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TECHNICAL FIELD
This invention relates generally to a method and apparatus for determining
the position of the armature of an electromagnetic actuator, and more
particularly, to a method and apparatus for measuring the magnitude and
the time derivative of the current in the coil of an electromagnetic
actuator and responsively determining the position of the armature of an
electromagnetic actuator.
BACKGROUND ART
Electromagnetic actuators, such as linear or rotary solenoids, typically
include a coil in electromagnetic communication with a movable armature.
The coil is generally connected to a controllable driving circuit which
varies the magnitude of current flowing in the coil and resultantly varies
the strength of the magnetic field being produced by the coil. As the
strength of the magnetic field is changed, the armature moves in response
to the resulting change in the magnetic force being exerted on the
armature.
Typically, the position of the armature is a function of both the magnitude
of current flowing in the coil and the magnitude and direction of
mechanical forces being exerted on the armature. The mechanical forces are
exerted on the armature in response to the operating conditions of the
system in which the electromagnetic actuator is operating. It is therefore
advantageous to have a method of determining the position of the armature
so that the operating conditions of the system can be indicated and used
in connection with system diagnostics or a closed-loop control for the
driving circuit.
The most common method of determining the position of the armature of an
electromagnetic actuator is to connect an external sensor to the actuator.
Such sensors often take the form of potentiometers or linear voltage
differential transformers (LVDTs). While the addition of these sensors
provides the desired information, they increase the cost and warehousing
requirements of the actuator.
Attempts to provide position information without utilizing additional
sensors have generally taken the form described in Japanese Patent Appl.
No. 61-157418, published Jan. 20, 1988, and in Proceedings: 39th Relay
Conference, Apr. 22-24, 1991, National Association of Relay Manufacturers,
pp. 9-1 through 9-4. Both of the above publications disclose systems which
determine the position of the armature by measuring the inductance of the
coil in the actuator. Since inductance is a function of the air gap
between the armature and the coil, the size of the air gap, and hence
armature position, is determined by comparing measured inductance values
to empirically determined inductance versus position characteristics.
Systems of this type are generally incapable of providing accurate results
for actuators exhibiting second-order characteristics since such actuators
do not have explicit inductance values. Furthermore, as described in the
Japanese Application, additional measurements and comparisons, e.g. coil
temperature and magnetomotive force, are required to provide accurate
indications of armature position.
Devices for determining armature position are particularly useful in
connection with solenoids and electrohydraulic valves. Electrohydraulic
valves are often used to control the engagement/disengagement of
transmission clutches. The engagement of a hydraulic clutch consists of
two stages: the fill mode and the pressure modulation mode. In the fill
mode, the displaced clutch volume is filled with hydraulic fluid. In the
pressure modulation mode, the pressure within the clutch volume is
modulated (increased) to a pressure level to ensure proper and full
engagement of the clutch. To actuate the clutch, the solenoid is
therefore, first energized to begin filling the clutch. When the clutch is
filled, the current applied to the solenoid is modulated (typically, in an
increasing linear ramp function) to continue the flow of hydraulic fluid
to the clutch and increase the pressure to a level sufficient to properly
engage the clutch.
Typically, a timing strategy has been used to determine when the clutch has
reached the end of fill condition. In this situation, the solenoid's coil
would be energized and the clutch would begin to fill with hydraulic
fluid. After a predetermined time period, the transmission controller
would begin to modulate current in an effort to fully engage the clutch.
This procedure has several limitations. For example, operating conditions
change the actual time required to fill the clutch. Since pump flow is a
function of engine speed, pump flow will vary with engine speed. Other
factors (for example, other hydraulic systems being supplied by the pump)
may also affect pump flow. As the pump flow varies, the time required to
fill the clutch will also vary. Other operating conditions which affect
the clutch fill times are present gear ratio, desired gear ratio,
transmission load, and inclination of the vehicle.
