Brake master cylinder

Abstract

The utility model provides a brake master cylinder which can restrain curl and cracking of a cup component. A brake master cylinder (1) is provided with: a cylinder body (11) in which liquid chambers (14, 15) are formed; pistons (12, 13) capable of advancing and retreating within the cylinder (11) according to the operation of the brake pedal (2); and cup members (18, 19, 22, 23) that seal the space between the pistons (12, 13) and the cylinder (11) and that can slide with respect to the inner peripheral surface of the cylinder (11) as the pistons (12, 13) move forward and backward. At least the sliding surfaces of the cup members (18, 19, 22, 23) that slide with respect to the inner peripheral surface of the cylinder (11) are formed from a resin material in which the frictional force received by the cup members (18, 19, 22, 23) and the reactive force of the cup members (18, 19, 22, 23) satisfy the relationship (reactive force / frictional force) > 1. The surface roughness Rz of the inner peripheral surface of the cylinder (11) is 2.0 [mu] m or less.

Description

Technical Field

[0001] This utility model relates to a brake master cylinder, and more particularly to a brake master cylinder having a cup component. Background Technology

[0002] A brake master cylinder is a device used in a vehicle's braking system that converts the operation of the brake pedal into hydraulic pressure to brake the wheels. A brake master cylinder comprises: a cylinder body made of iron or aluminum; a piston that moves forward and backward within the cylinder body according to the operation of the brake pedal; and a cup component that slides relative to the inner circumferential surface of the cylinder body as the piston moves forward and backward, and seals the piston and cylinder body.

[0003] Cup components are required to have high strength, excellent durability, and a good seal. Therefore, various technologies have been proposed. For example, Patent Document 1 discloses a cup component in which the sliding surface that slides relative to the inner circumferential surface of the cylinder is made of rubber, while other parts are made of materials different from rubber, such as resin or metal.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2007-271073

[0005] However, when rubber materials are used for the sliding surfaces, the following problems arise, such as the tendency for the cup component to curl and crack. Specifically, rubber materials have a high coefficient of friction and a low modulus of elasticity compared to metals like iron and aluminum. When applied to the cup component, the frictional force experienced by the cup component due to sliding relative to the inner circumferential surface of the metal cylinder is greater than the reaction force (also called repulsive force or restoring force) caused by deformation. This leads to curling of the cup component. Furthermore, if the inner circumferential surface of the cylinder has a high roughness, the frictional force experienced by the cup component is even greater, potentially leading to cracking. Utility Model Content

[0006] This invention was developed to solve such a technical problem, and its purpose is to provide a brake master cylinder that can suppress the curling and cracking of the cup component.

[0007] The brake master cylinder of this invention comprises: a cylinder body having a liquid chamber formed therein; a piston capable of moving forward and backward within the cylinder body according to the operation of the brake pedal; and a cup member sealing the piston and the cylinder body, and capable of sliding relative to the inner circumferential surface of the cylinder body as the piston moves forward and backward. The invention is characterized in that at least the sliding surface of the cup member that slides relative to the inner circumferential surface of the cylinder body is formed of a resin material in which the frictional force borne by the cup member during sliding and the reaction force of the cup member satisfy the relationship (reaction force / frictional force) > 1, and the surface roughness Rz of the inner circumferential surface of the cylinder body is 2.0 μm or less.

[0008] In the brake master cylinder of this invention, at least the sliding surface of the cup component that slides relative to the inner circumferential surface of the cylinder body is formed of a resin material in which the frictional force borne by the cup component and the reaction force of the cup component satisfy the relationship (reaction force / frictional force) > 1. This increases the reaction force of the cup component and reduces the frictional force, thus suppressing the curling of the cup component. Furthermore, the surface roughness Rz of the inner circumferential surface of the cylinder body is 2.0 μm or less, thus also suppressing the cracking of the cup component.

[0009] According to this invention, it is possible to suppress the curling and cracking of cup components. Attached Figure Description

[0010] Figure 1 This is a simplified cross-sectional view of the brake master cylinder in the embodiment.

