Variable valve train with a rocker arm

Abstract

A variable valve train for a gas exchange lifting valve of an internal combustion engine. The valve can be moved between open and closed positions periodically by way of a cam via a rocker arm. The variable valve train includes a camshaft having at least first and second cams which are arranged offset in the longitudinal direction of the camshaft. The first and second cams having cam contours. The valve train includes a rocker arm mounted which pivots about a rocker arm axis and is assigned to the at least one first cam via a pressure roller at its camshaft-side end and is connected to at least one lifting valve at its valve-side end, and a roller lever which is assigned to the at least one second cam at its camshaft-side end and is articulated at its other end on the rocker arm and pivots about the rocker arm axis.

Claims

1. A variable valve train for a lifting valve, which valve is moved periodically indirectly by way of a cam via a rocker arm between a closed and an open position, the valve train comprising: (a) a camshaft, having at least one first cam and at least one second cam which are arranged offset in a longitudinal direction of the camshaft, the at least one first cam and the at least one second cam having different cam contours; (b) a rocker arm, having a camshaft-side end and a valve-side end, and mounted pivotally about a rocker arm axis, the rocker arm is assigned to the at least one first cam via a roller on the camshaft-side end and is operatively connected to at least one lifting valve on the valve-side end; (c) a roller lever assigned to the at least one second cam via at least one roller on a camshaft-side end of the roller lever and is articulated on another end of the roller lever on the rocker arm such that the roller lever pivots about the rocker arm axis; (d) a switchable hydraulic locking device, by way of which the rocker arm and the roller lever are selectively: (1) locked rigidly to one another, both following the at least one second cam, and (2) unlocked from one another, each following a respective one of the at least one first cam and the at least one second cam independently of one another, wherein the roller lever is connected to the rocker arm via a hinge, the hinge having an axis of rotation parallel to and spaced from the rocker arm axis.

2. The variable valve train according to claim 1, wherein the at least one lifting valve is a gas exchange valve of an internal combustion engine.

3. The variable valve train according to claim 1, wherein the at least one second cam includes two second cams respectively provided on first and second axial sides of the at least one first cam, and the roller lever extends from the camshaft-side end of the rocker arm and follows the cam contour of two second cams.

4. The variable valve train according to claim 1, wherein the at least one first cam includes two first cams respectively provided on first and second axial sides of the at least one second cam, and the camshaft-side end of the rocker arm extends from the roller lever and follows the cam contour of two first cams.

5. The variable valve train according to claim 1, wherein the rocker arm and the roller lever are braced against one another via at least one restoring spring in such a way that the roller of the rocker arm and the at least one roller of the roller lever are aligned with respect to one another in a base circle position.

6. The variable valve train according to claim 5, wherein the at least one restoring spring includes two restoring springs arranged on opposite sides of the rocker arm.

7. The variable valve train according to claim 1, wherein the switchable hydraulic locking device comprises a hydraulically actuable switching pin which is movable from a first position into a second position by way of loading with a predefined hydraulic pressure, the switching pin permitting a relative movement of the rocker arm and the roller lever with respect to one another about the rocker arm axis in the first position, and preventing a relative movement of the rocker arm and the roller lever about the rocker arm axis in the second position.

8. The variable valve train according to claim 7, further comprising a guide pin, a pin spring which is plugged onto the guide pin, and the switching pin which is screwed to the guide pin are arranged in the rocker arm in a sliding guide bore, and the switching pin loadable with the predefined hydraulic pressure via a pressure chamber fillable with oil in order to actuate a switching means, the locking device being configured in such a way that the switching pin, in a state in which the switching pin is not loaded with the predefined hydraulic pressure, is held by way of the pin spring which acts as a restoring spring and the guide pin, in the first position, and that the switching pin, in a state in which the switching pin is loaded with the predefined hydraulic pressure, is pressed into the second position, in which the switching pin protrudes out of the rocker arm towards the roller lever and moves into an aligned sliding guide seat of the roller lever.

9. The variable valve train according to claim 7, further comprising a guide pin, a pin spring which is plugged onto the guide pin, and the switching pin which is screwed to the guide pin are arranged in the rocker arm in a sliding guide bore, and the switching pin configured to be loaded with the predefined hydraulic pressure via a pressure chamber fillable with oil in order to actuate a switching means, the locking device being configured in such a way that the switching pin, in a state in which the switching pin is not loaded with the predefined hydraulic pressure, is held by way of the pin spring which acts as a restoring spring and the guide pin, in the second position, and that the switching pin, in a state in which the switching pin is loaded with the predefined hydraulic pressure, is pressed into the first position, in which the rocker arm moves in, with the result that the switching pin releases the aligned sliding guide seat of the roller lever.

10. The variable valve train according to claim 1, wherein the cam contour of the at least one first cam has a different cam elevation or a different phase position in comparison with the cam contour of the at least one second cam.

