DEFLECTION COMPENSATING UNIFIED TWO PART TRACK FOR SLIDING DOOR AND METHOD OF MAKING SAME
United States Patent 3842462
Suspension mechanism for a sliding door for a rapid transit type railway car comprises a unified two-part track which is anchored only at its ends to the car body. The two parts of each track comprise a track base portion with a seat extending lengthwise therein, and a track bar portion seated in the seat and secured therein. Each door is suspended from its individual track by a pair of hangers mounted one adjacent each end of the top of the door and both hangers in endwise sliding relation on the bar portion of the track. Since each track is supported only at its ends, the weight of the door suspended therefrom tends to bow the track downward, and this bowing or sagging effect varies as the hangers move back and forth along the track during each opening and closing operation of the door. This invention compensates for the sagging effect caused by the weight and movement of a door along its track by subjecting the base portion of the track to pre-bowing stresses within the elastic limit of the track base material during the cutting of a straight seat for the track bar portion, so that when these bowing stresses are removed, the base portion springs back to its normal straight condition, thereby causing the seat to assume an upwardly bowed or arched condition. When the track bar portion is seated and secured in its seat, it assumes a slightly arched condition, which is reduced toward a straight condition by the weight of the door suspended therefrom by its hangers. The magnitude and application point or points for the pre-bowing stresses for curving the base while cutting the seat in order to provide maximum straightness of the track bar portion in operation are carefully arrived at, preferably by means of computer calculations.
US Patent References:
/1225098.html
Addison - May 1917 - 1225098
Means for slidingly supporting folding doors
Phillips - June 1924 - 1496904
Arch joist and floor construction
Frease - June 1931 - 1812690
Supporting apparatus for sliding doors
Birkmeyer, Sr. - September 1959 - 2904821
PRESTRESSED CONCRETE MEMBERS AND METHOD OF PRESTRESSING THE SAME
Rajchman - January 1971 - 3552074
/1225098.html
Addison - May 1917 - 1225098
Means for slidingly supporting folding doors
Phillips - June 1924 - 1496904
Arch joist and floor construction
Frease - June 1931 - 1812690
Supporting apparatus for sliding doors
Birkmeyer, Sr. - September 1959 - 2904821
PRESTRESSED CONCRETE MEMBERS AND METHOD OF PRESTRESSING THE SAME
Rajchman - January 1971 - 3552074
Application Number:
05/075972
Publication Date:
10/22/1974
Filing Date:
09/28/1970
View Patent Images:
Export Citation:
Assignee:
Rohr Corporation (Chula Vista, CA)
Primary Class:
Other Classes:
49/409, 16/87R, 104/123, 52/291
International Classes:
B61D19/02; E05D15/06; B61D19/00; A47H1/04
Field of Search:
16/87,87.6,87.8,93,94,95,96,97 49/409,411 52/223,291 244/155D 104/123
US Patent References:
| 3604361 | AERIAL GUIDEWAY SYSTEM | September 1971 | Harbert |
Primary Examiner:
Gilliam, Paul R.
Assistant Examiner:
Aschenbrenner, Peter A.
Attorney, Agent or Firm:
Schlesinger, Patrick Gilliam Frank J. D.
Claims:
Having thus described my invention, what I claim as new and useful and desire to secure by U.S. Letters Patent is
1. A unified two part track for suspending a sliding door of known weight by a pair of hangers riding on, and spaced apart lengthwise of, the track for approximately straight line movement along one of the two track parts, said track comprising
2. A unified two part track as claimed in claim 1 wherein the bowing forces causing track deflections are due to the weight of the door.
3. A unified two part track as claimed in claim 2 wherein the bowing forces causing track deflections include lateral forces due to the center of gravity of such suspended door being offset laterally from a vertical plane including the suspension axis of such door.
4. A unified two part track as claimed in claim 1 wherein the bowing forces causing track deflections are due to combined vertical and lateral force components exerted on the track.
5. A unified two part track as claimed in claim 1 wherein the first long narrow track part, when subjected to bowing forces carefully calculated with respect to the bowing forces exerted by such door suspended from the unified track, reduces the bowed seat toward a straight condition.
6. A unified two part track as claimed in claim 1 wherein the track, with the exception of the mounting means at each end thereof, is spaced laterally from such supporting structure.
