Field of the Invention
[0001] The present invention relates to an engine.
Description of the Related Art
[0002] An engine is provided with a variable valve mechanism. The variable valve mechanism
includes a low-speed rocker arm used in a low-speed region of the engine rotation
speed, and a high-speed rocker arm used in a high-speed region of the engine rotation
speed.
[0003] For example, the low-speed rocker arm and the high-speed rocker arm are attached
to a rocker shaft side-by-side in the axial direction of the rocker shaft. The low-speed
rocker arm includes a first roller which rolls and comes into contact with a low-speed
cam of a camshaft. The high-speed rocker arm includes a second roller which rolls
and comes into contact with a high-speed cam of the camshaft.
[0004] The low-speed rocker arm is driven in the low-speed region of the engine rotation
speed by the low-speed cam thereby opening and closing a valve. The low-speed rocker
arm and the high-speed rocker arm are coupled in the high-speed region of the engine
rotation speed. Specifically, a coupling pin inserted into a hole in the low-speed
rocker arm is moved by an actuator and is inserted into a hole in the high-speed rocker
arm. As a result, the low-speed rocker arm and the high-speed rocker arm are coupled
together. In this state, the low-speed rocker arm is not driven by the low-speed cam
and the high-speed rocker arm is driven by the high-speed cam thereby opening and
closing a valve.
JP H01 110816 A discloses rocker arms for driving three intake valves and supported swingably by
a rocker shaft, the ends of two low speed rocker arms being in rolling contact with
the lower speed cams via a roller and the end of one high-speed rocker arm being in
sliding contact with the high-speed cam via a slipper.
Summary of the Invention
Technical Problem
[0005] Rollers are used in the low-speed rocker arm and the high-speed rocker arm and therefore
the weight is increased in the abovementioned engine. As a result, the effect of the
equivalent inertia weight of the rocker arms is increased when the engine rotation
speed is in the high-speed region. For example, the behavior of the rocker arms in
the high-speed region is affected when the equivalent inertia weight of the rocker
arms is large. As a result, there is a problem that the upper limit of the engine
rotation speed needs to be lowered in order to suppress any disturbance in the behavior
of the rocker arm.
[0006] Accordingly, the inventor of the present application considered changing both of
the rollers in the low-speed rocker arm and the high-speed rocker arm to slippers
in order to reduce the equivalent inertia weight. By using slippers, the weight of
the rocker arms can be reduced more in comparison to a case when rollers are used,
thereby reducing the equivalent inertia weight.
[0007] However, an oil film produced on the contact surfaces of the slippers becomes a thin
boundary lubrication because the frictional speed of the slippers with respect to
the cam is low in the low-speed region of the engine rotation speed. As a result,
there is a problem that the frictional resistance between the slippers and the cam
increases and the mechanical loss of the engine increases when a slipper is used in
the low-speed rocker arm.
[0008] Conversely, the frictional speed of the slipper with respect to the cam is greater
in the high-speed region of the engine rotation speed and therefore the mechanical
loss is relatively low. However, there is a problem that the allowable surface pressure
of the slipper is low in comparison to the roller. In particular, it is difficult
to increase the stiffness of the two rocker arms because the rocker arms are coupled
each other in the high-speed region of the engine rotation speed as discussed above.
As a result, partial contact between the slipper and the cam may occur due to the
deformation of the rocker arms. Localized surface pressure on the slipper increases
when partial contact occurs. This type of partial contact occurs more easily in the
high-speed region than in the low-speed region of the engine rotation speed. Specifically,
there is a problem that the partial contact must also be considered along with the
low allowable surface pressure of the slipper in the high-speed region of the engine
rotation speed.
[0009] Increasing the curvature radius of the contact surface of the slipper may be considered
as one means for reducing the surface pressure. However, the length of the slipper
increases if the curvature radius is increased. Moreover, the length of the arm section
for supporting the slipper also tends to increase if the length of the slipper is
increased. The equivalent inertia weight of the rocker arm may increase due to the
aforementioned factors and thus the effect of reducing the equivalent inertia weight
is limited even when a slipper is used in place of a roller.
[0010] An object of the present invention is to reduce mechanical loss in the low-speed
region of the engine rotation speed and increase the upper limit of the engine rotation
speed.
Solution to Problem
[0011] An engine according to a first aspect includes a cylinder head, a valve, a rocker
unit, a camshaft, and an open/close timing changing unit. The valve is attached to
the cylinder head. The rocker unit presses the valve and opens and closes the valve.
The camshaft drives the rocker unit. The open/close timing changing unit changes the
opening and closing timing of the valve.
[0012] The rocker unit includes a rocker shaft, a first rocker arm, a second rocker arm,
and a coupling pin. The rocker shaft is supported by the cylinder head. The first
rocker arm includes a roller and a pressing member. The roller is provided in a manner
to allow contact with the camshaft. The pressing member presses the valve. The first
rocker arm rotates around the axis of the rocker shaft due to the roller coming into
contact with the camshaft. A second rocker arm includes a slipper. The slipper is
arranged to be contact with the camshaft. The second rocker arm is aligned with the
first rocker arm in the axial direction of the rocker shaft. The second rocker arm
rotates around the axis of the rocker shaft due to the slipper coming into contact
with the camshaft. The coupling pin is configured to move between a coupling position
and a release position due to the open/close timing changing unit. The coupling pin
couples the second rocker arm to the pressing member in the coupling position. The
coupling pin releases the second rocker arm from the pressing member in the release
position.
[0013] When the engine rotation speed is in a predetermined low-speed region, the open/close
timing changing unit positions the coupling pin in the release position whereby the
pressing member presses the valve according to the rotation of the first rocker arm.
When the engine rotation speed is in a predetermined high-speed region, the open/close
timing changing unit positions the coupling pin in the coupling position whereby the
pressing member presses the valve according to the rotation of the second rocker arm.
[0014] The roller comes into rolling contact with the camshaft. The slipper comes into sliding
contact with the camshaft. The tip end of the slipper is closer to the axis of the
rocker shaft than the tip end of the roller as seen from the axial direction of the
rocker shaft. The maximum width of the slipper is greater than the width of the roller
in the axial direction of the rocker shaft.
[0015] The roller is used in the first rocker arm for low speeds in the engine according
to the present aspect. As a result, the frictional resistance between the roller and
the camshaft can be reduced in the low-speed region of the engine rotation speed.
The mechanical loss can thereby be reduced in the low-speed region.
[0016] Furthermore, the slipper is used in the second rocker arm for high speeds. As a result,
the equivalent inertia weight of the second rocker arm can be reduced. Moreover, because
the frictional speed of the slipper with respect to the camshaft in the high-speed
region of the engine rotation speed is high, a thick oil film can be produced on the
contact surface of the slipper. As a result, mechanical loss can be reduced even when
the slipper is used in the second rocker arm for high speeds. By using the roller
in the first rocker arm for low speeds and the slipper in the second rocker arm for
high speeds in this way, the equivalent inertia weight can be reduced while limiting
mechanical loss in all regions of the engine rotation speed.
[0017] Furthermore, the maximum width of the slipper is greater than the width of the roller
in the axial direction of the rocker shaft. As a result, the surface pressure of the
slipper can be limited and the generation of partial contact can be suppressed. Moreover,
the tip end of the slipper is closer to the axis of the rocker shaft than the tip
end of the roller as seen from the axial direction of the rocker shaft. That is, the
surface pressure of the slipper can be reduced by making the maximum width of the
slipper greater than the width of the roller, whereby the need to increase the curvature
radius in order to reduce the surface pressure is reduced. As a result, a slipper
with a shorter configuration is possible. Consequently, an increase in the equivalent
inertia weight can be suppressed in comparison to when the length of the slipper is
increased and the curvature radius of the slipper is increased. As a result, the upper
limit of the engine rotation speed can be increased.
[0018] The slipper may include a curved contact surface for contact with the camshaft. The
curvature radius of the curved surface may be greater than the curvature radius of
the roller. In this case, the surface pressure of the slipper can be reduced.
[0019] The center of gravity of the second rocker arm is closer to the axis of the rocker
shaft than the center of gravity of the first rocker arm. In this case, the equivalent
inertia weight of the second rocker arm can be reduced even further.
[0020] The weight of a portion of the second rocker arm positioned further on the tip end
side of the slipper than an imaginary plane including the axis of the camshaft and
extending in the cylinder axial direction of the cylinder head may be less than the
weight of a portion of the first rocker arm positioned further on the tip end side
of the roller than the imaginary plane. In this case, the equivalent inertia weight
of the second rocker arm can be reduced even further.
[0021] The second rocker arm may include a boss portion and an arm portion. The boss portion
may include a hole through which the rocker shaft passes. The arm portion may extend
from the boss portion to the slipper. The slipper may include a contact surface for
contact with the camshaft.
[0022] The maximum width of the contact surface of the slipper may be less than the width
of the boss portion in the axial direction of the rocker shaft. In this case, the
weight of the slipper can be reduced while limiting the surface pressure of the slipper,
and consequently the equivalent inertia weight of the second rocker arm can be further
reduced.
[0023] The arm portion may include a recessed portion positioned between the contact surface
and the boss portion. In this case, the weight can be further reduced than if the
contact surface continued as far as the boss portion and the equivalent inertia weight
of the second rocker arm can be reduced even further. Moreover, interference with
a jig for machining when machining the contact surface can be avoided due to the recessed
portion.
