Poor Plastic Selection Caused Gas Pedal Failures

DN Staff

February 11, 2010

3 Min Read
Poor Plastic Selection Caused Gas Pedal Failures

Toyota says ahigh-performance plastic used as friction levers in accelerator pedalassemblies causes the gas pedal to malfunction in certain weather conditions. Toyota outlined theproblem in a recent letter to the National Highway Traffic SafetyAdministration, including details of problems dating to March, 2007, when internaltesting on the plastic accelerated.

Chris Santucci, manager of technical & regulatory affairsfor Toyota Motor North America, says:

"Due to the manner in which the friction lever interactswith the sliding surface of the accelerator pedal inside the pedal sensorassembly, the sliding surface of the lever may become smooth during vehicleoperation. In this condition, if condensation occurs on the surface, as mayoccur from heater operation (without A/C) when the pedal assembly is cold, thefriction when the accelerator pedal is operated may increase, which may resultin the accelerator pedal becoming harder to depress, slower to return or in theworst case, mechanically stuck in a partially depressed position."

The problem was first reported in March, 2007 when Toyota received fieldtechnical information of accelerator pedals demonstrating symptoms such asrough operation or being slow to return to the idle position.

The accelerator pedal assemblies in the vehicles (Tundras) containeda friction lever made of the polyamide (nylon) 4/6 material. Toyota's investigation found that thematerial was susceptible to humidity, which could cause the friction lever toabsorb moisture and swell. It is well known that nylon is a hygroscopic(water-absorbing) polymer.

In February 2008, the material of the friction arm waschanged to PPS while investigations continued. "In June 2008, Toyotaconcluded that while accelerator pedal feeling could change under certain conditions,Toyota considered it to be a drivability issueunrelated to safety," said Toyota'sSantucci in a Jan. 21 letter to Daniel C. Smith, associate administrator forenforcement at the National Highway Traffic Safety Administration.

Starting in December of 2008, Toyotareceived field technical information from Europethat the accelerator pedals using the PPS were also sticking. The reportspredominantly involved right hand drive versions of the Toyota Aygo and Yaris vehicles.Toyota began adetailed investigation of returned pedals in March of last year.

"Internal inspection of the sliding surface of the frictionlever and the pedal arm was found to be partially smooth," wrote Santucci. "Toyota conducted someduplication tests, and it was found that the internal friction could increaseif moisture was attached to the sliding surface of the friction lever as thesurface became smooth. This made the accelerator pedal stick in a partiallydepressed position under the condition where condensation occurs on theaccelerator pedal."

When air conditioning was operating, the phenomenon did notoccur.

As a result, Toyotalengthened the arm of the friction lever and changed its material to preventsmoothing on all vehicles produced in Europe,starting in mid-August of last year.

Starting last October, reports surfacedof problems in North America with pedals usingthe PPS material. The design solution is still being investigated.

Toyota Outlines Technical Problems in Letter to the NHTSA

Friction builds up on contact points (left) when condensation forms on smooth plastic surfaces. Toyota says that insertion of a precision-cut steel reinforcement bar (right) eliminates the excess friction. Illustration: Toyota

Poor Plastic Selection Caused Gas Pedal Failures A

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