U.S. patent application number 13/766829 was filed with the patent office on 2014-08-14 for transmission gear shift control.
This patent application is currently assigned to FORD GLOBAL TECHNOLOGY OPERATIONS, LLC. The applicant listed for this patent is FORD GLOBAL TECHNOLOGY OPERATIONS, LLC. Invention is credited to Anuradha Annaswamy, James William Loch McCallum, Gregory Michael Pietron, Sarah M. Thornton, Diana Yanakiev.
Application Number | 20140229080 13/766829 |
Document ID | / |
Family ID | 51177974 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140229080 |
Kind Code |
A1 |
Pietron; Gregory Michael ;
et al. |
August 14, 2014 |
TRANSMISSION GEAR SHIFT CONTROL
Abstract
A method for controlling pressure applied to a displaceable
piston in a cylinder, piston displacement actuating a control
element of an automatic transmission during a gearshift, includes
determining whether piston displacement exceeds a free length of an
isolation spring located between the piston and a friction plate of
the control element; calculating the pressure using A the
cross-sectional area of the piston; K a coefficient of a return
spring extending between the piston and a reference position in the
cylinder; x the piston displacement; F.sub.0 a pre-load of the
return spring; x.sub.free the free length of the isolation spring;
and K.sub.is a coefficient of the isolation spring; and applying
the calculated pressure to the piston.
Inventors: |
Pietron; Gregory Michael;
(Canton, MI) ; Thornton; Sarah M.; (Sacramento,
CA) ; Yanakiev; Diana; (Birmingham, MI) ;
McCallum; James William Loch; (Ann Arbor, MI) ;
Annaswamy; Anuradha; (W. Newton, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FORD GLOBAL TECHNOLOGY OPERATIONS, LLC |
Dearborn |
MI |
US |
|
|
Assignee: |
FORD GLOBAL TECHNOLOGY OPERATIONS,
LLC
DEARBORN
MI
|
Family ID: |
51177974 |
Appl. No.: |
13/766829 |
Filed: |
February 14, 2013 |
Current U.S.
Class: |
701/51 |
Current CPC
Class: |
F16D 2500/30822
20130101; F16D 2500/30814 20130101; F16D 2500/5012 20130101; F16D
2500/50236 20130101; F16D 48/06 20130101; F16H 61/061 20130101;
F16D 2500/70605 20130101; Y10T 477/69383 20150115; F16D 2500/7061
20130101; F16D 2500/70406 20130101; F16D 2500/7044 20130101; Y10T
477/6939 20150115; F16D 2500/3026 20130101; F16H 63/3026 20130101;
F16D 2500/50653 20130101; F16H 2061/064 20130101 |
Class at
Publication: |
701/51 |
International
Class: |
F16H 61/00 20060101
F16H061/00 |
Claims
1. A method for controlling pressure applied to a displaceable
piston in a cylinder, piston displacement actuating a control
element of an automatic transmission during a gearshift, comprising
the steps of: (a) determining whether piston displacement exceeds a
free length of an isolation spring located between the piston and a
friction plate of the control element; (b) calculating said
pressure using A, a cross-sectional area of the piston; K, a
coefficient of a return spring extending between the piston and a
reference position in the cylinder; x, the piston displacement;
F.sub.0 a pre-load of the return spring; x.sub.free the free length
of the isolation spring; and K.sub.is a coefficient of the
isolation spring; (c) applying said calculated pressure to the
piston.
2. The method of claim 1, wherein step (a) further comprises:
comparing the piston displacement to the free length of the
isolation spring.
3. The method of claim 1, wherein step (b) further comprises:
setting x.sub.contact equal to 0 provided that the free length of
the isolation spring is equal to or greater than the piston
displacement; setting x.sub.contact equal to 1 provided that that
the free length of the isolation spring is not equal to or greater
than the piston displacement; and calculating said pressure from
the following equation P=1/A(F.sub.0-K
x+x.sub.contact(x.sub.free-x)K.sub.is).
4. The method of claim 1, further comprising: (d) determining a
difference between said calculated pressure and a commanded
pressure; (e) calculating Q a flow rate of fluid in the cylinder
using K.sub.1 a laminar flow coefficient; K.sub.2 a turbulent flow
coefficient; and said difference; (f) updating displacement of the
piston using the flow rate of fluid in the cylinder, a cross
sectional area of the piston, and the length of a period between
executing steps (a) and (f).
5. The method of claim 4, wherein step (d) further comprises
determining the commanded pressure to be applied to the piston.