[0024] The arm portion includes a protruding portion that extends from the slipper up to
the boss portion and protrudes from the surface opposite the contact surface of the
slipper. In this case, the stiffness of the arm portion can be assured by the protruding
portion while reducing the weight of the arm portion.
[0025] The width of the protruding portion may be less than the width of the contact surface
in the axial direction of the rocker shaft. In this case, the weight of the arm portion
can be reduced and consequently the equivalent inertia weight of the second rocker
arm can be further reduced.
[0026] The surface of the arm portion opposite the contact surface may have a shape that
is recessed toward the contact surface as seen from the axial direction of the rocker
shaft. In this case, the weight of the arm portion can be reduced and consequently
the equivalent inertia weight of the second rocker arm can be further reduced.
[0027] The slipper may include a hardened layer. The hardened layer may come into contact
with the camshaft and may have a coefficient of friction less than that of the base
material of the slipper and may have a hardness greater than that of the base material
of the slipper. In this case, the abrasion resistance of the slipper can be improved.
Effects of Invention
[0028] According to the present invention, mechanical loss in the low-speed region of the
engine rotation speed is reduced and the upper limit of the engine rotation speed
can be increased.
Brief Description of Drawings
[0029]
FIG. 1 is a side view of the straddle-type vehicle according to an embodiment.
FIG. 2 is a cross-sectional view of a portion of an engine for a straddle-type vehicle
according to the embodiment.
FIG. 3 is a cross-sectional view of a cylinder head and a head cover as seen from
a direction perpendicular to the cylinder axis and the cam axis.
FIG. 4 is a perspective view of the inside of the cylinder head.
FIG. 5 is a perspective view of the inside of the cylinder head.
FIG. 6 is a view of the inside of the cylinder head as seen from the cylinder axial
direction.
FIG. 7 is a cross-sectional view of the inside of the cylinder head as seen from the
cam axial direction.
FIG. 8 is a perspective view of an intake rocker unit.
FIG. 9 is a view of the intake rocker unit as seen from the direction perpendicular
to the cam axis.
FIG. 10 is a view of the intake rocker unit as seen from the cam axial direction.
FIG. 11 is a view of the second rocker arm as seen from below.
FIG. 12 is a view of the second rocker arm as seen from the cam axial direction.
FIG. 13 is a cross-sectional view in the vicinity of a second shaft supporting portion
and an arm urging member.
FIG. 14 is a cross-sectional view of the inside of the cylinder head as seen from
the cam axial direction.
FIG. 15 is a perspective view of the intake rocker shaft.
FIG. 16 illustrates changes in loss torque with respect to the engine rotation speed
when a roller is used and when a slipper is used in the rocker arm.
FIG. 17 is a view of the intake rocker unit as seen from the cylinder axial direction
according to a first modified example.
FIG. 18 is a view of the intake rocker unit as seen from the cylinder axial direction
according to a second modified example.
FIG. 19 is a view of the inside of the cylinder head according to a third modified
example as seen from the cylinder axial direction.
Description of Embodiment
[0030] The following is an explanation of a straddle-type vehicle and an engine for a straddle-type
vehicle according to an embodiment with reference to the drawings. FIG. 1 is a side
view of a straddle-type vehicle 100. The straddle-type vehicle 100 is a so-called
scooter-type motorcycle. As illustrated in FIG. 1, the straddle-type vehicle 100 includes
a front wheel 101, a seat 102, a rear wheel 103, a power unit 104, a steering device
105, and a vehicle body cover 106.
[0031] The front wheel 101 is rotatably supported on the steering device 105. A handle 113
is attached to the upper end of the steering device 105. The seat 102 is disposed
to the rear of the steering device 105. The power unit 104 is disposed below the seat
102. The power unit 104 includes an engine 1 and a transmission 107. The power unit
104 rotatably supports the rear wheel 103.
[0032] The vehicle body cover 106 includes a rear cover 108, a lower cover 109, and a front
cover 110. The rear cover 108 is disposed under the seat 102. The front cover 110
covers the vicinity of the steering device 105. The lower cover 109 is disposed between
the front cover 110 and the rear cover 108. The upper surface of the lower cover 109
includes a foot board 111 and a tunnel portion 112.
[0033] The tunnel part 112 is arranged in the middle portion in the vehicle width direction
on the upper surface of the lower cover 109. The tunnel portion 112 protrudes upward
higher than the foot board 111. The foot board 111 is disposed on the right and left
of the tunnel portion 112. The foot board 111 is provided for a rider to place his
or her feet. The tunnel portion 112 may be omitted. That is, the upper surface of
the lower cover 109 may have a flat foot board that extends in the left-right direction.
[0034] FIG. 2 is a cross-sectional view of a portion of an engine 1 for a straddle-type
vehicle according to the embodiment. The engine 1 according to the present embodiment
in a water-cooling type single-cylinder engine. As illustrated in FIG. 2, the engine
1 includes a crankcase 2, a cylinder body 3, a cylinder head 4, and a head cover 5.
[0035] The crankcase 2 houses a crankshaft 6. The cylinder body 3 is connected to the crankcase
2. The cylinder body 3 may be integrated with the crankcase 2 or may be a separate
body. The cylinder body 3 houses a piston 7. The piston 7 is coupled to the crankshaft
6 via a connecting rod 8.
[0036] The direction from the cylinder head 4 toward the head cover 5 in the cylinder axis
Ax1 direction of the cylinder body 3 is referred to as the "head cover side" in the
present embodiment. Moreover, the direction from the cylinder head 4 to the cylinder
body 3 in the cylinder axis Ax1 direction is referred to as the "cylinder body side."
[0037] The cylinder head 4 is disposed on the head cover side of the cylinder body 3. The
cylinder head 4 is attached to the cylinder body 3. The head cover 5 is disposed on
the head cover side of the cylinder head 4. The head cover 5 is attached to the cylinder
head 4.
[0038] FIG. 3 is a cross-sectional view of the cylinder head 4 and the head cover 5 as seen
from a direction perpendicular to the cylinder axis Ax1 and a cam axis Ax3. As illustrated
in FIG. 3, the cylinder head 4 includes a side wall 4a that extends in the cylinder
axis Ax1 direction. The head cover 5 includes a side wall 5a that extends in the cylinder
axis Ax1 direction. An end portion 4b (referred to hereinbelow as "side wall end 4b")
of the side wall 4a of the cylinder head 4 is disposed face to face with an end portion
5b (referred to hereinbelow as "side wall end 5b") of the side wall 5a of the head
cover 5. Specifically, the side wall end 4b of the cylinder head 4 is disposed face
to face with the side wall end 5b of the head cover 5 with a seal member 9 disposed
therebetween. The cylinder head 4 may be integrated with the cylinder body 3 or may
be a separate body.
[0039] As illustrated in FIG. 2, the cylinder axis Ax1 is perpendicular to a central axis
Ax2 (referred to hereinbelow as "crankshaft axis Ax2") of the crankshaft 6. The cylinder
head 4 includes a combustion chamber 11. A spark plug 12 is attached to the cylinder
head 4. The tip end portion of the spark plug 12 is disposed so as to face the combustion
chamber 11. The base end portion of the spark plug 12 is disposed outside of the engine
1. A valve mechanism 13 is housed in the cylinder head 4 and the head cover 5.
[0040] The valve mechanism 13 is a mechanism for opening and closing belowmentioned exhaust
valves 25 and 26 and intake valves 27 and 28. A single overhead camshaft (SOHC) mechanism
is used in the valve mechanism 13. A so-called variable valve mechanism which switches
the timing for opening and closing the intake valves 27 and 28 is used in the valve
mechanism 13.
[0041] The valve mechanism 13 includes a camshaft 14. The camshaft 14 is supported on the
cylinder head 4. The center axis Ax3 (referred to hereinbelow as "cam axis Ax3") of
the camshaft 14 runs perpendicular to the cylinder axis Ax1. The cam axis Ax3 runs
parallel to the crankshaft axis Ax2.
[0042] As illustrated in FIG. 3, the camshaft 14 includes a first camshaft end portion 141
and a second camshaft end portion 142.
[0043] A sprocket 29 is attached to the first camshaft end portion 141. A cam chain 15 illustrated
in FIG. 2 is wound onto the sprocket 29. As illustrated in FIG. 2, a cam chain chamber
16 is provided in the cylinder head 4 and the cylinder body 3. The cam chain 15 is
disposed in the cam chain chamber 16. The camshaft 14 is coupled to the crankshaft
6 via the cam chain 15. The rotation of the crankshaft 6 is transferred through the
cam chain 15 to the camshaft 14 thereby rotating the camshaft 14.
[0044] A water pump 17 is coupled to the first camshaft end portion 141. The water pump
17 is connected to a liquid coolant passageway (not illustrated) and a radiator 19
in the engine 1 through a liquid coolant hose 18. The water pump 17 is driven by the
rotation of the camshaft 14 thereby circulating a liquid coolant for the engine 1.
