Double-section oil pushing stroke brake upper pump capable of preventing sudden pressure relief

Abstract

A double-section oil pushing stroke brake upper pump capable of preventing sudden pressure relief comprises a brake pump body which is provided with a piston cavity and an oil storage cavity. A piston oil pushing assembly; the brake handle is in transmission fit with the piston oil pushing assembly through a push rod assembly; a tubing assembly; the piston oil pushing assembly comprises a small-diameter piston push rod, a large-diameter piston push sleeve, a small-diameter piston oil seal, a large-diameter piston oil seal, a reset elastic piece and an assistance elastic piece. The small-diameter piston push rod is arranged in the large-diameter piston push sleeve in a penetrating manner; the power-assisted elastic piece is propped between the small-diameter piston push rod and the large-diameter piston push sleeve; the reset elastic piece abuts against the position between the small-diameter piston push rod and the inner wall of the piston cavity. The large-diameter piston oil seal is arranged on the large-diameter piston push sleeve, and the small-diameter piston push rod is arranged on the small-diameter piston push rod; a first limiting step is arranged in the piston cavity, and the large-diameter piston push sleeve can abut against the first limiting step to form limiting fit. In the using process, the situation of short-time pressure drop is prevented, and a stable, reliable and safe braking function is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of braking equipment, and in particular to a brake master cylinder with a dual-stage oil-pushing stroke that prevents sudden pressure relief. Background Art

[0002] Hydraulic brakes are a type of braking system that transmits pressure through a liquid and are widely used in automobiles, motorcycles, bicycles, and industrial equipment. Its core principle is to utilize the incompressibility of the liquid to efficiently convert the force applied by the driver into braking force, achieving precise and stable braking effects.

[0003] The brake master cylinder of a bicycle (also known as the brake master cylinder or brake handle assembly) is one of the core components of a hydraulic braking system and is mainly responsible for converting the pressing force of the rider's hand into the pressure of hydraulic oil, thereby driving the brake caliper to clamp the disc and achieve the braking effect.

[0004] In an ideal bicycle brake master cylinder, a piston oil seal with a larger size needs to act in the front stage of oil pushing, so that the brake master cylinder quickly delivers brake oil to the brake slave cylinder, and then pushes out the brake pads in the brake slave cylinder and quickly contacts the brake disc, and the braking starts to take effect; in the middle and later stages of oil pushing, a piston oil seal with a smaller size needs to act. At this time, a static pressure environment (Pascal's principle) is formed between the piston oil seal and the brake slave cylinder. At this time, compared with the piston oil seal with a larger size, the piston oil seal with a smaller size has a smaller pressure brought by the reaction force when achieving the same braking force, so it is easier to squeeze and hold, giving the user a better braking feel.

[0005] Example of the prior art 1, referring to the patent document CN216969898U, discloses a variable hydraulic brake structure related to a hydraulic braking system. The variable hydraulic brake structure includes: a body having an activity space and an oil outlet inside, and the oil outlet communicates with the activity space; a first piston disposed in the activity space of the body and movable along the activity space between a first position and a second position; the first piston has a driving part; a second piston disposed in the activity space of the body and movable along the activity space between a third position and a fourth position; the second piston has a driven part; wherein, when the first piston is in the first position and the second piston is in the third position, the driving part of the first piston is separated from the driven part of the second piston by a predetermined distance; and a brake handle pivotally connected to the body to drive the first piston to move. It can provide a more secure and flexible pressing feel for the brake handle of the user. The structural features and effects shown in Example of the prior art 1 are exactly the opposite of those of an ideal bicycle brake master cylinder, so it does not have market competitiveness.

[0006] Prior Art Example 2. Referring to patent document CN118545202A, a double-cylinder piston hydraulic oil pump and a hydraulic disc brake are disclosed. This double-cylinder piston hydraulic oil pump is used in conjunction with the handlebar cross tube of a bicycle frame and includes an upper pump body. One end of the upper pump body is movably connected to a brake lever member. A double-cylinder oil chamber is provided on the side of the upper pump body close to the brake lever member. The double-cylinder oil chamber includes a first oil cylinder chamber and a second oil cylinder chamber that are coaxially connected and have gradually decreasing inner diameters. A double-cylinder piston member is movably assembled in the double-cylinder oil chamber, and a piston rod is movably assembled at the first end of the double-cylinder piston member. The other end of the piston rod extends out of the oil cylinder chamber and is fixedly assembled at the lower end of the brake lever member to drive a large braking force ratio of oil to be input into the oil outlet when the brake lever member swings at a small angle. In this application, the swing angle movement stroke of the brake is divided into two stages. In the first stage, when the brake lever member swings at a small angle, a small stroke can be achieved to eliminate the preset gap between the brake pads and the disc. In the second stage, when the brake lever member is further squeezed, a strong braking effect is obtained while the brake lever member swings at a small angle.

[0007] Prior Art Example 3. Referring to patent document ZL202520084516.2, a brake upper pump with double oil seals and lateral pressure relief is disclosed, which includes a brake pump body provided with a piston chamber and an oil storage chamber that communicate with each other; a brake handle that forms a rotational fit with the brake pump body and a transmission fit with a piston mechanism; a tubing assembly that communicates with the piston chamber; a piston mechanism including a piston body, a first oil seal, and a second oil seal, where the second oil seal is on the front side of the first oil seal and the effective oil-pushing area S1 of the second oil seal is smaller than that of the first oil seal; a return spring that acts on the piston body; a pressure relief valve mechanism installed in the pressure relief chamber of the brake pump body; the piston chamber at least has a large-diameter chamber section, a small-diameter chamber section, and a variable-diameter chamber section, and the pressure relief chamber communicates with the variable-diameter chamber section through a pressure relief passage. The utility model adopts a double-piston oil seal structure with large and small diameters to achieve the effect that the front section has a relatively large oil seal area and the rear section has a relatively small oil seal area, and the overall braking performance will be more linear.

