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Downhill driving


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16 replies to this topic

#1 OFFLINE   John A Smith

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Posted 10 March 2015 - 04:21 PM

When I use the downhill switch on my gear shift what exactly happens?  Hopefully it uses maximum regen before using the transmission to slow descent.  It actually doesn't seem to but I could be wrong.    









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#2 OFFLINE   rbort

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Posted 10 March 2015 - 05:04 PM

Think of it as a variable L gear setting John.  D is minimal regen slight drag similar to taking your foot off the gas in an ICE car.

 

DHA is variable L, increases with the slope and decreases with a level road, varying from D to L, but not in my opinion as much as L on the high side.  Variable is used to hold the car speed constant down a hill, but the car can speed up a bit if the slope it steeper than DHA can handle.

 

L is maximum regen, should slow the car down but there is always a steep slope that even L can't hold you back on.  However, I believe that L can handle a little steeper slope than DHA can without speeding up the car.

 

Hope this helps,

 

-=>Raja.



#3 OFFLINE   drdiesel1

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Posted 10 March 2015 - 06:38 PM

DHA uses regen to maintain vehicle speed at the set point. Sometimes the decent

can over power it and the vehicle can gain a few extra MPH on steeper grades.



#4 OFFLINE   fotomoto

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Posted 11 March 2015 - 07:55 AM

I've only use DHA on a mountain trip in my former CMax Hybrid and it would spin up the ICE (no fuel burn AFAICT) to use as both compression braking and burning off excess charge from regen since the battery was full (see photo).  Energi drivers have notice the same thing happening when leaving with a full charge and immediately going down a hill but without DHA activated.

 

null_zps68517abf.jpg


Edited by fotomoto, 11 March 2015 - 07:56 AM.


#5 OFFLINE   dontfret

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Posted 11 March 2015 - 08:12 AM

When I use the downhill switch on my gear shift what exactly happens?  Hopefully it uses maximum regen before using the transmission to slow descent.  It actually doesn't seem to but I could be wrong.    

This car doesn't have a transmission to slow decent.  D, L, and DHA are all just adjusting the regen braking level and have nothing to do with the ICZE motor.


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#6 OFFLINE   John A Smith

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Posted 11 March 2015 - 02:23 PM

This car doesn't have a transmission to slow decent.  D, L, and DHA are all just adjusting the regen braking level and have nothing to do with the ICZE motor.

No transmission??  Of course it does, it is a continually variable transmission (CVT).  You don't feel gears changing because it is a step-less range from its lowest to its highest ratio.  I have always assumed the L position locked the CVT in a low ratio.  Am I wrong?  



#7 OFFLINE   stevedebi

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Posted 11 March 2015 - 03:21 PM

No transmission??  Of course it does, it is a continually variable transmission (CVT).  You don't feel gears changing because it is a step-less range from its lowest to its highest ratio.  I have always assumed the L position locked the CVT in a low ratio.  Am I wrong?  

Well, I suppose so. The computer sets the transmission to put power back into the generator (and therefore the batteries). So I think the generator is what is causing the "drag". If the battery gets full, the engine spins up (but burns no fuel) to take care of the excess power generated.

 

I know someone will chip in with a more technical description, but I think this pretty well describes what happens.



#8 OFFLINE   drdiesel1

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Posted 11 March 2015 - 05:11 PM

The ICE can come on when the HVB has been charged to the systems threshold limit.

The ICE will only function as an engine brake to slow/control the vehicles speed.

It has nothing to do with power use. They use the ICE to slow the vehicle down when MG1 is turned off

because the HVB has reached it charge limits. This disables regen, but they still need a way to keep the vehicle from

freewheeling and gaining speed downhill.

 

The ICE spins in fuel cut mode to slow the vehicle down. It will rev pretty high too. I never use my ICE as an engine brake :runaway:



#9 OFFLINE   dr61

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Posted 11 March 2015 - 06:26 PM

L does no locking in a 'low' gear. It is entirely increased regen from the electric motor (plus spinning up the ICE if battery is full).  There really are no variable gear ratios, just variable resistance from the electric motors and ICE when it is allowed to spin.

 

It works very much like the Toyota power split transmission:

http://auto.howstuff...hybrid-car7.htm

also:

http://eahart.com/prius/psd/



#10 OFFLINE   stevedebi

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Posted 12 March 2015 - 08:01 AM

The ICE can come on when the HVB has been charged to the systems threshold limit.

The ICE will only function as an engine brake to slow/control the vehicles speed.

It has nothing to do with power use. They use the ICE to slow the vehicle down when MG1 is turned off

because the HVB has reached it charge limits. This disables regen, but they still need a way to keep the vehicle from

freewheeling and gaining speed downhill.

