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 Post subject: Driving 100% in B mode?
PostPosted: Thu Dec 13, 2018 3:32 pm 
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Joined: Sun Jul 22, 2018 4:18 pm
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Location: Ottawa, Canada
OK, so I searched the forum for info on driving in B mode. I found a few opinions but nothing really definitive.

What I want to know is there any problem driving all the time in B mode?

My opinion is that coasting is giving away energy as coasting is merely another way of slowly slowing down. Coasting or during or whatever you call it makes sense in an ICE since increased rpm's means more fuel consumption, but it seems to me that the loss of rpm's (read momentum) in an EV is just loss of energy. So why not recuperate as much energy as possible?

I also noticed that on my 2017 the brake lights only come on when I completely take my foot off the accelerator. So going downhill with my foot partially on the a-pedal leaves the dial in the green (regenerating) without the lights coming on (not affecting the cars behind me). And I have to admit I kinda like the feel of the "hard" regen as it reminds me of go-carting!

Anybody know?
Jon.

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 Post subject: Re: Driving 100% in B mode?
PostPosted: Thu Dec 13, 2018 4:43 pm 
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I think it has more to do with your driving style than efficiency. I like to let my car coast towards a light, waiting for it to turn green, with my foot off the pedal. If it is in B mode, it slows down quickly, then I have to accelerate again when the light turns green.
I understand the eGolf goes into regen if you press the brake pedal lightly. If you press it hard, then braking kicks in. Charge and discharge have efficiency loss.

I also have a tesla. To "coast", I need to balance my foot on the "gas" pedal so it is neither powering the motor or doing regen.


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 Post subject: Re: Driving 100% in B mode?
PostPosted: Thu Dec 13, 2018 9:05 pm 
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Coasting is the most efficient. Any time you convert one form of energy into another, there are entropic losses. Regen converts kinetic energy into chemical energy, and there are losses. If you were to drive on a perfectly flat road, the most efficient way to travel is to just put enough energy into keeping the car moving and never braking because in an ICE car braking generates heat (lost energy) and regen in an EV charges the battery (not 100% efficient buy still very good). I drive in B slot around town because I’m not good at anticipating how long I’ll be able to coast, so for quick stops with no friction braking from a slow speed, B is best.

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 Post subject: Re: Driving 100% in B mode?
PostPosted: Fri Dec 14, 2018 2:50 am 
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Joined: Sat Jul 25, 2015 2:24 am
Posts: 782
Location: SoCal
If I expect to do a lot of braking (city driving, rush hour freeway), then I use B mode. If I don’t expect to be doing much braking, I use D, maybe D1 or D2 on the really steep stretches.

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 Post subject: Re: Driving 100% in B mode?
PostPosted: Fri Dec 14, 2018 7:12 am 
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Joined: Sat Nov 17, 2018 5:08 pm
Posts: 48
Location: Boston area, MA
Thorallophon wrote:
I also noticed that on my 2017 the brake lights only come on when I completely take my foot off the accelerator. So going downhill with my foot partially on the a-pedal leaves the dial in the green (regenerating) without the lights coming on (not affecting the cars behind me).
Jon.


I might be wrong about this, but from what I've experienced so far in my limited experience, putting the car in D3 mode with your foot off the accelerator pedal has the same or very similar effect to driving in B mode and leaving your foot partially on the accelerator, except that coasting in D3 mode with your foot completely off the pedal will not turn on the brake lights.

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 Post subject: Re: Driving 100% in B mode?
PostPosted: Fri Dec 14, 2018 10:18 am 
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Joined: Mon Oct 05, 2015 2:01 pm
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I almost always drive in D mode, and downshift to D1 or D2 when slowing down, using my foot brake last, so that the idiot driving behind me will at least see some brake lights to indicate to them they need to use the brakes and slow down, too.

I get 6.0 to 6.3 or 6.4 miles per kWh driving this way in the spring, summer and fall, whenever overnight temps stay warm, and it doesn't take much time to warm up the whole drive train /gearbox /CV joint /bearing grease stuff.

Now that it's a little cooler here in So CA, I am seeing 5.9 to 5.8 miles per kWh. It will be that way, probably through March.

Rain really lowers my miles per kWh, and shortens my range significantly, so I try to drive something else when it's raining, the e-Golfs range per recharge really suffers in the rain.

