Hybrid electric vehicle particulate regeneration method and system

A method is applied to regenerate particulate matter in a particulate filter of a hybrid electric vehicle having a combination of a combustion engine and an electric motor for propelling the vehicle, the hybrid electric vehicle having an electrically heated catalyst disposed in flow communication with the particulate filter in an exhaust system of the vehicle. The method determines whether the combustion engine is or is not combusting fuel, and under a condition where the combustion engine is not combusting fuel, the catalyst is electrically heated until it has reached a temperature suitable to cause ignition of the particulate matter. The electric motor is used to facilitate rotation of the combustion engine at a rotational speed suitable to draw air into and be exhausted out of the combustion engine into the exhaust system, across the catalyst, and into the particulate filter to facilitate ignition of the particulate in the filter.

FIELD OF THE INVENTION

The subject invention relates to hybrid electric vehicles (HEVs), and more particularly to a particulate regeneration method and system for HEVs or plug-in hybrid electric vehicles (PHEVs).

BACKGROUND

PHEVs can have significant periods of engine-off operation during charge depletion modes of operation, creating a situation where the engine may be cold-started multiple times that potentially increases the creation and emission of particulate matter (PM).

Accordingly, it is desirable to provide a method and system for collecting and regenerating PM to avoid an increase in PM emissions in HEVs and PHEVs.

SUMMARY OF THE INVENTION

In one exemplary embodiment of the invention a method is applied to regenerate particulate matter (PM) in a particulate filter (PF) of a hybrid electric vehicle (HEV) having a combination of a combustion engine and an electric motor for propelling the HEV, the HEV having an electrically heated catalyst (EHC) disposed in flow communication with the PF in an exhaust system of the HEV. The method determines whether the combustion engine is or is not combusting fuel, and under a condition where the combustion engine is not combusting fuel, the EHC is electrically heated until the EHC has reached a temperature suitable to cause ignition of the PM in the PF. The electric motor is used to facilitate rotation of the combustion engine at a rotational speed suitable to draw air into and be exhausted out of the combustion engine into the exhaust system, across the EHC, and into the PF to facilitate ignition of the PM in the PF.

In another exemplary embodiment of the invention a particulate regeneration system is configured for a hybrid electric vehicle (HEV), the HEV having a combination of a combustion engine and an electric motor for propelling the HEV. An electrically heated catalyst (EHC) is disposed in exhaust flow communication with an exhaust system of the combustion engine. A particulate filter (PF) is disposed in exhaust flow communication with and downstream of the EHC. A controller is operably disposed in signal communication with a control system of the combustion engine, a control system of the electric motor, a control system of the EHC, and a control system of the PF, the controller being responsive to computer executable instructions which when executed by the controller facilitate a method to regenerate particulate matter (PM) in a PF. The method includes determining whether the combustion engine is or is not combusting fuel, and under a condition where the combustion engine is not combusting fuel, electrically heating the EHC until the EHC has reached a temperature suitable to cause ignition of the PM in the PF, and using the electric motor to facilitate rotation of the combustion engine at a rotational speed suitable to draw air into and be exhausted out of the combustion engine into the exhaust system, across the EHC, and into the PF to facilitate ignition of the PM in the PF.

DESCRIPTION OF THE EMBODIMENTS

In accordance with an exemplary embodiment of the invention that is directed to an HEV, or a PHEV, having both an electric motor (EM) and an internal combustion engine (ICE), a control strategy and system as described herein leverages the operational characteristics of an electrically heated catalyst (EHC) and a particulate filter (PF) to initiate regeneration of the particulate matter (PM) collected in the PF, and the operational characteristics of an unfueled ICE to provide air flow to control the PM regeneration temperature, where the PM becomes the fuel that powers the PF regeneration process, and the unfueled air flow from the ICE becomes a control element in the PF regeneration process.

