Variable valve drive

Abstract

The disclosure relates to a variable valve drive, in particular with a sliding cam system, for an internal combustion engine. The variable valve drive has a cam carrier which has a first and second cam and a first, second, and third engagement track. A first actuator is designed to engage into the first engagement track in order to displace the cam carrier in a first axial direction. A second actuator is designed to engage into the second engagement track in order to displace the cam carrier in a second axial direction which is opposite to the first axial direction, and to engage into the third engagement track in order to displace the cam carrier in the first axial direction. The variable valve drive can have the advantage that, even in the event of a failure of the first actuator, a displacement of the cam carrier that is normally effected by means of the first actuator is possible by means of the second actuator.

Claims

1. A variable valve drive comprising: a shaft; a cam carrier which is arranged rotationally conjointly and axially displaceably on the shaft and which has a first cam, a second cam, a first engagement track, a second engagement track, and a third engagement track; a first actuator which is designed to engage into the first engagement track in order to displace the cam carrier in a first axial direction; and a second actuator which is designed to engage into the second engagement track in order to displace the cam carrier in a second axial direction which is opposite to the first axial direction, and to engage into the third engagement track in order to displace the cam carrier in the first axial direction.

2. The variable valve drive according to claim 1, wherein: an engagement of the first actuator into the first engagement track effects a displacement of the cam carrier from a first axial position into a second axial position; and an engagement of the second actuator into the third engagement track effects a displacement of the cam carrier from the first axial position into the second axial position or an engagement of the second actuator into the second engagement track effects a displacement of the cam carrier from the second axial position into the first axial position.

3. The variable valve drive according to claim 2, further comprising: a force transmission device that, in the first axial position of the cam carrier, produces an operative connection between the second cam and a gas exchange valve, wherein the second cam is designed as an engine braking cam, or an internal combustion engine that, in the first axial position of the cam carrier, is operated in an engine braking mode.

4. The variable valve drive according to claim 1, wherein: when the second actuator engages into the third engagement track, an end of a throw-out portion of the third engagement track is reached before the cam carrier reaches a second axial position; or when the second actuator engages into the third engagement track, the cam carrier is accelerated such that the cam carrier, after the throw-out of the second actuator of the third engagement track, moves yet further in free flight as far as the second axial position; or a pin of the second actuator is thrown out of the third engagement track before the cam carrier reaches the second axial position.

5. The variable valve drive according to claim 1, further comprising a control unit which is designed to activate the first actuator or the second actuator.

6. The variable valve drive according to claim 5, wherein the control unit is designed to activate the second actuator to engage into the third engagement track if the first actuator or an axial displacement by the first actuator exhibits a malfunction.

7. The variable valve drive according to claim 5, wherein: the control unit is designed to lower an engine rotational speed of an internal combustion engine to below or to, and/or keep an engine rotational speed of the internal combustion engine below or at, a predetermined limit value before or while the control unit activates the second actuator to engage into the third engagement track; or the control unit is designed to lower an engine rotational speed of the internal combustion engine to, or keep an engine rotational speed of the internal combustion engine at, an idle rotational speed before or while the control unit activates the second actuator to engage into the third engagement track.

8. The variable valve drive according to claim 5, wherein the control unit is designed to activate the second actuator in multiple successive attempts to engage into the third engagement track until such time as the cam carrier has been displaced into a second axial position.

9. The variable valve drive according to claim 5, wherein the control unit is designed to, in an event of a malfunction of the first actuator, prevent an axial displacement of the cam carrier by engagement of the second actuator into the second engagement track.

10. The variable valve drive according to claim 1, wherein an arc length of the third engagement track is shorter than an arc length of the first engagement track or an arc length of the second engagement track.

11. The variable valve drive according to claim 1, wherein an arc length of the third engagement track lies in a range of less than or equal to 90 camshaft angle or greater than or equal to 20 camshaft angle.

12. The variable valve drive according to claim 1, wherein a depth of the third engagement track is smaller than a depth of the first engagement track or a depth of the second engagement track.

13. The variable valve drive according to claim 1, wherein a depth of the third engagement track lies in a range of less than or equal to 2 mm and/or greater than or equal to 1 mm.

14. The variable valve drive according to claim 1, wherein a gradient of the third engagement track is steeper than a gradient of the first engagement track or a gradient of the second engagement track.

