US2655114A

US2655114A - Drop pit apparatus

Info

Publication number: US2655114A
Application number: US181264A
Authority: US
Inventors: Lloyd H Holdeman; Hugh K Hybarger
Original assignee: Manning Maxwell and Moore Inc
Current assignee: Manning Maxwell and Moore Inc
Priority date: 1950-08-24
Filing date: 1950-08-24
Publication date: 1953-10-13
Anticipated expiration: 1970-10-13

Description

13, 1953 L. H. HOLDEMAN ETAL. 9

DROP PIT APPARATUS Filed Aug. 24, 1950 4 sheets-sheet 1 I i mvwmfiamw Llo d, W Wolelevmmm :431.

Oct. l3 1953 L. H. HOLDEMAN ETAL 296559114 DROP PIT APPARATUS Filed Aug. 24, 1950 4 Sheets-Sheet 2 a5 [3 -Hakiemp m nem q .Q-l bur Oct. 13, 1953 L. H. HOLDEMAN ETA'L 2,655,114

DROP PIT APPARATUS Filed Aug. 24, 1950 4 Sheets-Sheet 4 m Ln mad LIO d. wodemclm Q-hgkQ-Q-lgkaargew Prom EV Patented Oct. 13, 1953 DROP PIT APPARATUS Lloyd H. Holdeman and Hugh K. Hybarger,

Muskegon, Mich., assignors to Manning, Maxwell & Moore, Inc., Muskegon, Mich., a corporation of New Jersey Application August 24, 1950, Serial N 0. 181,264

21 Claims. 1

The invention relates to drop pit apparatus of the type used in railroad shops for removing, replacing or repairing the trucks or Wheels of locomotives and other vehicles and for trans porting the trucks and wheels between the various service tracks of the shop.

One object of the invention is to provide improved elevator mechanism for drop pit apparatus of the above general character which affords smoother action in all movements of the mechanism and more precise control of such movements.

A more specific object is to provide a dual elevator drop pit apparatus in which the operation of the elevator mechanisms is coordinated so that each is brought into action automatically at the proper time, thus allowing the attendant to devote his attention to other duties involved in the operation of drop pit apparatus and correspondingly increasing the operating efficiency and safety of the apparatus.

Another object is to provide an improved arrangement for insuring accurate alinement of a drop pit table with the pit structure by which the table is supported.

A further object is to provide an elevator table of improved construction which especially adapts it for operation with a dual elevator mechanism.

It is also an object of the invention to provide improved mechanism for disengageably coupling the elevator mechanism with the elevator table.

Other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment illustrated in the accompanying drawings, in which:

Figure 1 is a perspective view of drop pit apparatus embodying the features of the invention.

Fig. 2 is an end elevational view of the apparatus showing the drop table raised above its normal pit bridging position.

Fig. 3 is a fragmentary side view of the apparatus showing the drop table in an intermediate position.

Fig. 4 is a view similar to Fig. 3 showing the drop table lowered to transport position.

Fig. 5 is a fragmentary transverse sectional view of the pit showing the guide means for locating the drop table in alinement with the service track.

Fig. 6 is a front view of the guide mechanism shown in Fig. 5.

Fig. 7 is a fragmentary sectional view taken in offset planes substantially on the line 1-1 of Fig. 4.

Fig. 8 is a fragmentary sectional view taken 2 in a plane substantially on the line 8-8 of Fig. 2.

Fig. 9 is a diagrammatic view of the hydraulic and electrical circuits for the apparatus.

While the invention is susceptible of various modifications and alternative constructions, we have shown in the drawings and will herein describe in detail the preferred embodiment, but it is to be understood that We do not thereby intend to limit the invention to the specific form disclosed, but intend to cover all modifications and alternative constructions falling Within the spirit and scope of the invention as expressed in the appended claims.

By way of illustration the invention has been shown as incorporated in apparatus adapted to operate in a pit H) which intersects and extends beneath a series of railroad tracks II (Figs. 5 and 6) such as those commonly provided in railroad repair shops and generally known as service or release tracks. To permit locomotives or other vehicles to be run over the pit and their wheels or trucks to be positioned for lowering therein, releasable drop tables 12 are provided for bridging the pit at the various track intersections. These tables [2 may be of any preferred type of either one piece or sectional construction, such, for example, as shown in the Minty Patent 2,196,468, issued April 9, 1940.

