Method for operating a hybrid powertrain system in a plug-in hybrid vehicle

Abstract

A method for operating a hybrid powertrain system (20) in a plug-in hybrid vehicle (5), comprising: first operating the hybrid powertrain system (20) in a charge-depleting mode to reduce a state of charge, SOC, of ​​an energy storage device (25); and in response to a driver request, determine whether the SOC is less than a maximum threshold; if the SOC is less than a maximum threshold, determining whether conditions for opportunity charging are met, the conditions for opportunity charging including that the vehicle speed is within an allowable window, that an output torque request is within an allowable window, and that the internal combustion engine (40) is not operating in a catalyst light-off mode; when conditions for opportunity charging are met, operating the hybrid powertrain system (20) in an opportunity charging mode comprising operating an internal combustion engine (40) to generate torque to charge the energy storage device (25) to opportunity charge the energy storage device (25) to increase the SOC of the energy storage device to the maximum threshold during a trip prior to reaching a minimum SOC associated with initiating operation in a charge-sustaining mode.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for operating a hybrid powertrain system in a plug-in hybrid vehicle. BACKGROUND

[0002] Powertrain architectures for vehicles include hybrid powertrain systems that utilize multiple torque-generating devices, including internal combustion engines and non-combustion torque machines, that transmit mechanical torque, either directly or through a transmission device, to a drive system for use as propulsive force. Known internal combustion engines can also generate torque that can be transmitted to a torque machine to produce power storable as potential energy in an on-board storage device. An on-board storage device can be coupled to a remote power supply for charging during a period when the vehicle is stationary, e.g., parked. Vehicles designed with an on-board storage device that can be coupled to a remote power supply are often referred to as plug-in hybrids.

[0003] Common internal combustion engines include multi-cylinder heat engines that convert stored fuel into mechanical power through combustion processes. Common non-combustion torque machines include multi-phase electric motors that convert electrical power into mechanical power. An electrical energy storage device, such as a battery, stores direct electrical power, which can be transferred and converted to alternating electrical power using an inverter device to drive the multi-phase electric machine to generate mechanical power to perform work. Parameters associated with energy storage devices include a state of charge (SOC) and battery efficiency.

[0004] Hybrid powertrain systems can operate in charge-sustaining and charge-depleting modes. A hybrid powertrain system operating in a charge-sustaining mode generates mechanical power from an internal combustion engine and an electric machine to a vehicle propulsion system in response to a driver torque demand, while maintaining the SOC of the energy storage device within a predetermined window, e.g., during a trip, at an SOC between 50% and 60%. Thus, power outputs from the internal combustion engine and the electric machine are controlled to respond to the driver torque demand and to temporarily charge and discharge the energy storage device during each trip.

[0005] A hybrid powertrain system operating in a charge-depleting mode generates mechanical power from an internal combustion engine and an electric machine to a vehicle propulsion system in response to a driver torque request and while depleting a SOC of the energy storage device from an initial SOC to a predetermined minimum SOC during a trip. When the SOC decreases to the predetermined minimum SOC during a trip, the hybrid powertrain system begins operating in the charge-sustaining mode, which includes operation to maintain the SOC at or near the minimum SOC. Thus, power outputs from the internal combustion engine and the electric machine are controlled to respond to the driver torque request while discharging the energy storage device during each trip.A hybrid powertrain system operating as a plug-in hybrid system and operating in a charge-depleting mode preferably charges the energy storage device during periods when the vehicle is not operating, using available electrical power, e.g., from a power grid.

[0006] US 2011 / 0 166 733 A1 discloses a charge state maintenance function and energy management for a battery of a plug-in hybrid vehicle. DE 10 2010 018 447 A1 describes a method for controlling a vehicle powertrain and a vehicle control system. US 6 362 602 B1 discloses a strategy for controlling a battery charge state based on vehicle speed. US 2012 / 0 072 063 A1 discloses a hybrid vehicle and a control method therefor.

[0007] Further prior art can be found in DE 10 2011 051 439 A1, which, however, was not yet known on the priority date relevant here.

