Potting boat heat sink

A potting boat adapted to receive a printed circuit board is described. The boning boat includes a base plate and a plurality of sidewalls projecting from the base plate, a plurality of cooling fins, a recessed portion, and an arm. The plurality of cooling fins are formed on one of the sidewalls. The cooling fins extend laterally outward from the one of the sidewalls. The recessed portion is in a first sidewall of the plurality of sidewalls, and extends laterally inward. The arm has a first end fixed to the sidewall and an opposite, second end not connected with the first sidewall. The arm at least partially overlays the recessed portion to define a void within which electrical wires connected to the printed circuit board are retained proximate the first sidewall.

FIELD OF THE INVENTION

The present invention relates to power tools, and more particularly to power tools having potting boat heat sinks.

BACKGROUND OF THE INVENTION

Potting boats are typically used to dissipate heat from printed circuit board assemblies in power tools. Such potting boats are made of thermally conductive material to accumulate heat generated by the electrical components for subsequent discharge from the potting boat.

SUMMARY OF THE INVENTION

The invention provides, in one aspect, a potting boat adapted to receive a printed circuit board. The potting boat comprises a base plate and a plurality of walls projecting from the base plate. The potting boat further comprises a plurality of cooling fins formed on one of the sidewalls, the cooling fins extending laterally outward from the one of the sidewalls. The potting boat further comprises a recessed portion in a first sidewall of the plurality of sidewalls, extending laterally inwardly. The potting boat further comprises an arm having a first end fixed to the first sidewall and an opposite, second end not connected with the first sidewall, the arm at least partially overlying the recessed portion to define a void within which the electrical wires are connected to the printed circuit board are retained proximate the first sidewall.

The invention provides, in another independent aspect, a power tool comprising an electric motor configured to provide torque to a rotating component in the power tool when activated, a printed circuit board including a plurality of heat-generating electrical components, and a potting boat in which the printed circuit board is received. The potting boat comprises a comprises a plurality of cooling fins formed on one of the sidewalls, the cooling fins extending laterally outward from the one of the sidewalls. The potting boat further comprises a recessed portion in a first sidewall of the plurality of sidewalls, extending laterally inwardly. The potting boat further comprises an arm having a first end fixed to the first sidewall and an opposite, second end not connected with the first sidewall, the arm at least partially overlying the recessed portion to define a void within which the electrical wires are connected to the printed circuit board are retained proximate the first sidewall. The electrical wires are routed through the void and over the first sidewall to connect with the printed circuit board.

DETAILED DESCRIPTION

FIG.1schematically illustrates a power tool (e.g., a rotary hammer10) including a brushless DC electric motor14, a gear train34athat receives torque from the motor14to rotate a spindle38, and a reciprocating mechanism34boperable to impact axial impacts to a tool bit (e.g., a drill bit) driven by the spindle38. The rotary hammer10also includes a potting boat18in which a printed circuit board (i.e., PCB22) is positioned and an onboard power source (e.g., a battery pack26). Wires W electrically connect the motor14, the PCB22, and the battery pack26. Field effect transistors (i.e., FETs30) are mounted on the PCB22and are operable to function as an inverter bridge circuit to direct electrical current from the battery pack26to the motor14. During use of the rotary hammer10, the FETs30are rapidly and sequentially switched, which generates heat, to transmit power from the battery pack26to the motor14. The potting boat18is configured as a heat sink to dissipate heat generated by switching of the FETs30.

FIGS.3-9illustrate the potting boat18in detail. With reference toFIG.3, the potting boat18includes a base plate46, which is generally planar and defines a closed end50of the potting boat18. Sidewalls54a-54dproject from the base plate46and terminate in an open end58of the potting boat18. As such, the potting boat18is shaped generally as a cuboid having an open end58. In the illustrated embodiment, there are four sidewalls54a-54d, and each sidewall extends perpendicular from the base plate46to the open end58.

