Vehicle Anti-lock brake rotor system, increase horsepower, Brake Rotor takes 175 ft-lbs, 36 Hp to spin up, really? free wheeling the brake rotor

[kaazx9r]

Hello, I wanted to see if it would be possible to create an anti-lock brake rotor that would unlock on non-braking events to free up the power it takes to spin them to speed.

But my numbers seem pretty high. My calculation

Taking a typical Shelby GT500 brake rotor(I know you all have these laying around like me), consider this brake Rotor laying flat on your screen, where z-axis is coming out of the screen, and rotating, with an outer radius is 7.5”, inner radius is 4.5”, thickness is 1.25” and mass of 31.4 lbs, what is the inertia? Then find the torque and horsepower to accelerate the brake rotor to a target rotational speed of 700 rpm to 1500 rpm in 4 seconds about its z-axis. (Basically a tire diameter of 28.5" to get wheel rpm from 60mph to 130mph, gives 700rpm to 1500rpm wheel/rotor speed.



So as the title states I got 175 ft-lb and 36Hp. But torque acting on the hub given a 3.55 rear diff gear ratio, we'll get 49ft-lb and 10.14 Hp is what the engine needs if you go through a 1:1 4th gear ratio. Multiply this by 4 wheels (say rear wheels have 75% smaller brake rotors), you're looking at 172 ft-lb and 35Hp from the engine just to turn the brake rotors. Seems reasonable?

So what kind of system would disengage, Chatgpt solutions:
1. Sprag or Overrunning Clutch
A sprag or overrunning clutch allows torque transmission in only one direction. When braking force is applied, it locks the rotor to the hub, but when no braking force is applied, it allows the rotor to spin freely.

2. Pneumatic or Hydraulic Actuator with a Locking Pin
3. Mechanical Locking Hub (Manually or Automatically Controlled)
4. Electromechanical Braking System (e.g., Electric Park Brake Actuator)
5. Electromagnetic Clutch



Chatgpt creates some strange images but anyway, the system would have to be normally closed for safety. And the added weight is another thing to consider. You need to engage it a split millisecond before the braking event but that should be doable or you can gradually bring the freewheeling rotor to match the hub speed where it would take a lot less torque over the greater time.

I think a synchro dog teeth transmission style system would also work but may not be normally closed. And spinning it up to speed to match the hub speed would have to start before the braking event but on a straight away this is not an issue due to the extra time, but still creates more load on the vehicle. You want the rotor freewheeling when accelerating to save that horsepower and enough to take over another vehicle, once at cruising speed, the system would start to match the rotor and wheel/hub speed.

Kindly discuss.

Edit to add cleaner calculations.

 

[Orange_kun]

I still don't understand the problem statement. EVs have already solved this with regenerative braking. You lose energy getting the brake rotor up to the same rotational speed as the rest of the wheel. Yes. You can also regain nearly all of that energy with very little added complexity if you use a hybrid powertrain.

What problem do you think this is solving? Heavy unsprung mass? Change materials, increase cooling, go lighter. Fuel efficiency? Same deal. Complexity? Uh, no. wrong direction. Lack of vehicle acceleration performance? Again, make it lighter, change gear ratios... add a hybrid system.

Step 1 with (all?) engineering problems is to ask yourself: what problem does the solution address? Step 2 is to get into the tradeoffs. To me, this is as much of a potentially good idea as an aircraft with a lead fuselage. Could you do it? Sure. Should you do it? Probably not.

Same goes for Imperial units. Just use SI, and you'll make fewer enemies and even fewer mistakes. I have no idea how many slugs are in the garden patch, but it's pretty easy to how many joules I have stored in some mass spinning at some rad/s and if it's worth reducing that number.

 

[3DDave]

This is trying to squeeze 1% more performance out of a race car over a couple percent of the race at the expense of having no brakes when the complicated mechanism fails. It is to do this by removing the inertia of the brake rotors from the drive train during acceleration like those stupid free-wheeling spinner hubcaps do. Unlike the spinner hubcaps, this seeks to re-attach them for braking, but that means waiting for the rotors to come up to speed, then locking them to the axle and only then can the brakes be applied.

Same sort of thinking about why airliners should use hub motors to spin up tires to reduce tire wear on landing.

Imperial units are fine. They don't cause mistakes. A slug is a unit mass just like a kilogram is. If I took a drink every time I saw a reference to the weight of something measured in kilograms I would be permanently pickled; SI doesn't fix knowing the difference.

 

[Orange_kun]

I suspect Brembo has already built a better compromise than this. Something to do with ultralight carbon/carbon discs and 1-piece calipers. It's pretty wild watching those test videos of F1 brake simulators. The disc goes beyond red-hot and back in less than a few seconds. Fantastic heat dissipation, from an impressively light rotor.

And ultimately, you're trying to reduce unsprung mass. That's higher priority than the rotational inertia. So I'm still confused about this whole thought exercise.

I won't get too bogged down into another units debate. The non-American world seems to prefer SI. I prefer the simplicity of having the base unit easily convertible to other forms. That's probably due to what I was educated with, and work with daily. But I would also argue in this day and age of precision the inch standard is obsolete, depending what you're designing. For me, it's the 4th decimal place that makes it a bit silly. Tenths of thous vs the same 3 decimal places getting you down to microns if in mm scale. I can see why machinists prefer inch standard - historically 3 decimals was all you really needed for a lot of stuff. But when you start really splitting hairs and there's a lot of work in 10ths, I would say the mm comes out ahead. Fortunately, we can automate the dual dimensions these days.