[0045] As illustrated in FIG. 3, the camshaft 14 includes a rod portion 143, a first intake
cam portion 144, a second intake cam portion 145, and an exhaust cam 146. The rod
portion 143 is rotatably supported by a first shaft support portion 21 and a second
shaft support portion 22 of the cylinder head 4. The first intake cam portion 144,
the second intake cam portion 145, and the exhaust cam 146 are disposed on the outer
circumference of the rod portion 143. The first intake cam portion 144, the second
intake cam portion 145, and the exhaust cam 146 are aligned in the cam axis Ax3 direction.
[0046] FIGS. 4 and 5 are perspective views of the inside of the cylinder head 4. FIG. 6
is a view of the inside of the cylinder head 4 as seen from the cylinder axis Ax1
direction. As illustrated in FIGS. 3 to 6, the cylinder head 4 includes the first
shaft support portion 21 and the second shaft support portion 22. The first shaft
support portion 21 and the second shaft support portion 22 are formed integrally with
the cylinder head 4. The first shaft support portion 21 and the second shaft support
portion 22 are aligned in the cam axis Ax3.
[0047] The first shaft support portion 21 and the second shaft support portion 22 rotatably
support the camshaft 14. As illustrated in FIG. 3, the first shaft support portion
21 includes a first camshaft hole 211 into which the camshaft 14 is inserted. A first
shaft bearing 23 is attached to the first camshaft hole 211. The first shaft support
portion 21 supports the camshaft 14 via the first shaft bearing 23. The second shaft
support portion 22 includes a second camshaft hole 221 into which the camshaft 14
is inserted. A second shaft bearing 24 is attached to the second camshaft hole 221.
The second shaft support portion 22 supports the camshaft 14 via the second shaft
bearing 24.
[0048] An end portion 21a on the head cover side of the first shaft support portion 21 is
positioned further to the head cover side than the side wall end 4b of the cylinder
head 4. That is, the first shaft support portion 21 protrudes further to the head
cover side than the side wall end 4b of the cylinder head 4. An end portion 22a on
the head cover side of the second shaft support portion 22 is positioned further to
the head cover side than the side wall end 4b of the cylinder head 4. That is, the
second shaft support portion 22 protrudes further to the head cover side than the
side wall end 4b of the cylinder head 4.
[0049] As illustrated in FIG. 6, the intake valves 27 and 28 and the exhaust valves 25 and
26 are attached to the cylinder head 4. FIG. 7 is a cross-sectional view of the inside
of the cylinder head 4 as seen from the cam axis Ax3 direction. As illustrated in
FIG. 7, the cylinder head 4 includes an intake port 31 and an exhaust port 32 that
communicate with the combustion chamber 11.
[0050] The intake valves 27 and 28 open and close the intake port 31. As illustrated in
FIG. 6, the intake valves 27 and 28 include a first intake valve 27 and a second intake
valve 28. The first intake valve 27 and the second intake valve 28 are aligned in
the cam axis Ax3 direction.
[0051] As illustrated in FIG. 4, an intake valve spring 271 is attached to the first intake
valve 27. The intake valve spring 271 urges the first intake valve 27 in the direction
in which the first intake valve 27 closes the intake port 31. An intake valve spring
281 is also attached to the second intake valve 28 in the same way and urges the second
intake valve 28 in the direction in which the second intake valve 28 closes the intake
port 31.
[0052] The exhaust valves 25 and 26 open and close the exhaust port 32. The exhaust valves
25 and 26 includes a first exhaust valve 25 and a second exhaust valve 26. The first
exhaust valve 25 and the second exhaust valve 26 are aligned in the cam axis Ax3 direction.
[0053] As illustrated in FIG. 5, an exhaust valve spring 251 is attached to the first exhaust
valve 25. The exhaust valve spring 251 urges the first exhaust valve 25 in the direction
in which the first exhaust valve 25 closes the exhaust port 32. An exhaust valve spring
261 is also attached to the second exhaust valve 26 in the same way and urges the
second exhaust valve 26 in the direction in which the second exhaust valve 26 closes
the exhaust port 32.
[0054] As illustrated in FIG. 7, the valve mechanism 13 includes an exhaust rocker unit
33 and an Intake rocker unit 34. The exhaust rocker unit 33 presses the exhaust valves
25 and 26 and opens and closes the exhaust valves 25 and 26. The intake rocker unit
34 presses the intake valves 27 and 28 and opens and closes the intake valves 27 and
28. The exhaust rocker unit 33 and the intake rocker unit 34 are driven by the camshaft
14.
[0055] The exhaust rocker unit 33 includes an exhaust rocker shaft 35, an exhaust rocker
arm 36, and a pressing member 38. The exhaust rocker shaft 35 is disposed parallel
to the camshaft 14. The exhaust rocker shaft 35 is supported on the cylinder head
4. Specifically, the exhaust rocker shaft 35 is supported on the first shaft support
portion 21 and the second shaft support portion 22.
[0056] The exhaust rocker arm 36 is supported on the exhaust rocker shaft 35 in a swingable
manner centered on the exhaust rocker shaft 35. The exhaust rocker arm 36 is configured
to act on the exhaust valves 25 and 26. The exhaust rocker arm 36 includes a roller
37 and an arm portion 39.
[0057] The arm portion 39 includes a through-hole 364 and the exhaust rocker shaft 35 passes
through the through-hole 364. As illustrated in FIG. 6, the arm portion 39 rotatably
supports the roller 37. The rotational center axis of the roller 37 runs parallel
to the cam axis Ax3. The roller 37 comes into contact with the exhaust cam 146 and
rotates due to the rotation of the exhaust cam 146.
[0058] The pressing member 38 is formed integrally with the arm portion 39. As illustrated
in FIGS. 5 and 6, a first adjuster screw 365 and a second adjuster screw 366 are provided
on the tip end of the pressing member 38. The tip end of the first adjuster screw
365 faces the stem end of the first exhaust valve 25. As illustrated in FIG. 7, the
tip end of the second adjuster screw 366 faces the stem end of the second exhaust
valve 26.
[0059] When the roller 37 is lifted upward by the exhaust cam 146, the exhaust rocker arm
36 swings whereby the pressing member 38 presses the first exhaust valve 25 and the
second exhaust valve 26 downward. As a result, the exhaust port 32 is opened. When
the roller 37 is not pressed upward by the exhaust cam 146, the first exhaust valve
25 and the second exhaust valve 26 are respectively lifted upward by the exhaust valve
springs 251 and 261 and the exhaust port 32 is closed.
[0060] FIG. 8 is a perspective view of the intake rocker unit 34. FIG. 9 is a view of the
intake rocker unit 34 as seen from the direction perpendicular to the cam axis. FIG.
10 is a view of the intake rocker unit 34 as seen from the cam axial direction. As
illustrated in FIGS. 8 to 10, the intake rocker unit 34 includes an intake rocker
shaft 41, a first rocker arm 42, a second rocker arm 43, a pressing member 44 (see
FIG. 6), and a coupling pin 45. While the intake rocker shaft 41 is omitted in FIG.
10, the position of the axis of the intake rocker shaft 41 is indicated by the reference
numeral Ax4.
[0061] The intake rocker shaft 41 is disposed parallel to the camshaft 14. The intake rocker
shaft 41 is supported on the cylinder head 4. Specifically, the intake rocker shaft
41 is supported on the first shaft support portion 21 and the second shaft support
portion 22.
[0062] The first rocker arm 42 is supported on the intake rocker shaft 41 in a swingable
manner centered on the intake rocker shaft 41. The first rocker arm 42 is configured
to act on the intake valves 27 and 28. As illustrated in FIG. 3, the first rocker
arm 42 includes a first attachment portion 421. The first attachment portion 421 is
a hole provided in the first rocker arm 42. The intake rocker shaft 41 passes through
the first attachment portion 421.
[0063] The first rocker arm 42 includes a first coupling hole 422. The first coupling hole
422 is positioned further to the head cover side than the intake rocker shaft 41.
The first coupling hole 422 extends in the cam axis Ax3 direction. The coupling pin
45 is inserted into the first coupling hole 422.
[0064] As illustrated in FIG. 8, the first rocker arm 42 includes a first arm portion 420
and a roller 423. The roller 423 is arranged to come into contact with the first intake
cam portion 144. The roller 423 is rotatably supported by the first arm portion 420.
The roller 423 comes into rolling contact with the first intake cam portion 144. The
roller 423 rotates due to the rotation of the first intake cam portion 144. The rotational
center axis of the roller 423 runs parallel to the cam axis Ax3. The roller 423 comes
into contact with the first intake cam portion 144 whereby the first rocker arm 42
rotates around the axis Ax4 of the intake rocker shaft 41.
[0065] As illustrated in FIG. 7, the second rocker arm 43 is supported in a swingable manner
centered on the intake rocker shaft 41. The second rocker arm 43 is aligned with the
first rocker arm 42 in the cam axis Ax3 direction. The second rocker arm 43 is disposed
on the cam chain chamber 16 side of the first rocker arm 42. As illustrated in FIG.
3, the second rocker arm 43 includes a second attachment portion 431. The second attachment
portion 431 is a hole provided in the second rocker arm 43. The intake rocker shaft
41 passes through the second attachment portion 431.
[0066] The second rocker arm 43 includes a second coupling hole 432. The second coupling
hole 432 is positioned further to the head cover side than the intake rocker shaft
41. The second coupling hole 432 extends in the cam axis Ax3 direction. The second
coupling hole 432 is disposed so as to overlap the first coupling hole 422 in the
cam axis Ax3 direction. Therefore, the coupling pin 45 can be inserted into the second
coupling hole 432 of the second rocker arm 43.
[0067] As illustrated in FIGS. 8 and 10, the second rocker arm 43 includes a boss portion
430, a slipper 433, and a second arm portion 434. The boss portion 430 includes the
abovementioned second attachment portion 431. The second arm portion 434 extends from
the boss portion 430 to the slipper 433. The second arm portion 434 supports the slipper
433. The slipper 433 comes into contact with the second intake cam portion 145 and
is provided in a slidable manner with the second intake cam portion 145. The boss
portion 430, the second arm portion 434, and the slipper 433 are formed integrally.
The slipper 433 comes into slide contact with the second intake cam portion 145 whereby
the second rocker arm 43 rotates around the axis Ax4 of the intake rocker shaft 41.
[0068] As illustrated in FIG. 9, the maximum width of the slipper 433 is greater than the
width of the roller 423 in the axial direction of the intake rocker shaft 41. FIG.
11 is a view of the second rocker arm 43 in FIG. 10 as seen from below. As illustrated
in FIGS. 10 and 11, the slipper 433 includes a contact surface 435 that comes into
contact with the second intake cam portion 145. The maximum width of the contact surface
435 of the slipper 433 is less than the width of the boss portion 430 in the axial
direction of the intake rocker shaft 41. The second arm portion 434 includes a protruding
portion 439 that protrudes from the surface opposite the contact surface 435 in the
slipper 433. The protruding portion 439 extends from the slipper 433 through the second
arm portion 434 to the boss portion 430. The width of the protruding portion 439 is
less than the width of the contact surface 435 in the axial direction of the intake
rocker shaft 41.
[0069] As illustrated in FIG. 10, the second arm portion 434 includes a recessed portion
436. The recessed portion 436 is positioned between the contact surface 435 and the
boss portion 430. More specifically, the recessed portion 436 has a shape that is
recessed toward the head cover side from an imaginary plane Q that extends along the
contact surface 435 as far as the boss portion 430. The recessed portion 436 has a
shape that is recessed toward the head cover side from the contact surface 435 as
seen in the axial direction of the intake rocker shaft 41. The recessed portion 436
has a shape that is curved in a circular arc. The recessed portion 436 extends in
the axial direction of the intake rocker shaft 41. The tip end of the slipper 433
is closer to the axis Ax4 of the intake rocker shaft 41 than the tip end of the roller
423 as seen from the axial direction of the intake rocker shaft 41.
[0070] The contact surface 435 has a curved shape. The curvature radius of the contact surface
435 is greater than the curvature radius of the roller 423. As illustrated in FIG.
10, the contact surface 435 has a shape that is curved around a center of curvature
C1. The center of curvature C1 extends in the axial direction of the intake rocker
shaft 41. The center of curvature C1 is positioned on the head cover side with respect
to the contact surface 435. The center of curvature C1 is positioned so as not to
overlap the intake rocker shaft 41 as seen from the axial direction of the intake
rocker shaft 41. The center of curvature C1 is positioned further to the head cover
side than the axis Ax4 of the intake rocker shaft 41 as seen from the axial direction
of the intake rocker shaft 41.
[0071] The surface 438 opposite the contact surface 435 of the second arm portion 434 has
a shape that is recessed toward the contact surface 435 as seen from the axial direction
of the intake rocker shaft 41. Specifically, the opposing surface 438 includes a first
surface 438a and a second surface 438b. The first surface 438a extends in a direction
that approximately follows the contact surface 435. The second surface 438b extends
in a direction from the first surface 438a toward the head cover side. The opposing
surface 438 has a curved shape between the first surface 438a and the second surface
438b.
[0072] The weight of a portion of the second rocker arm 43 positioned further on the tip
end side of the slipper 433 than an imaginary plane P1, Is less than the weight of
a portion of the first rocker arm 42 positioned further on the tip end side of the
roller 423 than the imaginary plane P1. The imaginary plane P1 extends in the cylinder
axial direction and includes the axis Ax4 of the intake rocker shaft 41.
[0073] FIG. 12 is a view of the second rocker arm 43 as seen from the cam axial direction.
G1 in FIG. 12 indicates the location of the center of gravity of the first rocker
arm 42. G2 indicates the location of the center of gravity of the second rocker arm
43. As illustrated in FIG. 12, the center of gravity G2 of the second rocker arm 43
is closer to the axis Ax4 of the intake rocker shaft 41 than the center of gravity
G1 of the first rocker arm 42.
[0074] The contact surface 435 of the slipper 433 includes a hardened layer 437 formed with
a surface treatment. The hardened layer 437 has a coefficient of friction less than
the base material of the slipper 433 and a hardness greater than the base material
of the slipper 433. The coefficient of friction of the hardened layer 437 is lower
than the coefficient of friction of a chromium nitride coating or of the surface of
a sintered material. In other words, the hardened layer 437 has a high seize resistance.
Specifically, the hardened layer 437 is preferably a carbon-based hard coating, or
more specifically, is preferably a diamond-like carbon (DLC). DLC exhibits self-lubrication,
which is a property of a graphite structure, and therefore has a low coefficient of
friction and a high seize resistance. Moreover, DLC has a diamond structure and therefore
has a higher maximum hardness and higher abrasion resistance than the chromium nitride
coating. The base material is, for example, a chrome molybdenum steel.
[0075] As illustrated in FIG. 6, the pressing member 44 is connected to the first rocker
arm 42. The pressing member 44 is formed integrally with the first rocker arm 42.
A first adjuster screw 441 and a second adjuster screw 442 are provided on the tip
end of the pressing member 44. The tip end of the first adjuster screw 441 faces the
stem end of the first intake valve 27. The tip end of the second adjuster screw 442
faces the stem end of the second intake valve 28. The pressing member 44 rotates around
the axial direction of the intake rocker shaft 41 and presses the first intake valve
27 and the second intake valve 28.
[0076] The intake rocker unit 34 includes an arm urging member 46, a first supporting member
47, and a second supporting member 48. The arm urging member 46 urges the second rocker
arm 43 in the direction for pressing slipper 433 against the camshaft 14. The arm
urging member 46 in the present embodiment is a coil spring and the intake rocker
shaft 41 passes through the arm urging member 46.
[0077] The first supporting member 47 supports one end of the arm urging member 46. The
first supporting member 47 has a pin-like shape and protrudes from the second rocker
arm 43 in the cam axis Ax3 direction.
[0078] The second supporting member 48 supports the other end of the arm urging member 46.
The second supporting member 48 is configured as a curved plate. FIG. 13 is a cross-sectional
view in the vicinity of the second shaft support portion 22 and the arm urging member
46. As illustrated in FIG. 13, a step portion 222 is provided on the second shaft
support portion 22, and the second supporting member 48 is supported on the step portion
222.
[0079] As illustrated in FIG. 3, the coupling pin 45 is movable in the axial direction of
the camshaft 14 and is configured to move between a coupling position and a release
position. The coupling pin 45 is disposed across the first coupling hole 422 and the
second coupling hole 432 in the coupling position. As a result, the coupling pin 45
couples the first rocker arm 42 and the second rocker arm 43. That is, the coupling
pin 45 couples the pressing member 44 to the second rocker arm 43 via the first rocker
arm 42 in the coupling position. As a result, the pressing member 44 swings integrally
with the first rocker arm 42 and the second rocker arm 43.
[0080] The coupling pin 45 is disposed in the first coupling hole 422 and is not disposed
in the second coupling hole 432 of the second rocker arm 43 in the release position.
As a result, the coupling pin 45 does not couple the first rocker arm 42 and the second
rocker arm 43 in the release position. That is, the coupling pin 45 releases the second
rocker arm 43 from the pressing member 44 in the release position. As a result, the
pressing member 44 and the first rocker arm 42 swing independently of the second rocker
arm 43.
[0081] The valve mechanism 13 includes an open/close timing changing unit 49. The open/close
timing changing unit 49 changes the opening and closing timing of the first intake
valve 27 and the second intake valve 28. The open/close timing changing unit 49 is
attached to the head cover 5.
[0082] The open/close timing changing unit 49 is an electromagnetic solenoid and switches
the position of the coupling pin 45 from the release position to the coupling position
by pressing the coupling pin 45 in the axial direction of the camshaft 14 when the
open/close timing changing unit 49 is energized. When the energization of the open/close
timing changing unit 49 is stopped, the position of the coupling pin 45 is returned
from the coupling position to the release position due to the elastic force of a belowmentioned
pin urging member 59.
[0083] The open/close timing changing unit 49 includes a rod 491 for pressing the coupling
pin 45, and a body portion 492 for driving the rod 491. The center axis of the rod
491 runs parallel to the cam axis Ax3. The rod 491 is disposed so as to overlap the
coupling pin 45 as seen from the cam axis Ax3 direction in the swing range of the
coupling pin 45. The rod 491 presses the coupling pin 45 due to being driven by the
body portion 492.
[0084] As illustrated in FIG. 3, the intake rocker unit 34 includes the pin urging member
59. The pin urging member 59 is disposed inside the first coupling hole 422. The pin
urging member 59 urges the coupling pin 45 from the coupling position toward the release
position. Therefore, the coupling pin 45 is held in the release position by the pin
urging member 59 when the coupling pin 45 is not pressed by the open/close timing
changing unit 49. When the coupling pin 45 is pressed by the open/close timing changing
unit 49, the coupling pin 45 resists the urging force of the pin urging member 59
and moves from the release position to the coupling position.
