Normally-open solenoid valve including plunger formed with pressure receiving portion

A solenoid valve includes a solenoid coil, a yoke of magnetic material, an armature of magnetic material to move in an axial direction of the solenoid coil when the solenoid coil is energized, a plunger to be moved with the armature, a valve seat member including a seat portion formed with a valve hole to be closed and opened by a forward end portion of the plunger, and a coil spring which is disposed between a spring receiving portion of the plunger and the valve seat member, around the plunger. The plunger includes a pressure receiving portion (such as a flat portion) which extends in a radial direction of the plunger at a position between the forward end portion and the spring receiving portion of the plunger, and which faces to the seat portion.

BACKGROUND OF THE INVENTION

The present invention relates to normally-open type solenoid valve or electromagnetic valve.

A patent document JP2008-121721A shows a normally-open solenoid valve including a damper chamber behind a plunger, and an elastic member disposed between the damper chamber and a valve chamber receiving a valve element, and designed to define a throttle passage. The elastic member functions to increase the cross sectional size of the throttle passage by deformation just after opening of the valve, and thereby to facilitate the flow of an operating fluid toward the damper chamber, to suppress self excited vibrations.

SUMMARY OF THE INVENTION

In order to design a solenoid valve capable of treating a greater flow rate, it is generally desirable to increase a seat diameter and to decrease the diameter of a forward end of a plunger. However, the flow of the operating fluid between the valve seat and plunger becomes fast with increase of the flow rate, and tends to develop a negative pressure which acts to pull the plunger, and induce vibrations of the plunger. The addition of a damper chamber as in the above-mentioned patent document is disadvantageous in that the size of the valve is increased. Therefore, it is an object of the present invention to provide a solenoid valve for suppressing vibrations and preventing a size increase of the valve.

According to one aspect of the present invention, a solenoid valve includes a plunger formed with a pressure receiving portion spreading radially.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

[Structure of Solenoid valve] A solenoid valve or electromagnetic valve1according to a first embodiment of the present invention is a normally-open valve to be used in a brake system of a vehicle.FIG. 1shows the solenoid valve1in section. Solenoid valve1includes a solenoid coil2to produce an electromagnetic force when energized, an armature3made of magnetic material and arranged to actuated by the electromagnetic force, a plunger4to move as a unit with armature3, a valve seat5having an orifice hole5bopened and closed by plunger4, and a valve body10housing the plunger4.

The valve seat5includes a seat portion5a, a spring receiving (or retaining) portion5d(serving as a base from which the seat portion5aprojects axially) and a fluid passage5c. The seat portion5ais formed at a first end of valve seat5extending axially or longitudinally from the first end to a second end. Seat portion5ais a funnel-shaped portion having a recess tapering to the orifice hole5b(or valve hole). The spring receiving portion5dis formed around the seat portion5a, and arranged to retain one end of a coil spring11. The fluid passage5cextends axially from the orifice hole5bto the second end of valve seat5.

The plunger4is a non-magnetic member made of a resin, extending from a first end connected with armature3, to a second end or forward end4b. Plunger4includes a spring receiving (or retaining) portion4awhich is formed between the first and second ends of plunger4and which is arranged to retain the other end of coil spring11. Plunger4includes a base portion extending from the first end to the spring receiving portion4a, and a shaft portion having an outside circumferential surface4eand extending from the spring receiving portion4atoward the second end4b. The shaft portion is a tapering portion tapering from the spring receiving portion4atoward the second end4b. Plunger4further includes a forward end portion including the forward end or tip4b, which is formed as a valve element4bfor abutting against the seat portion5a. The valve element4bis a hemispherical portion shaped like a half of a sphere. Plunger4further includes a pressure receiving portion4c(which can correspond to a flat portion) formed between valve element4band spring receiving portion4a, as explained below more in detail.

The valve body10is a tubular member having a bore10aextending axially through. The plunger4and valve seat5are received in the bore10aof valve body10. The base portion of plunger4is slidable axially in bore10a.

