I be interested in knowing what kind of testing and what group of people got to try this concept out. Is this something that the driver will get used to and won't mind. Or is it more of a situation that people just won't notice. I would assume it's something that most people would notice. So I guess it;'s one of those things that people learned to put up with the goal of feeling good because they are driving green.
Based on my experience test-driving a Chevy Volt -- and I realize I'm being entirely subjective here -- the regenerative braking system was easier getting used to than ABS was when I first confronted that. The Volt's brake pedal has a "squishy" feel to it, which on first use makes one think there's something wrong with it. It's simply the regen kicking in.
Full electric braking will be less effective than friction brakes, from the energy standpoint because at rthe low no-regen. speeds the computers will be forced to run the motors backward. (I know it isn't really running backward but in effect it is and consumes energy.) I am also less inclined to trust a full eletric system, things do fail occationally. Even Hydraulic friction brakes usually have a back up cable activated parking brake. We must also start NOW to develop a battery recycling system or when these cars reach end of life we will have a horrible disposal (battery) problem on our hands.
@Walt: You bring up a good point. I do not know anything about battery powered cars, but I do know I have destroyed numerous batteries in the past by improper charging.
I also know I do not want my vehicle to put the brakes on as soon as I lift my foot off of the accelerator. This article makes me think there are people making decisions based on Feel Good rather than what really improves the product.
Hi. I believe the best option for regen is to blend it with mechanical braking. The first portion of the brake pedal would regen as much as possible but continuing to press the pedal would engage mechanical braking. Regen should always be proportional to the brake pedal position and not an on/off function of a present regen amount. IMHO, coasting when lifting the foot off the accelerator is better than engaging regen at that point. You get much more (range) out of letting the car coast than braking it with regen in hopes to recover some of that energy. Proportional regen, blended with mechanical braking is tough to do. First, you want a certain amount of braking to always be present at a certain brake pedal position. Nothing is scarier that pushing the brake pedal to what you're used to and finding the car is not stopping as expected. Second, regen braking capacity varies depending on how much current the battery pack can sink. If you live on a hilltop you will not get much regen braking when you set off in the morning after changing your batteries all night. Regen also varies with speed which complicates things even further. Third, the transition from electrical to mechanical braking must be seamless to make it effective and elegant. I guess that's why we compromise and get regen on accelerator in most implementations.
There does seem to be a driving technique issue here, in that the most efficient driving includes a bit of coasting, as opposed to braking. Regenerative braking when you want to brake is fine, but when I want to coast, that is different, and I DO NOT want to be braking. In many cases it works very well to take my foot off the throttle and coast up to a red light, since It was clear that it would still be red when I arrived.
As for those folks concerned about"overheating the regenerative braking mechanism", clearly they are not aware that it is all the same parts, just a different controls setting. The problem with regenerative braking is that when needed most, for hard decelleration, there is only so much energy the batttery can absorb in a short time. The solution would be to have a bank of super-capacitors, which can absorb a charge much faster, and then return it much more rapidly. The challenge is that supercapacitors are sort of expensive, and would need to be installed someplace, taking room away from the battery bank. But, they could absorb the power as fast as it was generated, and then deliver it for the next accleration. That has been demonstrated already.
The "depends" part of the regenerative breaking is the system condition. The Volt attempts to keep the battery full until the engine runs out of fuel leaving little charge space for regenerative breaking. The exception is when the Volt is driven slowly and is on battery only.
In the mountains with long downhills, regeneration dose not happen with a full battery. Breaking is all mechanical.
Regeneration is most effective in city driving and only when the car is driven agressively. Fast and hard acceleration takes from the battery leaving room to regenerate. This is why the Prias and Volt have good MPG numbers for the city driving circuit.
For the two footed key in and drive folkes, the "feel" of the gas and break functions emulate the bulk of automatic cars. The indirect method of setting the more agressive one peddle regenerative breaking keeps the numb drives from getting into the mode by accident.
Effeciency and heat. If the motor is 90% and the controller is 90% and the battery is 90% then the total is 72.9%. At a stated 75%, there is no abnormal heat present.
Think of how hot normal brakes get. Now if 75% of that gets converted back to stored electricity, the other 25% turns into heat. It is distributed between the electronics, the motor, and the battery. If there are any engineers left at GM they probably designed for this situation, with temp sensors on all the components.
Some advantage is gained from regenerative braking, but not much. It is a known fact that batteries do not recharge quickly, regardless of the method. The gain is a surface charge more quickly used than the deep charge that comes with time. Granted, regenerative braking is better than having none at all but IMHO (since I am no electrical/battery engineer) it probably results in longer life for the brakes than in significantly improved efficiency. Worth the extra cost and wear and tear on the drive system? Time will tell.
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