US 3598020 A
Description (OCR text may contain errors)
United States Patent Petrus Blok Coymansstraat 7, Moerkapelle; Taco J. Viersma, Julianalaan 26, Pijnacker,
 Inventors both of, Netherlands  Appl. No. 825,869  Filed May 19, 1969  Patented Aug. 10, 1971  Priority May 31, 1968 [3 3] Netherlands  6807776  MAIN CONTROL SYSTEM FOR HYDRAULIC SERVOMOTORS 6 Claims, 3 Drawing Figs.
 U.S.Cl 91/416, 91/216A,9l/376,9l/417,91/461,137/82  Int.Cl ..F15b15/11, Fl5b9/l0,FOlbl5/OO  Fieldoi'Seai-ch 91/3,49,
Primary Examiner- Paul E. Maslousky Attorney-Imirie & Smiley ABSTRACT: A control system for a hydraulic servomotor, comprising a cylinder chamber containing a diaphragm which is borne, between two circular bearing edges so that a central and an annular compartment are produced on either side of the diaphragm, each of the annular compartments being connected to a pilot system, the first central compartment being connected to a cylinder of a servomotor, and the second to a discharge, in each central compartment an outflow member discharging towards the center of the diaphragm the member in the first compartment connected to a high-pressure supply and the other member to said cylinder.
PATENTEUAUGIOIB?! SHEET 1 OF 2 INVENTOR:
PETRIJS 51 3K ATTORNEYS MAIN CONTROL SYSTEM FOR HYDRAULIC SERVOMOTORS The invention relates to a main control system for a hydraulic servomotor, comprising a supply of high-pressure liquid at substantially constant pressure, which can be connected via an adjustable inlet aperture to a cylinder chamber of the servomotor, the main control system also having a discharge to a low-pressure reservoir, which can also be connected via an adjustable outflow aperture to the aforementioned cylinder chamber, a displaceable member being provided to adjust the size of the inlet and outlet apertures, whose condition can be adjusted by means of a control system, while the pressure in the cylinder chamber so acts on the displaceable member that when the pressure rises, the inlet aperture increases in size and the outlet aperture decreases in size, and vice versa.
A main control system of the kind specified is disclosed on page 48 of the thesis entitled Investigations into the accuracy of hydraulic servomotors" by Dr. of Engineering T. J. Viersma, Delft Technical University 1961.
In this known system, the displaceable member is a control disc whose movement inside a casing opens the inlet and outlet apertures to varying degrees. The reaction of the pressure in the cylinder chamber is obtained by making this pressure act on a diaphragm to which the control disc is connected. One disadvantage of this system is its rather complicated construction and the fact that the control disc has a relatively large mass, thus reducing the control speed.
It is an object of the invention to provide a main control valve of the kind specified which is of simple, robust and very compact construction and in which the mass of the displaceable member is small, so that control speed is very high.
To this end the main control system according to the invention is characterized in that it comprises a closed cylinder chamber containing a circular diaphragm which has a diameter at least substantially the same as that of the cylinder chamber and over smaller diameter than that of the outer periphery ofthe diaphragm is borne between two circular eonstructional members bearing in sealingtight relationship against the end walls of the cylinder chamber and the diaphragm, so that an annular compartment and a central compartment are produced on either side of the diaphragm, and each of the annular compartments can be connected to a pilot control system delivering two control pressures one central compartment being connectable to the aforementioned cylinder chamber of the servomotor, the other central compartment being connectable to the discharge, while the highpressure liquid supply discharges via an outflow aperture directed towards the center of the diaphragm into the compartment which can be connected to said cylinder chamber, and an outflow member whose outflow aperture is directed towards the center of the diaphragm and whose other side can be connected to the said cylinder chamber of the servomotor is disposed in the compartment which can be connected to the discharge.
The result is a main control valve of very compact construction which is well adapted to be incorporated in the piston of the servomotor, thus making the servomotor itself more compact. Sensitivity and control speed are high, due to the small mass of the moving diaphragm. The main control valve can also be controlled by a hydraulic or pneumatic pilot valve.
Also advantageously according to the invention. each ofthe constructional members bearing the diaphragm is formed by the combination of a number of balls received in an annular cage with an O-ring gasket on one or both sides thereof.
The invention will now be described in greater detail with reference to the drawings, wherein:
FIG. 1 shows diagrammatically (not to scale) a servomotor main control system cooperating with a pilot control system;
FIG. 2 shows diagrammatically (not to scale) a variant embodiment of the main control system shown in FIG. 1, and
FIG. 3 shows diagrammatically (not to scale) an embodiment of a servomotor in which the main control system is incorporated in the servomotor piston.
