AngryCorvair
AngryCorvair MegaDork
12/18/19 9:59 p.m.

Over the years, there has been a lot of interest on this forum in the SAE Applied Vehicle Dynamics seminar which I help teach. Well, I am glad to announce that this January we will be teaching a two-day seminar called Applied Brake Controls, at a vehicle test facility in the beautiful Upper Peninsula of Michigan. We will get a lot of seat time on snow, ice, and combined surfaces as we delve into the topics of:

DAY ONE - ABS & TCS

  • ABS Part I: Performance on Homogeneous Surfaces
    • Mu-slip curves and the friction circle
    • Defining stability, steerability, stopping distance 
    • ABS objectives and strategies
    • ABS performance on homogeneous surfaces
    • Driving exercise - combined braking and steering on low-coefficient surfaces
  • ABS Part II: Performance on Splits and Transitions
    • Basics of ABS wheel control
    • Why splits and transitions require unique control
    • ABS performance on split-mu surfaces
    • ABS performance during transitions
    • Driving exercise - ABS transitions and split-mu deceleration 
  • TCS Part I: Performance on Homogeneous Surfaces
    • Revisiting stability, steerability, acceleration performance 
    • TCS objectives and strategies
    • Basics of TCS wheel control
    • TCS performance on homogeneous surfaces
    • Driving exercise - combined accelerating and steering on low-coefficient surfaces

DAY TWO - TCS & ESC

  • TCS Part II: Performance on Splits and Transitions
    • Why splits and transitions require unique control
    • TCS performance on split-mu surfaces
    • TCS performance during transitions
    • Driveline architecture implications
    • Driving exercise - TCS transitions and split-mu acceleration
  • ESC Performance 
    • The physics of turning
    • ESC objectives and strategies
    • Basics of ESC wheel control 
    • ESC performance on homogeneous surfaces
    • Driving exercise - double lane changes on low-coefficient surfaces
  • ABS, TCS, and ESC Interactions 
    • Review of ABS, TCS, and ESC wheel control
    • Moding considerations
    • Driving exercise - low-coefficient handling course

Seats are still available, and it would be cool to see someone from this forum, and/or someone from GRM, in attendance. More info at the link below:

https://www.sae.org/learn/content/c0610/

Mods / Magazine folks, please LMK if this oversteps the boundaries of free advertising.

ShawneeCreek
ShawneeCreek HalfDork
12/19/19 9:09 a.m.

I'm interested, and it's actually applicable to my work at the moment. Even better, I've got approval from my manager. Now I'm just waiting on approval from his manager and HR. I'm hopeful. :)

AngryCorvair
AngryCorvair MegaDork
12/19/19 10:30 a.m.
ShawneeCreek said:

I'm interested, and it's actually applicable to my work at the moment. Even better, I've got approval from my manager. Now I'm just waiting on approval from his manager and HR. I'm hopeful. :)

Outstanding! And it’s early in the calendar year when training budgets are full!

David S. Wallens
David S. Wallens Editorial Director
12/21/19 9:48 a.m.

Sounds cool. 

AngryCorvair
AngryCorvair MegaDork
12/21/19 9:57 a.m.
David S. Wallens said:

Sounds cool. 

I can hold a seat for you... :-)

David S. Wallens
David S. Wallens Editorial Director
12/21/19 10:03 a.m.
AngryCorvair said:
David S. Wallens said:

Sounds cool. 

I can hold a seat for you... :-)

If it weren't the days after the Rolex At Daytona....

ShawneeCreek
ShawneeCreek HalfDork
1/14/20 8:43 a.m.

Much success. See you in the UP.

mazdeuce - Seth
mazdeuce - Seth Mod Squad
1/14/20 8:50 a.m.

In reply to ShawneeCreek :

Be sure to report back. I bet you totally dig the course. 

ShawneeCreek
ShawneeCreek HalfDork
1/31/20 1:27 p.m.

Now that I’ve caught back up with work and life let’s get a summary for everyone.

