# Honda Jazz Converstion Idea



## MaverickNZ (May 14, 2008)

I was thinking of converting a Honda Jazz to electric. I thought one with a cvt trasmission would be ideal because the motor can stay at its ideal range and the gear ratio changes.

Im just not sure how the CVT gearbox is controlled though. im hoping that it would be possible to adapt the gearbox control systems to be used.

Anyone know anything about he honda CVT gearboxes?

The eventual idea once i got my converstion working would be to design a kit for sale so that more people can catch that EV grin lol


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## Warren Walker (Jun 8, 2008)

hi,

the cvt is computer controlled and keeps the revs in the engnies ideal torque range 2500-3500rpm.

so in terms of an EV, the cvt would be tricky, not impossible, to install and have operate. i would imagine the cvt wouldnt keep the electric motor up the 5-6krpm range of its efficency.

ideally you want a vehicle that doesnt need information from the AT and engine to run. if you considered an AT for a conversion maybe a modified stall/torque converter for be somewhere to look.


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## MaverickNZ (May 14, 2008)

I realise it would be tricky. its just an idea at this stage. i was trying to think of ways of getting the most efficiency from the electric motor and cvts are great when it comes to that.

as far as the efficiency point goes that can be fixed by putting a microcontroller between the cvt computer and the motor controller. that way the microcontroller acts as a signal adapter so the cvt computer thinks the motor in in the normal motor range while it is acctually controlling the motor through a wider rpm range.

Like i said its just an idea at this stage im just trying to see if its feasible first before i go starting to design anything or buy parts. i might go talk to honda and see if they have any info that might help


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## Warren Walker (Jun 8, 2008)

well its your lucky day. what info do you need?


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## MaverickNZ (May 14, 2008)

I'm not sure really. I suppose if there is a technical manual on teh gearbox describing the way the systems operate and describing the control interfaces. At this stage any info i could get on it would be great. im just trying to decide if its an avenue worth persuing


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## NZVideoguy (Jun 26, 2008)

Hey guys, I also have a Honda Jazz and was thinking exactly the same thing. My thoughts on the cvt are that it would work well given it's great efficiency.
Anyway, just joined the forum. I live in Christchurch and as the user name suggests, I'm a professional videographer.
Cheers Paul


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## MaverickNZ (May 14, 2008)

yeh i think so as well but for the life of me i cant find any info on it. might have to go ask honda after all


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## NZVideoguy (Jun 26, 2008)

More thoughts on the Jazz cvt. I was watching a video clip of Gavin Shoebridge last night where he talks about putting the car in 2nd gear for around town driving. I have to be honest, it took a while for my brain to figure out that when the car is stopped, the electric motor is also stopped so there's no need to change gears or use a clutch. How this relates to the vtc transmission on the Honda Jazz is that you always have the option of selecting 1st, 2nd or drive with each gear giving almost identical efficiency of a manual trans. So, for example on hills, drop to 1st. For around town (and probably country) select 2nd. I can do well over 100kmh in 2nd so it's quite a high gear. Anyway, bottom line is with a choice of 3 "speeds" and infinitely variable on top, I can't see how it wouldn't be a great trans for an electric motor. I have to add that I'm feeling really excited about the possibility of doing this conversion on my Honda. Tell the oil companies to shove it right up their ring gear.


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## MaverickNZ (May 14, 2008)

the idea of using a cvt is that if it in cvt mode it will keep the engine in its max efficiency range and you would get more range out of each charge because its not wasting so much current when accelerating


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## Heretic (May 8, 2008)

I had a 2006 nissan primera with CVT, and it did not like torque, not one bit - it would sit at 5000rpm at full throttle from 10km/h to nearly 100km/h. Check to see if you can change the RPM at which it sits at, otherwise you may get a gearbox that wastes alot of torque


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## Kiwi_ME (May 29, 2008)

I'm not clear on why a sophisticated transmission like a CVT needs to be part of the equation. The electric motor doesn't have a "powerband" nor does it need to be running at idle speed to start off. Compared to an IC engine the efficiency is relatively constant at all speeds and torque levels. I could see two fixed ratios being of some use to improve acceleration at low speeds but transmission losses must be at an absolute minimum to make it all worthwhile. And using a torque convertor or any part of a conventional automatic? - forget it. I don't even like the idea of a hypoid gearset, a FWD helical gearset final drive is as good as it's going to get without going to direct drive.

