Internal-combustion engines – Poppet valve operating mechanism – Tappet
Patent
1997-01-14
1998-01-06
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
Tappet
123 9049, F01L 124, F01L 146
Patent
active
057043191
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a hydraulic clearance compensation element for valve control units of internal combustion engines comprising a piston guided slidably in a housing, piston and housing defining therebetween a pressure chamber which communicates through a one-way valve arranged on a lower end of the piston with a reservoir disposed within the piston, an elastic securing ring being arranged in a circumferential groove of the housing.
Different structural embodiments of such clearance compensation elements are known such as, for example, the clearance compensation element of GB 619,535 which comprises an outer cylindrical body and a piston mounted slidably therein with slight play. A snap ring is disposed in a circumferential groove provided in an open end of the outer cylindrical body. In a position of maximum lift, a shoulder of the piston abuts against this snap ring so that the piston cannot come free of the cylindrical body. The radial dimensions of the groove and the piston are interadapted so that when the spring force is overcome during disassembly, the snap ring can be pressed by the piston into a free space within the groove i.e., the diameter of the groove is larger than the diameter of the securing ring.
One drawback of this structure is that the securing ring is not centered and can shear off during disassembly of the clearance compensation element.
A further drawback of such a securing arrangement is that the housing cannot be utilized up to its upper edge for the guidance of the piston, that is to say, the supporting length on the housing is reduced. Moreover, the annular groove reduces the cross-sectional area and thus also the strength of the piston in the upper region. The largest possible supporting length and an unweakened cross-section in the upper region are, however, particularly important in the case of short elements which are subjected to high shearing forces.
The object of the invention is therefore to improve the securing arrangement between the cylinder and the piston of a clearance compensation element using a securing ring while avoiding the hitherto encountered drawbacks.
The invention achieves this object by the fact that the groove is arranged in the housing so that a piston supporting length remains above the groove in every position of lift of the piston, and a diameter of the groove is larger than a diameter of the securing ring which is radially centered by a recess of the piston comprising a ramp at least at its lower end.
An advantage of this solution is that, because the securing ring is centered, it cannot be damaged during disassembly of the clearance compensation element. A further advantage results from the fact that the arrangement of the groove avoids a weakening of material in the upper region of the piston, and an improved guiding or supporting length is obtained between the piston and the housing because support is consistently effected at the upper end of the housing.
To begin with, the securing ring is placed in the groove. The piston is then pushed into the housing whereby the bevel on the piston centers and expands the securing ring which is thus displaced completely into the groove of the housing. When the piston is moved so far into the housing that its bevel passes the securing ring, this latter, due to its pre-tension, snaps back out of the groove of the housing i.e., the diameter of the securing ring becomes smaller, so that the securing ring now acts as a lock to prevent the piston from being pushed out of the housing by the force of the piston resetting spring. In the present context, a ramp is to be understood as a part inclined to the longitudinal axis of a rotationally symmetrical body and joining two regions of different diameter to each other. If, for disassembling the clearance compensation element, a force clearly larger than the force of the resetting spring of the piston is applied, the ramp of the piston presses the securing ring into the groove of the housing and the piston can be removed from the housing without any problem, the sec
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patent: 2784706 (1957-03-01), Humphreys
patent: 3358660 (1967-12-01), Cornell
patent: 4864982 (1989-09-01), Speil
patent: 4867114 (1989-09-01), Schaeffler
patent: 5119774 (1992-06-01), Krieg et al.
Engelhardt Helmut
Schmidt Dieter
INA Walzlager Schaeffler KG
Lo Weilun
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