Information
-
Patent Grant
-
6736095
-
Patent Number
6,736,095
-
Date Filed
Tuesday, December 4, 200122 years ago
-
Date Issued
Tuesday, May 18, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Denion; Thomas
- Corrigan; Jaime
Agents
-
CPC
-
US Classifications
Field of Search
US
- 123 9015
- 123 9016
- 123 9017
- 123 906
- 074 569
-
International Classifications
-
Abstract
An output cam for a variable valve mechanism includes a body configured for being pivotally associated with and driven by an input shaft. A lift profile of the output cam includes a base circle portion, a cam portion and a fixed radius portion. The base circle portion is adjacent to and continuous with the cam portion, and the cam portion is adjacent to and continuous with the fixed radius portion. The base circle portion has a base radius, the cam portion has a cam radius and the fixed radius portion has a fixed radius. The base and fixed radii are substantially constant. The fixed radius is a predetermined amount greater than the base radius. The cam radius increases from a value approximately equal to the base radius adjacent the base circle portion to a value approximately equal to the fixed radius adjacent the fixed radius portion.
Description
TECHNICAL FIELD
This invention generally relates to variable valve actuation mechanisms for internal combustion engines and, more particularly, to an output cam for use with a variable valve mechanism.
BACKGROUND OF THE INVENTION
A conventional internal combustion engine utilizes an air throttling device and a timing device. The throttle device is typically a valve that, in response to driver input, regulates the flow of air to the engine intake valves. The timing device includes a crankshaft that drives a rotary, lobed camshaft. Engine intake valves are opened and closed at predetermined angles of crankshaft rotation to allow the descending piston to draw air into the combustion chamber. The shape or lift profile of the cam lobes, in part, fixes the crankshaft angle at which the valves open/close and the amount by which the valves are lifted. The plot of valve lift relative to crankshaft angular position is referred to as a valve lift profile. A conventional engine has an intake valve lift profile that is generally parabolic in shape.
A modern internal combustion engine may incorporate a more advanced throttle control system, such as, for example, an intake valve throttle control system. An intake valve throttle control system, in general, controls the flow of gas and air into the cylinders by varying the timing and/or the amount of intake valve lift. The timing and/or amount of lift is varied dependent upon and in response to engine operating parameters, such as, for example, engine load, speed, and driver input. Intake valve throttle control systems vary the valve lift profile through the use of various mechanical and/or electromechanical configurations, generally referred to herein as variable valve actuating (VVA) mechanisms. One example of a VVA mechanism is detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is incorporated herein by reference.
Conventional VVA mechanisms typically include an output cam lobe that is pivotally oscillated through a predetermined and fixed range of motion. The pivotal motion of the output cam lobe is transferred to opening and/or closing of a corresponding valve. More particularly, the output cam typically engages a roller finger follower that, in turn, engages a corresponding intake valve. The shape or lift profile of the pivoting output cam lobe causes a corresponding displacement or pivot of the roller finger follower and, in turn, a corresponding actuation or lifting of the intake valve. The amount and timing of the valve lift is varied by changing the angular position of the output cam lobe relative to the roller finger follower and/or a central axis of the cam lobe such that the roller finger follower is engaged by a desired portion of the output cam lift profile as it is pivoted.
For example, to impart a large amount of lift to the intake valve, the angular position of the output cam lobe relative to the roller finger follower is established such that the nose or peak of the lift profile is disposed within the fixed range of motion of the output cam. Thus, as the output cam lobe is pivoted through its fixed range of motion the peak of the lift profile engages the roller finger follower thereby actuating or lifting the valve a corresponding and relatively large amount. Conversely, to achieve a small amount of or zero lift the angular position of the output cam lobe relative to the roller finger follower is established such that the roller finger follower is engaged primarily or only by the base circle of the lift profile as the output cam lobe pivots through its fixed range of motion. Thus, the roller finger follower is pivoted and the corresponding valve is actuated a relatively small or zero amount.
Conventional VVAs vary the amount and timing of valve lift in order to, for example, increase engine power, reduce pumping work and/or improve charge preparation. The output cams of such VVAs incorporate conventional lift profiles. Since only the amount and/or timing of the valve lift is varied, the valve lift profiles remain generally parabolic in shape. The amount of valve lift in a given engine is fixed not only by the lift profile of the output cam lobe but also by the valve springs and other valve train components. The limited available or maximum amount of valve lift, in turn, limits the amount of air flow/intake and thereby limits engine power. The limited maximum lift also limits the resolution of, i.e., the difference in lift between, the valve lift profiles. The peak valve lift achieved by the lower-lift profiles must be a certain amount less than the maximum lift.