A housing6of the brake system includes a valve receiving hole6afor receiving the solenoid valve1. Into this valve receiving hole6aof housing6, a filter7, the valve seat5equipped with a first seal8, and the valve body10equipped with a second seal9are inserted one after another. Valve body10is fixed to housing6, by stalking in this example. Plunger4is connected with armature3and inserted into the bore10aof valve body10. In this operation, the coil spring11is set around the shaft portion extending from the spring receiving portion4ato the valve element4b, and disposed between the spring receiving portion4aof plunger4and the spring receiving portion5dof valve seat5so that the coil spring11urges the plunger4toward armature. Thus, plunger4is urged by coil spring11in a direction away from the seat portion5aof valve seat5(that is, the valve opening direction).

Armature3is received in a cylinder12having a rounded bottom shaped like a hemisphere. An open end portion of cylinder12is fixed to valve body10by welding in this example. Solenoid coil2is received in a yoke14which is made of a magnetic material and attached so that armature3is surrounded by yoke14. In the open valve state, the operating fluid is supplied from a master cylinder to a wheel cylinder of the brake system of a vehicle, by the route of the filter7, fluid passage5cof valve seat5, orifice hole5b, the bore of valve body10, a through hole which is formed through the side wall of valve body10to convey the fluid from the bore to the outer side of valve body, and a fluid passage formed in the housing6.

[Structure of Plunger]FIG. 2shows the valve element4bof plunger4and the seat portion5aof valve seat5in enlarged section. The pressure receiving portion4cis a flat portion extending in a radial direction of plunger4at a intermediate position between valve element4band spring receiving portion4a. Pressure receiving portion4cis formed continuously between a large diameter portion4dof valve element4band an outside circumferential surface4eof the shaft portion. The outside diameter P1of pressure receiving portion4cis greater than a hole diameter (or seat diameter) φ2of seat portion5a. Furthermore, the outside diameter φ1of pressure receiving portion4cis smaller than the inside diameter φ3of coil spring11. The height h from the forward end of valve element4bto the pressure receiving portion4cis approximately equal to a quantity which is once and half times as long as the seat diameter φ2of seat portion5a.

FIG. 3shows the forward end portion of plunger4in an enlarged scale, andFIG. 4is a view for illustrating a process of forming the plunger4. Plunger4is formed by injecting a resin into a mold or forming or molding die13including a cavity13ein the form of plunger4. The resin is injected through an injection hole formed in mold13. The mold13is a mold which can be divided into a first mold13a, a second mold13band a third mold13c. Mold13has first and second parting lines13fand13galong which mold13is parted. First parting line13fbetween first and second molds13aand13bis located at the position of pressure receiving portion4c. Second parting line13gbetween the second and third molds13band13cis located at the position of spring receiving portion4a.

[Operation] To increase the flow rate of the solenoid valve, it is desirable to increase the seat diameter and to reduce the diameter of the forward end of the plunger. However, the flow velocity of the operating fluid flowing between the seat and plunger becomes higher with increase of the flow rate. Therefore, the negative pressure increases in a direction to pulling in or sucking down the plunger, and increases the possibility of vibration of the plunger.

FIG. 5is a view showing a pressure distribution appearing when the operating fluid flows through an interspace opened between the valve element4bof plunger4and the seat portion5aof valve seat5. As shown inFIG. 5, a negative pressure or vacuum is produced between valve element4band seat portion5a. By this negative pressure, the plunger4moves in the valve closing direction toward valve seat5, and thereby decreases the flow quantity of the fluid flow through the interspace between valve element4band seat portion5a. With the decrease of the flow quantity, the flow velocity decreases, and the negative pressure diminishes, so that the plunger4moves in the valve opening direction away from valve seat5. By repeating this cycle, the plunger4tends to vibrate.

FIG. 6is a time chart showing a fluid pressure of a wheel cylinder in the case of a plunger having no pressure receiving portion4c. As shown inFIG. 6, the wheel cylinder pressure fluctuates because the supply quantity of the operating fluid is inconstant due to vibrations of plunger4. A solenoid valve including a damper chamber formed behind the armature3, and a fluid passage for supplying the operating fluid to the damper chamber may be effective for preventing vibrations of plunger4. However, this solenoid valve increases the size of the valve and complicates the structure. Therefore, the plunger4according to the first embodiment is formed with the pressure receiving portion4cdesigned to prevent vibrations. The pressure receiving portion4cextends radially at the position between the valve element4band spring receiving portion4a, and has the size (or the outside diameter) smaller than the inside diameter of coil spring11.

