Internal-combustion engines – Poppet valve operating mechanism – Camshaft drive means
Patent
1999-01-20
2000-08-01
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
Camshaft drive means
123 9015, 123 9017, 123 9052, 123 906, 731181, 73119R, F01L 120
Patent
active
060951044
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method for the dimension checking of the timing system of an internal combustion engine comprising at least a camshaft with cams and main journals, and a cylinder head with valves and seats for housing the main journals and defining the position of the mentioned camshaft in a longitudinal direction, the method including the steps of detecting and processing values relating to diametral dimensions of the main journals of the camshaft and radial dimensions of the cams, detecting and processing values relating to diametral dimensions of the seats of the cylinder head, and the transversal arrangement of the valves with respect to the formerly mentioned longitudinal direction, and calculating--on the basis of the detected values and in the course of the camshaft rotation--a clearance value between each cam and its associated valve. The invention also relates to an apparatus for checking the timing system of an internal combustion engine according to the formerly mentioned method.
BACKGROUND ART
There are known internal combustion engines with mechanical tappet comprising elements commonly called "bucket type tappets" positioned between the cylinder head valves and the associated cams of the camshaft and having the purpose of remaining in contact with the valves and cooperating with the cams lobes in the course of the camshaft rotation. In order to ensure a correct performance in the valve opening and closure phases, it is necessary that the clearance existing between the base circle of each cam and the related bucket type tappet be determined in an accurate way.
In fact, if on the one hand no clearance, or an extremely limited amount of clearance, would not allow the proper closure of the valves, on the other hand an excessive clearance would detrimentally affect the performance and the life of the engine and, among other things, increase noise.
In order to attain, for each single cam/bucket type tappet coupling the required amount of clearance, generally there is foreseen the insertion--in a suitable bucket type tappet recess, at the cam or valve side--of a specifically thick adjustment shim so that the clearance between the base circle of the cam and the bucket type tappet (or the shim) be of the desired value. According to a variant, that does not involve the insertion of shims, there can be foreseen, for each cam/valve coupling, the selection of an appropriate bucket type tappet among a series of bucket type tappets that have different predetermined thicknesses. The English abstract of Japanese patent application JP-A-57013205 shows a device for calculating the gaps existing between the top faces of the valve lifters 3 and the base circles of the relevant cams of a camshaft when the latter is assembled to the cylinder head. The thickness of the shims to be inserted are chosen on the basis of the values of the calculated gaps and of the desired clearances. Two measurements are taken to calculate each gap. A first measurement is taken on the cylinder head, substantially corresponding to the distance between the top surface of each bucket type valve lifter and a camshaft bearing surface 9 of the cylinder head. A second measurement is taken on the camshaft, corresponding to the distance between the surfaces of the base circle of the cam and a bearing journal of the camshaft.
The calculations for determining the thickness of the adjustment shims, or that of the bucket type tappets, are troublesome due to various reasons among which the radial clearance existing between the main journals of the camshaft and the cylindrical seats of the cylinder head in which these journals are seated. This clearance is limited, but necessary for guaranteeing a correct rotation of the camshaft and allowing an appropriate lubrication. Devices like the one shown in the English abstract of JP-A-57013205 do not take into account such radial clearance in the calculation of the gaps.
A checking method presently used for determining the thicknesses foresees the use of apparatuses that check
REFERENCES:
patent: 3988925 (1976-11-01), Seccombe et al.
patent: 4521863 (1985-06-01), Solaroli
patent: 4966107 (1990-10-01), Imajo
Patent Abstracts of Japan, Kokai No. 57-13205, Jan. 1982.
Bolognesi Antonio
Danielli Franco
Ghielmi Antonio
Lo Weilun
Marposs Societa'per Azioni
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