Patent Publication Number: US-2021178567-A1

Title: Power tools with high-emissivity heat sinks

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/865,417, filed on Jun. 24, 2019, the entire content of which is hereby incorporated by reference. 
    
    
     FIELD 
     Embodiments described herein relate to power tools including heat sinks. 
     BACKGROUND 
     Some power tools include a brushless direct current motor to drive a tool bit to perform work on a workpiece. The motor is driven by a power switching network, such as, for example, an inverter switch bridge, an H-bridge, or the like. The power switching network includes a plurality of transistors (e.g., six field effect transistors [FETs]) that are switched at high-frequencies to drive the motor. These FETs used in the power switching network may generate heat during operation. 
     SUMMARY 
     In certain scenarios, the heat generated by the FETs may damage the FETs or other electrical components in the power tool. To remove the heat generated by the FETs, some power tools include a fan attached to and driven by the motor. The fan generates a cooling air flow within the power tool that may remove some of the heat generated by the FETs. In power tools that drive motors for a prolonged period of time, for example, drills, saws, and the like, the fan may generate sufficient air circulation to dissipate the heat generated by the FETs. In contrast, in power tools that drive motors intermittently for shorter periods of time, for example, nailers and the like, air circulation generated by the fan may not be sufficient to dissipate the excess heat generated by the FETs. 
     In one example, a roofing nailer may be used to complete about 400 actuations at an ambient temperature of 130° F./55° C. The roofing nailer is expected to deliver this performance even at elevated temperatures. However, the motor of the roofing nailer spins for a limited amount of time with an actuation being completed in, for example, under 0.25 seconds. The motor-driven fan generates limited airflow to cool the electronics compared to, for example, a drill. To compensate for the limited airflow, a heat sink may also be used to dissipate heat from the FETs of the power switching network. However, even with a heat sink, the power tool may shutdown in certain scenarios because the tool reaches a predetermined high temperature threshold (e.g., 90° C.). 
     Power tools described herein include a power source, a motor, and a power switching network coupled between the power source and the motor. The power switching network includes a plurality of switches. A heat sink is in a heat-transfer relationship with the plurality of switches. The heat sink includes a high emissivity material having an emissivity of greater than or equal to 0.1. 
     Power tools described herein include a power source, a motor, and a power switching network coupled between the power source and the motor. The power switching network includes a plurality of switches. A heat sink is in a heat-transfer relationship with the plurality of switches. The heat sink includes a high emissivity finish to increase the emissivity of the heat sink. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a power tool in accordance with some embodiments. 
         FIG. 2  is a plan view of the power tool of  FIG. 1 , with the housing removed, illustrating a lifting mechanism. 
         FIG. 3  is a plan view of the power tool of  FIG. 1 , with the housing removed, illustrating an electronics assembly. 
         FIG. 4  is a perspective view of an electronics assembly of a power tool in accordance with some embodiments. 
         FIG. 5  is a perspective view of an electronics assembly of a power tool in accordance with some embodiments. 
         FIG. 6  is a perspective view of an electronics assembly of a power tool in accordance with some embodiments. 
     
    
    
