Automotive braking trends – the inside track

This is the first of a series of blogs highlighting the most important trends facing the manufacturers of cars, brake systems and brake pads.

You can’t cut corners when manufacturing car brakes. Huge stresses are concentrated on small surface areas every time a car brakes – tens of thousands of times over a pad’s life. Pads must keep giving the same pedal feel and smooth deceleration in all conditions.

In a slow-moving and safety-conscious industry, demands are changing quickly, particularly faced with new emissions laws and regulations. Friction material compounders must develop different formulations with alternatives to copper and other raw materials for H&S reasons.

Our recent introductory article discussed the trends in automotive braking. Here, we’d like to expand on three areas that are most important to car and brake system manufacturers: reducing brake wear and emissions, standardizing pads globally, and electrification and driver automation.

Brake pad wear and emissions continue to reduce

Research is continually reducing brake pad wear, which is also important to reduce brake emissions. Over 90% of PM10 particulate matter emissions from traffic are now estimated to come from non-exhaust emissions. Up to half of that comes from brake wear, and legislation for emissions is being written in various countries and regions right now.

The legislation will most likely include details of particle sizes and possibly emissions chemistry. Car manufacturers are working closely together with legislators. Once legislation is introduced, it will set up a chain reaction where the car manufacturer has to comply, and this may change requirements for brake pads. In the short term, filters or vacuum pumps could reduce emissions to legal levels while longer-term solutions are worked on. At the moment, though, the extra weight makes manufacturers reluctant to add them, and filters are inconvenient when replacing brake pads in the aftermarket.

Standardizing brake pads and Global NAO

Different legislation in different geographic regions is making life difficult for car (and brake system) makers. Car manufacturers are increasingly looking to avoid the expensive process of customizing production lines for the different regions. European cars at the moment need low-steel (LS) brake pads that incorporate steel fibres. US and Far Eastern brakes instead use Non Asbestos Organic (NAO) also called ceramic friction materials.

^{Brake pad formulations differ around the world.}

LS pads have a higher friction coefficient and therefore the shortest stopping distances but score less on comfort. NAO materials have zero steel content, have a lower friction coefficient, but better comfort. An NAO pad for example doesn’t result in dirty rims which are common in Europe.

NAO materials give less disc wear, and tend to have better NVH (noise, vibration and harshness) particularly near end of life, and can be reinforced by materials like Lapinus’ mineral fibres. These fibres are (uniquely) certified bio-soluble and completely safe for humans and the environment.

The future of brake pads lies in a Global NAO standard. A normal combustion-engine car has 60-70% of its weight on the front wheels. Stresses are therefore particularly high on the front brakes, and these absorb most of the braking energy. The first Global NAO brake pads will therefore target the rear axle of smaller vehicles.

One obstacle holding back global NAO is European-focused legislation. The AMS (Auto, Motor and Sport) test sets the bar high when it comes to stopping under extreme conditions. AMS is widely accepted for maintaining safety, even with end customers, but is hard to achieve using NAO brake pads. However, more intelligent sensors in cars and a push towards lower maximum speeds on European roads could change this perception. In future, the test could be seen as over specified for normal traffic, which could open up the market for Global NAO.

Electrification & automation: corrosion, pad life & NVH

The most exciting automotive trend is undoubtedly alternative propulsion. This should grow from under 10% of cars today to around 60% by the end of the decade, mostly for hybrid EVs. Here, regenerative braking is a given because of the great increases in fuel efficiencies and range. Even in purely electric vehicles, though, regenerative braking simply won’t be strong enough to do away with car brake pads for many years yet. Cars must stop quickly in an emergency, and also during a car power-out.

Electric vehicles

EVs were sold globally in 2018, up 44% from the prior year

Brake pads on EVs and hybrids actually have to have a larger surface area than on conventional cars because of the weight of the batteries. This shifts the weight to the rear axle from 30-40% up to 50%. Increasing friction levels is therefore most important for rear brakes.

Brakes and brake pads for EVs and hybrids face a major issue: rotor and pad corrosion. Steel rotors on all cars corrode, but in normal traffic the rotor is cleaned on a daily basis. Regenerative braking however uses pads much less frequently, and both rotors and pads can therefore corrode. This can reduce safety and performance. Using an electronic parking brake can result in stiction, and after releasing the parking brake the rotor should be cleaned from corrosion.

Car manufacturers are looking at brake pad and rotor manufacturers to come up with a solution. In the high-end market coated, non-corroding rotors can solve the problem. Their additional cost, though, gives brake pad manufacturers a strong incentive to meet this new increasing customer demand.

Besides reducing brake pad life, pad wear leads to environmental emissions. These are more significant for EVs because of the lack of tailpipe emissions. Reducing brake noise would seem particularly important for EVs because of the (lack of) engine sound.

Although autonomous vehicles aren’t (yet) living up to their initial hype, sales of driverless cars with human override (level 4) will grow steadily. This is inevitable with 70-95% of all accidents being related to driver decisions, and autonomous cars being better at predicting traffic. Subjective feelings of safety will be critical, though, and automated cars will therefore have a very defensive driving style: no last-second overtaking manoeuvres or high speed travelling even if technically possible. That means less braking, and less demand on the brakes.

^{Three major areas of NAO research.}

Our next blog discusses the importance of manufacturing quality and consistency. That means consistent operation of the pad across its lifetime, and consistency between different production runs.