33 replies to this topic

[Rediscoveryx]

I'm trying to settle a discussion here, and I thought maybe someone in here knows the correct answer. There was a lot of talk about "fly by wire" in the early 90's - my question is simply; what is this? Does it differ from Traction control, and if so; in what sense? When would it be useful and what teams were using it?

I would be very grateful for any answers

Best Regards, RDX

[wati]

You probbably mean drive by wire. The throttle is connected with engine by cable (wire) and controlled by electronics. Roughly speaking.;)

Wattie

[Rediscoveryx]

And how would this affect the cars performance?

[DEVO]

Rather then the control being mechanical... it is now digital. So you could have software optimize throttle response in any given situation.

[blkirk]

Traditionally, the pedal under the driver's right foot is connected directly to the throttle in the engine by a mechanical linkage. Pedal up, throttle closed. Pedal down, throttle open. There was nothing to prevent the driver from doing something crazy like full power in 1st gear.

With drive-by-wire, the pedal is connected to a sensor that tells the engine computer what the driver wants. The computer can then have a different throttle response for different conditions. Now when the driver pushes the pedal to the floor in 1st gear, the throttle only opens as far as the engineers think it should. The possibilities are limited only by your imagination and ability to get sensor data.

[AdamLarnachJr]

GM uses this on the Corvette and Camaro LS1 V8's, you can check out their corporate site for some technical info.

[Rediscoveryx]

Ok, is it performance enhancing?

[david_martin]

Originally posted by Rediscoveryx
Ok, is it performance enhancing?

Not in the strictest interpretation of "performance enhancing". It does eliminate a lot of mechanical parts and simplifies things greatly, and it does make the engineers job a lot easier. The Honda engine guys designed the most fabluous and complex mechanical throttle mechanism at Senna's request for the 1989 engine to improve the linearity of the throttle response of the rather peaky V10. I am sure it was a blessed relief to them to be able to replace all of those mechanical linkages with a resolver , a servo motor and some software ;)

A drive-by-wire throttle is also the launching pad for a lot of other integrated drivetrain functions like launch control, and traction control.

[Rediscoveryx]

Thanks for the help guys, let's see if I understood this properly (hope you excuse my poor prior knowledge of this particular subject).

"Drive by wire" has been around since the 80's - it's not a "driver aid", like Active Suspension or Traction Control in the sense that it enhances the drivers performance. It is a "driver aid" in the sense that it prevents the driver from making "silly" mistakes like giving full power in first gear.
It is also an "underlying" system that allows traction control and launch control.

Is that correct?

[int2str]

Not quiet...

The term fly-by-wire (original use of technology), just means that in the aviation industry, planes replaced the long cables running from the cockpit to the wings (rudders & elevators) were replaced by wires and servos in the wings. That greatly improves steering response and avoids cables getting "stuck".

Adapted to the car "drive-by-wire" it simply means the same. As others mentioned - the throttle cable on the car (pedal->carbs) has been replaced by a wire controling a servo and the engine control unit. Only direct benefits are much better (and quicker) throttle response (an electric position sensor reacts much finer to pedal movement than a wire).

That's all about "drive-by-wire". Nooooowwww, as others mentioned, once you have the drivers throttle input electronicly, you can play with it! You can prevent 1st gear full throttle (never heard of it, though), and use the throttle position as an input in your traction control calculation.
But these are other electronic helpers. "drive-by-wire" is just what I stated in the paragraphs above.

Only if you count quicker & smoother throttle control a "performance enhancement", you could say it is one....

Hope that helps!

Cheers,
Andre

[DEVO]

an analogy can be made that an analog watch (mechanical watch that you have to wind up) is to mechanical linkage throttle as a digital watch is to drive-by-wire (fly by wire)... that's as simple as I can make it.

[goGoGene]

The fly by wire technology is a necessity for modern stealth aircraft, which are aerodynamically unstable, and are basically uncontrollable, so the computer gets input from the pilot where he wants to fly (direction/throttle, etc) are calculates how it can best achieve this result. What you'll often see is an elevator/aileron fluttering to maintain stability. So the reason for using fly by wire was to take control away from the pilot since his/her responses weren't quick enough. The same is true for F1, if the pilot asks for something that will result in the car losing control/traction/etc the computer will do the best it can without overstepping the line. The logical extreme is to control both the steering wheel and throttle as parameters for the computer to take as input, and then do the best it can to achieve. But Steer by wire is currently not allowed under the regs.

ggg

[wati]

Originally posted by david_martin

am sure it was a blessed relief to them to be able to replace all of those mechanical linkages with a resolver , a servo motor and some software ;)

Servo motor? You mean the potentiometer?

