Hello,I would like to control the speed using curve.Because I want to reproduce the acceleration of a specific car.There is a way to convert rpm or km\h to torque? Or an other way to obtain the acceleration (I have the curve in f(x)). 250 Km/h max. Max torque 140. 2880 rpm

Well that's depends on how you want to do it and what kind of curve you have. Is it a distance vs time or speed vs time, or something else?

I have a speed/time curve and it's a smooth curve. You need the équation ? With 140 of torque,my car go to the full speed ,but so fast... The full speed on thé curve is obtained at 24 seconde.

So what you need is torque to be a function of engine speed, as it would be with a real car. Torque(rpm) = ...math stuff... You could use a simple parabolic approximation for your torque curve, Torque(rpm) = -a(x – h)2 + k Where k is your peak torque at an engine speed of h. The coefficient a is a parameter defining the flatness of your torque curve. Smaller values will result in something more peaky, and higher values for something flatter. I'd recommend putting in your desired peak torque (k) at the desired engine speed (h) and play with the parameter a until you have the jump from a standing start you want. You could use a lookup table or a higher-order polynomial model if you wanted to model a curve you've obtained from a dyno, but a reasonably flat parabola will get you close.

Time (s) / Speed (Km/h) To be honest, I don't understand (I speak French).My peak torque is k = 140 ,okay for a ,h is for rpm speed ? but it's not static ? And after how do I apply this curve to the car ? Else I have this f(x) = 0.004166667 + 0.004077778 * x + 0.0005274167 * x^2 - 0.000003814444 * x^3 + 1.27e-8 * x^4

So based on your Time vs Velocity graph, I was able to calculate an Acceleration vs. Velocity function. I inverted your function to get Velocity vs Time, then took the derivative to get the acceleration (a = dv/dt). From there, I was able to generate a plot of A vs. V and fit a polynomial to it. This won't give you torque, but for a fixed mass car with a fixed radius wheel, the difference is only a multiplicative factor.

Here's a good read: http://entitycrisis.blogspot.com/2010/12/unity3d-wheelcollider-and-motortorque.html