Electromagnetic valve

Abstract

Electromagnetic valve (100) comprising a valve body assembly (110) housed in a casing (101) and an electromagnetic coil (141), wherein the valve body assembly (110) comprises: a piston (120) having a groove section (121) on a cylindrical outer circumferential surface of the piston (120), wherein the groove section (121) extends in a cylinder axial direction, wherein the piston (120) moves in the cylinder axial direction by an electromagnetic force generated by the electromagnetic coil (141); a rod (111) attached to the piston (120), wherein the rod (111) abuts a valve seat (151) to open and close the electromagnetic valve (100) when the piston (120) is moved to close the electromagnetic valve (100), and the abutment of the rod (111) against the valve seat (151) is lifted when the piston (120) is moved to open the electromagnetic valve (100); a cylindrical sleeve (122) designed to cover the outer circumferential surface of the piston (120) and formed integrally with the piston (120); and a communication passage (125) defined by the groove section (121) of the piston (120) and an inner circumferential surface of the sleeve (122) and extending in the cylinder axis direction, where the valve body unit (110) is designed such that an arc length of an opening of the groove section (121) along the circumferential direction of the piston (120) is less than or equal to 20 times a thickness of the sleeve (122) along the radial direction of the sleeve (122), the electromagnetic valve (100) is an electromagnetic vehicle valve that is mounted in a vehicle and is arranged such that the cylinder axis direction of the piston (120) is horizontal when the electromagnetic valve (100) is mounted in the vehicle, and the piston (120) has: a covering area (123) in which the groove section (121) is covered by the sleeve (122); and a non-covering area (124) in which the groove section (121) is not covered by the sleeve (122), wherein the groove section (121) corresponding to the uncovered area (124) communicates with a space outside the sleeve (122) at least in the horizontal direction and in the direction orthogonal to the horizontal direction.

Description

TECHNICAL AREA

[0001] The invention relates to a configuration of an electromagnetic valve for activating a valve body unit using an electromagnetic force. STATE OF THE ART

[0002] An example of this type of electromagnetic valve is described in JP 2011 - 38 542 A, which is mounted in a vehicle. This electromagnetic valve is designed such that a valve body assembly and an electromagnetic coil are housed in a casing, the valve body assembly has a piston that can slide in the casing, and a valve chamber and a spring chamber communicate with each other via a communication passage that penetrates the piston.

[0003] US Patent 3,523,676 A discloses an electromagnetic valve comprising a valve body assembly housed in a casing and an electromagnetic coil, wherein the valve body assembly has: a piston having a groove section on a cylindrical outer circumferential surface of the piston, the groove section extending in a cylinder axial direction, the piston moving in the cylinder axial direction by an electromagnetic force generated by the electromagnetic coil; a rod attached to the piston, the rod striking a valve seat to open and close the electromagnetic valve when the piston is moved to close the electromagnetic valve, and the rod striking the valve seat is released when the piston is moved to open the electromagnetic valve;a cylindrical sleeve designed to cover the outer circumferential surface of the piston (120) and formed integrally with the piston; and a communication passage defined by the groove section of the piston and an inner circumferential surface of the sleeve, extending in the cylinder axial direction.

[0004] JP 2011-38542A describes a solenoid valve with a housing containing working fluid passages, a rod separably arranged in a valve seat, and a piston that maintains a passage for communication with a valve chamber via a spring chamber. The piston contains the rod at one end of the valve chamber, with the spring chamber positioned between a body and the piston. A spring biases the piston in the valve closing direction of the rod. SUMMARY OF THE INVENTION

[0005] According to the valve body assembly described in JP 2011-38542A, the communication passage is provided by mechanically machining a penetration through the piston. This results in high costs. To reduce costs, the communication passage can alternatively be formed by a groove section with a recessed shape, provided on the piston's outer circumferential surface, for example, by forging. However, in this case, the piston's outer profile, which incorporates the groove section with the recessed shape on the piston's outer circumferential surface, is not a true circle, and thus the sliding resistance between the piston and the housing in which the piston is located increases. Therefore, the valve body assembly cannot operate reliably.Furthermore, such a problem can occur in the electromagnetic valve that is installed in the vehicle, as well as in an electromagnetic valve that is installed in various types of other devices instead of the vehicle.

