Boronized brake disc rotor

Abstract

A brake rotor, a brake system including the brake rotor, and a method of boronizing the brake rotor, where the brake rotor includes a rotor body including a brake face. The rotor body includes an iron alloy, and the braking face includes a layer of Fe2B phase in the braking face. The brake system includes a brake rotor and a brake pad engageable with a brake surface. The method includes boronizing the braking surface and forming a Fe2B phase on the braking surface and cooling the rotor body to an ambient temperature.

Description

Technical Field

[0001] The present disclosure relates to the automotive field, and more particularly, to a boronized brake disc rotor. Background Art

[0002] Vehicle brakes use friction to stop the wheels from turning and bring the vehicle to a stop. When the brake pedal is depressed or the brakes are otherwise actuated, hydraulic pressure is applied to one or more brake pads associated with a given wheel. The brake pads press against a rotor connected to each wheel, causing the wheel's rotation to slow and eventually stop. During this process, kinetic energy is converted to heat, which can result in relatively high local temperatures on the rotor. Contact between the brake pads and rotor can cause material loss in the pads and rotors, and the formation of particulates. Depending on the composition, as some rotors wear, they can develop track patterns or grooves in the brake pads or rotors.

[0003] So while brake pads and disc rotors have served their intended purpose, there is still room for further advancement. Summary of the invention

[0004] According to several aspects, the present disclosure is directed to a brake rotor. The brake rotor includes a rotor body including a braking surface. The rotor body includes an iron alloy, and the braking surface includes a layer of an iron boride phase (Fe2B phase) having a chemical formula of Fe2B in the braking surface.

[0005] In the above-described embodiments, the iron alloy includes grey cast iron.

[0006] In any of the above embodiments, the layer further comprises an iron boride phase (FeB phase) having a chemical formula of FeB. Optionally, the iron boride phase in the layer consists of a Fe2B phase.

[0007] In any of the above embodiments, the hardness of the braking surface is in the range of 1500 to 2000 Vickers hardness (HV).

[0008] In any of the above embodiments, the layer has a depth in the range of 0.02 mm to 2.5 mm.

[0009] In any of the above embodiments, the rotor body is a disk and includes a central hub and an annulus defined around the central hub, wherein the annulus includes a braking surface. In further embodiments, the annulus includes cast iron. In further embodiments, the central hub is formed of a second material.

[0010] In any of the above embodiments, the rotor body is a drum including a central hub and a wall extending from the central hub, wherein an inner surface of the wall includes the braking surface.

[0011] According to several further aspects, the present disclosure is directed to a braking system. The braking system includes a brake rotor according to any of the above embodiments. The brake rotor includes a rotor body having a braking surface. The rotor body includes an iron alloy and the braking surface includes a layer of an iron boride phase (Fe2B phase) having a chemical formula of Fe2B. The braking system also includes a brake pad engageable with the braking surface.

[0012] In the above-mentioned embodiment, the layer further comprises iron boride having a chemical formula of FeB (FeB phase). Optionally, the iron boride phase in the layer consists of a Fe2B phase.

[0013] In any of the above embodiments, the hardness of the braking surface is in the range of 1500 to 2000 Vickers hardness (HV).

[0014] In any of the above embodiments, the ferrous alloy includes gray cast iron.

[0015] In any above embodiment, the rotor body is a disc.Alternatively, in any above embodiment, the rotor body is a drum.

[0016] In any of the above embodiments, the brake system further includes a brake actuator, a master cylinder connected to the brake actuator, and a piston connected to the brake pad and the master cylinder, wherein the piston is connected to the master cylinder via one or more hydraulic lines.

[0017] According to several further aspects, the present disclosure is directed to a method of forming a brake disc rotor. The method includes removing contaminants from a brake rotor. The brake rotor includes a rotor body having a braking surface. The rotor body includes an iron alloy. The method also includes boriding the braking surface and forming a layer of an iron boride phase (Fe2B phase) having a chemical formula of Fe2B on the braking surface, and cooling the rotor body to ambient temperature.

