JP4890498B2 - Piston position detection device in master cylinder - Google Patents

Description

The present invention comprises a cylinder body having a cylinder bore, a piston is engaged before Symbol slidably fitted in the cylinder bore, the piston, a radially outer and a piston main portion, from the outer peripheral surface of the piston main unit And a plurality of annular protrusions that protrude in the axial direction and are arranged at intervals in the axial direction of the cylinder hole, and a master cylinder in which a hydraulic chamber is formed in the cylinder body to face the front end of the piston In particular, the present invention relates to a piston position detection device that detects the position of a piston in a direction along the axis of a cylinder hole.

In order to detect the axial position of the piston in the cylinder body and light the brake lamp, etc., a magnet that operates with the piston is arranged in the cylinder body, and the magnet is detected by a switch or a magnetic sensor arranged on the cylinder body side. This is already known from Patent Document 1, Patent Document 2, and the like.
Japanese Utility Model Publication No. 3-120261 JP-T-2006-521960

  However, in the ones disclosed in Patent Document 1 and Patent Document 2, a space for arranging the magnet in the cylinder body must be secured, and the magnet is attached to the piston in order to operate the magnet together with the piston. It is necessary to add a structure for fixing, and it is necessary to greatly change the structure inside the master cylinder.

  Therefore, it is conceivable that a magnetic sensor capable of detecting the piston itself made of a magnetic material is provided on the outer periphery of the cylinder body made of a non-magnetic material, and the piston is directly detected by the magnetic sensor. It is not necessary to change the structure greatly. However, when the outer periphery of the piston has an uneven shape with a plurality of flanges for holding the cup seal and a plurality of annular protrusions such as stoppers, depending on the stroke position of the piston, There is a problem that the position of cannot be detected accurately.

  The present invention has been made in view of such circumstances, and a piston position detection device in a master cylinder that can accurately detect the axial position of a piston while eliminating the need to greatly change the configuration inside the cylinder body. The purpose is to provide.

To achieve the above object, a first aspect of the present invention, includes a cylinder body having a cylinder bore, a front Symbol piston slidably fitted in the cylinder bore, the piston, and the piston main portion A plurality of annular protrusions projecting radially outward from the outer peripheral surface of the piston main portion and arranged at intervals in the axial direction of the cylinder hole, and the front end of the piston is disposed in the cylinder body. in the master cylinder fluid pressure chamber is formed for exposing, said annular projection and a plurality of magnetic sensors are the same number is, the annular projection of the piston is formed of a magnetic material detection and their annular projection so as to output an output signal Te, spaced in the axial direction of the cylinder bore to the outer periphery of the cylinder body made of non-magnetic material, at the middle of the forward operating said piston from the non-operating position Each of the plurality of annular protrusions close to each of the plurality of magnetic sensors when in position, so that all of the plurality of magnetic sensors output an output signal, and when the piston is in an inoperative state The relative positions of the plurality of annular protrusions and the plurality of magnetic sensors are such that the combination of the output signals of the plurality of magnetic sensors is different from any of the combinations of the output signals of the magnetic sensor when the piston moves forward. position is set, the plurality of piston position determining means for output of the magnetic sensor is inputted, it determines the position of the piston in the direction along the axis of the cylinder bore in combination of the output signals of the magnetic sensors It is characterized by that.

The invention according to claim 2, in addition to the configuration of the invention according to claim 1, wherein the width along the axial direction of the forwardmost annular protrusion of the plurality of annular projections, the other of said annular projection is set larger than the width along the axial direction, characterized in that the rearmost magnetic sensor of the plurality of magnetic sensors are positioned to detect the front-most annular protrusion during non-operation of the piston .

Further the third aspect of the present invention, in addition to the configuration of the invention according to claim 1 or 2, at least one of said plurality of annular protrusions, as elastically sliding contact with the inner periphery of the cylinder bore The piston is provided on the piston so as to hold a cup seal interposed between the cylinder body and the piston.

