CA2383669A1

CA2383669A1 - Regeneration circuit

Info

Publication number: CA2383669A1
Application number: CA002383669A
Authority: CA
Inventors: Gerald T. Perkins
Original assignee: RAYMOND Co
Current assignee: Individual
Priority date: 2000-07-05
Filing date: 2001-07-02
Publication date: 2002-01-24
Also published as: WO2002006679A2; AU2001270281A8; WO2002006679A3; AU2001270281A1

Abstract

A regeneration hydraulic circuit which increases the speed of one action of a double action cylinder. The hydraulic circuit includes first hydraulic line in fluid communication with one end of the double action cylinder, and a second hydraulic line in fluid communication with an opposing end of the double action cylinder. A third hyraulic line connects the first hydraulic line and the second hydraulic line. A pilot check valve is disposed in the third hydraulic line, and has a pilot line. The pilot line is connected to the fir st hydraulic line, wherein the pilot check valve is open when hydraulic fluid flows through the first hydraulic line and into the one end of the double action cylinder The pilot check valve is closed when hydraulic fluid flows o ut of the end of the double action cylinder and through the first hydraulic lin e. A check valve is disposed in the second hydraulic line, wherein hydraulic fluid flowing out of the opposing end of the double action cylinder is diverted into the third hydraulic line.

Description

REGENERATION CIRCUIT
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of U.S. Provisional Patent Application No. 60/216,041 filed on July 5, 2000.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] Not Applicable Back~,round Of The Invention [0003] The present invention relates to regeneration circuits, and more particularly to hydraulic regeneration circuits in lift trucks.

[0004] Known lift trucks, such as Reach-Fork~ and Swing-Reach~ trucks available from The Raymond Corporation in Greene, New York, include a vertically extendible mast supporting a carriage having horizontally extendible forks. The trucks are used with rack systems for storing and retrieving loads such as pallets in the racks. Efforts continue to reduce the time to perform each store or retrieve operation, and thus increase the efficiency of the truck and operator.

[0005] Each store or retrieve operation requires similar steps. For example in a retrieve operation, the truck performs the following steps; raising the forks vertically to a level below the desired load , extending the forks horizontally underneath the load, raising the forks to lift the load off of the rack supports; and retracting the forks horizontally. The store operation is essentially the same except instead of extending the forks underneath the load and then raising the forks, the forks are extended into the rack storage location and then lowered until the load is supported by the rack supports. Once the load is supported by the rack supports, the forks are then retracted without the load on board.

[0006] One method of decreasing the time required to perform these operations is to increase the vertical speed of the mast and the horizontal speed of the forks.
In hydraulic systems, this can be accomplished by increasing the size of the hydraulic pump and hydraulic lines to handle the increase flow of hydraulic fluid, or providing separate systems sized for the maximum desired speed for individual functions. These modifications, however, increase the cost of the lift truck. Moreover, certain functions of the lift truck, such as retracting the forks horizontally with a load on board, is often limited due to the potential for tipping. As a result, increasing the top speed of certain functions does not always provide a reduction in cycle times.

[0007] Reducing the cycle time of an operation can often be accomplished by increasing the speed of one particular function, such as horizontally extending the forks when a load is not on the forks. Horizontal fork movement is often accomplished using one or more double action hydraulic cylinders. As noted above, in the prior art, increasing the speed of one function, such as horizontal fork extension, may increase the speed of another function, such as horizontal fork retraction, beyond what is required.
Therefore, in a hydraulic system for use in a lift truck, a need exists for economically increasing the speed of one function without increasing the speed of another related function.

Summary Of The Invention [0008] The present invention provides a regeneration hydraulic circuit which increases the speed of one action of a double action cylinder. The hydraulic circuit includes first hydraulic line in fluid communication with one end of the double action cylinder, and a second hydraulic line in fluid communication with an opposing end of the double action cylinder. A third hydraulic Line connects the first hydraulic line and the second hydraulic line. A pilot check valve is disposed in the third hydraulic line, and has a pilot line. The pilot line is connected to the first hydraulic line, wherein the pilot check valve is open when hydraulic fluid flows through the first hydraulic line and into the one end of the double action cylinder The pilot check valve is closed when hydraulic fluid flows out of the one end of the double action cylinder and through the first hydraulic line. A check valve is disposed in the second hydraulic line, wherein hydraulic fluid flowing out of the opposing end of the double action cylinder is diverted into the third hydraulic line.

[0009] A general objective of the present invention is to increase the speed of one action of a double action cylinder without increasing the size of a pump pumping hydraulic fluid into the cylinder. This objective is accomplished by diverting hydraulic fluid being forced out of one end of the hydraulic cylinder to combine with fluid being pumped into the other end of the cylinder.

