METHOD AND SYSTEMS FOR CONTROLLING FUEL INJECTION

Abstract

Method for an engine that includes the following: Measuring fuel rail pressure, Determining a threshold cylinder pressure based on the fuel rail pressure during a hot engine restart, adjusting the fuel injection timing into an engine cylinder such that for the entire duration that a fuel injection device is open, the cylinder pressure is greater than a threshold cylinder pressure and during a cold engine start, the setting of a fuel injection timing into an engine cylinder, wherein the fuel injection device is open at least when the cylinder pressure is below the threshold cylinder pressure, where the specified threshold cylinder pressure is increased when the measured fuel rail pressure increases.

Description

Technical area

[0001] The present application relates to methods and systems for controlling injection timing and fuel pulse width in an internal combustion engine. General state of the art and brief description

[0002] Direct fuel injection, where fuel is delivered directly into an engine's combustion chamber, can be used to deliver fuel to an engine. The fuel injector can receive high-pressure fuel from a rail pressurized by a high-pressure fuel pump. Direct injection can allow flexibility in the timing of fuel delivery to the cylinder depending on operating conditions.

[0003] DE 10 2006 000 172 A1 discloses a control unit for an internal combustion engine. A fuel pressure sensor is used to measure the pressure between a fuel pump and an injection device. Furthermore, an in-cylinder pressure sensor and an ECU are disclosed, which controls the injection based on the pressures.

[0004] US Pat. No. 7,234,440 B2 discloses a fuel injection strategy for reducing cold-start emissions from direct-injection gasoline engines. Fuel injection occurs via several separate injection processes.

[0005] US Pat. No. 5,941,209 A discloses a fuel injection device and method for direct-injection engines. An ECU, which calculates the opening and closing times of the injector, is used to calculate a reference point in time to determine when the pressure in the combustion chamber reaches the injection pressure in the valve.

[0006] DE 10 2006 042 086 A1 discloses a hybrid vehicle system with an engine featuring variable valve timing. During engine operation, the opening and closing timing of the intake and exhaust valves can be variably adjusted.

[0007] The inventors herein have recognized that during hot engine restarts, due to the high pressure in the fuel rail caused by the high-temperature fuel, combined with minimal injector opening times, a higher fuel flow than required may be delivered to the engine. Therefore, the air-fuel ratio cannot be maintained due to the increased amount of fuel delivered to the engine. As a result, effective emission control may be reduced because engine emissions may increase.

[0008] Thus, in one example, the above problems may be at least partially addressed by a method for an engine. An example method includes, during a hot engine restart, adjusting fuel injection timing into an engine cylinder such that, for an entire duration that a fuel injector is open, the cylinder pressure is greater than a threshold cylinder pressure. In this way, it is possible to harness the compression created by the piston during the compression stroke to counteract the effects of the minimum injector opening time.

[0009] In one example, the threshold cylinder pressure may increase with an increase in fuel rail pressure. Therefore, the fuel injection opening and closing timings may be retarded compared to a cold-start condition or a hot-restart condition where injection timing is not significantly modified based on cylinder pressure. By retarding fuel injection to a condition where cylinder pressure is higher, the higher cylinder pressure increases a fuel pulse width necessary to achieve a desired amount of injected fuel for a given rail pressure. In this way, the fuel pulse width may be more easily modified, for example, in response to air-fuel ratio requirements for emissions control.

[0010] It should be understood that the above summary is provided to introduce, in a 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 clearly defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any disadvantages noted above or in any part of this disclosure. Short description of the drawings Fig. Figure 1 shows a schematic diagram of an engine. Fig. Figure 2 shows a schematic diagram of a cylinder of an engine coupled to a fuel system. Fig. Figure 3 shows timing charts illustrating fuel injection in relation to cylinder pressure and piston position. Fig. 4 shows a flowchart illustrating a routine for controlling fuel injection into an engine during an engine cold start. Fig. 5 shows a flowchart illustrating a routine for controlling fuel injection into an engine during a hot engine restart. Fig. 6 shows a flowchart illustrating a routine for controlling fuel injection into an engine during a hot engine restart. Fig. Figure 7 shows timing charts illustrating fuel injection in relation to engine speed and fuel pulse width. Detailed description

