US2554145A - Apparatus for servicing the trucks or wheels of railway vehicles - Google Patents

Description

L. H. APPARATUS FOR SERVICING THE TRUCKS OR HOLDEMAN May 22, 1951 WHEELS OF RAILWAY VEHICLES Filed Nov. l, 1949 5 Sheets-Sheet 1 NVSNTQM @Aw/mx @frommen/W l L. H. HOLDEMAN APPARATUS FOR SERVICING THE TRUCKS OR May 22, 1951 WHEELS 0F RAILWAY VEHICLES l Y 5 Sheets-Sheet 2 Filed Nov. l, 1949 IIIHHIIIIU Fr. I l

May 22, 1951 L. H. HOLDEMAN APPARATUS TOR sERvIcTNG THE TRUCKS 0R WHEELS 0F RAILWAY VEHICLES 5 Sheets-Sheet 3 Filed Nov. l, 1949 mnnwmhu.)

, JVliLw 1.. H. HoLDEMAN 2,554,145 APPARATUS FOR SERVICINGTHE TRUCKS OR WHEELS 0F RAILWAY VEHICLES May 22, 1951 Filed NOV. l, 1949 5 sheets-sheet 4 HOLDEMAN APPARATUS FOR SERVICING THE TRUCKS OR May 22, 1951 y WHEELS OF RAILWAY VEHICLES Filed NOV. l, 1949 5 Sheets-Sheet 5 :Egg

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Patented May 22, 1951 APPARATUS FOR SERVICING THE TRUCKS v `OR. WHEELS 10F RAILWAY VEHICLES Lloyd H..Holdeman,Muskegon, Mich., assignor to `Manning, Maxwell & Moore, Inc., .Muskegom Mich., a corporation of New Jersey Application November 1, 1949, Serial N o. 124,808

.11;Claims. (Cl. 1-04-32) The invention relates to apparatus .for removing and replacing the trucks, wheels or other parts of the running gear of railway vehicles .and more particularly to apparatus of thetype adapted to operate in apit below the vehicle.

A general object of the invention is to extend the eld of usefulness of `such apparatus by improvements in construction and organization which particularly adapts it for the repair, servicing or replacement of the trucks or running gear of Diesel locomotives.

Another object is to provide apparatus of the above general character requiring .only a relatively shallow drop pit `for its accommodation, thereby affording substantial savings in .the construction of thekpit andreducing equipment costs to a minimum.

A more specific object is to providea combined drop pit table and .pit carriage including built-in elevator mechanism .embodied in a simple unitary structure which can be .manufactured at .relatively low cost.

Still another object is to provide improved mechanism for `supporting a vehicle Abody while the trucks or wheels arebeing removed and replaced.

A further object is to provide improved controls for coordinating the operation of the drop pit table and the vehicle body supportingmechanism to afford maximum safety in the handling of heavy equipment.

Other objects andadvantages of the 'invention will become apparent from the following detailed description of `the ,preferred embodiment .illustrated in the accompanying drawings, in which:

Figure l is a fragmentary plan Yview of a drop pit installation equipped with a drop pit table and vehicle body supporting mechanism embodying the features of the invention.

Fig. 2 is a sectional View takenin :a vertical plane substantially on the line 2-2 of Fig. 1, showing details of the vehicle body supporting mechanism.

Fig. 2a is an end view of the body support latch taken in a verticalplane substantially on the line 2a-2a of Fig. 2.

Fig. 3 is a View taken transversely of the drop pit showing the pit table in pit-bridging position.

Fig. 4 is a side elevational view of thepit table in raised or pit-bridging position.

Fig. 5 is a view taken'transversely of the drop pit showing the Vtable raisedabove track level and with the supporting mechanismin operative position.

Fig. 6 is a View similar to lFig.5 showing the table lowered to drop the trucks of the vehicle.

Fig. 7 isa diagram of the electrical and hydraulic circuits of the drop pit apparatus.

Fig. 8 is a diagram of the electrical and hydraulic circuits `of the supporting mechanism.