[0006] Accordingly, the invention arose with regard to the aspects described above, and it is an object of the invention to provide an effective technique for reducing the cost of the valve body assembly and for improving the utilization of the electromagnetic valve, in which the valve body assembly is operated using electromagnetic force. This object is achieved with an electromagnetic valve according to the features of claim 1. The dependent claims relate to preferred embodiments of the invention.

[0007] According to the invention, the cost of forming the communication passage is reduced compared to the cost of forming the communication passage by machining the piston through its penetration. Furthermore, the circularity of the sleeve can be improved by using a desired strength for the cylindrical sleeve. This reduces the sliding resistance between the sleeve and the housing. As a result, the utilization of the valve body assembly can be improved.

[0008] The arc length of the groove opening along the circumferential direction of the piston is less than or equal to 20 times the sleeve thickness along the radial direction of the sleeve. Therefore, if a value suitable for the sleeve thickness is set for the arc length of the groove opening, the desired circularity of the sleeve can be ensured. The circularity of the sleeve (the difference between the geometric true circle of the circular body and the circle corresponding to the shape of the sleeve) can, for example, be reduced to approximately 1 µm. On the other hand, if the arc length of the groove opening exceeds 20 times the sleeve thickness, the arc of the sleeve corresponding to the groove opening will likely deform into a straight line. Thus, it is difficult to ensure the desired circularity of the sleeve.

[0009] According to a further aspect of the electromagnetic valve according to the invention, the sleeve can preferably be made of a non-magnetic material, and a dimension greater than or equal to the dimension of the sliding gap between the outer circumferential surface of the sleeve and the housing can preferably be defined as the radial thickness of the sleeve. Accordingly, the magnetic force generated by the electromagnetic coil does not act on the sleeve, which is made of the non-magnetic material. Thus, the friction (the sliding resistance) generated between the outer circumferential surface of the sleeve and the housing can be reduced. In this case, a value corresponding to the sliding gap between the outer circumferential surface of the sleeve and the housing can be defined as the thickness of the sleeve.

[0010] According to a further aspect of the electromagnetic valve according to the invention, it is advantageous if the housing has a valve chamber located in a region corresponding to one end of the piston for accommodating the rod, and a spring chamber located in a region corresponding to the other end of the piston for accommodating a spring for elastically pre-tensioning the piston against the electromagnetic force generated by the electromagnetic coil, and the valve chamber and the spring chamber communicate with each other via the communication passage. Accordingly, the communication passage for communication between the valve chamber and the spring chamber in the electromagnetic valve can be defined by the groove section of the piston and the inner circumferential surface of the sleeve.

[0011] Furthermore, the electromagnetic valve according to the invention is an electromagnetic vehicle valve mounted in a vehicle, and the electromagnetic valve is arranged such that the direction of the piston's cylinder axis corresponds to the horizontal direction when the electromagnetic valve is mounted in the vehicle. The piston has: a covered area where the groove section is covered by the sleeve, and an uncovered area where the groove section is not covered by the sleeve. The groove section corresponding to the uncovered area communicates with a space outside the sleeve at least in the horizontal direction (the first direction) and in the direction (the second direction) orthogonal to the horizontal direction. Accordingly, the area of ​​the groove opening between the covered area and the uncovered area of ​​the piston is increased.As a result, gas bubbles present in the space outside the sleeve can be easily introduced into the communication passage from the groove section corresponding to the uncovered area by the flow of hydraulic fluid in at least two directions, in order to release the gas bubbles from the groove section corresponding to the uncovered area. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0012] As described above, according to the invention, the costs of the valve body unit can be reduced and the use of the valve body unit in the electromagnetic valve for opening and closing the valve body unit using electromagnetic force can be improved. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a system diagram of a brake control device 10 according to an embodiment of this application. Fig. Figure 2 is a view showing a cross-sectional configuration of an electromagnetic valve 100 according to the embodiment. Fig. Figure 3 is a top view showing a valve body unit 110, which is in Fig. 2 is shown. Fig. Figure 4 is a sectional view of the valve body unit 110 along a line AA of the Fig. 3. Fig. 5 is a partially enlarged view of the Fig. 4. Fig. Figure 6 is a view showing a positioning state of the valve body unit 110 when the electromagnetic valve 100 is installed in the vehicle. DESCRIPTION OF THE EXECUTION FORMS

[0013] In the following, an embodiment of the present invention is described with reference to the associated drawings.