[0011] The following description relates to various embodiments of methods and systems for controlling fuel injection into an engine. In one example method for operating an engine, during a hot engine restart, the fuel injection timing of a cylinder of the engine is adjusted such that, for an entire duration that a fuel injector is open, the cylinder pressure is greater than a threshold cylinder pressure. In such an example, the opening and closing timings of a fuel injection may each be retarded so that fuel is injected at a later time when the cylinder pressure is greater. For example, the threshold cylinder pressure may be adjusted in response to the fuel rail pressure such that the threshold cylinder pressure increases with increased fuel rail pressure.When fuel is injected at a higher cylinder pressure, when the difference between the cylinder pressure and the fuel rail pressure is smaller, the flow rate of fuel to the cylinder decreases, and the fuel injector must stay open longer to deliver a desired amount of fuel to the cylinder. Therefore, there is less opportunity to deliver a larger amount of fuel than required to the cylinder during a hot engine restart, and a desired air-fuel ratio can be maintained. The hot engine restart may include an engine start from rest shortly following previous engine operation such that the engine temperature is elevated above a threshold and elevated relative to the ambient temperature.In contrast, an engine cold start may involve an engine start from rest, where the engine has cooled to ambient temperature, for example, below the threshold temperature. Various alternative approaches may also be used to identify engine cold starts or hot restarts, such as engine coolant temperature, engine cylinder block temperature, and various others.

[0012] Fig. 1 is a schematic diagram illustrating one embodiment of a cylinder of a multi-cylinder engine 10, which may be included in a propulsion system of an automobile. The engine 10 is controlled at least in part by a control system including a controller 12 and by input from a vehicle operator 132 via an input device 130. In this example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. A combustion chamber (i.e., a cylinder) 30 of the engine 10 includes combustion chamber walls 32 with a piston 36 disposed therein. As depicted, the piston 36 is coupled to a crankshaft 40 such that reciprocating motion of the piston is translated into rotary motion of the crankshaft. The crankshaft 40 may be coupled to at least one drive wheel of a vehicle through an intervening transmission system.Furthermore, a starter motor may be coupled to the crankshaft 40 via a flywheel to enable a starting process of the engine 10.

[0013] As in the example of Fig. 1, the combustion chamber 30 receives intake air from an intake manifold 44 via an intake passage 42 and expels combustion gases via an exhaust passage 48. The intake manifold 44 and the exhaust passage 48 may be selectively connected to the combustion chamber 30 via a respective intake valve 52 and exhaust valve 54, respectively. In some embodiments, the combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.

[0014] In this example, intake valve 52 and exhaust valve 54 are controlled by cam actuation via respective cam actuation systems 51 and 53. Cam actuation systems 51 and 53 may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems, which may be actuated by controller 12 to vary valve operation. The positions of intake valve 52 and exhaust valve 54 are determined by position sensors 55 and 57, respectively. In alternative embodiments, intake valve 52 and / or exhaust valve 54 may be controlled via electrical valve actuation.For example, cylinder 30 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including a CPS and / or a VCT system.

[0015] Furthermore, the fuel injector 66 is shown coupled directly to the combustion chamber 30 to inject fuel directly therein, in proportion to the pulse width of the signal FPW received from the control unit 12 via an electronic driver 68. In this way, the fuel injector 66 provides what is known as direct injection of fuel into the combustion chamber 30. The fuel injector may be mounted, for example, in the side of the combustion chamber or in the top of the combustion chamber (as in Fig. 1). The fuel may be supplied to the fuel injector 66 through a fuel system 70, which, as described below with reference to Fig. 2, includes a fuel tank, a fuel pump, and a fuel rail. In some embodiments, the combustion chamber 30 may alternatively or additionally include a fuel injector disposed within the intake manifold 44 in a configuration that provides what is known as port injection of fuel into the intake port upstream of the combustion chamber 30.

[0016] As in Fig. 1, the intake passage 42 includes a throttle valve 62 having a throttle plate 64. In this particular example, the position of the throttle plate 64 may be varied by the controller 12 via a signal sent to an electric motor or actuator integrated with the throttle valve 62, a configuration commonly referred to as electronic throttle control (ETC). In this manner, the throttle valve 62 may be actuated to vary the intake air provided to the combustion chamber 30 among the other engine cylinders. The position of the throttle plate 64 is provided to the controller 12, for example, by a throttle position signal TP. The intake passage 42 further includes a mass air flow sensor 120 and a manifold air pressure sensor 122 for providing respective MAF and MAP signals to the controller 12.

[0017] In some embodiments, the combustion chamber 30 or one or more other combustion chambers of the engine 10 may be operated in a compression ignition mode, with or without an ignition spark. In other examples, the engine 10 may additionally or alternatively include an ignition system that, under select operating modes, provides an ignition spark to the combustion chamber 30 via a spark plug in response to a pre-ignition signal received from the controller 12.

