Tension member for an elevator

Abstract
A tension member for an elevator system has an aspect ratio of greater than one, where aspect ratio is defined as the ratio of tension member width w to thickness t (w/t). The increase in aspect ratio results in a reduction in the maximum rope pressure and an increased flexibility as compared to conventional elevator ropes. As a result, smaller sheaves may be used with this type of tension member. In a particular embodiment, the tension member includes a plurality of individual load carrying ropes encased within a common layer of coating. The coating layer separates the individual ropes and defines an engagement surface for engaging a traction sheave.
Description




TECHNICAL FIELD




The present invention relates to elevator systems, and more particularly to tension members for such elevator systems.




BACKGROUND OF THE INVENTION




A conventional traction elevator system includes a car, a counterweight, two or more ropes interconnecting the car and counterweight, a traction sheave to move the ropes, and a machine to rotate the traction sheave. The ropes are formed from laid or twisted steel wire and the sheave is formed from cast iron. The machine may be either a geared or gearless machine. A geared machine permits the use of higher speed motor, which is more compact and less costly, but requires additional maintenance and space.




Although conventional steel ropes and cast iron sheaves have proven very reliable and cost effective, there are limitations on their use. One such limitation is the traction forces between the ropes and the sheave. These traction forces may be enhanced by increasing the wrap angle of the ropes or by undercutting the grooves in the sheave. Both techniques reduce the durability of the ropes, however, as a result of the increased wear (wrap angle) or the increased rope pressure (undercutting). Another method to increase the traction forces is to use liners formed from a synthetic material in the grooves of the sheave. The liners increase the coefficient of friction between the ropes and sheave while at the same time minimizing the wear of the ropes and sheave.




Another limitation on the use of steel ropes is the flexibility and fatigue characteristics of steel wire ropes. Elevator safety codes today require that each steel rope have a minimum diameter d (d


min


=8 mm for CEN; d


min


=9.5 mm (⅜″) for ANSI) and that the D/d ratio for traction elevators be greater than or equal to forty (D/d≧40), where D is the diameter of the sheave. This results in the diameter D for the sheave being at least 320 mm (380 mm for ANSI). The larger the sheave diameter D, the greater torque required from the machine to drive the elevator system.




With the development of high tensile strength, lightweight synthetic fibers has come the suggestion to replace steel wire ropes in elevator systems with ropes having load carrying strands formed from synthetic fibers, such as aramid fibers. Recent publications making this suggestion include: U.S. Pat. No. 4,022,010, issued to Gladdenbeck et al.; U.S. Pat. No. 4,624,097 issued to Wilcox; U.S. Pat. No. 4,887,422 issued to Klees et al.; and U.S. Pat. No. 5,566,786 issued to De Angelis et al. The cited benefits of replacing steel fibers with aramid fibers are the improved tensile strength to weight ratio and improved flexibility of the aramid materials, along with the possibility of enhanced traction between the synthetic material of the rope and the sheave.




Even ropes formed from aramid fiber strands, however, are subject to the limitations caused by the pressure on the ropes. For both steel and aramid ropes, the higher the rope pressure, the shorter the life of the rope. Rope pressure (P


rope


) is generated as the rope travels over the sheave and is directly proportional to the tension (F) in the rope and inversely proportional to the sheave diameter D and the rope diameter d (P


rope


≈F/(Dd). In addition, the shape of the sheave grooves, including such traction enhancing techniques as undercutting the sheave grooves, further increases the maximum rope pressure to which the rope is subjected.




Even though the flexibility characteristic of such synthetic fiber ropes may be used to reduce the required D/d ratio, and thereby the sheave diameter D, the ropes will still be exposed to significant rope pressure. The inverse relationship between sheave diameter D and rope pressure limits the reduction in sheave diameter D that can be attained with conventional ropes formed from aramid fibers. In addition, aramid fibers, although they have high tensile strength, are more susceptible to failure when subjected to transverse loads. Even with reductions in the Did requirement, the resulting rope pressure may cause undue damage to the aramid fibers and reduce the durability of the ropes.




