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DESMODROMIC a distinctiveness of the Ducati engines
Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 DESMODROMIC a distinctiveness of the Ducati engines Stefano Fantoni Engine Simulation Manager Ducati Motor Holding spa Summary • • • • • What’s DESMODROMIC timing system Hystory Design techniques Special characteristics Conclusions Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Summary • • • • • What’s DESMODROMIC timing system Hystory Design techniques Special characteristics Conclusions Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Desmodromic timing system Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Cam Sealing spring Slider Valve Bilateral constraint Bignan, 1920 From the Greek words: DESMOS controlled-linked DROMOS stroke-path Valve timing systems Spring Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Pneumatic Desmodromic Opening cam Closing cam Closing rocker Lashes adjuster Air spring Air Sealing Spring Opening finger Summary • • • • • What’s DESMODROMIC timing system Hystory Design techniques Special characteristics Conclusions Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Hystory Development Trends of Motorcycles Mercedes–Benz W196 (1954) • • • • Engine: 8 cylinder inline, 2500 cm3 Gasoline direct injection Engine power: from 250 to 295 CV @ 8500 giri/min Desmodromic valve train 5th Internaltional Conference 18th October 2012 Two times F1 World champion (1954 e 1955) with M.Fangio Hystory Development Trends of Motorcycles Ducati 125 Desmo (1956) • Motore: single cylinder, 125 cm3 • First Ducati engine with 5th Internaltional Conference 18th October 2012 Desmodromic valve train Three overhead camshafts More performance and durability Victory at the first race History Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 70’s: TWIN CYLINDERS 80’s: DESMOQUATTRO 2001: TESTASTRETTA 2003:DESMOSEDICI 2011: SUPERQUADRO 2 valves engine 4 valves engine 4 valves engine MotoGP series New engine with low S/B First Ducati twin cylinders engine with single overhead camshaft Double overhead camshaft, beginning of the SBK era New design to reduce the angle between valves New desmo ready to compete with pneumatic valve train Desmo valve train driven by chain. High performance, low maintenance Summary • • • • • What’s DESMODROMIC timing system Hystory Design techniques Special characteristics Conclusions Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Kinematic Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Geometrical definition of desmo y6 y6 rbase1 Rbase1 rbase0 Rbase0 •Cams: 6 •position rb0 4 Rb0 B0 44 0 Rc0 C0 55 Cam-Finger Radius rc0 Lash.Finger Radius x6 Cam-Rocker Radius y5 y5 x6 y4 y4 x4 Lash-Rocker Radius x4 x5x5 rc1 C1 1 rb1 Rc1 B1 O (0; 0) Rb1 yy x 5 of cam rotation center •base radius of opening and closing cam •Opening finger: •position of finger rotation center •finger geometry •Closing rocker: •position of rocker rotation center •rocker geometry Kinematic Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Maximum valve acceleration limited by geometry Target Lift The kinematic limits are the maximum acceleration |aLIM | (maximum positive-minimum negative) available for valve motion aLIM = f(geometry, ω, L, V, ρ) where: ω = camshaft velocity L, V = vave lift and velocity ρ = maximum admisible curvature radius of cam profile Acceleration Kinematic Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Kinematc limits Closing rocker Horizontal head Opening finger Same rotation with mirrored geometry Kinematic Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Kinematc limits Closing rocker Horizontal + Vertical head Opening finger Kinematic Total kinematic limits Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Due to the conjugate movement of opening and closing parts of the desmo the effective valve acceleration is limited by minimum absolute value of accleration considering all the geometry (opening-closing, vertical and horizontal). 𝑎𝑒𝑓𝑓 ≤ |𝒂𝒍𝒊𝒎 | Kinematic Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Cam profile curvature affects the kinematic limits max a+ ρ→∞ => av>0 ρ maximum (∞ or negative curvature) Opening finger min a- ρ minimum (ρ→0 ) ρ→0 => av<0 ρ→∞ => av<0 max a+ ρ minimum (ρ→0) Closing rocker min a- ρ maximum (∞ or negative curvature) ρ→0 => av>0 Kinematic Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 ρ: interference or undercutting No interference condition 1 1 + 𝑅 𝜌 R = radius of cutter or follower ρ = cam curvature radius 1 1 + 𝑅 𝜌 ≥0 𝑅+𝜌 ≥0 𝑅∙𝜌 𝑖𝑓𝜌 ≥ 0 𝑎𝑙𝑤𝑎𝑦𝑠 𝑜𝑘 . 