US2517153A

US2517153A - Telescopic power down hoist

Info

Publication number: US2517153A
Application number: US691108A
Authority: US
Inventors: Louis S Wood
Original assignee: Gar Wood Industries Inc
Current assignee: Gar Wood Industries Inc
Priority date: 1946-08-16
Filing date: 1946-08-16
Publication date: 1950-08-01
Anticipated expiration: 1967-08-01

Description

1, 1950 s. WOOD 2,517,153

TELESCOPIC POWER DOWN HOIST Filed Aug. 16, 1946 4 Sheets-Sheet l f l E. E3.

INVENTOR. 44:01.5 in pad BY M,% 1/

Aug. 1, 1950 L. s. WOOD TELESCOPIC POWER DOWN HOIST 4 Sheets-Sheet 2 Filed Aug. 16, 1946 Aug. 1, 1950 s. WOOD 2,

TELESCOPIC POWER DOWN HOIST Filed Aug. 16, 1946 4 Sheets-Sheet 4 Inf.

m I INVENTOR.

Patented Aug. 1, 1950 UNITED STATES PATENT OFFICE.

TELESCOPIC POWER DOWN HOIS T Louis S. Wood, Burlingame, Califi, assignor to Gar Wood Industries, Inc., Detroit, Mich, a 1 corporation of Michigan; Application August 16, 1946, Serial No. 691,108,

The present invention relates to hydraulic hoists, particularly for dump-type cargo vehicle bodies.

In the design and construction of dump-type truck bodies for hauling dirt and other loose loads, it has become common practice to hinge the body near its back end, and to provide a tail gate adapted to be opened, dumping means being incorporated comprising hoist mechanism for swinging the portion of the body lying forward of the hinge axis upwardl so that the load may slide or pour from the gate opening.

The hoist mechanism mayconveniently take the form of a plurality of telescopically arranged cylindrical sections, the outer and. inner ones of which are provided with suitable pivot-type coupling means whereby one may be connected to the frame or chassis of the truck or vehicle and the other connected to the pump body at a point spaced forwardly from the aforementioned hinge axis. Thus, fluid under pressure, asfrom a hydraulic system, may be applied to the telescopic cylinder assembly to extend the same and tilt and dump the body in the manner above-mentioned. Where the hoist mechanism incorporates no means for retracting the several sections into one another by positive application of actuating fluid, the dump angle to which the body is lifted must as a practical matter be limited to such value that the center of gravity of the empty body does not pass through a vertical line projected upwardly from the hinge axis, since if this were per mitted, power would be required to lower the body. Provision has been made for such positive retraction by the application of hydraulic power to the telescopic hoist unit in such manner as to retract the sections into one another, in constructions heretofore proposed which have been designed to permit tilting the body over-center the aforementioned manner, such positive re traction in certain prior art devices involving conducting the hydraulic fluid to an outer portion of the telescopic assembly through flexible hoses. While such constructions utilizing hose connections possess the advantage of permitting a greater dump angle and. are therefor of assistance both in the dumping of sticky or coherent loads and with respect to rapidity of dumping, the provision of flexible hoses extending to the outer telescopic sections in the manner mentioned has several serious disadvantages of these disadvantages is of course the difficulty of arranging such hoses to avoid all danger of their being caught and injured by the movable. parts of the body and hoist mechanism. It is also necesemployed in thesystem;

sary when employing hoses in the indicated manner to incorporate positive keying means'between each pair of telescopic sections, in order to prevent the outermost sectidn to'which the hose' is attached from rotating andtthereby injuring the hose. Such lengthy keying means are of course relatively fragile and if the entire mechanism is not to be seriously weakened by the incorporation thereof, it is necessary toumake the structure more massive than would oth'erwise be necessary.

An important object of the :present invention is accordingly to provide an improved telescopic hoist of the indicated character incorporating positive fluid-operatedretracting means requiring no external hoses or other fluid conducting means outside the hoist' structure itself and-arranged in such manner that rotation may bepermitted between the several telescopic sections without injury to thepartst in l Another object of the invention is to provide such a telescopic hoist of 'thepositive retraction or power-down type arranged so that circulation of hydraulic fluidto andfromthepurnp is permitted at both ends of itswork'i'ng stroke.

