US 3843003 A
Description (OCR text may contain errors)
United States Patent [191 Frank Oct. 22, 1974 EXTENDED REACH MECHANISM FOR A TRUCK  Inventor: Gary D. Frank, Battle Creek, Mich.
 Assignee: Clark Equipment Company,
 Filed: July 7, 1972  Appl. No.: 269,855
 U.S. C1 214/762, 214/763, 214/770  lint. Cl E02f 3/86  Field Of Search 214/763, 762, 764, 770, 214/730  References Cited UNlTED STATES PATENTS 3,070,244 12/1962 Lull 214/770 3,410,433 11/1968 Brown 214/763 3,463,335 8/1969 Brownell i 214/762 3,698,580 10/1972 Carlson 214/1 CM 3,713,557 1/1973 Seaberg 214/763 3,726,423 4/1973 Lark 214/764 Primary ExaminerRobert J. Spar Assistant Examiner-John Mannix Attorney, Agent, or FirmHobbs & Green [5 7 ABSTRACT An extended reach mechanism for a lift truck in which a generally vertically positioned post is pivotally connected at its lower end to the rear end of the truck, and a boom connected to the upper end of the post extends forwardly therefrom and has an attachment at the forward end for raising and lowering a load. A first power means pivots the post forwardly and rearwardly to advance and retract the boom, and a second power means spaced forwardly from the: post raises and lowers the forward end of the boom. in order to maintain the boom and the load on the attachment on a plane as the boom is advanced and retracted, an electrical system is incorporated in the mechanism which is responsive to the movement of the post for adjusting the second power means as the load is advanced and re tracted. The first and second power means are preferably hydraulic cylinders controlled by a hydraulic system having a manually controlled valve for each cylinder and an electrically controlled valve for the second power cylinder responsive to a rheostat operated by the pivotal movement of the post.
10 Claims, 5 Drawing Figures BAIENIEnmzzzsu smaur FIG. 3
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EXTENDED REACH MECHANISM FOR A TRUCK An extended reach mechanism for a truck has special applications and advantages in the construction field in that loads can be picked up, delivered to the construction or building site, and lifted to and placed on scaffolding, without the necessity of special or separate handling to transfer the load from the truck load carrying attachment to the scaffold platform or other work supporting structure. This type of truck has the further special advantage of being able to pick up a load immediately in front of the truck where the ground is firm, transport the load to the work site, and deliver it to the scaffolding platform or partially completed building and yet avoid driving onto the usually soft backfill around the outside of the building. The extended reach trucks of the standard or well known construction utilize a parallelogram arrangement for the members supporting the forwardly extending support or boom, with the members pivotally connected to one another and to the truck frame. Movement of the members forwardly to a point approaching the fully extended position results in a drooping of the forward end of the boom, thus causing difficulty in picking up a load and positioning it at the desired level and maintaining it at that level while advancing the load until it is deposited onto the scaffold platform or other work support. Further, the problem caused by the failure of the prior extended reach trucks to advance the load on a horizontal plane, particularly as the load approached its fully extended position, was compounded by the effect of heavy loads compressing the tires on the front wheels adjacent the load attachment and by thedip caused by soft ground traversed by those wheels as the truck approached the place where the load was to be discharged. While movement of the load ona horizontal plane would not eliminate the difficulty caused by the load on the tires or soft ground, it would result in easier and more effective control of the extended reach mechanism and load attachment under those adverse conditions. It is therefore one of the principal objects of the present invention to provide an extended reach truck in which the load supporting mechanism will operate automatically to maintain the load on the fork or bucket ona plane as it is moved forwardly or rearwardly between its maximum and minimum limits of reach, regardless of the tendency of the load to dip as a result of compressing the tires or soft ground, and which can be operated by a single control means for advancing and retracting the load.
Another object of the invention is to provide a truck having an extended reach mechanism which has the ability to pick up a load below ground level, and which can be controlled either manually or automatically to compensate for compression of the truck tires by the load or downward or upward tilting of the forward end of the truck as a result of the terrain,'to obtain move ment of the load on the horizontal plane under those conditions.
Still another object of the invention is to provide a material handling truck of the extensible reach type, in which the reach mechanism is controlled by an electrical and hydraulic system which will provide effective control of the lift and reach mechanism and which will perform efficiently under various adverse operating conditions.
A further object of the invention is to provide a mate rial handling truck having an extended load mechanism of the aforesaid type which is so constructed and designed that it has maximum stability in all load handling positions and can be adapted to various types of truck designs without any appreciable modifications in the basic structure of the mechanism.
