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Take a Brake: Read About Start&Stop and Regenerative Braking
You’re going to hear more and more about these features, so might as well know what they’re talking about. That way you can impress them at the water cooler with your impressive knowledge.
First of all, you should know that an idling engine consumes between ½ and 2 litres of fuel an hour, depending on engine displacement and the accessories that are being used (air conditioning, heating, lights, etc.). Furthermore, when idling, energy is lost pure and simple, and produces useless greenhouse gases. The Start&Stop provides a solution to this problem.
If the engine is turned off at a red light, energy consumption will be nil if the energy used during the stop and that needed to restart comes from another source than the fuel tank. However, if the battery is emptied during the stop and that it recharges when the engine is running, there’s no gain to be made. That’s why the Start&Stop system is always associated with regenerative braking, which I’ll explain further on.
In order for S&S to work properly, an additional energy source is required: mechanical components (air conditioning, electrical power steering, automatic transmission) must also be designed with the system in mind. Furthermore, the starter must be reinforced as the number of starts will be multiplied, or another starting mechanism proposed altogether. Transition from one mode to another has to be kept simple and almost imperceptible to the driver.
In a “normal” car, electrical energy (that which is stored in the battery and used to power accessories) is generated exclusively by the combustion engine’s alternator. So all the energy used by the car ultimately comes from burned fuel. Regenerative braking produces electrical energy (stored in another battery of greater capacity) by converting energy normally lost through the friction and heat produced during braking. The “free” electricity can be used to power accessories during the stopped phase at red lights in addition to giving a small boost during acceleration.
In all cases, a reversible electric motor is used to slow down the car and produce electricity. It’s a bit like the small generator we had on our bikes as kids, the one produced electricity for the headlamp by using one of the wheels to drive it. Do you remember how it made pedalling more difficult? Well, the S&S uses the same principle. The simplest reversible electric motor is the alternator-starter of light hybrid systems. In a nutshell, this is a beefed up reversible alternator: it will charge the battery when the car is coasting with no throttle, and it can act as an electric motor when that battery sends it some juice. It is belt driven, and normally recharges the battery only when coasting. When the engine is turned off at a stoplight, the alternator acts as a powerful motor for re-starting and can supply additional power when accelerating.
It’s interesting to note that regenerative braking doesn’t call upon the vehicle’s brakes. It’s the slowing down that is used, not the actual braking itself. Normal braking power is always available for emergency braking and at to keep the vehicle immobile.
S&S and regenerative braking should become more widespread in the next few years: they don’t cost that much, their effectiveness has been proved, and they’re relatively easy to install on a conventional axle system.
So, what do you think? Let’s talk.
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