Track Tested: 2011 Nissan Leaf SL

It is odd they only use direct drive trans. Seems logical a few more gears would make a world of difference.

Years ago I knew a guy who converted an old Nissan pickup into electic. He used a large forklift electric motor and connected it to the stock 5 speed gearbox, seemed to work really well. If he could do it in his garage then why not?

Good stuff. I'm disappointed that it doesnt get to 60 quicker, though. Why doesn't Nissan put their CVT into this thing? Also, why not offer a 5-speed like the CR-Z?

Let's do a thought experiment. An object of a fixed weight is traveling 50mph. You can have the option of using an electric motor rotating at 8000 rpm vs. 3000 rpm. The electrical motor is 90% efficient at 8000 rpm, and 75% efficient at 3000 rpm. Is it a good idea to add the weight of a gearbox?

Automotive engineers aren't stupid.

There's no reason to use gears to lower electric motor rpms. It isn't as if higher rpm means lower efficiency in an electric motor, most electric motors don't peak their efficiency curve until they're at 80% of maximum operating rpm.

That is good to know. I wasnt aware of the efficiency component of the equation. But still, I think having the option to have a more performance oriented transmission would be good for future models. Otherwise performance enthusiasts will not adopt the electric vehicle until they have no other choice (if it ever gets to that point).

Single gear direct drive transmissions work great in EV's. The LEAF isn't supposed to be a performance car but it does do what it was designed to do.
Hop in a single gear Tesla and tell me how it feels. :)

Uh...what exactly will a "performance tranismission" do for a motor?

abcyard,

All motors, including electric, have a power band. The higher you gear it, the less power you can bring to the wheels. It's a matter of striking a balance. Direct drive is easier, less expensive, and works in a lot of cases. I don't blame the automotive companies for starting with direct drive, but I believe we will see two speed transmissions in the future. Even Tesla wants a multip-speed transmission. They had a two speed for the Roadster, but couldn't get it to work. They've stated that they still want a two speed.

Again, I don't blame them for using a single speed, but that doesn't make a two speed a bad idea.

My 168 hp Outback weighs about the same as the Leaf with 107 hp. The Leaf isn't all that much slower than my car. So, the electric motor is doing a great job, in my opinion.

Also, back 40-50 years ago, cars that broke the 10 second 0-60 time were considered peppy. For the intended owners, this Leaf is powerful enough.

Electric motors have such linear power curve the additional cost and weight of a transmission negates any theoretical advantages.

In a heat engine, because there are limitations as to the lowest/highest reliable rpm, and torque doesn't kick in at low rpms, you need to adapt the output of the internal combustion engine to the drive wheels.

In an electric motor? The engineers just design to have the right number of copper loops to achieve what a heat engine + transmission does.

After all that effort to get a vehicle with a full charge for testing, why didn't you do the acceleration testing first?

As good to drive as anyone expected it to be, for sure, but somehow I thought it would be quieter.

Electric or gas the advantage of gears comes from it taking much more power (torque) to accelerate a car from a stop then it does to cruise at speed. Direct drive means you need a larger electric motor to give that amount of power people expect these days.

Gears let you have the best of both worlds.

A multispeed gearbox would allow the use of a smaller, lighter, cheaper, lower powered electric motor then direct drive would.

At this time would the extra benefits outweigh the costs? Hard to say, maybe not. Not my area of engineering.

acbayard said earlier "Automotive engineers aren't stupid" and that's true. However product planners can be cheap and short sighted.

I`ll bet most electric cars will have CVTs before long (even if it is my least favourite transmission).

A transmission would require a heat exchanger to cool transmission fluid, introduce more inefficiencies, and also means the transmission would be the least reliable item on the car - as an electric car transmission would be going at a few thousand higher rpms than most gasoline engines.

It just doesn't make sense. Electric motors have much much much higher torque capacities at low rpm than equivalent weight/sized gasoline engines.

I'm not sure what a CVT needs but manuals don't need extra cooling. They are also extremely reliable.

Maybe the old guy I knew with the electric Nissan pickup had the right idea after all.

No question really, there is a reason why every car (and motorbike, bicycle, etc) built in the last century has had a multispeed gearbox.

CVTs and automatic transmissions need to be cooled either through a heat exchanger using the cooling capacity of the engine radiator - or have a separate transmission cooler.

I think there's a disconnect regarding how electric motors operate and their operational advantages... the inherent limitations in a heat engine simply don't exist.

As much as I appreciate the efforts IL goes to to test a car with afull charge, how is that at all relevant in the real world? Unless the freeway on-ramp is at the end of your driveway, the 0-60 time with a 100% charge has no meaning. What is important in an EV is who far can it go on a charge and how much does it's performance degrade at 33% charge. In other words, will I be able to beat that semi across the intersection on my way home from work, which just happens to be 25 miles? Anyone who's driven a bumper car at the fair knows electric cars are fast with full juice. What happens after they've been unplugged for awhile?

