VALVE-ACTUATING MECHANISM

Abstract: A valve-actuating mechanism for a multicylinder internal combustion engine has, for each inlet valve (E) of a cylinder, a low engine speed cam (2) and a high engine speed cam (8). A first drag lever (4) cooperates with the low engine speed cam (2) and the valve (E), while a second drag lever (9) cooperates only with the high engine speed cam (8) and in the high engine speed range can be coupled to the first drag lever (4) in order to operate the valve (E) in accordance with the contour of the high engine speed cam (8). The coupling between the first and second drag levers (4, 9) is effected by means of a piston (13) which can be moved by a pressure medium and which is acted on by the latter only when sufficient time remains to bring the piston (13) into its coupling position before the commencement of the lifting phase of the valve in question.

Description: Valve-actuating Mechanism Description The invention relates to a valve-actuating mechanism according to the preamble of Claim 1. In a valve-actuating mechanism of this kind, which is for example known from EP 0 213 759, the problem arises that on the change-over, that is to say when the second or high engine speed cams are to come into action through the coupling of the two drag levers of each valve, the pistons serving as coupling elements of all the coupling devices are loaded with the pressure medium, so that so-called edge bearers may result, because after the commencement of the pressure loading the pistons need a certain period of time to pass into their second position. If the pressure loading starts at a moment in time only shortly before the commencement of the lifting phase of the drag levers in question, the piston will not yet be in its second end position when the lifting phase starts and will therefore, for example, project only slightly into the bore in the second drag lever, with the consequence that a considerable surface pressure will occur, which leads to heavy wear. In order to solve this problem it is known (DE-C 35 26 543) to provide a mechanical locking means for the piston, which will free the piston only during the lifting phase of the respective valve, so that sufficient time will be available for the movement of the piston before the commencement of the next lifting phase. This solution of the problem discussed is however relatively expensive and is limited to one very specific valve-actuating mechanism. The problem underlying the invention is that of ensuring by simple means, in a valve-actuating mechanism of the type defined, a complete movement of each coupling element to its second end position in the coupling operation. According to the invention this problem is solved by the features indicated in the characterizing part of Claim 1. Through the proposal according to the invention the effect is thus achieved that after the commencement of the pressure loading sufficient time will be available for each coupling element to reach its second end position, through the fact that the device for controlling the pressure loading of the coupling element, normally a control valve in the pressure medium supply pipe, is opened at the appropriate moment, which is possible with the aid of the usual electronic engine control devices without additional expense, since these devices already for example determine the ignition timing selectively for each cylinder, that is to say the upper dead centre position of the internal combustion engine piston and thus also the position of the cams for the valves of the respective cylinder. τhe proposal according to the invention can be applied to different valve-actuating mechanisms, for example also those described in DE-A 42 05 230, which is not a prior publication. In the shaft on which all the drag levers are mounted a longitudinal channel is normally provided, through which the pressure medium is fed to the bores which are provided in the drag levers in question and which contain the pistons. With a configuration of this kind, in order to apply the principle of the invention a shut-off valve may be provided upstream, in the direction of flow of the pressure medium in the longitudinal channel, of each of the drag levers of the inlet or outlet valve of a cylinder, while, when the change-over is made, the shut-off valves lying one behind the other in the direction of flow are opened one after the other, in each case at a moment of time such that sufficient time is left for the pistons in the following drag levers to reach their end position. It is thereby ensured that, after initiation of the change-over operation, all the pistons will be loaded with pressure one after the other at the correct moment in time. In some cases it is not necessary to provide a shut-off valve in the longitudinal channel upstream of the drag lever of the valves of each cylinder, namely when in successive cylinders the "permissible" change¬ over times - that is the change-over times within which pressure loading of the coupling pistons must take place to ensure reliable movement of the pistons into their second end position - overlap. In an internal combustion engine having a bank of four cylinders and with the ignition sequence 1-3-4-2, this is for example the case for the drag levers of the valves of cylinders 1 and 2 and of cylinders 3 and 4. It therefore becomes possible to provide in the supply channel a first shut-off valve upstream of the drag levers for the inlet or outlet valve of the first cylinder, and a second shut-off valve upstream of the drag levers for the inlet or outlet valve of the third cylinder. The first shut-off valve can then be formed by the control valve which initiates the coupling operation in dependence on engine speed and/or load. In the embodiments according to Claims 2 and 3 it was assumed that the pressure medium is fed to the longitudinal channel at one end, while the other end is closed. It would however also basically be possible to provide the drag levers of the valves of determine d cylinder groups with their own longitudinal channels in the common drag lever shaft, for example by interrupting the longitudinal channel between the second and thir d cylinders in a bank of four cylinders, and supplying the pressure medium from