7. A unified two part track for suspending a sliding door of known weight by a pair of hangers riding on, and spaced apart lengthwise of, the track for approximately straight line movement along one of the two track parts, said track comprising,
1. A unified two part track for suspending a sliding door of known weight by a pair of hangers riding on, and spaced apart lengthwise of, the track for approximately straight line movement along one of the two track parts, said track comprising
2. A unified two part track as claimed in claim 1 wherein the bowing forces causing track deflections are due to the weight of the door.
3. A unified two part track as claimed in claim 2 wherein the bowing forces causing track deflections include lateral forces due to the center of gravity of such suspended door being offset laterally from a vertical plane including the suspension axis of such door.
4. A unified two part track as claimed in claim 1 wherein the bowing forces causing track deflections are due to combined vertical and lateral force components exerted on the track.
5. A unified two part track as claimed in claim 1 wherein the first long narrow track part, when subjected to bowing forces carefully calculated with respect to the bowing forces exerted by such door suspended from the unified track, reduces the bowed seat toward a straight condition.
6. A unified two part track as claimed in claim 1 wherein the track, with the exception of the mounting means at each end thereof, is spaced laterally from such supporting structure.
7. A unified two part track for suspending a sliding door of known weight by a pair of hangers riding on, and spaced apart lengthwise of, the track for approximately straight line movement along one of the two track parts, said track comprising,
Description:
BACKGROUND OF THE INVENTION
In the past it has been common practice to suspend the sliding doors commonly used on rapid transit cars from roller type hangers, the rollers of which ride in channel track means mounted above each door opening. In order to have a reasonable life expectancy these rollers are usually of substantial diameter, for example, of the order of 3 or 4 inches, and are mounted with a close fit in the channel track to avoid rattles and side play. As a result, unless the bottoms of the doors are positioned and guided to hold the rollers centered in their channel tracks there is a tendency for the rollers to bind, which prevents free roller movement and increases wear on the suspension mechanism. Available statistics indicate that approximately 80 percent of the failures in existing sliding doors of this type occur in the suspension mechanism.
The problem of providing a satisfactory sliding door for a railway type car is complicated by the fact that since the car body is supported on bolsters located near its ends, the entire car body tends to bow downwardly toward its center, and the amount of such bowing varies with the car loading. Such deflection of the car body in the past has caused a bending of the door support tracks, which tends to cause binding of the doors and increased maintenance problems.
In use these prior art door mounting structures are subjected not only to the wear and tear caused by their constantly recurring opening and closing at every station stop, but also that caused by the substantial side loads to which they are recurrently subjected, such as those imposed by wind, high speed travel, entering and leaving tunnels and occasional pressure by passengers. All of these factors tend to swing the doors about their suspension tracks as an axis, and in the case of existing wheel or roller type hangers fitted closely into channel tracks, they produce destructive forces acting through substantial lever arms.
A companison case, U.S. Patent application Ser. No. 74,045, filed 9/21/70, now U.S. Pat. No. 3,727,349 is based on the structural arrangement of the door mounting mechanism.
SUMMARY OF THE INVENTION
The present invention has for its primary objective the provision of a two part track for supporting a sliding door for a rapid transit type railway car wherein a straight seat is formed lengthwise along one side of one part of the two part track while said one part is subjected to carefully determined transverse bowing stresses within the elastic limit of the material from which said one part is made. When the bowing stresses are relieved the seat assumes an arched configuration. The other track part is seated in said seat and secured therein, the two track parts being relatively bowed as required during such seating and securing. The unified two part track thus formed is supported only at its ends, and sagging of the track under the weight of a door suspended from the other track during opening and closing of the door tends to reduce the arched condition of the other track part toward a straight condition, so that a door suspended therefrom travels in a substantially straight line.
A further objective of the invention is to provide a unified, two-part support track for a sliding door wherein the door rides along one part of the two part track, which part is so pre-arched that the weight of the door on the track at selected stages between open and closed positions of the door causes sagging which is calculated to reduce the pre-arched condition of said one track part toward a straight condition.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing objectives and advantages of the invention will be apparent from the following description and the accompanying drawings, wherein:
FIG. 1 is a fragmentary, horizontal, sectional view through a car body track support beam with one unified, two part, door supporting track shown in top elevation, one door hanger also being shown, portions being broken away.
