US3530893A - Sliding plate type directional control valve - Google Patents

Description

I United States. Patent 13,530,893

[72] Inventor Kenzl Masuda [55 Rgfe e Cited 21 A l N 23%;? Japan UNITED STATES PATENTS m 11 2,832,561 4/1958 Holl 251/2s3x [73] Assignee Daik'h ogyo Co Ltd 3,353,557 11/1967 Faisandier 25 l/282X Osaka, Japan Primary Examiner- Henry T. Klinksiek a corporation of Japan Attorney-Christen and Sabol [32] Priority Dec. 13, 1966 I v v [33] Japan [31] til/81,703 ABSTRACT: A sliding plate type directional control valve comprising a movable or sliding plate member disposed within the valve chamber for sliding movement, said movable member having, solely or together with a valve body member, [54] SLIDING PLATE TYPE DIRECTIONAL CONTROL stepped fluid passages each comprising a large diameter VALVE assa e portion and a small diameter assage portion, each of P B P 6 claims'so Dmwmg Figs I said-stepped fluid passages is always in communication with [52] 11.8. C1 137/625.25,' i her one f he valv p rts. a piston being disposed in each of 137/6252], III/625.65, 251/282,251/283 the large diameter portions, the cross-sectional area of said [51] Int. Cl ..Fl6k 11/02, large diameter passage portion being equal to or greater than F161: 39/04 the effective pressure acting area of the corresponding port so [50] Field of Search 1 37/625 .25, that the movable member may be constantly urged toward the 625.48, 625.63, 625.64, 625.65, 625.68, 625.21; valve port under the influence of the pressure difference act- 251/282, 283 ing thereon.

3 l4 I6 40 l q l r 1. w a A 3/- V i 4 I w B P "A 7' Patented Sept. 29, 1970 l of 14 Sheet MW 3 wt Patented 'Sept. 29, 1970 v 3,530,893

Sheet 3 of 14 Patented Sept. 29, 1970 -3,530,893

Sheet 4 0114 Sheet Paten ted Sept. 29, 1970 Patented Sept. 29, 1970 Sheet 7 of 14 5Q QM v Patented Sept. 29, 1970 Sheet 8 M14 FIG /7 12: FIG: /8

a/ a b) 4 9) 4.?(P/ 43 m; b 445m r I l l II w .m v Y L i3 m O0 f G QC Patented Sept. 29, 1970 3,530,893

Sheet 9 of 14 FIG. 23

Patented Sept. 29, 1970 Sheet 10 of 14 Pa tented Sept. 29, 1970 3,530,893

Sheet 11 01'14 FIG. Z70

Patented Sept. 29, 1970 7 Sheet '3 01'14 awn Qu QM wt Patented Sept.' 29, 1970 3,530,893

Sheet I4 of 14 SLIDING PLATE TYPE DIRECTIONAL CONTROL VALVE 1 BACKGROUND OF THE INVENTION The present invention relates to a fluid control valve, and more particularly to a sliding plate type directional control valve having a sliding member disposed within valve chamber for sliding movement so as to control fluid flow.

In the past, as means for providing a directional control of fluid flow, there have been proposed two different types of directional control valves, namely, a spool valve and a 'sliding plate type valve. However, both of 'these known types have disadvantages. in a spool type directional control valve, a cylindrical spool is slidably received within a valve body which has a plurality of ports such as a pump port, tank port and one or more cylinder ports respectively communicating with a fluid pump, fluid reservoir or tank and one or more fluid cylinders or the like through suitable pipings. Said spool is provided with a plurality of circumferential grooves and serves to effect communication between selected two of said ports when it is slidably and axially moved. In other words, when the spool is moved in one direction, the pump port is placed in communication with one of the cylinder ports and the other of the cylinder ports is placed in communication with the tank port. while when the spool is moved in the other direction, the pump port and the tank port are respectively put into communication with said other of the cylinder ports and said one of the cylinder ports. Thus, the flow of fluid can be switched over simply by the axial sliding movement of the spool. In this type of directional control valve, problems have been encountered in that a foreign material enters between the spool and the valve body causing sticking of the valve spool, that there often occurs fluid leakage from the gap between the spool and the valve body, and that, through the extended usage, either or both of the spool land and the inner wall surface of the valve chamber are substantially worn and results in an excessively large clearance between them so that the volumetric efficiency of the valve is substantially reduced.

