Patent Application
20080127922
1. Field of the Invention
The invention relates to a valve gear for load change valves of internal combustion engines, that are held in the closed position by spring force. An intermediate element is articulated onto a lever mounted in a fixed position in the cylinder head, so as to pivot, in order to activate the load change valves. This intermediate element rests against an adjustable counter-bearing and engages a cam of a camshaft mounted in the cylinder head.
2. The Prior Art
Valve gears of this type are shown in FIG. 1 of German Patent No. DE 38 33 540 C2. A load change valve held in the closed position by spring force is indirectly activated by a cam, via a pivot lever mounted in a fixed location, by way of an intermediate element articulated onto the pivot lever, in accordance with the cycle, but with variably adjustable opening characteristics.
The cam, with its control curve, forces the triangle-shaped intermediate lever articulated onto the pivot lever against a roller that is fixed in place, but is adjustable by pivoting in its position. The pivoting for changing the roller position takes place about the imaginary articulation axle of the intermediate element on the pivot lever, specifically in the position that the articulation axle assumes when the valve is closed.
Depending on the position of the roller, the control curve converts the movement transferred by the cam into different valve opening curves, all the way to non-opening of the valve, by the articulation on the pivot lever.
With the valve gear embodiment described above, it is disadvantageous that only a slight valve stroke is performed when the opening time is short, due to the kinematics.
It is therefore an object of the invention to configure a valve gear where the full valve stroke is effective even in the case of slight opening, and the opening angle is reduced in the case of full or approximately full valve stroke.
According to the invention, this is achieved by means of a combination of the following characteristics:
the cam has a known plateau region for maximal valve lift that follows the lift phase,
the lever for activating the load change valves is configured as a rocker arm, onto which the intermediate element is articulated so as to pivot,
the intermediate element has a fork-shaped parallel guide that engages a guide cylinder of the camshaft, over the center axis of which a guide groove in the shape of a circular ring segment extends, in which a roller axle of a roller that engages the cam is guided in a displaceable manner,
the inner and the outer delimitations of the guide groove describe arcs or curves that approximate the ring segment, which are configured centrally or with a slight deviation from the centered progression, relative to the plateau region, when the roller engages on the plateau region of the cam,
in the position of the intermediate element in the case of maximal lift of the valve(s), the guide groove extends, starting from the plane of engagement of the roller on the cam, approximately at the same or a smaller angle than the plateau region of the cam opposite the direction of rotation of the camshaft,
a spring is supported on the roller axle of the roller that engages the cam, and forces the roller axle against a control curve of a guide element that is directed in the direction of rotation of the cam, counter to the forces that will be considered below, when it passes through the plateau region, and lies against it, and
the control curve is guided so that the guide groove is more or less covered by the cam, depending on its position, proceeding from the plane of lifting of the roller.
With the invention, the load will flow evenly when the valve(s) is/are fully open, even with short opening times, and an intentional load movement in the cylinder space can be effectively initiated in this manner.
Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.
In the drawings, wherein similar reference characters denote similar elements throughout the several views:
In
The structure of the valve gear according to the invention will be explained using
Cam 11, following the lift phase, has a known plateau region P for maximal valve lift. Subsequently, a lowering phase follows, which leads back to the cam base circle.
Intermediate element 5 is coupled onto the rocker arm end of rocker arm 3 that lies opposite load change valve 2, by way of an articulation axle 31. It has a fork-shaped parallel guide 51 that engages a guide cylinder 12 of camshaft 1. Over the center axis of camshaft 1, a recess in the shape of a circular ring segment extends as a guide track 50, in which a roller axle 53 of a roller 52 that engages cam 11 is guided in displaceable manner. The inner radius Ri and the outer radius Ro of the guide track 50 in the shape of a circular ring segment describe arcs that run central to the camshaft axis when roller 52 engages on plateau region P of cam 11. Alternatively, the radii describe curves that approximate such arcs, which are configured to deviate slightly from the central progression to the plateau region P, when roller 52 engages on plateau region P of cam 11. A slight deviation of the curves that approximate the arcs Ri and Ro might be necessary and is advantageous for lifting roller 52 from the base circle or lowering it to the base circle, respectively, in the case of shortened opening angles for the load change valve(s) 2. In this regard, see the explanations relating to
In setting intermediate element 5 for maximal lift Emax of load change valve 2, guide track 50 in the shape of a circular ring segment extends, proceeding from the plane of engagement of roller 52 on cam 11, approximately at the same or a smaller angle than plateau region P of cam 11, opposite the direction of rotation DR of camshaft 1.
