Regenerative braking in reverse down a steep driveway

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JackHickey

Member
Joined
Jan 22, 2015
Messages
19
I have had my Spark EV for a year with 8,000 miles on it. Most of those miles are in L mode. I have no problem maintaining a constant speed or a coasting speed. My mileage in warmer weather ranged from 100 to 120 on a full charge. Those numbers are with lights off. I also shift to neutral at stop lights.

My daily round trips are 6 miles, with an elevation change of 350 feet. I charge up at the higher elevation at home. With a FULL charge, I see little regenerative braking while going down the hill.

My carport is 15 feet above the street level.(a 4000 pound car takes 60,000 ft.lbs of energy to get up my driveway) When I back down my driveway there is no regenerative braking(even without a full charge).

I would like to see GM correct that problem. Braking in reverse should be regenerative. Also, it would help my mileage if they provided a means to set the maximum charge level to 90 or 95%. That way I would recover the energy used to climb the hill. (mostly the 1/10th of a mile from my home)

I may have to put in a circular driveway. ;)
 
JackHickey said:
In D or L there is creep which requires a foot on the brake. That takes charge from the battery.
No, it does not take charge from the battery. Creep only happens when your foot is off the brake. Look at the display.

If shifting to neutral and finding a 'coast' driving in L makes you happy, fine !
I like the 'coast' the car provides by driving in D.
Also, lately I've been driving on ice and slick snow. There is NO WAY I would try to drive this car in L in those conditions.

If you live on the top of a mountain you should not charge 100%. There is nowhere for the Regen power to go so you end up using friction brakes like and old fashioned Gasser.

Lack of Regen in reverse concerns you !!?? Awesome !
 
JackHickey,

Boy I love this Spark! What a fun toy.

Regarding reverse. Here's something fun to try. Put in reverse, grab your balls :eek: and head down that steep hill and without putting on the brakes slide the shifter into forward. Whalla, regenerative breaking in reverse ! Nice and smooth, just like in when moving forward. Press the gas to stop quicker !

If the hill isn't steep enough the car will come to a complete stop. On wimpy hills you may have to roll in neutral for a little to gain speed (a few mph) before shifting to forward. (Don't touch that brake pedal, thats what the gas is for :eek: ) The regen (braking effect) is more pronounced than L when moving forward on the same hill.

Not sure if theres any difference between D & L when doing this, I'll have to go play some more to find out !

Almost forgot:
1. Leave the wife at home when practicing this.
2. I have no idea if this hurts the car so I'll keep testing :)
3. Someone on the great internet will take this to extremes and break something :lol:
 
NORTON said:
If you live on the top of a mountain you should not charge 100%. There is no where for the Regen power to go so you end up using friction brakes like and old fashioned Gasser.
I happen to live near top of a mountain, picking up 2 bars on the way down to town. I try to keep it at 80% or less, but sometimes I forget to disconnect (sleep through the alarm clock at 3 AM), and charge to 100%. It's annoying that I can't set it to automatically stop at X%.
 
bicycleguy said:
Put in reverse, grab your balls :eek: and head down that steep hill and without putting on the brakes slide the shifter into forward. Whalla, regenerative breaking in reverse ! Nice and smooth, just like in when moving forward. Press the gas to stop quicker !
Umm. Doesn't this cause the motor to be powered even more to try to keep the car moving forward? Trying to creep forward takes power, not regen, no?
 
Restating using words for the actual direction and letters fro the gear position:

Regarding reverse (and R). Here's something fun to try. Put in R, grab your balls :eek: and head down that steep hill in reverse and without putting on the brakes slide the shifter into D. Whalla, regenerative breaking in reverse ! Nice and smooth, just like in when moving forward. Press the gas to stop quicker !

If the hill isn't steep enough the car will come to a complete stop. On wimpy hills you may have to roll in N for a little to gain speed (a few mph) before shifting to D. (Don't touch that brake pedal, thats what the gas is for :eek: ) The regen (braking effect) is more pronounced than L when moving forward down the same hill.

Not sure if theres any difference between D & L when doing this, I'll have to go play some more to find out !

Almost forgot:
1. Leave the wife at home when practicing this.
2. I have no idea if this hurts the car so I'll keep testing :)
3. Someone on the great internet will take this to extremes and break something :lol:
4. Put on your thinking cap before trying this. Once you try it all becomes obvious. (to me)
 
bicycleguy said:
.. in reverse and without putting on the brakes slide the shifter into D. Whalla, regenerative breaking in reverse ! Nice and smooth, just like in when moving forward. Press the gas to stop quicker !....
This sounds like you are USING power to slow from reverse to a stop. Sort of like Electric Brakes, NOT Regen Brakes. Don't look at the display. Look over your shoulder !!

Is all this to avoid using those pesky friction brakes?
You know, the way this BEV goes through those brake pads you may have to install a new $45 set every 150-200 k miles.

You know, GM did a great job engineering the 'Blended Brakes' in this car. You are not using the friction brakes when driving in D and stepping on the brake pedal, until you feel that little bump at 2-3 mph when slowing to a stop. That's when the friction brakes take over. Of course any time you are pressing hard and go beyond the 'Regen' display limit those brake pads start working.

Brand T and B do not have blended brakes on their BEV brake pedal. The brake pedal is friction brakes, Only. They demand you drive this new '1 Pedal Method' in their BEV's. Lazy engineering?
I've been driving in ice and snow lately. There is no way I want full regen when I lift off the Go pedal
 
NORTON said:
This sounds like you are USING power to slow from reverse to a stop.
That's what I thought, too, and posted as such. But he repeated himself, maybe there's some firmware bug that allows this? I'm not about to try it on my SparkEV.

NORTON said:
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.
 
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.
 
JackHickey said:
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.
 
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". ;)
 
SparkevBlogspot said:
NORTON said:
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....
 
Zoomit said:
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.
 
bicycleguy said:
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.
 
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.
 
bicycleguy said:
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.
 
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.
 
NORTON said:
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:
 
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