US2670811A - Multicylinder hydraulic lift truck - Google Patents

Description

March 2, 1954 w. M. SHAFFER 2,670,811

MULTICYLINDER HYDRAULIC LIFT TRUCK Filed Jan. 17, 1949 5 Sheets-Sheet 1 4 INVENTOR. WAA 22? .44. JAM/TEE March 2, 1954 w. M. SHAFFER MULTICYLINDER HYDRAULIC LIFT TRUCK 5 Sheets-$heet 2 Filed Jan. 17, 1949 INVEN TOR. 14 44 726? M J/MF/Z'E ram/[V5 March 2, 1954 Filed Jan. 17, 1949 W. M. SHAFF ER MULTICYLINDER HYDRAULIC LIFT TRUCK 5 Sheets-Sheet 3 March 2, 1954 Filed Jan. 17, 1949 W. M. SHAF F ER MULTICYLINDER HYDRAULIC LIFT TRUCK 5 Sheets-Sheet 4 IN V EN TOR. WAZ 727? M JHAFFEE March 2, 1954 w. M. SHAFFER MULTICYLINDER HYDRAULIC LIFT TRUCK 5 Sheets-Sheet 5 Filed Jan. 17, 1949 Fj 1E INVENTOR.

W41 me M. SHA Fit? A NE Y5 Patented Mar. 2, 1954 MULTICYLINDER HYDRAULIC LIFT TRUCK Walter M. Shaffer, Cleveland, Ohio, assignor to Towmotor Corporation, Cleveland, Ohio, a corporation of Ohio Application January 17, 1949, Serial No. 71,373

This invention relates to industrial lift trucks and, more particularly, to the mast structure thereof, the principal objects of the invention being to improve the mast so as to provide a high maximum lift, a high free lift, and improved visibility for the lift truck operator.

Industrial lift trucks are very well-known and widely used in handling materials of many kinds in warehouses, factories, freight terminals, and so forth. The use of such machines has so facilitated the stacking of boxes and cartons, as well as-many more articles, that far more efficient utilization of warehouse space has been made possible. This is particularly true where the lift truck is capable of elevating the load to considerable height so that a maximum quantity of goods can be tiered and stored in a given floor area.

Since it is usually necessary for lift trucks to pass through doors of conventional height the provision of a high lift has necessitated the use of telescoping mast structures, and various arrangements of telescoping mast rails are known.

It isalso desirable that a lift truck be capable of stacking articles close to a low ceiling in many cases, as, for example, when the machine is used for loading box cars and vans. With certain known types of machines the inherent construction of the machine is such that elevation of the extensible mast section takes place concurrently with elevation of the load-supporting carriage, or, in other words, as the load is elevated the height of the mast is increased, usually at a considerably slower rate. However, in some cases, the carriage may be elevated through a certain range before the total height of the mast begins to increase and this range is known as the free lift of the machine. A high free lift has been obtained in machines using a drum and cable or an endless chain operated by a rotating shaft, but thesearrangements have certain disadvantages, as they involve a rather complicated mechanical system and they are not well-suited for hydraulic operation.

In general a lift truck that employs a hydraulic cylinder for elevating the carriage has many advantages, but no satisfactory arrangement, has heretofore been proposed through which an appreciable amount of free lift is possible, because, even though the mast itself is not extended, the distention of the hydraulic ram increases the over-all height of the machine.

Ithas been proposed to increase the free lift by employing block and tackle arrangements to multiply the movement of the cylinde so tha 14 Claims. (Cl. 187-9) a relatively short hydraulic cylinder could be employed. These arrangements also involve structural complications and are undesirable in that they tend to obscure the view of the operator of the truck.

This invention presents a superior solution to the problem of providing maximum free lift in an industrial truck characterized by efficiency, simplicity, economy, and improved visibility. In brief, this object is accomplished through the provision of a plural cylinder assembly and by utilization therewith of a simple set of motion-multiplying chains such as are known to be highly satisfactory in lift trucks. The chains are used to double the movement of the larger cylinder, which is capable of exerting sufiicient force to handle the contemplated load. The chain may be limited to a single pair of strands which, in contradistinction to the multi-chain structures heretofore in use, will improve the operators visibility, yet elevate the carriage to'the top of the fixed or unextendible portion of the mast. The extension of the mast and further elevation of the carriage" is effected in one embodiment of the invention by a second cylinder of smaller diameter which may have a stroke substantially as great as the minimum height of the mast and which operates without multiplication of motion.

In a second form of the invention the principle outlined above is carried one step further to provide an extremely high lift structure; in other words, one in which the maximum elevation of the lift truck carriage is relatively great in relation to the height of the lowered or telescoped mast. This is achieved by the use of a mast having three sections, two of which are extensible with respect to the base section which is mounted on the lift truck, in combination with a cylinder assembly of the type previously discussed but provided with an additional plunger in the mast cylinder so that the cylinder is extensible to approximately three times its contracted length.

