Master cylinder device

Abstract

To provide a master cylinder device capable of miniaturizing a magnet as one example.SOLUTION: A master cylinder device according to an embodiment includes, for example, a piston having an inner peripheral surface extending around a central axis and facing the central axis and an outer peripheral surface extending around the central axis and facing the inner peripheral surface, the piston being configured to move in an axial direction along the central axis and being configured to be restricted from rotating around the central axis, a sensor spaced apart from the outer peripheral surface in a direction orthogonal to the central axis and configured to detect magnetism, and a detection target component having a magnet located between the central axis and the sensor and being partially provided on the outer peripheral surface around the central axis.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a master cylinder device. [Background technology]

[0002] A master cylinder device has been known that includes a piston and a stroke sensor that detects the position of the piston. The stroke sensor detects the position of the piston based on the magnetism of a magnet provided in the piston, for example (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-178098 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional configurations, the magnet is located on the central axis of the piston, for example. Meanwhile, the stroke sensor is located radially adjacent to the piston. This results in a long distance between the magnet and the stroke sensor. Since the stroke sensor detects the magnetism of the magnet, the master cylinder device must be equipped with a large magnet.

[0005] The present invention has been made in view of the above, and provides a master cylinder device in which the magnet can be made smaller. [Means for solving the problem]

[0006] A master cylinder device according to an embodiment of the present invention includes, as an example, a piston having an inner circumferential surface extending about a central axis and facing the central axis, and an outer circumferential surface extending about the central axis and facing the inner circumferential surface, configured to move axially along the central axis but restricted from rotating about the central axis; a sensor spaced from the outer circumferential surface in a direction perpendicular to the central axis and configured to detect magnetism; and a detection target part having a magnet located between the central axis and the sensor and partially disposed on the outer circumferential surface around the central axis. Therefore, as an example, by disposing the detection target part on a portion of the outer circumferential surface close to the sensor, the distance between the magnet and the sensor is shortened. Therefore, even if the magnet is made smaller, the sensor can detect the magnetism of the magnet. In other words, the master cylinder device allows the magnet to be made smaller. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view showing a brake system according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a part of the master cylinder device of the embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing a part of the master cylinder device of the embodiment taken along line F3-F3 in FIG. [Figure 4] FIG. 4 is an exploded perspective view of the piston and the component to be detected according to the embodiment. 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, "suppress" is defined as, for example, preventing an event, action, or influence from occurring, or reducing the severity of an event, action, or influence. Also, in the following description, "restrict" is defined as, for example, preventing movement or rotation, or allowing movement or rotation within a predetermined range and preventing movement or rotation beyond the predetermined range.

[0010] Fig. 1 is a perspective view showing a brake system 10 according to this embodiment. The brake system 10 is mounted on a vehicle 1, such as a four-wheeled automobile. The brake system 10 includes a master cylinder device 11 and a brake pedal 12, which is shown schematically in Fig. 1. The brake system 10 further includes various components, such as a wheel cylinder, a reservoir, a pump, and an electronic control unit (ECU).

[0011] The master cylinder device 11 is connected to the brake pedal 12, and can generate pressure in the brake fluid in response to the driver's operation of the brake pedal 12. However, the master cylinder device 11 is not limited to this example.

[0012] FIG. 2 is a cross-sectional view showing a portion of the master cylinder device 11 of this embodiment. As shown in FIG. 2, the master cylinder device 11 has a cylinder body 21, a piston 22, a cylinder cover 23, an input rod 24, multiple seals 25, 26, 27, and 28, a spring 29, a detection target component 31, a substrate 32, and a stroke sensor 33. Note that the master cylinder device 11 may have multiple pistons. The seal 25 may also be referred to as a primary cup. The seal 26 may also be referred to as a secondary cup.

[0013] A hole 41 is provided in the cylinder body 21. The hole 41 is a substantially cylindrical hole provided along the central axis Ax. Hereinafter, the direction along the central axis Ax will be referred to as the axial direction, the direction perpendicular to the central axis Ax as the radial direction, and the direction around the central axis Ax as the circumferential direction.

