JPH09207761A - Booster - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum booster device favourable as a mechanical brake device of an electric car. SOLUTION: A sleeve 27 consisting of a magnetic body is fit on an outer peripheral part of a valve plunger 26 free to slide by holding airtightness. A vacuum valve 44 is constituted of a valve body 31 and a vacuum valve seat 31 provided on a sleeve 27, and a breather valve 38 is constituted of the valve body 31 and a breather valve seat 25. Additionally, a solenoid 47 is arranged on the rear side of the sleeve 27. When the solenoid 47 is magnetized, the sleeve 27 is held at a retreating end position where its rear side end part comes in contact with a step part 47a of the solenoid 47. Consequently, even when a brake pedal is stepped on from this state and the valve plunger 26 is made to advance (to the left), the sleeve 27 remains held at the retreating end position, and accordingly, a valve system 24 does not work and consequently, a vacuum booster device does not work.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a booster used for a brake of an automobile or the like, and more particularly to a booster suitable for use in a mechanical braking device of an electric vehicle.

[0002]

2. Description of the Related Art Conventionally, a booster having the following configuration is known. That is, a roughly cylindrical valve body slidably provided in the shell, a power piston provided on the outer peripheral portion of the valve body, a constant pressure chamber and a variable pressure chamber defined in front of and behind the power piston, and the valve described above. A booster provided in a body and provided with a valve mechanism for controlling opening / closing of a flow passage in the valve body is known. In such a conventional booster, an output can be obtained at a predetermined servo ratio according to the pedal effort of the brake pedal. By the way, in recent years, an electric vehicle has been put into practical use, and in this electric vehicle, a braking system using both a mechanical braking device using the booster having the above-described configuration and a regenerative braking device is adopted. In such a braking system for an electric vehicle, until the mechanical braking device operates,
The regenerative braking force is increased / decreased according to the increase / decrease in the pedal effort of the brake pedal, and when the mechanical braking device starts braking and outputs the braking force, the regenerative braking force is kept constant. . Therefore, the increase / decrease of the regenerative braking force only by the regenerative braking device and the increase / decrease of the total braking force of the regenerative braking force and the mechanical braking force can be smoothly continued.

[0003]

However, in the above-described braking system for an electric vehicle, the regenerative braking force is increased in response to an increase in the pedal effort of the brake pedal only until the mechanical braking device starts braking. Therefore, the regenerative braking force when the mechanical braking device starts braking cannot be increased, and the regenerative braking force by the regenerative braking device cannot be effectively used. That is, in order to increase the regenerative braking force when the mechanical braking device starts braking and to effectively use the braking force, it is necessary to set the mechanical braking device to start braking only by giving a large pedaling force. Well, for that purpose, the set load of the return spring of the booster and the return spring of the master cylinder that constitute the mechanical braking device may be increased. However, if such a setting is made, and if the regenerative braking device does not operate, the pedaling force until the start of operation of the mechanical braking device becomes large, so the braking effect is felt to be poor, It is also dangerous. Furthermore, the maximum value of the regenerative braking force is not always constant, but varies depending on the rotation speed of the drive motor that drives the electric vehicle, so if the set load is made too large, even if the maximum regenerative braking force is obtained, the mechanical type There may be a case where the braking device does not start operating, which causes a drawback that the brake feeling is deteriorated.

[0004]

[Means for Solving the Problems] In view of such circumstances,
The present invention provides a generally cylindrical valve body slidably provided in a shell, a power piston provided on an outer peripheral portion of the valve body, a constant pressure chamber and a variable pressure chamber defined in front of and behind the power piston, In a booster equipped with a valve mechanism provided in the valve body for controlling opening and closing of a flow path in the valve body, the valve mechanism is formed on the inner peripheral portion of the valve body toward the front side. An atmosphere valve seat, a valve plunger slidably fitted in the valve body and interlocking with the input shaft, and a valve plunger that is slidably fitted in the valve plunger while keeping airtightness, and is made of a magnetic material. A sleeve, a vacuum valve seat formed on the inside of the atmosphere valve seat toward the front side of the sleeve, a valve element seated on both valve seats from the front side, and the valve element To urge towards A spring and a second spring that positions the sleeve at the forward end position with respect to the valve plunger, and a solenoid is disposed on the rear side of the sleeve in the valve body, and the solenoid is excited to excite the solenoid. The operation of the valve mechanism is prevented by retracting the sleeve with respect to the valve plunger.

