Patent Application
20190178116
The following documents are incorporated herein by reference as if fully set forth: German Patent Application No. 10 2017 129 419.8, filed Dec. 11, 2017.
The invention relates to a variable valve train of an internal combustion engine with at least two functionally identical gas-exchange valves for each cylinder, whose valve strokes can be generated by at least one primary cam and one secondary cam of a camshaft and can be transferred by a switchable cam follower selectively to the allocated gas-exchange valves, wherein each cam follower has a primary lever in tapping contact with the associated primary cam and in switching contact with the associated gas-exchange valve and also a secondary lever in tapping contact with the associated secondary cam and can be coupled with the primary cam by an axial displacement of a control pin guided in a transverse hole. Each control pin of the cam follower is connected by connecting elements formed as leaf springs to an elongated switching element that is arranged above the cam follower parallel to the camshaft and can be moved longitudinally by a linear actuator against the restoring force of a spring element from a home position into a switched position.
Switchable valve trains of internal combustion engines are known in different constructions. For example, valve trains of individual cylinders or groups of cylinders of an internal combustion engine can be deactivated by switching off the transmittable valve stroke and in this way, in connection with switching off the fuel injection for the affected cylinders, the fuel consumption and CO2 emissions and other harmful emissions of the internal combustion engine in partial load operation can be reduced. On the other hand, the stroke profiles that can be transferred by valve trains of intake and/or exhaust valves of an internal combustion engine can be changed by switching the strokes and in this way can be adapted to the current operating state of the internal combustion engine as a function of operating parameters, such as the engine speed and engine load, whereby the engine output and torque are increased and the specific fuel consumption of the internal combustion engine can be reduced.
In valve trains that can be switched off, typically two components that can move or rotate relative to each other are provided in a switchable stroke transmission element, of which one component is in switching connection with the associated cams of a camshaft and the other component is in switching connection with the valve shaft of the associated gas-exchange valve. Both components can be coupled with each other or decoupled from each other by a coupling element usually constructed as a coupling pin. In the coupled state, the valve stroke of the associated cam is transmitted to the affected gas-exchange valve, but is not transmitted in the decoupled state, so that the gas-exchange valve then remains closed. The coupling pin is typically guided so that it can move axially in a hole of one component and can move into a coupling hole of the other component. By the use of a spring element, the coupling pin is held in a home position and displaced and held there by the loading with a switching force against the restoring force of the spring element in an actuation position. In valve trains that can be deactivated, the home position of the coupling pin usually corresponds to the coupled state of the components of the stroke transmission element and the actuation position usually corresponds to the decoupled state of the components. The stroke transmission elements that can be deactivated can be cup tappets, roller tappets, cam followers, rocker arms, or support elements that can be deactivated.
In valve trains that can be switched, at least two components that can move or rotate relative to each other are provided in a switchable stroke transmission element, of which one component is in switching contact with an associated primary cam of a camshaft with a certain valve stroke and with the valve shaft of the associated gas-exchange valve and the other component is in switching contact with an associated secondary cam of the camshaft with a larger valve stroke or with an additional stroke. Both components can be coupled with each other or decoupled from each other by a coupling element usually constructed as a coupling pin. In the decoupled state, the valve stroke of the primary cam is transmitted to the affected gas-exchange valve, but in the coupled state, the larger valve stroke of the primary or secondary cam is transmitted to the gas-exchange valve. Here, the coupling pin can also typically move in a hole of one component and into a coupling hole of the other component. By the use of a spring element, the coupling pin is held in a home position and pushed into an actuation position and held there by the loading with a switching force against the restoring force of the spring element. In valve trains that can be switched, the home position of the coupling pin usually corresponds to the decoupled state of the components of the stroke transmission element and the actuation position usually corresponds to the coupled state of the components. Stroke transmission elements that can be switched are usually cup tappets, cam followers, or rocker arms that can be switched.
