WO2005077017A2

WO2005077017A2 - Improved brush card apparatus and method

Info

Publication number: WO2005077017A2
Application number: PCT/US2005/003906
Authority: WO
Inventors: Robert Alan Colwell
Original assignee: Motor Products Corporation
Priority date: 2004-02-06
Filing date: 2005-02-07
Publication date: 2005-08-25
Also published as: WO2005077017A3

Abstract

A brush card (10) for a DC motor is molded around a lead frame system (16) and includes integral brush card holders (12) and a connector housing (14). Gaskets are molded to the upper and lower peripheries of the brush card and provide interfaces between the brush card and the housing and the end-frame casting (30), respectively, of the motor. There is no direct mechanical connection between the brush card and the housing or the end-frame casting (30) to thereby provide for some resiliency reducing the transmission of brush card vibrations to the motor shell (28) and end frame (30). A portion of the lead frame system (16) extends above the molded plastic for directly attaching a bimetallic circuit breaker (26) to the lead frame (16). A contact (36) for the contact attached to the bimetallic blade (34) of the circuit breaker (26) is attached to the lead frame system before the plastic is molded around it. A capacitor (20) is attached to the lead frame system in an area proximate to the connector housing to increase the filtering effectiveness of the capacitor.

Description

IMPROVED BRUSH CARD APPARATUS AND METHOD

TECHNICAL FIELD

The present invention relates to permanent magnet DC brush motors, and more particularly, to brush cards used in such motors.

BACKGROUND OF THE INVENTION Insert molding, integral connectors, and molded-in-place gaskets are common knowledge in the permanent magnet DC brush motor industry, and molded plastic brush cards with integral brush tubes are also commonly used. In the past the brush cards have generally been encased and staked in a metal casting and a separate circuit breaker assembly mounted onto the brush card. The placement of the brush card in the casting and the staking of the brush card to the casting results in a direct mechanical fastening of the brush card to the motor housing providing an unimpeded path for the vibrations generated in the brush card to be passed to the motor housing. It can therefore be appreciated that a brush card which provides some mechanical isolation between the brush card and the motor housing, and in which a separate circuit breaker assembly can be eliminated is highly desirable. SUMMARY OF THE INVENTION Briefly described is a molded plastic brush card for use in DC permanent magnet brush motors having an integral circuit breaker. Also described is the utilization of gaskets formed on the brush card to both seal the motor and to resiliently mount the brush card thereby providing sound and vibration damping. Further described is a brush card assembly incorporating the particular combination of features presented below.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become appreciated and be more readily understood by reference to the following detailed description in conjunction with the accompanying drawings, wherein: Fig. 1 is a perspective top view of the improved brush card of the present invention; Fig. 2 is a perspective bottom view of the brush card assembly of the present invention; Fig. 3 is a perspective exploded side view of the brush card, shell, & end frame; Fig. 4 is a perspective bottom view of the assembled position of brush card, end-frame, & shell of Fig. 3; Fig. 5 is a perspective top view of the brass conductor system used in the brush card of Fig. 1; Fig. 6 is a perspective top view of the plastic molded around brass conductor system of Fig. 5; Fig. 7 is a perspective bottom view of a portion of the brush card of Fig.