[0005]

With this structure, it is possible to provide a booster suitable for use in the mechanical braking device of the electric vehicle described above. That is, when the above-described booster is adopted as the mechanical braking device of the above-described braking system for the electric vehicle, when the solenoid is excited, the brake pedal is depressed and the valve plunger interlocked with the input shaft is advanced. However, since the sleeve is retracted by the magnetic force of the solenoid, the valve mechanism does not operate. That is, it is possible to prevent the booster from operating. On the other hand, the regenerative braking device starts braking with the depression of the brake pedal described above. Then, the vehicle is decelerated by the regenerative braking device, and the vehicle speed is reduced. When the vehicle speed becomes equal to or lower than a predetermined value, the regenerative braking force decreases, so if the solenoid is deenergized when the decrease in the regenerative braking force is detected, the second
The spring moves the sleeve to the advanced position relative to the valve plunger, actuating the valve mechanism and actuating the booster. Thus, the regenerative braking force of the regenerative braking device can be effectively used while the mechanical braking device (boost device) is not operated. When the solenoid is not energized, the sleeve is positioned at the forward end position with respect to the valve plunger by the second spring, and when the brake pedal is depressed from that state, the valve plunger and the sleeve that interlock with the input shaft are released. Be advanced. Therefore, the vacuum valve seat provided on the sleeve sits on the valve body, while the valve body separates from the atmosphere valve seat, so that the fluid circuit in the valve body is switched and the difference between the constant pressure chamber and the variable pressure chamber is reached. Pressure is generated and the booster operates. As a result, if the regenerative braking device in the braking system of the electric vehicle fails, the booster as the mechanical braking device operates.
Accordingly, when the regenerative braking device fails, it is possible to reliably prevent the braking effect from being delayed, and prevent the brake feeling of the driver from being hindered. Therefore, it is possible to provide a booster suitable for use in the mechanical braking device of an electric vehicle.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a braking system for an electric vehicle will be described below. In FIG. 1, the braking system for an electric vehicle increases or decreases the regenerative braking force according to the increase or decrease in the pedal effort of the brake pedal 1. A braking device 2 and a mechanical braking device 3 that increases / decreases the mechanical braking force according to an increase / decrease in the pedal effort of the brake pedal 1 are provided. The regenerative braking device 2 has a conventionally known configuration, and uses a drive motor 4 that drives the front wheels to perform a regenerative braking action during braking. The regenerative braking device 2 includes a sensor 5 that detects the pedal effort of the brake pedal 1, and the pedal effort of the brake pedal 1 detected by the sensor 5 is input to the control device 6. Then, based on the input from the sensor 5, the control device 6 increases the regenerative braking force of the regenerative braking device 2 to the maximum regenerative braking force according to the increase in the pedaling force of the brake pedal 1. It is well known that the maximum regenerative braking force obtained by the regenerative braking device 2 is not always constant but varies depending on the rotation speed of the drive motor 4. Further, as the sensor 5, a sensor that detects a stroke amount instead of the depression force of the brake pedal 1 may be adopted. Next, the mechanical braking device 3 is provided with a tandem master cylinder 7 having a conventionally well-known configuration, and a vacuum booster 8 interlocking with the tandem master cylinder 7. When the brake pedal 1 is stepped on and the regenerative braking operation is performed by the regenerative braking device 2 as described above, the input shaft 11 of the vacuum booster 8 connected to the brake pedal 1 is also advanced, so that the brake is applied. The pedal effort of the pedal 1 is boosted by the vacuum booster 8 and then transmitted to the tandem master cylinder 7. Then, the hydraulic pressure generated in the tandem master cylinder 7 is supplied to the front wheel cylinder 13 and the rear wheel cylinder 14 via the brake fluid passage 12, whereby a braking action can be obtained. As shown in FIG. 2, the vacuum booster 8 includes a substantially tubular valve body 1 in a shell 15 as a hermetic container.
6 is provided slidably. A power piston 17 is connected to the outer peripheral portion of the valve body 16, and a diaphragm 18 is stretched on the back surface of the power piston 17. The diaphragm 18 divides the shell 15 into a constant pressure chamber A and a variable pressure chamber B. doing. As shown in FIG.
The inside of the constant pressure chamber A is connected to a negative pressure pump 22 via a negative pressure introducing pipe 21. Motor 2 as a driving source of the negative pressure pump 22