Still another object is to providesuch a telescopic hoist of the power-downtype which incorporates novel hydraulic cushioning means for controlling the rate of descent of the body. Other objects and advantages willbe apparent upon consideration of the present disclosure in its entirety. l I r i In the drawings:

w Fig. 1 is a side elevationalview of amotor truck provided with a dump body operable by hoist means constructed in accordance with the present invention, l

Fig. 2 isa substantially diametric, longitudinal sectional view of the hoist, centrally broken away, showing the parts intheir retracted positioning;

Fig.3 is a viewsimilar to Fig. 2:b'ut on a smaller scale and showing the hoistextended;

Fig. l is a detail diametric sectional view on a larger scale showing the outer extremity of the hoist assembly with the parts in an intermediate position; i l l l Fig. 5 is a schematic diagram, and l Fig. 6 is a sectional view of a control valve Referring now to the drawings; reference character l0 designates generally a motor truck, shown equipped' with a dump-typebody l2 pivotally attached as by trunnion bearing means M 'to the frame l5 of the truck for swinging movement about a transverse-horizontal axis. In

' Fig? 1 the body 12 is shownin full lines in. its normal lowered running position, while the tilted or dumping position is fragmentarily illustrated in the same View in dot-dash lines. It is to be noted that in tilting the body to the fully raised position the center of gravity of the empty body passes through and beyond a vertical line projected upwardly from the hinge axis defined by the trunnion bearing means l4.

Power for hoisting the body and for returning it to the lowered, running position is derived from a hoist unit comprising a plurality of telescopically disposed cylindrical sections, the outermost of which, designated 20, is connected to the truck frame 5 for swinging movement about a transverse axis, as by means of the trunnion pivot pin 22, while the innermost section is provided with an end coupling portion 24 similarly pivotally connected as by the pivot pin 25 to the bottom of the dump body 2 at a point so spaced forwardly from the hinge axis l4 that the body is tilted to a desired angle when the hoist assembly is fully extended, as indicated in Fig. 1.

The hoist unit maybe operated by means of a suitable hydraulic fluid (not shown) the bull: of which is normally stored in a reservoir tank I6 from which the fluid is forced under suitable pressure developed by a pump I8, through a control valve assembly, the body of which is generally designated 26, and through suitable flexible conduits as UP and DN to the hoist unit. The control means is so arranged that when hydraulic fluid is being delivered to the. hoist unit throughconduit UP, to extend the hoist, a return. connection to the reservoir is provided by way of conduit DN, while conduit UP serves as a return line when fluid is being delivered to the unit through conduit DN to lower the body under power.

Fluid is conducted from the tank IE to the pump I8. by way of a pipe or conduit and forced through pumpoutlet conduit 32 to the control valve inlet 3.4. A suitable filter as 35 may be incorporated in the line from. the pump to the valve, as indicated.

The upper section 27 of the valve casing 26 incorporates a piston-type. pressure-limiting valve 36 which opens when the pump pressure exceeds a predetermined value to provide a direct return to the reservoir by way of conduit 38-, which is connected to the escape port 31. of the valve. The pressure-limiting valve spring 40 is so calibrated as to maintain a desired maximum, pump pressure, and the setting of the spring-controlled pressure is variable by a suitable adjusting screw 42- which permits changing the preloading of the helical compression-type spring, trapped behind the valve element 36 in the usual manner, as shown in Fig. 6.

The control valve is of the balanced spool piston type, having a pair of central reduced areas 52, 54 separated by a central piston or spool section 55 and constituting means for selectively diverting the supply fluid to either of the pipes UP and DN through channels presently to be described. A second pair of symmetrically disposed outer reduced areas 55, 58 in the valve form annular channels through which the fluid may be returned to the. reservoir during. extension. and retraction of the telescopic sections. With the valve inthe centered position shown in Fig. 6 fluid from the pump enters at inlet 34, flows through. the head chamber 55 of the pressure limiting valve to a pair of branching passages 46U, 46D, the former terminating in a port 48H which. communicates with, the outer end of valve chamber 52 when the valve is in its centered position, while passage 46D similarly communicates with valve chamber 54. When the valve is in the centered position, both of its chambered portions 52, 54, open into a return passage 6!] communicating with valve outlet 62, which is connected as by conduit means 64, 65 to the reservoir IS.

