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Friction Material (brake pads) for Metal Matrix Drums


OBJECTIVE: To develop dual-use friction material (brake pads) for use with the new family of aluminum metal matrix composite (AL MMC) brake drums for use on both unique military applications and commercial vehicle brake systems. DESCRIPTION: Aluminum MMC (Al MMC) brakes can provide significant weight savings, increased fade performance, lower operating temperatures, increased corrosion resistance and longer component life on a wheeled vehicle braking system[1][2]. Metal matrix composite brakes provide benefits to both military and commercial vehicles by reducing fuel requirements and reducing life cycle costs. These benefits are in alignment with S & T focus area 4b."Sustainability/Logistics-Transport, Distribute & Retrograde as the increased reliability of the tactical trucks will increase the reliability and timeliness of supplies. This product will reduce brake fade and thus increase vehicle safety while increasing the efficiency by increasing vehicle payload or improving fuel economy. Inherent lower operating temperatures, resultant of increased thermal capacity and thermal conduction, of AL MMC brakes both increase the life of the braking components and increase the fade performance of the braking system. Al MMC brakes have much better corrosion resistance than cast iron components which eliminates the"brake stick"phenomena that cast iron brakes exhibit after sitting in a wet or salty environment for a period of time. Al MMC brakes operate with a transfer layer between the brake drum and the friction material which creates very little wear of the brakes resulting in increased life of the brakes as compared to cast iron. Typical friction solutions for cast iron brake systems are not applicable to Al. MMC brake components due to higher operating temperatures of cast iron. To realize the full benefits of AL MMC brakes the matching friction material has to be chosen. The material will provide sufficient frictional torque to the brakes during normal and extreme operating conditions while also providing the static holding torque required for parking on grades up to 60% for military vehicles. To achieve these performance requirements a material with the correct coefficient of friction has to be chosen that provides a balance between brake stopping power and static holding torque. The variables that affect the frictional torque requirement for a vehicle include gross vehicle weight (GVW)and tire diameter, the braking performance requirements which include the vehicle speed and deceleration requirement (stopping distance) and the brake system which uses various mechanisms such as wedges or cams to generate force applied to the friction material. With all of these variables changing for each application, the frictional requirements are also unique. As there are families of friction materials that have been developed and tested for various applications regarding cast iron brakes, friction materials have to be developed and tested for various applications regarding AL MMC brakes as well. The objective of this topic is to develop a family of friction materials compatible with AL MMC brakes for both military and commercial applications. This family of friction materials would consist of a base formulation that is optimized for AL MMC brake drums. Modifications can be made to this base formulation to further develop solutions based on specific vehicle parameters and operating conditions. The friction materials developed will target current medium to heavy wheeled vehicles that employ various brake actuation systems such as S-cam, single wedge and dual wedge, among others. The appropriate friction material will generate consistent dynamic and static braking torque as well as providing long life and not doing any irrevocable damage to the AL MMC brakes for a given application. It would also be desirable for a given friction material to be used for multiple military and commercial applications. PHASE I: Identify base formulation materials to match the operating characteristics of al. MMC brakes, the goal is to create a family of friction materials which will operate at the lower MMC brake operating temperature and optimize the friction characteristics of the ceramic/aluminum MMC drum/rotor formulas. Determine reinforcement and additive materials for each unique application. These materials will fall under the classifications of binder, filler, abrasives, lubricants, and fillers. Start catalog or spider diagram demonstrating various formulations and potential applications for each. Create a development plan that includes friction formulation development, testing and production along with identification of military and commercial vehicle platforms. Metrics for evaluating reinforcement and additive materials include their effect on ultimate friction level, effect on stopping distance, effect on fade response, effect on recovery response, noise vibration harshness (NVH) concerns, effect on the wear of friction material, effect on the wear of al. MMC brake drum, and the any swell or growth concerns that could arise due to various operating conditions such as extreme cold weather or salt spray. PHASE II: Optimize base friction materials for stopping distance, fade performance and durability of both the brake drum and pad while operating at the lower MMC temperature while optimizing the friction characteristics of the ceramic/aluminum MMC drum/rotor formulas under varying application forces (each brake system applies forces in a different manner). Focus will be on current military and commercial, medium and heavy vehicles with GVW"s of 25,000 lbs and above. Main metrics will be cost, coefficient of friction and wear. Typically there is a trade-off between coefficient of friction and wear rates, certain materials can have high coefficient of friction, but high wear rates will also be evident. There are various brake actuation systems that are common to commercial and military trucks including single wedge, dual wedge, and S-cam systems. Each of these systems has a different brake factor and to meet these brake factors varying levels for coefficient of friction are required. The main goal of Phase II will be optimizing individual formulations within the larger family that work for each brake system. Coefficient of friction will be evaluated utilizing the SAE J661 procedure [4] with an aluminum MMC brake drum (effectively a coupon test). The full scale materials can then be evaluated on a dynamometer utilizing the FMVSS 121 Performance Test [5] and ATPD 2354 Jennerstown Fade and Laurel Mountain Hotstop among others. Some of the Phase II deliverables may be subject to International Traffic in Arms Regulation (ITAR) control if ITAR controlled vehicle parameters are part of the dynamometer test plan. PHASE III: Currently General Dynamics Land Systems is testing US Army developed and supplied AL MMC brake drums (using brake pads optimized for cast iron brake drums, so optimal performance will not be realized) for the purpose of adopting this technology on future LAV and Stryker suspension upgrades. This SBIR's optimized brake pads will be implemented concurrent with the AL MMC drums. Commercial interest includes Bendix and Webb wheel, the on highway semi-truck is the leading candidate for this technology and could use a common solution to our 915/916 truck platforms. Final feasibility and material performance assessments will be completed during phase III. Integrated friction formulations for existing product lines including commercial, military, and industrial will be provided for US Army use. REFERENCES: 1. Kero, M., Light-weight Aluminum Composite Fade Response and Speed Sensitivity Results, SAE Technical Paper 2011-01-2146, 2011, doi:10.4271/2011-01-2146. 2. Kero, M. and Halonen, A.,"Development and Testing of Lightweight Aluminum Composite Brake for Medium to Heavy Duty Vehicles,"SAE Technical Paper 2010-01-1705, 2010, doi:10.4271/2010-01-1705. 3. Buckman, Leonard."Commercial Vehicle Braking Systems: Air Brakes, ABS and Beyond". SAE International SP-1405. 4.
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