Valve drive for an internal combustion engine, internal combustion engine comprising such a valve drive, and method for operating an internal combustion engine comprising such a valve drive

Abstract

A valve drive for an internal combustion engine, including a gas exchange valve; a first mechanically driven drive mechanism; and a second drive mechanism connected to the gas exchange valve to move same. The first and second drive mechanisms connected via a hydraulic coupling device that has a pressure chamber, which can be relieved of pressure via a valve device and is designed to couple the drive mechanisms by hydraulic pressure and to decouple same in a pressure-relieved state. The valve device has two switch valves fluidically connected to the pressure chamber in parallel and via which the pressure chamber is relieved of pressure in the open state of at least one of the switch valves. The valve drive has a controller that actuates the switch valves in a delayed manner to provide a variable valve stroke of the gas exchange valve during a stroke movement.

Claims

1. A valve drive for an internal combustion engine, comprising: at least one gas exchange valve; a first, mechanically driven, drive mechanism; a second drive mechanism connected to the at least one gas exchange valve for repositioning the at least one gas exchange valve; a hydraulic coupling installation that operatively connects the first drive mechanism to the second drive mechanism, wherein the hydraulic coupling installation has a pressure chamber which is capable of being relieved of pressure and which under hydraulic pressure is specified for coupling the first drive mechanism to the second drive mechanism, and in a pressure-relieved state is specified for decoupling the first drive mechanism from the second drive mechanism; a valve installation connected to the pressure chamber to relieve the pressure in the pressure chamber, wherein the valve installation has at least two switch valves which are fluidically connected in parallel to the pressure chamber and by way of which the pressure chamber in an opened state is capable of being relieved of pressure by at least one of the switch valves; and a control apparatus configured to actuate the switch valves in a temporally offset manner for representing a variable valve stroke of the at least one gas exchange valve during a stroke movement of the gas exchange valve, wherein the at least one gas exchange valve includes a plurality of gas exchange valves assigned to different combustion chambers of the internal combustion engine, wherein a common end stage of the control apparatus is in each case assigned to at least two of the switch valves that are assigned to different combustion chambers, said different combustion chambers having gas exchange cycles that are temporally mutually separated.

2. The valve drive according to claim 1, wherein the switch valves of the valve installation are of identical construction.

3. The valve drive according to claim 1, wherein the switch valves are high-speed valves.

4. The valve drive according to claim 1, wherein the control apparatus is configured to vary the temporal offset between the actuation of the switch valves.

5. An internal combustion engine comprising a valve drive according to claim 1.

6. The internal combustion engine according to claim 5, further comprising a plurality of combustion chambers, wherein each combustion chamber is assigned at least one gas exchange valve as well as at least one hydraulic coupling installation of the valve drive.

7. A method for operating an internal combustion engine having a valve drive according to claim 1, comprising the step of actuating switch valves that are fluidically connected in parallel to a common pressure chamber of a hydraulic coupling installation of the valve drive in a temporally mutually offset manner during a stroke movement of a gas exchange valve that is assigned to the hydraulic coupling installation.

8. The method according to claim 7, further including varying the temporal offset in the actuation of the switch valves.

Description

(1) The invention will be explained in more detail hereunder by means of the drawing in which:

BRIEF DESCRIPTION OF THE DRAWING

(2) FIG. 1 shows a schematic illustration of an exemplary embodiment of an internal combustion engine having a valve drive; and

(3) FIG. 2 shows a schematic illustration of the functioning mode of the valve drive according to FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows a schematic illustration of an exemplary embodiment of an internal combustion engine 1 having a valve drive 3. The valve drive 3 here is assigned plurality of gas exchange valves, in the schematic illustration two gas exchange valves 5, 5′, said gas exchange valves 5, 5′ in turn being assigned to different combustion chambers 7, 7′ (likewise only schematically illustrated here) of the internal combustion engine 1.

(5) The functioning mode of the valve drive 3 will first be explained in the context of the first gas exchange valve 5. Identical and functionally equivalent elements which are assigned to the second gas exchange valve 5′ herein are provided with respective corresponding reference signs with an apostrophe, such that a separate explanation of said elements and the functioning mode thereof is not required; to this extent, reference is rather made to the explanation pertaining to the elements provided with reference signs without apostrophes. The interaction of the actuation of the different gas exchange valves 5, 5′ in the case of the valve drive 3 will subsequently be explained in more detail.

(6) The gas exchange valves 5, 5′ are preferably configured as inlet valves. However, it is also possible for said gas exchange valves 5, 5′ to be configured as outlet valves, or for the valve drive 1 to be assigned corresponding outlet valves in addition to the inlet valves 5, 5′. The internal combustion engine 1 preferably has more than two combustion chambers 7, 7′. The number of combustion chambers 7, 7′ herein is not delimited in principle. The internal combustion engine 1 can in particular have four, six, eight, ten, twelve, sixteen, eighteen, twenty, or twenty-four, combustion chambers 7, 7′.

(7) The first gas exchange valve 5 is assigned a first, mechanically driven, drive mechanism 9 which here has in particular a first piston 11 and a first piston rod 13, wherein the first piston rod 13 here is operatively connected to a cam 15 of a camshaft, the first piston rod 13 and thus the first piston 11 being contemporaneously activatable by said cam 15 so as to move in the manner of a stroke.

(8) A second driving mechanism 17 which, for repositioning the gas exchange valve 5, is mechanically connected to the latter and which in particular has a second piston 19 and a second piston rod 21 is moreover provided, wherein said second driving mechanism 17 furthermore has a deflection mechanism 23 by way of which the second piston rod 21 is mechanically coupled to the gas exchange valve 5.

(9) The first drive mechanism 9 and the second drive mechanism 17 are operatively connected to one another by way of a hydraulic coupling installation 25, wherein the hydraulic coupling installation 25 has in particular a pressure chamber 27 which by way of a valve installation 29 is capable of being relieved of pressure, wherein the pressure chamber 27, under hydraulic pressure, is specified for coupling the first drive mechanism 9 to the second drive mechanism 17, and to decouple said first drive mechanism 9 and said second drive mechanism 17 in the pressure-relieved state. To this end, the two pistons 11, 19 are collectively disposed in the pressure chamber 27 such that the second piston 19, when the pressure chamber 27 is under hydraulic pressure, follows a stroke movement of the first piston 11, in a manner transmitted by way of the hydraulic means, wherein the second piston 19 can be decoupled from the first piston 11 in that the pressure chamber 27 is relieved of pressure such that the coupling by way of the hydraulic means is cancelled, wherein the second piston 19 in this instance can no longer follow a stroke movement of the first piston 11.

(10) A variable stroke for the gas exchange valves 5 can be correspondingly represented by way of the hydraulic coupling installation 25, wherein sub-curves in terms of a valve stroke curve that is defined by the shape of the cam 15 can in particular be obtained. The valve drive 3 is therefore configured as a variable valve drive 3 and in particular as a fully variable valve drive 3.

(11) The valve installation 29 has at least two, here exactly 2, switch valves 31, 33 that are fluidically connected in parallel to the pressure chamber 27, specifically a first switch valve 31 and a second switch valve 33, wherein the pressure chamber 27 in the opened state is capable of being pressure-relieved by at least one of the switch valves 31, 33.

(12) The valve drive 3 moreover has a control apparatus 35 of which only two end stages, specifically a first end stage 37 and a second end stage 39, are schematically illustrated here. The control apparatus 35, for representing a variable valve stroke during a same stroke movement of the gas exchange valve 5, is specified for actuating, in particular actuating so as to open, the switch valves 31, 33 in a temporally offset but preferably temporally overlapping manner.

(13) Instead of a single switch valve by way of which the pressure chamber 27 is capable of being pressure-relieved, as is known in the case of conventional valve drives, said valve drive in the case of the valve drive 3 proposed here is accordingly assigned at least the two switch valves 31, 33, on account of which it becomes possible for a comparatively high flow cross section to be released and pressure in pulses in the pressure chamber 27 to be contemporaneously minimized, specifically in that a temporally staged release of the cross section in the form of the temporally offset actuation of the switch valves 31, 33 is carried out. Steeper valve stroke flanks, in particular steeper valve closing flanks, can thus be achieved for the gas exchange valve 5, on account of which overall more corpulent stroke curves result. Furthermore, a use of interchangeable parts is possible not only on the internal combustion engine 1 but also in the case of an entire construction series or in the case of different construction series, in particular different sizes or performance classes, of internal combustion engines 1, because the same switch valve for providing larger flow cross sections can be provided in multiples.

(14) To this extent, it is in particular provided that the switch valves 31, 33 as well as the switch valves 31′, 33′ of the second gas exchange valve 5′ are configured so as to be of identical construction.

(15) The switch valves 31, 33, 31′, 33′ are preferably configured as high-speed valves, in particular as high-speed solenoid valves (HSSV).

(16) The control apparatus 35 is preferably specified for varying the temporal offset between the actuation of the switch valves 31, 33, 31′, 33′ that are assigned to a same valve installation 29, 29′, wherein the variation of the temporal offset can in particular be performed as a function of momentary operating point of the internal combustion engine 1, most particularly preferably as a function of a characteristic diagram. A suitable valve stroke curve and a dedicated suitable switching behavior of the switch valves 31, 33, 31′, 33′ can thus be represented for each operating point of the internal combustion engine 1.

(17) Each of the switch valves 31, 33, 31′, 33′ is assigned an end stage 37, 39. For example, the first switch valves 31, 31′ are assigned the first end stage 37, and the second switch valves 33, 33′ are assigned the second end stage 39.

