Abstract:
A power tool includes a drive motor and at least one auxiliary device, which is coupled to the drive motor, for activating at least two different operating states. The drive motor and the at least one auxiliary device are controllable using at least one operating device. The output of the drive motor is changed when the at least one auxiliary device is activated. As a result, the operating forces are reduced when switching between operating states, and the load on components is reduced.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
       [0001]    The invention described and claimed hereinbelow is also described in German Patent Application DE 10 2009 001 132.3 filed on Feb. 25, 2009. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to power tools. 
         [0003]    Publication U.S. Pat. No. 6,800,045 B1 makes known a power tool, in the form of a drill, the gearbox of which is coupled to the drive motor and is connected to an auxiliary gear device. The auxiliary gear device automatically lowers the gear ratio during operation in accordance with the resistance to rotation presented. This means, for instance, that the rotational speed of the gearbox is reduced during drilling operation if the hardness of the material to be drilled increases. This is made possible via the known auxiliary gear device without the need to stop the drive. 
         [0004]    Furthermore, it is made known in JP 7308813A to provide a shifting device on a column drill, the shifting device making it possible to change gears rapidly during operation. Further details, in particular those regarding the control of rotational speed during gear shifting, are not provided in the document. 
         [0005]    From U.S. Pat. No. 6,978,846 it is known, with regard for a torque-controlled impact driver, to adapt the rotational speed of the drive to the torque required to drive a screw, and to the screw-driving status. In the case of the known impact driver, it is not possible to shift gears while driving a screw. 
         [0006]    From U.S. Pat. No. 5,754,019 it is known to control the electric motor of a power tool such that it is automatically switched to another operating state once a limiting torque is reached. In this other operating state, the tool switches to indexed operation, e.g., when a screw is being driven, and the screw is driven completely into place. The motor speeds and/or time intervals of motor operation that occur during the other operating state may be adapted as needed. 
         [0007]    From U.S. Pat. No. 6,398,678 B1 it is known to change the rotational speed of the drive motor of a power tool without having to stop the drive motor. This is realized via manual input to a wheel that changes the position of a transmission belt located between bevel gears. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is based on the object of developing a power tool in a manner such that the switch from a first operating state to a second operating state, e.g., by switching gears or changing the operating mode, is carried out on an as-needed basis and in a manner that is gentle on the components of the power tool. 
         [0009]    This is attained in the present invention by changing the output of the drive motor during activation of the at least one auxiliary device. As a result, it is possible to reduce, in particular, the output of the drive motor in order to go easy on, e.g., the gears of a gear box while switching between two gears. In this manner it is also possible to ensure that, when an operator changes an operating state, this does not result in damage occurring to components, even in a parameter range that has not been adapted, and that the operating forces required to switch to the new operating state are reduced. In all, a power tool according to the present invention therefore has a robust design, non-critical handling, and a long component service life. 
         [0010]    All combinations of at least two features disclosed in the description, the claims, and/or the figures are included in the scope of the present invention. 
         [0011]    Particularly advantageously, the present invention may be used in a power tool that is designed as an electrical screwdriver, an electrical drill/driver, an electrical impact driver, a drill, an impact drill, or a rotary hammer, and that includes a multistage gearbox and/or a plurality of operating modes (e.g., drilling/impact drilling) since this results in a reduction of operating forces and minimal damage to the gearbox components. Preferably, the power tool may also include an axial drive device, in particular an impact drilling device. 
         [0012]    It is also possible to provide a common operating element for the drive motor and the auxiliary device in order to simplify operation and enable automatic switching between operating modes. 
         [0013]    By reducing the output of the drive motor, it is possible to reduce the load on the components during operation of the power tool, and to reduce the operating forces that occur when switching between the operating states. 
         [0014]    However, it is also possible to reduce the load on the components and to switch easily between operating states when the output of the drive motor is temporarily increased. This is the case, e.g., when the aim is to switch between two gears of a gearbox while the operator does not foresee operating the power tool otherwise. Blockage and/or increased wear on gearbox components is prevented as a result. 
         [0015]    The power tool according to the present invention may be designed, particularly advantageously, as an electrical screwdriver, and electrical drill/driver, an electrical impact driver, a drill, an impact drill, or a rotary hammer. 
         [0016]    The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a cordless drill, in a simplified depiction in accordance with the present invention, 
           [0018]      FIG. 2  shows the graph of current I of the drive motor of the cordless drill according to  FIG. 1 , plotted against actuation path S of a switch lever in accordance with the present invention, 
           [0019]      FIG. 3  shows a modified cordless drill, in a simplified depiction in accordance with the present invention, and 
           [0020]      FIG. 4  shows the graph of current I of the drive motor of the cordless drill according to  FIG. 3 , in various operating modes in accordance with the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]      FIG. 1  shows a cordless drill  10  which includes a housing  11 . A rechargeable battery pack  13 , which is used as the energy source for the drive (motor) and electronics of cordless drill  10 , is also shown on the lower end of handle  12 . Furthermore, a switch lever  15 , which may be moved by an operator in the direction of arrow  16 , is supported on handle  12 . A movement of switch lever  15  in the direction of arrow  16  will also be referred to below as displacement path S of switch lever  15 . 
         [0022]    Cordless drill  10  includes, in its interior, a drive motor  20  which is coupled to a drill chuck  18  or a spindle via a gearbox  19 . Drive motor  20  is connected via lines  21 ,  22  to an output control switch  23  which is connected via a line  24  to switch lever  15 , and is controlled by the same. 