The above art notwithstanding, scientists and engineers under the direction of Applicants'Assignee are working to develop more efficient and durable methods and apparatus to drive elevator systems.




DISCLOSURE OF THE INVENTION




According to the present invention, a tension member for an elevator has an aspect ratio of greater than one, where aspect ratio is defined as the ratio of tension member width w to thickness t (Aspect Ratio=w/t).




A principal feature of the present invention is the flatness of the tension member. The increase in aspect ratio results in a tension member that has an engagement surface, defined by the width dimension, that is optimized to distribute the rope pressure. Therefore, the maximum pressure is minimized within the tension member. In addition, by increasing the aspect ratio relative to a round rope, which has an aspect ratio equal to one, the thickness of the tension member may be reduced while maintaining a constant cross-sectional area of the tension member.




According further to the present invention, the tension member includes a plurality of individual load carrying ropes encased within a common layer of coating. The coating layer separates the individual ropes and defines an engagement surface for engaging a traction sheave.




As a result of the configuration of the tension member, the rope pressure may be distributed more uniformly throughout the tension member. As a result, the maximum rope pressure is significantly reduced as compared to a conventionally roped elevator having a similar load carrying capacity. Furthermore, the effective rope diameter ‘d’ (measured in the bending direction) is reduced for the equivalent load bearing capacity. Therefore, smaller values for the sheave diameter ‘D’ may be attained without a reduction in the D/d ratio. In addition, minimizing the diameter D of the sheave permits the use of less costly, more compact, high speed motors as the drive machine without the need for a gearbox.




In a particular embodiment of the present invention, the individual ropes are formed from strands of non-metallic material, such as aramid fibers. By incorporating ropes having the weight, strength, durability and, in particular, the flexibility characteristics of such materials into the tension member of the present invention, the acceptable traction sheave diameter may be further reduced while maintaining the maximum rope pressure within acceptable limits. As stated previously, smaller sheave diameters reduce the required torque of the machine driving the sheave and increase the rotational speed. Therefore, smaller and less costly machines may be used to drive the elevator system.




In a further particular embodiment of the present invention, a traction drive for an elevator system includes a tension member having an aspect ratio greater than one and a traction sheave having a traction surface configured to receive the tension member. The tension member includes an engagement surface defined by the width dimension of the tension member. The traction surface of the sheave and the engagement surface are complimentarily contoured to provide traction and to guide the engagement between the tension member and the sheave. In an alternate configuration, the traction drive includes a plurality of tension members engaged with the sheave and the sheave includes a pair of rims disposed on opposite sides of the sheave and one or more dividers disposed between adjacent tension members. The pair of rims and dividers perform the function of guiding the engagement of the tension member with the sheave.




In another embodiment, the traction drive includes a guidance device disposed proximate to the traction sheave and engaged with the tension member. The guidance device positions the tension member for proper engagement with the traction sheave. In a particular configuration, the guidance device includes a roller engaged with the tension member and/or the sheave to define a limited space for the tension member to engage the sheave.




In a still further embodiment, the traction surface of the sheave is defined by a material that optimizes the traction forces between the sheave and the tension member and minimizes the wear of the tension member. In one configuration, the traction surface is integral to a sheave liner that is disposed on the sheave. In another configuration, the traction surface is defined by a coating layer that is bonded to the traction sheave. In a still further configuration, the traction sheave is formed from the material that defines the traction surface.




Although described herein as primarily a traction device for use in an elevator application having a traction sheave, the tension member may be useful and have benefits in elevator applications that do not use a traction sheave to drive the tension member, such as indirectly roped elevator systems, linear motor driven elevator systems, or self-propelled elevators having a counterweight. In these applications, the reduced size of the sheave may be useful in order to reduce space requirements for the elevator system. The foregoing and other objects, features and advantages of the present invention become more apparent in light of the following detailed description of the exemplary embodiments thereof, as illustrated in the accompanying drawings.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is perspective view of an elevator system having a traction drive according to the present invention.





FIG. 2

is a sectional, side view of the traction drive, showing a tension member and a sheave.





FIG. 3

is a sectional, side view of an alternate embodiment showing a plurality of tension members and a roller guide assembly.