The operation of No. 3 is controlled by the control device 6 to obtain a negative pressure of a predetermined value. Therefore, a negative pressure having a predetermined value is introduced into the constant pressure chamber A. The valve body 16 of the vacuum booster 8 is provided with a valve mechanism 24 that switches a fluid circuit between the constant pressure chamber A, the variable pressure chamber B, and the atmosphere. The valve mechanism 24 includes an annular atmospheric valve seat 25 provided on the valve body 16, a valve plunger 26 slidably fitted on the valve body 16, an annular vacuum valve seat 28 provided on a sleeve 27, and A substantially cylindrical valve body 31 seated on both valve seats 25 and 28, and this valve body 31
A first spring 32 that urges and seats against 5, 28;
Further, a second spring 33 for biasing the sleeve 27 having the vacuum valve seat 28 toward the front side is provided.
Further, the valve mechanism 24 is provided with a third spring 34, and the third spring 34 urges the valve plunger 26 and the input shaft 11 connected thereto to the rear side so that the valve plunger 26 and the input shaft 11 are positioned at the inoperative position in the drawing. ing. Therefore, in the present embodiment, the valve mechanism 24 is configured as follows so that the operation of the vacuum booster 8 can be prevented when the brake pedal 1 is depressed. That is, an annular protrusion 16a extending toward the front side is formed on the inner peripheral portion of the valve body 16, and the atmospheric valve seat 25 is constituted by the tip end of the annular protrusion 16a. Further, the atmosphere passage 36 is constituted by the axial hole 16b on the outer side of the atmosphere valve seat 25 and the internal space of the valve body 16 continuous to the rear side thereof. The atmosphere is always introduced into the atmosphere passage 36. Next, the valve body 31 made of an elastic body is
It is arranged toward the rear side so as to face the atmosphere valve seat 25 and the vacuum valve seat 28. The front end of the valve body 31 is made thick, and the end thereof is formed into a cylindrical plug 37.
The front end of the valve body 31 and the outer peripheral portion of the plug 37 in this state are fitted into the annular groove provided on the rear outer peripheral portion of the valve body 16 in the inner peripheral portion of the valve body 16 from the front side. The first spring 32 is elastically mounted over the back surface of the seat portion of the valve body 31 and the stepped portion of the plug 37. Due to the elastic force of the first spring 32, the seat portion of the valve body 31 has both the valve seats. It is designed to sit on 25 and 28. In the present embodiment, the atmosphere valve 38 that opens and closes the atmosphere passage 36 by the atmosphere valve seat 25 and the seat portion of the valve body 31 that comes in contact with and separates from the atmosphere valve seat 25.
Is composed. The plug 37 of this embodiment substantially forms a part of the valve body 16. Next, the valve plunger 26 has an annular groove 26 at its axial center.
In addition to forming a, an annular protrusion 26b is formed on the outer peripheral portion on the front side of the annular groove 26a. The sleeve 27 is slidably fitted to the outer peripheral portion of the annular projection 26b adjacent to the rear side, and at the same time, the rear outer peripheral portion of the sleeve 27 is slidably fitted to the reduced diameter portion 16c of the valve body 16. It is fitted. Annular groove 26a
Another annular groove is formed slightly on the rear side, and the seal member 41 is mounted in this annular groove. This seal member 4
1, the inner peripheral surface of the sleeve 27 and the valve plunger 26
The airtightness is maintained between the outer peripheral portion and the outer peripheral portion. A seal member 42 is also attached to the inner peripheral portion of the reduced diameter portion 16c of the valve body 16 with which the sleeve 27 is in sliding contact, so that the airtightness between the inner peripheral portion of the valve body 16 and the outer peripheral surface of the sleeve 27 is achieved. Holding And the valve body 1
The key member 43 is engaged with the annular groove 26a of the valve plunger 26 through the radial hole 16d formed in the sleeve 6 and the notch formed in the axial center portion of the sleeve 27. As a result, the valve plunger 26 moves into the valve body 16
To prevent it from falling out. Next, the sleeve 27 of the present embodiment is made of a magnetic material, and is provided with a flange portion 27a extending outward in the radial direction at the end portion on the front side, and a position facing the valve body 31 on the outer peripheral portion of the flange portion 27a. Is an annular projection that bulges to the front side, and this serves as the vacuum valve seat 28. The second spring 33 is elastically mounted over the flange portion 27a and the stepped end surface of the valve body 16 facing the flange portion 27a, so that the entire sleeve 27 is attached to the front side relative to the valve plunger 26. I am energetic. In the non-actuated state of the vacuum booster 8 shown in FIG. 2, the flange portion 27a of the sleeve 27 is located at the forward end position where it abuts on the annular protrusion 26b of the valve plunger 26. The vacuum valve seat 28,
