Abstract:
A hammer drill comprising: a body; a motor mounted within the body; a transmission housing mounted within the body, a transmission mechanism mounted within the transmission housing which is capable of rotatably driving and/or repetitively striking a cutting tool held by the hammer drill in response to rotation of an output shaft of the motor; wherein the transmission housing comprises a pair of housing portions adapted to engage each other to support the component parts of the transmission mechanism within the transmission housing; wherein the first housing portion is made from metal and the second housing portion is made from a plastic material, each of the components of the transmission mechanism being supported jointly be the first and second housing portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority, under 35 U.S.C. §119, to UK Patent Application No. 1404968.8 filed Mar. 20, 2014 and UK Patent Application No. 1405612.1 filed Mar. 28, 2014, titled “Hammer Drill.” 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a hammer drill incorporating a transmission housing. 
       BACKGROUND OF THE INVENTION 
       [0003]    Hammer drills are power tools that can often operate in three modes of operation. The hammer drill will have a tool bit that can be operated in a hammering mode, a rotary mode and a combined hammer and rotary mode. The hammer drill will typically comprises an electric motor and a transmission mechanism by which the rotary output of the electric motor rotationally drives the tool bit and/or repetitively strikes the tool bit to perform the hammer function. Such a transmission mechanism can be mounted within a transmission housing which is in turn mounted within an external housing of the hammer drill. The use of a transmission housing allows the transmission mechanism to be assembled within the transmission housing prior to its insertion into the external housing as a single sub-assembly. The transmission housing may also be moveably mounted within the external housing so that the hammer drill can be vibrationally damped. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    EP1674215 discloses a hammer drill which has a transmission mechanism mounted within a transmission housing which is mounted within an external housing. EP1674215 indicates that the transmission housing can be made from metal or plastic. It is widely understood that if metal is used to make the transmission housing, the whole of the transmission housing is constructed using metal clam shells. Similarly, it is widely understood that if plastic is used to make the transmission housing, the whole of the transmission housing is constructed using plastic clam shells. This is to ensure the physical properties of the whole of the transmission housing are consistent to provide a balanced support to the components supported within it. 
         [0005]    Accordingly there is provided a hammer drill comprising: 
         [0006]    a body; 
         [0007]    a motor mounted within the body; 
         [0008]    a transmission housing mounted within the body, 
         [0009]    a transmission mechanism mounted within the transmission housing which is capable of rotatably driving and/or repetitively striking a cutting tool held by the hammer drill in response to rotation of an output shaft of the motor; 
         [0010]    wherein the transmission housing comprises a pair of housing portions adapted to engage each other to support the component parts of the transmission mechanism within the transmission housing; 
         [0011]    characterised in that a first housing portion is made from metal and the second housing portion is made from a plastic material, each of the components of the transmission mechanism being supported jointly be the first and second housing portions. 
         [0012]    It has been assumed by engineers that the clam shells of a transmission housing should be made from the same material to provide consistent properties. However, the inventor has found that, when the transmission housing is used to support components of a transition mechanism, the use of a combination of a metal clam shell with a plastic one, where both clam shells support each of the components of the transmission mechanism, provides unusual benefits. The metal clam shell provides rigidity and therefore provides support. However, it needs to be cast and then machined. In existing designs, where two metal clam shells are used, the manufacturing needs to be precise. Plastic material is more flexible but cheaper. Plastic clam shell can be designed with ribs to provide addition support. By using a single metal clam shell, rigidity and support can still be provided. By connecting it to a plastic clam shell, which can flex, the tolerance during the manufacture of the metal clam shell can be reduced as the plastic clam shell can flex to accommodate a wider range of tolerances. It has been assumed that, by having the components supported in a metal clam shell on one side and a plastic clam shell on the other, the support provided to the components would be unbalanced and therefore not desirable. However, to the surprise of the inventor, this has not been found to be the case. 