[0014] The in Fig. The brake control device 10 shown in Figure 1 is mounted in a vehicle to control a braking force exerted on the vehicle's wheels and has a function for independently controlling the four wheels in response to the actuation of a brake pedal 11 by a driver. The brake pedal 11 has a stroke sensor 12 for detecting the actuation stroke of the brake pedal 11 and is connected to a master cylinder 13. The master cylinder 13 is connected to a reservoir tank 14 for storing hydraulic fluid (or brake oil) and has output channels 13a and 13b for dispensing the hydraulic fluid in response to the actuation of the brake pedal 11.

[0015] A lifting simulator 16 is connected to the output channel 13a of the master cylinder 13 via an electromagnetic valve 15. The electromagnetic valve 15 is energized so that it opens when the driver's application of the brake pedal 11 is detected. The lifting simulator 16 has a function for generating a reaction force corresponding to the driver's application of the brake pedal 11. A first hydraulic line 17 for the right front wheel is connected to the output channel 13a. The first hydraulic line 17 is connected to a wheel cylinder 21 for applying the braking force to the right front wheel. A second hydraulic line 18 for the left front wheel is connected to the output channel 13b. The second hydraulic line 18 is connected to a wheel cylinder 22 for applying the braking force to the left front wheel.The electromagnetic valve 15 and a hydraulic actuator 60 are each controlled by an electronic control unit (ECU) 70.

[0016] A first master interrupt valve 19 is arranged in the first hydraulic oil line 17 in the hydraulic actuator 60, and a second master interrupt valve 20 is arranged in the second hydraulic oil line 18 in the hydraulic actuator 60. The first master interrupt valve 19 interrupts the communication between the master cylinder 13 and the wheel cylinder 21 when the master interrupt valve 19 is energized, causing it to close. The second master interrupt valve 20 interrupts the communication between the master cylinder 13 and the wheel cylinder 22 when the master interrupt valve 20 is energized, causing it to close. On the other hand, the first master interrupt valve 19 causes communication between the master cylinder 13 and the wheel cylinder 21 when the master interrupt valve 19 is not energized, so that it is open, or when the excitation level of the master interrupt valve 19 is reduced, so that it opens.The second master interrupt valve 20 enables communication between the master cylinder 13 and the wheel cylinder 22 when the master interrupt valve 20 is not energized, so that it is open, or when the excitation level of the master interrupt valve 20 is reduced, so that it opens.

[0017] Furthermore, a pressure sensor 17a for detecting the master cylinder pressure is arranged on the right front wheel side at the first hydraulic oil line 17 in the hydraulic actuator 60. A pressure sensor 18a for detecting the master cylinder pressure on the left front wheel side is arranged on the second hydraulic oil line 18 in the hydraulic actuator 60. The actuation force of the brake pedal 11 is obtained based on the master cylinder pressures detected by the pressure sensors 17a and 18a.

[0018] The hydraulic actuator 60 has a pump 26 driven by a motor 27. A pump inlet of the pump 26 is connected to a hydraulic oil line 25, which communicates with the reservoir tank 14. A pump outlet of the pump 26 is connected to a hydraulic oil line 30, which branches off from the hydraulic oil line 25. An accumulator 31, a relief valve or pressure relief valve 32, and a pressure sensor 33 are arranged in the hydraulic oil line 30. The accumulator 31 converts pressure energy from the brake fluid, generated by the pump 26, into pressure energy of a filling gas and stores this pressure energy. The relief valve 32 opens to return the high-pressure brake fluid to the hydraulic oil line 25 when the pressure of the accumulator 31 exceeds a predetermined value. The relief valve 32 is operated according to the pressure of the accumulator 31, which is detected by the pressure sensor 33.

