| MDX350 |
On earlier MDX models, if both rear wheels AND one front wheel lost traction, the X wouldn't move.
NOW, with VSA, it should move as long as ANY ONE wheel has traction, front or rear, since VSA will brake the spinning wheels, so even the front axle now has a sort of limited slip differential.
Is that correct?
If Yes, that's good, should improve its snow handling even more. |
|
|
| renov8r |
I think that must be the reasoning behind the wording in the press release. The said something about VSA improving traction...I'd not want to test this too harshly... For condtions so severe,mechcanical torque limiting solution seems like a more durable way to go.
quote:
Originally posted by MDX350
On earlier MDX models, if both rear wheels AND one front wheel lost traction, the X wouldn't move.
NOW, with VSA, it should move as long as ANY ONE wheel has traction, front or rear, since VSA will brake the spinning wheels, so even the front axle now has a sort of limited slip differential.
Is that correct?
If Yes, that's good, should improve its snow handling even more.
|
|
|
| MDX350 |
mercedes has 3 open differentials in the ML, but uses traction control to brake slipping wheels - no mechanical locks. the ML has performed superbly in off-road car rallies (e.g. the Paris Dakar rally, etc.). So this way of improving traction must work! The ML has been out 5 years, mercedes has been making 4WD vehicles for ages, so I assume they know what they are doing.
I just want to understand Acura's VSA a little more - if it indeed brakes individual slipping wheels, then the VTM system becomes somewhat redundant, isn't it? I hope they don't counteract each other - two systems trying to do the same thing, end up interferring with each other's work! |
|
|
| wmquan |
VSA does not brake slipping wheels to manage the bleeding of power.
VSA brakes the wheel(s) that its CPU thinks will counteract a skid and put the vehicle back on track. Often it may be the wheel(s) that are not skidding. The main point of VSA is to measure steering, throttle, ABS sensor input, and vehicle yaw to determine if the vehicle is going off of its intended direction, and to correct the directional error by selectively modulating braking force to the correct wheels.
It is not intended to provided 4WD-type capability.
So the MDX will still get stuck in those rear cases when only one front tire has traction. The other front tire will spin unfettered, and even if VTM-4 tries to kick in, the torque will go to the rear and spin the rear tires.
MB's 4ETS has three open differentials and will brake slipping wheels. It doesn't actually "clamp down" on a wheel, as much as it modulates the spin of the wheel through braking (basically pulsing braking force through). Thus, power does not bleed out of the open differential and any wheel with grip gets power. This works well on the ML because it has power being sent to all four wheels, rather than waiting for slippage to occur. |
|
|
| tigmd99 |
Hey all,
As WMQUAN said, the addition of VSA does NOT mean that one front wheel will get power if the other is slipping. VSA is a stability control...it is NOT a traction control system.
Mercedes ML's system has been WIDELY criticized by the off-roading crowd as being weak and crappy! Why? See reasons:
1. If the traction control system is activated, it will shut down engine power...therefore, if you are in sand or mud, the ML may get stuck because of too much engine braking. In other systems (including those in Toyota, like my 4Runner), you can disable this "cut-engine-power" feature.
2. ML system allows for TOO much wheelspin before it engages...by that time, you have lost momentum. In contrast, the Land Rover system is very quick to react. Toyota system is somewhere between ML and Land Rover.
Thanks. |
|
|
| wmquan |
| Was the ML's off-roading improved somewhat in 2001? I heard they came up with an upgraded version called "4ETS+" which was specifically meant to address off-roading. Something about "pressure preload" when the vehicle is in low-range. Whatever that is. |
|
|
| tigmd99 |
WM,
According to this year's (2002) Fourwheeler magazine, the ML500 did a LITTLE BIT better with the "improved" system. It now features a 2-feet something that allows you to creep over a big rock slowly. Basically, you are able to put one feet on gas pedal and one on brake pedal and have the ML still move slowly forward. In addition, Mercedes quicken the response time of the traction control system. It did improve in mild off-roading. However, according to Fourwheeler, the ML system got totally confused in deep sand and was stuck.
Thanks. |
|
|
| MDX350 |
quote:
Originally posted by tigmd99
Mercedes ML's system has been WIDELY criticized by the off-roading crowd as being weak and crappy!
