Why don’t electric cars have gears? Car reviews praise the torque at zero revs but also say they tend to run out of puff as speed increases. Seems to me torque at zero revs would be perfect for multiplying speed via a gearbox, and the motor wouldn’t need as much battery power?
Seems to be not done, so there is probably a good reason, so why not?
AwesomeO said:
Why don’t electric cars have gears? Car reviews praise the torque at zero revs but also say they tend to run out of puff as speed increases. Seems to me torque at zero revs would be perfect for multiplying speed via a gearbox, and the motor wouldn’t need as much battery power?Seems to be not done, so there is probably a good reason, so why not?
I’d say weight, they would lose a lot of their advantage maybe?
AwesomeO said:
Why don’t electric cars have gears? Car reviews praise the torque at zero revs but also say they tend to run out of puff as speed increases. Seems to me torque at zero revs would be perfect for multiplying speed via a gearbox, and the motor wouldn’t need as much battery power?Seems to be not done, so there is probably a good reason, so why not?
By having lots of torque at zero to low speeds and then having it drop off as the speed builds up is very similar to a typical petrol/diesel engine with gears. So because the electric motor behaves like that there’s no need for a gearbox.
Some petrol engines can do clever tricks like changing the valve timing and/or lift to improve power at high revs without sacrificing good power at low revs, but you can also easily do that with an electric motor by likewise changing the timing of the fields as the rpms change.
You’d probably do that if you were building a racing electric car, but for ordinary road vehicles it probably isn’t necessary. Yes, the torque drops off with higher speeds but at those speeds the car is normally going into cruise anyway so doesn’t need a big burst of acceleration.
Spiny Norman said:
AwesomeO said:
Why don’t electric cars have gears? Car reviews praise the torque at zero revs but also say they tend to run out of puff as speed increases. Seems to me torque at zero revs would be perfect for multiplying speed via a gearbox, and the motor wouldn’t need as much battery power?Seems to be not done, so there is probably a good reason, so why not?
By having lots of torque at zero to low speeds and then having it drop off as the speed builds up is very similar to a typical petrol/diesel engine with gears. So because the electric motor behaves like that there’s no need for a gearbox.
Some petrol engines can do clever tricks like changing the valve timing and/or lift to improve power at high revs without sacrificing good power at low revs, but you can also easily do that with an electric motor by likewise changing the timing of the fields as the rpms change.
Well no, not typical, in the reviews of the Tesla in multi car tests they show the initial surge beating ICE cars but then they claw it back, I would think a gearbox would assist that. It would or should also increase range whereas high speed in a battery car depletes the battery very quickly, but with high torque at zero you could have the motor not working as hard at high speed.
AwesomeO said:
Spiny Norman said:
AwesomeO said:
Why don’t electric cars have gears? Car reviews praise the torque at zero revs but also say they tend to run out of puff as speed increases. Seems to me torque at zero revs would be perfect for multiplying speed via a gearbox, and the motor wouldn’t need as much battery power?Seems to be not done, so there is probably a good reason, so why not?
By having lots of torque at zero to low speeds and then having it drop off as the speed builds up is very similar to a typical petrol/diesel engine with gears. So because the electric motor behaves like that there’s no need for a gearbox.
Some petrol engines can do clever tricks like changing the valve timing and/or lift to improve power at high revs without sacrificing good power at low revs, but you can also easily do that with an electric motor by likewise changing the timing of the fields as the rpms change.Well no, not typical, in the reviews of the Tesla in multi car tests they show the initial surge beating ICE cars but then they claw it back, I would think a gearbox would assist that. It would or should also increase range whereas high speed in a battery car depletes the battery very quickly, but with high torque at zero you could have the motor not working as hard at high speed.
