Torque vectoring  enhances the driving experience

Customers want electric or hybrid vehicles to be fun to drive, in addition to being economical and environmentally friendly. One of the ways of achieving this is by providing more power to the rear wheels through new axle technology.

Automotive Industries (AI) asked Dr Joachim Horst, Vice President Engineering at global engineering group GKN how the company’s electric “torque-vectoring” axle technology will help make the next generation hybrid vehicles more dynamic.

Horst: The eAxle system integrates GKN’s Twinster dual-clutch drive module, which distributes more torque to an individual wheel to help the vehicle turn faster. This greatly enhances cornering response – or “torque vectoring”. With the Twinster we can control the lateral dynamics of the car. We want the eAxle to be more than an add-on to a normal primary axle. Building it in will give us the ability to do some torque vectoring to enhance the stability and the lateral dynamics of the car.

This technology has a number of application opportunities, from automakers that want to produce hybrids with great off-road performance to performance-focused cars that require greater levels of on-road traction and cornering capability. Automakers are already using GKN eAxles to build more driver-focused plug-in hybrids such as the Porsche 918 Spyder and BMW i8 that blend efficiency with all-wheel drive performance. GKN’s new torque vectoring eAxle module comprises a 60kW, 240Nm GKN EVO electric motor which drives an electric axle with a transmission ratio of 1:10. A dual-clutch Twinster system then vectors the resulting 2,400Nm of torque between the rear wheels.

AI: AI asked Dr Rainer Link, Managing Director eDrive Systems at GKN how the new technology compares against conventional powertrains on performance and efficiency.

Link: The electric “torque-vectoring” axle technology will make the next generation hybrid vehicles more dynamic. The technology will help hybrids compete successfully against conventional powertrains on performance, not just efficiency.

AI: Dr Andreas Mair, Senior Director Product Technology eDrive Systems was asked how the new eAxle system for Volvo XC90 helps to integrate a plug-in hybrid powertrain into a global platform.

Mair: GKN’s systems integration capabilities resulted in an eAxle that minimizes packaging, and maximizes performance. Designed to fit in the same space as the rear drive module on the XC90 AWD (all wheel drive) driveline, the eAxle solution provided by GKN gives Volvo the ultimate flexibility to meet the customer demand mix between all versions of the XC90 driveline. Our technology enables new, axle-split hybrid architectures that make it simpler to integrate a plug-in hybrid powertrain into a global platform. It offers consumers a compelling mix of electric-drive efficiency and all-wheel drive capability.

By using the electric motor’s output as the transmission input shaft, the result is a smaller, lighter and higher performance electric drivetrain. GKN’s eAxle system incorporates an intelligent disconnect clutch technology that provides a more efficient eDrive mode by disconnecting the eAxle in the high speed driving range.

JH: How does the new AWD system Ford Focus RS work?

Mair: For the Ford Focus RS we developed a new version of the Twinster torque vectoring all-wheel drive (AWD) system. It is a combination of new gearing ratios and control algorithms that have helped Ford to create a car with unprecedented dynamics, feel and handling. The Ford Focus RS uses a GKN AWD system with a PTU (power transfer unit) and a RDM (rear drive module) utilizing the Twinster twin clutch system. GKN’s Twinster technology can apply torque to one or both wheels independently, enabling the vehicle’s dynamic torque vectoring functions across its entire speed range.

The latest version of the Twinster in the Focus RS uses new gearing ratios that deliver more torque to the rear wheels than previous applications. When AWD is engaged, the Twinster drives the rear wheels slightly faster than the front. This 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. In Ford’s “drift mode,” the AWD system delivers even more torque to the rear axle, enabling the RS to achieve a controlled “drift” through corners.

AI: How can GKN help car makers to achieve the crucial tipping point for electric drives in mass production?

Mair: It started with a mild all-wheel hybrid drive which we developed 10 years ago in Japan. Then we did some hybrids in the range of maximum of 30% of the electrical power compared to the mechanical power. The first application we had with 20kW nominal power on the eAxle and 120kW mechanical power was in 2008. With the i8 we have exceeded that. But, what we are working on is products which provide more than 50% electrical energy compared to the mechanical energy of the car. Our goal is to provide more power through a transmission with higher capacity. We are able to offer integrated systems with reduced packaging, high torque and backed up by our global manufacturing capability. We are ready to support our customers with mass production.

Hybrid vehicles are moving now into volume production and everything in the driveline that we are developing for hybrid vehicle could potentially be used for pure electric vehicles. The tipping point for battery electric vehicles will be determined by the battery, and we have no influence on that. The tipping point for the fuel cell will be the actual infrastructure and what we have to offer there is our hydrogen storage technology. GKN is developing a hydrogen storage system, which is a very safe, low pressure solution for hydrogen storage.

The success of our eAxle systems in sports cars for Porsche and BMW demonstrated how the right kind of hybridization creates new value propositions for the driver. We are now preparing mass-production versions of the technology that can also deliver torque vectoring.

AI: How is the technology affecting GKN as a company?

Mair: Our company has evolved in the last five years from being the world’s largest supplier of limited slip differentials, constant velocity joints and lightweight driveshafts into a leader in intelligent hybrid and all-wheel drive systems. We worked closely with Porsche and BMW on the launch of the companies’ flagship plug-in hybrid programs: the Porsche 918 Spyder and the BMW i8.

The development and introduction of this critical technology will support widespread adoption of plug-in hybrids. We will accelerate the downsizing of eAxles and make it simpler to integrate electric torque vectoring into vehicle platforms. AI: How can you make hybridization easier for vehicle manu­facturers and at same time more compelling for car buyers?

Link: As the car becomes more and more attractive for the end customer, the more hybridization is built in from the CO2 point of view and also from a power point. This is one direction that we are pursuing quite heavily at the moment. In generic terms, we are helping with systems development, getting rid of interfaces, increasing the power of whole modules and not just developing gearboxes, but integrating e-machine, power and electronics. The objective is offer modules that are both cheaper and easy to integrate. On one hand we want to help our customers to produce attractive solutions within a reasonable price range and on the other, to make the vehicle fun to drive for the end user. Everybody expects to have good experience in an electric or hybrid vehicle.

AI: How early do you get involved in a new project with a carmaker?

Link: GKN has a very good, longstanding relationship with the advanced engineering departments. We understand that our customers, the OEMs, want much more than a component manufacturer. The full range of services that we provide to the customer in the early stages of development includes simulation, consulting on operating strategies, and electronics development. You see mainly the hardware, but the software and the deep knowledge of the systems is something that opens doors that we couldn’t open in the past. This is our development direction.