ZF: Multi-Speed Transmissions Coming Soon For Electric Cars

MAR 22 2015 BY STAFF 48

06 i8 Workshops 750x500 Multi Speed Transmissions Coming To Electric Vehicles

Multi-Speed Transmissions Coming To Electric Cars Soon

For electric vehicles, power delivery is sent to the wheels via a single-speed transmission. The new BMW i3 also uses a single-speed box to rotate the rear wheels. But according to a report by Wards Auto, a multi-speed transmission for EVs is just a few years away.

For most electric vehicles today, the 1-speed transmission is sufficient since it can handle plenty of torque. Tesla is one of the automakers that tried a 2-speed transmission, but the product wasn’t found fit. Model S uses a single-speed gearbox designed by ZF.

But the gearbox maker says that could change within five or six years.

*Editor’s Note: This post appears on BMWBLOG.  Check it out here.

Multi-Speed Transmissions Coming To Electric Cars Soon

Multi-Speed Transmissions Coming To Electric Cars Soon

In the BMW i8, the electric motor drives the front wheels via a GKN two-speed automatic gearbox which always run in first gear while in eDrive mode but switches directly to second gear in the mixed modes.

“For passenger cars, I would say we will probably eventually rise up to 3- or 4-speeds,” James Potter, controls manager for ZF Powertrain Technology, says to Wards Auto.

“Two-speeds are coming out, and that will be the next generation,” he says.

Four speeds are the maximum gears that ZF foresee for EVs.

The first benefit of more speeds for electric vehicles is an improvement in driving range by up to 20 percent.

Relative to a 1-speed, a multi-gear transmission would deliver greater efficiency on the highway and in suburban driving, says the ZF executive. But in the city, the 1- or 2-speed transmission would probably suffice.

Potter says that with batteries cost going down, he doesn’t expect a price increase of the EV overall package, and multi-speed transmission could become an option for the buyer based on his or hers driving habits.

ZF is also working on a new form of hybrid transmission with electric motor integrated which will hit the market around 2020. The evolved transmission could replace the one currently found in the 3, 7 and 7 Series BMW hybrids.

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48 Comments on "ZF: Multi-Speed Transmissions Coming Soon For Electric Cars"

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CVT ?

No way. CVT’s cannot handle anywhere near the amount of torque a good electric motor can put out.

Depends…

Mechanical CVT like those used in the ICE powertrain can’t handle it due to the belt/chain durability.

But the electric CVT used in the Voltec, or Prius or Honda system can handle the higher torque application. In fact, that is what they use to transmit torque from those monster trucks.

“CVT” can also built using a hydraulic system…

Tesla Roadster had an EPA range increase when they went from 2 speed transmission to single speed transmission.

Tesla’s d still has a single speed transmission. It has two different different motors that reach peak torque at different speeds though. Range improvement is only 1.9%, not enough to justify the additional cost and complexity of a multi-speed transmission.

Volt 2.0 also does this with the 2 motors. I am sure we will see more of this in the future.

The Tesla Roadster also had significantly better reliability when they got rid of the transmission and went to a reduction gear.

That’s why I love my EV: It’s simple. Keep your stupid transmissions out of my car please.

More complexity and cost? Sign me up!

I’d rather just spend whatever the increased cost of the transmission is on more/better batteries.

This. I have a hard time believing that the added performance & efficiency you get will be worth the added cost & complexity.

Transmissions are complicated mechanical things that will eventually break. If you can do without them, that would seem the better way to go.

Cost-wise, it may be more expensive and would certainly be a bit more complex. However, a multi-speed transmission could potentially give a 20% range boost in a much smaller package than just adding more batteries. You basically would get more bang for your buck. And we’re only talking about 2 to 4 speeds, not the crazy 6,7, or 8 speed multi-clutched transmissions that the OEMs are developing and building now.

this article is evidence of the cleverness of the engineering of the chevrolet Volt. GM has already anticipated this development. the Volt uses a planetary gearset in which the ring gear can be counterspun using a second motor/ICE such that the electric traction motor can operate in its most efficient RPM range. the planetary gearset of the Volt makes such a multispeed transmission, as described in this article, unnecessary.

unfortunately, too many people, it seems, see a “BMW” nameplate on a car and find it hard to believe that a car with a “Chevrolet” nameplate could be better engineered than one with a “BMW” nameplate.

Good Point!

+1

Does it really surprise anyone that a gearbox maker thinks that EVs should have a transmission? In the two wheeled EV world Brammo bet on a transmission and lost.

be that as it may, this is only good news. EVs will need transmissions in the high end market to satisfy drivers who drive fast. Think autobahn. Think track days. Think electric racecars and supercars.

