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Drive by wire - electric throttle
v8kid - 29/1/13 at 08:01 PM

How does it work?

Is it just a stepper motor with a controller operated by a variable resistance on the throttle pedal?

What is the equivalent of a throttle return spring at the throttle body?

Cheers!

richmars - 29/1/13 at 08:28 PM

Just guessing, but in principle yes.
In practice, there'll be all sorts of complicated control theory going on, compering the input (your foot) with the output (engine revs). May also be some sort of variable gain, so it's more sensitive at low speeds.
The control theory is needed to ensure you don't get unstable hunting (which wouldn't be fun), but still responds quickly to a step input.

T66 - 29/1/13 at 08:38 PM

My Suzuki GV has got one....do you want the text from my techy manual ?

MikeRJ - 29/1/13 at 09:33 PM

quote:
Originally posted by v8kid
How does it work?

Is it just a stepper motor with a controller operated by a variable resistance on the throttle pedal?

What is the equivalent of a throttle return spring at the throttle body?

Cheers!


They still have a throttle return spring even if you can't see it; if the actuator loses power it has to fail safe (i.e. closed). There are numerous other safety related systems built in as well, such as dual sensors in the throttle pedal, and position sensors within the throttle body. The throttle pedal signal is processed by the ECU, and manufactures do all sorts of tricks such as retarding the ignition on sharp throttle inputs to give a smoother response.

[Edited on 29/1/13 by MikeRJ]

T66 - 29/1/13 at 09:36 PM

I noticed it on mine for the first time last week, my brakes were squeeling so I hit the brake with my left foot to clear the krud off them.


The ecu spotted what was happening and the engine power dropped right back.

coyoteboy - 30/1/13 at 12:15 AM

That occurs (some) cars even without fly by wire throttle.

Fbw throttle control is often very complex, used to limit the rate of change of throttle movement to limit emissions, but also van be used to adjust the feel of thecar.

Slimy38 - 30/1/13 at 06:28 AM

quote:
Originally posted by T66
I noticed it on mine for the first time last week, my brakes were squeeling so I hit the brake with my left foot to clear the krud off them.


The ecu spotted what was happening and the engine power dropped right back.


This is the most annoying thing I find about my throttle by wire. If my brakes are a bit rusty after sitting still, I tend to try and lightly 'ride' them until they're clear and I have a good braking effort. Normal cars a bit of left foot braking takes care of them pretty well, but in mine if you touch the brake it kills the power so you come to a halt very quickly. Which I guess is what brakes are meant to do, but not in my case!! I've even had to change my bedding in procedure, although that's not a bad thing.

MikeRJ, I have to admit I don't remember mine having a throttle return spring. Certainly when the engine is off and I manually manipulate it, it stays in the position I leave it. It made cleaning it rather easy though.

It's only when I plug it in and turn the ignition on does it reset to 'nearly closed' (for idling I guess?). And of course when I've done that, the ECU has no idea what is open or closed so I have to do an ECU reset before the car will even drive!!

You're right about there being numerous fallbacks etc, and from memory if any one of them registers as even remotely faulty the car does it's 'limp home' trick.

MikeRJ - 30/1/13 at 06:57 AM

quote:
Originally posted by Slimy38
MikeRJ, I have to admit I don't remember mine having a throttle return spring. Certainly when the engine is off and I manually manipulate it, it stays in the position I leave it. It made cleaning it rather easy though.


That's interesting, not seen one that wasn't sprung before. What car is it?

v8kid - 30/1/13 at 08:10 AM

quote:
Originally posted by T66
My Suzuki GV has got one....do you want the text from my techy manual ?


Ta for the offer but it would take me too long to work out what was going on I just needed an overview thanks

Slimy38 - 30/1/13 at 08:10 AM

quote:
Originally posted by MikeRJ
quote:
Originally posted by Slimy38
MikeRJ, I have to admit I don't remember mine having a throttle return spring. Certainly when the engine is off and I manually manipulate it, it stays in the position I leave it. It made cleaning it rather easy though.


That's interesting, not seen one that wasn't sprung before. What car is it?


SEAT Toledo, it's the VW 2.3 V5 engine?

Of course, it could have just been broken!

v8kid - 30/1/13 at 08:12 AM

quote:
Originally posted by MikeRJ
quote:
Originally posted by v8kid
How does it work?

Is it just a stepper motor with a controller operated by a variable resistance on the throttle pedal?

