U.S. patent application number 09/741068 was filed with the patent office on 2001-06-21 for variable-valve-actuation apparatus for internal combustion engine.
This patent application is currently assigned to UNISIA JECS CORPORATION. Invention is credited to Hara, Seinosuke, Nakamura, Makoto, Takeda, Keisuke.
Application Number | 20010003973 09/741068 |
Document ID | / |
Family ID | 18475862 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010003973 |
Kind Code |
A1 |
Nakamura, Makoto ; et
al. |
June 21, 2001 |
Variable-valve-actuation apparatus for internal combustion
engine
Abstract
A VVA apparatus includes an operating mechanism that changes a
valve-lift amount, and a microcomputer-based controller that
controls the operating mechanism to change the valve-lift amount in
accordance with engine operating conditions. A first portion of the
valve-lift amount between a high lift and a low lift is changed
continuously, and a second portion of the valve-lift amount between
the low lift and zero lift is changed with one of the low lift and
zero lift selected.
Inventors: |
Nakamura, Makoto; (Kanagawa,
JP) ; Hara, Seinosuke; (Kanagawa, JP) ;
Takeda, Keisuke; (Kanagawa, JP) |
Correspondence
Address: |
Foley & Lardner
3000 K Street, N.W.
P.O. Box 25696
Washington
DC
20007-8696
US
|
Assignee: |
UNISIA JECS CORPORATION
|
Family ID: |
18475862 |
Appl. No.: |
09/741068 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
123/90.16 ;
123/90.17 |
Current CPC
Class: |
F01L 13/0026 20130101;
F01L 13/0021 20130101; F01L 2305/00 20200501 |
Class at
Publication: |
123/90.16 ;
123/90.17 |
International
Class: |
F01L 001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 1999 |
JP |
11-362086 |
Claims
What is claimed is:
1. A variable-valve-actuation (VVA) apparatus for an internal
combustion engine with valves, comprising: an operating mechanism
that changes a lift amount of the valves; and a microcomputer-based
controller that controls said operating mechanism to change said
lift amount in accordance with operating conditions of the engine,
a first portion of said lift amount between a predetermined high
value and a predetermined low value being changed continuously, a
second portion of said lift amount between said predetermined low
value and zero being changed with one of said predetermined low
value and zero selected.
2. The VVA apparatus as claimed in claim 1, wherein said
predetermined low value of said lift amount is more than twice as
large as a clearance of the valves.
3. The VVA apparatus as claimed in claim 1, wherein said controller
is provided with a map used for controlling said lift amount, said
map comprising first and second areas and a boundary between said
first and second areas.
4. The VVA apparatus as claimed in claim 3, wherein said first area
of said map is such that said lift amount of the valves is fixed to
zero, and said second area of said map is such that said lift
amount of the valves is changed continuously from said
predetermined low value to said predetermined high value.
5. The VVA apparatus as claimed in claim 3, wherein said first area
of said map is such that said lift amount of particular valves is
fixed to said predetermined low value and said lift amount of the
other valves is fixed to said predetermined low value, and said
second area of said map is such that said lift amount of all valves
is changed continuously from said predetermined low value to said
predetermined high value.
6. The VVA apparatus as claimed in claim 5, wherein on said
boundary between said first and second areas, output torque of the
engine when said lift amount of said all valves is fixed to said
predetermined low value is approximately equal to that of the
engine when said lift amount of said particular valves is fixed to
zero and said lift amount of said the other valves is fixed to said
predetermined low value.
7. The VVA apparatus as claimed in claim 5, wherein on said
boundary between said first and second areas, output torque of the
engine when said lift amount of said all valves is fixed to said
predetermined low value is greater than that of the engine when
said lift amount of said particular valves is fixed to zero and
said lift amount of said the other valves is fixed to said
predetermined low value.
8. The VVA apparatus as claimed in claim 5, wherein in a
low-rotation and high-load range of the engine, output torque of
the engine when said lift amount of said particular valves is fixed
to zero and said lift amount of said the other valves is fixed to
said predetermined low value is greater than that of the engine
when said lift amount of said all valves is fixed to said
predetermined high value.
9. The VVA apparatus as claimed in claim 3, wherein said boundary
between said first and second areas is moved in accordance with
said operating conditions of the engine.
10. The VVA apparatus as claimed in claim 9, wherein said boundary
between said first and second areas is moved to a side of said
predetermined high value when a temperature of air inhaled into a
combustion chamber is lower than a predetermined value.
11. The VVA apparatus as claimed in claim 9, wherein said
controller controls said boundary between said first and second
areas and said predetermined low value on said boundary in
accordance with a result of learning.
12. The VVA apparatus as claimed in claim 1, wherein said operating
mechanism comprises a driving shaft rotated by a crankshaft of the
engine and provided with a crank cam at an outer periphery thereof,
a valve operating (VO) cam coming in slide contact with a top face
of a valve lifter disposed at an upper end of each valve to open
and close it, a transmission mechanism connected between said crank
cam and said VO cam, and an alteration mechanism for variably
controlling an operation position of said transmission mechanism to
change a position of contact of said VO cam with respect to said
top face of said valve lifter.
13. A variable-valve-actuation (VVA) apparatus for an internal
combustion engine with valves, comprising: an operating mechanism
that changes a lift amount of the valves, said operating mechanism
comprising a driving shaft rotated by a crankshaft of the engine
and provided with a crank cam at a outer periphery thereof, a valve
operating (VO) cam coming in slide contact with a top face of a
valve lifter disposed at an upper end of each valve to open and
close it, a transmission mechanism connected between said crank cam
and said VO cam, and an alteration mechanism for variably
controlling an operation position of said transmission mechanism to
change a position of contact of said VO cam with respect to said
top face of said valve lifter; and a microcomputer-based controller
that controls said operating mechanism to change said lift amount
in accordance with operating conditions of the engine, a first
portion of said lift amount between a predetermined high value and
a predetermined low value being changed continuously, a second
portion of said lift amount between said predetermined low value
and zero being changed with one of said predetermined low value and
zero selected.
