Reduction of particulate emissions from vehicle braking systems

Abstract

A vehicle braking system reduces particulate emissions resulting from wear of the brake pad and rotor during stopping or slowing of a vehicle. The rotor includes at least one friction surface, that has an outer coating of a corrosion and wear-resistant material. This uoter coating can optionally include a first layer comprising a crystalline material and a second layer overlaying and contacting the first layer and comprising an amorphous material. The first layer and the second layer can optionally have an inter-layer period of less than 10 nm such that the structure of the outer coating is that of a superlattice. A brake member that includes a friction material is mounted to a caliper on the vehicle with the friction material disposed opposite the at least one friction surface so that the friction material reversibly engages with the outer coating of the corrosion and wear-resistant material when the braking system is operated to stop or slow the vehicle. Contact between the friction material and the outer coating results in substantially reduced conversion of the friction material to dust while producing an improved coefficient of friction relative to standard braking systems. Related systems, apparatus, methods, and/or articles are also described.

What is claimed: 
     
         1 . A brake rotor comprising:
 a friction surface;   a plurality of raised island formations disposed on the friction surface, the raised island formations separated by spaced air flow channels between the island formations, the raised island formations comprising braking surfaces configured to interact with a brake pad;   a wear and corrosion resistant coating applied to at least the braking surfaces of the raised island formations, the wear and corrosion resistant coating comprising a first layer comprising a metal and a second layer comprising a nitride, boride, carbide or oxide of the metal; and   a surface geometry on the braking surfaces of the raised island formations, the surface geometry comprising peaks and valleys, the surface geometry causing the braking surfaces to exhibit a three dimensional appearance of a woven texture with the wear and corrosion resistant coating applied thereto.   
     
     
         2 . A brake rotor as in  claim 1 , wherein the first layer has an amorphous structure or a crystalline structure. 
     
     
         3 . A brake rotor as in  claim 1 , wherein the second layer overlays and contacts the first layer and comprises one or more metal nitrides, metal borides, metal carbides and metal oxides. 
     
     
         4 . A brake rotor as in  claim 1 , wherein the second layer comprises a super lattice structure that includes thin films formed by alternately depositing two different components to form layered structures. 
     
     
         5 . A brake rotor as in  claim 1 , wherein the first layer comprises one or more amorphous metals and the second layer comprises one or more binary metals. 
     
     
         6 . A brake rotor as in  claim 5 , wherein the amorphous metal of the first layer is selected from titanium, chromium, zirconium, aluminum, hafnium and an alloy combination thereof; and wherein the binary metal of the second layer is selected from a metal nitride, a metal boride, a metal carbide and a metal oxide. 
     
     
         7 . A brake rotor as in  claim 5 , wherein the second layer further comprises one or more nitrides, borides, carbides or oxides of the amorphous metal of the first layer. 
     
     
         8 . A brake rotor as in  claim 1 , wherein the rotating braking element comprises a brake disk or rotor. 
     
     
         9 . A brake rotor as in  claim 1 , wherein active engagement of the brake pad and the brake rotor results in conversion of the friction surface to dust at a coated loss rate that is approximately 10 to 30 times slower than an uncoated loss rate that results from active engagement of the brake member and a bulk structural material of the brake rotor without the wear and corrosion resistant coating. 
     
     
         10 . A brake rotor as in  claim 1 , wherein active engagement of the brake pad and the brake rotor results in the friction surface having a coated useful lifetime that is approximately 10 to 30 times longer than an uncoated useful lifetime that results from active engagement of the brake pad and a bulk structural material of the brake rotor without the wear and corrosion resistant coating. 
     
     
         11 . A method for reducing particulate emissions from a vehicle braking system, the method comprising:
 installing a rotating braking element as part of the vehicle braking system, the rotating braking element comprising a bulk structural material and a friction surface, the friction surface comprising an outer coating that comprises a corrosion and wear-resistant material;   mounting a brake member to a caliper of the vehicle braking system, the brake member comprising a friction material having a friction material composition, the brake member being mounted with the friction material disposed opposite the at least one friction surface so that the friction material reversibly engages with the outer coating of the corrosion and wear-resistant material when the braking system is operated to stop or slow the vehicle, contact between the friction material and the outer coating producing a coated coefficient of friction that is substantially equivalent to or greater than an uncoated coefficient of friction produced by contact between the friction material and the bulk structural material without the outer coating, active engagement of the brake member and the rotating brake element resulting in conversion of the friction material to dust at a coated loss rate that is at least 30% slower than an uncoated loss rate that results from active engagement of the brake member and the bulk structural material of the rotating braking element without the outer coating.   
     
     
         12 . A method comprising:
 forming a rotating brake element from a bulk structural material such that the rotating brake element comprises a friction surface;   applying an outer coating of a wear and corrosion resistant material to the friction surface, the outer coating having a coated coefficient of friction with a friction material of a movable brake member adapted to contact the friction surface during engagement of a braking system, the coated coefficient of friction being substantially equivalent to or greater than an uncoated coefficient of friction between the friction material and a second friction surface of a second rotating brake element that does not have the outer coating applied, release of a chemical species i from the friction material during use of the braking system occurring at a release rate, R release,i , according to
     R   release,i   =C   pad,i   ×D   pad    
   where C pad,i  is a mass concentration of the chemical species i in the friction material and D pad  is an average degradation rate at which the friction material loses mass; and wherein D pad  is reduced by at least 30% for use of the movable brake member with the rotating brake element having the outer coating applied relative to use of the movable brake member with the second rotating brake element having a second friction surface without the outer coating applied.   
     
     
         13 . A method as in  claim 12 , wherein the outer coating of the corrosion and wear-resistant material comprises a first layer comprising a crystalline material and a second layer overlaying and contacting the first layer and comprising an amorphous material. 
     
     
         14 . A method as in  claim 13 , wherein the first layer and the second layer have an inter-layer period of less than 10 nm and the outer coating comprises a superlattice structure. 
     
     
         15 . A method as in  claim 13 , wherein the first layer comprises one or more amorphous metals and the second layer comprises one or more binary metals. 
     
     
         16 . A method as in  claim 15 , wherein the amorphous metal of the first layer is selected from titanium, chromium, zirconium, aluminum, hafnium and an alloy combination thereof, the binary metal of the second layer is selected from a metal nitride, a metal boride, a metal carbide and a metal oxide. 
     
     
         17 . A method as in  claim 15 , wherein the second layer further comprises one or more nitrides, borides, carbides or oxides of the amorphous metal of the first layer. 
     
     
         18 . A method as in  claim 12 , further comprising machining the friction surface prior to applying the outer coating of the wear and corrosion resistant material such that the friction surface comprises a plurality of raised island formations separated by channels or gaps that permit air flow to cool the rotating braking element during active engagement with the brake member. 
     
     
         19 . A method as in  claim 12 , wherein the rotating braking element comprises a brake disk or rotor. 
     
     
         20 . A method as in  claim 12 , wherein D pad  is reduced by a factor of approximately 10 to 30 for use of the movable brake member with the rotating brake element having the outer coating applied relative to use of the movable brake member with the second rotating brake element having a second friction surface without the outer coating applied.