Piston and a liquid pressure control device

Abstract

To provide a piston of which the cost of manufacture can be reduced.SOLUTION: A piston comprises a wall including an outer peripheral surface, an end face connected to an end of the outer peripheral surface in a first axial direction and an inner face which extends from the end face in a second axial direction and forms a groove which is opened on the outer peripheral surface. The inner face includes a bottom face which is provided on a bottom of the groove, an inclined face which is provided between an end of the bottom face and the outer peripheral surface in the second axial direction, a first curved face which is provided between an end of the inclined face and the outer peripheral surface in the second axial direction and continued to the outer peripheral surface; and a second curved face which is provided between the end of the bottom face and the outer peripheral surface in a circumferential direction and continued to the outer peripheral surface. An angle between the inclined face and the outer peripheral surface is 20 to 70°, a length of the first curved face along a central axis is 1.5 mm or less and the second curved face includes a first region which is continued to the first curved face and of which the width is reduced toward the first curved face.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to a piston and a hydraulic control device. [Background technology]

[0002] Conventionally, there is known a hydraulic control device that adjusts the pressure of, for example, brake fluid. The hydraulic control device has a piston that pressurizes the brake fluid. A groove is provided on the outer peripheral surface of the piston. When the piston advances until the end of the groove passes over the seal, for example, the seal and the piston separate the fluid chamber from the flow path. On the other hand, when the piston retreats until the end of the groove passes over the seal, the groove connects the fluid chamber to the flow path (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5976545 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional configurations, the grooves may be formed by, for example, cutting or electric discharge machining. Furthermore, the shape of the conventional grooves is prone to burrs when the outer circumferential surface of the piston is cut or ground. The burrs are then removed by machining. Using these types of machining to form the grooves increases the manufacturing cost of the piston.

[0005] The present invention has been made in view of the above, and provides a piston and a hydraulic pressure control device that can reduce manufacturing costs. [Means for solving the problem]

[0006] As an example, a piston according to an embodiment of the present invention includes a wall having a cylindrical outer peripheral surface, an end surface connected to an end of the outer peripheral surface in a first axial direction along a central axis of the outer peripheral surface, and an inner surface extending from the end surface in a second axial direction opposite to the first axial direction and forming a groove opening on the outer peripheral surface, the inner surface including a bottom surface provided at a bottom of the groove in a radial direction perpendicular to the central axis, a sloped surface provided between an end of the bottom surface and the outer peripheral surface in the second axial direction, and a sloped surface provided between an end of the sloped surface and the outer peripheral surface in the second axial direction. The piston has a first curved surface that is convex outward from the wall, and a second curved surface that is convex outward from the wall and is provided between the end of the bottom surface and the outer peripheral surface in the circumferential direction around the central axis, and is convex outward from the wall. The angle between the inclined surface and the outer peripheral surface is 20° to 70°, the length of the first curved surface along the central axis is 1.5 mm or less, and the second curved surface is continuous with the first curved surface and has a first region that narrows toward the first curved surface in a radial projection. Thus, for example, the portion where the outer peripheral surface and the inner surface are connected is rounded. Therefore, grooves can be formed by forging, such as press working. Generally, the outer peripheral surface is machined or ground to smooth the sliding of the piston. Because the obtuse angle between the inclined surface and the outer peripheral surface and the first and second curved surfaces that are continuous with the outer peripheral surface are provided, the piston is less likely to produce burrs due to machining or grinding. Furthermore, if the radius of the first curved surface is large, the position of the groove end in the second axial direction will vary greatly when the outer peripheral surface is cut or ground. The length of the first curved surface along the central axis is set to be small, 1.5 mm or less. This improves the accuracy of the position of the groove end in the second axial direction. As described above, the piston has the desired performance, and the groove can be formed by forging, reducing burrs. Therefore, the piston can reduce manufacturing costs. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view that schematically illustrates a brake system according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a part of the piston of the embodiment. [Figure 3] FIG. 3 is a plan view showing a part of the piston of the embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing a part of the piston of the embodiment taken along line F4-F4 in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment will be described below with reference to FIGS. 1 to 4. In this specification, components according to the embodiment and descriptions of the components may be described using multiple expressions. The components and their descriptions are merely examples and are not limited by the expressions in this specification. The components may also be identified by names different from those in this specification. Furthermore, the components may also be described using expressions different from those in this specification.

[0009] In the following description, "inhibit" is defined as, for example, preventing an event, action, or effect from occurring or reducing the magnitude of an event, action, or effect.

[0010] 1 is a cross-sectional view that schematically shows a brake system 10 according to this embodiment. The brake system 10 is mounted on a vehicle 1 such as a four-wheeled automobile. However, the brake system 10 is not limited to this example.

[0011] The brake system 10 includes a hydraulic control device 11 and a plurality of wheel cylinders 12. The brake system 10 may further include various other components such as a master cylinder, a pump, and a solenoid valve.

[0012] The hydraulic pressure control device 11 controls, for example, the hydraulic pressure of at least one of the plurality of wheel cylinders 12. The hydraulic pressure control device 11 includes an electric cylinder device 21, a reservoir 22, an electronic control unit (ECU) 23, and a plurality of hydraulic paths 24.

[0013] The electric cylinder device 21 is connected to at least one of the plurality of wheel cylinders 12 and the reservoir 22 via a fluid path 24. The electric cylinder device 21 increases the pressure of the brake fluid in the wheel cylinder 12 to generate braking force for the vehicle 1. The electric cylinder device 21 has a housing 31, a piston 32, two seals 33 and 34, a rotary-to-linear motion conversion mechanism 35, a motor 36, and a reduction mechanism 37.

