Brake-based park systems, where an electric parking brake system becomes fully responsible for vehicle immobilization and enables elimination of the traditional driveline-based parking pawl, has increased in popularity, especially in full Electric Vehicles. At face value, the promise of saving mass, cost, and critical packaging space in an electric drive unit is compelling. However, this must be weighed carefully against less obvious impacts, which include engineering in added redundancy, significant changes in “real world” duty cycle of EPB components, risk of brake pad and rotor crevice corrosion, and perhaps most acutely because it affects every drive cycle, the impact to residual drag and therefore vehicle energy use. The present work endeavors to present a balanced view of the considerations, both advantages and tradeoffs, for brake-based park systems, with a special focus on the residual drag behavior because it is perhaps the most difficult to characterize, most variable in its behavior, but most impactful to the vehicle effect.

The use of reinforced phenolic composite material in application to hydraulic pistons for brake calipers has been well established in the industry - for sliding calipers (and certain fixed calipers with high piston length to diameter ratios). For decades, customers have enjoyed lower brake fluid temperatures, mass savings, improved corrosion resistance, and smoother brake operation (less judder). However, some persistent concerns remain about the use of phenolic materials for opposed piston calipers. The present work explores two key questions about phenolic piston application in opposed piston calipers. Firstly, do opposed piston calipers see similar benefits? Do high performance aluminum bodied calipers, where the piston may no longer be a dominant heat flow path into the fluid (due to a large amount of conduction and cooling enabled by the housing), still enjoy fluid temperature reductions? Are there still benefits for judder with the much shorter length to diameter ratio the pistons have in these applications? Secondly - it is clear that the much shorter length to diameter ratio of the piston in opposed piston calipers will result in significant increases in contact stress on the piston material at its contact points to the bore, when it is pressurized against pads with significant taper wear - will the phenolic material have adequate durability to withstand this? Can a simple “application guideline” for phenolic pistons be defined, potentially based on piston diameter (governing peak clamp load) and length to diameter ratio (which determines the correlation between clamp load and contact stress in the piston material at the bore contact points)? To address the first question, a battery of comparative tests was run on a high performance 6 piston aluminum-bodied brake calipers with high performance low-metallic brake pads and a large 18” wheel envelope two piece, cast iron plate and aluminum hub rotor. Fluid consumption, drag, brake torque variation, and fluid temperatures were measured through tests designed to exercise these behaviors, with both the production aluminum pistons and prototype phenolic piston calipers. The second question was explored through lab-based durability testing, abusive inertia dyno testing, and analysis of parts failed during testing. Pistons of the same phenolic material (Durez 29504B) were prototyped in opposed-piston caliper configurations in two sizes (51mm and 34mm) and tested to failure. The analysis of the data changed the authors’ initial thinking substantially about the failure mechanics of the piston in severe use, but still resulted in a simple, free body diagram based application guideline and a clear path for future work.

Previously published research [1] covering the role of piston material properties in brake torque variation sensitivity and roughness concluded that phenolic pistons have significantly higher low-pressure range compliance than steel pistons, which promotes lower roughness propensity. It also determined that this property could be successfully characterized using a modern generation of directacting servo hydraulically actuated brake component compression test stands.This paper covers a subsequent block of research into the role of the caliper piston in brake torque variation sensitivity (BTV sensitivity) and thermal roughness of a brake corner. It includes measurements of hydraulic stiffness of pistons in a "wet" fixture, both with and without a brake pad and multi-layer bonded noise shim. Inertia dynamometer measurements of BTV sensitivity against a machined 20-micron thickness variation rotor with multiple (prototype) phenolic piston geometries, as well as steel pistons with two different piston to bore clearance levels followed. Finally, higher-temperature thermal roughness testing of multiple phenolic piston geometries and steel pistons with tighter and looser piston to bore clearances were run.The results of these studies give some insight into the role of the caliper piston - its material properties, geometry, and clearance to the bore - in brake roughness and performance.

Eine Ausfuhrungsform umfasst ein Reibungsmaterial und ein Verfahren zur Herstellung desselben, wobei das Reibungsmaterial eine Ubertragungsschicht auf einer ferritisch nitrocarburierten Komponente umfasst, wobei die Ubertragungsschicht aus Glas, Kautschuk, Kohlenstoff, Aramidfaser, Fullstoffmaterial, Abrasivstoff oder einem Hochtemperaturharz hergestellt werden kann.

The brake caliper piston plays a key role in caliper function, taking significant responsibility for qualities such as fluid consumption, insulation of the brake fluid from heat, seal rollback function, and brake torque variation sensitivity to disc thickness variation. It operates in a strenuous environment, being routinely subjected to high stresses and elevated temperatures. Given all of the demands on this safety-critical component (strength, stiffness, wear resistance, stable friction against rubber, thermal stability, machinability, manageable thermal conductivity, and more), there are actually relatively few engineering materials suitable for use as a caliper piston, and designs tend to be limited to steel, aluminum, and engineered plastics (phenolic composites). The lattermost - phenolic composites - has been of especial interest recently due to mass savings and possible reduction in brake corner judder sensitivity to disc thickness variation. This paper focuses on characterizing two important mechanical characteristics, stiffness and damping, of the most common piston materials, steel and phenolic. Data are shown first suggesting the effect of piston material on brake performance, and then stiffness and damping data from different methodologies are presented. From these data, a preferred methodology is recommended and results are reconciled with brake corner subsystem performance and modeling.

During the automotive brake system design and development process, a large number of performance characteristics must be comprehended, assessed, and balanced against each other and, at times, competing performance objectives for the vehicle under development. One area in brake development that is critical to customer acceptance due to its impact on a vehicle's perceived quality is brake pedal feel. While a number of papers have focused on the specification, quantification and modeling of brake pedal feel and the various subsystem characteristics that affect it, few papers have focused specifically on brake corner hoses and their effect on pedal feel, in particular, during race-track conditions. Specifically, the effects of brake hose fluid consumption pedal travel and brake system response is not well comprehended during the brake development process. This paper introduces the basic construction of automotive brake hoses, the test methodologies and test results used to quantify brake hose fluid consumption under various operating conditions, and it illustrates the influence of hose performance at the vehicle-level using simple analyses on an example race track-capable sports car.