[0008] It is an object of the present invention to provide an improved method for managing charge degradation in a plug-in hybrid vehicle. SUMMARY

[0009] This object is achieved by the features of patent claim 1. Advantageous further developments are described in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] One or more embodiments will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 illustrates a plug-in hybrid vehicle (PHV) including an embodiment of a hybrid powertrain system coupled to a propulsion system and controlled by a control system according to the invention; Fig.Figure 2 illustrates a charge management control scheme for controlling the operation of a PHV according to the invention: Fig. 3 shows a process according to the invention for enabling a HOLD+ SOC strategy, which includes determining whether the conditions for using the HOLD+ SOC strategy, which includes opportunity charging to increase the SOC, are met; and Fig. 4 illustrates several battery discharge curves for a PHV operating according to the charge management control scheme of Fig. 2 and Fig. 3 works according to the invention. DETAILED DESCRIPTION

[0011] Referring now to the drawings, in which the figure is for the purpose of illustrating certain exemplary embodiments only, Fig.1 schematically illustrates a plug-in hybrid vehicle (PHV) 5 including a hybrid powertrain system 20 coupled to a propulsion system 60 and controlled by a control system 10. The PHV 5 described herein is configured as a hybrid electric vehicle utilizing an internal combustion engine 40 and first and second electrically operated torque machines 35 and 36, respectively. The PHV 5 described herein is provided to illustrate the concepts of this invention applicable to other configurations of hybrid electric powertrains and other hybrid systems configured with a remotely chargeable, non-combustion onboard energy storage system 25, including, for example, a pneumatic hybrid vehicle utilizing an internal combustion engine and pneumatically operated torque machines, and a hybrid hydraulic vehicle utilizing an internal combustion engine and hydraulically operated torque machines.Like numbers refer to like elements throughout the description. The PHV 5 may be configured to operate in an electric vehicle (EV) mode or a hybrid vehicle (HV) mode. Operating the PHV 5 in the EV mode includes generating all of the propulsion torque from one or more of the torque machines 35, 36 powered by electric power. In an all-electric EV mode, the electric power comes from the energy storage system 25, e.g., an onboard electrical energy storage system 25, and the engine 40 is in a shut-down state. In a partially electric EV mode, the electric power comes from an onboard energy storage system 25 in combination with electric power from a generator device, e.g., the first or second torque machines 35, 36, that is mechanically coupled to and driven by the engine 40.Engine operation may begin and stop during operation in the partially electric EV mode. Operating the PHV 5 in the HV mode includes generating at least some drive torque by the engine 40. A portion of the drive torque may be generated by the first or second torque machines 35, 36. The HV mode may include one or more operating conditions where all drive torque is generated by the engine 40.

[0012] The hybrid powertrain system 20 utilizes communication paths 55, mechanical power paths 57, and high-voltage electrical power paths 59. The mechanical power paths 57 mechanically couple elements that generate, utilize, and / or transmit torque, including the internal combustion engine 40, the first and second torque machines 35, 36, a hybrid transmission 50, and a drive system 60. The high-voltage electrical power paths 59 electrically connect elements that generate, utilize, and / or transmit high-voltage electrical power, including the energy storage system 25, an inverter module 30, and the first and second torque machines 35, 36. The high-voltage electrical power paths 59 include a high-voltage bus 29.The communication path 55 includes high-speed data transmission lines to effect communications between various elements of the PHV 5 and may include one or more of a direct connection, a local area network bus, and a serial peripheral interface bus, and includes a high-speed communication bus 18.

[0013] The energy storage system 25 may be any suitable energy storage system. An exemplary energy storage system 25 is a high-voltage battery constructed from a plurality of lithium-ion cells. It is understood that the energy storage system 25 may include a plurality of electrical cells, ultracapacitors, and other suitable devices configured to store electrical energy on the vehicle.