FIG. 4

is another alternate embodiment showing a traction sheave having an hour glass shape to center the tension member.





FIG. 5

is a further alternate embodiment showing a traction sheave and tension member having complementary contours to enhance traction and to guide the engagement between the tension member and the sheave.





FIG. 6



a


is a sectional view of the tension member;

FIG. 6



b


is a sectional view of an alternate embodiment of a tension member;

FIG. 6



c


is a sectional view of a further alternate embodiment of a tension member; and

FIG. 6



d


is a sectional view of a still further embodiment of a tension member.











BEST MODE FOR CARRYING OUT THE INVENTION




Illustrated in

FIG. 1

is a traction elevator system


12


. The elevator system


12


includes a car


14


, a counterweight


16


, a traction drive


18


, and a machine


20


. The traction drive


18


includes a tension member


22


, interconnecting the car


14


and counterweight


16


, and a traction sheave


24


. The tension member


22


is engaged with the sheave


24


such that rotation of the sheave


24


moves the tension member


22


, and thereby the car


14


and counterweight


16


. The machine


20


is engaged with the sheave


24


to rotate the sheave


24


. Although shown as an geared machine


20


, it should be noted that this configuration is for illustrative purposes only, and the present invention may be used with geared or gearless machines.




The tension member


22


and sheave


24


are illustrated in more detail in FIG.


2


. The tension member


22


is a single device that integrates a plurality of ropes


26


within a common coating layer


28


. Each of the ropes


26


is formed from laid or twisted strands of high strength synthetic, non-metallic fibers, such as commercially available aramid fibers. The ropes


26


are equal length, are spaced widthwise within the coating layer


28


and are arranged linearly along the width dimension. The coating layer


28


is formed from a polyurethane material that is extruded onto the plurality of ropes


26


in such a manner that each of the individual ropes


26


is retained against longitudinal movement relative to the other ropes


26


. Other materials may also be used for the coating layer


28


if they are sufficient to meet the required functions of the coating layer: traction, wear, transmission of traction loads to the ropes


26


and resistance to environmental factors. The coating layer


28


defines an engagement surface


30


that is in contact with a corresponding surface of the traction sheave


24


.




As shown more clearly in

FIG. 6



a


, the tension member


22


has a width w, measured laterally relative to the length of the tension member


22


, and a thickness t


1


, measured in the direction of bending of the tension member


22


about the sheave


24


. Each of the ropes


26


has a diameter d and are spaced apart by a distance s. In addition, the thickness of the coating layer


28


between the ropes


26


and the engagement surface


30


is defined as t


2


and between the ropes


26


and the opposite surface is defined as t


3


, such that t


1


=t


2


+t


3


+d.




The overall dimensions of the tension member


22


results in a cross-section having an aspect ratio of much greater than one, where aspect ratio is defined as the ratio of width w to thickness t


1


or (Aspect Ratio=w/t


1


). An aspect ratio of one corresponds to a circular cross-section, such as that common in conventional round ropes


26


. The higher the aspect ratio, the more flat the tension member


22


is in cross-section. Flattening out the tension member


22


minimizes the thickness t


1


and maximizes the width w of the tension member


22


without sacrificing cross-sectional area or load carrying capacity. This configuration results in distributing the rope pressure across the width of the tension member


22


and reduces the maximum rope pressure relative to a round rope of comparable cross-sectional area. As shown in

FIG. 1

, for the tension member


22


having five individual round ropes


26


disposed within the coating layer


28


, the aspect ratio is greater than five. Although shown as having an aspect ratio greater than five, it is believed that benefits will result from tension members having aspect ratios greater than one, and particularly for aspect ratios greater than two.




The separation s between adjacent ropes


26


is dependant upon the weight of the materials used in the tension member


22


and the distribution of rope stress across the tension member


22


. For weight considerations, it is desirable to minimize the spacing s between adjacent ropes


26


, thereby reducing the amount of coating material between the ropes


26


. Taking into account rope stress distribution, however, may limit how close the ropes


26


may be to each other in order to avoid excessive stress in the coating layer


28


between adjacent ropes


26


. Based on these considerations, the spacing may be optimized for the particular load carrying requirements.