[0008] Technical Example 2 and Technical Example 3 both have large and small piston oil seals, and the working sequence satisfies the ideal bicycle brake master cylinder described above. However, both of these two technical solutions have the same defect, specifically: in the front, middle, and rear sections of squeezing the brake handle, the large-size piston oil seal and the small-size piston oil seal always move forward synchronously. Therefore, there is a handover point for the actually working piston oil seals. That is, during the movement after the large-size piston oil seal switches to the small-size piston oil seal for work, the space between the large-size piston oil seal and the small-size piston oil seal changes. At this time, the large-size piston oil seal is still boosting the brake oil between the large-size piston oil seal and the small-size piston oil seal. In order to prevent this part of the brake oil from interfering with the use of the small-size piston oil seal, both Example 2 and Example 3 apply a pressure relief structure, which is used to offset and discharge the brake oil pressure between the large-size piston oil seal and the small-size piston oil seal. However, due to the continuous change of the space between the large-size piston oil seal and the small-size piston oil seal, the brake oil pressure also continuously changes, and the function of the pressure relief structure cannot be completely unified and stable. Therefore, there will be an obvious pressure relief (pressure drop) phenomenon in a short time, and in severe cases, it will be completely depressurized, which will lead to the sudden failure of the brake in a short time, posing a very serious safety hazard. Summary of the Invention

[0009] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a brake master cylinder with a double-stage oil pushing stroke to prevent sudden pressure relief.

[0010] The technical solution of the present invention to solve its technical problems is: a brake master cylinder with a double-stage oil pushing stroke to prevent sudden pressure relief, including:

[0011] A brake pump body, which is provided with a piston chamber and an oil storage chamber. The piston chamber and the oil storage chamber are filled with brake oil, and the oil storage chamber is communicated with the piston chamber through an oil return hole;

[0012] A piston oil pushing assembly, which is located in the piston chamber;

[0013] A brake handle, which forms a rotational fit with the brake pump body through a pivoting mechanism, and the brake handle forms a transmission fit with the piston oil pushing assembly through a push rod assembly;

[0014] A tubing assembly, which is connected to the brake pump body and is in communication with the piston chamber;

[0015] The piston oil pushing assembly includes a small-diameter piston push rod, a large-diameter piston push sleeve, a small-diameter piston oil seal, a large-diameter piston oil seal, a reset elastic member, and an assisting elastic member;

[0016] At least a part of the small-diameter piston push rod is inserted into the large-diameter piston push sleeve, and a clearance fit is formed between the outer wall of the small-diameter piston push rod and the inner wall of the large-diameter piston push sleeve;

[0017] The described boosting elastic member abuts between the rear end of the small-diameter piston push rod and the rear end of the large-diameter piston push sleeve;

[0018] The described reset elastic member abuts between the small-diameter piston push rod and the inner wall of the piston cavity. The reset elastic member acts on the small-diameter piston push rod so that the small-diameter piston push rod always has a tendency to move backward;

[0019] The described large-diameter piston oil seal is arranged on the large-diameter piston push sleeve, and the described small-diameter piston push rod is arranged on the small-diameter piston push rod, and the small-diameter piston oil seal is located in front of the large-diameter piston oil seal;

[0020] The piston cavity has at least a first equal-diameter section and a second equal-diameter section. The inner diameter size of the first equal-diameter section is larger than the inner diameter size of the second equal-diameter section. The large-diameter piston oil seal contacts the inner wall of the first equal-diameter section and forms a sealing fit. The small-diameter piston oil seal can contact the inner wall of the second equal-diameter section and form a sealing fit. And there is a first limiting step between the first equal-diameter section and the second equal-diameter section. The front end of the large-diameter piston push sleeve can abut against the first limiting step and form a limiting fit.

[0021] For further description of the present invention, a supplementary oil hole is also provided between the oil storage cavity and the piston cavity. The supplementary oil hole is located behind the oil return hole. When the user pinches the brake handle, the brake oil in the oil storage cavity is supplemented into the piston cavity behind the large-diameter piston oil seal through the supplementary oil hole;

[0022] In the first stage when the user pinches the brake handle, the large-diameter piston oil seal is located behind the oil return hole. Thus, when the piston oil pushing assembly moves forward, the small-diameter piston push rod and the large-diameter piston push sleeve move forward together. Thus, the large-diameter piston oil seal transports the brake oil in the piston cavity to the oil storage cavity through the oil return hole;

[0023] In the second stage when the user pinches the brake handle, the large-diameter piston oil seal is located in front of the oil return hole. Thus, when the piston oil pushing assembly moves forward, the small-diameter piston push rod and the large-diameter piston push sleeve move forward together. Thus, the large-diameter piston oil seal and the small-diameter piston oil seal together transport the brake oil in the piston cavity to the brake lower pump through the oil pipe assembly;

[0024] In the third stage when the user pinches the brake handle, the front end of the large-diameter piston push sleeve abuts against the first limiting step and stops moving forward, and the small-diameter piston push rod continues to move forward. Thus, the small-diameter piston oil seal transports the brake oil in the piston cavity to the brake lower pump through the oil pipe assembly;

[0025] When the user pinches the brake handle in the first stage and the second stage, the boosting force applied by the boosting elastic member to the large-diameter piston push sleeve forward is greater than the retracting force applied by the brake oil to the large-diameter piston push sleeve backward.

[0026] Regarding the preferred solution of the large-diameter piston push sleeve in the present invention, the large-diameter piston push sleeve includes a first support section, a first groove section, and a first accommodation section arranged in sequence from back to front;

[0027] The large-diameter piston push sleeve has a through hole that penetrates through the first support section, the first groove section, and the first accommodation section, and at least part of the small-diameter piston push rod passes through the through hole;

[0028] The front end of the boosting elastic member abuts against the first support section;

[0029] The large-diameter piston oil seal is installed in the first groove section;

[0030] The small-diameter piston oil seal can retract into the first accommodation section or / and extend out of the first accommodation section.

[0031] A further setting of the above technical solution is that an accommodation cavity is provided in the first accommodation section, and the small-diameter piston oil seal can retract into the accommodation cavity or / and extend out of the accommodation cavity;

[0032] In the first stage and the second stage when the user pinches the brake handle, the small-diameter piston oil seal retracts into the accommodation cavity, and the small-diameter piston oil seal contacts the inner wall of the accommodation cavity and forms a sealing fit;

[0033] In the third stage when the user pinches the brake handle, the small-diameter piston oil seal extends out of the accommodation cavity.

[0034] It should be noted that a first flow channel groove is provided on the inner wall of the through hole, and the piston cavity behind the large-diameter piston push sleeve is communicated with the accommodation cavity through the first flow channel groove;

[0035] A second flow channel groove is provided on the outer wall of the first accommodation section; in the first stage and the second stage when the user pinches the brake handle, the first equal-diameter section is communicated with the second equal-diameter section through the second flow channel groove.

