US1924321A - Braking system - Google Patents

Description

H. D. JAMES BRAKING SYSTEM Aug. 29, 1933.

Filed April 18, 1930 4 Sheets-Sheet l IINVENTOR Henry D. Jam es,

ATTORNEY H. D. JAMES BRAKING SYSTEM Aug. 29, 1933.

Filed April 18, 1930 4 Sheets-Sheet 2 INVENTOR Henrgl) James.

ATTORNEY Aug. 29, 1933. H. D. JAMES 1,924,321

BRAKING SYSTEM Filed April 18, 1930 4 Sheets-Sheet 3 Fig. 5.

INVENTOR Hen/"g5. James.

ATTORNEY H. D. JAMES BRAKING SYSTEM Aug. 29, 1933.

4 sheets-sheet 4 Filed April 18, 1950 Fig. 4.

INVENTOR Harv-9D. James.

ATTORNEY Patented Aug. 29, 1933 UNITED STATES PATENT OFFICE BRAKING SYSTEM Application April 18, 1930. Serial No. 445,318

8 Claims. (0]. 187--29) My invention pertains to braking systems and more specifically to brakes associated with elevator systems in addition to the regular brakes.

In prior elevator systems, it has been difiicult to provide for the operation of the elevator car at a proper landing speed after slow-down has been initiated. In order to quickly check the speed of the rapidly moving elevator car, it is necessary to apply a high degree of braking efiort when slow-down is initiated. When the speed of the car has been diminished to a value suitable for approaching the floor, it is necessary to again reduce the braking force in order that the car may be accurately landed.

When the brake is applied with full force, it is difficult for the operator to accurately judge the speed and reduce the braking force at the proper instant. If the brake is not released at the proper instant, the car will be brought to a dead stop before the floor is approached, and, if it is released too soon, the car will overrun.

Furthermore, the sudden application of the brake with full force, and its equally sudden reduction from full force to zero, causes a very rough and jerky operation of the elevator car. This efiect is still further accentuated by the fact that it is often necessary to apply and release the brake several times before the car is level with the. floor.

In elevator systems of the variable-voltagecontrol type, it is common to depend upon regenerative braking to check the speed of the elevator car when slow-down is initiated. However, it is difiicult and complicated to maintain a suitable landing speed with this type of control.

' In those elevator systems in which the elevator motor is of the alternating-current induction type, regenerative braking can not be utilized.

It is, acordingly, an object of my invention to provide a movable conveyance with a braking means and control therefor such that the conveyance may be brought to a stop smoothly and accurately.

It is also an object of my invention to provide a motor-driven vehicle, or a motor-driven load of any kind, with a braking means such that it will be brought to a smooth and accurate stop when slow-down is initiated and Which will be automatically released when the car speed has been reduced to a low rate suitable for approaching the floor to make an accurate landing.

It is another object of my invention to provide an elevator system with auxiliary braking means which, when slow-down is initiated, is automatically applied with a maximum braking force the intensity of which is gradually diminished as .the speed of the car is reduced and which will be entirely released when the car speed has been reduced to a low rate suitable for approaching the floor to make an accurate landing.

It is also an object of my invention to provide an elevator system with braking means which will be automatically applied, when slow-down is initiated, with a force which depends upon the speed of travel of the car at the time when slowdown is initiated.

Other objects of my invention will be evident from the following detailed description, taken in conjunction with the accompanying drawings, in which Figure 1 is a diagrammatic view of an elevator system provided with a braking device which is controlled in accordance with my invention.

Fig. 2 is a diagrammatic view of a similar elevator system provided with a braking device and controlling means in accordance with a modified form of my invention, and

Fig. 3 is a diagrammatic view of another modification of my braking device and control therefor, as applied to an alternating-current elevator system.

Fig. 4 is an end elevational view of a brake that may be used in the systemshown in Fig. 1.

Referring to the drawings, the apparatus shown diagrammatically in Fig. 1 comprises an elevator car C supported by a hoist cable Ca which passes over a 'hoist drum D to a counterweight Cw in the hatchway, in the usual manner.

