Eng-Tips is the largest engineering community on the Internet
Intelligent Work Forums for Engineering Professionals
Regenerative Braking
- Thread starter iamyo
- Start date
GregLocock
Automotive
regen is using the electrical generator (of whatever form) as a brake. So you'll need some way of detecting braking, some way of handling huge amounts of power, quickly, and some way of modulating the force, I suspect. Typically the power absorption requirement under braking is about three-10 times the maximum power of the engine (that's not how it is worked out, but as a rule of thumb it works). Your battery will not be able to accept charge at that rate so you either have to limit the proportion of the braking supplied electrically, or burn the additional power off in a resistor. I suspect the first makes more sense.
Cheers
Greg Locock
Cheers
Greg Locock
magnograil
New member
It depends upon the braking system. The most efficient is probably hydraulics. It can deliver and absorb large amounts of power in a short time.
Northrop used electric motors to drive/brake their "Swords to Plowshares" bus boondoggle. I was stuck with doing the software and simulation of the energy system. Braking was by using the motors as generators with the power going into batteries (which is only 50% efficient) and the excess into heating elements. The batteries were dumped as it took more power to haul them uphill than recovered going down. So it ended up being a natural gas powered electrically driven bus.
Northrop used electric motors to drive/brake their "Swords to Plowshares" bus boondoggle. I was stuck with doing the software and simulation of the energy system. Braking was by using the motors as generators with the power going into batteries (which is only 50% efficient) and the excess into heating elements. The batteries were dumped as it took more power to haul them uphill than recovered going down. So it ended up being a natural gas powered electrically driven bus.
patprimmer
New member
Unless you really gear them up and turn them really fast, and use large diameter peripheral weighted construction, flywheels are also very heavy
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
Railroad locomotives reverse the traction motors and dump the energy to massive resistor grids that one can sometimes see glowing red hot when the roadway is above the railroad tracks in mountainous country.
Electric vehicle retarders used in trucks busses, and trailer axles have pairs of massive (50Kg or more) steel flywheels with fan blades built into them where the downhill energy is dumped as eddy currents. They glow red hot when in maximum usage.
If you are going to get any effective braking, regen or otherwise, since we all agree that charging batteries is not a very good way to go, wasting the energy in a similar fashion after you have stored all you possibly can is the only option.
What about charging up diodes?? (easy to ask, since I am not an electrical engineer)
rmw
Electric vehicle retarders used in trucks busses, and trailer axles have pairs of massive (50Kg or more) steel flywheels with fan blades built into them where the downhill energy is dumped as eddy currents. They glow red hot when in maximum usage.
If you are going to get any effective braking, regen or otherwise, since we all agree that charging batteries is not a very good way to go, wasting the energy in a similar fashion after you have stored all you possibly can is the only option.
What about charging up diodes?? (easy to ask, since I am not an electrical engineer)
rmw
MikeHalloran
Mechanical
I knew a guy once who was trying to sell the idea of using an axial flow fan, e.g. a turbojet's compressor, as a truck retarder. He said the power requirement went up as the fifth power of rpm. At the time, it sounded like a good idea.
Of course, in order to be lightweight, it has to turn fast enough to put the blades at a high sress level, and when you do that, it becomes a single speed device, which doesn't match a truck application very well. I don't think he had researched the subject enough to learn about compressor stall, where the power requirement suddenly falls off, and because of the subsequent overspeed, the maximally stressed blades fall off too.
Uh, diodes don't store anything, so you can't charge them up. You can charge capacitors, but the energy density doesn't approach that of batteries.
The whole concept of 'charging' something for regenerative braking implies the existence of a device that doesn't actually exist; a high power level Continuously Variable Transmission, that can accept power from a decelerating low speed drive, and transfer it with minimal waste to an accelerating or constant speed high speed drive.
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
Of course, in order to be lightweight, it has to turn fast enough to put the blades at a high sress level, and when you do that, it becomes a single speed device, which doesn't match a truck application very well. I don't think he had researched the subject enough to learn about compressor stall, where the power requirement suddenly falls off, and because of the subsequent overspeed, the maximally stressed blades fall off too.
Uh, diodes don't store anything, so you can't charge them up. You can charge capacitors, but the energy density doesn't approach that of batteries.
