U.S. patent application number 11/545715 was filed with the patent office on 2008-04-10 for pulse width modulated fluidic valve.
Invention is credited to Thomas R. Chase, Perry Y. Li.
Application Number | 20080083894 11/545715 |
Document ID | / |
Family ID | 38871774 |
Filed Date | 2008-04-10 |
United States Patent
Application |
20080083894 |
Kind Code |
A1 |
Li; Perry Y. ; et
al. |
April 10, 2008 |
Pulse width modulated fluidic valve
Abstract
A pulse width modulated fluidic valve includes a cylinder having
an elongate bore, a length and first and second ports which extend
from outside the cylinder into the bore. A rotatable spool is
carried in the bore and movable in a direction of the length of
cylinder. The spool has a variable blocking feature which blocks
passage of fluid between the first and second ports as a function
of angular position relative to the first and second ports and as a
function of linear position along the length of the cylinder.
Inventors: |
Li; Perry Y.; (Maple Grove,
MN) ; Chase; Thomas R.; (Minneapolis, MN) |
Correspondence
Address: |
WESTMAN CHAMPLIN & KELLY, P.A.
SUITE 1400, 900 SECOND AVENUE SOUTH
MINNEAPOLIS
MN
55402-3319
US
|
Family ID: |
38871774 |
Appl. No.: |
11/545715 |
Filed: |
October 10, 2006 |
Current U.S.
Class: |
251/129.05 |
Current CPC
Class: |
F16K 7/10 20130101; F04B
49/24 20130101; Y10T 137/0318 20150401 |
Class at
Publication: |
251/129.05 |
International
Class: |
F16K 31/02 20060101
F16K031/02 |
Claims
1. A pulse width modulated fluidic valve, comprising: a housing
having an elongate bore, a length and first and second ports which
extend from outside the housing into the bore; and a rotatable
spool carried in the bore and movable in a direction of the length
of housing, the spool having a variable blocking feature which
selectively blocks passage of fluid between the first and second
ports as a function of angular position relative to the first and
second ports and as a function of linear position along the length
of the housing.
2. The apparatus of claim 1 including a rotary driver coupled to
rotatable spool configure to rotate the rotatable spool.
3. The apparatus of claim 2 wherein a speed of rotation is
controllable.
4. The apparatus of claim 2 wherein the speed of rotation is
fixed.
5. The apparatus of claim 1 includes a linear displacement driver
coupled to the rotatable spool configured to move the spool in a
direction along the length of the housing.
6. The apparatus of claim 5 wherein the linear displacement driver
is responsive to a linear position control input.
7. The apparatus of claim 1 wherein the variable blocking feature
comprises a seal which provides a seal between the spool and a wall
of the bore.
8. The apparatus of claim 1 wherein the seal extends linearly along
a length of the spool and radially along a circumference of the
spool.
9. The apparatus of claim 8 wherein the seal is helical.
10. The apparatus of claim 1 wherein the variable blocking feature
comprises two seals which provide fluidic seals between an outer
circumference of the rotatable spool and a wall of the elongate
bore of the housing.
11. The apparatus of claim 7 wherein the seal is formed relative to
a cut out region of the spool.
12. The apparatus of claim 7 wherein the seal comprises a raised
portion on an outer circumference of the spool.
13. The apparatus of claim 1 wherein the rotatable spool is
hollow.
14. The apparatus of claim 1 wherein the rotatable spool includes a
fluidic passageway which extends radially through the spool.
15. The apparatus of claim 14 wherein the passageway extends from
one side of the variable blocking feature to another side of the
variable blocking feature.
16. A method of controlling flow of a fluid, comprising: providing
flow of a fluid into a housing; receiving the flow of the fluid
into the housing; rotating a spool within the housing, the spool
including a variable blocking feature; moving the spool linearly
within the housing; and receiving the fluid at an exit from the
housing.
17. The method of claim 16 including actuating a rotary driver
coupled to rotatable spool configure to rotate the rotatable
spool.
18. The method of claim 17 wherein a speed of rotation is
controllable.
19. The method of claim 17 wherein the speed of rotation is
fixed.
20. The method of claim 16 includes actuating a linear displacement
driver coupled to the rotatable spool configured to move the spool
in a direction along the length of the housing.
21. The method of claim 20 wherein the linear displacement driver
is responsive to a linear position control input.
22. The method of claim 16 wherein the variable blocking feature
comprises a seal which provides a seal between the spool and a wall
of the bore.