[0018] An exhaust gas sensor 126 is shown coupled to the exhaust passage 48 upstream of an emissions control device 70. The sensor 126 may be any suitable sensor for providing an indication of the exhaust gas air-fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a dual-state oxygen sensor or EGO, a HEGO (heated EGO), a NO x-, HC, or CO sensor. The emission control device 70 is shown arranged downstream of the exhaust gas sensor 126 along the exhaust passage 48. The device 70 may be a three-way catalyst (TWC), a NO x -catchers, various other emission control devices, or combinations thereof. In some embodiments, the emission control device 70 may be periodically reset during operation of the engine 10 by operating at least one cylinder of the engine within a particular air-fuel ratio.

[0019] The control unit 12 is in Fig. 1 as a microcomputer including a microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values, shown in this particular example as a read-only memory chip 106, random access memory 108, battery-powered memory 110, and a data bus. In addition to those previously discussed signals, control unit 12 may receive various signals from sensors coupled to engine 10, including induced mass air flow (MAF) measurements from mass air flow sensor 120, engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114, an ignition profile pickup (PIP) signal from a Hall effect sensor 118 (or other type) coupled to crankshaft 40, throttle position (TP) from a throttle position sensor, and a manifold absolute pressure (MAP) signal from sensor 122.An engine speed signal, RPM, may be generated by controller 12 from the PIP signal. The manifold pressure signal, MAP, from a manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold. Note that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor, for example, may provide an indication of engine torque. Further, this sensor, along with the sensed engine speed, may provide an estimate of the charge (including air) introduced into the cylinder. In one example, sensor 118, also used as an engine speed sensor, may generate a predetermined number of equally spaced pulses during each revolution of the crankshaft.

[0020] The storage medium read-only memory 106 may be programmed with computer-readable data representing instructions executable by the processor 102 to perform the methods described below, as well as other variations contemplated but not specifically listed.

[0021] As described above, Fig. 1 only one cylinder of a multi-cylinder engine, it should be understood that each cylinder may similarly include its own set of intake / exhaust valves, fuel injector, spark plug, etc.

[0022] Fig. Figure 2 shows another embodiment of a cylinder, such as the combustion chamber 30 of the engine 10, described above with reference to Fig. 1. As described in Fig. 2, the combustion chamber 30 is fluidly coupled to the fuel system 70. Fig. 1 and Fig. 2 include like parts and are therefore designated by like reference numerals, and some of the parts may not be described in detail again.

[0023] As in Fig. 2, the fuel system 70 includes the fuel tank 72, the fuel pump 74, and the fuel rail 76. The fuel tank 72 contains a suitable fuel for combustion, which is supplied to the combustion chamber 30. As one example, the fuel tank 72 may contain diesel fuel. In other examples, the fuel tank 72 may contain gasoline or an alcohol-containing fuel blend, such as E85 (containing approximately 85% ethanol and 15% gasoline) or M85 (containing approximately 85% methanol and 15% gasoline).

[0024] The pump 74 may be a high-pressure pump that supplies the fuel rail 76 with high-pressure fuel. The fuel rail 76 may, for example, be a high-pressure accumulator that stores the fuel at high pressure until it is delivered to the combustion chamber 30. The fuel system 70 further includes a pressure sensor 78 in communication with the controller 12 and configured to send a signal indicative of the fuel rail pressure to the controller 12. The pressure sensor 78 may be any suitable sensor for measuring pressure. In some examples, more than one pressure sensor may be arranged at multiple locations in the fuel rail. As one example, each fuel injector may have a corresponding pressure sensor. As shown in Fig. 2, the fuel is injected from the fuel rail 76 via the fuel injector 66 directly into an upper portion of the combustion chamber 30. In the Fig. In the example shown in Figure 2, the fuel injector 66 is actuated by the controller 12. For example, the fuel injector may be actuated by a solenoid controlled by the controller 12.

[0025] Fig. Figure 3 shows a series of timing charts illustrating fuel injection during different conditions of cylinder pressure and piston position. Fig. 4 to 6 show flowcharts illustrating control routines for injecting fuel into a cylinder of an engine, such as the combustion chamber 30 of the engine 10, described above with reference to Fig. 1 and Fig. 2 during various in Fig. 3 described conditions. Fig. For example, Figure 4 shows a routine for determining the timing and pulse width of fuel injection under a cold start condition. Fig. Figure 5 shows a routine for determining the timing and pulse width of fuel injection under the condition of a hot engine restart, and Fig. 6 shows a routine for determining the timing and pulse width of fuel injection based on the cylinder pressure under a hot engine restart condition.

