U.S. patent application number 09/870309 was filed with the patent office on 2002-12-05 for clutch calibration and control.
This patent application is currently assigned to Eaton Corporation. Invention is credited to Chan, Kwok Wah, Hawarden, Jeffrey Philip, Kelly, Timothy Peter, Mack, William Joseph, Speranza, Donald, Stasik, Anthony, Wheeler, Robert Stanley.
Application Number | 20020183165 09/870309 |
Document ID | / |
Family ID | 25355112 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020183165 |
Kind Code |
A1 |
Mack, William Joseph ; et
al. |
December 5, 2002 |
CLUTCH CALIBRATION AND CONTROL
Abstract
A control system and calibration method are provided for a
vehicle drive line having an automated master friction clutch. The
control system utilizes engine torque data supplied by a serial
communication data link to identify a clutch control parameter
value corresponding to an urge-to-move position of the clutch. The
clutch control parameter value identified by the calibration method
is stored and utilized by the control system to control the
engagement position of the automated clutch in an "urge to move"
mode of operation. The inventive calibration method can be utilized
across multiple vehicle platforms having different engine, clutch
and transmission system components.
Inventors: |
Mack, William Joseph;
(Kalamazoo, MI) ; Speranza, Donald; (Kalamazoo,
MI) ; Stasik, Anthony; (Coppull, GB) ; Chan,
Kwok Wah; (Middleton, GB) ; Hawarden, Jeffrey
Philip; (Helmshore, GB) ; Wheeler, Robert
Stanley; (Preston, GB) ; Kelly, Timothy Peter;
(Lymm, GB) |
Correspondence
Address: |
RADER, FISHMAN & GRAUER PLLC
Suite 140
39533 Woodward Avenue
Bloomfield Hills
MI
48304
US
|
Assignee: |
Eaton Corporation
|
Family ID: |
25355112 |
Appl. No.: |
09/870309 |
Filed: |
May 30, 2001 |
Current U.S.
Class: |
477/174 |
Current CPC
Class: |
F16D 48/06 20130101;
B60W 10/02 20130101; B60W 30/18027 20130101; B60W 30/18 20130101;
B60W 2510/0275 20130101; B60W 30/1819 20130101; B60W 2710/022
20130101; F16D 2500/1026 20130101; F16D 2500/3026 20130101; B60W
30/18063 20130101; F16D 2500/50281 20130101; B60W 2510/0657
20130101; B60W 10/04 20130101; F16D 2500/7109 20130101; F16D
2500/30814 20130101; F16D 2500/50254 20130101; F16D 2500/30412
20130101; F16D 2500/3065 20130101; F16D 2500/10412 20130101; F16D
2500/30421 20130101; B60W 2050/0045 20130101; B60W 10/06 20130101;
Y10S 477/902 20130101 |
Class at
Publication: |
477/174 |
International
Class: |
B60K 041/02 |
Claims
What is claimed is:
1. A method for determining the value of a clutch control parameter
signal corresponding to an urge-to-move position of a vehicular
master friction clutch drivingly interposed between an engine
having a rated engine reference torque and a multi-speed
transmission having an input shaft, the method comprising the steps
of: (a)(i) determining an unloaded engine torque, (ii) preventing
rotation of the input shaft, (iii) applying the clutch until a
loaded engine torque minus the unloaded engine torque exceeds an
urge-to-move reference torque, (iv) sensing a first control
parameter signal when the loaded engine torque minus the unloaded
engine torque exceeds the urge-to-move reference torque, and (v)
releasing the clutch; (b)(i) preventing rotation of the input
shaft, (ii) applying the clutch in at least one pulse until the
loaded engine torque minus the unloaded engine torque is greater
than or substantially equal to the urge-to-move reference torque
and less than or substantially equal to two times the urge-to-move
reference torque, and (iii) sensing a second clutch control
parameter signal when the loaded engine torque minus the unloaded
engine torque is greater than or substantially equal to the
urge-to-move reference torque and less than or substantially equal
to two times the urge-to-move reference torque; (c) offsetting the
second clutch control parameter signal a predetermined amount to
determine a clutch control parameter signal corresponding to an
urge-to-move position of the master friction clutch.
