Haldex

Haldex is not a differential but a coupling joint that also manages to perform the function of a central differential. The Haldex joint used in all-wheel-drive vehicles allows for the management of various torque values between the two axles by continuously adjusting the percentage of torque allocated to the front and rear wheels.

Haldex Coupling of All-Wheel Drive – How It’s Made

The Haldex coupling present in an all-wheel-drive vehicle consists of a cylindrical casing containing two sets of plates, one connected to the front axle and one connected to the rear axle, which make up the package of the electrohydraulic multidisc clutch managed through electronic control.

Haldex Coupling – How It Works and When It Engages

Under normal driving conditions, the Haldex clutch is open, so the two axles are independent as are the two sets of plates connected to them. When the wheel speed sensor of the ABS detects that the front axle is rotating faster than the rear axle, the control unit activates the hydraulic pump which, by increasing the oil pressure in the actuators, brings the two sectors of the clutch closer together (the clutch pack tightens), allowing the transfer of torque between the two axles, thanks to increased friction between the plates. The system’s intervention is very quick: it is sufficient for the slip angle between the front and rear wheels to exceed 90 degrees. The Haldex clutch is then reopened when the slip ceases or if the brake is applied. The distribution of torque can vary from 90% front and 10% rear up to 100% rear, depending on the specifications desired by the manufacturer. Of course, 100% rear is a limit situation that occurs, for example, when one of the front wheels loses grip and there are no electronic slip limiters on the front.

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