In order to overcome the above described disadvantages, a sliding plate type directional control valve has been proposed. In this type of valve, a valve body is constructed by a pair of port members having a pump port and one or more cylinder ports respectively and opposingly disposed so as to form a valve chamber therebetween, and an intermediate member disposed between the port members and having a tank portv Within said valve chamber, a sliding plate having a plurality of fluid passages is axially slidably received.

It is important to note that the valve of this type includes a wear compensation mechanism for compensating the possible wear of the valve components which may be experienced through the extended usage of the valve. To this end, in this type of valve, the sliding plate is disposed within the valve chamber with a sufficient clearance between it and the port members so that the sliding plate may not directly contact with either of the port members. At each port, the clearance between the sliding plate and the port member is sealed by means of a so-called balanced piston which is disposed in the fluid passage communicating with a port and is resiliently pushed onto the surface of the sliding plate by thrust of the spring so that the balanced piston may sealingly engage with the sliding plate for preventing the leakage from the gap between the sliding plate and the port member. The piston may be so constructed that the differential fluid pressure act ing thereon may assist to push it toward the sliding plate. By this arrangement, the internal fluid leakage in the valve can be effectively prevented, and moreover any wear of the valve components can be compensated.

However, the sliding plate type valve is also disadvantageous in that all of the ports are simultaneously opened or put into communication during operation or transition period of the sliding plate in which the plate is moved from one position to the other, and therefore the pressure in each port is instantaneously released to zero pressure. Accordingly,

this type of directional control valve can have but a few limited uses unless the circuit in which it is disposed are provided with specially designed additional means.

SUMMARY OF THE INVENTION The present invention is aimed to overcome the disadvantages as encountered in the known types of directional control valves.

The present invention has a particular relation to a directional control valve adapted to be disposed in a fluid circuit including for example a fluid pressure pump and a pressurized fluid operated actuator such as a fluid cylinder for controlling the fluid flow, and more particularly to a sliding plate type directional control valve having a sliding member slidably disposed within a valve chamber for controlling the fluid flow.

An object of the present invention is to provide a directional control valve in which internal fluid leakage is substantially eliminated without any increase of sliding resistance, and which is easily operated and is suitable even as a high pressure valve.

Another object of the present invention is to provide a directional control valve in which all -of the ports are prevented from being simultaneously opened even when a transition period in which the sliding member is moved from one position to the other or another position so that the pressurized fluid from the pump port is prevented from escaping into the low pressure or tank port.

A further object of the present invention is to provide a directional control valve in which the sliding resistance is substantially reduced by a perfect pressure balancing arrangement for eliminating any moment acting on the sliding member due to the fluid pressure.

Still another object of the present invention is to provide a directional control valve in which means are incorporated for compensating any wear of sliding surfaces such as the sliding member and the valve body.

Still further object of the present invention is to provide a directional control valve in which the tank port can be subjected to a back pressure by preventing all of the ports from being opened during said transition period.

A further object of the present invention is to provide a directional control valve which may be modified to several different types such as the open-center type. closed-center type or partially open center type, etc., by applying only a simple machining to the sliding member.

Another object of the present invention is to provide a semiopen center type directional control valve or such a valve that can effect an inching action.

Still further object of the present invention is to obtain a directional control valve of such a type that has all of the afore-mentioned and other functions which may be obtainable by a conventional spool valve.

With these and other objects in view, the dll'CCIiOl'i'ui control valve in accordance with the present invention comprises a ported member and a movable member provided with stepped fluid passages each of which having a large diameter and a small diameter passage portions, and normally communicating with either the pump port or one of the cylinder ports, a piston being disposed in each of the large diameter passa e portions, the cross-sectional area of said large diameter passage portion being equal to or larger than the effective pressure acting area of the corresponding port so that the movable member may be constantly urged toward the ported member under the influence of the differential pressure acting thereon.

ln one aspect of the present invention, the stepped fluid passage is provided in a sliding member.

in another aspect of the present invention, a floating member is provided in the valve chamber, and the stepped fluid passage is provided in the floating member or between it and the valve body.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings; FIG. 1 is a longitudinal section of a conventional balanced piston type three position four way reciprocating electric solenoid valve;

FIG. 1a is a symbol ofthe valve shown in FIG. 1;

FIG. 2 is an enlarged sectional view showing in detail the balanced piston employed in the valve shown in FIG. 1;

FIG. 3 is a longitudinal section of a conventional three position four way rotary type directional control valve of the balanced piston type, the section being taken along the line III-III of FIG. 4;

FIG. 3a symbolically show the type of the valve shown in FIG. 3;

FIG. 4 is a sectional view taken along the line IV-IV of FIG.

