CN115419662A

CN115419662A - Brake system for automatic driving automobile

Info

Publication number: CN115419662A
Application number: CN202211055036.0A
Authority: CN
Inventors: 陈阔; 崔臻; 王远东; 沈玉平; 蒋剑; 耿强; 孔维强; 陶广华; 朱福雄; 杜克虎
Original assignee: Hangzhou Hemei Automobile Technology Co Ltd
Current assignee: Hangzhou Hemei Automobile Technology Co Ltd
Priority date: 2022-08-31
Filing date: 2022-08-31
Publication date: 2022-12-02
Anticipated expiration: 2042-08-31
Also published as: GB202300763D0; CN115419662B

Abstract

The invention relates to the technical field of automobile braking, and discloses a braking system for an automatic driving automobile, which comprises a braking caliper, wherein fixed plates are symmetrically arranged on the inner side of the braking caliper, a brake pad is arranged on one side of each fixed plate, a fixed sleeve is arranged on the other side of each fixed plate, a groove is arranged on one side of each fixed plate close to the corresponding fixed sleeve, a locking mechanism is arranged in each groove, and a fixed seat is arranged on the outer side of the braking caliper. According to the invention, the brake caliper with the first oil cylinder, the second oil cylinder and the fixed seat is arranged, the brake pad can be pushed to abut against the brake disc through the first oil cylinder to perform braking, and the fixed plate and the brake pad can be pulled in the opposite direction through the second oil cylinder and the second piston, so that the gap between the brake pad and the brake disc of the automobile is enlarged, and the clamped hard object automatically falls off, therefore, the clamped hard object can be treated without manual cleaning in the driving process, and the brake caliper is convenient and safe.

Description

Brake system for automatic driving automobile

Technical Field

The invention relates to the technical field of automobile braking, in particular to a braking system for an automatic driving automobile.

Background

An automatic driving automobile is also called an unmanned automobile or a computer driving automobile, and is an intelligent automobile which can realize unmanned driving through a computer system. The automatic driving automobile depends on the cooperation of artificial intelligence, visual calculation, radar, monitoring device and global positioning system, so that the computer can operate the motor vehicle automatically and safely without any active operation of human.

In a conventional automobile or an autonomous automobile, the brake is mainly performed by a drum brake or a disc brake, and compared with the drum brake, although the disc brake has a general braking effect, the disc brake has better reactivity and stability, good heat dissipation and convenient maintenance, so the disc brake is widely applied. Although the disc brake has many advantages, since the disc brake is not totally enclosed, during driving, hard objects such as stones may enter the disc brake and get stuck between the brake pad and the brake disc, when the hard objects are stuck between the brake pad and the brake disc, on one hand, the braking effect is greatly reduced, on the other hand, the hard objects may also increase the abrasion of the brake disc and the brake pad, and in severe cases, the brake pad or the brake disc may be directly scrapped.

In the prior art, when finding that the card has the hard thing between brake block and the brake disc, generally park earlier, then inspect four wheels of vehicle, after confirming the fault point, artifical manual clear up the hard thing, efficiency is lower, if in highway or bridge etc. difficult highway sections of parkking break down, the maintenance of parking is very dangerous moreover, but if do not handle, the existence of hard thing again causes the influence to the brake effect, has the potential safety hazard equally.

Disclosure of Invention

The invention provides a braking system for an automatic driving automobile, which has the beneficial effect of automatically processing the clamping hard object between a brake pad and a brake disc, and solves the problem that only manual processing can be carried out when the clamping of the hard object between the brake pad and the brake disc is found in the background technology.