15. The variable valve drive according to claim 1, wherein an axial extent of the third engagement track along an axial axis of the cam carrier is shorter than an axial extent of the first engagement track along the axial axis of the cam carrier or an axial extent of the second engagement track along the axial axis of the cam carrier.

16. The variable valve drive according to claim 1, wherein the third engagement track is dimensioned to be smaller than the first engagement track or the second engagement track.

17. The variable valve drive according to claim 1, wherein a start of a run-in portion of the third engagement track adjoins an end of a throw-out portion of the second engagement track.

18. The variable valve drive according to claim 1, wherein a start of a run-in ramp of the third engagement track adjoins an end of a throw-out ramp of the second engagement track in a circumferential direction around the cam carrier.

19. The variable valve drive according to claim 1, wherein: the cam carrier has a fourth engagement track; and the first actuator is designed to engage into the fourth engagement track in order to displace the cam carrier in the second axial direction, or an engagement of the first actuator into the fourth engagement track effects a displacement of the cam carrier from a second axial position of the cam carrier into a first axial position of the cam carrier.

20. A motor vehicle or a utility vehicle comprising a variable valve drive according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-described embodiments and features of the disclosure may be combined with one another in any desired manner. Further details and advantages of the disclosure will be described below with reference to the appended drawings. In the drawings:

(2) FIG. 1 shows an isometric view of an exemplary variable valve drive according to the present disclosure;

(3) FIG. 2 shows a plan view, or a view from above, of the exemplary variable valve drive; and

(4) FIG. 3 shows a detail illustration of a portion of a cam carrier of the exemplary variable valve drive.

(5) The embodiments shown in the figures at least partially correspond, and therefore similar or identical parts are denoted with the same reference designations, and for the explanation of the parts, reference is also made to the description of the other embodiments or figures in order to avoid repetitions.

DETAILED DESCRIPTION

(6) FIGS. 1 and 2 show a variable valve drive 10. The variable valve drive 10 has a shaft (camshaft) 12, a sliding cam system 14, a force transmission device 16, a first gas exchange valve 18 and a second gas exchange valve 20. The gas exchange valves 18, 20 may for example be inlet valves or outlet valves of a cylinder of an internal combustion engine.

(7) The variable valve drive 10 may be used for adapting the valve control curves of the first and second gas exchange valves 18, 20. The variable valve drive 10 is assigned to an internal combustion engine (not illustrated). The internal combustion engine may for example be part of a utility vehicle, for example a bus or a heavy goods vehicle. The internal combustion engine may have one or more cylinders.

(8) The sliding cam system 14 has a cam carrier 22 and an actuator device with a first actuator 24 and a second actuator 26.

(9) The cam carrier 22 is arranged rotationally conjointly and axially displaceably on the shaft 12, for example by means of an axial profiling of the outer circumference of the shaft 12 and of the inner circumference of the cam carrier 22 (for example toothed shaft connection or spline connection). It is possible for multiple cam carriers 22 to be able to be arranged on the shaft 12, for example in order to actuate gas exchange valves of multiple cylinders of the internal combustion engine. The cam carrier 22 has four cams 28-31, a first engagement track (switching slotted guide) 32, a second engagement track (switching slotted guide) 34 and a third engagement track 36 (see FIG. 3, not visible in FIGS. 1 and 2). As described in detail elsewhere herein, the third engagement track 36 serves in particular as an emergency engagement track in the event that the first actuator 24 fails.

(10) The cam carrier 22 forms, together with the shaft 12, a camshaft. The shaft 12 with the cam carrier 22 is arranged as an overhead camshaft (OHC). The shaft 12 with the cam carrier 22 may be provided as part of a double camshaft system (double overhead camshaftDOHC) or as a single camshaft (single overhead camshaftSOHC).

(11) The four cams 28-31 may have different cam contours in order to generate different valve control curves for the gas exchange valves 18, 20. The cams 28-31 may at least partially also be formed as zero-lift cams. The different cam contours of the cams 28-31 be used for example for reducing fuel consumption, for thermal management or for realizing an engine brake. In the exemplary embodiment described here, the second cam 29 is designed as an engine braking cam. An engine braking function by means of the engine braking cam may be realized for example by virtue of an outlet valve actuated by the engine braking cam initially being held closed in the compression stroke and/or in the discharge stroke, and then being opened. In this way, a (twofold) decompression into the exhaust-gas tract is effected, which brakes the internal combustion engine. The associated cylinder is not fired. Furthermore, the fourth cam 31 may for example be designed as a zero-lift cam.

(12) The four cams 28-31 are arranged offset with respect to one another along a longitudinal axis of the cam carrier 22. The first cam 28 is arranged adjacent to the second cam 29. The third cam 30 is arranged adjacent to the fourth cam 31. The first and second cams 28, 29 serve selectively for the actuation of the first gas exchange valve 18. The third and fourth cams 30, 31 serve selectively for the actuation of the second gas exchange valve 20. The cams 28, 29 and 30, 31 are arranged at opposite ends of the cam carrier 22. In other embodiments, it is possible for additional cams, fewer cams and/or alternative arrangements of the cams to be provided, for example a central arrangement of the cams on the cam carrier.

(13) The actuators 24, 26 may be electrically (for example electromotively, electromagnetically), pneumatically and/or hydraulically actuated. In the embodiment illustrated, the actuators are electrically actuated (see the electrical terminals at the upper ends thereof).

(14) The sliding cam system 14 may additionally have a locking device (not illustrated). The locking device may be designed so as to secure the cam carrier 22 axially on the shaft 12 in the desired axial positions. For this purpose, the locking device may for example have an elastically preloaded blocking body. The blocking body may, in a first axial position of the cam carrier 22, engage into a first recess of the cam carrier 22 and, in a second axial position of the cam carrier 22, engage into a second recess of the cam carrier 22. The locking device may for example be provided in the shaft 12.

(15) The force transmission device 16 has a first force transmission element 40, a second force transmission element 41, a lever axle 42 and a multiplicity of bearing blocks 43. The force transmission elements 40, 41 are arranged rotatably on the lever axle 42 so as to be pivotable about the lever axle 42. The lever axle 42 is mounted or held in the bearing blocks 43. The shaft 12 is mounted rotatably in the bearing blocks 43. It is for example also possible for separate bearing blocks to be provided for the lever axle 42 and the shaft 12. The actuators 24 and 26 are carried on the lever axle 42 by a carrying device 46.

(16) In the embodiment shown, the force transmission elements 40, 41 are formed as rocker levers, and the lever axle 42 is thus formed as a rocker lever axle. It is however for example also possible for the force transmission elements 40, 41 to be formed as valve levers, and for the lever axle 42 to thus be formed as a valve lever axle.

(17) In the embodiment illustrated, the first force transmission element 40 serves for actuating the first gas exchange valve 18, and the second force transmission element 41 serves for actuating the second gas exchange valve 20. It is however also possible, for example, for multiple gas exchange valves to be actuated by means of only one force transmission element, for example with the interposition of a valve bridge.

(18) The force transmission elements 40, 41 have in each case one cam follower 44, 45, for example in the form of a rotatably mounted roller. The cam followers 44, 45 follow a cam contour of the cams 28-31 in a manner dependent on an axial position of the cam carrier 22.

(19) Referring to FIGS. 1 to 3, the functioning of the actuators 24, 26 in interaction with the engagement tracks 32, 34 and 36 will be described below.

(20) The first engagement track 32, the second engagement track 34 and the third engagement track 36 (visible only in FIG. 3) are provided centrally on the cam carrier 22. It is also possible for the engagement tracks to be arranged eccentrically, for example at the ends on the cam carrier. Engagement tracks 32, 34 and 36 extend helically as depressions (grooves or slotted guides) in the cam carrier 22 about a longitudinal axis of the shaft 12.

(21) For the axial displacement of the cam carrier 22, it is possible for pins 24A, 26A (see FIG. 3), which are displaceable radially with respect to the longitudinal axis of the shaft 12, of the actuators 24, 26 to engage selectively into the engagement tracks 32, 34, 36. In detail, a pin 24A of the first actuator 24 can engage selectively into the first engagement track 32 in order to displace the cam carrier 22 from a first axial position to a second axial position. FIGS. 1 to 3 illustrate the cam carrier 22 in the second axial position by way of example. The pin 24A of the first actuator 24 can only engage into the first engagement track 32 for the displacement into the second axial position if the cam carrier 22 is in the first axial position.

