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Date Registered: 05-2012
Location: Sunshine Coast
TOTAL POSTS: 481
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A tuners guide from "Modified Magazine"


This is a cut and paste from Modified Magazine & covers a lot of groundwork with the QR25DE motor.

What I found very interesting is the section on how the 'drive by wire' accelerator works with that engine.

It is very different to the normal cable mechanism & it seems to indicate that slight accelerator pressure would seem to give the same throttle response as a heavy accelerator but without wasting fuel as the electronics interpret the accelerator position as an indicator of how much torque is wanted rather than how wide the throttle should be opened.

(I don't use much accelerator to keep up with or beat other cars at the lights & I do get good fuel economy.)

 A Tuner's Guide Inside the QR25DE
A look at Nissans QR25DE
Modified Mag, April 08, 2009


Up top, air enters through a drive-by-wire throttle body, shown in photo #3. Instead of a throttle cable, there is simply a sensor on the gas pedal and a small motor on the throttle plate. Between them is the computer, and like many drive-by-wire systems, there is no direct relationship between your foot position and the throttle position. Push down 50 percent on the pedal, for instance, and the ECU will open the throttle the appropriate amount to give you 50 percent of the torque available. That may mean a 30 percent throttle opening, or it may mean 80 percent, but you'll never know.


Interestingly, although the rev limiter could be implemented by simply having the ECU close the throttle (as Porsche does), that was deemed too smooth, so the rev limiter is done conventionally, by shutting down the fuel injectors.

Being drive-by-wire in itself doesn't make it any harder to reprogram the ECU, but it does make the consequences of tripping over the wrong bit much bigger. Since the ECU is completely new, it will probably take a few years for anyone to crack it.





Late Edit 21/11: Your reply is noted. Sorry Jalal, I didn't see the home page reference.

Once again, I seem to have re-invented the wheel. Damn - and I thought it was 'new' emoticon

So I've removed the majority of the article and left only that which applies to optimal use of the accelerator in a drive- by -wire system.

As such, that part might still be useful in the Fuel & Oil section.

Apparently the d-b-w digital accelerator method of proportioning fuel intake to accelerator position is very different to the cable (analogue) version.


Last edited by DogTrail, 21/Nov/2013, 8:04 pm


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2011/12 Australia:- 2.5 litre petrol 4WD, Series IV ST, CVT : + some gadgets and cosmetic add-on's. Dirt, (it protects the paintwork) X-2429(c).
19/Nov/2013, 12:08 am Link to this post Send Email PM   Send Private Message
 
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Date Registered: 02-2004
Location: SUTHERLAND, SYDNEY
TOTAL POSTS: 29094
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Re:


This article has already been posted and linked to our forum main page HERE quite a while ago now emoticon

It does pay to visit our own home page sometimes emoticon



Last edited by jalalski, 23/Nov/2013, 8:48 pm


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19/Nov/2013, 6:07 am Link to this post Send Private Message MSN Blog
 
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Date Registered: 02-2004
Location: SUTHERLAND, SYDNEY
TOTAL POSTS: 29094
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Re:


I have re-opened the thread if you want to talk about this further.

P.S. I don't get notified when you edit your post, so if you were waiting for me to re-act and re-open the thread after you have edited it, please make sure you either send me a PM or email to action it. I monitor the entire forum, so it can get quite busy as you can imagine emoticon

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23/Nov/2013, 8:50 pm Link to this post Send Private Message MSN Blog
 
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Date Registered: 05-2012
Location: Sunshine Coast
TOTAL POSTS: 481
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Re: Re:


Thank you for re-opening the thread.

I do experience a difference using d-b-w vs my lifelong use of cable driven accelerators.

At the time I was looking for a new car, the Subaru dbw was so bad with such unexplained over-run that I walked away from that car after one test drive.

I did give it every opportunity to respond to my foot but it resolutely refused to do so.

Driving the X-Trail, I was surprised to find that it was also dbw as the response to my every movement was instant. I thought it was cable for months, until I was otherwise informed on this forum.

It might be that I misunderstand the process and it may be a pointless exercise for me to draw attention the subtle difference but I've found that driving by wire to attain good fuel economy seems to require a different approach to the accelerator.

This is what works for me to keep fuel usage low with that electronic system:

At take-off, set the accelerator position at the same point you would usually keep it at the speed allowed for the area.

The car 'brain' does the rest to get you to that point as quickly as possible with due regard to economy.

In my experience, flooring the accelerator to reach 60 kph adds little to acceleration but much to fuel usage.

With dbw, lightly moving the accelerator to the 20 cm point tells the car you want to reach a particular speed (say 60 kph), so it it does that as efficiently as it sees fit using the CVT gearbox.

With cable, that accelerator position tells the car that it should do 2000 rpm.

I see that as a world of difference.



Last edited by DogTrail, 23/Nov/2013, 9:38 pm


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2011/12 Australia:- 2.5 litre petrol 4WD, Series IV ST, CVT : + some gadgets and cosmetic add-on's. Dirt, (it protects the paintwork) X-2429(c).
23/Nov/2013, 9:27 pm Link to this post Send Email PM   Send Private Message
 


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