WO2013172520A1

WO2013172520A1 - Solenoid valve

Info

Publication number: WO2013172520A1
Application number: PCT/KR2012/009418
Authority: WO
Inventors: Chang Hoon Lee; Eui Dong Roh; Chan Shik Ahn
Original assignee: Unick Corporation
Priority date: 2012-05-14
Filing date: 2012-11-08
Publication date: 2013-11-21

Abstract

A solenoid valve includes a valve configured to control a flow of a fluid; and a solenoid configured to operate the valve. The valve includes a pipe-like holder; a supply chamber, a control chamber and an exhaust chamber formed in the holder separately from each other in a longitudinal direction thereof; a supply port, a control port and an exhaust port formed on an outer peripheral surface of the holder, to be respectively connected to the supply chamber, and the control chamber and the exhaust chamber; a spool movably provided in the holder; an annular groove formed on an outer peripheral surface of the spool, the annular groove serving to connect the control chamber and the supply chamber or the exhaust chamber when the spool is moved; and a feedback passage formed in the spool, to be connected to the control chamber.

Description

SOLENOID VALVE

The present invention relates to a solenoid valve; and, more particularly, to a solenoid valve used as one of hydraulic pressure control valve units for controlling a hydraulic pressure to be supplied to an automatic transmission.

A vehicle transmission is a device that converts and transmits the rotary speed and power of an engine to be suitable for various driving environments. Such a transmission is classified into a manual transmission through which a gear-shifting process is manually performed by a driver and an automatic transmission through which a gear-shifting process is automatically performed in a certain pattern. The automatic transmission includes a torque converter; an actuator; a planetary gear system; a hydraulic control unit; and an electronic control unit. The hydraulic control unit is provided with a hydraulic pressure control valve unit to control a hydraulic pressure.

Korean Patent No. 10-1009266 (2011.01.12) discloses a solenoid valve used as one of hydraulic pressure control valve units. The solenoid valve includes a solenoid which is actuated according to whether a power is switched on or off; a holder coupled to the solenoid; and a spool provided in the holder.

In the holder, a supply chamber, a control chamber, an exhaust chamber and a feedback chamber are formed. Formed on an outer peripheral surface of the holder are a supply port, a control port, an exhaust port and a feedback port connected to the supply chamber, the control chamber, the exhaust chamber and the feedback chamber, respectively. A feedback passage through which the feedback chamber and the control chamber are connected to each other is also formed on the outer peripheral surface of the holder.

In the meantime, one end of the aforementioned feedback passage has an open groove-like shape. Accordingly, the feedback passage can function as a complete passage only when the open end of the feedback passage is closed by forming a mounting hole in a valve body of the solenoid valve. Therefore, when a gap is formed between the holder and the mounting hole due to a processing tolerance, an assembly tolerance and/or the like, it is difficult to completely seal spaces between the ports, causing abnormal movement of fluid between the chambers. This makes it difficult to reliably control a hydraulic pressure to be supplied to the automatic transmission.

In view of the above, the present invention provides a solenoid valve capable of improving the responsiveness of a valve by reliably controlling a hydraulic pressure to be supplied to the automatic transmission.

The present invention also provides a solenoid valve capable of minimizing a hydraulic pressure loss caused by abnormal movement of a fluid by filling a gap between a holder and a mounting hole and by completely sealing spaces between ports.

In accordance with an aspect of the present invention, there is provided a solenoid valve including a valve configured to control a flow of a fluid; and a solenoid configured to operate the valve wherein the valve includes a pipe-like holder; a supply chamber, a control chamber and an exhaust chamber formed in the holder, the chambers being arranged separately from each other in a longitudinal direction thereof; a supply port, a control port and an exhaust port formed on an outer peripheral surface of the holder, the supply port, the control port and the exhaust port being respectively connected to the supply chamber, and the control chamber and the exhaust chamber; a spool movably provided in the holder; an annular groove formed on an outer peripheral surface of the spool, the annular groove serving to connect the control chamber and the supply chamber or the exhaust chamber when the spool is moved; and a feedback passage formed in the spool, the feedback passage being connected to the control chamber.