An electric car has the disadvantage of having to drag around a lot of heavy batteries. A petrol car doesn’t. An advantage of electric cars is that they can control the power at the wheels far more accurately and faster than a petrol car can, hence they get off the line better. Also, for a given road speed a petrol car has the variables of engine revs & gears. You need to be in the right gear to minimise the fuel consumption and that’s usually the highest gear that you can use; not always though. With an electric car the power needed is, like a petrol car, the amount to combat aero drag, mechanical drag, and tyre friction, etc. The different is that the electric car, not matter what revs it’s doing, can always tailor the power requirement to be a minimum.
Also take a look at the upcoming Tesla Roadster. It’s reported as being able to do an 8.9 1/4 mile, 0 – 60 mph in 1.9 seconds, and a top speed of around 400 km/h. It’s also supposed to have a good 1,000 km range. Name me one road-legal petrol car that can do all those things.
Also take a look at the upcoming Tesla Roadster. It’s reported as being able to do an 8.9 1/4 mile, 0 – 60 mph in 1.9 seconds, and a top speed of around 400 km/h. It’s also supposed to have a good 1,000 km range. Name me one road-legal petrol car that can do all those things.
Reported from any car manufacturer on a developing car is fantasy figures. I can see a 1000 km range, and the 400 kmh, it’s just a matter of batteries, what I can’t see is the two together.
AwesomeO said:
Reported from any car manufacturer on a developing car is fantasy figures. I can see a 1000 km range, and the 400 kmh, it’s just a matter of batteries, what I can’t see is the two together.
Tesla has been pretty reliable so far on performance figures for their upcoming cars. So yeah it may not quite be as fast as that, but it’ll still be massively faster than any other petrol car for some time to come.
AwesomeO said:
Also take a look at the upcoming Tesla Roadster. It’s reported as being able to do an 8.9 1/4 mile, 0 – 60 mph in 1.9 seconds, and a top speed of around 400 km/h. It’s also supposed to have a good 1,000 km range. Name me one road-legal petrol car that can do all those things.Reported from any car manufacturer on a developing car is fantasy figures. I can see a 1000 km range, and the 400 kmh, it’s just a matter of batteries, what I can’t see is the two together.
…and with Tesla the fantasy level is quite high.
Spiny Norman said:
AwesomeO said:
Reported from any car manufacturer on a developing car is fantasy figures. I can see a 1000 km range, and the 400 kmh, it’s just a matter of batteries, what I can’t see is the two together.
Tesla has been pretty reliable so far on performance figures for their upcoming cars. So yeah it may not quite be as fast as that, but it’ll still be massively faster than any other petrol car for some time to come.
Every single real world road test of an electric car remarks that if you use the available performance you can’t use the available range, sometimes drastically so, which is why I said I can see the two, but not both together.
party_pants said:
…but for ordinary road vehicles it probably isn’t necessary. Yes, the torque drops off with higher speeds but at those speeds the car is normally going into cruise anyway so doesn’t need a big burst of acceleration.
Probably the best reason given so far, but what about range? Gears not so much for maintaining high speed but for increased range?
AwesomeO said:
party_pants said:
…but for ordinary road vehicles it probably isn’t necessary. Yes, the torque drops off with higher speeds but at those speeds the car is normally going into cruise anyway so doesn’t need a big burst of acceleration.
Probably the best reason given so far, but what about range? Gears not so much for maintaining high speed but for increased range?
I assume that reducing the revs in an electric motor at cruising speed does not increase the efficiency, otherwise they would do it.
So trucks coming down the range, they use the gearbox to come down slowly.
They don’t use the brakes because they’d have none left by the time they got to the bottom.
AwesomeO said:
Every single real world road test of an electric car remarks that if you use the available performance you can’t use the available range, sometimes drastically so, which is why I said I can see the two, but not both together.
So if you thrash an electric car it won’t go as far as it would if you drove economically? How is that different to a petrol car? An example being a car I had a few years back. With the engine management system it had I could log the injector duty cycle. Cruising steadily at 100 km/h the injectors would be running at 8% duty cycle. At full power they’d be running at 62%. If I drove the car economically I could get about 600 km from it. Based on the full-power figures I’d only get about 77 km from it.
