US3766832A - Hydraulic control system - Google Patents

Hydraulic control system Download PDF

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US3766832A
US3766832A US00234094A US3766832DA US3766832A US 3766832 A US3766832 A US 3766832A US 00234094 A US00234094 A US 00234094A US 3766832D A US3766832D A US 3766832DA US 3766832 A US3766832 A US 3766832A
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sections
valve
pressure
land
control system
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P Hayner
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Lockheed Corp
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Sanders Associates Inc
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00—Details of servomotor systems ; Valves for servomotor systems
    • F15B13/02—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors
    • F15B13/04—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor
    • F15B13/042—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor operated by fluid pressure
    • F15B13/043—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor operated by fluid pressure with electrically-controlled pilot valves
    • F15B13/0438—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor operated by fluid pressure with electrically-controlled pilot valves the pilot valves being of the nozzle-flapper type
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
    • B22D17/20—Accessories: Details
    • B22D17/32—Controlling equipment

Definitions

  • This invention relates generally to hydraulic control systems and particularly to such systems which are capable of controlling selectively either the rate of flow or the pressure of fluid furnished to a useful load.
  • a typical program requires that the acceleration and velocity of the ram be controlled closely regardless of the pressure exerted until a predetermined pressure is reached, after which the pressure is controlled closely regardless of velocity.
  • Various kinds of equipment have been used in the past to execute such programs but difficulty has been experienced in executing the change in mode of control from velocity control to pressure control. This is because, when the charge has substantially filled the die, the pressure rises very rapidly, making it difficult to change modes at the proper pressure and quickly enough to prevent excessive rise in pressure and/or excessive loading of the equipment. This difficulty has been experienced whether the change over has been done manually or automatically.
  • Automatic changeover in response to a predetermined pressure may present an additional problem because, during normal velocity control, the pressure may vary erratically, exhibiting transient peaks" which, although of very short duration, may be of sufficient magnitude to actuate the changeover apparatus prematurely.
  • a valve incorporating the present invention that land which meters the flow to the high pressure side of the load is made in two sections, moveable with respect to each other, with their junction at the associated groove. Suitable means are provided for injecting fluid under pressure to the junction between sections, thereby separating the sections and closing the passageway quickly.
  • FIG. 1 there is shown in block form the die casting machinery 21 which is to be controlled by the equipment of the present invention. More particularly, it is to be controlled by a hydraulic ram 22 having a piston 23 which is mechanically connected to the machinery 11 as indicated by the dotted line. The piston. 23 is also mechanically connected to operate a switch bank 24 which comprises several switches operated as the piston 23 reaches various predetermined positions. .
  • the ram 22 is actuated by a flow control valve 25 and also by a pressure control valve 26.
  • the valve 25 is a single stage spool valve, as will be more fully explained, and is controlled by a pilot valve 29 which is preferably a two stage valve as will be more fully explained.
  • This valve in turn is controlled by a force motor 31 to which is applied an electric signal, preferably a current, obtained from a velocity signal source 32.
  • i i i The signal source 32 maybe a conventional arrangement of electronic components such as power supplies, variable resistors and the like capable of generating a wide variety of patterns of output signals and of repeating them at will.
  • the output may rise at a predetermined rate to a predetermined value where it may be held for a predetermined time oruntil an externally applied signal dictates a change, such as a further increase at a different rate to a second predetermined value.
  • signalsources are of conventional construction and the details thereof do not form any part of the present invention.
  • One suitable signal source is available commercially from Sanders Associates, Inc., Nashua, N.H. and is designated a Model SC Controller.
  • the pressure control valve 26 is preferably a two stage valve, as will be more fully explained, and it is controlled by a force motor 33 which receives signals from a pressure signal source 34 which may be identical to the source 32.
  • the ram 22 is controlled by the valve 25 while the valve 26 is shut off.
  • the valve 25 causes fluid to flow into the conduit 27 at a rate determined by the signal from the source 32.
  • the velocity of the piston 23 is, of course, directly proportional to the rate of flow of fluid through the conduit 27 into the head end of the ram 22.
  • a transfer valve 35 shuts off the valve 25 and activates the valve 26 which controls the pressure in conduit 27 in accordance with the signal from the source 34.
