Deaglán Ó Meachair filed the following post, “Inside the eye of the dust storm,” on BrakeBetter.com concerning the evolution of vehicle-emission management from exhaust-pollution control to include that of brake systems. The post is excerpted with emphasis on the braking portion.
In September 2015, the automotive world learned a powerful new phrase. The phrase came to embody a damaging lack of transparency and trust in multinational OEMs as well as weakness in gatekeeping. In Europe, particularly, the scale of the problem was so widespread that it was clear a systemic reset was urgently needed. While OEMs scrambled to salvage public reputations and legislators searched for a more robust defence, prosecuting teams across the region responded with dramatic dawn raids on corporate offices and high profile arrests. Affected consumers were encouraged to allow their vehicles to be modified, so that the original non-compliant systems could be brought into line. Resulting changes in vehicle performance and value are still being fought through the courts.
PM from Brakes Greater Threat than from ICE
The background to the World Harmonised Light Vehicle Test Protocol (WLTP) exhaust emissions standards introduced in Europe in 2017 was informed primarily by the events described above, namely Dieselgate. The new standard was unforgiving, and was specifically aimed at ensuring non-compliant vehicles could not reach the market. Air quality had to be protected, and if that meant certain vehicle or engine variants were no longer viable, so be it. Even the standard industry plea to protect jobs and prosperity was only effective in briefly tapering the new requirements . . .
Particulate emissions controls were also strengthened, with the familiar Diesel Particle Filters being joined by equivalent devices on Petrol models. And the interest in particles (in particular!) also allowed for a widening of the scope of vehicle emissions beyond the exhaust, to consider other sources. The easiest non-exhaust source to measure scientifically has proven to be the brakes. Agreed test methods are established, formal legislation is being created, and it is clear that every vehicle manufacturer needs to pay close attention. What’s not yet agreed (publicly, at least) is when, and how much (or how few, if you will). Some assumptions exist regarding both these unknowns, and they feed into a very uncomfortable picture for the braking top brass.
How do you solve a problem like emissions?
There are three main approaches to reduce brake emissions; i) vehicle level measures, ii) brake adaptions and iii) near-brake devices. The vehicle level measures would include regenerative braking, automated driving and other similar approaches to reduce the use of friction brakes for appropriately configured vehicles. It appears such vehicle level measures offer significant benefit, and are likely to be effective, where available. However, for the (majority of) cars without these systems, adaptions within the brakes, or fitting specific treatment devices are required.
To adapt brake discs and pads to emit less particles will mean significant changes to the chemistry of either or both elements. These changes don’t come without cost or compromise, specifically with regard to friction levels and durability. Achieving an acceptable brake performance across all conditions for an acceptable cost is not always possible. Coupled with these fundamental concerns are the remaining level of emissions with such solutions (best case typically a 40 percent reduction). As the legislative limits aren’t yet known, this is no silver bullet.
Changing the friction behavior of the brake changes the fundamental behavior of every aspect. Therefore, as well as solving these challenges, the ABS, TCS and ESP systems need to be recalibrated to take account of the new basic performance. NVH performance must also be revisited, but typically, this can be done in parallel with the brake control calibration. If we predict that legislation were to come into force in 2025 (along with Euro 7, for example), that gives OEMs just over 40 months to finish. A typical base brake and ESP program would take 36 months, if the winter testing falls in the right place. Remembering that there isn’t a shovel-ready fix, we don’t yet know the targets, and ALL vehicles need to be ready, this is a difficult moment to be a brakes manager. (Much like the exhaust emissions labs bottlenecks, it’s likely there aren’t enough brake dynos, nor enough calibration manpower to deliver all variants simultaneously)
An alternative approach is to utilize near-brake devices which trap the emitted particles, preventing them from leaving the vehicle, and can be safely disposed of during service. The sealed drum brake found on Volkswagen’s MEB platform is one such solution, albeit with a slightly different motivation. Encapsulation of the brake disc and caliper allows for a similar range of benefits for electric vehicles, but with the added braking performance of disc brakes. At the recent EuroBrake conference, Advanced Braking Technology demonstrated the comprehensive performance of their Terra Dura encapsulation system. As well as offering complete encapsulation of the emissions, the solution provides excellent protection of the brake hardware and NVH benefits, while allowing continued use of existing friction materials, thus avoiding the potential recalibration activities on a large volume of vehicle variants.
The lessons learnt from the introduction of WLTP loom large for OEMs as they navigate the future of brakes emissions. As evidenced by the recent significant downtick in exhaust emissions limits, the industry is on the back foot. Brake emissions levels are a firm focus of the regulators, and it is likely that there will be progressive tightening of these targets once the initial levels are introduced. The sprint to clear the initial limits is necessary due to the timing scenarios discussed, but it would seem difficult to believe that the race will stop at the first hurdle.
To view the entire post, click HERE.