The whole concept of 'charging' something for regenerative braking implies the existence of a device that doesn't actually exist; a high power level Continuously Variable Transmission, that can accept power from a decelerating low speed drive, and transfer it with minimal waste to an accelerating or constant speed high speed drive.
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
I worked three years for a trolleybus manufacturing company, it is standard equipment at trolleybuses, tramcars and metro-coaches in Europe.
When braking, the electrical engine is the main brake, and only at lower speeds these vehicles use classical friction brakes. When braking, the electrical engine becomes generator and pumps current up into the electrical network. Only there is one problem: there should be in the neighbouring area an other vehicle, which is accelerating right at that time, then you have a user, which will use the power pumped into the network, by the braking vehicle. If there is nobody to use that current, every vehicle has braking resistors, and the generated current is routed there, and all the current will go out on the resistors into the air as heat, and will be lost.
That's why in some European cities they interconnect the tramcar and trolleybus current network, this way doubling the possibility of beeing somebody around already accelerating, when somebody else is braking.
This kind of equipment manufacturers are Kiepe, Ganz Transelektric, Siemens, IKPE SAERP and I belive Bombardier also has this kind of equipment. You can try their websites for further info.
By!
When braking, the electrical engine is the main brake, and only at lower speeds these vehicles use classical friction brakes. When braking, the electrical engine becomes generator and pumps current up into the electrical network. Only there is one problem: there should be in the neighbouring area an other vehicle, which is accelerating right at that time, then you have a user, which will use the power pumped into the network, by the braking vehicle. If there is nobody to use that current, every vehicle has braking resistors, and the generated current is routed there, and all the current will go out on the resistors into the air as heat, and will be lost.
That's why in some European cities they interconnect the tramcar and trolleybus current network, this way doubling the possibility of beeing somebody around already accelerating, when somebody else is braking.
This kind of equipment manufacturers are Kiepe, Ganz Transelektric, Siemens, IKPE SAERP and I belive Bombardier also has this kind of equipment. You can try their websites for further info.
By!
If the flywheel is used for regenerative braking only, and not as the prime mover, the size can be kept quite reasonable and can be made of 4340.
I have a prototype IVT system in my basement that I designed and built about five years ago. The problem as you stated is sizing up the torque capability, not impossible for one of the big three but certainly way beyond my means.
GregLocock
Automotive
Yes and yes. Didn't Ford have a showcar (well truck) with a hydraulic accumulator?
Cheers
Greg Locock
Cheers
Greg Locock
Back in the late seventies, somebody put one of these systems in a Granada. The engine was set up to pump up the accumulator, and the drive was hydraulic only. Doubled the fuel economy when driven side by side with a conventional Granada. I think I still have the Popular Mechanics or Science article somewhere.
I had heard that Ford was implementing this on the F-350 as a power aid. Has seventeen years passed already?
magnograil
New member
Warpspeed, TOHCan - it was also done in '70 using a Bradley GT bodied VW chassis, Tecumseh 18 HP lawn mower motor to recharge the hydraulics when necessary, variable displacement hydraulic motor driving the stock VW transaxle. Braking was by reversing the flow from the hydraulic motor from low to high pressure reserviors. All off the shelf parts. 70 mpg, 0-60 in 7 seconds.
Nobody was interested.
".. got fuel to burn, got roads to drive.
Keep on rockin' in the free world." - NY
Nobody was interested.
".. got fuel to burn, got roads to drive.
Keep on rockin' in the free world." - NY
Very interesting, it was just an idea that suddenly came to me when I spotted this thread.
I suppose cost and complexity, and the unusual layout would discourage many car manufacturers from taking up something like this. I am not surprised that the hydraulic idea has already been tried. When gasoline is ten dollars a gallon some of these ideas might be looked at again with more interest.
Unless there is a major breakthrough with battery technology (unlikely) hydraulics may hold more promise. At least the hydraulic accumulator will not slowly die and need frequent replacement every few years like batteries.
I suppose cost and complexity, and the unusual layout would discourage many car manufacturers from taking up something like this. I am not surprised that the hydraulic idea has already been tried. When gasoline is ten dollars a gallon some of these ideas might be looked at again with more interest.