In accordance with an exemplary embodiment of the invention, and with reference toFIG. 1, a particulate regeneration system100is illustrated in one-line block diagram form for use with an HEV or a PHEV. As used herein and in accordance with an embodiment of the invention, reference to an HEV is intended to encompass both HEVs and PHEVs. That said, since HEVs typically do not have a long engine-off time as compared to PHEVs due to HEVs having a comparatively smaller battery, an embodiment of the invention disclosed herein may be more applicable to PHEVs than to HEVs. However, since a PHEV is a specialized form of an HEV (plug-in versus not plug-in), the foregoing reference to the term HEV intending to encompass both HEVs and PHEVs, remains. A typical HEV, only partially depicted by reference numeral10, includes both an ICE102, and an EM104powered by a battery set106suitably sized to provide sufficient DC power to operate the EM104over a desired distance, for example. In an embodiment, the battery set106provides DC voltage in the range of 250-400Vdc and DC power in the range of 8-80 KW-hrs (Kilowatt-hours).

An exhaust manifold108directs exhaust gases from the ICE102to the regeneration system100, which in an embodiment includes an EHC110, a PF112, and a controller200. An exemplary EHC suitable for a purpose disclosed herein is an extruded EHC available from NGK Insulators, Ltd., with positive and negative electrodes placed on opposing surfaces of the extruded form. An exemplary PF suitable for a purpose disclosed herein is described in U.S. Pat. No. 7,524,360. The EHC110is disposed in exhaust flow communication with the exhaust manifold108, and the PF112is disposed in exhaust flow communication with and downstream of the EHC110. In an embodiment, a three-way catalyst (TWC)114may be optionally disposed in exhaust flow communication with and upstream of the PF112.

The controller200is operably disposed in signal communication with a control system202of the ICE102, a control system204of the EM104, a control system of the EHC110, and a control system of the PF112. In an embodiment, control system202is an electronic control module that monitors operational characteristics of the ICE102, such as fuel consumption and engine RPM (revolutions per minute) for example, and provides regulatory control to the ICE102, such as control of the fuel-air ratio used for combustion for example. In an embodiment, control system204is an electronic control module that monitors operational characteristics of the EM104, such as power consumption and torque output for example, and provides regulatory control to the EM104, such as control of the power delivery used for torque production for example. In an embodiment, control systems202and204may be integrally formed into a single electronic control module. In an embodiment, the control system of the EHC110includes an oxygen sensor (O1)205disposed in the exhaust flow upstream of the EHC110, and a switch206disposed and configured to connect and disconnect power from the battery set106to the EHC110. In an embodiment, the control system of the PF112includes an oxygen sensor (O2)208disposed in the exhaust flow downstream of the EHC110and upstream of the PF112, an inlet temperature sensor (T1)210disposed in the exhaust flow downstream of the EHC110and upstream of the PF112, an outlet temperature sensor (T2)212disposed in the exhaust flow downstream of the PF112, and delta pressure sensors (P1, P2)214,216across the inlet and outlet ports of the PF112. With reference toFIGS. 1 and 2, temperature sensors (T1, T2)210,212are closely coupled to the respective inlet and outlet ports118,120of PF112so that a temperature of particulate matter (PM)116, best seen with reference toFIG. 2, under ignition inside the PF112can be determined either directly or indirectly, such as by being inferred. In the embodiment depicted inFIG. 2, ignition of the PM116occurs first at the inlet port118and progresses toward the trapped PM116′ proximate the outlet port120. Exhaust flow entering and passing through the PF112is generally depicted inFIG. 2by reference numerals250(exhaust flow entering the PF112),252(pre-filtered exhaust flow) and254(filtered exhaust flow).

In an embodiment, controller200is responsive to computer executable instructions which when executed by the controller200facilitate a method to regenerate the PM116inside the PF112, which will now be discussed with reference toFIG. 3depicting an exemplary control flowchart (method)300.

Block302of flowchart300is representative of a start point for a hybrid PM regeneration continuous loop, where an embodiment of the invention runs the illustrated process in a continuous loop to facilitate continuous regeneration of the PM116in the PF112of the HEV10. In an embodiment, method300continuously cycles unless otherwise interrupted, such as when the HEV10is turned off and not in use for example.

