Method and device for operating an internal combustion engine

The disclosure relates to a method for operating an internal combustion engine having a plurality of cylinders, the method comprising, during one working cycle, distributing fuel for each cylinder of the plurality of cylinders among a plurality of injection processes according to settable split factors which respectively define a setpoint fuel mass and/or injection duration and time setting of each respective injection process for the plurality of individual injection processes, wherein random variation is carried out for at least one injection process.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to German Patent Application No. 102012209785.6, filed on Jun. 12, 2012, the entire contents of which are hereby incorporated by reference for all purposes.

FIELD

The disclosure relates to a method and to a device for operating an internal combustion engine. In particular, the disclosure relates to a method and to a device for operating an internal combustion engine by means of which instability in the running of the engine which occurs during operation of the engine and is due to the generation of pressure waves can be avoided or at least reduced.

BACKGROUND AND SUMMARY

The operation of an internal combustion engine with multiple injections (also referred to as “split injection”) is used, inter alia, for reducing particle emissions. In this context, the conventional injection of an individual fuel injection during the working cycle is replaced by the injection of a plurality of chronologically distributed fuel injections, wherein comparatively less fuel is used for each individual injection process than in the case of an individual injection.

However, a problem which occurs in practice in the case of multiple injections is that pressure waves which occur in the fuel line of systems with high fuel pressure during operation in a mode with multiple injections can cause the internal combustion engine to operate in an unstable fashion.

This instability is caused by undesired deviation in the actual injection quantity brought about by pressure pulsations in the common fuel line. Depending on the distribution and chronological arrangement of the multiple injections at all the cylinders, these high pressure pulsations can occur due to unfavorable superimposition of the excitation as a result of the respective extraction of fuel.

The inventors herein have recognized the above issues and provide a method to at least partly address them. In one embodiment, a method for operating an internal combustion engine having a plurality of cylinders comprises, during one working cycle, distributing fuel for each cylinder of the plurality of cylinders among a plurality of injection processes according to settable split factors which respectively define a setpoint fuel mass and/or injection duration and time setting of each respective injection process for the plurality of individual injection processes, wherein random variation is carried out for at least one injection process.

Thus, the method according to the disclosure for operating an internal combustion engine comprising a plurality of cylinders, during one working cycle, the fuel injection for each of the cylinders is distributed among a plurality of injection processes according to settable split factors which respectively define the setpoint fuel mass and/or the injection duration and the time setting of the respective injection process for the individual injection processes, wherein random variation is carried out for at least one injection process.

The present disclosure is based, in particular, on the concept of performing random variation of the split factors for individual injection processes within a range defined by a tolerance value during an operating mode of the internal combustion engine with multiple injections. By means of such a device or by increasing the splitting or apportioning of the fuel injection for the individual injection processes it is possible as a result to reduce the pressure waves within the fuel line. In this context, a reduction in pressure waves within the fuel line can already be achieved by marginal change in the split factors for each injection process and each cylinder.

DETAILED DESCRIPTION

Engines may be configured to operate under a split injection mode, wherein more than fuel injection is performed to a given cylinder during a cylinder cycle. Depending on the frequency of the injections, pressure waves may build in the fuel system, leading to degradation of the system components. To disrupt and/or prevent such waves, various parameters of the fuel injections may be randomly adjusted. For example, the fuel mass of a first injection event of a plurality of injection events of a cylinder may be randomly adjusted away from the setpoint fuel mass determined based on operating conditions. The adjusted fuel mass may be compensated by adjusting a later fuel injection event (performed to the same cylinder during the same cylinder cycle).

According to the disclosure, the random variation can occur in the time setting for at least one injection process. According to a further embodiment, the random variation is carried out by means of the time setting of at least one injection at one cylinder in such a way that the excitation of the pressure pulsations is detuned.

According to one embodiment, the random variation of the setpoint fuel mass and/or of the injection duration therefore takes place for at least two injection processes in such a way that pressure waves which occur are reduced in comparison with an analogous operation without the random variation.