14. The VVA apparatus as claimed in claim 13, wherein said
predetermined low value of said lift amount is more than twice as
large as a clearance of the valves.
15. The VVA apparatus as claimed in claim 13, wherein said
controller is provided with a map used for controlling said lift
amount, said map comprising first and second areas and a boundary
between said first and second areas.
16. The VVA apparatus as claimed in claim 15, wherein said first
area of said map is such that said lift amount of the valves is
fixed to zero, and said second area of said map is such that said
lift amount of the valves is changed continuously from said
predetermined low value to said predetermined high value.
17. The VVA apparatus as claimed in claim 15, wherein said first
area of said map is such that said lift amount of particular valves
is fixed to said predetermined low value and said lift amount of
the other valves is fixed to said predetermined low value, and said
second area of said map is such that said lift amount of all valves
is changed continuously from said predetermined low value to said
predetermined high value.
18. The VVA apparatus as claimed in claim 17, wherein on said
boundary between said first and second areas, output torque of the
engine when said lift amount of said all valves is fixed to said
predetermined low value is approximately equal to that of the
engine when said lift amount of said particular valves is fixed to
zero and said lift amount of said the other valves is fixed to said
predetermined low value.
19. The VVA apparatus as claimed in claim 17, wherein on said
boundary between said first and second areas, output torque of the
engine when said lift amount of said all valves is fixed to said
predetermined low value is greater than that of the engine when
said lift amount of said particular valves is fixed to zero and
said lift amount of said the other valves is fixed to said
predetermined low value.
20. The VVA apparatus as claimed in claim 17, wherein in a
low-rotation and high-load range of the engine, output torque of
the engine when said lift amount of said particular valves is fixed
to zero and said lift amount of said the other valves is fixed to
said predetermined low value is greater than that of the engine
when said lift amount of said all valves is fixed to said
predetermined high value.
21. The VVA apparatus as claimed in claim 15, wherein said boundary
between said first and second areas is moved in accordance with
said operating conditions of the engine.
22. The VVA apparatus as claimed in claim 21, wherein said boundary
between said first and second areas is moved to a side of said
predetermined high value when a temperature of air inhaled into a
combustion chamber is lower than a predetermined value.
23. The VVA apparatus as claimed in claim 21, wherein said
controller controls said boundary between said first and second
areas and said predetermined low value on said boundary in
accordance with a result of learning.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a variable-valve-actuation
(VVA) apparatus for an internal combustion engine that can vary,
particularly, the lift amount of valves such as an intake valve and
exhaust valve in accordance with engine operating conditions.
[0002] As disclosed in U.S. Pat. No. 6,029,618 issued Feb. 29, 2000
to Hara et al., the VVA apparatus typically comprises a crank cam
arranged at the outer periphery of a driving shaft that rotates in
synchronism with a crankshaft and having an axis eccentric to an
axis of the driving shaft, and a valve operating (VO) cam to which
torque of the crank cam is transmitted through a transmission
mechanism to have a cam face coming in slide contact with the top
face of a valve lifter arranged at the upper end of an intake valve
for opening and closing operation thereof.
[0003] The transmission mechanism includes a rocker arm disposed
above the VO cam and swingably supported to a control shaft, a
crank arm having an annular base engaged with the outer peripheral
surface of the crank cam and an extension rotatably connected to a
first arm of the rocker arm through a pin, and a link rod having a
first end rotatably connected to a second arm of the rocker arm
through a pin and a second end rotatably connected to an end of the
VO cam through a pin.
[0004] Moreover, fixed on the outer peripheral surface of the
control shaft is a control cam having an axis eccentric to an axis
of the control shaft by a predetermined amount and rotatably fitted
in a support hole formed substantially in the center of the rocker
arm. The control cam changes a rocking fulcrum of the rocker arm in
accordance with the rotated position to change the position of
contact of the cam face of the VO cam with respect to the top face
of the valve lifter, carrying out variable control of the lift
amount of the intake valve.
[0005] Specifically, when the engine operating conditions are in
the low-rotation and low-load range, for example, in order to urge
an actuator to rotate the control shaft clockwise, for example, for
rotation of the control cam in the same direction, the rocking
fulcrum of the rocker arm is moved to a certain position. Then,
pivotal points of the rocker arm with the crank arm and link rod
are moved leftward to draw up an end or cam nose of the VO cam,
moving the position of contact of the VO cam with respect to the
top face of the valve lifter to a base portion of the VO cam. Thus,
the intake valve is controlled to have zero lift in the valve-lift
characteristic, achieving the valve-stop state so called.
[0006] On the other hand, when the engine operating conditions are
in the high-rotation and high-load range, the actuator rotates the
control cam counterclockwise from the certain position through the
control shaft, moving the rocking fulcrum of the rocker arm
downward. Then, the cam nose of the VO cam is pushed downward by
the link rod, etc. to move the position of contact of the VO cam
with respect to the top face of the valve lifter to a lift top
portion of the VO cam. Thus, the intake valve is controlled to have
greater lift in the valve-lift characteristic.
