How to find the roadTorqueImpulse?

[Jonathan Dion]

I am programming a vehicle for a company with as much realism as possible, but I have a little problem right now. I calculate the rolling resistance and the angular momentum. The problem is that I cannot calculate the longitudinal force, the lateral force as well as the slip ratio in order to be able to calculate the necessary torque.

 

[Baluncore]

Welcome to PF.

I guess you need to look at tyre forces in the plane of the road.
Rolling resistance will be vertical and will heat the tyre.
The tyre torque applied to the road becomes a longitudinal force which must balance the vehicle aerodynamic drag, the acceleration or braking, and the change in potential energy when climbing or descending hills.

How are you modeling the vehicle. What are your sub-systems and what are the state variables.

 

[Jonathan Dion]

Right now I have 3 subsystems.

I have the motor which sends the torque directly to the wheels by being multiplied by the final gear ratio * the current gear ratio.
The wheels then calculate its rolling resistance as well as its angular momentum which are added as resistance force (as a negative force).

The transmission then receives these values from each wheel in order to calculate its rotation speed by adding it to the result of the multiplication of the clutch pulse * final gear ratio * the current gear ratio.

The clutch takes the rotation value of the transmission and calculates it again with the final gear ratio * the current gear ratio. It then calculates the dragImpulse based on the maximum motor impulse, the difference in rotation speed in the clutch and that of the motor.

The dragImpulse value is used to simulate the vehicle's weight during acceleration and deceleration. It is this value which is miscalculated due to the fact that I cannot find the right formula which would allow me to calculate the resistance of the wheels when they receive torque.

 

[jack action]

The words you are using makes it very difficult to understand what you don't understand:

1. What is a dragImpulse?
2. What is the maximum motor impulse?
3. The dragImpulse value is used to simulate the vehicle's weight; I have no clue what that means and why you need to simulate the weight.

Check this page to understand the equation you need to evaluate the acceleration of the vehicle.

The acceleration of the rotating components are linked to the acceleration of the vehicle. Just like inertia of the rotating components are linked to the inertia (i.e. weight) of the vehicle. Check out this page to find out how.

You cannot evaluate the acceleration/velocity for one component at a time and use some sort of feedback to reevaluate the acceleration/velocity. You have to see it as a whole machine with a defined inertia, acceleration and velocity for a particular point in your machine (usually either the input or the output).

 

[Jonathan Dion]

@jack action
The dragImpulse, in this case, is used to represent the pulse difference between the rotational speed of the clutch and that of the engine when the wheels receive the torque.
Example: During acceleration, the motor receives a reverse force which causes it to lose torque.
When changing from second to first speed, in the case of a manual transmission, all depends on the speed of the wheels, the rpm will increase due to the fact that the transmission rotates faster than that of the engine.

Regarding the maximum motor impulse, I take into account the maximum torque that the motor can produce and I convert it into impulse in order to be able to keep in memory the "range" (min-max) depending on the clutch between the two "discs" (always keeping in mind that this is a "program" of simulation).

In terms of simulating the vehicle's weight, a 1,200 kg car will not accelerate at the same speed as a 14,000 kg truck. As mentioned above, it is not from a physical system, but simulated for driving training.

 

[jack action]

The dragImpulse, in this case, is used to represent the pulse difference between the rotational speed of the clutch and that of the engine when the wheels receive the torque. But I'm not sure if this is what you mean.

For info, this is an impulse in physics. I'm still not sure what you mean by pulse. But the difference in rotational speed between the output & input of a clutch under a change in torque, will depends a lot on the friction force between the two.

During acceleration, the motor receives a reverse force which causes it to lose torque.

The motor creates the force, so it cannot "loose" it. It is a given. But its acceleration can change though.

When changing from second to first speed, in the case of a manual transmission, all depends on the speed of the wheels, the rpm will increase due to the fact that the transmission rotates faster than that of the engine.

The rpm of what will increase? The rpm increases because there is an acceleration, period. The acceleration depends on force and inertia. Changing from 2nd to 1st could lead to an increase in engine rpm, but it could also lead to a decrease in wheel rpm; it all depends on the force analysis. Think of the case where your vehicle is on a very slippery icy road.

I take into account the maximum torque that the motor can produce

What counts is the torque that your motor is actually producing.

I convert it into impulse in order to be able to keep in memory the "range" (min-max) depending on the clutch between the two "discs"

I have absolutely no clue what this means. I refer to you again to the definition of impulse and I don't understand the concept of "memory" in physics.

As mentioned above, it is not from a physical system, but simulated for driving training.

It doesn't matter, you should be using equations representing physical systems. And in those, the weight is just a known parameter.

It is really about doing a free body diagram. One similar to the following one for a planetary gear set:

​

Just decoupled every component and do a force analysis on each of them.