According to a further embodiment, the random variation takes place both in the time setting for at least one injection process and in the setpoint fuel mass and/or injection duration for at least two injection processes.

According to a further embodiment, the random variation of the setpoint fuel mass takes place for at least two injection processes in a predefined tolerance range. According to a further embodiment, the random variation of the setpoint fuel mass takes place for at least two injection processes in such a way that pressure waves which occur are reduced in comparison with an analogous operation without the random variation.

According to one embodiment, the random variation of the setpoint fuel mass takes place for each of the cylinders in such a way that the sum of the setpoint fuel masses which are to be injected in all the injection processes remains unchanged for the respective cylinder.

According to one embodiment, the method also has a fault diagnosis step in which a fault message is generated as a function of the value of the sum of the split factors. This can take place, in particular, when the sum of the split ratios for a respective combustion cycle is greater than one (and/or is greater than 100%).

The disclosure also relates to a device for operating an internal combustion engine comprising a plurality of cylinders and which is configured to carry out a method having the features described above.

FIG. 1shows a schematic depiction of a vehicle system6including an engine system8. The engine system8may include an engine10having a plurality of cylinders30. Engine10includes an engine intake23and an engine exhaust25. Engine intake23includes a throttle62fluidly coupled to the engine intake manifold44via an intake passage42. The engine exhaust25includes an exhaust manifold48eventually leading to an exhaust passage35that routes exhaust gas to the atmosphere. Throttle62may be located in intake passage42downstream of a boosting device, such as turbocharger50, or a supercharger, and upstream of an after-cooler (not shown). As such, the after-cooler may be configured to reduce the temperature of the intake air compressed by the boosting device. Turbocharger50may include a compressor52, arranged between intake passage42and intake manifold44. Compressor52may be at least partially powered by exhaust turbine54, arranged between exhaust manifold48and exhaust passage35, via turbine shaft56.

Engine exhaust25may include one or more emission control devices70, which may be mounted in a close-coupled position in the exhaust. One or more emission control devices may include a three-way catalyst, lean NOx filter, SCR catalyst, PM filter, etc.

Engine system8may further include one (as depicted) or more knock sensors90distributed along engine block11. When included, the plurality of knock sensors may be distributed symmetrically or asymmetrically along the engine block. Knock sensor90may be an accelerometer, or an ionization sensor.

The vehicle system6may further include control system14. Control system14is shown receiving information from a plurality of sensors16(various examples of which are described herein) and sending control signals to a plurality of actuators81(various examples of which are described herein). As one example, sensors16may include exhaust gas sensor126(located in exhaust manifold48), knock sensor(s)90, temperature sensor127, and pressure sensor129(located downstream of emission control device70). Other sensors such as pressure, temperature, air/fuel ratio, and composition sensors may be coupled to various locations in the vehicle system6, as discussed in more detail herein. As another example, the actuators may include fuel injectors66, and throttle62. The control system14may include a controller12. The controller may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on instruction or code programmed therein corresponding to one or more routines. Example control routines are described herein with reference toFIGS. 6-8.

FIG. 2depicts an example embodiment of a combustion chamber or cylinder of internal combustion engine10(ofFIG. 1). Engine10may receive control parameters from a control system including controller12and input from a vehicle operator130via an input device132. In this example, input device132includes an accelerator pedal and a pedal position sensor134for generating a proportional pedal position signal PP. Cylinder (herein also “combustion chamber”)30of engine10may include combustion chamber walls136with piston138positioned therein. Piston138may be coupled to crankshaft140so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft140may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Further, a starter motor may be coupled to crankshaft140via a flywheel to enable a starting operation of engine10.