both sides by way of a control valve, which is then actuated both in dependence on operating parameters and in dependence on the position of the cams in question. The valve-actuating mechanism according to the invention can be used for an internal combustion engine having more than one inlet valve per cylinder, that is to say also for an internal combustion engine having two inlet valves (DE-C 35 26 543) or having three inlet valves per cylinder (DE-A 42 05 230), while it is possible to actuate not all, but only one or two of the inlet valves by means of different cams. The longitudinal channel carrying the pressure medium in the drag lever shaft is normally connected by branch channels to the bearings of the drag levers on the drag lever shaft, in order to lubricate said bearings. In order to ensure lubrication of the drag lever bearings in the case of the proposal according to which shut-off valves are provided in the longitudinal channel, the closure members of the shut-off valves may be provided with throttle channels which permit a throttled flow to the drag lever bearings when the shut-off valves are closed. The shut-off valves are in this case preferably disposed in the bearings of the drag lever shaft. One examplary embodiment of the invention is described below with reference to the drawings, in which: Figure 1 shows a valve gear provided with a valve-actuating mechanism according to the invention for two inlet valves per cylinder, in a vertical section along the line 1-1 in Figure 2, Figure 2 shows a section along the line 2-2 in Figure 1, and Figure 3 shows the valve lift curves for the inlet valves of a four-cylinder internal combustion engine with the ignition sequence 1-3-4-2. Figures 1 and 2 illustrate a valve gear for a four-cylinder internal combustion engine having two inlet valves E for each cylinder I to IV. Each valve E is loaded by a spring 1 in the closing direction. Each valve E is actuated by its own cam 2 of a camshaft 3 with the aid of a drag lever 4. The drag levers 4 are mounted pivotally on a common stationary shaft 5, which in turn is held in bearings 6 in the cylinder head of the inter¬ nal combustion engine. Between the drag levers 4 associated with the inlet valves of a cylinder there is disposed in each case a second drag lever 7 cooperating with a cam 8 which is disposed between the two cams 2 associated with the drag levers 4 and which has a cam profile designed for conditions in the upper engine speed range of the internal combustion engine, that is to say, for example, which produces a greater valve lift and a longer opening time than the cams 2. In the upper engine speed range each second drag lever 7 can be coupled to the neighbouring first drag levers 4, so that in this engine speed range the valves E are actuated in accordance with the contour of the cam 8. The free end of each second drag lever 7 has a cross member 9 which extends in front of and at a short distance from the free ends of the first drag levers 4. In the first drag levers 4 bores 11 are provided, which extend radially in relation to the shaft 5 and which are in line with bores 12 in the cross member 9 when the valves E are closed, that is to say when all the drag levers 4 and 7 lie against the base circles of their cams 2 and 8 respectively. Each bore 11 contains a piston 13 which, by means of a pressure medium supplied through a channel 14 in the shaft 5, is pushed outwards and engages in the bore 12 in the cross member 9, whereby the drag levers 4 and 7 are coupled together. Each piston 13 is acted on by a spring 15, which is supported at one end against an insert 16 fixed in the bore 11 and at the other end against the end of a sleeve 17 fastened to the piston 13 and extending through the insert 16. The spring 15 returns the piston 13 to its uncoupled position when the supply of pressure medium to the bore 11 is inter¬ rupted, the insert 16 acting as a stop for the piston 13. The channel 14 is in communication by way of bores 19 with the bearings of the drag levers 4 and 7 on the shaft 5, so that these bearings are lubricated. The channel 14 is closed by a stopper 18 at its left-hand end (in Figure 2) , while its right-hand end can be brought into communication with a pressure source 21 when the pistons 13 are to be moved to their coupling position, as will be described later on. Each drag lever 4, 7 has a sliding surface 20 by which it lies against its cam 2 or 8 respectively. The second drag levers 7 are held against their cams 8 by spring elements (not shown) . When the valves E are to be actuated by the cams 8, pressure medium, normally lubricating oil, is fed from the oil circuit of the internal combustion engine to the channel 14. The pistons 13 need a certain time to move, against the action of the springs 15, from their uncoupled first end position shown in Figures 1 and 2 to their second end position, in which they engage in the bores 12 in the cross member 9 of the second drag levers 7 and lie against the end of said bores 12. This complete engagement of the pistons 13 can occur only when the bores 11 and 12 are in line with one another during the entire period of time t 8 (Figure 3). Because of the different contours of the cams 2 and 8, this is the case substantially only during the period of time in which the drag levers 4 and 7 are running on the bases circles of their cams 2 and 8. If the period of time from the application of pressure to the pistons 13 until the commencement of the lifting phases of the drag levers 4 and 7 is shorter than the period of time required for the complete movement of the pistons 13, the piston 13 will not go as far as the end of the bore 12 because the drag levers 4 and 7 make a movement relative to one another in the lifting phase, which leads to jamming of the piston 13. This causes a high surface pressure with corresponding wear. Only when, after further rotation of the camshaft, the drag levers 4 and 7 are running on the base circles of their cams can the piston 13 pass into its second end position. This process is unavoidable if all the pistons 13 are loaded simultaneously, because the cams associated with the valves of the various cylinders are offset relative to one another, for example by 90° in the case of a four-cylinder