[0085] FIG. 14 illustrates the state while the slipper 433 is being pressed upward by the
second intake cam portion 145 when the coupling pin 45 is positioned in the coupling
position. When the coupling pin 45 is positioned in the coupling position, the first
rocker arm 42 is coupled to the second rocker arm 43 and swings integrally with the
second rocker arm 43. As a result, when the slipper 433 is pressed upward by the second
intake cam portion 145, the second rocker arm 43 swings around the intake rocker shaft
41 whereby the first rocker arm 42 also swings in the direction for lowering the pressing
member 44.
[0086] As a result, the tip end of the first adjuster screw 441 presses the first intake
valve 27 down and the tip end of the second adjuster screw 442 presses the second
intake valve 28 down. Consequently, the first intake valve 27 and the second intake
valve 28 open the intake port 31. In this way, the pressing member 44 presses the
first intake valve 27 and the second intake valve 28 according to the rotation of
the second rocker arm 43 while the coupling pin 45 is in the coupling position. When
the slipper 433 is not being lifted upward by the second intake cam portion 145, the
first intake valve 27 and the second intake valve 28 are lifted upward respectively
by the intake valve springs 271 and 281 and the intake port 31 is closed.
[0087] When the coupling pin 45 is positioned in the release position, the first rocker
arm 42 swings independently of the second rocker arm 43. As a result, when the roller
423 is lifted upward by the first intake cam portion 144, the first rocker arm 42
swings around the intake rocker shaft 41 in the direction for lowering the pressing
member 44.
[0088] As a result, the tip end of the first adjuster screw 441 presses the first intake
valve 27 down and the tip end of the second adjuster screw 442 presses the second
intake valve 28 down. Consequently, the first intake valve 27 and the second intake
valve 28 open the intake port 31. In this way, the pressing member 44 presses the
first intake valve 27 and the second intake valve 28 according to the rotation of
the first rocker arm 42 while the coupling pin 45 is in the release position. When
the roller 423 is not being pressed upward by the first intake cam portion 144, the
first intake valve 27 and the second intake valve 28 are lifted upward respectively
by the intake valve springs 271 and 281 and the intake port 31 is closed.
[0089] The shapes of the first intake cam portion 144 and the second intake cam portion
145 are set such that the second intake cam portion 145 lifts the slipper 433 upward
before the tip end of the first intake cam portion 144 reaches the roller 423. As
a result, when the coupling pin 45 is positioned in the coupling position, the first
rocker arm 42 is acted upon due to the rotation of the second intake cam portion 145
whereby the rotation of the first intake cam portion 144 is not transmitted to the
first rocker arm 42.
[0090] Therefore, when the coupling pin 45 is positioned in the coupling position, the first
intake valve 27 and the second intake valve 28 are opened and closed in response to
the rotation of the second intake cam portion 145. Conversely, when the coupling pin
45 is positioned in the release position, the rotation of the second intake cam portion
145 is not transmitted the first rocker arm 42. As a result, when the coupling pin
45 is positioned in the release position, the first intake valve 27 and the second
intake valve 28 are opened and closed in response to the rotation of the first intake
cam portion 144.
[0091] When the engine rotation speed is in the predetermined low-speed region, the open/close
timing changing unit 49 positions the coupling pin 45 in the release position. For
example, the open/close timing changing unit 49 positions the coupling pin 45 in the
release position when the engine rotation speed is less than a predetermined switching
threshold. As a result, the pressing member 44 presses the first intake valve 27 and
the second intake valve 28 according to the rotation of the first rocker arm 42. Consequently,
the first intake valve 27 and the second intake valve 28 are opened and closed in
response to the rotation of the first intake cam portion 144.
[0092] When the engine rotation speed is in the predetermined high-speed region, the open/close
timing changing unit 49 positions the coupling pin 45 in the coupling position. For
example, the open/close timing changing unit 49 positions the coupling pin 45 in the
coupling position when the engine rotation speed is equal to or greater than a predetermined
switching threshold. As a result, the pressing member 44 presses the first intake
valve 27 and the second intake valve 28 according to the rotation of the second rocker
arm 43. Consequently, the first intake valve 27 and the second intake valve 28 are
opened and closed in response to the rotation of the second intake cam portion 145.
[0093] The following is a detailed description of the structure of the intake rocker shaft
41. FIG. 15 is a perspective view of the intake rocker shaft 41. As illustrated in
FIG. 15, the intake rocker shaft 41 includes a shaft member 51 and a collar member
52. The shaft member 51 and the collar member 52 are separate from each other. The
collar member 52 has a tube-like shape. The shaft member 51 is inserted into a hole
521 of the collar member 52. The shaft member 51 is not fixed to the collar member
52. Therefore, the collar member 52 is able to rotate with respect to the shaft member
51.
[0094] The shaft member 51 includes a first end portion 511 and a second end portion 512.
The first end portion 511 is one end portion in the axial direction of the intake
rocker shaft 41. The second end portion 512 is the other end portion in the axial
direction of the intake rocker shaft 41. The first end portion 511 protrudes one way
from the collar member 52 in the axial direction of the intake rocker shaft 41. The
second end portion 512 protrudes the other way from the collar member 52 in the axial
direction of the intake rocker shaft 41.
[0095] As illustrated in FIG. 3, the first end portion 511 is supported on the first shaft
support portion 21. The first shaft support portion 21 includes a first rocker shaft
hole 212. The first rocker shaft hole 212 is disposed adjacent to the first camshaft
hole 211. The first rocker shaft hole 212 penetrates the first shaft support portion
21 in the cam axis Ax3 direction. The first end portion 511 is inserted into the first
rocker shaft hole 212. The end surface of the first end portion 511 is disposed facing
toward the cam chain chamber 16.
[0096] The second end portion 512 is supported on the second shaft support portion 22. The
second shaft support portion 22 includes a second rocker shaft hole 223. The second
rocker shaft hole 223 is disposed adjacent to the second camshaft hole 221. The second
rocker shaft hole 223 does not penetrate the second shaft support portion 22. However,
the second rocker shaft hole 223 may penetrate the second shaft support portion 22.
The second end portion 512 is inserted into the second rocker shaft hole 223.
[0097] As illustrated in FIG. 8, a boundary B between the first coupling hole 422 of the
first rocker arm 42 and the second coupling hole 432 of the second rocker arm 43 is
closer to the second end portion 512 than an intermediate position M of the interval
L between the first end portion 511 and the second end portion 512. More specifically,
a distance L2 from the boundary B to the second end portion 512 is less than a distance
L1 from the boundary B to the first end portion 511 (L2 < L1).
[0098] As illustrated in FIG. 15, a locking groove 513 is provided on the end surface of
the first end portion 511. A tool is locked to the locking groove 513 whereby the
shaft member 51 can be attached or removed to and from the first rocker shaft hole
212.
[0099] A locking hole 514 is formed in the second end portion 512. The locking hole 514
penetrates the second end portion 512 in the direction perpendicular to the axis of
the shaft member 51. As illustrated in FIG. 5, a hole 224 which extends perpendicular
to the axial direction of the second rocker shaft hole 223 is provided in the second
shaft support portion 22. The hole 224 opens on the upper surface of the second shaft
support portion 22. A fastening member 53 illustrated in FIG. 6 is inserted into the
hole 224 of the second shaft support portion 22 and the locking hole 514 of the second
end portion 512 whereby the shaft member 51 is locked to the second shaft support
portion 22.
[0100] The collar member 52 is separate from the shaft member 51. The collar member 52 is
disposed between the first end portion 511 and the second end portion 512 in the axial
direction of the intake rocker shaft 41. The collar member 52 is disposed between
the first shaft support portion 21 and the second shaft support portion 22. The first
rocker arm 42 and the second rocker arm 43 are attached to the collar member 52. That
is, the first attachment portion 421 of the first rocker arm 42 and the second attachment
portion 431 of the second rocker arm 43 are inserted into the collar member 52. The
arm urging member 46 and the second supporting member 48 are also attached to the
collar member 52.
[0101] The outer diameter of the collar member 52 is larger than the outer diameter of the
shaft member 51. The outer diameter of the collar member 52 is larger than the outer
diameter of the exhaust rocker shaft 35. The outer diameter of the collar member 52
is larger than the outer diameter of the first end portion 511 and larger than the
outer diameter of the second end portion 512. The inner diameter of the first rocker
shaft hole 212 is smaller than the outer diameter of the collar member 52. The inner
diameter of the second rocker shaft hole 223 is smaller than the outer diameter of
the collar member 52.
[0102] The roller 423 is used in the first rocker arm 42 for low speeds in the engine 1
according to the present embodiment as explained above. Furthermore, the slipper 433
is used in the second rocker arm 43 for high speeds. The weight of the slipper 433
and the portion supporting the slipper 433 is less than the weight of the roller 423
and the portion supporting the roller 423. Consequently, the equivalent inertia weight
of the second rocker arm 43 can be reduced. Therefore, by using the slipper 433 in
the second rocker arm 43 for high speeds, the effect of the equivalent inertia weight
of the second rocker arm 43 when the engine rotation speed is in a high-speed region
is smaller in comparison to when a roller is used in the second rocker arm 43 is for
high speeds. As a result, the upper limit of the engine rotation speed can be increased.