In accordance with another aspect of the present invention, there is provided a solenoid valve including a valve configured to control a flow of a fluid; and a solenoid configured to operate the valve, wherein the valve includes a pipe-like holder; a supply chamber, a control chamber and an exhaust chamber formed in the holder, the chambers being arranged separately from each other in a longitudinal direction thereof; a supply port, a control port and an exhaust port formed on an outer peripheral surface of the holder, the supply port, the control port and the exhaust port being respectively connected to the supply chamber, and the control chamber and the exhaust chamber; a spool movably provided in the holder; an annular groove formed on an outer peripheral surface of the spool, the annular groove serving to connect the control chamber and the supply chamber or the exhaust chamber when the spool is moved; and a feedback passage formed in the spool, the feedback passage serving to connect or disconnect the control chamber to or from the feedback chamber when the spool is moved.

In accordance with the aspects of the present invention, since the feedback passage is formed in the spool, it is possible to minimize a processing tolerance, an assembly tolerance and the like caused by the feedback passage. Accordingly, it is possible to remove a gap between the holder and a mounting hole and to prevent abnormal movement of a fluid by sealing spaces between the ports. Especially, by providing the O-rings on the outer peripheral surface of the holder, it is possible to completely prevent the abnormal movement of the fluid. This makes it possible to a hydraulic pressure loss caused by the feedback passage and to reliably control a hydraulic pressure to be supplied to an automatic transmission, thereby improving the responsiveness of the valve.

Further, when the spool is moved by supplying a power to the solenoid valve, a fluid in the control chamber is partially flowed into the feedback passage (or feedback chamber) or a fluid flowed into the feedback passage (or feedback chamber) is exhausted to the control chamber. Accordingly, it is possible to obtain a linearity with regular variation of the hydraulic pressure by preventing the hydraulic pressure from being rapidly varied while the fluid is flowed in or out through the control port.

The objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which:

Fig. 1 is a cross sectional view showing a solenoid valve in accordance with a first embodiment of the present invention;

Fig. 2 is an enlarged view of a valve of the solenoid valve in accordance with the first embodiment of the present invention;

Fig. 3 is an enlarged view of a portion A of Fig. 1;

Figs. 4 and 5 show an operation state of the solenoid valve in accordance with the first embodiment of the present invention;

Fig. 6 is a cross sectional view showing a solenoid valve in accordance with a second embodiment of the present invention;

Fig. 7 is an enlarged view of a valve of the solenoid valve in accordance with the second embodiment of the present invention;

Fig. 8 is an enlarged view of a portion B of Fig. 7; and

Figs. 9 and 10 show an operation state of the solenoid valve in accordance with the second embodiment of the present invention. 12

Embodiments of the present invention will now be described with reference to the accompanying drawings which form a part hereof. Further, in the following description and drawings, components having substantially the same configuration and function are denoted by as like reference characters as possible even in different figures.

As shown in Figs. 1 to 3, a solenoid valve in accordance with an embodiment of the present invention includes a valve 100 for controlling the flow of a fluid; and a solenoid 200 for operating the valve 100.

The valve 100 includes a holder 110; a spool 120 movably provided in the holder 110; an elastic member, e.g., a spring, 130 provided above the spool 120; and a pressure-adjusting screw 140.

The holder 110 is of a pipe-like shape having a circular cross section in such a way as to move the spool 120 therein. In the holder 110, a supply chamber 150, a control chamber 160 and an exhaust chamber 170 are formed separately from each other in a longitudinal direction thereof. Formed on an outer peripheral surface of the holder 110 are a supply port 152, a control port 162 and an exhaust port 172 connected to the supply chamber 150, the control chamber 160 and the exhaust chamber 170, respectively. In the holder 110, the chambers 150 to 170 and the ports 152 to 172 are arranged successively vertically from a lower portion of the holder 110 to an upper portion thereof.

The supply chamber 150 and the supply port 152 serve to supply a fluid from the outside into the holder 110. The control chamber 160 and the control port 162 serve to control the fluid flowed into the holder 110 to a predetermined pressure and exhausting the fluid to a clutch (not shown) of the automatic transmission. The exhaust chamber 170 and the exhaust port 172 serve to exhaust to the outside the fluid that has been flowed after being exhausted to the clutch of the automatic transmission.

The ports 152 to 172 are respectively radially arranged along the circumferences of the chambers 150 to 170, and annular filters 116 are respectively provided at portions on the outer peripheral surface of the holder 110 where the

ports

152 and 162 are formed.

