U.S. patent application number 10/462194 was filed with the patent office on 2004-01-08 for piezoelectric valve actuation.
Invention is credited to Brower, David R., Gatecliff, George W., Novak, Keith A., Rado, Gordon E..
Application Number | 20040003786 10/462194 |
Document ID | / |
Family ID | 29718049 |
Filed Date | 2004-01-08 |
United States Patent
Application |
20040003786 |
Kind Code |
A1 |
Gatecliff, George W. ; et
al. |
January 8, 2004 |
Piezoelectric valve actuation
Abstract
A piezoelectric valve actuation system for an internal
combustion engine includes a piezoelectric driver in the form of a
pre-stressed wafer or strip including a layer of piezoceramic
material such as lead zirconate titanate (PZT). The driver has a
central portion which includes an aperture for direct engagement
with a valve stem so that the valve is moved between open and
closed positions directly by the piezoelectric driver. The
piezoelectric driver can have end portions which attach to the
engine cylinder head proximate the valve location. The
piezoelectric actuator is driven by an electronic control module
(ECM) providing electrical signals to control valve operation based
various engine parameters along with user input.
Inventors: |
Gatecliff, George W.;
(Saline, MI) ; Brower, David R.; (Beaver Dam,
WI) ; Rado, Gordon E.; (Plymouth, WI) ; Novak,
Keith A.; (Depere, WI) |
Correspondence
Address: |
BAKER & DANIELS
111 E. WAYNE STREET
SUITE 800
FORT WAYNE
IN
46802
|
Family ID: |
29718049 |
Appl. No.: |
10/462194 |
Filed: |
June 16, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60389463 |
Jun 18, 2002 |
|
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Current U.S.
Class: |
123/90.11 |
Current CPC
Class: |
F16K 31/005 20130101;
F01L 2301/02 20200501; F01L 9/20 20210101; F01L 9/24 20210101; F01L
2301/00 20200501 |
Class at
Publication: |
123/90.11 |
International
Class: |
F01L 009/04 |
Claims
What is claimed is:
1. A piezoelectric actuated valve mechanism for an internal
combustion engine having at least one valve with a valve stem, the
valve mechanism comprising: a curved, pre-stressed piezoelectric
drive member having a central portion operatively coupled to the
valve of the engine and a peripheral portion captively engaged by a
portion of the engine proximate the valve; and a controller input
for exciting said drive member; whereby the valve moves between an
open position and a closed position based on a predetermined set of
engine operating parameters and user input.
2. The mechanism of claim 1 wherein said central portion of said
drive member defines an aperture in engagement with the valve
stem.
3. The mechanism of claim 2 wherein said aperture is keyhole shaped
and includes a first portion that receives the valve stem
therethrough, and a second portion, smaller than said first
portion, configured to receive a reduced diameter of a retaining
groove in the valve stem.
4. The mechanism of claim 1 wherein said peripheral portion of said
drive member includes first and second opposite ends.
5. The mechanism of claim 4 wherein said ends are planar in shape,
the engaging portion of the engine further including at least one
retaining groove captively engaging said ends.
6. The mechanism of claim 4 wherein said ends are rolled, the
engaging portion of the engine further including a pair of mounting
pins receivable in a respective one of said rolled ends.
7. The mechanism of claim 1 wherein said peripheral portion of said
drive member is circular in shape, the engaging portion of the
engine further including at least one retaining groove captively
engaging said circular peripheral portion.
8. The mechanism of claim 1 wherein said drive member includes at
least one layer of a piezoceramic material.
9. The mechanism of claim 8 wherein said piezoceramic material is
lead zirconate titanate (PZT).
10. An actuator for a valve having a valve stem, the actuator
comprising: a drive member including a curved, pre-stressed wafer
having at least one layer of piezoceramic material, said wafer
having an aperture in a central portion thereof configured for
direct attachment to the valve stem whereby the valve is moved
between an open position and a closed position by said drive
member.
11. The actuator of claim 10 wherein said piezoceramic material
comprises lead zirconate titanate (PZT).
