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Hydraulic question for Senior Design

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Hurst View Drop Down
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    Posted: 07 Nov 2011 at 5:41pm
So for my senior design in engineering school, I am designing and building a small hydraulic drivetrain with regenerative braking.  I have a couple of questions:

We are looking at running the system at 1000psi and at full speed would be operating around 3gpm.  One of the goals is to be able to shut off the pump and run the car (which in this case is going to be a small go kart) for a period of time (shooting for around 1 minute or so of medium speed driving, so around 1.5-2 gpm flow at most).  This means I need at least 2, probably closer to 3 gallon capacity hydraulic accumulator. 

Does anyone know where I can obtain one or more good hydraulic accumulators for a good price (We have a budget of $1500 for the whole project and the motors, pump, control valves, and fittings will eat into that)? 

Also, does anyone have any in depth hydraulic experience that would be willing to give me and my team some assistance with designing accumulator charging and control system?

Additionally, right now we are looking at using a gear motor/pump for the wheel drive, as it is reversible and can operate as a motor and pump.  However, this gives us a fixed displacement, so we cannot vary our torque to operate more efficiently.  Is there a variable displacement hydraulic motor that works as a pump and is reversible?  And how much money would we be talking if such a thing exists off the shelf?

Thanks

Hurst
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Russ-neia Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2011 at 8:33pm
Look for old accumulators on Gleaner or other makes of combines for header flotation.  Not sure if the displacement will be enough, but they are large.  Another source would be auto-reset moldboard plows.

As far as a motor/pump - would the reel drive pump (variable displacement with electrically controlled swashplate) from a Gleaner 300 series grain header work?  Not sure if they can be reversed, though.
The innovators offer what others will imitate.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2011 at 8:48pm
I didn't think about the headers on combines.  I had seen them on the plows.  Right now I found a good 10 Liter accumulator on evilbay for 225+100 shipping, which would be the right size, but it a good chunk of our budget.  I'll have to look into the reel drive pumps.  That would be pretty nice to have the electrically controlled swash plate, as that would allow us to better tie it into a simple control system for the setup.  If it can't work for the drive motor, it may be the cat's meow for the drive pump if it's not too big...

Hurst
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Coke-in-MN Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2011 at 8:58pm
A radial or axial piston pump will give you directional rotation at the same volume in either direction. For brakeing the use of a variable reliev valve will give you that by controlling the flow from the piston pump.
 We replaced a 200 ft pound magnetic clutch we used for brakeing a tension roller with a vickers piston pump, using a variable spool relief valve for the adjustment of tension, using a 10 gallon tank the heat disipated from fluid to ambient temp of room and life of unit was 5 years until pump repair compaired to 3 month rebuild on magnetic clutch-brake.
 A gear pump has a loss of about 15% or more efficency where the piston pump is less. We used a fixed displacement pump with a set angle of swash plate . by going to a power supplied from a variable swash plate the speed control could be obtained easily in drive power and speed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote james6600 Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2011 at 9:40pm
    Put a check valve after pump then the accumulator after that, your accumulator will have to have a large nitrogen reservoir to offset pressure loss as fluid is used. There are other ways but the price rises quickly, as for finding parts check with the iron recycle centers in your area that deal with the local factories. They sell their old machines for scrap and during tax time throw alot of stuff away out of inventory. If you know any one who works at a factory they can probably get what you want for scrap price or less, most all factories have a junk yard of old machines laying somewhere when it gets so full they call the scrap buyer to pick it up. You will have a better chance at smaller mom & pop shops as they will be more willing to help you than say the big three auto makers. Foundries and stamping facilities any place that has presses will have a full range of valves servos and accumulators, also hydraulics seem to go cheap on ebay when they dont know the application of the part, I bought a brand new eaton power steering pump for my wd45 for $10 (char lynn system).  hope that helps you.  James
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 8:52am
Coke, I had a quick question about the axial piston pumps.  We want the drive motor for the wheels to also be able to act as a pump during braking and it would be nice if it would work in both directions (so the vehicle could reverse and move forward).  Would this type of pump generally be capable of performing such a task (working as both a driven hydraulic pump and a driving hydraulic motor)?  If so, do they exist in something that would be around .2 cu in/rev (looking for around 2-3 gpm at full speed at 1000 psi, would be about half that if we upped the pressure to 2000 psi, as we are aiming for using a 2hp electric motor for demonstration as that closely matches the go-kart's original 3 hp gas engine's output)?  Russ' idea about the reel pump may be about the right size, but I would venture to guess it may be a bit bigger, like around 4 or 5 gpm at rated speed? But, that wouldn't necessarily be a huge problem, just operate at slower speeds and change the gearing.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote TimNearFortWorth Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 9:10am
Hurst,
Search Hydraulic Closing Unit on the web by searching Oilfield Service/Rental companies.
Then you can research manufacturers of the units as the service companies buy-out the units they use on the well sites for hydraulic valve and blowout preventer operations.
These units are required to have multiple operating capacity without the use of the electric or diesel driven pump that provides the required 1500-3000 psi operating pressure, in-case all means of power is lost during hydraulic operation; think blow-out of a well and this backup feature is mandatory.
Backup pressure is obtained by precharge of the volume bottle via a bladder which is typically N2 charged and lasts for a number of years. Bladder is inside the accumulator bottles and allows the stored hydraulic fluids to be pressurized without constant pump pressure applied as normal. They are fair size as we require approximately 20-30 gallon "bottles" x 4, 6 or 8, depending on the number of applied functions required.
We can typically operate 2-3 functions open/close if the N2 bottles were properly maintained and we are cycling through 75-100' of 1.00" hoses.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gerald J. Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 9:41am
Down load the hydraulics chapters of the Baum Hydraulics Catalog. They have a wide selection. www.baumhydraulics.com and some tutorials. Look at Burden's Surplus Center for interesting hardware too, www.surpluscenter.com. A surplus 5 or 6" cylinder pushing on a spring might make a hydraulic reservoir too.

