US3760840A

US3760840A - Dynamic modulator

Info

Publication number: US3760840A
Authority: US
Inventors: P Gates
Original assignee: Applied Power Inc
Current assignee: Enerpac Tool Group Corp
Priority date: 1972-03-10
Filing date: 1972-03-10
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25

Abstract

A dynamic modulator for modulating fluid pressure transients in the hydraulic lines to a hydraulically actuated device, the modulator including a metering piston to control the flow of fluid bypassed through the modulator; a modulating piston positioned to respond to the movement of the metering piston and to control the response of the metering piston; and a bypass duct network connected across the metering piston and including metering valves to control the time interval of response of the metering piston to pressure variations across the metering piston.

Description

United States Patent 1191 Gates Sept. 25, 1973 DYNAMIC MODULATOR [75] Inventor: Paul Gates, Waukesha, Wis.

[73] Assignee: Applied Power Inc., Milwaukee, Wis.

[22] Filed: Mar. 10, 1972 [2]] Appl. N0.: 233,488

[52] US. Cl. 137/493 [51] Int. Cl. F16k 17/26 [58] Field of Search 137/493; 91/436, 91/437 [56] References Cited UNITED STATES PATENTS 3.138072 6/1964 Gray 91/437 3,378,028 4/1968 Mosher 137/493 Primary 'ExaminerHenry T. Klinksiek Attorney-James E. Nilles 57 ABSTRACT A dynamic modulator for modulating fluid pressure transients in the hydraulic lines to a hydraulically actuated device, the modulator including a metering piston to control the flow offluid bypassed through the modulator; a modulating piston positioned to respond to the movement of the metering piston and to control the response of the metering piston; and a bypass duct network connected across the metering piston and including metering valves to control the time interval of response of the metering piston to pressure variations across the metering piston.

11 Claims, 6 Drawing Figures PATENTED SEPZS I973 SHEU 1 BF 2 DYNAMIC MODULATOR BACKGROUND OF THE INVENTION In hydraulically actuated devices such as hydraulic motors and hydraulic piston and cylinder assemblies, it is desirable to have the device accelerate anddecelerate smoothly under control of the operator. When these devices are used to operate heavy duty construction equipment such as lift trucks, derricks, shovels and winches, high static friction and inertia must be overcome in the equipment each time the device is actuated, often resulting in oscillations in the movement of the equipment as well as thehydraulic device. For instance, when hydraulic pressure is applied to the piston and cylinder assembly operating a shovel, boom or fork lift truck, or when pressure is applied to a hydraulic motor, theinput pressure on the hydraulic device rises considerably before load movement begins. On breakout, a surge of fluid into the device results due to the pressure drop in the device. (Breakout refers to the initial movement of the hydraulically actuated device when the fluid pressure is sufficient to overcome the static friction or load on the device.) At breakout, the movement of the device accelerates rapidly, producing a high mass movement in the construction equipment. The accelerated movement of this mass will eventually exceed the speed of movement of the hydraulic device and cause the boom to vibrate. Each momentary stop will produce a pressure transient in the device resulting in an oscillation of the device. In boom type equipment such as a shovel or derrick, high dynamic loads can be imposed on the boom if excessive oscillations or vibrations occur which can result in damage to the boom.

SUMMARY OF THE INVENTION The dynamic modulator of the present invention can be used to relieve hydraulic pressure transients in hydraulic devices used in lift trucks, shovels, derricks, winches and the like. The modulator responds to hydraulic pressure transients and modulates those transients on a bidirectional and dynamic basis. The modulator includes a metering piston that responds to pressure. variarions to bypass fluid across the hydraulic lines. A modulating piston is used to control the response characteristic of the movement of the metering piston which prevents oscillation of the metering piston. The time response of the metering piston is controlled by a bypass duct network provided in the modulator. Adjustable metering valves are provided in the bypass duct network to adjust the length of the time delay interval of response to the metering piston. It should be noted that the modulator is not complicated, and hence is precise, durable and relatively inexpensive.

DRAWINGS in a back hoe showing the dynamic modulator connected across the hydraulic lines.

FIG. 4 is a load pressure-time chart showing a comparison between ideal startup conditions, actual startup conditions and modulated startup conditions.

