JP2017114407A - Master cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a master cylinder in which erroneous detection of insufficiency of fluid volume of a brake fluid can be suppressed.SOLUTION: A detection part for detecting a fluid volume of a brake fluid comprises: a first terminal 111 connected to a power source 122; a second terminal 112 connected to a determination part 123 for determining the fluid volume; a switch 113 for electrically connecting the first terminal 111 and the second terminal 112 together when the fluid volume is less than a first predetermined value, and disconnects the electrical connection between the first terminal 111 and the second terminal 112 when the fluid volume is equal to a second predetermined value or more; and an RC circuit 118 provided between the switch 113 and the second terminal 112 and comprising a resistor 115 and capacitors 116, 117.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a master cylinder that supplies hydraulic pressure to a brake cylinder of a vehicle.

  In a master cylinder, a liquid level sensor that detects the amount of brake fluid is provided in a reservoir tank that stores brake fluid (see, for example, Patent Document 1).

Japanese Patent No. 3906400

  The amount of brake fluid at the position detected by the sensor varies depending on the behavior of the vehicle. For this reason, there is a possibility that the shortage of the liquid amount is erroneously detected even though the whole liquid amount is not short.

  An object of the present invention is to provide a master cylinder capable of suppressing erroneous detection of insufficient brake fluid amount.

  In order to achieve the above object, according to the present invention, a detection unit that detects the amount of brake fluid is a second terminal that is connected to a first terminal connected to a power source and a determination unit that determines the amount of fluid. A terminal and the first terminal and the second terminal are electrically connected when the liquid amount is less than a first predetermined value, and the first terminal and the second terminal are electrically connected when the liquid amount is equal to or greater than a second predetermined value; A switch that cuts off electrical connection between the first terminal and the second terminal; and an RC circuit that is provided between the switch and the second terminal and includes a resistor and a capacitor. .

  According to the master cylinder of the present invention, it is possible to suppress erroneous detection of insufficient brake fluid amount.

It is a side view which shows the master cylinder of embodiment. It is a sectional side view which shows the reservoir tank of the master cylinder of embodiment. It is a plane sectional view showing a reservoir tank of a master cylinder of an embodiment. It is a circuit diagram which shows the detection part etc. of the master cylinder of embodiment. It is a perspective view which shows the level indicator switch unit of the master cylinder of embodiment. The level indicator switch unit of the master cylinder of embodiment is shown, (a) is a top view, (b) is a side view, (c) is a bottom view. It is A arrow directional view of FIG. It is a B arrow view of FIG. It is sectional drawing of the level indicator switch unit and its vicinity which follow the CC line of FIG. It is a figure which shows the voltage characteristic of the 2nd terminal at the time of ON / OFF of a switch, Comprising: (a) shows embodiment and (b) shows the former.

  The master cylinder of this embodiment is demonstrated based on drawing. A master cylinder 10 according to the present embodiment shown in FIG. 1 is mounted on a vehicle such as a four-wheel automobile, and includes a reservoir tank 11 and a master cylinder main body 12. Here, the posture shown in FIG. 1 is a posture of the master cylinder 10 in a vehicle-mounted state, and the master cylinder 10 is mounted on the vehicle so that the left side in FIG. 1 is the front side when the vehicle moves forward. In the following description, front, rear, left and right are front, rear, left and right when the vehicle is moving forward.

  The master cylinder main body 12 is a brake master cylinder that constitutes a part of a brake device that brakes wheels. The reservoir tank 11 stores brake fluid, and is connected to the master cylinder body 12 to supply brake fluid thereto. Although not shown, the master cylinder main body 12 generates a brake fluid pressure to be introduced into a wheel cylinder that is provided on a wheel and generates a braking force in accordance with a driver's brake operation or the like. Although not shown, the master cylinder main body 12 of the present embodiment is a tandem type having two hydraulic chambers at the front and rear so that brake hydraulic pressure can be generated in two brake lines.

