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 Post subject: EV Idle Behavior Question
PostPosted: Wed May 08, 2013 7:17 pm 
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Joined: Mon Feb 18, 2013 9:46 pm
Posts: 20
It seems like the R4EV (as well as a Highlander Hybrid I used to own) goes out of its way to copy the "idling" behavior of an automatic gas vehicle. Basically at under 3mph when take your foot off the gas, power "trickles" to the motor causing a ~ 1mph/s acceleration. Likewise over 3mph, when you take your foot off the accelerator, the regeneration system kicks in and power "trickles" back to the battery causing a ~-1mph/s deceleration. Shifting to "B" increases the deceleration to what I am guessing is the maximum (?) capacity of the regen system. (I don't think "B" does anything else.)

My point is that this "dumb" legacy behavior takes no consideration of the current grade, either uphill or downhill.

An EV system has potential for so much more. Why an EV should have to creep forward (or backward if your on an uphill slope) is confounding.

What I propose as a better behavior is basically this:

v - current velocity
v_idle - idle target velocity (+/- hysteresis) - make this a user preference from 0-4 mph

Releasing brake at stop (0<=v<v_idle)
accelerate at a_rest, where a_rest is a user preference from 0-2 mhp/s

Coasting (v_idle < v)
decelerate at a_coast, where a_coast is a user preference from -3-0.mph/s

AND follow these equations REGARDLESS of incline. Imagine not drifting backward when stopped on steep inclines, or not having to shift to "B" or "ride" the brake (and wondering whether you were still in the regen envelope or wearing the pads).

Also I not sure what the purpose of shifting to neutral is in an EV, but it would simply set a_rest=0, likewise in this proposal the purpose of "B" become moot?


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 Post subject: Re: EV Idle Behavior Question
PostPosted: Wed May 08, 2013 9:23 pm 
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Joined: Sat Sep 22, 2012 9:37 pm
Posts: 4
FWIW, I can't speak to the specific behavior of the RAV4EV, but about a dozen years ago I drove a Think City for a week. It lacked any idle creep. During the course of testing it I found that parallel parking it in a small space on flat ground was almost impossible if I wanted to avoid hitting the cars ahead or behind me. The problem was the 'throttle' mapping, which from stop went nothing, nothing, nothing, TOO MUCH! Even with left foot braking it was pretty easy to get into trouble, so I only parallel-parked it when I had at least one open space ahead or behind me, which was ridiculous for a small city car. Part of the issue was that the steering was unassisted and much too heavy, so you needed fine low-speed control to turn the wheel, and with the notchy 'throttle' things were happening too fast.

Better slow speed power control (without idle creep) might solve the problem, but I can't say for sure. I don't think it was due to any lack of ability on my part, as I learned how to drive in a '65 Impala with manual transmission and steering, and that was far easierto parallel park than the Think, as has been true of all my subsequent (all manual transmission) cars.

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 Post subject: Re: EV Idle Behavior Question
PostPosted: Thu May 09, 2013 3:22 am 
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Joined: Wed Nov 14, 2012 9:50 pm
Posts: 3872
Location: San Diego
The transmission creep apparently can't be selected off (at least I can't find a setting listed) and my dealer said it couldn't.

I was under the impression that the Model S could select between creep and zero power.


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 Post subject: Re: EV Idle Behavior Question
PostPosted: Mon May 13, 2013 10:10 pm 
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Joined: Mon Feb 18, 2013 9:46 pm
Posts: 20
Its more than just zero power, its zero velocity as well. I especially dislike rolling backward when stopped on an uphill grade. Its got a AC induction motor, can't it lock the rotor or something?


Also - what is the purpose of N? I can't even reliably shift into neutral to determine what it does.

Anyone know what inside the gearbox? Is it more than a reduction gear and parking pawl?


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 Post subject: Re: EV Idle Behavior Question
PostPosted: Mon May 13, 2013 10:23 pm 
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Joined: Thu Mar 14, 2013 12:05 am
Posts: 311
ToddR wrote:
Also - what is the purpose of N? I can't even reliably shift into neutral to determine what it does.

I used "N" today for the vehicle to be pulled up on the flat bed truck transport to the dealership for the Screen of death - Check EV System message I got this morning. Also I use "N" for going thru the car wash. :)

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 Post subject: Re: EV Idle Behavior Question
PostPosted: Mon May 13, 2013 10:45 pm 
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Joined: Wed Nov 14, 2012 9:50 pm
Posts: 3872
Location: San Diego
ToddR wrote:
Its more than just zero power, its zero velocity as well. I especially dislike rolling backward when stopped on an uphill grade. Its got a AC induction motor, can't it lock the rotor or something?


Also - what is the purpose of N? I can't even reliably shift into neutral to determine what it does.

Anyone know what inside the gearbox? Is it more than a reduction gear and parking pawl?


You're not moving any actual gears or clutches by putting it in Neutral. It is just a denergizing the motor.

To shift to neutral, push the Prius gear shifter to the left for two seconds. Easy. I use it a lot for coasting down hills.


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 Post subject: Re: EV Idle Behavior Question
PostPosted: Mon May 13, 2013 11:42 pm 
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Joined: Mon Feb 18, 2013 9:46 pm
Posts: 20
It was the "2 seconds" that fooled me.


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