In general, drop pit tables of the above general character comprise a rectangular frame adapted to be supported in pit bridging position by retractible latch bars i3 cooperating with supporting ledges l4 (Figs. 5 and 6) on the side walls of the pit. Spaced guide elements H on the table l2 cooperate with guide bars [4' adjacent the ledges M to aline the latch bars with the ledges as the table is raised.

The latch bars i3 may be projected and retracted manually or by power, as preferred. In the case of sectional drop pit tables, a separate subtop I2 is supported from the main top by retractible latches l3 (Fig 2). The table [2 is provided on its upper face with rails i5 extending across both the main top and subtop and spaced apart to aline with the rails of the service track ll, thus extending such tracks across the pit when the table is latched in pit bridging position.

Drop pit apparatus of the type with which the present invention is concerned is conveniently provided with elevator means for raising and lowering the drop table [2 and with means for transporting the same along the pit l6 for a sso ciation with the various service and release tracks in the shop. For this purpose the elevator means is mounted on a carriage I6 equipped with flanged wheels II adapted to run on rails I8 forming a track at the bottom of the pit.

The exemplary carriage I6 as shown comprises longitudinal girders I9 built up, in this instance, of heavy channel members secured together in parallel spaced relation. These girders are connected at opposite ends by cross beams 20. Intermediate members 2| extending between the cross beams generally centrally of the carriage provide a platform for supporting the power drive mechanism of the apparatus including a motor M for traversing the carriage on the pit track I8. As shown, the motor M is drivingly connected with one of the wheels I! at each side of the carriage by means of a suitable speed reducing transmission 22 and a drive shaft 23 (Figs. 1 and 2). At each corner of the carriage an upright post 24 is provided for guiding a vertically movable elevator table assembly 25.

When a truck or set of wheels is to be removed from a vehicle the drop table I2 is latched in pit bridging position at one of the service tracks and the vehicle is run over the pit so as to spot such wheels or truck on the table track I5. To facilitate the disconnection of the wheels or truck from the vehicle it is usually necessary to compress their springs and thus relieve the pressure on the retaining bolts. This is done by raising the table I2 a short distance above track level. A relatively small vertical movement is sufiicient for this operation, but it will be evident that a relatively heavy thrust is required to produce it.

Upon disconnection of the wheels or truck from the vehicle, the table I2 is lowered until the load 1 clears the running gear of the locomotive and any other drop tables bridging the pit at other service tracks. With the table in such lowered or transport position the carriage IE is traversed along the pit to another service track and the drop pit table is raised to track level to permit the wheels or trucks to be rolled off for repairs or other attention. To replace the wheels or trucks the sequence of operations above described is simply reversed.

In accordance with one aspect of the invention. the elevator means is constructed and arranged so that each phase of the table raising and lowering operation may be carried out in the quickest,

most efiicient manner by mechanism especially suited for the character of the operation. More particularly. the invention provides dual elevator mechanisms, one for raising and lowering the drop table through the range in which heavy loads are imposed upon it, and the other for raising and lowering the drop table through the range in which lighter loads are involved and high speed operation is desirable. These elevator mechanisms may be conveniently identified as heavy duty and light duty mechanisms, and will be so referred to hereinafter.

The raising and lowering of the drop table I2 is effected by the elevator mechanisms through the medium of the elevator table assembly 25. To accommodate the action of the two mechanisms the table is constructed in two superimposed relatively movable sections, including a lower section 26 and an upper section 27 each associated individually with one of the elevator mechanisms. In the preferred form shown, the lower table 26 comprises a generally rectangular frame made up of end members 28 and side members 29 welded or otherwise secured together to form a strong and rigid structure. At each corner of this frame there is an upright box-like housing 30 open at its lower end to receive one of the carriage guide posts 24 and adapted to cooperate with the post in guiding the table section in its up and down movements.

The upper elevator table section 21 also comprises a rigid rectangular frame having end members 3I and side members 32 joined to form a tion is somewhat narrower than the lower section tion is some what narrower than the lower section so as to afford clearance between the

side members

29 and 32 of the table sections for the accommodation of the heavy duty elevator mechanism and other parts of the structure, as will appear presently. The length of the upper table section is such, however, that the end members 3| are adapted to rest on the corresponding members of the lower table section to support the upper section thereon when the heavy duty elevator mechanism is idle.

