► In-motor brakes for electric cars on the cards
► Mercedes is investigating the technology
► Designed to reduce weight and complexity
Mercedes is looking to the future of electric cars, and is investigating how it can reduce the weight and complexity of an EV by engineering brakes into an e-motor thereby removing traditional discs in the wheel hubs.
Other benefits, Mercedes says, include a reduction in maintenance, aerodynamic improvements and a reduction in brake dust particulates – that latter point being a key improvement for Euro7 emissions standards.
‘The bottom line is, even with high energy regeneration when slowing down with an EV, we still need a friction brake,’ says Christoph Schildhauer, lead engineer on the in-motor brake project. ‘Around 98 per cent of braking [with our EVs] are below 0.3G, but the ones that are above that are harder to handle, so we still need physical brakes for the last two per cent.
‘That explains two things in the market of EVs,’ adds Schildhauer. ‘It explains why customers are reporting rust on the rear wheel axle brakes, and that recuperation allows us to design a brake concept to last a car’s lifetime.’
Merc’s new braking system, then, is integrated into an electric motor. For the engineering demo, the team have added on an in-motor brake to the same electric drive unit that is used on the new Mercedes Modular Architecture – the platform that will underpin an all-new CLA and three more models.
It’s still a physical disc brake, but a smaller one and one where the brake pad covers 100 per cent of the rotating disc, rather than a section in conventional disc brakes. Mercedes claims that is ‘subject to minimal wear, doesn’t rust and is virtually maintenance-free.’
‘A conventional disc brake is around 22kg,’ says Schildhauer. ‘If we take this weight [times four] out of the car, we’re estimating around 40 per cent less unsprung mass, improving driving comfort and lighter dampers. Also, if you have a lighter wheel, it means you can accelerate faster.’
The idea also potentially frees up wheel and car design. Conventional brake discs need cooling, either via the wheel designs themselves or via ducts in the car – if not both.
But if it still uses a conventional brake pad and disc, just hidden away, what about brake dust that will be still emitted? ‘The brake dust generated will be stored into a cavity in the unit, which designed to hold a lifetime of dust,’ adds Schildhauer.
Ah, yes – a ‘lifetime.’ How does Mercedes define that? ‘We say that’s around 300,000km, or 15 years,’ Schildhauer responds. Far longer than the average someone owns a car for in some cases, but only in some cases.
What happens if someone has their car for longer, and needs to have the dust cavity emptied, repair or replace the brake components? That’s the part Mercedes is still working on. ‘For us, the design for good service quality is important, so we want to make sure that the effort for servicing the car is as little as possible,’ says Schildhauer.
For now, Mercedes is keen to stress that this is still in the experimental phases, and isn’t likely to launch onto a car in the near future. But it shows how far into the future Mercedes engineers are looking.