Abstract:
Landing gear for selectively supporting a semitrailer and a method of assembly of the landing gear is provided. The landing gear includes a leg having an upper section and a lower section telescopingly received in the upper section. A lead screw extends and retracts the upper and lower sections relative to each other upon rotation thereof. An input shaft applies a torque to the lead screw to drive rotation thereof, the input shaft being rotatable about a rotation axis and movable in translation along the rotation axis for shifting between a first position for low gear operation and a second position for high gear operation. An output shaft, axially aligned with the input shaft, has an output gear for transmitting torque to the lead screw. A gearing subassembly is received in the upper leg section and is configured to augment lift when the input shaft is in the first position and augment speed in the second position.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 10/405,079, filed on Apr. 1, 2003, now U.S. Pat. No. 7,055,859, titled LANDING GEAR AND METHOD OF ASSEMBLY. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to landing gear used in the support of semitrailers and more particularly to gearing configurations of a landing gear. 
     Landing gear of the present invention has particular application in the support of semitrailers when they are not attached to a tractor. The landing gear conventionally includes a pair of telescoping legs capable of extending to engage the pavement or other supporting surface to hold up the front end of the semitrailer, and of retracting to move up out of the way when the semitrailer is being pulled over the road by a tractor. The extension and retraction is most often carried out by the driver manually turning a crank connected by gearing to a lead screw in the leg. The lead screw interconnects telescoping leg sections of the leg so as to retract a lower leg section into an upper leg section or extend the lower leg section from the upper leg section depending on the direction the screw is rotated. 
     The semitrailers are very large and heavy by themselves, and further carry large loads. In order to lift such loads when extending the legs, the gearing provides a mechanical advantage in addition to the crank. In providing the mechanical advantage, the rotation of the lead screw is very much retarded in relation to the rotation of the crank. In other words, it will require numerous turns of the crank to achieve a very small linear travel of the lower leg section relative to the upper leg section. The high ratio of turns per inch of travel is acceptable when the legs are actually bearing the load of the trailer because of the accompanying mechanical advantage. Once the load is relieved from the leg, such as when the semitrailer is supported by the tractor, the slow linear movement of the lower leg section becomes an issue because of the long time it takes to get the lower leg section retracted far enough above the ground for safe travel over the road. Likewise, slow extension of the lower leg section into engagement with the pavement is also highly undesirable. It is known to provide for shifting between a low gear and a high gear in the gearing, with the low gear providing the mechanical advantage needed for lifting large loads and high gear providing for more rapid linear movement of the lower leg section (i.e., a lower turns per inch ratio). Co-assigned U.S. Pat. No. 4,187,733 discloses gearing of this type. Generally, a large difference between the turns per inch ratio in low gear versus high gear is desirable. 
     One way to assist in providing greater lift in low gear is to provide a gear on an idler shaft located between the input shaft (of the crank) and the output shaft connected to the lead screw. This arrangement is typically referred to as a double reduction. An idler shaft requires additional space in the gear box, which is at a premium. In addition, there are two additional openings in the gear box containing bearings for the idler shaft. These openings provide an additional place from which leakage of lubricant becomes more likely over the life of the landing gear. 
     Conventionally, the gearing has been located in a gear box which is formed separately from the leg. For instance, the gear box may be formed from two halves which are individually stamped and later bolted together. The gears making up the gearing may be installed in one half of the gear box before it is completed. The gear box is welded or otherwise attached to the landing gear leg on the inside or outside of the leg. The input shaft from the crank, and the output shaft which is connected to the lead screw, are held by bearings located in the landing gear leg. The conventional construction requires a number of parts in addition to the landing gear leg and several manufacturing steps to assemble the gearing in the gear box with the input and output shafts and the leg. It is known to incorporate some of the gearing in the leg, but significant manufacturing steps are required to assemble component parts of the gearing together with the input and output shafts. 
     SUMMARY OF THE INVENTION 
     Among the several objects and features of the present invention may be noted the provision of landing gear which is of simplified construction; the provision of such landing gear having a compact gear arrangement; the provision of such landing gear which provides additional torque in low gear and augmentation of crank rotation in high gear to increase speed; the provision of such a landing gear which inhibits leakage of lubricant; the provision of such landing gear which has fewer external bearings receiving shafts; the provision of such landing gear which has fewer parts; the provision of such landing gear which is lighter in weight; and the provision of such landing gear which can be efficiently assembled. 
     Further among the several objects and features of the present invention may be noted the provision of a method of assembling landing gear which can be carried out rapidly and with precision; the provision of such a method which reduces the number of externally exposed shaft bearings to minimize leakage; and the provision of such a method which reduces the number of steps to complete manufacture of the landing gear. 