2. The method of claim 1, wherein the urge-to-move reference torque
is a percentage of the rated engine reference torque required to
transfer a predetermined amount of torque from the engine to the
transmission.
3. The method of claim 1, wherein the predetermined amount of
torque transferred from the engine to the transmission is in the
range of 20-60 lb-ft.
4. The method of claim 1, wherein the predetermined amount of
torque transferred from the engine to the transmission is
approximately 35 lb-ft.
5. The method of claim 1, wherein the pulse comprises applying the
clutch to a position corresponding to a clutch control parameter
signal, pausing a predetermined amount of time to allow the engine
and clutch to stabilize, and then releasing the clutch.
6. The method of claim 1, wherein a first pulse corresponds to the
first control parameter signal minus a predetermined offset.
7. The method of claim 6, wherein a subsequent pulse corresponds to
a control parameter signal used in the preceding pulse plus a
predetermined amount if the loaded engine torque minus the unloaded
engine torque is less than the urge-to-move reference torque.
8. The method of claim 6, wherein a subsequent pulse corresponds to
a control parameter signal used in the preceding pulse minus a
predetermined amount if the loaded engine torque minus the unloaded
engine torque is greater than two times the urge-to-move reference
torque but less than three times the urge-to-move reference
torque.
9. The method of claim 8, wherein the method is restarted when the
loaded engine torque minus the unloaded engine torque is greater
than three times the urge-to-move reference torque.
10. The method of claim 1, wherein the clutch includes a
solenoid-controlled valve and a source of pulse width-modulated
electric power applied to the solenoid of the valve, the first and
second clutch control parameter signals comprising the pulse width
modulation of the electric power.
11. The method of claim 1, further including the step of verifying
that the second clutch control parameter signal is accurate.
12. The method of claim 11, wherein the verification step comprises
engaging the clutch to a position corresponding to the second
clutch control parameter signal and determining if the loaded
engine torque minus the unloaded engine torque is greater than or
substantially equal to the urge-to-move reference torque and less
than or substantially equal to two (2) times the urge-to-move
reference torque.
13. The method of claim 11, wherein the verification step is
repeated a predetermined number of times.
14. In a combination including a source of motive power having an
unloaded idle torque at a predetermined idle speed and a friction
clutch for controllably transferring torque from the source of
motive power to an input shaft of a multi-speed transmission, a
calibration method for determining a clutch control parameter
signal corresponding to the clutch urge-to-move position comprising
the steps of: determining if conditions exist to begin calibration;
operating the source of motive power at the idle speed; applying a
predetermined brake torque to the transmission input shaft;
determining an urge-to-move reference torque that is greater than
the unloaded idle torque; applying the friction clutch in a ramping
rate of application; sensing a first clutch control parameter
signal when the measured engine torque minus the unloaded idle
torque exceeds the urge-to-move reference torque; releasing the
clutch and re-applying the clutch according to at least one pulse;
sensing a second clutch control parameter signal when the measured
engine torque minus the unloaded idle torque at least attains the
urge-to-move reference torque; and offsetting the second clutch
control parameter signal a predetermined amount to determine a
clutch control parameter signal corresponding to the urge-to-move
position of the master friction clutch.
15. A control system for determining a clutch control parameter
signal corresponding to an urge-to-move position of a vehicular
master friction clutch drivingly interposed between an engine
having a rated engine reference torque and a multi-speed
transmission having an input shaft, the control system comprising:
an electronic control unit in communication with the engine for
receiving and processing engine torque data according to control
logic, the electronic control unit including an engine torque and
calibration processor for comparing the engine torque data with an
urge-to-move reference torque; and a clutch controller in
communication with the electronic control unit for controlling
engagement of the clutch, the clutch controller configured to
receive instructions from the electronic control unit corresponding
to a commanded clutch position.
16. The system of claim 15, wherein the electronic control unit
includes an output for selectively transmitting a command output
signal, the clutch controller having an input that selectively
receives the command output signal, the clutch controller
configured to produce a pulse width modulated control signal that
corresponds to the command output signal.
17. The system of claim 16, wherein the pulse width modulated
control signal is ramped at a predetermined rate to selectively
control the engagement of the clutch to determine a value of a
clutch control parameter signal that transfers a predetermined
amount of torque between the engine and the transmission.