         [0013]    In an embodiment the first housing portion comprises a recess; wherein a seal is integrally moulded within a groove formed around the recess; wherein the second housing portion comprises a recess; wherein a groove is formed around the recess; and wherein the seal locates within the groove in the second housing portion when the first and second housing portions are engaged with each other. 
         [0014]    In an embodiment, a semi-circular groove is formed in the first housing portion; where a semi-circular seal is moulded into the groove; wherein a semi-circular recess is formed in the second housing portion; where a semi-circular seal is moulded into the recess; and wherein the semi-circular seal in the first housing portion aligns with the semi-circular seal in the second housing portion when the first and second housing portions are engaged with each other to form a circular seal within the transmission housing. The use of fully circular seals in a transmission mechanism requires that the seals are incorporated during the assembly of the transmission mechanism which can difficult. By manufacturing a circular seal using two semi-circular seals formed within the housing portions improves the ease of manufacture. The semi-circular seals can be moulded into the clam shells prior to the assembly of the transmission mechanism taking place. This is simple and ensures their location remains fixed during assembly. The transmission mechanism can then be simply assembled in one of the housing portions and then the other located on top of it, sandwiching the transmission mechanism inside of it. 
         [0015]    In an embodiment, the semi-circular seal in the first housing portion is integral with the seal around the recess. 
         [0016]    The first housing portion further extends to provide a housing portion for a motor housing. This provides a structural support to the motor in relation to the transmission mechanism. 
         [0017]    In an embodiment, there is provided a third housing portion made from a plastic material which engages with the first housing portion to form a motor housing. By using a third housing portion made from plastic material, it can be ensure that the motor is surrounded by a non conductive housing. 
         [0018]    In an embodiment, a semi-circular groove is formed in an edge of a wall of the first housing portion; wherein a semi-circular seal is moulded into the groove; wherein a groove is formed in an edge of a wall of the third housing portion; where a semi-circular seal is moulded into the groove; wherein the semi-circular seal in the first housing portion aligns with the semi-circular seal in the third housing portion when the first and third housing portions are engaged with each other to form a circular seal within the first and third housing portions. The use of fully circular seals requires that the seals are incorporated during the assembly of the transmission mechanism which can difficult. By manufacturing a circular seal using two semi-circular seals formed within the housing portions improves the ease of manufacture. The semi-circular seals can be moulded into the clam shells prior to the assembly of the transmission mechanism taking place. This is simple and ensures their location remains fixed during assembly. The transmission mechanism can then be simply assembled in one of the housing portions and then the other located on top of it, sandwiching the transmission mechanism inside of it. 
         [0019]    In an embodiment, the third housing portion comprises grooves formed in an outer wall of the third housing portion; wherein a seal is integrally moulded into the grooves; wherein, when the first, second and third portions are engaged with each other, the seal engages with an outer surface of the second housing portion to form a seal between the second and third housing portions. The circular seal in the third housing portion can be integral with the seal moulded into the grooves. 
         [0020]    The semicircular seal in the first portion can be integral with the seal surrounding the recess. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    An embodiment of the present invention will now be described by way of example only and not in any limitative sense, with reference to the accompanying drawings in which: 
           [0022]      FIG. 1  is a perspective view of an example of a hammer drill; 
           [0023]      FIG. 2  is a side cross-sectional view of the hammer drill of  FIG. 1 ; 
           [0024]      FIG. 3  is an enlarged side cross-sectional view of part of the hammer drill of  FIG. 2 ; 
           [0025]      FIG. 4  is a partially cut away perspective view of part of the piston drive mechanism of  FIG. 1  in its rearmost position; 
           [0026]      FIG. 5  is a partially cut away perspective view of part of the piston drive mechanism of  FIG. 1  advanced through a quarter of a cycle of reciprocation from the position shown in  FIG. 4 ; 
           [0027]      FIG. 6  is a partially cut away cross section of part of the piston drive mechanism of  FIG. 1  advanced through half a cycle from the position shown in  FIG. 4  to its foremost position; 
           [0028]      FIG. 7  shows the design of the assembled transmission housing in accordance with the embodiment of the present invention; 
           [0029]      FIG. 8  shows the first part of the transmission housing of  FIG. 7  with the integral motor housing from a first side; 
           [0030]      FIG. 9  shows the first part of the transmission housing of  FIG. 7  with the integral motor housing from a second side opposite to that shown in  FIG. 8 ; 
           [0031]      FIG. 10  shows the second part of the transmission housing of  FIG. 7  from a first side; 
           [0032]      FIG. 11  shows the second part of the transmission housing of  FIG. 7  from a second side opposite to that shown in  FIG. 10 ; 
           [0033]      FIG. 12  shows the third part of the housing which form part of the motor housing of  FIG. 7  from a first side; and 
           [0034]      FIG. 13  shows the third part of the housing which forms part of the motor housing of  FIG. 7  from a second side opposite to that shown in  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    An example of a known hammer drill will now be described in relation to  FIGS. 1 to 6 . 
