Abstract:
A power tool having a housing, a motor, especially an electric motor, a drive shaft that can be driven by the motor, a belt drive for transmitting the driving force of the motor to a tool, and a first fan that serves to generate a first air path in the housing as well as to cool at least the motor. The first fan and the belt drive can be driven by the drive shaft. The power tool has a second fan that serves to generate a second air path in the housing as well as to cool at least the belt drive.

Description:
[0001]    The invention relates to a power tool that has a housing, a motor, especially an electric motor, a drive shaft that can be driven by the motor, a belt drive for transmitting the driving force of the motor to a tool, and a first fan that serves to generate a first air path in the housing as well as to cool at least the motor. The first fan and the belt drive can be driven by means of the drive shaft. 
       BACKGROUND 
       [0002]    With some power tools such as, for instance, core drills, the power take-off of the motor is effectuated by a belt drive. Here, a belt (timing belt) is connected to the drive shaft via a gear wheel or belt pulley and the drive shaft, in turn, is driven by the motor. Elevated temperatures can arise at the contact site between the belt pulley and the belt. Damage can occur to the belt drive due to these elevated temperatures and this can also result in a complete failure of the belt drive. This is why there is normally some kind of cooling measure to appropriately cool the belt drive. Prior-art cooling measures for power tools with belt drives usually entail active cooling with an air path. This air path is generated by means of a fan (blower). Here, the fan is often positioned in the power tool in such a way that, in addition to the belt drive, the motor as well as the electronics are appropriately cooled. The air flow (air path) generated by the fan to cool the motor, the electronics and the belt drive is often first directed at the motor so as to achieve a maximum cooling of the motor while the air flow that is still relatively cool. Subsequently, the air flow is directed at the electronics for cooling purposes. In this process, the air flow is additionally warmed up. Lastly, the air flow reaches the belt drive in order to cool it. Since the air flow generated by the fan is first directed at the motor and at the electronics in order to cool them, and only directed at the belt drive after that, the temperature of the air flow will already have risen markedly as a result its having cooled the motor and the electronics, so that the belt drive can no longer be optimally cooled. If the belt drive is not optimally cooled, the temperature of the belt drive, especially at the contact site between the belt pulley and the belt, can rise to such an extent that there is a risk of damage to and/or complete failure of the belt drive and of the entire power tool. 
       SUMMARY OF THE INVENTION 
       [0003]    It is an object of the present invention to provide a power tool entailing an improved cooling of the belt drive in order to reduce the susceptibility to wear and failure on the part of the belt drive or of the power tool. 
         [0004]    The present invention provides a power tool that has a housing, a motor, especially an electric motor, a drive shaft that can be driven by the motor, a belt drive for transmitting the driving force of the motor to a tool, and a first fan that serves to generate a first air path in the housing as well as to cool at least the motor, whereby the first fan and the belt drive can be driven by means of the drive shaft. 
         [0005]    According to the present invention, the power tool has a second fan that serves to generate a second air path in the housing as well as to cool at least the belt drive. In this manner, an additional air path or air flow is made available exclusively for cooling the belt drive. As a result, the cooling of the belt drive is greatly improved and a heat-induced failure of the belt drive is appropriately countered. 
         [0006]    According to another embodiment of the present invention, it can be provided that the second fan can be driven by means of the drive shaft. In this manner, it is possible to dispense with an additional drive for the second fan, and the driving force of the drive shaft can be utilized very efficiently to drive the second fan. Moreover, the installation space of the housing can be used efficiently owing to the serial arrangement of the two fans relative to each other. 
         [0007]    In order to prevent dirt particles from being drawn into the interior of the housing of the power tool along with the air that is drawn in from the surroundings to cool the fans, it is advantageous for the first air path to have an intake opening on the outside of the housing and for the second air path to have an intake opening on the outside of the housing, and whereby the first and second intake openings are positioned on a side of the housing facing away from the tool. There are fewer dirt particles in the ambient air on the side of the housing facing away from the tool, since, on this side of the housing, fewer dirt particles are created during the operation of the tool that then get into the ambient air. 
