MODULAR ARRANGEMENT OF A

DOUBLE WRAP TRACTION ELEVATOR MACHINE

WITH DYNAMIC BRAKING BACKGROUND

The present disclosure relates generally to an elevator system, and more particularly to an elevator system including a plurality of motors for a double wrap traction elevator.

A typical traction elevator system includes a car and a counterweight disposed in a hoistway, a plurality of ropes that interconnect the car and counterweight, and a machine having a traction sheave engaged with the ropes. The drive machine of the traction elevator can have a traction sheave with grooves for the hoisting ropes of the elevator and an electric hoist motor driving the traction sheave either directly or through a transmission. The ropes are driven by rotation of the traction sheave motor that results in repositioning of the car and counterweight within the hoistway. The traction machine, and its associated electronic equipment, along with peripheral elevator components, such as a governor and safety features, are commonly housed in a machine room located above the hoistway.

Conventional traction machines make use of alternating current (AC) permanent magnet hoist motors, which have permanent magnets in the rotor in order to improve the efficiency of the machine. The conventional machines, however, are limited to relatively low duty cycles and low speeds. These types of machines are impractical for newer buildings, which are constructed at greater and greater vertical heights that the elevators must service. Existing machines can approach their design limits for these newer structures, which is becoming more and more common.

One of the problems encountered in gearless elevator machines of conventional construction has been their large size and weight. The hoist motors take up considerable space and are difficult to transport to the site and to install. In large elevator machines, transmitting the torque from the hoist motor to the traction sheave can be a problem. For elevators designed for loads of several thousand kilograms and speeds of several meters per second, conventional machines with a single motor are not capable of developing a sufficient torque and speed of rotation with a size and weight that is suitable for installation in a building. This imposes special requirements on the electric drive of the hoist motor to allow full-scale utilization of the motor, and the size of the motor becomes unwieldy. Specialized equipment and large cranes are required for getting such hoist motors in place during construction of structures of great vertical height. Further, the size of the motors and machines and area required might be greater than that of the cross- sectional area of the hoistway of the elevator, again requiring specialized mounting arrangements. Special requirements generally result in a complicated system or a high price, or both.

Thus there is a need in the art to develop elevator systems that efficiently utilize the available space and meet the duty load and speed requirements over a broad range of elevator applications, including tall vertical structures. Further, there is a need for a machine that is easily installed, and can be positioned by hoisting the machine through the hoistway with common building cranes.

Another issue in traction elevator applications involves the need for synchronous management of two or more elevator power train subunits propelling one elevator, with a single or double deck car. There needs to be a proper transition from normal operation into emergency braking in case of a power supply interruption. The application of passive dynamic braking to elevator drive motors is a critical part of elevator tandem operation. This braking system is most often the sole means of stopping the elevator when overspeed and overtravel conditions occur.

SUMMARY In one embodiment, a drive for a gearless elevator in what is known as a double wrap traction elevator machine includes a first hoist motor adapted to drive a first sheave and a second hoist motor for driving a second sheave. The rope system comes up vertically from the counterweight to the first machine sheave, then it wraps about 160° around the first sheave, travels down to the second sheave. Next the rope system goes around the second sheave and back to the first sheave, thus wrapping 180° around the second sheave. From the first sheave, the rope system goes to the elevator car. Both the first and second sheaves are motor driven, thus greatly increasing the lifting capacity without the use of extremely large motors. The motors are permanent magnet synchronous motors.

The motors that drive the first and second sheaves are not mechanically coupled. In another embodiment, a dynamic braking system is disclosed. This dynamic braking system comprises connecting both motors in parallel to a common motor drive while providing that each motor will operate from its inverter and control logarithm. A single resistive load bank is provided with a resistance value based upon the size of the load, the inverter, and the motors. The resistive load bank is connected between the two motors through semiconductor switches. When dynamic braking is operating, the motors are disconnected from the inverters, and switches in a commonly connected matrix switch box provide for smooth dynamic braking.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a double wrap gearless traction elevator with motors on the first and second sheaves.

