U.S. patent application number 10/585782 was filed with the patent office on 2008-03-06 for port arrangment for a rotary valve engine.
Invention is credited to Andrew Donald Thomas.
Application Number | 20080053395 10/585782 |
Document ID | / |
Family ID | 34812595 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080053395 |
Kind Code |
A1 |
Thomas; Andrew Donald |
March 6, 2008 |
Port Arrangment for a Rotary Valve Engine
Abstract
A axial flow rotary valve rotatable within a bore in a cylinder
head (9) of an internal combustion engine has a port extending from
a peripheral opening (4) to an axial opening at one end of the
valve. The peripheral opening (4), which periodically communicates
with a combustion chamber (30) through a window (8) in the bore,
has a first trailing edge (13). The window (8) has a second
trailing edge (12). The port closes from the combustion chamber
(30) as the first trailing edge (13) passes the second trailing
edge (12). The edges (12, 13) are disposed such that the
instantaneous intersection point (17) of the two edges (12, 13)
progressively moves away from the axial opening over at least 50%
of the length of the window (8) as the port closes.
Inventors: |
Thomas; Andrew Donald; (New
South Wales, AU) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
34812595 |
Appl. No.: |
10/585782 |
Filed: |
January 28, 2005 |
PCT Filed: |
January 28, 2005 |
PCT NO: |
PCT/AU05/00092 |
371 Date: |
July 11, 2006 |
Current U.S.
Class: |
123/190.2 |
Current CPC
Class: |
F01L 7/023 20130101;
F01L 3/06 20130101; Y02T 10/12 20130101; Y02T 10/146 20130101 |
Class at
Publication: |
123/190.2 |
International
Class: |
F01L 7/02 20060101
F01L007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2004 |
AU |
2004900377 |
Claims
1. A rotary valve assembly for an internal combustion engine
comprising a cylinder head and an axial flow rotary valve rotatable
within a bore in said cylinder head, said valve having a port
extending from a peripheral opening on the periphery of said valve
to an axial opening at one end of said valve, said peripheral
opening periodically communicating with a combustion chamber
through a window in said bore as said valve rotates, said
peripheral opening having a first trailing edge and said window
having a second trailing edge whereby said port closes from said
combustion chamber as said first trailing edge passes said second
trailing edge as said valve rotates, characterised in that said
first and second trailing edges are disposed such that as said port
closes from said combustion chamber the instantaneous intersection
point of said first and second trailing edges progressively moves
away from said axial opening over at least 50% of the length of
said window.
2. A rotary valve assembly as claimed in claim 1 wherein said port
is an inlet port.
3. A rotary valve assembly as claimed in claim 1 wherein said first
and second trailing edges are disposed such that as said port
closes from said combustion chamber the instantaneous intersection
point of said first and second trailing edges progressively moves
away from said axial opening over substantially the whole length of
said window.
4. A rotary valve assembly as claimed in claim 1 wherein at least
50% of said first trailing edge is substantially linear and oblique
to the axis of said valve, and said second trailing edge is
substantially linear and parallel to the axis of said valve.
5. A rotary valve assembly as claimed in claim 4 wherein said first
trailing edge is substantially linear and oblique to the axis of
said valve.
6. A rotary valve assembly as claimed in claim 1 wherein said
window is substantially rectangular.
7. A rotary valve assembly as claimed in claim 1 wherein the length
of said window is at least 60% of the bore diameter of the cylinder
that said rotary valve assembly is adapted to suit.
8. A rotary valve assembly for an internal combustion engine
comprising a cylinder head and an axial flow rotary valve rotatable
about an axis within a bore in said cylinder head, said valve
having a port extending from a peripheral opening on the periphery
of said valve to an axial opening at one end of said valve, said
peripheral opening periodically communicating with a combustion
chamber through a window in said bore as said valve rotates,
characterised in that every axial portion of said peripheral
opening, said window or both that is longer than one half of the
length of said window is asymmetric about a plane passing through
the axial mid-point of said portion, perpendicular to said
axis.
