fly by wire?

[Phil]

Hi

What exactly is a fly by wire throttle and how does it work?

Thanks Phil

[OliverSedlacek]

A 'fly by wire' throttle is actuated by an electric motor rather than by the pedal through some form of linkage. The pedal is the main input to an ECU, which sends a signal to the motor through an electrical connection. The benefit of 'fly by wire' is that the pedal is not the only input, so it can do traction control, cruise control and rev limiting.

[Roger King]

It's other main use is to stop the engine from doing things that will make emissions worse. You may ask the throttle to do something, but it's not going to unless Big Brother feels you should be allowed to.

It's a brilliant idea. I found this out when my wife's Tigra suffered a flat battery and on replacing it, the throttle would not work. We had to call out a specialist to reset the ECU so that it would recognise the relevant hardware.

Can you imagine such a conversation twenty years ago? "Yes sir, you're battery has gone flat and this naturally means that your accelerator no longer works"

[Instigator]

Caterhams are just about the only cars on sale that do not have electronically actuated throttles, as IVA only includes a basic exhaust emission test. That said, Caterham's export models all feature fly by wire as they need to meet EU5 regulations.
In addition to having cleaner tailpipes the fly by wire cars are more fuel efficient, but throttle response is noticably less direct and, while the Ford sourced throttle position sensor and actuator are very reliable, Caterham's wiring to both is not. 

 

[Phil]

Thanks

I now have a better understanding of what they are and why Caterham maybe fitting them as standard on next years models.

 

[ChrisC]

Isnt the 160 fly by wire?

[Jonathan Kay]

... but throttle response is noticably less direct...

Why is that? Sensor, actuator or algorithm? And if it's the algorithm is it deliberate... and reprogrammable?

Thanks

Jonathan

[Mankee]

It's common for VAG 1.8T/2.0TFSI tuners to remap the throttle versus load map so that the driver has more control over the specified load. The factory throttle map on my Skoda does my head in as it tries to be clever and sometimes gives me more load than I actually want, resulting in rampant boost and wheelspin in his weather.

[Grubbster]

If the throttle response is less direct it could be to do with the algorithm it uses (my renault RS Megane I can change it to make it stupidly sharp or dim-witted!) or maybe to do with the stepper motors that operate the throttle - could they have a short delay to react?

[Roger King]

If you slam the throttle open on a car with mechanical throttle (be it carbs or injection), you will see a large spike of hydrocarbons popping out of the exhaust just a tad later (see SI units for definition of "tad").

If the throttle is opened just a little more gently this spike is greatly reduced. You also get a similar effect if you shut the throttle suddenly at high load. Fly by wire can stop all of this happening, although at the cost of the throttle feeling as though it is connected to the pedal via a rice pudding, an elastic band and a lump of warm blu-tak. There are many other scenarios where big brother control of the throttle will reduce naughty emissions.

If you're used to such things it can be quite a shock to blip the throttle of a car equipped with well set up DCOE's - the response is instant.

[Moggie]

Could Caterham use two maps, one to be EU5 compliant and another 'track' mode which replicates the exact peddle position with no interference?  Is a drive-by-wire capable of being as responsive as a mechanical throttle?

[rj]

I don't think they'd be allowed to according to the regs, at least not in the EU. A road registered car must be roadworthy at any time, even if not in use. You can take off the registration and alter the car, but if you want to re-register it, then it has to be roadworthy.

[Moggie]

I meant in a way that the driver could select the map via a switch on the dash.  Such as the Ferrari race mode settings.  Would that mean that a Ferrari 458 in race mode is still EU5 compliant?

It would be win-win if Caterham could have a 'road' and 'track' setting whereby only road was required to be EU5 compliant.

[Jonathan Kay]

Is a drive-by-wire capable of being as responsive as a mechanical throttle?

The engineering aspects of this aren't particularly difficult and the technology could easily offer that. But there are two additional constraints: keeping the production costs down, and the compromises in the algorithm if you have multiple objectives such as economy and low emissions as well as responsiveness.

I don't know whether the cost constraints in production versions limit the responsiveness you can get by changing the algorithm. Any more "remapping" experiences that could throw light on this?

You can get more responsiveness (in one sense) with smart systems than fully manual (or pedal!) systems. One example of this the braking on eg Mercedes road cars. At high speeds drivers are known to underbrake : the systems are designed to compensate for this. The output is matched to need rather than input alone.

Jonathan