     In general, one embodiment of the invention is directed to landing gear for selectively supporting a semitrailer. The landing gear includes a leg having an upper section and a lower section in telescoping arrangement with each other and a lead screw mounted for extending and retracting the upper and lower sections relative to each other upon rotation of the lead screw. The landing gear also includes an input shaft for applying a torque to the lead screw to drive rotation thereof, the input shaft being rotatable about a first rotation axis and movable in translation along the first rotation axis for shifting between a first position for low gear operation and a second position for high gear operation. The landing gear also includes an output shaft including an output gear for transmitting torque to the lead screw, the output shaft being mounted for rotation about a second rotation axis and being generally axially aligned with the input shaft. The landing gear also includes a gearing subassembly configured so that for each rotation of the input shaft, the output shaft rotates less than one rotation for low gear operation and interconnecting the generally axially aligned input and output shafts in the second position so that for each rotation of the input shaft, the output shaft rotates more than one rotation, whereby the gearing subassembly augments lift when the input shaft is in the first position and augments speed in the second position. 
     The invention is also directed to landing gear for selectively supporting a semitrailer. The landing gear includes a leg having an upper section and a lower section in telescoping arrangement with each other and a lead screw mounted for extending and retracting the upper and lower sections relative to each other upon rotation of the lead screw. The landing gear also includes an input shaft rotatable about a first rotation axis and an output shaft rotatable about a second rotation axis and connected for driving rotation of the lead screw. The landing gear further includes an idler shaft rotatable about a third rotation axis and gearing associated with the input shaft, output shaft, idler gear and lead screw for operatively connecting input shaft to the lead screw for driving rotation thereof. The landing gear also includes a bearing member located within the upper section of the leg and including a bearing element bearing the idler shaft for rotation, the bearing member being supported by the upper section at a location above the location of the bearing element. 
     Another embodiment of the invention is directed to landing gear for selectively supporting a semitrailer. The landing gear includes a leg having an upper section and a lower section in telescoping arrangement with each other and a lead screw mounted for extending and retracting the upper and lower sections relative to each other upon rotation of the lead screw. The landing gear also includes an input shaft rotatable about a first rotation axis and movable in translation along the first rotation axis for shifting between a first position for low gear operation and a second position for high gear operation and an output shaft mounted for rotation about a second rotation axis. The landing gear further includes a first idler shaft mounted for rotation about a first idler shaft axis spaced from the axis of rotation of the input shaft and a second idler shaft mounted for rotation about a second idler shaft axis spaced from the axis of rotation of the input shaft. The input shaft and the first idler shaft are arranged such that in the first position torque from the input shaft is transmitted through the first idler shaft to the lead screw and the output shaft and the input shaft and the second idler shaft are arranged such that in the second position torque from the input shaft is transmitted through the second idler shaft to the output shaft and lead screw. 
     Another embodiment of the invention is directed to landing gear for selectively supporting a semitrailer. The landing gear includes a leg having an upper section and a lower section in telescoping arrangement with each other. The upper section has opposing walls, a first of the walls having a slot therein at an upper end. The landing gear also includes a lead screw mounted for extending and retracting the upper and lower sections relative to each other upon rotation of the lead screw and an input shaft rotatable about a first rotation axis and connected in operation to the lead screw for driving rotation thereof. The input shaft extends into the upper section of the leg through the slot in the first wall. The landing gear further includes a cover plate attached to the upper section generally over the slot, the cover plate including a bearing receiving the input shaft there through. 
     Another embodiment of the invention is directed to a method of assembling a landing gear leg. The method includes the steps of mounting at least one shaft on a bearing located in a bearing member and inserting the bearing member mounting the shaft into an upper section of the landing gear leg. 
     Another embodiment of the invention is directed to a subassembly for use in manufacturing a landing gear leg. The subassembly includes a bearing member adapted to be mounted on the leg in an open top thereof and a shaft mounted on the bearing member for rotation. The subassembly also includes gearing associated with the shaft for use in transmitting rotation, whereby the shaft and gearing are supported for rotation independently of mounting in the leg. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation of a semitrailer unhitched from its truck tractor, and having landing gear thereon supporting the front end of the semitrailer; 
         FIG. 2  is an enlarged perspective view of a landing gear leg of the landing gear depicted in  FIG. 1 ; 
         FIG. 3  is a front side elevation of the landing gear leg of  FIG. 2 ; 
         FIG. 4  is a right side elevation of the landing gear leg of  FIG. 2 ; 
         FIG. 5  is an exploded perspective view of the landing gear leg of  FIG. 2  capable of receiving a gearing subassembly for both conventional and reverse mounted legs; 
         FIG. 6  is a side elevation of a mounting plate of the landing gear leg of  FIG. 2 ; 
         FIG. 7  is a side elevation of an upper portion of the landing gear leg; 
         FIG. 8  is a plan view of an upper section of the landing gear leg; 