FIG. 5 is a longitudinal sectional view of a hand operated reciprocal type three position four way valve embodying the present invention, the valve being shown in the neutral position;

FIG. 5a is a symbol showing the type of the valve shown in FIG. 5;

FIG. 6 is a sectional view substantially taken along the line VI-VI of FIG. 5;

FIG. 7 is a plan view of the port member employed in the valve shown in FIG. 5;

FIG. 8 is a sectional view substantially taken along the line VIII-VIII of FIG. 7;

FIG. 9 is a sectional view substantially taken along the line IX-IX of FIG. 7;

FIG. 10 is a plan view of the sliding member employed in the valve shown in FIG. 5;

FIG. 11 is a sectional view substantially taken along the line Xl-XlofFlG. 10;

FIG. 12 is a longitudinal sectional view similar to FIG. 5, but showing the sliding member shifted to the extreme left position;

FIG. 13 is a sectional view showing a modification of the embodiment shown in FIGS. 5-12, the valve being an all port open type four way valve:

FIG. 13a is a symbol of the valve shown in FIG. 13;

FIG. 14 is a further modification of the embodiment shown in FIGS. 5-l2, the valve being a center-bypass type four way valve;

FIG. 14a is a symbol of the valve shown in FIG. 14;

FIG. 15 is a longitudinal sectional view showing the fluid pressure relationship in the valve shown in FIGS. 512;

FIG. 16 is a longitudinal sectional view of the second embodiment of the present invention, the valve being a hand operated reciprocal type and shown in the neutral position;

FIG. 16a is a symbol showing the type of the valve of FIG. 16;

FIG. 17 is a plan view of the port member employed in the valve shown in FIG. 16;

FIG. 18 is a sectional view of the port member substantially taken along the line XVIII-XVIII of FIG. 17;

FIG. 19 is a sectional view of the port member substantially taken along the line XIX-XIX of FIG. 17;

FIG. 20 is a plan view of the sliding member employed in the valve shown in FIG. 16;

FIG. 21 is a sectional view of the sliding member substantially taken along the line XXI-XXI of FIG. 20;

FIG. 22 is a plan view of the floating member employed in the valve shown in FIG. 16;

FIG. 23 is a longitudinal sectional view similar to FIG. 16 but showing the sliding member shifted to .the extreme left position;

FIG. 24 shows a modification of the embodiment shown in FIGS. 16-23, in which the sliding member has no through hole but each port and the stepped fluid'passage is communicated through a separate passage;

FIG. 24a is a symbol of the valve shown in FIG. 24;

FIG. 25 shows a member for subjecting the tank port to a back pressure;

FIG. 25a is a symbol showing the type of the valve of FIG. 25;

FIGS. 26 and 27 show modified stepped fluid passage;

FIG. 270 shows the type of the valve of FIG. 27;

FIG. 28 is a sectional view substantially taken along the line XXVIII-XXVIII of FIG. 27;

FIG. 29 is a longitudinal section of an all port open type four way directional control valve;

FIG. 30 is a longitudinal section of a partial open center type four way directional control valve;

FIG. 31 is a longitudinal sectional view of a center by-pass type four way directional control valve;

FIG. 32 is a longitudinal sectional view of a valve which is provided with.,a choke between the shifted positions of the sliding member so as to obtain an inching, shock free and flow control features;

FIG. 33 is a longitudinal section of a rotary type three position four way directional control valve;

FIGS. 29a, 30a, 31a, 32a and 33a diagrammatically show the type of the valve of FIGS. 29, 30, 31, 32 and 33 respectivey;

FIG. 34 is a plan view of the port member employed in the valve shown in FIG. 33;

FIG. 35 is a plan view of the sliding member employed in the valve shown in FIG. 33; and