12. The actuator of claim 10 wherein said aperture is keyhole
shaped and includes a first portion configured to receive the valve
stem therethrough, and a second portion, smaller than said first
portion, configured to receive a reduced diameter of a retaining
groove in the valve stem.
13. An internal combustion engine comprising: a block portion
defining at least one cylinder; at least one cylinder head attached
to said block portion and defining at least one combustion chamber
in said at least one cylinder, said cylinder head supporting at
least two valves for said at least one cylinder; an actuation
mechanism for operating said valves between an open position and a
closed position, said actuation mechanism including a curved,
pre-stressed piezoelectric drive member for each said valve, each
said piezoelectric drive member having a central portion thereof
operatively coupled to a respective one of said valves; and a
controller input for exciting said actuation mechanism; whereby
said valve moves between said open position and said closed
position based on a predetermined set of engine operating
parameters and user input.
14. The engine of claim 13 wherein said actuation mechanism
includes a pre-stressed wafer having at least one layer of
piezoceramic material.
15. The engine of claim 14 wherein said piezoceramic material
comprises lead zirconate titanate (PZT).
16. The engine of claim 13 wherein said valve includes a valve stem
and said central portion of said drive member includes a keyhole
shaped aperture having a first portion configured to receive said
valve stem therethrough, and a second portion, smaller than said
first portion, configured to receive a reduced diameter of a
retaining groove in said valve stem.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a valve actuation system;
and in particular, to a piezoelectric valve actuation system in an
internal combustion engine.
[0003] 2. Description of the Related Art
[0004] Valve systems in internal combustion engines are typically
driven from a camshaft either directly or through a mechanical
linkage. The valves of the system are preloaded in a closed
position by a valve spring with the cam opening the valve against
the force of the spring. Valve movement, in terms of lift and
duration, is determined by the cam profile such that rotation of
camshaft actuates the valves. The camshaft is indexed with respect
to the engine crank shaft so that valve timing relative to the
engine crank shaft rotation is predetermined.
[0005] In mechanically actuated systems, valve operation influences
several engine characteristics such as horsepower, torque, fuel
economy and emissions. Most often, the designer must make
compromises such as having less than optimum horsepower or torque
to achieve acceptable performance throughout the engine's operating
range from engine idle to maximum speed.
[0006] It has been recognized in the prior art that advantages can
be achieved by the development of an actuation mechanism that is
not controlled by engine camshaft position. A valve system of this
type would have the potential for providing infinitely variable
valve timing. Efforts have been made to develop electromagnetic or
solenoid actuated systems, however, with limited effectiveness due
to the bulk and complexity of these systems combined with
relatively high current requirements for such applications.
[0007] In a further effort, piezoelectric materials have been used
in valve actuation mechanisms. U.S. Pat. No. 4,593,658 to Moloney
discloses a valve actuation system that uses a piezoelectric device
including a stack of piezoelectric discs or rings to actuate the
valve. One end of the piezoelectric stack is fixed to a housing
while the other end is freely movable. A pin attached to the
movable end of the piezoelectric stack engages a lever pivoted on a
carrier mounted to the engine block. The lever is connected to an
actuator rod of the valve for operation thereof. Such actuators,
however, are bulky and rather expensive due to the number of
piezoelectric elements required to form the piezoelectric stack.
These actuators also require a linkage, such as the lever and
actuator arms of Moloney, to operate the valve.
[0008] What is needed is a simple, economical, and compact
piezoelectric valve actuator capable of directly operating a valve
in an internal combustion engine without the need of a lever or
linkage mechanism.
SUMMARY OF THE INVENTION
[0009] The present invention provides a piezoelectric valve
actuation system for an internal combustion engine. A piezoelectric
drive member is directly connected to the valve stem of the valves
such that the drive member directly drives the valves toward both
open and closed positions. This eliminates the need for a return
spring to bring the valve back to a closed position once it has
been opened. The curved, pre-stressed piezoelectric drive member
has a central portion operatively coupled to the valve of the
engine and a peripheral portion captively engaged by a portion of
the engine proximate the valve. The ends of the piezoelectric drive
member may be pivotally mounted in the cylinder block of the
engine. The piezoelectric drive member may include a keyhole shaped
aperture that engages a retaining groove formed near one end of the
valve stem.