What is the equivalent of a throttle return spring at the throttle body?

Cheers!


They still have a throttle return spring even if you can't see it; if the actuator loses power it has to fail safe (i.e. closed). There are numerous other safety related systems built in as well, such as dual sensors in the throttle pedal, and position sensors within the throttle body. The throttle pedal signal is processed by the ECU, and manufactures do all sorts of tricks such as retarding the ignition on sharp throttle inputs to give a smoother response.

[Edited on 29/1/13 by MikeRJ]


So I guess it would not be a stepper motor then i think they lock in the same position when there is no power and it takes a pulse input to shift them - unless there is some sort of magnetic coupling.

v8kid - 30/1/13 at 08:15 AM

quote:
Originally posted by T66
I noticed it on mine for the first time last week, my brakes were squeeling so I hit the brake with my left foot to clear the krud off them.


The ecu spotted what was happening and the engine power dropped right back.


Ah! that's an easy way to build a fail safe in - could have some sort of link to the clutch as well to allow blipping the throttle on downchanges.

Cheers!

renetom - 30/1/13 at 09:52 AM

Hi
I may be old & may not have understood the post .
But fail to see any point or benefit of this at all
what's wrong with a cable or rod throttle ?
Why put in something else to go wrong
If its for disabled people that need the
Throttle on the steering wheel or elsewhere
Then I can understand otherwise it seems to be
as useful as tits on a boar.

v8kid - 30/1/13 at 11:22 AM

quote:
Originally posted by renetom
Hi
I may be old & may not have understood the post .
But fail to see any point or benefit of this at all
what's wrong with a cable or rod throttle ?
Why put in something else to go wrong
If its for disabled people that need the
Throttle on the steering wheel or elsewhere
Then I can understand otherwise it seems to be
as useful as tits on a boar.


Bit like a locost car used to go shopping

Anyhow I think you are right what I need is not drive by wire throttle but a throttle blipper!

PS I'm old too but that does not stop me

[Edited on 30-1-13 by v8kid]

Slimy38 - 30/1/13 at 12:50 PM

quote:
Originally posted by renetom
Hi
I may be old & may not have understood the post .
But fail to see any point or benefit of this at all
what's wrong with a cable or rod throttle ?
Why put in something else to go wrong
If its for disabled people that need the
Throttle on the steering wheel or elsewhere
Then I can understand otherwise it seems to be
as useful as tits on a boar.


It helps to put a 'computer' in the way for emissions, cruise control, avoiding overfuelling and probably a fair few other things. But probably in all situations you could switch back to a mechanical throttle and still keep all those benefits.

coyoteboy - 30/1/13 at 01:17 PM

Fly by wire offers quite a few nice benefits but as mentioned the main ones are emissions, cruise control and some jiggery pokery you won't need on a kit car. But they would offer the option of a throttle blip if you knew how to achieve it and your ECU supported it.

MarcV - 30/1/13 at 03:25 PM

The electronic throttle has a DC motor with some reduction gears to drive the throttle plate. Normally (indeed all I have seen) have a spring which does not return to fully closed, but leaves a slight opening.

It either has dual potmeters or dual hall sensors for feedback of throttle position. These go to the ECU. The ECU outputs a PWM signal to the DC motor to achieve the desired position. Normally the throttle pedal would have two sensors as well, either resistive or hall.

On road cars it is indeed just for traction control, cruise control etc. Also the throttle response can be easily changed (exponential curve or something) (sport button). It also opens the throttle while coasting to reduce engine braking. It might actually slam shut again when the brakes are depressed to aid in braking. Also speed and rev limiting are incorporated in the functioning of the system. Probably a bit more as well.

Reason for a return spring which doesn't fully close is when a complete malfunction occurs, you end up with a high idle which gives a little more speed for getting your car somewhere safe.

You might have luck with the early cars that adopted drive by wire. The BMW E38 springs to mind which had two EML modules to control the two throttles. These have some interaction with other systems, but might work stand alone?

v8kid - 30/1/13 at 03:25 PM

Thanks for the input chaps you got the grey stuff working and ebay was my friend.

I found a pneumatic pin cylinder for a few quid that screws into the throttle stop and blips it for downshifts. I can then control the revs by cutting ignition.

Bit roundabout but lightweight and hopefully effective. The only issue is will a 20mm lift at the throttle stop be enough? I think so but we shall see - eventually.

Cheers!