Further, a first and a second

auxiliary chamber

190a and 190b are respectively formed inside an upper and a lower end portion of the holder 110. In the pressure-adjusting screw 140, a first auxiliary port 192a connected to the first auxiliary chamber 190a is formed. On a lower outer peripheral surface of the holder 110, a second auxiliary port 192b connected to the second auxiliary chamber 190b is formed. The

auxiliary chamber

190a and 190b and the

auxiliary ports

192a and 192b respectively serve to ensure the smooth movement of the spool 120 by removing remaining pressures inside the upper and the lower end portion of the holder 110.

Furthermore, mounting grooves 112a to 112c are formed on the outer peripheral surface of the holder 110, and O-rings 114a to 114c are respectively provided at the mounting grooves 112a to 112c. Substantially, a first mounting groove 112a and a first O-ring 114a are provided between the supply port 152 and the second auxiliary port 192b, and a second mounting groove 112b and the second O-ring 114b are provided between the supply port 152 and the control port 162. A third mounting groove 112c and the third O-ring 114c are provided between the control port 162 and the exhaust port 172.

The spool 120 serves as a multi-stage unit having an outer peripheral surface on which

annular grooves

122a and 122b are formed. Formed in the spool 120 is a feedback passage 182 extended in a longitudinal direction of the spool 120. A feedback port 184 connecting the feedback passage 182 and the control chamber 160 is formed at the center of the spool 120. At an inner upper portion of the spool 120, a feedback chamber 180 connected to the feedback passage 182 is formed.

The

annular grooves

122a and 122b include a first and a second

annular groove

122a and 122b that are positioned successively from a lower side of the spool 120 to an upper side thereof. When the spool 120 is moved upwardly, the first annular groove 122a connects the supply chamber 150 and the control chamber 160. When the spool 120 is moved downwardly, the second annular groove 122b connects the control chamber 160 and the exhaust chamber 170.

The feedback chamber 180 serves as a space having a diameter that is larger than that of the feedback passage 182. A lower end of the feedback chamber 180 is of a taper shape whose diameter is decreased toward the feedback passage 182. The feedback chamber 180 having such a shape is connected to the control chamber 160 through the feedback passage 182 and the feedback port 184.

The pressure-adjusting screw 140 is provided at an upper end portion of the holder 110 to adjust a moving distance of the spool 120 to thereby control the control pressure to be applied to the clutch through the control port 162.

The spring 130 is provided between the pressure-adjusting screw 140 and the spool 120 to downwardly elastically support the spool 120 and to absorb the shock generated when the spool 120 is moved.

With the above-mentioned configuration of the valve 100, the feedback passage 182 is formed inside the spool 120. Accordingly, it is possible to manipulate the holder 100 into a pipe shape having a complete circular cross section. As such, by manufacturing the holder 110 into the pipe shape having a complete circular cross section, it is possible to minimize a processing tolerance generated in the manufacture of the holder 110 and an assembly tolerance in the assembling of the holder 110. Therefore, it is possible to remove a gap between the holder 110 and a mounting hole (into which the holder 110 is inserted) (not shown) and to prevent abnormal movement of a fluid by sealing spaces between the ports 152 to 172. Especially, by providing the O-rings on the outer peripheral surface of the holder 110, it is possible to completely prevent the abnormal movement of the fluid. This makes it possible to a hydraulic pressure loss caused by the feedback passage 182 and to reliably control a hydraulic pressure to be supplied to an automatic transmission, thereby improving the responsiveness of the valve 100.

The solenoid 200 serves to move a plunger 250 by generating a magnetic field when a power is applied thereto and to operate the valve 100 through a rod 270 connected to the plunger 250. As shown in Fig. 1, the solenoid 200 is configured to include a case 210; a bobbin 220 provided in the case 210; a coil 230 wound around an outer peripheral surface of the bobbin 220; a yoke 240 insulted through a lower end of the bobbin 220; the plunger 250 provided in the yoke 240; a core 260 connected to an upper end of the yoke 240; a rod 270 coupled with the core 260 in such a way as to extend through an upper end of the core 260; and a connector 280 coupled with a lower end side of the yoke 240.

In this embodiment, the solenoid 200 has such a configuration, but is not limited thereto. Alternatively, the solenoid 200 may have any configuration capable of operating the valve 100 depending on whether or not a power is applied thereto.

An operating process of the solenoid valve in accordance with the first embodiment of the present invention will be described as follows with reference to Figs. 4 and 5.

Fig. 4 shows a state of the solenoid valve to which a power is supplied. Specifically, a magnetic field is generated by supplying a power to the solenoid valve, and the plunger 250 is moved by the action of the generated magnetic field to raise the rod 270 and the spool 120. When the spool 120 is moved upwardly through these steps, the supply chamber 150 and the control chamber 160 are connected to each other and the control chamber 160 and the exhaust chamber 170 are disconnected from each other.

