Vehicle fuel control based on vacuum-assisted brake component actuation

A control method for an engine of a vehicle includes generating a brake value indicative of an operating condition of a brake system of the vehicle, and selectively adjusting one of a fuel control value of the engine and a fuel adjustment diagnostic value for the engine based on the brake value. In the method, a mass of fuel delivered to the engine is based on the fuel control value, and a diagnostic result indicative of lean operation of the engine is based on the fuel adjustment diagnostic value. The brake operating condition is selected from a group including a state of operation, a pedal displacement, an actuation period, a fluid operating pressure, and a power assist pressure. The fuel control value is provided.

FIELD

The present disclosure relates to control systems and methods for controlling an internal combustion engine of a vehicle, and more particularly, to control systems and methods for fuel control and fuel control diagnostics.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art. The background information provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Motorized vehicles may include a powertrain that includes a powerplant (e.g., an engine, an electric motor, and/or a combination thereof), a multispeed transmission, and a differential or final drive train. The powerplant may include an engine that produces drive torque that is transmitted through one of various gear ratios of the transmission to the final drive train to drive wheels of the vehicle. The engine may produce drive torque by combusting an air-fuel mixture in cylinders of the engine. The air-fuel mixture may be controlled by one or more electronic control modules.

Motorized vehicles may also include a brake system connected to the wheels that may be selectively actuated to decelerate and thereby stop the vehicle. Typically, the brake system is actuated by a driver of the vehicle by depressing a brake pedal and thereby generating pedal force. In vehicles equipped with a hydraulic brake system, the pedal force may be converted by a master cylinder to a pressure of brake fluid used to actuate brakes connected to the wheels.

In a conventional brake system, the pedal force may be directly transmitted to the master cylinder for generating fluid pressure. Conventional power brake systems may include a vacuum-actuated brake booster that amplifies the pedal force transmitted to the master cylinder and thereby provides braking assistance.

Power brake systems that include a vacuum-actuated brake booster may use engine vacuum to actuate the brake booster. In such systems, a vacuum chamber of the brake booster may be fluidly connected with an intake manifold of the engine. Engine vacuum generated in the intake manifold during induction strokes may generate vacuum in the vacuum chamber that is used to actuate a diaphragm assembly housed in the brake booster. The diaphragm assembly moves in response to a pressure differential that is created between the vacuum chamber located on one side and a working chamber located on an opposite side when the brake pedal is depressed. The pressure differential acts against the diaphragm assembly, causing the diaphragm assembly to translate (i.e. move) within the brake booster and transmit a force to the master cylinder in proportion to the pressure differential.

SUMMARY

The present disclosure provides a control system for an engine of a vehicle that includes an input that receives a brake value indicative of an operating condition of a brake system of the vehicle, and a compensation module that selectively adjusts one of a fuel control value of the engine and a fuel adjustment diagnostic value for the engine based on the brake value. The brake operating condition is selected from a group including a state of operation, a pedal displacement, an actuation period, a fluid operating pressure, and a power assist pressure.

In one feature of an exemplary embodiment, the fuel control value is an air induction value of the engine and the compensation module selectively adjusts the air induction value. The air induction value is an estimated volumetric efficiency of the engine, and the compensation module determines an offset value based on the brake value and selectively adjusts the estimated volumetric efficiency based on the offset value.

In another feature of the exemplary embodiment, the compensation module selectively adjusts the fuel adjustment diagnostic value based on a first difference between a current value and a previous value of a learned fuel adjustment value. The learned fuel adjustment value is based on a second difference between a desired air-fuel ratio and an actual air-fuel ratio of the engine.

In a related feature, the compensation module selectively adjusts the fuel adjustment diagnostic value when the first difference is positive. In another related feature, the compensation module adjusts the fuel adjustment diagnostic value when an actuation period of the brake system is less than a threshold period. The threshold period is based on a comparison of a previous value of the fuel adjustment diagnostic value and a threshold value. In yet another related feature, the compensation module adjusts the fuel adjustment diagnostic value by a product of a scalar value and the first difference. The scalar value is a real number that varies between zero and one. The scalar value is based on a first comparison of a previous value of the fuel adjustment diagnostic value and a threshold value, and a second comparison of an actuation period of the brake system and a threshold period. The threshold period is based on the first comparison.

The present disclosure also provides a control method for an engine of a vehicle that includes generating a brake value indicative of an operating condition of a brake system of the vehicle, and selectively adjusting one of a fuel control value of the engine and a fuel adjustment diagnostic value for the engine based on the brake value. In the method, a mass of fuel delivered to the engine is based on the fuel control value, and a diagnostic result indicative of lean operation of the engine is based on the fuel adjustment diagnostic value. The brake operating condition is selected from a group including a state of operation, a pedal displacement, an actuation period, a fluid operating pressure, and a power assist pressure.

In one feature of an exemplary method, the fuel control value is an air induction value of the engine and the selectively adjusting includes selectively adjusting the air induction value. The air induction value is an estimated volumetric efficiency of the engine. The selectively adjusting the air induction value includes determining an offset value based on the brake value and adjusting the estimated volumetric efficiency based on the offset value.

In another feature of the exemplary method, the selectively adjusting includes selectively adjusting the fuel adjustment diagnostic value based on a first difference between a current value and a previous value of a learned fuel adjustment value. The learned fuel adjustment value is based on a second difference between a desired air-fuel ratio and an actual air-fuel ratio of the engine.

