Patent Publication Number: US-4921732-A

Title: Railroad tie service vehicle and method for spray application of a preservative

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention. 
     The present invention relates generally to the servicing of railroad ties, and in particular to a vehicle for and a method of applying preservative to existing wooden railroad ties in situ. 
     2. Description of the Prior Art. 
     Wood has traditionally been, and will probably continue to be, the predominant material for railroad track ties. Wood has several advantages over alternative tie materials, such as concrete. Wood is a renewable natural resource and is available in many parts of the world at reasonable cost. Another important advantage of wood is its natural resiliency, which enables wooden railroad ties to absorb the dynamic loads that are associated with railroad traffic. Wooden railroad ties tend to be lighter in weight than comparable concrete railroad ties, and therefore can be relatively easily handled by installation and maintenance crews and equipment. 
     A significant disadvantage to wood railroad ties, on the other hand, is that they can be susceptible to decay and deterioration. Since wood is a cellulose material, it is subject to damage from fungus, decay, termite infestation, and exposure to the elements in unprotected, outdoor environments. 
     Preservatives including coal tar creosote are commonly applied to structural wood members, such as railroad ties, that will be exposed to the elements. However, the protection provided by such preservatives tends to lessen over time because the preservatives are susceptible to the deteriorating effects of sunlight, precipitation, freeze-thaw cycles, etc. Thus, the useful service life of a railroad tie is generally limited by the effectiveness of its preservative treatment. 
     Railroad ties are particularly susceptible to damage and deterioration in the connection areas adjacent to each end where the tracks are attached. The normal construction of a railroad track involves the placement of ties at intervals of about eighteen to thirty inches in a roadbed of ballast comprising crushed rock or the like. A pair of steel plates are then placed on the connection areas of each tie to support the rails, and spikes are driven through the plates and into the railroad ties, the spike heads securing the rails in place by clamping the lower rail flanges to the plates. 
     The spikes penetrate interior portions of the ties that may have received little or no preservative. The tie ends are often split by the spikes, exposing other untreated interior portions. Under railroad traffic, these connection areas are naturally subjected to more stress than any other part of the railroad tie, whereby they tend to experience the greatest amount of wear. Moreover, the plates tend to collect and retain moisture, thereby exacerbating deterioration at the connection areas. On most wooden ties the condition of these connection areas tends to deteriorate more rapidly than other portions, yet the connection areas are the most critical for providing rail support and maintaining the integrity of the railroad. Hence, the useful service life of an entire railroad tie is generally limited by the structural integrity of its connection areas. 
     Several methods have heretofore been employed to correct railroad tie deterioration problems. For example, wood preservative can be injected into the tie connection areas, generally through the holes in the plates that are not occupied by spikes. In normal railroad construction two spikes per plate are used, although the plates typically have at least four holes. Thus, each such plate has two holes available for preservative injection. Although railroad tie life can be prolonged somewhat by this method, a substantial amount of damaged or decayed wood material often remains. The additional preservative may slow the deterioration process, but generally it will not significantly improve the condition of the tie. When enough ties become so deteriorated that a railroad track is deemed unusable, the ties must be replaced at great expense in time and labor. 
     An intermediate procedure is sometimes employed whereby the tracks are removed, the connection areas are planed down by a resurfacing vehicle, preservative is applied to the exposed wood at the connection areas, and the tracks are remounted. Railroad maintenance equipment is available for removing the spikes, setting the rails aside, scooping out the surrounding ballast and planing the connection areas of the existing ties. Heretofore the preservative has generally been applied manually. However, manual application of the preservative is not particularly desirable because of the inherent difficulties in accurately dispensing predetermined quantities of preservative with manual applicators, the limitations on the amount of preservative that a worker can carry and the hazards to the worker associated with handling the preservative. Creosote-based preservatives are generally toxic and can irritate the skin and eyes of a worker exposed to them. Respirators, face masks and other protective clothing must normally be worn when handling such preservatives. 
     The present invention addresses these problems associated with preservative application by providing a device and a method for applying the preservative automatically, efficiently and safely. 
