Direct current motor with crescent shaped brushes

Abstract: A single speed, two pole permanent magnet motor (10) has compact brush card (56) assembly with crescent shaped brushes (68) mounted within the volume form by a plurality of ring shaped laminations (48) forming the armature (38) to allow the height "X" of the motor to much less than a standard motor. In addition, there is shown a two speed, four pole permanent magnet motor (100) having a height much less than a standard two speed motor. In each motor there are electrically connected to the supply lines a choke means (64) and across each supply line is a capacitor (146) for suppressing radio frequency interference.

Description: This invention relates to a direct current motors in general and more particularly to brush cards for one and two speed four pole permanent magnet motors having crescent shaped brushes. Background of the Invention Prior Art The most conventional type of brushes for direct current, 'd.c.' motors is a straight brush. Examples of which are found in several US Patents such as 5,006,747, entitled 'Dynamoelectric Machine Brush Rigging and Method Assembly'. US Patent 4,596,941, entitled 'Electric Motor', illustrates brushes affixed to spring levers resiliently mounted on the end wall of the motor. This is still a straight brush. An example of the use of such brushes may be found in Japanese Patent Serial number 58222768(A), in which such brushes are mounted on a base member, and arranged to be mounted on a commutator of a direct current electrical motor via an aperture in the base member. Such an arrangement serves to provide a means for reducing the axial height of the motor in combination with a suitably formed recess in an inner surface side of the motor. Another type of brush is called the hammer brush and is illustrated by US Patent 4,638,204 entitled 'Hammer Brush Holder Assembly for a Commutator Motor' issued on January 20, 1987 by Siemens Aktiengessellschaft. This brush is mounted in a brush holder that is pivoted to bring the brush into contact with the commutator. The brush is curved to follow the pivoting arc of the moveable brush holder. A further type of brush may be found in German Gebrauchsmuster Rollennummer G 89 06 558.1, which discloses a brush card upon which a pair of arcurate brushes is disposed in arcurate guide members and urged to electrically connect to a commutator by biasing springs. Summary of the Invention It is a principle advantage of the motor to reduce the overall height or width of the motor for applications wherein the motor length or width is an advantage. It is another advantage to provide a two speed, four pole motor wherein the brushes are substantially contained within the armature laminations. According to the present invention there is provided a direct current motor comprising a commutator mounted axially on a rotatably mounted armature shaft, an armature connected to said armature shaft for rotation therewith, and a brush card having an aperture adapted to receive said commutator, and at least one pair of brush means being mounted on a peripheral region of said brush card about said aperture and arranged to form electrical contact with said commutator, thereby causing said armature to rotate by action of electrical current flowing through a plurality of armature coils disposed thereon, in combination with a magnetic field provided by a permanent magnet, characterized in that said armature is comprised of a plurality of ring shaped laminations peripherally mounted on a web member, said peripherally mounted ring shaped laminations forming first and second volumes either side of said web member, said brush card means being mounted on one side of said web member within said first volume, and said commutator having a plurality of commutator bars each with a hook means for connecting each bar of the commutator to one of said armature coils, wherein said hook means are arranged to extend through radially extending slots in said web member so as to occupy said second volume, said commutator and said brush card in combination with said hook means being disposed on either side of said web member within said first and second volumes formed by said ring shaped armature so as to substantially reduce the axial height of said direct current motor. In a second embodiment, there is illustrated a two speed, four pole motor wherein the brush card contains brushes for each speed within the periphery of the ring shaped armature. Thus this motor is also reduced in height or width. Detailed Description of the Drawings In the drawings: Fig. 1 is a plan view of a two pole, single speed permanent magnetic motor of the preferred embodiment; Fig. 2 is a sectional view of the motor of Fig. 1 taken along line 2-2 of Fig. 1; Fig. 3 is a plan view of the brush card assembly of the motor of Fig. 1; Fig. 4 is section view of the armature assembly of the motor of Fig. 1; Fig. 5 is a plan of the armature web taken along line 5-5 of Fig. 4; Fig. 6 is plan view of the brush; Fig. 7 is a sectional view taken along line 7-7 of Fig. 6; Fig. 8 is an elevation view of the brush tube taken in the direction of arrow 8 in Fig. 9; Fig. 9 is a plan view, partially in section, of the brush tube; Fig. 10 is a sectional view, similar to Fig. 2, of a four pole, two speed permanent magnetic motor of an alternate embodiment; Fig. 11 is a plan view of the low speed brush card assembly of the motor of Fig. 10; Fig. 12 is a plan view of the high speed brush card assembly of the motor of Fig. 10; Fig. 13 is a plan view of the common brush card assembly of the motor of Fig. 10; Fig. 14 is an electrical schematic of the control of the motor of Fig. 1; Fig. 15 is a truth table for the control of the