ELECTROMAGNETIC DIRECTIONAL CONTROL VALVE

Abstract: An electromagnetic directional control valve for chang­ ing over flow paths of fluid comprises a plunger (16) disposed in a case (10, 10′, 42) and being capable of moving from a neutral position in one axial direction by a first solenoid (12A) and in the other axial direction by a second solenoid (12B) to participate in the changeover of the flow paths. First and second stoppers (17A, 17B) bearing against the plunger (16) are moved together with the plunger respectively in one axial direction and the other axial direction. First and second springs (18A, 18B) biase the first and second stopper (17A, 17B) respectively in the direction of abutting against the plunger (16). The plunger (16) is stopped at the first neutral position held by the first and second springs (18A, 18B), at a second position to which the plunger is moved in one axial direction by the first solenoid (12A) against the first spring (18A) and a third position to which the plunger is moved in the other axial direction by the second solenoid (12B) against the second spring (18B).

Description: BACKGROUND OF THE INVENTION Field of the Invention: This invention relates to an electromagnetic directional control valve capable of changing over flow paths of fluid to three different positions and, more particularly to a compact electromagnetic directional control valve which can be housed in a tubular member having a relatively small size such as a piston rod. Description of the Prior Art: A prior electromagnetic directional control valve as disclosed in the US-PS 3 701 366 In the case of this known valve a plunger is provided for opening and closing the flow paths. This plunger is held in its neutral position by means of the biasing means. At both sides of the plunger electromagnetic means are provided in the axial direction; by activating them the plunger is adjustable in one axial direction. An actuating member, which is displaced axially when the corresponding electromagnetic means is activated and at least partly transmits this axial displacement to the plunger by means of mechanical engagement of its pusher with its plunger, serves to adjust the plunger in each case. By means of the thus effected axial shift of the plunger the flow paths of the valve are opened and closed. The plunger serves exclusively as a valve element. Its actuation is effected by means of the two actuating members. One actuating member is disposed in the axial direction on the right side of the plunger, the other on the left side of the plunger. In addition, every actuating member is fixedly connected to the corresponding pusher extending in the axial direction. Thus, the entire axial extension of the electromagnetic directional control valve known from the US-APS 3 701 366 is comparatively long. Moreover, it has a large number of individual parts, which leads to a correspondingly complex assembly. SUMMARY OF THE INVENTION It is the object of the invention to develop the electromagnetic directional control valve according to the preamble such that its axial extension is diminished and the number of its individual parts is reduced. According to the application this object is achieved by an electromagnetic directional control valve in which, the plunger is made of magnetic material and has flow paths capable of affording communication with the flow path provided in the tubular case. Thus the plunger serves as a valve body. Furthermore, this plunger or valve body is actuated immediately and directly by the electromagnetic means, i.e. without interposing any kind of actuating members. Delays between the excitation of the electromagnetic means and the adjustment of the plunger are eliminated. It is no longer necessary to dispose actuating members between the plunger and the electromagnetic means. Since in the case of the subject matter of the application it is possible to dispense with the actuating members and due to the design of the flow paths within the plunger itself the electromagnetic directional control valve according to the subject matter of the application can be built significantly smaller and more compact compared to the prior art. BRIEF DESCRIPTION OF THE DRAWINGS The other objects and features of the present invention will become apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings, in which; Fig. 1 is a longitudinal sectional view showing a first embodiment of an electromagnetic control valve according to the present invention; Fig. 2 is a sectional view taken along the line 2-2 in Fig. 1; the electromagnetic control valve according to the present invention. PREFERRED EMBODIMENTS OF THE INVENTION Reference numeral 10 designates a yoke serving as a case and made generally cylindrically. In Fig. 1, a first electromagnetic means having a first bobbin 11A including a cylindrical portion, a first coil 12A and a first core 13A is fixed to an upper interior of the yoke 10. To the inside of the cylindrical portion of the first bobbin 11A is fixed a first sleeve 14A made of non-magnetic material. A second electromagnetic means having a second bobbin 11B, a second coil 12B and a second core 13B is fixed to a lower interior ofthe yoke 10 coaxially with the first electromagnetic means. A second sleeve 14B is fixed to the inside of the cylindrical portion of the second bobbin 11B. To an intermediate position between the first and second electromagnetic means, as shown in Fig. 2, is fixed a third cylindrical core 15 formed radially with four first ports 15c. The yoke 10 is formed on an inner peripheral surface with an annular groove 10a, from which are provided four holes 10b to an outer peripheral surface. Therefore, a necessary area of flow path is ensured even if the third core 15 is rotated to move the port 15c out of the hole 10b of the yoke 10. A cylindrical plunger 16 made of magnetic material is movably housed inside of the third core 15. In the embodiment shown, the plunger 16 is formed on an outer peripheral surface at an