Pressure oil supply/discharge circuit and valve device for use in said circuit

Abstract: A check valve (14) with a forcibly valve opening function and a bypass passage (16) are disposed in parallel in a pressure oil supply/discharge passage (3) connected in communication to A hydraulic actuation chamber (2). A residual pressure holding valve (17) and a flow resistance application means (21) are disposed in series in the bypass passage (16). The supply/discharge passage (3) and a discharge passage (7) are connected in communication by a pressure compensation valve (12). While the aforementioned valve (17) is adapted to be pushed to its valve closing side by means of a pressure of a check valve inlet (14a) and a residual pressure holding spring (19), it is adapted to be pushed its valve opening side by means of a pressure of a check valve outlet (14b). Incidentally, the valve (17) comprises a valve member (38) resiliently urged to a valve seat (40) by means of the spring (19).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure oil supply/discharge circuit with a residual pressure holding function and a residual pressure holding valve device for use in the pressure oil supply/discharge circuit, which are adapted to leave a predetermined pressure remaining within a hydraulic actuation chamber even in case that a breakage of a hydraulic hose and the life cause an oil leak in a pressure oil supply/discharge passage connected to the hydraulic actuation chamber of a hydraulic cylinder. 2. Description of the Prior Art Such pressure oil supply/discharge circuits with a residual pressure holding function have been conventionally known (e.g. the ones disclosed in Japanese Patent Laid Open Publication No. 1979 - 108156 and EP-A-0 019 597). As shown in a circuit diagram of Fig. 12, the Japanese publication discloses a hydraulic cylinder applied to a clamping device. That is, a clamping hydraulic actuation chamber 403 is disposed in one side of a piston 402 of a double-acting type hydraulic cylinder 401, a check valve 405 with a forcibly valve-opening function is disposed in a clamping pressure oil supply/discharge passage 404 connected to the hydraulic actuation chamber 403, and an unclamping pressure oil supply/discharge passage 407 is connected to an unclamping actuation chamber 406 disposed in the other side of the piston 402. At the time of clamping, a pressure oil is discharged from the unclamping hydraulic actuation chamber 406 as well as the pressure oil is supplied to the clamping hydraulic actuation chamber 403, so that the hydraulic cylinder 401 is operatively contracted to press and fix a fixed object 410 by means of a clamping member 409. Under this clamping condition, when a pressure on the inlet side of the check valve 405 abnormally lowers due to a breakage of a hydraulic hose and the like, the check valve 405 serves to prevent a counter flow so as to leave a pressure remaining within the clamping hydraulic actuation chamber 403 and thus to prevent a shift and/or a fall of the fixed object 410. Incidentally, a very little leakage of a pressure from the check valve 405 is adapted to be supplemented by means of an accumulator 411. On one hand, at the time of unclamping, when the pressure oil is supplied from the unclamping pressure oil supply/discharge passage 407 to the unclamping hydraulic actuation chamber 406, the check valve 405 is opened by means of a hydraulic pressure of a pilot oil passage 413, so that a pressure oil is allowed to be discharged from the clamping hydraulic actuation chamber 403 and the hydraulic cylinder 401 is operatively extended. The above-mentioned prior art has such an advantage that the clamping condition can be held by means of a checking function of the check valve 405 even though a pressure oil leakage is caused on the inlet side of the check valve 405, but there is the following problem associated therewith. For example, like in a hydraulic clamping device for a metal mould of an injection moulding machine, when the hydraulic cylinder is subjected to a raised temperature under the clamping condition, a pressure within the clamping hydraulic actuation chamber 403 gradually increases due to a cubical expansion of the pressure oil. Thereby, a clamping force of the hydraulic cylinder 401 excessively increases and resultantly it is apprehended that the fixed object 410 might be damaged. SUMMARY OF THE INVENTION It is an object of the present invention to make a leaving of a pressure remaining within a hydraulic actuation chamber by means of a check valve compatible with a prevention of an excessive pressure increase within the hydraulic actuation chamber. For accomplishing the above object, according to the present invention, a pressure oil supply/discharge circuit with the features of claim 1 is provided. As shown Figs. 2 through 4, a bypass passage 16 is connected to a pressure oil supply/discharge passage 3 in parallel with a check valve 14. A relief type residual pressure holding valve 17 and a flow resistance application means 21 are disposed in series in the bypass passage 16. A valve opening operation of the