Author Topic: Speaking of fuel efficiency, a random idea for hybrids  (Read 1877 times)

Offline TaviRider

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Speaking of fuel efficiency, a random idea for hybrids
« on: January 23, 2014, 12:18:14 AM »
So a hybrid like the Prius I drive has a limited battery capacity. The electronics also have to avoid charging the batteries too quickly to avoid shortening their life. It also must avoid completely depleting the batteries to avoid leaving the driver with only the gas engine for power.

My daily commute involves going uphill briefly, then downhill for a good distance. During the uphill, my Prius uses some battery and some gas at the same time, and at the top of the hill the battery is at about 50%. But the downhill is more than enough to fully charge the batteries. Some of the potential power is lost. If only the car knew that it was about to have a surplus of charge during the uphill. It could rely mite heavily on the batteries then, perhaps almost completely draining them before the long downhill.

Well now we have navigation systems, GPS, and elevation maps. It seems like the system could predict upcoming battery loads and adjust the balance between electric motor and gas engine to minimize losses.

Does this make sense? Is it plausible?

Offline adrive7

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Re: Speaking of fuel efficiency, a random idea for hybrids
« Reply #1 on: January 23, 2014, 07:37:20 AM »
100% plausible, and almost already in use. There are two systems that come to mind which are similar to your idea:

1) The Chevrolet Volt has a button for "Mountain Mode" which essentially tells the car to run the engine and save battery power for later. They call it mountain mode, but a better name might be "EV Delay. It's ideal for a situation where you drive on the highway for a while before dropping into a city. You're better off using the gas engine on the highway and saving the EV power for the city.



2) The latest MINI Cooper (2015) just unveiled at the LA Autoshow has a predictive shifting feature ("MINI Predictive Drivetrain") which uses GPS data to figure out what gear you're going to need for an upcoming corner. This is probably more for performance than efficiency, but the concept is similar. Also, it's for automatic transmissions only, obviously.

Joe
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Offline Grawk1

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Re: Speaking of fuel efficiency, a random idea for hybrids
« Reply #2 on: January 24, 2014, 06:53:16 PM »
Related question, why don't current electric cars have a mechanism to charge their batteries using the energy lost during braking?

 I understand the safety concerns of having less efficient brakes in emergencies, but surely there's a way to deploy an induction coil instead of a brake pad in the cases of slower, controlled braking, such as when going down a large hill or driving in city traffic. Seems like TaviRider could turn off the petrol engine entirely, go into neutral and brake all the way down the mountain, generating a significant percentage of the energy he will need to go back up later.

Offline TaviRider

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Re: Speaking of fuel efficiency, a random idea for hybrids
« Reply #3 on: January 24, 2014, 09:45:01 PM »
Related question, why don't current electric cars have a mechanism to charge their batteries using the energy lost during braking?

They do. It's called regenerative braking. They also have regular friction brakes as well. When you decelerate in a Prius, a portion of that energy is stored back in the batteries. However if you brake hard, the generator can't slow down the car fast enough, so the braking system automatically adds in some of the friction brakes. The ideal way to slow a Prius to a stop is to do it steadily and gently so that the friction brakes aren't used at all, ensuring the maximum energy is recovered. In fact, I once considered an after-market modification for my Prius like this one to add an indicator that tells me whether I'm using the friction brakes.

So in my original post, the problem is that going downhill for a long distance and gently braking almost the whole time completely fills the Prius batteries through regenerative braking. By the time I get close to the bottom of the hill the Prius actually stops regenerative braking because it has nowhere to put the power, and it relies more on the friction brakes. It also automatically engages the gas motor to help slow the car down, just like switching a standard gas car into a low gear. I want to avoid all that by making sure the battery is as drained as possible at the top of the hill.

Offline Grawk1

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Re: Speaking of fuel efficiency, a random idea for hybrids
« Reply #4 on: January 24, 2014, 10:18:27 PM »
Ah, understood! thanks for explaining