BRUSH HOLDER FOR AN ELECTRIC MOTOR

Abstract: A unitary bifurcated brush holder (52) for a small electric motor (10), has a pair of spaced coplanar terminal tabs (134, 136). The tabs are laterally offset from the brush holder sleeve (110), and extend axially of the motor for direct plug-in engagement with terminals (38) at the commutator end (12) of a stator assembly (24). The brush holder (50) is made from a single sheet metal stamping. The terminal tabs (134, 136) are carried at the end of a support arm (114) extending from a wall (122) of the brush holder sleeve (110). In assembly, the brush holder is mounted in an insulator (50) which includes support bosses (92, 94) for engaging and augmenting the support of the rear end of the terminal tabs.

Description: BACKGROUND OF THE INVENTION The invention concerns brush holders and brush holder subassemblies and their electrical connection, particularly for small motors of the type typically used in portable tools and domestic appliances. Given the high production volumes and strong competition in the portable tool and appliance markets, economical design is essential for profitability. Design efforts to simplify and eliminate parts and to facilitate automation of assembly are potentially very rewarding. Brush holder design and arrangement, the subject matter of the present invention, has been included in these cost saving design activities. For example, U.S. Patents 4,613,781-Sanders, and 4,498,230-Hayes, sharing a common assignee with the present invention, both disclose brush holders of simple rectangular shape formed from a stamped flat pattern of sheet material and including an integral terminal for direct plug-in connection of the brush holder to other motor elements. U.S. Patent 4,056,749-Carlson discloses a brush holder of similar construction supported by a motor end bracket and oriented so that in assembly the brush terminal, extending axially, may be inserted directly into a fixed terminal of a terminal board on an end of the stator assembly of the motor. Electrical connection from a field winding to the brush is thus completed without the need for a jumper or additional terminals, simplifying assembly and facilitating its automation. In the known simple formed sheet metal brush holder designs it is typical for the single terminal to be "close coupled" to the sleeve of the brush holder and, for strength and stability reasons, to be of limited length. The simple form of these brush holder designs largely predetermines and limits the disposition of the terminal relative to the brush holder sleeve and also its reach from the sleeve. This, in turn, limits the adaptability of the design concept in motor configurations where direct plug-in connection of brush to field, by way of the brush holder, is desired and the axial spacing between field and brush is relatively great. And they are not, for example, obviously adaptable to more complex motors which may require two connections to each brush, for example in a dynamically braked motor using a dedicated secondary winding for the braking mode. SUMMARY OF THE INVENTION According to one aspect of the invention, there is provided a brush holder subassembly for an electric motor, the motor having an axis of rotation and including a motor housing and field coils, comprising: an insulator including a body having a through bore and a support element disposed externally of the body; and a brush holder of conductive material, including a sleeve portion for slidably receiving a brush, housed in fixed position in the bore of the insulator body, and an elongated terminal portion fixedly connected to the sleeve portion, disposed externally of the insulator body and extending perpendicular to the longitudinal axis of the insulator body bore and including a free connecting end for electrical connection to the field coils, and an opposite support end for engaging the support element of the insulator to stabilize the terminal portion relative to the sleeve portion. The brush holder terminal portion preferably extends parallel to the axis of rotation of the motor and preferably includes two spaced terminal tabs extending perpendicular to the longitudinal axis of the insulator body. The brush holder is preferably formed from a single piece of sheet material. The brush holder preferably includes an elongated support member extending through a slot in the insulator body for connecting the brush holder sleeve portion to the terminal portion. The insulator may include a guide surface extending perpendicular to the longitudinal axis of the insulator bore for engaging and at least partially fixing the brush holder subassembly in the housing. A portion of the insulator body is preferably interposed between the brush holder sleeve and the terminal portion. The support element of the insulator is preferably contoured at a plane perpendicular to the axis of the insulator body bore. The terminal portion support end may include a mating contour for supportively engaging the insulator support element. The insulator preferably includes a second support element. Each terminal tab is substantially independently stabilized by the support elements. The