Abstract:
A power tool, such as a hammer drill and/or a chiseling hammer, includes a lubricated transmission arranged in a sealed transmission box. The transmission box is in fluid connection with the atmosphere via a venting channel. A sealing element is arranged in the venting channel. The sealing element cooperates with the venting channel to create a meandering pathway for air to pass through the venting channel so that leakage of lubricant between the sealing element and the venting channel is at least substantially prevented.

Description:
RELATED APPLICATION 
     This application is related to, and claims priority from, European Patent Application No. 08 010 192.6, filed Jun. 4, 2008, entitled “POWER TOOL HAVING A TRANSMISSION VENT,” the entirety of which is incorporated by reference herein and made a part of the present specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a power tool, preferably a hammer drill or a chipping hammer comprising a lubricated transmission arranged in a sealed transmission box, in particular in an air-tight transmission box, wherein the transmission box is in fluid connection with the atmosphere via a venting channel, and an air-permeable sealing element arranged in the venting channel. 
     2. Description of the Related Art 
     Such a power tool is, for example, known from EP 1 252 976 A1, wherein the transmission box is open towards the atmosphere via a narrow channel and a filter connecting to this channel. The filter element may, for example, be a felt. 
     If the transmission is lubricated by oil or an oil-like lubricant, there is the danger that the felt soaks up the oil through capillary action and that the transmission starts to leak after a short time (oil leakage by capillary action). A similar problem arises also when using grease or grease-like lubricants. Here, the felt works similar to a sieve and separates the grease into its components. The base oil is soaked up by the felt through capillary action, whereas the soaps from the grease remain sticking on the surface of the felt and form a thick layer. This layer seals the felt so that a further loss of lubricant is avoided but at the same time no more venting of the transmission housing is warranted. However, the venting is necessary because the air pressure within the transmission housing of the hammer drill or chipping hammer is subject to continuous oscillations due to changes in temperature and the operation of the hammer mechanism, and a pressure compensation with the atmosphere has to be provided. 
     SUMMARY OF THE INVENTION 
     In view of the above discussion, it is an object of the present invention to further develop a power tool of the specified type so that a secure and permanent venting without any substantial loss in lubricant may be ensured. 
     This object is achieved by the features of one or more embodiments of the claimed invention. Further preferred embodiments are defined in the dependent claims. 
     A preferred embodiment of the present invention is based upon the notion to provide a meander-like sealing element in the path or channel taken by the air for the pressure compensation of the transmission box towards the atmosphere, which upon over- or underpressure allows air to circulate in the transmission box by extending the path from the transmission box to the outside, without any lubricant leaking from the transmission by capillary action. 
     Thus, the power tool, which preferably is a hammer drill or a chipping hammer, comprises a lubricated transmission arranged in a sealed transmission box, in particular in a substantially air-tight transmission box, wherein the transmission box is in fluid connection with the atmosphere via a venting channel, and an air-permeable sealing element arranged in the venting channel, which upon over- or underpressure in the transmission box allows air to circulate between the atmosphere and the transmission box. According to the invention, this sealing element is configured so as to extend the venting channel meander-like so that the air may continue to circulate but lubricant is prevented from leaking from the transmission box to the atmosphere by-passing the sealing element. Preferably, the sealing element may be formed of rubber or a rubber-like material. 
     According to a particularly preferred embodiment, the venting channel comprises an aperture open to the transmission box, wherein it is preferred that the sealing element substantially immediately adjoins the aperture. Thereby, leakage of lubricant from the transmission box is substantially avoided without the need for additional elements or laborious structures in order to seal other regions of the venting channel against leakage of the lubricant. 
     A particularly economical and space-saving construction may be achieved if the power tool comprises a switching member, preferably a transmission switch, wherein the switching element preferably has a socket (stub or boss) protruding into the transmission box, within which the venting channel having the sealing element is formed. To operate the power tool, such a switching element is operable from the outside so as to switch a component in the interior of the power tool. Thus, such a switching element is an interface between the interior of the power tool and the environment and, therefore, the atmosphere. This interface may be configured as leaky (untight or unsealed) location and may be utilized for forming the venting channel in a space-saving and economical way. Here, a transmission switch is particularly preferred. For example, this can be used to switch between a hammer drill mode and a chipping hammer mode or, conversely between a pure drill mode and a hammer drill mode. Here, there may be a mechanical connection between the switching element and one or more transmission elements. In other words, there is a connection between the switch and the transmission box so that substantially no additional elements may to be provided in order to form the venting channel. 
