US3180514A

US3180514A - Control system for a load handling attachment on an industrial truck

Info

Publication number: US3180514A
Application number: US265213A
Authority: US
Inventors: Earl A Horton
Original assignee: Yale and Towne Inc
Current assignee: Yale and Towne Inc
Priority date: 1963-03-14
Filing date: 1963-03-14
Publication date: 1965-04-27
Anticipated expiration: 1982-04-27
Also published as: GB986656A

Description

April 27, 1965 E. A. HORTON CONTROL SYSTEM FOR A LOAD HANDLING ATTACHMENT ON AN INDUSTRIAL TRUCK 3 Sheets-Sheet Filed March 14, 1963 INVENTOR. t". 14. HORTON ATTORNEY April 27, 1965 E. A. HORTON 3, 8 ,514

CONTROL SYSTEM FOR A LOAD HANDLING ATTACHMENT ON AN INDUSTRIAL TRUCK Filed March 14, 1965 3 Sheets-Sheet 2 16a INVENTOR.

f. 4 How To/v A nl 27, 1965 HORTON 3,180,514

CONTROL SYSTEM FOR A LOAD HANDLING ATTACHMENT ON AN INDUSTRIAL TRUCK Filed March 14, 1963 3 Sheets-Sheet 3 15 454 I I :Ilijfi I 1 LJ l 1 I 1 160/ 16 INVENTOR 5 4 #0R TON r; BY

United States Patent CQNIRQL SYSTEM F023; A ELQAB HANELLYG ATTACHIl EENT ON AN @IBUdTRlAL TRUCK Earl A. Horton, Philadelchia, Pa, assignor, by usesne assignments, to Yale 8; Towne, inc, New York, N.Y., a eorncany of (E hic Filed Mar. 14, 1963, Ser. No. 265,213 5 Clair-"us. (Cl. 214-652} This invention relates to industrial trucks. More particularly, the invention relates to a control system for operating a plurality of hydraulically actuated load manipulating devices mounted on the lifting carriage of such a truck.

It has heretofore been proposed to control such hydraulically actuated devices through a hydraulic directional control valve mounted on the truck, adjacent the operators seat, and electrically operated valves mounted on the load carriage, with the valves being operated by electric switches mounted on the truck. This arrangement provides individual control of the plurality of hydraulically actuated devices on the load carriage, while utilizing only one pair of hydraulic hoses and a relatively small multiple conductor electric cable leading from the truck to the load carriage.

With an arrangement of this type, however, it is possible, particularly if the switches are mounted on the handle for the directional control valve, for the operator to accidentally release a switch thereby stopping operation of one hydraulic device and immediately start operation of a second hydraulic device. This can be dangerous. Thus, the operator may release a switch to stop operation of a hydraulic device on the load carriage for rotating a load, and by doing so, simultaneously start operation of a load clamping device, with resulting crushin or drop ping of a load.

This invention provides an improved arrangement of this type in which either actuating or releasing a switch is ineffective to operate the electric valve on the load carriage, unless the directional control valve is in a neutral position in which no fluid is supplied to the hydraulic devices. Thus, with this arrangement, it is impossible to stop operation of one hydraulic device and simultaneously start operation of a second hydraulic device.

The invention and its advantages having been described, a more detailed description of two forms of the invention is given hereafter by reference to the accompanying drawings w erein:

FIG. 1 is a side elevational view of a lift truck of the type on which the control system of the invention may be advantageously used;

FIG. 2 is a top plan view of the truck shown in FIG. 1;

FIG. 3 is a combined electrical and hydraulic diagram showing one form of control system constructed in accordance with the invention for controlling operation of three hydraulically operated load manipulating devices mounted on the lifting carriage of the truck shown in FIGS. 1 and 2; and

FIG. 4 is a combined electrical and hydraulic diagram showing a second control system constructed in accordance with the invention for controlling operation of three hydraulically operated manipulating devices mounted on the lifting carriage of the truck shown in F168. 1 and 2.

Referring to the drawings and in particular to FIGS. 1 and 2, there is shown an industrial truck T of the type on which the control system of the invention may be used advantageously.