The valve 50 is yieldably maintained in the centered position shown in Fig. 6 by centering means including a spring 10 acting upon a reduced extension portion 63 projecting from one end of the valve and from its casing 26. Spring i0 is of the helical compression type and is trapped between a pair of slidable spring abutment pieces H, 12, the former engageable by an abutment formed by the reduced right-hand extremity of the valve, as the same is viewed in Fig. 6, which reduced portion forms the plane of demarkation between the valve per se and the e: tension stem 63. The spring abutment 12 is also slidable upon the stem section 53 and engageable with a casteilated nut M mounted upon the outer end of the stem portion. The outer end of the abutment i2 is also urged by the spring against a shoulder formed in the outer end of the cap 15 carried upon the end of the valve casing in axial alignment with the valve and enclosing the centering mechanism. When the valve is moved to the left, as viewed in Fig. 6, its relieved portion 52 provides communication between feed passage GGU and a port EBU connected to the main hoist cylinder 20 by the conduit UP. At the same time the port 68D, which is connected to the main hoist cylinder Ell by the conduit DN is brought into communication with the fluid return outlet coupling portion 62 of the valve by the valve section 58, which then provides communication between port 68D and a passage 61D formed in the valve body and communicating with the fluid return portions 68, 62. When the valve is reversed in position by moving it to the right of the centered position shown, communication is similarly provided between conduit UP and the return line portions 64, 65, and the reservoir by the reduced valve section 56, which then bridges and provides connection between port 68U and a passage BTU connected to return outlet 62 and corresponding to the passage 61D previously described.

Valve member 59 also projects from the other end of casing 25, through suitable packing means as 853, and is provided with a reduced and apertured extremity as 8.2 by which it may be actuated, either manually or through the agency of suitable actuating mechanism and/or connecting means (not shown).

The hoist assembly comprises four cylindrical sections slidable within one another, the outer cylinder 26 having a lower head or end plate 8 welded or otherwise rigidly secured'in place and rigidly supporting in a central position the downwardly projecting trunnion bearing support into which the trunnion bearing pin 22 is tightly fitted to rockably support the hoist assembly with respect to the vehicle frame in the manner described above and best indicated in Fig. 1. The bottom plate 8% is also provided with a coupling portion to which the conduit UP is coupled and through which fluid for extending the hoist is introduced. Three telescopically arranged inner cylindrical hoist sections are provided, successively designated 92, 94 and 96, the last-mentioned, innermost cylinder projecting from the rest and carrying the coupling element connected by the pivot pin 25 to the bottom of the dump body as previously indicated. Coupling element 24 is welded to the-inner cylinder 06, as shown in Fig. 2.

Cylinders

92, 94, 96 are actuated by piston portions I02, I04, I06, respectively rigidly attached to their lower extremities and somewhat exceeding the diameter of and serving as spacers for the respective cylindrical sections, to which they are attached as by welding. I Each piston is provided with packing means such as the piston rings I05 slidably engaging the interior of the next outermost cylindrical section into which the piston portion is in each instance fitted. The bottom closure or head for the piston I02 attached to cylindrical section 82 is formed by a plate I01 welded to the piston. A similar head plate I08 provides a closure for the piston I04, while piston portion I06 forms a closure for the bottom of the cylindrical section 96 as well as filling the space between the cylinders '94, 96. Each of the cylindrical sections or

sleeve

20, 92, 90, carries a packing nut at IIO, =II2, II4, screwed in place or otherwise suitably attached at its outer end and co-operating with packing means as M5, H5 H5 providing a sliding seal between the sleeve by which the nut and packing are carried and the sleeve mounted next therewithin. supplemental packing means such as felt rings H8, H6 H6 and resilient O-rings H8 may also be provided, the felt rings being arranged to supplement the compressible packings I I5, I i 5 I I5 and being located at the other extremities of the packing nuts, and serving as wipers adapted to remove foreign matter from the outer surfaces of the slidable cylinders, while the O-rings IE8 seal the threads of packing nuts I I2, H4, since the compressible packing material H5 H5 associated with these nuts is notfso arranged as to seal the nut threads as will be apparent. i

A Toy-pass or feed tube I20 extends through and is rigidly secured in axial position with respect to main cylinder head plate 84, and projects into the interior of the assembly far enough tomaintain slidable connection with a similar tube I22, extending through and rigidly carried by plate I01 and slidably fitted upon the tube I20, the tubes being of such length that their connection is maintained even when the hoist is fully extended. A similar tube I24 slidably surrounding the tube I22 is supported in corresponding position by the plate I08, tube I24 beingslidably surrounded by a sleeve I25 attached to and movable with piston I08 and sleeve 95.