residual pressure holding valve 17 is adapted to be carried out by a differential force between a received pressure of a check valve outlet 14b and a resultant force of a received pressure of a check valve inlet 14a and a resilient force of a residual pressure holding spring 19. A pressure compensation valve 12 is disposed along the pressure oil supply/discharge passage 3 and the pressure oil discharge passage 7 in parallel with the pressure oil supply/discharge changeover means 4. The pressure compensation valve 12 is adapted to discharge only a very slow increased portion of the hydraulic pressure within the hydraulic actuation chamber 2. This circuit operates as follows. Under a normal pressure condition in which a pressure of the check valve inlet 14a is within a first pressure range R₁, when the pressures of the hydraulic actuation chamber 2 and of the check valve outlet 14b increase very slowly due to the cubical expansion of the pressure oil caused by the heat reception of the hydraulic cylinder 1, the residual pressure holding valve 17 is opened by that hydraulic pressure so that the aforementioned increased portion of the hydraulic pressure can be released to the pressure oil discharge passage 7 through the valve 17, the pressure oil supply/discharge passage 3 and the pressure compensation valve 12 in order. As a result, the pressure of the hydraulic actuation chamber 2 can be prevented from being excessively increased. Further, under the normal pressure condition in which the pressure of the check valve inlet 14a is within the first pressure range R₁, also when the pressure on the side of the check valve inlet 14a abnormally lowers due to an abrupt oil leakage caused by a breakage of a hydraulic hose 10 and a little oil leakage from pipings, similarly to the aforementioned case, since the received pressure from the check valve outlet 14b overcomes a resultant force of the received pressure from the check valve inlet 14a and the spring force of the residual pressure holding spring 19 to open the residual pressure holding valve 17, the pressure oil within the hydraulic actuation chamber 2 can be discharged slowly to the pressure port P through the valve 17 and the flow resistance application means 21. But, when the pressure on the side of the check valve outlet 14b has lowered to the second pressure range R₂, the spring 19 serves to close the valve 17 so as to prevent a further lowering of the pressure and to hold the pressure of the chamber 2 within the second pressure range R₂. Therefore, according to the invention, it is possible to make a leaving of a pressure remaining within the hydraulic actuation chamber at the time of abnormal lowering of the check valve inlet side pressure compatible with a prevention of an excessive pressure increase within the hydraulic actuation chamber. Incidentally, in the aforementioned construction, in the case that the resilient force of said residual pressure holding spring is set at a smaller value than the fluid force which the valve member of said residual pressure holding valve receives from the check valve outlet when the pressure of said check valve outlet ( the pressure of the working port ) has reached a working set pressure H, since the pressure of the hydraulic actuation chamber of the hydraulic cylinder can be provided with at least two kinds of pressure ranges such as the first pressure range R₁ and the second pressure range R₂, the following advantages can be provided. That is, in the case that the hydraulic cylinder is used as a hydraulic clamp for a metal mould of an injection moulding machine and as a hydraulic clamp for a metal mould of a press machine, since it can be changed over to a high pressure clamping condition after completion of a fitting of moulds under its low pressure clamping condition, the mould fitting becomes easy. Further, in the case that the hydraulic cylinder is used as a hydraulic clamp for a work of a cutting machine, since it becomes possible to finish the work under the low pressure clamping condition after completion of a powerful rough machining under the high pressure clamping condition, a machining time can be shortened as well as a machining accuracy can be improved. Further, by making the resilient force of the residual pressure holding spring as small as possible, a difference between an upper limit and a lower limit of the first pressure range R₁ becomes small and a variable range of the pressure of the working port A can be small. Advantageously, as shown in Figs. 1 and 7, said bypass passage 16 is disposed in such a portion as extending from the pressure port P to said working port A, in parallel with the check valve seat 28 and the check valve chamber 29 within a valve casing 27. Said residual pressure holding valve 17 and said flow resistance application means 21 having a throttling passage 44 are disposed in series in the bypass passage 16. The valve 17 is of the relief type and comprises a residual pressure holding valve member 38 resiliently urged for valve closing to a residual pressure holding valve seat 40 by means of a residual pressure holding spring 