23. The method of claim 22 wherein the seal extends linearly along
a length of the spool and radially along a circumference of the
spool.
24. The method of claim 22 wherein the seal is helical.
25. The method of claim 16 wherein the variable blocking feature
comprises two seals which provide fluidic seals between an outer
circumference of the rotatable spool and a wall of the elongate
bore of the housing.
26. The method of claim 22 wherein the seal is formed relative to a
cut out region of the spool.
27. The method of claim 22 wherein the seal comprises a raised
portion on an outer circumference of the spool.
28. The method of claim 16 wherein the rotatable spool is
hollow.
29. The method of claim 16 wherein the rotatable spool includes a
fluidic passageway which extends radially through the spool.
30. The method of claim 16 wherein the spool includes a passageway
which extends from one side of the variable blocking feature to
another side of the variable blocking feature.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to fluidic valves of the type
used to control flow of a fluid. More specifically, the present
invention relates to pulse width modulated control of such fluid
flow.
[0002] Fluidic valves have many applications and are generally used
to control flow of a fluid between two locations. One simple valve
configuration is a simple blocking element positioned in a pipe, or
the like, which can be moved between at least two positions. In one
position, fluid is allowed to flow through the pipe while in the
other position, the blocking element seals or partially seals
against the pipe and blocks or restricts flow of fluid. If multiple
positions are available between the fully "on" position (with large
opening) and the fully "off" position (completely closed), flow of
fluid can be further controlled accordingly. Valves with adjustable
partial openings are the most prevalent means of controlling the
pressure or flow in a hydraulic circuit. However, flow through
partially open valves induces pressure drops across the valve, and
consequently throttling energy loss, given by the product of the
pressure drop across the valve and the flow, is incurred. Thus,
such throttling valves are inherently inefficient.
[0003] On the other hand, valves with binary positions--fully on or
fully off, are inherently more efficient, since pressure drop is
small when it is fully open, and flow is cut off when it is fully
close. Thus, throttling loss in either positions can be zero or
very small. In order to allow such on/off valves to achieve
variable flow, the valve can be pulsed on and off at different
times during the operation of the system. One such mode of
operation is via pulse width modulation (PWM). In a pulse width
modulated valve, the valve is rapidly switched between the fully on
position and the fully off position. By changing the relative
duration that the valve is in either the fully on position or the
fully off position to the total period of an on/off cycle, the
average flow rate can be accurately controlled between a maximum
flow rate and zero flow rate. Such pulse width modulated valves can
be used in many applications, for example, in achieving variable
displacement functions from fixed displacement pumps and
motors.
[0004] One example pulse width modulated valve configuration uses
an obstruction which is moved linearly in a flow conduit between a
fully blocking or closed position and a fully open position. The
linear driving element can be, for example, an electromagnetic
solenoid, a PZT actuator or the like. A critical factor in the
performance of a pulse width modulated or other binary on/off valve
configurations is the time it takes to transition between the fully
on state, and the fully off state. Since the valve is throttling
the flow during transition, it induces inefficiency. In a PWM
valve, the proportion of time the valve is in transition relative
to the time when it is fully on or fully off should be small to be
efficient. On the other hand, a short cycling time (which consists
of the fully on, fully off, and transition times) should be small
for responsiveness and for precision. Thus, a short transition time
is required for both efficiency as well as responsiveness and
precision.
SUMMARY OF THE INVENTION
[0005] A pulse width modulated valve consists of an element which
is in continuous unidirectional rotational motion. This element is
driven by an external power source, or by the energy in the fluid
flow. The motion of the rotating element is then translated to
periodic high speed relative movement between a valve obstacle
(land) and an inlet or exit port. By providing a means to modulate
the relationship between the duration when the valve obstacle does
or does not cover the inlet or exit port, the duty cycle of the PWM
operation is modulated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a simplified schematic diagram of a mechanical
hydraulic boost converter including a pulse width modulated fluidic
valve in accordance with the present invention.
[0007] FIG. 2A is a perspective view of a pulse width modulated
fluidic valve where the cylinder has been cut away through its axis
to reveal the spool which travels in its bore in a first
position.
[0008] FIG. 2B is a perspective view of a pulse width modulated
fluidic valve where the cylinder has been cut away through its axis
to reveal the spool which travels in its bore in a second
position.
[0009] FIG. 3 is a perspective view of a rotatable spool shown in
FIGS. 1 and 2.