The vacuum valve 4 is formed by the seat portion of the valve body 31 coming into contact with or separated from
4. A vacuum passage 45 is formed by the inner space of the vacuum valve 44 and the valve body 31 and the axial hole 37a of the plug 37 continuous from the space. The vacuum passage 45 is always in communication with the constant pressure chamber A, and since the negative pressure is always introduced into the constant pressure chamber A through the negative pressure introducing pipe 21 described above, the vacuum passage 45 is always negative. Pressure is acting. The space between the atmosphere valve 38 and the vacuum valve 44 communicates with the variable pressure chamber B via a variable pressure passage 46 formed by the radial hole 16d of the valve body 16. The valve mechanism 24 of this embodiment is configured as described above. Further, in this embodiment, the annular solenoid 47 is fitted into the inner peripheral portion of the valve body 16 from the rear side, and is brought into contact with the step end surface on the rear side of the reduced diameter portion 16c. An annular retainer 48 having an engaging claw on the outer peripheral portion is press-fitted from the rear side of the solenoid 47 into the inner peripheral portion of the valve body 16 and is brought into contact with the solenoid 47. As a result, the solenoid 47 is fixed to the inner peripheral portion of the valve body 16. Further, on the front side of the inner peripheral portion of the solenoid 47 fixed in this way, the reduced diameter portion 1
The outer peripheral portion on the rear side of the sleeve 27 that penetrates 6c is inserted. The elastic force of the second spring 33 that biases the sleeve 27 toward the front side is weaker than the biasing force that the sleeve 27 is attracted toward the rear side by the magnetic force when the solenoid 47 is excited. . Therefore, when the solenoid 47 is excited based on a command from the control device 6, the magnetic force of the solenoid 47 causes the sleeve 27 to move to the valve plunger 26 and the valve body 16.
The rear end of the sleeve 27 is urged relatively to the rear side with respect to the rear end, and is maintained at the retracted end position where the rear end of the sleeve 27 contacts the step 47a on the inner circumference of the solenoid 47. In this state, even if the brake pedal 1 is stepped on and the input shaft 11 and the valve plunger 26 are advanced, the sleeve 27 is maintained at the retracted end, so the valve mechanism 24 does not operate, and therefore the vacuum is not applied. The booster 8 is deactivated. Further, the third spring 34 is elastically mounted over the retainer 48 and the flange portion formed at the rear side end portion of the valve plunger 26, thereby positioning the valve plunger 26 and the input shaft 11 in the inoperative position shown in the drawing. It is like this. Next, the plug 3
A front side outer peripheral portion of the valve plunger 26 is slidably fitted to the inner peripheral portion of 7, and a disk-shaped reaction disk 51 is attached to the end surface of the annular projection 37b formed on the plug 37. Abutting. The reaction disc 51 is provided with a recess 5 provided at the base of the push rod 52.
2a, and the tip of the recess 52a is slidably fitted on the annular projection 37b of the plug 37. The front end of the push rod 52 (not shown) is interlocked with the piston rod of the tandem master cylinder 8. In addition, the push rod 52
An annular retainer 53 fitted to the front side of the plug is fitted to the inner peripheral portion of the valve body 16 from the front side, and is brought into contact with the front end surface of the plug 37 and the stepped end surface of the valve body 16. This prevents the push rod 52 and the plug 37 from falling off the valve body 16 toward the front side. Further, the return spring 54 is elastically mounted over the retainer 53 and the wall surface of the shell 1 on the front side, so that the valve body 16 and the like are biased to the rear side and are located in the inoperative position in the drawing. . (Description of Operation) In the above configuration, when the vacuum booster 8 shown in FIG. 2 is in a non-operating state and the solenoid 47 is excited based on a command from the controller 6, the valve body 16 is It abuts against the key member 43 that abuts against the end face of the step portion of the shell 1 and stops at the retracted end. Further, the valve plunger 26 and the input shaft 11 are
The end surface of the annular groove 26a on the front side stops at the retracted end where it abuts the key member 43. In this state, the valve body 31
When the seat portion of the seat is seated on the atmosphere valve seat 25, the atmosphere valve 38
Is closed. Further, the sleeve 27 is retracted to the rear side by the magnetic force of the excited solenoid 47, and the rear side end thereof is stopped at the retracted end in contact with the stepped portion 47a of the solenoid 47. Further, the vacuum valve seat 28 is separated from the seat portion of the valve body 31, and the vacuum valve 44 is opened. Therefore, the constant pressure chamber A and the variable pressure chamber B communicate with each other through the vacuum passage 45 and the variable pressure passage 46, and a negative pressure is introduced into both chambers A and B. Next, when the brake pedal 1 is depressed from the inoperative state, the input shaft 11 is interlocked with it.