  The master cylinder main body 12 is attached to the vehicle body side in a posture inclined slightly upward to the horizontal, and the cylindrical mounting boss portion 14 is located on the front side of the upper portion and the rear side of the upper mounting boss portion 14. A cylindrical mounting boss portion 15 is formed in each. The reservoir tank 11 is fitted and attached to the mounting boss portions 14 and 15, and the inside of the reservoir tank 11 communicates with each hydraulic pressure chamber in the master cylinder body 12 in this attached state.

  The reservoir tank 11 includes a synthetic resin reservoir body 20 and a synthetic resin cap 21 that can be attached to and detached from the reservoir body 20.

  The reservoir body 20 has a bottom portion 30, an upper plate portion 31, a front wall portion 32, a rear wall portion 33 and a side wall portion 34 shown in FIG. 2, and a side wall portion 35 shown in FIG. The brake fluid is accommodated in the brake fluid chamber 37 shown in FIG.

  Similar to the master cylinder main body 12 shown in FIG. 1, the bottom 30 is inclined slightly upward in front of the horizontal as a whole. As shown in FIG. 2, the front wall portion 32 extends vertically upward from the front edge portion of the bottom portion 30, and the rear wall portion 33 extends upward from the rear edge portion of the bottom portion 30. The side wall portion 34 extends upward from the right edge portion on one side of the bottom portion 30 in the left-right direction, and the side wall portion 35 shown in FIG. 3 extends from the left edge portion on the opposite side of the bottom portion 30 in the left-right direction. It extends upward. The front wall part 32, the side wall part 34, the rear wall part 33, and the side wall part 35 are connected in a frame shape in this order. The upper plate portion 31 shown in FIG. 2 extends inward from the upper edge portions of the front wall portion 32, the side wall portion 34, the rear wall portion 33, and the side wall portion 35 so as to close the inside thereof. Yes. The front wall portion 32 is disposed so as to be orthogonal to the front-rear direction, the side wall portions 34, 35 are disposed along the front-rear direction, and the upper plate portion 31 is disposed horizontally.

  The reservoir body 20 has an injection port portion 38 at a substantially central position of the upper plate portion 31. The inlet portion 38 has a cylindrical shape, and protrudes upward from the inner position of the upper plate portion 31 perpendicular to the upper plate portion 31. The inlet portion 38 has an inner passage that allows the brake fluid chamber 37 of the reservoir body 20 to communicate with the outside. The inlet portion 38 is closed by attaching the cap 21 to the upper end portion.

  The bottom 30 includes a front-side front component 41, a rear-side intermediate component 42, and a rear-side rear component 43. The front component 41 and the rear component 43 are slightly inclined upwards with respect to the horizontal, and the intermediate component 42 projects upward from between the front component 41 and the rear component 43.

  The bottom part 30 has a pair of attachment opening parts 45 and 46 in the front and rear. The attachment port portions 45 and 46 are both cylindrical, and the attachment port portion 45 protrudes downward from the front component portion 41 in a direction perpendicular thereto, and the attachment port portion 46 extends from the rear component portion 43 perpendicular thereto. Projecting downward. The attachment openings 45 and 46 allow the respective inner passages to communicate the brake fluid chamber 37 of the reservoir body 20 to the outside. The reservoir main body 20 is attached to the master cylinder main body 12 with the fitting opening portions 45 and 46 fitted inside the attachment boss portions 14 and 15 shown in FIG. In this state, the passages inside the attachment ports 45 and 46 can communicate with the hydraulic chambers of the master cylinder body 12 via the passages inside the attachment bosses 14 and 15.

  The bottom portion 30 has a pair of mounting plate portions 51 shown in FIG. 2 and a mounting plate portion 52 shown in FIG. The attachment plate portions 51 and 52 protrude downward from the intermediate component portion 42 shown in FIG. 2, and the attachment plate portion 51 is arranged on the right side and the attachment plate portion 52 is arranged on the left side. The mounting plate portions 51, 52 are along the vertical direction and along the front-rear direction, and the mounting plate portion 51 shown in FIG. 2 has mounting holes 53 penetrating in the left-right direction in the mounting plate portion 52 shown in FIG. A mounting hole 54 penetrating in the left-right direction is formed. The reservoir body 20 is connected to the master cylinder body 12 by a cylindrical spring pin 55 fitted in the mounting holes 53 and 54.

