Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TWO-CYCLE ENGINE INCLUDING IMPROVED EXHAUST VALVE MECHANISM,
AND METHOD
FIELD OF THE INVENTION
The present invention relates to two-cycle engines, and more particularly to a
mechanism and method for controlling the exhaust of a two-cycle engine.
BACKGROUND OF THE INVENTION
to
So that two-cycle engines can deliver peak performance at high speeds, it is
desirable that they receive a full charge and that charge losses are kept as
small as
possible. This is achieved, on the one hand, by appropriately early opening of
the
exhaust port and, on the other, by exploiting the resonance of the exhaust
system.
is Matching the exhaust system to the peak output of the engine, however,
typically
results in a noticeable loss of usable piston travel and a marked increase in
charge
losses in the middle of the engine-speed range, because of the comparatively
high
level of exhaust. This, in turn, is concomitant with a reduction in torque and
an
increase in fuel consumption.
In the lower speed range, torque can be increased with a simultaneous
reduction in fuel consumption by reducing the exhaust. As such, US Patent No.
4,399,788 discloses an exhaust valve (restricting member) slideable within a
passageway in the wall of an associated exhaust duct. This exhaust valve is
2s proximate to the cylinder head and subtends an acute angle with the axis of
the
cylinder. At its unattached end, the exhaust valve forms a restricting edge
that is
matched to the cylinder bore. In its working position, the exhaust valve is
advanced
toward the cylinder and partially covers the exhaust port, thereby varying its
axial
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extent. This results in a corresponding reduction of the time the exhaust port
is
open.
In order to ensure that the exhaust duct is largely obstructed in the exhaust
s valve's working position it may be flush with the cylinder bore across the
whole width
of the exhaust port. For example, German Patent Document DE 195 35 069 A1
disclosed an exhaust valve including a parallel-slide gate valve having a
curved
guide surface, in a plane that is at right angles to the direction of movement
of the
valve.
io
In other known two-stroke engines, secondary exhausts for the cylinder are
provided in addition to the primary exhaust in order to enhance exhaust
performance, and thereby increase the maximal throughput of gas. Typically,
secondary exhausts are connected to the primary exhaust duct by way of
secondary
is ducts. In order to shorten the effective exhaust time, these secondary
exhausts may
be closed. This is typically effected by roller-like blocking members that
pass
through the secondary ducts and can rotate between a closed position and an
open
position, about an axis of rotation perpendicular to the axis of the cylinder
(JP 8-
158870). The roller-like blocking members incorporate a recess for opening the
2o secondary ducts. So that the blocking members can be actuated using a valve
mechanism for a sliding exhaust valve in the primary exhaust duct, the roller-
like
blocking bodies are typically connected to the valve mechanism through a
complicated linkage.
2s Still other engines, such as those disclosed in European patent document EP
0 141 650 A2 incorporate secondary exhausts, controlled by a valve in
dependence
on the engine speed, so that the secondary exhaust is only opened at higher
engine
speeds. These known engines, however, do not also control the exhaust of the
primary exhaust.
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Accordingly, there is a need for a two-cycle engine with an improved
mechanism for controlling the engine exhaust.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a two-cycle
engine
including primary and secondary exhaust ducts and associated control valves
operable to vary the duration of an open exhaust using a mechanism that may be
easily constructed.
io
In accordance with an embodiment of the present invention a two-cycle
engine includes a primary exhaust valve that is installed so as to be able to
slide
within a guiding passageway in a wall proximate to the cylinder head, so as to
subtend an acute angle with the axis of the cylinder. A slidable secondary
exhaust
is valve that may be moved in a direction parallel to the primary exhaust
valve can be
used to restrict flow through a secondary exhaust for the cylinder.
Conveniently, by providing a primary exhaust valve having an actuating
movement that is parallel to movement of the secondary exhaust valve, the
2o secondary exhaust valve need only be installed so as to slide in a bore in
the wall of
the exhaust duct that is parallel to the guiding passageway for the primary
exhaust
valve. Conveniently, this bore may pass through the secondary duct, so that in
its
forward, working position, the secondary exhaust valve closes off the
secondary
duct, leaving it open when the secondary exhaust valve is in its retracted,
normal
2s position.