𝑖𝑓 𝜌 < 0 𝑡ℎ𝑒𝑛 𝜌 ≤ −𝑅 In case of concave cam profile the radius of curvature is limited by the radius of the cutter (or follower) ≥0 Kinematic Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Offset contact between follower-lash adjuster During the valve motion the contact point between follower and lash adjuster is not always on the valve’s center line. It’s important to control the maximum offset to reduce the moment of force applied on the valve Fba Fbc Offset = f (valve lift) It’ is important to reduce the offset during the active phase of each parts (openigng-closing). Dynamic Development Trends of Motorcycles Dynamic analysis: finger and rocker design 5th Internaltional Conference 18th October 2012 Simulated valve acceleration Pivot stiffness Lashes Experimental valve acceleration A validated dynamic model of the valve train is useful for design the finger and rocker arm, in terms to stiffness and durability Dynamic Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Dynamic analysis: finger and rocker design Contact force Cam-Finger It’s possible to test virtually differnet shape of members to find the optimal solution 139MPa 157MPa F F Fcam-bil Fcam-bil a reg a cam a cam a reg Desmo design Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Efficiency: friction power loss 𝑃𝑓 = 𝑓 ∙ 𝐹 ∙ 𝑣𝑠 Sliding velocity Friction coefficient Load A kinematic index of the friction loss is the product of velocity and acceleration. It is better to impose higher acceleretion when the velocity is lower. 𝑃𝑓 ∝ 𝑎 ∙ 𝑣 Using special coating or surface finiture is possible to reduce the friction coefficient Desmo design Performance Design Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Kinematic Limits 𝑎𝑙𝑖𝑚 Friction Loss Offset – Valve Load Compact design Stiffnes - Weight Base Radius Arm Lever Ratio Arm lenght The valve train design is a trade-off process. In general, a mechanis with hight kinematic lmits results to have highter friction and to be less compact . Summary • • • • • What’s DESMODROMIC timing system Hystory Design techniques Special characteristics Conclusions Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Performances Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Desmo Vs Spring: hertzian contact stress 𝜎∝ 1 1 ± 𝜌 𝑅 Maximum hertzian stress are located at minimum curvature radius Spring limit In a Desmo mechanism the zone with minimum curvature radius are not active zone. It’s possible to impose the same valve acceleration value during positive and negative phase ρ = cam curvature radius R = radius of follower a+ zone a- zone Efficiency Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Desmo Vs Spring: power loss I: inertial load S: spring force Spring valve train Mean Force during a cycle applied to the camshaft 𝐹∝ 𝐼 𝑑𝜗 + 𝑆 𝑑𝜗 I 𝐼 𝑑𝜗 = 0 S Spring valve train Desmo I 𝐹∝ 𝑆 𝑑𝜗 Fm = cost Desmo 𝐹∝ 1 2 𝐼 𝑑𝜗 + 0 3 𝐼 𝑑𝜗 + 1 𝐼 𝑑𝜗 2 Fm α ω2 Efficiency Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Desmo Vs Spring: power loss Spring valve trian Fm = cost Desmo is more efficient at middle and low engine rev. Desmo Ploss α ω Fm α ω2 Ploss α ω3 This point is influenced by te design of each mechanism Summary • • • • • What’s DESMODROMIC timing system Hystory Design techniques Special characteristics Conclusions Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Conclusions Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 •Desmo is a quite complex (and expensive) mechanism that allows to control the valve lift even at high engine revolutions. •It’s possible to increase negative valve accleration, generating more performance valve lift curve •Desmo is an efficient mechanism for middle-low rpm the end of the design process it’s important to define a mechanism well balanced in all its parts: for example, the kinematic limits of opening and closing parts heve to be similar as well the stiffnes of opening and closing rocker arms •At Development Trends of Motorcycles 5th Internaltional Conference 18th October 2012 Thank you for your attention