[0011] Figure 2 (a) is a graph showing the ratio of reaction force to friction force for each resin material. Figure 2 Figure (b) shows the relationship between the surface roughness and wear of the inner circumferential surface of the cylinder body for PTFE and PA6. Figure 2 (c) is a graph showing the survey results of the wear amount of each resin material.

[0012] Figure 3 (a) is a schematic perspective view used to illustrate the reciprocating friction test. Figure 3 (b) is a schematic perspective view used to illustrate the measurement of wear.

[0013] Explanation of reference numerals in the attached figures

[0014] 1…Master cylinder; 2…Brake pedal; 3…Piston rod; 11…Cylinder body; 11a…Bottom; 12…First piston; 13…Second piston; 14…First fluid chamber; 15…Second fluid chamber; 16…First spring; 17…Second spring; 18…First cup component; 19…Second cup component; 20…First atmospheric pressure chamber; 21…First inlet; 22…Third cup component; 23…Fourth cup component; 24…Second atmospheric pressure chamber; 25…Second inlet; 26…First outlet; 27…Second outlet. Detailed Implementation

[0015] Figure 1 This is a simplified cross-sectional view showing the brake master cylinder of the embodiment. In this embodiment, the brake master cylinder 1 is used in the vehicle's braking system as a device that converts the operation of the brake pedal 2 into hydraulic pressure to brake the wheels. Figure 1As shown, the brake master cylinder 1 includes: a cylinder body 11, in which liquid chambers (a first liquid chamber 14 and a second liquid chamber 15) are formed; a piston (a first piston 12 and a second piston 13) is disposed inside the cylinder body 11 and is capable of moving forward and backward along the axial direction of the cylinder body 11; and cup members (a first cup member 18, a second cup member 19, a third cup member 22 and a fourth cup member 23) seal the piston and the cylinder body 11 and are capable of sliding relative to the inner circumferential surface of the cylinder body 11 as the piston moves forward and backward.

[0016] The cylinder body 11 is made of iron or aluminum and is a bottomed cylindrical shape. That is, the entire cylinder body 11, including the inner circumferential surface, is made of iron or aluminum. The surface roughness Rz of the inner circumferential surface of the cylinder body 11 is less than 2.0 μm.

[0017] The first piston 12 is formed into a generally cylindrical shape from a metal material such as iron or aluminum, and is slidably housed inside the cylinder body 11. A recess 12a is formed at one end of the first piston 12, and a piston rod 3 connected to the brake pedal 2 is pressed into the recess 12a. The second piston 13 is formed into a generally cylindrical shape from a metal material such as iron or aluminum, and is slidably housed inside the cylinder body 11. Furthermore, the first piston 12 and the second piston 13 are arranged in a row along the axial direction of the cylinder body 11 in a coaxial manner.

[0018] A first liquid chamber 14 is formed between the first piston 12 and the second piston 13, and a second liquid chamber 15 is formed between the second piston 13 and the bottom 11a of the cylinder body 11. Additionally, a first spring 16 is disposed between the first piston 12 and the second piston 13, and this first spring 16 exerts a force on the first piston 12 and the second piston 13 in a direction of separation. A second spring 17 is disposed between the second piston 13 and the bottom 11a of the cylinder body 11, and this second spring 17 exerts a force on the second piston 13 towards the first piston 12.

[0019] Two annular peripheral grooves are formed on the outer peripheral wall of the first piston 12 at a predetermined distance. A first cup component 18 is embedded in one of the two peripheral grooves (the one closer to the piston rod 3), and a second cup component 19 is embedded in the other (the one closer to the first liquid chamber 14). The first cup component 18 and the second cup component 19 are cup-shaped sealing rings made of resin material. The first cup component 18 and the second cup component 19 are configured to seal between the first piston 12 and the cylinder 11, and are capable of sliding relative to the inner peripheral surface of the cylinder 11 as the first piston 12 moves forward and backward.