FIG. 36 is a plan view of the floating member employed in the valve shown in FIG. 33.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, particularly to FIGS. 1 and 1a, there is shown by a longitudinal sectional view a kind of conventional sliding plate type directional control valve, i.e., a reciprocating type two position four way solenoid valve. As shown in the drawing, the valve includes a pair of port members 101 and 102 having a pump port P and a pair of cylinder ports A and B respectively. The port members 101 and 102 are so arranged that a valve chamber 103 is defined therebetween, and an intermediate member 104 is interposed between the port members 101 and 102. The port members and the intermediate member are secured together so as to form a rigid valve body. Within the valve chamber 103, a sliding member 108 is axially slidably received. The sliding member has flow passages 105, 106 and 107. The member 108 is constantly urged toward right by a coil spring 111 which acts through a spring seat 110 on the left end of the sliding member 108. An electric solenoid 109 is disposed at the right hand side of the sliding member 108 and acts, when energized, on the member 108 to urge it toward left. Thus, the sliding member 108 is selectively shifted toward right or left so as to connect the port P selectively to the port A or B through the passage 105 or 107. It has been known, in this type of valve, to provide a wear compensation mechanism for the purpose of preventing fluid leakage from the clearance between the port members 101 and 102 and the sliding member 108 and compensating any wear of the members which may occur through the extended usage of the valve. A typical example of the compensating mechanism is shown in FIG. 1. In the valve construction shown in FIG. 1, the sliding member 108 is arranged with a sufficient clearance with port members 101 and 102 so 5 that the former may not directly contact with the latter. The

port members 101 and 102 carries, at each of the passages leading to the ports P, A and B, a so-called balanced piston 112?, 112A or 1128 which is urged by means of a spring 1131, 113A or 1138 toward the sliding member 108 so as to seal the clearance between the sliding member 108 and the port member 101 or 102 even when either of the members is subjected to wear. The balanced piston is different in effective area at the opposite ends so that the pressure difference acting thereon may assist to urge the piston toward the sliding member 108. Thus, when the sliding member 108 is shifted to one of their positions, for example to the position shown in FIG. 1 in which the port P is connected with the port A through the passage 105'and the tank port T is connected with the port 8 through the passage 106, the balanced pistons 1121 and 112A are urged toward the sliding member 108 by the pressure difference acting thereon and the springs 113P and 113A so as to make a fluid tight contact with it. Therefore, the pressurized fluid from the pump port P is prevented from leaking into the valve chamber and is introduced into an actuator (not shown). Even when either or both of contact surfaces of the sliding member 108 and the balanced piston 112 are worn, the fluid tight contact at the contact surfaces can be maintained because the pistons are pushed onto the sliding member 108 by means ofthe springs l 13.

Thus, the known form of sliding plate type directional control valve may be effective in preventing any internal fluid leakage and compensating any wear of the valve components. However, in this type of valve, since all ports such as the pump port P and the cylinder ports A and B are fixed in its position while the passages 105, 106 and 107 are shifted their positions in response to the shifting movement of the sliding member 108, the valve components assumes the condition somewhat as shown in FIG. 2 during the transition period when the member 108 is shifted from one position to the other. FIG. 2 shows a condition which may be experienced during leftward movement of the sliding member 108. As shown in FIG. 2, during the transition period, the pump port P or the passage 1141 in the balanced piston 1121 and the passage 105 are partially opened to valve chamber 103, and the pressurized fluid in the pump port P is allowed to escape from the gap between the port member 101 and the sliding member 108 through the valve chamber 103 into the return line or the tank. Therefore, there instantaneously prevails zero pressure in the valve. A similar phenomenon will be seen when the pump port P comes into partial communication with the passage 107. Due to this disadvantageous feature, a valve of this type is limited in its use unless the circuit is specifically designed by incorporating additional components. In other words, if a plurality of valves of this type are connected with a single pump and each of the valves is combined with an actuator so that, by operating the valve, the corresponding actuator can be operated, when one of the valves is shifted from one position in which fluid under pressure is directed to the corresponding actuator, to another position in which fluid under pressure is exhausted from said actuator, fluid pressure in the pump port P of said valve may be allowed to escape into the low pressure line and thus the fluid pressure therein is suddenly decreased. Therefore, the pressure in the other actuators will be simultaneously exhausted through said valve. Thus, by this type of valve, it is very difficult to always maintain the fluid pressure in all of the actuators.

