US1692121A - Truck - Google Patents

Description

` Noi-20, 1928,

G. HOLMES TRUCK Filed Aug. 6, 1923 4 Sheets-Sheet vwamtoz, GRANT HL MES.

@Hardw/L3 Nov. 2o, 1928. 1,692,121'

G. HOLMES TRUCK Filed Aug. 6. 1923 .4 sheets-smet 2 l It 36 IMA l-Il 11347 4 29 29 4 5 4743 ze 29 I8 '7 29 29 Z9 v 50H '6 l5' I Z9 l0 9 8.23 Z! 6mm/471L 25 3024 5 Y Nov. 2o, '1928. 1,692,121.

G. HOLMES TRUCK Filed Aug. 6, 1925 4 Sheets-Sheet 5 Nov. 2o, 1928. l 1,692,121

G. HOLMES TRUCK I Filed'Aug. 6. 1923 4 Sheets-Sheet 4 28 26 2'9 24./ 29/ GRANTHoL/v Patented Nov. 20, i928.

UNITED STATES 1,692,121 PATENT OFFICE..

GRANT HOLMESj OF DANVILLE, ILLINOIS, ASSIGNOR TO THE MARION STEAM SHOVEL COMPANY, OF MARION, OHIO, A. CORPORATION OF OHIO.

TRUCK.

Application inea August e, 1923. serial No. 655,850

This invention relates to trucks and more particularly to trucks for selr1 propelled machines, such as excavating` machines7 which are advanced 'from one position to another as the work progresses.

The invention is designed primarily for use with large excavating machines, such as rotary steam shovels, which are used tor stripping the over-burden from surface deposits ci' coal, ore and the like. These machines are of very large size and great weight and they are usually supported by four separate trucks. one arranged at each cornerof the machine. Each of these trucks comprises tour track wheels which travel over tracks formed ot sections oi railroad rails which "ray be mounted either on ties or directly on the surface ot the coal from which the overburden has been removed. Theserails are necessarily in comparatively short sections so that they be readily disconnected and the rear sect-ions moved to the front as the machine advances. The rail sections are connected one to the other by fish plates in the nsti-al manner but the oints between the rail sections constitute weak points in the track.

particularly it the joint happens to be located above a sott spot in the ground or coal, which are likely to yield under the immense dit to which they are subjected, thus g' the joint downwart ly. elevating the other ends ot the rails and permitting the truck and that portion ot the machine supported thereby, to sag or follow the depressed joint downwardly. 'I' his not only imposes a in upon the machine which is very det rimental thereto but, even in the absence injury to the machine itself. it causes seriour delays, and the elevation ot the machine. thL relniilding` of the track and the remounting otl the trucks on the tracks involves a great. deal otvlabor and expense. Even though the yielding of a joint may not be sufficient to injure the machine or wreck the track it is very l"kely to derail the truck. Further. the tracks re tormedot standard railroad rails having a relatively narrow base and these rails have a tendency to tilt under the strains to which they are ajected. epcfally when they are moiinted upon the sur'race ot the coal itselt'. In order to over-corre these ditliculties it is one object ot the iniv 'on to provide truck .ni thetracli; sect-unis will be witliout joints and will be advanced from time to time relatively to the truck wheels to provide at in whi el all times a track surface in front ot the wheels over which they may travel.

A further object of the invention is to provide means whereby the track members or sections may be relieved ot their load to permit of their being advanced beneath the wheels and relatively thereto.

A further object ot' the invention is to provide a truckot` this character in which the weight of the machine may be utilized for advancing the track members.

-A further obj ect ot the invention is to provide a truck ot this character which will be comparatively simple in its construction and operation and which will be of a strong durable character; and in which the track members will have wide base portions which will prevent them from tilting.

Other objects ot the invention will yappear as the device is described in detail.