  • An arming valve 36 prevents premature operation of the transfer valve 35.
  • a program timer 37 generates signals a predetermined time after the operation of the transfer valve 35.
  • FIG. 2 there is shown a graph indicating the variation in velocity of the piston 22 and the pressure in the conduit 27 during one cycle of the operation of the die casting machinery 21.
  • Velocity variations are indicated by solid lines while pressure variations are indicated by dashed lines. Both curves are idealized to simplify explanation and it will be understood that actually the various corners of the curves would be rounded.
  • the ordinates represent velocity and pressure in percent of maximum while the abscissa represents time although not to any particular scale.
  • the velocity and pressure curves shown are typical of programs which have been found to produce satisfactory castings.
  • step one indicates the beginning of the operation at which time a start signal is applied to the velocity signal source 32.
  • This source then applies to the force motor 31 a current which rises substantially uniformly at a predetermined rate as indicated by the portion 41 of the graph until it reaches a predetermined value after which it remains constant as indicated by the curve 42.
  • a correlation between elapsed time and the distance traveled by the piston 23 and step two is initiated when the piston 23 has traveled sufficiently to close one of the switches in the switch bank 24.
  • the resultant signal is passed to the source 32 which changes its connections so as to generate an output signal which rises at a steeper rate, as indicated by the curve 43, until it reaches its maximum value where it remains steady as indicated by the curve 44.
  • the curves 41 to 44 represent velocity of the piston 23 which, as previously explained, is determined by the rate of flow of fluid from the valve 25 into the ram 22. During this time the pressure control valve 26 is closed and has no effect.
  • the arming valve 36 is provided which inhibits operation of the transfer valve during the early stages of operation. For any particular casting, it is known approximately where in the travel of the piston 23, the pressure will tend to rise and one of the switches in the switch bank 24 is adjusted to be actuated a short distance before this point is reached as indicated by step 3 in FIG. 2. Such a switch actuation operates the arming valve 36 which enables operation of the transfer valve 35 so that changeover will occur the next time the pressure rises to the level of the dotted line 45.
  • Step 4 occurs the first time the pressure reaches the level of the dotted line 45 subsequent to enabling of the valve 35. At this time, the flow control valve 25 is suddenly shutoff in a manner to be fully explained. Also, signals are sent to the velocity signal source 32 and the pressure signal source 34 so as to terminate control by the valve 25 and initiate the control by the valve 26.
  • the source 34 generates a signal specifying the desired pressure and the valve 26 responds by controlling the pressure in the conduit 27 accordingly.
  • the pressure falls to zero as indicated by the curve 49.
  • the timer 37 sends a signal to the velocity source 32 which generates a signal directing the piston 23 to again move forward, although at a slow rate, thereby ejecting the biscuit," or completed casting.
  • Step 6 shows the initiation of this operation which is concluded at step 7 by the actuation of a switch within the switch bank 24.
  • the program timer 37 generates another signal which is passed to the velocity signal source 32 directing the piston to retract as shown by step 8.
  • the timer 37 sends another signal to the source 32 calling for zero velocity, as indicated by step 9 thus conpleting one cycle of operation.
  • the valve 25 comprises a valve body 51 formed to define a hollow cylinder 52 in which is inserted a spool or piston indicated generally by the reference character 53.
  • the overall length of the spool 53 is less than that of the cylinder thereby leaving end spaces 54 and 55.
  • the end space 54 contains a weak compression spring 56 which urges the spool 53 to the right.
  • the end space 54 is connected by means of a conduit 57 to a source of fluid under pressure indicated schematically by the letter P, and which may have, for example, a pressure of 2,300 psi. (pounds per square inch).
  • the end space 55 is connected by means of a conduit 58 to the pilot valve 29. A control pressure generated within the valve 29 is transmitted over the conduit 58 so as to position the spool 53.
  • the spool 53 includes a land 60 adjacent to the end space 54 and also includes a land denoted generally by the reference character 59 but which is comprised of two discrete sections 59a and 59b.
  • the junction of these sections is generally perpendicular to the axis of the spool and one of the sections, in this case the section 59b, is relieved on that side, or face, adjacent to section 59a so as to define a small chamber 61 between these sections.