Incidentally, the rear piston 14 of the embodiment corresponds to the piston of the present invention, the rear fluid pressure chamber 25 of the embodiment corresponds to the hydraulic chamber of the present invention.

According to the first aspect of the present invention , the plurality of magnetic sensors having the same number as the plurality of annular protrusions of the piston made of the magnetic material detects and outputs the plurality of annular protrusions by the proximity of the protrusions. In order to output a signal, the cylinder body made of a non-magnetic material is provided at an interval on the outer periphery, and each of the plurality of annular protrusions is provided when the piston is in a predetermined position during forward operation from the non-operating position. The relative positions of the plurality of annular protrusions and the plurality of magnetic sensors are set so that all of the plurality of magnetic sensors output an output signal by approaching each of the plurality of magnetic sensors, and the output signals of these magnetic sensors Since the piston position in the direction along the axis of the cylinder hole is judged by the combination of the cylinders, the axial position of the piston having a plurality of annular protrusions is greatly changed in the structure inside the cylinder body. It can be detected Rukoto without accurately. In particular , the combination of the output signals of the magnetic sensor when the piston is not operating is different from the combination of the output signals of the magnetic sensor when the piston is moving forward. It is possible to reliably detect without detection, and to determine the brake operating state more accurately.

Further , according to the invention of claim 2, since the width of the foremost annular protrusion detected by the rearmost magnetic sensor when the piston is not operated is set larger than the width of the other annular protrusion, Even if there is an error in mounting the magnetic sensor on the outer circumference of the cylinder body, the foremost annular protrusion is reliably detected by the rearmost magnetic sensor when the piston is not in operation, The combination of the output signals of the magnetic sensor more reliably prevents the combination of the output signals of the magnetic sensor during the forward movement of the piston, and the initial position when the piston is inactive is reliably detected. can do.

Further, according to the invention described in claim 3, since at least one of the plurality of annular protrusions holds the cup seal, the outer shape of the piston is greatly changed from the conventional outer shape of the piston. It is not necessary to form a piston on the surface.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on one embodiment of the present invention shown in the accompanying drawings.

  1 to 8 show an embodiment of the present invention. FIG. 1 is a longitudinal sectional view of a master cylinder in a non-operating state, FIG. 2 is an enlarged view of a main part of FIG. 1, and FIG. FIG. 4 is a cross-sectional view corresponding to FIG. 2 in a state in which the rear piston is advanced from the position shown in FIG. 3, and FIG. 5 is a cross-sectional view corresponding to FIG. FIG. 6 is a cross-sectional view corresponding to FIG. 2 in a state where the rear piston is advanced from the position of FIG. 5, and FIG. 7 is a rear piston being advanced from the position of FIG. 6. FIG. 8 is a cross-sectional view corresponding to FIG. 2 in a state where the rear piston has advanced from the position of FIG. 7.

  First, in FIG. 1, this master cylinder M is a tandem type used in a vehicle brake device, and has a cylinder hole 11 whose front end is closed by an end wall 12a, and is made of a nonmagnetic material such as an aluminum alloy. 12 and a front piston 13 and a rear piston 14 slidably fitted in the cylinder body 12. At the top of the cylinder body 12, a front boss 15 and a rear boss 16 formed in a cylindrical shape are integrally provided so as to protrude upward at a position spaced in the axial direction of the cylinder hole 11, A flat plate-like connecting projection 17 projecting upward at an intermediate portion between the bosses 15 and 16 is integrally provided.

  A reservoir R made of synthetic resin is attached to the master cylinder M, and the lower portion of the reservoir R is connected to the front and rear bosses 15 and 16 of the cylinder body 12 via grommets 18 and 19, respectively. Cylindrical front and rear supply tubes 20 and 21 to be fitted, and a flat connecting arm 22 abutting on the side of the connecting protrusion 17 of the cylinder body 12 are integrally provided. Is fastened to the connecting projection 17 by a bolt 23.

