Title: Variable valve control system and method for an internal combustion engine
Abstract: A variable valve control system for an internal combustion engine includes first and second variable valve control mechanisms capable of varying valve lift characteristics of one of an intake valve and exhaust valve, and a controller that controls the first and second variable valve control mechanisms. The controller includes a detecting section for detecting a malfunction of the first variable valve control mechanism, and a control section that controls the second variable valve control mechanism upon detection of the malfunction of the first variable valve control mechanism so that an intake valve opening timing coincides with or is retarded from an exhaust valve closing timing. A variable valve control method is also provided.
Patent Number: 6,990,937 Issued on 01/31/2006 to Shindou, et al.
| Inventors:
|
Shindou; Shigeki (Yokohama, JP);
Toriumi; Masaki (Yokohama, JP);
Nohara; Tsuneyasu (Kanagawa, JP)
|
| Assignee:
|
Nissan Motor Co., Ltd. (Yokohama, JP)
|
| Appl. No.:
|
834119 |
| Filed:
|
April 29, 2004 |
Foreign Application Priority Data
| May 22, 2003[JP] | 2003-144625 |
| Current U.S. Class: |
123/90.15; 123/90.16; 123/90.11 |
| Current Intern'l Class: |
F01L 1/34 (20060101) |
| Field of Search: |
123/901,901.1,901.2,901.5,901.6,901.8,198.D
|
References Cited [Referenced By]
U.S. Patent Documents
| 6135077 | Oct., 2000 | Moriya et al.
| |
| 6189512 | Feb., 2001 | Kawasaki et al.
| |
| 6679206 | Jan., 2004 | Takagi.
| |
| Foreign Patent Documents |
| 5-98916 | Apr., 1993 | JP.
| |
Other References
U.S. Appl. No. 10/953,365, filed Sep. 30, 2004, Shindou.
|
Primary Examiner: Mohanty; Bibhu
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
What is claimed is:
1. A variable valve control system for an internal combustion engine comprising:
first and second variable valve control mechanisms capable of varying valve lift
characteristics of one of an intake valve and exhaust valve; and
a controller that controls the first and second variable valve control mechanisms;
the controller including:
a detecting section for detecting a malfunction of the first variable valve control
mechanism; and
a control section that controls the second variable valve control mechanism upon
detection of a malfunction of the first variable valve control mechanism so that
an intake valve opening timing coincides with or is retarded from an exhaust valve
closing timing.
2. A variable valve control system according to claim 1, wherein the first variable
valve control mechanism comprises a valve timing control mechanism capable of varying
a valve timing of the intake valve, and the second variable valve control mechanism
comprises a valve event and lift control mechanism capable of varying an operation
angle and a valve lift of the intake valve continuously.
3. A variable valve control system according to claim 2, wherein the valve event
and lift control mechanism comprises an intake camshaft rotatable in timed relation
to a crankshaft of the engine, an oscillation cam fixedly mounted on the intake
camshaft for driving the intake valve of the engine, a circular drive cam eccentrically
and fixedly mounted on intake cam shaft, a pivotal link pivotally mounted on drive
cam, a control shaft, a circular control cam eccentrically and fixedly provided
to the control shaft, a rocker arm pivotally mounted on the control cam and having
an end portion pivotally connected to a protruded arm portion of the pivotal link,
a connecting link having an upper end portion pivotally connected to another end
portion of the rocker arm and a lower end portion pivotally connected to the oscillation
cam, and an actuator for changing a rotational angle of the control shaft.
4. A variable valve control system according to claim 3, wherein at the time
of the malfunction of the first variable valve control mechanism and in case a
center phase of an intake valve operation angle is retarded from a reference center
phase that is a phase at the center between an exhaust valve closing timing and
a bottom dead center, the controller controls the valve event and lift control
mechanism so that the intake valve closing timing comes closer to the bottom dead center.
5. A variable valve control system according to claim 3, wherein at the time
of the malfunction of the valve timing control mechanism and in case the center
phase of the intake valve operation angle is advanced from a reference center phase
that is a phase at the center between an exhaust valve closing timing and a bottom
dead center, the controller controls the valve event and lift control mechanism
so that the intake valve opening timing approximately coincides with the exhaust
valve closing timing.
6. A variable valve control system according to claim 1, wherein the controller
controls the first and second variable valve control mechanisms only at a particular
engine operating condition including starting of the engine.