Variations in the engine and operating characteristics of the transmission
components can be expected over the life of the vehicle due to wear. This
will also affect the clutch fill time.
Furthermore, variations in the system components, including the clutches,
due to manufacturing tolerances will also affect clutch fill time.
If the proper fill time is not known or accurately estimated, the clutch
will be in an overfill or underfill condition when the controller attempts
to modulate clutch pressure to fully engage the clutch.
Operation of the transmission by modulating the clutch pressure in an
underfill or overfill condition will cause a "jerky" shift action and
increase the rate at which wear and tear occurs.
In an attempt to predict fill times, sensors are often added to the
transmission controller. For example, U.S. Pat. No. 4,707,789 issued to
Robert C. Downs et al., on Nov. 17, 1987, uses a transmission input speed
sensor to detect underfill/overfill condition. The time delay used to
estimate clutch fill is adjusted based upon the transmission input speed.
However, transient changes, that is, changes in the operating conditions
that the controller has not adapted to, will affect the shift quality.
Furthermore, a transient condition will have a negative effect on the fill
time for the next shift without the transient condition.
In another attempt to accurately predict the end of fill condition, it is
known to add additional valves to the controller. One such system is shown
in the Komatsu technical guide, "K-ATOMICS Komatsu-Advanced Transmission
with Optimum Modulation Control". A flow sensing valve is used to sense a
pressure differential. The spool of the flow sensing valve closes a switch
in response to the pressure differential, thereby, signalling the end of
fill condition. In still another attempt, hydraulic pressure is used to
predict the end of fill condition. U.S. Pat. No. 4,942,787 issued to
Takashi Aoki et al., on Jul. 24, 1990, discloses the use of a pressure
detection switch for that purpose. However, the cost added by the
additional components in both these systems, plus, the added manufacturing
cost due to the increased complexity, make these systems undesirable.
The present invention is directed at overcoming one or more of the problems
as set forth above.
DISCLOSURE OF THE INVENTION
The invention avoids the disadvantages of known devices for determining the
position of an armature with respect to its associated coil and provides
an accurate and flexible indication of armature position with respect to
the coil and end-of fill conditions in a hydraulic clutch without the need
for external sensors.
In one aspect of the present invention, an apparatus is provided for
determining the position of an armature of an electromagnetic actuator
having a coil. A controller measures a magnitude and a rate of change of
current in the coil and responsively determines the position of the
armature with respect to the coil.
In another aspect of the present invention, an apparatus is provided for
determining the position of an armature of an electromagnetic actuator
having a coil. A controller measures the frequency of the voltage applied
to the coil and responsively determines the position of the armature with
respect to the coil.
In yet another aspect of the present invention, a method is provided for
determining the position of an armature of an electromagnetic actuator
having a coil. The method comprises the steps of measuring the magnitude
of current in the coil, measuring the rate of change of current in the
coil, and determining the position of the armature with respect to the
coil in response to the magnitude and rate of change.
BRIEF DESCRIPTION OF THE DRAWING
For a better understanding of the present invention, reference may be made
to the accompanying drawings, in which:
FIG. 1 is a graphical representation of the relationship between flux
linkage, coil current, and armature position;
FIG. 2 is a graphical representation of the relationship between applied
voltage, coil current, and the rate of change of coil current;
FIG. 3 is a schematic representation of an embodiment of the present
invention;
FIG. 4 is a schematic representation of an embodiment of the present
invention;
FIG. 5 is a graphical representation of the relationship between the
applied voltage, coil current, and inductance;
FIG. 6 is a schematic representation of an embodiment of the present
invention;
FIG. 7A is a diagrammatic view of an electrohydraulic valve operated clutch
piston including an embodiment of the present invention;
FIG. 7B is a diagrammatic view of a clutch piston controlled by a dual
stage spool valve design including an embodiment of the present invention;
FIG. 8A is an exemplary graph illustrating coil current and voltage during
clutch actuation;
FIG. 8B is an exemplary graph illustrating spool position during clutch
actuation;
FIG. 8C is an exemplary graph illustrating control pressure during clutch
actuation; and
FIG. 8D is an exemplary graph illustrating clutch position during clutch
actuation.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIG. 1, flux linkage versus coil current characteristics of a
generalized electromagnetic actuator are shown. The variable x represents
the size of an airgap between the armature and the coil of the actuator.