The invention provides the following technical scheme: a braking system for an automatic driving automobile comprises a braking caliper, wherein fixed plates are symmetrically arranged on the inner side of the braking caliper, a brake pad is arranged on one side of each fixed plate, a fixed sleeve is arranged on the other side of each fixed plate, a groove is formed in one side, close to the fixed sleeve, of each fixed plate, a locking mechanism is arranged in each groove, a fixed seat is arranged on the outer side of the braking caliper, a first oil cylinder and a second oil cylinder are arranged on each fixed seat, a fixed cavity is formed in each fixed seat, an oil path switching mechanism is arranged in each fixed cavity, and a brake fluid recovery port is formed in the outer side of each fixed seat;

the brake system comprises a brake caliper, a first oil cylinder, a second oil cylinder, a fixed sleeve, a brake fluid inlet and a brake fluid outlet, wherein the first oil cylinder and the second oil cylinder are fixedly connected with the brake caliper, a first piston is arranged in the first oil cylinder, one end of the first piston is inserted into the fixed sleeve and is elastically connected with the fixed sleeve through a connecting spring, one side of the first oil cylinder is provided with the brake fluid inlet and outlet, a second piston is arranged in the second oil cylinder, and one end of the second piston is elastically connected with the second oil cylinder through a tension spring.

As an alternative to the brake system for an autonomous vehicle according to the invention, wherein: one end, close to the fixing seat, of the second oil cylinder is provided with a fixing groove, a supporting spring is arranged in the fixing groove, and the fixing groove is communicated with the fixing cavity.

As an alternative to the brake system for an autonomous vehicle according to the invention, wherein: and a through hole is formed in one side of the fixed cavity and communicated with the first oil cylinder.

As an alternative to the brake system according to the invention for autonomous vehicles, the following features are provided: the oil circuit switching mechanism comprises a limiting plate and a supporting block, the supporting block is located at one end, close to the first oil cylinder, of the fixed cavity, the supporting block is fixedly connected with the fixed seat, the limiting plate is rotatably connected with the supporting block through a rotating shaft, one end of the limiting plate is fixedly connected with the supporting spring, and the other end of the limiting plate is provided with a plug.

As an alternative to the brake system for an autonomous vehicle according to the invention, wherein: the one end of fixing base is equipped with the spread groove, the one end of spread groove is equipped with the opening, just the other end of spread groove with the mouth intercommunication is retrieved to the brake fluid, spread groove department is equipped with the case, just the one end of case pass through fixed spring with fixing base elastic connection, the other end of case pass the spread groove and with the limiting plate is inconsistent, just be equipped with the valve opening on the case.

As an alternative to the brake system for an autonomous vehicle according to the invention, wherein: the locking mechanism comprises a clamping block, the clamping block is in sliding connection with the groove, the clamping block is elastically connected with the groove through a limiting spring, a clamping protrusion is arranged at one end of the clamping block, and a triangular block is arranged at the other end of the clamping block.

As an alternative to the brake system for an autonomous vehicle according to the invention, wherein: and a clamping groove matched with the clamping protrusion is formed in the end part of the second piston.

As an alternative to the brake system for an autonomous vehicle according to the invention, wherein: the brake caliper is characterized in that a pipe connector is arranged at the top of the brake caliper, brake fluid recovery pipes are arranged at two ends of the pipe connector, and one end of each brake fluid recovery pipe is communicated with the corresponding brake fluid recovery port.

As an alternative to the brake system for an autonomous vehicle according to the invention, wherein: and a cavity is arranged in the middle of the first piston, and a third piston is arranged in the cavity.

The invention has the following beneficial effects:

1. this a braking system for autopilot car, have first hydro-cylinder through the setting, the braking pincers of second hydro-cylinder and fixing base, can promote brake block and brake disc conflict through first hydro-cylinder, brake, when the card has hard thing between brake block and the brake disc, can stimulate fixed plate and brake block in the opposite direction again through second hydro-cylinder and second piston, thereby make the clearance grow between brake block and the car brake disc, make the hard thing of blocking drop automatically, at the in-process of traveling like this, need not manual clearance and can handle the hard thing of blocking, it is convenient and safe.

2. This a braking system for autopilot car seals the through-hole through the limiting plate that sets up to have the end cap, because first hydro-cylinder is great at during operation internal pressure, consequently sets up the supporting shoe in the one end that the fixing base is close to the through-hole, and at this moment, the limiting plate just is equivalent to a lever, and under supporting spring's effect, the limiting plate can just be stopped up the through-hole with less power, compact structure.

