Ignoring the load and potential damage to the ring and pinion, do we have a qualified engineer that can confirm once and for all an engineering question my colleagues and I have had for the past 12 months.
Diff Ratio 2:1, 10" diameter Disc Brakes x 1 on each wheel
vs
Diff Ratio 2:1 with 1 x 10" Disk Brake mounted on the Tailshaft
Will the single Disc apply the same braking force?
Will the single disc experience the same friction and heat?
(Ignoring the additional heat build up caused by the higher speed and the pads rubbing slightly.
Now the real scenario:
4.56:1 Diff, 2 x 14" rotors at each wheel
vs
Single 10" disc mounted on the tails haft
The disc is smaller 10/14, but the diff advantage is higher, will the single disc still provide the same braking force. (Think of the H1 Hummer with the Inboard Brakes)
I know my maths and theories, but keen to see you all try to add your 0.02 worth.
The single disk will experience exactly the sum of the two disks heat (if we ignore the very important heat due to running drag).
It might be easiest to think of this: The moving car has X energy that must be converted to heat to stop it. You can have X/2 heat in two disks, X/4 heat in four disks, or X/1 heat in one disk.
My thoughts exactly. Energy cannot be created or destroyed but it can transfer. All of the kinetic energy (ignoring friction from tires and drivetrain) will be converted to thermal energy by the brakes. How well each rotor set up can get rid of heat is another issue. Wheel brakes not too much issue, driveline brakes definite heat fade problems. But what I think you are asking is this, which is stonger brake effort at the wheel? Your simple version is exacty even, same brake force at the wheel. Real world version, smaller brakex4.56, yes it will have more brake force than 2 wheel brakes. No major calcluations needed. Ever see a rockwell axle jeep with pinion brakes stand on it's nose because the driver jabbed the brakes? A driveline brake will have more stopping power due to mechanical advantage but can't function as well in duration as wheel brakes because of the excessive heat
That's fine, but you need to be very cognizant of surface feet per minute through the pads. The obvious answer is to reduce rotor diameter, but then you lose brake torque due to the smaller lever. The challenge will be finding the balance.
I would also do some investigation into titanium pistons or titanium shields on the pads to keep the heat out of the fluid and you'll likely need some ducting with those rotor locations.
Brakes mounted on the diff outputs would be limited to 300mm (Same diameter as the diff) unless we are braking via our reduction hubs, asking a 300mm rotor to pull up our 37 or 39" tyres is a big ask.
We run between 330 and 380mm rotors at the wheel now and if we want to run 12" 300mm in board rotors, we would need the portal mechanical advantage.
Running a 10" Rotor (Again limited by the diff dimensions as the pinion is 1.125" below the ring gear centreline) on the tails haft at 4.56:1, should provide 4.56 x 10" brake ability.
2 x 330mm rotors is less braking ability than 4.56 x 250mm rotors...
Perhaps if we ran a brake booster and MASSIVE line pressure on a 300mm or smaller disc mounted to the diff would provide the same sort of braking force?? We have measured passenger cars and found that their pressures are between 1200 and 2000 PSI, where as our mechanical pedal only provides 1200 PSI at present...
We might actually do some testing of 300mm rotors on each side of the diff one day to confirm if it is possible.
As do the hummer H1's I believe. If you combined those inboard brakes with 2:1 portals you'd get the same kind of mechanical advantage, fun to think about.
Had been discussing and the concern that someone brought up was an axle/CV failure and actually being able to stop the wheel. Inboard brakes are kind of useless if that happens. Risk/Reward tradeoff on safety perhaps? How do hummers deal with this?
In the case of the OP I believe they are using a spool, so a broken axle shaft would net a loss of braking traction from one tire, but the clamping force and heat dissipation would remain constant. I would guess that they would tend to break more axles in a low speed crawling section of a course than the go fast desert section as well.
Other tire/wheel still has inertia though. What happens when you've got three tires braking and one still going still trying to go forward in the go fast? In my mind (could be wrong) it would result in an unbalanced system and potential hazard there. Obviously going slow not a big deal. Only potential issue that's came up in some of the discussions. Not sure how braking against the pinion or CVs impacts their lifespan or if it has any significant impact.