Most hydraulic motors will work as a pump, the limits are often in the shaft seals. A motor that's reversible is the first step to being useful as a pump. Gear pumps/motors are most common but aren't variable flow for a given shaft speed. You have to be careful reversing the power flow (motor to pump) in any variable flow device, if you change to a pump but have it set for very small or very large displacement it may develop piston forces beyond survival.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orange Blood Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 9:42am
I have some  questions?
 
In order to get enough stored energy, you will have to be braking for some time?
The braking action will be greatest when you are trying to store the highest pressure, this will occur at the end of the braking cycle, when you have little momentum left to do any work?
You could use two or three or more gleaner accumulators to offset there size.
 
But what about weight, the heavier it is the better energy to store pressure, but the more will be required to get it rolling again.  Seems like a loosing battle?
 
As for the varable displacement pump/motor, the vikers eaton style on the 7000 series allis, can be made to work both ways, it would be a challange, but could be done.  There are motors like these on genie manlifts, that esetually do the same thing, and are nearly ready to go.  You just have to be able to reverse the swash plate.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 2:27pm
The main idea for the braking system is to just recover as much energy as possible and store it, then turn around and use it to help accelerate the gokart from a stop.  We are not planning on weighing the cart down.  For a fixed displacement wheel motor, the braking would be easy at first and most aggressive at the end when the pressure in the accumulator builds up, but we are also planning on holding the accumulator at a set pressure and allowing the hydraulic motor to reverse and charge the accumulator further, thus there will be even more pressure available upon start-up.  So for example, the accumulator may remain charged at 950 psi while the vehicle is driving, then as the flow path to the wheel motor is reversed through a reversing valve so it will start acting as a pump charging the accumulator further to say, 1500 psi, as the vehicle decelerates from the hydraulic motor acting as a pump.  It's a little confusing to put into words without drawing some things and we are still working on quite a few fine details.  Ideally, the system would have a variable displacement pump and wheel motor (that could also act as a pump), would be controlled in a manner that the wheel motor's displacement would vary depending on the accumulator pressure and the desired braking power when the vehicle is being braked.  However, that is a little bit out of the scope of our project, mainly in terms of time and money (and then there's the electrical control system that would have to be built to control and modulate the swash plates of both the variable driven pump and the wheel motor).  If I could find a good candidate for a wheel motor/pump that is priced so it wouldn't kill our budget and so we can make use of it, it would be something I'd like to try, although our controls would be much more crude than what one would expect to see in production, but it would work great for demonstrating varying braking power and drive power from a constant pressure source (the accumulator being charged by a variable displacement pressure-compensated vane pump or piston pump).  Kind of rambled on there, but hopefully that gives a little more insight.  Please feel free to post any ideas or any more possible places / donor machines I could find these parts.  My team and I are all for scrounging salvage yards if we can find machine models with suitable parts.  

Thanks for all the help and ideas!  I have passed the link on to my group members so they can follow and keep up with your guys' feedback and ideas!

