Abstract:
A control system for controlling the fueling of an engine assembly. The engine assembly includes an internal combustion engine, a fuel control system, a fuel vapor storage canister and a purge control system for purging the fuel vapor storage canister. The control system includes a purge fuel vapor measuring device for measuring an amount of purge fuel vapor flowing from the vapor storage canister to the internal combustion engine, a fuel corruption estimating device for estimating an amount of fuel corruption as a function of the amount of purge fuel vapor flowing from the vapor storage canister to the internal combustion engine and a controller for adapting the control of the internal combustion to the estimate of the amount of fuel corruption. A method for fueling an engine assembly having an internal combustion engine is also provided.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to purge control systems for internal combustion engines and more particularly to a method for controlling a vapor storage canister for a purge control system of an internal combustion engine. 
     2. Discussion 
     Stricter Federal and California evaporative emission standards for automotive vehicles require that Federal Test Procedure (FTP) emission levels be measured with a loaded vapor canister. The standards require that the automotive vehicle undergo an FTP emission cycle, after which the vehicle is placed in a variable temperature shed and resting loss emissions re measured over a predetermined time period. 
     Under normal automotive vehicle operating conditions, fuel vapors present within the vehicle&#39;s fuel tank are temporarily stored inside a vapor storage canister. These devices are known in the art as purge canisters or vapor storage canisters. A typical vapor storage canister contains a quantity of activated charcoal as the preferred medium for storing the fuel vapors. The storage capacity of the vapor storage canister is limited by the mass and volume of charcoal after becoming saturated with absorbed fuel vapor. Therefore, it is necessary to periodically purge the vapor storage canister with fresh air to remove the fuel vapor and restore the storage potential of the canister. 
     Typically, a purge control system is used to purge the vapor storage canister. The purge control system includes a purge solenoid which is turned ON and OFF to control fuel vapor purged from the vapor storage canister. An example of such a purge control system is disclosed in U.S. Pat. No. 4,821,701 to Nankee II et al. Another example of a purge control system for controlling and varying the amount of purge flow from the vapor storage canister to the internal combustion engine is disclosed in U.S. Pat. No. 5,263,460 to Baxter et al. 
     One problem associated with the use of such purge control systems is that the amount of fuel which they deliver to the internal combustion engine during a purge cycle is not quantified. Accordingly, in situations where a substantial amount of fuel vapor is being generated (e.g., where the vehicle is operating in a relatively hot environment or where the vehicle is fueled with an oxygenated fuel), operation of the purge control system in an ON condition is likely to be frequent and provide the internal combustion engine with a relatively large supply of fuel. The delivery of fuel to the internal combustion engine via the purge control system is likely to cause erratic engine operation, particularly when the vehicle is idling and a heavy load is applied to the engine, as when actuating an air conditioning compressor. 
     When the engine is idling and the purge control system is turned ON, for example, the additional fuel being delivered to the internal combustion engine causes a rich burn situation wherein the ratio of fuel to air is higher than a desired stoichiometric ratio. This situation is typically detected via an oxygen sensor. In response to the detection of a rich burn situation, the engine controller typically reduces the amount of fuel that is being delivered to the internal combustion through the primary fueling means (e.g., injectors) to return the fuel-to-air ratio to the desired stoichiometric ratio. In response to the application of a heavy load to the engine, the idle speed motor opens the throttle, causing the engine to ingest relatively more air and altering the fuel-to-air ratio to create a lean bun situation and reducing the available engine torque. The lean burn situation is the result of the failure to estimate or predict the quantity of fuel that is being delivered to the engine for combustion from the purge canister and the corresponding need to retard the rate with which the injectors are permitted to change the amount of fuel that is delivered to the engine so as to avoid over reacting to variances in the amount of fuel that is being delivered from the purge canister. The speed of the engine will vary widely until a sufficient amount of time has elapsed to permit the fuel-to-air ratio to return to the desired stoichiometric ratio. 
     Accordingly, there remains a need in the art for a device for controlling the fueling of an engine assembly which estimates the amount of fuel that is being delivered to the engine for combustion from a purge canister. There also remains a need in the art for a method of fueling an engine that more accurately accounts for the amount of fuel that is being delivered to the engine for combustion from a purge canister. 