Therefore, what is needed in the art is an output cam for use with a VVA mechanism that extends the duration of the valve event.
Furthermore, what is needed in the art is an output cam for a VVA mechanism that increases air flow/intake for a given amount of valve lift.
Still further, what is needed in the art is an output cam for a VVA mechanism that increases engine power for a given amount of valve lift.
Moreover, what is needed in the art is an output cam for a VVA mechanism that increases the resolution of valve lift profiles by providing lower lift curves that represent a larger percentage of peak or maximum valve lift.
SUMMARY OF THE INVENTION
The present invention provides an output cam for a variable valve mechanism.
The invention comprises, in one form thereof, a body configured for being pivotally associated with and driven by an input shaft. A lift profile of the output cam includes a base circle portion, a cam portion and a fixed radius portion. The base circle portion is adjacent to and continuous with the cam portion, and the cam portion is adjacent to and continuous with the fixed radius portion. The base circle portion has a base radius, the cam portion has a cam radius and the fixed radius portion has a fixed radius. The base and fixed radii are substantially constant. The fixed radius is a predetermined amount greater than the base radius. The cam radius increases from a value approximately equal to the base radius adjacent the base circle portion to a value approximately equal to the fixed radius adjacent the fixed radius portion.
An advantage of the present invention is that a longer duration lift event is achieved.
A further advantage of the present invention is that engine power is increased for a given amount of valve lift.
A still further advantage of the present invention is that low-lift valve lift profile resolution is improved.
An even further advantage of the present invention is that longer duration lift events are achieved without requiring modifications to associated valve train components.
Yet further, an advantage of the present invention is that the peak or maximum amount of valve lift can be reduced without sacrificing power or air intake/flow.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become apparent and be better understood by reference to the following description of one embodiment of the invention in conjunction with the accompanying drawings, wherein:
FIG. 1
is a side view of one embodiment an output cam of the present invention;
FIG. 2
is a perspective view of a VVA mechanism incorporating the output cam of
FIG. 1
; and
FIG. 3
is a plot of exemplary valve lift profiles obtained with the VVA mechanism of FIG.
2
.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and particularly to
FIG. 1
, there is shown one embodiment of an output cam of the present invention. Output cam
10
includes lift profile
12
. Generally, and as will be described with more particularity hereinafter, lift profile
12
of output cam
10
increases the duration of the valve lift event.
Output cam
10
includes body
14
. Body
14
is generally annular in shape, and defines central orifice
16
that is substantially concentric relative to a central axis A. Central orifice
16
is configured for receiving a camshaft of an internal combustion engine. Body
14
further defines peripheral orifice
18
that is substantially concentric relative to central axis B, which is substantially parallel to and spaced apart from central axis A. Peripheral orifice
18
is configured for receiving a coupling member, such as, for example, a pin, that couples output cam
10
to a link member of a variable valve mechanism. Body
14
is constructed of, for example, stainless steel or aluminum.
Lift profile
12
is affixed to and/or integral and monolithic with body
14
. Lift profile
12
includes three distinct portions or segments, base circle portion
20
, cam portion
22
and constant radius portion
24
. Base circle portion
20
is adjacent to and continuous with cam portion
22
, and cam portion
22
is adjacent to and continuous with constant radius portion
24
.
Base circle portion
20
has a substantially constant radius r
BASE
. Cam portion
22
has a radius r
CAM
that increases in a clockwise direction or in a direction toward constant radius portion
24
. Constant radius portion
24
has a substantially constant radius r
CONSTANT
, that is a predetermined amount greater than r
BASE
.
Referring now to
FIG. 2
, one embodiment of a variable valve actuation (VVA) mechanism incorporating output cam
10
is shown. VVA
50
is operably installed within engine
52
. More particularly, VVA
50
is operably associated with rotary camshaft
54
of engine
52
. Camshaft
54
has central axis C and includes at least one input cam
56
that engages roller
58
. Roller
58
is carried by first link member
60
, which is pivotally interconnected with second link member
62
. Second link member
62
is, in turn, pivotally interconnected with output cam
10
. Frame
64
is pivotally associated with camshaft
54
, and is pivotally interconnected with the end of first link member
60
that is opposite second link member
62
. Control gear
66
is disposed upon control shaft
68
, and engages a corresponding gear (not referenced) carried by or integral with frame
64
.
