It has in some form but I believe it's only very recently got to a stage where it's energy density has been good enough to start making them viable for cars
Going Electric.. present small car options.. confusing
- Thread starter varesecrazy
- Start date
Currently reading:
Going Electric.. present small car options.. confusing
It has in some form but I believe it's only very recently got to a stage where it's energy density has been good enough to start making them viable for cars
- Joined
- Mar 1, 2014
- Messages
- 4,579
- Points
- 828
I see! I don't think it's used in consumer electronics either atm.
It just wouldn't, at high speed it's aerodynamic drag that is killing the range not the speed of the motor. An electric motor can spin to many many thousand rpm and not lose efficiency, but a gearbox will add drive train losses that weren't there before.
The Porsche Taycan is 2 speed but 1st is only used for launch control otherwise it's in the higher gear at all times.
Last edited:
- Joined
- Mar 1, 2014
- Messages
- 4,579
- Points
- 828
I see! I stand corrected.
2 speed is about as far as its got..
( some of that is to aid regeneration )
( some of that is to aid regeneration )
An electric motor has a constant power torque throughout the Rev range, therefore if you have a 500hp electric motor theoretically it has the full 500hp available no matter if you’re doing 2rpm or 2000rpm,
An internal combustion engine only has its power in a narrow band on a power/torque curve and so we fit a gearbox to keep the revs of the engine in that power band which is why if you try to drive up a hill in a high gear the car might slowdown or even stall because it doesn’t have the power, change into a lower gear and the engine can then tackle the hill. Not a problem for an electric motor it will pull up the hill no matter.
Basically an electric car doesn’t need a gear box.
As pointed out above you need to put energy into something to make it move so if you need 1000 joules to push a car forward at 30mph then you change gear, you still need 1000 joules to move the car forward, you’re just now in a different gear. So if you fitted a gearbox to an electric car to travel at a higher speed it would not reduce the amount of energy needed to keep the car moving so high or low gearing it’s still going to need the same amount of battery power.
Fitting a high gear ratio to an electric motor is not really any different to driving up a hill so fit a gear box to an electric car and you might actually need more energy and battery power to keep the car moving at the same speed.
Logically if you could just fit a higher gear without any costs we’d just be fitting more and more gears to a car to make it go faster and faster, we can’t do that because you’ll only get out what you put in and a gearbox doesn’t change that.
An internal combustion engine only has its power in a narrow band on a power/torque curve and so we fit a gearbox to keep the revs of the engine in that power band which is why if you try to drive up a hill in a high gear the car might slowdown or even stall because it doesn’t have the power, change into a lower gear and the engine can then tackle the hill. Not a problem for an electric motor it will pull up the hill no matter.
Basically an electric car doesn’t need a gear box.
As pointed out above you need to put energy into something to make it move so if you need 1000 joules to push a car forward at 30mph then you change gear, you still need 1000 joules to move the car forward, you’re just now in a different gear. So if you fitted a gearbox to an electric car to travel at a higher speed it would not reduce the amount of energy needed to keep the car moving so high or low gearing it’s still going to need the same amount of battery power.
Fitting a high gear ratio to an electric motor is not really any different to driving up a hill so fit a gear box to an electric car and you might actually need more energy and battery power to keep the car moving at the same speed.
Logically if you could just fit a higher gear without any costs we’d just be fitting more and more gears to a car to make it go faster and faster, we can’t do that because you’ll only get out what you put in and a gearbox doesn’t change that.
Power and Torque are very different engineering terms.
Torque is a measurement of how hard the shaft is being rotated in that time interval.
Torque = Force at the end of a lever x how long the lever is.
So you need torque on a wheel to overcome friction, and to accelate the mass of the car overall. At constant speeds you need torque to overcome drag or climb a hill.
Power is a measure of rate of energy delivery.
Power = Torque x Speed (with a factor for whatever units you want)
Units include Horse power or KW.
So a car with constant power output slows down going up a hill as it has to reduce speed for more torque to overcome gravity.
To properly understand an engine you need to know its torque delivery vs speed curve.
A petrol engine has a minimum speed of say 750 RPM or it will stall. So you need a slipping clutch to allow the gearbox to bring the drive shaft and wheels up to a no slip speed for a car at standstill.
Your acceleration is limited by clutch slip. Then by engine torque until you hit a torque drop off at high engine revs, so you have to change gear. Car engines deliver little useful above 3000 Rpm. Diesels will stay between 1500 and 2000 RPM for best service ( busses and lorries) needing several gears.
An engine might spin up to a high speed with a nominal torque delivery and therefore calculate to a high power but that is frankly useless. Peak torque at any speed is little more than the rated, they are easy to stall.
An electric motor also has a rated power, that being calculated at a max speed where it can deliver a continuous torque rating.
