Generalized cold start emissions reduction strategy

A system providing an approach for catalytic converter warmup mode is applicable to multiple vehicle applications including hybrid vehicles. The system determines exhaust enthalpy during conditions including transient engine speed and transient engine load for a catalytic converter receiving exhaust output from an engine. Multiple exhaust parameter measurement devices each measure exhaust conditions entering the catalytic converter. A processor receives output from each of the exhaust parameter measurement devices and continuously calculates an enthalpy of the catalytic converter. The calculated enthalpy of the catalytic converter is repeatedly compared to a predetermined enthalpy threshold required to achieve catalytic light-off saved in a memory.

INTRODUCTION

The present disclosure relates to automobile vehicle engine cold start emission reduction and catalyst operation.

Vehicle cold start emission reduction strategy is normally implemented during stable engine speed and load conditions. A predetermined time is normally allowed for catalyst warm-up of a catalytic converter before emission strategies are executed. An elevated engine idle employing one or both of a spark retard together with engine rpm elevation is normally performed for a predetermined time period, for example approximately 10 to 20 seconds, after which it is assumed catalytic converter light-off has occurred and catalytic converter oxidation and reduction processes are occurring.

Newer propulsion technologies may necessitate execution of emission reduction regardless of engine state, which may therefore require catalyst warm-up be executed during transient engine speed and load. Under these conditions, the predetermined time period for elevated engine idle is not available or is not achieved, therefore the set target for both spark retard and accumulated engine rpm has not been achieved. A new approach for managing cold start emissions reduction during conditions of transient engine speed and load is therefore required.

Thus, while current vehicle cold start emission reduction strategies achieve their intended purpose, there is a need for a new and improved system and method for implementing emission cold start strategy.

SUMMARY

According to several aspects, a system for determining catalytic light-off conditions during transient engine speed and transient engine load includes a catalytic converter receiving exhaust output from an engine. At least one exhaust parameter measurement device measures at least one parameter of the exhaust entering the catalytic converter. A processor receives output from the at least one exhaust parameter measurement device and continuously calculates an enthalpy of the catalytic converter. The calculated enthalpy of the catalytic converter is repeatedly compared to a predetermined enthalpy threshold required to achieve catalytic light-off saved in a memory.

In another aspect of the present disclosure, a calculation block receives inputs including an exhaust input temperature, a mass air flow, a mass fuel flow, and a catalytic converter warmup mode state for calculating the enthalpy of the catalytic converter.

In another aspect of the present disclosure, in the calculation block, the catalytic converter warmup mode state being True is determined prior to initiating calculation of the enthalpy of the catalytic converter, the catalytic converter warmup mode state being True identifies the catalytic converter is at a temperature below that required for catalytic light-off.

In another aspect of the present disclosure, a cumulative mass flow past the catalytic converter is calculated by the processor; and in a comparative block a determination is made if a) the calculated enthalpy of the catalytic converter is greater than the predetermined enthalpy threshold, and b) if the cumulative mass flow is less than a predetermined cumulative mass flow threshold.

In another aspect of the present disclosure, if an output from the comparative block for (a) and (b) is affirmative, a diagnostic pass signal is generated.

In another aspect of the present disclosure, if an output from the comparative block for (a) and (b) is negative, a diagnostic fail signal is generated.

In another aspect of the present disclosure, a cumulative mass flow past the catalytic converter is calculated by the processor; and in a determination block it is determined that the catalytic converter warmup mode state is False and if the cumulative mass flow is greater than a predetermined minimum threshold.

In another aspect of the present disclosure, if an output from the determination block is positive, a diagnostic test indeterminate signal is generated.

In another aspect of the present disclosure, a catalytic converter warmup mode enabled status is determined in a determination block, and if an output from the determination block is positive indicating the catalytic converter warmup mode is enabled, a request for a torque reserve is made to increase an exhaust temperature; and the torque reserve is computed and integrated following the request for the torque reserve in a first computation block.

In another aspect of the present disclosure, a result from the computation block is entered as a first variable in a comparison block; and a second computation block provides a second variable defining an energy threshold necessary to achieve catalyst light-off to the comparison block.

