U.S. patent application number 14/808263 was filed with the patent office on 2016-02-04 for drive apparatus.
The applicant listed for this patent is DENSO CORPORATION. Invention is credited to Toshihiro TAKAHARA, Yuuya TAKAHASHI.
Application Number | 20160032796 14/808263 |
Document ID | / |
Family ID | 55179536 |
Filed Date | 2016-02-04 |
United States Patent
Application |
20160032796 |
Kind Code |
A1 |
TAKAHASHI; Yuuya ; et
al. |
February 4, 2016 |
DRIVE APPARATUS
Abstract
A profile radius change rate, which is an amount of change in a
profile radius of a drive cam relative to a rotational angle of the
drive cam in a pocket boundary section located between a
progressively changing portion and a pocket portion, is set such
that a boundary sound pressure, which is a sound pressure generated
when a contact point between a roller and the drive cam passes
through the pocket boundary section in response to the rotational
movement of the drive cam, is included in a reference sound
pressure range, which is a range of variation in a sound pressure
generated when the contact point passes through the progressively
changing portion.
Inventors: |
TAKAHASHI; Yuuya;
(Tokai-city, JP) ; TAKAHARA; Toshihiro;
(Kariya-city, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DENSO CORPORATION |
Kariya-city |
|
JP |
|
|
Family ID: |
55179536 |
Appl. No.: |
14/808263 |
Filed: |
July 24, 2015 |
Current U.S.
Class: |
123/90.18 |
Current CPC
Class: |
F01L 13/0042
20130101 |
International
Class: |
F01L 13/00 20060101
F01L013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2014 |
JP |
2014-158712 |
Claims
1. A drive apparatus that adjusts a control amount of a controlled
subject in response to an axial position of a control shaft member,
the drive apparatus comprising: a drive source; a driving-side gear
that is joined to an output shaft of the drive source; a
driven-side gear that receives a drive force of the drive source
directly from the driving-side gear or indirectly from the
driving-side gear through at least one intermediate gear; a drive
cam that is rotatable about a camshaft member, which is joined to
the driven-side gear, wherein a profile radius of the drive cam,
which is a distance from a rotational center of the drive cam to an
outer peripheral surface of the drive cam, is not uniform in a
circumferential direction of the drive cam; a contact portion that
is placed on one radial side of the drive cam in a radial direction
of the rotational center of the drive cam, wherein the contact
portion is urged by the controlled subject to contact the outer
peripheral surface of the drive cam at a contact point; a support
member that supports the contact portion, wherein the support
member makes linear reciprocating movement in a direction
perpendicular to an axial direction of the camshaft member in
response to a change in the profile radius at the contact point
upon rotational movement of the drive cam; and the control shaft
member that is joined to the support member, wherein the control
shaft member makes linear reciprocating movement in an axial
direction of the control shaft member together with the support
member, wherein: the drive cam includes: a progressively changing
portion, in which the profile radius progressively changes in
response to the rotational movement of the drive cam; and a pocket
portion, which is placed adjacent to the progressively changing
portion in the circumferential direction, wherein the profile
radius increases in both of a forward rotational direction and a
reverse rotational direction of the drive cam in the pocket
portion; and a profile radius change rate, which is an amount of
change in the profile radius relative to a rotational angle of the
drive cam in a pocket boundary section located between the
progressively changing portion and the pocket portion, is set such
that a boundary sound pressure, which is a sound pressure generated
when the contact point passes through the pocket boundary section
in response to the rotational movement of the drive cam, is
included in a reference sound pressure range, which is a range of
variation in a sound pressure generated when the contact point
passes through the progressively changing portion.
2. The drive apparatus according to claim 1, wherein the profile
radius change rate at the pocket boundary section is defined as an
inclination of a straight line, which connects between an apex of
the pocket boundary section and an inflection point that is closest
to the apex and is located in one of the progressively changing
portion and the pocket portion.
3. The drive apparatus according to claim 2, wherein: the
progressively changing portion is formed such that the profile
radius is changed at a constant gradient in response to the
rotational movement of the drive cam; and the profile radius change
rate at the progressively changing portion side is defined as a
gradient of the progressively changing portion.
4. The drive apparatus according to claim 1, wherein the
driven-side gear receives the drive force of the drive source
indirectly from the driving-side gear through the at least one
intermediate gear.
5. The drive apparatus according to claim 1, wherein: the
driving-side gear is a spur gear; and the driven-side gear is a
spur gear.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2014-158712 filed on Aug.
4, 2014.
TECHNICAL FIELD
[0002] The present disclosure relates to a drive apparatus, which
converts rotational movement of a drive source into linear
reciprocating movement of a control shaft member and adjusts a
control amount of a controlled subject according to an axial
position of the control shaft member.
BACKGROUND
[0003] A previously known drive apparatus converts rotational
movement of a drive source into linear reciprocating movement of a
control shaft member through a drive cam and adjusts a control
amount of a controlled subject according to an axial position of
the control shaft member. In this drive apparatus, when a drive
force of the drive source is stopped, it is required to hold a
given constant position of the drive cam and a given constant
position of the control shaft member against a load applied from
the controlled subject to the control shaft member.
[0004] For example, a drive cam of a drive apparatus disclosed in
JP2014-134194A (corresponding to US2014/0116197A1) has a pocket
portion. In the pocket portion of the drive cam, a profile radius,
which is a distance from a rotational center of the drive cam to a
profile (i.e., an outer peripheral surface) of the drive cam,
increases in both of a forward rotational direction (also referred
to as a normal rotational direction) and a reverser rotational
direction of the drive cam. When the drive force of the motor is
stopped in a state where the pocket portion contacts the roller,
the rotation of the drive cam is locked at a corresponding
rotational position, at which the profile radius is minimized in
the pocket portion. Thereby, each of the rotational position of the
drive cam and the axial position of the control shaft member can be
held at the given constant position.
[0005] The drive cam of JP2014-134194A (corresponding to
US2014/0116197A1) has a progressively changing portion (also
referred to as a gradually-varying portion), in which the profile
radius progressively increases in response to rotation of the drive
cam. A drive force of a motor control device is transmitted from a
motor gear, which is connected to an output shaft of the motor, to
a cam gear, which is connected to the drive cam.