Further, when a plurality of valves such as tandem center type valves are connected in series by connecting the tank port T of the preceding valve with the pump port P of succeeding valve and the oil port of each valve is connected with an actuator, the fluid pressure in the pump port P of the succeeding valve has some influence on the tank port T of the preceding valve. Describing in detail, when the succeeding valve is shifted to the position in which the fluid pressure is supplied to the corresponding actuator, the operating pressure in this actuator is supplied through the tank port of the preceding valve and the pump port of the succeeding valve. In this condition, if the valves are of said type, when the preceding valve is operated, the tank port T of the preceding valve is instantaneously allowed to communicate with the valve chamber of the same valve during transition period, so that high pressure fluid is allowed to enter from the tank port into this valve chamber. Thus, the valve chamber of the preceding valve is filled with high pressure fluid resulting in the malfunctioning or failure of the valve. For this reason, the valve of said type cannot be used in such a system. Further, in a system having said type of valve, an accumulator, which is intended to charge a predetermined amount of pressurized fluid in order to provide a large amount of flow when such is required or which is intended to charge an excess amount of pressurized fluid so as to provide compensation for the leakage of fluid from the system, is also allowed to discharge the fluid under pressure through the valve during the transition period of the valve. Still further, the valve of this type cannot be used in such a system that gives an inching motion to an actuator due to said disadvantageous feature.

The same disadvantages as possessed by the conventional reciprocation-type change-over valve are experienced in a conventional rotary type directional control valve as shown in FIGS. 3, and 4. The illustrated valve isof two position four way 1 type and has a valve body comprising a portrnember 121 and a casing 123 mounted on the member 121 to form a valve chamber therebetween. The'port member 121 is provided with a pumpaport P, a tank port T and cylinder ports A and B, and within the valve chamber there is rotatably disposed a rotatable member 122 having four openings for co-operating with the ports formed in the port member. Two of the openings in the rotatable member 122 are connected together as shown in FIG. 3 by a fluid passage 105, and the other two are also connected together by a similar fluid passage (not shown).The rotatable member 122 has a rotatable shaft 124 which is fixed thereon at one end and extends through the easing 1 23.At the outer end of the shaft 124, there is secured an operating lever 125 so that the rotatable member 122 can be rotated by operating the lever 125 manually. The port member 121 has balanced pistons 112 which are identical in construction to those employed in the reciprocating type valve shown in FIGS. 1 and 2. As in the previously described valve, each of the balanced pistons is urged into a sealing contact with the rotatable member 122 by means of a spring 113 and a pressure difference acting thereon. In this type of valve, since the ports P, A and B are stationary while the passages such as the passage are shiftable, the same problems as in the previously described valve will be encountered during the transition period of the rotatable member 122.

These disadvantages of the conventional valve can be overcome by the novel and'improved construction of the present invention as will become clearin the following descriptions with respect to the preferred embodiments shown in the drawings,

Referring now to FIGS. 5, 5a and 6, there is shown a three position four way directional control valve of a sliding plate type. The valve includes a valve body comprising port members 31 and 35 superposed together, a stationary member 33 and a housing 34 assembled so as to form a valve chamber V. Within the valve chamber V, there is disposed a movable or sliding plate member 22. The port member 35 has a pump port P which is in communication with a suitable fluid pressure source (not shown), a pair of cylinder ports A and B which is adapted to be selectively connected with the pressure port P for directing the fluid under pressure to a selected actuator (not shown), and a tank port T which is in communication with a fluid tank (not shown). The port member 31 is provided with holes 1, 2, 3 and 4 which are in registered communication with the ports B, P, A and T respectively. The port member 31, the stationary member 33 and the housing 34 interposed between the members 31 and 33 are fluid tightly assembled with sealing means such as gaskets 29 and form, said valve chamber V. The sliding plate member disposed in the valve chamber V is substantially rectangular in shape as shown in FIGS. 6 and 10, and arranged so as to make a face-to-face contact with the upper surface of the port member 31 and the lower surface of the stationary member 33. A rear rod 37 extends through the left end wall of the housing 34 and is connected at its inner end with the left end of the sliding member 22 while its outer end is projected from the left end of the valve body. A front rod 38 which extends through the right end wall of the housing 34 is connected at its inner end with the right end of the sliding member 22 and at its outer end with a lever 39 for effecting axial movement of the front rod 38. The rear rod 37 is provided with a plurality of recesses which are adapted to be engaged by a detentspring and ball assembly 40 so as to hold the sliding member 22 in a selected position. Thus, in this valve, when the lever 39 is manually actuated, the assembly of the front rod 38, the sliding plate 22 and the rear rod 37 is shifted against the action of the detent means 40 until the means engages with another recess of the rear 37. Therefore, the sliding member 22 is selectively shifted so as to connect the ports P and T with the ports A and B respectively or vice versa.

