HYDRAULIC CONTROL VALVE

Abstract: A hydraulic control valve in a construction machine, wherein a parallel port (20b) and a bridge port (20c) which are provided in avalve body (40) of the hydraulic control valve are formed by machining, cylinder drain ports (20e) are limited to through holes opened on opposite sides of the valve body (20) and caused to join together in a tank port block (39). Accordingly, when the valve body (40) is manufactured by casting, only a main core (19) forming a spool port (13h) need be used, so that the control valve can be made compact in size. Furthermore, portions (20', 21') where a passage of a neutral port of the core has heretofore been formed by jointing the main core (19) to joint cores (20, 21) are formed by machining a manual operation process of jointing can be dispensed with and the working efficiency and casting accuracy are improved. Further a safety valve (43) and a suction valve (44) are formed separately from each other, and these valves are provided separately on the valve body (40), so that the valve body has a simplified construction and is made compact in size.

Description: TECHNICAL FIELD The present invention relates to a hydraulic control valve adapted for use in a construction machine such as a power shovel. BACKGROUND TECHNOLOGY A conventional power shovel as known from JP-U-56-139064 comprises, as illustrated in Fig. 9, a lower self-propelled movable body 1 driven by a propelling motor, not shown, an upper turntable 2 capable of being turned by a turning motor, not shown, and a working machine 3 mounted at the front portion of the turntable 2. The working machine 3 has a boom 6 which can be swung rightward and leftward by a swinging cylinder 4 and movable vertically at the tip end thereof by a boom cylinder 5 and an arm 8 pivotally mounted at the tip end of the boom 6 which is turned by an arm cylinder 7. The arm 8 has a tip end to which a bucket 10 is attached so as to be turned by a bucket cylinder 9. A blade 12 which is vertically movable by a blade cylinder 11 is mounted at the front portion of the movable body 1. A hydraulic control valve 13 provided at each actuator controls the propelling motor, the turning motor and hydraulic actuators composed of various cylinders. Each hydraulic control valve 13 is, as illustrated in Fig. 10, normally connected with one another. Each hydraulic control valve 13 comprises, as illustrated in Fig. 11, a valve body 13a, a spool 14 housed in the valve body 13a for switching oil passages in the valve body 13a, the spool 14 normally retained at a neutral position by a return spring 13b wherein an oil under pressure supplied to a pump port 13c is drained through a drain port 13d into a tank 16 by way of a port block 15. The valve body 13a of the hydraulic control valve 13 is, as illustrated in Fig. 12, conventionally formed integrally by casting. However, in the conventional hydraulic control valve 13, a main core for forming a spool port 13h is complex so that narrow passages can not be formed in the hydraulic control valve 13 since a cylinder drain port 13e, a bridge port 13g and the spool port 13h are separately formed in three stages. As a result, this was the obstacle to make the hydraulic control valve compact in size since the diameter of the spool port 13h could not be less than that ranging from 11 mm to 12 mm. The present invention has been made in view of the problem set forth above and is to provide a hydraulic control valve capable of manufacturing a valve body without using cores having complex structures. Particularly, the conventional control valve body is, as described above, integrally formed by casting and a passage of a neutral port in a valve chamber is also formed by casting wherein cores are employed for forming the passage of the neutral port at the time of casting. The core is formed, as illustrated in Fig. 13, by casting a main core 19 for forming the spool port 13h and thereafter by jointing joint cores 20 and 21 to the main core 19. There was a problem in that a mold can not be splitted along the line X-X when forming the core if the jointing cores 20 and 21 are integrated with each other, which involves the following drawbacks. (1) A jointing operation of the cores is manually made which results in preventing an automatic assembly of the cores, hence this is inefficient. (2) Jointing deviation between the cores is liable to occur which involves a deteriorated casting accuracy. (3) Casting flash is liable to occur at the jointing portions of the cores. (4) Jointing agent causes generating gas at the time of casting which is likely to generate a casting porosity. Accordingly, it is a second object of the present invention to provide a hydraulic control valve capable of manufacturing a valve body by machining the passage without using the conventional jointing cores, whereas the passage was conventionally formed by the jointing cores. The valve body 13a of the conventional control valve 13 forms therein, as illustrated in Fig. 14, a parallel port 13f, the bridge ports 13g, cylinder ports 13i and the cylinder drain port 13e wherein a load check valve 17 for allowing the oil under pressure only to flow from the parallel port 13f into the bridge port 13g is provided between the parallel port 13f and the bridge port 13g and a hydraulic cylinder 18 is connected to the cylinder ports 13i therebetween. If the spool 14 of the control valve 13 having