Purge fueling delivery based on dynamic crankshaft fueling control

A fuel control system is provided for enhancing the fueling strategy of a vehicle at start up when fueling is being supplemented with purge vapors from the fuel tank. The system includes monitoring the purge vapor flow rate from the purge vapor control system to the engine at start-up. A dynamic crankshaft fuel control fuel multiplier is then calculated based on engine roughness. If the engine is operating rough during purge vapor fueling, the amount of injected fuel is adjusted according to the fuel multiplier. Once oxygen sensor feedback is available, the dynamic crankshaft fuel control fuel multiplier is recalculated based on the oxygen sensor goal voltage. If necessary, the amount of injected fuel may be readjusted with the updated fuel multiplier. Once the engine is warm, the purge vapor fueling stops and the present methodology ends.

BACKGROUND OF THE INVENTION
 1. Technical Field
 The present invention generally relates to fuel control systems and, more
 particularly, to a method of using a dynamic crankshaft fuel control fuel
 multiplier to control fuel injection in conjunction with the delivery of
 fuel vapors from a fuel tank to an engine during cold engine operation.
 2. Discussion
 Modern automotive vehicle engines commonly employ injected fuel for
 combustion. At start-up, when the engine is not fully warm, the injected
 fuel is commonly cold and in a liquid state. Cold, liquid fuel is not as
 easily vaporized as warm fuel. As such, the cold, liquid fuel poorly
 combusts at start-up. This may lead to poor emissions.
 Attempts have been made before and after combustion to improve emissions
 quality. One pre-combustion treatment has been to heat the fuel prior to
 its injection. By heating the fuel, it becomes more easily vaporized
 thereby improving its combustibility. While successful, such pretreatment
 heating is complex and expensive to implement. A common post-combustion
 treatment involves the employment of a catalyst in the engine exhaust gas
 stream. The catalyst burns the undesirable exhaust gas constituents prior
 to their passage to the atmosphere. While also successful, such
 post-combustion treatment is still expensive and complex to implement.
 Modern automotive vehicles are also commonly equipped with a fuel vapor
 purge control system. Fuel within the fuel tank tends to vaporize as
 temperatures increase. The vaporized fuel collects in the fuel tank and is
 periodically removed by the purge vapor control system. The fuel vapors
 from the tank are initially collected and stored in a canister. When the
 engine operating conditions are conducive to purging, a purge valve is
 opened thereby allowing the engine to draw the fuel vapors from the purge
 canister to the engine for combustion.
 While such purge fuel vapor control systems are very efficient, some fuel
 vapor is commonly present in the dome portion of the fuel tank at
 start-up. Advantageously, it has recently been discovered that this fuel
 vapor can be used for combustion during cold engine operation instead of
 the liquid fuel normally supplied from the fuel injectors. In this
 process, fuel vapor from the fuel tank is delivered to the engine at
 start-up while a commensurate amount of normally injected fuel is
 simultaneously removed from the fueling strategy. As such, the total
 amount of fuel delivered, i.e., fuel vapor plus injected fuel, is
 controlled.
 However, prior to the present invention, there was no way to optimize the
 amount of injected fuel in the purge vapor start-up fueling strategy for
 providing smooth engine operation. As such, the potential for rough engine
 operation exists.
 SUMMARY OF THE INVENTION
 A fuel control system is provided for enhancing the fueling strategy of a
 vehicle at start-up when fueling is being supplemented with purge vapors
 from the fuel tank. The system includes monitoring the purge vapor flow
 rate from the purge vapor control system to the engine at start-up. A
 dynamic crankshaft fuel control fuel multiplier is then calculated based
 on engine roughness. If the engine is operating rough during purge vapor
 fueling, the amount of injected fuel is adjusted according to the fuel
 multiplier. Once oxygen sensor feedback is available, the dynamic
 crankshaft fuel control fuel multiplier is recalculated based on the
 oxygen sensor goal voltage. If necessary, the amount of injected fuel may
 be readjusted with the updated fuel multiplier. Once the engine is warm,
 the purge vapor fueling stops and the present methodology ends.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 The present invention is directed towards a method of controlling the purge
 vapor fueling of an internal combustion engine during cold engine
 operation. During a cold start, fuel vapor from the fuel tank is directed
 to the engine for combustion. Simultaneously, a commensurate amount of
 injected fuel is removed from the fueling strategy such that a desired
 amount of total fuel is delivered to the engine. Thereafter, the engine is
 monitored for roughness and, if necessary, the amount of injected fuel
 delivered to the engine is adjusted based on dynamic crankshaft control.