Piston portion I01 is slidably sealed with respect to tube I20 as by means of the chevron packing assembly generally designated I26. A

similar seal between piston I08 and the tube I22 is provided by corresponding chevron packing l28. Additional chevron packing means as I may be provided to furnish a running seal between the sleeve I25 and its connected piston I06 and the tube I24 connected to the headplate ing I28, the parts being secured together and the its attached piston packing compressed by means of screws I44.

Packing I30 may be compressed by a conventional packing screw I46, threaded into the lower end of the sleeve I25.

The assembly comprising sleeve I25, packing I30, and other elements supported by the sleeve, is slidable in a surrounding sleeve I45 flanged at its lower end to underlie the piston I06, to which it is secured as by screws I48, sleeve I25 being yieldably positioned with respect to sleeve I45 and the connected piston I06 and tube 96 by means of a coil-compression spring I50 trapped between a shouldered portion (undesignated) of sleeve I45 and the head of an abutment screw I52 secured in the outer end of sleeve I25. Springinduced outward movement of the sleeve I25 is limited by the head of packing screw I46, which head overlies the lower end of the sleeve I45. The sleeves I25, I45, are provided with oil passages and ports the purpose and arrangement of which will presently be described. Outward movement of the abutment screw I52 and so of sleeve I25, sleeve I45, piston I06 and attached piston sleeve 86, is limited by an abutment washer I55 retained upon the end of tube I24 by lock nuts I55 threaded upon a nipple I58 welded in the end of tube I24. As indicated in Fig. 3, abutment screw I52 brings up against the washer I 55 when the hoist is fully extended, the spring I50 being compressed as the piston and sleeve assembly I06, 86, continues its outward movement, the limit being reached when the outer end of sleeve I45 brings up against the underside of the nut I52.

Coupling member 24 forms a fluid-tight closure for the outer end of cylinder 95 and it will be seen that the slidable tubes I28, I22, I24, provide fluid conductive communication between the supply conduit DN and the interior of cylinder 96. Conduit DN is connected to a coupling nipple I secured to the trunnion-supporting block 25 as by means of the screws I 62 and projecting through and tightly fitted in said block to provide communication between the conduit DN and tube I20. The inner end of the nipple I50 may be welded to tube I '20 and also sealed with respect to head 84 as by means of packing washers I64. Nipple I50 also extends through an appropriately dimensioned and positioned aperture in trunnion shaft 22 and may serve to retain such shaft in the block 85.

It is believed that the remaining components of the hoist mechanism and connected hydraulic system may best be considered in connection with a description of their operation. I When the hoist is to be extended, valve 50 is moved to the left, as viewed in Fig. 6, thereby establishing communication between the fluid-supply conduit 32 from the pump and the flexible conduit UP coupled to the lower cylinder head 84, the fluid being routed through valve chambers and

passages

45, 46U, 52 and 68U, the latter constituting the outlet port and being permanently connected to the conduit UP. The fluid flows through ports I10 in plate I01 and through similar ports I12 in plate I08, so that fluid pressure is applied to the underside of piston I08 and the fluid fills all of the space between the plates 35, I61, E08, and piston I06. There is at this time no avenue of escape for the fluid fed into the space beneath the piston I86, since the ball check valve I15 incorporated in piston I08 has no efiective outlet un der the conditions being considered. Fluid pressure accordingly projects the several telescopic sections. Although the fluid pressure tends at this time to lift the ball check I15 from its seat,

Llief valves.

