# How to Calculate Torque from Desired Acceleration in a Powertrain Model?

• Vivek Vijay
In summary: Equivalent mass is a way to model rotational inertia.I am looking for an equation that will give me the power at a given moment in time.You are looking for an equation that will give you the power at a given moment in time.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.If you are looking for an equation that will give you the power at a given moment in time, then using 'dt' is
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 ?

Have a look at the units:

[ Nm ] = [ N ] * [ m ]

Hesch said:
Have a look at the units:

[ Nm ] = [ N ] * [ m ]

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 ?

Vivek Vijay said:
F tractive = F air + D drag + F accel
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.

Vivek Vijay said:
But will this be dynamic enough ?
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.

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

Vivek Vijay said:
But will this be dynamic enough ?

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).

strive said:
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).
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

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?

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.

## What is desired acceleration?

Desired acceleration refers to the rate of change of an object's velocity over time, or how quickly an object is speeding up or slowing down. It is typically measured in meters per second squared (m/s^2).

## What is torque?

Torque is a measure of the rotational force or moment of an object. It is calculated by multiplying the force applied to an object by the distance from the point of rotation to the point where the force is applied. It is typically measured in units of newton-meters (N*m).

## How are desired acceleration and torque related?

In order to achieve a desired acceleration, an object must have a certain amount of torque applied to it. This is because torque is responsible for causing rotational motion, which in turn leads to acceleration. The amount of torque required will depend on the mass and shape of the object, as well as the desired acceleration.

## What is the difference between linear and angular acceleration?

Linear acceleration refers to the change in an object's velocity in a straight line, while angular acceleration refers to the change in an object's rotational velocity. Torque is responsible for causing angular acceleration, while force is responsible for causing linear acceleration.

## How can desired acceleration and torque be calculated?

To calculate desired acceleration, you can use the equation a = ∆v/∆t, where a is acceleration, ∆v is the change in velocity, and ∆t is the change in time. To calculate torque, you can use the equation τ = F*d, where τ is torque, F is the applied force, and d is the distance from the point of rotation to the point where the force is applied. Keep in mind that both of these calculations may involve other variables and factors, such as mass and inertia, depending on the specific scenario.

Replies
4
Views
3K
Replies
22
Views
2K
Replies
58
Views
6K
Replies
8
Views
5K
Replies
2
Views
2K
Replies
18
Views
1K
Replies
17
Views
3K
Replies
4
Views
3K
Replies
6
Views
2K
Replies
19
Views
3K