The size of the airgap changes as the armature moves through its range of
motion. As is well-known in the art of electromagnetics, the flux linkage
is a positive function of coil current and a negative function of the size
of the airgap in the magnetic circuit. Thus, for a given current
magnitude, the flux linkage decreases as the airgap increases. The
relationship that is illustrated by the graph of FIG. 1 allows the size of
the airgap, and hence the position of the armature with respect to the
coil, to be determined if the flux linkage and coil current are known.
The voltage across the coil can be described by the following equation:
V=iR+d(Li)/dt (1)
where
i is the magnitude of current in the coil;
R is the resistance in the coil;
L is the inductance of the coil; and
Li is the flux linkage (lambda).
By dividing both sides of equation (1) by di/dt, the following equation is
derived which, following manipulation, provides an expression for the
slope of the characteristics illustrated in FIG. 1 as a function of coil
voltage, coil current, resistance, and the rate of change of coil current.
d(Li)/di=(V-iR)/(di/dt) (2)
Equation (2) indicates that since d(Li)/di is a function of armature
position (see FIG. 1). Therefore, one method for determining the position
of the armature is provided by storing empirically determined data
representing a series of characteristics similar to those illustrated in
FIG. 1, and comparing the stored data to a measured magnitude of the coil
current and a calculated value for d(Li)/di. In the preferred embodiment,
a two-dimensional look-up table of a type well-known in the art is used to
complete the comparison and select the proper armature position value. The
number of characteristics stored in memory is dependent upon the desired
precision of the system. Interpolation may be used to determine the actual
position of the armature in the event that the measured and calculated
values fall between the discrete values stored in memory.
Referring now to FIG. 3, an electromagnetic actuator control system 10
which determines the position of the armature in response to d(Li)/dt and
coil current magnitude is diagrammatically illustrated. A solenoid driver
12 is shown in electrical connection to a solenoid 14. The solenoid 14
includes a coil 16 and an armature 18 that is movable with respect to the
coil 16. In one embodiment, the armature is linearly actuatable in
response to the magnitude of current flowing in the coil 16, such as a
linear solenoid. In an alternative embodiment, the armature is pivotally
actuatable in response to the magnitude of current flowing in the coil 16,
such as a rotary solenoid. As the armature moves, the size of the airgap
between the coil and the armature changes dimensions which causes the
magnetic characteristics of the solenoid to change as described above.
A shunt resistor 20 is connected to and between the solenoid driver 12 and
the solenoid 14. The magnitude of current flowing in the coil is
determined 56 by measuring the voltage across the shunt resistor 20. The
signal representing the magnitude of coil current is differentiated 58.
The signal representing the magnitude of coil current is also multiplied
60 by a value representative of the internal resistance of the coil 14.
The voltage across the first and second terminals 62,64 of the coil 16 is
determined 66 and a voltage signal is produced. The signal representing
the current magnitude multiplied by the internal coil resistance is
subtracted 66 from the voltage signal to produce a signal that is
indicative of the reactive component of the voltage across the first and
second terminals 62,64. The signal representing the reactive voltage
component is then divided 70 by the derivative of current with respect to
time in order to produce a flux linkage signal that is indicative of the
derivative of flux linkage with respect to current in the coil 16.
The controller 52 includes a memory circuit 54 which has empirically
determined data relating to the above-described d(Li)/dt, coil current
magnitude, and armature position characteristics. The controller 52
receives the coil current magnitude signal and the flux linkage signal.