the arrangement set forth above is moved rightward, the oil under pressure introduced into the pump port 13c reaches the parallel port 13f and pushes the load check valve 17, then flows into the bridge ports 13g. The oil under pressure is further introduced into a bottom side of a hydraulic cylinder 18 from cylinder ports 13i which communicates with the spool 14 by the movement of the spool 14 so as to stretch the hydraulic cylinder 18 whereas the oil under pressure at the side of the cylinder rod flows from the cylinder ports 13i to the cylinder drain port 13e and thereafter drained into a tank 16. During the operations set forth above, if a shock is applied to the hydraulic cylinder 18 or a tensile force acts on the hydraulic cylinder 18 for some reasons, an anomalous pressure or a negative pressure is generated in the hydraulic circuit which causes the hydraulic cylinder 18 to be damaged or unstable. As a result, this is likely to cause an obstruction for working. To prevent such a problem, a suction safty valve 120 is conventionally provided, as illustrated in Fig. 15, between the cylinder ports 13i and the cylinder drain port 13e for preventing the anomalous pressure or the negative pressure from being generated. That is, when the anomalous pressure is generated in the cylinder ports 13i a poppet 121 provided inside the suction safty valve 120 is released so that the pressure inside the cylinder ports 13i is relieved into the cylinder drain port 13e to prevent the anomalous pressure from being generaed in the hydraulic circuit. When the negative pressure is generated in the cylinder port 13i, a suction valve 122 is released by the negative pressure so that the oil under pressure in the tank 16 is introduced into the cylinder port 13i from the cylinder drain port 13e whereby the negative pressure is prevented from being generated in the hydraylic circuit. Inasmuch as the conventional hydraulic control valve 13 has the suction safty valve 120 serving as the safty valve function and the suction valve function combined in a single valve so that the structure of the valve is complex which impedes the miniaturization thereof. DISCLOSURE OF THE INVENTION To achieve the above object, a hydraulic control valve according to the present invention is provided with the features of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a lateral cross sectional view of a hydraulic control valve according to an embodiment of the present invention, Fig. 2 is a vertical cross sectional view of the hydraulic control valve in Fig. 1, Figs. 3 and 4 are view showing operations of the hydraulic control valve in Fig. 1, Figs. 5(a) and 5(b) are views showing hydraulic control valves according to another embodiment of the present invention wherein a main core forming a spool port and the shape of casting are respectively explained illustratively which are cross sectional views taken along V-V in Fig. 12, Fig. 9 is a perspective view of a construction machine which is an object to be controlled by the hydraulic control valve, Fig. 10 is a plan view of a conventional hydraulic control valve, Fig. 11 is a lateral cross sectional view of Fig. 10, Fig. 12 is a cross sectional view of a valve body, Fig. 13 is a cross sectional view explaining a main core for forming a spool port of the valve body of the conventional hydraulic control valve, Fig. 14 is an enlarged vertical cross sectional view of the conventional hydraulic control valve and Fig. 15 is an enlarged view of a suction safety valve of the conventional hydraulic control valve. BEST MODE FOR CARRYING OUT THE PRESENT INVENTION Embodiments of the present invention will be described with reference to drawings. Referring to Figs. 1 and 2, designated at 40 is a valve body, 41 is a spool slidably housed in a spool port 20a of the valve body 40, 22 is a return spring for retaing the spool 41 at a neutral position, 43 is a safety valve, 44 is a suction valve and 25 is a load check valve. The valve body 40 has a parallel port 20b and bridge ports 20c which are respetively formed by machining by way of a hole 20h to which a load check valve 25 is attached. The load check valve 25 is attached between the parallel port 20b and the bridge ports 20c for allowing an oil under pressure to flow merely from the parallel port 20b into the bridge ports 20c. Cylinder ports 20d are formed at both sides of the bridge ports 20c and connected to a bottom side of a hydraulic cylinder 27 and a rod side of the hydraulic cylinder 27 by way of lines 28. Cylinder drain ports 20e are provided as through holes at both sides of the cylinder ports 20d so as to penetrate both side surfaces of the valve body 40. A drain passage 30a in a tank port block 39 attached to the side surface of the valve body 40 is connected to the cylinder drain ports 20e. The drain passage 30a in the tank port block 39 is also connected to drain ports 20e of the valve body 40 so that the oil under pressure discharged from a pump port 20g to the drain ports 20e is drained into a tank 31 through the drain passage 30a when the spool is retained at the neutral position. Operations of the hydraulic control valve will be described hereinafter. If the spool 41 is moved e.g. rightward in order to control the hydraulic cylinder 27 provided in the construction machine and the like, the oil under pressure introduced into the pump port 20g flows into the parallel port 20b to push the load check valve 