FIG. 5 is a schematic view of a hydraulic circuit for a hydraulically actuated motor showing the modulator connected across the hydraulic lines.

FIG. 6 is a. quantity-load pressure chart showing the pressure flow characteristic for various valve openings.

DESCRIPTION OF THE INVENTION The dynamic modulator 10 of this invention is used to control transient pressure surges in the hydraulic lines to a hydraulically actuated device. This modulator has particular application in a fluid circuit for a doubleacting hydraulic piston and cylinder assembly 12 as seen in FIG. 2 and 3 or a hydraulically actuated motor 14 as seen in FIG. 5. In the fluid circuit shown in FIGS. 2 and 3, the flow of fluid from a pump 15 through hydraulic lines l6and 18 to the piston and cylinder assembly 12 and back to the reservoir 17 is controlled by means of a control valve 19. In the fluid circuit shown in FIG. 5, the flow of fluid from the pump 15 through

hydraulic lines

16 and 18 to the motor 14 and back to he reservoir 17 is controlled by means of a four-way control valve 21.

The modulator 10 is connected across the

hydraulic lines

16 and 18 to relieve pressure transients that occur in the assembly 12 or motor 14. In FIG. 3, the piston and cylinder assembly 12 is shown connected to control the movement of the boom 20 for a backhoe, 22. In a device of this type, considerable hydraulic pressure has to be built up in the assembly 12 in order to overcome static friction and interia in the boom. Once static friction is overcome, rapid acceleration of the movement of the piston in the cylinder of the assembly 12 occurs due to the build up of high fluid pressure in the cylinder with a corresponding sudden drop in pressure in the cylinder assembly. The boom 20 will start to decelerate and the pressure will again build up in order to continue to move the boom. This fluctuation in pressure continues until the hydraulic force required to move the boom is stabilized.

In this regard and referring to FIGS. 4 and 6 a graphic representation is shown of the flow characteristics of the hydraulic fluid. The parabolic lines X X and X indicate the functional relation of fluid quantity and pressure of fluid for different valve openings of the control valves 19 and 21. Referring to FIG. 6 a fluid quantity-fluid pressure chart is shown. It will be noted that ordinarily there is a pressure buildup to a pressure PI for a valve opening indicated by X on the chart. Since no flow occurs until there is movement of the piston, the pressure buildup is a straight line relation on the chart. Once static friction has been overcome, the piston moves rapidly and pressure drops off rapidly to pressure line P2 with a rapid increase in the volume of flow as indicated by line Q When the piston begins to slow the pressure will again rise from point P in a straight line back to line X In FIG. 4 a load pressure, X -time, t, chart is shown for an ideal startup condition A (no static friction or inertia), an actual startup condition B, and a modulated startup condition C. The ideal startup condition A is in the form of an arcuate line that rises in a relatively straight line relation up to the load condition, X However, under nonnal operating conditions, in order to overcome static friction, load pressure X increases rapidly as shown in line B to a pressure P1 above load condition. On startup, pressure drops rapidly to a pressure P2 below load condition X as described above in connection with FIG. 6. Pressure then again builds up to a point P3 above load pressure and oscillates above and below the load pressure until a stable condition is achieved.

When the modulator of th present invention is connected across the

hydraulic lines

16 and 18, pressure will build up as shown in line C to a point above load condition X on a more gradual slope due to the modulating action of the modulator 10. In startup, pressure will drop to a point below load condition X The modulator 10 will respond to this transient pressure wave and again produce a more gradual slope in pressure drop so that the line C assumes the load condition line X with a minimum of pressure fluctuations. In other words, a single oscillation of pressure will occur above and below the load condition.

DYNAMIC MODULATOR In accordance with the invention, the modulator 10 as seen in FIG. I generally includes a housing 24, having a cylindrical bore 26 and a counterbore or chamber 25, 27 at each end. The hydraulic line 16 is connected to the bore 26 through a first passage 28 and to the chamber 25 by means of a duct 29. The flow rate through duct 29 is controlled by means of a metering valve 31. The hydraulic line 18 is connected to the bore 26 through a second passage 30, chamber 27, a third passage 34 and a pair of passages 56 and 58. The flow of hydraulic fluid through the bore 26 is controlled by means of a metering piston 36 which is responsive to pressure variations in chamber 25, chamber 27, and bore 26.

