Torque based engine speed control

A method of achieving a desired engine speed of an internal combustion engine includes determining the desired engine speed, calculating a slow response torque value based on the desired engine speed and calculating a fast response torque value based on the desired engine speed. A slow response actuator command and a fast response actuator command are generated based on the slow response torque value and the fast response torque value, respectively. Operation of the engine is regulated based on the slow response actuator command and the fast response actuator command to achieve the desired engine speed.

FIELD

The present invention relates to engines, and more particularly to torque-based speed control of an engine.

BACKGROUND

Internal combustion engines combust an air and fuel mixture within cylinders to drive pistons, which produces drive torque. Air flow into the engine is regulated via a throttle. More specifically, the throttle adjusts throttle area, which increases or decreases air flow into the engine. As the throttle area increases, the air flow into the engine increases. A fuel control system adjusts the rate that fuel is injected to provide a desired air/fuel mixture to the cylinders. As can be appreciated, increasing the air and fuel to the cylinders increases the torque output of the engine.

Engine control systems have been developed to accurately control engine speed output to achieve a desired engine speed. Traditional engine control systems, however, do not control the engine speed as accurately as desired. Further, traditional engine control systems do not provide as rapid of a response to control signals as is desired or coordinate engine torque control among various devices that affect engine torque output.

SUMMARY

Accordingly, the present disclosure provides a method of achieving a desired engine speed of an internal combustion engine. The method includes determining the desired engine speed, calculating a slow response torque value based on the desired engine speed and calculating a fast response torque value based on the desired engine speed. A slow response actuator command and a fast response actuator command are generated based on the slow response torque value and the fast response torque value, respectively. Operation of the engine is regulated based on the slow response actuator command and the fast response actuator command to achieve the desired engine speed.

In other features, the slow response actuator command is a desired throttle area. The method further includes determining a desired air per cylinder (APC) value based on the slow response torque value and determining the desired throttle area based on the desired APC and a manifold absolute pressure (MAP) of the engine.

In other features, the fast response actuator command is a desired spark timing. The method further includes determining the desired spark timing based on the fast response torque value and a measured APC of the engine.

In other features, the method further includes determining a minimum torque value based on the desired engine speed and a transmission gear ratio. The slow response torque value is determined based on the minimum torque value. The method further includes determining at least one of a reserve torque value, a feed-forward torque value and a proportional-integral torque value. The slow response torque is further based on the at least one of a reserve torque value, a feed-forward torque value and a proportional-integral torque value. The method further includes calculating an engine speed error based on a measured engine speed and the desired engine speed. The proportional-integral torque value is determined based on the engine speed error.

In still other features, the method further includes determining at least one of a reserve torque value, a run torque value and a proportional torque value. The fast response torque is further based on the at least one of a reserve torque value, a run torque value and a proportional torque value. The method further includes calculating an engine speed error based on a measured engine speed and the desired engine speed. The proportional torque value is determined based on the engine speed error.

In yet another feature, the method further includes limiting each of the slow response torque value and the fast response torque value between respective minimum and maximum values.

The present disclosure provides a torque-based engine speed control that improves the overall flexibility of the engine control system, simplifies the software requirements for implementing such control and provides for an automated calibration process. In this manner, overall implementation and development costs for an engine system can be reduced.

DETAILED DESCRIPTION

Referring now toFIG. 1, an engine system10includes an engine12that combusts an air and fuel mixture to produce drive torque. Air is drawn into an intake manifold14through a throttle16. The throttle16regulates mass air flow into the intake manifold14. Air within the intake manifold14is distributed into cylinders18. Although a single cylinder18is illustrated, it can be appreciated that the coordinated torque control system of the present invention can be implemented in engines having a plurality of cylinders including, but not limited to, 2, 3, 4, 5, 6, 8, 10 and 12 cylinders.

A fuel injector (not shown) injects fuel that is combined with the air as it is drawn into the cylinder18through an intake port. The fuel injector may be an injector associated with an electronic or mechanical fuel injection system20, a jet or port of a carburetor or another system for mixing fuel with intake air. The fuel injector is controlled to provide a desired air-to-fuel (A/F) ratio within each cylinder18.

An intake valve22selectively opens and closes to enable the air/fuel mixture to enter the cylinder18. The intake valve position is regulated by an intake cam shaft24. A piston (not shown) compresses the air/fuel mixture within the cylinder18. A spark plug26initiates combustion of the air/fuel mixture, which drives the piston in the cylinder18. The piston, in turn, drives a crankshaft (not shown) to produce drive torque. Combustion exhaust within the cylinder18is forced out an exhaust port when an exhaust valve28is in an open position. The exhaust valve position is regulated by an exhaust cam shaft30. The exhaust is treated in an exhaust system and is released to atmosphere. Although single intake and exhaust valves22,28are illustrated, it can be appreciated that the engine12can include multiple intake and exhaust valves22,28per cylinder18.

