Brake discs

Abstract

Provided is a brake disc having excellent cracking resistance. A brake disc 1 according to an aspect of the present invention comprises a plurality of drain recesses 3, each formed in an area against which a brake pad is abutted, wherein the angle of a shoulder portion 31 formed by a friction surface against which the brake pad is abutted and an inner peripheral surface of an opening of the drain recess 3 is an acute angle.

Description

[Technical field]

[0001] The present invention relates to a brake disc. [Background technology]

[0002] For example, disc brake devices are widely used as braking devices for vehicles, in which a brake disc that rotates together with a rotating shaft is sandwiched between brake pads to stop the rotation of the rotating shaft by frictional force. In such disc brake devices, if foreign matter such as water or dust gets between the brake disc and the brake pads, the braking force decreases, so a technology is known in which a drain hole is provided in the brake disc to remove such foreign matter (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-38030 A Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, motorcycle brake discs are made of special stainless steels having high strength, but in some cases, brake discs are made of relatively inexpensive carbon steel. If a drain hole is formed in the brake disc, thermal stress tends to concentrate, and cracks may occur starting from the drain hole. Therefore, the present invention aims to provide a brake disc with excellent crack resistance. [Means for solving the problem]

[0005] A brake disc according to one embodiment of the present invention is a brake disc having a plurality of water-draining recesses formed in an area where the brake pads contact, and the shoulder angle formed by the friction surface against which the brake pads contact and the inner surface of the opening of the water-draining recesses is an obtuse angle.

[0006] In the above brake disc, the angle of the shoulder may be greater than or equal to 135° and less than or equal to 175°.

[0007] In the above-mentioned brake disc, the water drainage recess may be conical.

[0008] In the above-described brake disc, the water drainage recess may be formed at a different position on one of the friction surfaces from that on the other of the friction surfaces.

[0009] In the above-described brake disc, the opening diameter of the water drainage recess may be equal to or greater than 7 mm and equal to or less than 15 mm.

[0010] The brake discs described above may be made from carbon steel, cast iron or stainless steel having a tensile strength of up to 800 MPa.

[0011] The brake discs described above may be made from carbon steel or cast iron. Effect of the Invention

[0012] According to the present invention, a brake disc having excellent crack resistance can be provided. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a front view of a brake disc according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a partial cross-sectional view of the brake disc of FIG. 1. [Diagram 3] FIG. 6 is a partial cross-sectional view of a brake disc according to a second embodiment of the present invention. [Figure 4] FIG. 11 is a partial cross-sectional view of a brake disc according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a front view (axial view) of a brake disc 1 according to a first embodiment of the present invention. Fig. 2 is a partial cross-sectional view of the brake disc 1 of Fig. 1.

[0015] The brake disc 1 is used in a disc brake device. Specifically, the brake disc 1 is formed in a flat, annular plate shape that is doughnut-shaped when viewed from the front, and is fixed to a rotating shaft (not shown) (typically an axle) so as to rotate together with the rotating shaft, and is sandwiched between brake pads (not shown) to brake the rotating shaft. In other words, both sides of the brake disc 1 form friction surfaces 11 and 12 against which the brake pads come into contact.

[0016] When viewed from the front, the brake disc 1 has a number of mounting holes 2 on its inner circumference for fixing it to a hub provided on a rotating shaft, and a number of water-draining recesses 3 formed in the area outside the mounting holes 2 where the brake pads abut.

[0017] The thickness of the brake disc 1 depends on the output of the rotating shaft to be braked, and can be, for example, 2 mm or more and 60 mm or less. The inner diameter of the brake disc 1 is selected according to the hub provided on the rotating shaft, and can be, for example, 40 mm or more and 300 mm or less. The outer diameter of the brake disc 1 is selected so as to ensure the contact area of ​​the brake pads required to obtain the required braking force within the installation space of the disc brake device, and can be, for example, 100 mm or more and 400 mm or less.

[0018] The brake disc 1 can be formed from, for example, carbon steel, cast iron, stainless steel, etc., but the effect of improving crack resistance by the present invention is remarkable when the brake disc 1 is formed from a material having a mechanical property of tensile strength of 800 MPa or less, such as relatively inexpensive structural carbon steel, typically mechanical structural carbon steel such as S50C, S53C, S55C, S58C (JIS-G4051:2016), or cast iron, typically gray cast iron (JIS-G5501:1995), spheroidal graphite cast iron (JIS-G5502:2007), etc.

