Rx300 Awd Not!
09-30-01, 02:37 PM
#1
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Rx300 Awd Not!
My 2001 RX300 AWD with Trac and VSC will not move itself forward unless the front wheels have traction. Also Trac does not prevent ANY single wheel nor both front wheels or both rear wheels from from spinning freely.
See detailed post in Edmunds town hall re: RX300.
Has anyone seen any actaul LEXUS material stating how RX AWD actually works? Or TRAC?
See detailed post in Edmunds town hall re: RX300.
Has anyone seen any actaul LEXUS material stating how RX AWD actually works? Or TRAC?
10-01-01, 07:03 PM
#3
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Traction applies brakes on the wheel that is NOT getting traction [spining freely]. {for FWD, the TRAC senses spin of front two wheels only. for AWD ?]
Once you know how a system works, one can create a situation where the vehicle would not operate. Competitors exploit this fact.
RX is certainly not a vehicle for every one/use.
Salim
Once you know how a system works, one can create a situation where the vehicle would not operate. Competitors exploit this fact.
RX is certainly not a vehicle for every one/use.
Salim
Last edited by salimshah; 10-01-01 at 07:05 PM.
10-03-01, 03:53 PM
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After a more thorough analysis of the RX300 AWD setup I have realized that prior to the 2001 model year (when the TRAC system was incorporated) the RX300 could get "stuck" with only one wheel having lost traction. If you ordered the vehicle with a limited slip rear differential then EITHER front wheel, or both rear wheels having lost traction would get you stuck.
Absent having ordered the LSD, all three differentials are of the open type, and with any one wheel having lost traction all engine torque would be routed to that ONE wheel.
That's why neither the 99 nor the 2000 Rx300 would climb that test ramp that all of us keep hearing about.
What the 2001 TRAC system is SUPPOSED to do is automatically apply the brakes to any wheel having lost enough traction to spin faster than other wheels. I hope it works as well as the ML320 did from the get-go.
They now share the exact same AWD setup.
Absent having ordered the LSD, all three differentials are of the open type, and with any one wheel having lost traction all engine torque would be routed to that ONE wheel.
That's why neither the 99 nor the 2000 Rx300 would climb that test ramp that all of us keep hearing about.
What the 2001 TRAC system is SUPPOSED to do is automatically apply the brakes to any wheel having lost enough traction to spin faster than other wheels. I hope it works as well as the ML320 did from the get-go.
They now share the exact same AWD setup.
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10-15-01, 01:40 PM
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More bad news...
I was looking through the shop manual for the 2000 Chrysler T&C AWD this morning. The T&C AWD sysetm is virtually the saem as the RX300 with two noteable exceptions. The T&C has an over-running clutch in series with the rear drive shaft so that during severe braking the front wheels can turn slower than the rear. The T&C also has a reverse gear "dog-clutch" to bypass over-running clutch so the T&C still has AWD in reverse.
So the question became, why does the T&C need this additional mechanization if the RX doesn't.
Because the T&C has a much higher preload on the viscous clutch, meaning the latent torque distribution to the rear axle on the T&C is much greater than in the RX. That's why the RX wouldn't apply enough torque to the rear wheels (with the fronts elevated) to move the vehicle forward. The RX300 viscous clutch latent "preload" is low enough not to cause harm to the drive train in heavy braking when it is extremely likely the rear wheels will turn faster than the front. But a lower preload also means less torque to the rear axles.
Shame on Lexus! The Chrysler T&C has a betetr AWD setup.
I was looking through the shop manual for the 2000 Chrysler T&C AWD this morning. The T&C AWD sysetm is virtually the saem as the RX300 with two noteable exceptions. The T&C has an over-running clutch in series with the rear drive shaft so that during severe braking the front wheels can turn slower than the rear. The T&C also has a reverse gear "dog-clutch" to bypass over-running clutch so the T&C still has AWD in reverse.
So the question became, why does the T&C need this additional mechanization if the RX doesn't.
Because the T&C has a much higher preload on the viscous clutch, meaning the latent torque distribution to the rear axle on the T&C is much greater than in the RX. That's why the RX wouldn't apply enough torque to the rear wheels (with the fronts elevated) to move the vehicle forward. The RX300 viscous clutch latent "preload" is low enough not to cause harm to the drive train in heavy braking when it is extremely likely the rear wheels will turn faster than the front. But a lower preload also means less torque to the rear axles.
Shame on Lexus! The Chrysler T&C has a betetr AWD setup.