4The presentinvention 4may be used `with various `pit and .trackage -arrangements for servicing a wide varietyof railway vehicles. For purposes .of illustration, .themechanism has been shown in connection with a drop pit .I 0 (Figs. l, 3, 5 and 6) intersecting and extending beneath a service track comprised of rails 4.I I. When -intended for servicing certain types of vehicles, such as ADiesel locomotives, an .inspection pit I2 is -usually provided vbelow theservice trackat opposite sides of `the drop pit table. .Usually the droppit I0 is eX- tended across a plurality of service or `transfer tracks 4between which vehicle wheels or trucks may be transferredby elevating and transporting mechanism 4operating on rails I3 .extending longitudinally of the .drop pit and forming `a pit track.

In accordance withone aspectofthe invention theelevating and transporting mechanism is constructed asasimple, self-contained unitor combined drop pit table and pit carriage -I.5 .particularly `adapted foroperation ina relativelyshallow pit. Considerable saving .in initial construction costs is thus afforded as compared with deep pit installations required with conventional droppit apparatus. Furthermore, construction of the apparatusis simplied, enabling it `to be manufac tured vat lower cost and .to be maintained eco' nomically. Referring more particularly to Figs. 1, 3.-and 4 of the drawings, `the apparatus Vunit I5, which may be conveniently termed a drop .pit table, comprises .a rigid Vgenerally rectangular .table structure I6 built up of heavyI-beams or other structural shapes sufficiently strong .and rugged to supportthe weight of a heavyrailway vehicle such as a Diesel locomotive. The table structure 'I6 ris dimensioned so as to span .the -drop pit transversely and is arranged for movement .vertically and longitudinally within the pit. Rails yI'I on the upper face of the table structure form an extension track adapted to bridge the gap in the 'service track II when the table structure occupies the pit-bridging position in which it is showninFig. 3. Flanged wheels I8 are provided on the'table structure for supportingit on the pit track I3 when lowered to transport position. Preferably the top of the table structure is floored between and on opposite :sides of the rail I1 b y metal lplates I9 and I9a which are located flush with 'the 'shop `floor when the ltable structure is supported at the position shown in Fig. 3.

To insure adequate stability when a locomotive is run over the pit, the drop pit table I5 is releasably supported in pit-bridging position by latches 20 engageable with suitable ledges 2| on the side walls of the pit I0. Where an inspection pit |2 is installed, the ledges 2| are conveniently formed on or carried by upright members 22 disposed at opposite sides of the inspection pit.

The latches 20 as herein shown comprise heavy metal bars mounted in suitable guides formed in the table structure for endwise movement from the projected or active position in which they are shown in Fig. 3 to an inactive or withdrawn position as shown in Figs. 5 and 6 in which they are retracted to clear the ledges 2|.

While projection and retraction of the latches may be effected by any suitable means, it is preferred to employ a power-operated actuator 23 for that purpose. The actuator 23 as herein shown is of the pressure fluid operated type adapted to receive pressure fluid from a suitable source and vunder control of valve kmeans described in detail hereinafter. In its preferred form, the poweroperated actuator comprises a cylinder 23 (Figs. 3 Aand 7) having a working piston 24 connected vby a piston rod 25 and linkage with the latches 20, of which there are four in the exemplary drop pit table. The linkage includes a rockshaft 26 extending across the table structure and having suitably positioned oppositely directed radial arms '21 connected by links 23 with the respective latches. The arrangement is such that the latches may be projected or retracted simultaneously by appropriate rocking of the shaft 26, Such rocking is effected throughthemedium of a crank arm on the shaft operatively connected with the piston rod 25.

As indicated above, the drop pit table'lii is provided with built-in elevator mechanism for raising and lowering the table structure in the pit I0. 'Ihis mechanism, while capable of lifting the table structure from its transport position on the pit track I3, as shown in Fig. 6, to a position several inches above the level of the service track I I, as

shown in Fig. 5, is characterized by its simplicity and ruggedness, and more particularly by its compactness which is an important consideration in reducing the pit depth required for the accommodation of the apparatus. This factor, together with the construction of the table for service as a pit carriage, permits the apparatus to function efficiently in a pit of minimum depth.

Referring now to Figs. 1, 3, 4 and 7 of the drawings, the elevator mechanism is of the pressure iiuid operated .type comprising a plurality of fluid operated actuators 3G mounted on the table structure IG and adapted to exert a thrust against the pit floor to raise the table from the pit track I3. The actuators 30 are preferably of the cylinder and piston type, each comprising a cylinder 3| with a working piston 32 (Fig. 7) having a piston rod 33 projecting from one end of the cylinder.