[0014] 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. The rearward direction Db is the opposite direction to the forward direction Df. The forward direction Df and the rearward direction Db may be different from the fore-and-aft direction of the vehicle 1.

[0015] The end of the hole 41 in the rear direction Db is open to the outside of the cylinder body 21. That is, the hole 41 is recessed from the outer surface of the cylinder body 21 in the forward direction Df. The cylinder body 21 has an inner circumferential surface 41a and a bottom surface 41b. The hole 41 is defined by the inner circumferential surface 41a and the bottom surface 41b. However, the hole 41 is not limited to this example.

[0016] The inner circumferential surface 41a is a substantially cylindrical curved surface that extends around the central axis Ax and faces the central axis Ax. The inner circumferential surface 41a may have multiple cylindrical curved surfaces that are different in diameter and aligned in the axial direction. The bottom surface 41b is located at the end of the hole 41 in the forward direction Df and faces substantially in the rearward direction Db.

[0017] A groove 45 is further provided in the cylinder body 21. The groove 45 opens to the inner circumferential surface 41a and extends in the axial direction. The cylinder body 21 further has a recessed surface 45a. The groove 45 is defined by the recessed surface 45a. However, the groove 45 is not limited to this example.

[0018] Fig. 3 is a cross-sectional view showing a part of the master cylinder device 11 of this embodiment taken along line F3-F3 in Fig. 2. As shown in Fig. 3, the concave surface 45a is a roughly semi-cylindrical curved surface extending around another central axis that is substantially parallel to the central axis Ax. However, the concave surface 45a is not limited to this example.

[0019] The concave surface 45a has an arc-shaped edge A1 in a cross section perpendicular to the central axis Ax as shown in Fig. 3. The edge A1 is an example of a first edge. The radius of each of the concave surface 45a and the edge A1 is smaller than the radius of the inner circumferential surface 41a.

[0020] FIG. 4 is an exploded perspective view of the piston 22 and the detected component 31 of this embodiment. The piston 22 is made of a non-magnetic material such as an aluminum alloy. As shown in FIG. 4, the piston 22 has a piston body 51 and a connecting rod 52. However, the piston 22 is not limited to this example.

[0021] The piston body 51 and the connecting rod 52 are each formed in a generally cylindrical shape extending along the central axis Ax. Note that the central axes of the hole 41, the inner circumferential surface 41a, the piston body 51, and the connecting rod 52 may be slightly misaligned from one another.

[0022] 2, the piston body 51 has two end faces 51a and 51b and an outer circumferential surface 51c. The end face 51a is formed substantially flat and faces the forward direction Df. The end face 51b is located on the opposite side to the end face 51a. The end face 51b is formed substantially flat and faces the rearward direction Db.

[0023] 3, the outer peripheral surface 51c is a substantially cylindrical curved surface extending around the central axis Ax. In this embodiment, two notches 55 are provided in the piston body 51. Therefore, the outer peripheral surface 51c includes two substantially semi-cylindrical curved surfaces each extending around the central axis Ax. However, the outer peripheral surface 51c is not limited to this example.

[0024] 2, the piston body 51 is disposed in the hole 41 of the cylinder body 21. The diameter of the outer peripheral surface 51c is slightly smaller than the diameter of the inner peripheral surface 41a, so that the outer peripheral surface 51c faces the inner peripheral surface 41a with a small gap therebetween.

[0025] The connecting rod 52 protrudes in the rear direction Db from the end face 51b of the piston body 51. The connecting rod 52 has an end face 52a and an outer surface 52b. The end face 52a is provided at the end of the connecting rod 52 in the rear direction Db. The outer surface 52b is a substantially cylindrical curved surface extending around the central axis Ax. The outer surface 52b has a smaller diameter than the outer peripheral surface 51c of the piston body 51. A portion of the outer surface 52b faces the inner peripheral surface 41a.

[0026] An insertion hole 56 is provided in the connecting rod 52. The insertion hole 56 is recessed from the end face 52a in the forward direction Df along the central axis Ax. One end of the input rod 24 is received in the insertion hole 56 and attached to the connecting rod 52. The other end of the input rod 24 is connected to the brake pedal 12.

