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.
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.

Does nobody have a pen?

The reality inside powertrain departments during this time was grim, to say the least. The sign-off criteria for new powertrains were suddenly strenuous, the burden of proof onerous, and very few powertrain configurations were able to meet the new requirements without remedial action. A significant bottleneck (ironically) proved to be emissions lab availability, as solutions needed to be developed alongside the expanded testing requirements of WLTP. Every current model program was affected, but alongside that, products already in the market had to be fixed, and these solutions also needed to be developed and qualified. Many powertrains were either temporarily withheld from markets, or abandoned altogether. Porsche even took the extraordinary step of suspending all new orders for a number of months, to buy time to fix it’s vehicles. Signing off a powertrain program against these new requirements was no laughing matter, especially with many top managers either already incarcerated or awaiting trial. While the operational effects of this maelstrom could be seen in sales charts and balance sheets, the cultural effects were a little harder to appreciate from the outside.

Fig. 1: The VW Golf GTI, like many, was unavailable while awaiting WLTP compliance

Braking into the crosshairs

While some of the effects inside OEMs were discernible in the marketplace, there was another factor which was not so easy to spot. Legislative efforts to clean air quality were significantly bolstered, as were the resources dedicated to this subject. The research and testing capabilities of governments across the world increased, and in Europe specifically, this coincided with a renewed vigour in demanding more (or less, if you will) from automobiles. Fleet-wide CO2 targets for the first half of this decade were pushed down significantly, and the next major exhaust emissions package, Euro 7, was envisaged as the final one – the last framework under which internal combustion would be allowed enter the market. So strenuous were these requirements, that OEMs claimed that emissions control devices now represented over 60% of the cost of a powertrain (up from just under 50% under Euro 6).
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% reduction). As the legislative limits aren’t yet known, this is no silver bullet.
Changing the friction behaviour of the brake changes the fundamental behaviour 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)

Fig. 2: An enclosed brake disc offers complete entrapment of all emissions

An alternative approach is to utilise 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.

Race Strategy

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.