EV transmissions are coming

I think this is wishful thinking on ZF's part. Drive a tesla, part of that great acceleration is no shifts, just pure torque to the wheels. I'm going to test drive the P85D next weekend. here we get part of what they are talking about, 2 different motor speeds, but it comes with awd ;-) I think the KISS principal applies. No need for a multi-speed transmission if you can save the cost and weight.

PHEVs are different of course and need more than a single speed transmission for the ice, so the volt, ford energis and prius phv have a variable speed psd type transmission. The upcoming hyundai phev has a traditional transmission and two clutches like its hybrid version.

 

I still like the concept of a multi-speed tranny. It is almost like having a v12 engine in a Corolla because there is only one speed tranny.

The point of the tranny is to maximize the power being used at higher speeds. I am not sure 3 or 4 speed tranny is needed. But I think Tesla originally had it right with 2-speed tranny concept. City and Highway gearing to reduce the amount of electricity needed, and reduce the EV motor size/cost too.

 

I won't ever buy another daily driver with a shifting transmission if I can help it. All my Toyota/Lexus hybrids have no shifts, the Leaf has no shifts, there is no reason for it.

 

I would rather see power-electronics switching of the stator coils from serial to parallel. Use serial at slow speed and parallel to handle high-speed.

Bob Wilson

 

I see no reason for a transmission unles you are on a race track.
Far from increasing efficiency, I suspect you will loose efficiency, increase cost, and add points of failure.

 

The Toyota and Ford transmissions can't power split the EV motors so the big MG-2 motor is effectively single speed. The original Volt does power split the EV motors at freeway speeds so the Volt's big MG-B motor can run slower. However, this feature has been traded for other gains in the 2nd generation Volt so it will be single speed in EV driving. Improvements in the new inverter and motor designs offset the loss of the EV power splitting.

 

I suspect the shift on a two speed EV would be above 60mph. It would be just there to improve efficiency on the highway, and I bet in any came to market, the driver will be able to hold the car in first gear for acceleration.

I think many of the DIY BEV conversions used donor cars with manual transmissions. An automatic would require keeping the readiator and possibly an external oil pump.

 

A clutchless, manual transmission is also possible but not necessarily needed. It has to do with back-EMF.

Bob Wilson

 

What ever they offer us the public, I would lean toward Tesla and Toyota solutions before the other guys.

 

Remember, low EV range is what prevents most from considering a BEV. A working transmission solution can increase that without the costs of a larger battery; price, weight, and size.

 

A multi speed transmission may actually drop city mpg and combined mpg, while increasing high speed acceleration and top speed. bmw i3-rex has single speed transaxle and gets 117 mpge, the leaf 114 mpge. The volt has a transmission (psd to electric motors) and gets 98 mpge. The volt is more aerodynamic than both of those cars. Electric motors in the leaf and i3 are very efficient from 0 to 70mph. Adding a multigear transmission would like cause losses that are only overcome by increased motor efficiency at high speeds.

 

I'm not sure of your point.

Between around 5 mph and 70 mph a well designed motor for a plug-in should be within 5% of its peak efficiency except at very low or high loads (low power inefficiency doesn't matter, high power acceleration is only a tiny portion of operating time). If you are taking a 3% hit in transmission efficiency it becomes difficult to overcome this loss. This applies to the motors in the leaf, tesla S, and bmw i3.

The volt's mgb's efficiency drops faster than this (perhaps less expensive or less well specified motor) and it uses 2 motors and a psd variable ratio transmission to increase efficiency at higher loads. It doesn't overcome the transmissions losses well though at least on the epa test. It only gets the mpge of the much heavier tesla S 60kwh model. At high speeds the S should be more efficient (8% lower cdA no transmission losses) than the volt. The i3-rex was tested against the volt real world highway and it beat it too, despite higher drag. In places like the bay area and LA traffic is so bad that people end up going far bellow the speed limit, and you can set your cruise at 65mph or lower for longer trips longer range when traffic isn't there. No real efficiency gain with a multi gear transmission.

The epa test is outdated and does have 55% city, 45% highway and cycles like 1940s LA. That doesn't mean these cars need anymore than the right motor and a single speed transaxle or 2 motors on 2 transaxles for iawd.

 

The Leaf and i3 are 440 to 720 pounds lighter than the Volt. Plus the Volt transmission has to accomodate an ICE along with the two motors.

This seems to imply that the Leaf efficiency is nearly half going 70mph vs. 35mph.

 

That is the thing, Tesla believed in it (rather Elon Musk believe it that he kept delaying the roadster release)... until his investors were about to kick him out before he locked his tranny.

And for those that keep saying they do not want to feel the gear shift. Elon Musk even said you do not have to shift. You can keep on whichever gear you want and it still works.

 

That is overall efficiency, it in no way shows anything about the drivetrain efficiency.
Most, if not all of that is due to air resistance increasing as speed does.

And Musk was one that didn't want a transmission.
Martin Eberhard was the founder that wanted a dual speed transmission.

It is unneeded. Adds complexity, inefficiency, and points of failure.

I'll believe it actually increases efficiency when someone puts both a simple one speed and two speed transmission in the same model EV and tests them.

 

ZF is one of the big transmission suppliers.

I didn't have any luck finding something on just the motor's efficiency, but overall efficiency what matters in the end.

My commute has about 20 miles on a 4 lane highway with a posted speed of 55mph. Most do 60+mph, like in most of the rest of the country. Yes, they could just slow down to increase efficiency and range, but we all know that the typical person won't do so, and they want farther range than what most EVs give right now for 'just in case'. I've been passed by plenty of Prii, so the majority simply isn't going to change their habits.

To get people into a BEV, they need more range and also come down in price. A transmission with a second, overdrive, gear could provide this. The 200 mile BEV for the 'masses' will arrive soon, they are still going to be over $30k and the incentives won't last forever. We will need a cheap BEV to be a daily commuter for most people, and still have enough range from the public to be comfortable enough to buy it.

Even with battery prices dropping, BEVs will still have limitations when it comes to longer trips. PHVs are an answer, but we also look into diversifying. Non-ICE range extenders, like fuel cells and Al-air batteries, will benefit from greater efficiency on the interstate. The fuel cell could be smaller and require smaller tanks. An Al-air requires a bit more than simply filling a tank after its current claimed 1000 miles are up. The longer between those, the better.

 

Yes, overall efficiency is what matters.
My point is, I don't believe any of the loss of efficiency is due to drive train efficiency, it is all due to the higher wind resistance.

So increasing the complexity of the drive train will decrease efficiency at all speeds and gain almost no efficiency at high speeds.
It will also add cost.

If you want a low cost BEV, the last thing you want to do is increase cost and cut range.

I'm not surprised a manufacturer of transmissions would SAY they have a better mousetrap.
I would be surprised if that turned out to be true anywhere but the racetrack.

 

Correct, but their products are contracted by the manufactures for existing and/or new.