How does ATRAC work?? - Page 3 - Toyota

Thai · 08-08-2004, 08:51 PM

Iowa,

Details, details...yeah, thanks for the physics lesson.

Like i said, i hope that everyone else found my explanation to be adequate. :rolleye2:

Don't forget, when you're stuck in mud/snow, VSC will activate because you're sliding around, which will be interpreted by the computer as oversteer/understeer. Also, the effects of ATRAC can be interpreted by some as cutting engine power (even though it doesn't when center diff is locked). If you're gentle on the gas pedal, it will feel like you're not getting power to the ground. That's why you need to really press on the gas pedal to overcome ATRAC when going up a sandy hill (or getting out of a mud hole). Like posted above, when the rpms go past about 3000 rpms, ATRAC intervention decreases.

Now, i know for a FACT that ATRAC shuts off after about 40 mph in Land Rovers and Mercedes systems. I can't imagine that Toyota's system would be any different. Both Mercedes and LR started using ATRAC before Toyota did. I think that Mercedes designed the first system. It may also be that at high speed, brake pulsing a wheel may create even more dynamic instability, especially in situation where a wheel loses traction only a split second (ex: hitting an oil spot on the road). Thus, any braking situation at high speed is reserved to bail you out of trouble (e.g. oversteer and understeer).

From my experience off-road, ATRAC is NOT instantaneous in it's activation...it does require a little bit of wheel spin before coming on. So, there's a "reaction time." You can imagine what kind of problem this will be when one tire hit a small oil spot on the road...by the time ATRAC kicks in, your tire has regained traction...this can create a lot of problem (and lawsuits!).

Or, if you don't believe me, then READ up on Toyota's definition of VSC or any other manufacturer's system.

Thai · 08-08-2004, 08:54 PM

Here is an article on VSC's:

Vehicle Stability Control Systems
by Jim Kerr

First, there was anti-lock braking. Then came traction control systems. Stability control is the third step in electronic systems that help us control our vehicles. Almost all automobile manufacturers offer a stability control system on select models. Most of them are on cars, although trucks are quickly adding stability control to the option list.

While all systems are similar in concept, one system has important market significance. AdvanceTrac, the stability control option on the 2001 Ford Focus is the first system offered on an economy car, and it brings vehicle stability controls within the financial grasp of the majority of the buying public. AdvanceTrac is available on two of the Focus models, the economical and sporty ZX3 three-door, and the top of the line ZTS four-door sedan.

AdvanceTrac came from Ford's involvement with Formula One racing. Although active vehicle controls like AdvanceTrac are no longer used in F1 racing, their benefits are very real in everyday driving. Ford first offered AdvanceTrac in the Lincoln LS. This system, on the Focus, brings a new level of safety to small cars.

Stability control systems are especially beneficial on wet, snowy, or icy conditions, although they do offer handling benefits during emergency maneuvers on dry pavement. The design intent of stability control is to keep the vehicle going in the direction the driver is steering the car. To do this, the brakes are applied on one wheel to help steer the car in the correct direction. For example, if poor traction causes the front end of the car to slip sideways when you are going around a corner, the computer will apply the wheel brake on the inside of the corner causing the car to turn and slow down. If the back end of the car slips sideways, the brake on the outside of the corner is applied to bring the car back into line. The system works when the car starts to slide on a straight road the same as it does when turning corners.

Not all stability control systems feel the same. The difference is mainly in the computer programming. I find systems on Mercedes and Lexus cars react aggressively by reducing engine power and vehicle speed at the first instance of vehicle instability. Their emphasis is on always keeping the car in total control. Other systems, such as the Subaru Outback Vehicle Dynamic Control system, allow the vehicle to move around a bit for a more sporty feel, but as soon as the movement is too much, control is smoothly engaged. The Subaru system operation is my personal favourite. Most systems, including AdvanceTrac, fall somewhere between these two. Control is smooth and seamless.

Several inputs are required for stability control operation. The wheel speed sensors for the anti-lock brakes are used to detect wheel spin. A steering wheel position sensor is used to determine where the driver is wishing the car to go. A yaw rate sensor measures the speed at which the car is rotating around its centre, while a lateral acceleration sensor measures sideways force on the car. The AdvanceTrac computer monitors these sensors 150 times per second and can react within milliseconds to briefly apply individual brakes, re**** ignition timing, and cut back on fuel delivery to keep the vehicle under control.

Stability control systems are a fantastic safety system. According to Johnny Unser, race car driver and performance driving consultant, "the yaw control is phenomenal in avoiding an accident by keeping the car pointing in the right direction, instead of getting out of control."

There is one caution about stability control. It can't overcome the laws of physics. Trying to corner at excessive speeds or driving beyond the limits of tire traction can cause the car to lose control. The stability system will help, but there is only so much it can do.