The truck '1 is of conventional construction and includes uprights ill and a lifting load carriage 11 which is mounted for vertical movement on the uprights ll Three conventional hydraulically actuated load maniput" dtldfil s: cc Patented. 2?, 1%55 lating devices are shown mounted on the lifting carriage T e first device is a load clamping device, generally indicated at 312, and includes a pair of clamping arms 13 and 1'4 and a pair of hydraulic rams 1d and 16 for moving the clamping arms toward and away from each other to clamp or release a load.

The second device is a rotating device, generally indicated at 17, and includes a hydraulic ram or motor 18 by which the clamping device 12 may be rotated about a horizontal axis relatively to the load carriage 11.

The third device is a side shifting device, generally indicated at id, and includes a hydraulic ram 26 by which the clamping device 12 and rotating device 17 may be shifted as a unit in a direction transversely of the load carriage ll. Each of these hydraulic devices are of conventional, well-known constructions, and the details thereof for 3. no part of the invention.

Fluid for operating the rams i5, i6, 18 and 2% is supplied from a single pair of

hoses

21 and 22, extending between the load carriage ll and a fluid pump, or other pressure source, mounted on the truck. The direction of flow of tluid through the hoses is controlled through a reversing valve 23 mounted on the truck body, which is actuated through movement of a handle 24. As will be described in detail, fluid from the

hoses

21 and 22 is selectively directed to rams 15' and 16 or to ram 1% or ram through electrics-ll actuated valves mounted on the load carriage and operated by switches which are mounted on the truck body and connected to the valves by a multiple conductor electric cable 25. By this arrangement, individual control of the three hydraulically actuated devices l2, l7 and 1% is obtained, while utilizing only a single pair of hoses and a relatively small multiple conductor electric cable leading from the truck to the load carriage.

Referring now to PEG. 3, there is shown diagrammatically, one form of control system constructed in accordance with the invention for controlling operation of the rams of the three devices 12, 1'7 and 19. In the system illustrated in El 3, two solenoid operated valves 26 and 2?, which are mounted on the carriage H, are used to selectively control the flow of fiuid from the pair of hoses 2.1 and 22 to the rams 15, l6, l3 and 20. As will be described in detail hereafter, these two valves are actuated by push buttons and 29, which are conveniently moun ed on the handle 24 of the reversing valve 23.

in FIG. 3, each of the solenoid operated valves 26 and 27 are shown in the non-actuated position and the various relays are shown in the non-energized condition. Reversing valve 23 is shown in a neutral position in which the

hoses

21 and 22 are disconnected from the pump 36), or other source of fluid pressure.

Assuming that the operator wishes to clamp 21 load, he moves the hande 24 in the direction of the arrow A, without operating push buttons 23 and 2d. This moves the reversing valve 23 to a position in which the hose 21 is connected with a pressure line 31 from a fluid pressure source Eli), while hose 2?. is connected with a return line 32 to the pressure source 39. Fluid under pressure flows from the fluid pressure source through the hose 21, through solenoid operated valve 26, and through solenoid operated valve 27 to the left-hand side of the ram 15, causing the piston a thereof to move to the right.

The ram 15 is connected in parallel with the ram by a conduit 33, so that fluid from the hose 21 also flows to the right-hand side of the ram to, causing the piston lea thereof to move to the left. As the piston 15a moves to the right and the piston lea moves to the left, fluid on the right-hand side of piston 15:: and the fluid on the leit-hand side of piston lea flows through a conduit 33a, which connects the opposite ends of the rams in parallel,

3. through the solenoid operated valve 27, the solenoid operated valve 26, the hose 22, the reversing valve 23 and the return line 32 back to the pressure source 39.

