Seamless Gearboxes (aka blowing in the shifts)

[autogyro]

It seems that certain F1 teams are increasing the gearshift 'GAP' to allow use of the engine being 'disengaged from the gearbox' during the shifts, to blow a higher volume of exhaust gas over the diffuser during deceleration and corner entry.

The 'GAP' in the gearshift allows this to be done because there is zero or minus torque being transffered during the shifts.

So mush for all the 'seamless' gearbox BS.

[Richard]

Any evidence?

[Steven]

There indeed seems to be something strange going on at Mercedes AMG. Check the pole lap of Nico Rosberg and the strange noise the car makes when Rosberg shift down into a corner. He also seems to start downshifting later than what is otherwise optimal, and it appears that Hamilton is doing the same.

[youtube]http://www.youtube.com/watch?v=CAwt35ER_tg[/youtube]

Perhaps unrelated to this case, but I have checked some Ferrari onboard footage, and although it's less unusual, both Ferrari drivers shift down at around 14000rpm. They usually keep revs higher in high speed corners though.

Both Red Bull drivers on the other hand usually shift down around 16000rpm (having seen onboard quali footage from 3 of the 4 races so far in 2013).

[autogyro]

Gearing for maximum exhaust blowing at gearshift points on deceleration and corner entry will leave the gearing lower, resulting in a lower maximum top speed.
This will negate full use of DRS.
It will also result in the engine rpm during acceleration being slightly higher through the gears than the other cars.
Early in the race with a high fuel load a longer time will be spent with the engine rpm further above maximum torque than the others.
The car will as a result, accelerate at a lower rate than the other cars with early race high fuel loads.
However it will hit a higher performance window somewhere around mid race.

It is of course a balancing act.
If the coander exhaust worked better and the aero design was as good as the RB, the gearing could be changed.
Throw hydo/pneumatic suspension in to the mix that IMO collapsed on Hamiltons car on the left rear during Quali and you have a lot of problems to solve.

[bhall]

Gearing for maximum exhaust blowing at gearshift points on deceleration and corner entry will leave the gearing lower, resulting in a lower maximum top speed.
This will negate full use of DRS.
It will also result in the engine rpm during acceleration being slightly higher through the gears than the other cars.
Early in the race with a high fuel load a longer time will be spent with the engine rpm further above maximum torque than the others.
The car will as a result, accelerate at a lower rate than the other cars with early race high fuel loads.
However it will hit a higher performance window somewhere around mid race.

[...]

“I wanted to get a good start, I got a terrible start. And then I was just so slow.”

“I was nowhere, had no speed at all. Nothing I could do, no matter what I did to the car it wouldn’t get faster and the gap was just growing in front.

“And all of a sudden something happened, after the second pit stop I think it was, all of a sudden the car started reacting differently and I was able to push, I had grip again.”

[langwadt]

Gearing for maximum exhaust blowing at gearshift points on deceleration and corner entry will leave the gearing lower, resulting in a lower maximum top speed.
This will negate full use of DRS.
It will also result in the engine rpm during acceleration being slightly higher through the gears than the other cars.
Early in the race with a high fuel load a longer time will be spent with the engine rpm further above maximum torque than the others.
The car will as a result, accelerate at a lower rate than the other cars with early race high fuel loads.
However it will hit a higher performance window somewhere around mid race.

It is of course a balancing act.
If the coander exhaust worked better and the aero design was as good as the RB, the gearing could be changed.
Throw hydo/pneumatic suspension in to the mix that IMO collapsed on Hamiltons car on the left rear during Quali and you have a lot of problems to solve.

last year RB ran out of rpms with DRS all the time

[riff_raff]

It seems that certain F1 teams are increasing the gearshift 'GAP' to allow use of the engine being 'disengaged from the gearbox' during the shifts, to blow a higher volume of exhaust gas over the diffuser during deceleration and corner entry.

With regards to the impact of exhaust gas flows improving diffuser performance, I believe it's the energy content of the exhaust gas flow that matters. Thus an unloaded engine exhaust flow would have little energy to contribute to the diffuser airflow. However, there would be some benefit to maintaining high engine revs at the corner exit such that the engine would be operating close to its optimum rpm point when the driver gets back on the throttle.