Because the directions of movements of primary and secondary exhaust
valves coincide; it is much simpler to couple the drives for the primary
exhaust valve
and the secondary exhaust valve slide. The secondary exhaust valve and the
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primary exhaust valve can be operated in an advantageous manner by way of a
common actuating head that works against a spring. The spring may act in the
direction of the working position or in the direction of the normal position.
s In order to even out unequal actuating travel but at the same time permit
actuation of the primary exhaust valve and of the secondary exhaust valve that
is
staggered over time-which can also allow the timing of the exhaust to be
adapted
to a wide range of engine speeds-the secondary exhaust valve can be installed
so
as to be able to slide relative to the primary exhaust valve. This sliding can
be
io limited by a stop, without the need to provide separate drive systems for
the two
valves. In this regard, a particularly simple construction will result if the
primary
exhaust valve and the secondary exhaust valve are acted upon by separate
springs
in the direction of their working positions. So arranged, the secondary
exhaust
valve, for example, can be moved within the mutual displacement travel
relative to
is the primary control valve, when urged into its working position. As such,
when the
primary exhaust valve is in its working position, the secondary exhaust may be
moved independently.
The common actuating head can be driven pneumatically. For example, a
2o diaphragm that is accommodated in a diaphragm cell and connected to the
actuating
head through a rod as disclosed in US Patent No. 4,399,788 may be employed.
Alternatively, the common actuating head may be positioned by a rack and
pinion. A
toothed rack may be arranged on the guide shaft of the actuating head, and a
pinion
may engage this rack. Alternatively, the guide shaft of the actuating head may
2s include a thread or a side pin to be driven by a threaded bushing that is
associated
with the thread or by a guideway bushing associated with the pin.
Another advantageous arrangement for operating the primary and secondary
exhaust valves includes a common guide rod having guideways machined therein.
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Primary and secondary exhaust valves can be controlled completely
independently
of each other, depending only on the particular shape of the guideways.
In accordance with an aspect of the present invention, there is provided a
s two-cycle combustion engine comprising: a combustion cylinder having a
cylinder
axis; a primary exhaust duct in flow communication with an exhaust port for
the
cylinder; a secondary exhaust duct in flow communication with the primary
exhaust
duct; a primary exhaust valve slidably mounted to the cylinder, and moveable
along
an axis of movement between a normal position and a working position whereat
the
1o primary exhaust valve extends into the primary exhaust duct, to partially
obstruct the
primary exhaust duct; a secondary exhaust valve, moveable along an axis of
movement generally parallel to the axis of movement of the primary exhaust
valve,
between a normal position and a working position whereat the secondary exhaust
valve at least partially obstructs the secondary exhaust duct. A drive
operably
is connects the primary exhaust valve and the secondary exhaust valve to move
the
primary exhaust valve and the secondary exhaust valves between their normal
and
working positions.
In accordance with another aspect of the present invention there is provided a
2o method of controlling the exhaust flow of a two-cycle engine comprising a
cylinder
having primary and secondary exhaust ducts associated therewith. The method
includes driving an actuator to sequentially extend a secondary exhaust valve
along
an axis of movement to at least partially obstruct flow through the secondary
exhaust
duct, and thereafter extend a primary exhaust valve along an axis parallel to
the axis
2s of movement of the secondary exhaust valve to obstruct flow through the
primary
exhaust duct.
In accordance with a further aspect of the present invention there is provided
an exhaust valve mechanism for a two stroke engine including primary and
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secondary exhausts. The mechanism includes an actuator slideable along an axis
of movement; a primary exhaust valve moveable to at least partially obstruct
the
primary exhaust, a secondary exhaust valve moveable to at least partially
obstruct
the secondary exhaust, the primary exhaust valve and the secondary exhaust
valve
s coupled to the actuator for movement therewith along axes parallel to the
axis of
movement.