  The front piston 13 is slidably fitted into the cylinder hole 11 so as to form a front hydraulic pressure chamber 24 between the end wall 12a of the cylinder body 12, and the rear piston 14 13 is slidably fitted into the cylinder hole 11 so as to form a rear hydraulic chamber 25 therebetween. The cylinder body 12 is provided with a front output port 27 that communicates with the front hydraulic chamber 24 and a rear output port 28 that communicates with the rear hydraulic chamber 25. Further, a front return spring 29 for urging the front piston 13 rearward is housed in the front hydraulic chamber 24, and the rear piston 14 is interposed between the front piston 13 and the rear piston 14 in the rear hydraulic chamber 25. The rear return spring 30 that biases toward the rear side is contracted.

  The front piston 13 includes a pair of front and rear piston portions 13a and 13b that are integrally connected via a small-diameter coupling portion 13c. The front piston portion 13a is connected to the front hydraulic chamber 24 side. A cup seal 31 slidably in contact with the inner surface of the cylinder hole 11 while allowing the hydraulic fluid to flow in is attached, and a cup seal 32 slidably in contact with the inner surface of the cylinder hole 11 is attached to the piston portion 13b on the rear side.

  Between the outer periphery of the front piston 13 and the inner surface of the cylinder hole 11, a replenishing liquid chamber 33 is formed in an annular shape between the pair of front and rear piston parts 13 a and 13 b, and the front boss 15 always communicates with the replenishing liquid chamber 33. A replenishment port 34 opened in the cylinder body 12 is formed in the cylinder body 12, and the hydraulic fluid replenished from the front replenishment cylinder 20 of the reservoir R is supplied to the replenishment fluid chamber 33.

  The front piston 13 is equipped with a center valve 35 for communicating between the front hydraulic chamber 24 and the replenishing fluid chamber 33 when the front piston 13 returns to the retreat limit position.

  The center valve 35 is coaxially mounted on the front end portion of the front piston 13 and coaxially formed in the piston portion 13a of the front piston 13 through the replenishing liquid chamber 33 and the valve box 36. An axial passage 37 that opens to the front end of the piston portion 13a, a valve body 38 that is accommodated in the valve box 36 so that the front end opening of the axial passage 37 can be closed and moved back and forth, and a valve body 38. A valve spring 39 that is housed in the valve box 36 by exerting a spring force that urges the valve body 36 rearward, that is, in the closing direction of the axial passage 37, and when the front piston 13 is in the retreat limit, the valve body 38 is moved to the valve spring 39. A stopper pin 40 that allows the valve body 38 to move backward, that is, closes when the front piston 13 moves forward, while being held at the forward position against the spring biasing force.

  The small-diameter coupling portion 13c of the front piston 13 is provided with a long hole-like through hole 41 extending in the axial direction of the small-diameter coupling portion 13c so as to extend along the radial direction of the cylinder hole 11. Is communicated with the replenishing liquid chamber 33. The stopper pin 40 also functions to restrict the retreat limit of the front piston 13, is fixed to the cylinder body 12, passes through the through hole 41, and is connected to the valve body 38 to be axially connected. The rear end of the valve stem 42 inserted through 37 is brought into contact with the stopper pin 40.

  According to such a center valve 35, when the front piston 13 is in the retreat limit, the valve stem 42 is pressed by the stopper pin 40, so that the valve body 38 is opened to the axial passage 37, and the valve is opened. Thus, the front fluid pressure chamber 24 and the through hole 41 are communicated with each other, so that the replenisher from the replenisher fluid chamber 33 can be replenished to the front fluid pressure chamber 24. Further, when the front piston 13 moves forward from the retreat limit, the stopper pin 40 moves relative to the front piston 13 so as to be positioned in the rear in the through hole 41, so that the valve body 38 has a spring force of the valve spring 39. As a result, the axial passage 37 is moved to a position where the axial passage 37 is closed, and the space between the replenishing fluid chamber 33 and the front fluid pressure chamber 24 is blocked.