In a related feature, the selectively adjusting includes selectively adjusting the fuel adjustment diagnostic value when the first difference is positive. In another related feature, the selectively adjusting includes adjusting the fuel adjustment diagnostic value when an actuation period of the brake system is less than a threshold period. The threshold period is based on a comparison of a previous value of the fuel adjustment diagnostic value and a threshold value.

In yet another related feature, the selectively adjusting includes adjusting the fuel adjustment diagnostic value by a product of a scalar value and the first difference. The scalar value is a real number that varies between zero and one. The scalar value is based on a first comparison of a previous value of the fuel adjustment diagnostic value and a threshold value, and a second comparison of an actuation period of the brake system and a threshold period. The threshold period is based on the first comparison.

DETAILED DESCRIPTION

On vehicles equipped with a power brake system that includes a vacuum-actuated brake booster, operation of the brake booster may cause an uncompensated increase in the mass of air inducted into the engine. The uncompensated increase in the mass of air may temporarily result in lean operation of the engine. During open-loop fuel control, uncompensated increases in the mass of air may result in prolonged lean operation of the engine. An increase in the mass of air entering the engine may occur as the diaphragm assembly moves within the brake booster and decreases the volume of the vacuum chamber. As the volume of the vacuum chamber decreases, the absolute pressure in the vacuum chamber may temporarily increase (i.e. vacuum decreases) and cause a corresponding transient increase in the pressure of the air within the intake manifold.

Accordingly, the present disclosure provides exemplary control systems and methods for selectively adjusting an estimated mass of air entering the engine based on one or more operating conditions of the brake system. Additionally, the present disclosure provides exemplary control systems and methods for selectively adjusting a learned fuel adjustment diagnostic value used to generate a diagnostic result indicative of prolonged lean engine operation based on the brake system operating conditions. Selectively adjusting the estimated mass of air provides for more accurate control of air-fuel ratios. Selectively adjusting the learned fuel adjustment diagnostic value inhibits drift in the learned fuel diagnostic control value that may otherwise result during periods of high manifold vacuum, such as during engine idle. One or both the estimated mass of air and the fuel adjustment diagnostic value may be selectively adjusted according to the principles set forth in more detail below. Example embodiments will now be described more fully with reference to the accompanying drawings.

With particular reference toFIG. 1, a functional block diagram illustrating an exemplary vehicle system10is shown. The vehicle system10includes a powerplant12and a brake system14. The vehicle system10may further include a vehicle control module (VCM)16that regulates operation of the powerplant12and the brake system14. As discussed herein, the VCM16may regulate operation of the powerplant12based on the operation of the brake system14.

The powerplant12produces drive torque that may be used to accelerate the vehicle and maintain a desired vehicle speed. The drive torque may be transferred through a transmission20at varying gear ratios to a drivetrain22to drive one or more wheels24of the vehicle. The powerplant12may be a hybrid powerplant that includes an internal combustion engine26and a hybrid drive system28as shown.

With particular reference toFIG. 2, the engine26may be of any conventional type. The engine26may include one or more cylinders for combusting an air-fuel mixture and thereby produce drive torque. For example only, a single cylinder30is shown. The engine26may include a piston (not shown) that reciprocates within the cylinder30to draw air into the engine26and compress the air-fuel mixture. During induction strokes, air may be drawn into the cylinder30through a throttle31and an intake manifold32. The flow of air entering the cylinder30may be controlled by an intake valve34that periodically opens to enable air to flow into the cylinder30and closes to permit combustion of the air-fuel mixture within the cylinder30. Although a single intake valve34is shown, two or more intake valves may be provided with each cylinder30.

One or more fuel injectors may supply fuel to the engine26. For example only, a single fuel injector36is shown. The fuel injector36may be located in the intake manifold32and inject fuel that mixes with the air therein and is carried to the cylinder30. The air-fuel mixture may enter the cylinder30and be ignited by a spark plug38located in the cylinder30. Combustion of the air-fuel mixture forces the piston down, thereby driving a rotating crankshaft (not shown). The piston then moves up, forcing the byproducts of combustion (i.e. exhaust gas) out of the cylinder30through an exhaust valve40. The exhaust valve40periodically opens to enable the byproducts to enter an exhaust system42and closes to permit combustion within the cylinder30. Exhaust gas entering the exhaust system42may be treated within the exhaust system42and expelled to the atmosphere.

The engine26may also include a camshaft assembly44that actuates (i.e. opens and closes) the intake and exhaust valves34,40. The camshaft assembly44may be drivingly coupled to the crankshaft and rotate at a speed proportional to the rotational speed of the crankshaft. Alternatively, the camshaft assembly44may include solenoids (not shown) that actuate the intake and exhaust valves34,40.

The engine26may further include a plurality of sensors that measure various operating conditions of the engine26. The engine sensors may generate output signals, hereinafter referred to and shown in the drawings (e.g.,FIG. 3) as engine signals48, that are communicated to the VCM16. For example only, the engine26may include sensors such as, but not limited to, a manifold air pressure (MAP) sensor50, a manifold air temperature (MAT) sensor52, a camshaft position sensor54, a crankshaft position sensor56, and an oxygen sensor58.

The MAP sensor50may be located in the intake manifold32and may sense an absolute pressure of the air therein. The MAP sensor50may generate a MAP signal based on the absolute pressure sensed. The MAP signal may be used to determine a current MAP.

