Variable valve train for a cam-activated lifting valve of an internal combustion engine

Abstract

The invention relates to a variable valve train ( 1 ) for a cam-actuated lifting valve ( 13 ) of an internal combustion engine, which valve ( 13 ) is loaded by a closing spring ( 13 a ) acting against the direction of opening, with an approximately cylindrical force application element ( 2 ) located between a cam ( 14 ) and the valve ( 13 ), whose length can be adjusted hydraulically and whose exterior cylindrical wall face ( 3 ) is slidable in a fixed guide cylinder ( 4 ), said element ( 2 ) being provided with a pressure piston ( 6 ) longitudinally slidable in a cylinder ( 5 ), which piston ( 6 ) is adjacent to a pressure chamber ( 7 ) into which opens a pressure channel ( 8 ) departing from a port ( 9 ) in the wall face ( 3 ) of the force application element ( 2 ), a fixed pressure line ( 11 ) opening into the guide cylinder ( 4 ) in the area of the port ( 9 ), which line ( 11 ) can be subjected to hydraulic high pressure (p H ) permitting hydraulic activation of the valve ( 13 ). In order to obtain a variable valve train ( 1 ) independet of crank angle (KW) in as simple a manner as possible, a permanent flow connection is provided between pressure line ( 11 ) and pressure channel ( 8 ) independently of the position of the force application element ( 2 ).

What is claimed is:  
     
         1 . A variable valve train ( 1 ) for a cam-actuated lifting valve ( 13 ) of an internal combustion engine, which valve ( 13 ) is loaded by a closing spring ( 13   a ) acting against the direction of opening, with an approximately cylindrical force application element ( 2 ) located between a cam ( 14 ) and the valve ( 13 ), whose length can be adjusted hydraulically and whose exterior cylindrical wall face ( 3 ) is slidable in a fixed guide cylinder ( 4 ), said element ( 2 ) being provided with a pressure piston ( 6 ) longitudinally slidable in a cylinder ( 5 ), which piston ( 6 ) is adjacent to a pressure chamber ( 7 ) into which opens a pressure channel ( 8 ) departing from a port ( 9 ) in the wall face ( 3 ) of the force application element ( 2 ), a fixed pressure line ( 11 ) opening into the guide cylinder ( 4 ) in the area of the port ( 9 ), which line ( 11 ) can be subjected to hydraulic high pressure (p H ) permitting hydraulic activation of the valve ( 13 ), wherein a permanent flow connection is provided between pressure line ( 11 ) and pressure channel ( 8 ) independently of the position of the force application element ( 2 ).  
     
     
         2 . A valve train ( 1 ) according to  claim 1 , wherein the end ( 11   a ) of the pressure line ( 11 ) opening into the guide cylinder ( 4 ) and the port ( 9 ) in the wall face ( 3 ) of the force application element ( 2 ) are designed to be overlapping in every position.  
     
     
         3 . A valve train ( 1 ) according to  claim 1  or  2 , where the force application element ( 2 ) can perform a lift corresponding to the cam lift, wherein a recess ( 12 ) is provided between pressure line ( 11 ) and pressure channel ( 8 ), which communicates with both pressure line ( 11 ) and pressure channel ( 8 ), the height (h) of which recess ( 12 ), as measured in the direction of the lift, will correspond to at least the maximum lift of the force application element ( 2 ).  
     
     
         4 . A valve train ( 1 ) according to  claim 3 , wherein the recess ( 12 ) is configured at least partially by a space in the guide cylinder ( 4 ).  
     
     
         5 . A valve train ( 1 ) according to  claim 3  or  4 , wherein the recess ( 12 ) is configured at least partially by a space in the exterior wall face ( 3 ) of the force application element ( 2 ).  
     
     
         6 . A valve train ( 1 ) according to any of  claims 1  to  5 , wherein the force application element ( 2 ) is located between the cam ( 14 ) and the lifting valve ( 13 ), and preferably, it is coaxial with the valve ( 13 ), and more preferably it is configured as a cup-shaped tappet.  
     
     
         7 . A valve train ( 1 ) according to any of  claims 1  to  5 , wherein the force application element ( 2 ) is configured as part of a valve arm bearing block supporting a valve arm for actuation of the lifting valve ( 13 ).  
     