A spring 6 configured as a wound bending spring is supported on roller axle 53 of roller 52 that engages cam 11, preferably on both sides, with one of its spring arms. The force F that is thereby exerted symmetrically on roller axle 53 is able to force roller axle 53 against a control curve 42 of a guide element 4, and lay roller axle 53 against control curve 42, counter to the forces that act during passage of the base circle.
Springs 6 are disposed in guided manner in cylinder head ZK, whereby one of the spring arms is also counter-mounted there. See
Guide element 4 with control curve 42 can pivot about an axle 41 that is mounted in cylinder head ZK, in a fixed location, and can be adjusted into different positions.
Control curve 42 is structured so that it constantly holds roller axle 53 in end contour 50E of guide track 50 in the shape of a circular ring segment of intermediate element 5, in the right end position of guide element 4. In this way, opening of load change valve 2 is set at max. time cross-section Omax.
Control curve 42 covers guide track 50 more or less, depending on the position of guide element 4, and forms a counter-bearing surface in different positions, against which roller axle 53 of roller 52 is forced and laid down, with its outside diameter D53, by force F of springs 6.
When roller 52 engages on plateau region P of cam 11, springs 6 have a greater bias, because of displacement of intermediate element 5 that has occurred, than in the case of engagement on the base circle, so that force F of springs 6 forces roller axle 53 against control curve 42 of guide element 4 and lays it down there, both counter to forces of roller friction that are in effect between roller 52 and cam 11, and counter to other friction and mass inertia forces.
It would also be possible for control cam 42 to be disposed on a guide element 4 that is guided in the cylinder head with a pushing movement, and adjustable.
The rocker arm 3 that activates load change valve 2 is coupled with intermediate element 5 by way of an axle, not shown, which is mounted in intermediate element 5 in guide supports 5a and 5b on both sides. The fork-shaped parallel guides 51 that engage diameter D12 of guide cylinders 12 of camshaft 1 are also disposed in guide supports 5a and 5b of intermediate element 5, on both sides.
In the representation in
In
In accordance with the position of control curve 42, roller axle 53 is constantly held in right end contour 50E of guide track 50. Roller 52 should therefore be considered to be fixed in place on intermediate element 5, so that the stroke of cam 11 is transferred to intermediate element 5 by way of roller 52, in accordance with the lift contour, to rocker arm 3 and load change valve 2 by way of articulation axle 31. During the stroke, intermediate element 5 is displaced, guided both by the articulation on rocker arm 3, by way of articulation axle 31, and by parallel guide 51 that engages on guide cylinder 12 of camshaft 1. In this connection, a maximal displacement Bmax of parallel guide 51 relative to camshaft 1 occurs at maximal valve lift Emax, as shown in
The force F of spring 6 acts in the same manner as explained with regard to
In the following, the movement progression and the function of the individual parts will be explained using
Spring force F of springs 6 has a greater bias than in the case of engagement on the base circle of cam 11, because of the displacement of intermediate element 5 that has occurred, see
Therefore, only a part ΦwminP of the extension angle ΦP of plateau region P becomes effective for full opening of valve 2. Proceeding from the position of roller axle 53 shown, lowering of intermediate element 5 takes place with constant contact between roller axle 53 and control curve 42, determined by the engagement of roller 52 on the lowering region of cam 11. Valve 2 increasingly closes.
In
In planes a and b of the lift diagram, the diagram for maximal valve opening time Omax is shown, in each instance, with one of minimal valve opening time Omin and with one for reduced valve opening time Ox, for comparison.
It can be seen that all of the settings of the valve opening times Omax, Omin, Ox have a similar opening contour OA-PA and closing contour PE-OE, as well as the maximal valve lift Emax, at all times.
The different duration of valve opening times is determined, in each instance, by the different angles ΦwmaxP; ΦwminP; ΦwxP of the effectiveness of the plateau region P.
The angle ΦwminP of the effectiveness of the plateau region PA/PE can never reach the value of zero, because the return time tr of roller 52 with roller axle 53 over the entire region of guide groove 50 cannot be infinitely short. This is due to the design and kinematics limitations of force F of spring 6, and to the mass inertia forces of roller 52 and roller axle 53, as well as the forces of rolling friction between roller 52 and cam 11 that must be overcome. Assuming that the return time tr of roller 52 when passing through plateau region P of cam 11 is constant at a position of control curve 42, in each instance, a proportion of the opening angle of valve 2 that is dependent on the speed of rotation occurs, in each instance. Therefore there is also a dependence on the speed of rotation of the entire opening angle of valve 2 at every position of control curve 42.
Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 003 002.8 | Jan 2006 | DE | national |
