Patent Publication Number: US-2022213953-A1

Title: Composite gearwheel for an electropneumatic hammer drill

Description:
The present invention relates to a composite gearwheel for an electropneumatic hammer drill, wherein the composite gearwheel has a basic body, consisting of a first material, and an encircling toothing. 
     BACKGROUND 
     Composite gearwheels of the type mentioned at the beginning are known in principle from the prior art. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a composite gearwheel, in particular for use in a transmission unit of an electropneumatic hammer drill, said gearwheel having comparatively high stability while having a comparatively low weight. 
     The present invention provides that the encircling toothing is formed, along a first circular arc, by a toothed body of the composite gearwheel, and is formed, along the remaining second circular arc, by the basic body itself, wherein the toothed body consists of a second material that is different than the first material. 
     The invention incorporates the finding that gearwheels—in particular when they are used in a transmission unit, cooperating with an impact mechanism, of an electropneumatic hammer drill—are exposed to a torque dependent on crank angle. This torque arises periodically and can vary by up to one order of magnitude around a circumference of 360 degrees. Since the encircling toothing of the composite gearwheel according to the invention is formed, along the first circular arc, by a toothed body that consists preferably of steel, a highly loadable but also comparatively heavy reinforcement of the encircling toothing can be restricted to a minimum. As a result, the composite gearwheel according to the invention then has comparatively high stability while having a comparatively low weight. Preferably, the encircling toothing is formed, along a first circular arc, exclusively by the toothed body of the composite gearwheel. 
     It has been found to be advantageous for the first circular arc to have a center angle of less than 90 degrees, preferably less than 45 degrees. 
     In a particularly preferred configuration, the basic body has a slot into which the toothed body has been at least partially introduced. In particular, the toothed body is held—both in the circumferential direction and in a radial direction—in a form-fitting manner in the basic body. The toothed body can be held in the basic body in a radial direction by a force fit, for example by being pressed in. Preferably, exactly one toothed body, which has a plurality of teeth of the encircling toothing, is provided. 
     In a particularly preferred configuration, the composite gearwheel has a balancing weight in order to compensate for an imbalance caused by the toothed body. Preferably, the balancing weight is provided as a separate weight, which is arranged on an opposite side of the composite gearwheel from the toothed body. Alternatively or in addition, the balancing weight can be formed in one piece with the basic body, for example by a material thickening. 
     It has been found to be advantageous for the first material to be a plastic, for example a thermoplastic or a thermosetting plastic. The second material is preferably metal, in particular a hardened metal. Particularly preferably, the second material is a steel material. Preferably, the composite gearwheel weighs less than 150 grams. 
     In a further preferred configuration, the composite gearwheel has a central hub, which is provided preferably to define a timing of the composite gearwheel. The central hub may be in the form of an insert and preferably has an internal toothing with eight teeth. The insert can be held in the basic body in a form-fitting, force-fitting or materially bonded manner. The hub in the form of an insert consists preferably of metal, in particular of a hardened metal, preferably steel. 
     According to the invention, an electropneumatic hammer drill is likewise provided, wherein the composite hammer has a composite gearwheel of the above-described type, wherein the composite gearwheel has been installed in a transmission unit of the hammer drill in such a way that only that part of the encircling toothing that is formed by the toothed body is exposed to an increased torque of an impact mechanism of the hammer drill. The electropneumatic hammer drill can be developed advantageously by the features described with reference to the composite gearwheel. 
     Further advantages will become apparent from the following description of the figures. Various exemplary embodiments of the present invention are illustrated in the figures. The figures, the description and the claims contain numerous features in combination. A person skilled in the art will expediently also consider the features individually and combine them to form useful further combinations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the figures, identical and similar components are denoted by the same reference signs. In the figures: 
         FIGS. 1  A,  1  B and  1  C show a first preferred exemplary embodiment of a composite gearwheel according to the invention; 
         FIG. 2  A shows an electropneumatic hammer drill having the composite gearwheel in  FIG. 1 ; and 
         FIG. 2  B shows the torque in the transmission unit plotted versus the crank angle KW. 
     