In this case, a fluid supplied through the supply port 152 is controlled to a predetermined pressure while passing through the supply chamber 150 and the control chamber 160 and then exhausted to the clutch (not shown) of the automatic transmission through the control port 162. At this time, some of the fluid flowed from the supply chamber 150 to the control chamber 160 is transferred to the feedback chamber 180 through the feedback port 184 and the feedback passage 182. In other words, since some of the fluid to be exhausted through the control port 162 is transferred to the feedback chamber 180, a control pressure of the fluid to be exhausted through the control port 162 is prevented from being rapidly varied. Further, a pressure is applied to a taper surface 186 of the feedback chamber 180 by the action of the fluid transferred to the feedback chamber 180, and thus the spool 120 is prevented from being rapidly raised.

With the aforementioned configuration, the control pressure of the fluid to be exhausted through the control port 162 is increased or decreased at a smooth gradient. This makes it possible to obtain a linearity with regular variation of the control pressure and to extend a control section of pressure to thereby more accurately control the control pressure.

On the other hand, when the power supplied to the solenoid 200 is turned off, the spool 120, the plunger 250 and the rod 270 are moved downwardly by the action of the spring 130 provided above the spool 120 (see Fig. 4). As such, when the spool 120 is moved downwardly, the connection between the supply chamber 150 and the control chamber 160 is released and the control chamber 160 and the exhaust chamber 170 are connected to each other.

In this case, even if a fluid is supplied through the supply port 152, the fluid is not transferred to the control port 162, and the fluid (whose pressure has been adjusted to the predetermined level) that has been exhausted to the clutch through the control port 162 is exhausted to an external fluid storage tank (not shown) through the exhaust port 172 after passing through the control chamber 160 and the exhaust chamber 170.

As shown in Figs. 6 to 8, a solenoid valve in accordance with a second embodiment of the present invention includes a valve 300 for controlling the flow of a fluid; and a solenoid 400 for operating the valve 300.

The valve 300 includes a holder 310; a spool 320 movably provided in the holder 310; an elastic member, e.g., a spring, 330 provided above the spool 320; and a pressure-adjusting screw 340.

The holder 310 is of a pipe-like shape having a circular cross section to move the spool 320 therein. In the holder 310, a supply chamber 350, a control chamber 360, an exhaust chamber 370 and a feedback chamber 380 are formed separately from each other in a longitudinal direction thereof. Formed on an outer peripheral surface of the holder 310 are a supply port 352, a control port 362 and an exhaust port 372 connected to the supply chamber 350, the control chamber 360 and the exhaust chamber 370, respectively. In the holder 310, the chambers 350 to 380 and the ports 352 to 372 are arranged successively vertically from a lower portion of the holder 310 to an upper portion thereof.

The supply chamber 350 and the supply port 352 serve to supply a fluid from the outside into the holder 310. The control chamber 360 and the control port 362 serve to control the fluid flowed into the holder 310 to a predetermined pressure and exhausting the fluid to a clutch (not shown) of the automatic transmission. The exhaust chamber 370 and the exhaust port 372 serve to exhaust to the outside the fluid that has been flowed after being exhausted to the clutch of the automatic transmission.

The ports 352 to 372 are respectively radially arranged along the circumferences of the chambers 350 to 370, and annular filters 316 are respectively provided on outer peripheral surfaces of the holder 310 where the

ports

352 and 362 are formed.

Further, a first and a second

auxiliary chamber

390a and 390b are respectively formed inside an upper and a lower end portion of the holder 310. In the pressure-adjusting screw 340, a first auxiliary port 392a connected to the first auxiliary chamber 390a is formed. On a lower outer peripheral surface of the holder 310, a second auxiliary port 392b connected to the second auxiliary chamber 390b is formed.

Furthermore, mounting grooves 312a to 312c are formed on the outer peripheral surface of the holder 310, and O-rings 314a to 314c are respectively provided at the mounting grooves 312a to 312c. Substantially, a first mounting groove 312a and a first O-ring 314a are provided between the supply port 352 and the second auxiliary port 392b, and a second mounting groove 312b and the second O-ring 314b are provided between the supply port 352 and the control port 362. A third mounting groove 312c and the third O-ring 314c are provided between the control port 362 and the exhaust port 372.

