The rationale behind "feathering the throttle"

[anko]

Jaap wrote in a different topic:

I found that the venerable practice of "feathering the throttle" (which means pushing the accelerator to obtain a certain speed/acceleration and then easing up marginally without losing the power - I've been doing that since the stone age on cars varying from an A Ford to a Morgan, so it is an automatism for me) works well and reduces racing the ICE significantly.

I have heard more about it, but with all due respect, to me it sound a bit like magic: easing up on the throttle without losing power. Is there any rational on how this would work?

 

[jaapv]

Whew - I don't know, on a carburettor I can dream up an explanation including air flows, vortexes etc. but I suspect that it has to do with mechanical tolerances.
All I know that the technique does save fuel on ICE cars and seems to reduce the revving on the PHEV without perceptible loss of performance.

It is just that I am from an older generation of drivers who had to ride the mechanism, I still double-declutch on a gearbox car when changing down, I can use a crash box, can do four-wheel drifts on rear-driven sports cars, even get home with a broken clutch. And feather the throttle and brakes as a matter of routine.

 

[Titan]

I'm not sure I would have described it as a process I used as such but I do concur. When I'm driving in Charge mode I watch the power gauge and power flow meters and will "feather" to ensure the battery is getting charged. It's possible to play the throttle with little change in forward momentum yet achieve improved charging rate (I assume, as the power meter drops, so therefore more juice must be going to the battery).

(also an older driver, used to double de - clutch, can ride a clutch beautifully on a hill, used crash box on Formula Fords and regularly used to get home with broken clutch cable on my motor , love tear wheel drive cars and power slides)

 

[jthspace]

I have heard more about it, but with all due respect, to me it sound a bit like magic: easing up on the throttle without losing power. Is there any rational on how this would work?

I have been riding motorcycles, driving cars and other vehicles for over 45 years and "feathering" has always been a part of the way of driving, the last car that I drove that feathering definately had a positive effect on was a Nissan Juke with CVT - it was noticable that you could get up to speed and by easing the throttle "a cats whisker" could drop the revs by 500 or more and maintain the same speed. This was probably a function of the CVT, but it is still the way I learned to drive - listen to and "feel" the engine so as to use the sweet-spots in rev range and get the best out of the engine/gearbox. Much more difficult these days as engine management systems and good insulation removes the driver from the "sharp end" - no bad thing either! I have my motorcycle when I need to get back to nature as it was intended.

Jeff

Cats Whisker - technically, it should be described as «a gnats c*ck» but . . .

 

[Regulo]

Further to this discussion: When I travel at a steady rate, I notice that without moving the accelerator, if I paddle from B0 to B5 the power meter changes. Although the car seems to run easier on B0, the power meter moves up i.e. away from the "charge" area. B5 drops the gauge back, but the car doesn't seem to run freer, if you see what I mean. Any explanations? We're told the motors can't be re-generating while driving the car, so why this difference on the power meter, and in the "feel" of the car?

 

[Neverfuel]

I have noticed this as well, I assumed that it was because the paddles change the detente position on the accelerator pedal. Maybe someone can enlighten us?

 

[anko]

Further to this discussion: When I travel at a steady rate, I notice that without moving the accelerator, if I paddle from B0 to B5 the power meter changes. Although the car seems to run easier on B0, the power meter moves up i.e. away from the "charge" area. B5 drops the gauge back, but the car doesn't seem to run freer, if you see what I mean. Any explanations? We're told the motors can't be re-generating while driving the car, so why this difference on the power meter, and in the "feel" of the car?

Indeed, when changing from B5 to B0 the gas-pedal is remapped. You can actually change speeds by charing B-levels while holding your pedal stationary. In B0, less pressure is needed to obtain the same speed. Many people interpet this as if the car is mor light footed.

 

[anko]

had a positive effect on was a Nissan Juke with CVT - it was noticable that you could get up to speed and by easing the throttle "a cats whisker" could drop the revs by 500 or more and maintain the same speed.

Let us take CVTs out of the equation as so much mor is going on there that does not apply to our cars. Like you said, easing off the throttle almost automatically results in change of gear ratio which will impact efficiency (when driven like a CVT). It wil only complicate the discussion. Is that okay?

 

[anko]

I'm not sure I would have described it as a process I used as such but I do concur. When I'm driving in Charge mode I watch the power gauge and power flow meters and will "feather" to ensure the battery is getting charged. It's possible to play the throttle with little change in forward momentum yet achieve improved charging rate (I assume, as the power meter drops, so therefore more juice must be going to the battery).

