U.S. patent application number 09/891488 was filed with the patent office on 2001-11-08 for computer readable storage medium for controlling engine torque.
This patent application is currently assigned to Ford Global Technologies, Inc.. Invention is credited to Pallett, Tobias John, Robichaux, Jerry Dean.
Application Number | 20010037793 09/891488 |
Document ID | / |
Family ID | 23458793 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010037793 |
Kind Code |
A1 |
Robichaux, Jerry Dean ; et
al. |
November 8, 2001 |
Computer readable storage medium for controlling engine torque
Abstract
A computer readable storage medium having instructions for
controlling an engine includes instructions for determining a
desired engine brake torque and modifying the desired engine brake
torque based on current engine operating conditions to determine a
requested engine brake torque prior to determination of control
parameters, including at least one of an airflow and a fuel
quantity, to effect the requested engine brake torque. Preferably,
the desired engine brake torque is modified by combining the
desired engine brake torque with an idle speed torque to generate a
first intermediate torque, comparing the first intermediate torque
to an actual engine brake torque to generate a second intermediate
torque, generating a feedback correction torque based on the second
intermediate torque, and combining the first intermediate torque,
the feedback correction torque, and a third intermediate torque to
determine the requested engine brake torque.
Inventors: |
Robichaux, Jerry Dean;
(Riverview, MI) ; Pallett, Tobias John;
(Ypsilanti, MI) |
Correspondence
Address: |
David S. Bir
Brooks & Kushman P.C.
1000 Town Center, 22nd Floor
Southfield
MI
48075-1351
US
|
Assignee: |
Ford Global Technologies,
Inc.
Dearborn
MI
|
Family ID: |
23458793 |
Appl. No.: |
09/891488 |
Filed: |
June 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09891488 |
Jun 25, 2001 |
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09370234 |
Aug 9, 1999 |
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6279531 |
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Current U.S.
Class: |
123/339.19 ;
123/350; 701/110 |
Current CPC
Class: |
F02D 2041/1409 20130101;
F02D 2250/18 20130101; Y02T 10/40 20130101; F02D 41/083 20130101;
F02D 41/1497 20130101; F02D 2200/1004 20130101; F02P 5/1504
20130101; F02D 41/0087 20130101; F02D 2041/0017 20130101; F02D
2041/1422 20130101; Y02T 10/46 20130101; F02D 2200/1006
20130101 |
Class at
Publication: |
123/339.19 ;
123/350; 701/110 |
International
Class: |
F02D 041/00 |
Claims
What is claimed is:
1. A computer readable storage medium having stored data
representing instructions executable by a computer to control an
engine, the computer readable storage medium comprising:
instructions for determining a desired engine brake torque based on
accelerator pedal position, barometric pressure, and speed;
instructions for adjusting the desired engine brake torque to
generate a requested engine brake torque based on current operating
conditions; and instructions for controlling at least one operating
parameter of the engine based on the requested engine brake torque
to deliver the desired engine brake torque.
2. The computer readable storage medium of claim 1 wherein the
instructions for adjusting the desired engine brake torque
comprise: instructions for combining the desired engine brake
torque with an idle speed torque, the idle speed torque determined
at least in part based on a desired engine speed; instructions for
determining an actual engine brake torque; and instructions for
comparing the actual engine brake torque to the desired engine
brake torque to generate a torque error.
3. The computer readable storage medium of claim 2 wherein the
instructions for determining an actual engine brake torque comprise
instructions for estimating an actual engine brake torque based on
current engine operating parameters.
4. The computer readable storage medium of claim 3 wherein the
instructions for adjusting the desired engine brake torque further
comprise instructions for generating a requested brake torque based
on the torque error to drive the torque error toward zero.
5. The computer readable storage medium of claim 3 wherein the
instructions for generating a requested brake torque based on the
torque error comprise: instructions for applying the torque error
to a PID feedback controller having associated proportional,
integral, and derivative terms; and instructions for setting the
proportional and derivative terms to zero and holding the integral
term constant during transient torque control modes.
