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Electronic Locking Differential for VW Golf GTI Mk7

February 21, 2013

Volkswagen’s new Mk7 Golf GTI, due later this year, will be available with an optional performance pack which includes the “VAQ” differential (front axle transverse differential lock) in the front (driven) axle.

Unlike the electronic EDL or XDS traction systems, which use a standard differential in conjunction with individual electronic control of the front brakes, the VAQ is an active mechanical clutch pack-based device located between the differential cage and the right-hand drive shaft. The pressure required to actuate the clutch pack is produced and regulated by an electrically-powered hydraulic pump. The VAQ is a Haldex unit similar to that already used in VW 4MOTION four-wheel drive systems.

The locking differential prevents the driven wheel with the least grip from spinning by “vectoring” torque to the wheel with most grip. A typical example of this in a powerful front-wheel drive car is during cornering. Weight is transferred away from the wheel on the inside of the curve, causing it to break traction, or even spin. Should that happen, drive can be reduced or lost, and steering is adversely affected.

The VAQ responds to changes in vertical wheel forces monitored by sensors, allowing the vehicle’s handling to remain neutral and agile, with precise steering close to its performance limits. VW claims that the traction problems typically associated with powerful front-wheel drive cars have been virtually eliminated using the system.

A new, progressive electromechanical steering system has variable tooth spacing on the steering rack and a more powerful electric motor. The new system gives a more progressive transition between relatively indirect steering during straight-line driving and more direct response at larger steering angles.

The Mk7 Golf is based on a new VW Group platform called MQB (Modularer Querbaukasten) or Modular Transverse Matrix. The objective of MQB is to streamline production, reducing both weight and cost, the latter making it possible to deliver higher specifications to the customer for less money. It extends beyond the components used to manufacture a car, making it much easier and cheaper to install the plant employed to build the vehicles and, particularly, to establish all-new production facilities. Vehicle chassis are constructed using a tool kit of standard components. So it becomes easy, for example, to substitute a rear floor section capable of accommodating a battery in a hybrid version without any re-engineering.

Almost all VW, Audi, Seat and Skoda models up to C-Segment level will be based on the new platform. At VW, this covers everything from the Polo to the Golf and will extend to the Passat. MQB is a highly modular platform based on certain fixed chassis dimensions, while allowing flexibility in others. It also incorporates a high degree of standardization, with common engine mountings and exhaust configurations across diesel and gasoline powertrains.

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