Cruise Control

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lanceaz

Member
Joined
Feb 23, 2011
Messages
7
Location
Tucson, AZ
It seems to me that the cruise control could easily hold the speed down while descending a hill using the motor as a brake. It would apply a regenerative charging load to the motor much like the brake pedal does when lightly applied. I would hope this would be a very simple software modification. How about an update to the software, Nissan?
 
Why do you think it doesn't do that? Every cruise control
I've ever used limits the speed as well as maintains it... :shock:
 
GeekEV said:
Why do you think it doesn't do that? Every cruise control
I've ever used limits the speed as well as maintains it... :shock:

None of the cars I ever had slowed the vehicle down to maintain cruise control speed. Basically the behavior is the same as if you weren't using cruise and lifted your foot off the accelerator. Most cars (all that I've driven) will not actually "downshift" or anything to slow the car any more, it just relaxes the accelerator.

Same in the Leaf, as far as I can tell. In D, it will do a very slight regen (1 bubble), and in eco it will do more (3, I think?) but its exactly the same behavior as if you were not using cruise and you just lifted your foot off the accelerator.

I think what the OP was implying is that it would automatically cause MORE regen if your speed increased, meaning it would go up to 4 or 5 bubbles of regen going down a significant hill, which would be DIFFERENT than just lifting off the accelerator.

I think that would be clever and useful, but on the other hand it would make it behave differently than other "normal" vehicles, so they might have avoided doing that simply because they want it to behave normally. Similar to the "idle creep" that they built in, which doesn't really make much sense in an EV.
 
blorg said:
GeekEV said:
Why do you think it doesn't do that? Every cruise control
I've ever used limits the speed as well as maintains it... :shock:
None of the cars I ever had slowed the vehicle down to maintain cruise control speed. Basically the behavior is the same as if you weren't using cruise and lifted your foot off the accelerator. Most cars (all that I've driven) will not actually "downshift" or anything to slow the car any more, it just relaxes the accelerator.
Yep, The cruise control in every car I've had, including the LEAF, controls only the accelerator, and will accelerate above the set speed on downhills if they're steep enough to overcome engine braking. All the cruise control does is not give gas. ECO mode makes it appear different because it takes a steeper hill to accelerate the car, but it will accelerate.

I live at the top of a hill, and have tried it on multiple routes down.
 
I have driven some cars that downshift to increase engine braking to limit downhill speed.
Just how far over the set speed is the Leaf getting up to?
 
My BMW 330i uses brake to control speed on downhills. This is the first car I've ever owned that does that.
 
lanceaz said:
It seems to me that the cruise control could easily hold the speed down while descending a hill using the motor as a brake. It would apply a regenerative charging load to the motor much like the brake pedal does when lightly applied. I would hope this would be a very simple software modification. How about an update to the software, Nissan?
Excellent idea. Conventional cars have nothing but the brakes to slow the car on a steep downhill, and a system that applies the brakes automatically is more expensive, and so will be found only on high-end cars. But a car with regen capability (any well-designed EV or hybrid) should use its full regen capacity (limited by how much electricity the battery can accept) to limit downhill speeds when cruise control is engaged.

Maybe they think people want to speed up on the downhills in order to use the kinetic energy on the following uphill?
 
My BMW does as well. It will also downshift a gear for more engine breaking if necessary and cut off the fuel flow on overrun to save gas.

scharlj said:
My BMW 330i uses brake to control speed on downhills. This is the first car I've ever owned that does that.
 
mogur said:
My BMW does as well. It will also downshift a gear for more engine breaking if necessary and cut off the fuel flow on overrun to save gas.

scharlj said:
My BMW 330i uses brake to control speed on downhills. This is the first car I've ever owned that does that.

That's pretty cool that it would actually use the brake. My Murano does downshift a LITTLE bit with the CVT, and they call it "downhill assist" but it's not a significant hold-back.

I think most engines will cut fuel flow when going downhill (or, rather, when it's in "compression braking" mode, for lack of my brain figuring out the real term).
 
mogur said:
My BMW does as well. It will also downshift a gear for more engine breaking if necessary and cut off the fuel flow on overrun to save gas.

scharlj said:
My BMW 330i uses brake to control speed on downhills. This is the first car I've ever owned that does that.