[0103] FIG. 16 illustrates changes in loss torque with respect to the engine rotation speed
when the roller 423 is used and when the slipper 433 is used in a rocker arm. The
loss torque indicates the size of the output torque of the engine 1 lost in the rocker
arm. In FIG. 16, L_roller indicates a case when the roller 423 is used in the rocker
arm. L_slipper indicates a case when the slipper 433 is used in the rocker arm. As
illustrated in FIG. 16, the loss torque when the slipper 433 is used is greater than
the loss torque when the roller 423 is used.
[0104] However, because the frictional speed of the slipper 433 with respect to the camshaft
14 in the high-speed region of the engine rotation speed is high, a thick oil film
is produced on the contact surface 435 of the slipper 433. As a result, the frictional
resistance between the slipper 433 and the camshaft 14 is reduced in the high-speed
region. Consequently, the difference in loss torque decreases as the engine rotation
speed increases as can be seen in FIG. 16. Therefore, by using the slipper 433 in
the second rocker arm 43 for high speeds, the mechanical loss during high speeds can
be limited while reducing the equivalent inertia weight.
[0105] Conversely, the difference in the loss torque increases in the low-speed region of
the engine rotation speed. Accordingly, by using the roller 423 in the first rocker
arm 42 for low speeds, the frictional resistance of the roller 423 and the camshaft
14 can be decreased. As a result, the mechanical loss can be limited in the low-speed
region. Moreover, because the effect of the equivalent inertia weight is reduced more
in the low-speed region in comparison to the high-speed region, the effect of the
equivalent inertia weight of the second rocker arm 43 can be reduced even when the
roller 423 is used.
[0106] As described above, by using the roller 423 in the first rocker arm 42 for low speeds
and the slipper 433 in the second rocker arm 43 for high speeds, the equivalent inertia
weight can be reduced while limiting the mechanical loss in all regions of the engine
rotation speed.
[0107] Further, the maximum width of the slipper 433 is greater than the width of the roller
423 in the axial direction of the intake rocker shaft 41. As a result, the surface
pressure of the slipper 433 can be limited and the generation of partial contact can
be suppressed.
[0108] Further, the tip end of the slipper 433 is closer to the axis of the exhaust rocker
shaft 35 than the tip end of the roller 423 as seen from the axial direction of the
exhaust rocker shaft 35. That is, the surface pressure of the slipper 433 can be reduced
by making the maximum width of the slipper 433 greater than the width of the roller
423, whereby the need to increase the curvature radius to reduce the surface pressure
is reduced. As a result, the slipper 433 can have a shorter configuration. Consequently,
an increase in the equivalent inertia weight can be suppressed in comparison to when
the length of the slipper 433 is increased and the curvature radius of the slipper
433 is increased. As a result, the upper limit of the engine rotation speed can be
increased.
[0109] Moreover, the slipper 433 includes the hardened layer 437. Consequently, the abrasion
resistance of the slipper 433 can be improved.
[0110] The maximum width of the contact surface 435 of the slipper 433 is less than the
width of the boss portion 430 in the axial direction of the exhaust rocker shaft 35.
As a result, the weight of the slipper 433 can be reduced while limiting the surface
pressure of the slipper 433, and consequently the equivalent inertia weight of the
second rocker arm 43 can be further reduced.
[0111] The weight of the portion of the second rocker arm 43 positioned further toward the
tip end side of the slipper 433 than the imaginary plane P1, is less than the weight
of the portion of the first rocker arm 42 positioned further toward the tip end side
of the roller 423 than the imaginary plane P1. The maximum width of the contact surface
435 of the slipper 433 is less than the width of the boss portion 430 in the axial
direction of the exhaust rocker shaft 35. The width of the protruding portion 439
is less than the width of the contact surface 435 in the axial direction of the exhaust
rocker shaft 35. Moreover, the surface opposite the contact surface 435 of the second
arm portion 434 has a shape that is recessed toward the contact surface 435 as seen
from the axial direction of the exhaust rocker shaft 35. The weights of the slipper
433 and the second arm portion 434 can be further reduced due to the aforementioned
shapes of the slipper 433 and the second arm portion 434. Consequently, the weight
of the slipper 433 side of the second rocker arm 43 is reduced. Consequently, the
equivalent inertia weight of the second rocker arm 43 can be further reduced.
[0112] The second arm portion 434 includes the recessed portion 436 positioned between the
contact surface 435 and the boss portion 430. The weight can be reduced in comparison
to when the contact surface 435 is joined to the boss portion 430, and thus the equivalent
inertia weight of the second rocker arm 43 can be further reduced. Consequently, interference
with tools for machining can be avoided due to the recessed portion 436 when machining
the contact surface 435. As described above, the slipper 433 can be brought closer
to the boss portion 430 by bringing the tip end of the slipper 433 closer to the axis
Ax4 of the intake rocker shaft 41 than the tip end of the roller 423. Due to the formation
of the recessed portion 436 even with the above configuration, tools for machining
are not hindered by the boss portion 430 and the machining (for example, polishing)
of the curved contact surface 435 is possible.
[0113] The second arm portion 434 includes the protruding portion 439. Consequently, the
weight of the second arm portion 434 can be reduced and the stiffness of the second
arm portion 434 can be assured.
[0114] The center of gravity G2 of the second rocker arm 43 is closer to the axis of the
rocker shaft 41 than the center of gravity G1 of the first rocker arm 42. As a result,
the equivalent inertia weight of the second rocker arm 43 can be further reduced.
Consequently, the spring load (urging force) of the arm urging member 46 can be reduced
and wear of the arm urging member 46 can be limited. Moreover, mechanical loss due
to the arm urging member 46 can be limited. Although an embodiment of the present
invention has been described so far, the present invention is not limited to the above
embodiments and various modifications may be made within the scope of the invention,
which is defined by the appended claims.
[0115] The engine is not limited to a water-cooling type single-cylinder engine. For example,
the engine may be an air-cooling type. The engine may be a multi-cylinder engine.
[0116] The number of exhaust valves is not limited to two and may be one or three or more.
The number of intake valves is not limited to two and may be one or three or more.
[0117] While a mechanism for switching the timing for opening and closing the valves with
the open/close timing changing unit 49 is used for the intake valves in the above
embodiment, the switching mechanism may also be used for the exhaust valves. The structure
of the rocker shafts including the shaft member 51 and the collar member 52 may also
be used for the exhaust rocker shafts.
[0118] The collar member 52 may be attached to the shaft member 51 in a manner that does
not allow rotation. The collar member 52 may be omitted.
[0119] The pressing member 44 may be separate from the first rocker arm 42 and the second
rocker arm 43 as illustrated by the first modified example in FIG. 17. For example,
the second rocker arm 43 and the pressing member 44 may be coupled by the coupling
pin 45 when the abovementioned coupling pin 45 is in the coupling position, and the
first rocker arm 42 and the pressing member 44 may be coupled by the coupling pin
45 when the coupling pin 45 is in the release position.
[0120] The coupling pin 45 may be driven by a hydraulic pump (open/ close timing changing
unit). For example, a first oil chamber 42r and an oil path 42m are formed in the
first rocker arm 42 in the second modified example in FIG. 18. Oil in the first oil
chamber 42r can be used to raise and lower the pressure via the oil path 42m. Similarly,
a second oil chamber 44r and an oil path 43m are formed in the second rocker arm 43.
Oil in the second oil chamber 43r can be used to raise and lower the pressure via
the oil path 43m. A pin hole 45r is formed in the pressing member 44. The pin hole
45r communicates with the first oil chamber 42r and the second oil chamber 43r. The
coupling pin 45 is housed in the pin hole 45r. By displacing the coupling pin 45 with
oil pressure in the above configuration, the pressing member 44 can be selectively
coupled to the first rocker arm 42 and the second rocker arm 43.
[0121] Pressing members 44a and 44b may be provided respectively on the first rocker arm
42 and the second rocker arm 43 as illustrated by the third modified example in FIG.
19. That is, a first pressing member 44a may be provided on the first rocker arm 42
and a second pressing member 44b may be provided on the second rocker arm 43. In this
case, the pressing member 44a provided on the first rocker arm 42 may press the first
intake valve 27 according to the rotation of the first rocker arm 42 while the coupling
pin 45 is in the release position. Moreover, the second pressing member 44b provided
on the second rocker arm 43 may press the second intake valve 28 according to the
rotation of the second rocker arm 43 when the coupling pin 45 is in the coupling position.
Industrial Applicability
[0122] According to the present invention, mechanical loss in the low-speed region of the
engine rotation speed is reduced and the upper limit of the engine rotation speed
can be increased.
