The Nitty Gritty On Why Electric Cars Only Have 1 Gear (Update) – Videos

SEP 5 2017 BY DOMENICK YONEY 38

One gear or some gears.

It’s an argument that has raged among EV fans and engineers for some time and shows few signs of abating. Even when videos, such as the one above, (bias alert*) lays it all out quite nicely why a single gear is preferred.

Videos: the first episode of a five-part series looking at the issue (above), which just goes to demonstrate it’s not as straight forward as some might think.  The second episode has just been released, and asks the question, “Could Electric Cars Have A Manual Transmission? You can check it out in all its geeky goodness below.

All joking aside, there are times when a multi-speed gearbox, i.e. a transmission, makes perfectly good sense, and the video above from Engineering Explained mentions some of them: the motor is smallish, and so doesn’t produce lots of torque; the motor has a low maximum rpm, etc.

For most use cases, a single speed motors works quite fine, and that’s what you’ll find in just about every purchasable electric vehicle today. The Nissan Leaf? Check. Every Tesla ever (aside from the first few Roadsters, which had a 2-speed transmission that was deemed too fragile for that drivetrain and was replaced) Check. Every model from Zero Motorcycles? Check.

To answer the question of why this is, and using the Formula E paddock as a back drop, the Engineering Explained folks employ some math and fancy graphics to make their point: unlike internal combustion engines (ICE), electric motors are high revving, can produce lots of torque at low RPMs, and have a flat, long torque curve. So, no need to make up for shortcomings using mechanical torque multipliers (a transmission) like an ICE does.

 

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38 Comments on "The Nitty Gritty On Why Electric Cars Only Have 1 Gear (Update) – Videos"

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That could be an effective marketing strategy. “Imagine never having to pay for a transmission rebuild again”.

That doesn’t mean it is reliable… Just far less complex which “correlates” to the possibility of higher reliability.

Far less complex, because it is a reduction gear only. No shifting gears, no moving (just rotating) parts, no torque converter.

Unless it’s poorly built, a single-speed reduction gear will be more reliable.

“Unless it is poorly built”..

Well, there is that reason that trumps complexity..

I think that with most modern cars, the transmission will never have to be rebuilt.

That’s like saying, “Avoid the theatre and you’ll never get the bubonic plague.” In reality, bubonic plague is also very rare.

Both manual and automatic transmissions eventually need the transmission fluid replaced. Every 30K miles or every 60K miles, depending.

It is obvious…

Typical ICE only has usable rpm band of 2,500rpm to about 5,500 rpm (yes it can go higher but often they aren’t used outside that range). That is ONLY 3,000rpm wide band.

Typical Electric Motors can go between 0rpm to 12,000rpm. That is 4x as wide as typical ICE band.

So, a 1 speed is easily replacing at least 4 speed transmission which is what all the older ICE had/need for a long time. (Modern high speed transmissions are only needed for fuel efficiency and top speed).

If EVs want more efficiency as well as higher top speed, then it would need about 2-3 gears AT MOST EVER (as formula E has shown). A 2 speed gear box is probably more than sufficient for most EVs out there.

Putting a 2 speed gear box into cars like the Bolt, LEAF, eGolf or Spark EV, they can easily go 130mph instead of their 90mph ish top speed.

“Spark EV, they can easily go 130mph instead of their 90mph ish top speed.”

It looks like you did the homework! 🙂

SparkEV will achieve about 130 MPH with gearing optimized for top speed. eGolf and Leaf may not get there due to lower power and more drag (more area). Bolt could hit much more; I haven’t done the math, but I’d guess about 150 MPH for Bolt.

Yes, I think if it has right gearing and right tires, it can do that.

With a 2 speed, it can do both.

One limitation for a BEV running at sustained high speed is the battery pack overheating due to such high power output. I certainly can’t speak to how that affects all BEVs, but the Tesla Model S can’t sustain a run at 125 MPH for more than ~12 minutes. Or at least, older Model S’s can’t. I understand Tesla’s 100 kWh battery packs have improved cooling systems, so perhaps those could support that speed longer without overheating.

“One limitation for a BEV running at sustained high speed is the battery pack overheating due to such high power output.”

That sounds like an improperly designed battery pack rather than the battery pack itself.

In fact, I think the issues are more likely to be the motors and motor drives than the battery since the motor is super dense energy device that even with 10% loss can result in huge heat build up.

Either way, it isn’t a limitation to all BEVs but rather a particular design. Formula E doesn’t have this problem, do they?