(22) The pin 26A of the second actuator 26 can in turn engage selectively into the second engagement track 34 if the cam carrier 22 is in the second axial position. Then, the cam carrier 22 is displaced from the second axial position back to the first axial position (to the right in FIG. 3).

(23) In the second axial position, illustrated in FIGS. 1-3, of the cam carrier 22, the gas exchange valves 18, 20 are actuated by the first cam 28 and the third cam 30. Specifically, the first gas exchange valve 18 is actuated by the first cam 28 and the second gas exchange valve 20 is actuated by the third cam 30.

(24) In the first axial position of the cam carrier 22, the gas exchange valves 18, 20 are actuated by the second cam 29 and the fourth cam 31. Specifically, the first gas exchange valve 18 is actuated by the second cam 29 and the second gas exchange valve 20 is actuated by the fourth cam 31.

(25) As already mentioned, the second cam 29 may be designed as an engine braking cam, and the fourth cam 31 may be designed as a zero-lift cam. Thus, in the first axial position of the cam carrier 22, an engine braking mode of the internal combustion engine can be effected. By contrast to this, in the second axial position of the cam carrier 22, a normal mode of the internal combustion engine can for example be effected.

(26) The axial displacement of the cam carrier 22 is triggered by virtue of the fact that the deployed pin 24A, 26A of the respective actuator 24, 26 is positionally fixed with respect to an axial direction of the shaft 12. Consequently, the displaceable cam carrier 22 is, owing to the helical form of the engagement tracks 32, 34, displaced in a longitudinal direction of the shaft 12 if one of the deployed pins 24A, 26A engages into the respective engagement track 32, 34. At the end of the axial displacement process, the deployed pin 24A, 26A of the respective actuator 24, 26 is guided by the respective engagement track 32, 34 via a pushing-out ramp oppositely to the deployment direction and is thus retracted or thrown out. The pin 24A, 26A of the respective actuator 24, 26 passes out of engagement with the respective engagement track 32, 34.

(27) For as long as the actuators 24 and 26 are functional, it is possible for switching between the first axial position and the second axial position of the cam carrier 22 to be performed as desired. It is thus for example possible for an engine braking mode to be realized in the first axial position and for a normal mode of the gas exchange valves 18, 20 to be realized in the second axial position.

(28) It is however conceivably possible for the first actuator 24 to fail. As a consequence, it is no longer possible by means of the first actuator 24 to perform a switch from the first axial position of the cam carrier 22 for the engine braking mode to the second axial position of the cam carrier 22 for the normal mode. To nevertheless permit an axial displacement of the cam carrier 22 from the first axial position to the second axial position, the third engagement track 36 for the second actuator 26 is provided. In particular in the event of a malfunction of the first actuator 24, it is thus nevertheless still possible to switch to the normal mode by means of the second actuator 26.

(29) The third engagement track 36 is designed as an emergency engagement track which is expediently utilized by the second actuator 26 only if the first actuator 24 fails. This may be detected for example by means of a control unit 38 which is schematically illustrated in FIG. 2. The control unit 38 may have a communication connection to the first actuator 24 and to the second actuator 26, and for example to one or more further components of the internal combustion engine, in particular for the closed-loop control of a rotational speed of the internal combustion engine. It is possible for the control unit 38 to directly or indirectly activate the first actuator 24 and/or the second actuator 26.

(30) The third engagement track 36 may at least partially likewise extend helically. The third engagement track 36 may in particular be shallower (less deep) and shorter (less long) than the engagement tracks 32, 34. For example, an arc length of the third engagement track may lie in a range between 20 camshaft angle and 90 camshaft angle, for example between 30 camshaft angle and 60 camshaft angle, whereas an arc length of the engagement tracks 32, 34 may be greater, for example between 120 camshaft angle and 160 camshaft angle. It is possible for a depth of the third engagement track 36 to lie in a range between 2 mm and 3 mm, whereas a depth of the engagement tracks 32, 34 may be greater, for example 3 mm to 6 mm, in particular approximately 4.5 mm. Furthermore, the third engagement track 36 may have a steeper gradient than the engagement tracks 32, 34.

