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The Tufts technology is regenerative shock absorbers.
http://www.greencarcongress.com/2008/11/electric-truck.html
quote comment
Good find, John. What's your take on the viability of such a system? I have trouble believing that all the extra complication and weight would justify the minimal energy gain.
The shock absorber from Tufts University- it does make sense, though I wonder if it makes sense cost-wise. Think of regenerative braking- it reclaims the energy that would otherwise be lost in slowing a heavy, moving vehicle- in fact, the heavier, and/or faster moving, the more energy required to stop the car, and therefore more energy to potentially recoup- this is not something for nothing- it takes more energy to move more weight, and to move it faster. The regenerative shock absorbers would to the same thing- except instead of normal shocks dampening the energy from the up and down movement of the car (think pot holes!), the Tufts shocks would recover this energy. If you have every ridden in a car with bad shocks, you feel every bump in the road- again, it is not reclaiming something for nothing- it takes more energy to move a vehicle over those bumps, but now Tufts offers a way to reclaim a percentage of that energy.
And John- why watch the tach instead of the speed? If I remember the show correctly, he was mainly touting the benefits of this on a hilly route, and suggested that when going up and down the hills, you maintain the same RPM's instead of maintaining the same speed- by maintaining RPM's, your speed will go up and down along with the terrain, but you optimize the engine efficiency, much like the Volt's engine will do I might add, when it acts as a constant speed generator.
Regarding the email from Fred, to allow GM to sell gliders without further testing? Can't- the different weight, and the different weight distribution, can markedly change the crash dynamics- what might be safe with an engine, may not be with several hundred pounds of batteries and other equipment. After decades of pushing through safety standards on our Automotive industry, we really do not want to go backwards on this- safety in a 2500 pound, fast-moving object, is not something to compromise on- especially when your life, or the life of your kids, depends on it;-)
Paul, Regarding,
"...he was mainly touting the benefits of this on a hilly route, and suggested that when going up and down the hills, you maintain the same RPM's instead of maintaining the same speed-..."
Tell me what I am missing here. If you maintain the same RPM, you will maintain the same speed. That was the whole point of my commment. RPM and SPEED are linked together by the transmission. If the RPM is constant, then the SPEED is constant. You can actually calibrate your tachometer as a speedometer for a specific gear. Perhaps I am missing something here, but this seems to be non-sense.
LaterJohn C. Briggs
Darrell, I think my gut feeling is the same as your. The system isn't worth the effort. But let's try to go beyond the gut. The article suggests that average power is will be between 1 to 6 KW. The comments seem to suggest this is really more for large trucks then cars. So let's think about delivery trucks that might run for 4 hours a day rather than cars that might run for 1 or 2 hours per day. Also, I think it is cleanest to look at this is to compare the value of the electricity generated over a 10 year life of the vehicle to the cost of the shock absorber system. Here are some numbers (sorry about the spacing).
So at the low end, perhaps US$2700 worth of electricity will be generated over 10 years and on the high end $16,000. So if the system costs less than $2700 then it pays for itself. Limitations: If the vehicle is driven less, then less energy will be generated and it will be very difficult to pay off the cost of the regenerative shock absorber system. Also, I have valued the electricity at $0.19/KWH and electricity is much cheaper in some parts of the country. In the end, it seems like the idea has merit for a heavily used vehicle assuming the 1 to 6 KW power output can be achieved. On the flip side, we would all save more money by having smoother roads.
With regard to the constant RPMs, I think I remember the point being not to maintain constant RPM, but rather constant load on the ICE. With the scangauge II on a Prius for example, I think it is possible to track the ICE load (and operational mode) in addition to RPM. Keeping the ICE load at the ICE's optimal point while allowing speed to vary makes sense to me.
Steve
There was a discussion of maintaining constant load on the engine and letting the speed vary a little as you go up and down hills. That makes sense.
The comment that I am having a problem with is listed below.
Time marker 31:00
"One of the things that we always wish for is that we could have a cruise control that wasn’t hooked up to the speedometer but instead hooked up to the tachometer. ‘cause if you can keep your RPMs constant, instead of your speed constant, you generally do a lot better."
My point is that if your SPEED is constant, your RPMs will be constant.
Clearly these gentleman know a lot about hypermiling and have been very successful. So I don't mean to pick on this one point. However, it seems like a basic misunderstanding in how the car operates.