Referring to FIG. 1, a main control system 1 comprises a closed cylindrical casing 2 receiving a circular diaphragm 3 having substantially the same diameter as the casing 2. Over a diameter smaller than its peripheral diameter, the diaphragm 3 is loosely borne between two circular knife-edge-like bearing edges 4, 5 which bear in sealingtight relationship against the diaphragm 3 and and are also rigidly connected to the walls of the casing 2, thus forming two annular compartments 6, 7 and two central compartments 8, 9. Disposed in the center of each of the end walls of the casing 2 is an outflow member 10, 11 whose outflow apertures 12, 13 respectively are turned towards the diaphragm 3. The outflow member 10 is connected via a supply line 14 to cylinder chamber 15 of a servomotor 16. The chamber 15 is connected via a line 17 to a pump (not shown) delivering high-pressure liquid at a substantially constant pressure. The central compartment 8 into which the supply line 14 discharges via outflow aperture 12 is connected via a line 18 to chamber 19 of the servomotor 16. The chamber 19 is also connected via a discharge duct 20 to the outflow member 11, which discharges via its outflow aperture 13 into the central compartment 9 which is in open communication via aperture 21 with a collecting reservoir (not shown). A pilot control system 22 delivers, in dependence on an input signal, two control pressures p,, p, which pass via lines 23, 24 to the compartments 6, 7.
Operation is as follows: in the state of equilibrium (with the servomotor piston 25 at rest), the pressures p p delivered by the pilot system 22 are identical with one another, and the diaphragm 3 occupies a position in which the liquid flow passing via supply line 12, compartment 8 and line 18 to chamber 19 is equal to the liquid flow leaving the chamber 19 via duct 20, outflow aperture 13, compartment 9 and aperture 21. The pressure p in the chamber 19 exerts on the piston 25 a leftwardly directed force which is precisely equal to the rightwardly directed force exerted on the piston by the pressure p, in the chamber 15 and the load. When the pilot system 22 receives an input signal such that the control pressure p, delivered rises, and the pressure p falls, the pressure in the compartment 7 falls-As a result, the diaphragm 3 occupies the position shown in chain lines. In this position the distance between the diaphragm and the outflow member 10 is reduced, and that between the diaphragm and the outflow member 11 is increased. Consequently, the liquid flow from the supply duct 14 to the compartment 8 and therefore to the chamber 19 is reduced, while the liquid flow from the chamber 19 via duct 20 and outflow aperture 13 is increased. As a result, the piston 25 moves to the right.
On the other hand, if the pilot system 22 receives a signal such that the control pressure p in line 24 and compartment 7 rises, and the control pressure p in line 23 and compartment 6 falls, the diaphragm 3 occupies the chain-dash line, in which the distance between the diaphragm and outflow aperture 12 is increased and the distance between the diaphragm and outflow aperture 13 is reduced. As a result, the liquid flow to the chamber 19 is increased, and the liquid flow from the chamber 19 is reduced, so that the piston 25 moves to the left.
If an external force is exerted on the piston 25, for instance, towards the right, the consequence is that the pressure 11,. in the chamber 19 rises. Since compartment 8 is in open communication with chamber 19, the pressure rises therein also. The result is that the diaphragm 3 is forced to the right. Consequently, the outflow resistance of outflow aperture 12 is reduced, while at the same time the outflow resistance of outflow aperture 13 is increased, so that even though p, increases, the liquid flows entering and leaving remain equal to one another, and the piston 25 does not move to the right. The same thing happens, but in the opposite direction, when an external leftwardly directed force is exerted on the piston 25. The control system effects very satisfactory load compensation, and the piston remains substantially unmoved by loading.
FIG. 2 shows a slightly different embodiment of the main control system illustrated in FIG. 1. In the embodiment shown in FIG. 2, the place of the bearing edges 4, 5 is taken by a number of balls 31 received in a circular cage 30 and having an O-ring gasket 32, 33 on both sides thereof. The advantage is that the diaphragm 8 cannot get jammed between its bearings, thus possibly impeding the deformation of the diaphragm. Being borne on balls ensures that when it is deformed, the diaphragm can move to a slight extent between the balls. Since the pressure in compartment 9 is always lower than the pressure in compartment 7, if necessary the O-ring 33 can be omitted from compartment 9 without any adverse effeet on sealingtightness.
FIG. 3 shows diagrammatically a servomotor with the main control system incorporated in its piston. In FIGS. 1 and 3 like elements have like references.
The servomotor 16 comprises a cylinder 27 which can move over a fixed guide 28 to which a piston rod 29 is rigidly connected. The piston rod 29 is connected to a piston 25 containing a main control system as illustrated in FIG. 1. To this end, the piston 25 has a cylindrical chamber containing a diaphragm 3 borne by circular bearing edges 4, 5, thus forming compartments 6, 7, 8, 9. The center of the end face of the piston 25 is formed with an outflow member 11 whose outflow aperture 13 points towards the diaphragm 3 and which is also in open communication with the cylinder chamber 19 containing a pressure p Disposed on the other side of the diaphragm is an outflow member whose outflow aperture 12 also points towards the diaphragm and whose other side is connected via duct 14 to cylinder chamber 15 in which there is a constant pressure p,. The chamber 15 is connected via a line 17 to a pump (not shown) delivering liquid at a substantially constant pressure. The compartment 8 is connected to the chamber 19 via a duct 18, while the compartment 9 is connected via a duct 21 to a low-pressure reservoir (not shown).
