US3057426A - Lift truck with counter-rotating dual trction motors - Google Patents

Description

Oct. 9, 1962 R. HASTINGS, JR 3,057,426

LIFT TRUCK WITH COUNTER-ROTATING DUAL TRACTION MOTORS 4 Sheets-Sheet 1 Filed June 8, 1959 ww l) INVENTOR.

RUSSELL HASTINGS JR.

ATTORNEY Oct. 9, 1962 R. HASTINGS, JR 3,057,426

LIFT TRUCK WITH COUNTER-ROTATING DUAL TRACTION MOTORS 4 Sheets-Sheet 2 Filed June 8, 1959 INVENTOR.

RUSSELL HASTINGS JR.

ATTORNEY 0d. 9, 1962 R. HASTINGVS, JR 3,057,426

LIFT TRUCK WITH COUNTER-ROTATING DUAL TRACTION MOTORS 4 Sheets-Sheet 5 Filed June 8, 1959 i 2 i 74 100 102 t, 76 72 I I 1Z2 INVENTOR.

RUSSELL HASTINGS JR.

ATTORNEY Oct. 9, 1962 R. HASTINGS, JR

LIFT TRUCK WITH COUNTER-ROTATING DUAL TRACTION MOTORS Filed June 8, 1959 4 Sheets-Sheet 4 INVENTOR.

RUSSELL HASTINGS JR.

ATTORNEY United States Patent Ofilice 3,057,426 Patented Oct. 9, 1962 This invention relates to driving mechanism for vehicles and may be found particularly useful in industrial truck applications wherein a vehicle capable of making very short turns, such as right angle turns within a narrow passage in order to pick up, deposit or tier a load at right angles to the general direction of the passage, and to make right angle turns from one narrow passage to another, is required.

Trucks of the above mentioned type are commonly referred to as narrow-aisle trucks. Several version of so-called narrowaisle trucks have heretobefore been contemplated and some of them have heretofore been marketed to a limited extent.

To conserve space or provide for more efficient utilization of existing space, the development of narrow-aisle lift trucks which can turn in an aisle only slightly wider than the truck wheel base has become an important consideration because of the relatively high cost of building. Some previously manufactured narrow-aisle trucks have been provided with lifting forks which can be retracted during normal truck travel and extended during loading and unloading operations with the components so arranged that the weight of the overhanging extended fork and its load is properly balanced to preclude tipping of the vehicle. In certain ones of such trucks, the lifting forks are constructed for extension and retraction in a horizontal path from either a floor level position or at any selected elevated stacking position.

Briefly, such trucks normally provide a U-shaped pocket at the loading end the legs or Outriggers of which are supported at their free ends on ground engaging wheels, and an upright mast structure and lifting fork assembly mounted for longitudinal movement relative to such legs such that the lifting forks can be retracted and extended within and beyond the U-shaped pocket, respectively. A truck framework extends rearwardly of the base of the U-shaped pocket and provides rear wheel traction means for the truck as well as control elements therefor. With the lifting forks in retracted position the load may be transported above the main frame and between the front and rear wheels.

For unloading in a location beside an aisle, narrowaisle trucks are driven through the aisle to the unloading location and then are turned transversely of the aisle to bring the extendable forks into alignment with the opening or storage space in the row. The lifting forks with a palletized load are first positioned at the desired level and then projected from the truck into the storage space. Thereafter, the forks are lowered slightly to deposit the pallet either on the floor or in stacked relation to another load, as the case may be, and then retracted in a straight line path until they are located without the pallet whereupon the truck may be swung into the aisle and driven away.

For removing the palletized load from any selected storage position in a row, the truck with its lifting forks retracted i brought into alignment with a pal-let and then, in succession, the forks are extended in a straight line under the pallet, raised to pick up the load, and then retracted to bring the loaded forks outside the storage row whereupon the truck is ready to be turned and driven through the aisle. Straight line extension and retraction of the lift forks is of importance for proper handling of pallets.

It will be seen that with the forks fully retracted there is no substantial overhang thereof beyond the main frame, thereby enabling a turning clearance and the use of narrow aisles, with consequent maximum utilization of storage area.

Of various narrow-aisle truck constructions which have been designed heretofore, one of the more widely accepted types has provided a space at the rear of the truck on which the operator is enabled to ride in a stand-up position and wherein the truck is supported by four wheels, two at the front for supporting the load receiving end of the main frame and two at the rear for steering the truck,

one of the two rear steerable wheels being also a driving and braking wheel receiving its power from a single drive unit rotatable with the wheel during steering thereof and located in a corner portion of the truck frame. Examples of such a construction are disclosed in US. Patents Nos. 2,564,002 and 2,752,058, both issued in the name of Gibson.

