Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TWO-CYCLE ENGINE
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to two-cycle engines and
more particularly to two-cycle engines with means for varying
a port timing in accordance with the engine speed to improve
power output.
Prior Art
As is well known, in a two-cycle internal combustion
engine, an exhaust port is selectively closed by a
reciprocating piston in a cylindqr during the operation ox the
engine.
One conventional port timing control device as disclosed
in Japanese Patent Publication No. 47-36047 comprises a port
timing control valve comprising an elongated valve element of
an arcuate plate and a lever carrying at one end the valve
element and pivotally mounted on an upper portion of a wall of
the exhaust passage, so that the valve element is movable
between an open position where the valve element is received
.in a recess formed in a lower portion of the wall of the
exhaust passage and a closed position where the valve element
closes an upper portion of the exhaust port to delay an
exhaust timing. This conventional port timing control device
has been found not entirely satisfactory, however, in that
when the valve is in its open position with the valve element
received in the recess, the pivotal lever extends through the
exhaust passage diametrically thereof adjacent to the exhaust
port and therefore affects the flow of the exhaust gas from
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the exhaust port.
Another conventional port timing control device, as
disclosed in Japanese Patent Application Laid-Open (Kokai) No.
5~-42868 and Japanese Utility Model Publication No. 58-5063,
comprises a port timing control valve of a generally semi-
cylindrical shape mounted on a wall of an exhaust passage for
angular movement about an axis perpendicular to the axis of
the cylinder between an open position where the valve is held
in a recess formed in an upper portion of the exhaust passage
wall and a closed position where the valve is held in the
exhaust passage with a peripheral surface thereof, serving as
a timing control surface, closing a upper portion of the
exhaust port to delay an exhaust tlmin~. the timing control
surface of the valve it held in slidin~3 contact with a
complementarily-contoured surface of the recess. Unburned
products, such as carbon, contained in an exhaust gas
discharged from the combustion chamber via the exhaust port
tends to deposit on the timing control surface of the valve
when the valve is in its closed position. Therefore, it is
quite possible that the deposited products prevent the valve
from moving smoothly between its open and closed positions.
In addition, the generally semi-cylindrical valve is reduced
in cross-sectional area progressively from its opposite ends
toward a center thereof, so that it is rather difficult for
the peripheral timing control surEace to be closely fitted on
the peripheral surface of the piston when the valve is in its
closed position.
SUMMARY OF THE INVENTION
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tt .is therefore an object ox this invention to provide a two-
cycle engine incorporating a port timing control means in which a
port timing control valve can be operated in a reliable manner for
a prolonged period of time and will not affect the flow of exhaust
gas discharged from the exhaust portO
According to the present invention, there is provided a two-
cycle engine comprising:
(a) a cylinder block having a cylinder head thereon, said
cylinder block having a cylinder and an exhaust port formed in
a side wall of said cylinder, and said cylinder block having an
exhaust passage ct~municating with said exhaust port wherein a
main flow of exhaust gases are expelled from said cylincler through
said exhaust port and in a direttion along the exhaust pa.5sage;
(b) a piston received in saitl cylinder Eor reciprocal movement
therealong; and
c) a port timing control means ccmprising a port timing
control valve which is mounted on said cylinder block and has a
timing control surface, said control valve being movable in a
plane substantially perpendicular to the axis of said cylinder
between a closed position wherein said valve is disposed in said
exhaust passage with said control surface closing the end por-
tion of said exhaust port closer to said cylinder head and an
open position wherein said valve is retracted out of said exhaust
passage in a direction perpendicular to the flow of said exhaust
gases to open said end portion of said exhaust port, said control
surface being of an arcuate toncave shape and having a curvature
suhstantially equal to that of an inner peripheral surface of said
cylinder so as to be smoothly continuous with the inner peripheral
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surface of said cylinder.
BRIEF DESCRIPTION OF THE DRAW_NGS
Fig. 1 is a horizontal cross-sectional view of a two-
cycle engine provided in accordance with the present
invention;
Fig. 2 is fragmentary vertical cross-sectional view of
the engine;
Fig. 3 is a fragmentary cross-sectional view showing a
centrifugal governor;
Figs. 4A and ~B are fragmentary views as viewed in the
dlrection of arrow IV of Fig. 1, showing the operattQn of a
port tirning control valve;
Figs. 5 and 6 are views similar to Fig. 1 but showing
modified engines;
Fig. 7 is a view similar to Fig. 1 but showing a further
modified engine;
Fig. 8 is a fragmentary cross-sectional view taken along
the line XIII-XIII of Fig. 7;
Fig. 9 is a cross-sectional view taken along the line IX-
IX of Fig. 7;
Fig. 10 is a view similar to Fig. 7 but showing a port
timing control valve in its open position;
Fig. 11 is a cross-sectional view taken along the line
XI-XI of Fig. 7;
Fig. 12 is a view similar to Fig. 7 but showing a further
modified engine;
Fig. 13 is a cross-sectional view taken along the line
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XIII-XIII of Fix. 12;
Fig. 14 is a view similar to Fig. 12 but showing a port
timing control valve in its open positisn;
Fig. 15 is a block diagram of a valve control system;
Fig. 16 is a graph showing the relation between the
pressure in the cylinder and the opening of the control valve;
Fig. 17 is a graph showing the relation between the
opening of the control valve and the engine speed;
Fig. 18 is a flow chart of the operation of the valve
control system;
Fig. 19 is a block diagram of a modified valve control
system;
Fig. 20 is a block (diagram oE another typo ox ~alv~
control system;
Fig. 21 is a graph showing power output characteristics
of a conventional engine;
Fig. 22 is a graph showing power output characteristics
of the engine incorporating the valve control system of Fig.
20;
E`ig. 23 is a cross-sectional view of a further modified
engine;
Fig. 24 is a perspective view of a motorcycle
incorporating the engine of E`ig. 23;
Fig. 25 is a cross-sectional view of a further modified
engine;
Fig. 26 is a fragmentary cross-sectional view of the
engine of Fig. 25;
Figs. 27 and 28 are cross-sectional views of further
modified engines;
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Fig. 29 is an enlarged plan view of the portion of the
engine indicated by a circle A of fig. 28;
Fig. 30 is a cross-sectional view taken along the line
XXX-XXX of Fig. 29;
Fig. 31 is a schematic view of a modified drive means;
Fig. 32 is a cross-sectional view of a further modified
engine; and
Fig. 33 is a perspective view of the engine of Fig. 32.
' DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The invention will now be described with reference to the
accompanying drawings in which like reference numerals denote
corresponding parts in several viows.
E`igs. 1 and 2 show a two-cycle internal combustion engine
10 which comprises a cylinder block 12 hatring a cylinder head
14 thereon, the block having a cylinder 16. A piston 18 is
received in the cylinder 16 for reciprocal movement
therealong. The piston 18 is connected to a crankshaft 20
(Fig. 3) via a connecting rod (not shown). An exhaust port 22
is formed in a side wall of the cylinder 16, and an exhaust
~0 passage 24 is formed in the cylinder block 12 and opens to the
exhaust port 22 at one end thereof. An intake pork (not
shown) for introducing an air/fuel mixture from a carburetor
(not shown) into the engine 10 is formed in a wall of a
crankcase (not shown) secured to the cylinder block 12.
Scavenge ports 26 are also formed in the wall of the cylinder
16 and communicate with a crankcase chamber. The exhaust port
22 and the scavenge ports 26 are opened and closed by the
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piston 18 moving along the cylinder 16. A spark plug 28 is
threaded through the cylinder head 14 for igniting the
air/fuel mixture in a combustion chamber clefined by the
cylinder 16 and the cylinder head 14.
A partition wall 30 extends between upper and lower
portions of the wall of the exhaust passage 24 along the axis
of the cylinder 16 centrally of the width of the exhaust port
22 and is disposed immediately adjacent to the exhaust port
22, so that the exhaust port 22 is divided by the partition
wall 30 into a pair of first and second portions 22a and 22b
which are juxtaposed circumferentially of the cylinder 16 and
are d:isposed symmetrically with respect to the partition wall
30. the partitlon wall 30 serves to cause the exhaust gas
prom the combustion chamber to slow smoothly and also to
reinforce the exhaust port 22.
A port timing control means is provided for varying an
exhaust port timing in accordance with the engine speed. The
port timing control means comprises a port timing control
valve 34 and a drive means 36 for driving the control valve 34
into and out of a closed position, as will hereinafter more
fully be descrlbed.
The control valve 34 comprises a pair of first and second
elongated valve elements 34a and 34b of a rectangular cross-
section disposed coaxially with each other, the valve elements
34a and 34b being slidably received respectively in a pair of
guide recesses 38a and 38b formed in the cylinder block 12 for
movement toward and away from each other along respective
their respective axes lying in a plane perpendicular to the
axis of the cylinder 16. In other words, the first and second
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valve elements 34a and 34b are movable toward and away from
each other along respective straight paths lying on a common
plane. The guide recesses 38a and 38b are disposed in opposed
relation to each other and opening to the exhaust passage 24.
Each of the valve elements 34a and 34b hays a timing control
surface 34c, 34d of an arcuate concave shape formed in one
side face facing the exhaust port 22 at an inner portion
thereof. A curvature of each control surface 34c and 34d is
substantially equal to or slighter greater than that of the
inner peripheral surface of the cylinder 16.
Each of the first and second valve elements 34a and 34b
is movable between a closed positioh, indicated in solld lLnes
in Fiq. 1, where the first and sQcond valve el~men~s 3~a and
34b are disposed in the exhaust passage 24 with their
respective control surface 34C and 34d closing the upper end
portions of the first and second portions 22a and 22b of the
exhaust port 22, respectively fig. 4A), and an open position,
indicated in dot and dash lines in Fig. 1, where the valve
elements 34a and 34b are held out of the exhaust passage 24
and fully received in the guide recesses 38a and 38b,
respectively, to open the upper end portions (Fig 4A~. In
the closed positions of the first and second valve elements
34a and 34b, the first and second control surfaces 34c and 34d
are smoothly continuous with the inner peripheral surface of
the cylinder 16 and the surface of the partition wall 30
facing the cylinder. Also, in these closed positions, the
distal tip ends of the first and second valve elements 34a and
34b are held in contact with the opposite side surfaces of the
partition wall 30.
The drive means 36 comprises a centrifugal governor 40
and a linkage or power transmission means 42. The centrifugal
governor 40 comprises a shaft 44 mounted on the crankcase
through bearings 45 and 4i for rotation about an axis thereof
and having an integral gear 44a at one end, a disc 46 fixedly
mounted on the shaft 44, a sleeve 48 mounted on the shaft 44
for movement therealong and having a dish-shaped portion 48a
at one end and a rack portion 48b around the other end, balls
50 received by the dish-shaped portion 48a, and a compression
coil spring 52 wound around the shaft 44 and acting between
the gear 44a and the end face of the sleeve 48 for normally
urglng the ball 50 against the disc ~6. An output shaEt 54
i9 supported by the cylinder block 12 or rotation about an
axis thereon and has a pinion 56 secured thereto by a pin 58
and meshingly engaging the rack portion 48b, the output shaft
54 extending parallel to the axis of the cylinder 16. A gear
60 is mounted on the crankshaft 20 and meshingly engages the
gear 44a. The coil spring 52 is so preloaded that when the
crankshaft 20 is rotated at above a preselected speed, the
balls 50 are moved outwardly under the influence of a
centriEugal force, thereby causing the sleeve 48 to move along
the shaft 44 toward the gear 44a to rotate the output shaft 54
in a direction R indicated in Fig. 3. Thus, when the engine
speed reaches a predetermined level, the centrifugal governor
40 is operated.
Referring to the linkage 42, a first lever 62 is fixedly
secured at one end to the output shaft 54, and the other end
of the lever 62 is received in a recess 34e formed in the
outer end of the first valve element 34a~ The other end of
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the first lever 62 has a slot 62a, and a pin 64 is secured to
the outer end of the first valve element 34a and extends
through the slot 62a. A second lever 66 is fixedly secured at
one end to a shaft 68 rotatably mounted on the cylinder block
12 and extending parallel to the axis of the cylinder 16, and
the other end of the lever 66 is received in a recess 34e
formed in the outer end of the second valve element 34b. A
pin 64 is secured to the outer end of the second valve element
34b and extends through a slot ~6a formed in the other end of
the second lever S6. A pair of first and second links 70 and
72 are fixedly connected at their one ends to the output shaft
54 and the shaft 68, respectively, and are pivoted at the
other ends to opposite ends of a interconnecting link 74.
