Brake Assisted Steering

[spectre6000]

The Porsche 918 (and I think the newest 911s as well) supposedly handles like a much smaller car partly due to its ability to actuate the brakes on the inside corner. I was noodling on cutting brakes the other day and got the crazy idea to rig something up to help with handling in turns. If a cutting brake setup could somehow be rigged up to a steering box to actuate the inside brake, it could feasibly perform the same task as the Porsche system.

The simplest approach would be to have it actuate at a certain number of turns, say half a turn in either direction. This could be done by simply actuating the cylinders with levers or pushrods attached to the dog bone or something on a stock steering box, or something similar on a rack and pinion setup.

A more advanced and useful approach would be to have a gear on the steering column drive a second gear with essentially a small rack and pinion box to actuate the cylinders. This would provide for a much more even and smooth actuation.

The downside I see to this is potentially that, at least using the readily available cutting brake system concepts, you're only actuating the rear brakes, but I'm not sure that's necessarily detrimental to performance... I'm sure I'm missing some other major flaw in this design exercise; anyone care to point it out?

[Ol'fogasaurus]

I am sure that there has to be some electronic brake management system(s) tied to the braking to control pressure and when to release the brake(s). The driver's arms might be awful busy at times with a manual secondary braking system: steering with the wheel, shifting and using the aux turning brake all at the same time. It is also going to wear on the pads on one side faster as road courses are still a loop/circle.

I would suspect that one would want to put a single handle (probably a line-lock system rather than a single handle push/pull system) system in each front brake lines after the master cylinder rather than a single line out of the master cylinder then use either a single handle (push/pull) or two handle system. Finesse would be the watch word here but on the other-hand, drifters do use braking systems to get the rear of the car lose allowing them to drift on asphalt like dirt trackers have done for years.

Noodling is a good term for working things out in your ka-noggin'.

[E_bug]

Vehicle stability control as per Toyota .
It uses the input from the yaw rate sensor plus the g sensor along with the TRC inputs from the wheels.
It is meant to keep you on the road .

You are thinking to implement this for spirited driving?

[spectre6000]

I'm talking about building this into the steering system; no additional controls for the driver. You turn the wheel, all of this is driven off either the steering box or the steering shaft as discussed above. Totally passive. Maybe it would need to be defeatable somehow for more regular driving.

This is bouncing around in my noodle because I live up in the mountains, and because of all the flooding we've had recently, I have a lot of really long windy drives between me and just about anything I might need to drive to. Taking the switchbacks at speed is fun, but cutting the brakes could make it even more fun. This also has obvious race implications as well.

Actually, I might have just settled my concern about only braking the rears... I was looking for some literature of some sort from Porsche about the system to better explain it, and found this little gem:

PTV in conjunction with the manual gearbox, or PTV Plus with Porsche Doppelkupplung (PDK), are available as options for the 911 Carrera models and standard in the 911 Carrera S models. Both systems actively enhance vehicle dynamics and stability. Operating in conjunction with a mechanical (PTV) or electronic (PTV Plus) rear differential lock, they work by braking the rear wheels as the situation demands.

As a function of steering angle and steering speed, accelerator pedal position, yaw rate and vehicle speed, PTV and PTV Plus are able to improve steering response and steering precision by specific braking of the right or left rear wheel.

To be more precise, this means that when the car is driven assertively into a corner, moderate brake pressure is applied to the inside rear wheel. Consequently, a greater amount of drive force is distributed to the outside rear wheel, inducing an additional rotational pulse (yaw movement) around the vehicle’s vertical axis. This results in a direct and sporty steering action as the car enters the corner.

At low and medium vehicle speeds, PTV and PTV Plus significantly increase agility and steering precision. At high speeds and when accelerating out of corners, the rear differential lock ensures greater driving stability. With PTV, the differential lock is regulated mechanically; with PTV Plus, it is regulated electronically and the torque distribution is infinitely variable. Whichever system is fitted, it interacts with Porsche Stability Management (PSM) to improve driving stability on a range of surface conditions, including the wet and snow.

For the driver, this means remarkable stability, easier handling and outstanding traction as well as greater agility at every speed with precise steering and stable load transfer characteristics. What else? Unrivaled driving pleasure at every twist and turn.