[0027] An oil passage 57 is provided in the piston 22. One end of the oil passage 57 opens to the end surface 51a of the piston body 51. The other end of the oil passage 57 opens to the outer surface 52b of the connecting rod 52. Note that the oil passage 57 is not limited to this example.

[0028] As shown in Fig. 4, the piston body 51 is further provided with a recess 61 and a mounting hole 62. The recess 61 is recessed from the outer peripheral surface 51c toward the central axis Ax. The mounting hole 62 is recessed from the bottom of the recess 61 toward the central axis Ax. As shown in Fig. 3, the oil passage 57 is spaced apart from the recess 61 and the mounting hole 62 in the circumferential direction.

[0029] The piston body 51 further has two side surfaces 61a and a bottom surface 61b. The recess 61 is defined by the two side surfaces 61a and the bottom surface 61b. However, the recess 61 is not limited to this example.

[0030] The two side surfaces 61a are each connected to the outer peripheral surface 51c. One side surface 61a is formed substantially flat and faces the forward direction Df. The other side surface 61a is formed substantially flat and faces the rearward direction Db. The two side surfaces 61a face each other.

[0031] The bottom surface 61b is provided at the end (bottom) of the recess 61 on the inside in the radial direction. The bottom surface 61b is formed to be approximately flat and faces outward in the radial direction. Note that the bottom surface 61b is not limited to this example and may be, for example, a curved surface. The mounting hole 62 opens to the bottom surface 61b.

[0032] 2, the cylinder cover 23 is formed in a substantially cylindrical shape extending around the central axis Ax. For this reason, a through hole 71 is provided in the cylinder cover 23. The through hole 71 axially penetrates the cylinder cover 23 along the central axis Ax.

[0033] The cylinder cover 23 is fitted into the hole 41 and attached to the cylinder body 21 by, for example, screwing. The cylinder cover 23 has two end faces 23a and 23b, an inner face 23c, and an outer face 23d.

[0034] The end surface 23a is provided at an end of the cylinder cover 23 in the forward direction Df. The end surface 23a faces the bottom surface 41b of the cylinder body 21. The end surface 23b is located on the opposite side of the end surface 23a. The through hole 71 opens to the two end surfaces 23a, 23b.

[0035] The inner surface 23c is a substantially cylindrical curved surface that extends around the central axis Ax and faces the central axis Ax. The inner surface 23c defines the through hole 71. The outer surface 23d is located on the opposite side of the inner surface 23c. The outer surface 23d is a substantially cylindrical curved surface that extends around the central axis Ax. The outer surface 23d faces a portion of the inner circumferential surface 41a of the cylinder body 21.

[0036] The cylinder cover 23 is provided with a plurality of seal grooves 72, 73, 74, 75 and an oil passage 76. The seal grooves 72, 73 are provided on the inner surface 23c. The seal groove 73 is spaced apart from the seal groove 72 in the rear direction Db. The seal grooves 74, 75 are provided on the outer surface 23d. The seal grooves 74, 75 are spaced apart from each other in the axial direction.

[0037] One end of the oil passage 76 opens to the inner surface 23c between the two seal grooves 72, 73. The oil passage 76 opens to the inner surface 23c near the seal groove 72. The other end of the oil passage 76 opens to the outer surface 23d between the two seal grooves 74, 75.

[0038] The piston body 51 is located between the bottom surface 41b of the cylinder body 21 and the cylinder cover 23. Therefore, the end surface 23a of the cylinder cover 23 faces the end surface 51b of the piston body 51. The connecting rod 52 extends through the through-hole 71. The outer surface 52b of the connecting rod 52 faces the inner surface 23c of the cylinder cover 23 with a small gap therebetween.

[0039] Seals 25, 26, 27, and 28 are fitted into seal grooves 72, 73, 74, and 75. Seals 25 and 26 seal the gap between the inner surface 23c of the cylinder cover 23 and the outer surface 52b of the connecting rod 52. Seals 27 and 28 seal the gap between the outer surface 23d of the cylinder cover 23 and the inner circumferential surface 41a of the cylinder body 21.