So how is that surprising?
Peak Warming Man said:
So trucks coming down the range, they use the gearbox to come down slowly.
They don’t use the brakes because they’d have none left by the time they got to the bottom.
And electric trucks will not only use engine braking, they also re-charge the battery at the same time.
AwesomeO said:
party_pants said:
…but for ordinary road vehicles it probably isn’t necessary. Yes, the torque drops off with higher speeds but at those speeds the car is normally going into cruise anyway so doesn’t need a big burst of acceleration.
Probably the best reason given so far, but what about range? Gears not so much for maintaining high speed but for increased range?
I am not sure it would make much difference. In order to move car a certain distance at a certain speed it takes a certain amount of energy, which people far cleverer than can work out with a pen and paper. That is the energy required, doing it in a different gear in an electric car is not really going to make much difference in my way of thinking, you can’t save energy by going to a different gear.
Spiny Norman said:
AwesomeO said:
Every single real world road test of an electric car remarks that if you use the available performance you can’t use the available range, sometimes drastically so, which is why I said I can see the two, but not both together.
So if you thrash an electric car it won’t go as far as it would if you drove economically? How is that different to a petrol car? An example being a car I had a few years back. With the engine management system it had I could log the injector duty cycle. Cruising steadily at 100 km/h the injectors would be running at 8% duty cycle. At full power they’d be running at 62%. If I drove the car economically I could get about 600 km from it. Based on the full-power figures I’d only get about 77 km from it.
So how is that surprising?
I didn’t say it was different, I said you can’t have both.
AwesomeO said:
party_pants said:
…but for ordinary road vehicles it probably isn’t necessary. Yes, the torque drops off with higher speeds but at those speeds the car is normally going into cruise anyway so doesn’t need a big burst of acceleration.
Probably the best reason given so far, but what about range? Gears not so much for maintaining high speed but for increased range?
I don’t know enough about electric motors to comment on that but I’d suspect that they would only use as much power as they need to for that constant speed. In a petrol car you typically have a shorter range below about 80 km/h or so, then up past about 100 km/h it starts to decrease again. There’s usually a fairly small rev range where the engine works best to minimise fuel burn and that again varies with speed; Get too far from that sweet spot and the range starts to decrease. I’d be guess that it’d be far less critical for an electric car as no matter what the engine speed it’s only going to use the minimum amount of electrical power to do that.
AwesomeO said:
Spiny Norman said:
AwesomeO said:
Every single real world road test of an electric car remarks that if you use the available performance you can’t use the available range, sometimes drastically so, which is why I said I can see the two, but not both together.
So if you thrash an electric car it won’t go as far as it would if you drove economically? How is that different to a petrol car? An example being a car I had a few years back. With the engine management system it had I could log the injector duty cycle. Cruising steadily at 100 km/h the injectors would be running at 8% duty cycle. At full power they’d be running at 62%. If I drove the car economically I could get about 600 km from it. Based on the full-power figures I’d only get about 77 km from it.
So how is that surprising?
I didn’t say it was different, I said you can’t have both.
You mostly can with an electric car. Unlike a petrol car where the engine is the engine and the gearbox is the gearbox, in an electric car the batteries are the engine and the motor is the gearbox. So with something like the Tesla Sportster it has a huge battery pack which give it a very long range. But if you choose to give it a thrash you’ll go through the battery reserves much faster and hence reduce the range. Nothing surprising about that.
Bear in mind also that having a gearbox in an electric car means having to lug extra weight around. If the performance difference in having gears on an electric car was marginal to begin with, adding the extra weight might make it even more marginal.