the projected position by the spring I50. As the sections approach the fully projected positioning, sleeve I45 is moved outwardly over sleeve I25, as the latter is restrained by abutment washer I55,

until channel I80 is brought into registry with an external annular channel I82 in the surface of sleeve I25, as best shown in Fig. 3. The fluid may then flow from the check valve through port H9, channel I90, chamber I 92 and through a port I84 in sleeve I49 to the interior of cylinder 99. From cylinder 95 the fluid returns to conduit DN through the several telescopic by-pass tube sections I24, I22, I20, previously described. Thus, if the valve 50 is held in the left-hand position while the hoist is extended, the fluid is returned through valve port 681), valve chamber 50, and valve passages 97D, 62, to the return conduits :3, 65, through which it flows back to the reservoir I6. The hydraulic fluid may thus circulate continuously while the hoist is in its extended positioning, thereby eliminating any danger of overloading the pump or hydraulic system, or any necessity for reliance upon overload pressure re- It will be understood by those skilled in the art that this arrangement also reduces the tendency to overheat the oil which would be present if overload relief valves were relied upon.

To initiate power retraction of the hoist assembly, the valve 50 is moved to the right, as viewed in Fig. 6, to establish communication between ports 48D, 98D, through the agency of which fluid delivered to the valve body from the pump by way of conduit 32 is conducted to the conduit DN, whence it is delivered to the telescopic bypass tube assembly I20, I22, I24, by conducting and connecting means previously described, the fluid pressure being thereby introduced into the interior of the cylinder 99, whence it ma flow into the interior of the surrounding cylinders, but only in the spaces above the piston sections of each, in a'controlled manner. With the assembly initially extended, the interior of cylinder 9% communicates through a port I88 of restricted cross section with a chamber I90 defined by the area between cylinders 94 and 99 above piston I06. It will be understood that if desired, in order to prevent undue straining of the hoist mechanism, the upward tilting movement of the dump body as I2 may be limited so that the hoist sections are never extended as fully as they are shown in Fig. 3, which indicates the extreme limit of possible movement. Although the lower port I88 in the wall of cylinder 99 is shown in Fig. 3 as moved upwardly slightly above the abutting faces of the piston portion 506 and the head of cylinder 94, it will be appreciated that at the start of power down operation, the fluid will force its way between such piston and head portions to drive the piston IBG downwardly. The fluid cannot move upwardly because of the packing H5 and the fit of the slidable metal parts will not, as a practical matter, prevent the fluid from entering the space I90 in this manner, even if the cylinder 96 is moved outwardly to the extreme limit as shown in Fig. 3. The cross-sectional area of the head portion of piston E06 exposed to the interior of chamber i530 exceeds in area the cross section of the active inner face of couplingclosure member 24, so. that the fluid-supply pressure urges the piston I06 inwardly with greater effort than it exerts in an outward direction against the inner head of cylinder 96 represented by the under surface of member 24. Cylinder 96 is accordingly forced inwardly by the fluid pressure, a port I92 of greater cross-sectional area. than port I88 being uncovered as cylinder 96 commences its inward movement, permitting the fluid to flow rapidly into the chamber I90 and slide the sleeve 96 inwardly. As the cylinder 96 completes its inward movement, piston I06 uncovers a port I94 formed in the wall of cylinder 94 near the inner end of the latter, and the fluid then flows through port I94 into the space 200 between the

cylinders

92, 94, forcing the piston section I04 downwardly to slide its connected cylinder 94 into the cylinder 92. As the piston I04 and connected cylinder 94 complete their inward movement, the piston I04 uncovers a port I96 positioned .in the wall of cylinder 92 near the inner end of the latter, and the fluid then flows under pressure into the chamber 2I0 between the

cylinders

20, 92, and above the piston I02, forcing the cylinder 92 inwardly with respect to the main cylinder 20 and bringing the parts to the fully telescoped positioning shown in Fig. 2.

