U.S. patent application number 12/300653 was filed with the patent office on 2009-04-23 for controller of variable valve actuator.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Shuichi Ezaki, Akio Kidooka.
Application Number | 20090101090 12/300653 |
Document ID | / |
Family ID | 39765735 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090101090 |
Kind Code |
A1 |
Kidooka; Akio ; et
al. |
April 23, 2009 |
CONTROLLER OF VARIABLE VALVE ACTUATOR
Abstract
The present invention provides a variable valve mechanism
control device that is capable of reducing the power consumption
and rating of an electric motor by allowing camshaft rotary inertia
torque to reduce spring reaction force during a valve lift.
Camshaft rotary inertia force is increased to a value not smaller
than a predetermined value before the start of a valve lift. During
the time interval between the instant at which the valve lift
starts and the instant at which the maximum lift is provided, the
spring reaction force of a valve spring is used as deceleration
torque for the camshaft rotary inertia force. During the time
interval between the instant at which the maximum lift is provided
and the instant at which the valve lift terminates, the spring
reaction force is used as acceleration torque for the camshaft
rotary inertia force. The camshaft rotary inertia force cancels the
spring reaction force so that motor torque generated during a valve
lift is composed of counter-friction torque only.
Inventors: |
Kidooka; Akio;
(Kanagawa-ken, JP) ; Ezaki; Shuichi;
(Shizuoka-ken, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi ,Aichi-ken
JP
|
Family ID: |
39765735 |
Appl. No.: |
12/300653 |
Filed: |
March 7, 2008 |
PCT Filed: |
March 7, 2008 |
PCT NO: |
PCT/JP2008/054142 |
371 Date: |
November 13, 2008 |
Current U.S.
Class: |
123/90.11 ;
123/90.17 |
Current CPC
Class: |
F01L 2009/2126 20210101;
F01L 2800/08 20130101; F01L 13/0015 20130101; F02D 13/02 20130101;
F01L 2001/0537 20130101; F01L 2820/035 20130101; F01L 1/356
20130101; F01L 2001/0475 20130101; F01L 9/20 20210101; F02D 13/0207
20130101; F01L 1/08 20130101; F02D 13/0269 20130101; F01L 9/22
20210101; F01L 2800/01 20130101; F01L 1/143 20130101; Y02T 10/12
20130101; F01L 1/053 20130101; F01L 2820/042 20130101 |
Class at
Publication: |
123/90.11 ;
123/90.17 |
International
Class: |
F01L 9/04 20060101
F01L009/04; F01L 1/344 20060101 F01L001/344 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 2007 |
JP |
2007-072220 |
Jan 22, 2008 |
JP |
2008-011830 |
Claims
1. A variable valve mechanism control device for an internal
combustion engine, comprising: a camshaft on which a cam is mounted
to drive a valve that is biased by a valve spring; an electric
motor which rotationally drives the camshaft; and control means for
exercising drive control over the electric motor; wherein the
control means controls the rotary inertia force of the camshaft so
as to be equal to or more than a predetermined value at the
beginning of a valve lift so that the rotary inertia force cancels
the spring reaction force of the valve spring.
2. The variable valve mechanism control device according to claim
1, wherein the control means controls the rotational position of
the electric motor so that the rotation speed of the camshaft is
decreased by the spring reaction force exerted during the time
interval between the instant at which a valve lift starts and the
instant at which the maximum lift position is reached, and that the
rotation speed of the camshaft is increased by the spring reaction
force exerted during the time interval between the instant at which
the maximum lift position is reached and the instant at which the
valve lift terminates.
3. The variable valve mechanism control device according to claim
1, wherein the control means employs the spring reaction force
exerted during the time interval between the instant at which the
valve lift starts and the instant at which the maximum lift
position is reached as deceleration torque for the rotary inertia
force, while employing the spring reaction force exerted during the
time interval between the instant at which the maximum lift
position is reached and the instant at which the valve lift
terminates as acceleration torque for the rotary inertia force.
4. The variable valve mechanism control device according to claim
1, wherein, when the rotary inertia force exerted at the end of the
valve lift is smaller than the predetermined value, the control
means requires during a cam base circle slide to the electric motor
to generate such torque that causes said rotary inertia force to be
equal to or more than the predetermined value.
5. The variable valve mechanism control device according to claim
1, wherein the control means inhibits the electric motor to
generate torque opposing the spring reaction force and requires the
electric motor to generate only torque opposing the friction of the
cam and valve during a valve lift.
6. The variable valve mechanism control device according to claim
1, further comprising: engine speed change means which raises an
engine speed to a value equal to or more than a predetermined value
when a requested engine output value is equal to or more than a
predetermined value and the engine speed is in a low rotation speed
region where the engine speed is equal to or lower than the
predetermined value.
7. The variable valve mechanism control device according to claim
1, further comprising: an inertia force increase member which is
installed in a cam drive system having the camshaft and the
electric motor to increase the camshaft rotary inertia force;
wherein the inertia force increase member adjusts the enlargement
range for an actual operating angle in a low rotation speed region
where an engine speed is equal to or lower than a predetermined
value.
8. The variable valve mechanism control device according to claim
1, further comprising: an inertia force change mechanism which can
change the camshaft rotary inertia force when the operating angle
of the valve is to be changed within a low rotation speed region
where an engine speed is equal to or lower than a predetermined
value.
9. The variable valve mechanism control device according to claim
1, wherein, when the cam is to be driven from a stopped state, the
control means requires the electric motor to generate such torque
that causes the rotary inertia force to be equal to or more than a
predetermined value during a cam base circle slide before the start
of a valve lift.
10. The variable valve mechanism control device according to claim
1, wherein, when the cam is to be driven from a stopped state, the
control means requires the electric motor to generate such torque
that causes the rotary inertia force to reach a predetermined
initial value during a cam base circle slide before the start of a
valve lift, and then requires the electric motor to generate such
torque that causes the rotary inertia force at the end of the valve
lift to reach a predetermined value greater than the predetermined
initial value.
11. The variable valve mechanism control device according to claim
1, wherein, when the cam is to be driven in a normal rotation
direction, the control means changes the rotation speed of the
camshaft during a cam base circle slide in accordance with an
engine speed so that the rotation of the camshaft synchronizes with
the rotation of a crankshaft.
12. A variable valve mechanism control device for an internal
combustion engine, comprising: a camshaft on which a cam is mounted
to drive a valve that is biased by a valve spring; an electric
motor which rotationally drives the camshaft; and control means for
exercising drive control over the electric motor; wherein the
control means controls the rotational position of the electric
motor so that the cam rotation speed during a valve lift is equal
to or lower than the cam rotation speed during a cam base circle
slide.
13. The variable valve mechanism control device according to claim
1, wherein the control means increase the rotary inertia force to a
value equal to or more than a predetermined value by imparting
torque of the electric motor during a cam base circle slide so as
to swingingly drive the cam, and then synchronizes the rotation of
the camshaft with the rotation of a crankshaft.
14. The variable valve mechanism control device according to claim
13, further comprising: startup request acquisition means for
acquiring a startup request for the internal combustion engine;
wherein the control means changes the period for swingingly driving
the cam to increase the rotary inertia force in compliance with the
startup request acquired by the startup request acquisition
means.
15. The variable valve mechanism control device according to claim
14, wherein the control means includes judgment means for
determining the degree of requested acceleration indicated by the
startup request, applies the torque of the electric motor only
during a cam base circle slide if the degree of requested
acceleration is smaller than a predetermined value, and applies the
torque of the electric motor not only during a cam base circle
slide but also during a valve lift if the degree of requested
acceleration is equal to or more than the predetermined value.
16. A variable valve mechanism control device for an internal
combustion engine, comprising: a camshaft on which a cam is mounted
to drive a valve that is biased by a valve spring; an electric
motor which rotationally drives the camshaft; and a control unit
for exercising drive control over the electric motor; wherein the
control unit controls the rotary inertia force of the camshaft so
as to be equal to or more than a predetermined value at the
beginning of a valve lift so that the rotary inertia force cancels
the spring reaction force of the valve spring.
17. A variable valve mechanism control device for an internal
combustion engine, comprising: a camshaft on which a cam is mounted
to drive a valve that is biased by a valve spring; an electric
motor which rotationally drives the camshaft; and a control unit
for exercising drive control over the electric motor; wherein the
control unit controls the rotational position of the electric motor
so that the cam rotation speed during a valve lift is equal to or
lower than the cam rotation speed during a cam base circle slide.
Description
TECHNICAL FIELD
[0001] The present invention relates to a variable valve mechanism
control device with an electric motor, and more particularly to
drive control over an electric motor.
BACKGROUND ART
[0002] A variable valve mechanism control device with an electric
motor is known (refer, for instance, to Patent Document 1). The
control device disclosed in Patent Document 1 includes a torque
reduction mechanism for imparting counter-torque in consideration
of valve spring torque, inertia torque, and in-cylinder compression
torque, which arise while an intake valve or exhaust valve is being
opened or closed. This decreases the torque applied to the electric
motor, thereby reducing the rating of the electric motor.
[0003] Patent Document 1: Japanese Patent Laid-open 2005-171786
[0004] Patent Document 1: Japanese Patent Laid-open 2005-171937
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
[0005] However, the control device disclosed in Patent Document 1
entails a cost increase because it newly includes the torque
reduction mechanism. In addition, the use of the torque reduction
mechanism may result in increased friction torque between a cam and
a valve.
[0006] The present invention has been made to solve the above
problem. An object of the present invention is to provide a
variable valve mechanism control device that is capable of reducing
the power consumption and rating of an electric motor by using
camshaft rotary inertia torque to reduce spring reaction force
during a valve lift.
Means for Solving the Problem
[0007] The first aspect of the present invention is a variable
valve mechanism control device for an internal combustion engine,
comprising:
[0008] a camshaft on which a cam is mounted to drive a valve that
is biased by a valve spring;
[0009] an electric motor which rotationally drives the camshaft;
and
[0010] control means for exercising drive control over the electric
motor;
[0011] wherein the control means controls the rotary inertia force
of the camshaft so as to be equal to or more than a predetermined
value at the beginning of a valve lift so that the rotary inertia
force cancels the spring reaction force of the valve spring.
[0012] The second aspect of the present invention is the variable
valve mechanism control device according to the first aspect of the
present invention, wherein the control means controls the
rotational position of the electric motor so that the rotation
speed of the camshaft is decreased by the spring reaction force
exerted during the time interval between the instant at which a
valve lift starts and the instant at which the maximum lift
position is reached, and that the rotation speed of the camshaft is
increased by the spring reaction force exerted during the time
interval between the instant at which the maximum lift position is
reached and the instant at which the valve lift terminates.
[0013] The third aspect of the present invention is the variable
valve mechanism control device according to the first aspect of the
present invention, wherein the control means employs the spring
reaction force exerted during the time interval between the instant
at which the valve lift starts and the instant at which the maximum
lift position is reached as deceleration torque for the rotary
inertia force, while employing the spring reaction force exerted
during the time interval between the instant at which the maximum
lift position is reached and the instant at which the valve lift
terminates as acceleration torque for the rotary inertia force.
[0014] The fourth aspect of the present invention is the variable
valve mechanism control device according to the first aspect of the
present invention, wherein, when the rotary inertia force exerted
at the end of the valve lift is smaller than the predetermined
value, the control means requires during a cam base circle slide to
the electric motor to generate such torque that causes said rotary
inertia force to be equal to or more than the predetermined
value.
[0015] The fifth aspect of the present invention is the variable
valve mechanism control device according to the first aspect of the
present invention, wherein the control means inhibits the electric
motor to generate torque opposing the spring reaction force and
requires the electric motor to generate only torque opposing the
friction of the cam and valve during a valve lift.
[0016] The sixth aspect of the present invention is the variable
valve mechanism control device according to any one of the first to
fifth aspects of the present invention, further comprising:
[0017] engine speed change means which raises an engine speed to a
value equal to or more than a predetermined value when a requested
engine output value is equal to or more than a predetermined value
and the engine speed is in a low rotation speed region where the
engine speed is equal to or lower than the predetermined value.
[0018] The seventh aspect of the present invention is the variable
valve mechanism control device according to any one of the first to
fifth aspects of the present invention, further comprising:
[0019] an inertia force increase member which is installed in a cam
drive system having the camshaft and the electric motor to increase
the camshaft rotary inertia force;
[0020] wherein the inertia force increase member adjusts the
enlargement range for an actual operating angle in a low rotation
speed region where an engine speed is equal to or lower than a
predetermined value.
[0021] The eighth aspect of the present invention is the variable
valve mechanism control device according to any one of the first to
fifth aspects of the present invention, further comprising:
[0022] an inertia force change mechanism which can change the
camshaft rotary inertia force when the operating angle of the valve
is to be changed within a low rotation speed region where an engine
speed is equal to or lower than a predetermined value.
[0023] The ninth aspect of the present invention is the variable
valve mechanism control device according to the first aspect of the
present invention, wherein, when the cam is to be driven from a
stopped state, the control means requires the electric motor to
generate such torque that causes the rotary inertia force to be
equal to or more than a predetermined value during a cam base
circle slide before the start of a valve lift.
[0024] The tenth aspect of the present invention is the variable
valve mechanism control device according to the first aspect of the
present invention, wherein, when the cam is to be driven from a
stopped state, the control means requires the electric motor to
generate such torque that causes the rotary inertia force to reach
a predetermined initial value during a cam base circle slide before
the start of a valve lift, and then requires the electric motor to
generate such torque that causes the rotary inertia force at the
end of the valve lift to reach a predetermined value greater than
the predetermined initial value.
[0025] The eleventh aspect of the present invention is the variable
valve mechanism control device according to claim 1, wherein, when
the cam is to be driven in a normal rotation direction, the control
means changes the rotation speed of the camshaft during a cam base
circle slide in accordance with an engine speed so that the
rotation of the camshaft synchronizes with the rotation of a
crankshaft.
[0026] The twelfth aspect of the present invention is a variable
valve mechanism control device for an internal combustion engine,
comprising:
[0027] a camshaft on which a cam is mounted to drive a valve that
is biased by a valve spring;
[0028] an electric motor which rotationally drives the camshaft;
and
[0029] control means for exercising drive control over the electric
motor;
[0030] wherein the control means controls the rotational position
of the electric motor so that the cam rotation speed during a valve
lift is equal to or lower than the cam rotation speed during a cam
base circle slide.
[0031] The thirteenth aspect of the present invention is the
variable valve mechanism control device according to the first
aspect of the present invention, wherein the control means increase
the rotary inertia force to a value equal to or more than a
predetermined value by imparting torque of the electric motor
during a cam base circle slide so as to swingingly drive the cam,
and then synchronizes the rotation of the camshaft with the
rotation of a crankshaft.
[0032] The fourteenth aspect of the present invention is the
variable valve mechanism control device according to the thirteenth
aspect of the present invention, further comprising:
[0033] startup request acquisition means for acquiring a startup
request for the internal combustion engine;
[0034] wherein the control means changes the period for swingingly
driving the cam to increase the rotary inertia force in compliance
with the startup request acquired by the startup request
acquisition means.
[0035] The fifteenth aspect of the present invention is the
variable valve mechanism control device according to the fourteenth
aspect of the present invention, wherein the control means includes
judgment means for determining the degree of requested acceleration
indicated by the startup request, applies the torque of the
electric motor only during a cam base circle slide if the degree of
requested acceleration is smaller than a predetermined value, and
applies the torque of the electric motor not only during a cam base
circle slide but also during a valve lift if the degree of
requested acceleration is equal to or more than the predetermined
value.
ADVANTAGES OF THE INVENTION
[0036] According to the first aspect of the present invention, the
spring reaction force is cancelled by the camshaft rotary inertia
force. It means that, since the spring reaction force generated
during a valve lift is reduced by the camshaft rotary inertia
force, the torque that should be generated by the electric motor
during a valve lift can be reduced. This makes it possible to
reduce the power consumption and rating of the electric motor.
[0037] According to the second aspect of the present invention, the
rotational position of the electric motor is controlled so that the
camshaft rotation speed is decreased by the spring reaction force
generated during the period between the instant at which a valve
lift starts and the instant at which the maximum lift position is
reached, and that the camshaft rotation speed is increased by the
spring reaction force generated during the period between the
instant at which the maximum lift position is reached and the
instant at which the valve lift terminates. This enables the
camshaft rotary inertia force to reduce the spring reaction force
during a valve lift.
[0038] According to the third aspect of the present invention, the
spring reaction force generated during the period between the
instant at which a valve lift starts and the instant at which the
maximum lift position is reached is used as deceleration torque for
the camshaft rotary inertia force, and the spring reaction force
generated during the period between the instant at which the
maximum lift position is reached and the instant at which the valve
lift terminates is used as acceleration torque for the camshaft
rotary inertia force. This enables the camshaft rotary inertia
force to reduce the spring reaction force during a valve lift.
[0039] According to the fourth aspect of the present invention, in
a case where the camshaft rotary inertia force is smaller than a
predetermined value at the end of a valve lift, the electric motor
is required to generate such torque that makes the camshaft rotary
inertia force equal to or more than the predetermined value during
a cam base circle slide. The torque required to the electric motor
to generate can be smaller during a cam base circle slide than
during a valve lift. It is therefore possible to avoid an increase
in the power consumption and rating of the electric motor.
[0040] According to the fifth aspect of the present invention, the
electric motor is required to generate no
counter-spring-reaction-force torque but only counter-friction
torque during a valve lift. This makes it possible to reduce the
torque required to the electric motor to generate during a valve
lift. Thus, the rating of the electric motor can be reduced since
the rating of the electric motor can be determined merely by
considering the counter-friction torque.
[0041] According to the sixth aspect of the present invention, in a
case where the requested engine output value is equal to or more
than a predetermined value in a low rotation speed region, engine
speed is increased to equal to or more than a predetermined value
by the engine speed change means. Here, since the camshaft rotary
inertia force becomes smaller in the low rotation speed region than
in a high rotation speed region, the enlargement range for the
actual operating angle becomes greater in the low rotation speed
region. When the operating angle is large, it may not be possible
to achieve a requested engine output value, since the Atkinson
cycle is implemented so that adequate torque cannot be generated.
The sixth aspect of the present invention can reduce the
enlargement range for the actual operating angle by switching
toward the high rotation speed side. This makes it possible to
generate adequate torque and achieve a requested engine output
value.
[0042] According to the seventh aspect of the present invention,
the enlargement range for the actual operating angle in the low
rotation speed region is adjusted by increasing the camshaft rotary
inertia force by the inertia force increase member. This makes it
possible to achieve target values for fuel efficiency and
torque.
[0043] According to the eighth aspect of the present invention, the
inertia force change mechanism can change the camshaft rotary
inertia force when the valve operating angle is changed in the low
rotation speed region. In other words, the enlargement range for
the actual operating angle can be changed by changing the camshaft
rotary inertia force, so as to implement a desired valve operating
angle.
[0044] According to the ninth aspect of the present invention, when
a stopped cam is to be driven, the electric motor is required to
generate such torque that makes the camshaft rotary inertia force
equal to or more than the predetermined value during a cam base
circle slide before the start of a valve lift. The camshaft rotary
inertia force, which has been increased before the start of the
valve lift, cancels the spring reaction force during the valve
lift. Further, since the spring reaction force does not act on the
camshaft during the cam base circle slide, the camshaft rotary
inertia force can be increased even if the torque required to the
electric motor to generate is small. This makes it possible to
reduce the power consumption of the electric motor when the cam is
to be driven from its stopped state. Consequently, the rating of
the electric motor can be reduced.
[0045] According to the tenth aspect of the present invention, when
a stopped cam is to be driven, the electric motor is required to
generate such torque that makes the camshaft rotary inertia force
reach to the predetermined initial value during a cam base circle
slide before the start of a valve lift. Subsequently, the electric
motor is required to generate such torque that makes the camshaft
rotary inertia force reach to a predetermined value greater than
the predetermined initial value at the end of the valve lift. As
the torque required to the electric motor to generate is divided,
the torque required to the electric motor to generate before the
start of a valve lift is reduced. Therefore, the tenth aspect of
the present invention can accept a lower electric motor rating than
the ninth aspect.
[0046] According to the eleventh aspect of the present invention,
the rotation of the camshaft can be synchronized with that of the
crankshaft by changing the camshaft rotation speed during a cam
base circle slide in accordance with the engine speed.
[0047] According to the twelfth aspect of the present invention,
the rotational position of the electric motor is controlled so that
the cam rotation speed during a valve lift is equal to or lower
than the cam rotation speed during a cam base circle slide. This
makes it possible to minimize the torque that is required to the
electric motor to generate during a valve lift.
[0048] According to the thirteenth aspect of the present invention,
the camshaft rotary inertia force is increased to a value equal to
or more than the predetermined value necessary for normal rotation
drive by applying the torque of the electric motor during a cam
base circle slide to swingingly drive the cam. Subsequently, the
cam is driven in the normal direction so that the rotation of the
camshaft is synchronized with that of the crankshaft. The camshaft
rotary inertia force does not drastically increase to a value equal
to or more than the predetermined value, but gradually increases
through repeated cam swings. This makes it possible to decrease the
electric motor torque, thereby reducing the rating of the electric
motor.