[0014] The internal combustion engine 40 is preferably a multi-cylinder, direct fuel injection (SIDI) internal combustion engine that converts fuel into mechanical power through a combustion process. The internal combustion engine 40 is equipped with a plurality of sensing devices and actuators configured to monitor operation and deliver fuel to form a combustion charge to generate torque. In one embodiment, the internal combustion engine 40 is configured to operate as a spark-ignition (SIDI) engine with controlled combustion timing, and the associated engine torque is controlled by advancing or retarding the spark ignition timing. In one embodiment, the internal combustion engine 40 is configured as a spark-ignition (SIDI) engine.Spark-Ignition Direct Injection (SID) engine operating in either a spark-ignition combustion mode or a controlled compression-ignition combustion mode (HCCI). Alternatively, engine 40 is configured to operate as a compression-ignition engine with timing control of combustion, and wherein the associated engine torque is controlled by advancing or retarding the timing of fuel injection events. Engine 40 is configured to execute auto-start and auto-stop control schemes and fuel cutoff (FCO) control schemes during ongoing operation of vehicle system 5. Engine 40 is considered to be in a shut-down state when it is not receiving fuel and is not rotating. Engine 40 is considered to be in an FCO state when it is rotating but not receiving fuel.

[0015] The first and second torque machines 35, 36 preferably comprise multi-phase electric motor / generators electrically connected to the inverter module 30 and configured to convert stored electrical energy into mechanical power and convert mechanical power into electrical energy that can be stored in the energy storage system 25. The first and second torque machines 35, 36 have limitations on their power outputs in the form of minimum and maximum torques and speeds.

[0016] The inverter module 30 includes first and second inverters 32 and 33, which are electrically connected to the first and second torque machines 35, 36, respectively. The first and second torque machines 35, 36 cooperate with the respective first and second inverters 32 and 33 to convert stored electrical energy into mechanical power and to convert mechanical power into electrical energy that can be stored in the energy storage system 25. The first and second inverters 32 and 33 serve to convert high-voltage direct current to high-voltage alternating current and also serve to convert high-voltage alternating current to high-voltage direct current. Electrical power generated in the first torque machine 35 can be electrically transmitted to the energy storage system 25 via the inverter module 30 and the high-voltage bus 29, and to the second torque machine 36 via the inverter module 30.Electrical power generated in the second torque machine 36 can be electrically transmitted to the energy storage system 25 by means of the converter module 30 and the high-voltage bus 29 and to the first torque machine 35 by means of the converter module 30 and the high-voltage bus 29.

[0017] The hybrid transmission 50 preferably includes one or more differential gears and controllable clutch components to effect torque transfer over a range of speeds between the internal combustion engine 40, the first and second torque machines 35, 36, and an output member 62 connecting to the drive system 60. In one embodiment, the hybrid transmission 50 is a dual-mode transmission device configurable to transmit torque in an input-split mode or a compound-split mode. Mechanical power generated in the internal combustion engine 40 can be transferred to the first torque machine 35 via an input member 42 and to the output member 62 via the hybrid transmission 50.Mechanical power generated in the first torque machine 35 can be transferred to the internal combustion engine 40 via the hybrid transmission 50 and the input member 42, and can be transferred to the output member 62 via the hybrid transmission 50. Mechanical power generated in the second torque machine 36 can be transferred to the output member 62 via the hybrid transmission 50. Mechanical power can be transferred between the hybrid transmission 50 and the drive system 60 via the output member 62. Operating parameters associated with the transfer of mechanical power include power between the internal combustion engine 40 and the hybrid transmission 50, indicated by an input torque Ti and an input speed Ni, and power between the hybrid transmission 50 and the drive system 60, indicated by a propulsion torque To and an output speed No.The drive system 60 may include a differential gear assembly 65, which in one embodiment mechanically couples to an axle 64 or half-shaft, which mechanically couples to a ground-contacting wheel 66. The differential gear assembly 65 is coupled to the output member 62 of the hybrid powertrain system 20 and transmits output power therebetween. The drive system 60 transmits propulsive power between the hybrid transmission 50 and a road surface.

[0018] If the energy storage system 25 is a high-voltage battery, it stores potential electrical energy and electrically connects via the high-voltage bus 29 to the inverter module 30, which connects to the first and second torque machines 35, 36 to transfer electrical power therebetween. An external connector 26 electrically connects to the high-voltage battery and is connectable to an external AC power source to provide electrical power for charging the high-voltage battery during periods of vehicle inactivity.