As the piston I02 completes its inward travel, it uncovers a port 598 in the lower portion of the wall of cylinder 20. Port I98 communicates with the upper chamber portion 202 of a check valve body 204 containing a ball check valve 205 arranged to be unseated by the fluid under pressure thus introduced. As the ball 205 is moved away from its seat, against the resistance of its closing spring 206, fluid enters the lower check valve chamber 208 which communicates through a connecting nipple 2I2 with the space within the cylinder 20 beneath the piston I02, which area is in direct communication with the conduit UP. After the telescopic sections are fully retracted, therefore, and while the valve 50 remains in the right-hand or down position fluid may return to the reservoir by way of'check valve body 204, conduit UP, and valve ports and passages 08U, 56, STU, and 62, whence it returns to the reservoir by Way of connecting conduits 64 and 65. It will thus be apparent that the oil may circulate freely with the hoist in the down position in a manner analogous to the abovementioned free-circulating action which is provided when the hoist is extended.

It will be apparent that while the hoist is being extended, fluid is returned to the reservoir by counterflow through the telescopic by-pass tubes I20, I22, I24 and conduit DN as the fluid is forced out of the areas I90, 2.00, 2H as such areas diminish in size with projection of the telescopic sections. Correspondingly, during power-induced retraction of the hoist section the fluid is forced out of the areas between the plates 84, I07, I08, and piston I06, through the several passages I70, I12, previously mentioned and returned by Way of conduit UP to port 681T, whence it is delivered to the return lines 64, 65, in the manner previously mentioned.

- When in the downward movement of the te1escopic sections the body passes over center, so that its weight tends to augment the inward closing effort exerted upon the hoist sections, the pressure developed as a result of the weight of the body and the compressive force it exerts upon the telescopic hoist sections may exceed the pump pressure delivered to conduit DN from the pump in the manner previously described. In that event a check valve 2I5 is opened to permit the fluid thereby returned under the augmented pressure torecirculate to the line DN and back through the hoist unit, so that the pump l8 then need only supply such excess fluid as is required to fill the increasing

areas

1,90, 200, 2H], as the, hoist sections collapse.

While it will be apparent that the preferred embodiment of my invention herein disclosed is well calculated to fulfill the objects and attain the advantages set forth in the introductory portion of this specification, it will be appreciated that the invention is susceptible to modification and change without departure from the spirit and scope of the following claims.

What is claimed is:

1. In a fluid-operable motor unit of the type including a cylinder, a piston slidable therein, and means for selectively directing fluid into the cylinder upon either side of the piston whereby the piston may be driven in either direction, a tubular member attached ,to and movable with the piston and slidably projecta-ble from one end of the cylinder, said member being closed at its outer end, said means for directing fluid into the cylinder upon one side of the piston comprising a feed tube of lesser diameter than said first mentioned tubular member extending into the opposite end of said cylinder and projecting slidably through the piston and into the first mentioned tubular member and substantially sealed with respect to said member and piston, the effective cross sectional area of the piston outside the tubular member exceeding th effective cross sectional area of said tubular member, and passage-defining means connecting the interior of the tubular member with the space within the cylinder upon the same side of the piston as that from which the tubular member projects, whereby fluid introduced into the tubular member through said tube may act upon the piston to move the same in a direction to retract said tubular member with respect to the cylinder, means for introducing fluid directly into the cylinder upon said opposite side of the piston to project the tubular member with respect to the cylinder,

passage-defining means providing direct communication between the portions of said cylindeif upon opposite sides of the piston, means including a check valve and normally closed port-defining means incorporated-in the aforementioned passage-defining means, the port-defining means being adapted to be opened by movement of the piston to one extreme of its travel.

2. In a fluid-operable motor unit of the type inciuding a cylinder, a piston slidable therein, and means for selectively directing fluid into the cylinder upon either side of the piston whereby the piston may be driven in either direction, a tubular member attached to and movable with the piston and slidably projectable from one end of the cylinder, said member being closed at its outer end, said means for directing fluid into the cylinder upon one side of the piston comprising a feed tube of lesser diameter than said first mentioned tubular member extending into the opposite end of said cylinder and projecting slidably through the piston and into the first mentioned tubular member and substantially sealed with respect to said member and piston, the effective cross sectional area of the piston outside the tubular member exceeding the effective cross sectional area of said tubular member, and passage-defining means connecting the interior of the tubular member with the space Within the cylinder upon the same side of the piston as that by fluid introduced into the tubular me ber through said tube may act upon the piston to move the same in a direction to retract said tubular member with respect to the cylinder, means for introducing fluid directly into thecylinder upon said opposite side of the piston to project and means for selectively directing fiuid into the cylinder upon either side of the piston whereby the piston may be driven in either direction, a

