The debate over the role of tin whiskers in Toyota's unintended acceleration case has returned, and government administrators are expected to answer more questions on the subject this week.
Even after the National Highway Traffic Safety Administration (NHTSA) declared in 2011 that there was no electronic cause for Toyota's problems, the debate had quietly continued. It rose to prominence again this month, when a US senator stepped in.
"Recently, whistleblowers have provided my office with information, supported by documentation, which raises concerns that the scope of the NHTSA and NASA investigations may have been too narrow," Sen. Charles E. Grassley (R-IA) wrote in a letter (PDF) to NHTSA Administrator David Strickland on July 12. The letter went on to pose questions about the agency's methodology, and it called for answers to be delivered by July 26.
Toyota's Matrix is one of the vehicles recalled during the automaker's "unintended acceleration" studies. (Source: Toyota)
Tin whiskers -- small metal dendrites that sometimes form on electroplated tin -- are an important topic for design engineers, because they can cause short circuits and arcing in electrical equipment. In Toyota's case, tin whiskers were considered a potential culprit in the "unintended acceleration" claims that grabbed headlines three years ago.
Much of the debate over tin whiskers died down in February 2011, after Secretary of Transportation Ray LaHood called on teams of NHTSA and NASA engineers to search for the cause of Toyota's problems. "The verdict is in," LaHood declared emphatically after the scientists reached their conclusion. "There is no electronic-based cause for unintended high-speed acceleration in Toyotas. Period."
After that conclusion was announced, the National Academy of Sciences said that all available data indicated there was no electronic or software problem on the Toyotas.
Still, the buzz about tin whiskers continued in some quarters, especially after a separate team of NASA scientists published a study (PDF) of Toyota accelerator pedals on the Internet in September 2011. The scientists said they found tin whiskers in an accelerator assembly, and "a tin whisker induced short was responsible for the failure of a 2003 Toyota Camry Accelerator Pedal Position (APP) Sensor based on a Dual Potentiometer Design."
In his letter, Grassley cited that study and its author, Henning Leidecker of NASA Goddard, to support his claim that more questions needed to be answered.
In response to the latest volley, Toyota officials argued that tin whiskers may cause failure of pedal sensors, but they've never caused unintended acceleration. "We know that tin whiskers can form -- we've never said they couldn't," Brian Lyons, a spokesman for Toyota, told us. "But when pedals fail -- for whatever reason -- the vehicle enters into a fail-safe situation, a limp-home mode."
Lyons also said that the September 2011 study specifically linked tin whiskers to sensor failure in the accelerator assemblies, not to unintended acceleration.
When reports of unintended acceleration originally surfaced, Toyota engineers examined multiple potential culprits: the accelerator's friction lever, heater condensation, corrosion, electronics, and floor mats. Toyota has since examined the mats, shortened the pedals, lengthened the friction lever, added a spacer, and changed the linkage materials. It also employs a brake-throttle override on its vehicles to cut off gas flow if the brake and accelerator pedals are depressed simultaneously.
Until Grassley sent his letter to the NHTSA, the focus had shifted away from electronics and toward floor mat entanglements. In June, the NHTSA mandated a recall of 154,000 more Toyota vehicles for problems associated with "unsecured or incompatible floor mats."
Seems to me the EU in it's quest to eliminate lead as a pollution source has signed the death warrant of untold millions of electronic devices around the world. It isn't just automobile electronics that will suffer a premature death, it is just about all devices we buy and use everyday, washers, dryers, TV's cell phomes etc. There have been numerous post placed here over the last few years about tin whiskers causing electronic failures in all types of electronics. If indeed electronic throttle controls on cars are susceptable to this same fate as other electronic devices, then there should be a loud outcry worldwide to suspend ROHS compliance until a workable solution is found.