[0049] According to the fourteenth aspect of the present invention,
the period for swingingly driving the cam to increase the rotary
inertia force is changed in accordance with an internal combustion
engine startup request. Therefore, the cam can switch from swing
drive to normal rotation drive with optimum timing according to the
internal combustion engine startup request.
[0050] According to the fifteenth aspect of the present invention,
the torque of the electric motor is applied only during a cam base
circle slide if the degree of requested acceleration indicated by
the internal combustion engine startup request is smaller than the
predetermined value. This provides a relatively long period for
swinging the cam to increase the camshaft rotary inertia force. If,
on the other hand, the degree of requested acceleration is not
smaller than the predetermined value, the torque of the electric
motor is applied not only during a cam base circle slide but also
during a valve lift. This makes it possible to increase the
camshaft rotary inertia force in a short period of time.
Consequently, the cam can switch from swing drive to normal
rotation drive in a short period of time.
BRIEF DESCRIPTION OF DRAWINGS
[0051] FIG. 1 is a perspective view illustrating the configuration
of a variable valve mechanism 10 according to a first embodiment of
the present invention;
[0052] FIG. 2 is an axial view of the first camshaft 18 shown in
FIG. 1;
[0053] FIG. 3 is a drawing for describing the configuration of the
engine 1 in which the variable valve mechanism 10 shown in FIG. 1
is mounted
[0054] FIG. 4 is a drawing for describing the configuration of a
hybrid vehicle system according to the first embodiment of the
present invention;
[0055] FIG. 5 is a perspective view illustrating the essential part
configuration of a drive mechanism in the hybrid vehicle system
shown in FIG. 4;
[0056] FIGS. 6A and 6B are drawings for describing the spring
reaction force that acts on a camshaft during a valve lift;
[0057] FIG. 7 is a drawing for describing the motor torque to be
generated when the cam rotation speed is constant;
[0058] FIGS. 8A to 8C show how the spring reaction force acting on
the camshaft affects the cam speed in the first embodiment of the
present invention;
[0059] FIG. 9 shows how the camshaft rotary inertia force changes
in the first embodiment of the present invention;
[0060] FIGS. 10A to 10E show valve lift characteristics and cam
rotation speed changes at various engine speeds in the first
embodiment of the present invention;
[0061] FIG. 11 is a drawing for describing a first modification of
the first embodiment of the present invention;
[0062] FIG. 12 is a drawing for describing a second modification of
the first embodiment of the present invention;
[0063] FIGS. 13A to 13C show how the spring reaction force acting
on a camshaft acts on the cam speed in a second embodiment of the
present invention;
[0064] FIG. 14 shows a map that defines a target value for the cam
rotation speed during a cam base circle slide;
[0065] FIG. 15 shows how the camshaft rotary inertia force changes
in the second embodiment of the present invention;
[0066] FIG. 16 shows how the cam rotation speed changes in the
second embodiment of the present invention;
[0067] FIG. 17 shows the relationship between the engine speed NE
and actual operating angle in a third embodiment of the present
invention;
[0068] FIG. 18 is a collinear drawing for describing a distribution
change operation that the power distribution mechanism 51 performs
when the engine speed NE is to be shifted toward a high rotation
speed side;
[0069] FIG. 19 shows an inertia force increase section provided in
a cam drive system according to a fourth embodiment of the present
invention;
[0070] FIG. 20 shows an inertia force increase section provided in
a cam drive system according to a modification of the fourth
embodiment of the present invention;
[0071] FIG. 21 shows an inertia force change mechanism according to
a fifth embodiment of the present invention;
[0072] FIG. 22 shows cam rotation speed changes and motor torque in
the sixth embodiment of the present invention;
[0073] FIG. 23 shows cam rotation speed changes and motor torque in
the seventh embodiment of the present invention;
[0074] FIGS. 24A and 24B show cam phase changes and valve lifts in
the eighth embodiment of the present invention;
[0075] FIGS. 25A to 25C show an example of motor torque that is
imparted in the ninth embodiment when an engine startup request is
generated in accordance with a catalyst warm-up request;
[0076] FIGS. 26A to 26C show an example of motor torque that is
imparted in the ninth embodiment when an engine startup request is
generated in accordance with an acceleration request; and
[0077] FIG. 27 is a flowchart illustrating a routine that the ECU
30 executes in the ninth embodiment. will now be described with
reference to.
DESCRIPTION OF REFERENCE NUMERALS
[0078] 1 Engine [0079] 3 Crankshaft [0080] 10 Variable Valve
Mechanism [0081] 14; 15; 16; 17 Cam [0082] 18; 19 Camshaft [0083]
20; 21; 23; 24; 25 Gear [0084] 22; 26 Motor [0085] 27 Weight [0086]
30 ECU [0087] 44 Transmission [0088] 51 Power transfer mechanism
[0089] 52 Generator [0090] 54 Motor [0091] 60 Battery
BEST MODE FOR CARRYING OUT THE INVENTION
[0092] Embodiments of the present invention will now be described
with reference to the accompanying drawings. Like elements in the
drawings are designated by the same reference numerals and will not
be redundantly described.
First Embodiment
Configuration of Variable Valve Mechanism
[0093] FIG. 1 is a perspective view illustrating the configuration
of a variable valve mechanism 10 according to a first embodiment of
the present invention. As shown in FIG. 1, the variable valve
mechanism 10 is provided to an engine 1 at the side of an intake
valve 11. The variable valve mechanism 10 is capable of changing
the operating angle and lift amount of the intake valve 11.
[0094] The engine 1 is, for example, an in-line four-cylinder
gasoline engine. In FIG. 1, the reference numerals #1 to #4
respectively represent the first to fourth cylinders of the engine
1. In the engine 1, explosion occurs in the order of the first,
third, fourth, and second cylinders, as is the case with a common
engine.
[0095] Two intake valves 11 provided for each cylinder 2 are biased
toward valve lifters 13 by the spring reaction force of valve
springs 12. Cams 14, 15, 16, 17, each of which is related to each
cylinder 2, are positioned above the valve lifters 13.
[0096] The cam 14 related to the first cylinder #1 and the cam 17
related to the fourth cylinder #4 are fastened to a first camshaft
18. The cam 15 related to the second cylinder #2 and the cam 16
related to the third cylinder #3 are fastened to a second camshaft
19. These camshafts 18, 19 are coaxially positioned and capable of
rotating each other.
[0097] The first camshaft 18 is coaxially fastened to a first
driven gear 20. The first driven gear 20 is engaged with a first
output gear 21. The first output gear 21 is fastened to the same
axis as for the output shaft of a first motor 22. The configuration
described above makes it possible to transmit the torque of the
first motor 22 to the first camshaft 18 through the gears 20, 21.
In other words, the first motor 22 directly drives the cams 14, 17
without regard to a later-described crankshaft 3, thereby
controlling the intake valve opening characteristics of the first
cylinder #1 and fourth cylinder #4.
[0098] The second camshaft 19 is coaxially fastened to a second
driven gear 23. A second output gear 25 meshes with the second
driven gear 23 is engaged, via an intermediate gear 24, with a
second output gear 25. The second output gear 25 is fastened to the
same axis as for the output shaft of a second motor 26. The
configuration described above makes it possible to transmit the
torque of the second motor 26 to the second camshaft 19 through the
gears 23, 24, 25. In other words, the second motor 26 directly
drives the cams 15, 16 without regard to the crankshaft 3, thereby
controlling the intake valve opening characteristics of the second
cylinder #2 and third cylinder #3.
[0099] The operation of the variable valve mechanism 10 described
above is controlled by an ECU (Electronic Control Unit) 30, which
serves as a control device. More specifically, the ECU 30 issues
drive instructions to the first motor 22 and second motor 26 in
accordance with outputs from various sensors to control the
rotational positions of the motors 22, 26.
[0100] FIG. 2 is an axial view of the first camshaft 18 shown in
FIG. 1. As shown in FIG. 2, the two cams 14, 17 mounted on the
first camshaft 18 are arranged so that their cam noses 14a, 17a are
positioned 180.degree. apart from each other in the circumferential
direction of the first camshaft 18. The two cams 14, 17 are shaped
the same and symmetrical with respect to a straight line passing
through the cam center and cam nose.
[0101] There are two drive modes for the cams 14, 17: normal
rotation drive mode and swing drive mode. In the normal rotation
drive mode, the first motor 22 continuously rotates in one
direction to continuously rotate the cams 14, 17 in a normal
rotation direction. In the swing drive mode, on the other hand, the
first motor 22 changes its rotation direction during a lift of the
intake valve 11 to reciprocate the cams 14, 17.
[0102] Although the two cams 15, 16 mounted on the second camshaft
19 are not shown in the figure and will not be described in detail,
these two cams 15, 16 are also arranged so that their cam noses
15a, 16a are positioned 180.degree. apart from each other in the
circumferential direction of the second camshaft 19. Further, the
second motor 26 can exercise drive control over these cams 14, 17
to place them in either the normal rotation drive mode or swing
drive mode.
[Configuration of Engine]
[0103] FIG. 3 illustrates the configuration of the engine 1 in
which the variable valve mechanism 10 shown in FIG. 1 is mounted.
The engine 1 has a cylinder block 6, which includes a piston 5. The
piston 5 is connected to the crankshaft 3 through a crank
mechanism. A crank angle sensor 4, which detects the rotation angle
of the crankshaft 3, is installed near the crankshaft 3.
[0104] A cylinder head 7 is attached to the top of the cylinder
block 6. The cylinder head 7 includes an ignition plug 9, which
ignites an air-fuel mixture in a combustion chamber 8. The cylinder
head 7 has an intake port 31 that communicates with the combustion
chamber 8. The aforementioned intake valve 11 is positioned in the
joint between the intake port 31 and combustion chamber 8. The
intake valve 11 is connected to the above-mentioned variable valve
mechanism 10. An injector 32 is installed near the intake port 31
to inject fuel into the neighborhood of the intake port 31.
[0105] The intake port 31 is connected to an intake path 32. A
throttle valve 33 is installed in the middle of the intake path 32.
The throttle valve 33 is an electronically controlled valve that is
driven by a throttle motor 34. The throttle valve 33 is driven in
accordance with an accelerator angle AA, which is detected by an
accelerator angle sensor 36. A throttle angle sensor 35 is
installed near the throttle valve 33 to detect a throttle angle TA.
An air flow meter 37 is installed upstream of the throttle valve
33. The air flow meter 37 is configured to detect an intake air
amount Ga.
