I’m assuming based on the AWD setup of the G35x that it doesn’t have a mechanical rear LSD, even in the Sport models. Since it doesn’t, does the AWD system (somewhat) make up for that since it will transfer power to tires with grip? Does this technology apply to side-to-side tire slip as well as rear-to-front slip? For example - during a corner when breaking the rear tires loose, the LSD will lock up and both tires will hook up... does the AWD system in the X do this (or something similar anyway) through it's computer?

I’m just curious, since I’m the new owner of a new G35x Sport and have only owned RWD sports cars w/ mechanical LSD’s, and appreciate the performance benefits they provide. My understanding anyway is that while the AWD might not work exactly as well as a normal LSD, that it is a decent substitute with the Infiniti being much more rear-biased than most other AWD cars.

 

There's plenty of information on the ATTESA E-TS system if you google and dig around.
I've had mine since April 07.

On dry roads, it's fantastic and I'm happier with it than I expected to be.
In the winter, with Blizzaks installed, it's been awesome.

Here's a good description of the system.

 

the LSD transfers power side to side. Both tires grip, or neither tire grips.

without the LSD, VDC will brake the slipping wheel, which simulates the effect of a LSD, albeit at a lesser level of performance.

the AWD only transfers power from the rear to the front, not side to side like the ATESSA-ETS on the (older) GT-Rs

 

So based on the above scenarios, if the VDC is turned OFF, how would the AWD system react if/when the inside rear tire breaks loose? Would it then send power to the front inside tire only? That's too bad it's not side to side, that would function much more like a normal LSD I'm guessing.

 

Keep in mind that the AWD system deployed in the x is not a performance option, and instead listed as a safety option only. Obviously, it is very difficult for a manufacturer to guess what types of environments and uses the customers of their product will eventually drive in, but the AWD system we have is not the same as what the Japanese have (of course, the bastitches!), the x was given a system designed for snow, ice and other slippery soups and certainly not intended for performance numbers on the street or strip. Japan keeps all those wonderful toys for themselves...

Even if the hardware is the same, the purpose of the AWD system is changed for USDM x's, and therefore you're going to get as Mike@RiversideInfiniti said, an all-grip or no-grip scenario (safety over performance).

It may be possible to reflash the firmware or change the environment maps for the system controlling the behavior, but the design is meant to keep you out of slipping-and-sliding-trouble, not into it, so if the system detects slip it (in a perfect scenario) will throttle down and reduce torque to the wheels slipping. Maybe you could rally the x and it might actually work that AWD system...

LOL. Maybe not.

Anyway...point is, Nissan engineers decided safety over performance, so it'll require some fiddlin' to get a system that behaves more like the Evolution X or the new WRX STi. My $16.38

 

So then, my next question would be - how come they have a switch to shut off the VDC? Based on your description of the AWD system in my x, the AWD system automatically reduces wheel spin by reducing torque, so what exactly does VDC do in excess of that? In my old G35 (2005 6MT Coupe) it would elimilate wheel spin when it detected it at the rear wheels; turning VDC off would allow wheel spin. What does turning VDC off on the AWD system allow, or how is it different from leaving it on?

 

VDC = Vehicle Dynamic Control

It's designed to keep the car neutral in over-torque/wheel spin situations, control throttle response, keep RPMs level and keep the car from being generally unpleasant at speed.

There may be other aspects the VDC does in the x over the standard S model, so perhaps someone here on the forums knows further details as to what, exactly, is disabled/neutralized when the VDC is turned off, but what I described is largely a function of the VDC system. I remember, at one point, my salesman that sold me my S told me it was 'a software LSD'...

LOL...that is patently not true. It is additional control over throttle mostly (limiting throttle input will in essence reduce torque delivery, etc. etc. and so forth...), it is primarily the LSDs job to maintain exactly what its acronym implies...Limited Slip Differential, keeps the one-wheel-that-slips-while-the-other-grips routine to an acceptable minimum.