Further objects and advantages of the present invention will become apparent from the following description and accompanying drawings, wherein:
FIG. 1 is a perspective view of an extended reach truck embodying the present invention showing the extended reach mechanism in both its lowered position in full lines and in its raised position in broken lines;
FIG. 2 is a side elevational view of the presentlift truck illustrating the extended reach mechanism in its lowered and elevated positions;
FIG. 3 is a frontelevational view of the truck shown in FIGS. 1 and 2;
FIG. 4 is a rear elevational view of the truck shown in the preceding figures; and
FIG. 5 is a schematic diagram of the operating and control systems of the extended reach mechanism.
Referring more specifically to the drawings, numeral 10 indicates generally a lift truck on which the extended reach mechanism 12 is mounted, the truck having from drive wheels 14 and 16 and rear steerable wheels 18 and 20. While only the front wheels are driven and the rear wheels are steerable, the truck may be one in which the front and rear wheels are steerable and in which both sets of wheels are drive wheels. The motor driving the truck and providing the power for operating the extended reach mechanism is under hood or cover 22 and is mounted on frame 24, and the truck is controlled by an operator from cab 26 wherein the manual controls shown in FIG. 5 are located. While the extended reach mechanism may be mounted on various types of trucks and truck frames, the one shown has two longitudinal side members anda plurality of cross members forming the support for the motor, controls and cab, and also forming the basic support for the extended reach mechanism. Various changes in the truck structure can be made to adapt it to the desired operation to be performed thereby.
The extended lift mechanism. 12 includes a pair of posts 30 and 32 normally assuming a substantially upright position and being pivotally mounted on a shaft 34 secured to the rear end of frame 24 by mounting fixture 36. The two posts are rigidly joined to one another by a steel plate 38 to form a bifurcated structure which is adapted to tilt forwardly and rearwardly on the two pivot means 40 and 42, respectively, at opposite ends of shaft 34. Boom or arm 44 consisting of two longitudinal members 45 and 46 is pivotally connected to the upper ends of posts 30 and 32, respectively, and ex tends forwardly therefrom generally parallel laterally to the two sides of frame 24, the two members being adapted to pivot on the upper ends of the posts from a position such as that shown in solid lines in FIG. 2 to an elevated position shown in broken lines. Longitudinal boom arms 45 and 46 are pivotally connected to the upper end of posts 30 and 32 by shafts 48 and 50, respectively. A plurality of cross members 52 tie the two longitudinal arms together so that they operate in unison in moving loads from one position to another, both forwardly and rearwardly and up and down. Joined to the forward end of the arms and forming a part thereof are extensions 54 and 56 joined rigidly at one end to the main portion of the arms and pivotally supporting an upright 60 at the other end. Pivot pins 62 and 64 Y connect the forward end of the extensions to fixtures 66 and 68, respectively, on the upright. The upright, which may be considered conventional for the purpose of the present description and which is shown here fragmentarily to assist in fully understanding the invention, supports a fork lift attachment 70 mounted on the front of upright 60 on vertically spaced tracks 72 and 74, and is moved to various vertical positions on the upright by a suitable power mechanism such as a hydraulic cylinder 76. The fork attachment is provided with two spaced tines 78 and 80 rigidly connected to and supported by carriage 82.
Posts 30 and 32 are pivoted forwardly and rearwardly on pivots 40 and 42 by cylinder assemblies on opposite sides of the truck which are connected at one end to frame 24 by fixture 92 and connected at the other end through the piston rod 93 to pivot means 94, the two hydraulic cylinders being operated together from the same hydraulic system. The boom is raised and lowered and pivoted relative to posts 30 and 32 by a pair of hydraulic cylinder assemblies, one of which is shown at numeral 100, the lower end of each cylinder being connected to the frame by a fixture 102 on each side, and the other end through piston rod 103 to the arms by a fixture 104 on each side, and the two cylinder assemblies being operated in unison from the same hydraulic system. The cylinders 90 and and the interconnecting frame andarm form a trapezoid configuration which permits the mechanism easily to dip forwardly well below ground level to pick up or deposit a load. It is seen that fixture 104 for the upper end of cylinder assembly 100 is spaced further from pivot 48 than fixture 102 for the lower end of the assembly is from pivot means 40. The upright is moved to various angular positions or maintained in a vertical position as the arms are raised and lowered by a pair of hydraulic cylinders, one of which is indicated by numeral and is pivotally connected to extension 54 by a fixture 112 and to one of the side members of the upright by a fixture 114. The hydraulic cylinder 76 on the upright may be operated from the hydraulic system of the truck as part of the system which operates the hydraulic cylinders of the extended reach mechanism or by a separate hydraulic system, as desired.