[aussiegman]

With regards to the impact of exhaust gas flows improving diffuser performance, I believe it's the energy content of the exhaust gas flow that matters.

Can you define what do you mean by "energy content"??

Thus an unloaded engine exhaust flow would have little energy to contribute to the diffuser airflow.

Not sure I agree with this. Less but not "little"

However, there would be some benefit to maintaining high engine revs at the corner exit such that the engine would be operating close to its optimum rpm point when the driver gets back on the throttle.

[bhall]

You can hear it at work in this video.

As promised, here is my footage of Filepe's Ferrari during Friday practice.
https://www.dropbox.com/s/m2hsfd892hqu2 ... .50.00.mp4

[...]

[autogyro]

So much for 'seamless' gearboxes.

Here is an extract from a letter I received from Adrian Newey when he was technical director at McLaren in1999.

"The current layout may be crude but it is light, small and has a good efficiency with only a very short torque interruption during gear changes".

Signed Adrian Newey.

I was offering Adrian a planetary gear set for F1 use at that time.

Now we can see the layshaft stepped ratio gearbox gives gaps during the shifts which allow the engine to be throttled up to blow exhaust gas over the rear diffuser.

So retaining an unchanged design creates a loophole with opportunities for aerodynamics.

Proper technical development in powertrains would have eliminated that loophole.

[Tommy Cookers]

Gearing for maximum exhaust blowing at gearshift points on deceleration and corner entry will leave the gearing lower, resulting in a lower maximum top speed.
This will negate full use of DRS.
It will also result in the engine rpm during acceleration being slightly higher through the gears than the other cars.
Early in the race with a high fuel load a longer time will be spent with the engine rpm further above maximum torque than the others.
The car will as a result, accelerate at a lower rate than the other cars with early race high fuel loads.
However it will hit a higher performance window somewhere around mid race.

don't we know that there is only 18 ratios (combinations of gearbox gear pair ratios and final drive pair ratios) for the season ?
at any event a car must have chosen 7 of these and use them throughout practice, qualification, and the race
despite changes in weight and grip, nominally seamless gearboxes mean that only the top gear ratio is crucially important
presumably the undergearing concept is related to that

the desired top gear ratio is unpredictable in the gamble that is slipstreaming/DRS vs. hard rev limit
but whenever driver has fuel to spare for richening he can alleviate the top speed penalty of undergearing
because richening speeds combustion and increases power by raising the efficient rpm
(no car would be so undergeared as to top out at the hard rev limit in economy mixture)

best (top) gearing for car A leading by 2 sec is lower than that best for car B making a DRS/slipstreaming pass
but car B is overgeared for closing to DRS distance on car A
so, what's undergearing anyway ?

(a given amount of) 'undergearing' must surely be better at high weights than low ?
(lower weight means the car is potentially faster than high weight, so the undergearing will impede it more)

different gearing does not force different revs (except in top), typically it will only move shift points on the track
but it's pot luck whether undergearing gains or loses this way

[autogyro]

I disagree that it is 'pot luck' how gearing affects performance. (if that is what you are saying)

It is possible to work out gearing to a very high accuracy.

Unfortunately, exhaust diffuser blowing adds another variable that has to be added to the math.
Depending on how well the aero works generaly and specificaly how much exhaust blow is deemed necessary for the desired cornering downforce, sets the importance that the gearing plays in that part of the sum.

Listening to the cars it could be concluded that the Ferrari's use most exhaust blow the Mercedese is next and the RB uses less.
This would point to the RB having a better overall aero package with better unblown downforce and less need to augment this with diffuser blowing.
The Ferrari almost certainly has some other performance benefit that overcomes the use of so much diffuser blowing.
The Merc sits in the middle with potential both ways but with problems to solve.
It will be interesting to see how McLaren deal with being 'not there' in all areas, I hope Button can supply enough input now that Hamilton is no longer there.