[0006] When the drive cam is rotated in a direction, along which
the profile radius progressively increases, in a state where the
roller contacts the progressively changing portion of the drive
cam, a tooth of the motor gear, which serves as a driving-side
gear, always acts to push a corresponding tooth of the cam gear,
which serves as a driven-side gear.
[0007] However, when a contact point of the roller, which contacts
the drive cam, is moved into the pocket portion through a boundary
between the progressively changing portion and the pocket portion,
the profile radius, which has been progressively increased in
response to the rotation of the drive cam, is progressively
decreased. Therefore, a force is exerted from the roller to rotate
the drive cam to move the contact point of the roller to the bottom
(the profile radius minimum point) of the pocket portion. Because
of this rotational force, the tooth of the cam gear, which is the
driven-side gear, collides against the tooth of the motor gear,
which is the driving-side gear, to disadvantageously generate a
tooth hitting sound (a sound that is generated by hitting the tooth
of the motor gear with the tooth of the cam gear). Particularly, in
a case where the motor gear and the cam gear are formed as spur
gears, respectively, the tooth hitting sound tends to be
increased.
SUMMARY
[0008] The present disclosure is made in view of the above
disadvantage. According to the present disclosure, there is
provided a drive apparatus that adjusts a control amount of a
controlled subject in response to an axial position of a control
shaft member. The drive apparatus includes a drive source, a
driving-side gear, a driven-side gear, a drive cam, a contact
portion, a support member, and the control shaft member. The
driving-side gear is joined to an output shaft of the drive source.
The driven-side gear receives a drive force of the drive source
directly from the driving-side gear or indirectly from the
driving-side gear through at least one intermediate gear.
[0009] The drive cam is rotatable about a camshaft member, which is
joined to the driven-side gear. A profile radius of the drive cam,
which is a distance from a rotational center of the drive cam to an
outer peripheral surface of the drive cam, is not uniform in a
circumferential direction of the drive cam. The contact portion is
placed on one radial side of the drive cam in a radial direction of
the rotational center of the drive cam. The contact portion is
urged by the controlled subject to contact the outer peripheral
surface of the drive cam at a contact point. The support member
supports the contact portion. The support member makes linear
reciprocating movement in a direction perpendicular to an axial
direction of the camshaft member in response to a change in the
profile radius at the contact point upon rotational movement of the
drive cam. The control shaft member is joined to the support
member. The control shaft member makes linear reciprocating
movement in an axial direction of the control shaft member together
with the support member. The drive cam includes a progressively
changing portion, and a pocket portion. In the progressively
changing portion, the profile radius progressively changes in
response to the rotational movement of the drive cam. The pocket
portion is placed adjacent to the progressively changing portion in
the circumferential direction. The profile radius increases in both
of a forward rotational direction and a reverse rotational
direction of the drive cam in the pocket portion. A profile radius
change rate, which is an amount of change in the profile radius
relative to a rotational angle of the drive cam in a pocket
boundary section located between the progressively changing portion
and the pocket portion, is set such that a boundary sound pressure,
which is a sound pressure generated when the contact point passes
through the pocket boundary section in response to the rotational
movement of the drive cam, is included in a reference sound
pressure range, which is a range of variation in a sound pressure
generated when the contact point passes through the progressively
changing portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The drawings described herein are for illustration purposes
only and are not intended to limit the scope of the present
disclosure in any way.
[0011] FIG. 1A is a schematic diagram showing a transmitting
portion of a drive apparatus according to an embodiment of the
present disclosure;
[0012] FIG. 1B is a cross-sectional view taken along line b-b in
FIG. 1A;
[0013] FIG. 2 is a perspective view showing a speed reducing gear
mechanism of the drive apparatus of the embodiment;
[0014] FIG. 3 is a schematic view of a valve lift control system,
in which the drive apparatus of the embodiment is applied according
to the present disclosure;
[0015] FIG. 4 is a cross sectional view taken along line IV-IV in
FIG. 3;
[0016] FIG. 5 is a schematic diagram, showing details of the speed
reducing gear mechanism shown in FIG. 2;
[0017] FIG. 6 is a schematic diagram of a drive cam according to
the embodiment;
[0018] FIG. 7A and 7B are schematic diagrams showing application of
a drive torque, which is exerted by a motor torque and a roller, to
the drive cam;
[0019] FIGS. 8A and 8B are schematic diagrams showing a collision
phenomenon between a driving-side gear and a driven-side gear;
[0020] FIGS. 9A and 9B are diagrams of time charts for describing
the collision phenomenon between the driving-side gear and the
driven-side gear;
[0021] FIG. 10 is an enlarged view showing a pocket boundary
section of a drive cam of a second sample;
[0022] FIGS. 11A is a diagram indicating a profile radius change
rate at a second pocket boundary section of a drive cam of a first
sample;
[0023] FIG. 11B is a diagram indicating a profile radius change
rate at a third pocket boundary section of the drive cam of the
first sample;
[0024] FIG. 12A is a diagram indicating a profile radius change
rate at a second pocket boundary section of the drive cam of the
second sample;
[0025] FIG. 12B is a diagram indicating a profile radius change
rate at a third pocket boundary section of the drive cam of the
second sample;
[0026] FIG. 13A is a diagram indicating a change in a stroke of a
control shaft member relative to a rotational angle of the drive
cam at the time of rotating the drive cam of the first sample;
[0027] FIG. 13B is a diagram indicating a measured sound pressure
relative to the rotational angle of the drive cam of the first
sample;
[0028] FIG. 14A is a diagram indicating a change in a stroke of a
control shaft member relative to a rotational angle of the drive
cam at the time of rotating the drive cam of the second sample;
[0029] FIG. 14B is a diagram indicating a measured sound pressure
relative to the rotational angle of the drive cam of the second
sample;
[0030] FIG. 15 is a schematic diagram indicating a sound pressure
measuring method; and
[0031] FIG. 16 is a schematic diagram showing a transmitting
portion of a drive apparatus according to another embodiment of the
present disclosure.
DETAILED DESCRIPTION
[0032] A drive apparatus according to an embodiment of the present
disclosure will be described with reference to the accompanying
drawings.