FIG. 7is a view for illustrating hydrodynamic forces acting on plunger4. InFIG. 7, hatching is omitted for simplification. A force F acting on plunger4in the valve opening direction due to the operating fluid is given by a following equation.
F=p×S+ρ×Q×u1−ρ×Q×u2×cos φ+ρ×Q×u3
In this mathematical expression: p is a differential pressure between the fluid pressure in fluid passage5cof valve seat5and the fluid pressure in valve body10; S is a fluid passage area of orifice hole5b, ρ is the density of the operating fluid; Q is a flow quantity or flow rate of the operating fluid; u1is a flow speed of the fluid flowing through orifice hole5b; u2is a flow speed of the fluid flowing through the interspace between seat portion5aand valve element4b; u3is a flow speed of the fluid flowing toward the pressure receiving portion4c; and φ is an angle between the direction of the force F and the direction of the fluid flowing through the interspace between seat portion5aand valve element4b. The term ρ×Q×u2×cos φ represents a negative pressure force acting in the valve closing direction. The term ρ×Q×u3represents a force acting on the pressure receiving portion4cin the valve opening direction.

As shown by the above-mentioned equation, in opposition to the negative pressure force drawing in the plunger4, the fluid flowing out of the orifice hole5bof valve seat5and bumping against the pressure receiving portion4cof plunger4applies the pressure on the plunger4in the valve opening direction away from valve seat5a.FIG. 8is a time chart of the wheel cylinder fluid pressure supplied through the solenoid valve including the plunger4formed with pressure receiving portion4c. As shown inFIG. 8, fluctuation of the fluid pressure is prevented. This is because vibrations of the plunger4is prevented, and the supply of the operating fluid is held constant. The pressure receiving portion4creceives the pressure in the valve opening direction of moving plunger4away from seat portion5a, and hence the plunger4receives the force opposing the negative pressure. Therefore, this solenoid valve can prevent vibrations of plunger4. Pressure receiving portion4cis in the form of a flat portion formed between valve element4band spring receiving portion4a. Therefore, pressure receiving portion4ccan be formed without increasing the axial length of plunger4and without increasing the size of solenoid valve1. Moreover, the outside diameter of pressure receiving portion4cis smaller than the inside diameter of coil spring11. Therefore, it is possible to prevent interference of plunger4with coil spring11and to prevent plunger4from being caught by coil spring11.

In the illustrated example, the valve element4bis hemispherical, and the pressure receiving portion4cis formed continuously between the large diameter portion4dof valve element4band the outside circumferential surface4e. Moreover, the recessed corner formed between pressure receiving portion4cand large diameter portion4dis curved or rounded to have a radius of curvature equal to R0.03, and the projected corner between pressure receiving portion4cand outside circumferential surface4eis curved or rounded to have a radius of curvature equal to or smaller than R0.1. Therefore, the receiving portion4ccan have a sufficient area for preventing vibrations effectively.

Furthermore, in the illustrated example of the first embodiment, the plunger4is formed by injection molding of a resin using the mold13having the parting line13fat the position of pressure receiving portion4c. This arrangement makes it possible to reduce the radius of curvature at the corner between pressure receiving portion4cand large diameter portion4d, and the radius of curvature at the corner between pressure receiving portion4cand outside circumferential surface4e, and to facilitate the formation of pressure receiving portion4chaving a wider area.

Moreover, in the illustrated example, the height h measured from the forward end of valve element4bto the so pressure receiving portion4cis approximately one and half times as long as the seat diameter φ2of seat portion5a.FIG. 9shows various fluid pressure waveforms of the wheel cylinder fluid pressure in the form of time chart, obtained when the height h from the forward end of valve is element4bto the pressure receiving portion4cis changed. The upper row ofFIG. 9shows three waveforms of the wheel cylinder fluid pressure when the solenoid valve1is opened from the fully-closed state to the fully-open state. The lower row ofFIG. 9shows three waveforms of the wheel cylinder fluid pressure when the solenoid valve1is opened at an intermediate opening degree. In the case of the solenoid valve1opened from the fully-closed state to the fully-open state, the plunger4is liable to vibrate since the flow speed is higher. In the case of the intermediate opening degree, the plunger4is less likely to vibrate since the flow speed is relatively low. However, in the case of the intermediate opening degree, it is desirable to avoid the generation of an inflection point in the wheel cylinder fluid pressure in order to hold the flow rate constant.

