US2294754A - Brush lifting relay - Google Patents

Description

Sept.-1, 1942. R. M. HEINTZ BRUSH LIFTING RELAY Filed May 10, 1940 INVENTOR,

RALPH M. HE/NTZ.

A TTORNEYS Patented Sept. 1, 1942 BRUSH LIFTING RELAY Ralph M. Heintz, Palo Alto, Calif., assignor, by mesne assignments, to Jack 8: Heintz, Inc., Cleveland, Ohio, a corporation of Ohio Application May 10, 1940, Serial No. 334,386

MW 2 Claims. I (Cl. 172- -239) This invention relates to relays for starting and operating electric motors, and is particularly adapted for use in such motors as used in connection with engine starters.

Among the objects of this invention are: To provide a means of lifting the brushes of an engine starter motor, in order to relieve the friction thereof andto permit the permanent connection of the motor to the starter so that the inertia of the motor armature may be utilized in addition to that of a flywheel for providing starting effort; to provide a brush-lifting mechanism which, by decreasing the friction on an impulse starter, will permit the same to be hand cranked without the necessity for disengaging the motor from the starting mechanism: to provide a starting relay for a small motor which will handle relatively large currents without the necessity for either excessive contact area or excessive pressure; to provide a brush-lifting mechanism and relay which has the requisite compactness and lightness to make its use desirable in aircraft; and, specifically, to provide a starting relay adaptable for use in connection with the starter shown and described in my copending application, Serial No. 333,376, flied May 4, 1940, now Patent No. 2,271,640, patented Feb. 3, 1942, to which reference is made for the description of parts which are not directly pertinent to the present invention, but which are used. in connection therewith and upon which the present invention is, in part, predicated.

Other objects of this invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

In the drawing:

Fig. 1 is an end view, partly in section, of the commutator end of a motor embody ng. the brushlifting mechanism of this invention.

Fig. 2 is a view partly in section, the section line being indicated by the line 2-2 of Fig. 1.

The impulse type of starter for an airplane engine is utilized in order that a relatively small electrical motor may be employed in order to supply the extremely large power necessary to turn the engine over through one or more cycles of. operation until firing occurs and the engine starts. In order to do this, the motor exerts its starting eflort over a relatively long period in order to bring a flywheel up to a speed so high that the energy stored in the flywheel is suincient to supply the starting effort required. Since the necessity for light weight throughout the equipment is paramount, the motor should preferably operate at as high a speed as possible, and since it is also desirable that it develop as much power as is possible at these high speeds,

relatively large current must be supplied to it, and this involves large commutator areas and adequate brush pressure, so that a relatively large part of the motor power is absorbed in brush friction. When the flywheel has been brought up to speed the additional torque which would be supplied by the motor upon engaging the starter with the engine is immaterial, whereas the friction load remains important. Furthermore, in the event of the failure of starting power, it may be necessary to hand crank the starter. In order to do so, an extremely high gear ratio must be used between the hand crank and the flywheel, and in this event the friction load of the brushes, if they be in contact with the commutator, is so great as to render this practically impossible.

It has been customary, therefore, to disconnect the motor from the starter when the starter is to be engaged with the engine, or in the case of hand cranking. This necessitates the provision of a clutch mechanism between the motor and the flywheel, and also eliminates the effect of the moment of inertia of the motor armature, which would be a desirable addition to the energy stored for supplying the starting torque.

As has already been indicated, the power demands for a motor of this type are relatively high, and since it is necessary, in order to meet installation demands, that relay starting be employed, a starting relay must be provided which will handle adequate current. This ordinarily means the provision of contacts of large diameter, operated with heavy pressure, in order to prevent over-heating, pitting, and sticking, and this, in turn, means the use of a relatively large amount of power in the relay circuit. Thus. in order to handle. the current demands of the present installation, with a relay of the ordinary type, a contact pressure of at least thirty pounds is indicated, and it will be appreciated that a relay capable of exerting such pressures would require an appreciable amount of power, and this on anairplane where power is precious.

The conditions on a commutator contact are, however, different. It has recently been realized that the conduction under a brush. against a commutator is an electronic phenomenon, rather than a solid conduction one, and that the movement of the commutator beneath the brush besides oifering cooling of the commutator surface also serves by preventing the formation of continuing and growing arcs to maintain an inherently unstable electronic discharge in a stab e condition. It is as a result of this fact that a commutator-brush combination with a pressure of approximately one pound will carry the same current that would require a thirty pound pressure between stationary contacts, Furthermore, the brush contacts are necessary to supply the motor in any event, and if the brush contacts be used as the starting relay-the necessary result is obtained without introducing additional contact; and additional voltage drops across such contacts.

Considered in broad terms, therefore, the present invention comprises the combination with a commutator and its brushes, having means for holding the brushes against the commutator when the motor is in operation of means for normally holding the brushes out of contact with the commutator and electrical relay means for releasing the brushes to bear against the commutator in order to place the motor in operation.