In a third form of the invention the principle,

is employed to provide a lift truck which provides normal mast extension and a maximum amount of free lift and in which, when the carriage is lowered, there is no obstruction whatever to the vision of the operator of the lift truck from the mechanism which elevates the carriage and mast. In this form a plural cylinder assembly in which no cylinder is of substantially greater length than half the height of the low-'- ered mast is employed, and thus the operator may, readily see over the cylinder assembly when the carriage is lowered, as it normally is when the load is being transported from one place to another.

The invention thus overcomes the disadvantages or system that employ a short hydraulic cylinder with a high motion multiplication wherein the relatively large cylinder and multiplechains greatly impair visibility. Th invention is also superior to simple telescopic cylinder arrangements sinc the improved cylinder assembly is shorter and lighter and facilitates a much greater free lift movement than heretofore attained.

The pricipal object of the invention is to provide an improved system for obtaining relatively great free elevation in lift trucks; a further object of the invention is to obtain high free lift with maximum visibility, a minimum of complexity, and relatively high efliciency; a further object of the invention is to secure the foregoing advantages without sacrifice of any of the utilities of former mast and carriage structures.

Other objects and advantages of the invention, more or less ancillary in nature, will be apparent to those skilled in the art from the description herein of the preferred embodiment of the invention.

Referring to the drawings:

Fig. 1 is a front elevation of a mast structure embodying the present invention with the carriage lowered, the mast being shown in place on a lift truck illustrated schematically;

Fig. 2 is a similar View of the mast structure with the carriage raised to its maximum free lift position;

Fig. 3 is a similar view with th carriage fully raised and the mast extended Fig. 4 is a longitudinal view, partly in section, of the cylinder assembly of the mast shown in Figs. 1 to 3;

Fig. 5 is an elevation view, partially in section, of the lower end of the mast illustrating one manner of mounting the cylinder;

Fig. 6 is a horizontal sectional view of the lower end of the mast;

Fig. '7 is a front elevation of a second form of mast structure embodying the present invention, this form providing an extremely high lift, the carriage being shown in its lowered position;

Fig. 8 is a front elevation of the same with the a carriage elevated to its maximum free lift;

Figs. 9 and 10 are similar views showing progressive steps in the elevation of the carriage and concomitant extension of the mast;

Fig. 11 is a longitudinal view partly in section of the cylinder assembly employed in th mast of Figs. '7 to 10;

Fig. 12 is a longitudinal view partly in section of a third form of cylinder assembly; and

Figs. 13 to 16 are elevational views of a mast incorporating the cylinder of Fig. 12 illustrating the progressive stages in the elevation of the carriage.

Lift trucks in which the mast structures of the invention may be employed are well known and therefore it is considered that no extended description of such machines is required for an understanding of this invention. Th preferred environment for the invention is the well-known Towmotor lift truck, but the invention may obviously be employed in lift trucks of other types. A truck in which the invention may be employed is described in the copending application of Elverton W. Weaver for Industrial Trucks, Serial No. 750,914, filed May at, 194;7.

Such trucks include a chassis in (Fig. 1) supported by wheels H. A mast structure including parallel upright channel members I2 is supported at its lower end upon the frame of the truck by means which are not material to the present invention. A load-supporting carriage l3, which may be fitted with any desired arrangement for engaging and supporting the load, is elevated on the mast by a hydraulic cylinder assembly.

Considering now the form of the invention shown in Figs. 1 to 6, in Fig. l the carriage is shown lowered to a position adjacent the floor, in Fig. 2 it has been elevated to a position adjacent the top of the channels 12, and in Fig. 3

the carriage has been elevated still further and the mast is extended. The mast structure includes an inner channel assembly or slide l4 which recip-rocates in the outer channel members I2; the carriage l3 reciprocates within the channels l4- untilthe carriage reaches the position illustrated in Fig. 2. With this construction considerable lift may be obtained without extending the mast. Additional elevation is accommodated by vertical movement of the upper mast structure comprising the channels M. Extensible mast structures such as thos formed by the channels [2 and i4 and mechanism for guiding the carriage for movement on the mast are known in the art and the details thereof are not essential to an understanding of this invention. The mast structure preferably comprises a bottom cros plate [6 uniting the channels I2. which are further united by additional cross members such as lfia. The inner channels 14 are connected at their upper ends by a cross member H. The carriage l3 may be provided with rearwardly directed members [8 on which are mounted rollers I9 which traverse the channels l4.

A cylinder assembly 20 is supported at its lower and upper ends by the cross members [6 and H respectively. The manner in which the cylinder assembly serves to lift the carriage and extend the mast may be best understood after a description of the structure of the cylinder assembly, which is shown principally in Fig. 4. This assembly comprises generally an inner cylinder or ram united with an outer cylinder or ram which, in its retracted position, is approximately half the length of the inner ram and may be extended to approximately the entire length of the inner ram. The inner ram is connected to the base cross member and. therefore supports the assembly and is also provided with a single fluid connection through which both rams are actuated.

