Solenoid valve

Abstract

 A solenoid valve (1) comprises a fixed core (10), a bottomed tube (20) formed of a non-magnetic material and having a bottom (21), a movable core (30) slidably received within the bottomed tube (20) and opposed to the fixed core (10) with a gap therebetween, and a solenoid (60) for causing the movable core (30) to operate. The solenoid valve (1) also comprises a protruding portion (25,25') which is formed on the bottom (21) of the bottomed tube (20) and which protrudes in a direction of sliding of the movable core (30). The protruding portion (25,25') may comprise a plurality of convex-shaped protruding portions (25), a ridge-shaped protruding portion (25,25') extending along a whole circumference of the bottom (21) of the tube (20) or a plurality of ridge-shaped protruding portions (25,25') formed at circumferential equal intervals along a circumference of the tube bottom (21). The or each protruding portion (25,25') has a predetermined height.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] This invention relates to a solenoid valve.

Description of the Prior Art

[0002] A conventional solenoid valve includes a fixed core, a movable core slidably received within a bottomed tube formed of a non-magnetic material such that it is opposed to the fixed core via the non-magnetic material of the bottomed tube, and a solenoid which causes the movable core to operate.

[0003] FIG. 1 is an enlarged partial cross-sectional view showing a portion of a conventional solenoid valve e.g. of a spool valve type arranged in a hydraulic system for controlling the flow path of hydraulic oil to thereby control the pressure of the hydraulic system.

[0004] In the conventional solenoid valve 100, a movable core 130 is received within in a bottomed tube 120 formed of a non-magnetic material to thereby separate the movable core 130 from a fixed core 110 by the non-magnetic material for smooth sliding of the movable core 130.

[0005] According to the solenoid valve 100, a solenoid, not shown, is energized or excited by sending electric current therethrough to drive a spool to thereby control the flow path of hydraulic oil flowing in the hydraulic system whereby the pressure of the hydraulic system is controlled.

[0006] However, when the movable core 130 is magnetically attracted by the fixed core 110 and is moved close to the same, due to a short stroke (distance between the movable core 130 and the fixed core 110), an electromagnetic attractive force acting between the fixed core 110 and the movable core 130 can be sharply increased to cause the movable core 130 to be fixedly attracted to the fixed core 110.

[0007] In this state, the force of attraction acting between the fixed core 110 and the movable core 130 exceeds the expansive force of a spring 91 (see FIG. 2), so that even if the electric current is reduced by a normal control amount, the flow path of hydraulic oil is not changed according to the controlled decrease of electric current and hence the pressure of the hydraulic system is not changed according to the amount of electric current. That is, the pressure of the hydraulic system becomes uncontrollable.

[0008] Once the solenoid valve has entered this condition, only after the attractive force of the solenoid valve decreases to a level which the expansive force of the spring 91 can overcome, the flow path of hydraulic oil comes to be changed according to the amount of electric current and hence the pressure of the hydraulic system becomes controllable.

[0009] In the conventional solenoid valve 100, with a view to securing a normal controllable state in which the pressure of the hydraulic system can be changed according to the amount of electric current, a non-magnetic spacer 125 is arranged on a bottom 121 of the bottomed tube 120 such that a predetermined gap "s" can be formed between the movable core 130 and the fixed core 110 when the movable core 130 is attracted to a position closest to the fixed core 110, to thereby prevent the movable core 130 from being fixedly attracted to the fixed core 110.

[0010] However, the conventional solenoid valve 100 suffers from the following inconveniences:

[0011] Firstly, there is a fear of the solenoid valve being carelessly assembled without the spacer 125.

[0012] Secondly, since the spacer 125 is simply placed on the bottom 121 of the bottomed tube 120, the spacer 125 can be inclined to interfere with the spring 181, i.e. the spacer 125 is caught in the spring 185 during operation of the solenoid valve.

[0013] Thirdly, spacers 125 are generally stored in a state immersed in oil so as to prevent formation of rust thereon, so that a plurality of spacers 125 sticking to each other can be erroneously mounted in a solenoid valve during assembly thereof.

[0014] Fourthly, depending on the tape of product (solenoid valve), a plurality of kinds of spacers 125 are used, so that a spacer 125 having an improper thickness can be erroneously placed in the valve. For instance, when it is required to use a spacer 125 having a normal thickness, and yet a spacer 125 having a larger thickness than the normal thickness is erroneously assembled in a solenoid valve, the solenoid valve cannot operate to allow predetermined pressure to be produced, which makes it impossible for the solenoid valve to function as a hydraulic valve.

[0015] This erroneous assembly of the spacer 125 is difficult to detect, e.g. by reason of the spacer 125 being extremely thin. If a spacer 125 having an improper thickness is erroneously assembled in a solenoid valve, the erroneous assembly of the spacer 125 can be detected, for instance, only by causing the solenoid valve to operate.