Other aspects and features of the present invention will become apparent to
those of ordinary skill in the art, upon review of the following description
of specific
io embodiments of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following figures which illustrate, by way of example only, embodiments
is of the invention:
FIG. 1 is a cross sectional view of an exemplary exhaust valve mechanism for
a cylinder of a two-cycle engine, exemplary of an embodiment of the present
invention, taken through the cylinder axis proximate its exhaust duct;
FIG. 2 is a cross section of FIG. 1 taken along the line II-II;
2o FIG. 3: is a front cross-sectional view of another exemplary exhaust valve
mechanism for a two-cycle engine, exemplary of another embodiment of the
present invention;
FIG. 4: is a cross-sectional view of yet another exemplary exhaust valve
mechanism for a two cycle engine, exemplary of yet a further embodiment of
2s the present invention; and
FIGS. 5, 6 are simplified cross-sectional views of additional exemplary
exhaust valve mechanisms including alternate exhaust valve drive
arrangements.
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DETAILED DESCRIPTION
FIG. 1 illustrates a cylinder 1 of a two-cycle engine, exemplary of an
s embodiment of the present invention. As illustrated, cylinder 1 includes an
exhaust
duct 3 contiguous with an engine exhaust port 2. Two side secondary exhausts 4
are symmetrically arranged about primary exhaust port 2. Secondary ducts 5
connect secondary exhausts 4 to exhaust duct 3.
io A wall 6 of exhaust duct 3 that is proximate to the cylinder head also
forms a
passageway 7 for guiding movement of a primary exhaust valve 8. At its
unattached
end, primary exhaust valve 8 forms a restricting edge 9 that is matched to the
cylinder bore, as best illustrated in FIG. 2. This primary exhaust valve 8 can
be
moved between a retracted (normal) position and an extended (working) position
is along an axis of movement at an acute angle to the axis of cylinder 1. In
its working
position, the primary exhaust valve 8 is moved forward toward wall 6 of
exhaust duct
3, proximate the cylinder head, and thus toward cylinder 1. Primary exhaust
valve 8
is biased by a spring 10 towards this working position. To this end, spring 10
(illustrated as a coil spring) bears against a stop surface 11 that is fixed
to cylinder 1.
2o By moving primary exhaust valve 8 towards its working position, the axial
extent of
port 2 is effectively reduced.
Two receiving bores 12 illustrated in FIG. 2 extend parallel to passageway 7
proximate secondary ducts 5. Receiving bores 12, receive secondary exhaust
2s valves 13. Each secondary exhaust valve 13 slides within an associated bore
12
between a normal position that leaves an associated secondary duct 5
unobstructed
and a working position that substantially obstructs this secondary duct 5.
Secondary
exhaust valves 13 may be formed in numerous ways known to those of ordinary
skill
CA 02355038 2001-08-14
in the art. In the preferred embodiment of FIG. 2, secondary exhaust valves 13
are
formed as rotationally symmetrical cylinders.
A bridge-like actuating head 14 is provided to move the two secondary
s exhaust valves 13. Actuating head 14 is acted upon by a spring 15 in the
direction
of the working position of the two secondary exhaust valves 13 and may be
retracted
into its normal position by an actuating drive 16, acting against the force of
spring
15. Conveniently, a drive lug 17 extends from the top of each secondary
exhaust
valve 13 toward primary exhaust valve 8. The valve assembly including primary
io exhaust valve 8 includes a complementary pair of lug stops 18.
In operation, actuating drive 16 moves actuating head 14 and thereby
secondary exhaust valves 13 between their normal and working positions.
Primary
exhaust valve 8, in turn may be retracted into its normal position by drive 16
as lugs
15 17 of secondary exhaust valves 13 move primary exhaust valve 8 by exerting
upward force against the lug stops 18. As such, secondary exhaust valves 13
may
be moved into their working positions by drive 16 before primary exhaust valve
8 is
moved, as driving lugs 17 move along an idle path. Thus, in this embodiment,
primary exhaust valve 8 is moved along with secondary exhaust valves 13 only
after
2o secondary ducts 5 have been opened by actuating drive 16. Retraction of
primary
exhaust valve 8 and secondary exhaust valves 13 advantageously opens the
cylinder exhaust completely as is desired for peak performance of the engine
(FIGS.