[0019] The mounting holes 2 are usually used to fix the brake disc 1 to a hub by bolts. Therefore, the diameter and number of the mounting holes 2 are selected according to the required braking torque. In general, the mounting holes 2 are formed equidistant from the center of the brake disc 1 and at equal intervals in the circumferential direction.

[0020] The water-draining recess 3 has a water-draining effect that drains water adhering to the surface of the brake disc 1 and a cleaning effect that smoothes out the rough surface of the brake pad caused by dust and other particles trapped therein, thereby reducing the frictional force generated between the brake disc 1 and the brake pad and suppressing the occurrence of abnormal wear.

[0021] The drainage recesses 3 are each formed in a circular shape when viewed from the front. The drainage recesses 3 are preferably formed at different positions on one friction surface 11 and the other friction surface 12. This allows the positions at which stress is concentrated to differ between the friction surfaces 11 and 12, thereby suppressing the maximum value of thermal stress. The drainage recesses 3 on one friction surface 11 and the drainage recesses 3 on the other friction surface 12 are preferably formed in the same pattern with an angle shifted in the circumferential direction in order to equalize the drainage effect on both sides.

[0022] The brake disc 1 may have a plurality of groups of water drainage recesses 3 at different distances from the center. In this embodiment, a first group of five water drainage recesses 3 formed at a first distance from the center and at equal intervals in the circumferential direction and a second group of five water drainage recesses 3 formed at a second distance from the center and at equal intervals in the circumferential direction are formed on each of the friction surfaces 11 and 12. By providing the water drainage recesses 3 at different distances from the center in this manner, the water drainage effect can be improved.

[0023] The diameter of the water drain recess 3 expands at least at the opening toward the friction surfaces 11, 12 against which the brake pads abut, and the angle α of the shoulder 31 formed by the friction surfaces 11, 12 against which the brake pads abut and the inner peripheral surface of the opening of the water drain recess 3 is an obtuse angle. This reduces stress concentration on the shoulder 31, thereby suppressing the maximum value of thermal stress caused by frictional heat. Note that the inner peripheral surface of the opening does not mean a small surface formed by fine chamfering, but means a surface having a width of 1 mm or more that substantially defines the shape.

[0024] In this embodiment, the drainage recess 3 is formed in a conical shape, and the inclination angle of the inner peripheral surface is constant overall. In this way, by forming the drainage recess 3 in a conical shape, the maximum value of thermal stress can be effectively reduced. In addition, the conical drainage recess 3 is easy to form. Specifically, the conical drainage recess 3 can be easily formed in a single step by drilling.

[0025] The lower limit of the angle α of the shoulder portion 31 is preferably 135°, more preferably 155°. On the other hand, the upper limit of the angle α of the shoulder portion 31 is preferably 175°, more preferably 165°. By setting the angle α of the shoulder portion 31 to the lower limit or more, the maximum value of the thermal stress can be reduced. Furthermore, by setting the angle α of the shoulder portion 31 to the upper limit or less, the volume of the water draining recess 3 can be secured and a sufficient water draining effect can be obtained. Furthermore, by reducing the angle α of the shoulder portion 31, the formation of the water draining recess 3 becomes easy. For example, since the tip angle of a drill is a maximum of about 140°, a water draining recess 3 that forms a shoulder portion 31 having an angle α of 160° or less can be easily formed using a drill.

[0026] The lower limit of the opening diameter of the water drainage recess 3 is preferably 7 mm, and more preferably 8 mm. Meanwhile, the upper limit of the opening diameter of the water drainage recess 3 is preferably 15 mm, and more preferably 12 mm. By making the opening diameter of the water drainage recess 3 equal to or greater than the lower limit, the volume of the water drainage recess 3 is ensured, and an effective water draining effect is obtained. Also, by making the opening diameter of the water drainage recess 3 equal to or less than the upper limit, the frictional force between the brake disc 1 and the brake pad can be stabilized.

[0027] 3 is a partial cross-sectional view of a brake disc 1A according to a second embodiment of the present invention. In the following description, descriptions that overlap with the embodiments described above may be omitted.