[0019] The hydraulic oil line 30 is connected to the wheel cylinder 21 via a pressure booster valve 41 for the right front wheel, to the wheel cylinder 22 via a pressure booster valve 42 for the left front wheel, to the wheel cylinder 23 via a pressure booster valve 43 for the right rear wheel, and to the wheel cylinder 24 via a pressure booster valve 44 for the left rear wheel. These pressure booster valves 41, 42, 43, and 44 increase the wheel cylinder pressures when the respective pressure booster valves 41, 42, 43, and 44 are open. Conversely, these pressure booster valves 41, 42, 43, and 44 do not increase the wheel cylinder pressures when the respective pressure booster valves 41, 42, 43, and 44 are closed. Wheel cylinder 21 is connected to a pressure reducing valve 51 for the right front wheel. Wheel cylinder 22 is connected to a pressure reducing valve 52 for the left front wheel.Wheel cylinder 23 is connected to a pressure-reducing valve 53 for the right rear wheel. Wheel cylinder 24 is connected to a pressure-reducing valve 54 for the left rear wheel. The pressure-reducing valves 51, 52, 53, and 54 reduce the wheel cylinder pressures when they are open. Conversely, they do not reduce the wheel cylinder pressures when they are closed. The pressure of wheel cylinder 21 is detected by a pressure sensor 21a. The pressure of wheel cylinder 22 is detected by a pressure sensor 22a. The pressure of wheel cylinder 23 is detected by a pressure sensor 23a. The pressure of the wheel cylinder 24 is detected by a pressure sensor 24a.

[0020] In the following, a configuration of an electromagnetic valve 100 according to the present embodiment is described in more detail with reference to the Fig. 2 to 5 described. The electromagnetic valve 100 can be used for various electromagnetic valves mounted in a vehicle and can, for example, be used as the pressure reducing valve 51, 52 described above. Note that the electromagnetic valve 100 can also be used for the other pressure reducing valves 53 and 54 or other opening / closing valves. The electromagnetic valve 100 corresponds to the electromagnetic valve according to the invention.

[0021] As it is in Fig. As shown in Figure 2, the electromagnetic valve 100 comprises a valve body assembly 110, which is housed in a casing 101, and an electromagnetic unit 140. The valve body assembly 110 is operated by the electromagnetic force generated by the electromagnetic unit 140 (an electromagnetic coil 141). The valve body assembly 110 has a rod 111, a piston 120, and a sleeve 122 and extends in the longitudinal direction corresponding to the operating direction of the valve body assembly 110. The valve body assembly 110 corresponds to the valve body assembly according to the invention.

[0022] The rod 111 has an insertion part 111a, which is to be inserted into and attached to a mounting hole 120a located in the piston 120. The rod 111 is attached to the piston 120 by inserting the insertion part 111a into the mounting hole 120a. The rod 111 has a hemispherical tip 111b on the side opposite the insertion part 111a, and the tip 111b can abut a valve seat (a valve seat 151 described later) to open and close the electromagnetic valve. Accordingly, the rod 111 abuts the valve seat when the piston 120 is moved to close the electromagnetic valve, and the rod 111 releases the abutment against the valve seat when the piston 120 is moved to open the electromagnetic valve. The rod 111 corresponds to the rod according to the invention.

[0023] The piston 120 is made of a magnetic material and divides a space formed in the housing 101 into valve and spring chambers 112 and 113. In this case, the housing 101 has the valve chamber 112 in a region corresponding to one end of the piston 120 and the spring chamber 113 in a region corresponding to the other end of the piston 120. The rod 111 and a seat 150 are arranged in the valve chamber 112, and a spring 130 is arranged in the spring chamber 113. The piston 120 is elastically pre-tensioned in a closing direction D1 of the valve body assembly 110 by a spring force of the spring 130 such that the rod 111 approaches the valve seat 151 of the seat 150. As will be described in more detail later, a sleeve 122 covers the piston 120 to form a communication passage 125 for communication between the valve chamber 112 and the spring chamber 113.The piston 120 and the sleeve 122 each correspond to the piston and sleeve according to the invention.