The MAT sensor52may be located in the intake manifold32and may sense a temperature of the air therein. The MAT sensor52may generate a MAT signal based on the temperature sensed. The MAT signal may be used to determine a current MAT.

The camshaft position sensor54may be located proximate the camshaft assembly44and may sense a rotational position of the camshaft assembly44. The camshaft position sensor54may generate a CAM signal based on the rotational position of the camshaft assembly44. The CAM signal may be used to determine a current position of the intake valve34and the exhaust valve40.

The crankshaft position sensor56may be located proximate the crankshaft and may sense a rotational position and/or speed of the crankshaft. The crankshaft position sensor56may generate a CPS signal based on the rotational position and/or speed of the crankshaft. The CPS signal may be used to determine a rotational speed (RPM) of the engine26.

The oxygen sensor58may be located within the exhaust system42and may sense a concentration of oxygen within the exhaust gas therein. The oxygen sensor58may generate an O2 signal based on the concentration of oxygen sensed.

Referring again toFIG. 1, the hybrid drive system28may be one of several types and may be a belt alternator starter system (BAS) as shown. Accordingly, the hybrid drive system28may include an engine accessory drive60that transfers torque between an electric motor/generator62and the engine26. The hybrid drive system28may further include a power package assembly64.

In a motoring mode, the motor/generator62provides drive torque to the engine26while receiving electrical power from the power package assembly64. In a regenerating mode, the motor/generator62supplies an electrical charge to the power package assembly64while being driven by the engine26. The power package assembly64may include a battery (not shown) that stores energy supplied by the motor/generator62and supplies the energy to the various components of the vehicle system10, including the motor/generator62.

Referring again toFIG. 2, the brake system14may be of the conventional, power-assisted hydraulic type. The brake system14may include hydraulically-actuated brake assemblies70connected to the wheels24. The brake assemblies70may be friction brakes that produce a brake torque in proportion to a pressure of brake fluid supplied to the brake assemblies70.

The brake system14may further include a master cylinder72coupled to a brake booster74. The master cylinder72supplies brake fluid under pressure to the brake assemblies70in response to an external force applied to the master cylinder72by the brake booster74.

The brake booster74may be of the vacuum-actuated type and may include a housing80, a diaphragm82, a push rod84, a piston rod86, and a fluid valve88. The housing80may be fastened on one end to the master cylinder72. The diaphragm82is disposed within an interior volume defined by inside walls90of the housing80and may be fixed along a periphery to the walls90. The diaphragm82is movable between a first, retracted position and a second, extended position as indicated by the arrow inFIG. 2. In the retracted position, the diaphragm82does not exert a force on the master cylinder72. In the extended position, the diaphragm82exerts a force on the master cylinder72via the push rod84. A return spring92may be included with the housing80and may bias the diaphragm82in the retracted position.

The diaphragm82separates the interior volume into a vacuum chamber94and a working chamber96. The vacuum chamber94is disposed on a side of the diaphragm82proximate the master cylinder72and is defined by the walls90and the diaphragm82. The vacuum chamber94may be fluidly connected to the intake manifold32by a vacuum line98and check valve100included with the housing80. The check valve100is a one-way valve that permits air to be drawn out of the vacuum chamber94and inhibits air from entering the vacuum chamber94. The working chamber96is disposed on an opposite side of the diaphragm82and is defined by the walls90and the diaphragm82.

The push rod84abuts the master cylinder72on one end and is secured to the diaphragm82on an opposite end. The push rod84extends through the end of the housing80defining the vacuum chamber94and is slidably supported therein. The piston rod86is connected on one end to a brake pedal assembly102and operably connected on an opposite end to the valve88. The valve88is a double valve disposed within the housing80and moveable between a first position and a second position via the piston rod86. In the first position, the valve88provides fluid communication between the vacuum chamber94and the working chamber96. In the second position, the valve88inhibits fluid communication between the chambers94,96(i.e. isolates chambers94,96) and vents the working chamber96to atmosphere.

With continued reference toFIG. 2, operation of the brake booster74will now be described. During periods when the brake pedal assembly102is not depressed, the valve88remains in the first position and the vacuum within the vacuum chamber94and the working chamber96remains equal to the vacuum in the intake manifold32. Depressing the brake pedal assembly102causes the piston rod86to move in the direction of the vacuum chamber94and the valve88to move from the first position toward the second position.

As the valve88moves into the second position, the valve88isolates the chambers94,96and vents the working chamber96to atmosphere. As a result, air enters the working chamber96, causing the pressure to rise and become greater than the pressure in the vacuum chamber94. The pressure differential between the chambers94,96causes the diaphragm82to move from the retracted position toward the extended position against the return spring92and exert a force proportional to the pressure differential on the master cylinder72via the push rod84.

The movement of the diaphragm82causes the volume of the vacuum chamber94to decrease and may temporarily cause the pressure within the vacuum chamber94to rise above (i.e. become greater than) the pressure of the air within the intake manifold32. Thus, movement of the diaphragm82may cause a pressure transient within the intake manifold32during a period the pressure within the vacuum chamber94differs from the pressure within the intake manifold32.