25 so that the parallel port 20b communicates with the bridge ports 20c and the oil under pressure flows into the bridge ports 20c as illustrated in Fig. 3. The oil under pressure thus flown into the bridge ports 20c flows into the cylinder ports 20d which communicate with the bridge ports 20c by the movement of the spool 41 and further flows into the bottom side of the hydraulic cylinder 27 so as to stretch a rod of the hydraulic cylinder 27. The oil under pressure at the rod side of the hydraulic cylinder 27 is introduced into the cylinder drain ports 20e communicating with the cylinder ports 20d by the movement of the spool 21 and further flows into the drain passage 30a of the tank port block 39 as illustrated in Fig. 4 (a cross sectional view taken along IV-IV in Fig. 3), and is finally drained into the tank 31. When the spool 41 is moved leftward, the operation of the hydraulic control valve is same as that mentioned just above excepting that the rod of the hydraulic cylinder 27 is moved inside the cylinder. Accordingly, the explanation of the operation in this case is omitted. Inasmuch as the parallel port 20b and the bridge ports 20c inside the valve body 40 are respectively formed by machining and jointing portions of the right and left cylinder drain ports 20e are provided outside the valve body so that the port formed inside the valve body at the time of casting employs only the main core for forming the spool port, which facilitates the manufaturing of the valve body. As illustrated in Fig. 12, the passage of the neutral port in the valve chamber is formed by casting and the core is used for forming this passage at the time of casting wherein the spool port 13h is formed by the main core 19. The embodiment of the present invention is characterized in that the passage portion of the neutral port, which was conventionally formed by jointing the joint cores 20 and 21 to the main core 19, can be formed by machining. That is, the portions as denoted 20' and 21' in Fig. 5(b) are passage portions conventionally formed by the cores but they can be formed by machinig according to the present invention. As a result, the joint cores can be eliminated and the formation of the core can be composed of only the main core 19 as illustrated in Fig. 5(a) which solves the various drawbacks accompanied by the adoption of the conventional joint cores and improves the casting accuracy. INDUSTRIAL UTILIZATION As mentioned in detail above, according to the present invention, the parallel port and the bridge ports in the valve body are formed by machining and the jointing portions of the right and left cylinder drain ports are provided outside the valve body so that the ports formed in the valve body at the time of casting comprises only the spool port which can be formed by one main core. With the arrangement set forth above, since the valve body can be casted with use of the single-stage core, a narrow spool port can be formed in the control valve, so that the spool having a diameter less than 10 mm can be manufactured with ease which facilitates the miniaturization thereof and reduction of weight thereof. Since the passage portion conventionally formed by the joint core jointed to the main core for forming the spool port can be formed by machining, it is possible to dispense with the joint cores so that the core is formed by only the main core. As a result, it is possible to automatically form the core assembly whereby the working efficiency can be improved conspicuously and the jointing deviation of the core and the casting flash at the jointing portion and the casting porosity due to the generation of the gas of the jointing agent can be respectively eliminated. As a result, the casting accuracy can be improved.

Claims: A hydraulic control valve for controlling an actuator provided in a construction machine, comprising a parallel port (20b), bridge ports (20c), cylinder ports (20d) for connection to the hydraulic actuator, cylinder drain ports (20e) for connection to a tank (31), a pump port (20g) for connection with a hydraulic pump, said pump port (20g) being connected to said parallel port (20b) and said parallel port (20b) being connected to said bridge ports (20c) through a single load check valve (25); said ports (20) being respectively provided in a valve body of the hydraulic control valve, and a spool (41) movably provided in the valve body for controlling fluid flow between said cylinder ports (20d) and a said bridge port and a said cylinder drain port respectively, thus controlling the movement of said hydraulic actuator, characterized in that said parallel port (20b) and said bridge ports (20c) are formed by machining, and said cylinder drain ports (20e) are merely through holes opened to both sides of the valve body, said cylinder drain ports jointing into a drain passage (30a) in a tank port block (39) attached to a surface of the valve body (40). A hydraulic control valve according to Claim 1, characterized in that a core to be used for forming a neutral port in a valve chamber at the time of casting the valve body is formed only by a main core and a passage portion which was conventionally formed by joint cores jointing to the main core is formed by machining.

Inventors: TOMINAGA HIROYOSHI, TOMINAGA, HIROYOSHI
Applicants: KOMATSU ZENOA KK, KOMATSU ZENOAH KABUSHIKI KAISHA
Application year: 1991
Main classification: F16K27
IPC codes: F15B13, F16K27