Who's Afraid Of Electric Power Steering?

Edward Niedermeyer
by Edward Niedermeyer

Here’s a challenge: try to find a review of the Toyota Corolla that doesn’t bemoan its numb steering. Now try with a Chevy Cobalt. Or a Venza, or Vibe, Or Rav4, or Equinox. What do these vehicles have in common? Column-mounted electric power steering systems from JTEKT, a Toyota spin-off supplier which has done a brisk business in these fun-eliminating steering systems. And though the motor press has been bashing electric power assist steering (EPAS or EPS) for its deleterious effect on handling, the explosive growth in these systems may put more at risk than mere enthusiast-approved steering feel.

This anesthetization of steering systems has not taken place because manufacturers appreciate the proliferation of words like “numb” and “overboosted” in reviews of their products. EPS offers improved efficiency due to its reduction of parasitic losses, and is cheaper to manufacture than traditional hydraulic systems. This killer combination offers manufacturers a combination of improvements that have proven near-impossible to resist, resulting in the broad proliferation of EPS systems. And if reduced steering feel were the only casualty of the switch, it would be a tradeoff that any manufacturer would be willing to run.

But as EPS has exploded onto the market, a number of troubling issues has plagued the system. The National Highway Traffic Safety Administration has opened investigations into the Chevy Cobalt and Toyota Corolla, which share the column-mounted JTEKT EPS system. Cobalt, which moved to an EPS system for the 2005 model year has been haunted by an accelerating number of failures since the switch, while the Corolla investigation centers on Corollas built since the 2009 model-year switch to EPS.

In both of these vehicles, pinning down exact steering defects is proving to be difficult. Many of the Corolla complaints are related to sudden veering, particularly at speeds above 40 mph. The Cobalt, meanwhile, seems to experience complete EPS failure, causing momentary loss of steering and/or the need for drastically increased steering effort. Again, the inability to stay in a set traffic lane is being targeted as the most dangerous symptom of the possible defect.

These symptoms fit conveniently into a category that an early report (by Amit Rohidas Bendale of the Vishwakarma Institute of Technology, publication date unknown) on EPAS technology posted at college-seminars.com calls “auto steer,” a term the paper asserts “has crept into the lexicon as an adjunct to the development of EPAS system.” Bendale attempts to explain this phenomenon in his paper’s section on the disadvantages of EPS thusly:

To-date, technical and product liability concerns have precluded the introduction of such systems in the U.S. market through it is expected that niche application may be expected in the near-to-mid term mix of future vehicles. Such system design have yet to prove themselves sufficiently reliable and safe to prevent dangerous “auto steer” events. “Auto steer” has crept into the lexicon as an adjunct to the development of EPAS system. As the name implies “auto steer” denotes an uncontrolled steering event neither commanded nor stoppable by the vehicle’s driver due to catastrophic failure in the electron hardware or software. In truth, these systems are control servo systems, similar in function to aircraft control servo systems, and must have multiple redundancy. Although these new EPAS systems are said to have multiple redundancy , their design and broad application within the automotive industry have been, and will continue to be, subject to economic pressure more extreme then found in the aircraft industry. For instance one obvious safety related item has been universally deleted from such system specifications: a clutch for physically disengaging the reduction gear box and drive motor assist assembly from the host steering system in the event of system failure. This means that a driver encountering an EPAS system failure will have to exert additional force to “back drive” (i.e. manually over ride) the systems reduction gear box and drive motor assist assembly while attempting to maintain control of the vehicle in the absence of normal power steering assist.

Already, the parallels between these EPS issues (which are admittedly theoretical, but reflect NHTSA complaints) and Toyota’s gas pedal issues are plain to see. The first is the issue of economic pressure towards cost-cutting, which leads to the reduction of fail-safes and redundancy. Another parallel is the fragility of by-wire control systems: in Toyota gas pedals, tiny amounts of moisture was enough to cause the pedals to stick. In the case of EPS steering, there’s evidence to suggest that even cell phone interference could cause system failure. This is not to say that these two situations are directly comparable, but both cases indicate that earlier mechanical systems offer few clues as to possible malfunctions of electronic systems. Finally, the most important parallel between Toyota’s “unintended acceleration” and EPS “unintended veering” is the complicated dynamic between the driver and the system at the moment of malfunction or failure. Bendale continues:

Unlike the manual system described above, PAS with the presence of supplementary steering force to that provided solely by the operator introduces additional engineering challenges in terms of maintaining the desired steering linearity described previously. In fact, with respect to steering linearity, a poorly designed power steering assist system may have almost no relationship between the hand wheel torque applied by the operator and the actual required steering force imposed by the wheel or tires. There no longer may exist the uniform, consistent and predictable relationship between the “input and outputs” to facilitate “tactile reference driving.” Restated, the tactile sense of the driver to maintain directional control, and the magnitude and modulation of the “input” force may not bear a direct, proportional relationship to the required “output” force delivered by the steering system. Tactile reference steering is simply not possible with such vehicles. Rather their drivers must continuously engage in “visual reference steering” to maintain directional control. The result is that such vehicles are very tiring to drive for any length of time or distance. Further their drivers are constrained to continuously look at the road. If such driver should look away even momentarily (i.e., to check a rearview mirror or a child in the car), he or she has minimal tactile reference as to the actual position of the vehicle during that period of time. This is dangerous because, depending upon the road topography and condition, the vehicle may have moved transversely in significant amount relative to where the driver thought his or her vehicle was positioned. This can and often does lead to serious trouble.

This helps explain the varying accounts of unintended veering, as the ability to handle sudden changes in steering response varies greatly from driver to driver. Like unintended acceleration, this makes the task of narrowing down the primary causes of EPS failure or malfunction impossible based on recorded accounts alone.