7. A variable valve control system for an internal combustion engine comprising:
first and second variable valve control mechanisms capable of varying valve lift
characteristics of one of an intake valve and exhaust valve;
detecting means for detecting a malfunction of the first variable valve control
mechanism; and
control means for controlling the second variable valve control mechanism upon
detection of the malfunction of the first variable valve control mechanism so that
an intake valve opening timing coincides with or is retarded from an exhaust valve
closing timing.
8. A variable valve control method for an internal combustion engine having first
and second variable valve control mechanisms capable of varying valve lift characteristics
of one of an intake valve and exhaust valve, the method comprising:
detecting a malfunction of the first variable valve control mechanism; and
controlling the second variable valve control mechanism upon detection of the
malfunction of the first variable valve control mechanism so that an intake valve
opening timing coincides with or is retarded from an exhaust valve closing timing.
9. A variable valve control method according to claim 8, wherein the first variable
valve control mechanism comprises a valve timing control mechanism capable of varying
a valve timing of the intake valve, and the second variable valve control mechanism
comprises a valve event and lift control mechanism capable of varying an operation
angle and a valve lift of the intake valve continuously, and wherein at the time
of the malfunction of the first variable valve control mechanism and in case the
center phase of the intake valve operation angle is advanced from a reference center
phase that is a phase at the center between the exhaust valve closing timing and
a bottom dead center, the controlling comprises controlling the valve event and
lift control mechanism so that the intake valve opening timing approximately coincides
with the exhaust valve closing timing.
10. A variable valve control method according to claim 8, wherein the first variable
valve control mechanism comprises a valve timing control mechanism capable of varying
a valve timing of the intake valve, and the second variable valve control mechanism
comprises a valve event and lift control mechanism capable of varying an operation
angle and a valve lift of the intake valve continuously, and wherein at the time
of the malfunction of the first variable valve control mechanism and in case the
center phase of the intake valve operation angle is advanced from a reference center
phase that is a phase at the center between an exhaust valve closing timing and
a bottom dead center, the controlling comprises controlling the first and second
variable valve control mechanisms only at a particular engine operating condition
including starting of the engine.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a variable valve control system for an internal
combustion engine, which has two variable valve control mechanisms for varying
valve lift characteristics of intake and exhaust valves, and more specifically
to a failsafe technique upon malfunction of one of the variable valve control mechanisms.
The present invention further relates to a variable valve control method for an
internal combustion engine.
For the purpose of improving the output and fuel consumption of an internal combustion
engine, there have heretofore been proposed various variable valve control systems
for variably controlling the valve lift characteristics of intake and exhaust valves.
For example, in a system having valve timing control mechanisms provided to the
respective groups of engine cylinders for varying the valve timings of intake and
exhaust valves, when a malfunction of one of the valve timing control mechanisms
is detected, the valve timing of the other valve timing control mechanism is forcedly
controlled so as to coincide with the actual valve timing of the valve timing control
mechanism having been detected in malfunctioning, as disclosed in Unexamined Japanese
Patent Application No. 5-98916.
SUMMARY OF THE INVENTION
In the meantime, in case, a plurality of variable valve control mechanisms are
provided to predetermined intake and exhaust valves for variably controlling the
valve lift characteristics thereof, a malfunction of one of the variable valve
control mechanisms disables the engine to attain desired valve lift characteristics
of the intake and exhaust valves, e.g., a valve overlap may possibly be caused
inadvertently, thus increasing the exhaust gas remaining in the cylinders excessively
and disabling the engine to attain a good combustion stability necessary for preventing
a malfunction at starting and misfire.
It is accordingly an object of the present invention to provide a variable valve
control system having a plurality of variable valve control mechanisms, which can
attain such a performance ability and combustion stability that are sufficient
for avoiding a defective or poor start and misfire even upon a malfunction of one
of the variable valve control mechanisms.
It is a further object of the present invention to provide a variable valve control
method for an internal combustion engine having a plurality of variable valve control
mechanisms, which enables the engine to have the foregoing characters.
To achieve the above object, there is provided according to an aspect of the
present
invention a variable valve control system for an internal combustion engine comprising
first and second variable valve control mechanisms capable of varying valve lift
characteristics of one of an intake valve and exhaust valve, and a controller that
controls the first and second variable valve control mechanisms, the controller
including a detecting section for detecting a malfunction of the first variable
valve control mechanism and a control section that controls the second variable
valve control mechanism upon detection of a malfunction of the first variable valve
control mechanism so that an intake valve opening timing coincides with or is retarded
from an exhaust valve closing timing.