The above described oifcenter drive wheel construction and control means therefor, best disclosed in the above mentioned Patent No. 2,564,002, have proved to date to be one of the more acceptable stand-up types of narrowaisle truck which have been developed, but are inherently limited to such an extentin application that the relatively high percentage of the market which the narrow-aisle type of truck should theoretically command has never materialized.

One of the more serious problems which has limited general application of such trucks concerns the utilization of the one-wheel off-center drive principle and arrangement. It has been found that such trucks are inherently limited to a maximum speed of approximately 3 /2 to 4 miles per hour. If these trucks were designed to travel ata higher rate of speed, they would be unable to stop within a safe distance because of the limited braking force available in braking on only one wheel. It is, of course, desirable to attain much higher rates of speed for most economical warehousing operation.

Another important consideration is the rate of acceleration of the truck. Satisfactory rates of acceleration are not readily attainable with the one-wheel off-center type of drive because of the limitations in tractive effort inherent therein. Again, because of inherently limited power and traction, such trucks are generally unable to satisfactorily climb grades or bridgeplates. In an attempt to secure a maximum of tractive effort, such trucks have normally been of a type providing a vertically movable suspension consisting of either a spring mounting or pivoted axle mounting for one of the rear wheels, generally the nondriving wheel at the rear of the truck, in order to provide continuous contact of the driving wheel with the floor, particularly when driving over uneven surfaces.

One of the most common types of lateral articulation constructions has been an arrangement for spring mounting one of the four main wheels, namely the rear caster wheel on the operators side of the truck. This lateral articulation results in inherently poor lateral stability of the truck, particularly when stacking or removing loads at considerable heights above the main frame.

The one-wheel off-center drive arrangement of the prior art trucks may also result in an arrangement whereby the torque of the traction motor effects a reaction in the steerable wheel which is transmitted through he steering linkage and must be compensated for by the operator exerting a constant force tending to overcome such reaction.

With the foregoing in mind, it is a primary object of the present invention to provide an improved structure and arrangement of driving and braking means for a vehicle of the type above described which overcomes the inherent disadvantages which have heretofore existed.

One of the principal objects of the present invention is to provide a novel traction wheel and motor arrangement for a truck of the type described which renders the truck capable of travel at higher rates of speed.

Another important object of the present invention is to provide a new and novel arrangement for a truck of the character described which has increased braking force available whereby the truck may be stopped in a safe distance even through capable of traveling at a high rate of speed.

It is another important object of the present invention to provide a driving means for a truck of the type specified which eliminates the need for any lateral articulation, whereby the lateral stability of such truck is greatly enhanced.

It is a further object of the present invention to provide a drive means for a vehicle of the character specified which eliminates any torque reaction being transmitted from the steerable wheels through the steering linkage to the operators hand, thereby to eliminate the need for a continuous compensating force being applied by the operator.

It is a still further object of the present invention to provide an improved arrangement for mounting the traction motor or motors whereby the motors may be firmly secured in a non-rotatable manner relative to the frame of the vehicle, thereby eliminating the requirement for flexible power leads thereto with their attendant disadvantages.

It is a still further object of the present invention to provide a combined driving, braking, and steering arrangement for a vehicle of the character specified which is efficient, compact, reliable in operation, and which may be manufactured at a minimum of cost.

The above and other objects and advantages of this invention which will appear to those skilled in the art after a reading of this description, are essentially realized as the result of the provision of a pair of laterally spaced drive wheels at the rear of the truck and a separate nonrotatably mounted tract-ion motor associated with each such wheel, such motors being adapted and arranged to rotate in opposite directions to thereby eliminate undesirable motor torque reaction in that one motor olfsets the opposite torque reaction of the other motor. In this manner, turning force which would otherwise have to be restrained by the operator exerting an opposed force through the steering linkage is eliminated. The need for lateral articulation of the rear wheels is also eliminated since tractive effort is applied to both wheels by means of an independent drive to each wheel and the lateral stability of the truck is thereby greatly enhanced when it is used for high elevation stacking. Further, an independent drive to each wheel eliminates the disadvantages of drives operating from a common power source through a differential arrangement wherein lack of traction of one of the wheels causes all of the tractive effort to cease. In the present invention, failure of one of the two drive Wheels to maintain contact with the floor in no way reduces the tractive effort available and applied to the other drive wheel. My improved traction arrangement is readily adapted for use with various sizes and classes of vehicles by suitable variation in design particulars which will be readily determinable by those skilled in the art following a study of the description which follows, and of the accompanying drawings wherein:

