Patent Publication Number: US-10786888-B2

Title: Twin hammer impact tool

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Taiwanese Patent Application No. 107117860, filed on May 25, 2018. 
     FIELD 
     The disclosure relates to an impact tool, and more particularly to a twin hammer impact tool. 
     BACKGROUND 
     A conventional single hammer impact tool has a single hammer and an output hammer. The single hammer is driven to reciprocally move along and rotate about an axial line for striking the output hammer engaging a workpiece. To produce a relatively large impact force, the conventional single hammer impact tool is generally designed to increase mass so as to improve rotational inertia. However, such a design can produce relatively large vibration, which reduces operational ability and comfortability during a hammering operation. 
     A conventional twin hammer impact tool, as disclosed in Chinese Patent Application No. 107175610 A, includes a primary hammer and a secondary hammer. The primary hammer is reciprocally movable along and rotatable about an axial line. The secondary hammer is rotatable together with the primary hammer while being immobilized along the axial line. Compared with the conventional single hammer impact tool, the conventional twin hammer impact tool is advantageous to enhance rotational inertia and to reduce vibration. However, the conventional twin hammer impact tool has to be provided with a plurality of needle rollers respectively inserted into roller channels formed between the primary and secondary hammers for transmitting driving movements. To retain the needle rollers, it is required to additionally provide an elastic retention ring. Furthermore, there are other disadvantages that can lead to an unsmooth operation and an increased vibration. For instance, the needle rollers can swing due to positional deviation; the accuracy of processing the needle channels can be insufficient; frictional forces between the needle rollers and needle channels can be overly high. 
     SUMMARY 
     Therefore, an object of the disclosure is to provide a twin hammer impact tool that can alleviate at least one of the drawbacks of the prior art. 
     According to the disclosure, a twin hammer impact tool includes a motor, a drive unit, a hammer unit and a housing unit. 
     The motor includes a motor shaft. 
     The drive unit is driven by the motor, and includes a gear set connected to the motor shaft. 
     The hammer unit is connected to the drive unit, and includes a hammer spindle, an inner ring hammer, an outer ring hammer, a plurality of rolling beads, and an output hammer. 
     The hammer spindle extends along and is rotatable about an axial line of the motor shaft. The hammer spindle has a driven end connected to the gear set, and an output end opposite to the driven end. 
     The inner ring hammer is sleeved on the hammer spindle. The inner ring hammer has a plurality of bead grooves each having a ball half-shape, and a plurality of angularly spaced-apart hammer projections disposed around the output end of the hammer spindle. The inner ring hammer is reciprocally movable relative to the hammer spindle along the axial line while rotating together with the hammer spindle. 
     The outer ring hammer is disposed around the inner ring hammer. The outer ring hammer has a plurality of guiding grooves disposed around and extending along the axial line. The bead grooves respectively face and open toward the guiding grooves. 
     Each of the rolling beads is received within one of the bead grooves and one of the guiding grooves. 
     The output hammer is connected to the output end of the hammer spindle, and has a main body extending along the axial line for engaging a workpiece, and a plurality of angularly spaced engagement projections protruding radially from the main body for engaging the hammer projections. 
     The housing unit covers the motor, the drive unit and the hammer unit, and has an opening for the main body of the output hammer to extend outwardly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the disclosure will become apparent in the following detailed description of the embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  is a perspective view illustrating a first embodiment of a twin hammer impact tool according to the disclosure; 
         FIG. 2  is an exploded perspective view of the first embodiment; 
         FIG. 3  is an exploded view of the first embodiment illustrating a motor, a drive unit and a hammer unit of the twin hammer impact tool; 
         FIG. 4  is a fragmentary sectional view of the first embodiment; 
         FIG. 5  is a fragmentary sectional view of the first embodiment taken along line V-V of  FIG. 4 ; 
         FIG. 6  is a partly exploded perspective view illustrating a second embodiment of a twin hammer impact tool according to the disclosure; and 
         FIG. 7  is a fragmentary sectional view of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Before the disclosure is described in greater detail, it should be noted that where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics. 
     Referring to  FIGS. 1 to 5 , there is shown a first embodiment of a twin hammer impact tool according to the disclosure. The twin hamper impact tool includes a motor  1 , a drive unit  2 , a hammer unit  3  and a housing unit  4 . The hammer unit  3  has a hammer spindle  31 . 
     The motor  1  includes a motor shaft  11 . 