These arrangements of the valve components are in principle well known in the act, however, according to the present invention, the port member 31, passages and grooves provided in the sliding member 22 and balanced pistons are specially designed so as to prevent the fluid leakage, to reduce the sliding resistance, to facilitate the operation of the valve, and to prevent the ports from being simultaneously opened to the tank or any low pressure return line during the transition period when the sliding member 22 is shifted from one position to another.

According to the present invention, the port member 31 is provided, as shown in FIGS. 7, 8 and 9, on the surface a which contacts with the sliding member 22 a groove b registering to the tank port T and a series of passages l, 2, 3 and 4 for communication with the port B, P, A and T of the port member 35 respectively as described above. Further, as shown in FIGS. 10 and 11, the sliding member 22 is provided with three stepped passages 11, 12 and 13 comprising three passages of small diameter 5, 6 and 7 and three passages of large diameter 8, 9 and 10. The small diameter passages 5, 6 and 7 open at the side of the sliding member 22 facing to the port member 31, while the large diameter passages 8, 9 and 10 open at the side of the sliding member 22 facing to the stationary member 33. The ports B, P and A, the passages 1, 2 and 3 and the passages 5, 6 and 7 are so arranged that the passages 1, 2 and 3 and thus the ports B, P and A are always maintained in communication with the small diameter passages 5, 6 and 7 respectively irrespective of the position of the sliding member 22. Further, the sliding member 22 is formed with relief grooves 49 and 50 on the side facing to the port member 31. Thus, when the valve is in the neutral position as shown in FIG. 5, the ports P, T, A and B are blocked with each other, however, when it is shifted to the position as shown in FIG. 12, the passage 6 connects the passages 1 and 2, and the reliefgroove 50 comes into communication with the passage 3. Therefore, the pump port P is connected with the port B, while the cylinder port A is connected with the tank port T. On the other hand, when the sliding member 22 is shifted to the extreme right position, the pump port P comes in communication with the port A through the small diameter passage 6 and the port B communicates with the tank port T through the reliefgroove 49.

Further, in order to provide seal means for preventing the fluid leakage from the gap between the sliding member 22 and the members 31 and 33, the sliding member 22 is constantly urged toward the port member 31 so that they make a face-toface contact together, and hollow balanced pistons 14, 15 and 16 are disposed in the large diameter passages 8, 9 and 10 respectively with interposition of suitable seal means such as O-rings. The balanced pistons 14, 15 and 16 are constantly urged toward the stationary member 33. When there is fluid pressure prevailing in the passages l, 2 and 3, the fluid will have a tendency of escaping through the gap between the port member 31 and the sliding member 22, and the fluid pressure in the gap between the members 31 and 22 tends to force the members apart. The pressure receiving areas on which the leaking fluid pressure acts are shown by shadow lines in FIG. 7 and designated by reference letters 0, d and e. In the illustrated embodiment, the cross-sectional area of the large diameter passages 8, 9 and 10 are equal to or larger than the area 0, d and e so that the sliding member 22 is urged to a fluid tight contact with the port member 31 under the influence of the fluid pressure in the passages 8, 9 and 10. As shown in H08. and 12 and as previously described, the balanced pistons 14,

' 15 and 16, which are in themselves well known in the art and have different effective areas on opposite ends, are disposed in the large diameter passages 8, 9 and 10. The balanced pistons 14, 15 and 16 are pushed into sealing contact with the stationary member 33 by the fluid pressure acting thereon. Further, in each of the large diameter passages 8, 9 or 10, there is disposed a coil spring 23, 24 or 25 acting between the balanced piston 14, 15 or 16 and the stepped portion 17, 18 or 19 formed between the large diameter passage 8, 9 or 10 and the small diameter passage 5, 6 or 7. Each of the springs 23, 24 and 25 serves to urge the piston 14, 15 or 16 into the fluid tight contact with the stationary member 33, and the sliding member-22 with the port member 31 so as to prevent fluid leakage even when there is sudden increase in pressure in the ports P, A and B which may be experienced for example at the starting period. By this arrangement, the spring force and the fluid pressiirifserve to prevent fluid leakage between the sliding member 22 and the members 31 and 33.