[0007] Therefore, outstanding engine performance can be obtained,
e.g. improvement in fuel consumption by valve stop in the engine
low-rotation and low-load range and increase in engine output, etc.
by improved intake-air charging efficiency in the engine
high-rotation and high-load range. It is noted that an improvement
in fuel consumption by valve stop is achieved by stopping actuation
of the intake and exhaust valves of particular cylinders, i.e.
carrying out reduced cylinder operation so called, or actuation of
one of the two intake valves to produce swirl in a combustion
chamber.
[0008] However, the VVA apparatus generally have dimensional errors
of components produced upon manufacture thereof, which are
naturally included in the respective cylinders to which the
apparatus are mounted and have different magnitudes. The lift
amount of the valves variably controlled by the VVA apparatus is
not seriously affected by a dimensional error of the components in
the region of medium lift to high lift since the engine can be in
high rotation therein. It is, however, greatly affected by a
dimensional error of the components in the region of low lift,
particularly, very low lift since the engine can be in low rotation
therein, where engine rotation is apt to vary.
[0009] Moreover, variation in the machining accuracy of components
of the VVA apparatus results in variation in the lift amount of the
valves, which are the greatest in the region of very low lift with
respect to in the region of medium lift to high lift. Thus, during
engine operation in the very low lift area, the mixture charging
efficiency and gas flow conditions in the combustion chamber may be
apt to vary between the cylinders, resulting in unstable engine
rotation and lowered engine performance.
[0010] This causes need of enhanced machining accuracy of the
components of the VVA apparatus, raising an inevitable technical
challenge of increased manufacturing cost.
SUMMARY OF THE INVENTION
[0011] It is, therefore, an object of the present invention to
provide a VVA apparatus for an internal combustion engine, which
contributes to an improvement in the engine performance without any
increase in manufacturing cost.
[0012] The present invention provides generally a
variable-valve-actuation (VVA) apparatus for an internal combustion
engine with valves, comprising:
[0013] an operating mechanism that changes a lift amount of the
valves; and
[0014] a microcomputer-based controller that controls said
operating mechanism to change said lift amount in accordance with
operating conditions of the engine, a first portion of said lift
amount between a predetermined high value and a predetermined low
value being changed continuously, a second portion of said lift
amount between said predetermined low value and zero being changed
with one of said predetermined low value and zero selected.
[0015] One aspect of the present invention is to provide a
variable-valve-actuation (VVA) apparatus for an internal combustion
engine with valves, comprising:
[0016] an operating mechanism that changes a lift amount of the
valves, said operating mechanism comprising a driving shaft rotated
by a crankshaft of the engine and provided with a crank cam at a
outer periphery thereof, a valve operating (VO) cam coming in slide
contact with a top face of a valve lifter disposed at an upper end
of each valve to open and close it, a transmission mechanism
connected between said crank cam and said VO cam, and an alteration
mechanism for variably controlling an operation position of said
transmission mechanism to change a position of contact of said VO
cam with respect to said top face of said valve lifter; and
[0017] a microcomputer-based controller that controls said
operating mechanism to change said lift amount in accordance with
operating conditions of the engine, a first portion of said lift
amount between a predetermined high value and a predetermined low
value being changed continuously, a second portion of said lift
amount between said predetermined low value and zero being changed
with one of said predetermined low value and zero selected.
[0018] The other objects and features of the present invention will
become understood from the following description with reference to
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a sectional view showing a first embodiment of a
VVA apparatus for an internal combustion engine according to the
present invention;
[0020] FIG. 2 is a perspective view showing the VVA apparatus;
[0021] FIG. 3 is a view similar to FIG. 2, showing a crank cam;
[0022] FIG. 4 is a fragmentary longitudinal section showing the VVA
apparatus;
[0023] FIG. 5 is a graph illustrating the profile characteristics
of a cam face of a VO cam;
[0024] FIG. 6 is a fragmentary perspective view showing a needle
bearing;
[0025] FIGS. 7A-7B are schematic drawings explaining operation of
the VO cam and an intake valve when the valve has zero lift;
[0026] FIG. 8A is a view similar to FIGS. 7A-7B, showing the intake
valve open when the valve has low lift;
[0027] FIG. 8B is a view similar to FIG. 8B, showing the intake
valve closed;
[0028] FIG. 9A is a view similar to FIG. 8B, showing the intake
valve open when the valve has high lift;
[0029] FIG. 9B is a view similar to FIG. 9A, showing the intake
valve closed;
[0030] FIG. 10 is a view similar to FIG. 5, illustrating the
valve-lift characteristics;
[0031] FIG. 11 is a lift control map illustrating the range from an
area of zero lift fixed to a continuously variable area of low lift
to high lift;
[0032] FIG. 12 is a view similar to FIG. 10, illustrating the
relationship between the valve-lift amount and the lift variation
ratio of the apparatus;
[0033] FIG. 13 is a view similar to FIG. 12, showing a second
embodiment of the present invention;
[0034] FIG. 14 is a view similar to FIG. 13, showing a third
embodiment of the present invention;
[0035] FIG. 15 is a view similar to FIG. 14, showing a fourth
embodiment of the present invention;
[0036] FIG. 16 is a flowchart illustrating a fifth embodiment of
the present invention;
[0037] FIG. 17 is a view similar to FIG. 16, illustrating a sixth
embodiment of the present invention; and
[0038] FIG. 18 is a view similar to FIG. 15, showing a seventh
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] Referring to the drawings, a description will be made with
regard to a VVA apparatus for an internal combustion engine
embodying the present invention. In embodiments of the present
invention, the VVA apparatus is applied to a multiple cylinder
engine with two intake valves and two exhaust valves per cylinder,
and operates with two intake valves and two exhaust valves of each
particular cylinder. A description is mainly provided with respect
to the intake valves, since the structure is the same in the intake
and exhaust valves.