[0026] As explained above, Fig. Figure 3 shows a series of graphs illustrating piston position, cylinder pressure, and fuel injection over time. This example illustrates fuel injection under various conditions to show its relationship to cylinder pressure and piston position.

[0027] Curve 302 shows the piston position during an intake stroke and a compression stroke of an engine cycle for the cylinder. For example, at time t3, the piston reaches bottom dead center (BDC), and the intake stroke ends, and the compression stroke begins. Curve 304 shows the corresponding pressure in the cylinder during the intake and compression strokes. For example, during the intake stroke, the intake valve opens, allowing charge air to enter the cylinder, and a volume of the combustion chamber increases as the piston approaches bottom dead center at time t3. As a result, the pressure in the cylinder drops. On the other hand, during the compression stroke, the pressure in the cylinder increases as the valve closes, and the volume of the combustion chamber decreases as the piston approaches top dead center (TDC) at time t6.Curve 304 is shown as an example of the in-cylinder pressure and may indicate an average pressure in the cylinder. For example, during a cold start condition, the in-cylinder pressure during the intake stroke may be greater than indicated by curve 304, and during a hot engine restart, the in-cylinder pressure may be less than indicated by curve 304.

[0028] Furthermore, Fig. 3 illustrates fuel injections A, B, and C, each corresponding to a different condition. Fuel injection A corresponds to fuel injection during an engine cold start. An engine cold start may include, for example, conditions such as coolant temperature less than a threshold temperature and engine shutdown immediately prior to start for more than a threshold duration. As shown, fuel injection during the engine cold start may occur in a window 306 between time t1 and time t5, where the earliest fuel injector open time is t1 and the latest fuel injector close time is t5. The window for fuel injection (e.g., window 306) may be determined based on conditions such as ambient temperature and pressure and fuel rail pressure, for example.

[0029] Fuel injection B corresponds to fuel injection during a hot engine restart. A hot engine restart may include, for example, conditions such as coolant temperature greater than a threshold temperature and engine shutdown immediately prior to start-up for less than a threshold duration. As shown, fuel injection during the hot engine restart may occur in a window 310 between time t2 and time t5, where the earliest fuel injector open time is t2 and the latest fuel injector close time is t5. As described above, the window for fuel injection (e.g., window 310) may be determined based on conditions such as ambient temperature and pressure and fuel rail pressure, for example.During a hot engine restart, the fuel rail pressure may be higher than during a cold engine start, so the start of the fuel injection window may be delayed relative to the cold start condition. For example, due to the high-pressure fuel in the fuel rail and the relatively low pressure in the combustion chamber during the intake stroke, the fuel flow rate from the fuel rail to the combustion chamber may be higher during a hot engine restart than during a cold engine start. Consequently, the fuel injection window may be delayed during a hot engine restart such that the fuel injection quantity (e.g., the pulse width) can be better controlled.However, even if the fuel injection window is delayed, in some examples, a higher amount of fuel than required may be delivered to the cylinder due to the higher pressure in the fuel rail and the increased fuel flow velocity to the combustion chamber. As shown in . Fig. 3, the window 310 corresponding to fuel injection B begins at time t2, which is later than the time t1 at which the window 308 corresponding to fuel injection A begins.

[0030] Furthermore, the Fig. In the example depicted in Figure 2, fuel injection A is shown at 308, and fuel injection B is shown at 312. As shown, fuel injection B has a much shorter duration (e.g., pulse width) than fuel injection A. As described above, this is due to the higher pressure in the fuel rail during a hot engine restart compared to a cold engine start, resulting in a higher fuel flow rate from the fuel rail to the combustion chamber when the injector is open. Consequently, a greater amount of fuel flows into the combustion chamber in a shorter period of time.

[0031] Fuel injection C corresponds to fuel injection based on cylinder pressure during a hot engine restart. As shown, fuel injection during the hot engine restart may occur in a window 314 between time t4 and time t5, where the earliest fuel injector open time is t4 and the latest fuel injector close time is t5. The fuel injection window (e.g., window 314) may be determined based on conditions such as ambient temperature and pressure, fuel rail pressure, and, in this example, cylinder pressure. As described above, during a hot engine restart, the fuel rail pressure may be higher than during a cold engine start; therefore, the start of the fuel injection window may be delayed relative to the cold start condition.By monitoring cylinder pressure, a time at which a threshold pressure occurs can be determined, and fuel injection can be scheduled to occur only after the threshold cylinder pressure is reached. In this way, a longer fuel pulse width can be delivered to the cylinder in a way that better controls the amount of fuel delivered to the cylinder. For example, fuel injection C is shown at 316. Fuel injection C has a longer duration than fuel injection B because fuel injection C begins at a later time than fuel injection B when the cylinder pressure is greater.