A major thing to consider is the torque load that the brakes can generate well above engine power.
Landing hard while on the brakes will load up the shafts unless you limit your braking torque to match what the shafts can handle.
Also consider the chatter or wrap up of the shafts on and off the breaks. When you unload the breaks the shafts will spring back and then reload when power is reapplied.
Very important point. Rod Hall learned about this when he started racing Hummers (H1) years ago. They actually broke axle shafts during hard braking when a tire would take a hard impact. Imagine the moment when you realize you're about to hit a washout in the race course and you lock up the brakes at the last second. That situation would break the shafts on impact. Not sure what component was breaking, but it was between the brakes and the portal.
I dont have any experience with the inboard or driveshaft brakes on a truck, but in the ATV world its fairly common. On a can am renegade the rear uses the rotor mounted on the pinon like you are talking about and it stops very well. Has good feel to the pedal, well handle in this case, but it works very well and protects it inside the frame.
ALSO- just like an H1.... it rocks back and forth when you come to a stop. brakes are held steady, the lash in the portal boxes rock back and forth..... i was in a H1 last week- it was noticable on 42" tires.
Ok, so how about multi plate brakes? Like the clutch basket in a dirt bike, but for breaking instead? Lower rotational mass, lower surface feet per minute, etc.
Need more brakes? Add more plates. Maybe smart? Maybe not?
I Think inboard rotors would be a nice choice, maybe with 2 calipers on each rotor ( like Unimogs do), but in this case heat transfer should be a problem....
Does anyone have a parts list of hydro boost units and suitable master cylinders showing booster shaft travel, amount of mechanical advantage of the booster?
Since you are starting from scratch and designing this from the ground up, why not try to adapt a sintered iron clutch disk pack as a "rotor" and steel plate as the "pad"? They are designed to be able slip under full power, high RPM, and handle insane amounts of heat. They are available with in sizes from 10-12" and in packs from 2-5(maybe more) and are used to hold 5000+ horsepower. It could potentially take care of the heat and surface speed concerns.
That would be the area to start looking into. I kicked around suggesting a wet brake also but I don't think it would work well at high speeds; works great on big slow stuff though.
My initial thought was towards a wet clutch/brake (hence the dirt bike talk) but I got to thinking that the fluid shear might end up being too big of a parasitic loss.
A more traditional dry disks setup could be the ticket.
Haven't there already been some pretty in depth discussions about pinion brakes on Rockwells? Seems like a pretty similar problem mechanically. I know the Rockwell guys usually tend to go with somewhat less sexy (and expensive) solutions, but it's an application with some real world testing.
but! there is light at the end of the tunnel. the new corvette ZR1 has the same diameter rotors- so we bought one from chevy, swapped the hats and were good to go :grinpimp:
the chevy guys were chuckling at us when we bought their 1600 dollar rotor...... if they only knew
so- AFAIK if you want a big ass carbon rotor that is "cheap" look at the ZR1 rotor.
edit: forgot to mention- you need special brake pads- they are almost 800 bucks!
calipers are about 750 bucks.
So back to a multi-plate brake. I'd like to see them on the wheel. Use something light and slim like the rotor from a sportbike. They are designed to float on 'loose rivets' or some such mechanism. You could stack a few of them (along with custom double sided brake pads) up in the thickness of a standard cast / finned rotor. Buckets and buckets of braking power would be yours. They probably wouldn't last for 30,000 miles, but this isn't about a long-lasting solution, this is about winning races!
I think the big difference with rockwells and this setup is the speed involved.
The sintered iron disc do wear quickly an you would have to account for additional wear or build in adjustability. Hopefully we get to see something like this done. It would be an interesting test.
Check out the inboard disk brakes on a humvee. They mount to the output shaft if the differential. Same airflow as a pinion brake, same mechanical advantage as wheel brake. In the case of the humvee they were chosen to clear the portals
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Pirate 4x4
18.7M posts
366.4K members
Since 2000
A forum community dedicated to custom off-road vehicle owners and enthusiasts. Come join the discussion about trail reports, builds, performance, modifications, classifieds, troubleshooting, fabrication, drivetrain, and more!