With this construction, when the output shaft 5~ is annularly
moved in the direction R (Fig. 3), the first and second valve
elements 34a and 34b are moved away from each other, that is,
from their respective closed to open positions, through the
linkage 42.
The operation of the engine 10 will now be described. In
a lower range of the engine speed, the centrifugal governor 42
is not operated since the coil spring 52 holds the balls 50
against outward movement. In this condition, the first and
second valve elements 34a and 34b are held in thelr respective
closed positions (Fig. 4A) with their respective control
surface 34C, 34d closing the upper end portions of the first
and second portions 22a and 22b of the exhaust port 22,
respectively. Therefore, it can be said that the effective
upper edge of the exhaust port 22 is lowered a distance equal
to the thickness of the first and second valve elements 34a
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and 34b, thereby delaying the exhaust timing.
When the engine speed reaches a predetermined higher
level, the centrifugal governor 40 is operated to angularly
move the output shaft 54 in the direction R, so that the first
and second valve elements 34a and 34b are moved from their
respective closed to open positions. Therefore, the exhaust
stroke starts earlier at this higher engine speed than at the
above lower engine speed. And, when the engine speed goes
below the above predetermined level, the first and second
valve members 34a and 34b are moved from their respective open
to closed positions through the drive means 36. Thus, the
engine 10 con produce a go powcr output over wide ma of
the engine speed, i.e., prom a low to a lli~h ran ox he
engine speed.
The arcuate control surfaces 34c and 34d are not
subjected to sliding contact with surfaces 38c and 38d of the
guide recesses 38a and 38b during the movement of the first
and second valve elements 34a and 34b between their closed and
open positions. Therefore, the deposition of unburned
products on the control surfaces 34c and 34d will not prevent
the first and second valve elements 34a and 34b from smoothly
moving into and out of the respective guide recesses 38a and
38b. It will be appreciated that the delay of exhaust port
timing is preselected by the thickness of the valve elements
34a and 34b in the direction of the axis of the cylinder 16,
and therefore this delay can be varied by changing the
thickness of the valve elements 34a and 34b.
Fig. 5 shows a modified two-cycle engine 1Oa which
differs from the engine 10 of Fig. 1 in that the centrifugal
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yovernor 40 of the drive means 36 is replaced by a rotary
solenoid 78. The rotary solenoid 78 comprises an output disc
80 for angular movement about an axis thereof in opposite
directions, and a pair of links 82a and 82b pivotally
connected at their one ends to the output disc 80 in
diametrically opposed relation and pivotally connected at the
other ends to the first and second levers 62 and 66,
respectively. The rotary solenoid 78 is electrically
connected to a power source 84 via a switch 86. A speed
detector 88 for detecting the engine speed to produce a
detecting signal is electrically connected to the switch ~6.
When thc engine spqed reaches a predetermined leYel, the
swltch ~6 is responsive Jo the de~ectin~ sicJnal erom the speed
detector 88 to be closed whereupon the output disc 80 is
angularly moved in a direction R to move the first and second
valve elements 34a and 34b from their respective closed to
open positions.
Fig. 6 shows another modified two-cycle engine 1Ob which
differs from the engine 10 of Fig. 1 in that first and second
elongated valve elements 34a and 34b are pivotal between their
respective closed and open positions. More specifically, the
first and second valve elements 34a and 34b are fixedly
mounted at their outer ends respectively on a pair of pins 92a
and 92b mounted on the cylinder block 12 for angular movement
about their respec-tive axes and extending parallel to the axis
of the cylinder 16. A pair of recesses 38a and 38b are formed
in the cylinder block 12 in opposed relation to each other and
open to the exhaust passage 24. As described above in the
preceding embodiments, each of the valve elements 34a and 34b
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has a timing control surface 34c, 34d of an arcuate concave
shape formed in one side face facing the exhaust port 22 at an
inner portion thereof. A curvature of each control surface
34c and 34d is substantially equal to or slightly greater than
that of the inner peripheral surface of the cylinder 16.
First and second driven levers 93a and 93b are fixedly
connected at their one ends to the pins 92a and 92b,
respectively. The other end ox the second driven lever 93b is
pivotally connected to one end of a link 94. First and second
drive levers 96a and 96b are fixedly connected at their one
ends to the output shaft 54 in angularly spaced relation.
Opposite ends oP a link 9~ are pivotally connected
respectively to the other end ox the firs drive lover 96a and
the other end ox the 1rst driven lever ~3a. l'he second drive
lever 96b is pivotally connected at the other end to the other
end of the link 94. The output shaft 54 is driven by the
centrifugal governor 40 but may be operated by the rotary
solenoid 78. Upon angular movement of the output shaft 54 in
a direction R, each of the first and second valve elements 34a
and 34b is pivotally movable about the respective pins 92a and
92b between a closed position where the first and second valve
elements 34a and 34b are disposed in the exhaust passage 24
with their respective control surface 34r and 34d closing the
upper end portions of the first and second portions 22a and
22b of the exhaust port 22, respectively, and an open position
where the valve elements 34a and 34b are completely received
in the recesses 38a and 38b, respectively. The first and
second valve elements 34a and 34b are pivotally movable in a
plane substantially perpendicular to the axis of the cylinder
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16, each of the valve elements 34a and 34b having a uniform
thickness in the direction of the axis of the cylinder 16.
Figs. 7 to 10 show a further modified two-cycle engine
10c which is similar in construction and operation to the
engine 10 of Eig. 1. A pair of coaxial guide tunes 100 and
102 are mounted on a cylinder block 12, and a pair of first
and second elongated valve elements 34a and 34b are received
respectively in the guide tubes 100 and 102 for sliding
movement therealong. The common axis of the guide tubes 100
and 102 is disposed in a plane perpendicular to the axis of
the cylinder 16.