  Referring also to FIG. 2, the rear piston 14 has a short cylindrical piston main portion 14a and a plurality of annular protrusions projecting radially outward from the piston main portion 14a, for example, a first and a pair of front and rear The second annular protrusions 14b and 14c are integrally formed, and the rear piston 14 is fluid-tight and slidable by a bearing member 43 that is liquid-tightly fitted to the rear end of the cylinder body 12. The piston rod 44 supported on the shaft is coaxially and integrally connected. Thus, an annular replenishing liquid chamber 45 is defined between the rear piston 14 and the bearing member 43, and the rear piston 14 has a rear portion from the replenishing liquid chamber 45 at a position in front of the replenishing liquid chamber 45. A cup seal 46 that allows the hydraulic fluid to flow into the hydraulic chamber 25 is mounted. The cup seal 46 is a rear return that is contracted between the first annular protrusion 14 b and the front piston 13 and the rear piston 14. The rear end of the rear piston 14 is held between the rear end of the spring 30 and the cup seal pressing member 49 attached to the front end of the piston main portion 14a. Further, the cylinder body 12 is provided with a replenishment port 47 that always communicates with the replenishment liquid chamber 45 and opens into the rear boss 16, and hydraulic fluid replenished from the rear refill cylinder 21 of the reservoir R is supplied to the replenishment liquid chamber 45. Will be supplied.

  Further, a relief port 48 opened in the rear boss 16 is formed in the cylinder body 12, and this relief port 48 communicates with the rear hydraulic chamber 25 when the rear piston 14 is in the retreat limit as shown in the drawing. .

  Between the front piston 13 and the rear piston 14, there is provided a maximum interval restricting means 50 for restricting the maximum interval between the pistons 13, 14, and when the front piston 13 is restricted to the backward limit by the stopper pin 40, The rear piston 14 is also in the backward limit. A cylindrical stopper 51 is mounted on the piston main portion 14 a behind the second annular protrusion 14 c in the rear piston 14, and the stopper 51 abuts on the bearing member 43 to contact the rear piston 14. The retreat limit will be regulated.

  According to such a master cylinder M, the rear piston 14 moves forward in response to a forward force being input from the piston rod 44, and the hydraulic pressure in the rear hydraulic chamber 25 increases in response to the forward movement of the rear piston 14. Accordingly, the front piston 13 moves forward. Therefore, by detecting the position of the rear piston 14 in the direction along the axis of the cylinder hole 11, the front piston 13 in the direction along the axis of the cylinder hole 11 is detected. The position of the rear piston 14 in the direction along the axis of the cylinder hole 11 is detected by the configuration according to the present invention.

  In order to detect the axial position of the rear piston 14, the rear piston 14 having a piston main portion 14a and a pair of annular protrusions 14b and 14c projecting radially outward from the piston main portion 14a is formed of a magnetic material. The cylinder body 12 having the cylinder hole 11 into which the rear piston 14 is slidably fitted is formed of a nonmagnetic material, and the outer periphery of the cylinder body 12 is the same as the annular protrusions 14b and 14c of the rear piston 14. In this embodiment, the first magnetic sensor 52 on the front side and the second magnetic sensor 53 disposed behind the first magnetic sensor 52 are the axis of the cylinder hole 11. It is provided on the outer periphery of the cylinder 12 with an interval in the direction.

  The first and second magnetic sensors 52, 53 are Hall element sensors that detect the first and second annular protrusions 14b, 14c of the rear piston 14 by the proximity of the annular protrusions 14b, 14c, The first magnetic sensor 52 outputs an ON signal of “1” when the first annular protrusion 14b or the second annular protrusion 14c is in the detection position P1 in the direction along the axis of the cylinder hole 11, and the second The magnetic sensor 53 outputs an ON signal of “1” when the first annular protrusion 14b or the second annular protrusion 14c is in the detection position P2 in the direction along the axis of the cylinder hole 11.