9. A rotary valve assembly as claimed in claim 8 wherein said
peripheral opening has a first trailing edge and said window has a
second trailing edge whereby said port closes from said combustion
chamber as said first trailing edge passes said second trailing
edge as said valve rotates, and said first and second trailing
edges are disposed such that as said port closes from said
combustion chamber the instantaneous intersection point of said
first and second trailing edges progressively moves away from said
axial opening over at least 50% of the length of said window.
10. A rotary valve assembly as claimed in claim 8 wherein said
peripheral opening has a first leading edge and said window has a
second leading edge whereby said port opens to said combustion
chamber as said first leading edge passes said second leading edge
as said valve rotates, and said first and second leading edges are
disposed such that as said port opens to said combustion chamber
the instantaneous intersection point of said first and second
leading edges progressively moves towards said axial opening over
at least 50% of the length of said window.
11. A rotary valve assembly as claimed in claim 8 wherein said
peripheral opening is narrower at its end proximate to said axial
opening than at its end remote from said axial opening.
12. A rotary valve assembly as claimed in claim 11 wherein the
width of said peripheral opening progressively decreases from a
maximum at its end remote from said axial opening to a minimum at
its end proximate to said axial opening.
13. A rotary valve assembly as claimed in claim 11 or 12 wherein
the trailing edge of said peripheral opening is substantially
parallel to said axis.
14. A rotary valve assembly as claimed in claim 8 wherein said
window is narrower at its end proximate to said axial opening than
at its end remote from said axial opening.
15. A rotary valve assembly as claimed in claim 14 wherein the
width of said window progressively decreases from a maximum at its
end remote from said axial opening to a minimum at its end
proximate to said axial opening.
16. A rotary valve assembly as claimed in claim 14 or 15 wherein
the trailing edge of said window is substantially parallel to said
axis.
17. A rotary valve assembly as claimed in claim 8 wherein said
window is substantially rectangular.
18. A rotary valve assembly as claimed in claim 8 wherein said port
is an inlet port.
Description
TECHNICAL FIELD
[0001] The present invention relates to a means of improving the
volumetric efficiency of an axial flow rotary valve internal
combustion engine. It is applicable to all internal combustion
engines incorporating hollow cylindrical axial flow rotary valves,
where the rotary valve accommodates one or more ports terminating
as openings in the valve's periphery.
BACKGROUND
[0002] Most internal combustion engines regulate the flow of inlet
and exhaust to and from the cylinder, through a combustion chamber,
by means of poppet valves. An alternative means of regulating these
flows is the rotary valve, and in particular the axial flow rotary
valve. Although many rotary valve arrangements have been tested
unsuccessfully in the past, recent developments have opened the way
for the commercial exploitation of axial flow rotary valves, which
have many advantages compared to poppet valves.
[0003] Axial flow rotary valves are well known and examples are
described in U.S. Pat. No. 5,526,780 (Wallis) and U.S. Pat. No.
4,852,532 (Bishop). An axial flow rotary valve rotates within a
bore in the cylinder head of an engine, and each port in the valve
extends from a peripheral opening on the periphery of the valve to
an axial opening at one end of the valve. A significant portion of
each port is substantially parallel to the axis of rotation of the
valve. Typically, there is a single axial flow rotary valve for
each cylinder of the engine and each axial flow rotary valve
incorporates both an inlet and exhaust port terminating at opposite
ends of the valve. During rotation of an axial flow rotary valve
the peripheral openings periodically communicate with the
combustion chamber through a window in the bore of the cylinder
head to allow passage of fluids to and from the cylinder via the
combustion chamber. The valve opening of an axial flow rotary valve
is the opening through which the fluid passes when it travels
between the ports and the combustion chamber. At any rotational
position of the valve, the valve opening is the overlap area
between the peripheral openings and the window.
[0004] Typically, an inlet passageway extends from the axial
opening at the end of the inlet port of an axial flow rotary valve.
This passageway opens to atmospheric pressure, or in the case of a
supercharged or turbocharged engine this passageway opens to the
source of pressurised air. The passageway may contain a throttle
valve. The combination of the inlet passageway and the inlet port
forms an inlet tract. Similarly, an exhaust passageway, usually in
the form of an exhaust pipe, typically extends from the axial
opening at the end of the exhaust port to atmosphere, and the
combination of the exhaust passageway and the exhaust port forms an
exhaust tract.