When the brake pedal assembly102is released, the piston rod86retracts, moving the valve88from the second position toward the first position. In the first position, the valve88isolates the working chamber96from the atmosphere and provides a fluid communication path between the chambers94,96, causing the pressure within the chambers94,96to equalize. As the pressure equalizes, the force of the return spring92against the diaphragm82causes the diaphragm to move from the extended position toward the retracted position.

With continued reference toFIG. 2, the brake system14may also include a brake modulator, such as an anti-lock brake (ABS) module104. The ABS module104modulates the fluid pressure supplied by the master cylinder72to the brake assemblies70as may be desired to inhibit wheel slip and/or maintain vehicle control. The brake system14may further include one or more sensors that sense various operating conditions of the brake system14, such as the working pressure of the brake fluid, the pressure of the air within the brake booster74, and a position of the brake pedal assembly102. The brake system sensors may generate signals, hereinafter collectively referred to and shown in the figures (e.g.,FIG. 3) as brake system signals106, that are communicated to the VCM16.

For example only, the brake system14may include a brake fluid pressure sensor108, a booster pressure sensor110, and a brake pedal sensor112. The pressure sensor108may be located at an outlet of the master cylinder72and sense the working pressure of the brake fluid supplied. The pressure sensor108may generate a brake fluid pressure (BFP) signal based on the working pressure sensed. The booster pressure sensor110may be located in the housing80and may sense the pressure of the air within the vacuum chamber94. The booster pressure sensor110may generate a booster air pressure (BAP) signal based on the pressure sensed within the vacuum chamber94. The brake pedal sensor112may be included with the brake pedal assembly102and may sense a pedal position of the brake pedal assembly102. The brake pedal sensor112may be a two-position switch that generates a pedal position (PEDAL) signal indicating whether the pedal assembly is depressed based on the pedal position. In this manner, the PEDAL signal may indicate a brake request by the driver of the vehicle. The foregoing brake system signals106may be output to the VCM16as shown.

Referring still toFIG. 2, the VCM16may regulate operation of the powerplant12and the brake system14based on various signals it receives. The input signals may include the engine signals48and the brake system signals106previously discussed herein. The input signals may further include other signals generated by sensors and devices included with other components of the vehicle system10, including the hybrid drive system28.

The VCM16may further regulate operation of the powerplant12and the brake system14based on signals it receives from one or more driver interface devices120(FIG. 1) manipulated by a driver of the vehicle. The driver interface devices120may include devices such as, but not limited to, the brake pedal assembly102previously discussed herein, an accelerator pedal122, and a transmission gear selector (not shown). The accelerator pedal122may generate an accelerator pedal (ACCEL) signal indicating a desired drive torque of the driver of the vehicle. The signals generated by the driver interface devices120will be collectively referred to hereinafter and in the drawings (e.g.,FIG. 3) as driver signals124. While discussed as part of the brake system14, the brake pedal assembly102also may be considered one of the driver interface devices120. The driver signals124may be output to the VCM16as shown.

The VCM16regulates operation of the powerplant12and the brake system14by generating various control signals that control operation of various actuators of the powerplant12and the brake system14. The control signals may be timed signals. The actuators may include, but are not limited to, the throttle31, the fuel injector36, and the spark plug38previously discussed herein. For example only, the VCM16may generate a throttle control (THROTTLE) signal, a fuel control (FUEL) signal, and a spark control (SPARK) signal that control operation of the throttle31, the fuel injector36, and the spark plug38, respectively. The VCM16may further generate a brake control (BRAKE) signal that controls operation of the ABS module104and thereby regulates the pressure of the fluid supplied to the brake assemblies70.

As discussed herein, the VCM16may generate the various control signals based on one or more operating conditions of the brake system14. With particular reference toFIG. 3, an exemplary VCM16according to the principles of the present disclosure is shown. The VCM16includes a brake control module130, an engine control module (ECM)132, and a diagnostic module134. Although the VCM16is described with reference to the foregoing modules, the VCM16may include additional or fewer modules that generate the various control signals discussed herein.

The brake control module130receives the brake system signals106and generates the BRAKE signal that controls operation of the ABS module104. The brake control module130may also generate a signal indicating a brake state (not shown). The brake control module may generate the brake state signal to indicate whether one or more components of the brake system14is actuated. The brake control module130may receive other signals used to generate the BRAKE signal, such as a wheel speed signal indicating a speed of one or more of the wheels24. The brake control module130may output one or more of the brake system signals106and the BRAKE signal to the ECM132.

The ECM132receives one or more of the engine signals48, the brake system signals106, and the driver signals124. The ECM132generates the control signals, such as the SPARK, the THROTTLE, and the FUEL signals previously described, based on the signals received. In particular, the ECM132may generate the THROTTLE and the FUEL signals based on one or more brake system signals106as discussed in further detail below.

The ECM132may also generate diagnostic control values that may be used by the diagnostic module134. For example, the ECM132may generate a learned fuel adjustment diagnostic value (LTMf) indicating whether the engine26has operated in a lean air-fuel mixture condition for a prolonged period. More specifically, the ECM132may generate LTMf based on the O2 signal and one or more of the brake system signals106. A lean air-fuel mixture condition may exist when the mass of air drawn into the engine26exceeds an estimated mass of air used to determine a desired mass of fuel. A lean air-fuel mixture condition may also exist when the actual mass of fuel delivered to the engine26is less than the desired mass of fuel. The ECM132may output LTMf to the diagnostic module134as shown. Additionally, the ECM132may store LTMf in memory136of the VCM16.