internal combustion engine. In order to ensure that each piston 13 will reach its second end position when pressure is applied to it for the first time, an electromagnetic shut-off valve 22 is disposed in the channel 1 , upstream of each cylinder I to IV in the direction of flow of the pressure medium indicated by the arrow P, said valve having a closure member 23 which is slidable transversely to the longitudinal direction of the channel 14, and, in its closed position shown in Figures 1 and 2, shuts off the supply of pressure medium to the drag levers 4 following in the direction of flow P, or to their bores 11, and is drawn back when the valve 22 is energized and frees the flow of pressure medium. When the valves E are to be actuated by the high engine speed cams 8, the valves 22a to 22d are actuated, that is to say opened, one after the other in the direction of flow P of the pressure medium delivered from the pressure source 21, in such a manner that the supply of pressure medium to the pistons 13 of the drag levers associated with the valves of the following cylinder takes place at a moment in time which precedes the commencement of the lifting phase of these drag levers by at least the period of time t. required by the pistons 13 to reach their second end position. The valve 22a is thus opened first, in good time before commencement of the lifting phase of the valves of cylinder I, then the valve 22b, followed by the valve 22c and finally the valve 22d. It is thus ensured that none of the pistons 13 is loaded with pressure medium only during the period of time t, required, before the commencement of the lifting phase of the respective valve, to bring the piston into its second end position. At least this period of time is thus always available for the coupling operation. The valves 22a to 22d are operated with the aid of the usual electronic engine control system by which the ignition timing for the individual cylinders is controlled and which, for example by means of a Hall effect device, detects the angular position of the camshaft and thus also the angular positions of the individual cams. The first valve 22a serves at the same time as a control valve, which is additionally controlled in dependence on operating parameters, particularly engine speed and the load on the internal combustion engine, in order for example to initiate, at a determined engine speed, the actuation of the valves by means of the high engine speed cams 8. Figure 3 shows a valve lift diagram for the inlet valves of a four-stroke internal combustion engine which has four cylinders I, II, III and IV and the ignition sequence 1-3-4-2. The period of time required by the piston 13 to reach its second end position is designated t a . During this period of time the piston 13 must not be loaded with pressure medium, since otherwise there will be a risk that it will not reach its second end position before the commencement of the lifting phase and will therefore be subjected to increased surface pressure and increased wear. The change-over operation, that is to say the opening of the valve 22 in question, must therefore occur within the period of time t*. If the ranges t^ for cylinders following one another in the direction of flow p of the pressure medium overlap, it is possible to control by means of a single valve the flow of pressure medium to the pistons of the drag levers for the valves of these cylinders. This is the case in the examplary embodiment for the cylinders I and II and for the cylinders III and IV. The hatched bar A represents the period of time during which the change-over to the high engine speed cams 8 for the valves I and II can be made. The hatched bar B applies to the valves of cylinders III and IV. It can thus be seen that for this special case of a four- cylinder internal combustion engine with the ignition sequence 1-3-4-2 the valves 22b and 22d can be dispensed with. As can be seen in Figure 3, the pressure loading is preferably already effected during the lifting phase of the valve in question, in order to be sure of having the entire base circle phase, that is to say the period of time between the lifting phases, available for the change-over operation. It is true that the bores 11 and 12 in the first drag levers 4 and in the cross member 9 of the second drag lever 7 are at first not yet in line, but this does no harm because they will come into line after completion of the lifting phase, that is to say after a very short time, and the piston 13 can then be pushed into the bore 12 to reach its second end position. As previously mentioned, the bearings of the drag levers 4 and 7 are normally supplied with the pressure medium, as lubricant, through the channel 14 and the bores 19. Since this lubrication must also be effected when the valves 22 are closed, each closure member 23 is provided with a throttle point in the form of an annular groove 24 which, when the valve is closed, lies in the channel 14 and permits the supply of pressure medium as lubricant to the drag lever bearings under lower pressure. On the closing of the first valve 22a, the pressure in the channel 14 is thus lowered by the throttle groove 24 of said valve to such an extent that all the pistons 13 can be returned by their spring 15 to their first end position. Numerous modifications of the examplary embodiment illustrated are obviously possible without going beyond the scope of the invention. Thus, in the examplary embodiment illustrated, the channel 14 could be interrupted between the cylinders II and III and the pressure medium could be introduced not only from the right (in Figure 2) but also from the left, the closure stopper 18 being dispensed with, in which case a valve corresponding to the valve 22a, and therefore also controlled by operating parameters, would then be provided in front of the left-hand end of the channel 14, and the valves 22b, 22c and 22d lying therebetween could be dispensed with. It is obvious that the valve-actuating mechanism proposed is also suitable for an internal combustion engine which has only one inlet valve or more than two inlet valves per cylinder. The proposal according to the invention can also basically be applied to the outlet valves of the internal combustion engine.