 

[Jonathan Dion]

For info, this is an impulse in physics. I'm still not sure what you mean by pulse. But the difference in rotational speed between the output & input of a clutch under a change in torque, will depends a lot on the friction force between the two.

I know what an impulse is. It may be a bad term that I use, but this variable represents the impulse of resistance between the rotation speed of the clutch and the rotation speed of the engine according to the torque that the wheels receive.

The motor creates the force, so it cannot "loose" it. It is a given. But its acceleration can change though.

By losing torque, I meant that this value is used to change the motor rotation speed (rpm) according to the torque of the motor converted into impulse. In other words, the result of the calculation (the torque pulse - the resistance pulse / the engine inertia) represents the variation of the angular speed of the engine (rad / s)..

The rpm of what will increase? The rpm increases because there is an acceleration, period. The acceleration depends on force and inertia. Changing from 2nd to 1st could lead to an increase in engine rpm, but it could also lead to a decrease in wheel rpm; it all depends on the force analysis. Think of the case where your vehicle is on a very slippery icy road.

As for the example of the past from the second to the first, this variable (the resistance pulse) should be positive, therefore increases the revolution of the motor and applies a negative torque to the wheels to slow them down.

 

[jack action]

I'm pretty sure the answer to your problem lies in a free body diagram. If you show us one that you've made, we can help you find mistakes in it, if there are some.

I will ask others, see if they can help you in any other way.

 

[Jonathan Dion]

@jack action All I want to know is having the right formula knowing that I have the angular momentum, the rolling coefficient, the coefficient of friction and the rolling resistance in order to have the momentum necessary to turn the wheel depending on its angular speed and the torque it receives.

 

[chemisttree]

I know what an impulse is. It may be a bad term that I use, but this variable represents the impulse of resistance between the rotation speed of the clutch and the rotation speed of the engine according to the torque that the wheels receive.

When you say things like this, you should know that you are speaking your very own language that nobody else may understand.
Please define “impulse of resistance” for example. Is this actually some complex form of inertia?
Apparently you are dealing with a speed mismatch between the engine and the clutch. Someone might reasonably call that “slip.”
And measuring speed according to torque has no meaning at all unless you have created a lookup table to tie those two together somehow.

 

[jrmichler]

knowing that I have the angular momentum, the rolling coefficient, the coefficient of friction and the rolling resistance

Not completely correct, but you (sort of) have the idea.

momentum necessary to turn the wheel depending on its angular speed and the torque it receives

Completely wrong.

A wheeled vehicle has mass, velocity, position, rolling friction, and aerodynamic drag. If you are working on a driving simulator, additional inputs include engine torque, transmission gear ratio, final drive ratio, and effective tire diameter. It sounds like you want to simulate a manual transmission without a clue as to how to model a clutch. I strongly recommend that you start with an automatic transmission until the program works, then and only then, add a clutch.

Additional inputs after the above is working include rotational inertia of wheels and tires and torque converter/flywheel, driveline friction, wind speed, wind direction, road grade. But only after getting the above to work.

And, like @jack action said above, you NEED a free body diagram. After that is, you study the meaning of torque, momentum, and impulse (search those terms).

I think I understand your problem, but I cannot communicate the solution to you because you are using incorrect language. The correct language starts with a simplified free body diagram showing only net horizontal forces. Then use torque, inertia, and drag correctly to describe the motion. After you have done that, you should be able to figure out or derive the necessary equations using only the basic $F = ma$ equation from high school physics.

Suggestion: Start by assuming that net forward force is proportional to throttle position. Add in ratios, torque, driveline friction, and driveline inertia as a second step. Wind and road grade would be a third step.

 

[Tom.G]

Hey folks, It's a language/culture thing:

"Impulse" (or "pulse") is used as most of us would use "energy". Try that substitution in the OPs posts and see if thinga are a bit clearer.

 

[Jonathan Dion]

Everything about the transmission I already take it into account and it is already all programmed. Even if I would take an automatic transmission, I would still have the problem about the wheels.

To make it simpler in this case, to all of you, due to the fact of the poor pronunciation of the terms because I am not an expert in physics / mathematics, I seek to be able to calculate the fx on this image:

 

[jack action]

From the previous reference I pointed out to you earlier, assuming for all powered wheels:
$$F_x = \min\left(\frac{P}{v}; \mu F_z\right) - F_R$$
and:
$$F_x = \lambda_m ma$$Where:
$P$: wheel power
$v$: vehicle velocity
$\mu$: tire-road coefficient of friction
$F_z$: Normal force acting on the tire
$F_R$: Sum of all resistance forces (rolling resistance, drag, grade, etc.)
$\lambda_m$: total inertia vs vehicle inertia ($\frac{m_e}{m}$ in this reference)
$m$: mass of the vehicle
$a$: acceleration of the vehicle