# Desired Accelaration to Torque

1. Nov 22, 2016

### Vivek Vijay

Hello,

I would like to know the basic eqns in a simple Powertrain model. Where i have the Desired accelaration and the other quantities to calculate the tractive force.

But i need to calculate the torque to the wheels. can anyone help me ?

2. Nov 22, 2016

### Hesch

Have a look at the units:

[ Nm ] = [ N ] * [ m ]

3. Nov 22, 2016

### Vivek Vijay

Yeah, perhaps my question was too short.

I want to calculate the drive torque to the wheels, taking into consideration of the tractive forces.

Torque [wheels] = F tractive * dynamic wheel radius

F tractive = F air + D drag + F accel

But will this be dynamic enough ?

4. Nov 22, 2016

### Hesch

How will you calculate Fair? Read the weather forecast, wind direction, will it rain? Will you calculate the cw-value for each wagon with its load?

Drag is not constant. It goes uphill/downhill.

You are the one to know.

If an exact time of arrival is important, I would install a speed/acceleration control in the train, increasing the turbo pressure if needed.

5. Nov 23, 2016

### Vivek Vijay

Nice pun !! But you are mistaken - I am not looking to calculate for a power TRAIN, but i am talking about vehicle powertrain (automobile)...

Sorry for the typo...
But what i meant is air resistance (drag). Let me rephrase it..
F tractive = F air resistance + F rolling resistance + F accelaration
=0.5*(air density*drag co-eff*cross sec area*(velocity)^2) + m*g*coeff-roll resistace + (m*desired accel)

In this case i take air density constant - 1.2 kg/m3
Cross sec area - i have example data for the vehicle

6. Nov 23, 2016

### strive

What do you mean by dynamic?

If you want to calculate Force/Power at a given instant in time your equation is ok.
If you wish to plot Force/power over a given time period for a constant acceleration value, you need to either use 'dt' or do the calculation numerically (iteration per iteration).

7. Nov 23, 2016

### Vivek Vijay

Yes , i am doing a simulation of my mathematical model therefore numerical calculation by iteration is dynamic .

My question of dynamics was that, i try to make a simple physical equation of powertrain using the formula i mentioned above. When i do that, without considering driveline dynamic is that a right approach.

Or is my question too vague to comprehend ? please let me know

8. Nov 23, 2016

### strive

Well, i am missing some data in your explanation, but if you don't like sharing the details, that's allright. We'll find a way around it.

What do you mean with 'driveline dynamic'?

If you are worried about using your non-dt formula, don't worry, just use a sufficiently small timestep in your iteration. 0.1s should do, but if you are using a computer to churn out the results you might as well go with 0.01s. Difference will be minimal though.

What order of accuracy are you looking for?

9. Nov 23, 2016

### jack action

I use a mass factor to model the rotational inertia like shown here (I think that is what you are talking about). Learn more about the 'equivalent mass' theory.