[0020] The first cup component 18 and the second cup component 19 are configured such that their respective openings face the bottom 11a of the cylinder body 11. Furthermore, inside the cylinder body 11, a first atmospheric pressure chamber 20 is formed between the first cup component 18 and the second cup component 19. The first atmospheric pressure chamber 20 communicates with a reservoir (not shown) for storing brake fluid via a first inlet 21 provided on the wall of the cylinder body 11.

[0021] Two annular peripheral grooves are also formed on the outer peripheral wall of the second piston 13 at a predetermined distance. A third cup component 22 is embedded in one of the two peripheral grooves (the one closer to the first liquid chamber 14), and a fourth cup component 23 is embedded in the other (the one closer to the second liquid chamber 15). The third cup component 22 and the fourth cup component 23 are cup-shaped sealing rings made of resin material. The third cup component 22 and the fourth cup component 23 are configured to seal between the second piston 13 and the cylinder 11, and are capable of sliding relative to the inner peripheral surface of the cylinder 11 as the second piston 13 moves forward and backward.

[0022] like Figure 1 As shown, the third cup component 22 is configured with its opening facing the first piston 12. On the other hand, the fourth cup component 23 is configured with its opening facing the bottom 11a of the cylinder 11. Furthermore, inside the cylinder 11, a second atmospheric pressure chamber 24 is formed between the third cup component 22 and the fourth cup component 23. The second atmospheric pressure chamber 24 communicates with a reservoir for storing brake fluid via a second inlet 25 provided on the wall of the cylinder 11.

[0023] Furthermore, a first output port 26 communicating with the first liquid chamber 14 and a second output port 27 communicating with the second liquid chamber 15 are respectively provided on the wall of the cylinder body 11.

[0024] In this embodiment, at least the sliding surfaces of each cup component (first cup component 18, second cup component 19, third cup component 22, and fourth cup component 23) that slide relative to the inner circumferential surface of the cylinder 11 are formed of a resin material in which the frictional force borne by each cup component during sliding and the reaction force of each cup component satisfy the relationship (reaction force / frictional force) > 1. Here, an example is given. Figure 1 The second cup component 19 is shown in the enlarged cross-sectional view for explanation, but the first cup component 18, the third cup component 22 and the fourth cup component 23 are the same as the second cup component 19, so repeated descriptions are omitted.

[0025] like Figure 1As shown in the enlarged cross-sectional view, the second cup component 19 has a sliding surface 19a that slides relative to the inner circumferential surface of the cylinder 11. The sliding surface 19a may be only the portion of the outer circumferential surface of the second cup component 19 that contacts the inner circumferential surface of the cylinder 11, or it may be the entire outer circumferential surface of the second cup component 19 including the contact portion. Moreover, the sliding surface 19a is formed of a resin material in which the frictional force and reaction force generated when the second cup component 19 slides relative to the inner circumferential surface of the cylinder 11 satisfy the relationship (reaction force / frictional force) > 1.

[0026] For example, when the first piston 12 moves in the direction indicated by arrow F1, the second cup component 19 moves in the same direction as the first piston 12. At this time, the sliding surface 19a experiences a frictional force F2 in the opposite direction to the direction of movement, and also generates a reaction force F3 in the second cup component 19 due to the elastic deformation of the second cup component 19. Moreover, it is preferable that the sliding surface 19a is formed of a resin material that satisfies the relationship (F3 / F2) > 1. Examples of such resin materials include PA46 (polyamide 46), PA6 (polyamide 6), PA66 (polyamide 66), POM (polyacetal), PBT (polybutylene terephthalate), PPS (polyphenylene sulfide), and PEEK (polyether ether ketone).

[0027] The following describes the process of completing this utility model.

