TypeSAddict

Could somebody please explain to methedifferences between VSA and this new LSD? Which one is better?

Fabvsix

I don't think they are the same. LSD (Limited Slip Diferential), which has to do with Oversteer and understeer. VSA is a whole different tool if you will, that deals with traction as opposed to oversteer/understeer.

I could be wrong !

EricL

The LSD will transfer power to the wheel needing it. The VSA doesn't transfer power so much as it clamps the "binders"; it clamps the brake disk and retards the timing to keep forward traction (when hauling off the line, it keeps the tires from “chirping” too badly). If traction gets really dicey with the VSA, it will actually close a second intake throttle to really kill your power.

The LSD will transfer power with minimal losses and it will also change the vehicle dynamics in a very simple and natural way (it gets power to the wheel that needs it without dumping the engine power (as the VSA does). The VSA does its work through the application of selecting braking, and power reduction.


The LSD will not do all of the fancy oversteer and understeer correction that the VSA will do to help keep the car under control..


BTW -- the LSD only works on the front in a FWD car (as ours is).

jdl75

LSD - limited slip differential (also know on some cars as positraction, if that helps) - it keeps one wheel from spining out when you lose traction. It is primarilly a mechanical system for transfering torque to the wheel with traction.

VSA - Vehicle stability assist - An electronic system capable of applying selective braking forces and retarding ignition to

1. Keep the ass end from passing the front end, and
2. Get you moving on slippery surfaces (uses braking and ignition retardation to accomplish the same things as LSD).

Type S

LSD-when one of wheel slip or lose traction.it will be locked and transfered torque to other wheels.
VSA-once wheel lose traction.the fuel supply cuts.throttle close.until wheels regain traction.
basically VSA is more comlicated than LSD
i believe cls does not have LSD...my jeep does have LSD...

pgatour1

You are all correct isn't that nice to hear.

I thought this was gonna be a post about being on LSD and how VSA helped hahah.

THe Alero has LSD< sort of the same system as the Subuaru Wheels that slip to grip system but in a FWD method. That car is sick handling, let me tell you. Shit is crazy

EricL

LSD city links:

FAQ on Differentials (Open, LSD, and so on)

http://www.houseofthud.com/differentials.htm

http://platz.com/pca/pnwrpca/tech/20...mitedslip.html

http://www.globalwest.net/torsen_tra...fferential.htm

http://www.roadraceengineering.com/quaife.htm

bioyuki

Don't Subaru's have viscous coupling locking differentials?

Anyways, here are the types of LSDs that Honda uses. HLSD is the gear type correct? (cut and paste from some website)

Gear Types have gears inside of them that mesh/engage together when load is detected. This type is good to have because you'll probably never have to replace worn internal LSD parts, unlike the clutch type. The downside is that they can internally break if your into rough circut racing. Lifting a front wheel in a turn and landing back on it is how the LSD can break. Real stiff suspension is a major factor in making a car lift during a turn.

Clutch Types have small clutches inside that engage when load is being detected. These LSD's won't break if you happen to lift a wheel. The only real downside to this type of LSD is, wearing of the clutches. Just like the clutch disc inside of your tranny, the clutches inside this LSD wear out too, and needs replacement.

Viscous Type are similar to the viscous LSD's used in some AWD vehicles. The way these work is that a special fluid is used in the differential THICKENS, when excessive slip is induced. Stators and impellors in the diff make this even more efficient. Although there is a slight delay in locking of the differential, they work very well and last a long time.
According to my resources, these were 'special order' LSD's for JDM 96-97 ITR integra's only. No other countries would receive this optional LSD, only Japan. The cost was about twice as much as a the common Gear type found in all ITR's and CTR's. One odd thing though, Honda of Japan does NOT have this optional LSD type for 98+ ITR's! We're (EB & I) pretty sure it fits in 98+ ITR tranny's though...

EricL

Let me know if this doesn't cover them all (or at least most of them)...

http://www.houseofthud.com/differentials.htm

bioyuki

Hey you quoted me wrong! Anyways, I said those were the types that Honda uses, not all the possible types of differentials.

EricL

Don’t get your knickers in a knot -- if I had a dime for every time someone actualy cut my quotes to alter the context, I'd be rich...

Mea culpa

bioyuki

You're forgiven . Anyways, while we're on the topic, what catagory does Mitsubishi's AWD system (Lancer Evolution VII) fall under?