The clamping

arms

13 and 14 are thus moved toward each other by the

rams

15 and 16 to clamp the load. When the load is properly gripped by the clamping

arms

13 and 14, the operator moves the handle 24 back to the neutral-position, thereby disconnecting the

hoses

21 and 22 from the pressure source 3% and trapping. the fluid in the rams 15 and-16 so that the load is held clamped between the clamping

arms

13 and 14. 7

As the handle 24 is moved in the direction of the arrow A, to actuate the

rams

15 and 16, electrical contacts 3 which are held open by a cam 24a on the handle 24 when the handle 24 is in the neutral position, close, and contacts 35, which are held closed by the cam 24:: of the handle 24 in the neutral position of the handle open. The opening of contacts 35' prevents a circuit from being completed to the solenoid 26a of the solenoid operated valve 26 and also to the solenoid 27a of the solenoid operated valve 27, so that if either push button 28 or push button 29 is accidentally pressed while the valve 23 is shifted to operate the

rams

15 and 16, the pressing of the

buttons

28 and 29 is ineffective to operate the

rams

18 and 20. Thus once the operator has moved the handle 24 from the neutral position to operate the

rams

15 and 16, he cannot accidentally start operation of the

ram

18 or 20, without firstreturning the handle 24 to neutral position.

To unclamp the load, the handle 24 is moved in the direction of the arrow Bf The system then functions in the same manner as in clamping the load except that the direction of the flow of fluid is reversed so that the clamps V energize the solenoid 26a of the solenoid operated valve 7 26 to shift the valve 26 and to energize a relay 39 cansing normally closed contacts 39a thereof to open and causing normally open contacts 3% thereof to close.

The'shifting of valve 26 by energizing the solenoid 26a connects hose 21 to the lower end of ram 13' and connects hose 22 to the upper end of ram 18, so that when the reversing valve 23 is shifted to the left by movement of the handle 24 in the direction of the arrow A, fluid under pressure is applied to the ram 18 to extend the piston and rotate the load. At the same time, fluid is held trapped in the

rams

15 and 16 so that the load remains clamped. As the handle 24 is moved from the neutral position, contacts 34 close and contacts open.

Closing of contacts 34' forms a holding circuit through closed contacts 3% around the contacts 28a, so that once the button 28 is pressed and the handle 24 is moved from the neutral position, accidental releasing of the push button 28 to open contacts 28a is ineffective to de-energize the solenoid 2% of the solenoid operated valve 26. Thus, once the push button 28 has been pushed and the handle 24 moved from the neutral position, solenoid 26a cannot bode-energized with resulting simultaneous operation of the

clamping rams

15 and 16, except by first moving the handle 24 back to the neutral position.

- The opening of contacts 39a of the relay 39 opens the circuit through contacts 39a of push button 29 so that accidental closing of push button 22 is ineffective at this time to energize the solenoid 27a of the solenoid operated valve 27 to operate the ram 219.

Assuming that the load has been rotated to the desired position by operation of the ram 18, the operator moves the handle 24 back to the neutral position thereby discona i I necting the hoses 2,1 and 22 from the fluid pressure source 30. As the handle 24 is moved back to the neutral position, contacts 34 are again opened and contacts 35 are closed. As the contacts 34 are again opened, the holding circuit through the closed contacts 3% is broken so that the relay 39 and the solenoid 25a of the solenoid operated valve 26 are de-energized and valve 26 moves back to the initial position, as shown in the drawing, trapping the fluid in the ram 18 to hold the load in'the rotated position.

To rotate the load in the opposite direction, push button 2% is pressed and the handle 24' moved in the direction of the arrow B. The system then functions in the same manner as just described with the flow of fluid to the ram 18 being reversed to reverse the direction of rotation of v the load.

Assuming now that the operator wishes to side shift the load, he presses push button 29 and moves the handle 24 in the direction of the arrow A to shift the valve 23 to the right.

Pressing push button 29 closes contacts 29a to complete a circuit through closed contacts 35, closed contacts 39a of the relay 39 and the battery 36 to energize the solenoid 27a of the solenoid operated valve 27 to'shift the valve 27 and to energize relay 38 to open contacts 38a thereof and close contacts 38b.

The shifting of the valve 27 connects the

hoses

21 and 22 to the ram 29, sothat when the handle 24 is moved in. the direction of the arrow A, fluid is applied to the ram 20 to shift the load. As the handle 24 is moved from the neutral position, contacts 34 again close and contacts 35' open. Closing of contacts 34 completes a holding circuit through the closed contactsisdb, around contacts 29a, to hold the relay 38 and the solenoid 27a of the solenoid operated valve 27 energized should the push button 29' accidentally be released. Thus, the solenoid 27a cannot be de-energized to shift the valve 27 except by movement r of the handle 24 back to the neutral position.