axial interval with annular grooves 16a,16b. Three orifices 16d,16e are radially formed to afford communication between a flow path 16c provided in the plunger 16 and said annular grooves 16a,16b respectively. Thus, the plunger 16 serves also as a valve body. Each of the orifices 16d is different from each of the orifices 16e in the size of bore so that different quantity of liquid can flow therethrough. All of orifices 16e do not align with all of ports 15c even if the plunger 16 is rotated, since the number of orifices 16e differs from that of the ports 15c. As a result, change of flow resistance hardly occurs. The plunger 16 is provided on both ends with a first non-magnetic stopper 17A moved from a neutral position of the plunger in one axial direction together with the plunger 16 and a second non-magnetic stopper 17B moved from the neutral position in the other axial direction together with the plunger 16. The first and second stoppers 17A,17B are pressed to bear against the end faces of the plunger 16 respectively by first and second springs 18A,18B supported by the first and second cores 13A,13B and having relatively small spring constant respectively. The first stopper 17A is regulated not to move from a position in which it contacts one end 15a of said third core 15 to the lower portion of Fig. 1, i.e., toward the second electromagnetic means. Similarly, the second stopper 17B is regulated not to move from a position in which it contacts the other end 15b of the third core 15 toward the first electromagnetic means. Under these conditions occupies the plunger 16 the neutral position. Further, in the drawing, reference numeral 13c designates a flow path provided in the center of the second core 13B, 19 a sealing O-ring, 20 a second port formed in the yoke 10, 21 lead wires for supplying current to the first and second coils 12A,12B and 22 terminals. Next will be described the operation of the valve on the basis of said constitution. Normally, i.e., when the both first and second coils 12A,12B are not excited, the plunger 16 is pressed by the first and second springs 18A,18B through the first and second stoppers 17A,17B to be located at the first position (hereinafter referred to as the neutral position). As a result, the first and second ports 15c,20 communicate to each other through the orifices 16e in the plunger 16. When the first coil 12A is excited and the second coil 12B is not excited, the plunger 16 is attracted upward as viewed in Fig. 1. Then the second stopper 17B abuts against the end 15b of the third core 15 to be restrained from the movement above that position so that the plunger 16 is moved easily to the second position (hereinafter referred to as one side position) against only the set load of the spring 18A. As a result, the first and second ports 15c,20 are closed by the plunger 16 into the completely closed condition. Next, when the first coil 12A is not excited and the second coil 12B is excited, the plunger 16 is attracted downward as viewed in Fig. 1. Then, the plunger 16, reversely to the above mentioned, is moved easily to the third position (hereinafter refered to as the other side position) against only the set load of the second spring 18B. As a result, the first and second ports 15c,20 will communicate to each other through the orifices 16d in the plunger 16, the path area, i.e., flow resistance of the orifices 16d being different from that of the orifices 16e at said neutral position. As above mentioned, a directional control valve is provided which is operatively changed over to three positions by controlling the current supply to the first and second coils 12A,12B. Next will be described the effects of the present invention with reference to said embodiment. First, the prior directional control valve shows characteristics shown in Fig. 3. That is, a press force of the spring constant composed of two springs multiplied by the stroke of movement of the valve body, i.e., the press force proportional to the stroke acts on the valve body. Thus, when a upward force +P is applied to the valve body or a downward force -P is applied to same, the valve body is moved upwardly or downwardly by the stroke S proportional to the force P from the neutral position in which it is held by the two springs so that the valve body is not stationarily stabilized in the neutral position. On the other hand, the present invention has characteristics shown by the solid line in Fig. 11. Namely, when the plunger is moved upwardly from the neutral position by a small distance, the second spring 18B is regulated by the second stopper 17B as above described, so that the plunger 16 receives the load P set by the first spring 18A (hereinafter referred to as P for convenience) and when moved, further receives a press force proportional to the stroke (with the spring constant of only the first spring 18A being the proportional constant ). Similarly, when the plunger is moved downwardly, it receives same press force. Accordingly, when the force acting on the plunger 16 and the valve body 26 is less than P, both are stabilized stationarily in the neutral position. Thus, even if the respective spring constants of the first and second springs 18A,18B are reduced, the plunger 16 and the valve body 26 are stopped stationarily by a certain stationary force when the predetermined set load P is applied to the spring by the compression thereof and the vibration force is less than P. Further, when a small clearance R exists between the plunger 16 and the first and second stoppers 18A,18B, as shown by the dotted line in Fig. 4, the plunger is moved by the small stroke R. However, it goes without saying that the plunger can receive a certain stationary force against the movement larger than the clearance R. Also, the certain stationary force can be obtained even by reducing the spring constants of the first and second springs 18A,18B so that the present invention has excellent effects of providing the compact first and second coils 12A,12B.