The continuous torque rating is available from standstill.
More than that, it can deliver a peak torque (for short periods) if it stays within the overall power rating.
Typically this is 3x the continuous torque rating.
So an electric motor can accelerate the car from zero very aggressively with a high torque. It will continue to accelerate until rated power is reached, whereby the car would be at max speed. As a motor can reach a few thousand RPM without screaming like a piston engine no clutch or gearbox is required.
Torque is a measurement of how hard the shaft is being rotated in that time interval.
Torque = Force at the end of a lever x how long the lever is.
So you need torque on a wheel to overcome friction, and to accelate the mass of the car overall. At constant speeds you need torque to overcome drag or climb a hill.
Power is a measure of rate of energy delivery.
Power = Torque x Speed (with a factor for whatever units you want)
Units include Horse power or KW.
So a car with constant power output slows down going up a hill as it has to reduce speed for more torque to overcome gravity.
To properly understand an engine you need to know its torque delivery vs speed curve.
A petrol engine has a minimum speed of say 750 RPM or it will stall. So you need a slipping clutch to allow the gearbox to bring the drive shaft and wheels up to a no slip speed for a car at standstill.
Your acceleration is limited by clutch slip. Then by engine torque until you hit a torque drop off at high engine revs, so you have to change gear. Car engines deliver little useful above 3000 Rpm. Diesels will stay between 1500 and 2000 RPM for best service ( busses and lorries) needing several gears.
An engine might spin up to a high speed with a nominal torque delivery and therefore calculate to a high power but that is frankly useless. Peak torque at any speed is little more than the rated, they are easy to stall.
An electric motor also has a rated power, that being calculated at a max speed where it can deliver a continuous torque rating.
The continuous torque rating is available from standstill.
More than that, it can deliver a peak torque (for short periods) if it stays within the overall power rating.
Typically this is 3x the continuous torque rating.
So an electric motor can accelerate the car from zero very aggressively with a high torque. It will continue to accelerate until rated power is reached, whereby the car would be at max speed. As a motor can reach a few thousand RPM without screaming like a piston engine no clutch or gearbox is required.
This is kind or relevant and does affect motorway range but the added weight/complexity almost outweighs the pros, also EVs are expensive and adding more R&D to the costs to create a 2 speed gearbox that the computer controls will only make an already expensive car more expensive.
Not entirely true, my Ampera has a sort of gearbox to engage the ICE when the batteries are depleted or when you ask it to so you can reserve your battery for later use, obviously this is far from a traditional gearbox and more a series of clutches but it does add significantly more efficiency to the electric motor at the cost of much more complexity.
The car has 2 electric motors, one is the primary drive motor and the other motor acts as the generator for the ICE but can also drive the car (as motors can act as generators or motors depending on which way the current is going)
When you're accelerating on purely electric the 111kW primary motor accelerates you through one fixed ratio to the limited top speed of 100mph where the motor is at around ~8500rpm iirc, this is not as efficient as running the electric motor at a lower RPM even discounting wind resistance etc
Given my car has the second motor generator, when cruising at a set speed the car clutches in the secondary motor and reduces the rpm of the primary motor instead using both motors at a low RPM (something like 3000rpm at 70mph). As a result the Ampera is capable of very high efficiency when operating at a constant speed despite being a very heavy car lugging around an ICE and fuel tank etc. 4.5mi/kWh is achievable in good weather in an Ampera which is very impressive and it is down to this dual motor low rpm setup.
It adds a lot of complexity and only really made sense to implement on the Ampera because it already needed that second motor/generator for the range extender to work but it does prove a lower RPM motor is more efficient than high RPM, don't ask me the technicalities because I don't understand exactly how. I will also point out to avoid confusion this is all without the ICE running, adding the ICE into the mix changes all of this considerably given you are then using two fuel sources.
There is a video the explains the above much better if interested.
Obviously the volt is a lot more complicated than a straightforward battery electric vehicle. But if I’m understanding that video correctly the limitations of the volt drive motor is that it can only propel the car up to 70mph, using one gear, then if you want to push faster than that a series of clutches and a new gear ratio switch in the generator that can be used in reverse as a drive motor and due to the design of the generator has more power at lower revs so a different gear ratio is used when running with the generator, and the motor also switches in to provide yet more power.
If the battery is dead then the engine needs to be running and then connected to the generator to provide power to the motor, I assume in this configuration the car would be limited to 70mph max speed.
This isn’t really what’s being talked about above and while it’s clearly quite a clever solution to the limitations of the motor, it’s not necessary on a BEV that has a motor capable of +100mph without the engine and generator.
My understanding was that most single speeds dont Regen brake at 100mph..
They let drag ..and / Or footpressure for the speed to tail of.. with the Regen kicking in from 70 mph down
If the motor is 'geared' then it can potentially get better refinement whilst still giving better range.