[0010] FIG. 4A is a graph of flow versus time for the fluidic valve
of FIGS. 2A and 2B in which the rotatable valve spool is in a first
linear position.
[0011] FIG. 4B is a graph of flow versus time for the fluidic valve
of FIGS. 2A and 2B in which the rotatable valve spool is in a
second linear position.
[0012] FIG. 5 is a perspective view of another configuration of a
rotatable spool.
[0013] FIG. 6 is a schematic diagram of another embodiment.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0014] One problem associated with the pulse width modulated valves
described in the background section is that they must be positioned
linearly at a relatively fast rate. Such linear positioning
requires motion of the blocking element in one direction to be
stopped, and the blocking element be accelerated rapidly in the
opposite direction. This requires a large amount of force and
energy, is difficult to control, and is stressful on the components
of the valve. The force and power required to accelerate and
decelerate the blocking element only are proportional to the second
and third power of the velocity respectively. Additional force and
power, proportional to first and second power of the velocity, are
needed to overcome the friction. Thus, a large actuator and a
significant amount of power are needed to achieve short transition
times.
[0015] The present invention provides a pulse width modulated
fluidic valve in which a unidirectional rotating element is used to
generate high speed relative motion between a valve obstacle and an
inlet/exit port. The invention further provides a means to modulate
the relationship between the duration when the valve obstacle does
or does not cover the inlet or exit port, thus modulating the pulse
width. In the preferred embodiment, the rotating element is a
rotatable spool which rotates within a cylinder. The rotatable
spool provides a passage therethrough and the speed of rotation can
be used to control the frequency of the fluidic pulses through the
valve. Further, the configuration of the spool allows it to be
moved axially relative to the cylinder such that the width of the
pulse can be controlled. [0016] When the obstacle covers the
inlet/exit port, the valve is fully off, when the obstacle does not
cover the inlet/exit port, the valve is fully on. Unlike a PWM
valve that moves linearly requiring starting and stopping, the
unidirectional motion of the proposed valve allows for the actuator
to always tend to accelerate the valve. Thus, the relative speed
between the valve obstacle and the port will be consistently high,
achieving a short transition time. A means to modulating the
relationship between the duration when the valve obstacle does or
does not cover the inlet or exit port is also provided. This serves
to modulate the duty cycle of the PWM operation. Various
embodiments can be developed based on this concept.
[0017] Our preferred embodiment of the proposed pulse width
modulated fluidic valve includes a cylinder having an elongated
bore. A first port and a second port extend from outside the
cylinder into the bore. A rotatable spool is carried in the bore
and is movable in a direction of the length of cylinder. The spool
contains passages which allows fluid to flow between the
non-blocking portion of the spool surface and the center bore of
the spool. The spool has a variable blocking feature, which
selectively blocks passage of fluid from the first and second ports
to the center of the spool, as a function of angular position
relative to the first and second ports and a function of linear
position along the length of the cylinder. The rotatable spool is
constantly rotating unidirectionally at high speed. This achieves a
high relative speed between the spool and the inlet/exit port,
achieving a short transition time. By translating the spool axially
along the bore, the inlet/exit port will be exposed to varying
blocking features, which can be designed to achieve variable
duration when the valve is fully on or fully off.
[0018] FIG. 1 is a simplified diagram showing one application of a
pulse width modulated fluidic valve in a mechanical-hydraulic boost
converter. In this example, a continuously running pump 102 is
driven by a motor 104 through a fly wheel 106. The pump 102 draws
fluid from reservoir 110. A pulse width modulated fluidic valve 112
receives a control signal which controls the amount of fluid from
pump 102 which is recirculated. The fluid which is not recirculated
is pumped through a check valve 116 and an accumulator 114 is used
to smooth out the pulses in the flow of the fluid. This provides a
controllable flow of fluid to a hydraulic load, for example, a
piston/cylinder arrangement. Thus, the fixed displacement pump 102
is allowed to achieve the function of a variable displacement
pump.