As illustrated inFIG.3, sidewall54aand sidewall54care each provided with cooling fins60on the exterior surface thereof. In other words, the cooling fins60extend laterally outward from the sidewalls54a,54c. The sidewalls54a,54care opposite from each other in the lateral direction. The cooling fins60extend laterally outward from the sidewalls54a,54cbetween the open end58and the closed end50. In the illustrated embodiment, the cooling fins60axially extend the entire height of the potting boat18between the open end58and the closed end50.

As best illustrated inFIG.8, the potting boat18includes rounded corners62between each of the sidewalls54a-54d. The corners62are rounded at the interfaces between each of the sidewalls54a-54din a planar direction parallel with the base plate46.

As illustrated inFIG.3, the potting boat18includes an intermediate surface66extending from the closed end50to an intermediate position between the open end58and the closed end50. The intermediate surface66is in the form of a generally planar plateau that projects from the base plate46towards the open end58. In the illustrated embodiment, the plate46is generally planar to facilitate the flow of potting material beneath the PCB22in directions parallel to the planar plate46. Other embodiments may include another void or a different height intermediate surface66(i.e., separate faces) projecting from the plate46. This may further assist flow of potting material in assembly of the PCB22with the potting boat18. The depth of the plate46is deep enough to provide enough clearance from through-hole components and/or wire solder joints to mitigate electrical shorts between the PCB22, or any terminals or wires extending from the PCB22with the potting boat18. In the illustrated embodiment, the intermediate surface66only extends over a portion of the base plate46such that a portion of the interior depth of the potting boat18extends from the base plate46to the open end58, and another portion of the potting boat18extends from the intermediate surface66to the open end58. The illustrated potting boat18includes a plurality of intermediate surfaces66which are separated (i.e., non-contiguous) from each other. The intermediate surfaces66are also generally planar such that when the PCB22is located within the potting boat18, efficient thermal transfer is achieved between the PCB22and the potting boat18. Finally, as illustrated in at leastFIG.3, the intermediate surfaces66may further include chamfered or rounded edges E to avoid wear or abrasion on the wires extending from the PCB22that may otherwise cause electrical shorts with the potting boat18.

Returning toFIG.8, the sidewalls54a,54bof the potting boat18include respective recessed portions70a,70b. The recessed portion70aof the sidewall54aextends laterally inward from the remaining length of the sidewall54a. The recessed portion70aspans a length L1in a direction between the sidewall54band the sidewall54dand a width W′ in a direction between the sidewall54aand the sidewall54c. The recessed portion70bof the sidewall54bextends inward from the remaining length of the sidewall54b. The recessed portion70bspans a length L2in a direction between the sidewall54aand the sidewall54cand a width W″ in a direction between the sidewall54band the sidewall54c. Each of the recessed portions70a,70bof the potting boat18extend from the open end58to the closed end50.

With continued reference toFIG.8, an arm74(e.g., a cantilevered arm) is located adjacent the recessed portion70aof the sidewall54a. The arm74includes a first end74a(i.e., a fixed end) connected to the sidewall54aand a second end74b(i.e., a free end) opposite the first end74a. The arm74spans between the first end74aand the second end74band has a length L3that is less than the length L1of the recessed portion70aof the sidewall54a. The length L3of the arm74is measured parallel to the sidewalls54a,54cbetween the first end74aand the second end74b. A gap G1extending parallel with the sidewalls54a,54cis defined between the second end74bof the arm74and the recessed portion70a. A gap G2is defined between the arm74and the recessed portion70a. The gap G2extends parallel with the sidewalls54b,54dand opens into a void V defined by a combination of the closed end58, the open end50, the recessed portion70a, and the arm74. In some embodiments of the potting boat14, the arm74has a finger78(FIG.8) at the second end74bthereof. The finger78projects inwardly from the second end74btowards the recessed portion70aand the sidewall54cin a direction parallel with the sidewalls54b,54d. The gap G2is formed as the length L3of the arm74is less than a length L1of the recessed portion70a.

