US3834569A

US3834569A - Extended reach truck

Info

Publication number: US3834569A
Application number: US00221346A
Authority: US
Inventors: R Rabbitt; D Holtkamp; W Chichester
Original assignee: Clark Equipment Co
Current assignee: Doosan Bobcat North America Inc
Priority date: 1972-01-27
Filing date: 1972-01-27
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10
Also published as: BE794565A; FR2169189A1; CA980728A; AR195586A1; DE2261306A1; JPS5529918B2; BR7300010D0; FR2169189B1; AU5132973A; JPS4886249A; ZA73497B; GB1416494A; AU476648B2

Abstract

An extended reach mechanism for trucks in which the mechanism has a vertical member pivotally attached to the rear portion of the vehicle for pivoting forwardly and rearwardly, and an arm connected to the upper end of the vertical member and extending forwardly for supporting a load attachment such as a fork mounted on an upright. The vertical member and forwardly extending arm are operated by power means consisting of hydraulic cylinders, and a compensating means is included in the mechanism which adjusts the power means for the arm to cause the arm and the load attachment to move on a horizontal plane as the arm moves forwardly and rearwardly with the load. The compensating mechanism may include an adjustable hydraulic linkage for operating a valve to control the fluid to the hydraulic cylinder operating the arm for raising and lowering the load.

Description

United States Patent [191 Holtkamp et al.

[451 Sept. 10, 1974 EXTENDED REACH TRUCK [75] Inventors: Donald A. Holtkamp; Willard L.

Chichester; Robert R. Rabbitt, all of Battle Creek, Mich.

[73] Assignee: Clark Equipment Company,

Buchanan, Mich.

[22] Filed: Jan. 27, 1972 [21] Appl. No.: 221,346

[52] US. Cl. 214/762, 214/770 [51] Int. Cl E021 3/86 [58] Field of Search 214/762, 763, 764, 770, 214/773 [56] References Cited UNITED STATES PATENTS 3,024,933 3/1962 Albert 214/770 3,410,433 11/1968 Brown 214/763 3,494,495 2/1970 Alderman 214/762 3,695,474 10/1972 Blakely 214/763 Primary Examiner-Robert G. Sheridan Assistant Examiner-John Mannix Attorney, Agent, or Firml-lobbs & Green [5 7] ABSTRACT An extended reach mechanism for trucks in which the mechanism has a vertical member pivotally attached to the rear portion of the vehicle for pivoting forwardly and rearwardly, and an arm connected to the upper end of the vertical member and extending forwardly for supporting a load attachment such as a fork mounted on an upright. The vertical member and forwardly extending arm are operated by power means consisting of hydraulic cylinders, and a compensating means is included in the mechanism which adjusts the power means for the arm to cause the arm and the load attachment to move on a horizontal plane as the arm moves forwardly and rearwardly with the load. The compensating mechanism may include an adjustable hydraulic linkage for operating a valve to control the fluid to the hydraulic cylinder operating the arm for raising and lowering the load.

16 Claims, 5 Drawing Figures PATENIE SEP I man SHEU 5 BF 4 EXTENDED REACH TRUCK An extended reach lift 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 usual 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 pivoted 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 support, thus causing difiiculty in locating the load at the desired level and maintaining it at that level while advancing the load until it is positioned 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 the dip 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 on a 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 on a plane as it is moved forwardly or rearwardly between its maximum and minimum limits of reach, 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 movement of the load on the horizontal plane under those conditions.

Still another object of the invention is to provide a material 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. I is a perspective view of an extended reach truck embodying the present invention and 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 present lift truck showing the extended reach mechanism in its lowered and elevated positions;

FIG. 3 is a front elevational 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 system of the extended reach mechanism.

Referring more specifically to the drawings, numeral 10 indicates generally a lift truck on which the present extended reach mechanism 12 is mounted, the truck having

front 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 and a 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 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. Arm 44 consisting of two

longitudinal members

45 and 46 is pivotally connected to the upper ends of

posts

30 and 32, respectively, and extends forwardly therefrom parallel to the two side members 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. Arm member 45 is pivotally connected to the upper end of post 30 by a shaft 48, and arm member 46 is pivotally connected to the upper end of post 32 by a shaft 50. A plurality of cross members 52 tie the two arm members 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, rig idly 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 connect the forward end of the extensions to

fixtures

66 and 68, respectively, on the upright. The upright, which may beconsidered 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

twospaced tines

78 and 80 rigidly con nected to and supported by carriage 82.