FIG. 2 is an exterior, side elevational view of the fragments shown in FIG. 1 looking in the direction of the arrows 2--2 of FIG. 1, a fragment of a door also being shown.
FIG. 3 is a somewhat diagrammatic, transverse, vertical sectional view in reduced scale showing one of the doors suspended from its track, and its bottom guided to maintain it in position during opening and closing.
FIGS. 4 and 5 are diagrammatic side and end views, respectively, showing the track base portion biased from a normal straight condition for cutting the seat for the track bar, the bowing stresses being indicated by an arrow, and the track end supports by triangular fulcrums.
FIGS. 6 and 7 are diagrammatic side and end views respectively of the track base portion, generally similar to FIGS. 4 and 5 but with the biasing stresses removed.
FIGS. 8 and 9 are generally similar diagrammatic views showing the track bar seated in its seat.
FIG. 10 is a diagrammatic, front elevational view showing on the left an end portion of the left track shown in FIGS. 1 - 9, and on the right a similar, but end-to-end reversed, right hand track of an aligned pair thereof, both tracks being shown subjected to the loads of their respective doors, the broken lines showing the doors moved to closed position at the adjacent or inner ends of their respective tracks.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to the drawings in detail, an illustrative embodiment of the invention is shown in FIGS. 1 - 3 of the drawings, while FIGS. 5 - 10 illustrate diagrammatically the incorporation of the present invention therein, said its operation. Since the structure of FIGS. 1 - 3 is more fully illustrated, described, and claimed in the companion case referred to previously herein, such structure is described only briefly herein.
For mounting a pair of sliding doors for a door opening of a rapid transit type railway car, a support beam 10, FIGS. 1 - 3, preferably is incorporated in the car body over a door opening therein, and a pair of two-part door support tracks, such as the track 11 in FIGS. 1 - 3, and the tracks 11 and 11' in FIG. 10, aremounted on this beam 10 in aligned, relatively end-to-end reversed relation with their inner ends adjacent each other and centered over the door opening. Each door extends laterally beyond the door opening a distance equal substantially to the width of the door suspended therefrom.
The doors separate to open and converge to close, as indicated in FIG. 10, where the left hand track is designated by the numeral 11 and the right hand track by the numeral 11', and the left hand door is designated by the numeral 19, and the right hand door by the numeral 19'. Since the two tracks 11 and 11' and the doors and the suspension mechanisms therefor are similar except that they are relatively reversed end-for-end, the parts for the right hand track, door and suspension mechanism are designated by the same reference numerals as their left hand counterparts with the prime (') added. Only the left hand track and other suspension mechanism is described structurally herein.
The track 11 comprises a channel shape base portion 13, see FIGS. 1 - 3, with an integral central ridge 14 of truncated wedge shape extending lengthwise thereof. A seat groove 15 is cut lengthwise in the truncated top surface of the ridge 14 to receive a track bar 17 in seated relation therein. The track bar 17 is secured in seated relation in its seat 15 by screws 18, see FIG. 1, inserted at selected spaced intervals in counterbored holes in the base and screwed into registering threaded holes in the track bar.
A car door 19, see FIGS. 2 and 3, is suspended from its track bar 17 by a pair of identical hangers, one of which is mounted adjacent each end of the top and the door. One of these hangers 21 is shown in FIGS. 1 - 3, while a pair thereof 20' and 21' are shown diagrammatically in FIG. 10. An open type, linear motion ball bearing 22, see FIGS. 1 - 3, is fitted into the C-shape upwardly extending portion of each hanger, and rides on the track bar of its respective track. The base ridge 14 rides in the open operations of the C-shape upper hanger portion and in the usual gap in the open type bearing 22.
The two part track 11 is supported at its outer end by a bracket 23, see FIGS. 1 and 2, secured to an end plate 24 of the beam 10 by screws 25. The bracket has a notch 27 therein into which the outer end of the track base 13 is fitted and anchored for limited pivotal adjustment by a shoulder screw 28. A peel-off shim 29 is interposed between the bracket 23 and the beam end plate 24 to snugly fill any space which otherwise might exist therebetween.
