Technical Field ^r -t This invention relates to elevators in general, 5 and more specifically to the roping of an elevator in a ^* hoistway.

Background Art

Elevators typically consist of an elevator car and a counterweight for travel within a hoistway. A pair of

10 sheaves fixed within the hoistway above the car and counterweight guide a plurality of ropes which attach the car and the counterweight. One end of each rope attaches to the car and the other end attaches to the counterweight. The ropes extend from the car up the

15 hoistway to the sheaves, around the sheaves, and back down the hoistway to the counterweight. Movement of either the car or the counterweight a distance causes the other to travel a like distance in the opposite direction.

20 Tubular linear motors having a cylindrical shaped secondary and a tubular shaped primary may be used to power an elevator. The secondary is received within the center of the primary and an air gap is maintained between the secondary and the inner diameter of the

25 primary. Introducing electrical current into the primary creates magnetic flux which travels between the primary and secondary. The magnetic flux, in turn, creates attractive and repulsive forces between the primary and the secondary, thereby causing relative

30 motion between the two. Λ A disadvantage of the tubular linear motor, however, is that the travel of the motor is limited (and

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therefore the travel of the car in a conventionally roped elevator) since the secondary may only be attached on the ends. Attaching the secondary on the ends causes two problems in elevator applications. First, the sinusoidal nature of the attractive forces created by the magnetic flux can cause the secondary to deflect and vibrate. A secondary attached only at the ends is more susceptible to deflection and vibration. Second, there are practical material limits to the length of a secondary which is supported only at each end. The longer the secondary is, the less rigid it will be. A vibrating or flexible secondary will compromise the air gap between the primary and the secondary, and thereby negatively effect the performance of the motor.

Disclosure of the Invention

It is an object of the present invention to provide an elevator driven by a tubular linear motor which minimizes the necessary travel of the linear motor, thereby allowing a shorter, more rigid secondary to be used which increase the efficiency of the motor.

It is a further object of the present invention to provide an elevator driven by a tubular linear motor in which the length of travel of the motor does not limit the travel of the elevator car. It is a still further object of the present invention to provide a method for altering the length of travel of an elevator counterweight in a hoistway, relative to the travel of an elevator car in the hoistway. It is a still further object of the present invention to minimize the space necessary in the hoistway of an elevator.

According to the present invention, an elevator is provided having a car for travel within a hoistway. A tubular linear motor, comprising a movable member and a fixed member, propels the car through the hoistway. A first sheave is attached to the movable member and a second sheave is fixed within the hoistway. A plurality of ropes wrap around the first and second sheaves and attach to the car, thereby connecting the movable member of the linear motor and the elevator car. According further to the present invention, a method for altering the length of travel of an elevator counterweight relative to the travel of an elevator car in a hoistway is provided, where the car and counterweight are attached to one another by a plurality of ropes. The first step includes providing a linear motor for propelling the car in the hoistway. The linear motor comprises a movable member attached to the counterweight and a fixed member. The second step includes providing at least one first sheave attached to the movable member. The third step includes providing at least one second sheave fixed within the hoistway above the car and the counterweight. The fourth step includes fixing one end of the ropes either within the hoistway or to the counterweight. The fifth step includes extending the ropes to and around the first and second sheaves. The sixth step includes attaching the other end of the ropes to the car.

An advantage of the present invention is that the roping arrangement permits the elevator car to travel a multiple of the distance traveled by the movable member of the linear motor. As a result, a shorter tubular linear motor secondary may be used.

A further advantage of the present invention is that a shorter, more rigid secondary may be used. A

shorter, more rigid secondary is less susceptible to vibration and deflection and is therefore less likely to compromise the air gap between the movable and fixed members of the linear motor. As a result, the motor efficiency increases.

A still further advantage of the present invention is that the shorter required stroke of the counterweight in the present invention minimizes the hoistway space requirements in a building. These and other objects, features and advantages of the present invention will become more apparent in light of the detailed description of the best mode embodiment thereof, as illustrated in the accompanying drawings.

Brief Description of the Drawings

FIG.l is a perspective view of an elevator having a car and a counterweight.

FIG.2 is a diagrammatic side view of the elevator shown in FIG.l. FIG.3 is a cross-sectional view of the diagrammatic view shown in FIG.2

FIG.4 is a cross-sectional view of the diagrammatic view shown in FIG.2

Best Mode for Carrying Out the Invention Now referring to FIGS.l and 2, an elevator 10 is shown having a car 12 and a counterweight 14 capable of traveling through a hoistway 16. A pair of guide rails 18 guides the travel of the car 12 from the top 20 to the bottom 22 of the hoistway 16. A second set of guide rails 24 guides the travel of the counterweight 14 along a path parallel to the travel of the elevator car 12. The counterweight 14 includes a frame 26 and a plurality

of weights 28. A first 30 and a second 32 sheave are attached to opposite sides of t a counterweight 14.