My BMW would call me names (I assume they were bad....they were in German) and then it would mumble something about 'hippy' and it would actually hit the GAS when I tried to slow down!!

Apparently, my 330 ZHP didn't like going slow. So I sold it! :twisted:
 
I've driven several Chryslers that would downshift in order to maintain the set speed going down a hill and use engine compression to hold them back. With the built-in regeneration capability in the Leaf, it seems that it would be easy to hold the car down to the set speed going down the hill rather than to just let it coast and gain speed. I have not experienced any motor braking going down hills with the cruise on and set. It picks up speed as if it is coasting.
 
What I would really like to see is a constant power cruise as a second option to constant speed cruise. This way, the car will speed up downhill and slow down uphill. The power setting can be changed (just like a throttle setting for an aircraft) to produce a certain reference speed as the driver chooses for the driving conditions. Constant power will optimize the range of the car for a given power setting. Once up to speed, the lower the power setting (ideally at the "0" or neutral setting in the power circles display) the longer the range. A constant speed cruise wastes power both in the uphill and downhill phase (by using regen). Minimizing regen and using just the right amount of power would be the way to go IMHO.
 
wishboneash said:
What I would really like to see is a constant power cruise as a second option to constant speed cruise. This way, the car will speed up downhill and slow down uphill. The power setting can be changed (just like a throttle setting for an aircraft) to produce a certain reference speed as the driver chooses for the driving conditions. Constant power will optimize the range of the car for a given power setting. Once up to speed, the lower the power setting (ideally at the "0" or neutral setting in the power circles display) the longer the range. A constant speed cruise wastes power both in the uphill and downhill phase (by using regen). Minimizing regen and using just the right amount of power would be the way to go IMHO.

I agree. Constant power would be a nice option, traffic permitting.
 
I would call for a balance of speed and power. Let it drift down 3 to 7 mph going up and drift up 3 to 7 mph when going downhill. Maybe just in ECO mode.
 
wishboneash said:
What I would really like to see is a constant power cruise
If you tried constant power around here (let's say 20 kW to maintain 70 mph) you'd be doing 45 mph up hill and 85 mph down hill.

Open up the energy monitor and try it - it won't work safely for the vast majority of situations.

What would be better would be if setting that let the car wander +- 5 mph (configurable?) letting the car slow a bit for uphills and pick up some speed downhill before engaging regen.
 
smkettner said:
I would call for a balance of speed and power. Let it drift down 3 to 7 mph going up and drift up 3 to 7 mph when going downhill. Maybe just in ECO mode.
I think 7 mph is a bit much. If you want greater than 10 mph variation between min and max you should turn off the CC. But 3 or 4 would be good and, yes, it should definitely be a feature of ECO mode. Leave the speed tightly controlled as at present in D. That would make it easy to switch behaviors depending on traffic conditions.

Ray
 
smkettner said:
Just how far over the set speed is the Leaf getting up to?
A lot!

I have two long steep hills in my 4-mile commute; I have tried cruise control at least once going up & down the hills. The LEAF speeds up a lot downhill when on cruise control, so much so that I am invariably too preoccupied with the rapidly gaining speed to even notice whether there was being as much re-gen as when going the same hill w/o cruise control.
 
aqn, are you 80% charged? ECO mode? What speed? Seems like less regen braking at lower speeds.
I have yet to see more than a few mph gain going downhill with ECO mode.
 
smkettner said:
aqn, are you 80% charged? ECO mode? What speed? Seems like less regen braking at lower speeds.
I have yet to see more than a few mph gain going downhill with ECO mode.
Finally had a chance to confirm it yesterday.

I set the cruise control at 35 mph (the speed limit in my housing development) and the car proceeds for about 3-4 seconds at that speed before I reach the steep downhill. I am in ECO, which I'm in 99% of the time. 1214 feet later, with the re-gen max'ed at 5 dots/30 kWh, I'm doing 52 and gaining speed rapidly. I hit the brakes at that point.

Info from Google Earth:
Start (on Jester Blvd at Winterberry): 30'22'30.45"N 97'47'54.85"W 943 ft elevation
End (just before the big right hander): 30'22'20.51"N 97'47'55.79"W 795 ft elevation
148 feet drop over 0.23 miles (1214 feet) = 12% grade
 
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