[0033] As shown in FIGS. 3 and 4, the drive apparatus of the
present disclosure is implemented as a drive apparatus 10 of a
valve lift control system 100, which controls a lift amount L of an
intake valve 91 of, for example, a four cylinder internal
combustion engine 90 based on an axial position of a control shaft
member 30.
[0034] The valve lift control system 100 includes the drive
apparatus 10, an extension shaft 35, a plurality of helical splines
34, a plurality of rollers 36, and a plurality of rocker cams 38.
The drive apparatus 10 includes a control shaft member 30, which is
configured to linearly reciprocate. The extension shaft 35 is
connected to the control shaft member 30. The number of the helical
splines 34, the number of the rollers 36 and the number of the
rocker cams 38 correspond to the number of cylinders of the engine
90.
[0035] For example, an inner wall of the helical spline 34 is
meshed with an outer wall of the extension shaft 35 through helical
gear teeth. The helical spline 34 is rotated in response to the
linear reciprocating movement of the control shaft member 30 and
the extension shaft 35. In this way, an opening angle .psi. (see
FIG. 4) between an imaginary line s1, which connects between a
center of the extension shaft 35 and the roller 36, and an
imaginary line s2, which connects between the center of the
extension shaft 35 and a nose 381 of the rocker cam 38, is
changed.
[0036] The roller 36 contacts a cam portion of an intake valve
camshaft 93. When the position of the roller 36 is changed in
response to the rotation of the intake valve camshaft 93, the
rocker cam 38 is swung. The nose 381 of the rocker cam 38 contacts
a base end of the intake valve 91. The intake valve 91 is lifted in
response to the swing motion of the rocker cam 38. Therefore, the
lift amount L of the intake valve 91 can be adjusted by changing
the opening angle .psi. (see FIG. 4) through the adjustment of the
axial position of the control shaft member 30 and the extension
shaft 35.
[0037] The valve lift control system 100 of the present embodiment
does not adjust the lift amount of respective exhaust valves 92,
which are lifted through rotation of an exhaust valve camshaft
94.
[0038] Here, each intake valve 91 is urged in a valve-opening
direction thereof, which is an upward direction in FIG. 4, by an
urging force Fs of a valve spring 95 that contacts a flange 911.
The urging force Fs upwardly pushes the nose 381 of the rocker cam
38 and generates a rotational force Fr to the helical spline 34 in
a counterclockwise direction in FIG. 4. In the present embodiment,
the rotational force Fr of the helical spline 34 is converted into
a load Fa, which is exerted in a direction (an upward direction in
FIG. 3) of pulling the extension shaft 35 and the control shaft
member 30.
[0039] As discussed above, in the present embodiment, the load Fa
is applied from the helical spline 34, which serves as a driven
subject, to the control shaft member 30 in a direction of moving
the control shaft member 30 away from the drive cam 50.
[0040] Next, the structure of the drive apparatus 10 will be
described with reference to FIGS. 1A to 2 and 5. As shown in FIG.
2, the drive apparatus 10 includes an electric motor (serving as a
drive source) 20, the control shaft member 30, a support frame 41,
a roller 44, the drive cam 50 (see FIG. 1), and an angle sensor 70.
In the drive apparatus 10, the motor 20 generates a rotational
drive force according to a command received from an electronic
control unit (ECU) 76 and an electronic drive unit (EDU) 78.
[0041] The motor 20 is, for example, a DC motor and includes a
rotor 22, and permanent magnets 24. A coil is wound around the
rotor 22, and the permanent magnets 24 are placed on a radially
outer side of the rotor 22. A motor gear 62, which serves as a
driving-side gear, is installed to an end part of a shaft (an
output shaft) 26 of the motor 20, which is rotated integrally with
the rotor 22.
[0042] The control shaft member 30 is generally perpendicular to
the shaft 26 of the motor 20. One end part of the control shaft
member 30 is joined to a connecting portion 42 of the support frame
41 through a clip 43.
[0043] The support frame 41, which is configured into a rectangular
form, is placed on one radial side of the rotational center (the
rotational axis) P of the drive cam 50 in the radial direction and
is placed on an opposite side, which is opposite from the control
shaft member 30. As shown in FIG. 1B, the roller 44, which is
configured into a cylindrical form, is rotatably supported by a pin
411 that is fixed to the support frame 41.
[0044] The support frame 41 serves as a support member of the
present disclosure, and the roller 44 serves as a contact portion
of the present disclosure. The support frame 41 and the roller 44
form a transmitting portion 40, which converts the rotational
movement of the drive cam 50 into the linear reciprocating movement
and transmits the converted linear reciprocating movement to the
control shaft member 30.
[0045] The drive cam 50 has a profile radius (also referred to as a
cam radius) R, which is a radial distance from the rotational
center P to a profile of the drive cam 50 (i.e., an outer
peripheral surface of the drive cam 50). The profile radius R of
the drive cam 50 is riot uniform in a circumferential direction of
the drive cam 50. The drive cam 50 is placed in an inside of the
support frame 41 in such a manner that the drive cam 50 is
rotatable together with the camshaft member 51 about the rotational
center P. Furthermore, the roller 44, which is connected to the
control shaft member 30 through the support frame 41, is urged by
the load Fa discussed above to contact the profile of the drive cam
50 at a contact point C.
[0046] The rotational center P of the drive cam 50, the axis Q of
the roller 44, and the contact point C are placed along an axis J
of the control shaft member 30. The contact point C between the
roller 44 and the drive cam 50 is a line that extends in a
top-to-bottom direction of FIG. 1B, so that the contact point C is
a contact line in a correct sense. However, in this description,
for the sake of two-dimensional interpretation of the structure
shown in, for example, FIG. 1A, this contact line is referred to as
the contact point C.
[0047] When the drive cam 50 is rotated, the profile radius R at
the contact point C changes. Thereby, the roller 44, the support
frame 41 and the control shaft member 30 are linearly reciprocated
in the left-to-right direction in FIG. 1A in response to the
rotation of the drive cam 50.
