EVs and gearboxes, why not?

Bug One said:
How?
Click to expand...

In simplistic terms it's the same principle as in an ICE - trying to get the motor to operate in a more efficient part of it's operating window.

Given the completely different torque and efficiency profile of a motor compared to an ICE, this wouldn't however be an exercise in trying to make the motor run at the lowest possible RPM all the time. An ICE has appalling efficiency away from it's sweet spot, whereas an electric motor won't see such an extreme drop off.

Whilst slapping a 2 speed or 3 speed gearbox on an EV now might well permit some efficiency improvements (i.e. you might be able to turn 85% at 70mph to 90%), these would be offset by the additional weight and cost - weight in particular probably ultimately resulting in not much tangible benefit to range overall, even if you can make the efficiency better. If you can't make the benefit tangible, then the added cost is somewhat pointless. So outside of applications like the Taycan which have used it more as an aid to improving acceleration /top speed numbers rather than an attempt to make the car more efficient, the cost vs benefit balance isn't really there yet but that doesn't mean it never will be.

Edit - this will also become more apparent once people start expecting more equivalent products to ICE cars - the EQS 53 for example tops out at 137mph. Whilst arguably entirely unnecessary to be going faster, eventually people will start expecting the same sort of 160mph+ (186 in the case of the AMG E Class) capability you used to get in the top spec ICE equivalents. Trying to deliver that sort of top end speed, along with low end acceleration and keeping things in the efficient operating window is going to become challenging without adding another gear.
 
Last edited:
The MG HS PHEV has a 4 speed gearbox on its electric motor, I guess because it is a small cheap motor, the EV gearbox in the HS is comically slow.

You'll notice they advertise it as 10 speed, 6 for ICE and 4 for EV motor.

The Porsche Taycan has a 2 speed box.
 
Last edited:
Yeah was going to mention the Porsche and Audi have two gears.

Tesla Model S Plaid can hit 216mhp without multiple gears though, guess they just engineered their two motors to cover the range. Has an incredibly flat power curve over 30mph. Maybe it isn't as efficient at 23k rpm, but I don't suppose anyone cares enough to want gear box complexity and weight.

Edit: I just checked some EV motor maps and basically it's all fine over around 500rpm. So sure they have poor efficiency below that, but everything else looks fine.
 
Last edited:
What’s all fine mean ?

Going from 90 to 95% efficiency at 70mph is a decent increase in range
 
Last edited:
Plaid: It’s pretty much traction limited anyway so the 3 motors just holds that torque to a much later speed, which is then higher max rpmwith the carbon wrapped rotors to deal with the load and also improve electromagnetic field. That said the rear axle layout does kind of limit you to twin motors rather than multi-speed #platform
 
Last edited:
Simon said:
What’s all fine mean ?

Going from 90 to 95% efficiency at 70mph is a decent increase in range
Click to expand...
We don't have effiency maps of Teslas motors, so we can only guess. Seems unlikely that coasting at 70mph is anything near the edge for the plaid motors though, for all we know they are peak efficiency at that point.
 
I never mentioned Teslas. You did. Along with some assumption that ‘cause telsa they are perfect at 70mph

Normal cars will be setup for optimum WLTP and hence the best range numbers. Not 200+mph

Anyway. Wet Multi speed EV motors with oil cooling are coming. Current tech are bulky dry motor technology, with water cooling so no real possibility of downsizing and improving copper fill of the motor to then add multispeed like a wet motor can.
 
Last edited:
Simon said:
I never mentioned Teslas. You did. Along with some assumption that ‘cause telsa they are perfect at 70mph

Normal cars will be setup for optimum WLTP and hence the best range numbers. Not 200+mph

Anyway. Wet Multi speed EV motors with oil cooling are coming. Current tech are bulky dry motor technology, with water cooling so no real possibility of downsizing and improving copper fill of the motor to then add multispeed like a wet motor can.
Click to expand...

Please excuse my ignorance, but model 3, Y and new S are all completely oil cooled, inside the motor. So I would suggest it's already current tech.
 
It’s a bit annoying tbh. Someone asks a question. I answer it. Then people add random thoughts/assumptions and get upset and call me a pedant for correcting them :)

Tesla use a oil cooled casing /stator rather than water/glycol. It’s not a direct cooled wet motor. They use a dexron IV ATF too
 
Last edited:
Bug One said:
Simon, you're clearly wasted with us ignorant lot.

Perhaps Tesla might appreciate your help, seeing as you seem to know more than them.
Click to expand...

To be fair I’m working on stuff like this and that doesn’t seem to matter when the power of Google and the Tesla media reports people like to lean on as some sort of professional knowledge on the subject that is then used as some sort of evidence in a perceived battle people need to “win” on a rather obscure section of a forum.

Few of the guys I work with may well help
Tesla but us UK types don’t really like 70hr weeks and next to no holidays you would then have to endure… so instead theres an ex Tesla guy I work with on the inverter design and integration.

But that doesn’t matter when we can pick up a brochure and cite what’s now as the future trends? Whilst also ignoring the last of their previous Roadster attempt that never made it to production whilst discussion the application of gears.

As mentioned the Taycan does it to balance two attributes, standing start accel and high speed. The suspension setup allows more space at the rear of the subframe to allow the large motor and gearbox to package which is where they have had time to think about the application as the knowledge of EVs grow. It’s naive to think Tesla started off perfectly with the model S to where it is today. No space for a gearbox… so
Mental tech applied to get that single speed motor to twin for initial torque and then carbon wrap etc to allow the speed.

Let’s not go around throwing shade at each other just cos we are reading stuff on the internet.

PS. That link to a job is closer to a mechanic than a design engineer.
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom