Solenoid Valve

Proportional solenoid valve and control method therefor

Solenoid Valve Abstract:
BACKGROUND OF THE INVENTION

The present invention relates to a device for controlling the flow of a fluid, and particularly for controlling the supply of water to a washing machine, such as a washing machine for laundry or a dishwasher.

More specifically, the invention relates to a device comprising a solenoid valve of the bistable type, controlled by an operating winding, and circuit means connected for operation to an electrical power source such as the electrical mains, and capable of supplying to the winding of the said solenoid valve a first and a second current pulse for opening and closing the said solenoid valve respectively.

The use of solenoid valves of the bistable type is widespread, particularly because of their low energy consumption. This is because a brief pulse is sufficient to open such a device, and another brief pulse is sufficient to subsequently close it. In the time interval between these first and second pulses, the bistable solenoid valve is not energized, and therefore does not consume any energy.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a solenoid valve device for controlling the flow of a fluid, particularly for controlling the supply of water to a washing machine, which overcomes some problems encountered in the operation of devices using solenoid valves of the bistable type. This and other objects are achieved according to the invention with a device whose principal characteristics are for controlling the flow of a fluid in a domestic electrical appliance, particularly for controlling the water supply to a washing machine.

Further characteristics and advantages of the invention are shown clearly in the following detailed description, provided purely by way of example and without restrictive intent, with reference to the attached drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a first embodiment of a device according to the invention;

FIG. 2 is a partial sectional view of a bistable solenoid valve;

FIG. 2a is a partial view which shows a detail of FIG. 2 on an enlarged scale;

FIG. 3 is a view similar to that of FIG. 2, showing the bistable solenoid valve in the open condition; and

FIG. 4 is a partial sectional view of a bistable solenoid valve included in a second embodiment of a device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, the number 1 indicates the whole of a device for controlling the flow of a fluid, particularly for controlling the supply of water to a washing machine, made according to the present invention.

With particular reference to the diagram in FIG. 1, a device 1 according to the invention comprises a solenoid valve 2 of the bistable type, connected to an electrical power supply and control circuit indicated as a whole by 3.

The bistable solenoid valve 2 itself comprises an operating winding 4, connected to two terminals 5 and 6 of the circuit 3.

Also with reference to FIG. 1, the circuit 3 has two further terminals 7 and 8, designed to be connected to an electrical power source, particularly to the alternating current mains.

The terminal 7 of the circuit 3 is connected to the terminal 5 through a normally open switch 9, a rectifier diode 10, a switching device indicated as a whole by 11, and a capacitor 12.

The switch 9, which can be, for example, a solid state switch or an electromechanical switch, is controlled in a known way, for example by means of an electronic unit which is not illustrated, or by what is known as a "timer", to cause the opening of the bistable solenoid valve 1.

In the illustrated example of embodiment, the switching device 11 is of the electromechanical type, and comprises a moving contact 13 controlled by a winding or coil 14. The moving contact 13 is normally in the position shown in broken lines in FIG. 1, in which it connects the cathode of the diode 10 to the capacitor 12. When the winding 14 is energized, the moving contact 13 moves to the position shown in solid lines, in which it connects the capacitor 12 to the terminal 6 of the circuit 3; in other words it connects the capacitor 12 directly to the operating winding 4 of the bistable solenoid valve 2.

The circuit 3 comprises a further capacitor 15 connected between the anode of the diode 10 and a double half-wave rectifier circuit 16. In the illustrated example of embodiment, the rectifier circuit 16 comprises four diodes 17 in a quadrilateral arrangement, in the configuration also known as a Graetz bridge. One end of a diagonal of this bridge circuit is connected to the capacitor 15 and the other end is connected to the terminal 6. The energizing winding 14 of the switch 11 is connected in parallel with the other diagonal of this bridge circuit.

The power supply terminal 8 of the circuit 3 is connected to the output terminal 6.

In the example of embodiment shown in FIGS. 2, 2a and 4, the bistable solenoid valve 2 comprises a structure including two shaped bodies, namely a lower body 20 and an upper body 21, joined in a watertight way to form a chamber 22 between them.

The lower body 20 forms an inlet connector 23 and an outlet connector 24. The latter is connected in its part facing the chamber 22 to an annular wall 25 whose top edge 26 can act as a valve seat.

Inside the lower body 20 and around the annular wall 25 there is formed an inlet passage 27, which is also annular and which communicates with the inlet connector 23.

The number 28 indicates the whole of a main plug, comprising a flexible annular membrane 29, whose peripheral edge is gripped between the bodies 20 and 21, and a rigid body 30 pierced by an axial passage 31, whose upper termination forms a valve seat 32.

The plug 28 is designed to interact, in the way which is described more fully below, with the valve seat 26.

As shown in particular in FIG. 2a, passages 33 and 34, by means of which the chamber 22 can communicate with the inlet connector 23 when the solenoid valve 2 is closed, are formed in the body 30 and in the thickened central portion of the membrane 29 (FIGS. 2 and 2a).

The plug 28, as described more fully below, can interact with the valve seat 26 to control the flow of liquid between the annular inlet passage 27 and the outlet connector 24.

The upper part of the body 21 forms a tubular receptacle 35 closed at its top by an end wall 36.

The operating winding 4 of the bistable solenoid valve 2 is positioned around the said tubular receptacle 35. A core 37 is mounted in an axially slidable way in this receptacle, this core being made at least partially of ferromagnetic material and having in its lower part an auxiliary plug 38 which can interact with the valve seat 32 formed in the rigid body 30, forming a pilot valve with the said seat.

A permanent magnet 39 is fixed to the terminal wall 36 of the receptacle 35.

A coil spring 40 is positioned between this permanent magnet and the moving core 37, and tends to push the latter downwards, in such a way that its plug closes the seat 32 (FIGS. 2 and 2a), against the action of the magnet 39 which would tend to keep the core in the raised position (FIG. 3).

The solenoid valve described above operates essentially in the following way.

In FIG. 2, the solenoid valve 2 is shown in the closed condition. In this condition, the plug 28 closes the valve seat 26. Under the action of the spring 40, the moving core 37 is in the lowered position in which its plug 38 closes the valve seat 32. The chamber 22 is filled with liquid which has flowed into it previously from the inlet connector 23, through the passages 33 and 34 of the plug 28. The pressure acting on the upper face of the plug 28 is greater than that acting on its lower surface or face, and the plug therefore presses on the valve seat 26.

When the winding 4 is energized by a first pulse of current flowing in a predetermined direction, the magnetic field developed as a result overcomes the force of the spring 40 and causes the moving core 37 and the associated plug 38 to move upwards to the position shown in FIG. 3. In this condition, the attractive force exerted by the magnet 39 on the moving core 37 is sufficient in itself to retain this moving core and the plug 38 in the raised position. Thus, when the first energizing pulse ceases, the core 37 and the plug 38 remain in the raised position. The liquid contained in the chamber 22 can then flow through the passage 31 towards the outlet connector 24. The consequent pressure drop in the chamber 22, and the simultaneous action of the pressure exerted by the inflowing liquid on the lower face of the plug 28, cause the latter to rise from the valve seat 26, as shown in FIG. 3, and the flow of liquid supplied to the inlet connector 23 can thus pass directly to the outlet connector 24 through the said valve seat and the tubular wall 25.

When the bistable solenoid valve 2 is to be closed, a second current pulse must be sent to the winding 4, in the opposite direction to the direction of the first current pulse. This second pulse can be sent in a known way to the winding 4 by an electronic control unit which is not shown in FIG. 1. The magnetic field generated in this way now acts on the moving core 37 in conjunction with the spring 40, in such a way that it overcomes the retaining force exerted on the said moving core 37 by the permanent magnet 39. The plug 38 closes the valve seat 32, and the liquid which flows from the inlet connector 23 to the chamber 22 through the passages 33 and 34 no longer finds an outlet and gradually increases the pressure acting on the upper face of the plug 28, until this plug returns to a position of engagement with the valve seat 26. Thus the flow of liquid between the inlet connector 23 and the outlet connector 24 is cut off.

With the bistable solenoid valve 2 described above, the following problem may arise. If the mains power is cut off while the solenoid valve 2 is open (with the winding 4 de-energized after the first opening pulse), the solenoid valve 2 remains in the open condition, potentially for an indeterminate time. This can entail the risk of flooding of the domestic appliance with which the solenoid valve 2 is associated for controlling its filling with water from the water mains.

This problem can be overcome by means of the solution described above with reference to the electrical circuit diagram of FIG. 1. With reference to this figure, the power supply circuit 3 comprises the capacitor 12 which is designed to act as a source of auxiliary voltage during operation.

When the switch 9 is closed, the energizing winding 14 of the switch 11 is energized, and causes the moving contact 13 to move from the position shown in solid lines to the position shown in broken lines. The positive half-waves of current can then flow towards the capacitor 12 and the operating winding 4 of the solenoid valve 2. The capacitor 12, which is initially discharged, acts initially as a short circuit. The operating winding 4 is energized, and the bistable solenoid valve 2 is opened. As soon as the capacitor 12 has been charged, it acts essentially as an open circuit, and disconnects the winding 4 of the solenoid valve 2 from the power supply terminals 7 and 8, and therefore from the mains.

If the supply voltage at the terminals 7 and 8 of the circuit 3 is cut off while the solenoid valve 2 is open, the winding 14 of the switch 11 is de-energized, and the moving contact 13 moves to the position shown in solid lines in FIG. 1. The capacitor 12 is then coupled directly to the winding 4 of the solenoid valve 2, and is discharged into it, causing a current pulse to flow through it, in the opposite direction to the direction of the preceding current pulse, and, by the discharge of the charge stored in the capacitor 12, causes the solenoid valve 2 to close automatically.

By this means, the problem of bistable solenoid valves described above is easily overcome.

It should be noted that any other auxiliary voltage source can be used in place of the capacitor 12. Furthermore, any other known switch device, particularly a solid-state electronic switch, can be used in place of the electromechanical switch 11 described above.

With the circuit described above, if the supply voltage applied to the terminals 7 and 8 is cut off while the bistable solenoid valve 2 is closed, the circuit 3 again operates in the way described above, and the current pulse flowing in the winding 4 as a result of its coupling to the capacitor 12 has no practical effect, since the solenoid valve is already closed.

FIG. 4 shows a variant embodiment. In this figure, the same reference numbers are given to parts and elements described previously.

In the embodiment according to FIG. 4, the permanent automatic retention magnet 39 is positioned not inside the tubular receptacle 35 but outside it, and is carried by a central formation 41 of a membrane 42 whose peripheral edge is gripped in a watertight way between an upper half-shell 43 and a lower half-shell 44 forming in combination a capsule connected in a watertight way to the upper end of the tubular receptacle 35.

Between the membrane 42 and the lower half-shell 44 there is formed a chamber 45 of variable volume, which can be made to communicate with the washing chamber of a washing machine by means of a connector 46 and a tube (not shown) which passes into the said washing chamber. The arrangement is such that, during operation, as the water level rises in the washing chamber of the domestic appliance with which the solenoid valve 2 is associated, the air pressure in the chamber 45 of the capsule 43, 44 increases. When the level in the washing chamber exceeds a predetermined danger level, the air pressure in the chamber 45 can cause the raising of the membrane 42 and the associated permanent magnet 39.

The solenoid valve device of FIG. 4 essentially operates in the following way.

As long as the water level in the washing chamber of the domestic appliance with which the solenoid valve 2 is associated remains below the aforesaid threshold, the permanent magnet 39 is adjacent to the terminal wall 36 of the receptacle 35. In this condition, it can act as a retaining element to hold the moving core 37 and the plug 38 in their raised position when the solenoid valve is open and the initial current pulse (which has caused it to open) has ceased.

If the mains power is cut off while the bistable solenoid valve 2 is open, the valve remains open and the water level in the washing chamber continues to rise. As soon as this level reaches the hazard or danger level specified above, the air pressure in the chamber 45 causes the permanent magnet 39 to rise. The action of the spring 40 is then sufficient to cause the moving core 37 and the plug 38 to return to the lowered position in which the valve seat 32 is closed. This causes the solenoid valve 2 to close, cutting off the flow of liquid between its inlet connector 23 and its outlet connector 24 essentially as described above.

The solution described above with reference to FIG. 4 is moreover capable of automatically closing the solenoid valve 2 not only after an interruption of the power supply and the reaching of a danger level by the liquid in the washing chamber. This is because the solution shown in FIG. 4 enables the solenoid valve 2 to be closed automatically even when the supply voltage is present, for example if there is an accidental interruption of the circuit between the supply terminals and the operating winding 4 of the solenoid valve, or an interruption of the continuity of this winding. In such a case, the winding 4 would not be able to receive the energizing pulse or pulses for closing the solenoid valve. However, as soon as the water level in the washing chamber exceeds the predetermined danger threshold, the permanent magnet 39 will still be raised, thus causing the automatic closing of the solenoid valve.

Clearly, provided that the principle of the invention is retained, the forms of its embodiment and the details of construction, which have been described and illustrated purely by way of example and without restrictive intent, can be varied considerably without departure from the scope of the invention as defined in the attached claims.

Solenoid Valve Claims:
1. A proportional solenoid valve comprising:

an input port to which a fluid is supplied;

an output port that communicates with the input port;

a drain port from which a part of the fluid supplied to the input port is discharged;

a cylindrical valve seat member that includes an input/output-side passage provided between the input port and the drain port and between the output port and the drain port, a seat portion that is provided in an end portion of the input/output-side passage, and a drain-side passage provided between the seat portion and the drain port;

a ball-shaped valve element that is brought into and out of contact with the seat portion; and

a valve drive portion that includes a coil and displaces the valve element in accordance with a current applied to the coil, thereby changing an amount of the fluid flowing from the input/output-side passage to the drain port through the drain-side passage and changing an output pressure from the output port,

wherein the drain-side passage is formed by exhaust passage holes whose number is an even number equal to four or more than four and which are arranged at regular intervals in a circumferential direction of the valve seat member,

wherein a total sectional area of all of the exhaust passage holes is set as equal to a seat area of the seat portion.

2. A proportional solenoid valve comprising:

an input port to which a fluid is supplied;

an output port that communicates with the input port;

a drain port from which a part of the fluid supplied to the input port is discharged;

a cylindrical valve seat member that includes an input/output-side passage provided between the input port and the drain port and between the output port and the drain port, a seat portion that is provided in an end portion of the input/output-side passage, and a drain-side passage provided between the seat portion and the drain port;

a ball-shaped valve element that is brought into and out of contact with the seat portion; and

a valve drive portion that includes a coil and displaces the valve element in accordance with a current applied to the coil, thereby changing an amount of the fluid flowing from the input/output-side passage to the drain port through the drain-side passage and changing an output pressure from the output port,

wherein the drain-side passage is formed by exhaust passage holes whose number is an even number equal to four or more than four and which are arranged at regular intervals in a circumferential direction of the valve seat member, and

wherein the input port is provided with an input port orifice and the input/output-side passage is provided with an input/output-side passage orifice having a sectional area that is two to six times as large as a sectional area of the input port orifice.

3. A proportional solenoid valve comprising:

an input port to which a fluid is supplied;

an output port that communicates with the input port;

a drain port from which a part of the fluid supplied to the input port is discharged;

a cylindrical valve seat member that includes an input/output-side passage provided between the input port and the drain port and between the output port and the drain port, a seat portion that is provided in an end portion of the input/output-side passage, and a drain-side passage provided between the seat portion and the drain port;

a ball-shaped valve element that is brought into and out of contact with the seat portion; and

a valve drive portion that includes a coil and displaces the valve element in accordance with a current applied to the coil, thereby changing an amount of the fluid flowing from the input/output-side passage to the drain port through the drain-side passage and changing an output pressure from the output port,

wherein the drain-side passage is formed by exhaust passage holes whose number is an even number equal to four or more than four and which are arranged at regular intervals in a circumferential direction of the valve seat member, and

wherein the input port is provided with an input port orifice and the output port is provided with an output port orifice having a sectional area that is two to six times as large as a sectional area of the input port orifice.

4. A proportional solenoid valve comprising:

an input port to which a fluid is supplied;

an output port that communicates with the input port;

a drain port from which a part of the fluid supplied to the input port is discharged;

a cylindrical valve seat member that includes an input/output-side passage provided between the input port and the drain port and between the output port and the drain port, a seat portion that is provided in an end portion of the input/output-side passage, and a drain-side passage provided between the seat portion and the drain port;

a ball-shaped valve element that is brought into and out of contact with the seat portion;

a valve drive portion that includes a coil and displaces the valve element in accordance with a current applied to the coil, thereby changing an amount of the fluid flowing from the input/output-side passage to the drain port through the drain-side passage and changing an output pressure from the output port; and

a cylindrical valve guide portion that is inserted into the valve seat member and guides the displacement of the valve element,

wherein a length of the valve guide portion is set so that when the valve element is brought into contact with the seat portion, a tip portion of the valve guide portion protrudes from a center of the valve element towards the seat portion side by 4% to 14% of a diameter of the valve element.

5. A control method for a proportional solenoid valve provided with: an input port to which a fluid is supplied; an output port that communicates with the input port; a drain port from which a part of the fluid supplied to the input port is discharged; a cylindrical valve seat member that includes an input/output-side passage provided between the input port and the drain port and between the output port and the drain port and a seat portion that is provided in an end portion of the input/output-side passage; a ball-shaped valve element that is brought into and out of contact with the seat portion; and a valve drive portion that includes a coil and displaces the valve element in accordance with a current applied to the coil, thereby changing an amount of the fluid flowing from the input/output-side passage to the drain port and changing an output pressure from the output port,

the control method comprising:

adjusting a supply pressure to the input port when a temperature of the fluid becomes equal to or higher than a preset temperature so that a pressure difference between the output pressure from the output port and the supply pressure to the input port becomes larger than a pressure difference with which self-induced vibration of the valve element occurs.