[0019] Parameters associated with the energy storage system 25 include a state of charge (SOC), temperature, available electrical voltage, and available battery power, which are preferably monitored by the control system 10. The available battery power is represented by battery power limits that encompass an allowable range between a minimum and maximum allowable battery power, represented as minimum SOC and maximum SOC. It is understood that battery power is measured in terms of a parameter that can be regularly monitored, e.g., the SOC or another suitable parameter. The allowable battery power limits are preferably set at threshold values ​​to prevent either overcharging or overdischarging of the energy storage system 25, which may result in damage that reduces its service life.

[0020] The PHV 5 may utilize an electric power management system that includes a charge-harvesting mode and a charge-sustaining mode. The terms "charge-harvesting" and "charge-sustaining" define and refer to operating modes for the use and management of stored electric power in a hybrid vehicle, e.g., the PH5, during a trip. By definition, a trip includes vehicle operation during a single key-on cycle by a driver. During each trip, the PHV 5 operates in a charge-harvesting mode to generate drive torque using power solely from the high-voltage battery through the torque machines 35, 36 until the SOC of the energy storage system 25 is less than a minimum threshold, as long as the first and second torque machines 35, 36 can generate sufficient drive torque to respond to an output torque request.When the SOC of the energy storage system 25 reaches the minimum threshold, the internal combustion engine 40 may be activated to generate torque for propulsion torque generation or electric power generation, or both. The PHV 5 operates in the charge-sustaining mode to generate propulsion torque using both the internal combustion engine 40 and the torque machines 35, 36 with the intention of maintaining the SOC of the energy storage system 25 within a predetermined range of the minimum threshold.

[0021] The magnitudes of threshold conditions described herein are determined and correspond to system requirements, including minimum and maximum thresholds for the SOC of the energy storage system 25. The PHV 5 is also configured to effect opportunity charging of the energy storage device by utilizing the engine to drive the first or second torque machine 35, 36 to generate electrical power, preferably when the engine is operating at or near peak engine operating efficiency. Other forms of electrical charging during ongoing vehicle operation include, for example, regenerative braking.

[0022] The control system 10 includes a control module 12 signal-connected to a driver interface 15. The control module 12 includes a low-voltage power supply for providing regulated electrical power thereto. The driver interface 15 includes a plurality of human-machine interface devices through which the vehicle driver commands and controls the operation of the PHV 5, including, for example, an ignition switch to enable a driver to initiate vehicle operation via a key-on operation, an accelerator pedal, a brake pedal, a transmission range selector (PRNDL), cruise control, and a load selector actuator 14. The vehicle driver's commands include a driver torque request indicating a driver request for a magnitude of propulsion torque supplied to the drive system 60 to effect vehicle acceleration.Vehicle acceleration includes positive and negative acceleration events. The charge selector actuator 14 may be in the form of a switch or other suitable device by which the vehicle driver indicates a preferred powertrain operating mode. The preferred powertrain operating modes preferably include selecting a charge-depleting mode, which includes operating in an EV mode, and a charge-sustaining mode, which includes operating a HOLD SOC strategy or a HOLD+ SOC strategy, which includes operating the hybrid powertrain system to opportunity charge the energy storage device to increase the SOC of the energy storage device.

[0023] Although the control module 12 and the driver interface 15 are shown as individual, separate elements, such representation is for ease of description. It should be understood that the functions described as being performed by the control module 12 may be combined in one or more devices, e.g., implemented in software, hardware, and / or application-specific integrated circuitry (ASIC) and sub-circuitry that are separate and distinct from the control module 12. It should be understood that information transfer to and from the control module 12 may be accomplished using the communication paths 55, including, e.g., the high-speed communication bus 18. The control module 12 is preferably signal-coupled and operatively connected to the individual elements of the hybrid powertrain system 20 by means of the high-speed communication bus 18.The control module 12 is signal-connected to the sensing devices of the energy storage system 25, the inverter module 30, the first and second torque machines 35 and 36, the internal combustion engine 40, and the hybrid transmission 50, respectively, to monitor operation and determine parameters thereof.

