Multi-gear EVs are probably the future

[Mattias]

No gearing required.

Makes more sense to drive the gearing down, thus giving the engine more top speed. This isn't an ICE, and there is more than plenty of torque available from rest. To compensate for the lost acceleration the manufacturers will just increase the engines output, cooling is a non issue if you design them right. In industrial applications there are engine running at the near MW level continuously for years on end without problems. As the batteries get larger capacities, we can afford drain higher and higher currents from them without the risking damage to the battery. The P85D for example, is most likely limited to it's acceleration by it's battery, not the electric motors.

Thus future battery development will offset the need for a gearbox. It's just not needed.

Also remember that the engines are more efficient at higher loads, so this would also aid the range, both at low and high speeds.

 

[scaesare]

I'm 94.83% sure it's going to be much less expensive to design the (already-necessary) motor to operate at the RPM range you want, and design the (already-necessary) inverter to supply the necessary power.

Once IGBT's became available to handle the electrical power necessary, it's what allowed them to eliminate the gearbox in the roadster by allowing the inverter to simply supply enough power that the motor could provide the torque/RPM to operate with a single gear.

Adding a multi-gear transmission is going to add to the cost/complexity, not reduce it.

 

[JRP3]

Adding a multi-gear transmission is going to add to the cost/complexity, not reduce it.

Exactly, which is why it won't show up in less expensive vehicles, but could have a place in high performance cars and trucks.

 

[Skotty]

If EVs are the future, I think eventually you will see performance EVs with gearboxes. Probably both automatic and also manual for those that like to row their own gears. There will probably be fewer gears though, probably no more than 4, and likely only 2 or 3. This would have the added benefit of calming down good ole boys who are either offended by the idea of vehicles without transmissions or insist on having a manual transmission. I have to admit myself, if I have the choice, I always go for the manual gearbox. Shifting myself, for me, is just a better driving experience. I know most of you reading this probably go the other way on that though.

 

[FlasherZ]

If EVs are the future, I think eventually you will see performance EVs with gearboxes. Probably both automatic and also manual for those that like to row their own gears. There will probably be fewer gears though, probably no more than 4, and likely only 2 or 3. This would have the added benefit of calming down good ole boys who are either offended by the idea of vehicles without transmissions or insist on having a manual transmission. I have to admit myself, if I have the choice, I always go for the manual gearbox. Shifting myself, for me, is just a better driving experience. I know most of you reading this probably go the other way on that though.

Speaking from a marketing point of view, the performance segment is the only one where this tends to be the norm, and even then the minds are being changed. The reason people like to jam gears? They simply were forced to in the past, and there's a bit of a reputation attached to it (I admit to loving the 4-speed Muncie with Hurst shifter in my '65 Pontiac GTO). Shifting still addresses that performance aspect that just isn't possible in a clutched automatic gearbox: managing the peak power points for your own needs. But what happens when you combine an EV motor with a multi-speed automatic gearbox? The need for managing the peak power points largely goes away: so now is it just a nostalgia thing?

I hate having to remember to turn off the headlights in that same GTO. I hate having to use the key to lock my Mustang each time I get out of the car (65/66 Mustangs can't be locked using the inside knob - closing the door just unlocks it automatically). Fun for nostalgia, a blast to drive, but eventually the convenience wins out - let me step out of my car and the lights automatically turn off and the doors lock when I walk away.

It's getting more difficult to find manual gearboxes, except for the enthusiasts. And even then, the car manufacturers are concluding that it's a dying segment and leaving it for the enthusiasts:

Understanding What's Really Killing the Manual Transmission

I wouldn't be surprised if we saw performance EV's with gearboxes, but I think they're limited-run at best.

 

[ScepticMatt]

If EVs are the future, I think eventually you will see performance EVs with gearboxes.

With a given gear ratio the higher the power output the higher a car is going to be traction limited. So you can get away with taller gearing for higher top-speed performance without reducing low-speed performance (without slicks).

As an extreme example, the 1500 hp Koenigsegg Regera can reach 249 mph without gearbox
just two drive trains that work at different speed ranges like what Tesla is speculated doing with their D versions.