To Mr Weaver: with all due respect, it appears your comparison of the relative ease of servicing different brands of cars was comparing a standard transmission with an automatic. Manual transmissions will always have a threaded (and inconvenient) plug to check the lubrication level, rather than a dipstick as do automatics; the fluids have different purposes and viscosities. The same is true with Toyota stick shifts. Having had a number of BMWs as well as a number of Toyotas (and 2 Lexuses), I know the engineering levels vary. However, the downfall of the German engineering is their electronics, not their mechanics. My 1984 BMW 635CSi drive train was darn-near bulletproof and still cranked out well in excess of 130 MPH before I got too scared to push my luck, and traded it off last year (for, oddly, an older Toyota MR2). I fear Toyota, "German cars," and any other manufacturer in the spotlight can be found "guilty" of cost/benefit tradeoffs. My wife (the Lexus driver) calls it a witch hunt.
"In fact, NHTSA only knows of four occurrences of tin whiskers in a population of 1.7 million Camry vehicles. None of those occurrences involved any crashes or injuries and in each case, the vehicle entered a form of fail-safe operation that was so noticeable that the consumer quickly brought the vehicle in for repair."
What kind of rubbish is that? It implies that they inspected 1.7 million vehicles. How many did they actually look at? four? four thousand? forty thousand? Certainly wasn't 1.7 million.
I have a 2006 Malibu, over 100k miles on it, virtually no problems. Easily gets mid 30's on the highway, mid 20's driving around town. Got 80k miles on the original tires.
I drive a 1992 Cadillac Deville that has 202k miles on it. Runs like a champ. Springs a leak here and there every once in a while (my plumbing aint' what it used to be either!), but other than that it gets me around. I get about 20 mpg, almost all around town driving.
I don't believe that the "J factor" cars are ultimately any better than "A factor" cars. I have had both over the years, and I have had good experiences with both. I prefer current American built sedans to anything built.
I remember dealing with tin wiskers on wire wrap terrestrial sysems back in the 70's. They were occuring between pins with 1/16 in spacing. Ok, so now I've been working with spacecraft and satellites for 25 years where there is one rule on this: don't use pure tin. I feel like saying "duh".
I am interested to know how the computer can distinguish between a throttle position giving a certain resistance and a tin whisker coincidentally producing the same resistance.
Would not encapsulation of soldered areas solve this problem?
The typical method is to use a voltage divider so that a short to either rail or an open is an invalid reading. monitoring for noise is also used to determine if the connection is intermittent, which is what will happen when the sensor starts to fail. They usually open in the throttle position that is used the most, like at a highway cruise or idle.
I have thought of the encapsulation method myself, such as a spray on coating after assembly, but am not sure if this would prevent whisker growth. Perhaps someone with direct experience with the issue could chime in and answer the question. The real scary part of this is that any commercial aircraft built in the last 30 years are controlled by fly-by wire systems.
Charles, I hate to tell you "I told you so" , because I did comment on your previous blog where you definitevely rejected a possibility of whiskers "because NHTSA said so". Few cases in 1.7 million cars? Just a good cover-up.Most of customer have no idea what a dealer is doing to a car that was left for "car mat replacement".Anyhow , why would I take a word of NHTSA agains NASA? Only one of them consists of really credible scientists (no pun intended to the other one)It is a serious problem and it has to be addressed as such.A driver of a car does not quite know what to do in a panic situation.Sorry to say that but after seeing thousands "whisker cases" in many other devices I would dismiss car mats...
Tin whiskers are not a new phenomena, but we used to have a bit of lead in our solder which prevented it. But with everyone going RoHS compliant, this is one of those results of the law of unintended consequences.
Keep in mind, when RoHS was first proposed and adopted, the primary usage of lead in electronics, was a pigment fixative in plastics. The darker the color, the more fixative was used. In the average consumer electronics equipment, something like >90% of the lead was in the plastic.
RoHS was never originally meant to touch our solders, because that was considered (at the time) too little a percentage to be worthwhile. If memory serves, the day that RoHS was adopted, Nokia dropped their 5 year warranty to 1 year because they were afraid of tin whiskers. Ahh, how times change!
Using almost 200 light-emitting diodes in the front and back of the new 2014 CTS, Cadillac designers are showing how LEDs can change the character of a vehicle.
We looked at a number of sources to determine this year's greenest cars, from KBB to automotive trade magazines to environmental organizations. These 14 cars emerged as being great at either stretching fuel or reducing carbon footprint.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
4 