I would be interested to hear Gavin's take (based on his experience) as to how many ratios are really needed.


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## John (Sep 11, 2007)

NZVideoguy said:


> Hey guys, I also have a Honda Jazz and was thinking exactly the same thing. My thoughts on the cvt are that it would work well given it's great efficiency.


I think the CVT's claim to efficiency has more to do with it keeping the ICE at its most efficient revs. From what I've read the parasitic power demand of a CVT is worse than a standard auto but keeping the ICE in its efficiency sweet spot more than makes up for it. This would not be particularly useful in an EV.


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## Kiwi_ME (May 29, 2008)

When Audi introduced the CVT in the US market A4 some years ago I recall it had the same EPA fuel economy numbers as the manual transmission. I don't think these things would have even appeared on the scene without have less losses than a conventional auto with lock-up torque converter.


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## John (Sep 11, 2007)

The CVT still has a torque converter just like a conventional auto. It also has a hydraulic system like a conventional auto but from what I understand the CVT's hydraulic system has higher flow and pressure demand than a conventional auto and hence a higher parasitic power demand. The torque converter in the CVT locks at much lower engine revs than in an auto which produces some efficiency gain. It also can hold the engine revs at its most efficient power production revs independently of vehicle speed while the car accelerates which is something neither an auto nor a manual can do. This makes the ICE more efficient and lowers its emissions. The efficiency gain in the ICE offsets the extra transmision losses.

When a vehicle accelerates energy is absorbed to build the vehicles inertia. This is not just the vehicles linear inertia but also the inertia of all its rotating parts as well whose angular velocity increases with the vehicles linear velocity. By the CVT "decoupling" the engines angular velocity (revs) from the vehicle velocity the engine is no longer accelerating when the vehicle accelerates and is hence not absorbing energy to increase its inertia. This should provide a subtle improvement in the vehicles performance by freeing up more energy for acceleration. Performance being the flip side of the efficiency coin this gain can be taken as an efficiency gain instead by reducing power demand.

The ICE's efficiency varies from 0% at idle up to about 35% maximum probably averaging about 15% to 20% depending on the vehicle. So there is a very large variability in its efficiency. The DC series electric motor will vary from about 70% to 90% efficiency giving a much narrower variability. This means the scope for a CVT to improve the efficiency of a vehicle is much greater with an ICE powered vehicle than an electric powered vehicle. Given the CVT's higher internal power consumption and hence lower efficiency and the narrow scope for improvement the overall net position is likely to be worse in an EV.


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## Kiwi_ME (May 29, 2008)

Thanks, I'm pretty clear on the details of general automotive engineering! Indulge me a moment, have a look at the blow-up of the Audi CVT on this review. Perhaps the Honda Jazz CVT has a TC, but not this one. The multi-plate clutch is clearly visible:

http://www.canadiandriver.com/articles/hl/03a4.htm

To quote, "The strong but flexible chain also provides other benefits: There's more than a 6:1 ratio between lowest and highest gears, and a power-sapping and fuel-gobbling torque converter is not required with this CVT."

But certainly I agree, a CVT in general is mostly pointless in an electric vehicle, and no doubt the benefits of narrowing the working RPM range on IC engines is why we are seeing 7 and 8-speed conventional autos. 

Also, see the docs I posted in another thread on the EV1 sales magazine. The drivetrain is pretty simple in that well-engineered vehicle, one ratio only.