6. The computer readable storage medium of claim 1 wherein the
instructions for adjusting the desired engine brake torque
comprise: instructions for combining an accessory brake torque with
the desired engine brake torque; instructions for combining a
frictional torque based on engine temperature with the desired
engine brake torque; instructions for compensating for torque
reducing effects of spark retard and air/fuel ratio; and wherein
the instructions for controlling at least one operating parameter
include instructions for controlling at least one of airflow and
fuel flow.
7. Apparatus for controlling an engine comprising: means for
determining a desired engine brake torque based on accelerator
pedal position, barometric pressure and speed; means for adjusting
the desired engine brake torque to generate a requested engine
brake torque based on current operating conditions; and means for
controlling at least one operating parameter of the engine based on
the requested engine brake torque to deliver the desired engine
brake torque.
8. The apparatus of claim 7 wherein the means for determining a
desired engine brake torque determines a desired engine brake
torque based on vehicle speed.
9. The apparatus of claim 7 wherein the means for determining a
desired engine brake torque determines a desired engine brake
torque based on engine speed.
10. The apparatus of claim 7 wherein the means for adjusting the
desired engine brake torque combines the desired engine brake
torque with an idle speed torque, the idle speed torque determined
at least in part based on a desired engine speed.
11. The apparatus of claim 7 wherein the means for adjusting the
desired engine brake torque determines an actual engine brake
torque and compares the actual engine brake torque to the desired
engine brake torque to generate a torque error.
12. The apparatus of claim 11 further comprising means for
estimating an actual engine brake torque based on at least engine
speed, engine temperature, airflow, ignition angle, and relative
camshaft timing.
13. The apparatus of claim 10 wherein the means for adjusting the
desired engine brake torque generates a requested brake torque
based on the torque error to drive the torque error toward
zero.
14. The apparatus of claim 7 wherein the means for adjusting the
desired engine brake torque combines an accessory brake torque with
the desired engine brake torque.
15. The apparatus of claim 14 wherein the accessory brake torque
includes an estimate of torque required to operate an air
conditioning compressor.
16. The apparatus of claim 14 wherein the accessory brake torque
includes an estimate of frictional losses based on engine
temperature and engine speed.
17. A computer readable storage medium having stored data
representing instructions for controlling an engine, the computer
readable storage medium comprising: instructions for determining a
desired engine brake torque; and instructions for modifying the
desired engine brake torque based on current engine operating
conditions to determine a requested engine brake torque prior to
determination of control parameters, including at least one of an
airflow and a fuel quantity, to effect the requested engine brake
torque by combining the desired engine brake torque with an idle
speed torque to generate a first intermediate torque, comparing the
first intermediate torque to an actual engine brake torque to
generate a second intermediate torque, generating a feedback
correction torque based on the second intermediate torque, and
combining the first intermediate torque, the feedback correction
torque, and a third intermediate torque to determine the requested
engine brake torque.
18. The computer readable storage medium of claim 17 wherein the
third intermediate torque represents torque required to operate at
least one engine accessory.
19. The computer readable storage medium of claim 17 wherein the
third intermediate torque varies as a function of temperature and
engine speed.
20. A computer readable storage medium having stored data
representing instructions executable by a computer to control an
internal combustion engine, the computer readable storage medium
comprising: instructions for determining a desired engine brake
torque; instructions for adjusting the desired engine brake torque
to generate a requested engine brake torque by combining an
accessory brake torque with the desired engine brake torque; and
instructions for controlling at least one operating parameter of
the engine based on the requested engine brake torque to deliver
the desired engine brake torque.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of application Ser. No.
09/370,234, filed on Aug. 9, 1999, entitled "System And Method for
Controlling Engine Torque", now U.S. Pat. No. 6,______,______
B1.
TECHNICAL FIELD
[0002] The present invention is directed to a computer readable
storage medium for controlling engine torque using feedback and
feed forward control.
BACKGROUND ART
[0003] Electronic airflow control systems, such as variable cam
timing systems and electronic throttle control systems, replace
traditional mechanical throttle cable systems with an "electronic
linkage" provided by sensors and actuators in communication with an
electronic controller. This increases the control authority of the
electronic controller and allows the airflow and/or fuel flow to be
controlled independently of the accelerator pedal position.
[0004] To control the actual output engine brake torque to achieve
the driver demanded engine brake torque, it is desirable to
calculate a corresponding desired airflow and fuel flow.
