METHOD FOR REDUCING SOOT FORMED BY AN ENGINE

Abstract

A method of operating an engine (10), comprising: Supplying a quantity of fuel from a fuel vapor storage tank (144) to a cylinder (30) and Setting a number of fuel pulses delivered to the cylinder (30) via a fuel injector (66) during a cycle of the cylinder (30) in response to the fuel vapor supplied to the cylinder (30) from the fuel vapor storage canister (144) amount of fuel supplied during the cylinder cycle and a minimum pulse width of the fuel injection valve (66), wherein the amount of fuel is injected directly to the cylinder (30) and wherein a pulse width of at least one fuel pulse supplied to the cylinder (30) is reduced while the amount of fuel supplied to the cylinder (30) from the fuel vapor storage canister (144) increases.

Description

[0001] Soot can form in an engine where fuel is injected directly to the engine's cylinders. In particular, soot can form when fuel is injected to an engine cylinder while the engine is operating at higher speeds and loads. The soot can form from incomplete combustion of hydrocarbons because there is less time to atomize fuel injected to the cylinder at higher engine speeds. Soot formation can also be influenced by introducing hydrocarbons to the cylinder via purging of fuel vapors stored in a fuel vapor storage canister. Because the purged fuel vapors may mix with air entering the engine before the air enters the cylinder, fuel injected to the cylinder in particular may have more difficulty vaporizing and mixing with the air-fuel mixture entering the cylinder.Consequently, the amount of soot produced by an engine may increase as stored fuel vapors are purged to the engine.

[0002] DE 101 35 758 A1 discloses a method for ensuring the combustion of vaporizing fuel in a stratified charge engine using multiple fuel injection pulses. The method includes controlling the purge flow from a fuel vapor storage canister and the injected fuel supply. The supplied fuel quantity is adjusted based on the purge flow supplied to the cylinder, thus ensuring a homogeneous air / fuel ratio.

[0003] Document US 2007 / 0 215 111 A1 discloses a system and method for reducing knock and pre-ignition in an internal combustion engine. A fluid and fuel are introduced into the combustion chamber in different ratios via a supply system.

[0004] The document DE 11 2005 000 875 B4 discloses a method for predicting the purging of a reservoir for an engine fuel and air control system.

[0005] EP 2 147 205 B1 discloses a method for equalizing cylinders in an internal combustion engine to achieve the smoothest possible running. This method involves injecting and post-injecting fuel into the combustion chamber of at least one cylinder.

[0006] The object of the invention is to reduce soot formation in the combustion chamber of an engine cylinder in connection with fuel vapors supplied from the fuel vapor storage tank. This object is achieved by the features of the independent patent claim. Advantageous developments of the invention are the subject of the dependent claims.

[0007] The inventor of the present invention has recognized the above-mentioned limitations and has developed a method of operating an engine comprising: supplying an amount of fuel from a fuel vapor storage canister to a cylinder and adjusting a number of fuel pulses supplied to the cylinder via a fuel injector during a cycle of the cylinder in response to the amount of fuel supplied to the cylinder from the fuel vapor storage canister during the cylinder cycle and a minimum pulse width of the fuel injector, wherein the amount of fuel is injected directly to the cylinder and wherein a pulse width of at least one fuel pulse supplied to the cylinder is reduced while the amount of fuel supplied to the cylinder from the fuel vapor storage canister increases.

[0008] By delivering fuel to a cylinder in multiple fuel pulses, while also delivering fuel to the cylinder via a fuel vapor storage canister, it may be possible to reduce soot formation in the cylinder's combustion products. Specifically, cylinder soot formation may be reduced by performing multiple fuel injections during a cylinder cycle. In one example, multiple fuel pulses delivered to a cylinder during a cylinder cycle may be maximized to promote fuel vaporization, even though a mixture of air and fuel enters the cylinder via a cylinder's intake valve.

[0009] The present description may offer several advantages. In particular, the approach may provide reduced soot formation in combustion byproducts. Furthermore, the method may reduce engine system costs by reducing the possibility of requiring the provision of a particulate trap for the engine. Furthermore, if the engine system includes a particulate filter, the particulate filter may need to be regenerated less frequently when applying the approach.

[0010] The above advantages and other advantages and features of the present description will be readily apparent from the following detailed description, considered alone or in conjunction with the accompanying drawings.

[0011] It should be understood that the above summary is intended to introduce, in simplified form, a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any of the disadvantages noted above or in any other part of this disclosure. SHORT DESCRIPTION OF THE CHARACTERS Fig. 1 shows a schematic representation of an engine; Fig. 2 shows an exemplary fuel injector transfer function; Fig. 3 and Fig. 4 show exemplary fuel injection sequences when fuel vapors are supplied to a cylinder; and Fig. 5 shows a flowchart of an exemplary method for operating an engine. DETAILED DESCRIPTION

[0012] The present description relates to controlling fuel injection to a cylinder to reduce soot formation in the cylinder. In one example, a fuel injector that supplies fuel to a cylinder of an engine may be Fig. 1, as described. The fuel injection valve opening control can be adjusted as shown in the Fig. 3 and Fig. 4. The control of the opening of the fuel injector is based on a minimum pulse width of the fuel injector, as shown in Fig. 2. The procedure of Fig. 5 can be the basis for adjusting the fuel injection valve operation as shown in the Fig. 3 and Fig. 4 be.