 After exhaust gas oxygen sensor feedback becomes available, the amount of
 injected fuel is fine tuned.
 Turning now to the drawing figures, a fuel vapor purge control system is
 illustrated schematically at FIG. 1. The fuel vapor purge control system
 10 includes a fuel tank 12, a fuel vapor purge canister 14, and an
 internal combustion engine 16. The fuel tank 12 includes a fuel fill tube
 18 and a dome portion 20. The fuel tank 12 is interconnected with the fuel
 vapor purge canister 14 by a fuel tank vapor line 22. The fuel tank vapor
 line 22 is coupled to the dome portion 20 of the fuel tank 12. As is
 known, fuel vapors in the fuel tank 12 migrate through the tank vapor line
 22 and are stored in the fuel vapor purge canister 14.
 The fuel vapor purge canister 14 is interconnected with the internal
 combustion engine 16 by a purge vapor line 24. The purge vapor line 24 is
 coupled to the intake manifold 26 of the internal combustion engine 16.
 The fuel vapor purge canister 14 communicates with atmosphere by way of a
 vent line 28 coupled thereto. A canister vent valve 30 is disposed along
 the vent line 28 to selectively seal the fuel vapor purge canister 14 from
 atmosphere. A purge valve 32 is disposed along the purge vapor line 24 for
 selectively isolating the fuel vapor purge canister 14 and the fuel tank
 12 from the internal combustion engine 16.
 During normal purging operations, the canister vent valve 30 is open
 thereby allowing the fuel vapor purge canister 14 to communicate with
 atmosphere. Also, the purge valve 32, which is typically closed during
 operation of the internal combustion engine 16, is opened when engine
 operations are conducive to purging, thereby allowing the lower pressure
 within the intake manifold 26 to draw purge vapors from the fuel vapor
 purge canister 14 through the purge vapor line 24 and into the internal
 combustion engine 16 for combustion.
 At start-up, only a small amount of fuel vapors are present in the fuel
 vapor purge canister 14. In fact, the vast amount of fuel vapors reside in
 the dome portion 20 of the fuel tank 12 at start-up. By closing the
 canister vent valve 30 and opening the purge valve 32 at start-up, the low
 pressure of the intake manifold 26 draws the fuel vapors from the dome
 portion 20 of the fuel tank 12 into the internal combustion engine 16. As
 such, this fuel vapor can be used for combustion at start-up instead of
 the normal injected fuel.
 As more fully described in co-pending U.S. application Ser. No. 09,377,324
 entitled "Purge Vapor Start Feature" to Weber et al. (99-827), which is
 commonly assigned to the assignee of the present invention and hereby
 expressly incorporated by reference herein, a methodology for controlling
 the above-described fuel vapor purge system includes replacing a percent
 of liquid injected fuel with the fuel vapor from the fuel tank at
 start-up. The percent of fuel to be replaced is targeted as a function of
 time since the start-up event.
 The desired percentage of fuel vapor to be delivered is preferably the
 maximum amount possible as prescribed by certain limits. For instance, at
 idle, a minimum pulse width requirement sets the maximum limit of fuel
 vapors. The minimum pulse width sets the minimum amount of fuel that can
 be accurately injected by the fuel injectors based on the operating
 parameters of the engine. The fuel injectors are never completely turned
 off to avoid transient fuel concerns at a throttle tip-in event. During
 off idle conditions, a maximum rate of vapor flow from the fuel tank is
 the maximum limit.
 The methodology also tracks the actual mass flow rate of the fuel delivered
 from the purge system. As the mass flow rate of fuel vapor from the fuel
 tank decreases (due to the change in the pressure difference between the
 intake manifold and the fuel tank over time), the amount of fuel required
 to be injected increases. After the mass flow rate of the purge fuel vapor
 drops below a minimum threshold, complete fuel delivery is supplied by the
 fuel injectors.
 Turning now to FIG. 2, a methodology for controlling the amount of injected
 fuel to be supplied in conjunction with the purge vapors from the purge
 vapor control system is illustrated. The methodology starts in bubble 34
 and falls through to decision block 36. In decision block 36, the
 methodology determines if the engine has reached a fully warm condition.
