Abstract:
A knob assembly for a power tool comprising: a knob having a slot and knob recess, the slot and knob recess intersecting each other at an intersection within the knob; a latch slideably mounted within the slot; a peg located within the knob recess; wherein the peg and latch engage with each other via the intersection in order for the peg to retain the latch within the slot and for the latch to retain peg within the knob recess.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to UK Application No. GB 1413293.0, filed on Jul. 28, 2014, entitled “Mode Change Knob Assembly.” The content of this application is incorporated herein by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a knob assembly, particularly a mode change knob assembly for a hammer drill. 
       BACKGROUND OF THE INVENTION 
       [0003]    A hammer drill comprises a tool holder in which a cutting tool, such as a drill bit, can be supported and driven by the hammer drill. The hammer drill can often drive the cutting tool in three different ways, each being referred to as a mode of operation. The cutting tool can be driven in a hammering mode, a rotary mode and a combined hammer and rotary mode. A hammer drill will typically comprise an electric motor and a transmission mechanism by which the rotary output of the electric motor can either rotationally drive the cutting tool to perform the rotary mode or repetitively strike the cutting tool to perform the hammer mode or rotationally drive and repetitively strike the cutting tool to perform the combined hammer and rotary mode. 
         [0004]    EP1157788 discloses a typical hammer drill. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In order to change the mode of operation, there is provided a mode change mechanism. The mode change mechanism is typically operated using a mode change knob assembly. EP0437716 discloses an example of a mode change knob assembly. 
         [0006]    Accordingly, there is provided a knob assembly in accordance with claim  1  and a method in accordance with claim  11 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    An embodiment of the present invention will now be described with reference to the accompanying drawings of which: 
           [0008]      FIG. 1  shows a side view of a hammer drill in accordance with the present embodiment of the invention; 
           [0009]      FIG. 2  shows a vertical cross sectional view of the hammer drill of  FIG. 1 ; 
           [0010]      FIG. 3  shows a top perspective view the mode change knob assembly of the hammer drill of  FIG. 1 ; 
           [0011]      FIG. 4  shows a bottom perspective view the mode change knob assembly of the hammer drill of  FIG. 1 ; 
           [0012]      FIG. 5  shows a top view of the knob and latch only; 
           [0013]      FIG. 6  shows a rear view of the latch, biasing spring and indicator peg only; 
           [0014]      FIG. 7  shows a top view of the latch, biasing spring and indicator peg only; 
           [0015]      FIG. 8  shows a first perspective view of the slot of the knob with the latch, peg and biasing spring omitted; 
           [0016]      FIG. 9  shows a second perspective view of the slot of the knob with the latch, peg and biasing spring omitted; and 
           [0017]      FIG. 10  shows an underside view of the mode change knob assembly. 
       
    
    
       [0018]    Referring to the  FIGS. 1 and 2 , the hammer drill comprises a motor housing  50  which connects to a transmission housing  52  via intermediate housing  54 . 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Mounted within the motor housing  50  is an electric motor  2  having a rotor  4  mounted within a stator  6 . The motor  2  is powered via an electric cable  8  which connects to the motor via an electric switch  10 . Depression of the switch causes the rotor  4  to rotate. A fan  44  is mounted on the output spindle  12  of the motor to draw air over the motor  2 . 
         [0020]    The transmission mechanism will now be described. 
         [0021]    The output spindle  12  of the motor comprises teeth which mesh with a gear  14  on an intermediate shaft  16  to rotatingly drive the intermediate shaft  16 . A wobble bearing  18  is mounted on the intermediate shaft  16  which, when activated, is rotationally driven by the intermediate shaft  16  to reciprocatingly drive a piston  20  located within a hollow spindle  22 . The piston reciprocatingly drives a ram  24  via an air cushion. The ram  24  in turn repetitively strikes a beat piece  26  which strikes the end of a cutting tool when held in a tool holder  28  attached to the end of the hollow spindle  22  at the front of the transmission housing  52 . Also mounted on the intermediate shaft  16  is a second gear  30  which meshes with a third gear  32  mounted on the hollow spindle  22 . When activated, the intermediate shaft  16  rotationally drives the hollow spindle  22  via the second and third gears, the third gear  32  driving the hollow spindle  22  via a torque clutch  36 . Rotation of the hollow spindle  22  results in the rotation of the tool holder  28 . The wobble bearing  18  and rotary drive are activated via a mode change mechanism  40 . The operation of such a hammer drill is well known in art and therefore will not be discussed any further. 