And valve plunger 26 is advanced, but solenoid 4
Since the sleeve 27 is held at the retracted position by the magnetic force of 7, the vacuum valve seat 28 is not moved and the valve mechanism 24 is not operated. That is, the vacuum booster 8 is not activated. On the other hand, the pedaling force of the brake pedal 1 is detected by the sensor 5 and input to the control device 6, and the control device 6 regeneratively brakes based on the input from the sensor 5 in accordance with the increase of the pedaling force of the brake pedal 1. By increasing the regenerative braking force of the device 2 to the maximum regenerative braking force, the vehicle speed is reduced and the vehicle speed is reduced. Then, when the vehicle speed becomes equal to or lower than the predetermined value, the regenerative braking force becomes lower than the maximum regenerative braking force. Therefore, when the decrease in the regenerative braking force is detected, the control device 6 causes the solenoid 47 to operate.
To extinguish Therefore, the sleeve 27 is moved by the urging force of the second spring 33 so that the valve plunger 26 and the valve body 1 move.
6 is moved to the front side with respect to the flange portion 2
7a is located at the forward end position where it abuts the annular projection 26b of the valve plunger 26. In the process of moving the sleeve 26 toward the front side, after the vacuum valve seat 44 is seated on the seat portion of the valve body 31 and the vacuum valve 44 is closed, the seat portion of the valve body 31 is separated from the atmosphere valve seat 25. Then, the atmospheric valve 38 is opened. Therefore, the communication state between the constant pressure chamber A and the variable pressure chamber B is blocked, while the atmosphere in the atmosphere passage 36 is introduced into the variable pressure chamber B via the opened atmospheric valve 38, so that the constant pressure chamber A and the variable pressure chamber B are transformed. Since a differential pressure is generated between the valve body 16 and the chamber B and the push rod 52 is moved forward, it is possible to obtain an output of a predetermined servo ratio according to the pedaling force of the brake pedal 1. In other words, the solenoid 47 that was excited
Since the vacuum booster 8 is actuated by deactivating, the braking force by the mechanical braking device 3 and the regenerative braking device 2 can be obtained. There is. Then, as described above, after increasing the regenerative braking force of the regenerative braking device 2 to the maximum regenerative braking force according to the increase in the pedaling force of the brake pedal 1, the mechanical braking device 3 (vacuum booster 8) is activated. By doing so, the regenerative braking force of the regenerative braking device 2 can be effectively used. In addition,
When the depression of the brake pedal 1 is released from the above-described operating state, the return spring 34 returns the valve body 16 to the inoperative position in the drawing, and the valve body 3
1, the valve plunger 26 and the sleeve 27 return to the inoperative position shown. Next, as shown in FIG. 2, when the vacuum booster 8 is in the non-operating state and the solenoid 47 is not excited, the sleeve 27 has its flange portion 27a due to the elastic force of the second spring 33. Is in the forward end position where it comes into contact with the annular projection 26b of the valve plunger 26. When the brake pedal 1 is depressed from this state, the input shaft 11 is advanced in conjunction with this. Then, the input shaft 1
The valve plunger 26 and the sleeve 27 integrated with the valve plunger 26 are also moved forward in association with 1. As a result, the vacuum valve seat 4
After 4 is seated on the seat portion of the valve body 31 and the vacuum valve 44 is closed, the seat portion of the valve body 31 is separated from the atmosphere valve seat 25 and the atmosphere valve 38 is opened. Therefore, the communication state between the constant pressure chamber A and the variable pressure chamber B is blocked, while the atmosphere in the atmosphere passage 36 is introduced into the variable pressure chamber B via the opened atmospheric valve 38, so that the constant pressure chamber A and the variable pressure chamber B are transformed. Since a differential pressure is generated between the valve body 16 and the chamber B and the push rod 52 is moved forward, it is possible to obtain an output of a predetermined servo ratio according to the pedaling force of the brake pedal 1. In other words, when the brake pedal 1 is stepped on while the solenoid 47 is not excited, the vacuum booster 8 is operated to obtain an output of a predetermined servo ratio according to the stepping force of the brake pedal 1. it can. Therefore, in the case where the regenerative braking device 2 fails, the mechanical braking device 3 (vacuum booster 8) is immediately activated when the brake pedal 1 is depressed by not exciting the solenoid 47.
Therefore, if the regenerative braking device 2 fails, the braking effectiveness will not be delayed. Therefore, it is possible to prevent the driver from feeling uneasy due to the delayed braking. In this way, the vacuum booster 8 of this embodiment is
Is a booster suitable for use in a mechanical braking device of an electric vehicle.

