surface of bearing seat  40  is a pressure-compensation channel  42 , formed by a threaded-type recess that opens through, counter to a venting direction of gear compartment  10 , into an annular groove  44 . Pressure-compensation channel  42  forms a labyrinth seal and, in addition, has a lubricant-recirculating effect during operation. A bearing gap between inner ring  84  and outer ring  86  of ball bearing  36  is sealed airtight and lubricant-tight via a sealing ring  90 . 
     List of reference numerals 
       10  compartment 
       12  pressure-compensation device 
       14  pressure-compensation device 
       16  bearing 
       18  bearing 
       20  component 
       22  component 
       24  lubricant seal 
       26  lubricant seal 
       28  bearing seat 
       30  bearing seat 
       32  component 
       34  pressure-compensation device 
       36  bearing 
       38  lubricant seal 
       40  bearing seat 
       42  pressure-compensation channel 
       44  annular groove 
       46  filter element 
       48  bearing 
       50  pressure-compensation channel 
       52  pressure-compensation channel 
       54  component 
       56  motor compartment 
       58  drive motor 
       60  tool holder 
       62  bit 
       64  hand grip 
       66  hand grip 
       68  drive shaft 
       70  partition wall 
       72  outer ring 
       74  inner ring 
       76  sealing washer 
       78  shoulder 
       80  fan impeller 
       82  pinion gear 
       84  inner ring 
       86  outer ring 
       88  shoulder 
       90  sealing ring 
       92  bore hole 
       94  recess 
       96  inner ring 
       98  outer ring 
       100  ball bearing 
       102  bearing seat 
       104  housing 
       106  partition wall