Suitable guide means is provided to maintain the two table sections in alinement while permitting raising or lowering of the upper table section with respect to the lower section. For this purpose spacer guide plates 33 are ri idly attached to each of the end members ill of the upper table section with the plates positioned to slide through the open central portion of the end members 28 of the lower table section, as shown in Fig. 8. One of the guide plates 33, preferably the outer one, is provided at each end with a vertically disposed outwardly projecting guide rail 34 adapted to slide in a channel formed by parallel spaced guide bars 34a secured to the adjacent face of the member 28.

In the long range high speed movements of the elevator table assembly the

table sections

26 and 27 operate as a unit. The light duty elevator mechanism is, therefore, associated with the lower table section 26 and is operative to raise and lower it through a predetermined range of vertical travel. During such movements the lower table section acts as a support for the upper table section 21. In the working or heavy duty range, which has its lower limit substantially coincidental with the upper limit of the range of the lower table section, the upper table section 21 alone is active and provision is therefore made for associating it individually with the heavy duty elevator mechanism.

In the preferred form of the apparatus both elevator mechanisms are of the pressure fluid operated type and both are preferably of the type having operating elements movable vertically upwardly or downwardly in accordance with the manner in which pressure fluid is supplied thereto. Thus the light duty elevator mechanism comprises a plurality of pressure fluid operated actuators each including a cylinder 35 closed at one end and having a working piston 36 (Figs. 3 and 9) with the piston rod 3'! projecting from the other end. In the exemplary apparatus four of the actuators are provided, one interposed between each corner of the carriage I5 and the corresponding corner of the lower table section 26. Preferably each actuator cylinder 35 is supported in an upright position with its closed end down and with the piston rod 3'! projecting into the housing 33. Support for each cylinder may be conveniently provided by a supporting plate 38 carried by the girders I9. Within each of the housings as there is provided a transverse plate or block 39 (Figs. 3 and 9) forming an abutment for engagement by the upper end of the associated actuator piston rod 31. The abutments 39 are located so as to clear the post 24 when the elevator table is lowered to the transport position in which it rests directly on the carriage 16 shown, for example, in Figs. 4 and 5.

The light duty elevator mechanism of the exemplary apparatus is designed to move the elevator table assembly between the lowered or transport position shown in Fig. 4 and an intermediate position shown in Fig. 3 in which the drop table [-2 is located slightly below floor level. Raising of the drop table from the inter-mediate position to and above floor level (see Fig. 2) is effected by the heavy duty elevator mechanism through the movement of the upper table section 2'1, while the lower table section 216 remains stationary at the intermediate position. The heavy duty elevator mechanism also comprises a plurality of pressure fluid operated actuators, four in the present instance, supported on the carriage 16 adjacent the four corners of the table section 21. Each actuator comprises .a cylinder 40 (Figs. 2-4 and 9) closed at one end and having a Working piston ill with a piston rod 42 projecting from its other end.

As the working range of the drop table 12 is small, the cylinder 40 may be relatively short and is preferably of substantially larger diameter than the cylinder of the light duty elevator mechanism. To position the actuators for cooperation with the upper table section, each of the cylinders is supported on the carriage l6 in an elevated position conveniently on a shelf or ledge 43 formed by a laterally ofiset extension of one of the guide posts .24.

To allow the light duty elevator mechanism to function without interference from the heavy duty mechanism, provision is made for releasably associating the latter with the upper table section :27. For this purpose the table section is provided with a series of retractible abutment members 45, one at each corner of the section, for cooperation with the piston rods 42. The members 45 may conveniently comprise heavy steel bars supported in suitable guides for horizontal endwise sliding movement into and out of the paths of the piston rods 42. As herein shown the bars 45 are supported for movement between the retracted positions in which they are shown in Figs. 3 and 4, and the operative position shown in Figs. 2 and 9.

Suitable actuating means, preferably power operated, is provided for projecting and retracting the abutment bars 45. Preferably the actuating means is pressure fluid operated and, as shown,

includes a cylinder .46 (Figs. 2 and .9) Supported on a side member of the upper table section. A

piston 41 working in the cylinder 46 is connected by a piston rod 48 with a crank arm 49 fixed on a rockshait 59 journalled on and extending across the table section. This rockshait is operatively connected with each of the four abutment bars by crank arms and links 5i whereby all of the bars may be projected or retracted simultaneously.