The hoist drum D is connected, by a shaft S, to the armature EM of a motor EM by which it is driven in either direction, depending upon the polarity of the current supplied to the armature. The shaft S also carries a brake drum Bdwhich, with a cooperating brake'shoe 1, constitutes a brake, hereafter referred to as a hydraulic brake, for checking the speed of the elevator car when Slow-down is initiated. The brake shoe 1 is normally pressed against the brake drum by a spring 2 acting through a rod 3. The rod 3 passes through a cylinder 4 and carries a piston 5. Under normal running conditions, sulficient pressure is admitted to the cylinder 4, through a pipe '6; to hold the brake shoe disengaged from the brake drum-in opposition to the spring 2.

The shaft 3 also carries a brake drum Bd2 which, with a cooperating brake shoe 8, biasing spring 9 and electromagnet l0 constitutes the usual magnetic or machine brake.

The motor EM is provided with a field winding E. M. F. which is separately excited from the main-line conductors L1 and L2. The armature EM of the motor is energized by a generator G and is, for this purpose, connected in a loop circuit with the armature of the generator.

The field winding GF of the generator is separately excited from the main-line conductors L1 and L2 through a control system by means of which its energization may be reversed and varied in intensity, in either direction, by the operator. By varying the excitation of the generator in this manner, the voltage applied to the armature EM of the elevator motor is likewise varied or reversed, and its speed of rotation is correspondingly varied in either direction.

The armature G of the generator is driven continuously by a motor M which is connected directly across the line conductors L1 and L2. The control apparatus for this motor is of a usual type and not shown because it would unnecessarily complicate the disclosure.

A governor cable 11 is secured to the car by a detachable tension clip 12 to run over a sheave 13 above the hatchway. A speed-responsive device 14 is associated with the sheave 13 to be driven thereby at a speed corresponding to the speed of travel of the elevator car in the hatchway. The speed-responsive device 14 may be the usual centrifugal governor provided for tripping the car-safety means (not shown).

, A bracket 15, which may be of insulating material, is associated with the governor whereby it will be raised or lowered as the speed of the elevator car increases or decreases, respectively. Contact segments 16, 1'7 and 18 are carried by a conducting support 19 which is mounted on the bracket 15 and are moved into engaging relation with stationary brushes 21, 22, and 23 mounted adjacent thereto.

The contact segments are of diiferent lengths, and the stationary brushes are mounted in spaced relation adjacent thereto in such relative positions that the brushes will all be disengaged when the elevator car travels at full speed but will be engaged in succession as the speed of the elevator car decreases. When the elevator comes to rest, all the brushes may be disengaged (as shown in Fig. 1).

Pressure is supplied to the brake cylinder 4 from a pump 24 which is driven by an electric motor PM. The pump motor PM is connected in parallel with the motor M of the motor generator set and operates continuously whenever the elevator is in use.

The pump is connected to the pressure tank ,25 from which it supplies pressure through the pipe line 6, to the brake cylinder 4. In order to maintain a constant predetermined maximum pressure in the line, a pressure regulator 26 is provided therein. This may be any suitable escape valve which, when the pressure exceeds a certain value, will open a by-pass and return aportion of the pressure fluid through the pipe 2'? to the exhaust tank 28. The pressure regulator 26 will be set to maintain a pressure in the brake cylinderwhich is high enough to completely release the brake and to hold the brake shoe disengaged from the brake drum. This pressure will be different for difierent installations but we will assume that, in this spe cific case, the regulator is set to maintain a pressure of 10 lbs. per square inch.

To vary the pressure applied to the brake piston in accordance with the speed of the elevator car, a series of electromagnetically controlled regulator or bleedervalves 31,, 32, and 33 are provided. Each of these valves is provided with an electromagnetic depresser which, when energized, holds the valve seated. When the electromagnetic depresser of any valve is deenergized, the valve is urged to seating position only by the force of its associated spring which is adjusted to maintain a certain predetermined pressure.

It will be apparent, from Fig. l of the drawings, that the releasable regulator valves are connected from the line 6 to the exhaust tank 28 in parallel with the high-pressure regulator 26. When two or more regulators are connected in parallel in this manner, the one that is set for the lowest pressure will determine the pressure in the line. Hence, by adjusting the regulators 31, 32 and 33 for various pressures lower than that maintained by the high-pressure regulator 26, and by deenergizing various of the associated electromagnetic depressers, it is possible to set the system to maintain various pressures on the brake piston. The energization of the electromagnets is controlled by the brushes associated with the governor contact segments, and the brake pressure is automatically varied in accordance with the speed of the elevator car.