     
         8 . A valve train ( 1 ) according to any of  claims 1  to  5 , wherein the force application element ( 2 ) is located between a cam ( 14 ) and a valve arm for actuation of the lifting valve.  
     
     
         9 . A valve train ( 1 ) according to any of  claims 1  to  8 , wherein the pressure line ( 11 ) is connected to an external pressure generating unit ( 16 ) comprising at least one pump ( 17 ,  28 ), and at least one pressure tank ( 18 ,  21 ) with at least one pressure regulator ( 20 ), and at least one pressure control element ( 19 ).  
     
     
         10 . A valve train ( 1 ) according to  claim 9 , wherein the pressure control element ( 19 ) is configured as an electromechanical element with at least one electromechanically actuated valve.  
     
     
         11 . A valve train ( 1 ) according to  claim 9  or  10 , wherein the pressure control element ( 19 ) is configured as a piezo-mechanical element with at least one piezomechanically actuated valve.  
     
     
         12 . A valve train ( 1 ) according to any of  claims 9  to  11 , wherein several lifting valves ( 13 ) can be actuated by means of one and the same pressure control element ( 19 ).  
     
     
         13 . A valve train ( 1 ) according to any of  claims 9  to  12 , wherein the pressure control element ( 19 ) is configured as a 3/2-way valve.  
     
     
         14 . A valve train ( 1 ) according to any of  claims 9  to  13 , wherein the working medium and/or control medium of the pressure generating unit ( 16 ) is water, fuel, or lubricating oil.  
     
     
         15 . A valve train ( 1 ) according to any of  claims 1  to  13 , wherein the pressure generating unit ( 16 ) is part of a further subsystem of the engine other than the valve train.  
     
     
         16 . A valve train ( 1 ) according to  claim 15 , wherein the pressure tank ( 18 ,  21 ) is part of a fuel injection system.  
     
     
         17 . A valve train ( 1 ) according to  claim 15 , wherein the pressure tank ( 18 ,  21 ) is part of an hydraulic gear system of the vehicle.  
     
     
         18 . A valve train ( 1 ) according to  claim 15 , wherein the pressure tank ( 18 ,  21 ) is part of an hydraulic braking system of the vehicle.  
     
     
         19 . A valve train ( 1 ) according to  claim 15 , wherein the pressure tank ( 18 ,  21 ) is part of a coolant circulation system of the vehicle.  
     
     
         20 . A valve train ( 1 ) according to any of  claims 9  to  19 , wherein the pressure generating unit ( 16 ) has a high pressure level (p H ) and a medium pressure level (p M ), permitting the pressure chamber ( 7 ) of the force application element ( 2 ) to be flow-connected to either high pressure level (p H ) or medium pressure level (p M ) via the pressure control element ( 19 ), the high pressure level (p H ) preferably being provided by a high pressure tank ( 18 ) connected to a high pressure pump ( 17 ).  
     
     
         21 . A valve train ( 1 ) according to  claim 20 , wherein the medium pressure level (p M ) is provided by a medium pressure pump ( 28 ).  
     
     
         22 . A valve train ( 1 ) according to  claim 20 , wherein the medium pressure level (p M ) is provided by a medium pressure tank ( 21 ), which is connected via a relief valve ( 22 ) to a high pressure tank ( 18 ) for the high pressure level (p H ).  
     
     
         23 . A valve train ( 1 ) according to any of  claims 9  to  22 , wherein the force application element ( 2 ) is connected to the medium pressure level (p M ) via a pressure relief line ( 26 ) preferably provided with a check valve ( 27 ) opening in the direction of the force application element ( 2 ).  
     
     
         24 . A valve train ( 1 ) according to any of  claims 1  to  23 , wherein the pressure piston ( 6 ) is designed as a stepped piston.  
     
     
         25 . A method for operating an internal combustion engine with a variable valve train according to any of  claims 1  to  24 , wherein the lifting valve will be hydraulically activated and given an additional lift during the mechanical lifting phase performed by the cam.  
     
     
         26 . A method for operating an internal combustion engine with a valve train according to any of  claims 1  to  24 , wherein the lifting valve will be re-opened hydraulically at least once after the mechanical lifting phase performed by the cam has come to an end.  
     
     
         27 . A method for operating an internal combustion engine with a valve train according to any of  claims 1  to  24 , wherein the lifts of subsequent charge exchange processes are alternatingly determined mechanically and hydraulically.