Article

Quick Spin: TRW's Smart Power Steering

May 2015, TruckingInfo.com - Department

by Jim Park, Equipment Editor - Also by this author

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TRW Automotive showed off a new commercial steering technology at the 2015 Mid-America Trucking Show. Called ReAx, it merges the company’s hydraulic power steering system with an electrically powered drive. The result reduces steering effort at low speeds, while increasing on-center stiffness at highway speed to enhance lane-keeping stability. That’s a tall order, but ReAx handles it deftly.

ReAx is not an add-on or a switchable driver assist system. It’s fully integrated into the traditional hydraulic power steering gear – built right onto the gear itself, in fact. The control module, electric motor, gearbox and the steering column position sensors are all inside, so the system functions as a single unit, not an electric-over-hydraulic arrangement.

The traditional power steering system provides the torque needed to steer the vehicle, while the electric motor and its sensors and electronics provide precision control to the hydraulic gear. Together, they exercise proportional control over the steering, based, in this case, on vehicle speed.

At low speeds, the system reduces the steering effort to nearly zero, yet it retains the feel drivers would expect from a truck steering system. It returns quickly to center as you are pulling out of a turn. While reversing, it resists the steering geometry’s natural inclination to return to center.

At higher speed, the steering feels stiffer, more like the driver would expect. And at highway speeds, TRW says the system actually adds stiffness to the steering to enhance stability and lane position retention.

ReAx uses proprietary torque and angle sensors, coupled with other vehicle signals such as a speed sensor, to prompt the ECU to calculate the required electrical assistance to provide the desired steering feel.

“Because the system is electronically controlled, OEs can dial in the precise ‘feel’ they want in their trucks, or customize the level of assistance to suit different applications,” explained Mark Cartwright, chief engineer of systems integration at TRW, who was along on our short evaluation of the system. “Drivers will appreciate how much their steering effort is reduced at low speeds and how much more stable the steering feels at high speed. It really gives them the best both ends of the steering spectrum.”

It’s failsafe, too. ReAx will revert to normal straight hydraulic power in the event of a failure of the electric drive. It’ll feel just like regular power steering.

I had a chance to try ReAx during the Mid-America Trucking Show in March, in a parking lot adjacent to the fairgrounds. We were without a trailer, but I don’t think that made much of a difference. It was installed in a Peterbilt 387, which, like most Peterbilts, has a very nice feel to the steering, good on-center stability and good cornering. It’s on the firm side, making quick full-swing turns of the wheel a bit of work. For all the times I would have preferred an easier turning while backing into a tight spot, I would never have agreed to lightening up the feel while driving on the highway. ReAx gives us the best of both worlds.

The ReAx electric drive is fully integrated into the body of the power steering gear.
The ReAx electric drive is fully integrated into the body of the power steering gear.

The truck had an on/off switch to make the comparison easier, so we ran a couple of laps around the parking lot and through a backing maneuver with the system off and then with the system on.

The difference was like night and day. I didn’t get much higher than 20 mph in the parking lot, so I never experienced the proportional transition from full electric assist to minimal at higher speeds and extra stability at highway speed.

It was an unaccustomed luxury having to use no more energy than I would while reversing a boat trailer with a pickup truck. I suspect drivers will warm to this idea pretty quickly. It was very useful, too, in making those quick full-cut turns sometimes necessary to shoehorn the truck into tight loading docks. ReAx would be equally welcome on a downtown street with 90-degree corners and no room to spare. Here again, getting the wheels cut around while covering the shortest possible distance will be very advantageous.

I’m trying to imagine a possible downside to ReAx, but I can’t. Short of an electrical problem or a sensor failure, the system seems almost bullet proof. Even its complete failure would leave you no worse off than you are today with full hydraulics. It won’t add much weight, though it will likely cost more. I think the real benefits will become quickly obvious once drivers get a hold of it.

TRW says ReAx should be on the market by 2017.

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