motor of Fig 14; Fig. 16 is a prior art electrical schematic of the control of the motor of Fig. 10; and Fig. 17 is a prior art truth table for the control of the motor of Fig 16. Detailed Description Referring to the drawings by the characters of reference there is illustrated in Fig. 1 a plan view of a single speed, two pole permanent magnet motor 10. The housing 12 of the motor is essentially tubular shaped and enclosed at one end. As shown in the end of the housing 12 are a plurality of holes 14 which function to allow the passage of air into and out of the interior of the housing. Illustrated are three mounting brackets 16 which are connected to or formed from an end bell 18 of the motor 10. Referring to Fig. 2 there is illustrated in section the direct current motor 10 of Fig. 1 having the housing 12 open at one end and an aperture 20 centrally located in the closed end. As shown, the aperture is contained in a pocket of the housing 12 which is formed to be inside the plane 21 formed by the end of housing 12. Supported in the aperture 20 is a bearing member 22 which is illustrated as a ball bearing, and a spring member 24 to hold the bearing member in place. Mounted along the inside of the housing 12 are a plurality of permanent magnets 26, for providing the magnet flux of the motor 10. An end bell 18 encloses the housing 12 at its open end and in the preferred embodiment has the plurality of mounting brackets 16 connected to or formed thereof which function to support the motor in its application. The end bell 18 has a bearing means 28, illustrated as a solid bearing formed from a bearing material, which is centrally located and is aligned with the bearing member 22 in the aperture 20 at the closed end of the housing 12. A spring means 30 for locating and maintaining the bearing means 28 is supported in the end bell 18 and in particular is located in a well in the end bell. An armature means 32, as illustrated in Fig. 4, including an armature shaft 34, a commutator 36, and an armature 38, is supported for rotation by the bearing member 22 and the bearing means 28. Mounted on the armature shaft 34 and between the bearings is the commutator 36 having a plurality of commutator bars 40 each with a hook means 42 for connecting each bar of the commutator 36 to a winding coil 44 in the armature 38. The hook means 42 are illustrated in a reverse direction, compared to conventional hook means, to allow a more compact motor width or height "X" in Fig 2. Also mounted on the armature shaft is a web member 46, as illustrated in Fig. 4, supporting the laminations 48 of the armature 38. The laminations 48 are ring-shaped and are mounted on both flat surfaces 49-50 of the web member 46 with an equal number of laminations on both sides of the web member for balancing the armature, as shown in Fig. 4. If the number of laminations is not equal, a balancing weight, not shown, may be added to the short stack of laminations for balancing. As illustrated in FIG. 5, the web member 46 has a plurality of radially extending slots 52 extending from the hub 54 to allow the hook means 42 from the commutator 36 to extend therethrough. The brush card means 56, as illustrated in Fig. 3, is mounted in the end bell 18 and has at least one pair of diametrically opposed brush means 58 mounted on an electrically non-conductive base member 60. As shown, there are two pair of brush means mounted to the brush card means 56. The base member 60 has a central aperture 62 with a diameter larger than the diameter of the commutator 36, thereby allowing the commutator to extend therethrough. In the preferred embodiment, the base member 60 is substantially circular in shape and supports the pair of brush means 58 inside the outer periphery or circumference of the base member. As illustrated in Fig. 3, the brush card means 56 additionally includes choke means 64 electrically connected for reducing electromagnetic interference. The brush means 58 comprises a round shaped brush tube 66, illustrated in Figs. 8-9, having a crescent shaped or arcuate shaped brush 68, illustrated in Figs. 6-7, supported therein. The brush card means 56 is positioned so that the brushes 68 are in contact with the commutator 36. The arcuate brush tube 66 retains and guides the crescent shaped brush 68 to remain in contact with the commutator 36. This is illustrated in Fig. 3. Mounted on the base member 60 is a torsion spring 70 for biasing each of said brushes 68 in an arcuate direction toward the commutator 36. The torsion spring 70 is located on a post 72 which is proximate the center of the arc of the brush 68. In this manner, as the brushes 68 wear, the torsion spring 70 will apply the same amount of pressure to the brush during the time the brush is wearing out. As illustrated in Fig. 4, the commutator 36 is mounted adjacent to the hub 54 and substantially within the cylinder formed by the ring shaped armature 38. By so doing, this allows the height, X, of the motor 10 to be reduced. The brush card means 56 which is mounted to the end bell 18, is nestled in and is substantially contained within the inner volume formed by the ring shaped laminations 48 of the armature 38. As illustrated in FIG. 2, the commutator 36 maybe formed to provide a pocket 74 for the bearing means 28 in the end bell 18 in order that the bearing means extends further into the motor 10 to reduce the height, X, of the motor. Referring to Figs. 14 and 15, there is an electrical schematic and truth table respectively, of a two pole, single speed motor of the present invention. This schematic and truth table are well known. Referring to Fig. 10, there is illustrated a four pole two speed motor 100. The basic four pole, two speed motor is described in