BMW's New Regenerative Braking Technology

[JoshCalkins]

The new 5-Series GT is currently making its rounds through the major automotive review publications pending its release towards the end of this year. While the debate as to whether or not the vehicle is warranted in BMW's lineup and whether or not it will sell is an interesting one, we will be leaving it behind today in order to look at a new technology that the 5-Series GT has onboard: BMW's Regenerative Braking System. Now, regenerative braking systems have been around for awhile now, and have found homes on many hybrid vehicles, but BMW's system is, as expected, far more elegant.

Regen Display In Dash

In a nutshell, all regenerative braking works by taking the kinetic energy of a spinning brake rotor and converting it to electricity when the brakes are applied. BMW's system does this as well, but what makes it special is the pairing of this system with an alternator clutch. The 5-Series GT's alternator will be disengaged most of the time. Whenever the throttle is applied, in either acceleration or maintaining speed, the alternator will disengage so as not to use valuable energy that is better used propelling the car. Whenever the brakes are applied and you want to slow down, the alternator will engage and begin drawing power from the turning engine, while at the same time the regenerative brakes also create electricity.

This accomplishes a few things all at once: first, the engaged alternator will act as a drag brake on the engine, gradually slowing it down while adding electricity; second, the regenerative braking will transfer the kinetic energy of the brake rotors to electricity, further slowing the vehicle down; and third, you brakes will have a much easier job bringing the car to a stop, meaning they will last longer.

5-Series GT

Of course, there are also computer controls governing the larger-than-average-size battery's charge so that if it gets to low, the alternator will engage regardless of driving situation. In essence, the kinetic energy that you want to get rid of when braking will be used to power your car's electronics, and the kinetic energy you want as you accelerate will be left alone. Quite an ingenious solution. BMW hasn't released any information on how much this system costs, so whether or not the technology will make its way to anything other than high-end models (the 5-Series GT is expected to retail at about 68,000 USD) is uncertain.