     Before any embodiments are explained in detail, it is to be understood that the embodiments are not limited in its application to the details of the configuration and arrangement of components set forth in the following description or illustrated in the accompanying drawings. The embodiments are capable of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. 
     In addition, it should be understood that embodiments may include hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic-based aspects may be implemented in software (e.g., stored on non-transitory computer-readable medium) executable by one or more processing units, such as a microprocessor and/or application specific integrated circuits (“ASICs”). As such, it should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components, may be utilized to implement the embodiments. For example, “servers,” “computing devices,” “controllers,” “processors,” etc., described in the specification can include one or more processing units, one or more computer-readable medium modules, one or more input/output interfaces, and various connections (e.g., a system bus) connecting the components. 
     Relative terminology, such as, for example, “about,” “approximately,” “substantially,” etc., used in connection with a quantity or condition would be understood by those of ordinary skill to be inclusive of the stated value and has the meaning dictated by the context (e.g., the term includes at least the degree of error associated with the measurement accuracy, tolerances [e.g., manufacturing, assembly, use, etc.] associated with the particular value, etc.). Such terminology should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4”. The relative terminology may refer to plus or minus a percentage (e.g., 1%, 5%, 10%, or more) of an indicated value. 
     It should be understood that although certain drawings illustrate hardware and software located within particular devices, these depictions are for illustrative purposes only. Functionality described herein as being performed by one component may be performed by multiple components in a distributed manner. Likewise, functionality performed by multiple components may be consolidated and performed by a single component. In some embodiments, the illustrated components may be combined or divided into separate software, firmware and/or hardware. For example, instead of being located within and performed by a single electronic processor, logic and processing may be distributed among multiple electronic processors. Regardless of how they are combined or divided, hardware and software components may be located on the same computing device or may be distributed among different computing devices connected by one or more networks or other suitable communication links. Similarly, a component described as performing particular functionality may also perform additional functionality not described herein. For example, a device or structure that is “configured” in a certain way is configured in at least that way but may also be configured in ways that are not explicitly listed. 
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 and 2 , a power tool  10 , for example, a gas spring-powered fastener driver  10  is operable to drive fasteners (e.g., nails) held within a canister magazine  14  into a workpiece. The fastener driver  10  includes a housing  16 , a cylinder  18  positioned within the housing  16 , and a moveable piston  22  positioned within the cylinder  18 . The fastener driver  10  can be powered by a power source, such as, for example, a removable and rechargeable battery pack. The fastener driver  10  further includes a driver blade  26  that is attached to the piston  22  and moveable therewith. The fastener driver  10  does not require an external source of air pressure, but rather includes a storage chamber cylinder  30  of pressurized gas in fluid communication with the cylinder  18 . In the illustrated embodiment, the cylinder  18  and moveable piston  22  are positioned within the storage chamber cylinder  30 . 
     With reference to  FIG. 2 , the cylinder  18  and the driver blade  26  define a driving axis  38 , and during a driving cycle the driver blade  26  and piston  22  are moveable between a ready position (i.e., top dead center) and a driven position (i.e., bottom dead center). The fastener driver  10  further includes a lifting mechanism  42 , which is powered by a motor  46 , and which is operable to move the driver blade  26  from the driven position to the ready position. 
     In operation, the lifting mechanism  42  drives the piston  22  and the driver blade  26  to the ready position by energizing the motor  46 . As the piston  22  and the driver blade  26  are driven to the ready position, the gas above the piston  22  and the gas within the storage chamber cylinder  30  is compressed. Once in the ready position, the piston  22  and the driver blade  26  are held in position until released by user activation of a trigger  44 . When released, the compressed gas above the piston  22  and within the storage chamber cylinder  30  drives the piston  22  and the driver blade  26  to the driven position, thereby driving a fastener into a workpiece. The illustrated fastener driver  10  operates on a gas spring principle utilizing the lifting mechanism  42  and the piston  22  to further compress the gas within the cylinder  18  and the storage chamber cylinder  30 . 
       FIG. 3  illustrates an electronics assembly  50  for driving the motor  46 . As illustrated in  FIGS. 4 and 5 . The electronics assembly  50  includes a printed circuit board (PCB)  54  and a power switching network  58 . The power switching network includes a plurality of switches  62 , such as field effect transistors (FETs), mounted on the PCB  54 . The electronics assembly  50  also includes a heat sink  66  in a heat-transfer relationship with the plurality of FETs  62 . 
     In the example illustrated in  FIGS. 4 and 5 , the heat sink  66  is mounted on the PCB  54  and extends in a direction perpendicular to the PCB  54 . The heat sink  66  is more particularly identified as heat sink  66   a  in  FIG. 4  and heat sink  66   b  in  FIG. 5 . However, heat sink  66  is used to generically refer to both heat sinks  66   a  and  66   b . In the embodiment illustrated in  FIG. 4 , the heat sink  66   a  includes a T-shape such that a horizontal surface  70  is provided parallel to the PCB  54  and a vertical surface  74  extends from the horizontal surface  70  to the PCB  54  in a direction perpendicular to the PCB  54 . In the embodiment illustrated in  FIG. 5 , the heat sink  66   b  includes the vertical surface  74  extending away from the PCB  54  in a direction perpendicular to the PCB  54 , but does not include the horizontal surface  70 . 
