Author Topic: Dynamometer - a friend questioned and i have no idea.  (Read 2835 times)

Offline NeoTech

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Dynamometer - a friend questioned and i have no idea.
« on: September 10, 2015, 01:33:40 PM »
Dynamometers is a interesting subject.. So i started to pondering this a couple of days ago. And i could not wrap my head around it really..

But here is my theory anyway.. And this is for a inertia brake simulator type dynamometer.

Let us say we a have a high volume high rpm gear pump connected to the output shaft of an engine/transmission. It would be free to rotate with the motor so a 1m torque arm would be attached to the pump, that inturn connects to a loadcell so the arm is pulling on the loadcell.

Now to take a sweep measurement of this, you would i imagine read a some form of rpm signal, and you do that like 30 or 60 times a second. And control the braking action on the gearpump by basicly making it  harder to pump oil through an orifice. I imagine this could be hooked into a micro controller that reads the torque and rpm sensor and adjusts the brake by means of actuating a stepper motor or something and then just read the signal from a serial connection on a pc.


Am i completely off my rockers?
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/

Offline redshift

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Re: Dynamometer - a friend questioned and i have no idea.
« Reply #1 on: September 10, 2015, 02:19:13 PM »
Neo, show this to your friend.  http://dtec.net.au/Inertia%20Dyno%20Design%20Guide.htm
What engine does he want to test? Let me know I maybe able to help.
Dave

Offline NeoTech

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Re: Dynamometer - a friend questioned and i have no idea.
« Reply #2 on: September 10, 2015, 03:36:37 PM »
Ah well we build drag racing cars basicly. So it would be Bigblock chevy V8 engines, at around 1000-1200hp and 900-1400lbs/ft.
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/

Offline redshift

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Re: Dynamometer - a friend questioned and i have no idea.
« Reply #3 on: September 10, 2015, 03:53:35 PM »
Mmmm, a little different to the 6 - 30 bhp Kart engines I pay with. So I cant be of help but would be very interested in the solution you come up with. Eddy current or water brake? Water brake looks more like a possible solution at that level of power. Have you any pics of the vehicle that the engine is used in?
Dave

Offline NeoTech

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Re: Dynamometer - a friend questioned and i have no idea.
« Reply #4 on: September 10, 2015, 07:21:19 PM »
That motor sits in this car atm; http://www.roughedge.se/blogg/wp-content/uploads/2014/06/20140619-184902-67742825.jpg

And are awaiting fuel injection and a new rear axle cuz i shot the 12 bolt gm axle to hell this summer..  *wiiih* And with the multipoint fuel injection i hope to find the last bit of power out of it.

I am looking at waterbrake solutions now, it all seems like a damn hassle tho, how would one control the inflow of water in relation to the RPM and at the same time have it to be exact enough to retard the motor enough for a controlled rpm curve...  The best would be to find 2 telma 1700lbs, 6000rpm eddy current brakes froma lorry.

The benefits of water or eddy current brakes tho is that you can self learn the engine efi under simulated load and create the complete map without getting on the road at all.
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/

Offline bhowden

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Re: Dynamometer - a friend questioned and i have no idea.
« Reply #5 on: September 12, 2015, 06:11:19 PM »
That level of hp might be out of range for this but many years ago (40 ish) I saw a dyno somebody had made out of a torque converter.  The torque converter mated up to the engine and the other side was attached to a lever resting on a scale.  They had tapped the torque converter with fittings and ran the oil out through a large cooler and controlled the amount of oil let into the converter to control how much resistance was applied to the motor.  Do any really large trucks use automatic transmissions now?

Another thought might be to have strain gauges mounted in the motor mounts so you could get a data log of every run and convert that to hp.

Brian

Offline NeoTech

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Re: Dynamometer - a friend questioned and i have no idea.
« Reply #6 on: September 13, 2015, 02:37:31 AM »
Well all bench brakes use some sort of strain gauge and an arm like you said there.
Usually the brake is mounted in pillow blocks allowing it to rotate but are stopped on a gauge..

The HP is then calculated by doing (rpm*torque)/5252 - and you will be in the correct ballpark.
For a sweep curve, you would read the rpm, and control the inflow of braking media (water or electricity if using a telma) and then make sure the engine under full load can't accelerate more than 300rpm / s.

That would make several datapoints availabe by rpm and torque..  You would need something around 200hz in polling rate for this, and an algorithm that sorts out all the crud or averages the reading during each second. Its here i have decided to use an FPGA from Xilinx - cuz everything can be connected to it, its blazing fast and you can just connect an USB to it for dataread out, stream or buffer. =)
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/

Offline NeoTech

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Re: Dynamometer - a friend questioned and i have no idea.
« Reply #7 on: September 13, 2015, 02:41:35 AM »
The stator housing would need to look something like this. with squar vanes, and a return "area" for the medium, the impeller would also be of the square wanes typ but with no center opening so it pushes the water outwards and it will hit the vanes, return to the center and go out again.. in flow on both sides and an exit at the bottom of the stator housing.
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/