[0014] The housing 31 is formed in a substantially cylindrical shape. A cylinder 41 is provided inside the housing 31. The cylinder 41 is a substantially cylindrical space extending along a central axis Ax. The central axis Ax is, for example, a virtual central axis of the cylinder 41. Note that the central axis of the cylinder 41 may be different from the central axis Ax.

[0015] For convenience, the axial direction, radial direction, and circumferential direction are defined in this specification. The axial direction is a direction along the central axis Ax. The axial direction includes a forward direction Df and a rearward direction Db. The forward direction Df is a direction along the central axis Ax and is an example of a first axial direction. The rearward direction Db is the direction opposite to the forward direction Df and is an example of a second axial direction. Note that the rearward direction Db and the forward direction Df may be different from the fore-and-aft direction of the vehicle 1. The radial direction is a direction perpendicular to the central axis Ax. The circumferential direction is a direction around the central axis Ax.

[0016] The housing 31 has an inner circumferential surface 41a and an end face 41b of a cylinder 41. The inner circumferential surface 41a and the end face 41b form (define, define) the cylinder 41. The inner circumferential surface 41a is formed in a substantially cylindrical shape extending along the central axis Ax and facing radially inward. The end face 41b is provided at an end of the cylinder 41 in the forward direction Df.

[0017] The housing 31 is further provided with an output port 42 and an input port 43. The output port 42 is an example of a first flow path. The input port 43 is an example of a second flow path. The output port 42 and the input port 43 each open to the inner circumferential surface 41a and communicate with the cylinder 41. In the axial direction, the input port 43 is spaced from the output port 42 in the rearward direction Db.

[0018] The piston 32 extends in the axial direction and has a generally cylindrical shape with a closed end in the forward direction Df. The piston 32 has an outer circumferential surface 32a, an end face 32b, and a curved surface 32c. The curved surface 32c is an example of a fourth curved surface.

[0019] The outer peripheral surface 32a is formed in a cylindrical shape extending in the axial direction. The outer peripheral surface 32a is disposed substantially concentrically (coaxially) with the cylinder 41. Therefore, the central axis Ax is not only the central axis of the cylinder 41 but also the central axis of the outer peripheral surface 32a. The outer peripheral surface 32a may have an uneven surface.

[0020] The end face 32b is connected to the end of the outer circumferential surface 32a in the forward direction Df via a curved surface 32c. The end face 32b is formed to be substantially flat and faces the forward direction Df. The curved surface 32c is continuous with the outer circumferential surface 32a and the end face 32b. That is, the curved surface 32c is directly connected to the outer circumferential surface 32a and the end face 32b. The curved surface 32c forms an arc-shaped edge extending between the outer circumferential surface 32a and the end face 32b in a cross section along the central axis Ax as shown in FIG. 1.

[0021] The piston 32 is housed in the cylinder 41. The piston 32 is able to move axially inside the cylinder 41. The piston 32 defines a part of the cylinder 41 as a liquid chamber 45. The liquid chamber 45 is provided between an end face 32b of the piston 32 and an end face 41b of the cylinder 41 in the axial direction.

[0022] The output port 42 communicates with a fluid chamber 45. The fluid chamber 45 is connected to the wheel cylinder 12 through the output port 42 and the fluid passage 24. The piston 32 reduces the volume of the fluid chamber 45 by moving forward Df. This allows the electric cylinder device 21 to increase the pressure of the brake fluid in the fluid chamber 45 and the wheel cylinder 12.

[0023] On the other hand, the piston 32 moves in the rear direction Db to increase the volume of the fluid chamber 45. This allows the electric cylinder device 21 to reduce the pressure of the brake fluid in the fluid chamber 45 and the wheel cylinder 12.

[0024] A gap 46 is provided radially between the inner circumferential surface 41a of the cylinder 41 and the outer circumferential surface 32a of the piston 32. The inner circumferential surface 41a of the cylinder 41 faces the outer circumferential surface 32a of the piston 32 via the gap 46. The gap 46 allows the piston 32 to move axially relative to the housing 31.

[0025] The two seals 33, 34 seal the gap 46. In the axial direction, the seal 33 is spaced forward Df from the input port 43. The seal 34 is spaced rearward Db from the input port 43. The output port 42 opens to the inner circumferential surface 41a at a position spaced forward Df from the seal 33. The seal 33 can seal between the liquid chamber 45 and the input port 43.

[0026] The reservoir 22 is connected to the input port 43 through the fluid passage 24. The reservoir 22 stores brake fluid. For example, the reservoir 22 is open to the atmosphere, so that the pressure of the reservoir 22 is maintained at atmospheric pressure.

[0027] The rotary-to-linear motion conversion mechanism 35 is disposed inside the cylinder 41. In this embodiment, the rotary-to-linear motion conversion mechanism 35 is, for example, a ball screw. The rotary-to-linear motion conversion mechanism 35 has a rotating member 51, a linear motion member 52, and a plurality of balls 53.

[0028] In this embodiment, the rotating member 51 may also be referred to as a screw shaft. The linear motion member 52 may also be referred to as a nut. However, the rotary-linear motion conversion mechanism 35 is not limited to this example. For example, the rotating member may have a nut, and the linear motion member may have a screw shaft.

[0029] The rotary member 51 is supported by the housing 31 so as to be rotatable about the central axis Ax. The linear motion member 52 is attached to the piston 32. The piston 32 and the linear motion member 52 may be formed integrally.

