VALVE-ACTUATING MECHANISM

Abstract: A valve-actuating mechanism for a plurality of identical valves of a cylinder of an internal-combustion engine has first drag levers (5) which each actuate a valve and which are actuated by a cam for a lower speed range, and second drag levers (7) which are arranged between adjacent first drag levers (5) and which are actuated by specific identical cams for the upper speed range. The first and the second drag levers (5, 7) can be coupled to one another in the upper speed range by means of a rotatable switching shaft (11) which extends through all the drag levers and which can be actuated by an outer electromagnet (21), so that the valves are then actuated according to the contour of the cams acting on the second drag levers (7).

Description: VALVE-ACTOATI G ME-CHAN-I--3Ϊ The invention relates to a valve-actuating mechanism for an internal-combustion engine according to the pre-characterising clause of Claim 1. In a known valve-actuating mechanism of this type (EP-A-34.2,007) , two coupling pins butting against one another are provided in the bores of the drag levers and can be displaced counter to a spring force, by an elec- tromagnet arranged in one of the drag levers, in such a way that they bridge the separating gaps between adjacent drag levers and thus connect all the drag levers rigidly to one another, so that the first drag levers acting on the valves are now moved by the second drag levers according to the cam contour of the second cams. One problem in this construction is that the coupling pins have to be positioned very accurately, in order to ensure that the first two drag levers can move freely in the uncoupled position. Furthermore, accommodating an elec- tromagnet, by means of which the necessary short switching times of approximately 5 ms can be achieved, in the drag lever presents considerable problems as do the dissipation of the heat generated and the current supply. Finally, in the event of repair, the valve drive has to be at least partially dismantled. The object on which the invention is based is to provide a valve-actuating mechanism of the relevant generic type, in which the first drag levers can be connected to the second drag levers or be separated from these in a simpler way by means of an electromagnetically actuable coupling device. This object is achieved, according to the inven¬ tion, by means of the features of the characterising clause of Claim 1. In the proposal according to the invention, the coupling device is a rotatable switching shaft which can extend outwards, so that the electromagnet can be arranged at a suitable point next to the switching shaft in the cylinder head, where there is, of course, more space than in a drag lever and the dissipation of the heat generated presents no problems. A further advantage is that, if a defect occurs, the electromagnet can be exchanged easily, whereas, in such a case, an at least partial dismounting of the valve drive would be necessary in the known mechanism. Advantageous developments of the invention emerge from the subclaims. An exemplary embodiment of the invention is described below with reference to the drawings. In these: Figure 1 shows a valve drive with a valve- actuating mechanism according to the invention for three inlet valves in a vertical section along the line 1-1 in Figure 2, Figure 2 shows a section along the line 2-2 in Figure 4, Figure 3 shows a section along the line 3-3 in Figure 2, the switching shaft being shown in the position according to Figure 1, Figure 4 shows a section corresponding to that of Figure 1, the coupling device being shown in a second position, Figure 5 shows a section corresponding to that of Figure 3, the switching shaft being shown in the position according to Figure 4, and Figure 6 shows a section along the line 6-6 in Figure 2. The drawings show a valve drive for three inlet valves 1, of which, however, only one is shown in Figure 1. Each valve 1 is loaded in the closing direction by a spring 2. The valves are actuated by specific cams 3 of a camshaft 4 via drag levers 5 which are mounted pivot- ably on a common axle fi of fixed location. The cams 3 can have different cam profiles for the individual inlet valves, in order to obtain a different valve stroke, a different opening duration and/or different control times and to afford optimum preconditions in the lower and medium speed range of the internal-combustion engine. Arranged on the axle 6 between adjacent first drag levers 5 are second drag levers 7 actuated by second cams 8 having an identical cam profile which is designed for the conditions in the upper speed range of the internal- combustion engine, that is to say, for example, brings about a larger valve stroke and a longer opening dura¬ tion. The second drag levers 7 have extensions which extend rearwards and on which is supported a spring 7a which endeavours to keep the second drag levers bearing against their cams 8. The second drag levers 7 can be coupled to the first drag levers 5 in the upper speed range, so that, in this speed range, the valves 1 are actuated according to the contour of the second cams 8. For this purpose, the first and the second drag levers 5 and 7 have bores 9 and 10 which extend parallel to their pivot axis and which are aligned with one another when the valves are closed. Through all the bores 9, 10 extends a rotatable switching shaft 11 which is mounted in the bores 10 of the second drag levers 7 and which has cutouts 12 in the region of the bores 9 in the first drag levers 5. As is evident from Figures 3 and 5, the bores 9 in the first drag levers 5 are opened downwards over a part region 13. When the switching shaft 11 is in the position shown in Figure 5, the second drag levers 7 can pivot downwards, without taking along the first drag levers 5, since, as a result of the cutouts 12 and the open regions 13 of the bores 9, the switching shaft 11 can slide out of these bores. The valves are thus actuated according to the contours of the cams 3. When the switching shaft 11 is rotated into the position shown in Figures 1 and 3, a positive coupling of the first drag levers 5 with the second drag levers 7 takes place, since the switching shaft 11 cannot slide en*" of the bores 9, but is supported on the walls of the bores 9 via the circumferential region 14. To rotate the switching shaft 11, the latter is provided with an eccentric extension 15 at its end on the left in Figure 2. Mounted on a pivot pin 16 on the outer face of the first drag lever 5 on the left in Figure 2 is a two-armed switching lever 17, the first arm 18 of which has an arcuate slot 19, into which the extension 15 engages, and the second arm 20 of which extends in the form of an arc of a circle and is concentric to the pivot axis of the drag levers in the position shown in Figure 1. The switching lever 17 is pivoted by means of an electromagnet 21 into the position shown in Figure 1, in which the drag levers 5 and 7 are coupled to one another, as previously described and as shown in Figure 3. For this purpose, there is pivotably mounted at 23 on the housing of the electromagnet 21 an angle lever 22, one arm 24 of which cooperates with the armature 25 of the electromagnet and the other arm 26 of which bears against a second lever arm 20 of the switching lever 17 when the electromagnet 21 is energised. After the deenergisation of the electromagnet 21, a torsion spring 27 returns the armature 25 and the angle lever 27 into the position shown in Figure 4. In this position, the switching shaft 11 is rotated by a torsion spring 28 (Figure 2), seated on the right-hand end of the switching shaft 11 and connected at one end to the switching shaft and at the other end to the adjacent drag lever 5, back into the position shown in Figure 5, in which the first drag levers 5 are uncoupled from the second drag levers 7, that is to say the valves 1 are actuated according to the contour of the first cams 3. As is evident from Figure 4, when the electromag¬ net 21 is not energised the arm 26 of the angle lever 27 is out of contact with the second arm 20 of the switching lever 17, so that no friction is generated. The housing of the electromagnet 21 has a flange 30 which is screwed to a corresponding face 31 in the cylinder head, and the lower end 32 of the armature 25 is seated in a corresponding bore 33 in the cylinder head. The electromagnet 21 can thereby be mounted and dis¬ mounted, without the need to take action in the valve- actuating mechanism. The exemplary embodiment shows a valve-actuating mechanism for three inlet valves. This mechanism can, of S course, also be used for a larger or smaller number of inlet valves. If a plurality of outlet valves is provided for each cylinder, these can, if necessary, likewise be actuated by means of a mechanism of this type.

