Variable timing mechanism for a rotary valve

Details Variable timing mechanism for a rotary valve Variable timing mechanism for a rotary valve

2002-11-25

2004-07-20

Yuen, Henry C. (Department: 3747)

Internal-combustion engines

Four-cycle

Rotating valve

C123S190800

Reexamination Certificate

active

06763788

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a variable valve timing mechanism for a rotary valve assembly used in an internal combustion engine, and more particularly to a variable valve timing mechanism where both the inlet port and the exhaust port are in the same rotary valve.
BACKGROUND
Rotary valve arrangements have been proposed by many people. One recent example is that proposed by U.S. Pat. No. 5,526,780 (Wallis). Common to all these valve arrangements is an opening in the rotary valve's periphery that periodically aligns with a similar shaped window in the combustion chamber. When the opening in the rotary valve's periphery aligns with the window in the combustion chamber, fluid can pass into (in case of the inlet stroke) and out of (in the case of the exhaust stroke) the combustion chamber. When the opening in the valve's periphery is not aligned with the window in the combustion chamber the contents of the cylinder are trapped during the compression and combustion stroke.
In most prior art arrangements the rotary valve is driven at a fixed angular velocity ratio to the crankshaft. This is achieved by way of mechanical drive mechanisms such as gear trains, chain drives or belt drives which transmit constant angular velocity ratios.
“Angular velocity ratio” is the ratio obtained when the angular velocity of the rotary valve is divided by the angular velocity of the crankshaft. Unless the context requires otherwise any reference made to varying the angular velocity of the rotary valve is made in the context of the angular velocity of the crankshaft remaining constant.
These arrangements all suffer from an inability to vary the engine's valve timing. The duration of the inlet and exhaust process is fixed by the geometry of the window and the respective openings in the rotary valve. In the event that the rotary valve incorporates both, inlet and exhaust ports in the same rotary valve, the angular phase relationship between the inlet and exhaust process is also fixed by the rotary valve geometry.
This inability to vary the valve timing of rotary valve engines is a significant impediment to its widespread adoption in production car engines. Increasingly, more stringent government regulations in the areas of emissions and fuel economy can only be addressed by internal combustion engines that have the ability to vary the engine's valve, timing.
Valve timing is generally expressed as the location of the inlet open, inlet close, exhaust open and exhaust close points relative to the crankshaft position. The crankshaft position is generally specified as an angle relative to a reference location. This is generally chosen to be the location where the piston is at the top of its stroke (i.e. top dead centre—tdc). If the exhaust closes 15° after tdc the exhaust port will cease communication with the cylinder when the crankshaft has rotated 15° from the position where the piston was at top dead centre.
Alternatively valve timing can be thought of as a combination of durations—inlet duration, exhaust duration, close duration and overlap duration, together with an initial position and phase. The initial position determines the relationship between the crankshaft position and the rotary valve position at some point.
“Overlap” is that portion of the engine cycle where both inlet and exhaust ports are both simultaneously open to the combustion chamber.
“Duration” is the angle the crankshaft rotates through between any two events.
“Inlet duration” is the angle the crankshaft rotates through when the inlet port is in communication with the combustion chamber i.e. between inlet open and inlet close. Similarly “exhaust duration” is the angle the crankshaft rotates through when the exhaust port is in communication with the combustion chamber i.e. between exhaust open and exhaust close. “Close duration” is the angle the crankshaft rotates through when neither the inlet nor the exhaust port are open to the combustion chamber i.e. between inlet close and exhaust open. This occurs during the compression and power strokes on a four-stroke, engine. “Overlap duration” is the angle the crankshaft rotates through when both the inlet and exhaust ports are simultaneously open to the combustion chamber i.e. between inlet open and exhaust close.
In all internal combustion engines synchronization of the valve events to their correct position in the engine cycle is essential. Phase is used to describe this synchronization. If the phase is constant from cycle to cycle the valve events will occur in exactly the same position in the cycle from one cycle to the next.
The position in the cycle is defined by the crankshaft position. The position of the rotary valve is described by the angle the valve has rotated from a reference location usually chosen as one of the easily observable valve events—i.e. inlet valve open (ivo), inlet valve close (ivc), exhaust open (evo) or exhaust valve close (evc). For ease of reference in this specification we have chosen the reference location to be ivo. “Rotary valve position” is defined as the angle the valve has rotated from the ivo point.
For conventional rotary valve internal combustion engines using drive mechanisms that deliver constant angular velocity ratio the position of the rotary valve relative to the cycle position can be represented by a graph of the type shown in FIG.
10
A. Line
56
defines the position of the rotary valve for all crankshaft positions. So long as the relationship defined by this line occurs on successive cycles, phase has remained constant (and equal to zero i.e. &sgr;=0). In the event the relationship between rotary valve position and crankshaft position is at some other time represented by line
57
a phase change is said to have occurred and its magnitude is &sgr;. In the event line
56
is chosen as the reference, the phase is a &sgr;°.
“Phase” in this context is the distance in crankshaft degrees (° crankshaft) that the line
57
defining constant phase has shifted relative to reference line
56
defining (nominally) zero phase.
In the event an arrangement was used where the drive mechanism delivers a varying angular velocity ratio during the cycle, another relationship represented by lines
58
in
FIG. 10B
may occur. So long as the mechanism maintains this relationship from cycle to cycle there is no phase change. In the event the rotary valve at some other time follows the relationship shown by lines
59
a phase shift of &sgr;° has occurred and, in the event lines
58
are the reference lines (nominally) defining zero phase, the phase will be a &sgr;°.
In the event the drive mechanism can vary the angular velocity ratio within the cycle and also vary the shape of the angular velocity ratio curve plotted against crankshaft position from cycle to cycle we have a situation shown in FIG.
10
C. Lines
60
represents the relationship between valve position and cycle position in one cycle and lines
61
represent the same relationship in the next cycle. Clearly there is a change in synchronization at all points within the cycle. Instantaneous phase changes are occurring at all points within the cycle (at rotary valve position 120° a phase change of &sgr;° has occurred). However the relationship between rotary valve position and cycle position is unaltered at the start and end points of the cycle i.e. there is no change in synchronization or phase at these points.
FIG. 10D
shows an alternative outcome from this mechanism. Lines
62
represents the relationship during the first cycle and lines
63
represents the relationship during the next cycle. In this case the end point of the cycle represented by lines
63
is different from the end point of the previous cycle. The phase has been changing within the cycle and at the end of the cycle i.e. there is a change of synchronization both during the cycle and at the end of the cycle.
To distinguish between an arrangement that maintains phase at the start and end of each successive cycle and one that doesn't and also to distinguish between an arrangement

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