2. DESCRIPTION OF THE PRIOR ART Elevator systems typically include a car that moves within a hoistway to transport passengers or items between various levels in a building. The elevator car is typically balanced during installation when the car is stationary at a midpoint of the hoistway. The elevator car is properly balanced when the center of gravity of the complete assembly lies vertically below the suspension point. The elevator car includes weights placed within a weight trough to counteract any unbalanced force when the elevator car is at the midpoint of the hoistway.

During typical operation, forces and weight distribution on the elevator car change. Typically, an elevator system will include compensation ropes attached to an underside of the elevator car. The compensation ropes includes a length supported by the elevator car during operation. Often, the speed and rise of the elevator car will cause an unbalanced condition. The unbalanced condition causes a corresponding increase in pressure on the roller assemblies large enough to affect ride quality.

Another contributor to unbalanced elevator car conditions is a traveling cable that includes a plurality of control wires and conductors that communicate electricity to the elevator car. The traveling cable is typically attached to the elevator car in a manner causing an unbalanced condition. The traveling cable is attached between a controller within the elevator system at a fixed point within the hoistway and the elevator car. The traveling cable attached to the elevator car cannot be installed at the center of gravity or center point of the elevator car. The traveling cable is therefore attached to the elevator car in an offset position.

The length of the traveling cable and compensation ropes and the respective corresponding weight supported by the elevator car changes dynamically during

movement within the hoistway. As the elevator car moves upward, the amount of the traveling cable and compensation rope supported by the elevator car increases.

Typically, the traveling cable weights between 1 and 2 pounds per liner foot.

In high-rise applications, the elevator car may travel hundreds of feet, and the weight of the compensation rope supported by the elevator car can exceed several hundred pounds. Further, the weight of the traveling cable and compensation rope may drop to only a few pounds at a lower most point within the hoistway where only a small section of the traveling cable is supported by the elevator car. The weight compensation provided in the elevator car diminishes toward the bottom of the hoistway.

The varying weights exerted by the compensation rope and the traveling cable cause an overturning moment on the elevator car that produces an increase in guide roller pressure. Balancing the elevator car promotes good ride quality defined as a smooth and quiet ride. Further, a balanced car provides the best conditions for safety applications or buffer engagement. A balanced car also minimizes wear on the guide shoes, rails and the rollers.

A known system includes a weight that is shiftable relative to the elevator car to dampen vibrations. Another known system includes a movable support for the elevator car roping that changes the lift point dynamically as the elevator car moves within the hoistway. Such approaches are complicated and costly to implement.

Such systems increase overall weight, in some instance requiring a larger motor for lifting the elevator car. Further, such devices add to the complexity of the elevator system, reduce reliability and increase the likelihood that maintenance will be needed.

Accordingly, it is desirable to develop a system to dynamically maintain a proper balance or orientation of the elevator car by accounting for changes in forces exerted on the elevator car during system operation.

SUMMARY OF THE INVENTION This invention is a system and method for balancing an elevator car by selectively distributing fluid in a container associated with the elevator car.

In one embodiment, an elevator system includes a fluid container supported for movement with the elevator car and a fluid moving device that selectively distributes fluid to desired portions of the container In one particular example, the elevator car includes balance tanks located at each corner of the elevator car and a centrally located fluid reservoir. A device for transferring fluid to each of the balance tanks moves fluid between the balance tanks and the reservoir to control orientation of the elevator car. Controlling the amount of fluid within the balance tanks counters changes in forces on the elevator car to maintain a desired balanced condition.

Accordingly, this invention provides a simple effective, accurate, and efficient means of dynamically balancing an elevator car within the hoistway.

BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows : Figure 1 is a schematic view of an elevator car supporting a fluid container; Figure 2A is a schematic view of an elevator car within a hoistway at a lower most position ; Figure 2B is a schematic view of the elevator car within the hoistway at midrise ; Figure 2C is a schematic view of the elevator car within the hoistway at an upper most position; Figure 3 is a schematic view of an example balance system designed according to this invention ; and Figure 4 schematically illustrates selected portions of another embodiment of a balance system designed according to this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figures 1 and 3, an elevator car 12 supports a distribution container 14 containing fluid 26. Fluid 26 is moved within the distribution container

14 by a fluid moving device. In one example, the fluid moving device is a pump 16.

Although a pump 16 is used in the illustrated embodiment, other known devices are within the scope of this invention.

The container 14 includes a reservoir 22 and balance tanks 20. The fluid moving device 16 moves fluid within the distribution container 14 to balance the elevator car 12 in response to instructions from a controller 18. The controller 18 can be a separate controller or a part of an overall elevator system controller. Further, given this description, those skilled in the art will be able to program a commercially available controller or to develop dedicated hardware, software or both to achieve the desired control over distribution of fluid.

Movement of fluid within the distribution container 14 shifts weight associated with the elevator car 12 to accommodate and counter changes in force and load distributions that typically occur during elevator system operation. The controller 18 represents that part of a controller, located within the elevator car 12 or within the elevator system controller 56 (shown in Figure 2A-2C), that controls movement of fluid within the distribution container 14. The controller 18 determines whether the car 12 is properly balanced and changes the fluid distribution as needed to maintain a desired car orientation or balance.