         FIG. 9  is a bottom side perspective of a top cover and associated idler shaft and gearing of a single idler landing gear leg according to one embodiment of the invention; 
         FIG. 10  is an inverted view of the top cover and idler shaft of  FIG. 9  with the parts exploded to illustrate assembly; 
         FIG. 11  is a schematic fragmentary cross section of the single idler landing gear leg of  FIG. 9  with the input shaft in the low gear position; 
         FIG. 12  is a schematic fragmentary cross section of the single idler landing gear leg of  FIG. 9  with the input shaft in the high gear position; 
         FIG. 13A  is an end view of the idler shaft of the single idler landing gear of  FIG. 9 ; 
         FIG. 13B  is a sectional view of the idler shaft taken along line  13 B- 13 B of  FIG. 13A ; 
         FIG. 14  is a bottom side perspective of a top cover of the single idler landing gear leg; 
         FIG. 15  is an inverted perspective view of the top cover of  FIG. 14  with the parts exploded to illustrate assembly; 
         FIG. 16  is a schematic, fragmentary cross section of another version of the single idler landing gear leg having an idler shaft supported from the side internally of the leg; 
         FIG. 17  is a bottom side perspective of a top cover and associated dual idler shafts and gearing according to one embodiment of the invention; 
         FIG. 18  is an inverted perspective view of the top cover and dual idler shafts of  FIG. 17  with the parts exploded to illustrate assembly; 
         FIG. 19  is a schematic, fragmentary side elevation of a dual idler landing gear leg with a wall of the leg and other selected parts broken away to reveal construction with the input shaft in the high gear position; 
         FIG. 20  is a schematic, fragmentary side elevation of a dual idler landing gear leg with a wall of the leg and other selected parts broken away to reveal construction with the input shaft in the low gear position; 
         FIG. 21  is an enlarged fragmentary side elevation of the dual idler landing gear; 
         FIG. 22A  is an end view of the low idler shaft of the dual idler landing gear; 
         FIG. 22B  is a sectional view of the low idler shaft taken along line  22 B- 22 B of  FIG. 22A ; 
         FIG. 23A  is an end view of the high idler shaft of the dual idler landing gear; 
         FIG. 23B  is a sectional view of the high idler shaft taken along line  23 B- 23 B of  FIG. 23A ; 
         FIG. 24  is a bottom side perspective of the top cover of the dual idler landing gear leg; 
         FIG. 25  is an exploded perspective of the top cover of  FIG. 24 ; 
         FIG. 26  is a fragmentary front elevation of a single idler landing gear leg having components substantially identical to the dual idler landing gear leg of  FIGS. 20 and 21 ; and 
         FIG. 27  is a fragmentary side elevation of the single idler landing gear leg with a wall of the leg and other selected parts broken away to reveal construction. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates landing gear, indicated generally at  10 , for the support of semitrailers when not attached to a tractor. The landing gear  10  typically includes a pair of legs  11  (only one leg is shown) located near respective front comers of a semitrailer  12 . Each leg  11  is capable of extending to engage the pavement S or other supporting surface to hold up the front end of the semitrailer as is well understood in the art. A shoe  14  of the landing gear  10  is pivotally mounted on the leg  11  for engaging the pavement S. The legs  11  are also capable of retracting to move up out of the way when the semitrailer  12  is being pulled over the road by a tractor (not shown). A crank handle  16  is used to extend and contract the length of the leg  11 , as will be described below. The following description is confined to one of the legs  11 . The other leg (not shown) has a similar construction, but if it is connected to gearing of the illustrated leg such as by an output shaft extending underneath the front of the semitrailer  12 , the other leg need not have some of the gearing present in the illustrated leg. Such constructions are well understood by those of ordinary skill in the art and will not be further described herein. 
     Referring to  FIGS. 2-5 , the landing gear leg  11  includes a lower leg section  13  ( FIG. 5 ) telescopingly received in an upper leg section  15 . The lower leg section  13  is a steel square tube. The upper leg section  15  is preferably a square tube made of steel or other like material. The upper leg section  15  has internal dimensions larger than that of the lower leg section  13  so that the lower leg section is telescopingly received in the upper leg section. The lower and upper leg sections  13 ,  15  could also have other cross sectional shapes, such as rectangular, round or the like. In an alternate version, the upper leg section is a steel channel having an open front side extending the length of the upper leg section. A mounting plate  17  for attaching the leg  11  to the trailer  12  is attached by bolts and/or welding to the upper leg section  15 . Holes  17 A in the mounting plate  17  may receive fasteners (not shown) for attaching the leg  11  to the trailer  12 . The leg  11  can be attached to the trailer in either a “conventional mount” and “reverse mount”. These labels will be understood by those of ordinary skill in the art and will not be discussed further. 
       FIG. 5  illustrates that the upper leg section  15  has two U-shaped cutouts  18 ,  20  extending axially downward from the upper end of the upper leg section on opposite sides of the upper leg section. In the final assembly, the cutouts  18  and  20  are closed by an outside cover plate  19  and an inside cover plate  21 , respectively. For illustrative purposes, with the conventionally mounted leg  11 , the “outside” cover plate  19  faces out to the side of the semitrailer and the “inside” cover plate  21  faces in toward the center of the semitrailer. The upper leg section  15  is formed with two pockets  22  extending outward from the upper leg section on opposite sides of the upper leg section. The pockets  22  are formed on the sides of the upper leg section that do not have the cutouts  18 , 20 . The pockets  22  are sized to accommodate an idler gear as will be described below. 