[0030] For example, a male screw provided on the rotating member 51 and a female screw provided on the linear moving member 52 are fitted together via a ball 53. As a result, the linear moving member 52 and the piston 32 move in the forward direction Df or the backward direction Db in response to the rotation of the rotating member 51.

[0031] The motor 36 is disposed outside the housing 31. The motor 36 has an output shaft 55 and rotates the output shaft 55 under the control of, for example, the ECU 23. The reduction mechanism 37 has a plurality of gears and transmits rotation between the rotating member 51 and the output shaft 55.

[0032] The piston 32 has a main body 60. The main body 60 is an example of a wall. The main body 60 has a peripheral wall 61 and an end wall 62. The peripheral wall 61 is formed in a substantially cylindrical shape extending along the central axis Ax and has an outer peripheral surface 32a. The end wall 62 is connected to the end of the peripheral wall 61 in the forward direction Df and has an end surface 32b. The main body 60 has a curved surface 32c at a corner where the peripheral wall 61 and the end wall 62 are connected.

[0033] A plurality of grooves 65 are provided in the main body 60 of the piston 32. Each of the plurality of grooves 65 extends from the end face 32b and the curved surface 32c in the rear direction Db and opens to the outer circumferential surface 32a. The main body 60 further has a plurality of inner surfaces 66. Each of the plurality of inner surfaces 66 forms (defines, defines) a groove 65. The plurality of grooves 65 and the plurality of inner surfaces 66 are arranged at approximately equal intervals around the central axis Ax.

[0034] Fig. 2 is a cross-sectional view showing a part of piston 32 of this embodiment. Fig. 3 is a plan view showing a part of piston 32 of this embodiment. Fig. 4 is a cross-sectional view showing a part of piston 32 of this embodiment along line F4-F4 in Fig. 3.

[0035] As shown in Fig. 3, each of the multiple inner surfaces 66 has a bottom surface 71, an inclined surface 72, a curved surface 73, a curved surface 74, a pair of curved surfaces 75, and a pair of curved surfaces 76. The curved surface 74 is an example of a first curved surface. The curved surface 75 is an example of a second curved surface. The curved surface 76 is an example of a fifth curved surface.

[0036] The bottom surface 71 is provided at the bottom of the groove 65 in the radial direction. The bottom surface 71 has two curved surface regions 71a and 71b. Note that the bottom surface 71 is not limited to this example. The curved surface region 71a is an example of a sixth curved surface and a second region. The curved surface region 71b is an example of a third curved surface.

[0037] As shown in Fig. 4, the curved surface region 71a has a substantially semi-cylindrical curved surface that protrudes inward from the main body 60 and extends substantially in the axial direction. Therefore, the central axis C1 of the curved surface region 71a is located outside the main body 60. The curved surface region 71a is also substantially perpendicular to the end face 32b. However, the curved surface region 71a is not limited to this example. For example, the curved surface region 71a may be inclined with respect to the central axis Ax so as to taper in the forward direction Df.

[0038] 2, the curved surface region 71b is provided between the end face 32b and the end of the curved surface region 71a in the forward direction Df, and is continuous with the end face 32b. The curved surface region 71b has a curved surface that is convex outward from the main body 60. Therefore, the center line C2 of the curved surface region 71b is located inside the main body 60.

[0039] The curved surface region 71b does not have to be smoothly connected to the end face 32b. At the position where the curved surface region 71b and the end face 32b are connected to each other, the angle between the tangent to the curved surface region 71b and the end face 32b is smaller (shallower) than 90°.

[0040] In a radial projection view such as that shown in Fig. 3, the width W1 of the curved region 71b is, for example, 2.2 mm to 2.8 mm. That is, the width W1 is 0.5 mm or more, and also 1 mm or more. However, the width W1 is not limited to this example.

[0041] 2, the inclined surface 72 is provided between the end of the bottom surface 71 in the rear direction Db and the outer circumferential surface 32a. In this embodiment, the inclined surface 72 is connected to the end of the curved surface region 71a in the rear direction Db via a curved surface 73.

[0042] The angle θ between the inclined surface 72 and the outer peripheral surface 32a is smaller than a right angle. The angle θ is, for example, 43.5° to 46.5°. That is, the angle θ is 20° to 70°, or 30° to 60°. However, the angle θ is not limited to this example.

[0043] The curved surface 73 is provided between the end of the inclined surface 72 in the forward direction Df and the end of the bottom surface 71 in the rearward direction Db. The curved surface 73 is a curved surface that convexly faces inward of the main body 60. Therefore, the center line C3 of the curved surface 73 is located outside the main body 60.

[0044] The curved surface 74 is provided between the end of the inclined surface 72 in the rear direction Db and the outer peripheral surface 32a, and is continuous with the outer peripheral surface 32a. The curved surface 74 is a curved surface that convexly extends outward from the main body 60. Therefore, the center line C4 of the curved surface 74 is located within the main body 60.

[0045] In a radial projection view such as that shown in FIG. 3, the width W2 of the curved surface 74 is, for example, 0.4 mm or less. That is, the width W2 is 1.5 mm or less, or even 1 mm or less. Note that the width W2 is not limited to this example. The width W2 is equal to the length of the curved surface 74 along the central axis Ax.

[0046] In a radial projection as shown in Fig. 3, the boundary B1 between the outer circumferential surface 32a and the curved surface 74 is an arc-shaped curve. Note that the boundary B1 is not limited to this example. The boundary B1 forms the end of the groove 65 in the rear direction Db.