     The drive unit  2  is driven by the motor  1 , and includes a gear set  21  connected to the motor shaft  11 . The gear set  21  has a sun gear  210  connected to the motor shaft  11 , a carrier  213 , a plurality of planetary gears  211  mounted to the carrier  213  and meshed with the sun gear  210 , and a ring gear  212  meshed with the planetary gears  211 . The carrier  213  is connected to the hammer spindle  31 . The ring gear  212  is disposed around the planetary gears  211  and positioned to the housing unit  4 . 
     The hammer unit  3  is connected to the drive unit  2 , and further includes an inner ring hammer  32 , an outer ring hammer  33 , a plurality of rolling beads  34 , an output hammer  35 , a spring  36 , a first packing ring  37  and a second packing ring  38 . 
     The hammer spindle  31  extends along and rotatable about an axial line (L 1 ) of the motor shaft  11 . The hammer spindle  31  has a driven end  311  connected to the carrier  213 , an output end  312  opposite to the driven end  311 , an outer surface  313 , and two V-shaped grooves  314  indented from the outer surface  313 . 
     The inner ring hammer  32  is sleeved on the hammer spindle  31 . Further, the inner ring hammer  32  has a plurality of bead grooves  321  each having a ball half-shape, a plurality of angularly spaced-apart hammer projections  322  disposed around the output end  312  of the hammer spindle  31 , and two sliding grooves  323  respectively facing the V-shaped grooves  314 . The bead grooves  321  are arranged annularly around the axial line (L 1 ) and are equiangularly spaced apart from each other. In addition, the hammer unit  3  further includes two rolling elements  315 . Each rolling element  315  is disposed between one of the V-shaped grooves  314  and one of the sliding grooves  323 . While the bead grooves  321  are arranged annularly around the axial line (L 1 ) and are equiangularly spaced apart from each other for uniform stress distribution the disclosure is not limited to this embodiment. 
     The output hammer  35  is connected to the output end  312  of the hammer spindle  31 , and has a main body  351  extending along the axial line (L 1 ) for engaging a workpiece, and a plurality of angularly spaced engagement projections  352  protruding radially from the main body  351  for engaging the hammer projections  322 . 
     The outer ring hammer  33  is disposed around the inner ring hammer  32 . The outer ring hammer  33  has a plurality of guiding grooves  331  disposed around and extending along the axial line (L 1 ), a first end  332  disposed around a portion of the main body  351  of the output hammer  35  proximal to the output end  312  of the hammer spindle  31 , and a second end  333  opposite to the first end  332 . Each guiding groove  331  has a curve-shaped cross section. The bead grooves  321  respectively face and open toward the guiding grooves  331 . 
     Each rolling bead  34  is received within one of the bead grooves  321  and one of the guiding grooves  331 . 
     The spring  36  is sleeved on the hammer spindle  31  and connects between the carrier  213  and the inner ring hammer  32 . 
     The first packing ring  37  is disposed around the main body  351  of the output hammer  35  and abuts the first end  332  of the outer ring hammer  33 . 
     The second packing ring  38  is disposed around the hammer spindle  31  and abuts the second end  333  of the outer ring hammer  33 . The first and second packing rings  37 ,  38  are stationarily positioned inside the housing unit  4 . In particular, the first packing ring  37  is positioned to an inner surface of the housing unit  4 . 
     It should be noted that the disclosure is not limited to the numbers of the bead grooves  321 , the guiding grooves  331 , the rolling beads  34 , the hammer projections  322  and/or the engagement projections  352  of the first embodiment. 
     The housing unit  4  covers the motor  1 , the drive unit  2  and the hammer unit  3 , and has an opening  41  for the main body  351  of the output hammer  35  to extend outwardly. 
     When the motor  1  is activated, the motor shaft  11  drives the planetary gears  211  to rotate together with the carrier  213  such that the hammer spindle  31  connected to the carrier  213  rotates about the axial line (L 1 ). Because the spring  36  connects between the carrier  213  and the inner ring hammer  32 , the inner ring hammer  32  rotates concomitantly with the carrier  213 . During rotation of the inner ring hammer  32 , the rolling elements  315  respectively slide in the V-shaped grooves  314  such that the inner ring hammer  32  is reciprocally moved along the axial line (L 1 ) relative to the hammer spindle  31  while being rotated together with the hammer spindle  31 . Because the rolling beads  34  connect the outer and inner ring hammers  33 ,  32 , the outer ring hammer  33  rotates concomitantly with the inner ring hammer  32  during rotation of the inner ring hammer  32 . Besides, because the rolling beads  34  are allowed to move within the guiding grooves  331  of the outer ring hammer  33  along the axial line (L 1 ), the movement of the inner ring hammer  32  along the axial line (L 1 ) will not be affected by the rolling beads  34 . Because the first and second packing rings  37 ,  38  are stationarily positioned inside the housing unit  4 , the outer ring hammer  33  is immobilized between the first and second packing rings  37 ,  38  and prevented from moving or vibrating along the axial line L 1  while being rotated about the axial line (L 1 ). In other words, the outer ring hammer  33  can only rotate about but not move along the axial line (L 1 ). 