11. The variable valve train according to claim 1, wherein at the rocker arm's valve-side end, the rocker arm has a seat, in which a hydraulic valve play compensating element or a screw with an elephant foot formation is received.

12. The variable valve train according to claim 1, further comprising a bearing system of the rocker arm, having a rocker arm bearing block, on which the rocker arm axis is arranged, onto which the rocker arm is plugged pivotally by way of an associated bore and is held by means of an axial positional securing means, the axial positional securing means being a guide connection as engagement element/counterelement connection between the bearing block and the rocker arm, in which an engagement element which is oriented transversely with respect to an axial direction engages into an associated counterelement with axial flank support in a pivotally movable manner.

13. A motor vehicle, in particular a commercial motor vehicle, having a variable valve train for a lifting valve, which valve is moved periodically indirectly by way of a cam via a rocker arm between a closed and an open position, the valve train comprising (a) a camshaft, having at least one first cam and at least one second cam which are arranged offset in a longitudinal direction of the camshaft, the at least one first cam and the at least one second cam having different cam contours; (b) a rocker arm, having a camshaft-side end and a valve-side end, and mounted pivotally about a rocker arm axis, the rocker arm is assigned to the at least one first cam via a roller on the camshaft-side end and is operatively connected to at least one lifting valve on the valve-side end; (c) a roller lever assigned to the at least one second cam via at least one roller on a camshaft-side end of the roller lever and is articulated on another end of the roller lever on the rocker arm such that the roller lever pivots about the rocker arm axis; (d) a switchable hydraulic locking device, by way of which the rocker arm and the roller lever are selectively: (1) locked rigidly to one another, both following the at least one second cam, and (2) unlocked from one another, each following a respective one of the at least one first cam and the at least one second cam independently of one another, wherein the roller lever is connected to the rocker arm via a hinge, the hinge having an axis of rotation parallel to and spaced from the rocker arm axis.

14. A variable valve train for a lifting valve, which valve is moved periodically indirectly by way of a cam via a rocker arm between a closed and an open position, the valve train comprising: (a) a camshaft, having at least one first cam and at least one second cam which are arranged offset in a longitudinal direction of the camshaft, the at least one first cam and the at least one second cam having different cam contours; (b) a rocker arm, having a camshaft-side end and a valve-side end, and mounted pivotally about a rocker arm axis, the rocker arm is assigned to the at least one first cam via a roller on the camshaft-side end and is operatively connected to at least one lifting valve on the valve-side end; (c) a roller lever assigned to the at least one second cam via at least one roller on a camshaft-side end of the roller lever and is articulated on another end of the roller lever on the rocker arm such that the roller lever pivots about the rocker arm axis; (d) a switchable hydraulic locking device, by way of which the rocker arm and the roller lever are selectively: (1) locked rigidly to one another, both following the at least one second cam, and (2) unlocked from one another, following a respective one of the at least one first cam and the at least one second cam independently of one another, wherein the rocker arm and the roller lever each include a pivot pin seat axially aligned with respect to one another so as to form a hinge with an inserted pivot pin, wherein the pivot pin has an axis parallel to and offset from the rocker axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantages of the present disclosure will be described in the following text with reference to the appended drawings, in which:

(2) FIG. 1 shows a perspective front view of a valve train according to one embodiment of the present disclosure,

(3) FIG. 2 shows a perspective side view of a valve train according to one embodiment of the present disclosure,

(4) FIG. 3 shows a perspective view from below of a valve train according to one embodiment of the present disclosure,

(5) FIG. 4 shows a side view of a rocker arm according to one embodiment of the present disclosure, and

(6) FIG. 5 shows a section A-A through FIG. 4.

DETAILED DESCRIPTION

(7) Identical parts are provided with the same reference numerals in the figures, with the result that the various views of the valve train which are shown in the figures are also comprehensible in themselves.

(8) FIGS. 1 to 3 show different perspective views of a variable valve train 1 according to one embodiment of the present disclosure. The valve train 1 serves to actuate a gas exchange valve (not shown) of an internal combustion engine, which gas exchange valve can be moved periodically indirectly by way of a cam via a rocker arm between a closed and an open position.

(9) The camshaft 7 has a middle cam 3, also called a first cam in this document, and two further cams 4, 5 which are arranged offset as viewed in the longitudinal direction of the camshaft 7. Said cams 4, 5 are also in each case called second cams in this document. The two cams 4, 5 are arranged on both sides of the middle cam and adjacently with respect to the latter. The middle cam 3 and the two second cams 4, 5 are of different design in terms of their cam contour. The second cams 4, 5 have a greater cam lift than the middle cam 3.