[0007]

As described above, according to the present invention, it is possible to provide an effect that a suitable booster can be provided for use in a mechanical braking device of an electric vehicle.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of the constituent member shown in FIG.

[Explanation of symbols]

 8 ... Vacuum booster 16 ... Valve body 17 ... Power piston 24 ... Valve mechanism 25 ... Atmospheric valve seat 26 ... Valve plunger 27 ... Sleeve 28 ... Vacuum valve seat 31 ... Valve body 32 ... First spring 33 ... Second spring 47 ... Solenoid A ... Constant pressure chamber B ... Transformer chamber

Claims (2)

[Claims] 1. A generally cylindrical valve body slidably provided in a shell, a power piston provided on an outer peripheral portion of the valve body, and a constant pressure chamber and a variable pressure chamber defined in front of and behind the power piston. A booster having a valve mechanism provided in the valve body for controlling opening and closing of a flow path in the valve body, wherein the valve mechanism is formed on an inner peripheral portion of the valve body toward a front side. The atmosphere valve seat, and a valve plunger slidably fitted in the valve body and interlocking with the input shaft,
A sleeve made of a magnetic material, which is slidably fitted to the valve plunger while keeping airtightness, and a vacuum valve seat formed on the inside of the atmosphere valve seat toward the front side of the sleeve. A valve body which is seated on both valve seats from the front side, a first spring which biases the valve body toward the valve seats, and a second which positions the sleeve at the forward end position with respect to the valve plunger. A solenoid is provided on the rear side of the sleeve in the valve body, and the solenoid is excited to retract the sleeve with respect to the valve plunger to prevent the operation of the valve mechanism. A booster characterized by being configured to. 2. The first spring is elastically mounted on the back surface of the seat portion of the valve body and the valve body, and the second spring is elastically mounted on the sleeve and the valve body.
Further, the solenoid is fixed by an annular retainer fitted to the inner peripheral portion of the valve body in a state of being brought into contact with the step portion of the valve body from the rear side, and further, the solenoid of the retainer and the rear portion of the valve plunger are fixed. A third spring for locating the valve plunger in the non-actuated position is elastically mounted over the outer peripheral portion on the side, and an annular projection is formed at a predetermined axial position of the valve plunger. The sleeve is fitted to the rear side with respect to the rear side, and the sleeve biased by the second spring comes into contact with the annular projection of the valve plunger from the rear side so that the sleeve is positioned at the forward end position. The booster according to claim 1, wherein the booster is configured as follows.