[0047] 4, the curved surface 75 is provided between the end of the bottom surface 71 and the outer peripheral surface 32a in the circumferential direction, and is also provided between the end of the inclined surface 72 and the outer peripheral surface 32a in the circumferential direction. The curved surface 75 is continuous with the outer peripheral surface 32a. The curved surface 75 is a curved surface that is convex outward from the main body 60. Therefore, the center line C5 of the curved surface 75 is located inside the main body 60.

[0048] Curved surface 75 does not have to be smoothly connected to outer peripheral surface 32a. At the position where curved surface 75 and outer peripheral surface 32a are connected to each other, the angle between the tangent to curved surface 75 and the tangent to outer peripheral surface 32a is smaller (shallower) than a right angle.

[0049] The curved surface 75 is continuous with the curved surface region 71a of the bottom surface 71 and the inclined surface 72. In this embodiment, the curved surface 75 is smoothly continuous with the curved surface region 71a. That is, at the position where the curved surface 75 and the curved surface region 71a are connected, the tangent to the curved surface 75 and the tangent to the curved surface region 71a substantially coincide with each other.

[0050] 3, curved surface 75 has gradually changing region 75a and linear region 75b. Note that curved surface 75 is not limited to this example. Gradual changing region 75a is an example of a first region. Linear region 75b is an example of a third region.

[0051] The gradually changing region 75a is continuous with the curved surface 74. In a radial projection such as that shown in Figure 3, the width of the gradually changing region 75a decreases toward the curved surface 74. The smallest width of the gradually changing region 75a is approximately equal to the width W2 of the curved surface 74.

[0052] The boundary B2 between the gradually changing region 75a and the outer peripheral surface 32a extends in a curved shape. The boundary B3 between the gradually changing region 75a and the bottom surface 71 or the inclined surface 72 also extends in a curved shape. The width of the gradually changing region 75a is the distance between the boundary B2 and the boundary B3. The boundary B2 has a larger radius of curvature than the boundary B3.

[0053] The linear region 75b extends in the forward direction Df from an end of the gradually changing region 75a in the forward direction Df. That is, the linear region 75b is directly connected to the gradually changing region 75a. In a radial projection view such as that shown in FIG. 3, the width W3 of the linear region 75b is substantially constant.

[0054] The width W3 is, for example, 1.3 mm. That is, the width W3 is 0.5 mm or more, and also 0.7 mm or more. Note that the width W3 is not limited to this example. The width W3 of the linear region 75b is greater than the width W2 of the curved surface 74.

[0055] The curved surface 76 is continuous with the end of the linear region 75b in the forward direction Df and with the curved surface 32c. The curved surface 76 is a curved surface that is convex outward from the main body 60. In a projection view seen in the radial direction as shown in FIG. 3, the width W4 of the curved surface 76 is 2.2 mm to 2.8 mm. That is, the width of the curved surface 76 is 0.5 mm or more, and also 1 mm or more. Note that the width of the curved surface 76 is not limited to this example.

[0056] The pair of gradually changing regions 75a and the pair of curved surfaces 76 cause the groove 65 to taper in the rear direction Db. Therefore, the width of the groove 65 in the circumferential direction is greatest at the position where the end face 32b and the inner surface 66 are connected to each other. In other words, the width of the groove 65 is greatest at the end of the groove 65 in the forward direction Df. The width of the groove 65 is shortest at the position (boundary B1) where the curved surface 74 and the outer peripheral surface 32a are connected to each other. In other words, the width of the groove 65 is greatest at the end of the groove 65 in the rear direction Db. Between the pair of straight line regions 75b, the width of the groove 65 is approximately constant.

[0057] The main body 60 of the piston 32 is formed by forging, such as press working, to form a plurality of grooves 65. The grooves 65 do not have portions that taper in the forward direction Df. The outer peripheral surface 32a, the end surface 32b, and the inner surface 66 are connected to one another by curved surfaces 32c, 74, 75, and 76. That is, the main body 60 does not have corners that could apply a large load or cause stress concentration on the press working die or the main body 60. Therefore, the grooves 65 can be easily formed by press working.

[0058] The grooves 65 are formed by pressing, which reduces costs compared to when they are formed by cutting or electric discharge machining. Also, the strength of the main body 60 can be prevented from decreasing compared to when the grooves 65 are formed by cutting.

[0059] After the body 60 of the piston 32 is formed by press working, the outer circumferential surface 32a and the end faces 32b are, for example, cut or ground. This reduces the surface roughness of the outer circumferential surface 32a and the end faces 32b and improves the roundness of the outer circumferential surface 32a. The outer circumferential surface 32a may be anodized.

[0060] 2, before the outer peripheral surface 32a and the end surface 32b are cut or ground, the main body 60 of the piston 32 has cutting allowances S1 and S2. The widths of the curved surfaces 32c, 74, 75, and 76 on the main body 60, including the cutting allowances S1 and S2, are greater than the widths of the curved surfaces 32c, 74, 75, and 76 after cutting or grinding.

[0061] For example, the cutting blade enters the curved surfaces 32c, 74, 75, and 76 of the main body 60, including the cutting allowance S1. In the vicinity of the outer peripheral surface 32a, the angles between the outer peripheral surface 32a and each of the curved surfaces 32c, 74, 75, and 76 are small. Furthermore, the angle between the outer peripheral surface 32a and the inclined surface 72 is also small (shallow). Therefore, burrs are less likely to occur when the outer peripheral surface 32a is cut or ground.