More specifically, the cylinder or ram structure constitutes an inner plunger 30, an inner cylinder 40, an outer plunger 50, and an outer cylinder -68. The inner plunger constitutes primarily a length of tubing 3| upon the lower end of which there is welded an end fitting 32, the diameter of which equals the .outside diameter of the tubing. The outer end of the fitting is bored for the reception of a pin 33 mounted in brackets afiixed to the cross member 16, and a fluid inlet 34 tapped for the reception of a hose fitting is provided in the side of the body 32 and discharges into the interior of the plunger. The upper end of the plunger 3! is partially closed by an annular disk 35 having a collar 36 thereon for guiding the plunger in the cylinder 4c. The cylinder 40 embodies a section Al of tubing of slightly greater inside diameter than the outside diameter of the plunger 30, one end of which is closed by a welded cylinder head 42. The cylinder head is drilled and tapped as indicated at 43 for cap screws 44' (Fig. 1) by which it is secured to the cross member ll. The lower end of the cylinder is provided with a packing retaining ring 45 welded to the tubing 4| and formed with an internal bore 46 for a sliding fit of the plunger 30. A packing nut 41 retains a packing material 48 which may be of any type, and supports a wiper ring 49. The inner face of the cylinder end ring 45 coacts with a ring 31 welded to the outer surface of the plunger 30 to limit the extension thereof from the cylinder to a safe and proper value.

The outer or carriage ram comprising the cylinder 60 and plunger 50 normally forms an annular structure surrounding the lower half of the cylinder 4|). B0 is provided with a ring 62 welded to the end member 44 of the inner cylinder. The cylinder sleeve or tube 6| is supported by the ring 62 and a packing retaining ring 63, both of which are welded to the tube. The internal diameter of the ring 63 is formed for a sliding fit upon the plunger 5!) and the joint is sealed against leak- The lower end of the cylinder age by a packing material 54 retained by a nut 65. The plunger 50 comprises a tube 5| slightly smaller than the tube SI and disposed in telescopic relation therewith. The outer end of the plunger extension tube 5| is provided with a ring 52 which is welded thereto and adapted to.

limit the extension of the plunger 50 when brought into abutting engagement with the packing retaining ring 63. The upper end of the plunger 50 has a ring 58 welded therein which is of sufficient length to afford an adequate bearing surface 53 for the cylinder 4|. The ring 58 is counterbored for the reception of a packing material 54 which is retained by a nut 55 threaded in the upper end of the ring. The retaining nut is of sufiicient length to extend through and protrude beyond the upper face of the crosshead 1|. The crosshead constitutes a part of the chain-elevating mechanism by which the movementof the plunger 52 is transmitted to the carriage and is formed with a counterbore 51 in the lower face thereof for the reception of the ring 52 so that the thrust of the cylinder may be transmitted directly to the crosshead member. 7

The outer cylinder has approximately onehalf the stroke of the inner cylinder, and the ring 58 slides over approximately one-half of the upper portion of the cylinder 40.

Both of the rams are of the single-acting type and are extended by the pressure of fluid from a suitably controlled hydraulic system. Retraction of the rams is effected by gravity under the combined weight of the carriage and mast.

As the pressure fluid delivered through the connection 34 enters the inner ram a portion thereof will be fed through the radial passages 38 in the inner tube 3| and the radial passages 39 in the tube 4| until the chamber within the plunger 50 and the upper end of the tube 3| are filled, whereupon the fluid acting on the larger cylinder head, i. e., the ring 58, will initiate the movement of the ram 50 and effect the extension thereof from the cylinder 60.

A bracket 68 welded or otherwise secured to the upper end of the'cylinder 6| is provided to accommodate the anchorage of the chains for elevating the carriage.