Cylinder30can receive intake air via a series of intake air passages142,144, and146. Intake air passage146can communicate with other cylinders of engine10in addition to cylinder30. In some embodiments, one or more of the intake passages may include a boosting device such as a turbocharger or a supercharger. For example,FIG. 2shows engine10configured with a turbocharger including a compressor174arranged between intake passages142and144, and an exhaust turbine176arranged along exhaust passage148. Compressor174may be at least partially powered by exhaust turbine176via a shaft180where the boosting device is configured as a turbocharger. However, in other examples, such as where engine10is provided with a supercharger, exhaust turbine176may be optionally omitted, where compressor174may be powered by mechanical input from a motor or the engine. A throttle20including a throttle plate164may be provided along an intake passage of the engine for varying the flow rate and/or pressure of intake air provided to the engine cylinders. For example, throttle20may be disposed downstream of compressor174as shown inFIG. 2, or alternatively may be provided upstream of compressor174.

Exhaust passage148can receive exhaust gases from other cylinders of engine10in addition to cylinder30. Exhaust gas sensor128is shown coupled to exhaust passage148upstream of emission control device178. Sensor128may be selected from among various suitable sensors for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), a NOx, HC, or CO sensor, for example. Emission control device178may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors (not shown) located in exhaust passage148. Alternatively, exhaust temperature may be inferred based on engine operating conditions such as speed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhaust temperature may be computed by one or more exhaust gas sensors128. It may be appreciated that the exhaust gas temperature may alternatively be estimated by any combination of temperature estimation methods listed herein.

Each cylinder of engine10may include one or more intake valves and one or more exhaust valves. For example, cylinder30is shown including at least one intake poppet valve150and at least one exhaust poppet valve156located at an upper region of cylinder30. In some embodiments, each cylinder of engine10, including cylinder30, may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper region of the cylinder.

Intake valve150may be controlled by controller12by cam actuation via cam actuation system151. Similarly, exhaust valve156may be controlled by controller12via cam actuation system153. Cam actuation systems151and153may 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 that may be operated by controller12to vary valve operation. The position of intake valve150and exhaust valve156may be determined by valve position sensors155and157, respectively. In alternative embodiments, the intake and/or exhaust valve may be controlled by electric valve actuation. For example, cylinder30may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems. In still other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system, or a variable valve timing actuator or actuation system.

In some embodiments, each cylinder of engine10may be configured with one or more fuel injectors for providing fuel thereto. As a non-limiting example, cylinder30is shown including one fuel injector166. Fuel injector166is shown coupled directly to cylinder30for injecting fuel directly therein in proportion to the pulse width of signal FPW received from controller12via electronic driver168. In this manner, fuel injector166provides what is known as direct injection (hereafter also referred to as “DI”) of fuel into combustion cylinder30. WhileFIG. 2shows injector166as a side injector, it may also be located overhead of the piston, such as near the position of spark plug192. Such a position may improve mixing and combustion when operating the engine with an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located overhead and near the intake valve to improve mixing.

Fuel may be delivered to fuel injector166from a high pressure fuel system80including fuel tanks, fuel pumps, and a fuel rail. For example, fuel tank19may store liquid fuel such as gasoline, fuel with a range of alcohol concentrations, various gasoline-ethanol fuel blends (e.g., E10, E85), and combinations thereof. As shown, fuel tank19may be coupled to a fuel pump21for pressurizing fuel delivered to fuel rail51. A fuel rail pressure sensor102in fuel rail51may be configured to sense the current fuel rail pressure and provide the sensed value to controller12of control system14. In some examples, pump21may be controlled based on the fuel rail pressure sensed by sensor102, and/or based on other parameter values. Fuel tank19may be refilled with liquid fuel via fueling port83. Fuel may be delivered from fuel tank19to the injectors of engine10, such as example injector166, via fuel rail51. While only a single injector coupled with the fuel rail is depicted, it will be appreciated that additional injectors are provided for each cylinder.

Alternatively, fuel may be delivered by a single stage fuel pump at lower pressure, in which case the timing of the direct fuel injection may be more limited during the compression stroke than if a high pressure fuel system is used. Further, while not shown, the fuel tank may have a pressure transducer providing a signal to controller12. It will be appreciated that, in an alternate embodiment, injector166may be a port injector providing fuel into the intake port upstream of cylinder30.