~5 described above for the engine 10 of Fig. 1, all
elongatecl partit:Lon wall 30 extends between uppqr and lower
portions of the wall of an exhaust passage 2~ along the axis
of the cylinder 16 and is disposed immediately adjacent to an
exhaust port 22, so that the exhaust port 22 is divided by the
partition wall 30 into a pair of first and second portions 22a
and 22b which are juxtaposed circumferentially of the cylinder
16 and are disposed symmetrically with respect to the
partition wall 30. The common axis of the guide tubes 100 and
102 is disposed perpendicular to the partition wall 30 as best
shown in Fig. 8.
Each of the valve elements 34a and 34b has a timing
control surface 34c, 34d of an arcuate concave shape formed in
one side face facing the exhaust port 22 at an inner portion
thereof. A curvature of each control surface 34c and 34d is
substantially equal to or slightly greater than that of the
inner peripheral surface of the cylinder 16.
As described above for the engine 10 of Fix. 1, each of
14
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the first and second valve elements 34a and 34b is movable
between a closed position ( Fig. 7) where their respective
control surface 34C and 34d close the upper end portions of
the first and second portions 22a and 22b of the exhaust port
22, respectively fig 8), and an open position (Fig. 10)
where their respective control surface 34c and 34d are held
out of the exhaust passage 24 to open the upper end portions.
In the closed positions of the first and second valve elements
34a and 34b, the first and second control surfaces 34c and 34d
are smoothly continuous with the inner peripheral surface of
the cylinder 16 and the surface of the partition wall 30
facing the cylinder. Also, in thesd closed positions, the
lnner ends ox the Elrst and second valve elements 3~ and 3~b
are held in contact with the opposite side surEaces oE the
partition wall 30. That portion of the inner edge of each
guide tube 100, 102 facing the exhaust port 22 is smoothly
continuous with the inner peripheral surface of the cylinder
16.
Each of the first and second elongated valve elements 34a
and 34b is of a square cross-section as best seen in Fig. 9.
Each of the guide tubes 100 and 102 has an outer cylindrical
surface and an internal bore 100a, 102a of a square cross-
section extending therethrough along an axis thereof. The
cross-section of each of the first and second valve elements
34a and 34b is substantially complementary to the cross-
section of a respective one of the internal bores 100a and
102a, and the valve elements 34a and 34b are slidable along a
respective one of the bores 100a and 102a. In the closed
positions of the valve elements 34a and 34b, the bottom
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surfaces 34f and 34g thereof are disposed parallel to the
upper edge 22d of the exhaust port 22 which upper edge is
disposed perpendicular to the axis of the cylinder 16 (Fig.
8).
The port timing control means further comprises a drive
means 106 for driving the first and second valve elements 34a
and 34b to move between their respective closed and open
positions in accordance with the engine speed. The drive
means 106 comprises an actuator 108 in the form of a
servomotor, and a power transmission means 110 for
transmitting an output of the actuator 108 to the valve
elements 34a and 34b to move them between their respective
closed end open positions. Reference numeral 88 de~qignates a
speed detector for detecting the engine speed to produce a
detecting signal.
The power transmission means 110 comprises a pair of
output shafts 112 rotatably mounted on the cylinder block 12
through bearings 114, a pair of levers 116 pivotally connected
at one ends respectively to the bifurcated outer ends of the
valve elements 34a and 34b remote from the control surfaces
34c and 34d by a pair of pins 118 and fixedly secured at the
other ends respectively to the output shafts 112 and 112, and
a drive shaft 120 rotatably mounted on the cylinder block 12
through bearings 122 and 122 and connected to the output
shafts 112 and 112 through a pair of worm gearings 124 and
124, a flexible joint l26 connected at one end to the output
shaft of the actuator 108 and connected at the other end to
the drive shaft 120 through a worm gearing 128. The worm
gearing 128 comprises a worm 128a rotatably mounted on the
16
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cylinder block 12 and coupled to the flexible joint 126, and a
gear 128b fixedly mounted on the drive shaft 120 and meshingly
engaging the worm 128a. Each of the worm gearings124 and 124
comprises a worm 124a (Fig. 11) fixedly mounted on thy drive
shaft 120, and a gear 124b fixedly mounted on a respective one
of the output shafts 112 and 112 and meshingly engaging the
worm 124a. The pitches of the two worms 1~4a and 124a on the
drive shaft 120 are reverse, so that upon rotation or angular
movement of the drive shaft 120, the two output shafts 112 and
112 are rotated in opposite directions. With this
arrangement, upon rotation of the actuator 108, the first and
second valve elements 34a and 3~b aye moved toward and away
from each other, that is to say, between their respecttvq
closed and open positions through the power transmission means
110.
For mounting the guide tubes 100 and 102 and the valve
elements 34a and 34b on the cylinder block 12, the guide tubes
100 and 102 are first forced into a pair of mounting holes 103
and 103 of a circular cross-section coaxially formed in the
cylinder block 12. Then, the valve elements 34a and 34b are
inserted into the cross-sectionally square internal bores 100a
and 102a of the guide tubes 100 and 102, respectively. Since
each of the mounting holes 103 and 103 has a circular cross-
section, the processing of the cylinder block 12 to provide
these holes can easily be carried out accurately. In
addition, since the separate guide tubes 100 and 102 are
employed, these guide tubes can easily be manufactured
accurately.
In operation, when the engine speed reaches a
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predetermined level, the actuator 10~ is responsive to the
detecting signal from the speed detector 88 to move the first
and second valve elements 34a and 34b from their respective
closed to open positions through the power transmission means
110, as described above or the engine 10 of Fig. l In the
closed positions of the valve elements 34a and 34b, the
effective upper edge of the exhaust port 22 is lowered a
distance equal to the thickness of the first and second valve
elements 34a and 34b, that is to say, from a level L1
representing the actual upper edge of the exhaust port 22 to a
level L2 representing-the lower suLfaces 34f and 34g of the
valve elements 3~a and 3~b (Fig. 8), thereby delayil1c~ the
exhaust timing.