Preferably, this computation accounts for variations in engine
operating parameters, such as engine operating temperature and
accessory losses.
[0005] Prior art approaches convert the desired engine torque to a
desired airflow using a two-dimensional lookup table with inputs
for desired torque and engine speed. However, such lookup tables
are typically calibrated for stoichiometric operation and for
maximum brake torque (MBT). The resulting desired airflow is then
modified by a function which relates engine operating temperature
and air/fuel ratio to engine torque to generate a modified or
corrected airflow. The corrected desired airflow is then achieved
via an appropriate airflow rate controller. This approach may be
seen by reference to U.S. Pat. Nos. 5,351,776 and 5,383,432, for
example.
[0006] While the prior art approaches may be acceptable for many
applications and operating conditions, it is desirable to provide a
more robust engine torque controller which improves powertrain
performance for current applications and is more amenable to new
engine technologies and control strategies such as direct
injection, lean burn, variable cam timing, and variable
displacement applications.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a
computer readable storage medium having stored data representing
instructions for controlling engine torque in an engine having
electronically controlled airflow and/or fuel flow.
[0008] Another object of the present invention is to provide engine
torque control which more accurately compensates for current
operating conditions such as additional frictional losses when the
engine is cold and for variable accessory losses which correct for
variations between desired and actual torque using a torque
feedback signal.
[0009] In carrying out the above object and other objects,
advantages, and features of the present invention, a computer
readable system and method for controlling engine torque includes
instructions for determining a desired engine brake torque based on
accelerator pedal position, barometric pressure, and speed;
instructions for adjusting the desired engine brake torque to
generate a requested engine brake torque based on current operating
conditions; and instructions for controlling at least one operating
parameter of the engine based on the requested engine brake torque
to deliver the desired engine brake torque. Preferably, the desired
engine brake torque is modified by combining the desired engine
brake torque with an idle speed torque to generate a first
intermediate torque, comparing the first intermediate torque to an
actual engine brake torque to generate a second intermediate
torque, generating a feedback correction torque based on the second
intermediate torque, and combining the first intermediate torque,
the feedback correction torque, and a third intermediate torque to
determine the requested engine brake torque, where the third
intermediate torque represents accessory load or a frictional
torque loss which varies with temperature.
[0010] The present invention provides a number of advantages over
prior art control strategies. The present invention compensates the
input to the engine torque controller prior to determination of the
control parameters, such as airflow and fuel flow, rather than
modifying the output of the engine torque controller as described
in the prior art. This provides a more robust torque controller
which is more easily applied to various engine technologies.
[0011] The above advantages and other advantages, objects, and
features of the present invention, will be readily apparent from
the following detailed description of the best mode for carrying
out the invention when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram illustrating a system and method
for controlling engine torque according to the present
invention;
[0013] FIG. 2 is a block diagram illustrating an output torque
based powertrain control strategy including determination of a
desired engine torque according to the present invention;
[0014] FIG. 3 is a block diagram illustrating an engine torque
controller according to the present invention; and
[0015] FIG. 4 is a flowchart illustrating a system and method for
controlling engine torque according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0016] FIG. 1 provides a block diagram illustrating operation of a
system or method for controlling engine torque according to the
present invention.
[0017] System 10 includes a vehicular powertrain 12 having an
internal combustion engine 14 coupled to an automatic transmission
16. Of course, the present invention is equally applicable to
manual transmission applications. Powertrain 12 may also include a
controller 18 in communication with engine 14 and transmission 16
for providing various information and control functions. Engine 14
is connected to transmission 16 via crankshaft 20 which is
connected to transmission pump 22 and/or torque converter 24.
Preferably, torque converter 24 is a hydrodynamic torque converter
including a pump or impeller 26 which is selectively fluidly
coupled to a turbine 28. Torque converter 24 may also include a
frictional converter clutch or bypass clutch 30 which provides a
selective frictional coupling between turbine shaft 32 and input
shaft 34.
[0018] Automatic transmission 16 includes a plurality of
input-to-output ratios or gear ratios effected by various gears,
indicated generally by reference numeral 36, and associated
frictional elements such as clutches, bands, and the like, as well
known in the art. Gears 36 provide selective reduction or
multiplication ratios between turbine shaft 32 and output shaft 38.
