All Wheel Drive Encyclopedia

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Haldex all wheel drive system

Haldex Generation I, 1998-

The design of the Haldex LSC gen. I, II, and III 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 in which the housing and an annular piston are connected to one shaft and a piston actuator is 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 shafts are rotating at the same speed, there is no pumping action. When a speed difference occurs, the pumping starts immediately to generate oil flow. It is a piston pump, so there is a virtually instant reaction with no low-speed pumping loss.

The oil flows to a clutch piston, compressing the clutch pack and braking the speed difference between the axles. The oil returns to the reservoir via a controllable valve, which adjusts the oil pressure and the force on the clutch package.

In traction/high slip conditions, a high pressure is delivered: in tight curves (i.e. parking), or at high speeds - a much lower pressure is provided.

Haldex Generation I and II based all wheel drive system is reactive. The coupling activates after a wheelspin is detected. However, the reaction is very quick and just 1/4 of a wheel turn is needed to engage all wheel drive. Electronics is capable of lowering the oil pressure only (when parking, ABS working, the handbrake is pulled, etc.), but cannot pre-tension the clutch.

Under normal driving conditions (driving at the constant speed, no silppage), the torque distribution is 90/10 front to rear. When the clutch is locked, torque is evently distributed between the axles (50/50).

Figure: Haldex clutch unit (2) insallation near the rear differential. Skoda Octavia.

Haldex unit cut away

Haldex Generation II, 2002-

This second generation of Haldex LSC is still using the mechanical hydraulic pump, but the linear throttle valve has been exchanged for a solenoid controlled proportional throttle valve.

Haldex Generation I and II based all wheel drive system is reactive. The coupling activates after a wheelspin is detected. However, the reaction is very quick and just 1/4 of a wheel turn is needed to engage all wheel drive. Electronics is capable of lowering the oil pressure only (when parking, ABS working, the handbrake is pulled, etc.), but cannot pre-tension the clutch.

Haldex Generation III, 2004-

A coupling with pre-tensioning capability of the hydraulic clutch by the means of existing feeder pump (PreX™ solution).

Haldex Generation III and IV based all wheel drive system is pro-active. The electronics can pre-tension the clutch and activate all wheel drive before a wheel slip occurs.

Haldex Generation IV, 2008-

The fourth generation does not have the mechanical pump any more. The clutch is activated using the feeder pump.

Haldex Generation III and IV based all wheel drive system is pro-active. The electronics can pre-tension the clutch and activate all wheel drive before a wheel slip occurs.

Haldex XWD� (Cross Wheel Drive), 2007-

A combination of two Haldex Couplings, one for the front/rear torque distribution, another for the torque distribution between the rear wheels. First introduced on Saab 9-3 in 2007 with earlier generation Haldex unit then replaced with Generation IV unit in 2008.

For further information, see the Haldex Web site: http://www.haldex.com/en/North-America/Applications-Products/Product-categories/AWD/

Last updated: 11-Jul-2010 13:38


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There are 5 comments
Klemen
July 13, 2010 - 16:52
Subject:

I own a Vw passat variant 2,0 tdi 4motion 2007, but i can't find out which generation of haldex does it use? Thank you for your answers.

Mark Schiller
July 05, 2010 - 22:54
Subject: 2007 Volvo S80 V8 AWD

Which version of Haldex is in the 2007 Volvo S80 and what is the percent of power to the wheels under normal conditions and what is the maxium split in power between the front and rear wheels under adverse conditions? Thank you.

Reply to Mark Schiller
awd.ee
July 06, 2010 - 21:20
Subject: Re: 2007 Volvo S80 V8 AWD

This one must have Haldex III. 90/10 split under normal conditions, 50/50 when the clutch is locked. The percentage of power can vary from 100/0 to 0/100. See "Understanding torque split" for more details. This is as much as I know at this moment.

Carl Warren
January 06, 2010 - 04:34
Subject: Does my 2010 Lincoln MKS Ecoboost have this type AWD?

This was an interesting presentation of the progression of HALDEX AWD system, and I would like to know if it is the system used in my new 2010 Lincoln MKS Ecoboost AWD.

Reply to Carl Warren
George
January 11, 2010 - 00:53
Subject: Re: Does my 2010 Lincoln MKS Ecoboost have this type AWD?

Ford is a big customer of Haldex, it stems from the days when they owned Volvo.
The Lincoln MKS utilizes the 4th iteration of the Haldex coupling.
Unfortunately it still has an open rear differential.

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