At the same time, the opening of contacts 38a by energizing relay 3% opens'the circuit through contacts 23a so that the accidental pressing of push button 28 is ineffective to energize the solenoid 2% of the solenoid operated valve 26, once the push button 29 has been pushed and the handle 24 moved from the neutral position.

Side shifting of the load is stopped by again returning the handle 24 to neutral position to' disconnect the hoses '21 and 22 from the pressure source 30 and to close contacts35 and open contacts 34. Opening of contacts 34 breaks the holding circuit through closed contacts 33b so that the relay 38 and the solenoid 27a are de-energized and valve 27 moves back to the original position, trapping the fluid in the ram 20.

To side shift the load in the opposite direction, the push button 29 is pressed and the handle 24 moved in the direction of the arrow B to reverse the. flow of fluid to th ram 20. V a

Thus, it can be seen that by this arrangement shown in FIG. 3, either actuating or releasing one of the

push buttons

28 or 29 is ineifective to operate the solenoid operated valves 26 and 27, unless the handle 24 and therefore the reversing valve 23 are in the neutral position, in which no fluid is supplied to the

hydraulic rams

15, 16, 18 and 20. Thus, with this arrangement, it is impossible to stop operation of one hydraulic device and simultaneously start operation of a second hydraulic device.

Referring now to FIG. 4,'there is shown aslightly dif ferent control arrangement which may be used when solenoid operated valves of the type shown in FIG. 3 are not available for the particular volumetric requirements of the system. In this arrangement, two solenoid operated valves are used for controlling the fluid to each hydraulic device. Thus, two

valves

41 and 42 are used for controlling the flow of fluid to the

rams

15 and 16 of the clamping device, two

valves

43 and 44 are used for controlling the flow of fiuidto the ram 18 ofthe rotating device and two valves .5 and 46 are used for controlling the flow of fluid to the ram Zll of the side shifting evice. Each of these solenoid operated valves is identical, and, when non-energized, as shown in PEG. 4, prevent return flow of fluid from each side of the rams while allowing fluid to be applied to each side of the rams. When energized, the valves allow fluid to flow in both directions from the ram.

Three push buttons 47, E3 and 49, conveniently mounted on the handle 24, are used to control the operation of the solenoid operated valves of the hydraulic devices.

Assuming that the operator wishes to clamp a load, he first presses push button 47 and moves the handle 24 in the direction of the arrow A. Pressing push button 47 closes contacts 470 completing a circuit from the battery 36 through closed contacts 35, closed contacts Sea of a relay 53 and closed contacts 54:: of a relay 54 to energize

solenoids

41a and 42a of the valves ll and 412, and also to energize a relay 5'5.

Energizing solenoids 41a and 22a shifts the valves to a position in which fluid may flow to the rams and 1%, so that shifting the reversing valve 23 to the left by movement of the handle 24 in the direction of the arrow A, applies fluid pressure through hose 21 to the left-hand side of the ram 15 and also to the right-hand side of ram 16 to move the piston 15a to the right and piston 16a to the left. As the piston 15:: moves to the right and the piston 16a moves to the left, the fluid on the opposite sides of the pistons flows through the valve 42; to the return hose 22. The clamping arms 13 and 1d are thereby moved together to clamp the load.

Energizing relay 55 causes normally open contacts 55a to close and normally closed contacts 55!: and 556 to open. Closing contacts 55a forms a holding circuit through contacts 34, which close as the handle 24 is moved in the direction of the arrow A, around the contacts 47a, so that once the button 47 is pressed and the handle 24 moved from the neutral position, accidental releasing of the button 47 to open the contacts 470 is ineifective to tie-energize the

solenoids

41a and 42a of the solenoid operated valves ll and 42. The opening of contacts 551) and 55s breaks the circuits through contacts 48a and 49:: so that accidental pressing of push buttons 43 and 49 is ineffective at this time to energize the solenoids of the

valves

43, 44, 45 and 4-5 to operate the rams 18 and 2% When the load has been properly clamped, the operator moves the handle 24 back to neutral position thereby disconnecting the

hoses

21 and 22 from the fluid pressure source 38. As the handle 24 is moved back to neutral position, contacts 34 are again opened and contacts 35 are closed. As the contacts are again opened, the holding circuit through the closed contacts 55:: is broken so that relay 55 and the

solenoids

41a and 42a of the

valves

41 and 42 are de-energized and the

valves

41 and 42 moved back to the initial position shown in the drawing, trapping the fluid in the rams 15 and in to hold the load clamped.