[0018] In the above embodiments, boriding includes contacting the ferrous alloy with a boron-containing composition, wherein the ferrous alloy is exposed to a temperature in the range of 700°C to 1000°C.

[0019] In a further embodiment of the above, the method includes mechanically finishing the braking surface after boriding.

[0020] In any of the above embodiments, the layer further includes an iron boride phase (FeB phase) having a chemical formula of FeB. In a further embodiment, the method includes removing the FeB phase from the braking surface.

[0021] In any of the above embodiments, the brake rotor further includes a central hub and an annulus defined about the central hub, wherein the annulus includes the braking surface. The method further includes assembling the central hub with the annulus. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0023] Figure 1 is a schematic diagram of a vehicle including a braking system according to an embodiment of the present disclosure.

[0024] Figure 2 is a diagram of a disc rotor according to an embodiment of the present disclosure.

[0025] Figure 3 is a diagram of a disc rotor according to another embodiment of the present disclosure.

[0026] Figure 4 is an illustration of a drum rotor according to an embodiment of the present disclosure.

[0027] Figure 5 is an illustration of a cross-section of a braking surface according to an embodiment of the present disclosure.

[0028] Figure 6 is a flow chart of a method for boronizing a braking surface of a rotor according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0029] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application or use. In addition, there is no intention to be bound by any express or implied theory present in the previous background technology, the invention summary or the following detailed description. It should be understood that in the accompanying drawings, corresponding reference numerals indicate the same or corresponding parts and features.

[0030] Although the present technology is primarily described herein in conjunction with passenger vehicles, the present technology is not limited to passenger vehicles. These concepts can be used in a variety of applications, such as commercial vehicles, off-road vehicles, military vehicles, motorcycles, mopeds, locomotives, aircraft, marine vessels, and other vehicles, as well as other applications that can incorporate disc rotors, such as in industrial applications, including conveyors, indexers, wind turbines, and hose reels.

[0031] Reference will now be made in detail to several examples of the present disclosure illustrated in the accompanying drawings. Whenever possible, the same or similar reference numerals are used in the drawings and description to refer to the same or similar components or steps. The drawings are in simplified form and are not to exact scale.

[0032] The present disclosure relates to borated brake rotors, borated brake rotor systems, and methods of boring brake rotors. Figure 1A vehicle 100 is shown that includes four wheels 102. A braking system 104 is associated with one or more of the wheels 102. The braking system 104 typically includes a brake actuator 110, such as a brake pedal or an electronic brake actuator. The brake actuator 110 is connected to a master cylinder 112. The master cylinder 112 is connected to a piston 114 or wheel cylinder associated with each wheel 102 by a hydraulic line 116 (see FIG. 1 ). Figure 4 ). The piston 114 or wheel cylinder is connected to a brake pad 118, which, when actuated by the brake actuator 110, can engage a brake rotor 120 connected to each wheel 102. The illustrated brake rotor 120 is a disc rotor; however, a drum rotor may also be used (see Figure 4 ).

[0033] Actuating the brake actuator 110, such as depressing a brake pedal or engaging an electronic brake actuator, generates pressure in the master cylinder 112. The pressure is hydraulically transmitted through hydraulic lines 116 to pistons 114, such as disc brake pistons or wheel brake cylinders (in the case of drum brakes), associated with each brake system 104 and brake rotors 120. The pressure causes the pistons 114 to expand and the brake pads 118 to engage the brake rotors 120 and apply force against the brake rotors 120. This force slows the rotation of the brake rotors 120 and the wheels 102 connected thereto, ultimately stopping the rotation of the wheels 102.

[0034] Figure 2 A brake rotor 120 is shown, and in particular a disc brake rotor 120a. The disc brake rotor 120a includes a rotor body 124, which includes one or more braking surfaces 126, which define an annular surface 132 around a central hub 130 on the rotor body 124. The central hub 130 is in the shape of a circular hat or bell. Figure 2 Only the first braking surface 126 is shown in FIG, with the second braking surface 126 present on the opposite side of the rotor body 124. The braking surface 126 may have a surface finish that varies by 2 microns or less, such as in the range of 0.3 microns to 2 microns.

