Manual Downshifting when driving hard - Page 5 - Alfa Romeo 4C Forums
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post #41 of 48 (permalink) Old 05-14-2017, 07:35 AM
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One time, because I had a sudden flat tire in the left-most lane of a four-lane highway, I had to drive about a mile on it to navigate my way safely to the only shoulder on the far right. It was that or risk being plowed into from trucks/lorries plowing along at high speeds.

So, it's okay to drive on a flat tire -- am I right? And since it was on the right side of the car, it provided natural pull to the right.


As a rule, downshifting is not for engine braking.

As a rule, don't drive on flat tires.

Etc.

Our robot overlords will conquer the earth once they start to master the lee-way of hard-and-fast rules vs. decision-making ability.

When decision-making ability overrides the rule that mandates action 95% of the time, the robots will have to 'know' the rule was not disproven as their prime directive.

To the humans here: As a rule, we don't downshift for engine braking.

Carry on.
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post #42 of 48 (permalink) Old 04-13-2019, 10:47 PM
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Bottas adjusted his engine brake 3 times in his pole lap. In the lower right corner (above "UP") it is noted (already a couple of seconds before it happens). The setting alters how much fuel is injected during overrun. This means they could eliminate engine braking if it would be advantageouse. But obviously it's an advantage to have an engine brake. Together with the brake balance changes he can alter the turn in behavior of the car.


Link to the video: https://streamable.com/3wi79



In the 4c e-learing manual, chapter braking system it says the following:


MSR: engine brake control by means of Powertrain Control Module management.
MSR: this is an engine brake control function during over-run. On particularly slippery surfaces, when
the accelerator is released the engine braking could cause the drive wheels to lock with serious
consequences for the control and stability of the vehicle. Under these circumstances the system increases
the engine torque to reduce engine braking and prevent the wheels from locking.



Basically the same systems like in F1 - we just miss a knob to adjust it manually in the 4c


Another sub system of the braking system:



CBC: when breaking with ABS active on bends, this function improves the distribution of the braking
pressure at the four wheels (to fully exploit the grip available on the ground). This improves stopping
distances and above all vehicle stability when cornering.



Both systems are part of ABS - so everybody should be save to exploit this extra brake power


The other mentions of the engine brake in the manual:


Automatic engagement of the clutch downhill with accelerator pedal released
If the vehicle picks up speed when travelling downhill with gear engaged and accelerator released, the
clutch is automatically closed when a pre-set speed is reached to supply engine brake function.



Automatic gear shift (auto mode)
The Alfa TCT is equipped with an automatic operating mode, very similar to that of a conventional
automatic transmission. The gear to be engaged is selected using a (double) map which correlates
the power required by the driver and the car speed. A double map is needed because two
AUTOMATIC control modes named Normal & Dynamic can be selected by pressing a button in the
dashboard. If the accelerator pedal is released in Dynamic mode, the system does not shift up to
maintain engine brake function. In Normal mode, instead, the gear is shifted up (if allowed) when the
accelerator is released to benefit in terms of consumption.





The engine brake force is dependent on gear and rpm. If you want the most of it downshift early.
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post #43 of 48 (permalink) Old 04-14-2019, 02:20 AM
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For some reason I find it much easier and natural to get the downshifting perfect in manual cars, in the 4C and my last car GQV I always bottle it and let the car do it's thing. Maybe over time I'll get the instinct for it. Maybe just through having driven manuals all my life it became a habit to have one hand on the gearstick ready to de clutch half way through a corner, it is almost like you feel it through the gearstick when the perfect revs are there.

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post #44 of 48 (permalink) Old 04-14-2019, 08:04 AM
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Engine braking in F1 is an engineering discussion that transcends this thread to say the least.

If you know anything more than squat about an F1 power unit (ICE, MGU-H, MGU-K) then I could save considerable breath. What happens when one lifts throttle and uses 'engine braking' is vastly different in F1. A whole array of programs come into play that address two forms of energy harvesting, and engine braking is working with kinetic braking and adjustable diffs. There is an entire strategy built on using engine braking or not to save fuel via lift/coast and/or harvest energy now (via engine braking) to deploy later (outright HP or faster turbo spool up or higher boost).