In the accompanying drawings Fig. l is a side elevation of a portion oi an excavating machine showing my invention applied thereto Fig. 2 is an end elevation oit such a machine; F 3 is an end elvationot one of the trucks, partly broken away; Fi i is a plan view ot' one of the trucks; Fig. 5 is a side elevation of a trucln partly broken away; Fig. 6 is a longitudinal section taken on the line 6 6 of Fig. 4; Fig. 7 is a section taken on the line 7 7 of l; and Fig. 8 is a section taken on the line 8 8 ot Fig. Il partly broken away.

In these drawings I have illustrated one embodiment of my invention and have shown the same as applied to a rotary stripping` shovel but it will be understood that the invention may be applied to excavating machines or other machines ot' various kinds and that the mechanism may take various terms without departing 'from the spirit of the invention.

In carrying out my invention I provide a plurality ot track members which are mounted for longitudinal movement over the groundor other supporting surface. These track members arranged below the truck frame and the wheels on the truck trame are adapted to travel over the respective traclf` members, thus supporting the load on the several track members. These track members being without joints throughout their length provide a very rigid and unyiel'ding supportor the machine. The len 'th ot the track members is such that the truck wheelsmay have a limited traveling movement thereon but as the wheels approach the limit of their movement on the track members the latter will advance relatively to the truck wheels and without otherwise displacing the same with relation thereto, so as to provide an additional track surface in front of the truck wheels. ln order that the track `members may be readily advanced means are provided for relieving the same of the weight of the load during the time of their forward movement. In order that the load may be adequately supported l prefer to arrange the track members in pairs and to alternately relieve the track members of each pair of their load and to advance the same while thus relieved of the load. These results may be aceomplished in various ways and the particular mechanism hereinafter described has been hosen for the purpose of illustration only.

As shown in these drawings the stripping machine comprises a base or main frame portion 1 which is preferably rectangular in shape and on which is mounted a rotating platform 2 which carries the power plant and operating mechanism and on which is mounted a boom 3 carrying the excavating dipper and its associated mechanism. The machine itself is of a well known construction and need not be here ldescribed in detail. Beneath each of the four corners of the base or main frame 1 of the machine is mounted a separate truck which carries the weight of the adjacent portion of the machine. yEhe several 'trucks are similar in construction and it will be necessary to describe but one of them.

In that particular embodiment of the invention which l have h-ere illustrated each truck comprises a main frame or body portion l havingl journaled therein two axles 5 and 6 on each of which are mounted four trackwheels 7. 8, 9 and 10, which are here shown as double flanged wheels. Means are provided for positively driving these truck wheels for the purpose of advancing' the machine when it is desired to move it from one position to another and preferably this is accomplished by connecting with the respective axles. 5 and 6, gears 11 and 12, which gears, in the present instance, are rigidly secured to the inner wheels 7 on each axle. Meshing` with both gear Wheels is a pinion 13 which, in the present instance, is rotatably mounted on a stud l/l rigidlyT secured vto the main truck frame 4l. This pinion is connected by means of a universal joint 15 to a transverse shaft 16 which is connected at its inner end by a second universal oint 17 with a short shaft 18, which in turn is connected by beveled gears 19 with a longitudinally extending driving shaft 2O having at its inner end a beveled `gear 21 by means of which it may be driven through a vertical shaft arranged at the axis of rotation of the platform Q and Legami driven from an engine on that platform, in a well known manner. Arranged' beneath the truck frame are a plurality of track members 22, 23, 2d and 25, upon which the wheels 7 8, 9 and 10, respectively, travel. These track members are separate one from the other and are individually capable of longitudinal movement relatively one to the other and relatively to the truck wheels. rllhe tracks may beef any suitable character but, as here shown., each track member comprises relatively wide base portion 26 having an upwardly extending longitudinal rib 27 which constitutes the rail on which the wheels travel. Each track member is without joints and to this end it is preferably formed in a single piece and is of suoli length that the wheels may have a limited traveling movement thereon. lnasmueh as the track members are designed for sliding movement over the ground, or other supporting surface, I have shown the end portions thereof as beveled or turned upwardly at 28, after the manner of sled runners.