[0010] In one embodiment, the cylinder head of the engine is
provided with retaining grooves in which the ends of a
substantially rectangular piezoelectric drive member are received.
The piezoelectric drive member then opens and closes the valve in
response to electrical signals from an electronic control module
(ECM).
[0011] In another embodiment, the cylinder head is provided with a
pair of mounting pins located on opposite sides of the valve. The
ends of the substantially rectangular piezoelectric drive member
are rolled to receive pins and pivotally mount the drive
member.
[0012] In a further embodiment, the piezoelectric drive member is
substantially disk shaped. Portions of the peripheral edge of the
drive member are received in grooved formed in retaining posts
secured to the cylinder block to pivotally mount the drive
member.
[0013] One form of the present invention provides a piezoelectric
valve actuation mechanism for an internal combustion engine having
at least one valve with a valve stem. The actuation mechanism
includes a curved, pre-stressed piezoelectric drive member having a
central portion operatively coupled to the valve of the engine and
a peripheral portion captively engaged by a portion of the engine
proximate the valve. A controller input is provided for exciting
the drive member such that the valve moves between an open position
and a closed position based on a predetermined set of engine
operating parameters and user input.
[0014] Another form of the present invention provides an actuator
for a valve having a valve stem. The actuator includes a drive
member including a curved, pre-stressed wafer having at least one
layer of piezoceramic material. The wafer has an aperture in a
central portion thereof is configured for direct attachment to the
valve stem whereby the valve is moved between an open position and
a closed position by the drive member.
[0015] A further form of the present invention provides an internal
combustion engine having a block portion defining at least one
cylinder and at least one cylinder head attached to the block
portion. At least one combustion chamber is defined in the at least
one cylinder with the cylinder head supporting at least two valves
for the at least one cylinders. An actuation mechanism is provided
for operating the valves between an open position and a closed
position. The actuation mechanism includes a curved, pre-stressed
piezoelectric drive member for each of the valves. The
piezoelectric drive member has a central portion thereof
operatively coupled to a respective one of the valves. A controller
input excites the actuation mechanism such that the valve moves
between the open position and the closed position based on a
predetermined set of engine operating parameters and user
input.
[0016] The present invention accomplishes a major objective of
providing a valve actuation system having infinitely variable valve
timing combined with variable valve lift over a predetermined range
under control of the piezoelectric actuator. The present invention
also enables bidirectional operation of the engine.
[0017] The invention accomplishes a further objective of providing
engine braking through valve control. The invention accomplishes
yet a further objective of eliminating the requirement for periodic
valve adjustments.
[0018] The invention accomplishes still a further objective of
eliminating a valve train and thus the eliminating cooling air
obstructions particularly in air cooled engines.
[0019] The invention accomplishes a still further objective of
providing a piezoelectric valve actuation system that operates with
minimum power consumption.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The above mentioned and other features and objects of this
invention, and the manner of obtaining them, will become more
apparent and the invention itself will be better understood by
reference to the following description of the embodiments of the
invention taken in conjunction with the accompanying drawings,
wherein:
[0021] FIG. 1 is a front sectional view of one embodiment of a
piezoelectric valve actuation system according to the present
invention mounted on an engine;
[0022] FIG. 2 is a top view of a portion of the piezoelectric
actuator of FIG. 1 showing a keyhole shaped aperture for engagement
with a valve stem;
[0023] FIG. 3 is a front sectional view of a piezoelectric valve
actuator according to the present invention showing an alternate
mounting of the actuator to the engine;
[0024] FIG. 4 is a top view of a disk shaped piezoelectric valve
actuator according to the present invention showing a still further
mounting technique; and
[0025] FIG. 5 is a front sectional view of the disk shaped
piezoelectric actuator of FIG. 4.
[0026] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplification set out
herein illustrates embodiments of the invention and such
exemplification is not to be construed as limiting the scope of the
invention in any manner.
DETAILED DESCRIPTION
[0027] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiments illustrated in the drawings and specific language will
be used to describe the same. It will nevertheless be understood
that no limitation of the scope of the invention is thereby
intended. The invention includes any alterations and further
modifications of the illustrated devices and described methods and
further applications of the principles of the invention which would
normally occur to one skilled in the art to which the invention
relates.