[0040] Referring to FIGS. 1-4, the VVA apparatus includes an
operating mechanism 10 for varying the lift amount of a pair of
intake valves 12 slidably arranged with a cylinder head 11 through
valve guides, not shown. The operating mechanism 10 includes a
hollow driving shaft 13 rotatably supported by a bearing 14 in an
upper portion of the cylinder head 11, a crank or eccentric
rotating cam 15 fixed to the driving shaft 13 through a connecting
pin 40, a pair of VO cams 17 swingably supported on an outer
peripheral surface 13a of the driving shaft 13 and coming in slide
contact with valve lifters 16 disposed at the upper ends of the
intake valves 12 to open and close them, and transmission means 18
connected between the crank cam 15 and the VO cams 17 for
transmitting torque of the crank cam 15 to the VO cams 17 as a
rocking force. The transmission means 18 have an operation position
variably controlled by alteration means 19.
[0041] The driving shaft 13 extends in the longitudinal direction
of the engine, and has one end with a follower sprocket, a timing
chain wound thereon, etc., not shown, through which torque is
received from a crankshaft of the engine. The driving shaft 13 is
rotated counterclockwise as viewed in FIG. 1. The driving shaft 13
is formed out of a material of high strength.
[0042] The bearing 14 includes a main bracket 14a arranged at the
upper end of the cylinder head 11 for supporting an upper portion
of the driving shaft 13, and an auxiliary bracket 14b arranged at
the upper end of the main bracket 14a for rotatably supporting a
control shaft 32 as will be described later. The brackets 14a, 14b
are fastened together from above by a pair of bolts 14c.
[0043] As shown in FIG. 3, the crank cam 15, which is a unitary
structure of a wear resistant material, is formed substantially
like a ring, and includes an annular main body 15a and a cylinder
15b integrated with the outer end face thereof. A though hole 15c
is formed axially through the crank cam 15 to receive the driving
shaft 13. An axis Y of the main body 15a is offset radially with
respect to an axis X of the driving shaft 13 by a predetermined
amount. The crank cam 15 is engaged with the driving shaft 13
through the through hole 15c for mounting thereto by the connecting
pin 40. A crescent flat surface is formed on one side face of the
cylinder 15b on the side of the cam main body 15a. The crank cam 15
is constructed to rotate counterclockwise or in the direction of
arrow as viewed in FIG. 1 with rotation of the driving shaft
13.
[0044] The valve lifters 16 are formed like a covered cylinder,
each being slidably held in a hole of the cylinder head 11 and
having a flat top face 16a with which the VO cam 17 comes in slide
contact. Referring to FIG. 8B, when the valve lifter 16 is pressed
to the VO cam 17 in a zero lift section, a slight valve clearance
with a set value .delta. is held between a lower face 16b of the
valve lifter 16 and the intake valve in consideration of a thermal
expansion difference between components upon engine start, a
deterioration thereof with time, etc.
[0045] Referring to FIGS. 1 and 7A-8B, the VO cam 17 is formed
roughly like a raindrop, and has a support hole 20a at a roughly
annular base end 20, through which the driving shaft 13 is arranged
for rotatable support. The VO cam 17 also has a pinhole 21a on the
side of a cam nose 21. A lower face of the VO cam 17 is formed with
a cam face 22 including a base-circle face 22a on the side of the
base end 20, a ramp face 22b circularly extending from the
base-circle face 22a to the cam nose 21, and a lift face 22c
extending from the ramp face 22b to a top face 22d with the maximum
lift arranged at an end of the cam nose 21. The base-circle face
22a, the ramp face 22b, the lift face 22c, and the top face 22d
come in contact with predetermined points of the top face 16a of
the valve lifter 16 in accordance with the rocking position of the
VO cam 17.
[0046] Specifically, referring to FIG. 5, in view of the valve-lift
characteristic, a predetermined angular range .theta.1 of the
base-circle face 22a corresponds to a base-circle section, and a
predetermined angular range .theta.2 of the ramp face 22b
subsequent to the base-circle section .theta.1 corresponds to a
ramp section, and a predetermined angular range .theta.3 of the
ramp face 22b from the ramp section .theta.2 to the top face 22d
corresponds to a lift section. As will be described later, the
amount of a low lift L1 of the intake valve 12 produced by the VO
cam 17 during valve-lift control is set to a predetermined value
more than twice as large as the set value .delta. of the valve
clearance.
[0047] An annular holding member 42 is arranged between one end
face of the base end 20 of the VO cam 17 and the crank cam 15. The
holding member 42 is of the outer diameter roughly equal to that of
the cylinder 15b of the crank cam 15, and has a center hole 42a for
engagement with the driving shaft 13.
[0048] The transmission means 18 include a rocker arm 23 disposed
above the driving shaft 13, a crank arm 24 for linking a first arm
23a of the rocker arm 23 with the crank cam 15, and a link rod 25
for linking a second arm 23b of the rocker arm 23 with the VO cam
17.
[0049] As shown in FIG. 1, the rocker arm 23 has in the center a
cylindrical base rotatably supported by a control cam 33 as will be
described later through a support hole 23c. The first arm 23a
protruding from an outer end of the cylindrical base has a pinhole
for receiving a pin 26, whereas the second arm 23b protruding from
an inner end of the cylindrical base has a pinhole for receiving a
pin 27 for connecting the second arm 23b and a first end 25a of the
link rod 25.
[0050] The crank arm 24 includes one end or relatively
large-diameter annular base end 24a and another end or extension
24b arranged in a predetermined position of the outer peripheral
surface of the base end 24a. The base end 24a has in the center an
engagement hole 24c rotatably engaged with the outer peripheral
surface of the main body 15a of the crank cam 15 through a needle
bearing 43. The extension 24b has a pinhole for rotatably receiving
the pin 26. An axis 26a of the pin 26 forms a pivotal point of the
extension 24b of the crank arm 24 with the first arm 23a of the
rocker arm 23.
