US2767272A - Speed governor - Google Patents

Description

J. NADER SPEED GOVERNOR Oct. 16, 1956- 2 Sheets-Sheet 2 Filed Jan. 9, 1952 1211 5 17 ZZTT Joseph Nader E7 7 El 2H5 SPEED GOVERNOR Joseph Nader, Chicago, Ill., assignor to Motordyne Incorporated, Monrovia, Calif, a corporation of California Application January 9, 1952, Serial No. 265,699

3 Claims. (Cl. 200-80) The present invention relates to an improved speed governor, particularly for electric motors.

One common form of speed governors used for small duty motors is described in the Lee Patent No. 1,767,146. T his governor includes a rotatable support member which is arranged to be secured on the shaft of a motor, and a pair of resiliently mounted contacts which open or close within a predetermined range of velocity, the contacts being employed in the energizing circuit of the motor to control the energization of the motor.

One of the major difficulties with speed governors of the type described resides in the fact that the operation of these speed governors is very adversely aifected by changes in temperature and humidity. Even relatively small changes in temperature of operation of the motor from the temperature at which the switch contact arms were initially set or adjusted can cause a substantial variation in the velocity at which the centrifugally operated switch elements operate. In general, changes in humidity also affect the operation of the device in a similar manner. As a result, changes in temperature and humidity make operation of this type of speed governor erratic. In installations where the motor is used as a frequency control device, as in inverters for alternating current supplies in aircraft, this erratic operation due to changes in temperature and humidity provides a serious problem,

One of the features of the present invention resides in a structure for a speed governor in which the effects of temperature are compensated for by proper selection of the materials used in the manufacture of the rotatable support element and the resiliently mounted switch elements. In a preferred embodiment of the present inven tion, the support member is made from a material having a low coefficient of thermal expansion, and a modulus of elasticity which decreases with increase in temperature. On the other hand, the switch arms are made from materials which also have a low coefficient of thermal expansion, but have the property of becoming more rigid rather than more flexible upon an increase in temperature, or at least do not become less rigid upon increase in temperature. As a result, as the resilient switch arms are shifted due to the thermal expansion of the support member, the increased rigidity of the resilient switch arms compensates for this effect with the result that the switch operates at a predetermined velocity substantially equal to the predetermined velocity desired, even though the motor is operated at a higher temperature than that at which the setting of the resilient switch arms was originally made.

Another feature of the present invention resides in an improved type of commutator construction in the assembly through which the polarity of the voltage being supplied to the contact elements is periodically reversed, thereby materially increasing the useful life of the contacts. In addition, the commutator structure of the present invention includes specially designed conducting rings having an increased resistance to the detrimental effects of relatively high humidity.

nited States Patent An object of the present invention is to provide an improved speed governor assembly for electromagnetic machines which will operate at a predetermined velocity over a wide range of temperature and humidity conditions.

Another object of the present invention is to provide an improved speed governor for electric motors that is rugged in construction, but simple and inexpensive to manufacture.

Another object of the present invention is to provide an improved electromagnetic machine assembly including the improved governor of the present invention.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its manner of construction and method of operation, together with further objects and advantages may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

Figure 1 is a plan view of a motor equipped with the improved governor assembly of the present invention, with parts thereof broken away to illustrate more clearly the structure;

Figure 2 is a view in elevation, on a magnified scale, of the support member and switch assembly of the governor;

Figure 3 is a cross sectional view, with parts in elevation, of the improved commutator of the present invention;

Figure 4 is an exploded view of the elements making up the commutator illustrated in Figure 3; and

Figure 5 is a diagram of the eelctrical circuit, of the motor, illustrating the manner in which the switch contacts of the governor are disposed in the electrical circuit of the motor.

As shown on the drawings:

Referring first to Figures 1 and 2 of the drawing, there is illustrated an electric motor 10 of the D. C. shunt type. It will be recognized, of course, that the invention is equally applicable to other types of motors such as series or compound motors. The motor 10 has a shaft 11 extending therefrom, what carries a governor assembly 12, a set screw 13 being provided to lock the governor 12 in fixed position along the shaft 11.

The governor assembly 12 includes a disc-like support 14 and a commutator 15. Structural details of the latter will be described more fully in connection with the description of Figures 3 and 4.

