Unusual ways to change gear, revisited

"Cé hé sin" (michael-m-mouse)
07/09/2020 at 18:50 • Filed to: Renault e-tech

!!!error: Indecipherable SUB-paragraph formatting!!! we looked at Renault’s new, weird and seemingly wonderful hybrid transmission which uses a dog clutch gearbox to mix and match the power provided by an electric motor and an engine. In short the box uses four gears for the engine (corresponding roughly to the upper four in a six speed) and two for the motor, all without synchomesh, and is able to use one of each at the same time as required . Here’s a picture, en francais because R enault. Boite multimodes sans embrayage means “mult i mode (gear) box without clutch”.

This diagram makes thing somewhat clearer. Only somewhat though. There aren’t actually six distinct gears because two (R1 and R3) are shared by both motor and engine. C1-C5 are the dog clutches. Roues AVG and AVD are front left and right wheels respectively. EV2 is the starter/generator.

Progress through all six speeds goes like this:

First electric gear: C1 is closed, motor EV1 drives R1 and the wheels

Second electric gear: C1 open, C2 closed, EV drives R3

First ICE gear: ICE starts, C1 and C3 closed, power taken from R1

Second ICE gear: C4 closed, power from R2

Third ICE gear: C2 and C3 closed, power from R3

Fourth ICE gear: C5 closed, power from R4

The ICE and EV gear ranges overlap

So, how does it work out in real life? The first lengthy road tests have now been published and the general opinion is “quite well, with a few issues”. Quite how significant the issues are is not that obvious because these are French tests of a French car fitted with a French hybrid transmission and the French are not known for being impartial about their own. We need to read between the lines a little.

What seemed to me the trickiest part- changing gear smoothly with a clutchless dog box - is handled well. Two electric motors are used to do the job normally done by clutch and syncho cones. One is a starter/generator attached directly to the engine which is used to match revs by speeding up or slowing it down so it’s turning at the speed needed by the next gear, the other is the traction motor which applies just enough power to fill in the gap created when the engine is throttled back during gearchanges. It all works seamlessly and gearchanges are pretty much imperceptible.

What would seem easier - changing between the two electric gears - isn’t quite so good as without anything to maintain power during the change ( I suppose you could use the engine but they don’t) there’s a noticeable delay and it feels rather like a single clutch automated manual.

Transitioning between EV and ICE mode is sometimes accompanied by a slight jerk and noises from the gears. Quite an amount of transitioning happens because the system is set up to use the battery as much as possible which extends to unexpectedly high speeds - after a few km at autoroute speeds the engine cuts out for maybe 800m and the motor takes over until the battery depletes and it hands traction duties back.

What you get overall, and what the designers were looking for, is a hybrid that is noticeably more economical at town speeds than the only immediate rival at the moment, the Toyota Yaris, and considerably so at higher speeds, something that aren’t a strong point with the Yaris.

What you definitely don’t get, despite the combined power of the engine and two motors being higher than conventional versions of the same car, is something that is in the least entertaining to drive. You can’t choose any of those six gears yourself, acceleration is less than nominally less powerful cars due I think to starting off using the electric motor only and the gearbox reacts to a floored accelerator with considerable pause for thought before a gear lower than the one you’re in is reluctantly summoned.

S o there we have it. A way to make your car burn less fuel without buying a diesel. Even though a diesel would be cheaper and feel quicker .

DISCUSSION (12)

sony1492 > Cé hé sin
07/09/2020 at 19:02

Good driving dynamics are rrrrreeeally taking a back seat to emissions.

Cé hé sin > sony1492
07/09/2020 at 19:09

Yup.

Who is the Leader - 404 / Blog No Longer Available > Cé hé sin
07/09/2020 at 19:46

So why not buy a diesel with a more fun and engaging transmission for cheaper with less complexity and more efficiency? The French.

Jb boin > Cé hé sin
07/09/2020 at 19:59

I t seems to actually be the best solution for the emissions while not being as terrible as a Toyota hybrid i n term of driving pleasure.

From what i read, it has similar performance metrics to the 130hp petrol with a DCT (which are not stellar ) while having a similar mileage as the 85hp diesel .

Leaving the ability to the driver to choose gears in such a car would probably be quite hard to do as the ECU itself seems to sometimes have a hard time knowing which gear on which gearbox change :)

At least , the test cars are in a nice color :

Kinja'd!!!

Demon-Xanth knows how to operate a street. > sony1492
07/09/2020 at 21:51

Welcome to 1972!

Cé hé sin > Who is the Leader - 404 / Blog No Longer Available
07/10/2020 at 17:51

NOx and the demonisation of diesels. Also, ever-stricter emissions requirements are making diesels expensive to buy and maintain (DPFs etc).

Who is the Leader - 404 / Blog No Longer Available > Cé hé sin
07/10/2020 at 17:59

So if you are going to buy an ICE powered car, which has the government’s taxation affected less?

Cé hé sin > Jb boin
07/10/2020 at 18:29

Renault do seem to like that version of blue for their test fleet!

According to this test one issue is a jerk if you lift the accelerator at just over 40 which I’m guessing is the main electric motor being engaged. Also, a Clio 130 automatic is rather better to drive on a winding road. There’s a price to pay for the hybrid’s low consumption I suppose.

Jb boin > Who is the Leader - 404 / Blog No Longer Available
07/10/2020 at 19:50

The car seems to be consuming like the less powerful diesel in mixed driving situations (including highway) while having similar performance as the most powerful petrol so it will most probably be even better in city driving than the diesel.

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Now even petrol engine have DPFs ; another thing to note is that hybrid and electric cars are supposed to wear less the braking system.

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In F rance the taxation on new cars is based on CO² so diesel cars is still favored over petrol while hybrid and PHEV are in most case not taxed at all (for this “bonus/malus écologique” tax) while you can have an incentive when buying an electric, hybrid of PHEV.

And SP95-E 10 (90 AKI with 10% of ethanol) is still 7.5% more expensive on national average than diesel.

Who is the Leader - 404 / Blog No Longer Available > Jb boin
07/10/2020 at 19:56

So diesels produce more CO² per liter but they are more efficient? But gasoline tends to provide more power per displacement. Interesting convergence of priorities that determine the choice there.

Jb boin > Who is the Leader - 404 / Blog No Longer Available
07/10/2020 at 20:33

Diesels are more efficient so they produce less CO² per kilometre (which is what is used for taxes).

Diesels have more torque in comparison to power than similar petrol engine so they tend to need less peak power figures for similar daily commuting driving.

Some “real world” mileage tests of European market cars are made by Motor1 France and Italy and most cars of the size of the Clio in both diesel and petrol can do less than 4l/100km (~60mpg) in the good conditions (and with “eco-driving”) .

On their 360km mixed test, the Clio TCe 100 (0. 9L inline 3 turbo petrol) averaged 3.7L/100KM (63.5MPG) ; while most probably won’t have figures as good as that, its still impressive that it’s achievable in the real world .

Who is the Leader - 404 / Blog No Longer Available > Jb boin
07/10/2020 at 21:15

Fascinating. Thank you.