[0062] For example, the cutting blade enters the curved surface 32c and the curved surface region 71b of the main body 60, including the cutting allowance S2. In the vicinity of the end face 32b, the angle between the end face 32b and the curved surface 32c and the angle between the end face 32b and the curved surface region 71b are small. Therefore, when the end face 32b is cut or ground, burrs are unlikely to occur.

[0063] While the outer peripheral surface 32a and the end face 32b are cut or ground, the inner surface 66 is not machined. Therefore, the surface roughness of the inner surface 66 is rougher than that of the outer peripheral surface 32a. Conversely, the surface roughness of the outer peripheral surface 32a is smoother than that of the inner surface 66. When the surface roughness is measured in terms of maximum height, the maximum height (Rz) of the surface roughness of the inner surface 66 is, for example, 12.5 μm or less. However, the surface roughness of the inner surface 66 is not limited to this example.

[0064] 1, when the piston 32 is retracted in the rearward direction Db until the end (boundary B1) of the groove 65 in the rearward direction Db passes over the seal 33, the fluid chamber 45 and the gap 46 communicate with each other at the boundary B1 in the rearward direction Db. That is, the fluid chamber 45 and the reservoir 22 communicate with each other. This allows the brake fluid to flow freely between the fluid chamber 45 and the reservoir 22, and the pressure in the fluid chamber 45 drops to atmospheric pressure.

[0065] The timing at which the liquid chamber 45 and the reservoir 22 communicate with each other is affected by the position of the boundary B1. If the angle θ between the inclined surface 72 and the outer peripheral surface 32a is too small, the position of the boundary B1 will vary greatly due to variations in the cutting or grinding of the outer peripheral surface 32a and variations in the formation of the grooves 65. Furthermore, if the radius of curvature of the curved surface 74 is large, the position of the boundary B1 will vary greatly due to variations in the cutting or grinding of the outer peripheral surface 32a and variations in the formation of the grooves 65.

[0066] In this embodiment, the angle θ between the inclined surface 72 and the outer peripheral surface 32a is not too small, and the length (width W2) of the curved surface 74 in the axial direction is also small. This reduces variation in the position of the boundary B1. In other words, the timing at which the liquid chamber 45 and the reservoir 22 communicate with each other can be controlled more accurately.

[0067] In the hydraulic pressure control device 11 according to the embodiment described above, curved surfaces 74, 75 that convex outward from the main body 60 are provided at the connection between the outer peripheral surface 32a and the inner surface 66. That is, the connection between the outer peripheral surface 32a and the inner surface 66 is rounded, avoiding corners that would impose a large load on the mold or the main body 60 of the piston 32. Therefore, the groove 65 can be formed by forging, such as press work. Furthermore, the outer peripheral surface 32a is generally machined or ground to facilitate smooth sliding of the piston 32. The obtuse angle between the inclined surface 72 and the outer peripheral surface 32a and the curved surfaces 74, 75 that are continuous with the outer peripheral surface 32a prevent burrs from being generated on the piston 32 due to cutting or grinding. Furthermore, if the radius of the curved surface 74 is large, the position of the end of the groove 65 in the rear direction Db will vary significantly when the outer peripheral surface 32a is machined or ground. When the piston 32 retracts in the rearward direction Db, the fluid chamber 45 of the cylinder 41 communicates with the input port 43 at the end of the groove 65 in the rearward direction Db. That is, the position of the end of the groove 65 in the rearward direction Db affects the timing at which the fluid chamber 45 communicates with the input port 43. The length (width W2) of the curved surface 74 along the central axis Ax is the remaining dimension of the curved surface 74 after cutting or grinding, and is set to a small value of 1.5 mm or less. This improves the accuracy of the position of the end of the groove 65 in the rearward direction Db, thereby improving the accuracy of the communication and blocking between the fluid chamber 45 and the input port 43 by the piston 32. As described above, the piston 32 has the desired performance, and the groove 65 can be formed by forging, reducing burrs. Therefore, the piston 32 can be manufactured at lower costs than when the groove 65 is formed by cutting or electric discharge machining, or when extensive burr removal processing is performed.

[0068] The portion where the end face 32b and the inner surface 66 are connected is provided with a curved surface region 71b that is convex outward from the body 60. That is, the portion where the end face 32b and the curved surface region 71a of the bottom surface 71 are connected is rounded and does not have a corner that would apply a large load to the mold or the body 60 of the piston 32. This allows the groove 65 to be formed by forging. The end face 32b may also be cut or ground. Because the curved surface region 71b that is continuous with the end face 32b is provided, the piston 32 can suppress the generation of burrs due to cutting or grinding.

[0069] A curved surface 32c that convexly extends outward from the body 60 is provided at the portion where the outer peripheral surface 32a and the end surface 32b are connected. Furthermore, a curved surface 76 that convexly extends outward from the body 60 is provided at the portion where the outer peripheral surface 32a and the inner surface 66 are connected, at the portion where the curved surface 75 and the curved surface 32c are connected, and at the portion where the end surface 32b and the inner surface 66 are connected. That is, the portions where the outer peripheral surface 32a, the end surface 32b, and the inner surface 66 are connected are rounded, avoiding corners that would apply a large load to the mold or the body 60 of the piston 32. Therefore, the groove 65 can be formed by forging, such as press working.

[0070] In a projection view seen in the radial direction, the width W3 of the linear region 75b is constant. Therefore, by moving the mold in the rear direction Db relative to the piston 32, it is possible to form the curved surface 75 having the gradually changing region 75a and the linear region 75b.