  As shown in FIG. 2, a mounting hole 61 is formed in the intermediate component 42 of the bottom 30 so as to extend in the left-right direction. The mounting hole 61 is formed so as to penetrate the intermediate component 42 in the left-right direction.

  The reservoir body 20 has a guide wall portion 71 extending vertically upward from the intermediate component portion 42 of the bottom portion 30. As shown in FIG. 3, the guide wall portion 71 has a cylindrical guide main body portion 73 formed with slits 72 extending in the axial direction, and projects radially inward from the inner peripheral surface of the guide main body portion 73 in the axial direction. It has a pair of extending guide ribs 74 and 75. The slit 72 is formed at an end position on one side in the left-right direction of the guide wall portion 71, and specifically, is formed at the left end position of the guide wall portion 71. The slit 72 allows the inside of the guide wall portion 71 to communicate with the outside. The guide rib 74 is formed at the front end position of the guide wall portion 71, and the guide rib 75 is formed at the rear end position of the guide wall portion 71.

  The reservoir body 20 includes an intermediate wall portion 81 that extends in the left-right direction from the front end position of the guide wall portion 71, a pair of end wall portions 82 and 83 that extend forward from both edge portions of the intermediate wall portion 81, and a guide wall portion. 71 includes an intermediate wall portion 85 extending in the left-right direction from the rear end position of the 71 and a pair of end wall portions 86 and 87 extending rearward from both edge portions of the intermediate wall portion 85. These intermediate wall portions 81, 85 and end wall portions 82, 83, 86, 87 are all connected to the bottom portion 30 at the lower edge. The front attachment port 45 is located in the inner range between the front intermediate wall portion 81 and the pair of end wall portions 82, 83, and The side mounting openings 46 are open.

  As shown in FIG. 2, the mounting hole 61 and the brake fluid chamber 37 are arranged with only one wall portion 88 therebetween. In other words, only one wall portion 88 is provided between the mounting hole 61 and the brake fluid chamber 37, the lower surface on one side of the one wall portion 88 forms the mounting hole 61, and the upper surface is the brake. A liquid chamber 37 is formed. The wall portion 88 is a part of the intermediate component portion 42 of the bottom portion 30.

  As shown in FIG. 3, the master cylinder 10 has a detection unit 91 that detects the amount of brake fluid stored in the reservoir tank 11. The detection unit 91 includes a float 92 that is movably disposed in the guide wall 71 of the reservoir body 20 and a level indicator switch unit 93 that is mounted in the mounting hole 61 of the bottom 30 of the reservoir body 20.

  As shown in FIG. 2, the float 92 includes a float body 101 made of synthetic resin and a magnet 102 fixed to the lower end portion of the float body 101. The float body 101 causes the float 92 to generate buoyancy that floats on the brake fluid. As shown in FIGS. 2 and 3, the float main body 101 has a columnar shape, and is formed with a pair of guide grooves 103 and 103 that are recessed from the outer peripheral surface. The pair of guide grooves 103, 103 are formed at positions that differ by 180 ° in the circumferential direction of the float main body 101, and extend in the axial direction of the float main body 101. When the float 92 is disposed in the guide wall portion 71 of the reservoir body 20, the pair of guide ribs 74 and 75 of the guide wall portion 71 are inserted into the pair of guide grooves 103 and 103 of the float body 101. Thereby, the float 92 moves up and down in the guide wall portion 71 while the rotation is restricted by the pair of guide ribs 74 and 75. The magnet 102 is fixed to the center position of the lower end of the float body 101 so as to protrude downward.

  The float 92 changes its height from the bottom 30 following the change in the height of the liquid level from the bottom 30 corresponding to the amount of brake fluid in the reservoir tank 11. Therefore, the magnet 102 provided in the float 92 also changes the height from the bottom 30 following the change in the height from the bottom 30 of the liquid level corresponding to the amount of brake fluid.