FIG. *1 is a side elevational view of one type of vehicle with which the present invention may be used; certain portions thereof being shown in phantom outline whereby details of other more important elements may be more clearly illustrated in a somewhat schematic manner to show a construction embodying my invention;

FIG. 2 is a plan view of the vehicle shown in FIG. 1 which shows in more detail the general arrangement of the driving elements together with one form of steering linkage for the vehicle;

FIG. 3 is an enlarged cross-sectional view taken substantially along the line 3-3 of FIG. 1 and shows in detail the arrangement of one of the driving motors together with the cooperating elements for transmitting the tractive effort of the motor to the traction wheel of the vehicle;

FIG. 4 is a top view of the brake drum, brake shoes and a portion of the actuating mechanism therefor;

FIG. 5 is a somewhat schematic view in perspective of an alternative arrangement of steering control and linkage for the vehicle; and

FIG. 6 is a perspective view showing in further detail the arrangement of certain of the elements shown in FIG. 5.

Referring now to the drawings, and in particular to FIGS. 1 and 2 thereof, an industrial truck of the narrowaisle type having in the embodiment illustrated a retractable and extendable mast, is shown generally at numeral 10 and comprises a forwardly extending U-shaped frame 12 having a vertically extending body section 14 at the rear portion thereof for housing a prime mover and a plurality of motors, pumps, and other components, not shown, for driving the truck 10 forwardly and rearwardly by means of a pair of rearwardly mounted dirigible traction wheels 16, each of which is operatively connected by a gear train generally indicated at 18 (to be described more fully hereinafter) to the output shaft of an electric drive motor 20.

Forwardly extending legs 22 of the U-shaped frame 12 are supported at the forward end thereof by a pair of laterally spaced trail Wheels 24 and comprise inwardly facing channel sections in which are mounted for extension and retraction a telescoping mast structure 26 of known construction on which is mounted a forwardly extending fork and carriage structure 23 actuatable upwardly along the upright 26 by means of hydraulic hoist means 36 which is suitably connected to the carriage 28 by sprocket and chain means, not shown. The upright structure 26 is mounted in the channel portions of the legs 22 by means of L-shaped brackets 32, the legs of each of which support a roller 34, which is mounted to roll along the top surface of the leg 22, and a roller 36, which is mounted for rolling movement along a track formed in the inwardmost portion of each of the legs 22. Suitable drive means, such as a worm gear drive, not shown, may be mounted in each of the legs 22 and adapted and arranged to synchronously drive the mast structure 26 forwardly or rearwardly in the leg members 22 in a manner well known in the art.

The body section 14 includes a rearwardly extending U-shaped portion having legs 38 which define a recess 4t in which an operator may stand to operate and work the truck 10 by means of various controls which are not shown except for a steering control lever 42, which is suitably mounted on the body portion 14.

In accordance with the present invention, and as better shown in FIG. 3, electric drive motor units 20 are rigidly mounted, as by bolting, on horizontally extending frame member 44 and plate 46 which are in turn rigidly connected to vertically extending frame members of the truck 10 in any suitable manner. FIG. 3 illustrates in detail the general arrangement of a turret assembly 48 for one of the steering and driving wheels together with the motor and transmission means connected to such wheel. The other turret assembly, motor, transmission unit, and wheel are substantially identical to the one illustrated except that the elements are assembled to form a unitary structure of opposite hand thereto, that is, one unit is right-hand and the other unit is left-hand.

The turret assembly 48 generally comprises an inverted cup-shaped cylindrical mounting element 50 having a radially outwardly extending flange 52 formed integrally therewith which is provided with a plurality of circumferentially spaced threaded apertures 54 for the reception of bolts (not shown) which rigidly secure the mounting element 50 to the horizontally extending framing member 44. The mounting element 50 also forms a lower end-bell for the motor assembly which is housed within a cylindrical sleeve element 56. A second inverted cupshaped cylindrical mounting element 58 is provided to form an upper end-bell for the motor assembly 20. The mounting element 58 is likewise provided with a plurality of circumferentially spaced threaded apertures in a top radially extending surface 60 thereof for the reception of bolts 62 and 64. The bolts 62 and 64 are arranged in alteration, the bolts 62 being relatively short and securing the mounting element 58 to the horizontally extending plate 46, while the bolts 64 are relatively long and extend downwardly through the motor assembly 20 into threaded apertures in the lower mounting element 50. The motor assembly 20 is thus rigidly secured as a unitary structure to the framing member 44 and plate 46.

