Why Don't Electric Cars Have Multi-Gear Transmissions?

[JatoTheRipper]

People on this site often ask about 2-speed transmissions in their RC vehicle. Most often people tell them to avoid the extra complexity and weight and stick with a single speed.

This is a good read. It's about 1:1 vehicles, but it would be applicable to RC as well.

Most electric cars have a single gear ratio. You probably understand the basic reasons for this, but the math is still super fascinating.

One of the biggest differences between electric cars and their conventional counterparts has to do with the drivetrain. An internal combustion vehicle has a multi-speed gearbox with numerous ratios; nearly every electric car has a single-speed transmission.

Implicitly, this makes sense. An electric motor delivers its maximum torque at zero RPM. Unlike an internal combustion engine, it doesn't need a system to disconnect it from the drivetrain to allow it to idle while the vehicle is stopped. But there's a more in-depth explanation to be had here, and it's fascinating.

Electric motors have a much larger RPM range than the typical internal combustion engine. And unlike a gas or diesel engine, an electric motor makes its best power output over an incredibly broad RPM range. So instead of packing the car with numerous gears to keep the engine in its happy zone, designers of electric cars just pick a gear ratio that provides a good compromise between acceleration and top speed. And with the typical electric motor capable of sustaining 20,000 RPM, the top speed often isn't even a limiting factor.

There's more that goes into this, too—delightful math and delicious graphics. And Jason Fenske of YouTube's Engineering Explained is here to go into the nerdy details like you've never had it explained to you before.

<iframe width="560" height="315" src="https://www.youtube.com/embed/36H9BVeMYMI" frameborder="0" allowfullscreen></iframe>

Source: Why Don't Electric Cars Have Multi-Gear Transmissions?

 

[Corrupt]

I don't know about other people on this site, but I think 2 speed transmissions still hold value to some in the RC crawling world. Trailing is a good example of it, where you might want the taller gear to avoid having to hold throttle wide open on flat parts of the trail, whereas the lower speed gives you more finesse over the rough, rocky parts of the trail. Is it ideal for everyone - no - but I have seen people use it and like it on their trail rigs. I personally don't use 2 speed transmissions, but I see the appeal.

-Corrupt

 

[OSRC]

I run several rigs with a 2 speed - your reasoning is spot on. Plus, it's fun to shift - adds a dynamic element to driving.

 

[DavidH]

If you have high enough motor rpms, and high enough voltage batteries, you can get away without shifitng gears in an ev - but, as detailed in the video, there are advantages to multi-gear transmissions. Tesla tried to put two-speeds in their earlier cars.

https://www.autoblog.com/2008/01/23/breaking-tesla-has-a-solution-for-their-transmission-woes-get/

Fortunately, the axial 2-speed transmissions have proven to be reliable.

And we may see more of them in 1:1 EVs.

"Gasoline cars currently have something electrics don't: a [multi-gear] gearbox. This may be about to change though, as the advantage of having a choice of gears is simply too great for electric carmakers to ignore."

Multi-Speed Gearboxes Are Coming to EVs | PluginCars.com


ZF: Multi-Speed Transmissions Coming Soon For Electric Cars

 

[JatoTheRipper]

I run several rigs with a 2 speed - your reasoning is spot on. Plus, it's fun to shift - adds a dynamic element to driving.

This is the only reason I'd try a 2 speed - just another button to push and play with on the trail.

 

[Ditchrat]

This is the only reason I'd try a 2 speed - just another button to push and play with on the trail.

I would assume a high speed used correctly would result in less battery consumption.

 

[hpiguy]

I have the AX2 two speed in my Wraith and really like it. The only downside is the cost of replacement parts for it. If you have a high HP setup, it chews up the internal gears much faster than I think it should, and the early ones had isses snapping some of the gear shafts as well.

 

[OSRC]

If you have a high HP setup, you don't really need a 2 speed. Although shifting is fun...

I run 2S on all my rigs, so the 2 speed gives great low end torque, and then wheelspeed when needed. For the most part, I run in low over obstacles and in technical sections, then shift into high for cruising along the trail, usually at 1/3 throttle or so. Saves a ton of battery.

I would think the same principle would work in a 1:1. Torque needs at highway speeds are far less than when accelerating. A simple transmission of some kind makes sense.