  As shown in FIG. 4, the level indicator switch unit 93 includes a switch circuit 110. The switch circuit 110 includes a first terminal 111, a second terminal 112, a first terminal 111, and a second terminal. A switch 113 that switches between electrical connection and disconnection between the terminal 112 and the RC circuit 118 that is provided between the switch 113 and the second terminal 112 and includes a resistor 115 and capacitors 116 and 117; It has.

  Here, in the level indicator switch unit 93, the first terminal 111 is connected to the power source 122 provided on the vehicle body 121 side, and the second terminal 112 is provided in the amount of liquid provided on the vehicle body 121 side. It will be connected to the determination part 123 which determines. The switch 113 is disposed on the circuit 131 of the switch circuit 110 that electrically connects the first terminal 111 and the second terminal 112, and switches connection and disconnection of the circuit 131. The determination unit 123 controls lighting of a warning lamp 124 provided on the instrument panel.

  In the RC circuit 118, the resistor 115 is provided between the switch 113 and the second terminal 112 in the circuit 131, and one end of each of the capacitors 116 and 117 is between the resistor 115 and the second terminal 112 of the circuit 131. Are connected in parallel to the circuit 132 of the switch circuit 110 that is electrically connected to the other end and grounded at the other end. The resistor 115 and the capacitors 116 and 117 are built in the level indicator switch unit 93.

  The switch 113 is a reed switch that opens and closes the circuit 131 by detecting magnetic force, and the magnet 102 of the float 92 shown in FIG. As a result, the distance between the switch 113 and the magnet 102 of the float 92 in which the magnet 102 rises and falls according to the amount of the brake fluid floats on the brake fluid. In other words, the float 92 has the magnet 102 and floats on the brake fluid, and the magnet 102 changes the distance from the switch 113 according to the amount of the brake fluid.

  The magnet 102 of the float 92 is turned on to electrically connect the switch 113 to the first terminal 111 and the second terminal 112 when the amount of brake fluid in the reservoir tank 11 is less than the first predetermined value. In the state, when the amount of brake fluid in the reservoir tank 11 is equal to or greater than a second predetermined value that is greater than the first predetermined value, the switch 113 is connected between the first terminal 111 and the second terminal 112. It is set to the OFF state that cuts off the electrical connection. In other words, the switch 113 is turned on when the amount of brake fluid in the reservoir tank 11 is less than the first predetermined value, and electrically connects the first terminal 111 and the second terminal 112. When the amount of brake fluid in the reservoir tank 11 is greater than or equal to a second predetermined value that is greater than the first predetermined value, the brake tank is turned off and between the first terminal 111 and the second terminal 112. Disconnect the electrical connection.

  As shown in FIGS. 5 and 6, the level indicator switch unit 93 has a flat shape and extends linearly. Each of the level indicator switch units 93 includes a synthetic resin unit main body 141 and a metal heat radiating plate 142 that constitute an outer portion of the level indicator switch unit 93.

  The unit main body 141 is a portion that mainly constitutes the level indicator switch unit 93 and has a flat shape and extends linearly. The unit main body 141 has a body 145 that extends linearly and a head 146 that is wider than the body 145 provided at one end in the length direction of the body 145. The head 146 is formed so as to protrude only on one side in the width direction with respect to the body 145, and has a bottomed cylindrical shape that opens to the opposite side of the body 145. A connector (not shown) on the vehicle body 121 side is fitted to the head 146 from the opening side. As shown in FIG. 7, the head portion 146 has a main body fitting portion 148 and an engaging portion 149, and the main body fitting portion 148 is fitted with a main body portion having a connector terminal (not shown). The engaging portion 149 is engaged with an engaging claw for preventing the connector from coming off.