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## John (Sep 11, 2007)

A CVT requires some sort of launch device. This would most often but not always be a torque converter. I cannot find a lot of info on the Jazz CVT but it looks like Honda in general use an acceleration clutch instead of a torque converter. The following file contains quite a lot of information on CVT efficiency. It’s quite a large file about 10 Mb. 

http://alexandria.tue.nl/extra2/200612241.pdf

About the Audi A4 CVT. Quote "_The problem seems to lie in the CVT's ultra-low lowest gear and the multiplate clutch that engages and disengages the transmission. The A4 creeps away from a stop like a car with a conventional automatic transmission, but when you first depress the throttle, nothing happens, so you continue pushing the pedal. Then, suddenly, the multiplate clutches, which provide the slippage that exists in a torque converter, lock up the lowest of the CVT ratios and, coupled with the torquey engine, spin the front wheels until the traction control restores the A4's dignity_." Perhaps a multiplate clutch is not the best launch device.

As you will see in the above file CVTs are quite torque specific. The clamping pressure is controlled to some margin over the torque that would cause the transmission to slip. As the transmissions loses are proportional to the clamping pressure it is important that this is optimised or the transmission loses will be horrendous. Also the motor torque available at start up in an EV could well be beyond the capability of a CVT.


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## locost_bryan (Aug 18, 2008)

As the owner of a new Jazz, a 1.3 with the CVT and flappy-paddle 7-speed pretend manual mode, I agree the CVT is a wonderful device when mated to an ICE with a wide torque band. Works really well when left to it's own devices.

Would it be any use with an electric motor? That depends...

I'm a newbie, so here's my understanding of a gearbox's role.

In an ICE, it's needed because of the ICE's peaky torque curve. Torque is required for acceleration (and power for speed). The gearbox (and diff) multiply the torque, so in 1st gear the engine's torque is mupltiplied by both the diff ratio and the 1st gear ratio, but in direct-drive 4th it is only multiplied by the diff ratio. The diff ratio for the EV would be chosen to give reasonable acceleration and a suitable top speed.

An example (Suzuki Swift GT engine in a 1999 Suzuki Carry van, 77 Nm @ 3500rpm to 113 Nm @ 5000rpm) :-
Gear Ratio Diff Overall Nm @ 3500 rpm Nm @ 5000 rpm
1st 3.652 4.555 16.635 1281 1880 
2nd 1.947 4.555 8.869 683 1002 
3rd 1.423 4.555 6.482 499 732 
4th 1.000 4.555 4.555 351 515 
5th 0.795 4.555 3.621 279 409
(any way to format a table?)

In an electric engine, peak torque is developed at low rpm, and only tails off at higher rpm (AC24LS is flat 87 Nm to 4000rpm, then down to 60 Nm @ 5000rpm, and drops 10 Nm per 1000rpm to 20Nm at 10,000rpm).

An example (Azure Dynamics AC24LS in 1999 Suzuki Carry van)
Gear Ratio Diff Overall Nm @ 3500 rpm Nm @ 5000 rpm
1st 3.652 4.555 16.635 1447 998 
2nd 1.947 4.555 8.869 772 532 
3rd 1.423 4.555 6.482 564 389 
4th 1.000 4.555 4.555 396 273
5th 0.795 4.555 3.621 315 217

Now, if I read some of the previous postings correctly, most EVs are only driven in one gear (1:1 4th). However, there are issues climbing hills, where a lower gear may sometimes be used.

If I understand correctly, 3 things limit the the maximum torque available from the electric motor :-
1) the rated power of the engine
2) the maximum amps from the inverter
3) the maximum amps from the batteries

So, in a "gearless" EV, the acceleration will ultimately be limited by the oomph from the batteries. 

Physics says acceleration will be limited by the available torque, and whether it is sufficient to move a given weight a certain distance (vertically and/or horizontally). 

If the EV struggles on hills, the options are a bigger motor and/or gruntier batteries, or using a lower gear to multiply the motor's torque. A bigger motor adds weight, but you only need enough power to maintain your top speed (say 100-110kmh). That requires less than 20kw in most cars and pickups, so the extra power goes to waste. But a 20kw motor may not create enough torque to give the required acceleration, so a traditional gearbox would be needed to give the torque multiplication effect (but needing fewer gears than an ICE).

Surely changing down to a lower gear will work the same for an EV as an ICE?

In this case, a CVT could be used to keep the EV motor at the rpm that generates maximum torque with minimum current draw for best acceleration, or lowest rpm to generate required power for cruising.

Of course, I could be talking utter bollocks 

Bryan Miller
Auckland


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