Auto Service World
Feature   April 1, 2001   by Andrew Ross


Most counterpeople know that a rack and pinion unit is really a hydraulic device. A turn of the steering wheel opens valves and the pressure from the pump helps the driver turn the wheels.

While speed sensitive steering has been around for some time in various guises, there were always limits to the range of boost available and some systems exhibited bumps and dropouts in the amount of boost supplied at various speeds. General Motors’ Magnasteer has ushered in a whole new level of electronics designed to do away with these shortcomings and more.

Introduced for the Cadillac line, Magnasteer variable-assist, speed-sensitive power rack and pinion steering system uses a variable magnetic field to increase or decrease steering effort as needed. Therefore, the range of adjustment is greater and has no steps or irregularities in the boost curves.

Low efforts are selected for ease of parking. Higher efforts are specified at higher speeds and when the driver needs a more confident sense of the road. Steering effort also is increased during traction control actuation and during ABS braking events. Using an electrically generated magnetic field instead of the previous permanent magnet design eliminates the chance of audible electrical interference through the entertainment system.

Besides the inevitable electronic controller, the key to the system is a unique device made up of a multiple-pole ring-style permanent magnet, a pole piece, and an electromagnetic coil assembly. What this piece does is add to what the spool valve is doing by adding or subtracting a little twist to the steering gear input shaft torsion bar. To do this the electromagnetic coil assembly is charged on command from the electronics.

An enhanced feature of Magnasteer is sensitivity to lateral acceleration. When sensors determine the cornering rate is up, steering effort is automatically increased to enhance the driver’s road feel.

Combined with StabiliTrak, GM’s stability control system, models with Magnasteer also feature steering effort compensation. During low-traction or emergency-maneuver situations, StabiliTrak commands the Magnasteer system to adjust the level of power assist in order to achieve a consistent steering feel. With the enhanced version of StabiliTrak, active steering effort compensation also is triggered by ABS and traction control operation. Combining steering assist level with stability control was achieved solely through software calibrations with no added hardware, cost or mass.

This means that varying the amount of steering effort becomes a programming exercise, so the system can be tuned to everything from the Cadillac to the Corvette, and it has been. Not everyone is happy with the way the system works however. I came across one case where a Grand Prix owner disabled his system by pulling fuse #28. The only problem is that it disabled the ABS, TCS and A/C too. And it set a code that wouldn’t extinguish when the fuse was replaced.

Also, on Magnasteer systems with a steering angle sensor (Magnasteer II and up) techs have to be careful to replace the steering wheel in the proper rotation, not 360 degrees out, or it will cause problems with the system.

Where other variable-effort steering systems have lots of wear-prone internal parts, Magnasteer does not, instead using electromagnetism and electronics.

With such a system, service concerns should be few, but the inevitable electronic malfunctions may yet prove elusive, especially for those not used to looking for electronics in a steering system.

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