Variable valve train of an internal combustion engine

Abstract

A variable valve train with at least two functionally identical gas-exchange valves per cylinder, having primary cam and a secondary cam generated valve strokes that are transmitted by a switchable cam follower selectively to the gas-exchange valves. The respective cam follower has a primary lever in tapping contact with the primary cam and in switching contact with the gas-exchange valve and a secondary lever that is in tapping contact with the secondary cam and is coupleable with the primary lever by a control pin. The respective control pins are connected by connecting elements to respective first and second elongated switching elements, which are arranged above the cam followers parallel to the camshaft and are displaceable longitudinally by a linear actuator from a home into a switched position. The control pins of the cam follower of functionally identical gas-exchange valves are in switching connection with a respective one of the first and second elongated switching elements for common movement.

Claims

1. A variable valve train of an internal combustion engine with at least two gas-exchange valves per cylinder, the variable valve train comprising: a camshaft with primary cams and secondary cams that are adapted to generate valve strokes; switchable cam followers that selectively transmit the valve strokes to associated ones of the gas-exchange valves; the switchable cam followers have primary levers in tapping contact with an associated one of the primary cams and in switching contact with an associated one of the gas-exchange valves and secondary levers in tapping contact with an associated one of the secondary cams; control pins that are configured to couple the secondary levers with the primary levers via axial displacement of the control pins, each said control pin being guided in a respective transverse hole; connecting elements connected to the control pins of the switchable cam followers, the connecting elements are constructed as leaf springs; first and second elongated switching elements arranged above the switchable cam followers, and the first and second elongated switching elements are parallel to the camshaft; first and second linear actuators that respectively displace the associated first or second elongated switching elements longitudinally against a restoring force of respective first and second spring elements from a home position into a switched position; the control pins of the switchable cam followers of first ones of the gas-exchange valves are in switching connection with the first elongated switching element by associated ones of the connecting elements, and are configured to move longitudinally by the first linear actuator; the control pins of the switchable cam followers of second ones of the gas-exchange valves are in switching connection with the second elongated switching element by associated ones of the connecting elements, and are configured to move longitudinally by the second linear actuator; the first and second elongated switching elements are arranged in parallel with a vertical spacing therebetween in a use position, one above the other, and are guided for axial movement in multiple vertically adjacent, housing-fixed guide openings of a cylinder head; the first elongated switching elements is provided with at least one passage opening dimensioned to receive the connecting elements of the second elongated switching element, and the second elongated switching element is provided with at least one passage opening dimensioned to receive the connecting elements of the first elongated switching element; a common actuator module having a housing in which the first and second linear actuators are arranged radially adjacent and are each in switching connection by a tappet that is held in the housing for axial movement with the first or second elongated switching element; and the first and second linear actuators are constructed as electromagnets each including an armature guided in a coil body for axial movement.

2. The variable valve train according to claim 1, further comprising bearing caps for the camshaft, the bearing caps include at least a few guide openings for the first and second elongated switching elements.

3. The variable valve train according to claim 1, wherein the armatures of the electromagnets are in switching connection with an associated one of the tappets via transmission levers supported for swiveling movement in the housing.

4. The variable valve train according to claim 3, wherein the transmission levers are each supported to swivel radially outward with respect to a plane of symmetry between the electromagnets and are each in switching contact with the tappets and the armatures of the electromagnets.

5. A variable valve train of an internal combustion engine with at least two gas-exchange valves per cylinder, the variable valve train comprising: a camshaft with primary cams and secondary cams that are adapted to generate valve strokes; switchable cam followers that selectively transmit the valve strokes to associated ones of the gas-exchange valves; the switchable cam followers have primary levers in tapping contact with an associated one of the primary cams and in contact with an associated one of the gas-exchange valves and secondary levers in tapping contact with an associated one of the secondary cams; control pins that are configured to couple the secondary levers with the primary levers via axial displacement of the control pins, each said control pin being guided in a respective transverse hole; connecting elements connected to of the control pins of the switchable cam followers; first and second elongated switching elements arranged parallel to the camshaft; first and second linear actuators that respectively displace the first or second elongated switching elements longitudinally against a restoring force of respective first and second spring elements from a respective home position into a respective switched position; the control pins of the switchable cam followers of first ones of the gas-exchange valves are connected to the first elongated switching element by associated ones of the connecting elements, and are configured to move longitudinally by the first linear actuator; the control pins of the switchable cam followers of second ones of the gas-exchange valves are connected to the second elongated switching element by associated ones of the connecting elements, and are configured to move longitudinally by the second linear actuator; the first and second elongated switching elements are arranged in parallel with a spacing therebetween in a use position, and are guided for axial movement in multiple adjacent, housing-fixed guide openings of a cylinder head; the first elongated switching element is provided with at least one passage opening dimensioned to receive the connecting elements of the second elongated switching element; a common actuator module having a housing in which the first and second linear actuators are arranged radially adjacent to one another and are each in contact with the associated one of the first or second elongated switching element; and the first and second linear actuators are constructed as electromagnets each including an armature guided in a coil body for axial movement.

6. The variable valve train according to claim 5, further comprising first and second tappets associated with the respective first and second elongated switching elements, the first and second tappets being driven by the armatures.

7. The variable valve train according to claim 6, wherein the armatures of the electromagnets are in switching connection with the tappets via transmission levers supported for swiveling movement in the housing.

8. The variable valve train according to claim 7, wherein the transmission levers are each supported to swivel radially outward with respect to a plane of symmetry between the electromagnets and are each in switching contact with the tappets and the armatures of the electromagnets.

9. The variable valve train according to claim 5, wherein each of the first and second elongated switching elements are guided in openings in camshaft bearing caps.

10. The variable valve train according to claim 5, wherein the second elongated switching element is provided with at least one passage opening dimensioned to receive the connecting elements of the first elongated switching element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For further illustration of the invention, drawings with an embodiment are provided. Shown in this drawing are:

(2) FIG. 1 a preferred embodiment of a variable valve train according to the invention in a combustion piston engine with three cylinders and two functionally identical gas-exchange valves for each cylinder with six switchable cam followers in a perspective overview,

(3) FIG. 2 the valve train according to FIG. 1 in the non-switched state of all switchable cam followers in a side view,

(4) FIG. 2A an enlarged detail A of the valve train according to FIG. 2,

(5) FIG. 3 the valve train according to FIG. 1 in the switched state of the switchable cam followers of functionally identical first gas-exchange valves and in the non-switched state of the switchable cam followers of functionally identical second gas-exchange valves in a side view,

(6) FIG. 3A an enlarged detail A of the valve train according to FIG. 3,

(7) FIG. 4 the valve train according to FIG. 1 in the non-switched state of the switchable cam followers of the functionally identical first gas-exchange valves and in the switched state of the switchable cam followers of the functionally identical second gas-exchange valves in a side view,

(8) FIG. 4A an enlarged detail A of the valve train according to FIG. 4,

(9) FIG. 5 the valve train according to FIG. 1 in the switched state of all switchable cam followers in a side view,

(10) FIG. 5A an enlarged detail A of the valve train according to FIG. 5,

(11) FIG. 6 an actuator module for switching the switchable cam followers in a perspective view, and

(12) FIG. 6A the actuator module according to FIG. 6 in a longitudinal middle section.

DETAILED DESCRIPTION

(13) In the perspective overview illustration of FIG. 1, a cylinder head 2 of an internal combustion engine is shown with three cylinders Z1, Z2, Z3 arranged in line and also one intake valve and two exhaust valves per cylinder together with components of a valve train 4 according to the invention. A camshaft carrier 6 screwed with the cylinder head 2 has four semicircular sliding bearing sections for supporting an intake camshaft 10 and also four semicircular sliding bearing sections for supporting an exhaust camshaft 12. The remaining sliding bearing sections for supporting the intake camshaft 10 and the exhaust camshaft 12 are part of bearing caps 8 that are placed and screwed on the camshaft carrier 6 after the camshafts 10, 12 are inserted. In FIG. 1, only the bearing caps 8 of the exhaust camshaft 12 are shown.

(14) The valve stroke of the first exhaust valves of all three cylinders that cannot be seen in the illustration of FIG. 1 can be switched by allocated first switchable cam followers 22. Likewise, the valve stroke of the second exhaust valves of all three cylinders that cannot be seen in FIG. 1 can be switched by allocated second switchable cam followers 26. For this purpose, the exhaust camshaft 12 for the first exhaust valves and also for the second exhaust valves has a centrally arranged primary cam 14, 18 and two secondary cams 16, 20 arranged on both sides of the respective primary cam 14, 18.

(15) 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 FIG. 1 and is supported so that it can move axially in a transverse hole of the respective secondary lever and projects with its axially outer end from the secondary lever and is in switching connection with this by an upward oriented, rod-shaped connecting element 30, 32 each with elongated switching elements 34, 42 constructed as a flat rod. The actual construction and the function of the switchable cam followers 22, 26 corresponds to that of the cam followers described in detail in DE 10 2017 101 792 A1, so that the contents of this publication should also be considered as incorporated herein by reference as if fully set forth. Therefore, further description will be omitted here.

(16) 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 (FIG. 2). The control pins 28 of cam followers 26 of the second exhaust valves are in switching connection by the connecting elements 32 also constructed as leaf springs and connected in an articulated way with the respective control pin 28 with a second elongated switching element 42 that can be moved longitudinally by a second linear actuator 64.

(17) 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.

(18) 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.

(19) 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.

(20) 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.

(21) 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.

(22) 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.

(23) In FIG. 2, the camshaft carrier 6 is shown together with the switchable cam followers 22, 26, the leaf springs 30, 32, the elongated switching elements 34, 42, and the actuator module 66 in a side view. In addition, in FIG. 2, hydraulic support elements 58, 60 are also shown, by which the cam followers 22, 26 are supported in the installed state on one end on the cylinder head 2.

(24) In the detail A from FIG. 2 shown enlarged in FIG. 2A, it can be seen that the two linear actuators 62, 64 are each in switching connection with an angled end 36, 44 of the associated elongated switching elements 34, 42 by a tappet 70, 72 that can move axially. The two elongated switching elements 34, 42 are each held in the home position 78, 80 shown in FIGS. 2 and 2A by a spring element 74, 76 that is constructed as a helical spring and is arranged between the angled end 36, 42 of the relevant elongated switching element 34, 42 and the adjacent end wall of the camshaft carrier 6. The elongated switching elements 34, 42 can be moved by the linear actuators 62, 64 each independently from each other against the restoring force of the respective helical spring 74, 76 by a longitudinal displacement in a switching direction 82 into the switched position 84, 86 shown in the following figures.

(25) In the side view of FIG. 3 and the section A from FIG. 3 shown enlarged in FIG. 3A, the first elongated switching element 34 is shifted by an actuation of the first linear actuator 62 against the restoring force of the affected helical spring 74 by the associated tappet 70 in the switching direction 82 into its switched position 84, in which the switchable cam followers 22 of the first exhaust valve are switched or will be switched by the associated leaf springs 30 through an axial displacement of their control pins 24 inward into the coupled switch state.

(26) 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.

(27) The second control rod 42 is in its home position 80 in the operating situation shown in FIGS. 3 and 3A, so that the switchable cam followers 26 of the second exhaust valves are in their not-switched state in which the relevant secondary levers are decoupled from the primary levers.

(28) In the side view of FIG. 4 and the section A from FIG. 4 shown enlarged in FIG. 4A, the second control rod 42 is shifted into its switched position 86 by an actuation of the second linear actuator 64 against the restoring force of the associated helical spring 76 by the associated tappet 72 in the switching direction 82, in which the switchable cam followers 26 of the second exhaust valves are switched or will be switched inward into the coupled switch state by the associated leaf springs 32 by an axial displacement of their control pins 28.

(29) 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.

(30) 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.

(31) In the side view of FIG. 5 and the section A from FIG. 5 shown enlarged in FIG. 5A, both the first elongated switching element 34 is shifted by an actuation of the first linear actuator 62 and also the second elongated switching element 42 is shifted by an actuation of the second linear actuator 64 against the restoring force of the associated helical springs 74, 76 by the associated tappets 70, 72 in the switching direction 82 into their switched positions 84, 86. In these switched positions 84, 86, the switchable cam followers 22 of the first exhaust valves and the switchable cam followers 26 of the second exhaust valves are switched or will be switched inward into the coupled switch state by the respective leaf springs 30, 32 by an axial displacement of their control pins 24, 28.

(32) 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.

(33) In the perspective view of FIG. 6 and the longitudinal middle section of FIG. 6A, a preferred construction of an actuator module 66 is shown with the two already mentioned linear actuators 62, 64. The two linear actuators 62, 64 are arranged radially adjacent a housing 68 of the actuator module 66 and each are in switching connection with an axially movable tappet 70, 72 supported in the housing 68. In the installed state, the tappets 70, 72 each contact the angled end 36, 44 of the associated elongated switching elements 34, 42 on the outside.

(34) As the section view according to FIG. 6A shows, in particular, the two linear actuators 62, 64 are constructed as electromagnets 88, 94 each with an armature 92, 98 guided axially movable in a coil body 90, 96. The armatures 92, 98 of the electromagnets 88, 94 are each in switching connection with the associated tappet 70, 72 by a transmission lever 100, 102 that is supported so that it can swivel.

(35) 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.

LIST OF REFERENCE SYMBOLS

(36) 2 Cylinder head 4 Valve train 6 Camshaft carrier 8 Bearing cap 10 Intake camshaft 12 Exhaust camshaft 14 Primary cam 16 Secondary cam 18 Primary cam 20 Secondary cam 22 Switchable cam follower 24 Control pin 26 Switchable cam follower 28 Control pin 30 Connecting element, leaf spring 32 Connecting element, leaf spring 34 Elongated switching means, first control rod 36 Angled end 38 Driver opening 40 Passage opening 42 Elongated switching means, second control rod 44 Angled end 46 Driver opening 48 Passage opening 50 Guide opening 52 Guide opening 54 Spring clip 56 Spring clip 58 Hydraulic support element 60 Hydraulic support element 62 First linear actuator 64 Second linear actuator 66 Actuator module 68 Housing 70 First tappet 72 Second tappet 74 Spring element, helical spring 76 Spring element, helical spring 78 Home position of the switching means 34 80 Home position of the switching means 42 82 Switching direction 84 Switched position of the switching means 34 86 Switched position of the switching means 42 88 First electromagnet 90 First coil body 92 First armature 94 Second electromagnet 96 Second coil body 98 Second armature 100 First transmission lever 102 Second transmission lever 104 Plane of symmetry 106 First bearing rib 108 Second bearing rib 110 Connector bushing A Drawing section Z1 First cylinder Z2 Second cylinder Z3 Third cylinder