The inner end of each track base 13 is secured to the car beam 10 by a bolt 30, a peel-off shim 31 being interposed between the track base 13 and the beam 10 to provide desired clearance therebetween. For adjusting the track about the shoulder screw 28 as a pivot upon loosening the bolt 30, a set screw 32 is screwed into a threaded hole provided in a bracket plate 33 welded to the beam 13 and bears endwise on the under side of a notched out portion of the track base 13.
In order to seal properly it is important that the doors of each pair fit snugly together when closed, and that they also fit closely with respect to the door opening in which they are mounted. To permit such close fits it is desirable that the doors travel as nearly as possible in a straight line as they move between open and closed position.
Since the track 11 is supported only at its ends, the weight of its car door 19 thereon as exerted by the hangers riding on the track bar 17 tends to cause a sagging or downward deflection of the track. In order to minimize such sagging, and to achieve a close approximation of a desired straight-line door travel, in accordance with the present invention the track base 13 is bowed downwardly by subjecting it to carefully arrived at transverse bowing stresses as indicated diagrammatically by the arrow 34 in FIG. 4 during the cutting of the track bar seat 15 therein. The track base 13 is not stressed beyond its elastic limit by this bending operation, so that when the straight seat 15 is cut therein as shown in FIGS. 4 and 5, and these transverse stresses are removed, the track base 13 springs back to it normal, straight, unstressed condition, and the seat 15 is arched thereby as shown in FIGS. 6 and 7.
The track bar 17 is then seated in the seat 15, either with the track base 13 stressed to straighten the seat 15, or with the track bar 17 bowed to fit the curvature of the seat, or both. When the track bar 17 is secured in seated relation in its seat 15 by the screws 18, see FIG. 1, both the track base 13 and the track bar 17 exert opposite bowing effects on each other as shown diagrammaticaly in FIGS. 8 and 9, which show the track bar 17 seated in its seat. This mutual bowing effect of the two track parts on each other is taken into consideration when calculating the sagging effect of the weight of a door on its track.
FIG. 10 shows diagrammatically portions of a left hand door 19 and its track 11, and a right hand door 19' and its track and suspension mechanism. The weight of the door 19' tends to cause its two-part track 11' to sag, and thereby bring the pre-arched track bar 17', along which the door hangers 20' and 21' ride, toward a straight condition. When the left hand door hanger 21' of the door 19' is moved by the closing of its door 19' to a position closely adjacent the supported left hand end of its track 11', as indicated in broken lines, the weight of this left hand hanger is exerted on the track through a lever arm of minimum length, while the other or right hand hanger 20' is at such time located near the mid-zone of the track and therefore bearing on the track through a lever arm of substantially maximum length. When the door 19' is centered on its track 11', as indicated in solid lines in FIG. 10, the loads on both hangers 20' and 21' bear on the track through medium length lever arms, while when the door 19' is in its right hand or open position (not shown) the loading is similar to that shown in broken lines but reversed.
Due to the shifting of the effective loading applied to the track as the doors travel between closed and open position it is desirable to calculate the sagging effect which the weight of the door has on its track, and the optimum corrections required, with the hanger loads imposed at successive, selected stages throughout the length of the track. The deflection of the track at each such stage is carefully measured or calculated so that the necessary arching of the groove 15 can be achieved for providing substantially straight line travel of the door in use.
The bottom of each door is provided with guide means 35, see FIG. 3, which positions the lower end of the door and guides it during opening and closing. Depending upon the design configuration of the car sides, the bottoms of the doors may be offset laterally either outwardly or inwardly from their suspension tracks 11 and 11', in which case each track under the weight of its door is subjected to bowing forces which include not only a vertical weight component, indicated by the arrow 37 in FIG. 3, but also a lateral component indicated by the arrow 38 in that figure. Usually the doors are mounted nearly upright, in which case the lateral component is negligible and is not corrected for.
However, the problem should be kept in mind so that in the event a car design configuration is adopted in which this lateral component becomes substantial it can be corrected for by subjecting the track to proportional bowing forces in both directions during the cutting of a straight bar seat therein in a manner which will be apparent to any ordinarily competent design engineer. It is assumed for the purposes of the present description that this lateral component is not sufficient to require correction and is not corrected for.
