Less engine, more gears

[cRiPpLe_rOoStEr]

Yesterday while I was walking in the neighborhood with my dog, I spotted one of the first eco-cars I fell in love for. The Fiat Palio Weekend 6 marchas was available only in '99 and 2000, with a 61hp/60lb.ft. 1.0L engine backed by a 6-speed (6 marchas) manual transmission, while the previous base versions had a 75hp/90lb.ft. 1.5L and a 5-speed manual instead.





Altough at some point a significantly lower displacement won't actually help, the gears always play an important role for both performance and efficiency.

[ksa8907]

Higher gear count transmissions are definitely gaining popularity, in the near future chrysler will be using solely 8 and 9 speed transmissions. Aerodynamics is also a hugely important aspect, the public doesn't want to drive slower so the only way to get those high mpg numbers is small turbo engines, lots of gears and very aerodynamic bodies.

[gone-ot]

...gears are becoming like Archimedes' geometric approximations of a circle, just use enough small-length, straight, segments to approximate a smooth circle made of straight pieces...ie, use enough 'staight' gears to approximate a 'smoothly curving' power-vs.-load curve: a geared CVT.

[jakobnev]

My car has six forward gears too: 1-2-3-4-5 and Neutral!

[nemo]

Originally Posted by jakobnev

My car has six forward gears too: 1-2-3-4-5 and Neutral!

And two reverse?

[Frank Lee]

What do you gain with all those gears? If your deal is max acceleration rate, that is what you gain. If your deal is fe, you lose from all that shifting- a most inefficient process what with all that throttle blipping and halting forward motion- and you lose from a transmission that has more moving parts and I would imagine more internal friction.

In the '80s the eco-stick trans options were 4-speed instead of 5.

With my 5-speeds I'm always skip shifting, like 1-3-5. I would like to only have the 1-3-5 gears and throw 2-4 away and save the internal trans losses.

[IamIan]

Like most things there are pros and cons.

• Pro: More gear ratio options allows a better ability to convert the real time road torque and RPM situation into a combination that is at more efficient point on a ICE's BSFC.
• Con: Manual transmissions has a loss of efficiency during the shifting period ... the more one has to shift the more shifting losses... more gears means more shifting over the same RPM and torque transition.
• Pro: Manual transmissions can be more energy efficient from input to output.
• Con: Finite Manual Transmissions have fewer gear options than other 'CVT' and the like ... ie they are less able to have the 'best' ICE gear ratio for all road torque and RPM conditions.

I have a interesting paper about the efficiencies of various transmissions.
Sadly it is not free... Link

But ... here are some teasers / interesting bits from the testing in it.

PumpCVT

Manual

Toroidal

BeltCVT

BallPump

FixedDisplacementPump

Automatic

[jamesqf]

Originally Posted by Frank Lee

What do you gain with all those gears? If your deal is max acceleration rate, that is what you gain. If your deal is fe, you lose from all that shifting- a most inefficient process what with all that throttle blipping and halting forward motion- and you lose from a transmission that has more moving parts and I would imagine more internal friction.

I dunno. My bikes seem to do pretty well with 21/24 speeds - though I could always use a few more :-)

[Frank Lee]

Right- and you go from 1st through each gear to 24th from a stop.

There was some guy on here that thought everything should have 18 or so speeds; maybe he likes to spend all his time shifting- I consider it a necessary evil.

[nemo]

If the vehicle is driven on relatively flat terrain, a manual transmission with four speeds is sufficient three was the norm for years. The problem is in most manual transmission the top gear does not get the rpms down low enough for best fuel economy. This seems to be the case whether equipped with a three, four or five speed. No personal experience with a six speed in a car. It’s as if the transmission is designed so under most driving condition you will not need to drop it down a gear. In the mountains it is nice to have multiple gear choices. In this case a 5 speed is better, especially if you have a low hp low torque car. Wouldn't it be nice if you had choices like the first four to be close ratio and fifth out in left field for economy.As gargantuan motors and the heard followers only want to sell the 20% of the vehicles that appeal to 80 % of the market. you are lucky to get what you want, to find it with a manual transmission a gem.

As for high gear count automatics just sounds more expensive to build and repair.