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OT: good design and why it's not used (e.g. Toyota pedal problem)

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  • OT: good design and why it's not used (e.g. Toyota pedal problem)

    The news about the Toyota accelerator pedal problem (btw my wife's RAV4 is affected) got me thinking about the wisdom of my car's design, one which I didn't really appreciate until Toyota's problem became a news.

    I drive a 2000 Saab 9-3. It's a throttle by wire, however the pedal is attached to a throttle cable like the traditional setup and the cable winds it's way to the throttle body. There the cable is attached to a shaft which is sensed by two separate potentiometer (POT). One of the POT increases in resistance as the throttle is depressed and the other decreases in resistance. Both of these values are read by the ECU to determined how much to open the throttle valve.

    The throttle valve is controlled by a servo motor, and just like the throttle position sensor, there are two POTs used. During the operation, ECU continually checks for the "sanity" of the throttle by wire system and should it sense that something is out of range, the ECU activates a solenoid in the throttle body which pushes a pin between the throttle position sensor and the the throttle valve. ECU then goes completely hands off the throttle, and allow the driver to control the throttle valve directly (and mechanically). Essentially allowing a manual override. Air/fuel mixture is still maintained by MAF, MAP, and O2 sensors.

    Originally, I thought why goes through so much trouble! Just put the sensor at the throttle pedal and do everything electronically. Now I see the wisdom of Saab's design. I actually think it's it's quite brilliant. No single point failure can cause the throttle system to fail completely (less the throttle cable breaking).

    So, my question is, "why are good designs replaced with inferior ones?" I see this all the time when they introduce new models. They had something that worked brilliantly but then they decided to change it and make it less effective (ergonomics being the primary examples). You may say that it's about cost reduction but in many cases I don't see that.

  • #2
    Heh, if car redesign was about cost reduction, we'd have $5000 new cars by now!
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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    • #3
      Originally posted by rotate
      The news about the Toyota accelerator pedal problem (btw my wife's RAV4 is affected) got me thinking about the wisdom of my car's design, one which I didn't really appreciate until Toyota's problem became a news.

      I drive a 2000 Saab 9-3. It's a throttle by wire, however the pedal is attached to a throttle cable like the traditional setup and the cable winds it's way to the throttle body. There the cable is attached to a shaft which is sensed by two separate potentiometer (POT). One of the POT increases in resistance as the throttle is depressed and the other decreases in resistance. Both of these values are read by the ECU to determined how much to open the throttle valve.

      The throttle valve is controlled by a servo motor, and just like the throttle position sensor, there are two POTs used. During the operation, ECU continually checks for the "sanity" of the throttle by wire system and should it sense that something is out of range, the ECU activates a solenoid in the throttle body which pushes a pin between the throttle position sensor and the the throttle valve. ECU then goes completely hands off the throttle, and allow the driver to control the throttle valve directly (and mechanically). Essentially allowing a manual override. Air/fuel mixture is still maintained by MAF, MAP, and O2 sensors.

      Originally, I thought why goes through so much trouble! Just put the sensor at the throttle pedal and do everything electronically. Now I see the wisdom of Saab's design. I actually think it's it's quite brilliant. No single point failure can cause the throttle system to fail completely (less the throttle cable breaking).

      So, my question is, "why are good designs replaced with inferior ones?" I see this all the time when they introduce new models. They had something that worked brilliantly but then they decided to change it and make it less effective (ergonomics being the primary examples). You may say that it's about cost reduction but in many cases I don't see that.
      The answer IS cost reduction aka increasing the company's profit.

      Change costs money and companies do not spend money unless they think there will be a cost benefit to THEM.

      Notice I did not say YOU.

      TMT

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      • #4
        Cast your mind back, say 20 years or so. The original "uncommanded acceleration" crisis was with Saab cars. The step on brake before shifting into drive interlock came from that. The system you are describing was meant to ensure that the problem never came back, Saab claimed that the real issue was drivers stepping on the gas by mistake, but one of their engineers found a single point failure in the throttle system and the whole thing got redesigned. A repeat would have really screwed them.

        Joe

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        • #5
          This is a sore point with me because I get to see a lot of bad design at work. There are several contributing factors -
          • "Let's not re-invent the wheel"
          • "We don't do it that way here"
          • "It's worked for the last x years - why do we need to change?"
          • "The cost of changing is too much"
          • "We can't change now - we need to get into test", followed by
          • "It's too late to change now - we need to get into production"
          • "We've already tested the design - we're not doing that again"

          Then again, some companies think that one designer is just as good as another, foregetting that like everything else, some people do and some don't have the knack for good design. For me the worst is the new graduates straight out of Uni/ College who are not trained how to design things properly but are thrown into design work as a learning experience without a mentor to watch over them.
          I could complain on and on...