With particular reference toFIG. 4, an exemplary ECM132according to the principles of the present disclosure is shown. The ECM132includes a spark actuator module140, a throttle actuator module142, and an injector actuator module144. The spark actuator module140receives a desired spark value (Des Spark) from a drive torque control module150, and the CPS signal. Based on Des Spark and the CPS signal, the spark actuator module140generates the SPARK signal that controls operation of the spark plug38. The Des Spark value may be a real value indicating the desired degrees of spark advance or retard with respect to a top dead center position of the piston within the cylinder30. The SPARK signal may be a timed signal used to energize the spark plug38at the desired time to initiate combustion within the cylinder30.

The throttle actuator module142receives a desired throttle position value (Des Throttle) from the drive torque control module150and the CPS signal. The throttle actuator module142generates the THROTTLE signal that controls operation of the throttle31. The Des Throttle value may be a real value indicating a desired rotational position of the throttle31corresponding to a desired mass of air to be inducted into the engine26. The throttle actuator module142generates the THROTTLE signal based on Des Throttle and the CPS signal.

The injector actuator module144receives a desired pulse width value (Des PW) from the drive torque control module150, and the CPS signal, and generates the FUEL signal that controls operation of the fuel injector36. The Des PW value may be a real value indicating the period of injector on-time corresponding to the desired mass of fuel for combustion within the cylinder30. The injector actuator module144generates the FUEL signal based on Des PW and the CPS signal. The FUEL signal may be a timed signal used to energize the fuel injector36at the desired time and for the period indicated by Des PW.

The drive torque control module150receives the engine and driver signals48,124. The drive torque control module150also receives a predicted air value (Pred Air) and a learned fuel adjustment value (LTMc) from a compensation module152. Based on the foregoing signals and control values, the drive torque control module150determines the Des Spark, the Des Throttle, and the Des PW values. In general, the drive torque control module150determines the Des Spark, the Des Throttle, and the Des PW to regulate the drive torque output of the engine26. The drive torque control module150may determine Des PW using the following formula (Equation 1):

DesPW=DesFuelLTMc×InjRate,
where Des Fuel is the desired mass of fuel (e.g., grams), InjRate is a base flow rate of the fuel injector36, and LTMc is the learned fuel adjustment value. The desired mass of fuel, Des Fuel, is the mass of fuel required to achieve a desired air-fuel ratio when mixed with the predicted mass of air, Pred Air. The base flow rate, InjRate, is the base mass flow rate of the fuel injector36as produced. Accordingly, when determining Des PW, the drive torque control module150may determine Des Fuel based on Pred Air and the desired air-fuel ratio. The drive torque control module150may look up InjRate in the memory136based on the engine operating conditions. LTMc is a learned scalar value that corrects for observed differences between an actual flow rate and the base flow rate of the fuel injector36. The drive torque control module150may look up LTMc in the memory136.

With particular reference toFIG. 5, an exemplary embodiment of the compensation module152according to the principles of the present disclosure is shown. The compensation module152determines Pred Air, LTMc, and LTMf. The compensation module152determines Pred Air based on an estimated volumetric efficiency (VEeng) of the engine26and a volumetric efficiency correction (VEcorr) value. The compensation module152may determine VEeng and LTMf based on one or more brake operating conditions. Additionally, the compensation module152may determine LTMc and LTMf using the engine signals48and control loop feedback.

With the foregoing in mind, the compensation module152may include an air compensation module160, a volumetric efficiency (VE) determination module162, an air module164, and a fuel compensation module166. The air compensation module160receives one or more of the brake system signals106and determines a brake compensation offset value (K1) based on the signals received. The air compensation module160outputs K1to the VE determination module162.

In general, K1may be a real value corresponding to an increase in volumetric efficiency of the engine26due to operation of the brake system14. K1may be zero during periods the brake system14is not operated. A temporary increase in volumetric efficiency may occur as a result of the increase in manifold air pressure caused by operation of the brake booster74. Accordingly, K1may be based on a state of operation of the brake system14. Where K1is based on the brake state, K1may further be based on a period since entering the current brake state. Additionally, K1may be based on the working pressure indicated by the BFP signal and/or the booster air pressure indicated by the BAP signal. Where K1is based on the working pressure, K1may further be based on a rate of change in the working pressure. Where K1is based on the booster air pressure, K1may further be based on a rate of change in the booster air pressure. K1may also be based on a difference between the booster air pressure and the manifold air pressure indicated by the BAP and MAP signals.

Increases in the volumetric efficiency due to operation of the brake booster74may be estimated using empirical methods (e.g., testing) and/or computational methods. In an empirical approach, operating conditions of the brake system14may be varied and the corresponding change in volumetric efficiency measured. The estimated increases in volumetric efficiency may then be used to determine values for K1.

Values for K1may be stored in data tables in the memory136. Accordingly, the air compensation module160may look up K1in the memory136based on one or more of the brake system operating conditions. K1may be a single value stored in the memory136based on the brake state. Accordingly, for example only, the air compensation module160may determine K1by looking K1up in the memory136based on the brake state.