Lower gearing can help with a high fuel load car but like everything else there is a point where reducing the gearing by to much gives a negative result.

[machin]

I disagree that it is 'pot luck' how gearing affects performance. (if that is what you are saying)

I think Tommy actually meant; "changing the gearbox ratios in this way improves acceleration at some road speeds but decreases it at others; you are robbing Peter to pay Paul".

imagine that with the 'standard' ratios you need to perform an upshift at 100mph, and now you fit a bigger ratio diff .... at 90mph the acceleration would be improved (by virtue of increased torque multiplication from the bigger diff ratio), but you'll now need to upshift at say 95mph, so the acceleration over the 95 to 100mph range will now be worse as you need to be in a higher gear at those speeds... the net effect is basically no change in acceleration when you consider a wide enough road speed range.

This is better understood if you work in the "power" realm rather than the "torque" realm: changing the diff ratio doesn't change the speed range over which the engine is operating, it just changes the road speed for a given RPM. Since the engine rpm range doesn't change then the average engine power output between upshifts also remains the same, and therefore acceleration also remains the same (over a wide enough road speed to negate the effect of the changing upshift points).

A better solution would be to keep first gear the same, but close up all the remaining gears (yes, you will lose a bit off topspeed). This reduces the RPM range over which the engine is operating: and therefore you can restrict engine usage to the part of the rev range which has the highest power... the result is that the average engine power output is now increased between upshifts in all gears except 1st (where is is unchanged), and therefore the acceleration through those gears will also increase (regardless of whether the car is heavy or light).

"Race" versions of standard road car gearboxes do something similar, but they INCREASE the length of first gear and close up the remaining gears. In this way you get the better acceleration through all gears except 1st by virtue of the smaller RPM band (over which the average engine power output is higher), without the loss of top speed (top gear remains the same ratio as the standard box). The lengthened first gear has no detrimental effect on performance since most tuned cars can generate enough motive force at the tyre contact patches to spin their wheels in 1st gear anyway (a shorter first gear would just mean the driver would need to apply less throttle to avoid wheelspin, and not gain any performance since changing gear ratios has no effect on the car's tyre's traction limit).

[autogyro]

I agree with what you say Machin but there is much more to consider.

First gear has to accelerate the car from stationary which takes lots of power to establish inertia.
Wheel spin increases and becomes progressively more uncontrollable the higher the first gear ratio.
A good start is much easier with a lower first gear, I am sure you know this Machin you yourself are pretty good at starts.

There are considerations to ratio choice to be made for corner entry speed and exit speed.
The length of straits and use of DRS.
The wind direction and wind speed.
Height above sea level and pressure AMSL.
Track construction and temperature.

There are many other considerations and the effect of each varies at each race.

The other major trade off, is aero drag.
With every increase in downforce there comes an increase in drag.
This drag is much larger at high speeds.
Unless the car can negate exhaust blown downforce (perhaps by breaking the 'coander' effect at high airflow speeds' the drag from this alone will slow the car by a large amount on high speed straits.
If the car does not have a good 'general downforce to drag co-efficient the gearing will be altered to compensate.
This negates many of the other gearing requirements.

Also consider the increased time taken undertaking gearshifts to achieve sufficient exhaust blowing.
This now uses several tens of meters of track distance and adds another dimension to gear ratio choice.

The situation is getting close to a point of aero development where it might be useful to do some calculations for the current high downforce cars against the concept of a much lower downforce car with better powertrain and mechanical handling innovations.
Unfortunately for 2014 the FIA is allowing 8 speed gearboxes and I think I can see why now.

[timbo]

I don't think the gear ratios play any role.
What matters is timing of the shift.
It was pointed out that the rpm has to be below 15k to exploit the engine mapping.
So as the car decelerates the shifting strategy would be to brake at the top gear until the rpms drop below 15k (say to 14k), now the driver should shift, normally gearchange would happen in an instant and rpms would raise up to say 16k, but instead the timing is that the gearbox is in neutral, and only engages next gear when the speed drops enough that the matching rpm is below 15k.