Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1995-03-28
1996-07-16
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9022, F01L 118, F01L 126, F01L 1300
Patent
active
055357040
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a valve-actuating mechanism for a multicylinder internal combustion engine.
In valve-actuating mechanisms for multicylinder internal combustion engines, which are, for example, known from EP-A-0 213 759 and DE-A-38 00 347, 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 rocker arms 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 rocker arms 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 rocker arm, 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.
Another solution of this problem is known from US-A-4 901 685. The coupling means disclosed therein for coupling a first and second rocker arm are controlled by control means such that they are inoperative during the initial interval of the valve opening motion. However, with this method of controlling the operation of the coupling means it can not be ensured that the movement of each coupling element is completed before the lifting phase of the respective rocker arm.
SUMMARY OF THE INVENTION
The problem underlying the invention is that of ensuring by simple means, in a valve-actuating mechanism of the type described, a complete movement of each coupling element to its second end position in the coupling operation.
According to the invention a control valve or a similar control device of the valve-actuating mechanism is actuated to apply pressure to the coupling elements such that after the commencement of the pressure loading to the coupling elements sufficient time will be available for each coupling element to reach its second end position. This is achieved 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 top dead center position of the internal combustion engine piston and thus also the position of the cams for the valves of the respective cylinder.
The proposal according to the invention can be applied to different valve-actuating mechanisms, for example also those described in DE-A-42 05 230.
In the shaft on which all the rocker arms are mounted, a longitudinal channel is normally provided, through which the pressure medium is fed to the bores which are provided in the rocker arms 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 rocker arms 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
REFERENCES:
patent: 4901685 (1990-02-01), Fukuo et al.
patent: 5297505 (1994-03-01), Doll et al.
patent: 5351661 (1994-10-01), Doll
patent: 5406835 (1995-04-01), Doll
Audi AG
Lo Weilun
LandOfFree
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