6. A proportional solenoid valve comprising:

an input port to which a fluid is supplied;

an output port that communicates with the input port;

a drain port from which a part of the fluid supplied to the input port is discharged;

a cylindrical valve seat member that includes an input/output-side passage provided between the input port and the drain port and between the output port and the drain port, a seat portion that is provided in an end portion of the input/output-side passage, and a drain-side passage provided between the seat portion and the drain port;

a ball-shaped valve element that is brought into and out of contact with the seat portion; and

a valve drive portion that includes a coil and displaces the valve element in accordance with a current applied to the coil, thereby changing an amount of the fluid flowing from the input/output-side passage to the drain port through the drain-side passage and changing an output pressure from the output port,

wherein the drain-side passage is formed by exhaust passage holes whose number is an even number equal to four or more than four and which are arranged at regular intervals in a circumferential direction of the valve seat member,

wherein a total sectional area of all of the exhaust passage holes is set as twice as large as a seat area of the seat portion.

7. A proportional solenoid valve comprising:

an input port to which a fluid is supplied;

an output port that communicates with the input port;

a drain port from which a part of the fluid supplied to the input port is discharged;

a cylindrical valve seat member that includes an input/output-side passage provided between the input port and the drain port and between the output port and the drain port, a seat portion that is provided in an end portion of the input/output-side passage, and a drain-side passage provided between the seat portion and the drain port;

a ball-shaped valve element that is brought into and out of contact with the seat portion; and

a valve drive portion that includes a coil and displaces the valve element in accordance with a current applied to the coil, thereby changing an amount of the fluid flowing from the input/output-side passage to the drain port through the drain-side passage and changing an output pressure from the output port.

wherein the drain-side passage is formed by exhaust passage holes whose number is an even number equal to four or more than four and which are arranged at regular intervals in a circumferential direction of the valve seat member,

wherein a total sectional area of all of the exhaust passage holes is set to have a value between an area equal to and an area twice as large as a seat area of the seat portion.

Solenoid Valve Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a proportional solenoid valve in which a valve element is displaced by applying a current to a solenoid to obtain an output pressure which is proportional to the value of the applied current, and a method for controlling the proportional solenoid valve.

2. Description of the Related Art

In a conventional proportional solenoid valve, a valve element is displaced in accordance with the value of a current applied to a coil while being guided by a cylindrical valve guide portion and is brought into and out of contact with a seat portion, thereby obtaining, from an output port, an output pressure proportional to the value of the applied current (see JP 2002-525524 A, for instance).

In a conventional proportional solenoid valve having this construction, self-induced vibration of the valve element is caused by operating temperature and disturbances such as pulsation. In particular, in recent years, due to rising oil temperatures and the like resulting from size reductions in proportional solenoid valve itself and transmissions, and arrangements in tight spaces, there occurs a situation where there is no choice but to perform control up to the temperature range in which the motion of the valve element becomes unstable. That is, when the oil temperature is high (120 degrees centigrade or higher, for instance) and the valve element is close to the seat portion, there is a danger of the self-induced vibration of the valve element occurring. When the self-induced vibration occurs in this manner, a control pressure is oscillated so that control becomes impossible. There is also a danger that the seat portion may be abraded due to friction between the valve element and the seat portion.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve the above problems, and is aimed at providing a proportional solenoid valve and a method for controlling the proportional solenoid valve with which it is possible to lower the self-induced vibration range of a valve element and improve resistance to oscillation.

According to the present invention, the proportional solenoid valve includes a drain-side passage formed by exhaust passage holes whose number is an even number equal to four or more and arranged at regular intervals in a circumferential direction of a valve seat member. As a result, it is possible to lower the self-induced vibration range of a valve element and to improve resistance to oscillation.

Further, according to the present invention, there is provided a proportional solenoid valve in which the length of a valve guide portion is set so that when the valve element is brought into contact with a seat portion, a tip portion of the valve guide portion protrudes from a center of the valve element towards the seat portion side by 4% to 14% of the diameter of the valve element. As a result, it is possible to lower the self-induced vibration range of the valve element and to improve resistance to oscillation.

Also, according to the present invention, in a method for controlling the proportional solenoid valve, a supply pressure to the input port is adjusted when the temperature of the fluid becomes equal to or higher than a preset temperature so that the pressure difference between the output pressure from the output port and the supply pressure to the input port becomes larger than the pressure difference with which self-induced vibration of the valve element occurs. As a result, it is possible to lower the self-induced vibration range of the valve element and to improve resistance to oscillation.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a cross-sectional view of a proportional solenoid valve according to a first embodiment of the present invention;

FIG. 2 is a magnified cross-sectional view showing the main portion of the proportional solenoid valve shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along the line III—III in FIG. 2;

FIG. 4 shows a relationship between an area ratio of the total cross-sectional area of exhaust passage holes to a seat area and the self-induced vibration range of a valve element;

FIG. 5 is a cross-sectional view of the main portion of a proportional solenoid valve according to a second embodiment of the present invention;

FIG. 6 shows a relationship between the length of a guide tip and the self-induced vibration range of the valve element;

FIG. 7 is a cross-sectional view of the main portion of a proportional solenoid valve according to a third embodiment of the present invention; and

FIG. 8 is a cross-sectional view of the main portion of a proportional solenoid valve according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described with reference to the accompanying drawings.