         [0036]    Referring to  FIG. 1 , a battery-powered hammer drill comprises a tool housing  22  and a chuck  24  for holding a drill bit (not shown). The tool housing  22  forms a handle  26  having a trigger  28  for activating the hammer drill  20 . A battery pack  30  is releasably attached to the bottom of the tool housing  22 . A mode selector knob  32  is provided for selecting between a hammer only mode, a rotary only mode and a combined hammer and rotary mode of operation of the drill bit. 
         [0037]    Referring to  FIG. 2 , an electric motor  34  is provided in the tool housing  22  and has a rotary output shaft  36 . A pinion  38  is formed on the end of output shaft  36 , the pinion  38  meshing with a first drive gear  40  of a rotary drive mechanism and a second drive gear  42  of a hammer drive mechanism. 
         [0038]    An embodiment of the rotary drive mechanism shall be described as follows. A first bevel gear  44  is driven by the first drive gear  40 . The first bevel gear  44  meshes with a second bevel gear  46 . The second bevel gear  46  is mounted on a spindle  48 . Rotation of the second bevel gear  46  is transmitted to the spindle  48  via a clutch mechanism including an overload spring  88 . The spindle  48  is mounted for rotation about its longitudinal axis by a spherical ball bearing race  49 . A drill bit (not shown) can be inserted into the chuck  24  and connected to the forward end  50  of spindle  48 . The spindle  48  and the drill bit rotate when the hammer drill  20  is in a rotary mode or in a combined hammer and rotary mode. The clutch mechanism prevents excessive torques being transmitted from the drill bit and the spindle  48  to the motor  34 . 
         [0039]    An embodiment of the hammer drive mechanism shall now be described as follows. The pinion  38  of motor output shaft  36  meshes with a second drive gear  42  such that rotation of the second drive gear  42  causes rotation of a crank plate  52 . A crank pin  54  is driven by the crank plate  52  and slidably engages a cylindrical bearing  56  disposed on the end of a hollow piston  58 . The hollow piston  58  is slidably mounted in the spindle  48  such that rotation of the crank plate  52  causes reciprocation of hollow piston  58  in the spindle  48 . A ram  60  is slidably disposed inside hollow piston  58 . Reciprocation of the hollow piston  58  causes the ram  60  to reciprocate with the hollow piston  58  as a result of expansion and contraction of an air cushion  93 , as will be familiar to persons skilled in the art. Reciprocation of the ram  60  causes the ram  60  to impact a beat piece  62  which in turn transfers impacts to the drill bit (not shown) in the chuck  24  when the hammer drill operating in a hammer mode or a in combined hammer and rotary mode. 
         [0040]    A mode change mechanism includes a first and a second drive sleeves  64 ,  66  which selectively couple the first and second drive gears  40 ,  42  respectively, to the first bevel gear  44  and the crank plate  52 , respectively, in order to allow a user to select between either the hammer only mode, the rotary only mode or the combined hammer and rotary mode. The mode change mechanism is the subject of UK patent application no. 0428215.8. 