[0010] This and still other objects and advantages of the present invention will be apparent from the description which follows. In the detailed description below, preferred embodiments of the invention will be described in reference to the accompanying drawings.
These embodiments do not represent the full scope of the invention. Rather the invention may be employed in other embodiments. Reference should therefore be made to the claims herein for interpreting the breadth of the invention.
Brief Description Of The Drawings [0011] Fig. 1 is a perspective view of a lft truck incorporating the present invention;

[0012] Fig. 2 is a hydraulic circuit schematic incorporating the present invention; and [0013] Fig. 3 is a detailed hydraulic circuit schematic showing the reach regeneration circuit of Fig. 2.
Detailed Description Of The Invention [0014] As shown in Figs 1 and 2 a lift truck 1 includes an extendible multi-stage mast assembly 2 mounted thereon. The mast assembly 2 lifts a carriage 3 and a pair of rotatable and extendible forks 4 fixed to the carriage 3. The forks 4 vertically support a pallet (not shown). The mast assembly 2 and forks 4 are actuated by a lift truck hydraulic circuit 10. The lift truck 1 can be any commercially available lift truck having a mufti-stage assembly, such as a Raymond Reach-Fork~, Easier Swing-Reach~, and Pacers Truck available from Raymond Corporation, Greene, New York.

[0015] Refernng to Fig. 2, the mast assembly 2 includes hydraulic lift cylinders 14 which lifts the carriage 3 and forks 4, to a predetermined height. An auxiliary lift cylinder 15 can lift the forks 4 independently of the carriage 3. A second set of hydraulic cylinders 16 extend and retract the forks 4. The forks 4 are rotated by a first rotary actuator 18 which rotates the forks in one direction, and a second rotary actuator 20 which urges the forks in the opposite direction. Although the preferred embodiment of the present invention is a hydraulically actuated cylinder, other fluid actuators, such as a pneumatically actuated cylinder and the like, are within the scope of the invention.

[0016] The lift truck hydraulic circuit 10 includes a reservoir 12 for holding hydraulic fluid which is pumped through hydraulic lines to actuate cylinders 14, 16 and rotary actuators 18, 20. Various valves 22 direct the hydraulic fluid to the cylinders 16, 18 and rotary actuators 18, 20 to actuate the desired cylinder 16, 18, or actuator 18, 20. One pump 24 pumps hydraulic fluid to the first set of cylinders 14, and a second pump 26 pumps hydraulic fluid to the carriage for operating the second set of cylinders I6 and rotary actuators 18, 20 mounted on the carriage.

[0017] As shown in Figs. 2 and 3, the hydraulic circuit 10 includes a regeneration circuit 30 for actuating the double action second set of cylinders I6 which extend and retract the forks. Each double action cylinder 16 includes a cap end 32 and a rod end 34. The cap end 32 and rod end 34 of each cylinder 16 are separated by a slidable diaphragm 36 having a rod 38 connected thereto. The rod 38 extends out of the cylinder 16, and is linked to the forks, such that as the rod 38 extends out of the cylinder 16 the forks extend, and as the rod 38 is retracted into the cylinder 16 the forks retract. Hydraulic fluid pumped in the cylinder cap end 32 slidably moves the diaphragm 36 which urges fluid in the cylinder rod end 34 out of the cylinder 16. Conversely, hydraulic fluid pumped into the rod end 34 slidably moves the diaphragm 38 which urges fluid in the cap end 32 out of the cylinder 16.
As the diaphragm 38 moves toward the rod end 34, the rod 38 extends further out of cylinder 16 to extend the forks, and as the diaphragm 38 moves toward the cap end 32, the rod 38 retracts into the cylinder 16 to retract the forks.

[0018] The regeneration circuit 30 causes the forks 4 to extend faster than the forks 4 can be extended without the regeneration circuit 30 by directing fluid being forced out of the cylinder rod end 34 back into the cap end 32. Referring to Fig. 2, in the regeneration circuit 30, when extending the forks, hydraulic fluid flows into the cylinder cap end 32 through a first hydraulic line 40, and out of the cylinder rod end 34 through a second hydraulic line 42.
In prior art hydraulic circuits, the hydraulic fluid exiting the cylinder rod end 34 is returned to the reservoir 12. However, in the present invention, the hydraulic fluid exiting the cylinder rod end 34 is diverted into the first hydraulic line 42 to increase the speed of the fork extension, and not back to the reservoir 12.

[0019] The hydraulic fluid is diverted to the first hydraulic Line 40 supplying the cylinder cap end 32 by check valves 44, 46. The first check valve 44 prevents hydraulic fluid from exiting the regeneration circuit 30 through the second hydraulic line 42.
The second check valve is a pilot check valve 46 in a connecting hydraulic line 48 connecting the first hydraulic line 40 to the second hydraulic line 42. A pilot line 50 of the pilot check valve 46 is connected to the first hydraulic line 40, such that the pilot check valve 46 is open when the first hydraulic line 40 is supplying hydraulic fluid to the cylinder cap end 32, and closed when the second hydraulic line 42 is supplying hydraulic fluid to the cylinder rod end 34.