[0005] Likewise, the inlet tract of a poppet valve engine extends
from the inlet poppet valve opening, through the inlet port and any
connected passageway, to atmosphere. The exhaust tract of a poppet
valve engine extends from the exhaust poppet valve opening, through
the exhaust port and any connected passageway, to atmosphere. The
valve opening of a poppet valve is the annular opening between the
valve seat and it's mating face on the poppet valve.
[0006] The fluids occupying the tracts of an internal combustion
engine are cyclically subjected to impulses from the cylinder,
which create pressure pulses in the tract. These pressure pulses
traverse the length of the tract at the local speed of sound
creating a time varying pressure wave within it. All modem internal
combustion engines utilise these pressure waves to improve the
flows of fluid into and out of the cylinder. The explanation of the
source of these pressure waves and how they are best harnessed in a
poppet valve engine is well known in the art. In order to better
explain the present invention, a brief simplified explanation of
the pressure waves in an inlet tract will now be provided.
[0007] At the start of the induction stroke, the acceleration of
the piston away from top dead centre (tdc) creates a negative
pressure pulse in the fluid residing in the inlet tract adjacent
the valve opening. This negative pressure pulse travels at the
local speed of sound towards the open or atmospheric end of the
inlet tract. At the open end of the tract the negative pressure
pulse is reflected as a positive pressure pulse which travels back
towards the cylinder at the local speed of sound. When this
positive pressure pulse reaches the valve opening it is again
reflected as negative pressure pulse that travels towards the open
end of the inlet tract. Depending on the length of the inlet tract
and engine speed, the pressure pulse may traverse the inlet tract
several times before the inlet port closes to the combustion
chamber. The inlet tract length is chosen to ensure that the return
of a positive pressure pulse to the valve opening coincides with
the end of the inlet stroke. The presence of this positive pulse
acts to increase the density of the charge being fed to the
cylinder and to overcome any adverse pressure gradient existing
between the cylinder and the inlet tract. Correct utilisation of
the pressure wave increases the volumetric efficiency of the
engine.
[0008] In high performance poppet valve engines, the inlet port is
arranged such that it is as close to coaxial with the poppet valve
as possible. Consequently any pulse reflected from the open end of
the tract will reach all parts of the poppet valve opening
simultaneously. However, in axial flow rotary valves a considerable
portion of the inlet port is approximately perpendicular to the
peripheral opening. Furthermore, the peripheral opening and the
window in the cylinder head bore are each generally approximately
rectangular in shape with the long side of the rectangle being
parallel to the axis of the rotary valve. As a consequence, the
reflected pressure pulse in the inlet tract does not reach all
parts of the valve opening simultaneously. Instead, the pressure
pulse axially traverses the valve opening at the local speed of
sound and as a result, at any instant in time, a pressure gradient
exists along the length of the valve opening. This situation does
not exist in poppet valve engines where the tract length can be
adjusted such that the peak pressure occurs at the appropriate time
over the entire poppet valve opening. In the case of typical axial
flow rotary valve engines, the inlet tract length can be adjusted
such that peak pressure occurs over a portion of the length of the
valve opening at an appropriate time, but not over its entire
length at the same time.
[0009] This particular problem is amplified by the fact that in
order to maximise the breathing capability of an axial flow rotary
valve engine the window length and consequently the length of the
peripheral opening is generally made very long. Typically the
window length may be greater than 60% of the cylinder bore size.
This compares to poppet valves in a four valve per cylinder head
where the valve head diameter is typically less than 35% of the
bore diameter. The problem is further amplified on rotary valve
engines designed for high speed where the inlet tract length
required to operate at high speed is relatively short. In these
engines the length of the peripheral opening represents a
significant portion of the tract length. The greater this portion,
the steeper the pressure gradient will be along the length of the
valve opening thus reducing volumetric efficiency. In certain cases
the pressure gradient can be steep enough such that air is being
pushed into the combustion chamber at one end of the valve opening
while at the other end air is being pushed from the combustion
chamber into the port.