A transmission will unlock the potential to have EV’s that can climb rapidly beyond the 100 mph mark without losing most of their efficiency.

Tesla didn’t get multi-speed transmissions to work because it’s not there yet.

Once the technology is suitable, it WILL be a range increase, as you’ll be able to run your motor at a higher efficiency at, say, highway speeds. As it currently stands the peak efficiency of these electric motors tapers off rapidly at highway speeds; even a 10% efficiency loss means you’re travelling the same distance on more battery.

You’ll get a bigger range increase on the highway by better optimizing aerodynamics. Many of the current crop of EVs have terrible aerodynamics (Volt and Tesla excepted). The problem is that current car buyers like the taller, easier-to-enter vehicles. They just happen to be aerodynamically inefficient.

Improving aerodynamics doesn’t reduce an EV’s reliability like adding a transmission does. Give me better aero any day.

I see highway speeds increasing with technologies such as autopilot. Texas already has a toll road with 85 mph speed limits and on I-95 south of Richmond the flow of traffic is around 80 mph. From what I understand diesels are popular on the Autobahn because they allow cars to travel at high speeds for longer distances between fill ups. So if EVs are going to compete they must get more efficient at speeds over 75 mph.

Gene,

Traffic on I-95 south of Richmond is generally only about 70 MPH, 75 MPH max. That is because that area is one of the biggest speed traps on the east coast. Have been on that road many, many times and it is very rare not to see VA State Police or the locals (primarily Emporia) with someone pulled over. Would not recommend running 80 MPH until you get to the NC border.

“transmission will unlock the potential to have EV’s that can climb rapidly beyond the 100 mph mark without losing most of their efficiency.”

Well that is great if you are building an EV race car. But for a consumer vehicle? It seems like a really stupid idea.

I’m intrigued by this because of the potential (hopefully) to increase efficiency at higher speed. One thing about EVs is how much speed affects range past ~60mph. I never noticed that in my previous ICE cars, at least not to the extent that it affects my Volt. IOW, it’s not just aerodynamics, me think. By the way, the funny thing is that it seems to be the opposite for acceleration, where a lead foot has relatively less impact on range.

No, you’ve just never noticed it in an ICE because of the relatively large fuel supply. ICEs don’t get nearly their advertised MPG when you drive them at 80 mph everywhere. The reason.. aerodynamics (same as EV).

I agree with Dan (and the article). The Volt1 suffers range loss more quickly on the highway, than mpg’s tend to go down.

More gears may bring more HP/Torque to the higher speeds, improving roll-on acceleration. I agree with “keep it simple”, but believe fun-factor currently suffers. It isn’t absolutely all about efficiency, for everyone.

Have your ICE cars ever reported instantaneous fuel consumption statistics, or just averages since your last trip-meter reset?

Dr. Miguelito Loveless

Of course, this means more complexity, more weight and more things to break. Also, how solid is the “20%” claim?

20% is way too much. AFAIK, the difference between peak efficiency and average efficiency of modern single-speed EVs is not more than 5-10%. In terms of efficiency, all multi-speed transmission can do is to help motor work closer to peak efficiency all the time.

Improved performance could be more significant advantage of multi-speed transmission.

With all the engineering brains behind the Formula E cars, they use a 5 speed transmission. Must be some advantage sacrifice the simplicity of a one speed drivetrain? Especially in carbon fiber race cars where weight and reliability is crucial.

Or they could just be doing it for the cool sound they make when they shift down for corners. Because that’s what fans expect.

With all the engineering brains behind the Formula E cars, they use a 5 speed transmission. Must be some advantage for them to sacrifice the simplicity of a one speed drivetrain? Especially in carbon fiber race cars where weight and reliability is crucial.

The first mainstream bicycles were called “Ordinaries”, or Penny Farthings. They relied on the size of their front wheel, for how fast they could go. People started racing these things. Wheels got bigger and bigger, as riders sought to increase speed.

Eventually, there was a physical limit to making a single wheel so big, the bike could not be mounted nor peddled optimally due to its weight. The safety bike was created and multiple gears were later used to more efficiently power the rear wheel. Clearly, having multiple gear ratios for the same human powerplant, actually works wonders.

Electric cars are still at the Penny Farthing stage, essentially relying on a single gear ratio to attain speed, because it’s easier, less costly and currently more reliable not to implement it.

That does not mean these qualities are eternal and static. Eventually, the cost will drop, they’ll be easy to add to EV drivetrains, and good engineering and design will conquer the reliability issues with high torque wear and tear.

But what is a good idea in race cars (where money is no object and high-speed performance is critical) may be a really bad idea in consumer cars (where money is critical and high-speed performance is not needed).