In use, camshaft
54
is driven to rotate by engine
52
, such as, for example, via a crankshaft (not shown). Camshaft
54
and input cam
56
rotate as substantially one body, and thus rotation of camshaft
54
results in the rotation of input cam
56
. As input cam
56
rotates, the lift profile thereof engages and displaces roller
58
toward and away from camshaft
54
in a generally radial direction. Roller
58
is carried by first link member
60
, and thus the rotation of input cam
56
is transferred to displacement of first link member
60
toward and away from camshaft
54
in a generally radial direction. The displacement of first link member
60
is transferred to a corresponding displacement of second link arm
62
toward and away from camshaft
54
in a generally radial direction. The displacement of second link arm
62
is, in turn, transferred to pivotal motion of output cam
10
relative to central axis C.
VVA
50
is configured such that rotation of input cam
56
results in pivotal oscillatory movement of output cam
10
relative to central axis C of a fixed and predetermined magnitude. For example, a full three-hundred and sixty degrees of rotation of input cam
56
results in pivotal motion of output cam
10
through, for example, a magnitude of approximately ninety degrees relative to central axis C (i.e., a forty-five degree pivot in the clockwise direction and a return pivot of forty-five degrees in the counterclockwise direction). As output cam
10
undergoes pivotal oscillatory motion, lift profile
12
engages roller finger follower
70
(schematically represented in
FIG. 2
) and thus the pivotal motion of output cam
10
displaces or pivots roller finger follower
70
in a generally radial direction away and toward from camshaft
54
.
Control shaft
68
is pivoted relative to central axis S thereof to thereby establish the angular position of output cam
10
relative to roller finger follower
70
. More particularly, pivoting of control shaft
68
relative to central axis S is transferred via control gear
66
to a corresponding but oppositely-directed pivotal movement of frame
64
relative to central axis C. The pivotal movement of frame
64
is transferred via first and second link arms
60
and
62
, respectively, to a corresponding pivotal movement of output cam
10
relative to central axis C. Thus, a “starting” angular position of output cam
10
relative to roller finger follower
70
and relative to central axis C is established by pivoting control shaft
68
to a predetermined angular position relative to central axis S. Placing output cam
10
in a predetermined angular position relative to roller finger follower
10
determines what portion of lift profile
12
(
FIG. 1
) engages the roller finger follower
70
to pivot.
Further details of the structure and operation of different embodiments of variable valve actuating mechanisms are provided in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which, as stated above, is incorporated herein by reference. It should be particularly noted that the structure and operation of VVA
50
from the mechanism viewpoint are substantially similar to the operation and structure of the VVA mechanisms described in U.S. Pat. No. 5,937,809. However, it should further be particularly noted that the valve lift curves obtained by VVA
50
are substantially different from those obtained by the VVA mechanisms disclosed in U.S. Pat. No. 5,937,809 due to the use of output cam
10
in VVA
50
.
Referring now to
FIG. 3
, a family of exemplary valve lift curves obtained with VVA
50
are shown. Valve lift curves
80
,
81
,
82
,
83
,
84
,
85
and
86
are obtained by establishing, via control shaft
68
, a corresponding angular position of output cam
10
relative to central axis C and/or roller finger follower
70
, as described above. For example, lift curve
80
is obtained by establishing the angular position of output cam
10
relative to central axis C such that constant radius portion
24
and a substantial portion of cam portion
22
are disposed at a relatively large angular distance from roller finger follower
70
. As output cam
10
is pivoted through its fixed range of motion roller finger follower
70
is engaged primarily by base circle portion
20
and by only a predetermined and relatively small segment of cam portion
22
. Thus, lift curve
80
has a relatively short duration and relatively low amount of lift.
Conversely, lift curve
83
is obtained by establishing the angular position of output cam
10
relative to central axis C such that a substantial portion, if not the entirety, of cam portion
22
is in relatively close angular proximity relative to roller finger follower
70
. As output cam
10
is pivoted through its fixed range of motion, roller finger follower
70
is engaged primarily by cam portion
22
up to approximately and/or including the peak thereof. Thus, lift curve
83
has a relatively long duration and a relatively high, if not maximum, peak amount of lift.