ln order that each trac-k member may be easily advanced relatively to the truck wheels it is desirable that it should, during its advancing movement, be relieved from the weight of the load.v To accomplish this I have, in the present form of the truck, providedthe tread portion of each of the truck wheels with a plurality of flattened surfaces, as shown at 29. These flattened surfaces are spaced apart equal distances about the periphery of the tread and are separated by the .normally rounded tread portions, which rounded portions are preferably of greater length than the flattened portions. To provide means for supporting the weight of the load during` the advancement of the tracks the flattened portions on adj arent wheels are arranged out of line one with the other so that when one wheel is out of supporting contact with its track member the adjacent wheel will be in sup aorting contact with its track member. ln t e present arrangement of the truck the track members are arranged in pairs, one pair, consisting of the track members 22 and 28, being arranged on one side of the longitudinal center of the truck and the other pair, consisting` of the track members 24e and 25, being arranged on the other side of the center of the truck. In the present arrangement the outer truck wheels 7 and 10 have their flattened portions arranged in line one with the other and the inner wheels 8 and 9 have their fla tened portions arranged in line one with the other but out of line with the flattened portions of the wheels 7 and 10. The rounded portions of the tread of each wheel being greater than the flattened portions thereof, it will. be apparent that as the wheels advance over the track members the flattened portions of the wheelsl 7 and 10, for example, will lie adjacent to the respective bers and the load will be supported on the track members 23 and 24. As the wheels travel` over the track members the rounded portions'o'f the treads ofthe wheels 7 and 10 will engage the respective track members some 'little time before the rounded portions of theV treads'of ther wheels 8 and 9 move out offengagementwith the track members 23 and 24i Gonsequ'entlyl atl fixed intervals during the ltiavelfof the truck wheels over the track all four of the wheels on each axle will be in supporting contact with their respective track members and as the wheels continue to advance the twotrack members ofeach pair will be'alternately relieved from the load so that they are free to be advanced. It will be obvious that the flattened portions of the wheels need not be strictly flat but that it will be sufficient if the radii ofthese portions areshortened so that they will be supported out of contact with the track members. It will also be apparent that either wheel on one pair of track membersmay have its flattened portions in line with the flattened portions of either wheel on' the other pair-"of track members.