[0028] The brake disc 1A has a plurality of drainage recesses 3A formed in the area where the brake pads come into contact. The brake disc 1A in Fig. 3 differs from the brake disc 1 in Figs. 1 and 2 only in the shape of each of the drainage recesses 3A.

[0029] The water drainage recess 3A in this embodiment has a shape like a part of a sphere cut out. More specifically, the inner surface of the water drainage recess 3A is spherical with the center located outside and larger than the friction surfaces 11 and 12. Such a water drainage recess 3A can be formed by, for example, a ball end mill. When the brake disc 1A has a small overall thickness, forming such a spherical water drainage recess 3A can prevent a decrease in strength caused by the thickness being too small in some places.

[0030] Fig. 4 is a partial cross-sectional view of a brake disc 1B according to a third embodiment of the present invention. The brake disc 1B has a plurality of water drainage recesses 3B formed in an area where the brake pads contact. The brake disc 1B in Fig. 4 differs only in the shape of each water drainage recess 3B from the shape of the water drainage recesses 3 of the brake disc 1 in Figs. 1 and 2.

[0031] The drainage recess 3B of this embodiment is a cylindrical recess whose opening is expanded into a cone shape. This drainage recess 3B can be formed by combining a drill to form a cone-shaped opening and a square end mill to form a cylindrical recess. The drainage recess 3B of this embodiment can be made larger in volume than the drainage recess 3 of FIG. 1, so that the drainage effect can be increased while suppressing the maximum value of thermal stress.

[0032] Although the brake discs according to the embodiments of the present invention have been described above, the configuration and effects of the brake discs according to the present invention are not limited to those described above. For example, the brake discs according to the present invention may be one in which, for example, a cup-shaped hub is integrally connected, or may have other structures, such as a notch on the outer periphery. EXAMPLES

[0033] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0034] For brake disc models 1 to 6, which were made of S50C and had a thickness of 7.5 mm, an inner diameter of 155 mm, and an outer diameter of 262 mm, a simulation was conducted to determine the maximum value of thermal stress acting due to frictional heat generated by pressing a brake pad against the friction surface.

[0035] Model 1 had a drainage recess with an opening diameter of 10 mm and a shoulder angle of 175°. Model 2 had a drainage recess with an opening diameter of 10 mm and a shoulder angle of 160°. Model 3 had a drainage recess with an opening diameter of 10 mm and a shoulder angle of 135°. Model 4 had a cylindrical non-through hole with a diameter of 10 mm. Model 5 had a through hole with a diameter of 10 mm. Model 6 had a through hole with a diameter of 12 mm.

[0036] The maximum thermal stress of model 1 was 450MPa. The maximum thermal stress of model 2 was 598MPa. The maximum thermal stress of model 3 was 798MPa. The maximum thermal stress of model 4 was 893MPa. The maximum thermal stress of model 5 was 989MPa. The maximum thermal stress of model 6 was 1013MPa.

[0037] From the above results, it was confirmed that brake discs with water-draining recesses having a large shoulder angle have a small maximum thermal stress and excellent crack resistance. [Explanation of symbols]

[0038] 1,1A,1B Brake disc 11,12 Friction surface 2 Mounting holes 3,3A,3B Drain recess 31 Shoulder

Claims

1. A brake disc having a plurality of water drainage recesses each formed in a circular shape in a front view in an area where the brake pads contact, A brake disc, wherein a shoulder angle formed by a friction surface against which the brake pad contacts and an inner peripheral surface of an opening of the water drain recess is 155° or more and 175° or less.

2. A brake disc having a plurality of conical drainage recesses formed in an area where the brake pads contact, A brake disc, wherein a shoulder angle formed by a friction surface against which the brake pad contacts and an inner peripheral surface of an opening of the water drain recess is 155° or more and 175° or less.

3. 3. The brake disc according to claim 1, wherein the water drainage recess is formed at a different position on one of the friction surfaces from the other of the friction surfaces.

4. 4. The brake disc according to claim 1, wherein an opening diameter of the water drainage recess is 7 mm or more and 15 mm or less.

5. 5. A brake disc according to claim 1, which is made of carbon steel, cast iron or stainless steel having a tensile strength of 800 MPa or less.

6. A brake disc according to any one of claims 1 to 5, made from carbon steel or cast iron.

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