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Someone got himself on Clean Technica today
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Thanks! I wasn't really thinking about doing a write up on the topic, but Jake from CleanTechnica reached out to me.
Thanks for the explanation. However a question I would really like to have addressed is when driving on the open road without regular braking what mode is better, D or L? A friend who also owns a Bolt claims that D mode doesn't slow the car as much as L mode every time the accelerator is let up a little and therefore he loses less momentum whereas L mode causes a loss in speed which has to be recovered. I'm only talking about highway speed driving without regular slowing. Which mode will give greater range over a long distance highway trip without traffic congestion?
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The highway choices are D, L or Cruise Control.
If you have focused attention controlling all movement in your right foot, D and L would be the same.
If you like to move your right foot occasionally during a long, or short trip, D allows this without the brake lights coming on and rapid deceleration when you release pressure on the Go Pedal.
(There is a possibility that allowing the car to slow on uphills and go faster on the downhills may be better than letting the cruise control lock onto a set speed. With EV's you have regen on the downhill side. Proving this would be difficult.)
If the accel / decel rates and cruise speeds are the same, D and L would be the same amount of miles/kWh.
Only one mode requires constant attention and no coasting.
Somewhere along the way Chevy marketing and other articles implied that there is an efficiency advantage to 1 Pedal Driving.
If regenerative braking/deceleration where 100% effective there would be no difference between D and L (any moment lost would be made up in battery regen). Since this is not the case (there are always going to be losses when going from one state to another) driving in D on the highway is the proper way to go from an efficiency stand point, in other words don't sacrifice momentum for regen. Even on long down grades where you might have to apply the brakes to prevent going too fast so long as the amount of braking applied doesn't activate the discs from contacting the rotors in which case momentum is wasted as heat as well. With effectively nothing in it between D and L in stop and go driving (whether you get regen from braking or from transmission the regen is coming from the same source) it is largely personal preference.
That is why I called out pedal control with L when hypermiling. Regenerative braking is inefficient (heck, braking alone is inefficient in any vehicle including ICE), so reducing the amount of regenerative braking you do is the best for efficiency. However, that is not synonymous with using D instead of L. If I let off the accelerator in D to coast with only 15 kW of regen, that is effectively the same thing as letting pressure off the accelerator in L until you are coasting with 15 kW of regen.
So efficiency isn't the reason to chose D over L in order to maximize efficiency. The most valid reason for using D over L is if someone lacks precise pedal control. In that case, leaving the settings in normal (not Sport) and D might work best.
That is true in that few second interval that may happen but in real world driving that is not the case.
The higher the amps through a cable (laminated ribbons), especially one that is well insulated will waste watts as the cable temperature rises. Keeping the lowest possible amps through the drive wires will incur the lowest wasted power.
Try a loop you do often. On one, while still maintaining the same top speed, use the pedal instead of the cruise. Try to minimize the amps when you must pick up speed and burn off speed.
Try a loop you do often. On one, while still maintaining the same top speed, use the pedal instead of the cruise. Try to minimize the amps when you must pick up speed and burn off speed.
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There seems to be a mindset among some people that regenerative braking is like some sort of magic elixir that gives you more juice. I've seen people lament that they don't benefit from regenerative braking when they drive on the freeway, which seems kind of silly to my way of thinking. It's as if they had the attitude "if only I could stop and then start again it would be better for me", which is patently false.
Rather than thinking of regen as "giving you more range", I think it's better to view it as "wasting less when you have to stop". That puts it into its proper perspective and makes it more obvious that stopping and starting is actually a bad thing and regen is just partially mitigating its negative effects.
Rather than thinking of regen as "giving you more range", I think it's better to view it as "wasting less when you have to stop". That puts it into its proper perspective and makes it more obvious that stopping and starting is actually a bad thing and regen is just partially mitigating its negative effects.
People seem to miss the "re" in regeneration.
The reason regenerative braking is valuable and useful is because real world driving is never ideal. In real world driving, you don't get to accelerate to speed, drive a constant speed without interference or changes in topography, and slowly coast while decelerating to your destination using only the car's momentum. If that's how driving actually went, regenerative braking wouldn't be of any use.
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In your example D is more efficient because in D you can start the coast sooner so the car doesn't have to provide as much power to get to the start of your coast. As a result you've used less power in D than in L.
The reason regenerative braking is valuable and useful is because it is an alternative to friction braking. Recharging the battery and reducing wear on brake pads and drums are bonus effects, not the primary goal. The regen tools (D, L, and paddle) provide driving style benefits, including the ability to mimic the use of friction brakes when braking. If it is not clear that regenerative braking is a method of reducing the speed of the vehicle, the expectation arises of somehow being able to develop a driving style that maximizes regen and recharges the battery as you move down the highway.
Discussion of regenerative braking in terms of how much more regen one can get from L than from D, and even more by using the paddle in combination with either L or D, seems to encourage poor driving habits in order to maximize regen levels... Drive in L, then use the paddle on top of L and you’ll get the strongest regen... But be prepared to step on the accelerator to keep yourself from stopping too soon...
What somehow gets glossed over is that the actual amount of regen captured as you slow down doesn’t really depend on the regen level used, does it? On level terrain, if you slow down from 40 mph to 20 mph because the traffic light ahead has changed to red and traffic is slowing, or if a stop sign ahead requires you to slow from 35 mph to a complete stop, isn’t the amount of regen you get as you reduce your speed by 20 mph, or come to a complete stop (using friction brakes when momentum is insufficient to create regen), about the same regardless of the level of regen you use (D, L, or paddle), and the primary difference is the distance and time it takes to slow down/stop?
