The Truth About Cars » gas pedal design http://www.thetruthaboutcars.com The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. Fri, 12 Dec 2014 19:16:55 +0000 en-US hourly 1 http://wordpress.org/?v=4.0.1 The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars no The Truth About Cars editors@ttac.com editors@ttac.com (The Truth About Cars) 2006-2009 The Truth About Cars The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars » gas pedal design http://www.thetruthaboutcars.com/wp-content/themes/ttac-theme/images/logo.gif http://www.thetruthaboutcars.com Why Toyota Must Replace Flawed CTS Gas Pedal With Superior Denso Pedal http://www.thetruthaboutcars.com/2010/02/why-toyota-must-replace-flawed-cts-gas-pedal-with-superior-denso-pedal/ http://www.thetruthaboutcars.com/2010/02/why-toyota-must-replace-flawed-cts-gas-pedal-with-superior-denso-pedal/#comments Tue, 02 Feb 2010 03:29:23 +0000 http://www.thetruthaboutcars.com/?p=343754 Update: a portal to all of TTAC’s 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 […]

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Update: a portal to all of TTAC’s 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 Toyota’s “shim fix”, and replicated the fix ourselves. Toyota’s 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 don’t 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.

Furthermore, Toyota has been facing similar issues in Europe going back to 2008:

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 didn’t 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 it’s difficult to imagining this assembly still functioning as intended that far down the road, nevertheless even five or ten years from now. Toyota’s 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 Toyota’s 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 Toyota’s 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.

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Exclusive: TTAC Takes Apart Both Toyota Gas Pedals http://www.thetruthaboutcars.com/2010/01/exclusive-ttac-takes-apart-both-toyota-gas-pedals/ http://www.thetruthaboutcars.com/2010/01/exclusive-ttac-takes-apart-both-toyota-gas-pedals/#comments Sat, 30 Jan 2010 21:26:02 +0000 http://www.thetruthaboutcars.com/?p=343512 Update: To see all of TTAC’s related articles on the subject of Toyota gas pedals, go here: In yesterday’s post , we offered a bounty for anyone to open up both the CTS (bottom) and Denso (top) Toyota gas pedal assemblies. No one took us up, and no one anywhere else has done it, so […]

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Update: To see all of TTAC’s related articles on the subject of Toyota gas pedals, go here:

In yesterday’s post , we offered a bounty for anyone to open up both the CTS (bottom) and Denso (top) Toyota gas pedal assemblies. No one took us up, and no one anywhere else has done it, so we took it upon ourselves . Here they are, both e-pedal assemblies taken apart and examined, in our quest to understand if and what the significant differences are, and how Toyota’s possible “shim” fix would work.  On initial observation, it appears that the CTS may be perceived as being the more solidly engineered/built unit, in that the pedal pivots on a traditional and solid steel axle whose bearings are brass or bronze sleeves. The Denso’s whole pivot and bearing surfaces are relatively flimsy-feeling plastic. But that can be deceptive, and we’re not qualified to judge properly if it is indeed inferior or superior.  So the question that goes beyond the analysis of these e-pedals is this: are these units really the full source of the problem, or are they scape goats for an electronics and/or software glitch? Pictures and tear down examination and analysis follows:

Update #2: It’s clear to me now that the CTS unit I took apart already had the side cover plates (sheet metal) removed before I examined it. One can see where they fit, and are obviously intended to protect the exposed axle pivot and bushing seen above and below:

(Update #3: Also see our follow-up stories on Toyota’s fix and our replication of the fix and its results)

Lets take a close look at the CTS unit:

We drove out the pivot pin with a C-clamp and screwdriver. It’s a very traditional design, like millions of plain-bearing (non roller-ball bearing) non-lubricated devices used in a huge variety of devices for decades, if not even centuries. The softer brass or bronze acts as relatively low-friction bearing. With the substantial pressure from the springs, it seems relatively unlikely that this would lock up, but that seems to be the concern. It’s possible that there is a greater potential for binding due to the tighter tolerances in the axle/sleeve assembly. A close up of the axle and bearing:

A big question for us was if there are dual springs, in the case one fails. Here is the CTS unit apart. Note that the pointed metallic part on the bottom of the pivot is the magnet that passes between the sensors in the case of the unit, which is how the sensor sends the throttle position signal to the engine controller.

The outer red spring surrounds the inner black coil spring. It seems that the possible “shim fix” that Toyota is considering would be a spacer on the bottom of this spring assembly, which would increase the pressure on it and presumably reduce the likelihood of the pedal sticking. I’m not an expert on springs, but the spring is already pre-loaded (compressed) to some degree when it is assembled, and unless these are variable rate springs, I wonder whether that would actually increase the working resistance of the spring unit. Since I had no problem taking the pedal/pivot unit apart which also houses the spring unit, and reassembling it as well, it would appear that if that route is taken, it should be easily done in a few minutes at the dealership.

To understand that part more clearly, here is a shot of the CTS unit assembled, with the main cover off, showing the pivot arm with the magnet and how it passes past  the sensors (Autoblog has a video explaining how the CTS sensor works, but no teardown):

Lets examine the Japanese Denso unit (below, which comes apart by removing the side cover held on by five screws. It is already apparent from the outside that there is no axle pivot that runs through this unit.

The Denso is a dramatically differently designed unit. The pivoting unit (green) is a plastic “bearing” that just sits inside the two outer units. One can see what it bears against in the side cover. The magnet is the square unit in the middle of the green pivot, and the sensor appears to be the round unit inside the side cover.  The numerous small bright metal protrusions on the side cover are not identified. I thought they were the sensors, but nothing runs over/past them. Here is a closer look at the spring assembly still installed and the plastic pivot “bearing” surface:

Here’s another view of the Denso unit:

The Denso spring unit, also a double coil unit, has a protective “sleeve” over the inner spring to reduce binding between them, since the Denso unit’s spring is in a substantially curved position inside the housing. The CTS does not have this feature, but it appears that its spring is less curved when installed.:

Subjective impressions of taking these two units apart are the opposite of what one typically would assume. The Denso unit feels “cheaper” in that the whole pivot bearing area is all plastic, and feels relatively more flimsy (that doesn’t necessarily mean it actually is). The CTS unit relies on very traditional steel and brass sleeve bearing that took some effort to take apart. The CTS pedal has no play or wiggle when assembled.

The big question is why Toyota completely redesigned the CTS unit from the older Denso unit. Perhaps they were actually trying to design a sturdier assembly because the Denso unit was in question. Perhaps the Denso unit is actually inferior in certain ways, but Toyota didn’t want to pay for new tooling to bring the Denso unit up to the newer CTS design? Source have told me that the Denso unit is likely to be recalled shortly, and the LA Times is reporting that there are known claims of pedal issues with the Japanese Denso unit.

From our perspective, it seems possible but rather highly unlikely that condensation is somehow causing the very solid CTS bearing pivot to lock up, given the spring tension and the units solidity. CTS claims it has only experienced a very limited degree of stiction at or near the idle point on a very few examples.

A key question is which unit was designed first. The CTS unit was used in Avalons since ’05 MY. Apparently Denso units have been in use before that. The question being: why did Toyota design two such fundamentally different units, and is the latter one designed to address any deficiencies of the older one?

Both units are surprisingly simple and obviously cheap, yet they feel robust when assembled. I believe Toyota has stated that the unit cost is $15 per pedal assembly. The retail price is about $120.

The overriding question is if these pedals are really the predominant or sole cause in any true (non-floor-mat caused) unintended acceleration, or whether electronics are the real 800 lb gremlin in this whole affair. Toyota has not acknowledged that…yet.

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