[0013] On Fig. 1 Referring to, a plurality of cylinders, one of which cylinder in Fig. 1, is controlled by an electronic engine controller 12. The engine 10 includes a combustion chamber 30 and cylinder walls 32 with a piston 36 positioned therein and connected to a crankshaft 40. The combustion chamber 30 is shown communicating with an intake manifold 44 and an exhaust manifold 48 via an intake valve 52 and an exhaust valve 54, respectively. Each intake and exhaust valve may be actuated by an intake cam 51 and an exhaust cam 53. Alternatively, one or more of the intake and exhaust valves may be actuated by an electromechanically controlled valve spool and armature assembly. The phase of the intake cam 51 and the exhaust cam 53 may be adjusted via cam phase actuators 59 and 69. The position of the intake cam 51 can be determined by the intake cam sensor 55. The position of the exhaust cam 53 can be determined by the exhaust cam sensor 57.

[0014] In the illustration, the fuel injector 66 is positioned to inject fuel directly into the cylinder 30, known to those skilled in the art as direct injection. The fuel injector 66 delivers liquid fuel proportional to a pulse width from the controller 12. Fuel is delivered to the fuel injector 66 from a fuel system including a fuel tank 140, a fuel pump 142, a fuel line 141, and a fuel rail (not shown). The fuel injector 66 receives operating power from the controller 12. Fuel vapors from the fuel tank 140 may be stored in the fuel vapor canister 144, which contains activated charcoal 146 or other hydrocarbon storage media.Fuel vapors enter the fuel vapor storage canister 144 from the fuel tank 140 via line 151 when the vent valve 150 is open or when fuel vapors are drawn into the intake manifold 44 via the purge line 143 and the purge valve 148. In addition, the intake manifold 44 is shown communicating with an optional electronic throttle 62 that adjusts a position of the throttle plate 64 to control airflow from the air intake 42.

[0015] A distributorless ignition system 88 delivers an ignition spark to the combustion chamber 30 via a spark plug 92 in response to the controller 12. The ignition system 88 may deliver a single or multiple sparks to each cylinder during each cylinder cycle. Furthermore, the timing of the spark delivered via the ignition system 88 may be advanced or retarded relative to the crankshaft timing in response to engine operating conditions.

[0016] A universal exhaust gas oxygen (UEGO) sensor 126 is shown connected to the exhaust manifold 48 upstream of an exhaust aftertreatment device 70. Alternatively, a dual-state oxygen sensor may be employed in place of the UEGO sensor 126. In some examples, the exhaust aftertreatment device 70 is a particulate filter and / or a three-way catalyst. In other examples, the exhaust aftertreatment device 70 is merely a three-way catalyst.

[0017] In the presentation of Fig. 1, the controller 12 is a conventional microcomputer including a microprocessor unit 102, input / output (I / O) ports 104, a read-only memory (ROM) 106, a random access memory (RAM) 108, a retained memory (RAM) 110, and a conventional data bus.In addition to the signals previously discussed, the controller 12 is shown receiving various signals from sensors coupled to the engine 10, including: engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; a position sensor 134 coupled to an accelerator pedal 130 for sensing the accelerator pedal position set by foot 132; a knock sensor for determining end gas ignition (not shown); an intake manifold pressure (MAP) measurement from pressure sensor 121 coupled to intake manifold 44; an engine position sensor from a Hall sensor 118 sensing the position of the crankshaft 40; a measurement of the mass of air entering the engine from sensor 120 (for example, a hot wire air flow sensor); and a measurement of throttle position from sensor 58. Barometric pressure may also be sensed for processing by the controller 12 (sensor not shown).According to a preferred aspect of the present description, the engine position sensor 118 generates a predetermined number of evenly spaced pulses for each revolution of the crankshaft from which the engine speed (RPM) can be determined.

[0018] In some examples, the engine may be coupled to an electric motor / battery system in a hybrid vehicle. The hybrid vehicle may have a parallel configuration, a series configuration, or variations or combinations thereof. Furthermore, in other embodiments, other engine configurations may be employed, for example, a diesel engine.

[0019] During operation, each cylinder in engine 10 typically experiences a four-stroke cycle: the cycle includes the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. During the intake stroke, exhaust valve 54 generally closes and intake valve 52 opens. Air is introduced into combustion chamber 30 via intake manifold 44, and piston 36 moves to the bottom of the cylinder to increase the volume in combustion chamber 30. The position where piston 36 is near the bottom of the cylinder and at the end of its stroke (for example, when combustion chamber 30 is at its largest volume) is typically referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, intake valve 52 and exhaust valve 54 are closed. Piston 36 moves toward the cylinder head to compress the air in combustion chamber 30.The point at which the piston 36 is at the end of its stroke and closest to the cylinder head (for example, when the combustion chamber 30 is at its smallest volume) is typically referred to by those skilled in the art as top dead center (TDC). In an event referred to herein as injection, fuel is introduced into the combustion chamber. In an event referred to herein as ignition, the injected fuel is ignited by a known ignition means, such as a spark plug 92, resulting in combustion. During the power stroke, the expanding gases push the piston 36 back to BDC. The crankshaft 40 converts piston movement into rotating shaft torque. Finally, during the exhaust stroke, the exhaust valve 54 opens to release the combusted air-fuel mixture to the exhaust manifold 48, and the piston returns to TDC.It should be noted that the above is described as an example only and that the timing of intake and exhaust valve opening and / or closing may vary to provide positive or negative valve overlap, late intake valve closing, or various other examples.

