# Patent

## Title
Method for operating a spark ignition internal combustion engine having at least two cylinders

## Abstract

An example for operating a spark ignition engine comprises discharging exhaust gases via an exhaust system comprising exhaust pipes from the at least two cylinders coming together to form an exhaust manifold; and initiating autoignition with exhaust gas from a first, exhaust-gas-supplying cylinder, which is discharged from the first cylinder into the exhaust system, the exhaust gas is introduced into an adjacent, exhaust-gas-receiving cylinder via the exhaust system. Exhaust gas from the first cylinder mixes with the air-fuel mixture of an adjacent cylinder raising the temperature therein. Under high loads the higher temperature and density of the aircharge is suitable to undergo autoignition.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims priority to European Patent Application No. 12165111.1, filed on Apr. 23, 2012, the entire contents of which are hereby incorporated by reference for all purposes.
TECHNICAL FIELD
The application relates to ignition initiation in spark ignition engines.
BACKGROUND AND SUMMARY
In a spark-ignition engine the load is generally controlled by a throttle valve provided in an intake tract. By adjusting the throttle valve it is possible to reduce the pressure of the intake air downstream of the throttle valve to a greater or lesser degree. In this way it is possible, for a constant combustion chamber volume, to adjust the air mass, that is to say the quantity of air, via the pressure of the intake air. Low loads use heavier throttling, that is to say extensive pressure reduction in the intake tract, so that large charge cycle losses have to be accepted, particularly in the partial-load range. In this respect the fuel-air mixture in the cylinder has a lower density at low loads than at higher loads.
The load-dependent variation of the aircharge density can present problems when initiating the spark-ignition. In order to ensure reliable ignition of the fuel-air mixture at low loads, that is to say, with a less dense mixture, the electrodes of the spark plug may have a relatively large gap, in order to form a large spark path for the ignition spark. A large electrode gap uses a high ignition voltage.
If the fuel-air mixture then becomes denser as the load increases, the voltage used in order to initiate reliable ignition is also increased, since the denser fuel-air mixture present between the electrodes has an insulating effect on the crossing of the ignition spark from one electrode to the other.
The high ignition voltage used can damage the spark plug itself and/or other components, in particular current supply components carrying a high voltage, that is to say components of the electrical system of the motor vehicle. In the event of an excessive ignition voltage demand, arcing may occur between the high-voltage leads and the chassis ground. No ignition spark is formed between the electrodes and misfiring may occur.
Besides the density of the mixture, the air/fuel ratio λ also has an influence on the initiation of the spark-ignition, in particular, however, on the combustion induced by ignition sparks. The fuel-air mixture of a spark-ignition engine can be enriched or made leaner as a function of the instantaneous load T prevailing, an enrichment preferably being undertaken, that is to say the air/fuel ratio λ being reduced, as the load increases.
Enrichment (λ<1) frequently ensues whenever high exhaust gas temperatures are to be anticipated, that is to say at high loads, in order to prevent a thermal overload of individual components of the internal combustion engine. This is done by injecting more fuel than can be burned with the quantity of air delivered, the excess fuel likewise being heated and vaporized, so that the temperature of the combustion gases falls. This approach is to be regarded as disadvantageous from various energy standpoints, particularly with regard to the fuel consumption of the internal combustion engine, and with regard to the pollutant emissions, but is recognized as admissible and practical.
Making the fuel-air mixture leaner as the load diminishes is a measure aimed at dethrottling of the internal combustion engine, less fuel being injected than could be burned with the quantity of air delivered, that is to say more fresh air is introduced into the cylinders than is necessary for combustion of the fuel introduced, thereby diluting the mixture. These variations in aircharge density and content may make spark initiation difficult.
The inventors have recognized the above mentioned problems and herein disclose a method for a spark ignition engine capable of initiating combustion via auto-ignition when it is advantageous. In the method according to the disclosure account is taken of the various load-specific demands of the spark plug in that the ignition of the fuel-air mixture is initiated either by spark-ignition or by auto-ignition—preferably as a function of load, T. In order to initiate auto-ignition, exhaust gas discharged from one cylinder into the exhaust discharge system, is introduced into another cylinder, in order to induce auto-ignition by this ignition gas.