19. The resilient force of said residual pressure holding spring 19 is set at a smaller value than the fluid force which the valve member 38 receives from the check valve outlet 14b when a pressure of the working port A has reached a working set pressure H. A valve opening operation of the valve member 38 is adapted to be performed by means of a differential force between a received pressure of the check valve outlet 14b and a resultant force of a received pressure of said check valve inlet 14a and a resilient force of the residual pressure holding spring 19. This valve device operates as follows. When the pressure of the pressure port P has lowered to the second pressure range R₂ from the first pressure range R₁, the residual pressure holding valve member 38 is brought into contact with the residual pressure holding valve seat 40 for valve closing by the resilient force of the residual pressure holding spring 19. Therefore, the residual pressure holding valve 17 can be made simple in construction by omission of an opening/closing operation device. Further, by setting the resilient force of the spring 19 at a small value, the spring can be made small in size as well as the valve device 11 can be made also small in size. and a valve-closing contact force between the valve member 38 and the valve seat 40 can be made small to prolong their sealing service times. In the case that the spring 19 is retained by a valve-opening hydraulic piston 33 as well as the resilient force thereof is set at a smaller value than a resilient force of a checking spring 31, a spring retaining construction can be simple as well as a relief accuracy can be improved. BRIEF DESCRIPTION OF THE DRAWINGS The above and other important features of the invention will be better understood from the following detailed descriptions of preferred embodiments and variants of the invention, made with reference to the accompanying drawings, in which: Figures 1 through 7 show an embodiment of the present invention: Figure 1 is an enlarged sectional view taken along the I - I directed line in Figure 5 and is a cross-sectional view of a residual pressure holding valve device; Figure 2 is a circuit diagram of a pressure oil supply/discharge circuit; Figure 3 is a view showing a change of a pressure of a working port with respect to the lapse of time; Figure 4 is a circuit diagram of a hydraulic clamping device to which the present invention is applied; Figure 5 is a sectional view taken along the V - V directed line in Figure 4; Figure 6 is a plan view of Figure 5; Figure 7 is a schematic view of an operational explanation, Figure 7(a) is a view showing a clamping condition. Figure 7(b) is a view showing a residual pressure holding condition, and Figure 7(c) is a view showing an unclamping condition; Figures 8 through 11 show a first variant through a fourth variant of above embodiment respectively and are views corresponding to Figure 1; Figure 12 shows a conventional embodiment and is a partial view corresponding to Figure 2. DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, embodiments of the present invention will be explained with reference to the drawings hereinafter. Figs. 1 through 7 show a first embodiment. Firstly, a construction of a pressure oil supply/discharge circuit with a residual pressure holding function and an operation thereof will be explained with reference to Figs. 2 and 3. A circuit diagram of Fig. 2 shows a device for operatively extending and contracting a single-acting spring-returned type hydraulic cylinder 1. A hydraulic actuation chamber 2 of the hydraulic cylinder 1 is adapted to be selectively connected to a hydraulic pressure source 6 at a starting end portion of a working pressure oil supply massage 5 and to an oil tank 8 at an ending end portion of a return pressure oil discharge passage 7 through a pressure oil supply/discharge passage 3 and a pressure oil supply/discharge changeover means 4. The changeover means 4 is composed of one changeover valve adapted to be changed over to a supply position M and to a discharge position N. A residual pressure holding valve device 11 is disposed between the hydraulic actuation chamber 2 and a hydraulic hose 10 of the pressure oil supply/discharge passage 3. A pressure compensation valve 12 is arranged along the pressure oil supply/discharge passage 3 and the pressure oil discharge passage 7 in parallel with the pressure oil supply/discharge changeover means 4. The residual pressure holding valve device 11 is provided with a check valve 14 with a forcibly valve-opening function, a forcibly valve opening means 15 of the hydraulic operation type, a bypass passage 16 connected to the check valve 14 in parallel, a residual pressure holding valve 17 and a flow resistance application means 21 both of which are disposed in series in the bypass passage 16. The valve member of the residual pressure holding valve 17 is adapted to be pushed to its valve closed side by a resultant force of a received pressure of a check valve inlet 14a and a resilient force of a residual pressure holding spring 19 as well as to be pushed to its