[0020] Thus, the system of Fig. 1. A control of an engine, comprising: an engine; a fuel vapor storage canister; a fuel injector that supplies fuel to a cylinder of the engine; a controller that includes instructions for injecting fuel to the cylinder in a plurality of fuel pulses during a cycle of the cylinder, the controller including further instructions for supplying fuel to the cylinder via the fuel vapor storage canister, the controller including further instructions for adjusting the number of fuel pulses during a cylinder cycle in response to a delivered amount of fuel when the fuel injector is operated at a minimum pulse width. In this way, the number of fuel injections during a cylinder cycle can be related to a characteristic of the fuel injector.

[0021] The system further includes additional instructions for maximizing the number of fuel pulses during the cylinder cycle. In some examples, the system further includes an air intake system that supplies air to the cylinders of the engine, and wherein the fuel vapor storage canister is in communication with the air intake system. The system further includes a fuel vapor purge valve; and wherein the controller further includes instructions for adjusting a duty cycle of the fuel vapor purge valve to adjust the flow of fuel vapors to the cylinder. The system further includes additional instructions for decreasing the pulse width of at least one fuel pulse in response to an amount of fuel supplied to the cylinder via the fuel vapor storage canister.The system further includes additional instructions to reduce the number of fuel pulses delivered to the cylinder when at least one fuel pulse delivered to the cylinder has a minimum fuel injector pulse width.

[0022] Now on Fig. 2, a simulated example diagram of a transfer function for a fuel injector is shown. The X-axis represents the fuel injector pulse width when a nominal voltage is supplied to the fuel injector. For example, a fuel injector rated for 14 volts may be supplied with a 5 ms 14-volt pulse to open the fuel injector and supply fuel to a cylinder. The Y-axis represents the mass of fuel injected by the fuel injector when voltage is supplied to the fuel injector at the nominal voltage. The transfer function of Fig. 2 can be set to operate when the fuel injector is supplied with a voltage that is less than or greater than the injector's nominal voltage. For example, the injected fuel mass can be reduced when a 10-volt, 5-ms pulse width is supplied to the fuel injector. The transfer function of Fig. 2 can be used for the Fig. 1 may be representative. Furthermore, the transfer function of Fig. 2 in the memory of the Fig. 1 shown control 12.

[0023] Fig. 2 shows that the fuel mass is essentially zero until the minimum fuel pulse width 202 is reached. In some examples, the fuel injector may inject a small amount of fuel that is not repeatable for fuel pulse widths below the minimum fuel pulse width. Therefore, the fuel injector will not operate with fuel pulse widths less than the minimum fuel pulse width. After a fuel pulse of at least the minimum fuel pulse width or greater is delivered to the injector, the injected fuel mass from the fuel injector increases linearly with increasing fuel pulse width. The minimum injected fuel mass is shown by distance 204 in the illustration. The minimum injected fuel mass corresponds to the minimum fuel pulse width.It should be noted that the minimum fuel mass injected and the minimum fuel pulse width are design considerations and may vary from one fuel injector design to another.

[0024] Now on Fig. 3, a simulated fuel injection sequence is shown when enhancing the purging of fuel vapors from a fuel vapor storage canister. The sequence of Fig. 3 can be done by the procedure of Fig. 5, which is controlled by instructions from the controller 12 in the system of Fig. 1 is executed.

[0025] The first diagram from the top in Fig. Figure 3 represents strokes of cylinder number 1 of a four-cylinder, four-stroke engine with a firing order of 1-3-4-2. The exhaust stroke is abbreviated as EXH, while the respective intake, compression, and power strokes are abbreviated as INT (intake stroke), COMP (compression stroke), and EXP (power stroke).

[0026] The second diagram from the top in Fig. Figure 3 illustrates the control of fuel injection events during the respective cylinder strokes of the first diagram from the top of Fig. 3. The injected fuel mass increases with increasing pulse width. The injector on-time or pulse width is shown as a pulse similar to 302. The injector off-time is shown by the absence of pulses similar to the time at 304. Likewise, the mass of injected fuel decreases with decreasing pulse width.

[0027] The third diagram from the top of Fig. 3 represents a fuel vapor storage container, such as 144 of Fig. 1, represents the amount of fuel vapor purge entering cylinder number one. The fuel mass entering cylinder number one increases in the direction of the Y-axis arrow.

[0028] The sequence is shown over more than three cylinder cycles; however, the events shown in the sequence can occur over several minutes during the purge of a fuel vapor storage canister. Furthermore, the first, second, and third diagrams of Fig. 3 occur simultaneously and on the same time scale.

[0029] The sequence starts at time T0, when the engine is running and cylinder number one begins an exhaust stroke. No fuel is purged from the fuel vapor storage canister at time T0, and no fuel injection occurs during the exhaust stroke.

[0030] At time T1, cylinder number one enters an intake stroke, and fuel injection to cylinder number one begins. At time T1, no fuel is purged from the fuel vapor storage canister.