Automatic transmission 16 is preferably electronically controlled
via one or more shift solenoids, indicated generally by reference
numeral 40, and a converter clutch control (CC) 41 to select an
appropriate gear ratio based on current operating conditions.
Transmission 16 also preferably includes an actuator for
controlling pump pressure (PP) 42 (or line pressure), in addition
to a shift lever position sensor (PRN) 44 to provide an indication
of the operator's selected gear or driving mode, such as drive,
reverse, park, etc. A line pressure sensor (LP) 46 can be provided
to facilitate closed loop feedback control of the hydraulic line
pressure during shifting or ratio changing.
[0019] Depending upon the particular application, output shaft 38
may be coupled to one or more axles 48 via a final drive reduction
or differential 50 which may include one or more gears, as
indicated generally by reference numeral 52. Each axle 48 may
include two or more wheels 54 having corresponding wheel speed
sensors 56.
[0020] In addition to the sensors described above, powertrain 12
preferably includes a plurality of sensors, indicated generally by
reference numeral 60, in communication with corresponding input
ports 62 of controller 18 to sense or monitor the current operating
and ambient conditions of powertrain 12. A plurality of actuators,
indicated generally by reference numeral 64, communicate with
controller 18 via output ports 66 to effect control of powertrain
12 in response to commands generated by controller 18.
[0021] The sensors preferably include a throttle valve position
sensor (TPS) 68 which monitors the position of throttle valve 70
which is disposed within intake 72. A mass airflow sensor (MAF) 74
provides an indication of the air mass flowing through intake 72. A
temperature sensor (TMP) 76 provides an indication of the engine
temperature which may include engine coolant temperature or engine
oil temperature, for example.
[0022] As also illustrated in FIG. 1, an engine speed sensor (RPM)
80 monitors rotational speed of crankshaft 20. Similarly, a turbine
speed sensor 82 monitors the rotational speed of the turbine 28 of
torque converter 24. Another rotational speed sensor, vehicle speed
sensor (VSS) 84, provides an indication of the speed of output
shaft 38 which may be used to determine the vehicle speed based on
the ratio of differential 50 and the size of wheels 54. Of course,
wheel speed sensors (WS1 and WS2) 56 may be used to provide an
indication of the vehicle speed as well.
[0023] Depending upon the particular application requirements,
various sensors may be omitted or alternative sensors provided
which generate signals indicative of related sensed parameters.
Values corresponding to ambient or operating conditions may be
inferred or calculated using one or more of the sensed parameters
without departing from the spirit or scope of the present
invention.
[0024] An accelerator pedal 58 is manipulated by the driver to
control the output of powertrain 12. A pedal position sensor 59
provides an indication of the position of accelerator pedal 58,
preferably in the form of counts. In one embodiment, an increasing
number of counts indicates a request for increased power output.
Preferably, redundant position sensors are used with at least one
position sensor having a negative slope such that a decreasing
number of counts corresponds to a request for increased power
output. A manifold absolute pressure (MAP) sensor, or equivalent,
may be used to provide an indication of the current barometric
pressure.
[0025] Actuators 64 are used to provide control signals or to
effect movement of various devices in powertrain 12. Actuators 64
may include actuators for timing and metering fuel (FUEL) 90,
controlling ignition angle or timing (SPK) 92, controlling
intake/exhaust valve actuators 93 (VCT) to implement variable cam
timing, setting the amount of exhaust gas recirculation (EGR) 94,
and adjusting the intake air using throttle valve 70 with an
appropriate servomotor or actuator (TVA) 96. As described above,
automatic transmission 16 may be selectively controlled by
controlling transmission pump or line pressure using an appropriate
actuator (PP) 42 in combination with shift solenoids (SS1 and SS2)
40 which are used to select an appropriate gear ratio, and a
converter clutch actuator or solenoid (CC) 41 used to lock, unlock
or control slip of the torque converter clutch 30. Also preferably,
a temperature sensor 106 is provided to determine the transmission
oil temperature (TOT).