A method is disclosed for operating a spark ignition engine, comprising: discharging exhaust gases from each of at least two cylinders via an exhaust system comprising exhaust pipes from the at least two cylinders coming together to form an exhaust manifold; and initiating compression ignition with exhaust gas from a first, exhaust-gas-supplying cylinder, which is discharged from the first cylinder into the exhaust system, the exhaust gas is introduced into an adjacent, exhaust-gas-receiving cylinder via the exhaust system. The hot exhaust gas from the first cylinder does not mix completely with the fresh charge of the adjacent cylinder. During the subsequent compression stroke the trapped hot exhaust gas is being compressed and its temperature further increased such that it can serve as ignition initiator in the same way like a spark plug does. Thus in contrast and in delimitation to the known auto-ignition this method provokes a more spark-ignition-like slower combustion and is therefore suitable for high loads. Additionally, the method of the present disclosure may be adapted such that spark ignition is still active under conditions for autoignition.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Further, the inventors herein have recognized the disadvantages noted herein, and do not admit them as known.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an example cylinder of an engine.
FIG. 2 schematically shows four cylinders of an in-line engine.
FIG. 3 shows an example exhaust manifold for four cylinders.
FIG. 4 shows an example exhaust manifold for two cylinders.
FIG. 5 shows a map of one embodiment of the spark ignition internal combustion engine in schematic form indicating the areas of use of spark ignition and autoignition.
FIG. 6 shows the process flow for initiating spark via autoignition in two adjacent cylinders under high load.
FIG. 7 shows a method depicting when an engine in accordance with the present disclosure is operated under spark ignition or autoignition.



DETAILED DESCRIPTION
FIG. 1 depicts an example embodiment of a combustion chamber or cylinder of internal combustion engine 10. Engine 10 may receive control parameters from a control system including controller 12 and input from a vehicle operator 130 via an input device 132. In this example, input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Cylinder (herein also “combustion chamber’) 30 of engine 10 may include combustion chamber walls 136 with piston 138 positioned therein. Piston 138 may be coupled to crankshaft 140 so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Further, a starter motor may be coupled to crankshaft 140 via a flywheel to enable a starting operation of engine 10.
Cylinder 30 can receive intake air via a series of intake air passages 142, 144, and 146. Intake air passage 146 may communicate with other cylinders of engine 10 in addition to cylinder 14. 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. 1 shows engine 10 configured with a turbocharger including a compressor 174 arranged between intake passages 142 and 144, and an exhaust turbine 176 arranged along exhaust passage 148. Compressor 174 may be at least partially powered by exhaust turbine 176 via a shaft 180 where the boosting device is configured as a turbocharger. However, in other examples, such as where engine 10 is provided with a supercharger, exhaust turbine 176 may be optionally omitted, where compressor 174 may be powered by mechanical input from a motor or the engine. A throttle 20 including a throttle plate 164 may 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, throttle 20 may be disposed downstream of compressor 174 as shown in FIG. 1, or alternatively may be provided upstream of compressor 174.
Exhaust passage 148 may receive exhaust gases from other cylinders of engine 10 in addition to cylinder 14. Exhaust gas sensor 128 is shown coupled to exhaust passage 148 upstream of emission control device 178. Sensor 128 may 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 device 178 may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof.
Exhaust temperature may be measured by one or more temperature sensors (not shown) located in exhaust passage 148. 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 sensors 128. 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 engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 30 is shown including at least one intake poppet valve 150 and at least one exhaust poppet valve 156 located at an upper region of cylinder 14. In some embodiments, each cylinder of engine 10, including cylinder 14, may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper region of the cylinder.
Intake valve 150 may be controlled by controller 12 by cam actuation via cam actuation system 151. Similarly, exhaust valve 156 may be controlled by controller 12 via cam actuation system 153. Cam actuation systems 151 and 153 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 that may be operated by controller 12 to vary valve operation. The operation of intake valve 150 and exhaust valve 156 may be determined by valve position sensors (not shown) and/or camshaft position sensors 155 and 157, respectively. In alternative embodiments, the intake and/or exhaust valve may be controlled by electric 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 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. A cam timing may be adjusted (by advancing or retarding the VCT system) to adjust an engine dilution in coordination with an EGR flow thereby reducing EGR transients and improving engine performance.
Cylinder 30 can have a compression ratio, which is the ratio of volumes when piston 138 is at bottom center to top center. Conventionally, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio may be increased. This may happen, for example, when higher octane fuels or fuels with higher latent enthalpy of vaporization are used. The compression ratio may also be increased if direct injection is used due to its effect on engine knock.
In some embodiments, each cylinder of engine 10 may include a spark plug 92 for initiating combustion. Ignition system 190 can provide an ignition spark to combustion chamber 30 via spark plug 92 in response to spark advance signal SA from controller 12, under select operating modes. However, in some embodiments, spark plug 92 may be omitted, such as where engine 10 may initiate combustion by auto-ignition or by injection of fuel as may be the case with some diesel engines.