It may be assumed that the spring 43 is adjusted to seat its associated valve 33 with a pressure of 5 lbs. per square inch and that the spring 42 is adjusted to seat its associated valve 32 with a pressure of 2 lbs. per square inch. The valve 31 is, however, much larger than the other valves, and its associated spring 41 is adjusted to seat it only very lightly, or its spring may be entirely omitted, so that, when its electromagnetic depresser is deenergized, it will open freely to discharge the pressure completely and permit the brake to be applied with full force.

However, my invention and its operation may be more readily described when considered in connection with an assumed operation thereof.

When the elevator car is standing at a floor, the parts will assume the positions shown in Fig. l of the drawings. If the operator desires to start the car upwardly, he will move the car switch CS in a clockwise direction, thereby energizing the winding of the up-direction relay UR.

The circuit through which the up-direction relay is energized may be traced from main-line conductor L1, through conductor 51, by way'of conducting segment 52 of the car switch CS, to conductor 53, the winding of relay UT and, by way of conductor 54 through the electromagnet winding 10 of the .usual electromagnetic machine brake to the other main-line conductor L2.

As a result of the energization of relay UR, it now pulls up its armature and closes its contact members a, b, c, d and e. The closing of contact members d and e will cause the field winding GF of the generator G to be energized, thereby applying a potential to the armature EM of the elevator motor. Closing contact members a, b and 0 will cause energization of the electromagnetic depressers of the valves 31, 32, and 33, whereby the valves will be seated, and a high pressure will be applied to the brake piston to release the brake.

The energizing circuit for the generator field winding GF may be traced from the main-line conductor L1, through conductors 61 and 62, contact member d of relay UR, conductors 63 and 64, winding GF, conductors 65 and 66, contact member e of relay UR, thence, by way of conductor 6'7, resistors R1 and R2 and conductor 68,

to line conductor L2. Energization of the field winding is limited by the resistors R1 and R2 which are included in series therewith and the elevator operates at low speed.

The energizing circuit for the electromagnetic valve depressers 31, 32 and 33 may be traced from line conductor L1, through conductors 61, 71, 72, contact members a, b, and c of relay UR, by way of the individual conductors '74, '75, and '76, to the respective windings 34, 35, and 36 of the magnetic valve depressers, and thence, by way of the common conductor 7, to the other line conductor L2. v

It will be observed that the energizing circuits for the electromagnetic depressers are in shunt to the circuits which may be completed through the governor contact segments 16, 17, 18 and brushes 21, 22 and 23, hence, the completion of these circuits by the governor will have no effect so long as either the up or the down-direction relay is energized. It is only when the car switch CS is centered and both the up and the downdirection relays are deenergized that the governoractuated brushes are effective to influence the brake.

To operate the elevator car at a higher rate of speed, the operator turns the car switch CS to its next operative position in the clockwise direction. The winding of the intermediate-speed relay IR will now be energized, thereby closing its contact and shunting the resistance R1 out of the circuit of the generator field winding. This will increase the potential applied to the armature of the elevator motor and will operate it at a higher rate of speed.

The energizing circuit for the winding of the intermediate-speed relay may be traced from line conductor L1, through conductor 51 to the conducting segment 52 of the car switch CS, thence,-

by way of conductor 81, to the winding of relay IR, continuing, by way of conductor 82, to the line conductor L2.

To operate the elevator at full speed, the operator now moves the car switch CS to the extreme position in a clockwise direction, thereby energizing the winding of the high-speed relay HR. Relay HR will now close its contact members, thereby shunting the resistance R2 out of the generator field circuit and still further increasing the excitation of the generator. A higher voltage will now be applied to the armature of the elevator motor which will be driven at full speed.

The energizing circuit for relay HR extends from line conductor L1, through conductor 51, conducting segment 52, conductor 91, the winding of relay HR and conductor 82, to line concluctor L2.