In another aspect of the present disclosure, the energy threshold required to achieve catalyst light-off defining the second variable is integrated as an exhaust flow accumulated value; and in the comparison block the second variable is compared to the first variable to determine if the second variable is greater than the first variable, and if an output from the comparison block is negative, the torque reserve is sufficient to meet the enthalpy threshold required for catalyst light-off.

In another aspect of the present disclosure, the at least one exhaust parameter measurement device defines each of a temperature sensor, a mass air flow sensor, and a mass fuel flow sensor.

According to several aspects, a method for determining catalytic light-off conditions of a catalytic converter during transient engine speed and transient engine load includes: measuring exhaust conditions entering the catalytic converter using an exhaust parameter measurement device; forwarding an output from the exhaust parameter measurement device to a processor; calculating an enthalpy of the catalytic converter in the processor; and repeatedly comparing the enthalpy of the catalytic converter to a predetermined enthalpy threshold required to achieve catalytic light-off saved in a memory.

In another aspect of the present disclosure, the method includes: confirming the catalytic converter is at or below a required temperature for catalytic light-off; and performing the calculating step in a calculation block, the calculation block receiving inputs including an exhaust temperature, a mass air flow, a mass fuel flow, and a catalytic converter warmup mode.

In another aspect of the present disclosure, the method includes: determining if the calculated enthalpy of the catalytic converter is greater than the predetermined enthalpy threshold.

In another aspect of the present disclosure, the method includes: determining that a catalytic converter warmup mode is enabled; and requesting a torque reserve to increase an exhaust temperature.

In another aspect of the present disclosure, the method includes: identifying a first variable defining an energy threshold necessary to achieve catalyst light-off and entering the first variable into a comparison block; entering a result from the computing step into the comparison block as a second variable; and comparing the first variable to the second variable to determine if the second variable is greater than the first variable, and if the comparison is negative, the torque reserve is deemed sufficient to meet an enthalpy threshold required for catalyst light-off.

According to several aspects, a method for determining catalytic light-off conditions of a catalytic converter during transient engine speed and transient engine load includes: measuring exhaust conditions entering the catalytic converter using at least one exhaust parameter measurement device; forwarding an output from the at least one exhaust parameter measurement device to a processor; continuously calculating an enthalpy of the catalytic converter in the processor; repeatedly comparing the calculated enthalpy of the catalytic converter to a predetermined enthalpy threshold required to achieve catalytic light-off saved in a memory; and calculating a cumulative mass flow past the catalytic converter.

In another aspect of the present disclosure, the method includes: calculating a cumulative mass flow past the catalytic converter; and determining if: a) the enthalpy of the catalytic converter is greater than the predetermined enthalpy threshold, and b) if the cumulative mass flow is less than a predetermined cumulative mass flow threshold.

In another aspect of the present disclosure, the method includes: requesting a torque reserve to increase an exhaust temperature; and computing and integrating the torque reserve.

DETAILED DESCRIPTION

The following description of one aspect is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, activated refers to operation using all of the engine cylinders. Deactivated refers to operation using less than all of the cylinders of the engine (one or more cylinders not active). As used herein, the term processor refers to an application specific integrated circuit (ASIC), an electronic circuit, a module (shared, dedicated, or group) and a memory that together execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality.

Referring now toFIG. 1, a vehicle10may be any type of automobile vehicle including internal combustion engine vehicles and hybrid vehicles, and includes an engine12that drives a transmission14. The transmission14is either an automatic or a manual transmission that is driven by the engine12through a corresponding torque converter or clutch16. Air flows into the engine12through a throttle18. The engine12includes N cylinders20. One or more of the cylinders20are selectively deactivated during engine operation. AlthoughFIG. 1depicts eight cylinders (N=8), it should be appreciated that the engine12may include additional or fewer cylinders20. For example, engines having 4, 5, 6, 8, 10, 12 and 16 cylinders are contemplated. Air flows into the engine12through an intake manifold22and is combusted with fuel in the cylinders20.

According to several aspects if the vehicle10is a hybrid vehicle, the vehicle10further includes an electric machine24and a battery26. The electric machine24is operable in each of a motor mode and a generator mode. In the motor mode, the electric machine24is powered by the battery26and drives the transmission14. In the generator mode, the electric machine24is driven by the transmission14and generates electrical energy that is used to charge the battery26. It should also be evident the battery26can power other vehicle accessories in addition to the electric machine24.

