Chassis Dynamometer / Rolling Road Dynamometer




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  1. #1
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    Default Chassis Dynamometer / Rolling Road Dynamometer

    My understanding is that the actual DynamoMeter machine can only measure 2 things. Speed of the drum/rollers (the wheels on the rollers) and the Rotational Force (torque). The rest is calculated.

    .

    Now my mind is pondering ...

    How does the Dyno know the engine revs. How does the Dyno know if you are in 1st (e.g. 3.55:1) or in 5th (e.g. 0.86:1) Do they select a gear with (what the operator think is) a 1:1 ratio and read the values off the engine tachometer (rev counter) ? Does he punch these values into the device as they go through the rev range.

    What about a vehicle with an auto transmission. I understand that you can only get maximum engine output throughout the rev range under wide open throttle (WOT). (You see were I'm going with this.) You will only be able to get values for the lower rev range in the lowest gear. Now it goes through the gears (WOT) and somewhere it will get to top gear at almost maximum revs. Now we are not in a gear with a 1:1 ratio.

    .

    If the Dyno only measure the physical speed on the rollers and the force applied, where does all the other figures come from.

    (Lets not discuss the altitude, temperature, flywheel and all the other corrections they do)

    .
    Last edited by KobusDJ; 2018/10/10 at 10:09 AM.
    Kobus

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  2. #2
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    Default Re: Chassis Dynamometer / Rolling Road Dynamometer

    Most dyno runs are done in one gear only as far as I know.

    And I think the dyno operator needs to identify the starting revs so that the dyno can understand the starting point and calculate from that.
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    Default Re: Chassis Dynamometer / Rolling Road Dynamometer

    Quote Originally Posted by jelo View Post
    Most dyno runs are done in one gear only as far as I know.
    Yes, that I know... but what gear. Highest or lowest, or somewhere in between. How can they calculate (accurately) the engine torque if they do not know the gear ratio. There will be a huge difference between a 0.9:1 and a 1.1:1 ratio.

    What about the auto at WOT ?
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    Default Re: Chassis Dynamometer / Rolling Road Dynamometer

    Quote Originally Posted by KobusDJ View Post
    Yes, that I know... but what gear. Highest or lowest, or somewhere in between. How can they calculate (accurately) the engine torque if they do not know the gear ratio. There will be a huge difference between a 0.9:1 and a 1.1:1 ratio.

    What about the auto at WOT ?
    Surely 4th gear as this is usually 1:1?
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    Default Re: Chassis Dynamometer / Rolling Road Dynamometer

    Take a look here and here.
    Cheers,
    John

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    Default Re: Chassis Dynamometer / Rolling Road Dynamometer

    The links are a lot to read in and take in.

    In a more simple explanation, a vehicles ecu or aftermarket ecu is connected to a pc or laptop, it gets rpm and speed etc from there plus any other info needed which the tuner/tester completes if necessary. Normally the tuner or tester selects 3rd gear, to measure the torque and horsepower, the tuner/tester administers load to the drums, in simple terms, breaking the drums, the software gets all the information from the equipment and inputs from tuner/tester and calculates the power the vehicle makes by overcoming the load/breaking of the drums.

    More powerful vehicles are tested in 4th gear because the breaking of the drum causes the wheels to spin/slip on the rollers because the force overcomes the traction on the drums and in turn the dynameter does not record the accurate power output of the vehicle. In many cases a higher gear is selected and weight applied to try and overcome the traction issues when load is applied.

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