(31) The third engagement track 36 is thus designed to permit a switch from the first axial position into the second axial position in a relatively small range, in particular in relation to the engagement tracks 32, 34. It must be taken into consideration here that the engagement tracks 32, 34 and 36 are expedient positioned only in the base circle range of the cams 28-31, because a switch between the cams 28-31 can be possible only here. The geometrical adaptations of the third engagement track 36 in relation to the engagement tracks 32, 34 are made possible by virtue of the fact that it is in particular used only as an emergency engagement track. The emergency switch may take place at a relatively low, predetermined engine rotational speed (and thus camshaft rotational speed). Here, relatively low forces act during the displacement of the cam carrier 22.

(32) If the control unit 38 detects for example that the first actuator 24 has a malfunction and a switch from the first axial position back into the second axial position is desired, the control unit 38 can lower the engine rotational speed to a predetermined rotational speed, for example an idle rotational speed for example around 600 rpm. After the pin 26A of the second actuator 26 has crossed or passed a run-out portion (for example run-out ramp or throw-out ramp) 34A of the second engagement track 34 without being actuated, the second actuator 26 is activated, for example electrically energized, by the control unit 38. The pin 26A of the second actuator 26 then runs into the run-in portion or the run-in ramp 36E of the third engagement track 36, which adjoins the run-out portion 34A of the second engagement track 34 with a small spacing or in the single-digit camshaft angle range (see FIG. 3). Owing to the low rotational speed of the shaft 12, sufficient time remains for the engagement into the third engagement track 36.

(33) The pin 26A of the second actuator 26 then effects a displacement of the cam carrier 22 from the first axial position in the direction of the second axial position. Here, the pin 26A may be thrown out of the third engagement track 36, by means of a throw-out portion or run-out portion 36A of the third engagement track 36, already before the cam carrier 22 actually reaches the second axial position. After the throw-out of the pin 26A, the cam carrier 22 moves, as it were, in defined free flight as far as the second axial position, in which it is locked by means of the locking device (not illustrated). The cam carrier 22 is thus accelerated by means of engagement of the pin 26A into the third engagement track 36, such that the cam carrier can reach the second axial position in free flight. At the same time, the acceleration may be selected such that the cam carrier 22 does not impact overly intensely against the corresponding axial stop of the second axial position, in order to prevent an overly intense rebound with the consequence of locking in the second axial position not being possible.

(34) It is possible for the control unit 38 to perform multiple attempts until the cam carrier 22 is, by engagement of the pin 26A into the third engagement track 36, actually moved into the second axial position and expediently locked therein.

(35) After a displacement of the cam carrier 22 by means of engagement into the third engagement track 36, the control unit 38 can permit a higher engine rotation speed again. Alternatively or in addition, the controller 38 may expediently prevent the cam carrier 22 from being displaced into the first axial position again by means of the second actuator 26.

(36) It is for example also possible for a fourth engagement track (not illustrated in the figures) to be provided in the cam carrier 22, by means of which fourth engagement track the first actuator 24 can, for example in the event of a malfunction of the second actuator 26, effect an axial displacement of the cam carrier 22 from the second axial position into the first axial position. The fourth engagement track may be designed and used analogously to the third engagement track 36.

(37) The disclosure is not restricted to the exemplary embodiments described above. In fact, numerous variants and modifications are possible which likewise make use of the concept of the disclosure and thus fall within the scope of protection.

LIST OF REFERENCE DESIGNATIONS

(38) 10 Variable valve drive

(39) 12 Shaft

(40) 14 Sliding cam system

(41) 16 Force transmission device

(42) 18 First gas exchange valve

(43) 20 Second gas exchange valve

(44) 22 Cam carrier

(45) 24 First actuator

(46) 24A Pin

(47) 26 Second actuator

(48) 26A Pin

(49) 28 First cam

(50) 29 Second cam

(51) 30 Third cam

(52) 31 Fourth cam

(53) 32 First engagement track

(54) 34 Second engagement track

(55) 34A Run-out portion

(56) 36 Third engagement track

(57) 36A Run-out portion

(58) 36E Run-in portion

(59) 38 Control unit

(60) 40 First force transmission element

(61) 41 Second force transmission element

(62) 42 Lever axle

(63) 43 Bearing block

(64) 44 Cam follower

(65) 45 Cam follower

(66) 46 Carrying device