Thermally efficient motor housing assembly

A thermally efficient motor housing assembly including a plurality of transistors and a printed wire board (pwb) for controlling a stepper motor and also including a plunger array and a spring array along with a combined heat sink and pwb enclosure.

BACKGROUND OF THE INVENTION

Stepper motors such as described in U.S. Pat. No. 5,369,324 entitled “Electrical Stepper Motor” often contain power transistors within the motor control circuit. Since the power transistors generate heat upon operation of the associated stepper motor, heat sinks are required to prevent the stepper motor and motor control circuit from overheating.

In some electric circuits containing power transistors, a heat sink is attached to the power transistor by means of a spring clip arrangement to insure close contact between the power transistor and the heat sink for efficient heat transfer away from the power transistor, per se. One example of a spring clip arrangement is found in U.S. Pat. No. 5,671,118 entitled “Heat Sink and Retainer for Electronic Integrated Circuits”

When the power transistor is arranged within an electrical enclosure, a heat sink in the form of a metal support plate is arranged on the bottom of the enclosure to allow air flow access to the heat sink. One example of such an arrangement is found in U.S. Pat. No. 6,249,435 entitled “Thermally Efficient Motor Controller Assembly”.

The attachment of the power transistors to the heat sink within an electrical enclosure is complicated when the heat sink is part of the enclosure, per se.

One purpose of the instant invention is to provide an electrical stepper motor enclosure whereby the power transistors employed within the motor control circuit automatically become spring-loaded into contact with a heat sink, which serves as the power transistor enclosure, upon attachment of the enclosure to the stepper motor support housing.

BACKGROUND OF THE INVENTION

Stepper motors such as described in U.S. Pat. No. 5,369,324 entitled “Electrical Stepper Motor” often contain power transistors within the motor control circuit. Since the power transistors generate heat upon operation of the associated stepper motor, heat sinks are required to prevent the stepper motor and motor control circuit from overheating.

In some electric circuits containing power transistors, a heat sink is attached to the power transistor by means of a spring clip arrangement to insure close contact between the power transistor and the heat sink for efficient heat transfer away from the power transistor, per se. One example of a spring clip arrangement is found in U.S. Pat. No. 5,671,118 entitled “Heat Sink and Retainer for Electronic Integrated Circuits”

When the power transistor is arranged within an electrical enclosure, a heat sink in the form of a metal support plate is arranged on the bottom of the enclosure to allow air flow access to the heat sink. One example of such an arrangement is found in U.S. Pat. No. 6,249,435 entitled “Thermally Efficient Motor Controller Assembly”.

The attachment of the power transistors to the heat sink within an electrical enclosure is complicated when the heat sink is part of the enclosure, per se.

One purpose of the instant invention is to provide an electrical stepper motor enclosure whereby the power transistors employed within the motor control circuit automatically become spring-loaded into contact with a heat sink, which serves as the power transistor enclosure, upon attachment of the enclosure to the stepper motor support housing.

SUMMARY OF THE INVENTION

A thermally efficient motor housing assembly including a plurality of transistors and a printed wire board (pwb) for controlling a stepper motor and also including a plunger array and a spring array along with a combined heat sink and pwb enclosure. Attachment of the combined heat sink and pwb enclosure to the motor housing with the plunger and spring array intermediate the the pwb and the motor housing automatically positions the transistors in spring-loaded contact with the heat sink and pwb enclosure to insure thermal transfer between the transistors and the heat sink upon the occurrence of heating caused by the transistors and the environment.

DESCRIPTION OF PREFERRED EMBODIMENT

The thermally efficient motor housing assembly10according to the invention is depicted inFIG. 1and includes a heat sink11, made from a metal having good thermal conductivity such as aluminum, in the shape of a hollow cylinder8with integral cooling fins8A, and a bottom plate9, having an inset9A, for attachment with a motor housing16.

The motor housing is a conventional housing of the type that includes a bottom surface21for attaching a stepper motor (not shown) along with an enclosure22for housing electrical components and connectors (not shown).

The motor housing is adapted to include spring retainer posts17extending from the top surface18thereof.

An array of transistors12, having depending connector pins12A, is positioned under the heat sink11and arranged for connection with the pwb13via first openings13A.

An array of plungers14, in the form of head caps19, which include recesses19A and tapered posts20, is positioned under the pwb13such that the tapered posts align with second openings13B in the pwb for contacting the transistors12in the manner to be described below in greater detail.

An array of compression springs15is positioned intermediate the plungers14and the motor housing16such that the springs15align with the recesses19A in the head caps19and the posts17extending upward from the top18of the motor housing16.

Once the transistors12are attached to the pwb13, the heat sink11is then moved in the down-ward indicated direction for connection with the motor housing16.

During the assembly of the heat sink to the motor housing; the inset9A within the bottom9of the heat sink11contacts the transistors12on the pwb13and moves the pwb into contact with the plungers14such that the tapered posts20pass thru the second openings13B and into contact with the transistors12to force the transistors into contact with the inset9A on the bottom plate9of the heat sink11.

The springs15become captured within the recesses19A formed in the ends of head caps19, and positioned over the posts17extending from the top18of the motor housing16.

The heat sink11is then fixedly attached to the motor housing16by means of metal fasteners (not shown).

The arrangement between the heat sink11and motor housing16within the completed thermally efficient motor housing assembly10of the invention is best seen by now referring toFIG. 2.

The positioning of the springs15over the posts17, extending from the top surface18of the motor housing16, and the capture of the springs within head caps19of plungers14fixedly holds the tapered posts20against the transistors12via second openings13B in the pwb13to force the transistors into good thermal contact with the inset9A on bottom plate9of the heat sink11under a wide range of operating temperatures.

A thermally efficient motor housing assembly wherein the power transistors on the motor control pwb are held in good thermal contact with the associated heat sink has herein been described. Although the invention has been described for use with electric motors, it is understood that other types of electrical equipment utilizing heat sinks, power transistors and pwbs can also be employed.