Drive-By-Wire Throttles

[brumster 135 1 Cars]

Here's one for the techie guys/mappers out there. Most modern cars, as I'm sure you're aware, have drive-by-wire throttles these days, where the pedal is not directly linked to the throttle butterflies by a cable (like our dear old 205s) but instead the ECU drives the throttle opening by a motor.

 

Now, looking at this purely from a "performance drivers" point of view, I've not driven one of these systems that doesn't feel utter s*ite compared to a good old carburettor and throttle cable. Typical areas of failure for me are poor throttle response and inconsistent range of pedal to opening of throttle (this really bugs me - where 80% of the actual engine throttle opening is controlled by the first 20% of the pedal!).

 

I like a long throttle pedal so I can modulate the power out of the engine, but modern cars seem to go completely the opposite way.

 

Now the problem is, my DbW experiences are limited to pretty mundane road cars - so chances are the likes of Porsche, Ferrari, Lamborghini, BMW, etc get this right.

 

Is it possible to make a DbW system that keeps the true petrol heads happy, or will you never attain that crispness and progressiveness that a piece of twisted steel wire gives you? Surely it must be possible, the microprocessors in some of these ECUs have a wealth of clock cycles free don't they?!

[Cameron 16]

Typical areas of failure for me are poor throttle response and inconsistent range of pedal to opening of throttle (this really bugs me - where 80% of the actual engine throttle opening is controlled by the first 20% of the pedal!).

 

I like a long throttle pedal so I can modulate the power out of the engine, but modern cars seem to go completely the opposite way.

 

I also find this really bloody irritating, and I have a feeling it's to make customers feel that they aren't ragging their engine too hard, if they had a long pedal the majority would complain of a lack of power and responsiveness. The same goes for modern brakes, I absolutely hate the way they're going with pedal effort. I like a linear relationship of input force to deceleration and a good firm pedal, but all manufacturers seem to be going well away from that.

 

I digress.. I have absolutely no reason to doubt that instant throttle response is achievable. I can't see how the response times could be below that of the throttle pot - injection / ignition timing relationship, so it should be possible to make a proper system where the response is equivalent to using a cable.

[brumster 135 1 Cars]

Good, I thought so too - it shouldn't be beyond the wit of man, should it? Maybe someone who's driven a high-end performance car with a DbW throttle can comment.

 

I'm always interested to see on some of these YouTube vids (Chris Harris for example) that when you put cars like a BMW M3 into "sport" mode it 'tightens up the throttle response' and I'm trying to understand what that means! If I was to put a car into sport mode I'd want the throttle pedal to go long-travel and linear!

[S@m 156]

The most 'performance' car that i have driven with a DbW throttle would be the DS3Racing and i have to say its just as rubbish as any other system i have tried - but then its still a citroen. Who knows about true performance cars.

 

Sam

[chipstick 382 1 Cars]

My Clio Cup has DBW. To be honest, I don't find it noticeable.

[welshpug 1,626]

Mk6 on transit vans are FBW, dont really notice it tbh! but then they dont have throttles per se.

[S@m 156]

My Clio Cup has DBW. To be honest, I don't find it noticeable.

 

I always found the clio cup throttle to be slow to respond, especially when pulling away at junctions and such. Maybe the one i used for a while was on its way out. Aside from that i liked the car.

 

Sam

[chipstick 382 1 Cars]

Perhaps so. This one is instant.

[CaptainK 11]

I too find the lack of response from DbW systems to be poor - especially after driving my now decased 205 GTi6 on ITBs with a super light and responsive throttle

 

Would be really nice if there was a way to tighten up throttle response. Maybe we can change the settings on the car's ECU to increase throttle response somehow as presumably its the ECU that tells the throttle motor how quickly to open and close ?

[Cameron 16]

I have a strong feeling that DBW having a delay is down to emissions, to slightly even out any small and rapid alterations in throttle pedal position - you'd be amazed at how many aspects of performance and driveability take second priority to emissions! My Mondeo Diesel had about a second of delay between pressing the pedal and something happening! (I'm not talking about turbo lag either)

 

I have a feeling that this is what the "tigtened throttle response" remarks in road tests of cars with a sport button relates to.. the normal map has more delay to average out the pedal positions and improve economy, then the sport map tightens everything up.

Edited June 15, 2012 by Cameron

[brumster 135 1 Cars]

I figured it might be emissions regulations to blame for these blasted things that and safety systems like traction control.

[GilesW 41]

You can get after market systems. Many displayed at autosports.And these are instant.

[d7ve_b 44 1 Cars]

When I had my S3 remapped I had the throttle response 'sharpened' as it is possible with the ME7.5 ECU in the later 8L S3's. Don't know what he did exactly but it certainly helped with throttle response.

[wracing 19]

I hate it so much on my car i spent a week of late nights reprogramming my ecu.

