Abstract:
An engine management system for a hybrid vehicle may include a hybrid vehicle controller that selects a power source to be one of an electric propulsion system and a combustion engine. The hybrid vehicle controller may include an engine operation module configured to determine when operation of the combustion engine is required based on a predetermined set of operating parameters associated with the combustion engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/883,855, filed on Jan. 8, 2007. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to hybrid vehicles, and more specifically to engine management for hybrid vehicles. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Internal combustion engines produce drive torque that is transferred to a drivetrain. The drive torque is transferred through a transmission that multiplies the drive torque by a gear ratio. Transmissions generally include multiple gear ratios through which the drive torque is transferred. Automatic transmissions automatically shift between gear ratios based on driver input and vehicle operating conditions. Hybrid powertrains typically include an electric machine and an energy storage device (ESD). In one mode, the electric machine drives the transmission using energy stored in the ESD. In another mode, the electric machine is driven by the engine to charge the ESD. 
     When operated in the first mode, the hybrid vehicle may be operated without the use of the engine. During operation in the first mode, extended periods of time may pass between consecutive operations of the engine. Due to these extended time periods of non-operation, the combustion engine may develop corrosion and lubrication issues. Additionally, when the engine is not operated, the fuel supply remains unused. When the fuel ages it may deteriorate, resulting in reduced engine performance, such as higher engine emissions when the engine is operated. Further, the on-board vapor recovery system can saturate during long periods of electric-only propulsion with fuel sloshing in the tank and when there is no purge flow through the vapor canister. 
     SUMMARY 
     Accordingly, an engine management system for a hybrid vehicle may include a hybrid vehicle controller that selects a power source to be one of an electric propulsion system and a combustion engine. The hybrid vehicle controller may include an engine operation module configured to determine when operation of the combustion engine is required based on a predetermined set of operating parameters associated with the combustion engine. 
     A method of controlling the hybrid vehicle may include providing motive power to the vehicle through the electric propulsion system, determining an elapsed time from when the combustion engine was last operated, and operating the combustion engine based on the elapsed time being greater than a predetermined value. 
     A method of controlling the hybrid vehicle may alternatively or additionally include determining the age of the fuel in a fuel reservoir for the combustion engine and determining whether engine-on operation is required based on the age of the fuel being greater than a predetermined value. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic illustration of a hybrid vehicle according to the present disclosure; 
         FIG. 2  is a functional block diagram of modules of the control module shown in  FIG. 1 ; and 
         FIG. 3  is a flow chart depicting a control logic for a hybrid vehicle according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an exemplary hybrid vehicle  10  is schematically illustrated. The hybrid vehicle  10  includes an engine  12  and an electric machine  14 , which selectively drive a transmission  16 . Hybrid vehicle  10  may be a plug-in type hybrid vehicle or any other type of hybrid vehicle that is capable of extended periods of operation without operation of engine  12 . Engine  12  is in communication with a source of fuel, such as fuel tank  18  and an on-board vapor recovery canister  19  in communication with fuel tank  18 . In one mode of vehicle operation, the electric machine  14  and the engine  12  provide drive torque to drive the transmission  16 . In this manner, fuel efficiency may be increased and emissions may be reduced. In another mode of operation, the engine  12  drives the electric machine  14  to generate power used to recharge an energy storage device (ESD)  20 , such as a battery. In another mode of operation, the electric machine  14  solely provides drive torque to the transmission  16  using energy from the ESD  20 . In yet another mode of operation, the engine  12  may solely provide the requisite drive torque to the transmission  16 . 
     The engine  12  and the electric machine  14  can be coupled via a belt-alternator-starter (BAS) system (not shown) that includes a belt and pulleys. Alternatively, the engine  12  and the electric machine  14  can be coupled via a flywheel-alternator-starter (FAS) system (not shown), wherein the electric machine  14  is operably disposed between the engine  12  and the transmission  16 . It is anticipated that other systems can be implemented to couple the engine  12  and the electric machine  14  including, but not limited to, a chain or gear system that is implemented between the electric machine  14  and a crankshaft. 
