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parasitic losses

parasitic losses

parasitic losses

We are going to measure the parasitic losses in a drivetrain with an IC engine.
one of the topics is the loss due to belt driven pulleys.
I could measure torques at all the pulleys with rpm or velocity of the belt.
Are there any other methods I could use?

RE: parasitic losses

another: replace the cranknose pulley with a pulley mounted on an electric motor, and measure the torque required to drive the whole FEAD.

another: replace the cranknose pulley with a two-part one using a clutch mechanism between the parts.  Measure engine output with all the accessories, then disengage the clutch and measure the new output with the accessories disconnected.  Could switch off/on a few times if desired.


RE: parasitic losses

How accurate a measurement would you like?
How big is your budget?
Are you intending to measure torques on a running engine?

Mike Halloran
Pembroke Pines, FL, USA

RE: parasitic losses

Hello Mike H,

the measurements must be reasonably accurate. We are trying to find losses with an accuracy of 5-10 Watts. But for first judgement in the range of 100 Watts.
Our budget is not unlimited, but I believe it to be sufficient.
We can buy sensors (we have logging equipment) or lend them.
We have the possibility to make alterations and have the budget to do so.
All measurements have to be done on a running engine, mounted in the vehicle.

RE: parasitic losses

Hello ivymike,

We already thought of driving the complete fead for a first judgement. Switching on and of the auxilliairies is one of the possibilities we are concidering.
We do not have enough space to replace the crank pulley with a complete electric motor. We can however replace the main pulley with a pulley with a torque measurement device.
The signal from the torque measurement device can be transmitted wireless.
The engine will be hooked up to the gearbox, so we do not have the possibility to measure the output on that side.
We can measure fuel usage, but this doesn't give us an accurate measurement unless the measurement time is very long.

RE: parasitic losses

I've never had the budget for instrumented pulleys or other forms of insertion dynamometer.  Which is sort of what you need, one per pulley, in order to measure losses associated only with the belt.

To at least rough out the problem, I'd start by mounting one of the belt idlers on a load cell, and infer whaat I could from that.


Mike Halloran
Pembroke Pines, FL, USA

RE: parasitic losses


Getting a value for a typical engine's belt drive parasitic losses within 5-10W is probably a bit unrealistic. 10W would be less than 0.20% of the power being transferred thru even a small engine's accessory belt drive.  You can expect an efficiency of between 90% to 95% for an average accessory belt drive.

Most accessory belts are multi rib serpentine type installations that transfer power thru friction.  Even when these belt drives are operating under optimum conditions (ie. with no slippage), they can still have fairly high and varying hysteresis losses within the elastomeric belt carcass.  These losses likely vary widely from installation to installation, and also with load.  So to get a statistically relevant measurement, you would need to sample many drives under a range of conditions.

Here's a reference with an experimental approach:


Good luck.

RE: parasitic losses

Hi tbuelna,

I know 5-10W is insane and I do not intend to measure in that range. I already had some indication of what to expect, but your pdf is very welcome
We are looking in to the power lost or transmitted to the auxiliairies. We are builing an accurate Sankey diagram, and one of the losses is due to the efficiency of the belt.
But as you're saying, the efficiency varies with installation, tension and wear. But we do not know how much it can vary. Your pdf helps there. Any other publications about this topic?


RE: parasitic losses

Another method to consider would be to install encoders on each shaft and measure the rpm to determine slip and transducers to measure torque. The crankshaft pulley transducer may have to be dampened so the firing spikes do not create measurement spikes that could make the net measurements less accurate.

Ed Danzer

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