Motor and Control System Having Cyclic Reversal and Unidirectional Capabilities

This invention relates to dynamoelectric machines, and in particular, to a novel motor system which develops high torque, instantaneous rotation reversal and simple speed control.

For some time, motor manufacturers have attempted to develop new motor systems for use in high volume appliances. One such motor system is disclosed in a copending United States application of the present inventor, U.S. Ser. No. 395,187, filed Sept. 7, 1973, now U.S. Pat. No. 3,858,098. The system disclosed in Ser. No. 395,187, like the invention disclosed hereinafter, provides a motor system operable continuously in either of two directions of rotation and permits instantaneous reversal between those rotational directions. This type of operation is particularly suitable for certain high volume consumer appliances. Thus, the systems may find application in a conventional washing machine, where cyclic rotation reversal of the motor is equivalent to an agitation or washing mode, and the continuous unidirectional run condition of the motor corresponds to the spin dry cycle of the appliance. Because of the unique motor operating characteristics, the motor may be connected mechanically to drive the wash basket directly, eliminating the need for transmissions now commonly found in washing machine applications. The invention described hereinafter, while dealing broadly with the same subject matter as Ser. No. 395,187, exhibits a number of improvements over previously known electronically controlled motors, in both the motor and circuit design aspects of the system.

Other prior art dealing with electronically controlled motors include, for example, the SCR manual, Fourth Edition, 1967, published by the General Electric Company; Principles of Inverter Circuits, John Wiley and Sons, Inc., 1964, by B. D. Bedford and R. G. Hoft; Complimentary Impulse Commutator Inverter, by R. Young, Poughkeepskie Lab., Technical Report TROO, 1973, dated Jan. 30, 1973, I.B.M.; and the U.S. Patents to Greenwell, No. 3,780,324, issued Dec. 18, 1973, and Offutt, No. 3,802,091, issued Apr. 9, 1974.

While this body of prior art generally discloses the use of electronic circuit means for controlling the operation of a dynamoelectric machine, very little information presently is available relating a motor which is continuously reversing its direction of rotation as a normal mode of motor operation. Under general motor design principles, it is highly desirable that the per unit current torque, of both the unidirectional and the reverse braking varieties, be as high as possible. Besides the obvious desirable feature of high torque from the application standpoint, if high per unit current torque can be obtained, the SCR circuits utilized in conjunction with motor operation need not be designed for high current handling capabilities and the cost of the motor system can be reduced appreciably.

The invention dislosed hereinafter utilizes an SCR circuit for controlling the application of electrical energy to a motor. The motor itself has a unique winding designed to deliver high per unit current torque. A position sensor used in conjunction with the motor is provided which includes adjustable elements for adjusting the speed torque characteristic of the motor. In addition, the control circuitry disclosed incorporates a number of improvements including means for limiting the current rate of change seen by the individual SCR elements, and a novel circuit arrangement for providing dual outputs from a single electrical input which operate independently of one another.

One of the objects of this invention is to provide an improved motor control system.

Another object of this invention is to provide a circuit arrangement for providing signal source voltage and motor voltage independent from one another from a single electrical input.

Another object of this invention is to provide an improved SCR circuit for controlling application of electrical energy to a dynamoelectric machine.

Still another object of this invention is to provide a position sensing device and reversing mechanism which is adjustable to vary the speed torque characteristic of a motor.

Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.

In accordance with this invention, generally stated, a motor system is provided that is capable of both unidirectional and bidirectional rotation and instantaneous direction reversal. A motor has a stator assembly including a core of magnetic material having a plurality of slots formed in it, and a two phase winding constructed from a plurality of wire turns arranged in coils. Each coil has a longitudinally extending portion and an end turn portion. The longitudinal portions of each coil occupies a separate slot of the stator core. A single rectifier circuit means is provided which supplies two power outputs, one to the motor and one to a position sensing and motor reversing circuit. The rectifier circuit means is designed so that the two power outputs are independent of one another. A silicon controlled rectifier (SCR) circuit is electrically connected to the position sensing and motor reversing circuit. The SCR circuit includes a novel arrangement for providing current rate of change protection to the individual SCR devices. The position sensing and motor reversing circuit is utilized to regulate the on times of individual elements of the SCR circuit. The position sensing portion also incorporates adjustable elements capable of varying the speed torque characteristic of the motor.