In operation, the controller 18 actuates the pump 16 to distribute fluid 2 6 between the balance tanks 20 in response to an unbalanced condition of the elevator car 12. Fluid 26 is dispersed in the specific proportions to the specific balance tanks 20 in a chosen manner to counter an overturning moment caused by the unbalance condition on the elevator car 12. The pump 16 also withdraws fluid through fluid conduits 24 to properly adjust fluid distribution as required to balance the elevator car 12.

Referring to Figures 2A-C, one example of force accommodation provided by this invention will be described. An elevator system 10 is partially, schematically shown including the elevator car 12 supported for movement within a hoistway 28.

The elevator car 12 supports the distribution container 14 that in the example includes the balance tanks 20 disposed at each corner of the elevator car 12. Fluid 26 transferred between the balance tanks 20 maintains a balanced condition of the elevator car 12 at any location within the hoistway 28.

The elevator car 12 is configured to ride within the hoistway 28 in a known manner. The elevator car 12 includes a platform 34 and an upright 36. Guide rollers 32 guide the elevator car 12 along guide rail 30. The elevator system controller 56 is electrically connected with appropriate components supported on the car 12 by way of a traveling cable 44. The traveling cable 44 is attached to the base portion 34 in an off-center manner a distance from the center of the elevator car 12 as known. In addition to the traveling cable 44, a compensation rope 45 is attached to compensate for dynamic changes to balanced conditions within the elevator car 12 during operation.

Ideally, the resultant force on the elevator car 12 must be aligned vertically with the center of gravity of the elevator car 12 and the centerline of the guide rails 30. The forces and weight supported and exerted on the elevator car 12 ideally combine to provide a balanced elevator car 12 (i. e. a level car orientation) at all locations within the hoistway 28. However, the traveling cable 44 and compensation rope 45 along with other items may not be attached to a central location on the elevator car 12.

For this reason, balance weights 54 are placed within the elevator car 12 as are known. Unbalanced weight supported by the elevator car 12 causes an over turning moment force on the elevator car 12. Example of items causing such unbalanced condition include the traveling cable 44 and the compensation rope 45 that are both mounted in an off-center position relative to the elevator car 12.

The counterbalance weight 54 counters the force of the weight of the traveling cable 44, and compensation rope 45 to balance the elevator car 12, but only at the mid-rise position within the hoistway 28 (Figure 2B). At the mid-rise position, the length 46 of the traveling cable 44 whose weight is supported by the elevator car 12 is balanced by the counterbalance weight 54. Further, a length 80 of the compensation rope 45 is also supported by the elevator car 12. However, as the length 46 of traveling cable 44, and length 80 of the compensation rope 45 changes during movement of the elevator car 12 away from the mid rise point, the counterbalance weight 54 no longer properly balances the elevator car 12.

Referring to Figures 2A-C, in operation, the system 10 senses the position of the elevator car 12 within the hoistway 28 by way of sensors 38. A pressure sensor

40 is also used to monitor pressure exerted on the rollers 32. Further, specific information on the load within the elevator car 12 can also be monitored and both the position and load information communicated to the controller 18. The controller 18 actuates the pump 16 to transfer fluid in proper proportions to the various balance tanks 20. Fluid 26 is transferred to counterbalance overturning moments caused by uneven loads on the elevator car 12.

Referring to Figure 2B, the elevator car 12 is in a mid-rise position where the weight of the traveling cable 44, and compensation rope 45 supported by the elevator car 12 are balanced against the counterbalance weight 54. Fluid 26 is either stored within the reservoir 22 or distributed as needed among the various balance tanks 20 to achieve a desired counterbalance effect.

As the elevator car 12 is lowered to a lower most position shown in Figure 2A, the sensors 38 communicate the movement of the elevator 14 to the controller 18. Further pressure sensors 40 communicate changes in pressure exerted on the rollers 32 to the controller 18. The controller 18 actuates the pump 16 and control valves 52 (Figure 3) to transfer fluid 26 within the balance tanks 20 to counteract the overturning moment 48 by the counterbalance weight 54. Raising the elevator car 12 to the upper most point within the hoistway 28 (Figure 2C) increases the length 46 of the traveling cable 44, and the compensation rope 45 supported by the elevator car 12. The increased length 46", 80"of the traveling cable 44 and the compensation rope 45 is much more than can be balanced by the counterbalance weight 54, and an overturning moment is exerted in the direction indicated at 49.

The controller 18 actuates the pump 16 to transfer fluid 26 between the balance tanks 20 to account for the additional weight and the overturning moment 48. The continual transference of fluid 26 between balance tanks 20 in response to the sensed unbalanced loads on the elevator car 12 maintains proper balance at any point within the hoistway 28.