Hurst
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Post Options Post Options   Thanks (0) Thanks(0)   Quote thomas davison Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 3:00pm
     Great project Hurst.  I am glad that there are intelligent young people like you who are interested in these kind of innovative projects.  However, I question wheither or not that you will generate enough power from braking to accumulate any meaningful amount of energy. If you think of how little you use your brakes, excetp in city traffic. I think that you will find that only a small amount of braking is done, and therefore only a small amount of energy would be generated.  A few mouintains in the Appalachians might be an exception.  Never the less, an interesting project and the best of luck to you with it.  Let us know the final results.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Coke-in-MN Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 3:00pm
Yes either a axial or radial piston pump will work for both drive and brake, space limitations make up the difference . I believe they both varry in the sizes you are looking for . In most of these pumps a charge pump is used to keep system full and also a case drain or fill is used to bleed excess air or oil that bypasses within the pump back to resivour.
 Your accumulator volume and pressure would also need to be bled off and controlled as if accumulator fills to capacity a bypass would be needed to hold or divert flow.
 Another unit one could look at is the trans-axle from hydrostat lawn mower as they use a piston pump within to transmit power. My ZT mower uses two units more or less with one axle blanked off on each so only one side drives. so fwd/rev unit is built into unit by variable swash plate. also speed is controlled by pump output and one can reverse one pump to countersteer.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote B26240 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 4:11pm
Great project Hurst!!! I also want to encourage you in this good to see young people interested in things like this ! I'm just a simple old guy who feels prowd just to make a loader go up and down-- I have learned from reading the posts such as a gear pump losing 15% of its eficency now can see why they go for the more expencive piston types good luck!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kcgrain Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 4:39pm
To bad you didnt start this about 3 months ago I had a Mack firetruck here that we disassembled for the motor, tranny, and service box it had a ladder on it originally and had a HUGE accumulater on it for the hydraulic system that controlled the ladder, you could have had it for free. If you look in slavage yards that have garbage, electric co digger derecks and fire trucks they may have an accumulator on them. I find your system interesting, but hyraulics are not the greatest system in place for motovating a vehicle, they are inefficient transfer of power and generate heat, which is wasted energy.Also the more valves, couplings, bends, etc rob more and more power, unlike electricity. Also 2-3 hp in a gas engine would probably require 5-6hp hydraulic. But if thats your classes project I guess that is the stuff you will be learning from your experiment, and I wish you the best of luck, to bad we are so far away have alot of hydraulic junk that we have removed from various equipment that you could have maybe used. Your $1500 budget is going to require alot of donations hydraulic components are not cheap, even hosing and ends can quickly gobble up a couple of hundred of your budget.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 4:47pm
I should have added in my earlier description, the regenerative braking will be focused for improving fuel economy in city driving mainly.  The idea is to show this is a feasible alternative to an electric-hybrid vehicle, especially in larger vehicles, as batteries become very costly and bulky, whereas hydraulic power can be scaled up in power without much increase in volume using higher pressure components.  The idea came from an article I read about Ford testing a similar system in their F150s.  

Here is a copy of the literature on the charging pump I am planning to use for the system (the one that will be driven by the electric or gas motor):


Basically, the plan is to make a closed center hydraulic system that will charge the accumulator to the "standby/operating" pressure, which is what the system would see under normal driving, and then have the hydraulic motor fed at a pressure equal to or greater than this standby/operating pressure (only would be greater when regenerative braking has been used to slow the vehicle) from the accumulator.  If I used a fixed displacement wheel motor, it will be easy to control the speed with a simple hydraulic "throttling" valve, but I will be losing out on efficiency, as I won't be effectively using the pressure from the accumulator.  Thus, if I could tie in together this flow adjusting throttling valve from the accumulator with a variable displacement motor, I could vary the displacement of the hydraulic motor so that it was operating efficiently (just enough flow from the throttling valve at the system pressure to generate the speed and torque needed).  So it's similar to a zero turn hydrostat mower's controls in some aspects, but they also use fixed displacement wheel motors with variable displacement pumps.  The way I want to break it down would be 2 basic sub systems:

1) charging section from engine powered pump
2) drive/regenerative charging section from wheel motors

The other idea is to be able to build a system that could possibly run with the engine shut off for a short time period, thus allowing the engine to run at a more optimal speed and load, then be shut off.  This would also benefit from a variable displacement motor, as it would allow me to increase flow as pressure drops and change the swash plate angle with this increase in flow so the total amount of work (function of pressure and flow) remains constant from the wheel motor even as pressure is bled off from the accumulator.  

I looked into a craftsman lawnmower transaxle, but the pumps and fluid passages were all cast/machined into the axle housing, so there wasn't a way to separate them from the axle assembly nor could I change the fluid path so I could utilize them with my accumulator...  But I am still on the look.  