At block304a determination is made as to whether the PF112requires regeneration, such as, for example, the filter is full (PF full), or not (PF not full). If it is determined that the PF112does not require regeneration, then method300continues on path330and cycles around to block302to continue with the monitoring of the state of the PF112until it does require regeneration or until the monitoring is otherwise interrupted. Such monitoring to determine whether the PF112requires regeneration or not may be accomplished using several techniques. A first technique uses the delta pressure sensors (P1, P2)214,216across the inlet and outlet ports of PF112to estimate PM loading, with a high pressure differential indicating a need for regeneration. A second technique uses a PM model to estimate PM loading. And a third technique uses mileage to estimate PM loading, with a mileage differential since the last regeneration being greater than a defined threshold indicating a need for regeneration. Any suitable technique or combination of techniques for determining a need for regeneration may be employed. The three techniques described may be employed together, where regeneration of PF112will be triggered depending on whichever technique crosses a defined calibration threshold.

If it is determined at block304that the PF112does require regeneration, then method300continues on path332to block306, where a determination is made whether the ICE102is or is not running and combusting fuel. In an embodiment, control system202provides the necessary information regarding the state of operation of ICE102. Under a condition where the ICE102is not combusting fuel, the control logic of method300passes to block308via path334where controller200causes switch206to turn on, i.e., close or activate, to electrically connect EHC110to battery set106to electrically heat EHC110until it has reached a temperature suitable to cause ignition of the PM116in PF112. In an embodiment, the ignition temperature of the PM116is 700 deg-C. At block310, controller200determines via information received from temperature sensor210whether EHC110has reached the ignition temperature or not. If not, then control logic of method300cycles back to block308via path336. When the temperature of PM116has been raised sufficiently for ignition, the logic of method300passes to block312via path338where controller200communicates with control system204to operate the EM104to facilitate rotation of the ICE102at a rotational speed suitable to draw air into and be exhausted out of the ICE102into the exhaust manifold108, across the EHC110, and into the PF112to facilitate continued ignition of the PM116in the PF112, and to turn off, i.e., open or inactivate, switch206to disconnect the EHC110from the battery set106. The EM104may be utilized to draw air into the ICE102with or without the HEV10being electrically propelled. The combination of heat from the EHC110and oxygen from the air drawn by ICE102, which when operating according to the above noted conditions acts as an air pump, ignites and maintains the ignition of the PM116in PF112. In an embodiment, the EM104acts through a transmission (TR)122, a clutched pulley and drive belt system (also referred to by reference numeral122), or any other suitable means (also referred to by reference numeral122) for mechanically coupling the EM104to the ICE102, to facilitate operation of the ICE102at a controlled RPM. While the above described logic at block312indicates that electrical power to the EHC110is turned off concurrent with EM104facilitating rotation of the ICE102, it will be appreciated that the EHC110may be turned off prior to or subsequent to the EM104being used to rotate the ICE102, depending on whether the PM116in the PF112is in a state of ignition or not, which may be determined by controller200via any suitable information from temperature sensor210for making this determination.

Under conditions where the PM116in the PF112is under ignition and the EHC110is off, control logic passes to block314where controller200monitors a temperature indicative of the PM116in the PF112, which in an embodiment is derived from information received from temperature sensor210. To maintain ignition of and regeneration of the PM116in PF112, controller200uses the EM104to raise, at block316, or lower, at block318, the RPM of the ICE102depending on whether the temperature of the PM116is indicated to be higher or lower, respectively, than a defined threshold value, such as 700 deg-C. That is, if the temperature of the PM116is higher than the threshold value, then control logic passes to block316via path340to increase the RPM of the ICE102, and if the temperature of the PM116is lower than the threshold value, then control logic passes to block318via path342to decrease the RPM of the ICE102.