[0048] Furthermore, three pocket portions 551, 552, 553 are formed
in the outer peripheral surface of the drive cam 50. One of the
pocket portions 551, 552, 553 contacts the roller 44 at the time of
stopping the drive force of the motor 20. As recited in JP
2014-134194A (corresponding to US 2014/0116197A1), the pocket
portion refers to a portion of the outer peripheral surface of the
drive cam 50, in which the profile radius R increases in both of a
forward rotational direction (also referred to as a normal
rotational direction) and a reverse rotational direction of the
drive cam 50 that is opposite from the forward rotational
direction. When the contact point C is located at one of two
circumferential end parts of the pocket portion, a rotational force
is generated in the pocket portion in a direction that is from the
one of the two circumferential end parts toward a circumferential
center part of the pocket portion. Furthermore, when the contact
point C is placed at the circumferential center part of the pocket
portion where the profile radius R is minimized in the pocket
portion, the rotational force becomes zero. Thereby, the drive cam
50 is held in the stable position at the circumferential center
part of the pocket portion. This effect is referred to as a pocket
effect.
[0049] The camshaft member 51 is placed generally parallel to the
shaft 26 of the motor 20. A cam gear (serving as a driven-side
gear) 68 is installed in one end part of the camshaft member 51,
which is located on a side where the motor 20 is placed, and a
sensor-side cam gear 74 is installed to the other end part of the
camshaft member 51, which is opposite from the motor 20.
[0050] In FIG. 2, a portion of a drive force transmission path from
the motor gear 62 to the cam gear 68 in a speed reducing gear
mechanism is simplified. Therefore, this portion of the drive force
transmission path will be described with reference to FIG. 5. As
shown in FIG. 5, for example, two intermediate gears, i.e., first
and second intermediate gears 63, 65 are installed between the
motor gear 62 and the cam gear 68 in the drive force transmission
path. The first intermediate gear 63 includes a first stage gear
630 and a second stage gear 64, which are concentric about a point
G1. The second intermediate gear includes a first stage gear 650
and a second stage gear 66, which are concentric about a point
G2.
[0051] The motor gear 62, which is centered at a point M, is meshed
with the first stage gear 630 of the first intermediate gear 63.
The second stage gear 64 of the first intermediate gear 63 is
meshed with the first stage gear 650 of the second intermediate
gear 65. The second stage gear 66 of the second intermediate gear
65 is meshed with the cam gear 68. In view of the meshed parts
between each adjacent two gears, one of the two adjacent gears,
which is located on the motor 20 side, corresponds to "a
driving-side gear", and the other one of the two adjacent gears,
which is located on the drive cam 50 side, corresponds to "a
driven-side gear". Alternatively, any one of the gears, which is
located on an upstream side (the motor 20 side) in the drive force
transmission path, may be referred to as the driving-side gear, and
another one of the gears, which is located on a downstream side
(the drive cam 50 side) of the one of the gears in the drive force
transmission path, may be referred to as the driven-side gear.
[0052] In the present embodiment, as discussed above, the drive
force (the motor torque) of the motor 20 is transmitted from the
motor gear 62 to the cam gear 68 through the intermediate gears 63,
65. In another embodiment, the motor gear 62 and the cam gear 68
may be directly meshed with each other, as indicated in FIG. 2.
[0053] Furthermore, the motor gear 62, the intermediate gears 63,
65 and the cam gear 68 of the present embodiment are spur gears,
respectively. In another embodiment, a bevel gear may be used as
the driving-side gear and the driven-side gear.
[0054] The angle sensor 70 senses a rotational angle of a sensor
gear 72, which is meshed with the sensor-side cam gear 74, through
a magnetic sensing device, such as a Hall element.
[0055] The ECU 76 receives a measurement signal of the angle sensor
70 and other measurement signals (e.g., a measurement signal from
an accelerator opening degree sensor). The ECU 76 outputs a control
signal to the EDU 78 based on the inputted sensor measurement
signals.
[0056] The EDU 78 drives the motor 20 based on the control signal
received from the ECU 76.
[0057] Next, details of the structure of the drive cam 50 will be
described with reference to FIG. 6.
[0058] As shown in FIG. 6, the drive cam 50 has the pocket portions
(the first to third pocket portions) 551, 552, 553, which are
formed one after another in the circumferential direction about the
camshaft member 51 and which are respectively configured into a
form of a planar surface at three locations in the outer peripheral
surface of the drive cam 50. A cam angle .theta. is defined to have
a positive value on one side (a counterclockwise side) of a
reference axis x (.theta.=.theta.0) in a counterclockwise direction
in FIG. 6. Furthermore, a clockwise direction in FIG. 6 is defined
as the forward rotational direction, and the counterclockwise
direction in FIG. 6 is defined as the reverse rotational
direction.
[0059] The first pocket portion 551 is set to extend over the
reference axis x between a cam angle 81 and a cam angle .theta.1e e
in the circumferential direction and includes a portion having a
profile radius R1. The second pocket portion 552 is set to extend
between a cam angle .theta.2 and a cam angle .theta.2e and includes
a portion having a profile radius R2. The third pocket portion 553
is set to extend between a cam angle 83 and a cam angle 83e and
includes a portion having a profile radius R3. The profile radius
R1 of the first pocket portion 551, the profile radius R2 of the
second pocket portion 552, and the profile radius R3 of the third
pocket portion 553 satisfy a relationship of R3>R2>R1. In
FIG. 6, the cam angle 82 is indicated as 82 by using a subscript
2.
[0060] A first progressively changing portion 531 is formed to
extend from the first pocket portion 551 to the second pocket
portion 552. In the first progressively changing portion 531, the
profile radius R progressively increases in response to the forward
rotation of the drive cam 50. A second progressively changing
portion 532 is formed to extend from the second pocket portion 552
to the third pocket portion 553. In the second progressively
changing portion 532, the profile radius R progressively increases
in response to the forward rotation of the drive cam 50.
Particularly, in the present embodiment, a rate of change in the
profile radius R (hereinafter referred to as a profile radius
change rate) relative to the cam angle .theta. is constant in each
of the first progressively changing portion 531 and the second
progressively changing portion 532. In other words, the profile
radius R is increased at a constant gradient in each of the first
progressively changing portion 531 and the second progressively
changing portion 532.