3. This a braking system for automatic pilot's car, come to use with the cooperation of way switching mechanism through the spread groove that sets up the case in the fixing base, when brake fluid backs down the end cap and gets into fixed chamber through the through-hole, the limiting plate can take place to deflect, after having lost blockking of limiting plate, the case can be to the motion of second piston direction, valve opening and spread groove on the case this moment stagger, the unable brake fluid that gets into brake fluid recovery mouth through the spread groove of fixed intracavity, when the limiting plate returns the normal position, valve opening and spread groove on the case are in the connected state, brake fluid can get into brake fluid recovery mouth through the spread groove this moment, then discharge through brake fluid recovery mouth, the existence of spread groove and case, make the recovery of brake fluid become simpler, and convenient.

Drawings

FIG. 1 is a schematic structural diagram of the present invention.

Fig. 2 is a front view of the present invention.

Fig. 3 is a schematic diagram of a fixing plate structure according to the present invention.

Fig. 4 is a schematic diagram of a fixture block structure according to the present invention.

Fig. 5 is a sectional view of the fixing base, the first oil cylinder and the second oil cylinder of the present invention.

In the figure: 1. a brake caliper; 2. a fixing plate; 3. a brake pad; 4. fixing a sleeve; 5. a groove; 6. a fixed seat; 7. a first oil cylinder; 8. a second cylinder; 801. a card slot; 9. a fixed cavity; 10. a first piston; 11. a brake fluid inlet and outlet; 12. a second piston; 13. a tension spring; 14. a brake fluid recovery port; 15. fixing grooves; 16. a support spring; 17. a through hole; 18. a limiting plate; 19. a support block; 20. a plug; 21. connecting grooves; 22. a valve core; 23. fixing the spring; 24. a valve bore; 25. a clamping block; 2501. clamping a convex head; 2502. a triangular block; 26. a limiting spring; 27. a connecting spring; 28. a pipe interface; 29. a brake fluid recovery pipe; 30. a chamber; 31. a third piston.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Referring to fig. 1-3, a brake system for an automatic driving automobile comprises a brake caliper 1, wherein a fixed plate 2 is symmetrically arranged on the inner side of the brake caliper 1, a brake pad 3 is arranged on one side of the fixed plate 2, a fixed sleeve 4 is arranged on the other side of the fixed plate 2, a groove 5 is arranged on one side of the fixed plate 2 close to the fixed sleeve 4, a locking mechanism is arranged in the groove 5, a fixed seat 6 is arranged on the outer side of the brake caliper 1, a first oil cylinder 7 and a second oil cylinder 8 are arranged on the fixed seat 6, a fixed cavity 9 is arranged in the fixed seat 6, an oil path switching mechanism is arranged in the fixed cavity 9, and a brake fluid recovery port 14 is arranged on the outer side of the fixed seat 6;

first hydro-cylinder 7 and second hydro-cylinder 8 all with braking pincers 1 fixed connection, be equipped with first piston 10 in the first hydro-cylinder 7, and the one end of first piston 10 pegs graft in fixed cover 4 and through connecting spring 27 and fixed cover 4 elastic connection, one side of first hydro-cylinder 7 is equipped with brake fluid access & exit 11, is equipped with second piston 12 in the second hydro-cylinder 8, and the one end of second piston 12 passes through extension spring 13 and second hydro-cylinder 8 elastic connection.

In this technical scheme, braking pincers 1 are installed in one side of car brake disc, can promote first piston 10 and fixed plate 2 through first hydro-cylinder 7 and move, fixed plate 2 can promote brake block 3 and make it inconsistent with the car brake disc to produce friction torque in order to reach the purpose of braking, can only manual cleaning's problem in order to solve some hard things of card between brake block 3 and the car brake disc, this technical scheme has improved on original braking pincers 1, fixing base 6 and second hydro-cylinder 8 have been increased.