The controller 52 retrieves the stored characteristics from the memory 54
and compares these characteristics to the coil current magnitude signal
and flux linkage signal to determine the position of the armature 18 with
respect to the coil 16. In the preferred embodiment, a two-dimensional
look-up table of a type well-known in the art is used to complete the
comparison and select the proper armature position value. The number of
characteristics stored in memory is dependent upon the desired precision
of the system. Interpolation may be used to determine the actual position
of the armature in the event that the measured and calculated values fall
between the discrete values stored in memory.
The controller 52 can then use this information in a diagnostic function to
determine whether the solenoid 14 is operating properly, in a closed-loop
control to vary the duty cycle of the PWM driving signal in response to
the desired and actual positions of the armature, or in a hydraulic clutch
control to indicate an end-of-fill condition.
It is to be recognized that FIG. 3 is a functional description and that a
variety of different specific circuits for providing the features of the
position detecting circuit could be designed by a person skilled in the
art.
It should be appreciated that since it was illustrated that d(Li)/di is a
function of coil current and armature position, equation (2) indicates
that di/dt is likewise a function of coil current and armature position.
Thus another method for determining the armature position is provided by
storing a series of empirically determined characteristics representing
the relationship between di/dt, coil current, and armature position in
memory and comparing the stored characteristics with measured values
representing the magnitude and rate of change of the coil current. As
described above, interpolation may be used to determine the actual
position of the armature in the event that the measured and calculated
values fall between the discrete values stored in memory.
The relationships between the voltage of the driving signal across the
terminals of the coil, the magnitude of the coil current, and -(di/dt) are
shown in FIG. 2. The driving signal is advantageously a Pulse-Width
Modulated (PWM) signal having a variable duty cycle. As voltage is applied
to the coil, the magnitude of current in the coil exponentially increases
toward a steady-state value; similarly, as voltage is removed from the
coil, the magnitude of current in the coil exponentially decreases. As the
duty cycle of the driving signal increases, the average magnitude of coil
current increases which increases the force on the armature. Similarly, as
the duty cycle of the driving signal decreases, the magnetic force
impressed on the armature decreases.
It is advantageous to have a single value representative of the inductive
characteristics of the coil which can be compared to the coil current
magnitude and armature position information stored in memory. Since di/dt
is a function of armature position and coil current magnitude, the range
through which the di/dt signal varies during each cycle of the driving
signal is also a function of coil current magnitude and armature position.
By measuring the peak of the di/dt signal, the size of the range through
which the the di/dt signal varies during each cycle is indicated. The peak
di/dt signal can thus be stored in memory and compared with the stored
coil current magnitudes and armature positions to obtain an indication of
armature position. Advantageously, the peak values of di/dt can be
measured for either energization or deenergization of the coil, or both.
It is noted that the peak value of di/dt given by equation (2) ignores eddy
current effects. In some cases eddy currents may substantially effect the
magnitude of the peak di/dt signal. Advantageously, the instant invention
is adapted to detect the peak di/dt signal even if the peak di/dt signal
is dominated by eddy current effects.
Referring now to FIG. 4, an armature position sensing circuit 10 which
determines the position of the armature in response to di/dt and coil
current magnitude is shown. More particularly, the peak di/dt signal is
detected along with the average value of the current traveling through the
coil to determine the position of the armature. As shown, opposing ends of
the shunt resistor 20 are preferably connected to a differential amplifier
22 via buffers 24,26. The differential amplifier 22 produces a signal that
is indicative of the coil current magnitude and is of a type well-known in
the art. The differential amplifier 22 comprises a first operational
amplifier 28, a resistor 30 connected between the output and inverting
input of the first operational amplifier 28, and a resistor 32 connected
between the non-inverting input of the first operational amplifier 28 and
circuit ground.
The output of the differential amplifier 22 is connected to a controller 52
and a differentiator 34. The differentiator 34 includes a second
operational amplifier 36 and a resistor 38 and a capacitor 40 connected in
series between the output of the first operational amplifier 28 and the
inverting input of the second operational amplifier 36. A resistor 42 is
also connected between the inverting input and the output of the second
operational amplifier 36. The non-inverting input of the second
operational amplifier is connected to circuit ground.
