Patent Publication Number: US-9403266-B2

Title: Power tool

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending International Application No. PCT/CN2012/078178 filed Jul. 4, 2012. 
     FIELD OF THE DISCLOSURE 
     The present invention relates to a power tool, in particular to an angle grinder, and more in particular, to a toggle switch for an angle grinder. 
     SUMMARY 
       FIGS. 1 to 3  which discloses a prior art design of angle grinder, the angle grinder comprises a plastic rear motor housing  2  which is connected to a metal gear housing  4  via bolts (not shown) located within threaded passageways  6  formed in the two housings. The rear motor housing comprises two clam shells  8 ,  10  which are attached to each other with bolts (not shown) along a vertical plane  12  as best seen in  FIG. 3 . 
     An electric motor (generally indicated by the dashed lines  14  in  FIG. 2 ) is mounted within the motor housing  2 . A motor spindle (generally indicated by the dashed lines  16  in  FIG. 2 ) of the motor  14  rotationally drives an output spindle  18  of the grinder via a gear box (generally indicated by the dashed lines  20  in  FIG. 2 ). The gear box  20  is mounted within the gear housing  4  and typically comprises a bevel gear. The gear box  20  alters the rotational speed of the output spindle  18  versus the motor spindle  16 , as well as allowing the axis of rotation of the output spindle  18  to be located perpendicularly relative to the axis of rotation of the motor spindle  16 . 
     Forward vents  22  are formed in the side of the motor housing  2  adjacent the front end of the motor  14  to allow a fan (generally indicated by the dashed lines  60  in  FIG. 2 ), mounted on the motor spindle  16 , to draw air into the motor housing and then force it to flow over the motor  14  to cool it. Rear vents  24  are formed in the motor housing  2  to allow the warm air to be expelled from the motor housing after it has passed over the motor  14 . 
     Removable access caps  26  are formed the side of the motor housing adjacent each of the brushes (not shown) of the motor  14  to enable the brushes to be replaced without dismantling the angle grinder. 
     The electric motor  14  is powered by a mains electricity supply which is provided to the grinder via an electric cable  28  which enter the motor housing  2  of the grinder at the rear. The electric cable comprises electrically insulted wires,  46 ,  47 ,  48  which form a circuit. The electric cable  28  connects to the motor  14  via a toggle switch  30  which enables the operator to switch the motor  14  on and off. 
     An example of such a toggle switch is  30  shown at  FIG. 4 . 
     The toggle switch  30  comprises body  32 , extending from which are two metal plates  34  which act as electric terminals for the switch  30 . The toggle switch  30  is connected in series with the wires  46 ,  47  of the electric circuit  36  of the motor  14  as shown in  FIG. 5 . The plates  34  are connected by being soldered to exposed ends of the wires  46 ,  47 . Alternatively, the ends of the wires may comprise female connectors which receive the plates  34  within them in an electrically conductive manner, and which may then be crimped. A pivotal toggle  38  extends from the body  32  which can be pivoted between two positions, a first position  40  shown in  FIGS. 4 and 5  by solid lines and a second position  40 ′ shown in  FIGS. 4 and 5  by the dashed lines. When the toggle is in its first position, an electrical connection is made between the two plates  34  allowing the motor  14  to run. When the toggle  38  is in its second position, the electrical connection between the plates  34  is broken and the flow of electrical current through the switch is prevented. As such, the motor  14  is switched off. A rubber boot  42  connects between the toggle  38  and the body  32  to prevent the ingress of dirt into the body of the switch via the opening in the body  32  through which the toggle  38  projects. 
     During use, a grinding or cutting disks is rigidly attached to the output spindle  18 . The motor is then activated using the toggle switch  30  and the operator manually manipulates angle grinder to use the grinding or cutting disk to grind or cut a work piece. Often the work piece is made from metal such as a metal girder. 
     However, a problem has been found with the operation of existing designs grinder. During use, metal filings generated by the cutting action of the grinder are drawn inside of the housing  2  via the vent  22  of the grinder due to the air flow generated by the fan  60 . Whilst a proportion of these will be subsequently expelled from the housing, a residual amount will collect on internal components located inside of the motor housing  2 . This includes the body  32  and metal plates  34  of the toggle switch  30 . In existing designs of grinder, parts or all of the plates  34  remain exposed. As such, when a sufficient amount of metal filings has congregated on the body  32  and plates  34  of the toggle switch, a short circuit is formed directly between the plates  34 . When electric power is provided to the grinder, the electrical power short circuits the toggle switch by being able to conduct between the plates  34  via the metal filings. This is dangerous for two reasons. Firstly, as soon as electrical power is connected to angle grinder, it will immediately commence to operate with the operator unable to stop its operation without removing the power supply. Secondly, the short circuit can lead to the switch setting fire which, as the motor housing is made of plastic, results in the housing setting on fire. 