In the showing of the drawing, the housing I within which the commutator and brush mechanism are mounted forms a continuation of the motor frame or casing 3, and bears upon its end 5 the bearing 1 upon which the motor shaft 9 is journaled. The armature II and commutator l3 are mounted upon the shaft in the ordinary manner. The housing I is horseshoe shaped, the open side being covered by a closure l5, formed integral with a fitting ll for receiving the electrical connections to the motor, and carrying the brush and relay mechanism, which therefore may be removed as a whole by removing the cover plate 15.

Rising from the face of the closure l5 are two supporting posts is, which carry the two brush mechanisms but are insulated therefrom by insulating strips .20 and bushings 2|. A conducting strip 23, preferably of brass, lies against the insulating strip for substantially its whole length, except where it is bent into an arch 25, to which the brush guide 21 is fixed, as, for example, by silver solder, The brush 29 slides within the brush guide, and is normally urged against the commutator by a spring 3|, mounted on an insulated stud 33. Y

The brush is provided with the usual pigtail 35, riveted to the brush and against a lug 3'! which slides within a suitable slot form d in the brush guide, and the pigtail terminates, at its other end, in a connecting lug 39.

An insulated bracket arm 41 carries a stub shaft on which the brush-retracting lever 43 is journaled, this lever extending up toward the brush to a suilicient distance so that its end can engage the lugs 31.

This structure is repeated on both sides of the commutator, the only difference being the disposition of the terminal lugs, one of which, as shown on the left of Fig. 1, connects to the motor winding while that shown on the right of this figure connects to the external circuit. Between the two brush-retractor levers 43 is positioned the solenoid 45 of the starting relay.

The solenoid is symmetrical, and within each end a plunger 41 is slidably mounted. The two plungers are similar, and are urged apart by a spring 49, which has suillcient strength to overcome the resistance of the brush springs 3|. The plungers are provided at their ends with a flange 5!, which prevents their inner ends coming in contact, and in the flanged end of each there is pressed a button 53 of insulating material which isolates the plungers from the brushretracting levers and prevents them from shorting the brush mechanism.

The device is actuated by pressing the starter button 55, which excites the winding of the solenoid from a battery or other source 51. The two plungers 41 are thereupon attracted, compressing the spring 49, and releasing the pressure exerted thereby upon the brush-retracting levers I, so that the brush springs 33 can urge the brushes into contact with the commutator, completing the motor-circuit in the usual and obvious manner. The flanges 5| prevent actual contact between the two plungers, which might cause sticking.

When the starting button 55 is released, the two plungers are urged apart by the spring 4!, pressing against the brush-retractor levers 43, which in turn engage the lugs I! and open the motor circuit by disengaging the brushes from the commutator.

For the sake of completeness, the complete circuit of motor and relay is included schematically in Fig. l. The relay solenoid 45 is excited by the same battery as supplies the motor, the circuit being completed through the motor frame to ground and'thence back to the battery. The motor circuit through the armature and thence through the series field coils 59 and commutating pole coils 6| is entirely conventional,

I claim:

1. In combination with a commutator, a combined relay and brush-liiting'mechanism comprising an opposed pair of brush guides, brushes slidably mounted in said guides, to bear on said commutator, resilient means for urging said brushes against said commutator, a pair of electrically operated brush retractors engageable with instrumentalities on said brushes to positively and simultaneously force the brushes out of contact with said commutator, a solenoid mounted between said brush retractors, a pair of magnetic plungers slidably mounted within said solenoid; a spring mounted between said plungers to urge them outward against said brush retractors and of suiiicient strength to overcome the resistance of said resilient means and positively and simultaneously lift said brushes out of contact with said commutator, and means for exciting said solenoid to compress said spring and permit the engagement of said brushes with said commutator, said brush retractors being of electrical conducting material, and insulating buttons atfixed to the ends of said plungers to prevent electrical contact between said plungers and said brush retractors.

2. In combination with a commutator, a com bined relay and brush-lifting mechanism comprising an opposed pair of brush guides, brushes slidably mounted in said guides to beer on said commutator, resilient means for urging said brushes against said commutator, a pair of electrically operated brush retractors engageable with instrumentalities on said brushes to positively and simultaneously force the brushes out of contact with said commutator, a solenoid mounted between said brush retractors, a pair of magnetic plungers slidably mounted within said solenoid, a spring mounted between said plungers to urge them outward against said brush retractors and of suflicient strength to overcome the resistance of said resilient means and positively and simultaneously lift said brushes out of contact with said commutator, and means for exciting said solenoid to compress said spring and permit the engagement of said brushes with said commutator, said magnetic plungers being provided with limiting means at their outer ends for stopping the movement of the plungers as they are shifted toward each other when the solenoid is energized to compress the spring coacting with the plungers.

RALPH M. HEHN'IZ.

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