First Embodiment

A proportional solenoid valve according to a first embodiment of the present invention is a hydraulic circuit of an electronically controlled automatic transmission for an automobile (hereinafter simply referred to as an "automatic transmission"), and is used to change the operating oil pressure in an operating portion of the automatic transmission.

FIG. 1 is a cross-sectional view of the proportional solenoid valve according to the first embodiment of the present invention. Note that in this drawing, a proportional solenoid valve of normally high type is illustrated. In the drawing, a coil 1 is accommodated in a cylindrical case 2 made of metal and a terminal 3 for connecting the coil 1 to a power supply is arranged outside of the case 2. Further, the coil 1 and the terminal 3 are molded in a resin portion 4 and a plunger accommodating cavity 4a that passes through the hollow portion of the coil 1 while extending in the axial direction of the coil 1 is provided in the resin portion 4.

To one end portion of the resin portion 4, a core 5 made of metal is coupled. This core 5 includes a cylinder portion 5a inserted into one end portion of the plunger accommodating cavity 4a and a flange portion 5b that is abutted against an end surface of the resin portion 4. The flange portion 5b is welded to the case 2 at the outer periphery of its joining surface with the case 2.

A first plain bearing 6 is inserted into the cylinder portion 5a. Also, a cylindrical adjuster 7 is press-fitted into the cylinder portion 5a.

To the other end portion of the resin portion 4, a guide member 8 made of metal is coupled. This guide member 8 includes an annular-shaped flange portion 8a abutted against an end surface of the resin portion 4, a cylindrical fit portion 8b that protrudes from the flange portion 8a, and a cylindrical valve guide portion 8c that extends from one end portion of the fit portion 8b. The flange portion 8a is welded to the base 2 at the outer periphery of its joining surface with the case 2. The diameter of the valve guide portion 8c is smaller than the diameter of the fit portion 8b.

A second plain bearing 9 is inserted into the valve guide portion 8c. Into the first plain bearing 6 and the second plain bearing 9, a rod 10 is inserted so as to be slidable. This rod 10 is arranged inside of the core 5, the plunger accommodating cavity 4a, and the guide member 8 so as to be capable of reciprocating in the axial direction of the coil 1.

To the middle portion of the rod 10, a cylindrical plunger 11 is fixed. That is, the rod 10 is press-fitted into the plunger 11. A first spring 12 is arranged between the plunger 11 and the first plain bearing 6, while a second spring 13 is arranged between the plunger 11 and the second plain bearing 9. The plunger 11 is capable of reciprocating integrally with the rod 10 inside of the plunger accommodating cavity 4a.

A ball-shaped (spherical) valve element 14 is inserted into the valve guide portion 8c. A tip portion of the rod 10 abuts against the ball-shaped valve element 14. The load of the first spring 12 energizing the plunger 11 toward the valve element 14 is adjusted by the press-fit position of the adjuster 7. The valve guide portion 8c is press-fitted into and is fixed to a valve seat member 15. The valve seat member 15 includes a cylindrical fixing portion 15a into which the valve guide portion 8c is press-fitted, a seat portion 15b which the valve element 14 is brought into and out of contact with, an input/output-side passage 15c, and a drain-side passage 15d. The seat portion 15b is provided at an end portion of the input/output-side passage 15c.

To the guide member 8, a housing 16 that forms the flow path of oil, which is of course a fluid, is attached. This housing 16 is welded to the flange portion 8a at the outer periphery of its joining surface with the flange portion 8a. Also, the housing 16 includes an input port 16a to which the oil is supplied, an output port 16b that communicates with the input port 16a, and a drain port 16c from which a part of the oil supplied to the input port 16a is discharged.

The output port 16b communicates with the input/output-side passage 15c, and the drain port 16c communicates with the drain-side passage 15d. Also, the housing 16 is provided with a valve seat insertion portion 16d into which an end portion of the valve seat member 15 is inserted. Between the inner peripheral surface of the valve seat insertion portion 16d and the valve seat member 15, a space having a predetermined size is provided and a seal member 17, such as an O-ring made of an elastic material, is provided in the space.