[0106] The cylinder head 7 also includes an exhaust port 38, which
communicates with the combustion chamber 8. An exhaust valve 39 is
mounted in the joint between the exhaust port 38 and combustion
chamber 8. The exhaust valve 39 is connected to a variable valve
mechanism 40 that has the same configuration as the aforementioned
variable valve mechanism 10. The exhaust port 38 is connected to an
exhaust path 41. A catalyst 42 is installed in the exhaust path 41
to purify exhaust gas. An air-fuel ratio sensor 43 is installed
upstream of the catalyst 42 to detect an exhaust air-fuel ratio.
The catalyst 42 includes a catalyst bed temperature sensor 45,
which detects a catalyst bed temperature.
[0107] The ECU 30 has its output end connected, for instance, to
the ignition plug 9, injector 32, throttle motor 34, and
transmission 44 in addition to the aforementioned motors 22, 26.
The transmission 44 may be either an automatic transmission or a
continuously variable transmission. The ECU 30 has its input end
connected, for instance, to the crank angle sensor 4, throttle
angle sensor 35, accelerator angle sensor 36, air flow meter 37,
air-fuel ratio sensor 43, and catalyst bed temperature sensor 45.
The ECU 30 calculates an engine speed (also hereinafter referred to
as the "engine revolution speed") NE in accordance with an output
from the crank angle sensor 4.
[Configuration of Hybrid Vehicle System]
[0108] The power supply infrastructure of a hybrid vehicle system
can be used to drive the above-mentioned motors 22, 26. FIG. 4
illustrates the configuration of a hybrid vehicle system according
to the first embodiment of the present invention. The hybrid
vehicle system shown in FIG. 4 includes the aforementioned engine
1, which is one driving source, and two other driving sources,
namely, a motor generator (hereinafter referred to as the
"generator") 52 and a motor generator (hereinafter referred to as
the "motor") 54.
[0109] As shown in FIG. 4, the hybrid vehicle system includes a
triaxial power distribution mechanism 51. The power distribution
mechanism 51 is a later-described planetary gear mechanism. The
power distribution mechanism 51 is connected to the generator 52
and motor 54 in addition to the crankshaft 3 of the aforementioned
engine 1. The power distribution mechanism 51 is also connected to
a speed reducer 53. The speed reducer 53 is connected to a rotation
shaft 57 of a driving wheel 55. The driving wheel 55 is provided
with a wheel speed sensor 56. The wheel speed sensor 56 is
configured to detect the number of revolutions or the rotation
speed of the driving wheel 55.
[0110] The generator 52 and motor 54 are connected to a common
inverter 58. The inverter 58 is connected to a boost converter 59.
The boost converter 59 is connected to a battery 60. The boost
converter 59 converts the voltage (e.g., 201.6 VDC) of the battery
60 to a high voltage (e.g., 500 VDC). The inverter 58 converts the
high DC voltage, which is generated by the boost converter 59, to
an AC voltage (e.g., 500 VAC). The generator 52 and motor 54
exchange electrical power with the battery 60 through the inverter
58 and boost converter 59.
[0111] As shown in FIG. 4, the ECU 30 is connected not only to the
aforementioned engine 1 but also, for instance, to the power
distribution mechanism 51, generator 52, speed reducer 53, motor
54, wheel speed sensor 56, inverter 58, boost converter 59, and
battery 60. The ECU 30 controls the drive amount or power
generation amount of the generator 52 and motor 54. The ECU 30 also
acquires information about the state of charge (SOC) of the battery
60.
[Essential Part Configuration of Drive Mechanism]
[0112] FIG. 5 is a perspective view illustrating the essential part
configuration of a drive mechanism in the hybrid vehicle system
shown in FIG. 4.
[0113] As shown in FIG. 5, the power distribution mechanism 51
includes a sun gear 61, a ring gear 62, a plurality of pinion gears
63, and a carrier 64. The sun gear 61, which is an external gear,
is fastened to a hollow sun gear shaft 65. The crankshaft 3 of the
engine 1 runs through the hollow of the sun gear shaft 65. The ring
gear 62, which is an internal gear, is concentric with the sun gear
61. The plurality of pinion gears 63 are positioned so as to engage
with both the sun gear 61 and ring gear 62. The pinion gears 63 are
rotatably retained by the carrier 64. The carrier 64 is coupled to
the crankshaft 3. In other words, the power distribution mechanism
51 is a planetary gear mechanism that performs a differential
operation by using the sun gear 61, ring gear 62, and pinion gears
63 as rotational elements.
[0114] The speed reducer 53 includes a motive power outputting gear
66, which is used for transmitting motive power. The motive power
outputting gear 66 is coupled to the ring gear 62 of the power
distribution mechanism 51. The motive power outputting gear 66 is
also coupled to a power transmission gear 68 through a chain 67.
The power transmission gear 68 is coupled to a gear 70 through a
rotation shaft 69. The gear 70 is coupled to a differential gear
(not shown) that rotates the rotation shaft 57 of the driving wheel
55.
[0115] The generator 52 includes a rotor 71 and a stator 72. The
rotor 71 is mounted on the sun gear shaft 65, which rotates
together with the sun gear 61. The generator 52 is configured so
that it can be driven not only as an electric motor for rotating
the rotor 71 but also as a power generator for generating
electromotive force by using the rotation of the rotor 71. Further,
the generator 52 functions as a starter at engine startup.
[0116] The motor 54 includes a rotor 73 and a stator 74. The rotor
73 is mounted on a ring gear shaft 75, which rotates together with
the ring gear 62. The motor 54 is configured so that it not only
can function as an electric motor for rotating the rotor 73 but can
also be driven as a power generator for generating electromotive
force by using the rotation of the rotor 73.
[0117] The power distribution mechanism 51 can distribute the
motive power of the engine 1, which is input from the carrier 64,
to the sun gear 61, which is connected to the generator 52, and to
the ring gear 62, which is connected to the rotation shaft 57, in
accordance with their gear ratio. The power distribution mechanism
51 can also combine the motive power of the engine 1, which is
input from the carrier 64, and the motive power of the generator
52, which is input from the sun gear 61, and output the combined
motive power to the ring gear 62. Further, the power distribution
mechanism 51 can combine the motive power of the generator 52,
which is input from the sun gear 61, and the motive power input
from the ring gear 62, and output the combined motive power to the
carrier 64.
[0118] The ECU 30 calculates the torque required for the overall
vehicle in accordance with the rotation speed of the driving wheel
55, which is detected by the wheel speed sensor 56, and the
accelerator angle AA, which is detected by the accelerator angle
sensor 36. To obtain the torque required for the overall vehicle,
the ECU 30 distributes driving force to the engine 1, generator 52,
and motor 54 while considering the state of charge (SOC) of the
battery 60. In other words, the ECU 30 calculates the torque
required for the engine 1 (hereinafter referred to as the "required
engine torque") and the torque required for the generator 52 and
motor 54.
[0119] The ECU 30 can provide improved fuel efficiency by stopping
the engine 1 during deceleration, braking, or low-speed rotation
(e.g., at a rotation speed of lower than 1000 rpm).
Features of First Embodiment
[0120] The variable valve mechanism 10 described above uses the
motors 22, 26 to rotate the camshafts 18, 19. The motor rating is
determined so as to support the load imposed on the motors. The
load imposed on the motors includes, for instance, valve spring
reaction force, camshaft rotary inertia force, and friction torque.
The spring reaction force, in particular, greatly affects the motor
size and rating.
[0121] FIGS. 6A and 6B illustrate the spring reaction force that
acts on a camshaft during a valve lift. More specifically, FIG. 6A
shows the spring reaction force that acts during a valve lift
ascent, whereas FIG. 6B shows the spring reaction force that acts
during a valve lift descent. For the sake of brevity, the cam 17
mounted on the camshaft 18 is not shown in the figures or described
below.
[0122] During a valve lift ascent (for valve opening), the cam 14
pushes down a valve spring 12 as shown in FIG. 6A. Therefore, the
spring reaction force oriented in a direction opposite the rotation
direction of the cam 14 (hereinafter referred to as the "cam
rotation direction") acts on the camshaft 18.
[0123] During a valve lift descent (for valve closing), on the
other hand, the spring reaction force of the valve spring 12 pushes
the cam 14 as shown in FIG. 6B. Therefore, the spring reaction
force oriented in the same direction as the cam rotation direction
acts on the camshaft 18.
[0124] Meanwhile, the motors 22, 26 provide phase control over the
cam. It means that the rotation of the cam is synchronized with
that of the crankshaft. Conventionally, control is exercised to
provide a constant cam rotation speed (half the engine speed
NE).
[0125] FIG. 7 illustrates the motor torque to be generated when the
cam rotation speed is constant. When control is exercised to
provide a constant cam rotation speed, it is necessary, as shown in
FIG. 7, that a motor generate torque opposing the aforementioned
spring reaction force (hereinafter referred to as the
"counter-spring-reaction-force torque"). In this instance, the
motor torque is the sum of the counter-spring-reaction-force torque
and friction torque. When the counter-spring-reaction-force torque
is to be generated with a motor, the power consumption of the motor
increases. Thus, a high motor rating is required.
[0126] According to Patent Document 1 described above, the use of a
torque reduction mechanism reduces the spring torque (spring
reaction force). However, the addition of the torque reduction
mechanism entails a cost increase. It should also be noted that the
use of the torque reduction mechanism results in increased friction
torque.
[0127] Under the above circumstances, the first embodiment
increases the rotary inertia force of the camshaft 18 (hereinafter
referred to as the "camshaft rotary inertia force") before the
start of a valve lift, as described in detail below. The camshaft
rotary inertia force is employed to cancel the spring reaction
force of the valve spring 12.
[0128] FIGS. 8A to 8C illustrate how the spring reaction force
acting on the camshaft affects the cam speed in the first
embodiment. FIG. 9 shows how the camshaft rotary inertia force
changes in the first embodiment.
[0129] First of all, as shown in FIG. 9, the camshaft rotary
inertia force is increased to a value equal to or more than a
predetermined value (e.g., 2 Nm) before the start of a lift. The
predetermined value represents the camshaft rotary inertia force
that can achieve a valve lift without causing the motor to generate
the counter-spring-reaction-force torque during a valve lift.
[0130] During a valve lift ascent (during the time interval between
the instant at which the lift starts and the instant at which the
maximum lift is provided), the spring reaction force oriented in a
direction opposite the direction of cam rotation acts on the
camshaft 18 as shown in FIG. 8A. In this instance, the motor is not
required to generate the counter-spring-reaction-force torque. In
other words, the motor does not generate the
counter-spring-reaction-force torque. Then, the spring reaction
force reduces the cam rotation speed. In other words, the spring
reaction force works as deceleration torque for the camshaft rotary
inertia force. Consequently, the camshaft rotary inertia force
gradually decreases from the aforementioned predetermined value as
shown in FIG. 9.