     SUMMARY OF THE INVENTION 
     In the practice of the present invention, a railroad tie service vehicle is provided which includes a chassis system, a drive system and an application system. The chassis system includes front and back ends, opposite sides and a deck. Containers of preservative may be transported on the chassis deck. The drive system includes an internal combustion engine driving a hydraulic pump. Front and rear pairs of wheels are mounted on the chassis, the rear wheels being driven by a live axle connected to the hydraulic motor. A pair of track subassemblies are mounted on swing arms at the front and back ends of the chassis, and are extendable and retractable between drive and transport positions. The track subassemblies include endless tracks driven by hydraulic motors. 
     The application system includes a preservative pump communicating with a preservative container, an actuating subassembly adapted to selectively engage railroad ties and a sprayer subassembly adapted to spray preservative in response to engagement by the actuating subassembly with railroad ties. 
     In the practice of the method of the present invention, the rails along one side of a section of railroad track to be treated are removed. The vehicle wheels on one side of the chassis engage the remaining rails, and on the other side the vehicle is supported and driven by the track subassemblies. As the actuating subassembly engages the railroad ties, a discharge valve opens and preservative is sprayed onto the railroad tie connection areas. When the actuating subassembly disengages railroad ties, the discharge valve is closed. 
     OBJECTS OF THE INVENTION 
     The principal objects of the present invention are: to provide a service vehicle for railroad ties; to provide such a vehicle for applying preservative to railroad ties; to provide such a vehicle which automatically dispenses preservative; to provide such a vehicle which minimizes preservative waste; to provide such a vehicle which uniformly applies preservative to railroad ties; to provide such a vehicle which substantially separates an operator from the preservative; to provide such a vehicle which is relatively safe for an operator to use; and to provide such a vehicle which is efficient in operation, capable of a long operating life, economical to manufacture and particularly well adapted for the proposed usage thereof. Further objects of the present invention include: to provide a method of servicing railroad ties in situ; to provide such a method wherein preservative is applied to the railroad ties automatically; to provide such a method which is relatively safe and efficient; and to provide such a method which is particularly well adapted for the proposed usage thereof. 
     Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
     The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a vehicle for applying preservative to railroad ties, embodying the present invention. 
     FIG. 2 is a top plan view of the vehicle. 
     FIG. 3 is a rear elevational view of the vehicle. 
     FIG. 4 is a fragmentary, side elevational view of the vehicle, particularly showing an application system. 
     FIG. 5 is an enlarged, horizontal, cross-sectional view of the vehicle, taken generally along line 5--5 in FIG. 4. 
     FIG. 6 is an enlarged, side elevational view of the application system, with a preservative valve in its open position. 
     FIG. 7 is an enlarged, fragmentary, vertical cross-sectional view of the vehicle taken generally along line 7--7 in FIG. 1. 
     FIG. 8 is an enlarged, fragmentary, horizontal cross-sectional view of the vehicle taken generally along line 8--8 in FIG. 7 and particularly showing the application system. 
     FIG. 9 is an enlarged, fragmentary, side elevational view of the application system particularly showing an actuating switch thereof. 
     FIG. 10 is an enlarged, fragmentary, vertical cross-sectional view of the vehicle taken generally along line 10--10 in FIG. 1 and particularly showing a drive arrangement for a live rear axle with a rear wheel engaged on a rail. 
     FIG. 11 is an enlarged, fragmentary, vertical cross-sectional view of the vehicle, particularly showing a hydraulic drive motor for the rear axle. 
     FIG. 12 is a top plan view of the vehicle in operation on a section of railroad track with the right-hand rail removed. 
     FIG. 13 is a top plan view of the vehicle in operation on a section of railroad track with the left-hand rail removed. 
     FIG. 14 is a side elevational view of the vehicle as it enters a street crossing. 
     FIG. 15 is a side elevational view of the vehicle in the street crossing. 