Claims: An electromagnetic directional control valve for changing over flow paths of fluid comprising a tubular case (10), first and second electromagnetic means (11A, 12A, 13A, 11B, 12B, 13B) fixed spaced axially from each other in said tubular case (10), a plunger (16) disposed in said case (10) and being capable of moving from a neutral position in one axial direction by said first electromagnetic means (11A, 12A, 13A) and in the other axial direction by said second electromagnetic means (11B, 12B, 13B) to participate in the changeover of said flow path, and first and second biasing means (18A, 18B) for biasing said plunger (16) toward its neutral position, said plunger (16) also having a second position to which said plunger (16) is moved in one axial direction by said first electromagnetic means (11A, 12A, 13A) against said first biasing means (18A) and a third position to which said plunger (16) is moved in the other axial direction by said second electromagnatic means (11B, 12B, 13B) against said second biasing means (18B), characterized in that said plunger (16) is made of magnetic material and has flow paths (16d, 16e) capable of affording communication with flow paths (10b) provided in said tubular case (10), the plunger thereby also serving as a valve body. An electromagnetic directional control valve according to claim 1, further comprising a first stopper member (17A) bearing against said plunger (16) to be moved in one axial direction together with said plunger (16) and a second stopper member (17B) bearing against said plunger (16) to be moved in the other axial direction together with said plunger (16), said first and second stopper members (17A, 17B) being made of non-magnetic material and being biased by said first and second biasing means (18A, 18B), respectively, in the directions of abutting said plunger (16). An electromagnetic directional control valve according to claim 2, wherein said plunger (16) is disposed movably in a tubular core (15) and said first and second stopper members (17A, 17B) abut against said core (15) to be blocked from further movement. An electromagnetic directional control valve according to claim 3, wherein said plunger (16) occupies its neutral position when said first and second stopper members (17A, 17B), respectively, bear against said tubular core (15). An electromagnetic directional control valve according to claim 2, wherein said first and second stopper members (17A, 17B), respectively, bear against end faces of said plunger (16). An electromagnetic directional control valve according to one of the claims 1 to 5, wherein said flow paths of the plunger (16) are two (16d, 16e) extending diametrally and spaced axially from each other and afford communication through small and large flow path sections. An electromagnetic directional control valve according to claim 6, as far as claim 6 is directed to claims 3 and 4, wherein said tubular core (15) has a flow path (15C) extending radially and communicating with said flow path (10b) of the case (10), the flow path (15C) being capable of communicating with said two flow paths (16d, 16e). An electromagnetic directional control valve according to claim 7, wherein said respective flow paths (16d, 16e) of said plunger (16) consist of a plurality of ports, and said flow path (15C) of said tubular core (15) consists of a number of ports different from that of each of said flow ports in said plunger (16).

Inventors: MASAKI, KAZUO, MURATA, SYUUJI, NAKAGAWA, KIYOHARU, SANADA, YUKITOMO, SATO, HIROKI, YOKOYA, YUJI
Applicants: NIPPONDENSO CO., LTD., TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1985
Main classification: B60G17
IPC codes: B60G17, F16F9