  The first terminal 111 and the second terminal 112 described above are arranged at the bottom of the body fitting portion 148 on the body 145 side. Note that the arrangement of the first terminals 111 and the second terminals 112 shown in FIG. 7 is an example, and the arrangement may be reversed. When the connector on the vehicle body 121 side is fitted to the head 146, the first terminal 111 and the second terminal 112 are connected to each terminal of the connector, resulting in the circuit configuration shown in FIG.

  As shown in FIGS. 6B, 6 </ b> C, and 8, the body portion 145 has a stepped portion 151 that is recessed in the thickness direction on one side in the thickness direction. An engagement protrusion 152 for preventing the retainer body 20 from being engaged with the reservoir body 20 when the reservoir body 20 is fitted into the mounting hole 61 is formed.

  As shown in FIG. 5 and FIG. 6A, the heat radiating plate 142 is disposed on one side in the thickness direction of the end portion of the body portion 145 opposite to the head portion 146. As shown in FIG. 9, the heat radiating plate 142 is fixed to the unit main body 141 with its outer surface positioned slightly outside the unit main body 141. That is, the heat radiating plate 142 is provided at a position exposed to the outside of the level indicator switch unit 93. The above-described capacitors 116 and 117 are attached to the inner surface of the heat sink 142 on the inner side of the level indicator switch unit 93 via a heat conductive material 155 such as a heat conductive adhesive having high heat conductivity and adhesion. Yes. The capacitors 116 and 117 are provided such that the level indicator switch unit 93 is aligned in the thickness direction and the length direction and aligned in the width direction. Capacitors 116 and 117 are supported by heat radiating plate 142 only through heat conductive material 155. Here, as the heat conductive material 155, for example, grease can be used.

  When the level indicator switch unit 93 is fitted into the mounting hole 61 of the bottom 30 of the reservoir body 20 and the engagement protrusion 152 is engaged, the level indicator switch unit 93 is fixed to the bottom 30. Here, the broken line in FIG. 3 shows the level indicator switch unit 93 that is fixed to the bottom 30 in this way. The level indicator switch unit 93 is fixed to the bottom 30 and the switch 113 shown in FIG. 4 is positioned in the bottom 30 vertically below the magnet 102 shown in FIG. As a result, the magnet 102 of the float 92 changes its height from the switch 113 following the change in the height of the brake fluid level in the reservoir tank 11 from the switch 113.

  In a state where the level indicator switch unit 93 is fixed to the bottom 30 of the reservoir body 20, the heat radiating plate 142 comes into contact with the wall 88 forming the brake fluid chamber 37 by surface contact as shown in FIG. Thus, the capacitors 116 and 117 transmit heat to the brake fluid only through the heat conducting material 155, the heat radiating plate 142, and the single wall portion 88 made of synthetic resin.

  In the master cylinder 10 described above, the magnet 102 of the float 92 floated on the brake fluid stored in the reservoir tank 11 follows the change in the height of the brake fluid level in the reservoir tank 11 from the switch 113. Thus, the height from the switch 113 changes. When the amount of brake fluid in the reservoir tank 11 at the position of the float 92 decreases and becomes less than the first predetermined value, the magnet 102 of the float 92 causes the switch 113 to be connected to the first terminal 111 and the second terminal by the magnetic force. The terminal 112 is turned on to be electrically connected. Then, a current flows from the power source 122 to the circuit 131, and the voltage of the second terminal 112 increases. At that time, the RC circuit 118 provided between the switch 113 and the second terminal 112 moderates the voltage increase of the second terminal 112 per unit time as shown in FIG. When the voltage at the second terminal 112 exceeds the threshold voltage, the determination unit 123 determines that the amount of brake fluid has decreased and turns on the warning lamp 124.

  In the master cylinder described in Patent Document 1 described above, a liquid level sensor that detects the amount of brake fluid is provided in a reservoir tank that stores brake fluid. That is, a cylindrical portion is provided at the bottom of the reservoir tank, and the liquid level sensor is fitted and held in the mounting hole inside the cylindrical portion.