As a non-limiting example, cylinder 30 is shown including one fuel injector 166. Fuel injector 166 is shown coupled directly to cylinder 30 for injecting fuel directly therein in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 168. In this manner, fuel injector 166 provides what is known as direct injection (hereafter also referred to as “DI”) of fuel into combustion cylinder 14. While FIG. 1 shows injector 166 as a side injector, it may also be located overhead of the piston, such as near the position of spark plug 92. Fuel may be delivered to fuel injector 166 from a high pressure fuel system 8 including fuel tanks, fuel pumps, and a fuel rail. 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 tanks may have a pressure transducer providing a signal to controller 12. It will be appreciated that, in an alternate embodiment, injector 166 may be a port injector providing fuel into the intake port upstream of cylinder 14.
As described above, FIG. 1 shows 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.
While not shown, it will be appreciated that engine may further include one or more exhaust gas recirculation passages for diverting at least a portion of exhaust gas from the engine exhaust to the engine intake. As such, by recirculating some exhaust gas, an engine dilution may be affected which may improve engine performance by reducing engine knock, peak cylinder combustion temperatures and pressures, throttling losses, and NOx emissions. The one or more EGR passages may include an LP-EGR passage coupled between the engine intake upstream of the turbocharger compressor and the engine exhaust downstream of the turbine, and configured to provide low pressure (LP) EGR. The one or more EGR passages may further include an HP-EGR passage coupled between the engine intake downstream of the compressor and the engine exhaust upstream of the turbine, and configured to provide high pressure (HP) EGR. In one example, an HP-EGR flow may be provided under conditions such as the absence of boost provided by the turbocharger, while an LP-EGR flow may be provided during conditions such as in the presence of turbocharger boost and/or when an exhaust gas temperature is above a threshold. The LP-EGR flow through the LP-EGR passage may be adjusted via an LP-EGR valve while the HP-EGR flow through the HP-EGR passage may be adjusted via an HP-EGR valve (not shown).
Controller 12 is shown in FIG. 1 as a microcomputer, including microprocessor unit 106, input/output ports 108, an electronic storage medium for executable programs and calibration values shown as read only memory chip 110 in this particular example, random access memory 112, keep alive memory 114, and a data bus. Controller 12 may receive various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor 122; engine coolant temperature (ECT) from temperature sensor 116 coupled to cooling sleeve 118; a profile ignition pickup signal (PIP) from Hall effect sensor 120 (or other type) coupled to crankshaft 140; throttle position (TP) from a throttle position sensor; and manifold absolute pressure signal (MAP) from sensor 124. Engine speed signal, RPM, may be generated by controller 12 from 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. Still other sensors may include fuel level sensors and fuel composition sensors coupled to the fuel tank(s) of the fuel system.
Storage medium read-only memory 110 can be programmed with computer readable data representing instructions executable by processor 106 for performing the methods described below as well as other variants that are anticipated but not specifically listed.
Turning to FIG. 2, four cylinders 1, 2, 3, 4 of a four-cylinder in-line engine are shown. Each cylinder may be coupled to a common crankshaft through a connecting rod, connecting rods 202, 204, 206, and 208, may couple cylinders 1, 2, 3, and 4 respectively, to crankshaft 40.
In the snapshot shown, the pistons 210, 212 of the first and second cylinders 1, 2 are situated at bottom dead center, and the pistons 214, 216 of the third and fourth cylinders 3, 4 are situated at top dead center.
Turning now to FIG. 3 an exhaust manifold of one embodiment of the spark-ignition internal combustion engine is shown. Each cylinder 30 comprises two exhaust ports 20, 21 for discharging the exhaust gases via the exhaust discharge system, to which ports the exhaust pipes 41 are joined.
The exhaust pipes 41 of cylinders 2 and 3 join and the exhaust pipes of cylinders 1 and 4 join. The cylinder head and exhaust manifold may be in fluidic communication with exhaust passage 48 (shown in FIG. 1). Furthermore, the exhaust manifold may comprise and integrated exhaust manifold and shown components may be largely integrated into a cylinder head.
A wall portion 6, projects into the exhaust discharge system, separating the exhaust pipes 41 of adjacent cylinders 1 and 2 or 3 and 4 from one another over a segment of the exhaust discharge system starting from the exhaust ports 20, 21 of the cylinders 30. The exhaust manifold joins exhaust from cylinders 2 and 3, and separately, from 1 and 4. The separate exhaust pipes 41 merge again to form a single exhaust passage. The exhaust manifold may receive engine coolant flow to cool the cylinder head. The engine may be boosted with a turbocharger in some examples, the turbine of the turbocharger coupled to a combined exhaust manifold outlet in the cylinder head.