[0032] Thus, as described in more detail below, in one embodiment, a method for operating an engine during a hot restart includes estimating a fuel rail pressure and estimating a cylinder pressure in a cylinder of the engine. The method further includes scheduling fuel injection timing such that fuel is injected directly into the cylinder only when the cylinder pressure is greater than a threshold cylinder pressure, where the threshold cylinder pressure is based on the fuel rail pressure. The injection timing may include, for example, injector opening timing, injector closing timing, and average injection time.

[0033] Fig. 4 shows a flowchart illustrating a routine 400 for controlling fuel injection into a cylinder of an engine during an engine cold start.

[0034] As an example, routine 400 of the Fig. 3 illustrated and described above.

[0035] At 402 of routine 400, engine operating conditions are determined. The operating conditions may include coolant temperature, ambient temperature and pressure (e.g., barometric pressure), air-fuel ratio, and the like.

[0036] Once the operating conditions are determined, a determination is made at 404 as to whether the engine is under a cold start. As an example, the engine may be determined to be under cold start conditions if the engine coolant temperature is less than a threshold temperature and / or if a duration for which the engine was off immediately prior to starting is greater than a threshold duration. Further, engine start may be determined if the engine is cranking or idling for a duration less than a threshold duration. If it is determined that the engine is not under cold start conditions, the routine moves to 416, and ongoing operation continues.

[0037] On the other hand, if it is determined that the engine is under a cold start, routine 400 proceeds to 406, where ambient temperature and pressure are determined. For example, during an engine cold start, before the engine is warmed up, a temperature and pressure in the intake manifold may be close to ambient pressure. Therefore, a cylinder pressure may be greater by an amount corresponding to the ambient temperature and pressure during an intake stroke under cold start operation than during warmed-up operation.

[0038] At 408, the routine determines a window for injecting fuel. The fuel injection window may be determined based on parameters such as the desired air-fuel ratio, the in-cylinder air-fuel mixture, intake valve timing, and the like. Once the fuel injection window is determined, routine 400 proceeds to 410, where a fuel injection amount is determined. The fuel injection amount may be determined based on the desired air-fuel ratio, cam timing, and the like.

[0039] Once the fuel injection window and fuel injection amount are determined, routine 400 proceeds to 412, where the fuel injection timing and pulse width are adjusted based on operating conditions. For example, based on ambient pressure during a cold start, fuel may be injected as early as possible when ambient pressure is higher due to a smaller pressure differential between the fuel rail and the combustion chamber. This allows the fuel to have a maximum amount of time to mix with intake air before combustion occurs. Further, the pulse width may be adjusted to be longer or shorter depending on the ambient temperature and pressure and the time at which injection begins.In some examples, fuel injection may be set such that fuel injection is split and fuel is injected into the cylinder at multiple times (e.g., 2 injections, 3 injections, 4 injections, etc.) in a single combustion cycle. In such an example, the total desired amount of fuel to be injected into the engine may be distributed across the multiple injections such that the pulse width for each injection is reduced during the combustion cycle. Thereafter, at 414 of routine 400, fuel injection is performed at the set time and with the set pulse width.

[0040] As a result, the timing and pulse width of fuel injection can be scheduled based on ambient conditions while the engine is warming up. This allows fuel injection to be scheduled to ensure efficient engine operation under cold-start conditions.

[0041] As you progress to Fig. 5, a flowchart is shown illustrating a routine 500 for controlling fuel injection into a cylinder of an engine during a hot engine restart. As an example, routine 500 may be Fig. 3 illustrated and described above.

[0042] At 502 of routine 500, engine operating conditions are determined. The operating conditions may include coolant temperature, ambient temperature and pressure (e.g., barometric pressure), air-fuel ratio, and the like.

[0043] Once the operating conditions are determined, routine 500 proceeds to 504 where it is determined whether the engine is under a hot restart. For example, the engine may be determined to be under a hot restart if the engine coolant temperature is greater than a threshold temperature and / or if a duration of an engine shutdown immediately preceding starting is less than a threshold duration. Further, engine starting may be determined if the engine is cranking or idling for a duration less than a threshold duration. If it is determined that the engine is not under a hot restart, routine 500 moves to 516 where ongoing operation continues.