I would think that, as the power meter drops, less power is going to the wheels and acceleration stops or the car slows down. But that is not what we are looking for, I would say ....

 

[jaapv]

had a positive effect on was a Nissan Juke with CVT - it was noticable that you could get up to speed and by easing the throttle "a cats whisker" could drop the revs by 500 or more and maintain the same speed.

Let us take CVTs out of the equation as so much mor is going on there that does not apply to our cars. Like you said, easing off the throttle almost automatically results in change of gear ratio which will impact efficiency (when driven like a CVT). It wil only complicate the discussion. Is that okay?

I seem to recall that you referred to the whole series hybrid system as a "virtual CVT" once.

 

[Trex]

had a positive effect on was a Nissan Juke with CVT - it was noticable that you could get up to speed and by easing the throttle "a cats whisker" could drop the revs by 500 or more and maintain the same speed.

Let us take CVTs out of the equation as so much mor is going on there that does not apply to our cars. Like you said, easing off the throttle almost automatically results in change of gear ratio which will impact efficiency (when driven like a CVT). It wil only complicate the discussion. Is that okay?

I seem to recall that you referred to the whole series hybrid system as a "virtual CVT" once.

:lol: Ok I am definitely staying out of this discussion. :lol:

But then again I am already in it. :roll: :lol:

And that folks is my "tongue in cheek" Australian sense of humour.

Regards Trex.

 

[anko]

had a positive effect on was a Nissan Juke with CVT - it was noticable that you could get up to speed and by easing the throttle "a cats whisker" could drop the revs by 500 or more and maintain the same speed.

Let us take CVTs out of the equation as so much mor is going on there that does not apply to our cars. Like you said, easing off the throttle almost automatically results in change of gear ratio which will impact efficiency (when driven like a CVT). It wil only complicate the discussion. Is that okay?

I seem to recall that you referred to the whole series hybrid system as a "virtual CVT" once.

Indeed, a virtual CVT.

 

[Trex]

Jaap wrote in a different topic:

I found that the venerable practice of "feathering the throttle" (which means pushing the accelerator to obtain a certain speed/acceleration and then easing up marginally without losing the power - I've been doing that since the stone age on cars varying from an A Ford to a Morgan, so it is an automatism for me) works well and reduces racing the ICE significantly.

I have heard more about it, but with all due respect, to me it sound a bit like magic: easing up on the throttle without losing power. Is there any rational on how this would work?

Hi folks,

As I am already involved. :lol:

I have heard this expression "feathering the throttle" as well as "feathering the brakes" from old truckies that worked for me.

As a mechanical engineer and the owner (and sometimes driver) of the trucks with 18 speed Roadranger gearbox I will say what I told them.

"If I believed in that I believe in the Tooth Fairy" or words to that effect including some that I cannot print here.

Sorry I do not wish to be too blunt.

Regards Trex.

 

[Phevourite]

Not sure if this adds anything to the discussion as you all probably know this stuff far better than me but all controls exhibit hysteresis. Old-fashioned throttles probably more than many. When I was a young child working large machine tools (it was a hard life) I got used to setting controls and backing them off to get consistent performance - not necessarily better performance in that case just more consistent. These days similar machines have much less hysteresis thankfully. I thought then and I still think it is odd that hysteresis is not on the school curriculum given that it is such an important and ever-present phenomena. Should be taught in maths I guess. Anyway; I suspect that electronic controls on devices as complex as the Outlander have a fair bit still and for reasons I could only guess at.

 

[jaapv]

Jaap wrote in a different topic:

I found that the venerable practice of "feathering the throttle" (which means pushing the accelerator to obtain a certain speed/acceleration and then easing up marginally without losing the power - I've been doing that since the stone age on cars varying from an A Ford to a Morgan, so it is an automatism for me) works well and reduces racing the ICE significantly.

I have heard more about it, but with all due respect, to me it sound a bit like magic: easing up on the throttle without losing power. Is there any rational on how this would work?

Hi folks,

As I am already involved. :lol:

I have heard this expression "feathering the throttle" as well as "feathering the brakes" from old truckies that worked for me.

As a mechanical engineer and the owner (and sometimes driver) of the trucks with 18 speed Roadranger gearbox I will say what I told them.

"If I believed in that I believe in the Tooth Fairy" or words to that effect including some that I cannot print here.