[0061] Furthermore, a transition portion 57, in which the profile
radius R is linearly and rapidly decreased, is formed between the
third pocket portion 553 and the first pocket portion 551.
[0062] Furthermore, a boundary section between the first
progressively changing portion 531 and the second pocket portion
552 will be defined as a second pocket boundary section 542, and a
boundary section between the second progressively changing portion
532 and the third pocket portion 553 will be defined as a third
pocket boundary section 543. When the drive cam 50 is rotated in
the forward rotational direction, the contact point C between the
drive cam 50 and the roller 44 is moved from the first
progressively changing portion 531 to the second pocket portion 552
through the second pocket boundary section 542. Geometric
characteristics of the pocket boundary sections 542, 543 will be
described in detail later.
[0063] Now, the operation of the drive apparatus 10 will be
described.
[0064] When the motor 20 is driven by the command outputted from
the EDU 78, the drive force of the motor 20 is conducted to the
camshaft member 51 and the drive cam 50 through the motor gear 62,
the intermediate gears 63, 65, and the cam gear 68. When the drive
cam 50 is rotated, the support frame 41, which supports the roller
44 that is in contact with the drive cam 50, is reciprocated in the
direction that is perpendicular to the camshaft member 51 in
response to the change in the profile radius R at the contact point
C. Thereby, the control shaft member 30, which is joined to the
support frame 41, is linearly reciprocated, so that the extension
shaft 35 of the valve lift control system 100 is linearly
reciprocated.
[0065] In response to the axial position of the control shaft
member 30 and the axial position of the extension shaft 35, each
helical spline 34 of the valve lift control system 100 is rotated
to change the opening angle .psi. (see FIG. 4), which is defined
according to the position of the roller 36 and the position of the
rocker cam 38. Thus, the lift amount L of the intake valve 91 is
changed.
[0066] At the time of stopping the engine 90, the ECU76 selects one
of the first to third pocket portions 551-553 of the drive cam 50,
which corresponds to the axial position of the control shaft member
30 at the time of stopping the engine 90, and the ECU76 commands
the selected one of the first to third pocket portions 551-553 to
the EDU 78. The EDU 78 stops the energization of the motor 20 in
such a manner that the drive cam 50 stops at a corresponding
position where the commanded one of the first to third pocket
portions 551-553 contacts the roller 44 in response to the command
outputted from the ECU 76.
[0067] When the drive force of the motor 20 is stopped in this
manner, the rotational position of the drive cam 50 can be
maintained at the corresponding cam angle, which corresponds to the
minimum profile radius of the selected one of the first to third
pocket portions 551-553, and thereby the axial position of the
control shaft member 30 can be maintained at a selected one of a
most retarded position, an intermediate position and a most
advanced position.
[0068] Next, the objective of the present disclosure will be
described with reference to FIGS. 7A to 9B.
[0069] In FIGS. 7A and 7B, the progressively changing portion of
the drive cam 50 (serving as a generalized representation of the
progressively changing portions of the drive cam 50 of the
embodiment) is indicated by reference numeral 53, and the pocket
boundary section of the drive cam 50 (serving as a generalized
representation of the pocket boundary sections of the drive cam 50
of the embodiment) is indicated by reference numeral 54.
Furthermore, the pocket portion of the drive cam 50 (serving as a
generalized representation of the pocket portions of the drive cam
50 of the embodiment) is indicated by reference numeral 55. Here,
it is assumed that the roller 44 sequentially contacts the
progressively changing portion 53, the pocket boundary section 54,
and the pocket portion 55 in this order. In such a circumstance,
FIG. 7A indicates a time point when the roller 44 contacts the
progressively changing portion 53, and FIG. 7B indicates a time
point when the roller 44 contacts the pocket portion 55. In both of
FIGS. 7A and 7B, the motor torque Tm is exerted to rotate the drive
cam 50 in the clockwise direction in FIGS. 7A and 7B.
[0070] At this time, the drive cam 50 is driven in a profile radius
decreasing direction, along which the profile radius R is
progressively decreased, by the roller 44, which is urged toward
the center P of the drive cam 50. In the state of FIG. 7A, the
drive torque Tr of the roller 44 is exerted in the profile radius
decreasing direction, along which the profile radius Rn of the
progressively changing portion 53 is progressively decreased, i.e.,
in an opposite direction, which is opposite from a direction of the
motor torque Tm (more specifically, the direction of the motor
torque vector). Furthermore, in the state of FIG. 7B, the drive
torque Tr of the roller 44 is exerted in the profile radius
decreasing direction, along which the profile radius Rp of the
pocket portion 55 is progressively decreased, i.e., in the
direction of the motor torque Tm (more specifically, the direction
of the motor torque vector). Therefore, in the state of FIG. 7B,
the large torque, which is larger than the motor torque Tm, is
applied to the drive cam 50.
[0071] FIGS. 8A and 8B indicate a relationship of forces exerted
between the driving-side gear and the driven-side gear. Here, as an
example, the second stage gear 66 of the second intermediate gear
65 shown in FIG. 5 is used as the driving-side gear, and the cam
gear 68 sown in FIG. 5 is used as the driven-side gear.
[0072] In the state of FIG. 8A, which corresponds to FIG. 7A, a
tooth 672 of the driving-side gear (the second stage gear) 66
contacts and urges a tooth 692 of the driven-side gear (the cam
gear) 68, which is located on a front side of the tooth 672 of the
driving-side gear (the second stage gear) 66 in the rotational
direction, so that the motor torque Tm is conducted from the tooth
672 of the driving-side gear (the second stage gear) 66 to the
tooth 692 of the driven-side gear (the cam gear) 68. At this time,
backlash (also referred to as play) is formed between the tooth 672
of the driving-side gear (the second stage gear) 66 and a tooth 691
of the driven-side gear (the cam gear) 68, which is located on a
rear side of the tooth 672 of the driving-side gear (the second
stage gear) 66 in the rotational direction. The presence of the
backlash enables the smooth rotation of the gears 66, 68.