[0024] Control module, module, controller, ECU, control unit, processor, and similar terms mean one or more combinations of one or more application-specific integrated circuits (ASICs), electronic circuitry, central processing unit(s) (preferably microprocessor(s)), and associated memory and storage (read-only, programmable read-only, random access, hard disk, etc.) that execute one or more software or firmware programs or routines, combinational logic circuitry, input / output circuitry, and components to provide the described functionality. Software, firmware, programs, instructions, routines, code, algorithms, and similar terms mean any set of instructions executable by an ECU, including calibrations and lookup tables.The control module includes a set of control routines that are executed to provide the desired functions. Routines are executed, for example, by a central computer and serve to monitor inputs from sensing devices and other networked control modules and to execute control and diagnostic routines to control the operation of actuators. The routines can be executed at regular intervals, for example, every 3.125, 6.25, 12.5, 25, and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, routines can be executed in response to the occurrence of an event.

[0025] Monitored parameters of the internal combustion engine 40 preferably include engine speed, engine torque or load, and temperature, including input torque Ti and input speed Ni. Monitored parameters of the hybrid transmission 50 preferably include speeds, including propulsion torque To and output speed No, and hydraulic pressure at multiple locations, from which parameters, including the use of specific torque-transfer clutches, can be determined. Monitored parameters of the first and second torque machines 35, 36 preferably include speeds and power flows, e.g., a flow of an electric current, from which motor torque can be determined. Monitored parameters of the energy storage system 25, in one embodiment, may include battery power, SOC, and battery temperature.

[0026] The control module 12 operatively interfaces the actuators of the inverter module 30, including the first and second inverters 32 and 33, the internal combustion engine 40, and the hybrid transmission 50, to control their operation according to executed control schemes stored in the form of routines and calibrations. It will be appreciated that, depending on torque inputs and operating conditions, both the first and second inverters 32 and 33 convert electrical power in a manner suitable for generating torque with one or both of the first and second torque machines 35, 36 and convert mechanical power in a manner suitable for generating electrical power with one or both of the first and second torque machines 35, 36.

[0027] The control module 12 executes control schemes 11 to control operation of the engine 40 in coordination with the first and second torque machines 35, 36 to control a transfer of mechanical power to the drive system 60 in response to the driver torque request concurrently with the controlling operation of the inverter module 30 to control the flow of electrical power. Such control schemes include balancing operation of the engine 40 with allowable power limits associated with the energy storage system 25. This includes controlling operation of the engine 40 to achieve a preferred engine speed / load operating point that achieves peak or otherwise preferred efficiency.

[0028] Fig. Figure 2 illustrates a charge management control scheme 200 for controlling the operation of a PHV, e.g., the one described with reference to Fig.1 described PHV 5. Table 1 is used as a key for Fig. 2, where the fields designated by numbers and the corresponding functions are defined as follows. Table 1 FIELD FIELD CONTENT 202 Key-In 204 Monitor SOCSelect charge-sustaining mode or charge-depleting mode 206 Is HOLD+ SOC strategy activated? 208 Working in a charge-reducing mode 210 Controlling engine ON / OFF in response to output torque demand, battery power / SOC, and engine torque constraints 212 Is SOC > SOC_HOLD+ maximum threshold? 214 Hold SOC at current value using SOC_HOLD strategy 216 Are the intermediate charging conditions met? 218 Use of the HOLD+ SOC strategy including opportunity charging to increase SOC 220 Hold SOC at current value using SOC_HOLD strategy 230 Working in charge-sustaining mode to maintain SOC

[0029] The charge management control scheme 200 triggers operation with a key-on (202) of the vehicle. Initially, the PHV preferably operates in the all-electric EV mode, which includes the charge-depleting mode, if the battery was fully charged using a remote power supply during an immediately preceding key-off period. Battery performance parameters are regularly monitored, including those from which the SOC can be determined. Based on the SOC, the charge-sustaining mode or the charge-depleting mode is selected. In one embodiment, the charge-sustaining mode is selected only when the SOC decreases to a minimum SOC threshold, triggering operation of the powertrain system in the charge-sustaining mode, which includes engine operation to maintain the battery SOC at or above the minimum SOC threshold (204).If the PHV is operating in the charge-sustaining mode (204)(1), the PHV continues to operate in the charge-sustaining mode (230) and execution of this iteration of the charge management control scheme 200 ends (232).