The thickness t


2


of the coating layer


28


is dependant upon the rope stress distribution and the wear characteristics of the coating layer


28


material. As before, it is desirable to avoid excessive stress in the coating layer


28


while providing sufficient material to maximize the expected life of the tension member


22


.




The thickness t


3


of the coating layer


28


is dependant upon the use of the tension member


22


. As illustrated in

FIG. 1

, the tension member


22


travels over a single sheave


24


and therefore the top surface


32


does not engage the sheave


24


. In this application, the thickness t


3


may be very thin, although it must be sufficient to withstand the strain as the tension member


22


travels over the sheave


24


. On the other hand, a thickness t


3


equivalent to that of t


2


may be required if the tension member


22


is used in an elevator system that requires reverse bending of the tension member


22


about a second sheave. In this application, both the upper


32


and lower surface


30


of the tension member


22


is an engagement surface and subject to the same requirement of wear and stress.




The diameter d of the individual ropes


26


and the number of ropes


26


is dependant upon the specific application. It is desirable to maintain the thickness d as small as possible in order to maximize the flexibility and minimize the stress in the ropes


26


. The actual diameter d will depend on the load required to be carried by the tension member


22


and the space available, widthwise, for the tension member


22


.




Although illustrated in

FIG. 2

as having a plurality of round ropes


26


embedded within the coating layer


28


, other styles of individual ropes may be used with the tension member


22


, including those that have aspect ratios greater than one, for reasons of cost, durability or ease of fabrication. Examples include oval shaped ropes


34


(

FIG. 6



b


), flat or rectangular shaped ropes


36


(

FIG. 6



c


), or a single flat rope


38


distributed through the width of the tension member


22


as shown in

FIG. 6



d


. An advantage of the embodiment of

FIG. 6



d


is that the distribution of rope pressure may be more uniform and therefore the maximum rope pressure within the tension member


22


may be less than in the other configurations. Since the ropes are encapsulated within a coating layer, and since the coating layer defines the engagement surface, the actual shape of the ropes is less significant for traction and may be optimized for other purposes.




Referring back to

FIG. 2

, the traction sheave


24


includes a base


40


and a liner


42


. The base


40


is formed from cast iron and includes a pair of rims


44


disposed on opposite sides of the sheave


24


to form a groove


46


. The liner


42


includes a base


48


having a traction surface


50


and a pair of flanges


52


that are supported by the rims


44


of the sheave


24


. The liner


42


is formed from a polyurethane material, such as that described in commonly owned U.S. Pat. No. 5,112,933 or any other suitable material providing the desired traction with the engagement surface


30


of the coating layer


28


and wear characteristics. Within the traction drive


18


, it is desired that the sheave liner


42


wear rather than the sheave


24


or the tension member


22


due to the cost associated with replacing the tension member


22


or sheave


24


. As such, the liner


42


performs the function of a sacrificial layer in the traction drive


18


. The liner


42


is retained, either by bonding or any other conventional method, within the groove


46


and defines the traction surface


50


for receiving the tension member


22


. The traction surface


50


has a diameter D. Engagement between the traction surface


50


and the engagement surface


30


provides the traction for driving the elevator system


12


.




Although illustrated as having a liner


42


, it should be apparent to those skilled in the art that the tension member


22


may be used with a sheave not having a liner


42


. As an alternative, the liner


42


may be replaced by coating the sheave with a layer of a selected material, such as polyurethane, or the sheave may be formed or molded from an appropriate synthetic material. These alternatives may prove cost effective if it is determined that, due to the diminished size of the sheave, it may be less expensive to simply replace the entire sheave rather than replacing sheave liners.




The shape of the sheave


24


and liner


42


defines a space


54


into which the tension member


22


is received. The rims


44


and the flanges


52


of the liner


42


provide a boundary on the engagement between the tension member


22


and the sheave


24


and guide the engagement to avoid the tension member


22


becoming disengaged from the sheave


24


.




An alternate embodiment of the traction drive


18


is illustrated in FIG.


