Reasons for Throttle Delay and Throttle Dead Zones

[RobM77]

I just found this patent filed:

http://www.freepatentsonline.com/5146886.html

Does anyone know if this is used in DBW production cars at the moment? I was trying to find a reason for the dead zone at the top of DBW throttle pedals, which seems to be present even in expensive carefully engineered sports cars such as the latest 911.


Secondly, this is rather worrying:

http://my.is/forums/f62/is300-throttle-cable-space...

Lexuses appear to have a spring between the throttle pedal and the throttle pot!!! That might explain a few things!

[bertelli_1]

Are you talking about the fact the pedal has no effect from around 70% to 100% of its travel? This is usually due to the way DBW throttles are set from the factory. To make the car feel more responsive when you press the pedal to say 50% it actually opens the butterfly more than 50%, making you think 'Wow, this car is quick!'.

You can even buy aftermarket gadgets now that 'improve the response of your engine' - all they do is change the output of the pedal to increase the butterfly opening even further. Is anyone actually stupid enough to buy one of these?

[RobM77]

bertelli_1 said:

Are you talking about the fact the pedal has no effect from around 70% to 100% of its travel? This is usually due to the way DBW throttles are set from the factory. To make the car feel more responsive when you press the pedal to say 50% it actually opens the butterfly more than 50%, making you think 'Wow, this car is quick!'.

You can even buy aftermarket gadgets now that 'improve the response of your engine' - all they do is change the output of the pedal to increase the butterfly opening even further. Is anyone actually stupid enough to buy one of these?

Hmm.. I didn't have my DBW car long.. I've now got three cars with cable throttles for this very reason. However, I think it's a time delaym rather than a pedal travel delay. If you hold your foot a cm down you can measure the same time delay as if you floor the throttle. In fact, in my 330ci is was possible to tap your foot to music on the accelerator and nothing happens!! BMW said that it was "within specification".

[Mr Whippy]

Just FYI, my throttle has as imperceptible throttle delay as I would care to want, it's as good as my 306 GTi6 was anyway, and there is no dead zone.
If you ever had the chance Rob, I'd let you have a go in my car as I am surprised how good a diesel DBW can actually be considering what I have experienced in petrol DBW's. I worry for my engine mounts and gearbox if I tap my accelerator to the music while driving, anywhere above 2000rpm that is


It seems today half the issues are mapped into the lookup tables to basically cover off cretin drivers, cover off emissions legislation by letting the engine change state more slowly and so controlling it better, and then making throttles top-heavy to make them feel 'responsive' again.

My current car was dire standard. Now all the crap is ripped off, and with a huge intercooler added in place, and with suitable throttle mapping changes, it's a dream to drive wrt response and dead-zone. Ie, it's mapped to need 98% throttle to get peak fuelling, wheras standard on some modern cars you can see them need only 60% throttle to get full fuelling.


Just generally, after learning about how modern ECU/DBW works, I'd certainly want to edit these files on any car I have in future, if they prove to be setup badly for what I want. At least on old cars you could see that 0% input = a closed throttle and 100% input = open throttle plate. Today you might need 5% to get the throttle moving, and then 70% to get the throttle wide open... naff in my view. Tuned for the lowest common denominator.

DIY tweaks are relatively easy and hugely fulfilling and can improve driveability no end! (again, it's all personal, I've seen some tuners see 'driveability' improvements as making 50% throttle input = 100% output )


Dave

Edited by Mr Whippy on Friday 12th December 17:13

[RobM77]

Thanks for your post. Diesels don't seem to have much of a delay actually. I did read why recently, but I've forgotten I'll post again if I can remember the reason!

[Mr Whippy]

Well, I think the throttle may be part of it. The diesel just tells the injection ecu to pump more fuel in, so it's at the top of the ladder in a way.

In a petrol the driver input tells the butterfly to open more, or the valves to open further, whatever, but then the resultant fuel change isn't seen until the exhaust gasses are assessed and then the change of fuelling is controlled, but of course we don't want a second running too lean or rich for emissions reasons, so the throttle will probably open slowly (relatively) as the current new fuelling AFR is detected and deemed 'clean', at which point the system will open the throttle a bit more, and so on.

I'm assuming. Bit of a feedback loop there, to satisfy regs. I'm sure a great deal of manufacturers now just deem good enough to be 'good enough'

Not sure how you get around it really, sort of fitting your own management and having it mapped up without such silly modern emissions concerns.

[eliot]

my 540 is dbw and seems fine. I've had the diagnostics on it and there is a 1:1 relationshoip between the pedal and the value the ECU sees. (what it does with that value is another matter)

[RobM77]

The situation with the E46 330ci that I owned was that when you opened the throttle, even gently, there was a noticeable and measurable delay before the actual throttle on the engine opened and the car responded. This made the car impossible to balance in the bends, which was a great shame as I'd paid the money for a rear drive car with a balanced chassis but I couldn't use it! Gear changes and hill starts were also very difficult. Alarmingly, this delay was also present when backing off. I like to back off when traffic slows ahead of me rather than brake, and the 330ci continued on the power for a second, which was rather scary! The car went in to BMW to be "fixed" innumerable times and eventually they just told me that the delay was "within specification". The car cost me £16k and BMW offered me £8k on trade in!! I now just own a 1999 E36 328i, which is beautifuly to drive and ever so smooth. I plan on looking after it!