[0030] If the PHV is operating in the charge-depleting mode (204)(0), it is determined whether operation in a HOLD+ SOC strategy has been activated by the vehicle driver (206). If operation in the HOLD+ SOC strategy has not been activated by the vehicle driver (206)(0), the PHV operates in the charge-depleting mode (208), with the engine selectively operating in response to vehicle operating parameters, including an output torque demand, a present battery power, and output torque limitations of the first and second electrically powered torque machines 35, 36 (210). Execution of this iteration of the charge management control scheme 200 ends.

[0031] If the HOLD+SOC strategy has been activated by the vehicle driver (206)(1), a determination is made as to whether the SOC is greater than a maximum HOLD+SOC threshold (212). The maximum HOLD+SOC threshold has a calibratable magnitude that can range from the minimum SOC threshold associated with charge-sustaining mode to a charge-termination SOC associated with a maximum SOC charge. The maximum HOLD+SOC threshold, in one embodiment, is a 65% SOC. If the SOC is greater than the maximum HOLD+SOC threshold (212)(1), the PHV preferably operates to maintain the SOC at its current value using a HOLD SOC strategy (214). If the SOC is less than the HOLD+SOC threshold (212)(0), a determination is made as to whether opportunity charging conditions are met (216).If the conditions for opportunity charging are not met (216)(0), the PHV operates to maintain the SOC at its current value using the HOLD SOC strategy (220). If conditions for opportunity charging are met (216)(1), the PHV uses the HOLD+ SOC strategy to opportunity charge the battery to raise the SOC to the HOLD+ SOC threshold (218). Alternatively, the charge management control scheme 200 may operate to allow the SOC to be fully depleted to the minimum SOC threshold associated with the charge-sustaining mode before allowing opportunity charging of the battery by operating the HOLD+ SOC strategy to raise the SOC to the HOLD+ SOC threshold. The HOLD+ SOC strategy involves operating the PHV in either charge-depleting mode or charge-sustaining mode with the possibility of opportunity charging when conditions are met.Stored energy can then be used later in a drive cycle to enable operation in the charge-depleting mode again and allow operation in the all-electric EV mode.

[0032] Fig. 3 illustrates a process 300 for activating the HOLD+ SOC strategy, which includes determining whether the conditions for utilizing the HOLD+ SOC strategy, including opportunity charging to raise the SOC, are met. The process 300 may be used as an embodiment of block 216 of the charge management control scheme 200. Table 2 is provided as a key for Fig. 3, with the fields designated by numbers and the corresponding functions listed as follows. Table 2 FIELD FIELD CONTENT 302 Go to Hold+ Load 304 Are there system errors? 306 Catalyst light-off mode activated? 308 Vehicle speed within the permitted window? 310 Output torque requirement within the permissible window? 312 Other conditions met? 318 Use of the HOLD+ SOC strategy including opportunity charging to increase SOC 320 Working in charge-maintaining mode (HOLD SOC strategy) to maintain SOC

[0033] If the HOLD+ SOC strategy is activated, such as with reference to Fig.2 (302), whether the conditions for opportunity charging are met is determined by evaluating several vehicle and powertrain conditions. As shown, the operating conditions are evaluated sequentially. It is understood that the operating conditions may be evaluated simultaneously or in any selected order without limitation. The operating conditions selected for evaluating opportunity charging are related to determining whether the engine is operating at or near a peak efficiency level or whether any engine or vehicle faults preclude opportunity charging.

[0034] The operating conditions include determining whether any system faults, such as on-board diagnostic (OBD) faults, have been detected (304) that preclude opportunity charging. For example, faults that preclude opportunity charging include excessive high-voltage battery temperature, a high-voltage battery current sensing fault, a high-voltage battery capacity test fault, and a fault that activates a vehicle malfunction indicator lamp (MIL). If OBD faults are present (304)(1), the PHV operates to maintain the SOC at its current value using the HOLD SOC strategy (320). If no OBD faults are present (304)(0), opportunity charging is not disabled by this operating condition.

[0035] The operating conditions include determining whether the engine is operating in a catalyst light-off mode (306). This precludes avoiding operating the engine for battery charging concurrently with operating the engine to effect catalyst light-off. If the engine is operating in a catalyst light-off mode (306)(1), the PHV operates to maintain the SOC at its current value using the HOLD SOC strategy (320). If the engine is not operating in a catalyst light-off mode (306)(0), opportunity charging is not disabled by this operating condition.