[0073] In a state of FIG. 8B, which corresponds to FIG. 7B, the
driven-side gear (the cam gear) 68, which is joined to the camshaft
member 51 of the drive cam 50, is rotated by the drive torque Tr of
the roller 44. Thus, the tooth 691 of the driven-side gear (the cam
gear) 68, which is located on the back side of the tooth 672 of the
driving-side gear (the second stage gear) 66, collides against the
tooth 672 of the driving-side gear (the second stage gear) 66
before occurrence of contact of the tooth 672 of the driving-side
gear (the second stage gear) 66 against the tooth 692 of the
driven-side gear (the cam gear) 68, so that tooth hitting sound
(commonly known as rattle sound) may possibly be generated. This
collision may possibly occur between other adjacent two of the
gears in the drive force transmission path from the motor gear 62
to the cam gear 68 shown in FIG. 5. In the case of the drive
apparatus 10, which is installed on the vehicle, this tooth hitting
sound may possibly deteriorate the salability of the vehicle.
[0074] FIGS. 9A and 9B indicate diagrams showing the behavior at
this time. As shown in FIG. 9A, at the time point tx, at which the
roller 44 passes through the pocket boundary section 54, the tooth
691 of the driven-side gear (the cam gear) 68 is accelerated by the
drive torque Tr exerted by the roller 44. In contrast, the teeth
671, 672 of the driving-side gear (the second stage gear) 66 are
rotated at a constant speed by the motor torque Tm.
[0075] In FIG. 9B, a width of the tooth 691 is ignored for the
descriptive purpose. At the time when the roller 44 contacts the
progressively changing portion 53, the tooth 691 of the driven-side
gear (the cam gear) 68 is rotated while the tooth 691 of the
driven-side gear (the cam gear) 68 is pushed by the tooth 671 of
the driving-side gear (the second stage gear) 66, which is located
on the rear side of the tooth 691 of the driven-side gear (the cam
gear) 68. However, when the tooth 691 of the driven-side gear (the
cam gear) 68 is accelerated at the time point tx, the tooth 691 of
the driven-side gear (the cam gear) 68 is spaced from the tooth 671
of the driving-side gear (the second stage gear) 66 located on the
rear side of the tooth 691 of the driven-side gear (the cam gear)
68 in the rotational direction and then collides against the tooth
672 of the driving-side gear (the second stage gear) 66.
[0076] In order to reduce the tooth hitting sound caused by this
kind of collision, it is effective to alleviate the rapid
acceleration at the time point tx, as indicated by an arrow
(countermeasure) in FIG. 9B. It is the objective of the present
disclosure to provide an appropriate configuration of the pocket
boundary section 54 of the drive cam 50, which is appropriate for
reducing the tooth hitting sound.
[0077] Next, cam profiles of two types of samples (i.e., samples A
and B) of the drive cam 50, which are prepared for achieving the
above objective, as well as a result of a sound pressure
measurement experiment will be described with reference to FIGS. 10
to 15.
[0078] In the sample (the first sample) A, the progressively
changing portion 53 (531, 532), in which the profile radius R is
increased at the constant gradient, is simply connected to the
pocket portion 55 (552, 553), which is configured into the form of
the planar surface, through an apex S (see FIG. 6).
[0079] In contrast, as shown in FIG. 10, in the sample (the second
sample) B, a transition portion 54n, which corresponds to an angle
.psi.n, is formed on one side of the apex S where the progressively
changing portion 53 is placed, and a transition portion 54p, which
corresponds to an angle .psi.p, is formed on the other side of the
apex S where the pocket portion 55 is placed. On the one side of
the apex S where the progressively changing portion 53 is placed,
the gradient is progressively decreased from a positive constant
value to 0 [mm/deg] during a period of increasing the profile
radius R from a inflection point In to the apex S by As. In other
words, the pressure angle is progressively decreased from the
positive constant value to 0 [deg]. Furthermore, on the other side
of the apex S where the pocket portion 55 is placed, the pressure
angle is kept to be 0 [deg] in an angular range between the apex S
and a inflection point Ip, and the profile radius R becomes
constant. It is desirable that the angle .psi.n of the transition
portion 54n eand the angle .phi.p of the transition portion 54p are
set to be as large as possible.
[0080] FIG. 11A is a diagram indicating a relationship between the
cam angle .theta. and the profile radius R at the second pocket
boundary section 542 in the sample A, and FIG. 11B is a diagram
indicating a relationship between the cam angle .theta. and the
profile radius R at the third pocket boundary section 543 in the
sample A. FIG. 12A is a diagram indicating a relationship between
the cam angle .theta. and the profile radius R at the second pocket
boundary section 542 in the sample B, and FIG. 12B is a diagram
indicating a relationship between the cam angle .theta. and the
profile radius R at the third pocket boundary section 543 in the
sample B.
[0081] In FIGS. 11A to 12B, the cam angle .theta. indicated at the
axis of abscissas is set such that the position of the apex S of
the pocket boundary section serves as a reference (0 degrees), and
a right direction along the axis of abscissas corresponds to the
forward rotational direction. Furthermore, in FIGS. 11A, 11B, 12A,
and 12B, a scale of the axis of abscissas and a scale of the axis
of ordinates are equally set.
[0082] The profile radius change rate corresponds to an inclination
of a straight line (=.DELTA.R/.DELTA..theta.). Here, the profile
radius change rate in the second pocket boundary section 542 is
indicated by k2, and the profile radius change rate in the third
pocket boundary section 543 is indicated by k3. Furthermore, a
third character A added after k2 or k3 indicates the sample A.
Also, a third character B added after k2 or k3 indicates the sample
B. Furthermore, a fourth character + added after k2 or k3 indicates
the forward rotational direction. Also, a fourth character - added
after k2 or k3 indicates the reverse rotational direction.
[0083] As shown in FIG. 11A and 11B, in the sample A, the apex S is
formed as an edge, and the pocket boundary section 54 (the pocket
boundary sections 542, 543) is indicated as a dot. In the
progressively changing portion 53 (the progressively changing
portions 531, 532), the gradient is constant up to the apex S, and
an inflection point does not exist in the middle of the
progressively changing portion 53 (the progressively changing
portions 531, 532). Therefore, in the forward rotational direction
for moving the roller 44 from the progressively changing portion 53
to the pocket portion 55 (from the progressively changing portions
531 to the pocket portion 552 and from the progressively changing
portions 532 to the pocket portion 553), the profile radius change
rates k2A+, k3A+ is defined as a gradient of the progressively
changing portion.