(10) Furthermore, the phase position of the middle cam 3 can differ from the second cams 4, 5. Depending on the application, the first cam can also be configured as a zero cam, with the result that the valves remain closed.

(11) Of the two cam contours, only one is always relevant for the valve movement in a switching state, which will be explained in the following text.

(12) Furthermore, the valve train comprises a rocker arm arrangement, having a rocker arm 10 which is mounted such that it can be pivoted about a rocker arm axis 2 and is assigned to the first cam 3 via a pressure roller 13 at its camshaft-side end 11, in order to follow said first cam 3, and is operatively connected to at least one lifting valve at its valve-side end 12.

(13) The rocker arm 10 is secured on a rocker arm bearing block (not shown), the rocker arm axis 2 being arranged on the rocker arm bearing block, onto which rocker arm axis 2 the rocker arm 10 is plugged pivotably by way of an associated bore and is held by means of an axial positional securing means.

(14) The axial positional securing can take place, for example, in a manner known per se via bearing faces on the rocker arm flanks. Said flanks can be produced, for example, by calibration of the cast blank or by machining. On the bearing block side, the fixing can likewise take place via correspondingly machined surfaces and by means of washers and securing rings. Furthermore, axial positional securing means between a rocker arm and the axis are known. For example, a region of the axis which is enclosed by the bore of the rocker arm has an annular groove for this purpose, in which annular groove a circlip runs which at the same time runs with its outer annular section in an annular groove of the rocker arm.

(15) In the present exemplary embodiment, the axial positional securing means is configured as an engagement element/counterelement connection between the bearing block and the rocker arm, in which connection an engagement element which is oriented transversely with respect to the axial direction, for example in the form of an annular web 16, engages into an associated counterelement (not shown) with axial flank support in a pivotably movable manner.

(16) The valve-side lever arm 12 of the rocker arm 10 is configured as a two-valve lever arm, in order to actuate two gas exchange valves at the same time. To this end, the valve-side lever arm 12 is of fork-shaped configuration. A seat 15 is arranged at each valve-side end of the lever arm 12. The seat 15 can be used for mounting a hydraulic valve play compensating element (not shown) which is known per se. Instead of a hydraulic valve play compensating element, a screw with an elephant foot can also be received in the seat 15, by means of which screw a valve play can be readjusted manually.

(17) Hydraulic valve play compensating elements in internal combustion engines are known per se and serve, in particular, to compensate for the length dimensions of the gas exchange valves which change over the service life, in such a way that reliable valve closure is ensured in the base circle phase of the cam which actuates the valve. Here, the cam elevation is secondly to be transmitted to the valve without losses and thus to be converted into a valve lift movement. The method of operation of hydraulic valve play compensating elements of this type which are arranged in the force flow of a valve control means, in particular of an internal combustion engine, is assumed to be known.

(18) In order to configure a variable valve train, furthermore, the valve train 1 comprises a roller lever 20 which is assigned at its camshaft-side end 21 to the two second cams 4, 5 and is articulated at its other end on the rocker arm 10 such that it can be pivoted about the rocker arm axis 2.

(19) The rocker arm 10 is connected rotatably to the roller lever 20 via a pivot pin 25. A pivot pin seat 14 is situated on the rocker arm 10 and a pivot pin seat 24 is situated on the roller lever 20 for said connection. The pivot pin seats 14, 24 which are aligned with one another are arranged on an upper side of the rocker arm 10, that is to say a side which faces away from the cylinder head, to be precise in a middle region of the rocker arm 10 which forms the cylindrical recess of the rocker arm, in which the rocker arm axis 2 is received.

(20) The camshaft-side lever arm 11 of the rocker arm 10 guides a pressure roller 13 at its end, which pressure roller 13 is assigned to the middle cam 3, in order to follow the cam 3 or its rotational movement.

(21) The roller lever has two parallel arms 21 which extend towards the camshaft and also in each case extend on different sides from the camshaft-side lever arm 11 of the rocker arm 10 as viewed in the longitudinal direction of the camshaft.

(22) Each of the two arms 21 likewise guides a pressure roller 23 at the end. Each of the pressure rollers 23 is assigned to one of the two second cams 4, 5, in order to follow the latter.

(23) Both the rocker arm 10 and the roller lever 20 are therefore mounted rotatably with respect to the rocker arm axis 2 and can be pivoted with respect to the rocker arm axis independently of one another, at least when the rocker arm 10 and the roller lever 20 are not locked to one another by way of the switchable hydraulic locking device.

(24) Furthermore, the rocker arm 10 and the roller lever 20 are braced against one another via two restoring springs 6 which are fastened on both sides, with the result that the roller lever 20 is pressed permanently onto the rocker arm 10 while the camshaft is situated in a base circle position. Here, a base circle phase or cam base circle phase is to be understood, in particular, to mean an angular range of the cam unit, in which cam contours of all part cams of the cam unit assume a common base circle level.