The hydraulic system for operating cylinder assemblies 90 and 100 is shown schematically in FIG. 5, numeral indicating generally the portion of the system controlling cylinder 90, numeral 122 indicating generally the system controlling cylinder 100, and numeral 123 indicating generally a compensating system for leveling the boom to prevent droop or unintentional lift when the boom is moved forwardly and rearwardly, respectively. System 120 is connected to a hydraulic pump 124 which delivers oil from a tank or sump 126 through line 128 to valve 130. The valve is connected to cylinder 90 on opposite sides of piston 132 by lines 134 and 136, and line 128 is connected to the sump by line 138. When post 30 is to be moved forwardly, i.e., to the left as illustrated in FIG. 5, the valve 130 is moved to the left, thus connecting a supply line 128 with line 136 and line 134 with return line 138, causing piston 132 to move to the left and pivot post 30 forwardly. When the post is to be moved in the opposite direction, the valve is moved to the right, as viewed in the drawing, thus connecting line 128 with line 134 and line 136 with return line 138. After the post has been moved to the desired position, the valve is returned to its center position where the hydraulic fluid from the pump in line 128 is returned to the sump through line 138. A pressure relief valve (not shown) may connect lines 128 and 138 to limit the maximum pressure in line 128 for operating the piston when the pump is in Opera tion.
Hydraulic system 122 is connected to pump 124 by line 128' which is a branch of line 128, and line 128 is connected to valve 158 for controlling cylinder 100. The valve is connected to cylinder 100 on the under side of piston 160 by line 162 and to the cylinder above the piston by line 164. The valve is also connected to sump 126 through line 166. When boom 12 is to be raised, the valve is moved to the left, as viewed in FIG. 5, by connecting line 128 with line 162 beneath piston 130, thus causing the piston and piston rod 103 to move upwardly, elevating the forward end of the boom and the upright and attachment. When the valve is in the position for raising the boom, line 164 is connected through the valve to line 166 to sump 126. To lower the boom, the valve is moved to the right as viewed in FIG. 5, thereby connecting line 128' with line 164 and line 162 with return line 166 and sump 126, thus causing the piston 160 and rod 103 to move downwardly.
After the load has been moved to the desired height, the boom is often extended forwardly by the operation of cylinder assembly 90 moving posts 30 and 32 forwardly. This movement will normally. raise or lower the fork attachment and upright, thus creating a problem for the operator in maintaining the load at the desired height. In the present extended reach lift truck, a mechanism is incorporated which compensates for this otherwise change of level of the load as it is moved forwardly or retracted by the boom, the attachment and load being thus maintained on a horizontal plane during the foregoing movement. In the extension or retraction of the boom, the droop or rise, respectively, causes an error in positioning of the load. The linkage 170 transmits the direction of error to switch 172 which closes the corresponding circuit to a proportional valve 174. The valve is provided with two solenoids 176 and 178, and lead connects the source of 'power such as a battery indicated at numeral 182, to solenoid 176, and lead 184 connects solenoid 178 with the source of power. The switch, operated by the movement of post 30 or the operator, selects the position of switch 172, and hence the lead 180 or 184 energizes the proper solenoid 176 or 178 for operating valve 174. The valve is supplied with hydraulic fluid under pressure by pump 186 through line 188, and is connected to hydraulic cylinder 100 beneath piston 160 by a hydraulic line 190. When the valve is in this operating position, valve 158 is in neutral, and line 164, which is connected to cylinder 100 above the piston, is connected to sump 126 through valve 158 and line 166, thereby permitting effective operation of the cylinder by the fluid delivered through line 190 from valve 174.
Valve 174 is controlled during the operation by a potentiometer 200 operated in response to the pivotal movement of post 30, as indicated schematically by linkage 202. The greater the rise or drop of the load as a result of the horizontal movement of the boom, the further the potentiometer rotates, causing the corresponding current variation through switch 172 to operate valve 174 to raise or lower piston 160 and hydraulic cylinder 100 the degree necessary to make the correction for maintaining the movement of the load and boom on a horizontal plane. This maintains the load and boom at the level selected by the operator prior to the horizontal movement thereof. If movement of the fork and/or load to a different elevation is required, valve 158 is actuated to control cylinder 100.
Actuation of valve 158 closes a switch 204 and opens a clutch 206 through leads 208 and 210 to open switch 172, and thereby renders potentiometer 200 and system 123 inoperable. Centering of valve 158 opens switch 204 and engages clutch 206, thereby again placing the leveling system in operation.