[0035] The rotor body 124 is formed by cast iron, which is an iron alloy containing 2% to 4% by weight of carbon and 1% to 3% by weight of silicon, which is the total weight of the cast iron alloy. In an embodiment, the cast iron is a gray cast iron and the carbon is present in the form of graphite. The cast iron may also contain less than 1.0% by weight (e.g., in the range of 0.5% to 0.9% by weight) of manganese, and trace amounts of sulfur and phosphorus impurities, which are also less than 0.3% by weight of the total weight of the alloy. It should be noted that the total weight of the cast iron alloy is 100% by weight. Alternatively, the rotor body 124 may be formed by one or more alternative iron alloys, such as compacted graphite iron (CGI), ductile cast iron (ductile iron) and steel.

[0036] Figure 3 A brake rotor 120 is shown, also a disc brake rotor 120a, in which a central hub 130 and a surrounding annulus 132 of a rotor body 124 are formed of two distinct components rather than a single component. In various aspects, the central hub 130 is formed of a second material, which includes one or more metals, metal alloys, and ceramics. In an embodiment, the central hub is formed of aluminum or an aluminum alloy, and the annulus 132 surrounding the central hub 130 is formed of cast iron or an alternative iron alloy as described above. The central hub 130 is connected to the annulus 132 by one or more mechanical fasteners or fittings.

[0037] Further, the annular surface 132 of the rotor body 124 may include a plurality of vents 134 extending from the center of the rotor body 124 to an edge 135 of the disc brake rotor 120a, such as Figure 2 and Figure 3 As shown, or defined between the braking surface 126 through hole (not shown). In addition, the annular surface 132 of the rotor body may include a groove 139 in the braking surface 126 (such as Figure 3 126) or a through hole defined in the rotor body 124 and extending from the braking surface 126 through the rotor body 124 to the opposing braking surface.

[0038] Figure 4 An embodiment of a brake rotor 120 is shown, and a drum brake rotor 120b is specifically shown. The drum brake rotor 120b includes a rotor body 124 in the general form of a drum, which includes a central hub 130 and a wall 136 extending from the central hub 130. At least a portion of the inner surface 138 of the wall 136 includes a braking surface 126. As with the disc brake rotor 120a, the rotor body 124 is formed of cast iron, which is an iron alloy containing 2% to 4% carbon by weight and 1% to 3% silicon by weight. In an embodiment, the cast iron is gray cast iron and the carbon is present in the form of graphite. The cast iron may also contain less than 1.0% manganese by weight (e.g., in the range of 0.5% to 0.9% by weight), and trace amounts of sulfur and phosphorus impurities, also less than 0.3% by weight. Alternatively, the rotor body 124 may be formed of one or more alternative iron alloys, such as compacted graphite iron (CGI), ductile cast iron (ductile iron), and steel.

[0039] The braking surface 126 in any of the above embodiments and aspects is borated, i.e., surface treated with boron, wherein boron atoms diffuse into the surface 140 and subsurface (just below the surface 140) of the rotor body 124 to form an iron boride phase (Fe2B phase) 144 having a chemical formula of Fe2B above the iron alloy 150 (see Figure 5) of the iron boride layer 142. In an embodiment, the only iron boride phase in the iron boride layer is the Fe2B phase. A phase is understood as a physically homogeneous state of matter having a certain chemical composition and different types of atomic bonding and elemental arrangements. The iron boride layer 142 may also include a phase having a Figure 5 14 and 15. The graphite phase may be present in the iron boride layer 142 if a graphite phase is present in an iron alloy, such as gray cast iron. Additionally, an iron phase or other phases may be present in the iron boride layer, depending on the iron alloy from which the rotor body 124 is formed and whether the surface of the iron alloy has been previously treated with one or more of the following treatments.