 

[EeePee]

A CVT type to keep it at peak efficiency. I win.

 

[clm]

Any motor/engine will have an area in their power curve where their output is most efficient, gearboxes are designed to try to keep the power plant running in this efficient area to maximize their fuel/electricity and keep things from overheating.

 

[EeePee]

Yes and a CVT will keep it at that exact number RPM whilst a multi geared transmission cannot. They're trying to though with these recent 8 speeds. Trying to be all Formula 1 like.

 

[JatoTheRipper]

CVTs are relatively weak and inefficient.

 

[hpiguy]

CVTs are relatively weak and inefficient.

Weak and inefficient how? I have seen zero data to back this up. Matter of fact, CVT equipped cars almost always post higher average MPG than thier manual transmission equipped counterpart.

Unless you're talking about high HP applications, of which there are clearly better designed transmissions out there for that job.

 

[JatoTheRipper]

Weak and inefficient how? I have seen zero data to back this up. Unless you're talking about high HP applications, of which there are clearly better designed transmissions out there for that job.

Yes, exactly. In higher HP applications. A high power electric motor would most likely destroy CVTs.

Nissan uses CVTs in some of their vehicles. But CVTs aren't as efficient as manual transmissions.

 

[EeePee]

https://en.m.wikipedia.org/wiki/List_of_automobiles_with_continuously_variable_transmissions

 

[hpiguy]

Neither are automatics, or DSG or anything else, and they never will be as efficient as a manual transmission from a pure engineering standpoint. The CVT was never designed for go fast stuff, quite the contrary. Lots of manufacturers use them with varying success these days. If you haven't driven a new car with a well designed CVT, they've came a long way since Nissan started using them 10 or so years ago. For the record, Subie has one of the best reliability records on their CVTs, and I love mine for a daily driver.

 

[ElChupacabra]

I can't stand driving my wife's Honda Insight with CVT. It makes me insane. It just sits at 4500 RPM all the time and it has zero punch or passing power. I plan my passes on the highway with a calendar. I'm mostly against owning an electric car and definitely against driving a CVT daily. I just need motor sounds and the ability to shift when I want, how I want.

 

[Ninomaniac]

Calendar

FWIW I drove a BMW 118d with an 8 speed auto the other day and it sucks donkey balls. It has a sport+ mode in which it sucks donkey balls too, but louder and less fuel efficient.

 

[hpiguy]

I can't stand driving my wife's Honda Insight with CVT. It makes me insane. It just sits at 4500 RPM all the time and it has zero punch or passing power. I plan my passes on the highway with a calendar. I'm mostly against owning an electric car and definitely against driving a CVT daily. I just need motor sounds and the ability to shift when I want, how I want.

They aren't all setup that way. My car behaves that way below 1/2 throttle, keeps you in the happy spot torque wise, and gets awesome mileage. Above 1/2 throttle, it runs through 6 gear changes up to redline just like a standard auto. Or throw it in M mode and use the paddle shifters if you want. Paddles also have overide in any mode, handy here in the mountains for gearing down on long steep descents. I get they aren't for everyone, but not all of them suck.

 

[JatoTheRipper]

https://en.m.wikipedia.org/wiki/List_of_automobiles_with_continuously_variable_tra nsmissions

Wow. I knew more than Nissan used CVTs, but I hadn't realized they became that popular. But notice how that list is mostly tiny engines.

Neither are automatics, or DSG or anything else, and they never will be as efficient as a manual transmission from a pure engineering standpoint. The CVT was never designed for go fast stuff, quite the contrary. Lots of manufacturers use them with varying success these days. If you haven't driven a new car with a well designed CVT, they've came a long way since Nissan started using them 10 or so years ago. For the record, Subie has one of the best reliability records on their CVTs, and I love mine for a daily driver.

I've driven old and new Nissan CVTs. I can't stand them. I specifically ruled out the Nissan Juke when I realized it had a CVT trans.

If I want a CVT I'll get a snowmobile.

I can't stand driving my wife's Honda Insight with CVT. It makes me insane. It just sits at 4500 RPM all the time and it has zero punch or passing power. I plan my passes on the highway with a calendar. I'm mostly against owning an electric car and definitely against driving a CVT daily. I just need motor sounds and the ability to shift when I want, how I want.

"thumbsup"