[0026] Controller 18 is preferably a microprocessor-based
controller which provides integrated control of engine 14 and
transmission 16 of powertrain 12. Of course, the present invention
may be implemented in a separate engine or transmission controller
depending upon the particular application. Controller 18 includes a
microprocessor 110 in communication with input ports 62, output
ports 66, and computer readable media 112 via a data/control bus
114. Computer readable media 112 may include various types of
volatile and nonvolatile memory such as random access memory (RAM)
116, read-only memory (ROM) 118, and keep-alive memory (KAM) 119.
These "functional" descriptions of the various types of volatile
and nonvolatile storage may be implemented by any of a number of
known physical devices including but not limited to EPROMs,
EEPROMs, PROMs, flash memory, and the like. Computer readable media
112 include stored data representing instructions executable by
microprocessor 110 to implement the method for controlling engine
torque according to the present invention.
[0027] FIG. 2 provides a block diagram of a representative control
architecture for use with a system and method for engine control
according to the present invention. As will be understood by one of
ordinary skill in the art, one of the advantages of the present
invention is its adaptability and robustness to various control
architectures and engine technologies. As such, the present
invention may be utilized in any of a number of applications and is
independent of the particular strategy illustrated for determining
a desired engine brake torque and for effecting a requested engine
brake torque.
[0028] In one embodiment of the present invention, a driver demand
is interpreted as represented by block 120 of FIG. 2 based on the
vehicle speed 122 accelerator pedal position 124 and barometric
pressure 126. In this embodiment, the driver demand is interpreted
as a wheel torque (TQWH_DD) and is provided as an input to block
130 which arbitrates the final wheel torque among various other
torque requesters, indicated generally by reference numeral 132.
Such torque requesters may include, for example, a cruise control
torque 134, a traction assist torque 136, and/or a vehicle speed
limiting torque 138. Block 130 selects the appropriate torque
depending upon the current operating conditions and provides this
final wheel torque (TQ_WHEEL) to block 140 which performs a number
of functions including scheduling the gear ratio and ratio changes.
Block 140 preferably includes determination of a torque converter
slip, and calculation of a desired engine brake torque based on the
final desired wheel torque. Inputs used in these determinations
include vehicle speed 122, barometric pressure 126, current gear
ratio 142, current torque converter slip 144, and bypass clutch
duty cycle 145. Determination of the desired engine torque is
explained in greater detail below.
[0029] The engine torque requested from block 140 is arbitrated
with various other engine torque limiting functions 146 as
represented by block 150. Transmission controller 152 may also
request torque limiting or modulation to provide cancellation of
the inertia phase to improve shift feel. Transmission controller
152 communicates with transmission solenoid control module 154
which energizes the appropriate shift solenoids to effect the ratio
change. Solenoid control module 154 preferably dynamically controls
the line pressure via transmission pump pressure actuator 42 during
a ratio change to improve shift feel. Alternatively, the apply and
release pressures for individual clutches or shifting elements may
be controlled during the ratio change to further improve shift
feel. Transmission controller 152 is also in communication with
bypass clutch controller 155 which controls the duty cycle of the
torque converter bypass clutch to control the state of the
clutch.
[0030] The final engine torque determined by block 150 is
communicated as a desired engine brake torque to engine controller
156, illustrated and described in greater detail with reference to
FIG. 3. The engine controller modifies the desired engine brake
torque based on current engine operating conditions to determine a
requested engine brake torque prior to determination of control
parameters such as air flow, spark, EGR, and fuel as represented by
blocks 158, 160, 162, and 164, respectively. Various other control
parameters may also be used, such as air/fuel ratio, and the like,
depending upon the particular application.
[0031] While the present invention is described with reference to a
system based on desired wheel torque, the present invention is
independent of the particular strategy used to determine the
desired engine brake torque. For example, the present invention
could be easily applied to a system which uses a desired tractive
effort or wheel power to determine a desired engine brake torque.
Likewise, the present invention is applicable to systems which
determine a desired engine brake torque directly from the operator
via an accelerator pedal or similar device.
[0032] FIG. 3 is a block diagram illustrating an engine torque
controller 156 according to the present invention. Engine torque
controller 156 includes three functional sections represented
generally by reference numerals 200, 202, and 204. Block 200
receives a desired engine brake torque (TQ_ENG) and adjusts the
desired engine brake torque to generate a requested engine brake
torque (TQ_SUM2) based on current operating conditions. The
requested engine brake torque is provided to block 202 which
controls at least one operating parameter of the engine based on
the requested engine brake torque to deliver the desired engine
brake torque. Block 204 includes an airflow-based idle speed
controller which generates an idle speed torque determined at least
in part based on a desired engine speed, preferably stored in a
lookup table.