“no need to make up for shortcomings using mechanical torque multipliers”

If you want acceleration, you need gears. Gassers have multiple gears instead of just two, because they want better acceleration. For EV, we deem the acceleration “good enough” and efficiency is more important (more range) so we don’t use multiple gears.

For example, if SparkEV has 3 speed gearbox where one is optimized for 0-30 MPH, another for 0-60 MPH, another factory stock, it would achieve 0-30 in about 1.5 seconds, 0-60 in 6.5 sec, and still maintain 119 MPGe. Scroll down to “Tangent thoughts: more gears” in this blog post for explanation.

http://sparkev.blogspot.com/2016/06/sparkev-performance-analysis.html

I am not sure what you mean when you say you need gears for acceleration. What you need is adequate torque to accelerate. This is proven countless times on you tube as various ICE cars up to 500kw (and better) are defeated by a Tesla P100D. In various drag racing classes two-speed powerglide transmissions regularly beat manual transmission competitors as well as >2 speed automatics.

Transmissions, torque converters and final drive (differential) gears all serve to multiply the torque generated by the ICE; engines with narrow torque curves benefit from more gear ratios. Notably in the most extreme classes, TF and FC, a controlled-slip clutch coupled directly to the differential conveys the torque from the ICE which revs to around 9,000 RPM.

you need proper gearing ratio for that instant torque to the wheel. yes. E-motor has broader curves, but it still NEEDS TO geared to be 10:1 as in (Model S P85) to achieve that acceleration.

That 10:1 gearing ratio isn’t good for efficiency at 75mph.

So a second gearing of 5:1 would be great for hwy cruising efficiency or higher top speed but won’t be good for 0-60mph.

Basically it seems like we could use two gears then. One for efficiency at speed, and one for acceleration. Of course there’s the question of whether the extra weight and complexity are worth the benefits.

Yes, 2 gears are more than sufficient for most “non-racing” related application.

It is almost an overdrive setting. Once you are cruising at hwy speed, up shift by 1 gear which can easily lower the RPM by 2x or any amount it needs to “center” the efficiency of the EV at 70mph around its “sweet spot”.

Of course, driver can also shift down in local/city driving to maximize performance.

Yes, complexity will increase and so will cost. But for those people who “value” the option of both would easily pay for it.

Formula E only uses up to 3 gears at most anyway…

I miss shifting about as much as I miss rewinding VCR tapes and dropping off film to be developed. I also don’t miss servicing my transmission or having it fail, like it did on my 90’s Chrysler minivan.

Technology offers some wonderful improvements and the lack of a transmission in an EV is definitely one of them.

The Detroit electric will have standard a 4 speed manual transmission.

This guy is spending an inordinate length of time explaining why EV’s have only 1 gear.

Except many of the plug-in hybrids which run in total electric mode on the battery and take advantage of differing reductions.

One thing he has not addressed – presumably since he doesn’t know about it, is the INEFFICIENCY of an EV with only one gear.

Hint: It happens both at low and high speeds, suggesting the need for a 3 speed transmission.

Bill – great minds think alike – you posted just ahead of me:)

An efficient planetary CVT could be useful. The efficiency of the motor is poor when it uses lots of current to start from a stop or accelerate hard.

Planetary gearset is very compact but it does has more loss than simple offset gearing.

That loss could be made up with less pack stress and longer range.

PHEV electric drive trains like the Gen 2 Volt have used a “trick” to optimize motor efficiency at various speeds through different gearing for each motor. They use two motors designed for different RPM/torque “sweet spots”, incorporated via the planetary gearing to blend their power. Either motor can become the “main” driver at different vehicle speed ranges, with power-sharing at the mid-range. No conventional “shifting”, but the software uses the ability to speed-match before “shifting for zero-slip clutching and de-clutching.

This technique is used now for just PHEV drivetrains, which must also blend ICE power to the drive line, but I would expect in the future that as the desire for top-end speeds increases, in dragsters or road racers, power-blended multi-motor/multi-geared drive trains conceptually similar to the Volt will find their niche.

It is a typical engineering trade off between efficiency, cost and performance to decide whether it needs 1 gear or multiple gears (2-3).

Electric motor’s far wider operating band gives engineer a much wider working rpm range to optimize the car for cost and low complexity without sacrificing too much efficiency and performance.

That is why the original Tesla P85 was geared to reach max torque at 43mph and max power at 71mph.