[0031] At higher engine speeds and loads, fuel injected directly to a cylinder can form soot in the cylinder during combustion. One way to reduce or limit soot from fuel injected directly to a cylinder may be to inject a desired amount of fuel in as many fuel injections as possible during a cylinder cycle. For example, a single 5-ms fuel pulse may be divided into five 1-ms pulses to improve fuel mixing and reduce soot formed in a cylinder during combustion. The additional fuel injections can help promote fuel mixing, allowing less soot to form in the number one cylinder. However, the number of fuel injections in a cylinder cycle may be limited by the fuel injector's minimum pulse width and / or a fuel injector's minimum off-time.In some examples, the minimum fuel injector off time may be defined as a period of time that energy supplied to the fuel injector must be suppressed in order to halt fuel flow from the injector between fuel injections. In this example, the desired amount of fuel may be delivered to the cylinder in four fuel injections spanning the intake stroke of cylinder number one. However, in other examples, the number of fuel injections may be increased or decreased based on engine speed, the minimum fuel injector on time, and the minimum fuel injector off time. At time T1, no fuel is being purged from the fuel vapor storage canister, so all fuel entering cylinder number one is through the sole fuel injector fueling cylinder number one.

[0032] Between time T1 and time T2, the purge control valve begins to open, and fuel vapor begins to flow into the engine intake manifold. The fuel vapors mix with air entering the engine and therefore require less fuel injection to the cylinder to meet a desired amount of fuel in the cylinder.

[0033] At time T2, fuel injection to cylinder number one begins for the second cycle of cylinder number one in Fig. 3. The engine is operating at the same speed and load between times T1 and T2. Therefore, the amount of air drawn to cylinder number one is the same between times T1 and T2. Furthermore, the target fuel amount for combustion cycles of cylinder number one beginning at times T1 and T2 is the same. However, because some of the fuel entering cylinder number one comes from purging fuel vapors in the fuel vapor storage canister, less fuel is injected to provide the same air-fuel ratio between cylinder cycles beginning at times T1 and T2.

[0034] During each individual fuel injection event, less fuel may be injected to the cylinder until the minimum fuel injector pulse width is reached. When the minimum fuel injector pulse width is reached, the number of fuel injections may be decreased, and the amount of fuel injected during each of the remaining fuel injections may be increased to provide the desired amount of fuel in the cylinder. When the number of fuel injections in a cylinder cycle is decreased, at least a portion of the amount of fuel injected during the eliminated fuel injection is added to the remaining number of fuel injections.The duration of the pulse widths of each of the remaining fuel injections increases so that the desired amount of fuel can be delivered to the cylinder even though one fuel injection event is missed during the cylinder cycle. Thus, during the intake strokes, beginning at times T1 and T2, essentially the same amount of fuel enters cylinder number one. The number of fuel injections is reduced, so fuel mixing may be less intense due to the three fuel injection events at time T2 compared to when there are four fuel injections, as shown at time T1. However, because some of the fuel entering the cylinder is already in the form of vapors, the one missed fuel injection event may not have as significant an impact, and therefore, low soot generation may still be provided.

[0035] Thus, at time T2, the number of fuel injections during a cylinder cycle is decreased in response to a condition where a first, higher number of fuel injection events would inject more fuel than desired if the fuel injector were operated at a minimum fuel injector pulse width. By decreasing the number of fuel injection events during the cylinder cycle, the fuel injector may deliver a desired amount of fuel to a cylinder with a fuel injection pulse width greater than the minimum fuel injection pulse width. In this way, the number of fuel injection events during a cylinder cycle may be adjusted to provide a maximum number of fuel injection events even in the presence of purge fuel vapors to the cylinder from a fuel vapor storage canister.

[0036] Between times T2 and T3, the amount of fuel vapor entering the engine intake manifold and cylinder number one continues to increase. The amount of fuel vapor flowing to the engine can be increased by increasing a duty cycle supplied to a purge valve that regulates flow from the fuel vapor canister.

[0037] At time T3, the engine continues to operate at the same speed and load as during times T1 and T2. Therefore, the target cylinder air quantity and the target cylinder fuel quantity remain the same between times T1, T2, and T3.

[0038] The amount of fuel vapor flowing to the engine via the fuel vapor storage canister has increased to a level that requires a reduction in the amount of injected fuel so that the desired amount of fuel can be delivered to the cylinder. Therefore, the amount of fuel injected during each fuel pulse is reduced from time T2 to time T3. If the fuel injector pulse width were not reduced, the cylinder air-fuel ratio would be reduced, resulting in a richer air-fuel mixture. By reducing the fuel injection pulse width, the cylinder air-fuel ratio can be maintained at a desired ratio. At time T3, the fuel injection pulse width has been reduced and is approaching the minimum fuel pulse width.

[0039] Between time T3 and time T4, the amount of fuel vapor entering the engine intake manifold and cylinder number one continues to increase. The amount of fuel vapor flowing to the engine may be increased over one or more cylinder cycles. In some examples, the amount of fuel vapor entering the engine cylinders may be measured via a hydrocarbon sensor, or it may be inferred via an oxygen sensor positioned in the engine's exhaust.

[0040] At time T4, the engine operates at the same speed and load as during times T1, T2, and T3. Consequently, the target cylinder air quantity and the target cylinder fuel quantity remain the same between times T1, T2, T3, and T4.

[0041] The increase in fuel vapors entering the engine via the fuel vapor storage canister has reached a level at which the desired amount of fuel in the cylinder cannot be provided over three fuel injections with the minimum fuel injector pulse width. In particular, if fuel were injected to the cylinder in three separate injections with the minimum fuel injector pulse width, more fuel than desired would be present in the cylinder. Therefore, the number of fuel injections to cylinder number one is reduced to two, and the duration of each fuel pulse width is increased. As a result, the cylinder can be operated with the same desired amounts of fuel at times T1, T2, T3, and T4, even though the amount of fuel vapor entering cylinder number one is increased.