The motor 10 also carries a pair of support brackets 17 and 13 having a pair of oppositely disposed brush holders 19 and 20 secured at the ends thereof. The brush holders 19 and 20 carry a pair of conventional springpressed brushes 21 and 22 which engage the commutator i5 and serves to reverse periodically the voltage applied to the switch arms of the governor.

As best seen in Figure 2, the support 14 includes an integral upstanding hub portion 24 having an internal bore of sufiicient diameter to receive the shaft 11 of the motor 10 in closely fitting relation. The hub 24 receives the commutator 15 in close fitting relation, as will hereinafter be described.

The support 14 is provided with suitable recesses to accommodate the switch elements of the governor assembly. These switch elements include a pair of resilient switch arms 26 and 27, each carrying a contact button 28 and 29, respectively. The fixed ends of the switch arms 26 and 27 are secured to an internal wall 30 of the support 14 by means of a pair of securing screws 31 and 32.

As shown in Figure 2, the commuator 15 is divided into conducting portions 34 and 35. The conducting portion 34 electrically connected to the switch arm 27 by means of a conductor 36 and 2. lug 37. An insulator strip 38 insulates the strip 37 from the wall 30. A pair of insulating strips 39 and 40 separate the switch arm 26 from the switch arm 27. The conducting portion 35 of the commutator 15 is electrically connected to the switch arm 26 by the provision of a conductor 42 and a lug 43. An insulator strip 44 insulates the switch arm 26, from a strip 45 into which the screws 31 and 32 are threaded. It will be appreciated that the screws 31 and 32 are electrically insulated from the switch contact arms 26 and 27, as by means of an insulating bushing about the screws 31 and 32.

The spacing between the contact buttons 28 and 29, which determines the angular velocity at which centrifugal force will cause the switch to operate is determined by means of a screw 48 adjustably threaded into a support member 49. The end of the screw 43 carries a glass ball St) or other insulating medium in abutting contact with the switch arm 27.

The material of the support 14 is chosen for its low coelficient of thermal expansion. A suitable material for this purpose is an aluminum-silicon alloy, such as one containing 12% silicon and 88% aluminum. However, even with materials having relatively low coeflicients of expansion, the expansion of the support 14 as a result of an increase in temperature causes a shift in the switch arms 26 and 27 such that the operating point, i. e., the velocity at which the contact arms 26 and 27 close, is varied. To compensate for this effect, the switch arms 26 and 27 are made from a material which also has a low coefficient of thermal expansion, but has the additional property of not increasing its flexibility as the temperature increases. Preferably, the material for the switch arms 26 and 27 is one which actually becomes less flexible as the temperature increases, that is, a material having a modulus of elasticity which increases with an increase in temperature.

Several types of alloys having these properties are available for the switch arms. A typical example of one such alloy is a nickel-iron alloy containing about 42% nickel, 4 /2% chromium, 2 /2% titanium, .06% carbon, .4% manganese, .5% silicon, .4% aluminum and the balance substantially all iron. The decreased flexibility at elevated temperatures of the metals described above has been found to compensate adequately for the expansion of the support member carrying the switch arms so that a relatively constant operating point can be achieved over a wide range of temperatures. Using a speed governor of the type described in an inverter assembly, I have found that the frequency in the generated A. C. voltage can be maintained to within an error of 1% over a temperature range from 55 C. to 75 C. This represents a substantial improvement over the operating characteristics of the conventional centrifugal type speed governors.

Another factor of importance in preventing erratic operation of the speed governor is the change in humidity which the governor encounters in use. The effects of humidity are especially troublesome in the commutator of the speed governor. The commutator structure illustrated with particularity in Figures 3 and 4 of the drawings effectively resists the adverse effects of changes in humidity. As best shown in the exploded view of Figure 4, the commutator includes a metallic spool 52 having an enlarged head portion 53. The spool has an axial bore 54 arranged to be received over the hub 24 of the support 14 in closely fitting relation. An inverted V- ring 55 of an electrical insulating material, such as mica, having a high resistance to moisture penetration is seated against the enlarged head 53 in nested engagement. A sleeve 56 of insulating and moisture resistant properties is next placed over the barrel of the spool 52 and against the inverted V-ring 55. The sleeve 56 preferably also composed of mica, forms a base support for the conducting segments making up the commutator structure. This structure consists of a plurality of individual, circumferentially spaced conducting segments 57 whose inner ends are dovetailed as indicated at 58 to be received in the insulator V-rings. Each of the segments 57 is preferably coated with a highly conductive material such as silver. The plurality of segments 57 is then arranged in a ring, and a pair of mica insulating strips 59 and 6% (Figure 2) are disposed at diametrically opposite portions of the conducting ring thus formed to provide the pair of conducting portions 34 and 35. The conducting segments may be pressed together with the mica strips interposed in a hydraulic press to cause a superficial bonding of the individual segments 57 into a composite ring. It will be appreciated that the commutator structure can be divided into more than two conducting portions, to thereby cause more than one cycle of current reversal during each revolution of the commutator.