[0016] Fifthly, since the bottomed tube 120 is formed of a sheet material by deep drawing, the wall thickness of the bottom 121 of the bottomed tube 120 is limited by the thickness of the sheet material. That is, if the wall thickness of the bottom 121 is increased, the wall thickness of a hollow cylindrical portion 122 is also increased, which makes the magnetizing force of the solenoid (or solenoid coil) ineffectual.

SUMMARY OF THE INVENTION

[0017] It is an object of the invention to provide a solenoid valve having a construction which dispenses with a spacer to thereby improve reliability of the solenoid valve and reduce manufacturing costs of the same.

[0018] To attain the above object, the present invention provides a solenoid valve including a fixed core, a bottomed tube formed of a non-magnetic material and having a bottom, a movable core slidably received within the bottomed tube and opposed to the fixed core with a gap therebetween, and a solenoid for causing the movable core to operate.

[0019] The solenoid valve according to the invention is characterized by comprising a protruding portion formed on the bottom of the bottomed tube, the protruding portion protruding in a direction of sliding of the movable core.

[0020] According to this solenoid valve, since the bottom of the bottomed tube is formed thereon with the protruding portion protruding in a direction of sliding of the movable core, it is possible to cause the fixed core and the movable core to be opposed to each other without interposing any member between the two cores such that the minimum required amount of the gap can be maintained even when the movable core is moved to a position closet to the fixed core,.

[0021] Preferably, the protruding portion comprises a plurality of convex-shaped protruding portions each having a predetermined height.

[0022] According to this preferred embodiment, the minimum required amount of the gap corresponding to the predetermined height of each convex-shaped protruding portion can be easily secured.

[0023] Further preferably, the protruding portion is formed in a manner protruding toward the movable core.

[0024] According to this preferred embodiment, the contact area at which the movable core and the protruding portion meet is small, so that it is possible to reduce collision noise produced when the movable core abuts against the protruding portion.

[0025] Alternatively, the protruding portion is formed in a manner protruding toward the fixed core.

[0026] According to this preferred embodiment, the movable core abuts on the bottom portion of the bottomed tube in a larger area, so that pressure acting on unit surface of the movable core is decreased, and hence abrasion of the movable core can be reduced.

[0027] Preferably, the protruding portion comprises a ridge-shaped protruding portion extending along a whole circumference of the bottom of the bottomed and having a predetermined height.

[0028] Preferably, the protruding portion comprises a plurality of ridge-shaped protruding portions formed at circumferential equal intervals along a circumference of the bottom of the bottomed tube and each having a predetermined height.

[0029] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 

FIG. 1 is an enlarged partial cross-sectional view showing essential parts of a conventional solenoid valve;

FIG. 2 is a longitudinal cross-sectional view showing a solenoid-related portion of a solenoid valve according to an embodiment of the invention;

Fig. 3 is an enlarged partial cross-sectional view showing essential parts of the FIG. 2 solenoid valve;

FIG. 4 is a longitudinal cross-sectional view of a bottomed tube appearing in FIG. 2;

FIG. 5 is a view taken from arrow A in FIG. 4; and

FIG. 6 is a longitudinal cross-sectional view of a variation of the bottomed tube of the solenoid valve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The invention will now be described in detail with reference to drawings showing a preferred embodiment thereof.

[0032] FIG. 2 shows a solenoid-related portion of a solenoid valve of a spool valve type for controlling the flow path of hydraulic oil, according to an embodiment of the invention.

[0033] The solenoid valve 1 includes a fixed core 10, a bottomed tube 20, a movable core 30, a lid member 40, a hollow cylindrical support block 50, a solenoid 60, and a socket 70.

[0034] The fixed core 10 has an outer periphery integrally formed with a case 11 in the form of a hollow cylinder. The case 11 has an open end formed with stepped portions 12, 13 at respective inner and outer peripheral wall surfaces of the open end. The hollow cylindrical support block 50 is mounted on the stepped portion 12, while the socket 70 is mounted on the stepped portion 13.

[0035] The fixed core 10 also is formed with a hollow cylindrical portion 15 having a predetermined height in a central portion thereof. The hollow cylindrical portion has a through hole 14 axially extending therethrough for arranging a spring 81 therethrough. The hollow cylindrical portion 15 has a top portion formed with a recess 16 in which a bottom 21 of the bottomed tube 20 can be fitted.

[0036] The bottomed tube 20, which is formed of a non-magnetic material, such as SUS304G, has the bottom 21 and a hollow cylindrical portion 22. The bottom 21 of the bottomed tube 20 is fitted in the recess 16 formed on the top portion of the hollow cylindrical portion 15 of the fixed core 10. The bottom 21 has a central portion thereof formed with an opening 23 opposed to the through hole 14 of the fixed core 10.