[0036] Preferably, the inner diameter size of the accommodation cavity is less than or equal to the inner diameter size of the second equal-diameter section, and the front end opening of the accommodation cavity has a circular arc chamfer portion.

[0037] Regarding the preferred solution of the small-diameter piston push rod in the present invention, the small-diameter piston push rod includes a rod body, a second support section, a second groove section, and a third support section arranged in sequence from back to front on the rod body;

[0038] The rear end of the reset elastic member abuts against the third support section;

[0039] The small-diameter piston oil seal is installed in the second groove section;

[0040] The second support section described above can abut against the large-diameter piston push sleeve to form a backward limiting and anti-retreat fit.

[0041] Optionally, the small-diameter piston push rod further includes a transmission joint;

[0042] The front end of the transmission joint is threadedly connected to the rod body through a threaded structure, and the effective mating length of the threaded structure is adjustable;

[0043] The rear end of the transmission joint has a transmission groove, and the push rod assembly extends into the transmission groove so that the push rod assembly forms a transmission fit with the rod body through the transmission joint;

[0044] A sealing ring is sleeved on the outer wall of the transmission joint, and the sealing ring contacts the inner wall of the large-diameter section so that a sealing fit is formed between the outer wall of the transmission joint and the inner wall of the large-diameter section.

[0045] In some preferred embodiments of the present invention, the front end of the first equal-diameter section extends inward to form a third equal-diameter section, the inner diameter size of the third equal-diameter section is larger than the inner diameter size of the second equal-diameter section, and the inner diameter size of the third equal-diameter section is smaller than the inner diameter size of the first equal-diameter section;

[0046] The first limiting step is located at the junction of the third equal-diameter section and the second equal-diameter section;

[0047] A second limiting step is formed at the junction of the first equal-diameter section and the second equal-diameter section, and the large-diameter piston oil seal can abut against the second limiting step to form a limiting fit.

[0048] The beneficial effects of the present invention are as follows:

[0049] First, in the solution of the present invention, during the process of the user squeezing the brake handle, the pressure borne by the piston push rod assembly (which may also be the pressure feedback to the user) is continuously increasing, so a stable, reliable and safe braking function is provided.

[0050] Second, the large-diameter piston oil seal and the small-diameter piston oil seal cooperate with each other to obtain the function of a large oil pushing amount and a larger oil pushing cross-sectional area in the early stage and a small oil pushing amount and a smaller oil pushing cross-sectional area in the later stage under different stages of squeezing the brake handle, that is, in the early stage, it can help the brake pads in the brake lower pump to be quickly pushed out, and in the later stage, the pressure received in the static pressure environment is smaller, and the user's hand feeling is softer and more linear, eliminating the wall-hitting feeling, so as to meet the requirements of the ideal bicycle brake upper pump for the change of the brake oil pushing amount.

[0051] III. When the small-diameter piston oil seal starts to work, the positions of the large-diameter piston push sleeve and the large-diameter piston oil seal remain stationary. Therefore, with the position of the large-diameter piston oil seal unchanged, the space between the large-diameter piston oil seal and the first limit step remains the same. As a result, the large-diameter piston oil seal will no longer push oil forward. Thus, there is no need for a pressure relief mechanism to relieve pressure during this stage, completely eliminating the pressure relief (pressure drop) phenomenon in a short period of time, avoiding the sudden failure of the brake in a short time, ensuring the normal use of the brake, greatly improving the brake safety, and guaranteeing the life and health safety of users.

[0052] IV. The front opening of the accommodation cavity has an arc chamfer portion, so that when the small-diameter piston oil seal retracts into the accommodation cavity, the small-diameter piston oil seal contacts the arc chamfer portion, achieving a smooth transition and playing a protective role to prevent the small-diameter piston oil seal from being scratched by sharp edges and causing seal failure, extending the maintenance and replacement cycle of the accessories and the overall service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a schematic diagram of the overall structure of the present invention.

[0054] Figure 2 is a schematic diagram of the overall structure comparison at each stage when the user squeezes the brake handle.

[0055] Figure 3 is a schematic diagram of the piston oil-pushing assembly comparison at each stage when the user squeezes the brake handle.

[0056] Figure 4 is an exploded view of the structure of the brake master cylinder in the present invention.

[0057] Figure 5 is a sectional view and a partial enlarged view of the structure of the brake handle in the first stage.

[0058] Figure 6 is a sectional view and a partial enlarged view of the structure of the brake handle in the second stage.

[0059] Figure 7 is a sectional view and a partial enlarged view of the structure at the switching node between the second stage and the third stage of the brake handle.

[0060] Figure 8 is a sectional view and a partial enlarged view of the structure of the brake handle in the third stage.

[0061] Figure 9 is a schematic diagram of the structural comparison of the front side and the rear side of the large-diameter piston push sleeve.

[0062] Figure 10 is a schematic diagram of the structure of the small-diameter piston push rod.

[0063] Figure 11It is a structural sectional view and a partial enlarged schematic diagram of the transmission joint after adjustment.

[0064] Figure 12 It is a comparison schematic diagram of the piston oil-pushing assembly before and after the adjustment of the transmission joint.

[0065] In the figure: 1. Brake pump body; 11. Piston cavity; 111. First equal-diameter section; 112. Second equal-diameter section; 113. Third equal-diameter section; 114. First limiting step; 115. Second limiting step; 12. Oil storage cavity; 13. Oil return hole; 14. Oil replenishing hole; 2. Piston oil-pushing assembly; 21. Small-diameter piston push rod; 211. Rod body; 212. Second supporting section; 213. Second groove section; 214. Third supporting section; 215. Transmission joint; 2151. Transmission groove; 2152. Thread structure; 2153. Sealing ring; 22. Large-diameter piston push sleeve; 221. First supporting section; 222. First groove section; 223. First accommodating section; 2231. Accommodating cavity; 2232. Arc chamfer part; 224. Through hole; 225. First flow channel groove; 226. Cavity; 227. Second flow channel groove; 23. Small-diameter piston oil seal; 24. Large-diameter piston oil seal; 25. Reset elastic part; 26. Boosting elastic part; 3. Brake handle; 31. Pivoting mechanism; 32. Push rod assembly; 3a. Initial stage; 3b. First stage; 3c. Second stage; 3d. Third stage; 4. Oil pipe assembly. Specific implementation manners

