JP2020011609A - Pneumatic booster - Google Patents

Abstract

To facilitate required stepping of a brake pedal when starting an engine.SOLUTION: A pneumatic booster is configured so that a relation during non-braking is first clearance C1≥second clearance C2>third clearance C3 when clearance in a direction along an axial direction between a rod holder 38 and a large diameter section 36a of an output rod 36 is defined as the first clearance C1, clearance relatively movable between a plunger 25 and a stop key 39 is defined as the second clearance C2, and clearance between the other surface 66 of a reaction force member 64 and a second tip surface 25b of the plunger 25 is defined as the third clearance C3. Therefore, since the output rod 36 can be advanced by prescribed amount before receiving spring force of a return spring 37, a brake pedal can be easily stepped up to stroke amount required for starting an engine of an automobile even in a state in which negative pressure is released and assist by differential pressure cannot be obtained.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic booster.

  As a pneumatic booster, the interior of the housing is defined by the power piston as a constant pressure chamber and a variable pressure chamber, and the valve means is opened by moving the plunger arranged in the valve body connected to the power piston by the input rod. The working gas (atmospheric pressure) is introduced into the variable pressure chamber, and a differential pressure is generated between the constant pressure chamber where the engine negative pressure is introduced and the variable pressure chamber. This differential pressure generates a thrust on the power piston. This thrust acts on the output rod supported by the rod holder via a reaction disk disposed at the tip of the valve body, thereby resisting the spring force of the return spring provided between the valve body and the housing. To move the output rod forward and transmit a part of the output reaction force to the input rod via the reaction disk and plunger. There is the. For example, in Patent Document 1, in a pneumatic booster having such a structure, the structure of the rod holder is devised to contribute to a reduction in the manufacturing cost of the rod holder while stably supporting the output rod. Things are disclosed.

  FIG. 3 is a cross-sectional view of a portion around a plunger of a pneumatic booster having a conventional structure as described above. That is, in the structure shown in FIG. 3, when the brake pedal is depressed and the input rod 100 is moved to the left side in the figure, the plunger 102 constituted by the valve member 104 and the reaction force receiving member 106 is accordingly moved to the left side in the figure. And the valve means 108 is opened. Thus, the thrust of the power piston (valve body 110) to the left in the drawing is generated by utilizing the differential pressure generated between the constant pressure chamber and the variable pressure chamber, and this thrust is applied to the reaction disk 112 and the output rod 114. Output to the master cylinder.

JP 2007-230306 A

  By the way, in recent years, automobiles of a type in which an engine is started by a push button or the like have become widespread. In order to start an engine in an automobile of this type, it is necessary to depress a brake pedal to some extent. However, if the car is left unused for several days, the negative pressure in the constant-pressure chamber of the pneumatic booster may decrease depending on the situation. Assist due to a large differential pressure cannot be obtained, and the pedal effort increases. As a result, there have been cases where the pedal cannot be depressed up to the stroke amount necessary for starting the engine and the engine cannot be started.

  The present invention has been made in view of the above problems, and an object of the present invention is to make it easy to depress a brake pedal required when starting an engine of an automobile.

  As a means for solving the above-mentioned problems, the present invention provides a valve body having a hollow boss portion inside and moving inside a shell defined by a constant pressure chamber and a variable pressure chamber, and a tip of the hollow boss portion. The thrust is transmitted from the reaction disk through a reaction disk, and the output rod having a large-diameter portion abutting on the reaction disk, a rod portion abutting on a piston of a master cylinder, and a return spring for biasing the valve body. A rod holder that is pressed and fixed to the body, supports the output rod so as to cover at least a part of the large diameter portion of the output rod, and receives the input rod and moves together with the input rod. A small-diameter portion having a diameter smaller than the inner diameter of the hollow inside of the hollow boss is disposed slidably in the hollow inside of the hollow boss along the axial direction. The first end face, which is provided on the end side, is opposed to the reaction disk at the tip end of the small-diameter portion, and the second tip surface extends radially outward from the base end of the small-diameter portion. Further, the plunger is provided with a locking groove of a predetermined width on the outer peripheral portion, and is disposed slidably along the axial direction in a counterbore provided in the opening on the distal end side of the hollow boss. One surface of the plunger is opposed to the reaction disk, and the other surface is partially opposed to the second distal end surface of the plunger, and one end protrudes into the hollow boss. A stop key inserted into the hollow boss portion to limit a relative movement amount between the valve body and the plunger, wherein the one end side is engaged with the locking groove of the plunger. , The rod ho A first clearance is defined as a clearance in a direction along an axial direction between the damper and the large-diameter portion of the output rod, and a second clearance is defined as a clearance that allows relative movement between the plunger and the stop key. Assuming that the clearance between the other surface of the member and the second end surface of the plunger is a third clearance, the relationship between the clearances when no braking is performed is the first clearance ≧ the second clearance> The third clearance is provided.