  By the way, in addition to the case where the total amount of brake fluid decreases and the amount of fluid at the position of the float 92 decreases, the amount of fluid at the position of the float 92 decreases momentarily due to acceleration / deceleration or turning of the vehicle. The magnet 102 may turn on the switch 113. In such a case, if the RC circuit 118 is not provided, the voltage increase per unit time at the second terminal 112 when the switch 113 is turned on is as shown in FIG. Even if the switch 113 turns off immediately after that, the voltage of the second terminal 112 exceeds the threshold voltage. As described above, when the voltage at the second terminal 112 exceeds the threshold voltage, the determination unit 123 determines that the amount of brake fluid has decreased and turns on the warning lamp 124.

  On the other hand, in the master cylinder 10 of the present embodiment, since the RC circuit 118 is provided between the switch 113 and the second terminal 112, the liquid amount becomes less than the first predetermined value and the switch 113. As shown in FIG. 10 (a), the voltage increase per unit time of the second terminal 112 when is turned on. Therefore, even if the liquid amount is instantaneously less than the first predetermined value and the switch 113 is turned on, the rise in the voltage at the second terminal 112 is delayed, so the liquid amount is the second predetermined value. If the switch 113 is immediately turned off as described above, the voltage of the second terminal 112 does not exceed the threshold voltage. Therefore, it is less likely that the determination unit 123 determines that the amount of brake fluid is insufficient when the detection unit 91 detects that the amount of fluid has decreased instantaneously. Therefore, it is possible to suppress erroneous detection of insufficient brake fluid amount.

  More specifically, even if the liquid amount at the position of the float 92 decreases instantaneously and becomes less than the first predetermined value and the magnet 102 turns on the switch 113, it is provided between the switch 113 and the second terminal 112. Since the rise of the voltage at the second terminal 112 is delayed in the RC circuit 118, the liquid amount at the position of the float 92 immediately returns to the second predetermined value or more and the magnet 102 turns off the switch 113. In this case, the voltage at the second terminal 112 does not exceed the threshold voltage. Therefore, it is less likely that the determination unit 123 determines that the amount of brake fluid is insufficient when the amount of fluid at the position of the float 92 decreases instantaneously. Therefore, it is possible to suppress erroneous detection of insufficient brake fluid amount.

  The time from when the switch 113 is turned on until the voltage value of the second terminal 112 reaches 100% is set by a combination of the resistance value of the resistor 115 and the capacitance values of the capacitors 116 and 117. Therefore, the time from when the switch 113 is turned on until the voltage value of the second terminal 112 exceeds the threshold voltage can be adjusted.

  In addition, since the RC circuit 118 is provided between the switch 113 and the second terminal 112, it is easy to make a mistake in the shortage of the brake fluid amount in a short period of time compared with the case where measures are taken by reviewing the internal structure of the reservoir tank 11. Measures can be taken. In other words, when reviewing the internal structure, it is necessary to create a sample and conduct an experiment, which leads to a long lead time. It is possible to suppress the lead time.

  Moreover, since the detection part 91 is provided with the heat sink 142 which contacts the wall part 88 which forms the brake fluid chamber 37 which stores the brake fluid of the reservoir tank 11, the heat of the heat sink 142 is braked via the wall part 88. Can be released into the liquid. Therefore, the heat dissipation efficiency of the heat sink 142 can be improved. As a result, the heat of the capacitors 116 and 117 attached to the heat radiating plate 142 via the heat conducting material 155 can be released to the brake fluid. Therefore, by disposing the master cylinder 10 in a high temperature atmosphere in the engine room, even if the capacitors 116 and 117 are subjected to heat, it is possible to suppress a decrease in service life due thereto.

  Since the two capacitors 116 and 117 are provided in parallel in the RC circuit 118, the reliability against the loss of capacitance of the capacitor due to aging can be improved. Of course, three or more capacitors may be provided in parallel. That is, it is preferable to provide a plurality of capacitors in parallel. One capacitor can be used for the purpose of cost reduction.