Four of the cylinder and piston actuators 30 are provided in the exemplary pit table. These actuators are arranged in pairs on opposite sides of the table structure and in vertical alinement with the rails I3 of the pit track. For this purpose each of the cylinders 3| has at one side a flat mounting plate 34 (Figs. 1, 3 and 4) adapted to be secured to the table structure I6 as by -bolts 35. The cylinders are mounted in upright positions with the piston rods 33 projecting downwardly. Preferably each piston rod is provided at its lower end with a channel-shaped'ho@ 35 adapted to engage and rest on the rail I3. Accordingly upon introduction of pressure fluid in the upper ends of the cylinders 3|, pistons 32 and their piston rods 33 are shifted downwardly until shoes 36 engage rails I3. Thereafter the cylinders 3| are shifted upwardly relative to the piston rods and the entire table structure is raised.

To cushion the shock at the upper ends of the stroke, each of the cylinders 3| is formed at its lower end with a recess 3l (Fig. '7) of reduced diameter for the reception of a collar-like enlargement 38 on the piston rod 33 adjacent the piston 32. The recess and piston rod enlargement are dimensioned so as to restrict the exhaust of fluid from the cylinder and thus slow down the rate of movement as the cylinder approaches the piston. The pit table may therefore be brought to rest with a minimum of shock.

Power means is also provided for traversing the pit table I5 along the pit track I3. This power means may conveniently comprise a reversible rotary pressure fluid operated motor TM (Figs. l, 3 and 7). As shown in Fig. l the motor TM is mounted on the table structure I6 intermediate one pair of wheels I8 and is drivingly connected by speed reduction gearing G with a shaft 4| extending across the table. The shaft 4| is drivingly connected with the wheels by a pinion 42 coacting with gears 43 rigid with the wheelst In accordance with another aspect of the invention, the latch bar actuator 23, the elevator actuators 33 and the table driving motor TM are organized in a unitary hydraulic system and are supplied with pressure from a common source such as a pump P (Figs. l and 7) driven by ari electric motor M. As the pump and motor, along' with other elements of the hydraulic system, are mounted on the traveling pit table, electric cu'r'l rent for operating the motor and the controls associated with the system is supplied through a flexible cable 44 (Fig. 4) adapted to be reeled iriand paid out by a spring-actuated cable reel 115 which may be supported on the table structure or located at one end of the pit IQ, as preferred. As shown in Fig. 1 a trap door is provided in the central floor plate I9 to provide access to the motor M and pump P for adjustment or repair.

Referring to Fig. 7 of the drawings, pump P draws fluid such as oil from a sump or reservoir R and delivers it under pressure to a uid supply conduit 41 by way of a pressure responsive relief valve RV. One branch 48 of the supply conduit extends to a reversing valve V-I operated in one position to direct pressure fluid through a conduit 49 and check valve CV and flow equalizer E to the upper ends of the actuator cylinders 3|. The now equalizer E may be of any of the several well-known types in general use and provides a uniform now of fluid to each actuator cylinder under all load conditions, thereby insuring movement of the actuators in step and maintaining the table structure level at all times.

In its other position the valve V-I directs pressure fluid by way of a conduit 5|, check valve r CV-I and flow equalizer E-I to the lower ends of the cylinders 3|. The conduits 49 and 5| are connected alternately with a drain conduit 52 in the respective positions of the valve V-I.

y The particular reversing valve shown in the exemplary hydraulic system is spring-biased to a central position in which both conduits 49 and 5| are blocked. Fluid is thus trapped in the cylinders 3| and movement of the pistons in either direction is effectively prevented when the reversing valve is in neutral position. Movement of the vale V-I vto the position for raising the Ltablestructure is effected by a solenoid'SQL--I energized uponclosure of a manually-operable S-o-I connected between the switch RSjand 'the solenoid SOL-I and adapted to be opened :by a cam -53 on one of the cylinders'3 I.