The output of the second operational amplifier 36 is connected to a peak
detection circuit 44 that includes an RC circuit having a resistor 46 and
a capacitor 48 connected in parallel between the circuit ground and the
cathode of a diode 50. The cathode of the diode is also connected to the
controller 52. The anode of the diode 50 is connected to the output of the
second operational amplifier 36. The component values associated with the
resistor 46 and capacitor 48 are chosen to provide a time constant for the
RC circuit that allows the peak value to remain steady enough to provide a
useful signal to the controller 52 but yet will allow the output signal to
change rapidly enough that the control system 10 accurately indicates the
position of the armature as it moves.
The controller 52 includes a memory circuit 54 which has empirically
determined data relating to the above-described di/dt, coil current
magnitude, and armature position characteristics. The controller 52
receives a signal that is indicative of the coil current magnitude from
the differential amplifier 22 and a signal that is indicative of the peak
value of the rate of change of the coil current from the peak detection
circuit 44. The controller 52 retrieves the stored characteristics from
the memory 54 and compares these characteristics to the current magnitude
and rate of change signals to determine the position of the armature 18
with respect to the coil 16. In the preferred embodiment, a
two-dimensional look-up table of a type well-known in the art is used to
complete the comparison and select the proper armature position value. The
number of characteristics stored in memory is dependent upon the desired
precision of the system. Interpolation may be used to determine the actual
position of the armature in the event that the measured and calculated
values fall between the discrete values stored in memory.
The controller 52 can then use this information in a diagnostic function to
determine whether the solenoid 14 is operating properly, in a closed-loop
control to vary the duty cycle of the PWM driving signal in response to
the desired and actual positions of the armature, or in a hydraulic clutch
control to indicate an end-of-fill condition. It is to be noted that the
present invention is not limited to these applications and it may be
evident to those skilled in the art that other uses may be possible.
The circuit shown in FIG. 4 is exemplary, and the manner of design and
construction of this, or a similar, circuit would be commonly known to a
person skilled in the art.
Yet another method for determining the armature position is provided by
measuring the frequency of the applied voltage. To further illustrate
this, the relationships between the voltage of the driving signal across
the terminals of the coil, the magnitude of the coil current with respect
to time, and the inductance of the coil are shown in FIG. 5. As voltage is
applied to the coil, the magnitude of current in the coil exponentially
increases towards a predetermined maximum value (MAX); similarly, as
voltage is removed from the coil, the magnitude of current in the coil
exponentially decreases to a predetermined minimum value (MIN). As is well
known, changes in inductance brings about changes in the rate of growth or
decay of the current. Shown on the time graph, the inductance changes from
a larger value, L.sub.1, to a smaller value, L.sub.2. Accordingly, the
rate of change of the coil current changes with the changing inductance.
This particular method requires that the coil current is controlled by a
"on-off" or "bang-bang" type solenoid driver which utilizes current
feedback. This type of solenoid driver operates with a predetermined
switching hysteresis to achieve a constant current "ripple" magnitude. The
"ripple" magnitude defines the predetermined minimum and maximum current
values. The driver generates the driving signal by applying the voltage to
the coil either full "on" or full "off" in accordance with the switching
hysteresis. More particularly, a desired current value is compared to a
measured current value and an error signal is generated which represents
the difference of the two values. The switching hysteresis controls the
voltage applied to the coil thereby reducing the error signal to zero.
Thus, the average coil current value is controlled to the desired current
value. This method of current control is well known in the art and will
not be further discussed.
From the above discussion it follows that as the inductance of the coil
increases, the frequency of the driving signal decreases in order to
control the coil current to the desired value. Similarly, as the
inductance of the coil decreases, the frequency of the driving signal
increases to control the coil current to the desired value.
