Synergy success story: the disc brake for commercial vehicles.

Mid-1980s: developers are testing brake discs on the friction dynamometer at Knorr-Bremse in Munich. 2019: children in the USA are making safer bus journeys to school. What happened in the intervening 35 years? It's a fascinating success story for truck disc brakes. One key reason lies in the technology transfer between the two Knorr-Bremse divisions Rail Vehicle Systems and Commercial Vehicle Systems.

Fresh off the assembly line in Bowling Green, Kentucky: Bendix's three millionth disc brake for the North American commercial vehicle market. The current US milestone appears relatively modest compared to over 17 million truck disc brakes supplied by Knorr-Bremse worldwide. It is significant nonetheless, underscoring the improvement in road traffic safety - a trend that follows the transition from drum brakes to disc brakes on the huge market for commercial vehicles in the USA.

USA: disc brake market share is on the rise

More than 25 percent of North American new builds for Class 6-8 air-braked wheel-ends are now equipped with ADBs – a 100 percent increase in overall market share since 2014. The Bendix® ADB22X™ accounts for about 80 percent of that increase and has found a broad range of applications, including in trucks, delivery vehicles, school buses, transit buses and coaches. In October 2019 the National School Bus Safety Week will be held again in the USA, sponsored by the National Association for Pupil Transportation (NAPT). It aims to continually improve the safety of buses in the USA. One significant contribution is made by Bendix Spicer Foundation Brake (BSFB) with its disc brakes for trucks. They stand for short braking distances and stable stops. The system is said to offer a "car-like feel".

Local development know-how pays off

In 2014, nine years after the introduction of disc brakes for trucks in the USA, the 400,000th unit was delivered; by 2017 it was two million and today three million disc brakes have been delivered. Nicole Oreskovic, product line director for air disc brakes at Bendix Spicer Foundation Brake (BSFB), spent a long time working towards this breakthrough: “Air-disc-braked trucks had been the European norm for years, and we were excited to pioneer their advantages on this side of the Atlantic. Fourteen years of research and development, optimization, sustained fleet adoption, and road-proven ROI later, we couldn’t be prouder of how our air disc brakes have helped make vehicles and roadways safer.” These current market developments in the USA have their basis in synergy ideas from Knorr-Bremse that were put into practice 35 years ago in Munich.

The disc brake: from rail to truck

It’s the mid-1980s and Knorr-Bremse is carrying out a major research project. A development team is testing brake discs, calipers and brake pads to their limits on the friction dynamometer. So far, so unremarkable. What is unusual, though, is that even all those years ago colleagues from Knorr-Bremse’s Rail Vehicle Systems and Commercial Vehicle Systems divisions were working side by side on the test rig. 30 years ago, the engineers were tasked with developing a Knorr-Bremse disc brake for commercial vehicles that would ideally become just as successful as its rail vehicle counterpart.

The ultimate example of technology transfer

Rail vehicles were using disc brakes as long ago as the 1950s. They proved themselves as the standard technology in trains and cars over a long period, with benefits including excellent braking force control, short braking distances and ease of maintenance. At this time, commercial vehicles used drum brakes exclusively.

How disc brakes work

When Knorr-Bremse started systematically developing disc brakes for commercial vehicles in the 1980s, the company was able to draw on its experience in the rail vehicles sector. Ultimately, all disc brakes are based on the same operating principle: Brake pads press against the disc, converting kinetic energy into heat. Effective heat dissipation to prevent the brake from overheating is one of the key challenges in developing disc brakes.

Drum brake vs. disc brake

Knorr Bremse’s engineers knew that disc brakes produce a more even braking force than drum brakes. As trucks got ever faster and heavier, this would help to improve handling and steering while braking. In addition, drum brakes require shorter maintenance intervals. In today’s parlance, disc brakes offer lower total costs of ownership (TCO). Knorr-Bremse therefore decided to develop its own disc brakes for commercial vehicles and began marketing and mass-producing them in the 1980s.

Harnessing synergies: Two divisions, one development center

The sharing of existing test rigs between the two divisions was a key factor in the disc brake success story and a sign of things to come. Since 2016, some 650 highly specialized engineers and technicians from both sides of the business have been working together across disciplines on the 100 state-of-the-art test systems in Knorr-Bremse’s new Munich Development Center.

The disc brake today

Back to the present: The next-generation disc brakes are called SYNACT for heavy-duty trucks and NEXTT for light and medium-duty trucks and trailers . They stand for the development of a digital and networked brake system and related components. As such, they are a key technology on the path towards a largely accident-free future for road traffic.


From rail...

Rail vehicles were using disc brakes as long ago as the 1950s. Their benefits included excellent braking force control, short braking distances and ease of maintenance. As time went by, plans were therefore devised to replace the standard drum brakes on commercial vehicles with disc brakes. road

Disc brakes produce a more even braking force on commercial vehicles, too. This helps to improve handling and steering while braking, which is particularly important for vehicles that are both fast and heavy. As a result, Knorr-Bremse started developing and massproducing disc brakes for commercial vehicles in the 1980s.

In our product development activities across both business segments, we are focusing on the global megatrends of urbanization, eco-efficiency, digitalization, and automated driving. In this way, we are generating sustainable growth potential for our company.

Dr. Peter Laier – Executive Board Member Knorr-Bremse AG and responsible for the Commercial Vehicle Systems Division

Building the future together

As well as individual components, future collaboration between the two divisions will increasingly be driven by solutions for megatrends such as digitalization, eco-efficiency and automated driving. Examples include the use of sensors for collision avoidance systems. Other cross-divisional R&D initiatives include condition monitoring, remote diagnostics and predictive maintenance solutions that were originally developed for rail vehicles but now also have applications for commercial vehicles. Moreover, research in the field of electric mobility promises to deliver basic technological solutions that can be used for both electric buses and rail vehicles. It is no wonder so many projects are underway: Knorr-Bremse’s total investment in research as a percentage of its revenues is double that of its competitors.

Synergies across the business: Technological benefits and economies of scale between rail and commercial vehicles

Cooperation today

  • Identical core technologies
  • Cooperation on development

Future technologies

  • Joint research centers
  • Electric mobility
  • Automated driving
  • Condition monitoring and predictive maintenance
  • Electromechanical brakes

Economies of scales

  • Technology leadership enabled by shared financial resources
  • Overlap between future road and rail technologies
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