[0020] In operation, when hydraulic fluid is being supplied to the cylinder cap end 32 through the first hydraulic Iine 40, the pilot check valve 46 is open, and the first check valve 44 is closed which causes hydraulic fluid exiting the cylinder rod end 34 to flow from the second hydraulic line 42 through the connecting line 48 and into the first hydraulic line 40.
The hydraulic fluid exiting the rod end 34 combines with the fluid pumped by the carriage pump 26 being supplied to the cap end 32 to increase the volumetric flow of hydraulic fluid into the cylinder cap end 32. Increasing the volumetric flow of hydraulic fluid by diverting the fluid exiting the cylinder rod end 38 increases the extension speed of the forks over the speed which would be attained by hydraulic fluid pumped by the carriage pump 26 alone.
Advantageously, the fork extension speed is increased without increasing the pump size.

[0021] When the forks are retracted, hydraulic fluid is supplied to the cylinder rod end 34 by the second hydraulic line 42, and fluid exits the cylinder cap end 32 through the first hydraulic line 40 and into the reservoir 12. The pilot check valve 46 prevents the flow of hydraulic fluid into first hydraulic line 40, and forces the fluid flowing through the second hydraulic line 42 into the cylinder rod end 34.

[0022] Advantageously, the present invention can provide a simple modification to an existing hydraulic circuit to increase the speed of one actuation direction of a double actuation cylinder, or other circuitry, such as in use with a torque motor, valves, and the like, without increasing the pump size. The modification includes providing a connection hydraulic line which connects a hydraulic line which supplies hydraulic fluid to the cap end of a cylinder and a hydraulic line which receives hydraulic fluid from the rod end of the hydraulic cylinder. A check valve is installed in the hydraulic line supplying fluid to the rod end of the cylinder, such that hydraulic fluid exiting the cylinder rod end is diverted into the connection hydraulic line. A pilot check valve is installed in the connecting hydraulic line with a pilot line connected to the hydraulic line supplying hydraulic fluid to the cap end of the cylinder, such that the pilot check valve is open when fluid is being supplied to the cap end of the cylinder, and the pilot check valve is closed when fluid is exiting the cylinder cap end. Of course, the portion of the hydraulic line downstream of the merging point of the connection line and the hydraulic line supplying fluid to the cap end of the cylinders (i.e. the portion of the hydraulic line between the merging point and the cap end) must be sized to accommodate the hydraulic fluid from the pump and the rod end of the cylinders.

[0023] Another advantage of the present invention, is that a circuit incorporating the present invention prevents a cylinder from "overrunning." Overrunning exists when a cylinder load tries to pull, or extend the cylinder rods. This can occur in a lift truck carrying a Ioad on extendible forks when braking.

[0024] While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention defined by the appended claims. For example, a different fluid, such as air, can be used.
_g_

Claims

I Claim:

1. In a fluid circuit having a first fluid line in fluid communication with one end of a double action cylinder, and a second fluid line in fluid communication with an opposing end of the double action cylinder, a combination therewith:

a third fluid line connecting the first fluid line and the second fluid line;
a pilot check valve disposed in said third fluid line, and having a pilot line connected to the first fluid line, wherein said pilot check valve is open when fluid flows through the first fluid line and into the one end of the double action cylinder, and said pilot check valve is closed when fluid flows out of the one end of the double action cylinder and through the first fluid line; and a check valve disposed in the second fluid line, wherein fluid flowing out of the opposing end of the double action cylinder is diverted into said third fluid line.

2. The fluid circuit of claim 1, in which said double action cylinder extends and retracts forks of a lift truck.

3. The fluid circuit of claim 1, in which the fluid flowing through the first fluid line is hydraulic fluid.

4. A method for increasing the speed of one actuation direction of a double action fluid cylinder having a first fluid line supplying fluid to one end of the cylinder and a second fluid line supplying fluid to another end of the cylinder, said method comprising:
connecting said first fluid line to said second fluid line with a fluid connecting line;
installing a check valve in said second fluid line such that fluid exiting the cylinder through the second fluid line is diverted to the first fluid line;
installing a pilot check valve having a pilot line in the connecting line;
connecting the pilot line to the first fluid line, such that the pilot check valve is open when fluid is being supplied to the cylinder through the first fluid line and the pilot check valve is closed when fluid is exiting the cylinder through the first fluid line.

5. The method of claim 4, in which said double action cylinder extends and retracts forks of a lift truck.

6. The method of claim 4, in which the fluid flowing through the first fluid line is hydraulic fluid.

7. A method of increasing the actuation speed of an action of a double action cylinder having a slidable diaphragm interposed between a rod end and a cap end, wherein fluid forced into one of the ends slidably moves the diaphragm toward the other one of said end and forces fluid in the other one of said end out of the other one of said end, said method comprising:

forcing fluid into one end of the double action cylinder to slidably move the diaphragm toward the other end of the cylinder and force fluid out of the other end of the cylinder;
directing fluid exiting the other end of the cylinder into the one end of the cylinder to increase the volumetric flow of fluid into the one end of the cylinder and increase the speed at which the diaphragm slidably moves toward the other end of the cylinder.

8. The method of claim 7, in which said double action cylinder extends and retracts forks of a lift truck.

9. The method of claim 7, in which the fluid is hydraulic fluid.