     SUMMARY OF THE INVENTION 
     In one preferred form, the present invention provides a control system for controlling the fueling of an engine assembly. The engine assembly includes an internal combustion engine, a fuel control system, a fuel vapor storage canister and a purge control system for purging the fuel vapor storage canister. The control system includes a purge fuel vapor measuring device for measuring an amount of purge fuel vapor flowing from the vapor storage canister to the internal combustion engine, a fuel corruption estimating device for estimating an amount of fuel corruption as a function of the amount of purge fuel vapor flowing from the vapor storage canister to the internal combustion engine and a controller for adapting the control of the internal combustion to the estimate of the amount of fuel corruption. A method for fueling an engine assembly having an internal combustion engine is also provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic diagram of a vehicle constructed in accordance with the teachings of the present invention; and 
     FIG. 2 is a schematic illustration in flowchart form of the method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1 of the drawings, a vehicle constructed in accordance with the teachings of a preferred embodiment of the present invention is generally indicated by reference numeral  8 . Vehicle  8  is shown to include an engine assembly  10  having an internal combustion engine  12  and a purge control system  14 . Internal combustion engine  12  includes a fuel control system  16  for delivering a primary charge of fuel to internal combustion engine  12  for combustion. In the particular embodiment illustrated, fuel control system  16  includes a controller  18 , an oxygen sensor  20  and a plurality of fuel injectors  22 . Controller  18  includes an adaptive memory  24  and a timer  26 . Fuel injectors  22  are operable for injecting fuel into internal combustion engine  12  for subsequent combustion. Fuel injectors  22  are electronically actuated to dispense fuel into internal combustion engine, with the amount of fuel that is dispensed being proportional to the bandwidth of an electronic pulse that is operable for actuating each of the fuel injectors  22 . Oxygen sensor  20  is positioned to monitor the exhaust of internal combustion engine  12  and responsively generate an oxygen sensor signal which is employed by fuel control system  16  to determine if internal combustion engine  12  is operating at a fuel-to-air ratio which is different than a predetermined stoch ratio. 
     Purge control system  14  includes a fuel tank  30  connected by a conduit  32  to a purge or vapor storage canister  34 . Under normal operating conditions, fuel vapors form in fuel tank  30  and are directed through conduit  32  into vapor storage canister  34 . Purge control system  14  also includes a purge solenoid  36  connected by a conduit  38  to vapor storage canister  34 . Purge control system  14  is coupled to controller  18  which controls the flow (ON or OFF) of the purge solenoid  36 . Controller  18  may conventionally include a microprocessing unit, an input/output module, communication lines, and other hardware and software necessary to control tasks of engine control such as fuel to air ratios, fuel spark timing, or exhaust gas recirculation. When controller  18  turns purge solenoid ON, fuel vapor is purged from vapor storage canister  34  and through a conduit  50  and into a fuel actuator  52 . Fuel actuator  52  delivers a mixture of fuel and vapors through a conduit  54  to internal combustion engine  12 . It should be appreciated that purge control system  14  may include other sensors, transducers or the like in communication with controller  18  to carry out the method to be described. It should also be appreciated that unless otherwise detailed herein, purge control system  14  may be similar to that disclosed in U.S. Pat. Nos. 4,821,701 to Nankee II et al. and U.S. Pat. No. 5,263,460 to Baxter et al. 
     Referring to FIG. 2, the method of the present invention is schematically illustrated in flowchart form. The method begins at bubble  100  and proceeds to decision block  104  where the methodology determines if fuel control system  16  is operating in a closed loop manner. In the particular embodiment disclosed, fuel control system  16  is operating in a closed loop manner when data from oxygen sensor is employed to tailor the amount of fuel that injectors  22  dispense to maintain the fuel-to-air ratio at the predetermined stoichiometric ratio. If fuel control system  16  is not operating in a closed loop manner (e.g., during engine start-up), the methodology proceeds to bubble  102  where the methodology terminates. If the fuel control system  16  is operating in a closed loop manner in decision block  104 , the methodology proceeds to decision block  108 . 
     In decision block  108 , the methodology determines if adaptive memory  24  is permitted to update. If adaptive memory is not permitted to update, as when adaptive memory  24  is running a diagnostic program or is damaged, the methodology proceeds to bubble  102  where the methodology terminates. If adaptive memory  24  is permitted to update in decision block  108 , the methodology proceeds to decision block  112 . 