[0033] Idle speed controller 204 determines the required airflow to
provide idle speed control and dashpot modes of operation. As known
in the art, dashpot mode operates to modify the engine deceleration
rate to smoothly approach the desired idle speed when the
accelerator pedal is released. Idle speed controller 204 includes a
feed forward idle speed control 206 having various inputs including
a desired engine idle speed (N_BASE), engine coolant temperature
(ECT), air charge temperature (ACT), and flags or switches to
determine the state of various accessories such as air conditioning
(A/C) and power steering (P/S).
[0034] PID and adaptive control feedback block 208 generates an
appropriate output based on an RPM error which is combined with the
output from block 206 and a dashpot input to determine a desired
airflow (DESMAF). This value is provided to section 202 as
explained in greater detail below. The desired airflow is also used
to generate a torque trim term to provide smooth transitions
between idle speed control and other operation modes. The torque
trim term is produced by generating an airflow error which is
operated on by PID controller 210 to reduce the error toward zero.
The airflow value is converted to a torque trim value by block 212
which is then combined with the desired engine brake torque value
at summing junction 214. As such, the desired engine brake torque
(TQ_ENG) is adjusted or modified first by combining the desired
engine brake torque with an idle speed torque (TQ_TRIM) to generate
a first intermediate torque (TQ_SUM) according to:
TQ_SUM=TQ.sub.--ENG+TQ_TRIM
[0035] The first intermediate torque is compared at block 218 to an
actual engine brake torque (TQ_NET) generated by block 216 to
generate a torque error (second intermediate torque) according
to:
TQ_ERROR=TQ_SUM-TQ_NET
[0036] The actual engine brake torque (TQ_NET) may be an estimated
or a measured value for actual torque. The second intermediate
torque or torque error is provided to a PID controller 220 which
generates a feedback correction torque based on the second
intermediate torque.
[0037] Preferably, controller 220 includes proportional, integral,
and derivative terms but is not active during certain transient
torque limiting control modes, which may include idle speed
control, dashpot, engine speed limiting, traction assist,
transmission gear shifting, and fail safe cooling, among others. In
one embodiment, controller 220 sets the proportional and derivative
terms to zero while holding the integral term constant during these
control modes. Alternatively, the integral term of controller 220
may be reset during transient torque control modes while setting
the proportional and derivative terms to zero. The torque feedback
controller is preferably deactivated during these transient modes
to prevent interference between the control parameters for air and
fuel flow and th transient torque control parameters such as spark
retard or injector/cylinder cutout. An example of a method for
reducing engine torque through coordinated control of spark retard,
cylinder cutout, and air/fuel scheduling can be seen in U.S. Pat.
No. 5,479,898, for example.
[0038] Block 216 preferably provides an estimate of the actual
engine brake torque based on current engine operating parameters
including ignition angle, air/fuel ratio, number of cylinders,
variable CAM timing angle, engine coolant temperature, engine
speed, airflow, and operation state of accessories such as the air
conditioning compressor. Of course, various other parameters may be
included in determining the actual engine brake torque.
Alternatively, an appropriate sensor may be provided to directly
determine the actual engine brake torque. Determination of an
estimated actual torque is described in greater detail in U.S. Pat.
No. 5,241,855, assigned to the Assignee of the present
invention.
[0039] The feedback correction torque generated by PID controller
220 (TQ_PID) is provided to a summing block 222 where it is
combined with the first intermediate torque and a third
intermediate torque (ETC_TQ_LOSS) to determine the final requested
engine brake torque according to:
TQ_ENG.sub.--DES=TQ_SUM+TQ.sub.--PID+ETC.sub.--TQ_LOSS
[0040] The third intermediate torque may represent an accessory
brake torque and/or the additional torque required to overcome
increased frictional losses during cold engine operation.