  • This chamber occupies only a central portion of the land and does not extend as far as the outer circumference thereof.
  • the land section 59a, the land 60 and the portion of the spool 53 joining them are formed to define a small passageway 62 which communicates at one end with the chamber 61 and at the other end with a groove 63 formed in the outer circumference of the land 60.
  • the valve body 51 is formed to define a passageway 64 communicating with the groove 63 at one end and connected to an external conduit 65 on the other, which conduit in turn is connected to the transfer valve 35 for a purpose which will be explained subsequently.
  • the spool 53 also includes a land denoted generally by the reference character 66 but which is comprised of two discrete sections 66a and 66b.
  • the former is rigidly and permanently connected to the land but has been shown separately because, during manufacture, it is preferred to make the sections separately and then to join them together.
  • the portions of the faces of the sections 66a and 66b facing each other are relieved to define a chamber containing a compression spring 67 which urges these sections apart. In the position of the parts illustrated in FIG. 3, the sections 66a and 66b are separated by a small distance while the sections 59a and 59b are in engagement with each other.
  • the spool 53 also includes a land 68 adjacent to the end space 55. This land is integral with the land section 66b.
  • the land 68, the land sections 66b, 66a and 59b, and those portions of the spool 53 which interconnect certain of these land sections are formed to define an axial bore 69.
  • the portion of this bore at the right end of the spool that is, extending from the end space 55 to a point between the land 68 and the land section 66b, is of a relatively small diameter and beginning at that point is of increased diameter for the remainder of its length.
  • a shoulder portion 71 is defined by the transition in diameters.
  • a rod 72 makes a sliding fit within the enlarged portion of the bore and in the position of the parts as shown in FIG.
  • the left end of this rod abuts the right face of the land section 59a while the right end of this rod abuts the shoulder portion 71.
  • the integral land sections 5% and 66a are slideable on the rod 72 as are the land sections 6612 and 68. 0 rings 73 and 74 are provided to prevent fluid leakage.
  • the right end of the rod 72 from a point approximately at the right face of the land section 59b and extending to the shoulder portion 61 is hollow and in communication through the bore 69, with the end space 55.
  • the portion of the spool 53 adjacent to the right end of the right hand section 59b is formed to define a small upstanding portion 75, which, after assembly of the apparatus, amounts to a boss on the right face of the land section 5912.
  • This portion 75 is formed to define a small rectangular radially extending slot 76 one wall of which is the right hand face of the land section 59b.
  • This slot extends from the outer circumference of the land 59b inward to an annular groove 77 formed in the central portion of the spool 53.
  • the rod 72 is formed with several apertures 78 in the outer wall which provide communication between the groove-77 and the interior of the rod 72 and the bore 69. There is thus complete communication from the end space to the slot 76.
  • This arrangement is similar to that described in U.S. Pat. No. 3,561,488 granted Feb. 9, 1971 to James Otto Byers and entitled Fluid Flow Control Valve.
  • the interior of the hollow cylinder 52 between the land and the land 59a is connected to the return, or reservoir, indicated schematically by the letter R.
  • the interior of the cylinder 52 in the region between land 68 and land section 66b is also connected to return.
  • the portion of the cylinder between land sections 59b and 66a is connected to the aforementioned source P of fluid under pressure.
  • the valve body 51 is formed with an annular groove 841 on its interior surface located so as to embrace the junction between the land sections 59a and 59b and of a width slightly less than the combined widths of the land sections 59a and 59b so that, in the neutral position of the valve shown, the groove 81 and the conduit27 connected thereto are completely blocked.
  • the valve body 51 is also formed with another annular groove 82 which embraces the junction between the land section 66a and 66b and is of such a width so that, in the neutral position shown in the drawing, the groove 82 and the conduit 28 connected thereto are completely blocked.
  • valve 25 is quite similar to the valves described in the aforementioned patent.
  • the land 68 When a control pressure is applied to the conduit 58, the land 68 will be displaced to the left and, through the rod 72, will similarly displace land 59a and the land 60.
  • the spring 67 will cause the land section 59b to remain in engagement with the section 59a.