1 and 2). Conveniently, a single drive 16 moves both primary exhaust valve 8
and
secondary exhaust valves 13 along generally parallel axes.
Of course, primary exhaust valve 8 and secondary exhaust valves 13 could
be rigidly coupled to each other through the bridge-like actuating head 14, so
that
the primary exhaust valve 8 and secondary exhaust valves 13 move in
synchronism,
and so that there is no relative movement between them. Although simpler, such
an
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embodiment would likely require primary exhaust valve 13 to extend into wall 6
in its
normal position, to allow a delay between closing secondary exhaust valves 13
and
primary exhaust valve 8, by allowing for longer actuating travel of secondary
exhaust
valves 13. This, in turn, would not allow primary exhaust valve 8 to rest
flush with
s wall 6, thus forming a cavity (not shown) extending into wall 6, which could
degrade
the performance of the engine.
In the engine of FIGS. 1 and 2, drive 16 may include a conventional
pneumatic actuator including a diaphragm cell that accommodates a diaphragm,
and
io an actuating rod (not shown) as, for example, disclosed in US patent no.
4,399,788.
In alternate embodiments, as for example illustrated in FIG. 3, it is possible
to
form an exhaust valve mechanism, exemplary of an embodiment of the present
invention, having a reduced height. To this end, as illustrated, two secondary
is exhaust valves 13' are secured to a common actuating head 14' installed in
a
housing 20, over a cylindrical stem 21 so as to be able to slide thereon.
Housing 20
includes a guide 22 for cylindrical stem 21. Actuating head 14' and secondary
exhaust valves 13' are held in their forward (working) position by two springs
15'. An
assembly including primary exhaust valve 8' includes a driving rod slidably
mounted
2o in the interior of guide 22, allowing relative movement of primary exhaust
valve 8'
relative to actuating head 14'. This rod includes lug stops 18'. Actuating
head 14'
includes complementary lugs 17'. A spring 10' bears against housing 20, and
against the top of lug stops 18', biasing primary exhaust valve 8' forward,
away from
housing 20. A drive 23 further controls the vertical motion of actuating head
14'.
In operation, actuating head 14' and secondary exhaust valves 13' are
retracted from their working position toward their normal position by a drive
23 as
required. If actuating head 14' is only slightly retracted, primary exhaust
valve 8' will
initially remain in its working position, biased by spring 10'. If actuating
head 14' is
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retracted far enough, driving lugs 17' of the actuating head 14' after moving
along an
idle path, will come into contact with the lug stop 18' associated with
primary exhaust
valve 8'. Thereafter, primary exhaust valve 8' and secondary exhaust valves
13'
move in unison with actuating head 14', until the cylinder exhaust is
completely
s open.
Optionally, as also shown in FIG. 3 primary exhaust valve 8' may be
independently driven by a pinion that secured to housing 20 so as to be able
to
rotate and engage a rack that is attached to the cylindrical stem 21 (the rack
and
io pinion are indicated by dashed lines in FIG 3). The pinion may be driven by
a
Bowden-cable and actuator 23, 24 or, alternatively by a servomotor, or the
like.
Primary exhaust valve 8' could, of course be pneumatically actuated as, for
example, described in connection with FIGS. 1 and 2. As such, the extension of
primary exhaust valve 8' relative to the position of secondary exhaust valves
13'
is may be adjusted. This in turn allows for control of the relative delay and
position
between secondary exhaust valves 13' and primary exhaust valve 14', as these
move from their normal to working positions.
Other possible drive systems for the primary exhaust valve 8 (or primary
2o exhaust valve 8') and secondary exhaust valves 13 (or 13'), or for the
common
actuating head 14, are shown in FIGS. 5 and 6. For simplicity, only an
exemplary
primary exhaust valve 8" (like primary exhaust valve 8 or 8') is shown.