I have enjoyed driving many cars in the $35,000 and up price range that were equipped with stability control. The systems work even better than they sound. Now that stability control is available on a Ford Focus at under $22,000, I look forward to the safety benefits on even more cars.

Thai · 08-08-2004, 09:04 PM

Quote:

Originally posted by Iowa4Runner
If Larry Leadfoot is cruising along an icy road at 40MPH and starts to spin the tires, the systems should get control right away instead of waiting until the vehicle starts fishtailing all over the place.

Larry Leadfoot is not very smart (and i am using kind words)!

In your situation, no system in the world will save him. Remember, to RE-EMPHASIZE, VSC cannot alter physics...it will only work to an extent...praying will help the rest of the way!

Iowa4Runner · 08-08-2004, 09:42 PM

Quote:

Originally posted by Thai
Larry Leadfoot is not very smart (and i am using kind words)! In your situation, no system in the world will save him. Remember, to RE-EMPHASIZE, VSC cannot alter physics...it will only work to an extent...praying will help the rest of the way!

Alter physics??? Don't be ridiculous. It's not like Larry is heading into an icy corner at 120 MPH. All that's required is some dethrottling and/or brake modulation to get the wheelspin under control. It'd be a piece of cake for today's vehicle control systems.

Thai · 08-08-2004, 11:04 PM

Quote:

Originally posted by Iowa4Runner
It'd be a piece of cake for today's vehicle control systems.

Only if your tires have traction....

Iowa4Runner · 08-09-2004, 12:20 AM

Quote:

Originally posted by Thai
Only if your tires have traction....

No. The computer doesn't need traction to dethrottle the engine and modulate the brakes.

Thai · 08-09-2004, 07:26 AM

Quote:

Originally posted by Iowa4Runner
No. The computer doesn't need traction to dethrottle the engine and modulate the brakes.

All those actions ain't gonna work if you have no traction at the tires...in fact, you can even shut off the engine if you like!

On a more serious note, there's no need to further discuss this topic unless you have some additional info.

I hope that you found the above info helpful in reading up on VSC's.

Iowa4Runner · 08-09-2004, 10:31 AM

Quote:

Originally posted by Thai
All those actions ain't gonna work if you have no traction at the tires...in fact, you can even shut off the engine if you like!

Ain't gonna work??? I've done it 100's of times with my right foot!!! If your wheels start to slip you simply reduce or close the throttle and your tires regain grip. The idea is to minimize the wheelspin before it leads to fishtailing and total loss of control. It's a very simple concept. Have you ever driven on icy roads?

boston_kevin · 08-09-2004, 11:38 AM

Iowa - Thai is simply stating that if the tires can't get a grip in the snow/ice, all of the stability systems in the world can't stop or control the vehicle. That being said, all systems are designed with the intent that there will be at least mininmal friction between the tires and the surface you are driving on (ice skating rinks, loose sand on pavement, oil slicks, all have near zero friction). To that end, I have seen a $70k land rover in Colorado hit a patch of snow covered black ice (about 3 years ago), and end up about 500 yards down the mountain... So much for VSC and TRAC on that car.

Thai - Iowa is restating what you are saying. I believe he is already assuming that there must be minimal friction, and the systems do in fact, work beautifully.

As far as systems reacting before any wheel slip occurs... Acura claims this with their MDX, but if you read the test results very carefully, wheel slip did occur and the system engaged within 1 millisecond, therefore the driver felt no slip whatsoever (and even with this system in Vail, many of the test drivers still ended up in the snow bank because of the laws of physics).

ATRAC and other related systems are phenomenol compared to what was offered before (lockers and previous gen's of TRAC), but it is not a perfect system. Don't think that will ever exist until we have flying cars, then who needs 4WD???

Thanks for the info Thai!! You are a wealth of knowledge.

Iowa4Runner · 08-09-2004, 12:45 PM

Quote:

Originally posted by boston_kevin
Iowa - Thai is simply stating that if the tires can't get a grip in the snow/ice, all of the stability systems in the world can't stop or control the vehicle.

I know, and that's the problem. I'm not talking about stopping or cornering. I'm talking about the wheelspin that results from applying too much throttle in slippery conditions. Wheelspin doesn't mean you're out of control. It simply means the wheel RPM is too high for the speed you're traveling.

Over the last century, MILLIONS of slow reacting humans have kept their cars under control by simply letting off the gas when wheelspin occured. A modern vehicle control system could easily accomplish this.

Thai · 08-09-2004, 04:29 PM

Quote:

Originally posted by Thai
All those actions ain't gonna work if you have no traction at the tires...in fact, you can even shut off the engine if you like!

On a more serious note, there's no need to further discuss this topic unless you have some additional info.