  • the land 59b will be displaced until the flow of fluid from the conduit 58 through the bore 69 and the slot 76 is sufficient to reduce the pressure in the end space 55 to that in the end space 54, namely, the pressure of the source P.
  • Fluid also flows from the source P to the groove 81 and the conduit 27 and the total flow will be exactly proportional to the flow occurring in the conduit 58. All this in accordance with the previously mentioned patent. If the pressure in conduit 58 is reduced below that of the source P, then the entire valve spoolwill be displaced to the right and conduit 57 will be connected to return while conduit 28 will be connected to the pressure source.
  • This valve comprises a force motor 31, a flappervalve stage 85 and to the right thereof a spool valve second stage.
  • the valve 29 is similar to the valve described in U.S. Pat. No. 2,896,588 granted July 28, 1959 to Paul F. I-Iayner and Zenny Olsen, and entitled Electro-I-Iydraulic Servo Valve.
  • the force motor section and the flapper valve section are substantially identical and the only substantial difference is in the spool.
  • the spool includes lands 86, 87, 88 and 89.
  • a source of fluid under pres sure, P which may, for example, be at a pressure of 2,800 psi, is connected to a groove which, in the neutral position of the valveshown, is completely occluded by the land 87.
  • the return is connected to a similar groove which is completely occluded by the land 88.
  • the space between the lands 87 and 88 is connected to the conduit 58 which, it wil be recalled, conducts the control pressure to the main flow control valve 25.
  • the flapper valve supply is designated Pp and may, for example, be at a pressure of 2,000-psi. It will be recalled I that the source P for the main flow control valve may,
  • the lands 86 and 89 are formed with small circumferential grooves and the body of the valve 29 is formed with annular grooves adjacent thereto which are connected to a sump designated R (return and drain) which may be completely opened to the atmosphere.
  • R return and drain
  • the reason for this is to minimize the leakage of fluid from the source P to the pilot source P
  • the valve 29 operates in substantially the same way as described in the aforementioned US. Pat. No. 2,896,588. It is sufficient for present purposes to note that a signal from the source 32 applied to the force motor 31 operates, through the flapper valve 85 and conduits to the end spaces, to displace the second stage spool by an amount substantially proportional to the magnitude of the signal.
  • the pressure control valve 26 is shown in more detail.
  • the previously mentioned source of pilot pressure, P is led by means of a conduit 87 through two restrictors 88 and 89 to two nozzles 91 and 92 which act on opposite sides of aflapper 93.
  • the differential pressure thus generated is applied to opposite ends of a valve piston or spool 94 which includes two lands 95 and 96.
  • the previously mentioned source of fluid under pressure, P is connected to a groove 97 and, in the position of the spool 94 shown in the drawing, the land 95 has partially opened a passageway between the groove 97 and the space between the lands 95 and 96.
  • a groove 98 is connected to the return, and, in the position of the parts shown in FIG.
  • the land 96 has partially opened a passageway between the groove 98 and the space between the lands 95 and 96. This space between the lands is connected through a groove 99 to the load conduit 27. With the position of the parts shown in FIG. 5, fluid will flow from the source P through the interior of the valve to the return R, and the load conduit 27 will be subjected to a pressure intermediate that of the source P and thereturn R.
  • the load conduit 27 is also connected to an internal passageway 101 where the pressure of this conduit acts on a small piston 102 which bears against the flapper 93.
  • the force motor 33 also acts on the flapper 93.
  • the piston 102 will displace the flapper ina direction shown in FIG. as upwards, thereby substantially increasing the pressure on the upper end of the land 95 and pushing the entire spool downward thereby completely occluding the groove 97 leading to the source and also the groove 99 leading to the load conduit 27. This has the effect of simply shutting off the load conduit 27 so that the valve 26 has no effect.
  • the transfer valve 35 includes a valve body 105 formed to define a hollow cylinder 106 which includes two annular grooves, 107 and 108. Within the cylinder 106 is a valve spool 109 which includes an upper land 111 and a lower land 112. The upper end of the cylinder 106 opens into a chamber 113 which is connected by means of a conduit 114 to the load conduit 27 so that the pressure in this conduit bears on the upper surface of the land 111.
  • a switch 115 which is actuated to one position when the land 111 is in the position shown in the drawing and which is actuated to another position when the land 111 is displaced downward from the position shown.