EricL

Well, I thought is is "viscous" and here is a pic and stolen excerpt:

"While Torsen 4WD is too expensive, Viscous-Coupling LSD is part-time only, most 4WD cars, including the rally ace Celica GT4, Subaru Impreza, Mitsubishi Lancer and Ford Escort RS Cosworth adopted another kind of center differential - basically it has a regular center differential which distribute torque to front and rear under normal condition, an additional Viscous Coupling Differential Lock provides anti-slip function when needed.
Characteristic of this system
The Viscous-Coupling Differential Lock is virtually the same as what we have learned earlier, therefore it also has slight delay and non-linear characteristic. However, in reality this might not be as serious as we thought, otherwise it would have been impossible that all the top rally cars use it. Moreover, Viscous-Coupling Differential Lock system is lighter and cheaper than Torsen system, while having superior effectiveness over the part-time Viscous-Coupling LSD system.

...




...

Who use it? * Mitsubishi Lancer GSR, 3000 GT VR4. (with Viscous-Coupling LSD in rear axle)


..."


And then there is this reference:

"Various features on the Evo 7 include vented front and rear disc brakes with ABS, 235/45ZR17 tires and the unchanged suspension layout from previous model, although with revised geometry and an overall wider track and longer wheelbase. The big piece de resistance, however, is the new ACD (Active Center Differential) which uses an electronically controlled clutch that gives better grip compared to the standard VCU type to improve traction, as well as the AYC (Active Yaw Control) stystem, which gives better torque distribution between the rear wheels. The Lancer goes on sale in Ferbuary 2001, for the equivalent of about $25,500 USD for the GSR and $21K for the RS in Japan. Look for the Evo in North America as well, as a 2003 model possibly detuned to 230 horsepower. "

bioyuki

Here we go...straight from the Mitsubishi brochure:

Active Center Differential
MMC became a pacesetter in offering highperformance
4-wheel drive production models
when it introduced a full-time 4WD system using
a viscous coupling-type center differential in 1987.
On-going research and development since then has
enabled the company to adopt electronic control
and to evolve its 4WD systems in other ways.
In the field of motor sports, virtually all works
teams have to date employed similar viscouscoupling
or mechanical limited slip differentials in
their competition machines, leaving much room
for further development. Seizing this opportunity,
MMC has developed an electronically controlled
Active Center Differential capable of fully
withstanding the rigors of use in all motor sports
events. Evolution VII uses this cutting-edge
technology to achieve a dramatic improvement in
road performance and gain a significant
competitive edge in the motor sports arena.
The Active Center Differential replaces the viscous
coupling-type differential used in the past with a
hydraulically actuated multi-plate clutch. This
revolutionary 4WD system regulates differential
limiting force to match driver operation of his
vehicle and driving conditions.
Developed with the motor sports arena firmly
in mind, the ACD uses a center differential to
distribute drive torque equally between front and
rear wheels and thereby improve steering response
at the same time as enhancing traction - a vital
factor in reducing stage and other race times.
Ensuring optimal transmission of drive torque from
the engine to the road surface under all conditions,
ACD's multi-plate clutch delivers up to three times
the differential limiting force of a viscous coupling-
type unit. To achieve this level of performance, the
multi-plate clutch employs the same kind of steel
plates as mechanical limited-slip differentials,
thereby offering superior durability and response
under high clutch plate load conditions. Using
sensors, the system electronically optimizes the
cover clamp load to match driver input and vehicle
operating status. Thus able to regulate center
differential limiting action from free to locked, as
conditions require, the ACD realizes the ideal
4WD system.
Under hard acceleration, the ACD reduces
slippage and approaches a locked state, thereby
transmitting more torque to the road surface for
better traction and acceleration. When the driver
makes rapid steering inputs, meanwhile, the ACD
operates virtually as an open differential to
improve steering response and feel through
corners while retaining outstanding 4WD stability.
The ACD also enables the driver to manually
select one of three modes - Tarmac, Gravel, Snow
- giving optimum traction for paved, un-paved and
snow-covered roads according to preference or to
suit conditions. And, for the rigors of rally,
gymkhana or other competitive use, the ACD
operates in a virtually open state when the parking
brake is used, thereby enabling rapid and effective
side brake turns.