FIG. 9shows a first example in which the step position (h) is approximately one and a half times as long as the seat diameter φ2in a left side column ofFIG. 9, a second example in which the step position (h) is approximately 1.2 times as long as the seat diameter φ2in a center column, and a third example in which the step position (h) is approximately 2.0 times as long as the seat diameter φ2in a right side column. In the second example (in which the height h is approximately equal to φ2×1.2), the solenoid valve can prevent vibrations of plunger4. However, a point of inflection is produced in the fluid pressure when the opening degree of the solenoid valve is intermediate between the minimum setting (fully-closed) and the maximum setting (fully-open). In the third example (in which the height h is approximately equal to φ2×2.0), there is produced no inflection in the intermediate opening state. However, plunger4vibrates when the solenoid valve is opened from the fully-closed state to the fully-open state. In the first example (in which the height h is approximately equal to φ2×1.5) which is a practical example according to the first embodiment, the solenoid valve can prevent vibrations of plunger4, and prevent the formation of inflection at the intermediate opening state.

Moreover, in this practical example according to the first embodiment, the outside diameter φ1of pressure receiving portion4cis set greater than the seat diameter φ2of seat portion5a. Therefore, the fluid discharged from seat portion5acan impinge on the pressure receiving portion4cefficiently, and thereby restrains vibrations efficiently.

[Effects] The first embodiment can provide following effects.

(I) A solenoid valve comprises: a solenoid coil (2) to produce a magnetic field when electric current is supplied; a yoke (14) of magnetic material receiving the solenoid coil; an armature (3) of magnetic material disposed on an inner peripheral side of the yoke, and arranged to move in an axial direction of the solenoid coil when the solenoid coil is energized; a plunger (4) of nonmagnetic material arranged to move with movement of the armature; a valve seat (5) including a seat portion (5a) formed with an orifice hole (or valve hole)5bto be closed and opened by a forward end portion or a valve element (4b) of the plunger; and an coil spring (11) disposed between a spring receiving portion (4a) formed in the plunger and the valve seat or the valve seat member, around the plunger, and arranged to urge the plunger in a (valve opening) direction toward the armature (away from the seat portion). The plunger includes a pressure receiving portion (4c) which extends in a radial direction of the plunger at a position between the valve element (4b) of the plunger and the spring receiving portion (4a), and which has an outer circumference smaller than an inside diameter of the coil spring.

The operating fluid flows out of orifice hole (5b) of valve seat (5) and then impinges on the pressure receiving portion (4c) of plunger (4). Therefore, the plunger (4) receives pressure in the valve opening direction, and the force due to the pressure acts against the negative pressure and thereby prevents vibrations of plunger (4). The pressure receiving portion (4c) is the flat portion (4c) formed between the valve element (4b) and the spring receiving portion (4a). This arrangement makes it possible to form the pressure receiving portion without increasing the axial length of the plunger (4) and to prevent a size increase of the solenoid valve (1). Moreover, the size (or outside diameter) of the pressure receiving portion (4c) is smaller than the inside diameter of the coil spring (11). Therefore, it is possible to prevent the plunger (4) from being caught by, or interfering with, the coil spring (11).

(II) The valve element (4b) is shaped like a hemisphere, and the pressure receiving portion (4c) of the plunger (4) is formed continuously between a larger diameter portion (4d) of the hemispherical portion and an outside circumferential surface (4e) of the plunger. A first corner is formed between the pressure receiving portion (4c) and the larger diameter portion (4d), and a second corner is formed between the pressure receiving portion (4c) and the outside circumferential surface (4e) so that a radius of curvature of the first corner is smaller than or equal to R0.03 and/or a radius of curvature of the second corner is smaller than or equal to R0.1.