     The lower and upper leg sections  13 ,  15  are connected together by a lead screw  23  (only the very upper portion of which is illustrated in  FIG. 5 ) for extension and retraction of the lower leg section  13  relative to the upper leg section  15  upon rotation of the lead screw. The lead screw  23  has a bevel gear  25  mounted on its upper end for use in driving the lead screw as will be described. The landing gear leg  11  includes an input shaft  27  received through the outside cover plate  19  into the leg and an output shaft  31  received through the inside cover plate  21  of the leg. The input shaft  27  and output shaft  31  are connected together a subassembly  32  further including gearing as will be described below. More specifically, the gearing subassembly  32  is preferably constructed and arranged to fit substantially within the cross sectional area of the upper leg section  15 . In one embodiment, the output shaft  31  would extend to the aforementioned other leg (not shown) of the landing gear to drive the rotation of the lead screw in that leg. The crank handle  16  ( FIG. 1 ) is preferably attached to the outer end of the input shaft  27  for manually applying torque to rotate the input shaft. 
     Assembly of the landing gear leg  11  may performed by dropping the top cover  47  and associated components of the subassembly  32  onto the open top of the upper leg section  15 . Thus, in one preferred embodiment, the gearing components of the subassembly, such as the idler shafts, the output gear, the pinion gear and the large diameter input gear, as will be described below, are all received within the upper leg section  15 . The input shaft  27  passes through the cutout  18  on the outside of the upper leg section  15  and the output shaft  31  passes through the cutout  20  on the inside of the upper leg section. Cover plate bolts extend through holes in respective cover plates  19 ,  21  and into the top cover  47  to secure the subassembly  32  to the leg  11 . The cover plates  19 ,  21  may also be welded to the upper section  15  and/or a gasket (not shown) may be provided between the cover plate ( 19 ,  21 ) and upper section. 
     Preferably, the leg  11  is constructed selectively for either conventional mounting on a semitrailer or reverse mounting by turning the subassembly  32  to the upper section  15  through 180 degrees. Nothing else about the construction of the leg changes, which simplifies manufacturing. It maybe seen that the upper end of the upper leg section  15  has the opposite laterally outwardly formed pockets  22 . In addition, the front side of the upper leg section  15  has an outwardly formed portion  24 . The pockets  22  provide space for the gears of the idler shafts (not shown) without regard to the orientation of the subassembly  32 . The outwardly formed portion  24  keeps the distance from a center of the upper section  15  to the respective cutouts  18 ,  20  equal. Thus, a beveled pinion gear member (described below with reference to  FIG. 9 ) in the subassembly  32  will mesh with the bevel gear  25  at the top of the lead screw  23  no matter which direction the top cover subassembly is oriented.  FIG. 5  shows the top cover subassembly  32  oriented for both conventional mount and for reverse mount. In either orientation, the subassembly  32  can be dropped into the open top of the upper leg section  15  for assembling the leg  11 . 
       FIG. 6  illustrates a mounting plate  17 ′ used with an upper leg portion (not shown) shaped as a channel and is configured to cover the open front side of the upper leg portion.  FIGS. 7 and 8  illustrate a modified version of an upper section  15 ″ of a landing gear leg having the shape of a square tube. The upper section  15 ″ has a mounting plate  17 ″ attached thereto. The upper end of the upper section  15 ″ is belled outwardly to form pockets  22 ″ and outwardly formed portions  24 ″. The pockets  22 ″ and outwardly formed portions  24 ″ extend over a substantial portion of the width of their respective side walls. Otherwise, the construction of the upper section  15 ″ is substantially the same as upper section  15 . The upper leg section  15  at its upper end is symmetrical about a central plane P. 
       FIGS. 9-16  illustrate a subassembly, generally designated at  32 , and parts thereof separately and in combination with the leg  11 . Referring to  FIGS. 9 and 10 , the subassembly  32  comprises a single idler shaft  45  ( FIG. 13 ) for mechanically connecting the input shaft  27  with the output shaft  31 . The input shaft  27  is received through a bearing  29  in the outside cover plate  19  into the leg  11  and the output shaft  31  is received through a bearing  33  in the inside cover plate  21  of the leg. The top cover  47  has been removed from  FIG. 9  for clarity. 
     The inner end of the input shaft  27  has a reduced diameter and is received and borne in an axial opening of an output gear  35  of the output shaft  31  for free rotation relative to the output gear and for axial movement relative to the output gear. Alternately, the output shaft has a reduced diameter end portion (not shown) which is received in an axial opening in the input shaft, or the shafts could be supported independently of each other. Thus, the input and output shafts  27 ,  31  are coaxial. The bearing  29  supporting the input shaft  27  in the outside cover plate  19  permits the input shaft to both rotate and move axially relative to the bearing. As to axial movement, a ball and spring mechanism (not shown) is provided to engage the bearing  29  to releasably lock the input shaft  27  in two axial positions, corresponding to low gear ( FIG. 11 ) and high gear ( FIG. 12 ), respectively. 
