Abstract:
A power tool includes a housing having a front portion and a handle portion. The front portion defines a cavity that encloses a motor and includes a gripping portion surrounding the cavity. An insulating cover is provided on the gripping portion of the housing and includes a gripping surface. A thermoelectric cooling unit is located between the gripping portion of the housing and the insulating cover. The thermoelectric cooling unit has a cold side positioned in thermal contact with an inner surface of the insulating cover and a hot side positioned in contact with an outer surface of the gripping portion of the housing. The thermoelectric cooling unit is configured to absorb thermal energy from the insulating cover via the cold side of the thermoelectric cooling unit and to release the absorbed heat via the hot side of the thermoelectric cooling unit.

Description:
TECHNICAL FIELD 
       [0001]    The disclosure relates generally to power tools, and, in particular, to systems and methods for cooling gripping surfaces of power tools. 
       BACKGROUND 
       [0002]    During operation, the motors and drive assemblies of power tools generate heat within the housing which can be transmitted to the user via the gripping surfaces of the tool. Heating is a concern particularly with power tools which utilize portions of the motor housing of the tool as a gripping region for the operator. For example, reciprocating saws typically utilize the front portion of the housing as a gripping region for an operator of the tool to use to stabilize the tool with one hand while the other hand holds the handle at the rear portion of the housing. The front gripping portion is located around and essentially directly over the motor and drive system of the reciprocating saw. As a result, the front gripping surface is exposed to a high level of heat during operation of the tool. 
         [0003]    Power tools are often provided with features that are designed to minimize the amount of heat that an operator of the tool may be exposed to during operations. For example, the gripping surfaces of power tools, such as reciprocating saws, are often provided with an insulating covering or boot formed of rubber or urethane which can absorb heat to a certain degree and lessen their impact on the operator of the tool. To further facilitate cooling, some insulating boots are provided with ribs on the inner surface that define air flow channels between the insulating boot and the outer surface of the tool housing. The air flow through the channels cools the outer surface of the housing which in turn helps to keep the insulating boot cooler than it would be otherwise. 
         [0004]    However, an insulating boot, with or without air flow channels, is only capable of cooling to the extent that an increase in temperature of the gripping surface is prevented or limited by dissipating heat from and/or minimizing heat transference to the gripping surface. A reduction in temperature of the gripping surface relative to ambient temperature is generally not possible using these methods. What is needed is a method or system for a power tool that enables active cooling of the gripping surfaces in a simple and inexpensive manner. 
     
    
     
       DRAWINGS 
         [0005]      FIG. 1  is a side view of an embodiment of a power tool having a thermoelectric cooling system for active cooling of a gripping surface of the tool in accordance with the disclosure. 
           [0006]      FIG. 2  is a side view of the preferred embodiment of the wobble plate assembly shown in  FIG. 1  with portions removed to illustrate interior construction. 
           [0007]      FIG. 3  is a schematic view of a thermoelectric cooling unit incorporated into the power tool of  FIGS. 1 and 2 . 
           [0008]      FIG. 4  is a schematic illustration of the thermoelectric cooling unit of  FIG. 3   
       
    
    