     In decision block  112  the methodology determines if the value in timer  26  exceeds a predetermined timer value. Timer  26  is employed to limit the frequency with which the methodology of the present invention is performed so as to avoid adversely affecting the operation of internal combustion engine  12 . If the value in timer  26  does not exceed the predetermined timer value, the methodology loops back to decision block  104 . If the value in timer  26  exceeds the predetermined timer value in decision block  112 , the methodology proceeds to block  116 . 
     In block  116 , the methodology causes controller  18  to control purge solenoid  36  such that the flow of purge vapor from the vapor canister  34  is OFF (i.e., fuel is not being supplied to internal combustion engine  12  from vapor canister  34  for combustion). 
     The methodology then proceeds to block  120  where a first value which is indicative of the operation of the internal combustion engine  12  when internal combustion engine  12  is not combusting fuel from the fuel vapor storage canister  34 . In calculating the first value, controller  18  monitors the oxygen sensor signal from oxygen sensor  20  and calculates a first median oxygen filter value. Controller  18  also determines a first median fuel correction value which is equal to the median fuel correction value during the times when internal combustion engine  12  is not combusting fuel from the fuel vapor storage canister  34 . In the particular example provided, the first value is equal to the product of the first median oxygen filter value and the first median fuel correction value. Those skilled in the art will understand that the first median fuel correction value tends to vary over a period of time, taking into account various factors including engine wear and the degree to which injectors  22  are plugged. Once the first median oxygen filter and the first median fuel correction values have been determined by controller  18 , the first value is then calculated by multiplying the first median oxygen filter value by the first median fuel correction value. 
     The methodology next proceeds to block  124  where controller  18  is actuated to control purge solenoid  36  such that the flow of purge vapor from the vapor canister  34  is ON (i.e., fuel is being supplied to internal combustion engine  12  from vapor canister  34  for combustion). The method then proceeds to block  128 . 
     In block  128 , the methodology calculates a second value indicative of the operation of internal combustion engine  12  when internal combustion engine  12  is combusting fuel from the vapor storage canister  34 . In calculating the second value, controller  18  monitors the oxygen sensor signal from oxygen sensor  20  and calculates a second median oxygen filter value. Controller  18  also determines a second median fuel correction value which is equal to the median fuel correction value during the times when internal combustion engine  12  is combusting fuel from the fuel vapor storage canister  34 . Those skilled in the art will understand that like the first median fuel correction value, the second median fuel correction value tends to vary over a period of time, taking into account various factors including engine wear and the degree to which injectors  22  are plugged. Once the second median oxygen filter and the second median fuel correction values have been determined by controller  18 , the second value is then calculated by multiplying the second median oxygen filter value by the second median fuel correction value. Those skilled in the art will understand that as the amount of fuel being delivered to internal combustion engine  12  via the fuel injectors  22  is known, the step of calculating the second value is analogous to measuring an amount of purge fuel vapor flow from the fuel tank to the engine and responsively producing a purge fuel vapor flow signal (i.e., the second value). 
     The methodology next proceeds to block  132  where the first and second values are employed to calculate a correction term or corruption signal that estimates the magnitude of fuel corruption. In the particular example provided, the correction term is equal to the difference between the first value and the second value and provides a number between zero (0) and one (1), with a value of zero (0) indicating no fuel corruption and a value of one (1) indicating the highest level of fuel corruption. The methodology proceeds to block  136  where timer  26  is reset and controller  18  adapts the control of the engine as a function of the correction term (corruption signal). The methodology then proceeds to decision block  140 . 
     In decision block  140 , the methodology determines if the value in timer  26  exceeds the predetermined timer value previously mentioned in decision block  112 . If the value in timer  26  does not exceed the predetermined timer value, the methodology loops back to block  128  where the second value is recalculated based on updated or current values of the second median oxygen filter and the second median fuel correction values. If the value in timer  26  exceeds the predetermined timer value in decision block  140 , the methodology proceeds to block  144  where the timer  26  is reset. Thereafter, the methodology loops back to block  116  to permit the first value to be recalculated. Those skilled in the art will understand that other predetermined conditions, such as a fuel temperature which exceeds a predetermined fuel temperature limit, may alternatively or additionally be employed to trigger the recalculation of the first value. As those skilled in the art will understand, a fuel temperature sensor  200  (FIG. 1) may be employed for monitoring the temperature of the fuel that is being delivered to engine  12  for combustion and generating a fuel temperature sensor signal in response thereto. 
     While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the description of the appended claims.