Generally, lift curves
84
,
85
and
86
illustrate how the duration of the valve event is extended by constant radius portion
24
of lift profile
12
. More particularly, lift curve
84
is obtained by establishing the angular position of output cam
10
relative to central axis C such that cam portion
22
and a predetermined portion of constant radius portion
24
are in relatively close angular proximity to roller finger follower
70
. As output cam
10
is pivoted through its fixed range of motion, roller finger follower
70
is first engaged by cam portion
22
and is then engaged by the predetermined portion of constant radius portion
24
. The engagement roller finger follower
70
by cam portion
22
lifts the valve in a substantially similar profile as curve
83
up until the crank angle where constant radius portion
24
engages roller finger follower
70
. The engagement of roller finger follower
70
by constant radius portion
24
maintains the lift at a generally constant level, i.e., the peak lift achieved by the engagement of roller finger follower
70
by cam portion
22
. Thus, the engagement of roller finger follower by constant radius portion
24
extends the crank angle over which the peak amount of lift is maintained, and thereby extends the duration of the valve event.
The amount (i.e., the crank angle range) by which the valve event is extended is determined by the radial length of constant radius portion
24
that engages roller finger follower
70
during the oscillation of output cam
10
. As the radial length of constant radius portion
24
that engages roller finger follower
70
is increased the crank angle range for which peak lift is maintained (i.e., the duration of the valve event) is increased correspondingly. Thus, lift curve
84
is achieved by increasing relative to lift curve
83
the radial length of constant radius portion
24
that engages roller finger follower
70
during the pivotal oscillation of output cam
10
. Similarly, lift curves
85
and
86
are achieved by respective increases relative to lift curve
84
in the radial length of constant radius portion
24
that engages roller finger follower
70
during the pivotal oscillation of output cam
10
. As described above, the portion or radial length of constant radius portion
24
that engages roller finger follower
70
is determined by the angular position of output cam
10
relative to central axis C.
VVA
50
, by extending the duration of the valve event, provides several distinct advantages relative to a conventional VVA. The extended duration valve events provided by VVA
50
increase airflow for a fixed or given amount of valve lift. Thus, installing VVA
50
on an existing engine increases the airflow and power of the engine. It should be particularly noted that the other valve train components, such as, for example, valve springs, would not need to be redesigned if the amount of lift is not changed.
Furthermore, it is desirable to have a design lift curve, i.e., the peak lift curve without any extension in duration and as exemplified by lift curve
83
, of a relatively short duration in order to have short duration lower lift curves. By extending the duration of the valve event, VVA
50
enables a desirable reduction in the duration of the design lift curve. Where engine loads require a lift curve above the peak lift curve, i.e., one that provides greater airflow, VVA
50
is adjusted to provide a lift curve having an extended duration to thereby provide the required increased airflow.
Moreover, VVA
50
can be applied to reduce the amount of lift required to provide a given airflow. Generally, for valve lifts above approximately six to eight millimeters, airflow into an engine is limited by the port flow characteristics rather than by the amount of valve lift. Thus, a lower lift valve event having duration extended by VVA
50
provides airflow equivalent to the airflow provided by a higher lift but normal duration (i.e., not extended) valve event.
In the embodiment shown, VVA
50
includes a single output cam
10
to thereby actuate a single valve. However, it is to be understood that VVA
50
can be alternately configured, such as, for example, having a second output cam and associated structure to thereby be configured for use with a cylinder having two intake valves.
In the embodiment shown, VVA
50
is configured to actuate one or more intake valves. However, it is to be understood that VVA
50
can be alternately configured, such as, for example to actuate exhaust valves. It should be particularly noted that configuring VVA
50
to actuate one or more exhaust valves extended exhaust valve duration and expanded charge dilution control capabilities are achieved.
In the embodiment shown, VVA
50
is configured for use with an internal combustion engine. However, it is to be understood that VVA
50
can be alternately configured, such as, for example, for use with various other mechanisms or machinery, such as, for example, air compressors, which may advantageously utilize variable or extended duration of one or more moving components.