[0044] On the other hand, if it is determined that the engine is undergoing a hot restart, routine 500 proceeds to 506, where a window for injecting fuel is determined. The fuel injection window may be determined based on parameters such as the desired air-fuel ratio, the in-cylinder air-fuel mixture, intake valve timing, and the like. Once the fuel injection window is determined, routine 400 proceeds to 410, where a fuel injection amount is determined. The fuel injection amount may be determined based on the desired air-fuel ratio, cam timing, and the like.

[0045] At 510, the fuel rail pressure is determined. The fuel rail pressure may be determined, for example, by a pressure sensor located in the fuel rail and in communication with a control module. As described above, during a hot engine restart, the pressure in the fuel rail may be higher than during a cold engine start. Due to a higher pressure differential between the combustion chamber and the fuel rail, fuel may flow to the cylinder at a higher velocity. Therefore, the fuel injection timing (e.g., the start of injection, the end of injection, and / or the average injection time) may be retarded.

[0046] Once the fuel rail pressure is determined, at 512 the fuel injection timing and pulse width are adjusted based on the operating conditions. As an example, the injector opening timing, the injector closing timing, and / or the average duration the injector is open may be adjusted in response to the operating conditions. For example, due to the higher fuel rail pressure during a hot engine restart, fuel injection (e.g., injector opening timing) may begin at a later time than during a cold engine start. Furthermore, due to the higher pressure differential between the fuel rail and the combustion chamber, the pulse width may have a shorter duration than during a cold engine start, as demonstrated by fuel injection B in Fig. 3. In some examples, fuel injection may be set such that fuel injection is split and fuel is injected into the cylinder at multiple times (e.g., 2 injections, 3 injections, 4 injections, etc.) in a single combustion cycle. In such an example, the total desired amount of fuel to be injected into the engine may be distributed across the multiple injections such that the pulse width for each injection is reduced during the combustion cycle. Thereafter, at 514 of routine 500, fuel injection is performed at the set time and with the set pulse width.

[0047] In this way, fuel injection during a hot engine restart may be scheduled to maintain, for example, a desired air-fuel ratio. However, due to the high pressure in the fuel rail, the pulse width may be relatively short, thereby increasing the need for precise control of the injector if pulse width modulation is desired to control the air-fuel ratio. In some examples, the desired pulse width may be less than a minimum or threshold pulse width. Consequently, fuel injection may be scheduled based on cylinder pressure, as described in more detail below with reference to Fig. 6 is described.

[0048] As you progress to Fig. 6, a flowchart illustrating a routine 600 for controlling fuel injection into a cylinder of an engine based on cylinder pressure during a hot engine restart is shown. As an example, routine 600 may be the Fig. 3 illustrated and described above.

[0049] At 602 of routine 600, engine operating conditions are determined. The operating conditions may include coolant temperature, ambient temperature and pressure (e.g., barometric pressure), air-fuel ratio, and the like.

[0050] Once the operating conditions are determined, routine 600 proceeds to 604 where it is determined whether the engine is under a hot restart. As described above, the engine may be determined to be under a hot restart if the engine coolant temperature is greater than a threshold temperature and / or if a duration of an engine shutdown immediately preceding starting is less than a threshold duration. Further, engine starting may be determined if the engine is cranking or idling for a duration less than a threshold duration. If it is determined that the engine is not under a hot restart, routine 600 moves to 622 where ongoing operation continues.

[0051] On the other hand, if it is determined that the engine is under a hot restart, routine 600 proceeds to 606, where the routine determines a window for injecting fuel. The fuel injection window may be determined based on parameters such as the desired air-fuel ratio, the in-cylinder air-fuel mixture, intake valve timing, and the like, as described above. Once the fuel injection window is determined, routine 600 proceeds to 608, where a fuel injection amount is determined. The fuel injection amount may be determined based on the desired air-fuel ratio, cam timing, and the like.

[0052] At 610, the fuel rail pressure is determined. The fuel rail pressure may be determined, for example, by a pressure sensor disposed in the fuel rail and in communication with a control module. As described above, during a hot engine restart, the pressure in the fuel rail may be higher than during a cold engine start, resulting in a higher pressure differential between the combustion chamber and the fuel rail. Therefore, the fuel flow rate from the fuel rail to the combustion chamber may be increased, and the injection timing (e.g., the start and / or end of injection) may be delayed.

[0053] At 612, the cylinder pressure is determined. In one example, the cylinder pressure may be estimated by calculating it according to a polytropic equation of state such as: P2=(V1V2)γP1, where P2 is the in-cylinder pressure, V2 is the volume in the cylinder as determined by the crankshaft angle, and P1, V1, and γ are determined by testing. In another example, cylinder pressure may be estimated based on a lookup table stored in the engine control unit's software. For example, cylinder pressures may be measured during an engine compression stroke, and the cylinder pressures may be inserted into a curve as a function of crank position (e.g., cam timing), and the equation and / or coefficients may be stored as the lookup table.