[0040] A fluid chamber R is provided between the bottom surface 41b of the cylinder body 21 and the end surface 51a of the piston body 51. The fluid chamber R is a part of the hole 41. The fluid chamber R is filled with, for example, brake fluid.

[0041] The spring 29 is interposed between the bottom surface 41b of the cylinder body 21 and the end surface 51a of the piston body 51. The spring 29 is supported by the bottom surface 41b and pushes the piston body 51 in the rear direction Db toward the end surface 23a of the cylinder cover 23.

[0042] The piston 22 is movable in the axial direction. That is, the outer peripheral surface 51c of the piston body 51 is slidable in the axial direction relative to the inner peripheral surface 41a of the cylinder body 21. When the piston 22 moves forward Df, the volume of the liquid chamber R decreases. On the other hand, when the piston 22 moves backward Db, the volume of the liquid chamber R increases.

[0043] 3, the detection target component 31 has a magnet 81, a resin cover 82, and a protrusion 83. Note that the detection target component 31 is not limited to this example, and may have, for example, only the magnet 81.

[0044] The magnet 81 is, for example, a permanent magnet. However, the magnet 81 may be another type of magnet. The magnet 81 is partially housed in the recess 61 of the piston body 51. A part of the magnet 81 protrudes radially outward from the outer circumferential surface 51c of the piston body 51. However, the entire magnet 81 may be housed in the recess 61.

[0045] The magnet 81 has a bottom surface 81a, an outer surface 81b, and two side surfaces 81c. The bottom surface 81a is located at the radially inner end of the magnet 81. The bottom surface 81a is formed to be approximately flat and is arranged approximately parallel to the bottom surface 61b of the piston body 51. The outer surface 81b is located at the radially outer end of the magnet 81. The outer surface 81b is a roughly semi-cylindrical curved surface extending around another central axis that is approximately parallel to the central axis Ax. The two side surfaces 81c each connect an end of the bottom surface 81a to an end of the outer surface 81b in the circumferential direction. The side surfaces 81c are formed to be approximately flat and are approximately perpendicular to the bottom surface 81a. The two side surfaces 81c are located opposite each other and arranged approximately parallel to each other.

[0046] The resin cover 82 and the protrusion 83 are made of, for example, synthetic resin. That is, the resin cover 82 and the protrusion 83 are non-magnetic. The resin cover 82 and the protrusion 83 are integrally formed. However, the resin cover 82 and the protrusion 83 are not limited to this example.

[0047] The resin cover 82 covers the entire magnet 81. That is, the magnet 81 is disposed inside the resin cover 82. Note that the magnet 81 may be partially exposed to the outside of the resin cover 82.

[0048] The resin cover 82, together with the magnet 81, is partially housed in the recess 61 of the piston body 51. A portion of the resin cover 82 protrudes radially outward from the outer circumferential surface 51c of the piston body 51.

[0049] The detection target component 31, which has the magnet 81 and the resin cover 82, protrudes radially outward from the outer circumferential surface 51c. That is, the detection target component 31 is provided on the outer circumferential surface 51c by being fitted into a recess 61 provided on the outer circumferential surface 51c. Note that the detection target component 31 is not limited to this example. For example, the detection target component 31 may be provided on the outer circumferential surface 51c by being attached to the outer circumferential surface 51c.

[0050] The detection target component 31 protrudes from a portion of the outer peripheral surface 51c in the circumferential direction. That is, the detection target component 31 is provided partially on the outer peripheral surface 51c around the central axis Ax. In this embodiment, the detection target component 31 is provided on the outer peripheral surface 51c within a range smaller than 180° around the central axis Ax. Note that the detection target component 31 is not limited to this example.

[0051] The resin cover 82 is formed integrally with the magnet 81 by, for example, insert molding. The outer shape of the resin cover 82 is similar to the outer shape of the magnet 81. However, the resin cover 82 is not limited to this example. The resin cover 82 has a bottom surface 82a, an outer surface 82b, and a side surface 82c.

[0052] The bottom surface 82a is located at the radially inner end of the resin cover 82. The bottom surface 82a is formed to be approximately flat and is disposed approximately parallel to the bottom surface 61b of the piston body 51. The bottom surface 82a of the resin cover 82 contacts the bottom surface 61b of the piston body 51. The bottom surfaces 82a and 61b may be spaced apart from each other.