[0066] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0067] Refer to Figures 1 to 12, A brake master cylinder with a double-stage oil-pushing stroke to prevent sudden pressure relief, comprising: a brake pump body 1, which is provided with a piston chamber 11 and an oil storage chamber 12. Brake oil is filled in the piston chamber 11 and the oil storage chamber 12, and the oil storage chamber 12 is communicated with the piston chamber 11 through an oil return hole 13; a piston oil-pushing assembly 2, which is located in the piston chamber 11; a brake handle 3, which forms a rotational fit with the brake pump body 1 through a pivoting mechanism 31, and the brake handle 3 forms a transmission fit with the piston oil-pushing assembly 2 through a push rod assembly 32; a tubing assembly 4, which is connected to the brake pump body 1 and is in communication with the piston chamber 11. When in use, the user holds and squeezes the brake handle 3. The brake handle 3 rotates relative to the brake pump body 1 with the pivoting mechanism 31 as the rotation center, and the rotational force of the brake handle 3 is converted into a forward boosting force of the piston oil-pushing assembly 2 through the push rod assembly 32. During the forward pushing process of the piston oil-pushing assembly 2, the brake oil in the piston chamber 11 is delivered to the brake slave cylinder through the tubing assembly 4 to achieve the braking function. Among them, the structural solutions of the pivoting mechanism 31 and the push rod assembly 32 are the same as those in the prior art and will not be elaborated here one by one.

[0068] It should be particularly emphasized that, in order to solve the defects of the prior art, the present invention provides a structural composition solution of the piston oil-pushing assembly 2 that is different from the prior art. Specifically: The piston oil-pushing assembly 2 includes a small-diameter piston push rod 21, a large-diameter piston push sleeve 22, a small-diameter piston oil seal 23, a large-diameter piston oil seal 24, a reset elastic member 25, and an assisting elastic member 26. Among them, the setting methods of the above-mentioned components are as follows:

[0069] First, at least a part of the small-diameter piston push rod 21 is inserted into the large-diameter piston push sleeve 22, and a clearance fit is formed between the outer wall of the small-diameter piston push rod 21 and the inner wall of the large-diameter piston push sleeve 22. The small-diameter piston push rod 21 and the large-diameter piston push sleeve 22 are not in a fixed connection relationship. Therefore, the small-diameter piston push rod 21 can move independently relative to the large-diameter piston push sleeve 22.

[0070] Second, the assisting elastic member 26 abuts between the rear end of the small-diameter piston push rod 21 and the rear end of the large-diameter piston push sleeve 22. The assisting elastic member 26 mainly acts on the large-diameter piston push sleeve 22 to enable the large-diameter piston push rod to move forward after receiving a thrust. The working condition is that the push rod assembly 32 directly drives the small-diameter piston push rod 21 to move forward. When the small-diameter piston push rod 21 moves forward, it applies a forward thrust to the assisting elastic member 26 and drives the rear end of the assisting elastic member 26 to move forward. As a result, the assisting elastic member 26 is compressed and releases a greater elastic boosting force forward. The elastic boosting force acts on the large-diameter piston push sleeve 22 to enable the large-diameter piston push sleeve 22 to also overcome the resistance and achieve a forward displacement.

[0071] 3. The reset elastic member 25 abuts between the small-diameter piston push rod 21 and the inner wall of the piston chamber 11. The reset elastic member 25 acts on the small-diameter piston push rod 21 so that the small-diameter piston push rod 21 always has a tendency to move backward. Once the user releases the brake handle 3, in the absence of external force, the reset elastic member 25 will be released. Thus, the reset elastic member 25 (and possibly also in combination with the oil pressure of the brake oil) will apply a reset elastic force to the small-diameter piston push rod 21 to cause the small-diameter piston push rod 21 to reset backward. At the same time, components such as the large-diameter piston push sleeve 22 and the push rod assembly 32 will also be reset together.

[0072] 4. The large-diameter piston oil seal 24 is arranged on the large-diameter piston push sleeve 22, and the small-diameter piston push rod 21 is arranged on the small-diameter piston push rod 21, and the small-diameter piston oil seal 23 is located in front of the large-diameter piston oil seal 24; similar to the prior art, the large-diameter piston oil seal 24 is at the rear and the small-diameter piston oil seal 23 is at the front, but their specific installation positions are different. In order to respectively match the sizes of the large-diameter piston oil seal 24 and the small-diameter piston oil seal 23, the piston chamber 11 at least has a first equal-diameter section 111 and a second equal-diameter section 112. The inner diameter size of the first equal-diameter section 111 is larger than the inner diameter size of the second equal-diameter section 112. The large-diameter piston oil seal 24 is in contact with the inner wall of the first equal-diameter section 111 and forms a sealing fit. The small-diameter piston oil seal 23 can be in contact with the inner wall of the second equal-diameter section 112 and form a sealing fit. It should be particularly noted that there is a first limit step 114 between the first equal-diameter section 111 and the second equal-diameter section 112. The front end of the large-diameter piston push sleeve 22 can abut against the first limit step 114 and form a limit fit. The first limit step 114 is a switching node for the function of the oil pushing amount. That is, when the front end of the large-diameter piston push sleeve 22 is not in contact with the first limit step 114, the large-diameter piston oil seal 24 and the small-diameter piston oil seal 23 push oil forward together. Therefore, when the brake handle 3 is pinched by the same amplitude, a larger oil pushing amount will be obtained, and the actual oil pushing cross-sectional area of the piston oil pushing assembly 2 is larger; when the front end of the large-diameter piston push sleeve 22 is in contact with the first limit step 114, physical limitation is formed. After that, when the brake handle 3 is pinched, the large-diameter piston push sleeve 22 and the large-diameter piston oil seal 24 will no longer move forward. Therefore, the small-diameter piston oil seal 23 pushes oil forward alone. Therefore, when the brake handle 3 is pinched by the same amplitude, a smaller oil pushing amount will be obtained, and the actual oil pushing cross-sectional area of the piston oil pushing assembly 2 is smaller.

