US 3871266 A
A hydraulic phasing system including a phasing valve for a multiple cylinder lift truck upright is disclosed. The phasing valve senses line pressure and automatically controls the sequence of extension and retraction between a first stage lift cylinder and a second stage lift cylinder.
Description (OCR text may contain errors)
United States Patent 11 1 1111 3,871,266 Schwab et al. Mar. 18, 1975  HYDRAULIC CYLINDER PHASING SYSTEM 2,301,028 11/1942 Esch 91/412 X 1 Inventors: e a ,GtssbmpiMn k 92332133 13/132? Si-$399.5? 111'. 1411731 5? James Portland, both Of 2,674,092 4/1954 0611111161.... 60/422 x g- 2,737,196 3/1956 Eames 91/412 x  Assignee: Hyster Company, Portland, Oreg. 22 Filed; July 16, 7 Primary ExaminerEdgar W. Geoghegan 211 Appl. NO.I 379,754 2  ABSTRACT  U.S. Cl 1. 91/412, 60/420, 60/484,
329 A hydraulic phasing system includlnga phasing valve 511 1111.01. Fl5b .11/20 for a multiple cylinder lift truck upright is disclosed-  Field of Search 91/412; 60/97 SE, 422, The Phasing Valve Senses line P s and automati' 6O/420 484, 329 cally controls the sequence of extension and retraction between a first stage lift cylinder and a second stage  References Cited 11ft y UNITED STATES PATENTS 3 Claims, 2 Drawing Figures 1,994,974 3/1935 Wledmann 91/412 X 1 HYDRAULIC CYLINDER PHASING SYSTEM BACKGROUND .OF THE 1 INVENTION 1. Field of the Invention The present invention pertains to hydraulically operated lift truck uprights in general and more particularly to those uprights having a plurality of cylinders which extend sequentially.
2. Description of the Prior Art Two common methods for controlling the phasing of sequentially operating hydraulic cylinders are disclosed by the prior art. The first employs mechanical latches and the second relies on the difference in effective pressure of the different cylinders. Mechanical latching mechanisms are positive but lack reliability and require careful adjustment.
Effective pressure difference between the cylinders is a useful method within a narrow temperature range. But as temperature drops, oil viscosity increases and hydraulic line losses begin to overcome the cylinder pressure differential. M isphasing will then occur. Space limitations and acceptable speed differences between the cylinders make it difficult to increase the effective cylinder pressure differentials sufficiently to cover the range of operating temperatures within which the system must function.
SUMMARY OF THE INVENTION The invention is directed to improvements in the construction and operation of lift truck uprights having a plurality of hydraulic hoisting cylinders which operate sequentially. To overcome the prior difficulties associated with cylinder phasing, the present invention utilizes a small differential in cylinder operating pressure along with line loss pressure sensing to automatically signal a hydraulic valve to route oil to the cylinders in proper sequence.
A primary object of the invention is to provide correct phasing of the cylinders during raising and lowering over a wide range of temperature variations.
A further object of the invention is to provide a minimum time delay between the reaching of full extension of the first stage cylinder and start of extension of the second stage cylinder. This provides a smooth transition with a minimum of bounce and noise.
A further object of the invention is to provide a minimum of restriction to flow for both cylinders during their lifting and lowering modes.
Throughout the following description the further objectives of the invention will become apparent to those skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a hydraulic schematic of the circuitry including the phasing valve of a lift truck having two lifting cylinders.
FIG. 2 shows the internal construction of the phasing valve.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 shows a hydraulic circuit which has an oil reservoir 1, a pump 3 which draws oil from the reservoir 1 and routes it to a spool control valve 5 via line 7. A pressure relief valve 9 is contained in the circuit and will allow oil to return to reservoir 1 when the pressure exceeds a preset level.
From valve 5 the pressure oil is applied to phasing valve 11. This valve routes oil to a first stage cylinder 13 through a line 15. Valve 11 senses the pressure drop due to flow restriction in line 15 via pilot line 21. Valve 11, under conditions to be described below, controls the routing of oil flow through line 17 to the second stagecylinder 19. Within phasing valve 11 is contained a control spool 23 having an orifice 25 and a plurality of openings 14. This spool is operatively connected to pilot line 21 and to line 17. The check valve 29 within passageway 18 is contained within valve 11. Oil from line 7 enters the valve via supply port 31 and moves through passageway 12, and line 15 to the first stage cylinder 13. At the same time, oil flows through openings 14 into passageway 16 and on through line 17 to the second stage cylinder 19. Oil is blocked from How ing from line 12 through passageway 18 by check valve 29. Spool 23 is biased to the open position via spring 22. Pilot line 21 runs from the first stage cylinder 13 to pilot port 26.