Posts

30 and 32 are pivoted forwardly and rearwardly on

pivots

40 and 42 by cylinder assemblies 90 on opposite sides of the truck which are connected at one end to frame 24 by fixtures 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. Arm 44 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 and the other end through piston rod 103 to the arm members by a fixture 104, and the two cylinders being operated in unison from the same hydraulic system. The

cylinders

90 and 100 and the interconnecting frame and arm 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 110 and is pivoted 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 cylinders

90 and 100 is shown schematically in FIG. 5, numeral 120 indicating generally the portion of the system controlling the cylinder 90, and numeral 122 indicating generally the portion of the system controlling cylinder 100. System 120 is connected to a hydraulic pump 124 which delivers oil from a tank or sump 126 through line 128 to a valve 130. The valve is connected to the cylinder on opposite sides of piston 132 by

lines

134 and 136, and line 128 is connected through the valve to the sump by line 138. Line 128 is also connected to the valve by a branch line 140 which has a check valve 142 therein, and the return line for the valve is connected to line 138 and to the sump by a line 144. When post 30 is to be moved forwardly, i.e. to the left as illustrated in FIG. 5, the valve is moved downwardly as viewed in the drawing, thus connecting branch line 140 with line 136 and line 134 with line 144, thus causing piston 132 and piston rod 93 to move to the left, as viewed in FIG. 5, and to swing post 30 forwardly. When the post is to be moved in the opposite direction, the valve is moved upwardly as viewed in the drawing, thus connecting line 140 with line 134 and line 136 with line 144. After the post has been moved to the desired position, the valve is returned to its centered position where the valve permits hydraulic fluid to pass therethrough. A pressure relief valve indicated generally by numeral connects line 128 with line 138, thus limiting the maximum pressure in line 128 for operating the piston when the pump is in operation.

Hydraulic system 122 is connected to pump 124 by line 128, which is an extension of line 128. Line 128' is connected to valve 158 by a branch line 160 containing a check valve 161, and to the return line 138 by a line 162 when the valve is in its centered position. The valve is connected to cylinder 100 by lines 164 and 166. When arm 44 is to be raised, the valve 158 is moved upwardly, as viewed in FIG. 5, thus connecting branch line 160 with line 164 and with the cylinder on the underside of piston 168 and connecting line 166 with return line 169, thus causing piston rod 103 to move the arm upwardly. When the arm is to be lowered, the valve is moved downwardly, connecting branch line 160 with line 166 and line 164 with return line 169. Since system 122 depends on valve 130 being in its neutral position for operation, valve 158 cannot control cylinder 100 while valve 130 is being controlled to operate cylinder 90, since movement of the valve in either direction disrupts the flow of fluid through line 128'.

As cylinder 100 pivots forwardly with post 30, a compensating hydraulic system and mechanism prevent drooping of the load held on the fork attachment 70 and maintain the movement of the arms and load on a horizontal plane. This hydraulic system is indicated generally by numeral and includes a valve 182 connected by rod 184 to the frame 24 and to arm 44 by cylinder 186 and

rods

188 and 190, the cylinder and

rods

188 and 190 forming an adjustable linkage for the valve, and the piston 192 in cylinder 186 being connected by rod 190 to arm 44. The linkage including cylinder 186 and rod 188 is held in operating position by a lever 194 pivotally connected to the upper end of rod 188 by pin 195, and to the pivoted connection 48 between post 30 and arm 44. The opposite sides of piston 192 are connected by

lines

196, 198 and 200 and

lines

196 and 200 have

check valves

202 and 204, respec tively, therein opened by the pressure from branch line 160 through line 206. When valve 158 is open, the two check valves are opened, thus permitting the fluid to flow freely between the opposite sides of piston 192. A sump 208 is provided for an adjustment in fluid to allow for the differences in piston area as the piston is moved from one position to another. During the time that valve 158 is operating cylinder 100, communication is maintained between the opposite sides of piston 192, thus permitting free movement of the piston as arm 44 is pivoted upwardly or downwardly. When valve 130 is controlled to operate piston 90 the communication between the pump and the