1 ; Fig. 8 is a perspective top view of the circuit breaker blade shown in Fig. 1 ; Fig. 9 is a perspective top view of the brush attachment of the brush card of Fig. 1 ; Fig. 10 is a perspective top view of capacitor attachment of the brush card of Fig. 1 ; Fig. 11 is a perspective top view of the spring and retainer assembly together with the brush card of Fig. 1 ; and Fig. 12 is a perspective side view of a portion of the brush card of Fig. 1 showing the circuit breaker blade and contact. It will be appreciated that for purposes of clarity and where deemed appropriate, reference numerals have been repeated in the figures to indicate corresponding features, and that the various elements in the drawings have not necessarily been drawn to scale in order to better show the features of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The improved brush card of the present invention comprises a novel brush card design, wherein the cost associated with brush card assembly is reduced. Following is a description and drawings of this novel apparatus and method. As illustrated in Figs. 1 and 2, the novel apparatus of the present invention comprises brush card 10 constructed of molded plastic with brush tubes 12 and a connector housing 14 molded as an integral part of the card. The embodiment further comprises a brass conductor system 16 (shown in Fig. 5) wherein the brass conductor system 16 is molded inside the brush card 10. The leads of the brushes 18 and RFI capacitor 20 may be connected to the brass conductor system 16 by soldering, resistance welding, ultrasonic welding, or crimping. Furthermore, injection-moldable elastomeric gaskets 22 and 24 are molded in place as illustrated. Additionally, the brush card of the present invention further comprises a circuit breaker 26 that is attached directly to the brass conductor system 16. An additional feature of the present invention is that the brush card 10 may be assembled into the motor without direct mechanical fastening. However, the brush card may also be attached to the motor by any suitable method, such as, riveting, screwing, or staking. Referring now to Figs. 3 and 4, the brush card 10 is positioned between the motor shell 28 and end-frame casting 30. The brush card 10 is placed into the end-frame casting 30, and is held in place radially by a thin wall feature of the end-plate casting 30 that extends part way up the side of the brush card. One of the brush card gasket surfaces seals against the casting, and another gasket surface extends axially slightly beyond the thin wall feature of the casting so as to be compressed by the motor shell when the motor is assembled. This compression of the gaskets forms a seal and holds the brush card securely in position. Additionally, the assembly allows for some resiliency thereby reducing the transmission of brush card vibrations to the motor shell and end frame. Furthermore, the brush card of the present invention is an insert- molded design. The first step in the manufacturing process is to stamp and form a brass conductor system 16, such as the one shown in Fig. 5. An electrical contact 32 is attached to the brass conductor system for later use as part of a circuit breaker. The second step in the process is to place the brass conductors in a mold and to mold plastic around the conductors. In a particular embodiment of the invention, the brush tubes and a connector housing are molded as integral parts of the plastic card as shown in Fig. 6. The electrical contact 32 and certain areas of the brass conductors are left exposed for later attachment of components. The next step is to place the plastic card into another mold and to injection mold gaskets. The gasket material may be an injection-moldable elastomer. Fig. 7 shows a particular configuration for these gaskets. As shown in Fig. 8, the circuit breaker 26 assembly comprises a current-carrying bi-metal blade 34 that is stamped and formed in such a way so as to "snap" from a concave shape to a convex shape at a temperature slightly below the safe thermal limits of the motor components. An electrical contact 36 may be welded or riveted to the blade. Furthermore, the blade 34 may be attached to the brass conductor system by welding or riveting. Additionally, the blade is positioned so the electrical contact 36 on the blade is centered, and in contact with the electrical contact 32 attached to the brass conductor system 16 as shown in Fig. 12. In operation, the current flowing to the motor goes through the circuit breaker blade 34 and contacts 32 and 36. In the case of abnormally high operating conditions or motor overload conditions, the blade 34 snaps and the two electrical contacts 32 and 36 are pulled apart, opening the electric circuit and stopping current flow to the motor, protecting it from thermal damage. When the blade 34 cools, it snaps back to the original operating position and automatically re-energizes the motor. As shown in Figs. 9 and 10, the motor brushes 18 are attached to the card at two points 38 where the brass conductors were left exposed. These connections may be made by welding, crimping, or soldering. For applications requiring RFI suppression, capacitor 20 is attached at two additional points 40 to the card, also by welding, crimping, or soldering. In a particular embodiment of the present invention, the RFI filter capacitor 20 is placed as near the point where the power conductors exit the motor shell as possible. Keeping the capacitor leads as short as possible serves to increase the filtering effectiveness of the capacitor. The capacitor is placed adjacent to the connector housing 14 and attached to the brass conductor system 16 by welding, crimping, or soldering. In the assembled motor of Fig. 4, the brushes 18 are held against the commutator by spring pressure. As illustrated in Fig. 11 , brush springs 42 are inserted into the brush tubes 12 so as to press against the back of the brush 18. In this configuration, a plastic cap 44 snaps into place on the end of the brush tube 12 and retains the spring 42. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, the foregoing description is to be considered exemplary, rather than limiting.

Claims

CLAIMS:

I claim: 1. A brush card for use in a DC motor, wherein said brush card comprises a molded plastic body having brush tubes and a connector housing molded as an integral part of the plastic body.

2. The brush card of claim 1 , further comprising at least one gasket for sealing said brush card within said DC motor.

3. The brush card of claim 1 , further comprising a brass conductor system wherein said brass conductor system is molded substantially inside said plastic body.

4. The brush card of claim 3 further comprising a circuit breaker having a bi-metal blade that is attached directly to said brass conductor system.

5. The brush card of claim 3 further including a capacitor attached to said lead frame system and located proximate to said connector housing.

6. An electric motor comprising: a) a metallic housing; b) a metallic end frame; c) a molded plastic brush card having upper and lower gaskets molded thereto, wherein said metallic housing engages said upper gasket and said metallic end frame engages said lower gasket such that there is no direct mechanical attachment between said metallic housing and said brush card, and between said brush card and said metallic end frame.

7. The electric motor of claim 6 wherein said molded plastic brush card includes a molded connector housing.

8. The electric motor of claim 6 further comprises a brass conductor system wherein said brass conductor system is molded substantially inside said plastic body.

9. The electric motor of claim 8 further comprising a circuit breaker having a bi-metal blade that is attached directly to said brass conductor system.

10. The electric motor of claim 6 further including a capacitor attached to said lead frame system and located proximate to said connector housing.

11. A method for making an electric motor comprising the steps of: a) making a brush card comprising the steps of: i) Molding a plastic body around a metallic lead frame while leaving exposed a plurality of predetermined areas of said lead frame; ii) molding a first and second gasket to said plastic body; iii) inserting brushes into brush holders formed in said plastic body; iv) adding means to said brush holders for urging said brushes toward a center opening in said plastic body; v) forming an electrical contact between each of said brushes and said lead frame; b) placing a rotor through said center opening of said plastic body; c) placing an metallic housing onto said first gasket and placing a metallic end frame onto said second gasket without forming a direct mechanically attachment between said metallic housing and said brush card and between said brush card and said metallic end frame.

12. The method of claim 11 further including attaching a blade of a circuit breaker to said lead frame.

13. The method of claim 11 further including attaching a capacitor to said lead frame proximate to a region of said lead frame that physically connects to electrical connections to said motor.

14. The method of claim 11 wherein a metallic contact is attached to said lead frame before said plastic body is molded to said lead frame.

15. The method of claim 11 wherein said molding step includes molding a connector housing.