[0073] The above content is the basic structural solution of the present invention. On the one hand, the large-diameter piston oil seal 24 and the small-diameter piston oil seal 23 cooperate to obtain the functions of a large oil pushing amount and a larger oil pushing cross-sectional area in the early stage and a small oil pushing amount and a smaller oil pushing cross-sectional area in the later stage when the brake handle 3 is pinched at different stages. That is, in the early stage, it can help the brake pads in the brake lower pump to be quickly pushed out, and in the later stage, the pressure received in the static pressure environment is smaller, and the user's hand feeling is softer and more linear, eliminating the wall-hitting feeling, so as to meet the requirements of the ideal bicycle brake upper pump for the change of the brake oil pushing amount. On the other hand, when the small-diameter piston oil seal 23 starts to work, the positions of the large-diameter piston push sleeve 22 and the large-diameter piston oil seal 24 remain stationary. Therefore, when the position of the large-diameter piston oil seal 24 remains unchanged, the space between the large-diameter piston oil seal 24 and the first limit step 114 remains unchanged. Therefore, the large-diameter piston oil seal 24 will no longer push oil forward. Therefore, in this stage, there is no need for a pressure relief mechanism to relieve pressure, completely eliminating the pressure relief (pressure drop) phenomenon in a short time, avoiding the situation of sudden brake failure in a short time, ensuring the normal use of the brake, greatly improving the brake safety, and ensuring the life and health safety of users.

[0074] In short, a very important improvement of the present invention is that in the prior art Examples 1 and 2, during the process of the user pinching the brake handle 3, the pressure borne by the piston push rod assembly 32 (which may also be the pressure feedback to the user) first increases, suddenly decreases (due to pressure relief), and then increases. Therefore, there are risks of instability, pressure drop, and brake failure. In the solution of the present invention, during the process of the user pinching the brake handle 3, the pressure borne by the piston push rod assembly 32 (which may also be the pressure feedback to the user) continuously increases. Therefore, a stable, reliable, and safe brake function is provided.

[0075] Embodiment 2

[0076] On the basis of the structure of Embodiment 1, as a more complete structural solution of the present invention, an oil replenishing hole 14 is further provided between the oil storage cavity 12 and the piston cavity 11. The oil replenishing hole 14 is located behind the oil return hole 13. When the user pinches the brake handle 3, the brake oil in the oil storage cavity 12 is replenished into the piston cavity 11 behind the large-diameter piston oil seal 24 through the oil replenishing hole 14 to maintain the oil pressure balance on both the front and rear sides of the large-diameter piston oil seal 24. The situations at each stage when the user pinches the brake handle 3 are described as follows:

[0077] Refer to Figure 5, in the first stage 3b when the user pinches the brake handle 3, the large-diameter piston oil seal 24 is located behind the oil return hole 13. Thus, when the piston oil pushing assembly 2 moves forward, the small-diameter piston push rod 21 and the large-diameter piston push sleeve 22 move forward together, so that the large-diameter piston oil seal 24 transports the brake oil in the piston chamber 11 to the oil storage chamber 12 through the oil return hole 13; this stage is usually referred to as the empty stroke stage, that is, in this stage, although the piston push rod assembly 32 moves forward, no sealed environment is formed between the large-diameter piston oil seal 24 or / and the small-diameter piston oil seal 23 and the brake lower pump, and no static pressure is generated. Therefore, the brake pads will not be pushed out, the brake pads do not contact the brake disc, and thus no braking effect will be generated.

[0078] Refer to Figures 6 to 7 , in the second stage 3c when the user pinches the brake handle 3, the large-diameter piston oil seal 24 is located in front of the oil return hole 13. Thus, when the piston oil pushing assembly 2 moves forward, the small-diameter piston push rod 21 and the large-diameter piston push sleeve 22 move forward together, so that the large-diameter piston oil seal 24 and the small-diameter piston oil seal 23 together transport the brake oil in the piston chamber 11 to the brake lower pump through the oil pipe assembly 4; in this stage, the large-diameter piston oil seal 24 and the small-diameter piston oil seal 23 act simultaneously and form a sealed environment with the brake lower pump, mainly to realize the action of pushing the brake pads outwards. Once the brake pads contact the brake disc, the braking effect starts to be generated, but the braking force in this stage is generally small.

[0079] In the above situation, it is worth mentioning that when the user pinches the brake handle 3 in the first stage 3b and the second stage 3c, the boosting force applied by the boosting elastic member 26 to the large-diameter piston push sleeve 22 forward is greater than the retreating force applied by the brake oil to the large-diameter piston push sleeve 22 backward, so as to achieve the effect of the large-diameter piston push sleeve 22 moving forward. It should be noted that the basic properties of the boosting elastic member 26, such as wire diameter, number of turns, free length, material, etc., can be customized according to actual needs and are not specially limited here.

[0080] Refer to Figures 7 to 8, in the third stage 3d when the user pinches the brake handle 3, the front end of the large-diameter piston push sleeve 22 abuts against the first limit step 114 and stops advancing, while the small-diameter piston push rod 21 continues to advance. As a result, the brake oil in the piston chamber 11 is conveyed to the brake lower pump through the oil pipe assembly 4 by the small-diameter piston oil seal 23. In this stage, a sealed environment is formed between the small-diameter piston oil seal 23 and the brake lower pump. Therefore, the small-diameter piston oil seal 23 alone plays a role in pushing the oil. And in fact, in this stage, since the brake pads have already contacted the brake disc and it is difficult to continue moving, and the brake oil is a liquid and difficult to be compressed, the displacement of the small-diameter piston oil seal 23 is relatively small. It applies to Pascal's principle (in an incompressible and static fluid, a change in pressure applied to a part of the enclosed fluid will be transmitted to all parts of the fluid and the container wall without change in magnitude). Satisfying the formula F1 / A1 = F2 / A2 = P, A1 refers to the effective boosting area between the brake master cylinder and the brake oil, and A2 refers to the effective contact area between the brake master cylinder and the brake oil. Therefore, the smaller the effective boosting area, the smaller the pressure and pressure borne by the brake master cylinder. Since the effective boosting area of the small-diameter piston oil seal 23 is smaller than that of the large-diameter piston oil seal 24, the pressure and pressure borne by the piston push rod assembly 32 in this stage are smaller, and thus the force feedback to the brake handle 3 is smaller, that is, it is easier for the user to operate, and the feeling of pinching the brake handle 3 is more gentle and linear, greatly reducing the sense of hitting a wall. On the other hand, it can also be understood that when the user pinches the brake handle 3 with the same force in this stage, the force acting on the brake lower pump is greater, so a stronger braking force will be obtained.