  Since the present invention is configured as described above, it is possible to easily depress the brake pedal required when starting the engine of the automobile.

It is a sectional view showing the whole structure of the pneumatic booster concerning an embodiment of the invention. 2A and 2B are cross-sectional views of the pneumatic booster of FIG. 1 around a plunger, in which FIG. 1A illustrates a state where a brake pedal is not depressed, and FIG. 2B illustrates a state where the brake pedal is depressed by a predetermined amount. It is sectional drawing of the periphery of the plunger of the conventional pneumatic booster.

Hereinafter, embodiments will be described with reference to the drawings. In FIGS. 1 and 2, common parts are denoted by the same reference numerals, and the left side of each figure is shown as a front side (front side) and the right side is shown as a rear side (rear side). .
1 and 2 schematically show the configuration of a pneumatic booster 50 according to an embodiment of the present invention. First, referring to FIG. 1, a pneumatic booster 50 according to an embodiment of the present invention is configured as a tandem type having two power pistons 7 and 8, and includes a front shell 1 and a rear shell 2. The interior of the housing 3 is divided into two chambers, a front side and a rear side, by a center shell 4.

  The front chamber is divided into a constant pressure chamber 9 and a variable pressure chamber 11 by a power piston 7 having a diaphragm 5. On the other hand, the rear chamber is partitioned into a constant pressure chamber 10 and a variable pressure chamber 12 by a power piston 8 having a diaphragm 6. Each of the power pistons 7 and 8 has a structure supported by a valve body 13, and the valve body 13 is inserted into the center shell 4 and the rear shell 2 in an airtight and slidable manner. The rear end extends to it. The rear shell 2 has a small-diameter cylindrical portion 2a in which the valve body 13 is inserted, and a dust boot 14 is mounted on the small-diameter cylindrical portion 2a. The dust boot 14 covers the hollow shaft portion 13b of the valve body 13 extending from the housing 3.

  The valve body 13 includes a cup-shaped main body portion 13a and a hollow shaft portion 13b connected to each other. The main body portion 13a serves as a sliding portion for the center shell 4 and the hollow shaft portion 13b corresponds to the rear shell 2. Each is configured as a sliding portion. Further, a substantially cylindrical hollow boss portion 13c is formed in the cup-shaped bottom portion of the main body portion 13a. The main body 13a of the valve body 13 communicates the two constant-pressure chambers 9 and 10 with each other and connects each of the constant-pressure chambers 9 and 10 to a valve mechanism 22 provided in the hollow shaft portion 13b. Passages 15a and 15b are provided. Further, the main body portion 13a of the valve body 13 is provided with a first atmospheric passage 16 that connects the rear-side variable pressure chamber 12 to a valve mechanism 22 in the hollow shaft portion 13b.

  On the other hand, a plurality of (two in the present embodiment) cylindrical communication pipes 18 are disposed in the rear-side constant pressure chamber 10, and inside the communication pipes 18, a rear-side variable pressure chamber 12 is provided. A second atmospheric passage 17 is provided for communicating the pressure chamber 11 with the front-side transformer chamber 11. Further, one end of each communication pipe 18 is press-fitted and fixed to the center shell 4, and the other end thereof is airtightly and slidably inserted into the power piston 8 on the rear side, and comes close to the rear shell 2. It has been extended to the site. In each of the communication pipes 18, there is inserted a penetrating rod 41 that penetrates the front shell 1 and the rear shell 2 in a gas-tight manner, and extends through the power piston 7 on the front side in a gas-tight manner. Stud bolts 42, 43 are integrally provided at both ends of the through rod 41, and these stud bolts 42, 43 are arranged in a state of standing upright on the rear surface of the rear shell 2 and the front surface of the front shell 1. I have. The two penetrating rods 41 and stud bolts 42 and 43 are provided at 180-degree intervals in the circumferential direction, but the rear shell 2 and the front shell 1 are out of phase with each other by 90 degrees. At the position, two general-purpose stud bolts 44 are erected. On the other hand, an engine negative pressure, for example, is introduced into the constant pressure chamber 9 on the front side through a pipe joint 19 provided on the front shell 1, and this negative pressure is transmitted through the negative pressure passages 15 a and 15 b to the rear side. Is introduced also into the constant pressure chamber 10 of FIG.