[0084] In contrast, in the reverse rotational direction for moving
the roller 44 from the pocket portion 55 to the progressively
changing portion 53 (from the pocket portion 552 to the
progressively changing portion 531 and from the pocket portion 553
to the progressively changing portion 532), the minimum point V at
the bottom of the pocket portion 55 (the pocket portions 552, 553)
is an inflection point, which is closest to the apex S, and thereby
the inclination of the straight line, which connects between the
minimum point V and the apex S, is defined as the profile radius
change rates k2A-, k3A-.
[0085] When a predetermined change rate threshold value is defined
as K, as indicated in FIGS. 11A and 11B, a relationship between
each profile radius change rate and the threshold value K of the
sample A is expressed as follows.
k2A+>K, k3A+.ltoreq.X, k2A->K, k3A->K
[0086] As shown in FIGS. 12A and 12B, in the sample B, the pocket
boundary section 54 (the pocket boundary sections 542, 543)
includes the apex S and is expressed by a cam angle range from the
inflection point In, which is closest to the apex S on the
progressively changing portion 53 side (the progressively changing
portion 531 side and the progressively changing portion 532) side,
to the inflection point Ip, which is closest to the apex S on the
pocket portion 55 side (the pocket portion 552 side and the pocket
portion 553 side). With respect to the profile radius change rate,
the inclination of the straight line, which connects between the
inflection point In and the apex S, is defined as k2B+, k3B+ in the
forward rotational direction, and the inclination of the straight
line, which connects between the inflection point Ip and the apex
S, is defined as k2B-, k3B- in the reverse rotational
direction.
[0087] A relationship between each profile radius change rate and
the threshold value K of the sample B is expressed as follows.
k2B+.ltoreq.K, k3B+>K, k2B-.ltoreq.K, k3B->K
[0088] FIG. 13A indicates a change in a stroke of the control shaft
member 30 relative to the rotational angle of the drive cam 50 at
the time of rotating the drive cam 50 of the sample A in the
forward rotational direction and the reverse rotational direction
in the drive apparatus 10. FIG. 14A indicates a change in a stroke
of the control shaft member 30 relative to the rotational angle of
the drive cam 50 at the time of rotating the drive cam 50 of the
sample B in the forward rotational direction and the reverse
rotational direction in the drive apparatus 10. A rotational angle
.theta.2, at which the inclination of the stroke changes,
corresponds to the second pocket boundary section 542 (see FIG. 6).
Furthermore, a rotational angle .theta.3, at which the inclination
of the stroke changes, corresponds to the third pocket boundary
section 543 (see FIG. 6).
[0089] FIG. 13B indicates a result of measurement of the sound
pressure generated from the drive apparatus 10 during the
rotational operation shown in FIG. 13A. FIG. 14B indicates a result
of measurement of the sound pressure generated from the drive
apparatus 10 during the rotational operation shown in FIG. 14A.
[0090] Now, a sound pressure measuring method will be briefly
described with reference to FIG. 15. The sound pressure measurement
is performed at a place where another sound source or another
vibration source is eliminated as much as possible. In a state
where the drive apparatus 10 is installed to a jig 89, which is
used in placed of the engine 90 (see FIG. 3), a distal end of a
microphone 82 connected to a sound pressure measuring device 81 is
set at a position that is spaced from an end of the drive apparatus
10 by about 10 mm. In this way, the sound pressure of the tooth
hitting sound, which is generated by the non-driving-side gear (the
driven-side gear) at the time of rotating the motor 20, is
measured.
[0091] In the sample A shown in FIG. 13A, a reference sound
pressure range A0 is about .+-.2 Pa at the time when the contact
point C of the roller 44 passes through the progressively changing
portion 531, 532 in response to the rotation of the drive cam 50 A
boundary sound pressure is compared with this reference sound
pressure range A0. Here, the term "boundary sound pressure" is
defined as a sound pressure that is generated at the time when the
contact point C of the roller 44 passes through the pocket boundary
section 542, 543 in response to the rotation of the drive cam 50.
In a case where the boundary sound pressure measured at the
corresponding rotational angle 82 or 83 is within the reference
sound pressure range A0, a blank circle is indicated at the top
side of the corresponding rotational angle .theta.2 or .theta.3 in
FIG. 13B. Also, in a case where the boundary sound pressure
measured at the corresponding rotational angle .theta.2 or 03
exceeds the reference sound pressure range A0, a multiplication
mark is indicated at the top side of the corresponding rotational
angle .theta.2 or .theta.3 in FIG. 13B.
[0092] At the rotational angle .theta.3 in the reverse rotational
direction, the boundary sound pressure is within the reference
sound pressure range A0. In contrast, at the rotational angles
.theta.2, .theta.3 in the forward rotational direction and the
rotational angle .theta.2 in the reverse rotational direction, the
boundary sound pressure exceeds the reference sound pressure range
A0. That is, a user may possibly hear the tooth hitting sound
generated at the pocket boundary section as a noisy sound (annoying
sound).
[0093] In the sample B shown in FIG. 14B, the reference sound
pressure range A0 is about .+-.2 Pa like the sample A shown in FIG.
13B, and the blank circle and the multiplication mark are indicated
at the top side of FIG. 14B in a manner similar to that of FIG.
13B.
[0094] As shown in FIG. 14B, at the rotational angle .theta.3 in
the forward rotational direction and the reverse rotational
direction, the boundary sound pressure exceeds the reference sound
pressure range A0. However, at the rotational angle .theta.2 in the
forward rotational direction and the reverse rotational direction,
the boundary sound pressure is within the reference sound pressure
range A0. Thus, with respect to the second pocket boundary section
542, the hitting sound is reduced in comparison to the sample
A.