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 Post subject: Re: Driving 100% in B mode?
PostPosted: Fri Dec 14, 2018 6:52 pm 
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Joined: Sat Dec 19, 2015 4:16 pm
Posts: 114
manybees wrote:
Thorallophon wrote:
I also noticed that on my 2017 the brake lights only come on when I completely take my foot off the accelerator. So going downhill with my foot partially on the a-pedal leaves the dial in the green (regenerating) without the lights coming on (not affecting the cars behind me).
Jon.


I might be wrong about this, but from what I've experienced so far in my limited experience, putting the car in D3 mode with your foot off the accelerator pedal has the same or very similar effect to driving in B mode and leaving your foot partially on the accelerator, except that coasting in D3 mode with your foot completely off the pedal will not turn on the brake lights.

Same experience here, except one time I was turning into a tight driveway in D3 and the brake lights definitely did come on (it was night and I could see the CHMSL reflect in the rear window). I think if you give the car a lot of steering angle it will scrub off speed fast enough in D3 to trigger the brake lights.

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 Post subject: Re: Driving 100% in B mode?
PostPosted: Sat Dec 15, 2018 8:55 pm 
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Joined: Sun Jul 22, 2018 4:18 pm
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Location: Ottawa, Canada
f1geek wrote:
Coasting is the most efficient. Any time you convert one form of energy into another, there are entropic losses. Regen converts kinetic energy into chemical energy, and there are losses. If you were to drive on a perfectly flat road, the most efficient way to travel is to just put enough energy into keeping the car moving and never braking because in an ICE car braking generates heat (lost energy) and regen in an EV charges the battery (not 100% efficient buy still very good). I drive in B slot around town because I’m not good at anticipating how long I’ll be able to coast, so for quick stops with no friction braking from a slow speed, B is best.


I think I understand what you are saying f1geek, but I'm still having a hard time wrapping my head around the benefits of coasting in an EV. So, bare with me as I work through the thought puzzle.

If I understand you, given a perfect scenario: distance travelled will be more when coasting than when using regen, assuming same min and max speed. This would mean that there would be more accelerations per km travelled, therefore coasting is better (acceleration = energy loss, and regen does not recoup that energy spent to accelerate to max speed).

However this does not account for terrain, traffic, weather, etc. So, for example, you arrive at the top of a steep downward slope. The cost of accelerating to get to the top is the same in both cases (regen vs coasting), so it's a wash from that standpoint.

if the slope isn't steep enough, you have to keep your foot on the accelerator to maintain speed, so, again, the same energy losses in both cases.

If the slope is steep enough that the vehicle accelerates, you would then have to brake to satisfy one of the real world factors, such as to keep the vehicle under the speed limit, or from piling into the back end of the car in front, or...

So, in this scenario we then we have to determine how much energy is retrieved if using regen without braking vs coasting and braking slightly. Either case will be highly dependant on the situation and/or the driver, though one might assume that on average, in highway scenarios, coasting might be slightly better.

So, long story short, Twocars is correct, it's mostly down to how you drive. I'm with RonDawg, in that most of my driving is either during rush hour or short in town trips. Therefore B mode. The exception is the longer trips, which I am now trying to find out which mode is best to drive in to maximize the distance. I guess it will depend. :P

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 Post subject: Re: Driving 100% in B mode?
PostPosted: Sat Dec 15, 2018 9:53 pm 
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Joined: Thu Nov 16, 2017 4:53 pm
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Here is the simplest way to understand it. We know energy cannot be created or destroyed and that no machine is 100% efficient. So use the minimum amount of energy as possible if you want max range. The less often you set on the accellerator the less energy you will use. If you step on it more than necessary then regen will capture some of that energy but not 100%. Probably more like 2/3rd of it. The rest goes to waste as heat.


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 Post subject: Re: Driving 100% in B mode?
PostPosted: Sun Dec 16, 2018 1:24 am 
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Joined: Sat Jul 25, 2015 2:24 am
Posts: 782
Location: SoCal
Thorallophon wrote:
I'm with RonDawg, in that most of my driving is either during rush hour or short in town trips. Therefore B mode.


Keep in mind that I use B mode in the city because of having to frequently slow down. It doesn’t capture any more energy than using the brake pedal, it just means I can better modulate my speed using just the accelerator pedal instead.

On EV’s, when depressing the brake, the car first will try to use regen before the actual friction pads, unless you need a lot of braking power now (as in you slammed on the brakes) or the battery is too full to accept more charge. So I could drive around in D in the city and use the brake pedal more and get the same results. It’s more of a convenience thing.

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