6. The method of claim 4, wherein step (e) further comprises
calculating Q the flow rate of fluid in the cylinder using the
following equation: Q=K.sub.1.DELTA.P+K.sub.2(.DELTA.P).sup.1/2
wherein .DELTA.P is the a difference between said calculated
pressure and the commanded pressure.
7. The method of claim 4, wherein step (f) further comprises
updating displacement of the piston using the following equation:
x(t+1)=x(t)+1/A*Q*.DELTA.t wherein x (t+1) is the updated
displacement of the piston, x(t) is an immediately previous
displacement of the piston, A is the cross-sectional area of the
piston, Q is the flow rate of fluid in the cylinder, and .DELTA.t
is the length of said period.
8. The method of claim 1, wherein step (b) further comprises
calculating said pressure from the following equation provided that
piston displacement is greater than x.sub.free: P=1/A (F.sub.0-K
x).
9. The method of claim 1, wherein step (b) further comprises
calculating said pressure from the following equation provided that
piston displacement is between x.sub.free and zero: P=1/A(F.sub.0-K
x+(x.sub.free-x)K.sub.is)
10. A method for controlling pressure applied to a displaceable
piston in a cylinder, piston displacement actuating a control
element of an automatic transmission during a gearshift, comprising
the steps of: (a) determining the displacement of the piston, and
controlling the pressure based at least in part on a calculated
piston displacement; (b) determining whether piston displacement
exceeds at least one of: a free length of an isolation spring
located between the piston and a friction plate of the control
element, and a free length of a return spring located between the
piston and a non-axial moving member; (c) calculating estimated
pressure using A, a cross-sectional area of the piston; K, a
coefficient of a return spring extending between the piston and a
reference position in the cylinder; x, the piston displacement;
F.sub.0 a pre-load of the return spring; x.sub.free the length of
the isolation spring; xmax, this maximum displacement of the
piston, and K.sub.is a coefficient of the isolation spring; (d)
applying the estimated pressure to the piston.
11. The method of claim 10, wherein step (a) further comprises:
comparing the piston displacement to the free length of the
isolation spring.
12. The method of claim 10, wherein step (b) further comprises:
setting x.sub.contact equal to 0 provided that the free length of
the isolation spring is equal to or greater than the piston
displacement; setting x.sub.contact equal to 1 provided that that
the free length of the isolation spring is not equal to or greater
than the piston displacement; and calculating said pressure from
the following equation P=1/A(F.sub.0-K
x+x.sub.contact(x.sub.free--x)K.sub.is).
13. The method of claim 10, further comprising: (d) determining a
difference between said calculated pressure and a commanded
pressure; (e) calculating Q a flow rate of fluid in the cylinder
using K.sub.1 a laminar flow coefficient; K.sub.2 a turbulent flow
coefficient; and said difference; (f) updating displacement of the
piston using the flow rate of fluid in the cylinder, a cross
sectional area of the piston, and the length of a period between
executing steps (a) and (f).
14. The method of claim 13, wherein step (e) further comprises
calculating Q the flow rate of fluid in the cylinder using the
following equation: Q=K.sub.1.DELTA.P+K.sub.2(.DELTA.P).sup.1/2
wherein .DELTA.P is the a difference between said calculated
pressure and the commanded pressure.
15. The method of claim 13, wherein step (f) further comprises
updating displacement of the piston using the following equation:
x(t+1)=x(t)+1/A*Q*.DELTA.t wherein x (t+1) is the updated
displacement of the piston, x(t) is an immediately previous
displacement of the piston, A is the cross-sectional area of the
piston, Q is the flow rate of fluid in the cylinder, and .DELTA.t
is the length of said period.
16. The method of claim 10, wherein step (b) further comprises
calculating said pressure from the following equation provided that
piston displacement is greater than x.sub.free: P=1/A (F.sub.0-K
x).
17. The method of claim 10, wherein step (b) further comprises
calculating said pressure from the following equation provided that
piston displacement between x.sub.free and zero: P=1/A(F.sub.0-K
x+(x.sub.free-x)K.sub.is).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to controlling the
actuation of a transmission control element actuated by the piston
of a hydraulic servo on the basis of the piston's position during a
gear shift.
[0003] 2. Description of the Prior Art
[0004] Knowing input shaft torque or output shaft torque is
considered beneficial for improving the quality of gear shift
control of an automatic transmission for a vehicle. Measurement of
input shaft torque or output shaft torque allows feedback control
that is more robust to unknown disturbances to be utilized.