Then factor in the economic side of things in the added manufacturing cost of building and installing gearboxes in the production line then it is easy to see the accountants saying “nah fuck it, if we can manage without a gearbox we will do it” for economic reasons, and giving orders to the engineers who might have wanted one for technical purity.
party_pants said:
Bear in mind also that having a gearbox in an electric car means having to lug extra weight around. If the performance difference in having gears on an electric car was marginal to begin with, adding the extra weight might make it even more marginal.
Then factor in the economic side of things in the added manufacturing cost of building and installing gearboxes in the production line then it is easy to see the accountants saying “nah fuck it, if we can manage without a gearbox we will do it” for economic reasons, and giving orders to the engineers who might have wanted one for technical purity.
Yeah, I can agree with that, if the gain is marginal not worth it. Plus you lose the marketing gimmick of having only 3 moving parts in the engine.
Some electric vehicles have two or four wheel hub motors, mounted inside the wheel. This means no transmission problems.
https://en.wikipedia.org/wiki/Wheel_hub_motor#Concept_cars
When that’s the case, gears are impossible.
mollwollfumble said:
Some electric vehicles have two or four wheel hub motors, mounted inside the wheel. This means no transmission problems.
https://en.wikipedia.org/wiki/Wheel_hub_motor#Concept_carsWhen that’s the case, gears are impossible.
Not quite, it’s still possible. The Massive Mercedes Unimog has a set of gears in the ends of the axles, used to increase torque at the wheels. You could also use an epicyclic system built into the wheel hub, and that would give you two gear ratios, by locking/unlocking the planetary gears.
mollwollfumble said:
Some electric vehicles have two or four wheel hub motors, mounted inside the wheel. This means no transmission problems.
https://en.wikipedia.org/wiki/Wheel_hub_motor#Concept_carsWhen that’s the case, gears are impossible.
It could get messy if your front left wheel computer got hacked by the Russians and your back right wheel computer got hacked by the Chinese and your spare wheel got hacked by a Cornish separatist collective.
gears lose power, even when you add oil for lubrication, in fact it takes energy to move and squeeze oil, and there’s the added complexity, there has to be ways to make electric cars cheap, that’s sort of the idea, like modest complexity. Takes energy to make a gearbox too.
transition said:
gears lose power, even when you add oil for lubrication, in fact it takes energy to move and squeeze oil, and there’s the added complexity, there has to be ways to make electric cars cheap, that’s sort of the idea, like modest complexity. Takes energy to make a gearbox too.
of course there’s the weight of gears/gearbox, they wear out too. Something else to break.
https://www.osti.gov/servlets/purl/5529813
3.4 ELECTRIC CONTINUOUSLY VARIABLE TRANSMISSIONS
https://ieeexplore.ieee.org/document/1658340/
https://www.ugent.be/ea/eemmecs/en/research/eelab/drivesystems/electrical-variable-transmission
https://teslamotorsclub.com/tmc/threads/cvts-for-electric-vehicles.9982/
https://www.quora.com/How-come-there-are-no-electric-CVT-cars-Wouldn-t-it-be-advantageous-since-it-can-keep-the-electric-motors-within-the-power-and-torque-band-while-keeping-the-amps-low
AwesomeO said:
Why don’t electric cars have gears? Car reviews praise the torque at zero revs but also say they tend to run out of puff as speed increases. Seems to me torque at zero revs would be perfect for multiplying speed via a gearbox, and the motor wouldn’t need as much battery power?Seems to be not done, so there is probably a good reason, so why not?
amateur electric vehicles can have an electric vehicle bolted onto the transmission and you treat the vehicle as a normal vehicle – you can change gears etc – given the strength of the motor though you can leave the car in 5th gear and it will take off just as strongly as in first – electric motors can create tremendous torque instantly.
modern electric vehicles leave the gears/ transmission out mainly to weight – a motor controller using PWM can accelerate the vehicle as fast or slow as you like. when you decelerate regenerative braking uses the motion of the vehicle to generate power back into the battery.
the battery power thats forecast to be used is clearly not that hard to muster on any EV designed to cover any decent range.