tubular member attached to and movable with the piston and slidably projectable from one end of the cylinder, said member being closed at its outer end, said means for directing fluid into the cylinder upon one side of the piston compris- 1 ing a feed tube of lesser diameter than said first mentioned tubular member extending into the opposite end of said cylinder and projecting slidably through the piston and into the first mentioned tubular member and substantially sealed with respect to said member and piston, a seci ond cylinder within which the first-mentioned cylinder is slidable but from which it projects at one end, said cylinders being of substantially different diameters and being in substantially sealed sliding, relation at the inner end of the first mentioned cylinder and at the outer end of the second cylinder, to provide a chamber therebetween, and means providing communication between the outer end of said first mentioned cylinder and said chamber when the tubular member is fully retracted into the first mentioned cylinder, the sealing means atthe inner end of the first mentioned cylinder being then adapted to serve as a piston to actuate the first mentioned cylinder inwardly with respect to the second cylinder.

4. In a fluid-operable motor unit of the type including a cylinder, a piston slidable therein, and means for selectively directing fluid into the cylinder upon either side of the piston whereby the piston may be driven in either direction, a

tubular member attached to and movable with cylinder within'which the first-mentioned cylinder is slidable but from which it projects at one end, said cylinders being of substantially different diameters and being in substantially sealed sliding relation at theinner end of the first mentioned cylinder and at the outer end of the second cylinder, to provide a chamber therebetween, and

means providing communication between the outer end of said first mentioned cylinder and said chamber when the tubular member is fully retracted into the first mentioned cylinder, the

tram which the tubular member projects, wherem sealing means at the inner end of the first m n.

tioned cylinder being then adapted to serve as a piston to actuate the first mentioned cylinder inwardly with respect to the second cylinder, and a second feed tube slidably interfitted with respect to the first mentioned feed tube and projecting into the opposite end of the second cylin-.- der to that from which the first mentioned cylinder proj ects. I

5. In a fluid operable motor unit of the type including a cylinder, a piston slidable therein, and means for selectively directing fluid into the cylinder upon" either side of thepiston whereby the" piston may be driven in either direction, a tubular member attached to and movable with the piston and slida'bly projectable from one end of the cylinder, said member being closed'at-its outer end, said means for directing fluid into the cylinder upon one side of the piston comprising a feed tube'oi'lesser diameter than said first mentioned tubular member extending into the opposite end of said cylinder and projecting slidably through the piston and into the-first mentioned tubular member and substantially sealed with respect to said member and piston, the effective cross sectional area of the piston outside the tubular member exceeding the effective cross sectional area of said tubular member, passagedefining means connecting the interior of the tubular member with the space within the cylinder upon the same side of the piston as that from which the tubular memberprojects, whereby fluid introduced into the tubularmember through said tube may act upon the piston to move the same in a directionto retract said tubular member with respect to the cylinder, means for introdu cing fluid directly into the cylinder upon said opposite sideof the piston toproject the tubular member with respect to the cylinder, passagedefining means'providing direct communication between the portions of said cylinder upon opposite sides of'the piston, a check valve carried by said piston and adapted to provide one directional fluid communication therethrough from the inner to the outer side of the piston, and valve means also carried by the pistonand positively preventing fluid flow through said check valve in either direction except when the piston approaches one extreme of its movement.

6. In a fluid-operable motor unit of the type including a cylinder, a piston slidable therein, and means for selectively directing fluid into the cylinder upon either side of the piston whereby the piston may be driven in either direction, a tubular member attached to and movable with the piston and slidably projectable from one end of the cylinder, said member being closed at its outer end, said means for directing fluid into the cylinder upon one side of the piston comprising a feed tube of lesser diameter than said first mentioned tubular member extending into the opposite end of said cylinder and projecting slidably through the piston and into the first mentioned tubular member and substantially sealed with respect to said member and piston, the effective cross sectional area of the piston outside the tubular member exceeding the eilective cross sectional area of said tubular member, passagedefining means connecting the interior of the tubular member with the space within the cylinder upon the same side of the piston as that from which the tubular member projects, whereby fluid introduced into the tubular member through said tube may act upon the piston to move the same in a direction to retract'said tubular member with respect to the cylinder, means 12 for introducing fluid directly into the cylinder upon said opposite side of the piston to project the tubular member with respect to the cylinder, passage-defining means providing direct communication between the portions of said cylinder upon opposite sidesof the piston, and valve means normally closing on" such communication comprising a sleeve valve slidable with said piston and tubular member and slidably encircling said feed tube, said valve being actuatable to a position to establish such communication as the piston approaches one extreme of its movement.