[0095] The location of the pocket boundary section, at which the
boundary sound pressure is within the reference sound pressure
range A0, in FIGS. 13B and 14B, coincides with the location of the
part, at which the profile radius change rate is equal to or less
than the threshold value K in FIGS. 11A to 12B. According to the
above result, it is understood that the profile radius change rate
and the boundary sound pressure correlate with each other. Thus,
when the cam profile is set such that the profile radius change
rate is equal to or less than the threshold value K in all of the
pocket boundary sections in the forward rotational direction and
the reverse rotational direction, the tooth hitting sound in the
entire rotational angle range can be reduced.
[0096] As discussed above, in the sample A and the sample B, which
are exemplified above, the boundary sound pressures at all of the
pocket boundary sections are not kept within the reference sound
pressure range A0. However, a person skilled in the art can
implement the present disclosure based on the above disclosure,
which clearly and sufficiently discloses the principle of the
present disclosure. The threshold value K may be appropriately
designed in view of results of experiments and/or simulations based
on the specifications of the structure and the gears of the drive
force transmission system, which may or may not include
intermediate gear(s).
[0097] Now, advantages of the embodiment will be described.
[0098] (1) In the present embodiment, the profile radius change
rate at the pocket boundary section 54 is set such that the
boundary sound pressure, which is the sound pressure generated at
the time when the contact point C passes through the pocket
boundary section 54 in response to the rotation of the drive cam
50, is within the reference sound pressure range, which is a range
of variation in the sound pressure generated at the time when the
contact point C passes through the progressively changing portion
53. Thereby, when the contact point C passes through the boundary
section 54 between the progressively changing portion 53 and the
pocket portion 55 in response to the rotation of the drive cam 50,
it is possible to limit or reduce the tooth hitting sound that is
generated through the collision of the driven-side gear (e.g., the
cam gear 68) against the driving-side gear (e.g., the second stage
gear 66 of the second intermediate gear 65).
[0099] (2) The profile radius change rate at the pocket boundary
section 54 is defined as an inclination of a straight line that
connects between the apex S of the pocket boundary section 54 and
the inflection point In, Ip, which is closest to the apex S and is
located in the progressively changing portion 53 or the pocket
portion 55. Furthermore, in the case where the progressively
changing portion 53 is formed to have the profile radius, which
changes at the constant gradient in response to the rotation of the
drive cam 50, the profile radius change rate at the progressively
changing portion 53 side is defined as the gradient of the
progressively changing portion 53. Based on this definition, the
profile radius change rate [mm/deg] can be objectively compared and
evaluated.
[0100] (3) In the present embodiment, the drive force (the motor
torque) of the motor 20 is transmitted from the motor gear 62 to
the cam gear 68 through the intermediate gears 63, 65, so that the
tooth hitting sound is more likely generated in comparison to the
case where the motor gear 62 and the cam gear 68 are directly
meshed with each other. Therefore, the advantage of limiting or
reducing the tooth hitting sound can be particularly prominent in
such a case.
[0101] (4) The motor gear 62, the intermediate gears 63, 65, and
the cam gear 68 are formed as the spur gears. Therefore, the tooth
hitting sound is more likely generated in the present embodiment in
comparison to the case where the bevel gears are used in place of
the spur gears. Thus, when the present embodiment is adapted, the
tooth hitting sound can be effectively reduced while using the
inexpensive spur gears.
Other Embodiments
[0102] (A) The specific configuration of the profile of the drive
cam is not limited to the one discussed in the above embodiment.
For example, the number of the pocket portions is not limited to
three and may be changed to any number, which is equal to or larger
than one. Furthermore, the change of the profile radius of the
progressively changing part does not need to have the constant
gradient.
[0103] (B) The structure, which urges the roller 44 against the
drive cam 50, is described as follows in the above embodiment. That
is, the load Fa is applied from the driven subject to the control
shaft member 30 in the direction of pulling the control shaft
member 30. Besides this, the drive apparatus of the present
disclosure may be also applied to a case where the control shaft
member 30 pushes the drive cam 50 directly or indirectly through
another member.
[0104] For example, in another embodiment shown in FIG. 16, a load
Fb is applied from a right side of FIG. 16 to a control shaft
member 49 in a direction of pushing the control shaft member 49. A
ball 492, which is formed separately from the control shaft member
49, is rotatably received in a recess 491, which is formed at a
distal end of the control shaft member 49, in a manner that enables
rotation of the ball 492 in all directions. While the ball 492
makes point contact with the pocket portion 55 of the drive cam 50
at the contact point C, the control shaft member 49 reciprocates in
the left-to-right direction of FIG. 16 in response to the rotation
of the drive cam 50. The control shaft member 49 of this embodiment
shown in FIG. 16 is a member, in which the support member and the
control shaft member of the present disclosure are formed
integrally, and the ball 492 serves as the contact portion of the
present disclosure.
[0105] (C) The drive source of the present disclosure is not
limited to the DC motor of the above embodiment. That is, the drive
source of the present disclosure may be an AC motor or another type
of electric motor, or an actuator, which is operated by hydraulic
pressure (oil pressure), compressed air or electromagnetic
force.
[0106] (D) The mechanism, which adjusts the lift amount at the
valve lift control system, is not limited to the above described
structure. Furthermore, the valve lift control system is not
limited to the one, which controls the lift amount of the
respective intake valves. That is, the valve lift control system of
the present disclosure may be one, which controls, for example, the
lift amount of the respective exhaust valves.
[0107] (E) The details of the specification of the sound pressure
measuring device and the measurement conditions discussed with
reference to FIG. 15 are not limited to the above described ones.
That is, according to the present disclosure, the reference sound
pressure range and the boundary sound pressure are simultaneously
measured with the measuring device and under the predetermined
condition. The reference sound pressure range and the boundary
sound pressure are relatively evaluated, so that the degree of the
boundary sound pressure can be objectively evaluated.
[0108] (F) The drive apparatus of the present disclosure is not
necessarily provided in the valve lift control system. That is, the
drive apparatus of the present disclosure may be provided in any
apparatus, which can control the control amount of a corresponding
controlled subject in response to the axial position of the control
shaft member.
[0109] As discussed above, the present disclosure is not limited
the above embodiments and modifications thereof. That is, the above
embodiments and modifications thereof may be modified in various
ways without departing from the principle of the present
disclosure.
* * * * *