When a stop is to be made, the operator restores the car switch CS to its central position, thereby deenergizing the speed relays HR and IR the up-direction relay UR and the electromagnet 10 of the machine brake is then applied. The opening of contact members (1 and e of the up-. direction relay will cause the field winding GF of the generator G to be deenergized.

The contact members a, b and c of relay will be simultaneously opened, thereby deenergizing all the electromagnetic valve depressers, since, as previously set forth, the stationary brushes associated with the governor will be disengaged when the car is traveling at high speed. The high-speed position of the govemor-actuated contact seg-- ments is shown in dotted lines. The valves will now be free to open and discharge the line pressure except as restrained by their I associated springs. The spring 41, associated with the large valve 31, is adjusted very lightly, as previously set forth, hence, this valve will practically discharge the pressure in the brake cylinders to zero, thereby permitting the spring 2 to set the hydraulic brake with its full force, and thereby apply a braking force which is supplemental to that applied by the usual brake.

When the car speed has decreased to a certain predetermined value, the brush 21 will be engaged by the contact segment 16 which will have moved down from the position shown in dotted lines, and the electromagnetic depresser of valve 31 will be energized. The pressure. in the brake cylinder will now increase to a pressure determined by valve 32 which, as previously set forth, may be adjusted to release at 2 lbs. per square inch. The pressure in the cylinder will now exert a force upon the piston which will oppose the braking force applied by the brake spring 2.

When the car speed has been still further decreased to a certain predetermined value, the

brush 22 will be engaged by contact segment 17 and will energize the electromagnetic depresser of valve 32 to force the associated valve into engagement with its seat. The pressure in the brake cylinder will now increase to a still higher pressure, as determined by valve 33 which, as previously set forth, may be adjusted to release at a pressure of 5 lbs. per square inch. The increasing pressure in the brake cylinder tends to still further reduce the force with which the brake shoe is urged into-engagement with the brake drum Ed by the spring 2.

When the speed of the elevator car has been reduced to a speed suitable for approaching the floor, for example, 30 feet per minute, the brush 23 is engaged, by contact segment 18, thereby energizing the depresser of the valve 33 and forcing the valve into engagement with its seat. The pressure in the brake cylinder will now rise to a pressure determined by the pressure regulator 26, which, as previously set forth, is such that the brake will be entirely released.

The hydraulic brake having been released, the operator may control the elevator to approach the floor at slow speed in the usual manner, and the car will be brought to rest by the usual brake. If desired, the contact segments actuated by the governor may be of such length that the stationary brushes will all be disengaged when the car comes to rest, whereby the pressure in the hydraulic brake cylinder will be released, and the hydraulic brake will be applied with full force to aid the regular brake in holding the car, or to hold the car if the regular brake is omitted.

If it is desired to operate the elevator car in the down direction, it is necessary to rotate the car switch in the counter-clockwise direction. The operation of the elevator in this direction is identical with the operation above set forth in the up direction except that the downdirection relay DR is now energized and this relay connects the field winding GF of the gen- An assumed operation of the device disclosed 150 in Fig. 1 has been considered and it has been shown that the hydraulic brake 1 will be released when the car switch is moved from its center position to start the car. It has also been shown that, when slow-down is initiated by restoring the car switch CS to its central position to deenergize the motor and apply the usual magnetic machine brake, the hydraulic brake 1 will be set with full force, which is reduced by steps as the speed of the elevator car decreases, thereby enabling the operator to bring the car to a smooth stop.

In Fig. 2 is shown an elevator system similar to that shown in Fig. 1 to which a modified form of my invention has been applied. The preceding description will also sufiice for Fig. 2, so far as it pertains to the elevator system and its operation, and will not be repeated since the elevator control systems are similar.

The hydraulic brake disclosed in Fig. 2 comprises a brake drum Bd2 engaged by a pair of spring-tensioned brake shoes 201 and 202. The spring 203 tends to pull the brake shoes together to engage the brake drum. To hold the brake shoes disengaged from the brake drum, a pair of expansible sylphon devices 204, and 205 are provided. When the sylphons are connected to a suitable source of pressure, they will expand and force the brake shoes apart, thereby disengaging the brake drum. The expans'iblesylphon devices are flexible, operate with a minimum of friction and are very sensitive to slight pressure variations.