According to another aspect of the present invention, there is provided
a variable valve control method for an internal combustion engine having first
and second variable valve control mechanisms capable of varying valve lift characteristics
of one of an intake valve and exhaust valve, the method comprising detecting a
malfunction of the first variable valve control mechanism, and controlling the
second variable valve control mechanism upon detection of the malfunction of the
first variable valve control mechanism so that an intake valve opening timing coincides
with or is retarded from an exhaust valve closing timing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a variable valve control system for an internal
combustion engine according to a first embodiment of the present invention;
FIG. 2 is a time chart for illustrating detection of a malfunction of a valve
timing control mechanism of the variable valve control system of FIG. 1;
FIG. 3 is a flowchart of a control executed by the variable valve control system
of FIG. 1;
FIG. 4 is a view for illustrating an operation of the variable valve control
system of FIG. 1;
FIG. 5 is a flowchart of a control executed by a variable valve control system
according to a second embodiment of the present invention; and
FIGS. 6A to 6C are views for illustrating an operation of the variable
valve control system according to the second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, an internal combustion engine is provided with
a pair of intake valves
18 for each cylinder. To intake valves
18
are provided two variable valve control mechanisms capable of varying the valve
lift characteristics of intake valves
18, i.e., valve timing control (VTC)
mechanism
30 capable of varying the valve timing of intake valves
18
and valve event and lift (VEL) control mechanism
20 capable of varying the
operation angle and lift of intake valves
18.
To intake cam shaft
19 is transmitted from a crankshaft (not shown) a
rotational
drive force by way of a pulley or sprocket (also not shown) so that intake cam
shaft
19 is rotatable in timed relation to the crankshaft.
VEL control mechanism
20 includes a pair of oscillation cams
21
fixedly mounted on intake cam shaft
19 for driving respective intake valves
18 by way of valve lifters
17, circular drive cam
23 eccentrically
and fixedly mounted on intake cam shaft
19, pivotal link
27 pivotally
mounted on drive cam
23, control shaft
24 extending in parallel with
intake cam shaft
19 and in the direction in which the cylinders (not shown)
are arranged, circular control cam
25 eccentrically and fixedly mounted
on control shaft
24, rocker arm
26 pivotally mounted on control cam
25 and having an end portion pivotally connected to a protruded arm portion
of pivotal link
27, connecting link
28 having an upper end portion
pivotally connected to another end portion of rocker arm
26 and a lower
end portion pivotally connected to one of oscillation cams
21, and electric-powered
VEL control changing device
22 that serves as an actuator for changing the
rotational angle of control shaft
24.
With the above-described structure, when intake cam shaft
19 is rotated
in timed relation to the crankshaft, drive cam
23 causes pivotal link
27
to move up and down. Movement of pivotal link
27 causes rocker arm
26
to pivot about the axis of control cam
25. Connecting link
28 connected
to rocker arm
26 thus causes oscillation cams
21 to oscillate and
drive intake valves
18 to open and close by way of valve lifters
17.
Further, by varying the rotational or angular position of control shaft
24 by means of VEL control changing device
22, the axis of control
cam
25 that is the pivotal axis of rocker arm
26 is varied, thus
causing the initial position of oscillation cams
21 (i.e., the center phase
of the oscillation angle) to be varied. This enables the intake operation angle
and valve lift to be varied continuously with the center phase of the intake operation
angle being maintained nearly constant.
Such VEL control mechanism
20 is compact and therefore excellent in the
installability since rocker arm
26 and links
27,
28 are collectively
disposed around intake cam shaft
19. Further, such VEL control mechanism
20 has a good durability and reliability in operation since many connecting
portions of the constituent parts such as the bearing portions of drive cam
23
and pivotal link
27 and control cam
25 and rocker arm
26 are
structured so as to be in surface-to-surface contact with each other and therefore
lubrication thereof can be attained with ease and further since it does not require
a biasing means such as return springs. Further, VEL control mechanism
20
is adapted for adoption to a direct-drive type valve operating system so that it
can make higher the rotational limit with a simple and compact structure.
An example of VTC mechanism
30 is disclosed in Unexamined Japanese Patent
Publication No. 5-98916, and VTC mechanisms of the type using helical splines and
of the vane type are well known. Brief description being made thereto, VTC mechanism
30 includes outer rotor
31 having a cam pulley or sprocket rotatable
in timed relation to the crankshaft and an inner rotor (not shown) disposed inside
outer rotor
31 and rotatable with intake camshaft
19. The rotors
are rotated relative to each other by means of hydraulic VTC changing device
32
thereby advancing or retarding the center phase of the intake valve operation angle
(i.e., the phase at which the lift of the intake valve becomes maximum).