To unclarnp the load, the operator again presses push button 47 and moves handle 24 in the direction of the arrow B. The system then functions in the same manner as just described with the flow of fluid to the

rams

15 and 15 being reversed to move the clamping arms away from each other.

Assuming that the load has been properly clamped and the handle 24 returned to neutral position, the operator may operate ram 18 to rotate the clamped load by pressing button 48 and then again moving the handle 24- in the direction of the arrow A.

Pressing push button 43 closes contacts 48:: completing a circuit from the battery 3-? through closed contacts 35 and closed contacts 551) and 54b of relays 55 and S l to energize solenoids 43a and 44a of the solenoid operated valves 43 and 44- to shift the

valves

43 and 44. The closing of the contacts 43a also completes a circuit to energize the relay 53 to open contacts 530 thereof and to close contacts 531) and 530.

,lsasis The shifting of the

valves

43 and 44 connects hose 2f to the upper end of the ram 13 and connects hose 22 to the lower end of ram 18, so that when the reversing valve 23 is shifted to the left by movement of the handle 24 in the direction of the arrow A, fluid under pressure is applied to the ram 13 to extend the piston 13a thereof to rotate the load. I

The closing of contacts 53b forms a holding circuit through closed contacts 34 around the contacts 43a, so that once the button 4% is pressed and the handle 24 is moved from the neutral position, accidental releasing of the push button 48 to open contacts 48a is ineffective to rte-energize the solenoids 43a and 44a of the solenoid operated

valves

43 and 44.

The opening of

contacts

53a and 530 breaks the circuit through contacts 47!: and 49a so that accidental pressing of buttons 47 and 49 is ineffective to energize the solenoids of the solenoid operated

valves

41, 42, 45 and as.

When the load has been rotated to the desired position by operation of the ram 18, the operator moves the handle 24 back to the neutral position, thereby disconnesting the hoses Z1 and 22 from the fluid pressure source 3%). As the handle 24 is moved back to neutral position, contacts 34 are again opened and contacts 35 are closed. As the contacts 34 are again opened, the holding circuit through the closed contacts 531) is broken so that the relay S3 and the solenoids 43a and 44:: are de-energized and

valves

43 and 44 moved back to the initial position, shown in the drawing, trapping the fluid in the ram 18 to hold the load in the rotated position.

To rotate the load in the opposite direction, push button 48 is again pressed and the handle 24 moved in the direction of the arrow B. The system then functions in the same manner as just described with the flow of fluid to the ram 18 being reversed to reverse the direction of rotation of the load.

Assuming now that the operator wishes to side shift the load, he presses push button 49 and moves the handle 24 in the direction of the arrow A to shift the valve 23 to the left.

Pressing push button 4% closes contacts 4% to complete a circuit from the battery 36 through the closed contacts 35 and closed contacts 53c and 550 to energize the relay S4 and to energize the solenoids 45a and ida of the solenoid operated valves 35 and 4K to shift these valves.

The shifting of the valves 4-5 and 46 connects the hose 21 to the left-hand end of the ram 20 and connects the hose 22 to the right-hand end of the ram 29, so that when the handle 24 is moved in the direction of the arrow A, fluid is applied to the ram 26 to shift the load. The closing of contacts 540 when the relay 54- is energized completes a holding circuit through contacts 34, around the contacts 49a, so that once the button 49 is pressed and the handle 24 moved from the neutral position, accidental releasing of the button 49 is inelfective to de-energize the

solenoids

45a and 46a of the valves 45 and 46.