  The present embodiment described above includes a master cylinder body, a reservoir tank connected to the master cylinder body and storing brake fluid, and a detector that detects the amount of the brake fluid, and the detector Are a first terminal connected to a power source, a second terminal connected to a determination unit for determining the liquid amount, and the first terminal when the liquid amount is less than a first predetermined value. A switch that electrically connects the second terminal, and disconnects the electrical connection between the first terminal and the second terminal when the liquid amount is equal to or greater than a second predetermined value; An RC circuit provided between the switch and the second terminal and including a resistor and a capacitor. Thus, since the RC circuit is provided between the switch and the second terminal, the voltage increase per unit time of the second terminal when the switch is turned on becomes moderate. Therefore, even if the switch is turned on instantaneously, a delay occurs in the rise of the voltage of the second terminal. Therefore, if the switch is immediately turned off, the voltage of the second terminal will not exceed the threshold voltage. . Therefore, it is less likely that the determination unit determines that the amount of the brake fluid is insufficient when the detection unit detects that the amount of fluid has decreased instantaneously. Therefore, it is possible to suppress erroneous detection of insufficient brake fluid amount.

  Further, the detection unit further includes a float that has a magnet and floats on the brake fluid so that the magnet changes a distance from the switch in accordance with the amount of the brake fluid. When the switch is less than the first predetermined value, the switch is in a state of electrically connecting the first terminal and the second terminal, and when the liquid amount is equal to or greater than the second predetermined value, The switch is brought into a state in which electrical connection between the first terminal and the second terminal is cut off. For this reason, even if the liquid amount at the position of the float decreases momentarily and becomes less than the first predetermined value and the magnet causes the switch to electrically connect the first terminal and the second terminal, Since the RC circuit provided between the second terminal causes a delay in the rise of the voltage at the second terminal, the liquid amount at the float position immediately returns to the second predetermined value or more, and the magnet switches the switch. When the electrical connection between the first terminal and the second terminal is cut off, the voltage at the second terminal does not exceed the threshold voltage. Therefore, the possibility that the determination unit determines that the amount of brake fluid is insufficient when the amount of fluid at the float position decreases momentarily is reduced. Therefore, it is possible to suppress erroneous detection of insufficient brake fluid amount.

  In addition, since the detection unit includes a heat radiating plate in contact with a wall portion that forms a brake fluid chamber for storing the brake fluid of the reservoir tank, the heat radiating plate releases heat to the brake fluid through the wall portion. Become. Therefore, the heat dissipation efficiency of the heat sink can be improved.

DESCRIPTION OF SYMBOLS 10 Master cylinder 11 Reservoir tank 12 Master cylinder main body 37 Brake fluid chamber 88 Wall part 91 Detection part 92 Float 102 Magnet 111 1st terminal 112 2nd terminal 113 Switch 115 Resistor 116,117 Capacitor 118 RC circuit 122 Power supply 123 Determination Part

Claims (3)

The master cylinder body,
A reservoir tank that is connected to the master cylinder body and stores brake fluid;
A detection unit for detecting the amount of the brake fluid,
The detector is
A first terminal connected to a power source;
A second terminal connected to a determination unit for determining the liquid amount;
The first terminal and the second terminal are electrically connected when the liquid amount is less than a first predetermined value, and the first terminal when the liquid amount is equal to or greater than a second predetermined value. And a switch for disconnecting an electrical connection between the second terminal and the second terminal;
A master cylinder comprising an RC circuit provided between the switch and the second terminal and including a resistor and a capacitor. The detector is
A float that floats on the brake fluid and has a magnet that changes the distance between the magnet and the switch according to the amount of the brake fluid;
The magnet
When the liquid amount is less than the first predetermined value, the switch is in a state of electrically connecting the first terminal and the second terminal;
2. The master cylinder according to claim 1, wherein when the liquid amount is equal to or greater than the second predetermined value, the switch is in a state in which electrical connection between the first terminal and the second terminal is cut off. .   The master cylinder according to claim 2, wherein the detection unit includes a heat radiating plate in contact with a wall portion that forms a brake fluid chamber for storing the brake fluid in the reservoir tank.

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