BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This device relates to the servicing of vehicles that require access to the underside and specifically to large vehicles such as trucks and the like. 
     2. Description of Prior Art 
     Prior art devices of this type are typically defined as excavated pits that are built in place which are used for vehicle servicing to eliminate the need to lift a vehicle in the air to gain access to the underside serviceable components. Such service pits are located in garage service areas and are typically custom built in place for strength and durability and ease of construction. Access to such service pits are by ladder or underground access tunnels with remote stairs as typically found in vehicle oil changing facilities. Service pits of this type are particularly useful and required in the service of large heavy vehicles such as trucks where it is often impossible to elevate the vehicle for service. 
     Examples of in ground service pits can be seen in U.S. Pat. Nos. 3,866,624, 4,960,150, 5,701,706, and 5,738,160. 
     In U.S. Pat. No. 3,866,624 an automobile service lane with servicing pit can be seen wherein a pit is provided adjacent gasoline pumps. A retractable pit shield is disclosed disposed within a recess portion along one side of the pit. 
     In U.S. Pat. No. 4,960,150 a movable safety cover for vehicle service pits is shown in which a cover configuration is positioned over the service pit in multiple retractable overlapping sections which have wheel assemblies on their adjacent corners. 
     In U.S. Pat. No. 5,701,706 an underground service bay for vehicles and process for constructing same is disclosed. The service bay is formed of a tunnel like structure of molded fiberglass that is buried in the ground with a concrete cap to provide vehicle support. 
     Finally, in U.S. Pat. No. 5,738,160 a removable cover for automobile service pit and method of installation is claimed in which a safety cover made up of a webbing material is deployable between tracks positioned on either side of the longitudinal edge openings of the service pit. 
     Applicant&#39;s device illustrates a pre-fabricated base structure that has a plurality of rigid cover grates that are deployable from inside the bay. A retractable folding stairway allows for select access upon activation to the bay. 
     SUMMARY OF THE INVENTION 
     A self-contained pre-fabricated in ground service bay for providing an access opening to the underside of vehicles to be serviced. The service bay has deployable safety closure grates and a movable stairway access assembly that can be retracted within the bay during use. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational section with portions broken away of the service bay of the invention; 
     FIG. 2 is an end elevation section illustrating the access stairway assembly; 
     FIG. 3 is a perspective view of a portion of the service bay with the access stairway deployed; 
     FIG. 4 is a perspective view of an installed service bay; 
     FIG. 5 is an enlarged side elevational view of the stairway railing retraction and activation assembly in deployed position; 
     FIG. 6 is an enlarged side elevational view of the stairway railing ratchet and activation assembly in closed position; 
     FIG. 7 is an end elevational view of a fixed access ladder assembly within the bay; and 
     FIG. 8 is a partial top plan view of the fixed ladder assembly shown in FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2 of the drawings, an underground service bay  10  of the invention can be seen installed within the ground G. The service bay  10  is of a generally elongated rectangular configuration having oppositely disposed sidewalls  11  and  12  with a floor  13  extending therebetween and respective end walls  14  and  15  as best seen in FIG. 1 of the drawings. A pair of oppositely disposed elongated flanges  16  and  17  extend at right angles from along the respective top perimeter edges of the sidewalls  11  and  12 . Elongated lighting retention brackets  18  extend vertically from the flanges  16  and  17  in spaced relation to said respective sidewalls  11  and  12  forming lighting channels at  19  inwardly and along the top of the respective sidewalls  11  and  12 . Lighting fixtures  20  are positioned within the lighting channels  19  as will be well understood by those skilled within the art. 
     A number of longitudinally spaced flange support posts  21  extend vertically from the floor  13  to the flange  16  with a plurality of intermediately positioned angle support brackets  22  extend between the sidewall  11  and the top flange  16  as will best be seen in FIG. 2 of the drawings. 
     A plurality of longitudinally spaced exterior stabilization braces B extend around the exterior surfaces  24  of the walls  11  and  12  exterior surface of the floor  13  to stiffen and support same. 
     It will be evident from the above description that the service bay  10  will have an elongated rectangular service opening at  26  between the respective flanges  16  and  17  for access to the undersides of a vehicle (not shown). Accordingly, a series of safety panels  27  are pivotally secured to the sidewalls  12  by multiple apertured brackets  28 . Each of the panels  27  is formed from surface grating  29  on a frame  30  as best seen in FIGS. 1 and 2 of the drawings. Support arms  31  extend from the panels  27  to the apertured brackets  28  and are pivotally secured by pivot pins  32 . The support arms  31  are longitudinally offset at  33  so as to position the respective surface grating  29  flush within the opening at  26 . Alignment stop brackets  34  extend from the respective panels to engage the flange  16  restricting the panels  27  for the flush alignment hereinbefore described. Each of the panels  27  have multiple hydraulic piston and cylinder actuation assemblies  35  pivotally secured to wall mounting brackets  36  and pairs of activation arms  31  pivoted to the respective apertured brackets  28 . 