[0081] In the present disclosure, the effective oil-pushing area (radial dimension) of the large-diameter piston oil seal 24 referred to is larger than the effective oil-pushing area (radial dimension) of the small-diameter piston oil seal 23. The advancing distance of the piston oil-pushing assembly 2 when pinching the brake handle 3 in the first stage 3b is less than the advancing distance of the piston oil-pushing assembly 2 when pinching the brake handle 3 in the second stage 3c, and the advancing distance of the piston oil-pushing assembly 2 when pinching the brake handle 3 in the second stage 3c is less than the advancing distance of the piston oil-pushing assembly 2 when pinching the brake handle 3 in the third stage 3d.

[0082] Embodiment III

[0083] Based on the structure of any of the foregoing embodiments, this embodiment provides a preferred structural solution for some components, which is as follows:

[0084] I. Large-diameter piston push sleeve 22: Refer to Figures 3 to 9 , the large-diameter piston push sleeve 22 includes a first support section 221, a first groove section 222, and a first accommodation section 223 arranged in sequence from the rear to the front;

[0085] The large-diameter piston push sleeve 22 has a through hole 224 that penetrates through the first support section 221, the first groove section 222, and the first accommodation section 223. The small-diameter piston push rod 21 at least partially passes through the through hole 224, that is, the front end of the small-diameter piston push rod 21 can extend to the front of the through hole 224, the rear end of the small-diameter piston push rod 21 is located behind the through hole 224, and a certain part in the middle of the small-diameter piston push rod 21 is located in the through hole 224. The front end of the boosting elastic member 26 abuts against the first support section 221, so that the elastic boosting force can be transmitted to the large-diameter piston push sleeve 22 (the first support section 221) by physical contact; the large-diameter piston oil seal 24 is installed in the first groove section 222 so that the large-diameter piston oil seal 24 can be stably installed on the large-diameter piston push sleeve 22, and thus the large-diameter piston oil seal 24 can move forward together with the large-diameter piston push sleeve 22; the small-diameter piston oil seal 23 can retract into the first accommodation section 223 and / or extend out of the first accommodation section 223.

[0086] Regarding the further setting of the large-diameter piston push sleeve 22, an accommodation cavity 2231 is provided in the first accommodation section 223, and the small-diameter piston oil seal 23 can retract into the accommodation cavity 2231 and / or extend out of the accommodation cavity 2231.

[0087] The situation during operation is as follows: during the first stage 3b and the second stage 3c when the user pinches the brake handle 3, the small-diameter piston oil seal 23 retracts into the accommodation cavity 2231, and the small-diameter piston oil seal 23 contacts the inner wall of the accommodation cavity 2231 and forms a sealing fit; during the third stage 3d when the user pinches the brake handle 3, the small-diameter piston oil seal 23 extends out of the accommodation cavity 2231.

[0088] Preferably, the inner diameter dimension of the accommodation cavity 2231 is less than or equal to the inner diameter dimension of the second equal-diameter section 112, so that when the small-diameter piston oil seal 23 previously extends out of the accommodation cavity 2231, it can more smoothly enter the second equal-diameter section 112 and form a sealing fit with the second equal-diameter section 112. Moreover, the front end opening of the accommodation cavity 2231 has an arc chamfer 2232, so that during the process of the small-diameter piston oil seal 23 retracting into the accommodation cavity 2231, the small-diameter piston oil seal 23 contacts the arc chamfer 2232 to achieve a smooth transition and play a protective role to prevent the small-diameter piston oil seal 23 from being scratched by sharp edges and causing sealing failure.

[0089] II. Scheme for oil pressure balance: On the one hand, in the third stage 3d when the user squeezes the brake handle 3, the large-diameter piston oil seal 24 remains stationary and the small-diameter piston oil seal 23 alone realizes the function of pushing oil forward. In this stage, as the small-diameter piston oil seal 23 advances, a cavity 226 is formed between the small-diameter piston oil seal 23 and the accommodating cavity 2231 and gradually increases. If brake oil is not replenished into the cavity 226, a certain additional pressure difference will be generated between the front and rear sides of the small-diameter piston oil seal 23, resulting in a tendency for the small-diameter piston oil seal 23 to move backward. The user needs to apply a greater operating force to push the small-diameter piston oil seal 23 forward, leading to a reduction in the braking force under the same operating force. To eliminate the above defects, a first flow channel groove 225 is provided on the inner wall of the through hole 224, and the piston cavity 11 behind the large-diameter piston push sleeve 22 is communicated with the accommodating cavity 2231 through the first flow channel groove 225; thus, once the small-diameter piston oil seal 23 moves independently relative to the large-diameter piston push sleeve 22, the brake oil in the piston cavity 11 behind the large-diameter piston push sleeve 22 can be replenished into the cavity 226 of the accommodating cavity 2231 through the first flow channel groove 225 to eliminate the cavity 226, playing a role in balancing the pressure, and thus obtaining a greater braking force under the same operating force. It should be added that after the brake oil in the piston cavity 11 behind the large-diameter piston push sleeve 22 is replenished into the accommodating cavity 2231, the brake oil in the oil storage cavity 12 is replenished into the piston cavity 11 behind the large-diameter piston push sleeve 22 through the oil replenishing hole 14 to maintain the internal pressure balance.

[0090] On the other hand, a second flow channel groove 227 is provided on the outer wall of the first accommodating section 223; in the first stage 3b and the second stage 3c when the user squeezes the brake handle 3, the first equal-diameter section 111 is communicated with the second equal-diameter section 112 through the second flow channel groove 227 to realize the function of pushing oil forward for the large-diameter piston oil seal 24. In the third stage 3d when the user squeezes the brake handle 3, the large-diameter piston oil seal 24 remains stationary. Therefore, theoretically, the large-diameter piston oil seal 24 maintains a local pressure balance of the brake oil with the first limiting step 114 through the second flow channel groove 227.

