Is engine braking really necessary?

[autogyro]

When harvesting energy the motor/generator also supplies overrun braking effect as well as the engine.
This has to be balanced to the wheel brakes and it is a main reason why variable diff control is essential in this operating faze.
(as well as for power out of corners)
With the motor/generator on the nose of the crankshaft, it is impossible to disengage the engine from the gearbox to eliminate the braking effect of the engine with all its energy losses, without also disengageing the energy harvesting/drive motor/generator.
The layout of the KERS systems used is a compromise forced by regulations and is an artificial use of new technology, in an attempt to force the continued use of conventional concepts in powertrains.
With flywheel energy storage thrown out in favour of dangerously placed batteries under the fuel tank, IMO it proves the sacrifice of sensible safe development for a future using a now fully regulation restricted formula.
Not only have regulations hamstrung development they have also resulted in dangerous energy storage systems.

[Tommy Cookers]

Thanks guys !

I'm still thinking that defuel/WOT will substantially reduce engine braking (even without changing valve timing, because the losses by compression are substantially recovered by the subsequent expansion). Surely the EB is much less in a diesel car, for this reason.
(Also, power-off the F1 valve timing won't give good cylinder filling ?)

One would think that non-ideal/uncontrolled EB must impede good KERS action.
A few years ago many? drivers set the gearchange control program to eliminate unneccessary/undesirable changes, eg if braking in top gear for a 4th gear corner it was best to let the 'box (at the right time) go from top directly to 4th. In this case EB is smooth and tends to resist incipient rear wheel locking (weak front/rear ABS effect). These days drivers are forced to change sequentially, ie go through all the gears ? This is disruptive of smooth EB.

We know that, additional to any EB the driving of the KERS demands a substantial force, ie this is electrical braking.
A freewheel (not allowed?) seems a natural way to go, ie allowing the engines rotational energy to be recovered independent of the need for braking of the car (it could be said that a freewheel/declutch system would allow engine running at tickover speed to give a false KERS effect).

I assume the drivers currently change down sequentially to keep the engine at high rpm to aid rapid KERS action in the favoured (brief) window, straightline braking from high speed.
In part, the drivers are milking the engine for easy, but false, KERS action (do we even know that no engine power is deliberately involved in this ?).

KERSing appears to make it even harder to brake optimally from high speed, with rapidly falling downforce. Surely such optimal braking is crucial to race performance.


BUT !!!


KERS has an inherent characteristic of giving substantial front/rear ABS effect (incipient locking of the rear wheels under braking will cause a sudden and large reduction in generator load, so strongly resisting locking). This is very useful for optimal braking from high speed.
I'm sure that this has been enhanced by the electrical designers in a way that the rule makers did not anticipate and cannot police (this covert ABS action counts against my suggestions regarding EB). This enhancement is simple to do, even in a 'passive/fixed' system.


The diff will give some L/R rear ABS effect from both EB and KERS ?



I am now starting to appreciate some aspects of the 2014 engine rules !

[alelanza]

Of course but open diffs have been used in the past with success.
Mainly when proper tyres were used.

What's a proper tyre?

It is a simple matter with modern electronics to control the differential traction via the brakes to achieve the ideal for any traction limit requirement.

Well that's the cheap approach to achieving the same effect, and in practice the tyres behave similarly to an LSD. But not even street performance cars rely solely on such an approach, they still have a % of locking happening inside the diff.

The diff slipper settings you mention are essential with high downforce, because there is insufficient 'feel' for the driver to apply power in any other way without braking traction.
Of course, without high downforce, the speed in corners would be lower but the skill level would be far higher.

It has nothing to do with high downforce, in fact they're all the more necessary in slow tight radius corners where you're allowed a very open diff mid corner that will allow the car to turn in easier and conserve the tyres better while still being able to rely on a stable rear end during entry and on exit.

[alelanza]

I'm still thinking that defuel/WOT will substantially reduce engine braking

Again, current rules don't allow ECU controlled WOT. But even when they did (as recent as last year) i don't believe the teams went for it. i suspect that was partially in order to allow a better transiton to on-power and as Tim said it allowed the resisting torque that kept both rear wheels linked and allowed for a more stable rear end.

I assume the drivers currently change down sequentially to keep the engine at high rpm to aid rapid KERS action in the favoured (brief) window, straightline braking from high speed.

Well they changed just the same prior to KERS.

I'm sure that this has been enhanced by the electrical designers in a way that the rule makers did not anticipate and cannot police (this covert ABS action counts against my suggestions regarding EB).

How are you sure of this? rules disallow it and teams run a std ECU on FIA software.

[autogyro]

Well that's the cheap approach to achieving the same effect, and in practice the tyres behave similarly to an LSD. But not even street performance cars rely solely on such an approach, they still have a % of locking happening inside the diff.

I disagree and having designed mechanical and hydraulic diffs so my opinion is qualified.

The reasons why biased braking has not replaced diff control is mainly because of restrictions in the regulations.

True, it is difficult to electronicaly control mechanical friction brakes to achieve the same result.

It is not as stated a cheap way to do it.

It is however, a simple matter to control electric induction braking as part of an energy recovery system, which is where the technology should be by now.

It is then an easy matter to include a full cross axle torque control.

[autogyro]

What's a proper tyre?

A tyre that is designed to fully meet the traction demands of a particular vehicle and results in the highest performance potential for that vehicle.

Not a tyre designed to wear at a much higher rate artificially to pander to downforce reguirments at the expense of ALL possible developments in powertrain technology.

[autogyro]

It has nothing to do with high downforce, in fact they're all the more necessary in slow tight radius corners where you're allowed a very open diff mid corner that will allow the car to turn in easier and conserve the tyres better while still being able to rely on a stable rear end during entry and on exit.

It has everything to do with high downforce both directly as I explained and indirectly because of the regulations that pander to it.

[g-force_addict]

According to ScarbsF1 they use "engine mapping" and "pedal maps" (euphemisms for still legal traction control) to prevent rear wheel lockup.
http://scarbsf1.wordpress.com/2012/05/1 ... anagement/

[Tommy Cookers]

I assume the drivers currently change down sequentially to keep the engine at high rpm to aid rapid KERS action in the favoured (brief) window, straightline braking from high speed.

Well they changed just the same prior to KERS.

I'm sure that this has been enhanced by the electrical designers in a way that the rule makers did not anticipate and cannot police (this covert ABS action counts against my suggestions regarding EB).

How are you sure of this? rules disallow it and teams run a std ECU on FIA software.[/quote]



ANSWER !


I think drivers change down sequentially because the rules were changed to force this (before KERS), this was to cut down on conspicuous involvement of software.

Sequential changes are easier for KERS, that's why they do them.

KERS is presented as regenerative braking, recovering (a very small part of the car's) KE otherwise dumped by the brakes. This KE includes rotational KE in the engine.
Any unneccessary downchange (raising the rpm and rotational KE) creates unneccessary, ie bogus, rotational KE and its recovery.

Even if there was a control (ie mandatory) MGen there would be a front/rear ABS effect, amounting to covert active control of brake balance.
Incipient locking of the rear wheels (slowing the MGen) will reduce the backdriving torque at the wheels, thereby resisting locking.

That's how a generator works.

This generator is designed and controlled to work at (equivalent) 17500-15500 rpm?, the load will fall to zero below the lower limit. It must do, and it will.

How is this not some ABS/brake balance proxy ?

This is all in the design of the MGen and its control circuitry (ie hard wired), not in some software implemented functionality.
This is basic stuff. IMO the rules allow it.

The only practical way to stop it is to issue mandated MGens etc.

Of course software would allow the full potential for the KERS to give an ABS/brake balance effect. This would be policeable. That's why they don't do it.


The rules are in effect made by the teams, ie something that they can all accept as being workable.

[autogyro]

According to ScarbsF1 they use "engine mapping" and "pedal maps" (euphemisms for still legal traction control) to prevent rear wheel lockup.
http://scarbsf1.wordpress.com/2012/05/1 ... anagement/

Exactly.

Keeping engine torque on during overrun is essential to compensate for the huge deceleration from downforce which would otherwise create a sudden and uncontrolable change from the applied driving torque to the drive axle, to a huge force reducing that torque from deceleration gained from that downforce.
This is also why diff control is essential to prevent rear break away during braking.

Without this 'engine torque positive' on overrun,rear tyre wear would be unacceptably high with the artificial tyres now in use, even with gentle use of the throttle. Some teams have yet to deal with it it seems.

It is yet another case showing the completely artificial control and technology additions forced on powertrain engineering by high downforce.