As described above,FIG. 2shows only one cylinder of a multi-cylinder engine. As such each cylinder may similarly include its own set of intake/exhaust valves, fuel injector(s), spark plug, etc.

Controller12is shown inFIG. 2as a microcomputer, including microprocessor unit106, input/output ports108, an electronic storage medium for executable programs and calibration values shown as read only memory chip110in this particular example, random access memory112, keep alive memory114, and a data bus. Controller12may receive various signals from sensors coupled to engine10, in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor122; engine coolant temperature (ECT) from temperature sensor116coupled to cooling sleeve118; a profile ignition pickup signal (PIP) from Hall effect sensor120(or other type) coupled to crankshaft140; throttle position (TP) from a throttle position sensor; absolute manifold pressure signal (MAP) from sensor124, cylinder AFR from EGO sensor128, and abnormal combustion from a knock sensor and a crankshaft acceleration sensor. Engine speed signal, RPM, may be generated by controller12from signal PIP. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold.

Storage medium read-only memory110can be programmed with computer readable data representing instructions executable by processor106for performing the methods described below as well as other variants that are anticipated but not specifically listed.

FIG. 3first shows an overview of the components used in a method according to the disclosure for operating an internal combustion engine in the multiple injection mode. In one example, the components depicted inFIG. 3may be included as part of controller12described above.

According to the block diagram inFIG. 3, a split unit107serves to calculate the fuel mass to be injected from the required fuel mass for each injection process, which fuel mass to be injected is defined by a torque model. The calculated fuel mass is identical for the respective injection processes for all the cylinders. In this context, it is possible to set different split ratios for each state of the internal combustion engine.

An injection duration unit121serves to calculate the injection duration for each injection process. This calculation includes pressure differences over the respective injection process, which includes calculation of the internal pressure of the cylinder as a function of the valve timing and the dynamic fuel flow for each injection nozzle.

A time setting unit131serves to set the time of the individual injection processes, wherein this time setting for each injection process is defined by the start of injection (SOI) and the end of injection (EOI). Within the time setting unit131the start of injection (SOI) can be set manually for each engine state. Depending on the state of the internal combustion engine, the injection system can permit up to, for example, five injection processes per cylinder and engine cycle. In this context, the start of injection is typically set for the first, the second, the third and the fourth injection process, whereas for the fifth injection process the end of injection (EOI) is set. In the case of stratified combustion or stratified loading operation, the fifth injection process can also be coupled with the injection setting.

According toFIG. 4, the split unit107in the exemplary embodiment is divided into three functional blocks111,109and113. A first functional block111permits a ratio to be set which defines the splitting for each engine cycle and for all the cylinders. The ratio can be predefined for each engine state or set manually. Furthermore, according toFIG. 4simple multiplication of the individual split ratios by the fuel mass calculated on the basis of the torque model takes place.

For each of the five injection processes, according toFIG. 4a split ratio (or a split factor) can be set in the function block111, which split ratio (or split factor) defines the setpoint fuel mass (mf_inj), the injection duration (ti_dinj_dur) and the time setting (a_inj_soi/a_inj_eoi) determined by the start of injection and the end of injection. In this context, it is possible to set dynamically for each injection nozzle, in a different way, the Q parameter which is predefined conventionally by the supplier for the injection nozzle.

According toFIG. 4, the setpoint fuel masses (mf_inj_1 to mf_inj_5) are fed to a second function block109. This second function block109according toFIG. 4serves, as is explained below, to reduce the generation of pressure waves during operation of the internal combustion engine with multiple injections.

A detailed diagram for explaining this second function block109is illustrated inFIG. 54. If the function block109is activated, in the exemplary embodiment random variation of the fuel mass takes place for the first injection process and for the second injection process, whereas the third injection process remains unchanged. This variation takes place in a random block which is provided for this purpose, in a region which is defined by a predefined tolerance value. By means of such a reduction or increase in the splitting or apportioning of the fuel injection for the individual injection processes it is possible as a result to reduce the pressure waves within the fuel line.