     FIG. 16 is a side elevational view of the vehicle as it leaves the street crossing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     I. Environment and Introduction 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     Referring to the drawings in more detail, the reference numeral 1 generally designates a self-propelled preservative application vehicle embodying the present invention. Without limitation on the generality of useful applications for the vehicle 1, it is shown and described in an exemplary operation for repairing a railroad line 2 including a ballast roadbed 3, railroad ties 5 and rails 6 including connection areas 7 upon which steel plates 8 are placed for supporting the rails 6. The rails 6 and the plates 8 are secured to the ties 5 by spikes 9 in the normal manner. The tie connection areas 7 provide primary support for the railroad traffic loads through the rails 6 and the plates 8. Each connection area 7 is located adjacent to a respective railroad tie end 10. Before treatment with the preservative application vehicle 1, the connection areas 7 are preferably planed down with a vehicle (not shown) that is commercially available and commonly used for this purpose by the railroads. 
     After being planed down, shallow notches 11 are formed in the railroad ties 5 at the connection areas 7 whereat relatively sound, untreated wood is exposed. By planing the railroad ties 5 in the connection areas 7, an external layer of decayed wood is preferably removed, exposing a connection area surface 12 of relatively sound, raw wood that previously has received little or no preservative since most of the original preservative is concentrated at or near the exterior surfaces of the railroad ties 5. Without limitation on the generality of materials that may be applied with the vehicle 1, the preservative may comprise creosote-based preservative available under the trademark &#34;ADZ-LIFE&#34; from Osmose Wood Preserving, Inc. of Buffalo, New York. 
     The vehicle 1 generally comprises a chassis system 21, a drive system 22 and a preservative application system 23, which will be described below in detail. 
     II. Chassis System 
     The chassis system 21 includes a front 24, a back 25 and opposite sides 26. A framework 28 is fabricated from structural steel members and mounts a deck 29. Adjacent to the chassis front 24, a boom assembly 30 is provided for loading and unloading containers 31, e.g., fifty-five gallon drums, of preservative. Adjacent to the chassis back end 25 a storage locker 32 is provided and mounts an operator&#39;s seat 33. In front of the operator&#39;s seat 33 a pedestal 36 mounts a control panel 37. On both sides of the pedestal 36, the deck 29 includes application system access openings 40 selectively covered by hinged, sprayer access panels 39. 
     An engine base 41 is mounted on the deck 29 in front of the pedestal 36 and a preservative container area 44 is located in front of the engine base 41 and adjacent to the boom assembly 30. A superstructure frame 42 is mounted on the engine base 41 and includes front and back A-frame sections 45, 46 innerconnected at their tops by a longitudinally-extending superstructure beam 47. 
     III. Drive System 
     The drive system 22 includes a prime mover comprising, for example, an internal combustion engine 48 mounted on the engine base 41. A twenty-two horsepower diesel engine has been found to be sufficient to drive the vehicle 1 and to operate its application system 23. The engine 48 drives a hydraulic pump 51. A pair of freely rotatable front wheels 53 are mounted on a front axle 54 in proximity to the chassis system front end 24. It is not necessary that the front wheels 53 be driven. A pair of rear wheels 55 are mounted on the chassis system 21 in proximity to its back end 25 and are drivingly innerconnected by a live rear axle 56. A hydraulic drive motor 58 is mounted on top of the deck 29 in proximity to the chassis back end 25 and is drivingly innerconnected to the rear wheels 55 and the axle 56 by a chain 59 engaging a sprocket 60 coupled to the live rear axle 56 (FIGS. 10 and 11). 
     A pair of retractable drive track assemblies 63 are mounted on the chassis front and back ends 24, 25 and each includes a swing arm 64 with a proximate end 65 journaled in a respective pivot clevis 66 mounted on a respective chassis front or back end 24, 25 and a distal end 67. The swing arm distal ends 67 are each captured in one of the locking clevises 68 which are mounted in pairs on the chassis front and back ends 24, 25 in proximity to the chassis sides 26. 
     A pair of telescoping track jack subassemblies 71 are mounted on the swing arm distal ends 67 and each includes inner and outer telescopic tubes 72, 73 reciprocable with respect to each other by a hydraulic piston-and-cylinder unit 75 within the track jack subassembly 71. The track jack subassemblies 71 communicate with the hydraulic pump 51 via suitable hydraulic fluid lines 74. Although hydraulically-actuated track jack subassemblies 71 are disclosed, it will be appreciated that other actuating means may be provided, for example a pneumatic piston-and-cylinder unit or a screw-threaded rod with a motor drive. 