     The input shaft  27  carries a pinion gear  37  which is pinned to the reduced diameter portion of the input shaft for conjoint rotation with the input shaft. It is contemplated that the pinion gear  37  could be formed as one piece with the input shaft  27 . The pinion gear  37  has a small diameter, and has a first set of gear teeth  38  and a second set of gear teeth  40 . The input shaft  27  also mounts a large diameter input gear  39  for free rotation relative to the input shaft, except as will be described, but which is held from movement along the axis of the input shaft relative to the upper leg section  15 . A central, internally toothed opening  42  of the input gear  39  has a diameter which is larger than the input shaft  27  for receiving a part of the pinion gear  37  into the central opening. The large diameter input gear  39  includes a flat central portion  46  and an angled outer portion  48 . This construction permits the large diameter gear  39  to fit closely against the outside cover plate  19  and between the outside cover plate and the bevel gear  25  of the lead screw  23 . The annular outer portion  48  of the large diameter gear  39  angles outwardly and has teeth formed therein for meshing with another gear as will be described. 
     The output gear  35  is pinned to the output shaft  31  for conjoint rotation. The output gear  35  includes first gear member  41  which receives input torque to drive the gear and a second beveled pinion gear member  43  which is meshed with the bevel gear  25  of the lead screw  23 . The first gear member  41  is substantially planar and fits close against the inside cover plate  21  and between the bevel gear  25  and the cover plate. As illustrated, the output gear  35  is formed as a single piece of tubular material. However, it may be formed from multiple pieces which are separated and secured to a common tube, or directly to the output shaft  31 . 
     Driving connection of the input shaft  27  with the output gear  35  is achieved by way of an idler shaft  45  having three idler gears formed as one piece with the shaft. It would be possible to form the gears separately from the shaft and connect them to the shaft. As shown in  FIGS. 11 and 12 , the idler shaft  45  is supported for rotation within the upper leg section  15  by a top cover  47 . In certain statements of the present invention, the top cover  47  may be considered to be a “bearing member”. The top cover will be described more fully hereinafter. A first idler gear  49  has the smallest diameter of the gears on the idler shaft and is permanently meshed with the large diameter input gear  39 . A second idler gear  51  has the largest diameter and is located generally in the middle of the idler shaft  45  for selective engagement with the teeth  40  of the pinion gear  37  of the input shaft  27 . A third idler gear  53  located at the far left end of the idler shaft  45  has a diameter between that of the first and second idler gears and is permanently meshed with the first gear member  41  of the output gear  35 . 
     Referring to  FIGS. 14 and 15 , a top cover  47  of the single idler landing gear leg  11  is formed to rotatably mount the idler shaft  45 . Preferably, it is not necessary to have additional openings in the exterior of the leg  11  through which rotating shafts are received, which are prime locations for leaking lubricant. The top cover  47  is made either partially or entirely of a polymeric material such as nylon. However, it is contemplated that the top cover  47  may be made of other suitable materials, such as a ductile iron casting or aluminum casting, without departing from the scope of the present invention. It is believed no separate bearings will be necessary if the top cover  47  is made of nylon or a like material. In one version, side flange  70  of the top cover  47  has openings  72  therein for receiving bolts or screws to secure the cover plate  19  (see  FIG. 10 ) to the top cover. The top cover has a first outwardly formed pocket  74  extending from a top surface  75  thereof. The pocket  74  provides space for receiving the second idler gear  51  (see  FIG. 10 ). The top cover  47  also has a second outwardly formed pocket  76  extending from the top surface  75  for receiving the third idler gear  53 . Side flange  78  of the top cover  47  has openings (not shown) therein for receiving bolts or screws to secure the cover plate  21  (see  FIG. 10 ) to the top cover. 
     Referring now to  FIG. 15 , the top cover  47  includes a first yoke  81  which receives a section of the idler shaft  45  between the first idler gear  49  and the second idler gear  51 , and a second yoke  83  which receives a section of the idler shaft between the second idler gear and the third idler gear  53 . The first and second yokes  81 ,  83  each have a lower portion  81 A,  83 A which can be separated from an upper portion  81 B,  83 B to place the idler shaft  45  in the top cover  47 . Bolts  84  may be used to connect the lower portions  81 A,  83 A to respective upper portions  81 B,  83 B. The gearing subassembly  32 , top cover  47 , outside cover plate  19 , inside cover plate  21 , input shaft  27 , and output shaft  31  may be subassembled and dropped into the upper leg section  15  as shown in  FIG. 5 . 