Obviously we're skipping the limited slip diff (maybe not obviously, but that's the case regardless) and all the fancy fun sensors and doing the whole shooting match mechanically using passive hydraulic systems. I think making it defeatable would probably be necessary, and doing so from the driver's seat a huge plus. It would likely need to be pretty dead on center and for a few degrees of steering wheel turning, but once you get beyond a certain degree at the wheel (beyond the sort of turn you're likely to see just driving around town) cutting the inside brake could be very beneficial (as thoroughly investigated and vetted by Herr Porsche's boys). Rigging it as I stated in the OP along with a tunable amount of dead travel would make it build brake pressure the harder you turn into the corner.

[Ol'fogasaurus]

Installing it on the rear wheels makes more sense and would be less scary if you had grabby brakes.

I still think that you are going to need much more technology than you are considering right now. As was stated, the yaw/horizontal relationship of the car to the road needs to be dealt with also. I still think brake wear could be increased also.

Lee

[Piledriver]

What Could Possibly Go Wrong?

I actually love the idea.
Implementing it without computer control AND an ABS system will be iffy.

[spectre6000]

As was stated, the yaw/horizontal relationship of the car to the road needs to be dealt with also.

Please explain. The whole reason for posting this idea is to figure out exactly how I'm crazy.

Implementing it without computer control AND an ABS system will be iffy.

Why?

[Piledriver]

The reason the high end traction/stability control systems work is due to computer control AFAICT.

I visualize an analog // manual system to be ~an integrated steering brake that works off steering inputs.
You will need something to allow it to be speed sensitive, and not reduce control..

I can kinda see this working with an electric power steering setup...

[Ol'fogasaurus]

Reread you quote from Porche; I just used some different words; the body lean I added is part of what I think they said. That and as they said, road conditions must be considered.

Consider that it is wise that you turn off cruise control in inclement weather as it get dangerous as the computer is still a non-thinking thing. It can be helped with a lot of data but there is a point.... I kind of consider that this might be similar to be the same kind thing... I think.

One of the things my father instilled into me (e.g., 'why did you do that' or 'did you consider') and I keep telling my wife; you can't think just linear, you have to think in all directions; you (metaphoric you) can miss a lot of things thinking linear.

I have my buggy set up so that I don't have to use the turning brakes any more than I have to but on tight turns they do come in handy... as long as you release them soon enough. Also, remember some states frown very harshly on turning brakes on a street driven car. I don't know how the drifters (if they do) get by with them myself.

[spectre6000]

I see what you're saying about computers helping with things. My complaint with the computer driven traction control systems (and I think the complaint of most professional drivers that turn them off when they're driving aggressively, not that I'm a professional driver or anything) is that you can't always predict when it's going to do what. My noodles are telling me that this would feel a lot like variable ratio steering as the inside rear brake grabs harder and harder as you turn deeper and deeper into the turn. If it were to be a binary type system (1 or 0, on or off) I think it could lead to some very unpredictable results that would be unsafe, but if I could figure out how to adjust the braking force of the cutting brake, I think it could be all but transparent.

Speaking of transparency, I think the best way to implement this would be to have the cutting brake as a completely separate system from the regular brakes for wear, adjustability and safety reasons. It would be pretty simple to fab up a bracket that allows for two calipers on the same rotor; one for regular braking, a second for the turning brakes.

Any ideas on how to make the turning brake an adjustable system? Hydraulic expansion tanks? Are there calipers or masters that are adjustable? I'm sure there's a pretty straightforward way, I've just never dug too deep into braking systems. Tuning brakes seems like it's something that should have been done before.

[Ol'fogasaurus]

I see what you're saying about computers helping with things. My complaint with the computer driven traction control systems (and I think the complaint of most professional drivers that turn them off when they're driving aggressively, not that I'm a professional driver or anything) is that you can't always predict when it's going to do what. My noodles are telling me that this would feel a lot like variable ratio steering as the inside rear brake grabs harder and harder as you turn deeper and deeper into the turn. If it were to be a binary type system (1 or 0, on or off) I think it could lead to some very unpredictable results that would be unsafe, but if I could figure out how to adjust the braking force of the cutting brake, I think it could be all but transparent.

Speaking of transparency, I think the best way to implement this would be to have the cutting brake as a completely separate system from the regular brakes for wear, adjustability and safety reasons. It would be pretty simple to fab up a bracket that allows for two calipers on the same rotor; one for regular braking, a second for the turning brakes.

Any ideas on how to make the turning brake an adjustable system? Hydraulic expansion tanks? Are there calipers or masters that are adjustable? I'm sure there's a pretty straightforward way, I've just never dug too deep into braking systems. Tuning brakes seems like it's something that should have been done before.

Paragraph 1: Yep, headache city! I don't know what the answer would be as I am not really a computer person.