Claims: Patent Claims 1. Valve-actuating mechanism for an internal- combustion engine, with at least two identical (inlet and/or outlet) valves per cylinder, with a camshaft (4) having first and second cams (3, 8) with a different cam profile, with first drag levers (5) which each cooperate with a valve (1) and a first cam (3) and with second drag levers (7) located between adjacent first drag levers (5) and each cooperating with a second cam (8) , the drag levers (5, 7) having bores (9, 10), which extend parallel to their common pivot axis and are aligned with one another when the valves are closed and in which is arranged an electromagnetically actuable coupling device (11) which couples the first drag levers (5) to one another in a first speed range and uncouples them from one another in a second speed range, characterised in that the coupling device has a rotatable switching shaft (11) which extends through all the bores (9, 10) and is mounted in the bores (10) of the second drag levers (7) and which is provided with cutouts (12) in the region of the bores (9) in the first drag levers (5), in that the bores (9) in the first drag levers (5) are opened down¬ wards over a part region (13), and in that an electro¬ magnet (21) and a spring (28) are provided for rotating the switching shaft (11) between a first position, in which it can escape from the bores (9) in the first drag levers (5) as a result of the cutouts (12), and a second position, in which it couples the first and the second drag levers (5, 7) to one another. 2. Valve-actuating mechanism according to Claim 1, characterised in that one end of the switching shaft (11) has an eccentric extension (15), and in that there is rotatably mounted on the first drag lever (5) adjacent to this end of the switching shaft a two-armed switching lever (17) which engages with its first arm (18) on the extension (15) and the second arm (20) of which cooper¬ ates with the movable part (25) of the electromagnet (21). 3. Valve-actuating mechanism according to Claim 2, characterised in that the second arm (20) of the switch¬ ing lever (17) has the form of a segment of an arc of a circle, the centre of which is located on the pivot axis of the drag levers in the coupling position of the switching lever, and in that there is arranged between the switching lever (17) and the movable part (25) of the electromagnet (21) an angle lever (22) which is mounted rotatably on the housing of the electromagnet and which, when the electromagnet is not energised, comes out of contact with the second arm (20) of the switching lever (17). 4. Valve-actuating mechanism according to Claim 2, characterised in that the switching shaft (11), at its end facing away from the switching lever (17), projects from the first drag lever (5) adjacent to this end, and in that there is mounted on this end a torsion spring (28) which is supported at one end on the switching shaft (11) and at its other end on this drag lever (5).

Inventors: HANNIBAL WILHELM, HANNIBAL, WILHELM
Applicants: AUDI NSU AUTO UNION AG, HANNIBAL WILHELM, AUDI AG
Application year: 1993
Main classification: F01L1
IPC codes: F01L1, F01L13