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Automotive Vehicle and Engine Simulink Model Engine rpm calculation

  1. May 26, 2016 #1
    Hello Everyone,

    I am designing Simulink model for HIL testing. Basic concept:
    Input: Throttle angle ----> Injection timing from that I have calculated requested torque (% of max torque)(chekced and correct)
    Real torque follows requested torque with delay. (long list of conditions depending on engine design and parameters)
    Total torque = Real torque - Internal friction torque (bmep = imep - tfmep)
    Now this is the toque I have at crankshaft.

    My question
    a) Is it correct approach if I integrate this torque and divide it by engine inertia to find engine angular speed. (Torque = Inertia*angular accelaration)?

    Consideration: If I do that it would mean that my engine rpm is independant on external load and only on torque request, which is obviously not the case.

    b) External loads are calculated using coast down coefficients and gearbox, differential ratio and transmission efficiency. I feel the correct approach would be to create a close loop and subtract external loads from torque transmitted by flywheel and then integrate it to find rpm.

    Any suggestions?

    Last edited: May 26, 2016
  2. jcsd
  3. May 27, 2016 #2

    jack action

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    Science Advisor
    Gold Member

    The angular acceleration will depend on the engine inertia as well as the inertia from any rotating mass connected to the crankshaft (considering gear ratios if any) and, if you move an object like a car for example, you need to consider the mass of the car that is also accelerating as well.

    The angular acceleration will also depend on the engine torque minus the reaction torque coming from external loads (again considering gear ratios if any, and drag & rolling resistance acting on a car, if any).
  4. May 30, 2016 #3
    Thank you for your reply. I have followed same approach. As a first step, results are quite okay. Only I have to model internal friction as a function of Toil, Poil and rpm in a way that my final result looks like rpm vs torque curve as seen in literature or from test bench data.
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