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Mr. Daniel Herven, Haldex Brake Products AB, SWEDEN
Mr. Anders Nilsson, Haldex Brake Products AB, SWEDEN
The current brake technology for commercial vehicles based on pneumatics has gone through several evolutions of development with added electrical control options to support the development towards ABS, EBS and ESC.
With the trend towards autonomous and electrified commercial vehicles new requirements and opportunities on the brake system emerges such as new redundancy concepts and improved brake control accuracy.
An opportunity to meet these requirements is to introduce electromechanical brake systems that beside an impact on the actual brake system also have vehicle impacts such as legislation, packaging, efficiency, vehicle installation, truck & trailer interface, suspension control and NVH.
The purpose of this paper is to describe both challenges and opportunities based on the vehicle impact when electromechanical brakes are introduced on commercial vehicles.
Haldex has investigated in electromechanical brakes for many years. The main driver initially has been safety improvement through improved braking distances and improved driver control throughout the braking applications as well as lower maintenance cost compared to pneumatic system.
With the clear trend of electrified trucks and busses new opportunities can be seen with electromechanical brakes such as reduced complexity of the pneumatic system eliminating air tanks and making room for batteries and simplify installation of the brake system in the vehicle.
Autonomous vehicles require increased interaction of control signals, status information and diagnostics between subsystems. An obvious example is interaction between steering and brake system where the brake system can be used as a backup system to the steering system. The electromechanical brake system with intelligence and better diagnostic capability at every wheel can support the technology trend of autonomous vehicles.
The main challenge for introduction of this kind of brake system is the legislation to support both brake by wire and electrical energy supply to the brakes instead of pneumatic energy.
Another challenge is compatibility with trailers as they have a pneumatic interface why early adopters of electromechanical brakes most likely are busses and distribution trucks not requiring an interface to a trailer.
Vehicle performance impact
As discussed, the initial driver to investigate electromechanical brakes was to improve brake performance by optimizing the friction utilization between the road and the tire to optimise brake performance and stability. A more precise control of the braking also gives the driver a better feeling.
All components of the pneumatic braking system must be working properly for the ABS control to impact the individual wheel. Problems with automatic brake adjusters, chamber malfunctions, and air leaks cannot be corrected by current ABS systems. EMB technology will allow better braking stability by adjusting braking force at individual wheels instantaneously verses just an on/off application.
Autonomous truck technologies will require braking applications that can be operated
electronically. This will require braking capabilities for the vehicle combination to work in unison. While this is possible with the current air systems, it is anticipated that EMB will provide much better braking balance and response times through the vehicle combination compared to current pneumatic brake systems. EMB can also communicate brake force, temperature and lining wear status providing the autonomous vehicle with information regarding brake health and performance.
Knowing that some cities decided to limit the allowed NVH levels a further benefit will be NVH. In an electrified vehicle where the combustion engine no longer is the major NVH contributor the pneumatic system instead will be a focus where the electromechanical brakes have a clear benefit.
A pneumatic brake system has poor efficiency with conversion where the combustion engine drives the compressor that supply air to the tanks through the air treatment. The energy efficiency in electromechanical system is much higher and comparing energy consumption with pneumatic systems, electromechanical brakes has been measured to be 8-10 times more efficient. This is of course very dependent on driving cycle and the biggest saving is in cities with a lot of start and stops. This energy saving comes to very good use in an electrified vehicle as the energy saving can be used to either reduce the battery size saving overall system cost or to increase the driving range of the vehicle with the same battery capacity.
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