Patent Publication Number: US-2017362059-A1

Title: Tension member for an elevator

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 11/981,346 filed Oct. 31, 2007, which is a division of U.S. application Ser. No. 10/839,550 filed May 5, 2004, now U.S. Pat. No. 9,352,935, which is a division of U.S. application Ser. No. 09/218,990, filed Dec. 22, 1998, now U.S. Pat. No. 6,739,433, which is a continuation-in-part of U.S. application Ser. No. 09/031,108 filed Feb. 26, 1998, the entirety of which is incorporated by reference and which is now U.S. Pat. No. 6,401,871. 
    
    
     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 round 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 round steel ropes is the flexibility and fatigue characteristics of round 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. 
     Another drawback of conventional round ropes is that 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. 
     The above art notwithstanding, scientists and engineers under the direction of Applicants&#39; 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 cords encased within a common layer of coating. The coating layer separates the individual cords 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 cords are formed from strands of metallic material. By incorporating cords having the weight, strength, durability and, in particular, the flexibility characteristics of appropriately sized and constructed 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 complementarily 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 tension member to prevent gross alignment problems in the event of slack rope conditions, etc. 
     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; 
         FIG. 4  is another alternate embodiment showing a traction sheave having an convex 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  is a magnified cross sectional view of a single cord of the invention having six strands twisted around a central stand; 
         FIG. 7  is a magnified cross sectional view of an alternate single cord of the invention; 
         FIG. 8  is a magnified cross sectional view of another alternate embodiment of the invention; and 
         FIG. 9  is a schematic cross sectional view of a flat rope to illustrate various dimensional characteristics thereof. 
     
    
    
