simulating worn brake pads effect on wheel's rpm

Hi all,

I'm getting into simulink for academic use, and I'm trying to understand how to show the condition of brake pads on the wheel's rpm on a time series. The diagram should be simple, and values shouldn't be exact, it's a first attempt for me. This is what I have so far, but I'm failing to understand how get the wheel's rpm. On top of that, I'm thinking about making the kinetic friction a variable, and to control it separately. Is that possible? any suggestion on how to move forward? Thanks!

Answer 1

[Steve Miller]

I have rebuilt your model with some modifications and attached it to this answer.

Some notes:

1. You can measure the wheel speed with an Ideal Rotational Motion Sensor. You can also simply view all the Simscape simulation results in the Simscape Results Explorer, which means you do not have to have extra sensor blocks in your diagram
2. I put a transfer function in to smooth the application of pressure to the Disc Brake.
3. You can enable thermal effects in the Disc Brake, which would allow you specify lookup tables for the static and coulomb friction values as a function of temperature. You could vary the temperature of the brake to get different behaviors.
4. Another option for varying friction is the Loaded Contact Rotational Friction block.

[Gal Shraiter]

Wow! Thanks! this looks much more elegant than my digaram.

I've used the simscape result explorer up till now, as I wasn't familiar with the Ideal Rotational Motion Sensor.

May I ask, why the transfer function smooths the application of the pressure sensor?

I'll enable the thermal effects in the the Disk Brake, thaks for that. Is there some king of tutorial about all this? I'm scratching info from here and there.

[Steve Miller]

A general set of "Getting Started" materials is here:

https://www.mathworks.com/solutions/physical-modeling/resources.html

This covers all domains and a wide range of topics.

Specific to thermal modeling of driveline systems, look at this page:

https://www.mathworks.com/help/physmod/sdl/ug/simulate-thermal-losses-in-driveline-components.html

--Steve

[Steve Miller]

"why the transfer function smooths the application of the pressure sensor?"

The transfer function is a low pass filter. Instead of the pressure jumping from no pressure to full apply instantaneously, the time constant on the filter causes the pressure to ramp up more slowly. That is more consistent with reality - as fast as you can move your foot, it will take some time to fully apply pressure to the brakes.

[Gal Shraiter]

That's super interesting. Continuing that, is that why you also used a step function? so the transfer function will have a sudden but smooth impact?

Also, I can't find this exact transfer function, is that taken from the default simscape library?

Thanks!

[Steve Miller]

I used the Step input block as it is convenient to specify when the transition will take place. The transfer function provides a convenient way to control how rapid the change is.

The Transfer Function block is a Simulink block. The same thing could be done within Simscape, but since this is essentially a control signal, it was OK to do it in Simulink.

[Gal Shraiter]

Got it. Thanks. Is there a way to control when it takes place when using a constant as I did before?