  The outputs of the first and second magnetic sensors 52 and 53 are input to the piston position determining means 54. The piston position determining means 54 is a combination of the output signals of the first and second magnetic sensors 52 and 53, and The position of the rear piston 14 in the direction along the axis is determined.

  By the way, the width D1 along the axial direction of the first annular projection 14b located in the forefront among the first and second annular projections 14b, 14c of the rear piston 14 is the second annular projection 14c located on the rear side. The second magnetic sensor 53 located at the rear of the first and second magnetic sensors 52 and 53 is set to be larger than a width D2 along the axial direction of the first piston. As shown in FIG. 2, it arrange | positions in the position which detects the 1st cyclic | annular protrusion 14b.

  The distance L1 between the front end of the first annular protrusion 14b and the front end of the second annular protrusion 14c is larger than the distance L2 between the detection positions P1, P2 detected by the first and second magnetic sensors 52, 53. , L2> D1. That is, the relative positions of the first and second annular protrusions 14b and 14c and the first and second magnetic sensors 52 and 53 are set so that L1> L2> D1> D2.

  Moreover, the stopper 51 attached to the piston main portion 14a behind the second annular protrusion 14c in the rear piston 14 should not be detected by the first and second magnetic sensors 52, 53. For example, it is formed of a nonmagnetic material made of stainless steel. Similarly to the stopper 51, the rear return spring 30 and the cup seal pressing member 49 are also made of a nonmagnetic material.

  Thus, as shown in FIG. 2, when the rear piston 14 is in an inoperative state and is in the retreat limit within the cylinder body 12, the output of the first magnetic sensor 52 is “0”, and the second magnetic sensor 53 The output is “1”.

  Next, as shown in FIG. 3, when the rear piston 14 slightly moves forward from the retreat limit, both the first and second magnetic sensors 52 and 53 change any of the first and second annular protrusions 14b and 14c. Also, the outputs of the first and second magnetic sensors 52 and 53 are both “0”.

  When the rear piston 14 moves forward from the position shown in FIG. 3 to the position shown in FIG. 4, the first magnetic sensor 52 detects the first annular protrusion 14b, whereas the second magnetic sensor 53 has the first and first Neither of the two annular protrusions 14b, 14c is detected, and the output of the first magnetic sensor 52 is “1”, whereas the output of the second magnetic sensor 53 is “0”.

  When the rear piston 14 moves forward from the position shown in FIG. 4 to the position shown in FIG. 5, the first magnetic sensor 52 detects the first annular protrusion 14b, and the second magnetic sensor 53 detects the second annular protrusion 14c. The outputs of the first and second magnetic sensors 52 and 53 are both “1”.

  When the rear piston 14 moves forward from the position shown in FIG. 5 to the position shown in FIG. 6, the first magnetic sensor 52 detects the first annular protrusion 14b, whereas the second magnetic sensor 53 detects the second annular protrusion. The output of the first magnetic sensor 52 is “1” while the output of the second magnetic sensor 53 is “0”.

  When the rear piston 14 moves forward from the position shown in FIG. 6 to the position shown in FIG. 7, both the first and second magnetic sensors 52 and 53 detect both the first and second annular protrusions 14b and 14c. The outputs of the first and second magnetic sensors 52 and 53 are both “0”.

  When the rear piston 14 moves forward from the position shown in FIG. 7 to the position shown in FIG. 8, the first magnetic sensor 52 detects the second annular protrusion 14b, whereas the second magnetic sensor 53 Neither of the two annular protrusions 14b, 14c can be detected, and the output of the first magnetic sensor 52 is “1”, whereas the output of the second magnetic sensor 53 is “0”.

  Further, when the rear piston 14 moves forward from the position shown in FIG. 8 and enters a full stroke state, both the first and second magnetic sensors 52 and 53 are either of the first and second annular protrusions 14b and 14c. Cannot be detected, and the outputs of the first and second magnetic sensors 52 and 53 are both “0”.