     Referring again to  FIGS. 11 and 12 , the operation of the landing gear is as follows. Assuming the lower leg section  13  ( FIG. 2 ) is retracted into the upper leg section  15  and is to be extended, the driver first moves the input shaft  27  axially outwardly to the position shown in  FIG. 12 . In this position, the pinion gear  37  is partially received in the central opening  42  of the large diameter input gear  39 . The use of a small pinion gear  37  is adopted from co-assigned U.S. Pat. No. 4,187,733, the disclosure of which is incorporated by reference. The first set of teeth  38  on the right side of the pinion gear  37  mesh with the internal teeth of the large diameter gear  39  so that the large diameter gear is now fixed for conjoint rotation with the input shaft  27 . Thus, the engagement of the large diameter gear  39  with the first idler gear  49  is a driving engagement. As is understood by those of ordinary skill in the art, the idler shaft  45  will be rotated more rapidly than the input shaft  27 . The torque is transmitted by the idler shaft  45  to the third gear  53  meshed with the first gear member  41  of the output gear  35  for driving the output gear at a rotational rate which is greater than that of the input shaft  27 . For example and not by way of limitation, if the ratio of teeth of the larger diameter gear  39  to that of the first idler gear  49  is 31T/7T and the ratio of teeth on the second idler gear  53  to the first output gear member  41  is 13T/25T, the output shaft rotates 2.3 times faster than the input shaft. The ratio of the turns of the crank handle  16  (see  FIG. 1 ) per inch of travel of the lower leg section  13  for this version is 1.97. In this way, the lower leg section  13  can be more rapidly extended from the upper leg section  15  for bringing the leg into contact with the pavement S. 
     Once the leg  11  contacts the pavement, it will be necessary to increase the mechanical advantage provided by the gearing to lift the semitrailer  12  ( FIG. 1 ) off of the fifth wheel of the tractor (not shown). To do this, the driver moves the input shaft  27  axially inwardly so that the pinion gear  37  moves out of the central opening  42  of the large diameter input gear  39  and into engagement with the teeth of the second idler gear  51  (as shown in  FIG. 11 ). The large diameter input gear  39 , although still meshed with the first gear  49  of the idler shaft  45  does not transmit any torque from the input shaft  27  and does not rotate conjointly with the input shaft. The second set of teeth  40  on the left side of the pinion gear  37  mesh with the teeth of the second idler gear  51 . It will be readily apparent that rotation Of the input shaft  27  will be substantially reduced by the second idler gear  51 , producing an accompanying increase in torque. The higher torque is transmitted by the third idler gear  53  to the first gear member  41  of the output gear  35 , achieving a further (or “double”) reduction. Now rotation of the input shaft  27  produces extension of the lower leg section  13  at a slower rate, but with greater lift to raise the semitrailer  12  and its load. 
       FIG. 16  illustrates another version of the single idler landing gear leg  111 , where corresponding parts are indicated by the same reference numeral, but with the prefix “1”. An idler shaft  145  is supported by bushings associated with outside and inside cover plates  119 ,  121  rather than being supported by the top cover. In this embodiment, the top cover  147  is not used to support the idler shaft  145 . Otherwise, the construction is substantially identical to  FIG. 9  and will not be further described herein. Referring again to  FIG. 16 , it may be seen that the idler shaft  145  has a reduced diameter stub  185  at the right end thereof and an enlarged diameter portion  187  at its left end. The stub  185  is journaled in a bushing  189  which is fitted into an opening formed in the outside cover plate  121  for rotation of the idler shaft  145 . The bushing  189  blocks the opening to assist in sealing the leg  11 . A short axle  191  is received through an opening in the inside cover plate  121  and into a recess in the enlarged diameter portion  187  of the idler shaft to mount the idler shaft  145  for rotation. The axle  191  is sealably secured to the inside cover plate  121 , such as by welding. The fitted bushing  189  and the short axle  191  mount the idler shaft  145  for rotation between the outside and inside cover plates  119 ,  121 . Thus, there is no moving part extending through the outside and inside cover plates  119 ,  121 . Thus, although the idler shaft  145  is supported from the sides of the leg  11 , it does not extend through the sides. Accordingly, a prime site for the leakage of lubricant (through a rotating shaft bearing) is eliminated. 
     Some examples of possible high gear and low gear ratios for the single idler leg  11  are listed below in turns of the crank handle  16  per inch of travel of the leg. 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 Low Gear 
                 29.2 
                 Low Gear 
                 32.8 
                 Low Gear 
                 35.1 
               
               
                 High Gear 
                 1.8 
                 High Gear 
                 1.97 
                 High Gear 
                 3.3 
               
               
                 Low Gear 
                 38 
                 Low Gear 
                 41.8 
                 Low Gear 
                 35.1 
               
               
                 High Gear 
                 1.8 
                 High Gear 
                 1.97 
                 High Gear 
                 4.5 
               
               
                 Low Gear 
                 35.1 
               
               
                 High Gear 
                 3.9 
               
               
                   
               
             
          
         
       
     
       FIGS. 17-25  collectively show a landing gear leg  211  and components thereof, of another embodiment. Corresponding parts are indicated by the same reference numeral as for the landing gear leg  11 , but with the prefix “2”.  FIGS. 17 and 18  illustrate a gearing subassembly  232  and a top cover  247  of the dual idler shaft landing gear leg  211 . The subassembly comprises a dedicated low gear idler shaft  257  ( FIGS. 22A and 22B ) and a separate, dedicated high gear idler shaft  263  ( FIGS. 23A and 23B ) for mechanically connecting an input shaft  227  with an output shaft  231 . The input shaft  227  is received through a bearing  229  in an outside cover plate  219  into the leg  211  and the output shaft  231  is received through a bearing  233  in an inside cover plate  221  of the leg. A top cover  247  is formed to rotatably mount both the low gear idler shaft  257  and the high gear idler shaft  263  in the dual idler landing gear leg  211 . Preferably, it is not necessary to have additional openings in the exterior of the leg  211  through which rotating shafts are received, and which are prime locations for leaking lubricant. 