According to one embodiment of the present disclosure as the cylinders fire in a 1-3-4-2 order. Under high loads, valve timing is adjusted so that valve overlap exists between the exhaust valve events of the second cylinder during its exhaust stroke and the first during its expansion stroke. The same overlap exists between the third and fourth cylinders, first and third, and fourth and second. In this way as the first cylinder exhausts hot gas, the previously firing second cylinder, may intake some of the hot exhaust gas under at least partial avoidance of subsequent mixing with the residual and fresh charge of the second cylinder. Furthermore, as exhaust pipes 41 merge within the exhaust manifold cross talk may occur between cylinders 1 and 3, 3 and 4, 4 and 2, and lastly 2 and 1. Greater valve overlap may facilitate more exhaust crosstalk, for example. As a non-limiting example, advancing the opening of an exhaust valve (e.g. opening closer to TDC) of an exhaust-gas-supplying cylinder may build pressure in the cylinder such that when the exhaust valve is opened high pressure exhaust may contribute to higher crosstalk. In this way an engine may comprise four cylinders in an in-line configuration; variable valve timing; a firing order with the four cylinders fire in a 1-3-4-2 order; and a controller with memory having instructions stored therein to adjust the variable valve timing of cylinders under high loads to overlap an exhaust phase previously firing cylinders.
Turning now to FIG. 4, an example exhaust manifold for two cylinders is shown. Reference numerals are the same as those in FIG. 3. In the case of two cylinders, a single wall portion 6 separates the two cylinders. Valve timing adjustments are made such that exhaust gas crosstalk between two cylinders is encouraged.
Additional method variants are possible wherein an exhaust manifold is configured with a switchable port sequentially firing cylinders to facilitate the crosstalk of exhaust gases between those cylinders. To allow for crosstalk of hot exhaust gas into an adjacent cylinder the port, controllable by a shutoff element, may be provided in a dividing wall portion of an integrated exhaust manifold. The wall portion divides the exhaust pipes of the two cylinders—adjacent in the firing order—from one another over a limited distance. The port therein allows the transfer of exhaust gas from the one cylinder into the other cylinder. With the port opened, exhaust gas, serving as ignition gas, is introduced into the other cylinder via the exhaust discharge system and the opened port.
In the context of the present disclosure the designation of the cylinders as a first or exhaust-gas-supplying cylinder and adjacent or exhaust-gas-receiving cylinder serves to distinguish between the cylinders. Each of the cylinders may in turn serve as an exhaust-gas-receiving cylinder or exhaust-gas supplying cylinder dependent on powertrain timing.
The exhaust gas transferred from one cylinder into another cylinder is hotter than the exhaust gas returned by exhaust gas recirculation, and in particular is also hotter than the exhaust gas returned by internal exhaust gas recirculation, which by definition originates from the cylinder into which it is internally fed back again. This situation is particularly significant and particularly advantageous in view of the fact that the exhaust gas transferred is used here as ignition gas, since the temperature represents a decisive influencing variable in the initiation of auto-ignition: the higher the temperature of the ignition gas, the more reliable the initiation of auto-ignition.
In advantageous embodiments of the spark-ignition internal combustion engine the exhaust pipes of the first and the second cylinder unite in a common exhaust pipe, forming an integrated exhaust manifold inside at least the one cylinder head. In designing the exhaust discharge system the aim is to minimize the thermal inertia of the segment of the exhaust pipes between the exhaust port on the cylinder and the exhaust gas aftertreatment system, which can be achieved by reducing the mass and the length of this segment. It may be practical here to integrate the exhaust manifold as far as possible into the cylinder head.
In the case of internal combustion engines supercharged by exhaust turbochargers, the aim is to arrange the turbine as close as possible to the exhaust, that is to say the exhaust ports of the cylinders, so as to be able in this way to make optimum use of the exhaust gas enthalpy of the hot exhaust gases, which is decisively determined by the exhaust gas pressure and the exhaust gas temperature and to ensure a rapid response of the turbocharger. The thermal inertia and the volume of the pipe system between the exhaust ports of the cylinders and the turbine may also be minimized here, for which reason it is again practical to integrate the exhaust manifold as far as possible into the cylinder head.
It is also increasingly common to integrate the exhaust manifold extensively into the cylinder head in order to benefit from cooling provided in the cylinder head and so that the manifold may not be produced from highly heat-resistant materials, which are cost-intensive. Uniting the exhaust pipes as extensively as possible within the cylinder head leads to a more compact construction, whilst allowing a tighter packaging and moreover affording cost and weight advantages.