In the drawings,

FIG. 1 is a diagrammatic representation of one illustrated embodiment of motor system of this invention;

FIG. 2 is a diagrammatic representation of position sensing and motor reversing circuit utilized with the motor system of FIG. 1;

FIG. 3 is a diagrammatic representation of the winding distribution of a motor utilized in conjunction with the motor system of FIG. 1;

FIG. 4 is a sectional view of a motor useful in the motor system of this invention;

FIG. 5 is a winding diagram schematic for a rotor assembly of the motor shown in FIG. 4;

FIG. 6 is a diagrammatic representation of a wiring diagram for a stator assembly shown in FIG. 4;

FIG. 7 is a cross sectional view of an adjustable sensor element used in conjunction with the position sensing and motor reversing circuit shown in FIG. 2; and

FIG. 8 is a diagrammatic representation of speed versus torque curves exhibited by the motor of FIG. 4 in both forward and reverse directions, illustrating the variations obtained in the speed torque characteristic curves of the motor as the sensor element of FIG. 7 is adjusted.

Referring now to FIG. 1, reference numeral 1 indicates one illustrated embodiment of motor system of this invention. The motor system 1 includes a motor 2, a rectifier circuit 3, an SCR circuit means 4, and a position sensing and reversing circuit 5.

The motor system 1 has a pair of input terminals 6 and 7 respectively which are connected to a source of AC power, not shown. One side of a full wave bridge rectifier 8 is connected to the terminal 6 through an on/off switch 9. The bridge 8 includes legs 10 through 13, each of which have individual ones of a plurality of diodes 14 connected in a conventional manner so as to define AC connection nodes 15 and 17, and DC connection nodes 16 and 18. The node 15 is the side of the bridge 8 connected to the terminal 6 through the switch 9 by a conductor 19. A triac 22 has a terminal 23 electricaly connected to the node 17, and has a terminal 24 connected to a conductor 121. Conductor 121 is electrically connected to the input terminal 7. A resistor 21 and a capacitor 20 are connected in series with the conductor 121 between the terminal 23 and the terminal 24 sides of the triac 22. A gate electrode 25 of the triac 22 is connected to a first side of a silicon bilateral switch 26. A resistor 27 also is connected between the gate electrode 25 and the conductor 121. A second side of silicon bilateral switch 26 is connected to a conductor 28 at a node 122 which in turn is connected to the conductor 121 through a capacitor 29 and to a first side of a variable resistor 30. A second side of resistor 30 is connected to the switch 9 through a resistor 31.

The node 16 of bridge 8 is electrically connected to a rotor winding 32 of the motor 2 through a pair of brushes indicated generally by the numeral 33, and to a winding 34 of a stator assembly 35 of the motor 2. The brushes 33 are conventional and are not described in detail. As later set forth, the winding 34 includes four winding segments 36 through 39, respectively.

A conductor 41 is connected to the conductor 121 at a node 108 and to an anode of a diode 42. The cathode of diode 42 is connected to a node 45 through a resistor 43. A capacitor 46 and a resistor 44 are connected in parallel between the node 45 and a conductor 40. The conductor 40 is connected to the negative node 18 of the bridge 8. As described in more detail hereinafter, a zener diode 47 may be connected in parallel with the capacitor 46 and the resistor 44 between the node 45 and the conductor 40. A conductor 117 is electrically connected to the node 45 and supplies signal voltage power to the position sensing and reversing system 5 at an input terminal 120.

