bicycleguy
Posts: 45
Joined: Thu May 14, 2015 5:19 pm
Location: Torrance, Ca

Re: Regenerative braking in reverse down a steep driveway

Sun Jan 24, 2016 5:15 pm

I don't think what I described is a software bug and I don't think it hurts anything. The 'transmission' is in name only. The motor rotor is always connected to the output shafts thru the planetary gear reducer/differential, no mater the gear, including neutral. The only conventional electromechanical mechanism is a latch pawl for park. As long as you avoid shifting into Park all the action happens with software controlled changes to the electric fields the motor inverter provides.

A maybe less (sycologically) stressful way to see the effect is simply drive forward up a modest hill near zero speed and let off the gas. The car will come to a stop and then start falling in the reverse direction regening. As indicated by the gauges you are not using power. The power is coming from the potential energy from going from high to low on the hill. If you step on the accelerator you will regen even more as the kinetic energy of the vehicle is also converted, just like when stoping in the forward direction. This happens in the control logic automagically because it is looking at the difference in torque demand from the gas pedal vs what the car is doing to determine how much to power or regen.

The more likely software error is why it doesn't do this in R.

bicycleguy
Posts: 45
Joined: Thu May 14, 2015 5:19 pm
Location: Torrance, Ca

Re: Regenerative braking in reverse down a steep driveway

Sun Jan 24, 2016 5:56 pm

JackHickey wrote:In D or L there is creep which requires a foot on the brake. That takes charge from the battery.
That creep is the fairly awesome control system faking you out. It makes creep because that what drivers are used to. However, as soon as you put on the brake enough + fraction of a second the torque is shut off. When you lift your foot off the brake the control system turns it back on.

You can partially confirm this yourself. Sitting with the ignition on and your foot on the brake, in a quite place, shift between forward and reverse and back a few times. You will notice no surging, sounds or any indication of torque being applied like you feel on a conventional car.

Zoomit
Posts: 242
Joined: Sat Jun 13, 2015 1:54 pm
Location: SoCal

Re: Regenerative braking in reverse down a steep driveway

Sun Jan 24, 2016 6:16 pm

bicycleguy--I believe what you're saying, but I'd believe it more if you didn't refer to the right pedal as the "gas pedal". ;)
2015 Spark EV: 2LT, DCFC, Summit White

NORTON
Posts: 1380
Joined: Fri May 01, 2015 5:52 am
Location: KC,MO

Re: Regenerative braking in reverse down a steep driveway

Sun Jan 24, 2016 6:22 pm

SparkevBlogspot wrote:
NORTON wrote:Brand T and B do not have blended brakes on their BEV brake pedal. The brake pedal is friction brakes, Only.
Whoa? I had NO idea! I guess that's why T & B always complain about lack of 1 pedal driving, even for gas cars.
There really needs to be a 'Sarcasm Font' on forums like this, no? ;)
I think this is sarcasm, I'm not sure without some help..... :oops:

I test drove a Tesla P85D and a BMW i3. Both require the '1 foot driving' method. No 'adjusting yourself' or shifting around in the seat. You must keep your foot on the Go pedal at all times. (Not sure what you are talking about with the gassers.)
edit:
For a first time test drive of an EV this may feel strange and unusual. It is.
Some owners embrace this new method! Others like a plane old fashioned 'Coast' from the car and not have to work for it.

In fact the i3 uses power to bring the car to a complete stop if you take your foot off the Go pedal, and at a strong deceleration rate. The brake lights come on because of this.
(I would hate this in slick winter driving). I need a normal 'Coast' with foot off the Go pedal.

I didn't test this on the P85D. I have read that both can be config'd for different levels of regen with 'foot off the Go pedal'. And I read on both cars the brake pedal is just an old fashioned brake pedal, No regen from the brake pedal. This may be wrong....
Last edited by NORTON on Mon Jan 25, 2016 7:41 am, edited 1 time in total.
'14 Spark EV 2LT w/ DCFC. 91k miles.
'17 Bolt Premier w/ It All! 59k miles.
GM needs Modern Troubleshooting tools for Modern EV's.
3 step Trouble Tree, 1st try, nope, 2nd try / cost $800. 3rd try fixed it.

StevesWeb
Posts: 147
Joined: Tue Jan 07, 2014 5:36 pm

Re: Regenerative braking in reverse down a steep driveway

Mon Jan 25, 2016 4:29 am

Zoomit wrote:bicycleguy--I believe what you're saying, but I'd believe it more if you didn't refer to the right pedal as the "gas pedal". ;)
Yes, it's called the volt pedal, although I'm sure a lot is done with pulse width and such. That reminds me I own a domain I need to develop - voltpedal.com.
/off_topic

I was scared the first time I backed Sparky out of our carport. There is a steep ramp up to the house, and Sparky is very happy to roll downhill fast. The brakes felt entirely different, as if they needed pads or were under-specced, and just for a fraction of a second I was concerned I'd hit something. Of course I was not driving a 2100 lb car, these cars are heavy for their size.

