Patent Publication Number: US-9421679-B2

Title: Hand-held power tool

Description:
FIELD OF THE INVENTION 
     The present invention relates to a hand-held power tool having a housing and a tool holder which is disposed on a drive shaft that is rotationally mounted in at least one first and one second ball bearing, the first ball bearing having a first inner ring and the second ball bearing having a second inner ring. 
     BACKGROUND INFORMATION 
     Conventional hand-held power tools have a drive shaft in the form of a drive spindle, the first ball bearing being situated in the area of a gear unit assigned to the power tool, e.g., a planetary gear that is located in a gear housing and in whose area a spindle lock is provided, which is assigned to the drive spindle, and the second ball bearing being situated in the area of a tool holder assigned to the power tool. Felt rings are provided between the first and second ball bearings, in order to prevent a hard impact of the drive spindle into the spindle lock when switching off such a power tool. These felt rings are disposed on the drive spindle in such a way that, to generate a drag torque by way of the gear housing, a prestress is produced on the spindle to thus reduce noise and wear during operation of the power tool. 
     A disadvantage is that the felt rings are comparatively costly, and also lead to a disturbing frictional force during normal operation or no-load operation of the power tool. This may result in an undesirable reduction in the service life of the power tool. 
     SUMMARY 
     An object of the present invention is to provide a new hand-held power tool having a low-friction and cost-effective no-load design. 
     This objective may be achieved by providing an example hand-held power tool having a housing and a tool holder which is disposed on a drive shaft that is rotationally mounted in at least one first and one second ball bearing. The first ball bearing has a first inner ring and the second ball bearing has a second inner ring. A spring element is disposed between the first inner ring and the second inner ring in order to prestress the first ball bearing with respect to the second ball bearing. 
     Thus, the present invention makes it possible to provide a hand-held power tool in which the use of felt rings may be omitted by using an inexpensive spring element; in doing so, comparatively great running quietness being achieved during operation of the power tool. 
     According to one specific embodiment, the spring element is fixed in position on the first and second inner rings, in order to permit the spring element to rotate with the inner rings during rotation of the drive shaft. 
     Therefore, a low-friction and wear-free utilization, and thus a comparatively long service life of the spring element may be achieved. 
     The first ball bearing is preferably supported axially and radially immovably in the housing, and is disposed on the drive shaft in a sliding fit. The first ball bearing preferably has an outer ring, which is supported in a press fit in a clamping ring secured in the housing. 
     Thus, a stable and reliable mounting of the first ball bearing in the housing may be achieved in an easy manner. 
     The second ball bearing is preferably disposed axially immovably on the drive shaft, and is supported axially displaceably in the housing. The second ball bearing preferably has an outer ring, which is supported in a sliding fit in a ring-like element secured axially and radially immovably in the housing. 
     Thus, a stable and reliable mounting of the second ball bearing in the housing may be achieved in an easy manner. 
     According to one specific embodiment, the drive shaft is able to be propelled via a gear unit, the first ball bearing being disposed in the housing so that it is at least sectionally in the area of an end face of the gear unit facing an end face of the housing. The second ball bearing is preferably disposed in the housing so that it is at least sectionally in the area of an end face of the housing facing the tool holder. 
     The present invention therefore permits a simple and compact design of the power tool. 
     Preferably, a supporting element is provided for the axial support of the second ball bearing, in order to make it possible to limit an axial shift of the second ball bearing in the direction of the tool holder. 
     Thus, safe and reliable operation of the electric tool may be ensured in an easy manner. 
     According to one specific embodiment, a notched mechanism for impact generation for the drive shaft is formed between the second bearing and the tool holder. 
     Thus, the present invention permits a simple and compact design of the power tool, even when using an assigned notched mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is explained in greater detail below on the basis of exemplary embodiments shown in the figures. 
         FIG. 1  shows a schematic view of a hand-held power tool according to a first specific embodiment. 
         FIG. 2  shows an enlarged sectional view of a cut-away portion of the power tool from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIG. 1  shows a hand-held power tool  100 , which has a housing  110  having a grip  115 . According to one specific embodiment, power tool  100  is connectable mechanically and electrically to a battery pack  190  for cordless power supply. By way of example, power tool  100  in  FIG. 1  is in the form of a cordless drill/driver. However, it is stressed that the present invention is not limited to cordless drill/drivers, but rather may be used in various, especially battery-operated power tools in which a tool is set in rotation, e.g., in the case of a cordless screwdriver, a cordless impact drill, etc. 
     Disposed in housing  110  are an electric drive motor  180 , supplied with current by battery pack  190 , and a gear unit  170 . Illustratively, drive motor  180  is operable, that is, is able to be switched on and off, via a manual switch  195 , and may be any type of motor, e.g., an electronically commutated motor or a direct-current motor. Preferably, drive motor  180  is electronically controllable or regulable in such a way that both a reverse operation as well as setpoint selections with respect to a desired rotational speed are able to be realized. The functioning method and the design of a suitable drive motor are well known, so that a detailed description is dispensed with here in order to keep the specification concise. 