U.S. Patent 4,910,790, ('790), issued on March 20, 1990 to Kershaw and is assigned to a common assignee. The brush card means 102 in this embodiment is illustrated in Figs. 11-14. The two speed, direct current motor 100 includes a first and a second commutator 104, 106 mounted on the armature shaft 108 with the second commutator 106 overlying and insulated from the first commutator 104. The commutators are mounted on the armature shaft 108 intermediate the bearing means 110 and the bearing member 112. As illustrated, the armature means 114 comprises a plurality of ring shaped laminations 116 mounted to a web member 118 having a central hub 120 for mounting on the armature shaft 108 intermediate the first commutator 104 and the bearing member 112. The web member 118 is illustrated as a plurality of flat members each having a plurality of radially extending slots extending from the hub 120 through which the hook means 122 from each commutator 104, 106 extends. Mounted to the end bell 124 of the motor 100 of Fig. 10, is the brush card means 102 having a first, second and third base members 132, 134, 136. The first base card member 132 is similar to that illustrated in Fig. 4 and is illustrated in Fig. 11. The first base card member 132 is electrically active when the four pole two speed motor is being operated at its lower speed and the third base card member 134 is electrically active at the higher speed. The first base member 132 is illustrated in Fig. 11. The diameter of the first aperture 138 in the first base member 132 is larger than the diameter of the first commutator 104. The first base member supports two pairs of brush means 58 inside the outer periphery of the first base member. Illustrated are two pairs of brush means 58 on the base member 132. The brush means 58 has an arcuate brush tube 66 for retaining and guiding an arcuate or crescent shaped brush 68 and a torsion spring 70 mounted on a spring post 72 to the first base member 132 for biasing each of the brushes 68 in an arcuate direction toward the first commutator 104. The first base member supports a choke means 64. The third base member 136 is illustrated in Fig. 13. The diameter of the first aperture 138 in the second base member 136 is larger than the diameter of the first commutator 104. The second base member 134 is the negative, common or ground electrical member and receives the common electrical connection. Mounted to the second base member is a choke means 64. The second base member 134 is illustrated in Fig. 12. The diameter of the aperture 140 in the third base member 134 is larger than the diameter of the second commutator 106. The third base member supports two pair of brush means 58 inside the outer periphery of the third base member. The brush means 58 has an arcuate brush tube 66 for retaining and guiding the arcuate or crescent shaped brush 68 and a torsion spring 70 mounted on a spring post 72 to the third base member 134 for biasing each of the brushes 68 in an arcuate direction toward the second commutator 106. Mounted to the third base member is a choke means 64. The brush card means has 102 places the second or negative brush card 136 between the first 132 and third 134 base members. Together the three brush cards form a laminated brush card means 102. This is illustrated in Fig. 10. Since this motor has two commutators 104, 106, the axial length of the commutators is longer than that of the motor 10 shown in Fig. 2. Therefore the web member 118 does not have the same number of laminations 116 secured to each face of the web member. The side of the web member 118 with the larger stack of laminations 116 allows the brush card means 102 to be positioned so that the brush means 58, which rides on the second commutator 106, is within the volume formed by the ring shaped armature laminations 116. As taught in the '790 patent, there are two layers 128, 130 of armature windings wound through the laminations 116. The inner layer 128 of windings is connected to the second commutator 106 for high speed operation and the outer layer 130 of windings is connected to the first commutator 104 for the lower speed operation. Referring to Fig. 16, the two speed motor 100, may be controlled by a pair of control switches 142, 144 which are mutually exclusive, in that if one is closed the other must be open. This is shown in the truth table of Fig. 17. In fact both switches 142,144 may be open at the same time but both switches may not be closed or operated at the same time. The power supplied to both switches 142, 144 may be the full voltage of the power supply. The normally open contact of the first switch 142 is electrically connected to one pair of brushes on the low speed or first commutator 104 through the choke coil 64. The second pair of brushes on the first brush card 132 are connected to the second brush card 136. The normally open contact of the second switch 144 is electrically connected to one pair of brushes on the third brush card 140 on the high speed or second commutator 106 through the choke coil 64. The second pair of brushes are connected to the third base member 136. The ground line is connected to the third base member 136. Thus, in order to operate the motor at the second or low speed, the two windings are connected in series with the voltage drop across each winding proportional to the resistance of the winding. When the motor is run at the first or high speed, the power is connected through the second switch 144 and choke 64 to the brushes of the second commutator and the high speed winding. Connected across each supply line are first and second filter capacitors 146 which in cooperation with the three choke coils operates to suppress radio frequency interference.

