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wheel-drive systemsupplied byGKN. This represents the first application of this technology in amass-market,D- segment vehicle.GKNcurrently deploys the systemin theMkIII Ford FocusRS, a specialist performancemodelwith a low production volume (4,000 carswere initially allocated for sale in theUK). Figures fromtheEuropean

Mass market four D

ebuting at theGenevaMotor ShowinMarch, theMY2017 Opel/Vauxhall InsigniaGrand Sportwill feature the Twinster, a torque-vectoring (TV) all-

tomass-production vehicles is evident in the past 10 years,withmanufacturers increasingly using cross-range branding for their vehicles that offer the technology.An example isBMW’s dynamic performance control on their xDrive series, supported by aZF system.

AutomobileManufacturersAssociation (ACEA) showa steady increase in take-up of all-wheel drive (AWD) since 1990, now totalling 13 per cent ofmarket share. This European trend is closelymatched by figures for theUK.While a large portion of theACEAfigure can be attributed to the explosion in popularity of sport utility vehicles, the trend towardsAWDis also noted inmanufacturers increasingly offeringAWDvariants of their range of conventional passenger cars. The FocusRSwas the first roadgoing

AWDversion of the best-selling hatchback, a collaborative project between Ford andGKNto adapt the frontwheel-drive, using a power transfer unit (PTU) to deliver torque to the rear wheelswhen cornering.By driving the rearwheels faster than the front, and the outsidewheel faster than the inside, the yawmoment can be increased, tightening the turning trajectory. Torque-vectoring has its origins in

Japan,withMitsubishi developing its active yawcontrol systemin a successful attempt to gain a competitive edge in the WorldRallyChampionship. Subaru – Mitsubishi’smain sporting rival in the 1990s – first fielded a carwith an active differential in 1993.Meanwhile,Honda invested heavily in implementing fully- mechanical solutions in road vehicles such as the Prelude and theNSXsports car,which used a helical gear assembly to influence clutch action in tight cornering. Early systems combined a conventional

front-drive setupwith vectoring to individual rearwheels. Systemswith four-wheel vectoring have been developed inEurope byZF,GKNand Ricardo, and rapid growth in application

42 /// Environmental Engineering /// February 2017

TORQUE VECTORING EXPLAINED The basic principles of torque vectoring serve to enhance the function of a vehicle differential, by splitting the available torque unevenly between the fourwheels, improving steering response; however, intelligent intervention is required to improve lateral dynamic stability and prevent unintended consequences, such aswheel spin and locking.Atorque- vectoring systemrequires the ability tomonitor vehicle conditions – driver inputs and available traction at eachwheel – and respond by distributing torque to maintain predictable handling. This is particularly important in low-grip conditions, such as inwinter, where one side of the car may encounter a patch of ice, provoking a sudden loss of traction. In the Focus, theGKNsystem can direct up to 70 per cent of available torque to the rear axle, ofwhich up to 100 per cent can be diverted to a singlewheel. If a loss of grip is detected, power delivery can be redistributed to optimise stability and prevent the tractivewheel fromreceiving toomuch power, aswith an open differential. The Twinster is an evolution of the

systemdevelopedwith Jaguar Land Rover for use in the 2014RangeRover Evoque.GKNprovided the PTUand rear drivemodule. TheECUalso switches to 2WDduring steady-state driving above 22mph, improving fuel efficiencywhen AWDis not required. The system

GKN Driveline’s Twinster brings electronic torque-vectoring to the mass market, promising performance-enhancing technology without breaking the scales. Automotive correspondent Scott Kimber looks at the implications

monitors the vehicle’s operating conditions and re-engages the system when additional traction is needed. The Insignia systemutilises the current

Twinster principle of using a set ofwet clutches at the rearwheel to deliver torquewithout the need for a differential. GKNclaims this provides a significant offset to the traditionalweight gain associatedwith a switch toAWD. The hydraulic actuators that operate the clutches are electronically controlled, opening and closing by degrees in response to driver inputs and road conditions,with a refresh rate in the range of a fewmilliseconds.

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