engagement of the terminal portion with the support elements preferably supports the terminal portion in mutually opposing directions in a plane perpendicular to the axis of the bore of the insulator body. In accordance with a second aspect of the invention, there is provided: an elongated sleeve for slidably receiving a brush, the sleeve having walls and a longitudinal axis; a first elongated terminal tab having a free connecting end and an opposite support end spaced from the sleeve walls and offset with respect to the sleeve axis and extending in a plane perpendicular to the sleeve axis; and a support arm for carrying the terminal tab, cantilevered from one of the sleeve walls to the support end of the terminal tab. The brush holder preferably includes a second elongated terminal tab extending parallel to and spaced from the first tab. The second tab is carried by the support arm. The support arm preferably includes a transversely extending bridging strip having opposite ends. Each of the tabs is respectively carried by the bridging strip adjacent one of its ends. Preferably the brush holder is formed from a single sheet of material having, when flat, a substantially rectangular shape. Substantially, all of the material of the rectangular shape is used to form the brush holder. The rectangular shape of the piece of sheet material may comprise two side-by-side substantially rectangular portions. One portion is for forming the sleeve portion and the other portion is for forming the terminal portion. In accordance with a third aspect of the invention, there is provided a small electric motor for use in portable tools and appliances characterized by: an armature having a commutator; a stator substantially enclosing the armature and including a plurality of field windings and having opposite ends including a commutator end adjacent the commutator; at least one pair of spaced apart terminals carried by the stator commutator end, and facing axially outwards with respect to the stator commutator end, and connected electrically to the field windings; a pair of diametrically opposed radially extending brushes, for maintaining electrical contact with the commutator; and a unitary brush holder having a sleeve for slidably supporting one of the brushes and including a pair of axially extending terminal tabs registering with the terminal elements of the stator to directly electrically connect the brush holder with the field windings and complete electrical connection between the armature and the field windings. Preferably the brush holder terminal tabs are coplanar in a plane perpendicular to the axis of the brush holder sleeve. The motor preferably further includes a second brush holder having a pair of terminal tabs engaged in a second pair of terminal elemants on the commentator end of the stator for making electrical connect between the armature and field windings. The field windings are preferably electrically split into at least two field winding portions. The armature is preferably connected in series with the field winding portions and between at least one pair of the field winding portions. The electrical connection is maintained by the combination of the brush holders and brushes. The field windings may further include run winding and brake winding portions for running and dynamically braking the motor respectively. Preferably both the run and brake windings are electrically split with respect to the armature. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial, cut away, partially sectioned view of the commutator end of the drive motor portion of a power tool embodying the invention. Fig. 2 is a composite view including a semi-schematic representation of a portion of the commutator end of the stator assembly of the tool of Fig. 1 shown in conjunction with the corresponding brush holder subassembly, aligned for electrical connection with the stator. Fig. 3 is a partial end view of the commutator end of the stator assembly taken approximately on line 3-3 of Fig. 2. Fig. 4 is a radially outside view of the brush holder subassembly with the brush assembly and retaining cap removed taken approximately on line 4-4 of Fig. 2. Fig. 5 shows the sheet metal stamping (flat pattern) used to form the brush holder included in Figs. 2, 4 and 6-9. Fig. 6 is a radially outside view of the brush holder corresponding to the view of Fig. 4. Fig. 7 is a side view of the brush holder corresponding to the view of Fig. 2. Fig. 8 is a front view of the brush holder taken approximately on line 8-8 of Fig. 7. Fig. 9 is a cross-sectional view of the sleeve portion of the brush holder, taken on line 9-9 of Fig. 8. Fig. 10 is a side view similar to Fig. 7 of an alternative embodiment of the brush holder portion of the invention. Fig. 11 is a cross-sectional view of the sleeve portion of the second embodiment taken on line 11-11 of Fig. 10. Fig. 12 is a wiring schematic for a dynamically braked series wound universal motor which may be used in the motor portion of the tool of Fig. 1. DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is embodied in a power tool such as a circular saw, a part of the drive motor portion 10 of which is