The usual windings 66 of the motor unit 20 are centrally disposed within the cylindrical sleeve 56 and the motor has its driving shaft 68 turning about a vertical axis. The driving shaft 68 extends from both ends of the motor unit 20 and its lower extension is splined to a vertically extending stub-shaft 69 which carries a bevel pinion 70 that engages a bevel gear 72 on a horizontal shaft 74 mounted in bearings 76 and 78 in a housing 80 which encloses the transmission assembly 18.

The housing 80 is provided with a vertically upwardly extending cylindrical boss 82 which extends into the lower mounting element 50 and is spaced therefrom for the reception of a pair of annular bearings 84 which are held in place by shouldered portions on the element 50 and the boss 82. A suitable annular retaining ring 86 is disposed beneath the radially extending flange 52 of the mounting element 50 and is rigidly connected thereto by means of a plurality of circumferentially spaced bolts 88. The upper end of the cylindrical boss 82 is suitably threaded for the reception of a locknut 90 which bears against the upper bearing 84. The transmission assembly 18 is thus mounted upon the turret assembly 48 for rotation relative thereto about a vertical axis.

At this point it will be appreciated that due to the arrangement of pinion gear 70 and bevel gear 72, the output torque of motor 20 tends to rotate turret assembly 48 about the axis of shaft 68 as well as rotate bevel gear 72 about is axis of revolution. It is this tendency of the output torque to rotate turret assembly 48 which results in an undesirable torque reaction in the steering mechanism. By providing a pair of counter-rotating motors 20 such undesirable torque reactions cancel each other in the steering linkage so that an operator is not required to resist any such reaction at steering lever 158.

The stub-shaft 69 which carries the bevel pinion 70 is suitably mounted within the cylindrical boss 82 for rota- .tion relative thereto and suitable vertically spaced antifriction bearings 92 are provided therebetween. The bearings 92 are also held in place by means of suitable retaining rings 94 and 96 and a lock-nut 98 which is threaded upon the upper end of the stub-shaft 69.

Formed upon the right-hand end of the horizontal shaft 74 which carries the bevel gear 72 is a small driving pinion 100 which meshes with a larger idler gear 102 which is rotatably carried by means of a suitable antifriction bearing 104 upon an intermediate stub-shaft 106 suitably mounted within a depending extension 108 of the housing 80 for the transmission assembly 18. The idler gear 102 meshes with a driven gear 110 carried upon a horizontally extending driven shaft 112 which is rotatably mounted upon a pair of axially spaced anti-friction bearings 114 which are suitably retained within a horizontally extending cylindrical boss 116 formed upon the depending extension 168 of the housing 80.

Carried upon the outboard end of the driven shaft 112 for rotation therewith is an annular lug plate 118 which is provided with a plurality of circumferentially spaced threaded apertures which are adapted and arranged to receive a plurality of lug bolts 120 which pass through corresponding apertures in the side wall or disk 122 of the 6 wheel assembly 16. The disk 122 is suitably secured conveniently by welding, to the cylindrical rim 124 of the wheel assembly which is preferably provided with a tire 126 formed of rubber or other suitable material.

From the foregoing description of the transmission 18 connecting the driving shaft 68 of the electric motor 20 with the driving wheel 16, it will be seen that the relatively high speed of the shaft 68. is reduced by the transmission to a relatively low speed of turning of the drive wheel 16, preferably to a maximum speed in the neighborhood of six miles per hour. At the same time the torque of the motor shaft is converted into a relatively high turning torque upon the driven shaft 112 which carries the wheel assembly 16.