[0036] The operating conditions include determining whether the vehicle speed is within an allowable speed window, i.e., greater than a minimum speed associated, for example, with idle or low-speed operation, but less than a maximum speed associated, for example, with high-speed operation (308). This excludes avoiding running the engine for battery charging during vehicle operating conditions that include low vehicle speed / stopping, such as those encountered in slow-moving traffic conditions. If the vehicle speed is not within an allowable speed window (308)(0), the PHV operates to maintain the SOC at its current value using the HOLD SOC strategy (320).If the vehicle speed is within a permissible speed window (308)(1), opportunity charging is not deactivated by this operating condition.

[0037] The operating conditions include determining whether an axle torque request, i.e., an output torque request from the vehicle driver, is within a predetermined calibratable window (310). This avoids operating the engine for battery charging during vehicle operating conditions where the powertrain system is unable to meet an output torque request. If the axle torque request is not within a predetermined calibratable window (310)(0), the PHV operates to hold the SOC at its present value using the HOLD SOC strategy (320). If the axle torque request is within a predetermined calibratable window (310)(1), opportunity charging is not disabled by this operating condition.

[0038] The operating conditions include determining whether other conditions are met (312). Such conditions may include avoiding vehicle operating conditions at operating points that negatively affect drivability or NVH. Such conditions may only include allowing the use of the HOLD+ SOC strategy during vehicle operation when the SOC is below a predetermined threshold. If these conditions are not met (312)(0), the PHV operates to maintain the SOC at its current value using the HOLD SOC strategy (320). If these conditions are met (312)(1), opportunity charging is not disabled by this operating condition.

[0039] The HOLD+ SOC strategy is utilized, and opportunity charging is enabled when all of the aforementioned conditions are met (318). The process 300 for enabling the HOLD+ SOC strategy is preferably executed iteratively during operation, with a determination being made at each iteration to either utilize the HOLD+ SOC strategy to temporarily increase the battery SOC or utilize the HOLD SOC strategy to maintain the battery SOC at its current value.

[0040] Fig. Figure 4 graphically shows several battery discharge curves for an embodiment of the PHV 5 operating according to the charge management control scheme 200 described with reference to Fig. 2 and Fig.3. The battery SOC is shown on the vertical axis (410) with a maximum value 406 of 100%, in relation to the vehicle operating time on the horizontal axis (420). The battery SOC is an example of a suitable battery parameter. Other battery parameters with a similar effect may be used.

[0041] Line 412 shows the SOC in relation to operating time with the PHV operating in the charge-depleting mode. As shown, the PHV operates in the charge-depleting mode until the SOC decreases to a minimum SOC threshold, as shown at line 402, which triggers operation in the charge-sustaining mode, which begins at time 428 and includes engine operation to maintain the battery SOC above the minimum SOC threshold.

[0042] In one operating scenario, the driver may command operation in the HOLD+ SOC strategy where the SOC is greater than a HOLD+ SOC maximum threshold, illustrated at line 404. Such operation is shown with reference to line 413 beginning at time 422. If the SOC is greater than the HOLD+ SOC maximum threshold, the PHV operates to maintain the SOC at its present value using a HOLD SOC strategy. The command to operate using the HOLD+ SOC strategy may subsequently be revoked, as shown at time 424, triggering operation in the charge-depleting mode until the SOC decreases to the minimum SOC threshold shown at line 402, which triggers subsequent operation in the charge-sustaining mode beginning at time 430.