Referring now to Figs. 1 to 3, the ram 50 is coupled to the carriage |3 by chains 12 disposed generally between the cylinder and the mast rails. One end of each chain 12 is fixed to the bracket 68 and the other end of the chain is connected to the carriage |3. Each chain passes over a sheave 14 mounted on the crosshead and rotatable on a horizontal axis. This arrangement of the chains is similar in principle to that disclosed in the above-noted Weaver application except that the chains are anchored to the cylinder rather than to the mast. As will be apparent, the chains multiply the movement of the ram 50 so that the amount of movement of the carriage I3 is twice that of the ram and the length of the ram is such as to effect the'elevation of the carriage l3 from a position of rest at the bottom of the channel members l2 to the top of the members I2, thus taking full advantage of the length of the mast without the extension thereof. The effective area of the outer ram is more than twice that of the inner ram, and therefore the resistance to extension of the outer ram, notwithstanding the two-to-one multiplication of movement, is less than that of the inner ram. Therefore, when hydraulic fluid is forced into the cylinder assemblythrough the port 34 it will takethe path of least resistance through ports 38 and 39 into the outer cylinder until this cylinder is fully extended. Thus, when only moderate elevation of the carriage is required, such movement is accomplished by the outer cylinder. When it is desired to lower the carriage, fluid is allowed to escape through the port 34 and the weight of the carriage, chains, and rams is sufiicient to effect the retraction of the carriage and expel the fluid from the cylinder. When the outer ram reaches its fully extendedposition, that is, when the stop 52 engages the ring 63 and fluid continues to be supplied, the inner cylinder 40 will be forced upwardly carrying the outer cylinder 60, the chains, the carriage, and the mast extension channels I4 therewith, as shown in Fig. 3. In the latter cycle of operation there is no change in the relative "position of the carriage and the channels |4 since the position of the plunger 50 and cylinder 60 do not change. As will be apparent, the total elevation is approximately twice the amount of the elevation illustrated in Fig. 2, save for the overlapped relation of' the channel members I2 and I4. When the carriage is lowered, the fluid is-permitted to escape through the connection '34, and since the load-imposed upon the inner cylinder isgreaterfthe fluid will be discharged from this before the assembly is completely recylinder t'racted,

The dimensions of the cylinders will, of course,

depend upon the weight of the'parts, the load; for which the machine is designed, and the operating pressure chosen for the hydraulic system; The outer cylinder 60 need not be greatly larger than would be required for a simple ram acting through the force multiplying chain 12 j without the inner cylinder, and, as will be apparent from Figs. 1 and 3, the cylinder and chains form but slight obstruction to the operators view when the carriage is either above.

or below his normal line of vision.

The outer surface of the plunger 3| and the outer surface of the cylinder 4| may, if desired,

be chromium plated or otherwise treated to preserve the finish thereon. '...while, the .cylinder pa ts are hown ,@n

actual scribed as being, principally fabricated by weldn it is to be understood that. the invention is not limited to this method of manufacture and that other forms of assembly are, contemplated as falling within the scope and spirit of the claims.

The arrangement by which the ram 30 is cou- P cd to the lower cross member it may be of various types, the utilization of the fulcrum pin 33 in the plunger being merely one type of mounting that has been found practical and serviceable. As will be seen in Fig. 5, the port 34 is provided with a flexible hose 90 which leads to a source of fluid under pressure in the manner customarily employed in machines of this character. The mechanism by which the flow of oil to; and from the cylinder is controlled is well understood by those skilled in the art and a detailed description thereof is therefore deemed unnecessary herein.

The second form of the invention, which provides an unusually-high lift for the carriage, is illustrated in Figs. '7 to 11. The principle of this form may be readily understood in view of. the previous detailed discussion by stating that the second form difiers from the first primarily in the provision of a three-section telescoping mast instead of the two-section one of the first species and by the employment of two telescoping plungers in the mast-elevating cylinder to obtain the. additional elevation without increasing the collapsed height of the mast r cylinder. Since otherwise most of the structural features of the second form are substantially the same as those previously directed, detailed description of the mast and cylinder assembly will be omitted in the interest of brevity, except insofar as the construction is modified from that previously described; and parts which are common to both forms will be identified by the same reference character.

In addition to the lower section I2 and the upper section 14, the mast comprises an intermediate section ldl comprising channel members which slide in the sections I2 and within which sections l4 slide. The carriage l3 reciprocates within the channels M as previously described. With the channel sections all of the same length it is possible to extend the mast to approximately two and one-half times the length of the individual sections and preserve sufiicient overlap between the sections for stability.

In Fig. 7 the mast and carriage are shown in their lowermost positions. In Fig. 8 the car riage has been raised to the top of the unextended mast, the mast sections remaining in their previous conditions, this extension being accomplished by the annular cylinder and plunger assembly comprising the cylinder 69 and plunger 58, the plunger sliding over the outer surface of the mast cylinder 40. This movement is effected by means of chains 12 as previously described. In Fig. 9 the outer cylinder, the carriage, and the upper mast section [4 have been elevated to the maximum extension of the mast section 14 by extension of the plungers from the cylinder 40. In Fig. 9 the carriage, the carriage cylinder, the mast cylinder 40, plunger 30, and the mast sections l4 and fill have been lifted as a unit by an inner plunger "12 telescoping within the plunger 30. It may be noted that the upper end of the mast cylinder 40 is attached to the upper cross bar I! of the mast section M in any convenient manner and the lower end of the plunger m2 is attached to. the be tom cross member I6 of the lower mast section l2 in the same manner asthe plunger 30 is attached in he previously described form.

The channels of the mast section 14 are united at their lower end by a cross member H3 and thoseof the intermediate mast section llll likewise by a cross member I Hi. The upper ends of the channels of the intermediate mast section are tied together by across piece I 16. The lower end of the plunger-38 is fixed to the intermediate mast section l9! by a cross member H1 which serves both to brace the cylinder against lateral displacement and to insure that the mast section [01 descends with the plunger 30 when the fluid is exhausted, permitting retraction within the plunger '30. of the plunger I32.