[0131] During a subsequent valve lift descent (during the time
interval between the instant at which the maximum lift is provided
and the instant at which the lift is terminated), the spring
reaction force oriented in the same direction as the direction of
cam rotation acts on the camshaft 18 as shown in FIG. 8B. In this
instance, the motor is not required to generate the
counter-spring-reaction-force torque either as is the case with the
valve lift ascent described above. The spring reaction force then
increases the cam rotation speed. In other words, the spring
reaction force works as acceleration torque for the camshaft rotary
inertia force. Consequently, the camshaft rotary inertia force
gradually increases and reaches the aforementioned predetermined
value at the end of the lift, as shown in FIG. 9.
[0132] During a subsequent cam base circle slide, the cam rotation
speed is controlled and rendered equal to the engine speed
NE.times.1/2+correction term .alpha. in order to synchronize the
cam rotation phase with the rotation of the crankshaft 3 as shown
in FIG. 8C. Further, since the cam 14 does not come into contact
with a valve lifter 13 during a cam base circle slide, the spring
reaction force does not act on the camshaft 18. In this instance,
therefore, the motor is not required to generate the
counter-spring-reaction-force torque either. Consequently, the
camshaft rotary inertia force is kept constant as shown in FIG.
9.
[0133] As described above, the camshaft rotary inertia force
cancels the spring reaction force in the first embodiment. During
the interval between the start of a lift and the end of the lift,
therefore, it is necessary that only the counter-friction torque be
generated by the motor as shown in FIG. 9. This makes it possible
to reduce the power consumption and rating of the motor.
[0134] FIGS. 10A to 10E show valve lift characteristics and cam
rotation speed changes at various engine speeds in the first
embodiment. More specifically, FIG. 10A shows valve lift
characteristics and cam rotation speed changes at an engine speed
NE of 1000 rpm; FIG. 10B shows the same at an engine speed NE of
2000 rpm; FIG. 10C shows the same at an engine speed NE of 3000
rpm; FIG. 10D shows the same at an engine speed NE of 4000 rpm; and
FIG. 10E shows the same at an engine speed NE of 5000 rpm. In FIGS.
10A to 10E, a curve marked "Conventional" represents a case where
control is exercised so that the cam rotation speed is half the
engine speed NE at all times.
[0135] When the engine speed NE is 1000 rpm (that is, when the
engine speed is low), the cam rotation speed and camshaft rotation
speed are lower than when the engine speed is high, as indicated in
the upper half of FIG. 10A. The camshaft rotary inertia force is,
therefore, smaller at a low engine speed than at a high engine
speed. Thus, the spring reaction force changes the cam rotation
speed by a greater amount at a low engine speed. As a result, the
operating angle becomes larger and the lift curve becomes deformed
as compared to those in a conventional case.
[0136] The first embodiment controls the motor position so as to
obtain the indicated lift curves. More concretely, lift curve maps
indicated in the upper halves of FIGS. 10A to 10E are prepared for
various engine speeds NE. Further, the motor position is controlled
so that the valve lift amount changes in accordance with a lift
curve map for a particular engine speed NE. The indicated lift
curves are lift curves that are obtained when the motor torque is
minimized, that is, when the spring reaction force is completely
cancelled by the camshaft rotary inertia force.
[0137] When the motor is driven so as to obtain the lift curves
shown in the upper half of FIG. 10A, the cam rotation speed changes
as indicated in the lower half of FIG. 10A. The cam rotation speed
attained during a cam base circle slide before the start of a valve
lift is approximately 900 rpm. Therefore, the correction term
.alpha. shown in FIG. 8C is 900 rpm-500 rpm=400 rpm. The cam
rotation speed attained when the maximum lift is provided is 100
rpm.
[0138] Further, an increase in the engine speed NE reduces not only
the difference between conventional lift curves and lift curves
according to the present invention but also the correction term
.alpha. for the cam rotation speed.
[0139] As described above, the first embodiment can reduce the
spring reaction force between the start and end of a lift by
allowing the camshaft rotary inertia force to cancel the spring
reaction force. Thus, only the counter-friction torque becomes the
motor toque during a valve lift. Consequently, the power
consumption and rating of the motor can be reduced. This makes it
possible to drive the motor with only the power supply for a normal
engine system and without having to use the power supply
infrastructure of a hybrid system.
[0140] Further, the first embodiment can reduce the power
consumption and rating of the motor without using a torque
reduction mechanism disclosed, for instance, in Patent Document 1
described above. This makes it possible to achieve cost reduction
and avoid an increase in the friction torque.
(Modifications)
[0141] A first modification of the first embodiment will now be
described with reference to FIG. 11.
[0142] In the first embodiment, the cam rotation speed is constant
during a cam base circle slide (see FIGS. 10A to 10E); therefore,
the camshaft rotary inertia force is also constant. However, the
camshaft rotary inertia force may be increased during a cam base
circle slide.
[0143] FIG. 11 is a drawing for describing the first modification
of the first embodiment. More specifically, FIG. 11 shows a case
where the camshaft rotary inertia force is increased during a cam
base circle slide. As shown in FIG. 11, the camshaft rotary inertia
force is equal to the predetermined value at the start of a lift,
but smaller than the predetermined value at the end of a lift.
[0144] To further reduce the power consumption and rating of the
motor, the first modification generates a motor torque so that the
camshaft rotary inertia force reaches the predetermined value
during a cam base circle slide after the end of a lift. Since the
spring reaction force does not act on the camshaft during a cam
base circle slide, a small motor torque can increase the camshaft
rotary inertia force to the predetermined value. This makes it
possible to reduce the motor rating.
[0145] Further, the motor may be required to generate torque during
a lift so that the camshaft rotary inertia force reaches the
predetermined value at the end of a lift. This causes the motor to
generate the counter-spring-reaction-force torque during a lift as
in a conventional manner. In marked contrast to the conventional
case, however, part of the spring reaction force is cancelled by
the camshaft rotary inertia force. Therefore, the
counter-spring-reaction-force torque required to the motor to
generate is smaller than in the conventional case. As a result, the
power consumption and rating of the motor can be made lower than in
the conventional case.
[0146] FIG. 12 illustrates a second modification of the first
embodiment.
[0147] In the first embodiment, the spring reaction force and
camshaft rotary inertia force are completely cancelled.
[0148] In the second modification, the value (the predetermined
value) representing the camshaft rotary inertia force exerted
before the start of a valve lift is set to be smaller than
indicated in FIG. 9. Therefore, the camshaft rotary inertia force
does not cancel the entire spring reaction force; however, part of
the camshaft rotary inertia force is cancelled. The
counter-spring-reaction-force torque, which is against the spring
reaction force that is not cancelled, is required to the motor to
generate. Therefore, the motor torque according to the second
modification is the sum of the counter-spring-reaction-force torque
and friction torque as shown in FIG. 12. The second modification
provides a motor torque that is smaller than a conventional motor
torque, as shown in FIG. 12. Consequently, the power consumption
and rating of the motor can be made lower than in the conventional
case.
[0149] In the first embodiment and its modifications, the engine 1
corresponds to the "internal combustion engine" according to the
first aspect of the present invention; the variable valve mechanism
10 corresponds to the "variable valve mechanism" according to the
first aspect of the present invention; and the ECU 30 corresponds
to the "control means" according to the first to fifth aspects and
the ninth to twelfth aspects of the present invention. Further, in
the first embodiment and its modifications, the valve spring 12
corresponds to the "valve spring" according to the first aspect of
the present invention; the valve 11 corresponds to the "valve"
according to the first aspect of the present invention; the cams
14-17 correspond to the "cam" according to the first aspect of the
present invention; the camshafts 18, 19 correspond to the
"camshaft" according to the first aspect of the present invention;
and the electric motors 22, 26 correspond to the "electric motor"
according to the first aspect of the present invention.
Second Embodiment
[0150] A second embodiment of the present invention will now be
described with reference to FIGS. 13 to 16.
[0151] The hardware shown in FIGS. 1 to 5 can be used as a system
according to the second embodiment.
Features of Second Embodiment
[0152] The first embodiment has been described in conjunction with
a case where the cams 14-17 are driven in the normal rotation drive
mode. On the other hand, the second embodiment will be described in
conjunction with a case where the cams 14-17 are driven in the
swing drive mode. As described with reference to FIG. 2, the above
system can be used to execute the swing drive mode.
[0153] FIGS. 13A to 13C illustrate how the spring reaction force
acting on a camshaft acts on the cam speed in the second
embodiment. FIG. 14 shows a map that defines a target value for the
cam rotation speed during a cam base circle slide. FIG. 15 shows
how the camshaft rotary inertia force changes in the second
embodiment. FIG. 16 shows how the cam rotation speed changes in the
second embodiment.
[0154] During a cam base circle slide shown in FIG. 13A, that is,
before the cam 14 comes into contact with the valve lifter 13, the
cam rotation speed is raised to a target value. The map shown, for
instance, in FIG. 14 is referenced to determine the target value in
accordance with the operating angle and engine speed NE. The
camshaft rotary inertia force is then increased, as shown in FIG.
15, to a value equal to or more than the predetermined value before
the start of a lift as is the case with the first embodiment.
[0155] During a subsequent valve lift ascent (from a lift starts to
the maximum lift), the spring reaction force oriented in a
direction opposite the direction of cam rotation acts on the
camshaft 18 as shown in FIG. 13B. In this instance, the motor is
controlled so as not to generate the counter-spring-reaction-force
torque. The spring reaction force then reduces the cam rotation
speed as shown in FIG. 16. In other words, the spring reaction
force works as deceleration torque for the camshaft rotary inertia
force. Consequently, the camshaft rotary inertia force gradually
decreases from the aforementioned predetermined value as shown in
FIG. 15.
[0156] During a subsequent valve lift descent (from the maximum
lift to a termination of the lift), the spring reaction force
oriented in the same direction as the direction of cam rotation
acts on the camshaft 18 as shown in FIG. 13C. In the second
embodiment, the cam 14 is driven in the swing drive mode;
therefore, the cam rotates in a direction opposite the cam rotation
direction shown in FIG. 13B. In this instance, the motor is
controlled so as not to generate the counter-spring-reaction-force
torque either as is the case with the valve lift ascent described
above. The spring reaction force then increases the cam rotation
speed as shown in FIG. 16. FIG. 16 shows the cam rotation speed
relative to the cam rotation direction. Since the spring reaction
force works as acceleration torque for the camshaft rotary inertia
force, the camshaft rotary inertia force gradually increases.
[0157] In the second embodiment, the camshaft rotary inertia force
cancels the spring reaction force as described above. Therefore,
only the counter-friction torque needs to be generated by the
motor, as shown in FIG. 15, during the interval between the start
and end of a lift. This makes it possible to reduce the power
consumption and rating of the motor.
