Low voltage electronic motor wire termination

The present invention provides a simple and robust design implementing an easily accessible external terminal connection point for supplying drive current to an AC motor. An embodiment of the invention is directed to an insertion plug and a conductor formed within the insertion plug. Specifically, the conductor acts as a current bus through an insertion aperture defined in a motor housing. The interior end of the conductor acts as an interior connection terminal for an AC phase coil, whereas the exterior end of the conductor is configured to accept an external motor drive source power cable. Advantageously, the modularity of the insertion plug design and a modified insertion housing aperture stamping program provide significant flexibility with regard to placement of the connection terminal. This aspect of the invention allows the connection terminals, as well as a corresponding motor housing to be customized for pre-existing mechanical designs and assemblies.

FIELD OF THE INVENTION

This invention relates generally to alternating current (AC) motors and, more particularly, to connection terminals used to provide drive current to a motor.

BACKGROUND OF THE INVENTION

In the past, electric forklifts, wheel chairs and golf carts have traditionally been powered by direct current (DC) motors. Typically, DC motors are longer than a similarly powered AC motor, because they require additional operational elements such as a brush commutator. The commutator provides a connection point between the current driving the motor and the moving parts of the motor. DC motor elements often require additional maintenance because of this connection of moving mechanical parts. For instance, brush and commutator wear require disassembly of the machine and replacement of these parts.

As in the diagram illustrated inFIG. 1, conventional electric DC motor100incorporates three-phase threaded terminal stud connections105, which protrude through the non-drive end bell. These studs can be positioned at various angles to facilitate attachment of the drive cables. The M8 (8 mm) threaded termination studs105provide the primary external power connection point to the motor. Secondary DC electrical connections (e.g., brushes and commutator) are made internal to the motor100. In the DC motor lead wire is used to electrically connect the brush assembly to the terminals. Lead wire consists of many fine strands of wire that are uninsulated from each other—there is only an outer jacket of insulation around all of the wires. Once this outer jacket is removed, the group of fine wires can be readily terminated to the terminal conductor thru brazing or other means.

In contrast, AC motors are mechanically simpler and have a shorter frame size because they lack the DC motor's commutators and brushes. AC motors typically have either permanent magnet or squirrel cage rotors and therefore only need to supply drive current to the stationary portion of the motor. In a conventional three phase AC motor design200, shown inFIGS. 2A and 2B, lead wires205(lengths of wire connected to the individual AC phase coils) exit the center of the motor200at point225and are terminated at the center of the motor body. Each phase has a terminal mounted to an M8threaded stud210molded to a Rynite terminal block215. Simple corrugated tubing220is then used to cover each external phase205from the exit point225on the non-drive end bell to the terminal block215.

There are several design and safety concerns with the conventional AC wire terminals illustrated inFIGS. 2A and 2B. As illustrated, lead wires205are covered in simple corrugated tubing220and exposed to the motor's external operating environment. The wires are not substantially insulated. People working around the motor are therefore exposed to a significant risk of electric shock. Moreover, in day-to-day operation this type of motor design is often mishandled by users that attempt to lift the motor by wires205. The wires205are not designed to support the weight of the AC motor200. This type of misuse increases the risk of live electric wires becoming unfastened from their terminals210and further increases the risk of electric shock. Also, the AC lead wires are bundles of magnet wires that exit the phase coils at335U,335V, and335W (shown inFIG. 3E) respectively, each of the individual wires comprising the bundle have a minor layer of insulation on their exterior. The existence of the layer of insulation means that the bundle of wires cannot be readily terminated to the terminal conductor. This is due to the high temperatures required to vaporize off the layer of insulation which eliminates brazing and the contaminating effect of the vaporized insulation layer to the resulting bundle strength which makes electrical resistance fusing or welding a problem. Removal of the insulation layer on each individual wire is possible but time consuming.

One conventional solution involves a two step process: (1) placing a ring of conductive material, such as a conductive ferrule, around the bundle of magnet wire with the insulation still in place and electric resistance fusing the wire bundle and the ferrule together; and (2) connecting the ferrule to the terminal conductor by brazing, soldering or other means to provide an electrical connection.

Also, as illustrated inFIG. 2A, the power connection location is fixed at the center of the conventional AC motor. Typically, end users prefer power connection points that can be positioned at various angles around the exterior of the motor to accommodate varied cable lengths similar to the DC motor design.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a simple and robust design that resolves both the operational design and safety issues discussed above. An embodiment of the invention is directed to an insulating plug and a conductor to carry current between an exterior connection point and an internal connection point.

The conductor provides an external connection terminal on the motor housing to connect drive current cables. The conductor acts as a current bus through the insertion aperture into the motor housing. The interior end of the conductor acts as an interior connection terminal for an AC phase coil.