 

The ICE spins in fuel cut mode to slow the vehicle down. It will rev pretty high too. I never use my ICE as an engine brake :runaway:

dr,

See, I said someone would chime in!

 

I don't generally have any issues with this, since on the highway I will use my HVB to go uphill if it is steep. So my battery is never fully charged. I don't think I've had the engine run once on my Energi. It happened frequently on my 2008 FEH, but that was a small battery. I suppose in the mountains on a long downhill it might happen, but there aren't really any like that here in So Cal.

 

EDIT: When I said "excess power", I was referring to the potential kenetic energy available because of the hill.

 

BTW, it would be great if you used the quote feature, to help folks follow the stream.


Edited by stevedebi, 12 March 2015 - 08:03 AM.


#11 OFFLINE   John A Smith

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Posted 13 March 2015 - 03:34 PM

Thanks everyone.  Now I know I am not wasting that downhill energy when activating the DHA or even putting it in L.  There is an opportunity for me to put this to a test.   Driving from LosAngeles  to Bakersfield there is a 4,500' elevation that drops to about 600' at the Grapevine.  I gain about 5 miles of charge from that downhill.  Next time I will use the DHA and L, if needed, then compare the result.  In the past I have used the brake as gently as possible.  


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#12 OFFLINE   drdiesel1

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Posted 13 March 2015 - 05:12 PM

Thanks everyone.  Now I know I am not wasting that downhill energy when activating the DHA or even putting it in L.  There is an opportunity for me to put this to a test.   Driving from LosAngeles  to Bakersfield there is a 4,500' elevation that drops to about 600' at the Grapevine.  I gain about 5 miles of charge from that downhill.  Next time I will use the DHA and L, if needed, then compare the result.  In the past I have used the brake as gently as possible.  

Using the brake will accomplish the same results without set speed control.



#13 OFFLINE   drdiesel1

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Posted 13 March 2015 - 05:13 PM

dr,

See, I said someone would chime in!

 

I don't generally have any issues with this, since on the highway I will use my HVB to go uphill if it is steep. So my battery is never fully charged. I don't think I've had the engine run once on my Energi. It happened frequently on my 2008 FEH, but that was a small battery. I suppose in the mountains on a long downhill it might happen, but there aren't really any like that here in So Cal.

 

EDIT: When I said "excess power", I was referring to the potential kenetic energy available because of the hill.

 

BTW, it would be great if you used the quote feature, to help folks follow the stream.

Okay! :victory:



#14 OFFLINE   P=E/t

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Posted 13 March 2015 - 05:49 PM

What happens if one is driving in DHA and shifts into L?

 

I mean, I know what happens--the car doesn't blow up or anything. But I've wondered--does the L setting negate/override the DHA? Or does the DHA just keep doing its thing and ignore the shift from D to L? It seems to me that the former is what happens, but I haven't had a long enough and steep enough hill to really explore it on.

 

And then there's cruise control ... Three variables, L, DHA & CC; each can be in an "on" or "off" state independent of the others ... that's eight variations.



#15 OFFLINE   rbort

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Posted 13 March 2015 - 06:19 PM

 

 

What happens if one is driving in DHA and shifts into L?

 

Regen goes to about max and the car starts to slow down if the hill is not too steep.  You can use L to slow down instead of using brakes when necessary.  You can also shift to L on the highway to slow down for the exit ramp as you're getting off.  Shift at any speed no problem.

 

L overrides DHA.

 

DHA overrides D

 

D overrides N.

 

CC overrides all (except N) so you can be in D or L or DHA and the car will still go the same speed.

However, CC with D does not hold speed downhill,

CC with DHA hold speed tighter.

CC with L holds speed the tightest around your set speed.

 

-=>Raja.


Edited by rbort, 09 July 2015 - 07:38 PM.


#16 OFFLINE   P=E/t

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Posted 13 March 2015 - 06:57 PM

OMG it's like Rock Scissors Paper Lizard Spock.

Yes, I use L a lot, but mostly when I know I'll have to come to a complete stop. Like a stop sign at the bottom of a hill. Otherwise, it seems more finessed to feather the brakes as needed.

#17 OFFLINE   rbort

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Posted 13 March 2015 - 07:02 PM

You're doing good.  I went through a phase where I used L all the time and almost never the brakes, but got out of that habit and decided to feather the brakes instead which I do well now.  Better that way as people see the brake light if they are behind you.

 

I still use L on occasion, when there is a steep hill or a stop sign at the bottom like you said or if there is a sudden reason to slow down where you are unsure if you will dig into the brake pads with too much braking.  Also I still use it for the off ramps, seems to do me well to shift into L for a few seconds until the car's speed is right to take the curve off the ramp and then back to D.  If there is no traffic behind me on the highway I just let up on the gas and let the car coast down to the right speed for the ramp in D.

 

-=>Raja.










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