US1138299A - Electrical driving system. - Google Patents

Description

H.C.LEAKE ELECTRICAL DRIVING SYSTEM.

APPLICATION FILED JUNE 6, I910.

1,138,299. Patented May 4, 1915.

4 SHEETS-SHEET l- (mm Inventor H. C. LEAKE.

ELECTRICAL DRIVING SYSTEM.

APFLICATION FILED JUNE 6, 1910.

1,138,299. Patented May 4, 1915.

4 SHEETS-SHEET 2- H. C. LEAKE.

ELECTRICAL DRIVING SYSTEM.

APPLICATION ru n JUNE 6. 1910.

1,138,299, v Patented May 4, 1915.

4 SHEETS-SHEET 3- min m Inventor.

- M Maw 144114 H. C. LEAKE.

ELECTRICAL DRIVING SYSTEM.

APPLICATION man sum: 6. I910.

1,138,299. Patented May 4, 1915.

4 SHEETS-SHEET 4.

30 '1; I *5 iii: 1

(6mm Imenror unirnn STATES PATENT oEEioE.

HENRY COOK LEAKIE, F ALTRINCHAM, ENGLAND, ASSIGNOR TO VICKERS, SONS & MAXIM, LIMITED, OF WESTMINSTER, ENGLAND.

ELECTRICAL DRIVING SYSTEM.

Specification of Letters Patent.

' Patented May 4, 1915.

Application filed June 6, 1910. Serial No. 565,341.

To all whom it may concern Be it known that I, HENRY Coon LEAKE, a subject of the King of Great Britain, residing at Spring Hill, The Downs, Altrincham, in the county of Chester, England, have invented new and useful Electrical Driving Systems, of which the following is a specification.

This invention relates particularly to methods of actuating and controlling electric motors employed for driving thevarious mechanisms of turrets on warships. In. connection with such working it is of the utmost importance that starting and stopping should be effected with facility; that there should be a wide range of speed with steady ruiming at any speed; that the control should be delicate, and the working immediately responsive to the control.

.Hitherto the most successful method of operation of turrets and turret mechanism has been byhydraulic motors and rams. These have the properties indicated above in a high degree, and there is much to be said in their favor. In the application of electrical power to this work,vthei'efore, it is desirable that the electric motors should be made to imitate in their action as far aspossible the properties of a hydraulic systerm. For this purpose in the first place the motors employed are arranged upon a constant current system,, some or all of the motors for one or more turrets being supplied from a single generator. This generator may be driven by a motor connected to the ordinary electrical supply mains on the ship, or in any other desired fashion, but in any case it is provided with a special winding or regulator by means of which its 40 current output is kept constant in spite of changes in its external circuit. Such constant current motors have the advantage that they can be simply and easily regulated without the complication of starting rheostats and without the losses attending their use. The torque of such motors, however,

does not substantially Vary with the speed,

so that the controller when correctly set for any particular speed confines the motor torque to a certain corresponding value. The result of this is-that fora particular setting of the control devices the motor will increase in speed until its load opposes a torque equal to that which the control devices permit the motor to exert. Comparatively small variations in the load of such a motor may then produce great unsteadiwhich may conveniently be attained in the case of the field by providing an extra winding connected across the brushes, and in the case of the armature by providing ashunt. This property, however, should not be gained at the expense of the standstill torque, and it may. therefore be well to' compensate for the effect of such regulation on the standstill torque by increasing the field strength at standstill. It is of course usual to regulate ordinary direct current motors by means of armature shunts and field rheostats and such motors have been used in elevating guns, but they have not the valuable properties attained by the present invention.

The invention is illustrated in the accompanying drawings, in which- Figure 1 diagrammatically illustrates the constant current system applied for this purpose, Fig. 2 shows an arrangement for obtaining constant current from a generator. Fig. 3 illustrates the use of an armature shunt, and Fig. 4 the effect of such use upon thetorque speed characteristic of the machine. Fig. 5 shows a modified way of using the armature shunt, and its effect on the characteristic is illustrated in Fig. 6. Fig. 5 shows a modification of the arrangement illustrated in Fig. 5. Fig. 7 illustrates the application of the principle of Fig. 3 to a separately excited motor. Figs. 8 and 9 show other modified ways of using the armature shunt and Fig. 10 shows diagrammatr gun turrets, gun laying from the ordinaryships mains 3. The gen erator has aseparately excited field and is so regulated as to supply within the limits of its power a constant current to its external circuit whatever the condition of that circuit. The current from this generator is taken into the rotatable turret through suitable sliding connections, and is led to the main isolating switches 5, one for each motor or group of motors through which it reaches the motors 6 and 7 which are diagrammatically shown as series wound. Each motor has a controller of a suitable type which conveniently consists in a movable brush rocker and by the aid of which the torque exerted by the motor can be varied from zero to its maximum in either direction.

It is possible to control a constant current smotor by varying its field strength (its brushes being fixed in neutral position) instead of by varying the position of its brushes, and this can be eifected by use of a field shunt resistance if the machine is series wound, or by the'use of a field series resistance if the field is separately excited. By'short circuiting or interruption respectively, of the field circuit the motor may be stopped, and by reversal of the field current the motor may be reversed. As rapid variation of the field may be needed the magnets should-be laminated. This method of regulating the motor is liable to a certain amount of sluggishness in. response on account of the time taken for the field to grow or diminish. The objection is only likely to be serious, however, in actual reversal and it may therefore be desirable in some cases to effect reversal by reversing the armature connections without of course interrupting the main circuits. Or it is possible to employ a double winding on the armature, the two windings each having a commutator and being connected in opposite directions to a switch by which either may be inserted in the main circuit. Thus the motor may be reversed without it being necessary to destroy and remake the field. Preferably the controller, on whatever system it works, is so arranged that, when in the off position, it closes a switch which short circuits the respective motor so that unnecessary heatcurrent is obtained by the use of an automatic controller WhlCll moves the brush rocker of the generator.

In Fig. 2 there is illustrated an improved system by which such brush control may be obtained. Here again 1 is the main generator and 2 its driving motor. The brush rocker of the generator is operated by a small auxiliary motor 8, the field 9 of which is arranged across the supply mains of the motor 2. The armature 8 of the motor receives its current from the armature of an auxiliary generator 10 which has two fields, one 11' connected with the field 9 across the mains, which are supposed to be of constant voltage, and the other 12 connected in series with the main generator 1. The windings 11 and 12 are so designed that, when the current passing through 12 is the normal constant current required, the two wind 85 ings balance each other and the auxiliary generator has no field. If the current in 12 increases, current is supplied to the armature 8 and the brushes are so rotated as to lessen the terminal voltage of the generator 1. If the current in 12 diminishes, the armature 8 again receives a supply, but in the opposite direction, and so rotates the brush* rocker of the main generator 1 as to increase its voltage. Obviously the auxiliary motor may bearranged to operate a field regulator instead of the brush rocker for the same purpose. It will be readily seen that this method of supply allows of excellent control of the torque of the motors and so enables the various operations to be conducted at M any desired speed, and with considerable delicacy of regulation. Starting rheostats and automatic circuit breakers and like devices are to a large extent eliminated from the turret. There is no need to waste any power in the regulation nor is there any danger of the generator or any of the motors becoming overloaded. It is not necessary that the generator should be of such capacity as to .be able to supply all the motors in its external circuit at their full load, but in the design of the generator proper allowance will be made for the fact that only a certain proportion of the motors are to. be expected to come into operation at one time. If this should result in a number of motors at some time endeavoring to take up more power than the generator is designed to supply, the limit of voltage regulation of the generator tion andsensitiveness of'control it is better will be reached, and then the motors will that the torque of the motor-should fall with the speed. If the speed is to be determined merely by fixing the torque at some constant value by suitable regulation of the brush position or motor field, the motor may vary considerably in speed owing to slight and unavoidable changes in its load which becomes particularly serious at low speeds. Under such conditions quite a small change in the resistance against which the motor is working may produce a very large variation in its speed, or even stop it altogether. It is therefore highly desirable that the torque of the motor should be made to vary with the speed so that any change in speed tends to automatically correct itself by varying the torque in a compensating manner. A hydraulic motor or ram, which has already been mentioned as having ideal characteristics for the purpose particularly in view, viz :-operation of turrets and turret and gun mechanismdoes not suffer from this disadvantage; it is inherent in its nature to exert as large a torque with its control valve nearly shut as with it wide open.

before being brought to a standstill. To obtain in the constant current motor the characteristics of a hydraulic motor, low speeds must be secured, not by limiting the maximum torque available, but in part at least, by causing the torque to fall rapidly with increase of speed. It will be apparent that the motor should be subject to two different controls, viz: hand control dependent on the 'i will of the operator (or the equivalent) and an automatic or inherent control dependent on the speed. a

The torque of the motor depends on the field, the armature current, and the position of the brushes; so that one or other of these require to be made dependent on the speed to produce the automatic or inherent regulation. It is diflicult without introducing undesirable moving parts to make the speed directly control either of these variables; but the'volta-ge across the armature varies with the speed, and this may conveniently be employed to control either the field or the armature current.

The armature current is conveniently varied automatically with the speed by simply connecting a resistance in shunt across the brushes in the manner indicated'in Fig. 3, where 13 indicates the motor armature, 14: its field, and 15 a resistance which may be variable, connected across the brushes of the armature. When the motor is stationary, the constant current will divide itself between the armature winding and the shunt resistance in inverse proportion to their resistances. When the motor begins to rotate, the passage of current through the armature is opposed not only by the resistance but also by the back electromotive force. This increases with the speed and therefore the fraction of the current diverted through the shunt will also increase with the speed. The total current being constant, the current in the armature must diminish as the speed increasesand therefore the torque also will fall ofl. The rate at which the torque falls off with speed will depend upon the magnitude of the shunt resistance. If the machine reached such a speed, that the back E. M. F. was equal to the product of the shunt resistance, and the constant current of the system there would be no current through the armature and therefore no torque. Obviously the lower the shunt resistance, the lower the speed at which this condition is reached. By cutting out the shunt by a switch under the control of the operator, the motor is instantaneously restored at will to its usual condition in which it is capable of giving its maximum torque at the high speed.

Fig. 4 diagrammatically illustrates the effect of such a shunt upon the characteristics of the machine. In this figure the torque of the motor is plotted as ordinates against abscissae proportional to the speed. The line 16 indicates the constant torque of a constant current motor which has no shunt. The level of this line can of course be varied by varying the brush position or by varying the fieldexcitation, but these variations leave it horizontal. If a comparatively large resistance is put in shunt with the armature, the torque curve will slope a little, as indicated by the line 17; (it may be that the torque curve will not be a straight line, but that is not of importance for the purpose of the present argument). It is important to notice, however, that with this change in the slope of the torque curve there is also and necessarily ,(so far as the devices yet described are concerned) a diminution in the initial standstill torque. This is because the maximum current through the armature of the motor is no longer the constant current of the system, but a fraction of that current equal to the ratio of the shunt resistance to the sum of the resistances of armature and shunt. When the shunt resistance is diminished, the standstill torque is diminishedand the slope of the torque speed characteristic becomes steeper, as indicated in Fig. 4 at the lines 18, 19, 20. It has been stated that this falling torque characteristic may be obtained by causing the field to vary with the speed. This is simply done by connectin a field winding which opposes the main eld winding in shunt with the armature. Such a winding necessarily acts to some extent in the same way as the resistance 15, i. (2., simply as an armature shunt,

its effects in this respect being small if its resistance is large, but large if its resistance is small. Apart from its actlon as anarmature shunt, however, such a field winding will obviously diminish the strength of the field as the motor increases in speed. It does not matter for this purpose whether the motor has a series field or is separately excited. Moreover in the former case the reverse field winding, or any armature shunt which may be used, can be put across both field and armature instead of only across the armature. In the case ofthe simple armature shunt, as already stated, the shunt may be made variable to vary the slope of the torque speed curve; where a reverse field winding is desired its effect may be varied by the use of a resistance in series with it. It will be clear that this automatic variation of the field will have a similar effect to the variation of the armature current, but the shape of the series of falling torque curves will vary according to the details of the arrangement adopted.

. It is now important not to diminish the standstill torque of the motor to any great extent, for otherwise the disadvantage above referred to in connection with the simple constant current motor still exists, viz: that a small rise in the resistance which the motor has to overcome may suffice to actually stop it. This disadvantage may be overcome by compensating for the diminution of the standstill torque occasioned by the methods of regulation indicated. Conveniently the standstill torque when diminished by the connection of an armature shunt may be increased again to its initial value by increasing the field. In the case of a series field, this 'may be efiected by varying the number of turns in the field winding, as illustrated in Fig. 5. Here again 13 is the armature of the motor to be controlled, 14 is the series field, and 15 is the variable shunt. The turns of the field winding 14 and the segments of the rheostat 15 are arranged to be simultaneously variable by the movement of a single controller. This is diagrammatically illustrated by the slider, 21 which as shown is connected to one of the brushes on the armature 13 and makes contact on the one hand with the field winding 14 and on the other hand with the rheostat 15. As the resistance in shunt with the armature is diminished the number of turns in the field winding carrying current is increased. Such an arrangement gives a series of torque speed curves like those indicated in Fig. 6; that is to say, the simultaneous variation of the field and of the armature shunt causes a change in the slope of the torque speed characteristic without any diminution of the initial ordinate.

If the field of the motor is separately excited as indicated in Fig. 7, a rheostat 22 in series with the field is varied simultaneously with the rheostat 15 for the pur and a rheostat 23 provides for hand control of the motor by variation of the field. Instead the brush rocker may be moved to compensate for the connection of an armature shunt resistance.

Another method of compensating would consist in providing an auxiliary winding in the field connected in series with the armature shunt, as illustrated in Fig. 5 but this acts also to strengthen the field as the motor increases its speed. Such modifications, however, are obvious and no others need be further detailed.

If irregularities arise owing to variation in the contact resistance of the carbon brushes of the machine to which the armature shut is applied, such irregularities may be avoided by connecting the shunt resistances directly to the armature. winding.

For this purpose one or more resistances may be mounted on the armature and connected to points on the armature winding which are separated by an angle equal to the angular pitch of the pole. This somewhat alters the manner of operation since the shunt resistances are now traversed by varying or alternating current, while the torque is made to vary or alternate during the revolution in a corresponding manner, the average torque is, however, reduced.

In Fig. 8, for example, three such resistances are shown for a two pole machine. If desired, however, instead of joining points separated by the pole pitch, a number of symmetrically placed points may be connected to a common junction. In Fig. 9 several such resistances are shown joined to the armature winding on the one hand and on the other to one of a set of contacts arranged in a circle. Preferably the contacts are made conical and are adapted to be bridged by an insulated conical short circuiting ring mounted movably on the shaft of the motor so that the shunt resistances can be cut out of action when desired.

In all cases the resistances employed may if desired be of a material having a negative temperature coefiicient. This will have the effect of causing the torque speed characteristics to become gradually steeper, as

while on a fall of speed the speed increases,

increases and partially the shunt resistance restores the torque.

If desired instead of the above described compensating devices an electromagnetic switch or like device could be arranged to cut out any'shunt automatically as the speed falls, so as to restore the standstill torque to its maximum value.

In Fig. 10 which shows the system applied to a rotating turret, 24 indicates the motors for turning the turret through the worm gears 25, pinions 26 and rack 27. The

rack 27 with the.roller track 28 is fixed to q the deck. The motors 24- and inions 26,

however, rotate with the turret and the pinions 26 travel around the inside of the rack 27. The lower guns 29,,are elevated by the motors 80 through suitable worm gearing and the upper guns 31 are similarly actuated by the motors 32. The sprocket chain ammunition hoist is represented at 83 and is driven by the motor 34 through the gearing 35.

The simplicity and delicacy of the control of motors on the system herein described appears to render them suitable also for ap-- plieationto some of the smaller guns not mounted in rotating turrets and usually worked by hand, but with which a partial use of power might be advantageous to save considerable physical exertion. In such a case several guns might conveniently be operated from a single motor generator.

lVhat I claim is 1. The combination of an electric motor, means for supplying constant current to its terminals and a shunt across its terminals adapted to cause the ampere turns on the motor to vary inversely with the speed over a considerable range of speed.