OPERATION Pump 3 draws oil from reservoir 1 and sends it via line 7 to valve 5. When valve 5 is in the neutral position oil passes through line 8 and filter 10 back to reservoir 1. When the operator chooses to raise the lift truck upright (not shown) he positions the valve so that oil flows into line 7 and to phasing valve 11. Oil is routed via passageway 12 and through line 15 to first stage cylinder 13. At the same time, oil pressure is directed by spool 23 through openings 14 and to passageway 16 to second stage cylinder 19 via line 17. Flow in line 17 will not normally exist because the second stage cylinder 19 requires a higher operating pressure. When the rate of flow to cylinder 13 via line 15 is high, or when the temperature is low so that oil viscosity is high, a drop in pressure will occur in line 15. This pressure drop is sensed by valve 11 via pilot line 21. At a predetermined pressure drop, spool 23 begins to restrict openings 14 leading to passageway '16 and line 17. When the pressure drop exceeds a predetermined maximum, spool 23 will highly restrict openings 14 and remain in that position independent of any further line loss. This will prevent misphasing of the second stage regardless of the load on the cylinders.
While spool 23 is in the restricting position, upward creep in the second stage cylinder must be prevented. This is accomplished by including an orifice 25 in the end of spool 23. This orifice is used to maintain a fixed differential between second stage pressure in line 17 and first stage pressure in line 15. This fixed differential is lower than the operating pressure difference of the two cylinders. A small controlled oil flow will pass through orifice 25 and pilot line 21 to first stage cylinder 13. This controlled orifice flow is regulated through the restriction of openings 14 and spool 23. Therefore, spool 23 is maintained at its minimum overlap position to maintain the maximum response rate in controlling Absence of a pressure drop in the line allows spring 22 to keep spool 23 wide open as the second stage cylinder moves through its stroke.
In the lowering mode, the second stage cylinder will retract first since its operating pressure is higher than the first stage cylinder operating pressure. The returning oil will pass through line 17, passageway 16 through spool 23 and back to reservoir 1. Since flow does not pass through line 15 while the second stage cylinder is retracting there will be no pressure drop to cause spool 23 to shift to the restricting position. Oil will also pass through passageway 18, through check valve 29 into line 7 and back to reservoir 1. Check valve 29 also provides an alternate path of flow in the event that the spool 23 should shift to the restricting position during transient responses or for any other reason. As soon as the second stage is fully lowered the first stage cylinder will retract.
Although we have described and illustrated a preferred embodiment of our invention, it will be understood by those skilled in the art that modifications may be made in the structure, form, and relative arrangement of the parts herein disclosed without departing from the spirit and scope of the invention. It should be understood that the appended claims are intended to cover all such modifications and arrangements which fall within the scope of the invention.
We claim: 1. A hydraulic control system for regulating the extension and retraction of a plurality of hydraulic motors, said system comprising:
a first and second separate hydraulic motors; a pump operatively connected to said motors; said hydraulic control system including a hydraulic control circuit supplied with pressure fluid by said pump and including a pressure fluid reservoir;
valve means Within said circuit including means for sensing viscous flow losses and for sensing pressure loss within that portion of said circuit which supplies said first hydraulic motor; and means within said valve means reactive to said pressure loss and viscous flow loss to restrict pressure oil to said second hydraulic motor.
2. A hydraulic phasing system for controlling a plurality of hydraulic cylinders comprising:
first and second hydraulic cylinders, said first cylinder being separate from said second cylinder;
a hydraulic control circuit operatively connected to said first and said second cylinders; the circuit including a pilot line from the first cylinder to the second cylinder;
an oil reservoir including a high pressure pump for supplying pressure fluid to said hydraulic control circuit;
means within said circuit for selectively extending said first and said second hydraulic cylinders;
and hydraulic phasing means including valve means sensitive to viscous flow losses and insensitive to fluid flow ratewithin said pilot line whereby said phasing means permits extension of said second cylinder only after said first cylinder has extended completely.
3. A hydraulic cylinder phasing system for controlling a plurality of extensible hydraulic cylinders comprising:
first and second hydraulic cylinders, said second hydraulic cylinder being separate from said first hydraulic cylinder;
a hydraulic pump operatively connected to said cylinders;
a hydraulic control circuit supplied with pressure fluid from said pump and including a pressure fluid reservoir, said circuit including a first supply line furnishing fluid to said first cylinder and a second supply line furnishing fluid to said second cylinder;
first valve means for selectively controlling flow of pressure oil from said pump to said hydraulic circult;
second valve means including means for sensing loss of pressure in said first cylinder supply line; the valve means being further sensitive to viscous flow losses;
and means within said second valve means reactive to said pressure loss and to said viscous flow losses to restrict pressure oil to said second cylinder;
whereby said reactive means controls phasing of said first cylinder and said second cylinder and permits extension of said second cylinder only after said first cylinder has extended completely.