 

[thegruf]

per the thread title - No. Gearbox not for me the right way to go.
Mechanical simplicity is one of Tesla's strongest usp's. the cost/weight/complexity/difficulty in obtaining seamless shifts all = wrong direction.

These are road cars, worldwide speed limits are iro 130km/h or 80mph, except for Germany and even there it is only a limited set of roads.
Sure they can strip and track but that's just for a fun sideshow and doesnt sell cars in all honesty.

Tesla right on the money imho at the moment.
Steadily increase battery density, improve charge times and the cars technology and extend the model range is the stongest offering.
Licensing their drivetrain tech to another major automotive manufacturer could also be a possibility (my vote would be Jaguar - the brand is fresh enough these days and the company is definitely full of imagination, would work well and present a sufficiently distinct offer to Tesla so as not to conflict)

 

[Danal]

per the thread title - No. Gearbox not for me the right way to go.
Mechanical simplicity is one of Tesla's strongest usp's. the cost/weight/complexity/difficulty in obtaining seamless shifts all = wrong direction.

These are road cars, worldwide speed limits are iro 130km/h or 80mph, except for Germany and even there it is only a limited set of roads.
Sure they can strip and track but that's just for a fun sideshow and doesnt sell cars in all honesty.

Tesla right on the money imho at the moment.
Steadily increase battery density, improve charge times and the cars technology and extend the model range is the stongest offering.
Licensing their drivetrain tech to another major automotive manufacturer could also be a possibility (my vote would be Jaguar - the brand is fresh enough these days and the company is definitely full of imagination, would work well and present a sufficiently distinct offer to Tesla so as not to conflict)

Agreed.

 

[rabar10]

Mod note: A dozen or so posts were split off into their own thread.

Regen limiting -- capacity, temperature, etc.

 

[thegruf]

well I did try to bring it back to the title

 

[TEG]

I'm a big fan of the single-speed gearbox that Tesla and other vehicles have. But, costs will have to be cut. Manufacturing a motor to run at over 15,000RPM is expensive as the rotor requires improved balancing and cooling. A lower-cost design would have a two-speed manual gearbox with a less powerful, slower, cheaper motor. The first speed would cover almost all vehicle speeds up to 70mph improving 0-60 acceleration further. The second speed would cover speeds up to 155mph or beyond, as necessary...

I don't think 'balancing' the motor and the higher RPM really causes much in the way of higher costs. In any case, cheaper mass market cars could be offered with lower top speed or slower acceleration as necessary. Also, keep in mind that all other production EVs on the market right now (including the relatively cheap ones) are just using a single speed gearbox too.

 

[thegruf]

I don't think 'balancing' the motor and the higher RPM really causes much in the way of higher costs...

Agreed - it is the engineering and design strength required to stop the motor flying apart at those rotational speeds.

 

[Danal]

I'm going to bet on the opposite: No gear electric drive trains.

The one fixed gear ratio that exists indicates the Torque/RPM curves are not where they need them to be for the driveshaft to the wheel. I'm willing to bet we will see the development of torquier, lower RPM motors that can be direct. Get the expense, efficiency loss, and maintenance of even that one gear, get that out of the drivetrain.

This is what has happened on Radio Control Aircraft, with so called "outrunner" motors. A few years ago, gears (single ratio) were common on electric airplanes, and/or some very cheap ones used direct drive at horrible efficiency points. Now, direct drive is about the only thing you see, via the development of proper torque at the RPM where the propeller is 'happy'.

 

[Johan]

I'm going to bet on the opposite: No gear electric drive trains.

The one fixed gear ratio that exists indicates the Torque/RPM curves are not where they need them to be for the driveshaft to the wheel. I'm willing to bet we will see the development of torquier, lower RPM motors that can be direct. Get the expense, efficiency loss, and maintenance of even that one gear, get that out of the drivetrain.

This is what has happened on Radio Control Aircraft, with so called "outrunner" motors. A few years ago, gears (single ratio) were common on electric airplanes, and/or some very cheap ones used direct drive at horrible efficiency points. Now, direct drive is about the only thing you see, via the development of proper torque at the RPM where the propeller is 'happy'.