In this context, in order to maintain the engine load, it is necessary for the resulting sum of the setpoint fuel masses to be injected to remain unchanged. If, for example, in the above example the fuel mass which is used for the first injection process is reduced by three percent (%), the fuel mass which is used for the second injection process must be increased by a factor which results in the same setpoint fuel mass.

Furthermore, according toFIG. 5, the five injection ratios for an injection process are combined in one vector “rat_inj_spli”. As is also apparent fromFIG. 5, in a third function block113it is checked whether the sum of the split ratios for a respective injection cycle is greater than one (corresponding to a value above 100%), in which case a fault message is generated.

Turning now toFIG. 6, a method600for injecting fuel to an engine is depicted. Method600may be carried out by an engine controller, such as controller12ofFIGS. 1 and 2, according to instructions stored thereon. Method600sets the parameters of fuel injection for each combustion event of each cylinder of an engine based on operating conditions, and then if indicated, randomly varies at least one of the injection parameters to prevent or disrupt pressure pulsations within the fuel rail or other fuel system components.

At602, engine operating parameters are determined. The operating parameters may be determined from signals received from various engine sensors. For example, engine speed, engine load, engine temperature, duration since an engine start, fuel rail pressure, exhaust aftertreatment regeneration state, and other parameters may be measured, estimated, or inferred.

At604, fuel injection parameters are set based on the previously determined operating conditions. The fuel injection parameters include a split ratio, which includes the number of injections performed at each cylinder per combustion cycle and the fuel mass of each split injection, injection timing (start and/or end of injection), and injection duration. The injection parameters may be optimized for different operating parameters. For example, during an engine start sequence, fewer injection events may be performed than during engine running conditions. Further, a purge or regeneration of an exhaust aftertreatment device (such as a lean NOx trap or particulate filter) may rely on increased exhaust temperature; the fuel injection parameters may be adjusted during the purge to increase the exhaust temperature.

At606, method600includes split injecting fuel to a cylinder. Injecting fuel to a cylinder includes, at608, injecting a total fuel mass based on desired air-fuel ratio (AFR). That is, the total amount of fuel injected to one cylinder during one cylinder cycle may be selected to maintain air-fuel ratio at a desired ratio (such as stoichiometry) and deliver a requested amount of torque. Further, as indicated at610, this total fuel mass is distributed among the split injections according to the split ratio set at604.

Upon commencement of fuel injection, fuel injection pressure is monitored at612. The monitoring of fuel injection pressure may include monitoring fuel rail pressure, the pressure in one or more lines delivering fuel from the rail to the injectors, the pressure of the injectors themselves, and/or other suitable pressures. At614, method600determines if a repetitive pressure fluctuation is detected. The repetitive pressure fluctuation may include a pressure wave propagated in the fuel rail, fuel delivery lines, or other fuel system components. The repetitive pressure fluctuation may be detected based on the monitored fuel injection pressure. In one example, pressure waves with amplitudes below a threshold may not be detected as a repetitive pressure fluctuation. The threshold amplitude of the pressure wave may be an amplitude above which degradation to an engine component may occur, and/or it may be an amplitude above which vibrations may be noticeable to a vehicle operator. The pressure fluctuation may be repetitive, that is occurring at least more than one time in a give time period.

If a repetitive pressure fluctuation is not detected, method600proceeds to616to maintain the fuel injection parameters determined at604, and method600returns. If a repetitive pressure fluctuation is detected, method600proceeds to618to randomly vary one or more split injection parameters to disrupt the pressure fluctuation. This may include randomly adjusting the split ratio and/or duration, as indicated at620and explained in more detail below with regards toFIG. 7. Further, randomly varying one or more split injection parameters may include randomly adjusting injection timing, as indicated at622and explained in more detail below with regards toFIG. 8. The random adjustment to the fuel injection parameter or parameters may be performed on the current combustion cycle, or it may be performed on a subsequent combustion cycle. Further, this random adjustment may be applied to the fuel injection of a single cylinder of a multi-cylinder engine, while maintaining the initial injection parameters of the remaining cylinders, or it may be applied to the fuel injection events of more than one cylinder of the engine.