The VE determination module162receives K1along with one or more of the engine signals48. The VE determination module162determines VEeng based on K1and the engine operating conditions. The VE determination module162outputs VEeng to the air module164. In general, VEeng may depend, in addition to the brake system operating conditions as previously discussed, on the manifold air pressure, the engine speed, and the position of the intake valve34. For example only, the VE determination module162may determine VEeng using the following formula (Equation 2):

VEeng=K⁢⁢1+(K⁢⁢2×MAP+K⁢⁢3×MAP2)+(K⁢⁢4×RPM+K⁢⁢5×RRM2)+(K⁢⁢6×ICAM+K⁢⁢7×ICAM2),
where coefficients K2and K3, K4and K5, and K6and K7(hereinafter “engine k-values”) are compensation values corresponding to manifold air pressure, engine speed, and intake valve position, respectively. The engine k-values may be predetermined values stored in the memory136. Accordingly, the VE determination module162may determine VEeng using Equation 2 based on K1and the foregoing engine operating conditions by looking up the engine k-values in the memory136. Using Equation 2, the VE determination module162may work together with the air compensation module to selectively adjust VEeng based on one or more brake operating conditions.

The air module164receives VEeng and one or more of the engine signals48and determines the predicted air value, Pred Air, based on the signals received. The air module164may determine Pred Air using the following formula (Equation 3):

In Equation 3, VEcorr is a scalar value determined during steady state operation of the engine26that corrects for differences between the estimated and an actual volumetric efficiency of the engine26. VEcorr may be a learned value that compensates for differences between VEeng and the actual volumetric efficiency of the engine26. ChargeAirTemp is an estimated temperature of the air within the cylinder30, and MAP is the manifold air pressure at the beginning of the pressure transient. When determining Pred Air, the air module164may look up the value of VEcorr in the memory136.

The fuel compensation module166receives one or more of the brake system signals106and the engine signals48and determines the fuel adjustment value, LTMc, and the fuel adjustment diagnostic value, LTMf, based on the signals received. The fuel compensation module166may output LTMc to the drive torque control module150(FIG. 4) and may output LTMf to the diagnostic module134(FIG. 3).

As previously discussed herein, LTMc is a learned scalar value that corrects for observed differences between actual flow rates and a base flow rate of the fuel injector36. For example only, LTMc may be learned using a feedback control method and the O2 signal. Using the feedback control method, the fuel compensation module166may selectively adjust the value of LTMc when the O2 signal indicates the engine26did not produce the desired air-fuel mixture and is not running at the desired air-fuel ratio. The fuel compensation module166may adjust the value of LTMc upward by a predetermined incremental value when the engine26is operating leaner than desired and downward by the incremental value when the engine26is operating richer than desired. In the foregoing manner, the fuel compensation module166may selectively increment or decrement the value of LTMc based on whether the engine26is operating at the desired air-fuel ratio.

The fuel compensation module166determines the value of LTMf based on the value of LTMc. More specifically, the fuel compensation module166selectively increments and decrements the value of LTMf based on a change in the value of LTMc (ΔLTMc) over a predetermined period. Additionally, the fuel compensation module166determines LTMf based on one or more brake operating conditions. As discussed herein and for example only, the fuel compensation module166determines LTMf based on the brake state. While the brake pedal assembly102is not depressed the fuel compensation module166adjusts LTMf by the value of ΔLTMc. Thus, while the brake pedal assembly102is not depressed, a change in the value of LTMf (ΔLTMf) may be equal to ΔLTMc.

When the brake pedal assembly102is depressed, the fuel compensation module166may determine the value of ΔLTMf using the following formula (Equation 4):
ΔLTMf=Ks×AFC×ΔLTMc,
where Ks is a first scalar value and AFC, an accumulator filter coefficient, is a second scalar value used to scale the value of ΔLTMc used to determine ΔLTMf. The first scalar value, Ks, may vary between zero and one, and may be based on one or more brake operating conditions. The second scalar value, AFC, may vary between zero and one, and may be based on one or more engine operating conditions. Values for Ks and AFC may be predetermined and may be retrieved from the memory136based on one or more of the brake and engine operating conditions, respectively.

Referring again toFIG. 3, the diagnostic module134may detect sudden faults with the current operation of the components of the vehicle system10. Additionally, the diagnostic module134may detect faults related to prolonged operation of the vehicle system10. Accordingly, the diagnostic module134may receive one or more each of the brake system signals106, the engine signals48, and the driver signals124. The diagnostic module134may also receive the diagnostic control values, such as LTMf, generated by the ECM132.

The diagnostic module134may compare the signals and the diagnostic control values with corresponding predetermined threshold values when determining a diagnostic result. Based on the comparisons, the diagnostic module134may generate diagnostic data indicating whether faults and problems have been detected. For example only, the diagnostic module134may store diagnostic trouble codes (DTCs) in the memory136that may be used to identify the particular fault detected.

The diagnostic module134may also store corresponding diagnostic fault information and a fault status of the DTCs. Based on the faults and problems detected and their corresponding fault status, the diagnostic module134may generate a malfunction indicator lamp (MIL) signal that selectively illuminates a MIL lamp (not shown) visible to the driver to indicate a problem with the vehicle system10. The diagnostic module134may output the MIL signal to one of the driver interface devices120, such as an instrument panel cluster (not shown).

Accordingly, the diagnostic module134may compare LTMf and a diagnostic threshold (Dltm). The diagnostic control module may store a corresponding DTC in the memory136when LTMf exceeds Dltm to indicate prolonged lean engine operation. The diagnostic control module may illuminate the MIL lamp based on the diagnostic data stored with the corresponding DTC.