[0158] As described above, the second embodiment can reduce the
spring reaction force during the interval between the start and end
of a lift by allowing the camshaft rotary inertia force to cancel
the spring reaction force even in the swing drive mode. Therefore,
the second embodiment provides the same advantages as the first
embodiment, which has been described earlier.
Third Embodiment
[0159] A third embodiment of the present invention will now be
described with reference to FIGS. 17 and 18.
[0160] The hardware shown in FIGS. 1 to 5 can be used as a system
according to the third embodiment.
Features of Third Embodiment
[0161] In a low rotation speed region where, for example, the
engine speed NE is equal to or lower than 2000 rpm, the camshaft
rotary inertia force is smaller than in a high rotation speed
region. Therefore, in a case where the camshaft rotary inertia
force is employed to cancel the spring reaction force as in the
present invention, change amount in the camshaft rotary inertia
force due to the spring reaction force becomes large. In such an
instance, the actual operating angle is larger in the low rotation
speed region than in the high rotation speed region as indicated in
FIGS. 10A to 10E and FIG. 17. FIG. 17 shows the relationship
between the engine speed NE and actual operating angle. In an
example shown in FIG. 17, the employed cam has a base circle that
provides an operating angle of 210.degree. when the cam is
rotationally driven at a constant speed. In the example shown in
FIG. 17, the actual operating angle is increased to 280.degree.
when the engine speed NE is 1000 rpm.
[0162] A solid line in FIG. 17 shows how the actual operating angle
changes when the variable valve mechanism 10 is mounted in the
hybrid vehicle engine 1 shown in FIG. 4. A one-dot chain line in
FIG. 17, on the other hand, shows how the actual operating angle
changes when the variable valve mechanism 10 is mounted in a normal
engine that has no driving source other than an engine. When the
variable valve mechanism 10 is mounted in a normal engine,
provision is made so as not to exceed a maximum actual operating
angle of 270.degree. that allows an air-fuel mixture to be ignited
during idling (200 rpm).
[0163] Meanwhile, when the actual operating angle increases, the
Atkinson cycle is implemented so that the fuel efficiency improves,
although the torque decreases. If, in this instance, a great
driving force is requested in such a low rotation speed region, the
driving force may not be generated in compliance with such a
driving force request.
[0164] As such being the case, the third embodiment shifts the
engine speed NE toward a high rotation speed side if the requested
driving force is equal to or more than a predetermined value while
the engine speed is in a low rotation speed region. FIG. 18 is a
collinear drawing for describing a distribution change operation
that the power distribution mechanism 51 performs when the engine
speed NE is to be shifted toward a high rotation speed side. As
indicated in FIG. 18, increasing the amount of power supply to the
generator 52 increases the rotation speed of the sun gear 61. This
makes it possible to shift the engine speed NE toward a high
rotation speed side.
[0165] The actual operating angle can be made smaller than in a low
rotation speed region by shifting the engine speed NE toward a high
rotation speed side. Therefore, an actual compression ratio can be
increased to increase the torque. Consequently, the driving force
can be generated in compliance with a driving force request even
when a great driving force is requested.
(Modification)
[0166] In the third embodiment, the power distribution mechanism 51
shifts the engine speed NE toward a high rotation speed side.
Alternatively, however, the engine speed NE may be shifted toward a
high rotation speed side by controlling the speed reduction ratio
of the speed reducer 44. Even when the ECU 30 exercises speed
reduction ratio control, the actual compression ratio can be
increased; therefore, it is possible to provide the same advantages
as the third embodiment.
[0167] In the third embodiment and its modification, the power
distribution mechanism 51 and transmission 44 correspond to the
"engine speed change means" according to the sixth aspect of the
present invention.
Fourth Embodiment
[0168] A fourth embodiment of the present invention will now be
described with reference to FIG. 19.
[0169] FIG. 19 shows an inertia force increase section provided in
a cam drive system according to the fourth embodiment. As shown in
FIG. 18, the cam drive system includes the camshaft 18, gears 23,
24, 25, and motor 26. In the fourth embodiment, a weight 27 is
attached to an end of the camshaft 18 as shown in FIG. 18.
Features of Fourth Embodiment
[0170] As described in conjunction with the third embodiment, when
the camshaft rotary inertia force is employed to cancel the spring
reaction force as in the present invention, the amount of camshaft
rotary inertia force change increases in a low rotation speed
region. As a result, the enlargement range for the actual operating
angle is greater in the low rotation speed region than in the high
rotation speed region.
[0171] As regards an engine that places emphasis on fuel efficiency
in the low rotation speed region, the Atkinson cycle is
implemented; therefore, no particular problem arises no matter
whether the enlargement range for the actual operating angle is
great. For an engine that places emphasis on torque in the low
rotation speed region, on the other hand, it is preferred that the
enlargement range for the actual operating angle be minimized to
obtain the actual compression ratio.
[0172] Meanwhile, if the camshaft rotary inertia force can be
increased, change in the camshaft rotary inertia force during a
valve lift caused by the spring reaction force decreases. As a
result, the enlargement range for the actual operating angle can be
reduced.
[0173] In the fourth embodiment, the weight 27 is attached to an
end of the camshaft 18. The addition of the weight 27 provides a
greater camshaft rotary inertia force than when the weight 27 is
not added. Therefore, the enlargement range for the actual
operating angle in the low rotation speed region can be made
smaller than when the weight 27 is not added. Consequently, the
actual compression ratio can be obtained in the low rotation speed
region as well. This makes it possible to obtain an adequate
torque.
[0174] Further, the heavier the weight 27, the smaller the amount
of camshaft rotary inertia force change, and thus the smaller the
enlargement range for the actual operating angle in the low
rotation speed region. Therefore, a desired torque (according to a
design value) can be obtained in the low rotation speed region by
adjusting the weight of the weight 27.
(Modifications)
[0175] In the fourth embodiment, the weight 27 is attached to an
end of the camshaft 18. However, the weight 27 may alternatively be
attached to an end of a motor drive shaft 26A as shown in FIG. 20.
FIG. 20 shows the inertia force increase section for the cam drive
system according to a modification of the fourth embodiment.
Another alternative would be to attach the weight 27 to the gears
23, 24, 25. These modifications provide the same advantages as the
fourth embodiment because they can reduce the amount of camshaft
rotary inertia force change during a valve lift.
[0176] Further, the spring constant of the valve spring 12 may be
greater than its design value. In such an instance, it may not be
possible to minimize the motor torque by exercising motor control
so as to obtain the lift curves shown in the upper halves of FIGS.
10A to 10E. In other words, the actual spring reaction force may be
greater than the spring reaction force calculated in accordance
with the design value. Therefore, complete cancel may not be
provided by the camshaft rotary inertia force. Then, it may be
necessary to require the motor to generate the
counter-spring-reaction-force torque during a valve lift.
Consequently, adding the weight 27 causes the camshaft rotary
inertia force increase, thereby being capable of minimizing the
motor torque when the spring constant is greater than its design
value.
[0177] In the fourth embodiment and its modifications, the camshaft
18, gears 23, 24, 25, and motor 26 correspond to the "cam drive
system" according to the seventh aspect of the present invention;
and the weight 27 corresponds to the "inertia force increase
section" according to the seventh aspect of the present
invention.
Fifth Embodiment
[0178] A fifth embodiment of the present invention will now be
described with reference to FIG. 21.
[0179] FIG. 21 shows an inertia force change mechanism according to
the fifth embodiment of the present invention. As shown in FIG. 21,
the inertia force change mechanism 28 is mounted on the outer
circumference of the camshaft 18. The inertia force change
mechanism 28 includes an oil passage 28A, which communicates with
an oil passage 18A in the camshaft 18. A weight 28B is positioned
in the oil passage 28A. The oil passage 28A is provided with a
spring 28C that biases the weight 28B toward the inside of the
camshaft 18 (toward the center).
[0180] If the hydraulic pressure applied to the oil passage 28A
through the oil passage 18A is smaller than the biasing force of
the spring 28C, the weight 28B is biased toward the inside of the
camshaft 18. If, on the other hand, the hydraulic pressure applied
to the oil passage 28A is greater than the biasing force of the
spring 28C, the weight 28B moves outward.
Features of Fifth Embodiment
[0181] The power consumption and rating of the motor can be reduced
by allowing the camshaft rotary inertia force to cancel the spring
reaction force as described above.
[0182] Meanwhile, the variable valve mechanism 10 shown in FIG. 1
can control the camshaft rotation speed without regard to the
crankshaft 3, thereby can change the operating angle.
[0183] However, when the motor rating is reduced, no more extra
motor torque exists so that it may be impossible to change the
operating angle particularly in the low rotation speed region.
Further, if an attempt is made to obtain extra motor torque, the
motor rating becomes as high as in the conventional case.
[0184] Therefore, when the operating angle is to be decreased
within the low rotation speed region, the fifth embodiment moves
the weight 28B outward by applying engine oil pressure to the oil
passage 28A. The camshaft rotary inertia force can then be
increased. This makes it possible to reduce the aforementioned
enlargement range for the actual operating angle and switch to a
small operating angle.
[0185] When, on the other hand, the operating angle is to be
increased within the low rotation speed region, the fifth
embodiment moves the weight 28B inward by applying no engine oil
pressure to the oil passage 28A. The camshaft rotary inertia force
can then be decreased. This makes it possible to increase the
aforementioned enlargement range for the actual operating angle and
switch to a large operating angle.
[0186] Consequently, even when the motor rating is low, the fifth
embodiment can change the camshaft rotary inertia force by
repositioning the weight 28B. As a result, the operating angle can
be changed.
[0187] In the fifth embodiment, the inertia force change mechanism
28 corresponds to the "inertia force change mechanism" according to
the eighth aspect of the present invention.
Sixth Embodiment
[0188] A sixth embodiment of the present invention will now be
described with reference to FIG. 22.
[0189] The hardware shown in FIGS. 1 to 5 can be used as a system
according to the sixth embodiment.
Features of Sixth Embodiment
[0190] The first and second embodiments have been described in
conjunction with motor drive control that is initiated when the cam
and camshaft are rotating.
[0191] The sixth embodiment will be described in conjunction with
motor drive control that is initiated when the cam and camshaft are
stopped. FIG. 22 shows cam rotation speed changes and motor torque
in the sixth embodiment.
[0192] As shown in FIG. 22, the cam is stopped at a base circle
before the beginning of startup. Therefore, the cam rotation speed
and camshaft rotation speed are zero. Further, the camshaft rotary
inertia force is also zero.
