Is engine braking really necessary?

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.

Post Tue May 08, 2012 12:39 pm

Engine braking causes rear wheel lockup when braking or trail braking at the limit, doesn't it?
How do F1s prevent lockup?
Do they have a rev-match or torque-match downshifting mechanism?

Add transmission strain while engine braking.
g-force_addict
 
Joined: 17 May 2011

Post Tue May 08, 2012 1:31 pm

g-force_addict wrote:Engine braking causes rear wheel lockup when braking or trail braking at the limit, doesn't it?
How do F1s prevent lockup?
Do they have a rev-match or torque-match downshifting mechanism?

Add transmission strain while engine braking.


Rear wheel braking is balanced with KERS harvesting to prevent rear wheel lock up.
This control happens while there is huge downforce applied to the whole car during deceleration and this totaly masks rear traction problems by reducing the potential for rear wheel lock up. Because all items that effect potential rear wheel lock up are computer controlled there is little chance of lock up or missed shifts.
Railway lines in the track or real time remote control would do a similar job.

In the days of proper racing, the shifts were fully modulated and the speed of shifts varied manualy as part of the complete skills armoury of the drivers.
This was a main part of being a racing driver as a result of having FULL control over the race car.
autogyro
 
Joined: 4 Oct 2009

Post Tue May 08, 2012 2:21 pm

Short answer has to be NO

Long answer must include talk about what the differential can do to help the car into a corner when trail braking.

It's probably useful rather than necessary.

Unless you call 'necessary' helping a car go faster :wink:
RH1300S
 
Joined: 6 Jun 2005

Post Tue May 08, 2012 4:14 pm

g-force_addict wrote:Engine braking causes rear wheel lockup when braking or trail braking at the limit, doesn't it?


Not necessarily, no.
Grip is a four letter word.

2 is the new #1.
Jersey Tom
 
Joined: 29 May 2006
Location: Huntersville, NC

Post Tue May 08, 2012 11:18 pm

Jersey Tom wrote:
g-force_addict wrote:Engine braking causes rear wheel lockup when braking or trail braking at the limit, doesn't it?


Not necessarily, no.


Of course it does.

I personally experienced it. At a performance driving course we were driving on the skidpad at speed deemed the limit of adhesion.
Any rough input be it braking or downshifting w/o rev matching sent the car out of the skidpad in a blink.

Thus if you are braking or trail braking with all four wheels just below the limit of adhesion (as you should for lower lap times) any additional braking in this case engine-braking will lockup the rear wheels.

Supposedly ABS has been banned in F1 so I suspect they still have some brake modulation or downshifting rev-matching algorithm.
g-force_addict
 
Joined: 17 May 2011

Post Tue May 08, 2012 11:30 pm

Downshifting at the apex of a corner would be a rookie move, at best, for the reasons you state. Get the shifting done in a straight line on corner entry where you can use the brake bias to ensure spare stability on a poor downshift... then can focus on hitting the apex mark and getting into the throttle as you so please.

Given that the braking disc torque is generally immense compared to coasting engine braking, that's the dominant factor. I wouldn't be worried about spinning out just from being off throttle.
Grip is a four letter word.

2 is the new #1.
Jersey Tom
 
Joined: 29 May 2006
Location: Huntersville, NC

Post Wed May 09, 2012 12:31 am

Formula1.com, 27 Feb 2008 wrote:“The biggest difference you notice with the 2008 cars is not the loss of traction control, but the absence of engine braking control because the car is much more unstable, especially on used tyres,” says Nelson [Piquet Jr.]. “When you look at the telemetry, the brake pressure is now much less compared to last year. With EBS you could brake much harder; if you did that without the electronics, you will simply lock up your wheels.”

[Fernando] Alonso echoes Piquet’s sentiments and emphasises the need to adapt set-up accordingly. “Without EBS you do suffer with locking of the rear tyres because stopping a car travelling at 300 km/h is not easy,” he explains.

What was EBS?
bhall
 
Joined: 28 Feb 2006

Post Wed May 09, 2012 1:12 am

Electronic Brake Systems?

"stopping a car travelling at 300 km/h is not easy" What kind of race driver makes such a statement? Was he talking to his girlfriend?

Brian
hardingfv32
 
Joined: 3 Apr 2011

Post Wed May 09, 2012 1:24 am

I guess the kind that wins a couple of World Championships.

Perhaps I should have been more specific regarding EBS.

How was the banned engine braking system different from ordinary engine braking?
bhall
 
Joined: 28 Feb 2006

Post Wed May 09, 2012 3:41 am

im pretty sure ebs was used as an engine-controlled anti-lock. if the rears were about to lock, the engine would give a little gas to keep them rotating.
interesting how much the bias has changed. you never see a rear tire lock now, only fronts.
thisisatest
 
Joined: 16 Oct 2010

Post Wed May 09, 2012 10:57 am

g-force_addict wrote:
Jersey Tom wrote:
g-force_addict wrote:Engine braking causes rear wheel lockup when braking or trail braking at the limit, doesn't it?