In the operation of an extended reach truck having the lift mechanism described herein, starting with the fork attachment in its lowered position, the operator moves the truck forwardly to slip the tines of the fork attachment under a load, and lifts the load from the ground, normally using the upright to perform the initial lifting operation and the boom for the subsequent lifting operation. The truck is then maneuvered to the position where the load is to be discharged, such as, for example, on the platform of a scaffold, and cylinders 100 are operated to raise boom 44 and the load on the fork attachment to the level at which the load is to be discharged. This operation is performed through the operation of control valve 158. With the load in position at a level slightly above the platform, cylinder 90 is operated by the operation of valve 130 to pivot posts 30 and 32 forwardly. As this operation is taking place, valve 174 of the compensating mechanism is operated to operate cylinder 100 in the direction to raise the forward end of boom 44 and maintain the load on its original elevated plane throughout the pivotal movement of the posts and the horizontal movement of the boom.
When the load is being advanced, switch 172 is connected with line 184 to energize solenoid 178 of valve 174, thereby connecting line 188 from pump 186 with line 190, which is connected to cylinder 100 beneath piston 160. The current for operating solenoid 178 is controlled by potentiometer 200 which in turn is operated in response to the pivotal movement of post 30 through linkage 102. While valve 174 is being controlled by potentiometer 200, the amount of hydraulic fluid required to lift the boom to maintain the original plane of the load is delivered through line 190 to cylinder 100. The operation of the compensating system is rendered inoperable by switch 204 and clutch 206 when valve 158 is operated to operate cylinder 100. If valve 158 is operated, switch 204 energizes the circuit for disengaging clutch 206 to prevent the operation of the compensating system while valve 158 is supplying fluid to hydraulic cylinder 100.
When the boom is being retracted, switch 172 is connected to lead 180 which energizes solenoid 176 to move the valve in the direction to drain the hydraulic fluid from the lower end of cylinder 100 and return it to sump 126. This permits the piston to move downwardly and adjust the load and boom properly for maintaining them in the desired constant elevated plane. After switch 172 is closed, the potentiometer controls the operation of solenoid 176 in the same manner as it controlled the solenoid 178 as previously described.
One of the advantages of the electrical compensating system is that it can be programmed to provide the desired depth or lift under various operating conditions. The programming can be changed as required from one lift truck operating condition to another, and can be adjusted to meet various operating conditions, such as firmness of the ground and the weight of the load on the vehicle tires. This may be accomplished by adjusting the operation of potentiometer 200.
While only one embodiment of the present extended reach truck has been described in detail herein, various changes and modifications may be made without departing from the scope of the invention.
1. An extended reach mechanism for a lift truck having a frame with a forward end and a rearward end, comprising a substantially vertical post pivotally connected at its lower end to the rearward end of the truck frame, a boom pivotally connected to the upper end of said post and extending toward the forward end of the truck frame, a load attachment at the forward end of said boom, a first power means connected to said post for pivoting said post forwardly and rearwardly for extending and retracting said boom, a control means for said first power means, a second power means spaced forwardly from said post and being extensible and retractable for pivoting said boom upwardly and downwardly to raise and lower a load on said attachment, a first control means for controlling said second power means, a second control means operated electrically for said second power means, and an electrical means responsive automatically to the pivoting movement of said post for actuating said second control means to extend or retract said second power means to maintain the forward and rearward movement of the forward end said boom on a substantially constant horizontal plane for any given elevation of said forward end.
2. An extended reach mechanism for a lift truck as defined in claim 1 in which said first and second mentioned, power means include hydraulic cylinders, a source of hydraulic fluid under pressure, and a pair of valves for controlling the operation of the cylinders.
3. An extended reach mechanism fora lift truck as defined in claim 2 in which said second control means consists of an electrically controlled valve operated by said electrical means responsive to the movement of said post.
4. An extended reach mechanism for a lift truck as defined in claim 1 in which a power means interconnects the boom and said attachment to move said attachment angularly with respect to said boom.
5. An extended reach mechanism for a lifttruck as defined in claim 1 in which said second control means is operated by a solenoid means, and said electrical means responsive to the movement of the post for actuating said second control means includes a potentiometer.
6. An extended reach mechanism for a lift truck as defined in claim 3 in which said second control means is operated by a solenoid means, and said electrical means responsive to the movement of the post for actuating said second control means includes a potentiometer.
7. An extended reach mechanism for a lift truck as defined in claim 5 in which said electrical means responsive to the movement of said post is controlled by a switch and a circuit for energizing said second control means selectively to operate said second power means, either to advance or retract said second power means cuit and a switch responsive to the movement of the first control means for rendering said second control means inoperable 10. An extended reach mechanism for a lift truck as defined in claim 5 in which said second means includes a circuit and a switch responsive to the movement of the first control means and a clutch for rendering said potentiometer inoperable.