Figs. 12 to 14 show a further modiEied ~wo-cycle engine
1Od which differs from the engine 10c of Fig. 7 in that a pair
of auxiliary exhaust ports 134 and 134 are formed in the side
wall of the cylinder 16 so as to be communicable with the
exhaust passage 24. The auxiliary exhaust ports 134 and 134
are disposed on opposite sides of the exhaust port 22 adjacent
thereto, the ports 134 and 134 being of a rectangular cross-
section (Fig. 13) and extending perpendicular to the axis of
the cylinder 16. The upper edge 134a of each auxiliary
exhaust port 134 is disposed at the same level as the upper
edge 22d of the exhaust port 22 while the lower edge 134b is
disposed at a level above the lower surfaces 34f and 34g of
the first and second valve elements 34a and 34b.
Each of the guide tubes 100 and 102 has an aperture 13Z
formed therethrough adjacent to its front edge continuous with
the inner peripheral surface of the cylinder 16, each aperture
18
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136 being aligned with and continuous with a respective one of
the auxiliary ports 134 and 134.
As shown in Fig. 12, when the first and second valve
elements 34a and 34b are in their respective closed positions,
the pair of apertures 136 and 136 are closed respectively by
those portions of the side fac s of thP first and second valve
elements 34a and 34b disposed adjacent to their respective
control surfaces 34c and 34d. Therefore, in this condition,
the communication of the auxiliary exhaust ports 134 and 134
with the exhaust passage 24 is interrupted. On the other
hand, as shown in Fig. 14, when the first and second valve
elements 34a and 3~b are in their respective open positions,
the arcuate control surfaces 3~c and 34d are disposed in
opposed relation to the respective apertures 136 and 136, so
that the auxiliary exhaust ports 134 and 134 are in
communication with the exhaust passage 24 via the respective
internal bores 100a and 102a of the guide tubes 100 and 102 as
indicated by arrows.
By virtue of the provision of the auxiliary exhaust ports
134 and 134, the overall exhaust port area is increased, so
that a good exhaust can be achieved in a high range of the
engine speed.
Fig. 15 shows a block diagram of a valve control system
140 for controlling the port timing control valve 34 in the
engines 10c and 1Od. The valve control system 140 serves as
decompression means for reducing the pressure in the cylinder
16 on compression stroke at the start of the engine. As
described above, the control valve 34 is in its closèd
position at low engine speeds to delay the exhaust port timing
1 9
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to increase the effective compression stroke of the piston 18.
On the other hand, in the open position of the control valve
34, the effective compression stroke of the piston 18 is
decreased. With this method, the power output characteristics
of the engine are improved. However, much torque is required
for starting the engine since the control valve 34 is in its
closed position at the start of the engine. The valve control
system 140 enables the engine to be started without requiring
undue torque.
As shown in Fig. 16, the compression in the cylinder 16
is the maximum when the control valve 34 is in its fully
closed posltion, that is to say, the degree of opening of the
valve 34 is pro. And, tho compression in the cyllnd~r 16
decreases with an increase in the degree oP opening of the
valve 34. After the opening degree exceeds 1/4, the
compression in the cylinder 16 becomes generally constant.
Therefore, where the opening degree is at least 4/1,
satisfactory results can be achieved. In view of these, with
the valve control system 140, when the engine speed is in the
range of between 0 and a predetermined low level L (Fig. 17),
the degree of opening of the valve 34 is not less than 1/4.
In the range of between more than the lower point L and a
predetermined high level H, the opening degree is zero (i.e.,
the valve 34 is in its fully closed position). And, in the
range of above the high level H, the opening degree is 1
(4/4), that is to say, the valve is in its fully opened
condition.
The valve control system 140 will now be described with
reference to Fig. 15. An ignition device 142 generates a
~2~3~
pulse signal per revolution of the engine, the pulse signal
being applied to a waveform shaping circuit 144 by which it is
shaped. An output signal from the wavefoxm shaping circuit
144 is fed to a counter 146, the contents of the counter 146
representing the engine speed. The waveform shaping circuit
144 and the counter 146 constitute a detector 148 for
detecting the engine speed to output a signal to a control
unit 150 such as a microprocessor unit. A detector 152
detects the amount Th of throttling of a throttle valve 154 to
output a signal to the control unit 150, the throttle valve
154 controlling the flow of the air fuel mixture to the engine
in response to the operation of an accelerator means sigh as a
throttle grip and an accelerator pedal. The control unit lS0
calculates a target value of the opening of the control valve
34 from the engine speed Ne and the throttling amount Th of
the throttle valve in accordance with a program incorporated
in the control unit 150. The control unit 150 outputs a
signal representative of the target value to a drive circuit
156. An encoder 158 is connected to an output shaft of the
actuator or servomotor 108 for detecting the position of
rotation or angular movement of the servomotor 108 to feed an
output signal to the drive circuit 156. The drive circuit 156
drives the actuator 108 until the output of the encoder 158 is
brought into agreement with the target value, that is to say,
the degree of the opening of the control valve 34 is brought
into agreement with the amount of the opening thereof
represented by the target value.
The operation of the valve control system 140 will now be
described with reference to a flow chart (Fig. 18t of the
21
program for effecting the operation of the system 140.
The engine speed at the start ox the engine, i. en, the
low level L (Fig. 17) mentioned above, is, for example, 750
rpm. First, when the engine is started, pulse signals are fed
from the ignition device 142 to the engine speed detector 148,
so that the control unit 150 inputs thereto the output of the
counter 14~ representative of the engine speed Ne at a
predetermined time interval. In Block B1, the control unit
150 determines whether the engine speed Me reaches the low
level L (750 rpm). If the result is "NO", the processing
proceeds to Block B2 in which the control unit 150 determines
whether the throttllng arnount Th ox the throttle valve 15~ is
more than zero. It the result is "NO", that .i9 to say, the
throttling amount Th is zero, the processing proceeds to Block
B3 in which the control unit 150 feeds the output signal or
target value representative of not less than 1/4 of the
opening of the control valve 34. On the other hand, in Block
B2, if the throttle amount Th is more than zero, the
processing proceeds to Block B4 in which the control circuit
150 feeds the output signal or target value representative of
4/4 of the opening of the control valve 34, that is to say,
the full opening thereof.
Thus, the first and second valve elements 34a and 34b are
moved from their respective closed positions in accordance
~5 with the target value, so that the effective compression
stroke of the piston 18 is reduced, thereby reducing the
torque required for starting the engine.
