Robust commutator bar anchoring configuration with dove-tailed features

This Application is based on U.S. Provisional Application No. 60/633,578 filed on Dec. 6, 2004 and claims the benefit thereof for priority purposes.

This invention relates to commutators for electric motors (generators) and, more particularly, to an anchoring configuration of the commutator bars.

A conventional electric motor is generally described in the U.S. Pat. No. 5,977,666, and the structure and manufacture of commutators are generally described in U.S. Pat. No. 6,242,839 and U.S. Pat. No. 4,872,255.

The functionality of the electrodynamic machines such as motors and generators are based on proper commutation. The proper flow and distribution of the electrical energy to the armature windings is commonly solved by the use of commutators and brushes. In a permanent magnet direct current brush motor (PMDC BM) assembly the commutator bar segments are electrically connected to the armature windings and at least one pair of brushes (one positive and one negative) are in contact with the surface of the commutator bars. The armature windings are placed onto the core of the armature in a pattern relative to the commutator hooks. The winding pattern and the style of the winding are determined based on the number of magnetic poles (magnet angle) of the electric machine. Furthermore, the brushes are positioned relative to the permanent magnets of the electrical machine. Then, the electrical current is conveyed from a given power source through at least one positive brush to the armature windings. The current conducting windings under the magnetic fields will generate rotational torque on the armature at a desired angular speed to produce mechanical power.

For adequate commutator and brush interface, the commutator surface is machined after the armature winding is completed. Although the best process is selected to perform this operation, there is a certain force (tensile and compressive) transferred to the anchoring system of each commutator bar. Therefore, the anchoring configuration of each bar must be robust enough to withstand the machining forces with acceptable surface conditions such as TIR (Total Indicted Run-out) and BTB (Bar to Bar).

Since the proper function and durable life of an electric machine depends mainly on the robustness of the commutation interface components such as the commutator and brushes, a good motor configuration must ensure that the commutator bars have sufficient thickness and robust anchoring features. More specifically the commutator must withstand high rotational speeds, tensile and compressive forces from the surface cutting operation and thermal and mechanical stresses that may occur during the life of the product.

The current production commutators work well in low power ranges used by most of the auto manufacturers. However, based on forecasts of higher power motor requirements new validation testing was performed using the current commutator and the test results indicated that the current configuration did not provide adequate anchoring for higher power applications. Therefore, there is a need to improve the anchoring structure of the commutator bars for higher power applications.

An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by providing a commutator bar including a body having a top surface and a bottom surface, a proximal end, a distal end and two opposing sides. The top surface is constructed and arranged to contact brushes of a motor. A hook extends from the proximal end of the body and is constructed and arranged to receive a portion of a winding of a motor. A first pair of anchors, a second pair of anchors and a third pair of anchors is provided with each pair extending from the bottom surface. The first pair includes first and second anchors disposed in spaced relation. Each anchor of the first pair has one end coupled to the proximal end of the body. A free end of the first anchor extends in a direction towards the proximal end of the body, and a free end of the second anchor extends in a direction towards the distal end of the body. The second pair of anchors includes third and fourth anchors disposed in spaced relation. Each anchor of the second pair has one end coupled to a distal end of the body and a free end extending in a direction towards the proximal end of the body. The third pair of anchors includes fifth and sixth anchors. Each anchor of the third pair has one end coupled to the body at a location between the proximal and distal ends. A free end of the fifth anchor extends toward one side of the body and a free end of the sixth anchor extends toward the other side of body.

In accordance with another aspect of the invention, a commutator includes a base having a periphery, and a plurality of commutator bars coupled to the periphery of the base. Each commutator bar has a body including a top surface and a bottom surface, a proximal end, a distal end and two opposing sides. The top surface is constructed and arranged to contact brushes of a motor. Each commutator bar has at least one pair anchors. Each anchor has one end coupled to the body at a location between the proximal and distal ends. A free end of one anchor extends beyond one side of the body and a free end of the other anchor extends beyond the other side of body. The anchors engage the base, and the commutator bars are arranged about the periphery of the base such that anchors of one commutator bar overlap a domain of an adjacent commutator bar.

Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.

The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which:

FIG. 1 is a perspective view of a single bar of a twenty bar barrel-commutator showing the anchoring features of the invention.

FIG. 2 shows an end view of the commutator bar of FIG. 1 , illustrating anchoring features thereof in accordance with the invention.

FIG. 3 shows an assembled commutator of the invention, without the molded base, illustrating the position of the anchoring features relative to each other.

FIG. 4 is cross-sectional view of the commutator of the invention with the molded base.

This invention does not relate to the manufacturing methods of the commutators; however, it identifies that anchoring features can be added to both segmented commutator bars and barrel type commutators. The manufacturing methods of both types of commutators can be found in the prior art. However, for the sake of understanding the differences between segmented and barrel type commutators, a brief description is provided below.