Since di/dt is a function of armature position and coil current magnitude,
the frequency through which the coil current magnitude varies is also a
function of coil current magnitude and armature position. Correspondingly,
the frequency of the driving signal or applied voltage is a function of
coil current magnitude and armature position. By measuring the frequency
of the coil current or the frequency of the driving signal, the size of
the range through which the inductance varies is indicated. Thus, a signal
representing the coil current frequency or driving current frequency can
be stored in memory and compared with the stored coil current magnitudes
and armature positions to obtain an indication of armature position, in a
manner described above.
Referring now to FIG. 6, an armature position sensing circuit 10 which
determines the position of the armature in response to the frequency of
the driving signal and the magnitude of the coil current is shown.
However, rather than directly measure the coil current, the value
representing the desired current may be utilized instead since the average
coil current is controlled substantially at the desired current value. As
discussed above, the solenoid driver 12 is an "on-off" voltage driver
having current feedback control. As shown, a frequency to voltage (F/V)
converter 102 is connected between the solenoid driver 12 and the solenoid
14. The F/V converter 103 is adapted to measure the frequency of the
driving signal and convert the frequency value to a voltage value in a
well known manner. In the preferred embodiment, the F/V converter 102 is a
circuit manufactured by National Semiconductor as part no. LM 2917. The
output of the F/V converter 102 is connected to the controller 52.
The controller 52 includes a memory circuit 54 which has empirically
determined data relating to the above-described driving signal frequency,
the desired current value, and armature position characteristics. The
controller 52 receives a voltage signal representing the driving signal
frequency and a signal representing the desired current value. The
controller 52 retrieves the stored characteristics from the memory 54 and
compares these characteristics to the representative signals to determine
the position of the armature 18 with respect to the coil 16. In the
preferred embodiment, a two-dimensional look-up table of a type well-known
in the art is used to complete the comparison and select the proper
armature position value. The number of characteristics stored in memory is
dependent upon the desired precision of the system. Interpolation may be
used to determine the actual position of the armature in the event that
the measured and calculated values fall between the discrete values stored
in memory.
The controller 52 can then use this information in a diagnostic function to
determine whether the solenoid 14 is operating properly, in a closed-loop
control to control the driving signal in response to the desired and
actual positions of the armature, or in a hydraulic clutch control to
indicate an end-of-fill condition.
Referring primarily to FIG. 7, an embodiment of the instant invention
capable of indicating an end-of-fill condition in a hydraulically operated
clutch is shown. In this embodiment, the solenoid 14 forms a portion of an
electrohydraulic valve 72 and the controller 52 takes the form of an
end-of-fill detector. The end-of-fill detector is disposed within a
transmission controller 74 that is adapted to controllably engage and
disengage the clutches of a vehicle's transmission. The transmission
controller receives signals indicative of certain parameters of the
vehicle (for example, engine speed, accelerator pedal position, and ground
speed) and generates signals to engage/disengage the clutches in
accordance with a set of shifting rules. Typically, such controllers
include a microcontroller or microcomputer. Many variations of such
transmission controllers are well known in the art and are therefore not
discussed further.
In the preferred embodiment, the signal from the transmission controller
74, is a current applied to the coil 16 of the electrical solenoid 14. A
valve means 76 delivers hydraulic fluid from a source of pressurized fluid
to a clutch 78 in response to the current applied to the coil 16.
As hydraulic fluid is delivered to the clutch 78, the clutch or control
volume increases to a maximum or near maximum level. Since hydraulic fluid
is still being delivered to the clutch 78, the clutch pressure rises
rapidly.
