How to make a run on an old braked dyno.

[0PETER0]

Hello,

I am having problems understanding how one could make a dyno pull from low engine rpm to high engine rpm at full throttle on an old braked(telma) chassis dynamometer.

What should be done to the brake when making such a pull.

Could someone give a hint?

 

[GregLocock]

slowly release the brake

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[0PETER0]

If I understand you well I should put the brake at its maximum (meaning smallest km/hour).
Go with the car to full throttle and then release the brake (setting to a higher km/hour) in steps until fully released.
I suppose at each step I should give the dynamometer the time to reach it's setpoint and then read the it's hp at the wheels.

In this way I should then get a hp curve that normally increases as I release the brake (setting for a higher km/hour).

Is this correct?

 

[GregLocock]

Yes, that should work.

I haven't used that sort of dyno. The one I've used most recently is electrically controlled, so I can either run in speed control mode or force controlled. In the latter you just sit at cruise and then wind the force up until you have full throttle at the same speed, and then play with it from there.

However I don't use this dyno for power measurements, there may be better approaches.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

Normally with a manually operated water brake dyno, you gradually apply a little power then gradually apply brake and power to control speed until you have full power. you then adjust the brake to give a steady rpm at a desired rpm. Then adjust brake to get other rpm readings.

This takes some judgement, like throttle and clutch control when doing a hill start.

Regards

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.

 

[Bribyk]

You need the most brake when the engine is making the most torque (and vice versa) to get a smooth controlled pull. A water brake is similar, you increase water in the brake to increase resistance as torque increases.

 

[SomptingGuy]

All this reminds me of my "Engine Running Course" as a new graduate. Smoke, smells, water, steam, dynos, listening for the onset of knock. Winding the CR up and down. Every powertrain engineer needs such a course.

 

[Bribyk]

My experiences were more like the smell of fear-sweat, due to unknown engine condition, untuned maps and untested subsystems, and the sounds of a muffler dislodging itself at 14,000 rpm WOT.

Great learning experience though...

 

[Warpspeed]

I am right in the middle of building the control system for such a chassis dyno myself at this very moment.

My approach is to monitor the roller speed and compare that with a set reference speed, and use any resulting error to drive a dc current through the windings of the Telma eddy current retarder.

If the rollers are running slow, there will be no retarding action at all, so the vehicle can be brought up to the required speed by just opening the throttle. As soon as the set speed is reached, the Telma will then provide enough torque resistance to hold the set roller speed. As you open the throttle further, the roller speed remains constant.

That way you can map your fuel and ignition at a range of throttle openings at any desired fixed engine rpm.

To do a sweep test, as you are suggesting, just cause the set target speed reference to ramp upwards at a suitable rate. The vehicle will follow that rate of speed increase.

You can then go wide open throttle, and the speed will increase at whatever speed the reference speed increases. The Telma retarder will hold the engine to a constant rate of acceleration, whatever shape the torque curve happens to be.