[0024] The seat 150 has the valve seat 151, which is arranged on a section opposite the tip end 111b of the rod 111, and a flow passage 152 that communicates with the valve seat 151, and is attached to the housing 101. When the activation of the electromagnetic unit 140 is stopped, the tip end 111b of the rod 111 abuts the valve seat 151 to close the electromagnetic valve by the spring force of the spring 130. When the electromagnetic valve is closed, the flow of hydraulic oil in the flow passage 152 is interrupted.On the other hand, when the electromagnetic unit 140 is activated and the tip end 111b of the rod 111 is moved away from the valve seat 151 against the spring force of the spring 130 to close the electromagnetic valve, the flow of the hydraulic oil is such that the hydraulic oil flows from the flow passage 152 of the seat 150 through the valve chamber 112 into the flow passage 101a of the housing 101. In other words, the direction of the preload of the valve body unit 110 by the spring 130 is opposite to the direction of the preload of the valve body unit 110 by the electromagnetic unit 140.

[0025] The electromagnetic unit 140 comprises an electromagnetic coil 141, a coil yoke 142, and a ring yoke 143. The electromagnetic coil 141 is a solenoid located outside the housing 101. The coil yoke 142 surrounds the electromagnetic coil 141, and the ring yoke 143 is attached to the housing 101. The coil yoke 142 and the ring yoke 143 are each magnetic bodies. Accordingly, the electromagnetic coil 141 is enclosed by the coil yoke 142 and the ring yoke 143, respectively, which are magnetic bodies. When the electromagnetic coil 141 is energized in this case, the electromagnetic unit 140 enters an activated state, and a magnetic flux (electromagnetic force) is generated to bias the piston 120 of the valve body unit 110 in the opening direction D2 against the spring force of the spring 130. As a result, the piston 120 moves in the opening direction D2.Conversely, when the excitation of the electromagnetic coil 141 is stopped, the electromagnetic unit 140 enters a deactivated state, and the piston 120 of the valve body unit 110 is moved in the closing direction D1 by the spring force of the spring 130. The electromagnetic coil 141 corresponds to the electromagnetic coil according to the invention.

[0026] As it is in the Fig. 3 and Fig. As shown in Figure 4, the piston 120 has several groove sections 121 (in Fig. 4 Two groove sections 121 are formed on the cylindrical outer circumferential surface 120b, and each of the groove sections 121 has a cylindrical shape and extends in one direction along a cylinder axis. The direction of the cylinder axis corresponds to the direction of movement (the opening and closing directions D1 and D2) of the valve body assembly 110. The groove section 121 is formed over the entire length of the piston 120. The sleeve 122 covers the outer circumferential surface 120b of the piston 120 and is a cylindrical element that is integral with the piston 120. Typically, the piston 120 and the sleeve 122 are integrated together by pressing the piston 120 into the sleeve 122. The sleeve 122 is designed such that its length in the direction of the cylinder axis is shorter than the length of the piston 120 in the direction of the cylinder axis.Accordingly, the piston 120 has a covered area 123, where the groove sections 121 are covered by the sleeve 122, and an uncovered area 124, where the groove sections 121 are not covered by the sleeve 122. As a result, each of the communication passages 125 described above, extending in the direction of the cylinder axis of the piston 120, is defined by a section of the groove section 121 corresponding to the covered area 123 of the piston 120 and the inner circumferential surface 122a of the sleeve 122. The communication passage 125 corresponds to the communication passage according to the invention. On the other hand, the recess of the groove section 121 in the non-covering area 124 of the piston 120 is maintained, since the section of the groove section 121 corresponding to the non-covering area 124 is not covered by the inner circumferential surface 122a of the sleeve 122.

[0027] For the design of this type of valve body assembly, a technique for forming a communication passage, such as the communication passage 125 described above, is required at low cost while simultaneously reducing the sliding resistance between the valve body assembly and the housing. Accordingly, the communication passage 125 in the valve body assembly 100 according to the invention is defined by the groove section 121 of the piston 120 and the inner circumferential surface 122a of the sleeve 122. In this case, the cost of forming the communication passage 125 is lower than the cost of forming the communication passage 125 by machining the piston 120. Furthermore, the circularity of the sleeve 122 can be increased by forming the cylindrical sleeve 122 with a desired strength. Thus, the sliding resistance between the sleeve 122 and the housing 101 can be reduced.As a result, the usability of the valve body unit 110 can be improved.

