Why Toyota Must Replace Flawed CTS Gas Pedal With Superior Denso Pedal
By
Paul Niedermeyer on February 1, 2010
Update: a portal to all of TTACs articles on the subject of Toyota gas pedals is here:
Toyota uses two different electronic gas pedal designs in its cars. The version built by
CTS (lower) is the subject of a massive recall, and the 2.3 million units in affected Toyota cars are to be fixed by the insertion of a steel shim. This CTS design is also being modified for new Toyota production, currently suspended. To our knowledge, Toyotas built with the other design (by Denso, upper) are not subject to any recalls or NHTSA investigations,. We have spent the last two days
tearing down both units, and familiarized ourselves with their designs,
reviewed Toyotas shim fix, and
replicated the fix ourselves.
Toyotas planned fix will undoubtedly reduce the likelihood of sticky pedals in the short term, but after examining both units, we are convinced that the CTS unit is intrinsically a flawed design, and poses safety risks in the long term, even with the fix. The only right action for Toyota is to acknowledge the long history of problems with the CTS-type unit, and replace them all with the superior Denso or another pedal unit that lacks the intrinsic flaws of the CTS design.
Before we briefly review the key design differences, we must acknowledge that Toyota is ultimately responsible for both designs. CTS has stated that its product was built to Toyota specifications. What we dont know (or understand) is why Toyota has two such fundamentally different units in production. Is one unit cheaper to build? Or was CTS tooled up to produce its unit because of other similar units it builds for other manufacturers? What we do know is that the CTS unit has been used in Toyota products since 2005, whereas the Denso unit has been in use since well before that time. Toyotas sold in Europe are also subject to a similar recall, and based on the description of the issues and the unit, it appears that it is the same or similar design as the CTS unit, but we do not know if it was built by CTS or another supplier.
The key component in question is the friction arm of the CTS. It is both essential and desirable to have a certain defined degree of friction in these electronic gas pedal assemblies. The amount of friction is designed to be some degree less than the return spring, so that when the pedal is released, it returns to the closed position. But the friction (hysteresis) makes it easier to maintain a steady throttle setting, and relieves strain from pushing against the spring continuously. It simulates the intrinsic friction that is present in the traditional throttle cable as it passes through the cable housing.
The two units generate the desired degree of friction in very different ways. In the Denso unit (above), the return spring (steel coil) is squeezed on both sides of its housing. It rubs against the plastic housing as it compresses, which generates the desired amount of friction. Both sides of the full length of the Denso coil are in continuous contact with the rubbed are, spreading out the contact area size. And the metal to plastic interface seems to be relatively unproblematic.
The CTS unit is a fundamentally different design. The friction is generated by two teeth (A) that extend from the friction arm, and ride in two grooved channels of the housing (B). The friction arm is an extension of the pedal itself, and moves as the pedal is moved. Both the friction arm, its teeth and the surface it rubs against are plastic. Notice the small area of contact (dulled gray spot on tooth). This is the fundamental source of the problem with this unit, and one that Toyota has not come clean about. The friction unit assembled, showing the teeth engaged in the two grooves, is shown below.
In Toyota V.P. Jim Lentz
appearance on the Today show, he claimed that issues with the friction arm go back to only October of 2009. Not so. According to a letter from Toyota to the NHTSA , in 2007 Toyota changed the plastic material used in the friction arm (from PA46 to PPS) in response to problems similar to those occurring now.
Toyota has been modifying the friction-arm (CTS) type assembly since 2007. Yet to our knowledge, the Denso design has never been implicated in any sticking-pedal issue, and has presumably been in production for some ten years. Why didnt Toyota change over years ago?
Toyota claims it now has the solution to the pedal problem. Later this week, Toyota will be sending shims that will be inserted under the friction arm of the CTS-built pedal to reduce its tendency to stick. We understand how this fix will work, and have replicated it. It does reduce the degree of friction; the exact amount will depend on the height of the spacer. Our one-eighth inch spacer made a fairly dramatic difference in subjective friction, but we could not test it installed in a car to see how different it would feel on the road.
Regardless of the thickness Toyota chooses for the shim, real and perceived friction will by necessity decrease to the detriment of pedal feel. The original designed degree of friction was obviously chosen to maximize the balance between the two forces at play; any change can only deviate from that, and away from that original ideal balance. We believe the odds are high that drivers will feel the difference, and that some or many may not like it.
Furthermore, the CTS-built unit is prone to continual wear and change in friction level over the long haul. I do not claim to be an expert, but having two small plastic surfaces rubbing against plastic does not strike me as an
elegant, reliable or durable design, and one that is presumably subject to long term deterioration from natural and unnatural causes. There are a lot of twenty and thirty year-old Toyotas on the road. But its difficult to imagining this assembly still functioning as intended that far down the road, nevertheless even five or ten years from now. Toyotas well-documented de-contenting is graphically on display here. Yet Toyota is apparently staying with this design, with some further modification, for ongoing new car production.
Whereas the Denso unit (above) is not exactly inspiring in solidity of its all-plastic design and build, it seems to lack the most serious flaw of the CTS unit. The smooth metal coils rubbing against the plastic housing seems less prone to deterioration and change in friction level. There are no known issues or problems associated with it.
We are calling on Toyota to replace all CTS-friction arm type gas pedal assemblies with either the Denso unit, or another proven design that lives up to Toyotas legendary quality and the longevity expectations of its loyal owners. Propping up an intrinsically inferior and historically-proven inferior design with a piece of metal stamping is not going to restore Toyotas tarnished reputation. The two units are interchangeable; Toyota should do the right thing and switch production over, and insist on replacing all the CTS-type units even after they have had their temporary fix. A Band-Aid will stop the hemorrhaging for the moment, but nothing less than a transplant will do for the long haul.