         [0022]    The mode change mechanism is operated using a mod change knob assembly  100 . 
         [0023]    Referring to  FIGS. 3 and 4 , the mode change knob assembly  100  comprises a knob  102 , a latch  104 , a helical biasing spring  106  (see  FIG. 6 ), an indicator peg  108  and a seal  110 . The mode change knob assembly is mounted within an aperture formed in a wall of transmission housing  52 , the edge of the aperture locating within slots  112  formed between a wall  114  and protrusions  116  on the knob  102 . The mode change knob assembly  100  can rotate about an axis  120  within the aperture. The knob  102  comprises a peg  118  which engages with the mode change mechanism of the hammer drill. Rotation of the mode change knob assembly  100 , results in rotation of the peg  118  about axis  120  which results in the peg  118  adjusting the mode change mechanism to change the mode of operation of the hammer drill. The seal  110  surrounds the knob  102  and engages with the transmission housing  52  to provide a grease seal, thus preventing grease from within the transmission housing  52  exiting through the aperture for the mode change knob assembly  100  in the wall of the transmission housing  52 . 
         [0024]    A slot  122  (as best seen in  FIGS. 8 and 9 ) is formed within the knob  102 . Slideably mounted within the slot  122  is the latch  104 . Formed on an inner wall of the latch  104  is a projection  124  (as seen in  FIG. 7 ). One end of the helical biasing spring  106  is mounted on the projection  124 . The projection  124  and spring  126  are located within the slot  122  of the knob  102 , the spring  106  being sandwiched between inner wall of the latch  104  and a rear inner wall of the slot  122  under compression force. The spring  106  biases the latch  104  out of the slot  122 . 
         [0025]    Formed on each side of the latch  104  are two rearwardly extending arms  128 ,  130 . The arms  128 ,  130  are resiliently deformable and can be bent towards each other. Integrally formed on the rear end of the arms  128 ,  130  are two catches  132 ,  134 , which project sideways, perpendicularly to the arms  128 ,  130 . A chamfer  136 ,  138  is formed on the rear of each of the catches  132 ,  134 . Formed in one of the side walls  140  of the slot  122  is a rectangular recess  142  (as seen in  FIG. 8 ), the entrance to the rectangular recess  142  from the slot  122  forming an intersection. The rectangular recess  142  extends to the base of the knob  102  as best seen in  FIG. 10 . Formed in the other of the side walls  144  of the slot  122  is a triangular recess  146  (as seen in  FIG. 9 ), the entrance to the triangular recess  146  from the slot  122  forming an intersection. The triangular recess  146  extends to the top of the knob  102  as best seen in  FIG. 5 . A small hole  152  is formed in the base of the triangular recess  146  which extends to the base of the knob  102 . The triangular indicator peg  108  locates within the triangular recess  146 . The triangular indicator peg  108  has a recess  150  formed in one side. When the mode change knob assembly  100  is assembled, one of the catches,  132  extends into the rectangular recess  142  and is cable of sliding in a forward and rearward manner within the rectangular recess  142 . The other of the catches  134  extends into the recess  150  of the triangular indicator peg  108 , and is cable of sliding in a forward and rearward manner within the recess  150  of the indicator peg  108 . When the latch  104  is biased to its most forward position, one side  154  of one of the catches  132  engages with side of the rectangular recess  142 , one side  156  of the other catch  134  engaging with the side of the recess  150  in the indicator peg  108 , thus defining the latch&#39;s  104  outer most position and preventing the latch from being pushed completely out of the slot  122 . When the catch  134  is located within the recess  150  of the peg  108 , the peg  108  is held within the triangular recess  146  of the knob  102 , the catch  134  prevent the peg  108  from being removed from the triangular recess  146 . Similarly, the peg  108  restricts the movement of the catch  134  and thus retains the catch  134  within the slot  122 . 
         [0026]    Formed on the outer portion of the latch  104  is a finger grip  160 . Extending from the base of the finger grip  160  is a tooth  162 . Formed around edge of the aperture in the wall of the transmission housing  52  for receiving the mode change assembly  100  are a series of indentations. When the mode change knob assembly is rotated within the aperture so that the tooth  162  is aligned with one of the indentations, the tooth  162  is cable of entering the indentation due to the biasing force of the spring  106 . Each of the indentations is located at an angular position where the mode change knob assembly needs to be orientated in order to activate one of the modes of operation of the hammer drill. 