         [0041]    A transmission mechanism comprises the rotary drive mechanism, the hammer drive mechanism and the mode change mechanism. The transmission mechanism is disposed inside a transmission housing  80 . The transmission housing  80  also supports the electric motor  34 . The transmission housing is formed from two clamshell halves of durable plastics material or cast metal, the two clamshell halves compressing an o-ring  82  there between. In existing designs, the transmission housing is made from only durable plastics material or of only cast metal. The o-ring  82  seals the transmission housing  80  to prevent dust and dirt from entering the transmission housing and damaging the moving parts of the transmission mechanism. 
         [0042]    The transmission housing  80  is slidably mounted inside the tool housing  22  on parallel rails (not shown) and is supported against to the tool housing  22  by first and second damping springs  84  and  86  disposed at its rearward end. The transmission housing  80  can therefore move by a small amount relative to tool housing  22  in order to reduce transmission of vibration to the user during operation of the hammer drill  20 . The spring co-efficients of the first and second damping springs  84  and  86  are chosen so that the transmission housing  80  slides to a point generally mid-way between its limits of forward and rearward travel when the hammer drill  20  is used in normal operating conditions. This is a point of equilibrium where the forward bias of the damping springs  84  and  86  equals the rearward force on the transmission housing  80  caused by the user placing the hammer drill  20  against a workpiece and leaning against the tool housing  22 . 
         [0043]    Referring to  FIG. 3 , the hammer drive mechanism will be described in more detail. The crank pin  54  comprises a cylindrical link member  68  rigidly connected to a part-spherical bearing  70 . The part-spherical bearing  70  is slidably and rotatably disposed in a cup-shaped recess  72  formed in the crank plate  52 . The cup-shaped recess  72  has an upper cylindrical portion  72   a  and a lower generally semi-spherical portion  72   b.  The upper cylindrical portion  72   a  and a lower semi-spherical portion  72   b  have the same maximum diameter which is slightly greater than that of the part-spherical bearing  70 . As a result, the part-spherical bearing  70  can be easily inserted into the cup-shaped recess. The crank pin  4  can pivot, rotate and slide vertically relative to the crank plate whilst the part-spherical bearing remains within the confines of the cup-shaped recess  72 . 
         [0044]    The cylindrical link member  68  is slidably disposed in a cylindrical bearing  56  formed in the end of the hollow piston  58 . Sliding friction in the cup-shaped recess  72  is slightly greater than in the cylindrical bearing  56 . The cylindrical link member  68  therefore slides up and down in the cylindrical bearing  56  while the part-spherical bearing rocks back and forth in the cup-shaped recess. A cylindrical collar member  74  surrounds the cylindrical link member  68  of the crank pin  54  and can slide between a lower position in which it abuts the upper surface of the part-spherical bearing  70  and an upper position in which it abuts and the underside of the cylindrical bearing  56 . The collar member  74  is a precautionary feature that limits movement of the part-spherical bearing  70  towards the cylindrical bearing  56  so that it is impossible for the crank pin  54  and the part-spherical bearing  70  to move totally out of engagement with the cup-shaped recess  72 . The cylindrical collar member  74  can be mounted to the crank pin  54  after construction of the crank plate  52  and crank pin  54  assembly. 
         [0045]    Referring to  FIGS. 4 to 6 , as the crank plate  52  rotates in the anti-clockwise direction from the upright position shown in  FIG. 6 , to the position shown in  FIG. 7 , it can be seen that the crank pin  54  pushes the hollow piston  58  forwardly and also tilts to one side. As the crank pin  54  tilts, the cylindrical link member  68  slides downwardly in the cylindrical bearing  56 . As the crank plate  52  rotates from the position of  FIG. 5  to the position of  FIG. 6  to push the hollow piston  58  to its foremost position, the crank pin  54  re-adopts an upright position and the cylindrical link member  68  of the crank pin  54  slides upwardly inside cylindrical bearing  56 . It can be seen that by engagement of the collar member  74  with the underside of the cylindrical bearing  56  and the top of the part-spherical bearing  70 , the crank pin  54  is prevented from moving too far inside the cylindrical bearing and out of engagement with the crank plate  52 . There is therefore no need for an interference fit to trap the crank pin into engagement with the crank plate, which significantly simplifies assembly of the drive mechanism. 