[0028] Referring to FIG. 1, an internal combustion engine is
generally represented at 10. Engine 10 may be a two or four-stroke
engine, the general operation of which is described in U.S. Pat.
No. 4,982,705, which is assigned to the assignee of the present
invention, the disclosure of which is hereby incorporated herein by
reference. The engine includes a cylinder head 12 and block 14 with
a combustion chamber generally indicated at 16. Cylinder head 12
includes a number of ports 22 including at least one intake port
delivering an air fuel mix to the engine's combustion chamber 16
and at least one exhaust port through which exhaust gases exit the
combustion chamber 16, with intake and exhaust ports generally
present in equal numbers. A valve seat 24 is located at the entry
of each port 22 into the combustion chamber 16. The valve seat 24
may be machined to have a beveled profile 27. A valve 30 has a
valve stem 32 that extends through a valve guide 28 formed in the
cylinder head 12. The valve 30 has a head portion 34 that may
include a beveled edge 36 machined to have a profile complimentary
to profile 27 of the valve seat 24. The engagement of beveled edge
36 with valve seat 24 when the valve 30 is in a closed position
acts to seal combustion chamber 16.
[0029] A piezoelectric actuator, or driver, 40 is provided to
operate the valve 30. One piezoelectric actuator particularly
suitable for use with the present invention is of a design that is
sold under the trademark THUNDER and is commercially available
through Face International Corporation of Norfolk, Va. The actuator
is a layered ferroelectric composite, the technology of which is
described in U.S. Pat. Nos. 5,632,841 and 5,639,850, both of which
are assigned to the United States of America as represented by the
Administrator of the National Aeronautics and Space Administration
(NASA), and the disclosures of which are hereby incorporated by
reference. The devices are further described in the publication
"THUNDER White Paper", Face International Corporation, Feb. 21,
2001, the disclosure of which is also hereby incorporated herein by
reference.
[0030] Actuators such as the THUNDER actuator are low cost, high
efficiency piezoelectric devices having improved piezoelectric
characteristics including improved mechanical output. The actuator
has a piezoceramic layer 43 of a material such as lead zirconate
titanate (PZT) sandwiched and bonded between a stainless steel
lower layer 45 and an aluminum upper layer 47. The actuator is
pre-stressed which gives it a characteristic curve or bend which
can be observed in FIGS. 1 and 3. When a voltage is applied to
piezoelectric actuator 40, the actuator responds by changing its
curvature and/or direction of concavity depending on the magnitude
and polarity of the applied voltage. The changes in curvature,
illustrated in ghost outline in FIG. 1, produces a reciprocating
action which actuates valve 30.
[0031] In one embodiment of the invention, the piezoelectric
actuator 40 is a substantially rectangular strip (FIG. 2). The
actuator includes a drive member 41 and end portions 42 which are
secured for pivotal motion in retaining grooves 26 formed in a pair
of posts 25 integrally formed with engine cylinder head 12. This
arrangement provides for better lubrication because oil can enter
grooves 26 and lubricate the sliding surfaces. Furthermore, no
fasteners are required and the arrangement is more tolerant of
manufacturing processes. Alternatively, the retaining post may be
in the form of an annular wall encircling the valve stem 12 and
containing a single, continuous retaining groove.
[0032] The valve stem 32 of valve 30 is directly connected to the
piezoelectric drive member 41 by any suitable manner to open and
close the valve 30 by direct actuation, thus eliminating the need
for valve return springs to return the valve 30 to its closed
position. One method of securing valve 30 to piezoelectric drive
member 41 is to provide the drive member with a keyhole shaped
opening or aperture 44. The keyhole shaped aperture 44 includes an
enlarged, off-centered opening 46 having a diameter larger than the
diameter of the valve stem 32. Opening 46 is connected to a smaller
opening 48 centered in the drive member 41 and has a diameter
substantially equal to the diameter of a retaining groove (not
shown) formed about the circumference of the valve stem 32 and
sized for engagement with the groove. The end of the valve stem 32
is received through the opening 46 until the retaining groove 38
aligns with the smaller opening 48. The valve 30 is slid toward the
smaller opening 48 until the piezoelectric drive member 41 engages
the retaining groove 38.