valve opened side by a received pressure of a check valve outlet 14b. The pressure compensation valve 12 comprises a throttling valve 23 and a relief valve 24 connected in series to each other. At the time of extending operation of the hydraulic cylinder 1, the changeover means 4 is changed over to its supply position M as well as the forcibly valve opening means 15 is changed over to its pressure oil discharge position. Thereupon, a pressure oil of the hydraulic pressure source 6 flows into the hydraulic actuation chamber 2 through the pressure port P, the check valve inlet 14a, the outlet 14b and a working port A of the valve device 11 so as to operatively extend the hydraulic cylinder 1. The pressures of the hydraulic actuation chamber 2 and of the working port A increase as the extension resistance increases, and when it reaches a working set pressure H ( herein, 245 Kgf/cm² ) within the first pressure range R₁ as substantially the same pressure as that of the hydraulic pressure source 6, the extension of the hydraulic cylinder 1 is completed ( time t₁ ). In the midway course of increasing of the pressure on the side of the check valve inlet 14a, the residual pressure holding valve 17 is held in the valve closed position by means of the residual pressure holding spring 19. Under the extension completed condition, when the hydraulic cylinder 1 receives a heat externally, the pressure of the hydraulic actuation chamber 2 starts to increase very slowly due to a cubical expansion of the pressure oil ( time t₂ ) . When the pressure of the working port A increases to a pressure ( herein, around 300 ∼ 325 Kgf/cm² ) determined by both the resilient force of the residual pressure holding spring 19 of the residual pressure holding valve 17 and the spring force of the relief valve 24 ( time t₃ ), the valve 17 serves to discharge only a very slow increased portion of the hydraulic pressure from the pressure oil discharge passage 7 to the oil tank 8 through the pressure compensating valve 12. Thereby, the pressures of the working port A and of the hydraulic actuation chamber 2 can be held within the first pressure range R₁. Under the extended condition of the hydraulic cylinder 1, when the pressure of the pressure port P starts to lower abnormally and rapidly due to a breakage of the hydraulic hose 10 and so on ( time t₄ ) , the pressure of the working port A lowers ( refer to the figure indicated by the alternate long and short dash line ) because the residual pressure holding valve 17 is opened by the received pressure of the check valve outlet 14b so as to allow the pressure oil to flow out of the working port A to the pressure port P while the check valve 14 serves to block a counter flow from the side of the outlet 14b to the side of the inlet 14a. When the pressure of the working port A lowers to the residual pressure set pressure ( herein, 50 Kgf/cm² ) within the second pressure range R₂ ( time t₅ ), the valve 17 is closed by the spring 19. Thereby, the pressures of the working port A and of the hydraulic actuation chamber 2 can be held within the second pressure range R₂. Further, in the case that the pressure of the pressure port P starts to abnormally lower very slowly due to a little leakage from the piping and the like at the time of t₄ , also the pressure of the working port A lowers very slowly ( refer to the figure indicated by the alternate long and two short dashes line ). Thereupon, similarly to the aforementioned one, when the pressure of the working port A lowers to the aforementioned pressure within the second pressure range R₂ ( time t₆ ) , the valve 17 is closed so that the pressures of the port A and of the chamber 2 can be held within the second pressure range R₂. On one hand, under such a condition that the hydraulic actuation chamber 2 is held within the first pressure range R₁, when the hydraulic actuation chamber 2 is operatively contracted, the pressure oil supply/discharge changeover means 4 is changed over to the discharge position N as well as the forcibly valve opening means 15 of the hydraulic operation type is changed over to the pressure oil supply position ( time t₇ ). Thereupon, the checking condition of the check valve 14 is cancelled so that the pressure oil within the hydraulic actuation chamber 2 is discharged to the oil tank 8 through the working port A, the check valve outlet 14b, the check valve inlet 14a, the pressure port P and the changeover means 4 at the discharge position N in order. Accompanying therewith, the pressure of the hydraulic actuation chamber 2 lowers rapidly, and then the contraction of the hydraulic cylinder 1 is completed ( time t₉ ). Incidentally, the contractional operation of the hydraulic cylinder 1 may be performed according to the following procedure. Under such a condition that the pressures of the hydraulic actuation chamber 2 and of the working port A are held within the first pressure range R₁, firstly only the changeover means 4 is changed over to the discharge position N at the time of t₄. Thereupon, the residual pressure holding valve 17 is opened and then the pressure oil within the