     The inner telescopic tubes 72 terminate at lower ends 77 mounting track clevises 78, which in turn mount track subassemblies 79. Each track subassembly 79 includes an endless track 80 driven by a hydraulic motor 81 communicating with the hydraulic pump 51 by suitable hydraulic fluid lines 82. The track subassemblies 79 are pivotally mounted on the track clevises 78 by pivot pins 83 aligned on transverse pivotal axes whereby the track subassemblies 79 can rock fore and aft in response to conditions that are encountered along the path of travel. The control panel 37 mounts a set of lever controls 86 for controlling the flow of pressurized hydraulic fluid to the track jack subassemblies 71, the hydraulic drive motor 58 and the drive track hydraulic motors 81. The control panel 37 also includes suitable controls 87 for the engine 48. A two compartment diesel fuel and hydraulic fluid tank 89 is mounted on the engine base 41 adjacent one side 26 of the chassis system 21 and supplies the engine 48 with diesel fuel and the hydraulic pump 51 with hydraulic fluid. 
     A foot pedal 90 is provided on the deck 29 behind the pedestal 36 and is connected to a hydraulic clutch valve (not shown), which in turn is connected to the hydraulic drive motor 58. When the foot pedal 90 is depressed, the hydraulic clutch valve is open and fluid is allowed to circulate through the hydraulic drive motor 58. When the vehicle 1 is being driven by the track subassembly 79, the hydraulic clutch valve is preferably open so that the rear wheels 55 are thus permitted to rotate freely. Preferably the foot pedal 90 is provided with a latch (not shown) for holding it in its down position with the hydraulic clutch valve open so that an operator of the vehicle 1 does not have to hold the foot pedal 90 down continuously when the vehicle 1 is being driven by the track subassemblies 79. 
     When the foot pedal 90 is released and raised, the hydraulic clutch valve closes, whereby hydraulic fluid is prevented from circulating freely through the hydraulic drive motor 58. Closing the hydraulic clutch valve has the effect of blocking or restricting the flow of hydraulic fluid through the hydraulic drive motor 58. When the live rear axle 56 is rotated by movement of the vehicle 1, its connection to the hydraulic drive motor 58 causes the latter to rotate and pump hydraulic fluid through the hydraulic drive system. Therefore, a braking action is applied to the live rear axle 56 when the foot pedal 90 is released and raised and the hydraulic clutch valve blocks or restricts hydraulic fluid flow since the closed hydraulic system will resist rotation of the hydraulic drive motor 58 and the live rear axle 56. 
     A caliper and disc brake system (not shown) is also provided on the axles 54, 56 and may be applied by an operator of the vehicle 1. 
     IV. Application System 
     The application system 23 includes an air compressor 91 which is driven by the diesel engine 48 and is mounted on the engine base 41. The application system 23 is adapted for placement in one of the side access openings 40 whereby it is suspended below the chassis system 21 and above the railroad ties 5. A mounting subassembly 94 includes a channel member 95 secured to and depending downwardly from the chassis framework 28 at the front of a respective access opening 40. The channel member 95 pivotably mounts upper and lower U-shaped brackets 97, 98. Each U-shaped bracket 97, 98 includes a pair of outwardly-extending end flanges 92 fixedly mounting respective L-shaped bolts 93 which are pivotally received in respective side flanges 96 of the channel member 95. 
     The U-shaped brackets 97, 98 mount a skid runner subassembly 101 including a vertical standard 102 pivotably connected to the brackets 97, 98 and terminating at a lower end 103. Each bracket 97, 98 also includes a center section 99 fixedly mounting a forwardly-extending U-shaped bolt which is pivotably received in the skid runner subassembly standard 102. A freely translatable, parallelogram linkage arrangement is thus formed by the channel member 95 and the standard 102, which remain parallel with respect to each other, and with the parallel upper and lower brackets 97, 98. These components define a parallelogram and are pivotally connected at their respective intersections by the bolts 93, 100. 