Movement of the metering piston 36 in the bore 26 is modulated by means of a modulating piston 38 located in the bore 26 in a spaced relation to the metering piston 36. The modulating piston 38 responds to pressure variations in chamber 27 and bore 26 to provide a variable volume in said bore 26. The space 23 in the bore 26 between the metering piston 36 and the modulating piston 38 is connected to the chamber 25 by means of a bypass duct 42. The flow of fluid through duct 42 is controlled by means of a metering valve 35.

As will be more specifically described below, as pressure transients occur in he first passage 28 or the second passage 30, the pressure transient will be transmitted to the chamber 25 or 27 to produce a corresponding movement in the metering piston 36 and the modulating piston 38. A change in pressure will occur in the space 23 in the bore 26 between the metering piston 36 and modulating piston 38. The modulating piston will respond at a different rate than the metering piston changing the volume of space 23 and producing a damping effect on the movement of the metering piston.

Means are provided for controlling the time required for the change in pressure in space 23 to be transmitted to the chamber 25. Such means is in the form of the metering valves 31 and 35 provided in ducts 29 and 42 respectively. It should be noted that the metering piston 36 will return to neutral or close whenever the pressure in chamber 25 and space 23 are equal. Therefore, the time response characteristics of modulator 10 is dependent on the time required for the pressure between space 23 and chamber 25 to equalize.

METERING PISTON More particularly, the metering piston 36 includes a first land 50 and a second land 52 connected by a rod 54. Each of the lands 50 and 52 is positioned to control the flow of fluid through the bore 26 between passage 28 and the connecting passages 56 and 58, respectively. The metering piston 36 is biased to a neutral or closed position with respect to the connecting passages 56 and 58 by means of a bidirectional metering spring assembly 60 located in the chamber 25.

In this regard the metering spring assembly 60 includes a first or outer spring 62 positioned between a spring retainer plate 64 and an end cap 66 threadedly received and sealed in the end of the chamber 25. The plate 64 has a central opening 70 and is biased against the end of the chamber 25 in a position to engage one end of the metering piston 36. Movement of the metering piston 36 to the left will compress the first spring 62. A second or inner spring 68 is located within the firstspring 62 and is positioned between the spring plate 64 and an end plate 72 mounted on the end of a rod 74 connected to the metering piston 36 and extending through opening 70. The spring force of spring 68 can be adjusted by means of a nut 73 on the threaded end of rod 74. Movement of the metering piston 36 to the right will compress the second spring 68.

The metering piston 36 is positioned within the bore 26. The land 50 is exposed to the pressure of the fluid in space 23 and the land 52 is exposed to the pressure of the fluid in chamber 25. Since the cross sectional areas of the land 50 and 52 are equal, the metering piston 36 will remain in a fixed or closed position as long as the pressure in the space 23 and chamber 25 is equal.

MODULATING PISTON The modulating piston 38 is biased to a neutral position in the bore 26 by means of a bidirectional modulating spring assembly located in the chamber 27. The bidirectional modulating spring assembly 80 includes a third spring 82 positioned between a spring plate 84 and an end cap 86 threadedly received and sealed in the end of the chamber 27. The spring plate 84 includes an opening 88 and is biased into engagement with the end of the chamber 27 and is positioned in the path of motion of the modulating piston 38. On movement of the modulating piston 38 to the right, the third spring 82 will be compressed to bias the modulating piston 38 back to the neutral position. A fourth spring is positioned within third spring 82 between spring plate 84 and a end plate 90 mounted on the end of a rod 92 connected to the modulating piston 38 and extending through opening 88. The spring force of spring 85 can be adjusted by means of a nut 93 on the threaded end of rod 92. On movement of the modulating piston 38 to the left, the spring 85 will be compressed to bias the modulating piston 38 back to the neutral position.

It should be noted that the force of the modulating spring assembly 80 should be two or three times the force of the metering spring assembly 60. The modulating piston 38 will then respond to pressure changes either in space 23 or chamber 27 at a slower rate than the metering piston 36.