[gato azul]

ANSWER !

I think drivers change down sequentially because the rules were changed to force this (before KERS), this was to cut down on conspicuous involvement of software.

I would like to see, that rule you refereing to.
The main reason that they change down sequentially, lays in the layout/design of the gearbox/gear selection mechanism.

Ever since people stoped using H-pattern gear selectors, you will be hard pressed to "skip" a gear on downshift.

I don't think F1 rules, have ever mandated "sequential" gearboxes, it's just much easier to "automate/assist" an sequential g/box, than it is to do the same with an H-pattern shift.
(Subarus frist pedal shift in the Gr.A Legacy/Imprezzas,a.k.a. the "ghost box", would be the only one, which comes to my mind, when people "automated" an H-Pattern selector box.
There are may others, but I'm not aware of them in racing/rallying, BMW's first SMG would be a road car example).

Even in racing series, where there is no KERS, and no paddle shift (AGS), drivers racing sequential boxes, will still shift down in sequence, as you "can't skip a gear" with this boxes.

Having worked, in one of the few series, which until some years ago, still raced H-pattern g-boxes, I can tell you, that very few drivers, and only under some specific conditions, would change, let's say from 5th to 2nd, without "going through the box".
Most of the time, they would still downshift sequential, and make use of EB, to assist with decelleration/braking.
KERS would have nothing to do with it, as it is not used there.

[gato azul]

It has nothing to do with high downforce, in fact they're all the more necessary in slow tight radius corners where you're allowed a very open diff mid corner that will allow the car to turn in easier and conserve the tyres better while still being able to rely on a stable rear end during entry and on exit.

It has everything to do with high downforce both directly as I explained and indirectly because of the regulations that pander to it.

So that would mean, all diffs in Rally car (no downforce) drive trains, both RWD and AWD, use only & always, 0/90 deg ramp angles on the coast/braking side of the diff, and Zero preload?

[autogyro]

So that would mean, all diffs in Rally car (no downforce) drive trains, both RWD and AWD, use only & always, 0/90 deg ramp angles on the coast/braking side of the diff, and Zero preload?

There is no comparison between current F1 and rallycar drive trains in regard to what diff set ups are used in each sport.

High downforce in F1 dictates all of the F1 drive train and its settings.
Why and how overrun braking is used in F1 is also dictated by the needs of this high downforce.

Rally car overrun braking is a completely different requirement.

[Tommy Cookers]

Sequential downshift !

What I was thinking about was the 2 options when recovering KE

If the driver brakes at 200 mph and changes to 6th as soon as possible, the 5th as soon as possible, 4th as soon as possible, then stops braking heavily as he turns into a 100 mph corner ....... this is what I called sequential

If he brakes at 200 mph continuously down till at about 120 mph he changes 6,5,4 , arriving in 4th at 100mph etc ....... this is what I call minimising the disruption of unnecessary changes, as when programmed paddle changes were allowed drivers eg Alain Prost in some places would go eg 7th then 4th ( I assume the gearbox did 6,5,4 at this part of the track when the paddle was operated 1 time)

So what I called sequential maximises engine braking (and KERS?) but is less smooth, so does not help braking overall (unless the car's brakes are poor).
I think Prost agrees here. Today he would operate the paddle 3 times very quickly

So I think max EB 77777766666666555555544444444444 would be wrong

Prost min EB 77777777777777777777777777654444 would be better




BUT KERS recovery will be helped by the max EB method
as described before, I think KERS recovery is a bit naughty


SO I'm sorry if I have confused anyone !

I think max EB should have no place in the 21st century F1, but it helps naughty KERS and keeps out gearchange programming

[gato azul]

o.k. - so you talk about fully automated downshifts, which indeed are banned since a while.

Technically, there is nothing stopping the driver to still do the same, late downshift to minimize engine braking, if he does not want it, it's just a question of his timing, when does he requests the downshift.

The gearbox controller (at least the onces I know - not F1), will only prevent an too early downshift - if this would lead to an engine over rev.
In this case, the controller would just ignore, the downshift request, and the driver would need to pull/push the pedal again.

Anyway, if you read the Renault article, you get the impression, that they don't use much engine braking these days anyway.

And I'm sure, they found other ways to recharge the KERS batteries, which they allready did last year, with the EBD mappings.
maybe not all that much KER in KERS