10-15-01, 06:41 PM
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Check out how the viscous (silicon) system works at www.lexus.com. Go to RX300 Specifications. It's supposed to equalize slippage side to side and front to rear by using this system. I guess I'll have a chance to try it out the next time we get 4-6" of snow.
10-16-01, 10:51 AM
#10
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Recently you submitted a question to the Lexus Customer Satisfaction Department.
Subject:
Fw: Trac
Dear Mr. West:
Thank you for contacting Lexus Customer Satisfaction.
In a limited traction situation, the viscous coupling is "hardware-controlled" power delivery, which helps get power to the end of the car with more traction.
The four-wheel TRAC system is "software controlled" power delivery. In limited traction situations, this helps get power to the individual wheel(s) of the vehicle.
The two systems work together to provide increased traction control.
Your Question:
----- Original Message -----
From: Willard West
To: Customer_Satisfaction_Inquiries@lexus.com
Sent: Tuesday, September 04, 2001 12:32 PM
Subject: Trac
I have a 2001 RX300.
My understanding of the Trac system is that it will automatically brake any wheel or wheels which lose traction and begin to turn faster. It is also my understanding of the AWD system that the nominal torque distribution front to rear is 70/30 and if the front wheels lose traction the differential turning rate causes the fluid in the viscous clutch coupling to "stiffen" which increases the torque coupling to the rear wheels. I understand that the torque distribution can be as high as 51/49 front to rear once the viscosity of the fluid is increased through this circumstance..
My question is this: If the Trac is used to "quickly" prevent wheelspin, how is it possible for the viscous clutch (with a much longer "time constant") to "sense" differential turning rates long enough for it to have any positive affects?
Willard West
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If you have any further concerns, you can also reach the Lexus Customer Satisfaction Department at 1-800-255-3987, Monday through Friday, 6:00 a.m. to 5:00 p.m., Pacific Time. Sincerely, Jessica Caldwell Customer Satisfaction Representative
I think what Lexus is saying here is that TRAC is used to control traction distribution right to left or left to right and the viscous clutch is used front to back. The viscous clutch is located in the rear drive path so it can only increase the torque to the rear, and then only to about 49%
Subject:
Fw: Trac
Dear Mr. West:
Thank you for contacting Lexus Customer Satisfaction.
In a limited traction situation, the viscous coupling is "hardware-controlled" power delivery, which helps get power to the end of the car with more traction.
The four-wheel TRAC system is "software controlled" power delivery. In limited traction situations, this helps get power to the individual wheel(s) of the vehicle.
The two systems work together to provide increased traction control.
Your Question:
----- Original Message -----
From: Willard West
To: Customer_Satisfaction_Inquiries@lexus.com
Sent: Tuesday, September 04, 2001 12:32 PM
Subject: Trac
I have a 2001 RX300.
My understanding of the Trac system is that it will automatically brake any wheel or wheels which lose traction and begin to turn faster. It is also my understanding of the AWD system that the nominal torque distribution front to rear is 70/30 and if the front wheels lose traction the differential turning rate causes the fluid in the viscous clutch coupling to "stiffen" which increases the torque coupling to the rear wheels. I understand that the torque distribution can be as high as 51/49 front to rear once the viscosity of the fluid is increased through this circumstance..
My question is this: If the Trac is used to "quickly" prevent wheelspin, how is it possible for the viscous clutch (with a much longer "time constant") to "sense" differential turning rates long enough for it to have any positive affects?
Willard West
If your issue remains unresolved, please update this question here.
You may also update this question by replying to this message. Because your reply will be automatically processed, you MUST enter your reply in the space below. Text entered into any other part of this message will be discarded.
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If you have any further concerns, you can also reach the Lexus Customer Satisfaction Department at 1-800-255-3987, Monday through Friday, 6:00 a.m. to 5:00 p.m., Pacific Time. Sincerely, Jessica Caldwell Customer Satisfaction Representative
I think what Lexus is saying here is that TRAC is used to control traction distribution right to left or left to right and the viscous clutch is used front to back. The viscous clutch is located in the rear drive path so it can only increase the torque to the rear, and then only to about 49%
10-16-01, 10:57 AM
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Recently you submitted a question to the Lexus Customer Satisfaction Department.
Subject:
RX300
At 07/18/2001 07:36 AM we wrote -
Dear Mr. West:
I am following up with you regarding your inquiries on viscous coupling and the normal distribution ratio. The definition of "viscous coupling" found in the Lexus web site is a dictionary definition and does not necessarily mean this is how our system operates.