Under low loads, the method of the present disclosure does not initiate ignition by autoignition. Because of the decreased aircharge temperature and density under low loads autoignition may start or fail to occur completely, without there being any control, with the result that incomplete combustion or misfires and increased emissions of unburned hydrocarbons and carbon monoxide may occur. Consequently, it is advantageous to employ spark ignition at low loads.
In connection with the method according to the disclosure, in particular the transfer of exhaust gas from one cylinder of the internal combustion engine, via the exhaust system, into another cylinder, it must be taken into account that the cylinders of the internal combustion engine can influence each other in many different ways during exhaust and refill.
In advantageous embodiments of the spark-ignition internal combustion engine the succeeding cylinder in the firing order serves as exhaust-gas-supplying cylinder, which delivers exhaust gas serving as ignition gas, and the preceding cylinder in the firing order serves as exhaust gas-receiving cylinder, into which the ignition gas is introduced.
Two succeeding cylinders in the firing order have minimal offset in terms of their working processes and are therefore advantageous for the transfer of exhaust gas from one cylinder into the other cylinder, that is to say from the preceding cylinder in the firing order into the succeeding cylinder in the firing order.
Turning now to FIG. 5 an engine map of one embodiment of the spark ignition internal combustion engine is shown. The map shows the torque (T) and engine speed (n) regions where spark ignition and autoignition may be utilized.
According to the method represented by the map in FIG. 5, autoignition is used at high loads, whereas spark ignition is employed at low loads and toward relatively high engine speeds. It should be pointed out in this context that loads T are regarded as high particularly when: T>0.5 Tmax or T>0.65 Tmax, Tmax denotes the maximal load at a respective engine speed n.
Assuming that auto-ignition is activated, it is advantageous when the load falls below a predefined load Tthreshold to revert to spark-ignition, for which purpose the auto-ignition initiation measures cease, so that auto-ignition is deactivated.
The internal combustion engine according to the disclosure affords advantages particularly at high loads T. A spark plug serving to initiate the spark-ignition can be designed with a large electrode gap 93 (shown in FIG. 1), which ensures reliable ignition of a less dense fuel-air mixture at low loads. As the load increases or with a denser mixture there is a transition to an auto-ignition process or the auto-ignition assumes a supplementary role, in order to achieve ignition of the mixture. In this case adjustments to valve timing may be made to better facilitate crosstalk of exhaust gas from exhaust-gas-supplying cylinder 2 to exhaust-gas-receiving cylinder 1 as an example. Furthermore, an air-fuel mixture, or other parameters may be altered to further aid initiation of ignition by auto-ignition at high loads.
If the auto-ignition, that is to say the crosstalk of ignition gas for the purpose of auto-ignition, as already proposed above, is performed at high loads T, this also assists the initiation of auto-ignition by hot exhaust gases. On the one hand the ignition gas originating from the exhaust gas-delivering cylinder is hotter at higher loads than at low loads. On the other hand the basically high or higher pressure and temperature level at high loads creates good prerequisites for the initiation of auto-ignition in the exhaust gas-receiving cylinder.
In contrast to this the auto-ignition according to the disclosure is not suitable for low loads, since the onset of auto-ignition may be uncontrolled or entirely absent, so that incomplete combustion or misfiring and greater emissions of unburned hydrocarbons and carbon monoxide can occur. Consequently it may be advantageous to use spark-ignition at low loads.
Unlike the homogeneous-charge compression-ignition (HCCI) method, which is also referred to as the volume ignition method or as the controlled auto-ignition (CAI) method, known in the state of the art and in which the aim is a controlled auto-ignition of the homogenized fuel-air mixture, preferably concurrently throughout the entire cylinder or combustion chamber, in the internal combustion engine according to the disclosure the auto-ignition is initiated and locally confined by a limited quantity of hot exhaust gas, the ignition gas, as with a spark plug and in place of the spark plug. The maximum pressure and pressure gradient of the combustion are thereby limited compared to homogeneous auto-ignition and compression ignition is feasible for higher loads. It is to be assumed here is that the ignition gas originating from the exhaust gas-delivering cylinder does not mix completely with the fuel-air mixture present in the exhaust gas-receiving cylinder, but initiates the auto-ignition locally, and is to be regarded as the starting point for the combustion of the mixture.
The initiation of auto-ignition at high loads may render the spark-ignition dispensable at these loads, for which reason the high load-specific demands of the spark plug are no longer a problem, particularly the demand for a high ignition voltage at high loads, at which the internal combustion engine according to the disclosure is ignited by auto-ignition.