[0037] The movable core 30 is slidably received in the bottomed tube 20. The spring 81 is interposed between one end of the movable core 30 and a plunger 90 through the through hole 14 of the fixed core 10. In the other end of the movable core 30 opens a hole 31 circular in cross-section and extending axially to a predetermined depth.

[0038] The lid member 40 has an outer diameter equal to an outer diameter of the bottomed tube 20. The lid member 40 has an outer peripheral surface thereof formed with a stepped portion 41 for enabling the lid member 40 to be inserted into the bottomed tube 20 via an opening 24 thereof and preventing the whole lid member 40 from falling into the bottomed tube.

[0039] The lid member 40 has one end face, opposed to the movable core 30, formed therein with a recess 42 having the same diameter as the hole 31 formed in the movable core 30. A spring 82 is arranged within space defined by inner walls of the hole 31 and the recess 42. Further, the other end face of the lid member 40 opposite to the one end face thereof opposed to the movable core 30 is formed with a projection 43 for use in positioning the lid member 40.

[0040] The hollow cylindrical support block 50 receives the assembly of the bottomed tube 20 and the lid member 40 therein to cover an outer peripheral surface of the bottomed tube 20 and a top portion of the lid member 40. The hollow cylindrical support block 50 has a flange portion 51 which extends radially outward from an axially intermediate portion of the outer peripheral surface of the hollow cylindrical support block 50. The flange portion 51 is mounted on the stepped portion 12 formed on the inner peripheral surface of the open end of the case 11. The hollow cylindrical support block 50 has an inner closed end surface thereof formed with a recess 52 for engagement with the projection 43.

[0041] The solenoid 60 is comprised of a coil yoke 61 supported in a manner sandwiched between the fixed core 10 and the hollow cylindrical support block 50 via O rings 83, 84 and a coil 62 received in the coil yoke 61. The solenoid 60 is driven for excitation by sending current through the coil 62 to thereby drive a spool, not shown, by way of the movable core 30 and component parts associated therewith, whereby the flow path of hydraulic oil is controlled.

[0042] The solenoid 60 can be powered either with direct current or alternating current. The direct current power supply may be of DC12V or DC24V, while the alternating current power supply may be of AC100V (50/60Hz) or AC200V.

[0043] The socket 70 is formed therethrough with a through hole 71 having an inner diameter substantially equal to the outer diameter of the hollow cylindrical support block 50. The socket 70 has the hollow cylindrical support block 50 inserted through the through hole 71 thereof, and has its inner peripheral edge fitted on the stepped portion 13 formed along the outer peripheral surface of the open end of the case 11.

[0044] In the solenoid valve 1, when electric current is sent through the coil 62 to excite the solenoid, the movable core 30 is magnetically attracted toward the fixed core 10. The magnetically attractive force is transmitted to the spool via the spring 81, a spring 91 arranged on the plunger 90, and the plunger 90. At this time, the spring 91 is contracted, whereas the spring 81, which is set to have a larger spring constant than the spring 91, is only slightly contracted to thereby serve as a damper.

[0045] On the other hand, when the supply of the electric current to the coil 62 is stopped to inhibit the solenoid from being excited, an expansive force of the contracted spring 91 causes the movable core 30 to return to its original position.

[0046] FIG. 3 shows essential parts of the FIG. 2 solenoid valve, on an enlarged scale. FIG. 4 is a longitudinal cross-sectional view of the bottomed tube, and FIG. 5 a view taken from an arrow A in FIG. 4.

[0047] The bottom 21 of the bottomed tube 20 is formed with protruding portions 25 each having a convex shape and a predetermined height from the inner surface thereof and protruding upward (toward the movable core 30) so as to maintain a gap between the movable core 30 and the fixed core 10 even when the movable core 30 is moved to a position closest to the fixed core 10 (see FIG. 4).

[0048] The protruding portions 25 are arranged on the bottom 21 of the bottomed tube 20 at angular intervals of 90 degrees about the vertical axis of the bottomed tube 20.

[0049] In the embodiment, when the movable core 30 is magnetically attracted toward the fixed core 10 to move to a predetermined position, the movable core 30 abuts the protruding portions 25, which prevent the movable core 30 from moving further downward. Therefore, it is possible to maintain a predetermined gap "g" between the movable core 30 and the fixed core 10 (see FIG. 3) even when the movable core 30 moves to the position closest to the fixed core 10 at which the stroke of the movable core 30 is the smallest.

