[brian_]

It isn't the transmission which is expensive; it is all of the modifications required to make an ancient automatic transmission intended for a gas engine suitable for an electric motor.

This transmission setup was developed for old brushed DC motors, and it works for them, but I don't see much point in this if using a Leaf motor. Like any other modern EV motor, the Leaf motor can produce full power over a broad speed range, so it only needs a single reduction ratio.

 

[hiura]

I'm quite new to the world of EVs, so my understanding is lacking. So, how exactly would I connect the Leaf motor to the rear diff? Torque tube?

The Leaf is FF and I would prefer a FR car as it was made RWD from the factory. What is the ideal setup for transferring power from a Leaf motor to the rear wheels if a 2-speed Powerglide is not optimal?

 

[brian_]

First, a bit of terminology: the combination reduction gearbox and differential is a 'transaxle'; the combination of electric motor and transaxle (usually with controller/inverter as well) can be called a 'drive unit' (at least it is for Teslas, and other brands have the same arrangement).

The Leaf is FF and I would prefer a FR car as it was made RWD from the factory. What is the ideal setup for transferring power from a Leaf motor to the rear wheels if a 2-speed Powerglide is not optimal?

There are at least a couple of people building projects which place the entire Leaf drive unit in the rear, in place of the original final drive (differential) to use the Leaf motor (and transaxle) in a car which was front engine and rear wheel drive. That has the advantages of being able to use the drive unit unmodified, avoiding the need to build parts to mate the motor to some other transmission, and leaving the engine compartment free. Unfortunately, since the car wasn't designed to have anything as large as the Leaf drive unit there, this is a major project involving structure and bodywork.
Example project: 300ZX Electric Conversion

At the opposite extreme, the traditional conversion approach is to just put the (Leaf) motor where the engine was, connected to the car's original transmission (which then still connects the original final drive (differential). The only reason to change the original transmission to a modified Powerglide would be to avoid shifting, but most people just shift the original manual transmission as necessary.

A compromise is to put the motor and a small single-ratio reduction gearbox in the original transmission tunnel, driving the final drive unit (diff) the same way the original engine and transmission did. If using a low-speed motor (not the Leaf) or building a car intended for high speeds (not regular street use) the reduction gearbox can even be omitted, so it's just a motor connected by the driveshaft to the final drive (diff).

One builder in this forum even managed to fit a motor in directly ahead of the final drive (essentially in the driveshaft tunnel under the rear seats), connected to the final drive by just a short coupling and with the motor housing mounted to the final drive housing by a custom bracket (which acts like a short torque tube): Latvian mazda RX-8 project

I'm quite new to the world of EVs, so my understanding is lacking. So, how exactly would I connect the Leaf motor to the rear diff? Torque tube?

In any solution which involves keeping the original final drive (differential), you connect to it the same way as the original car: you use the original propeller shaft (driveshaft), modified if necessary to fit your chosen gearbox (or directly to the motor).

A torque tube is a non-rotating box-shaped or tube-shaped structure which connects two parts (such as an engine in the front and a transaxle in the rear, or a transmission in the front and a final drive unit in the rear) to handle the torque in reaction to shaft torque. In a car which doesn't use a torque tube, those parts (engine, etc) must be mounted so that the body can handle the torque and keep those parts from twisting... and that's the normal setup, which is why final drive (differential) housings in typical cars have two widely-spaced rear mounts. As far as I know, no Nissan has ever used a torque tube. Of course anything with the engine and transaxle at the same end of the car (FF or mid/rear engined) has no torque tube because there is no distance to fill between the parts.

 

[Emyr]

A torque tube is a non-rotating box-shaped or tube-shaped structure which connects two parts (such as an engine in the front and a transaxle in the rear, or a transmission in the front and a final drive unit in the rear) to handle the torque in reaction to shaft torque. In a car which doesn't use a torque tube, those parts (engine, etc) must be mounted so that the body can handle the torque and keep those parts from twisting... and that's the normal setup, which is why final drive (differential) housings in typical cars have two widely-spaced rear mounts. As far as I know, no Nissan has ever used a torque tube. Of course anything with the engine and transaxle at the same end of the car (FF or mid/rear engined) has no torque tube because there is no distance to fill between the parts.

"Torque tube" is also (mis)used to describe a prop shaft when the engine is in the front but the transmission is in the back with the diff, a la Volvo 340.