[0010] The peripheral openings and windows of axial flow rotary
valve engines are typically approximately rectangular to maximise
the valve opening area. Each peripheral opening has a leading edge
and a trailing edge on opposite sides of the opening. The window
also has a leading edge and a trailing edge. As the valve rotates,
it opens to allow communication between the combustion chamber and
a port when the leading edge of that port's peripheral opening
passes the leading edge of the window. Similarly, the valve closes
as the trailing edge of the peripheral opening passes the trailing
edge of the window. The leading edges of the peripheral openings
and the window are typically deliberately designed to be parallel
to each other to maximise the rate at which the valve opens.
Similarly, the trailing edges of the peripheral openings and the
window are also typically parallel to each other to maximise the
rate at which the valve closes.
[0011] Various rotary valves have been proposed that have
peripheral openings or windows shaped other than rectangular, but
none of these arrangements address, or attempt to address, the
problem of the pressure gradient along the length of the valve
opening of an axial flow rotary valve.
[0012] Some rotary valve arrangements have been proposed where the
window is substantially round in shape. The round window is usually
dictated by the use of a `shoe` type gas sealing arrangement. These
arrangements necessarily limit the opening and closing rate of the
valve and consequently suffer from poor breathing capacity. In
these cases, the peripheral openings and window are still typically
symmetric about their respective axial mid-points.
[0013] In a few exceptional cases, asymmetric windows or peripheral
openings have been proposed. These arrangements generally fall into
two categories. Firstly there are arrangements where the peripheral
openings or window are asymmetric for packaging or construction
reasons. Secondly, there are arrangements where asymmetry has been
introduced to create variation in valve timing.
[0014] An example of the first category is shown in FIG. 2 of U.S.
Pat. No. 4,022,178 (Cross et al) depicting an asymmetric peripheral
opening. The shape of this peripheral opening is similar to that
shown in FIG. 8 of this specification. The asymmetry results from
the encroachment of the common wall between the inlet and exhaust
ports into the peripheral openings in the valve. In this case, the
asymmetry is limited to a small axial portion of the peripheral
opening. One way of defining the degree of asymmetry of a
peripheral opening is to specify the portion of its overall axial
length that is symmetrical about a plane, perpendicular to the
valve axis, passing through the axial mid-point of that portion. It
can be seen from FIG. 2 of U.S. Pat. No. 4,022,178 that an axial
portion of the peripheral opening greater than 70% of the overall
length of the opening (ignoring the corner radii) is axially
symmetrical about its mid-point.
[0015] An example of the second category is U.S. Pat. No. 4,163,438
(Guenther et al). In this case the rotary valves are axially
movable. This axial movement is controlled to effect a change in
valve timing. However, as the full length and width of the window
cannot be utilised in these arrangements breathing is poor. It is
important to note that, unlike the present invention, the rotary
valves described in U.S. Pat. No. 4,163,438 are radial flow rotary
valves, rather than axial flow rotary valves. The geometry of
radial flow rotary valves, like poppet valves, is such that they do
not suffer from the problems of non-uniform pressure distribution
along the valve opening. This is because the ports of a radial flow
rotary valve extend from one side of the periphery of the valve to
the other side without any changes of flow direction. So, like a
poppet valve engine, all parts of the valve opening are
substantially the same distance to the open end of the inlet
tract.
[0016] The present invention seeks to improve the volumetric
efficiency of an axial flow rotary valve engine.
SUMMARY OF INVENTION
[0017] In a first aspect, the present invention consists of a
rotary valve assembly for an internal combustion engine comprising
a cylinder head and an axial flow rotary valve rotatable within a
bore in said cylinder head, said valve having a port extending from
a peripheral opening on the periphery of said valve to an axial
opening at one end of said valve, said peripheral opening
periodically communicating with a combustion chamber through a
window in said bore as said valve rotates, said peripheral opening
having a first trailing edge and said window having a second
trailing edge whereby said port closes from said combustion chamber
as said first trailing edge passes said second trailing edge as
said valve rotates, characterised in that said first and second
trailing edges are disposed such that as said port closes from said
combustion chamber the instantaneous intersection point of said
first and second trailing edges progressively moves away from said
axial opening over at least 50% of the length of said window.