The segmented type commutator is such that each individual bar is manufactured separately, then the bars are positioned in a some type of cylindrical/circular fixture and a base (such as a phenolic based) is molded in at the surface B of the bars ( FIG. 1 ) to hold the bar assembly together.

The barrel type commutator is such that the anchoring features are added to a strip of sheet metal (commonly used copper or copper alloys) that is rolled up to form a cylindrical shape shell. Then, the base is molded into the shell at the surface B of the bars to hold the structure together. Next, at some point of the manufacturing process, the metallic shell is sliced up to electrically isolate the individual commutator bars from each other.

FIG. 1 and FIG. 2 show only a single commutator bar, generally indicated at 10 , of a commutator assembly 20 ( FIG. 3 ) to clearly illustrate the inventive anchoring features. However, the anchoring features of the embodiment can be used in commutators manufactured by both type of manufacturing processes mentioned above, or other types of manufacturing processes.

The commutator bar 10 shown in FIG. 1 has a body 11 defining a bottom surface B, where all the anchoring features are located; a top surface T that is to be in contact with the brushes in a motor assembly in the conventional manner, a proximal end H, a distal end O, and two opposing sides 30 and 32 . An armature winding (not shown) is connected and fused to the hook 12 in an armature assembly in the conventional manner. The hook 12 is provided at the proximal end H of the body 11 and preferably integral therewith.

In the embodiment, the anchoring features extending from surface B consist of three pairs of anchors and these anchors are configured and placed such to maximize the degree of freedom of each commutator bar 10 relative to the commutator base 21 and each axis 23 , 26 , and 27 shown in FIG. 4 ; where axis 23 , 26 and 27 is relative to axis x, y, and z, respectively, of the Global Coordinate System.

As best shown in FIG. 1 , the first pair of anchoring features includes a first anchor 13 and a second anchor 14 disposed in spaced relation. Each anchor 13 and 14 has one end coupled to the proximal end H of the body 11 . A free end of the first anchor 13 extends in a direction towards the proximal end H of the body 11 , and a free end of the second anchor 14 extends in a direction towards the distal end O of the body 11 . These dove-tailed anchors 13 and 14 are configured to provide sufficient bar stability to resist a pulling force from the armature winder.

The second group of anchoring features includes a third anchor 17 and a fourth anchor 18 disposed in spaced relation at the distal end O of body 11 to avoid bar lift up in case of the base 21 separates from surface B, since it is known that the base 21 does not bound very well to copper surface B. Each anchor 17 and 18 has one end coupled to the distal end O of the body 11 and a free end extends in a direction towards the proximal end H of the body 11 . As shown in FIG. 2 , each of the third and fourth anchors 17 and 18 has an outer side surface 34 , 36 , respectively, defining an acute angle 19 there-between.

The third pair of anchoring features includes a fifth anchor 15 and a sixth anchor 16 that are also dove-tailed anchors and staggered to allow an extension of the anchors 15 and 16 beyond the bounds defined by angle 19 illustrated in FIG. 2 . Thus, each anchor 15 and 16 has one end coupled to the body 11 at a location between the proximal and distal ends. A free end of the fifth anchor 15 extends toward side 30 of the body 11 and a free end of the sixth anchor 16 extends towards the other side 32 of body 11 . The anchors 15 and 16 are of arcuate shape, preferably generally U-shaped, and are configured to provide bar stability in base 21 during commutator machining, and long-term durability. The anchors 15 and 16 have deep rooting into the base 21 to avoid bar lift-up. Also, each pair of anchoring features is positioned on surface B to provide maximum side support for the commutator bar 10 , to minimize the BTB movement, and to eliminate “rocking” type bar movement during the commutator cutting/machining process. BTB is defined as the height difference between the trailing edge of one bar ( 10 ) to the leading edge of the adjacent bar ( 10 ′).

FIG. 3 shows the finished commutator 20 of the invention without the molded base 21 to illustrate the position of the anchoring features relative to each other in the final finished commutator. The staggered dove-tailed anchors 15 and 16 on bar 10 overlap into the domain of adjacent commutator bar segments 10 ′ and 10 ″ without interference and electrical contact (e.g., without shorting) with anchors 16 ′ or 15 ″.

A cross-sectional view of the assembled commutator 20 is shown in FIG. 4 . At the distal end O, there is a recessed feature 24 of the base 21 to allow a more compact, shorter axial motor assembly. There is a shoulder 25 at proximal end H to support/hold cross-link winding wires for a four pole two brush applications. The commutator has a bore 22 there-through, extending along centerline 23 , that is used to press the commutator onto an armature/motor shaft. There are also clearly visible the staggered anchoring features of bars 10 and 10 ′″.

The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims.