US2353900A

US2353900A - Electromagnetic brake

Info

Publication number: US2353900A
Application number: US458973A
Authority: US
Inventors: Clinton S Janes
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1942-09-19
Filing date: 1942-09-19
Publication date: 1944-07-18
Anticipated expiration: 1961-07-18

Description

- 'July 18,1944. CQ'SJANES 2,353,900

ELECTROMAGNETIC BRAKE Filed Sept. 19, 1942 INVENTOR. BY (lg/don 1S. Lia/mes Patented July 18, 1944 ELECTROMAGNETIC BRAKE Clinton S. Janes, Elmira Heights, N. 1., minor to Bendix Aviation Co poration, South Bend, Ind., a corporation of Delaware Application September 19, 1942, Serial No. 458,973

6 Claims. (Cl. zoo-as) The present invention relates to an electromagnetic brake for motors and" more particularly to an arrangement for automatically arresting the rotation of an engine starting motor when the starting switch is opened.

In electrical starters for internal combustion engines of the type in which a pinion is projected into mesh with an engine gear by the initial acceleration of the starting motor, and is thrown out of mesh when the engine starts, it is desirable to have the starting motor stop quickly when it is de-energized so that it it be start, and the consequent kinetic energy which must be transmitted to the engine may be destructive to the starter drive. This hazard is particularly serious in heavy duty-installations where the rotating parts are heavy, and the drive is usually operating close to the limit of its safe load capacity.

Moreover, in those forms 0! starter drive in which the demeshingoi' thepinion is aided or eflected by the deceleration of the startin motor when it is de-energized, some form of braking means for the starting motor is often desirable to assist the demeshing action, such for instance as shown in the patents to Loehr et al., 2,135,620, or Janes, 2,167,891.

It is an object of the present invention to provide a novel automatic electrical braking arrangement for motors which is eilicientand reliable in operation and simple and economical ,in- 9Qmn- ,Q

It is another'bbiect to provide such a device which secures the braking eflect by maintaining or strengthening the fleld of the starting motor while reducing or stopping the flow of current from the battery through the armature.

It is another object to provide such a device in which the braking eflect is secured by short-circuiting the armature either partially or completely.

It is another object to provide such a device which is automatically brought into action by the opening of the starting switch.

in which the braking eflect is removed as soon as the starting motor comes substantially to rest.

It is another object to provide such a device including means for maintaining the braking eilect for a predetermined time after the starting switch is opened.

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawing, in which:

Fig. l is a diagrammatic representation of a starting system showing a preferred embodiment of the present invention;

Fig. 2 is a similar view of such an arrangement in which the brake-applying magneto switch is also used as the remote controlled starting switch; and

Fig. 3 is a similar view of an embodiment of the invention incorporating a positive time delay mechanism which maintains the braking eflect for a measured interval of time.

In Fig. 1 01' the drawing there is illustrated a starting circuit comprising a battery 1 grounded at 2 and connected by a lead 3 to a starting switch 4. Switch 4 is connected by a lead 5 to a conventional type or series wound starting motor com-prising a pair of field coils l and I, an armature having a commutator 8,

"and two sets of commutator brushes 9, ii and II, II, brushes 9 and Ii being connected to the field coils I and 1 respectively, and brushes i2 and I! being grounded to complete the starting circuit.

A shunt circuit around the starting switch 4 is provided comprising a lead I, a resistor i5 and a magnetic switch it. The value of the resistance It is not at all critical, but may conveniently be such that when the starting switch 4 is open and the battery is connected to the starting motor through the shunt circuit, the

yoltage drop through the resistor i5 will be a substantial fraction of the battery voltage. Means for closing the switch i6 during rotation of the starting motor and for holding it closed until the starting motor comes substantially to rest is provided in the form of a coil il connected at one end by a lead it to the junction I! between-the field coil 1 and brush ILzthe opposite end of coil I! being grounded at In this embodiment oi the invention, the electromagnetic "braking eflect is secured by grounding the Junction between field coil 6 and brush I when the starting switch 4 is opened,

It is another object to provide such a device thus increasing the current flow through said field coil and at the same time short circuiting that part of the armature which is served by the brush 9. As here shown, this is accomplished by means of an electromagnetic switch 22 connected by a lead 2| with the junction 24 between field coil 6 and brush 9, and connected by a lead 25 to the ground. Grounding switch 22 is provided with an actuating coll 2| which is arranged to close said switch responsive to opening of the starting switch 4. This is brought about by connecting the coil 2| in shunt with the resistor ,l! by means of

leads

21 and 28 so that the voltage drop across the resistor i is impressed on said coil.

In the operation of this embodiment of the invention, starting with the parts in the positions illustrated, closure of the starting switch 4 by the operator completes the starting circuit in the usual manner whereby the motor is energized by the battery to rotate and perform its cranking operation. When the armature oi the starting motor rotates, a counter-electromotive force is generated therein causing a substantial voltage to be built up between the brushes and II and the grounded brushes l2, The potential of the brush ii is impressed on the ccoil I! of magnetic switch l6 by means of the connection whereby said switch is closed, thus closing the shunt circuit through resistor although no current flows therethrough so long as the starting switch 4 is held closed.

When the engine starts, the operator opens the starting switch 4, whereupon the battery current is caused to flow through the shunt circuit including resistor i5 and switch II. The consequent voltage drop across the resistor I! is impressed on the coil 26 of the grounding switch 22, causing it to close, thus groundinrthe field coil and short circuiting the armature through the brush 9. The field coil is consequently strengthened by the removal of the counterE. M. I". of the armature therefrom, and at the same time a current caused by the counter E. M. l". or the armature is permitted to flow throughthe circuit comprising brush 9, connection 2|, switch, ground connection 25 and the grounded brushes l2, l8. This current is in a direction to cause reversal oi the rotation of the armature and thus quickly arrest its forward rotation.

When the armature comes substantially to-rest, the counter E. M. F. of the armature disappears and the brush consequently is at approximate- 1y ground potential. The 0011 I1 oi shunt switch i6 is thus de-energized, thereby permitting said switch to open. The shunt circuit being thus broken, coil 2| oi the grounding switch I! is de-energized, permitting said switch to open, placing the starting mechanism in condition for re-actuation.

It will be noted that the resistor ll performs two functions. It provides a potential ior controlling the operation of the grounding switch 22, and it also serves to limit the fiow or current through the field coil 0, when grounded, to prevent overheating.

In the embodiment of the invention illustrated in Fig. 2 the magnetic grounding switch is caused to serve double duty as a remoteecontrolledstarting switch. As there shown, a battery |l groundedatflisconnectedbyaleadlltoastarting switch contact 34. A corresponding switch contact II is connected by a lead to a series-wound starting motor comprising parallel field coils 81 and commutator brushes 4| connected to the fields respectively, and brushes 4!, 4| grounded to complete the starting circuit. Means for connectingcontacts |4,||toclosethestartiu 2,sse,ooo

circuit is provided in the form of a bridging contact 44 actuated by acoil 4| grounded at one end at 4| and connected at the other end through lead 41 and push button 4| to the battery lead It will be understood that the push button 4| will be located conveniently to the operator to provide a remote control oi the starting operation.

A shunt circuit around the starting contacts N is provided comprising a magnetic switch 4| and a resistor II, which are arranged to connect the battery lead N with the starting motor lead 3|. Switch 4| is provided with a coil '2, one end of which is grounded at U and the other end connected by a lead 54 to the Junction 5! between the field coil 3| and armature brush 4|, whereby said coil is energized by voltage corresponding to the counter E M. F. .of the armature when it is in rotation.

Means for grounding the field coil I1 and short circuiting the armature through the brush is provided, comprising a grounding switch contact ll connected by a lead 51 to the junction ll between the field coil and brush and a contact 5| grounded at 6|. Contacts II, I! are positioned so as to be normally connected by the bridging contact 44, this engagement being maintained by suitable means such as a spring H.

In the operation of this embodiment of the invention, closure of the push button 4| by the operator causes energization of coil 4| which moves the bridging contact 44 out of engagement with the grounding contacts N and into engagement with the starting switch contacts |4, ll. The starting motor is thereby energized to cause the engine to be cranked in the usual manner. When the armature rotates, the counter E. M. F. thereof is impressed on the coil I! of shunt switch 4| by virtue of the connection 4 to brush 4|, causing said switch to close and com- .plete the shunt circuit around the starting switch.

when the engine starts, the operator releases the push button 4|, thereby disconnecting contacts M, II and closing the ground connection through contacts thus grounding the field coil |l as the operation of the grounding switch is eoncerned, it may be omitted altogether and the shunt switch 4| connected directly with the bat-, tery lead 3|. In such case, however, the braking efiect may be undesirably energetic. and the field coil I1 and grounding contacts 44, may become over-heated alter continued repetitious operation of the starter. It is preferred therefore to retainithe resistor ll simply for the purpose of preventing overloading of the field coil and contacts.

Fig. 3 shows the utilization oi a positive form 01 time delay mechanism for maintaining the electromagnetic braking efiect for a predetermined time after opening the starting switch. Inthisfigure a battery ll grounded at I: is connected by a lead H to a starting switch II. Switch 14 is connected by a lead II to the usual starting motor comprising parallel field coils 1| and I1, commutator brushes II and II connected to said field coils, and groimded commutator brushes and I2.

A shunt circuit around the starting switch I8 is provided comprising a lead 88, a resistor 88 and a shunt magnetic .switch 88 having an actuating coil 88. One end of coil 88 is grounded at 81 and the other end is connected through a resistor 88 to the starting motor lead l8. value of resistor 88 is not critical but is preterably oi the same order as the resistance of the coil 88. C011 88 is designed to close switch 88 when actuated by battery current flowing through resistor 88. v Q

Means for grounding both oi the field coils l8, l1, and completely short-circuiting the armature through both brushes I8, 18 is provided in the form of a grounding switch 88 connected by leads 88, 8| and 82 to the junction points 88 and 88 between the field coils I8, I! and brushes I8, 18 respectively and connected to the ground through a lead 88.. Grounding switch 88 is provided with an actuating coil 88 which is energized by the voltage drop across the resistor 88 by virtue of connections 81, 88.

Means are provided for opening switch 88 a predetermined time after the starting switch 18 is opened. As here shown this means comprises a fixed contact 88 connected by a lead IM to one The the bob I 88 of reed I88, setting the reed in vibra- 7 tion. After a period of time predetermined by necessarily energetic, the operation of the deend of the coil 88, and a movable contact I82 connected by a lead I88 to the opposite end of said coil, contact I82 being mounted on a flexible reed I88 anchored at I88 and provided with a weighted bob I88 on its free end whereby when the bob is flicked, the reed will vibrate for a predetermined time before permitting the contact I82 to come to rest against the contact 88. Means are provided for opening contacts I82, 88, dur-' ing the cranking operation comprising a solenoid I81. grounded at one end at I88 and connected at the other end by a lead I88 to the Junctions of the field coils I8, TI and commutator brushes 18, I8 through leads 8|, 82. A plunger II8 arranged to be actuated by the solenoid I81 is connected to a lever III pivoted at H2 and having a roller M3 on its free end in position to engage the bob I88 of the vibrator reed I 88 and bend the reed back to open contacts I82, 88.

, In operation, with the partsin the positions illustrated, closure of the starting switch 18 completes the starting circuit through the motor causing it to crank the engine in the usual manner. Closure of the starting switch also completes a circuit to the ground through resistor 88, lead I83, contacts I82, 88 and lead-|8I.

when the armature oi the motor rotates, the counter E. M. F. thus generated is impressed upon the solenoid I81 by virtue oi connections 8|, 82, I88, thus causing plunger II8 to move the lever III to open contacts 88, I82. Thereupon the 001188 of the shunt switch. 88 is energized by vice may be rendered less drastic by omitting one of said ground connections 8| or 82 without otherwise ailecting the operation of the braking system.

While the operation of a-vibrator type time delay to retard closure of a switch is old, as shown for instance in the patent to Loehr et 9.1.. 12,904, the use oi such a mechanism to delay the opening of a switch is believed to be novel. Applicant's understanding of the theory of operation in this case is as follows: When the contacts I82,, 88 are opened, thus removing the short circuit around the coil 88, the coil becomes energized by the current traversing the resistor 88, thus building up a magnetic field around the coil until the flow of current through the coil reaches a substantially constant value, and the magnetic circuit thereof is substantially saturated. The inductive reactance of the coil is therefore very low, and practically the only resistance to the flow 0! current through said eoil'is now its pure ohmic resistance. When the plunger H8 of solenoid I81 is released, thus flicking the reed I88, the fluttering of the contacts I82, 88 produces the eilect oi an intermittent current applied to the coil 88 during the intervals when the con- 40 tacts are open. Since as above pointed out, the

the current flowing through the resistor 88 to cause closure of said switch.

When the engine starts, the starting switch 18 is opened by the operator whereupon the current to the starting motor is forced to traverse the shunt circuit including resistor 88 and shunt switch 85. The consequent voltage drop across the resistor 84 is impressed on the coil 88 of the grounding switch 88, thus causing said switch to close and ground the field coils .18, "and short-circuit the armature by connecting both the brushes 18, [8 to the ground. Closure of the grounding switch 88 also grounds and de-energi zes the solenoid I81 which releases the plunger III), permitting the lever III to return to its idle position by suitable means such as a spring I I8. 'I'his'return motion oi the lever II I flicks coil has very little reactance, this pulsating current traverses it freely, and the self-inductance of said coil smooths out these pulsations into a substantially continuous current flow through the coil which accordingly maintains the magnetic field until the contacts 88, I82 come to rest in engagement. Then the coil 88 is short-circuited and de-energized and the shunt switch 88 permitted to open.

Whether or not this is the precisely correct theory of operation of the device is believed to be immaterial, since the operation thereof has been carefully observed and has been found to take place as described in the statement of operation above set forth.

The device as at present constructed utilizes a non-inductive resistor as the resistance 88, by virtue 01' its economy and convenience, and no undue amount of sparking at contacts 88, I82 has been observed. Obviously an inductive resistor 88 would be still more efllcient.

While certain embodiments of the invention have been shown and described in detail, it will be understood that other embodiments are possible and that various changes may be made in the design and arrangement of the parts without departing from the spirit 0! the invention as deof said armature during rotation of the starting motor, and means actuated by the voltage drop across the resistor when the starting switch is opened, operative to short-circuit the armature.

2. In combination with a starting circuit including a battery, a starting switch and a starting motor having a field and an armature, means responsive to opening of the starting switch for diverting the fiow oi battery current from the armature while maintaining said'fiow through the field, and means for opening the starting circult when the starting motor comes substantially to rest.

3. In combination with a starting circuit including a battery, a starting switch and a starting motor having a field and an armature, means responsive to opening the starting switch for short circuiting the armature while maintaining a connection from the battery through the field of the motor, and means for breaking said connection after a time delay sufficient to allow the armature to come substantially to rest.

4. In an engine starter a starting circuit including a motor and a switch, closure 01' which causes energization of the motor to crank the engine, and means responsive to opening of the switch for short circuiting the armature oi the motor while maintaining a connection from the battery through the field ot the motor.

5. In an engine starter a starting circuit including a motor having a field and armature connected in series, and a double-throw magnetic switch normally short-circuiting the armature. manually operable means for energizing the switch to open the short-circuit and to close the starting circuit, and means including a second magnetic switch energized by the counter E. M. 1". of the armature for maintaining the starting circuit closed aiter de-energization oi the first switch until the armature comes substantially to rest.

6. In an engine starter a starting circuit including a battery, a starting switch and a serieswound motor having parallel fields and parallel commutator brushes, one set or brushes being connected to the field coils and the other set being grounded to complete the starting circuit; a circuit in shunt with the starting switch comprising a resistor and a magnetic switch having a coil, one end 01' which is grounded and the other end connected to the junction of one field coil with its connected commutator brush, and a second magnetic switch arranged when closed, to ground the Junction of another field coil with its connected commutator brush, and having an actuating coil connected in shunt with said resister.

CLINTON S. JANES.