Therefore, the pressure receiving portion (4c) can be formed to have a sufficient area to prevent vibrations effectively.

(III) The plunger (4) is formed by plastic injection molding with a mold (13) having a parting line (13f) at which the position of the pressure receiving portion (4c) is located. Therefore, it is possible to form a sharper corner having a smaller radius of curvature at the corner between the pressure receiving portion (4c) and the larger diameter portion (4d) and the corner between the pressure receiving portion (4c) and the outside circumferential surface (4e), and thereby to increase the pressure receiving area of the pressure receiving portion (4c).

[Other Embodiments] Although the invention has been described above with reference to the first embodiment of the invention, the invention is not limited to the embodiment described above. Various modifications, variations and design changes are within the purview of the invention. For example, although, in the illustrated example of the first embodiment, the corner between pressure receiving portion4cof plunger4and large diameter portion4dis curved to have a radius of curvature smaller than or equal to R0.03 and the corner between pressure receiving portion4cand outside circumferential surface4eis curved to have a radius of curvature smaller than or equal to R0.1, it is optional to employ the arrangement in which the corner between pressure receiving portion4cof plunger4and large diameter portion4dis curved to have a radius of curvature greater than R0.03 and/or the corner between pressure receiving portion4cand outside circumferential surface4eis curved to have a radius of curvature greater than R0.1.

Furthermore, although in the illustrated example of the first embodiment, the height h from the forward end of the valve element4bof plunger4to the pressure receiving portion4cis approximately equal to a product obtained by multiplying the seat diameter φ2by 1.5 to obtain stable controllability and vibration preventing characteristic, it is not always necessary to set the ratio (h/φ2) of the height h to the seat diameter φ2, equal to 1.5. It is optional to set the ratio (h/φ2) of the height h to the seat diameter φ2properly in consideration of the distance of the pressure receiving portion4cfrom the seat portion5awhich tends to cause inflection in the fluid pressure at an intermediate opening degree if the pressure receiving portion4cis too close to seat portion5a, and which tends to cause vibrations of the plunger in the operation of opening the solenoid valve1from the fully closed position to the fully open position if the pressure receiving portion4cis too far from the set portion5a.

In the illustrated example of the first embodiment, the coil spring11is disposed between the spring receiving portion4aof plunger4and the spring receiving portion5dof valve seat5. However, it is optional to employ the arrangement in which the coil spring11is disposed between the spring receiving portion4aof plunger4and a spring receiving portion formed in valve body10, and arranged to urge the plunger4in the valve opening direction.

According to the first embodiment, a solenoid valve comprises: a valve seat member formed with a hole (or valve hole or orifice hole), and a plunger arranged to close the hole of the valve seat member (in a valve closing position, and to open the hole to open the valve). The plunger includes a pressure receiving portion facing to the valve seat member. The solenoid valve may further comprise any one or more of following features (F1)˜(F27). (F1) The pressure receiving portion of the plunger is an annular step portion including an annular shoulder surface facing toward the valve seat member in an axial or longitudinal direction of the plunger (that is the direction in which the plunger moves toward and away from the valve seat). (F2) The pressure receiving portion of the plunger includes a flat shoulder surface (such as an annular flat shoulder surface) extends radially from an inner circumference to an outer circumference.

(F3) The plunger includes a shaft portion, and a forward end portion. The pressure receiving portion is formed between the shaft portion and the forward end portion. (F4) The shaft portion of the plunger includes an outside circumferential surface (4e), the forward end portion (4b,4d) includes an outside circumferential surface, and the pressure receiving portion (4c) includes a shoulder surface extending radially outwards from an inner circumference forming an inner (recessed or reentrant) corner with the outside circumferential surface of the forward end portion, to an outer circumference forming an outer (projected or salient) corner with the outside circumferential surface of the shaft section. (F5) The inner corner is rounded to have a first radius of curvature and the outer corner is rounded to have a second radius of curvature which is greater than the first radius of curvature. (F6) The outside circumferential surface of the shaft portion and the outside circumferential surface of the forward end section are in the form of surface of revolution (such as conical surface, cylindrical surface, or spherical surface), formed coaxially around a center axis of the plunger. (F7) The inner (recessed) corner and the outer (projected) corner extend circumferentially around the center axis of the plunger.