check valves

202 and 204 is interrupted, thus causing the compensating cylinder to fonn a rigid linkage between arm 44 and valve 182. The valve is connected to a pump 210 by a line 212 and to sump 12.6 by a line 214. A pressure relief valve 216

interconnects lines

212 and 214 limiting the maximum pressure in the line. When valve 130 is operated to move piston 132 in the forward direction, for example, the linkage consisting of cylinder 186 and

rods

188 and 190 moves the valve downwardly to connect line 212 with line 230 and line 232 with line 214, thereby causing the piston 168 to move upwardly and maintain the arm and load attachment in a substantially level position regardless of the extent to which posts 30 and 32 are pivoted forwardly by cylinder 90. When the posts are moved in the opposite direction, i.e. to the right as viewed in FIG. 5, the valve 182 is moved upwardly to connect line 230 with line 214 and line 232 with line 212, thereby lowering the arm and load attachment to maintain the two on a substantially constant level plane throughout the rearward movement of the arms.

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 arms for the subsequent lifiting 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 arm 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, 7

valve 182 of the compensating mechanism is operated to operate cylinder 100 in the direction to raise the forward end of arm 44 and maintain the load on its original elevated position throughout the pivotal movement of the posts and the movement of the arm. While valve 158 is being operated to control cylinder 100, communication is established between the chambers on either side of piston 192 in cylinder 186 by the pressure transmitted through line 206 to the pressure

control check valves

202 and 204. When the pressure from line 206 is applied to the check valves, they are held in open position. These check valves have not been described in detail herein since their construction is well known, and they are available on the market as a standard item. As cylinder 100 is being controlled by the operation of valve 158, any movement of arm 44 is sensed by the compensating mechanism to position piston 192 in cylinder 186, thus increasing or decreasing the length of the linkage between arm 44 and valve 182. After cylinder 100 has been operated to place arm 44 and the load on the fork attachment in the desired position, valve 130 may be operated to shift the load horizontally. When the piston in fixed position, the linkage is moved by the movement of the arm and posts in either direction, causing valve l82 to move in the direction to operate cylinder 100 to correct any tendency of arm 44 to droop or otherwise deviate from the horizontal or other single and constant plane of movement. After the load has been deposited, the reverse operation is performed to return the fork attachment to its original position illustrated in FIGS. 1 and 2.

It is seen that the foregoing extended reach mechanism not only permits a wide load elevating range, from a position below the ground level of the truck to a position well above the truck, but also delivers a load sub stantially forwardly of the truck on a level plane, from the fully loaded withdrawn position to the fully loaded extended position. This permits the load to be readily placed in any desired location on a scaffolding platform, through an elevated door or window of the building being constructed, without requiring the truck to move directly beneath the scaffolding or building wall, and without requiring separate or special handling of the load.

A further circuit similar to that shown at numeral 122 would be included in the hydraulic system of the truck for the purpose of operating cylinder to maintain the upright and load attachment in various angular positions, details of this system being conventional in construction and operation and hence not described in detail herein.

While only one embodiment of the present extended reach mechanism for a truck has been described in detail herein, various changes and modifications maybe made without departing from the scope of the present invention.

We claim:

1. An extended reach mechanism for a truck having a frame with a forward end and a rearward end, comprising a substantially vertical post pivotally connected to the rear end of the truck frame, an arm pivotally connected to the upper end of said post and extending toward the forward end of the truck frame, a load carrying attachment connected to the forward end of said arm, a power means connected to said post for pivoting said post forwardly and rearwardly' and moving said arm and load attachment forwardly and rearwardly, a power means for pivoting said arm upwardly and downwardly to raise and lower the forward end of said arm and thereby to elevate and lower said load attachment, a control means with a linkage connected to saidarm and having a means for adjusting the length thereof in response to the operationof said second mentioned power means, and means operatively connecting said control means to said second mentioned power means for controlling said second mentioned power means in response to the movement of the aforesaid adjusted linkage when said first mentioned power means is operated, to maintain the movement of the forward end of said arm on a substantially constant horizontal plane for any given elevation of said forward end as said first mentioned power, means pivots said post forwardly or rearwardly and thereby moves said arm forwardly or rearwardly.

