VSA and SH-AWD
01-02-2010, 10:31 AM
#1
Instructor
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VSA and SH-AWD
I am curious to learn how VSA and SH-AWD function together on the 09 TL.
As I understand it, AWD distributes power to the wheels as deemed necessary.
VSA changes the engine's output and selectively applies the brake.
Are these two things in contradiction?
On snowy, sleety, or rain slicked roads is it best to turn off VSA?
In normal weather and road conditions is it best to leave VSA on?
As I understand it, AWD distributes power to the wheels as deemed necessary.
VSA changes the engine's output and selectively applies the brake.
Are these two things in contradiction?
On snowy, sleety, or rain slicked roads is it best to turn off VSA?
In normal weather and road conditions is it best to leave VSA on?
01-02-2010, 11:11 AM
#2
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If you are an experienced track driver, somebody who might drive in NASA Group 3 (California 4) or Group 4 (California 5) or Instructor Groups, then I would certainly turn off VSA on the track.
The only other time I can think of off hand that I'd switch off VSA is if I am trying to free the car from snow or mud where it is temporarily stuck.
The VSA cuts on much farther down the list of things to do than you would suppose.
In dry, wet, icy and muddy conditions the car will try to use SH-AWD before VSA is used as a last resort to stabilise the car.
It happens in the wink of an eye.
Don't try to second guess the car. It's well designed.
I'd leave VSA turned ON in all conditions except the two conditions I mentioned, personally. :-)
The only other time I can think of off hand that I'd switch off VSA is if I am trying to free the car from snow or mud where it is temporarily stuck.
The VSA cuts on much farther down the list of things to do than you would suppose.
In dry, wet, icy and muddy conditions the car will try to use SH-AWD before VSA is used as a last resort to stabilise the car.
It happens in the wink of an eye.
Don't try to second guess the car. It's well designed.
I'd leave VSA turned ON in all conditions except the two conditions I mentioned, personally. :-)
01-02-2010, 01:44 PM
#3
Instructor
Well put George. I'd add that SH-AWD is largely a proactive system for dry grip with an added bonus when needed in the rain/snow and VSA is a reactive safety system for any adverse condition (even blowouts, which is why VSA cannot be disabled if TPMS has an issue).
01-02-2010, 02:17 PM
#4
I am curious to learn how VSA and SH-AWD function together on the 09 TL.
As I understand it, AWD distributes power to the wheels as deemed necessary.
VSA changes the engine's output and selectively applies the brake.
Are these two things in contradiction?
On snowy, sleety, or rain slicked roads is it best to turn off VSA?
In normal weather and road conditions is it best to leave VSA on?
As I understand it, AWD distributes power to the wheels as deemed necessary.
VSA changes the engine's output and selectively applies the brake.
Are these two things in contradiction?
On snowy, sleety, or rain slicked roads is it best to turn off VSA?
In normal weather and road conditions is it best to leave VSA on?
Electronic Controls and Parameters
The control logic for SH-AWD® is integrated with the TL’s Vehicle Stability Assist™ (VSA®) ECU. The Powertrain Control Module (PCM) provides information on engine rpm, airflow and transmission gear selection, while the VSA® ECU provides wheel-speed data. The SH-AWD® ECU also monitors steering angle, lateral G-forces, yaw rate, and electromagnetic clutch engagement for the right and left rear axle shafts. Drive torque is calculated from PCM information, and then the acceleration situation, wheel spin, lateral G forces and steering angle are used to determine the front-to-rear torque distribution and the torque split between right and left rear wheels.
The control logic for SH-AWD® is integrated with the TL’s Vehicle Stability Assist™ (VSA®) ECU. The Powertrain Control Module (PCM) provides information on engine rpm, airflow and transmission gear selection, while the VSA® ECU provides wheel-speed data. The SH-AWD® ECU also monitors steering angle, lateral G-forces, yaw rate, and electromagnetic clutch engagement for the right and left rear axle shafts. Drive torque is calculated from PCM information, and then the acceleration situation, wheel spin, lateral G forces and steering angle are used to determine the front-to-rear torque distribution and the torque split between right and left rear wheels.
01-02-2010, 02:47 PM
#5
I would certainly turn off VSA on the track.
The only other time I can think of off hand that I'd switch off VSA is if I am trying to free the car from snow or mud where it is temporarily stuck.
I'd leave VSA turned ON in all conditions except the two conditions I mentioned, personally. :-)
The only other time I can think of off hand that I'd switch off VSA is if I am trying to free the car from snow or mud where it is temporarily stuck.
I'd leave VSA turned ON in all conditions except the two conditions I mentioned, personally. :-)
Toyota has a terrible design in their camry as you cant turn the VSA system on or off manually. I tried pushing my friends 2009 out of the snow last week and the engine just kept cutting power making it horribly difficult to get it out.
last spring he almost got T-boned trying to get across a busy intersection because when he stepped on the gas it initially shot him out into the intersection then killed the engine power due to wheel spin from the pea gravel/salt on the road. He wanted to turn it off in this situation because he was afraid that it may happen but couldnt.
I never realized there where many vehicles out there that wouldnt let you disable the VSA. IMO thats a horrible and potentially dangerous decision by the manufacture.
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