'1. A telescopic fluid motor unit comprising a plurality of telescopically interfitted cylinders having walls radially spaced from one another sufficiently to define annular chamber therebetween, each cylinder except the innermost having an inwardly overhanging head portion slidably engaging-the cylinder next therewithin, and each cylinder except the outermost having an outwardly extending piston portion slidably engaging the next outermost cylinder, whereby chambers are provided between the cylinders, means for applying fluid to the interiors of at least some of the cylinders to project them with respect to one another, and means for applying r'iuid to the chambers between the cylinders to retract them, including a plurality of telescopic feed tubes carried by and extending through the interiors of at least some of said cylinders.

A telescopic fluid motor unit comprising a plurality of telescopically interfitted cylinders having walls radially spaced from one another sumciently to define annular chambers there-- between, each cylinder except the innermost having an inwardly overhanging head portion slidably engaging the cylinder next therewithin, and each cylinder except the outermost having an outwardly extending piston portion slidably engaging the cylinder next radially outermost whereby chambers are provided between the cylinders, means for applying fluid to the interiors of at least some of the cylinders to project them with respect to one another, means for applying fluid to the chambers between the cylinders to retract them, means providing communication between the interiors 01' all of said cylinders except the outermost thereof, means providing communication between the interior of the outer most cylinder and said chambers, and means for selectively delivering fluid either to the interior of said outermost cylinder or to the interiors of the other cylinders, said last-named means comprising a plurality of telescopic i'eed tubes, one such feed tube being carried by and extending through the interior of each of said other cylinders and opening into said outermost cylinder.

9. A telescopic fluid motor unit comprising a plurality of telescopically interfitted cylinders having walls radially spaced from one another sumciently to define annular chambers therebetween, each cylinder except the innermost having an inwardly overhanging head portion slidably engaging the cylinder next therewithin, and

each cylinder except the outermost having an outwardly extending piston portion slidably en gaging the next outermost cylinder whereby chambers are provided between the cylinders, means for applying fluid to the interiors of at "leastsome or the cylinders to project them with respect to one another, means for applying fluid to the chambers between the cylinders to retract them, means providing communication between the interiors of all of said cylinders except the outermost thereof, means providing communication between the interior of the outermost cylinder and said chambers, means for selectively do livering fluid either to the interior of said outermost cylinder or to the interiors of the other cylinders, said last-named means comprising a plurality of telescopic feed tubes extending through the interiors of said other cylinders and opening into said outermost cylinder, and means providing communication between said chambers comprising port-defining portions successively providing communication therebetween as the several cylinders approach the inner extremities of their individual travel.

10. A telescopic fluid motor unit comprising a plurality of interfitted cylinders of materially variant diameters to provide substantial spacing therebetween, each cylinder except the innermost having an inwardly overhanging head portion slidably engaging the cylinder next therewithin, and each cylinder except the outermost having an outwardly extending piston portion slidably engaging the next outermost cylinder, whereby chambers are provided between the cylinders, means for applying fluid to the interiors of at least some of said cylinders to project them with 25 respect to one another, and means for applying fluid to the chambers between the cylinders to retract them, said last-named means including a plurality of axially arranged telescopically in- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 298,224 Morgan May 6, 1884 501,26 Kampf July 11, 1893 513,493 Evered Jan. .30, 1894 2,233,521 Ernst Mar. 4, 1941 2,398,999 Obecny Jan. 12, 1943 2,399,702 Gail Dec. 11, 1945 2,438,295 Houldsworth Mar. 23, 1948 2,453,359 Stegeman Nov. 9, 1948 FOREIGN PATENTS Number Country Date 801,573 France May 23, 1936