Electric Steering Gets a Boost
With the move to 42-volt electrical architectures on indefinite hold, OEMs are looking for ways to provide the benefits of electric steering while still using traditional hydraulic systems.
Usually automotive high-tech innovations are introduced on large luxury models and trickle down to lesser vehicles. But in the case of electric steering, just the opposite is true. Many entry-level cars have had electric steering for years while expensive sedans and SUVs continue to make do with hydraulic systems. Why? The heavier the front axle load requires more power than the current 12V architecture can provide to turn the wheels. 42V systems could have provided the power, but as OEMs have gotten more clever with the current electrical architecture, the desire to make the expensive switch has faded.
"Initially 42V was coming in 2012, now some say 2015, but I really don't know when it will come," says Alois Seewald, director, Global Research & Development, Steering, Linkage and Suspension, TRW Automotive GmbH (www.trw.com). That leaves automakers in a quandary. They don't want to pay to migrate every system to higher voltage, but they want the benefits of electric steering in their higher-end units nonetheless.
According to Seewald one potential answer is to combine a standard hydraulic system with an electric assist motor running at higher voltage. TRW's research has identified a range between 23 and 26V as sufficient to provide the needed boost, and has targeted capacitors as the most efficient supplemental power source. Seewald points out that going to a higher voltage not only provides the power that 12V can't, it also allows the motor to run on less current and with thinner wires, which reduces the chances of overheating. He estimates that the system will add 10% to the load capacity, making the system able to meet the peak load requirements incurred during high-speed maneuvers.
Moreover, larger vehicles could be programmed with steering torque overlay that allows for automatic steering adjustments based on sensor input. One example of this technology is the Volks-wagen Golf's electric steering system that is programmed to compensate for sidewinds so the driver doesn't have to maintain a constant torque on the wheel. In the future, as functions based on torque overlay like lane keeping and automatic parallel parking proliferate, luxury vehicles without the capability could be at a disadvantage.
Seewald says TRW's research on its electric/hydraulic system continues to move forward, and it could be ready for production by 2010. However, potential customers have yet to decide which direction they want to pursue. "There are two camps," he explains. "One wants to enhance the existing hydraulic system, the other wants to move totally to electric assist." Until that debate is settled, TRW's electric boost system will remain in the lab. In the meantime, expect lower weight vehicles to move to electric steering as they undergo full model changes. Plus, says Seewald, the addition of supplementary power sources like capacitors might allow small cars to jump to true steer-by-wire systems while still using 12V architecture. That could postpone 42V's introduction even more.—KW
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