Car doors, hangers and tracks embodying the invention are now in process of manufacture for a large mass transit operation, and the pre-bowing effect calculated and employed in the manufacture thereof has been found to require a maximum track base deflection of the order of 0.015 inch when cutting the seat 15, the loads imposed on the track by the hangers being computer-calculated for each 2 inches of door travel.
The invention provides a highly effective door mounting arrangement which in current production of doors and tracks embodying the invention results in almost straight line travel of the doors when moving between open and closed position, thereby permitting effective sealing, and long, trouble-free operation of the doors. In a test still in progress a set of doors embodying the invention has been operated successfully in excess of 2,500,000 two stroke cycles without lubrication, other maintenance, or servicing, and although this test is being conducted on a stationary base, rather than upon a moving car, it has continued many times beyond the life expectancy of any prior art doors of this type within knowledge.
In the past it has been common practice to suspend the sliding doors commonly used on rapid transit cars from roller type hangers, the rollers of which ride in channel track means mounted above each door opening. In order to have a reasonable life expectancy these rollers are usually of substantial diameter, for example, of the order of 3 or 4 inches, and are mounted with a close fit in the channel track to avoid rattles and side play. As a result, unless the bottoms of the doors are positioned and guided to hold the rollers centered in their channel tracks there is a tendency for the rollers to bind, which prevents free roller movement and increases wear on the suspension mechanism. Available statistics indicate that approximately 80 percent of the failures in existing sliding doors of this type occur in the suspension mechanism.
The problem of providing a satisfactory sliding door for a railway type car is complicated by the fact that since the car body is supported on bolsters located near its ends, the entire car body tends to bow downwardly toward its center, and the amount of such bowing varies with the car loading. Such deflection of the car body in the past has caused a bending of the door support tracks, which tends to cause binding of the doors and increased maintenance problems.
In use these prior art door mounting structures are subjected not only to the wear and tear caused by their constantly recurring opening and closing at every station stop, but also that caused by the substantial side loads to which they are recurrently subjected, such as those imposed by wind, high speed travel, entering and leaving tunnels and occasional pressure by passengers. All of these factors tend to swing the doors about their suspension tracks as an axis, and in the case of existing wheel or roller type hangers fitted closely into channel tracks, they produce destructive forces acting through substantial lever arms.
A companison case, U.S. Patent application Ser. No. 74,045, filed 9/21/70, now U.S. Pat. No. 3,727,349 is based on the structural arrangement of the door mounting mechanism.
SUMMARY OF THE INVENTION
The present invention has for its primary objective the provision of a two part track for supporting a sliding door for a rapid transit type railway car wherein a straight seat is formed lengthwise along one side of one part of the two part track while said one part is subjected to carefully determined transverse bowing stresses within the elastic limit of the material from which said one part is made. When the bowing stresses are relieved the seat assumes an arched configuration. The other track part is seated in said seat and secured therein, the two track parts being relatively bowed as required during such seating and securing. The unified two part track thus formed is supported only at its ends, and sagging of the track under the weight of a door suspended from the other track during opening and closing of the door tends to reduce the arched condition of the other track part toward a straight condition, so that a door suspended therefrom travels in a substantially straight line.
A further objective of the invention is to provide a unified, two-part support track for a sliding door wherein the door rides along one part of the two part track, which part is so pre-arched that the weight of the door on the track at selected stages between open and closed positions of the door causes sagging which is calculated to reduce the pre-arched condition of said one track part toward a straight condition.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing objectives and advantages of the invention will be apparent from the following description and the accompanying drawings, wherein:
FIG. 1 is a fragmentary, horizontal, sectional view through a car body track support beam with one unified, two part, door supporting track shown in top elevation, one door hanger also being shown, portions being broken away.
FIG. 2 is an exterior, side elevational view of the fragments shown in FIG. 1 looking in the direction of the arrows 2--2 of FIG. 1, a fragment of a door also being shown.
FIG. 3 is a somewhat diagrammatic, transverse, vertical sectional view in reduced scale showing one of the doors suspended from its track, and its bottom guided to maintain it in position during opening and closing.
FIGS. 4 and 5 are diagrammatic side and end views, respectively, showing the track base portion biased from a normal straight condition for cutting the seat for the track bar, the bowing stresses being indicated by an arrow, and the track end supports by triangular fulcrums.