I never saw any indication of regen in reverse, and my guess was that the absence of regen as compared to going forward was a factor in why the car feels difficult to stop when backing up downhill.

It's only that one very steep spot that produces this effect.

SparkevBlogspot
Posts: 499
Joined: Mon May 25, 2015 12:19 pm

Re: Regenerative braking in reverse down a steep driveway

Tue Jan 26, 2016 11:44 am

bicycleguy wrote:You can partially confirm this yourself.
I see it, but I don't believe it! I have over 500 ft long driveway that's about 75 ft elevation (give or take; it's steep). When the brakes are applied at standstill then allowed to move back in D, there is no regen. After bit of trying to move forward, it becomes like neutral.

But when it's in R then shift to D quickly, it regens as it's moving back. Well, at least the display is reporting the regen.

I saw up to 1kW regen in D going backwards doing this, because I was going pretty slow. It's much stronger than 1kW regen in D going forward. Being so strong with 1kW, I'm still skeptical if it's actually doing regen or using the battery power, but it's a neat party trick.

bicycleguy
Posts: 45
Joined: Thu May 14, 2015 5:19 pm
Location: Torrance, Ca

Re: Regenerative braking in reverse down a steep driveway

Tue Jan 26, 2016 12:34 pm

Yaa!, somebody finally tried it.

I feel much safer using this technique than the non-linear brakes backing down steep hills. The great rearward visibility :? doesn't help..
I see it, but I don't believe it! I have over 500 ft long driveway that's about 75 ft elevation (give or take; it's steep). When the brakes are applied at standstill then allowed to move back in D, there is no regen. After bit of trying to move forward, it becomes like neutral.
Don't do that, at least the stall part. As the User Manual p.9-21 notes: "... holding the vehicle in one place on a hill using only the accelerator pedal may damage the electric drive unit." I'm thinking this is because of uneven temperature distribution in the rotor and armature when the rotors not spinning. The cooling oil pump is separate (and doesn't spin backwards :D ) but the rotor movement helps it disperse the cooling oil.

The control system noticed the lack of movement and turned off the motor/generator. Same thing happens in hill start assist if you sit stalled for more than a second or two. Sparky's big brother is always watching you ! Also note that big brother doesn't try to stop you as long as your moving.

SparkevBlogspot
Posts: 499
Joined: Mon May 25, 2015 12:19 pm

Re: Regenerative braking in reverse down a steep driveway

Tue Jan 26, 2016 7:29 pm

bicycleguy wrote:Yaa!, somebody finally tried it.
Ya. I found it lot easier after more attempts. It turns out that it goes into "neutral" for a second or so before regen turns on. When you tap the brake, it also goes to neutral for a second or so. After that second, when I'm in D and rolling back, it always regens.

Also for strong regen I felt, I don't know if that's true or just perception. I am leaning back on hill, so additional regen feels stronger. Still, if I had to back into my driveway, I can use this to save on brake wear.

NORTON
Posts: 1380
Joined: Fri May 01, 2015 5:52 am
Location: KC,MO

Re: Regenerative braking in reverse down a steep driveway

Wed Jan 27, 2016 4:55 am

Another point of view:
You are now using your shift linkage, (the cable, lever, related mechanism on the drive unit) a lot more than if you just drove like normal person.
You are jockeying back and forth between Go and Stop pedals, while probably glancing at your display, when you should be paying attention looking back.
Plus you are passing through that '0 RPM' area of the motor, which the manual says you should avoid.
Brake pads are one of the least expensive maintenance items to replace, and the way they are used on this BEV, they will have phenomenal life driving like a normal person. Shift mechanism=expensive.
Brake pads and the brake discs need to 'meet' now and then to knock off the dust.

All these geek driving methods may be fun, and you should enjoy life with this little EV hot rod.

Just be aware that displaying all this stuff to someone new to EV's may be overwhelming .
This is kind of my position on 'Driving in L' and the '1 Foot' method of driving other EV brands demand.
It might be nice if you could jump into your first EV and not have to 'adopt' in anyway.
'14 Spark EV 2LT w/ DCFC. 91k miles.
'17 Bolt Premier w/ It All! 59k miles.
GM needs Modern Troubleshooting tools for Modern EV's.
3 step Trouble Tree, 1st try, nope, 2nd try / cost $800. 3rd try fixed it.

SparkevBlogspot
Posts: 499
Joined: Mon May 25, 2015 12:19 pm

Re: Regenerative braking in reverse down a steep driveway

Wed Jan 27, 2016 5:19 am

NORTON wrote:All these geek driving methods may be fun, and you should enjoy life with this little EV hot rod.
Well, yeah. One will quickly find that it's too much hassle for most circumstances unless the driveway is 500+ft and 100 ft in elevation and must back up and brakes are shot and killer turtles are chasing you and ... As such, it could be useful in the future to at least know this is possible. The circumstance under which this would be essential would be interesting, though.

Still, as I pointed out before, it's a neat party trick. "Look ma! I can regen going backwards!" :lol:

Return to “Engineering and Features”