More importantly, this helps explain the link between numb, overboosted and uncommunicative steering and safety. At highway speeds, any failure or malfunction would be registered and reacted to by touch (tactile feedback) before the brain would be able to register visual cues that vehicle control has been compromised. Because of EPS’s deficits in tactile feedback, and consistency between wheel and steering wheel positions, that all-important emergency tactile feedback would be more difficult for even a well-trained driver to interpret, making a crash more likely even if the unassisted steering system were still functioning (as has been reported in certain Cobalt incidents).

This is clearly an issue that companies like JTEKT have known about, as a 2008 paper on EPS [ PDF] by a JTEKT engineer admits that making EPS feel like the hydraulic systems the buying public is used to has been a major challenge. Another paper from the JTEKT Engineering Journal [ PDF] indicates that on higher-power versions of column-mounted EPS,

sensitivity to such inverse inputs as flutter and brake vibration has become higher. J-ISM [JTEKT’s EPS assist control algorithm] has adopted a suppression system that can detect inverse input vibration as torque differentiation value, and by providing assist in the direction of canceling the vibration, the vibration is not transmitted to the steering wheel.

In short, tactile feedback is actively canceled, not only reducing the driver’s ability to respond to an emergency based on steering feel, but also further loading the EPS system with compensation duties in addition to pure steering control.

The point of all this is not to merely raise unwarranted fears about EPS. Improved efficiency and lower costs are the very definition of a successful automotive system, and as long as EPS offers these benefits, its use will continue to grow. As this trend continues, it will be important for safety watchdogs to pay close attention to these systems. Without pressure to include redundancy, fail-safes and extremely robust sensor units, suppliers will continue to cut the cost of these systems to remain competitive with the growing number of firms that offer similar systems. Just as importantly, these new electronic systems require a new approach to safety that pays as much attention to driver reaction to malfunctions as to the malfunctions themselves. Only in this way can we be sure that relatively minor malfunctions don’t yield an epidemic of inexplicable accidents and recalls.

Join the conversation
2 of 91 comments
  • Boxingbarry Boxingbarry on Aug 19, 2012

    " I own or should I say used to own a 2006 Honda Civic Lx with a 5 speed manual transmission. I’m not sure if my car has EPS but I assume it does from reading other peoples post’s that have the identical car." The 2006 Honda Civic Lx is equipped with hydraulic steering. Only the SI models were equipped with electric assist.

  • Brandloyalty Brandloyalty on Nov 30, 2013

    "Road feel" is one matter, but EPAS failure is another. Toyota Prius, Camry and Highlander hybrids use EPAS, as did the Ford Escape Hybrids. All have had dozens of EPAS failures reported. Hybrids typically have EPAS because they need to maintain steering boost when the gas engine is shut off. The symptom is sudden total loss of the boost from the electric power steering. There is no warning. Because there is a physical column, steering is still possible but very difficult. Loss of boost while initiating a turn can and will result in accidents. Applying the brakes and/or shutting the vehicle off and on again seems to correct the problem. The failure does not trigger OBDII codes. Toyota has recalled their faulty hybrids, while Ford has not. So Ford is comfortable making their normal profits on this approximately $2000 repair for a design failure that endangers their customers. I have a 2009 Escape Hybrid, have experienced this problem once. I'm having the steering column assembly replaced. 2008 Escape Hybrids most commonly suffer this problem, followed by the 2009, then the pre-2008's. The 2010-2012's rarely have the problem. Ford variously says they don't think it's a safety problem because not enough of their customers have died, or it's not a significant safety problem to begin with. NHTSA in the US and Transport Canada are aware of this, but so far have not required Ford to do a recall. I urge anyone with a Toyota hybrid to have the recall/repair done, and anyone whose Escape Hybrid has had an EPAS failure to report it. It makes no sense to be driving a ticking time bomb, and the more Escapes are reported the sooner Ford will have to deal with it.

  • Wjtinfwb Instead of raising fines, why don't the authorities enforce the laws and write tickets, and have judges enforce the penalty or sentence of a crime. I live across the street from an Elementary School on a 4-lane divided state highway. every morning the cop sits in his car and when someone sails through the School Zone well above the 10 mph limit, he merely hits his siren to get their attention but that's it. I've never, in 5 years, seen them get out of the car and actually stop and driver and confront them about speeding. As a result, no one pays attention and when the School Zone light is not lit, traffic flies by at 50-60 mph in the 45 zone. Almost no enforcement occurs until the inevitable crash, last year some zoned out girl rolled her beater Elantra 3 times. On a dry, straight, 4 lane road with a 45 mph limit. I'm no Angel and have a heavy foot myself. I've received my share of speeding tickets, lots of them when younger. Traffic enforcement in most locales has become a joke these days, jacking prices because someone has a higher income in as asinine as our stupid tax policy and non-existent immigration enforcement.
  • Jeff S If AM went away I would listen to FM but since it is insignificant in the cost to the car and in an emergency broadcast it is good to have. I agree with some of the others its another way to collect money with a subscription. AM is most likely to go away in the future but I will use AM as long as its around.
  • BEPLA I think it's cool the way it is.If I had the money, time and space - I'd buy it, clean it up, and just do enough to get it running properly.Then take it to Cars and Coffee and park it next to all the newer Mustangs.
  • Dave M. I suppose Jethro’s farm report comes via AM, but there’s a ton of alternative ways to get that info. Move forward people. Progress is never easy.
  • BEPLA For anything but the base model, I'd rather have a pre-owned Polestar 2.