I hope that you found the above info helpful in reading up on VSC's.

Again, Iowa, i was half-kidding with my comment above...please see smilie.

Please read the rest of the post...if you have more info to counter what i have said above, then please post it. If not, then this discussion should end. I feel like i am stating the same things over and over again. PLEASE read up on VSC's.

Thanks.

Iowa4Runner · 08-09-2004, 04:50 PM

Quote:

Originally posted by Thai
Again, Iowa, i was half-kidding with my comment above...please see smilie.

Please read the rest of the post...if you have more info to counter what i have said above, then please post it. If not, then this discussion should end. I feel like i am stating the same things over and over again. PLEASE read up on VSC's.

Thanks.

Well, as a matter of fact you are stating things over and over again and I have no idea why. Your statements have no relevance to the scenario I'm describing.

I did add more info- Myself and many other drivers have done this type of control in the real world, and it works. If people have done it, why can't a control system do it?

I've yet to see an article on vehicle control systems stating this type of wheelspin control is impossible or detrimental in any way. Have you found one?

GatorGreg · 08-09-2004, 04:54 PM

Are you guys STILL going back and forth about the stupid VSC?

Thai · 08-09-2004, 04:57 PM

Quote:

Originally posted by Iowa4Runner
Well, as a matter of fact you are stating things over and over again and I have no idea why. Your statements have no relevance to the scenario I'm describing.

I did add more info- Myself and many other drivers have done this type of control in the real world, and it works. If people have done it, why can't a control system do it?

I've yet to see an article on vehicle control systems stating this type of wheelspin control is impossible or detrimental in any way. Have you found one?

Good...go out and do it to your 4runner. There's no article...hmmm...because VSC's main function is NOT for your situation. It's very simple. Go and have fun with your 4runner.

Thai · 08-09-2004, 04:58 PM

Quote:

Originally posted by GatorGreg
Are you guys STILL going back and forth about the stupid VSC?

Tell me about it...Iowa is very persistent....:o

08-08-2004, 08:51 PM	#31 (permalink)
Thai Snowflake, Guns, & Texas! Join Date: Nov 2002 Location: Texas Posts: 11,905	Iowa, Details, details...yeah, thanks for the physics lesson. Like i said, i hope that everyone else found my explanation to be adequate. :rolleye2: Don't forget, when you're stuck in mud/snow, VSC will activate because you're sliding around, which will be interpreted by the computer as oversteer/understeer. Also, the effects of ATRAC can be interpreted by some as cutting engine power (even though it doesn't when center diff is locked). If you're gentle on the gas pedal, it will feel like you're not getting power to the ground. That's why you need to really press on the gas pedal to overcome ATRAC when going up a sandy hill (or getting out of a mud hole). Like posted above, when the rpms go past about 3000 rpms, ATRAC intervention decreases. Now, i know for a FACT that ATRAC shuts off after about 40 mph in Land Rovers and Mercedes systems. I can't imagine that Toyota's system would be any different. Both Mercedes and LR started using ATRAC before Toyota did. I think that Mercedes designed the first system. It may also be that at high speed, brake pulsing a wheel may create even more dynamic instability, especially in situation where a wheel loses traction only a split second (ex: hitting an oil spot on the road). Thus, any braking situation at high speed is reserved to bail you out of trouble (e.g. oversteer and understeer). From my experience off-road, ATRAC is NOT instantaneous in it's activation...it does require a little bit of wheel spin before coming on. So, there's a "reaction time." You can imagine what kind of problem this will be when one tire hit a small oil spot on the road...by the time ATRAC kicks in, your tire has regained traction...this can create a lot of problem (and lawsuits!). Or, if you don't believe me, then READ up on Toyota's definition of VSC or any other manufacturer's system. __________________ 2010 Toyota Prius V with ATP (daily driver) 2008 Toyota Sienna Salsa Red Pearl 2wd Limited (urban family "land cruiser") 2009 Acura TSX Palladium (wife's car) Off-roading Videos of My G I AM FAMOUS!! "Everyday is Halloween on the Internet"