Redundant braking system... Somewhere in the back of my mind I seem to remember someone selling a dual caliper braking kit (http://www.bing.com/images/search?q=dua ... &FORM=IGRE) An interesting concept I must admit.

I have only seen Armstrong (arm strong/manual) units but look into what the drifters are using. Again, I have a memory of watching drifting and a comment being made that gave me the idea that what they have might just be a bit different than us'n off-roads might be using. http://www.ebay.com/sch/i.html?_nkw=drifting+e+brake http://www.driftsession.com/drifting_te ... _drift.htm (I did a search using "drifting turning brake" and came up with a whole passle of URLs. On the second URL, read what is said about drifting a stick)

[spectre6000]

The fact that dual caliper setups are commercially available is another encouraging thing. Allowing the brakes to properly vent and cool with two calipers seemed like it might be a limiting factor, but that mitigates the concern somewhat.

I'm pretty sure drifters actuate both rear brakes equally; essentially just a run of the mill e-brake. Maybe with a second caliper setup for similar considerations. The off road set seems to have the closest readily available thing to what I'm getting at.

Unfortunately, I don't yet have a race car to try this on or the facilities to do so. My '57 Ghia DD is not a good test mule either. If I already had discs in the rear, this would likely be a pretty inexpensive feat to accomplish assuming I can figure out a decent way to handle actuation at the steering column end.

[Ol'fogasaurus]

I am pretty sure you are right about them working with both wheels (e-braking) to hang the rear of the car out. That is what they used to do with FWD vehicles that were running closed course/sections Pro Rallying around here years ago; similar to what I have heard Rally-X is about... but different.

Like I said, I think it is going to be a hand full dealing all the handles, foot to do things, and arm waving things at the same time while still concentrating on where you are going. If the water gets high enough then you are going to need controls for a propeller and a rudder too.

Lee

[Jadewombat]

This question was posed to the Torsen guys a couple of years. Not this exact question, but they were asked to comment why some manufacturers use the same word "traction control" or pulsing of the brakes to the wheel that slips is the same as a true LSD system. The guy from Torsen said no, then paused, maybe in the future they will be equal.

I know this wasn't your question, but their answer was very similar to what you proposed. The Torsen guy said the technology has to be so advanced to take into account all of these things, speed, yaw, turn of the steering wheel, power applied, etc. The system can apply braking, the trick is to get it exactly right. Just enough brake to grab that wheel and not lock it up.

Just for clarity, you're talking about braking into a corner, correct? This poses the inevitable question, if you're trying to go fast you want to use the brakes only when you have to (not slow you down more).

[spectre6000]

Nope. Not what I'm talking about. I tried to make some sort of paintbrush type drawing, but I can't figure out how to convey the things that need conveying within my skill level.

Imagine you have a regular brake system. A disc at each wheel. Nothing out of the ordinary whatsoever. Nothing. Brakes are normal.

Imagine you have your regular steering setup. Steering box, pitman arm, tie rods, etc. Nothing out of the ordinary.

Here's the part that deviates from the norm: You have a 4" diameter sprocket welded to the steering column between the steering column tube and the coupling disc (I'm imaging this on a Ghia, but it's the same on a beetle). From this sprocket is a chain going to another 2.5" diameter sprocket (the ratio can be whatever, but for illustrative purposes I'm trying to be as detailed as possible). This sprocket drives the input shaft of a small rack and pinion-type steering box. Smallest you can find. All of this is on top of the frame head, under the gas tank. With this arrangement, as the steering column is turned, the secondary steering box also turns, albeit not as quickly. Instead of the steering box pushing and pulling tie rods, it has pushrods that actuate single circuit brake master cylinders. Each master cylinder has a line that runs to a second caliper mounted to the rear brakes. As you turn the steering wheel, the inside rear brake starts to actuate. Slowly at first as if you're going from 55 to 50; but as you turn harder the brake grabs harder. Adjustment of the system can be done by changing the ratios of the sprockets and adjusting the play in the pushrods (extra play to eliminate it from action on center).

Here's a video of Porsche's snooty sounding narrator describing the system:
http://www.youtube.com/watch?v=xKSHIZRE-xM

They say that it works if you're driving a "certain way", so this would be always on (unless I can figure out an easy way to make it defeatable). It doesn't just grab on and hold, it gradually increases pressure as you're actively turning into the curve. It should never lock up. You'd have to be in a pretty tight hair pin to even get it to be super noticeable outside of the reduced turning radius.

It may just be something I have to build (eventually) to see if it works and/or show what I'm trying to convey...