Shifting of the reversing valve V-I `toitsalternate or lowering position iseffected by asolenoid SOL- 2. The energizing circuit for the flatter solenoid includes a normally open manually ,operable switch LS and a limit switchS-:Z operable vb y a cam 54 on one of the rail engaging shoes 36 which limit switch is normally closed when the elevatormechanism is supporting the table structure on the rails I3, and an interlocking safety switch SS--I (Fig. 8) associated with the vehicle body supporting mechanism. The arrangement is such that the operation of that mechanism and the hoist is always properly coordinated, as explained hereinafter. Assuming that the limit and safety switches are closed, .the lowering action of the elevatormechanism continues only while .the switch LS isheld closed and is interrupted when .the switch is released. .In-

itiallyyr lof course, the cylinders 3| descend with reference to their pistons -32 until the wheels I8 ofthe table structure engage the rails I3. 'Thereafter, the pistons 32 are shifted to the upper ends l of their associated cylinders and thus raise Hthe shoes 36 from the rails i3 so that thepit'table may be traversed thereon without interference.

The equalizers E and E-I in thefluidsupply circuits for the actuators insure operation kof the actuators at the same .rate and thus maintain the table structure level under all operating conditions. Clontrol of the raising or lowering speeds is effected by metering the exhaust from the respective actuator cylinders. Forltliis purpose, adjustable metering valves MV and 'MV-I are connected in parallel relation respectively with the check valves CV andCV-JL '.Ilhe arrangement is such that vfluid flow 'toward A.the actuators passes freely through the check .valves 4while flowfrom the actuators is divertedthrough the metering valves.

Pressureiiuid for operating the latch .bar actuator 2 3 is supplied through a secondbranch-conduit 55 and under control of a reversing .valve V-3. This valve, which may be operatedmanually byimeansof a hand lever 56, connects ,the opposite ends ofthe actuatorcylinder 23 Aalternately with the branch conduit A55 and thedrain conduit `52.

A third branch conduit .'51 supplies .pressure fluid to the traverse motor TM under controlpf a reversing valve V-4 which determines thedirection of rotation of the motor Vanolfherefore the direction of travel of' the'table I5. This valve is normally spring-biased to a central Lor neutral position in which both ports leading totheinro'tor are blocked. vA solenoid SOL- 4 `energized upo'n closure of `a normally `open manually operable forward switch FS shifts the -va1vefto1'aposition to effect aforwardmovement-of the pitltable.

Shifting ofthe valve V-4 to its `alternate position, thereby reversing the direction of movement of the table, is effected by 'a solenoid SOL-5 energized upon closure of a normally ,open manually operable reverse switch RS-I. An 4adjustable metering valve MV-Z maybe interposed in the branch conduit 5l for regulating the speed of the traverse motor TM.

Means is provided for instantly unloading the hydraulic system in the case of an emergency. This means includes a valve V-5 interposed in a branch conduit 58 leading from therelief valve 'RV to the .drain 5.2. Valve V-5 is spring-biased to an open position but when the system is in operation, itis held closed by .a solenoid SOL-f6 energized in a circuit including a normally closed manually operable stop switch SS. Thus, upon power failure or in response to the actuation Iof the stop switch, solenoid SOL-6 Vis deenergized and valve V-5 opens to divert vall .pressure iluid from the pump, thereby immediately interrupting any function of the pit table that may be in progress.

The electrical controls above described are preferably arranged for low voltage operation and may be supplied with current from the motor supply circuit through a suitable step-down transformer 59. A suitable contactor or control switch (not shown) is provided in the motor circuit for starting and stopping the motor. The various manually operable switches are desirably of the push-button type and for convenience of operation may be mounted on a portable hand set connected with the solenoids and other elements of the system by a llexible conductor cable.

Associated with and forming a part of the drop pit apparatus above described is a novel mechanism providing support for the body of a vehicle while a set of wheels or truck is removed therefrom with the assistance of the pit table I5. The supporting mechanism in its preferred form comprises a column 6G (Figs. 2, 5, 6 and 8) supported `between the rails of the service track Il in a rigid frame 5I carried by the uprights 22 at the sides of the inspection pit and at one side of the drop pit Ill. The column (il) is slidable vertically in the frame from the extended position in which it is shown in Figs. 2 and 8 to a retracted position .in which its top portion is approximately at or below the level of the service track as shown in Fig. 1 so that the vehicle may be run over it without interference.