2. An extended reach mechanism for a truck as defined in claim 1 in which said first and second mentioned power means are hydraulic cylinders and a source of hydraulic fluid under pressure, and a pair of valve means controls the operation of said cylinders.

3. An extended reach mechanism for a truck as defined in claim 2 in which the means connected to said arm for controlling the second mentioned power means includes adjustable hydraulic means, and a control valve operated thereby, said valve being connected to a source of hydraulic fluid under pressure and to said second mentioned hydraulic cylinder for actuating said cylinder to maintain the movement of the am and load attachment in a horizontal plane.

4. An extended reach mechanism for a truck as defined in claim 3 in which said hydraulic means includes a cylinder, a piston in said cylinder connected to said arm, lines interconnecting the cylinder on opposite sides of said piston, check valves in said lines which are closed when the valve means for said first mentioned hydraulic cylinder is opened for operating said first mentioned cylinder to provide a solid linkage between said arm and said control valve.

5. An extended reach mechanism for a truck as defined in claim 4 in which a line is connected to the hydraulic line between the source of fluid under pressure and the valve means for said second mentioned hydraulic cylinder to maintain said check valves in open position except when said first mentioned hydraulic cylinder is in operation.

6. An extended reach mechanism for a truck as defined in claim in which said load attachment includes an upright, a fork mounted on said upright, and a hydraulic cylinder connected to said upright and to said arm to position said upright angularly with respect to said arm.

7. An extended reach mechanism for a truck as defined in claim 2 in which said second cylinder is spaced further from said post at the top than at the bottom and said arm includes a downwardly extending portion to facilitate lowering said load carrying attachment to a point below the level of the ground on which the truck is supported.

8. An extended reach mechanism for a truck as defined in claim 6 in which said second cylinder is spaced further from said post at the top than at the bottom and said arm includes a downwardly extending portion to faciliate lowering said load carrying attachment to a point below the level of the ground on which the truck is supported.

9. An extended reach mechanism for a truck, comprising a substantially vertical member pivotally connected at its lower end to the truck near one end thereof, an arm structure pivotally connected at one end to the upper end of said vertical member and extending toward the other end of the truck, a load carrying attachment connected to said other end of the arm structure, a power means connected to said vertical member for pivoting said vertical member forwardly and rearwardly and moving said arm structure and load attachment forwardly and rearwardly, a power means for pivoting said arm structure upwardly and downwardly to raise and lower said other end of said arm structure and thereby to elevate and lower said load attachment, a control means with a linkage connected to said arm structure and having a means for adjusting the length thereof in response to the operation of said second mentioned power means, and means operatively connecting said control means to said second mentioned power means for controlling said second mentioned power means in response to the movement of the aforesaid adjusted linkage when said first mentioned power means is operated, to maintain the movement of said other en of said arm structure on a sub stantially constant horizontal plane for any given elevation of said other end as said first mentioned power means pivots said vertical member forwardly or rearwardly and thereby moves said arm structure forwardly and rearwardly.

10. An extended reach mechanism for a truck as defined in claim 9 in which said first and second mentioned power means are hydraulic cylinder and a source of hydraulic fluid under pressure, and a pair of valve means controls the operation of said cylinders.

11. An extended reach mechanism for a truck as defined in claim 10 in which the means connected to said arm structure for controlling the second mentioned power means includes adjustable hydraulic means, and a control valve operated thereby, said valve being connected to a source of hydraulic fluid under pressure and to said second mentioned hydraulic cylinder for actuating said cylinder as required to maintain the movement of the arm structure and load attachment in a horizontal plane.

12. An extended reach mechanism for a truck as defined in claim 11 in which said hydraulic means includes a cylinder, a piston in said cylinder connected to said arm structure, lines interconnecting the cylinder on opposite sides of said piston, check valves in said lines which are closed when the valve means for said first mentioned hydraulic cylinder is opened for operating said first mentioned cylinder to provide a solid linkage between said arm and said control valve.

13. An extended reach mechanism for a truck as defined in claim 12 in which a line is connected to the hy draulic line between the source of fluid under pressure and the valve means for said second mentioned hydraulic cylinder to maintain said check valves in open position except when said first mentioned hydraulic cylinder is in operation.

14. An extended reach mechanism for a truck as defined in claim 13 in which said load attachment includes an upright, a fork mounted on said upright, and a hydraulic cylinder is connected to said upright and to said arm structure to position said upright angularly with respect to said arm.

15. An extended reach mechanism for a truck as defined in claim 9 in which said second cylinder is spaced further from said vertical member at the top than at the bottom and said arm structure includes a downwardly extending portion to facilitate lowering said load carrying attachment to a point below the level of the ground on which the truck is supported.

16. An extended reach mechanism for a truck as defined in claim 14 in which said second cylinder is spaced further from said vertical member at the top than at the bottom and said arm structure includes a downwardly extending portion to facilitate lowering said load carrying attachment to a point below the level of the ground on which the truck is supported.

Claims

1. An extended reach mechanism for a truck having a frame with a forward end and a rearward end, comprising a substantially vertical post pivotally connected to the rear end of the truck frame, an arm pivotally connected to the upper end of said post and extending toward the forward end of the truck frame, a load carrying attachment connected to the forward end of said arm, a power means connected to said post for pivoting said post forwardly and rearwardly and moving said arm and load attachment forwardly and rearwardly, a power means for pivoting said arm upwardly and downwardly to raise and lower the forward end oF said arm and thereby to elevate and lower said load attachment, a control means with a linkage connected to said arm and having a means for adjusting the length thereof in response to the operation of said second mentioned power means, and means operatively connecting said control means to said second mentioned power means for controlling said second mentioned power means in response to the movement of the aforesaid adjusted linkage when said first mentioned power means is operated, to maintain the movement of the forward end of said arm on a substantially constant horizontal plane for any given elevation of said forward end as said first mentioned power means pivots said post forwardly or rearwardly and thereby moves said arm forwardly or rearwardly.

3. An extended reach mechanism for a truck as defined in claim 2 in which the means connected to said arm for controlling the second mentioned power means includes adjustable hydraulic means, and a control valve operated thereby, said valve being connected to a source of hydraulic fluid under pressure and to said second mentioned hydraulic cylinder for actuating said cylinder to maintain the movement of the arm and load attachment in a horizontal plane.

6. An extended reach mechanism for a truck as defined in claim 5 in which said load attachment includes an upright, a fork mounted on said upright, and a hydraulic cylinder connected to said upright and to said arm to position said upright angularly with respect to said arm.

9. An extended reach mechanism for a truck, comprising a substantially vertical member pivotally connected at its lower end to the truck near one end thereof, an arm structure pivotally connected at one end to the upper end of said vertical member and extending toward the other end of the truck, a load carrying attachment connected to said other end of the arm structure, a power means connected to said vertical member for pivoting said vertical member forwardly and rearwardly and moving said arm structure and load attachment forwardly and rearwardly, a power means for pivoting said arm structure upwardly and downwardly to raise and lower said other end of said arm structure and thereby to elevate and lower said load attachment, a control means with a linkage connected to Said arm structure and having a means for adjusting the length thereof in response to the operation of said second mentioned power means, and means operatively connecting said control means to said second mentioned power means for controlling said second mentioned power means in response to the movement of the aforesaid adjusted linkage when said first mentioned power means is operated, to maintain the movement of said other end of said arm structure on a substantially constant horizontal plane for any given elevation of said other end as said first mentioned power means pivots said vertical member forwardly or rearwardly and thereby moves said arm structure forwardly and rearwardly.

13. An extended reach mechanism for a truck as defined in claim 12 in which a line is connected to the hydraulic line between the source of fluid under pressure and the valve means for said second mentioned hydraulic cylinder to maintain said check valves in open position except when said first mentioned hydraulic cylinder is in operation.