The conductor 40 also is electrically connected to the SCR circuit 4, serving as a common negative for that circuit. As later described in detail, and as observable in FIG. 1, a rectifier system is disclosed in which a DC voltage is supplied to the motor 2 and is controllable by the rectifier system 4 which voltage is adjusted by the operation of the triac 22 and resistor 30, while signal voltage is applied to the position sensing and reversing circuit 5 independently of voltage application to the motor 2 and SCR circuit 4.

The SCR circuit 4 includes four SCR devices 48, 49, 50 and 51 having their anodes connected to the winding segments 36, 37, 38 and 39 respectively through a diode 52 and an inductor 53. While each of the SCR devices 48, 49, 50 and 51 and related circuit components generally are similar to one another, certain specific circuit arrangements require that the entire SCR circuit mean 4 be described in more detail than might be necessary from either function or operation standpoints. However, like numerals are used for like components where appropriate. For example, the inductor 53 is important in that it has been found that use of the inductor 53 in the position sown and described provides better protection for the SCR devices against high current rate of change than other arrangements used in analogous circuit designs. The cathode of each of the SCRs 48 through 51 is electrically connected to the conductor 40.

A capacitor 54 and a series resistor 55 are connected between the conductor 40 and a node 56 located on the anode side of the SCR 48 between the diode 52 and the inductor 53. Similar arrangements of the resistor 55-capacitor 54 series circuit are connected between the conductor 40 and nodes 66, 69 and 70 located on the anode sides of SCRs 49, 50 and 51 respectively. A gate electrode 57 is connected to the conductor 40 through a capacitor 58 and to the position sensing and reversing circuit 5 through an inductor 59 and a conductor 60. The capacitor 58 serves as a harmonic filter and reduces application noise to insure that the SCR circuit means 4 is not triggered falsely.

A coasting path for load current includes a conductor 61 and a resistor 62 which are connected to the conductor 40 and a connection point 109. Individual ones of a plurality of diodes 63 are connected between the conductor 61 and a node 64 on the anode side of diode 52 for each of the SCR devices 48, 49, 50 and 51.

A capacitor 118 is connected in series with an inductor 65 between node 56 and the node 66, on the anode sides of SCRs 48 and 49. A similar series arrangement of a capacitor 67 and an inductor 68 is connected between the nodes 69 and 70 on the anode sides of the SCRs 50 and 51.

Elements of the position sensing and reversing circuit 5 are best described with reference to FIGS. 2, 4, and 7. As shown in FIG. 4, the motor 2 includes a stator assembly 71, and a rotor assembly 72 mounted to a shaft 73. The shaft 73 is journalled for rotation along a first end shield 74 and a second end shield 75.

End shield 74 is conventional and includes a central hub portion 76 which receives one end of the shaft 73. The end shields 74 and 75 may be joined to the stator assembly 71 and the rotor 72 by any convenient method. Conventional threaded fasteners, indicated generrally at 77, inserted through the end shields and through or along the ouer diameter of the stator assembly 71 work well, for example. A retaining ring 78 is positioned inboard of the hub 76 which acts to limit axial movement of the shaft 73 rotor 72 combination and to maintain the proper alignment of the rotor 72 and stator 71.

A slip ring assembly 80 is mounted for rotation with the shaft 73 and is positioned inboard of the end shield 75. The assembly 80 includes a disc body 110 having a first ring 81 and a second ring 82 formed on it. The rings 81 and 82 are conductive electrically and the ring 82 is disposed coaxially inwardly of the ring 81. The brushes 33 are mounted to the end shield 75 so that one each of the brushes 33 contacts an individual one of the rings 81 and 82. Location of the brushes on the end shield 75 may vary in embodiments of this invention. I find it convenient to mount the brushes 33 vertically through the end shield 75, although other arrangements are compatible with the broader aspects of this invention.

End shield 75 includes a central hub 83 which houses a bearing means 84. As indicated, bearing means 84 rotatably supports the shaft 73.