As shown in Fig. 2, the column 60 is in the form of a hollow cylinder with an auxiliary jack screw .62 threaded into its upper end. The jack screw vis provided with a flat head element 64 for engaging the pad which is ordinarily provided on 4the vehicle body for jacking purposes. By screw-- ing the jack in or out, the effective length of the' Asupport may be adjusted to conform to variations in the spacing of the jacking pad with respect to the track level.

Movement of the column El) between extended and retracted positions is effected by a pressure fluid operated actuator comprising, in this instance, a cylinder 65 supported in an upright position on a cross beam 66 extending transversely ofthe inspection pit. The cylinder is ttedwith a piston 61 (Fig. 8) having a piston .rod v58 :extending upwardly into the column and operatively connected with it by means or a cross pin 69. Accordingly, when fluid under pressure is admitted to the lower end of the cylinder t5, the column is raised ito extended position. When the cylinder is vented, the column returns to retracted position by gravity.

Due to the relatively heavy loads imposed on the column 60 and to the necessity of maintaining it in position to support a load irrespective of power failures or the like, means is provided for positively locking it in the extended position independently of the pressure huid operated actuator. Since this locking means is arranged to sustain the load on the column mechanically independently of the actuator, the latter may be of relatively light and inexpensive construction. Such positive locking of the column provides maxmum safety in the operation of the pit apparatus as it electually prevents accidental lowering of a vehicle into the open pit in which men may be working.

The column locking means in its preferred form comprises a locking bar 'l5 supported at opposite sides by guide bars l! (Figs. 2 and 2a) on the frame Si so that it may slide under the column wlien the latter is raised to its extended position. Accordingly, when a load is imposed on the column it is transmitted through the locking bar to the frame 6l independently of the pressure fluid actuator. As will be seen by reference to the drawing, the locking bar 1S is formed with a longitudinal slot l2 providing clearance for the cylinder 65 when the bar is advanced to operated or locking position.

Movement of the bar 'l0 between locking and release positions is eected by power-actuated means, herein shown as a pressure iiuid operated actuator comprising a cylinder' 'i3 having a work-- ing piston 'lil (Fig. 8) connected by a piston rod 'l5 with the locking bar. The cylinder is disposed in a substantially horizontal position and in the present instance is anchored at its closed end to one of the uprights 22 as by a pin i6.

Operation of the column and latch actuators in proper timed relation is insured by the novel erative to connect the lower end of the cylinder 65 alternatively with the supply conduit or with a drain conduit 19. Pressure fluid flows from the valve to the cylinder by way of a check valve CV-I while fluid exhausted from the cylinder returns to the reversing valve by way of a rnetering valve NIV-3 connected in parallel with the check valve. The metering valve is preferably adjustable to provide for regulating the speed of retraction of the column 60.

The reversing valve V- is shifted toits alternate positions by means of solenoids SOL-l' and SOL-8. Solenoid SOL-l is energized upon closure of a normally open manually operable raise switch RS-2 to initiate the raising of the column 60. The circuit of the solenoid 'SOIFS is controlled by the latch bar l0 through the medium of a limit switch S-3 closed by a cam 'E9s on the bar when the latter is fully retracted. The circuit for the solenoid SOL-8 also includes a set of normally closed contacts RS-Za associated with the raise switch to insure deener gization of the solenoid when the valve is to be shifted to its alternate position. Preferably, the solenoids and control switches are operated in a low voltage circuit herein shown as receiving its current supplyfrom the main circuit by way of a transformer 59s. Motor M-I operatesv in the main circuit which is controlled by the usual switches or contactors (not shown).

A second branch of the supply conduit ll extends to a conventional two-position reversin,T valve V-T from which conduits 8| and 82 extend respectively to opposite ends of the latch actuator cylinder 73. The valve may thus be shifted to direct fluid into either end of the cylinder 'f3 while venting the other end to the drain conduit 19. Such shifting is eiected by means of solenoids SOL-9 and SOL-lll. Solenoid SOL-9 is energized by closure of a limit switch S-V-d upon movement of the column B to its extended position. Such actuation of the switch is effected in this instance by a cam 83 carried by the column. Thus the full extension of the column initiates the shifting of the latch bar 'I8 into supporting relation to the column.