The random adjustment to the fuel injection parameters may alter the mass of fuel delivered during two or more split injections. To ensure that the total mass of fuel is delivered to the cylinder, the fuel mass of each split injection may be summed and compared to the target total fuel mass, set based on desired air-fuel ratio. At624, it is determined if 100% of the total fuel mass is delivered. If no, that is, if more or less fuel than desired is actually delivered, method600proceeds to624to set an error flag, and take default action. For example, the random adjustment may be ceased, additional fuel may be injected in a subsequent combustion event, etc.

If 100% of the total fuel mass is delivered, method600optionally proceeds to626to repeat the random variation for subsequent combustion cycles, and then method600returns.

Turning now toFIG. 7, a method700for randomly varying a split ratio of a cylinder fuel injection event is illustrated. Method700may be performed by a controller, during the execution of method600explained above, responsive to an indication to randomly vary the mass and/or duration of a given split fuel injection. Method700includes, at702, determining an initial fuel mass of a first split injection. The initial fuel mass may be determined based on a total fuel mass to be delivered to the cylinder and a fraction of that fuel mass that is to be delivered by the first injection, otherwise referred to as the split ratio. For example, if three fuel injections of equal mass are to be performed on a single cylinder during a given combustion cycle, the initial fuel mass of the first split injection may be ⅓ of the total fuel mass.

At704, a tolerance function is applied to maintain the first fuel mass in a threshold range. For example, the tolerance function may limit the random variation, described below, to adjusting the first fuel mass by less than a threshold amount, such as 10%. Because the fuel injection parameters are set based on operating conditions (to deliver the fuel in amounts and timings optimized for maximizing power, minimizing particulates, or other desired outcomes), major adjustments to the amount of fuel delivered by a split injection could result in diminished torque, excess particulates, or other undesired conditions. Thus, the tolerance function may maintain the variation to the injection parameters within a range that allows disruption of the pressure waves without perturbations to fuel efficiency, emissions, or other parameters.

The range of variation imposed by the tolerance function may be a suitable range. For example, it may be a fixed range, such as a variation of less than 10%. In other examples, the tolerance may depend on the initial injection parameters. As an example, if the initial fuel mass that the first split injection is intended to deliver is relatively small, the tolerance may only allow a 2% decrease in the fuel mass, to prevent metering errors that may occur when delivering small amounts of fuel, while allowing a larger increase in the fuel mass, such as 5%.

At706, a random variation function is applied to the initial fuel mass of the first split injection. The random variation function may be a random number generator, bounded by the tolerance described above, such as a true random number generator or a pseudo-random number generator. In one example, the fuel mass and/or duration of fuel injection may be adjusted by a percentile amount specified by the random variation function. Further, in some embodiments, other filters or functions may be applied to generate the variation applied to the fuel mass, such as a Gaussian function. Further still, additional functions may be applied to the random number generated by the random number generator, to ensure the number is different from the last random number generated, for example.

At708, the fuel mass and/or duration of the first split injection may be adjusted based on the random variation applied at706. For example, the fuel mass of the first split injection may be increased by 5%. To deliver the adjusted fuel mass, the injection duration may also be adjusted. For example, at a steady fuel injection pressure, in order to increase the fuel mass of the first split injection by 5%, the duration that the fuel injector is open may be increased to deliver the extra fuel. At710, the fuel mass and/or injection duration of the second split injection may be adjusted by a corresponding amount. To maintain a desired or commanded total fuel injection mass for the whole cylinder cycle, the second split injection may be adjusted to compensate for the change to the first split injection. For example, if the fuel mass of the first injection is increased by 5%, the fuel mass of the second split injection may be decreased by 5%. In this way, the random adjustment to the first injection may be compensated by an adjustment to the second injection in order to deliver the same amount of fuel to the cylinder as would be delivered without the random variation. The compensation is typically performed on one other split injection of the cylinder cycle, and thus if a third split injection is performed, its mass and duration are maintained and not adjusted, as indicated at712.

