Electric Power Steering

In a previous blog article, I discussed how complicated products were becoming as a result of the rapidly changing technology industry.  In another example of complex technology, electric power steering is replacing hydraulic power steering.  For the most part, this isn’t news.  Two years ago however, GM began recalling 2010 Chevrolet Cobalt vehicles because the power steering motor would fail.  Keep in mind that in a hydraulic system, pressurized fluid would assist the driver in turning the front wheels either left or right.  In an electric system, the power steering motor does this job.  But, when it fails, power steering disappears.  When power steering disappears, more effort is required from the driver in order to maintain control of the vehicle.  If the driver is unprepared for the additional strength required, then the risk of a crash increases. This is also true for a hydraulic system.  It is understood that the power steering motor depends upon input from sensor(s) in order to determine the steering wheel’s position and whether to move the front wheels right or left.  GM has stated in their recall that the power assist will return the next time that the vehicle is restarted.  This statement implies that somehow, something in the motor has a tendency to fix itself and return to normal until the next time the “something” decides to cause the motor to fail.  It should be noted that although not proven, the power steering motor might have a tendency to alternately stop operating and then start again causing the steering wheel to oscillate back and forth. Doing so, will likely cause the vehicle to move sideways, back and forth.  We are investigating a situation with just this type of movement.  Just one more thing for the driving public to have to worry about. If you have experienced a power steering problem you are urged to have it checked.  The recall for this vehicle can be seen on the NHTSA website or on the GM website.

About R.J. Hill, P.E.
R. J. Hill is the author of two blogs: R.J. Hill Consulting and the Descendants of James Alexander Hill. Mr. Hill is a registered professional (mechanical) engineer with 42 years of experience, 37 years in private practice. Please visit www.rjhill.com to see the kinds of forensic investigations that Mr. Hill performs.

One Response to Electric Power Steering

  1. Chris1970 says:

    I have driven several cars with EPS and read dozens of blogs and articles about the subject online, along with comparisons to conventional(hydraulic) steering assist. There are lots of complaints of “lack of road feel”, “numbness”, or poor return to center from turns. Other examples, such as the 2011-2014 Hyundai Sonata, of which I own, garnerd complaints such as twitchy, or wandering.

    After having my local Hyundai dealer switch the steering mode on my 2013 Limited to “Sport”, the steering became considerably tighter and more centered. No more twitching or constant corrections, and a lot *less* wandering than before, at the factory mode. Hyundai since about 2013 has had a Tech. Service Bulletin guiding service dept techs on what to look for to do this for their customers.

    My conclusions? Most EPS/MDPS systems actually pack a lot of punch for their size, compared to HPS(hydraulic power steering) and it is too easy for engineers to build ‘too much’ assist into them, resulting in many of the complaints two paragraphs above. My recommendation?

    Turn it down!!

    Engineer less voltage, or watts, or whatever into MDPS or Electronic Steering systems. Or provide, as Hyundai and some other car manufacturers have – modes of decreasing levels of assist, such as the Sport or Hard mode on Hyundais and Kias. Something else to consider is a broader implementation of the electric version of ‘variable assist’ or speed-sensitive steering: High boost(assist) at parking speeds, or under 15mph, then progressively less boost at 20, 40, 60mph, etc.

    I hope my suggestions find you and other industry members well.


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