Pressure fiuid for operating the several actuators of the apparatus is supplied by a pump P (Figs. 1, 2 and 9) driven by an electric motor MI assembled as a unit therewith and mounted on a casing which serves as a sump or reservoir for the fluid used in the system. The entire assembly may be conveniently supported on a platform formed by the cross members 21 of the carriage, as shown in Figs. 1 and 2. The pump P is arranged to draw fluid from the sump by way of an intake ondui 6 and to dis ar e t f i under pressure throu h a sup ly c n uit 5 i which is interposed a pressure control and unloading valve VI of conventional construction. This valve may be set by operation of a control valve V2 to maintain a predetermined pressure in the supply conduit when in the closed position shown in Fig. 9. The valve i effective to bypass substantially all of the fluid delivered by the pump to the sump at relatively low pressure when operated to its alternate or open position. A drain -58 conducts the fluid to the sump when the valve is open while a branch of the drain connects to the lower end of the valve to carry off fluid leaking around the valve plunger. The control valve as shown is operated by a sole- 11011152.

The supply conduit 5 has one branch 59 extending to a reversing valve V3 operable by solenoids S3 and S4 to direct fluid to the cylinders 35 of the light duty elevator mechanism for raising or lowering the table assembly, as required. For this purpose the valve is connected with opposite ends of the cylinders by conduits 60 and -61, in which are interposed suitable flow dividers FD for insuring uniform how to each of the cylindens irrespective of the distribution of the load on the table. Check valves V4 interposed in the conduit El together with associated by-passing needle valves V5 provide for adjustment of the speed of the actuators when lowering the table.

A second branch 6.2 of the supply conduit 51 extends to a reversing valve V6 connected by conduits 3 and with opposite ends of the cylinders ii} of the heavy duty elevator actuators. These conduits are likewise equipped with flow dividers FD, check valves V6, and bypass valves V5. Solenoids S5 and S6 are provided for operating the reversing valve.

Branch 52 of the supply conduit is also extended to reversing valves V1 and V8. Valve 'Vl, which is arranged for operation by solenoids S7 and st. directs pressure fluid by way of n ui 55 and to the cylinder 45 of the abutment positioning actuator to project or retract the abutment bars 65. Valve V8 is a manually operable valve mounted on the drop table '12 and adapted to direct fluid to a cylinder 5'. constituting a part of the power actuator for projecting retracting the table latch bars I 3. This cylfinder is fitted with a piston 68 having its piston rod 59 connected with the latch bars by a linkage 'l'll of well known construction. Since the cylinder- 46 is mounted on the table section 21, the connecting conduits 65 and 66, or at least portions of such conduits, are constructed of flexible tubing to accommodate the relative movements of the cylinder with respect to the control valve which is preferably assembled directly with the pressure fluid unit. Gylinder 6'1 and its control valve V3 are both mounted on the drop table l2. Accordingly, both the fluid supply conduit ll and the exhaust conduit l2 for this valve are in the form of flexible tubes and are preferably connected with the system by separable couplings 13 of the type arranged to close automatically when the conduits are disconnected, as when the table i separated from the elevating and transport apparatus.

the exemplary apparatus the traverse motor M is of the pressure fluid operated type and receives its supply or pressure fluid from the pump P by way of a b an h conduit 14.. Sp n pressure fluid is returned to the sump by way of a b a ch of the d ain c nduit .A r v s ng valv V9 operat d by ol n ids 9 d SH) on ols the direction of rotation of the motor and thus the direction of travel of the pit carriage 16. For controlling travel speed a suitable metering valve VIU may be interposed in the conduit l4.

Control of the functioning of the apparatus is effected through the medium of an electrical control system designed to simplify the work of the operator and to afford maximum safety in the use of the apparatus. The electric current for operating the control system and for driving the pump motor M is supplied to the apparatus from the shop power lines through a flexible cable anchored to a conventional take-up reel '15 (Fig. 2) mounted on the carriage [6.

Referring to Fig. 9 of the drawings, it will be observed that the control system of the exemplary apparatus is of the low voltage type and that current is supplied thereto by way of a step down transformer T. For starting the motor Ml the control system includes a manually operable starting switch SS1 which, when momentarily closed, energizes a magnetic starter MS which may be of any preferred construction. The starter locks in by closing a sealing switch MSI so as to maintain the motor circuit closed upon release of the starting switch. The starter may be deenergized and the motor stopped by actuation of a normally closed manually operable stop switch SS2.