     DETAILED DESCRIPTION 
       [0009]    For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to a person of ordinary skill in the art to which this disclosure pertains. 
         [0010]    An embodiment of a power tool  10  including a cooling system in accordance with the present disclosure is depicted in  FIGS. 1 and 2 . The power tool  10  includes a gear housing  12  having a nose portion  14  and a handle portion  16 . The housing  12  is typically formed of metal, such as die cast aluminum, although any suitable material(s) may be used. A motor  20  and a drive assembly  40  is enclosed in the housing  12 . The motor  20  comprises an electric motor having an output shaft  34  that is configured to be rotated by the motor. The drive assembly  40  includes a tool holder  26  that is configured to retain a working tool  24  that extends from the nose portion  14  of the housing. 
         [0011]    Power to the motor  20  is controlled by a trigger switch  18  provided on the handle portion  16  of the housing  12 . In one embodiment, the power tool is configured to be powered by a rechargeable battery (not shown), such as a rechargeable lithium-ion battery, which can be connected to the handle portion of the housing. Alternatively, the power tool may be configured to receive power from an external power source, such as an AC outlet, via a power cord (not shown). 
         [0012]    The drive assembly  40  is coupled to the output shaft  34  and is configured to convert the rotational motion of the output shaft  34  into an appropriate drive motion for driving a working tool  24 . In one embodiment, the power tool  10  comprises a reciprocating saw. In this embodiment, the drive assembly comprises a plunger  28  that is slideable in front and rear bushing assemblies  30 ,  32 , respectively. A pinion gear  36  is mounted on the output shaft  34  that engages a larger gear  38  that is connected to a reciprocating drive assembly in the form of a wobble plate assembly, for example. The wobble plate assembly drives the plunger  28  in a reciprocating manner as the gear  38  drives the wobble plate assembly. The tool holder  26  is provided on the end portion of the plunger  28  located externally with respect to the nose portion  14  of the housing. The tool holder  26  is configured to retain a cutting blade  24  in alignment with the reciprocating axis. A shoe  22  is attached to the nose portion of the housing. The shoe  22  provides a surface that can be positioned in contact with a work piece to guide movement and control the depth of the blade while making cuts. 
         [0013]    During operation, the motor and drive assembly of the tool generate heat and vibrations within the housing which can be transmitted to the user via the gripping surfaces of the tool. The reciprocating power tool includes two primary gripping surfaces. One gripping surface is on the handle where the trigger switch is located. The other gripping surface is provided on the front portion of the housing. As can be seen in  FIG. 1 , the front portion of the housing is flared outwardly to provide an ergonomic shape for a user to grasp. The handle portion and the front portion of the housing may each be provided with a rubber covering as can be seen in  FIG. 1 . 
         [0014]    To minimize the transference of heat and vibrations to an operator, at least the front gripping region is provided with an insulating covering or boot  42  formed of rubber or urethane which can absorb heat and vibrations to a certain degree and lessen their impact on the operator of the tool. To further facilitate cooling in the front gripping portion, a thermoelectric cooling system  50  is incorporated into the rubber boot to provide active cooling of the gripping surface. As used herein, “active cooling” refers to the ability of the cooling system to cool the gripping surface to below ambient temperatures. 
         [0015]    Referring to  FIGS. 3 and 4 , the thermoelectric cooling system  50  includes a thermoelectric cooling unit  52  and a heat sink  54 . The thermoelectric cooling unit  52  comprises a pair of thermally conductive plates  56 ,  58 , such as ceramic plates, having two dissimilar semi-conductors  60 ,  62  arranged therebetween. The two dissimilar conductors  60 ,  62  may be n-type and p-type conductive elements which are connected electrically in series and thermally in parallel. The thermoelectric cooling unit  52  is configured to receive a DC current via wiring conductors  64  which are coupled to a power source  66 , such as the internal electronics of the tool. Alternatively, power to the cooling unit may be provided by a separate battery or batteries which may be incorporated into the device and supported within the rubber boot. 
         [0016]    To activate cooling, a voltage is applied to the free ends of the two different conducting materials, resulting in a flow of current through the two semiconductors  60 ,  62  in series. The cooling unit  52  may be connected such that the voltage is applied to the cooling unit  52  whenever the motor is operating so that cooling is provided at all times. In alternative embodiments, the cooling system may include a switch (not shown) that enables the cooling system to be activated and deactivated as needed. In some embodiments, the cooling system may include a switch or a controller to control electronics to maintain the setting. 
         [0017]    When activated, the flow of DC current across the junction of the two semi-conductors  60 ,  62  creates a temperature difference. As a result of the temperature difference, Peltier cooling causes heat to be absorbed into the device from one side, i.e., the “cold” side, and moved to the other side, i.e., the “hot” side. Referring to  FIG. 4 , the cold side  68  of the thermoelectric cooling unit  52  is positioned in thermal contact with the interior of the rubber boot  42  while the hot side  70  of the thermoelectric cooling unit  52  is positioned in thermal contact with the outer surface  72  of the housing  12 . As a result, the thermoelectric cooling unit  52  causes a temperature difference that results in heat being absorbed from the rubber boot  42  on the cold side  68  and transferred to the hot side  70  of the thermoelectric cooling unit  52 . In some embodiments, the cold side  68  of the thermoelectric cooling unit  52  is positioned in thermal contact with the interior of the rubber boot  42  while the hot side  70  of the thermoelectric cooling unit  52  is positioned in thermal contact with an inner surface of the housing  12 . 
         [0018]    To help dissipate heat absorbed into the thermoelectric cooling unit  52 , the hot side  70  of the cooling unit is thermally coupled to a heat sink  74  which releases heat from the thermoelectric cooling unit  52  so that that the hot side of the thermoelectric cooling unit  52  remains at ambient temperature, while the cool side goes below ambient temperature (i.e., active cooling). The thermoelectric cooling unit  52  is positioned preferably (although not necessarily) under the location where a user&#39;s hands are likely to be located. The heat sink  74  is preferably located outside of the gripping region  76  so that the released heat is not reabsorbed by the rubber boot  42  and/or so the released heat does not adversely impact the operation of the thermoelectric cooling unit  52 . 
         [0019]    As depicted in  FIGS. 3 and 4 , the heat sink  74  may be located remotely from the thermoelectric cooling unit  52 , and thermal conductors  78 , such as heat pipes, may be used to conduct heat from the thermoelectric cooling unit  52  to the heat sink  74 . In one embodiment, the heat sink  74  is located inside the housing  12  in the internal air stream  80  generated by the motor fan  82  ( FIG. 2 ). For example, the housing may include air flow channels  84  which are located inside the housing  12  which are configured to direct a cooling air flow  80  from the motor fan  82  over the drive components in the housing. The heat sink  74  can be mounted in a position where the heat transported from the TEC can be released in the air flow generated by the motor fan. Any suitable type of heat pipe  78  may be used to conduct heat from the thermoelectric cooling unit  52  to the heat sink  74 . 
         [0020]    The cooling system  50  may be incorporated onto the power tool in any suitable manner. In one embodiment, the components of the thermoelectric cooling system  50  may be embedded into the interior portion of the insulating boot  42 . Alternatively, the cooling system  50  components may be installed on the housing  12  of the tool prior to the placement of the insulating boot  42 . 
         [0021]    Although not depicted in the drawings, thermoelectric coolers may be used in other locations on the tool such as in the rear handle portion  16 . In addition, although the thermoelectric cooling system has been described in conjunction with a reciprocating saw, thermoelectric coolers may be used for active cooling of the gripping surfaces of any tool. 
         [0022]    While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.