The pressure for actuating the expansiblesylphon devices may be supplied by a third sylphon device 206. The three expansible sylphon devices are connected together to form a closed system which is filled with any suitable pressure-transmitting fluid. By bringing an external pressure to bear upon the third sylphon member 206, the pressure within the system will be varied and the sylphons 204 and 205 will be expanded.

In order to apply suitable external pressures to the third sylphon device 206, I provide an armature 207 in connection therewith and an associated electromagnetic winding 208. The system is so designed that, when the electromagnetic winding 208 is deenergized, the brake will be applied by the spring 203 with full force, and, when the winding 208 is energized by the application of the full line voltage, the brake will be entirely released.

To vary the excitation of the winding 208 in accordance with the speed of the elevator car, I have provided a variable-voltage generator VG which is driven at speeds corresponding, or proportional, to the speed of travel of the elevator car. The generator is so connected in the energizing circuit of the winding 208 that its generated voltages will be in opposition to the line voltage.

Under normal running conditions, the generator is shunted out of the exciting circuit of the brake winding 208, and the winding receives its maximum excitation from the line to completely release the brake.

To increase the sensitivity of the system, a resistor R3 is connected in series in the exciting circuit of the brake winding. The resistance of R3 may be relatively high so that only a small portion of the line voltage is impressed upon the brake winding when the generator is shortcircuited. The winding 208, is so designed that it will be fully excited to release the brake when the full line voltage is impressed upon the winding, and the resistor is in series therewith.

When slow-down is initiated, the shunting contact members are opened, and the generated voltage is effectively connected in the energizing circuit of the brake winding 208. At high speeds, this voltage will be greater than at low speeds and, since it is in opposition to the line voltage, the brake winding will be deenergized, and the brake will be applied with full force, when the shunting contacts are opened by the initiation of slow-down.

As the speed of the elevator car decreases,

the generated voltage will decrease, and the.

difference between line voltage and the generated voltage will increase, consequently, the excitation of the brake winding will be increased thereby releasing the brake. This reduction of braking force will occur gradually. The generator can be driven at a suitable speed ratio to regulate the braking effect, as desired.

When the speed of the elevator car has been sufiiciently reduced for approaching the floor to make a landing, it is desirable to completely release the auxiliary brake and this may be accomplished by a governor-controlled contactor 209 which is moved to circuiteclosing position by the governor when the car speed has been suitably reduced. As shown in Fig. 2, the contactor 209 is so connected that when closed, it shunts the generator out of the exciting circuit of the brake winding 208, thereby releasing the brake. The operator may then control his car to approach the floor in the usual manner by the regular brake (not shown).

The circuit which excites the brake winding 208 to release the brake under normal running conditions may be traced from the line conductor L1, through conductors 211, 212 and 213 to the contact member 0 of the relay UR, thence, by way of conductor 214, winding 208, conductor 215, resistor R3, and conductor 216, to line conductor L2. It will be seen that, during operation of the elevator, the generator VG is normally shunted out through the conductor 214, contact member 0 of relay UR, conductors 213 and 212, resistor R4 and field winding VGF.

Although the field winding VGF of the generator VG is shown excited in series, through a permanent connection, a reversing switch may obviously, be provided for reversing the connections'when the direction of elevator travel is reversed, to render the automatic control effective for both directions. The field winding VGF may be excited in various other relations, depending upon the characteristics desired. If desired, the field winding may be separately excited from the main line through a reversing switch actuated in accordance with the direction of travel ,of the elevator car, as for example by the rotation of the hoist sheave.

In Fig. 3 I have disclosed another form of my invention as applied to an alternating-current elevator system. As shown here, the elevator hoist motor M is of the alternating-current induction type and is excited from the mains I, II, and III.

The elevator system is controlled by a slowspeed relay SR, a high-speed relay HR, and a reversing relay RR. The relays are actuated by the car switch CS.

A machine brake is provided comprising a brake drum Bd3 and a spring-pressed brake shoe 301. Two electromagnetic windings 302 and 303 are provided, either one of which will hold the energized. The energization of the winding 302 is controlled by contact members (I of the highspeed relay HR which will be closed when the relay is energized to operate the elevator at high speed. The energization of the other brake winding 303 is controlled through a set of governoractuated contact members 304 in series with contact members actuated by the car switch. The contact members 304 of the governor are closed at slow speeds suitable for approaching a floor for accurate landing, and may, for example, close at a speed of approximately 30 feet per minute. The system is more readily disclosed, however, when considered in connection with an assumed operation thereof.