[0051] As best seen in FIG. 1, the link rod 25 is formed
substantially like a letter L having a concave on the side of the
rocker arm 23, and has first and second ends 25a, 25b formed with
pinholes 25c, 25d through which ends of the pins 27, 28 press
fitted in the respective pinholes of the second arm 23b of the
rocker arm 23 and the cam nose 21 of the VO cam 17 are rotatably
arranged.
[0052] Arranged at one ends of the pins 26, 27, 28 are snap rings
for restricting axial movement of the crank arm 24 and the link rod
25.
[0053] The needle bearing or ball bearing member 43 is interposed
between the main body 15a of the crank cam 15 and the inner
peripheral surface 24c of the base end 24a of the crank arm 24
engaged with an outer peripheral surface 15d of the cam main body
15a. Referring to FIG. 6, the needle bearing 43 includes an annular
holder 44 and a plurality of needle rollers 45 rotatably held by
the holder 44. Although FIG. 6 illustrates only about half of the
needle bearing 43 for easy understanding, the actual needle bearing
43 is formed annularly.
[0054] The holder 44 is formed like an annulus ring having a
plurality of rectangular openings 44a disposed circumferentially
equidistantly. On the other hand, the needle rollers 45 are
rotatably held in the respective openings 44a to have an inner
periphery rotatably directly contacting the outer peripheral
surface 15d of the cam main body 15a and an outer periphery
rotatably directly contacting the inner peripheral surface 24c of
the base end 24a of the crank arm 24.
[0055] As best seen in FIG. 4, the needle bearing 43 is held in its
entirety on the outer peripheral surface of the cam main body 15a
such that both edges of the holder 44 are held by one side face 41a
of the crank cam 15 and one side face 42a of the holding member 42
in the direction of the driving shaft 13. As being formed out of a
wear resistant material, both the crank cam 15 and the holding
member 42 achieve a restraint of wear caused by slide movement with
the holder 44.
[0056] The alteration means 19 include the control shaft 32
disposed above the driving shaft 13 and rotatably supported on the
bearing 14, and the control cam 33 fixed at the outer periphery of
the control shaft 32 to form a rocking fulcrum of the rocker arm
23.
[0057] As best seen in FIG. 2, the control shaft 32 is disposed
parallel to the driving shaft 13 to extend in the longitudinal
direction of the engine, and is constructed to be rotatable within
a predetermined angular range by means of an electromagnetic
actuator 29 arranged at one end of the control shaft 32 and a worm
gear mechanism 34.
[0058] The control cam 33 is formed like a cylinder, and has an
axis P1 offset with respect to an axis P2 of the control shaft 32
by an amount .alpha. corresponding to a thick portion 33a.
[0059] The actuator 29 for controllably rotating the control shaft
32 is driven in accordance with a control signal derived from a
controller 30 for detecting engine operating conditions. The
controller 30, which includes a microcomputer, serves to detect
actual engine operating conditions in accordance with a signal of
an engine-speed detected by a crank angle sensor and detection
signals out of various sensors such as an accelerator
opening-degree sensor, intake-air temperature sensor, vehicle G
sensor, transmission gear-position sensor, etc. Moreover, the
controller 30 provides a control signal to the actuator 29 in
accordance with a detection signal out of a potentiometer 31 for
detecting the rotated position of the control shaft 32 that
corresponds to an actual valve lift.
[0060] Next, operation of the first embodiment will be described.
When the engine is at low velocity and at low load, the control
shaft 32 is rotated clockwise by the actuator 29 in accordance with
a control signal out of the controller 30. Thus, the axis P1 of the
control cam 33 is kept in a rotation-angle position located in the
top left direction of the axis P2 of the control shaft 32 as shown
in s in FIG. 7A, so that the thick portion 33a of the control cam
33 is moved upward with respect to the driving shaft 13. Thus, the
rocker arm 23 is moved in its entirety upward with respect to the
driving shaft 13, so that the VO cam 17, having the cam nose 21
forcibly slightly drawn up through the link rod 25, is rotated
counterclockwise in its entirety.
[0061] Therefore, referring to FIGS. 7A-7B, when rotation of the
crank cam 15 pushes the first arm 23a of the rocker arm 23 upward
through the crank arm 24, the corresponding lift amount,
transmitted to the VO cam 17 and the valve lifter 16 through the
link rod 25, is kept zero.
[0062] Thus, in such low-velocity and low-load range, referring to
FIG. 10, the two intake valves 12 are held at zero lift, i.e. in
the valve-closed state. This allows lowering of friction, etc.,
resulting in greatly improved fuel consumption. Moreover, in the
first embodiment, so-called reduced cylinder operation is carried
out wherein the two intake valves 12 of each particular cylinder
are at zero lift or in the valve-stop state, and the two exhaust
valves of the same cylinder are also at zero lift or in the
valve-stop state, but the intake and exhaust valves of the other
cylinders are not in the valve-stop state. This reduces a pumping
loss, resulting in further improvement in fuel consumption.
[0063] When depressing an accelerator pedal to pass the engine
operating conditions from the low-rotation and low-load range
(state as shown in FIGS. 7A-7B) to the low-rotation and medium-load
or medium-rotation and low-load range, the control shaft 32 is
rotated slightly counterclockwise in an instant by the actuator 29
in accordance with a control signal out of the controller 30. Thus,
referring to FIGS. 8A-8B, this rotates the control cam 33 slightly
counterclockwise in an instant from the position as shown in FIGS.