Edit: SIGH... valid insight into technical specs of how the 4C operates are nice, but please leave F1 out of it.
.
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Last edited by Philster; 04-14-2019 at 08:20 AM.
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post #45 of 48 (permalink) Old 04-14-2019, 08:31 AM
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Quote:
Originally Posted by goldmax View Post
For some reason I find it much easier and natural to get the downshifting perfect in manual cars, in the 4C and my last car GQV I always bottle it and let the car do it's thing. Maybe over time I'll get the instinct for it. Maybe just through having driven manuals all my life it became a habit to have one hand on the gearstick ready to de clutch half way through a corner, it is almost like you feel it through the gearstick when the perfect revs are there.
Goldmax,

Once you and your 4C are in-tune, you will be able to brake at maximum rate and pull the down-shift paddle at the right moment.... if the computer agrees, your request will be granted, if not, the beep will tell you that you still have much to learn about your 4C.

The 4C makes amazingly quick down shifts when you have smashed the brake pedal and pull the downshift paddle in quick succession at exactly the right time.... so much faster than the purists in ther manual sports car can ever dream of.

Cheers,

Alf.
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post #46 of 48 (permalink) Old 04-14-2019, 08:33 AM
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Quote:
Originally Posted by Philster View Post
Engine braking in F1 is an engineering discussion that transcends this thread to say the least.

If you know anything more than squat about an F1 power unit (ICE, MGU-H, MGU-K) then I could save considerable breath. What happens when one lifts throttle and uses 'engine braking' is vastly different in F1. A whole array of programs come into play that address two forms of energy harvesting, and engine braking is working with kinetic braking and adjustable diffs. There is an entire strategy built on using engine braking or not to save fuel via lift/coast and/or harvest energy now (via engine braking) to deploy later (outright HP or faster turbo spool up or higher boost).

Edit: SIGH... valid insight into technical specs of how the 4C operates are nice, but please leave F1 out of it.
.
Love your insight into the F1 world Philster

Cheers,

Alf.
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post #47 of 48 (permalink) Old 04-14-2019, 11:10 AM
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Quote:
Originally Posted by Philster View Post
Engine braking in F1 is an engineering discussion that transcends this thread to say the least.

If you know anything more than squat about an F1 power unit (ICE, MGU-H, MGU-K) then I could save considerable breath. What happens when one lifts throttle and uses 'engine braking' is vastly different in F1. A whole array of programs come into play that address two forms of energy harvesting, and engine braking is working with kinetic braking and adjustable diffs. There is an entire strategy built on using engine braking or not to save fuel via lift/coast and/or harvest energy now (via engine braking) to deploy later (outright HP or faster turbo spool up or higher boost).

Edit: SIGH... valid insight into technical specs of how the 4C operates are nice, but please leave F1 out of it.
.

The relevant part is that they have a setting called engine brake. Out of the drivers perspective it doesn't really matter which part of the car delivers the engine brake force. The driver feels a brake force from the drivetrain at the wheels but he can't tell you if it's the IC or the mgu-k and it doesn't matter for the driver. The only thing the F1 driver (like every other driver) cares about is that the drivetrain brake force suits the situation. The 4c driver is in the comfortable situation that the car electronic does the EB management on it's own.




I didn't mention PU harvesting because it's just irrelevant for the comparsion with the 4c. Sure there are more components involved in a F1 car than in the 4c in therms of PU/engine braking. There is also no need to look inside this black box - everything what's matter for this thread topic is what's happening at the wheels. For me it was a nice bridge to an actual race car, both have smiliar characteristic - even when the technical execution differs.
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post #48 of 48 (permalink) Old 04-14-2019, 03:09 PM
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It's relevant, because removing all hybrid systems creates a platform where shifts are fired off in seconds late and straight before rotation, and where virtually all legacy braking happens, I think the fairest thing you can do with analogies is get F1 out if it (engine braking because we have to) and turn to sports car racing GT classes, such as the pro and pro am cars, found in IMSA and WEC. GTD, GTLM and GT3 specs assorted series.

Cherry picking a series, such as F1, is just disingenuous. Broad use of engine braking because of tech and regulations hardly helps build a case for how often and how effective and how reasonable it is in very unrelated cars.

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Last edited by Philster; 04-14-2019 at 03:13 PM.
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