[0054] Once the cylinder pressure is estimated, a threshold cylinder pressure is determined at 614. The threshold cylinder pressure may be a minimum cylinder pressure for fuel injection to begin. For example, above the threshold cylinder pressure, a longer base pulse width may be employed such that there is greater scope for pulse width modulation for emissions control and the air-fuel ratio may be maintained. The threshold cylinder pressure is determined in response to the measured fuel rail pressure. For example, the threshold cylinder pressure may be a cylinder pressure needed to equalize the fuel rail pressure during a hot engine restart compared to the fuel rail pressure during cold start conditions. Therefore, the threshold cylinder pressure may increase as the fuel rail pressure increases.In some examples, the threshold cylinder pressure may be determined, at least in part, based on a minimum fuel injection amount. For example, the system may have a minimum fuel injection amount that may be exceeded in a certain crank angle range when the fuel rail pressure is relatively high. In such an example, the fuel injection opening-to-closing timing may be delayed until a crank angle duration over which the cylinder pressure is greater than the threshold pressure, such that an amount of fuel greater than the minimum fuel injection amount may be delivered to the combustion chamber.

[0055] At 616 of routine 600, the fuel injection timing and pulse width are adjusted based on the operating conditions. For example, the opening and closing timing of the fuel injector may be adjusted compared to a cold start condition ( Fig. 4) or a hot engine restart condition where fuel injection is not determined based on cylinder pressure ( Fig. 5), may be delayed. During a hot engine restart, fuel injection timing may be adjusted in response to cylinder pressure, for example, by holding the fuel injector open only when cylinder pressure is greater than the threshold cylinder pressure. Further, fuel pulse width (e.g., the duration the injector is open) may be increased due to the later start of injection timing and the smaller difference between cylinder pressure and fuel rail pressure. In one example, fuel injection may be scheduled to occur entirely during the compression stroke. Further, fuel injection may be scheduled such that the injector is only open when cylinder pressure is greater than the threshold cylinder pressure.In other words, the cylinder's fuel injection timing may be adjusted such that for an entire duration that the fuel injector is open, the cylinder pressure is greater than the threshold cylinder pressure. Still further, in some examples, fuel injection may be adjusted such that fuel injection is split and fuel is injected into the cylinder at multiple times (e.g., 2 injections, 3 injections, 4 injections, etc.) in a single combustion cycle. In such an example, the total desired amount of fuel to be injected into the engine may be distributed across the multiple injections such that the pulse width for each injection is reduced during the combustion cycle.

[0056] At 618, a determination is made as to whether the cylinder pressure is greater than the threshold pressure. If the cylinder pressure is not greater than the threshold pressure, the routine waits until the cylinder pressure is greater than the threshold cylinder pressure. Once the cylinder pressure is greater than the threshold cylinder pressure, routine 600 proceeds to 620, where fuel injection is performed according to the adjusted settings.

[0057] Consequently, fuel injection during a hot engine restart can be controlled such that the fuel injector is only open when the cylinder pressure is greater than a threshold cylinder pressure. As described above, the threshold pressure can be adjusted in response to the fuel rail pressure. For example, as the fuel rail pressure increases, the threshold pressure increases. In this way, fuel injection can occur when the pressure difference between the combustion chamber and the fuel rail is smaller, allowing a longer pulse width to be used and allowing pulse width modulation, which is used to control the air-fuel ratio, to be more easily implemented.

[0058] Fig. Figure 7 shows a series of timing charts illustrating examples of engine speed, fuel pulse width, and fuel injection timing for a cold start condition and a hot restart condition. In the example of Fig. 7 the motor is at rest before time t1 and the motor starts running at time t1.

[0059] After the engine is cranked, the fuel pulse width increases such that the first combustion can occur at time t2. As the engine speed (RPM) 702 increases, the desired fuel pulse width may be decreased, for example, to reduce engine torque. During the cold start indicated by curve 704, the fuel pulse width remains above the minimum fuel pulse width (p Wmin ). Therefore, the injection timing during the cold start, indicated by curve 708, can be adjusted compared to the condition where the cylinder pressure exceeds the threshold cylinder pressure (Pthresh ) is reached, remain advanced. However, during the hot restart, the fuel pulse width drops below the minimum fuel pulse width between times t3 and t4. Therefore, the fuel injection timing is retarded between times t3 and t4 such that fuel injection occurs at a higher cylinder pressure, as indicated by curve 710. Consequently, because the cylinder pressure is higher, the same amount of fuel can be injected over a longer pulse width such that the pulse width is at least equal to the minimum pulse width, as indicated by curve 706.