         [0027]    During the normal use of the hammer drill, the tooth  162  is located in one of the indentations and the hammer is operated in particular mode of operation. When the operator wishes to alter the mode of operation of the hammer drill, the operator must do so by rotating the mode change knob assembly  100 . In order to do, the operator presses the finger grip  160  of the latch  104  to push the latch  104  into the slot  122  of the knob  102  against the biasing force of the spring  106 . As the latch  104  moves the catches  132 ,  134  slide rearwardly within the recesses  142 ,  150  and the tooth  162  disengages from the indentation. Once clear of the indentation, the operator can rotate the mode change knob assembly  100  until the tooth becomes aligned with another indention when the tooth  162  will enter this indentation under the biasing force of the spring  106  to lock the mode change knob assembly against further rotation and in an angular position which it needs to be in for the mode change mechanism to operate in a new mode of operation. The operator can then commence to use the hammer drill in the new mode of operation. 
         [0028]    Molded onto the outer surface of the transmission housing  52 , around the mode change knob assembly  100 , are a number of symbols  164  (see  FIG. 1 ) which represent the modes of operation of the hammer drill. The indicator peg  108  acts as an arrow and provides a visual indicator to the operator as to where the operator should rotate the knob  102  and to what mode of operation the hammer drill will operate in when it is in that angular position. When the indicator peg  108  points to a symbol, it indicates that the tooth  162  is aligned with an indentation and therefore can be locked in that position. The particular symbol the indicator peg  108  is pointing to will inform the operator what mode of operation the hammer drill will operate in when the mode change knob assembly is in that angular position. 
         [0029]    The method by which the mode change knob assembly  100  is assembled and disassembled will now be described. 
         [0030]    Firstly, the seal  110  is placed on the knob  102 . The spring  106  is placed onto the projection  124  of the latch  104 . The triangular indicator peg  108  is inserted into the triangular recess  146  with the recess  150  facing towards the slot  122  of the knob  102 . The latch  104  and spring is then slid into the slot  122  with the rearwardly extending arms  128 ,  130  entering the slot  122  first. As the arms  128 ,  130  enter the slot  122 , the two chamfers  136 ,  138  engage with the side walls  140 ,  144  of the slot  122  and push the arms  128 ,  130  inwardly towards each other against the biasing force of the arms  128  allowing them and the latch  104  to enter the slot  122 . The latch is pushes into the slot  122  until the catches  132 ,  134  align with and then engage with the rectangular recess  142  on one side and the recess  150  of the peg  108  on the other due to the biasing force of the arms  128 ,  138 . The arms  128 ,  130  then hold the catches  132 ,  134  in the rectangular recess  142  and recess  150  of the peg  108 . As the latch  104  is slid into the slot  122 , the spring  106  becomes compressed. Whilst the catches  132 ,  134  are in the rectangular recess and recess  150  of the peg  108 , the latch  104  is locked inside of the sot  122  and is prevent from escaping. The mode change knob assembly is then inserted into the aperture of the transmission housing with the  118  engaging the mode change mechanism  40 . The edges of the wall of the transmission housing are located within the slots  112  to hold and guide the knob  102 . The mode change knob assembly  100  is secured to the transmission housing  52 . 
         [0031]    The advantage of this design of mode change knob mechanism is that peg  108  is used to secure the latch  104  within the slot  122 . Furthermore, the latch  104  is used to secure the peg  108  within the triangular recess  146 . Furthermore, the peg  108  is used to act as a visual indicator for the operator to inform the operator of the alignment positions of the mode change knob assembly  100  and the mode the hammer drill will operate in when in that angular position. 
         [0032]    To disassemble the mode change knob assembly, the mode change knob assembly  100  is removed from the transmission housing  52 . A tool is then inserted in the entrance of the rectangular recess  142  on the base of the knob  100  (shown in  FIG. 10 ) and engages with the catch  132  located within the rectangular recess  142 . The catch  132  is then pushed out of the rectangular recess  142  using the tool and into the slot  122 , bending the arm  128  as it does so. The latch  104  is then twisted within the slot  122  about an axis parallel to the rotational axis of the knob  102  to draw out the latch  104 , both arms  128 ,  130  bending as it brought out. The size of slot  122  and the flexibility of the arms  128 ,  130 , is sufficient to allow the latch  104  to be removed. The peg  108  can then be pushed out of the triangular recess  146  by inserting a pin through the small hole  152  in the base of the triangular recess  146  to engage with the peg  108  and then subsequently push the peg  108  out. The seal  110  and spring can then be removed.