Internal-combustion engines – Poppet valve operating mechanism – Tappet
Patent
1998-07-07
1999-11-09
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
Tappet
123 9051, F01L 124
Patent
active
059793856
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns a valve tappet actuated by a cam of an internal combustion engine comprising a cup made of a ferrous material and having a hollow cylindrical skirt and a cup bottom which closes the skirt at one end, said skirt comprising a peripheral groove on an outer surface and at least one bead on an inner surface, there being arranged concentrically within the cup, an inner element comprising a casing which bears against the constriction, while a hydraulic valve clearance compensation element is guided for axial displacement in the inner element.
BACKGROUND OF THE INVENTION
In valve tappets of the pre-cited type, known, for example, from DE-A 4325610, the soft, unhardened inner element is inserted into the soft, unhardened cup and the peripheral groove is then formed by roller burnishing. Inside the cup, the casing of the inner element and the bead formed by the roller burnished peripheral groove are pressed against each other so that the inner element is firmly connected to the cup. Following this, this partly assembled valve tappet is subjected to a heat treatment whereby the cup and the inner element are hardened. At the end of the heat treatment, the inner element has been somewhat deformed so that, to assure a proper guidance of the hydraulic valve clearance compensation element, machining, particularly grinding work, is required on the inner element. For example, the inner element of the prior art valve tappet comprises a guide sleeve in which the hydraulic valve clearance compensation element is guided for longitudinal displacement. After the common heat treatment of the cup and the inner element, the guide sleeve no longer has a circular cylindrical shape so that the inner wall of the guide sleeve has to be ground.
It is the object of the invention to improve a valve tappet of the generic type so that the machining of the cup after its heat treatment can be dispensed with.
SUMMARY OF THE INVENTION
The invention achieves the above object by the fact that the cup is hardened in a heat treatment process, and the inner element is unhardened. This simple solution offers the advantage that, for example, the guide sleeve no longer has to be machined prior to insertion of the hydraulic valve clearance compensation element into the inner element. Altogether, a deformation of the inner element due to thermal loading can be excluded because only the cup is hardened.
For supplying oil to the hydraulic valve clearance compensation element, the known valve tappet comprises an oil channel situated between the skirt and the casing, through which channel, the oil can be pumped to the hydraulic valve clearance compensation element. In an advantageous development of the invention, an annular chamber is defined by the casing and the skirt, which annular chamber serves to delimit the oil channel. Advantageously, the outer diameter of the casing and the clear diameter of the circumferential bead can be configured for forming a press fit with each other. A further bead can advantageously be arranged on the end of the skirt adjacent the cup bottom, against which further bead the inner element then bears. This guarantees, on the one hand, a firm connection between the inner element and the cup. The cylindrical casing of the inner element is supported in both its axial end regions on the beads so that the inner element cannot tilt. On the other hand, the annular chamber which is used to form the oil channel is formed without any additional costs. Appropriately, the peripheral groove comprises an opening communicating with this annular chamber so that oil present in the peripheral groove can be pumped into the annular chamber i.e., into the oil channel.
The inner element of the known valve tappet comprises a funnel which widens towards the cup bottom and merges at its widened end into the casing, while the narrower end of the funnel continues into a guide sleeve in which the hydraulic valve clearance compensation element is arranged. A transition section from the funnel to th
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patent: 5673662 (1997-10-01), Rigamonti
Schmidt Dieter
Speil Walter
Ina Walzlager Schaeffler OHG
Lo Weilun
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