In addition the exhaust gas originating from the auto-ignition has a relatively low concentration of nitrogen oxides (NOx) and virtually no soot, which has an advantageous effect on the emission characteristics of the internal combustion engine.
In connection with the transfer of exhaust gas from one cylinder of the internal combustion engine into another cylinder via the exhaust discharge system allowance may be made for the fact that in the charge cycle the cylinders of the internal combustion engine may have a reciprocal influence on one another in a variety of ways.
These effects are known and under low loads valve timing may be adjusted to avoid exhaust gas crosstalk. In a four-cylinder in-line engine, the cylinders of which are operated with the firing order 1-3-4-2, the fourth cylinder, for example, may have a detrimental influence during the charge cycle on the third cylinder adjacent to it in the firing order, that is to say the, exhaust gas originating from the fourth cylinder may get into the third cylinder, before its exhaust valves close. The evacuation of the combustion gases from the fourth cylinder here is substantially based on two different mechanisms. When an exhaust valve opens at the beginning of the charge cycle, the combustion gases flow at high velocity through the exhaust port into the exhaust pipe, due to the high pressure level prevailing in the cylinder towards the end of combustion and due to the associated high pressure differential between the combustion chamber and the exhaust discharge system. This pressurized flow process is all the more pronounced the greater the load T and is accompanied by a high peak pressure, which is also referred to as a pre-exhaust surge and which travels along the exhaust pipe. In the further course of the charge cycle the pressures in the cylinder and in the exhaust pipe largely equate to one another, so that the combustion gases are now expelled due to the piston movement.
In order to counter this effect at low loads the opening period of the exhaust valves and the exhaust ports is curtailed, that is to say the exhaust is opened later or closed earlier. The shortened opening period of the exhaust valves, however, may have disadvantages with regard to the output at high engine speeds and loads
In the internal combustion engine according to the disclosure the transfer of exhaust gas from one cylinder into another cylinder is not prevented but encouraged in order to utilize this exhaust gas for initiating auto-ignition at high loads. Accordingly, it may be advantageous according to the present disclosure to increase an opening duration of the at least one exhaust port of each cylinder in order to assist the transfer of exhaust gas serving as ignition gas.
The spark-ignition can basically be deactivated as soon as ignition shifts to auto-ignition and auto-ignition is induced by ignition gas. Nonetheless it may be advantageous to apply both ignition methods in parallel, thus undertaking spark-ignition also when initiating the auto-ignition.
In advantageous embodiments of the spark-ignition internal combustion engine each cylinder is equipped with a spark plug for initiating spark-ignition.
In advantageous embodiments of the spark-ignition internal combustion engine the electrode gap of each spark plug is here designed for low loads.
A spark plug serving for the initiation of spark-ignition may be designed with a large electrode gap, which ensures the reliable ignition of a less dense fuel-air mixture at low loads. As the load increases or with less dense mixtures auto-ignition is then activated, for which purpose, among other things, valve timing is adjusted for the transfer of exhaust gas.
As has already been explained, the aim during the charge cycle is for a rapid opening of the largest possible flow cross sections, in order to minimize the throttling losses in the exhaust gas outlet flows and to ensure an efficient discharge of the exhaust gases. For this reason it is advantageous to equip the cylinders with two or more exhaust ports.
In internal combustion engines, in which each cylinder comprises at least two exhaust ports for discharging the exhaust gases from the cylinder, advantageous embodiments of the spark-ignition internal combustion engine are those in which the exhaust port, which faces and is nearest to the succeeding cylinder in the firing order, has an earlier opening time, and the exhaust port, which is arranged remotely and further away from the succeeding cylinder in the firing order, has a later opening time.
The exhaust port of the first, exhaust gas-supplying cylinder, which faces and is nearest to the succeeding cylinder in the firing order, is the exhaust port which has the shortest distance via the exhaust discharge system to the adjacent, exhaust gas-receiving cylinder. In this respect this nearest exhaust port is the exhaust port suited to the transfer of exhaust gas, the function of which, namely the transfer of ignition gas, can be suitably assisted by opening this exhaust port earlier, thereby allowing more time for the exhaust gas transfer.
The other exhaust port, which is arranged remotely and further away from the succeeding cylinder in the firing order, may be opened later.
In internal combustion engines in which each cylinder comprises at least two exhaust ports for discharging the exhaust gases from the cylinder, advantageous embodiments of the spark-ignition internal combustion engine are those in which the exhaust port, which faces and is nearest to the preceding cylinder in the firing order, has a later closing time, and the exhaust port, which is arranged remotely and further away from the preceding cylinder in the firing order, has an earlier closing time.