7A-7B to slightly move the axis P1 of the control cam 33 in an
instant. As a result, the valve-lift amount passes from zero to L1
in an instant.
[0064] Referring to FIG. 11, the fact that the valve-lift amount
passes from zero to L1 in an instant will be described in the
concrete in accordance with a lift control map. In FIG. 11, an
x-axis designates an engine speed NE (rpm), and a y-axis designates
an accelerator opening degree Aa (deg) corresponding to an engine
load. The engine speed NE is given from a cranking speed N.sub.0 to
an allowable maximum speed Nmax, and the accelerator opening degree
Aa is given from full closing to full opening of the accelerator.
It is noted that the y-axis corresponding to the engine load may
provide a throttle-valve opening degree, an intake-air amount, or
an intake-pipe internal pressure in place of the accelerator
opening degree.
[0065] There is a boundary from the low-rotation and medium-load
range to the medium-rotation and low-load range, at which the
valve-lift amount passes from zero to the low lift L1. The
low-rotation and low-load side of the boundary is an area A wherein
the valve-lift amount is fixed to zero lift. The high-rotation and
high-load side of the boundary is an area B wherein the valve-lift
amount is changed continuously with an increase in engine speed or
load. Thus, the boundary shows a limit between the area A or an
area of zero lift fixed and the area B or an area of continuously
variable lift.
[0066] Assuming, for example, that actual engine operating
conditions correspond to a point Q1 in the area of zero lift fixed
or area A. When depressing the accelerator pedal here, the engine
operating conditions reach a point Q2 on the above boundary, at
which the lift control map changes from zero to L1 in an instant.
As a result, the controller 30 causes the control shaft 32 to
rotate slightly counterclockwise in an instant as described above,
adjusting the valve-lift amount to the low lift L1. Lift control
passes merely instantaneously through a very low lift area between
zero lift and the low lift L1, and selectively changes the
valve-lift amount substantially between zero and the low lift
L1.
[0067] Since lift control is not carried out in the very low lift
area, variation can be prevented in the valve-lift amount between
cylinders from occurring during very low lift due to variation in
the machining accuracy of components.
[0068] Referring to FIG. 12, an effect produced by lift control
wherein the valve-lift amount is selectively changed between zero
and the low lift L1 will be described in comparison to lift control
wherein the valve-lift amount is changed continuously.
[0069] FIG. 12 shows the relationship between the valve-lift amount
L and the lift variation ratio .DELTA.L/L when the machining
accuracy of components varies. The lift variation ratio .DELTA.L/L
is given as a value, for example, when the pitch length between the
pinholes 25c at both ends of the link rod 25 of each apparatus
varies by a predetermined amount.
[0070] As seen from FIG. 12, even with a reduction in the
valve-lift amount L, a variation .DELTA.L of the valve-lift amount
L does not decrease in proportion to the reduced valve-lift amount
L, so that the lift variation ratio .DELTA.L/L increases with a
reduction in the valve-lift amount L. It has a greater value,
particularly, in the very low lift area wherein the valve-lift
amount L is smaller than the low lift L1 and greater than zero,
which is an example when the length of the link rods 25 varies. The
lift variation ratio .DELTA.L/L also becomes a greater value in the
very low lift area when the machining or positional accuracy of
other portions varies, such as the rocker arm 23, the driving shaft
13, etc. This causes greater variation in the intake-air charging
efficiency and gas flow conditions between cylinders of a
particular cylinder group, resulting in unstable engine
performance.
[0071] However, variation in the valve-lift amount L can be
prevented from occurring with the valve-lift amount being set to
zero lift and not to very low lift. This is due to the fact that a
valve clearance is held between the lower face 16b of the valve
lifter 16 and the upper end face of the valve, which ensures
preservation of zero lift.
[0072] In the first embodiment, since lift control is not carried
out in the very low lift area wherein the lift variation ratio
.DELTA.L/L is greater, variation is restrained in the intake-air
charging efficiency and gas flow conditions between cylinders of a
particular cylinder group.
[0073] Further, in the first embodiment, switching from zero lift
to the low lift L1 and vice versa can smoothly be carried out by
the operating mechanism 10. Specifically, the control shaft 32
transiently passes at the intermediate rotated position of very low
lift during rotation from the rotated position of zero lift to that
of the low lift L1, enabling a full restraint of occurrence of
torque shock.
[0074] Furthermore, in the first embodiment, the amount of the low
lift L1 is more than twice as large as the set value .delta. of the
valve clearance as seen in FIGS. 8A-8B.
[0075] The lift variation ratio .DELTA.L/L is calculated in
excluding variation in the valve clearance, change thereof with
time, etc. Actually, the valve clearance includes not only such
errors, but undergoes another change with time due to wear of a
valve shaft end or formation of a deposit. Those errors produce a
variation .DELTA..delta. in the valve clearance, which changes
.DELTA.L to .DELTA.L.+-..DELTA..del- ta., resulting in change in
the lift variation ratio .DELTA.L/L (see FIG. 12).
[0076] The valve clearance has set value .delta. which can prevent
the valve clearance from being zero (occurrence of valve thrusting)
or excessive (occurrence of noise) even with the above errors.
[0077] Specifically, the variation .DELTA..delta. in the valve
clearance is smaller than the set value .delta.. Thus, by setting
the low lift L1 to 2.delta. or more, the actual lift amount can be
.delta. or more, and secure the minimum lift even with variation in
the valve clearance, change thereof with time, etc., enabling a
restraint of unstable engine performance. It is noted that when the
set value .delta. of the valve clearance is 0.4 mm, the low lift L1
is set to 0.8 mm or more.
