Thursday 9 October 2014

GKN unveils first 'disconnect' AWD

GKN has developed the world’s first 'disconnect' All-Wheel Drive (AWD) system for A-, B- and C-segment vehicle platforms. The company claims the system improves fuel economy during steady state cruising by up to four per cent.

The innovative 'disconnect' function enables vehicles to combine the enhanced traction, dynamics and stability of all-wheel drive with improved on-highway fuel efficiency.

Senior Programme Director Hannes Prenn said: “As global demand for smaller, more efficient SUVs continues to grow, GKN’s Disconnect AWD system will help open new markets. This compact new system enables manufacturers to offer customers more capable and dynamic vehicles with improved fuel-efficiency and CO2 emissions.”

The system responds to driver inputs and road conditions, connecting and disengaging drive to the rear axle on demand. By eliminating rotating losses from the driveline, during steady state cruising fuel efficiency can be improved by up to four per cent compared to permanent all-wheel drive systems which are well known for their heavier use of fuel.

The result, according to GKN, is a tightly packaged all-wheel drive system, which replaces features such as the standard power transfer unit (PTU) with a monoblock housing that fully integrates the propshaft’s constant velocity joint. The arrangement also yields superior NVH characteristics, benefiting the overall refinement of the vehicle. The clutch system at the heart of the disconnect system is a development of the system used in the Range Rover Evoque.

With all production, engineering and software development in-house, GKN Driveline claims it is the only supplier able to develop and supply such a tightly integrated all-wheel drive system. The result is the lightest, most compact and capable disconnect all-wheel drive system available in the market, according to GKN.

The same hardware can support models built on a common platform but with different performance requirements. GKN’s software engineers can fine-tune the electronic control to deliver specific brand characteristics.”
GKN Driveline’s 'disconnect AWD system includes a power transfer unit (PTU), linked to the transmission’s final drive differential. The PTU contains a fast-disconnect device and brake that can bring the all-wheel drive system to rest upstream of the PTU’s hypoid gears. An electro-mechanically actuated clutch located in the rear axle both biases drive torque and disengages the all-wheel drive system downstream of the hypoid gears to save fuel.

A dedicated driveline control unit continuously monitors vehicle dynamics and environmental conditions, disconnecting the AWD system during steady-state driving speeds when the AWD
function is not needed. If the driver or conditions require more traction, the AWD system reconnects within 300 milliseconds.

An active torque biasing function provides precise control of the distribution of torque between the front and rear wheels, optimising traction, stability and performance. Torque vectoring between the individual rear wheels is also possible with the system and has already been introduced on the Range Rover Evoque.

1 comment:

Anonymous said...

Perhaps you could tell us the manufacturer of an identical type of system introduced in the Chrysler 200 AWD last year? And the Cherokee the year before?

The prop shaft is shut down, and rear half-shafts are disconnected from the rear differential in the Chrysler system. This takes three electromechanical clutches to achieve. The re-engage time is 400 milliseconds, mainly spent spinning up the stopped prop shaft. And if that isn't perfect, you'll experience instability as the rear wheels are connected, particularly in low friction conditions.

American Axle have for sale a system like GKN's, shown on their web pages. However, I don't know which manufacturer FCA uses. Chrysler also has a system that fully disconnects the front wheels on their bigger nominally rear drive cars as well - that one still uses an active gear centre differential, rather than these cheap electromagnetic clutches. What a waste.

As an owner of Subaru's VTD AWD, and two quattros before that, I found the Chrysler 200 a bit of a lumberer - 400 millisecond engagement time means it's FWD most of the time. Exactly what I don't want in snow and ice! I want AWD all the time - I paid for it.

I wish these car companies would wake up - I want AWD for its safety, not to maximize fuel economy. At 60 kph, you travel a long way in 0.4 seconds before the AWD system module spins up the prop shaft from stopped to synchronicity. Utterly useless to even buy it! Adds 100 kg to lug around and hardly ever operates.

The original Haldex was criticized for taking 100 milliseconds to engage,but by comparison it was a sprint champions compared to these new "AWD"systems. These new systems save a tiny bit of fuel, but are fast asleep and snoring their heads off just when you need them. The V6 Chrysler will break traction at the front wheels and cause tire squeal on the first to second gearshift at full throttle, so the AWD is obviously not engaged.

Speaking as a mechanical engineer, I rate these disconnect systems as not worth having. They're included to tick off a box in the spec sheet for the clueless customer, not to do anything useful.