Withdrawal of the latch bar 'l0 and retraction of the column S0 is initiated by closure of a nor.- mally open manually operable lower switch LS-l which completes an energizing circuit for the solenoid SOL-itl. Associated with the lower switch is a normally closed switch LS- la which opens the circuit of the solenoid SOL- 9 to enable the companion solenoid to shift the valve to its alternate position. Upon full retraction of the latch bar lil, switch S-3 is closed to energine the solenoid SOL-8 and initiate the lowering of the column.

In an emergency, the hydraulic system may be unloaded by operation of a stop switch SSS-2 to deenergize a solenoid SOL-l l which normally holds a stop valve V-l in closed position. When the solenoid is deenergized, the valve is opened by a spring and diverts all pressure fluid from the pump P- l to the sump by way of a drain conduit 19h.

Reference has been made heretofore to the interlocking of the drop pit table elevator con- ,trols with the controls for the vehicle body supporting mechanism. For this purpose conductors 85 and 86 from the limit switch S-2 and the solenoid SOL-2 of the elevator controls are carried through the transmission cable 44 and connected by way of contact rings 8l and 88 of the cable reel 45 with conductors 89 and 9G leading to the .safety switch SS-l. This switch is supported in a position such that it is closed by the latch bar 'l0 upon movement of the latter to op erated or latching position. A cam 9| on the supporting column 6l] is also arranged to close the safety switch when the column is in its lowered or retracted position.

With the above arrangement, the lowering of the vehicle body onto the supporting column while the column is being raised or before it is securely latched in operating position is effectively prevented. However, normal operation of the elevator mechanism is permitted when the column is fully retracted.

In the operation of the improved drop pit apparatus, the table structure I5 is latched in pit bridging position, as shown in Fig. 3, and the vehicle is run over the pit with the truck to be removed spotted on the table. The raise switch RS is then closed, initiating the operation of the actuators 30 to raise the table above pit level, as shown in Fig. 5, thus removing the load from the latch bars 2li. The latch bars may then be retracted by operation of the valve V-3.

While the elevator table is in its uppermost position, the supporting column 60 is extended assises..

. 9 by closure of the raise switch RST-2. Whenv the column reaches its fully extended position closure ofV limit. switch S--lt initiates operation of the latch actuator mechanism to shift the latch. bar into supporting relation to the column. In practice the column is usually so constructed that it does not reach the jacking pad ofv the vehicle and accordingly the screw jack 62.v is turned up until the head 64 engages the jacking pad.

After the trucks are detached from the vehicle they may be lowered into the pit for transportation to another service or transfer track. Such lowering is initiated by` operation of thev'1ower switch LS. As the table structure. descends into the pit the weight of the vehicle body is transferred onto the column 69 and through the latch bar IIJ to the supporting framework in thepit` To replace the wheels or truck, the above sequence of operations is reversed. The table is run under the vehicle and elevated to the position shown in Fig. 5. This relieves the column 60 of the load so that the latch bar lll may be withdrawn and the column retracted upon closure ofv the lower switch LS-l. The .table is now lowered to the pit-bridging position and the latches 2D operated to latch the table in position. It will be apparent from the foregoing that the invention provides drop pit apparatus of novel and advantageous construction. The Vimproved apparatus is particularly well adapted for the repair, servicing or replacement ofthe running gear of Diesel locomotives. By reason of its novel construction, only a relatively shallow pitis required, thus affording substantial savings in the cost of constructing the pit and reducing equipment costs to a minimum.

The vehicle body supporting means is characterized by the ease with which it may be conditioned for operation or retracted to an out of the way position when not required. A novel interlocking arrangement between the pit elevator mechanism and the supporting mechanism effectively coordinates their actions for safe operation.

I claim as my invention:

1. Apparatus for use in a pit intersecting and extending beneath a service track and having rails providing a pit track extending transversely of the service track, said apparatus comprising, in combination, a rigid table structure'dimensioned to lit within the pit and movable vertically therein, said table structure having means f or carrying a track section, retractable latch members on said table structure engageable with the pit walls for supporting the table structure adjacent the top of the pit with the Vtrack section thereonV bridging the gap in the service track, a plurality of wheels on said table structure'engageable with the rails of the pit track and operative to support the table structure thereon substantially below the top of the pit, elevatorl mechanism mounted on said table structurefor shifting it between said two supported positions,

said mechanism including a pair of vertically disposed cylinders mounted at each end of said table structure substantially in alinement with the rails of the pit track, a piston Vworking in each cylinder and having a downwardly extending piston rod terminating in a rail engaging shoe, a source of fluid under pressure, and valve means operable to control the flow of pressure fluid to and from said cylinder to effect ,thellifting or lowering of said table structure.