[0078] On the other hand, when depressing the accelerator pedal
further to pass the engine operating conditions to the
high-rotation and high-load range, the control shaft 32 is rotated
counterclockwise by the actuator 29 in accordance with a control
signal out of the controller 30. Thus, referring to FIGS. 9A-9B,
this rotates the control cam 33 further counterclockwise from the
position as shown in FIGS. 8A-8B to move the axis P1 (thick portion
33a) of the control cam 33 downward. As a result, the rocker arm 23
is moved in its entirety in the direction of the driving shaft 13
or downward, so that the first arm 23b pushes the cam nose 21 of
the VO cam 17 downward through the link rod 25, rotating the VO cam
17 in its entirety clockwise by a predetermined amount.
[0079] Therefore, the position of contact of the cam face 22 of the
VO cam 17 with respect to the top face 16a of the valve lifter 16
is moved rightward or in the direction of the lift portion 22d as
shown in FIG. 9A. This rotates the crank cam 15 as shown in FIG. 9A
to push the first arm 23a of the rocker arm 23 through the crank
arm 24, obtaining a larger lift L2 with respect to the valve lifter
16.
[0080] Thus, the valve-lift characteristic is greater in the
high-rotation and high-load range than in the low-rotation and
low-load range, so that the valve-lift amount L has a greater value
L2 as shown in FIG. 10. This results in advanced opening timing and
delayed closed timing of each intake valve 12, obtaining improved
intake-air charging efficiency, allowing achievement of sufficient
engine output.
[0081] Moreover, since variation in the valve-lift amount L is
carried out continuously from the low-rotation and low-load range
to the high-rotation and high-load range (L1 to L2), the valve lift
can be controlled continuously accurately in accordance with engine
operating conditions, i.e. actual engine speed and load condition.
This allows achievement of the maximum engine performance such as
engine torque in any engine operating condition. Moreover, in the
lift range from L1 to L2, variation in the intake-air amount or the
like does not occur between the cylinders as seen from FIG. 12.
[0082] When the valve-lift amount L of particular cylinders is
fixed to zero lift, the valve-lift amount of the other cylinders
than the particular cylinders is fixed to the low lift L1, whereas
when the former is controlled in the range from L1 to L2, the
latter is controlled in the same range. Specifically, the minimum
lift of particular cylinders except zero lift is set to be equal to
the minimum lift of the other cylinders. Thus, immediately after
switching to all cylinder operation, there is no lift difference
between the cylinders, producing no difference in intake-air
charging efficiency between the cylinders.
[0083] FIG. 13 shows a second embodiment of the present invention
wherein a set value of the low lift L1 is changed so that the low
lift L1 at a point with the engine speed NE=N1 (rpm) and the
accelerator opening Aa=Aa1 (deg) in the lift control map as
illustrated in FIG. 11 is set to a value such that output torque at
zero lift for intake valves of particular cylinders and the low
lift L1 for intake valves of the other cylinders is roughly equal
to output torque at the low lift L1 for intake valves of all
cylinders. This allows a restraint of occurrence of torque shock
when the valve lift of particular cylinders is switched from the
zero lift to the low lift L1.
[0084] Specifically, output torque in the operating range with zero
lift for particular cylinders with the accelerator fully open is of
course smaller than that in the operating range with the low lift
L1 for all cylinders. This is due to the fact that since a throttle
valve is fully open when the accelerator is fully open, contraction
of intake air hardly occurs at this portion, but mainly appears at
intake valves, which results in reduced intake-air amount in terms
of the whole of the multiple cylinder engine when the valve-lift
amount of particular cylinders is set to zero lift. However, the
difference between the two torques is smaller as an engine load is
lower or the accelerator opening degree is smaller. When the
accelerator opening degree reaches a certain value, the two torques
are equal to each other, and when the accelerator opening degree
becomes further smaller, the output torque with zero lift becomes
higher than that with the low lift L1. This is due to the fact that
as the accelerator opening degree is smaller, contraction of intake
air carried out by the throttle valve is dominant, and the effect
of the valve lift is smaller. With zero lift, the combustion
efficiency becomes higher, and driving friction of a valve gear
becomes smaller, so that greater work is possible with respect to
the same intake-air amount, resulting in higher output torque with
zero lift.
[0085] FIG. 14 shows a third embodiment of the present invention
wherein a set value of the low lift L1 is changed further.
Specifically, in the lift control map as illustrated in FIG. 11,
the low lift L1 is set to a value such that output torque at the
low lift L1 for all cylinders is greater than that at zero lift for
particular cylinders and the low lift L1 for the other cylinders.
Thus, when the valve-lift amount is switched from zero lift to the
low lift L1, increased output torque is obtained, improving the
vehicular acceleration performance. This results in increased
applicable range of zero lift, i.e. possible setting of the
boundary on the high load side, also obtaining improved fuel
consumption.
[0086] FIG. 15 shows a fourth embodiment of the present invention
wherein the boundary is changed in accordance with engine operating
conditions, i.e. the intake-air temperature. Specifically, when the
intake-air temperature is higher than a predetermined temperature,
the boundary is changed to the side of zero lift or the side of the
area A, whereas when the intake-air temperature is lower than the
predetermined temperature, the boundary is changed to the side of
high lift or the side of the area B.
[0087] As is well known, as the intake-air temperature falls, the
density of intake mixture increases generally, improving the
mixture charging efficiency, resulting in improved engine torque.
Therefore, by moving the boundary to the side of the area B as in
the illustrative embodiment, the operating range with zero lift can
be enlarged in the high-rotation and high-load direction. This
results in enlarged operating range with zero lift, thus obtaining
improved fuel consumption with necessary torque secured.