[0060] In this way, it is possible to take advantage of the compression generated by the piston during the compression stroke to counteract the effects of the minimum opening time (e.g. pulse width) of the injector during a hot engine restart.

[0061] It should be noted that the exemplary control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The specific routines described herein may embody one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Therefore, various illustrated steps, operations, or functions may be performed in the illustrated sequence, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages described herein, but is provided for ease of illustration and description. One or more of the illustrated steps or functions may be performed repeatedly depending on the particular strategy employed.Furthermore, the described steps may graphically represent code to be programmed into the computer-readable storage medium in the engine control system.

[0062] It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered limiting, as numerous variations are possible. For example, the above technology may be applied to V6, R4, R6, V12, horizontally opposed four, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and the other features, functions, and / or characteristics disclosed herein.

[0063] The following claims particularly highlight certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims should be understood to encompass the inclusion of one or more such elements, neither requiring nor excluding two or more such elements.

Claims

[1] Method for an engine comprising: Measuring a fuel rail pressure, Determining a threshold cylinder pressure based on the fuel rail pressure during a hot engine restart, adjusting a fuel injection timing into an engine cylinder such that for an entire duration that a fuel injector is open, the cylinder pressure is greater than a threshold cylinder pressure, and during an engine cold start, setting a fuel injection timing into an engine cylinder, wherein the fuel injection device is open at least when the cylinder pressure is below the threshold cylinder pressure, wherein the determined threshold cylinder pressure is increased as the measured fuel rail pressure increases. [2] The method of claim 1, further comprising adjusting an injection pulse width based on the fuel rail pressure and the cylinder pressure. [3] The method of claim 1, wherein the hot engine restart includes the engine being off for a threshold duration and the coolant temperature being greater than a threshold temperature. [4] The method of claim 1, wherein the fuel injection timing includes a time at which the injector opens and a time at which the injector closes. [5] The method of claim 1, wherein the fuel injection timing includes an average time that the fuel injector is open. [6] The method of claim 1, further comprising retarding the injection timing for a fuel injection amount less than a threshold, wherein the opening to closing time is retarded until a crank angle duration over which the cylinder pressure is greater than the threshold cylinder pressure. [7] The method of claim 1, further comprising injecting fuel directly into the engine cylinder at multiple times during a combustion cycle. [8] Engine procedure which includes: Measuring a fuel rail pressure; Setting a threshold cylinder pressure in response to the fuel rail pressure, including increasing the threshold cylinder pressure in response to an increase in the fuel rail pressure; during a hot engine restart, injecting fuel directly into a cylinder, the injector being open only when the cylinder pressure is above a threshold cylinder pressure, the threshold cylinder pressure being adjusted in response to the fuel rail pressure, and during an engine cold start, injecting fuel directly into the cylinder, wherein the injection device is open at least when the cylinder pressure is below the threshold cylinder pressure. [9] The method of claim 8, further comprising, during the hot engine restart, adjusting an injection pulse width based on cylinder pressure and fuel rail pressure. [10] A method according to claim 8, wherein, during the hot engine restart, the opening and closing timing of the fuel injection are delayed. [11] The method of claim 8, wherein during engine cold start, fuel injection timing is based on ambient temperature and ambient pressure. [12] The method of claim 8, further comprising estimating the cylinder pressure based on a lookup table of predetermined values. [13] System for an engine, comprising: a fuel system having a direct injection device fluidly coupled between a fuel rail and a cylinder of the engine and configured to inject fuel directly into the cylinder, and a controller in communication with the direct injector and configured to identify a fuel rail pressure and a cylinder pressure of the cylinder and to control the direct injector to inject fuel into the cylinder during a hot engine restart only when the cylinder pressure is greater than a threshold cylinder pressure, wherein the threshold cylinder pressure is increased in response to the fuel rail pressure, the controller further configured to inject at least some fuel into the cylinder during an engine cold start when the cylinder pressure is less than the threshold cylinder pressure. [14] The system of claim 13, wherein the controller is configured to identify the cylinder pressure based on a polytropic equation of state. [15] The system of claim 13, wherein the controller is further configured to adjust an injection pulse width in response to the cylinder pressure and the fuel rail pressure. [16] The system of claim 13, wherein the controller is further configured to delay the opening and closing timing of the injector during the hot engine restart in response to the threshold cylinder pressure.

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