That is very true. However, 95% of us never go off-roading. On the road, ML's system work extremely well.
The MDX also has a very nice system, just wanted to know more about it. wmquan's post was very insightful. I now understand the difference between traction control and stability control clearly!!!! |
|
|
| mogur |
No, VSA, at least as implimented by Honda, does nothing for traction per se and is not traction control. It only intervenes when a skid or incipent skid is detected. Thus, it will have no bearing on the single wheel scenario.
quote:
Originally posted by MDX350
On earlier MDX models, if both rear wheels AND one front wheel lost traction, the X wouldn't move.
NOW, with VSA, it should move as long as ANY ONE wheel has traction, front or rear, since VSA will brake the spinning wheels, so even the front axle now has a sort of limited slip differential.
Is that correct?
If Yes, that's good, should improve its snow handling even more.
|
|
|
| MDX350 |
quote:
Originally posted by mogur
No, VSA, at least as implimented by Honda, does nothing for traction per se and is not traction control.
This is not correct. The 03 X brochure clearly states - "VSA also incorporates a traction control function". And in the summary they say "VSA with traction control".
So what really is the truth? Does it, or does it not have traction control?? |
|
|
| wmquan |
It's quite possible that Honda is stretching the definitions a bit. I'll do a little more research, as the 2003 MDX details on www.hondanews.com sure make it sound like there is at least a traction control equivalent between VSA and VTM-4 (see below).
Generally, traction control does not mean stability control. Stability control is implemented with traction control as a component, along with ABS and other newer items (e.g. throttle sensors, steering sensors, yaw sensor). Thus stability control in its own right is not = traction control, but traction control is a component.
I have also seen Honda refer to VTM-4 as a traction control system for the Pilot. It's not truly traction control but provides some similar benefits.
VSA on other Honda vehicles leverage traction control. It's quite possible that Honda is pushing the definition of VSA for the MDX, which doesn't have a true traction control system.
From hondanews.com (under MDX, Technical).
quote:
If conditions are really slippery and wheel spin is unavoidable, VTM-4 instantly reacts by adding rear-wheel torque in proportion to both the slippage and the rate of increase of slippage. This enhances performance on low traction surfaces and also improves steering trace and feel during acceleration. In addition, the new VSA system further enhances traction in different conditions by providing a limited-slip differential effect for the front wheels. For 2003, the front-to-rear torque distribution has been remapped to provide up to a 30 percent increase in rear torque.
quote:
For 2003, system mapping was modified to redistribute up to 30 percent more torque to the rear for improved performance, especially on low friction surfaces. In addition, the new VSA system provides a limited-slip differential effect by applying braking force to a slipping front wheel thereby directing driving force to the wheel with more grip.
Taking those at face value, it would seem that it still isn't true traction control, but some benefit seems to have been achieved for the front. And perhaps the MDX won't get stuck in those rare situations when only one wheel has traction.
But again, I'll do some more research on this. |
|
|
| tigmd99 |
WM,
If Acura does indeed have traction control (as we know it) on the front wheels, then the '03 MDX is pretty damn nice! This will give it similar TRACTION capability as the Hummer H2! Nice!
Still, VTM-4 and VSA are two things that i cannot think can co-exist peacefully. One system (VTM-4) engages rear axle to drive the rear wheels when slippage, while the other system (VSA) brakes the wheel that is slipping...Acura must be doing some overtime to put these two systems together.
thanks. |
|
|
| N_Jay |
Seems the original concern is the very unlikely condition where you have only one front wheel having enough traction to move the vehicle, and are stuck well enough that the torque it does get will not move you.
Hmm, just ride the brakes till you get rolling!
When you press the brakes lightly it will slow the spinning front wheel and trasnfer torque to the other.
If you are still stuck, give it up! |
|
|
| MDX350 |
quote:
Originally posted by N_Jay
Hmm, just ride the brakes till you get rolling!
That's fine. However, the original question still remains - does the 03 X have traction control (thru VSA) or not? The brochure claims it does, but no details are given. |
|
|
| MDX350 |
| Any updates on this, or nobody knows the answer? |
|
|
|
