AWD Braking Discussion: Ideal Brake Force Distribution

[SUMOTOY]

SAE Studies on ABS vs non ABS vs Control

• Do anti-lock brakes really work?
  Anti-lock brakes really do help you stop better. They prevent wheels from locking up and provide the shortest stopping distance on slippery surfaces. But do they really prevent accidents? This is the true measure of the effectiveness of ABS systems.
  The Insurance Institute for Highway Safety (IIHS) has conducted several studies trying to determine if cars equipped with ABS are involved in more or fewer fatal accidents. It turns out that in a 1996 study, vehicles equipped with ABS were overall no less likely to be involved in fatal accidents than vehicles without. The study actually stated that although cars with ABS were less likely to be involved in accidents fatal to the occupants of other cars, they are more likely to be involved in accidents fatal to the occupants of the ABS car, especially single-vehicle accidents. There is much speculation about the reason for this. Some people think that drivers of ABS-equipped cars use the ABS incorrectly, either by pumping the brakes or by releasing the brakes when they feel the system pulsing. Some people think that since ABS allows you to steer during a panic stop, more people run off the road and crash.

I did some digging around my files and found the SAE papers of the above summary, so that I could confirm some of my bag-o-stats I quote quite often in Vehicle Control Discussions

SAE 1999-01-1288 "Driver Crash Avoidance Behavior with ABS in an Intersection Incursion Scenario on Dry Versus Wet Pavement"

SAE 1999-01-1290 "Driver Crash Avoidance Behavior with ABS in an Intersection Incursion Scenario on the Iowa Driving Simulator"

NHTSB Stats
TO ABS Credit
Fatalities in multivehicle (M-V) accidents
DECREASED 24% in Wet Conditions
Non Fatalities in M-V Accidents
DECREASED 14% in Wet Conditions

That's the best it gets....

The Stats are sobering In Accident Avoidance in Single Vehicle Accidents WITH ABS:
Fatalities in Rollovers INCREASED 51% on Dry Road
Fatalities in Side Impact INCREASED 69% on unfavorable roads
Fatalities in Side Impact INCREASED 61% on favorable roads
Fatalities in Run Off Road INCREASED 29% in Dry
Fatalities in Run Off Road INCREASED by 17% in Wet


The interesting stat in the 1290 Simulator Avoidance Test Study investigating possible causes of the above stats, they found in controlled Accident Avoidance Tests:
23% of Females ran off road during Avoidance with ABS
50% of Females ran off road during Avoidance with non-ABS
(One of the admitted few statistically significant conclusions in the test)
Compared to
40% of Males ran off road during Avoidance with ABS
35% of Males ran off road during Avoidance with non-ABS

These studies and the resulting Final NHTSB report concluded that ABS on wet pavement was good, but could find no correlation to any factor regarding increases in other ABS accidents. It is suggested that having no steering control with conventional brakes may be better.

ABS may give the ability to have more control over *Steering* under braking, the SAE studies don't appear to support many of the positions here that Vehicle Steering wtih ABS VS. Vehicle Control with ABS has a positive correlation in terms of safety.


ST

 

[GeoRoss]

To be valid, these fatalities should be sorted by highway vs town and DUI. If they are, they are sobering. If they are not, much of the single car can be adjusted due to increase in the % of SUV's on the road and the increase in highway speed limits.

I did some digging around my files and found the SAE papers of the above summary, so that I could confirm some of my bag-o-stats I quote quite often in Vehicle Control Discussions

SAE 1999-01-1288 "Driver Crash Avoidance Behavior with ABS in an Intersection Incursion Scenario on Dry Versus Wet Pavement"

SAE 1999-01-1290 "Driver Crash Avoidance Behavior with ABS in an Intersection Incursion Scenario on the Iowa Driving Simulator"

NHTSB Stats
TO ABS Credit
Fatalities in multivehicle (M-V) accidents
DECREASED 24% in Wet Conditions
Non Fatalities in M-V Accidents
DECREASED 14% in Wet Conditions

That's the best it gets....

The Stats are sobering In Accident Avoidance in Single Vehicle Accidents WITH ABS:
Fatalities in Rollovers INCREASED 51% on Dry Road
Fatalities in Side Impact INCREASED 69% on unfavorable roads
Fatalities in Side Impact INCREASED 61% on favorable roads
Fatalities in Run Off Road INCREASED 29% in Dry
Fatalities in Run Off Road INCREASED by 17% in Wet


The interesting stat in the 1290 Simulator Avoidance Test Study investigating possible causes of the above stats, they found in controlled Accident Avoidance Tests:
23% of Females ran off road during Avoidance with ABS
50% of Females ran off road during Avoidance with non-ABS
(One of the admitted few statistically significant conclusions in the test)
Compared to
40% of Males ran off road during Avoidance with ABS
35% of Males ran off road during Avoidance with non-ABS

These studies and the resulting Final NHTSB report concluded that ABS on wet pavement was good, but could find no correlation to any factor regarding increases in other ABS accidents. It is suggested that having no steering control with conventional brakes may be better.