I bet you would have choosen faster horses….

Variable pole motors would be better then multi gear transmissions that would then need a clutch as well.

They would not need a clutch as the do not idle. Upshfting and dwonshifting does not require a clutch, it ust required the motor to recue its torque input to zero for a moment. That can be done via the electronic motor control. It even works with gas engines, like the race shifter in the BMW S1000R bike.

More moving parts, more bearings to fail, more to maintain, higher weight, higher cost.

Looks like a solution in search of a problem.

Not necessarily higher weight or cost, if multi-speed transmission allows same performance with smaller and cheaper motor.

Multi-speed tarnsmission has benefits, but further development of motor technology could make it obsolete. Time will tell.

Agree – who wants or need the greater complexity for parts to fail.

Here’s a tip design a multi speed in wheel motor ZF – that is the real future and engineering challenge.

Adding extra speeds… sorry that is so yester year engineering approach.

I will never buy an EV with multiple gears. Point.

Hmmm, a few days ago on the Volt forum someone asked how hte Volt would compare to his Mazda 3 hatch in terms of “hot hatch” fun to drive factor. He asked specifically about the loss of his manual transmission. My reply as it relates to “automatics” and the “one speed transmission”: One thing folks have trouble understanding is how the “slow” 0-60 time of cars like the Focus EV, Leaf, and Volt relates in real world driving. I describe it like this. The VAST majority of cars on hte road these days have automatic transmissions so let’s look at their driving characteristics. When you are taking off from a stop you are either headed straight or about to make a turn onto another road. If someone is in front of you, they typically take off slowly and then accelerate (whether in a straight line or after you have rounded the turn). You are behind them and take off slowly as well. Today’s automatics are set to upshift as quickly as possible to achieve the desired EPA mileage figures. So what happens is the car is quickly in second or third gear (maybe even fourth) by the time you want… Read more »

You all may be interested in the discussion of this topic on ES.

http://endless-sphere.com/forums/viewtopic.php?f=7&t=67112

One of the participants is an engineer at Zero Motorcycles. He makes the point that the new Honda Accord hybrid has gotten rid of the transmission altogether. It has better EPA mileage than either the comparable Toyota Camry hybrid, or the Toyota Prius V.

Honda says it’s e-CVT, when it in fact isn’t any kind of CVT. Very odd. In reality it’s almost simplest possible form of hybrid transmission (excluding pure series). ICE is either disconnect from final drive with clutch (series mode) or connected with fixed ratio reduction gear (parallel mode). It’s a little wonder that this set up hasn’t been used before.

*sigh*… So many blind BEV purist here that just can’t see the bigger picture. The multi-speed transmission is NOT designed to lower performance or efficiency. For a fact, it is designed to increase efficiency and performance. Single speed transmission has its limitation. With the awesome power of the Model S and its superior battery voltage, it still can’t reach the 170mph or 200 mph top speed where it should be able to with its low Cd and power. Why? B/c it is single speed transmission. Sure, you can argue that you don’t need it. But that is NOT the point of discussion here. The discussion is about the tradeoff. Telsa traded top speed and hwy efficiency with its low end performance. In order to get that awesome 0-60mph times, it geared the darn thing to 9.74:1. So, by the time 43mph rolls around, the motor reached its max torque. By the time 71mph rolls around, it reached max hp. So, if you cruise at 75mph, the efficiency of the electric motor and gearbox in the Tesla would be much worse than if it was operated at a much lower RPM. You can’t get around the magnetic saturation of the electric… Read more »

No one needs 250 km/h top speed on a public road.
If you want to speed, build a dedicated racing car and go on a private track.

Why do we need more top speed than 90mph then?

It is about bragging right. That is where it sells cars in that price range.

Also, efficiency also matters, you can have even higher efficiency when the motor is geared at higher ratio instead of the ultra low ratio which will reduce wear and tears in the gear box.

Higher rpm single speed gearset isn’t necessarily more durable than a lower rpm dual speed gearbox when everything else are the same.

Lots of variability here.

I don’t see anything more than a 2 speed gearbox helping anything other than the smallest electric motor.

A 4 speed gearbox might be necessary/desirable for a drivetrain where it had a gas engine ‘helper’, and the gearbox was more for the engine than the motor.

I have much to say, but I think I’ll hold my tongue..

Teslas in my opinion could have increased reliability and better overall performance with the single reduction by choosing a larger, somewhat heavier, slower motor in the first place. Then there would be no frequency concerns, nor overheating concerns, nor huge efficiency penalty at high speed since there would not really BE a high speed.

Nobody needs to go faster than 25 mph. Nature will sort this all out within the lifetime of today’s kids. Sorry kids, we were “exceptional.”