It is an object of the invention to provide an easily accessible apparatus to conduct drive current from an external AC power supply to the individual AC phase coils that constitute the AC motor's stator. During motor assembly, the insulating plug is inserted through an insertion aperture in the motor housing. The invention thereby, implements a close-profile robust exterior connection point. Accordingly, the invention provides an easily accessible solution to the problems discussed above. The accessibility of the connections significantly reduces the steps necessary to produce a robust operational motor.

It is another object of the invention to reduce the complexity of an AC motor manufacturing process and provide design flexibility. Specifically, the invention facilitates a significant degree of flexibility with regard to the placement of the external terminals around the motor housing. Depending on the specified operational requirements, the insulating plug aperture may be defined within the motor housing anywhere that is convenient for the AC motor design. For example, if a specific operating environment had been previously designed for a DC motor terminal configuration, the present invention allows the AC motor exterior terminal connections to replicate the DC configuration. Previously, it was necessary to re-design the operating environment to suit the AC motor's centrally located external terminal connections. Moreover, the housing apertures may be changed during manufacturing the motor housing to any location by adjusting the stamp template used to form the aperture in the housing.

The flexibility of terminal placement in the invention ensures compatibility with any existing DC terminal and cable locations in mature products. For example, if desired, a stamping program typically used to create the motor housing could be easily modified to replicate the pattern shown in the DC Motor illustrated inFIG. 1A.

DETAILED DESCRIPTION

The invention provides a greater degree of flexibility for AC motor connection terminal designs, as well as addressing a variety of safety concerns related to conventional AC motor connection terminal designs. Previously, AC motor drive current was supplied to a conventional AC motor through power cables connected to an exterior AC connection terminal block (illustrated inFIGS. 2A and 2B). The connection terminal block facilitated an external connection with lead wires that run externally from the connection terminal block to an end of the AC motor. The lead wires entered the AC motor through an aperture in the center of an end bell of the motor and were connected directly to the respective AC phase coils.

In contrast to the conventional AC motor, the invention as illustrated inFIGS. 3A and 3B, provides a simple, low profile, robust means of terminating AC phase coil windings. The lead wire connections are made internal to the motor housing.

FIG. 3Ais a black and white photograph of a side external view of an exemplary embodiment of the invention, specifically a TSW AC connection terminal design.FIG. 3Bis a diagram of the motor shown inFIG. 3Aand illustrates the exterior of the motor housing310and the three connection terminals305corresponding to the three phases of the AC motor300. As illustrated, terminals305allow current from an AC drive to supply the AC motor300. It is to be understood that there is a great deal of flexibility regarding the placement of the terminal connections in the motor housing to facilitate various motor designs and operating environments.FIGS. 3C and 3Dillustrate different views of the embodiment of the invention shown inFIG. 3A.FIG. 3Cshows the embodiment fromFIG. 3Aas a perspective view, whereasFIG. 3Dshows the embodiment fromFIG. 3Aas an end view.

FIG. 3Eis a cross-sectional end view of the AC motor shown inFIG. 3Btaken along line A-A. Specifically,FIG. 3Eshows the end of each AC phase coil335for each of the respective phases (U, V, and W). As shown, the insertion apertures330U,330V and330W are defined in the motor housing (310). Bundles of the copper coil comprising a given phase exit at points335U,335V, and335W, respectively, and run to their respective apertures330U,330V, and330W where they connect to a conductor bus.

An embodiment of the invention is directed to an insertion plug formed by a conductor disposed within an insulator block. The insertion plug is provided to connect an exterior motor drive source with an interior magnetic wire coil within an AC motor. The conductor is formed with two end extensions, an internal connection terminal and an external connection terminal, each disposed on a respective end of a conductor. The internal connection terminal is configured as a connection point for a lead from an AC motor coil, whereas the external connection terminal is configured as a connection point for an AC drive current cable. Various aspects of these elements are shown in greater detail inFIGS. 4A-4C.

FIGS. 4A and 4Binclude cross-sectional views taken along a central axis B-B and show elements that constitute an external connection terminal, exemplary insulator plug, conductor and interior connection terminal. External connection terminal305provides a connection point for a current drive cable (now shown) with a minimal external profile. Exterior connection terminal305(shown in greater detail inFIG. 4B) is connected with a conductor415, e.g., a current bus, which conducts current from the exterior connection terminal305to an interior connection terminal435.