Also, the case 2, the core 5, the guide member 8, and the plunger 11 collectively constitute a magnetic circuit. The core 5 functions as a magnetic attraction portion for the plunger 11. A valve drive portion 20 in this first embodiment includes the coil 1, the case 2, the terminal 3, the resin portion 4, the core 5, the first plain bearing 6, the adjuster 7, the guide member 8, the second plain bearing 9, the rod 10, the plunger 11, the first spring 12, and the second spring 13. To the housing 16, a flange member 18 for attachment to a valve body constituting the oil hydraulic circuit is fixed.

Next, the operation of this embodiment will be described. Under a state where the coil 1 is not excited, the plunger 11 is pressed towards the valve element 14 side by the spring force of the first spring 12. Consequently, the valve element 14 is pressed against the seat portion 15b by the rod 10, and the oil flow path to the drain port 16c is closed. As a result, a high-pressure output is obtained from the output port 16b.

When the coil 1 is excited and an electromagnetic force attracting the plunger 11 exceeds a predetermined size, the plunger 11 and the rod 10 are displaced against the spring force of the first spring 12 in a direction in which the distances of the plunger 11 and the rod 10 from the seat portion 15b increase. At that time, oil pressure acts on the valve element 14, so that the valve element 14 is displaced within the valve guide portion 8c along with the rod 10. As a result, the valve element 14 is spaced from the seat portion 15b, an amount of oil corresponding to the opening degree is output to the drain port 16c side, and the pressure output from the output port 16b is reduced. The valve element 14 is displaced in accordance with the value of the current applied to the coil 1 and an output proportional to the current value is obtained from the output port 16b.

In the hydraulic circuit for an automatic transmission in which this proportional solenoid valve is arranged, the oil accumulated in an oil pan 21, that is, an automatic transmission fluid is pumped by an oil pump 22. The oil pump 22 is driven in synchronization with an engine 23. The automatic transmission fluid pumped by the oil pump 22 is adjusted to a predetermined pressure by a regulator (not shown), and then it is sent to the input port 16a under pressure.

Then, by the output pressure from the output port 16b, the opening/closing of a control valve 24 is controlled and a clutch 25 is controlled, thereby performing a shifting operation. Also, the automatic transmission fluid discharged from the drain port 16c is recovered by the oil pan 21.

Next, FIG. 2 is a magnified cross-sectional view of the main portion of the proportional solenoid valve shown in FIG. 1, while FIG. 3 is a cross-sectional view taken along the line III—III in FIG. 2. In these drawings, the drain-side passage 15d is formed by exhaust passage holes 15e whose number is an even number of at least four and which are arranged at regular intervals in the circumferential direction of the valve seat member 15.

Also, each exhaust passage hole 15e has the same sectional area (sectional area measured perpendicular to the direction in which the oil flows). Further, the total sectional area of all of the exhaust passage holes 15e is set as equal to or twice as large as the seat area of the seat portion 15b (area of a tangent circle between the valve element 14 and the seta portion 15b). That is, the following equations are satisfied:

In such a proportional solenoid valve, the exhaust passage holes 15e, whose number is an even number of four or more than, are provided for the valve seat member 15 at regular intervals in the circumferential direction of the valve seat member 15, so that it becomes possible to lower the self-induced vibration range of the valve element 14 and to improve resistance to oscillation. As a result, it also becomes possible to prevent wear or abrasion of the seat portion 15b. Stipulations concerning these exhaust passage holes 15e were obtained by producing a number of samples having different arrangements and numbers of exhaust passage holes 15e and measuring their control pressures (output pressures) at a high oil temperature (120 degrees centigrade).

FIG. 4 shows a relationship between the area ratio of the total sectional area of the exhaust passage holes 15e to the seat area and the self-induced vibration range of the valve element 14. The relationship between the area ratio and the self-induced vibration range was obtained by producing a number of samples having different area ratios and measuring their control pressures at a high oil temperature (120 degrees centigrade).

As can be seen from FIG. 4, by setting the total sectional area of all of the exhaust passage holes 15e as equal to or twice as large as the seat area of the seat portion 15d, it becomes possible to further lower the self-induced vibration range of the valve element 14 and to further improve the resistance to oscillation. As a result, it becomes possible to more reliability prevent the wear or abrasion of the seat portion 15b.

Second Embodiment

Next, a second embodiment of the present invention will be described. FIG. 5 is a cross-sectional view of the main portion of a proportional solenoid valve according to the second embodiment. In the drawing, the length of the valve guide portion 8c is set so that when the valve element 14 is brought into contact with the seat portion 15b, the tip portion of the valve guide portion 8c protrudes from the center of the valve element 14 towards the seat portion 15b side by 4% to 14% of the diameter of the valve element 14. Other constructions are the same as those in the first embodiment.