The normal torque distribution ratio front to rear generally has a ratio of 50/50, but there are factors that can affect this ratio (ex. going around a corner, accelerating up a hill, etc.)
If you need any further assistance, you can also reach the Lexus Customer Satisfaction Department at 1-800-255-3987, Monday through Friday, 6:00 a.m. to 5:00 p.m., Pacific Time.
Your Question:
Dear sirs,
At Lexus.com under RX "specifications", "viscous coupling" "window", you state that the coupling compensates for slippage right to left and front to rear, is this statement actually correct? I can see how the viscous coupling "clutch" can "tighten" the coupling coefficient between the directly driven front axle and the rear axle (driven only through the viscous clutch) when there is a differential turning rate between the two but I don't see how this can happen left to right with the intervention of the VSC or Trac system.
Is your statement on viscous coupling specifications correct, or am I wrong?
Also, I'm quite sure that my salesman, when I bought the 2000 RX ( I have since upgraded to the 2001 RX for the added benefits of VSC, Trac, and HID), told me that the normal torque distribution ratio front to rear was something in the range of 70/30. I have since seen many statements in various automotive media stating a ratio of 50/50. As I understand the setup the torque coupling can increase under front/rear slippage conditions to very close to 50/50, but never actually greater than 51/49 front to rear.
Which is correct?
Thanks for your time,
Willard West
If your issue remains unresolved, please update this question here.
You may also update this question by replying to this message. Because your reply will be automatically processed, you MUST enter your reply in the space below. Text entered into any other part of this message will be discarded.
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If you have any further concerns, you can also reach the Lexus Customer Satisfaction Department at 1-800-255-3987, Monday through Friday, 6:00 a.m. to 5:00 p.m., Pacific Time. Sincerely, Kevin Saylan Customer Satisfaction Representative
Subject:
RX300
At 07/18/2001 07:36 AM we wrote -
Dear Mr. West:
I am following up with you regarding your inquiries on viscous coupling and the normal distribution ratio. The definition of "viscous coupling" found in the Lexus web site is a dictionary definition and does not necessarily mean this is how our system operates.
The normal torque distribution ratio front to rear generally has a ratio of 50/50, but there are factors that can affect this ratio (ex. going around a corner, accelerating up a hill, etc.)
If you need any further assistance, you can also reach the Lexus Customer Satisfaction Department at 1-800-255-3987, Monday through Friday, 6:00 a.m. to 5:00 p.m., Pacific Time.
Your Question:
Dear sirs,
At Lexus.com under RX "specifications", "viscous coupling" "window", you state that the coupling compensates for slippage right to left and front to rear, is this statement actually correct? I can see how the viscous coupling "clutch" can "tighten" the coupling coefficient between the directly driven front axle and the rear axle (driven only through the viscous clutch) when there is a differential turning rate between the two but I don't see how this can happen left to right with the intervention of the VSC or Trac system.
Is your statement on viscous coupling specifications correct, or am I wrong?
Also, I'm quite sure that my salesman, when I bought the 2000 RX ( I have since upgraded to the 2001 RX for the added benefits of VSC, Trac, and HID), told me that the normal torque distribution ratio front to rear was something in the range of 70/30. I have since seen many statements in various automotive media stating a ratio of 50/50. As I understand the setup the torque coupling can increase under front/rear slippage conditions to very close to 50/50, but never actually greater than 51/49 front to rear.
Which is correct?
Thanks for your time,
Willard West
If your issue remains unresolved, please update this question here.
You may also update this question by replying to this message. Because your reply will be automatically processed, you MUST enter your reply in the space below. Text entered into any other part of this message will be discarded.
[===> Please enter your reply below this line <===]
[===> Please enter your reply above this line <===]
If you have any further concerns, you can also reach the Lexus Customer Satisfaction Department at 1-800-255-3987, Monday through Friday, 6:00 a.m. to 5:00 p.m., Pacific Time. Sincerely, Kevin Saylan Customer Satisfaction Representative
10-16-01, 12:51 PM
#12
Lexus Champion
Willard, I'm not sure that your question was answered by someone who could consistently get oil in the crankcase and water in the radiator.
And their remark re "dictionary definition"!!! As you know, prevarication can occur over the definition of "is"........I think Aldous Huxley would be proud of the CS rep's doublespeak.
The mystery continues............
And their remark re "dictionary definition"!!! As you know, prevarication can occur over the definition of "is"........I think Aldous Huxley would be proud of the CS rep's doublespeak.
The mystery continues............
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