18. The system of claim 17, wherein the pulse width modulated
control signal is ramped at a rate of approximately 4 mA per 350
ms.
19. The system of claim 17, wherein the clutch controller includes
a solenoid-actuated hydraulic system and a source of pulse width
modulated electric power in communication with the solenoid of the
hydraulic system, the clutch control parameter signal comprising
the pulse width modulation of the electric power.
20. The system of claim 15, wherein the control logic includes
rules for: (a)(i) determining an unloaded engine torque, (ii)
preventing rotation of the input shaft, (iii) applying the clutch
until a loaded engine torque minus the unloaded engine torque
exceeds an urge-to-move reference torque, (iv) sensing a first
control parameter signal when the loaded engine torque minus the
unloaded engine torque exceeds the urge-to-move reference torque,
and (v) releasing the clutch; (b)(i) preventing rotation of the
input shaft, (ii) applying the clutch in at least one pulse until
the loaded engine torque minus the unloaded engine torque is
greater than or substantially equal to the urge-to-move reference
torque and less than or substantially equal to two times the
urge-to-move reference torque, and (iii) sensing a second clutch
control parameter signal when the loaded engine torque minus the
unloaded engine torque is greater than or substantially equal to
the urge-to-move reference torque and less than or substantially
equal to two times the urge-to-move reference torque; (c)
offsetting the second clutch control parameter signal a
predetermined amount to determine a clutch control parameter signal
corresponding to an urge-to-move position of the master friction
clutch.
21. The system of claim 20, wherein the control logic further
includes a rule for verifying that the second clutch control
parameter signal is accurate.
22. The system of claim 21, wherein the verification step comprises
engaging the clutch to a position corresponding to the second
clutch control parameter signal and determining if the loaded
engine torque minus the unloaded engine torque is greater than or
substantially equal to the urge-to-move reference torque and less
than or substantially equal to two times the urge-to-move reference
torque.
23. The system of claim 20, wherein the urge-to-move reference
torque is a percentage of the rated engine reference torque
required to transfer a predetermined amount of torque from the
engine to the transmission.
24. The system of claim 20, wherein the pulse comprises applying
the clutch to a position corresponding to a clutch control
parameter signal, pausing a predetermined amount of time to allow
the engine and clutch to stabilize, and then releasing the
clutch.
25. The system of claim 20, wherein a first pulse corresponds to
the first control parameter signal minus a predetermined
offset.
26. The system of claim 25, wherein a subsequent pulse corresponds
to a control parameter signal used in the preceding pulse plus a
predetermined amount if the loaded engine torque minus the unloaded
engine torque is less than the urge-to-move reference torque.
27. The system of claim 25, wherein a subsequent pulse corresponds
to a control parameter signal used in the preceding pulse minus a
predetermined amount if the loaded engine torque minus the unloaded
engine torque is greater than two times the urge-to-move reference
torque but less than three times the urge-to-move reference torque.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to controls for vehicular
master clutches, preferably wet friction clutches, utilized in
partially or fully automated mechanical transmission systems. In
particular, the present invention relates to an urge-to-move point
calibration method/system utilizing an electronic data link.
BACKGROUND OF THE INVENTION
[0002] Partially and fully automated vehicular mechanical
transmission systems utilizing automated friction master clutches
are known in the art. These systems are typically employed in a
vehicle that includes an engine, a multi-speed transmission having
an input shaft brake and at least one traction wheel connected to
an output of the transmission. At engine idle speeds with the
transmission engaged in a low ratio, such as first gear, it is
desirable that the engine generate at the flywheel a small amount
of torque sufficient to cause slow or creeping movement of the
vehicle if the vehicle brakes are not applied. This mode of
operation is analogous to conditions experienced by drivers of
passenger automobiles equipped with torque converter-type
transmissions. The advantages of this "urge-to-move" feature in an
automatic friction master clutch control is that the vehicle will
feel and act like a familiar passenger car equipped with an
automatic transmission, the vehicle may be maneuvered at slow
speeds using the brake pedal only, and vehicle launches will be
quicker with less lurch. The amount of flywheel or output torque
generated by an engine at idle speed, and transferable by a clutch
in the "urge-to-move" engagement condition, should be sufficient to
allow creeping if the brakes are not applied but small enough to
allow the clutch to dissipate the heat energy developed when the
clutch is slipped due to application of the vehicle brakes.