Referring to Figure 2A, the elevator car 12 is shown at a lower most point of the hoistway 28. The length 46', 80'of the traveling cable 44 and compensation rope 45 that is suspended below the car 12 is much shorter than the length 46,80 at the balanced, mid-rise position (Figure 2B). Therefore, the counterbalance weight 54 is greater than the weight of the traveling cable 44 and compensation rope 45

supported by the elevator car 12, and exerts an overturning moment force in the direction indicated by arrow 48. Such forces tend to cause undesirable wear on the guide rollers 32 and decrease the smoothness and quality of the ride.

Referring to Figure 2C, the elevator car 12 is shown at an upper most position and supports a much greater length 46 of traveling cable 44 than that supported at the mid-rise position shown in Figure 2B. Therefore, the counterbalance weight 54 is not sufficient to counteract the overturning moment in the direction indicated at 49.

Referring to Figures 2A-C and 3, an embodiment the elevator car 12 includes the reservoir 22 containing fluid 26 and the pump 16 for selectively distributing a desired amount of fluid to each of the balance tanks 20. The balance tanks 20 are disposed within a balance weight trough 58 at the front and back of the elevator car 12. In this example, the trough 58 comprises a known structure otherwise used to support the static counter balance weight 54. The balance tanks 20 and the fluid reservoir 22 through fluid conduits 24. In this example, each fluid conduit 24 includes a valve 52 that is controlled by the controller 18. Although the pump 16 is shown, it is within the contemplation of this invention to use other known devices to transfer fluid between the balance tanks 20 and the fluid reservoir 22.

As appreciated, the specific type of fluid used within the balance tanks 20 is preferably a n on-corrosive, n on-toxic f luid t hat i s r esistant toe ontamination. It i s within the contemplation of this invention to use any fluid fulfilling the application- specific requirements of a particular situation. The balance tanks 20 are disposed at corners of the elevator car 12 such that a desired amount of fluid 26 can be transferred to each specific balance tank 20 to counterbalance overturning moments exerted on the elevator car 12.

Depending on the selected manner of determining whether the car 12 is balanced (i. e. , all forces on the car are balanced and the car is level), the controller 18 uses the available information. In one example, position information regarding the car position in the hoistway is used. In another example, weight sensors associated with the car provide force distribution information. In another example, a level sensor associated with the car provides car orientation information. Those who have the benefit of this description will be able to select appropriate sensors or

sources of car position information and to suitably program a commercially available microprocessor or controller to meet the needs of their particular situation.

Sensors 38 (Figures 2A-C) within the hoistway 28 monitor the position of the elevator car 12 and communicate that information to the controller 18. The controller 18 controls the pump 16 and valves 52 to distribute appropriate amounts of the fluid 26 to the specific balance tanks 20 required to balance the elevator car 12 against tipping caused by otherwise unbalanced forces that change with different heights or positions of the car in the hoistway.

Sensors dedicated to the balancing system, such as sensors 38 disposed within the hoistway and pressure sensors 40 on the rollers 32, or information from the machine motor provide car position information to the controller 16 to initiate fluid to specific balance tanks 20. Further, sensor 41 disposed on the elevator car 12 communicates information indicative of elevator car 12 orientations to the controller 18.

In one example, the pressure sensors 40 sense changing loads on the rollers 32. The overturning moment forces causes unbalanced loads on the rollers 32. The sensors 40 monitor forces on the rollers 32 and communicate that information to the controller 18. The controller 18 in turn controls the pump 16 to distribute fluid between the balance tanks 20 to counter unbalanced forces on the elevator car 12.

Another example of the use of sensors is to sense the load distribution within the elevator car 12 with sensors disposed within the elevator car 12 or on the car supporting structure. Sensors 42 monitor loads on the elevator car 12 in a known manner and communicate that information to the controller 18. Sensing loads within the elevator car 12 allows adjustment of fluid 26 within the balance tanks 20 in response to specific weights or loads and their specific position within the elevator car 12. The controller 18 will then account for the load configuration within the elevator car 12 by transferring fluid 26 to the proper balance tank 20. This provides counter balance not only against the known weight of items always associated with the e levator c ar 12 s uch a s t he t raveling c able 4 4, b ut a Iso a gainst unequal 1 oads caused by passengers, equipment and other items transported within the elevator car 12.

Referring to Figure 4, another embodiment of the fluid moving device is illustrated and generally indicated at 6 0. The fluid moving device 6 0 includes an expandable member 66 actuated by a pneumatic device 64. The expandable member 66 is disposed within a container 70. The container 70 represents the centrally located fluid reservoir 22 in one example and the balance tanks 20 in another example. The controller 18 actuates the pneumatic device to fill the expandable member 66 to evacuate fluid 26 from the container 70 through conduits 68. As the expandable member 66 fills the space within the container 70, fluid 26 is driven to other free space within the distribution container 14. Selectively actuating expandable members positioned within the container 14 supported on the elevator car 12 distributes fluid 26 to counter any unbalanced forces or uneven weight distributions.

The pneumatic device 64 may be a pump or a tank containing a pressurized gas. It should be understood that it is within the contemplation of this invention that any type of pump or gas tank to provide a pressurized gas or fluid to actuate the expandable member 66 is within the contemplation of this invention.

The foregoing description is exemplary and not limiting. The invention has been described in an illustrative manner, and it should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Modifications and variations are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.