     According to a particularly preferred embodiment the sealing element is configured in a way that it has a mouth opening facing the transmission box, that is an opening open directly or indirectly towards the transmission box. Further, two flow channels continuing from the mouth opening are provided so that air flowing out of the transmission box upon overpressure, for example, may flow into the mouth opening and from there flow in different directions into the two separate flow channels. This is especially expedient in order to avoid an accumulation of lubricant, for instance an accumulation of grease. In case of an accumulation of grease in the mouth opening, in a situation of overpressure the accumulated grease is pushed out of the mouth opening into only one of the two flow channels, so that there always remains a flow channel for air to flow through. This contributes to a reliable and secure venting. 
     Further, it is preferred that the sealing element comprises at least one, but preferably several levels (or stages) respectively composed of at least one (preferably only one) mouth opening leading into the respective level and two flow channels continuing from the mouth opening. By arranging several levels connected in series and configured in this manner, the above-mentioned advantage regarding the prevention of an accumulation of grease and a secure and reliable venting is ensured and, on the other hand, it is avoided that the lubricant (accumulated grease) finds its way to the point of leaking out of the power tool. 
     Advantageously, the sealing element, which as mentioned may be made of rubber or a rubber-like material, may be molded, in particular injection-molded. In order to realize the above-mentioned configuration of mouth openings and continuing flow channels being arranged in several levels in the easiest way and at low production costs, it is hence preferred that the sealing element comprises several grooves sequentially arranged in direction of the venting channel. In other words, the sealing element comprises several grooves that are circumferentially arranged perpendicular to a longitudinal axis of the venting channel and distanced in the longitudinal direction of the venting channel. These grooves respectively form the mentioned flow channels and are separated by walls that are circumferentially arranged perpendicular to the longitudinal direction of the venting channel and distanced in the longitudinal direction of the flow channel. These walls each comprise a through hole, preferably only one through hole which forms the mouth opening. The wall is penetrated completely from one side to the other in the longitudinal direction of the venting channel so that by means of the through hole a connection between two grooves or flow channels that are adjacent in the longitudinal direction of the venting channel is created. These through holes are alternately provided on opposite sides of the sealing element, for example a front- and backside, so that a rectilinear flow from one through hole into the next is not possible. Here, it is also conceivable that the through holes or mouth openings are not arranged centrally in the walls and on the corresponding sides but are arranged in the walls and offset in an arbitrary manner. 
     Moreover, it is preferred that the walls seal circumferentially against the venting channel in a substantially air-tight manner so that neither a flow of lubricant nor a flow of air is permitted between the surface of the walls and the inner surface of the venting channel and past the sealing element. In order to achieve this, it may be preferred to provide a sealing lip surrounding the walls except for the through holes, or several sealing lips arranged in parallel. 
     Further advantages and features of the present invention, that may be employed on its own or in combination within a power tool according to the present invention, are apparent from the following description of a preferred embodiment given with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a power tool according to the invention, which is broken open in the region of the venting channel having the sealing element. 
         FIG. 2  shows an enlarged view of the venting channel having the sealing element arranged therein, corresponding to the illustration of  FIG. 1 , seen from the front in  FIG. 2   a , from a side in  FIG. 2   b , and from behind in  FIG. 2   c.    