     The standard lower end 103 fixedly mounts a skid runner 105 having a body 106 and front and back ends 107, 108 whereat the body 106 is undercut with its front and back ends 107, 108 forming acute angles A1, A2 respectively with respect to the horizontal. The skid body 106 also includes upper and lower edges 109, 110. Front and rear skid ramp plates 111, 112 are mounted on the body front and back ends 107, 108 respectively and slope in respective directions upwardly and away from the center of the body 106. The skid ramp plates 111, 112 have upturned inner (lower) ends 113 to prevent the skid runner 105 from catching a railroad tie 5 and damaging the skid subassembly 101. The inner (lower) end 113 of the front skid ramp plate 111 is mounted flush with the skid body lower edge 110. The inner (lower) end 113 of the rear ramp plate 112 is spaced slightly (e.g., about one-fourth inch) above the skid body lower edge 110 (FIGS. 4 and 6). 
     A drumhead subassembly 119 is mounted on a respective preservative drum 31 and includes a pneumatic motor 120 driving a stirring device (not shown) for stirring the preservative contents of the container 31. The pneumatic motor 120 is connected to an air compressor 91 which communicates with an air tank 88. The drumhead assembly 119 also includes a preservative suction line 121 connected to a preservative pump 122 powered by the air compressor 91. A preservative supply line 125 extends from the pump 122 to a sprayer subassembly 127 mounted on the skid subassembly standard 102. 
     The sprayer subassembly 127 includes a discharge valve 128 connected to a T-fitting 129, which forms a manifold 130 connected to a pair of spray heads 131 each having a discharge nozzle 132. An actuating subassembly 143 is mounted on the supply line 125 and includes a pneumatic line 124 communicating with the air compressor 91 and an electrical line 145 including first and second leads 146, 147 (comprising, e.g., positive and negative) connected to an electrical power source (not shown). 
     The first electrical lead 146 communicates with a single pole, normally open, momentary contact actuating switch 149 mounted on the skid body 106 by bolts 150. The switch mounting bolts 150 are received in slots 151 in the skid body 106 so that the position and orientation of the switch 149 can be adjusted. The switch 149 includes a trigger 152 movable between a first position shown in solid lines in FIG. 9 whereat the switch 149 is open and a second position shown in phantom lines in FIG. 9 whereat the switch is closed. A jumper lead 155 and the second lead 147 are attached to a normally-closed, solenoid-actuated pneumatic valve 156. When the switch 149 closes, current flows from the first lead 146, through the switch 149 and through the jumper lead 155 whereby the pneumatic valve 156 opens. When the pneumatic valve 156 opens, pressurized air from the pneumatic line 144 passes through the pneumatic valve 156, through a coupling 159 and into one end of a pneumatic piston-and-cylinder unit 160 with a reciprocating piston rod 161. The piston rod 161 is coupled to an actuating lever 162 on the sprayer subassembly valve 128. The actuating lever 162 is connected to the skid body 106 by a return spring 163. 
     A preservative roller 166, which may comprise a paint roller, is suspended from the chassis system 21 behind the skid subassembly 101. 
     V. OPERATION 
     A section of railroad track 2 to be treated with the vehicle 1 according to the method of the present invention is taken out of service and the rails 6 along one side are removed and set aside. However, as will be explained more fully hereinafter, neither of the rails 6 at a street crossing 171 (FIGS. 14-16) are removed. A respective front wheel 53 and a respective back wheel 55 at the other chassis side 26 engage the remaining rail 6 and the track jack subassemblies 71 lower the drive track assemblies 63 to their extended driving positions whereby the wheels 53, 55 on the one side 26 are raised above the roadbed 3. The vehicle 1 is thus supported on a pair of wheels 53, 55 on one side and on the drive track assemblies 63 on the other side where the rail 6 has been removed. The drive track assemblies 63 are syncronized in operation and the vehicle 1 may be driven entirely by them. 
     As shown in FIG. 6, the skid lower edge 110 has a length between the ramp plate ends 113 approximately equal to the center-to-center spacing between the railroad ties 5. The skid runner 105 is thus designed to rest substantially continuously on the notched connection areas 7 of the railroad ties 5. Preferably the notched connection areas 7 are relatively level, whereby the skid runner 105 will travel on a substantially level path. 
