GKN Driveline is claiming a “world first” for its new compact disconnect system for all-wheel drives (AWD) that can be incorporated into the powertrains of A, B and C-segment vehicles.
The campaign to reduce vehicle fuel consumption involves all aspects of vehicle design but it can be complicated by market trends. The increasing international popularity of small AWD SUVs brings particular challenges but GKN engineers claim their new system can alleviate the problems, with fuel consumption during cruise reduced by up to 4%, and CO2 emissions also lowered.
The entire system including software was developed in-house, said Rob Rickell, Senior Vice President of Engineering. It replaces the usual standard power transfer unit (PTU) with a monobloc housing that also fully integrates the propshaft’s CV joint. A dedicated driveline control unit continuously monitors vehicle dynamics and environmental conditions.
The PTU is linked to the vehicle’s final drive differential and contains a fast-disconnect capability and a braking system to stop the AWD system upstream of the unit’s hypoid gears. An electro-mechanically-actuated clutch located on the rear axle biases drive torque and disengages the AWD system downstream of the hypoid gears in low-load cruise conditions. The clutch system is a development of that used in the Range Rover Evoque.
Connection and disengagement of the disconnect system responds on demand to driver inputs and road conditions, with NVH levels improved as a consequence. AWD reconnection can be established in 300 ms, according to company engineers. When AWD is engaged, an active torque-biasing system looks after distribution to front or rear of the vehicle, and torque vectoring is used between the vehicle’s rear wheels.
Rickell emphasized that the same hardware can support models built off a common platform but with different performance requirements. The software can be fine-tuned to create specific brand characteristics, he said.
GKN’s compact disconnect solution promises to make an important efficiency contribution, though the general technology is not novel. For example Jeep’s 2014 Cherokee, based on a Fiat-Chrysler FWD architecture instead of a traditional rear-drive configuration, offers rear-axle disengagement when 4×4 capability is unnecessary.
The Cherokee uses American Axle & Manufacturing’s EcoTrac rear axle disconnect system, itself claimed as a “first” for a midsize SUV. [See Automotive Engineering cover story June 3, 2014: http://www.nxtbook.com/nxtbooks/sae/14AUTP06/index.php]. Featured on each of the Jeep’s three Active Drive systems available for the Cherokee, a wet clutch in the rear drive module automatically senses input torque and engages AWD when required.
According to Rickell, GKN Driveline is the only supplier able to develop and supply such a tightly integrated AWD system, which he claimed is the lightest, most compact and capable of any available.