FIGS. 6 and 7 are diagrammatic side and end views respectively of the track base portion, generally similar to FIGS. 4 and 5 but with the biasing stresses removed.
FIGS. 8 and 9 are generally similar diagrammatic views showing the track bar seated in its seat.
FIG. 10 is a diagrammatic, front elevational view showing on the left an end portion of the left track shown in FIGS. 1 - 9, and on the right a similar, but end-to-end reversed, right hand track of an aligned pair thereof, both tracks being shown subjected to the loads of their respective doors, the broken lines showing the doors moved to closed position at the adjacent or inner ends of their respective tracks.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to the drawings in detail, an illustrative embodiment of the invention is shown in FIGS. 1 - 3 of the drawings, while FIGS. 5 - 10 illustrate diagrammatically the incorporation of the present invention therein, said its operation. Since the structure of FIGS. 1 - 3 is more fully illustrated, described, and claimed in the companion case referred to previously herein, such structure is described only briefly herein.
For mounting a pair of sliding doors for a door opening of a rapid transit type railway car, a support beam 10, FIGS. 1 - 3, preferably is incorporated in the car body over a door opening therein, and a pair of two-part door support tracks, such as the track 11 in FIGS. 1 - 3, and the tracks 11 and 11' in FIG. 10, aremounted on this beam 10 in aligned, relatively end-to-end reversed relation with their inner ends adjacent each other and centered over the door opening. Each door extends laterally beyond the door opening a distance equal substantially to the width of the door suspended therefrom.
The doors separate to open and converge to close, as indicated in FIG. 10, where the left hand track is designated by the numeral 11 and the right hand track by the numeral 11', and the left hand door is designated by the numeral 19, and the right hand door by the numeral 19'. Since the two tracks 11 and 11' and the doors and the suspension mechanisms therefor are similar except that they are relatively reversed end-for-end, the parts for the right hand track, door and suspension mechanism are designated by the same reference numerals as their left hand counterparts with the prime (') added. Only the left hand track and other suspension mechanism is described structurally herein.
The track 11 comprises a channel shape base portion 13, see FIGS. 1 - 3, with an integral central ridge 14 of truncated wedge shape extending lengthwise thereof. A seat groove 15 is cut lengthwise in the truncated top surface of the ridge 14 to receive a track bar 17 in seated relation therein. The track bar 17 is secured in seated relation in its seat 15 by screws 18, see FIG. 1, inserted at selected spaced intervals in counterbored holes in the base and screwed into registering threaded holes in the track bar.
A car door 19, see FIGS. 2 and 3, is suspended from its track bar 17 by a pair of identical hangers, one of which is mounted adjacent each end of the top and the door. One of these hangers 21 is shown in FIGS. 1 - 3, while a pair thereof 20' and 21' are shown diagrammatically in FIG. 10. An open type, linear motion ball bearing 22, see FIGS. 1 - 3, is fitted into the C-shape upwardly extending portion of each hanger, and rides on the track bar of its respective track. The base ridge 14 rides in the open operations of the C-shape upper hanger portion and in the usual gap in the open type bearing 22.
The two part track 11 is supported at its outer end by a bracket 23, see FIGS. 1 and 2, secured to an end plate 24 of the beam 10 by screws 25. The bracket has a notch 27 therein into which the outer end of the track base 13 is fitted and anchored for limited pivotal adjustment by a shoulder screw 28. A peel-off shim 29 is interposed between the bracket 23 and the beam end plate 24 to snugly fill any space which otherwise might exist therebetween.
The inner end of each track base 13 is secured to the car beam 10 by a bolt 30, a peel-off shim 31 being interposed between the track base 13 and the beam 10 to provide desired clearance therebetween. For adjusting the track about the shoulder screw 28 as a pivot upon loosening the bolt 30, a set screw 32 is screwed into a threaded hole provided in a bracket plate 33 welded to the beam 13 and bears endwise on the under side of a notched out portion of the track base 13.
In order to seal properly it is important that the doors of each pair fit snugly together when closed, and that they also fit closely with respect to the door opening in which they are mounted. To permit such close fits it is desirable that the doors travel as nearly as possible in a straight line as they move between open and closed position.