08-08-2004, 08:54 PM	#32 (permalink)
Thai Snowflake, Guns, & Texas! Join Date: Nov 2002 Location: Texas Posts: 11,905	Here is an article on VSC's: Vehicle Stability Control Systems by Jim Kerr First, there was anti-lock braking. Then came traction control systems. Stability control is the third step in electronic systems that help us control our vehicles. Almost all automobile manufacturers offer a stability control system on select models. Most of them are on cars, although trucks are quickly adding stability control to the option list. While all systems are similar in concept, one system has important market significance. AdvanceTrac, the stability control option on the 2001 Ford Focus is the first system offered on an economy car, and it brings vehicle stability controls within the financial grasp of the majority of the buying public. AdvanceTrac is available on two of the Focus models, the economical and sporty ZX3 three-door, and the top of the line ZTS four-door sedan. AdvanceTrac came from Ford's involvement with Formula One racing. Although active vehicle controls like AdvanceTrac are no longer used in F1 racing, their benefits are very real in everyday driving. Ford first offered AdvanceTrac in the Lincoln LS. This system, on the Focus, brings a new level of safety to small cars. Stability control systems are especially beneficial on wet, snowy, or icy conditions, although they do offer handling benefits during emergency maneuvers on dry pavement. The design intent of stability control is to keep the vehicle going in the direction the driver is steering the car. To do this, the brakes are applied on one wheel to help steer the car in the correct direction. For example, if poor traction causes the front end of the car to slip sideways when you are going around a corner, the computer will apply the wheel brake on the inside of the corner causing the car to turn and slow down. If the back end of the car slips sideways, the brake on the outside of the corner is applied to bring the car back into line. The system works when the car starts to slide on a straight road the same as it does when turning corners. Not all stability control systems feel the same. The difference is mainly in the computer programming. I find systems on Mercedes and Lexus cars react aggressively by reducing engine power and vehicle speed at the first instance of vehicle instability. Their emphasis is on always keeping the car in total control. Other systems, such as the Subaru Outback Vehicle Dynamic Control system, allow the vehicle to move around a bit for a more sporty feel, but as soon as the movement is too much, control is smoothly engaged. The Subaru system operation is my personal favourite. Most systems, including AdvanceTrac, fall somewhere between these two. Control is smooth and seamless. Several inputs are required for stability control operation. The wheel speed sensors for the anti-lock brakes are used to detect wheel spin. A steering wheel position sensor is used to determine where the driver is wishing the car to go. A yaw rate sensor measures the speed at which the car is rotating around its centre, while a lateral acceleration sensor measures sideways force on the car. The AdvanceTrac computer monitors these sensors 150 times per second and can react within milliseconds to briefly apply individual brakes, re**** ignition timing, and cut back on fuel delivery to keep the vehicle under control. Stability control systems are a fantastic safety system. According to Johnny Unser, race car driver and performance driving consultant, "the yaw control is phenomenal in avoiding an accident by keeping the car pointing in the right direction, instead of getting out of control." There is one caution about stability control. It can't overcome the laws of physics. Trying to corner at excessive speeds or driving beyond the limits of tire traction can cause the car to lose control. The stability system will help, but there is only so much it can do. I have enjoyed driving many cars in the $35,000 and up price range that were equipped with stability control. The systems work even better than they sound. Now that stability control is available on a Ford Focus at under $22,000, I look forward to the safety benefits on even more cars. __________________ 2010 Toyota Prius V with ATP (daily driver) 2008 Toyota Sienna Salsa Red Pearl 2wd Limited (urban family "land cruiser") 2009 Acura TSX Palladium (wife's car) Off-roading Videos of My G I AM FAMOUS!! "Everyday is Halloween on the Internet"

08-09-2004, 11:38 AM	#39 (permalink)
boston_kevin Member Join Date: Apr 2004 Location: Outside of Boston Posts: 1,228	I think you guys are saying the same thing... Iowa - Thai is simply stating that if the tires can't get a grip in the snow/ice, all of the stability systems in the world can't stop or control the vehicle. That being said, all systems are designed with the intent that there will be at least mininmal friction between the tires and the surface you are driving on (ice skating rinks, loose sand on pavement, oil slicks, all have near zero friction). To that end, I have seen a $70k land rover in Colorado hit a patch of snow covered black ice (about 3 years ago), and end up about 500 yards down the mountain... So much for VSC and TRAC on that car. Thai - Iowa is restating what you are saying. I believe he is already assuming that there must be minimal friction, and the systems do in fact, work beautifully. As far as systems reacting before any wheel slip occurs... Acura claims this with their MDX, but if you read the test results very carefully, wheel slip did occur and the system engaged within 1 millisecond, therefore the driver felt no slip whatsoever (and even with this system in Vail, many of the test drivers still ended up in the snow bank because of the laws of physics). ATRAC and other related systems are phenomenol compared to what was offered before (lockers and previous gen's of TRAC), but it is not a perfect system. Don't think that will ever exist until we have flying cars, then who needs 4WD??? Thanks for the info Thai!! You are a wealth of knowledge.

08-09-2004, 04:54 PM	#43 (permalink)
GatorGreg Self-Appointed SUV Expert Join Date: Nov 2002 Location: Gator Country Posts: 2,568	Are you guys STILL going back and forth about the stupid VSC? __________________ 2003 Dorado Gold Pearl GX470 (2003 Four Wheeler & 4x4 of the Year) 2000 Millennium Silver Metallic SR5 4x4 5spd - RIP

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