First off, this class SAE C0610 - Applied Brake Controls Test Track Experience: ABS, TCS, and ESC is taught by James Walker, Jr. who also teaches the class that mazdeuce - Seth took last year (SAE C0414 - Applied Vehicle Dynamics). You can read all about his experience with that class here. https://grassrootsmotorsports.com/forum/grm/sae-co414-applied-vehicle-dynamics/151662/page1/.

First up, the training facility was graciously loaned and prepared for the SAE by BWI Group (formerly part of Delphi, aka General Motors). This is a huge deal. There are several winter test facilities in the Upper Peninsula (UP) of Michigan owing to its snow, low temperatures, and proximity to the automotive industry in Detroit. The winter test season usually runs only from December to March and is highly dependent on the weather.

Unlike a pavement racecourse or test track a winter test facility will include an ice field, a snow field, traction hills, snow circles, snow handling tracks, and split-mu (pronounced “mew”) areas. All of these require maintenance before, after, and sometimes during use. The ice must be cleaned of snow and smoothed with the high traction (high mu) run up and run off areas clean and dry. And all the snow fields and tracks must be kept clear of new snow and precisely groomed and packed into a consistent, testable surface. This means that there are 4-6 employees out there running broom trucks, plow trucks, and snow groomers just to maintain a relatively constant surface in the face of temperature changes, changes in solar load (cloudy or sunny), and lake effect snow showers from Lake Superior.

And while our SAE class was out on the surfaces the many other paying customers of BWI could not. This SAE course hasn’t been run since 2008 or so in part because they lost access to a winter test facility. I’m very grateful to the staff of BWI for letting us in and being wonderful hosts.

Fun fact, since the test vehicles on the snow courses never touch the pavement, you can set up a different course every year in the open space available. What was a handling course one year could be a circle the next year, and part of the snow field the next year. In the picture below I outlined the courses that we use this year. For a sense of scale, that’s a runway on the right side of the picture and the snow circle is a mile in circumference.

ShawneeCreek
ShawneeCreek HalfDork
1/31/20 1:28 p.m.

The students in my class were an interesting mix across industries. There were three test technicians from another vehicle test facility, a chassis system manufacturing engineer from Honda, an engineer who designs the electric motors and control systems for 1 million pound GVW mining dump trucks and two engineers from the company that designs those dump trucks, an engineer who is designing and integrating rear steering systems, and me. It was interesting where the discussions went. Because what might be useful on a Honda could be entirely dangerous in a million-pound dump truck. And do you know what you need if you have a million-pound dump truck? A 2-million-pound scale. The size is staggering. And those engineers are working on anti-lock brakes (ABS), traction control systems (TCS), and electronic stability control (ESC) for those dump trucks. At first glance you would wonder why such a slow vehicle would need these “performance” systems. But then you think that if you were moving one million pounds at 45 miles per hour on mud or gravel near large drop offs and up hills, you want as much control as you can get.

Much like Seth’s experience in Thermal, CA I found the lead instructor and driving instructors very, very knowledgeable. Collectively they know more about vehicle control and systems tuning that I could ever hope to learn. As you might expect, they are all car guys of one sort or another and have lots of good stories. I also enjoyed meeting AngryCorvair and hearing more about his current project. And to give him E36 M3 about trying to fit 325 rear tires, because does it really need it? He countered with, “and this coming from the man who put a flying-eagle-painted minivan body on a Pontiac G6?” :)

ShawneeCreek
ShawneeCreek HalfDork
1/31/20 1:28 p.m.

As you can see from AngryCorvair’s original post the class was divided into six modules and covered how brake controls are used for ABS, TCS, and ESC both on homogenous (constant) surfaces and on splits and transitions (side to side and/or front to back). There is no way to cover everything here, so I’ll just hit a few of my highlights. You can take the class if you want to learn more. It is really interesting stuff.

First, we need to grab a concept that Seth talked about: amax ≡ µpeak. This means that the maximum acceleration (or deceleration, aka braking) is exactly equal to the peak coefficient of friction (aka, mu). That means that regardless of how big your big brake kit is on your Miata, or how sticky your tires are, the car cannot generate more than 0.1 g of acceleration on a surface with a mu of 0.1. It’s a seemingly simple idea with large implications. One of which is that no matter how good you tune your anti-lock brakes you are always limited by the laws of physics. It may be able to react better than a human driver in certain situations like split-mu, but it can’t stop faster than physics will allow.