In the embodiment shown, the amount of valve lift obtained by VVA
50
is adjusted by establishing the angular position of output cam
10
relative to central axis C to thereby engage roller finger follower
70
with a desired portion of lift profile
12
as output cam
12
undergoes a fixed degree of pivotal movement/oscillation. However, it is to be understood that the present invention can be alternately configured, such as, for example, as changing the degree range over which the output cam is pivotally oscillated relative to central axis C to thereby engage the roller finger follower with more, less or different portions of the lift profile of the output cam.
In the embodiment shown, output cam
10
is illustratively shown and the method of operation thereof illustratively described by reference to an exemplary variable valve actuating mechanism. However, it is to be understood that output cam
10
and the method of operation thereof is compatible with virtually any of the various configurations of known variable valve actuating mechanisms, such as, for example, belt-driven, linkless, cam link and eccentric variable valve actuating mechanisms, and those yet to be developed.
In the embodiment shown, VVA
50
includes link members and a roller that operate to convert rotary motion of the input cam lobe to pivotal oscillatory motion of the output cam. However, it is to be understood that VVA
50
can be alternately configured with various other means to convert rotary motion of the input shaft and/or input cam to pivotal oscillatory motion of the output cam. Such other means include, for example, one or more belts, chains or other links transferring rotation of the input or cam shaft and/or the input cam to pivotal motion of the output cam.
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the present invention using the general principles disclosed herein. Further, this application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
Claims
- 1. An output cam for a variable valve mechanism, comprising:a body configured for pivotal movement relative to a central axis; and a lift profile that is one of affixed to and integral with said body, said lift profile having a base circle portion, a cam portion and a fixed radius portion, said base circle portion being adjacent to and continuous with said cam portion, said cam portion being adjacent to and continuous with said fixed radius portion, said base circle portion having a base radius, said cam portion having a cam radius and said fixed radius portion having a fixed radius, said base radius and said fixed radius being substantially constant, said fixed radius being a predetermined amount greater than said base radius, said cam radius increasing from a value approximately equal to said base radius adjacent said base circle portion to a value approximately equal to said fixed radius adjacent said fixed radius portion.
- 2. The output cam of claim 1, wherein said body defines a central orifice, said central orifice configured for receiving a shaft to thereby pivotally associate said output cam with said shaft.
- 3. The output cam of claim 1, wherein said body defines a periphery orifice, said periphery orifice for coupling said output cam to a link member.
- 4. A variable valve actuation mechanism, comprising:an output cam having a body; means for transferring rotary motion of an input shaft to pivotal movement of said output cam; and a lift profile that is one of affixed to and integral with said body, said lift profile having a base circle portion, a cam portion and a fixed radius portion, said base circle portion being adjacent to and continuous with said cam portion, said cam portion being adjacent to and continuous with said fixed radius portion, said base circle portion having a base radius, said cam portion having a cam radius and said fixed radius portion having a fixed radius, said base radius and said fixed radius being substantially constant, said fixed radius being a predetermined amount greater than said base radius, said cam radius increasing from a value approximately equal to said base radius adjacent said base circle portion to a value approximately equal to said fixed radius adjacent said fixed radius portion.
- 5. The variable valve mechanism of claim 4, wherein said body defines a central orifice, said central orifice configured for receiving a shaft to thereby pivotally associate said output cam with said shaft.
- 6. The variable valve mechanism of claim 5 wherein said shaft comprises a camshaft of an engine.
- 7. The output cam of claim 4, wherein said body defines a periphery orifice, said periphery orifice configured for coupling said output cam to a link member.
- 8. An internal combustion engine, comprising:a variable valve actuation mechanism including: an output cam, said output cam having a body; means for transferring rotary motion of an input shaft of said engine to pivotal movement of said output cam; and a lift profile that is one of affixed to and integral with said body, said lift profile having a base circle portion, a cam portion and a fixed radius portion, said base circle portion being adjacent to and continuous with said cam portion, said cam portion being adjacent to and continuous with said fixed radius portion, said base circle portion having a base radius, said cam portion having a cam radius and said fixed radius portion having a fixed radius, said base radius and said fixed radius being substantially constant, said fixed radius being a predetermined amount greater than said base radius, said cam radius increasing from a value approximately equal to said base radius adjacent said base circle portion to a value approximately equal to said fixed radius adjacent said fixed radius portion.
US Referenced Citations (4)