[0050] According to this embodiment, the protruding portions 25 provide the same effect as obtained by the aforementioned spacer 125 of the prior art provided on the bottom 121 of the bottomed tube 120. Further, since the spacer 125 used in the prior art can be dispensed with, they also provide an advantageous effect of reduction of the cost of the material.

[0051] Further, the embodiment provides the following advantageous effect by eliminating the spacer:

[0052] Firstly, there is no fear of a spacer having a thickness larger than required being erroneously used, and hence solenoid valves of uniform performance and high quality can be provided.

[0053] Secondly, no spacer can be caught in a spring during operation of the valve, causing no malfunction ascribable to the spacer.

[0054] Thirdly, there is no fear of a solenoid valve being assembled without placing a required spacer therein, or with a plurality of spacers placed one upon another, so that it is not required to carry out any conventional operations for mounting a spacer and inspection of proper mounting thereof, which makes it possible to reduce costs of assembly and inspection.

[0055] Fourthly, a contact area at which the movable core 30 and the protruding portions 25 meet is smaller than a contact area at which the movable core 130 and the spacer 125 of the prior art meet, so that it is possible to reduce collision noise produced when the movable core abuts against the bottom 21 of the bottomed tube 20.

[0056] Fifthly, the protruding portions 25 are formed on the bottom 21 of the bottomed tube 20, so as to ensure that the predetermined gap is maintained between the movable core 30 and the fixed core 10 even when the movable core 30 moves to the position closest to the fixed core 10, so that it is not required to increase the wall thickness of the bottom 21. As a result, the hollow cylindrical portion 22 of the bottomed tube 20 can be formed to have a thin wall, which makes it possible to prevent the magnetizing force of the solenoid 60 from being decreased.

[0057] Although in the above embodiment, four protruding portions 25 are formed on the bottom 21 of the bottomed tube 20, this is not limitative, but more than four protruding portions may be formed. Further, it is possible to form a ridge-shaped protruding portion 25 having a predetermined width and extending along the whole circumference of the bottom 21. Also, it is possible to form a plurality of ridge-shaped protruding portions 25 having a predetermined width and extending at equal intervals along the circumference of the bottom 21.

[0058] FIG. 6 is a longitudinal cross-sectional view showing a variation of the bottomed tube. Component parts and elements corresponding to those of the above embodiment are indicated by identical reference numerals.

[0059] In the variation, protruding portions 25' are formed in a manner protruding downward (toward the fixed core 10) from the bottom 21 of the bottomed tube 20 such that the protruding portions 25 are in contact with the fixed core 10 (see FIG. 6).

[0060] This variation provides the same effects as obtained by the above embodiment. Further, since the movable core 30 abuts on the bottom 21 of the bottomed tube 20 in a larger area than in the above embodiment, pressure acting on the surface of the movable core 30 is decreased, and hence abrasion of the movable core 30 can be reduced.

[0061] It should be noted that in the conventional solenoid valve, a plurality of kinds of spacers 125 having different heights are used according to respective uses of the solenoid valve, while in the solenoid valve of the invention, a plurality of kinds of bottomed tubes 20 which are different from each other in height of protruding portions 25 thereof may be used according to different uses of the solenoid valve.

[0062] It is further understood by those skilled in the art that the foregoing is the preferred embodiment and variation of the invention, and that various changes and modification may be made without departing from the spirit and scope thereof.

Claims

1. A solenoid valve (1) comprising a fixed core (10), a bottomed tube (20) formed of a non-magnetic material and having a bottom (21), a movable core (30) slidably received within the bottomed tube (20) and opposed to the fixed core (10) with a gap therebetween, and a solenoid (60) for causing the movable core (30) to operate,
   characterised by a protruding portion (25,25') formed on the bottom (21) of the bottomed tube (20) and protruding in a direction of sliding of the movable core (30).

2. A solenoid valve (1) according to claim 1, wherein the protruding portion (25) is formed in a manner protruding toward the movable core (30).

3. A solenoid valve (1) according to claim 1, wherein the protruding portion (25') is formed in a manner protruding toward the fixed core (10).

4. A solenoid valve (1) according to claim 1, 2 or 3, wherein the protruding portion (25,25') comprises a plurality of convex-shaped protruding portions (25,25') each having a predetermined height.

5. A solenoid valve (1) according to claim 1, 2 or 3, wherein the protruding portion (25,25') comprises a ridge-shaped protruding portion (25,25') extending along a whole circumference of the bottom (21) of the bottomed tube (20) and having a predetermined height.

6. A solenoid valve (1) according to claim 1, 2 or 3, wherein the protruding portion (25,25') comprises a plurality of ridge-shaped protruding portions (25,25') formed at circumferential equal intervals along a circumference of the bottom (21) of the bottomed tube (20) and each having a predetermined height.

Drawing