With particular reference toFIG. 6, an exemplary control method200for determining LTMf according to the principles of the present disclosure is shown. The method200compensates for operation of the brake system14when determining LTMf and thereby inhibits drift in the value of LTMf that may prematurely result in a stored DTC code and/or illumination of the MIL lamp. The method200may be run periodically during operation of the vehicle system10. The method200may be implemented with one or more modules included with the vehicle system10, such as the VCM16.

The method200begins in step202where control determines whether the brake system is actuated. Control may determine whether the brake system is actuated based on one or more of the brake system signals106. If the brake system is actuated, control continues in step202, otherwise control continues in step230.

In step204, control determines a current change in the value of LTMc since the last control loop (ΔLTMc(i)). Control may determine ΔLTMc(i) by subtracting a previous value of LTMc (LTMc(i−1)) from a current value of LTMc (LTMc(i)). Next in step206, control determines whether ΔLTMc(i) is greater than zero (i.e. positive). If ΔLTMc(i) is greater than zero, control proceeds in step208, otherwise control proceeds in step230. In step208, control compares a previous value of LTMf (LTMf(i−1)) with a predetermined threshold (Cltm). Control may compare the value of LTMf determined in the previous control loop and stored in memory (e.g., memory136). The predetermined threshold, Cltm, may be less than the diagnostic threshold, Dltm. If LTMf(i−1) is less than Cltm, then control proceeds in step210, otherwise control proceeds in step216.

In step210, control compares an actuation period and a first threshold period (T1). If the actuation period is less than T1, control proceeds in step212, otherwise control proceeds in step230. In general, the actuation period is a period since one or more components of the brake system14was actuated. Thus, the actuation period may be determined by monitoring one or more of the brake system signals106. Depending on the signal monitored, the actuation period may correspond, more particularly, to operation of a particular component of the brake system14. As one example, the actuation period may correspond to operation of the brake pedal assembly102where the PEDAL signal is monitored to determine the actuation period. As another example, the actuation period may correspond to operation of the brake booster74and the master cylinder72where the BFP signal is monitored to determine the actuation period.

The first threshold period, T1, may correspond to an estimated period of brake system operation during which the operation of the brake system14may affect the mass of air inducted into the engine26. Values for T1may be determined in a variety of ways. For example only, values for T1may be determined using empirical methods and/or computational methods. For simplicity, a single value of T1may be stored in memory and retrieved in step210.

In step212, control determines current values for the first scalar value, Ks1(i), and the second scalar value, ACF(i) based on the current brake operating conditions and the current engine operating conditions, respectively. For example only, control may retrieve values for Ks1(i) and ACF(i) from memory based on the current brake and engine operating conditions. As previously discussed, Ks1(i) and ACF(i), each may be a real value between zero and one used scale the value of ΔLTMc subsequently used to determine a current value of LTMf, LTMf(i). For simplicity, a single value less than one for Ks1(i) may be stored in memory.

Control continues in step214, control determines a desired current change in the value of LTMf (ΔLTMf(i)) based on Ks1(i), AFC(i) and ΔLTMc(i). Control may determine ΔLTMf(i) using the following formula (Equation 5):
ΔLTMf(i)=Ks1(i)×AFC(i)×ΔLTMc(i).
From step214, control continues in step234.

In step216, control compares the actuation period and a second threshold period (T2). If the actuation period is less than T2, control continues in step218, otherwise control continues in step230. In general, the second threshold period T2, like T1, may correspond to an estimated period of brake system operation during which the operation of the brake system14may affect the mass of air inducted into the engine26. However, the value of T2may be different from T1to provide a different period during which control compensates for operation of the brake system14when determining LTMf. For example only, T2may be greater than T1to provide for a longer period of compensation where LTMf has exceeded the predetermined threshold, Cltm.

In step218, control determines current values of a third scalar value (Ks2(i)) and a fourth scalar value. For example only, control may determine the fourth scalar value in the same manner as the accumulator filter coefficient, ACF(i), previously discussed with reference to step212.

The third scalar value, Ks2(i), like Ks1(i), may vary between zero and one and may be used to scale the value of ΔLTMc subsequently used to determine a current value of LTMf (LTMf(i)). The value of Ks2(i) may be less than the value of Ks1(i). In this manner, Ks2(i) may be used to reduce the effect of ΔLTMc(i) on LTMf(i) where LTMf(i−1) is greater than Cltm. The value of Ks2(i) may be a predetermined value retrieved from memory based on one or more of the brake operating conditions. For simplicity, Ks2(i) may be a single, predetermined value stored in memory.

In step220, control determines ΔLTMf(i) based on Ks2(i), AFC(i) and ΔLTMc(i). Control may determine ΔLTMf(i) using the following formula (Equation 6):
ΔLTMf(i)=Ks2(i)×AFC(i)×ΔLTMc(i).
From step220, control continues in step234.

In step230, control determines a fifth scalar value used to scale the value of ΔLTMc subsequently used to determine the LTMf(i). For example only, control may determine the fifth scalar value in the same manner as the accumulator filter coefficient, ACF(i), previously discussed with reference to step212.

Control continues in step232where control determines ΔLTMf(i) based on AFC(i) and ΔLTMc(i). Control may determine ΔLTMf(i) using the following formula (Equation 7):
ΔLTMf(i)=AFC(i)×ΔLTMc(i).
From step232, control continues in step234.