Thanks
John C. Briggs
John -
I actually phoned in this answer, so you might hear it twice now. If I make just ONE assumption, I can answer your concern on tach vs speedo.
Most hypermiling that I deal with is in regard to the Prius. (The Prius drivers are the ones who love the ScanguageII so they can determine the RPM and load of the engine.) The Prius has a continuously variable transmission, so there is zero correlation between speed and RPM.
In the case of the Prius, the RPM (and load) is all that matters. Not the speed.
The Prius EV switch enables a 2 minute run on all Electric. calcars has a how-to installation guide at http://www.calcars.org/prius-evbutton-install.pdf
same on EVNut.comhttp://www.evnut.com/prius_ev_mode.htm
Hi again John- I am certainly not a gear head, so maybe this is more perception than reality, but if you go up a hill, or go down one, and maintain the same RPM, your speed will not stay the same- normally when you hit a hill, you have to give a car a bit more gas to get it up the hill at the same speed you were going, and therefore more RPM's. This is much easier with a stick-shift, since if you slow down too much, the car will kick into a lower gear with an Automatic transmission.
I appreciate the help from the posters, but I am not sure if we are quite there yet.
Darrell, My understanding of the Prius (and I do own one) is that it does NOT have a CVT. In fact, it doesn't have a transmission at all. The Prius has a sun gear that takes as input the gasoline engine shaft and the electric motor shaft, and output is the drive to the wheels. Now, the RPM in this case could refer to the gasoline engine RPM or the electric motor RPM (which are different). The gasoline engine spins at a constant RPM (5000 I do believe) and the speed of the electric motor is varied. So in this case, perhaps they are referring to keeping the RPM of the electric motor constant. Still there is a problem, as far as I can tell, the RPM of the electric motor is directly correlated to the vehicle speed. I really have to doubt the premise here because the Prius does NOT have a tachometer, so I don't think they would have been talking about the Prius.
Paul, I think there is confusion here between accelerator pedal position, versus, RPM, versus SPEED. Regardless of the accelerator position, the RPM and SPEED would be directly related, if this was not the case there would be slipping between the engine and the drivetrain. That does not happen in manual transmissions or modern automatic transmissions with lock-up torque converters.
Again, I appreciate the effort to answer this, but it still makes absolutely no sense to me.
ThanksJohn C. Briggs
I agree that the Prius doesn't have a CVT - that's just the term that most folks have heard before, and it explains the situation. The *result* is the same. There are no fixed gear ratios - and that's all that I meant to convey - regardless of the technology to get there.
The ICE certainly does not spin the same speed at all times, though it does try to spin at the most efficient RPM. If you nail the throttle at 10 mph, the ICE will spin up to max RPM and the car roars. If you pull away gently, the ICE will spin below the most efficient range. But accelerate like your average driver, and presto - the ICE spins at the sweet spot. Regardless, there are no fixed gear ratios, so there's no way to tell what the ICE is doing just from the speedo alone. And even if the ICE did try to always spin at 5,000 RPM, we still have a disconnect between speed and RPM.
And as you say... which RPM are we talking about? I assume it must be the ICE that we care about because the electric motor is almost equally efficient over its whole speed range. The ICE is not.
It could very well be that the original situation was not about the PRius - I admit that I didn't even listen to the original, and was just responding to the comments. My bad!
Gint -
The EV switch has no time component. How long it can be used is determined by the battery's state of charge, and what other demands are being placed on the HSD system. If you start the car in the cold with the heat blasting and want to accelerate hard, the EV switch will NOT allow you to go into EV mode - or will immediately switch out of it when high power demand is created. In mild weather and gentle driving, you can stay in EV mode for quite a long time, and several miles.
There is no time limit on it. The only thing that determines how long you can use it is energy supply and demand.
Darrell, OK thanks for the correction of the RPM of the ICE in the Prius. That drive system still has many surprises for me. I still say that for RPM versus SPEED, for non-hybrids, there should be a one-to-one correspondence.ThanksJohn C. Briggs
Whoa- see Paul back-pedaling at incredible speed! Actually John- as I think about what you said, I believe you are right- I was equating fuel flow with RPM and not thinking about it (this is why I fix computers and not cars;-)- it does make more sense that the RPM would maintain a one-to-one rate with the speed in a given gear.
Yup! I think we're in agreement now (and now maybe Bo can come back in and not be afraid).