[0071] The bottom surface 71 has a curved surface region 71a that is convex toward the inside of the main body 60. Therefore, the bottom surface 71 can be formed by forging.

[0072] The portion where the bottom surface 71 and the curved surface 75 are connected is smooth and continuous, without any corners that would apply a large load to the mold or the body 60 of the piston 32. Therefore, the groove 65 can be formed by forging, such as press working.

[0073] The boundary B1 between the outer peripheral surface 32a and the curved surface 74 does not form a corner that would apply a large load to the die or the body 60 of the piston 32. Therefore, the groove 65 can be formed by forging, such as by pressing.

[0074] The groove 65 tapers in the rear direction Db. Therefore, the mold can form the groove 65 by moving in the rear direction Db relative to the material of the piston 32.

[0075] The main body 60 has a plurality of inner surfaces 66 that are arranged around the central axis Ax and each of which forms a groove 65. Therefore, the plurality of grooves 65 can, for example, connect the liquid chamber 45 and the input port 43. Therefore, the piston 32 can set a large flow path area between the liquid chamber 45 and the input port 43.

[0076] The surface roughness of the inner surface 66 is rougher than the surface roughness of the outer peripheral surface 32a. That is, the outer peripheral surface 32a is cut or ground, for example, to allow the piston 32 to slide smoothly, but the inner surface 66 is not machined and can be maintained with the surface roughness formed by forging. Therefore, the piston 32 can be manufactured with less machining, which in turn reduces manufacturing costs.

[0077] The piston 32 can increase the hydraulic pressure in the cylinder 41 and the output port 42 by advancing in the forward direction Df to a position where the end of the groove 65 in the rear direction Db is spaced in the forward direction Df from the seal 33. On the other hand, the piston 32 can establish communication between the output port 42 and the input port 43 via the cylinder 41 by retreating in the rear direction Db to a position where the end of the groove 65 in the rear direction Db is spaced in the rear direction Db from the seal 33. The piston 32 can improve the accuracy of the position of the end of the groove 65 in the rear direction Db, and therefore can improve the accuracy of the piston 32 establishing and blocking communication between the output port 42 and the input port 43.

[0078] In the above embodiment, the bottom surface 71 has the curved region 71a. However, the bottom surface 71 may have a flat surface or a curved surface extending in the circumferential direction. In this case, the curved region 71a connects the flat surface or curved surface to the curved surfaces 73 and 75.

[0079] In the above embodiment, the piston 32 is provided in the electric cylinder device 21. However, the piston 32 may be provided in another device such as a master cylinder. In this case, the shape of the piston 32 is not limited to the above. For example, the end wall 62 may be provided with a hole through which a spring passes.

[0080] The piston according to at least one embodiment described above includes, for example, a wall having a cylindrical outer peripheral surface, an end surface connected to an end of the outer peripheral surface in a first axial direction along a central axis of the outer peripheral surface, and an inner surface extending from the end surface in a second axial direction opposite to the first axial direction and forming a groove opening on the outer peripheral surface, and the inner surface has a bottom surface provided at a bottom of the groove in a radial direction perpendicular to the central axis, a sloped surface provided between the end of the bottom surface and the outer peripheral surface in the second axial direction, and a sloped surface provided between the end of the sloped surface and the outer peripheral surface in the second axial direction. The piston has a first curved surface between the bottom surface and the outer peripheral surface, which is continuous with the outer peripheral surface and convex outward from the wall, and a second curved surface between the end of the bottom surface and the outer peripheral surface in the circumferential direction around the central axis, which is continuous with the outer peripheral surface and convex outward from the wall, wherein the angle between the inclined surface and the outer peripheral surface is 20° to 70°, the length of the first curved surface along the central axis is 1.5 mm or less, and the second curved surface is continuous with the first curved surface and has a first region whose width decreases toward the first curved surface in a projection view viewed in the radial direction. Thus, for example, the first curved surface and the second curved surface convex outward from the wall are provided at the portion where the outer peripheral surface and the inner surface are connected. That is, the portion where the outer peripheral surface and the inner surface are connected is rounded, without any corners that would apply a large load to the mold or the piston wall. Therefore, grooves can be formed by forging, such as press working. Furthermore, the outer peripheral surface is generally machined or ground to smooth the sliding of the piston. The obtuse angle between the inclined surface and the outer peripheral surface, and the provision of a first curved surface and a second curved surface that are continuous with the outer peripheral surface, prevent burrs from being generated on the piston due to cutting or grinding. Furthermore, if the radius of the first curved surface is large, the position of the groove end in the second axial direction will vary greatly when the outer peripheral surface is cut or ground. When the piston retracts in the second axial direction, the end of the groove in the second axial direction communicates with, for example, the fluid chamber of the cylinder and the flow path. In other words, the position of the groove end in the second axial direction affects the timing at which the groove communicates with the fluid chamber and the flow path. The length of the first curved surface along the central axis is the remaining dimension of the first curved surface after cutting or grinding, and is set to be small, for example, 1.5 mm or less.This improves the accuracy of the position of the groove end in the second axial direction, thereby improving the accuracy of communication and blocking between the fluid chamber and the flow path by the piston. As described above, the piston has the desired performance while allowing the groove to be formed by forging, reducing burrs. Therefore, the piston can be manufactured at a lower cost than when the groove is formed by cutting or electric discharge machining, or when a large amount of burr removal processing is performed.

[0081] In the piston, for example, the angle between the inclined surface and the outer circumferential surface is 30° to 60°. Therefore, for example, the piston can reduce manufacturing costs.