         FIG. 3  shows a perspective view only of the sealing element of  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The illustrated power tool is a hammer drill and chiseling hammer comprising an electric motor (not shown) as drive unit, which offers a hammer drill or chiseling hammer function through a transmission (not shown). It is possible to switch between a hammer drill mode and chiseling hammer mode by means of a transmission switch  20 . By virtue of a mechanical connection with the transmission, the transmission switch causes either the transmission of the rotational motion of the electric motor to the drill chuck (hammer drill mode) or causes a corresponding removal of this rotational motion (chipping hammer mode). The mechanical connection and the switching of the transmission is insubstantial for the present invention and, therefore, will not be explained in more detail. The transmission is received in a transmission housing which in the embodiment shown consists of a housing body  21  and a lid  22 . A transmission box  23  is formed in the housing  21 ,  22 , which in the present case houses an oil-lubricated transmission (not shown). Due to temperature changes during operation as well as the hammer function of the hammer mechanism, pressure oscillations are created in the transmission box  23  during the operation of the power tool. In other words, an over- or underpressure may be created, which can only be compensated to the atmosphere. To that end the transmission switch  20  comprises a socket (stub)  24  seated in a recess  25  of the lid  22  of the transmission housing and, at the same time, fixed on the lid  22  of the transmission housing in a rotatable manner via latching connections (not shown). 
     The interface between the outer surface of the socket (stub)  24  and the inner surface of the opening  25  is configured in a substantially tight manner (against the lubricant and air). Further, the transmission switch  20  comprises a handling member  27  that can be grasped in order to operate the transmission switch  20 . Facing the lid  22  of the transmission housing, a cavity  28  is provided in this handling member  27 , which is formed by a recess in the handling member  27  and is closed by a surface of the transmission housing lid  22 . However, In this case an air passage is provided between the lid  22  of the transmission housing or its outer surface and the support surface of the handling member  27  surrounding the space  28 . Moreover, a venting channel  26  is provided in the socket  24 , which communicates with space  28  via a connecting bore  29  (see also  FIG. 2   c ). The venting channel  26  has an aperture  30  leading into the transmission box  23 . By virtue of the fluid connection between the space  28  and the atmosphere via the interface between the handling member  27  and the outer surface of the lid  22  of the transmission housing, a fluid connection exists between the atmosphere and the transmission box  23  via space  28 , bore  29  and venting channel  26 . 
     Substantially immediately adjoining the aperture  30 , a sealing element  40  is seated in the venting channel  26 , which will be explained in more detail below by referring to  FIG. 3 . The sealing element  40  is preferably made of rubber or a rubber-like material and is, in the illustrated arrangement, molded, for example injection-molded. It is tapered from an end facing the aperture  30  toward the opposite end and the venting channel  26  illustrated in  FIGS. 1 and 2  is configured in the same way, that is tapering away from the aperture  30 . In particular, this is predetermined by the transmission switch  20 , which is an injection-molded part, so that the tapered shape of the recess forming the venting channel  26  is necessary for demolding. The sealing element is seated in a force-fitting or friction-fitting manner within the venting channel so that no additional fastening is necessary. 
     At the broader end, the sealing element  40  comprises a mouth opening  41 . In the assembled state, this mouth opening  41  is arranged on the side of the sealing element  40  facing the aperture  30  and, thus, the transmission box  23 . Two flow channels  42 ,  43  continue from this mouth opening  41 . 
     The sealing element  40  of the illustrated embodiment further comprises five levels  1 - 5  (see  FIG. 2 ), which respectively consist of a mouth opening  41  and the two flow channels  42 ,  43  continuing from the mouth opening  41 . 
     The sealing element  40  is formed by several grooves  44  forming the flow channels  42 ,  43  and arranged circumferentially and perpendicularly to the longitudinal direction of the sealing element  40 . The grooves  44  are distanced from each other in the longitudinal direction of the sealing element  40  and are separated from each other by walls  45 . The walls are configured circumferentially and perpendicular to the longitudinal direction of the sealing element  40  and comprise a through hole  46  each in the longitudinal direction. The perforation (through hole) of the walls is configured so as to connect two of the grooves  44  at a time. The through hole  46  provided closest to the transmission box  23 , that is at the stronger end of the sealing element  40 , connects the first groove  44  via aperture  30  to the transmission box  23  and is, therefore, the mouth opening facing the transmission box. As can be seen in particular from  FIGS. 2   a  and  c , the through holes  46  of neighboring walls  45  are provided diametrically opposite to each other on opposing sides of the sealing element  40 . The through holes  46 , however, do not necessarily have to be arranged on neighboring walls  45  in a diametrically opposite manner, that is offset by 180°, but may also be offset in a different arrangement. 