ABS may give the ability to have more control over *Steering* under braking, the SAE studies don't appear to support many of the positions here that Vehicle Steering wtih ABS VS. Vehicle Control with ABS has a positive correlation in terms of safety.


ST

 

[SUMOTOY]

To be valid, these fatalities should be sorted by highway vs town and DUI. If they are, they are sobering. If they are not, much of the single car can be adjusted due to increase in the % of SUV's on the road and the increase in highway speed limits.

Good point, why I went after the tests, not the stats. The SAE tests were an attempt to attribute the all encompassing statistics to come to some sort of conclusion regarding the statistics. That is not a factor in the controlled SAE tests (all participants were sober).

Remember the stats are 1996 (well after speed limit increases) and the tests took a cross section of vehicles.

SAE controlled tests couldn't make the statistics significant to any attributable cause. They hinted that non ABS lockup may yield less steering ability, not such a bad thing.

I assure you, these are sobering stats. And the reason you now see throttle control, drive-by-wire swithes (read if brakes are on, accelerator is off), yaw, pitch, and a plethora of steering correcting matricies. However, in my 202 thread, I spoke to Select Low Rear Braking, which is still the standard for ABS control systems. The nut behind the wheel is the factor in control (specifically lack thereof) not the ABS.

ST

 

[SUMOTOY]

What might be more interesting to explore in the SAE studies AND the NHTSB summary is the data showed maximum steering angle in accident avoidance testing was *higher* with conventional brakes than with ABS (that appears counterintuitive to ABS having more steering control). In the test conclusions, this was theorized to be attributed to ABS 'feel' (no significance found in the testing variables). My opinion is that the answer might be found by testing the relation of conventional rear brake pressures vs ABS Select Low rear brake pressures. The effect of these two systems in terms of vehicle dynamics vs rear braking pressures differs in terms of steering input angle and actual chassis steering angle.

ST

 

[Walking Eagle]

So is this how our system operates? If not, please reword, don't explain, just reword it.

Four-channel, four-sensor ABS - This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

Romer - if I may interject a much simpler answer than sumo gave

Thre-channel, four-sensor ABS - There is a speed sensor on all four wheels and a separate pair of valves for both front weels. The rear wheels are controled by one pair of valves. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force. It controls the front wheels independantly. The rear wheels are controled together as there is only one brake line feeding that axle - with a T- fitting.

The reason I say a pair of valves, is one controls in, and one controls out. I didn't know that till I started looking at more info. on ABS.

Now, this part I'll seperate, cause I"m not 100% on the 80 series. But it does seem that most all ABS systems use select low. Which means that the rear axle braking is determined by whichever tire has the least traction.

Does that work for ya'?

 

[Walking Eagle]

I should state that the opinions here-in represented by SUMOTOY are his opinions and do not represent the position of the forum Please consider this when evaluating SUMOTOYs opinions as they apply to your vehicle. This forum and the moderator do not recommend driving with the CDL engaged and the ABS off in normal driving conditions. Not saying he is wrong, just that it is his opinion.

X2.........................

I sometimes am extremelly envious of your self control Rome.

X3 -

X4 or 5 I guess

The one good thing is I figured out multi-quote!

Any thread that includes '101' from Sumo should also have this disclaimer. Actually, I personally feel that anything labled '101' aught to come from a better source than Sumo has. Say, a Automotive Engineer? A Toyota representative? Just seems anything that say's '101' is claiming to be teaching something, and if all it is supplying is someone's oppinions, '101' is not appropriate IMHO.

 

[SUMOTOY]

Romer - if I may interject a much simpler answer than sumo gave

The reason I say a pair of valves, is one controls in, and one controls out. I didn't know that till I started looking at more info. on ABS.

Now, this part I'll seperate, cause I"m not 100% on the 80 series. But it does seem that most all ABS systems use select low. Which means, according to Sumo and some of his sources, that the rear axle braking is determined by whichever tire has the least traction. The part I'm not 100% sure on is if they are in unison or if they are sequential on the 80. Unison would be one rear tire locks up, pressure to both brakes is released at the same time. Sequential would be the sensors show lockup of one wheel and pressure to that wheel is released, and then at some selected time interval, pressure is released at the opposing wheel. Sumo claims all ABS systems are in unison - facts (see links on other threads) say that at least some are sequential.

Does that work for ya'?

No, but you are closer to agreeing with me.... All ABS rear systems are in unison under ABS braking. Don't confuse 'independent rear control' with stability control or traction control (the "facts" in the other threads). What happens in Select Low/Select High is that any rear solenoid activation is in unison. Period. Hence my statement that all 4 channel ABS systems under an 'abs braking event" are 3 channel ABS by definition. 2 circuits in unison, or one circuit (93 and 94 80's) controlling 2 brakes in unison. Same thing. In fact, you can find several 4 sensor/3 channel ABS computer boxes that interchange with 4 sensor/4channel ABS systems. Channel 4 is just doubled up on channel 3.

I'm 100% sure all 80's use Select Low Rear braking ABS algorithums.