FIG. 6 shows a relationship between the length of the guide tip of the valve guide portion 8c (the length of the protrusion of the tip portion of the valve guide portion 8c from the center of the valve element 14 towards the seat portion 15b side under a state where the valve element 14 is brought into contact with the seat portion 15b) and the self-induced vibration range of the valve element 14. The relationship between the guide tip length and the self-induced vibration range was obtained by producing multiple samples having different guide tip lengths and measuring their control pressures at a high oil temperature (120 degrees centigrade).

As can be seen from FIG. 6, by setting the ratio of the guide tip length to the diameter of the valve element 14 in a range of 4% to 14% (lower than the 17% conventionally used), it becomes possible to further lower the self-induced vibration range of the valve element 14 and to further improve the resistance to oscillation. As a result, it becomes possible to more reliability prevent the wear or abrasion of the seat portion 15b.

Third Embodiment

Next, a third embodiment of the present invention will be described. FIG. 7 is a cross-sectional view of the main portion of a proportional solenoid valve according to the third embodiment. In the drawing, the input port 16a is provided with an input port orifice 31 and the input/output-side passage 15c is provided with an input/output-side passage orifice 32 having a sectional area that is two to six times as large as the sectional area of the input port orifice 31 (sectional area measured perpendicular to the direction in which the oil flows). Other constructions are the same as those in the first embodiment.

In such a proportional solenoid valve, since the input port 16a is provided with the input port orifice 31 and the input/output-side passage 15c is provided with the input/output-side passage orifice 32 having a sectional area that is two to six times as large as the sectional area of the input port orifice 31, it becomes possible to lower the self-induced vibration range of the valve element 14 and to improve the resistance to oscillation, which makes it possible to prevent the wear or abrasion of the seat portion 15b. Stipulations concerning these orifices 31 and 32 were obtained by producing multiple samples having different sectional areas for the orifices 31 and 32 and measuring their control pressures at a high oil temperature (120 degrees centigrade).

Fourth Embodiment

Next, a fourth embodiment of the present invention will be described. FIG. 8 is a cross-sectional view of the main portion of a proportional solenoid valve according to the fourth embodiment. In this drawing, the input port 16a is provided with an input port orifice 31 and the output port 16b is provided with an output port orifice 33 having a sectional area that is two to six times as large as the sectional area of the input port orifice 31 (sectional area measured perpendicular to the direction in which the oil flows). Other constructions are the same as those in the first embodiment.

In such a proportional solenoid valve, since the input port 16a is provided with the input port orifice 31 and the output port 16b is provided with the output port orifice 33 having a sectional area that is twice to six times as large as the sectional area of the input port orifice 31, it becomes possible to lower the self-induced vibration range of the valve element 14 and to improve the resistance to oscillation, which makes it possible to prevent the wear or abrasion of the seat portion 15b. Conditions concerning those orifices 31 and 33 were obtained by producing multiple specimens having different sectional areas of the orifices 31 and 33 and measuring their control pressures at a high oil temperature (120 degrees centigrade).

Fifth Embodiment

Next, a method for controlling a proportional solenoid valve according to a fifth embodiment of the present invention will be described. Here, the control method for the proportional solenoid valve shown in FIG. 1 will be described. In the fifth embodiment, when the temperature of the fluid becomes equal to or higher than a preset temperature, the supply pressure to the input port 16a is adjusted so that the pressure difference between the output pressure from the output port 16b and the supply pressure to the input port 16a becomes larger than the pressure difference with which self-induced vibration of the valve element 14 occurs.

Here, the set temperature is 120 degrees centigrade, for instance. Also, in a proportional solenoid valve that has a 4 mm seat diameter and a control pressure of 0 MPa to 0.6 MPa, by performing adjustment so that the pressure difference becomes larger than 0.05 MPa, it becomes possible to prevent the self-induced vibration of the valve element 14. In order to maintain such a large pressure difference, supply pressure is set somewhat excessively high and the output pressure is also increased although the degree of increase is slight. In this case, however, self-induced vibration is prevented, so that it becomes possible to improve the controllability of the output pressure. Further, as a result of the improvement in the controllability, it also becomes possible to reduce the cost of a control program for the proportional solenoid valve.

It should be noted here that it is possible to provide the effects of the present invention even if the constructions and methods in the first to fifth embodiments are each applied alone. The constructions and methods may also be combined with each other as appropriate. In that case, it becomes possible to suppress the self-induced vibration with more reliability.

Also, in the first to third embodiments, there was described a proportional solenoid valve of a normally high type whose output pressure is high at the time of non-energization and is decreased in accordance with an increase in an applied current. However, the present invention is also applicable to a proportional solenoid valve of a normally low type whose output pressure is low at the time of non-energization and is increased in accordance with an increase in an applied current.