The spool 320 serves as a multi-stage unit having an outer peripheral surface on which annular grooves 322a to 322c are formed. Formed in the spool 320 is a feedback passage 324 extended in a longitudinal direction of the spool 320. A first feedback port 326a is formed at the center of the spool 320 to connect the feedback passage 324 and the control chamber 360. A second feedback port 326b is formed at an upper end portion of the spool 320 to connect the feedback passage 324 and the feedback chamber 380.

The annular grooves 322a to 322c include a first, a second and a third annular groove 322a to 322c that are positioned successively from a lower side of the spool 320 to an upper side thereof. When the spool 320 is moved upwardly, the first annular groove 322a connects the supply chamber 350 and the control chamber 360. When the spool 320 is moved downwardly, the second annular groove 322b connects the control chamber 360 and the exhaust chamber 370. Further, the third annular groove 322c constitutes one side of the feedback chamber 380.

Here, the upper end portion of the spool 320 provided in the feedback chamber 380 has an outer peripheral surface that is formed in multiple stages to have different diameters. In other words, one end of the spool 320 is formed in multiple stages in such a way that an upper region 328a of the upper end portion of the spool 320 has a diameter d1 that is smaller than a diameter d2 of a lower region 328b thereof. As a result, the diameter d1 of the upper region 328a is formed to be smaller than the diameter d2 of the lower region 328b, so that a relative larger pressure is applied to the lower region 328b having a larger hydraulic pressure portion.

The pressure-adjusting screw 340 is provided at an upper end portion of the holder 310 to adjust a moving distance of the spool 320 to thereby control the control pressure to be applied to the clutch through the control port 362.

The spring 330 is provided between the pressure-adjusting screw 340 and the spool 320 to downwardly elastically support the spool 320 and to absorb the shock generated when the spool 320 is moved.

The solenoid 400 serves to move a plunger 450 by generating a magnetic field when a power is applied thereto and to operate the valve 300 through a rod 470 connected to the plunger 450. As shown in Fig. 5, the solenoid 400 has the same configuration as that of the solenoid 200 of the second embodiment, and thus the redundant description thereof will be omitted.

An operating process of the solenoid valve in accordance with the second embodiment of the present invention will be described as follows with reference to Figs. 9 and 10.

Fig. 9 shows a state of the solenoid valve to which a power is supplied. Specifically, a magnetic field is generated by supplying a power to the solenoid valve, and the plunger 450 is moved by the action of the generated magnetic field to raise the rod 470 and the spool 320. When the spool 320 is moved upwardly through these steps, the supply chamber 350 and the control chamber 360 are connected to each other and the control chamber 360 and the exhaust chamber 370 are disconnected from each other.

In this case, a fluid supplied through the supply port 352 is controlled to a predetermined pressure while passing through the supply chamber 350 and the control chamber 360 and then exhausted to the clutch (not shown) of the automatic transmission through the control port 362. At this time, some of the fluid flowed from the supply chamber 350 to the control chamber 360 is transferred to the feedback chamber 380 through the feedback ports 326a and 362b and the feedback passage 324. In other words, since some of the fluid to be exhausted through the control port 362 is transferred to the feedback chamber 380, a control pressure of the fluid to be exhausted through the control port 362 is prevented from being rapidly varied. Further, a relatively larger pressure is applied to the lower region 328b of the upper end portion of the spool 320 by the action of the fluid flowed into the feedback chamber 380, the lower region 328b having the larger hydraulic pressure portion, and thus the spool 320 is prevented from being rapidly raised.

As a result, the control pressure of the fluid to be exhausted through the control port 362 is increased or decreased at a smooth gradient. This makes it possible to obtain a linearity with regular variation of the control pressure and to extend a control section of pressure to thereby more accurately control the control pressure.

On the other hand, when the power supplied to the solenoid 400 is turned off, the spool 320, the plunger 450 and the rod 470 are moved downwardly by the action of the spring 330 provided above the spool 320 (see Fig. 10). As such, when the spool 320 is moved downwardly, the connection between the supply chamber 350 and the control chamber 360 is released and the control chamber 360 and the exhaust chamber 370 are connected to each other.

In this case, even if a fluid is supplied through the supply port 352, the fluid is not transferred to the control port 362, and the fluid (whose pressure has been adjusted to the predetermined level) that has been exhausted to the clutch through the control port 362 is exhausted to an external fluid storage tank (not shown) through the exhaust port 372 after passing through the control chamber 360 and the exhaust chamber 370.