[0053] The outer surface 82b is located at the radially outer end of the resin cover 82. The outer surface 82b is also located at the radially outer end of the detection target component 31. The outer surface 82b is a roughly semi-cylindrical curved surface extending around another central axis that is substantially parallel to the central axis Ax. The outer surface 82b of the resin cover 82 and the outer peripheral surface 51c of the piston body 51 are aligned in the circumferential direction, for example, via a notch 55.

[0054] The outer surface 82b has an arc-shaped edge A2 in a cross section perpendicular to the central axis Ax as shown in Fig. 3. The edge A2 is an example of a second edge. The radius of each of the outer surface 82b and the edge A2 is smaller than the radius of the inner circumferential surface 41a.

[0055] The two side surfaces 82c each connect an end of the bottom surface 82a to an end of the outer surface 82b in the circumferential direction. The side surfaces 82c are formed to be substantially flat and are substantially perpendicular to the bottom surface 82a. The two side surfaces 82c are located on opposite sides of each other and are disposed substantially parallel to each other.

[0056] In the radial direction, the side surface 82c is shorter than the side surface 81c of the magnet 81. The portion (corner) where the outer surface 82b and the side surface 82c are connected is located inside the recessed portion 61. In other words, the outer surface 82b and the edge A2 are partially located inside the recessed portion 61.

[0057] 4, the resin cover 82 further has two side surfaces 82d. One side surface 82d is formed substantially flat and faces the forward direction Df. The other side surface 82d is formed substantially flat and faces the rearward direction Db. The side surface 82d of the resin cover 82 and the side surface 61a of the piston body 51 face each other with a small gap therebetween.

[0058] 3, the protrusion 83 protrudes radially inward from the bottom surface 82a of the resin cover 82. The protrusion 83 fits into the mounting hole 62 of the piston body 51. As a result, the protrusion 83 and the mounting hole 62 restrict movement of the detection target component 31 in the axial and circumferential directions. The protrusion 83 and the mounting hole 62 are spaced apart radially from the central axis Ax.

[0059] A portion of the detection target component 31 protrudes from the outer peripheral surface 51c of the piston body 51 and fits into the groove 45. For example, the detection target component 31 restricts the rotation of the piston 22 around the central axis Ax by the outer surface 82b of the resin cover 82 abutting against the concave surface 45a of the cylinder body 21. Note that the outer surface 81b of the magnet 81 may abut against the concave surface 45a.

[0060] The outer surface 82b and edge A2 of the resin cover 82 are at least partially disposed in the groove 45. Furthermore, edge A2 faces edge A1 of the recessed surface 45a of the cylinder body 21. Edge A2 has a smaller radius than edge A1. This allows the outer surface 82b to abut against the recessed surface 45a over a relatively large area. Note that the radii of edges A1 and A2 are not limited to this example.

[0061] Other parts or elements may limit the rotation of the piston 22. For example, a key and groove may limit the rotation of the piston 22. In this case, the detected part 31 does not need to protrude from the outer peripheral surface 51c of the piston body 51.

[0062] The substrate 32 and the stroke sensor 33 are located outside the hole 41 (fluid chamber R). The substrate 32 is attached to the cylinder body 21. The substrate 32 is, for example, a printed circuit board. However, the substrate 32 is not limited to this example.

[0063] The stroke sensor 33 is, for example, a Hall IC. The stroke sensor 33 has an element 91. The element 91 is an example of a sensor. The element 91 is, for example, a Hall element, and detects magnetism. However, the stroke sensor 33 and the element 91 are not limited to this example.

[0064] The stroke sensor 33 is mounted on the substrate 32 so as to be located between the substrate 32 and the liquid chamber R. An element 91 of the stroke sensor 33 is spaced apart from the outer peripheral surface 51c of the piston body 51 in the radial direction.