     In the examples illustrated in  FIGS. 4 and 5 , the FETs  62  are stand up FETs such that the FETs  62  extend perpendicular to a connection surface of the PCB  54 . Each FET  62  includes a body portion  78 , connection terminals  82  extending from a first side of the body portion  78 , and a mounting portion  86  extending from a second side of the body portion  78 . In the examples illustrated, the connection terminals  82  and the mounting portion  86  are provided on opposite sides of the FET  62 . The plurality of FETs  62  are mounted on the PCB  54  by, for example, soldering the connection terminals  82  to corresponding wire traces on the PCB  54 . The body portion  78  includes, for example, a cuboid shape with two surfaces having a larger surfaces area compared to the other four surfaces. The body portion  78  extends away from the PCB  54  such that the larger surfaces of the body portion  78  are perpendicular to the PCB  54 . 
     The plurality of FETs  62  are also mounted to or in thermal communication with the heat sink  66 . Fasteners  90  are inserted through the mounting portions  86  and secured to the heat sink  66  to mount the plurality of FETs  62  to the heat sink  66 . The plurality of FETs  62  are mounted to the heat sink  66  such that one of the larger surfaces of the body portion  78  is facing and in contact with the vertical surface  74  of the heat sink  66 . Due to this facing relationship (e.g., heat-transfer relationship) between the body portion  78  and the vertical surface  74 , heat generated by the FET  62  during operation is absorbed and dissipated by the heat sink  66 . In the example illustrated, six FETs  62  (e.g., FETs  62  of an inverter bridge of the power tool  10 ) are mounted to the heat sink  66 , with three FETs  62  provided on a first side of the vertical surface  74  and the other three FETs  62  provided in a similar manner on a second side of the vertical surface  74  opposite the first side. 
     In the example illustrated in  FIG. 6 , the FETs  62  are surface mount FETs are mounted directed to the connection surface of the PCB  54 . Each FET  62  includes a body portion  78 , connection terminals  82  extending from a first side and a second side of the body portion  78 . In the examples illustrated, the connection terminals  82  are provided on opposite sides of the FET  62 . The plurality of FETs  62  are surface-mounted on the PCB  54  by, for example, soldering the connection terminals  82  to corresponding wire traces on the PCB  54 . The body portion  78  includes, for example, a cuboid shape with two surfaces having a larger surface area compared to the other four surfaces. The body portion  78  extends horizontally along the PCB  54  such that the larger surfaces of the body portion  78  are parallel to the PCB  54 . The FETs  62  are, for example, SO-8, Copperstrap SO-8, PowerPak, or DirectFET™ marketed and sold by Infineon Technologies. In the example illustrated, a total of twelve FETs  62 , six high-side and six low-side, are mounted to the PCB  54 . 
     In the example illustrated in  FIG. 6 , a first heat sink  66   c  and a second heat sink  66   d  are provided over the FETs  62  ( FIG. 6  illustrates the heat sinks  66   c ,  66   d  exploded away from the PCB  54 ). As described above, “heat sink  66 ” is used to generically refer to both heat sinks  66   c  and  66   d . The first heat sink  66   c  and the second heat sink  66   d  may be mounted to the PCB  54  such that a surface of the first heat sink  66   c  is in thermal communication or a facing relationship (heat-transfer relationship) with the body portion  78  of the high-side FETs  62  and the second heat sink  66   d  is in a facing relationship (heat-transfer relationship) with the body portion  78  of the low-side FETs  62 . The configuration between the PCB  54 , the heat sinks  66   c ,  66   d  and the plurality of FETs  62  is such that a first larger surface of the body portion  78  of the FETs  62  is in a facing relationship with the PCB  54  and a second larger surface of the body portion  78  of the FETs  62  is in a facing relationship (heat-transfer relationship) with one of the heat sinks  66   c ,  66   d . In other embodiments, a single heat sink  66  may be provided in a facing relationship (heat-transfer relationship) with the body portion  78  of all twelve FETs  62 . In some embodiments, the inverter bridge may include six FETs  62  as described above with respect to  FIGS. 4 and 5  above. 
     As described above, the motor  46  may be intermittently actuated for short durations, which results in short durations of air flow generated by the motor-driven fan to cool the plurality of FETs  62 . To increase the heat absorption and dissipation capability of the heat sink  66 , the heat sink  66  may be coated with a material having high emissivity. As used herein, emissivity refers to an emissivity coefficient that indicates the radiation of heat from a material compared with the radiation of heat from an ideal ‘black body’ radiator. For reference, the emissivity of an ideal black body radiator is 1, while the emissivity of polished aluminum is about 0.05. 
     In some embodiments, a material with high emissivity may have an emissivity greater than or equal to 0.1. In some embodiments, a material with high emissivity may have an emissivity greater than or equal to 0.3. In some embodiments, a material with high emissivity may have an emissivity greater than or equal to 0.4. In some embodiments, a material with high emissivity may have an emissivity greater than or equal to 0.5. In some embodiments, a material with high emissivity may have an emissivity over greater than or equal to. In other embodiments, a material with high emissivity may have an emissivity greater than or equal to 0.7. 
     In some embodiments, high emissivity materials, for example, carbon (emissivity=0.81), gold (emissivity=0.47), and the like may be used to coat the heat sink  66 . In one example, the heat sink  66  is coated with an anodized aluminum coating (emissivity=0.85) compared to bare aluminum (emissivity=0.05). In some embodiments, the emissivity of the heat sink  66 , or a material coating the heat sink  66 , is in a range of at least one selected from the group including: between 0.1 and 0.85, between 0.2 and 0.85, between 0.3 and 0.85, between 0.4 and 0.85, between 0.5 and 0.85, between 0.6 and 0.85, and between 0.7 and 0.85. 
     In other embodiments, in addition to or instead of the high emissivity coating, the finish of a heat sink  66  may be varied to increase the emissivity of the heat sink  66 . For example, the heat sink  66  may be finished to have a matte surface, a textured surface, a rough surface or the like may be used in place of heat sinks  66  having polished, shiny, or reflective surface finishes. In some embodiments, a rough surface in combination with a high emissivity coating may be used to further improve the heat absorbing properties of the heat sink  66 . 
     Providing additional heat dissipation as described above provides the advantage of avoiding tool shutdown due to overheating or at least increasing the number of power tool actuations before tool shutdown due to overheating. For example, the number of actuations of the fastener driver  10  may be significantly increased before the fastener driver  10  shuts down due to over-heating compared to a nailer having a similar construction but a lower emissivity heat sink. 
     Thus, various embodiments described herein provide for power tools including heat sinks having high emissivity. Various features and advantages are set forth in the following claims.