In the x, the consensus seems to be that there are additional parameters which further hamper bad behavior through some sort of firmware-driven 'virtual LSD'...at this point, you've driven beyond my small envelope of knowledge on the actual subcomponent design of the AWD system and you will likely need to view the link posted a few back.

However...unless the AWD system employes a viscous, locking, or disc-type center LSD or has an actual LSD incorporated into the front + rear, there is very little the system can do to "simulate" LSD behavior without actually having physical LSD components in the diffs. Imagine the technical wizardry in designing a system that can actively proportion torque to each wheel based on grip analysis and weight transfer. Which, in effect, is what the amazing systems in Evolution X and STi do. I doubt the AWD in the G is as sophisticated, but that doesn't make it impossible. Let me read up on how the system is designed, and I'll offer more if I happen to learn something new (likely).

 

Here's something I had on file about it, actually...this pretty much sums it up, the system is pretty much identical in all the Infiniti G's, including the x:

"VDC System VS VLSD System
Vehicle Dynamic Control - Viscous Limited-Slip Differential

Many people are wondering about this topic. Here's the info.

The VDC system is designed to help the driver maintain control in severe cornering or turning situations. Seven sensors determine wheel speed, brake pressure, steering angle, and lateral force. If a decrease in lateral stability is detected, the system reduces the engine's power and/or applies the brakes individually as necessary to help stabilize the vehicle. VDC enhances performance in emergency avoidance maneuvers, improves vehicle stability, and provides improved control even on a slippery road surface. VLSD is no longer needed because the Vehicle Dynamic Control (VDC) system, along with Traction Control System (TCS), provides the same function."

So perhaps my salesman was not quite so off the mark. LOL. Learn something new every day.

I'll just add, here, that having the VLSD is equal to having an 'always-on' performance feature, while the VDC is strictly reactive. However, again, it's a safety feature, not necessarily a performance feature, in the essence of the Evolution or the STi's system. Anyway...LOL...drive systems have since become a science, like everything else on these cars. The complexity is a given. :P

 

My guess is that this (further) ehnanced AWD system would be what the new Nissan GT-R would be employing; I can't imagine that they wouldn't have an AWD system similar to Evo X or STi on a car for $75K. This is also, as I understand anyway, something similar to what Acura employs on the SH-AWD system of the RL - regulating side-to-side in addition to back-to-front.

In the end, I'm just curious - where would power distribution go if I happen to, for example, be on sheer ice, turn VDC off, and floor it? 50-50 front-to-back? Or, does the AWD system automatically regulate wheelspin through torque regulation, and therefore VDC for the g35x only will squeeze a caliper here or there if you turn too hard into a corner?

Not that I'm expecting anyone to have the answer to this - I was just curious because based on reading an article on AWD cars, the previous-gen. G35x was described as the most RWD-biased of the bunch, with the "surprising" ability to toss out the back end without much difficulty given it's AWD setup. Not that I was planning on joining drifting competitions in the G35x or anything, just curious how it's possible given the AWD system. Maybe it's possibly off-throttle induced oversteer w/ the VDC turned off?

 

Of course, if I didn't still have only 230 miles on my G35x, I'd just go find out for myself how it all worked out Break-in is so long and painful!

 

I might add that what I posted above was the raw system as deployed in Japan. No word, really, on how exactly Nissan watered it down, but likely the individual wheel torque control is a bit beyond the G's price bracket and was nixed. Then again...I've been wrong before.

However, from my experience driving both versions of the G, (the S and the 'Sx') I can say that this behavior has not changed. Turning off the VDC would essentially disable these features of 'virtual LSD' as it is called (a more accurate term might be 'active LSD', perhaps), and you would basically over-torque and literally sit there and spin your wheels...

Heh...I love that. So much fun! I know, I know...simple minds, easily amused and all that. Story of my Life.