Why wouldn't you do the acceleration test first when the battery was 100%? Skidpad and slalom would not have been affected by battery charge while it is possible that acceleration would be.

The battery produces more power once its warmed up, so you would get better acceleration after you do the slalom tests. Its a moot point anyways, acceleration is software limited in the Leaf, there have been reports of faster 0-60 times with pre-production examples.

You use a transmission in a gas engine to get usable torque at a desired rpm level of the wheels, because the torque/rpm curve in a gas engine is not flat, transmissions match the engine to the wheels.. electric motors are not that way, they will happily produce infinite torque at 0 rpm until the windings burn up, thus all a transmission in an electric motor does is introduce losses. Note the Leaf does use a single speed transmission, ratio around 7:1

Can you put the Leaf on a dyno?

acbayard, GM admits that the electric motor in the Volt is less efficient at higher RPM. As a result, under certain circumstances, it will run at a higher effective gear, ala the planetary gear setup. As you said, the engineers aren't stupid. Electric motors have huge rpm and torque advantages over ICE, but they can sometimes use a little help too.

First point: the idea that the Leaf (or Volt or any modern EV) is using the maximum amount of power the batteries can physically source when you floor the accelerator is ludicrous. Given the current state of torque management on EVERYTHING, I suspect that even if the batteries lose power output capacity towards the end of the charge, they are still well within the max power the motor controller is programmed to extract at "WOT." These aren't backyard conversions...

Second point: This is slower than the Volt EV to EV (6mph trap speed slower). And the Volt picks up another 4-5mph of trap speed when the ICE is running (battery exhausted). That is very significant.

@brn: You're misunderstanding GM's engineering decision.

The reason why GM is opting to use the range extender's power directly during high speeds is not because of the electric motor's efficiency at higher speeds. It is because energy conversion losses at those speeds make the additional energy losses unappealing. It has more to do with losses converting kinetic energy to electrical potential, then back to kinetic energy.

acbayard,

I understand the efficiency loss in going from mechanical to battery storage to electrical back to mechanical. However if that were the only reason, wouldn't they always have a mechanical connection (at speed anyway)? GM did say in their statement that the electric motor is not as efficient at high speed.

We're both correct as to GMs reasoning. I will admit that when I read GM statement, I was a little surprised that they included the complication and weight of a planetary gear.

The Volt's much-maligned multi-clutch planetary arrangement effectively permits a CVT relationship between the two motors and the drive wheels. IIRC, the ratio varies 2:1. When the second motor clutches in, it reduces the RPM of the main motor.

Again with an IIRC caveat, this adds a couple miles to the EV range. As others above mentioned, it's nothing like an ICE engine, which absolutely requires multiple gears.

The downside is that when you floor it at highway speeds, it feels like you have to wait for a "downshift". I think what happens is that the 2nd motor is slowed to a stop and declutched before the main motor can apply full power.

@brn: However if that were the only reason, wouldn't they always have a mechanical connection (at speed anyway).

No. A gasoline engine operating at a fix rpm as a generator charging batteries + powering an electric motor that varies its load will be more efficient at all speeds up to the point where the energy produced curve intersects with (efficiency losses * energy demand).

@brn: "However if that were the only reason, wouldn't they always have a mechanical connection (at speed anyway)? GM did say in their statement that the electric motor is not as efficient at high speed."

Between about 40 and 70 mph, the most efficient choice in ICE mode depends on the exact circumstances and the Volt can move back and forth between serial and parallel hybrid configurations. Above 70, it's "always connected" but MotorTrend posted a chart of rpm-vs-speed which made me wonder if that's true in every circumstance. Since it's going through the planetary gear, the rpm-to-mph relationship is not fixed. I think this is where GM came up with the rationalization for their cute little "engine is not directly connected to the wheels" game. (In truth, planetary gears mess with my head).

If anyone *really* cares to know, there's a 36 minute presentation on the Volt powertrain by Pam Fletcher of GM on youtube. It's quite detailed for a to-the-media talk:
http://www.youtube.com/watch?v=d9-9atMw6Zs

If you're truly nuts, there are a number of SAE papers on the Volt powertrain and battery.

acbayard said it much more succinctly than I did.

BTW, I've hooked my OBDII scanner up under ICE mode. As you might expect, the engine runs at wide open throttle as often as possible to reduce pumping losses, loading it down with the generator. It's interesting to see 75% throttle (which is effectively WOT at low RPM from a pumping losses perspective according to my calibration friend) on the scanner while the engine is at a relatively sedate 1500rpm.

"@brn: However if that were the only reason, wouldn't they always have a mechanical connection (at speed anyway). "

A good question. My theory is that even though the electric motor is less efficient at higher speeds, it's still more efficient than the ICE. Don't engage ICE unless you have to.

The better question is why not mechanically engage the ICE at all speeds (when the battery is low)?