Claims: - 10 - Patent Claims 1. Valve-actuating mechanism for a multicyunder internal combustion engine having - at least one inlet or outlet valve (E) per cylinder, - a camshaft (3) which for each valve has a first cam (2) for a lower engine speed range and a second cam (8) for an upper engine speed range, - first drag levers (4) , each of which cooperates with a valve and a first cam (2), second drag levers (7) , each of which cooperates with a second cam (8) , - a shaft (5) on which all first and second drag levers of a bank of cylinders are pivotally mounted, and - a coupling device between the first and second drag levers of each valve, having a coupling element (13) which by means of a pressure medium can be moved, in dependence on operating parameters, from a first end position uncoupling the two drag levers from one another into a second end position coupling the two drag levers to one another, when both drag levers are running on the base circles of their cams, characterized by a device (22) for controlling the application of pressure to the coupling element (13) in such a manner that the application of pressure starts outside the period of time (t.) required, before the commencement of the lifting phase of the respective valve, by the coupling element to reach its second end position. 2. Valve-actuating mechanism according to Claim 1, having a piston (13) as coupling element, the two drag levers (4, 7) having bores (11, 12) receiving the piston and being in alignment with one another when both drag levers are running on the base circles of their cams, said piston in its first end position lying entirely in the bore (11) in the one drag lever (4) and, in its second end position, partly projecting into the bore (12) in the other drag lever (7) , while the shaft (5) common to the drag levers (4, 7) has a longitudinal channel (14) which is in communication with the bores (11) in all or some of the first or second drag levers and which can be connected by a control valve (22a) to a pressure source (21) in dependence on operating parameters, characterized in that a pressure medium shut-off valve (22) is provided in each case upstream, in the direction of flow (P) of the pressure medium in the longitudinal channel (14), of the drag levers for the inlet or outlet valve of a cylinder (I to IV), and in that on the change-over from one cam to the other the shut-off valves lying one behind the other in the direction of flow are opened one after the other at, in each case, a moment in time which precedes the commencement of the lifting phase of the following drag lever by at least the period of time (t.) required by the piston to reach its second position. 3. Valve-actuating mechanism according to Claim 2, for an internal combustion engine having a bank of four cylinders and the ignition sequence 1-3-4-2, characterized in that the bores (11) in the first drag levers (4) of the inlet and outlet valves of two successive cylinders (I, II or III, IV) are in communication with a common pressure medium supply channel (14) which is formed in the drag lever shaft (5) and in which a shut-off valve (22a, 22c) is in each case provided upstream, in the direction of flow (P) of the pressure medium, of the drag levers of the valve of the first of the two cylinders. 4. Valve-actuating mechanism according to Claim 2 or 3, characterized in that the shut-off valve (22a) which, in relation to the direction of flow (P) of the pressure medium, is disposed upstream of the drag levers of the inlet or outlet valve of the first cylinder (I) is formed by a control valve which brings the longitudinal channel (14) in the shaft (5) of the drag levers (4, 7) into communication with the pressure medium source (21). 5. Valve-actuating mechanism according to one of Claims 2 to 4, in which transverse channels (19) extend from the longitudinal channel (14) in the shaft (5) of the drag levers (4, 7) to the drag lever bearings, characterized in that the closure members (23) of the shut-off valves (22) are provided with throttle channels ( 24 ) which, when the shut-off valves are closed, permit a throttled flow to the drag lever bearings. 6. Valve-actuating mechanism according to Claim 5, characterized in that the closure members (23) of the shut-off valves (22) have a peripheral groove (24) which provides the throttle action and which lies in the longitudinal channel (14) of the shaft (5) when the shut- off valve is closed. η ' Valve-actuating mechanism according to one of the preceding claims, characterized in that the shaft (5 ) is mounted between the drag levers for the inlet or outlet valves of neighbouring cylinders, and in that the shut- off valves (22) are disposed in the bearings (6). 8 * Valve-actuating mechanism according to one of C laims 1 to 6, characterized in that the shut-off valves (22) are solenoid valves which are actuated not only in dependence on the position of the respective cams but also in dependence on operating parameters (engine speed, load) .

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