The position sensing and reversing circuit 5 includes a position sensing assembly 85 which is mounted to and is rotatable with the shaft 73 along the end shield 75 side of the motor 2. Assembly 85 includes a first member 86 and a second member 87, best shown in FIG. 7. The members 86 and 87 generally are cylindrical in cross section and are designed to be releasably rotatable with respect to one another. Means, for example, a set screw not shown and an opening 119 therefore, may be provided for securing the assembly 85 to the shaft 73.

The member 86 has a first circular electrically conductive ring 88 attached to it. The ring 88 has a plurality of position indicating, axially extending parts 89 integrally formed with it. Member 87 has a second circular, electrically conductive ring 90 attached to it. Ring 90 also has a plurality of position indicating axially parts 91 integrally formed with it. The members 86 and 87 preferably are constructed from a non-electrically conductive material, except for the rings 88 and 90 and their respective extensions 89 and 91, which preferably are copper or similar conductive material.

A diagrammatic illustration of the assembly 85 of FIG. 4 utilized in conjunction with a twelve pole, two phase winding is shown in FIG. 2. Individual poles of the two phase winding are positioned ninety electrical degrees apart, and are mounted on a core 104 of stator assembly 71. The rotor 72 is diagrammatically illustrated in FIG. 2 as a twelve pole wound rotor mounted on the shaft 73. The two members 86 and 87 of the position sensing assembly 85 also are mounted on the shaft 73. One is marked as the forward member for controlling rotation of the shaft 73 in a first direction, and another is marked as the reverse member for controlling rotation of the shaft in a reverse direction. Either member may function as the forward or reverse member, however, member 86 is designated as forward for purposes of description. The rings 88 and 90 are shown in axial aspect, while the axial extending parts are shown in plan. Again, this arrangement is used for purposes of description. The two rings 88 and 90 are energized through the two signal power brushes 92 and 93, electrically connected to a reversing switch 94 by a pair of electrical conductors 125 and 126 respectively. Switch 94 is conventional and is not described in detail. It may be located at any convenient location. Mounting the switch 94 on the end shield 75 works well, for example. In the embodiment illustrated, the brushes 92 and 93 are mounted through the hub 83. Brushes 92 and 93 may comprise any of a variety of commercially available devices and they are not described in detail. They appear in FIG. 2 and may be mounted on the end shield 75 at any convenient location. The brushes 92 and 93 ride on the continuous ring portions 88 and 90 of the respective members 86 and 87.

The angular position of the rings 88 and 90 are specified in FIG. 2 by the notations .alpha. (alpha) and .beta. (beta), where alpha represents the angular distance from the center of the slot between two rotor poles 95 to the center of an extending part 89, and beta represents the angular distance from the center of an extending part 91 to the center of the slot between two rotor poles 95. The selection of the angles .alpha. and .beta. directly influence the torque/speed characteristics of the motor. An example of the variations obtained is given in FIG. 8. As there illustrated, a set of torque/speed curves of a sample motor is plotted for different angles .alpha. and .beta.. The summation of the angles .alpha. and .beta. gives the angular distance between the two signal rings 88 and 90 as measured between the centers of two extending parts 89 and 91. The best operative region for this angular distance has been found to be in the range of 85.degree. or 85.degree. +N.times.360.degree. to 275.degree. or 275.degree.+N.times.360.degree. electrical degrees where N is an integer and equals a whole number. That is, the number N may be equal to one or more of the number of pole pairs for the motor 2. The extending parts of each of the rings 88 and 90, in the embodiment illustrated, are 360 electrical degrees apart as measured center to center. Consequently, any of the extending parts can be biased to set the relationship of the rings, i.e. choosing the angles .alpha. and .beta. within the above ranges. Although the motor 2 still operates at angles other than those given, performance generally is not as good as motors having the rings 88 and 90 set within the range given. The number of extending parts 89 and 91 is equal to the number of pole pairs of the rotor assembly 72. Consequently, for the 12 pole rotor illustrated, six of the extending parts 89 and 91 are utilized. That is to say, six of the extending parts are used in conjunction with each of the rings 88 and 90. The angular width of the extending parts 89 and 91 is indicated by an angle .theta. (theta) and is equal to 360.degree. divided by the number of poles.