Engine control unit
1 is made up of a known digital computer consisting
of CPU, ROM, RAM and an input/output interface and has a function of storing and
executing various control processings which will be described hereinafter. To engine
control unit
1 are inputted various signals such as water temperature signal
2 from a water temperature sensor, intake air amount signal
3 from
an airflow meter, throttle sensor signal
4 from a throttle sensor, crank
angle signal
5 from a crank angle sensor, O
2 sensor output signal
6 from an oxygen sensor disposed in an exhaust passage, engine speed signal
7 from an engine speed sensor, oil temperature signal
8 from an oil
temperature sensor, VEL control angle sensor signal
11 from VEL control
angle sensor
15 for detecting a rotational angle or an angular position
of control shaft
24 and cam angle sensor signal
12 from cam angle
sensor
16 for detecting a rotational angle or angular position of intake
camshaft
19. Based on those signals, engine control unit
1 outputs
control signals to various actuators, e.g., air/fuel ratio control signal
9,
ignition timing control signal
10, VEL control changing device control signal
13 and VTC changing device control signal
14 to a fuel injection
system, ignition system, VEL control changing device
22 and VTC changing
device
32, respectively, thereby controlling the operations thereof.
Referring to FIG. 3, a control executed by the variable valve control system
according to the first embodiment of the present invention will be described. In
the following control processings are executed in engine control unit
1.
Firstly, in step S
11, a target changing angle that is a target value
of a center phase of an intake valve operation angle to be attained by VTC mechanism
30 is determined based on an engine operating condition. The target changing
angle corresponds to a target value t
1 (refer to FIG. 2) of a phase difference
between the crank angle sensor signal and the cam angle sensor signal. In step
S
12, a control signal corresponding to the target changing angle to be attained
by VTC mechanism
30 is outputted to VTC changing device
32 thereby
driving VTC mechanism
30 so as to attain the target changing angle.
In step S
13, it is detected a condition in which VTC mechanism
30
cannot function or operate properly for some reason, i.e., it is detected a malfunction
of VTC mechanism
30 (malfunction detecting means or section). For example,
based on crank angle sensor signal
5 and cam angle sensor signal
12
is detected and calculated an actual changing angle of VTC mechanism
30,
and by comparing the actual changing angle with the target changing angle a detection
and judgment of malfunction is made. The actual changing angle corresponds to a
difference t
2 (refer to FIG. 2) between the crank angle sensor signal and
the cam angle sensor signal, i.e., a phase difference between the crankshaft and
camshaft
19. When t
2 and t
1 do not coincide with each other
and a difference therebetween exceeds a predetermined value, it is determined that
a malfunction of VTC mechanism
30 is caused and the control proceeds to
step S
14 where a control for avoiding a valve overlap by means of VEL control
mechanism
20 is executed. Further, though not shown, the driver is warned
of the malfunction of VTC mechanism
30 by means of a warning lamp or the like.
In step S
14, based on crank angle sensor signal
5 and cam angle
sensor signal
12, the malfunction position of VTC mechanism
30, i.e.,
center phase θ of the intake valve operation angle is calculated. As shown
in FIG. 4, center phase θ of the intake valve operation angle is represented
by an angle advanced from maximumly retarded phase θ
0 that is
an initial position of VTC mechanism
30 and becomes larger as it is advanced increasingly.
In step S
15, a target operation angle of VEL control mechanism
20
is calculated so that intake valve opening timing IVO coincides with (or is retarded
from) exhaust valve closing timing EVC, i.e., so that valve overlap period
41
(refer to FIG. 4) during which both of the intake valves
18 and the exhaust
valves are opened is eliminated. In step S
16, a control signal corresponding
to the target operation angle calculated in step S
15 is outputted to VEL
control changing device
22 thereby driving VEL control mechanism
20
so as to attain the target operation angle.
For example, in case a malfunction of VTC mechanism
30 is detected under
a condition where valve overlap
41 exists as shown in FIG. 4, VEL control
mechanism
20 is driven so as to attain a smaller operation angle and a smaller
valve lift so that IVO is retarded toward EVC.