         [0046]    An embodiment of the present invention will now be described with reference to  FIGS. 7 to 13 . The construction of the hammer drill is essentially the same as that disclosed in the above example except for the design of the transmission housing and the addition of an integral motor housing. Where the same features in the embodiment have previously been disclosed in the above example, the same reference numbers have been used. The same design of transmission mechanism, external housing handles, chuck and battery are used within the embodiment as in the example above. 
         [0047]      FIG. 7  shows the new design of the assembled transmission housing  600 . The transmission housing  600  is constructed from three component parts which are in the form of clam shells. 
         [0048]    The first part  602 , which is formed in a one piece construction from durable plastic material, forms one half of the transmission housing  600  on one side and half of the housing for the motor  34  as seen in  FIGS. 8 and 9 . The first part  602  forms two recesses  608 ,  610 , the first recess  608  for receiving part of the transmission mechanism, the second recess  610  for receiving the motor. 
         [0049]    The inside of the first recess  608  is shaped to directly support one half of the transmission mechanism. 
         [0050]    Formed inside of the first recess  608  within the wall of the recess  608  are semi-circular recesses  614  which receive and support one side of the support bearings  49 ,  604  (see  FIG. 2 ) of the transmission mechanism. Elongate troughs  618  provide further support for one side of the transmission mechanism. An aperture  620  is form through the wall at the base of the recess  608  through which the shaft of the mode change knob can pass from the transmission mechanism to outside of the housing to be operated by a user. 
         [0051]    A seal  622  is integrally moulded into a groove formed around the recess  608 . Small apertures  624  are formed in a number of places in the base of the groove through which some of the seal  622  can pass during the moulding procedure to secure the seal  622  within the groove. 
         [0052]    Formed within the wall  626  between the first  608  and second cavities  610  is a first semi-circular passageway  628 . The groove is formed within the edge of the wall  626  around the semi-circular passageway  628  and the seal  622  is integrally moulded within this groove to form a semi-circular seal  630  around the edge of the wall  626 . 
         [0053]    Formed within the inner wall of the recess  608  is a semicircular groove  632  which runs around a tubular section  634  of the transmission housing. The seal  622  is integrally moulded within this groove  632  to form a second semi-circular seal  636  around the tubular section  634 . 
         [0054]    Similar, the inside of the second recess  610  is shaped so that it directly supports one half of the motor  34 . Apertures  640  are formed through the side of the wall in the recess  610  so that an air flow can be drawn into the recess  610  and across the motor  34  by a fan and then is expelled from the recess  610 , to cool the motor  34 . A slot  642  is provided in which half of a brush card, for controlling the motor, can be inserted and held. 
         [0055]    The second part  644  of the transmission housing, which is formed in a one piece construction from cast aluminium, forms the second side of the transmission housing  600  only as seen in  FIGS. 10 and 11 . The second part  644  forms a recess  646  for receiving part of the transmission mechanism. 
         [0056]    The inside of the recess  646  is shaped to directly support one half of the transmission mechanism. 
         [0057]    Formed inside of the recess  646  within the wall of the recess  646  are semi-circular recesses  648  which receive and support the other side of the support bearings  49 ;  604  of the transmission mechanism. Whilst the second part  644  is cast to produce the overall part, the semi-circular recesses  648  are subsequently machined to ensure that their dimensions are matched perfectly with those of the bearings  49 ;  604  which are located within them. Elongate troughs  650  provide further additional support for the other side of the transmission mechanism. 
         [0058]    A semi-circular seal  652  is moulded into a groove formed in one of the semi-circular recesses  648 . Small apertures  654  are formed in a number of places in the base of the groove through which some of the seal  652  can pass during the moulding procedure to secure the seal  652  within the groove. 