         [0008]    According to another advantageous embodiment of the present invention, it can be provided that the second fan is positioned with respect to the belt drive in such a way that the belt drive that is to be cooled is at least partially situated in an excess-pressure area generated by the second fan. Owing to the excess pressure, the ambient air that is near the tool and that has been contaminated by dirt particles is prevented from getting into the belt drive. 
         [0009]    In order to avoid that the first air path, which serves at least to cool the motor, might influence or even warm up the second air path, according to another advantageous embodiment, it can be provided that the first air path and the second air path are positioned at least partially separately from each other in the housing. 
         [0010]    According to another advantageous embodiment of the present invention, it can be possible for the second fan to be made at least partially of metal. In this manner, a better thermal connection of the fan to the drive shaft as well as to the belt drive can be ensured, as a result of which a faster heat dissipation from the belt drive to the second air path is possible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Additional advantages ensue from the description of the drawings below. The drawings show an embodiment of the present invention. The drawings, the description and the claims contain numerous features in combination. In a practical manner, the person skilled in the art will also consider the features individually and will combine them into additional practical configurations. 
           [0012]    The following is shown: 
           [0013]      FIG. 1  a perspective view of a part of the power tool according to the invention; 
           [0014]      FIG. 2  a bottom view of the housing of the power tool; 
           [0015]      FIG. 3  an internal view along the sectional line A-A in  FIG. 2  of the power tool with a belt drive; 
           [0016]      FIG. 4  an internal view along the sectional line A-A in  FIG. 2  of the power tool without a belt drive; 
           [0017]      FIG. 5  an internal view of the power tool without a belt drive and with a partially opened housing; and 
           [0018]      FIG. 6  a bottom view of the power tool without a belt drive and with a partially opened housing. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  shows a power tool  1  according to a first embodiment. The power tool  1  is a core drill with a belt drive  50 . 
         [0020]    The power tool  1  configured as a core drill comprises a housing  10 , an electric motor  20 , a drive shaft  22 , a first fan  30 , a second fan  40 , and a belt drive  50 . 
         [0021]    The housing  10  comprises a top  11 , a bottom  12 , a right-hand side  13 , a left-hand side (not shown here), a front end  14  and a rear end  15 .  FIG. 1  shows the bottom  12 , the front end  14  and the right-hand side  13  of the housing  10 .  FIG. 2  especially shows the bottom  12  of the housing  10 . A tool in the form of a core bit (not shown here) can be positioned on the front end  14 . There is a handle  16  on the rear end  15  that allows a user (not shown here) to hold or guide the core drill  1 . The right-hand side  13  shown in  FIG. 1  is essentially identical to the left-hand side (not shown here). 
         [0022]    As is shown in  FIG. 3 , the electric motor  20  is positioned in the housing  10  and transmits a torque generated in the electric motor  20  to the drive shaft  22 , which is rotatably joined to the electric motor  20 . 
         [0023]    The first fan  30  as well as the second fan  40  are configured in the form of an axial blower, whereby the first fan  30  and the second fan  40  are of different sizes and especially of different diameters. The first fan  30  has a first side  31  and a second side  32 . Moreover, the second fan  40  also has a first side  41  and a second side  42 . According to the first embodiment, the first fan  30  is larger than the second fan  40 . The first fan  30  and the second fan  40  are non-rotatably positioned on the drive shaft  22 , so that the drive shaft  22  can cause them to rotate. When the fans  30 ,  40  are rotating, they generate a negative air pressure on the respective first sides  31 ,  41  and an excess air pressure on the respective second sides  32 ,  42 . Due to the generated negative air pressure, air can be drawn in by the fans  30 ,  40 . Accordingly, air can be pushed away from the fans  30 ,  40  due to the generated excess air pressure. As will be described in detail below, the fans  30 ,  40  blow air through the air paths. 
