BACKGROUND OF THE INVENTION

1. Technical Field

The present invention generally relates to fuel control systems and, more particularly, to a method of using fuel vapors from the fuel tank to power 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 fuel, which is not easily vaporized, is lesscombustible than warm fuel. As such, the 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 itscombustibility. 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 exhaustgas 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 thepurge 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 fromthe purge canister 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 now been discovered that this fuel vapor can be used for combustionduring cold engine operation instead of the liquid fuel normally supplied from the fuel injectors.

SUMMARY OF THE INVENTION

A fuel control system is provided including a fuel tank and a purge vapor collection canister interconnected with an internal combustion engine. A purge vapor canister vent valve selectively seals the purge vapor canister from atmosphere suchthat the fuel tank, purge vapor canister, and engine intake manifold form a closed system. Upon a cold engine start, a purge valve disposed between the purge vapor canister and the engine intake manifold is opened such that the pressure differentialbetween the engine intake manifold and the remainder of the system causes fuel vapor collected within the dome portion of the fuel tank to be drawn through the purge vapor canister and into the intake manifold. Simultaneously therewith, the amount offuel injected by the fuel injectors to the engine is reduced such that a desired amount of total fuel delivery is established. As the pressure differential between the intake manifold and the remainder of the closed system changes over time, the flowrate of purge vapors from the fuel tank slows down. Commensurate therewith, the amount of injected fuel is increased. During this time the engine is warming up such that the increased amount of injected fuel is more easily vaporized thereby yieldingbetter combustibility. When the engine reaches a filly warm operating condition, the purge valve is closed and complete fuel delivery is provided by the fuel injectors.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to appreciate the manner in which the advantages and objects of the invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in theappended drawings. Understanding that these drawings only depict preferred embodiments of the present invention and are not therefore to be considered limiting in scope, the invention will be described and explained with additional specificity anddetail through the use of the accompanying drawings in which:

FIG. 1 is a schematic illustration of a purge vapor control system according to the present invention; and

FIG. 2 is a flow chart depicting a control methodology for the purge vapor control system of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed towards a method of fueling an internal combustion engine during cold engine operation. More particularly, the present invention directs fuel vapor from the fuel tank to the intake manifold of the engineimmediately after start-up. A commensurate amount of injected fuel is removed during this time so that the appropriate total amount of fuel is delivered to the engine. As the engine warms, less fuel vapor is delivered until finally complete fueling isreturned to the fuel injectors.

Turning now to the drawing figures, a purge vapor control system according to the present invention 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 aninternal 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 thedome 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 canister14 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 purgevapor 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 internalcombustion 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 theinternal 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 andopening 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-upinstead of the normal injected fuel.

Turning now to FIG. 2, a methodology for controlling the above-described fuel vapor purge system is illustrated. The methodology starts in bubble 34 and falls through to decision block 36. In decision block 36, the methodology determineswhether the start-to-run transition of the internal combustion engine has occurred. If not, the methodology advances to bubble 38 and exits the routine pending a subsequent execution thereof. However, if the start-to-run transition has occurred atdecision block 36, the methodology continues to decision block 40.

In decision block 40, the methodology determines whether the engine has reached a warm condition. Preferably, this is accomplished by way of a timer although a direct temperature sensor reading may be taken if desired. If the engine has reacheda fully warm condition at decision block 40, the methodology advances to bubble 38 and exits the routine pending a subsequent execution thereof. However, if the methodology determines that the engine has not reached a fully warm condition at decisionblock 40, the methodology continues to block 41.

In block 41, the methodology determines whether a timer has expired. The timer setting corresponds to the predicted period of time that it will take to remove the resident purge vapors from the fuel tank and combust them in the engine. If thefuel tank is relatively full, less room is available in the tank for fuel vapors. As such, less vapor is present and less time is required to remove them. Therefore, the timer is set to expire relatively quickly. On the other hand, if the fuel tank isrelatively empty, more room is available in the tank for fuel vapors. As such, more vapor is present and more time is required to remove them. Therefore, the timer is set to expire after a longer period of time.

If the methodology determines that the timer has expired in decision block 41, the methodology advances to bubble 38 and exits the routine pending a subsequent execution thereof. However, if the methodology determines that the timer has notexpired in decision block 41, the methodology advances to decision block 42.

In block 42, the methodology calculates the percent of liquid injected fuel to replace with the fuel vapor from the fuel tank. Data block 44 dictates that the percent of fuel to be replaced is targeted as a function of time since start-up. Thedesired percentage of fuel vapor to be provided is preferably the maximum amount within certain limits. For instance, at idle, a minimum pulse width requirement sets the maximum limit. The minimum pulse width sets the minimum amount of fuel that can beaccurately delivered by the fuel injectors depending on the operating parameters of the engine. Preferably, the fuel injectors are never completely turned off to avoid transient fuel concerns at a throttle tip-in event. During off idle conditions, amaximum rate of flow from the fuel tank is the maximum limit. From block 42, the methodology continues to block 46.

In block 46, the methodology calculates the target purge fuel vapor mass flow rate. As described above, the target purge mass flow rate is that amount of fuel vapor required to replace the injected fuel calculated to be removed at block 42. From block 46, the methodology continues to block 48.

In block 48, the methodology commands the purge valve to open such that a desired amount of purge fuel vapor mass flow is attained. Over time, the pressure difference between the intake manifold and the fuel tank changes. As such, the rate offlow between the fuel tank and the intake manifold changes. Data block 50 dictates that the pressure change is based on tank volume and accumulated flow. Data block 52 dictates that the rate of flow change is based on the pressure change and thecurrent rate of flow. Conveniently, the pressure change in data block 50 and the purge flow in data block 52 can be mapped in a pair of tables as a function of time. From block 48, the methodology continues to block 54.

In block 54, the methodology calculates the actual mass flow rate of the fuel from the purge system. Data block 56 provides feedback to this calculation if it is available. For instance, a fuel modifier from a dynamic crankshaft fuel controlsystem could be input here to further vary the fueling strategy. After calculating the actual mass flow rate of the fuel from the purge system at block 54, the methodology continues to block 58. In block 58, the methodology subtracts the amount ofvapor fuel mass calculated at block 54 from the amount of fuel to inject. From block 58 the methodology continues to block 60.

In block 60, the methodology injects the amount of fuel calculated at block 58. As can be appreciated, as the mass flow rate of fuel vapor from the fuel tank decreases, the amount of fuel required to be injected at block 60 increases. When themass flow rate of the purge fuel vapors drops below a minimum threshold, complete fuel delivery is supplied by the fuel injectors. By this time, the intake valve and manifold port of the engine should be warm thereby heating the injected liquid fuelsuch that it is efficiently vaporized resulting in improved emissions. From block 60, the methodology continues to bubble 38 where it exits the routine pending a subsequent execution thereof.

Thus, a fuel control system is provided for fueling an internal combustion engine with fuel vapors from the fuel tank at start-up. In combination therewith, a reduced amount of fuel is injected into the engine. As the engine warms up, the ratioof fuel vapor to injected fuel changes such that engine operation eventually transitions completely to injected fuel. Advantageously, cold engine operation is primarily based on fuel vapors thereby eliminating poor emissions which may accompany thecombustion of cold injected fuel.

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 withparticular 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.

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