Longitudinalmovement may be imparted tothe respective track members in any suitable nia-nner but I prefer, when practical, to utilize the weight ofthe machine itself for imparting this movement to the track mem bers and, in thepresent construction, I have provided fluid operated devices for actuating the track members. Ashere shown, I have provided'adjacent to each pair of track members, 22'a1id 23', and 24 and 25, a forwardly extendingfluid cylinder in which is mounted a piston 31 havinga piston rod 32 extendbeyond the open forward end lof the cylinder. 'I his piston rod -is operatively connected with they two track members of that pair of track members with which-the cylinder is associated. In the present instance, the outer end ofthe piston rod 32 is pivotally connected with a floating lever 33 the upper end of which is connected by a link 34 with the frame 4-of the truck. The lower end of the lever beneath its point of connection with the piston l'rod is connected with a connecting rod 35 which extends rearwardly to a point near the rear end of the truck where it is pivotally connect-ed with an equalizing bar or lever 36, the point of connection beingv preferably midway between the ends of that'bar. The bar 3G is connected at each end with the rear ends of the respective track members and, as here shown, each end of the equalizing'bar is provided with a. longitudinal slot 37 through which extends a pin 38 mounted in the end of the track'member. Preferably the track members are provided with transverse slots 39 through which the ends ofthe eojualizingv bar loosely extend and the pins 33 are seated in th-e track member both above and below the slots 39, so as to provide a very strong connection. It willbe apparent that when the pistonBl is subjected to fluid pressure the lever 33 through the connecting rod 35, will exert pressure on the equalizing bar When one of the track members is relieved of its load this pressure on the equalizing bar will cause that track member to slide forward beneath the truck wheels, the flanges on the truck wheels serving as guides to prevent the lateral displacement of the track member. If desired, each pair of track members mayl be provided with a second operating cylinder 40 having a piston 4l and piston rod 42 which may be connected with the forward ends of the track members in order to move the same rearwardly when it is desired to reverse the direction of the movement of the machine. Inthe present instance, I have shown no connecting mechanism between the piston rod 42 and the forward ends of the track members, it being the intention to disconnect the lever 33, the connecting rod 35 and equalizing` bar 3G and reverse the same so that the equalizing bar will be connected with the forward ends of the track members and the lever willbe connected with the rearwardly extending piston rod 42. Obviously, however. the connecting devices may be duplicated, if desired, and one or the other ofthe operating` mech anisms may be disconnected from the tracks when the other operating mechanism is in use. Fluid under pressure may be supplier to the operating cylinders 30 and 40 in any suitable manner but, as has been stated, I prefer to utilize the weight of the machine for actuating the'track members and I have therefore provided the main truck frame 4 with a vertical cylinder 43 adapted to contain a suit able fluid and connected at its lower end, by means of conduits 44,.with the several operating cylinders 30 and 40. Suitable means are provided for controlling the connection between the cylinder 43 and the several operating cylinders and, in the present instance, I haveV provided individual valves 45 and 46 for controlling the several conduits, the valves 45 controlling theA connection between `the conduits and the forwardly extending cylinders 30 and the valves 46 controlling the conduits for the rearwardly extending cylinders 40.

lvlounted in the vertical cylinder 43, and sup ported by the fluid therein, is a piston 47 the upper end of which projects above the top of the cylinder and constitutes a support on which the corner of the base l rests, thus causing` the piston to be subjected to the entire weight of the adjacent portion of the machina the whole weight of the machine being` divided between the pistons 47 of the four trucks. This `great weight imposed upon the piston 47 subje'cts'the tluid in the cylinder 43 to a very high vpressure and when one of the controlling' valves, the valve 45 'for eX- ample, is opened, this pressure will be transmitted to the piston 3l in the operating cylinder 30. It will be understood that the valves 45 for the two forwardly operating cylinders are opened when it is desired to advance the machine, the valves :tor the rearwardly operating cylinders remaining closed. lli/*heu it is desired to reverse the direction ot the machine the valves 4G will be opened and the valves 45 will remain closed. When the valves 4:3 have been opened so that the pistons 3l are subjected to the pressure created by the weight ot' the load, power is applied to the truck wheels to advance the same along the 'track members. As soon as the flattened portions of one set o wheels move into positions adjacent to the respective track members. so that these track members are relieved of the weight of the load, the pressure on the piston 3l will aetuate the connecting rod 35, thus causing` the equalizing bar or lever 3G to i'iilcrum about its point of connection with that track member which supports the load and causing the opposite end ot the equalizing bar or lever to move forwardly, thus pushing the released track member forward beneath the wheels y which cooperate therewith. lt will be underwill be operated simultaneously in the same manner. Alfter the released track member has been fully advanced the rounded portions of all of the wheels will engage the track members so that all will be under load and will thus be held against movement relative to the truck wheels. As the wheels move torward on the stationary track members the truck frame will advance the cylinders 30 with relation to their pistons, which pistons are held against movement because of their connection with the track members, and will thus force the fluid out ol the cylinders 30 and back into the main vertical cylinder 43. rI`he interval during which all the truck wheels rest upon the track members is su'lticient to restore the pistons 3l to their normal positions. l/Vhen this has been accomplished the 'flattened portions of the second set of truck wheels are brought into positions adjacent to their respective track members and these track members are released. for movement and are advanced in the same manner that the first mentioned track members .were advanced. This operation will continue so long as the valves controlling the connections between the vertical cylinder and the operating cylinders remain open and power is applied to the truck wheels to rotate the same.