Wattie

[Jezztor]

i think rediscoveryx is still a bit confused...

in the simplest terms, drive by wire throttles are in a sense 'remote control'. instead of the accelerator / throttle being connected to a throttle wire that 'pulls' when you 'push' the throttle, there is a little motor which does it instead. i think it runs via similar digital waves as remote controlled vehicles...not sure, someone just clarify that.

jezz

[david_martin]

Originally posted by wati


Servo motor? You mean the potentiometer?

Wattie

Nope. A resolver or potentiometer is the pedal position sensor - the servo motor is the throttle actuator

[Top Fuel F1]

Originally posted by wati


Servo motor? You mean the potentiometer?

Wattie

Here's a very basic explanation of a SERVO MOTOR system:

http://www.rec.ri.cm...age/servo.shtml

Of course the control to such a motor can be either via RF or hardwire as it is in F1.
Don't forget to Click on "Gears", "Motors", "Rotational Sensor", "Programming: Rotational Sensor" at the bottom off the Web Page.

Rgds;

[Top Fuel F1]

Here's a Spec. for a real Servo Motor:

http://www.moog.com/...drives/g493.pdf

This one appears to be for industial use or possibly some aircraft. I haven't studied it yet.

[stevew]

So can we say that "drive-by-wire" is an electronic linkage as opposed to a mechanical linkage?

[Ben]

If you go looking at MOOG stuff, all the F1 cars apparently run Moog Type 35 valves for the throttle, clutch, diff and gearshift.

Ben

[Wolf]

Stevew, it is indeed a part of it's function. The other part I have problem with is that throttle is driver input, and it does fiddle with it, making it driver aid in strictest sense (even drive-by-wire systems in road cars fiddle with signal, making it smoother or ignoring parts of it*). If it was as David described it, only signal transmission from pedal to the engine it would be OK. For what other reason would that signal need to be digital, if not to be fed to a processor which decides on servo-motors input. So, unless analog potentiometer, actuators and servo-motor are used, with no A/D and D/A converters in between, that drive-by-wire system can be for all intents and purposes be considered a driver aid.

* just like most of 'tiptronic'-like systems in road-cars, which may or may not ignore drivers input (if revs are too low) or act w/o it (when rev limit is reached). hence, the things that are to be controlled exclusively by the driver (like throttle, brake, gearbox and steering) are not that way anymore. One can go as far to assume that a system could be made which would give pre-calculated amount of throttle regardless of drivers input...

[kos]

I think that it doesn't matter, if the signal is digital or analog. The only difference is that digital signals are processed using CPU and software, and analog signals are processed using hardware only. So it's more cheap and convinient to work with digital signal, but having analog signal doesn't guarantee that initial driver's input cannot be overriden/amplified/filtered etc...

[Wolf]

Yes, Kos, you have a point, but only to a certain extent. I belive that producing analog computers that complex would be more trouble than its worth... I belive that in case of analog signal, certain filters and modulation could be applied, but that would mean same modification regardless of conditions and type of signal; like fixed non-linear throtlle response (like in the case of da Silva's David mentioned) or damping the throttle pumping (like Hakkinen is said to use around apex of the corner).

[kos]

Wolf, I totally agree that it would be VERY complex and expensive (relative to digital signal processing), but I still think that you can provide all those 'driver aids' using analog signal.

Regardles of the signal type you need some sensor that will tell you that conditions have changed and you need to modify control algorythm.
So, if you have some sensor then you can mix-in its input into control loop.
I think that type of signal only determines HOW control algorythm is implemented, and not whether it can or can not be implemented.

Before microprocessors were invented in the middle of '70-s, majority of control systems were implemented using analog devices, simply because digital computers of that era were too large and heavy to be installed on aircrafts and so on.