(18) It is demonstrated herein that two switch valves 31, 31′, 33, 33′ which are assigned to different combustion chambers 7, 7′ are in each case assigned a common end stage 37, 39, wherein the gas exchange cycles of the combustion chambers 7, 7′ are temporally mutually separated. In the case of the combustion chambers 7, 7′ illustrated here, it is to this extent in particular provided that the phases of operating cycles of said combustion chambers 7, 7′ are mutually displaced by half an operating cycle period, thus by specifically 360° in terms of the angle of the crankshaft in the case of a four-stroke engine. Therefore, the respective two first switch valves 31, 31′ which are assigned to the different gas exchange valves 5, 5′ can be actuated by a common end stage, here specifically the first end stage 37, wherein the two second switch valves 33, 33′ can likewise be actuated by another common end stage, here specifically by the second end stage 39 which is different from the first end stage 37. The switch valves 31, 33, 31′, 33′ of the respective same gas exchange valve 5, 5′ herein are in each case actuated by different end stages 37, 39, such that the temporal offset in the actuation can be implemented. However, two switch valves 31, 31′, 33, 33′ that are in each case assigned to the different gas exchange valves 5, 5′ herein share a common end stage 37, 39.

(19) For example, when the first end stage 37 emits an actuation signal, the latter is received by the two first switch valves 31, 31′, on upon which said two first switch valves 31, 31′ are actuated so as to open. However, at the temporal point or crankshaft angle illustrated in FIG. 1, this leads only to an effect on the first gas exchange valve 5 since only the first drive mechanism 9 of the latter is momentarily mechanically activated by the first cam 15 such that the first gas exchange valve 5 is actuated to perform a valve stroke movement which can be varied by way of the actuation of the first switch valve 31. By contrast, the second cam 15′ is in a position in which the latter does not effect any valve stroke movement of the second gas exchange valve 5′ by way of the first drive mechanism 9′ of the latter, such that the second gas exchange valve 5′, independently of the switching behavior of the first switch valve 31′ assigned to said second gas exchange valve 5′, does not carry out any stroke movement. The actuation of the first switch valve 31′ that is assigned to the second gas exchange valve 5′, in addition to the actuation of the first switch valve 31 that is assigned to the first gas exchange valve 5, by the first end stage 37 thus does not develop any additional effect which is why it is possible for the two first switch valves 31, 31′ to be actuated by way of the common first end stage 37.

(20) The same applies in an entirely analogous manner to the second end stage 39 and to the second switch valve 33, 33′.

(21) The end stages 37, 39 are activated in a temporally offset manner such that the respective first switch valves 31, 31′ and the respective second switch valves 33, 33′ are actuated so as to open in a temporally offset but preferably temporally overlapping manner.

(22) FIG. 2 shows a diagrammatic illustration of the functioning mode of the valve drive 3 according to FIG. 1. At a) an actuation current I herein is schematically plotted in the diagram as a function of the camshaft angle of the internal combustion engine 1. The actuation current I for the first switch valves 31, 31′ that is outputted by the first end stage 37 is illustrated as a solid first curve K1, wherein the actuation current I of the second end stage 39 for the second switch valves 33, 33′ is illustrated as a dashed second curve K2. It is demonstrated herein that the first curve K1 and the second curve K2 temporally mutually overlap but have a mutual temporal offset Δt. Said temporal offset Δt is preferably variable, wherein said temporal offset Δt can preferably be chosen by the control apparatus 35 as a function of the operating point, in particular as a function of a characteristic diagram.

(23) At b), the product calculated from a flow cross section A of the switch valves 31, 33 and a coefficient of flow rate Cd is plotted as a function of the camshaft angle of the internal combustion engine 1. It is demonstrated herein that the release of the flow cross sections of the individual switch valves 31, 33 behaves in additive manner by virtue of the temporally offset actuation of said switch valves 31, 33. The profile of the overall flow cross section release for the two switch valves 31, 33 which are actuated so as to open in a temporally offset but mutually overlapping manner, thus behaves exactly like the sum calculated from the respective flow cross-section releases for the individual switch valves 31, 33.

(24) It is thus possible for the total flow cross section to be released in a temporally staged manner and for pressure pulses in the pressure chamber 27 to be contemporaneously minimized, preferably prevented.

(25) The temporal offset Δt for the actuation of the switch valves 31, 33′ herein can preferably be chosen such that pressure pulses created are interfered out of the way by virtue of the opening of the different switch valves 31, 33.

(26) It is overall demonstrated that a very efficient and cost-effective potential for implementing a fully variable valve drive 3 having steep flanks while avoiding pressure pulses is achieved by way of the valve drive 3 proposed here, the internal combustion engine 1, and the method.