While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

Claims

A solenoid valve comprising:

a valve configured to control a flow of a fluid; and

a solenoid configured to operate the valve,

wherein the valve includes:

a pipe-like holder;

a supply chamber, a control chamber and an exhaust chamber formed in the holder, the chambers being arranged separately from each other in a longitudinal direction thereof;

a supply port, a control port and an exhaust port formed on an outer peripheral surface of the holder, the supply port, the control port and the exhaust port being respectively connected to the supply chamber, and the control chamber and the exhaust chamber;

a spool movably provided in the holder;

an annular groove formed on an outer peripheral surface of the spool, the annular groove serving to connect the control chamber and the supply chamber or the exhaust chamber when the spool is moved; and

a feedback passage formed in the spool, the feedback passage being connected to the control chamber.
The solenoid valve of claim 1, wherein a feedback port is formed at a central portion of the spool to connect the feedback passage and the control chamber, and

a feedback chamber connected to the feedback passage is formed in an one end of the spool.
The solenoid valve of claim 2, wherein one end of the feedback chamber at a side of the feedback passage is of a taper shape.
The solenoid valve of claim 3, wherein the annular groove includes a first annular groove which connects the control chamber and the supply chamber when the spool is moved; and a second annular groove which connects the control chamber and the exhaust chamber when the spool is moved, and

the feedback port is provided between the first and the second annular groove.
The solenoid valve of claim 4, further comprising:

mounting grooves respectively formed, on the outer peripheral surface of the holder, between the supply port and the control port and between the control port and the exhaust port; and

O-rings respectively provided in the mounting grooves to seal spaces between the supply port and the control port and between the control port and the exhaust port.
The solenoid valve of claim 5, further comprising:

annular filters respectively provided at portions on the outer peripheral surface of the holder where the supply port is formed and where the control port is formed.
The solenoid valve of claim 5, further comprising:

an adjusting screw coupled to one end of the holder; and

an elastic member provided between the adjusting screw and the spool,

wherein the solenoid is provided at the other end of the holder.
A solenoid valve comprising:

a valve configured to control a flow of a fluid; and

a solenoid configured to operate the valve,

wherein the valve includes

a pipe-like holder;

a supply chamber, a control chamber and an exhaust chamber formed in the holder, the chambers being arranged separately from each other in a longitudinal direction thereof;

a supply port, a control port and an exhaust port formed on an outer peripheral surface of the holder, the supply port, the control port and the exhaust port being respectively connected to the supply chamber, and the control chamber and the exhaust chamber;

a spool movably provided in the holder;

an annular groove formed on an outer peripheral surface of the spool, the annular groove serving to connect the control chamber and the supply chamber or the exhaust chamber when the spool is moved; and

a feedback passage formed in the spool, the feedback passage serving to connect or disconnect the control chamber to or from the feedback chamber when the spool is moved.
The solenoid valve of claim 8, wherein a first feedback port is formed at a central portion of the spool to connect the feedback passage and the control chamber, and a second feedback port is formed at one end portion of the spool to connect the feedback passage and the feedback chamber, and

wherein an outer peripheral surface of one end of the spool is formed in multiple stages, and an outer peripheral surface of one end of the holder is formed in multiple stages corresponding to the one end of the spool.
The solenoid valve of claim 9, wherein the one end of the spool is formed in multiple stages in such a way that a diameter of one stage thereof at a side of the first feedback port larger than a diameter of another stage thereof at the opposite side with regard to the second feedback port.
The solenoid valve of claim 10, wherein the annular groove includes a first annular groove which connects the control chamber and the supply chamber when the spool is moved; and a second annular groove which connects the control chamber and the exhaust chamber when the spool is moved, and

the first feedback port is provided between the first and the second annular groove.
The solenoid valve of claim 11, further comprising:

mounting grooves respectively formed, on the outer peripheral surface of the holder, between the supply port and the control port and between the control port and the exhaust port; and

O-rings respectively provided in the mounting grooves to seal spaces between the supply port and the control port and between the control port and the exhaust port.
The solenoid valve of claim 12, further comprising:

annular filters respectively provided at portions on the outer peripheral surface of the holder where the supply port is formed and where the control port is formed.
The solenoid valve of claim 5, further comprising:

an adjusting screw coupled to one end of the holder; and

an elastic member provided between the adjusting screw and the spool,

wherein the solenoid is provided at the other end of the holder.