The preferred ring is then slipped over the mica sleeve 56, and a second V-ring 62 is then fitted over the barrel 52 to center the conducting ring between the V-rings and 62. Next, a metallic V-ring 63 is placed over the barrel 52. As indicated in Figure 3, an end 64 of the spool 52 may be flared outwardly to prevent the \.'-ring 63 from slipping off the end of the spool.

As another alternative, the conducting portions on the commutator can be made from solid machined bars of arcuate shape, and the body of the commutator which may be composed of synthetic resins such as Bakelite may then be molded around the preformed, solid conducting portions.

A circuit in which the speed governor of the present invention is included is schematically illustrated in Figure 5. In this drawing, a D. C. shunt motor having an armature 65 is energized by means of a shunt field winding 68. A current limiting resistor is in series with the shunt field winding 68. The electrical switch con tacts 26 and 27 are in parallel circuit relationship with the resistor 70, and as the motor builds up to a predeter mined speed, the centrifugal force on the governor closes the contacts 26 and 27, thus shorting out the resistor 70. The elimination of the resistor 70 from the circuit causes a corresponding decrease in the speed of the motor. As the motor speed decreases, the centrifugal force urging the contacts 26 and 27 closed also decreases, until the centrifugal force is insuflicient to hold the resilient contact arms 26 and 27 closed. At this time, the switch opens and the resistor 70 is again inserted in series with the shunt field winding 68, thereby increasing the angular velocity of the motor.

While the governor of the present invention has been specifically illustrated used in conjunction with a D. C. shunt motor, it will also be evident that the governor will find use in other types of motors and in electromagnetic machines generally where speed control is to be achieved.

The governor of the present invention has several distinct advantages over similar governors heretofore used. One of the main advantages arises from the novel correlation of the flexibility of the switch contact arm with the thermal expansion and increases flexibility of the rotatable support member due to increases in temperature. Further, the novel structure of the commutator of the present invention effectively resists the adverse effects of increased humidity. Furthermore, by the arrangement of the commutator segments in the manner indicated, the brushes which cooperate with the commutator act against the commutator along radial lines, rather than imposing an axial thrust against the rotating governor as in conventional governor assemblies. This structural feature is advantageous from the stand point of securing proper alignment between the commutator and the contracting brushes.

It will be evident that various modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. A speed governor assembly comprising a rotatable support member, a pair of switch arms carried by said support member, said support member being composed of a material which becomes more flexible upon an increase in temperature, and said switch arms being composed of a material which becomes less flexible on increase in temperature.

2. A speed governor assembly comprising a rotatable support member, a pair of resilient switch arms carried by said support member, said support member being composed of a material having a relatively low coefiicient of thermal expansion and a modulus of elasticity which decreases with an increase in temperature, and said switch arms being composed of a material having a relatively low coefiicient of thermal expansion and a modulus of elasticity which does not decrease with temperature.

3. In a speed governor assembly including a rotatable support member, and a pair of resilient switch arms carried by said support member arranged to close upon rotation of said support member at a predetermined angular velocity, a tension adjusting means comprising a screw carried by said support member in threaded engagement, and a contact member comprising a glass ball carried by one end of said screw and arranged to engage one of said switch arms to vary the spacing between said switch arms upon axial movement of said screw.

References Cited in the file of this patent UNITED STATES PATENTS 854,781 Underwood May 28, 1907 1,061,251 Burke May 6, 1913 1,415,370 Lehman May 9, 1922 1,551,598 Winter Sept. 1, 1925 1,632,565 Schmidt June 14, 1927 1,767,146 Lee June 24, 1930 1,855,703 Cloud Apr. 26, 1932 2,103,589 Lee et al. Dec. 28, 1937 2,444,799 Wood et a1. July 6, 1948 2,454,067 Kohl Nov. 16, 1948 2,480,590 Merrill Aug. 30, 1949 2,557,208 Thunberg et al. June 19, 1951

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