List of Reference Numerals
[0123]
- 4:
- Cylinder head
- 26:
- Intake valve
- 34:
- Intake rocker unit
- 14:
- Camshaft
- 49:
- Open/close timing changing unit
- 41:
- Intake rocker shaft
- 423:
- Roller
- 44:
- Pressing member
- 42:
- First rocker arm
- 433:
- Slipper
- 43:
- Second rocker arm
- 45:
- Coupling pin
- 435:
- Contact surface
- 430:
- Boss portion
- 434:
- Second arm portion
- 436:
- Recessed portion
- 437:
- Hardened layer
1. A straddle-type vehicle engine (1) comprising:
a cylinder head (4);
a valve (25, 26, 27, 28) attached to the cylinder head (4);
a rocker unit (33, 34) that presses the valve (25, 26, 27, 28) and opens and closes
the valve (25, 26, 27, 28);
a camshaft (14) that drives the rocker unit (33, 34) ; and
an open/close timing changing unit (49) that changes opening and closing timing of
the valve (27, 28),
wherein
the rocker unit (34) includes:
a rocker shaft (41) supported by the cylinder head (4);
a first rocker arm (42) including a roller (423) that comes into contact with the
camshaft (14), and a pressing member (44) pressing the valve (27, 28), first rocker
arm (42) rotating around an axis (Ax4) of the rocker shaft (41) when the roller (423)
comes into contact with the camshaft (14);
a second rocker arm (43) aligned with the first rocker arm (42) in an axial direction
(Ax3) of the camshaft (14), and including a slipper (433) that comes into contact
with the camshaft (14), the second rocker arm (43) rotating around the axis (Ax4)
of the rocker shaft (41) when the slipper (433) comes into contact with the camshaft
(14); and
a coupling pin (45) that moves between a coupling position and a release position
due to the open/close timing changing unit (49), the coupling pin (45) coupling the
second rocker arm (43) to the pressing member (44) in the coupling position and releasing
the second rocker arm (43) from the pressing member (44) in the release position;
and,
when an engine rotation speed is in a predetermined low-speed region, the open/close
timing changing unit (49) positions the coupling pin (45) in the release position
whereby the pressing member (44) presses the valve (27, 28) according to a rotation
of the first rocker arm (42), and
when the engine rotation speed is in a predetermined high-speed region, the open/close
timing changing unit (49) positions the coupling pin (45) in the coupling position
whereby the pressing member (44) presses the valve (27, 28) according to a rotation
of the second rocker arm (43), and
the roller (423) comes into rolling contact with the camshaft (14),
the slipper (433) comes into sliding contact with the camshaft (14),
a tip end of the slipper (433) is closer to the axis of the rocker shaft (41) than
a tip end of the roller (423) as seen from the axial direction of the rocker shaft
(41),
a maximum width of the slipper (433) is greater than a width of the roller (423) in
the axial direction of the rocker shaft (41),
a center of gravity (G2) of the second rocker arm (43) is closer to the axis (Ax4)
of the rocker shaft (41) than a center of gravity (G1) of the first rocker arm (42),
and
the intake rocker unit (34) includes an arm urging member (46) which urges the second
rocker arm (43) in the direction for pressing the slipper (433) against the camshaft
(14).
2. The engine (1) according to claim 1, wherein
the slipper (433) includes a curved contact surface (435) that comes into contact
with the camshaft (14), and
a curvature radius of the contact surface (435) is greater than a curvature radius
of the roller (423).
3. The engine (1) according to claim 1 or 2, wherein
a weight of a portion of the second rocker arm (43) positioned further on the tip
end side of the slipper (433) than an imaginary plane (P1) which includes the axis
(Ax3) of the camshaft (14) and extends in a cylinder axial direction of the cylinder
head (4), is less than a weight of a portion of the first rocker arm (42) positioned
further on the tip end side of the roller (423) than the imaginary plane (P1).
4. The engine (1) according to any one of claims 1 to 3, wherein
the second rocker arm (43) includes
a boss portion (430) including a hole through which the rocker shaft (41) passes,
and
an arm portion (434) extending from the boss portion (430) to the slipper (433), and
the slipper (433) includes a contact surface (435) that comes into contact with the
camshaft (14).
5. The engine (1) according to claim 4, wherein
a maximum width of the contact surface (435) of the slipper (433) is less than a width
of the boss portion (430) in the axial direction (Ax4) of the rocker shaft (41).
6. The engine (1) according to claims 4 or 5, wherein
the arm portion (434) includes a recessed portion (436) positioned between the contact
surface (435) and the boss portion (430).
7. The engine (1) according to any one of claims 4 to 6, wherein
the arm portion (434) includes a protruding portion (439) extending from the slipper
(433) to the boss portion (430) and protrudes from a surface (438) opposite the contact
surface (435) of the slipper (433).
8. The engine (1) according to any one of claims 4 to 7, wherein
a width of the protruding portion (439) is less than the width of the contact surface
(435) in the axial direction (Ax4) of the rocker shaft (41).
9. The engine (1) according to any one of claims 4 to 8, wherein
the surface (438) of the arm portion (434) opposite the contact surface (435) has
a shape that is recessed toward the contact surface (435) side as seen from the axial
direction (Ax4) of the rocker shaft (41).
10. The engine (1) according to any one of claims 1 to 9, wherein
the slipper (433) includes a hardened layer (437) that comes into contact with the
camshaft (14), and
the hardened layer (437) has a coefficient of friction less than that of a base material
of the slipper (433) and a hardness that is greater than that of the base material
of the slipper (433).
1. Motor (1) eines Grätschsitzfahrzeuges, umfassend:
einen Zylinderkopf (4);
ein Ventil (25, 26, 27, 28), das an dem Zylinderkopf (4) befestigt ist;
eine Kipphebeleinheit (33, 34), die auf das Ventil (25, 26, 27, 28) drückt und das
Ventil (25, 26, 27, 28) öffnet und schließt;
eine Nockenwelle (14), die die Kipphebeleinheit (33, 34) antreibt; und
eine Öffnungs-/Schließzeitänderungseinheit (49), die die Öffnungs- und Schließzeit
des Ventils (27, 28) ändert,
wobei
die Kipphebeleinheit (34) umfasst:
eine Kipphebelwelle (41), die von dem Zylinderkopf (4) getragen wird;
einen ersten Kipphebel (42) mit einer Rolle (423), die in Kontakt mit der Nockenwelle
(14) kommt, und einem Druckelement (44), das auf das Ventil (27, 28) drückt, wobei
sich der erste Kipphebel (42) um eine Achse (Ax4) der Kipphebelwelle (41) dreht, wenn
die Rolle (423) in Kontakt mit der Nockenwelle (14) kommt;
einen zweiten Kipphebel (43), der mit dem ersten Kipphebel (42) in einer axialen Richtung
(Ax3) der Nockenwelle (14) ausgerichtet ist und ein Gleitstück (433) aufweist, das
mit der Nockenwelle (14) in Kontakt kommt, wobei sich der zweite Kipphebel (43) um
die Achse (Ax4) der Kipphebelwelle (41) dreht, wenn das Gleitstück (433) mit der Nockenwelle
(14) in Kontakt kommt; und
einen Kupplungsstift (45), der sich zwischen einer Kupplungsposition und einer Freigabeposition
aufgrund der Öffnungs-/Schließzeitänderungseinheit (49) bewegt, wobei der Kupplungsstift
(45) den zweiten Kipphebel (43) mit dem Druckelement (44) in der Kupplungsposition
koppelt und den zweiten Kipphebel (43) von dem Druckelement (44) in der Freigabeposition
freigibt; und wobei,
wenn sich eine Motordrehzahl in einem vorbestimmten Niedrigdrehzahlbereich befindet,
die Öffnungs-/Schließzeitänderungseinheit (49) den Kupplungsstift (45) in der Freigabeposition
positioniert, wodurch das Druckelement (44) das Ventil (27, 28) entsprechend einer
Drehung des ersten Kipphebels (42) drückt, und
wenn sich die Motordrehzahl in einem vorbestimmten Hochgeschwindigkeitsbereich befindet,
die Öffnungs-/Schließzeitänderungseinheit (49) den Kupplungsstift (45) in der Kupplungsposition
positioniert, wodurch das Druckelement (44) das Ventil (27, 28) entsprechend einer
Drehung des zweiten Kipphebels (43) drückt, und
die Rolle (423) in Rollkontakt mit der Nockenwelle (14) kommt,
das Gleitstück (433) in Gleitkontakt mit der Nockenwelle (14) kommt,
ein vorderes Ende des Gleitstücks (433) näher an der Achse der Kipphebelwelle (41)
liegt als ein vorderes Ende der Rolle (423), gesehen von der axialen Richtung der
Kipphebelwelle (41),
eine maximale Breite des Gleitstücks (433) größer ist als eine Breite der Rolle (423)
in der axialen Richtung der Kipphebelwelle (41),
ein Schwerpunkt (G2) des zweiten Kipphebels (43) näher an der Achse (Ax4) der Kipphebelwelle
(41) liegt als ein Schwerpunkt (G1) des ersten Kipphebels (42), und
die Kipphebeleinheit (34) ein Armdruckelement (46) umfasst, das den zweiten Kipphebel
(43) in die Richtung drückt, um das Gleitstück (433) gegen die Nockenwelle (14) zu
drücken.
2. Motor (1) nach Anspruch 1, wobei
das Gleitstück (433) eine gekrümmte Kontaktfläche (435) aufweist, die mit der Nockenwelle
(14) in Kontakt kommt, und
ein Krümmungsradius der Kontaktfläche (435) größer ist als ein Krümmungsradius der
Rolle (423).