Since the illustrated valve is constructed as described above, when the sliding member 22 is positioned at the neutral position shown in H0. 5, all ports are blocked with each other, and when the sliding member 22 is shifted by means of the lever 39 to the position shown in FIG. 12, the pump port P is connected to the cylinder port B and the tank port T is connected to the cylinder port A, while when the member 22 is shifted to the extreme right position, the pump port P is connected to the cylinder port A and the tank port T is connected to the cylinder port B. Thus, by selectively shifting the sliding member 22, the pump port P can be selectively connected with either of the cylinder ports A and B. Further, in this valve, the small diameter passages 5, 6 and 7 are always maintained in communication with the passages 1, 2 and 3 respectively, and the cross-sectional area of the large diameter passages 8, 9 and 10 are equal to or larger than the forementioned effective area 0, d and e, so that the fluid force acting on the area 0, d and e and tending to urge the port member 31 and the sliding member 22 apart is overcome by the fluid force acting on the sliding member 22 so as to urge it toward the port member 31. Moreover, the latter fluid force is assisted by the spring force obtained through the action of the springs 23, 24 and 25. Further, the balanced pistons 14, 15 and 16 are urged to the stationary member 33 by the fluid pressure difference acting thereon and the said spring action, so that the leakage through the gap between the sliding member 22 and the stationary member 33 is always prevented. It should be noted that, in the illustrated valve, the aforementioned disadvantages of the conventional valve in that the pump port comes in communication simultaneously with the tank port T via the valve chamber can be effectively eliminated.

Further, in the aforementioned arrangement in which the sliding member 22 is provided with said stepped fluid passages 11, 12 and 13, the amount of the force acting on the sliding member 22 so as to force it toward the port member 31 is determined by the difference between the cross-sectional area of the large diameter passage and the small diameter passage and also by the spring force. Therefore, it is possible to select said area difference and the spring force to a minimum required value so that the valve may be operated with a minimum force even when it is used in an extremely high pressure line. Still further, the illustrated valve is advantageous in that, in addition to the perfect prevention of the fluid leakage through the gaps between the sliding member 22 and members 31 and 33 as described above, the fluid under pressure passing through the valve passes from each of the ports in the port member 3l through only the small diameter passage 6 of the stepped fluid passage 12, and does not pass through any one of the large diameter passages 8, 9 and 10 having the balanced pistons 14, 15 and 16 respectively disposed therein, so that the internal flow resistance can be substantially reduced and thus any efficiency loss due to the internal resistance of the valve can be prevented.

Further, the directional control valve in accordance with the present invention is advantageous over any known spool type directional control valve in that, even when the valve components such as the port member 31, the sliding member 22, the stationary member 33 and the balanced pistons 14, and 16 have worn through the extended usage, since they are so arranged that they are mutually brought into a.fluid tight contact by the fluid pressure, any wear on the sliding surfaces can be compensated and does not become unusable as in the case of a spool type valve. Thus, the valve of the present invention is extremely durable, and since all of the sliding surfaces are flat, uniform products can be obtained only by surface grinding. Accordingly, the valve structure of the present invention is very suitable for mass-production and is effective for obtaining high quality products.

Further, in the aforementioned embodiment, it is very important to note that the valve may be modified in various ways by simply changing the passages, grooves, etc. A few examples of the modifications will now be described.

1. Various types of valves can readily be obtained by slight modifications of the sliding member 22. For example, as shown in FIG. 13, by simply providing a relief groove 26 in the sliding member 22 so as to provide a communication among the ports P, B and A at the neutral position, an all port open type four way control valve (FIG. 13a) may be obtained. Further, as shown in FIG. 14, by providing a communication passage 27 for connecting the relief grooves 49 and 50, a tandem center type four way control valve (FIG 14a) may be obtained. Similarly, various modifications can be very easily made.

2 The present invention has been described with respect to a directional control valve having a pair of cylinder ports A and B, but the present invention can be embodied in a multiple control valve having a plurality of pairs of cylinder ports A, A etc. and B, B etc. Further, the valve in accordance with the present invention may be combined with one or more auxiliary mechanism. For example, a suitable unloading mechanism may be employed and operated with the sliding member 22, or a plurality of suitable load holding mechanism may be arranged in the cylinder ports A and B so as to obtain a plurality ofdifferent working pressure.

3. Although the present invention has been described with respect to an example embodied in a reciprocating type control valve, it can be embodied in a valve of rotary type without any inconvenience. Irrespective of whether the valve is of a reciprocating type or a rotary type, it can be designed as either a manual, an electro-solenoid or a solenoid controled pilot operated type.

4. In the above described embodiment, the tank port T has been explained as being opened to the tank. However, in the valve according to the present invention, since the ports P, A and B are not opened to the tank, the tank port T may be subjected to a back pressure by only providing a drain port and without necessity of designing as a pressure chamber type. This is one of the most important features of the present invention and will be described later in more detail.