  • the lower end of the cylinder 106 opens into a chamber 116 which is connected by means of a conduit 117 to the arming valve 36.
  • a compression spring 118 which acts between an upper spring seat 119 and a lower spring seat 121.
  • the upper spring seat 119 bears against the lower end of the spool 109 while the lower spring seat 121 bears against a set screw 122 by means of which the pressure exerted by the spring can be adjusted.
  • the groove 107 is connected to a conduit 123 which in turn is permanently connected, through a portion of the arming valve 36, to another conduit 124 which in turn is connected to the return R.
  • the lower groove 108 is connected by means of a conduit 125 to the source of pressure P
  • the portion of the cylinder 106 between the grooves 107 and 108 is connected to the conduit 65, which, it will be recalled, is connected to a portion of the flow control valve 25 for a purpose which will be fully explained.
  • the anning valve 36 is essentially a normal closed valve which is opened by the energization of a solenoid. More particularly, the arming valve 36 includes a valve body 131 formed to define a hollow cylinder 132.
  • the upper end of the cylinder 132 opens into a chamber 133 which communicates with the conduit 123 and also with the conduit 124 which, it will be recalled, is connected to the return.
  • the cylinder 132 is formed with a groove 134 which communicates by means of a passageway 135 with the chamber 133.
  • a spool 136 having an upper land 137 and a lower land 138.
  • a compression spring 141 which, on the top, bears against the valve body and which on the bottom bears against the spring seat 142 which in turn bears against the upper end of the land 137 so as to urge the spool 136 downward.
  • the cylinder 132 in the region between the lands 137 and 138 is connected to the conduit 117.
  • the spring M1 urges the spool 136 downward to the position shown and in this position the land 137 completely occludes the groove 134.
  • the conduit 117 is, in effect, blocked off.
  • the solenoid 145 when the solenoid 145 is energized, it attracts the armature 144 thereby raising the spool 136 and opening a passageway from the interior of the cylinder to the groove 13d and the conduit 135 thereby effectively connecting the conduit 117 to the return. It will be recalled that during the first stages of each cycle of operation, it is desired that the velocity of the piston 23 of FIG. 1 be controlled in accordance with the program illustrated in FIG. 2.
  • the flow control valve 25 is operative to dispense fluid to the ram 22 at such a rate that the desired velocity profile is followed.
  • the spool 53 of the valve 25 is displaced to the left of the position shown in this Figure so that the pressure source P is partially connected to the conduit 27 and the return R is partially connected to the conduit 23.
  • the chamber 61 is connected by means of the conduits 62, 641 and 65 to the transfer valve 35 (FIG. 6).
  • the valve 35 is in the position shown in FIG. 6 so that the conduit 65 is connected to the return. Therefore, the chamber 61 (FIG. 3) is at return pressure and the spring 67 holds the land section 59b in engagement with the section 59a, unopposed by any fluid pressure differential.
  • the conduit 65 is in communica-, tion with the chamber 61 and accordingly, when this conduit is connected to the sourceP the land section 59b is displaced to the right.
  • the only opposition to this displacement is the spring 67 (which is very weak indeed compared to the fluid pressures used) and the pressure in the conduit 28 which, at this time, is connected to the return R. Therefore the section 59b is displaced slightly to the right by this pressure.
  • the pressure source P is only a pilot pressure source and has very little flow capability, but as soon as the land 5912 separates from the land 59a the pressure of the conduit 27 and the flow capability of the pressure source P enter the chamber 61 and quickly displace the land section 59b to the right a distance sufficient to cause the land section 66a to engage the land section 66b. This distance is sufficient to completely close the groove 81 thereby shutting off the load conduit completely and preventing further flow to the ram. 22 from this source. The result is that the velocity of the piston 23 falls rapidly as shown in FIG. 2. At the same time, the switch 115 (FIG. 6) is actuated by the downward movement of the spool 109 and such actuation has three effects.
  • a signal is sent to the velocity signal source 32 (FIG. 1) directing it to remove the input signal from the force motor signal 31. This has the effect of returning the valve 29 (FIG. 4) to the neutral position shown with the conduit 58 effectively blocked. Such blocking creates a fluid lock which holds the spool 53 of the valve 25 (FIG. 3) in its then attained position with the groove 81 and the conduit 27 blocked.