shown in Fig. 1. The motor may be of the series wound universal type. The principal components and general arrangement of such motors are well known and need to be only briefly described. Fig. 1 shows the commutator end 12 of the motor including a portion of the armature 14 with its commutator 16 journaled in bearing 18. An end cap 20 registers with motor housing 22 which houses the stator assembly 24 shown only partially and only in Figs. 2 and 3. Contained between the end cap 20 and the stator assembly 24 are a pair of diametrically opposite brush holder subassemblies 26, partially held in place by resilient bolsters 28 carried by the end cap 20. The brush holder subassemblies 26 are an important part of the invention and will be described in more detail below. The stator assembly 24 (Figs. 2 and 3) is of known design including a laminated core 30 with pole pieces 32 carrying field coils 34. The commutator end of the stator assembly, shown in Figs 2 and 3, includes a plastic end ring or terminal board 36 which carries two diametrically opposite pairs of terminal posts 38 (only one pair is shown in the drawings). Each terminal post 38 has an axially extending bore (not shown in detail in the drawings). Each pair of terminal posts 38 is coplanar in a plane parallel to the axis of the motor armature and each post lies at an equal radial distance from the armature axis. The individual windings of the field coils 34 are terminated by crimping winding end leads 42 into terminals 44, which are inserted into the terminal post 38 (as seen best in Fig. 2). Turning now to the brush holder subassembly 26 and referring particularly to Figs. 2 and 4 - the two brush holder subassemblies 26 used in the embodiment of Fig. 1 are identical and only one is shown in detail in the drawings and need to described. Insulator 50, made of suitable plastic material for example, is in effect a vehicle for the electrically conductive brush holder 52. The generally conventional brush assembly 54 includes a rectangular cross section brush 56 which is free to slide radially in the brush holder 52 and is biased against the commutator 16 by a helical spring 58. Good electrical connection between the brush 56 and the brush holder 52 is ensured by a shunt 60 connecting the brush 56 to a connection disc 62 which is clamped securely against an end of the brush holder 52 by a screw threaded retaining cap 64 (shown only in Fig. 2). The insulator 50 has a semi-cylindrical body 70 with a through bore 72. The radially outward end of the bore 72 is enlarged to form a threaded well 74 (with a flat bottom 75) for receiving the retaining cap 64. The lower portion of the flat front face 76 of the body 70 contains a radially extending (with reference to the armature 16) central slot 78, indicated only in Fig. 2. The respective radially inner and outer end faces 80, 82 of the body 70 are substantially planar. A substantially rectangular guide flange 84 insert somewhat from the inner end face 80 has parallel inner and outer faces 86, 88 respectively, each perpendicular to the radially extending axis of the brush holder assembly. A symmetrically arranged pair of support elements 90, 92 extend forward from the flange 84. As seen best in Fig. 4 each support element is contoured to define a support boss 94, 96 spaced from the flange 84 by stem portions 98, 100. Details of the brush holder 52 are seen best in Figs. 5-9. The main elements of the brush holder are a sleeve or body portion 110, a terminal portion (terminal pair) 112 connected to the sleeve 110 by an angled support arm 114, the latter being stiffened by a central rib 116. In assembly, the support arm 114 emerges from the slot 78 of the insulator body 70. The cross section of the body 110 is essentially rectangular to match the conventional brush 56 and is formed of opposite side walls 118, 120, a front wall 122 and a rear wall 124. However, to accommodate the cylindrical form of the helical compression spring 58 in the radially outward portion of the sleeve, the sleeve form is modified to be partially cylindrical - see arcuate wall portions 126, 128 seen best in Fig. 9. The sleeve portion 110 is located axially in the bore 72 of the insulator body 70 by retaining lugs. At the radially inner end conventional lugs 130 are bent outwards to engage the body inner face 80. At the radially outer end of the sleeve 110, a pair of arcuate tangs 132, normally retracted before assembly, as indicated in Fig. 6, are bent outwards to engage the floor 75 of the insulator threaded well 74. (See Fig. 4.) As well as helping to anchor the brush holder 52 in the insulator 50, the tangs 132 provide a good electrically conductive support surface for the connection disc 62. In the terminal portion 112 of the brush holder 52 a pair of terminal tabs 134, 136 lie spaced apart in a plane perpendicular to the axis of the sleeve portion 110. The tabs 134, 136 are connected by a bridge strip 138 to the center of which the support arm 114 is connected. Each terminal tab 134, 136 has a connect end 140, 142 (which in assembly is free to mate with the terminal of another motor element) and a support end 144, 146. Each support end is notched 