Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2000-02-17
2001-07-03
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
Reexamination Certificate
active
06253719
ABSTRACT:
FIELD OF THE INVENTION
The present invention relate to a variable phase mechanism for use in a valve train of an internal combustion engine to permit the crank angles at which the valves open and close to be varied.
BACKGROUND OF THE INVENTION
As is well known, valve timing has a significant effect on engine performance and the optimum setting varies with engine operating conditions. To optimize performance under different operating conditions, it is necessary to be able to vary the valve timing.
Various variable valve timing mechanisms have been proposed in the past that achieve a variable phase. These mechanisms have suffered from various problems. Some, though feasible, have been costly to implement and some have developed excessive friction or not proved to be reliable. Furthermore, many could not be fitted as a modification to existing engines and required much of the valve train and cylinder head to be redesigned.
The most relevant prior art is believed to be the Applicants' own earlier proposal in EP-A-0 733 154. This discloses a valve operating mechanism comprising a hollow shaft, a sleeve journalled on the hollow shaft and fast in rotation with a cam, a coupling yoke connected by a first pivot pin to the hollow shaft and by a second pivot pin to the sleeve and means for moving the yoke radially to effect a phase change between the hollow shaft and the sleeve, wherein the means for moving the yoke radially comprise an actuating rod slidably received in the hollow shaft, a cam surface on the actuating rod and a plunger passing through a generally radial bore in the hollow sleeve to cause the yoke to move radially in response to axial movement of the actuating rod.
OBJECTS OF THE INVENTION
The present invention seeks to provide an improvement of the latter proposal which, in its different embodiments, can either allow a greater degree of angular movement to be achieved or can enable the same phase change mechanism to be used to vary the phase of both the intake and the exhaust camshafts of an engine.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a variable phase mechanism comprising a hollow shaft, first and second members rotatable about the hollow shaft, two yokes surrounding the hollow shaft, one yoke coupling the hollow shaft for rotation with first member and the other coupling the second member for rotation with the first member, an actuating rod slidably received in the hollow shaft, a cam surface on the actuating rod acting on the first yoke by way of a plunger passing through a generally radial bore in the hollow shaft to cause the first yoke to move radially in response to axial movement of the actuating rod so as to vary the angular position of the first member relative to the hollow shaft, rotation of the hollow shaft relative to the first member causing the outer surface of the hollow shaft to interact with the inner surface of the second yoke to cause the angular position of the second member to be varied in relation to the first member.
In the first aspect of the invention, a single variable phase mechanism can be used to drive two shafts, for example the intake and exhaust camshafts of a dual overhead camshaft engine. The first member may in this case be the drive sprocket connecting the engine crankshaft to the first camshaft, the latter being fast in rotation with the hollow shaft. The second member rotatable on the hollow shaft may be a drive sprocket serving to drive the other camshaft. The effect of axially displacing the actuating rod would be to advance the timing of one shaft while retarding the timing of the other.
The invention is not however restricted to its use in driving two camshafts using a single variable phase mechanism. It can also be used to drive a single camshaft while increasing the range of angular adjustment by the use of two yokes in tandem.
Hence, in accordance with a second aspect of the invention, there is provided a variable phase mechanism comprising a hollow shaft, first and second members rotatable about the hollow shaft, two yokes surrounding the hollow shaft, one yoke coupling the hollow shaft for rotation with the first member and the other coupling the first member for rotation with the second member, an actuating rod slidably received in the hollow shaft, a cam surface on the actuating rod acting on the first yoke by way of a plunger passing through a generally radial bore in the hollow shaft to cause the first yoke to move radially in response to axial movement of the actuating rod so as to vary the angular position of the first member relative to the hollow shaft, the resultant rotation of the first member about the hollow shaft causing the outer surface of the hollow shaft to interact with the inner surface of the second yoke to cause the angular position of the second member to be further varied in relation to the hollow shaft.
In this embodiment, the first member is not a drive member but simply a freely rotating disc arranged between the two yokes. Torque is transmitted from the second member to the first member and from the first member to the hollow shaft. The combined effect of the angular movements of the two yokes is to increase the angular displacement of the second member relative to the hollow shaft for a given movement of the actuating rod.
In a further aspect of the invention using two yokes in tandem to increase the angular adjustment range, it is possible to dispense with the first member rotatable on the hollow shaft and to connect the two yokes directly to one another.
Hence, in accordance with a third aspect of the invention, there is provided a variable phase mechanism comprising a hollow shaft, a member rotatable about the hollow shaft, two yokes surrounding the hollow shaft, the first yoke coupling the hollow shaft for rotation with the second yoke and the second yoke coupling the first yoke for rotation with the rotatable member, an actuating rod slidably received in the hollow shaft, a cam surface on the actuating rod acting on the first yoke by way of a plunger passing through a generally radial bore in the hollow shaft to cause the first yoke to move radially in response to axial movement of the actuating rod so as to vary the angular position of the second yoke relative to the hollow shaft, the resultant rotation of the second yoke about the hollow shaft causing the outer surface of the hollow shaft to interact with the inner surface of the second yoke to cause the angular position of the rotatable member to be further varied in relation to the hollow shaft.
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Mechadyne PLC
Patel Vinod D
Smith-Hill and Bedell
Walberg Teresa
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