Engine Brakes, what are they?

[ringo]

in fact if it were possible for the driver to press the throttle while on the brakes and then the fuel management would cut fuel to the engine. it may be very interesting the improvements in braking. If the rules did not stipulate that the throttle had to be controlled by the driver's foot at all times, there would be no need to step on the throttle pedal.
Any how i think engine braking strategies really play into the life of the engine, fuel saving and also vehicle dynamics.
And we can't forget the elephant in the room; the braking effect of all that drag force on the car.

the above seems to be a contradiction of the preceeding post, as it suggests that more throttle opening (fuel off) will increase engine braking, it will not
a major part of SI engine braking is always the suction load on the piston trying to suck air through a nearly closed throttle, feeding off the vehicles momentum
the effect was easy to demonstrate until vehicle design changes about 25 years ago, and was well known
eg it was easier to push-start a motorcycle with the throttle well open while pushing up to speed
a light aircraft will glide better engine-off if the everything is cut off and the throttle opened
80s cars could be modded by replacing the throttle microswitch (that told the injection that the driver was coasting) with a latching equivalent that would continue the fuel cutoff when the throttle was re-opened (once), this hugely improved coasting at speed

the compression losses are less, because there is re-expansion ?

I was looking on the point of view of having more mass of air to compress on the compression stroke; without combusting it of course. I guess we have to quantify the work done to compress air with the engine at max volumetric efficiency vs the work for the suction with closed throttle.
I don't think there is any system on an existing car that would cut the fuel when the throttle is fully open, maybe that's causing the contradiction. After all who would want to press the throttle and cut fuel?
But it would be an interesting application.

If it's a better braking technique, then the compression stroke of full throttle air, with no ignition must require more power than an intake stroke with a closed throttle.

edit: compression losses may be less if all 4 strokes are taken into account i suppose. I'll have to look into it.

[Tommy Cookers]

compression in this case will only start at inlet valve closure, ie it won't be the nominal CR (same for expansion of course)
the engine either has true zero fuelling, or otherwise (ie fuelling trending to idle) ?
there will still be a weak engine action (eg with open throttle) from residual heat in the combustion chamber/valves ?
throttle closed, some gas flow phases (exhausting) tend to reverse (when exposed at overlap to the induction side near-vacuum )

so, good luck with that thermo calculation !

in F1 EB can be maximised or minimised by gearchange strategy (which is now in effect determined by the rulemakers ?)

[nickf1boy]

Guys, Engine braking is the braking effect of the engine when off the throttle,. on f1 steering wheel, the engine brake knob is used to set how much of that you want, the ecu checks the front and rear wheel speed sensors, and compare them, if the rear is locking on braking, then the ecu injects more fuel to reduce the engine braking and prevent rear wheel lock, but like i said, they can adjust it for various corners and fuel saving strategies

[Tommy Cookers]

the engine brake knob is used to set how much of that you want, the ecu checks the front and rear wheel speed sensors, and compare them, if the rear is locking on braking, then the ecu injects more fuel to reduce the engine braking

recently we have been told by Renault Sport that the rules allow engine braking to be partly or completely cancelled
(they allow engine torque output to be raised to zero when the driver has lifted off the accelerator)
presumably this is referenced by a torque sensor (where I wonder relative to the KERS ?)
not by sensing wheel rpm (that would surely be in breach of some rules against traction control ?)

the KERS is recovering fake waste KE (the car has more KE than if it was zero fuelled on overrun like normal)
and the DF benefits from the exhaust flow of course

[autogyro]

Guys, Engine braking is the braking effect of the engine when off the throttle,. on f1 steering wheel, the engine brake knob is used to set how much of that you want, the ecu checks the front and rear wheel speed sensors, and compare them, if the rear is locking on braking, then the ecu injects more fuel to reduce the engine braking and prevent rear wheel lock, but like i said, they can adjust it for various corners and fuel saving strategies

They would certainly have to be sure of a decent fueling program if they richen up to compensate for excess engine braking.
I would suggest they program the Kers motor/generator on the crank nose, that would give far better control.
However, if the Kers motor/generator was part of the gearbox then under deceleration the engine need not be connected to the powertrain at all.