     The transmission  16  can include, but is not limited to, a continuously variable transmission (CVT), a manual transmission, an automatic transmission, an electrically variable hybrid transmission, and an automated manual transmission (AMT). Drive torque is transferred from the engine  12  and/or electric machine  14  to the transmission  16  through a coupling device  22 . The coupling device  22  can include, but is not limited to, a friction clutch or a torque converter depending upon the type of transmission implemented. In the case of a CVT, the coupling device  22  includes a torque converter and a torque converter clutch (TCC). The transmission  16  multiplies the drive torque through one of a plurality of gear ratios to drive a vehicle driveline (not shown). 
     A control module  24  regulates operation of the vehicle  10  based on the control system of the present disclosure. A current sensor  26  generates a current signal that is sent to the control module  24  and a voltage sensor  28  generates a battery voltage signal that is sent to the control module  24 . The control module  24  determines a state of charge (SOC) of the ESD  20  based on the current and voltage signals. There are several methods that can be implemented to determine the SOC. An exemplary method is disclosed in commonly assigned U.S. Pat. No. 6,646,419, issued on Nov. 11, 2003 and entitled State of Charge Algorithm for Lead-Acid Battery in a Hybrid Electric Vehicle, the disclosure of which is expressly incorporated herein by reference. 
     Control module  24  may signal operation of the engine  12  when required, as discussed below. Control module  24  may provide and/or receive signals for operation of a fuel pump  30  when operation of engine  12  is required. Control module  24  may receive signals from vehicle sensors  32 , such as ambient temperature, and signals from a fuel level sender  34  indicative of a fuel level in fuel tank  18 . Control module  24  may provide a signal to a vehicle display  36  indicative of vehicle operating conditions such as fuel age and elapsed time between engine operations. 
     With additional reference to  FIG. 2 , control module  24  may include a fuel fill module  38 , a fuel age module  40 , a fuel quality module  42 , an engine last start module  44 , an oil deterioration by fuel dilution module  45 , a vapor recovery canister loading module  47 , and an engine operation module  46 . The fuel fill module  38  may determine whether fuel has been added to fuel tank  18  and the quantity added. Fuel fill module  38  is in communication with fuel age module  40 . Fuel age module  40  may determine an age of the fuel in fuel tank  18 . The fuel age determination may be at least partially based on the fuel fill information provided by fuel fill module  38 . Fuel age module  40  is in communication with engine operation module  46  and fuel quality module  42 . 
     Fuel quality module  42  may determine a deterioration level of the fuel in fuel tank  18 . The determination of fuel deterioration level may be at least partially based on the fuel age information provided by fuel age module  40  and ambient storage temperature from vehicle sensors. Fuel quality module  42  may receive and evaluate information relating to fuel type, such as gasoline or ethanol blends, and provide a signal to engine operation module  46  to operate the engine  12  at the next vehicle start-up. Engine last start module  44  may determine the elapsed time between consecutive operations of engine  12 . Engine last start module  44  is in communication with engine operation module  46 . 
     Oil deterioration by fuel dilution module  45  may be in communication with engine operation module  46 . Oil deterioration by fuel dilution module  45  may determine the condition of engine lubricating oil based on a fuel dilution level thereof. Vapor recovery canister loading module  47  may be in communication with engine operation module  46 . Vapor recovery canister loading module  47  may determine the canister loading through vehicle driving statistics and temperature information. Engine operation module  46  may determine whether engine-on operation is required. 
     As seen in  FIG. 3 , the flow chart illustrates control logic  100  providing a method of controlling hybrid vehicle  10 . Once vehicle  10  has been powered on, determination block  101  determines whether a manual engine-start override is desired. If a manual engine-start override is desired, an engine start flag set and stored in control module  24  during a previous iteration may be reset at control block  103 . Control logic  100  may then proceed to determination block  102 . If a manual engine-start override is not desired, control logic  100  may proceed to determination block  102 . Determination block  102  evaluates whether an engine start flag was set and stored in control module  24  during a previous operation of vehicle  10 . If an engine start flag was previously set, control logic  100  proceeds to control block  104 , where engine  12  is automatically started. Engine  12  may then be operated for a predetermined period of time. Control logic  100  then proceeds to control block  106 , where the driver of vehicle  10  is notified of the reason for the engine start. After notification, control logic  100  proceeds to control block  108 . Referring to determination block  102 , if no flag was set during previous operation of vehicle  10 , control logic  100  proceeds to control block  108  as well. 