[0040] The Fe2B phase 144 develops first and penetrates deeper into the iron boride layer 142 than the FeB phase 146. In other words, when present, at least 60% by volume of the FeB phase is closer to the surface 140 than the Fe2B, which is generally deeper in the iron boride layer 142. The FeB phase 146 is susceptible to spalling, and the FeB phase 146 may be spalled or removed using a machining process as further described herein.

[0041] As previously mentioned, the rotor body 124, including the braking surface 126, can be treated with other surface treatments, including one or more of the following processes: flame hardening, induction hardening, and laser hardening. Additionally or alternatively, the rotor body 124, including the braking surface 126, can be treated by one or more of the following processes: laser cladding with additional iron alloys, austenitic carburizing, nitriding, nitrocarburizing, and ferrite nitrocarburizing. Such treatments can be performed before or after the braking surface 126 is borided. These treatments can affect the composition of the iron boride layer 142.

[0042] Figure 6 A method 600 of forming a boronized braking surface 126 is shown. Optionally, if not already provided, at block 602, the rotor 120 is formed by a method that may include melting and pouring a molten ferrous alloy into a mold or using additive manufacturing of a ferrous alloy feedstock. Once formed, molded-in stresses may be eliminated by applying one or more of heat and pressure to the ferrous alloy.

[0043] At block 604, the braking surface 126 of the rotor body 124 or the entire rotor body 124 is cleaned to remove contaminants such as debris, residue, oil, and oxides that may inhibit the diffusion of boron to the braking surface 126, which would inhibit the formation of an iron boride phase in the braking surface 126. Cleaning may be facilitated by using at least one of a solvent and water. Additionally or alternatively, the rotor body 124 may be immersed in an acid bath. In an embodiment, the selected cleaning method does not change the surface finish of the braking surface 126 of the rotor body 124, which may vary between 5 microns or less (e.g., 0.3 microns to 2 microns).

[0044] At box 606, the braking surface 126 and optionally the entire rotor body 124 are boronized. Boriding can be performed using at least one of the following treatment processes: phase homogenization in pressurized diffused gas boronizing, powder filled boronizing, and electrochemical boronizing. During the boronization process, boron or a boron-containing composition is contacted with an iron alloy exposed to a temperature of 700°C or higher (such as in the range of 750°C to 1000°C). In an embodiment of pressurized diffused gas boronizing, the iron alloy is exposed to a boron-containing gas at a temperature of 800°C to 950°C. The process can also be plasma-assisted. In an embodiment of powder filled boronizing, the iron alloy is filled in a powder mixture of boron carbide (B4C), an inert filler (such as silicon carbide (SiC)) and an activator (such as potassium tetrafluoroborate (KBF4)) and immersed in an inert environment with a furnace temperature in the range of 950°C to 1000°C. In an embodiment of phase homogenization in electrochemical boriding, the iron alloy is exposed to an electrolyte of molten borax and sodium carbonate at an elevated temperature ranging from 900° C. to 1000° C. It will be appreciated that the boriding process can be used to relieve stress in the rotor body 124 and the stress relief step in the forming process can be omitted.

[0045] In the above process, the Fe2B phase is formed first, and then the FeB phase is formed. An electric current is applied to the iron alloy for a period of time, typically less than one hour. The Fe2B and FeB phases (if present) are formed in the iron boride layer 142 formed below the surface 140 of the braking surface 126. Preferably, the selected process is adjusted to limit or prevent the formation of the FeB phase. Since the boriding process is performed at an elevated temperature, after the boriding at box 604, at box 608, the rotor body 124 is allowed to cool to an ambient temperature in the range of 18°C ​​to 30°C, including all values ​​and ranges therein, while maintaining the rotor body 124 in an environment with a temperature in the range of 18°C ​​to 30°C. Natural cooling can minimize warping and deformation of the rotor body 124; however, some distortion may be unavoidable.