3


. In this embodiment, the traction drive


18


includes three tension members


56


, a traction sheave


58


, and a guidance mechanism


60


. Each of the tension members


56


is similar in configuration to the tension member


22


described above with respect to

FIGS. 1 and 2

. The traction sheave


58


includes a base


62


, a pair of rims


64


disposed on opposite side of the sheave


58


, a pair of dividers


66


, and three liners


68


. The dividers


66


are laterally spaced from the rims


64


and from each other to define three grooves


70


that receive the liners


68


. As with the liner


42


described with respect to

FIG. 2

, each liner


68


includes a base


72


that defines a traction surface


74


to receive one of the tension members


56


and a pair of flanges


76


that abut the rims


64


or dividers


66


.




The guidance mechanism


60


is located on both sides of the sheave


58


and proximate to the take-up and take-off points for the tension member


56


. The guidance mechanism


60


includes a frame


78


, a pair of bearings


80


, a shaft


82


, and three rollers


84


. The bearings


80


permit rotation of the shaft


82


and rollers


84


. The rollers


84


are spaced apart such that each roller


84


is proximate to one of the grooves


70


of the sheave


58


in the region of contact with the corresponding tension member


56


. The arrangement of the roller


84


and the groove


70


,and liner


68


results in a limited space for the tension member


56


. The space restriction guides the tension member


56


during engagement and ensures that the tension member


56


remains aligned with the traction surface


74


of the liner


68


.




Alternative guidance mechanisms for the traction drive


18


are illustrated in

FIGS. 4 and 5

.

FIG. 4

illustrates a sheave


86


having an hour glass shaped traction surface


88


. The shape of the traction surface


88


urges the flat tension member


90


to remain centered during operation.

FIG. 5

illustrates a tension member


92


having a contoured engagement surface


94


that is defined by the encapsulated ropes


96


. The traction sheave


98


includes a liner


100


that has a traction surface


102


that is contoured to complement the contour of the tension member


92


. The complementary configuration provides guidance to the tension member


92


during engagement and, in addition, increases the traction forces between the tension member


92


and the traction sheave


98


.




Use of tension members and traction drives according to the present invention may result in significant reductions in maximum rope pressure, with corresponding reductions in sheave diameter and torque requirements. The reduction in maximum rope pressure results from the cross-sectional area of the tension member having an aspect ratio of greater than one. For this configuration, assuming that the tension member is such as that shown in

FIG. 6



d


, the calculation for maximum rope pressure is determined as follows:






P


max




=


(2F/Dw)






Where F is the maximum tension in the tension member. For the other configurations of

FIGS. 6



a-c


, the maximum rope pressure would be approximately the same although slightly higher due to the discreteness of the individual ropes. For a round rope within a round groove, the calculation of maximum rope pressure is determined as follows:






P


max




=


(2F/Dd)(4/π)






The factor of (4/π) results in an increase of at least 27% in maximum rope pressure, assuming that the diameters and tension levels are comparable. More significantly, the width w is much larger than the rope diameter d, which results in greatly reduced maximum rope pressure. If the conventional rope grooves are undercut, the maximum rope pressure is even greater and therefore greater relative reductions in the maximum rope pressure may be achieved. Another advantage of the tension member according to the present invention is that the thickness t


1


of the tension member may be much smaller than the diameter d of equivalent load carrying capacity round ropes. This enhances the flexibility of the tension member as compared to conventional ropes.




For instance, for a sheave typical low rise gearless elevator system, the use of three tension members, each with five 3 mm aramid fiber ropes, may result in reductions in approximately fifty percent in maximum rope pressure and eighty percent in rated torque, peak torque and sheave diameter as compared to conventional steel ropes (four 10 mm SISAL core steel wire ropes) and reductions of approximately sixty percent in rated torque, peak torque and sheave diameter as compared to conventional round ropes formed from comparable aramid fibers (three 8 mm aramid fiber ropes).




Although the invention has been shown and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that various changes, omissions, and additions may be made thereto, without departing from the spirit and scope of the invention.