Under normal conditions, the second oil cylinder 8 does not work, if a hard object is clamped between the brake pad 3 and an automobile brake disc, when the first oil cylinder 7 works, the fixed plate 2 and the brake pad 3 cannot be pushed to a preset position, the brake fluid pressure in the first oil cylinder 7 is increased, when the pressure exceeds a certain threshold value, the brake fluid pushes the plug 20 and the limiting plate 18 to move, then enters the fixed seat 6 through the through hole 17, the fixed seat 6 is internally provided with the fixed cavity 9, the fixed cavity 9 is also communicated with the second oil cylinder 8, the brake fluid enters the second oil cylinder 8 and pushes the second piston 12 to move, the second piston 12 is abutted against the fixed plate 2, and under the action of the locking mechanism, the second piston 12 is connected with the fixed plate 2;

after the brake is released, the brake fluid can be discharged through the brake fluid recovery port 14 and the brake fluid inlet and outlet 11, at this time, the brake fluid pressure in the fixed seat 6, the first cylinder 7 and the second cylinder 8 can be reduced, the limiting plate 18 can return to the original position under the action of the supporting spring 16, the second piston 12 can return to the original position under the action of the tension spring 13, the fixed sleeve 4 is arranged on the fixed plate 2, the fixed sleeve 4 is elastically connected with the first piston 10 through the connecting spring 27, a certain moving space is formed between the fixed sleeve 4 and the first piston 10, the fixed plate 2 can be pulled to move in the opposite direction through the second piston 12, so that the gap between the brake pad 3 and the automobile brake disc is enlarged, and the clamped hard object can automatically fall down.

This technical scheme has first hydro-cylinder 7 through the setting, second hydro-cylinder 8 and fixing base 6's braking pincers 1, can promote brake block 3 and brake disc conflict through first hydro-cylinder 7, brake, when the card has hard thing between brake block 3 and the brake disc, can stimulate fixed plate 2 and brake block 3 in the opposite direction again through second hydro-cylinder 8 and second piston 12, thereby make the clearance grow between brake block 3 and the car brake disc, make the hard thing of blocking drop automatically, at the in-process of traveling like this, need not manual clearance and can handle the hard thing of blocking, it is convenient and safe.

It should be noted that the specific structure and position of the automobile brake disc and the installation manner of the brake caliper 1 are the prior art, and therefore are not described in detail.

Example 2

Referring to fig. 1 and 5, in this embodiment, a fixing groove 15 is formed at an end of the second cylinder 8 close to the fixing seat 6, and a supporting spring 16 is disposed in the fixing groove 15, where the fixing groove 15 is communicated with the fixing cavity 9. One side of the fixed cavity 9 is provided with a through hole 17, and the through hole 17 is communicated with the first oil cylinder 7. The oil circuit conversion mechanism comprises a limiting plate 18 and a supporting block 19, the supporting block 19 is located at one end, close to the first oil cylinder 7, of the fixing cavity 9, the supporting block 19 is fixedly connected with the fixing seat 6, the limiting plate 18 is rotatably connected with the supporting block 19 through a rotating shaft, one end of the limiting plate 18 is fixedly connected with the supporting spring 16, and the other end of the limiting plate 18 is provided with a plug 20.

This technical scheme has set up two oil circuit switching mechanisms in fixing base 6, an oil circuit switching mechanism corresponds a first hydro-cylinder 7 and a second hydro-cylinder 8, under normal condition, first hydro-cylinder 7 is the exclusive work, consequently be equipped with solitary brake fluid access & exit 11 on first hydro-cylinder 7, end cap 20 through on the limiting plate 18 can be closed through hole 17, supporting shoe 19 plays a effect of supporting limiting plate 18, because first hydro-cylinder 7 is great at during operation internal pressure, consequently, set up supporting shoe 19 in the one end that fixing base 6 is close to the through-hole, at this moment, limiting plate 18 just is equivalent to a lever, under supporting spring 16's effect, limiting plate 18 can just be stopped up through hole 17 with less power, compact structure. When the brake fluid pushes the plug 20 open and enters the fixed cavity 9 through the through hole 17, the brake fluid enters the second cylinder 8 through the fixed cavity 9, and the second piston 12 is pushed to move.

Example 3

Referring to fig. 1 and 2, in this embodiment, a further improvement of embodiment 2 is provided, one end of the fixed seat 6 is provided with a connection groove 21, one end of the connection groove 21 is provided with an opening, and the other end of the connection groove 21 is communicated with the brake fluid recovery port 14, a valve core 22 is provided at the connection groove 21, one end of the valve core 22 is elastically connected to the fixed seat 6 through a fixed spring 23, the other end of the valve core 22 passes through the connection groove 21 and abuts against the limiting plate 18, and a valve hole 24 is provided on the valve core 22.