This embodiment also advantageously assists the transfer of exhaust gas, that is to say ignition gas. In contrast to the embodiment previously described, however, the transfer of exhaust gas is not assisted by suitable valve timings of the exhaust ports of the exhaust gas-delivering cylinder, but rather by suitable valve timings of the exhaust ports of the exhaust gas-receiving cylinder. The improvement obtained, however, is based on the same effects, an exhaust port of the exhaust gas-receiving cylinder remaining open for longer, that is to say being closed later, in order to afford the ignition gas already present in the exhaust discharge system more time for the transfer.
In advantageous embodiments of the spark-ignition internal combustion engine at least one supercharging device is provided.
The supercharging serves primarily for boosting the performance of the internal combustion engine. Here the air for the combustion process is compressed, so that a greater air mass can be fed to each cylinder per working cycle. This makes it possible to increase the fuel mass and hence the mean pressure. Supercharging is a suitable to increase the power output of an internal combustion engine for the same displacement, or of reducing the displacement for the same power output. In either case the supercharging leads to an increase in the power-to-volume ratio and to a more favorable power-to-weight ratio. For the same vehicle constraints the load population can thus be shifted towards higher loads, at which the specific fuel consumption is lower.
An exhaust turbocharger and/or a compressor, for example, may be used as supercharging device. In particularly advantageous embodiments of the spark-ignition internal combustion engine at least one exhaust turbocharger is provided as supercharging device. An exhaust turbocharger comprises a compressor and a turbine, which are arranged on the same shaft. The hot exhaust gas flow is fed to the turbine and expands, releasing energy in the turbine, so that the shaft is set in rotation. The energy which the exhaust gas flow delivers to the turbine and ultimately to the shaft is used to drive the compressor, also arranged on the shaft. The compressor delivers and compresses the charge air fed to it, thereby supercharging the cylinders. Charge-air cooling may be provided, which serves to cool the compressed combustion air before it enters the cylinders.
Various measures can be taken to optimize the torque characteristic of a supercharged internal combustion engine, for example by designing the turbine with a small cross section and simultaneous exhaust gas blow-off, but in particular through the use of multiple exhaust turbochargers, the turbines of which are arranged in parallel or in series.
In advantageous embodiments of the spark-ignition internal combustion engine direct injection is provided for introducing fuel into the cylinders.
The injection of fuel directly into the combustion chamber of the cylinder is regarded as a suitable measure for discernibly reducing the fuel consumption also on spark-ignition engines. The principle of direct injection is inherently associated with internal cooling of the combustion chamber and the mixture, thereby allowing higher compression and/or supercharging and minimized knocking.
Direct injection of the fuel into the combustion chamber is suitable for achieving stratified charging of the combustion chamber, which likewise contributes to the dethrottling of the spark-ignition operating process, since with the aid of stratified-charge operation the internal combustion engine can be made to run very lean, which affords thermodynamic advantages particularly in partial-load operation, that is to say in the low and medium load range, when small quantities of fuel are to be injected.
In internal combustion engines in which each exhaust port is equipped with an exhaust valve, which can be controlled by a valve actuating device and which opens or closes the exhaust port, advantageous embodiments are characterized in that the valve actuating device is of at least partially variable design for varying the valve timings, and the valve timings are varied according to whether a cylinder is an exhaust gas-delivering cylinder or an exhaust gas-receiving cylinder.
Turning now to FIG. 6, a method 400 is shown depicting the process flow for initiating spark via autoignition in two adjacent cylinders under high load. The cylinders in question may be, as a non-limiting example, cylinders 3 and 4 of an inline 4 cylinder engine as described above, as these cylinders are situated next to one another and fire sequentially. Furthermore, the circumstances under which an engine according to the present disclosure is adjusted to undergo auto ignition are discussed in greater detail below in reference to FIG. 7.
At step 402, a first cylinder fires under high load. This first cylinder may, for example be the third cylinder of an inline four cylinder engine fired in a 1-3-4-2 firing order. The first cylinders also fire by auto-ignition. To accomplish this, the first cylinders may have an adjusted valve timing, with positive valve overlap to retain or receive more of their own exhaust gases. In alternative embodiments, the first cylinder could be part of any engine with at least two cylinders wherein the first cylinder is next to an adjacent cylinder which fires immediately following the first cylinder in the firing order.
At step 404, the valve opening times are adjusted to allow hot exhaust gas from the first cylinder into the adjacent cylinder due to an increased open time as described above. At step 406 the exhaust valve of the adjacent cylinder has a delayed closing time, allowing it to intake the hot exhaust gas released into the exhaust pipe via the opened exhaust ports. The opening period of an exhaust port can be extended by closing the port later or in another example by opening the associated valve earlier. The extended opening period may on the one hand serve as a measure for allowing the process of transferring ignition gas to be initiated at all and in a departure from the normal operation of the internal combustion engine, that is to say a measure for starting the transfer. The extended opening period may however also serve as a measure used for improving the transfer of exhaust gas.