Considering now the construction of the cylinder assembly, which is shown in greater detail in Fig. 11, this comprises the outer cylinder 69, an annular plunger 50,, an inner or mast cylinder ii), .and a plunger 30 reciprocable therein as in the previously described form. The plunger 38 differs from the corresponding plunger of Fig. 4 in that it is provided at its lower end with means for attaching the cross member ill rather than the end fittin 32. The end fitting32 is, instead, welded to the lower end of the inner plunger )2 which reciprocates within the plunger 30, the cylinder 46 and plungers 3i and 462 thus constituting a double extension cylinder and plunger assembly. In this construction, hydraulic fluid entering through the port 34 and fitting S2 enters the chamber within the plunger Hi2 and passes through ports 163 in that plunger, ports 33 in plunger 39, and ports 39 in the inner cylinder 4!! to the outer ram where it is effective to extend, the plunger 53 and elevate the carriage. As in the previous form of the device, the effective area of this outer cylinder is such that it fills with fluid first. When the carriage has been raised to its maximum elevation, an

additional supply of hydraulic fluid projects the plungers 38 and T92 as a unit from the cylinder 40 as'illu strated in Fig. 9. When the stops 31 on the plunger 36 strike the head of the cylinder, an additional supply of hydraulic fluid accompanied by a slight increase in pressure extends the plunger 182 from the plunger 36 which acts as a cylinder therefor, as illustrated in Fig. 10. No detailed description of the construction of the cylinders is believed to'be necessary in view of the fact that the structural principles and details' in general are as previously described. The member H'l' which couples the lower end of the plunger 30'to the channels IOI may be coupled to the'plunge'r 30 in any convenient manner as by a collar H8 retained between the gland nut H9 and the ring l2! which reinforces the lower end of the plunger 30. It should be noted that the connection! ll need not lift the intermediate section ml, since this may be carried up by the upper channel section hiby provision of interengaging elements on these parts limiting the extension of the upper section 14 with respect to the intermediate section WI. It does assure, however, that the section I6] is lowered into the lower section 12 before the section M is lowered into the section iii i.

For a given load to be elevated and a given hydraulic pressure, it will be apparent that this form will require slightly larger diameter cylinders than that previously disclosed.

The third-form of the invention, illustrated in Figs. 12 to 16 is one withtwomas't sections,"

and has the same characteristics a to free lift and total lift as the device of Figs. 1 to 6. By the incorporation of a modified hydraulic system, the use of a relatively short hydraulic. cylinder assembly is permitted, thereby further improving the vision of the truck operator. The shorter cylinder assembly is made possible principally by the utilization of a multiple telescoping mast cylinder and plunger assembly which is in many respects similar to that of Fig. 11. In view of the fact that the mast is single-extension, a much shorter mast cylinder may be employed than that illustrated in Fig. 11, and the mast cylinder may be contained within the carriage cylinder.

' In Figs. 12 to 16, parts whichare similar in structure and function to those previously described will be identified by the same reference numerals.

' Referring to Figs. 13 to 16, the channels of the mast section I4 slide in the channel sect1ons of the fixed mast I2 and the carriage I3 reciprocates in channels I4. The carriage cylinder 60 is as previously described, and mounts slidably therein the carriage elevating plunger I50 which is generally similar to the plunger 50 except for the upper end construction. Since the mast cylinder is contained within the plunger I50 in its retracted position and the plunger does not slide over the mast cylinder, the plunger is fitted with a head I42 welded thereon in place of the packing gland assembly employed in the forms previously described. The head I42 is tapped as indicated at I43 for the securement thereto of a crosshead III, which may mount chain sprockets for the carriage elevating chains I2 as previously described. One end of each chain I2 is fixed to a member I68 which correspond to the previously described chain anchorage and is aflixed to the cylinder wall, but is extended as illustrated in Figs. 14 6016 to engage the channel members I4 to which it is secured in any convenient manner, thus uniting the cylinder 60 with the upper mast section for elevatin and lowering movement, and supporting the cylinder 60 in its proper parallel relation to the mast. The mast cylinder I40 is disposed within the plunger I50 and is joined to the cylinder 60 by a ring 62 welded to both cylinders at the lower end. As previously stated, the length of the cylinder I40 is substantially equal to that of the cylinder I60. Concentric plungers I30 and 202 are reciprocably mounted within the cylinder I40, the principles of construction being substantially the same as that described in connection with Fig. 11 except that no ports through the plungers or cylinder wall are required in this construction. A fitting 32 welded to the lower end of the plunger 202 is provided .with a fluid inlet port 34 connected tothe controlled source of hydraulic fluid. When fluid is introduced through the port 34, pressure is exerted against the cylinder head I32 and the ram I50 is extended, elevating the carriage I3 from the position illustrated in Fig. 13 to that illustrated in Fig. 14, thus providing a free lift to the total collapsed height of the mast. When the ram I50 has reached its limit of movement defined by engagement of the stop I52 against theupper end ring 63 of the cylinder 60, further supply of fluid .accompanied by a slight increase of pressure causes the plungers 202 and I30 to be concurrently extended from the cylinder I40 until the carriage cylinder and sliding mast section are elevated to the position illustrated in Fig. 15. With a slight additional increase in pressure, further supply of fluid extends the 10 plunger 202 from within the plunger I30, thus elevating the mast and carriage to the maximum height as illustrated in Fig. 16. The plunger 202 may besupported on the bottom cross member I6 of the lower mast section in th same manner as previously described.