[0028] To suppress the curling of the cup component, the inventors of this application focused on resin materials with a lower coefficient of friction and a higher elastic modulus compared to rubber components. PA46, PA6, PA66, POM, PTFE (polytetrafluoroethylene), PBT, PPS, LCP (liquid crystal polymer), and PEEK were selected as resin materials, and EPDEM rubber (ethylene propylene diene monomer rubber) was selected as the existing rubber component. The coefficient of friction and elastic modulus of each component were measured, and the measurement results are summarized in Table 1.

[0029] The coefficient of friction is determined by... Figure 3 The test results were obtained from the reciprocating friction test shown in (a). Specifically, as... Figure 3 As shown in (a), firstly, a flat plate made of the aforementioned materials is constructed. A container is then made with this plate as its bottom, and brake fluid is placed inside the container. Next, an iron disc is placed inside the brake fluid, and under a specified load applied to the disc, as shown... Figure 3 The disc was slid back and forth across the plate surface as indicated by the arrow in (a) to determine the coefficient of friction of each material. In the measurement, SH-H brake fluid was used, the load was 30 N, the amplitude was 14 mm, the frequency was 1.2 Hz, and the duration was 1800 s. The measurement was conducted at room temperature.

[0030] On the other hand, the elastic modulus is determined by conducting a tensile test.

[0031] [Table 1]

[0032]

[0033] As shown in Table 1, it can be seen that the coefficients of friction of each resin material are smaller compared to EPDEM rubber. As a result, PTFE has the lowest coefficient of friction among the resin materials. Furthermore, it can be seen that the elastic modulus of each resin component is also larger compared to EPDEM rubber. As a result, PTFE has the lowest elastic modulus among the resin components. Moreover, with a larger elastic modulus, the reaction force of the cup component due to deformation increases.

[0034] Next, the inventors of this application, for PA46, PA6, PA66, POM, PTFE, PBT, PPS, LCP, and PEEK, applied the same conditions (resin ε = 0.0001, resin area = 0.4 N / m²). cm 2 The vertical resistance (20N) was investigated to determine whether the relationship (reaction force / friction force) > 1 was satisfied, and the results are summarized in Table 2. Figure 2 In (a), in addition, for comparison, the frictional and reaction forces associated with EPDEM rubber were also investigated.

[0035] [Table 2]

[0036] Material Name Friction [N] Reaction force [N] Slope (reaction force / friction force) PA46 11.98 13.2 1.10 PA6 6.06 12 1.98 PA66 8.96 11.6 1.29 POM 10 10.8 1.08 PTFE 2.56 2 0.78 PBT 7.46 10.52 1.41 PPS 10.78 15.2 1.41 LCP 11.46 6.4 0.56 PEEK 9.04 16 1.77

[0037] As shown in Table 2 and Figure 2 As shown in (a), it can be seen that PA46, PA6, PA66, POM, PBT, PPS, and PEEK among the investigated resin materials all satisfy the relationship (reaction force / friction force) > 1. Therefore, it is believed that by using these resin materials on the sliding surface, the friction force borne by the cup component is reduced, and the reaction force of the cup component caused by elasticity is increased, thereby suppressing the curling of the cup component.

[0038] On the other hand, to suppress cracking of the cup component, it is known to use a resin material with a higher tensile strength than rubber. For example, the tensile strength of rubber is 150–200 kg / cm². 2 The tensile strength of resin materials is 300–1000 kg / cm². 2 .

[0039] Therefore, the inventors of this application measured the tensile strength of PA46, PA6, PA66, POM, PTFE, PBT, PPS, LCP, and PEEK respectively, and summarized the results in Table 1 above. Furthermore, the inventors of this application compared the measured tensile strength of each resin material with the tensile strength of rubber cup components described in Japanese Patent Application Publication No. 60-149645 (e.g., Tables 2 and 3).

[0040] According to Japanese Patent Application Publication No. 60-149645, this can be understood as follows: when the cup component is made of rubber material, if its tensile strength is 180 kg / cm², 2 The above measures can suppress the formation of cracks in the cup components. In contrast, as shown in Table 1, the tensile strengths of PA46, PA6, PA66, POM, PTFE, PBT, PPS, LCP, and PEEK all exceed 180 kg / cm². 2 Therefore, it is believed that these resin materials are resistant to cracking, and by using these resin materials on sliding surfaces, cracking can be prevented.