     Control block  108  determines the type of fuel used in vehicle  10 . This determination may be based on an input from a sensor or a driver input. Once the fuel type is determined, control logic  100  proceeds to determination block  110 . 
     Determination block  110  evaluates whether fuel has been added to fuel tank  18 . If fuel has been added, control logic  100  proceeds to control block  112  where a fuel age is reset within control module  24  to an adjusted value. Control logic  100  then proceeds to control block  114 . If fuel has not been added, control logic  100  proceeds to control block  114  as well. 
     Control block  114  determines a fuel quality level indicated by an age and deterioration level of the fuel. Fuel age and deterioration level may be determined based on a number of inputs including ambient temperature measurements from vehicle sensors  32 , calibration values, fuel tank level measurements from fuel level sender  34 , elapsed time between fuel fills and the amount of fuel added during fuel fills. Each of these inputs may be stored within or provided to control module  24 . Control logic  100  then proceeds to control block  116 . 
     Control block  116  determines operating criteria for engine  12 . Specifically, control block  116  begins with a nominal set of engine-on criteria. These criteria may include operating engine  12  when the load on ESD  20  exceeds a predetermined value or when the state of charge of ESD  20  falls below a predetermined level. Using the fuel age and deterioration level, or fuel quality level, determined at control block  114 , engine-on operating criteria may be biased toward an engine-on condition. For example, the values of maximum load on ESD  20  and the minimum charge level required prior to an engine-on condition may be adjusted to increase the occurrence of an engine-on condition. This may reduce the overall time that fuel will remain in fuel tank  18  unused. Control logic  100  may then proceed to control block  118 . 
     Control block  118  notifies the driver of a fuel age. The notification may include an indication of the amount of time since fuel was last used or some other indication of fuel aging. Control logic  100  then proceeds to determination block  120 . 
     Determination block  120  evaluates whether an elapsed time between engine-on conditions has exceeded a predetermined limit. Engine  12  may require a certain frequency of operation to ensure proper lubrication and corrosion control. If the elapsed time between engine-on conditions has exceeded a predetermined time limit, control logic  100  proceeds to control block  122  where an engine start flag is set. The engine start flag may be stored by control module  24  and may initiate an engine-on condition during a subsequent vehicle use when detected at determination block  102 . Alternatively, the engine start flag may initiate an engine-on condition automatically when set. Control logic  100  may then proceed to determination block  124 . At determination block  120 , if the elapsed time between engine starts does not exceed the predetermined limit, control logic  100  also proceeds to determination block  124 . 
     Determination block  124  evaluates whether a fuel age has exceeded a predetermined limit. If the fuel age has exceeded the predetermined time limit, control logic  100  proceeds to control block  126  where an engine start flag is set. The engine start flag may initiate an engine-on condition during a subsequent vehicle operation when detected at determination block  102 . Control logic  100  may then proceed to determination block  128 . At determination block  124 , if fuel age does not exceed the predetermined limit, control logic also proceeds to determination block  128 . 
     Determination block  128  evaluates whether the oil is diluted by fuel beyond a predetermined limit. If the oil dilution has exceeded the predetermined limit, control logic  100  proceeds to control block  130  where an engine start flag is set. The engine start flag may initiate an engine-on condition during a subsequent vehicle operation when detected at determination block  102 . Control logic  100  may then proceed to determination block  132 . If the oil dilution has not exceeded the predetermined limit, control logic  100  also proceeds to determination block  132 . 
     Determination block  132  evaluates whether the vapor canister is loaded by fuel vapor beyond a predetermined limit. If the vapor loading has exceeded the predetermined limit, control logic  100  proceeds to control block  134  where an engine start flag is set. The engine start flag may initiate an engine-on condition during a subsequent vehicle operation when detected at determination block  102 . Alternatively, the engine start flag may initiate an engine-on condition automatically when set. Control logic  100  may then terminate. If the vapor loading has not exceeded the predetermined limit, control logic  100  may terminate. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.