The system also comprises a pilot control system 22. The pilot control system 22 comprises a l-l-shaped yoke 40 bearing a sensor 41 cooperating with the cam 42. Disposed between the arms of the yoke are two outflow members 43, 44. The outflow member 43 has an outflow aperture 45 pointing to the left and its other side is sealed by a mobile ball 46 having a somewhat larger diameter than that of the outflow aperture. Chamber 47 in the outflow member 43 is connected via a constriction 48 to duct 49 connected to line 17 in which there is a substantially constant liquid pressure. The outflow member 44 has an outflow aperture 50 pointing to the right and its other side is sealed by a mobile ball 51 of somewhat larger diameter than the outflow aperture. Chamber 52 in the outflow member 44 is also connected via a constriction 53 to duct 49. The two outflow members 43, 44 are disposed in a structural member 55 rigidly COIII ICCIed to the cylinder 27. The yoke 40 is disposed on two resilient strips 56, 57 connected on their other sides to the cylinder 27.
Chamber 47 in the outflow member 43 is connected via a duct 23 to a compartment 6, while chamber 52 in the outflow member 44 is connected via a line 24 to compartment 7.
Operation is as follows: when the sensor 41 is moved to the right, the yoke 40 is entrained and the outflow resistance of outflow member 43 rises, while that of outflow member 44 falls. This means that the pressure P1 in chamber 47 rises, and the pressure p in chamber 52 falls. These pressures also occur in compartments 6, 7. The result is that the diaphragm 3 is so deformed that it bears more closely against the outflow aperture 12. Consequently, the liquid flow via outflow aperture 12, compartment 8 and duct 18 to chamber 19 is reduced, and the liquid flow from chamber 19 via outflow aperture 13, compartment 9 and duct 21 to the reservoir is increased. The cylinder 27 therefore moves to the right and thus follows the movement of the sensor. Together with the cylinder 7, the structural member 55 moves and so do the outflow members as well as the resilient strips 56,57. This movement continues until the equilibrium condition ,0, p is reached again. When the sensor moves to the left, the same events take place, but in the opposite direction.
If an external, for instance, rrghtwardly directed force is exerted on the chisel 60, the pressure p, in chamber 19 consequently rises. This rise in pressure also takes place in compartment 8, so that the diaphragm 3 is forced a small distance to the left. The outflow resistance of outflow aperture 12 is therefore reduced, while at the same time the outflow resistance of outflow aperture 13 is increased. As a result, even though p increases, the liquid flows entering and leaving remain equal to one another, so that the piston 25 is not displaced as a result of the external loading.
The foregoing clearly shows that the invention provides a very compactly constructed servomotor main control system in which external loadings are fully compensated.
What we claim is:
l. A main control system for a hydraulic servomotor, com prising;
a casing having a cylindrical inner wall and spaced sidewalls defining a cylindrical chamber;
a circular diaphragm of slightly smaller diameter than said chamber and disposed between and spaced with respect to said sidewalls;
a pair of retainer means, each disposed between a respective one of said sidewalls and a corresponding side of said diaphragm and each sealingly engaging its corresponding side of the diaphragm along a circular path inwardly offset from said inner wall to separate said chamber into a pair of annular compartments on opposite sides of the outer marginal area of said diaphragm and a pair of central compartments on opposite sides of the central area of said diaphragm;
a pair of fluid discharge nozzles, each discharging into a respective central compartment toward and in spaced relation to the corresponding side of said diaphragm;
means for conveying fluid from each of said central compartment; and
means for subjecting said annular compartments to different pressures to deflect said marginal area of the diaphragm and dish the central area thereof so that the spacing between said diaphragm and one nozzle is decreased while the spacing between the diaphragm and the other nozzle is increased, and vice versa, whereby differentially to modify the fluid flow through said nozzles.
2. The system as defined in claim 1 including a servomotor cylinder having a movable piston therein;
means for connecting said cylinder on one side of said piston to a source of pressurized fluid and to one of said nozzles; and
means for connecting that central compartment associated with said one nozzle to said cylinder on the other side of said piston and to the other central compartment whereby to slave said piston to pressure differences in said annular compartments.
3. The system as defined in claim 2 wherein each said retainer means comprises a circular wall having a knife edge bearing against a corresponding side of said diaphragm.
4. The system as defined in claim 2 wherein each said retainer means comprises a circular row of balls interposed between a corresponding side wall of the casing and a corresponding side of said diaphragm, and at least one O-ring concentric with and adjacent said row of balls.
5. The system as defined in claim 1 wherein each said retainer means comprises a circular wall having a knife edge bearing against a corresponding side of said diaphragm.
6. The system as defined in claim 1 wherein each said retainer means comprises a circular row of balls interposed between a corresponding side wall of the casing and a corresponding side of said diaphragm, and at least one O-ring concentric with and adjacent said row of balls.