[0018] Preferably, said port is an inlet port.
[0019] Preferably, said first and second trailing edges are
disposed such that as said port closes from said combustion chamber
the instantaneous intersection point of said first and second
trailing edges progressively moves away from said axial opening
over substantially the whole length of said window.
[0020] Preferably, said first trailing edge is substantially linear
and oblique to the axis of said valve, and said second trailing
edge is substantially linear and parallel to the axis of said
valve. Preferably, said first trailing edge is substantially linear
and oblique to the axis of said valve.
[0021] Preferably, said window is substantially rectangular.
Preferably, the length of said window is at least 60% of the bore
diameter of the cylinder that said rotary valve assembly is adapted
to suit.
[0022] In a second aspect, the present invention consists of a
rotary valve assembly for an internal combustion engine comprising
a cylinder head and an axial flow rotary valve rotatable about an
axis within a bore in said cylinder head, said valve having a port
extending from a peripheral opening on the periphery of said valve
to an axial opening at one end of said valve, said peripheral
opening periodically communicating with a combustion chamber
through a window in said bore as said valve rotates, characterised
in that every axial portion of said peripheral opening, said window
or both that is longer than one half of the length of said window
is asymmetric about a plane passing through the axial mid-point of
said portion, perpendicular to said axis.
[0023] In one preferred embodiment, said peripheral opening has a
first trailing edge and said window has a second trailing edge
whereby said port closes from said combustion chamber as said first
trailing edge passes said second trailing edge as said valve
rotates, and said first and second trailing edges are disposed such
that as said port closes from said combustion chamber the
instantaneous intersection point of said first and second trailing
edges progressively moves away from said axial opening over at
least 50% of the length of said window.
[0024] In another preferred embodiment, said peripheral opening has
a first leading edge and said window has a second leading edge
whereby said port opens to said combustion chamber as said first
leading edge passes said second leading edge as said valve rotates,
and said first and second leading edges are disposed such that as
said port opens to said combustion chamber the instantaneous
intersection point of said first and second leading edges
progressively moves towards said axial opening over at least 50% of
the length of said window.
[0025] In one preferred embodiment, said peripheral opening is
narrower at its end proximate to said axial opening than at its end
remote from said axial opening.
[0026] Preferably, the width of said peripheral opening
progressively decreases from a maximum at its end remote from said
axial opening to a minimum at its end proximate to said axial
opening. Preferably, the trailing edge of said peripheral opening
is substantially parallel to said axis.
[0027] In another preferred embodiment, said window is narrower at
its end proximate to said axial opening than at its end remote from
said axial opening. Preferably, the width of said window
progressively decreases from a maximum at its end remote from said
axial opening to a minimum at its end proximate to said axial
opening. Preferably, the trailing edge of said window is
substantially parallel to said axis.
[0028] Preferably, said window is substantially rectangular.
Preferably, said port is an inlet port.
BRIEF DESCRIPTION OF DRAWINGS
[0029] FIG. 1 is a cross sectional view of an internal combustion
engine having a first embodiment of rotary valve assembly in
accordance with the present invention.
[0030] FIG. 2 is a view of the cylinder head and valve, looking
into the window from the cylinder side of the cylinder head, of the
internal combustion engine shown in FIG. 1.
[0031] FIG. 3 is a side view of the rotary valve of the internal
combustion engine shown in FIG. 1.
[0032] FIG. 4 is a projection of the inlet peripheral opening
geometry of the rotary valve shown in FIG. 3.
[0033] FIG. 5 is a view of the cylinder head and valve, looking
into the window from the cylinder side of the cylinder head, of an
internal combustion engine having a second embodiment of a rotary
valve assembly in accordance with the present invention.
[0034] FIGS. 6a-6l depict various alternative shapes of peripheral
openings or windows that may be utilised in axial flow rotary valve
assemblies in accordance with the present invention.
[0035] FIG. 7 is a view of an inlet peripheral opening in
accordance with the present invention, projected onto plane B of
FIG. 3.