[0042] In this way, the maximum number of fuel injection events may be provided to a cylinder during a cycle of the cylinder to reduce soot formation in the cylinder. Furthermore, the number of fuel injection events may be adjusted to accommodate the minimum fuel injection time, the minimum fuel injector off time, and the amount of fuel vapor provided to the cylinder. It should be noted that the number of injection events, cylinder strokes, and fuel vapor amounts are shown for illustrative purposes only and are not intended to limit the scope of the present disclosure.

[0043] Now on Fig. 4, a simulated fuel injection sequence during the reduction of purging of fuel vapors from a fuel vapor storage canister is shown. The sequence of Fig. 4 can be done by the procedure of Fig. 5, which is controlled by instructions from the controller 12 in the system of Fig. 1 is executed. The diagrams of Fig. 4 are similar to those of Fig. 3. Therefore, for the sake of brevity, Fig. 4 only describes the differences.

[0044] The sequence begins at time T0, when the engine is running and cylinder number one begins an exhaust stroke. Fuel is purged from the fuel vapor storage canister at a relatively high rate at time T0, and fuel injection is not present during the exhaust stroke. Fuel vapors do not enter cylinder number one until the intake valve of cylinder number one opens during cylinder number one's intake stroke.

[0045] At time T1, cylinder number one enters an intake stroke, and fuel injection to cylinder number one begins. Fuel is injected in two fuel pulse widths, and fuel vapors enter cylinder number one when the intake valve of cylinder number one opens. If fuel were injected to cylinder number one in three pulse widths equal to the minimum fuel injector pulse width during the intake stroke beginning at time T1, the total amount of fuel entering the cylinder via the fuel injector and the fuel vapor storage canister would exceed the target fuel amount. Therefore, the number of fuel injections is limited to two fuel injections, and the fuel injection pulse widths are greater than the minimum fuel injection pulse width.

[0046] Between time T1 and time T2, the purge control valve begins to close, and fuel vapors flowing into the engine intake manifold are reduced. Alternatively, the amount of fuel vapors stored in the fuel vapor storage canister may be reduced as fuel vapors are exhausted from the fuel vapor storage canister.

[0047] At time T2, fuel injection to cylinder number one begins for a second cycle of cylinder number one in Fig. 3. The engine is operating at the same speed and load between times T1 and T2. Therefore, the amount of air introduced into cylinder number one is the same between times T1 and T2. Furthermore, the target fuel amount for combustion cycles of cylinder number one beginning at times T1 and T2 is the same. However, since the portion of fuel entering cylinder number one is reduced by the purge of fuel vapors in the fuel vapor storage canister, additional fuel is injected to cylinder number one to provide the same air-fuel ratio between cylinder cycles beginning at times T1 and T2.

[0048] Additional fuel can be injected to the number one cylinder by increasing the number of fuel injections at or above the minimum fuel injection time during the intake stroke of the number one cylinder. The number of fuel injections during a cylinder cycle can be increased if the amount of fuel entering the cylinder via the fuel vapor canister and the fuel injector does not exceed the target fuel amount when fuel is injected at the minimum fuel pulse width. When the number of fuel injections in a cylinder cycle is increased, at least a portion of the amount of fuel injected during each of the previous number of fuel injections is added to the amount of fuel injected during the additional fuel injection during the cylinder cycle.Thus, during the intake strokes beginning at times T1 and T2, essentially the same amount of fuel enters cylinder number one, although the amount of fuel vapor entering the cylinder decreases. The number of fuel injections is increased, so fuel mixing may be more intense due to the three fuel injection events at time T2 compared to when there are two fuel injections, as shown at time T1.

[0049] Thus, at time T2, the number of fuel injections during a cylinder cycle is increased in response to a condition where an initial, fewer number of fuel injection events would not provide as much in-cylinder mixing as is possible with a maximum number of fuel injections. By increasing the number of fuel injection events during the cylinder cycle when fuel vapors flowing into the cylinder are reduced, the fuel injector can improve in-cylinder fuel mixing and deliver a desired amount of fuel to a cylinder with a fuel injection pulse width greater than the minimum fuel injection pulse width.In this way, the number of fuel injection events during a cylinder cycle can be adjusted to provide a maximum number of injection events, even in the presence of a reduced amount of fuel vapor being purged from a fuel vapor storage canister to the cylinder. Between time T2 and time T3, the amount of fuel vapor entering the engine intake manifold and cylinder number one further decreases.

[0050] At time T3, the engine continues to operate at the same speed and load as during times T1 and T2. Therefore, the target cylinder air quantity and the target cylinder fuel quantity remain the same between times T1, T2, and T3.

[0051] The amount of fuel vapor flowing to the engine via the fuel vapor storage canister has decreased to a level that requires an increase in the amount of injected fuel so that the desired amount of fuel can be provided in the cylinder. Therefore, the amount of injected fuel is increased during each fuel pulse from time T2 to time T3. If the fuel injector pulse width were not increased, the cylinder air-fuel ratio would be increased, resulting in a leaner air-fuel mixture. By increasing the fuel injection pulse width, the cylinder air-fuel mixture can be maintained at a desired ratio. At time T3, the fuel injection pulse width has been increased, approaching an extent at which additional fuel injection can be provided at a minimum fuel pulse width or greater.