Claims: A direct current motor (10) comprising a commutator (36) mounted axially on a rotatably mounted armature shaft (34), an armature (38) connected to said armature shaft (34) for rotation therewith, and a brush card (56) having an aperture adapted to receive said commutator (36), and at least one pair of brush means (58) being mounted on a peripheral region of said brush card (56) about said aperture (62) and arranged to form electrical contact with said commutator (36), thereby causing said armature (38) to rotate by action of electrical current flowing through a plurality of armature coils (44) disposed thereon, in combination with a magnetic field provided by a permanent magnet (26), characterized in that said armature (38) is comprised of a plurality of ring shaped laminations (48) peripherally mounted on a web member (46), said peripherally mounted ring shaped laminations forming first and second volumes either side of said web member (46), said brush card (56) and said commutator (36) being mounted on one side of said web member (46) within said first volume, and said commutator having a plurality of commutator bars (40) each with a hook means (42) for connecting each bar of the commutator to one of said armature coils (44), wherein said hook means (42) are arranged to extend through radially extending slots in said web member (46) so as to occupy said second volume, said commutator (36) and said brush card (56) in combination with said hook means (42) being disposed on either side of said web member (46) within said first and second volumes formed by said ring shaped armature (38) so as to substantially reduce the axial height of said direct current motor (10). A direct current motor as claimed in Claim 1, further comprising a second commutator (106) mounted on said armature shaft (34), said second commutator (106) overlying and insulated from said first commutator (104), wherein said brush card (56) further comprises at least two electrically non-conductive base members (132, 134, 136) with a first of said at least two base members (132) having a central aperture (138) with a diameter larger than the diameter of the first commutator (36, 104) and a second of said at least two base members (134) having a central aperture (138) with a diameter larger than the diameter of the second commutator (106), said first and second base members (132, 134) being arranged to support at least one pair of brush means (58) arranged to form electrical connection respectively with said first and second commutators (104, 106), said brush card (56) being arranged such that said brush means (58) are contained within said first volume between said ring shaped armature (38) and said first and second commutators (104, 106), thereby reducing the height of the two speed motor. A direct current motor as claimed in Claim 2, wherein a third of said base members (136) has a central aperture (140) with a diameter larger than the diameter of the first commutator (104), and is disposed between said first and second base members (132, 134) and arranged to provide a negative, common or ground potential with respect to the first and second base members. A direct current motor as claimed in Claims 2 or 3, wherein hook means (42) connected to commutator bars of said second commutator (106) also extend through said radially extending slots (52) in said web member (46) and are arranged in combination with said web member (46) to provide corresponding electrical connection to second armature coils (130) whilst reducing the axial height of the motor. A direct current motor as claimed in any preceding Claim, wherein each of said at least one brush means (58) is comprised of arcurate brushes (68) and a torsion spring (70) for each brush, which torsion springs (70) urge said brushes (68) respectively to contact either of said first or said second commutators (104, 106).

Inventors: HORSKI MAREK, HORSKI, MAREK
Applicants: SIEMENS ELECTRIC LTD, SIEMENS ELECTRIC LIMITED
Application year: 1995
Main classification: H02K13
IPC codes: H02K5, H02K13, H02K11