  Thus, during forward operation from the rearward limit of the rear piston 14 to the full stroke, the combination of the output signals of the output 1 and the second magnetic sensors 52 and 53 varies depending on the forward position of the rear piston 14, and so on. The piston position determination means 54 can determine the position of the rear piston 14 in the direction along the axis of the cylinder hole 11 by changing the combination of the output signals. In addition, when the rear piston 14 is in the position shown in FIG. 5 during the forward operation from the rearward limit of the rear piston 14 to the full stroke, the first magnetic sensor 52 detects the first annular protrusion 14b, and the second magnetic The sensor 53 simultaneously detects the second annular protrusion 14c. Further, when the rear piston 14 is in an inoperative state, the output signal of the first magnetic sensor 52 is “1”, the output signal of the second magnetic sensor 53 is “0”, and the combination of such output signals is the rear piston 14. This is different from the combination of the output signals of both the magnetic sensors 52 and 53 during the forward movement operation.

  Next, the operation of this embodiment will be described. In the master cylinder M, the cylinder body 12 having the cylinder hole 11, the stopper 51, the rear return spring 30, and the cup seal pressing member 49 are formed of a nonmagnetic material, and the piston main portion 14a and The rear piston 14 having first and second annular protrusions 14b and 14c projecting radially outward from the piston main part 14a and slidably fitted into the cylinder hole 11 is made of a magnetic material. The first and second magnetic sensors 52 and 53, which are the same number as the first and second annular protrusions 14 b and 14 c, connect the first and second annular protrusions 14 b and 14 c of the piston 14 to the annular protrusions. 14b and 14c, and the first and second annular members are detected during the forward operation from the non-operating position of the rear piston 14 The parts 14b and 14c are individually and simultaneously detected so as to be provided on the outer periphery of the cylinder body 12 with an interval in the axial direction of the cylinder hole 11, and the outputs of the first and second magnetic sensors 52 and 53 are input. Since the piston position determining means 54 determines the position of the rear piston 14 in the direction along the axis of the cylinder hole 11 by the combination of the output signals of the first and second magnetic sensors 52 and 53, the first and first The axial position of the rear piston 14 having the two annular protrusions 14b and 14c can be accurately detected without greatly changing the structure inside the cylinder body 12.

  Further, the combination of the output signals of the first and second magnetic sensors 52 and 53 when the rear piston 14 is not operated is the combination of the output signals of the first and second magnetic sensors 52 and 53 when the rear piston 14 moves forward. Since the relative positions of the first and second annular protrusions 14b and 14c and the first and second magnetic sensors 52 and 53 are set so as to be different from any combination, the initial state of the rear piston 14 in the non-operating state is set. The position can be reliably detected without erroneous detection, and the brake operating state can be determined more accurately.

  A width D1 along the axial direction of the first annular protrusion 14b which is the foremost of the first and second annular protrusions 14b and 14c protruding radially outward from the piston main part 14a is a second annular protrusion. 14c is set to be larger than the width D2 along the axial direction, and the second magnetic sensor 53, which is the rearmost of the first and second magnetic sensors 52, 53, has the first annular protrusion 14b when the rear piston 14 is not operated. Even if there is an error in attaching the magnetic sensors 52 and 53 to the outer periphery of the cylinder body 12, the second annular sensor 14 causes the first annular protrusion 14b to be moved when the rear piston 14 is not operated. The combination of the output signals of the magnetic sensors 52 and 53 when the rear piston 14 is in the non-operating state is combined with the output signals of the magnetic sensors 52 and 53 when the rear piston 14 is advanced. It can be more reliably prevented that would match, detecting the initial position in the inoperative state of the rear piston 14 reliably.