It may be noted, as compared with the form of the invention first described, that the form of Figs. 12 to 16 is advantageous in that the vision of the operator of the truck is improved when the carriage is lowered and that a shorter mast cylinder is required. Thi form, however, requires an additional plunger in the mast cylinder and presumably a slightly larger overall diameter of the cylinder assembly. As in the previously described form, the effective area of the carriage cylinder is slightly more than twice thatof the plunger I30 so that the carriage may be elevated more readily than the mast and the mast will descend before the carriage descends on the mast.

The several forms of the invention described are all highly advantageous, but in certain types of service, one may be more suitable than another. It will be apparent to those skilled in the art that the general principles of the invention most satisfactorily solve the problems of maximum free lift, maximum total lift, and maximum visibility for the operator of the truck. The forms of the invention herein disclosed are the best modes of carrying out the invention presently known to me, but it will be apparent to those skilled in the art that many variations within the spirit of the invention are possible. A number of obvious modifications will be apparent in view of the principle that in general the inner and outer members of the cylinder may be reversed so that the cylinder travels over the plunger rather than the plunger within the cylinder, or that rams may be inverted so as to reverse the points of attachment of the cylinder and plunger.

Although the foregoing description is necessarily of a detailed character, in order that the invention may be completely set forth, it is to be understood that the specific terminology is not intended to be restrictive or confining, and that various rearrangements of parts and modifications of detail may be resorted to without departing from the scope or spirit of the invention as herein claimed.

Iclaim:

1. A lift truck comprising a chassis, a mast mounted thereon comprising a lower section coupled to the chassis and an upper section telescoping with the lower section, a load-supporting carriage movable along the mast, a mast ram for extending the mast comprising a cylinder coupled to the upper section and a plunger coupled to the lower section, a carriage ram comprising a cylinder surrounding said mast ram cylinder, said carriage ram cylinder being open at its upper end and fixed at its lower end to said mast ram cylinder and in fluid-tight relation therewith, a carriage ram plunger surrounding said mast ram cylinder, said plunger including a downwardly-directed extension tube for disposition between said mast and carriage ram cylinders, adjustable packing means between the upper end of said carriage ram cylinder and said carriage ram plunger as well as between the latter and said mast ram cylinder, a connection between the carriage ram plunger and the carriage to elevate the carriage relative to the upper mast section, and means for providing a comgar en" men supply of hydraulic fluid to the two rams,

the effective areas or the rams being so related to the loads efiective thereon that the carriage ram offers less resistance to extension upon entrance of fluid than does the mast ram.

2. A lift truck comprising a chassis, a mast mounted thereon comprising a lower section coupled to the chassis and an upper section telescopin with the lower section, a load-supporting carriage movable along the mast, a mast ram for extending the mast comprising a cylinder coupled to the upper section and a plunger coupled to the lower section, a carriage ram comprising a cylinder surrounding said mast ram cylinder, said carriage ram cylinder being open at its upper end and fixed at its lower end to said mast ram cylinder and in fluid-tight relation therewith, a carriage ram plunger surrounding said mast ram cylinders, said plunger including a downwardly-directed extension tube for disposition between said mast and carriage i'am cylinders, adjustable packing means between the upper end of said carriage ram cylinder and said carriage ram plunger as well as between the latter and said mast ram cylinder, a motion-multiplying connection between the carriage ram plunger and the carriage to elevate the carriage relative to the upper mast section, whereby the length of the carriage rain may be substantially less than the corresponding movement of the carriage, and means for providing a common supply of hydraulic fluid to the two rams, the efiective areas of the rams bein so related to the loads effective thereon that the carriage ram ofiers less resistance to extension upon entrance of fluid than does the mast ram.

3. A lift truck comprising a chassis, a mast mounted thereon comprising a lower section coupled to the chassis and an upper section telescoping with the lower section, a load-supporting carriage movable along the mast, a meet ram for extending the mast comprising a cylinder coupled to the upper section and a plunger coupled to the lower section, a carriage ram comprising a cylinder surrounding said inast ram cylinder, said carriage ram cylinder being open at its upper end and fixed at its lower end to said mast ram cylinder and in fluid-tight relation therewith, a carriage ram plunger surrounding said mast ram cylinders, said plunger including a downwardly-directed extension tube for disposition between said mast and carriage ram cylinders, a threaded stumng box assembly mounted on the upper end of said carriage ram cylinder and sealing with said carriage ram plunger, and another threaded stumng box assembly mounted on the upper end of said carriage ram plunger and sealing with said mast ram cylinder, a connection between the carriage rain plunger and the carriage to elevate the carriage relative to the upper mast section,

and means for providing a common supply of hydraulic fluid to the two rams, the-effective areas of the rams being so related to the loads efiective thereon that the carriage ram offers less resistance to extension upon entrance of fluid than does the mast ram.