  As shown in FIGS. 1 and 2A, the valve mechanism 22 links the variable pressure chambers 11 and 12 to the constant pressure chamber 9 in conjunction with an input rod 24 as an input shaft that moves forward and backward with respect to the front shell 1 and the rear shell 2. , 10 or the outside air, and includes a plunger 25, a poppet valve 27, a negative pressure valve 29, an atmosphere valve 31, and a valve spring 32. The plunger 25 is fitted inside the hollow boss 13c of the valve body 13 so as to be slidable along the axial direction, and is connected to an input rod 24 that works with a brake pedal (not shown). The rear end of the poppet valve 27 is fixed to the inner peripheral surface of the hollow shaft portion 13 b of the valve body 13 by a pressing member 26.

  The negative pressure valve 29 is configured such that the outer peripheral edge of the front end of the poppet valve 27 and the negative pressure valve seat 28 formed on the inner peripheral surface of the hollow shaft portion 13b (hollow boss portion 13c) of the valve body 13 are in contact with each other. It is configured with contact and separation. The atmosphere valve 31 is configured such that an inner peripheral edge of a front end of the poppet valve 27 and an annular atmosphere valve seat 30 formed at a rear end of the plunger 25 are in contact with and separated from each other. It is. One end of the valve spring 32 is locked to the input rod 24, and constantly biases the poppet valve 27 in the valve closing direction. As shown in FIG. 1, a return spring 33 is interposed between the holding member 26 and the input rod 24. When the plunger 25 is not operated with no input from the brake pedal, the return spring 33 is turned off. Thus, the state in which the atmosphere valve seat 30 at the rear end thereof is in contact with the inner peripheral edge of the front end of the poppet valve 27 is maintained.

  As shown in FIG. 2A, a small-diameter portion 60 having a diameter smaller than the inner diameter of the hollow interior of the hollow boss portion 13c is provided at the tip of the plunger 25, and the small-diameter portion 60 is provided. The distal end surface of the plunger 25 includes a first distal end surface 25a located at the distal end of the small diameter portion 60, and a second distal end surface 25b extending radially outward from the base end of the small diameter portion 60. The first distal end surface 25a is opposed to a reaction disk 35 described later so as to be able to abut, and the second distal end surface 25b is opposed to a reaction force member 64 described later. Further, in the present embodiment, an annular locking groove 62 having a predetermined width is formed in the outer peripheral portion on the rear end side of the plunger 25.

  A stop key 39 is inserted into a substantially boundary portion between the main body portion 13a and the hollow shaft portion 13b of the valve body 13, that is, the hollow boss portion 13c as a member for defining a retreat end from its radial direction. In this state, one end of the stop key 39 projects into the hollow interior of the hollow boss 13c, and the other end of the stop key 39 projects into the rear side transformer chamber 12, and one end of the stop key 39 projects into the hollow interior of the hollow boss 13c. The side is engaged with a locking groove 62 provided in the plunger 25 which is a configuration of the valve mechanism 22. The stop key 39 moves in the axial direction together with the valve body 13 or the input rod 24, and defines a retreating end of the valve body 13 and the input rod 24. The stop key 39 is provided on the small-diameter cylindrical portion 2a of the rear shell 2. The position in contact with the step portion 40 (see FIG. 1) is the original position. Further, the relative movement amount between the valve body 13 and the plunger 25 is regulated by the stop key 39.

  As shown in FIG. 2A, a counterbore 68 is formed at the opening on the distal end side of the hollow boss 13c of the valve body 13, and slides in the counterbore 68 along the axial direction. A reaction force member 64 is movably disposed. The reaction force member 64 has an annular shape in the present embodiment, and one surface 65 is opposed to a reaction disk 35 to be described later, and a part of the other surface 66 is a part of the plunger 25 based on the sliding direction. 2 is opposed to the front end surface 25b. Note that the remaining portion of the other surface 66 of the reaction force member 64 faces the seating surface of the counterbore portion 68 of the hollow boss portion 13c so as to be able to abut. On the other hand, at the tip of the hollow boss 13c of the valve body 13, a reaction disk 35 made of an elastic material such as rubber and a large diameter portion 36a of the output rod 36 are arranged. The rear surface of the reaction disk 35 can be abutted.