ACD AYC
1. Decelerating
2. Start of turn
(entering cor-ner)
3. End of turn
(leaving corner)
Mitsubishi's Active Yaw Control traction
enhancement system uses a computer to
optimally regulate torque transfer in the rear
differential on 4WD models and thereby tailor
rear wheel differentials to match driver
operation and vehicle operating status. In this
way, MMC's proprietary system both equalizes
the load on the four tires by adaptively
regulating the yaw moment that acts on the body
and improves cornering performance without
inducing any sense of deceleration.
On Evolution VII, control of the ACD and AYC
systems is integrated by computer. ACD control is
based on: (1) A feedback control strategy to
improve vehicle stability by keeping actual body
attitude as close as possible to pre-determined
attitudes as derived from steering angle and vehicle
speed and, (2) A feedforward control strategy that
responds rapidly to driver acceleration and
deceleration actions. By combining these strategies
in an optimal manner, ACD achieves the
outstanding stability of a full-time 4WD vehicle
and enhances steering response while realizing the
superior traction of locked up 4-wheel drive.
In the integrated system, ACD feedback and
feedforward information is transmitted to the AYC
control system using parameters in such a way that
the larger the ACD differential limiting force is, the
larger the yaw moment generated by the AYC
system.
This precise and integrated control operates so
that, for example when accelerating out of a corner,
ACD+AYC operation schematic
Active Yaw Control
Integrated ACD & AYC
system control
When accelerating through a corner, AYC
reduces understeer by transferring torque to the
outer wheel; when decelerating in a corner,
AYC enhances stability by transferring torque to
the inner wheel. AYC also improves traction on
surfaces with low or split friction coefficients
and has fully proven its worth since it was first
introduced in Evolution IV.
For Evolution VII, all parts of the torque
transfer mechanism of rear differential have
been uprated to match the increase in engine
Evolution of Mitsubishi 4WD system
the ACD enhances traction and the AYC enhances
steering response and cornering performance. And
because of its seamless nature, the driver is
unaware of the integrated system as it operates to
improve acceleration and handling more than the
ACD and AYC systems would if they were
operating independently.
ACD+AYC control schematic
Reduces slippage in proportion to deceleration
to improve stability.
Increases slippage in proportion to steering
angle and steering input speed to improve
steering through corner
Reduces slippage in proportion to throttle
opening to boost traction
Transfers torque to outer wheel to match steering
angle and steering input speed, to improve
steering through corner.
Transfers torque to outer wheel in proportion to
throttle opening to reduce understeer and
improve cornering performance
(In cornering under deceleration, reduces
oversteer by transferring torque to inside wheel)
torque, while breather and clutch operating
durability have been improved. The system
shares the same computer, hydraulic actuator
unit and sensors as the ACD, thus reducing
weight and improving reliability.
(
ACD transfer
Hydraulic multi-plate clutch
Front
differential
Hydraulic
pressure lines Wire harness
Steering angle ACD+AYC Joint ECU
ABS ECU
Display
Engine
Transmission
ACD mode switch
Parking brake switch
Throttle opening
Individual wheel speeds
Longitudinal G
Lateral G
Sensor data
Hydraulic unit
Rear differential
with AYC
Electric pump
with accumulator
Center differential
(50:50)
End of turn
ACD decreases slippage
AYC transfers large amount
torque to outer wheel
Reduces understeer
Improves traction
Deceleration
ACD decreases slippage
Better braking stability
1
Start of turn
ACD frees differential
AYC transfers small amount
torque to outer wheel
Better handling response
2
3

bioyuki

Sorry the text is all skewed...cut and paste it from a .pdf.

DtEW

Summarizing and commenting on the Mitsubishi technologies:

The Active Center Differential (ACD) is simply an electronically-controlled clutch-type differential. Understand that conventional clutch-type LSD is "on" all the time and can't tell whether the difference between front and rear axle RPM is due to just cornering (remember that the front and rear axles trace different paths) or real slippage (like spinning a wheel, or even driving sideways). Being so, the conventional clutch-type LSD resists the difference in RPM in both cases. While that's good in the case of real slippage, the resistance hampers cornering, introducing a degree of understeer in both corner entry and apexing.

The Mitsubishi brochure doesn't mention several things.

The Torsen-type (helical gear) LSDs used Audi and others don't suffer this problem, since it couldn't give a rat's ass about RPM differences (Torsen means TORque SENsing), and does "tell" between cornering and slippage. But Torsen-type differentials are relatively fragile, and one to match the strength of either a conventional clutch-type LSD or Mitsubishi's ACD is going to be much more massive.

