Overdriven transmission

[riff_raff]

Inertia of the rotating gearbox components is not a big concern with F1 cars. However, mechanical efficiency of the drivetrain is of concern. As I noted, since 100% of the engine output power must pass thru the drivetrain, even a tiny improvement in efficiency produces large benefits. The typical MT has two gear meshes the power transmits thru. The shift spur gear mesh and the spiral/hypoid gear mesh final drive. The shift spur gear mesh has 99% or better efficiency, and the final drive gear mesh has 98.5% or better efficiency. If you add in all of the other losses from bearings, seals and unloaded shift gears, the input-to-output efficiency of an F1 gearbox is probably better than 98%.

The biggest problem with running the shift gears at higher speeds is the significantly increased viscous/sliding/windage losses. You must remember that in a 2 shaft 7-speed constant mesh MT, at any given time there are over 14 gears, 3 shafts and 6+ bearings spinning, but only 4 gears transmitting power.

[andylaurence]

The shift spur gear mesh has 99% or better efficiency, and the final drive gear mesh has 98.5% or better efficiency. If you add in all of the other losses from bearings, seals and unloaded shift gears, the input-to-output efficiency of an F1 gearbox is probably better than 98%.

But the efficiency through those two gears alone is 97.515%, so there's no chance of >98% efficiency.

[autogyro]

Inertia of the rotating gearbox components is not a big concern with F1 cars. However, mechanical efficiency of the drivetrain is of concern. As I noted, since 100% of the engine output power must pass thru the drivetrain, even a tiny improvement in efficiency produces large benefits. The typical MT has two gear meshes the power transmits thru. The shift spur gear mesh and the spiral/hypoid gear mesh final drive. The shift spur gear mesh has 99% or better efficiency, and the final drive gear mesh has 98.5% or better efficiency. If you add in all of the other losses from bearings, seals and unloaded shift gears, the input-to-output efficiency of an F1 gearbox is probably better than 98%.

The biggest problem with running the shift gears at higher speeds is the significantly increased viscous/sliding/windage losses. You must remember that in a 2 shaft 7-speed constant mesh MT, at any given time there are over 14 gears, 3 shafts and 6+ bearings spinning, but only 4 gears transmitting power.

http://www.f1technical.net/forum/viewto ... &start=360

In direct top gear this stepped ratio gearbox has NO windage at all and only one support bearing.
Prevented from being used and developed further by regulations and 19th century thinking.

[gruntguru]

The shift spur gear mesh has 99% or better efficiency, and the final drive gear mesh has 98.5% or better efficiency. If you add in all of the other losses from bearings, seals and unloaded shift gears, the input-to-output efficiency of an F1 gearbox is probably better than 98%.

But the efficiency through those two gears alone is 97.515%, or better so there's some chance of >98% efficiency.

Did some fixing for you.

[Tommy Cookers]

the F1 transmission has at least 3 gear meshing stages

because after the gearset there is 2 stage CWP emulation ( a 90 deg spiral bevel gear pair backing a final straght spur gear pair)
and then the power goes through tripod CV joint pairs
(these are continuously working as for aero benefits the driveshafts are out of 'horizontal' alignment at normal ride height)

so the efficiency is maybe 96% ?

last year the usual bunch of technical semi-illiterates awarded the Dewar Trophy to the F1 Mercedes
in 1958 a similar bunch awarded it to the WCC winning F1 Vanwall
in top gear this used only 1 stage of gearing

btw the geared turbofans would have less windage due to the low ambient pressure in use (factored-in to the efficiency stated ??)

[autogyro]

Efficiencies of 96/98 percent in F1 gearboxes/transmissions/ drive trains has always been sufficient until today.
In the past it was always possible to burn a bit more fuel.
With the economy formula we now have it begins to show up the lay shaft stepped gearbox as the inefficient component it has always been.

[Tommy Cookers]

as the car layout benefits from having the crankshaft eg lower than the axles there is no penalty from the layshaft transmission
ie necessary positional step-up (drop gear) and the ratio step-down (CWP) are inherent to the layshaft transmission ie free of penalty
and the arrangement of output shaft above input shaft layout is narrow - this also helps aero

a planetary gear would need additional drop gearing
and would anyway tend towards less efficiency at the rather low overall ratio in F1 ?? and also be wider and so disadvantage aero

this layout effect also makes it hard for alternatives to compete eg in road cars
eg the automatic now has to bear the cost and efficiency penalty of added drop gearing (unless the standard transmission is coaxial)

[riff_raff]

The shift spur gear mesh has 99% or better efficiency, and the final drive gear mesh has 98.5% or better efficiency. If you add in all of the other losses from bearings, seals and unloaded shift gears, the input-to-output efficiency of an F1 gearbox is probably better than 98%.

But the efficiency through those two gears alone is 97.515%, or better so there's some chance of >98% efficiency.

Did some fixing for you.

gg- thanks for the assist. I qualified my estimates of gear mesh efficiency with the words "...or better..." since the efficiency of any gear mesh can vary with changes in speed. The losses in the gearbox will be lower when operating in 1st or 2nd gear than in higher gears, since the rotating speed of many components is lower. In 1st or 2nd gear, the mesh efficiencies might be 99.5% and 99% which would exceed 98% combined.

Some losses in a gearbox are speed dependent while others are load dependent. Windage, viscous and sliding losses in gears and rolling element bearings are mostly speed dependent, and they increase exponentially with PLV. While friction/rolling contact losses are more load dependent. Thus the worst case from an efficiency standpoint is a situation where the speed/PLV of gearbox components is high and loads are low. The gearbox power losses as a percentage of input power at this operating condition can be quite high. The best gearbox efficiency will likely be at some operating condition of high load combined with low speed of the rotating parts.