To eleminate any possibility of improper setting of the elements of the control switch when the pump P is idle, current for all functions of the system except motor starting is supplied through the sealing switch MSI when closed. Provision is also made for interrupting the current supply to the control system when the pressure fluid delivered by the pump P is diverted through the unloading valve Vl. For this purpose the solenoid S2 for the valve V2 which controls the unloading valve is incorporated in the control circuit so that it is normally energized when the control system is in operation and which maintains the valve V2 in the operating or pressure on position. The circuit for this solenoid may be interrupted manually by actuation of a normally closed locking type pressure stop switch SS3 thereby effecting release of the valve V2 and at the same time interrupting the current supply to the other elements of the control system. Release of the valve V2 sets the valve V! to by-pass fluid to the sump at reduced pressure. A signal lamp L connected in multiple with the solenoid S2 provides a visual indication of the pressure condition in the system.

In accordance with another aspect of the invention, the operation of the actuator for both the light duty and the heavy duty elevator mechanisms are controlled by a single set of manually operable controllers such as electrical switches through the medium of interlocking controls which automatically bring the actuators into action at the proper time during either the raising or lowering of the elevator table. This set of switches includes a raising switch RS and a lowering switch LS, each having two normally open contact sets designated A and B respectively and two normally closed contact sets C and D.

Cooperating with the raising and lowering switches in controlling the actuators are five limit switches LS-I, LS2, LS3, LS4 and LS5. Switch LSI has a single set of normally open switch contacts LSl-B which are closed as the lower table section 26 approaches its upper limit position. Switch LS2 has one set of switch contacts LSZ-A which are closed and a second set of contacts LS2-B which are open when the abutment bar 45 is in retracted position. Contacts LS2-A are opened and contacts LS2-B are closed when the abutment bar is projected to its fully advanced position. Switch LS3 also has two sets of contacts, LS3-A being open and LSi-B being closed when the table assembly is in its lower or transport position. The positions of the switches are reversed upon initial upward movement of the table assembly.

Switch LS4 is carried on the lower table section 26 and is actuated in accordance with the position of the upper table section. The switch has one set of contacts LS l-B which is closed when the upper table section is resting on the lower section. The contact set is opened, of course, when the upper table section is raised relative to the lower section. Switch LS5 is associated with the abutment bar 45 and has two sets of switch contacts. One set LS5-A is open when the bar is fully retracted and closes in the initial advance of the bar. The other set of contacts LS5-B is closed when the bar is fully retracted and opens incident to the advance of the bar.

Also included in the control system and cooperating with the above described elements are a pair of control relays RI and R2, respectively energized during the table raising and lowering operations. A second set of manually operable switches TF and TR respectively control the forward and reverse travel of the carriage [6 on the pit tracks. Each of these switches has a normally open contact set A, a normally closed contact set C and a normally closed contact set D.

Having in mind the switch and relay organization above described, the operation of the control system will now be explained. Assume first by way of example, that there is pressure in the hydraulic system, that the table assembly is in its lower position resting on the carriage l6 and that the abutment bars 45 are in retracted position. To raise the table assembly the raise" switch RS is momentarily actuated. This completes a circuit for the relay RI by way of normally closed contacts R2-I of relay R2 and manual switch contacts RS-A, LS-C, TF-D and TR-D. Relay RI becomes energized and closes switch Rl-l to complete a holding circuit over which it is maintained energized upon release of the switch RS and the consequent opening of its contacts RS-A.

Relay RI also closes a switch RI-3 to complete an energizing circuit for the solenoid S4 which shifts valve V3 into a position to direct pressure fluid to the lower ends of the cylinders 35 of the light duty elevator mechanism. The table assembly is now quickly raised to its upper limit position. In the initial upward movement of the table assembly, limit switch LS3-B is opened thus disabling the traverse mechanism of the carriage, as will appear presently. Limit switch LS3-A is closed to prepare the circuit for the lowering relay R2.

As the table assembly approaches its upper limit position, limit switch LSL-B is closed, thereby completing a circuit for the solenoid S8 which sets the valve V! for directing pressure fluid to the cylinder 46 to cause the abutment bar to be projected. The circuit for the solenoid S8 includes limit switch LSZ-A which opens immediately upon advance of the abutment bar, thus interrupting the circuit for the solenoid. Valve V1, however, remains set for advancing the bar until reoperated by its other solenoid ST.

upper table section is controlled automatically and at the proper phase of the operating cycle.