[0033] The valve 30 is constrained laterally by the valve guide 28,
only permitting travel of the valve 30 longitudinally along the
longitudinal axis of the valve stem 32. The movement of the valve
from a closed position to an open position is indicated by the
ghost outline in FIG. 1. It is required that the longitudinal axis
of the valve stem 32 be aligned with the central axis of the
smaller opening 48 in the piezoelectric drive member 41 so that the
motion of the actuator facilitates movement of the valve along the
longitudinal axis of the valve stem 32. If the axes of the valve
stem 32 and the smaller opening 48 are not aligned, linear movement
of the valve 30 may be hindered.
[0034] Referring to FIG. 1, in operation, the piezoelectric valve
actuator is electronically controlled, for example, by a computer
or an electronic control module (ECM), generally represented at 50.
The ECM 50 gathers information of selected engine operating
parameters and, along with user input, controls valve operation
through electrical connectors 88. Electrical connectors 88 are
electrically connected to the valve 30 at 51 to supply control
signals to the valve and facilitate opening and closing movement
thereof.
[0035] Turning now to FIG. 3, a second embodiment of a
piezoelectric valve actuation system is shown. In this embodiment,
a piezoelectric valve actuator 60 includes a piezoelectric drive
member 65 having layers similar to those of drive member 41
described previously. However, the stainless steel layer 66 of
drive member 65 is different from stainless steel layer 45 being
provided with rolled ends 67. In this embodiment, cylinder head 70
is provided with a pair of mounting pins 72 located on each side of
the valve stem 32 to which the rolled ends 67 of piezoelectric
drive member 65 are pivotally attached. Operation of this actuator
is identical to that of the embodiment previously described with
electrical connections at 68 receiving signals from the ECM 50 via
electrical connectors.
[0036] An additional embodiment of the piezoelectric valve
actuation system is shown in FIGS. 4 and 5. In this embodiment, a
piezoelectric valve actuator 80 includes a disk shaped
piezoelectric drive member 85 formed from a plurality of layers
similar to those of drive member 41 described previously. The
cylinder head 90 includes a plurality of retaining posts 92, each
including a retaining groove 94 in which a portion of the periphery
of the piezoelectric drive member 85 is received. At least four
retaining posts 92 are provided as shown in FIG. 4, however any
suitable number of retaining posts 92 may be used to mount drive
member 85 to the cylinder head 90. Alternatively, the retaining
posts could be replaced with an annular retaining wall completely
encircling the valve stem and containing a single, continuous
retaining groove. Piezoelectric drive member 85 includes a
centrally located keyhole shaped aperture 87 for engagement with a
valve stem 32 as previously described. The piezoelectric drive
member 85 is electrically connected at 96 to ECM 50 via electrical
connectors which receive signals from the ECM 50 for operation of
the drive member in the same manner described above.
[0037] The valve actuation system of the present invention provides
infinitely variable valve timing giving the ability to continuously
change gas flow characteristics of an engine based on feedback from
various engine sub-systems along with operator input. Valve lift
could also be varied over a predetermined range. Additionally, the
valves could also be left partially open during engine startup
thereby reducing the required size of starter motors and
batteries.
[0038] Other benefits deriving from the piezoelectric valve
actuator of the present invention include the provision of engine
braking through valve control and the lack of a requirement for
periodic valve adjustment. Also, the operation of individual
cylinders in a multicylinder engine could be suspended by closing
selected valves to improve fuel economy when full power is not
required. In addition, the valve actuation system of the present
invention provides the capability to effect combustion chamber
turbulence based on the use of additional tangential flow intake
valves.
[0039] As a further benefit of the present invention, the
elimination of the valve train simplifies engine mechanics and
eliminates cooling air obstructions, particularly for air cooled
engines. In addition, adding layers to the actuator which could
generate power back into the system when the valve direction is
reversed could minimize power consumption.
[0040] While this invention has been described as having an
exemplary structure, 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 invention using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains and which fall within the limits of
the appended claims.
* * * * *