TIME DELAY SYSTEM The time delay required for the pressure differential across the metering piston 36 to be equalized, determines the time response characteristic of the modulator. That is, once a pressure differential is set up across the metering piston, fluid flow will occur across the bore 26 between passage 28 and passage 56 or 58. The time to equalize pressure across the metering piston 36 is controlled by means of the metering valves 31 and 35 provided in the ducts 29 and 42.

In this regard, the metering valve 31 is threadedly received in a threaded bore 98 provided in housing 24 in a position to engage valve seat 99 in a duct 29. The metering valve 35 is threadedly received in a threaded bore 95 provided in housing 24 in a position to engage a valve seat 97 in duct 42. The metering valves 31 and 35 can be adjusted to provide a predetermined flow rate and thereby control the time required to equalize pressure across the metering piston 36.

OPERATION Increase in Pressure in Line 16 When the pressure increases in line 16 to the modulator the pressure wave or transient is bypassed through the bypass duct 29 through metering valve 31 and into the chamber adjacent the end of metering piston 36. The increase in pressure in the chamber 25 causes the piston 36 to move to the right against the bias of spring 68, allowing the fluid to flow from the passage 28 to the passage 56. The pressure in the space 23 in the bore between the metering piston 36 and the modulating piston 38 will increase. The modulating piston 38 will move to the right as the pressure in space 23 exceeds the spring rate of spring 82. The time of transfer of the increased pressure in space 23 to the chamber 25 is controlled by the setting of the metering valves 31 and 35. The modulating piston 38 maintains a positive pressure in the space 23 preventing the metering piston 36 from oscillating in the bore 26. the Decrease in Pressure in Line 16 When the pressure drops in line 16, the pressure drop will betransferred through the bypass duct 29 and metering valve 31 to the chamber 25 adjacent the metering piston 36. The pressure in in the space 23 in the bore 26 between the metering piston 36 and the modulating piston 38 is now greater than the pressure in the chamber 25 and the metering piston 36 will move to the left against the bias of spring 62. Fluid will flow into the inlet passage 28 from the passage 58. As pressure drops in the space 23 due to the movement of the metering piston 36, the metering piston will move to the right to close the passage 58 due to the force of spring 62. Increase of Pressure in the Line 18 A surge in pressure in the line 18 will produce an increase in pressure in the chamber 27 adjacent the modulating piston 38. The modulating piston 38 will move to the left, increasing the pressure in the space 23 between the modulating piston 38 and the metering piston 36. The increased pressure in the space 23 will act on land 50 moving the metering piston 36 to the left against the bias of spring 62, connecting the passage 58 to the passage 28. The increased pressure in the space 23 in the bore will be transferred through the duct 42 past the metering valve to the chamber 25 and through metering valve 31 in duct 29 to passage 28 in a time delay interval. When the pressure in the chamber 25 equals the pressure in the space 23, the metering piston 36 will move to the right, closing the flow path between the discharge passage and the inlet passage. Drop in Pressure in the Line 18 When the pressure drops in the line 18, a corresponding drop in pressure will occur in the chamber 27 adjacent the modulating piston 38. The modulating piston 38 will move to he right against the bias of the spring 82 producing a drop in pressure in the space 23 between the metering piston 36 and the modulating piston 38. The drop in pressure will allow the metering piston 36 to move to the right against the bias of internal spring 68, connecting the passage 56 to the passage 28. The drop in pressure in the space 23 in the bore will also produce a drop in pressure in the chamber 25 through the metering valve 35 and the bypass duct 42 metering valve 31 in duct 29 at a delay time interval When the pressure in the chamber 25 starts to drop, the spring 68 will return the metering piston 38 to the closed position.