A controller28communicates with the engine12, the electric machine24and receives various inputs from exhaust parameter measurement devices such as sensors as discussed herein. A vehicle operator manipulates an accelerator pedal30to regulate the throttle18. More particularly, a pedal position sensor32generates a pedal position signal that is communicated to the controller28. The controller28generates a throttle control signal based on the pedal position signal. A throttle actuator (not shown) adjusts the throttle18based on the throttle control signal to regulate air flow into the engine12.

The vehicle operator also manipulates a brake pedal34to regulate vehicle braking. As the brake pedal34is actuated, a brake position sensor36generates a brake pedal position signal that is communicated to the controller28. The controller28generates a brake control signal based on the brake pedal position signal. A brake system (not shown) adjusts vehicle braking based on the brake control signal to regulate vehicle speed. In addition to the pedal position sensor32and the brake position sensor36, an engine speed sensor38generates a signal based on engine speed. An intake manifold absolute pressure (MAP) sensor40generates a signal based on a pressure of the intake manifold22. A throttle position sensor (TPS)42generates a signal based on throttle position. A mass air flow sensor (MAF)44generates a signal based on air flow into the throttle18.

When the vehicle load requirements can be met using torque generated by less than all of the cylinders20, the controller28transitions the engine12to the deactivated mode. In an exemplary embodiment, N/2 cylinders20′ are deactivated, although one or more cylinders20′ may be deactivated. Upon deactivation of the selected cylinders20′, the controller28increases the power output of the remaining cylinders20by adjusting the position of the throttle18. The engine load is determined based on the MAP, MAF, RPM, and other inputs. For example, if an engine vacuum is above a threshold level for a given RPM, the engine load can be provided by less than all cylinders and the engine12is operated in the deactivated mode. If the vacuum is below a second threshold level for the given RPM, the engine load cannot be provided by less than all of the cylinders, and the engine12is operated in the activated mode.

The controller28provides engine speed control to adapt the engine output torque through intake air/fuel and spark timing controls in order to maintain a target engine speed. The controller28provides an electronic spark timing (EST) signal output via a line46to an ignition controller48. The ignition controller48responds to the EST signal to provide timed output of drive signals to spark plugs50for combusting the fuel charge in the engine cylinders20. The EST signal may also provide spark timing signals over a wide range of timing. Normally, it is desirable that spark timing occur before piston top dead center and, with increasing engine speed it is typical to further advance spark timing.

It is also known to those skilled in the art to retard spark timing to after-top-dead center. Spark timing may be retarded for example to quickly limit engine output torque or during engine cold starts to increase exhaust gas temperature, in essence trading engine output torque for heat. The exhaust from the engine12is discharged through at least one catalytic converter52, having a catalyst54which is required to reach a predetermined temperature (defining “catalyst light-off”) prior to optimally performing its oxidation and reduction reactions. Spark timing may be retarded during engine cold starts to more quickly increase exhaust gas temperature, and therefore to raise the temperature of the catalyst54as quickly as possible, thereby more quickly achieving fuel emissions standards. The predetermined temperature defining catalyst light-off and conditions defining a total enthalpy value also defining catalyst light-off may be saved in a memory59of the controller28.

As a further method to raise the temperature of the catalyst54during engine cold starts, an “elevated idle” may be performed, wherein the controller28signals for a temporarily increased engine idle speed above the normal engine idle speed. The elevated idle may extend for a period of approximately 10 to 40 seconds after engine start. A set target is used to control engine rpm and spark timing or retard during elevated idle operation.

During certain operational times the full period to perform elevated idle may not be available. For example, if the vehicle accelerates using the electric machine24powered by the battery26to drive the transmission14, but there is insufficient torque to meet the torque demand, an engine start and torque output may be required before the catalyst54can reach the minimum required temperature for catalyst light-off. Under such conditions, it is desirable to continue to achieve emission standards while the engine speed comes up to meet torque demand. To help determine how such operations as elevated idle are effecting catalyst light-off, one or more exhaust temperature sensors56may be used, which can be positioned either upstream or downstream or both upstream and downstream of the catalytic converter52. A mass fuel flow sensor58can also be provided.

