In modern four-stroke automotive engine technology, variable valve timing and lift control offer potential benefits for making a high-performance engine. In this paper, a novel design named dual-mode electrohydraulic fully variable valve train (EHFVVT) for both engine intake and exhaust valves is introduced. The system is mainly controlled by either proportional flow control valves or proportional pressure relief valves, and hence two different families of valve displacement patterns can be achieved. The construction of the mathematical model of the valve train system and its dynamic analysis are also presented in this paper. Experimental and simulation results show that the dual-mode electrohydraulic variable valve train can achieve fully variable valve timing and lift control, and has the potential to eliminate the traditional throttle valve in the gasoline engines. With the proposed system, the engine performance at various speeds and loads will be significantly improved. NOMENCLATURE A 1 : cross-section area of the master cylinder piston (m 2 ) A 2 : cross-section area of the valve cylinder piston (m 2 ) A c : cross-section area of check valve orifice (m 2 ) A r : cross area of pressure relief valve orifice (m 2 ) C d : discharge coefficient of valve orifice C tp1 : leakage coefficient of the master cylinder (m 3 / s·Pa) C tp2 : leakage coefficient of the valve cylinder (m 3 /s·Pa) D : tappet displacement (m) d : hydraulic pipe diameter (m) d p : poppet valve diameter (m) F st1max : maximum static friction force on the master cylinder piston (N) F st2max : maximum static friction force on the valve cylinder piston (N) F co1 : sliding friction on the master cylinder piston (N) F co2 : sliding friction on the valve cylinder piston (N) F r1 : friction force on the master cylinder piston (N) F r2 : friction force on the valve cylinder piston (N) ΔF 1 : resultant force on the master cylinder piston (N) ΔF 2 : resultant force on the valve cylinder piston (N) F : load on poppet valve (N) F 0 : preload in disk-spring stack (N) F pre : preload in valve spring (N) g : acceleration of gravity=9.81 m/s 2 K g : stiffness of valve spring (N/m) K 1 : stiffness of disk-spring stack (N/m) K : gain of proportional flow control valve (m/V) K' : gain of proportional pressure relief valve (Pa/V) l 2 : length of hydraulic pipe (m) m 1 : mass of the master cylinder piston (Kg) m 2 : mass of the valve cylinder piston (Kg) P o : set pressure (Pa) P 1 : operating pressure in the master cylinder (Pa) P 2 : operating pressure in the valve cylinder (Pa) P L : residual gas pressure in combustion chamber (Pa) ΔP : pressure drop along the pipe to the valve cylinder (Pa) Q 1 : hydraulic flow generated by the master cylinder (L/min) Q 2 : hydraulic flow into the valve cylinder (L/min) Re : reynolds number r : base circle radius of input cam (m) u : proportional valve control signal (V) V 1 : initial volume of the master cylinder (m 3 ) V 2 : initial volume of the valve cylinder (m 3 ) v 2 : flow velocity in the pipe to the valve cylinder (m/ ...
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