I claim:

1. A dynamic fluid pressure modulator for controlling fluid pressure transients in the hydraulic lines to a hydraulically actuated device, said modulator comprisa housing having a bore,

a chamber at one end of said bore,

a first fluid passage connecting said bore to one of the hydraulic lines,

a second fluid passage connecting said bore to the other of the hydraulic lines,

a metering piston positioned in said bore to control the flow of fluid between said first and second fluid passages,

said piston being positioned in said bore to respond to the pressure of fluid in said chamber,

means for biasing said piston to a neutral or closed position with respect to said first and second fluid passages, I

a first bypass duct connecting said first fluid passage to said chamber,

a first metering valve in said first bypass duct,

a second bypass duct connecting said chamber to said bore on the side of said piston remote from said chamber,

' a second metering valve in said second bypass duct whereby said metering piston will respond to variations in pressure across said metering piston.

2. The modulator according to claim 1 including a modulating piston positioned in said bore in a spaced relation to said metering piston, said modulating piston responding to pressure variations in the space between said metering piston and said modulating piston.

3. The modulator according to claim 2 including means for biasing said modulating piston to a neutral position in said bore.

4. The modulator according to claim 3 including a second chamber at the other end of said bore, said second fluid passage being connected to said second chamber, and a third fluid passage connecting said chamber to said bore.

5. The modulator according to claim 1 wherein said biasing means comprises a bidirectional metering spring assembly positioned in said first chamber.

6. A dynamic modulator for controlling fluid pressure transients in the hydraulic lines to a hydraulically actuated device,

said modulator comprising,

a housing having a bore,

a first fluid passage connecting said bore to one of the hydraulic lines,

a metering piston positioned in said bore to control the flow of fluid between said first fluid passage and said second fluid passage,

a modulating piston in said bore positioned in a spaced relation to said metering piston and being connected to respond to the pressure in said second passage,

a first fluid bypass duct connecting said first passage to the end of said bore adjacent to said metering piston, and

a metering valve in said first fluid bypass duct, whereby said metering piston responds to a fluid pressure transient in the hydraulic lines to bypass fluid through said first and second passages.

7. The modulator according to claim 6 including means for bidirectionally biasing said metering piston to a closed position with respect to said first passage and said second passage.

8. The modulator according to claim 6 including means for bidirectionally biasing said modulating piston to a neutral position in said bore.

9. The modulator according to claim 6 including a first chamber at one end of said bore connected to said first bypass duct and a second chamber at the other end of said bore connected to said second fluid passage, said metering piston responding to pressure changes in said first chamber and said modulating piston responding to pressure changes in said second chamber.

10. The modulator according to claim 6 including a second bypass duct connecting said one end of said bore to the space in said bore between said metering piston and said modulating piston.

11. The modulator according to claim 10 including a metering valve in said second bypass duct tocontro] the flow rate through said second bypass duct.

Claims

1. A dynamic fluid pressure modulator for controlling fluid pressure transients in the hydraulic lines to a hydraulically actuated device, said modulator comprising, a housing having a bore, a chamber at one end of said bore, a first fluid passage connecting said bore to one of the hydraulic lines, a second fluid passage connecting said bore to the other of the hydraulic lines, a metering piston positioned in said bore to control the flow of fluid between said first and second fluid passages, said piston being positioned in said bore to respond to the pressure of fluid in said chamber, means for biasing said piston to a neutral or closed position with respect to said first and second fluid passages, a first bypass duct connecting said first fluid passage to said chamber, a first metering valve in said first bypass duct, a second bypass duct connecting said chamber to said bore on the side of said piston remote from said chamber, a second metering valve in said second bypass duct whereby said metering piston will respond to variations in pressure across said metering piston.

6. A dynamic modulator for controlling fluid pressure transients in the hydraulic lines to a hydraulically actuated device, said modulator comprising, a housing having a bore, a first fluid passage connecting said bore to one of the hydraulic lines, a second fluid passage connecting said bore to the other of the hydraulic lines, a metering piston positioned in said bore to control the flow of fluid between said first fluid passage and said second fluid passage, a modulating piston in said bore positioned in a spaced relation to said metering piston and being connected to respond to the pressure in said second passage, a first fluid bypass duct connecting said first passage to the end of said bore adjacent to said metering piston, and a metering valve in said first fluid bypass duct, whereby said metering piston responds to a fluid pressure transient in the hydraulic lines to bypass fluid through said first and second passages.

11. The modulator according to claim 10 including a metering valve in said second bypass duct tocontrol the flow rate through said second bypass duct.