hydraulic actuation chamber 2 is discharged therefrom so that the pressure of the hydraulic actuation chamber 2 lowers to the second pressure range R₂ ( time t₅ ). Under this condition, the check valve 14 is opened by actuating the forcibly valve opening means 15 to the pressure oil supply position ( time t₈ ). Thereby, the pressure of the chamber 2 lowers so that the contraction of the cylinder 1 is completed ( time t₉ ). The concrete constructions of the aforementioned pressure oil supply/discharge circuit and of the residual pressure holding valve device 11 will be explained with reference to Figs. 4 through 7 and Fig. 1 hereinafter. Fig. 4 shows a hydraulic clamp device 50 for fixing a metal mould to a rotary table type injection moulding machine. A first metal mould 52 and a second metal mould 53 are fixedly secured to a circular rotary table frame 51 of the injection moulding machine by means of two hydraulic clamps 54, 54 respectively. Each hydraulic clamp 54 has its housing 55 whose opposite side walls are fixedly secured to the rotary table frame 51 by means of bolts 57, 57, and its clamping member 62 extended from the housing 55 is adapted to press upper and lower fixed portions 52a, 53a of each metal mould 52, 53. In order to enable to be mounted within the outer peripheral surface 51a of the rotary table frame 51, those hydraulic clamps 54 are adapted to move the clamping member 62 forward and backward in the inclined direction with respect to the metal moulds 52, 53. That is, as shown in a vertical sectional view of Fig. 5 and in a plan view of Fig. 6, a cylinder bore 58 of the hydraulic cylinder 1 is formed in the housing 55 of the hydraulic clamp 54 in a forwardly downwardly inclined manner. An inclination angle ϑ of the cylinder bore 58 is preferably defined at an angle of ab. 35 degree for making the housing 55 compact. A hydraulic piston 59 is inserted into the cylinder bore 58 through a packing 60 so as to be oil-tightly movable forwardly and backwardly. The hydraulic actuation chamber 2 is so formed in the cylinder bore 58 as to face the back surface of the piston 59. The clamping member 62 is protruded directly from the upper portion of the piston 59 toward its advancing side. A spring accommodation bore 66 is so formed in the piston 59 as to extend backward from its front surface. The axis K of the bore 66 is displaced to a lower side below the axis J of the piston 59. An unclamping spring 67 composed of a compression spring is inserted into the bore 66. This spring 67 is mounted between the piston 59 and a spring retaining pin 69 put into a pin insertion hole 68 of the housing 55. A pair of left and right guide grooves 71, 71 are formed in the opposite lateral side portions in the front opened state in order to avoid an interference with the pin 69. When the hydraulic clamp 54 is changed over to the clamping condition as illustrated, the pressure oil is supplied to the hydraulic actuation chamber 2. Thereupon, the piston 59 is advanced by the hydraulic pressure, so that the clamping member 62 can be advanced to the clamping position outside the front surface 55a of the housing 55. Thereby, the clamping member 62 serves to press and fix the fixed portions 52a of the metal mould 52 to the rotary table frame 51. The residual pressure holding valve device 11 is arranged in the housing 55 of the aforementioned hydraulic clamp 54. As shown in Fig. 1, the valve casing 27 of the valve device 11 comprises a wall portion 73 and a lid bolt 74. The pressure port P is connected in communication to the working port A through the check valve seat 28 and the check valve chamber 29 in order within the valve casing 27. A check valve member 30 inserted into the check valve chamber 29 is resiliently urged for valve closing to the check valve seat 28 by a checking spring 31. The forcibly valve opening means 15 is disposed outside ( above, in Figure ) the pressure port P and the check valve seat 28 and is provided with a valve-opening hydraulic piston 33 inserted into the valve casing 27. Above the piston 33 there are provided a hydraulic actuation chamber 34 and a pilot port F. By making the external dimension D of the piston 33 smaller than a cutoff diameter dimension E of the check valve seat 28 a piston pressure receiving cross-sectional area is sat at a smaller value than a pressure non-receiving cross-sectional area within the check valve seat 28. A valve opening member 35 disposed below the piston 33 is opposed to the check valve member 30 from the side of the pressure port P. The valve surface of the check valve member 30 is made of a resilient material such as fluoroplastic and the like. A bypass passage 16 is formed between the pressure port P to the working port A in parallel with the check valve seat 28 and the check valve chamber 29. The residual pressure holding valve 17 disposed in a midway portion of the bypass passage 16 is provided with a residual pressure holding valve member 38 inserted into an accommodation bore 75 of the hydraulic piston 33 and a residual pressure holding valve seat 40 formed in the check valve member 30. The