[0082] In the piston, for example, the length of the first curved surface along the central axis is 1 mm or less, which allows for reduced manufacturing costs.

[0083] In the above piston, for example, the bottom surface has a second region connected to the inclined surface and a third curved surface provided between the end surface and the end of the second region in the first axial direction, continuing from the end surface and convex outward from the wall. Therefore, for example, a third curved surface convex outward from the wall is provided at the portion where the end surface connects to the inner surface. That is, the portion where the end surface connects to the second region of the bottom surface is rounded and does not have a corner that would apply a large load to the mold or the wall of the piston. Therefore, grooves can be formed by forging. Furthermore, the end surface may be machined or ground. The provision of a third curved surface continuing from the end surface reduces the generation of burrs due to cutting or grinding.

[0084] In the piston, for example, the width of the third curved surface is 0.5 mm or more in a projection view seen in the radial direction, and therefore, for example, the piston can suppress the generation of burrs due to cutting or grinding.

[0085] In the piston, for example, the width of the third curved surface is 1 mm or more in a projection view seen in the radial direction, and therefore, for example, the piston can suppress the generation of burrs due to cutting or grinding.

[0086] In the piston, for example, the wall has a fourth curved surface that is continuous with the outer peripheral surface and the end surface, and the inner surface has a fifth curved surface that is continuous with the second curved surface and the fourth curved surface, and the width of the fifth curved surface is 0.5 mm or more in a radial projection. Therefore, for example, the fourth curved surface that is convex outward is provided at the portion where the outer peripheral surface and the end surface are connected. Furthermore, the fifth curved surface that is convex outward is provided at the portion where the outer peripheral surface and the inner surface are connected, the portion where the second curved surface and the fourth curved surface are connected, and the portion where the end surface and the inner surface are connected. That is, the portions where the outer peripheral surface, the end surface, and the inner surface are connected are rounded, without corners that would apply a large load to the mold or the piston wall. Therefore, the grooves can be formed by forging, such as press working.

[0087] In the piston, for example, the width of the fifth curved surface is 1 mm or more in a projection view seen in the radial direction. Therefore, for example, the groove can be formed by forging such as press working.

[0088] In the piston, as one example, the second curved surface has a third region extending from the first region in the first axial direction, and the width of the third region is constant in a projection view seen in the radial direction. Thus, as one example, the mold can form the second curved surface having the first region and the third region by moving in the second axial direction relative to the piston.

[0089] In the piston, for example, the width of the third region in a projection seen in the radial direction is 0.5 mm or more and is greater than the length of the first curved surface along the central axis. Thus, for example, the mold can form the second curved surface having the first region and the third region by moving in the second axial direction relative to the piston.

[0090] In the piston, for example, the width of the third region in a projection seen in the radial direction is 0.7 mm or more and is greater than the length of the first curved surface along the central axis. Thus, for example, the mold can form the second curved surface having the first region and the third region by moving in the second axial direction relative to the piston.

[0091] In the piston, for example, the bottom surface has a sixth curved surface that is convex toward the inside of the wall. Thus, for example, the bottom surface can be formed by forging.

[0092] In the piston, for example, the sixth curved surface is continuous with the second curved surface. Therefore, for example, the portion where the bottom surface and the second curved surface are connected does not have a corner that would apply a large load to the mold or the wall of the piston, but is smoothly continuous. Therefore, the groove can be formed by forging, such as press working.

[0093] In the piston, for example, in a projection view seen in the radial direction, the boundary between the outer peripheral surface and the first curved surface is a curved line. Therefore, for example, the boundary between the outer peripheral surface and the first curved surface does not have a corner that would impose a large load on the die or the piston wall. Therefore, for example, the groove can be formed by forging, such as press working.

[0094] In the piston, for example, the boundary is a circular arc in the radial projection. Thus, for example, the groove can be formed by forging, such as by pressing.

[0095] In the piston, for example, the width of the groove in the circumferential direction is greatest at the position where the end face and the inner face are connected to each other. Therefore, for example, the groove tapers toward the second axial direction. Therefore, the mold can be moved in the second axial direction relative to the piston material to form the groove.

[0096] In the piston, for example, the wall has a plurality of inner surfaces that each define a groove and are arranged around the central axis. Therefore, for example, the plurality of grooves can connect, for example, the liquid chamber and the flow path. Therefore, the piston can be configured to have a large flow path area between the liquid chamber and the flow path.

[0097] In the piston, for example, the surface roughness of the inner surface is rougher than the surface roughness of the outer surface. Therefore, for example, the outer surface is cut or ground to smooth the sliding of the piston, but the inner surface is not machined and can be kept as the surface roughness formed by forging. Therefore, the piston can reduce the amount of machining, and ultimately the manufacturing cost.

[0098] In the piston, for example, the maximum height of the surface roughness of the inner surface is 12.5 μm or less, which allows the piston to reduce processing and ultimately reduce manufacturing costs.

[0099]

[0013] As an example, the hydraulic pressure control device according to at least one embodiment described above includes: a housing having an inner circumferential surface facing the outer circumferential surface; and a seal spaced from the second circumferential surface in the first axial direction and sealing a gap between the outer circumferential surface and the inner circumferential surface. The housing includes: a piston; a cylinder that accommodates the piston; a first flow path communicating with the cylinder; and a second flow path communicating with the cylinder at a position spaced from the first flow path in the second axial direction. Thus, as an example, the piston can increase hydraulic pressure in the cylinder and the first flow path by advancing in the first axial direction to a position where an end of the groove in the second axial direction is spaced from the seal in the first axial direction. Meanwhile, the piston can communicate with the first flow path and the second flow path via the cylinder by retracting in the second axial direction to a position where an end of the groove in the second axial direction is spaced from the seal in the second axial direction. The piston can improve the accuracy of the position of the end of the groove in the second axial direction, and thus improve the accuracy of communication and blocking between the first flow path and the second flow path by the piston.

