h a l f b a k e r yOn the one hand, true. On the other hand, bollocks.
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Simple really, maybe no more than a little foot switch and a tweak of the transmission firmware.
So-called automatic transmissions are not quite as smart as a really dumb driver. If you drive over the crest of a hill the engine/transmission is not smart enough (at least in every car I have ever
driven) to shift to a lower ratio and utilise engine braking. The result is the driver cooks the brakes by riding them down to the bottom of the slope or needs to take a hand from whatever else it is being used for to push the shift handle back, usually the former as evidenced by the pattern of braking lights I see every time I drive.
The idea is a simple foot pedal (or switch) for the otherwise redundant left foot which when held down signals the transmission not to change up and when pushed further down causes the transmission to select an even lower ratio.
Apart from the down hill situation there is performance and safety potential too especially when overtaking on a single lane road. If the car has a big engine running at, say 1750 rpm at 100Kph (65mph(?)) pushing the accelerator pedal brings only a slow response, first the engine starts to accelerate, the manifold depression drops, at last the pedal hits the kick-down/tap-down, the transmission changes down and at last you are ready to begin that overtaking manouvre. But a driver with forsight can push the pedal/switch in advance, the transmission will already be in the lower ration and the engine will be running more into its power band and more ready to give a snappy acceleration when the driver presses the gas pedal to begin the overtaking.
I look forward to your negative comments, yes it is baked, thouroughly in fact, I fitted one to a V8 in 1973. But has it been baked by anyone else?
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So... did you ever mistake the brights switch for other? |
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I love the idea I am looking for something for my left foot to do anyway for some reason it does nothing... I guess the engineers-lawers-accountants figured that the typical person either has a bum left foot or it got blown off or something. |
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actually it shouldnt be much trouble to install...I will have to try this |
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"And the clutch pedal goes where?"
In a geared car. |
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I got caught out once in an automatic hire car. It changed up as I was overtaking and what started out as a casual and easy overtake with room for more turned into a narrower squeak than I would have liked. |
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My Pug 406 auto has a setting on the gearbox that holds gears longer thatn 'normal' for this reason. There's a button by the selector that engages it |
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Two things:
1) Every automatic transmission I've ever seen lets you select a gear other than "Drive"
2) I'd rather cook the brakes than the transmission. Brakes are cheaper and easier to replace. |
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Well, since you're expecting the negative comments ... |
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[shad]
Having been a driving instructer I can tell you the left foot( in an automatic) is used to brace yourself in the case of a collision, or under heavy braking.There is a flat area in most vehicles, near the left foot, called the dead pedal which you use to push yourself in to the seat.
Hope this explains things. |
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No Shad, I never got that switch confused with the head lamp dip switch. The one I installed it on was a GM vehicle with a foot dip switch but every modern car I have driven has that on a steering column stalk. |
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Yes oneofdave, I think most autos have something like that but my suggestion is to make it more convenient by moving, or adding, that control to the otherwise redundant left foot. |
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Phoenix, I would rather keep the brakes for when I need them, not as a speed adjustment device. I find it not unusual to follow traffic down a 2000' descent (in about 12 miles) and watch brake lights all the way down. Can you imagine what those brakes are like by then? |
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And yes Phoenix, automatic cars do have selections other than 'D', did you not read all of what I wrote? |
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Python, I am glad you did not teach me to drive, just how much effect do you think a braced foot will have after you have cooked your brakes? |
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Only SIX fish? What is wrong with you people? Can't you really dig deeper than that? Hahahahaha! |
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Shad, when I did it to my old GM vehicle I just paralleled the kick-down switch from under the throttle pedal. I do not know if modern electronic controlled transmissions would allow such an easy modification. |
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First off, every auto I have had the displeasure of driving has had an "intelligent" gearbox. If you need the extra power/acceleration from the engine, shove you foot to the floor and it knows not to change up until peak revs.
Secondly, as [phoenix] says, all autos have other gears than drive specifically meant for hill descents. Can you not just snick down to one of these gears?
Sorry, but I am going to have to show you the fish.