FIG. 2 is a side elevation view of the sheaves in FIG. 1 illustrating the double wrap arrangement.

FIG. 3 is a side elevation view of the sheaves in FIG. 2 illustrating the double wrap arrangement.

FIG. 4 A and 4B are electrical connection diagram of the dynamic braking system in normal (4A) and emergency (4B) operation of the motors.

FIG. 5 is a side elevation view of an alternative elevator system with two motors. DETAILED DESCRIPTION

FIG. 1 illustrates a gearless traction elevator system 10 with double wrap traction rope system 11. First sheave 13 is driven by hoist motor 15, and second sheave 17 is driven by hoist motor 19. A power source 21 (such as a power utility) provides electrical power via power lines 22 to drive unit 23. Alternating current (AC) drive power at a variable frequency is supplied by motor drive unit 23 to motors 15 and 19 via power lines 24. Hoist motors 15 and 19 are permanent magnet AC motors that vary the speed as a function of drive frequency. Motor drive unit 23 is controlled by controller 25 and control signals transmitted via line 26. Motor drive unit 23 may include a converter for converting AC input power to DC voltage on a DC bus, and an inverter (or inverters) to convert the DC voltage from the DC bus to AC drive power of a frequency determined by the control signals from controller 25.

Motors 15 and 19 drive sheaves 13 and 17 via shafts 27 and 28, and thus provide increased torque to permit the use of system 10 on heavier and/or taller elevator systems. Rope system 11 connects car 33 and counterweight 35. Rope system 11 may include one rope or may more commonly include a plurality of ropes, in some instances having as many as 20 ropes. Ropes are made from a variety of materials such as, for example, steel in the form of cable and as wound ropes. The number and type of ropes will determine the surface of the sheaves. It is contemplated that any rope system may be used with the present invention as long as the rope system is otherwise suitable for the size and lift distance of the elevator system.

Shown in FIG. 1 is a two rope system where the first rope 37 is attached to car 33 at a suitable termination 37a, rises up to first sheave 13, passes around sheave 13 at 37b and second sheave 17 at 37c. First rope 37 then again extends up to first sheave 13 at 37d, then around second sheave 17 at 37e, and down to counterweight 35 at a suitable termination 37f. Similarly, second rope 39 is attached to car 33 at a suitable termination 39a, rises up to first sheave 13, passes around sheave 13 at 39b and second sheave 17 at 39c. Second rope 39 then again extends up to first sheave 13 at 39d, then around second sheave 17 at 39e, and down to counterweight 35 at a suitable termination 39f. Although shown as a 1 : 1 roping arrangement, the present invention could be used with other roping arrangements (e.g. 2:1).

In order to increase the torque and duty potential of an elevator system, a double wrap traction sheave system is used in which the first or traditional drive sheave and the second sheave both have a motor drive. In conventional machines, the second sheave was an idler sheave. That is, a motor did not drive the second sheave. Both motors 15 and 19 may be the same size and power and are controlled by controller 25 as described in FIG. 1. Alternatively, motors 15 and 19 may be of different sizes due to their traction capabilities, such as when first and second sheaves 13 and 17 have different degreees of wrap. If the second sheave 17 has less traction, motor 19 may be of a smaller size, and, conversely, if second sheave has greater traction, motor 19 may be of a larger size. Hoist motors of the type described herein could, for example, operate at up to 7 meters/second in speed and can carry up to 4,500 kg of duty load, thus doubling the size of the elevator lifting capacity and/or the distance the elevator is to travel, such as in very tall buildings. FIG. 2 illustrates the manner in which the first sheave 13, with its axis 13c, is aligned so that the car centerline 41 is offset from centerline 43 of first sheave 13. Similarly, the centerline 45 of counterweight 35 is offset from centerline 47 of second sheave 17. with its axis 17c. Ropes 37 and 39 function as described above with reference to FIG. 1.