FIG. 8illustrates a method800for randomly adjusting injection timing of a split injection. Similar to method700, method800may be performed by a controller, during the execution of method600explained above, responsive to an indication to randomly vary the injection timing of a given split fuel injection.

At802, method800includes determining an initial timing of a first split fuel injection. The timing of the injection may include a start of injection, or an end of injection. The injection timing of the split injection may be determined based on operating parameters, as explained above. At804, a tolerance is applied to maintain the injection timing within a threshold range, similar to the tolerance applied at704above. At806, a random variation function is applied to randomly vary the timing of the split injection. The random variation may similar to the random variation performed at706of method700. At808, the timing of the first split injection is adjusted based on the random variation determined at806.

While the methods described above randomly adjust fuel mass or injection timing of a split injection, in some embodiments both fuel mass and injection timing may be adjusted. Further, in some embodiments the fuel mass of a first split injection may be adjusted, and the fuel mass and injection timing of a second split injection may also be adjusted. Further, the above-described methods randomly vary the fuel injection parameters responsive to an indication that a pressure wave is propagating the fuel system. However, in some embodiments, the random variation may be carried out proactively before a pressure wave has built, in order to prevent the build-up of the pressure wave. In such embodiments, the random variation may be performed automatically at each cylinder cycle or performed automatically on selected cylinder cycles.

Thus, the methods described provide for a method, comprising split injecting fuel in two or more injections into a cylinder during a single combustion cycle; and randomly varying at least one of the two or more injections. The randomly varying may include randomly varying one or more of a fuel injection mass, injection timing, and injection duration. In one example, the randomly varying includes randomly varying a fuel injection mass of a first injection of the two or more injections, and the method may further comprise adjusting a fuel injection mass of a second injection of the two or more injections based on, and to compensate for, the random variation of the first injection, where a desired total amount of injected fuel is maintained for the two or more injections even with the random variation. In another example, the randomly varying includes randomly varying an injection timing of one of the two or more injections.

In an embodiment, a method comprises split injecting fuel including at least a first fuel mass and a second fuel mass to a cylinder during a first cylinder cycle; and randomly varying a split ratio of the first fuel mass relative to the second fuel mass for each of a plurality of subsequent cylinder cycles. The method includes randomly adjusting the first fuel mass and adjusting the second fuel mass to compensate for the adjustment to the first fuel mass. Adjusting the first fuel mass comprises adjusting the first fuel mass by less than a threshold amount from an initial setpoint fuel mass. The initial setpoint fuel mass may be set based on engine operating conditions. In embodiments, the method may further comprise injecting a third fuel mass during the first cylinder cycle, wherein the third fuel mass is maintained over each subsequent engine cycle. A total mass of fuel injected to the cylinder may remain constant over each subsequent cylinder cycle.

As used in the disclosure, cylinder cycle or combustion cycle may refer to, in a four stroke engine, a complete cycle of intake, compression, expansion, and exhaust strokes of a given cylinder. Each cylinder may undergo a combustion or cylinder cycle in a complete engine cycle. Additionally, while the methods described above randomly adjust fuel mass, duration, and/or timing of a first injection, it is to be understood the random adjustment to an injection parameter may be applied to a suitable injection of the two or more injections performed in a cylinder cycle. For example, if a split injection includes five injection events, the first, second, third, fourth, or fifth injection may be randomly varied. Further, if an injection event is randomly varied such that its fuel mass is changed, a later fuel injection may be adjusted to compensate for the random variation. Thus, if a first injection is randomly varied, a second, third, fourth, or fifth injection may be adjusted to compensate for the variation. In some embodiments, to compensate for the variation of a first injection, both a second and a third injection may be adjusted. Other injection adjustments are possible, as discussed in more detail below.