V2. Apparatus for use in a 4pit intersecting and 10 Y extending beneath a service track and having rails providing a, pit track extending transversely of the service track, said apparatus comprising, in combination, a` rigid table structure dimensioned tofit Iwithin the pit and movable vertically therein, retractable latch members on said table structure engageable with, the pit walls for supporting theA table structure adjacent the top of the pit,l said table structure having means for carrying .a track section operable to bridge the gap, in the service track when the table structure is latched to the pit, a plurality of wheels on said, 'table structure engageableA with the rails of the pit track and operative to support the table structure thereon substantially below the top of the pit, elevator mechanism mounted on said tabl-e structure for shifting it between said two supported positions, said mechanism includ-1 ing a pair of vertically disposed cylinders mounted at each end of said table structure substantially in alinement, with the rails of the pit track, a

piston working in each cylinder and having a.

downwardly extending` piston rod terminating in a rail engaging shoe, a source of fluid under pressure, a reversing valve operable to direct fluid from said source to the opposite ends of said cylinders alternately, and manually operable control means for selectively operating said reversing valve.

3,. Apparatus for use in a pit intersecting and extending beneath a service track and having rails providing a pit track extending transversely of` the service track, said apparatus comprising, in combination, a rigid table structure having wheels adapted to travel on the pit track, said table structure having means for carrying a sectio-nV of track, elevator mechanism operative to raise said table structure from the pit track to a position adjacent the top of the pit with the track section thereon bridging the gap in the service track, said elevator mechanism including a plurality of pressure fluid operated actuators carried by the table structure and cooperating with the rails of the pit track, a fluid motor operative to drive saidtable structure along the pit track, a source of iiuid under pressure, independently operable reversing valves for respectiveliy controlling the ow of iluid from said source to said actuators and said motor, and ya stop valve 0perable to interrupt the flow of pressure fluid to said actuators and said motor independently of said reversing valves.

' 4. Drop pit apparatus for servicing the wheels and trucks of railway vehicles comprising, in combination, a table structure dimensioned to operate in a` pit intersecting `and extending beneath a service track, said table structure having means for carrying a track section operativeto extend the service track across the pit, elevator mechanism associated with said table structure operative to raise and lower th-e table structure, means for supporting the body of a vehicle when a set of wheels or truck is removed therefrom by lowering the elevator, said supporting means comprising a member movable vertically from a retracted position below the service track into engagement with the underside'of the vehicle body, power operated means for moving said member, a latch element shiftable into a position t0 mechanically retain said member in its raised position and to support the load imposed on the member, and control means operable by said latch elementfor preventing operating of said elevator mechanism to lower said table structureY until the latch element has been shifted into latching position.

5. Drop pit apparatus for servicing the wheels and trucks of railway vehicles comprising, in combination, a table structure dimensioned to operate in a pit intersecting and extending beneath a service track, said table structure having means for carrying a track section adapted to extend the service track across the pit, elevator mechanism associated with said table structure operative to raise and lower the table structure, means for supporting the body of a vehicle when a set of wheels or truck is removed therefrom by lowering the elevator, said supporting means comprising a member movable vertically from a retracted position below the service track into engagement with the underside f the vehicle body, power operated means for moving said member, a latch element shiftable into a position to mechanically retain said member in its raised position and to support the load imposed on the member, control devices for said elevator mechanism operable selectively to initiate the raising or lowering of the table structure, and an auxiliary control device actuated in accordance with the position of said latch element to render effective or ineffective the device for initiating the lowering of the table structure.

6. Drop pit apparatus for servicing the wheels and trucks of railway vehicles comprising, in combination, a table structure dimensioned to operate in a pit intersecting and extending beneath a service track, said table structure being adapted tocarry a track section for extending the service track across the pit, elevator mechanism associated with said table structure operative to raise and lower the table structure, means for supporting the body of a vehicle when a set of wheels or truck is removed therefrom by lowering the elevator, said supporting means comprising a member movable vertically from a retracted position below the service track into engagement with the underside of the vehicle body, power operated means for moving said i tor mechanism including an electrical circuit operative when closed to initiate a downward movement of the mechanism, a normally open safety switch in said circuit closed upon movement of said latch element into latching position.