[0003] A key feature of known automated friction clutch controls is
their ability to sense and control engine flywheel torque utilizing
an electronically controlled engine connected to a serial
communication data link, such as a data link conforming to SAE
J1939, and to control the engaged position of a master friction
clutch. To improve the controllability and response of prior art
master clutch control systems, it is known to determine a clutch
control parameter, such as a pulse width modulation (PWM) signal,
which corresponds to a clutch touch point position, i.e. the point
of initial clutch engagement. However, conventional friction clutch
control systems are not necessarily configured to determine a
clutch control parameter corresponding to the urge-to-move position
of the clutch. Moreover, conventional friction clutch control
systems for determining the touch point position are typically
designed for a specific vehicle platform rendering the control
system inflexible and uneconomical for inclusion in other vehicle
platforms having different engine, clutch and transmission system
components.
SUMMARY OF THE INVENTION
[0004] The present invention provides an innovative calibration
system/method for an automated master friction clutch, such as a
wet friction clutch, which utilizes information available on serial
communication data links, such as data links conforming to the SAE
J1939, to determine the value of a clutch control parameter
corresponding to the urge-to-move position of the master friction
clutch.
[0005] The inventive control system includes an electronic control
unit (ECU) that receives torque information from an engine via a
serial communication data link and processes the same according to
control logic. The ECU communicates with a clutch controller, which
is configured to control the engagement of the clutch.
[0006] The clutch operating parameter value corresponding to the
clutch urge-to-move position is determined by a calibration routine
that is executed according to a pre-determined schedule. Upon
determination that the vehicle conditions are safe to begin
calibration, the control system determines an approximation of the
clutch control parameter value by engaging the clutch until a
maximum loaded engine torque sensed during the engagement of the
clutch minus an unloaded engine torque exceeds an urge-to-move
reference torque. Due to the limited system response, the initial
engagement of the clutch will likely yield an approximation of the
clutch control parameter value higher than the actual control
parameter value (clutch over-engaged). The clutch is then returned
to the fully disengaged position and a more detailed search is
commenced. The detailed search is characterized by re-applying the
clutch in at least one pulse, where the pulse comprises applying
the clutch to a position corresponding to a clutch control
parameter value, pausing a predetermined time to allow the engine
and clutch to stabilize, and then releasing the clutch. The cycle
of applying and releasing the clutch is continued until a more
accurate control parameter value is determined. The control system
then verifies the accuracy of the control parameter value and
stores this value in computer memory.
[0007] In order to account for inaccuracies in engine torque
reporting, the control system subtracts a predetermined offset
constant from the verified control parameter value to arrive at a
control parameter value that corresponds to the urge-to-move
position of the clutch actuator. In most cases the urge-to-move
control parameter value is already established from previous
operation of the vehicle and stored in computer memory. Due to
factors such as clutch wear and temperature changes, the
urge-to-move control parameter value can change, and therefore is
updated each calibration. The new urge-to-move control parameter
value may be used as the updated urge-to-move control parameter
value, or a blend of the stored and the new values may be used to
determine the updated urge-to-move control parameter value.
[0008] The calibration system/method advantageously compensates for
variations in system components across multiple vehicle platforms
to determine a clutch control parameter value corresponding to the
urge-to-move position of the clutch. Various additional aspects and
advantages of this invention will become apparent to those skilled
in the art from the following detailed description of the preferred
embodiment, when read in light of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The features and inventive aspects of the present invention
will become more apparent upon reading the following detailed
description, claims, and drawings, of which the following is a
brief description:
[0010] FIG. 1 is a schematic illustration of a vehicular automated
mechanical transmission system advantageously utilizing the control
method/system of the present invention.
[0011] FIG. 2 is a schematic illustration of a pressurized
fluid-actuated control mechanism for controlling the engaged
condition of a vehicular master clutch.
[0012] FIG. 3 is a partial sectional view of a vehicular wet master
friction clutch of the type utilized in the system of FIG. 1.
[0013] FIG. 4 is a schematic illustration of the inventive control
system.
[0014] FIGS. 5A, 5B and 5C are flow charts illustrating the
inventive control logic.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] A typical vehicular automated mechanical transmission system
10 advantageously utilizing the master clutch control of the
present invention is schematically illustrated in FIG. 1. System 10
includes a fuel-controlled engine 12, a wet master friction clutch
14 and a multiple-speed mechanical transmission 16. Engine 12 is
typically a diesel or gasoline engine and has an output member or
crank shaft 18 that drives friction discs 14A of clutch 14, which
are interdigitated with friction discs 14B that are rotationally
fixed to input shaft 20 of transmission 16. Transmission 16 may be
of the simple or compound type, having an output shaft 22, which
drives a drive shaft 24 connected to the input 26 of a vehicle
drive axle mechanism 27.
[0016] An engine controller 28, which is preferably electronically
and microprocessor-controlled, is provided for controlling fuel
delivery to the engine and for providing output information to an
electronic data link DL, preferably conforming to the industry
standard SAE J1939 or a comparable protocol. A data link,
conforming to the SAE J1939 protocol or a comparable protocol,
transmits information by which engine output torque (also called
"flywheel torque") may be read or determined. By utilizing this
information and engine control capability, the master clutch 14 may
be controlled to provide enhanced system performance. A sensor 33
is preferably provided for sensing throttle 33A position and
providing a signal THL to engine controller 28 indicative thereof.
However, it is recognized that throttle position information also
may be obtained from the data link.
[0017] A microprocessor-based electronic control unit 34 (ECU) is
provided for receiving input signals 36 and processing the same
according to control logic to generate command output signals 38.
The ECU 34 may be separate or integral with the engine controller
28. Although not shown in FIG. 1, ECU 34 may be of general
construction having a central processing unit (CPU), various
co-processors, a read only memory (ROM), a random access memory
(RAM), an input for selectively receiving engine torque data via a
data link, an output for selectively transmitting command output
signals 38, and a bi-directional bus interconnecting the
components.
[0018] Clutch 14 is defined as a "wet clutch," as the friction
members thereof, 14A and 14B, are exposed to liquid, such as
Dextron III, for heat transfer and/or lubrication purposes. In the
illustrated embodiment, the clutch pack 14C is contained within a
housing 14D, which is connected to source conduit 14E and an
exhaust conduit 14F. While a forced coolant system is illustrated,
the present invention also is applicable to wet clutches wherein
the friction members are in a relatively static sump or the like.
While the illustrated preferred embodiment utilizes a multi-disc
wet clutch 14, the present invention also is applicable to
single-disc wet clutches and/or dry clutches.
[0019] A fluid pressure-operated clutch actuator assembly 30 is
schematically illustrated in FIG. 2. A clutch operator piston 42 is
received in a cylinder 44 and is biased in the disengaging
direction by springs 46. Pressurized fluid, such as a hydraulic
fluid or pressurized air, introduced into chamber 48 will act on
piston face 50 to move the piston 42 in the engaged direction
against the bias of the springs. A two-position, three-way,
solenoid-controlled valve 52 is provided to selectively pressurize
and exhaust chamber 48. A pressure controller 54, having an input
for selectively receiving command signals from ECU 34, controls the
energizing of the solenoid 52A of valve 52, preferably by pulse
width modulation (PWM). Although a pressurized fluid-type actuator
assembly 30 is illustrated, the present invention is also
applicable to clutch controls using other types of clutch
actuators, such as ball ramp actuators or the like.
[0020] The structure of a typical wet master friction clutch 14 may
be seen by reference to FIG. 3. Briefly, the engine output 18,
shown as a dampened flywheel, is connected to the transmission
input shaft 20 by an engageable and disengageable friction disc
pack 14C. The clutch is contained within a housing 14D, which will
hold the lubricating and cooling fluid, such as Dextron III or the
like. Annular piston 42 is slidably and sealingly contained in a
cylinder 44 and is biased in the disengaged direction by springs
46.
[0021] FIG. 4 is a schematic illustration depicting the inventive
control system 60 used to calibrate the urge-to-move position of
clutch 14. The ECU 34 includes an engine torque and calibration
processor 62 that processes engine torque data received from engine
12 via a serial communications data link. During operation, engine
12 will periodically broadcast an engine configuration map via the
serial communications data link. A typical engine configuration map
contains engine torque data corresponding to various engine speeds,
where the engine speed is typically characterized in revolutions
per minute (RPM) and the torque is characterized as a percentage
(%) of a rated engine reference torque. The engine reference torque
is typically specified and programmed into the electronics of
engine 12 by the engine manufacturer and is typically, but not
necessarily, the rated maximum engine torque. The engine torque and
calibration processor 62 processes the engine torque data according
to the stored control logic and communicates with pressure
controller 54 via a clutch operating signal controller 64, which is
preferably an element of ECU 34. Control system 60 further includes
an inertia brake 66 that is configured to slow down or stop the
rotation of input shaft 20 so that the engine may be loaded during
the calibration process.
[0022] As is well known, engine output or flywheel torque
(T.sub.FW) is equal to gross engine torque (T.sub.EG) minus the sum
of engine torque losses (T.sub.L), such as engine friction torque,
accessory torque, etc. The value of the sum of engine torque
losses, at idle speed, may be determined by measuring the value of
engine gross torque when the clutch is fully disengaged (therefore,
flywheel torque equals zero) and engine speed is stabilized at idle
speed (T.sub.EGD=T.sub.L if T.sub.FW=0). With a known value of
torque losses (T.sub.L) at idle speed, the value of output torque
while the clutch is engaged, at a stabilized idle speed, will equal
the value of gross engine torque minus the known value of torque
losses (T.sub.FW=T.sub.EGE-T.sub.L).
[0023] According to the present invention, a calibration method is
provided for identifying a clutch control parameter value (such as
the value of a pulse width modulated control signal) indicative of
the urge-to-move position of the clutch, where the urge-to-move
position is the partially engaged position of the clutch that
allows creeping of the vehicle if the brakes are not applied.
[0024] The calibration method of the present invention is described
with reference to the flow charts of FIGS. 5A, 5B and 5C. Referring
to FIG. 5A, the calibration process begins with the ECU 34 first
determining whether certain vehicle conditions are present to
commence the calibration, as shown in step 100. The correct vehicle
conditions required for entering a calibration state occur, for
example, when the vehicle is stationary, the transmission is in
neutral, the engine is running, disabling faults such as a J1939
fault are not present, and a minimum coolant temperature level is
achieved.
[0025] Once the calibration state is entered, ECU 34 starts a
calibration timer corresponding to a predetermined maximum
calibration period. Should the duration of the calibration period
exceed the predetermined maximum calibration period, the
calibration will be deemed to have failed and the calibration
process will not restart until the next pre-scheduled calibration,
such as the next vehicle power up. ECU 34 is programmed to refer to
a previously stored PWM control signal value to control actuation
of clutch 14 in the event the calibration fails.
[0026] The engine controller 28 will first maintain engine speed at
a desired idle RPM (about 600-850 RPM) with clutch 14 fully
disengaged. The engine torque data is transmitted via the J1939
data link to the engine and calibration processor 62, where it is
filtered, e.g. averaged, to determine a gross disengaged (unloaded)
engine torque (T.sub.EGD). In this state, the amount of torque
generated by the engine (T.sub.EGD) will be equal to that of the
engine torque losses (T.sub.L) at the desired idle RPM. The gross
disengaged engine torque (T.sub.EGD) is preferably characterized as
a percentage (%) of the rated engine reference torque. For example,
if the engine torque losses (T.sub.L) are equal to 68 lb-ft and the
engine reference torque is equal to 680 lb-ft, the gross disengaged
engine torque (T.sub.EGD) will be 10%.
[0027] Referring to step 102, the ECU 34 then turns on inertia
brake 66 to lock input shaft 20 and, thus, ground the driven side
14B of clutch 14 in order to load the engine. ECU 34 then
determines an approximate value of a PWM control signal (S.sub.1)
that causes clutch 14 to transfer a predetermined amount of torque
from engine 12 to transmission 16. Referring to step 104, ECU 34
provides a command output signal to pressure controller 54
instructing pressure controller 54 to provide a ramping PWM control
signal to the solenoid-actuated hydraulic system 52 causing clutch
14 to engage in a stepwise manner. The initial value of the ramping
PWM control signal preferably corresponds to a touch point position
of the clutch, i.e. the point where the clutch first starts
transmitting torque. In a preferred embodiment, the PWM control
signal is preferably ramped at a rate of approximately 4 mA per 350
mS and the predetermined amount of torque transferred from engine
12 to transmission 16 is about 35 lb-ft (47.5 Nm). Although it has
been determined that about 35 lb-ft (47.5 Nm) is the preferred
amount of torque transfer to allow urge-to-move operation of the
vehicle, it is recognized that an urge-to-move torque in the range
of approximately 20-60 lb-ft (27.1-54.3 Nm) may be used. It is also
recognized that other ramping rates may be employed to engage the
clutch.
[0028] As clutch 14 is engaged, the gross engaged (loaded) engine
torque (T.sub.EGE) is continuously being monitored and filtered,
e.g. averaged, by the engine and calibration processor 62. The
gross engine torque (T.sub.EGE) is preferably characterized as a
percentage (%) of the engine reference torque. The clutch 14 is
engaged until the maximum filtered gross engine torque (T.sub.EGE)
sensed during the ramping process minus the gross disengaged engine
torque (T.sub.EGD) is greater than an urge-to-move reference torque
(T.sub.REF), as shown in step 106. The urge-to-move reference
torque (T.sub.REF) is defined in ECU 34 as a percentage (%) of the
engine reference torque required to transfer the predetermined
amount of torque, e.g. 35 lb-ft (47.5 Nm), from engine 12 to
transmission 16. For example, if the engine reference torque is 680
lb-ft (922.8 Nm), the urge-to-move reference torque (T.sub.REF)
would be equal to 5.14% (680 lb-ft.times.5.14%=35 lb-ft).
Alternatively gross engaged engine torque (T.sub.EGE), gross
disengaged engine torque (T.sub.EGD) and urge-to-move reference
torque (T.sub.REF) may be expressed as an actual torque value, not
as a percentage of the engine reference torque.
[0029] The ramping engagement of clutch 14 is chosen to provide an
approximate measurement of first PWM control signal (S.sub.1). The
first PWM control signal (S.sub.1) is then recorded, step 108,
clutch 14 is returned to the fully disengaged position, step 110.
While clutch 14 is disengaged, and preferably during future periods
of disengagement, the ECU 34 monitors and filters the engine torque
data for a predetermined amount of time to account for any engine
accessories, such as an air conditioning compressor, that may have
been activated and would effect the gross disengaged engine torque
(T.sub.EGD). Once the gross disengaged engine torque (T.sub.EGD) is
re-determined, a more detailed search is commenced to find a more
accurate PWM control signal that generates the urge-to-move
reference torque (T.sub.REF).
[0030] The detailed search is characterized by re-applying clutch
14 in at least one pulse, where the pulse comprises applying clutch
14 to a position corresponding to a PWM control signal, pausing a
predetermined amount of time to allow engine 12 and clutch 14 to
stabilize, and then releasing clutch 14. The PWM control signal
corresponding to a first pulse is determined by offsetting the
recorded first PWM control signal (S.sub.1) a predetermined amount,
for example 8 mA, to generate a second PWM control signal
(S.sub.2). Referring to step 112, the clutch 14 is then pulsed
corresponding to the second PWM control signal (S.sub.2) and the
maximum filtered gross engine torque (T.sub.EGE) sensed during the
pulse is recorded.
[0031] Referring to steps 114 and 116, if ECU 34 determines that
the maximum filtered gross engine torque (T.sub.EGE) minus the
gross disengaged engine torque (T.sub.EGD) is less than the
urge-to-move reference torque (T.sub.REF), clutch 14 is disengaged
and then re-engaged corresponding to a new pulse PWM control signal
(S.sub.n) that equals the previous PWM control signal (S.sub.n-1)
plus a predetermined amount, for example 1 mA. If it is determined
that the maximum filtered gross engine torque (T.sub.EGE) minus the
gross disengaged engine torque (T.sub.EGD) is greater than three
(3) times the urge-to-move reference torque (T.sub.REF), as shown
in step 115, the calibration process is restarted. If, however, it
is determined that the maximum filtered gross engine torque
(T.sub.EGE) minus the gross disengaged engine torque (T.sub.EGD) is
greater than two (2) times the urge-to-move reference torque but
less than or substantially equal to three (3) times the
urge-to-move reference torque (T.sub.REF), clutch 14 is disengaged
and then re-engaged corresponding to a new pulse PWM control signal
(S.sub.n') that equals the previous PWM control signal (S.sub.n'-1)
minus a predetermined amount, for example 2 mA, as shown in step
118. Referring to step 120, the cycle of applying and releasing
clutch 14 is continued until the filtered gross engine torque
(T.sub.EGE) minus the gross disengaged engine torque (T.sub.EGD) is
greater than or substantially equal to the urge-to-move reference
torque (T.sub.REF) and less than or substantially equal to two (2)
times the urge-to-move reference torque (T.sub.REF). The
corresponding PWM control signal is then read (step 122) and stored
in computer memory (step 124).
[0032] Referring to FIG. 5B, once a more accurate PWM control
signal is identified, the calibration process enters a confirmation
state to verify that when the identified PWM control signal is
applied to solenoid valve 52, the urge-to-move reference torque
(T.sub.REF) is achieved. Referring to step 126, clutch 14 is
applied to a position corresponding to the identified PWM control
signal and the maximum filtered gross engine torque (T.sub.EGE) is
recorded. Referring to step 128, if it is determine that the
maximum filtered gross engine torque (T.sub.EGE) minus the gross
disengaged torque (T.sub.EGD) is not greater than or substantially
equal to the urge-to-move reference torque (T.sub.REF) or less than
or substantially equal to two (2) times the urge-to-move reference
torque (T.sub.REF), the confirmation is deemed to have failed and
clutch 14 is disengaged and then re-engaged in at least one pulse,
as described above, to determine a more accurate PWM control
signal. Otherwise, the confirmation process proceeds until the PWM
control signal is verified a predetermined number of times, for
example twice, and the verified PWM signal is stored in computer
memory, as shown in steps 130 and 132.
[0033] Referring to FIG. 5C, in order to account for control system
inaccuracies, such as inaccuracies in engine torque reporting, ECU
34 subtracts a stored predetermined offset constant from the
verified PWM signal to arrive at a PWM control signal (S.sub.UTM)
that corresponds to the urge-to-move position of clutch 14, as
shown in step 134. In a preferred embodiment, the ECU 34 subtracts
a predetermined offset constant of 16 mA, which is empirically
determined from a wide range of vehicle drive line configurations.
The PWM control signal (S.sub.UTM) is then stored in non-volatile
memory for future reference.
[0034] Due to factors such as clutch wear and temperature changes,
the urge-to-move PWM control signal (S.sub.UTM) can vary, and
therefore is updated during each calibration. Referring to steps
136 and 138, in order to allow new clutch control systems to
calibrate quickly, if it is determined that the current PWM control
signal (S.sub.UTM) differs from the previously stored PWM control
signal (S.sub.UTM-1) by more than a predetermined amount, for
example 20 mA, the new value is used by ECU 34 unfiltered.
Otherwise, a "filter" is employed by ECU 34, which calculates the
PWM control signal (S.sub.UTM) as a function of the current PWM
control signal (S.sub.UTM) and the previously stored PWM control
signal (S.sub.UTM-1), as shown in step 140. In a preferred
embodiment, ECU 34 utilizes approximately 80% of the stored PWM
control signal (S.sub.UTM-1) and approximately 20% of the current
PWM control signal (S.sub.UTM) to determine an updated PWM control
signal to be used by the control system to modulate clutch 14 to
the urge-to-move position. The use of a filter advantageously
reduces the susceptibility of changes in PWM control signal
(S.sub.UTM) and the corresponding urge-to-move position of clutch
14 due to noise in the electronics of control system 60.
[0035] Referring to steps 142 and 144, the updated urge-to-move PWM
control signal is then stored in non-volatile memory for future
access by ECU 34 and ECU 34 releases brake 66 to complete the
calibration process. The clutch control parameter value (S.sub.UTM)
is utilized by ECU 34 to control reengagement of the automated
clutch 14 while transmission 16 is in the "urge to move" mode.
[0036] Although certain preferred embodiments of the present
invention have been described, the invention is not limited to the
illustrations described and shown herein, which are deemed to be
merely illustrative of the best modes of carrying out the
invention. A person of ordinary skill in the art will realize that
certain modifications and variations will come within the teachings
of this invention and that such variations and modifications are
within its spirit and the scope as defined by the claims.
* * * * *