ST

 

[Walking Eagle]

No, but you are closer to agreeing with me.... All ABS rear systems are in unison under ABS braking. Don't confuse 'independent rear control' with stability control or traction control (the "facts" in the other threads). What happens in Select Low/Select High is that any rear solenoid activation is in unison. Period. Hence my statement that all 4 channel ABS systems under an 'abs braking event" are 3 channel ABS by definition. 2 circuits in unison, or one circuit (93 and 94 80's) controlling 2 brakes in unison. Same thing. In fact, you can find several 4 sensor/3 channel ABS computer boxes that interchange with 4 sensor/4channel ABS systems. Channel 4 is just doubled up on channel 3.

I'm 100% sure all 80's use Select Low Rear braking ABS algorithums.

ST

Dude, do you know what unison means?

 

[landtank]

Dude, do you know what unison means?

Ya, that's a buffalo with one horn, right.

 

[SUMOTOY]

Dude, do you know what unison means?

Actually Heath, you will find the Traction Control guys don't use the word 'unison'. For Select Low and Select High Rear braking, these engineers refer to rear circuits in terms of *phase*. Under Select Low/Select High, the 2 rear brake ciruits are operated in phase.

Now, this part I'll seperate, cause I"m not 100% on the 80 series. But it does seem that most all ABS systems use select low. Which means that the rear axle braking is determined by whichever tire has the least traction.

I see agreement and perspective. I'm 100% sure that the 3 channel 80's use select low rear braking, because it is by definition. I'm also 100% sure that the 4sensor/4channel equipped 80's also use select low. I'll go further and say *all current production ABS systems use select low abs strategy. Some use an additional yaw pitch defined Select High in phase rear ABS to control sudden lane change under braking (note: this is in addition to Select Low programming)*.

ST

 

[Walking Eagle]

Actually Heath, you will find the Traction Control guys don't use the word 'unison'. For Select Low and Select High Rear braking, these engineers refer to rear circuits in terms of *phase*. Under Select Low/Select High, the 2 rear brake ciruits are operated in phase. ST

Hummm.... Sounds like by operating in phase, that they're not operating in UNISON. Perhaps 'they' don't use the word unison because it's not the correct word? It's your word, not mine. Phase sounds kinda like a period of time has passed, sorta like the word sequential? Does this sound familiar?

 

[SUMOTOY]

Hummm.... Sounds like by operating in phase, that they're not operating in UNISON. Perhaps 'they' don't use the word unison because it's not the correct word? It's your word, not mine. Phase sounds kinda like a period of time has passed, sorta like the word sequential? Does this sound familiar?

In phase, not sequential phase, or out of phase. In Phase, means when one solenoid is activating, so is the other to the exact same time, duration and frequency.

HTH

ST

 

[Walking Eagle]

In phase, not sequential phase, or out of phase. In Phase, means when one solenoid is activating, so is the other to the exact same time, duration and frequency.

HTH

ST

That's fine. I guess I was going by the dictionary meaning of phase

verb;
10. to put in phase; synchronize: to phase one mechanism with another.

Idiom(s):
in phase
In a correlated or synchronized way.


I mistakenly thought you might admit that since the pattent for asychronized abs has been around for a decade, that perhaps not all operate 'in unison' anymore. Guess that's not going to happen eh?

 

[SUMOTOY]

That's fine....

I mistakenly thought you might admit that since the pattent for asychronized abs has been around for a decade, that perhaps not all operate 'in unison' anymore. Guess that's not going to happen eh?

Where is this sequential programming happening? That patent was the first attempt by bosch to look at yaw movement to institute an oversteer moment. That idea was replaced with a simpler patent using the Select High principle. Both accomplish the same thing, a moment of oversteer. Why address the variables of two different mu inputs? Again, just take the fact you have impending lockup and hit the ABS *in phase* to both rear wheels based on the wheel with the highest traction. Select Low in reverse, simple and easy.

Put more simply, when Bosch applied for the patent for out of phase sequential rear ABS you reference, they were 6 years from figuring out Select High was a much more effective application? And, Select High is now found in the latest Gen 8.0 Bosch ABS, and 'just' introduced (bosch licensed) in the Honda Accord for the JDM.

ST

 

[Walking Eagle]

Put more simply, when Bosch applied for the patent for out of phase sequential rear ABS you reference, they were 6 years from figuring out Select High was a much more effective application? ST

uhm, the patient I reference is a Lucas patient, not a Bosch patient.

 

[landtank]

uhm, the patient I reference is a Lucas patient, not a Bosch patient.

LOL, I don't know why you guys bother with him. He either doesn't read your replies or can't comprehend them. Either way it will never end.

 

[Grench]

LOL, I don't know why you guys bother with him. He either doesn't read your replies or can't comprehend them. Either way it will never end.

Unless Romer caps it like he did the other identical thread (thank you Romer!).

At least now the number of mind numbing repetitions of the same crap have narrowed.

 

[Walking Eagle]

Unless Romer caps it like he did the other identical thread (thank you Romer!).

Heck, I half wish he'd delete all three of them, and I'm one of the participants!