Preferably, the third intermediate torque is the sum of the
estimated accessory brake torques including the air conditioning
compressor, front end accessory friction, power steering pump
losses, and additional rotational friction attributable to cold
engine operation. The output of block 222 is then the requested
final engine brake torque which is provided to section 202 to
control the engine output. In the embodiment illustrated in FIG. 3,
section 202 uses airflow as the primary control parameter. Of
course, fuel delivery or fuel flow may also be controlled to
control the engine output torque. As such, the input to the torque
controller section 202 is compensated to request additional torque
to compensate for accessory losses and cold friction losses as
opposed to modifying the output of the torque controller as seen in
various prior art references.
[0041] As stated above, the present invention is independent of the
particular strategy or controller used to deliver the requested
engine brake torque. In this embodiment, airflow is used as the
primary control parameter to deliver the requested torque for
stoichiometric operation. Various other operational modes and/or
engine technologies, such as lean burn, may utilize airflow
control, fuel flow control, spark or ignition angle control, and
the like as well known in the art.
[0042] Once the requested brake torque is determined by section
200, it is provided to block 230 which provides feed forward
compensation to compensate for the non-linear effects of the
air/fuel ratio being rich or lean of stoichiometry, i.e., an
air/fuel ratio between about 12:1 and about 18:1. Likewise, block
230 compensates for the non-linear effects of the spark or ignition
angle being retarded from the steady-state operation conditions,
such as when in idle speed control mode. This is considered a feed
forward compensation because these terms modify the control input
to cause total or partial cancellation of the non-linear functions
of the model. Improved transient and steady-state control is
provided by combining the feed forward compensation of block 230
with the feedback operation of block 220.
[0043] Block 230 includes inputs representing the operating
air/fuel equivalence ratio (LAMBSE), spark retard from MBT
(SPK_DELTA), engine speed (RPM), and load. A lookup table is used
to generate a torque ratio parameter which defines a relationship
between indicated torque at a given air/fuel ratio relative to the
indicated torque at a stoichiometric air/fuel ratio according
to:
TQ_RATIO.sub.--LAMBSE=FN(LAMBSE)
[0044] This function is described in greater detail in U.S. Pat.
No. 5,241,855 assigned to the Assignee of the present invention.
Because this function is preferably defined for maximum brake
torque (MBT) ignition timing, any variation from MBT requires an
additional compensation. The effect of spark retard, such as may
occur during idle speed control, is preferably calculated from a
tabular function and is represented as a scalar determined
according to:
TQ_RATIO.sub.--SPK=FN(SPK.sub.--DELTA)
[0045] Such a function is described in greater detail in U.S. Pat.
No. 5,241,855. Preferably, this value represents the reduction in
torque due to an ignition timing which is varied from MBT during
steady-state conditions. Thus, the input torque to block 230
(TQ_ENG_DES) can be compensated for the effects of spark retard and
lean or rich LAMBSE according to: 1 TQ _ ENG _ TOT = TQ _ ENG _ DES
TQ _ RATIO_ LAMBSE * TQ _ RATIO_ SPK
[0046] The output of block 230 (TQ_ENG_TOT) is provided to block
232 which converts the torque to a required airflow (load) to
achieve the requested value of engine brake torque. Preferably,
this model (FNTQETC) is in the form of a lookup table referenced by
requested engine brake torque and engine speed. In one embodiment,
this model assumes minimal accessory losses, stoichiometric
operation, warm engine operation, and standard temperature and
pressure calibrations. The output of block 232 is in the form of a
desired engine cylinder load which may be represented by:
ETC.sub.--DES_LOAD=FNTZETC(TQ.sub.--ENG_TOT, RPM)
[0047] where load is defined as the percentage of maximum
theoretical cylinder air mass in the combustion chamber for a
naturally aspirated engine (SARCHG).
[0048] Block 234 converts the load to a desired intake airflow
(ETC_TQ_MAF) according to:
ETC.sub.--TQ_MAF_ETC.sub.--DES_LOAD * ENGCYL * RPM * SARCHG
[0049] where ENGCYL represents the number of intake strokes per
engine revolution. Block 236 operates as a multiplexer or switch to
switch between the real-time controller and the idle speed or
dashpot mode control. The appropriate input is selected and passed
to the output based on the APP (at part pedal) flag which is set to
zero or one when the accelerator pedal is either partly depressed
or fully depressed and equal to minus one when the accelerator
pedal is not depressed. Block 238 selects the higher value for the
airflow from the idle speed controller or the real-time engine
torque controller to ensure that the final requested airflow
(ETC_DESMAF) does not decrease below the idle speed control setting
(DESMAF) due to any modeling errors in the torque-to-load table
(FNTQETC) represented by block 232. As such, block 238 always
selects the maximum of its two inputs which is then provided at the
output.
