- #1
danja
- 13
- 0
Alright, I've re run this numerous times in my head, and on paper. It seems I must be missing something stupid here. Bottom line is, I am trying to calculate the amount of axle torque (post differential) required to stop a 1500 KG car from rolling down a 20 degree hill. Road to axle radius is assumed to be 8 inches. No, it's not a homework question =D though it does sound like one.
Anyways, here is the issue. I have arbitrarily picked 20 degrees since most roads don't slope higher than that. Since this is the torque to hold the car still, the angular acceleration is zero along with drag and the like.
Now, summing the torques will give the general equation (neglecting drag and friction):
Taxle = m*g*r*sin(hillangle) + m*r^2*(alpha)
In this case:
Taxle = 1500*9.8*0.2*sin(20) + 0
Or: Taxle = 1021.63 Nm (753.55 lbft)
Am I to believe that this is really correct?? Given that an average car has less than 200 Nm peak torque (at the wheels) this seems very off. Now what did I miss? This is driving me crazy!
Anyways, here is the issue. I have arbitrarily picked 20 degrees since most roads don't slope higher than that. Since this is the torque to hold the car still, the angular acceleration is zero along with drag and the like.
Now, summing the torques will give the general equation (neglecting drag and friction):
Taxle = m*g*r*sin(hillangle) + m*r^2*(alpha)
In this case:
Taxle = 1500*9.8*0.2*sin(20) + 0
Or: Taxle = 1021.63 Nm (753.55 lbft)
Am I to believe that this is really correct?? Given that an average car has less than 200 Nm peak torque (at the wheels) this seems very off. Now what did I miss? This is driving me crazy!