MATTTT

We all know it diverts torque to the rear when it detects the front wheels slipping but that begs the questions...

1) When does it revert back to FWD only? As soon as the front wheels stop slipping? A few seconds later? Minutes? Next time you hit the brakes?

2) What other conditions cause it to engage? If you give it full throttle from a standing start does it assume Quattro is required or does it still wait until the front slips?

3) Can it learn? Let's say the streets are slick and every light I've pulled away from has caused the Quattro to engage, can it predict the same will happen again?

4) If you take a curve fast and attempt to power out of it with full throttle does (or can) the Quattro engage to correct understeer? (Let's assume ESP is off). Or perhaps front wheel slip is an implicit feature of understeer and therefore a situation automatically handled by the Haldex?

jgriff

ANswers to your questions.
Haldex will supply torque to the front wheels as long as they can handle it without slip. The system responds quickly to changes in wheel slippage and therefore once the torque can be reapplied to the front it directs the torque in that manner.

Haldex does not assume anything. It simply responds to the need to apply torque to the wheels that can use it. It does not learn anything, it is an active system that responds to the conditions it is operating under. It has no predictive powers.

Haldex cannot repeal the laws of physics. If you are in an understeer situation it is because you have too much steering input for the traction that is available. Your car will continue to push until the speed is decreased or traction is increased through other means (better road surface, less steering input, or other). Haldex will transfer torque from the slipping wheel(s) to those that are not slipping, therefore, assuming the rear wheels are not slipping, the application of additional torque (more throttle) will be transfered by Haldex to the rear wheels, increasing your speed, and the understeer situation. This throttle application will have the further result of transfering weight aft decreasing the traction on the front wheels and increasing your understeer.<ul><li><a href="http://www.haldextraction.com/">http://www.haldextraction.com/</a</li></ul>

smallTTs

NEW HALDEX 4WD-SYSTEM FOR VW GOLF 4 MOTION

Swedish development gives increased performance and safety

The new Volkswagen Golf 4 Motion has one of the most advanced four-wheel drive systems yet developed. This new system, the Haldex Limited Slip Coupling (Haldex LSC) has
been developed by Haldex Traction AB, Landskrona, Sweden a company within the Haldex Group. The Haldex LSC provides fully controllable torque transfer characteristics to deal
with all potentially dangerous or difficult driving conditions and to enhance the vehicle dynamics and handling performances.

Automatic torque transfer actuation

Without intervention by the driver the Haldex LSC automatically adjusts torque transfer characteristics to deal with any situation, whether requiring maximum torque transfer in sand or at
acceleration, or reduced torque transfer when negotiating sharp corners or parking in confined spaces.

Volkswagen had been seeking a 4WD system with improved performance over existing systems which in many cases are based on a viscous coupling. VW adopted the Haldex LSC
after extensive testing and evaluation which demonstrated the ability of the Haldex system to eliminate virtually all the problems experienced with existing systems. Further development
and co-operation between Volkswagen and Haldex has finely tuned the system to the specific requirements of the VW Golf Syncro.

VW has placed an order for Haldex to supply their new system on 4WD models based on the A4 platform for the next 5-6 years, which could be worth some $130 million, depending
on 4WD sales.

Kenneth Hansen, the 1996 European rally-cross champion, has several years of positive experience of the Haldex LSC in extremely demanding conditions.

The Haldex LSC, a self-contained compact mechanical/hydraulic unit with an integral electronic control unit (ECU) and associated software, provides increased safety, performance and
driving comfort. The VW Golf Syncro is the first production vehicle to incorporate the new Haldex system, which will also be fitted in the new super-coupe Audi TT Quattro, due to be
launched in the autumn of 1998.

Compatible with all safety systems

Full compatibility with ABS, ESP and other safety systems is achieved without the need for additional components, such as an electromagnetic clutch or the freewheeling devices used in
many existing 4WD vehicles. The Haldex LSC connects to the Golf's electrical data distribution system (CAN) to gather information on the driver's actions, engine performance,
transmission and brakes in order to control the car's torque transfer characteristics.

Installed in the vehicle's drive train, the Haldex LSC distributes torque between front and rear axles by means of a wet multi-plate clutch. The hydraulic piston pump is activated
immediately by the speed difference when a driven wheel starts spinning. The ECU controls the hydraulic system, via a throttle valve, and hereby controls the amount of torque transfer in
accordance with the driving conditions being identified.

Immediate activation

So sensitive is the Haldex 4WD-system that within 10 degrees of wheel spin the coupling is activated and the spinning arrested. Even at differential wheel speeds as low as 3 to 4 rev/min.
the coupling reacts equally fast.

Controllability = Possibilities

Controllability of system functions is such that uneven tyre wear can be tolerated without affecting the performance of the vehicle, even the newly developed "Run-flat"-tyres will not cause
any problems. This is because the ECU detects the difference in the diameter of the tyres and adjusts the characteristics accordingly.

The controllability of the Haldex LSC offers virtually unlimited possibilities to customize the performance and characteristics of the vehicle.

Weight optimization

With the built-in torque transfer limitation the weight of the complete drive-train can be optimized resulting in reduced fuel consumption.

Further information from:

HALDEX TRACTION AB

email: info@htse.haldex.com

Jason Chen

Nicely said!