You should get a manual anyway! :) |
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Gromit, Holden 253 ute with Tri-matic. |
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Silverstormer, my point exactly, the kick-down will not change the ratio until the revs have come up which is not something very useful when you are looking for engine braking down-hill. |
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Yes, of course I could pull the handle back to a lower ratio (I think I already said that?) but my observation is that most people do not do this. Thank you for your fish, I will put it with the others. |
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Brakes are for wusses. Coast all the way down, I say. |
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Seriously though, I don't think bracing yourself with your left foot is going to prevent you from being thrown forward in an accident. |
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Gromit, I presently drive a 4 litre Ford 6 with an automatic and very rarely does it see a flat stretch of road. In its very short life I have replaced the pads a few times and the front disks once, unfortunately in this model the disks are integral with the hubs so the whole thing needs replacing at the one time, quite expensive, naturally enough I am trying to develop a less brake-dependant driving style. The suggested pedal/switch would be just so much more convenient than taking one hand off the wheel to pull the trans shifter handle while at the same time sneaking between the bus pulling out and the cement truck grinding up in the other direction. |
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Yea, a smarter cruise control would be nice, mine only mantains a minimum speed and does nothing to stop overspeeding on down grades, good point though but it still would not have the foresight that a competant driver should have. |
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[python] Actually I do use my left foot, for the brake -- I know this may greatly disturb you but it by far more efficient for xtreem off-roading (you dont waste any time switching feet - - very important - - -the differance between winning and loosing) I also tend to drive that way in seriously demanding situations even using both feet. |
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I have NEVER been in a situation that required me to use my left foot to assist my seat belt or 5 point from failing |
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the energy lost in the transmission durring deacceleration is turned into heat in the torque converter. most trannys have a trans cooler if it does not and the tranny is overheated dammage may result. deacceleration forces on the tranny going down the hill are similar to the forces going up the hill it would be extreemly unusual to overheat the tranny in this manner ( it is an accepted way to drive ) |
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I beleive that this is also true for the motor
the wear on the motor will possibly be slightly more than if you were to leave it in overdrive |
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BUT like you said I would like to have my brakes when I need them |
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Actually Shad I do not believe that all the energy is converted to heat in the torque convertor although that would certainly be the case if the engine was not turning! However the engine is turning and has quite a load from friction and from the forces needed to compress all that air that is being pumped through. |
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On the other hand the torque convertor is most likely not operating in it's most efficient manner during the over run so heat build up may be higher compared to the uphill direction? |
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As an aside, much of the compression load is recovered when the air expands on what would otherwise be the power stroke. This energy taken up by the engine is like the transmission heat disposed of via the radiator and some conducted away via the air and the exhaust path. |
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I can accept that there is more wear on the engine when used in this way rather than leaving the trans in overdrive but how far do I want to go down that path? There would be even less wear if I left the thing at home and took a bus. :-) |
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Exhaust braking like trucks have may be a nice enhancement to this idea. |
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Meanwhile, I have driven a few more hundred kilometres since posting this idea and if I may I will add an alternative. After thinking about it some more, and sitting on my motor bike (unfortunately not road worthy just now) I have concluded that a motor cycle type shift pedal for the 'PRNDL' would actually be a very good idea, has any car ever done this? |
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[KiwiJohn] - you mean sequential shifting between P,R,N,D and L (rather than between gear ratios)? Don't think anyone has.. can you imagine driving one flavour thinking it was the other?
L brrrmm D brrrrrmmm N briizzz huh? R boom! |
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I think you'd want any steering wheel mounted controls to be limited to selecting forward gears only. I'd be happy with the sport mode button(s) to be moved from the gearstick to the wheel. |
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to rephrase what I said. to keep myself from appearing to sound like an idiot |
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//the energy lost in the transmission durring deacceleration is turned into heat in the torque converter// |
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The energy THAT IS LOST in the transmission durring deacceleration is turned into heat - - - yeah what you said- - - |
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dont know about sequential PRD321 but they are doing sequential steering wheel paddles in formula 1 and a lot of high doller performance cars but I think that this is kind of a manual transmission |
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shucks, then there still wouldnt be anything for my left foot to do.. maybee I willl buy a motorcycle.... |
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"Car with a big engine...passing."
Ha. I have a 1957 Packard Clipper.
Weight, over 4000 pounds. Engine is
about 5 liters. Transmission: 3-speed
automatic. Normally, it will start in 2nd,
and shift to 3rd at about 30 mph. So I'm
doing 60 on the freeway, and decide to
pass. I step on the gas. The
transmission drops to 2nd gear pretty
much immediately (well under .5
seconds), the car roars forward, and by
the time I've passed the car, I'm well
over 80 mph. |
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Example B, my old 1990 Ford Probe. 4-
speed auto. I'm in 4th, and want to
force a downshift. Instead of a floor
pedal, there's a button on the shift
stick. It changes (D) 2 1 to (3) 2 1. That
is, it locks out 4th gear. So if I'm smart
enough to press your floor button, I'm
smart enough to squeeze the overdrive
lockout. I can even shift to 1 on the
freeway. The transmission will start
shifting downward to first gear, but
only when the vehicle speed isn't too
high. Engine braking with automatic
downshifting. |
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Most automatic transmissions don't provide much engine braking anyway, for the same reason you can't push-start them. |
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I think what you want is a hydraulically actuated "automatic mechanical" transmission, without the torque converter: an electronic control computer determining what gear the vehicle needs to be in, gear selection and clutch actuation by hydraulic pistons. Didn't Nissan make something like this? |
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"Engine braking", in a gasoline automobile, is actually performed by the throttle. Energy spent compressing air to pressures above atmospheric will be largely recovered during the power stroke. The throttle, however, forces the engine to waste energy pumping air through a constriction. This energy could be recovered if one tried to harvest useful energy from the vacuum, but most cars don't (they use the vacuum for things like power brakes, but the amount of energy used thereby is pretty tiny). |
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"Exaust braking," or "Jake Brake," or "Engine Retarders," as used in truck diesels, disables the fuel injectors and opens the exhaust valves at the top of the compression stroke, thus dumping the compressed air and the the energy used to compress the air in the cylinder. Gear selection is still important, because the Jake Brake isn't as effective at higher RPMs. Jake Brake operation is semi-automatic, in that it's disabled except when the engine is decelerating- this allows the driver to leave the brake switched on when driving in hilly country. The downside of Jake Brake operation is that it's noisy, and its use banned in some hilly areas (dead truckers apparently being preferred to noisy ones).
I can't think of a reason such a device couldn't be used with a gasoline engine, but I'm not an engine designer. It would still be cheaper to have it manually activated- an automatic system would be complex and expensive, I think.
As far as the foot-activated "kickdown" switch, I can see that it might be a tad more convenient for some, but learning proper hill/mountain driving technique is a far better solution- biometrics and wetware (dexterity and brains) can easily be transferred from vehicle to vehicle at no cost. |
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