Traverse of the apparatus on the pit tracks is controlled through the medium of simple forward and reverse direction control switches, whose action is coordinated with that of the elevator mechanism in a manner to insure safe operation. Accidental or premature engagement of the carriage drive mechanism is effectively presented by interlocks which maintain the drive inactive at all times when the table assembly is raised from the carriage l6.

We claim as our invention:

1. In a drop pit apparatus, in combination, a carriage adapted to travel in a pit extending beneath a service track, a table assembly including a lower section adapted to rest on said carriage, an upper section adapted to rest on said lower section, power operated elevator mechanism associated with said lower table section for raising and lowering both sections together, other power operated elevator mechanism including a plurality of vertically movable elements for raising and lowering said upper table section, and means on said upper table section defining abutments movable from operative positions overlying said movable elements into retracted positions affording clearance for the elements in the lowering of said upper table section below the upper ends of said elements when said upper table section is resting on said lower table section, said abutments when in operative positions acting to establish thrust transmitting connections between said upper table section and the movable elements of said other mechanism.

2. In a drop pit apparatus, in combination, a carriage adapted to travel in a pit extending beneath a service track, a table assembly ineluding a lower section adapted to rest on said carriage, an upper section adapted to rest on carriage, means carried by said upper table section for operatively associating and disassociating that section and said second elevator mechanism, and power actuated means for operating said associating and disassociating means.

3. In a drop pit apparatus, in combination, a

carriage adapted to travel in a pit extending beneath a service track, a table assembly including a lower section adapted to rest on said carriage, an upper section adapted to rest on said lower section, a first power operated mechanism supported on said carriage operative to raise and lower both table sections through a predetermined range of travel, a second power operated elevator mechanism supported on said carriage, power operated means for disengageably coupling said upper table section with said second mechanism, and means controlled in part by the position of said first power operated mechanism for controlling the operation of said power operated means.

4. In a drop pit apparatus, in combination, a carriage adapted to travel in a pit extending beneath a service track, a table assembly including a lower section adapted to rest on said carriage, an upper section adapted to rest on said lower section, a first power operated mechanism supported on said carriage operative to raise and lower both table sections through a predetermined range of travel, a second power operated elevator mechanism supported on said carriage, power operated means for disengageably coupling said upper table section with said second mechanism, and control means actuated in accordance with the position of said first mechanism for rendering said power operated means effective at a selected point in said predetermined range.

5. In a drop pit apparatus, in combination, a carriage adapted to travel in a pit extending beneath a service track, a table assembly including a lower section adapted to rest on said carriage, an upper section adapted to rest on said lower section, a first power operated mechanism supported on said carriage operative to raise and lower both table sections through a predetermined range of travel, a second power operated elevator mechanism supported on said carriage, power operated means for disengageably coupling said upper table section with said second mechanism, manually operable control means for controlling the operation of both of said mechanisms, and control means actuated in accordance with the position of said first mechanism for modifying the action of said manually operable means in controlling said second mechanism.

6. In a drop pit apparatus, in combination, a carriage adapted to travel in a pit extending beneath a service track, a table assembly including a lower section adapted to rest on said carriage, an upper section adapted to rest on said lower section, a first power operated mechanism supported on said carriage operative to raise and lower both table sections through a predetermined range of travel, a second power operated elevator mechanism supported on said carriage, power operated means for disengageably coupling said upper table section with said second mechanism, manually operable control means for controlling the operation of both of said mechanisms, and control means actuated in response to the movements of the lower table section for rendering said manually operable means effective to control said second mechanism only when said lower table section is in its upper limit position.

7. In a drop pit apparatus, in combination, a carriage adapted to travel in a pit extending beneath a service track, a table assembly including a lower section adapted to rest on said carriage, an upper section adapted to rest on said lower section, a first elevator mechanism including a plurality of pressure fluid operated actuators each having a vertically movable element engageable with the lower table section to raise or lower the section, a second elevator mechanism including a plurality of pressure fluid operated actuators each having a vertically movable element, and a plurality of abutment members supported on said upper table section for projection into and retraction out of the paths of the movable elements of said second mechanism.