Good observation. The current gearing ratio of 9.something:1 tells the motors will need to develop a lot though before this can occur in a full sized car.

 

[Robert.Boston]

I agree with Danal. Take a look at the wind turbine business: the big commercial units (1.5 MW+) from top manufacturers are increasingly direct-drive, eliminating an important wear and maintenance component.

 

[dhanson865]

I'm a big fan of the single-speed gearbox that Tesla and other vehicles have.
[snip]
Thoughts? I doubt Tesla will do this for Model 3 as they'd like to keep complexity down. But perhaps we'll see this for even further cost reduced models.

Someone brought this thread back. The OP posted in 2013 when the Model S was still a single gear car.

Now in 2015 we have a different situation in that the majority of the Model S cars sold have dual motors and each motor has a different gear ratio. Effefictively 9x% of the Model S cars sold in 2015 are two gear setups.

S70D - 2 gear
S85 - 1 gear
S85D - 2 gear
P85D - 2 gear

and the holdout S85 is hidden in the ordering process so most people have to ask how to order it.

So my question is: Isn't the dual motor setup enough to settle the desire for more gear ratios or do some of us still want 3 or more gear ratios in play?

 

[JRP3]

I'm going to bet on the opposite: No gear electric drive trains.

The one fixed gear ratio that exists indicates the Torque/RPM curves are not where they need them to be for the driveshaft to the wheel. I'm willing to bet we will see the development of torquier, lower RPM motors that can be direct. Get the expense, efficiency loss, and maintenance of even that one gear, get that out of the drivetrain.

So how will they make up for the loss of that 9.73 torque multiplier? 9.73 times the current? 9.73 times the motor diameter? Direct drive may work for wind turbines and propellers where start up torque isn't important but I'm not so sure about vehicle motors.

 

[Danal]

So how will they make up for the loss of that 9.73 torque multiplier? 9.73 times the current? 9.73 times the motor diameter? Direct drive may work for wind turbines and propellers where start up torque isn't important but I'm not so sure about vehicle motors.

The max torque point of an electric motor is 0 RPM. If it has run torque, it has start torque in excess. As proven by our various 0-to-60 times.

How will motor designers get run torque with direct drive? Not sure. That's why I'm typing this instead of flying my private jet (which is where I'd be if I'd been first with the RC model motors that can direct drive a prop, aka "Outrunner" motors. ).

 

[JRP3]

The max torque point of an electric motor is 0 RPM. If it has run torque, it has start torque in excess. As proven by our various 0-to-60 times.

Which were only achieved using a 9.73:1 gear ratio to multiply that torque. Chevy Spark is a prime example, their motor puts out 400 ft/lbs of torque, but since they used a higher gear ratio, (lower numeric), for increase efficiency the 0-60 times are 7.5 seconds, which isn't bad, but a small car with 400 ft/lbs of torque should do much better.

How will motor designers get run torque with direct drive? Not sure.

I explained it, higher current and/or larger diameter motors. There is a reason no wheel motors or direct drive motors have ever been successful in cars. For turning a prop power is more important than torque, and power is torque x RPM, so a prop can build up RPM before it ever starts to move a plane. As you know props need to reach a certain RPM before a plane starts to move, cars need to start moving from 1 RPM.

 

[bxr140]

The current gearing ratio of 9.something:1 tells the motors will need to develop a lot though before this can occur in a full sized car.

More importantly I think is the differential 'problem'. It stands to reason that the technology will advance to the point where the propulsion motor in an EV could be direct drive, but you'd then need a motor per wheel to manage the differential wheel speeds. Very feasible of course, but a second motor on the same axle increases the overall complexity that one is otherwise trying to drive down by implementing direct drive.

An interesting potential solution is an integrated dual-ish DD motor, where you have only one unit that has mostly one set of components and is thus mostly one motor (as opposed to two motors bolted together), but it doesn't push its power through a traditional-ish mechanical differential like the model S does now.