[0036] FIG. 8 is a view of a prior art inlet peripheral
opening.
BEST MODE OF CARRYING OUT THE INVENTION
[0037] FIGS. 1 to 4 depict an internal combustion engine having a
first embodiment of a rotary valve assembly in accordance with the
present invention. Referring to FIG. 1, rotary valve I rotates
within bore 11 of cylinder head 9 about axis A, supported by
bearings 26. Valve 1 is rotated by means not shown to be in timed
relationship with piston 20 as it reciprocates within cylinder 10.
There is a small clearance between the cylindrical portion 25 of
valve 1 and bore 11. An array of floating seals (not shown) spans
the small clearance between cylindrical portion 25 and bore 11 thus
preventing the loss of fluids. Valve I has an inlet port 2 and an
exhaust port 3. Inlet port 2 extends from inlet peripheral opening
4 on the periphery of valve 1 to inlet axial opening 6 at one end
of valve 1. Exhaust port 3 extends from exhaust peripheral opening
5 to exhaust axial opening 19, at the opposite end of valve 1 to
inlet axial opening 6. As valve 1 rotates, inlet and exhaust
peripheral openings 4, 5 periodically communicate with combustion
chamber 30 through window 8 in bore 11 of cylinder head 9. During
the compression and power strokes of the engine, cylindrical
portion 25 covers window 8 to prevent the escape of fluids from
combustion chamber 30.
[0038] Inlet passageway 28 extends from inlet axial opening 6 to
open end 29. Throttle valve 7 is mounted in inlet passageway 28.
The combination of inlet port 2 and inlet passageway 28 forms an
inlet tract. An exhaust pipe (not shown) extends from exhaust axial
opening 19, and the combination of exhaust port 3 with the exhaust
pipe forms an exhaust tract.
[0039] FIG. 2 is a view of cylinder head 9 and valve 1 looking into
window 8 from the side of cylinder head 9 that faces cylinder 10.
Valve 1 rotates in a direction indicated by arrow R such that inlet
peripheral opening 4 (indicated by broken lines where hidden) opens
then closes to window 8 as it moves from left to right as viewed,
thereby opening then closing inlet port 2 to combustion chamber 30.
In the position shown, inlet peripheral opening 4 is almost fully
closed to window 8. The remaining valve opening 16 at this instant
is the overlap between inlet peripheral opening 4 and window 8.
Window 8 is rectangular in shape and its trailing edge 12 is
substantially parallel to axis A. To maximise breathing capacity of
the engine, window 8 is long relative to the diameter of cylinder
10 in the direction of axis A. The trailing edge 13 of inlet
peripheral opening 4 is oblique to axis A by a predetermined
angular amount. As valve 1 rotates and inlet peripheral opening 4
closes to window 8, the instantaneous intersection point 17 of
inlet peripheral opening trailing edge 13 and window trailing edge
12 progressively moves axially away from inlet axial opening 6. Or
in other words, as inlet peripheral opening 4 closes, intersection
point 17 progressively moves from window end 14, proximate to inlet
axial opening 6, to window end 15, remote from inlet axial opening
6.
[0040] At the start of the induction stroke, piston 20 accelerates
away from top dead centre, creating a negative pressure pulse in
the fluid residing in inlet port 2 adjacent inlet peripheral
opening 4. This negative pressure pulse travels at the local speed
of sound through inlet port 2 and inlet passageway 28 until it
reaches open end 29. This negative pressure pulse is then reflected
back towards combustion chamber 30 as a positive pressure pulse
travelling at the local speed of sound. The pressure pulse may
traverse the inlet tract several times as discussed in the
background. The angle of inlet peripheral opening trailing edge 13
to axis A is predetermined such that at a particular desired engine
speed the return positive pressure pulse traverses the length of
window 8 at approximately the same rate that instantaneous
intersection point 17 moves along window 8 as inlet peripheral
opening 4 closes. Furthermore, the length of the inlet tract is
chosen such that at the same engine speed, a return positive
pressure pulse travels adjacent the instantaneous intersection
point 17 as the pressure pulse traverses the length of window 8.