It should be noted that by virtue of the above described construction, the motor 20 is non-rotatably mounted relative to the frame of the truck and that the wheels 16 and transmission assemblies 18 are mounted for swivel move ment relative thereto by means of the turret assemblies 48, the driving shaft 68 of the motor passing through and being disposed concentrically with the enlarged steering pivot the axis of which extends through the axis of rotation of the wheel 16. In prior art arrangements the motor shaft has been offset relative to the steering pivot and, therefore, the motor has been adapted and arranged for pivotal or swivel movement along with the wheels. This has resulted in the necessity for providing flexible electrical conductor cables fromthe power supply to the motor which complicates the construction and increases the cost thereof, not to mention the additional service problem in replacing cables which might become frayed or broken due to the constant flexing thereof as the wheel is swiveled during steering operations. Another advantage gained through this particular mounting of the motors is that the brake actuating mechanism can be simplified because provision does not have to be made for rotative movement of the portion of the brake means carrying the actuating mechanism as, for example, where the motor is mounted for rotation with the wheel assembly, thereby necessitating the use of flexible control cables or the like. Further, the braking torque will be absorbed in the vehicle frame in the case where the motor is fixedly mounted relative to the vehicle frame which is not the case where the motor is mounted for movement with the wheel assembly. In the latter case, braking torque exerts a reaction through the wheel assembly which tends to rotate the wheel assembly about its steering axis, thus creating large upsetting forces which are transmitted through the steering control.

That part of the driving shaft 68 of the motor unit 20 which extends above the upper end of the motor is suitable journaled within a suitable anti-friction bearing 128 retained within a cylindrical boss 130 formed upon the upper mounting element 58. Suitably secured for rotation with the upper end of the driving shaft 68, such as by means of a key 132, is the hub 134 of a brake drum 136. The brake drum 136 is held against axial movement by means of a suitable lock-nut 138 threaded onto the end of the shaft 68 and engaging the hub 134. The opposite end of the hub 134 engages the upper side of bearing 128.

The brake mechanism, as shown in FIG. 4, comprises the brake drum 136, hereina-bove described, which is connected to the upper end of the shaft 68, and a pair of brake shoes 140 which are carried on or integrally formed on levers 142. The levers 142 are fulcrumed upon studs 144 which may be carried by the horizontally extending frame member 46. The free ends of the brake levers 1-42 are biased toward one another by means of a tension spring 146 suitably connected thereto to thereby normally bias the brake shoes into braking engagement with the brake drum 136.

Near their outer ends the brake levers 142 are provided with suitable receptacles for receiving the free ends of a pair of opposed piston rods 148 which are connected to pistons 150 slidably disposed within a hydraulic brake release cylinder 152. A suitable conduit 154 is provided for supplying hydraulic fluid under pressure to the cylinder 152 and for draining fluid therefrom as necessary. When fluid under pressure is admitted to the cylinder 152, the pistons 150 will be forced outwardly away from one another and the brake levers 142 will be forced outwardly against the bias of the tension spring 146 whereby the brake shoes 140 will be released from engagement with the brake drum 136.

The details of the above described brake structure as well as control mechanism for operating same are more fully described in my co-pending application Serial No. 818,869, filed June 8, 1959.

As shown in FIG. 2, each of the transmission housing assemblies 18 is provided with outwardly projecting bifurcated lugs 156 for connection with the steering linkage for the truck. The steering linkage may be of any suitable type, either mechanically operated as shown in FIGS. 1 and 2 and more fully disclosed and claimed in co-pending application of Robert L. Carter Serial No. 594,571, filed June 28, 1956 now US. Patent No. 2,900,195, (common assignee), or it may be a manually controlled power steering system as hereinafter described by reference to the modification shown in FIGS. 5 and 6.

