Is engine braking really necessary?

[Agerasia]

To answer the original question and get back on topic....
F1 cars used to prevent rear wheel lock up in software you know It was a form of stability control. Engine braking is advantagous in certain circumstances.
Anyway I believe that F1 cars now have an advanced type of slipper clutch since standardised ECU's came in.

[Belatti]

To add something appart from the current discussion here:

I discourage the young formula drivers I work with to use engine braking, more or less following the reasons given by Smith in "drive to win".

As opposite, engine braking is absolutelly necesary in some touring cars series.

[Tim.Wright]

Remember, without engine braking, there is nothing to engage the locking effect on the diff to stabilise the car in the braking zone.

Tim

[munks]

So because the gearbox at that gear can´t spin as fast as the rear wheels want to do because they are travelling at 80km/h you will end up with locked rear wheels.

However, the locked rear wheels won´t stall the engine because the engine is dancing on the limiter.
The wheels will stop locking when you slow the car down to 50km/h.

You have one part that wants to do 80km/h the other wants to do 50km/h.

Just FYI guys, you two are using different definitions of 'locked'. xxChrisxx is using the more common definition where the wheel speeds are literally zero. If both rear wheels have stopped rotating and the clutch is engaged, then yes, the engine will also have stopped rotating. Nando is talking about what most of us would call a 'partial lock-up' where the tires are skidding but still turning. Since they are still rotating a bit, yes, the engine is still going.

[hardingfv32]

I believe that F1 cars now have an advanced type of slipper clutch since standardised ECU's came in.

Can you expand?

Under current rules I don't think the clutch can be used to help this issue, unless the driver is doing the clutch modulation.

Brian

[xxChrisxx]

Just FYI guys, you two are using different definitions of 'locked'. xxChrisxx is using the more common definition where the wheel speeds are literally zero. If both rear wheels have stopped rotating and the clutch is engaged, then yes, the engine will also have stopped rotating. Nando is talking about what most of us would call a 'partial lock-up' where the tires are skidding but still turning. Since they are still rotating a bit, yes, the engine is still going.

I'm glad you said that, I thought I was going a bit mad.
I've got pages written out deriving the conditions from first principles.

I came to the same conclusion as above, but it's nice for someone else to confirm it.

[Johnnyfartpants]

First post but back to the thread.

I come from a bike background and engine braking is both a help and hinderance. 2-strokes have virtually none, where as big 4-stroke twins have loads. Controlling it via the clutch, or fancy gizmos such as slipper clutches or air bleeds into the cylinders, or even auto-blippers, depends on how much cash you have. Most road riders will be well practiced in blipping the clutch before down changes and the better you get the more you can control you're breaking. You can actually turn the bike tighter using it, but generally corner faster without it. With a small 2-T the lack of engine braking and high corner speeds help as you don't have the spread of torque to pull you out of the corner.High torque 4-T's fire out of corners like rockets so squaring off he corner using a combination of balanced engine braking (Manual or mechanical) and the actual brakes is the trick.

I'd imagine in cars the same balance is required, but like everything else it will come down to driver styles and preferences. And with the kers balancing the engine braking I guess they can dial in what ever they want.

[Nando]

I guess i´m the problem sorry bit of a communication issue.

However, when it comes to the handbrake drift scenario i mean 100% completely locked wheels for half a second or more.

[olefud]

I'm currently doing a workthrough of traction from first principles, for posting in a seperate thread.

Could you elaborate a bit on that point.

What do you mean by snotty? When the track loses grip?
Did the wheel stop rotating and remain sliding or just break traction?
Was this under braking, thottle, lift off/overrun at high revs/low revs etc.
Was it on a straight or a corner?
Was it a specific wheel, ie the loaded or unloaded, or was it both?

Snotty was the result of watering the clay track a bit too much. After watering, the cars would pack the track at modest speed. If too damp it had poor grip.

Both rear wheels (locked diffential) would stop to the extent that the lug nuts could be seen. At the point of lockup, both braking and overrun were occurring.
This would be at max revs towards the end of the straight. The driver would feel the rear getting away, get off the brakes, and turn into the banking. This would scrub off speed and usually get the engine running again. Sometime just getting off the brakes would work. Probably getting into the banking would load the tires and help.

Run-what-you-brung (Fendered Formula Libre) was the standard so it hard to generalize about the equipment other than we used American V-8s.

Problem was that three of the engines four cycles consumed energy while only one produced energy. With a light flywheel, the energy needed to come from the car’s kinetic energy turning the rear wheels. With poor traction, the wheels slid and the engine stopped. With the throttle closed, the intake stroke has high pumping needs against the cylinder vacuum, though the compression stroke, while still needing energy, is less demanding.

[munks]

I guess i´m the problem sorry bit of a communication issue.

However, when it comes to the handbrake drift scenario i mean 100% completely locked wheels for half a second or more.

If I'm not mistaken, some rally cars can automatically disengage the clutch when the handbrake is used.

[gato azul]

I guess i´m the problem sorry bit of a communication issue.

However, when it comes to the handbrake drift scenario i mean 100% completely locked wheels for half a second or more.

If I'm not mistaken, some rally cars can automatically disengage the clutch when the handbrake is used.

It's (it was)normally not the "clutch between engine and gearbox" which disengages when the hand brake is applied.

In the past (Gr.A days), the car's I have worked on, had either a seperate clutch, to disconnect only the rear axle, or were using a "clutch pack" in the centre diff, so you would make the center diff fully open, when the hand brake is pulled.
Which had the same effect, turning your 4WD car into a FWD car for a moment.

There are maybe different systems used today - it's a while since I have seen a rally car drive line from close quarters.

[munks]

Ahhh, thanks for the clarification. Now that you mention it, I was actually remembering the center diff trick.

[riff_raff]

Remember, without engine braking, there is nothing to engage the locking effect on the diff to stabilise the car in the braking zone.Tim

Engine braking does not add heat load to the brake rotors. This can be significant with a heavy chassis and steel rotors, which may be subject to fade.

[autogyro]

Remember, without engine braking, there is nothing to engage the locking effect on the diff to stabilise the car in the braking zone.Tim

Engine braking does not add heat load to the brake rotors. This can be significant with a heavy chassis and steel rotors, which may be subject to fade.

True and a good reason to use engine braking.
Of course it then requires the driver to modulate that engine braking to balance the car if prper driver skill is to be natured.
With FI and other high downforce formula, when the throttle is lifted the retardation caused by the downforce both negates and masks any need for engine braking. The speed of this retardation makes it almopst impossible to change gear or manualy balance engine braking anyway.
It is only the regulations that define the energy harvesting components and how they are controlled that retains a need for any form of powertrain overrun in current F1 cars.
Controlled braking in F1 today is little different to throwing an anchor over the side.

[Tim.Wright]

Engine braking does not add heat load to the brake rotors. This can be significant with a heavy chassis and steel rotors, which may be subject to fade.

What I was talking about has nothing to do with using the engine braking to physically slow the car. Im talking about using the drag torque to apply locking to the diff and stabilise the car. I believe this is the primary use of engine drag torque these days.

You don't want to completely eliminate the engine drag torque (by rev matching, blipping etc) because there will be nothing engaging the diff locking to stabilise the car.

Tim