Assuming that the car is standing at a floor, the various elements of the system will assume the positions shown in Fig. 3.

When the operator desires to start the car upward, he rotates the car switch in a counterclockwise direction. This will cause the slowspeed relay SR to be energized. The brake winding 303 will also be energized, since the contact members 304 are closed by the governor at all speeds up to about 30 ft. per minute. The slowspeed relay SR will connect the motor to the line through the resistors R1, R2, and R3, and the brake winding 303 will simultaneously release the brake.

The energizing circuit for the slow-speed relay may be traced from main-line conductor II, through conductor 311, to contact segment 312 on the car switch, through the bridging segment on the car switch, to contact segment 313 thereon, thence, by way of conductors 314 and 315, through the winding of relay SR and conductor 316, to the main-line conductor III.

The circuit for energizing the induction motor M for slow speed may be traced; from main conductor I, through conductor 341, contact member 0 of relay SR, conductor 344, resistor R1, conductor 351, contact-bridging member a of relay RR and conductor 354', to the stator; from main conductor II, through conductor 342, contact member b of relay SR, conductor 345, resistor R2, conductor 352, contact-bridging member I) of relay RR and conductor 355, to the stator; from main-line conductor III, through conductor 343, contact member a' of relay SR, conductor 346, resistor R3 and conductor 353, to the stator.

The energizing circuit for the brake winding 303 may be traced from the line conductor I, through conductor 321, the winding 303, conductor 322, governor contact member 304, conductor 323, car switch contact segments 325 and 312, thence, by way of conductor 311, to the mainline conductor II.

In order to operate the car at high speed, the operator will now move the car switch CS to its extreme position in the counter-clockwise directioii. This will complete a circuit to energize the high-speed relay HR which will then pull up its armature and close its contact members a, b, and c to complete a shunt circuit around each of the resistors R1, R2, and R3, thereby operating the elevator motor at high speed. The contact members d of the relay I-IR will also be closed and will complete an energizing circuit for the brake winding 302. The elevator motor will now be operated at high speed, and the brake will be released, even after the governor contacts 304 open, and deenergize brake winding 303, since the winding 302 is energized. The energizing circuits for the high-speed relay may be traced from main-line conductor II, by way of conductor 311, to contact segment 312 and through the bridging contactor to contact segment 325 of' the car switch, to conductor 331, through the winding of relay HR and, by way of conductor 316, to main line conductor III.

The energizing circuit for the brake winding 302 is now completed from line I, through conductor 341 contact member 0 of relay SR, conductor 356, the winding 302, thence, by way of conductor 357, contact member d of the highspeed relay HR andby way of conductor 345, though contact member 6 of relay SR, through conductor 342, to line conductor II.

When slow-down is initiated by moving the car switch CS one step toward the center position, the high-speed relay HR will be deenergized, thereby opening its contacts. the resistors R1, R2 and R3, into the motor circuit. The brake winding 302 will be deenergized, and the brake will be applied, since both brake windings are now deenergized.

When the car speed has been reduced to a slow speed suitable for approaching the floor, the governor contact member 304 will close. This will cause the brake winding 303 to be energized and release the brake automatically. The operator may new approach the floor, since the car is free to move, and the motor is operating at slow speed through the resistors R1, R2, and R3.

To stop the car, the operator will center the car switch CS, thereby deenergizing the low-speed relay SR which will open its contact members and will disconnect the motor from the line. The opening of the contact between segments 325 and 312 of the car switch CS will deenergize the brake winding 303, thereby applying the brake and stopping the car. A regular brake may also be provided and used in the usual manner.

To operate the car in the opposite direction, it is necessary only to rotate the car switch in the clockwise direction. The operation is identical with that set forth above except that the reversing segment 361 on the car switch is now engaged by the bridging member thereby energizing the reversing relay RR in addition to the other relays. The reversing relay will now pull up and will reverse, or interchange the connection of mainline conductors II and Ill with the motor, thereby reversing its direction of rotation.