     When the inner ring hammer  32  rotates together with the hammer spindle  31 , because the engagement projections  352  of the output hammer  35  engage the respective hammer projections  322  of the inner ring hammer  32 , the output hammer  35  moves and rotates together with the inner ring hammer  32 . When the output hammer  35  engages the workpiece and is loaded, the inner ring hammer  32  moves and presses the spring  36  along the axial line (L 1 ) until the hammer projections  322  of the inner ring hammer  32  disengage from the engagement projections  352  of the output hammer  35 . The energy of the spring  36  is therefore released and the hammer projections  322  of the inner ring hammer  32  rotate at a high speed and strike the engagement projections  352  of the output hammer  35  to perform a screw-driving operation. 
     The twin hammer impact tool of the disclosure has the following effects: 
     1. The outer ring hammer  33  rotated by the inner ring hammer  32  can effectively increase rotational inertia to adjust the hammering force. 
     2. Compared with a conventional single hammer impact tool, the outer ring hammer  33  in the first embodiment can be effectively prevented from vibrating along the axial line L 1  during a hammering operation. 
     3. Unlike the conventional twin hammer impact tool disclosed in Chinese Patent Application No. 107175610 A, the first embodiment utilizes the rolling beads  34  which are not needle-shaped. Compared to needle rollers used in the conventional twin hammer impact tool, the rolling beads  34  have relatively small contact areas to contact respective bead grooves  321  and respective guiding grooves  311 . Therefore, frictional forces produced by the rolling beads  34  can be reduced to enhance smoothness of the hammering operation. 
     4. By using the rolling beads  34 , problems of positional displacement and undesired swinging motions encountered by the conventionally used needle rollers can be avoided, and the elastic retention ring required in the conventional twin hammer impact tool can be dispensed with. Therefore, vibration is much reduced and construction is simplified. 
     5. During manufacturing, because each rolling bead  34  has a relatively small length and relatively small contact area, the guiding grooves  311  can be easily formed without needing high level of processing accuracy, thereby reducing manufacturing costs. 
       FIGS. 6 and 7  illustrate a second embodiment according to a twin hammer impact tool of the disclosure, which has a structure generally similar to that of the first embodiment. 
     However, in this embodiment, the hammer unit  3  further includes a roller bearing unit  39  and the first packing ring  37  is omitted. The outer ring hammer  33  further has a head portion  334  disposed around a portion of the main body  351  of the output hammer  35  proximate to the output end  312  of the hammer spindle  31 , and a neck portion  335  extending from the head portion  334  toward the gear set  21 . The head portion  334  abuts an inner surface of the housing unit  4 . The second packing ring  38  (hereinafter referred to as “the packing ring  38 ”) is disposed around the neck portion  335  of the outer ring hammer  33 . The roller bearing unit  39  has a roller housing ring  391  and a plurality of cylindrical rollers  392 . The roller housing ring  391  is sleeved on the neck portion  335  of the outer ring hammer  33 , and is disposed between and in abutment with the packing ring  38  and a shoulder face  336  formed at the juncture of the head and neck portions  334 ,  335  of the outer ring hammer  33 . The cyndrical rollers  392  are rotatably received in the roller housing ring  391 . The packing ring  38  is stationarily positioned inside the housing unit  4  such that the outer ring hammer  33  is immobilized between the inner surface of the housing unit  4  and the packing ring  38 , and is prevented from vibrating along the axial line (L 1 ) while being rotated about the axial line (L 1 ). 
     In the second embodiment, the packing ring  38  does not abut the outer ring hammer  33 ; rather it abuts the roller housing ring  391 . Since a frictional force between the roller housing ring  391  and the packing ring  38  is greater than a frictional force between the outer ring hammer  33  and the roller bearing unit  39 , through an abutment with the roller bearing unit  39  frictional forces generated by the outer ring hammer  33  can be reduced, and operational smoothness can be enhanced. 
     In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent, however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. It should also be appreciated that reference throughout this specification to “one embodiment,” “an embodiment,” an embodiment with an indication of an ordinal number and so forth means that a particular feature, structure, or characteristic may be included in the practice of the disclosure. It should be further appreciated that in the description, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects, and that one or more features or specific details from one embodiment may be practiced together with one or more features or specific details from another embodiment, where appropriate, in the practice of the disclosure. 
     While the disclosure has been described in connection with what are considered the exemplary embodiments, it is understood that this disclosure is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.