[0043] In one operating scenario, the driver may command operation in the HOLD+ SOC strategy where the SOC is less than the HOLD+ SOC maximum threshold, which is illustrated at line 404 and is preferably pre-determined, and may be a driver-selectable amount. Such operation is shown beginning at time 426. If the SOC is greater than the HOLD+ SOC maximum threshold, the PHV does not utilize the HOLD+ SOC strategy. If the SOC is less than the HOLD+ SOC maximum threshold, the PHV operates to maintain the SOC at its current value and utilizes the HOLD+ SOC strategy to opportunity charge the battery to raise the SOC to the HOLD+ SOC threshold when opportunity charging conditions are met, as shown with reference to line 416. Line segments 415 and 417 indicate periods of operation during which opportunity charging occurs.Line segment 418 indicates another operating period in which the SOC is maintained at its current value. At time 432, the SOC increases to the HOLD+ SOC maximum threshold (line 404), at which time the HOLD+ SOC strategy disengages and the PHV operates in charge-sustaining mode. At time 434, the driver deactivates the HOLD+ SOC strategy. The PHV then operates in the charge-depleting mode shown at line segment 419 until the SOC decreases to the SOC minimum threshold shown at line 402, which triggers subsequent operation in charge-sustaining mode beginning at time 436.

[0044] The HOLD+ SOC strategy described herein can be advantageously used by a vehicle driver using a driving program that exceeds the vehicle's EV range capability, with a city drive at the end of a trip. In such circumstances, an acceptable EV experience can be achieved at the beginning of a trip with a full battery charge and at the end of a trip with EV drive and subsequent plug-in charging of the vehicle, with no degradation in fuel economy or drivability during the trip.

[0045] The HOLD+ SOC strategy involves operating in a charge-depleting mode with the possibility of opportunity charging when conditions are met.

[0046] This involves operating in charge-depleting mode with opportunity charging enabled once the battery has initially been depleted below a maximum threshold. Stored energy can then be used later in a drive cycle to re-enable charge-depleting mode and allow operation in pure electric EV mode. This allows the vehicle driver to choose when to use the battery charge and provides an opportunity for multiple charge depletion during a long-distance trip. Such operation can enable equivalent fuel economy and increased electric range for vehicle drivers who may not be able to access a stationary electric charging system.

[0047] The HOLD+ SOC strategy has been proven to achieve the same fuel economy and total trip energy cost as a system using only a charge depleting mode operated in series with a charge sustaining mode, while allowing additional working time in the all-electric EV mode over the course of the trip.

[0048] The HOLD+ SOC strategy enhances the vehicle driver's ability to fully discharge the battery during a trip and then charge the battery for use in a low-emissions zone at the end of a trip. This operation can be used in situations where a planned trip exceeds the vehicle's EV range capability and the trip involves urban driving toward the end of the trip, without compromising fuel economy or drivability over the course of the trip.

Claims

[1] A method for operating a hybrid powertrain system (20) in a plug-in hybrid vehicle (5), comprising: first operating the hybrid powertrain system (20) in a charge-depleting mode to reduce a state of charge, SOC, of ​​an energy storage device (25); and in response to a driver request, determine whether the SOC is less than a maximum threshold; if the SOC is less than a maximum threshold, determining whether conditions for opportunity charging are met, the conditions for opportunity charging including that the vehicle speed is within an allowable window, that an output torque request is within an allowable window, and that the internal combustion engine (40) is not operating in a catalyst light-off mode; when conditions for opportunity charging are met, operating the hybrid powertrain system (20) in an opportunity charging mode comprising operating an internal combustion engine (40) to generate torque to charge the energy storage device (25) to opportunity charge the energy storage device (25) to increase the SOC of the energy storage device to the maximum threshold during a trip prior to reaching a minimum SOC associated with initiating operation in a charge-sustaining mode. [2] The method of claim 1, further comprising operating the hybrid powertrain system (20) to maintain the SOC of the energy storage device at a driver-selected SOC value that is greater than the minimum SOC in response to the driver request. [3] The method of claim 2, wherein operating the hybrid powertrain system (20) to maintain the SOC of the energy storage device (25) at the driver-selected SOC value greater than the minimum SOC in response to the driver request comprises operating the hybrid powertrain system (20) in a partially electric electric vehicle mode. [4] The method of claim 1, further comprising operating the hybrid powertrain system (20) in a charge-sustaining mode when the SOC reaches the maximum threshold following operating the hybrid powertrain in the opportunity charge mode. [5] The method of claim 1, wherein operating the hybrid powertrain system (20) in the intermediate charging mode comprises operating the hybrid powertrain system (20) to charge the energy storage device (25) only when no diagnostic errors are present.

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