The car 12 and the counterweight 14 are propelled through the hoistway 16 by a tubular linear motor 31 having a tube-shaped primary 34 and a cylindrical-shaped secondary 36. The secondary 36 is a ferromagnetic cylinder fixed within the hoistway 16, secured at both ends with no supports in the middle. The primary 34 is attached to the frame 26 of the counterwaight 14, in between two stacks of weights 28. The primary 34 receives the secondary 36 within its center 38 and thereby completely surrounds the length of the secondary 36 received within the primary 34.

Structural beams 40 fixed within the hoistway 16 above the car 12 and counterweight 14 support a third sheave 42, a fourth sheave 44, and a fifth sheave 46. The third sheave 42 is positioned on the side of the beams 40 opposite the car 12 and the counterweight 14, above the counterweight 14. The third sheave 42 is aligned diagonally across the counterweight 14 (See

FIG.3) to enable the pay-on point 48 of the third sheave 42 to align with the pay-off point 50 of the first sheave 30 and the pay-off point 52 of the third sheave 42 to align with the pay-on point 54 of the second sheave 32. FIG.4 shows the rope path in phantom. Pay- on and pay-off points are defined as the points on a sheave at which a rope may enter and exit the sheave, respectively. The fourth 44 and fifth 46 sheaves are attached to the structural beams 40 on the side of the beams 40 facing the car 12 and counterweight 14. Like the third sheave 42, the fourth 44 and fifth 46 sheaves are arranged diagonally relative to the counterweight and car, thereby minimizing the necessary space, in the hoistway 16. The pay-on point 56 of the fourth sheave

44 is aligned with the pay-off point 58 of the second sheave 32. The pay-off point 60 of the fifth sheave 46 is positioned directly over the center of gravity of the elevator car 12. A plurality of ropes 62 connect the counterweight

14 to the car 12. One end of each rope 62 is fixed at a point 64 within the hoistway 16 (See FIG.3). From there, the ropes 62 extend downward to the first sheave 30 attached to the counterweight 14, wrap around the first sheave 30 and return upward to the third sheave

42. The ropes 62 enter the third sheave 42, wrap around it and extend down to the second sheave 32. The ropes 62 then enter the second sheave 32, wrap around it and return upward to the fourth sheave 44. The ropes 62 then enter the fourth sheave 44, partially wrap around it and exit to the fifth sheave 46. After partially wrapping around the fifth sheave 46, the ropes 62 extend down and attach to the elevator car 12 directly below the fifth sheave 46. In the operation of the elevator 10, as is known in the art an electrical current is introduced into the primary 34 of the linear motor 31 to create motion between the primary 34 and secondary 36 of the linear motor 31. Specifically, the electrical current creates magnetic attractive and repulsive forces between the tubular primary 34 and the cylindrical secondary 36. The forces cause the movable primary 34, and therefore the counterweight 14, to move along the fixed secondary 36. Movement of the counterweight 14 causes movement of the elevator car 12 by virtue of the ropes 62, which are fixed on one end to a position 64 within the hoistway 16 and on the other end to the elevator car 12. Specifically, movement of the counterweight 14 either up

or down causes the elevator car 12 to travel in the opposite direction.

As described above, the ropes 62 travel between the first 30, second 32, third 42, fourth 44, and fifth 46 sheaves. The first 30 and second 32 sheave are mounted on the counterweight 14 and are therefore capable of displacement within the hoistway 16. The third 42, fourth 44, and fifth 46 sheaves, conversely, are attached to structural beams 40 and are therefore fixed in the hoistway 16. Movement of the counterweight 14 in either direction causes a change of length in each length of rope 62 extending between the displaceable sheaves 30,32 on the counterweight 14 and the sheaves 42,44,46 fixed within the hoistway as well as the length 68 of rope 62 between the attachment point 64 in the hoistway 16 and the first sheave 30.

Now referring to FIG.l, an upward movement of "x" distance by the counterweight 14, for example, causes the rope lengths between: (a) 68, the initial attachment point 64 and the first sheave 30; (b) 70, the first sheave 30 and the third sheave 42; (c) 72, the third sheave 42 and the second sheave 32; and (d) 74, the second sheave 32 and the fourth sheave 44, each to decrease by a distance of "x". Since the overall rope length remains constant, the total displacement of each rope is equal to "4x". The "4x" length of displaced rope increases the length of rope 76 between the fifth sheave 46 and the elevator car 12, thereby lowering the car 12 a distance of "4X". If, on the other hand, the counterweight 14 were moved downward a distance equal to "x", then the elevator car 12 would move upward a distance equal to "4x", and so forth.

A person skilled in the art will recognize that the number of sheaves mounted on the displaceable

counterweight 14 may be altered to tailor the distance travel by counterweight 14 versus the distance traveled by the elevator car 12. Moreover, a person of skill will also recognize that the ropes 62 may be initially attached to the displaceable counterweight 14 rather than fixed within the hoistway 16. In any of the possible embodiments, an advantage of the present invention is that the travel of the counterweight 14 can be designed as a fraction of the travel of the elevator car 12. As a result, the length of the linear motor secondary 36 may be minimized and the travel of the car 12 extended.

Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.