8. In a drop pit apparatus, in combination, a carriage adapted to travel in a pit extending beneath a service track, a table assembly including a lower section adapted to rest on said carriage, an upper section adapted to rest on said lower section, a first elevator mechanism including a plurality of pressure fluid operated actuators each having a vertically movable element engageable with the lower table section to raise or lower the section, a second elevator mechanism including a plurality of pressure fluid operated actuators each havin a vertically movable element, a plurality of abutment members supported 13 on said upper table section for projection into and retraction out of the paths of the movable elements of said second mechanism, and power operated means for projecting and retracting said abutment members.

9. In a drop pit apparatus, in combination, a carriage adapted to travel in a pit extending beneath a service track, a table assembly including a lower section adapted to reston said carriage, an upper section adapted to reston said lower section, a first elevator mechanism including a plurality of pressure fluid operated actuators each having a vertically movable element engageable with the lower table section to raise or lower the section, a second elevator mechanism including a plurality of pressure fluid operated actuators each having a vertically movable element, a plurality of abutment members supported on said upper table section for projection into and retraction out of the paths of the movable elements of said second mechanism, power operated means for projecting and retracting said abutment members, and control means for preventing operation of said second actuators to move said elements upwardly until said abutment members are fully projected.

10. In a drop pit apparatus, in combination, a carriage adapted to travel in a pit extending beneath a service track, a table assembly including a lower section adapted to rest on said carriage, an upper section adapted to rest on said lower section, a first elevator mechanism including a plurality of pressure fluid operated actuators each having a vertically movable element engageable with the lower table section to raise or lower the section, asecond elevator mechanism including a plurality of pressure fluid operated actuators each having a Vertically movable element, a plurality of abutment members supported on said upper table section for projection into and retraction out of the paths of the movable elements of said second mechanism, power operated means for projecting and retracting said abutment members, said elements engaging the projected members to raise said upper table section, and control means for preventing a retracting operation of said power operated means when said upper table section is in araised posi-' tion.

11. In a drop pit apparatus having a pit carriage and a table supported thereon, a plurality of cylinders mounted on the carriage in an upright position, a piston working in each cylinder and having a piston rod projecting from the upper end of the cylinder, means for directing pressure fluid alternately to opposite ends of said cylinders to move said piston rods upwardly and. downwardly, said cylinder and piston assemblies being disposed so that said piston rods clear the edges of the table, and a series of abutment bars supported on said table for sliding movement into and out of the paths of said piston rods.

12. In drop pit apparatus having a pit carriage and a table supported thereon, a plurality of cylinders mounted on the carriage in an upright position, a piston working in each cylinder and having a piston rod projecting from the upper end of the cylinder, means for directing pressure fluid alternately to opposite ends of said cylinders to move said piston rods upwardly and downwardly, said cylinder and piston assemblies being disposed so that said piston rods clear the edges of the table, a series of abutment bars supported and guided on said table for'projection into and retraction out of the paths of said piston 14 rods, and power operated means for projecting or retracting said bars simultaneously.

13; In drop pit apparatus having a pit carriage and a table supported thereon, a plurality of cylinders mounted on the carriage in an upright position, a piston working in each cylinder and having a piston rod projecting from the upper end of the cylinder, means for directing pressure fluid alternately to opposite ends of said cylinders to move said piston rods upwardly and downwardly, said cylinder and piston assemblies being disposed so that said piston rods clear the edges of the table, and a series of abutment bars supported and guided on said table for projection into and retraction out of the paths of said piston rods, power operated means for projecting or retracting said bars simultaneously, and control means operative to prevent delivery of pressure fluid to said cylinders for moving said piston rods upwardly when said bars are retracted.

14. in a drop pit apparatus having first and second elevator mechanisms for raising and lowering a table structure respectively through lower and upper ranges of travel, a control system for said. mechanisms including a manual controller, means operative upon momentary actuation of said controller for initiating operation of the first elevator mechanism, said mechanism continuing in operation until the table structure is raised to the limit of its lower range, and means operative upon actuation of said controller when said table structure is at said limit position for initiating the operation of the second elevator mechanism, such operation of the second elevator mechanism proceeding only while said controller is actuated.

15. In a drop pit apparatus having first and second elevator mechanisms for raising and lowering a table structure respectively through lower and upper ranges of travel, a control system for said mechanisms including a manually actuated controller, and control devices in said system automatically operative for rendering said controller effective to control the first mechanism only when the table structure is in its lower range and effective to control the second mechanism only when the table structure is in its upper range or at the upper limit of its lower range.

