AWD Braking Discussion: 80 Rear Proportioning Valve Adj and Service

[landtank]

That's not true.

At any given amount of force on the brake pedal the front braking will remain the same regardless of how the proportioning valve is adjusted. Adjusting the proportioning valve will on increase of decrease the amount applied to the rear brakes.

Adjusting the prop valve affects total brake capacity, and can put brake force distribution closer to the factory targets (in relation to Ideal).

That's pretty much what I wrote, just in different language.

 

[SUMOTOY]

Defining Select Low Principle

According to my 1992 Camry manual these cars which are front wheel drive only have a discrete 4 wheel ABS system.

Contained in the actuator assembly is 4 solenoids, 1 for each wheel. to control lockup.

Problem: Select Low Principle

Rick, 4 solenoids doesn't mean 4 independent channel ABS. Select Low Principle is a concept in ABS algorithum programming that means that the two rear solenoids are operated in unison to the rear wheel with the least amount of tractive force. This means the 2 rear solenoids are operated together.

A lot of 4w/4ch systems were installed in hardware anticipation of traction control systems.

I wrote a note to my traction control engineer bud to find out if Select Low Principle has been modified in the last couple years. To wit, are their any known ABS computers (under braking) that allow 4 different solenoid activations. My bet would be that the 1992 camry application of 4hcannel is to eliminate the rear proportioning valve hardware more than 4 independent activations of ABS.

I also see no way to incoporate 4 independent channel ABS without yaw sensing as a minimum requirement.

ST

 

[landtank]

My bet would be that the 1992 Camry application of 4hcannel is to eliminate the rear proportioning valve hardware more than 4 independent activations of ABS.

Nope, a rear tandem proportioning valve is present in the system.

I can't imagine going through the expense of the design and build cost of this system and not adding a chuck of software to take advantage of it.

 

[SUMOTOY]

...
I can't imagine going through the expense of the design and build cost of this system and not adding a chuck of software to take advantage of it.

I can. Here's from the 2006 Honda Ridgeline marketing blurb (the first time I've seen SL presented as propoganda). This is the Ridgline with stability control, traction contro, active yaw, EBD, and throttle control. And with all the latest and greatest gadgets, we find this in the braking section:

" Brake Assist is used to assist with brake function during accident avoidance maneuvers. At the rear, a select-low braking strategy is used to preserve directional stability in slippery driving. In the event one rear wheel verges on lock-up, triggering a pressure modulation at that wheel, brake pressure is also diminished at the adjoining wheel to preserve lateral stability. " = Definition of Select Low Rear Braking with ABS

I'm pretty sure Select Low is still the norm to this day. Marketing it as an advantage might be new. This is usually found buried pretty deep in the service training manuals IME. Even Bosch latest ABS 5.3 uses Select Low Rear proportioning under ABS braking. I'm trying to find if there is an exception yet. 4 ABS solenoids are usually there for EDL (electronic differential locking) on rwd/awd and for TCS (Traction Control Systems) on rwd/awd, and Stability Control on fwd/rwd/awd where independent rear abs activation is a function of acceleration torque vehicle dynamics, not braking torque vehicle dynamics.

I suspect that the 4ch solenoid system on the camry is a parts bin issue of the ABS box, not an exception to select low ABS programming.

ST

 

[landtank]

I can. Here's from the 2006 Honda Ridgeline marketing blurb (the first time I've seen SL presented as propoganda). This is the Ridgline with stability control, traction contro,l active yaw, EBD, and throttle control. And with all the latest and greatest, we find this:

" Brake Assist is used to assist with brake function during accident avoidance maneuvers. At the rear, a select-low braking strategy is used to preserve directional stability in slippery driving. In the event one rear wheel verges on lock-up, triggering a pressure modulation at that wheel, brake pressure is also diminished at the adjoining wheel to preserve lateral stability. "

I'm pretty sure Select Low is still the norm to this day. Marketing it as an advantage might be new. This is usually found buried pretty deep in the service training manuals IME. Even Bosch latest ABS 5.3 uses Select Low Rear proportioning under braking.

ST

There is no point in posting info that doesn't apply. Post up some technical info for a 1992 Camry or don't bother.

 

[SUMOTOY]

There is no point in posting info that doesn't apply. Post up some technical info for a 1992 Camry or don't bother.

Your Camry has Select Low in the rear Rick. Neither example is 80 related. Bosch 5.3 is the latest and most sophisticated ABS/EDL/Traction/Stability Control ABS box on the market today, and it uses Select Low Principle. There is no doubt in my mind if it has it, so does your Camry, and so does every single Toyota application.

I speak to a couple of engineers that do traction systems, one guy that travels worldwide as a supplier, the other for a specific US supplier. Right now, there are no exceptions to SL that either can find. I asked for an update from them both a few days ago. Both got back to me that it's going to be a 'search' to find the exception.

With all due respect, a 92 Camry isn't it?



ST