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Flywheel Design and Sizing Calculation Example 1 of 4 http://blog.mechguru.com/machine-design/flywheel-design-calculation-... Home MechGuru Categories Engineering design Manufacturing Engineering Fluid Engineering Engineering Calculator Material Engineering How it Works Thermal Engineering Engineering Math Engineering Softwares Vehicle Design Applied Math Electronics Advertise « Kinetic Energy Recovery System – How it Works Anti Lock Braking system vs Electronic Stability Program – Working » Print this Post Flywheel Design Calculation – Simplified What is a flywheel? A flywheel used in machines acts as a reservoir to store energy when the supply of energy is excess and the same is released when the requirement arises i.e. its primary function is to sort out variations in the speed of a shaft which are caused due to torque fluctuations. In case of I.C engines, energy is developed during power stroke and the engine is to run the whole cycle from the power generated from this stroke. When the flywheel absorbs energy, its speed goes on increasing and when it releases the acquired energy, it decreases. Flywheel Design Image source: Wiki Classification of fly wheel Based on the mode of operation, two kinds of flywheel designs are there: 1. Disc type – Suited for smaller sized engines/machines 2. Arm type – Suited for larger sized engines/machines Application of flywheels 1. IC engine 2. Sheet metals press 3. Kinetic energy recovery system (KERS) Fundamental Principles of Flywheel Design and Sizing Calculations Firstly, calculate the mass moment of inertia required by the flywheel to smoothing out the fluctuation/variations of kinetic energy in the system. This will be discussed in this article. Secondly, calculate the geometry/dimensions of the flywheel based on the calculated mass moment of inertia and material properties. This will be covered in another article. Design steps and formulas Step-1: Coefficient of fluctuation calculation Input required: Maximum & minimum speed Flywheel inertia/size depends upon the fluctuations in speed. The difference between maximum & minimum speeds during a cycle is called maximum fluctuation of speed. 11/11/2015 7:07 µµ Flywheel Design and Sizing Calculation Example 2 of 4 http://blog.mechguru.com/machine-design/flywheel-design-calculation-... The ratio between maximum fluctuations of speed to mean speed is called coefficient of fluctuation of speed (Cs). Consider, Ѡ max =Max. Speed during the cycle Ѡmin = Min. speed during the cycle Ѡmean =Mean speed = (Ѡ max + Ѡ min) /2…….eq.1 Therefore, Coefficient of Fluctuation of speed, Cs = [2*(Ѡmax–Ѡmin)]/[Ѡmax+Ѡmin]…….eq.2 Note: The smaller the Cs value, larger the flywheel, but smoother the operation. Step-2: Mass moment of inertia calculation Input required: kinetic energy of the system The general equation of kinetic energy for a flywheel system is given as, Ke = 0.5* I* (Ѡmax2 – Ѡmin2) ………..eq.3 Rewriting eq.3, we get Ke = 0.5 I (Ѡmax + Ѡmin) (Ѡmax – Ѡmin)…………eq.4 Substituting eq.1 & 2 in eq.4, we get I = Ke / Cs Ѡmean2……………..eq.5 eq.5 is used to obtain necessary flywheel inertia corresponding to variations in speed. We will try out a simplified problem on flywheel sizing and calculate the required moment of inertia. Regarding units ( Important ): Ke – N.m Ѡ – rad/sec I – Kg.m2 Example: Let us consider a punching machine driven by 3KW, 1000RPM powered motor with a gear set of 5:1 and a stroke length of 250mm. Rated capacity of the punching machine is 22KN. Consider coeff. of fluctuation of speed, Cs = 0.02 (Value to be considered by the designer) Since it is a small machine, diameter of the flywheel should be as small as possible. Consider 500mm to be the max size of the flywheel dia. Calculate the mass moment of inertia required for the flywheel of the punching press machine. Solution: Step-1: Coefficient of fluctuation (Cs) calculation The value is given as, Cs=0.02 Step-2: Mass moment of inertia (I) calculation Input required: kinetic energy of the system- to be calculated Kinetic energy of the system (Ke) calculation: Work done, W = 22*10^3*0.25*0.15 (Assume rated load delivered during 15% of power stroke) Therefore, W = 825Nm Thus, Energy absorbed is 825Nm. Now, let us calculate the mean torque acting on the shaft, Tmean = 3*10^3 / 2*π*(1000/60) Therefore, Tmean = 28.66Nm Work done per cycle is (Energy supplied), Wc= 2π*28.66*5 = 900 Nm Therefore, Kinetic energy of the system is, 11/11/2015 7:07 µµ Flywheel Design and Sizing Calculation Example 3 of 4 http://blog.mechguru.com/machine-design/flywheel-design-calculation-... Ke=W–Wc*0.08 (Energy absorbed – Energy supplied* factor for loss) Ke = 825 – 900 *0.08 (0.08 – factor for losses. Again dependent on the designer) Ke = 753Nm Therefore, mass moment of inertia as per eq.5 is I = 753 / 0.02 (2π*1000/60)2 I = 3.43 Kg.m2 Hence, the flywheel sizing/design calculation for the above example shows that the required mass moment of inertia for this application should be = 3.43 Kg.m2. Cheapest Stock Photos Professional Photos from $0.15. Low Regular Prices. About Gopinath K Gopinath is a Design Engineer by profession and a writer by passion. One who always wanted to share the knowledge gained of both technical and non-technical aspects. 8 4 3 Like this: Be the first to like this. Related Leave a Reply Anouncement Science or Engineering Graduate? Write for mechGuru Subscribe To get the latest post directly to your email box, Enter your email address: Recent Posts HPDC vs LPDC Friction welding vs Friction Stir welding 7 Important 3D Printing Technologies – You Must Know Automobile Traction Control System Basics and Application How Automobile Air Bag System Works? Why I-Section Beam is structurally better than same weight other sections? Micro vs Mild vs Full Hybrid Vehicle How Chocolates are Made How LCRV or LSPV Braking System Works How to calculate vehicle speed from engine RPM and vice versa The Challenges of New Eco-Friendly Tech – Are 11/11/2015 7:07 µµ Flywheel Design and Sizing Calculation Example 4 of 4 http://blog.mechguru.com/machine-design/flywheel-design-calculation-... Electric Cars Really That Green? 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