[0028] As it is in Fig. As shown in Figure 5, it is advantageous if, in the valve body unit 100 according to this embodiment, the arc length of an opening of the groove section 121 along the circumferential direction of the piston 120 is less than or equal to 20 times the radial thickness of the sleeve 122. If the outer diameter of the piston 120 is given as d [mm], the opening angle of the groove section 121 is given as θ [rad], and the thickness of the sleeve 122 is given as t [mm], the arc length L [mm] of the opening of the groove section 121 is equal to d*θ / 2. Therefore, if the condition described above is met, the relationship L / t = (d*θ) / (2*t) ≤ 20 applies. If this relationship holds, the arc length L of the opening of the groove section 121 can be determined such that the condition for the thickness t of the sleeve 122 is met. Accordingly, deformation of the sleeve 122 covering the piston 120 can be prevented, and the desired circularity of the sleeve 122 can be ensured.The circularity of the sleeve 122 (the difference between the circle defined by the outer surface of the cylinder body and the geometrically true circle) can be reduced to approximately 1 µm. However, if the arc length L of the opening of the groove section 121 exceeds 20 times the thickness t of the sleeve 122, the arc section of the sleeve 122 opposite the opening of the groove section 121 will likely deform in such a way that it generally has a straight shape. Therefore, it is difficult to ensure the desired circularity of the sleeve 122. Note that in the electromagnetic valve installed in the vehicle, the outer diameter d of the piston 120 is preferably about 6 to 20 mm.

[0029] Furthermore, according to this embodiment, the sleeve 122 in the valve body assembly 110 can preferably be made of a non-magnetic material (typically stainless steel), and it is advantageous if the relationship t ≥ s is satisfied when the dimension of the sliding gap between the outer circumferential surface 122b of the sleeve 122 and the inner circumferential surface 101b of the housing 101 is specified as s [mm]. Accordingly, the magnetic force generated by the electromagnetic coil 141 does not act on the sleeve 122, which is made of the non-magnetic material. Therefore, the friction (the sliding resistance) generated between the outer circumferential surface 122b of the sleeve 122 and the inner circumferential surface 101b of the housing 101 can be reduced.In this case, a value that satisfies the condition of the dimension of the sliding void s can be set for the thickness t of the sleeve 122, while a value to prevent fluttering of the sleeve 122 when the sleeve 122 slides can be set for the dimension of the sliding void s.

[0030] The electromagnetic valve 100 described above can be arranged in various orientations. However, in the case where the electromagnetic valve 100 is an electromagnetic vehicle valve mounted in a vehicle, as is the case in Fig. As shown in Figure 6, the electromagnetic valve 100 can preferably be arranged such that its direction along the cylinder axis of the piston 120 corresponds to the horizontal direction X (the piston 120 is arranged laterally) when the electromagnetic valve 100 is mounted in the vehicle. In this case, a section of the groove section 121, corresponding to the uncovered area 124 of the piston 120, communicates with the spring chamber 113 (a space outside the sleeve 122), preferably at least in both the horizontal direction X (hereinafter also referred to as the "first direction") and in a direction Y (hereinafter also referred to as the "second direction") that is orthogonal to the horizontal direction. Accordingly, the opening area of ​​the groove section 121 between the covered area 123 and the uncovered area 124 of the piston 120 is increased.As a result, by the flow of hydraulic fluid along at least two directions (the first and second directions), gas bubbles present in the spring chamber 113 can be easily introduced from the section of the groove section 121 corresponding to the uncovered area 124 into the communication passage 125 corresponding to the covered area 123 of the groove section 121, thereby releasing gas bubbles into the valve chamber 112. In this case, in . Fig. 6 The route of the gas bubbles flowing along the first direction X is indicated by an arrow R1, and the route of the gas bubbles flowing along the second direction Y is indicated by an arrow R2.

[0031] The present invention is not limited to the typical embodiment described above, and various applications and modifications are possible. The embodiments described below can, for example, be realized using the embodiment described above.

[0032] According to the embodiment described above, two communication passages 125 are arranged in the valve body unit 110. However, the number of communication passages according to the present invention is not limited to two. One communication passage 125 or three or more communication passages 125 can be arranged in the valve body unit 110. In particular, if the number of communication passages 125 is large, the costs can be reduced compared to the case in which the communication passages are formed by machining.