[0019] FIGS. 2A and 2B are perspective views of a pulse width
modulated fluid valve in accordance with one embodiment. The valve
cylinder has been cut away through its axis to reveal the spool
which travels in its bore. In FIG. 2A, the valve 112 is arranged in
a mostly closed position. While in FIG. 2B, the valve 112 is
arranged in a mostly open position. Valve 112 includes an elongate
cylinder 130 having a bore 132 therein. A rotatable spool 134 is
positioned within bore 132. Cylinder 130 also includes first and
second ports 136 and 138 which extend from outside of the cylinder
into the bore 132. Valve 112 also includes a rotary driver 144 and
a linear driver 146 responsive to control signals 148 and 150,
respectively. Drivers 144 and 146 couple to spool 134 through spool
armature 152. Rotary driver 144 is configured to rotate spool 134
relative to ports 136 and 138 of cylinder 130 in response to
control signal 148. Similarly, linear driver 146 is arranged to
move spool 134 linearly within cylinder 130 along an axial length
of the cylinder 130 in response to the control signal 150.
[0020] FIG. 3 is a more detailed perspective view of spool 134. As
illustrated in FIG. 3, spool 134 includes variable blocking
features 160, and end seals 162 and 164. These components are
configured to fluidically seal the spool 134 with respect to the
wall of bore 132 of cylinder 130. The variable blocking features
160 define a fluid blocking region 166 and a fluid flow region 168.
In fluid flow region 168, passageways 170 extend through spool
134.
[0021] In the configuration of FIG. 3, variable blocking feature
160 is formed as a ridge in the outer circumference of spool 134
and comprises a first helical portion 160A and a second helical
portion 160B.
[0022] Turning back to FIG. 2A, as spool 134 rotates, a fluidic
passageway between ports 136 and 138 will be opened or closed
depending upon the position of blocking features 160 relative to
ports 136 and 138. Because of the linear position of spool 134
relative to portions 136 and 138, as the spool 134 rotates, the
ports 136 and 138 will reside most of the time in the fluid flow
blocking region 166 and flow of fluid will be blocked by portions
160A and 160B of blocking feature 160. However, as spool 134
continues to rotate, the ports 136 and 138 will less frequently
reside within fluid flow region 168 such that there can be fluid
flow between ports 136 and 138 through passageway 170.
[0023] FIG. 4A is a graph of flow versus time for this
configuration. As shown in FIG. 4A, a series of relatively narrow
flow pulses are provided with the valve being mostly off between
each pulse. This provides a relatively small average flow
level.
[0024] Returning to the configuration shown in FIG. 2B, the spool
134 is shown positioned further within cylinder 130. In this
configuration, as spool 134 rotates, the ports 136 and 138 will
reside for a greater period of time in the fluid flow region 168 of
spool 134 than they will in the fluid blocking region 166. FIG. 4B
is a graph of flow versus time for this arrangement. As illustrated
in FIG. 4B, the flow comprises a series of relatively long flow
periods with brief flow blocking periods in between each peak. This
results in an average flow which is almost as great as the level of
the individual peaks, and much greater than the average flow level
shown in FIG. 4A. Thus, as illustrated above, the period of the
pulses can be controlled by adjusting the rotation speed of rotary
driver 144, while the width of the individual pulses can be
controlled by adjusting the linear position of the spool 134 within
the cylinder 130 using linear driver 146. Further, the relationship
between linear position and pulse width can be controlled by
changing the shape of the variable blocking features 160. As
illustrated in FIG. 3, the variable blocking features 160 have a
profile which is dependent upon both the angular position along the
circumference of spool 134 as well as the linear position along the
axis of spool 134.
[0025] FIG. 5 is a perspective view of another configuration of a
spool 200. In the configuration of FIG. 5, the variable blocking
feature 160 is formed as a step change in the outer surface of the
spool 200. Such a configuration may be easier to manufacture and
provide greater blocking abilities in comparison to that shown in
FIG. 3. However, spool 134 shown in FIG. 3 provides less surface
area against the wall of bore 132 and therefore should provide
lower journal friction.
[0026] In general, a pulse width modulated (PWM) fluidic valve is
provided. The valve can be cycled from on to off at high
frequencies, for example, on the order of 1000 Hz. The flow through
the valve is controlled by varying the fraction of each cycle that
the valve is open. The flow rate through the valve is infinitely
variable between zero flow and maximum flow. Despite its high
frequency, the valve can also provide high fluid flow rates with
low pressure drops. Pressure losses are minimized by providing
sufficiently large port openings, and by reducing the time during
which the switching port is partially obstructed by the valve
spool. The spool of the valve is driven by a linkage having two
degrees of freedom, one in a linear direction and one rotational.