The output of the extending parts 89 and 91 of the members 86 and 87 is sensed by a plurality of signal brushes 96 which are located along the center lines of predetermined ones of the poles of each phase of a stator winding 97. Stator winding 97 is described in detail hereinafter. For present purposes it is sufficient to note that the winding 97 is a two phase winding. That is, the winding includes two sets of wound coils defining a plurality of electrical poles which are predeterminately positioned with respect to one another. In the two phase motor diagrammatically shown in FIG. 2, the solid lines represent the phase 1 pole centers and the dotted lines represent the phase 2 pole centers. Two of the signal brushes 96 are located at each pole center for picking up the signals coming from the forward and the reverse signal rings 88 and 90. The brushes 96 ride on the parts extending 89 and 91 so that signal output from the members 86 and 87 is a pulse which is capable of initiating conduction of predetermined ones of the SCRs 48 through 51. Each set of the two signal brushes 96 located at a particular pole center are connected through a diode 98 and a resistor 99 to one of the gate electrodes of the SCRs 48, 49 50 and 51. That is, gate command is supplied from the signal brushes at 96 to the respective terminals a, b, c and d in FIG. 2 which correspond to the terminals a, b, c, and d shown in FIG. 1. Gate command turns certain ones of the SCRs devices on in accordance with the position of the rotor assembly 72. It also may be observed in FIG. 2 that the spacing between the axial extending parts 89 and 91 and the angular length of those extending parts are such that two of the brushes 96 will receive an input signal very nearly at the same time, so that the SCRs may be considered to operate in pairs. The diodes 98 are used to prevent electrical interferences between the rings 88 and 90 during operation of the motor 2, described hereinafter.

As indicated above, and diagrammatically illustrated in FIG. 5, rotor assembly 72 is a wound armature having a winding 100 arranged in slots of a plurality of stacked laminations not shown. Lamination design and slot configuration, while important in overall motor performance capabilities, form no part of this invention and are not described in detail. The winding 100 comprises a plurality of wire turns arranged in individual coils 101 and positioned in the slots of the rotor core. The coils 101 are serially connected and terminate in coil ends 102 and 103 which are electrically connected to the rings 81 and 82 of the slip ring assembly 80.

The stator assembly 71 includes the core 104 constructed from a plurality of individual, stacked laminations, not shown. In the motor 2 illustrated and described, each lamination has a central, rotor receiving opening through it, and has a plurality of slots extending radially outwardly from the central opening. The slots also extend axially through the stacked laminations to define winding receiving receptacles. The stator assembly 71 also includes the stator winding 97. The winding 97 is constructed from a plurality of wire turns formed into individual coils 106. The coils 106 include end turn portions 107, best observed in FIG. 4, and axially extending portions contained in the slots of the individual laminations forming the core 104 which are generally indicated by the numeral 111 in FIG. 4. The particular lamintion utilized in conjunction with the motor 2 has 48 slots, and the winding 97 is positioned so that an individual one of the axially extending portions 111 of the coils 106 is positioned within a single slot of the lamination. That is, none of the coils 106 share slots with any other of the coils forming in the winding 97. The ends of the winding 97, shown in FIG. 6, as A.sub.1 and A.sub.2, A.sub.3 and A.sub.4 ; B.sub.1 and B.sub.2, B.sub.3 and B.sub.4 ; are electrically connected in FIG. 1 at T.sub.1 and T.sub.2, and T.sub.3 and T.sub.4, and T.sub.5 and T.sub.6, and T.sub.7 and T.sub.8, respectively. The coils 106 between the ends A.sub.1 and A.sub.2 constitute the winding segment 36 while those between A.sub.3 and A.sub.4 constitute the winding segment 37. In like manner, the coils between the ends B.sub.1 and B.sub.2 constitute the winding segment 38 while those between B.sub.3 and .sub.4 constitute the winding segment 39. The coil 106 placement within the core 104 is diagrammatically illustrated in FIG. 3. The arrangement shown in FIG. 3 is carried out only for 16 slots of the 48 slots lamination, but those skilled in the art will recognize the coil placement merely is repeated for those slots in excess of 16. The segments 36 and 37 of the winding 97 constitutes one pahse of that winding, while the segments 38 and 39 constitute a second phase of that winding. Each phase of the winding 97 has 12 of the coils 106 associated with it, six between each of the ends A.sub.1 and A.sub.2, A.sub.3 and A.sub.4, B.sub.1 and B.sub.2, and B.sub.3 and B.sub.4.