148, 150 in a contoured form matching that of the insulator support elements 90, 92. The bridge strip 138 may be flat, or may be formed to suit a particular application or to establish a particular lateral spacing between the terminal tabs 134, 136 other than that established by the flat pattern. In this embodiment, as seen best in Fig. 8, the bridge strip 138 has a central hump 152, partly to clear mating parts (not shown) in the motor assembly and partly to control the lateral spacing of the terminal tabs 134, 136. Figs. 10 and 11 illustrate an alternative embodiment of brush holder 52'. This is formed from a flat pattern generally similar to that of Fig. 5, but not shown in the drawings. This brush holder is of the cartridge type and in assembly tabs 156 are bent inwards and downwards to retain the brush in the sleeve. Again, in locating the sleeve portion 110' in the bore of the insulator, conventional retaining lugs 130' are used at the radially inner end of the assembly. To complete the retention of the sleeve in the body of the insulator, side tabs 158 engage internal notches in the bore of the insulator. (Not shown in the drawings.) Brush holders according to the invention are particularly suited for use in motors having a wiring schematic requiring two connections to each brush, as in the exemplary schematic of Fig. 12. In this arrangement a secondary winding is dedicated to a dynamic braking function and both primary and secondary windings are electrically split. The motor is controlled by a double pole, single throw alternate contact switch 160 shown in the off or braking position in Fig. 12. In operation, actuation of the switch 160 connects the run windings 162, 164, in series with, but on opposite sides of, the armature 14' to an electrical power source 166. In the braking mode the power is disconnected and the brake windings 168, 170 are connected in shunt across the armature 14' but with the armature electrically between them. As indicated in Fig. 12 each brush 56' is connected simultaneously and permanently to one each of the run and brake windings. A motor with this wiring schematic is the subject of a co-pending U.S. patent application, Docket No. P-US-RA-0177, sharing a common assignee with the present invention. In assembly operations the brush holder subassembly 26 (Figs. 2 and 4) is a sturdy compact unit of good integrity, well adapted to mechanical handling in automated assembly. In a single, simple assembly move the brush holder subassembly 26 may be inserted axially into the motor housing 22 so that the insulator guide flange 84 engages suitable support slots (not shown in the drawings), thus guiding terminal tabs 134, 136 into plug-in electrical connection with the terminals 38 of the stator assembly 24. Thus substantially direct electrical connection may be made between brushes 56 and field coils 34 without the use of jumper wires and without manual intervention. In the brush holder (52) concept, removing the terminal tabs 134, 136 from the direct connection to the walls of the brush holder sleeve 110 by placing them at the end of a support member (arm 114) provides flexibility in application of the design. Both the axial spacing and the lateral offset between the terminal tabs and the brush (held in the sleeve portion of the brush holder) may be set to suit the application. In addition this separation makes it possible to interpose specific support structure for the terminal tab directly engaging the tab, thus reinforcing the support provided by the material of the brush holder alone. In this exemplary embodiment, as seen best in Figs. 2 and 4, notches 148, 150 of the terminal tabs closely fit the support bosses 94, 96 of the insulator 50. The bosses may be tapered somewhat so that as the brush holder is slid into the insulator a press fit is obtained between the notches and the bosses. The bosses are shaped so as to "interlock" the terminal tabs so as to stabilize the terminal tabs under axial loading in both directions as in connecting with and disconnecting from the terminals 38 of the stator assembly. A brush holder according to the invention is especially advantageous in the bifurcated form of the present embodiment which provides for two connections to one brush. As seen in Fig. 5, the substantially rectangular flat pattern 170 comprises two smaller component rectangular portions, sleeve port 172 and terminal portion 174 connected by the support arm 114. As the flat pattern indicates the brush holder may be manufactured with very little material waste. Relatively low manufacturing cost makes it cost effective to us a brush holder (52) according to the invention is motor assemblies requiring only one connection to each brush, leaving one terminal tab inactive. Clearly, either terminal tab 134, 136 may be used in such an application and a requirement for manufacturing specific left-hand or right-hand parts may be avoided. Although such an embodiment is not shown in the drawings it will be understood that the general form of brush holder and brush holder insulator or carrier combination according to the invention, may be embodied in a brush holder assembly with a single terminal tab.