Since the track 11 is supported only at its ends, the weight of its car door 19 thereon as exerted by the hangers riding on the track bar 17 tends to cause a sagging or downward deflection of the track. In order to minimize such sagging, and to achieve a close approximation of a desired straight-line door travel, in accordance with the present invention the track base 13 is bowed downwardly by subjecting it to carefully arrived at transverse bowing stresses as indicated diagrammatically by the arrow 34 in FIG. 4 during the cutting of the track bar seat 15 therein. The track base 13 is not stressed beyond its elastic limit by this bending operation, so that when the straight seat 15 is cut therein as shown in FIGS. 4 and 5, and these transverse stresses are removed, the track base 13 springs back to it normal, straight, unstressed condition, and the seat 15 is arched thereby as shown in FIGS. 6 and 7.
The track bar 17 is then seated in the seat 15, either with the track base 13 stressed to straighten the seat 15, or with the track bar 17 bowed to fit the curvature of the seat, or both. When the track bar 17 is secured in seated relation in its seat 15 by the screws 18, see FIG. 1, both the track base 13 and the track bar 17 exert opposite bowing effects on each other as shown diagrammaticaly in FIGS. 8 and 9, which show the track bar 17 seated in its seat. This mutual bowing effect of the two track parts on each other is taken into consideration when calculating the sagging effect of the weight of a door on its track.
FIG. 10 shows diagrammatically portions of a left hand door 19 and its track 11, and a right hand door 19' and its track and suspension mechanism. The weight of the door 19' tends to cause its two-part track 11' to sag, and thereby bring the pre-arched track bar 17', along which the door hangers 20' and 21' ride, toward a straight condition. When the left hand door hanger 21' of the door 19' is moved by the closing of its door 19' to a position closely adjacent the supported left hand end of its track 11', as indicated in broken lines, the weight of this left hand hanger is exerted on the track through a lever arm of minimum length, while the other or right hand hanger 20' is at such time located near the mid-zone of the track and therefore bearing on the track through a lever arm of substantially maximum length. When the door 19' is centered on its track 11', as indicated in solid lines in FIG. 10, the loads on both hangers 20' and 21' bear on the track through medium length lever arms, while when the door 19' is in its right hand or open position (not shown) the loading is similar to that shown in broken lines but reversed.
Due to the shifting of the effective loading applied to the track as the doors travel between closed and open position it is desirable to calculate the sagging effect which the weight of the door has on its track, and the optimum corrections required, with the hanger loads imposed at successive, selected stages throughout the length of the track. The deflection of the track at each such stage is carefully measured or calculated so that the necessary arching of the groove 15 can be achieved for providing substantially straight line travel of the door in use.
The bottom of each door is provided with guide means 35, see FIG. 3, which positions the lower end of the door and guides it during opening and closing. Depending upon the design configuration of the car sides, the bottoms of the doors may be offset laterally either outwardly or inwardly from their suspension tracks 11 and 11', in which case each track under the weight of its door is subjected to bowing forces which include not only a vertical weight component, indicated by the arrow 37 in FIG. 3, but also a lateral component indicated by the arrow 38 in that figure. Usually the doors are mounted nearly upright, in which case the lateral component is negligible and is not corrected for.
However, the problem should be kept in mind so that in the event a car design configuration is adopted in which this lateral component becomes substantial it can be corrected for by subjecting the track to proportional bowing forces in both directions during the cutting of a straight bar seat therein in a manner which will be apparent to any ordinarily competent design engineer. It is assumed for the purposes of the present description that this lateral component is not sufficient to require correction and is not corrected for.
Car doors, hangers and tracks embodying the invention are now in process of manufacture for a large mass transit operation, and the pre-bowing effect calculated and employed in the manufacture thereof has been found to require a maximum track base deflection of the order of 0.015 inch when cutting the seat 15, the loads imposed on the track by the hangers being computer-calculated for each 2 inches of door travel.
The invention provides a highly effective door mounting arrangement which in current production of doors and tracks embodying the invention results in almost straight line travel of the doors when moving between open and closed position, thereby permitting effective sealing, and long, trouble-free operation of the doors. In a test still in progress a set of doors embodying the invention has been operated successfully in excess of 2,500,000 two stroke cycles without lubrication, other maintenance, or servicing, and although this test is being conducted on a stationary base, rather than upon a moving car, it has continued many times beyond the life expectancy of any prior art doors of this type within knowledge.