I am also looking at these hydrostatic pumps like off of a zero turn as Coke was mentioning to use as a variable displacement hydraulic motor, but I don't know if they will work both ways, as I am not sure if they are vane or piston pumps:



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kcgrain Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 4:49pm
A though just came to me about your drive, rather than have a hyd drive wheel why dont you get yourself a hydrosatic tranny off of a garden tractor, even a craftsman can be bought cheap on craigslist, now you just need a drive motor, which could be a electric 12-24v run on batteries, than hook your brakes up to a generator so braking would create electric power stored in a battery to run the 24 or 12v electric motor .This would eleminate the accumulator, would take care of your forward and reverse, and could be put together cheap, and you rig a alt. to the braking system wouldnt be hard. Just a thought. Could also hook in a small hydraulic motor to the return pressure coming from the hydro to capture any left over energy and hook another alt/gen to it and create a liitle more electic charge for the battery.This would be way more efficient use of hyd drive sytstem than a bunch of comlplicated valving.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 4:50pm
Here is the article about the F150 that got me started on the whole idea for the project in case anyone is interested in reading:


Apparently Ford and Eaton got together a few years ago and designed a prototype f550 with a similar sytem and UPS has developed a test fleet, although I am not sure what ever came of either of those prototypes off the top of my head.  Best I could tell was UPS was still using their trucks, but not sure what happened to the f550...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 4:55pm
We had thought about using an electrical/hydraulic mix, but we had trouble coming up with advantages of it over the popular electric hybrid to present to our adviser and teaching staff, so we decided the use of an accumulator would be something more novel and could provide a size and environmental benefit over batteries, along with the ability to be charged somewhat quickly, where in an electrical hybrid, that requires some sort of super-capacitor, as charging over a certain rate will fry/reduce the life of the batteries.  We also considered pneumatic systems, but that was going to be $$$ and I felt like it would be difficult to store that much compressed air in a car safely given what we had available to use (I didn't want to blow anyone up with 10,000+ psi of air...)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kcgrain Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 4:58pm
Fords protoype was probably funded by a multi million dollar grant from the GOV to see what could be learned about hydraulic drives. The flaw in my eyes is the high pressure , the higher the pressures the more energy consumed to peak the hydraulics to store in a accumulator. I guess your expierementing will determine if it actually works. Again best of luck. Interesting though I will say that.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gerald J. Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 5:09pm
Baum Hydraulics has had zero turn mower drive units for decent prices. They do brake, though I doubt they store much energy in the process.

Whether braking will store energy depends a lot on the driver. If the driver zooms up to the stop sign and stands on the brakes, you can recover considerable kinetic energy. If, like me, the driver anticipates the stop and backs off on power and mostly lets friction to the stopping, you won't recover significant kinetic energy and my brakes last a long time.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote wjohn Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2011 at 5:25pm
Call up some companies! Some of them may be willing to donate parts or give you a good discount. Our 1/4 scale tractor pulling club has many components donated to us or discounted when we build each year's tractor. We did a hydro FWA tractor a couple years back that performed very well, but it sure didn't have regenerative braking. Good luck and keep us updated.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stan R Quote  Post ReplyReply Direct Link To This Post Posted: 12 Nov 2011 at 9:38pm
Did you work out calculations on the theoretical energy that you can store during braking, size of accumulator needed, efficiency of storing this kinetic energy (minus friction losses such as bearings,fluid friction loss, etc.)? Once you get that done you can then go from there with sizing the mechanical equipment.
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First, I assume you (or your prof) knows that the inefficiency of hydraulic systems (especially at low pressures) is hard to cover up with regenerative braking and that this is a " learning exercise."

As far as a piston pump and motor (much more efficient than a gear or gerotor pump), you might do some searching for and looking at a hydrostatic garden tractor that is being parted out and buy the drive unit.  Ebay has them for for under $500-------but buyer beware as they may be worn out.  It may also be hard to get an accumulator plumbed in between the pump and drive portions of the hydrostatic.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveKamp Quote  Post ReplyReply Direct Link To This Post Posted: 13 Nov 2011 at 10:44am
Hi Hurst!

I can help you with sorting out calculations for energy recovery- it's all basic thermodynamics, and I had an entire segment dedicated to this in each railroad braking/propulsion class I taught, regardless of wether the braking/propulsion system was utilizing electric propulsion dynamic braking, pneumatic friction, or hydraulic friction braking.