Im sure the only EV I can justify buying wont have such 'luxuries'
Travelling back for work last night.. My Diesel punto was slowly overhauling a Zoe
It was doing @63 mph.. then started gaining on me down hill perhaps the late 20's driver was using the 'econometer'
That was basically my cruising speed too
Anyhow.. 2 things amused me:
The car looked a Beige colour.. odd ..as nobody pays extra for paint on these..
It WAS white.. and had scrawls of a Horseshoe magnet and ..ahem..Jennytaylor in the masculine form
Then 1/2 an hour later it came flying past me at 80+..
Perhaps he needed to reach his destination before Lighting.up Time
It was doing @63 mph.. then started gaining on me down hill perhaps the late 20's driver was using the 'econometer'
That was basically my cruising speed too
Anyhow.. 2 things amused me:
The car looked a Beige colour.. odd ..as nobody pays extra for paint on these..
It WAS white.. and had scrawls of a Horseshoe magnet and ..ahem..Jennytaylor in the masculine form
Then 1/2 an hour later it came flying past me at 80+..
Perhaps he needed to reach his destination before Lighting.up Time
Last edited:
I’m not talking at all about regen braking, if you go see the video the generator on the volt flips and becomes an extra motor above 70mph because the main motor can’t push the car beyond that speed.
I don’t know the ins and outs of what limitations in BEV regen systems, but you could build a motor that would regen at higher speeds realistically if the motor can push the car that fast then it can cope with the energy of a higher speed regen, but you’d probably have a much better idea of what is and isn’t than I do
My understanding of the situation is, electric motors produce less torque the faster they are spinning so you need pick a gear ratio that produces enough torque to overcome air and rolling resistance and mass at your desired top speed.
In general they pick a low gear as 0-30 and 0-60 is more useful than being able to do a speed you cannot legally reach anywhere except Germany.
I'd imagine this is why alot of them do 90ish as very few places have speed limits in excess of 80mph.
Top speed of petrol car is a byproduct of the need for it not to be screaming at 70mph and horribly inefficient...electric cars don't have either of these issues.
You could have a 2 speed box or more to bring it back into the more torque heavy band of the motor at higher speeds but unless you want to accelerate hard (like the Porsche) and have a high top speed (again like the Porsche) it is not required.
In general they pick a low gear as 0-30 and 0-60 is more useful than being able to do a speed you cannot legally reach anywhere except Germany.
I'd imagine this is why alot of them do 90ish as very few places have speed limits in excess of 80mph.
Top speed of petrol car is a byproduct of the need for it not to be screaming at 70mph and horribly inefficient...electric cars don't have either of these issues.
You could have a 2 speed box or more to bring it back into the more torque heavy band of the motor at higher speeds but unless you want to accelerate hard (like the Porsche) and have a high top speed (again like the Porsche) it is not required.
No you have misunderstood, the 100mph is achieved using 1 motor. It has nothing to do with limitations of either motor, they are identical aside from one being used as a generator when you are using power from the ICE.
It is purely for energy saving reasons, at a constant speed two motors at a lower RPM is more efficient than 1 at high RPM. It adds plenty of complexity and doesn't make sense to do this in a typical BEV but I am making a point that electric motors are more efficient in certain RPM bands and a 2 speed EV could in theory save energy but the complexity outweighs the gains.
- Joined
- Sep 14, 2009
- Messages
- 19,492
- Points
- 3,294
Most EVs use permanent magnet motors requiring rare earth elements (neodymium, etc). This company has a multi pole a.c. motor that does not use rare earth magnets and presumably has less cogging effects.https://www.telegraph.co.uk/business/2021/03/28/british-firm-cracks-electric-car-motor-conundrum/ These could be used as brakes by feeding power against the direction of rotation. I'm not sure if that would be a regeneration or a load.
The idea of multi pole a.c. motors with variable speed drives goes back to the late 1970s when Class 58 railways locos began hauling coal trains. For coal unloading, the train had to move at 1/2 mph pretty much stalled. The diesel was going full load for around 30 minutes. The multipole motors and variable frequency speed controllers could handle the extreme currents of turning so slowly.
That was 40 years ago so hopefully these new motors will be on to something.
The idea of multi pole a.c. motors with variable speed drives goes back to the late 1970s when Class 58 railways locos began hauling coal trains. For coal unloading, the train had to move at 1/2 mph pretty much stalled. The diesel was going full load for around 30 minutes. The multipole motors and variable frequency speed controllers could handle the extreme currents of turning so slowly.
That was 40 years ago so hopefully these new motors will be on to something.
Last edited:
The Video shows at 70mph motor 1 has reached full RPM, therefore to go above this speed the generator is linked in presumably at a different gear ratio to the first motor as the generator achieves higher speeds at lower RPM, and the 1st motor is then linked by clutches to the the generator. Meaning that both motor and generator (operating as a motor) are providing drive to the wheels at a lower RPM.