       FIGS. 19 and 20  illustrates that the input shaft  227  and output shaft  231  are coaxial and a reduced diameter inner end of the input shaft is received and borne within the output shaft. Alternately, an output shaft has a reduced diameter end portion which is received in an axial opening in the input shaft (not shown). The bearing  229  supporting the input shaft  227  in the outside cover plate  219  permits the input shaft to both rotate and move axially relative to the bearing. As to axial movement, a ball and spring mechanism (not shown) is provided to engage the bearing  229  to releasably lock the input shaft  227  in two axial positions, corresponding to high gear and low gear, respectively. The subassembly  232  is shown in the high gear position in  FIG. 19  and in the low gear position in  FIG. 20 . 
     It is noted that a pinion gear  237  is formed as one piece with the input shaft  227  and an output gear  235  is formed as one piece with the output shaft  231 . It will be appreciated that the pinion gear  237  and output gear  235  may be formed separately from their respective shafts ( 227 ,  231 ). The pinion gear  237  contains a first set of teeth  238  and a second set of teeth  240 . A large diameter input gear  239  is somewhat smaller than the large diameter gear  39  of the first embodiment and is entirely planar, but is similarly mounted for free rotation on the input shaft  227  except when engaged by the first set of teeth  238  of the pinion gear  237 . The output gear  235  differs from the single idler output gear configuration by having a third, small diameter gear member  244 . More specifically, the dual idler landing gear leg includes a low gear idler shaft  257  including a large diameter first gear  259  engageable by the pinion gear  237  for driving the rotation of the low gear idler shaft, and a second small diameter gear  261  permanently meshed with the first gear member  241  of the output gear  235 . A separate high gear idler shaft  263  includes a first high gear idler gear  265  permanently meshed with the large diameter input gear  239 , and a second high gear idler gear  267  permanently meshed with the third gear member  244  of the output gear  235 . Accordingly, it is not necessary to balance speed in high gear against torque in low gear. The separate, dedicated idler shafts  257 ,  263  decouple these design features. 
     As shown in  FIG. 21 , the axis A 1  of the low gear idler shaft  257  and the axis A 2  of the high gear idler shaft  263  are offset on opposite sides of a vertical plane P including the common axis of rotation A 3  of the input and output shafts  227 ,  231 . Preferably, the offset is as small as necessary to permit the gears of both idler shafts  257 ,  263  to mesh with the coaxially arranged gears ( 235 ,  237 ,  239 ) of the input and output shafts  227 ,  231 . 
     The operation of the dual idler landing gear leg  211  is similar to the operation of the embodiment of the single idler landing gear  11  shown in  FIG. 5 , except that different idler shafts  257 , 263  are used for low and high gear. In high gear, the first set of teeth  238  of the pinion gear  237  is partially received in the large diameter input gear  239  so that the large diameter gear rotates conjointly with the input shaft  227  ( FIG. 19 ). It will be appreciated that the high gear idler shaft  263  rotates faster than the input shaft  227 . For example, with 19 teeth on the large diameter input gear  239  and 9 teeth on the high gear idler gear  265 , the idler shaft  263  rotates 2.11 times as fast as the input shaft  227 . The rotational speed is again increased by the second high gear idler gear  267  meshed with the third gear member  244  of the output gear. The low gear idler shaft  257  turns but does not transfer any torque in this configuration. For low speed, high torque operation the input shaft  227  is moved axially to the left so that the large diameter input gear  239  is disengaged and the second set of teeth  240  on the other end of the pinion gear  237  mesh with the first low gear idler gear  259  ( FIG. 20 ). The input shaft torque is now transferred by the low gear idler shaft  257  to the output gear by way of the second low gear idler gear  261  and the first gear member  241  of the output gear  235 . A substantial reduction is achieved both from the input shaft  227  to the low gear idler shaft  257  and from the low gear idler shaft to the output gear  235  by virtue of the relative sides of the meshed gears. 
     Preferably, the numerical values given in the range have units of turns of the crank per inch of travel of the leg are between 1.02 and 4.5 in high gear and 26 and 44 in low gear. However, one skilled in the art will understand that any combination of low and high ratios is possible. Preferably, the dual idler leg  211  provides good lift in low gear (e.g., 35 turns per inch), and an option for high gear. For example, the high gear could be either 1.02 or 4.5, with minimal change of gears and other components necessary to provide the desired high gear ratio. 