valve member 38 is resiliently urged for valve closing to the valve seat 40 by means of the residual pressure holding spring 19 mounted in a spring accommodation bore 76. The resilient force of the spring 19 is set at a smaller value than the resilient force of the checking spring 31. The bore 76 is connected in communication to the check valve inlet 14a through a communication groove 38a. Also the valve surface of the valve member 38 is made of a resilient material such as fluoroplastic and the like. The flow resistance application means 21 disposed in the midway portion of the bypass passage 16 is arranged between the pressure port P and the residual pressure holding valve 17 and comprises a throttling passage 44 composed of an annular fitting gap defined between the lid bolt 74 and the check valve member 30. An annular filter room 78 is formed between the pressure port P and the residual pressure holding valve 17 as well as the check valve 14. An annular primary filter 79 is mounted in the filter room 78. Further, a secondary filter 94 is mounted between the residual pressure holding valve 17 and the working port A. This secondary filter 94 is pushed to the check valve member 30 by the checking spring 31. The operation of the aforementioned valve device 11 will be explained with reference to Fig. 7. Fig. 7(a) shows the clamping condition. At the time of clamping operation, the pressure oil supplied from the pressure port P serves to push and open the check valve member 30 and flows into the hydraulic actuation chamber 2 from its peripheral grooves 30a through the working port A. After the pressure within the chamber 2 has increased, the check valve member 30 is brought into contact with the check valve seat 28 for valve closing by the checking spring 31. The residual pressure holding valve member 38 is brought into contact with the residual pressure holding valve seat 40 for valve closing by the residual pressure holding spring 19. Further, a valve opening clearance S is formed between the valve member 38 and the valve-opening hydraulic piston 33, and an abutment clearance T is formed between the valve opening member 35 of the hydraulic piston 33 and the check valve member 30. Under this clamping condition, when the pressure of the hydraulic actuation chamber 2 increases very slowly so that the pressure of the check valve outlet 14b is increased, the residual pressure holding valve member 38 is opened by that hydraulic pressure against a resultant force of the received pressure of the check valve inlet 14a and of the resilient force of the residual pressure holding spring 19, so that the very slow increased portion of the hydraulic pressure is released from the pressure port P. Fig. 7(b) shows the residual pressure holding condition. In case that the pressure within the pressure port P lowers abnormally, firstly the residual pressure holding valve member 38 is opened by the received pressure from the check valve outlet 14b against the residual pressure holding spring 19 while the check valve member 30 is held in such a condition that being kept in contact with the check valve seat 28 for valve closing. Thereby, the pressure oil within the working port A is discharged slowly from the pressure port P through the check valve outlet 14b, the residual pressure holding valve seat 40 and the flow resistance application means 21 in order as indicated by the arrow of the alternate long and two short dashes lines. When the pressure of the check valve inlet 14a lowers to a residual pressure set pressure L ( refer to Fig. 3 ) , the valve member 38 is brought into contact with the valve seat 40 for valve closing by the spring 19. As a result, the pressures of the working port A and of the hydraulic actuation chamber 2 are prevented from being lowered below the aforementioned pressure L. Fig. 7(c) shows the unclamping condition. By supplying the pressure fluid from the pilot port F to the hydraulic actuation chamber 34, the valve-opening hydraulic piston 33 serves to separate the the check valve member 30 from the check valve seat 28 through the valve opening member 35. Thereby, the pressure oil within the hydraulic actuation chamber 2 is discharged from the pressure port P. In this case an abutment preventing clearance G is provided between the residual pressure holding valve member 38 and the hydraulic piston 33. Thereby, the valve closing abutment force between the residual pressure holding valve member 38 and the residual pressure holding valve seat 40 can be provided only by the resilient force of the residual pressure holding spring 19. As a result, the valve surface of the valve member 38 can be prevented from being damaged, so that the service life thereof can be prolonged. Further, since the respective valve surfaces of the check valve member 30 and of the residual pressure holding valve member 38 are made of a resilient material, an oil leakage can be prevented more surely. As a result, the accumulator 411 employed in the conventional embodiment ( refer to Fig. 21 ) can be omitted, so that the whole of the valve device 11 can be made small. Incidentally, the