With continued reference toFIG.8, the potting boat18includes holes82. In the illustrated embodiment, the holes82extend through the entire thickness of the base plate46of the potting boat18. As illustrated inFIGS.11and12, the holes82are configured to receive fasteners86(e.g., screws) to secure the PCB22within the potting boat18. The holes82are optionally located at locations corresponding with intermediate surfaces66of the potting boat18. As the intermediate surfaces66are generally planar, when the PCB22is secured to the potting boat18via the fasteners86, any unintended strain imparted to the PCB22(e.g., as a result of the PCB22bending from being mounted to a non-planar surface) via the fasteners86is mitigated. Further, other types of fasteners86besides screws may be employed to secure the PCB22to the potting boat18. For example, other such fasteners may temporarily hold the PCB22against the potting boat18while the PCB22is potted and until the potting material has cured. Such temporary fasteners may provide mechanical support to the electrical components (e.g., the FETs30) of the PCB22during the potting process, until the potting material has cured at which time the cured potting material itself can primarily support the electrical components. The PCB22includes a first surface22a(FIGS.2and10) onto which the FETs30are mounted. The wires W engage (i.e., are soldered or otherwise connected to) the PCB22at the first surface22athereof. The PCB22includes an opposite second surface22b(FIG.2) onto which other electrical components are mounted. The other electrical components may be nested between the intermediate surface66and the base plate46. As illustrated inFIG.1, in the illustrated embodiment, the electrical components (e.g., the FETs30) are mounted upon the first surface22aof the PCB22. The first surface22afaces the open end58of the potting boat18.

As best illustrated inFIGS.2and10, a subset of wires W1extends from the PCB22, project from the open end58of the potting boat18, extend through the void V, and extend beyond the closed end50. Other wires W of the power tool10are connected to the PCB22through the open end58of the potting boat18without passing through the void V.

With continued reference toFIG.10, a combination of the void V, the arm74, and the finger78define a wire guide80through which the wires W1pass and in which the wires W1are retained. As the potting boat18includes the wire guide80, separate elements (e.g., wire ties, etc.) are not required to tether the wires W1together as they pass from the open end58of the potting boat18toward the closed end50. In the power tool10, the wire guide80provides space between the sidewall54aand in interior surface of the outer housing12(FIG.1) of the power tool10through which the wires W1may be routed to connect with electrical components beneath (i.e., beyond the closed end50of) the potting boat18. The arm74is rigid to prevent the wires W1within the wire guide80from being pinched or otherwise damaged in response to an impact on the outer housing12of the power tool10. In other words, the wire guide80nests or secures the wires W1with the potting boat18as they extend from the open end58, through the void V, and beyond the closed end50, thereby circumventing the need for additional guide structure for the wires W1within the power tool10. Additionally, the recessed portion70balso provides space between the sidewall54band the interior surface of the outer housing12of the power tool10through which other wires W may pass or extend through in the same manner as the wire guide80.

The illustrated potting boat18is made using a die cast process. The illustrated potting boat18is made of aluminum, which has relatively high thermal conductivity on the order of around 200 W/m-K, or an aluminum alloy. The high thermal conductivity of the potting boat18increases the rate at which accumulated heat from the PCB22can be transferred away from the PCB22, into the potting boat18, and to the environment via the cooling fins60.

FIG.12illustrates an alternate potting boat18′ for use with the rotary hammer10ofFIG.1. The potting boat18′ generally shares the same features as in the potting boat18. However, the arm74in the potting boat18′ is tapered between the first end74aand the second end74b. In the illustrated embodiment of the potting boat18′, the taper is formed on the interior of the arm74such that the width of the void V increases along the length of the arm74, from the first end74atoward the second end74b. The potting boat18′ does not have a finger78as described above with respect to the potting boat18. Additionally, the potting boat18′ does not have the recessed portion70bon the sidewall54b. The potting boat18′ has the intermediate surface66located at different portions of the base plate46than the potting boat18. The potting boat18′ also has a plurality of intermediate surfaces66which are separated (i.e., non-continuous) from each other. Finally, the cooling fins60of the potting boat18′ have a cross-sectional profile that is scalloped, as opposed to the generally rectangular cross-sectional profile of the cooling fins60of the potting boat18.