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There are two parts to the answer.
First of all, you get more juice back into the battery if you slow from 60mph to 40mph than you do if you slow from 35mph to 15mph. That's because the change in speed takes place over a larger distance, and therefore requires more work. The exact reverse is also true: it take more work to accelerate from 40mph to 60mph then it does from 15mph to 35mph. Anyone who's ridden a bicycle with multiple gears will understand this intuitively.
Secondly: yes, you essentially regain about the same amount of power by slowing from 35mph to 15mph whether you do it quickly or slowly. But there's a reason to do it slowly, especially when you're slowing for a red traffic light: the longer it takes you to reach a red traffic light, the greater the chance that it will turn green before you arrive - and if it does then you can accelerate without having lost as much speed. Since regen is only something like 66% efficient, any loss of speed that you can avoid will be a benefit.
Thanks, Sean, for the clarification. Clearly, the faster you’re moving when you first apply the regenerative brakes, the greater the energy that is being used to "crank the generator" and create the regen. Slowing from 60 mph to 40 mph will create more regen than slowing from 35 mph to 15 mph (actually, I suppose, the regen is capturing a portion of the energy used to accelerate the car, and it takes more energy to accelerate from 40 mph to 60 mph than from 15 mph to 35 mph). Nevertheless, the distance and time it takes to drop your speed by 20 mph is related to the level of regen used to slow the car, but the amount of regen you get by doing so isn’t.
Ladogaboy's discussion of one-pedal driving seemed to emphasize the methodology of maximizing the regen level readout on the display, when it wasn’t clear to me why one would want to do that if the amount of regen created by decelerating a given amount is not dependent upon the level of regen used to do that.
I am pleased to read your reason for slowing at less than maximum regen levels (i.e., coasting in D instead of L)... you increase the chances the light will change and you won’t lose as much speed before you can accelerate back up to cruising speed. You "lose" some regen if you don’t have to decelerate as far as anticipated, but the amount of energy you then didn’t need to use to accelerate back up to speed will allow your car to travel much further when used to maintain cruising speed.
Ladogaboy's discussion of one-pedal driving seemed to emphasize the methodology of maximizing the regen level readout on the display, when it wasn’t clear to me why one would want to do that if the amount of regen created by decelerating a given amount is not dependent upon the level of regen used to do that.
I am pleased to read your reason for slowing at less than maximum regen levels (i.e., coasting in D instead of L)... you increase the chances the light will change and you won’t lose as much speed before you can accelerate back up to cruising speed. You "lose" some regen if you don’t have to decelerate as far as anticipated, but the amount of energy you then didn’t need to use to accelerate back up to speed will allow your car to travel much further when used to maintain cruising speed.
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This should be a fairly straight forward math problem. F = M x A. Unfortunately, it has been a long time since I have taken physics! This would be an awesome question in a 10th grade math textbook.
Bottom line though would be that the rate of acceleration/deceleration and the force required to slow or speed up are the two factors involved. One other factor involved too is distance and it is involved because that is how the car displays its efficiency. I suspect though that the math would show that the difference between the two would be minimal from an energy saved/used perspective based on the equation(Newton’s laws) unless the Volt is way less or more efficient at 70% regen vs 100% regen or likewise to the acceleration process.
I suspect that the green spinning efficiency leaf ball on my 2013 is using Newton’s second law math to display its deviation from Newton’s first law. Aside from the wheels on the road and the wind against me, I never want to experience Newton’s third law
while driving.
Bottom line though would be that the rate of acceleration/deceleration and the force required to slow or speed up are the two factors involved. One other factor involved too is distance and it is involved because that is how the car displays its efficiency. I suspect though that the math would show that the difference between the two would be minimal from an energy saved/used perspective based on the equation(Newton’s laws) unless the Volt is way less or more efficient at 70% regen vs 100% regen or likewise to the acceleration process.
I suspect that the green spinning efficiency leaf ball on my 2013 is using Newton’s second law math to display its deviation from Newton’s first law. Aside from the wheels on the road and the wind against me, I never want to experience Newton’s third law
while driving.
Not sure we can blame Chevy marketing for this one. People have misunderstood "maximum regen" between "peak regen" and "best regen" and its implications basically for as long as there's been regenerative braking.
That becomes an opinion. D allows more speed build up on downhills in cruise and is likely more efficient than L. Allowing the car to accelerate from gravity doesn't have the conversion losses of turning the generator and charging the battery. That could lead to exceeding the speed limit though and maybe going faster than the driver is comfortable with in some situations. L would maintain set speed better. In L the driver isn't as much loosing momentum as he is converting the extra momentum into battery charge. There are some efficiency losses doing this, but there are upper limits to how much you can allow the speed to increase on a downhill run. On a winding road with a 9% grade and 30-40 mph speed limit, it's unlikely I can safely just coast down the hill in D.
Not necessarily. You are controlling the accelerator the whole time, so it's not as though you magically start at a point of high regenerative braking and have to dial it back.
Yes, I agree. That is why I called out that point in the video and interview.
But to your point above, I feel that is why I feel it is important to assess maximum regenerative braking force. Again, real-world driving isn't ideal, so sometimes you must brake aggressively (even in non-emergencies). The stronger the regenerative braking force, the less the friction brakes are used.
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