[0193] During a subsequent cam base circle slide, that is, during
the time interval between the instant at which startup begins and
the instant at which a lift is about to begin, the cam rotation
speed is raised to a target value. As a result, the camshaft rotary
inertia force reaches a predetermined value. In this instance, no
spring reaction force acts on the camshaft. Therefore, acceleration
can be achieved by a smaller motor torque than when acceleration is
achieved during a valve lift. When an extra motor torque is
available, the acceleration is executed slowly so that the cam
rotation speed reaches the target value at the beginning of a lift.
The reason is that slow acceleration requires less motor power
consumption than sudden acceleration.
[0194] During the subsequent time interval between the instant at
which a lift starts and the instant at which the maximum lift is
provided, only the counter-friction torque is required to the motor
to generate without requiring the motor to generate the
counter-spring-reaction-force torque. Therefore, the spring
reaction force decreases the cam rotation speed, thereby gradually
decreasing the camshaft rotary inertia force.
[0195] During the time interval between the instant at which the
maximum lift is provided and the instant at which a valve lift
terminates, only the counter-friction torque is required to the
motor to generate also without requiring the motor to generate the
counter-spring-reaction-force torque. Therefore, the spring
reaction force increases the cam rotation speed, thereby gradually
increasing the camshaft rotary inertia force. Since the cam
rotation speed reaches the aforementioned target value again at the
end of a valve lift, the camshaft rotary inertia force reaches the
predetermined value again.
[0196] As described above, the sixth embodiment increases the cam
rotation speed before the start of a lift to increase the camshaft
rotary inertia force to a value equal to or more than the
predetermined value, thereby allowing the camshaft rotary inertia
force to cancel the spring reaction force. Therefore, it is
necessary that only the counter-friction torque be generated by the
motor during a valve lift as shown in FIG. 22. Further, during a
cam base circle slide before the start of a lift, the cam rotation
speed can be increased by a relatively small motor torque. In other
words, the motor torque for increasing the cam rotation speed is
smaller than the counter-spring-reaction-force torque. Therefore,
it is possible to reduce the power consumption and rating of the
motor.
[0197] In the sixth embodiment, the ECU 30 corresponds to the
"control means" according to the ninth aspect of the present
invention.
Seventh Embodiment
[0198] A seventh embodiment of the present invention will now be
described with reference to FIG. 23.
[0199] The hardware shown in FIGS. 1 to 5 can be used as a system
according to the seventh embodiment.
Features of Seventh Embodiment
[0200] In the sixth embodiment described earlier, the motor torque
for increasing the cam rotation speed before the start of a lift is
greater than the motor torque used during a valve lift. In such an
instance, the power consumption and rating of the motor are
determined by the motor torque used at the beginning of cam
drive.
[0201] As such being the case, the seventh embodiment will be
described in conjunction with a method of reducing the motor torque
during the time for cam drive start (that is, during the time for
cam rotation speed acceleration before the start of a lift) FIG. 23
shows cam rotation speed changes and motor torque in the seventh
embodiment.
[0202] As shown in FIG. 23, the cam rotation speed is raised to an
initial target value during a cam base circle slide, that is,
during the time interval between the instant at which startup
begins and the instant at which a lift is about to begin. The
initial target value is smaller than the target value used in the
sixth embodiment. Therefore, the motor torque required for raising
the cam rotation speed to the second target value is smaller than
the motor torque required for raising the cam rotation speed to the
above-mentioned target value.
[0203] During the subsequent time interval between the instant at
which a lift starts and the instant at which the maximum lift is
provided, only the counter-friction torque is required to the motor
to generate without requiring the motor to generate the
counter-spring-reaction-force torque. Therefore, the spring
reaction force decreases the cam rotation speed, thereby gradually
decreasing the camshaft rotary inertia force.
[0204] Before the start of a lift, the cam rotation speed is merely
raised to the initial target value. If this condition is allowed to
continue, the cam rotation speed does not reach the target value at
the end of a lift. Therefore, the torque for raising the cam
rotation speed is required to the motor to generate during the time
interval between the instant at which the maximum lift is provided
and the instant at which a valve lift terminates. The motor torque
required in this stage is equal to or smaller than the motor torque
required before the start of a lift. Generating such motor torque
ensures that the cam rotation speed reaches the target value at the
end of a lift.
[0205] As described above, the seventh embodiment increases the cam
rotation speed to the initial target value, which represents a
lower cam rotation speed than the target value, before the start of
a lift, and generates motor torque during a cam lift so that the
cam rotation speed reaches the target value at the end of a lift.
Therefore, the motor torque required for the start of cam drive is
smaller in the seventh embodiment than in the sixth embodiment.
Consequently, the power consumption and rating of the motor can be
reduced.
[0206] In the seventh embodiment, the ECU 30 corresponds to the
"control means" according to the tenth aspect of the present
invention.
Eighth Embodiment
[0207] An eighth embodiment of the present invention will now be
described with reference to FIGS. 24A and 24B.
[0208] The hardware shown in FIGS. 1 to 5 can be used as a system
according to the eighth embodiment.
Features of Eighth Embodiment
[0209] At the time of engine startup, no camshaft rotary inertia
force exists. If the camshaft rotary inertia force is smaller than
a peak torque Tp shown in FIG. 7, a cam lobe cannot be overridden.
It means that the cam cannot be driven in a normal rotation
direction.
[0210] In the seventh embodiment, which has been described earlier,
the cam rotation speed is raised to the initial target value by
imparting motor torque to the camshaft during a cam base circle
slide, that is, during the time interval between the instant at
which engine startup begins and the instant at which a valve lift
is about to begin. Subsequently, the cam rotation speed is raised
to the final target value by imparting motor torque during the time
interval between the instant at which the maximum lift is provided
and the instant at which the valve lift terminates. As described
above, the motor torque is imparted in two steps to reduce the
motor rating and increase the camshaft rotary inertia force to a
value not smaller than the peak torque Tp.
[0211] The eighth embodiment will be described in conjunction with
a method for further reducing the motor rating than that in the
seventh embodiment, which has been described earlier. FIGS. 24A and
24B show cam phase changes and valve lifts in the eighth
embodiment. More specifically, FIG. 24A shows cam phase changes,
whereas FIG. 24B shows the valve lifts of the first cylinder #1 and
fourth cylinder #4.
[0212] At time t0, which is indicated in FIGS. 24A and 24B, an
engine startup sequence begins. This engine startup sequence is
also employed as an engine restart sequence. Motor torque is
imparted to the camshaft during the interval between time t0 and
time t1, which is the time for starting a valve lift for the first
cylinder #1, that is, during a cam base circle slide between the
beginning of engine startup and the start of a valve lift. The cam
rotation speed then increases to increase the camshaft rotary
inertia force. The motor torque imparted between time t0 and time
t1 can be smaller than the motor torque imparted before the start
of a lift in the seventh embodiment. Therefore, the motor rating
can be reduced.
[0213] During a subsequent valve lift between time t1 and time t2,
no motor torque is imparted to the camshaft. Then, during the
interval between time t2 at which the valve lift for the first
cylinder #1 terminates and time t3 at which a valve lift for the
fourth cylinder #4 starts, motor torque oriented in a direction
opposite the torquing direction employed between time t0 and time
t1 is imparted to the camshaft. This ensures that the cam rotation
speed at time t3 is higher than the cam rotation speed at time t1.
As a result, the camshaft rotary inertia force at time t3 is
greater than the camshaft rotary inertia force at time t1. The cam
phase then increases to increase the cam swing range.
[0214] During the subsequent interval between time t4 at which the
valve lift for the fourth cylinder #4 terminates and time t5 at
which a valve lift for the first cylinder #1 starts, motor torque
oriented in a direction opposite the torquing direction used
between time t2 and time t3 is imparted to the camshaft. This
ensures that the cam rotation speed at time t5 is higher than the
cam rotation speed at time t3. As a result, the camshaft rotary
inertia force at time t5 is greater than the camshaft rotary
inertia force at time t3. As a result, the cam phase further
increases so as to further increase the cam swing range.
[0215] During a subsequent cam base circle slide between time t6
and time t7, between time t8 and time t9, and between time t10 and
time t11, motor torque is imparted to the camshaft in the same
manner as described above. Then, the cam rotation speed increases
as the time elapses from t7 through t9 to t11, thereby gradually
increasing the camshaft rotary inertia force. As a result, the cam
phase gradually increases so as to gradually increase the cam swing
range. This causes the valve lift amount to gradually increase.
[0216] When the camshaft rotary inertia force necessary for driving
the cam in a normal rotation direction is obtained at time t11,
switching is made at time t12 to drive the cam in a normal rotation
direction. In other words, normal rotation drive of the cam
synchronizing with crankshaft rotation arises after time t12.
[0217] As described above, the eighth embodiment gradually
increases the cam rotation speed by imparting motor torque to the
camshaft so as to drive the cam to swing during a cam base circle
slide after the beginning of engine startup. As a result, the cam
phase gradually increases to gradually increase the camshaft rotary
inertia force. When the camshaft rotary inertia force later reaches
a predetermined value necessary for normal rotation drive, normal
rotation drive of the cam synchronizing with crankshaft rotation
arises. When the camshaft rotary inertia force is gradually
accumulated while the cam is driven to swing as described above, a
predetermined value (peak torque) necessary for normal rotation
drive can be attained even using a motor with a low rating.
Therefore, the eighth embodiment can provide lower motor resistance
than the seventh embodiment, which has been described earlier.
Ninth Embodiment
[0218] A ninth embodiment of the present invention will now be
described with reference to FIGS. 25 to 27.
[0219] The hardware shown in FIGS. 1 to 5 can be used as a system
according to the ninth embodiment.
Features of Ninth Embodiment
[0220] The eighth embodiment, which has been described earlier,
gradually increases the cam swing range (phase) at engine startup
to increase the cam rotation speed and camshaft rotary inertia
force, and then switches the cam from the swing drive mode to the
normal rotation drive mode. In the eighth embodiment, however, no
motor torque is imparted to the camshaft during a valve lift. This
scheme is employed to reduce the power consumption of the motor
during a valve lift.
[0221] An engine startup request is not only generated in
compliance with an acceleration request, which is based on a
vehicle driver's accelerator operation, but also generated in
compliance with a catalyst warm-up request, which is issued when
the catalyst bed temperature is low. If the catalyst bed
temperature is not higher than a predetermined value while the
engine is stopped, the ECU 30 judges that an engine startup request
is generated in accordance with a catalyst warm-up request. The
catalyst bed temperature can be detected by the catalyst bed
temperature sensor 45 shown in FIG. 3. Further, if an accelerator
pedal is depressed while the engine is stopped, the ECU 30 judges
that an engine startup request is generated in accordance with an
acceleration request. A depressed accelerator pedal can be detected
by the accelerator angle sensor 36 shown in FIG. 3.