[0088] FIG. 16 is a flowchart illustrating a fifth embodiment of
the present invention wherein the controller 30 carries out
learning control of the low lift area placed on the boundary in
accordance with variation in engine operating conditions.
[0089] Referring to FIG. 16, first, at a step S1, an actual valve
lift is read from the position sensor, and at a step S2, an actual
gear position is read from the gear-position sensor. Next, at a
step S3, an actual acceleration G1 of the vehicle is read from the
G sensor. At a subsequent step S4, the actual acceleration G1 is
compared with a target acceleration G obtained in accordance with
engine torque estimated out of information such as the actual valve
lift and accelerator opening degree and the gear position so as to
determine whether or not the actual acceleration G1 reaches the
target acceleration G. If it is determined that the actual
acceleration G1 reaches the target acceleration G, flow proceeds to
a step S5 where the low lift L1 is learned and stored in a storage
in the controller 30.
[0090] On the other hand, if it is determined that the actual
acceleration G1 fails to reach the target acceleration G, flow
proceeds to a step S6 where the low lift L1 is increased, which is
the minimum lift when excluding zero lift. This allows the
valve-lift amount L except zero lift to be increased in a relative
way, improving the actual acceleration G1. And the valve-lift
amount L is increased up to a given value of the low lift L1 at
which the actual acceleration G1 corresponds to the target
acceleration G, which is learned and stored in the storage.
[0091] Learning control is always carried out in such a way with
regard to the low lift L1, so that lowering of the vehicular
performance can be prevented even if friction of a vehicle or a
valve gear is increased with time.
[0092] FIG. 17 is a flowchart illustrating a sixth embodiment of
the present invention. In the fifth embodiment, learning is carried
out with regard to the low lift L1, whereas in the sixth
embodiment, the boundary between the area A and the area B is
learned to produce the same effect.
[0093] Referring to FIG. 17, processing from a step S11 to a step
S14 is similar to that from the step S1 to the step S4 as shown in
FIG. 16. At the step S14, if it is determined that the actual
acceleration G1 reaches the target acceleration G, flow proceeds to
a step S15 where the boundary is learned and stored in the storage
in the controller 30. On the other hand, if it is determined that
the actual acceleration G1 fails to reach the target acceleration
G, flow proceeds to a step S16 where the boundary is moved to the
side of zero lift. This allows the valve-lift amount L to be
changed in the low-rotation and low-load range, improving the
actual acceleration G1. And the valve-lift amount L is increased up
to a given value on the boundary at which the actual acceleration
G1 corresponds to the target acceleration G, which is learned and
stored in the storage.
[0094] FIG. 18 shows a seventh embodiment of the present invention
wherein a set value of the low lift L1 is set to a reasonably small
value between zero lift and the high lift L2.
[0095] In the aforementioned embodiments, in the event that the
actuator 29 cannot produce torque due to, e.g. its failure such as
disconnection, the valve-lift amount L of the intake valves 12 of
particular cylinders is fixed to zero lift by a biasing force of a
valve spring, whereas the valve-lift amount of the intake valves of
the other cylinders is fixed to the low lift L1. This may bring a
lack of engine torque, resulting in greatly deteriorated operating
performance in the ordinary low-rotation range.
[0096] On the other hand, in the seventh embodiment, the valve-lift
amount L of the intake valves of particular cylinders is set to
zero lift, whereas the valve-lift amount of the intake valves of
the other cylinders is set to a reasonably small lift L1',
obtaining the high-load output torque characteristic as illustrated
in FIG. 18. Specifically, when widely depressing the accelerator
pedal to achieve full opening of the accelerator, and the
valve-lift amount L of all cylinders has a predetermined larger
value L2, output torque varies along a curve as illustrated by
one-dot chain line in FIG. 18, obtaining high output torque in the
high-rotation range due to high lift and wide operating angle.
However, in the low-rotation range, as a result of high lift and
wide operating angle, mixture once inhaled in cylinders is
discharged into the intake pipe due to larger valve lift after the
piston bottom dead center and lagged closing timing of the intake
valves, lowering the mixture charging efficiency, resulting in
certain torque reduction.
[0097] On the other hand, when setting a set value of the low lift
L1 to the reasonably small value L1', a discharge of mixture during
low rotation is smaller even with smaller number of actuated intake
valves, so that torque in the low-rotation and high-load range is
greater than that when the valve-lift amount L of all intake valves
has the maximum lift L2 as illustrated by fully drawn line in FIG.
18.
[0098] In the seventh embodiment, a set value of the low lift L1 is
set to the reasonably small value L1' in such a way, so that even
if the valve-lift amount L of particular intake valves 12 is fixed
to zero lift, and the valve-lift amount of the other intake valves
is fixed to the low lift L1 due to failure of the actuator 29,
torque in the low-rotation and high-load range can be greater than
that obtained by fixing the valve-lift amount of all intake valves
to the maximum lift L2, preventing greatly deteriorated operating
performance in the ordinary low-rotation range due to lack of
engine torque.
[0099] Having described the present invention with regard to the
illustrative embodiments, it is noted that the present invention is
not limited thereto, and various changes and modifications can be
made without departing from the scope of the present invention. By
way of example, in the illustrative embodiments, the present
invention is applied to a two-valve-stop engine so called wherein
the intake valves for each cylinder have both zero lift. The
present invention is not limited thereto, and it is of course
applicable to a one-valve-stop engine so called wherein one of the
two intake valves has zero lift to enhance swirl in the cylinder
for improved fuel consumption.
[0100] The entire contents of Japanese Patent Application 11-362086
are incorporated hereby by reference.
* * * * *