The adjustment of coupling elements of switchable stroke transmission elements is typically performed hydraulically in that a switching pressure line leading to pressure chambers of the coupling elements is connected or switched without pressure, for example, by means of a magnetic switching valve, selectively to an oil pressure source. A known construction of a switchable cam follower that is provided with a hydraulically adjustable coupling pin and is provided in an internal combustion engine for switching off the stroke of a gas-exchange valve is described in DE 10 2006 057 894 A1. In contrast, DE 10 2006 023 772 A1 describes a known construction of a switchable cam follower with a hydraulically adjustable coupling pin that is provided in an internal combustion engine for switching the stroke of a gas-exchange valve. The feeding of the switching pressure oil from the respective switching pressure line into a switchable cam follower is usually realized by a two-channel hydraulic support element, as is known, for example, from DE 103 30 510 A1.
If gas-exchange valves of an internal combustion engine can be switched off or switched selectively in groups, then for a hydraulic adjustment of the coupling elements, separate switching pressure lines are required each with an associated switching valve. A corresponding hydraulic control device for the selective group-wise adjustment of the coupling elements of a variable valve train in an internal combustion engine with two intake valves and two exhaust valves per cylinder is described, for example, in DE 102 12 327 A1. The switchable stroke transmission elements of the valve train are formed, in this case, as switchable cup tappets.
The coupling elements of switchable stroke transmission elements, however, can also be adjusted electromagnetically, in that the coupling elements are each in active connection with an electromagnet and the electromagnets are selectively energized or switched to a de-energized state. A known construction of a switchable cam follower that is provided with an electromagnetically adjustable coupling pin in an internal combustion engine for deactivating the stroke of a gas-exchange valve is disclosed in U.S. Pat. No. 5,544,626 B1. The coupling pin and the electromagnet, whose armature is connected to the coupling pin, are arranged longitudinally oriented in a primary lever of the cam follower, wherein a greater structural length of the cam follower and a correspondingly larger width of the affected cylinder head are produced.
In contrast, in DE 10 2016 220 859 A1, a valve train of an internal combustion engine with electromagnetically switchable cam followers is described, which is provided in an internal combustion engine for switching the stroke of the affected gas-exchange valves. The coupling pins are each arranged oriented longitudinally in the respective primary lever of the cam follower and can be brought into contact with a ramp surface of an armature rod of an associated electromagnet and can also be moved axially into a coupling position. The electromagnets are arranged with essentially vertical orientation above the cam follower and the associated camshaft on a carrier plate mounted on the affected cylinder head, wherein a larger structural height of the cylinder head is produced.
Because the arrangement of separate hydraulic switching pressure lines or electrical switching lines in a cylinder head of an internal combustion engine is relatively difficult and expensive due to the tight space requirements, in the not previously published DE 10 2017 101 792 A1, a variable valve train of an internal combustion engine was proposed in which the valve stroke of multiple functionally identical gas-exchange valves can be deactivated or switched by a single actuator.
The switchable cam followers of this valve train each have a primary lever and a secondary lever. The primary lever is supported with its one end on an associated support element supported on the housing side and with its other end on the valve shaft of the associated gas-exchange valve and is in tapping contact with the associated primary cams between its ends. The secondary lever is supported so that it can swivel on the primary lever, is in tapping contact with the associated secondary cams, and can be coupled with the primary lever by a movable coupling element. The coupling elements of the switchable cam followers are each constructed as a coupling pin that is guided so that it can move axially in a transverse hole of the primary lever and can be moved by a control pin supported so that it can move axially in a transverse hole of the secondary lever against the restoring force of a spring element into an opposing coupling hole of the secondary lever. Each control pin projects with its outer end from the secondary lever and is in switching connection with a control rod constructed as a flat rod on this lever by means of a rod-shaped connecting element directed upward. The control rod is arranged above the cam follower parallel to the allocated camshaft and can be moved longitudinally from a home position into a switched position by means of a linear actuator against the restoring force of a spring element.
Another valve train according to the class is known from JP 2004 108 252 A, in which an elongated switching elements can likewise be moved by a linear actuator against the restoring force of a spring laterally from a home position into a switched position. Control pins that couple or release valve switching elements with each other are also arranged there in transverse holes of the same.
In addition, from DE 10 2004 058 997 A1, a valve train is known, in which according to one embodiment, an elongated switching element that can be moved laterally by an electric actuator can be used for switching the valve stroke.
Moreover, from WO 2015/139 692 A1, an electromagnetic double actuator is known, by which two adjacent control elements can be displaced laterally.
Finally, from WO 2017/060 496 A1, a valve train of an internal combustion engine is known, in which a shaft that can be driven by an electric motor carries leaf spring-like control elements, with which control pins arranged on switching cam followers can be actuated by these cam followers in the longitudinal direction. By the use of these control pins, the inner lever and the outer lever of the respective switching cam followers can be coupled with each other or released from each other.
Based on this background, the present invention concerns the objective of providing a variable valve train of an internal combustion engine of the type noted above, in which the valve stroke of functionally identical first gas-exchange valves and functionally identical second gas-exchange valves of at least a few cylinders can be deactivated or switched independent from each other in groups with a space-saving and economical construction.
This objective is achieved by a valve train with one or more features of the invention. Advantageous constructions and refinements of the valve train according to the invention are described below and in the claims.
Accordingly, a variable valve train of an internal combustion engine with at least two functionally identical gas-exchange valves per cylinder is provided, whose valve stroke can be generated by at least one primary cam and one secondary cam of a camshaft and can be transmitted by a switchable cam follower selectively to the associated gas-exchange valves, wherein the respective cam follower has a primary lever in tapping contact with the associated primary cam and in switching contact with the associated gas-exchange valve and a secondary lever in tapping contact with the associated secondary cam and can be coupled with the primary lever by an axial displacement of a control pin guided in a transverse hole, wherein the respective control pins of the cam follower are connected by connecting elements constructed as leaf springs to an elongated switching element that is arranged above the cam follower parallel to the camshaft and can be shifted longitudinally by a linear actuator against the restoring force of a spring element from a home position into a switched position, wherein the control pins of the cam follower of the functionally identical first gas-exchange valves are in switching connection by the associated connecting elements with a first elongated switching element that can be moved longitudinally by a first linear actuator, wherein the control pins of the cam followers of functionally identical second gas-exchange valves are in switching connection by the associated connecting elements with a second elongated switching element that can be moved longitudinally by a second linear actuator, wherein the two elongated switching elements are arranged parallel one above the other with a small vertical distance and are guided so that they can move axially in multiple vertically adjacent, housing-fixed guide openings of a cylinder head, wherein the two elongated switching elements are each provided with passage openings with appropriately sized dimensions for the contactless passage of the connecting elements of the other elongated switching element, wherein the linear actuators are arranged radially adjacent in a housing of a common actuator module and are in switching connection by a tappet that is supported so that it can move axially in the housing with the associated elongated switching element and in which the linear actuators are formed as electromagnets each with an armature guided so that it can move axially in a coil body.
Due to the switching connection of the control pins of the cam followers of functionally identical first and second gas-exchange valves with separate elongated switching elements that can be moved longitudinally by separate linear actuators that are, however, arranged adjacent in a housing of a shared actuator module, in a simple way the ability is created to deactivate or switch the first valve stroke of the first gas-exchange valves and the second gas-exchange valves independent from each other.
Here, it is an especially space-saving arrangement that the two elongated switching elements are arranged in parallel one above the other with a slight vertical distance and are guided so that they can move axially in multiple vertically adjacent housing-fixed guide openings of a cylinder head. Because this arrangement of the control rods maintains the geometry of the switching connections between the control pins and the control rods above the leaf springs, the switchable cam followers of the first gas-exchange valves and the second gas-exchange valves can also have a structurally identical design.
For enabling the vertically stacked arrangement of the two elongated switching elements, these are each provided with passage openings with appropriately sized dimensions for the contactless passage of the connecting elements of the other control rods.
At least a few guide openings of the elongated switching elements are arranged preferably in bearing caps of the associated camshaft, so that no additional components are needed for guiding the elongated switching elements and no additional installation space is claimed.
To keep the installation space requirements of the two linear actuators to a minimum and to simplify their assembly and energy supply, the two linear actuators are advantageously arranged radially adjacent in a housing of a common actuator module and they are in switching connection by a tappet that is supported so that it can move axially in the housing with the associated elongated switching element.
The two linear actuators are preferably constructed as electromagnets each with an armature guided so that it can move axially in a coil body and are in switching connection by a transmission lever that is supported so that it can swivel in the housing with the relevant tappet. By this construction and arrangement of the transmission lever, the switching path of the tappet relative to the switching path of the armature and also the radial distance of the tappet relative to the radial distance of the armature can be changed in a suitable way.
In order to increase the switching path of the tappet in comparison to the switching path of the armature and in order to reduce the radial distance of the tappet relative to the radial distance of the armature, preferably such an arrangement of the transmission lever is provided in which the transmission levers are supported so that they can swivel radially outward with respect to a plane of symmetry between the electromagnets and radially inward with the associated tappet and are also in switching contact in-between with the armature of the associated electromagnet.
The elongated switching elements can be constructed, for example, as switching rods, flat bars, or as elongated switching plates.
For further illustration of the invention, drawings with an embodiment are provided. Shown in this drawing are:
In the perspective overview illustration of
The valve stroke of the first exhaust valves of all three cylinders that cannot be seen in the illustration of
The first and second switchable cam followers 22, 26 have essentially identical constructions here and each have a primary lever and a secondary lever. In the not-switched state of the cam followers 22, 26 in which the respective secondary lever is decoupled from the affected primary lever, the stroke profile of the primary cams 14, 18 is transmitted to the associated exhaust valves. In the switched state of the cam followers 22, 26 in which the respective secondary lever is coupled with a positive fit with the affected primary lever, the larger stroke of the primary cams 14, 18 or of the secondary cams 16, 20 is transmitted to the associated exhaust valves. The switching of the cam followers 22, 26 into the coupled state is realized by an axial displacement of a control pin 24, 28 that cannot be seen in
The control pins 24 of cam followers 22 of the first exhaust valves are in switching connection by the associated connecting elements 30 that are constructed as leaf springs and are connected in an articulated way with the respective control pins 24 with a first elongated switching means 34 that can be moved longitudinally by means of a first linear actuator 62 (
The two linear actuators 62, 64 are arranged in a housing 68 of a common actuator module 66 that is screwed with the cylinder head 2.
The leaf springs 30, 32 are each mounted on the relevant control pins 24, 28 according to a type of retaining plate by the placement and engagement with its hole that is open at the end in an annular groove arranged on the outer end of the respective control pin 24, 28. Possible constructions of such an articulated connection are indicated, for example, in the not previously published DE 10 2017 119 653 A1.
The elongated switching elements 34, 42 are arranged above the switchable cam followers 22, 26 parallel to the exhaust camshaft 12 at a small vertical distance in parallel one above the other and guided so that they can move axially in multiple adjacent housing-fixed guide openings 50, 52. In the present case, the first elongated switching element 34 is arranged above the second elongated switching element 42.
The housing-fixed guide openings 50, 52 for the two control rods 34, 42 are arranged in the bearing caps 8 of the camshaft carrier 6 for the exhaust camshaft 12.
The connecting elements 30, 32 constructed as leaf springs in the switchable cam followers 22, 26 each engage with play in a slot-shaped driver opening 38, 46 of the associated elongated switching elements 34, 42. In this way, the leaf springs 30, 32 can move with low wear in the driver openings 38, 46 of the elongated switching elements 34, 42 during the operation of the internal combustion engine. In addition, in this way, production tolerances in the arrangement and size of the driver openings 38, 46 and the elongated switching elements 34, 42 themselves can be equalized in a simple way by an enlarged switching path of the linear actuators 62, 64.
On their wider outer wall facing away from the cam followers 22, 26, the elongated switching elements 34, 42 are provided on each driver opening 38, 46 on the switching direction side with an arc-shaped spring clip 54, 56, whose free end for the elastic support of the associated leaf springs 30, 32 projects in the longitudinal direction into the affected driver opening 38, 46. In this way, the leaf springs 30, 32 are supported elastically and movable longitudinally in the driver openings 38, 46 of the elongated switching elements 34, 42, wherein the mechanical wear to the contact surfaces and the transmission of transverse forces to the control pins 24, 28 of the cam followers 22, 26 is reduced. For the contactless passage of the leaf springs 30, 32 of the other elongated switching elements 34, 42, the elongated switching elements 34, 42 are each provided with passage openings 40, 48 with appropriately sized dimensions.
In
In the detail A from
In the side view of
For those cam followers 22 in which the primary and secondary cams 14, 16 of the exhaust camshaft 12 are tapped by the primary and secondary levers just in the reference circle, the switching happens immediately. For those cam followers 22 in which the primary and secondary cams 14, 16 of the exhaust camshaft 12 are barely not tapped in the reference circle by the primary and secondary levers, the affected control pins 24 are initially only pretensioned in the axial direction. The actual switching takes place when the exhaust camshaft 12 continues to rotate, that is, when the primary and secondary cams 14, 16 are tapped by their primary and secondary levers simultaneously in the reference circle.
The second control rod 42 is in its home position 80 in the operating situation shown in
In the side view of
In those cam followers 26 in which the primary and secondary cams 18, 20 of the exhaust camshaft 12 are just tapped in the reference circle by the primary and secondary levers, the switching happens immediately. In those cam followers 26 in which the primary and secondary cams 18, 20 of the exhaust camshaft 12 are barely not tapped in the reference circle by the primary and secondary levers, the affected control pins 28 are initially pretensioned only axially and the actual switching takes place when the exhaust camshaft 12 continues to rotate, as soon as the primary and secondary cams 18, 20 are tapped by their primary and secondary levers simultaneously in the reference circle.
The first elongated switching element 34 is in its homes position 78, so that the switchable cam followers 22 of the first exhaust valves are in their not-switched state, in which the relevant secondary levers are decoupled from the primary levers.
In the side view of
When the linear actuators 62, 64 are switched off, the control rods 34, 42 are restored opposite the switching direction 82 into their home position 78, 80 by the restoring force of the respective helical springs 74, 76. The decoupling of the switchable cam followers 22, 26 is realized by an axial displacement of the affected control pins 24, 28 outward, which is realized by the restoring force of an internal spring element and is possible with the simultaneous tapping of the primary and secondary cams 14, 16; 18, 20 of the exhaust camshaft 12 by the primary and secondary levers, that is, for control pins 24, 28 free of transverse force.
In the perspective view of
As the section view according to
The two transmission levers 100, 102 are supported so that they can swivel with respect to a plane of symmetry 104 between the electromagnets 99, 94 on the radial outer side on a bearing rib 106, 108 inserted into the housing 68 and are in switching contact radially on the inner side with the associated tappet 70, 72 and in-between with the armatures 92, 98 of the associated electromagnets 88, 94. Through this arrangement of the transmission levers 100, 102, the switching path of the tappets 70, 72 is increased relative to the switching path of the armature 92, 98 and the radial distance of the tappets 70, 72 is significantly reduced relative to the radial distance of the armature 92, 98 of the electromagnets 88, 94. For powering the electromagnets 88, 94, the housing 68 of the actuator module 66 is provided with a molded connector bushing 110.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102017129419.8 | Dec 2017 | DE | national |