  As shown in FIG. 1, a return spring 37 for returning the valve body 13 to its original position is disposed in the cup-shaped main body 13a of the valve body 13 in the constant pressure chamber 9 on the front side. The return spring 37 has one end on the front side at the back of the concave portion 1a of the front shell 1 and the other end on the rear side at the bottom of the cup (hollow boss) of the main body 13a of the valve body 13 via the rod holder 38. The parts 13c) are arranged so as to be in contact with each other. That is, the rod holder 38 is pressed and fixed to the valve body 13 by the return spring 37.

  Further, as shown in FIG. 2A, the rod holder 38 has a cup portion 38a that partially covers the large-diameter portion 36a of the output rod 36, and a flange portion 38b with which the return spring 37 abuts. Are formed in the shape of a hat. An insertion hole 47 having a diameter larger than the outer diameter of the rod portion 36b, through which the rod portion 36b of the output rod 36 is inserted, is formed at the center of the bottom surface portion 38c of the cup portion 38a. The space formed by the cup portion 38a of the rod holder 38 and the output rod 36 is a negative pressure passage 15c connecting the constant pressure chamber 9 to the valve mechanism 22, and the insertion hole 47 and the rod portion of the output rod 36. An annular space formed between the pressure chamber 36b and the pressure mechanism 36b forms a negative pressure passage 15d connecting the constant pressure chamber 9 to the valve mechanism 22. Further, an annular space formed between the outer periphery of the flange portion 38b of the rod holder 38 and the inner peripheral surface of the main body portion 13a of the valve body 13 forms a negative pressure passage 15e (which connects the constant pressure chamber 9 to the valve mechanism 22). (See FIG. 1). Here, the negative pressure passage 15 is composed of each of the negative pressure passages 15a, 15b, 15c, 15d, and 15e, and the negative pressure passage 15 constitutes a communication passage in the present embodiment. The valve body 13 is constantly urged toward the rear side (return direction) by the return spring 37. The rod holder 38 also functions as a stopper for preventing the reaction disk 35 and the output rod 36 from being detached from the valve body 13.

  Further, the pneumatic booster 50 according to the embodiment of the present invention is configured so as to satisfy the following magnitude relationship of clearance. Specifically, as can be seen in FIG. 2A, the clearance in the axial direction between the cup portion 38a of the rod holder 38 and the large diameter portion 36a of the output rod 36 is a first clearance. C1 and the second movable clearance C2 (the relative movable amount between the plunger 25 and the valve body 13) between the plunger 25 and the stop key 39, and the other of the reaction force members 64. The clearance between the surface 66 and the second end surface 25b of the plunger 25 is defined as a third clearance C3. The relationship between the clearances C1 to C3 when the pneumatic booster 50 is not braking is such that the first clearance C1 ≧ the second clearance C2> the third clearance C3. The magnitude relationship between the clearances C1 to C3 is realized by appropriately adjusting the shape, size, arrangement, and the like of related members.

  The pneumatic booster 50 is connected to a vehicle body (not shown) and a master cylinder (not shown) via stud bolts 42 and 43 at both ends of the penetrating rod 41 and general-purpose stud bolts 44. At this time, as shown in FIG. 1, a master cylinder (not shown) is coupled to a concave portion 1a provided on the front surface of the front shell 1. A cylindrical body 48 of the master cylinder is hermetically inserted into the bottom of the recess 1 a and extends into the main body 13 a of the valve body 13. The rod portion 36b of the output rod 36 extends into the cylindrical body 48 and is connected to a piston (not shown) of the master cylinder.