7. Drop pit apparatus for servicing the wheels and trucks of railway vehicles comprising, in combination, a table structure dimensioned to operate in a pit intersecting and extending beneath a service track, said table structure being adapted to a carry a track section for extending the service track across the pit, elevator mechanism associated with said table structure operative to raise and lower the table structure, means for supporting the body of a vehicle when a set of wheels or truck is removed therefrom by lowering the elevator, said supporting means comprising a member movable vertically from a retracted position below the service track into engagement with the underside of the vehicle body, power operated means for moving said member, a latch element shiftable into a position to mechanically retain said member in its raised position and to support the load imposed on the member, a control system for said elevator mechanism including an electrical circuitY operative when closed to initiate a downward movement of the mechanism, a normally open manually operable switch in said circuit, a second switch in said circuit closed when the table structure is in araised position, and a third switch in said circuit closed incident to the movement of said latch element to latching position.

8. Drop pit apparatus for servicing railway vehicles comprising, in combination, a table structure dimensioned to operate in a pit intersecting and extending beneath a service track, said table structure having means for supporting a track section operative to extend the service track across the pit, elevator mechanism associated with said table structure operative to raise and lower the same, means for supporting the body of a vehicle spotted over the pit when a set of wheels or truck is removed therefrom by lowering the elevator mechanism, said supporting means comprising a member supported between the rails of the service track at one side of the pit for movement vertically from a retracted position at or below the level of the service track to a raised position in engagement with the underside of the vehicle body, power operated means for moving said supporting member to raised position, a rigid element shiftable into a position to mechanically retain said member in raised position and to support the load imposed on the member, other power operated means for shifting said element to and from supporting position, and controls governing the operating sequence of said two power operated means.

9. Drop pit apparatus for servicing railway vehicles comprising, in combination, a table structure dimensioned to operate in a pit intersecting and extending beneath a service track, said table structure having means for support'- ing a track section operative to extend the service track across the pit, elevator mechanism associated with said table structure operative to raise and lower the same, means for supporting the body of a vehicle spotted over the pit when a set of wheels or truck is removed therefrom by lowering the elevator mechanism, said supporting means comprising a member supported between the rails of the service track at one side of the pit for movement vertically from a retracted position at or below the level of the service track to a raised position in engagement with the underside of the vehicle body, power operated means for moving said supporting member to raised position, latch means operative to retain said supporting mechanism in raised position, control devices for said elevator mechanism operable selectively to initiate the raising or lowering of the table structure, and an auxiliary control device actuated by said latch means cooperating with the control device for initiating the lowering of the table structure to control the operation of said elevator mechamsm.

10. Vehicle body supporting mechanism comprising, in combination, a supporting member mounted between the rails of a service track for movement from a position substantially at or below track level to a raised position in engagement with the underside of the body of a vehicle standing on the track, a power-operated actuator for raising and lowering said supporting member, a latch element shiftable transversely of saidsupporting member into or out of latching engagement therewith, a power-operated actuator for shifting said latch element, control means operative upon the movement of said supporting member to its raised position for initiating the operation of the latch element actuator to shift the element into latching engagement With the member, manually operable means for initiating the operation of said latch element actuator to withdraw the element from latching engagement with the member, and control means rendered effective incident to the Withdrawal of the latch element for initiating the operation of said first-mentioned actuator for lowering said supporting member to retracted position.

11. Vehicle body supporting mechanism comprising, in combination, a supporting member mounted between the rails of a service track for movement from a position substantially at or below track level to a raisedv position in engagement with the underside of the body of a vehicle standing on the track, a power-operated actuator for raising and lowering said support- REFERENCES CITED The following references are of record in 'the file of this patent:

15 UNITED STATES PATENTS Number Name Date 304,562 Ramsey Sept. 2, 1884 1,632,256 Walter June 14, 1927 20 2,262,121 Snider Nov. 11, 1941 2,454,226 Skinner Nov. 16, 1948

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