     As set forth above with respect to the single idler embodiment, the top cover  247  is preferably made of a polymeric material such as nylon. However, it may be made of other suitable materials, such as a ductile iron casting or aluminum casting, without departing from the scope of the present invention. It is believed no separate bearings will be necessary if the top cover  247  is made of nylon or a like material. The input and output shafts  227 ,  231  are also supported by the top cover  247  in a first yoke  269  depending from the top cover. A second yoke  271  is provided for supporting one end of the low gear idler shaft  257  and a third yoke  273  is provided to support one end of the high gear idler shaft  263 .  FIGS. 24 and 25  illustrate the top cover  247  of the double idler landing gear leg  211  which mounts the idler shafts  257 ,  263  for rotation. It may be seen that each yoke  269 ,  271 ,  273  (broadly, “bearing member”) includes a respective removable lower portion  269 A,  271 A,  273 A which is attached to an upper portion  269 B,  271 B,  273 B by a respective pair of bolts. It is also envisioned that the top cover  247  and yokes  269 ,  271 ,  273  may be made as a single, unitary piece. In that event, the idler shafts  257 ,  263  would be made in two pieces (not shown) to permit their insertion into holes in the yokes  269 ,  271 ,  273 . After insertion the two pieces of the idler shaft would be connected together. In the illustrated embodiments, the first yoke  269  has three holes, including a first hole  275 A which receives the output shaft  231 , a second hole  275 B which receives the low gear idler shaft  257  and a third hole  275 C which receives the high gear idler shaft  263 . The second yoke  271  has a single hole  277  for another portion of the low gear idler shaft  257  and the third yoke  273  similarly has a single hole  279  for receiving another portion of the high gear idler shaft  263 . The output shaft  231  is received in the first hole  275 A of the first yoke  269  and is supportingly engaged by the first yoke. 
     To place the idler shafts  257 ,  263  in the first, second and third yokes ( 269 ,  271 ,  273 ), the lower portions ( 269 A,  271 A,  273 A) of the yokes are removed, opening up the second and third holes  275 B,  275 C of the first yoke and the holes  277 ,  279  of the second and third yokes. The low gear idler shaft  257  is placed on the top cover  247  (which is preferably inverted for assembly) so that a section of the shaft adjacent to the first low gear idler gear  259  is received in the exposed portion of the second hole  275 B of the upper portion  269 B of the first yoke  269  still associated with the top cover. At the same time, a section of the low gear idler shaft  257  nearer the second low gear idler gear  261  is received in the portion of the hole  277  in the upper portion  271 A of the second yoke  271  which is still associated with the top cover  247 . Similarly, the high gear idler shaft  263  is placed so that a section of the shaft adjacent to the first high gear idler gear  265  is received in the exposed portion of the hole  279  of the upper portion of the third yoke  273  still associated with the top cover  247 . At the same time, a section of the high gear idler shaft  263  nearer the second high gear idler gear  267  is received in the exposed portion of the third hole  275 C in the upper portion  269 B of the first yoke  269 . 
     The idler shafts  257 ,  263  are secured in place by bolting the lower portions  269 A,  271 A,  273 A to the respective upper portions  269 B,  271 B,  273 B, thereby encircling the idler shaft sections. In this way, the idler shafts  257 ,  263  are mounted entirely by the top cover  247 . The outside cover plate  219  may be preassembled with the input shaft  227  and the inside cover plate  221  may likewise be preassembled with the output shaft  231 . The input and output shafts (and associated cover plates) can be brought together with the top cover  247  as shown in  FIG. 18 . The output shaft  231  is received through the first hole  275 A in the first yoke  269  and the reduced diameter portion of the input shaft  227  is inserted into the output shaft. Bolts are passed through the cover plates  219 ,  221  and into the top cover  247 . This completes the subassembly  232  which includes all of the gearing of the landing gear leg  211  except for the bevel gear  225  attached to the top of the lead screw (not shown but essentially the same as the screw  23  of  FIG. 5 ). It is further contemplated that the single idler leg  11  may use a top cover substantially similar to the top cover  247  used by the dual idler leg  211  and leave one of the yokes  271 ,  273  unused, as described below. The subassembly  232  so formed may be dropped into the open top of the leg  211  in manufacture. The cover plates  219 ,  221  are secured to the leg  211  to assemble the subassembly  232  with the upper section  215  of the leg. 
       FIGS. 26 and 27  illustrate another version of the single idler landing gear leg  211 ′ that uses a top cover  247 ′ having yokes  269 ′,  271 ′ and  273 ′ substantially identical to the top cover described above with respect to the dual idler landing gear leg  211 . Thus, the same top cover and leg sections can be used to manufacture both single and dual idler landing gear legs. In the version illustrated in  FIGS. 27 and 28 , the input and output shafts  227 ′,  231 ′ are also supported by the top cover  247 ′ in the first yoke  269 ′ depending from the top cover. Either the second yoke  271 ′ or the third yoke  273 ′ receives and supports the idler shaft  245 ′. The other yoke  273 ′ or  271 ′ is not used by the subassembly  232 ′. The operation of this version would be substantially similar to the operation of the single idler leg  11  described above. With this version, both a single idler subassembly  232 ′ and the dual idler subassembly  232  would use a common top cover to facilitate manufacture. 
     When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.