In Fig. 4, I have shown a specific embodiment of a hydraulic brake which maybe used in the system shown in Fig. 1. This braking device may comprise a brake-drum Bd afiixed to the driving shaft S to which a braking effect is to be applied. Surrounding the brake-drum Ed is a yoke or frame 403 which carries and supports a pair of brake levers 404 and 405 and a piston-and-cylinder assembly 406 for actuating the brake levers to their brake-releasing positions.

As shown, the brake levers 404 and 405 are disposed on opposite sides of the drum 13d with their lower ends pivotally connected by pivot pins 407 and 408 to the frame 403 and are provided with a pair of brake shoes 409 and 410 for engaging the brake drum Bd.

It will be noted that each of the brake shoes 409 and 410 is seated on its supporting brake 'lever by means of a universal joint in the form of a ball-and-socket connection comprising a ball 412 formed on the shoe and a socket 413 formed in the central portion of the lever. Each shoe is bolted to its supporting lever by means of-an eye bolt 415, the inner end of which is secured This will reinsert in a slot 416 in the ball portion of the shoe by pivot pin 417. As shown, the inner end of the eye bolt 415 is mounted on the pivot pin 417 in the shoe with sufiicient play to permit the shoe to rotate, to a limited degree, in any direction. The outer end of the eye bolt 415 is provided with a nut 418 for drawing the bolt and shoe tightly against the brake lever, thereby causing the ball to be frictionally retained in the socket.

In view of the small area of the engaging surfaces of the ball-and-socket connection, as compared with the large areas of contact between the shoes and the drum, the shoes will be accurately aligned with the drum the first time they are applied thereto by the brake, regardless of the degree to which the eye bolts may be tightened, and, by reason of the frictional engagement of the balls in the sockets, will retain their alignment when they are withdrawn from the drum. Inasmuch as the shoes are held tightly against the levers by the eye bolts under all conditions, no lost motion can occur between the shoes and the levers.

The means for applying the brake shoes 409 and 410 to the brake drum Bd comprises a pair of compression springs 420 and 421 which are mounted on the outer ends of a pair of eye bolts 422 and 423 in position to press against the upper ends of the brake levers 404 and 405. The inner ends of the eye bolts 422 and 423 are secured to the frame 403 by a pair of pivot pins 424 and 425, and the outer ends are provided with a pair of nuts 426 and 427 by which the tension of the springs 420 and 421 may be adjusted.

The piston-and-cylinder assembly 406 for releasing the brake shoes is mounted on the upper central portion of the frame 403 and is suitably connected to the brake levers 404 and 405 to separate them against the force of the springs 420 and 421. As shown the cylinder'438 is provided with a movable piston 439 and rod 431, the lower end of which engages the inner arms of a pair of bell-crank levers 432 and 432' which are pivotally mounted on a pair of pivot pins 433 and 434 in the upper part of the frame 403.

- The bell-crank levers 432 and 432' are positioned in the frame 403 in such manner that the outer ends impinge against the inner ends of a pair of set screws 435 and 436 in the brake levers 404 and 405 and thus act as a means for separating the brake levers when the electro-magnet 406 is energized. Each of the set screws 435 and 436 is provided with a locking nut 437 for retaining it in any position to which it may be adjusted.

The clearance between the brake shoes 409 and 410 and the brake drum Bd when the brake levers 404 and 405 are separated by the piston rod 431 may be adjusted by loosening the locking nuts 437 and rotating the set screws 435 and 436 in the proper direction.

It will be observed that the brake mechanism is arranged in such manner that all of the forces' exerted by the brake shoes 409 and 410 and by the piston rod 431 are directed against the inner sides of the brake levers 404 and 405 at points between the pivotal supports of the levers and the compression springs 420 and 421 and, therefore, that the forces exerted by the springs keep the lower ends of the levers pressed against the inner sides of the pivot pins 407 and 408 at all times.

With the brake arranged in the manner de-. scribed, no lost motion can occur in the movement of the various parts during the operation of the brake, and, therefore, the brake can be adjusted with a minimum amount of clearance between the drum and the shoes. Also, forces that tend to deflect the lever 404 act in the same direction when the brake is applied or released, and, therefore, there is no effect of lost motion, due to deflection of the arm 404 under the influence of pressure of the spring 420 or the lever 432.