          Michael

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          • #6
            Originally posted by Optics Curmudgeon
            Cast your mind back, say 20 years or so. The original "uncommanded acceleration" crisis was with Saab cars. The step on brake before shifting into drive interlock came from that. The system you are describing was meant to ensure that the problem never came back, Saab claimed that the real issue was drivers stepping on the gas by mistake, but one of their engineers found a single point failure in the throttle system and the whole thing got redesigned. A repeat would have really screwed them.

            Joe
            The problem you described was with Audi 5000s, not Saabs.

            Back to rotate's point - I think a good bit of it has to do with engineers on staff who try to find something to "improve" to justify their continued employment. This is a huge problem IMHO in the software industry.

            Steve.

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            • #7
              Call me crazy but I think the highest level of reform is simplicity! What is wrong with a straight cable to the throttle body with a spring that drives the throttle to idle if the cable snaps? And why not use a cam shaped pulley to create a better response curve than to use a drive by wire system?

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              • #8
                My Chevy truck drive-by-wire system with automatic trans backs off the throttle during upshifts. Smoother acceleration and longer trans life presumably.

                Major reason for drive-by-wire or a side benefit I don't know.

                I'm accustomed to harder shifts like a quick shifting th400 behind a big block 454 so it was a little unnerving at first but I don't even notice it anymore.

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                • #9
                  Drive by wire is stupid plain and simple. There is no need for it. It is just a problem waiting to happen. I frown upon car manufactures today. Everything is built in china or japan, there is no american car anymore. They get the same gas mileage as cars 20 years ago and they are no more if not less reliable. But hey, it has blondstar and some useless plug in feature on the radio!
                  Andy

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                  • #10
                    I prefer the Saab method over anything I have read about so far but I too am dead against any throttle by wire, steer by wire or brakes by wire all of which they call drive by wire.

                    What is going on, are we so stupid we are no longer able to drive and we have to have a computer do it for us. The aircraft use fly by wire but the systems they use are far superior to anything the auto industry would use.

                    The only thing I see when I read about drive by wire is a whiz bang techy attitude and practicality was thrown out with the wash water.

                    I see nothing but trouble using the drive by wire systems.
                    It's only ink and paper

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                    • #11
                      The dual pot system is USELESS!

                      Useless UNLESS the lack of sanity requires the vehicle to stop and refuse to work until the problem is resolved. Refusing to start on the next attempt would probably be the most practical, but not the best method.

                      Single redundancy has no "limp home" mode..... you must stop.

                      A three pot system would take the two best signals, and then require a 'service engine soon, safety systems failing" message.
                      1601

                      Keep eye on ball.
                      Hashim Khan

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                      • #12
                        Originally posted by vpt
                        They get the same gas mileage as cars 20 years ago and they are no more if not less reliable.
                        There is really no way you can compare cars today to cars from 20 years ago. Especially when talking about gas mileage. I used to have a 1987 nissan sentra that would get 38 miles to the gallon no matter how it was driven. My 2009 corolla gets about 34 mpg in town and about 40 on the highway. But, the sentra would barely do 80 mph and was really dangerous when trying to merge into traffic on the interstate because the engine was very underpowered. The corolla has no problem at all getting into traffic and can run well over 100, yet still gets mileage in the same range as the sentra without putting my life in danger trying to get on the interstate. Plus it don't sound like it's about to puke it's guts out when it gets up to highway speeds and is a lot more fun to drive. I wouldn't want to have to go back to an engine like the sentra even though I really liked that car when I had it then.
                        Jonathan P.

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                        • #13
                          Sorry to hear about your gutless sentra. My 180HP 1989 civic will bury the speedo in 14 seconds (100mph+) and gets 35mpg religiously. Oh and it has a cable controlled throttle body that has never gave me problems.
                          Andy

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                          • #14
                            Originally posted by vpt
                            Sorry to hear about your gutless sentra. My 180HP 1989 civic will bury the speedo in 14 seconds (100mph+) and gets 35mpg religiously. Oh and it has a cable controlled throttle body that has never gave me problems.
                            VPT, those cars were the exception, not the rule. Honda had several civic engines in those years that had around 80 to 90 hp too, much like the sentra. Look around a little, you'll find more of the low hp versions than you will of the one like you have. And they were quite gutless just like the sentra engine.
                            Jonathan P.

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                            • #15
                              The 80-90hp hondas of those years got up to 75mpg. What does it take to get that kind of mileage now days?

                              Gas mileage winner this last year, what was it? Oh yes a 1989 honda!

                              http://ecomodder.com/blog/20-yearold...l-economy-run/
                              Andy

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