Focus RS: Ford and GKN create an AWD masterpiece

  • 14-May-2016 01:29 EDT
Ford04-16 Focus RS Tyrone Johnson 2.jpg

Vehicle Engineering Manager Tyrone Johnson said the RS's rear-wheel overspeeding means the rear of the car is constantly trying to overtake the front, giving a lively feel. But the bad news is "the back of the car works against the front.” 

If an international TV quiz show had the new Ford Focus RS as one of its subjects, Tyrone Johnson would have all the answers.

As Vehicle Engineering Manager for Global Ford Performance—and as Chief Engineer for Formula One and rallying before that—Johnson has seen the latest RS mature to become a truly global car. And like the Mustang and a growing number of other models, it is conforming to the company’s “One Ford” philosophy.

Despite being a specialized sports model, the RS had to be built on the same line as the regular Focus at Ford’s Saarlouis, Germany, plant without causing any hint of a hold up in the output of some 2000 cars per day.

“Stop the line and you get a lot of attention at Ford!” said Johnson. So although the RS is something of an exotic machine, it still contains the essential elements that define a Focus. “It had to be an everyday usable car—not just a one purpose vehicle, even though we planned to introduce some innovative solutions for track and handling, with aerodynamics (achieving zero-lift balance is difficult for a 5-door car) and chassis systems driving its design,” he told Automotive Engineering.

A 'less efficient' intercooler

The new RS packs an impressive specification. Power comes from a Honeywell-turbocharged 2.3-L 4-cylinder driving a 6-speed manual gearbox and GKN all-wheel-drive system with torque vectoring and drift control. The Ecoboost engine's claimed 257 kW (345 hp) is kept in check with launch control and is capable of propelling the RS to 266 km/h (165 mph) max velocity, with 0-100 km/h (0-62 mph) acceleration in a claimed 4.7 s.

RS front suspension is by MacPherson struts with semi-isolated subframe. The rear short-long arm suspension features Ford's "control blade" setup designed by former Ford vehicle-development boss Richard Parry-Jones. First used in the Focus ST, this unique trailing arm multilink system offers the packaging benefits of a trailing arm suspension with the geometry of a double wishbone system.

The thin stamped-steel control-blade trailing arm handles two degrees of freedom—longitudinal wheel movement and brake-torque reaction. So only three lateral links are needed to fully control toe and camber, with the added benefit of good anti-dive geometry.

Braking the 1599-kg (3525-b) RS is handled by Brembo 4-piston Monobloc calipers clamping 350 x 25-mm ventilated rotors in front, and solid 302 x11-mm discs in the rear. Claimed fuel consumption on the combined NEDC is 7.7 L/100km and CO2 emissions of 175 g/km.

Johnson noted that his development teams sweated the details on this car. That's immediately evident to drivers, but in one area the technology developed was just a little too good.

“We had to decide 2½ years ago on air intake opening size. This could not be changed later in the development program so we decided bigger is better, as durability cooling was very important," he said. "However, the intercooler proved to be too efficient; under some specific conditions water vapor was created in the intake system, which is not good. So we made the intercooler a little less efficient by using a blanking plate.”

There may be applications in the future for the super cooler, he noted. Peak engine torque is quoted at 440 N·m (325 lb·ft) but Johnson explained that an overboost to 470 N·m (347 lb·ft) is available for 15 seconds. But a driver only need lift off the throttle for a millisecond and back would come the added 30 N·m (22 lb·ft); so effectively it is available all the time.

The sound effects accompanying the engine are supported by an exhaust system “as straight through possible” with an active valve system to balance NVH and power and stay within noise legislation.

“One of our metrics is: ‘Rewarding to rev.’ Sound in this type of car is incredibly important but it has to be legal.” Achieving just the right balance involved three redesigns to meet what seemed like opposing criteria. “We are legal, including pops and burbles, something that officials looked at very closely, as they are achieved by misfires, not burning fuel efficiently and leaving hydrocarbons!”

GKN's clever Twinster AWD

The RS features a twin-clutch GKN Twinster driveline, rather than a Haldex AWD. Ford and GKN worked closely to integrate the system that can apply torque independently, enabling the vehicle’s dynamic torque vectoring functions across its entire speed range.

The GKN system incorporates a PTU (Power Transfer unit) and an RDM (Rear Drive Module) utilizing the Twinster twin clutch system that can apply torque to one or both wheels independently. The Twinster drives the rear wheels faster than the front.

The overspeeding (2%) at the rear, fundamentally changes the way the car feels and handles. The result is a car of competence and character sampled recently by Automotive Engineering on track, frozen lakes, and regular roads. It’s fun.

Through corners, the Twinster makes the vehicle turn in more sharply, responding more immediately to the driver’s inputs. In the Focus’s track-only drift mode, the AWD system delivers even more torque to the rear axle, making it easy for the RS to achieve a controlled drift through corners.

A dedicated ECU controls the hydraulics and solenoid valves to continuously vary the pressure at each clutch pack, redistributing the torque to the wheels.

The software updates the hydraulic control settings 100 times per second to provide quick, accurate torque control, the clutches continuously moving as required anywhere between fully open and fully locked, delivering the required performance.

Johnson explains that the system allows the car to be steered into and through a corner without the usual understeer effect of most AWD set-ups, facilitating a very fast exit from the corner. “We did not want a fixed input of torque to the rear wheels, typically 70% for other systems,” he noted. 

The rear-wheel overspeeding means the rear of the car is constantly trying to overtake the front because the system is running faster, explained Johnson: “This gives the car its lively feel. That’s the good news; the bad is that the back of the car works against the front.”

Ford, working with GKN, took more than two years to develop the AWD for the RS, successfully achieving compensating solutions for the forces generated and the systems’ “in-fighting”.

Said Johnson: “Engineers spent hundreds of hours calibrating every possible drive situation in order to get the reactions we wanted. We experienced extreme situations where we had upwards of 95% of torque going to the back of the RS!”

There is also a launch control for rapid take-offs.

Other chassis technologies for the RS include a unique electric PAS; brake cooling aided by an upside-down airfoil to accelerate airflow; unique dampers, spring and subframe assemblies; and exclusive Michelin tires.

The body gets additional stiffening to enhance torsional rigidity.

And all this has been done for a global buyer base, stressed Johnson. “It’s probably the most global car we have ever built," he said, "yet I can count on the fingers of one hand the different parts between the U.S. and Europe.”

Former Ford CEO Alan Mulally, father of the company’s “One Ford” doctrine, might allow himself a satisfied smile at hearing that.

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