[0052] Between time T3 and time T4, the amount of fuel vapor entering the engine intake manifold and cylinder number one further decreases. The amount of fuel vapor flowing to the engine may be reduced over one or more cylinder cycles. In some examples, the amount of fuel vapor entering the engine cylinders may be measured via a hydrocarbon sensor or inferred via an oxygen sensor positioned in the exhaust of the engine.

[0053] At time T4, the engine operates at the same speed and load as during times T1, T2, and T3. Consequently, the target cylinder air quantity and the target cylinder fuel quantity remain the same between times T1, T2, T3, and T4.

[0054] The decrease in fuel vapors entering the engine via the fuel vapor storage canister has essentially reached zero, and the target fuel quantity can be delivered to cylinder number one via four separate fuel injections during the cylinder cycle. Therefore, the number of fuel injections to the cylinder is increased while the fuel pulse width of each injection is reduced. As a result, the cylinder can be operated with the same target fuel quantities at times T1, T2, T3, and T4, even though the amount of fuel vapor entering cylinder number one decreases.

[0055] In this way, the maximum number of fuel injection events may be provided to a cylinder during a cycle of the cylinder to reduce soot formation in the cylinder. Furthermore, the number of fuel injection events may be adjusted to accommodate the minimum fuel injection time, the minimum fuel injector off time, and the amount of fuel vapor provided to the cylinder. It should be noted that the number of injection events, cylinder strokes, and fuel vapor amounts are shown for illustrative purposes only and are not intended to limit the scope of the present disclosure.

[0056] Furthermore, it should be mentioned that in some examples of the consequences of Fig. 3 and Fig. 4 Fuel injection can continue into at least part of the compression stroke. Consequently, the number of fuel injections providing fuel participating in combustion during a cylinder cycle can be set to a maximum number when fuel vapors are purged or reduced to engine cylinders.

[0057] Now on Fig. Referring to Figure 5, a method of operating an engine is disclosed. The method of Fig. 5 sets a number of fuel injections during a cylinder cycle, the fuel injections supplying fuel participating in combustion within the cylinder. The number of fuel injections during a cylinder cycle is maximized in the presence or absence of fuel vapors delivered to the engine from a fuel vapor storage canister.

[0058] At 502, method 500 determines the engine operating conditions. The engine operating conditions may include, but are not limited to, engine speed, engine load, engine torque demand, engine temperature, fuel vapor storage amount in the fuel vapor canister, and time since engine stop. Method 500 proceeds to 504 after determining the engine operating conditions.

[0059] At 504, method 500 determines an amount of fuel (fuel_Ibm) to be delivered to one or more engine cylinders during a cycle of the cylinder. In one example, the amount of fuel may be determined by multiplying an amount of air entering a cylinder by a desired air-fuel ratio. The desired air-fuel ratio may be determined empirically and stored in a table or function indexed using engine operating conditions. For example, a desired engine air-fuel ratio may be determined to be 14:1 at engine start-up conditions, with the engine partially warmed up. The air-fuel ratio may be adjusted (e.g., made richer or leaner) for different engine operating conditions and to improve catalyst efficiency.The air entering a cylinder can be determined using an air mass sensor or an intake manifold pressure sensor and the ideal gas law PV = nRT, where P is pressure in the engine cylinder, V is the cylinder volume, n is the number of moles of air, R is a gas constant and T is the temperature in degrees Kelvin.

[0060] In other examples, the cylinder fuel amount may be based on a desired or requested engine torque level. The requested engine torque is converted into a desired air mass and a desired fuel amount to provide the desired engine torque level. One such method is described in U.S. Patent No. 7,321,821, which is hereby incorporated by reference in all respects. Method 500 proceeds to 506 after determining the desired fuel amount to be delivered to the cylinder.

[0061] At 506, method 500 determines a desired amount of purged fuel vapors entering the engine cylinders. Alternatively, an actual amount of fuel vapor entering a cylinder may be determined. In one example, the amount of fuel vapor entering a cylinder via the fuel vapor storage canister (vapor_lbm) may be determined as described in U.S. Pat. No. 6,523,531, which is hereby incorporated by reference in all respects. The canister purge fuel flow rate in lb mass per minute from the fuel vapor storage canister may be converted to fuel mass flow per cylinder event by multiplying the canister purge flow rate by the number of minutes per cylinder intake event.Furthermore, the canister purge flow rate and the concentration of hydrocarbons (e.g., the air-fuel ratio of the purge vapor mixture) flowing from the canister to the engine cylinders may be adjusted for the engine operating conditions (e.g., engine temperature, stored vapor amount). After determining the canister purge fuel vapor mass flowing into the engine cylinder, method 500 proceeds to 508.

[0062] At 508, method 500 determines the maximum number of fuel injections during a cylinder cycle. In one example, the maximum number of fuel injections may be determined based on engine speed, the minimum fuel injector pulse width, and the minimum fuel injector off time. Specifically, the total available fuel injection duration may be determined using the following equation: tot_avail_inj_period=crankshaft_deg_duration⋅1 / N⋅1 rev / 360 degrees where tot_avail_inj_period is a total period of time during which fuel injection is permitted, crankshaft_deg_duration is a predefined crankshaft interval in crankshaft degrees during which fuel injection is permitted (for example, TDC intake stroke to 20 crankshaft degrees after BDC intake stroke), and N is engine speed in rpm. The variable tot_inj_period can then be represented by the sum of the minimum fuel injector pulse width and the minimum fuel injector off time, expressed as: tot_tim_limited_injections=int(tot_inj_period÷(min_inj_on_pw+min_inj_off_tm)) where tot_tim_limited_injections is the total number of fuel injections limited by the amount of time available to inject fuel, min_inj_on_pw is the minimum pulse width of the fuel injector, min_inj_off_tm is the minimum off time of the fuel injector, and int is a function that yields the integer part of the operation in parentheses. Thus, the integer part of the result is the total number of fuel injections possible under the current engine operating conditions (for example, at the current engine speed). Method 500 proceeds to 510 after determining the total number of fuel injections limited by the time available to inject fuel.