The brake caliper 1 is provided at the top thereof with a tube connector 28, and both ends of the tube connector 28 are provided with brake fluid recovery tubes 29, one end of each brake fluid recovery tube 29 being communicated with the brake fluid recovery port 14.

In order to facilitate the recovery of brake fluid, the technical scheme is that a connecting groove 21 with a valve core 22 is arranged in a fixed seat to be matched with an oil way conversion mechanism for use, when the brake fluid jacks a plug 20 and enters a fixed cavity 9 through a through hole 17, the brake fluid enters a second oil cylinder 8 through the fixed cavity 9 so as to push a second piston 12 to move, when the pressure of the brake fluid is reduced, a limiting plate 18 returns to the original position under the action of a supporting spring 16, at the moment, the through hole 17 is sealed again, so that the brake fluid in the second oil cylinder 8 and the fixed cavity 9 cannot flow back into the first piston 10 through the through hole 17 and is discharged through a brake fluid inlet and outlet 11;

in order to solve the above problems, according to the technical scheme, the connecting groove 21 is used in cooperation with the oil path switching mechanism, one end of the valve core 22 is elastically connected with the fixed seat 6 through the fixed spring 23, and the other end of the valve core 22 is abutted against the limiting plate 18, when brake fluid pushes the plug 20 open and enters the fixed cavity 9 through the through hole 17, the limiting plate 18 deflects, after the blocking of the limiting plate 18 is lost, the valve core 22 moves towards the second piston 12, at the moment, the valve hole 24 on the valve core 22 is staggered with the connecting groove 21, the brake fluid in the fixed cavity 9 cannot enter the brake fluid recovery port 14 through the connecting groove 21, when the limiting plate 18 returns to the original position, the valve hole 24 on the valve core 22 is in a communication state with the connecting groove 21, because the second piston 12 is elastically connected with the second cylinder 8 through the tension spring 13, after the brake fluid pressure, the second piston 12 returns to the original position under the action of the tension spring 13, the brake fluid in the second cylinder 8 can be reversely pushed through the second piston 12, at the brake fluid can enter the brake fluid recovery port 14 through the connecting groove 21, and then is discharged through the brake fluid recovery port 14.

Two second oil cylinders 8 are arranged on one side of the brake caliper 1, the pipe joint 28 is a three-way pipe joint, three joints are provided, the pipe joint 28 is communicated with the brake pump through a pipeline, and the brake fluid at the brake fluid recovery port 14 on one side of the brake caliper 1 can be uniformly recovered through the pipe joint 28.

Example 4

Referring to fig. 3 and 4, the locking mechanism includes a locking block 25, the locking block 25 is slidably connected to the groove 5, the locking block 25 is elastically connected to the groove 5 through a limiting spring 26, one end of the locking block 25 is provided with a locking protrusion 2501, and the other end of the locking block 25 is provided with a triangular block 2502. The end of the second piston 12 is provided with a catch 801 that engages with the catch 2501. A chamber 30 is provided in the middle of the first piston 10, and a third piston 31 is provided in the chamber 30.

The fixture block 25 can slide along the groove 5, when the second piston 12 abuts against the fixture block 25, the fixture block 25 is pushed upward first, then under the action of the limiting spring 26, the fixture block 25 returns to the original position, at this time, the clamping protrusion 2501 abuts against the clamping groove 801 on the second piston 12, the third piston 31 is arranged on the first piston 10, after brake fluid enters the first cylinder 7, the third piston 31 is pushed to move first, then the first piston 10 is pushed to move, the third piston 31 abuts against the triangular block 2502 on the fixture block 25 when moving, due to the inclined surface on the triangular block 2502, the third piston 31 pushes the fixture block 25 and the triangular block 2502 to move, so that the clamping protrusion 2501 is separated from the clamping groove 801, and the second piston 12 can be connected with the fixing plate 2 more tightly by arranging the locking mechanism.