This means that at each point along the length of window 8, once
the positive pressure pulse has passed that point then that point
is closed to prevent the fluid flowing back out of the combustion
chamber into the lower pressure that follows behind the positive
pressure pulse. This relative arrangement of inlet peripheral
opening trailing edge 13 and window trailing edge 12 therefore
improves the volumetric efficiency of an axial flow rotary valve
engine by utilising the reflected positive pressure pulse over the
whole length of window 8.
[0041] FIGS. 3 and 4 illustrate how the shape of inlet peripheral
opening 4 is defined. Plane D is perpendicular to the axis A of
valve 1 and passes through the mid-point 31 of inlet peripheral
opening 4. Mid-point 31 is axially halfway between ends 32 and 33
of inlet peripheral opening 4, and circumferentially halfway
between points 34 and 35, which are defined by the intersection of
plane D with inlet peripheral opening trailing edge 13 and inlet
peripheral opening leading edge 18 respectively. Axis A and
mid-point 31 lie in plane C. Plane B is perpendicular to both
planes C and D, and passes through intersection points 34 and 35.
In this specification, all discussions relating to the shape of
inlet peripheral opening 4 refer to its shape as projected onto
plane B, as shown in FIG. 3. Likewise all discussions referring to
the shape of any other peripheral opening or window refer to the
shape as projected onto a plane constructed in the same manner as
plane B for that particular opening.
[0042] FIG. 4 shows the specific points required to define the
angular orientation of inlet peripheral opening trailing edge 13 to
axis A. Axis A lies in both planes E and F, and planes E and F pass
through end points 21 and 22 respectively of inlet peripheral
opening trailing edge 13. Taper angle a is the angle between planes
E and F.
[0043] The amount of taper angle a required to obtain the benefit
of the present invention is typically small. The maximum taper
angle a required for a four stroke engine can be calculated using
the following formula. Maximum .alpha.=(window length L/local speed
of sound).times.(engine speed in rpm.times.3). This assumes the
pressure pulse is rectangular in shape and very narrow. In reality
the pulse is neither rectangular nor narrow and consequently the
required taper angle a will generally be smaller than that
calculated by the above formula. The taper angle a required
increases with the length L of window 8 and engine speed.
[0044] FIG. 5 shows an internal combustion engine having a second
embodiment of a rotary valve assembly in accordance with the
present invention viewed in the same manner as FIG. 2. The only
differences between this rotary valve assembly and that of FIGS. 1
to 4 are that the trailing edge 12a of window 8a is oblique to axis
A by a predetermined amount, and the trailing edge 13a of inlet
peripheral opening 4a is substantially parallel to axis A. As the
valve rotates and inlet peripheral opening 4a closes to window 8a,
the instantaneous intersection point 17 of inlet peripheral opening
trailing edge 13a and window trailing edge 12a progressively moves
axially away from inlet axial opening 6 in the same manner as the
rotary valve assembly of FIGS. 1 to 4. As such this arrangement
also improves the volumetric efficiency of an axial flow rotary
valve engine by utilising the reflected positive pressure pulse
over the whole length of the window.
[0045] The present invention is not limited to the shape and
configuration of the peripheral openings or windows shown in the
two abovementioned embodiments. For example, in other not shown
embodiments both the inlet peripheral opening trailing edge and
window trailing edge may both be oblique to the axis of the valve
and each other.
[0046] It is preferable that the intersection point of the inlet
peripheral opening and window trailing edges progressively moves
away from the inlet axial opening over substantially the whole
length of the window as the valve rotates, as in the two
abovementioned embodiments. However, arrangements where the
intersection point progressively moves away from the inlet axial
opening over at least 50% of the window length still improve the
volumetric efficiency of an axial flow rotary valve engine. Such
rotary valve assemblies have the geometrical attribute that every
axial portion of the inlet peripheral opening and/or the window
that is longer than 50% of the length of that opening is asymmetric
about a plane perpendicular to the axis of the valve, passing
through the mid-point of that portion. For the purposes of this
test, the corner radii of the opening should be ignored and the
geometry of the opening should be considered to be that generated
by projecting the leading edge, trailing edge and ends of the
opening to their intersection points.