Regarding F1, 'drive-by-wire' appeared here when analog control electronics was almost forgotten, but in the aviation industry 'fly-by-wire' was implemented long before, if I can remember correctly, F-15 Eagle was first American fighter to employ that technique and it was designed around 1972. And from what I read about it, it uses analog computer in the control loops for pitch and bank channels

[JForce]

Of course the sytem needs to be progremmed correctly: Audi's sensatinaolly fast RS4 wagon uses a "drive-by-wire" throttle system that has become one of the most criticised parts of the car. Say you're in a long right hander, and you want to settle the car a little (which, being 4WD, understeers like a pig...), you may want to tap the brake with your left foot, whilst still accelerating.

The Audi senses that you have braked, and assumes you want to stop. It cuts all acceleration.

This can be very dangerous.

Obviously, if you were using mechanical linkages, you could brake and accelerate at the same time...

[Wolf]

JForce- I guess it shows that letting the car decide what to do isn't neccessarily the best thing to do; just like those 'clever' tiptronic-like gearboxes which decide if and when to shift. They present the danger when one downshifts too close to the entry to the bend and gearbox decides to shift (I've heard thet it sometimes takes up to half a second) during turn-in and one finds himself in a corner and no drive... Apparently it's best to downshift, when using those contraptions, way before the corner.

[Melbourne Park]

Originally posted by JForce
...Audi's sensatinaolly fast RS4 wagon uses a "drive-by-wire" throttle system that has become one of the most criticised parts of the car. Say you're in a long right hander, and you want to settle the car a little (which, being 4WD, understeers like a pig...), you may want to tap the brake with your left foot, whilst still accelerating.

The Audi senses that you have braked, and assumes you want to stop. It cuts all acceleration.

This can be very dangerous. ...

It also stops keeping the boost at a high level, by applying the brakes while holding the throttle open ... this technique can make the brakes quite hot as well, maybe Audi think that its not a good technique.

Incidentally, a couple of big benefits of drive by wire are being able to have a light weight throttle, and also they lower noise levels as there is no hole in the firewall for the throttle cable.

I can imagine in the future being able to get a car's computer to adjust the average weight of the steering, brakes, clutch and accellerator to suit one's individual preferences ...

[Melbourne Park]

For instance you can put a variable resister into the circuit of a Lexus' steering, and one can dial up the weight of the steering. And that is not a fly by wire steering system, that's just adjusting the way the power assistance recognises steering effort.

It would be fun to have such personal adjustments in cars for things like steering weight; my wife prefers lighter steering than I do ...

[desmo]

Surely the day cannot be far off- if it hasn't already arrived without my noticing- when the car's "brain" will recognize who's key has been used and automatically adjust seat and steering wheel, pedals, auto transmission upshift and downshift preferences, climate control, steering and braking weights, even suspension settings etc. etc. to suit the user. I suppose one could use a default setting for valet parking or loaning the car out to a friend.

[Ursus]

I guess you missed it desmo At least for seat/mirror/steering wheel adjustments etc.

[david_martin]

Originally posted by desmo
Surely the day cannot be far off- if it hasn't already arrived without my noticing- when the car's "brain" will recognize who's key has been used and automatically adjust seat and steering wheel, pedals, auto transmission upshift and downshift preferences, climate control, steering and braking weights, even suspension settings etc. etc. to suit the user. I suppose one could use a default setting for valet parking or loaning the car out to a friend.

It has arrived - check the the "iDrive" integrated electronics system on new BMW 7-series. It does everything on you wish list

[desmo]

I obviously need to read more car mags!

[Melbourne Park]

Does the 7 still have a key?

[david_martin]

Yeah, of sorts - a little smart card with a remote entry button that plugs into the centre console. I understand that as of late this year or early next year the remote entry button disappears and the system becomes truly keyless.

[Melbourne Park]

Originally posted by david_martin
Yeah, of sorts - a little smart card with a remote entry button that plugs into the centre console. I understand that as of late this year or early next year the remote entry button disappears and the system becomes truly keyless.

It sounds as if the car might do that upgrade all by itself ... maybe oneday an owner will injest a "key", and when you walk into the car park your smart car will recongise your proximity, it'll start its engine in anticipation, honk its horn and flash its lights; buy the deluxe model, and it'll come on over to you ...