Next, the operation of the pneumatic booster 50 according to the embodiment of the present invention will be described.
Here, first, when a negative pressure is introduced into the front and rear constant pressure chambers 9 and 10 due to the operation of the engine, or when the engine is stopped, the front and rear constant pressure chambers are used. A case in which a negative pressure remains in 9 and 10 will be described. In these cases, when the brake pedal is depressed from the non-braking state as shown in FIG. 2A, the plunger 25 moves forward together with the input rod 24, and the air valve seat 30 at the rear end of the plunger 25 is opened. However, the air valve 31 is opened apart from the inner peripheral edge of the front end of the poppet valve 27. As a result, the air flows into the hollow shaft portion 13b of the valve body 13 through the silencer and the filter, and this air is introduced into the rear-side transformer chamber 12 through the first air passage 16 and the communication pipe 18 Is also introduced into the front-side transformer chamber 11 through the second air passage 17. As a result, a pressure difference is rapidly generated between the front and rear variable pressure chambers 11 and 12 into which the atmosphere is introduced and the front and rear constant pressure chambers 9 and 10 into which the negative pressure is introduced. I do. The pressure difference causes the front and rear power pistons 7 and 8 to be propelled, and the thrust is transmitted from the tip of the hollow boss 13 c of the valve body 13 via the reaction disk 35 and the output rod 36 to the master cylinder. Output to the side.

  On the other hand, when the depression force on the brake pedal is released, the input rod 24 is retracted by the spring force of the return spring 33, and the plunger 25 is also retracted. As a result, the atmosphere valve seat 30 of the plunger 25 contacts the inner peripheral edge of the front end of the poppet valve 27 to close the atmosphere valve 31, while the poppet valve 27 is lifted by the plunger 25, and the valve is closed. The negative pressure valve 29 is opened apart from the negative pressure valve seat 28 of the body 13, and the negative pressure is reduced through the negative pressure passages 15 a and 15 b and the first and second atmospheric passages 16 and 17, Introduced at 12, the pressure differential is eliminated. Thereafter, with a time lag from the input rod 24, the valve body 13 is retracted by the return spring 37 in the constant pressure chamber 9 on the front side, and the stop key 39 in contact with the valve body 13 is moved to the step portion 40 in the rear shell 2. After returning to the original contact position, the negative pressure valve 29 is closed.

  On the other hand, the brake pedal is depressed to start the engine in a state where no negative pressure remains in the front-side and rear-side constant pressure chambers 9, 10 due to, for example, the fact that the car has not been used for several days. When the atmosphere valve 31 is opened, the front and rear transformation chambers 11 and 12 into which the atmosphere is introduced, and the front and rear constant pressure chambers 9 at a pressure substantially equal to the atmospheric pressure. No pressure difference is generated between the pressure difference and the pressure difference, and no assist is obtained due to the pressure difference. In this case, the plunger 25 advances further after the atmospheric valve 31 is opened, the first end surface 25a of the plunger 25 is pressed against the reaction disk 35, and the second end surface 25b of the plunger 25 is further pressed. Is pressed against the other surface 66 of the reaction member 64, the plunger 25 and the reaction member 64 press the reaction disk 35, and the output rod 36 advances in response. At this time, the advancement of the output rod 36 by the plunger 25 and the reaction force member 64 causes the stop key 39 engaged in the locking groove 62 of the plunger 25 to move the locking key 62 as shown in FIG. Is carried out until it comes into contact with the wall portion 62a. During this time, the plunger 25 does not push out the valve body 13 or the rod holder 38 due to the relationship of the first clearance C1 ≧ the second clearance C2> the third clearance C3. Absent. Thereafter, when the depression force on the brake pedal is released, the plunger 25 moves back together with the input rod 24 by the spring force of the return spring 33, and the atmosphere valve 31 is closed.

  As described above, the pneumatic booster 50 according to the embodiment of the present invention includes the rod holder 38 (cup portion 38a) and the large diameter portion 36a of the output rod 36, as shown in FIG. Between the plunger 25 and the stop body 39 (in other words, the relative clearance between the plunger 25 and the valve body 13). When the clearance between the other surface 66 of the reaction force member 64 and the second distal end surface 25b of the plunger 25 is the third clearance C3, the clearances are defined as the second clearance C2. The magnitude relation between C1 and C3 is determined as follows. That is, the relationship between the clearances C1 to C3 when the pneumatic booster 50 is not braking is such that the first clearance C1 ≧ the second clearance C2> the third clearance C3.