[0222] When an engine startup request is generated in accordance
with an acceleration request, it is necessary to start the engine
in a short period of time. To achieve engine startup in a short
period of time, it is preferred that the cam is switched from the
swing drive mode to the normal rotation drive mode in a short
period of time. The reason is that the normal rotation drive mode
for the cam provides a larger time area and higher intake
performance than the swing drive mode.
[0223] When, on the other hand, an engine startup request is
generated in accordance with a catalyst warm-up request, there is
no need to start the engine in a short period of time unlike in the
case of the aforementioned engine startup request based on an
acceleration request.
[0224] However, if the accelerator angle is significantly small, it
is not always necessary to start the engine in a short period of
time no matter when an engine startup request is generated in
accordance with an acceleration request.
[0225] Under the above circumstances, the ninth embodiment
determines whether or not to impart motor torque to the camshaft
during a valve lift in accordance with the degree of requested
acceleration indicated by the engine startup request. In other
words, the ninth embodiment changes a motor assist pattern in
accordance with the engine startup request.
[0226] More specifically, the degree of requested acceleration is
small when an engine startup request is generated in accordance
with a catalyst warm-up request. In this instance, therefore, no
motor torque is imparted to the camshaft during a valve lift as
indicated in FIGS. 25A to 25C. FIGS. 25A to 25C show an example of
motor torque that is imparted in the ninth embodiment when an
engine startup request is generated in accordance with a catalyst
warm-up request. More specifically, FIG. 25A shows a valve lift;
FIG. 25B shows a motor angular velocity; and FIG. 25C shows a motor
torque (control instruction value). The motor angular velocity
correlates with (is proportional to) the camshaft rotation
speed.
[0227] When an engine startup request based on a catalyst warm-up
request is acquired, an engine startup sequence begins at time t20,
which is shown in FIGS. 25A to 25C. As indicated in FIG. 25B, the
motor angular velocity is zero at time t20. During a cam base
circle slide between time t20 and time t21 at which a valve lift
for the first cylinder #1 starts, motor torque is imparted to the
camshaft. The motor angular velocity and camshaft rotation speed
then increase. During a subsequent valve lift between time t21 and
time t23, no motor torque is imparted to the camshaft. Therefore,
the spring reaction force oriented in a direction opposite the
camshaft rotation direction reduces the motor angular velocity and
camshaft rotation speed before the maximum lift is provided at time
t22. After time t22, the camshaft rotation direction reverses so
that the spring reaction force oriented in the same direction as
the reversed camshaft rotation direction increases the motor
angular velocity and camshaft rotation speed.
[0228] During a subsequent cam base circle slide between time t23
at which the valve lift terminates and time t24 at which a valve
lift for the fourth cylinder #4 starts, motor torque oriented in
the same direction as the camshaft rotation direction is imparted.
As a result, the motor angular velocity (absolute value) at time
t24 is higher than the motor angular velocity (absolute value) at
time t21.
[0229] During a subsequent valve lift between time t24 and time
t26, no motor torque is imparted to the camshaft as is the case
with the interval between time t21 and time t23. Therefore, the
spring reaction force oriented in a direction opposite the camshaft
rotation direction reduces the motor angular velocity and camshaft
rotation speed before the maximum lift is provided at time t25.
After time 25, the camshaft rotation direction reverses so that the
spring reaction force oriented in the same direction as the
camshaft rotation direction increases the motor angular velocity
and camshaft rotation speed.
[0230] During a subsequent cam base circle slide after time t26 at
which the valve lift terminates, motor torque oriented in the same
direction as the camshaft rotation direction is imparted. As a
result, the motor angular velocity and camshaft rotation speed for
normal rotation drive are reached at time t27. Therefore, the motor
torque is changed to a torque composed of friction torque only.
After time t27, the cam is switched to the normal rotation drive
mode, and control is exercised to synchronize the cam with the
crankshaft. Consequently, the cam is driven in a normal rotation
direction to perform a valve lift for the first cylinder #1 during
the interval between time t28 and time t30. This makes it possible
to perform ignition for the first cylinder #1.
[0231] On the other hand, when an engine startup request based on
an acceleration request is acquired, motor torque is imparted to
the camshaft during a valve lift as shown in FIGS. 26A to 26C.
FIGS. 26A to 26C show an example of motor torque that is imparted
in the ninth embodiment when an engine startup request is generated
in accordance with an acceleration request. More specifically, FIG.
26A shows a valve lift; FIG. 26B shows a motor angular velocity;
and FIG. 26C shows a motor torque (control instruction value)
[0232] When an engine startup request based on an acceleration
request is acquired, an engine startup sequence begins at time t40,
which is shown in FIGS. 26A to 26C. As indicated in FIG. 26B, the
motor angular velocity is zero at time t40. During a cam base
circle slide between time t40 and time t41 at which a valve lift
for the fourth cylinder #4 starts, motor torque is imparted to the
camshaft. The motor angular velocity and camshaft rotation speed
then increase.
[0233] During a subsequent valve lift between time t41 and time
t43, motor torque is also imparted to the camshaft unlike in the
case shown in FIGS. 25A to 25C. More specifically, the same motor
torque as for a period preceding time t41 is imparted during the
interval between time t41 at which a valve lift starts and time t42
at which the maximum lift is provided, and motor torque oriented in
an opposite direction is imparted during the interval between time
t42 and time t43 at which the valve lift terminates. As a result,
the motor angular velocity (absolute value) at time t43 at which
the valve lift terminates is higher than the motor angular velocity
(absolute value) at time t41 at which the valve lift starts.
[0234] During a subsequent cam base circle slide after time t43 at
which the valve lift terminates, the same motor torque as for the
interval between time t42 and time t43 is imparted. As a result,
the motor angular velocity and camshaft rotation speed for normal
rotation drive are reached at time t44. Therefore, the motor torque
is changed to a torque composed of friction torque only. The
interval between time t40 and time t44 is shorter than the interval
between time t20 and time t27, which are shown in FIGS. 25A to 25C.
In other words, the example shown in FIGS. 26A to 26C makes it
possible to switch to the normal rotation drive mode in a shorter
period of time than the example shown in FIGS. 25A to 25C.
[0235] After time t44, the cam is switched to the normal rotation
drive mode, and control is exercised to synchronize the cam with
the crankshaft. Consequently, a valve lift is performed for the
first cylinder #1 during the interval between time t45 and time
t47. This makes it possible to perform ignition for the first
cylinder #1.
Details of Process Performed by Ninth Embodiment
[0236] FIG. 27 is a flowchart illustrating a routine that the ECU
30 executes in the ninth embodiment. The routine is started at
predetermined time intervals while the engine is stopped due, for
instance, to the use of an EV mode.
[0237] First of all, the routine shown in FIG. 27 judge whether an
engine startup request is generated performs (step 100). In step
100, if the catalyst bed temperature is equal to or lower than the
predetermined value, it is judged that an engine startup request is
generated in accordance with a catalyst warm-up request. If, on the
other hand, a vehicle driver has operated an accelerator (stepped
on the accelerator pedal), it is judged that an engine startup
request is generated in accordance with an acceleration request. If
it is judged in step 100 that no engine startup request is
generated, the routine terminates.
[0238] If it is judged in step 100 that an engine startup request
is generated, the engine startup request is acquired (step 102).
Next, it is judge whether the degree of requested acceleration
indicated by the engine startup request acquired in step 102 is
equal to or larger than a predetermined value (step 104). Step 104
is performed to judge whether engine startup in a short period of
time is requested. More specifically, this step is performed to
judge whether the accelerator angle is equal to or larger than a
predetermined value.
[0239] If it is judged in step 104 that the degree of requested
acceleration is smaller than the predetermined value in a
situation, for instance, where the accelerator pedal is slightly
stepped on or where catalyst warm-up is requested with the
accelerator pedal insignificantly stepped on, it is concluded that
engine startup in a short period of time is not requested. In this
instance, motor torque is imparted to the camshaft only during a
cam base circle slide (step 106). In step 106, motor torque control
shown, for instance, in FIGS. 25A to 25C is exercised.
[0240] If, on the other hand, it is judged in step 104 that the
degree of requested acceleration is equal to or more than the
predetermined value in a situation, for instance, where the
accelerator pedal is considerably stepped on, it is concluded that
engine startup in a short period of time is requested. In other
words, it is concluded that the cam needs to be driven in a normal
rotation direction in a short period of time. In this instance,
motor torque is imparted to the camshaft not only during a cam base
circle slide but also during a valve lift (step 108). In step 108,
motor torque control shown, for instance, in FIGS. 26A to 26C is
exercised.
[0241] After completion of step 106 or 108, it is judge whether the
camshaft rotary inertia force is equal to or more than a
predetermined value (step 110). The predetermined value (that is,
the peak torque) represents the camshaft rotary inertia force
required for driving the cam in a normal rotation direction and is
used as a reference value for judging whether it is possible to
switch the cam from the swing drive mode to the normal rotation
drive mode. If it is judged in step 110 that the camshaft rotary
inertia force is smaller than the predetermined value, flow returns
to step 110. If, on the other hand, it is judged in step 110 that
the camshaft rotary inertia force is equal to or more than the
predetermined value, the camshaft is placed in the normal rotation
drive mode and control for synchronizing the camshaft with the
rotation of the crankshaft is exercised (step 112). Upon completion
of step 112, the routine terminates.
[0242] As described above, when the degree of requested
acceleration indicated by the engine startup request is high, the
ninth embodiment imparts motor torque not only during a cam base
circle slide but also during a valve lift. Since this allows the
camshaft rotary inertia force to increase in a short period of
time, it is possible to switch from the swing drive mode to the
normal rotation drive mode in a short period of time. As a result,
a high degree of requested acceleration can be achieved in
compliance with a request. When, on the other hand, the degree of
requested acceleration indicated by the engine startup request is
low, the ninth embodiment imparts motor torque only during a cam
base circle slide. Since this causes the cam to be switched from
the swing drive mode to the normal rotation drive mode in a
relatively long period of time, the power consumption of the motor
can be reduced. Consequently, the ninth embodiment can not only
reduce the motor rating but also switch from the swing drive mode
to the normal rotation drive mode with optimum timing according to
the degree of requested acceleration.
[0243] In the ninth embodiment, the "control means" according to
the thirteenth aspect of the present invention is implemented when
the ECU 30 performs steps 108, 110, and 112; the "startup request
acquisition means" according to the fourteenth aspect of the
present invention is implemented when the ECU 30 performs step 102;
the "control means" according to the fourteenth aspect of the
present invention is implemented when the ECU 30 performs steps
104, 106, and 108; the "judgment means" according to the fifteenth
aspect of the present invention is implemented when the ECU 30
performs step 104; and the "control means" according to the
fifteenth aspect of the present invention is implemented when the
ECU 30 performs steps 106 and 108.
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