(25) Said restoring springs 6 press onto the bearing point 17 of the rocker arm 10 (see FIG. 3) and also against the bearing point 27 of the roller lever 20 (see FIG. 1 or 2). Pre-assembly of the entire switchable rocker arm arrangement 10, 20 is possible as a result of the mutual bracing.

(26) Furthermore, the variable valve train 1 comprises a switchable hydraulic locking device or a hydraulic switching element 30, by way of which the rocker arm 10 and the roller lever 20 are locked rigidly to one another when said switching element 30 is switched on, and both follow the movement of the second cams 4, 5.

(27) To this end, the switchable hydraulic locking device 30, the construction of which will be explained in greater detail using FIGS. 4 and 5, is situated in the rocker arm 10.

(28) The switchable hydraulic locking device 30 comprises a guide pin 34, onto which a pin spring 33 is plugged. The guide pin 34 and the pin spring 33 are situated in a sliding guide bore 37 which is made in the camshaft-side lever arm 11 of the rocker arm 10. The guide pin 34 is screwed in the sliding guide bore 37 with a switching pin 31. The pin spring 33 comes into contact with a spring stop 32. Moreover, the switching pin 31 has a zero point rest 36. In a basic state (no pressure loading), the switching pin 31 is pressed by the pin spring 33 onto the zero point rest 36. A pressure chamber 35 which is filled with oil in order to actuate the switching means is situated behind the switching pin 31. The switching pin 31 is pressed out with the screwed guide pin 34 by way of the oil pressure in the pressure chamber 35, with the result that the pin spring 33 is compressed. Here, the guide pin 34 comes into contact with the bearing face 38, with the result that there is a defined end position in the extended state of the two pins 31, 34.

(29) In said extended state of the switching pin 31, the latter protrudes out of the rocker lever arm 11, in the direction of an adjacent arm 21 of the roller lever 10, and engages into a sliding guide seat (not shown) of the roller lever 10, which sliding guide seat is provided in an aligned manner. As a result, the switching pin 31 locks the rocker arm 10 to the roller lever in the extended state. In said state, the rocker arm 10 and the roller lever 20 can no longer be pivoted about the rocker arm axis 2 independently of one another, but rather only jointly. In said locked state, the rocker arm 10 and the roller lever 20 follow the cam contour of the second cams 4, 5, since the latter have the greater lift.

(30) If the oil pressure diminishes, the switching pin 31 including the guide pin 34 is pressed against the zero point rest 36 again by way of the spring force of the pin spring 33, and the roller lever 20 is decoupled again from the rocker arm 10.

(31) The rocker arm 10 and the roller lever 20 are therefore mounted such that they can be rotated about the rocker arm axis 2 independently of one another when the hydraulic locking device 30 is not switched on, with the result that the second cams 4, 5 are inactive, that is to say, although the second cams 4, 5 actuate the roller lever 20, it performs only tilting movements, without influence on the valve. In contrast, the rocker arm and the roller lever are connected to one another fixedly so as to rotate together when the locking device is switched on, with the result that both can be pivoted about the rocker arm axis 2 only jointly.

(32) By way of selective loading of the pressure chamber 35 with a hydraulic pressure, a switchover can therefore be made at a desired time, for example as a function of operating parameters, from the first cam contour of the middle cam 3 to an alternative cam contour of the second cams 4, 5 or vice versa, in order to operate the gas exchange valves of the internal combustion engine in a variable manner with different opening and closing times and/or with different valve opening lifts.

(33) Although the present disclosure has been described with reference to defined exemplary embodiments, a person skilled in the art can see that various amendments can be carried out and equivalents can be used as a replacement, without departing from the scope of the present disclosure. In addition, many modifications can be performed, without departing from the associated scope. As a consequence, the present disclosure is not to be restricted to the disclosed exemplary embodiments, but rather is to comprise all exemplary embodiments which fall within the scope of the appended patent claims. In particular, the present disclosure also claims protection for the subject matter and the features of the subclaims independently of the claims which are referred to.

LIST OF REFERENCE NUMERALS

(34) 1 Valve train 2 Rocker arm axis 3 First cam, for example middle cam 4, 5 Second cam 6 Restoring spring 7 Camshaft 10 Rocker arm 11 Camshaft-side lever arm 12 Valve-side lever arm 13, 23 Pressure roller 14, 24 Pivot pin seat 15 Seat 16 Annular web 17, 27 Bearing point for restoring spring 20 Roller lever 21, 22 Lever arm 23 Bearing point for restoring spring 25 Pivot pin 30 Hydraulic locking device 31 Switching pin 32 Spring stop 33 Pin spring 34 Guide pin 35 Pressure chamber 36 Zero point rest 37 Sliding guide bore 38 Bearing face