Innovation in steering systems for light duty vehicles: The advantages of electric power steering systems
Innovation in steering systems for light duty vehicles
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The electric power steering market is forecast to grow by 13.44% globally by 2016. Power steering has become so commonplace in our vehicles today that we tend to take it for granted, but the automotive industry does not stand still, and hydraulic power steering is slowly being replaced by electric systems.
The main industry driver for this change is better fuel efficiency, but the cost of electric power steering systems could affect this growth, and producing systems which are acceptable to consumers is another concern. Previous incarnations of electric power steering systems have been criticised for not giving the correct ‘feel’ to the driver, and creating a digital, and unnatural experience. The key for OEM’s and their suppliers is to create systems which generate the right amount of feedback from the road surface and supply the right amount of torque to the steering wheel. The steering wheel is the driver’s foremost tool for interaction with the road, and electric systems must give an accurate representation of a natural driving experience.
The advantages of electric power steering systems
The use of electric power steering systems can contribute to enhanced safety, comfort, and driving precision. The increasing use of electric motors rather than hydraulic systems to control the power steering offers better control of steering assistance to suit the driver’s requirements, and to overlay additional torque as necessary. Sensors detect the steering torque being applied by the driver and send this information, via a control unit, to an electric motor. The motor then applies the necessary steering to the wheels via the steering rack. The big advantage to an electric system is that the amount of steering torque applied to the wheels is not just reliant on the torque applied by the driver, but can also be regulated by software depending on a range of other variable data supplied by the vehicles electric systems.
Source: ZF Lenksysteme GmbH
Speed-sensitive power steering can be linked to an electric system, offering better comfort at high speeds for the driver, and more manoeuvrability at lower speeds. It is also possible to have a variety of different parameters for different driving styles, such as comfort and sports driving styles. Enhanced steering functions can also take advantage of information fed to the ECU by other sensors throughout the vehicle, by using algorithms built into the software to control directional stability. External forces such as an inclined road surface or a heavy crosswind can be offset by the power steering to prevent additional torque on the steering wheel.
Other functions which can be supported by electric power steering include parking assistance, whereby the driver retains control of the accelerator and brake, but the electric power steering takes care of automatically guiding the vehicle into the parking space. We are also already seeing lane-keeping systems in production which utilise the electric power steering to keep the car in lane if a driver accidentally drifts across the road. Further functions will enable assistance to the driver as required to respond to critical situations, providing additional torque in the case of oversteer, for example.
This is the first in a three part series on innovation in steering systems by Colin Pawsey. Part 2 focuses on real examples from several OEMs.