Referring toFIG. 2and again toFIG. 1, according to several aspects, exhaust enthalpy during conditions including transient engine speed and transient engine load are used as an input in a diagnostic method defining a parameter to control engine cold start emission reduction mode. The determination of an exhaust enthalpy to identify when catalytic light-off occurs provides an alternative approach to determining exhaust measurement deviations during a prescribed steady state engine operating condition such as during elevated idle when the steady state operating condition may not be available. Exhaust enthalpy can be determined by catalytic converter input or output temperature, using for example the exhaust temperature sensor56. With continuing reference toFIG. 1, one or more temperature sensors, with only a single exhaust temperature sensor56shown as an example, are located upstream of the catalytic converter(s)52which are used to identify exhaust temperatures. Additional temperature sensors (not shown) may be positioned downstream of each catalytic converter52.

Exhaust enthalpy may also be determined by a summation of the energy input to the catalytic converters52. In this approach, exhaust enthalpy determined as an overall energy input to the catalytic converters52is calculated using the output from sensors such as the temperature sensor56, the mass air flow sensor (MAF)44and the mass fuel flow sensor58described in reference toFIG. 1.

According to several aspects, in an enthalpy summation algorithm60, an exhaust temperature62, a mass air flow64, a mass fuel flow66, and a catalytic converter warmup mode state68are each inputs to a calculation block70. In the calculation block70, it is initially identified if the catalytic converter warmup mode state is True72, which identifies the catalytic converter is at a temperature below that required for catalytic light-off, for example the catalytic converter52is at an ambient temperature. If the catalytic converter warmup mode state is True72, an exhaust enthalpy74is calculated, and a cumulative mass flow76past the catalytic converter52for the exhaust enthalpy74is also calculated. These values may each be integrated in determining if the energy and temperature conditions for catalytic converter light-off have been achieved.

The exhaust enthalpy74determined in the calculation block70can be calculated using integral equations (1) and (2) below:
QIn Flow=∫{dot over (m)}*Cp(T)*TindtEquation (1):
mIn Flow=∫({dot over (m)}air+{dot over (m)}fuel)dtEquation (2):
Where QIn Flowis the cumulative energy flow into the catalytic converter52, and mIn Flowis the cumulative mass flow going past the catalytic converter52.

As a diagnostic tool, in a following comparative block78it is determined if a) the calculated exhaust enthalpy74is greater than a predetermined enthalpy threshold, AND b) if the cumulative mass flow76is less than a predetermined cumulative mass flow threshold. If an output82from the comparative block78for items (a) and (b) above is affirmative, a diagnostic pass signal84is generated. If an output86from the comparative block78is negative, in a cumulative block88it is determined if the cumulative mass flow76is less than a predetermined mass flow threshold. If an output92from the cumulative block88is negative, a diagnostic fail signal94is generated.

If an output96from the cumulative block88is positive, in a determination block98it is determined if the catalytic converter warmup mode state68is False100and if the cumulative mass flow76is greater than a predetermined minimum threshold102. If an output104from the determination block98is negative, the program returns to the calculation block70. If an output106from the determination block98is positive, the diagnostic test is deemed indeterminate, and a diagnostic test indeterminate signal108is generated. Enthalpy into the catalytic converter52is measured until a predetermined energy level is achieved to assume catalytic converter light-off is achieved. The diagnostic compares both energy and mass flows. When energy flow is greater than mass flow, catalytic light-off can occur and the diagnostic pass is identified. If mass flow is greater than energy flow, the diagnostic fails and is repeated. The diagnostic is not time dependent, and continues unless a “fault pending” state is identified defining the indeterminate outcome. The indeterminate outcome may result for example when an engine start occurs, but the engine is shut off before a time period sufficient to achieve catalytic light-off has been reached.

Referring toFIG. 3and again toFIGS. 1 and 2, according to other aspects, a method for determining exhaust enthalpy integrates a torque reserve as a parameter for an exit strategy from catalyst warmup mode. Torque reserve is defined as a crankshaft torque potential value. A torque reserve may be available due to retarded spark timing during an engine cold start mode which delays combustion and therefore creates a difference between the potential value of torque and an actual delivered torque. Values of torque reserve are integrated over time, and upon reaching a threshold based on an exhaust flow accumulated value, the torque reserve value is used as a basis to conclude if the necessary increased exhaust enthalpy has been reached to achieve catalytic light-off.

