Regenerative Braking

Regenerative Braking In Hybrid Vehicles

Hybrid vehicles and all electric powered vehicles use a system called regenerative braking to conserve energy. Regenerative braking creates power to recharge electric batteries.

Let's break this down further. What is clear is that in hybrid or all electric vehicles regenerative braking is a system that captures the vehicles motion or momentum energy and turns it into electricity. This same electricity being produced is what recharges or "regenerates" the electric battery when the vehicle decelerates or comes to a stop. The battery being charged is what powers the vehicle's electric motor. In all-electric powered vehicles, this motor is the only power source for vehicle operation. In hybrid cars, the electric motor works in tandem with an internal combustion engine. In the case of hybrids, the electric motor is not only used for propulsion, but it also functions as a generator. So how does this help your brakes?

In all-electrics and hybrids, the motor is referred to as a motor/generator (M/G). To get deeper into the generation of electric in this regenerative braking system you need a basic knowledge of how a motor/generator operates.

So How Does a Motor/Generator Work in an Electric or Hybrid Vehicle?

Regardless of vehicle design, a mechanical connection has to exist between the motor/generator and the drive train. The set up in all-electric vehicles could contain a motor/generator at each wheel or a motor/generator located in the center fitted to the drivetrain through a gearbox.

In hybrids, the motor/generator might be a single piece driven by an accessory belt originating from the vehicle's engine. It may also be a flat or pancake motor/generator bolted between the vehicle's engine and the transmission. This is the set up found in the Toyota Prius and is the most common. The set up could also be multiple motor/generators that are mounted within the hybrid's transmission. This is the set up for dual mode hybrids. In all these cases the motor/generator is still responsible for propulsion.

Propulsion with Motor/Generator

Most hybrid and electric vehicles use what's called an electronic throttle control system. Once the throttle pedal is pressed, the onboard computer receives a signal, which further turns on a relay in the controller. The relay sends current from the electric battery through to an inverter/converter that sends it to the motor/generator producing propulsion. Current is controlled by how much force is exerted on the throttle pedal. The more force is applied to the pedal, the more electric current flows and the faster the vehicle can drive.

In hybrid vehicles, taking into account the weight of the load, battery charge and drive-train design, a heavy throttle will activate the internal combustion engine to get more power. On the other hand, reducing exertion on the throttle will decrease electric flow to the motor causing the vehicle to decelerate. Lifting even more force off the throttle further or being completely off it will cause the electric current to reverse direction. This will move the vehicle from motor/generator mode to just generator mode and start the regenerative braking process.

Once the electronic throttle control is closed and the vehicle is still in motion, the energy sent out from that motion or momentum can be used. Another name for this energy is kinetic energy. It can be captured and used to decelerate the vehicle or recharge the battery. The hybrid's computer signals the electric battery to stop transferring electricity through the relay and, instead, receive it via the charge controller. As this happens the motor/generator stops receiving electric current and instead sends the current out to the electric battery for recharging.

Basically, when the motor/generator has electricity it makes mechanical power for propulsion. When the motor/generator has mechanical power it creates electricity. Electric current actually causes the vehicle to slow down via magnetic friction. This magnetic friction reduces the vehicles momentum and speed.

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