4. In a load transporting and tiering mechanism for use in industrial trucks, a telescopic mast means comprising an outer upright frame adapted to be supported by the truck and a movable frame structure elevatably supported on the first frame structure, a load elevating carriage operatively supported by the second frame struc'- ture, a unitary hydraulic ram mechanism disposed within the telescopic mast means for erecting elevation of the carriage and elevation of the movable frame structure, said ram mecha nism being compound in its function and comprising a fixed hollow cylindrical member supported by the outer upright frame, a cylindrical slide member slidable on and coaxial to the fixedsprockets having ends thereof attached to the; carriage whereby the carriage is moved upwardly;

relative to the movable frame structure by action of the sprockets on the chains upon up:

ward thrust of the cylindrical piston, the opposite ends of the chains being held immovable: relative to the movable frame during elevation of the carriage with respect to the movable frame, and said sprocket piston being elevatable together with the carriage and the elevatable frame structure to maintain the carriage inmaximum elevated relation to the movable frame structure.

5. In a load transporting and timing mechanism adaptable for use on industrial trucks, a unitary hydraulically operated mechanism comprising multiple ram means, the respective pis tons and cylinders of which are telescopingly and substantially coaxially arranged to operaterelatively longitudinally means whereby the said,

multiple ram means are in fluid communication with each other, an upright frame structure adapted to be relatively fixed on the truck, a movable frame structure elevatably supported by the fixed frame structure, a load elevating car-- riage elevatably supported by the second frame structure, one of the hydraulic ram means having one of the telescoping elements thereoi coupled to the movable frame structure and the; other element thereof coupled to the fixed frame structure thereby to effect a relatively elevated movement between the two 'frame structures, a flexible element having one end thereof attached to the load elevating carriage, means for maintaining the other end of the flexible element fixed during movement of the carriage relative to the movable frame, one of said ram means being arranged to slide upon an element of the other ram means, a reeving means actuated by said sliding ram means and acting on the nexible element to enact an elevating movement bf the carriage relative tothemovable frame, packm gland means carried by the slidin ram means at the top thereof in sliding contact with, the ram element which is bb'upled to the mo'v-' able frame and packing gland means at the bottom of said element in sliding contact with the ram element coupled to the fixed frame.

6. In "a load trans orting and hearing mechanism adaptable m use on industrial trucks, a primary and a secondary hydraulic lly operated piston and cylinder meansfthe several piston and cylinder means being substantially'cbaxially airranged to operate relatively longitudinally "and being pro vided with fluid communication means whereby hydraulic pressure fluid may pass from one or said means to the a telescopl'c'mast means'comprising anouter upright irame ada ted to be supported by the truck end, a movable;

frame structure cperauvely sup orted by me fist frame structure, a load elevating carriage opera tively supported by the second frame structure, means coupling said secondary means to the movable frame for elevating said movable frame, said primary hydraulically operated; piston and cylinder means being disposed, within the telescopic mast means and coupled to'the loadcarriage through a flexible element having, one end thereof attached to the load ,elevatingcarriage and the other endheld relative to an element of the said secondary means and through means actuated by the said primary piston and cylinder means and acting on the flexible element to effect an elevating movement of the carriage relative to the movable frame before the secondary hydraulic means has effected elevation of the movable frame.

7. In a load transporting and tiering mechanism adaptable for use on industrial trucks, two coaxially arranged hydraulically operated ram means with one serving as a pressure fiuid conduit for the other and th several piston and cylinder means of the two ram means being substantially coaxially and telescopingly arranged to operate relatively longitudinally, a telescopic upright frame means comprising an upright frame structure adapted to be relatively fixed on the truck and a movable frame structure operatively supported by the fixed frame structure, a load elevating carriage elevatably supported by the second frame structure, one of the hydraulic ram means having one of the telescoping elements thereof coupled to the movable frame structure and the other element thereof coupled to the fixed frame structure thereby to effect a relatively elevated movement between the two frame structures, the second ram means being slidably supported by an element of the first ram means, a flexible element having one end thereof attached to the load elevating carriage and the other end secured relative to an element of the first said ram means, and a reeving means actuated by the said second ram means and acting on the flexible element to effect an elevating movement of the carriage relative to the movable frame before the other ram means has extended the frame.