They also suggest that an open differential distributing power between the front and rear axles is the best setup for corner entry and apexing. While that's true relative to clutch-type differentials, viscous-locking differentials and viscous couplings, they fail to mention that the very best setup for corner entry and apexing is sending no torque whatsoever to the front axle, aka RWD, or simulation thereof. This is of course why part-time AWD systems are employed in premium sports cars such as the Porsche 959, 911 Turbo, Lamborghini Diablo, Murcielago, and the Nissan Skyline GT-R.

(If RWD is so hot for cornering, why AWD at all for for these premium sports cars? A torque-sensing AWD setup is optimal for putting down the power for the corner exit, esp. if the car is ultra-powerful, has a strange torque curve, and/or the driver tends to be a little ham-footed. Powerful rear-engine Porsches especially need this to counter the configuration's natural tendency to oversteer. Amongst the cars listed, the front-engine Skyline GT-R needs the AWD system the least. It shouldn't surprise you to find out that competing in the JGTC, Skylines are actually "only" RWD.)

The Active Yaw Control (AYC) is a conceptual cousin of the Honda ATTS system that came in the Prelude Type SH. Accelerating in a corner, it biases torque to the outside wheels. Think about how a tank turns, and you'll get the idea. (I don't think a lot of the people here are going to grasp a reference to tire stagger of NASCAR or IRL.)

An additional function of AYC is that of a LSD in deceleration. What happens when you trail-brake hot into a corner? Weight transfers to the front and outside wheels, giving the front outside wheel the highest possible traction. Assuming:

1. You have a simple braking system without Electronic Braking Distribution (EBD), which means that brake fluid pressure is distributed equally between both sides of the car.
2. You're braking so hard you're at the edge of lockup.

Which wheel locks up first?

The inside wheels, starting with the inside rear wheel, of course. Those wheels aren't being presed to ground nearly as hard as the outside wheels, which allows the same degree of brake application of lock them up while the outside wheels still roll. (Rear wheel lockup is a function of front-rear brake bias, which is kind of involved in this discussion, but I'm already over my head in terms of post length already.)

Remember that a LSD resists either differences in RPM or torque? The presence of one (or AYC) lets the rolling wheel try to spin the locked wheel, and conversely allowing the locked wheel to try to stop the rolling wheel. What happens is that some of wasted braking power that has locked up the inside wheel is allowed to add to the braking power acting on the still-rolling outside wheel. The rolling outside wheel gets the locked inside wheel to roll a little bit, which improves traction (I'm assuming you guys know the whole kinetic and static friction discussion) and steering ability/consistency, now that you have two rolling wheels to steer with instead of one rolling and one locked.

There's a shitload of theory that would be otherwise fun to discuss were it not for the fact that it's 5:45AM.

gavriil

ATTS was the first thing that came to mind when I saw that our CLS is getting an LSD. So, isnt what our CLS is getting basically the same thing that they put in the Prelude SH in the 90s?

TypeSAddict

Yes, and :ahem: I believe it was yours truly who said that ATTS would be on the new CL

gavriil

I also wonder why they pulled the VSA off. Cant they make VSA and a LSD coexist. or maybe have the LSD intervene only in the front wheels and teh VSA only the rear wheels. I wonder.

While the appripriate front wheel is given more torque from the LSD, at the same time the appropriate rear wheel is being applied the appropriate braking force to create the appropriate transfer of weight to bring the car back.

I know though that in my other car, a 2001 Lexus RX300, they pulled the LSD off in 2001 because all RX300s came with VSC as standard. Plus the car is AWD. I wonder if that car has ANY differentials then.

EricL

Guess #1 --- time to delivery...

TypeSAddict

Those pussys, I wanted a six speed, but I WILL NOT buy a car w/o some kind of stablity/traction assist.

typeR

why dont you drive the car first...

TypeSAddict

Mainly because if I test drive the car, chances are I will not take it to through the set of conditions that would set VSA into action, so I would not feel a difference until I got it home and broke the car in a bit and see how it performs in all conditions.

typeR

howabout this...if the 6mt out performs the auto with vsa engaged in the slalom and g pad????

gavriil

I dont think that by pulling off the VSA automatically it means that they pulled out the Traction Control. Those are 2 different systems that work at different speeds, etc. The 6 Speed might be equipped with Traction Control but not VSA. I think that is the case with the 2001-2002 CLP cars. Anyone?