[0046] At box 610, the brake surface 126 is mechanically finished to the desired tolerance. Mechanical finishing at this stage can remove all or at least part of the FeB phase that may be present in the iron boride layer 142, and reduce the variation that may be caused by the boriding process. In an embodiment, before the cleaning at box 604 and the boriding at box 606, the brake surface 126 is mechanically finished to a tolerance of + / -0.7 mm or less, including all values ​​and ranges therein, such as + / -0.5 mm or + / -0.25 mm, and then mechanically finished again to reduce the variation caused by the boriding process. The brake surface can be mechanically finished using various techniques, including one or more of the following: precision milling and grinding, such as double disc grinding. In addition, if the rotor body 124 has not yet been formed, the rotor body 124 can be drilled or slotted. At box 612, the brake surface 126 is finished by polishing the brake surface 126.

[0047] If other treatments are performed, including one or more of flame hardening, induction hardening, laser hardening, laser cladding with additional ferrous alloys, austenitic carburizing, nitriding, nitrocarburizing, and ferritic nitrocarburizing, these treatments may be applied before or after boriding the brake surface 126 at box 604 but before finishing at box 610.

[0048] In an embodiment, the resulting brake rotor 120 may present an iron boride layer 142 including Fe2B having a depth in the range of 0.02 mm to 2.5 mm, including all values ​​and ranges therein. Additional phases present in the iron boride layer may include one or more of iron, graphite, and FeB. In addition, the borided surface of the Fe2B phase may exhibit a hardness greater than the underlying iron alloy. The hardness of the braking surface may be in the range of 1500 HV to 2000 Vickers hardness (HV, HV.01) measured according to the International Organization for Standardization test protocol ISO 6507-1:2018; while gray cast iron, for example, may exhibit a hardness in the range of 180 HV to 250 HV. In addition, the borided surface may exhibit greater wear resistance than the underlying iron alloy. The resulting brake rotor 120 may be assembled into a vehicle braking system or used in other braking applications as described above.

[0049] The borided brake disc rotor and brake system of the present disclosure provide a number of advantages. These advantages include the formation of a hardened and wear-resistant braking surface. In addition, the boriding process can be used to replace the stress relief step in casting. Another advantage is that the braking surface of various types of rotors (e.g., drum rotors, one-piece disc rotors, or two-piece rotors) can be treated using the above process.

[0050] The description of the present disclosure is merely exemplary in nature, and variations that do not depart from the gist of the present disclosure are intended to fall within the scope of the present disclosure. Such variations should not be regarded as departing from the spirit and scope of the present disclosure.

Claims

1. A brake rotor, comprising: A rotor body having a braking surface, wherein the rotor body comprises an iron alloy and the braking surface comprises a layer of an iron boride phase (Fe2B phase) having a chemical formula Fe2B in the braking surface.

2. The brake rotor according to claim 1, wherein: The rotor body comprises grey cast iron.

3. The brake rotor according to claim 1, wherein: The layer also includes an iron boride phase (FeB phase) having the chemical formula FeB.

4. The brake rotor according to claim 1, wherein: The hardness of the braking surface is in the range of 1500 to 2000 Vickers hardness (HV).

5. The brake rotor of claim 1, wherein: The iron boride phase in the layer consists of a Fe2B phase.

6. The brake rotor of claim 1, wherein: The depth of the layer is between 0.02 mm and 2.5 mm.

7. The brake rotor of claim 1, wherein: The rotor body is a disk and includes a central hub and an annulus defined around the central hub, wherein the annulus includes the braking surface.

8. The brake rotor of claim 7, wherein: The annulus comprises grey cast iron.

9. The brake rotor of claim 8, wherein: The central hub is formed from a second material.

10. A method of forming a brake disc rotor, comprising: removing contaminants from a brake rotor, wherein the brake rotor comprises a rotor body having a braking surface, wherein the rotor body comprises an iron alloy; boriding the braking surface and forming a layer of an iron boride phase (Fe2B phase) having a chemical formula of Fe2B on the braking surface; and The rotor body is cooled to ambient temperature.

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