     The object of the present invention is to provide an improved design which overcomes or at least reduces the problems associated with existing designs.  FIGS. 1 to 3  which discloses a prior art design of angle grinder, the angle grinder comprises a plastic rear motor housing  2  which is connected to a metal gear housing  4  via bolts (not shown) located within threaded passageways  6  formed in the two housings. The rear motor housing comprises two clam shells  8 ,  10  which are attached to each other with bolts (not shown) along a vertical plane  12  as best seen in  FIG. 3 . 
     An electric motor (generally indicated by the dashed lines  14  in  FIG. 2 ) is mounted within the motor housing  2 . A motor spindle (generally indicated by the dashed lines  16  in  FIG. 2 ) of the motor  14  rotationally drives an output spindle  18  of the grinder via a gear box (generally indicated by the dashed lines  20  in  FIG. 2 ). The gear box  20  is mounted within the gear housing  4  and typically comprises a bevel gear. The gear box  20  alters the rotational speed of the output spindle  18  versus the motor spindle  16 , as well as allowing the axis of rotation of the output spindle  18  to be located perpendicularly relative to the axis of rotation of the motor spindle  16 . 
     Forward vents  22  are formed in the side of the motor housing  2  adjacent the front end of the motor  14  to allow a fan (generally indicated by the dashed lines  60  in  FIG. 2 ), mounted on the motor spindle  16 , to draw air into the motor housing and then force it to flow over the motor  14  to cool it. Rear vents  24  are formed in the motor housing  2  to allow the warm air to be expelled from the motor housing after it has passed over the motor  14 . 
     Removable access caps  26  are formed the side of the motor housing adjacent each of the brushes (not shown) of the motor  14  to enable the brushes to be replaced without dismantling the angle grinder. 
     The electric motor  14  is powered by a mains electricity supply which is provided to the grinder via an electric cable  28  which enter the motor housing  2  of the grinder at the rear. The electric cable comprises electrically insulted wires,  46 ,  47 ,  48  which form a circuit. The electric cable  28  connects to the motor  14  via a toggle switch  30  which enables the operator to switch the motor  14  on and off. 
     An example of such a toggle switch is  30  shown at  FIG. 4 . 
     The toggle switch  30  comprises body  32 , extending from which are two metal plates  34  which act as electric terminals for the switch  30 . The toggle switch  30  is connected in series with the wires  46 ,  47  of the electric circuit  36  of the motor  14  as shown in  FIG. 5 . The plates  34  are connected by being soldered to exposed ends of the wires  46 ,  47 . Alternatively, the ends of the wires may comprise female connectors which receive the plates  34  within them in an electrically conductive manner, and which may then be crimped. A pivotal toggle  38  extends from the body  32  which can be pivoted between two positions, a first position  40  shown in  FIGS. 4 and 5  by solid lines and a second position  40 ′ shown in  FIGS. 4 and 5  by the dashed lines. When the toggle is in its first position, an electrical connection is made between the two plates  34  allowing the motor  14  to run. When the toggle  38  is in its second position, the electrical connection between the plates  34  is broken and the flow of electrical current through the switch is prevented. As such, the motor  14  is switched off. A rubber boot  42  connects between the toggle  38  and the body  32  to prevent the ingress of dirt into the body of the switch via the opening in the body  32  through which the toggle  38  projects. 
     During use, a grinding or cutting disks is rigidly attached to the output spindle  18 . The motor is then activated using the toggle switch  30  and the operator manually manipulates angle grinder to use the grinding or cutting disk to grind or cut a work piece. Often the work piece is made from metal such as a metal girder. 
     However, a problem has been found with the operation of existing designs grinder. During use, metal filings generated by the cutting action of the grinder are drawn inside of the housing  2  via the vent  22  of the grinder due to the air flow generated by the fan  60 . Whilst a proportion of these will be subsequently expelled from the housing, a residual amount will collect on internal components located inside of the motor housing  2 . This includes the body  32  and metal plates  34  of the toggle switch  30 . In existing designs of grinder, parts or all of the plates  34  remain exposed. As such, when a sufficient amount of metal filings has congregated on the body  32  and plates  34  of the toggle switch, a short circuit is formed directly between the plates  34 . When electric power is provided to the grinder, the electrical power short circuits the toggle switch by being able to conduct between the plates  34  via the metal filings. This is dangerous for two reasons. Firstly, as soon as electrical power is connected to angle grinder, it will immediately commence to operate with the operator unable to stop its operation without removing the power supply. Secondly, the short circuit can lead to the switch setting fire which, as the motor housing is made of plastic, results in the housing setting on fire. 