InFIG. 4A, the conductor415and interior connection terminal435are illustrated as a single element, specifically flag terminal415. The shape of the insertion plug is primarily defined by a pair of insulators425and430. Insulators425and430electrically isolate the conductor from the motor housing310and provides a support structure for fastening receptacle450(described in greater detail below). Insulator430electrically isolates current bus415as the drive current flows to the interior connection terminal435. The interior connection terminal435provides the connection point for the lead wires330U,330V and330W, described inFIG. 3Eof stator coils440. The lead wires may be connected to the interior connection terminal by any conventional securing method (e.g. brazing, soldering, crimping, etc . . . ). In the exemplary embodiment ofFIG. 4Athe interior connection terminal435is configured so that the lead wire extending from stator coil440may be crimped to the interior connection terminal and thereby provide an electrical conducting path for AC current to drive the AC motor.

FIG. 4Bshows the elements of the exterior connector terminal305in greater detail. Specifically, in an exemplary embodiment, a current drive cable (not shown) is secured to the insertion plug by fastener400. The fastener400shown inFIG. 4Bis a threaded bolt, assembled in coordination with fastening receptacle450. The fastening receptacle is simply a threaded area seated in a support portion of the insulator425, which receives the fastener400. The fastening receptacle could simply be a threaded portion of the insulator itself. The threaded bolt400is inserted through apertures defined in the conductor415and support element410to engage threaded nut450. Forming the aperture420in conductor415with a diameter greater than the bolt's diameter allows for flexibility in the location of the insertion plug and the fastener400within the housing.

The support element410, which may be a conical spring washer, a bevel washer, or another type of supporting element, provides additional support to the connection between the drive current cable (not shown), the exterior connection terminal305and the conductor415. Furthermore, support element410maintains pressure on the joint through a range of temperature and torque conditions (i.e., preventing rotation of the assembly). Also, it is to be understood that a wide variety of fasteners could be used, depending on design specifications. In the embodiment illustrated inFIGS. 4A and 4B, the fastener400is an M8×20 mm long steel Hex Head Bolt.

As shown inFIG. 4C, the conductor, i.e., current bus,415is formed as a flag terminal that includes an aperture420for securing the fastener400and the power cable (not shown) at the exterior connection terminal305. The use of the flag terminal incorporating substantially a right angle bend, provides a connection that is quite compact and robust both radially and axially. Conductor415also includes a cylindrical extension providing a stable connection point for the lead wire extending from stator440(shown inFIG. 4A) at the interior connection terminal435. It is to be understood that the current bus415may be modified in accordance with different AC motor designs and operating environments. For example, the current bus may be adapted to accommodate a wide range of phase coil winding length variations and varying radial end turn exit locations. At it's simplest, the conductor is simply any conducting material passing through the insulator.

The invention incorporates a ring of conductive material as part of the terminal conductor, the interior connection terminal435, which allows the process to require just one step: to place the bundle of magnet wire with the insulation within the interior connection terminal435and then use crimping and electric resistance fusing to make the connection. In this invention the interior connection terminal435is formed as an open circle and the final gap is closed by a brazing process.

Typically, the crimped and resistance fused electrical connections between bundles of magnet wire and the internal connection terminal are made with a roughly circular electrode which serves as both the crimping tool and the electrode. The circular electrode limits the amount of surface area contact to the connection and thereby limits the area that is crimped and the heat conducted into the joint to fuse the connection. As the number of wires in the lead bundle increases, the quality of the joint degrades.

In this invention, an elongated electrode is used where the length of the long axis of the electrode approximately equals the width of the internal connection terminal. This serves to increase the surface area contact to the connection and increases the area that is crimped and the heat conducted into the joint to fuse the connection. The additional heat at the joint provides for better vaporization of the wire insulation layer and thereby a better electrical connection. The brazed closing of the final gap in the interior connection, a terminal is required to ensure that the wires in the lead bundle remain in intimate contact with each other and therefore maintain a low resistance joint.

As shown inFIG. 5, the lead wire bundle460, has been inserted into the conductor415, and the interior connection terminal has been formed or crimped470, as well as electrical resistance fused to the lead wire bundle. The brazed joint480is also shown inFIG. 5, which fills the remaining gap in the formed interior connection terminal.

It is to be understood that the above description is only representative of illustrative embodiments. For the convenience of the reader, the above descriptions have focused on a representative sample of possible embodiments, a sample that teaches the principles of the invention. The description has not attempted to exhaustively enumerate all possible variations. That alternate embodiments may not have been presented for a specific portion of the invention or that further undescribed alternate embodiments may be available for a portion is not to be considered a disclaimer of those alternate embodiments. It will be appreciated that many of those undescribed embodiments incorporate the same principles of the invention and others are equivalent. Thus, it is to be understood that the embodiments and variations shown and described herein are merely illustrative of the principles of this invention and that various modifications may be implemented without departing from the scope and spirit of the invention.