 

The control algorithms are quite simple, they tend to look at rate of change as well as position, hence why small fast or large very slow movments dont affect throttle position.

 

after quite a while i manganged to get 10% pedel to equal 10% throttle not an easy task..

 

James

[Lan 24 1 Cars]

I'm limited to experience of d-b-w mostly to Mercedes vehicles, Diesels in particular and unsurprisingly its rather good certainly on the more sporty cars when you put it into sport mode it essentially changes the whole "feeling" of the response and the way the vehicle shifts and on the recent cars with the 7Gtronic box they shift even better and even smoother and have the "fun" extra of wheel mounted shift paddles, the d-b-w is pretty good on the vans too there is a bit of delay like with a car in comfort mode but in day-to-day driving you wouldn't notice it.

[feb 47]

Yes, the buttlerfly opening vs accelerator pedal angle relationship can be altered.

 

The throttle on my 2004 FSTi -that is standard- feels a bit lazy.

 

On the other hand the very cprispy throttle response of my 2006 FSTi can make the car a little annoying to drive especially when you are tired as you have to be very alert; a tiny movement of the accelerator's angle causes the car to get on boost immediately; I am pretty sure the butterly opening vs accelerator pedal angle table has been altered by the person who mapped it but I can't tell as I haven't read the map.

 

I requested him to have as much torque low down as possible and he may have done this to "trick" me as I believe I get 100% of the butterly open with only about 60-80% of the pedal's travel.

 

This is something that I would like to do and make it more linear:

http://www.wrx.com.au/forum/viewtopic.php?f=31&t=50862&view=next

[Sandy 189]

DbW throttles have never really impressed me, even the latest BMW M3 feels laggy in sports mode compared to a decent ITB engine with a cable. None of us are really party to what the exact thinking of the manufacturers is, but from my own mapping/economy experiments, I know that one of the biggest wastes of fuel for no extra motion, is pump enrichment (for those that don't know, it's the injection equivalent to the extra squirt of fuel a carb gives on quick throttle openings to compensate for the sudden change in air speed/volume/pressure). If you drive a car in a manner of smooth throttle openings and gradual, measured changes in load, then economy improves considerably. What DbW can do, is act as a damper between the driver's pedal movements and the engine's load/speed changes, so that the management can anticipate better and waste less fuel.

The other aspect, which intrigues us, is that particularly with large throttle bodies, peak torque at low to medium revs is often reached around half-two thirds throttle openings and beyond that it drops off, also quick throttle openings at low revs create a change of air speed/pressure, that produces a less potent response than a gentler climb. If you could mitigate that, it would improve performance and make mapping much easier, perhaps, as suggested, with more throttle pedal travel (precision/resolution). What alot of bike engines have, are a secondary ECU controlled set of butterflies, which I can only assume are designed to limit the effects of throttle openings in those situations, an obvious solution, while retaining proper manual cable control of the main throttles. I intend to test using the extra butterflies at some stage, we use alot of bike bodies with them removed, so it would be nice to retain them and experiment.

[Baz 421]

My Clio Cup has DBW. To be honest, I don't find it noticeable.

 

I've driven a few and didn't notice tbh, i was told afterwards and was quite surprised!

[Baz 421]

There was a decent article regarding DBW in an old issue of Track Driver written by Dave Walker iirc i stumbled across a few weeks ago, was quite interesting.

[brumster 135 1 Cars]

I've got an Octavia vRS myself (a petrol one; yes, I'm one of the 3 who bought one!) and I find it quite hard to push it hard but smooth. It's not the engine or the power delivery as it's quite a tractable, torquey lump with a flat spread of torque from 2000 onwards, but when you're on the limits of adhesion and trying to feed the power in mid-bend, it's really hard to not overwhelm the front wheels. Considering it's only specced at 205Nm (that's a rather pitiful 150ft.lb) it gives up the grip quite easily. I'm sure the figure is wrong, to be honest, it feels soooo much more grunty than 150ft.lb.

 

Turning off the traction control is just pointless.... with no ability to modulate the throttle, it just offers no practical benefit whatsoever (that I can see, at least).

 

Jumping into the Pug afterwards is a pure delight no flywheel mass and instant throttle response...

[Baz 421]

The VAG stuff annoys me more as it cuts the throttle when you left foot brake, very aggrevating!

[GLPoomobile 958]

I figured it might be emissions regulations to blame for these blasted things that and safety systems like traction control.

 

My Alfa V6 has STR (Sports Throttle Response) which pretty much all owners leave engaged all the time. I've heard that Alfa had to dampen the throttle response considerably in order to meet emissions (the Busso V6 being a stupidly thirsty beast), so they added the STR button in order that owners wouldn't have to suffer. With it switched off the car is horrible. With it switched on it's more like you'd expect a normal cable operated throttle to be, but still not quite good enough.