The opening of

contacts

54a and 54b breaks the circuits through contacts 48a and 47a so that accidental pressing of push button 47 or 49 is inetfective at this time to energize the solenoids of the valves ll, 42, 43 and 44 to operate the

rams

15, 16 and 18. The side shifting of the load is stopped by again returning the handle 24 to neutral position to disconnect the

hoses

21 and 22 from the pressure source 39 and to close contacts 35 and open contacts 34. The opening of contacts 34 breaks the holding circuit through contacts 540 so that the relay 54 and the

solenoids

45a and 46a are de-energized and the valves 4-5 and 46 moved back to the original position, trapping the fluid in the ram 20.

To side shift the load in the opposite direction, the push button 49 is pressed and the handle 24 is moved in the direction of the arrow B to reverse the flow of fluid to the ram 29.

Thus, it can be seen by the arrangement shown in FIG. 4, that either actuating or releasing the

push buttons

47, 48 and 49 is ineffective to operate the solenoid operated

valves

41, 42, 43, 45 and 46, unless the handle 24 and therefore the reversing valve 23 are in the neutral position in which no fluid is supplied to the hydraulic rams. Thus with this arrangement, it is impossible to start operation of one hydraulic device and simultaneously start operation of a second hydraulic device. 7

From the preceding description, it can be seen that there is provided a novel arrangement in which either actuating or releasing a switch is ineffective to operate the electric valve on the load carriage, unless the directional control valve is in a neutral position in which no fluid is supplied to the hydraulic device. Thus accidental stopping of one operation and simultaneous starting of a second operation resulting in the creation of a dangerous situation is effectively prevented.

While two embodiments of the invention have been shown and described, it will be appreciated that this is for the purpose of illustration and that changes'and modifications may be made therein without departing from the spirit and scope of the invention.

I now claim:

' 1. In an industrial truck having a main frame, a lifting carriage mounted for movement on said mainframe, a

' plurality of hydraulically actuated load manipulating devices on said carriage, a source of fluid pressure on said main frame, flexible conduit means extending between said main frame and said lifting carriage, a hydraulic control valve on said main frame movable between a neutral position in which said flexible conduit means is disconnected from said source of fluid pressure and a power position inwhich said flexible conduit means is connected to said source of fluid pressure, power operated hydraulic valve means on said carriage operable to selectively direct fluid from said conduit means to one of said hydraulically actuated load manipulating devices, control means on said truck for selectively operating said power operated valve means, and means interconnecting said hydraulic control valve and said power operated valve means for preventing operation of said power operated valve means when said hydraulic control valve is in said power position while permitting operation of said power operated valve means when'said hydraulic control valve is in neutral. position whereby simultaneous stopping of the operation of one hydraulic device and starting operation of a second hydraulic device is prevented.

2. In an industrial truck having a main frame, a lifting carriage mounted for movement on said main frame, a plurality of hydraulically actuated load manipulating devices on said carriage, a source of fluid pressure on said main frame, flexible conduit means extending between said main frame and said lifting carriage, a hydraulic control valve on said main frame movable between a neutral position in which said flexible conduit means are disconnected from said source of fluid pressure and a power position in which said flexible conduit means are connected'to said source of fluid pressure, electrically operated hydraulic valve means on said carriage operable to selectively direct fluid from said conduit means to one plurality of hydraulically actuated load manipulating devices on said carriage, a source of fluid pressure on said main frame, flexible conduit means extending between said main frame and said lifting carriage, a hydraulic.

control valve on said main frame including handle means for moving said valve between a neutral position in which said flexible conduit means is disconnected from said source of fluid pressure and a power position in which said flexible conduit means is connected to said source of fluid pressure, electrically operated hydraulic valve means on said carriage operable to selectively direct fluid from said conduit means to one of said hydraulically actuated load manipulating devices, switch means on said handle electrically operated valve means when said hydraulic control valve is in said power position while permitting operation of said electrically, operated valve means by said switch means when said hydraulic control valve is in neutral position whereby stopping operation of one hydraulic device and simultaneous starting operation of a second hydraulic device is prevented.