It should be noted that, in this document, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the technical principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A braking system for autonomous vehicles, comprising a brake caliper (1), characterized in that: the brake caliper is characterized in that fixing plates (2) are symmetrically arranged on the inner side of the brake caliper (1), a brake pad (3) is arranged on one side of each fixing plate (2), a fixing sleeve (4) is arranged on the other side of each fixing plate (2), a groove (5) is formed in one side, close to the fixing sleeve (4), of each fixing plate (2), a locking mechanism is arranged in each groove (5), a fixing seat (6) is arranged on the outer side of the brake caliper (1), a first oil cylinder (7) and a second oil cylinder (8) are arranged on each fixing seat (6), a fixing cavity (9) is formed in each fixing seat (6), an oil way switching mechanism is arranged in each fixing cavity (9), and a brake fluid recovery port (14) is formed in the outer side of each fixing seat (6);

first hydro-cylinder (7) with second hydro-cylinder (8) all with braking pincers (1) fixed connection, be equipped with first piston (10) in first hydro-cylinder (7), just the one end of first piston (10) is pegged graft in fixed cover (4) and through connecting spring (27) with fixed cover (4) elastic connection, one side of first hydro-cylinder (7) is equipped with brake fluid access & exit (11), be equipped with second piston (12) in second hydro-cylinder (8), just the one end of second piston (12) through extension spring (13) with second hydro-cylinder (8) elastic connection.

2. A braking system for autonomous vehicles as claimed in claim 1, characterized in that: one end, close to the fixing seat (6), of the second oil cylinder (8) is provided with a fixing groove (15), a supporting spring (16) is arranged in the fixing groove (15), and the fixing groove (15) is communicated with the fixing cavity (9).

3. A braking system for an autonomous vehicle as claimed in claim 1, characterized in that: one side of the fixed cavity (9) is provided with a through hole (17), and the through hole (17) is communicated with the first oil cylinder (7).

4. A braking system for an autonomous vehicle as claimed in claim 2, characterized in that: the oil circuit conversion mechanism comprises a limiting plate (18) and a supporting block (19), the supporting block (19) is located at one end, close to the first oil cylinder (7), of the fixed cavity (9), the supporting block (19) is fixedly connected with the fixed seat (6), the limiting plate (18) is rotatably connected with the supporting block (19) through a rotating shaft, one end of the limiting plate (18) is fixedly connected with the supporting spring (16), and a plug (20) is arranged at the other end of the limiting plate (18).

5. A braking system for autonomous vehicles as claimed in claim 4, characterized in that: the one end of fixing base (6) is equipped with spread groove (21), the one end of spread groove (21) is equipped with the opening, just the other end of spread groove (21) with mouthful (14) intercommunication is retrieved to brake fluid, spread groove (21) department is equipped with case (22), just the one end of case (22) through fixed spring (23) with fixing base (6) elastic connection, the other end of case (22) pass spread groove (21) and with limiting plate (18) are inconsistent, just be equipped with valve opening (24) on case (22).

6. A braking system for an autonomous vehicle as claimed in claim 1, characterized in that: the locking mechanism comprises a clamping block (25), the clamping block (25) is connected with the groove (5) in a sliding mode, the clamping block (25) is elastically connected with the groove (5) through a limiting spring (26), a clamping protrusion (2501) is arranged at one end of the clamping block (25), and a triangular block (2502) is arranged at the other end of the clamping block (25).

7. A braking system for an autonomous vehicle as claimed in claim 6, characterized in that: the end part of the second piston (12) is provided with a clamping groove (801) matched with the clamping protrusion (2501).

8. A braking system for an autonomous vehicle as claimed in claim 1, characterized in that: the brake caliper comprises a brake caliper body (1), and is characterized in that a pipe connector (28) is arranged at the top of the brake caliper body (1), brake fluid recovery pipes (29) are arranged at two ends of the pipe connector (28), and one ends of the brake fluid recovery pipes (29) are communicated with the brake fluid recovery ports (14).

9. A braking system for an autonomous vehicle as claimed in claim 1, characterized in that: a cavity (30) is arranged in the middle of the first piston (10), and a third piston (31) is arranged in the cavity (30).