Not necessarily, no.

Of course it does.


I can see why you are saying it, but from a physical/mechanical perspective the way you are saying it doesn't make sense.

Engine braking alone can't lock the wheels. As using the engine as a brake doesn't acutally doesn't stop the wheels from spinning, it causes them to slow down by using them to do work (pump air through the engine). If the engine did cause the wheels to stop spinning the car would stall (as it's directly connected 0 wheel rpm = 0 engine rpm).

Brakes are the things actually physically try to stop the wheels from spinning.

So to clarify:
Engine braking + 'real' brakes = total braking input.
When the total braking input exceeds traction, you get a lock up.

The root cause of the lock up is attributed to too much 'real' brakes rather than the engine braking component. Fine tutning between engine braking and physical braking increases feel.

A downshift to increase engine braking will make the wheels spin too fast and brake traction.

The reason why engine braking is not strictly necessary but extremely useful is that it reduces brake wear.
xxChrisxx
 
Joined: 18 Sep 2009

Post Wed May 09, 2012 11:04 am

xxChrisxx wrote:If the engine did cause the wheels to stop spinning the car would stall (as it's directly connected 0 wheel rpm = 0 engine rpm).


Not always. If you are in fourth gear and put it in second then release the clutch you would have 0 wheel speed but the engine would still be alive, a bit too much alive. And the gearbox would take an immense beating.

Now i know F1 cars are sequential and there´s no jumping of gears but just wanted to point out that you can have the rear wheels locked and still have the engine running.
"Il Phenomeno" - The one they fear the most!

"2% of the world's population own 50% of the world's wealth."
Nando
 
Joined: 10 Mar 2012

Post Wed May 09, 2012 11:15 am

Nando wrote:Not always. If you are in fourth gear and put it in second then release the clutch you would have 0 wheel speed but the engine would still be alive,


I was going to edit the post to say without the clutch bein pulled in, but thought that was obvious. If the clutch is disengaged the engine is no longer connected to the road wheels.

Nando wrote:Now i know F1 cars are sequential and there´s no jumping of gears but just wanted to point out that you can have the rear wheels locked and still have the engine running.


If you lock the driving wheels, and don't slip or disengage something along the transmission. You will stall. F1 have anti stall, which pulls in the clutch when the rears lock. In your car your brain tells you to push the clutch.


Rather than launching into a merry go round discussing clever systems to prevent it, getting the basic simple concept sorted first makes some sense. The concept of stalling at high speed or stalling when pulling away is no different.
xxChrisxx
 
Joined: 18 Sep 2009

Post Wed May 09, 2012 11:26 am

xxChrisxx wrote:If the clutch is disengaged the engine is no longer connected to the road wheels.

Obviously you engage the clutch again after putting the gearbox in second gear.



xxChrisxx wrote:If you lock the driving wheels, and don't slip or disengage something along the transmission. You will stall. F1 have anti stall, which pulls in the clutch when the rears lock. In your car your brain tells you to push the clutch.

Nope because the forward momentum of the car will eventually slow down enough for the rear wheels to start rolling again.
You can lock the rears and have the gearbox hitting the limiter without stalling the car.

Another view on this is the handbrake. You don´t stall the engine just by locking the rears for a second while performing a nice slide.
You just have to push the clutch in before you stop the car.


My brain only tells me to push the clutch in because of fear of destroying the gearbox, but it doesn´t change the fact that you can lock the rear wheels while moving and not stall the engine.
"Il Phenomeno" - The one they fear the most!

"2% of the world's population own 50% of the world's wealth."
Nando
 
Joined: 10 Mar 2012

Post Wed May 09, 2012 11:39 am

I can see why you are saying it, but from a physical/mechanical perspective the way you are saying it doesn't make sense.

Engine braking alone can't lock the wheels. As using the engine as a brake doesn't acutally doesn't stop the wheels from spinning, it causes them to slow down by using them to do work (pump air through the engine). If the engine did cause the wheels to stop spinning the car would stall (as it's directly connected 0 wheel rpm = 0 engine rpm).

Brakes are the things actually physically try to stop the wheels from spinning.

So to clarify:
Engine braking + 'real' brakes = total braking input.
When the total braking input exceeds traction, you get a lock up.

The root cause of the lock up is attributed to too much 'real' brakes rather than the engine braking component. Fine tutning between engine braking and physical braking increases feel.

A downshift to increase engine braking will make the wheels spin too fast and brake traction.
The reason why engine braking is not strictly necessary but extremely useful is that it reduces brake wear

I dont think so Chris. Surely you mean a downshift to increase engine braking will make the engine spin too fast therefore applying a higher retardation of rear wheel rotational speed speed, which if coupled with high rear disc brake retardation could break traction.
autogyro
 
Joined: 4 Oct 2009

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