 

[brian_]

"Torque tube" is also (mis)used to describe a prop shaft when the engine is in the front but the transmission is in the back with the diff, a la Volvo 340.

That's really confusing, because for some vehicles that would mean calling both the (rotating) prop shaft and (non-rotating) housing that it is in "torque tube".

I'm familiar with the DAF/Volvo 300 series only because of the famous CVT transaxle, but I didn't recall the rest of the mechanical details. Wikipedia says that it has a torque tube (from engine to transaxle), but only with the 2.0 litre engine... the others would have an open propeller shaft, and the reaction torque transmitted through the vehicle structure (just like most other cars).

 

[hiura]

A compromise is to put the motor and a small single-ratio reduction gearbox in the original transmission tunnel, driving the final drive unit (diff) the same way the original engine and transmission did. If using a low-speed motor (not the Leaf) or building a car intended for high speeds (not regular street use) the reduction gearbox can even be omitted, so it's just a motor connected by the driveshaft to the final drive (diff).

Still learning after a life in the ICE world. This seems the most realistic option for money, time and skill. I'm in Japan over the summer break to work on a father-son project. My understanding and plan would be to put the leaf unit in the front replacing the ICE but leaving the rear alone (maybe changing the final gear ratio if need be). This is why I was thinking the PowerGlide making sense being a 2-speed.

I am not certain that I can go online or to a shop to purchase a small single-ratio reduction gearbox (Thunderstruck's website is dead and have to go through archive.org to see their $900 gear reduction as opposed to a typical $200-$300 PowerGlide) and I know that I do not have the skill to make one. OZ Motors is near Yokohama and the only Japanese EV shop that I know of, so it's not like looking for SR20DET/RB engine parts that you can easily find.

I'm a teacher, so I always prefer to begin with the end in mind and then work to the beginning. This way, less likely to hit a snag that completely ends a project. Plus, Japan requires a complete description of all the parts used in a swap for the application for approval before even starting. People watch Tokyo Drift while living in the (car) freedoms of the US and think that...yeh, Japan is going to be like Florida with no problem modifying a car.

 

[hiura]

Potential good news for anyone reading about a Leaf motor swap for a RWD car. Engineering Explained let me know about a Nissan Toroidal CVT that I never knew of:

https://www.youtube.com/watch?v=5jIeSgq7ewI

I think this is an affordable and realistic option.

 

[brian_]

Potential good news for anyone reading about a Leaf motor swap for a RWD car. Engineering Explained let me know about a Nissan Toroidal CVT that I never knew of:

...

I think this is an affordable and realistic option.

I think that's way too much complication and inefficiency for an electric motor. Continuously variable transmissions exist to keep an engine closer to their ideal operating speed (for the current conditions) than is possible with a finite number of distinct gear ratios, but the tolerable range of speeds for an modern high-voltage AC motor is quite broad. The loss of power going through a gear set is low, but CVTs like this use a friction drive which is inherently less efficient. As with a conventional (planetary gears and torque converter) transmission, this CVT requires the motor to turn at idle to maintain hydraulic pressure, and uses a torque converter (which slips at low speed) to achieve that, which is just throwing energy away.

As with any automatic, controlling the transmission without the complete control systems of the car it was originally in would be a challenge.

I don't understand the determination to use an automatic transmission. With a Leaf motor, there is no need to have a transmission which changes gears at all. If more than one ratio is really wanted, a manual transmission works... and just about anyone who is capable of driving a car can learn to shift a manual transmission.


Also, most CVTs are of the type which uses a steel belt running between variable pulleys - even from Nissan. This toroidal design is mechanically interesting, but obscure. It was probably only used on one Nissan model.

 

[Jack-Lee]

Obscure? My lathe from 1964 Made in hungary use the same type of gearing.

 

[brian_]

Obscure? My lathe from 1964 Made in hungary use the same type of gearing.

Interesting, but a design used on only one transmission used by one manufacturer in a single model of car for a few years a quarter century ago is certainly obscure, in an automotive context.