Then, when the engine speed Ne reaches the low level L
and is not more than the high level H (Fig. 17), the target
~33~'1~t3
value or the output of the control unit 150 represents "O" of
the opening of the control valve 34, that is to say, the full
closing thereof, regardless of the throttling amount Th of the
throttle valve 154 (slocks s5 to B7~. Therefore, the first
and second valve elements 34a and 34b are moved to their
respective closed positions. On the other hand, when the
engine speed Ne exceeds the high level H (slock B6), the
contxol unit 150 feeds the output or target value
representative of 4/4 of the opening of the control valve 34,
that is to say, the full opening thereof. Therefore, the
first and second valve elements 34a and 34b are moved to their
respective open positions.
Fig, 19 shows a block diagram ox a modlfied valve control
system 140a which differs from the valve control system 140 of
Fig. 15 in that the throttling detector 152 is omitted. More
specifically, when the engine speed Ne is less than the
predetermined low level L, the control unit 150 outputs the
target value representative of the opening of the control
valve 34. When the engine speed Ne reaches the low level
and is not more than the high level H, the target value or the
output of the control unit 150 represents "O" of the opening
of the control valve 34, that is to say, the full closing
thereof. When the engine speed exceeds the high level H
(Block B6), the control unit 150 feeds the output or target
value representative of the opening of the control valve 34,
that is to say, -the full opening thereof.
Fig. 20 shows a block diagram of a valve control system
160 for controlling the opening of the control valve 34 in the
engines 10c and 1Od. In the engines 10c and 1Od, the control
~Z33~8
valve 34 is switched from its closed to open position when the
engine speed reaches a predetermined level regardless of the
amount Th of throttling of a throttle valve 154, the throttle
valve controlling the flow of the air-fuel mixture to the
engine in response to the operation of an accelerator means
such as a throttle grip and an accelerator pedal. Therefore,
as the amount Th of throttling of the throttle valve 154
decreases, power output characteristics of the engine becomes
irregular, as shown in Fig. 21.
An ignition device 142 generates a pulse signal per
revolution of the engine, the pulse signal being applied to a
waveform shaping circuit 1~4 by kick it is shaped. A output
signal prom thq waveform shaping clrcuit 144 i9 End to an ~'/V
converter 164 whlch converts the frequency of the pulses into
voltage and outputs data, representative of the voltage
corresponding to the engine speed, the output data being fed
to a control unit 166 such as a microprocessor unit. The
waveform shaping circuit 144 and the converter 164 constitute
a detector 16~ for detecting the engine speed. A detector 152
detects the amount of throttling of the throttle valve 154 to
output a signal to an address control circuit 170. The
throttling detector 152 is composed of a 3-bit encoder
operatively connected to the throttle valve 154. memory 172
stores valve-switching data representative of the optimum
values of the engine speed at various amounts of throttling of
the throttle valve 154 at which values the control valve 34
should be switched from one of its closed and open positions
to the other to render the power output characteristics
smooth, the valve-switching data being determined through
24
3LZ33~
experiments. The address control circuit 170 outputs address
data to the memory 172 to access the addresses thereof to read
the valve-switchin~ data therefrom. Thus, the data
representative of the optimum value of the engine speed and
the data representative of the actual engine speed are fed to
the control unit 166, and in accordance with these data, the
control unit 166 determines a target value of the opening of
the control valve 34, the target value representing either the
full closing or full opening ox the valve 34. The control
unit 166 outputs a signal representative of the target value
to a drive circuit 156. on encoder 158 is connected to an
output sham ox the actuator ox servomotor 10~ for detecting
the position ox ro~lon or annular m~vem~nt ox k s~rvomotor
108 to weed an output signal to the drive circuit 156. The
drive circuit 156 drives the actuator 108 until the output of
the encoder 158 is brought into agreement with the target
value, that is to say, the degree of the opening of the
control valve 34 is brought into agreement with the amount of
the opening thereof represented by the target value.
In operation, when the engine speed reaches the
predetermined level and when the throttle valve 154 is opened
to a certain extent, the amount of throttling of the valve 154
is detected by the throttling detector 152. Then, the valve-
switching data is read from that address ox the memory 172
corresponding to the throttling amount, and is fed to the
control unit 166. Then, the control unit 166 compares the
valve-switching data with the data outputted from the engine
speed detector 148 to determine whether the target value of
the opening of the control valve 34 should represent the full
~3~
opening or full closing of the control valve 34. If the
target value represents the full opening of the valve 34, in
which case generally the engine speed is high, the first and
second valve elements 34a and 34b are moved to their
respective open positions through the actuator 108. On the
other hand, if the target value represents the full closing of
the valve 34, the first and second valve elements 34a and 34b
are moved to their respective closed positions. Thus, in this
embodiment, the control valve 34 is controlled depending on
two parameters, that is, the amount of throttling of the
throttle valve 154 and the engine speed, a smooth power output
characteristics can be achieved as shown in Fig. 22~
ig~ 23 show a ~ur~h~r modt~led two-cycl~ engine IOe
which differs from the engine 10 of Fig. 1 in that a single
valve element 3~a of a port timing control valve 34 is
employed and in that a modified drive means 106 is provided
for moving the valve element 34a between its closed and open
positions. The valve element 34a has a timing control surface
34c of an arcuate concave shape formed in one side face facing
an exhaust port 22 at an inner portion thereof. A curvature
ox the control surface 34c is substantially equal to or
slightly greater than that of the inner peripheral surface of
the cylinder 16.
In its closed position of the valve element 34a, the
control surface 34c is smoothly continuous with the inner
peripheral surface of the cylinder 16 as described in the
preceding embodiments. And, in its open position, the valve
element 34a is held out of the exhaust passage 24 and received
in a recess 38 formed in the cylinder block 16. A guide hole
~L;233~8
39 is wormed in the cylinder block 12 and leads to the recess
38 at one end and to the exhaust passage 24 at the other end.