By this embodiment, in case a malfunction of VTC mechanism
30 is detected,
VEL control mechanism
20 is driven so as to eliminate valve overlap
41
at once, thus making it possible to attain a good engine performance and a good
combustion stability that are sufficient to prevent such a malfunction in starting
and misfire that may otherwise be caused by an excess amount of exhaust gas remaining
in the cylinders due to valve overlap
41.
Further, since VEL control changing device
22 is of the electric-powered
type that is excellent in the responsiveness, the overlap can be eliminated rapidly
at the time of occurrence of the malfunction.
Referring to FIG. 5, a control executed by the variable valve control system
according to a second embodiment of the present invention will be described. The
second embodiment is substantially the same as the first embodiment except for
the control executed in ECU
1.
The control processings in steps S
11 to S
14 are the same as those
of the first embodiment. Namely, in step S
11, a target changing angle of
VTC mechanism
30 is determined. In step S
12, VTC mechanism
30
is driven so as to attain the target changing angle. If in step S
13 a malfunction
of VTC mechanism
30 is detected, the control proceeds to step S
14
where a center phase θ of the intake valve operation angle, corresponding
to the malfunction position of VTC mechanism
30 is calculated.
In the following steps S
21 to S
24, VEL control mechanism
20
is driven so as not to cause a valve overlap but to cause intake valve closure
timing IVC to come closer to bottom dead center BDC.
Namely, in step S
21, it is determined whether the center phase θ
of the intake valve operation angle that is representative of the malfunction position
is equal to or larger than reference center phase θ
1. Reference center
phase θ
1 is the phase in the middle of the period between exhaust
valve closure timing EVC and bottom dead center BDC and corresponds to the center
phase that enables IVO to coincide with EVC and IVC to coincide with BDC.
As shown in FIG. 6A, in case center phase θ of the intake valve operation
angle is advanced from reference center phase θ
1 (θ>θ
1),
IVC is advanced from BDC if the intake valve operation angle is of such one that
causes IVO and EVC to coincide with each other. Accordingly, if the intake valve
operation angle is increased in order to make IVC come closer to BDC, IVO is advanced
from EVC, thus causing a possibility of a valve overlap. Accordingly, in this embodiment,
in case center phase θ of the intake valve operation angle is advanced from
reference center phase θ
1, the control proceeds to step S
22
where similarly to step S
15 in the first embodiment the target operation
angle of VEL control mechanism
20 that causes IVO to nearly coincide with
or be retarded from EVC is calculated.
As shown in FIG. 6C, in case center phase θ of the intake valve operation
angle is retarded from reference center phase θ
1 (θ<θ
1),
IVC is retarded from BDC if the intake valve operation angle is of such one that
causes IVO and EVC to coincide with each other. Accordingly, when the intake valve
operation angle is made smaller in order to make IVC coincide with BDC, IVO is
caused to go apart from EVC toward the retard side, thus increasing so-called minus
overlap
42 but never causing a valve overlap. Thus, in case center phase
θ of the intake valve operation angle is retarded from reference center phase
θ
1, the control proceeds to step S
23 where a target operation
angle of VEL control mechanism
20 that causes IVC to nearly coincide with
bottom dead center BDC is calculated. Then, in step S
24, VEL control mechanism
20 is driven so as to attain the target operation angle calculated in step
S
22 or S
23.
By such a second embodiment, in addition to the similar effect attained by the
first embodiment, it becomes possible to make IVC come closer to BDC without causing
a valve overlap, thus making it possible to make the actual compression ratio higher
thereby further improving the combustion stability.
The control processing shown in FIGS. 3 and 5 at the time of a malfunction of
VTC mechanism
30 can be performed in all of the engine operation ranges
or in a particular engine operation range. For example, at engine start, a malfunction
in starting may possibly be caused when desired valve lift characteristics cannot
be attained due to a malfunction of VTC mechanism
30. Accordingly, it will
suffice to perform the control of FIGS. 3 and 5 only at engine start or at an engine
operating range including engine start.
The entire contents of Japanese Patent Application P2003-144625 (filed May 22,
2003) are incorporated herein by reference.
Although the invention has been described above by reference to certain
embodiments of the invention, the invention is not limited to the embodiment described
above. Modifications and variations of the embodiment described above will occur
to those skilled in the art, in light of the above teachings. For example, a malfunction
of VEL control mechanism
20 may be detected and VTC mechanism
30
may be controlled or driven in a way as to eliminate a valve overlap upon detection
of a malfunction of VEL control mechanism
20.
*