The outward movement of the floating tlattened portions may be provided on theY treads oi each wheel but when more than two iiat portions are provided the length o1 the rounded portions of the several wheels which will simultaneously engage their respectivel track members is comparatively short and may, in some instances, result in a movement ot the track members which is objectionably short. rlhis will be due to the fact that both track members are not held against movement long enough to permit the cylinder to be advanced for the ull length of the piston stroke. Should this happen means may be provided for locking that track member which has been advanced against further movement until the other track member has been released, thus holding both track members against movement for a length of time sullicient to permit the cylinder to be advanced for substantially the full length of the piston stroke. This may be accomplished in various ways. As here shown, the two track members of each pair are each provided with a pair of lugs, the lugs on the track niemeer 24 being indicated by Vlugs 51 and 52 y and the lugs on the track member 25 being indicated by the lugs 53 and 54. The lugs 5l and 52 are spaced apart agreater distance than are the lugs 53 and 54 and the latter lugs extend between the lugs 5l and 52 and are so arranged with relation thereto that when the track member 24 has been moved to its foremost position the lug 52 on that track member will engage the lug 54 on the track member 25, which is held against movement, and will thereby prevent the further forward movement of the track member 24 as the frame of the truck advances, it being understood that this locking device holds the track member 24 against movement until the wheels resting thereon have rotated far enough to bring the rounded portions or the tread into contact with the track member. The lug 53 in the track member 25 is so arranged with relation to the lug 5l on the track member 24 that itwill engage the same when the track member 25 has advanced to the limit of its forward movement with relation to the truck, the operation in this instance being the same as that above described.

lWhen the desired movement of the machine has been accomplished the rotation of the truck wheels isstopped and the valves may be closed if desired but this is not necessary. The truck wheels are preferably stopped in such positions that all eight of the'wheels of,

ieu

lllfiV Iam the truck will rest upontheir respective track members, thus providing an eight point support for themach ine uponthe wide base track `members, which support is very rigid and absolutely unyielding.

In the old type of truck above referred to the constant vibration or hammering on the wheels results in the treads thereof being bodiment of my invention I wish it to be understood that I do not desire to be limited to the details thereof as various modifications may appear to a person skilled in the art.

Having now fully described my invention, what I claim as new and desire to secure by Letters Patent, i

l. In a truck, a main frame, wheels mounted thereon, a pair of separate track members upon which the respective whe-els are adapted to travel, means for actuating said wheels to more the same along said track members, said wheels having means for alternately relieving said track members of the load thereon, a power operated actuating device carried by said truck. frame, and a' connecting member operatively connected with both track members and with said actuating device and so arranged that the force applied thereto by the actuating device will cause whichever track member ris relieved of its load to be advanced with relation to the other track member.

2. In a truck, a main frame, wheels mounted thereon, a pair of separate track members upon which the respective wheels are adapted to travel, means for actuating said wheels Vto move the same along said track members, said wheels having means for alternately relieving .said track members of the loady thereon, a power operated actuating device carried by said truckframe, and alever connected at its endswith the' respective track members and connected between its ends with said actuating device, whereby the actionof said actuating` device on said lever will advance that track member which has been relieved of its load.

3. Ina truck, a main frame, wheels mounted thereon, a plurality of separate track members upon which the respective wheels are adapted to travel, means for actuatingsaid wheels to move the same. along vsaid track i members, said wheels having means for alternately relieving said track members of the load thereon, an actuating device carried by said truck frame, a connecting member opvsure tosaid cylinder.

eratively connected with both track members and with said actuating device and so arranged that the force applied thereto by said actuating device will advance whichever track member is relieved of its load, and means controlled by the weight of the load on said truck for operating said actuatingdevice. y

el, A truck comprising a pair of track members, wheels adapted to travel on the respec-` tive track members, each of said Wheels having` Vits tread provided with a flattened portion, said flattened portions of the Vrespective wheels being arranged out of line one with the other, a lever connected atits ends with the respective track members, and means for applying power to said lever near the center thereof, whereby when one of said track members isrelieved of its load because of the proximity of the'flattened portion of its .wheel thereto, the thrust on saidlever will impart longitudinal movement to said track member.