As illustrated, the primary exhaust valve 8" may be coupled to rods installed
2s in a guide bushing 29 (only indicated herein) so as to be able to slide in
the direction
of the axis of movement 30 of the primary exhaust valve 8". In order to adjust
the
position of the primary exhaust valve 8" (or an actuating head 14" connected
thereto) the shaft of the exhaust valve is provided with a thread 31 (FIG. 5)
or with a
guide pin 32 (FIG. 6).
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If provided with a thread 31, as illustrated in FIG. 5, thread 31 may engage a
threaded bushing 33 that is prevented from motion along the axis of motion of
valve
8" yet supported in a guide bushing 29 so as to be able to rotate. As such,
when
s threaded bushing 33 is rotated, the primary exhaust valve 8" is moved
between its
working position and normal positions. The threaded bushing 33 can be moved
either by a notched belt 34, by gearing, a servo motor, hydraulically,
pneumatically,
or otherwise.
io Alternatively, in order to allow long travel of primary exhaust valve 8"
with very
little rotational movement, an actuating rod of exhaust valve 8" may engage a
bushing 35 as illustrated in FIG. 6. As illustrated, bushing 35 includes a
guideway
machined therein. Pin 32 on the actuating rod of exhaust valve 8" engages the
guideway of the bushing 35. Of course, alternatively bushing 35 could be
provided
is with one or more pins, and a complementary guideway could be formed as part
of
an actuating rod of primary exhaust valve 8".
A further embodiment allowing the largely independent actuation of primary
exhaust valve 8"' (like valves 8, 8', 8") and of secondary exhaust valves 13"'
(like
2o valves 13, 13', 13") is illustrated in FIG. 4. As illustrated, primary
exhaust valve 8"'
and secondary exhaust valves 13"' are once again guided by the cylinder
housing.
Secondary exhaust valves 13"' are moved by a guide rod 25 that can slide
transversely to the direction of movement of the primary exhaust valve 8"'.
The
guide rod 25 is installed either in a housing that is secured to the cylinder,
or directly
2s within the cylinder, and is once again moved by a cable, actuator motor, or
pneumatically. Guideways 26 are machined into the guide bar 25 and the slides
engage in this by way of pins or bolts 27.
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If guide rod 25 is moved in the direction indicated by the arrow 28, primary
exhaust valve 8"' and then secondary exhaust valve 13"' are moved toward the
cylinder, into their working positions. On subsequent retraction of the guide
in the
direction opposite that indicated by the arrow 28, first the secondary exhaust
valve
s 13"' and then the primary exhaust valve 8"' is retracted. Depending on the
particular
shape (rise, travel) of guideways 26, the primary exhaust valve 8"' and the
secondary exhaust valve 13"' can be moved as desired, largely independently of
each other. This, in turns, allows great flexibility in timing the primary and
the
secondary exhaust valves.
to
The arrangement described above can be used to particular advantage in
multicylinder, in-line engines. In such engines all valves may be operated by
a
common guide rod 25, greatly reducing the number of engine components.
is The present invention is not, of course, confined to the embodiments shown
and described herein. Many modifications are possible. For example, only one
secondary exhaust could be provided in place of two such exhausts.
The described drives for the primary exhaust valve 13 (or 13', 13", 13"') and
2o secondary exhaust valves 8 (or 8', 8", 8"') may be extensively modified so
that
secondary exhaust valves and the primary exhaust valve are actuated in a
predetermined dependency on each other. Conveniently, this is simplified as
both
the primary and secondary exhaust valves are moved along generally parallel
axes,
in generally the same direction.
Finally, it should be remembered that the primary exhaust valve 8 (or 8', 8",
8"') may also be configured as a double slide (as described in Austrian Patent
Document AT 399204) so that the exhaust time can in addition be controlled
incrementally.
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As such, it will be appreciated that the described embodiments of carrying out
the invention are susceptible to many modifications of form, arrangement of
parts,
details and order of operation. The invention, rather, is intended to
encompass all
such modification within its scope, as defined by the claims.
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