     Drive motor  180  is connected via gear unit  170  to a drive shaft  120 . It is rotationally mounted in housing  110  by way of a bearing configuration  130 , and is provided with a tool holder  140  situated in the area of an end face  112  of housing  110 . Bearing configuration  130  may be attached to housing  110 , e.g., via assigned fastening elements, or may be disposed in an assigned intermediate element, e.g., a separate gear housing in which gear unit  170  is situated, or a separate motor housing in which motor  180  and gear unit  170  are disposed, the gear housing and the motor housing, respectively, being located in housing  110 . Tool holder  140  is used to receive a tool  150  and may be an integral part of drive shaft  120  or be joined to it in the form of an attachment. By way of example, in  FIG. 1 , tool holder  140  is attachment-like, and is secured to drive shaft  120  via a fastening device  122  provided on drive shaft  120 . 
     According to one specific embodiment, bearing configuration  130  has a first bearing  134  and a second bearing  132  set apart from it. For example, first bearing  134  is situated at least sectionally in the area of end face  112  of housing  110 , and hereinafter, is therefore also denoted as “tool-holder-side bearing.” Second bearing  132 , for example, is situated at least sectionally in the area of an end face  172  of gear unit  170  facing end face  112  of housing  110 , and is therefore also denoted hereinafter as “gear-unit-side bearing.” 
     According to one specific embodiment, a notched mechanism  160  is disposed between tool-holder-side bearing  134  and tool holder  140 . During operation of power tool  100 , this permits the realization of an impact operation, during which a percussive movement of drive shaft  120  is generated. Notched mechanism  160  is described in detail below with reference to a sectional view of a cut-away portion  200  shown enlarged in  FIG. 2 . 
       FIG. 2  shows cut-away portion  200  of hand-held power tool  100  from  FIG. 1  in normal operation, that is, in drilling operation or screwing operation without impact generation, or in no-load operation of power tool  100 . Cut-away portion  200  shows clearly an exemplary form of tool  150  and of tool holder  140 , of gear unit  170 , of bearing configuration  130  and of drive shaft  120 , as well as of notched mechanism  160  for the impact generation for drive shaft  120  during impact operation of power tool  100 . 
     By way of example, tool holder  140  has a drill chuck  240  which is attached to fastening device  122  of drive shaft  120 . For example, fastening device  122  is formed as an external thread, which is engaged with an internal thread  222  provided on drill chuck  240 . Moreover, drill chuck  240  has a predefined number of clamping members  242 ,  244 , e.g., three or four, for clamping tool  150 , as well as a clamping sleeve  246  which generally sheaths drill chuck  240 . Tool  150  is turned by a rotation of drive shaft  120  during operation of power tool  100 . 
     According to one specific embodiment, gear unit  170  is a planetary gear, formed with various gear steps or planetary steps, which is rotationally driven by drive motor  180  during operation of power tool  100 . For instance, planetary gear  170  has an internal ring gear  206 , at least one planet gear  205  as well as a driver  204 , and transmits the torque of drive motor  180  via the planetary steps with the aid of a rotary driving contour of driver  204 , to drive shaft  120 . 
     As evident from  FIG. 2 , bearings  132 ,  134  of bearing configuration  130  provided for the mounting of drive shaft  120  are preferably in the form of ball bearings. For example, drive shaft  120  is formed as a drive spindle having a support flange  255 , so that in the present exemplary embodiment, bearings  132 ,  134  are used as spindle bearings. However, it is stressed that other types of bearing are also usable within the scope of the present invention. For instance, alternatively, bearings  132 ,  134  may be implemented as friction bearings, drawn cup needle roller bearing with open ends, roller bearings or other types of rolling-contact bearings. 
     For example, gear-unit-side bearing  132  has an outer ring  291 , as well as an inner ring  292 , and is disposed axially and radially immovably in housing  110 . Illustratively, outer ring  291  is joined by a press fit to a clamping ring  232  secured in housing  110 . According to one specific embodiment, inner ring  292  is disposed in a sliding fit on drive spindle  120 , so that spindle  120  is axially displaceable relative to bearing  132 . By way of example, tool-holder-side bearing  134  has an outer ring  293 , as well as an inner ring  294 , and is disposed on drive spindle  120  in axially immovable fashion, e.g., in a press fit, via inner ring  294 . As an alternative, bearing  134 , i.e., its inner ring  294 , may be integrally molded on drive spindle  120 , and thus formed in one piece with it. Outer ring  293  is disposed in a sliding fit in a ring-like element  266 , which is formed according to a type of retention sleeve and is secured axially and radially immovably in housing  110 , that is, in the area of its end face  112 . Therefore, bearing  134  is supported radially immovably in retention sleeve  266 , but axially displaceably relative to it, and thus is supported in a sliding fit in housing  110 . 
     According to one specific embodiment, bearing  134  is acted upon in the direction of drill chuck  240  by a spring element  250 , e.g., a compression spring, situated between bearing  134  and gear-unit-side bearing  132 . Thus, bearings  132 ,  134  are prestressed with respect to each other. Spring element  250  preferably abuts with its axial end areas against inner rings  292 ,  294  of bearings  132  and  134 , respectively, and is therefore fixed in position on them in such a way that, during operation of power tool  100 , spring element  250  rotates with the same speed as drive spindle  120  and inner rings  292 ,  294 . Moreover, spring element  250  may also be secured to inner rings  292 ,  294 . 