Claims: A brush holder subassembly (26) for an electric motor (10), the motor having an axis of rotation and including a motor housing (22) and field coils (34), characterized by: an insulator (50) including a body (70) having a through bore (72) and a support element (90, 92) disposed externally of the body (70); and a brush holder (52) of conductive material, including a sleeve portion (110) for slidably receiving a brush (56), housed in fixed position in the bore (72) of the insulator body (70), and an elongated terminal portion (112) fixedly connected to the sleeve portion (110), disposed externally of the insulator body (70) and extending perpendicular to the longitudinal axis of the insulator body bore (72) and including a free connecting end (140, 142) for electrical connection to the field coils (34), and an opposite support end (146) for engaging the support element (90, 92) of the insulator (50) to stabilize the terminal portion (112) relative to the sleeve portion (110). The brush holder subassembly of Claim 1 characterized in that the insulator (50) includes a guide surface extending perpendicular to the longitudinal axis of the insulator bore (72) for engaging and at least partially fixing the brush holder subassembly in the housing (22). The brush holder subassembly of Claim 1 characterized in that assembly, the brush holder terminal portion (136) extends parallel to the axis of rotation of the motor (10). The brush holder subassembly of Claim 1 characterized in that: the insulator body (70) includes a slot (78) communicating with the bore (72); and brush holder (52) includes an elongated support member (114) extending through the slot (78) and connecting the brush holder sleeve portion (110) to the terminal portion (112). The brush holder subassembly of Claims 1 or 4 characterized in that the terminal portion (112) comprises two spaced terminal tabs (134, 136) extending perpendicular to the longitudinal axis of the insulator body 70. The brush holder subassembly of Claim 5 characterized in that: the insulator (50) includes a second support element (90, 92); and each terminal tab is substantially independently stabilized by the support elements (90, 92). The brush holder subassembly of Claim 1 characterized in that the brush holder (52) is formed from a single piece of sheet material. The brush holders subassembly of Claim 1 characterized in that: the support element (90, 92) of the insulator (50) is contoured in a plane perpendicular to the axis of the insulator body bore (72); and the terminal portion support end (144, 146) includes a mating contour (148, 150) for supportively engaging the insulator support element (90, 92). The brush holder subassembly of Claim 8 characterized in that the engagement of the terminal portion (112) with the support elements (90, 92) supports the terminal portion (112) in mutually opposing directions in a plane perpendicular to the axis of the bore (72) of the body (70). The brush holder subassembly of Claim 1 characterized in that a portion of the insulator body (70) is interposed between the brush holder sleeve (110) and terminal portions (112). A unitary brush holder for an electric motor characterized by: an elongated sleeve (110) for slidably receiving a brush (56), the sleeve having walls (118, 120, 122, 124) and a longitudinal axis; a first elongated terminal tab (134, 136) having a free connecting end (140, 142) and an opposite support end (144, 146), spaced from the sleeve walls and offset with respect to the sleeve axis and extending in a plane perpendicular to the sleeve axis; and a support arm (114) for carrying the terminal tab (134, 136) cantilevered from one (122) of the sleeve walls to the support end (144, 146) of the terminal tab. The brush holder of Claim 11 characterized by a second elongated terminal tab (136) extending parallel to and spaced from the first tab (134) and also carried by the support arm (114). The brush holder of Claim 12 characterized in that the support arm (114) includes a transversely extending bridging strip (138) having opposite ends and each of the respective terminal tabs (134, 136) is carried respectively by the bridging strip 138 adjacent one of its ends. The brush holder of Claim 12 characterized in that: the brush holder (52) is formed from a single piece of sheet material (170) having, when flat, a substantially rectangular shape; and substantially all of the material of the rectangular shape is used to form the brush holder. The brush holder of Claim 14 wherein the rectangular shape of the piece of sheet material (170) comprises two side-by-side, substantially rectangular portions (172, 174), one for forming the sleeve portion (110) and the other for forming the terminal portion (112). A small electric motor (10) for use in portable tools and appliances characterized by: an armature (14) having a commutator (16); a stator (24) substantially enclosing the armature (14) and including a plurality of field windings (34) and having opposite ends including a commutator end (12) adjacent the commutator (16); at least one pair of spaced apart terminal (38) carried by the stator commutator end (24), and facing axially outwards with respect to the stator commutator end, and connected electrically to the field windings (34); a pair of diametrically opposed radially extending brushes (56) for maintaining electrical contact with the commutator (16); and a unitary brush holder (52) having a sleeve (110) for slidably supporting one of the brushes (56) and including a pair of axially extending terminal tabs (140, 142) registering with the terminal elements (38) of the stator (24) to directly electrically connect the brush holder (52) with the field windings (34) and complete electrical connection between the armature (14) and the field windings (34). The electric motor of Claim 16 characterized in that the brush holder terminal tabs (140, 142) are coplanar in a plane perpendicular to the axis of the brush holder sleeve (110). The electric motor of claim 16, characterized by a second pair of terminal elements (38) at the commutator end of the stator, a second brush holder (56) holder having a pair of terminal tabs (140, 142) engaging said second pair of terminal elements (38) for completing electrical contact between the armature (14) and field windings (34), the field windings (34) electrically split into at least two field winding portions (162, 164, 168, 170), the armature (14) connected electrically in series with the field winding portions and between at least one pair (162, 164; 168, 170) of field winding portions, and said connection being maintained by the brush holders and brushes in combination. The electric motor of Claim 18 characterized in that: the field windings (34, 34) include run winding and brake winding portions (162, 164, 168, 170) for running and dynamically braking the motor respectively; and both the run and brake windings are electrically split with respect to the armature (14).

Inventors: LENTINO, LYNN E., TURNER, TERRY L.
Applicants: BLACK & DECKER INC.
Application year: 1990
Main classification: H02K5
IPC codes: H02K13, H01R39, H02K23, H02K5