The implication of this is there is not enough power in the one motor to achieve 100mph on its own as that configuration does not appear in the video and they state in single motor mode that the motor is operating at full RPM when it reaches 70mph.
This is how the video explains it.
Above 70 mph the two motors work together to achieve the higher speed either powered from the battery or if needed the engine kicks in for more power.
I'm guessing that having a motor that will power the car up to 70mph then a second motor to go above that speed means that the single motor is more battery efficent than if you had one massive motor trying to push a car along at 30mph,
No different to a 5litre V8 using more fuel than a little 1 litre 4 cylinder for plodding around town.
This is more akin to a V8 that turns off half its cylinders when at low speeds.
However if i've got that wrong i'd be interested to see some other info you've got some links because the video is not brilliantly clear.
Other way round, an electric motor produces all of its torque from near 0 RPM all the way up to the maximum electrical load of the motor.
EVs need to have a motor that is able to get the car moving from a stand still but then able to take that car all the way up to full speed, and they can do that very well because where as a car might sit at 2000rpm on a cruise, the motor can easily achieve 13,000-16,000 rpm
Say you have a car with a normal engine that at 1500 RPM in first gear can achieve 15km/h with a 10:1 ratio between the engine and the wheels.
Then at 15,000 RPM you'll get 150km/h which is about 93mph. The motor will have the same amount of torque at 1500 rpm as it does at 15,000 RPM there will come a point where the motor can't carry any more electricity and at that point the torque drops off dramatically therefore the an electric motor tends to hit a wall.
This is why electric cars tend to be able to accelerate at ridiculous velocity, but then will stop at about 100ish mph or for something like a tesla 130mph
So this is why electric cars don't need gears, what something like they taycan has is probably a lower gear ratio for quicker starts and performance and a higher (normal) gear ratio for normal driving.
as most cars don't need to do sub 2 second 0-60s, the majority of electric cars will never need a gearbox.
There is going to be a 200mph version of the tesla model s and I suspect that will use some sort of gearbox to keep the low speed 0-60 of under 2 seconds and then be able to continue up to 200mph, with a higher gear ratio than it currently has for the speed and a new low ratio for still remaining as quick off the mark.
nothing new about them, the reluctance motor (which these are) have been around nearly 200 years. its one of the earliest forms of electric motors.
The only thing they have done in this instance is to refine the electronics needed to drive them to make them suitable for automotive use. But in other articles you'll see they are only currently suitable for trucks and lorries because they still lack the refinement for use in cars.
The latest model 3 Tesla uses a type of magnet assisted reluctance motor.
The cogging you mentioned I'm going to say is much worse in a reluctance motor because of what's called torque ripple as the motor rotates, its basically a big stepper motor with less poles than a stepper motor, its this torque ripple that makes refinement of these motors more difficult.
Obviously progress is good and being able to do away with permanent magnets in a motor would save cost but I notice you've posted this article in multiple places on the forum and honestly progress is good but this isn't something to get that excited about.
The bars on the RHS are just for demonstration purposes and do not reflect the actual maximum RPM of the motor. If you had driven one you would know this, there is a very noticeable delay (1-2seconds) whilst it switches in and out of series mode, this would be extremely inconvenient if it happened every time you accelerated beyond 70mph because acceleration would completely pause.
If you're travelling at 70mph and the car has switched to series mode, when you plant your foot there is the aforementioned pause whilst it comes out of series mode, often you lose 1mph of speed whilst it does this before the car will start accelerating as only fairly gradual acceleration is possible in series mode.
Here is an even more detailed investigation into this although apparently the poster initially also assumed 70mph was when a switchover occurred, perhaps due to the same video being a bit misleading. You'll find single motor mode tops out at 102mph at 9,465rpm.
I'm not going to argue this any further because its leading the topic astray, was only commenting on a possible 2 speed EV having potential to be more economic.
I genuinely don't think its an argument, its actually all very interesting.
In the volts case i'm going to presume the two gears comes from the fact it has two motors.
Its too motors are more energy efficient working together in a higher gear ratio than one big motor that has only one gear.
The second motor/generator was present anyway as its needed to harvest energy from the engine when its running therefore they've come up with a rather neat solution to gain more electric efficiency from what they already had without adding any more weight than was needed.
The ability to accelerate up to 102mph on one motor is going to seriously drain the battery, but as you said the switch to two motor mode has a delay/hesitation in it so you need a way to bring the second motor in smoothly, therefore if someone accelerated up to 80mph which is a normal highway speed all over Europe you'd not want a horrible pause in acceleration that could be quite dangerous if you where trying an over take with limited room to complete the maneuver