4. In an industrial truck having a main frame, a lifting carriage mounted for movement on said main frame, a plurality of hydraulically actuated load manipulating devices on said carriage, a source of fluid pressure on said main frame, flexible conduit means extending between said main frame and said lifting carriage, a hydraulic control valve on said main frame movable between a neutral position in which said flexible conduit means are of said hydraulically actuated load manipulating devices, I

switch means on said truck for selectively operating said electrically operated valve'means, and means interconnecting said hydraulic control valve and said electrically operated valve means for preventing operation of said electrically operated valve means when said hydraulic control valve is in said power position while permitting operation of said electrically operated valve means when said hydraulic control valve is in neutral position whereby simultaneous stopping of the operation of one hydraulic device and starting operation of a second hydraulic device is prevented. 1 I

3. In an industrial truck having a main frame, a lifting carriage mounted for movement on said main frame, a

disconnected from said source of fluid pressure and a power position in which said flexible conduit means are connected to said source of fluid pressure, electrically operated hydraulic valve means on said carriage for each hydraulically operated device for connecting the hydraulic devices with said conduit means, switch means on said truck for selectively operating the electrically operated hydraulic valve means of each hydraulically operated device, and means interconnecting said hydraulic con- 5. In an industrialtruck having a main frame, a lift ing carriage mounted for movement on said main frame, at least two hydraulically actuated load manipulating devices on said carriage, a source of fluid pressure on said main frame, flexible conduit means extending between said main frame and said lifting carriage, a hydraulic control valve on said main frame movable between a neutral position in which said flexible conduit means is disconnected from said source of fluid pressure and a power position in which said flexible conduit means is connected to said source of fluid pressure, electrically operated hydraulic selector valve means on said carriage operable to selectively direct fluid from the said conduit means to either one of said hydraulically actuated load manipulating devices, switch means on said truck for operating said electrically operated selector valve means, and means interconnecting said hydraulic control valve and said electrically operated selector valve means for rendering said switch means ineffective to change the position of said selector valve means when said hydraulic control valve is in power position while permitting changing of the position of said selector valve means by said switch means when said'hydraulic control valve is in neutral position whereby stopping operation of one hydraulic device and simultaneous starting operation of a second hydraulic device is prevented.

References Cite by the Examiner UNITED STATES PATENTS Harsch 60-52 Tyler 121-41 Balch 200-157 Schroeder 214-652 Randall 121-40 Schenkelberger 219-653 Quayle 60-97 Troche 60-97 MacMillin 60-97 Bullard 200-157 X 10 HUGO O. SCHULZ, Primary Examiner.

MORRIS TEMIN, Examiner.

Claims

1. IN AN INDUSTRIAL TRUCK HAVING A MAIN FRAME, A LIFTINBG CARRIAGE MOUNTED FOR MOVEMENT ON SAID MAIN FRAME, A PLURALITYH OF HYDRAULICALLY ACTUATED LOAD MANIPULATING DEVICES ON SAID CARRIAGE, A SOURCE OF FLUID PRESSURE ON SAID MAIN FRAME, FLEXIBLE CONDUIT MEANS EXTENDING BETWEEN SAID MAIN FRAME AMD SAID LIFTING CARRIAGE, A HYDRAULIC CONTROL VALVE ON SAID MAIN FRAME MOVABLE BETWEEN A NEUTRAL POSITION IN WHICH SAID FLEXIBLE CONDUIT MEANS IS DISCONNECTED FROM SAID SOURCE OF FLUID PRESSURE AND A POWER POSITION IN WHICH SAID FLEXIBLE CONDUIT MEANS IS CONNECTED TO SAID SOURCE OF FLUID PRESSURE, POWER OPERATED HYDRAULIC VALVE MEANS ON SAID CARRIAGE OPERABLE TO SELECTIVELY DIRECT FLUID FROM SAID CONDUIT MEANS TO ONE OF SAID HYDRAULICALLY ACTUATED LOAD MANIPULATING DEVICES, CONTROL MEANS ON SAID TRUCK FOR SELECTIVELY OPERATING SAID POWER OPERATED VALVE MEANS, AND MEANS INTERCONNECTING SAID HYDRAULIC CONTROL VALVE AND SAID POWER OPERATED VALVE MEANS FOR PREVENTING OPERATION OF SAID POWER OPERATED VALVE MEANS WHEN SAID HYDRAULIC CONTROL VALVE IS IN SAID POWER POSITION WHILE PERMITTING OPERATION OF SAID POWER OPERATED VALVE MEANS WHEN SAID HYDRAULIC CONTROLS VALVE IS