In the preferred embodiment, the valve means 76 includes a spool (control)
valve 80. The spool valve 80 is connected between the clutch 78 and a
source of pressurized fluid S, and includes a spool 82. The spool 82 is
connected to the armature 18 of the solenoid 14. When no current is being
applied to the solenoid 14, the spool valve 80 is said to be in a no-flow
position. That is, there is no fluid flow between S and the clutch volume,
C. When maximum fluid flow is allowed between S and C, the spool valve is
said to be in a full flow position. A tank of hydraulic fluid T, is also
provided to allow the clutch 78 to drain. The pressurized hydraulic fluid
is created by a pump arrangement (not shown). Many such arrangements are
known in the art, and are therefore not further discussed.
A clutch volume, C, is defined by the walls of the clutch 78 and a piston
84. The clutch 78 includes a number of clutch plates (not shown). When the
clutch volume, C, is pressurized to its end-of-fill pressure, the clutch
plates are pinned together and the clutch 78 is said to be engaged. For
the purpose of illustration, the clutch plates are modeled by a rod 86 and
a spring 88. The spring 88 acts to bias the piston 84 to the left, thereby
acting to decrease the clutch volume and to disengage the clutch 78.
Feedback means 90 provides a restricted flow of fluid from the clutch
volume, C back to the valve means 76. In the preferred embodiment, the
feedback means 90 includes a restrictive orifice 92.
With reference to FIGS. 8A-8D, graphical representations of the coil
current and voltage, spool position, control pressure, and clutch position
are shown for the purpose of illustrating the operation of the end-of-fill
detector during a typical fill operation.
At time, t.sub.0, the clutch 102 is disengaged, coil current and voltage
are zero (0), there is no flow of hydraulic fluid to the clutch, the spool
is at its minimum position, and the piston is at its minimum position.
Before t.sub.0, the clutch 102 is said to be fully disengaged.
Prior to time t.sub.1, the controller 74 signals the solenoid 14 to actuate
the valve means 76 and to fill (engage) the clutch 78. In the preferred
embodiment, the controller 74 includes a pulse width modulated (PWM)
solenoid driver for controlling the current supplied to the coil 16.
At t.sub.1, the solenoid driver circuit 12 delivers a first current level
to the coil 16, as shown in FIG. 8A. The current within the coil 14
creates a magnetic force within the solenoid 16 which moves the armature
18 with respect to the coil 16. To begin filling the clutch volume, the
first current level from the solenoid driver acts to move the armature 18
and therefore the spool 82, from the minimum or original position towards
a maximum position, see FIG. 8B.
As shown in FIG. 8D, the flow of hydraulic fluid into the clutch volume
acts against the piston 84 and the spring 88, moving the piston 84 (also
to the right), and thereby, increasing the clutch volume.
As the piston 84 moves to the right, the clutch plates begin to compress.
At time t.sub.2, the piston is near its maximum position, the clutch
plates are nearly locked, the pressure within the clutch volume increases
sharply due to the increased resistance from the clutch plates and the
continued flow of hydraulic fluid from S. The increase in pressure exerts
force on the spool 82 via the feedback means 90. This pressure flux
creates a transient reverse pressure differential across the spool valve
80 which causes the spool 82 to move to an equilibrium position as shown
in FIG. 8B.
The movement of the spool 82 from the maximum position to the equilibrium
position is sensed by the transmission controller 74 which responsively
produces an end-of-fill signal that causes the solenoid driver circuit 12
to increase the coil current. As illustrated in FIGS. 8A and 8C, the
increase in coil current increases the magnitude of the magnetic force
acting on the armature which responsively increases the pressure of fluid
in the clutch 78 to engage the clutch plates.
For large clutches, a multistage design may be needed to gain the benefits
of higher fluid flow. With reference to FIG. 7B, a dual stage spool valve
design includes a first spool or pilot valve 94 and a second spool or
control valve 96. The solenoid 14 is connected to the first spool 98 of
the first spool valve 94. The first spool 98 is movable in response to
energization of the coil 16 and allows fluid to flow from S to the first
control volume, C.sub.1. The first spool valve 94 controls the flow of
fluid to a second control volume, C.sub.2 (the clutch volume). The control
valve 96 has a second spool 100. The second spool 100 allows fluid to flow
from the first control volume, C.sub.1 to the second control volume,
C.sub.2 through a conduit in the second spool 100. The second spool 100 is
spring biased to close the path between the source, S and the clutch
volume. The first spool valve 94 creates a pressure differential across
the second spool valve 96. When the pressure differential becomes large
enough to overcome the biasing force, the spool moves and fluid is allowed
to pass directly from S to the clutch through the second spool valve 96.