Referring now toFIG. 9, an example split fuel injection sequence is shown. The sequence ofFIG. 9may be provided by the system ofFIGS. 1 and 2executing the method ofFIG. 6. Cylinder timing for an engine including cylinders1,2,3, and4is shown. Note that actual fuel injection times may differ from the timings shown inFIG. 9sinceFIG. 9is intended to illustrate the method described herein rather than show particular fuel injection timings.

The first, third, fifth, and seventh plots from the top ofFIG. 9represent cylinder strokes for cylinders number one, three, four, and two of a four cylinder engine. Intake strokes are abbreviated INT while compression strokes are abbreviated as COMP. Expansion strokes are abbreviated as EXP while exhaust strokes are abbreviated as EXH.

The second, fourth, sixth, and eighth plots from the top ofFIG. 9represent fuel injection events for cylinders number one, three, four, and two of the engine. As illustrated inFIG. 9, three injection events (or split injections) occur for each cylinder during each combustion cycle. The first split injection, second split injection, and third split injection for a first cylinder cycle of cylinder number one are indicated as902a,904a, and906a, respectively. The first split injection, second split injection, and third split injection for a first cylinder cycle of cylinder number three are indicated as908a,910a, and912a, respectively. The first split injection, second split injection, and third split injection for a first cylinder cycle of cylinder number four are indicated as914a,916a, and918a, respectively. The first split injection, second split injection, and third split injection for a first cylinder cycle of cylinder number two are indicated as920a,922a, and924a, respectively.

Likewise, the first split injection, second split injection, and third split injection for a second cylinder cycle of cylinder number one are indicated as902b,904b, and906b, respectively. The first split injection, second split injection, and third split injection for a first cylinder cycle of cylinder number three are indicated as908b,910b, and912b, respectively. The first split injection, second split injection, and third split injection for a first cylinder cycle of cylinder number four are indicated as914b,916b, and918b, respectively. The first split injection, second split injection, and third split injection for a first cylinder cycle of cylinder number two are indicated as920b,922b, and924b, respectively.

The number of split injections, as well as the injection timing, fuel mass, and duration for each split injection may be determined based on operating conditions, as explained above. In the illustrated example, the engine may be operating at idle with stratified combustion, and as such, for each combustion event at a given cylinder, three split injections are performed, with the third split injection timing corresponding with ignition timing.

During the injections for the first cylinder cycle of cylinder one, each injection event902a,904a, and906adelivers an equal fuel mass. However, at the second cylinder cycle, a random variation has been applied to the fuel mass of the first injection902b, resulting in a decrease of the fuel mass. The second injection904bis increased by a corresponding amount. The third injection906bdelivers the same mass of fuel as the third injection906aof the first cylinder cycle.

For cylinder three, the random variation has been applied to the first injection908aof the first cylinder cycle, increasing the fuel mass. The second injection910ais decreased by a corresponding amount, and the third injection912adoes not change from the initial setpoint fuel mass. For the second cylinder cycle, the first injection908bis increased due to the random variation and the second injection910bis decreased.

For cylinder four, the fuel mass of the first injection914a, second injection916a, and third injection918aof the first cylinder cycle are equal to the initial setpoint fuel mass. However, the injection timing of the first injection914ahas been retarded. For the second cylinder cycle, the timing of the second injection916bhas been advanced.

For cylinder two, the fuel mass of the first injection920aof the first cylinder cycle has been increased and the fuel mass of the second injection922ahas been decreased. Also, the injection timing of the second injection922ahas been retarded. For the second cylinder cycle, the fuel mass of the first injection920bhas been decreased, the fuel mass of the second injection922bhas been increased, and the injection timing of the second injection922bhas been advanced.

Thus, the sequence illustrated inFIG. 9includes random variation to fuel mass alone in some examples, random variation to injection timing alone in other examples, and random variation to both fuel mass and injection timing in other examples. Whether random adjustment to the injection parameters is performed only on one parameter or multiple parameters may depend on the amplitude of the pressure wave, tolerance of the random variation of each injection parameter (for example, if the tolerance for adjusting the fuel mass is very narrow, the injection timing may also be adjusted), and other parameters.

Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system.