     The roadbed 3 on which the drive track assemblies 63 ride, however, is often not level so that the vehicle 1 may tilt slightly from one side to the other in motion. The application system 23, however, is designed to compensate for such tilting and to maintain the sprayer subassembly 127 in substantially continuous contact with the railroad ties 5. This is accomplished by the pivotal, parallelogram linkage between the channel member 95, the brackets 97, 98 and the skid standard 102. Since the entire sprayer and actuating subassemblies 127, 143 are mounted on the skid standard 102, they likewise &#34;float&#34; with the skid subassembly 101 to compensate for the slight tilting of the vehicle 1. The purpose of this arrangement is to maintain the skid runner 105 in substantially continuous contact with the railroad tie connection areas 7. The operator of the vehicle 1 can level it with the track jack subassemblies 71. Alternatively, an automatic leveling mechanism can be provided. 
     The front skid ramp plate 111 is normally the first part of the vehicle 1 to engage a railroad tie 5, and its inner (lower) end 113 is mounted flush with the skid body lower edge 110 so that the weight of the application system 23 may be distributed across the width of the front skid ramp plate 111 where it slidably contacts a respective railroad tie connection area 7. Upon engaging a railroad tie 5, the switch trigger 152 will swing from its open position shown in solid lines in FIG. 9 to its closed position shown in phantom lines in FIG. 9 whereby the switch 149 will close and electrical current will flow through the first lead 146, through the switch 149, through the jumper lead 155 and to the pneumatic, solenoid-actuated valve 156. The valve 156 will thus open, pressurized air will flow through the pneumatic line 144, through the pneumatic valve 156, through the coupling 159 and into the pneumatic piston assembly unit 160 whereby the piston rod 161 will be retracted and will lift the actuating lever 162, opening the sprayer valve 128. Preservative will thus flow through the supply line 125, the valve 128, the T-fitting 129, the manifold 130, the spray heads 131 and be sprayed from the nozzles 132 on either side of the skid runner 105. 
     The nozzles 132 are oriented forwardly and downwardly whereby most of the preservative sprayed therefrom is placed on the railroad tie connection area 7. By properly adjusting the actuating subassembly 143, relatively little of the preservative will be wasted on the roadbed 3, and maximum preservation and benefit will be obtained. 
     The inner (lower) end 113 of the rear skid ramp plate 112 is spaced above the skid body lower edge 110 so that preferably only the skid body lower edge 110 contacts the railroad tie connection area 7 which has just been coated with the preservative. By spacing the inner (lower) end 113 of the rear skid ramp plate 112 above the railroad tie connection area 7, in normal operation most of the preservative will remain on the railroad tie connection area 7 and will not be pushed off by the inner (lower) end 113 of the rear skid ramp plate 112 as it passes over the railroad tie connection area 7. The preservative roller 166 then rolls over the connection area 7 to which preservative has just been applied to distribute the preservative thereover. 
     In the method of the present invention, both rails 6 are left in place at a street crossing 171. As the vehicle approaches the street crossing 171, the front drive track assembly 63 is raised to a retracted travel position with a respective track jack subassembly 71 whereby both front wheels 53 engage the rails 6 (FIG. 14). 
     The rear drive track assembly 63 is then raised (FIG. 15) whereby all four wheels 53, 55 are on the rails 6. In this configuration the vehicle 1 is driven by the hydraulic drive motor 58 which is coupled to the live rear axle 56. When the vehicle 1 leaves the street crossing 171 (FIG. 16), the procedure is reversed whereby first the front drive track assembly 63 is lowered and then the rear drive track assembly 63 is lowered to resume normal operation. 
     When converting the vehicle 1 for operation on the other side, the drive track assemblies 63 are raised whereby the vehicle 1 is supported on all four wheels 53, 55. The swing arms 64 are then released from the locking clevises 68, swung to the other side and locked into respective locking clevises 68 adjacent the other chassis side 26. The application system 23 is then removed from one of the access openings 40 and placed in the access opening 40 adjacent the other chassis side 26 by lifting the other access panel 39. The vehicle 1 can then be driven onto a track section where one of the rails 6 has been removed, whereat the drive track assemblies 63 would be lowered to resume normal operation. 
     It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.