[0033] According to the embodiment described above, the communication passage 125 for communication between the valve chamber 112 and the spring chamber 113 is defined by the groove section 121 of the piston 120 and the inner circumferential surface 122a of the sleeve 122. However, the present invention can be used for a configuration of the communication passage 125 that has a different function than the communication passage 125.

[0034] Furthermore, according to the embodiment described above, the sleeve 122 is used, which is made of a non-magnetic material. However, if required, the sleeve 122 can be made of a magnetic material.

[0035] In the embodiment described above, the piston 120 has the covering area 123, in which the groove section 121 is covered by the sleeve 122, and the uncovered area 124, in which the groove section 121 is not covered by the sleeve 122. According to the present invention, however, the piston 120 can have a configuration without the uncovered area 124, in other words, a configuration in which the groove section 121 is completely covered by the sleeve 122.

[0036] Furthermore, according to the present invention, if the desired strength of the sleeve 122 can be ensured by suitable selection of the material of the sleeve 122 and the like, the arc length L of the opening of the groove section 121 can be greater than 20 times the thickness t of the sleeve 122.

[0037] Furthermore, in the embodiment described above, the pressure-reducing valves 51 and 52 of the brake control device 10 are, for example, the electromagnetic valve 100 that is mounted in the vehicle. However, the present invention can be used for an electromagnetic valve for an anti-lock braking system (ABS) that is installed in the vehicle, or for an electromagnetic valve that is installed in various other devices instead of the vehicle.

Claims

[1] An electromagnetic valve (100) comprising a valve body unit (110) housed in a housing (101) and an electromagnetic coil (141), the valve body unit (110) comprising: a piston (120) having a groove portion (121) on a cylindrical outer peripheral surface of the piston (120), the groove portion (121) extending in a cylinder axis direction, the piston (120) moving in the cylinder axis direction by an electromagnetic force generated by the electromagnetic coil (141); a rod (111) fixed to the piston (120), the rod (111) abutting against a valve seat (151) for opening and closing the electromagnetic valve (100) when the piston (120) is moved to close the electromagnetic valve (100), and the abutment of the rod (111) against the valve seat (151) is canceled when the piston (120) is moved to open the electromagnetic valve (100); a cylindrical sleeve (122) which is designed to cover the outer peripheral surface of the piston (120) and which is formed integrally with the piston (120); and a communication passage (125) defined by the groove portion (121) of the piston (120) and an inner peripheral surface of the sleeve (122) and extending in the cylinder axis direction, where the valve body unit (110) is designed such that an arc length of an opening of the groove portion (121) along the circumferential direction of the piston (120) is less than or equal to 20 times a thickness of the sleeve (122) along the radial direction of the sleeve (122), the electromagnetic valve (100) is a vehicle electromagnetic valve mounted in a vehicle and arranged such that the cylinder axis direction of the piston (120) is horizontal when the electromagnetic valve (100) is mounted in the vehicle, and the piston (120) has: a covering region (123) in which the groove portion (121) is covered by the sleeve (122); and a non-covering area (124) in which the groove portion (121) is not covered by the sleeve (122), wherein the groove portion (121) corresponding to the non-covering area (124) communicates with a space outside the sleeve (122) at least in the horizontal direction and the direction orthogonal to the horizontal direction. [2] The electromagnetic valve (100) according to claim 1, wherein the sleeve (122) is made of a non-magnetic material, and the thickness of the sleeve (122) along the radial direction of the sleeve (122) is greater than or equal to a dimension of a sliding clearance between the outer peripheral surface of the sleeve (122) and the housing (101). [3] Electromagnetic valve (100) according to claim 1 or 2, wherein the housing (101) comprises: a valve chamber (112) arranged in a region corresponding to one end of the piston (120), the rod (111) being housed in the valve chamber (112); and a spring chamber (113) arranged in a region corresponding to the other end of the piston (120), wherein a spring (130) for elastically biasing the piston (120) against the electromagnetic force generated by the electromagnetic coil (141) is accommodated in the spring chamber (113), wherein the valve chamber (112) and the spring chamber (113) communicate with each other via the communication passage (125).

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