FIG. 3, which is a side view of FIG. 2, illustrates the double wrap arrangement for rope 39 about first sheave 13 and second sheave 17. Of course, the same description is true for all the ropes used in the present invention. One end 39a of rope 39 extends down to an elevator car, not shown here but in the same manner as in FIG. 1, and the other end 39f extends to a counterweight, also not shown for convenience of illustration. Car 33 and counterweight 35 of FIG. 1 to raise and lower an elevator car. Rope 39 is arranged so that when the rope system raises an elevator car, rope 39 travels from rope end 39a around sheave 13 at 39b, down to sheave 17 at 39c at a wrap angle, such as about 160°, and back to sheave 13 from sheave 17 at 39e at an angle of 180°, around sheave 13 at 39f and back to sheave 17 at 39g, and then down at a final angle of 20° at 39h to the counterweight by end 39f. The wrap angle may range from less than 150° to more than 170°, and specifically about 160°. The return angle is calculated by subtracting the wrap angle from 180°, and would be about 20° when the wrap angle is about 160°.

FIGS. 4A and 4B illustrate a dynamic braking system 61 in two modes. During normal operation of an elevator system, the braking system 61 shown in FIG. 4A, and the system 61 is shown in FIG. 4B in an emergency braking system.

The dynamic braking system 61 includes a pair of motors 15 and 19, such as those shown in the previous figures where each motor drives a separate sheave. Dynamic braking system 61 motors 15 and 19 are powered by a source of AC signals 63, such as a 60 Hz signal that is converted to direct current (DC) in motor drive 23 as controlled by controller 25. Motor drive 23 then smooths the DC signal into a flat signal and inverts it to an AC signal such as from 0 Hz to 100 Hz, for example, to drive motors 15 and 19 through drive lines 73 and 75. Energy flows into and out of motor drive 23 as the elevator rises and descends in a normal manner. FIG. 4A illustrates the operation of system 61 during normal use. However, in the event that there is over speed and/or over travel conditions, particularly when any mechanical brake system fails, dynamic braking will be needed. It should be noted that there is at least one mechanical brake associated with motors used in elevator systems and that those mechanical brakes normally are adequate to stop the movement of the elevator. System 61 provides for those times when the mechanical brakes do not function as intended.

FIG. 4B illustrates a dynamic braking embodiment. Motor drive 23 is adapted to sense that the elevator system is in an emergency mode, such as when a rope brakes or other mechanical or electrical failures occur. Occupants may also trigger an emergency switch or button indicating an emergency. Motor drive 23 then disconnects the power to motors 15 and 19, as shown by the x through power lines 73 and 75. Matrix switch box 77 activates switches contained therein from a signal from motor drive 23 via line 79 to create a switching state that avoids causing equal and opposite phase currents between motors 15 and 19 to avoid a zero retarding torque that won't function as a dynamic brake. Matrix switch box 77 maintains an equality of speed between motors 15 and 19 as the current generated by these motors is fed into a resistive bank 81, dissipating the energy into heat and causing motors 15 and 19 to come to a stop, and thus stop the elevator car.

In the case of two motors, as described above, matrix switch box 77 is arranged such that each motor 15 and 19 sees the winding of the other as braking resistors dissipating braking energy. This produces instantaneous braking torque on the rotors of both motors 15 and 19. Controller 25 synchronizes the speed and torque of both motors 15 and

19 during normal operation as well as during emergency stopping.

FIG. 5 illustrates a two-dimensional view of a tandem system 101 incorporating two permanent magnet (PM) motors 103 and 105 that are decoupled mechanically from each other. Motors 103 and 105 drive sheaves 107 and 109 via rope system 111 to raise and lower elevator car 113 and counterweight 115. The rope system 111 comprises a first rope I l ia operating with sheave 107 and a second rope 111b operating with sheave 109, such that wherein the first rope I l ia and the second rope 111b are offset to raise and lower the elevator car 113 and the counterweight 115 past one another.

The tandem system 101 of FIG. 5 is also adaptable for use with the dynamic braking system 61 shown above in FIGS. 4A and 4B, such that motors 103 and 105 are also controlled by a controller, such as motor drive 23 during normal operation and a matrix switch box 77 in dynamic braking, in the manner described above. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.