The valve element 34a is closed fitted in the guide hole 39
for sliding movement therealong. The drive means 106
comprises an actuator 108 in the form of a servomotor, and a
power transmission means 110 which comprises an output shaft
44 mounted on the cylinder block 16 for angular movement about
an axis thereof extending along the axis of the cylinder 16,
and a lever 62 fixedly mounted at one end on the shaft 44 and
having at the other end a slot 62c in which a pin 34g, secured
to the end of the valve element 34a remote from the control
surface 34a, is received. The power transmission means 110
further comprises a flexible joint 126 connected at one and ~.o
an output shaEt ox tha actuator 1OB and also connected a the
lS other end to the drive shaft 44 via a worm gearing snot shown)
or the like. With this construction, upon actuation of the
actuator 108, the lever 62 is angularly moved about the axis
of the drive shaft 44 for moving the valve element 34a between
its closed and open positions along a straight path in a plane
substantially perpendicular to the axis of the cylinder 16.
The cylinder block 12 has a hollow projection 176 in
which the recess 38 is formed and in which part of the power
transmission means 110 is accommodated, the projection 176
extending generally radially outwardly from a cylinder block
body 12a. In the preceding embodiments, two such projections
are provided on the cylinder block. Thus, tha engine 1Oe in
this embodiment is compact in size because of the provision of
the single valve element 34a.
Fig. 24 shows a motorcycle 178 incorporating the engine
3~
1Oe of Fig. 15, the engine 1Oe being mounted on a body 180.
An exhaust pipe 182 extending from the exhaust passage 24, and
that portion 182a of the exhaust pipe 182 forming an exhaust
chamber is disposed adjacent to the engine 10e on that side of
the cylinder 16 opposite to the projection 176. With this
arrangement, the exhaust pipe 182 can be positioned closer to
the engine a distance D than an exhaust pipe 182b which would
be incorporated in the engine 10 of Fig. 1.
Fig. 25 shows a further modified two-cycle engine 10f
which differs from the engine 10c of Fig. 7 in that guide
means 186 is provided for guiding the movement of first and
second valve elements 34a and 34b between thelr respective
closed al1d open posiklon~ he flrsl: and second valve
elements 34a and 34b are similar in configuration to those in
the embodiment of Fig. 7 except that the former is shorter
than the latter. In addition, as best shown in Fig. 26, each
of the first and second valve elements 34a and 34b has an
integral tubular slider portion 188 extending parallel to the
body thereof, and a connecting arm 190 extending from the end
of the body remote from the control surface 34c, 34d and
interconnecting the body and the slider portion 188. The
guide means l86 comprises a pair of coaxial guide rods 192 and
194 of a circular cross-section fixedly mounted on the
cylinder block 12 and extending parallel to guide tubes 100
and 102, and the tubular slider portions 188 of the valve
elements 34a and 34b fitted on the guide rods 192 and 194,
respectively, for sliding movement therealong. Each of the
slider portions 188 has a rack portion 196 on a upper surface
thereof. In this embodiment, instead of the levers 116 in the
28
~L~33~
embodiment of Fig. 7, a pair of first and second pinions 198
are fixedly mounted on the output shafts 112 and 112 and
meshingly engage the rack portions 196 and 196 on the slider
portions 188 and 188, respectively. Upon rotation of the
output shafts 112 and 112, the first and second valve elements
34a and 34b are moved between their respective closed and open
positions, as described above for the preceding embodiments.
By virtue of the provision of the gu:ide rods 192 and 194
and the slider portions 188 and 188, the valve elements 34a
and 34b and the guide tubes 100 and 102 can be substantially
reduced in length without affecting the accurate sliding
movement of the valve elements 3qa'and 34b along the
respectlve guide tubcs 100 and 102. Therefore, the overall
wldth of the engine 10~ can also be substantially reduced, so
that the engine 10f can be of a compact size. More
specifically, although the areas of sliding contact of each
guide tube 100, 102 with a respective one of the first and
second valve elements 34a and 34b are reduced, the cooperation
of the slider portions 188 and 188 with the respective guide
rods 192 and 193 positively prevent the first and second valve
elements 34a and 34b from rattling during the movement thereof
between their respective closed and open positions. As
described above for the embodiment of Fig. 7, since the first
and second valve elements 34a and 34b of a square cross-
section are slidably received respectively in the cross-
sectional7y square bores 100a and 102a of the guide tubes 100
and 102, the valve elements 34a and 34b are prevented from
rotation or angular movement along the axls thereof.
Fig. 27 shows a further modified two-cycle engine 10g
29
~;233~
which differs from the engine 1 Oc of Fig. 7 in that modified
drive means 106 is provided for moving the first and second
valve elements 34a and 34b between its closed and open
positionsO The drive means 106 comprises an actuator 202 in
the form of a servomotor mounted on the cylinder block 12, and
power transmission means 204 for transmitting the output of
the actuator 202 to the first and second valve elements 34a
and 34b for moving them between its respective closed and open
positions. The power transmission means 204 comprises a drive
rod 206 borne at its opposite ends by a pair of bearings 208
and 208 for movement along an axis thereof. The drive rod 206
has a square cross-sectiQn, and the opposite ends oE the drive
God 206 arq slidably received respectively in compl~mf3nt~rily-
shaped bores of the bearing 208 and 208, so that the drive rod
206 is prevented from rotating about its axis. A first lever
210 is Eixedly mounted at one end on a rotatable output shaft
(not shown) of the actuator 202, and a first pinion 212 is
fixedly secured to the upper end of the output shaft. The
first lever 210 has at the other end a slot 210a in which a
pin 214 secured to the first valve element 34a is received. A
second lever 216 is fixedly mounted at one end on a shaft (not
shown) rotatably mounted on the cylinder block 12, and a
second pinion 218 is secured to the upper end of this shaft.
The second lever 216 has at the other end a slot 21 6a in which
a pin 214 secured to the second valve element 34b is received.
The drive rod 206 has a pair of rack portions 206a and 206a on
opposite sides thereof adjacent to the opposite ends thereof.