location where a sealing resilient member is disposed may be at the check valve seat 28 and the residual pressure holding valve seat 40. The residual pressure holding valve device 11 having the aforementioned construction may be used as shown in Fig. 4. The pressure ports P of the respective valve devices 11 are selectively connected to the booster pump ( the hydraulic pressure source ) 6 at the starting end portion of the working pressure oil supply passage 5 and to the oil tank 8 at the ending end portion of the return pressure oil discharge passage 7 through the pressure oil supply/discharge passage 3 and the pressure oil supply/discharge changeover means 4. The booster pump 6 is adapted to operatively deliver an oil within the oil tank 8 when a compressed air is supplied thereto from a pneumatic source 80 through a pressure reduction valve 81. In the midway portion of the pressure oil supply/discharge passage 3 there are provided two flexible hydraulic hoses 10, 10, and the pressure compensation valve 12 is disposed along both the passage 3 and the passage 7 in parallel with the changeover means 4. The pilot ports F of the respective valve devices 11 are selectively connected to a valve-opening pressure oil supply passage 84 and to a valve-opening cancellation pressure oil discharge passage 85 through the pressure oil supply/discharge passage 82 and the pressure oil supply/discharge changeover means 83. The changeover means 83 employs a hydraulic changeover valve having the same construction as that of the pressure oil supply/discharge changeover means 4. The pressure oil supply passage 84 is connected to the working pressure oil supply passage 5, and the pressure oil discharge passage 85 is connected to the return pressure oil discharge passage 7. Also in the midway portion of the passage 82 there are interposed two flexible hoses 87, 87. The aforementioned two changeover means 4, 83 are operatively changed over to the supply position M and to the discharge position N by means of an electromagnetic pneumatic changeover valve 89. When the pneumatic changeover valve 89 is changed over to the clamping position C, one changeover means 4 is changed over to the supply position M as well as the other changeover means 83 is changed over to the discharge position N. Thereby, the pressure oil of the booster pump 6 is supplied to the pressure port P of the valve device 11, so that four hydraulic clamps 54 are actuated for clamping. This clamping operational condition is detected by means of a pressure switch 91. To the contrary, when the pneumatic changeover valve 89 is changed over to an unclamping position U, the one changeover means 4 is changed over to the discharge position N as well as the other changeover means 83 is changed over to the supply position M. Thereby, the pressure oil of the booster pump 6 is supplied to the pilot port F of the valve device 11. As a result, the pressure oil within the hydraulic actuation chamber 2 is discharged from the pressure port P to the oil tank 8 through the changeover means 4, so that the respective hydraulic clamps 54 are actuated for unclamping. This unclamping operational condition is detected by means of a pressure switch 92. Incidentally, the forcibly valve opening means 15 may be of the pneumatic actuation type or of the manual operation type. Figs. 8 through 11 show a first variant through a fourth variant of the first embodiment respectively. In the respective variants, component members having the same constructions as those in the aforementioned embodiment are in principle designated by the same symbols. (First Variant) Fig. 8 shows a first variant and is a partial view corresponding to Fig. 1. To a portion facing the working port A within the valve casing 27, a secondary filter 94 is pressed and fixed oil-tightly by means of the resilient forces of the checking spring 31. (Second Variant) Fig. 9 shows a second variant and is a view corresponding to Fig. 1. The residual pressure holding valve seat 40 is formed in the midway portion of the check valve member 30, and the residual pressure holding valve member 38 is inserted into the check valve member 30. Incidentally, the secondary filter 94 shown in Fig. 1 and Fig. 8 is omitted. (Third Variant) Fig. 10 show a third variant which is different form the variant of the Fig. 9 in the following constructions. The residual pressure holding spring 19 is received by a stop ring 96 fitted to the check valve member 30. The flow resistance application means disposed in the midway portion of the bypass passage 16 is composed of a throttling passage 44 between the valve casing 27 and the check valve member 30 and a throttling passage 98 between the check valve member 30 and a throttling valve member 97. (Fourth Variant) Fig. 11 show a fourth variant and is a view corresponding to Fig. 1. An projected portion of the valve-opening hydraulic piston 33 is inserted oil-tightly and movably into the check valve member 30. The residual pressure holding valve seat 40 is formed in the projected portion, and the residual pressure holding valve member 38 is inserted therein.

