The balance of power

Written by: Justin Cunningham | Published:

Torque vectoring certainly sounds cool, but is it something that is actually useful? Justin Cunningham investigates.

If Jeremy Clarkson was an engineer, it’s possible he may have worked on a recent transmission innovation from Redditch based GKN Driveline. The presenter famous for his catchphrase, ‘POWER!!’ would almost certainly approve of the torque vectoring technology it’s developed.

While the automotive industry has been keen to talk about downsizing engines in recent years, many are complaining the fun is being taken out of driving. Bucking the trend is the 2016 Ford Focus RS. Despite using Ford’s ‘EcoBoost’ engine, the Focus RS will produce 350hp, and if that isn’t enough to bring the fun factor back, the car will use a torque vectoring all-wheel drive (AWD) transmission system.

GKN Driveline was awarded the development programme just 18 months ahead of its cars’ launch, which didn’t give its engineers much time to design and integrate the system it is calling the Twinster. It consists of a Torque Vectoring Rear Drive Module (RDM), the Power Transfer Unit (PTU) and Constant Velocity Joint (CVJ) side shafts into the front wheel drive platform. GKN’s in-house software and calibration teams also worked in collaboration with Ford and its vehicle dynamics engineers on new control algorithms to optimise the torque vectoring system.

The Twinster uses modular architecture to enable it to be tuned for various applications from stability and safety to higher speed handling and drivability. In this case, Twinster allows even a novice to feel like Lewis Hamilton behind the wheel by increasing the dynamic feel and handling of the Focus RS.

“It allows a non-professional driver to handle a car like a professional driver,” said GKN Driveline vice president of global product technology, Dr Ray Kuczera. “The transmission will know throttle position, steering wheel angle, what the vehicle is doing in terms of sliding, oversteering or understeering, and then work out where to apply power to get it to do what the driver wants.

“It’s modular so can be designed based on whatever it is you’re looking for. It can be tuned for off-road use, which is the way we tuned it for the Range Rover Evoque, or for safe, assured, on-road performance. But, you can also get extreme off-road or extreme driving from it that is at the limit of performance too.”

Computer generated drifting

For professional drivers, setting up a car to control oversteer and understeer is part of the job. Knowing when to apply power, brakes, add steering or counter steering, often all simultaneously within a split second, is a skill that is gradually developed.

The GKN Twinster system has essentially taken that experience and packaged it together to emulate the skill of professional drivers using clever algorithms in conjunction with its AWD capability. Essentially, the car knows how to corner better than you.

Professional drivers probably cringe at the thought of the Twinster, and are no doubt banned from using these kinds of systems anyway. However, for enthusiasts seeking to fulfil childhood dreams and push the limits corner by corner, the Twinster gives stability, control and a certain amount of forgiveness to those that are a little too keen.

Its rear driveline module (RDM) controls the power between the front and rear, and also between each rear wheel. The torque to the rear wheels is individually controlled by a pair of modulating clutches on each side between the transmission and each wheel.

“They are constantly being varied between being completely open (no torque) and full engagement (essentially locked),” said Dr Kuczera. “Any state in between is possible, it is not binary on or off, so can be anywhere between the two states based on the driving requirement. The system is designed to cope with the constant slip that occurs in the RDM. It has been extensively tested so the constant slip is not a problem for durability.

“The way power is distributed from the front to the rear is through a device called a Power Transfer Unit (PTU), which attaches to the transmission. The PTU takes torque from the front and sends it to the rear through the propshaft. The PTU is located at the end of the transmission, so whatever gear the vehicle is in, all of the wheels are in the same gear.”

The front wheels use a traditional differential with no clutches for active control, though there is normal transmission clutch.

Big challenge

A big challenge was how to handle the power. The engine developed by Ford is a 2.3L, 350hp 4-cylinder turbo, delivering 475Nm of torque at the wheels. Designing and controlling a transmission system that can not only put the power down but also modulate it millisecond by millisecond between all four wheels is nothing short of a technical marvel.

While the Twinster can have a similar result as Electronic Stability Control (ESC) systems, which artificially improve handling by applying subtle braking to individual wheel, this all-wheel drive (AWD) system increases power to certain wheels to increase control.

“We steer the vehicle by applying torque to a certain wheel,” said Dr Kuczera. “With brake based traction control and electronic stability programmes you’re robbing the vehicle of power. With torque vectoring you’re sending more power down, so instead of slowing the vehicle down, you’re speeding up certain wheels.”

The Ford Focus RS uses a selector on the dash to pick a driving mode, which can go from regular driving to the most extreme setting, ‘drift mode’. This has the effect of oversteering the rear of the car in a very aggressive manner.

“In this mode the Twinster drives the rear wheels faster than the front,” said Dr Kuczera. “This overspeeding of the rear fundamentally changes the way the car feels and handles. In curves, the Twinster makes the vehicle turn in more sharply, responding more immediately to the driver’s inputs.”

Of course, there is still a need to brake on occasion. And while this system adds stability during acceleration, it works in conjunction with stability control systems that work under braking.

“For driving and handling, torque vectoring is the best way to make the handling better,” said Dr Kuczera. “But for stability, if I’ve lost control of the car, then it makes perfect sense to use the brakes to bring the car back under control.”

The twin clutch system is also being applied elsewhere. The 2016 Cadillac XT5 premium SUV will also use similar technology. While it doesn’t have active torque vectoring, it’s used for on-road stability as well as off-road traction.

“It makes the car great to drive, makes it very safe, and gives you off-road capabilities in a luxury Cadillac SUV,” said Dr Kuczera.

At almost twice the price of a basic Focus (£15,995 vs £29,995), the Focus RS with its Twinster technology is a car for those that want to be engaged with their driving experience, and are willing to pay for it. Clearly, however, you’re not going to drive the vehicle to its limit to visit the supermarket, but what the Focus RS does offer is a commuter car that can double as a track day car.

The 2016 Ford Focus RS will produce 350hp and deploys the 'Twinster' transmission system

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