[0063] At 510, method 500 adjusts fuel injector timing to set the maximum number of fuel injections during the assigned engine crankshaft interval in the presence or absence of purged fuel vapors from the fuel vapor storage canister. In one example, method 500 begins by subtracting the amount of purged fuel vapors entering the cylinder (vapor_lbm), determined at 506, from the amount of fuel desired in the cylinder (fuel_lbm), as determined at 504. The result is the total amount of fuel to be injected to the cylinder during the subsequent cylinder cycle (inj_lbm).

[0064] The total amount of fuel to be injected into the cylinder during the subsequent cylinder cycle (inj_Ibm) is divided by the fuel mass injected by the fuel injector when the fuel injector is operated at the minimum fuel injector pulse width to determine a maximum number of fuel injections possible to inject the total amount of fuel to be injected during the cylinder cycle when the fuel is injected at a minimum fuel injector pulse width. The operation can be expressed as follows: max_num_inj=int(inj+lbm÷mass_inj_min_pw) where max_num_inj is a maximum number of fuel injections during the cylinder cycle to provide the target fuel quantity for the cylinder and where max_num_inj is limited by the minimum pulse width of the fuel injector, inj_Ibm is the total fuel quantity to be injected to the cylinder and where mass_inj_min_pw is the fuel mass that is injected when the fuel injector is operated with the minimum fuel pulse width and the minimum injector off time.

[0065] Thus, method 500 adjusts the number of fuel injections based on the desired engine air-fuel ratio, as well as the purge vapor air-fuel ratio and the total purge flow rate. If the concentration of fuel vapors flowing to a cylinder increases, the number of fuel injections may be decreased. If the concentration of fuel vapors flowing to the cylinder decreases, the number of fuel injections may be increased. If the desired engine air-fuel ratio is enriched, the number of fuel injections may be increased. If the desired engine air-fuel ratio is leaned, the number of fuel injections may be reduced.

[0066] The method 500 determines the maximum number of fuel injections into a cylinder during a cycle of the cylinder by determining the minimum total number of time-limited injections (tot_tim_limited_injections) and the total number of minimum fuel pulse width limited injections (max_num_inj), expressed as: tot_num_inj=min(max_num_inj,tot_tim_limited_injections) where tot_num_inj is the number of fuel injections to be provided during the subsequent fuel injection period. In this manner, method 500 selects the maximum number of fuel injections during a cylinder cycle, taking into account the minimum fuel injector pulse width, the minimum fuel injector off time, and the minimum amount of fuel injected when the fuel injector is operating at the minimum fuel pulse width.

[0067] Method 500 determines the amount of fuel to be injected during each fuel injection of the cylinder cycle by dividing the fuel mass to be injected (inj_Ibm) by the total number of fuel injections (tot_num_inj). The fuel mass to be injected during each of the injections is then determined by indexing a fuel injector transfer function, as shown in Fig. 2, with the fuel mass to be injected during each injection converted into a fuel injector pulse width. The fuel injector transfer function outputs the fuel injector on-time, which is output to the fuel injector beginning with the fuel injection duration described at 508 and following each fuel injector off-time. In some examples, the fuel injector off-time may be the minimum fuel injector off-time. Further, the injector on-time and off-time may be adjusted based on the number of fuel injections. For example, the determined number of fuel injections may be evenly spaced in time or crankshaft angle over the desired fuel injection interval.Alternatively, fuel injection pulses may be spaced unevenly in time or with respect to crankshaft position. In one example, the specific injector on and off timing may be retrieved from a table or function that empirically maintains determined injector opening (e.g., on) and closing (e.g., off) timings, possibly indexed based on the desired number of fuel injections, engine speed, and engine load.

[0068] Furthermore, method 500 may limit an amount of fuel vapor entering a cylinder by maintaining or reducing a duty cycle of a purge control valve to adjust the fuel vapor purge flow rate when a number of fuel injections during a cylinder cycle reaches a threshold. For example, if fuel is to be injected at least twice during a cylinder cycle, the purge flow may be limited to a threshold by limiting a duty cycle of a purge valve. If two fuel injections are desired and the engine air-fuel ratio is limited to a threshold rich limit, the purge flow rate may be reduced to allow two fuel injections. If desired, a minimum number of fuel injections may be provided under conditions where multiple fuel injection events are desired.

[0069] Additionally, method 500 may adjust the spark timing and the number of spark events provided to the cylinder as the number of fuel injections changes. For example, as the number of fuel injections increases, the spark timing may be retarded from the base spark timing (e.g., a spark timing based on engine speed and load) to account for the additional number of fuel injections. As the number of fuel injections decreases, the spark timing may be advanced from the base spark timing.