The first embodiment of the present invention has been described above, and it will be clear that in the above described valve the aforementioned problems of the known valve have substantially been overcome. However, it is not a perfect balanced type as explained below. Therefore, it is suitable for a low pressure or medium pressure use rather than a high pressure use. (A valve which is suitable for a high pressure use will be described later as the second embodiment of the present invention.)

In the first embodiment, there will be no problem when the sliding member 22 is in the neutral position. However, when it is shifted for example to the extreme left position as shown in FIG. 15 in which the pump port P is in communication with the cylinder port B through the small diameter passage 6 of the stepped fluid passage 12 and the cylinder port A is in communication with the tank port T through the relief groove 50, the sliding member 22 will be subjected to upwardly directed fluid forces acting at the center of the ports B, P and A and designated by reference letters R, S and T respectively, and downwardly directed fluid forces acting at the center of the large diameter passages 8, 9 and 10 and designated by the reference letters U, V and W. Since the illustrated valve is an internal drain type, the upwardly directed force T and the downwardly directed force W cancel each other, and as a result, the resultant force f of the upwardly directed forces R and S and the resultant force F of the downwardly directed forces U and V act on the sliding member 22 at different points as shown in FIG. 15. With regard to the moments of the forces f and F about an imaginary point M on the port member 31, unless the product of the resultant force F and the distance between the point M and the point on which the resultant force F acts is larger than that of the resultant force f and the distance between the point M and the point on which the resultant force facts, the sliding member 22 will have a tendency of aparting from the port member 31. Therefore, the resultant force F should be greater than the resultant force f. Thus, the pressures acting on the sliding member 22 are not perfectly balanced. Accordingly, in the above described valve, the slidingmemben 22 wil l be disturbed in its free sliding movement as the system pressure increases.

The second embodiment, which will now be described with reference to FIG. 16, is intended to eliminate the above disadvantages encountered in the structure of the first embodiment,

" "and has a movable member comprising a floating member and a sliding member, said floating member being provided with stepped fluid passages similar to those in the aforementioned structure. By this arrangement, the fluid pressure acting on the movable member is perfectly, balanced and thus the movable- :mernber will become operable with a small force even when the system pressure is high. Further, in the arrangement, the advantageous features of the above described embodiment are fully retained.

In FIG. 16, there is shown by a longitudinal section a reciprocating type directional control valve embodying the feature of the present invention. In this embodiment, the corresponding parts are designated by the same references as in the previous embodiment. This valve is a four way, all port block, no-spring, three detent position type valve as shown in 7 FIG. 16a, and comprises a valve body including a ported member 31, a stationary member 33 and a housing 34 assembled with interposition of gaskets 36 so as to define a valve chamber V. A port member 35 is mounted on the ported member 31. Within the valve chamber V, there is disposed a rectangular sliding member 22 and a floating member 30, the sliding member 22 being in face-to-face contact at its lower surface with the upper surface of the ported member 31 and at its upper surface with the lower surface of the floating member 30. The floating member 30 is disposed between the sliding member 22 and the stationary member 33 with some clearance in the vertical direction, while it is restricted in longitudinal movement by the housing 34. A rear rod 37 is connected at its inner end to the left end of the sliding member and extends outwardly through the housing. Similarly, a front rod 38 is connected at its inner end with the right end of the sliding member 22 and extending outwardly through the housing 34. An operating lever 39 is pivotally connected to the outer end of the front rod 38 for giving the reciprocal movements thereto. The rear rod 37 is provided with three recesses for engagement with a detent spring and ball means 40. By operating the lever 39, the sliding member 22 is selectively moved against the action of the detent means 40.

As shown in FIGS. 17, 18 and 19, the ported member 31 is formed, on the surface a which is in contact with the sliding member 22, with grooves 12 communicating through a passage 44 with the tank (not shown). The ported member 31 is further provided with passages 41, 42, 43 and 44 adapted to be connected respectively with the ports B, P, A and T of the member 35. The passages are so arranged that, irrespective of position of the sliding member 22, the passages 46, 48, and 47 provided in the sliding member 22 (refer to FIG. 20) are always in register with the passages 41, 42 and 43 respectively (FIG. 23). Further, as shown in FIGS. 20 and 21, the passages 46, 47 and 48 pass through the sliding member 22 so thatthe fluid pressure introduced into the passages 41, 42 and 43 does

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