The valve is applicable to many types of installation, for example,
a fixed displacement hydraulic pump in which the valve can control
the output of flow of the pump; or a fixed displacement motor in
which the valve can control the output speed of the motor at
constant flow. Such a valve configuration is for use with hydraulic
motors, hydraulic transformers, etc. This configuration provides a
high frequency response which makes for superior operation as a
pulse width modulated valve. The valve can be combined with a
controller to provide software enabled features. For example, such
software can be implemented in drivers 144 and 146, or in software
which controls such drivers. The valve can operate at high
frequencies which thereby improves controllability. The valve
varies flow rate without throttling the flow which thereby reduces
input power and lowers operating costs. Such a valve configuration
provides for improved size, weight and efficiency over other
configurations.
[0027] The above description of the present invention is for
illustrative purposes only. The techniques and description set
forth above may be modified as appropriate. For example, although
only two ports are shown, other configurations could be used. For
example, using additional ports will increase the fraction of each
pulse cycle during which each port is partially obstructed by the
blocking feature of the spool. In one configuration, three such
ports may be desirable due to the stable nature of a triangular
configuration. However, there is a trade off between additional
ports and efficiency of the valve. The spool and cylindrical
housing need merely be moved relative to one another. The actual
movement, rotational or linear, can be by movement of any one of
the spool or cylindrical housing or a combination of both. During
operation, the angular velocity should exceed some minimum
threshold for the valve to be operational. Once the minimal
velocity has been met, the flow rate should be nominally
independent of the angular velocity of the valve. Note that fluid
inertia may start to effect the actual flow rate at high rates of
pulsing. The rate of rotation of the spool sets the frequency of
the pulses. In some configurations, the valve is coupled to an
accumulator on the load side of the system, for example element 114
in FIG. 1. This enables averaging the discreet pulses of flow from
the valve into a steady flow applied to the load with a "ripple"
superimposed on top of the flow. Increasing the rate of pulsing
reduces the amplitude of the ripple which is typically desirable.
Further, increasing the angular velocity of the spool also
increases the potential to control the bandwidth of the valve,
i.e., the speed at which the valve can respond to a command to
change the flow rate. Therefore, with the present invention, given
flow rate the valve can pulse the flow at a higher rate than a
linear valve. However, in general, the rate of rotation does not
nominally change the average flow rate.
[0028] The particular actuator used to provide the relative
rotation can be configured as desired. Although the Figures show an
external motor configured to rotate the spool, other configurations
can be used. For example, power can be extracted from the flow of
fluid through the valve and used to rotate the spool. In other
words, the spool serves as a fluid turbine as well as the means for
starting and stopping the fluid flow. In such a configuration, the
rotary actuator 144 as shown in the Figures is not required.
Instead, ports through the cylinder sleeve, such as ports 136, 138
in FIG. 2A, may be configured tangentially to the circumference of
the cylinder sleeve. In another example configuration, element 144
comprises a sensor which can be used to sense the rate of rotation
of the spool as it is rotated by the fluid. This information can be
used by a control algorithm.
[0029] In contrast to linear valves, in the present invention the
fraction of the period that the fluid flow is partially blocked by
the blocking feature traveling over the fluid ports in the sleeve
is the same regardless of the frequency. In linear valves, the
fraction of the cycle that the flow is partially blocked increases
with frequency. The partially blocked state is undesirable in that
the flow is choked and power is lost. Further, if the valve of the
present invention is operated at high frequencies, the input power
is not reduced. The power improvement results from achieving a
variable flow without choking the flow through a variable orifice.
In addition, as mentioned above, the valve can be run at high
frequencies without increasing the relative small fraction of the
cycle that the flow is choked.
[0030] Although the specific embodiments shown above illustrate one
fluid path arrangement, of course, other arrangements can be used
in accordance with the present invention. For example, the spool
can be constructed to allow the flow of fluid out of the depression
in the spool and in the axial direction. For example, referring to
FIGS. 3 and 5, radial holes 170 may be removed. Alternatively,
slots may be cut in the end seal 162 whereby fluid may flow out of
the depression and along the axial direction. In yet another
configuration, the seal 162 may be removed altogether. However,
seal 162 may be advantageous in holding the spool concentrically
with the sleeve. In another configuration, the valve can be
constructed such that flow path is reversed, in other words, fluid
can enter through the spool and exit through the ports in the
sleeve. However, such a configuration may increase the volume of
the fluid which is subjected to pulsing and thereby lowers the
overall bandwidth of the valve system. In other words, a valve
using the reverse flow path may not be able to provide the same
performance of a valve using the forward path. However, such a
valve may provide sufficient service at lower pulse frequencies. In
yet another configuration, the center bore of the spool in FIG. 3
is divided into two separate chambers, one connected to spool
feature 168 as before, and the other connected to feature 166
through new passages similar to ports 170. The two chambers are
then connected to outlet ports. This configuration enables the
valve to act as a three way valve that allows flow through either
of the outlet ports.