3. Motor (1) nach Anspruch 1 oder 2, wobei
ein Gewicht eines Abschnitts des zweiten Kipphebels (43), der näher an der Spitzenendseite
des Gleitstücks (433) positioniert ist als eine imaginäre Ebene (P1), die die Achse
(Ax3) der Nockenwelle (14) einschließt und sich in einer axialen Zylinderrichtung
des Zylinderkopfs (4) erstreckt, geringer ist als ein Gewicht eines Abschnitts des
ersten Kipphebels (42), der näher an der Spitzenendseite der Rolle (423) positioniert
ist als die imaginäre Ebene (P1).
4. Motor (1) nach einem der Ansprüche 1 bis 3, wobei der zweite Kipphebel (43) umfasst:
einen Nabenabschnitt (430), der ein Loch enthält, durch das die Kipphebelwelle (41)
verläuft, und
einen Armabschnitt (434), der sich von dem Nabenabschnitt (430) zu dem Gleitstück
(433) erstreckt, und
das Gleitstück (433) eine Kontaktfläche (435) aufweist, die mit der Nockenwelle (14)
in Kontakt kommt.
5. Motor (1) nach Anspruch 4, wobei eine maximale Breite der Kontaktfläche (435) des
Gleitstücks (433) kleiner ist als eine Breite des Nabenabschnitts (430) in der axialen
Richtung (Ax4) der Kipphebelwelle (41).
6. Motor (1) nach Anspruch 4 oder 5, wobei der Armabschnitt (434) einen vertieften Abschnitt
(436) aufweist, der zwischen der Kontaktfläche (435) und dem Nabenabschnitt (430)
angeordnet ist.
7. Motor (1) nach einem der Ansprüche 4 bis 6, wobei der Armabschnitt (434) einen Vorsprungabschnitt
(439) aufweist, der sich von dem Gleitstück (433) zu dem Nabenabschnitt (430) erstreckt
und von einer Fläche (438) gegenüber der Kontaktfläche (435) des Gleitstücks (433)
vorsteht.
8. Motor (1) nach einem der Ansprüche 4 bis 7, wobei eine Breite des Vorsprungabschnitts
(439) kleiner ist als die Breite der Kontaktfläche (435) in der axialen Richtung (Ax4)
der Kipphebelwelle (41).
9. Motor (1) nach einem der Ansprüche 4 bis 8, wobei die Oberfläche (438) des Armabschnitts
(434), die der Kontaktfläche (435) gegenüberliegt, eine Form aufweist, die von der
axialen Richtung (Ax4) der Kipphebelwelle (41) aus gesehen zur Seite der Kontaktfläche
(435) hin vertieft ist.
10. Motor (1) nach einem der Ansprüche 1 bis 9, wobei
das Gleitstück (433) eine gehärtete Schicht (437) aufweist, die mit der Nockenwelle
(14) in Kontakt kommt, und
die gehärtete Schicht (437) einen Reibungskoeffizienten, der kleiner als der eines
Basismaterials des Gleitstücks (433) ist, und eine Härte, die größer als die des Basismaterials
des Gleitstücks (433) ist, aufweist.
1. Moteur (1) pour véhicule de type à enfourcher, comprenant :
une culasse (4) ;
une soupape (25, 26, 27, 28) fixée sur la culasse (4) ;
un bloc culbuteur (33, 34) qui appuie sur la soupape (25, 26, 27, 28) et ouvre et
ferme la soupape (25, 26, 27, 28) ;
un arbre à cames (14) qui entraîne le bloc culbuteur (33, 34) ; et
une unité (49) de modification de la synchronisation d'ouverture/fermeture qui modifie
la synchronisation d'ouverture et de fermeture de la soupape (27, 28),
dans lequel
le bloc culbuteur (34) comprend :
une rampe de culbuteurs (41) supportée par la culasse (4) ;
un premier culbuteur (42) comprenant un galet (423) qui entre en contact avec l'arbre
à cames (14) et un élément poussoir (44) qui appuie sur la soupape (27, 28), le premier
culbuteur (42) tournant autour d'un axe (Ax4) de la rampe de culbuteurs (41) lorsque
le galet (423) entre en contact avec l'arbre à cames (14) ;
un second culbuteur (43) aligné avec le premier culbuteur (42) dans une direction
axiale (Ax3) de l'arbre à cames (14) et comprenant un patin (433) qui entre en contact
avec l'arbre à cames (14), le second culbuteur (43) tournant autour de l'axe (Ax4)
de la rampe de culbuteurs (41) lorsque le patin (433) entre en contact avec l'arbre
à cames (14) ; et
une tige de couplage (45) qui est mobile entre une position de couplage et une position
de désolidarisation sous l'effet de l'unité (49) de modification de la synchronisation
d'ouverture/fermeture, la tige de couplage (45) couplant le second culbuteur (43)
à l'élément poussoir (44) dans la position de couplage et désolidarisant le second
culbuteur (43) de l'élément poussoir (44) dans la position de désolidarisation ; et
lorsqu'une vitesse de rotation de moteur se situe dans une zone de faible vitesse
prédéterminée, l'unité (49) de modification de la synchronisation d'ouverture/fermeture
positionne la tige de couplage (45) dans la position de désolidarisation, grâce à
quoi l'élément poussoir (44) appuie sur la soupape (27, 28) en fonction d'une rotation
du premier culbuteur (42), et
lorsque la vitesse de rotation de moteur se situe dans une zone de vitesse élevée
prédéterminée, l'unité (49) de modification de la synchronisation d'ouverture/fermeture
positionne la tige de couplage (45) dans la position de couplage, grâce à quoi l'élément
poussoir (44) appuie sur la soupape (27, 28) en fonction d'une rotation du second
culbuteur (43), et
le galet (423) entre en contact roulant avec l'arbre à cames (14),
le patin (433) entre en contact glissant avec l'arbre à cames (14),
une extrémité de bout du patin (433) est plus proche de l'axe de la rampe de culbuteurs
(41) qu'une extrémité de bout du galet (423), en vue de la direction axiale de la
rampe de culbuteurs (41),
une largeur maximale du patin (433) est supérieure à une largeur du galet (423) dans
la direction axiale de la rampe de culbuteurs (41),
un centre de gravité (G2) du second culbuteur (43) est plus proche de l'axe (Ax4)
de la rampe de culbuteurs (41) qu'un centre de gravité (G1) du premier culbuteur (42),
et
le bloc culbuteur côté admission (34) comprend un élément de poussée de culbuteur
(46) qui pousse le second culbuteur (43) dans la direction permettant d'appuyer le
patin (433) contre l'arbre à cames (14).
2. Moteur (1) selon la revendication 1, dans lequel
le patin (433) est pourvu d'une surface de contact (435) incurvée qui entre en contact
avec l'arbre à cames (14), et
un rayon de courbure de la surface de contact (435) est supérieur à un rayon de courbure
du galet (423).
3. Moteur (1) selon la revendication 1 ou 2, dans lequel
la masse d'une partie du second culbuteur (43) placée plus loin, sur le côté de l'extrémité
de bout du patin (430), qu'un plan imaginaire (P1) qui inclut l'axe (Ax3) de l'arbre
à cames (14) et s'étend dans une direction axiale de cylindre de la culasse (4) est
inférieure à la masse d'une partie du premier culbuteur (42) placée plus loin, sur
le côté de l'extrémité de bout du galet (423), que le plan imaginaire (P1).
4. Moteur (1) selon l'une quelconque des revendications 1 à 3, dans lequel
le second culbuteur (43) comprend
une partie formant protubérance (430) pourvue d'un trou à travers lequel passe la
rampe de culbuteurs (41), et
une partie formant bras (434) qui s'étend de la partie formant protubérance (430)
vers le patin (433), et
le patin (433) inclut une surface de contact (435) qui entre en contact avec l'arbre
à cames (14).
5. Moteur (1) selon la revendication 4, dans lequel
une largeur maximale de la surface de contact (435) du patin (433) est inférieure
à une largeur de la partie formant protubérance (430) dans la direction axiale (Ax4)
de la rampe de culbuteurs (41).
6. Moteur (1) selon les revendications 4 ou 5, dans lequel
la partie formant bras (434) inclut une partie évidée (436) positionnée entre la surface
de contact (435) et la partie formant protubérance (430).
7. Moteur (1) selon l'une quelconque des revendications 4 à 6, dans lequel
la partie formant bras (434) comprend une partie saillante (439) s'étendant du patin
(433) vers la partie formant protubérance (430) et avance depuis une surface (438)
opposée à la surface de contact (435) du patin (433).
8. Moteur (1) selon l'une quelconque des revendications 4 à 7, dans lequel
une largeur de la partie saillante (439) est inférieure à la largeur de la surface
de contact (435) dans la direction axiale (Ax4) de la rampe de culbuteurs (41).
9. Moteur (1) selon l'une quelconque des revendications 4 à 8, dans lequel
la surface (438) de la partie formant bras (434) opposée à la surface de contact (435)
a une forme qui est évidée en direction du côté de la surface de contact (435), en
vue de la direction axiale (Ax4) de la rampe de culbuteurs (41).
10. Moteur (1) selon l'une quelconque des revendications 1 à 9, dans lequel
le patin (433) comprend une couche trempée (437) qui entre en contact avec l'arbre
à cames (14), et
la couche trempée (437) a un coefficient de frottement inférieur à celui d'un matériau
de base du patin (433) et une dureté qui est supérieure à celle du matériau de base
du patin (433).