  Further, at least one of the first and second annular protrusions 14b and 14c, in this embodiment, the first annular protrusion 14b is elastically brought into sliding contact with the inner periphery of the cylinder hole 11, and the cylinder body 12 and Since it is provided in the rear piston 14 so as to hold the cup seal 46 interposed between the rear pistons 14, the rear piston 14 has an outer shape greatly changed from the outer shape of the rear piston used conventionally. It becomes unnecessary to form.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. It is.

  In the above embodiment, the case where the present invention is applied to the tandem master cylinder M has been described. However, the present invention also applies to a master cylinder in which a single piston is slidably fitted into a cylinder hole of a cylinder body. Is possible.

Longitudinal section of the master cylinder in non-actuated state 1 is an enlarged view of the main part of FIG. Sectional view corresponding to FIG. 2 with the rear piston advanced from its initial position Sectional view corresponding to FIG. 2 with the rear piston advanced from the position of FIG. Sectional view corresponding to FIG. 2 with the rear piston advanced from the position of FIG. Sectional view corresponding to FIG. 2 with the rear piston advanced from the position of FIG. Sectional view corresponding to FIG. 2 with the rear piston advanced from the position of FIG. Sectional view corresponding to FIG. 2 with the rear piston advanced from the position of FIG.

DESCRIPTION OF SYMBOLS 11 ... Cylinder hole 12 ... Cylinder body 14 ... Rear piston 14a which is a piston ... Piston main part 14b, 14c ... Annular protrusion 25 ... Rear hydraulic chamber which is a hydraulic chamber 52, 53 ... Magnetic sensor 46 ... Cup seal 54 ... Piston position determining means M ... Master cylinder

Claims (3)

The cylinder body having a cylinder bore (11) and (12), before SL and a piston (14) slidably fitted in the cylinder bore (11), the piston (14) is a piston main portion (14a ) And a plurality of annular protrusions (14b, 14c) that protrude radially outward from the outer peripheral surface of the piston main part (14a) and are arranged at intervals in the axial direction of the cylinder hole (11). In the master cylinder in which a hydraulic chamber (25) is formed in the cylinder body (12) to face the front end of the piston (14),
The plurality of magnetic sensors (52, 53), which are the same number as the annular protrusions (14b, 14c), form the annular protrusions (14b, 14c) of the piston (14) made of a magnetic material . Are provided on the outer circumference of the cylinder body (12) made of a non-magnetic material with an interval in the axial direction of the cylinder hole (11) so that an output signal is output when detected by the proximity of the parts (14b, 14c). ,
Each of the plurality of annular protrusions (14b, 14c) comes close to each of the plurality of magnetic sensors (52, 53) when the piston (14) is at a predetermined position in the middle of forward operation from the non-operating position. The combination of the output signals of the plurality of magnetic sensors (52, 53) so that all of the plurality of magnetic sensors (52, 53) output an output signal and the piston (14) is in an inoperative state. The plurality of annular protrusions (14b, 14c) and the plurality of magnetic sensors (() are different from any combination of output signals of the magnetic sensors (52, 53) during the forward movement of the piston (14)). 52, 53) is set,
Wherein the plurality of piston position determining means for output of the magnetic sensor (52, 53) is input (54), the axial line of the cylinder bore in combination with the output signals of the magnetic sensors (52, 53) (11) piston position detecting equipment in the master cylinder, characterized in that to determine the position of the piston (14) in the direction along. Of the plurality of annular protrusions (14b, 14c), the width along the axial direction of the foremost annular protrusion (14b) is set larger than the width along the axial direction of the other annular protrusions (14c). , the rearmost magnetic sensor of the plurality of magnetic sensors (52, 53) (53) is positioned to detect the front-most annular projection (14b) during non-operation of the piston (14) The piston position detecting device in the master cylinder according to claim 1 . The cylinder body (12) and the piston (14) are arranged such that at least one (14b) of the plurality of annular protrusions (14b, 14c) elastically slides on the inner periphery of the cylinder hole (11). The piston position detecting device in the master cylinder according to claim 1 or 2 , wherein the piston (14) is provided so as to hold a cup seal (46) interposed therebetween.

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