     A retractable stairway assembly  37  can be seen in FIGS. 1 and 2 of the drawings having multiple stair treads  37 A each of which is of an alternating tread depth extending between outer stair stringers  38  and  39  and defined therebetween by a center support stringer  40  as illustrated in FIG. 3 of the drawings. This alternating depth tread arrangement provides for a shortened stairway of increased angular ascension. The stairway  37  is supported on respective pairs of wheel assemblies  41  and  42  engageable in upper and lower guide support tracks  41 A and  42 A respectively inside the bay. 
     A hydraulic piston and cylinder assembly  43  secured to the sidewall  12  and lower wheel assembly  42  moves the stairway assembly  37  within the service bay from an access position indicated in solid lines to a non-use stored position as shown in broken lines. A collapsible stair handrail assembly  44  has a pair of spindles  45 A and  45 B pivotally secured to the stringer  39  and to a rail  45 . 
     Referring now to FIGS. 5 and 6 of the drawings, a tensioning and release mechanism  46  inner engages the stair spindle  45 B having a central hub  47  with a pair of annularly offset engagement arms  48  and  49  extending therefrom. An elongated coil spring  50  extends from a bracket  51  on the bay floor  13  around the hub  47  within a spring guard  52  to a link  53  that pivotally extends from the end of the hereinbefore-described engagement arm  48 . 
     A deployment cable  54  is adjustably secured to the end wall  14  of the service bay  10  and to a link  55  pivoted to the engagement arm  49 . With the stair assembly in open access position, the spring  50  is expanded applying tension to the engagement arm  48  and against the deployment cable  54 . As the piston and cylinder assembly  43  pushes the stairway back to its stored position, shown in broken lines, tension on the cable  54  releases and the spring  50  rotates the hub  47  via the engagement arm  48  pivoting the stair spindle  45 B in a clockwise direction as viewed in FIG. 5 illustrated by directional arrow C. 
     The rail  45  and spindles  45 A and  45 B pivot downwardly retracting the handrail assembly  44  to a closed position as illustrated in FIG. 6 of the drawings. 
     Referring now to FIGS. 1,  2 ,  3  and  6  of the drawings, to open the stairway assembly  37  and deploy the handrail assembly  44 , it will seen that as the piston and cylinder  43  pulls the stairway  37  forward on its respective wheel assemblies  41  and  42  that the cable  54  goes into tension, illustrated in broken lines in FIG. 6, rotating the hub  47  and attached spindle  45 B as indicated by arrow D, unfolding the handrail assembly  44  to an upright access position as seen in FIG. 3 of the drawings against the tension of the spring  50 . 
     Referring now to FIGS. 7 and 8 of the drawings, the end wall is of the service bay  10  can be seen having an auxiliary fixed ladder assembly  55  secured thereon. The ladder assembly  55  has a plurality of fixed generally U-shaped rungs  56  that are horizontally disposed at vertically spaced intervals and extend outwardly from the wall surface  15 . A pair of safety handrail assemblies  57  are positioned in oppositely disposed relation alongside the rungs  56 . Each of the rail assemblies  57  has a guide tube  58  with telescopically extensible handrails  59  within. 
     In use, the respective handrails  59  are raised manually so as to extend from the service bay  10  and secured by a locking assemblies  59 A to aid the user in climbing down or up out of the service bay  10 . 
     During installation of the service bay  10  of the invention, it will be noted that it is positioned within an excavated opening in the ground G, it will initially be stabilized by pouring concrete around its respective end areas  60  and middle area  61 . Once stabilized, back fill  62  is used to bury the service bay  10  as will be well understood by those skilled in the art. 
     A finished floor  63  which in this example is poured concrete will overlie the respective flanges  16  and  17  and be flush with an upper surface  64  of the lighting channels  19  as illustrated in FIG. 1 of the drawings. 
     It will thus be seen from the above detailed description that a new and useful modular self-contained service bay pit enclosure has been illustrated and described that provides a unique service access to the underside of large vehicles. It will also be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the spirit of the invention.
A pre-fabricated service bay used for providing service access to the underside of vehicles. The service bay is fabricated as a single monolithic unit and then positioned in an excavated hole within a service building. The service bay has multiple safety cover grids that are hydraulically activated to enclose the bay's opening when not in use. An access stairway is retractable within the bay during use with a deployable safety handrail that collapses upon stairway retraction.