EcoAnalog: Hybrid Vehicles

Blog Post created by tnelson654 Employee on Jun 15, 2017

On my bike ride downtown for coffee this morning, I waited in a double left turn lane surrounded by cars. I used to dread those moments because of the exhaust fumes. It's much better now thanks to hybrid vehicles and the new start/stop feature in traditional vehicles. Hybrid vehicles and stop/start gasoline-powered vehicles eliminate tons of carbon from polluting the atmosphere. Literally, tons!

According to the International Energy Agency in 2016, the transportation sector was responsible for approximately 23% of the world’s total carbon dioxide (CO2) emissions from fossil fuel consumption. On the occasion of their 9 millionth hybrid vehicle in April 2016, Toyota calculated that their hybrid vehicles produced approximately 67 million less tons of CO2 compared to conventional vehicles of similar size and driving performance. Today, almost every major automaker offers hybrid vehicles. So, certainly, that number is many times larger for the industry as a whole.


12V Stop Start

My first hybrid had the stop/start feature; it automatically shut off the engine at the first stop light and then started it back up when I wanted to go. It took some getting used to! And now that system has been applied to regular (non-hybrid) vehicles. For city driving, shutting off the engine at stop lights saves fuel and therefore CO2 emissions compared to idling at the stop light. Estimates range but many suggest 10% better fuel economy compared to the same model without stop/start. This has the potential to reduce much more CO2 than hybrid vehicles because there are so many more traditional vehicles on the road. I'm not going to attempt the math, but it's probably on the order of hundreds of millions of tons. Between the two technologies, that's a huge impact.


The algorithms differ by automaker. While traditional vehicles utilize a second lead-acid battery for restarting the engine, battery chemistry advances allowed hybrid vehicles to move from nickel-metal hydride to lithium-ion battery stacks. Accurately measuring and controlling the batteries is one of the keys to maximizing the performance of these systems. The stop/start system needs to be sure the battery is capable of restarting the engine before it stops it. The hybrid battery stack needs to keep each cell in the stack balanced with all the others, sharing equally and remaining fully charged. Isolating and level-shifting precision measurements of tiny voltages on a stack of hundreds of volts in an abusive environment is a challenge. It has to be robust, reliable and stable across temperature variations for the life of the battery system. And more systems use ADI than any other. Each generation is more integrated than the previous one, more precise, more reliable; and as they become more complex, the firmware support makes it easier to implement.


Schematic for battery monitoring


It's just what we do. So when I'm waiting at a red light on my bike, I don't have to breath all that exhaust, the planet doesn't have to absorb all that CO2 and I'm happy about that.