There are many variations of such multistage designs with parameters suited
to different applications. For example, different feedback schemes and
spool designs will give the system different operating characteristics.
Since the specific design of the valve means 76 is application specific
and has no bearing on the present invention, no further discussion is
given.
INDUSTRIAL APPLICABILITY
With reference to the drawings and in operation, the present invention is
adapted to indicate the position of an armature with respect to the coil
of an electromagnetic actuator and to signal a transmission controller 74
at the occurrence of an end of fill condition of a hydraulic clutch 78.
The following description is only for the purposes of illustration and is
not intended to limit the present invention as such. It will be
recognizable, by those skilled in the art, that the present invention is
suitable for a plurality of other applications.
The actuator control system 10 determines the magnitude and the rate of
change of current flowing in the coil 16 of a solenoid 14 and compares
this data to empirically determined data relating magnitude and rate of
change of coil current to the position of the armature 18 with respect to
the coil 16. This comparison is preferably performed by a simple
two-dimensional look-up scheme of a type well known in the art and
includes the ability to interpolate between the discrete values that are
stored in memory.
In one embodiment, the stored data directly relates the magnitude and rate
of change of coil current to the position of the armature 18. In an
alternative embodiment, the derivative of the flux linkage with respect to
the current in the coil 16 is determined from the rate of change of coil
current and the magnitude of the current and voltage in the coil 16. In
this embodiment, the stored data relates the derivative of flux linkage,
the magnitude of coil current, and armature position.
The position of the armature that is determined by the controller 52 is
then usable in connection with a number of control and diagnostic systems.
For example, the position information can be used to provide a closed-loop
control system for a solenoid by providing the controller with an actual
position that can be compared with a desired position in order to
responsively change the magnitude of current in the coil accordingly.
Alternatively, the position information can be used in a diagnostic system
to determine whether the armature or the device being actuated by the
armature is operating properly in response to the desired function being
indicated by the control system.
In particular, the position information can be used in connection with a
transmission controller 74 which controls the shifting of a transmission
on a vehicle (not shown) between a plurality of gear ratios. For example,
the transmission may include three forward and three reverse gear ratios.
The transmission controller 74 operates a plurality of electrical
solenoids. The solenoids are adapted to engage/disengage the
transmission's hydraulic clutches, such that the transmission is shifted
to the desired gear ratio.
The transmission controller 74 receives information related to the desired
operation of the vehicle and to the vehicle's operating environment and
energizes/deenergizes the solenoids. For example, the controller 74 may
receive information related to a desired or maximum gear ratio, the
position of the accelerator pedal (not shown), and/or the actual speed of
the vehicle.
Based on the received information, the transmission controller 74, operates
the hydraulic clutches through actuation of the solenoids in accordance
with a set of programmed shift rules. For example, in response to the
received information, the transmission controller 74 requires an upshift
to the third forward gear ratio. To implement this requirement, one or
more clutches need to be disengaged and one or more additional clutches
engaged. The exact clutch(es) to be engaged/disengaged are dependent upon
the structure of the transmission.
The transmission controller 74, begins to fill the required clutches 78 as
discussed above. When a clutch 78 reaches the end of fill condition, the
resulting movement of the spool 82 is sensed by the transmission
controller 74 which responsively produces an end-of-fill signal to cause
the solenoid driver circuit 12 to modulate the coil current to engage the
clutch 78.
Other aspects, objects, and advantages of this invention can be obtained
from a study of the drawings, the disclosure, and the appended claims.
* * * * *
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