Sorry I do not wish to be too blunt.

Regards Trex.

Well, don't feather brakes and have your passengers bend reverently as the car slams to a halt, do feather them and they will remain peacefully reclined in their seats...
I'm not quite convinced truckers are the ultimate authority on sensitive ( or should that be sensible ?) driving.

 

[jthspace]

had a positive effect on was a Nissan Juke with CVT - it was noticable that you could get up to speed and by easing the throttle "a cats whisker" could drop the revs by 500 or more and maintain the same speed.

Let us take CVTs out of the equation as so much mor is going on there that does not apply to our cars. Like you said, easing off the throttle almost automatically results in change of gear ratio which will impact efficiency (when driven like a CVT). It wil only complicate the discussion. Is that okay?

I was responding to the OP on feathering, and gave my experience on a recent vehicle - I thought, adding to the discussion but I am fine if you want to exclude specific reference to CVT's It would seem then that every vehicle that doesn't have four electric motors with one attached to each wheel will never form a part of a discussion???? :lol:

 

[Neverfuel]

had a positive effect on was a Nissan Juke with CVT - it was noticable that you could get up to speed and by easing the throttle "a cats whisker" could drop the revs by 500 or more and maintain the same speed.

Let us take CVTs out of the equation as so much mor is going on there that does not apply to our cars. Like you said, easing off the throttle almost automatically results in change of gear ratio which will impact efficiency (when driven like a CVT). It wil only complicate the discussion. Is that okay?

I was responding to the OP on feathering, and gave my experience on a recent vehicle - I thought, adding to the discussion but I am fine if you want to exclude specific reference to CVT's It would seem then that every vehicle that doesn't have four electric motors with one attached to each wheel will never form a part of a discussion???? :lol:

4 electric motors - imagine the graphs that we would see in the Technical Section! :lol:

Can we possibly keep moon buggies out of this and talk about the PHEV? :shock:

 

[jthspace]

:lol:

As you can see from my username, I understand moon buggies - I have been involved in the "space" industry for over 35 years and currently working with a team to 3D print a cubesat satellite chassis, assemple the electronics in-orbit and launch it from the Internationl Space Station next year - fun project but with fantastic future potential - getting a 3D printer to work in zero gravity, printing spare parts from data files instead of waiting months for a replacement to be flown up, inter-planetary or off-world spares and repairs . . . a simple use of new-ish technology that will absolutely change the future.

Jeff

 

[anko]

had a positive effect on was a Nissan Juke with CVT - it was noticable that you could get up to speed and by easing the throttle "a cats whisker" could drop the revs by 500 or more and maintain the same speed.

Let us take CVTs out of the equation as so much mor is going on there that does not apply to our cars. Like you said, easing off the throttle almost automatically results in change of gear ratio which will impact efficiency (when driven like a CVT). It wil only complicate the discussion. Is that okay?

I was responding to the OP on feathering, and gave my experience on a recent vehicle - I thought, adding to the discussion but I am fine if you want to exclude specific reference to CVT's It would seem then that every vehicle that doesn't have four electric motors with one attached to each wheel will never form a part of a discussion???? :lol:

Fair comment. My line of thinking was this: by easing of the throttle in a CVT, you basically tell the car you don't need to much power reservers and it will shift up a little bit. Higher engine load at lower RPM results in same amount of power at lower fuel consumption. Same as you would manually shift to a higher gear in a normal car. CVT puzzle solved. Does that make sense?

But although our car is indeed capable of CVT like behaviour at serial hybrid speeds (Jaap was correct when he said I mentioned this myself) to me that doesn't mean that feathering it would automatically result in higher load at less RPM. I would think it would result in less power and less speed.

 

[anko]

One way of driving is this: We can push the pedal in a certain position and the car will accelerate. At some point power generated by the engine is matched by (air)resistance and the car does not accelerate any further. But that is not how we typically drive. At least, not me.

We accelerate and when we reach the desired speed we lift the throttle a bit to prevent the car from going even faster. I assume this is not what we mean with feathering. Feathering would, if I understand correctly, be to lift the throttle a little bit further, after acceleration has already stopped. Right?

Now somebody explain to me, if I can, while driving at a constant speed, lift the pedal from (e.g.) 18% to 17.8%, without loosing power and thus without loosing speed, then why could I not do the same thing again a few seconds later and lift from 17.8% to 17.6% without loosing power or speed? And so on?