[0100] While the embodiments of the present invention have been described above, the above-described embodiments and modifications are merely examples and are not intended to limit the scope of the invention. The above-described embodiments and modifications can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. Furthermore, the configurations and shapes of each embodiment and each modification can be partially interchanged. [Explanation of symbols]

[0101] 11...hydraulic pressure control device, 31...housing, 32...piston, 32a...outer peripheral surface, 32b...end surface, 32c...curved surface (fourth curved surface), 33...seal, 41...cylinder, 41a...inner peripheral surface, 42...output port (first flow path), 43...input port (second flow path), 46...gap, 60...main body (wall), 65...groove, 66...inner surface, 71...bottom surface, 71a...curved surface region (second region, sixth curved surface) ), 71b...curved surface area (third curved surface), 72...inclined surface, 74...curved surface (first curved surface), 75...curved surface (second curved surface), 75a...gradually changing area (first area), 75b...straight line area (third area), 76...curved surface (fifth curved surface), Ax...central axis, Df...forward direction (first axial direction), Db...backward direction (second axial direction), W1, W3, W4...width, W2...width (length), θ...angle, B1...boundary.

Claims

1. a wall having a cylindrical outer peripheral surface, an end surface connected to an end of the outer peripheral surface in a first axial direction along a central axis of the outer peripheral surface, and an inner surface extending from the end surface in a second axial direction opposite to the first axial direction and forming a groove opening on the outer peripheral surface; Equipped with the inner surface has a bottom surface provided at the bottom of the groove in a radial direction perpendicular to the central axis, a sloped surface provided between an end of the bottom surface and the outer circumferential surface in the second axial direction, a first curved surface provided between the end of the sloped surface and the outer circumferential surface in the second axial direction, the first curved surface being continuous with the outer circumferential surface and convex outward from the wall, and a second curved surface provided between the end of the bottom surface and the outer circumferential surface in the circumferential direction around the central axis, the second curved surface being continuous with the outer circumferential surface and convex outward from the wall, The angle between the inclined surface and the outer circumferential surface is 20° to 70°, The length of the first curved surface along the central axis is 1.5 mm or less, the second curved surface is continuous with the first curved surface and has a first region whose width decreases toward the first curved surface in a projection view seen in the radial direction; piston.

2. The angle between the inclined surface and the outer circumferential surface is 30° to 60°. The piston of claim 1.

3. The length of the first curved surface along the central axis is 1 mm or less. The piston of claim 1.

4. the bottom surface has a second region connected to the inclined surface, and a third curved surface provided between the end surface and an end of the second region in the first axial direction, the third curved surface being continuous with the end surface and convex outward from the wall, The piston of claim 1.

5. In a projection view seen in the radial direction, the width of the third curved surface is 0.5 mm or more. The piston of claim 4.

6. In a projection view seen in the radial direction, the width of the third curved surface is 1 mm or more. The piston of claim 5.

7. the wall has a fourth curved surface that is continuous with the outer circumferential surface and the end surface, the inner surface has a fifth curved surface that is continuous with the second curved surface and the fourth curved surface, In a projection view seen in the radial direction, the width of the fifth curved surface is 0.5 mm or more. The piston of claim 1.

8. In a projection view seen in the radial direction, the width of the fifth curved surface is 1 mm or more. The piston of claim 7.

9. the second curved surface has a third region extending from the first region in the first axial direction; In a projection view seen in the radial direction, the width of the third region is constant. The piston of claim 1.

10. a width of the third region in a projection seen in the radial direction is 0.5 mm or more and is greater than a length of the first curved surface along the central axis; The piston of claim 9.

11. a width of the third region in a projection seen in the radial direction is 0.7 mm or more and is greater than a length of the first curved surface along the central axis; The piston of claim 10.

12. The bottom surface has a sixth curved surface that is convex toward the inside of the wall. The piston of claim 1.

13. the sixth curved surface is continuous with the second curved surface; The piston of claim 12.

14. In a projection view seen in the radial direction, a boundary between the outer circumferential surface and the first curved surface is a curved line. The piston of claim 1.

15. In the radial projection, the boundary is a circular arc.

15. The piston of claim 14.

16. The width of the groove in the circumferential direction is longest at a position where the end surface and the inner surface are connected to each other. The piston of claim 1.

17. the wall has a plurality of inner surfaces each defining the groove and arranged around the central axis; The piston of claim 1.

18. The surface roughness of the inner surface is greater than the surface roughness of the outer circumferential surface. The piston of claim 1.

19. The maximum height of the surface roughness of the inner surface is 12.5 μm or less.

20. The piston of claim 18.

20. a piston according to any one of claims 1 to 19; a housing provided with a cylinder that accommodates the piston, a first flow path that communicates with the cylinder, and a second flow path that communicates with the cylinder at a position spaced from the first flow path in the second axial direction, the housing having an inner circumferential surface facing the outer circumferential surface; a seal spaced from the second flow path in the first axial direction and sealing a gap between the outer circumferential surface and the inner circumferential surface; A hydraulic control device comprising:

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