5. In a truck, a main frame,.wheels mounted thereon, a plurality of separate track members on which the. respective wheels areV adapted to travel, means for actuating said wheels tofmove the same along said track members, said wheels having means for `alternately relieving said track members ofthe load thereon, a fluid operated device .mounted on said truck frame, a lever connectedwith said track members, means for operatively connecting said lever with said iluid operated device, whereby said fluid operated device will be caused to act upon that track .member which has been relieved of its load.

6. In a truck, Va pair of parallel track members, a frame arranged above said members, wheels carried by said frame and adapted'to tra-vel on said trackmenibers, means for rotating said wheels, said wheelshaving means for alternately relieving said track members from the load, a lever pivotally connected at its ends withthe respective track members, a cylinder, a piston mounted in said cylinder, a piston rod connecting said piston with said lever at a point Ibetween said track members, and means vfor Supplying fluid under pres- 7. In a machine of theeharacter described, a truck to support a portion of said machine, said truck comprising wheels, track members over `which said wheels travel, and means actuated by the weight of the load on said truck for imparting longitudinal movement to said track members.

8. In a machine of the character described, a truck on which a portion ofthe weight of said. machine is supported, a plurality of track members, wheels adapted to rtravel on the respective. track members, means controlled by said wheels to rrelieve one of said track members dits-load, and means actuated by the 'weight yof the machine on said same along said track, said wheels being so shaped and arranged with relation one to the other that said track members will be alternately relieved of the load on said truck, and means actuated by the weight of the load on said truck for imparting longitudinal movement to each track member when it is relieved of its load.

10. In a machine of the character described, a truck to support a portion of the weight of said machine and comprising a pair of track members, wheels adapted to travel on said track members, driving mechanism for said wheels, said wheels having portions of their treads flattened, the flattened portions of the treads of the two wheels being so arranged that said track members will be alternately7 relieved of the weight of the load on said truck, a mechanism for imparting longitudinal movement to the track member which has been so relieved, and means actuated by the weight of the load on said truck for imparting movement to said actuating mechanism.

11. In a machine of the character described, a truck to support a portion of the weight of said machine and comprising a pair of' track members, wheels adapted to travel over said track members, driving mechanism for said wheels, said wheels being of such a character and so arranged thatk said track members will be alternately relieved of the load on said truck, a fluid operated device for imparting longitudinal movement to the respective ltrack members when. they arel so relieved of their load, and means operated by the weight of the load on said truck for supplying fluid under pressure to said fluid actuated device.

l2. In a machine of the character described, a truck comprising a main frame, a

vertical fluid cylinderl carried by said-frame,

a piston mounted in said cylinder and arranged to support the load on said truck, wheels mounted on said fra-me, means for rotating said wheels, separate track members on which the respective wheels travel, said wheels having portions of their treads flattened, the flattened portions of the several wheels being so arranged that said track members will be alternately relieved of the weight of the load on said truck, a fluid operated device for imparting longitudinal move- `ment to the respective track members when theyy have been relieved of their load, and a conduit connecting said fluid actuating device with said cylinder. Y

13. In a machine of the character described, a frame, a cylinder carried by said frame and adapted to contain a fluid, a piston mounted in said cylinder and arranged to support the load on saidtruck, wheels carried by said frame, separate tracks over which said wheels are adapted t0 travel, means controlled by the movement of said wheels to alternately relieve said tracks of the load on said truck, and means actuated by the pressure of said piston on the fluid in said cylinder to impart longitudinal movement to that track member which has been relieved ofits load. Y