For an accumulator, the best suggestion I have, is to build it.  You'll need storage vessels suitable and safe in excess of your target pressures... I suggest you find a few big Argon or O2 cylinders, and re-purpose those for 'bladderless' function, and until you have had the system thoroughly inspected and blessed, run it only at below Kilopressure ratings.

You'll have very high efficiency losses due to plumbing restrictions, so make it flow very, very well.

Your drive units... keep in mind that under ANY common hydrostatic systems, that they're designed to be FULLY HYDROSTATIC... meaning, the prime mover is ALWAYS operating... and they self-cool by benefit of the nonrestricted return-flow.  You don't want thermal losses there, so you're not really a 'hydrostatic' system.  You CAN, however, utilize the variable flow pump/drive scheme to get what YOU need... it will take some doing.  Drop me a direct Email if you want long-form answers, and I'll pull whatever data, etc., I can to help you out.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joe(TX) Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2011 at 5:49pm
Surplus center normaly has accumalators.
Womack Machine Supply has some very good books on hydraulic design.
Full Hydrostatic does not give regenerative bracking. Regenerative means it is storing some of the braking energy. Hydrostatics just block the flow in braking and gernerate heat.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveKamp Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2011 at 12:49am
What Hurst is intending to do, is modify a variable-ratio device so that it can be utilized both as a variable-ratio drive unit, and when braking demand is needed, use it as a variable-ratio pump, so that kinetic energy of his kart can be recovered by pushing fluid back into the accumulator.  A variable-ratio hydrostatic pump is essentially already there, as you have two ports and a swashplate, it just needs to be appropriately coupled.

The prime mover need not be variable ratio... it can be started and stopped on-demand, and actually, if he uses clever valving, it can be started and stopped strictly off of accumulator pressure by virtue of some solenoid valves... when pressure falls below a certain point, one set of solenoid valves pushes accumulator pressure through the pump and whips the motor on, and once running, the valves reverse flow direction for the motor to pressurize the accumulator... and once at the setpoint, drop the valves (to tandem center) and kill ignition.  Hand-start would provide the initial pressurization.  (I would probably run a secondary accumulator dedicated to kicking the motor over, so that a 'kickon' operation doesn't sap from the main accumulator and cause the kart to 'buck'...

Once the accumulator is charged, the drive system would essentially be stand-alone mechanical linkage to swashplate, but I think what I would do (in the interest of efficiency) is fit the driveline with some sort of overruning clutch, so that the kart can coast, hence, conserve bottled energy.

Fun project.   Fair challenge!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KGood Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2011 at 7:17am

We run accumulators on our diecast machines to get speed on cylinders. They have a piston to separate oil and gas not bladder we use nitrogen as gas most are precharged 2/3 of operating pressure with gas unless there is no holding tank it's usually 1/2 precharge our operating press. is around 1500. Iam just afraid a 5 gallon acc. of ours is to heavy for a gokart there is a 21/2 or 3 gallon laying around here. The garden tractor rearend is a good Idea because most variable dis.pumps aren't going to have a manual lever for the squash plate to control displacement and direction. Something that is neat you might look up is intensifiers we use them to turn 1500psi into 4000psi with no more energy but less volume is abtained on the high pressure side. could be made to give you like a shot off nitro in take off or used to get a little extra pressure charge on accum. side.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote D17JIM Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2011 at 7:36am
Wjohn's suggestion on getting donations was one I thought of as I read this.  Great learning experience and many times companies want to donate to young people Working on inventive ideas. So while someone scrounges junk yards someone else can do some calling.  Best of luck on  the project !!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2011 at 8:26am
Thanks Jim!  We actually called up White Drive Products and they said they would send us a variable displacement axial piston hydraulic pump for the project, so that saves us quite a bit of money.

Hurst
1979 Allis Chalmers 7000
5800 Hours
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gerald J. Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2011 at 9:22pm
Stumbled on an interesting book in a box of mine today. Titled "Mechanical, Thermal, and Chemical Storage of Energy" edited by V. W. Hassenzahl, Benchmark Papers on Energy V. 9.LOC TJ165.M4.

The most interesting article is by Bruno V. Nordberg of Milwaukee, titled "The Compressed Air System of the Anaconda Copper Mining Co., Butte, MT" from Amercican Inst. Min. Eng. Trans, V 46: pages 826-888 (1913).

That article reminds me that you are really storing your recovered energy as compressed air and if you don't also hold the heat of compression to be applied during expansion, you will lose much energy.

The book has a section on flywheels, another on gravity storage, another on alternative fuels (chemical storage), and one on thermal energy storage. Copyright 1981 and is biased towards methanol instead of ethanol because those days methanol was CHEAP.

Gerald J.
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