[0065] At least a portion of the magnet 81 is located between the central axis Ax and the element 91. The cylinder body 21 is made of a non-magnetic material, at least between the magnet 81 and the element 91. For example, the cylinder body 21 is made of an aluminum alloy. Therefore, the element 91 can detect the magnetism of the magnet 81. An outer surface 81b of the magnet 81 faces the element 91 via the resin cover 82 and the cylinder body 21. However, the outer surface 81b is not limited to this example.

[0066] The magnet 81 is longer around the central axis Ax than the element 91. For example, in the circumferential direction, the outer surface 81b of the magnet 81 is longer than the element 91. Note that the stroke sensor 33 may be longer than the magnet 81 in the axial direction.

[0067] A gap is at least partially provided between the outer surface 82b of the resin cover 82 and the concave surface 45a of the cylinder body 21. For example, the piston 22 can rotate around the central axis Ax within the range of the gap. However, the difference between the length of the magnet 81 and the length of the element 91 around the central axis Ax is longer than the range in which the piston 22 can rotate.

[0068] 2, when the brake pedal 12 is not operated, the spring 29 presses the piston body 51 against the end surface 23a of the cylinder cover 23. In other words, the cylinder cover 23 supports the piston body 51. At this time, the oil passage 57 of the piston 22 communicates with the oil passage 76 of the cylinder cover 23.

[0069] The oil passage 76 of the cylinder cover 23 is connected to the reservoir, for example, through an oil passage in the cylinder body 21. Therefore, the brake fluid can flow between the fluid chamber R and the reservoir through the oil passages 57 and 76. The reservoir is, for example, open to the outside, and the pressure of the brake fluid is made approximately equal to atmospheric pressure.

[0070] When the brake pedal 12 is operated, the piston 22 moves forward Df against the elastic force of the spring 29. When the end of the oil passage 57 that opens to the outer surface 52b of the connecting rod 52 passes over the seal 25, the seal 25 seals the space between the two oil passages 57, 76.

[0071] The detection target component 31 also moves in the forward direction Df together with the piston 22. The stroke sensor 33 detects the magnetism of the magnet 81 with the element 91, thereby being able to detect the position (amount of movement) of the piston 22.

[0072] For example, the ECU of the brake system 10 obtains the amount of movement of the piston 22 from the stroke sensor 33. The ECU drives the pump to increase the pressure in the wheel cylinder based on the amount of movement of the piston 22. The brake system 10 presses the brake pads against the disc rotor using the pressure in the wheel cylinder, thereby braking the vehicle 1.

[0073] As shown in FIG. 1 , the master cylinder device 11 further includes a stroke simulator S. The stroke simulator S is connected to a fluid chamber R. Therefore, the brake fluid in the fluid chamber R flows into the stroke simulator S. The stroke simulator S applies a pseudo reaction force to the brake pedal 12.

[0074] When the brake pedal 12 is released, the piston 22 moves rearward Db due to the elastic force of the spring 29. The ECU reduces the pressure in the wheel cylinder based on the amount of movement of the piston 22, thereby releasing the braking of the vehicle 1.

[0075] When power is not supplied to the brake system 10, for example, a normally open solenoid valve connects the fluid chamber R to the wheel cylinder. On the other hand, for example, a normally closed solenoid valve blocks communication between the fluid chamber R and the stroke simulator S. In this case, when the piston 22 moves forward Df, the volume of the fluid chamber R decreases, and the pressure in the fluid chamber R and the wheel cylinder increases. That is, the master cylinder device 11 may change the pressure in the wheel cylinder directly by moving the piston 22, or may change the pressure in the wheel cylinder indirectly by electrical control. The stroke simulator S may also be omitted.

[0076] For example, the piston 22 may rotate around the central axis Ax due to a force input from the input rod 24 or brake fluid, or vibration. However, the detected component 31 limits the rotation of the piston 22, so that the outer surface 81b of the magnet 81 remains facing the element 91.

