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Is Tesla so fast compared to the price because is an electric car or this is totally unrelated and was just designed to have such an acceleration, without help

by antirez 10y ago

Is Tesla so fast compared to the price because is an electric car or this is totally unrelated and was just designed to have such an acceleration, without help from the fact it's an electric car? Thanks. EDIT: Thank you for the replies!

PietdeVries 10y ago
To my knowledge the essence of an electric engine is that is has max traction almost independent of the rpm. Where a petrol engine has an optimal rpm (4000 for instance) where it provides most power, the electric car does not. Consequence is that a petrol car needs a gearbox to keep the engine around this optimal RPM (and thus most power) while the electric engine does not need one - it accelerates and keeps on accelerating... So the Tesla is so fast because it is electric, not because it has other features.
- jackmott 10y ago
  Max torque, not traction. That, and being able to do all wheel drive efficiently and with less weight penalty and with less risk to drivetrain parts helps the quick acceleration. But you still have to make tons of power and not be too heavy of course.
  - usrusr 10y ago
    Yes and no. While the grandparent post was clearly confusing traction and torque quite a bit, the answer is still mostly about traction. At the supercar level, you can basically assume infinite power when looking at acceleration in the lower speed ranges. The limit is traction, not torque. A sufficiently strong EEV can continuously max out traction. An ICE supercar does the same, but with a few tiny gaps for shifting that add to the total time. The ICE supercars do not need a stronger engine to come closer to the Tesla, they need faster transmissions to minimize shifting gaps. I think that this is also the prime reason why manual transmissions are disappearing/have disappeared from supercar territory, dual clutch automatics provide shorter gaps.
- PinguTS 10y ago
  Which is only partly right. Also electric drives have a dependency of torque to rpm(1). But it is much more easy to control than an ICE. (1): http://lancet.mit.edu/motors/motors3.html http://lancet.mit.edu/motors/motors3.html
gravypod 10y ago
The reason why an EV would outperform most motors is mutli-fold 1. No cold starting. The engine is on as soon as you push power in. 2. Equal torque at all speeds 3. The lack of a need for a transmission. All "gears" can be controlled by how much power you're feeding The EV is more like a solid state transistor verses a relay. They do similar things, they're good for different applications, but the transistor has some nice features that makes it better in some key aspects (like raw performance).
- jaredraby 10y ago
  It's not equal torque at all rpm.
  - gravypod 10y ago
    Effectively it's more equal then an ICE. Also if you can get someone who has a lot of experience with motor control they can get you going pretty quickly. I'm assuming what's in the Tesla is a brush-less DC motor and there are a few things you can do (especially since you're on some serious batteries in the Tesla) to push some serious torque at the startup curve. You're probably only running a modulated power start for a few seconds. After the first few seconds you're shoving the full amperage into the motor.
    - CarVac 10y ago
      Teslas have AC induction motors.
      - gravypod 10y ago
        If they do that then they can also take advantage of mutli-phase power that they could modulate to change the speed thereby running it at a higher torque at lower speeds.
    - stevendhansen 10y ago
      As pointed out in other comments Tesla actually uses AC induction machines (asynchronous AC) instead of brushless machines (synchronous AC). To a first approximation an AC induction machine can produce constant torque up to a fixed speed. Above this speed the torque falls off as approximately 1/speed. You are right about the startup torque. AC induction machines can produce full breakdown torque at zero speed, but this does require high current (but luckily not high power because the applied voltage is still low due to low motor speed). Another limit is the junction temperature of the power semiconductors in the inverter(s). I think Tesla uses liquid cooled inverters, but this typically means there isn't much mass to act as a heatsink (relying on the liquid coolant instead), so overload times are typically very short. I'd would guess this is actually the limit in their design. In other words they can put very high currents into the motor for a long period of time before it thermally overheats, but way before that time they have to reduce the current in order to protect the power semiconductors in the inverter.

by antirez 10y ago

PietdeVries 10y ago

To my knowledge the essence of an electric engine is that is has max traction almost independent of the rpm. Where a petrol engine has an optimal rpm (4000 for instance) where it provides most power, the electric car does not. Consequence is that a petrol car needs a gearbox to keep the engine around this optimal RPM (and thus most power) while the electric engine does not need one - it accelerates and keeps on accelerating... So the Tesla is so fast because it is electric, not because it has other features.

jackmott 10y ago
Max torque, not traction. That, and being able to do all wheel drive efficiently and with less weight penalty and with less risk to drivetrain parts helps the quick acceleration. But you still have to make tons of power and not be too heavy of course.
- usrusr 10y ago
  Yes and no. While the grandparent post was clearly confusing traction and torque quite a bit, the answer is still mostly about traction. At the supercar level, you can basically assume infinite power when looking at acceleration in the lower speed ranges. The limit is traction, not torque. A sufficiently strong EEV can continuously max out traction. An ICE supercar does the same, but with a few tiny gaps for shifting that add to the total time. The ICE supercars do not need a stronger engine to come closer to the Tesla, they need faster transmissions to minimize shifting gaps. I think that this is also the prime reason why manual transmissions are disappearing/have disappeared from supercar territory, dual clutch automatics provide shorter gaps.
PinguTS 10y ago
Which is only partly right. Also electric drives have a dependency of torque to rpm(1). But it is much more easy to control than an ICE. (1): http://lancet.mit.edu/motors/motors3.html http://lancet.mit.edu/motors/motors3.html

gravypod 10y ago

The reason why an EV would outperform most motors is mutli-fold 1. No cold starting. The engine is on as soon as you push power in. 2. Equal torque at all speeds 3. The lack of a need for a transmission. All "gears" can be controlled by how much power you're feeding The EV is more like a solid state transistor verses a relay. They do similar things, they're good for different applications, but the transistor has some nice features that makes it better in some key aspects (like raw performance).

jaredraby 10y ago
It's not equal torque at all rpm.
- gravypod 10y ago
  Effectively it's more equal then an ICE. Also if you can get someone who has a lot of experience with motor control they can get you going pretty quickly. I'm assuming what's in the Tesla is a brush-less DC motor and there are a few things you can do (especially since you're on some serious batteries in the Tesla) to push some serious torque at the startup curve. You're probably only running a modulated power start for a few seconds. After the first few seconds you're shoving the full amperage into the motor.
  - CarVac 10y ago
    Teslas have AC induction motors.
    - gravypod 10y ago
      If they do that then they can also take advantage of mutli-phase power that they could modulate to change the speed thereby running it at a higher torque at lower speeds.
  - stevendhansen 10y ago
    As pointed out in other comments Tesla actually uses AC induction machines (asynchronous AC) instead of brushless machines (synchronous AC). To a first approximation an AC induction machine can produce constant torque up to a fixed speed. Above this speed the torque falls off as approximately 1/speed. You are right about the startup torque. AC induction machines can produce full breakdown torque at zero speed, but this does require high current (but luckily not high power because the applied voltage is still low due to low motor speed). Another limit is the junction temperature of the power semiconductors in the inverter(s). I think Tesla uses liquid cooled inverters, but this typically means there isn't much mass to act as a heatsink (relying on the liquid coolant instead), so overload times are typically very short. I'd would guess this is actually the limit in their design. In other words they can put very high currents into the motor for a long period of time before it thermally overheats, but way before that time they have to reduce the current in order to protect the power semiconductors in the inverter.