Method for operating an internal combustion engine with electrohydraulic valve control means
A method for operating an internal combustion engine ( 4 ) with an electrohydraulic valve train ( 1 ) for variable-lift drive of a gas exchange valve ( 3 ), including a camshaft ( 6 ) and a hydraulic system arranged in a drive path between the camshaft and the gas exchange valve, said hydraulic system being connected to a pressure medium supply ( 14 ) of the internal combustion engine, a first hydraulic piston ( 8 ) which is driven by a cam ( 5 ) of the camshaft and a second hydraulic piston ( 9 ) which drives the gas exchange valve in an opening direction, a variable-volume pressure chamber ( 10 ) which is delimited by the hydraulic piston and a control channel ( 12 ) which connects the pressure chamber to a pressure relief chamber ( 11 ), an electrically actuated hydraulic valve ( 15 ) which is arranged in the control channel and which, in an open position, permits a flow of hydraulic medium through the control channel and, in a closed position, blocks a flow of hydraulic medium through the control channel, and an electronic controller ( 16 ) for the actuation of the hydraulic valve as a function of operating parameters of the internal combustion engine. To improve the cold-start behavior of the internal combustion engine, it is provided that, during the starting phase, the hydraulic valve is closed and opened again at least once between two immediately successive lifts of the first hydraulic piston.
1. A method for operating an internal combustion engine with an electrohydraulic valve train for a variable-lift drive of a gas-exchange valve that is spring-loaded in a closing direction, comprising providing a camshaft and a hydraulic system arranged in a drive sense between the camshaft and the gas-exchange valve and that is connected to a pressurized medium supply of the internal combustion engine, with a first hydraulic piston driven by a cam of the camshaft and a second hydraulic piston driving the gas-exchange valve in an opening direction, and a pressure chamber limited by the first hydraulic piston and the second hydraulic piston with variable volume and a control channel connecting the pressure chamber to a pressure relief space, arranging an electrically controlled hydraulic valve in the control channel and allowing a flow of hydraulic medium through the control channel in an open position of the hydraulic valve and blocking said flow of the hydraulic medium in a closed position of the hydraulic valve, controlling the hydraulic valve with an electronic controller as a function of operating parameters of the internal combustion engine, and during a startup phase of the internal combustion engine, closing the hydraulic valve and reopening the hydraulic valve at least once between two immediately successive lifts of the first hydraulic piston.
2. The method according to claim 1 , further comprising during the startup phase, reopening the hydraulic valve closed during a lift of the first hydraulic piston before a maximum lift (h(max)) of the gas-exchange valve.