[autogyro]

as the car layout benefits from having the crankshaft eg lower than the axles there is no penalty from the layshaft transmission
ie necessary positional step-up (drop gear) and the ratio step-down (CWP) are inherent to the layshaft transmission ie free of penalty
and the arrangement of output shaft above input shaft layout is narrow - this also helps aero

a planetary gear would need additional drop gearing
and would anyway tend towards less efficiency at the rather low overall ratio in F1 ?? and also be wider and so disadvantage aero

this layout effect also makes it hard for alternatives to compete eg in road cars
eg the automatic now has to bear the cost and efficiency penalty of added drop gearing (unless the standard transmission is coaxial)

Look again TC.
The gear train fits into an 84mm box so there is no need for input step up.
There is no mechanical clutch and the unit fits into a slightly larger volume than the original clutch.
True the casing diameter also contains electronics and is bigger in diameter but no larger than the engine and only at the site of the original clutch, aero would be much better.
How can the design be less efficient than a lay shaft gearbox when there are NO gears moving in engagement at all in direct top gear, so no torque loss or windage and only the planet gears for each other ratio engaged in its own particular gear?

[Tim.Wright]

For what its worth, I've seen that a lot of manufacturers have overdriven upper gears. I don't know why though:
Audi R8 // Nissan GT-R // Porsche Turbo S
Porsche 918 Spyder
Jaguar F-Type // Lotus Elise S CR // Mercedes SLK 350 // Porsche Boxster

[autodoctor911]

I didn't realize how important efficiency was for F1. an extra gearset would be a serious loss then.

I assume they have gone away from transverse shaft gearboxes for this same reason(extra gear mesh to change sideways before gearbox).

In an all indirect gearbox, if you had all higher gear ratios, maybe some still underdrive, some overdrive and a shorter final drive, you could have reduced torque at the final drive at least, while maintaining engine speed for the dog clutches, but I think the reduced torque requirement may not reduce the actual mass of the Pinion and crownwheel if it has to be larger just to handle the ratio with decent tooth size and count on the pinion.

Basically, it would be the normal layout. the input shaft and the output at the axles would all remain at the same speed as before, but the secondary shaft/pinion shaft would spin much faster.

Well, I just looked at some recent F1 gearboxes, and although the layout is what I thought from the input through to the pinion, the crown wheel is smaller, and another spur gear reduction is used at the final drive to the differential. I couldn't find actual ratios, but the combination of the smaller crownwheel and the final spur gear seem to have more reduction than older pinion and crownwheel designs, so maybe the upper gears are overdrive?

Is this still the current setup?

Also, is there a rule that prevents using the KERS motor to create an ECVT with the engine in a planetary setup. This would be a change in gear ratio without driver control, correct?

[Tommy Cookers]

'recent F1 gearboxes' will presumably be the later N/A boxes
as these engines had an unprecedentedly short stroke the 'drop' height difference between crankshaft and axle was rather large
the (very high rpm and very low overall ratio) 2 stages from output to axle also contributes to getting the required drop

current boxes must have a greater distance between the input and output shaft centres to allow higher torque capacity
though the stroke is a bit longer, so the crankshaft will be about 4 mm higher
and haven't wheel diameters been increased ?

for now - I still can't see how autogyro's box deals with the drop

[autodoctor911]

If the tire diameter has increased, it should negate at least some of that increase in crankshaft height as far as the gearbox design goes, right?

Autogyro, is your design using the Kers motor to regulate the rpm difference between crankshaft and wheels?

If so, I would think it is not legal for F1, as it would allow computer control of gear ratio(automatic gear change).

[autodoctor911]

I read the 2015 regs and 9.6.5 specifically prohibits a continuously variable transmission system from transmissitting power from the PU.

The energy flow diagram also specifies the flow path for the MGU-K to 3 paths: the engine, engine ancillaries and other ancillaries.

[autogyro]

If the tire diameter has increased, it should negate at least some of that increase in crankshaft height as far as the gearbox design goes, right?

Autogyro, is your design using the Kers motor to regulate the rpm difference between crankshaft and wheels?

If so, I would think it is not legal for F1, as it would allow computer control of gear ratio(automatic gear change).

To be honest I have not looked at the gearbox regs lately.

My ESERU changes gear electronically, however it is a stepped ratio gear set.
The actual shifts are CV with torque transfer during the whole of the shift.
The method of operation as with any stepped ratio gearbox can be auto, semi auto, or manual up or down.
The gear set is the KERS, the annuli of each planetary set is one step of a multi segment electric generator/motor.
The first planetary set sun gear is directly driven by the crankshaft, there is no mechanical clutch.
The clutch operates by applying electrical energy to the forward electric motor coil which slows the forward planetary annulus from free wheel neutral to stationary where it is locked to the casing by an electric locker, establishing first gear and vehicle motion through CV operation.
The other planetary sets remain locked as units until required with no movement in gear mesh.

As explained there is no step up or down at input it is direct drive.
The step up is to the diff at the rear.

The reason for overdriven gears at least in road cars, is simply a ratio required issue balanced against engine rpm max requirement in top gear, road wheel size etc.
Just math.
Usually with over five gears it is difficult to choose ratios to suit without opening up the ratio spread.
As most modern lay shaft gearboxes are indirect output anyway, overdrive is the simple answer without increasing the already high torque and windage losses.
19th century technology thats why.