    
    
     DETAILED DESCRIPTION 
     A preferred exemplary embodiment of a composite gearwheel  10  according to the invention is illustrated in  FIGS. 1  A,  1  B and  1  C. The composite gearwheel  10  can be used in a transmission unit  30  of an electropneumatic hammer drill  100  (cf.  FIG. 2 ). 
     The composite gearwheel  10  has a basic body  1  consisting of a first material M 1 , in the present case for example a thermoplastic, and an encircling toothing  3 . The encircling toothing  3  is formed, along a first circular arc K 1 , only by a toothed body  5  of the composite gearwheel  10 . Exactly one toothed body  5  is provided, which has a plurality of teeth  3 ′ of the encircling toothing  3 . The second toothed body  5  is formed from a second material M 2 , which is different than the first material M 1 . In the presented here, the second material M 2  is a steel material. 
     As can be gathered from  FIG. 1  A, the encircling toothing  3  is formed, along the remaining second circular arc K 2 , by the basic body  1  itself. The first circular arc K 1  and the second circular arc K 2  are each in relation to an axis of rotation D of the composite gearwheel  10  and add together to form a full circle. 
     In the exemplary embodiment illustrated in  FIG. 1  A, the first circular arc K 1  has a center angle ZW of less than 45 degrees, in this case for example about 40 degrees. This corresponds to a sector with comparatively high torque loading (cf.  FIG. 2  B). 
     The composite gearwheel  10  in  FIG. 1  A also has a central hub  2  for defining a timing of the composite gearwheel  10 . 
       FIG. 1  B shows the composite gearwheel  10  from  FIG. 1  A in an exploded illustration. It is readily apparent that the toothed body  5  is in the form of a separate component, different than the basic body  1 . In order to hold the toothed body  5  in the basic body  1 , the basic body  1  has a slot  7 , into which the toothed body  5  has been at least partially introduced ( FIG. 1A  shows the toothed body  5  introduced into the slot  7 ). As can be gathered from  FIG. 1  B, the toothed body  5  has a cutout  6 . This serves for one part for saving weight. For the other part, the toothed body  5  can be fastened in a radial direction R via this cutout  6  and a corresponding cutout  6 ′, which is formed in the basic body  1 . This can take place for example by plugging in a pin, which is not illustrated here, or by joint casting of the cutouts  6 ,  6 ′. 
     As can be gathered from  FIG. 1  B, the composite gearwheel  10  has a balancing weight  9 , in order to compensate for an imbalance caused by the toothed body  5 . The balancing weight  9  is in the form of a separate body, in the present case made of steel, which is located entirely within the basic body  1  with the composite gearwheel  10  assembled (cf.  FIG. 1  A). For example, the balancing weight  9  can be held in the basic body  1  in a radial direction R by means of a pin, which is not illustrated here and is intended to be introduced through a pin hole  9 ′ formed in the basic body  1 . 
     As already mentioned, the composite gearwheel  10  has a central hub  2  for defining a timing of the composite gearwheel  10 . In the present case, the central hub  2  is in the form of an insert, which is held in the basic body in a form-fitting manner (by means of the external teeth  8 ). 
       FIG. 1  C shows, finally, a central hub  2  in detail. The hub  2  has for example an internal toothing  4  with eight teeth  4 ′, which are distributed uniformly along an inner circumference IU of the hub. The teeth  4 ′ are arranged at a spacing of 45 degrees, this corresponding approximately to the center angle ZW of the first circular arc K 1  of the toothed body  5 . As a result, the gearwheel can be installed in a transmission unit  30  of the hammer drill  100  in such a way that only that part of the encircling toothing  3  that is formed by the toothed body  5  is exposed to an increased torque of an impact mechanism  20  of the hammer drill  100 . 
       FIG. 2  A now shows such an electropneumatic hammer drill  100 . The latter has a preferably brushless electric motor  40 , which is operatively connected to an impact mechanism  20  via a transmission unit  30 . For its part, the impact mechanism has a piston  21 , which acts on a pneumatic spring  23 . The transmission unit  30  has the composite gearwheel  10 , which is driven about the axis of rotation D. In  FIG. 2  B, the torque in the transmission unit  30  (to be more precise at the measurement point  35 ) is plotted versus the crank angle KW. The crank angle KW is defined about the axis of rotation D. It is readily apparent that the torque M is comparatively low (Mmin) in the range from 0 degrees to 180 degrees and a peak torque (Mmax) arises in the range between 280 degrees and 320 degrees. This is absorbed by the toothed body  5  having an exemplary center angle ZW of 40 degrees. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Basic body 
           2  Hub insert 
           3  Encircling toothing 
           4  Internal toothing 
           4 ′ Tooth 
           5  Toothed body 
           6 ,  6 ′ Cutout 
           7  Slot 
           8  External tooth 
           9  Balancing weight 
           9 ′ Pin hole 
           10  Composite gearwheel 
           20  Impact mechanism 
           21  Piston 
           23  Pneumatic spring 
           30  Transmission unit 
           35  Measurement point 
           40  Electric motor 
           100  Hammer drill 
         D Axis of rotation 
         K 1  First circular arc 
         K 2  Second circular arc 
         KW Crank angle 
         M Torque 
         M 1  First material 
         M 2  Second material 
         R Radial direction 
         IU Inner circumference 
         ZW Center angle