8. A load tiering mechanism comprising a. telescopic mast structure consisting of a relatively fixed frame and an elevatable frame, a load carriage elevatable with respect to the elevatable frame, a unitary compound hydraulic ram mechanism disposed within the frame members comprising coaxial hollow pistons and cylinders hydraulically arranged to be in fluid communication whereby the ram mechanism is operable to effect complete vertical extension of the mast structure after a primary elevation of the load carriage, sprocket chain means anchored to the carriage, means to maintain the other end of the chain fixed with respect to the elevatable frame during primary operation of the carriage and sprocket means carried by a piston of the ram mechanism over which the sprocket chain means extends for acting on the sprocket chain means to effect the said primary elevating movement of the carriage relative to the movable frame.

9. A load tiering mechanism comprising a telescopic mast structure consisting of a relatively fixed frame and an elevatable frame, a load carriage elevatable on the elevatable frame, a duplex hydraulic mechanism disposed within the frame members comprising two hollow pistons and two cylinders hydraulically in communication and the pistons and cylinders being coaxially and telescopingly arranged to provide a directly acting inner piston, and cylinderand an indirectly acting outer piston and cylinder slidablerelative to the inner piston withthe inner piston and its cylinder being operably disposed to effect complete vertical extension .of the mast structure, a flexibl means connected to the carriage and to the outer cylinder of the hydraulic mechanism and a means carried by'the piston of the last mentioned cylinder over which the flexible means extends for acting on theflexible means to effect elevating movement of the carriage relative to the movable frame.

10. In a load transporting and tiering mechanism adaptable for use on industrial trucks, at primary and a secondary hydraulically operated piston and cylinder means, the respective piston and cylinder means being substantially coaxially arranged to operate relatively longitudinally, a telescopic mast means comprising an outer upright frame adapted to be supported by the truck end, a movable frame structure operatively supported by th first frame structure, a load elevating carriage operatively supported by the second frame structure, said primary hydraulically operated piston and cylinder means being disposed to effect a relatively elevated movement between the movable frame structure and the carriage, a flexible element having one end thereof attached to the load elevating carriage and the other end coupled to the movable frame and means coupling the said secondary piston and cylinder means directly to the movable frame lement to effect an elevating movement of the movable frame and the carriage relative to the fixed frame after the primary hydraulic means has effected a primary elevation of the carriage on the movable frame.

11. A lift truck comprising a chassis, a mast mounted thereon comprising a lower section coupled to the chassis and anupper section telescoping with the lower section, a load-supporting carriage movable along the mast, a mast ram for extending the mast comprising a cylinder coupled to the upper section and a plunger coupled to the lower section, a carriage ram comprising a cylinder movable with the upper mast section and a plunger movable relatively thereto, a motion-multiplying connection between the last-named plunger and the carriage to elevate the carriage relative to the upper mast section, whereby th length of the carriage ram may be substantially less than the corresponding movement of the carriage, and a common supply of hydraulic fluid to the two rams, the efiective areas of the rams being so related to the loads effective thereon that the carriage ram offers less resistance to entrance of fluid than the mast ram.

12. A lift truck comprising a chassis, a mast mounted thereon comprising a lower section coupled to the chassis and an upper section telescoping with the lower section, a load-supporting carriage movable along the mast, a mast ram for extending the mast comprising a cylinder coupled to the upper section and a plunger coupled to the lower section, a carriage ram comprising an annular cylinder mounted on the lower end of the mast ram cylinder and an annular plunger slidable on the ram cylinder, and a motion-multiplying connection between the lastnamed plunger and the carriage to elevate the carriage relative to the upper mast section, whereby the length of the carriage ram may be substantially less than the corresponding movement of the carriage,

18 -13. A lift truck comprising a chassis, n mast mounted thereon comprising a; lower seetion coupled to the chassis and an upper section telescoping with the lower section, a load-supporting carriage mevable-along the mas't,-a mast ram for extending the mast comprising a cylinder "coupled to the upper section and a'plunger coupled to the lower section, a carriage rem comprising an ennnlareylinder mounted on the lower end of the mast ram cylinder and an annular plunger snaeble on the ram cylinder, at motion-multiplying eennecti'oh between the last-plunger and the carriage to elevate the carriage relative to the upper mast section, whereby the length of the carriage ram may be substantially less than the corresponding movement of the carriage, the effective areas of the rams being so related to the loads effective thereon -that the carriage ram "ofiers less resistance to entrance of fluid than the mast mm, a connection for fluid under pressure 18 through the first-named plunger into the mast ram, and a conduit for fluid from the mast ram into the carriage ram, the said conduit being constantly open.

14. A mechanism of the character described in claim '7 wherein the said element coupled to the fixed frame structure is coupled therewith by an aligning support permitting of a limited alignin'g movement of the ram mechanism with the movable frame member.

WALTER M. SHAFFER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,480,066 Weaver l. Aug. 23, 1949 2,505,009 Schroeder flan--- Apn 25, 1950 2,595,959 Lawless l May 6, 1952

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