In the operation of the brake mechanism, the

- brake shoes 409 and 410 are normally held in engagement with the brake drum Ed by the compression springs 420 and 421. Assuming that it is desired to release the brake drum Ed, the

pipe 6 leading to the cylinder 438 is connected to a suitable source of pressure. The pressure on the piston 439 causes its rod 431 to move downwardly against the inner ends of the bell-crank levers 432 and 432 and actuate them to separate the brake levers 404 and 405 against the action of the springs 420 and 421, thereby releasing the brake shoes 409 and 410 from the brake drum Bd.

It will therefore, be understood that I have devised a brake that is exceedingly quick in action, by reason of the fact that no lost motion occurs in the operation of its movable parts, and one that is provided with shoes which are self-aligning in all directions, and that varying degrees of braking force may be applied by varying the releasing pressure applied to the piston.

It will also be observed that the brake shoes 409 and 410 are operated independently of each other and, therefore, that any defect in one shoe will not affect the operation of the'other shoe.

Although I have shown and described certain specific embodiments of my invention as applied to elevator systems, I am fully aware that many modifications and applications thereof are possible. I do not wish to be restricted to the specific structural details or circuit connections shown or to the specific pressures and braking forces which have been given merely by Way of examples, I desire, therefore, that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention:

1. The combination with an elevator system comprising anelevator car and a control system therefor,.of a brake, an auxiliary brake, means for applying said brakes simultaneously when slow-down is initiated, and means for gradually releasing said auxiliary brake as the speed of the elevator car decreases.

2. The combination with an elevator system comprising an elevator car and a control system therefor, of a brake comprising a brake drum and a' spring-pressed brake shoe, and hydraulic releasing means for releasing the brake in accordance with the pressure admitted to said hydraulic means, of means for admitting a high pressure to said releasing means to release the brake under normal running conditions, and means rendered effective by the initiation of slow-down to discharge said pressure and thereafter to increase it as the elevator speed decreases, whereby the brake is applied with greatest force when slow-down is,

' for controlling the application of said brake,

means for varying the excitation of said electromagnetic means to release the brake during normal running conditions and to apply the brake when slow-down is initiated, and means for varying the excitation of said electromagnetic means during the deceleration of said car to gradually release the brake in accordance with the decreasing speed of the car.

5. The combination with an elevator system comprising an elevator car, a control system therefor, and a brake, of electromagnetic means for controlling the application of said brake, means for varying the excitation of said electromagnetic means to release the brake during normal running conditions and to apply the brake when slow-down is initiated, and a variablevoltage generator driven by the elevator to vary the excitation of said electromagnetic means during the deceleration of said car, whereby the brake is gradually released in accordance with the decreasing speed of the elevator car.

6. The combination with an elevator system comprising an elevator car and a control system therefor, of a brake comprising a braking surface, a brake shoe, and a spring for biasing the brake shoe to engaging relation with the braking surface, hydraulic releasing means for holding the brake shoe disengaged from the braking surface in opposition to the spring, means for applying a high pressure to said hydraulic releasing means to completely release the brake during running conditions, means comprising valves rendered efiective by the initiation of slow-down to discharge said pressure to apply the brake, speedresponsive means for regulating said valves to increase the pressure applied to said hydraulic releasing means as the car speed-decreases, whereby the brake is released as the car decelerates.

'7. The combination of an elevator system comprising an elevator car and a control system therefor, of a machine brake, an auxiliary brake, a hydraulic releasing means for said auxiliary brake, means for applying said brakes simultaneously when slow-down is initiated and speedresponsive means for admitting increasing degrees of pressure to said hydraulic releasing meansto gradually release the auxiliary brake as the speed of the elevator car decreases.

8. The combination with an elevator system comprising an elevator car, a control systemtherefor and a brake, of pressure-responsive brake releasing means, a pressure generator connected thereto, electromagnetic means for actuating said pressure generator, means for varying the excitation of said electromagnetic means to release the brake during normal running conditions and to apply the brake when slow-down is initiated, and means for varying the excitation of said electromagnetic means during the deceleration of the car to gradually release the brake as the speed of the car decreases.

HENRY D. JAMES.

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