The first and second pinions 212 and 218 are in mesh with the
rack portions 206a and 206a, respectively
~33~
In operation, upon rotation or angular movement of the
output shaft of the actuator 202 in a counter-clockwise
direction (Fig. 27), the first lever 210 is annularly moved in
a counter-clockwise direction, and simultaneously the drive
rod 206 is moved in a right-hand direction through the first
pinion 212 and the rack portion 206a in mesh therewith to
angularly move the second lever 216 in a clockwise direction
through the second pinion 218 and the rack portion 206a in
mesh therewith, so that the first and second valve elements
34a and 34b are simultaneously moved away from each other,
that is to say, from their respective closed to open
positions. Since the drive rod 206 is adapted to be moved
linearly, the first and second levers 210 and 216 con by
angularly moved accurately in synchronism with each other, so
that the first and second valve elements 34a and 34b are also
accurately moved between their respective closed and open
positions. In this embodiment, although the actuator 202 is
coupled to the first lever 210, a suitable actuator such as a
solenoid may be directly connected to the drive rod 206 for
driving the same along the axis whereof.
Fig. 28 shows a further modified two-cycle engine 1Oh
which differs from the engine 10c of Fig. 7 in that modified
drive means 222 is provided for moving the first and second
valve elements 34a and 34b between its closed and open
positions, the drive means 222 including jeans for adjusting
the positions of the first and second valve elements 34a and
34b relative to the exhaust port 22, as hereinafter more fully
be described. The drive means 222 comprises a power
transmission means 224 which comprises a first lever 226 of a
~Z33~
generally L-shape is fixedly mounted intermediate opposite
ends on a shaft 22~ mounted on the cylinder block12 for
rotation about an axis thereof and extending substantially
parallel to the axis of the cylinder 16. The first lever 226
has at one end a slot 226a in which a pin 230 secured to the
first valve element 34a is received. A second lever 232 is
fixedly mounted at one end on a shaft 234 mounted rotatably on
the cylinder block 12 and extending substantially parallel to
the axis of the cylinder block 12, the second lever 232 having
at the other end a slot 232a in which a pin 236 secured to the
second valve element 34b is received. The first and second
levers 226 and 232 are disposed in a common plane
perpendicular to the axls ox the cylinder 16, A hind lever
238 of a generally triangular shape is rotatably mounted
intermediate opposite ends on the shaft 228 and disposed above
the first lever 226 in parallel relation thereto. A
connecting rod 240 has one end pivotally connected to one end
of the third lever 238 while the other end is pivotally
connected to the second lever 232 intermediate opposite ends
thereof.
As best shown in Figs. 29 and 30, the other ends 226c and
23~c of the first and third levers 226 and 238 are disposed in
overlapping relation and connected together through a fastener
member 242 defined by a disc-shaped base 242a and an eccentric
pin 242b extending perpendicularly from one side thereof in
eccentric relation to the center or axis of the base 242a.
The axis of the base 242a is indicated by X1 in Fig. 30 while
the axis of the pin 242b is indicated by X2. More
specifically, the base 242a is received in a slot 226b formed
~3~ 8
in the other end of the first lever 226. The eccentric pin
242b passes through an aperture 238a formed through the other
end of the third lever 238. A nut 244 is threaded on an upper
threaded end of the eccentric pin 242b to join the first and
third levers 226 and 238 together with the end 238c of the
third lever 238 clamped between the nut 244 and the end 226c
of the first lever 226, so that the first and third levers
can be angularly moved in unison upon angular movement of the
shaft 228. The drive means 222 comprises an actuator (not
shown) such as a servomotor which is connected to the shaft
~0 228 to drive the same for angular movement about its axis.
There may be occasions when the first and second valve
elements 34a and 34b con no be brought accuratqly into ~h~:Lr
respective prede~ermlned closed positions in the course of use
of the engine. For adjusting the positions of the valve
elements 34a and 34b relative to the exhaust port 22, a cover
member 246 is first removed from the cylinder block 12. Then,
the nut 244 is loosened, and the fastener member 242 is
slightly moved angularly about the axis of the eccentric pin
242a, so that the angular positions of the first and third
levers 226 and 238 wi-th respect to the shaft 228 are suitably
adjusted. Thus, the fastener member 242 is easily accessible,
and therefore the adjustment can be easily carried out.
The fastener member 242 may have a disc-shaped clamp
portion (not shown) formed integrally on the face of the base
242a facing away from the first lever 226, the clamp portion
being greater in diameter than the base 242a so that upon
tightening of the nut 244, the ends 238c and 226c of the first
and third levers 238 and 226 are clamped between the nut 244
33
~:33~8
and the clamp portion.
Further, as shown in Fig. 31, the third lever 238 and the
connecting rod 240 may be replaced respectively by a lever 250
having a pinion portion 250a and a connecting rod 252 having a
s pair of first and second rack portions 252a and 252b at
opposite ends thereof, the first rack portion 252 being in
mesh with the pinion portion 250a of the:Lever 250 while the
second rack portion 250b is in mesh with a pinion 254 mounted
on the shaft 234.
Fig. 32 shows a further modified two-cycle engine 10i
whieh differs from the engine 10f of Fig 25 in that cooling
means is provided or cooling the p'air of bearings 122 and 122
rotatably 3upportin~ the drive shift 120. More speelP:lcally,
a first water passageway 260 of a generally annular
eonfiguration is formed in the cylinder block 12 in
surrounding relation to the left-hand bearing 122 (Fig. 32),
and similarly a second water passageway 262 of a generally
annular configuration is formed in the cylinder block 12 in
surrounding relation to the right-hand bearing 122. The first
and second water passageways 260 and 262 are in communication
with a cooling water circulation system 264 Fig. 33) of the
engine. The circulating cooling water is fed from a water
pump 268 driven by the engine through a cylinder water jacket
270, a passage in the cylinder head 14, a radiator upper tank
272 and a radiator lower tank 274 and is returned to the water
pump 268 through a water hose 276. The lower portion of each
of the first and second water passageways 260 and 262
communicates with the cylinder water jacket 270 while the
upper portion communicates with the passage in the cylinder
34
~233~
head 14. With this arrangement, during the operation of the
engine, the circulating cooling water flows through the first
and second water passageways 260 and 262 in the vicinity of
the pair of bearings 122 and 122 to efficiently cool them.
Thus, the pair of bearings 122 and 122 are prevented from
displacing out of position due to thermal expansion, thereby
holding the drive shaft 120 in position to ensure an accurate
operation of the power transmission means 204.