[0050] Referring now to FIG. 4, a flowchart illustrating control
logic of one embodiment of a system or method according to the
present invention is shown. As will be appreciated by one of
ordinary skill in the art, the flowchart illustrated in FIG. 4 may
represent any of a number of known processing strategies such as
event-driven, interrupt-driven, multi-tasking, multi-threading, and
the like. As such, various steps or functions illustrated may be
performed in the sequence illustrated, in parallel, or in some
cases omitted. Likewise, the order of processing is not necessarily
required to achieve the objects, features, and advantages of the
invention, but is provided for ease of illustration and
description. Preferably, the control logic is implemented in
software which is executed by a microprocessor-based controller. Of
course, the control logic may be implemented in software, hardware,
or a combination of software and hardware. The flowchart of FIGS. 4
illustrate one "loop" and its operations are preferably repeated at
predetermined time intervals as known by those of skill in the
art.
[0051] Block 300 represents determining a desired engine brake
torque. As described above, various techniques may be used to
determine the desired engine brake torque. Preferably, the desired
engine brake torque is determined based on the vehicle speed,
accelerator pedal position, and current barometric pressure.
Depending upon the particular application, a driver demanded torque
may be represented by a wheel torque, wheel power, engine power, or
various other parameters which are converted to a desired engine
brake torque. Blocks 302-308 adjust the desired engine brake torque
to generate a requested engine brake torque based on current
operating conditions. Blocks 310-312 represent controlling at least
one of the operating parameters of the engine based on the
requested engine brake torque to deliver the desired engine brake
torque.
[0052] In particular, block 302 represents combining the desired
engine brake torque with an idle speed torque to generate a first
intermediate torque. Preferably, the idle speed torque is a torque
trim value which is used to provide smooth transitions between the
idle speed controller and the engine torque controller. The first
intermediate torque is compared to the actual engine brake torque
to generate a second intermediate torque as represented by block
304. Preferably, the first intermediate torque is also used in a
feed forward arrangement as illustrated in FIG. 3 and represented
by block 308.
[0053] Block 306 represents generating a feedback correction torque
based on the second intermediate torque. Preferably, a
proportional-integral-de- rivative (PID) controller is used to
generate the feedback correction torque. Preferably, the
proportional and derivative terms are set to zero while the
integral term is held constant during at least one engine control
mode where transient torque control is necessary, such as during
idle speed control, traction assist, and the like. The output of
the feedback correction torque block is used to adjust the
requested engine brake torque to drive the torque error toward
zero.
[0054] A third intermediate torque based on accessory loads and/or
engine frictional losses is determined as represented by block 308.
Preferably, block 308 represents determination of an estimated
accessory brake torque which includes the torque required to
operate various vehicle accessories including an air conditioning
compressor, power steering pump, and the like. Various losses may
also be compensated for by block 308 including the frictional
losses. As known, frictional losses generally vary as a function of
engine temperature and engine speed. As such, block 308 preferably
includes a term for frictional losses based on engine temperature
and engine speed.
[0055] The first intermediate torque, feedback correction torque,
and third intermediate torque are combined to determine the
requested engine brake torque as represented by block 310. The
requested engine brake torque is then compensated for the torque
reducing effects of spark retard and LAMBSE being rich or lean of
stoichiometry. The compensated requested engine brake torque is
then provided to block 312 where it is converted to appropriate
control parameters to control the engine as represented by block
312. The control parameters may include airflow, fuel, ignition
angle (spark), CAM timing, and the like, depending upon the
particular application.
[0056] As such, the present invention compensates the input to the
engine torque controller prior to determination of the control
parameters rather than modifying the output of the engine torque
controller as described in the prior art. This provides a more
robust torque controller which is more easily applied to various
engine technologies including lean burn, variable CAM timing, and
the like.
[0057] While the best mode for carrying out the invention has been
described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention as defined by the
following claims.
* * * * *