         [0059]    Formed within the wall  652  at the base of the recess is a semi-circular passageway  658 . 
         [0060]    The first part  602  is attached to the second part  644  by bolts which pass through apertures  646  in the first and second parts and are secured using nuts. When the two parts are secured to each other, the transmission mechanism is sandwiched between and supported by the two parts, half of each of the components of the transmission mechanism being supported in the first plastic part  602 , the second half of each of the components of the transmission mechanism being supported in the second metal part  644 . 
         [0061]    A groove  662  is formed around the recess  646  in the second part  644  to receive the seal  622  of the first part which is aligned with the groove  662  when the first and second parts are attached to each other. 
         [0062]    When the first and second parts are connected together, the second semi-circular seal  636  formed within the first part  602  aligns with the semi-circular seal  652  in the second part  644  to form a circular seal which located around a tubular section  634  within the housing. The seal  636 ,  652  surrounds and engages with the spindle  48  of the hammer drill which extends from the transmission mechanism in the transmission housing to outside of the hammer drill via an aperture  670 , to prevent grease and oil within the transmission housing from leaking out of the transmission housing  600 . 
         [0063]    The third part  672 , which is formed in a one piece construction from durable plastic material, forms the second half of the motor  606  for the motor  34  as seen in  FIGS. 12 and 13 . The third part  672  forms a recess  674  for receiving the motor  34 . 
         [0064]    The recess  674  is shaped so that it directly supports the second half of the motor  34 . Apertures  676  are formed through the side of the wall in the recess  674  so that an air flow can be drawn into the recess  674  and across the motor  34  by a fan, and then expelled to cool the motor. A slot  678  is provided in which the second half of the brush card, for controlling the motor  34 , can be inserted. 
         [0065]    A seal  680  is integrally moulded into grooves formed within the top wall of the third part  672 , outside of and facing away from the recess  674 . Small apertures (not shown) are formed in a number of places in the base of the grooves through which some of the seal  680  can pass during the moulding procedure to secure the seal  680  within the grooves. 
         [0066]    Formed within the top wall  682  is a semi-circular passageway  684 . A groove is formed within the edge of the wall  682  around the semi-circular passageway  684  and the seal  680  is integrally moulded within this groove to form a semi-circular seal  686  around the edge of the wall  682 . 
         [0067]    The third part  672  is attached to the first part  602  prior the second part  644  has been attached. It is attached by using bolts which pass through the apertures  688  in the first and third parts and are secured using nuts. When the second part  644  is attached to the first part  602 , the bottom section of the second part  644  sandwiches the top section of the third part  672 , the two bolts which pass through the lower two apertures  646  of the second part  644  also passing through the top two apertures  688  of the third part  672  prior to passing through the apertures of the first part  602 . When the two parts  602 ,  672  are secured to each other, the motor  34  and brush card are sandwiched between and supported by the two parts, half of each component being supported in the first plastic part  602 , the other half of each component being supported in the third plastic part  672 . 
         [0068]    When the first and third parts are connected together, the first semi-circular seal  630  formed within the first part  602  aligns with the semi-circular seal  686  in the third part  672  to form a circular seal which locates around a circular aperture formed by the semi-circular passageway  628  in the first part  602  and the semi-circular passageway  684  in the second part  672 , which are also aligned. The seal  630 ,  686  surrounds and engages with the shaft  36  of the motor  34  which passes from the motor  34  in the motor housing to the transmission mechanism in the transmission housing, to prevent grease and oil within the transmission housing from passing into the motor housing. 
         [0069]    Furthermore, when the first, second and third parts are connected together, the seal  680  on the top wall  626  of the third part  672  engages with the outer surface of the lower wall of the second part  644  to provide a seal between the two. 
         [0070]    It will be appreciated that the three parts could be designed so that, as an alternative, the third part  672  is attached to the first part  602  after the second part  644 .