  Of these, the second clearance C2> third clearance C3, the brake pedal is depressed, the input rod 24 advances, and the plunger 25 receives the axial force inside the hollow boss 13c along the axial direction. At the time of displacement, before the plunger 25 moves beyond the relative movable amount between the plunger 25 and the valve body 13, that is, before the plunger 25 contacts the stop key 39 and pushes out the valve body 13. First, first, the first end surface 25a of the plunger 25 is pressed against the reaction disk 35 and the reaction disk 35 is pushed out, whereby the output rod 36 advances in the axial direction. Further, since the reaction force member 64 is slidably disposed in the counterbore portion 68, the plunger 25 is moved until the second distal end surface 25b contacts a part of the other surface 66 of the reaction force member 64. When displaced, the reaction member 64 separates from the seating surface of the counterbore portion 68 and is displaced in the leftward direction together with the plunger 25 in the figure. Are pressed against the reaction disk 35, and the output rod 36 can be further advanced. At this time, the front end of the hollow boss portion 13c of the valve body 13 does not push out the valve body 13 until the wall portion 62a of the locking groove 62 of the plunger 25 contacts the stop key 39. Since it is performed only by the plunger 25 and the reaction force member 64 which can protrude from the valve body 13, the spring force of the return spring 37 urging the valve body 13 is not received.

  Moreover, due to the relationship of the first clearance C1 ≧ the second clearance C2, the output rod 36 is moved forward before the output rod 36 moves forward until the wall 62a of the locking groove 62 of the plunger 25 contacts the stop key 39. The large diameter portion 36a does not come into contact with the cup portion 38a of the rod holder 38. That is, also by this, it is possible to avoid receiving the spring force of the return spring 37 via the rod holder 38 pressed and fixed to the valve body 13 by the return spring 37. With such a configuration, since the output rod 36 can be advanced by a predetermined amount before receiving the spring force of the return spring 37, the negative pressure is released from the constant pressure chambers 9 and 10, and the assist by the differential pressure is performed. Even in a state where the brake pedal cannot be obtained, it is possible to easily depress the brake pedal to a stroke amount necessary for starting the engine of the automobile.

  Here, in the present embodiment, the tandem type pneumatic booster 50 having two power pistons 7 and 8 is applied. It is also possible to apply.

  1: front shell, 2: rear shell, 4: center shell, 9, 10: constant pressure chamber, 11, 12: variable pressure chamber, 13: valve body, 13c: hollow boss, 24: input rod, 25: plunger, 25a: 1st tip surface, 25b: 2nd tip surface, 35: reaction disk, 36: output rod, 36a: large diameter portion, 36b: rod portion, 37: return spring, 38: rod holder, 39: stop key, 50: pneumatic booster, 60: small diameter portion, 62: locking groove, 64: reaction member, 65: one surface, 66: the other surface, 68: counterbore, C1: first clearance, C2: second clearance, C3: third clearance

Claims (1)

A valve body having a hollow boss on the inside and moving inside a shell defined by a constant pressure chamber and a variable pressure chamber,
Thrust is transmitted from the tip of the hollow boss portion via a reaction disk, and a large-diameter portion abutting on the reaction disk, and an output rod having a rod portion abutting on a piston of the master cylinder,
A rod holder that is pressed and fixed to the valve body by a return spring that biases the valve body and supports the output rod so as to cover at least a part of the large-diameter portion of the output rod;
A small diameter having a diameter smaller than the inner diameter of the hollow boss portion is disposed slidably in the hollow interior of the hollow boss portion along the axial direction so as to move with the input rod in response to the movement of the input rod. By providing the portion on the distal end side, a first distal end surface that is opposed to the reaction disk at the distal end of the small diameter portion and a second radially outwardly extending from the base end of the small diameter portion. A plunger having a distal end surface, and further provided with a locking groove of a predetermined width on an outer peripheral portion;
The hollow boss portion is slidably disposed in a counterbore portion provided at the distal end side opening portion along the axial direction, and has one surface facing the reaction disk and a part of the other surface facing the plunger. A reaction member opposing the second end surface of
One end is inserted into the hollow boss so as to protrude into the hollow inside of the hollow boss, and the one end is engaged with the plunger in order to limit a relative movement amount between the valve body and the plunger. A stop key engaged in the groove,
With
A first clearance is defined as a clearance in a direction along an axial direction between the rod holder and the large-diameter portion of the output rod,
A clearance that allows relative movement between the plunger and the stop key is a second clearance,
When the clearance between the other surface of the reaction force member and the second end surface of the plunger is a third clearance,
The relationship of each clearance when not braking,
The first clearance ≧ the second clearance> the third clearance, wherein a pneumatic booster is provided.

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