[0047] FIGS. 7 and 8 depict two example inlet peripheral openings.
Consider an engine the same as that of FIGS. 1 to 4 except with an
inlet peripheral opening 4b shaped as shown in FIG. 7. More than
50% of the length of inlet peripheral opening trailing edge 13b is
oblique to axis A and the remainder is parallel to axis A. As such,
the instantaneous intersection point 17 (refer FIG. 2)
progressively moves away from inlet axial opening 6 over at least
50% of the length of window 8. Applying the above geometrical test
to inlet peripheral opening 4b, H represents any axial portion of
inlet peripheral opening 4b that is greater than 50% of L in
length. M is a plane perpendicular to axis A that passes through
the mid-point of portion H. It is clear from FIG. 7 that portion H
is asymmetric about plane M regardless of where along the length of
inlet peripheral opening 4b portion H is chosen.
[0048] Next, consider an engine the same as that of FIGS. 1 to 4
except with an inlet peripheral opening 4c shaped as shown in FIG.
8. Inlet peripheral opening 4c is similar to that of the prior art
in that only a small portion of inlet peripheral opening trailing
edge 13c is oblique to axis A. Again, H represents any axial
portion of inlet peripheral opening 4c that is greater than 50% of
L in length. It is clear from FIG. 8 that portion H as shown is
symmetric about plane M and therefore such a rotary valve assembly
does not meet the above geometric test. Therefore such an engine
would not have any appreciable improvement in volumetric efficiency
over the prior art.
[0049] The volumetric efficiency advantages of the present
invention may be further enhanced by disposing the leading edges of
the inlet peripheral opening and window such that as the inlet port
opens to the combustion chamber, the intersection point of these
trailing edges progressively moves towards the inlet axial opening.
In the prior art where both the inlet peripheral opening leading
edge and the window leading edge are parallel to the axis of the
valve, the downward motion of the piston as the inlet port opens
imparts an impulse to the fluid in the inlet port that is uniform
along the length of the window. The negative pressure pulse that
travels along the inlet tract resulting from this arrangement can
be thought of as the combination of an infinite number of small
pulses starting at different points along the length of the window
that will each reach the open end of the inlet tract at a slightly
different time. The pressure pulse as a whole is therefore broad,
rather than sharply defined. If however, the intersection points of
these trailing edges progressively moves towards the inlet axial
opening then the arrangement can be designed such that each small
pulse along the window reaches the open end of the inlet tract at
approximately the same time resulting in a sharper pressure pulse
that may be better used to improve the volumetric efficiency when
it is reflected back as a positive pulse. The shapes and relative
orientations of the leading edges to achieve an intersection point
that progressively moves towards the inlet axial opening are
similar to that described for the trailing edges, except mirrored
about the valve axis.
[0050] The trailing edge of the exhaust peripheral opening may also
be arranged such that the instantaneous intersection point of the
trailing edges of the exhaust inlet peripheral opening and the
window progressively moves away from the exhaust axial opening as
the exhaust port opens, in a similar manner as described in
relation to the opening of the inlet port. However given that the
window length is generally short compared to the length of the
exhaust tract the benefit will be of a lower order, compared to
applying the invention to the inlet port.
[0051] FIGS. 6a-6l depict various alternative shapes of peripheral
openings or windows that may be utilised in axial flow rotary valve
assemblies in accordance with the present invention provided that
the instantaneous intersection point of the trailing edges of the
peripheral opening and the window progressively moves away from the
axial opening of the port as the valve rotates, or the
instantaneous intersection point of the leading edges of the
peripheral opening and the window progressively moves towards the
axial opening of the port as the valve rotates, over at least 50%
of the window length. The examples shown here are not exhaustive.
It should be noted that the shapes shown in FIGS. 6a-6l all have
the geometrical attribute described above that every axial portion
that is longer than 50% of the length of that opening is asymmetric
about a plane perpendicular to the axis of the valve, passing
through the mid-point of that portion
[0052] It should be noted that the invention also applies to
engines having more than one axial flow rotary valve per cylinder,
or axial flow rotary valves where the inlet and exhaust ports are
in separate axial flow rotary valves.
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