August 17th, 2021
It’s a simple yet genius idea: capture the kinetic energy generated from braking, and use it to help power the vehicle. Electrified braking, known as regenerative braking, does exactly this. It stores the wasted braking energy, and uses this to power the vehicle. In this blog, we take a closer look at how this super-efficient system works.
The standard braking system uses a friction brake. When the driver puts their foot on the brake pedal, hydraulic fluid pushes the brake pads and discs together, and the friction caused by this slows the vehicle down. This process generates heat – which is wasted energy.
A regenerative brake on a modern petrol or diesel motor is used to charge the vehicle’s battery. It’s pretty low-key and just runs ancillary functions. However, in electric cars or hybrid electric vehicles, the regenerative braking system plays a more significant part in helping to charge the large battery.
The electric motor in an electric/hybrid car changes running direction, depending on whether the driver is accelerating or braking. When their foot moves from the gas to the brake pedal, the motor changes direction and this puts the braking energy into the battery, by acting as a generator.
Different makes of car have different levels of regenerative braking, which in some systems can be adjusted by the driver (although Tesla has now removed this feature). All models still have hydraulic brakes that works alongside the electric braking system and in some situations the hydraulic brake will override the regenerative brake for example, during an emergency stop.
There’s great potential for energy storage from braking. To give you an idea of the energy generated from friction braking, brake manufacturers Brembo claim that a Formula 1 car can generate temperatures of up to 1000°C (that’s quite an extreme driving example and most of us hopefully never experience this level of braking torque, but you get the idea).
The energy captured during deceleration is stored, and hybrid electric vehicles use this to recharge their batteries while they’re being driven. A pure electrified vehicle will still need plugging in to receive the right amount of energy, with the regenerative braking system helping to keep the battery topped up.
Naturally, driving style has a significant impact on energy regeneration, just as it has on fuel consumption in an internal combustion engine car. If there is little braking force applied, if the driver maintains a constant speed or is driving down a lot of low-speed roads, there’s less braking power generated to store.
Drivers new to electric vehicles simply need to adjust their driving styles and become more conscious of how they brake. A slow run-up style of braking is better for energy efficiency than a sharp, last-minute stab of the brake pedal (which would probably cause the hydraulic system to kick in, anyway). Switching to an electrified vehicle is about more than fuel economy and cutting down on emissions: it’s also about how your car can generate its own power in a virtuous circle.
There is another impact regenerative braking is having on electric vehicles, and that is moving back to drum brake systems. There was a trend to move to disc brakes all around, but with electric vehicles the braking systems are used much less (because of regenerative braking) and the friction brakes are only used in emergencies or right at the end of the braking cycle. A lot of electric vehicles are moving to discs at the front and drums at the back. Generative braking is also creating a rust issue on discs as they are not being used as much, making drum brake systems a more suitable solution as less of the braking components are exposed. The great advantage of this is that they need less maintenance and represent an opportunity to save some money too.
Regenerative braking isn’t just used in vehicles. Electric trains feed stored energy back into overhead power lines, while Otis’ ReGen’s lift uses energy efficiency tech to feed power back into its host building.
Challenges for the automotive industry include how to maximize the efficiency of regenerative braking systems in a range of vehicles. A large, powerful vehicle will naturally generate more kinetic energy so will be better able to charge up its own battery; however, we don’t all want to be driving truck-sized motors around our cities. Every electrified braking system helps, moving us collectively closer to a more energy efficient future: we look forward to seeing what the next gen of regen brings.
At Saint-Gobain, we work closely with the automotive industry, providing them with bespoke components for a range of applications. If you want to discuss your project, engineer to engineer, please get in touch with the team at Saint-Gobain.