         [0023]    Switch lever  15  is also connected via a connection  25  to an automatic shifting device  26  designed as an auxiliary device. Shifting device  26  may switch, e.g., the gear reduction of gearbox  19  coupled to drive motor  20  between two stages, namely a first stage having a high reduction (=low rotational speed of drill chuck  18 ), and a second gear having a low reduction (=high rotational speed of drill chuck  18 ). Shifting device  26  is notified via connection  25  to switch gears when displacement path S has reached a certain value. 
         [0024]    The operation of cordless drill  10  according to the present invention is explained in greater detail below with reference to  FIG. 2 . It is shown that, between actuation path S 0  and S 1 , current I does not yet flow through drive motor  20 . The path between S 0  and S 1  corresponds to the position of switch lever  15  in which the operator has placed his finger on switch lever  15  but does not yet want to drill. As a result, drive motor  20  is prevented from being accidentally started up via a slight movement of the operator&#39;s finger. 
         [0025]    If switch lever  15  is pressed further, a current I, which increases along displacement path S, flows through drive motor  20 , between positions S 1  and S 2 . This is equivalent to an increasing speed of drive motor  20  or drill chuck  18 , while gearbox  19  remains in its second gear (=low reduction). Current I max  associated with position S 2  corresponds to the limit value of current I through drive motor  20 , which is limited in terms of the (long-term) loadability of drive motor  20  in particular. 
         [0026]    If switch lever  15  is moved further, past S 2 , in the direction toward S 3 , shifting device  26  should shift to first gear, with increased reduction, in order to increase the torque. Therefore, as soon as position S 3  on switch lever  15  has been reached, shifting device  26  is actuated via connection  25 . At the same time, according to the present invention, current I through drive motor  20  is reduced between positions S 3  and S 4  while the gear is shifted. As a result, the torque present at the drive train of drive motor  20 , i.e., the torque present in shifting device  26 , in particular, is also reduced. As a result, the shifting procedure itself may be implemented by shifting device  26  using less torque. These reduced torques also make it possible to switchover or to shift gears when drive motor  20  should be blocked. 
         [0027]    In addition, when actuation path S is traversed in the opposite direction, between S 4  and S 3 , it is assumed that less torque is required, and so shifting takes place in drive motor  20  using less current I. Shifting device  26  shifts from the gear having a high reduction to the gear having low reduction. 
         [0028]    Modified cordless drill  10   a  shown in  FIG. 3  includes a manually actuatable gear-change switch  30  which is coupled to shifting device  26   a . In cordless drill  10   a , in contrast to cordless drill  10 , switch lever  15   a  is therefore coupled only to drive motor  20   a,    
         [0029]    Two different operating modes of cordless drill  10   a  are described in greater detail below with reference to  FIG. 4 . Curve A represents the case in which the operator initially increases the rotational speed continually (with the second gear engaged, with low reduction) between positions S 10  and S 11 , thereby resulting in a correspondingly continually increasing current I through drive motor  20   a . Maximum current I max  flows through drive motor  20   a  between positions S 11  and S 12 . To increase the torque present at the gearbox of cordless drill  10   a , it is necessary to switch to the first gear which has a higher reduction than the second gear. This is carried out manually by the operator via actuation of gear-change switch  30 . This should take place in position S 12 , although it is pointed out that this could also take place in another position of switch lever  15   a . As a result of the actuation of gear-change switch  30  in position S 12 , current I through drive motor  20   a  is temporarily reduced, and so shifting device  26   a  shifts gears in a manner analogous to cordless drill  10 , with less torque present in the drive train. Shifting has been complete in position S 13 . 
         [0030]    The second operating mode, represented by curve B, depicts the case in which the operator wants to shift gears, e.g., from second gear to first gear, without cordless drill  10   a  being operational and/or without drilling. Drive motor  20   a  is therefore (initially) at a standstill.  FIG. 4  therefore shows the graph of current I through drive motor  20   a  during gear-shifting event E. It should be mentioned that, if the gear is shifted while drive motor  20   a  is at a standstill, the driving toothing may come to rest on its end face between a shifting internal gear and its counterpart. This results in blockage occurring in shifting device  26   a . This is prevented, according to the present invention, in that, when the operator wants to shift gears by actuating gear-change switch  30  without also actuating switch lever  15   a , drive motor  20   a  is operated during the gear change at a low rotational speed, e.g., 10 revolutions per minute, as indicated in  FIG. 4  by the portion of the graph between points P 1  and P 2 , and so a small amount of current I temporarily flows through drive motor  20   a . This prevents gears or gearbox components in the gearbox of cordless drill  10   a  from becoming jammed. 
         [0031]    It is also mentioned that the present invention may also be used, of course, in power tools other than cordless drills  10 ,  10   a  described herein. Furthermore, the application is not limited to gear shifting as described herein. The current and/or output through a drive motor may also be reduced in an analogous manner, e.g., when changing an operating mode (e.g., from drilling to impact drilling). In addition, a plurality of functions (gear shifting, operating modes) may be realized on the same power tool, in which case every one of the functions may influence the current flow or power consumption of the drive motor of the power tool. 
         [0032]    It is furthermore mentioned that the output may be changed not only by changing the current profile, but also, e.g., by modifying a pulse width modulation or the like. 
         [0033]    It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
         [0034]    While the invention has been illustrated and described as embodied in a power tool, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
         [0035]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. 
         [0036]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.