[0070] Furthermore, method 500 may also adjust cam timing when adjusting the number of fuel injections. For example, with increasing numbers of fuel injections, cam timing may be retarded to keep an intake valve open later in a compression stroke. Closing the intake valve later may help further mix the cylinder contents. In this way, soot formation may be further reduced. Method 500 ends after determining the number and duration of fuel injections during a cylinder cycle.

[0071] The fuel valve on and off timing of each fuel injection valve of the engine can be adjusted according to the method of Fig. 5. Furthermore, the method of Fig. 5 may be repeated in each engine cycle for each fuel injector. In this way, the number of fuel injections during each cylinder cycle can be updated based on the amount of fuel vapor entering the cylinder from the fuel vapor storage canister, the minimum on-time or minimum pulse width of the fuel injector, and the minimum off-time of the fuel injector.

[0072] Thus, the procedure of Fig. 5 Operation of an engine, comprising: supplying an amount of fuel from a fuel vapor storage canister to a cylinder; and adjusting a number of fuel pulses supplied to the cylinder via a fuel injector during a cycle of the cylinder in response to the amount of fuel supplied to the cylinder from the fuel vapor storage canister during the cylinder cycle. In this way, the number of fuel injections during a cylinder cycle can be maximized for greater cylinder mixing.

[0073] The procedure of Fig. 5 further provides that the amount of fuel is injected directly to the cylinder and that a pulse width of at least one fuel pulse delivered to the cylinder is reduced while the amount of fuel delivered to the cylinder from the fuel vapor storage canister increases. The method includes delivering the number of fuel pulses delivered to the cylinder during an intake stroke of the cylinder. Further, the method includes delivering the number of fuel pulses delivered to the cylinder during an intake stroke and a compression stroke of the cylinder. Further, the method includes limiting the amount of fuel delivered to the cylinder from the fuel vapor storage canister to maintain a minimum number of fuel pulses delivered to the cylinder via a fuel injector.The method further includes wherein the number of fuel pulses delivered to the cylinder is further based on an engine torque request.

[0074] In some examples, the procedure of Fig. 5 further provides operation of an engine, comprising: supplying an amount of fuel from a fuel vapor storage canister to a cylinder; and adjusting a number of fuel pulses supplied to the cylinder via a fuel injector during a cycle of the cylinder in response to the amount of fuel supplied to the cylinder from the fuel vapor storage canister during the cylinder cycle and a minimum fuel injector pulse width. In this way, the method accommodates a minimum fuel injector pulse width, whereby repeatable amounts of injected fuel can be provided when the injector is operated at a nominal voltage and fuel pressure.

[0075] The method further includes where the minimum fuel injector pulse width is a fuel pulse width at which a substantially repeatable minimum amount of fuel is delivered via the fuel injector. The method further includes where the number of fuel pulses delivered to the cylinder is further based on a minimum fuel injector off time. The method further includes where the number of fuel pulses delivered to the cylinder is further based on an engine torque request.

[0076] In some examples, the method includes where the number of fuel pulses delivered to the cylinder is further based on an amount of fuel delivered to the cylinder when the fuel injector is operating at the minimum pulse width. Further, the method includes where the number of fuel pulses delivered to the cylinder is delivered during an intake stroke of the cylinder. Further, the method includes where at least one fuel pulse delivered by the fuel injector during the cylinder cycle is delivered during a compression stroke of the cylinder. Thus, the amount of time during which a number of fuel injections occur during a cylinder cycle may vary with operating conditions.Finally, the method includes adjusting the amount of fuel supplied to the cylinder from the fuel vapor storage canister by adjusting a duty cycle supplied to a purge control valve.

[0077] As is obvious to an average expert, this can Fig.5 may represent one or more of a number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Thus, various illustrated steps or functions may be performed in the order illustrated, in parallel, or in some cases omitted. Likewise, the processing order may not necessarily achieve the objects, features, and advantages described herein, but is provided for convenience of illustration and description. Although not explicitly illustrated, it will be apparent to one of ordinary skill in the art that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy employed.

[0078] This concludes the description. A reading thereof by one of ordinary skill in the art would reveal many changes and modifications without departing from the spirit and scope of the description. For example, single-cylinder, I2, I3, I4, I5, V6, V8, V10, V12, and V16 engines powered by natural gas, gasoline, diesel, or alternative fuel configurations could advantageously utilize the present description.

Claims

[1] A method of operating an engine (10), comprising: Supplying a quantity of fuel from a fuel vapor storage tank (144) to a cylinder (30) and Setting a number of fuel pulses delivered to the cylinder (30) via a fuel injector (66) during a cycle of the cylinder (30) in response to the fuel vapor supplied to the cylinder (30) from the fuel vapor storage canister (144) amount of fuel supplied during the cylinder cycle and a minimum pulse width of the fuel injection valve (66), wherein the amount of fuel is injected directly to the cylinder (30) and wherein a pulse width of at least one fuel pulse supplied to the cylinder (30) is reduced while the amount of fuel supplied to the cylinder (30) from the fuel vapor storage canister (144) increases. [2] The method of claim 1, wherein the minimum pulse width of the fuel injector (66) is a fuel pulse width wherein a substantially repeatable minimum amount of fuel is delivered via the fuel injector (66). [3] The method of claim 1, wherein the number of fuel pulses delivered to the cylinder (30) is further based on a minimum off time of the fuel injector (66). [4] The method of claim 1, wherein the number of fuel pulses delivered to the cylinder (30) is further based on an engine torque request.

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