 This may be accomplished by way of a timer or may be directly measured by
 a temperature sensor.
 If the engine is fully warm at decision block 36, start-up purge vapor
 fueling stops and the methodology advances to block 38. In block 38, the
 methodology starts normal closed loop fuel control. Normal closed loop
 fuel control does utilize fuel purge vapors and therefore the remainder of
 the present methodology is unnecessary. Therefore, from block 14, the
 methodology advances to bubble 40 and exits the subroutine pending a
 subsequent execution thereof, such as at the next start-up event.
 Referring again to decision block 36, if the engine has not yet reached a
 fully warm condition, start-up purge vapor fueling continues and the
 methodology advances to block 42. In block 42, the methodology calculates
 a dynamic crankshaft fuel control (DCFC) fuel multiplier based on engine
 roughness. According to DCFC systems, if the engine is operating too
 rough, an adjustment in fueling can be made to smooth the engine. A more
 thorough description of dynamic crankshaft fuel control fuel multiplier
 calculations can be found in U.S. Pat. No. 5,809,969 entitled "Method for
 Processing Crankshaft Speed Fluctuations for Control Applications" to
 Fiaschetti et al., which is assigned to the common assignee of the present
 application and is hereby expressly incorporated by reference herein.
 During the calculation of the DCFC fuel multiplier, the purge vapor flow
 rate from the purge vapor fuel control system is provided from data block
 44. This purge vapor flow rate may be acquired, if desired, from the
 position of the purge valve. Based on the purge vapor flow rate, the
 methodology determines a current amount of fuel being injected into the
 engine. In block 42, the methodology adjusts the amount of fuel injected
 into the engine with the calculated DCFC fuel multiplier.
 From block 42, the methodology advances to decision block 46. In decision
 block 46, the methodology determines if an exhaust gas oxygen sensor is
 ready by, for instance, determining if enough time has expired since
 start-up for the oxygen sensor to be reliable. If the oxygen sensor is not
 ready at decision block 46, the methodology advances to bubble 16 and
 exits the subroutine pending a subsequent execution thereof. However, if
 the oxygen sensor is deemed ready by the methodology at decision block 46,
 the methodology advances to decision block 48.
 In decision block 48, the methodology determines if the engine is operating
 smoothly on the fuel vapors from the fuel purge vapor control system and
 the injected fuel as modified by the DCFC fuel multiplier at decision
 block 42. In this case, the term "smoothly" contemplates an engine
 roughness level which is within certain pre-selected limits, i.e., within
 a range of smooth operation. If the engine is not operating smoothly at
 decision block 48, the methodology advances to decision block 40 and exits
 the subroutine pending a subsequent execution thereof. However, if the
 engine is deemed to be running smoothly by the methodology at decision
 block 48, the methodology advances to block 50.
 In block 50, the methodology recalculates the DCFC fuel multiplier based on
 the goal voltage for the exhaust gas oxygen sensor. In this way, the DCFC
 fuel multiplier determined at block 42 (which results in smooth engine
 operation at decision block 48) is fine-tuned with oxygen sensor feedback
 at block 50. The methodology then readjusts the amount of fuel being
 injected into the engine at block 50 with the updated DCFC fuel
 multiplier. As with the determination of the DCFC fuel multiplier at
 decision block 42, the recalculation of the DCFC fuel multiplier at block
 50 relies in part on the purge vapor flow rate from data block 44. From
 block 50, the methodology advances to bubble 16 and exits the subroutine
 pending a subsequent execution thereof.
 Thus, a fuel control system is provided for controlling the amount of fuel
 being injected into an internal combustion engine during fuel vapor
 fuelling at start-up. After start-up, the methodology tests the engine for
 roughness and adjusts the amount of injected fuel delivered to the engine
 with the fuel vapors accordingly. After oxygen sensor feedback is
 available, the methodology recalculates the fueling requirements. If
 necessary, the amount of injected fuel is readjusted. After the engine
 warms up, the delivery of fuel vapors stops and the present methodology
 ends.
 Those skilled in the art can now appreciate from the foregoing description
 that the broad teachings of the present invention can be implemented in a
 variety of forms. Therefore, while this invention has been described in
 connection with particular examples thereof, the true scope of the
 invention should not be so limited since other modifications will become
 apparent to the skilled practitioner upon a study of the drawings,
 specification, and following claims.