When Toyota started using a power-split transmission in the hybrids I was talking with a friend about it, and he said his parents' farm had equipment with a related power-split drive system. Most basic machine designs that are 'new' have had a prior life in a different application. But if you go out to buy a toroidal CVT, I think you'll find they're not common... and you can't use one out of a lathe. 😉

 

[brian_]

(Thunderstruck's website is dead and have to go through archive.org to see their $900 gear reduction as opposed to a typical $200-$300 PowerGlide)

Thunderstruck EV? Their website is working, but their $900 custom-ratio "gear reduction" unit is actually a toothed belt drive, intended for boats and not configured to fit in a car, and not likely capable of handling the torque wanted in this case.
https://www.thunderstruck-ev.com/custom-ac-gear-reduction.html

 

[hiura]

I don't understand the determination to use an automatic transmission. With a Leaf motor, there is no need to have a transmission which changes gears at all. If more than one ratio is really wanted, a manual transmission works... and just about anyone who is capable of driving a car can learn to shift a manual transmission.

I see. You have no experience with Japan. I am more than capable of driving a manual - it is not hard to do and I did so for more than a decade in the US - but Japan's driver's license system is run by a racist mafia that has dinosaurs who want to retire to the driving schools where they can get paid to yell at and fail people. It is all an extortion scam. No one can 'pass' a Japanese driving test. You either get passed or you do not without explanation. I have been 'failed' 5 times over the years in more than one prefecture and I only was allowed to get my AT license when my wife came on my third attempt for the AT license with a sob story of how I would have to drive because she was pregnant.

I will stop here because I can feel my blood pressure rising and I am serious. The Yakuza has never stolen my money but the government has. You can see why the AT is a must.

 

[brian_]

... You can see why the AT is a must.

That's good background about the situation in Japan.

A solution is single-speed: no clutch pedal, no shifter (just the forward/reverse switch), and thus no transmission to be shifted, and so no requirement for a manual transmission license to drive it.

Assuming the use of a motor salvaged from a production EV, the most efficient way to get a single-speed transmission is to use the transaxle which comes with the motor. That only works easily when replacing a transverse engine and transaxle, but has also been done in rear-wheel-drive cars with rear or mid or even front engines... but mounting the entire drive unit (motor with inverter and transaxle) in the rear of a car not designed with space for an engine there is difficult.

The most straightforward way to use a front-mounted motor with rear wheel drive is to use a single-speed gearbox, but potential difficulties with getting such a gearbox and getting it approved have already been discussed.

If necessary, a stock manual transmission could just be left locked in one gear (whatever turns out to be the most suitable ratio) to get a single-speed system; a direct coupler could replace the clutch. Of course the original shifter and clutch pedal would be omitted. You would need a forward/reverse selector, and could even use one from an EV... but the transmission wouldn't have a "park" mode so a selector with that mode should be avoided (as it would present a non-functioning choice to the driver, presumably causing confusion and issues with approval.


A transmission with multiple ratios can improve performance, but the inefficiency of an automatic transmission would negate much or all of that advantage. Even if no performance improvement and an efficiency loss are both acceptable to avoid a manual transmission, an automatic presents a substantial cost and complexity challenge... especially if you want to avoid spinning the motor at "idle" just to keep the transmission in gear.

 

[hiura]

I had not considered using a manual transmission locked into one gear with the possibility of a difference reverse option. Hmmmmmm, this causes some reconsideration.

Of course, some enterprising company may already be designing a "plug-n-play" single gear gearbox for a RWD swap. With so many Leafs now just at Copart alone, there are a plethora of choices. The Chevrolet Spark can be found cheap as well, while the Bolt is a good 2-4 more years away from salvage parts.

Here in Japan, it is not hard at all to find a complete Leaf dropout for $400-$500. But then, car DIY here is far smaller because of the authoritarianism of the Japanese government whose policy is to force people into buying NEW Japanese cars on a regular basis.

Safety and single-payer healthcare in Japan? Outstanding! If you like cars or motorcycles (especially for a father-son project), not so much. Yearly taxes and biannual inspections. At least I run my own inspections rather than pay $1000+ for some shop to run the 30 minute procedure.

 

[brian_]

Of course, some enterprising company may already be designing a "plug-n-play" single gear gearbox for a RWD swap. With so many Leafs now just at Copart alone, there are a plethora of choices. The Chevrolet Spark can be found cheap as well, while the Bolt is a good 2-4 more years away from salvage parts.

I realize that this is an old discussion, but this may still be useful...

The Chevrolet Spark EV used an unusual motor and gearing combination, with less than 4:1 reduction from the motor to the axles, and an unusually large and high-torque motor to work with the resulting need for more torque and less speed. The Spark EV motor may be usable when connected to a car's stock final drive unit (differential with ring-and-pinion gear reduction) when other common motors would need a reduction gearbox.

With the Bolt, GM returned to a more conventional combination of motor speed and reduction gearing ratio.