         [0024]    The belt drive  50  comprises a first belt pulley  51 , a second belt pulley  52 , a third belt pulley (not shown here), a fourth belt pulley (not shown here), a first belt  53  and a second belt  54 . The first belt pulley  51  serves to transmit the torque from the drive shaft  22  to the first belt  53 . The second belt pulley  52  transmits the torque from the drive shaft  22  to the second belt  54 . The first belt  53  transmits the torque to the third belt pulley, and the second belt  54  transmits the torque to the fourth belt pulley. The third and fourth belt pulleys transmit the torque further to a tool (for example, a core bit), (not shown here), by means of which a material can be worked. 
         [0025]    A shown in  FIGS. 3 and 4 , the first fan  30 , the first belt pulley  51 , the second belt pulley  52  and the second fan  40  are positioned one after the other on the drive shaft  22  in such a way that the torque of the drive shaft  22  is transmitted to them. The first fan  30  and the second fan  40  are made to rotate synchronously by means of the drive shaft  22 . A bearing plate  60  is positioned between the first fan  30  and the second fan  40 . The bearing plate  60  is situated especially between the first fan  30  and the first belt pulley  51 . The bearing plate  60  serves as a partition in order to create an air-tight separation between the space in front of the bearing plate  60  and the space behind the bearing plate  60 . 
         [0026]    The housing  10  comprises a first air path  70  or air channel as well as a second air path  80  or air channel (see  FIG. 4 ). The first air path  70  has a first opening  71 , a second opening  72  and an elongated channel  73 . The first opening  71  and the second opening  72  are positioned on the outer surface of the housing  10  (see  FIGS. 1 and 2 ). According to the first embodiment, the first opening  71  and the second opening  72  are not separated from each other and they share the same inlet into the housing  10  (see  FIGS. 1 and 4 ). According to a second embodiment (not shown here), however, it can also be provided that the first opening  71  and the second opening  72  are separated from each other and do not share the same inlet into the housing  10 . Here, the first opening  71  and the second opening  72  each have their own inlet into the housing  10 . 
         [0027]    Once the first fan  30  has been made to rotate by means of the drive shaft  22 , air is drawn in from the surroundings and it enters the first air path  70  through the first opening  71 , which serves as the inlet. Therefore, the first opening  71  can be referred to as an intake opening. Via the elongated channel  73 , the air that has been drawn in by the fan  70  ultimately reaches the second opening  72 . The second opening  72  serves as the outlet through which the air can then exit the housing  10 . The first air path  70  is positioned in the housing  10  in such a way that the elongated channel  73  extends past the electric motor  20 . In this manner, the air in the first air path  70  is conveyed past the electric motor  20 . When the air is conveyed past the electric motor  20 , heat from the electric motor  20  is transferred to the air due to thermal convection so that the electric motor  20  is cooled. 
         [0028]    The second air path  80  likewise has a first opening  81 , a second opening  82  and an elongated channel  83 . The first opening  81  and the second opening  82  are also positioned on the outer surface of the housing  10 . The second opening  82  is situated here on the side of the housing  10  facing away from the tool (not shown here). Once the second fan  80  has likewise been made to rotate by means of the drive shaft  22 , air is drawn in from the surroundings and it enters the second air path  80  through the first opening  81 , which serves as the inlet. Therefore, the first opening  81  can be referred to as an intake opening. For this purpose, in the flow direction of the air upstream from the second fan  80 , there is a negative air pressure that draws in the air. The flow direction of the air is shown by the small arrows in  FIG. 4 . The second fan  80  is positioned in the vicinity of the second opening  82  so that the second fan  80  pushes the air out of the housing  10  through the second opening  82 . For this purpose, the air downstream from the second fan  80  has an excess pressure that pushes the air away. Here, the second fan  80  is positioned relative to the belt drive  50  and especially relative to the first and second belt pulleys  51 ,  52  in such a way that the air is blown onto the belt drive  50  or onto the first and second belt pulleys  51 ,  52 . In this way, first of all, the belt drive  50  is cooled and secondly, excess pressure is generated so that the second opening  82  only discharges air, and consequently, no air can enter the housing  10  through the second opening  82  and no air can reach the belt drive  50 . The fact that the second opening  82  only discharges air and no air enters the housing  10  through the second opening  82  means that no ambient air that has been contaminated by dirt particles can penetrate (through the second opening) into the housing  10  and get into the belt drive  50 .