How does the RX300's 4WD work exactly?
06-07-21, 07:17 PM
#16
I hate diasgaree, but that's not how the Rex's AWD system works. It's 50/50 normally. Here's a a couple of reference points:
Edmunds review: http://www.edmunds.com/reviews/roadt...2/article.html
Lexus Technology press release, 9/7/200:
http://www.lexus.com/about/news/pr_archive.html
Enjoy the miles,
TC
Edmunds review: http://www.edmunds.com/reviews/roadt...2/article.html
Lexus Technology press release, 9/7/200:
http://www.lexus.com/about/news/pr_archive.html
Enjoy the miles,
TC
Any chance anyone has the content from the two links above? The links are old and no longer good.
Or perhaps someone has the info about the AWD system that Lexus shared with RX300 customers.
Thanks!
06-08-21, 02:07 AM
#17
AWD is same as RWD with the difference is the differential at the front is bolted to the transmission to power front it uses a planetary limit slip dif and computer controls power.
06-08-21, 09:58 AM
#18
Moderator
Note: Experts can simply skip/ignore my post.
Although the discussion here is among the enthusiasts, but let me break it down for lay readers. Please keep in mind there have been subtle changes and various offerings by Lexus in the first gen RX.
To go around a curve/turn the inside wheel should spin slower than the outside wheel. If wheels on both sides spin at the same rate under engine power, then the inside wheel will have two break traction and skid/slip. Sitting inside the vehicle you would feel it and it will ruin your tires over time. The solution that engineers came up with was a differential that allows asymmetric rotational speed on wheels on the same axle (or even missing/pseudo-axle).
Basic law: Vehicles must allow asymmetric-rotation of the rotated wheels [under power] which are on the left vs right side. If they free-wheel then they are inherently independent
Problem with this is that while trying to straight, if the traction is less on one wheel, it will end up spinning under engine power while the one that is well planted will not rotate.
In a 4 wheel/all-wheel the problem is compounded as not only left-to-right, you have an additional axle [with its own left/right], but we also have front and back which should allowed to spin at different rate.
Auto transmission inherently comes with torque converter that allows engine to be decoupled with the driven wheel [in manual with the clutch released and gear engaged there is a practically hard power coupling].
Engineers have to adhere to the basic law stated above and yet provide full (ideal) traction to each wheel. No solution is perfect and each has its limitations.
Getting into RX specific
First gen RX basic configuration was front wheel auto-trans and AWD. The rears were connected through a viscous coupling [this gives the slip from front to back and then decoupled].
For FWD, when there was no traction under front right (example), the front diff would transfer all the power to the front right wheel and it would spin freely. Engineering solution --> Traction-control [it was not a standard issue in the first year/s]. With the traction control the electronic-based brake [left-vs-right wheel rotation based difference] would apply brake to the free spinning wheel and thus redistribute the power to the wheel that had traction. [I purchased AWD with traction as an option]. My understanding is that there was nothing fancy done for front the back, so if the rears broke traction , the vehicle just became front wheel drive. This was the time when the only real competitor [Benz] set up platforms to poo poo the Lexus AWD design and showed that Lexus FWD with traction fared better that the AWD in various scenarios, but RX is not a true AWD system. Lexus responded by making Traction control a standard issue.
We are governed by the laws of physics. For a true 4 wheeling, a manual transmission is preferred and the above stated law in bold is broken and usually for a short time [comfort and tire wear and speed are all compromised]. Lexus RX does all the work for you automagically and will shine in some situations and can also leave you stranded too. Since there is no rigid power transfer mechanism at one point or another there will be a situation you will need a tow.
Side note: On sheet of ice even the real 4x4 is not drivable.
Salim
Although the discussion here is among the enthusiasts, but let me break it down for lay readers. Please keep in mind there have been subtle changes and various offerings by Lexus in the first gen RX.
To go around a curve/turn the inside wheel should spin slower than the outside wheel. If wheels on both sides spin at the same rate under engine power, then the inside wheel will have two break traction and skid/slip. Sitting inside the vehicle you would feel it and it will ruin your tires over time. The solution that engineers came up with was a differential that allows asymmetric rotational speed on wheels on the same axle (or even missing/pseudo-axle).
Basic law: Vehicles must allow asymmetric-rotation of the rotated wheels [under power] which are on the left vs right side. If they free-wheel then they are inherently independent
Problem with this is that while trying to straight, if the traction is less on one wheel, it will end up spinning under engine power while the one that is well planted will not rotate.
In a 4 wheel/all-wheel the problem is compounded as not only left-to-right, you have an additional axle [with its own left/right], but we also have front and back which should allowed to spin at different rate.
Auto transmission inherently comes with torque converter that allows engine to be decoupled with the driven wheel [in manual with the clutch released and gear engaged there is a practically hard power coupling].
Engineers have to adhere to the basic law stated above and yet provide full (ideal) traction to each wheel. No solution is perfect and each has its limitations.
Getting into RX specific
First gen RX basic configuration was front wheel auto-trans and AWD. The rears were connected through a viscous coupling [this gives the slip from front to back and then decoupled].
For FWD, when there was no traction under front right (example), the front diff would transfer all the power to the front right wheel and it would spin freely. Engineering solution --> Traction-control [it was not a standard issue in the first year/s]. With the traction control the electronic-based brake [left-vs-right wheel rotation based difference] would apply brake to the free spinning wheel and thus redistribute the power to the wheel that had traction. [I purchased AWD with traction as an option]. My understanding is that there was nothing fancy done for front the back, so if the rears broke traction , the vehicle just became front wheel drive. This was the time when the only real competitor [Benz] set up platforms to poo poo the Lexus AWD design and showed that Lexus FWD with traction fared better that the AWD in various scenarios, but RX is not a true AWD system. Lexus responded by making Traction control a standard issue.
We are governed by the laws of physics. For a true 4 wheeling, a manual transmission is preferred and the above stated law in bold is broken and usually for a short time [comfort and tire wear and speed are all compromised]. Lexus RX does all the work for you automagically and will shine in some situations and can also leave you stranded too. Since there is no rigid power transfer mechanism at one point or another there will be a situation you will need a tow.
Side note: On sheet of ice even the real 4x4 is not drivable.
Salim
06-08-21, 04:16 PM
#20
I entered 2000 Lexus RX300 into Edmunds and this was in the description:
Now in its second year of production, the RX 300 can be had in front-wheel drive, which improves both performance and gas mileage. To add to the front-wheel-drive model's capability in less than perfect weather, electronic traction control is optional. Full-time four-wheel drive is also available with a viscous center coupling that directs torque to the wheels with the most traction whenever slippage occurs.
Now in its second year of production, the RX 300 can be had in front-wheel drive, which improves both performance and gas mileage. To add to the front-wheel-drive model's capability in less than perfect weather, electronic traction control is optional. Full-time four-wheel drive is also available with a viscous center coupling that directs torque to the wheels with the most traction whenever slippage occurs.
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