[0091] III. Small-diameter piston push rod 21: Refer to Figures 3 to 8 、 Figure 10, the small-diameter piston push rod 21 includes a rod body 211, a second support section 212, a second groove section 213, and a third support section 214 that are sequentially arranged on the rod body 211 from the rear to the front; the rear end of the return elastic member 25 abuts against the third support section 214, so that the elastic return force can be transmitted to the small-diameter piston push rod 21 (the third support section 214) through physical contact; the small-diameter piston oil seal 23 is installed in the second groove section 213, so that the small-diameter piston oil seal 23 can be stably installed on the small-diameter piston push rod 21, and thus the small-diameter piston oil seal 23 can move forward together with the small-diameter piston push rod 21; when the user releases the brake handle 3 (provided that it is after the third stage 3d of squeezing the brake handle 3), under the action of the return elastic member 25, the small-diameter piston push rod 21 approaches the large-diameter piston push sleeve 22. During this process, the second support section 212 can abut against the large-diameter piston push sleeve 22 and form a backward limiting and anti-retreat fit to prevent the small-diameter piston push rod 21 from retreating excessively.

[0092] Embodiment 4

[0093] Based on the structure of Embodiment 3, as a further optional solution in this embodiment, the details are as follows: Refer to Figures 11 to 12 , the small-diameter piston push rod 21 further includes a transmission joint 215; the front end of the transmission joint 215 is threadedly connected to the rod body 211 through a thread structure 2152, and the effective mating length of the thread structure 2152 is adjustable; the rear end of the transmission joint 215 has a transmission groove 2151, and the push rod assembly 32 extends into the transmission groove 2151, so that the push rod assembly 32 forms a transmission fit with the rod body 211 through the transmission joint 215; a sealing ring 2153 is sleeved on the outer wall of the transmission joint 215, and the sealing ring 2153 contacts the inner wall of the large-diameter section, so that a sealing fit is formed between the outer wall of the transmission joint 215 and the inner wall of the large-diameter section.

[0094] In this embodiment, it should be emphasized that the effective mating length of the thread structure 2152 is adjustable, so that the initial state of the piston push rod assembly 32 in the piston cavity 11 is adjustable. Thus, in the initial case where the brake handle 3 is not squeezed, the distance between the large-diameter piston oil seal 24 and the oil return hole 13 (i.e., the distance of the dead stroke) is adjustable, so that the brake master cylinder has a specific dead stroke adjustment function.

[0095] Embodiment 5

[0096] Refer to Figures 5 to 8, on the basis of the structure of any of the foregoing embodiments, this embodiment provides a more stable usage solution for the large-diameter piston oil seal 24, specifically: the front end of the first equal-diameter section 111 extends inward to form a third equal-diameter section 113, the inner diameter of the third equal-diameter section 113 is larger than the inner diameter of the second equal-diameter section 112, and the inner diameter of the third equal-diameter section 113 is smaller than the inner diameter of the first equal-diameter section 111; the first limiting step 114 is located at the junction of the third equal-diameter section 113 and the second equal-diameter section 112; a second limiting step 115 is formed at the junction of the first equal-diameter section 111 and the second equal-diameter section 112, and the large-diameter piston oil seal 24 can abut against the second limiting step 115 to form a limiting fit.

[0097] Through the setting of the second limiting step 115, once the front end of the large-diameter piston push sleeve 22 abuts against the first limiting step 114 to form a limiting fit, the large-diameter piston oil seal 24 also abuts against the second limiting step 115 to form a limiting fit, reducing the impact of the internal pressure on the large-diameter piston oil seal 24 and making its shape more stable. Therefore, the first limiting step 114 and the second limiting step 115 in this embodiment provide limiting effects respectively. Especially during the process that the small-diameter piston push rod 21 moves forward alone relative to the large-diameter piston push sleeve 22, the large-diameter piston oil seal 24 and the large-diameter piston push rod can each maintain a stable static state.

[0098] The above is only a preferred embodiment of the present invention, and does not impose any limitations on the present invention. Any simple modification, change, and equivalent structural change made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A brake pump with a double-stage oil pushing stroke to prevent sudden pressure relief, comprising: A brake pump body (1) is provided with a piston chamber (11) and an oil storage chamber (12), wherein the piston chamber (11) and the oil storage chamber (12) are filled with brake oil, and the oil storage chamber (12) is connected to the piston chamber (11) through an oil return hole (13); A piston oil pushing assembly (2), which is located in the piston cavity (11); A brake handle (3) is rotatably matched with a brake pump body (1) via a pivot mechanism (31), and the brake handle (3) is transmission matched with a piston oil pushing assembly (2) via a push rod assembly (32); An oil pipe assembly (4) connected to the brake cylinder body (1) and communicating with the piston chamber (11); Features: The piston oil pushing assembly (2) comprises a small-diameter piston push rod (21), a large-diameter piston push sleeve (22), a small-diameter piston oil seal (23), a large-diameter piston oil seal (24), a reset elastic member (25) and a boosting elastic member (26); The small-diameter piston push rod (21) is at least partially inserted into the large-diameter piston push sleeve (22), and a clearance fit is formed between the outer wall of the small-diameter piston push rod (21) and the inner wall of the large-diameter piston push sleeve (22); The boosting elastic member (26) is in contact between the rear end of the small-diameter piston push rod (21) and the rear end of the large-diameter piston push sleeve (22); The reset elastic member (25) abuts between the small-diameter piston push rod (21) and the inner wall of the piston chamber (11), and the reset elastic member (25) acts on the small-diameter piston push rod (21) so that the small-diameter piston push rod (21) always has a movement tendency to move backwards; The large-diameter piston oil seal (24) is arranged on the large-diameter piston push sleeve (22), the small-diameter piston push rod (21) is arranged on the small-diameter piston push rod (21), and the small-diameter piston oil seal (23) is located in front of the large-diameter piston oil seal (24); The piston chamber (11) comprises at least a first equal-diameter section (111) and a second equal-diameter section (112); the inner diameter of the first equal-diameter section (111) is larger than the inner diameter of the second equal-diameter section (112); the large-diameter piston oil seal (24) contacts the inner wall of the first equal-diameter section (111) and forms a sealing fit; the small-diameter piston oil seal (23) can contact the inner wall of the second equal-diameter section (112) and form a sealing fit; a first limiting step (114) is provided between the first equal-diameter section (111) and the second equal-diameter section (112); and the front end of the large-diameter piston push sleeve (22) can abut against the first limiting step (114) and form a limiting fit.

