Unusual ways to change gear, cont'd

This, as not many here will know, is a Renault Clio.

Renault sell many cars in the EU so they’ll have substantial fines to pay unless their range averages no more than approx (approx because the actual target varies according to the weight of the cars a manufacturer produces) 95g of CO2 per km by 2021. By 2021 each maker will be levied a fine of €95 per car per gram over their target. Sell 100,000 at 10g over then and it’ll cost you 100,000 x 950 or €95m.

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Diesels are now seen as Satan personified so everybody’s going to have to go down the electric route, whether by full EV or hybrid. Renault then are optionally hybridising the Clio. There’ll be a conventional hybrid and if more money is spent a PHEV. Either way they need to mix and match power from engine and motor.

There are a number of ways of doing this.

One method is the deceptively simple sounding Toyota system which uses an epicyclic gearset to which are attached the engine, a motor/generator and the wheels (via a second motor/generator). By using the first motor/generator as either a motor or generator to either speed up or slow down one element of the epicyclic gearset you can blend electric and engine power and also vary the gearing.

Another method, used by VW and Merc amongst others, is to sandwich a motor/generator between engine and gearbox, whether DCT or conventional automatic, and clutching engine and motor in or out as required.

A third is the Honda twin motor setup where the engine drives a generator which in turn powers a motor/generator

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. The vehicle starts using battery power and then as speed rises the engine starts and provides electric power. At higher speeds the engine is clutched to the wheels and therefore provides power mechanically.

Yet another way is to split the two forms of power so that one drives the front wheels and the other the rear ones.

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Renault aren’t doing any of these.

They’re going to use a mechanical gearbox which consists of four gears. Two serve the motor and the other two the engine. The electric motor is used for starting and reversing so a clutch and reverse gear aren’t needed. Rather than use expensive synchromesh motorcycle type dog clutch gears are used. But there isn’t a clutch so another way of changing gear is needed. Bikes get over this by using a quickshift which momentarily cuts power but this isn’t smooth enough for car use so Renault employ a second electric motor to carry out rev matching. The idea is that the second motor spins the engine at just the right speed that the box can slip smoothly and silently to the other “engine” gear. On the other side the main electric motor does its own rev matching. Not only does this give you four speeds, but it goes beyond that because engine and motor can run at the same time so you can have the motor in first and the engine in second and vice versa.

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Renault describe this as if it’s their own work and will be building it themselves but Vitesco, formerly Continental’s drivetrain division, describe something that appears to be exactly the same system so who knows?

They’re not the only ones. Schaeffler, a company almost nobody has heard of but who have bits in every car that’s now made, have one too.

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It’s more complicated because it uses a total of five gears to give six speeds using the engine. On the left and in green, two EV gears. On the right and in yellow, two engine gears. In the middle and in blue a pair of “multiplier” gears which work like the high and low speeds on a truck. Mix and match all this lot and you get six speeds.

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What I don’t know is why these complex multi gear systems are though better than the single epicyclic that has served Toyota well for twenty plus years but I’m sure there’s a reason.

EDIT: There is. The Toyota powersplit system relies to a certain extent on the engine providing electricity to power the vehicle which is inefficient.

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