Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1990-09-17
1991-07-16
Okonsky, David A.
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9039, F01L 134
Patent
active
050315846
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an arrangement for varying the degree of valve lift in an internal combustion engine and in particular to an arrangement which permits such variation without at the same time altering the phase of opening of the valve.
The volume of the intake charge of any cylinder varies with the operating conditions and if a fixed degree of valve lift is used under all operating conditions, as is the case in conventional engines, then the velocity of the charge through the skirt area and the resultant turbulence in the charge will vary over the engine operating range. It is clearly desirable, therefore, to be able to vary the valve lift so as to enable the air flow conditions to be optimised over the full operating range and in particular to permit higher air velocities under low speed part load conditions.
The prior art discloses arrangements which permit the geometry of the intake port to be varied with the same aim in mind but these are less effective in the control of the air velocities since it is at the skirt area that the velocity is of importance and the closer the control mechanism is to this region, the more effective it will prove.
Variable lift valves have been proposed (see for example GB No. 1201872, GB No. 1201558 and GB No. 682628) in which the position of a fulcrum of a rocker acting between a push rod and a valve can be varied to alter the mechanical advantage of the rocker and thereby alter the valve lift. Such arrangement have the disadvantage that they cannot be used in a overhead camshaft engine in which the camshaft is mounted in line with and above the valve stems.
According to the present invention, there is provided a mechanism for achieving variable lift of a valve of an internal combustion engine having a fixed profile overhead camshaft, characterised by a lever arrangement interposed between the camshaft and the valve, which lever arrangement includes a first fixed fulcrum lever acted upon by the camshaft, a second fixed fulcrum lever arranged to actuate the valve and a coupling member movable relative to the fulcrums of the two levers for transmitting the movement of the first lever to the second lever.
Each of the two levers may be constructed as a single arm lever but, depending upon the geometry of the cylinder head, one or both of the levers may alternatively be two armed levers. It is important in all cases that one arm of the first lever should overlie an arm of the second lever so that movement of one can be directly transmitted to the other.
The travel of the second lever will vary with the position of the coupling member and in some cases, depending upon the lift height and the separation of the levers, the lower lever may overlap the position of the upper lever in a horizontal plane. Collision between the levers can be avoided by offsetting one of the levers to one side in the horizontal plane but this step alone would cause a bending moment to be applied to the coupling between the levers. It is therefore preferred in this case for the first lever to be bifurcated and to straddle the second lever. This bifurcation of the first lever is also effective to prevent direct collision between the first lever and the valve spring retainer plate.
The coupling member between the levers may comprise a roller movable along the length of the overlapping lever arms. Such a roller may be supported on a sheet metal cage and movement of the roller can be effected by a rack and pinion mechanism in which the rack is constituted by or supported on the cage while the pinion can be formed on or driven by the shaft on which one of the levers is journalled.
As an alternative, the coupling member may consist of a roller carried by a further lever pivotably mounted on the outer end of an arm projecting from the shaft on which one of the levers is journalled. As the latter shaft is turned, the further levers for all the cylinders are moved in unison to vary the positions of their respective rollers relative to the first and second levers of the valves.
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REFERENCES:
patent: 4397270 (1983-08-01), Aoyama
patent: 4438736 (1984-03-01), Hara et al.
patent: 4459946 (1984-07-01), Burandt
patent: 4572118 (1986-02-01), Baguena
patent: 4699094 (1987-10-01), Stegeman
patent: 4724822 (1988-02-01), Bonvallet
patent: 4911124 (1990-03-01), Bennett
Drouillard Jerome R.
Ford Motor Company
Lo Weilun
Okonsky David A.
Sadler Clifford L.
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