2. The brake upper pump with a double-stage oil pushing stroke for preventing sudden pressure release according to claim 1 is characterized in that: An oil replenishing hole (14) is also provided between the oil storage chamber (12) and the piston chamber (11), and the oil replenishing hole (14) is located behind the oil return hole (13). When the user squeezes the brake handle (3), the brake oil in the oil storage chamber (12) is replenished to the piston chamber (11) behind the large-diameter piston oil seal (24) through the oil replenishing hole (14); In the first stage (3b) when the user squeezes the brake handle (3), the large-diameter piston oil seal (24) is located behind the oil return hole (13), so that when the piston oil push assembly (2) moves forward, the small-diameter piston push rod (21) and the large-diameter piston push sleeve (22) move forward together, so that the large-diameter piston oil seal (24) transfers the brake oil in the piston chamber (11) to the oil storage chamber (12) through the oil return hole (13); In the second stage (3c) when the user squeezes the brake handle (3), the large-diameter piston oil seal (24) is located in front of the oil return hole (13), so that when the piston oil push assembly (2) moves forward, the small-diameter piston push rod (21) and the large-diameter piston push sleeve (22) move forward together, so that the large-diameter piston oil seal (24) and the small-diameter piston oil seal (23) together transport the brake oil in the piston chamber (11) to the brake pump through the oil pipe assembly (4); In the third stage (3d) when the user squeezes the brake handle (3), the front end of the large-diameter piston push sleeve (22) abuts against the first limit step (114) and stops moving forward, while the small-diameter piston push rod (21) continues to move forward, so that the small-diameter piston oil seal (23) transports the brake oil in the piston chamber (11) to the brake pump through the oil pipe assembly (4).

3. The brake upper pump with a double-stage oil pushing stroke for preventing sudden pressure release according to claim 1 is characterized in that: When the user squeezes the brake handle (3) in the first stage (3b) and the second stage (3c), the forward boosting force applied by the boosting elastic member (26) to the large-diameter piston push sleeve (22) is greater than the backward retreating force applied by the brake oil to the large-diameter piston push sleeve (22).

4. The brake upper pump with a double-stage oil pushing stroke for preventing sudden pressure release according to claim 1 is characterized in that: The large-diameter piston push sleeve (22) comprises a first supporting section (221), a first groove section (222) and a first accommodating section (223) which are arranged in sequence from back to front; The large-diameter piston push sleeve (22) has a through hole (224), the through hole (224) runs through the first supporting section (221), the first groove section (222) and the first accommodating section (223), and the small-diameter piston push rod (21) at least partially passes through the through hole (224); The front end of the assisting elastic member (26) abuts against the first supporting section (221); The large-diameter piston oil seal (24) is installed in the first groove section (222); The small-diameter piston oil seal (23) can be retracted into the first accommodating section (223) or / and extended out of the first accommodating section (223).

5. The brake upper pump with a double-stage oil pushing stroke for preventing sudden pressure release according to claim 4 is characterized in that: An accommodating chamber (2231) is provided in the first accommodating section (223), and the small-diameter piston oil seal (23) can be retracted into the accommodating chamber (2231) or / and extended out of the accommodating chamber (2231); In the first stage (3b) and the second stage (3c) when the user squeezes the brake handle (3), the small-diameter piston oil seal (23) retracts into the accommodating chamber (2231), and the small-diameter piston oil seal (23) contacts the inner wall of the accommodating chamber (2231) to form a sealing fit; In the third stage (3d) when the user squeezes the brake handle (3), the small-diameter piston oil seal (23) extends out of the accommodating cavity (2231).

6. The brake upper pump with a double-stage oil pushing stroke for preventing sudden pressure release according to claim 5 is characterized in that: A first flow channel groove (225) is provided on the inner wall of the through hole (224), and the piston chamber (11) behind the large-diameter piston push sleeve (22) is connected to the accommodating chamber (2231) through the first flow channel groove (225); A second flow channel (227) is provided on the outer wall of the first accommodating section (223); in the first stage (3b) and the second stage (3c) when the user squeezes the brake handle (3), the first equal-diameter section (111) is connected to the second equal-diameter section (112) via the second flow channel (227).

7. The brake upper pump with a double-stage oil pushing stroke for preventing sudden pressure release according to claim 5 is characterized in that: The inner diameter of the accommodating cavity (2231) is smaller than or equal to the inner diameter of the second equal-diameter section (112), and a circular arc chamfered portion (2232) is provided at the front end opening of the accommodating cavity (2231).

8. The brake upper pump with a double-stage oil pushing stroke for preventing sudden pressure release according to claim 1 is characterized in that: The small-diameter piston push rod (21) comprises a rod body (211), a second supporting section (212), a second groove section (213) and a third supporting section (214) which are sequentially arranged on the rod body (211) from the back to the front; The rear end of the resetting elastic member (25) abuts against the third supporting section (214); The small-diameter piston oil seal (23) is installed in the second groove section (213); The second supporting section (212) can abut against the large-diameter piston push sleeve (22) and form a rearward limiting stop fit.

9. The brake upper pump with a double-stage oil pushing stroke for preventing sudden pressure release according to claim 8, characterized in that: The small-diameter piston push rod (21) further includes a transmission joint (215); The front end of the transmission joint (215) is threadedly connected to the rod body (211) via a threaded structure (2152), and the effective matching length of the threaded structure (2152) is adjustable; The rear end of the transmission joint (215) has a transmission groove (2151), and the push rod assembly (32) extends into the transmission groove (2151), so that the push rod assembly (32) forms a transmission match with the rod body (211) through the transmission joint (215); A sealing ring (2153) is sleeved on the outer wall of the transmission joint (215), and the sealing ring (2153) contacts the inner wall of the first equal-diameter section (111), so that a sealing fit is formed between the outer wall of the transmission joint (215) and the inner wall of the first equal-diameter section (111).

10. The brake upper pump with a double-stage oil pushing stroke for preventing sudden pressure release according to claim 1, characterized in that: The front end of the first equal-diameter section (111) extends inward to form a third equal-diameter section (113), the inner diameter of the third equal-diameter section (113) is larger than the inner diameter of the second equal-diameter section (112), and the inner diameter of the third equal-diameter section (113) is smaller than the inner diameter of the first equal-diameter section (111); The first limiting step (114) is located at the junction of the third equal-diameter section (113) and the second equal-diameter section (112); A second limiting step (115) is formed at the junction of the first equal-diameter section (111) and the second equal-diameter section (112), and the large-diameter piston oil seal (24) can abut against the second limiting step (115) to form a limiting fit.

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