Claims: A pressure oil supply/discharge circuit having a hydraulic actuation chamber (2) of a hydraulic cylinder (1) adapted to be selectively connected to a working pressure oil supply passage (5) and to a return pressure oil discharge passage (7) through a pressure oil supply/discharge passage (3) and a pressure oil supply/discharge changeover means (4); a check valve (14) with a forcibly valve opening function disposed in said pressure oil supply/discharge passage (3); and said check valve (14) being adapted to block a counter flow from a check valve outlet side (14b) to a check valve inlet side (14a) under a checking condition in which a forcibly valve opening means (15) is not operated and to allow the pressure oil to be discharged from the pressure oil actuation chamber (2) under a checking cancelled condition in which the forcibly valve opening means (15) is operated, characterized in that a bypass passage (16) is connected to said pressure oil supply/discharge passage (3) in parallel with said check valve (14); a residual pressure holding valve (17) and a flow resistance application means (21) are disposed in said bypass passage (16) in series; said residual pressure holding valve (17) is of a relief type; a valve opening operation of said valve (17) is adapted to be performed by means of a differential force between a received pressure of said check valve outlet (14b) and a resultant force of a received pressure of said check valve inlet (14a) and a resilient force of a residual pressure holding spring (19); a pressure compensation valve (12) is disposed along said pressure oil supply/discharge passage (3) and said pressure oil discharge passage (7) in parallel with said pressure oil supply/discharge changeover means (4); and said pressure compensation valve (12) is adapted to discharge only a very slow increased portion of the hydraulic pressure within said hydraulic actuation chamber (2). A pressure oil supply/discharge circuit according to claim 1, characterized in that : a resilient force of said residual pressure holding spring (19) is set at a smaller value than the fluid force which the valve member (38) of said residual pressure holding valve (17) receives from the check valve outlet (14b) when the pressure of said check valve outlet (14b) has reached a working set pressure (H). A pressure oil supply/discharge circuit according to claim 1, characterized in that : a pressure port (P) is connected in communication to a working port (A) through a check valve seat (28) and a check valve chamber (29) in order within a valve casing (27); a check valve member (30) is inserted into the check valve chamber (29), said member (30) being resiliently urged for valve closing to the check valve seat (28) by means of a checking spring (31); said forcibly valve opening means (15) of said check valve (14) is disposed outside the check valve seat (28) within the valve casing (27), and a valve opening member (35) of said forcibly valve opening means (15) is opposed to said check valve member (30) from the side of said pressure port (P); under a checking condition in which the forcibly valve opening means (15) is not operated, said check valve member (30) is adapted to be brought into contact with the check valve seat (28) for valve closing so as to block a counter flow from the side of the check valve outlet (14b) to the side of the check valve inlet (14a); under a checking cancelled condition in which said forcibly valve opening means (15) has been operated, said check valve member (30) is adapted to be separated from the check valve seat (28) by means of the valve opening member (35) so as to allow the pressure oil to be discharged from the working port (A) to the pressure port (P); said bypass passage (16) is disposed in such a portion as extending from said pressure port (P) to said working port (A), in parallel with said check valve seat (28) and said check valve chamber (29); said residual pressure holding valve (17) and said flow resistance application means (21) having a throttling passage (44) are disposed in said bypass passage (16) in series; said residual pressure holding valve (17) is of the relief type and comprises a residual pressure holding valve member (38) resiliently urged for valve closing to a residual pressure holding valve seat (40) by means of a residual pressure holding spring (19); said resilient force of said residual pressure holding spring (19) is set at a smaller value than the the fluid force which the valve member (38) receives from the check valve outlet (14b) when the pressure of said working port (A) has reached a working set pressure (H); and a valve opening operation of said valve member (38) is adapted to be performed by means of a differential force between a received pressure of said check valve outlet (14b) and a resultant force of a received pressure of said check valve inlet (14a) and a resilient force of said residual pressure holding spring (19). A pressure oil supply/discharge circuit according to claim 3, characterized in that : one of a valve face of said check valve member (30) and said check valve seat (28) is made of a resilient material such as a synthetic resin and the like and the other thereof is made of a solid material such as a metal and the like, one of a valve face of said residual pressure holding valve member (38) and said residual pressure holding valve seat (40) is made of a resilient material such as a synthetic resin and the like, and the other thereof is made of a solid material such as a metal and the like. A pressure oil supply/discharge circuit according to claim 3 or to claim 4, characterized in that : said residual pressure holding valve seat (40) is disposed in said check valve member (30), and said residual pressure holding spring (19) is received by a valve-opening hydraulic piston (33) of said forcibly valve opening means (15) as well as the resilient force of said residual pressure holding spring (19) is set at a smaller value than that of said checking spring (31). A pressure oil supply/discharge circuit according to claim 5, characterized in that : said residual pressure holding valve member (38) is inserted into said valve-opening hydraulic piston (33), and a valve opening clearance (S) provided therebetween for said residual pressure holding valve member (38) is set at a larger value than a contact clearance (T) between said valve opening member (35) and said check valve member (30). A pressure oil supply/discharge circuit according to any one of claims 3 through 6, characterized in that : said valve casing (27) is fixedly secured to a cylinder body (1a) of a hydraulic cylinder (1).

Inventors: YONEZAWA KEITARO K K KOSMEK, YONEZAWA, KEITARO, K.K. KOSMEK
Applicants: KOSMEK KK, KABUSHIKI KAISHA KOSMEK
Application year: 1991
Main classification: F15B13
IPC codes: F15B13, F15B11, B29C45, F15B20