     The object of the present invention is to provide an improved design which overcomes or at least reduces the problems associated with existing designs. 
     Accordingly there is provided a power tool comprising: a housing; an electric motor mounted within the housing; an insulated electric wire electrically connected to the motor and which is capable of providing an electric current to the motor; an electric switch connected in series with the wire, the electrical switch comprising a body and at least one electrical terminal plate extending from the body wherein an exposed end of the insulated electric wire is electrically connected to the end of the terminal plate, the exposed end of the wire and the end of the terminal plate being enclosed within an insulating sleeve characterized in that a resilient insulating tube is mounted on and surrounds the terminal plate, the resilient insulating tube being positioned on the terminal plate between the insulating sleeve and the body of the switch to enclose the part of the terminal plate located between the body and the insulating sleeve. 
     Use of an insulating sleeve in isolation has resulted in small parts of the plate between the insulating sleeve and body of the switch remaining exposed due to manufacturing processes and tolerances in component parts. Therefore, the use of an insulating resilient tube in addition to an insulating sleeve ensures that whole of the plate is enclosed. The resilient nature of the tube ensures that any exposed part is enclosed as it expands to fill the gaps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of an existing design of angle grinder; 
         FIG. 2  shows a side view of the angle grinder of  FIG. 1 ; 
         FIG. 3  shows a rear view of the angle grinder of  FIG. 1 ; 
         FIG. 4  shows a side view of a toggle switch; 
         FIG. 5  show the electric circuit of the motor; 
         FIG. 6  shows a side view of a toggle switch in accordance with an embodiment of the present invention; 
         FIG. 7  shows a block of the resilient polyurethane flame retardant sponge material with aperture for a plate; 
         FIG. 8  shows a block of the resilient polyurethane flame retardant sponge material mounted on a plate of the toggle switch; and 
         FIG. 9  shows the plate with the block of the resilient polyurethane flame retardant sponge material attached to an electric wire. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the invention will now be described with reference to  FIGS. 6 to 9 . 
     The toggle switch  30  of the embodiment is mounted within the housing  2  and located within the circuit  36  in the same manner as that described previously. However, the electrical connection between each of the plates  34  of the toggle switch and the exposed ends of the electrical wires  46 ,  47  are encapsulated within an insulating sleeve  50  and an insulating resilient tube  52 . 
     The insulating sleeve  50  is a commercially available sleeve which is used to enclosed exposed parts of electric wires and the ends of the plates  34  to which they are connected. The sheaf can be made of plastic material. Such sheaths may be capable of being shrink fitted by being heated, causing the diameter of the sleeve to reduce thereby causing it to encapsulate the exposed part of the electric wire and sleeve. Alternatively, the sleeve may be a rubber sleeve which may be held in place by being tight fitted over the exposed part of the electric wire. 
     The resilient insulating tube  52  is shown in  FIG. 7  and comprises a block of polyurethane flame retardant sponge material. An aperture  54  is formed through the length of the block to enable the plate  34  of the switch to pass through it. 
     When the toggle switch is being assembled inside the motor housing  2 , each of the plates  34  is inserted into a resilient insulating tube  54  which is slid up against the body  32  of the switch, exposing the end of the plate  34  as shown in  FIG. 8 . The exposed end of the corresponding electric wire  46 ,  47  (and female connector if such a type connection is being used) is passed through an insulating sleeve  50  and then electrically and mechanically connected to the exposed end the plate  34 . The insulating sleeve  50  is then located to enclose the end of the plate  34  and the exposed end of the wire  46 ,  47  and then fixed in place (for example by being shrink wrapped). Due to the resilient nature of the resilient insulating tubes  52 , the resilient insulating tubes  52  enclose the each of the plates  34  between the body  32  of the switch and the insulating sleeve  50  as shown in  FIG. 9 . As such, the whole of the plates are enclosed. Therefore, any metal filings cannot provide a short circuit between the plates  34 . 
     Whilst the present embodiment has been described in relation to an angle grinder, it will be appreciated that the invention could be utilized on any type of power tool.