Referring to FIGS. 1 and 2, the truck is provided with a steering lever 158 which is mounted on the upper surface of a bearing member 160 for limited swinging movement in both directions from a neutral position thereof. Lever 158 is fixedly mounted on a downwardly extending shaft 162 which is rotatable in bearing 160*. A rearwardly extending link member 164 is fixedly connected at one end thereof to shaft 162 for rotation therewith and is pivotally connected at the opposite end thereof with a transversely extending link 166, which in turn is pivotally connected at the opposite end 168 thereof with another link 170. Link 170 is rigidly connected at one end thereof with a vertically extending shaft memher 172 which is rotatably at the upper end thereof in a truck body connected bearing member 174 and at the lower end thereof in a similar bearing member. At the lower end shaft 172 is fixedly connected as by bolting or keying, with a lever 176 which is pivotally connected at its opposite end with a drag link 178. The drag link 178 is pivotally connected at 180 with a lower forwardly extending arm portion 182 of a pitman or control arm 184 which is mounted on a fixed pivot or mounting means 186 connected to a fixed frame member 188, said pivot or mounting means 186 being laterally spaced a predetermined distance to one side of the longitudinal center line of the truck 10. The forward end 190 of the control arm 184 is a widened portion thereof for pivotally mounting at 192 one end of a center tie rod member 194, which may be adjusted to various lengths as requirements demand by a nut member 196, and for pivotally mounting at 198 one end of a curved left-hand tie rod 200 which is connected by pivot means 202 at the opposite end thereof to the bifurcated lugs 156 rigidly connected to and extending rearwardly from the housing of the gear train assembly 18. A second pitman or control arm 204 which is equal in length to control arm 184, is pivotally connected at a widened portion 206 thereof to the opposite end of center tie rod 194 at 208 and to one end of a right-hand tie 210 at 212. The tie rod 210 is equal in efiective length and is of the same configuration as is tie rod 200, and is pivotally connected at the opposite end 214 thereof to the bifurcated lugs 156 of the other transmission assembly 18 in the same manner as is tie rod 200. The rearward end of control arm 204 is pivotally mounted in a pivot or mounting means 216 which is laterally spaced from pivot means 186 in a plane transverse to the truck axis at the same predetermined distance from the longitudinal axis of the truck as is pivot means 186. The pivot or mounting means 216 is mounted at a somewhat higher elevation than is the pivot or mounting means 186 so that the control arm 204 crosses over the control arm 184 to form a crossed intermediate control arm steering linkage which generally comprises crossed control arms such as arms 184 and 204, respectively spaced pivotal fixed mountings therefor such as shown at 186 and 216, and a center tie rod member such as member 194 which fixes the lateral spacing between the forwardly and rearwardly extending ends of the control arms.

By virtue of the above described arrangement, actuation of the drag link 178 in either direction by means of the linkage connection thereof to steering lever 158 effects differential turning of the wheels 16 by means of the crossed intermediate control arm steering linkage to pre vent scrubbing action of the wheels during turning movement of the truck 10 as described in detail in the aforementioned Carter patent.

Referring now to FIGS. 5 and 6, which illustrate somewhat schematically and in perspective a modified form of steering linkage and wherein like parts have been numbered in the same manner as in FIGS. 1 and 2, a steering handle 218 is provided which occupies substantially the same position relative to the truck 10 as the steering lever 158 of the previously described steering linkage. The steering handle 218 is adapted and arranged to be grasped by the left hand of the operator and moved laterally to the left or right in an arcuate, but substantially horizontal, path of movement to effect, respectively, a left hand turn or a right hand turn. The steering handle 218 is mounted upon one end of vertically extending lever arm 220 which is pivotally connected at 222 (see FIG. 6) to an angle bracket member 224 which in turn is fixed secured, conveniently by welding, to a generally cylindrical contractible ring 226. The ring 226 fixedly secures the control linkage adjacent one end of a hydraulic steering booster cylinder 228 of well known type. Pivotally connected to the lever arm 220, intermediate the ends thereof as at 229, is a valve actuating link 230 which extends lengthwise of the steering booster cylinder 228 and terminates in a rearwardly extending arm portion 232 which is pivotally attached at 234 to a valve actuating element 236 which is formed as a selfcontained part of the steering booster cylinder 228.

Disposed within the steering booster cylinder 228 is a relatively movable piston having a piston rod 238 which extends outwardly beyond the left hand end of the cylinder. The piston rod 238 is fixedly secured to the truck body by means of a suitable connector assembly 240. By virtue of such connection of the piston rod 238 to the truck body, the entire steering linkage assembly above described together with the main body of the cylinder 228 moves laterally of the truck when steering is being effected with control thereof being accomplished by the relative movement between the valve actuating link 230 and the cylinder. As above stated, such relative movement is accomplished by the pivotal movement of the vertically extending lever arm 220 about its pivotal connection at 222, thereby moving the pivot connection 229 of the valve actuating link 230 arcuately to the right or left from a neutral position thereof. Suitable conduits will, of course, be provided for supplying and removing hydraulic fluid from the steering booster cylinder 228 as desired, which conduits may be connected into the hydraulic system of the truck 10 in any convenient manner suitable for satisfactory operation thereof. The remaining portion of the steering linkage shown in FIGS. 5 and 6 is identical in structure and operation to that described in connection with FIGS. 1 and 2.