If it had another gear, it could do that and still increase the efficiency with higher ratio at hwy cruising speed without sacrificing the low end acceleration.

But complexity and “typical use case” also shows that “need” is less thus Tesla decides against that.

But when will the VTECH kick in, yo?

From 0 RPM! 🙂

I think they (Tesla) should use a different differential.
“The ATB differential has many benefits over a standard open differential, including maximizing traction and minimizing wheel-spin, eliminating torque steer and snatching in front wheel drive cars compared to conventional LSD units, and a maintenance-free design which retains the standard oil lubrication.” evtv

Fact: It’s less safe to text and drive with a manual transmission… 😀

Theory: It is far less likely for anyone to text and driving while driving a manual transmission. In fact, driving transmission requires far more involved which would likely reduce driving distraction.

Invention of Automatic transmission, cruise control….now autopilot allows or encourages people to drive with more distractions!

Based on my own decades of driving experience, driving a stick shift by preference, I think that’s more than just a theory. I’d say there is some pretty good evidence that those driving a manual transmission won’t be texting on their phones as much as those driving an automatic transmission!

I always have driven a manual since my ’70 Saab. Always working the shifter on short trips.

“I think that’s more than just a theory. I’d say there is some pretty good evidence that those driving a manual transmission won’t be texting on their phones as much as those driving an automatic transmission!”

I think Consumer Report has shared similar “views”. They explained that driving manual requires the driver to pay attentions to the road which requires one to pre-plan for downshifting and upshifting that leads the driver to be less distracted.

With that said, I do know one person in my high school who was capable of driving a manual with his knee shifting and eating a hamburger at the same time. But he did still pay attention to the road though.

“Every Tesla ever (aside from the first few Roadsters, which had a 2-speed transmission that was deemed too fragile for that drivetrain and was replaced) Check.”

Those few Roadsters with the 1.0 drivetrain which were actually delivered, were locked into 2nd gear because the transmission couldn’t handle the strain of repeated gear shifts. And this was after Tesla rejected the first 2-speed transmission delivered by a supplier, and had another made for them by a second supplier. In the end, Tesla just beefed up the motor and eliminated the transmission.

So far as I know, no other EV maker has tried to build a production BEV with a multi-speed transmission. Contrariwise, the Formula E race cars started out with 5-speed transmissions in the first year, but have been eliminating gears since then. I think someone said last year’s top Formula E champion used a car with a single gear, but other cars in the competition are still using multiple gears.

” I think someone said last year’s top Formula E champion used a car with a single gear, but other cars in the competition are still using multiple gears.”

The winner of the Formula E was a single gear car but I believe the best lap time record holder was a 3-speed geared car.

Also, I think Detroit Electric is working on multi-speed transmission.

At the end, it is about weighing the trade off between efficiency/performance and simplicity/cost. Often “cost” wins.

In racing, cost isn’t nearly as big deal as performance/efficiency (fixed sized battery).

There are already EV’s with two gear ratios. There are AWD Tesla’s use different gear ratio’s and motors in front and back. That effectively makes them function much like a virtual CVT transmission, through delivering power at any ratio to front and back.

My guess is that the long-term solution for effectively having 2 gears will be matching different motors and different final drive ratio’s front and back. At some point it will simply be cheaper to stick in a second motor than it is to add a multi-speed transmission that can handle the instant torque banging in the gear change. The added benefit being zero shift lag.

“EVs.. have a flat, long torque curve.” They don’t. A Drag Times chart, showing torque over speed, for the P100D was referenced on Clean Technica: https://cleantechnica.com/2017/02/22/tesla-model-s-p100d-torque-stuns-drag-times-dyno-test/ EV torque curves aren’t flat. That’s why we frequently say “all available, at zero mph”. Torque then goes down. P100D supplies more than the rest of the car can handle, delaying the same effect until you’re already at most speed limits, while keeping above 500lbs until you get past ~90mph. -Gargantuan, to even have 500lbs all the way to this speed, but certainly not the 850+lbs you had all the way past 50mph. So, I think the article is flawed in that most EVs feature the same, highly spiked, torque chart with the spike happening sooner, and the effect felt much more as speeds increase. Yes, an ICE is even more spiked if allowed only one gear, but is that the point here? Posting two days afterward doesn’t help, but I think what Inside EVs needs is to drop complexity, stop talking about torque and horsepower, and instead show a table of elapsed time to speed. Vertically show 0-30, to 60, to 90, to 120, etc., and then provide the elapsed times to these… Read more »