Next, we need to understand the mu-slip chart. Along the bottom we have the slip axis from zero slip at the left to 100% slip (aka, a locked tire) on the right. The y-axis is the friction potential or mu of the system. For a tire to generate force it must generate slip. The more slip, the more force, up to a point. And that point is µpeak. Once a tire passes mu peak it locks up.

The goal of an ABS system is to stop as quickly as possible (max deceleration, aka amax) which means that it wants to keep the tires as close as it can to mu peak. amax ≡ µpeak. The problem for the ABS designer is that mu peak is a constantly moving and changing target that can be affected by ambient temperature, surface moisture, surface type, weight transfer, vehicle loading, road inclination, and more. And each of those variables can change over the course of a single stop.

So how do you go about finding mu peak and staying near it? The answer is you brake hard enough that you go past it, then brake less until the tire recovers, then brake hard again, and wait for the tire to recover, and repeat until the stop is complete. Engineers call this peak seeking control. Pretty cool, huh? But it’s not always that easy. What if you transition from dry pavement to ice (high mu to low mu)? Suddenly you need much less braking force. Or from ice to dry pavement (low mu to high mu)? More braking force. Or dry pavement to gravel (solid surface to deformable surface)? This is where the engineers and programmers earn their keep. They must figure out how to detect these transitions (usually with just the data from the four wheel-speed sensors) and react appropriately.

My favorite vehicle demonstration was related to these transitions, specifically the high to low and low to high. On the high to low we performed a panic level stop starting on dry pavement and ending on ice. The ABS started pulsing on the pavement portion of the stop, but once we transitioned to the ice the brake pedal was physically forced back against my foot as the ABS pump moved brake fluid away from the calipers and back into the master cylinder. On the low to high demonstration we did the same panic stop, just starting on ice and ending on dry pavement. In that case the ABS pulsed away on the ice and we were gradually coming to a stop (as you do on ice). Once we transitioned to the dry pavement, we didn’t stop any faster for a few brief moments because the ABS system hadn’t yet figured out that we were on dry pavement. Once it did figure that out the anchor was dropped, and we came to a rapid stop. But that moment of light braking was very interesting.

ShawneeCreek
ShawneeCreek HalfDork
1/31/20 1:29 p.m.

Overall, I really enjoyed this training course. It was informative, interesting, and the driving exercises really cemented in the concepts that were taught in the classroom. We missed out on a couple of the driving exercises simply because the weather was wrong. But that is just the nature of winter testing. I’m proud to say that over the two days I managed to not get the test vehicle stuck in the snow or stuffed into a snowbank. Now I just need to convince my boss that the SAE C0414 Applied Vehicle Dynamics course is applicable, because that looks like a lot of fun and like a lot more to learn. smiley

David S. Wallens
David S. Wallens Editorial Director
1/31/20 1:36 p.m.

That rocks. Thanks for the report. 

AngryCorvair
AngryCorvair MegaDork
1/31/20 1:47 p.m.
ShawneeCreek said:

The goal of an ABS system is to [edit]balance vehicle stability, steerability, and stopping distance, according to the driver's requests, and within the laws of physics, which is sometimes to [/edit] stop as quickly as possible (max deceleration, aka amax) which means that it wants to keep the tires as close as it can to mu peak. amax ≡ µpeak. ...

FTFY

ShawneeCreek
ShawneeCreek HalfDork
1/31/20 2:05 p.m.
AngryCorvair said:
ShawneeCreek said:

The goal of an ABS system is to [edit]balance vehicle stability, steerability, and stopping distance, according to the driver's requests, and within the laws of physics, which is sometimes to [/edit] stop as quickly as possible (max deceleration, aka amax) which means that it wants to keep the tires as close as it can to mu peak. amax ≡ µpeak. ...

FTFY

Gah. (hangs head in shame). Yes, you are correct. ABS is juggling all of those things. And for everyone else a few definitions:

  • stable vehicle has lots of rear lateral force capability (rear grip)
  • steerable vehicle has lots of front lateral force capability (front grip)
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