  • actuation of the switch 115 sends a signal to the pressure signal source 34 directing it to generate a signal to be applied to the force motor 33 (FIGS. 1 and 5) indicative of the desired pressure profile as shown by FIG. 2. It will be recalled that, before the application of the signal through the force motor 33, the flapper 93 (FIG.
  • the pressure control valve 26 continues to operate and causes the pressure in the conduit 27 (which, it will 7 be recalled is connected to the head end of the ram 22) to follow the dashed curves 47 and 48 of the FIG. 2.
  • the program timer 37 (FIG. 1) sends a signal to the pressure signal source 34 which in turn removes the signal entirely from the force motor 33 (FIG. 5).
  • the piston 102 rises pushing the flapper 93 upward thereby creating differential pressures which push the spool 94 downward.
  • the land first blocks off the groove 97 while the land 96 further opens the groove 98 thereby removing the pressure source P from the conduit 27 and connecting the con duit 27 solely to the return R.
  • Step 5 is completed by the generation of an additional Signal from the program timer 37 which is sent to the arming valve 36 (FIG. 6) to deenergize the solenoid 144.
  • This additional signal is delayed with respect to the previously mentioned step 5 signal (which was sent to the pressure signal source 34) sufficiently to allow time for the spool 109 of the valve 35 to be raised by the spring to the position illustrated in the drawing, as previously explained. Accordingly, the transfer valve 35 is now in its initial condition and its operation is again inhibited by the arming valve 36.
  • the program timer 37 sends a signal to the velocity signal source 32 which operates the valve in the usual manner to displace the spool 53 to the left and allow fluid from source P to flow through the conduit 27 at a slow rate. This ejects the die and when the ram has advanced sufficiently it actuates another switch at step 7 to cut off the signal from the source 32 and stop the ram.
  • the program timer 37 sends another signal to the velocity signal source 32 this time directing it to reverse the direction of the ram.
  • This signal is passed to the force motor 31 and the pilot valve 29 whichoperates in the opposite sense to connect the conduit 58 to the return line.
  • Such retraction is unopposed and does not take very long and a short time later another signal from the program timer 37 is sent to the signal source 32 which operates through the force motor 31 and the pilot valve 29 to return the flow control valve 25 to the neutral position ready for another cycle of operation.
  • a hydraulic control system comprising a valve including a valve body formed to define a hollow cylinder and including an enlarged diameter generally annular internal groove, a valve spool including a generally cylindrical land moveable in said cylinder,
  • said means for controlling the position of said spool and land so as to selectively close and variably open a passageway between the interior of said cylinder and said groove, 21 source of fluid under pressure, a load, and a hydraulic path including said passageway interconnecting said source and said load characterized in that said land comprises first and second discrete sections with their adjacent faces embraced by said groove and in that said system includes means for applying fluid pressure to the space between said sections.
  • a hydraulic control system in accordance with claim 1 which includes resilient means urging said second section into engagement with said first section.
  • a hydraulic control system including a spool having a land, and moveable within a hollow cylinder formed with an interior annular groove to open and close a passageway including said groove between a load and a source of fluid under pressure characterized in that said land is formed in two discrete sections moveable axially with respect to each other and positioned with their adjacent faces embraced by said groove and in that said system includes means for injecting fluid under pressure into the space between said sections.
  • a hydraulic control system including a spool having a land and moveable within a hollow cylinder formed with an interior annular groove to open and close apassageway including said groove between a load and a source of fluid under pressure characterized in that said land is formed in two discrete sections moveable axially with respect to each other and positioned with their adjacent faces embraced by said groove and in that said valve is formed to define a hydraulic path communicating with the junction of said sections and with the exterior of said valve.
  • a hydraulic control system in accordance with claim 7 in which said hydraulic path includes a passageway formed in one of said sections.