[rjsa]

Guys, Engine braking is the braking effect of the engine when off the throttle,. on f1 steering wheel, the engine brake knob is used to set how much of that you want, the ecu checks the front and rear wheel speed sensors, and compare them, if the rear is locking on braking, then the ecu injects more fuel to reduce the engine braking and prevent rear wheel lock, but like i said, they can adjust it for various corners and fuel saving strategies

I'm pretty sure this is not allowed by the rules. The comparing the front and rear wheel speeds I mean. That's closed loop control of traction/braking. It's a no no.

[Dragonfly]

I remember when KERS was going to be introduced BMW spoke about the problems with varying braking effect and that they had to make engine mapping so that KERS introduced force be neutralized by applying torque from the engine the driver had a consistent braking behavior before each corner.

[rjsa]

But all that without feedback from wheel speed. Never.

[Tommy Cookers]

I remember when KERS was going to be introduced BMW spoke about the problems with varying braking effect and that they had to make engine mapping so that KERS introduced force be neutralized by applying torque from the engine the driver had a consistent braking behavior before each corner.

this requires only a torque sensor (in the right place)
credible surely ?

[rjsa]

this requires only a torque sensor (in the right place)
credible surely ?

That's another point of feedback I'd bet money the SECU can't process.

No closed loop control of braking or acceleration, I'm pretty sure about that.

EDIT:Ohh, and pumping fuel to counter KERS while braking is as against the spirit of the freaking gadget as anything can get.

[Dragonfly]

this requires only a torque sensor (in the right place)
credible surely ?

That's another point of feedback I'd bet money the SECU can't process.

No closed loop control of braking or acceleration, I'm pretty sure about that.

EDIT:Ohh, and pumping fuel to counter KERS while braking is as against the spirit of the freaking gadget as anything can get.

I am sure there were similar comments back then. About burning fuel while trying to harvest kinetic energy which is illogical to the intention of the whole idea. But it will be a very difficult task for a driver to select a braking point with varying braking behavior. Don't know how they do it today, definitely there must have been some advance since 2008.

[Tommy Cookers]

according to Renault Sport is the driver selects how much overrun push he wants
(it's all in the mapping, the mapping rules limit this to zero torque output, ie 100% cancellation of engine braking)
that is the maps of engine throttle position and fuelling for all rpm when the driver is off the accelerator
there must be real-time torque sensor(s) somewhere (exactly where is significant)

the driver currently adjusts push level according to the condition of the tyres
the max push they use would consume up to 2kg of fuel (ie if used for the whole race)

given that the engines resistance on overrun would at high rpm be about 20% (of max torque)
full cancellation of engine braking could easily generate more power than the current KERS needs
and will presumably be used in 2014 when the Kinetic recovery power will be twice the 2013 power

(fuel will be freely available according to rpm at all times, even if the driver has lifted off the accelerator
the torque sensor position will determine whether engine driving the generator is treated as zero output torque)

[rjsa]

I doubt there is any kind of sensor feeding back torque into the SECU.

If they do have overrun push (I'm not doubting it, just never looked at the matter myself) then it was set up in the dine, with preset fuel quantities on the maps as you stated. But it's open loop, preset map only.

[Tommy Cookers]

I doubt there is any kind of sensor feeding back torque into the SECU.

If they do have overrun push (I'm not doubting it, just never looked at the matter myself) then it was set up in the dine, with preset fuel quantities on the maps as you stated. But it's open loop, preset map only.

if it is preset, this must be based on bench calibration runs with a bench torque sensor (or how is zero torque demonstrated ?)
would that be accepted as proving rule-compliance in the races ?

Renault say they monitor torque throughout the race, and adjust response accordingly

[rjsa]

I don't doubt they have telemetery reading torque, I just doubt it will be fed back into the SECU for on the fly adjustment.

'Monitor torque throughout the race, and adjust response accordingly' as stated implies to me the pit sending commands to the engine, what I assume is another no no. They might get the readings and advise the driver to turn knobs and push buttons, but never send instructions directly to the engine.