14. In a machine of the character described, a truck comprising a frame, a pair of track members arranged on each side of the center of said frame, axles journaled in said frame and extending transverselyV to said track members, wheels mounted on said arles and adapted to travel on the respective track members, means for driving said wheels, said wheels being so shaped and arranged with relation one tothe other that as they move over said `track members the latter will be alternately relie-ved of the weight of the load on said truck, a cylinder carried by said frame adjacent t0 each pair of track members, a piston mounted in each cylinder, an operative connection between cach piston and the adjacent pair of track members, a vertical' cylinder carried by saidframe and adapted to contain a fluid, a piston mountedV in said vertical cylinder and adapted to support the load on said truck, and a valve controlled connection between said vertical cylinder and the lirst mentioned cylinder.

15. In a machine of the character described, a truck comprising a frame, a pair of track members arranged on each side of the center of said frame, axles journaled in said frame and extending transversely to said track members, wheels mounted on said axles and adapted to travel on the respective track members, means for driving said wheels, said wheels being so shaped and arranged with relation one to the other that as they move over said track members the latter will be alternately relieved of the weight of the load on said truck, a cylinder carried by said frame adjacent to eac-h. pairof track members, a piston mountedin each cylinder, equalizing levers connectedat their ends with the track members lof the respective'pairs, rods connected with the respective levers between the ends thereof, oper- Yative connections between saidv connectingV rods and respective pistons, a vertical cylinder carried by'said frame and adapted to conf-' tain a fluid, a valve controlled connection i between said vertical cylinderand each of the Y ed in said vertical cylinder and adapted to support the weight of the load on said truck.

i6. ln a truck, a pair et track members, a frame arranged above said track members, wheels carried by said trame and adapted to travel on said track members, means for rotating said wheels, said wheels having means :tor alternately relieving said truck members from the load, a cylinder carried by said frame, a piston mounted in said cylinder, a connection between said piston and said track members, and means for supplying Huid nnder pressure to said cylinder whereby the track member which has been relievedro'f the load will be advanced, said wheels alsor having means tor holding both track members against movement for an interval be'- tween the movements of the respective track members, whereby the movement of said frame will move said cylinder with relation to said piston.

17. In a truck, a trame, wheels mounted thereon, driving means for said wheels, a plurality of separate track members on which the respective wheels are adapted to travel, the tread of each wheel having adjacent fiat and rounded portions, the iiat portion on one wheel being out of line with the flat portion )if another Wheel, whereby the respective track members will be alternately relieved of the load on said truck, said flat portions being so arranged that both track members will be held against movement tor an interval between the movements of the respective track members, a cylinder carried by said frame, a piston mounted in said cylinder, an operative connection between said piston and said track members, and means the flattened portions oli' the wheels for controlfluid under pressure te said cylinder to advance the track member which has been relieved, the for' ard movement of said 'trame during the interval that both track members are held against movement serving to move said cylinder relatively tothe piston to re4 store the piston to its initial position.

18. A truck comprising a pair of track membe s, wheels adapted to travel on the respective track members, each of said wheels having its tread provided with a flattened portion, said flattened portions of the respective wheels being` arranged out or' line one with the other, means or imparting longitudinal movement to said t ack members when are adja cent thereto, and locking means ling the longitudinal movement of said track members with relation one to the other.

19. A truck comprising a pair of track members, wheels adapted to travel on the resaective track members, each et said wheels having its tread provided with a 'liattened porti-on, said l'iattened portions et the respective wheels being arranged out of line one with the other, and means for imparting longitudinal movement to said track membersL when the 'flattened portions et' the wheels are adjacent thereto, the track members of each pair having cooperating lugs arranged to lock ene ot said track members against movement with relation to the other when the tirst mentioned track member has been moved predetermined position.

In testimony whereof, I aiiix .my signature hereto. Y

GRANT HOLMES.

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