According to a torque reserve enthalpy integration algorithm110, a catalytic converter warmup mode status112is determined at a determination block114. If an output116from the determination block114is positive, indicating the catalytic converter warmup mode is enabled, in a request step118a request for torque reserve is made to increase an exhaust temperature. Following the request for torque reserve118, in a computation block120a torque reserve is computed and integrated. The result from the computation block120is entered as a first variable into a comparison block122. A second variable, defining an energy threshold necessary to achieve catalyst light-off, is obtained from a second computation block124and entered into the comparison block122. As noted above, the energy threshold necessary to achieve catalyst light-off used as the second variable is integrated as an exhaust flow accumulated value. In the comparison block122, the second variable defining the energy threshold necessary to achieve catalyst light-off is compared to the first variable obtained from the computation block120to determine if the second variable is greater than the first variable. If an output126from the comparison block122is negative, the torque reserve available is sufficient to meet the energy threshold required for catalyst light-off, and the algorithm returns to and repeats the request step118.

If an output128from the comparison block122is positive, the torque reserve available is insufficient to meet the energy threshold required for catalyst light-off. The algorithm provides a response gate130which receives the output128from the comparison block122. In addition, if an output from the determination block114is negative, indicating the catalytic converter warmup mode is not enabled, the negative response from the determination block114is also forwarded to the response gate130. Any response received by the negative response gate130results in a flag132indicating torque reserve should not be requested, and the algorithm ends at a step134.

Referring toFIG. 4and again toFIGS. 1 through 3, according to other aspects, a method for determining exhaust enthalpy integrates a cumulative exhaust enthalpy as a parameter for an exit strategy from catalyst warmup mode. Torque reserve as defined above is applied to increase exhaust temperature. Values of exhaust enthalpy into the catalyst are integrated over time and upon reaching a threshold, the heat energy threshold for catalyst light-off is used as a basis to conclude if the necessary increased exhaust enthalpy has been reached to achieve catalytic light-off.

According to a catalyst exhaust enthalpy integration algorithm136, a catalytic converter warmup mode status138is determined at a determination block140. If an output142from the determination block140is positive, indicating the catalytic converter warmup mode is enabled, in a request step144a request for torque reserve is made to increase an exhaust temperature. Following the request for torque reserve144, in a computation block146an exhaust enthalpy into the catalyst54is computed and integrated. The result from the computation block146is entered as a first variable into a comparison block148. A second variable, defining an energy threshold necessary to achieve catalyst light-off, is obtained from a second computation block150and entered into the comparison block148. As noted above, the energy threshold necessary to achieve catalyst light-off used as the second variable is integrated as an exhaust flow accumulated value. In the comparison block148, the second variable defining the energy threshold necessary to achieve catalyst light-off is compared to the first variable obtained from the computation block146to determine if the second variable is greater than the first variable. If an output152from the comparison block148is negative, the exhaust enthalpy available is sufficient to meet the energy threshold required for catalyst light-off, and the algorithm returns to and repeats the request step144.

If an output154from the comparison block148is positive, the exhaust enthalpy available is insufficient to meet the energy threshold required for catalyst light-off. The algorithm provides a response gate156which receives the output154from the comparison block148. In addition, if an output from the determination block140is negative, indicating the catalytic converter warmup mode is not enabled, the negative response from the determination block140is also forwarded to the response gate156. Any response received by the negative response gate156results in a flag158indicating torque reserve should not be requested, and the algorithm ends at a step160.

A system and method for determining exhaust enthalpy during conditions including transient engine speed and transient engine load of the present disclosure offers several advantages. These include the use of exhaust enthalpy as an input to a diagnostic method as opposed to the use of measurement deviations from a prescribed steady engine operating condition. The present method also provides a generalized strategy for converter warm-up and the ability to diagnose a cold start emissions strategy during off-idle operations. The present method is energy based and can be used in both steady state and transient engine speed and load conditions. The strategy uses exhaust enthalpy which accounts for total heat energy into the catalyst, and applies as a maintenance parameter, and therefore can be applied during all driving conditions. According to several aspects, the present method provides two exit strategies, including a first strategy related to an amount of torque reserve needed to increase exhaust temperature to achieve catalyst light-off, and a second strategy related to a total exhaust enthalpy into the catalyst to achieve catalyst light-off.