[0031] The spool can be configured as desired. For example, the
spool can be hollow in order to reduce mass. However, the spool may
also be solid, or partially solid as desired. If a solid spool is
used, some type of exit path should be provided for the fluid. This
can be done in a number of different ways. In a first
configuration, an axial escape path is provided for the fluid as
discussed above. In another configuration, a hole is provided
radially down into the spool with axial ports extending into the
end of the spool to meet the radial holes. In yet another
configuration, holes may be skewed between the radial and axial
directions, i.e., to provide a single continuous hole which starts
in the depression of the spool and exits at an axial face of the
spool. This may also provide a rough technique for using fluid
forces to cause the spool to rotate as discussed above. If fluid
forces are used to spin the spool as discussed above, the rate of
the rotation will not be constant nor directly controllable.
However, as long as the fluid forces cause the spool to rotate
above some minimum angular velocity, the valve will still be
operational. The precise speed for proper valve operation is
dependent upon spool configuration. However, it is preferable that
the speed be maintained within some reasonable bounds.
[0032] A helical cut for the depression in the spool may be
beneficial in that it implements a linear relationship between the
axial position of the spool and the width of the "duty cycle" of
each pulse. However, the depression may be cut with some
alternative profiles to achieve the desired pulse profile. The
invention is not limited in particular to a helical cut. Similarly,
the ports in the cylindrical housing are not required to be
positioned perfectly radially. In fact, in order to implement a
spool which is driven by fluid flow forces, it may be desirable to
skew these ports off of the radial direction. Skewing the center
line of the port from the radial direction also has the negative
consequence of increasing the fraction of each duty cycle that each
port is partially obstructed by the blocking feature as discussed
above. Therefore, a trade-off arises between the efficiency of
pulsing the fluid flow and the efficiency of the fluid dynamics for
directly spinning the valve.
[0033] Although the valve is described to be a pulse width
modulated valve in that the duty ratio of the valve being fully on
versus the cycle time is modulated, more precise control of the
timing of when the valve is turned on and turned off can be
attained using the invention. This can be achieved for example, in
the configuration in FIG. 3, by moving the spool linearly so as to
enable the ports 136/138 to avoid or to approach the blocking
feature 160B in FIG. 3. This in turn lengthens or shortens the
individual pulse width.
[0034] Although FIG. 1 shows one potential application for a valve
of the present invention, the valve of the present application is
applicable to any appropriate configuration. One embodiment is
shown in FIG. 6 which consists of a rotating mechanism 250 with the
obstacle block or valve spool 252 connected to arms 254,256 of the
mechanism. A drive motor 258 coupled to ground 260 through link 262
drives the spool 252. Spool 252 moves in housing 264 and
selectively blocks port 266. While a sliding obstacle block is
suggested in FIG. 6, a rotating obstacle block could also be used.
The modulating function can be achieved by sliding or rotating
another link.
[0035] In general, the valve of the present invention allows
pulsing of the flow of the fluid without requiring accelerating or
decelerating of the valve spool. In the embodiment suggested in
FIG. 6, while the valve spool does accelerate and decelerate, the
rotating driving element does not require acceleration or
deceleration. In some configurations, it is possible to vary the
flow from zero flow to a maximum flow. However, the valve may also
be configured such that the flow is only variable over some smaller
fraction of the total possible range.
[0036] In one configuration, the spool is rotated continuously
relative to the sleeve. In another configuration, the spool is
rotated back and forth in the circumferential direction rather than
continuously rotated.
[0037] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention. For example,
although a cylindrical housing is shown the housing may be of any
appropriate configuration. Similarly, although a particular spool
configuration is illustrated, the spool can be of any appropriate
shape. In another example configuration, a linkage or armature is
connected radially offset from the spool and is used to rotate the
spool using a reciprocating motion. In general, the present
invention utilizes the continuous rotary motion of an element in
order to achieve high frequency periodic motion which is used to
move a valve obstacle.
* * * * *