Following intensive restructuring during the 1990s, opportunities for further consolidation in the light vehicle braking system segment have largely dried up. Today, three companies – Continental, Bosch and TRW– account for half of the global market for automotive foundation brakes. Matthew Beecham talks to braking system executives about recent technical advances.
Go deeper with GlobalData
Discover B2B Marketing That Performs
Combine business intelligence and editorial excellence to reach engaged professionals across 36 leading media platforms.
Foundation brake parts include disc brake assemblies and components, including callipers, rotors and knuckles, drum brake assemblies and parts, including drum brakes, drum-in-hat adapters, hubs and integral parking brakes.
The apparently simple issue of braking continues to be a major issue for engineers. Drivers are, of course, concerned that in an emergency, their vehicles should stop as quickly as possible. There is a practical limit to braking performance, set by the ability of the tyre contact patches to transmit the forces involved without sliding. However, advances in tyre design, soon to be complemented by the ability of electronically controlled braking systems to distribute effort according to wheel load (if, for example, the brakes are applied while the vehicle is cornering), mean that limit is now potentially very high, at least on dry road surfaces. This is throwing the onus very much back to the braking system developers.
The main engineering challenges in any braking system are to withstand the extremely high temperatures involved, to remove the very large amount of heat generated during hard deceleration, and to minimise the weight of the braking units.
Neil Geldard-Williams, managing director of Caparo AP Braking says weight reduction is very important across the braking system, but especially in the un-sprung area where it improves ride and handling as well as fuel consumption and CO2 emissions. He said: “We are also focusing on clever design that improves brake feel and reduces engineering costs. Caparo has considerable experience in materials manufacture and engineering, which is very complementary to our base braking business and provides a lot of performance and flexibility benefits for our customers.
For example, we have a unique formulation for our cast iron rotors which increases resistance to cracking during high thermal cycling giving our customers a choice of either increased performance or size and weight reduction. A good example of clever design is our new monobloc calipers, cast within the Caparo Group at Bridge Aluminium, which can be quickly adapted to virtually any vehicle by modifying the size of the pad box and adjusting the mounting points. This helps get vehicles to market faster, allows fast and cost-effective introduction of higher performance variants and provides significant cost savings where a number of niche vehicles are developed from a single platform.”
Demands for more performance with minimal cost or weight penalties are also pressurising brake system designers to come up with new ideas.
Guenther Plapp, executive vice president engineering of Bosch’s Chassis Systems Brakes division, said: “Our unit Buderus has developed a new disc material with low silicon and high carbon content. This leads to high damping values, low natural tension and, in connection with an optimized design, low coning values. In relation to conventional grey cast iron materials, this new material also manifests better thermal resistance and creates high reliability in operation. The customer benefits from a higher life-time due to less wear and optimum braking comfort. In order to reduce the weight of high performance discs, we have developed a disc that is made of aluminium at the hat and of newly composed cast iron derivates at the friction ring. Finally, we are investigating whether coating technologies can further improve endurance and other features relevant for brake comfort.”
Investigations have also been carried out on friction materials in terms of composition and organics. “Of the three major types of friction materials in global service – NAO, lomets and semimets – only the second is actively in use in the EU,” said Parimal Mody, vice president of Bosch’s Global Friction Engineering. “Currently, the primary development targets for these EU lomets are to reduce wheel dust and scoring or grooving of the discs, besides providing superior high-speed braking performance in conjunction with ever-stricter brake NVH requirements. The sourcing cost of metals and other raw materials has prompted the friction industry to find lower-cost substitutions, e.g. of lubricants. Unfortunately, these are not always adequately designed or validated, and can increase field NVH risk. Environmental aspects, e.g., reduced copper, will serve to further drive newer formulation directions. In short, a brake system has to continually accommodate and adapt to evolving market requirements and changes in friction material formulations.”
New materials such as aluminium or ceramic discs have been closely studied, as have the friction materials themselves, plus better caliper designs, and four-pot calipers are now relatively commonplace. The aim of the ceramic discs is to improve performance by allowing higher temperatures to be run, while the metal composite discs are intended to save weight without sacrificing wear resistance or performance. “Carbon ceramic discs will find their way into high-end car applications today and in the future,” added Plapp. “Since the manufacturing processes are rather complex, they will remain a special niche product for sports applications with high appeal and image potential. Good handling due to low weight is another attribute which sporty drivers will appreciate.”