[0077] In the brake system 10 according to the embodiment described above, the piston 22 is configured to be restricted from rotating around the central axis Ax. The element 91 is configured to detect magnetism by being spaced apart from the outer peripheral surface 51c in a radial direction perpendicular to the central axis Ax. The detection target component 31 has a magnet 81 located between the central axis Ax and the element 91 and is partially disposed on the outer peripheral surface 51c around the central axis Ax. Therefore, for example, by disposing the detection target component 31 on a portion of the outer peripheral surface 51c close to the element 91, the distance between the magnet 81 and the element 91 is shortened. Therefore, even if the magnet 81 is made small, the element 91 can detect the magnetism of the magnet 81. In other words, the master cylinder device 11 can have a smaller magnet 81, which in turn can be made smaller in the axial direction and reduce costs. Furthermore, the master cylinder device 11 can easily assemble the piston 22 and the detection target component 31 because the magnet 81 can be attached to the outer peripheral surface 51c, for example, in the radial direction.

[0078] The concave surface 45a defines a groove 45 that opens to the inner circumferential surface 41a and extends in the axial direction. The detection target component 31 protrudes from the outer circumferential surface 51c, fits into the groove 45, and abuts against the concave surface 45a to restrict rotation of the piston 22 around the central axis Ax. Therefore, as an example, the master cylinder device 11 can restrict rotation of the piston 22 around the central axis Ax with a simple configuration. Therefore, the master cylinder device 11 can prevent an increase in the number of components and reduce costs. Furthermore, the detection target component 31 allows the magnet 81 to be closer to the element 91 than when it is located inside the outer circumferential surface 51c. Therefore, the master cylinder device 11 can improve the accuracy of magnetic detection by the element 91 and further reduce the size of the magnet 81.

[0079] The concave surface 45a has an arc-shaped edge A1 in a cross section perpendicular to the central axis Ax. The detection component 31 has an arc-shaped edge A2 in a cross section perpendicular to the central axis Ax. The edge A2 is at least partially disposed in the groove 45, faces the edge A1, and has a smaller radius than the edge A1. Therefore, for example, the arc-shaped concave surface 45a (groove 45) can be easily formed using a rotary tool such as a drill or a milling cutter. Furthermore, because the radius of the edge A2 is small, the master cylinder device 11 can set a gap between the edges A1 and A2 so that the detection component 31 can move smoothly axially in the groove 45. Furthermore, the contact area between the detection component 31 and the concave surface 45a is wider. Therefore, compared to when the contact area between the detection component 31 and the concave surface 45a is small (point contact or line contact), the master cylinder device 11 can suppress wear and thereby maintain a constant angle at which the piston 22 can rotate.

[0080] The magnet 81 protrudes from the outer peripheral surface 51c. Therefore, for example, the magnet 81 can be closer to the element 91 than if the magnet 81 were positioned inside the outer peripheral surface 51c. Therefore, the master cylinder device 11 can improve the accuracy of detecting magnetism by the element 91 and can further reduce the size of the magnet 81.

[0081] The magnet 81 is longer around the central axis Ax than the element 91. Therefore, for example, even if the piston 22 rotates around the central axis Ax within an allowable range, the magnetism of the magnet 81 detected by the element 91 is unlikely to change. Therefore, the master cylinder device 11 can prevent the magnetism detected by the element 91 from changing due to the rotation of the piston 22.

[0082] The detection target component 31 has a resin cover 82. The magnet 81 is located inside the resin cover 82. Therefore, for example, the resin cover 82 can prevent the magnet 81 from being exposed to, for example, brake fluid, and thus can prevent the magnet 81 from corroding. Furthermore, the resin cover 82 can prevent the magnet 81 from directly contacting the concave surface 45a.

[0083] A recess 61 is provided on the outer peripheral surface 51c. A part of the detection target component 31 is housed in the recess 61. Therefore, as an example, the detection target component 31 can be easily provided on the outer peripheral surface 51c.

[0084] At least one embodiment of the master cylinder device described above includes, for example, a piston having an inner circumferential surface extending about a central axis and facing the central axis, and an outer circumferential surface extending about the central axis and facing the inner circumferential surface, configured to move axially along the central axis but restricted from rotating about the central axis; a sensor spaced from the outer circumferential surface in a direction perpendicular to the central axis and configured to detect magnetism; and a detection target part having a magnet located between the central axis and the sensor and partially disposed on the outer circumferential surface around the central axis. Therefore, for example, by disposing the detection target part on a portion of the outer circumferential surface close to the sensor, the distance between the magnet and the sensor is shortened. Therefore, even if the magnet is made smaller, the sensor can detect the magnetism of the magnet. In other words, the master cylinder device can have a smaller magnet, which in turn can be made smaller in the axial direction and reduce costs. Furthermore, since the master cylinder device allows the magnet to be attached to the outer circumferential surface in a direction perpendicular to the central axis, for example, assembly of the piston and the detection target part can be facilitated.

