Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1997-10-20
1998-10-20
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9055, F01L 1300, F01L 114, F01L 124
Patent
active
058231510
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a cam follower of a valve drive of an internal combustion engine or a support element for a finger lever having means for switching to at least two different lifts of at least one gas exchange valve, comprising an inner element (2) and an outer element (3) which are inserted axially into each other and can be coupled to each other at least indirectly by coupling means (4) which are displaceable radially or secant-like, so that, in a coupled state of said inner and outer element (2, 3), a larger valve lift, and in an uncoupled state thereof, a smaller valve lift is realized, the coupling means (4) effecting coupling of said inner and outer element (2, 3) under the force of a spring means (5) and uncoupling under hydraulic pressure, said cam follower (1) further comprising two separate channels (9, Z.sub.2 ; 8, Z.sub.1) starting from the outer element (3) and extending in the inner element (2) to supply hydraulic medium pressure to the coupling means (4) and to a hydraulic clearance compensation device (10), a control valve (11) being arranged in front of the channel (9, Z.sub.2) to the coupling means (4), which control valve (11), during warm running (operating temperature) of the internal combustion engine and during operation thereof in the partial and full load range, reduces the hydraulic pressure in the channel (9, Z.sub.2) to a level which is lower than and distinct from the hydraulic pressure which serves to displace the coupling means (4) for uncoupling the elements (2, 3) so that a coupled state of the two elements (2, 3) prevails.
A species-defining cam follower of the pre-cited type is known from DE-G 93 15 436.4. In this cam follower, a coupling of the inner and the outer element is likewise effected by spring force and an uncoupling by hydraulic medium pressure. This principle of switching proves to be expedient for application to disconnectable cam followers and support elements because, for the initial starting as well as for renewed starting of the internal combustion engine, all the cylinders are required. Thus, it is only necessary that the two sections be coupled to each other during the starting operation which begins with an idling speed, so that the valve concerned opens following the high lift cam and a proper gas exchange can take place. On the other hand, after warming-up of the internal combustion engine, in a range between idling and partial load running, the two tappet sections should be uncoupled i.e., the coupling elements should be displaced by hydraulic medium pressure in uncoupling direction against the spring force. If a common supply of hydraulic medium is provided, and the two tappet sections are to be uncoupled, say at an engine speed of about 3000 rpm, hydraulic pressure must be reduced so that the coupling means are displaced into their uncoupling position. However, since at these speeds, the clearance compensation device has a relatively high hydraulic pressure requirement due to the increasing foaming of the hydraulic medium at higher speeds, it is necessary to switch from a relatively high hydraulic pressure level which holds the coupling means in an uncoupling position to a low hydraulic pressure. But this low hydraulic pressure must, at the same time, be sufficient to assure an optimal pressure supply to the clearance compensation element (e.g. 2 to 2.5 bars) at normally run engine speeds. As a result, the uncoupling pressure of the hydraulic medium would have to be situated above the aforementioned value. This would necessitate a hydraulic pump which produces very high hydraulic pressures already in the idling range and up to the lower partial load range. This cannot be realized with conventional pumps. On the other hand, the spring forces which load the coupling means against hydraulic pressure for establishing the desired coupled state would then also have to be extremely high. A limit to this is set already by the disposable design space itself in the cam follower.
From DE-GM 93 19 435.8, a support element having the features of the gene
REFERENCES:
patent: 5361733 (1994-11-01), Spath et al.
patent: 5555861 (1996-09-01), Mayr et al.
Katogi Teiji, "Variable Valve Timing Device," vol. 16, No. 328, JP 4094405, Mar. 26, 1992 (abstract only).
Hirano Tomiyasu et al, "Valve System Having . . . Engine", JP 7317518, Dec. 5, 1995 (abstract only).
Elendt Harald
Haas Michael
Maas Gerhard
INA Walzlager Schaeffler KG
Lo Weilun
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