Hoping for more detail on how VSC works

I know this topic has been thoroughly discussed, and I've been through most of the previous threads. I believe I understand the philosophy, and I even made myself a cheat-sheet in Excel to carry with me in my Tacoma.

I own a 2015 TRD Off-Road DCSB

Now that's it is winter here in Michigan, I'm getting ample opportunity to play with these different options. Hence, a few questions;

When running in 2HI with VSC ON, I understand it is an engine-regulated limited slip configuration. I believe Toyota calls this TRAC. My first question is, besides the throttle being regulated, what exactly is happening at my rear axle? Is the system modulating the rear brakes independently to control wheel-spin, or is something happening within the differential itself to transfer torque? The specifics are not clear to me.

That said, when in 2HI with VSC OFF, can I assume what ever is happening at the rear axle when TRAC is on continues to happen, but without engine regulation? (And to be clear, when TRAC is turned off, Toyota now calls the configuration Auto LSD?) If I'm accurate thus far, what's the point? It seems like not regulating engine output would just require the limited-slip system to work harder. Is that problematic for reliability?

In short, I'm confused about what type of traction control Toyota is using. I know some companies use mechanical options in the differential, but the fact that I'm not required to use special additives in the differential gear oil makes me believe Toyota's traction control version is accomplished with the brakes and wheel sensors alone.

Can someone shed some light on this for me? Am I even in the ballpark? I'm an engineer, but certainly not an automotive mechanic.

Thank you in advance

 

Even after a year i still play around with the modes. So yesterday we had a couple inches of snow for the evening commute, and i decided to turn off vsc to see how it handles, wont do that again. Kicked out the rear end and almost took out a mailbox. I promptly placed the truck into 4wd

 

Subbed, I'm confused too. I thought VSC controlled the brakes individually to keep you from spinning out and auto LSD applies the brake to the wheel that's spinning if your peeling out on ice.

Another questions, if we have the option to turn on and off the auto LSD then what kind of diff do we have? Is it just an open diff or is also a mechanical LSD diff? I have an off road if that matters.

 

I think 2008 was the last year Toyota put mechanical LSDs in the tacoma; after that year, they were mechanically open diffs, with an electronically brake-simulated LSD effect going on like you describe

 

Wouldn't a TRD OR have A-TRAC? That's what I have in mine anyway.

So the default mode (when AUTO LSD is not illuminated on the gauges) is A-TRAC/VSC. Wheel spin is monitored and brakes/engine modulated as needed. I assume this applies at all drive wheels.

AUTO LSD (A-TRAC OFF) will only modulate the brakes to maintain traction, and maybe only on the rear axle?

 

someone needs to link to davidk's thread on this .


Atrac is ONLY active in 4low on 09+TRD OR 4x4's when the atrac button is pushed.

Otherwise its standard trac / vsc

trac / vsc brakes all 4 wheels independently.

Turning off engine regulation (a quick tap of the traction control button, which turns on auto lsd / trac off in 4hi) turns off the engine controlling the throttle body, the brake functions stay the same but are more pronounced due to higher tire speeds.

 

@David K , bless this thread with your wisdom.

 

https://www.tacomaworld.com/threads/a-trac-trac-auto-lsd-explained-easy-to-understand-i-hope.70551/

 

Thanks for the clarifications. It sounds to me like my truck uses independent braking as the limited slip functionality.

Per David K's post below, I'd like to ask a couple more questions about the 2WD modes;

1) 2WD: VSC and TRAC active, engine regulated ('Limited Slip Lite').

2) 2WD: 'AUTO LSD' ('TRAC OFF MODE'). No engine regulation for 'strong' limited slip.

3) 2WD: 'VSC OFF MODE' (TRAC is off for 'open differential').


I'm hoping someone can help me better understand the point of not regulating engine RPM, as is the case when TRAC is turned off. It seems like the engine and brakes would only be fighting each other. Can someone give me an example of where that would be beneficial?

Also, for us guys with the TRD Off-Road models that feature the electric-brake booster (instead of vacuum), can we assume our limited-slip functionality is more 'aggressive' than the other Tacoma models with the different braking system? Enough to where we'd be able to detect a difference? Just curious.

Thank you

 

the need for the lsd function without engine regulation comes when you need to keep momentum and wheelspin. mud, snow etc. Its real shitty when you are in mud and you put your foot to the floor and the engine doesnt rev above 2 grand.

And you are correct, the TRD off road's with the electric boosted master cylinder / abs unit all in one (vs the vacuum boosted master / seperate abs unit of all other models), has line pressures 2x as much as the vacuum assisted setups. The auto lsd is much stronger and quicker acting.

 

Okay. I'm beginning to understand. Thanks to everyone.

One last question;

Again, for those of us with the Off-Road model (electric boosted master cylinder) . . . is there really a difference between TRAC and A-TRAC?

What I mean is; no matter if it's 4HI or 4LO, the truck still using the same set of brake pads and the same master cylinder. So how exactly does 4LO's A-TRAC outperform 4HI's TRAC in terms of limiting slip? I'm either missing something important, or it's a marketing gimmick.

 

atrac puts the system into a hyper active mode. During trac / auto lsd it works about half has hard as it does in atrac.

 

Ah, I get it. More frequent, but not more brake pressure

 

I think my fellow TWers got you in the right pattern.
If I was to add anything, it would be to say:
TRAC (TRAC OFF MODE in H4) is great, but A-TRAC (L4) is in another level closer to "Locker Nirvana" because it doesn't just limit spin with brake pressure, it stops spin with cross-axle rotation matching sensors... so both tires rotate together, even when one is totally in the air... as a locking differential would.

It depends on speed as to which mode and system you are in, A-TRAC only works in Low Range, and Low Range is a slow, crawling speed for steep climbs and drops... slow and safe.. and nothing broken.
TRAC (TRAC OFF since 2012) is what you have available in High Range... normal speed or level stuff where you might have tire spin that could slow or stop forward movement.

The idea of throttle control (engine regulation) is to help reduce tire spin... then the brake action further slows a spinning tire. When you select TRAC OFF (since 2012) you stop the regulation so you can add more tire turning power to the traction tire to move you ahead... without the power held back, as it is in TRAC (since 2012). [2009-2011 in H4 is called TRAC, but it is traction control with regulation off]