Claims
  • 1. A traction drive for an elevator system, the elevator system including a car and a counterweight, the traction drive comprising:at least one tension member, each of which interconnects the car and counterweight, the tension member comprising a load carrying rope and a polyurethane coating encasing the load cog rope, the tension member having a width w, a thickness t measured in the bending direction, and an engagement surface defined on the polyurethane coating by the width dimension of the tension member, wherein he tension member has an aspect ratio, defined as the ratio of width w relative to thickness t, of greater than one; and a traction sheave driven by a machine and over which the tension member passes, the traction sheave including a traction surface configured to receive the engagement surface of the tension member between take-up and take-off points on either side of the traction sheave such that traction between the traction surface of the sheave and the tension member in a region between the take-up and take-off points is transmitted through the polyurethane coating to the load carrying rope and moves the car and counterweight.
  • 2. The traction drive according to claim 1, wherein the tension member includes a plurality of the load carrying ropes encased within a common layer of the coating, the coating layer separating the individual ropes and defining the engagement surface for the tension member.
  • 3. The traction drive according to claim 1, wherein the traction surface is contoured to complement the engagement surface of the tension member such that traction between the traction sheave and tension member is enhanced.
  • 4. The traction drive according to claim 1, wherein the traction surface is contoured to complement the engagement surface of the tension member to guide the tension member during engagement with the traction sheave.
  • 5. The traction drive according to claim 1, wherein the traction surface includes a diameter D, and wherein the diameter D varies laterally to provide a guidance mechanism during engagement of the tension member and traction sheave.
  • 6. The traction drive according to claim 1, wherein the traction sheave includes a pair of retaining rims on opposite sides of the traction sheave.
  • 7. The traction drive according to claim 1, including a plurality of the tension members.
  • 8. The traction drive according to claim 7, wherein the traction sheave includes a traction surface for each tension member, and further includes one or more dividers that separate the plurality of traction surfaces.
  • 9. The traction drive according to claim 1, further including a guidance device disposed proximate to the traction sheave, the guidance device engaged with the tension member to position the tension member for engagement with the traction sheave.
  • 10. The traction drive according to claim 9 wherein the guidance device includes a roller engaged in rolling contact with the tension member.
  • 11. The traction drive according to claim 1, wherein the traction surface is formed from a non-metallic material.
  • 12. The traction drive according to claim 11, wherein the traction surface is formed from polyurethane.
  • 13. The traction drive according to claim 1, wherein the rope is formed from non-metallic material.
  • 14. The traction drive according to claim 1, wherein the maximum rope pressure of the load carrying rope is approximately defined by the following equation:Pmax=(2F/Dw) Where F is the tension in the tension member and D is the diameter of the traction sheave.
  • 15. The traction drive according to claim 1, further including a sheave liner disposed about the traction sheave, wherein the sheave liner defines the traction surface.
  • 16. The traction drive according to claim 1, wherein the traction surface is defined by a coating layer that is bonded to the traction sheave.
  • 17. The traction drive according to claim 1, wherein the traction sheave is formed from the material defining the traction surface.
  • 18. The traction drive according to claim 17, wherein the traction sheave is formed from polyurethane.
Parent Case Info

This is a division of copending application Ser. No. 09/031/108 filed Feb. 26, 1998, the contents of which is incorporated herein by reference.

US Referenced Citations (13)
Number Name Date Kind
2017149 Greening Oct 1935 A
2326670 Patterson, Jr. Aug 1943 A
2685801 Tishman Aug 1954 A
3279762 Bruns Oct 1966 A
3797806 Demmert Mar 1974 A
3910559 Sapozhnikov et al. Oct 1975 A
4022010 Gladenbeck et al. May 1977 A
4030569 Berkovitz Jun 1977 A
4589861 Dodge May 1986 A
4620615 Morris et al. Nov 1986 A
4624097 Wilcox Nov 1986 A
4807723 Salmin et al. Feb 1989 A
5921352 Garrido et al. Jul 1999 A
Foreign Referenced Citations (4)
Number Date Country
2127934 Apr 1984 GB
2134209 Aug 1984 GB
2162283 Jan 1986 GB
1491804 Jul 1989 SU