[0041] Furthermore, a higher tensile strength results in less wear on the material (in other words, higher wear resistance). Therefore, the inventors of this application measured the wear of PTFE and PA6 at ring roughness Rz values ​​of 1 μm, 2 μm, and 3 μm, respectively.

[0042] Specifically, such as Figure 3 As shown in (b), flat plates made of PTFE or PA6 were fabricated. An iron (S45C) ring was placed on the surface of each plate. The ring was rotated and slid in the direction indicated by the arrow under a specified load. The wear amount of each resin material was measured, and the results are summarized in Table 3. Figure 2 (b) Here, the ring is conceived as a cylinder. Furthermore, in the measurement, the load was 1000 N, the sliding speed was 250 rpm, and the time was 1800 s. Additionally, the test was conducted at room temperature.

[0043] [Table 3]

[0044]

[0045] From Table 3 and Figure 2 As shown in (b), in the case of PA6, the wear is less if the ring roughness Rz is below 2.0 μm. On the other hand, it can be seen that PTFE with the same ring roughness has a greater wear than PA6.

[0046] Furthermore, to suppress leakage caused by poor sealing of the cup components, it is known to use resin materials with low abrasion. Therefore, the inventors of this application have developed resins based on PA46, PA6, PA66, POM, PBT, PPS, and PEEK. Figure 3 The wear amount was measured using the method shown in (b), and the results were summarized in Table 1 above. Figure 2 In (c), the load was 1000 N, the sliding speed was 250 rpm, and the time was 1800 s. The test was conducted at room temperature.

[0047] As shown in Table 1 and Figure 2 As shown in (c), it can be seen that among PA46, PA6, PA66, POM, PBT, PPS, and PEEK, PA6, PA66, POM, PPS, and PEEK exhibit relatively low wear, especially PEEK, which shows the least wear. Therefore, it is believed that using these resin materials on the sliding surface can enhance the wear resistance of the cup component and suppress leakage.

[0048] Based on the above measurement results, the inventors of this application discovered that if PA6, PA66, POM, PPS and PEEK are used on the sliding surface of the cup component, the curling and cracking of the cup component can be suppressed, thereby preventing leakage caused by poor sealing, thus completing this utility model.

[0049] In the brake master cylinder 1 of this embodiment, preferably, the sliding surfaces of at least the cup components (first cup component 18, second cup component 19, third cup component 22, and fourth cup component 23) that slide relative to the inner circumferential surface of the cylinder body 11 are formed of a resin material in which the frictional force borne by the cup component and the reaction force of the cup component satisfy the relationship (reaction force / frictional force) > 1 during sliding. Preferably, such resin materials are PA6, PA66, POM, PPS, and PEEK.

[0050] This increases the reaction force of the cup component and reduces friction, thus suppressing the curling of the cup component. Furthermore, the surface roughness Rz of the inner circumferential surface of the cylinder 11 is less than 2.0 μm, thus suppressing cracking of the cup component. Moreover, by using a resin material with low wear, the wear resistance of the cup component is enhanced, thus preventing leakage due to poor sealing.

Claims

1. A brake master cylinder comprising: a cylinder body having a liquid chamber formed therein; a piston capable of moving forward and backward within the cylinder body according to operation of a brake pedal; and a cup member sealing the piston and the cylinder body, and capable of sliding relative to the inner circumferential surface of the cylinder body as the piston moves forward and backward, characterized in that, At least the sliding surface of the cup component that slides relative to the inner circumferential surface of the cylinder is formed of a resin material in which the frictional force borne by the cup component during sliding and the reaction force of the cup component satisfy the relationship of reaction force / frictional force > 1. The surface roughness Rz of the inner circumferential surface of the cylinder block is less than 2.0 μm.

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