Operation of the motor system of this invention is simple. The motor 2 is installed in the desired application. As indicated above, the motor 2 has particular application when adapted for use in an appliance, in particular, to drive the wash basket of a conventional washing machine indicated generally by the numeral 115 in FIG. 1. In that application, the switch 94 may comprise a mechanical linkage which reverses the application of signal power to the members 86 and 87 after a predetermined angular movement, thereby altering the operation of the SCR circuit means 4 and reversing rotation direction of the rotor 73, and which may be locked in either of the two positions shown to permit rotor rotation in a single direction. This type of operation, of course, is directly comparable to the wash and spin modes of operation of conventional washing machines.

A single phase AC power source is connected to the terminals 6 and 7. The AC source is applied to the bridge rectifier 8 through the on/off switch 9 and the triac 22. The bridge 8 provides full wave rectification of the AC input and bridge 8 output is controlled by the triac 22. Application of the AC power through the switch 9 charges capacitor 29 through resistors 31 and 30. The rate at which capacitor 29 charges is adjusted by resistor 30. After capacitor 29 reaches a predetermined voltage, it discharges through the silicon bilateral switch 26 and resistor 27, thereby providing gate command to triac 22. Since triac 22 controls the AC input side of bridge 8, it also controls the DC output side of the bridge. The motor 2 operates similarly to a conventional series wound DC motor in that speed is directly proportional to the applied voltage. Since applied voltage is easily controlled by the circuit disclosed, it is evident that simple means for varying the speed of the motor 2 is provided.

An important feature of my invention is the circuit arrangement utilized to provide the supply voltage at the terminal 120. Upon activation of the switch 9, a current will flow through conductor 41, the rectifier diode 42 and resistor 43. The voltage at node 45 charges capacitor 46 until the breakdown voltage of zener diode 47 is reached, at which time capacitor 46 discharges through diode 47. Diode 42 is connected to the negative node 18 of bridge 8 through resistor 43 and the capacitor 46, resistor 44, diode 47 circuit between node 45 and the common negative conductor 40. Consequently, the rectifier circuit means 3 displays dual outputs, one variable for motor 2 speed control, and a second constant voltage for operating the position sensing and reversing means 5. The second output voltage is not affected by changes in the firing angle of the triac 22 because the diode 42 is connected to the AC power line conductor 19, while a simple circuit arrangement is made possible because of the use of the common negative connection to the negative node 18 of bridge 8 through the conductor 40. When a constant and smooth signal power voltage is not required, the zener diode 47 may be omitted, and for this reason, diode 47 is illustrated in phantom lines.