(F8) The forward end portion of the plunger includes a hemispherical tip end or tip. (F9) The valve seat member includes a seat portion (5a) which is a bowl-shaped or funnel-shaped portion including a recess recessed to a bottom in which the hole (5b) is open (like a funnel), and including a concave surface (such as a conical surface) spreading radially from the hole. (F10) The seat portion (5a) projects axially toward the plunger, from a base to a top end which is in the form of a rim or annular ridge confronting the pressure receiving portion (4c) of the plunger, and encircling the concave surface and the hole of the seat portion. (F11) The seat portion includes the concave surface (such as a conical surface) which extends from the bottom at which the hole is open, to an inner circumference of the rim encircling the concave surface, and the inside diameter of the inner circumference of the rim is smaller than the diameter of an outer circumference of the pressure receiving portion (which extends radially outwards from an inner circumference to the outer circumference).

(F12) The forward end portion of the plunger includes a frustum portion including an outside conical surface (4e), and a hemispherical tip end (4b) including a hemispherical surface formed continuously with the conical surface (so as to form a continuous surface of revolution). (F13) The conical surface of the frustum portion of the forward end portion of the plunger tapers from a larger base end (4d) surrounded contiguously by the pressure receiving portion, to a smaller top end from which the hemispherical tip end projects continuously toward the hole of the seat portion.

(F14) The solenoid valve further comprises a coil spring (11) arranged to urge the plunger (4) in a valve opening direction away from the hole (5b) of the seat portion (5a). (F15) The shaft portion and the forward end portion (4b,4d) of the plunger, and the seat portion (5a) of the valve seat member are disposed in, and surrounded by the coil spring (11). (F16) The plunger (4) includes a base portion extending axially from a first end (which may be connected or fixed with an armature (3)) to a second end from which the shaft portion projects in an axial direction away from the first end. (F17) The plunger includes a spring receiving annular shoulder surface (4a) for retaining a first end of the coil spring (11), and the spring receiving annular shoulder surface (4a) is formed between the base portion and the shaft portion of the plunger in the form of a step. (F18) The base portion of the plunger is a cylindrical portion slidably fit in an axial bore (10a) of a valve body (10), and the shaft portion is coaxial with the base portion and smaller in cross sectional size than the base portion. (F19) The shaft portion tapers and becomes gradually smaller in cross sectional size from a first end connected with the base portion to a second end connected with the forward end portion. (F20) The shaft portion includes a conical outside circumferential surface (4e). (F21) The valve seat member includes a spring receiving portion (5d) for retaining a second end of the coil spring (11). (F22) The seat portion (5a) is surrounded by the spring receiving portion (5d) of the valve seat member, and the seat portion (5a) projects axially from the spring receiving portion (5d) of the valve seat member, toward the plunger.

(F23) The plunger (4) is made of nonmagnetic material. (F24) The plunger is a resin molding. (F25) The plunger is a resin molding formed by using a mold having a parting line surface (13f) in which the pressure receiving portion (4c) is located or exposed. (F26) The valve seat member may comprise a valve seat (5) or may comprise a valve seat (5) and a valve body (10). (F27) The pressure receiving portion (4c) of the plunger includes a shoulder surface facing axially toward the seat portion and extending radially outwards from an imaginary inner cylindrical surface defining an inner circumference of the shoulder surface, to an imaginary outer cylindrical surface surrounding the inner cylindrical surface coaxially and defining an outer circumference of the shoulder surface, the forward end portion projects axially from the inner circumference of the shoulder surface to a tip end (4b) within the imaginary inner cylindrical surface, and the forward end portion of the plunger has a height (h) which is measured from the shoulder surface (4c) to the tip end (4b). (F28) The height (h) of the forward end portion measured from the shoulder surface (4c) to the tip end (4b) is smaller than the diameter of the imaginary outer cylindrical surface.

This application is based on a prior Japanese Patent Application No. 2009-215628 filed on Sep. 17, 2009. The entire contents of this Japanese Patent Application are hereby incorporated by reference.