The engine system10can include an intake cam phaser32and an exhaust cam phaser34that respectively regulate the rotational timing of the intake and exhaust cam shafts24,30. More specifically, the timing or phase angle of the respective intake and exhaust cam shafts24,30can be retarded or advanced with respect to each other or with respect to a location of the piston within the cylinder18or crankshaft position. In this manner, the position of the intake and exhaust valves22,28can be regulated with respect to each other or with respect to a location of the piston within the cylinder18. By regulating the position of the intake valve22and the exhaust valve28, the quantity of air/fuel mixture ingested into the cylinder18and therefore the engine torque is regulated.

The engine system10can also include an exhaust gas recirculation (EGR) system36. The EGR system36includes an EGR valve38that regulates exhaust flow back into the intake manifold14. The EGR system is generally implemented to regulate emissions. However, the mass of exhaust air that is recirculated back into the intake manifold14also affects engine torque output.

A control module40operates the engine based on the torque-based engine speed control of the present disclosure. More specifically, the control module40generates a throttle control signal and a spark advance control signal based on a desired engine speed (RPMDES). A throttle position signal generated by a throttle position sensor (TPS)42. An operator input43, such as an accelerator pedal, generates an operator input signal. The control module40commands the throttle16to a steady-state position to achieve a desired throttle area (ATHRDES) and commands the spark timing to achieve a desired spark timing (SDES). A throttle actuator (not shown) adjusts the throttle position based on the throttle control signal.

An intake air temperature (IAT) sensor44is responsive to a temperature of the intake air flow and generates an intake air temperature (IAT) signal. A mass airflow (MAF) sensor46is responsive to the mass of the intake air flow and generates a MAF signal. A manifold absolute pressure (MAP) sensor48is responsive to the pressure within the intake manifold14and generates a MAP signal. An engine coolant temperature sensor50is responsive to a coolant temperature and generates an engine temperature signal. An engine speed sensor52is responsive to a rotational speed (i.e., RPM) of the engine12and generates in an engine speed signal. Each of the signals generated by the sensors is received by the control module40. The engine system10can also include a turbo or supercharger54that is driven by the engine12or engine exhaust.

The torque-based engine speed (RPM) control of the present disclosure achieves RPMDESbased on ATHRDESand SDES. More specifically, the torque-based engine speed control regulates transitions between engine speed and torque control and engine speed control. As explained in further detail below, this is achieved through the application of open-loop torque control to transform an engine RPM command into different engine actuator commands including, but not limited to, spark timing (S), throttle position (ATHR) and cam phaser positions. This is further achieved through application of RPM feedback to maintain RPMDESunder coast down, transition to engine RPM control and idle speed control conditions, as well as through calculating a minimum torque (TMIN) required to maintain RPMDES.

The torque-based engine RPM control determines a slow response requested torque value (TREQSL) and a fast response requested torque value (TREQFS). TREQSLis determined based on the following relationship:
TREQSL=TRES+TFF+TMIN+TPI(1)
where: TRESis a reserve torque;

TMINis the minimum torque required to maintain RPMDES; and

TRESis an additional amount of torque that is incorporated to compensate for unknown loads that can suddenly load the engine. TFFis a feed-forward torque amount that indicates the additional amount of torque required as a result of a transmission range change (e.g., a change from neutral (N) to drive (D)). TPI, is determined in accordance with the following relationship:
TPI=kP* RPMERR+kI* ∫RPMERR(2)
where: RPMERRis an RPM error;

kPis a proportional constant; and

kIis an integral constant.

RPMERRis determined as the difference between RPMDESand an actual RPM (RPMACT) measured by the engine RPM sensor52. TREQSLis limited between minimum and maximum values based on the following relationship:

TREQSLis used to determine a slow response term using an inverse torque module. More specifically, a desired air per cylinder (APCDES) value is determined by processing TREQSLthrough the inverse torque model, as is represented in the following relationship:
APCDES=T−1(TREQSL, SUM, I, E, RPM)   (4)
where: SUMis an un-managed spark timing term;

I is the intake cam phase angle; and

E is the exhaust cam phase angle.

To improve the stability of the control, APCDESis filtered using a low-pass filter to provide a filtered APCDES.

The filtered APCDESis processed using a compressed flow (CF) model to provide a desired throttle area (ATHRDES). More specifically, a desired mass air flow (MAFDES) is determined based on the following relationship:

MAFDES=APCDES⁡(FILT)·RkCYL(5)
where kCYLis a cylinder constant. For example, kCYLis equal to 15 for an 8-cylinder engine, 20 for a 6-cylinder engine and 15 for a 4-cylinder engine. ATHRDESis determined based on the following relationship:

ATHRDES=MAFDES*R·TAMBB·Φ·(MAPB)(6)
where B is the measured barometric pressure, TAMBis the ambient air temperature and Φ is based on a pressure ratio (PR) according to the following relationships:

Φ={2⁢γγ-1⁢(1-PRγ-1γ)if⁢⁢PR>Pcritical=(2γ+1)γγ-1=0.528γ⁢(2γ+1)γ-1(γ-1)if⁢⁢PR≤Pcritical(7)
PRis the ratio of MAP to the ambient pressure (PAMB) and PCRITICAL. PCRITICALis defined as the pressure ratio at which the velocity of the air flowing past the throttle equals the velocity of sound. This condition is called choked or critical flow. The critical pressure ratio is determined by:

PCRITICAL=(2γ+1)γ/γ-1(8)
where γ is equal to the ratio of specific heats for air and range from about 1.3 to about 1.4.