     Illustratively, notched mechanism  160  is situated between tool-holder-side bearing  134  and drill chuck  240  and, for example, has at least one first notched disk  164  secured to drive spindle  120  and at least one second notched disk  162  secured to housing  110 . During impact operation of power tool  100  for the purpose of impact generation for drive shaft  120 , notched disks  162 ,  164  are in operative engagement with each other via a front-side toothing  263  provided on notched disk  162  and a front-side toothing  265  provided on notched disk  164 . During normal operation or no-load operation, toothings  263 ,  265  are set apart or separated from each other. 
     First notched disk  164  is secured axially and radially immovably on drive spindle  120 , e.g., in a press fit, and illustratively, is supported on support flange  255 . Alternatively, notched disk  164  may be integrally molded on drive spindle  120 , and thus formed in one piece with it. According to one specific embodiment, first notched disk  164  is facing drill chuck  240 , and is therefore also denoted hereinafter as “drill-chuck-side notched disk.” Preferably, it is situated, at least sectionally, radially within clamping members  242 ,  244  and/or clamping sleeve  246 . 
     Second notched disk  162  is joined to ring-like element  266 ; notched disk  162  may be secured to or integrally molded on ring-like element  266 , or formed in one piece with it. Therefore, hereinafter, second notched disk  162  is also denoted as “gear-unit-side notched disk.” Just like drill-chuck-side notched disk  164 , it is preferably disposed outside of housing  110 . For instance, end face  112  of housing  110  is formed by a plate-like fixation member  212 , that is used to fix ring-like element  266  in position in or on housing  110 . Illustratively, fixation member  212  is joined, e.g., screw-fitted, via a screw-like fastening element  299  to clamping ring  232  provided in housing  110 , so that fixation member  212  and clamping ring  232  are fixed in position on housing  110  by element  299 . 
     According to one specific embodiment, as described above, tool-holder-side bearing  134  is supported axially displaceably, but radially immovably in ring-like element  266 , or in gear-unit-side notched disk  162 . In order to limit an axial shift of bearing  134  in the direction of drill chuck  240 , gear-unit-side notched disk  162  has a supporting element  262  for the axial support of bearing  134 . It may likewise be formed from gear-unit-side notched disk  162 , that is, be an integral component of it, or, as illustrated in  FIG. 2 , may also be integrally molded on retention sleeve  266 . 
     In the direction of gear unit  170 , an axial shift of bearing  134  may be blocked by a blocking member  270 . Preferably, it is joined to an adjusting device, not shown for the purpose of clarity and simplicity of the illustration, with which, in particular, the normal operation or the impact operation of power tool  100  is selectively adjustable. 
     In order to seal off notched mechanism  160 , a sealing element  260  is provided to protect it against grease loss, dirt and dust, and thus to prevent its functionality from being impaired. For instance, sealing element  260  may be in the form of a bellows, so that its air balance is not influenced in response to an axial shift of drill-chuck-side notched disk  164 . In the same way, an O-ring, a radial shaft seal ring or a groove seal, that is, a seal formed by an air gap with axial extension, provided between notched disks  162 ,  164  may be used, so that a venting between drive spindle  120  and gear-unit-side notched disk  162 , or between tool-holder-side bearing  134  and gear-unit-side notched disk  162  is made possible. 
     During normal operation, or during no-load of the impact operation of power tool  100 , tool-holder-side bearing  134 , and thus drive spindle  120 , is pressed or pushed by compression spring  250  in the axial direction toward tool holder  140 . In this context, according to one specific embodiment, during normal operation, bearing  134  is pressed against supporting element  262  and blocked by blocking member  270 . Therefore, drive spindle  120  cannot be shifted in the direction of planetary gear  170 , so that notched disks  162 ,  164  are set apart from each other by a predefined distance  214 , and their front-side toothings  263 ,  265  can thus not be brought into operative engagement. 
     During impact operation of power tool  100 , tool-holder-side bearing  134  is released axially by the release of blocking member  270 , thus permitting an axial shift of drive spindle  120 . In this context, by way of a pressure force exerted by a user on power tool  100 , i.e., its housing  110 , an axial shift of housing  110  relative to tool holder  140  against the force of spring element  250  may now be achieved to the extent that front-side toothings  263 ,  265  of notched disks  162  and  164 , respectively, engage, and due to this operative engagement, impact generation is made possible for drive spindle  120 . Impact generation of this kind is known sufficiently from the related art, so that in order to keep the specification concise, a detailed description is dispensed with here. 
     Since, as described above, spring element  250  acts upon tool-holder-side bearing  134  in the direction of drill chuck  240 , this makes it possible to switch power tool  100  over to normal operation, or to operate in no-load of the impact operation. In order to switch over to normal operation, as described above, tool-holder-side bearing  134  is locked by blocking member  270  in an axial position assigned to the normal operation.