Anyway...yeah. They give you the option of turning it off doubtless because there are a few drivers who really know what they are doing, and having such a system enabled would only limit them and 'get underfoot' so-to-speak. Truly, if you are going deep into a corner and WANT wheel-spin (as a deft method of controlling torque--read 'old school') you certainly do not want the system interfering with your efforts. Naturally, most of us will never have that problem with the system...

Perhaps if you are interested enough, I encourage taking your G out and doing an active test. Being smart about it is paramount of course, but if you take it somewhere where you are not in any immediate danger of hitting anything more solid than a snowdrift, a little active science never hurt anyone.

 

I completely agree - no words can take fully take the place of seeing how it works first-hand.

I guess in a perfect world, I think the computer would be able to perfectly monitor the limits of the car, and be able to out-judge the driver as to it's limits. I do think there are some cars out there that can just about do that right now. However, in my '05 Coupe, when I left the VDC on, I would notice that the system was a little overly-intrusive in my opinion when it came to regulating the at-limit driving ability of the car - I could notice the VDC cutting my throttle earlier than I thought was necessary, mosty during exiting corners under throttle. So, I simply turned VDC off, and let the LSD do it's work instead, and made sure I didn't put the car completely sideways

Well, only 970 miles before I put the G35x through the test as well! Safely, of course

 

This, unfortunately, is the byproduct of 'predictive electronics'...i.e. making the car safe for every Tom, Dick and Harriet that drives one. That factory has to assume you don't know what you're doing, and try to take steps to prevent you from doing yourself in.

Sadly, a large portion of individuals have...lacking...driving skills.

I kind of have a ritual with any car I own. Especially a used car, but it is important--I feel--for all cars purchased which are new to you. I like taking my cars out to a barren parking lot (sometimes, if I'm lucky, I find an abandoned Vons/K-Mart parking lot with no concrete bump stops or islands to break up a smooth surface) and slog the car around until I know where its practical limits are. This helps me enormously in my track days...the worst thing a driver can be is uninformed and afraid of his machine. You can't read your machine if you've not taken it to the brink and back. Some cars, obviously, are better than others when it comes to communicating to the driver, but all cars speak and if you are attentive, there is significantly less chance of the car surprising you with any snap oversteer (a lesson well-learned by me during my MR2 Turbo-owning days) or understeer conditions when in any position in a corner trajectory. Knowledge = power.

Always be as safe as you can, however, but don't be afraid to leave some rubber on the pavement in trade-off for advanced knowledge of your rides' capabilities. Do it enough, and you'll remember it when in traffic and some assmunch pulls out in front of you, or that truck doesn't see you in his blindspot and starts movin' over into your lane with you in it. It won't always save you...but sometimes it can get you through with a near-miss.

My $86.00

 

Here is the link how it works with VDC on

http://nz.youtube.com/watch?v=ttOvLZHGFpQ
Here is when it is turned off

http://nz.youtube.com/watch?v=Qkl4aCRatFQ&feature=user
This is with all season tires.

Tg

 

Ugh.. just lost a long post i typed...

To summarize:

1. AWD kicks in before VDC. In a straight line, AWD is sufficient to prevent traction loss, even with brake torquing. Without AWD, VDC kicks in, first by braking the rear wheel(s), and then reducing/cutting power to eliminate the traction loss. In a turn, power is transferred forward to prevent wheelspin on the inner rear wheel, and if that is insufficient, that wheel is braked. If that is insufficient, power is reduced. If that is STILL insufficient, power is cut.

2. a LSD transfers power, VDC reduces power through braking, or engine output reduction. (this is why PORSCHE and BMW refuse to put a LSD on the Caymen and 3 series; they would encroach on the performance levels of the Carrera and M3 respectively)


on a side note, as mentioned above, AWD only transfers power from rear to front.

The new GT-R's AWD basically only does that as well; it doesnt transfer power like the old ATESSA-ETS, super HICAS, mitsubishi SYAC, etc