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Thread: Electric Vehicle torque requirements for a specific acceleration

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    Associate Engineer Nashty's Avatar
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    Apr 2012
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    Electric Vehicle torque requirements for a specific acceleration

    Hi, this is my first post here. Sorry in advance for the long introduction.

    Anyways, for whatever reason, I decided to dedicate my life to converting gasoline vehicles into battery electric or hydrogen fuel cell vehicles once the fuel cells become small and affordable enough. It seemed like a good idea at the time...

    I have a client who had someone else convert a 2004 Porsche 996. The person did a horrible job. They had a charging accident and hurt the LiFePO4 battery. He also mounted the power steering pump directly over the commutator of the motor that almost started a fire. My client paid way too much for the conversion and is now extremely reluctant to put any more money into the car since he went and bought a Tesla. He likes driving the Porsche much better than the Tesla for the handling and comfort, but drives the Tesla because it has the range and acceleration he wants. Unfortunately he would rather let the Porsche sit and rot rather than sell it for what it is actually worth.

    Anyways, my buddy and I took everything out of the car and designed the car so that it works fairly well now except that it does not have the range nor the performance that my client would like, the performance is much better but the battery is toast. What I want to do is design a battery system, find a motor and maybe upgrade the controller to get him the performance he wants. I am planning on putting my own money into this in the hopes that he will be impressed enough to pay me back or that the car will sell so I can get back some of my money.

    So my question is this:
    How do I determine the amount of torque required to get this car to accelerate from 0-60MPH in less than 3.7 seconds?

    Once I find that out I can start looking for a motor that can put out that kind of torque. Then I will find a controller that can push the motor that hard. Finally I will design a battery system that will give enough power to the controller. Unless someone can convince me why I would do differently, but I am pretty stubborn.

    Here are the particulars:
    • 2004 Porsche 911 Carrera (996) donor vehicle
    • Weight = 3,520 lbs after conversion
    • Cd = 0.34
    • CdA = 5.92 sq ft
    • Crr = 0.016

    Tires
    • Front - 225/40 ZR18
    • Rear - 285/30 ZR18

    Gear Ratios:
    • 1 - 3.82
    • 2 - 2.20
    • 3 - 1.52
    • 4 - 1.22
    • 5 - 1.02
    • 6 - 0.84
    • R - 3.55
    • Final - 3.44


    I have looked at the "Motor Accelerating Torque Calculator" in your Calculators section, but then it goes into moment of inertia questions and I get lost.

    Anyways, I do want the answer, but I am more interested in how to determine the answer on my own so I can do this for other people as well. Not just a formulae, but the how and why of it in case I forget the formulae and need to figure it out again.

    Thanks in advance. I am sure I will have more questions after I wrap my head around this answer.
    Last edited by Nashty; 04-24-2012 at 08:03 AM. Reason: Wrong tire size

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