The torque-based engine RPM control determines TREQFSbased on the following relationship:
TREQFS=TRUN−TRES+TP(9)
where: TRUNis a run torque value; and

TRUNis determined based on the following relationship:
TRUN=f(APCACT, RPM,SUM, I, E)   (10)
where APCACTis that actual air per cylinder value and is determined based on the MAF signal. TPis determined based on the following relationship:
TP=kFP·RPMERR(11)
where kFPis a proportional constant for the fast term. TREQFSis limited between minimum and maximum values based on the following relationships:

The desired spark timing (SDES) is determined based on the following relationship:
SDES=Ts−1(TREQFS, APCACT(FILT), R,I,S)   (13)
where APCDESis filtered using a low-pass filter to provide a filtered APCDES(FILT). In this manner, the stability of the control is improved. SDESis limited based on the following relationships:

SDES=[SMAX,if->S>SMAXSMIN,if->S<SMIN](14)
The torque-based engine RPM control subsequently regulates engine operation based on ATHRDESand SDESto achieve RPMDES.

Referring now toFIG. 2, exemplary steps executed by the torque-based engine speed control will be discussed in further detail. In step200, control determines whether the engine is on (i.e., running). If the engine is not one, control ends. If the engine is on, control generates RPMDESin step202. In step204, control determines TREQSLand TREQFSbased on RPMDES, as described in detail above. ATHRDESis determined based on TREQSLin step206, as described in detail above. In step208, control determines SDESbased on TREQFS, as described in detail above. Control operates the engine based on ATHRDESand SDESto achieve RPMDESin step210and control loops back to step200.

Referring now toFIG. 3, exemplary modules that execute the torque-based engine speed control will be discussed. The exemplary modules include an RPMDESmodule300, a TMINmodule302, a proportional-integral (PI) module304, a proportional (P) module306, limiting modules308a,308b,308c, inverse torque model (ITM) modules310a,310b, low-pass filter (LPF) modules312a,312b, a compressed flow (CF) module314and an engine control module (ECM)316.

The RPMDESmodule300generates RPMDESbased on a standard block of RPM control described in detail in commonly assigned U.S. Pat. No. 6,405,581 B1, issued on Jun. 18, 2002 and entitled System and Method of Controlling the Coastdown of a Vehicle, the disclosure of which is expressly incorporated herein by reference. RPMDESis output to the TMINmodule302and a summer module318. The TMIN302module determines TMIN, for example, from a look-up table, based on RPMDESand a current transmission gear ratio. TMINis output to a summer module320.

The summer module318determines an RPM error (RPMERR) as the difference between RPMDESand an actual RPM (RPMACT). RPMACTis determined using the engine RPM sensor52. RPMERRis output to the PI module304and the P module306. The PI module304determines TPIand the P module determines TP, as described above. TPIis output to the summer module320and TPis output to a summer module322. A summer module324determines a base torque (TBASE) as the difference between an unmanaged-filtered torque (TUMF) and TRES. TBASEis output to the summer module322.

The summer module320determines TREQSLas the sum of TRES, TFF, TMINand TPI. TREQSLis output to the limiting module308a, which limits the value of TREQSLbetween minimum and maximum values, as described in detail above. The limited TREQSLis output to the ITM module310a, which determines APCDESbased on TREQSL, SUMand other parameters, as discussed in detail above. APCDESis filtered in the LPF module312aand is output to the CF module314. The CF module314determines ATHRDESbased on the filtered APCDESand MAP, as described above. ATHRDESis output to the ECM316.

The summer module322determines TREQFSas the sum of TPand TERR. TREQFSis output to the limiting module308b. The limiting module308blimits the value of TREQFSbetween minimum and maximum values, as described in detail above. The LPF module312bfilters APCACTand outputs the filtered APCACTto the ITM module310b. The limited TREQFSis output to the ITM module310b, which determines SDESbased on TREQFSL, the filtered APCACTand other parameters, as discussed in detail above. The limiting module308climits the value of SDESbetween minimum and maximum values, as described in detail above. The limited SDESis output to the ECM316. The ECM316generates control signals based on ATHRDESand SDESto achieve RPMDES.

The torque-based engine speed control of the present disclosure improves the overall flexibility of the engine control system, simplifies the software requirements for implementing such control and provides for an automated calibration process. In this manner, overall implementation and development costs for an engine system can be reduced.

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.