  • a hydraulic control system comprising a valve including a valve body formed to define a hollow cylinder and including first and second enlarged diameter generally annular grooves, a valve spool including first and second generally cylindrical lands moveable in said cylinder, means for controlling the position of said spool and said lands so as to variably open first and second passageways between a first interior portion of said cylinder and said first groove and between a second interior portion of said cylinder and said second groove, a source of fluid under pressure, a load including first and second fluid connections, a reservoir, a first hydraulic path including said first passageway interconnecting said source and said first fluid connection, and a second hydraulic path including said second passageway interconnecting said reservoir and said second fluid connection; characterized in that said first and second lands comprise first and second discrete sections and third and fourth discrete sections respec tively, positioned with their adjacent faces embraced by said first and second grooves, respectively, and with said first and fourth sections remote from each other, means for joining said second and third sections so as to move as a
  • a hydraulic control system in accordance with claim 9 in which said second and third sections are mounted to be moveable axially with respect to said .first and fourth sections.
  • a hydraulic control system in accordance with claim 10 in which said sections are mounted to be relatively moveable from a first position at which said first and second sections are in engagement while said third while said third and fourth sections are in engagement.
  • a hydraulic control system in accordance with claim 10 including resilient means for urging said third and fourth sections apart and said first and second sections together.
  • a hydraulic control system in accordance with claim 14 which includes means for normally inhibiting operation of said means responsive and which is responsive to movement of said load beyond a predetermined position for enabling operation of said means responsive.
  • a hydraulic control system comprising, a first valve for controlling the flow of fluid to a load in accorand fourth sections are separated to a second position at which said first and second section are separated dance with a signal indicative of a desired velocity of movement of said load, a second. valve for controlling the flow of fluid to said load in accordance with a signal indicative of a desired fiuid pressure to be exerted against said load, and means responsive to the attainment of a predetermined pressure at said load for transferring control of fluid flow from said first valve to said second valve, characterized in that said system includes means for normally inhibiting operation of said means responsive and which is responsive to the movement of said load beyond a predetermined position for enabling operation of said means responsive.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • General Engineering & Computer Science (AREA)
  • Fluid-Pressure Circuits (AREA)
  • Servomotors (AREA)
  • Injection Moulding Of Plastics Or The Like (AREA)
US00234094A 1972-03-13 1972-03-13 Hydraulic control system Expired - Lifetime US3766832A (en)

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US (1) US3766832A (ja)
JP (1) JPS5232032B2 (ja)
AU (1) AU458389B2 (ja)
CA (1) CA984264A (ja)
CH (1) CH557475A (ja)
DE (1) DE2308628A1 (ja)
FR (1) FR2175742B1 (ja)
GB (1) GB1410422A (ja)
SE (1) SE396799B (ja)

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JPS5473390U (ja) * 1977-11-02 1979-05-24
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JPS591122Y2 (ja) * 1978-02-27 1984-01-13 三菱電機株式会社 高周波加熱装置
JPS53146598U (ja) * 1978-05-10 1978-11-18
JPS54176474U (ja) * 1978-06-01 1979-12-13
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JPS5820806Y2 (ja) * 1978-06-02 1983-05-02 三菱電機株式会社 高周波加熱装置
JPS5515505U (ja) * 1978-07-14 1980-01-31
JPS5912483Y2 (ja) * 1978-08-04 1984-04-16 三菱電機株式会社 高周波加熱装置
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JPS56148502U (ja) * 1981-03-26 1981-11-09
JPS5777829A (en) * 1981-09-08 1982-05-15 Matsushita Electric Ind Co Ltd Steam oven
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US1109022A (en) * 1913-12-15 1914-09-01 Elmer D Spicer Governor for engines, motors, or the like.
US1777293A (en) * 1926-12-20 1930-10-07 Benjamin J Curtis Liquid-measuring device
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Also Published As

Publication number Publication date
DE2308628A1 (de) 1973-09-27
GB1410422A (en) 1975-10-15
CH557475A (it) 1974-12-31
FR2175742B1 (ja) 1977-07-29
JPS5232032B2 (ja) 1977-08-18
AU4050072A (en) 1973-10-04
CA984264A (en) 1976-02-24
JPS49675A (ja) 1974-01-07
AU458389B2 (en) 1975-02-10
FR2175742A1 (ja) 1973-10-26
SE396799B (sv) 1977-10-03
SE7303504L (ja) 1973-09-14

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