At block320controller200determines whether regeneration of the PF112is complete or not, which may be determined from any information suitable for making this determination, including information received from temperature sensors210,212, delta pressure sensors214,216, or a combination thereof. For example, in an embodiment, complete regeneration may be inferred if the temperature profile between temperature sensor T1210and temperature sensor T2212has displayed over the course of regeneration a temperature rise at T1210, followed by a temperature rise at T2212, followed by a temperature fall at both T1210and T2212. In another embodiment, complete regeneration may be inferred if the pressure profile between pressure sensor P1214and pressure sensor P2216has displayed over the course of regeneration a high pressure differential between P1214and P2216followed by low pressure differential therebetween. If regeneration of the PF112is not complete, then the logic of method300cycles back to block314via path344. If regeneration of the PF112is complete, then the logic of method300continues to block322via path346where controller200signals the control system204of EM104to disconnect the EM104from the ICE102to stop rotation of the ICE102to prevent any further air from being drawn into and exhausted out of the ICE102and through the PF112. From block322, the logic of method300cycles back to block302via path348where the regeneration method300continuously cycles unless otherwise interrupted.

Referring back to block306, under a condition where the PF112was previously determined to require regeneration and the ICE102is running and combusting fuel, such as when an operator of the HEV10depresses an accelerator pedal of the HEV10resulting in a demand for speed and/or power that is beyond the capability of the EM104alone, the logic of method300passes to block324via path350where controller200signals the control unit202of the ICE102to provide an air-fuel ratio to the ICE102that is sufficient to terminate combustion, such as a ratio that is about equal to the stoichiometric ratio associated with the ICE102such that all of the oxygen used by the ICE102for combustion of the fuel is consumed, which serves to smother and extinguish combustion of the PM116in the PF112to prevent a thermal runaway condition within the PF112.

At block326the controller200monitors a temperature indicative of the temperature of the PM116in the PF112, such as using temperature sensor T1201for example, to determine whether regeneration of PF112is complete or not. If regeneration is determined to be not complete, temperature sensor T1201will register that a hot condition remains, that is, the temperature from sensor T1201will register a value higher than a defined threshold value, such as 700 deg-C for example, indicating that the combusting PM116has not yet been smothered and extinguished, resulting in the control logic of method300cycling back to block324via path353to maintain a condition that will extinguish combustion, such as the air-fuel ratio being maintained at about the stoichiometric ratio. If regeneration of PF112is determined at block326to be complete, temperature sensor T1201will register that a cold condition exists, that is, the temperature from sensor T1201will register a value lower than the defined threshold value, indicating that the combusting PM116has been smothered and extinguished, then the control logic of method300cycles back to block302via path354where the regeneration method300continuously cycles unless otherwise interrupted.

In an embodiment, the continuous regeneration loop of method300is implemented by controller200while the HEV10is being propelled by the EM104with no exhaust flow from the ICE102.

In view of the foregoing, it will be appreciated that an embodiment of the invention may be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. The present invention may also be embodied in the form of a computer program product having computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, USB (universal serial bus) drives, or any other computer readable storage medium, such as random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or flash memory, for example, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. The present invention may also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or wirelessly via electromagnetic radiation, wherein when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor-based controller, such as controller200for example, the computer program code segments configure the microprocessor to create specific logic circuits. A technical effect of the executable instructions is to regenerate PM in a PF to avoid an increase in PM emissions in HEVs and PHEVs in accordance with an embodiment of the invention described herein.

In view of the foregoing description and illustration, it will be appreciated that a method and system has been herein described having at least one of the following advantages: reduction of PM emissions resulting from multiple cold engine starts in an HEV; utilization of air flow from an unfueled ICE to facilitate control of PM regeneration in a PF; utilization of an EHC to provide sufficient catalyst temperature to initiate PM regeneration with no exhaust flow from the ICE, including periods while the HEV is propelled electrically; utilization of air flow from a rotating ICE absent fuel combustion to transfer thermal energy from the EHC to start combustion of PM on the upstream end of the PF; leverage of the inherent energy in PM for regeneration of the PF while closely controlling the combustion temperature using air flow from an unfueled ICE; a quick and fuel efficient PF regeneration process; and, controlled operation of a fueled ICE to smother and extinguish PM combustion, such as controlled utilization of the stoichiometric operation for example, to prevent uncontrolled PM regeneration temperatures.