As indicated above, terminal 120 is connected to rings 88 and 90 through the brushes 92 and 93. Rotational direction of a DC motor 5 may be changed in a variety of ways, for example, reversing the polarity applied to either the armature or the field winding of a conventional DC motor will reverse the rotational direction of the motor. This principal is applied in the motor 2, by use of the switch 94 and position sensing means 5 to energize certain ones of the winding segments 36 through 39, depending upon which direction of rotation is desired. Switch 94 in addition preferably is adapted to permit either cyclic reversal or continuous rotation of the rotor assembly 72. It is thus evident, that cyclic reversal of the motor 2 corresponds directly to the washing mode of the present day convenional washing machines, while the continuous rotation corresponds to the spin cycle of those machines. Energization of the winding segments, 37, 38, 39 and 40 is dependent upon position of the rotor assembly 72. That is to say, the signal brushes 96 initiate the gate signal for the SCR devices 48 through 51 which in turn determine which of the winding segments are energized. With the switch 94 in the position shown full line in FIG. 2, power will be applied to the ring 88. Two signal brushes 96a and 96b of the brush plurality 96, because they are in contact with an axial extending part 89 of the ring 88, will be energized and develop a voltage at terminals a and b. Terminals a and b provide gate command for SCRs 49 and 51, so that these SCRs will be gated on. As the rotor assembly 72 continues to rotate, the succeeding extending part 89 will come into contact with brushes 96c and 96d of the brush plurality 96, which provides gate signal voltage at terminals c and d, while the proceeding extending part 89 moves out of contact with brushes 96a and 96b, removing gate command from terminals a and b. It should be noted that the voltage and current at terminal 120 are extremely low as compared to the voltage supplied to the motor 2. Consequently, problems inherent in prior art systems arising because of the interruption of high voltage and current circuits are not a factor in the operation of the motor 2.

The SCR circuit system 4 is conventional in that it provides an SCR device for each of the winding segments 36 through 39. When gate command is present at terminals a and b, SCRs 49 and 51 conduct, permitting current flow through the winding segments 37 and 39 to the negative supply terminal node 18 of bridge 8 via conductor 40. SCRs 49 and 51 are commutated by removing their gate command and gating SCRs 48 and 50 to an on condition. Initial conduction by SCRs 49 and 51 will change capacitors 118 and 67. Taking the SCR 48 and 49 branch as an example, conduction by SCR 48 will discharge capacitor 118, thereby providing commutation current for SCR 49, turning that device to an off condition through a loop path comprising capacitor 118, SCR 48, conductor 40, SCR 49, and inductors 53 and 65. Those skilled in the art will recognize that while the turn on and turn off times of an SCR device is described as instantaneous, in actuality, the turn off time extends over some time period before the SCR device actually is in a final off condition. During this time period, it is common to provide a coasting path for the load current. I have found that the use of the resistor 62 in the coasting path to be beneficial in that initially current for communicating the on SCR will flow in the loop path described. Once commutation begins, however, the load current may transfer to the coasting path of resistor 62, conductor 61 and diode 63. This same operation cycle is repeated when SCR 48 is commutated and also is applicable to the SCR 50 and 51 branch operation.

It is thus evident that the motor system disclosed is one well adapted to attain all the ends and objects set forth, together with other advantages which are obvious and which are inherent to the structure disclosed.

Numerous variations, within the scope of the appended claims, will be apparent to those skilled in the art in the light of the foregoing description and accompanying drawings. For example, some latitude is permissible in component selection and placement. As indicated, zener diode 47 may be utilized or not, depending on whether regulated input voltage to terminal 47 is desired. Likewise, the silhouette and design characteristics of motor 2 may vary in other embodiments of this invention. While the motor 2 was described as a twelve pole motor, other electrical pole configerations are compatible with the broader aspects of this invention. Merely by way of example, the following components are suitable for use in the circuit illustrated in FIG. 1.

While conventional brushes were utilized for signal brushes 96, other forms of generating the gate signal may be utilized, if desired. For example, other embodiments of this invention are contemplated where Hall effect generators are utilized for gating the SCR devices into conduction. While various connection points were illustratively described as "Nodes," those skilled in the art will recognize that the diagrammatic illustration of a connection node merely facilitates the verbal discription of the circuit diagram under consideration and that individual nodes maybe combined into single connection points and need not appear as actual nodes in embodiments of this invention.

These variations are merely illustrative.