Bill VanderRoest, technical director, Foundation Brakes, TRW Automotive, added: “There have been some interesting developments in advanced materials such as carbon fibre discs which provide advantages under extreme braking conditions. Because of their cost premium, the application of such materials is limited to the very high-end performance vehicles.”
TRW Automotive has developed a so-called ‘thin wide bridge calliper technology’ (TWB) which, it claims, combines the benefits of increased fuel economy with longer brake life. With the thin wide bridge design, the calliper bridge thickness is reduced by 45% in comparison to a conventional brake calliper design, while the width is increased by 40%. This decrease in bridge thickness allows for an increase in piston effective radius which, when combined with larger pads and rotors, can equate to a significant increase in brake torque output. “Weight savings and enhanced performance were the primary objectives that led to the re-engineering of conventional brake parts to create highly mass-efficient structures for disc brake calliper housings,” said TRW braking engineering chief, Josef Pickenhahn. “The housings on the thin wide design are lighter than their predecessors, promoting better vehicle fuel economy. TWB housings also accommodate larger diameter rotors and friction pad areas, which tend to reduce rotor-running temperatures, brake fade and pad wear. Combined with larger rotors, this also results in increased brake torque output.”
Disc brakes, despite prediction of the past, have not completely superseded drum brakes; the latter are still being used at the rear of a number of entry-level small- and medium-segment volume passenger cars produced in Europe, in an effort to contain costs. While the same can be said of the North America and Japanese market, the proportional difference between disc and drum brakes is less marked. Vince Austin, director, product planning for TRW Automotive’s Global Braking Systems business said: “The fitment of drum brakes has declined dramatically in Europe over the last ten years for larger segments. AMS [Auto Motor & Sport], the consumer publication that evaluates and publishes braking performance results, was the primary reason OEMs increased the fitment of disc brakes. At the end of the AMS test procedure, the vehicle is evaluated for stopping distance and compared to other vehicles. Those vehicles with stopping distances in excess of 40 metres were considered to have relatively poor braking performance. As consumers became aware of these performance comparisons and started to insist on shorter stopping distances, OEMs incorporated this test within their brake system development. In Europe, the fitment of rear drum brakes remains high in A-segment (˜ 90%) and B-segment (˜ 80%). Larger segments are dominated by disc brakes at all four corners.”
Karl Friedrich Wörsdörfer, vice president, product development, Hydraulic Brake Systems, Chassis and Safety division, Continental believes that drum brakes are still part of our roadmaps and will stay for a long period. He said: “In small cars, drum brakes are still state-of-the-art and the behaviour of drum brakes during ABS control is much improved so that there is no disadvantage. In the North American car parc, especially mid-range cars more and more combined caliper will substitute drum brakes. In Europe this is state-of-the-art.”
Those OE trends are clearly affecting the aftermarket, too. Plapp added: “The aftermarket is certainly following the development in OE. But as the average lifetime of a car is about 15 years, there still are a lot of cars equipped with drums. Additionally, we can observe a renaissance of drums in the low cost area. So in total we assume that the market volume for brake shoes will be quite stable over the next five to ten years.”
Another major concern of braking engineers is, of course, to manage NVH. “There are numerous factors contributing to NVH that can involve nearly every component at the wheel end, the suspension, as well as the supporting structure,” said VanderRoest. “For a number of years now, TRW begins the NVH analysis at a very early stage using predictive simulation tools followed by noise rig testing using hardware to validate the performance of a system. Of course, our primary emphasis has been designing products that are inherently more robust against factors that cause noise, vibration, and harshness. We have made significant strides in these areas and the results are being seen in measurable warranty and customer satisfaction measures.”
Thierry Pasquet, Bosch’s director for NVH in Europe concluded: “The major market trend is to reduce noise propensity. There are two key factors to improve NVH performance: profound system know-how and close cooperation with our customers and suppliers. We need system know-how because NVH is a complex interaction between pad, rotor, caliper and corner components. NVH engineering requires the competences of our experts in more than six different domains of physics. The combination of process control and component stability provides the best results. And we need close cooperation with customers and suppliers because each customer platform is specific.”
See also: Global market review of foundation brakes – forecasts to 2014 (download)