MATTTT

that the car would start to behave more like RWD and tend towards oversteer. Maybe that's silly.

But back to your answer. If torque is directed to the rear then some of the traction required is performed by the rear. Surely it follows that now less traction is expected from the front, and now the traction required for the desired steering input is within the tire's operating range?

JustJeff

Controllability of the vehicle in all driving situations is becoming an
important promotional factor for All-Wheel-Drive. A AWD vehicle has
better road handling and is safer in all driving situations. Answering
these requirements, the Haldex LSC offers fully controllable torque
transfer characteristics and extremely rapid activation and deactivation
- automatically. Maximum performance and safety are achieved in all
driving situations, as shown here: Parking Low or zero torque transfer
needed for easy and comfortable manoeuvring. Acceleration High torque
transfer for maximum traction on all four wheels. High speed driving
Reduced torque transfer, to minimum, still adding dynamic stability.
Driving on slippery/wet roads Swift activation of the coupling for
maximum traction and safety depending on the slip of the wheels. The
coupling is in on-line communication with other safety systems in the
vehicle. Different tyre wear and pressure conditions Remained function
of the coupling. The algorithm in the ECU detects the diameter
difference of the tyres and compensate the characteristics accordingly.

Braking/ABS Immediate deactivation on ABS signal to ensure full function
of ABS system. Brake testing Coupling is not activated until a set value
of the engine speed is exceeded. This means no function of the coupling
even if the ignition is on. Towing Coupling is not activated until a set
value of the engine speed is exceeded. The ignition can be on for lights
etc. ESP Immediate deactivation on ESP signal to ensure full function of
ESP system. Alternative is to communicate with the ESP system for adding
the control possibility of the Haldex LSC to the ESP System.
Run-flat-tyre Software compensation for different wheel dimension - AWD
function maintained. Off-road Rapid activation with high torque transfer
for maximum traction. Alternative separate off-road mode (switch) to
lock the coupling.

The design of the Haldex LSC is based on a Swedish
patent acquired by the Haldex Group.
The unique design of the Haldex LSC
comprises three functional parts:
- The hydraulic pump driven by
- the slip between the axles/wheels.
- The wet multi-plate clutch.
- The controllable throttle valve
- with its electronics.
The unit can be viewed as a hydraulic pump, where the
housing and an annular piston are connected to one shaft
and a piston actuator connected to the other.
The two shafts are connected via the wet multi-plate
clutch pack, normally unloaded and thus transferring no
torque between the shafts.
When both shaft are rotating at the same speed, there is
no pumping action. Immediately as a speed difference
occurs, the pumping and starts to generate oil pressure.
As a piston pump there is virtually instant reaction with
no low speed pumping loss.
The oil flows to a clutch piston, compressing the clutch
pack, braking the speed difference between the axles.
The oil returns to the reservoir via a contollable throttle
valve, which controls the oil pressure and the force on
the clutch package.
In traction/high slip conditions a high pressure is
delivered, while in tight curves, i.e. parking, or at high
speeds a much lower pressure is provided.



Haldex LSC is fast! With instant activation on differential
speed Haldex LSC provides high torque transfer within
less than 15° wheel rotation.
Haldex LSC reacts equally fast against slow wheel spin.
The coupling is activated and starts transferring torque at
differencial wheel speeds of just a few rpm.
Haldex LSC is activated regardless of whether the input
shaft is rotating faster or slower than the output shaft.
This is a major advantage for the dynamic stability of the
vehicle in acceleration or deceleration in combination
with cornering or manoeuvring.
The torque transfer characteristics are controlled by the
ECU using the vehicle management information,
adjusting oil pressure via the throttle valve. With the
controllable torque transfer characteristics of Haldex LSC
the vehicle performance does not need to be a
compromise between traction demanding high torque
transfer and manoeuvrability demanding low torque
transfer. The torque transfer is optimized for each
individual driving situation - ensuring maximum safety
and performance.

JustJeff

Oops, beat me to it.

jgriff

In an understeer situation the front wheels are slipping laterally not rotationally (ie torque induced). Given a slipping condition the wheels will be unable to handle additional torque and the Haldex will redirect torque to the rear.

When that happens our condition is unchanged up front (wheels slipping laterally) and we are sending torque to the rear. The front tires are still slipping laterally therefore the understeer will continue unabated. The weight transfer to the rear will cause less traction at the front and thereby increase the understeer.

To induce oversteer we have to increase the traction on the front wheels and reduce it on the rear. this can be accomplished by hard braking during prior to turn-in and then continuing to brake (trail braking) during the turn. With quattro (fwd) throttle induced oversteer is not really possible unless all the wheels are slipping (front and rear). however the vehicle will tend to move laterally and rotate as you desire.

MATTTT

once the front wheels start to lose traction! Ouch! (If ESP was switched off)

You say that the tires are losing traction laterally but my original question was what happens if you apply full throttle coming out of a curve. I was thinking that there could be sufficient torque to break traction rotationally (I wasn't thinking laterally). Once you break traction rotationally, the lateral traction is also broken, hence power induced understeer. If it weren't for the extra torque applied there would have been no loss of traction. Now, are you still saying that the Haldex Quattro doesn't help in this situation?

TTop Gun

Enough throttle to break all 4 tires loose = throttle-induced four wheel drift, *not* understeer!