16. In a drop pit apparatus having an elevator table structure and first and second power operated elevator mechanisms for raising and lowering the table structure respectively through lower and upper ranges of travel, a control system for said mechanisms including a pair of manually operable controllers, one for initiating a raising action and the other for initiating a lowering action, and other control devices actuated in accordance with the position of said table structure for rendering said controller effectiv to control either of the mechanisms individually.

17. In a drop pit apparatus having an elevator table structure and first and second power operated elevator mechanisms for raising and lowering the table structure respectively through lower and upper ranges of travel, a control system for said mechanisms including a pair of manually operable controllers, one for initiating a raising action and the other for initiating a lowering action, and control devices operative when the tabl structure is at the upper limit of its lower range for rendering the lowering controller effective to control the operation of the first elevator mechanism and being further operative for rendering the raising controller effec- 1 5 tive for controlling the operation of the secon elevator mechanism.

18. In a drop pit apparatus having a horizontally movable carriage with a vertically movable table assembly supported thereon, pressure fluid operated elevator mechanism for raising and lowering the table assembly, pressure fluid operated drive means for traversing the carriage, a pump for supplying pressure fluid to said elevator mechanism and said drive means, an electric motor for driving said pump, a valve effective when operated to by-pass the fluid supplied by said pump, an electrical control system including means for starting and stopping said motor, for controlling the operation of said valve, for controlling the operation of said elevator mechanism and for controlling the operation of said drive mechanism, a first interlock device operative to disable all of the controls except the motor starting means when said motor is idle, and a second interlock device operative to disable the means for controlling the elevator mechanism and drive means when said by-pass Valve is operated.

19. In a drop pit apparatus, in combination, a generally rectangular carriage adapted to travel in a pit intersecting a service track, a table assembly includnig a pair of generally rectangular sections arranged one above the other, a first group of cylinders mounted adjacent the four corners of said carriage, each of said cylinders having a working piston and a piston rod projecting from its upper end for engagement with the lower table section, a second group of cylinders mounted adjacent the four corners of said carriage each having a working piston and a piston rod projecting from its upper end, and abutments on the upper table section engageabl by the piston rods of the second group, said abutments being retractible to afford clearance for the cylinders of the second group when the table assembly is being raised or lowered by the cylinders and pistons of the first group.

20. In a drop pit apparatus having a two section elevator table, in combination, a first power operated elevator mechanism for raising and lowering both table sections together, a second power operated elevator mechanism for raising and lowering one of the table sections alone, shiftable abutment members on said one table section adapted when projected to associate that section with said second mechanism for raising and lowering and when retracted to disassociate the section from the second mechanism, a power operated actuator for projecting and retracting said abutment members, a control system for the apparatus including a manually operable controller, control devices operative upon momentary actuation of said controller when the table sections are in a lowered position for initiating the operation of said first mechanism and continuing such operation until the table sections are raised to a predetermined position, other control devices operable upon movement of the table sections to said predetermined position for rendering said controller effective to initiate the operation of said actuator to project said abutment members, and still other control devices operative upon the projection of said abutment members for rendering said controller efiective to control said second mechanism.

21. In a drop pit apparatus having a two section elevator table, in combination, a first power operated elevator mechanism for raising and lowering both table sections together, a second power operated elevator mechanism for raising and lowering one of the table sections alone, shiftable abutment members on said one table section adapted when projected to associate that section with said second mechanism for raising and lowering and when retracted to disassociate the section from the second mechanism, a power operated actuator for projecting and retracting said abutment members, a control system for the apparatus including a pair of manually operable controllers, control devices operative in response to a momentary actuation of one of said controllers when the table sections are in a lowered position for initiating the operation of said first mechanism and continuing such operation until the table sections are raised to a predetermined position, other control devices operative upon movement of the table sections to said predetermined position for rendering said one controller efiective to initiate the operation of said actuator to project said abutment members, and still other control devices operative upon projection of said abutment members for rendering said one controller effective to control said second mechanism, said control devices being further operative to render the other controller effective to control said second mechanism when the abutment members are projected, to initiate the operation of said actuator for retracting the abutment members when said one table section is in its lower limit position, and to initiate the operation of said first mechanism for lowering the table sections when said abutment members have been retracted.

LLOYD H. I-IOLDEMAN. HUGH K. HYBARGER.

References Cited in the file of this patent UNITED STATES PATENTS Number