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Hybrid Vehicles Hybrid Vehicles - Archived Discussions How do Hybrids work? Newbie questions encouraged! 
139 messages, Last post on Aug 02, 2007 at 5:38 PM
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Replying to: robertsmx (Jan 03, 2005 10:39 am) . The answers provided here were for the Toyota. Honda works differently: - press the brake ~1/2 inch & it's pure generator braking - press the brake ~1 inch & it's friction braking - generator braking works down to ~10 mph & then turns off So my approach is this: - Lightly press the brake for pure generator braking - Until I hit 10 mph - Use friction braking to slow from 10 to 0. troy |
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Replying to: xcel (Jan 04, 2005 5:31 pm) I don’t care about whether or not these systems exist today. In current hybrids, it is more about following the safer/conventional route. It is a part of the lesson in economics. |
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The "regen" feature of the Hybrid braking systems "DO NOT" (I repeat, do not) make the brakes less effective or more unsafe. The systems are basically just like "regular brakes" in that they use pads and rotors and discs/drums. All that makes them different is that they have additional components to recapture the energy wasted by braking.
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Replying to: larsb (Jan 06, 2005 1:06 pm)
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Replying to: robertsmx (Jan 06, 2005 3:42 pm) That is a point largely being missed here. People are assuming that regenerative braking takes away something from actual braking, where as it is really using vehicle's inertia to generate electricity (on top of braking effort by the driver). ___No one is missing anything here except for you. Regenerative braking is good for one thing to date, regen. Why didn’t Toyota, Ford, and Honda just remove the mechanicals to save on costs? It is in the future after all. Because the regenerative action of release to engage and back again is far to slow by comparison to the electro-hydraulic-mechanicals that are in use in most of our automobiles today. ___Have you driven a hybrid yet? Until you have, you have no idea as to how fast the transition is between Regen, release, and back to regen in another gear actually is. With that, you can definitely feel how [b]slow[/b] the process is after a few taps of the pedals vs. locking up the binders and feeling the pulsation of ABS or TCS in a fast but slick corner from a particular wheel. There isn’t a maybe about it, it just is. Do you know why Hybrid’s have mechanical brakes with safety overrides in which Regen is locked out? You can argue whatever you want but the 1000’s of engineers at Ford, Honda, and Toyota know more about it then what you obviously think because they have overridden regen for the respective automobiles safety functions on every Hybrid other then possibly the Escape HEV (I haven’t read up enough about it just yet to say one way or the other). ___Good Luck ___Wayne R. Gerdes
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Replying to: xcel (Jan 06, 2005 7:36 pm) Remove what mechanicals? Specify. Also elaborate on “electro-hydraulic” mechanicals you’re talking about. If you still believe hydraulics in any way are more responsive than electrical systems, I will try to dig up some links for you. For time being you go with what you've got. This does not mean forever. |
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My Insight's regenerative braking slows at ~1 mph per second. If I'm about to slam into a pole at 60 miles an hour, I want faster slowing than 1 mph/second (a full minute to stop). I want the old-fashioned but highly effective friction brakes. Troy |
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I’m not sure how you could measure how regenerative braking is translating to deceleration (down to mph). I have my doubts on common understanding of what regenerative braking really is. Electric motors transform potential energy (electric charge) to kinetic energy and when they are run in reverse (i.e. as electric generator), they can capture kinetic energy to store potential energy. That’s all there is to the bottom line of regenerative braking. Vehicle is already moving, and when driver applies brakes, the controller knows to switch to generator mode and starts to capture whatever kinetic energy it can and before the vehicle comes to a complete stop (due to braking by the driver). Since some of the kinetic energy is being transformed into electric charge, there is lower loss to the atmosphere by way of transformation of the kinetic energy into heat energy. I’ve yet to understand why it is being assumed here that regenerative brakes is actually stopping the vehicle by itself (well it is but only in conjunction actual braking action by the driver, pretty much like engine braking except for the fact that there is less energy lost in translation).
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Consider the railroads which have used electric motors to brake trains for about 80 years. They still use friction brakes. The reason is simple. Regenerative (or dynamic braking in the case of Diesel/Electric locomotives) is only effective over a certain speed range. Once the vehicle is moving too fast or too slowly it doesn't work. In the case of the Prius regenerative braking stops working below about 6MPH. There just isn't enough kinetic energy left to resist the magnetism of the field. If you wanted to completely stop using just the motor, you'd have to apply so much field current that you'd defeat the purpose of rhe regenerative brakes (i.e. recharging the HV battery). There is another consideration which you need to consider w.r.t. use of regeneration during ABS conditions. There's a friction brake at each wheel, while there's only one electric motor/generator set. Since the regenerative brakes have to transmit force through the differential/transaxle, there's no way to modulate the braking force between the drive wheels (and no way at all to brake the rear wheels in a FWD system). One could remedy this by placing a traction motor at each wheel, but that would add weight and complexity to the system far more than having conventional brakes (which you'd still need because of the limitations mentioned above). Hope this helps to further clarify things. btw, the FEH is no different from the others w.r.t. overriding regen braking... |
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Replying to: robertsmx (Jan 07, 2005 12:38 pm) . Because I have a brain? It's not that difficult to observe my Insight's deceleration with generator braking is about 1 mph per second. troy
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