DYNAMICS AND FRICTION OF VALVE TRAINS

Transcription

1 WAYNE STATE UNIVERSITY CENTER FOR AUTOMOTIVE RESEARCH DYNAMICS AND FRICTION OF VALVE TRAINS BY DINU TARAZA, NAEIM A. HENEIN MIRCEA TEODORESCU, RADU CEAUSU WALTER BRYZIC ARC ANNUAL MEETING, MAY 25-26, 1999 UNIVERSITY OF MICHIGAN

2 DYNAMICS AND FRICTION OF VALVE TRAINS VALVE TRAINS are influencing: Engine performance by optimizing the gas exchange process Engine noise Engine friction losses GOALS: Increase flow areas controlled by the valves Reduced vibration of Valve Train elements, and corresponding Valve Train noise Reduce friction losses

3 Contents 1. Types of valve trains 2. Kinematics 3. Dynamics of valve trains 4. Friction in valve trains 5. Experimental investigation 6. Model validation 7. Conclusion 8. Future work

4 Types of Valve Trains Push-rod systems Used in large Diesel engines Reduce the number of gears necessary to drive the camshaft Increased mass of moveable parts and reduced stiffness of the systems Limit the maximum allowable acceleration Prone to larger vibration Variants: Roller follower

5 Overhead camshafts Reduces mass of movable parts Increased stiffness of the system Increased maximum allowable acceleration Better engine breathing Lower vibration Asymmetrical cam profile Concavities of the cam profile

6 Direct acting camshaft Higher cam profile Larger camshaft bearings Cannot avoid sliding friction

7 Valve motion Valve lift 1.E-02 8.E-03 6.E-03 4.E-03 2.E-03 0.E+00-2.E <deg> Essential for Better engine breathing Valve train dynamics (vibration) In use: - Polynomial cams - Continuos sinusoidal acceleration - Cubic spline continuous acceleration

8 Polynomial Cams t a t b θ θ θ θ θ hv = hmax + Ca + Cb + Cc + Cd + Ce θ θ θ θ θ t c t d t e Valve Lift for Three Different Polynomial Laws <m> 9.E-03 8.E-03 7.E-03 6.E-03 5.E-03 4.E-03 3.E-03 2.E-03 1.E-03 0.E <deg> Valve Lift Acceleration for Three Different Polynomial Laws <m/sec^2> 5.E+02 4.E+02 3.E+02 2.E+02 1.E+02 0.E+00-1.E+02-2.E <deg>

9 Continuos Sinusoidal Acceleration

10 Cubic Spline Continuos Acceleration Influence of Ramps Necessity of ramps: Blending the base cycle into the active cam profile

11 Types of Ramps Constant Acceleration Sinusoidal Acceleration a) Without Vibrations Forces in Valve Train

12 Dynamics of Valve Train Two Mass System One Mass System

13 n=1330 rpm Intake Valve Inlet Valve Lift [m] 9.00E E E E E E E E E E E Crank Angle [degree] <N> The Force on the Intake Cam 1.E+02 0.E+00-1.E E+02-3.E+02-4.E+02-5.E+02-6.E+02-7.E+02 <deg> Inlet Valve Speed [m/sec] 1.50E E E E E E E+00 Crank Angle [degree] <Nm> 6.E+00 4.E+00 2.E+00 0.E+00-4.E+00-6.E+00 The Contribution of the Intake Cam to the Total Torque -2.E <deg> Inlet Valve Acceleration [m/sec^2] 1.20E E E E E E E E E E+02 Crank Angle [degree] <Nm> The Total Torque for the Camshaft 6.E+00 4.E+00 2.E+00 0.E E E+00-6.E+00 <deg>

14 Friction Model ( ) u = R + h u 1 b c c 2 = 0 ω dv2 v 2 = ϖ c e a 2 = = dt &ω e c Velocity of contact point along the cam surface Radius of curvature s& = u + e& = ( R + h ) + e& 1 b c ωc Flat follower s& ds dt ds Rc = = = &γ dt dγ dγ R c s = & ω c e& Rc = Rb + hc + = Rb + hc + ω c a ω 2 2 c

15 ELASTOHYDRODYNAMIC (EHD) LUBRICATION Non dimensional Film Thickness (Dowson and Toyoda) EHD Oil film Thickness Non dimensional Velocity H = 2. 65U G W h = HR c U = ( u + u ) η E' R c η 0 E' G =αe α W F b c / E' R b c Viscosity at bulk lubricant temperature and ambient pressure Composite modulus of elasticity (207 Gpa) Material parameter Pressure-viscosity coefficient of lubricant (2.2*10-8 m 2 /N) Non dimensional load Cam Width RMR surface roughness of cam and follower s 1,s 2 Composite surface roughness 2 σ = σ + σ λ = HR c σ λ > 1 λ 1 0 < λ< 1 Film Thickness parameter EHD Lubrication Boundary Lubrication Mixed Lubrication F = F + F f b F = ff ( 1 λ) b c ν ( ) F = bη u + u ν for λ < 1 for λ > 1 Friction force Boundary friction component Viscous Friction Component ( ) M = F R + h f f b c ( ) M = F e + M c c f Frictional Torque Total torque required to drive the camshaft

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18 The Experimental and Modeled Cam Shaft Torque rpm 6.00E E E E E Model Experiment -4.00E E E+00 <deg>

19 The Amplitude for the first 100 Harmonics rpm Model Experiment 0.5 0

20 The Experimental and Modeled Cam Shaft Torque rpm 6.00E E E E E E Model Experiment -6.00E E E+01 <deg>

21 The Amplitude for the first 100 Harmonics rpm Model Experiment 0.5 0

22 Conclusion - Valve train is a very important engine component. It influences engine breathing, noise and friction losses - Cam profile and valve train parameters determine the dynamic response and valve train vibration - Friction losses are strongly influenced by the valve train design Future work - Further develop the dynamic model to include bending and torsional flexibility of the camshaft - Study the influence of different cam profiles on the valve train dynamics and friction - Instrument the engine for measuring valve acceleration in order to better validate the dynamic model - Develop a design method for low noise, low friction valve trains

23 Acknowledgments The authors acknowledge the technical support and sponsorship of the Automotive Research Center by the U. S. Army National Automotive Center and TARDEC, Warren Michigan.