2. The combination of an electric motor having a field winding and armature, means for supplying constant current to said motor, a shunt across the armature of said motor and independent of the field winding and means for varying the number of turns of the field winding and the resistance of said shunt simultaneously.

.3. The combination of an electric motor having an armature, means for supplying constant currentto said motor, a shunt across the armature of said motor and means for causing the current in the shunt to vary with the ampere turns on the field.

4. The combination of an electric motor,

means for supplying constant current to said motor and means for causing the ampere turns on the armature to vary inversely with the speed over a considerable range of speed and for changing the rate of variation of the ampere turns on the armature with the s cc 5. The combination of an electric motor having an armature and field winding, means for supplying constant current to its terminals, a shunt across the armature independent of the field and means for varying simultaneously said shunt and the ampere turns on the motor field.

6. The combination with an electric motor of means for supplying a constant current to its terminals, means for causing the torque to vary with the speed, and means for changing at will the rate of variation of torque with speed at any given speed.

7. The combination with an electric motor of means for supplying a constant current 55 to its armature terminals, means for supplying current to the field, a shunt across the armature, a resistance in series with the field, and means for varying simultaneously the armature shunt and the field resistance.

8. The combination with an electric motor of means for causing its torque to vary with speed, and for changing the rate of variation of torque with speed, and means for maintaining the standstill torque constant independently of the rate of variation of torque with speed.

9. In an electrical driving system, the combination of an electric motor, means for supplying a constant current to the terminals of the motor armature, means for supplyingcurrent to the field winding, an ohmic resistance in shunt with the armature winding, and means for varying simultaneously the resistance of said armature shunt and the current through the field winding.

10. In an electrical driving system the combination of an electric motor, means for supplying constant current to the terminals of the motor armature, means for supplying current to the field winding, a rheostat in series with the field winding, a rheostat in parallel with the armature winding, and means for varying the two rheostats simultaneously.

11. In an electrical driving system the combination with an electric motor of means for supplying a constant current to the terminals of the motor armature, and means for supplying current to the field winding, a resistance in shunt with the armature, means for varying the torque produced by a given current in the armature winding, and means for simultaneously varying the resistance in shunt with the armature windin I2. The combination with gun laying mechanism of an electric motor operatively connected thereto, means for causing the torque of said motor to vary with speed, and for regulating the rate of variation of torque with speed, and means for maintaining the standstill torque constant.

13. The combination of gun laying mechanism, an electric motor having an armature and field winding opcratively connected thereto, means for supplying constant current to its terminals, a shunt across the armature independent of the field, and means for varying simultaneously said isihpit and the ampere turns on the motor 14. The combination of gunlaying mechanisni, an electric motor operatively connected thereto, means for causing torque of said electric motor to vary with speed. means forchanging the rate of variation of torque with speed, and means for maintaining the standstill torque constant independently of the rate of variation of torque ,with speed.

15. The combination of an electric motor,

means for supplying constant current to its terminals and a shunt of negative temperature co-eflicient across its terminals adapted to cause the ampere turns on the motor to vary inversely With the speed over a considerable range of speed.

- 16. The combination of an electric motor having a field Winding and an armature Winding, means for supplying constant current to said motor and a resistance of negative temperature co-eflicient independent of the field Winding in shunt across the arma ture winding and regulable by hand.

17. The combination of an electric motor having a field Winding and armature, means for supplying constant current to said motor, a shunt of negative temperature 00- efiicient across the armature of said motor and independent of the field Winding and means for varying the number of turns of the field Winding and the resistance of said shunt simultaneously.

18. The combination of an electric motor having an armature, means for supplying constant current to said motor, a shunt of 25 negative temperature co-efiicient across the armature of said motor, and means for causing the current in the shunt to vary With the ampere turns on the field.

19. The combination of an electric motor 30 having an armature and field Winding, means for supplying constant current to its terminals, a shunt of negative temperature co-efficient across the armature independent of the field, and means for varying simulta- 35 neously said shunt and the ampere turns on vthe motor field.

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