Unless there is a major breakthrough with battery technology (unlikely) hydraulics may hold more promise. At least the hydraulic accumulator will not slowly die and need frequent replacement every few years like batteries.
magnograil
New member
Actually it can be done rather cheaply. The 3000 PSI and 100 PSI accumulators, variable displacement motor for drive/brake and the constant displacement motor for recharging were all off the shelf parts. Solenoids were used to change the flow from drive to brake. A modern adaptation would use software and pressure transducers to keep track of the accumulator and gearbox. Obviously, a lower gear produces more braking with the same motor displacement than a higher one. It would also turn the fuel motor on/off to keep enough capacity for accelerating but leave enough for braking. Could very easily be optimized much better than it was and use a modern motorcycle engine. The fuel motor has to be sized for the weight, drag and grade you design for.
I worked on the Northrop electric hybrid bus. Driven by electric for political reasons. Excuse for eliminatating hydraulics from the drive source was due to preceived mechanics inability to service hydraulics without it leaking.
Scrapped regenerative electric braking due to poor charge/discharge efficiency of batteries and penalty of carrying dead weight uphill. So braking energy was all dumped as heat in cooking elements. Of course none of it used to heat the cabin. That came from a 35,000 RPM 120db aircraft APU from Israel (read boondoggle trip). The positive note was the boom boxes were overwhelmed by the electrical noise of all the electrics.
Car manufacturers are entrenched in petrol engines and will not consider alternatives until public pressure demands it.
I worked on the Northrop electric hybrid bus. Driven by electric for political reasons. Excuse for eliminatating hydraulics from the drive source was due to preceived mechanics inability to service hydraulics without it leaking.
Scrapped regenerative electric braking due to poor charge/discharge efficiency of batteries and penalty of carrying dead weight uphill. So braking energy was all dumped as heat in cooking elements. Of course none of it used to heat the cabin. That came from a 35,000 RPM 120db aircraft APU from Israel (read boondoggle trip). The positive note was the boom boxes were overwhelmed by the electrical noise of all the electrics.
Car manufacturers are entrenched in petrol engines and will not consider alternatives until public pressure demands it.
karlbamforth
Aerospace
Never thought of using Hydraulics to drive a car.
I guess i always considered hydraulic systems to be relatively heavy. Has anyone got a link or drawing as to how the system would work? Finding it a little difficult to visualise how an 18hp engine can drive a car efficiently and still have good accel etc.
I guess i always considered hydraulic systems to be relatively heavy. Has anyone got a link or drawing as to how the system would work? Finding it a little difficult to visualise how an 18hp engine can drive a car efficiently and still have good accel etc.
patprimmer
New member
Not a new Idea. Ferdinand Porsche designed a 4WD car with hydraulic drive way back around WW1 times
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
magnograil
New member
Try looking at a non-electric forklift someday. The fuel motor runs the hydraulic pump which powers the hydraulic drive motor.
The 18 HP fuel motor was just to recharge the accumulator as needed. The variable displacement hydraulic motor drove the standard VW transaxle. The "gas" pedal varied the drive motor displacement which had 3000 PSI feeding it. At top speed the fuel motor is providing all the hydraulic fluid to the drive motor and none is going into the accumulator.
If you think hydraulics are heavy, think again. They are commonly used in aircraft to move the control surfaces. If there was a lighter method it would have been used in commercial aircraft that are highly dependent upon light weight for cost savings. Military systems are going to 5000 PSI. A leak in that would cut your fingers off.
The 18 HP fuel motor was just to recharge the accumulator as needed. The variable displacement hydraulic motor drove the standard VW transaxle. The "gas" pedal varied the drive motor displacement which had 3000 PSI feeding it. At top speed the fuel motor is providing all the hydraulic fluid to the drive motor and none is going into the accumulator.
If you think hydraulics are heavy, think again. They are commonly used in aircraft to move the control surfaces. If there was a lighter method it would have been used in commercial aircraft that are highly dependent upon light weight for cost savings. Military systems are going to 5000 PSI. A leak in that would cut your fingers off.
iamyo,
Hydraulics are the only practical (and cost effective method) currently available for capturing a significant portion of braking energy in an automotive application.
Ford/Eaton are working to bring a system to market for cars and light trucks:
Permo-Drive has a system for heavy vehicles:
Regards,
Terry
Hydraulics are the only practical (and cost effective method) currently available for capturing a significant portion of braking energy in an automotive application.
Ford/Eaton are working to bring a system to market for cars and light trucks:
Permo-Drive has a system for heavy vehicles:
Regards,
Terry
- Status
Similar threads
- Locked
- Question
- Locked
- Question
- Locked
- Question