     Moreover, at least one sealing lip  47  is circumferentially provided, except for the through holes  46 , on the surface of walls  45 , which seals the walls  45  circumferentially against the inner walls of the venting channel  26  so that leakage of air and lubricant between the outer surfaces of the walls  45  and the inner surface of the venting channel  26  is avoided. 
     In the following, with particular reference to  FIGS. 2   a - c , the mode of operation of the vent will be explained. This explanation is given for an overpressure present in the transmission box  23  and is correspondingly inverted for respective underpressure. When there is overpressure in the transmission box  23 , air in the transmission box  23  flows into the aperture  30  of the venting channel  26  and from there into the mouth opening  41  closest to the aperture  30  at an end of the sealing element  40 . As indicated by the arrows in  FIG. 2   a , the inflowing air divides in the two flow channels  42 ,  43  after leaving the mouth opening  41  and flows into the mouth opening  41  of the second level, too, and from there in turn into two flow channels  42 ,  43  running perpendicular to the longitudinal direction of the venting channel  26  and the sealing element  40 . From there, it in turn flows into the mouth opening  41  of the third level and the associated flow channels  42 ,  43 . This is repeated on the fourth level until the air flows into the mouth opening  41  of the fifth level, and from there into the associated flow channels  42 ,  43 , meeting In the region of an opening  32  leading into the bore  29 , so that the air may escape through the bore  29  into the space  28  and from there towards the atmosphere. Thereby, a pressure compensation between the transmission box  23  and the atmosphere is ensured. Due to the significantly longer flow path of the air through the maze created by means of the mouth openings  41  and the flow channels  42 ,  43  on the different levels and due to the offset arrangement of the mouth opening  41  on the front and back side, a leakage of lubricant or a passage into the bore  29 , the space  28  and from there out of the housing of the power tool is minimized or at least substantially or completely avoided. 
     With grease lubrication, if an accumulation of grease should form in the mouth opening closest to the transmission box  23 , for example, it would eventually leave the mouth opening  41  in the direction of the atmosphere upon further overpressure and would eventually enter into one of the two flow channels  42  or  43 , too. Even in such a case, however, the second flow channel would still be available for venting and the air can still escape via this channel from the mouth opening  41  of the first level to the mouth opening  42  of the second level and from there further via the third to fifth levels, the bore  29  and the space  28  towards the atmosphere, so that a secure and reliable venting is provided for without entailing a leakage of lubricant due to capillary action. 
     The inventive sealing element thus features numerous advantages. On the one hand, it can be economically produced. On the other hand, the placement and configuration in the transmission switch can easily be realized in a space-saving manner and without the integration or implementation of further elements or configurations. Without having to renounce these advantages, the sealing element of the present invention provides a secure and reliable venting without the risk of a leakage of lubricant and, thus, achieves the economical and space-saving replacement of the known filter as sealing element. 
     However, it is to be understood that the present invention is not limited to the illustrated embodiment but that various modifications within the scope of the patent claims may be effected. For example, the grooves  44  and thus the flow channels  42 ,  43  do not necessarily and unconditionally have to run perpendicular to the longitudinal extension of the venting channel  26  and/or of the sealing element  40  but may also be formed in an inclined manner or be composed of longitudinally and transversely extending elements or portions. Also, the mouth openings  41  formed by the through holes  46  do not necessarily have to run in the longitudinal direction but may also be inclined. As mentioned, the through holes  41  also do not necessarily have to be provided diametrically opposite to each other on different sides and alternately in the walls  45 , but may be configured so as to be offset in various ways. Further, one can do without the configuration of the sealing lips  47  if the surfaces of the walls  45  suitably seal with the inner surface of the flow channel  26 , which would, however, lead to a more difficult assembly (more effort) and smaller tolerances would need to be maintained. Finally, the venting channel does not necessarily have to be integrated in a switching element and/or the sealing element does not necessarily have to be seated in the venting channel of the switching element. For example, it is conceivable to provide in the lid  22  of the transmission housing, a suitable socket which leads into the transmission box  23  and communicates with the atmosphere, and in which the venting channel having the sealing element would then be provided. Also, the transmission does not necessarily have to be oil-lubricated, but a lubrication by grease and/or another oil-like or grease-like lubricant or any other lubricant could be used, too. Moreover, further modifications which allow the implementation of the present invention will be apparent to the skilled person.