     DETAILED DESCRIPTION 
     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 cords  26  within a common coating layer  28 . Each of the cords  26  is formed from preferably seven twisted strands, each made up of seven twisted metallic wires. In a preferred embodiment of the invention a high carbon steel is employed. The steel is preferably cold drawn and galvanized for the recognized properties of strength and corrosion resistance of such processes. The coating layer is preferably a polyurethane material which is ether based and includes a fire retardant composition. 
     In a preferred embodiment, referring to  FIG. 6 , each strand  27  of a cord  26  comprises seven wires with six of the wires  29  twisted around a center wire  31 . Each cord  26 , comprises one strand  27   a  which is centrally located and six additional outer strands  27   b  that are twisted around the central strand  27   a . Preferably, the twisting pattern of the individual wires  29  that form the central strand  27   a  are twisted in one direction around central wire  31  of central strand  27   a  while the wires  29  of outer strands  27   b  are twisted around the central wire  31  of the outer strands  27   b  in the opposite direction. Outer strands  27   b  are twisted around central strand  27   a  in the same direction as the wires  29  are twisted around center wire  31  in strand  27   a . For example, the individual strands in one embodiment comprise the central wire  31 , in center strand  27   a , with the six twisted wires  29  twisting clockwise; the wires  29  in the outer strands  27   b  twisting counterclockwise around their individual center wires  31  while at the cord  26  level the outer strands  27   b  twist around the central strand  27   a  in the clockwise direction. The directions of twisting improve the characteristics of load sharing in all of the wires of the cord. 
     It is important to the success of the invention to employ wire  29  of a very small size. Each wire  29  and  31  are less than 0.25 millimeters in diameter and preferably is in the range of about 0.10 millimeters to 0.20 millimeters in diameter. In a particular embodiment, the wires are of a diameter of 0.175 millimeters in diameter. The small sizes of the wires preferably employed contribute to the benefit of the use of a sheave of smaller diameter. The smaller diameter wire can withstand the bending radius of a smaller diameter sheave (around 100 millimeters in diameter) without placing too much stress on the strands of the flat rope. Because of the incorporation of a plurality of small cords  26 , preferably about 1.6 millimeters in total diameter in this particular embodiment of the invention, into the flat rope elastomer, the pressure on each cord is significantly diminished over prior art ropes. Cord pressure is decreased at least as n −1/2  with n being the number of parallel cords in the flat rope, for a given load and wire cross section. 
     In an alternate embodiment, referring to  FIG. 7 , the center wire  35  of the center strand  37  a of each cord  26  employs a larger diameter. For example, if the wires  29  of the previous embodiment (0.175 millimeters) are employed, the center wire  35  of the center strand only of all cords would be about 0.20-0.22 millimeters in diameter. The effect of such a center wire diameter change is to reduce contact between wires  29  surrounding wire  35  as well as to reduce contact between strands  37   b  which are twisted around strand  37   a . In such an embodiment the diameter of cord  26  will be slightly greater than the previous example of 1.6 millimeters. 
     In a third embodiment of the invention, referring to  FIG. 8 , the concept of the second embodiment is expanded to further reduce wire-to-wire and strand-to-strand contact. Three distinct sizes of wires are employed to construct the cords of the invention. In this embodiment the largest wire is the center wire  202  in the center strand  200 . The intermediate diameter wires  204  are located around the center wire  202  of center strand  200  and therefore makeup a part of center strand  200 . This intermediate diameter wire  204  is also the center wire  206  for all outer strands  210 . The smallest diameter wires employed are numbered  208 . These wrap each wire  206  in each outer strand  210 . All of the wires in the embodiment are still less than 0.25 mm in diameter. In a representative embodiment, wires  202  may be 0.21 mm; wires  204  may be 0.19 mm; wires  206  may be 0.19 mm; and wires  208  may be 0.175 mm. It will be appreciated that in this embodiment wires  204  and  206  are of equivalent diameters and are numbered individually to provide locational information only. It is noted that the invention is not limited by wires  204  and  206  being identical in diameter. All of the diameters of wires provided are for example only and could be rearranged with the joining principle being that contact among the outer wires of the central strand is reduced; that contact among the outer wires of the outer strands is reduced and that contact among the outer strands is reduced. In the example provided, (only for purpose of example) the space obtained between the outer wires of outer strands is 0.014 mm. 
     The cords  26  are equal length, are approximately equally 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, preferably a thermoplastic urethane, that is extruded onto and through the plurality of cords  26  in such a manner that each of the individual cords  26  is restrained against longitudinal movement relative to the other cords  26 . Transparent material is an alternate embodiment which may be advantageous since it facilitates visual inspection of the flat rope. Structurally, of course, the color is irrelevant. 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 cords  26  and resistance to environmental factors. It should further be understood that if other materials are used which do not meet or exceed the mechanical properties of a thermoplastic urethane, then the additional benefit of the invention of dramatically reducing sheave diameter may not be fully achievable. With the thermoplastic urethane mechanical properties the sheave diameter is reducible to 100 millimeters or less. 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. 9 , 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 cords  26  has a diameter d and are spaced apart by a distance s. In addition, the thickness of the coating layer  28  between the cords  26  and the engagement surface  30  is defined as t 2  and between the cords  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. 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 and load carrying capacity. As shown in  FIG. 2 , for the tension member  22  having five individual cords  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 cords  26  is dependant upon the materials and manufacturing processes 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 cords  26 , thereby reducing the amount of coating material between the cords  26 . Taking into account rope stress distribution, however, may limit how close the cords  26  may be to each other in order to avoid excessive stress in the coating layer  28  between adjacent cords  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 . It may also be desirable to groove the tension member surface  32  to reduce tension in the thickness t 3 . On the other hand, a thickness t 3  equivalent to that of t 2  may be required if the tension member  2 ′ 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 cords  26  and the number of cords  26  is dependent upon the specific application. It is desirable to maintain the thickness d as small as possible, as hereinbefore discussed, in order to maximize the flexibility and minimize the stress in the cords  26 . 
     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 . The diameter of a sheave for use with the traction member described hereinabove is dramatically reduced from prior art sheave diameters. More particularly, sheaves to be employed with the flat rope of the invention may be reduced in diameter to 100 mm or less. As will be immediately recognized by those skilled in the art, such a diameter reduction of the sheave allows for the employment of a much smaller machine. In fact, machine sizes may fall to ¼ of their conventional size in for example low rise gearless applications for a typical  8  passenger duty elevators. This is because torque requirements would be cut to about ¼ with a 100 mm sheave and the rpm of the motor would be increased. Cost for the machines indicated accordingly falls. 
     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  and a traction sheave  58 . 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 . Also as in  FIG. 2 , the liner  42  is wide enough to allow a space  54  to exist between the edges of the tension member and the flanges  76  of the liner  42 . 
     Alternative construction for the traction drive  18  are illustrated in  FIGS. 4 and 5 .  FIG. 4  illustrates a sheave  86  having a convex shaped traction surface  88 . The shape of the traction surface SS 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 cords  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. The calculation for approximate maximum rope pressure (slightly higher due to discreteness of individual cords) is determined as follows: 
         P   max ≡(2 F/Dw )
 
     Where F is the maximum tension in the tension member. For a round rope within a round groove, the calculation of maximum rope pressure is determined as follows: 
         P   max ≡(2 F/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 cord 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 using a flat tension member configuration. 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. 
     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.