In step234, control determines LTMf(i) based on LTMf(i−1) and ΔLTMf(i). For example only, control may determine LTMf(i) based on the value of LTMf determined in the previous control loop, LTMF(i−1), and stored in the memory. Additionally, it will be appreciated from the foregoing that control determines LTMf(i) based on the value of ΔLTMf(i) determined in one of steps214,220, and232in the current control loop. Control may determine LTMf(i) using the following formula (Equation 8):
LTMf(i)=LTMf(i−1)+ΔLTMf(i).
Control in the current control loop ends in step234and control returns to step202to begin another control loop of the method200.

In the foregoing manner, the method200selectively adjusts LTMf based on LTMc, the brake state, and the actuation period. In particular, when the brake system is actuated and the change in LTMc is positive, the method200selectively scales the change in LTMc used to determine LTMf. Control may determine LTMf in this manner to inhibit drift in the value of LTMf that may otherwise occur as a result of brake system operation during periods of high manifold vacuum.

With particular reference toFIG. 7, another exemplary control method300according to the principles of the present disclosure is shown. In general, it will be appreciated from the description herein, that the method300may be used to selectively adjust one or both of an air induction value used for fueling the engine26and a learned fuel adjustment diagnostic value based on the brake operating conditions. The air induction value may be the Pred Air value and the diagnostic control value may be the LTMf value previously discussed herein. Accordingly, the method300will be described with reference to the foregoing control values. Additionally, the method300may include steps of the method200. For simplicity, steps of the method200that may be included in the method300will be referred to where appropriate and will not be discussed in detail.

Control under the method300begins in step302where control determines whether the brake system is actuated. Control may determine whether the brake system is actuated based on one or more of the brake system signals106. If the brake system is actuated, control continues in step304, otherwise control continues in step308.

In step304, control determines whether to adjust Pred Air based on one or more brake operating conditions. Control may adjust Pred Air to compensate for additional air that may be drawn into the engine26due to operation of the brake booster74. Control may also determine whether Pred Air should be adjusted based on whether LTMf is adjusted in a subsequent step. In this way, control may determine whether one or both Pred Air and LTMf should be adjusted in the current control loop. If control determines Pred Air should be adjusted, control proceeds in step306, otherwise control continues in step308.

In step306, control determines the adjusted volumetric efficiency, VEeng, based on the brake compensation value, K1. Control may determine VEeng using Equation 2 as previously discussed herein. From step306, control continues in step310.

In step308, control determines the volumetric efficiency, VEeng, using the following formula (Equation 9):

VEeng=(K⁢⁢2×M⁢⁢A⁢⁢P+K⁢⁢3×M⁢⁢A⁢⁢P2)+(K⁢⁢4×R⁢⁢P⁢⁢M+K⁢⁢5×R⁢⁢P⁢⁢M2)+(K⁢⁢6×ICAM+K⁢⁢7×ICAM2),
where K2, K3, K4, K5, K6, and K7are the engine k-values previously discussed herein. Similarly MAP, RPM, and ICAM in Equation 9 are manifold absolute pressure, engine speed, and position of the intake valve34as previously discussed herein. From step308, control continues in step310.

In step310, control determines Pred Air based on VEeng. Control may determine Pred Air using Equation 3 as previously discussed herein. From the foregoing description of steps304-310, it will be appreciated that control may selectively adjust Pred Air based on the brake offset value, K1.

From step310, control proceeds in one of step314and step318depending on whether the brake system is actuated as indicated by step312. If in step302control determined the brake system is actuated, then control proceeds in step314, otherwise control proceeds in step318.

In step314, control determines whether to adjust LTMf based on the brake operating conditions. Control may determine whether to adjust LTMf based on whether control determined Pred Air should be adjusted in step304. If control determines LTMf should be adjusted, control proceeds in step316, otherwise control proceeds in step318.

In step316, control determines the change in LTMf, ΔLTMf, based on the change in LTMc, ΔLTMc, and one or more of the brake operating conditions previously discussed. For example only, control may determine ΔLTMf according to the steps204-232of the method200described above. Accordingly, control may selectively adjust ΔLTMf based on a comparison of LTMf and Cltm and a comparison of the actuation period with the first and second threshold periods, T1and T2. Additionally, control may selectively adjust ΔLTMf based on the scalar values Ks1, Ks2, and AFC.

In step318, control determines ΔLTMf based on ΔLTMc. For example only, control may determine ΔLTMf according to the steps230,232of the method200described above. Accordingly, control may determine ΔLTMf based on the scalar value AFC.

In step320, control determines a new value for LTMf based a previous value of LTMf and ΔLTMf. For example only, control may determine the new value for LTMf based on the value of LTMf determined in the previous control loop. Additionally, it will be appreciated from the foregoing that control determines the new value for LTMf based on the value of ΔLTMf determined in step316or step318in the current control loop. Control may determine LTMf using Equation 8 as previously described and store the new value in memory. From step320, control in the current control loop ends and control returns to step302to begin another control loop in the method300.

In the foregoing manner, control selectively adjusts one or both Pred Air and LTMf based on the brake operating conditions. Control may selectively adjust one or both Pred Air and LTMf to more accurately control combustion while also inhibiting drift in the value of LTMf that may otherwise occur during repeated operation of the brake system14.