However, the conventional approach of error-based closed-loop (CL)
control has limited authority during fast transients in the
torque-transfer phase of a gearshift due to the clutch actuators'
considerable nonlinearity, delay and lag.
[0005] A method for determining clutch torques during a gearshift
using references to input and output shaft torque measurements or
estimates , providing multiple opportunities for improving shift
control exist. While the off-going clutch torque signal and
on-coming clutch torque signal provide valuable feedback, essential
for changing the whole paradigm of synchronous torque transfer
control, that feedback is still not available during the initial
phases of clutch actuation.
[0006] The clutch has torque carrying capacity only after certain
nonlinear dynamic transients in the clutch actuator take place and,
unfortunately, there is no feedback information during that
transient response. To be able to command the clutch actuator
during those initial phases in a robust fashion, knowledge of the
internal state of the actuator would be essential.
SUMMARY OF THE INVENTION
[0007] A method for controlling pressure applied to a displaceable
piston in a cylinder, piston displacement actuating a control
element of an automatic transmission during a gearshift, includes
determining whether piston displacement exceeds a free length of an
isolation spring located between the piston and a friction plate of
the control element; calculating the pressure using A the
cross-sectional area of the piston; K a coefficient of a return
spring extending between the piston and a reference position in the
cylinder; x the piston displacement; F.sub.0 a pre-load of the
return spring; x.sub.free the free length of the isolation spring;
and K.sub.is a coefficient of the isolation spring; and applying
the calculated pressure to the piston.
[0008] The method provides internal estimates of the clutch state
based on the existing command and feedback signals including clutch
torque estimate. Executing the method on-board in real time is
simple, unlike existing high-fidelity simulation models. In order
to predict adequately the transients in the clutch body in
non-nominal conditions, the method captures the dominant physical
phenomena governing the movement of the clutch piston.
[0009] The availability of the clutch torque signal in region 3,
allows online adaptation of the clutch model parameters, to ensure
better representation of region 1 and 2 transients in subsequent
shifts. However, the need to use and adapt "boost duration" is
eliminated and the adaptation of "stroke pressure" can occur during
the gearshift, rather than after the gearshift.
[0010] The scope of applicability of the preferred embodiment will
become apparent from the following detailed description, claims and
drawings. It should be understood, that the description and
specific examples, although indicating preferred embodiments of the
invention, are given by way of illustration only. Various changes
and modifications to the described embodiments and examples will
become apparent to those skilled in the art.
DESCRIPTION OF THE DRAWINGS
[0011] The invention will be more readily understood by reference
to the following description, taken with the accompanying drawings,
in which:
[0012] FIGS. 1-4 are schematic diagrams showing clutch displacement
in various regions.
[0013] FIG. 5 is a logic diagram of an algorithm applicable to
region 2 and 3; and
[0014] FIG. 6 is a logic diagram of an algorithm applicable to
regions 1-4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] FIG. 1 provides insight about a conventional
hydraulically-actuated clutch 20 used in an automatic transmission.
The clutch piston 12, located in a hydraulic cylinder 14, is being
pushed rightward by the hydraulic pressure supplied to the
cylinder. Piston 12 first compresses two springs 16, 18 as it moves
rightward to compress the friction plates of clutch 20. The outer
return spring 18 is preloaded and pushes the piston 12 away from
the plates of clutch 20 when the clutch is commanded open. The
inner, isolation or cushion spring 16 is optional and it provides
resistance to the piston 12 touching the plates in the initial
stage of that transient.
[0016] Actuation of piston 12 is divided into four regions
according to the position of the clutch piston position. In region
1 illustrated in FIG. 1, the clutch piston 12 is at its maximum
distance X.sub.max from the friction plates of clutch 20.
Transmission fluid pressurizes the lines and overcomes the pre-load
of return spring 18, while the isolation spring 16 is
uncompressed.
[0017] In region 2 illustrated in FIG. 2, transmission fluid fills
the clutch cylinder 14 and moves the clutch piston 12 rightward
while compressing the return spring 18.
[0018] In region 3 illustrated in FIG. 3, transmission fluid
continues to fill the clutch cylinder 14. The isolation spring 16
compresses against the friction plates of clutch 20 as the clutch
piston 12 continues moving rightward. The torque transfer phase of
the gearshift begins and the clutch gains some torque transmitting
capacity as the friction plates begin to engage mutually.
[0019] In region 4 illustrated in FIG. 4, the clutch piston 12
stops traveling and touches the leftmost friction plate of clutch
20 when the clutch plates are in mutual contact. Clutch torque
capacity increases as the friction plates continue engaging. The
clutch pressure and torque capacity can be related linearly here.
Within region 4, the torque transfer phase of the gearshift ceases
and the inertia transfer phase of the gearshift occurs.
[0020] Although reference is made to the transmission control
element being a clutch, the control element may be a brake. A
clutch alternately connects and disconnects rotating members of the
transmission, whereas a brake alternately connects and disconnects
a rotating member of the transmission to a non-rotating component
such as a transmission housing.
[0021] The off-going clutch control and on-coming clutch control
during synchronous gearshifts has no on-board sensing that provides
feedback about the response of those clutches before the gearbox
speed measurements start changing. For a synchronous power-on
upshift, for example, there is no feedback during the initial
actuation of the clutches and through the torque transfer phase of
the gearshift. Only after the speed ratio change commences at some
time during region 4, is the real-time controller able to issue its
commands based on feedback information.
[0022] With the introduction of torque measurement or estimation,
that problem is alleviated, since clutch torque feedback is
available as soon as the on-coming clutch starts gaining torque
capacity, i.e., at the beginning of region 3, as described above.
Even then, since shaft twist can be greatly affected by
powertrain-induced or external disturbances, the linear
relationship between clutch actuation and the torque signal may not
be consistent instantaneously.
[0023] Line pressurization and return spring compression during
regions 1 and remain without any feedback. It is evident from the
balance of forces that, if the hydraulic pressure applied to piston
12 is not sufficient to overcome the force of return spring 18, the
clutch 20 can remain in the first or second region indefinitely.
However, if too much pressure is applied, the piston 12 can
progress too rapidly to engage the clutch plates and significant
disturbance to the driveline can occur. Hence, knowing the pressure
that results in the beginning of region 3, commonly referred as
"stroke" pressure, is key. While stroke pressure would be constant
for the ideal case of no part-to-part or environmental variations,
in reality stroke pressure varies. Stroke pressure is one of the
important parameters that a transmission controller would try to
adapt. Unfortunately, speed (or even pressure, if that were
available) feedback signals do not provide opportunity to adjust
that in time to avoid a bad gearshift.
[0024] Another factor in the control strategy can be introduced
with the so-called "boost phase." Boost is commonly employed to
speed the response in the initial phases (regions 1 and 2), by
commanding a higher pressure at the solenoid actuator until the
clutch pressure gets close to "stroke" pressure. Since neither
stroke pressure nor measured actual pressure at the piston 12 are
known, the boost phase duration is a calibrated parameter that is
adapted from shift-to-shift. Again, the wrong boost duration can
cause a bad shift, without the opportunity to correct as it
happens.
[0025] A production-suitable magneto-elastic shaft torque sensor
has been developed and is described in U.S. Patent Application
Publication Number 2012/0297895, which is assigned to the assignee
of the present patent application, the entire disclosure of which
is incorporated herein by reference. That torque sensor's ability
to measure torque directly at the transmission input or output
shaft enables many features in vehicle control. Its dynamic
response is within a fraction of a millisecond and its accuracy is
far superior to any currently available on-board torque estimates.
The clutch torque calculation based on these torque measurements or
estimates is described in U.S. Patent Application Publication
Number 2010/0318269, the entire disclosure of which is incorporated
herein by reference. This clutch torque determination would provide
feedback signal about the clutch actuation as soon as the beginning
of region 3.
[0026] The clutch model determines the movement of piston 12 as a
result of the force balance between the pressure in cylinder 14,
and the forces of springs 16, 18. This transient spans regions 2
and 3 in FIG. 1. The initial pressurization in region 1 can be
successfully captured with a system identification model, as well
as the fast-dynamics in region 4, which has additional feedback
information.
[0027] The availability of the clutch torque signal in region 3,
allows online adaptation of the clutch model parameters, to ensure
better representation of region 1 and 2 transients during
subsequent shifts. However, the need to use and adapt "boost
duration" is eliminated and the adaptation of "stroke pressure" can
occur during the gearshift, rather than after the gearshift.
PHYSICAL MODEL DESCRIPTION
[0028] Regions 2 and 3 define the part of the clutch actuation
wherein the piston 12 moves between the bounds of x.sub.max and
x.sub.0. As FIG. 1 shows, the origin of piston displacement xo is
located at the right-hand side of cylinder 14 with each plate of
the control element 20 touching another plate of the control
element. The maximum piston displacement xmax is shown in FIG. 1.
Using Newtonian dynamics to model the clutch piston movement, we
have
if ( x .ltoreq. x free ) x contact = 1 else x contact = 0 end x = 1
m ( PA + K x - F 0 - x contact ( x free - x ) K is - c x . ) , ( 1
) ##EQU00001##
wherein x is the clutch piston acceleration, m is the mass of the
clutch piston 12, P is the pressure in cylinder 14, A is the
cross-sectional area of the clutch apply piston 12, K is the
coefficient of return spring 18, x is the clutch piston position,
F.sub.0 is the pre-load of return spring 18, x.sub.contact is 0 or
1 depending on whether the clutch piston 12 is in region 2 or
region 3, x.sub.free is the height or free length of the isolation
spring 16, K.sub.is the coefficient of isolation of spring 18, c is
the damping coefficient, and {dot over (x)} is the clutch piston
velocity. However, we assume the flow of the transmission fluid
through the clutch body is quasi-static. Thus, {umlaut over (x)}
and {dot over (x)} are small, and Eq. (1) becomes
P = 1 A ( F 0 - K x + x contact ( x free - x ) K is ) ( 2 )
##EQU00002##
Note that when x=x.sub.max,
P = 1 A ( F 0 - K x ) ( 3 ) ##EQU00003##
and when x=x.sub.0,
P = 1 A ( F 0 + x free K is ) ( 4 ) ##EQU00004##
[0029] Equations (3) and (4) become the lower bound and upper
bound, respectively, of the model output pressure for regions 2 and
3, which can be used to help tune the initial model parameters.
[0030] To relate the control input, u, to the model output
pressure, P, we choose the clutch piston position, x, as the state.
The clutch piston position is modeled using a flow equation of the
pressure drop between a regulator valve 22 and the clutch 20. The
regulator valve 22 is located on the hydraulic line 24 between a
variable force solenoid 26, which provides the commanded pressure,
and clutch 10. Assuming there is no saturation of the regulator
valve, we have
.DELTA. P = u - P ( 5 ) Q = K 1 .DELTA. P + K 2 .DELTA. P ( 6 ) x =
x max - 1 A .intg. Q t ( 7 ) ##EQU00005##
wherein .DELTA.P is the difference in commanded and output
pressure, Q is the flow rate, K.sub.1 is the laminar flow
coefficient, and K.sub.2 is the turbulent flow coefficient.
[0031] The flow coefficients are most suitable for tuning the
model, since the other model parameters are geometric. As K.sub.1
and K.sub.2 vary, the desired output response is tuned. For
example, in the case of mostly laminar flow, or low .DELTA.P, the
flow coefficients may be chosen to be relatively slow. Also, the
difference between K.sub.1 and K.sub.2 should be considered in
order to tune the duration the model is within region 2 or region
3.
EXAMPLE ALGORITHMS (MODEL) DESCRIPTION
[0032] Region 1. For the first region, if the clutch piston 12 were
held at its maximum position and pressure were allowed to build up
to a commanded step input, the output pressure would be a second
order response. However, the clutch piston moves once the hydraulic
pressure overcomes the pre-load of the return spring. As a result,
the second order response is interrupted and the actual response
for this region looks like an unstable first order response. Since
a dynamic model of the true region 1 response would be difficult to
tune and align for the initial condition of region 2, we assume the
region 1 model to be constant, and defined as
P .ident. constant = 1 A ( F 0 - K * x max ) ( 9 ) ##EQU00006##
[0033] The duration of region 1 was found to be dependent on the
temperature of the transmission fluid.
Region 2. Using the condition from Eq. (1), x.sub.contact=0, and
Eq. (2) becomes
P = 1 A ( F 0 - K x ) ( 10 ) ##EQU00007##
Region 3. Again, using the condition from Eq. (1), x.sub.contact=1,
and Eq. (2) becomes
P = 1 A ( F 0 + K is x free - ( K + K is ) x ) , ( 11 )
##EQU00008##
wherein x is defined by Eq. (7). Region 4. Once the clutch piston
no longer travels, the dynamics of the hydraulic actuation system
are no longer present. The pressure response to command is almost
instantaneous, and can be represented with a first order transfer
function featuring a time constant T.sub.p and a time delay
T.sub.d.
P u ( s ) = 1 1 + T p s exp - T d s ( 8 ) ##EQU00009##
wherein x is defined by Eq. (7).
[0034] The control algorithm 30 shown in FIG. 5 performs a test at
step 32 to determine whether the piston displacement x(t) during
the current execution of the algorithm x(t) is equal to or less
than xfree. During the first execution of the algorithm x(t) is
initialized to xmax.
[0035] If the result of test 32 is false, control advances to step
34 where xcontact is set equal to 0. Otherwise, at step 36 xcontact
is set equal to 1.
[0036] At step 38 the magnitude of pressure in cylinder 14 that
actuates piston 12 is calculated using equation (2).
[0037] At step 40 equation (5) is used to calculate .DELTA. P. P
com (t) is determined by a closed-loop controller on the basis of
x(t).
[0038] At step 42 the flow rate of hydraulic fluid into cylinder 14
is calculated using equation (6).
[0039] At step 44 piston displacement is incremented by adding a
magnitude of piston displacement calculated using equation (7) to
the current piston displacement.
[0040] At step the number of the algorithm execution is
incremented, and control returns to step 32.
[0041] The control algorithm 50 shown in FIG. 6 performs a test at
step 52 to determine whether (t) is less than the time required for
piston 12 to move into region 2 from region 1. A look-up table
indexed by hydraulic fluid (ATF) temperature indicates the
magnitude of t12
[0042] If the result of test 52 is true, at step 54 Pclutch (t) for
region 1 is calculated and piston displacement is confirmed to be
equal to xmax.
[0043] Then control advances to step 56 where t is incremented and
control returns to step 52.
[0044] If the result of test 52 is false, at step 58 a test is
performed to determine whether piston displacement x(t) is equal to
or less than xfree.
[0045] If the result of test 58 is false, at step 60 xcontact is
set equal to zero, and at step 62 Pclutch (t) for region 2 is
calculated using equation (2).
[0046] Then control advances to step 64 where equation (5) is used
to calculate .DELTA. P. P com (t) is determined closed-loop by a
closed-loop controller on the basis of x(t).
[0047] At step 66 the flow rate of hydraulic fluid into cylinder 14
is calculated using equation (6).
[0048] At step 68 piston displacement x(t) is incremented by adding
a magnitude of piston displacement calculated using equation (7) to
the current piston displacement.
[0049] Then control advances to step 56 where t is incremented and
control returns to step 52.
[0050] If the result of test 52 is false and the result of test
step 58 is true, at step 70 xcontact is set equal to 1.
[0051] At step 72 a test is performed to determine whether x(t) is
equal to xfree. If the result of test 72 is true, at step 74 an
estimate of the time when piston 12 moved from region 2 into region
3 is recorded and stored in electronic memory.
[0052] At step 76 a test is performed to determine whether x(t) is
greater than zero.
[0053] If the result of test 76 is true, at step 78 Pclutch is
calculated and control returns to step 64 where equation (5) is
used to calculate .DELTA. P. P com (t) is determined closed-loop by
a PID controller on the basis of x(t).
[0054] At step 66 the flow rate of hydraulic fluid into cylinder 14
is calculated using equation (6).
[0055] At step 68 piston displacement x(t) is incremented by adding
a magnitude of piston displacement calculated using equation (7) to
the current piston displacement.
[0056] Then control advances to step 56 where t is incremented
again and control returns to step 52.
[0057] If the result of test 52 is false, the result of test step
58 is true, and the result of step 76 is false, at step 80 a test
is performed to determine whether x(t) is equal to zero.
[0058] If the result of test 80 is true, at step 82 an estimate of
the time when piston 12 first moved from region 3 into region 4 is
recorded and stored in electronic memory.
[0059] At step 84, Pclutch (t) is calculated for region 4 using the
equation of step 84, which is the discretized time domain version
of equation (8), wherein t.sub.delay is the period length that
passes between the controller issuing Pcom and completing the
calculation of Pclutch (t) at step 84 in response to Pcom.
[0060] Then control advances to step 56 where t is incremented
again and control returns to step 52.
[0061] In summary, the pressure output model consists of one state:
the clutch piston position, x. The model also has two main tuning
parameters, K.sub.1 and K.sub.2, for the hydraulic actuation. There
is also a time delay in the system modeled in Region 4.
[0062] In accordance with the provisions of the patent statutes,
the preferred embodiment has been described. However, it should be
noted that the alternate embodiments can be practiced otherwise
than as specifically illustrated and described.
* * * * *