[0085] As an example, the master cylinder device further includes a concave surface that opens onto the inner circumferential surface and defines a groove extending in the axial direction, and the detected component protrudes from the outer circumferential surface, fits into the groove, and abuts against the concave surface to restrict rotation of the piston around the central axis. Therefore, as an example, the master cylinder device can restrict rotation of the piston around the central axis with a simple configuration. Therefore, the master cylinder device can prevent an increase in the number of components and reduce costs. Furthermore, the detected component allows the magnet to be closer to the sensor than if it were located inside the outer circumferential surface. Therefore, the master cylinder device can improve the accuracy of magnetic detection by the sensor and further reduce the magnet's size.

[0086] In the master cylinder device described above, for example, the concave surface has an arc-shaped first edge in a cross section perpendicular to the central axis, and the detection component has an arc-shaped second edge in a cross section perpendicular to the central axis. The second edge is at least partially disposed in the groove, faces the first edge, and has a smaller radius than the first edge. Therefore, for example, the arc-shaped concave surface (groove) can be easily formed using a rotary tool such as a drill or a milling cutter. Furthermore, because the radius of the second edge is small, the master cylinder device can set a gap between the first edge and the second edge so that the detection component can move smoothly axially along the groove. Furthermore, the contact area between the detection component and the concave surface is larger. Therefore, compared to a master cylinder device in which the contact area between the detection component and the concave surface is small (point contact or line contact), the master cylinder device can suppress wear and thereby maintain a constant angle at which the piston can rotate.

[0087] In the master cylinder device, for example, the magnet protrudes from the outer peripheral surface. Therefore, for example, the magnet can be closer to the sensor than if it were positioned inside the outer peripheral surface. Therefore, the master cylinder device can improve the accuracy of magnetic detection by the sensor and further reduce the magnet size.

[0088] In the master cylinder device, for example, the magnet is longer than the sensor around the central axis. Therefore, even if the piston rotates around the central axis within an allowable range, the magnetism of the magnet detected by the sensor is unlikely to change. Therefore, the master cylinder device can prevent the magnetism detected by the sensor from being changed due to the rotation of the piston.

[0089] 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]

[0090] 11...master cylinder device, 22...piston, 31...detected part, 41a...inner surface, 45...groove, 45a...concave surface, 51c...outer surface, 81...magnet, 91...element (sensor), Ax...central axis, A1...edge (first edge), A2...edge (second edge).

Claims

1. an inner circumferential surface extending around a central axis and facing the central axis; a piston extending about the central axis and having an outer circumferential surface facing the inner circumferential surface, the piston being configured to move axially along the central axis and being restricted from rotating about the central axis; a sensor spaced apart from the outer circumferential surface in a direction perpendicular to the central axis and configured to detect magnetism; a detection component having a magnet located between the central axis and the sensor, the detection component being partially provided on the outer circumferential surface around the central axis; A master cylinder device comprising:

2. a concave surface defining a groove that opens to the inner circumferential surface and extends in the axial direction; Further comprising: The detected component is configured to protrude from the outer circumferential surface, fit into the groove, and abut against the concave surface to restrict the rotation of the piston around the central axis.

2. The master cylinder device according to claim 1.

3. the concave surface has a first edge that is arcuate in a cross section perpendicular to the central axis, the detection component has a second edge that is arc-shaped in a cross section perpendicular to the central axis, the second edge is at least partially disposed in the groove, faces the first edge, and has a smaller radius than the first edge; 3. The master cylinder device according to claim 2.

4. The magnet protrudes from the outer circumferential surface.

4. The master cylinder device according to claim 2 or 3.

5. The magnet is longer than the sensor around the central axis.

2. The master cylinder device according to claim 1.

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