As hereinbefore stated, the prior art arrangement of one-wheel off-center drive means for narrow-asile lift trucks have been such that the torque of the drive motor may result in a steering reaction being transmitted through the steering linkage to the steering wheel or lever which necessitates the constant application of an opposing force by the operator when driving the truck in a straight line of movement. In accordance with the present invention, as Viewed in FIG. 2, one of the motors 20 is arranged for rotation in a clockwise direction whereas the other motor is arranged for rotation in a counterclockwise direction. As a result of this arrangement the steering reaction resulting from the torque of the one motor is canceled out by the steering reaction result.- ing from the counter-rotation of the other motor. Thus, when utilizing a mechanical steering linkage such as described in connection with FIGS. 1 and 2, the operator is relieved from the tiring effort required to continuously overcome the steering reaction existent in the prior art type of arrangement. When utilizing a power steering system such as shown in connection with FIGS. 5 and 6, the operator is never required to exert any great degree of pressure even when steering is being done. The pro vision of power steering is, of course, more expensive than the manual steering arrangement. The arrangement of the present invention, therefore, overcomes the inherent steering reaction problem of many prior art manual steering constructions.

By providing two drive motors 20 together with transmission units 18 interconnecting such drive motors to each of the rear traction wheels 16 the arrangement of the present invention also overcomes the other inherent disadvantages of the prior art one-Wheel, off-center construction enumerated hereinbefore. That is, by providing a pair of traction motors connected to drive wheels at each rear corner of the truck the vehicle is capable of attaining higher rates of speed than heretofore inasmuch as each traction element is provided with separate braking means therefor and higher speeds are more practicable because of the provision of such additional braking force. Furthermore, by providing dual traction motors and wheels, the truck is capable of a higher acceleration rate and the increased power and traction enables the truck to be more effective in climbing grades and bridgeplates.

The arrangement of the present invention also eliminates the need for lateral articulation in order to provide continuous contact of the tractive effort with the ground. By eliminating the prior art type of lateral articulation, the lateral stability of the truck 10 of the present invention is greatly enhanced, particularly when stacking at a relatively high elevation.

The provision of dual motors and traction wheels also greatly enhances the flexibility of speed control for the truck 10 and provides for more economical utilization of the battery current. This may be accomplished by a novel arrangement of the electrical circuit and control means therefor which is described and claimed in my aforementioned co-pending application Serial No. 818,869, wherein means are provided for connecting the two motors in series or in parallel and for alternately utilizing one half of the battery cells to obtain a plurality of operating speeds.

While the present invention has been described hereinabove by way of reference to a particular illustrative embodiment thereof, it will be obvious to those skilled in the art that various alternative embodiments and modifications can be made without departing from the true spirit thereof. It is, therefore, not intended that the invention should be limited to any precise arrangement shown and described, nor otherwise than by the terms of the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A power driven material handling truck having, in combination, a base frame, front supporting wheels, a pair of laterally spaced rear combined driving and steering wheels mounted upon said base frame, each being arranged to pivot about a substantially vertical axis, steering means for said truck including a steering linkage operatively connected to each of said rear wheels, a pair of separate drive motor means each having a rotatable drive shaft connected to opposite ones of said rear wheels,

said pair of drive motor means being operable to drive said drive shafts in counter-rotation relative to one another and means mounting said drive motor means fixedly on said frame.

2. A power driven material handling truck having, in combination, a base frame, a pair of laterally spaced combined driving and steering wheels mounted upon said base frame to pivot in either direction about independent steering axes, separate drive motor means each having a rotatable drive shaft connected to respective ones of said wheels, means mounting said motor means fixedly on said frame and in locations wherein the drive shafts are substantially concentric with said steering axes, said drive shafts being driven by the respective motor means in opposite directions, said steering means connected to both said wheels for pivoting the wheels relative to the respective motor means.

3. A power driven material handling truck having, in combination, a base frame, a pair of laterally spaced combined driving and steering wheels mounted upon said base frame, each being arranged to pivot about a vertical steering axis, and separate drive motor means for each of said wheels, each of said drive motor means being nonrotatably mounted relative to said base frame and having the drive shaft thereof substantially concentric with the steering axis of the respective wheel, said motor means being constructed to effect counter-rotation of said drive shafts relative to one another for imparting to one of said wheels a drive motor torque reaction which is opposite to the drive motor torque reaction imparted to the other of said wheels.

4. A power driven material handling truck having, in combination, a base frame, a pair of laterally spaced driving and steering wheels mounted upon said base frame, each being arranged to swing about an independent steering axis, steering control means for said truck, a steering linkage interconnecting said steering control means with each of said wheels, and separate driving motor means for each of said wheels fixedly mounted relative to said frame, each of said motor means having a rotatable drive shaft essentially concentric with the steering axis of the respective wheel, said motor means being arranged to effect counter-rotation of said drive shafts relative to one another, and separate transmission means for connecting said separate motor means with said respective wheels such that the drive motor torque reaction imparted to one of said transmission means is opposed by an oppositely directed drive motor torque reaction imparted to the other of said transmission means, said steering linkage receiving such oppositely directed torque reaction, the effects of which are neutralized in said steering linkage.

5. A combination as set forth in claim 4 and including separate braking means for each of said wheels, each said braking means having a first brake element connected to the drive shaft of each of said motors and a cooperating second brake element connected to said base frame.

6. In a power driven vehicle, a base frame, a pair of laterally spaced combined driving and steering wheels, steering means including linkage interconnecting said wheels, a turret assembly for each of said wheels including bearing means mounting each wheel relative to said base frame for pivotal movement about a substantially vertical steering axis, separate transmission means connected to each of said wheels and mounted for pivotal movement therewith in each respective turret assembly, and a separate drive motor for each of said wheels, said drive motors having frame means nonrotatably mounted relative to said base frame and rotatable drive shafts extending into said turret assemblies for driving said wheels in rotation through said transmissions, said drive motors driving said drive shafts in opposite directions relative to one another to generate oppositely directed drive motor torque reactions which tend to pivot said turret assemblies in opposite directions whereby to tend to cancel said motor torque reactions in said steering means.

7. The combination as specified in claim 6, including separate braking means for each of said Wheels, each braking means comprising a [first brake element mounted for rotation with one of said motor drive shafts and a cooperating second brake element mounted upon the truck frame.

8. In a power driven vehicle having a base frame, a pair of laterally spaced combined driving and steering wheels secured to the base frame, each being arranged to pivot about a steering axis, a steering linkage interconnecti-ng said wheels, and separate driving motor means for each of said wheels, each of said driving motor means having frame means non-rotatably secured relative to the base frame and a rotatable drive shaft concentric with the steering axis of each of said wheels, said drive motors 'being arranged to effect counter-rotation of said drive shafts relative to one another for minimizing resultant motor torque reaction transmitted through said steering linkage.

9. In a vehicle having a main frame, a pair of laterally spaced turret assemblies, each turret assembly being secured to the main frame for pivotal movement about a substantially vertical steering axis, steering linkage operatively connecting said turret assemblies, and a pair of drive motors, each drive motor having a frame and a rotatable drive shaft substantially coaxial with one of said steering axes, said motor frames being fixedly secured to the main frame and said drive shafts being rotatable in opposite directions relative to each other in operation, each said turret assemblies including a ground engaging wheel and transmission means, each said transmission means connecting one of said drive shafts with one of said wheels and including a first shaft coaxial and connected with one of said drive shafts for rotation therewith and a second drive shaft rotatably mounted at an angle to said first drive shaft and operatively connected to one of said wheels, said first and second drive shafts 12 being mounted in driving relation to each other, whereby the drive motor torque reactions which tend to pivot said turret assemblies in opposite directions about the respective steering axes tend to be cancelled out or neutralized in said steering linkage.

10. A combination as set forth in claim 9 wherein each of said turret assemblies is mounted rotatably in the main frame by first bearing means and each of said first shafts is mounted rotatably in one of said turret assemblies by means of second bearing means, said first and second bearing means being coaxial and substantially coplanar.

11. A power driven material handling truck having, in combination, a base frame, front supporting wheels, a pair of laterally spaced rear combined driving and steering wheels mounted upon said base frame, each said rear wheel being arranged to swing about a vertical steering axis intersecting the axis of rotation thereof, steering means interconnecting said wheels, a pair of driving motors mounted in fixed relation to said frame means, said motors being connected in traction drive relation to respective ones of said rear wheels and having the drive shafts thereof arranged concentrically with the seering axes, separate power transmission means connecting said driving motors with respective ones of said rear wheels, said transmission means upon counter-rotation of said drive shafts causing said rear wheels to be rotatably driven in the same direction, the said counter-rotation of said motors being effective to minimize the resultant driving motor torque reaction of said transmission means which is transmitted through said steering means.

References Cited in the file of this patent UNITED STATES PATENTS 1,840,407 Norman Jan. 12, 1932 2,395,323 Framhein Feb. 19, 1946 2,462,201 Ki1gore Feb. 22, 1949 2,779,425 Miller Jan. 29, 1957 2,913,063 Brown Nov. 17, 1959

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