Extending the opening period of the exhaust ports serves to ensure that the exhaust strokes of the individual cylinders overlap or overlap to a greater degree in the course of the charge cycle. The transfer of exhaust gas serving as ignition gas from a first exhaust gas-delivering cylinder into a second exhaust gas-receiving cylinder is advantageously assisted.
In internal combustion engines in which each exhaust port is equipped with an exhaust valve, which can be controlled by an at least partially variable valve actuating device, advantageous embodiments are characterized in that the valve actuating device comprises at least two different cams for actuating the exhaust valve, at least the two different cams generating opening periods of different length of at least the one exhaust valve per cylinder.
This is advantageous with a view to the transfer of exhaust gas serving as ignition gas. In order to facilitate the transfer of exhaust gas, it is advantageous to extend the opening duration of at least the one exhaust port of each cylinder.
At step 408, hot intake gas is admitted into the adjacent combustion cylinder and mixed with the air-fuel mixture. Mixing with exhaust gases allows the aircharge to have a higher temperature than possible with intake air alone, or through traditional EGR. The higher temperature aids in initiation of autoignition.
At step 410, during the compression stroke of the adjacent cylinder the high density and temperature of the air-fuel mixture within the combustion cylinder result in autoignition. In some embodiments, as discussed above, it may be further possible to also use spark ignition in conjunction with increased valve open duration which allows hot exhaust gas into the adjacent cylinder.
Turning now to FIG. 7, a method 500 is shown depicting when an engine in accordance with the present disclosure is operated under spark ignition or autoignition conditions. The method 500 may be carried out by engine controller 12 and stored on ROM 110.
At step 502, it is determined if the load is greater than a predetermined threshold. The predetermined threshold may be T>0.5Tmax or T>0.65Tmax where T is the engine load, as non-limiting examples. The predetermined threshold for load may be based on a map such as the one shown in FIG. 5. If at 502, the engine load is not larger than the predetermined threshold (NO) the method proceeds to step 504 where spark ignition is maintained until the engine load exceeds the predetermined threshold.
If at step 502, the engine load exceeds the predetermined threshold the method proceeds to step 506 where it is determined if the exhaust temp is greater than a predetermined threshold. The predetermined threshold may be a temperature at which the exhaust gas may serve as an effective ignition starter. Exhaust gas temperature may be estimated based on engine load, air-fuel ratio, and engine speed for example or an exhaust gas temperature sensor may be arranged in exhaust passage 148. If the exhaust temperature is not greater than a predetermined threshold temperature, for example following a cold start, the method proceeds to 508 where spark ignition is maintained until the exhaust temperature is greater than the predetermined threshold.
If at step 506 the exhaust temperature is greater than a predetermined threshold (YES) the method proceeds to step 510 where the valve open times are adjusted to increased open duration allowing exhaust gas from the first cylinder to enter the adjacent cylinder. Allowing exhaust gas from the exhaust pipe of the first cylinder into the exhaust pipe of the second cylinder will result in the hot exhaust gas being taken into the combustion chamber and combined with the air-fuel mixture therein. The resultant higher temp, mixed with the high density of the aircharge within the cylinder will allow for autoignition upon compression.
Embodiments of the method in which spark ignition is deactivated as soon as a switch is made to autoignition and autoignition is induced by means of ignition gas are advantageous. The advantage of this variant of the method is that the high ignition voltages that are required for spark ignition at high loads are reliably avoided.
Nonetheless, it may be advantageous to employ both ignition methods together, e.g. to perform spark ignition even when autoignition has been initiated. If autoignition is successfully initiated, the subsequently performed spark ignition may be unnecessary, but may also not be a hindrance. If, on the other hand, initiation of autoignition accidentally fails, the continued activation of spark ignition, e.g. the maintenance of spark ignition, ensures that a misfire and the associated disadvantages may be reliably avoided. Embodiments of the method in which spark ignition is maintained even when autoignition is being induced by means of ignition gas are therefore also advantageous.
At step 512, it is again determined if the engine load is greater than the predetermined threshold. If the engine load is not below the predetermined threshold (NO) at step 512, the method proceeds to 514 where spark ignition is restored and standard valve open durations are adjusted such that exhaust gas is prevent from entering the adjacent cylinder.
Embodiments of the method in which, starting from activated autoignition, a switch back to spark ignition is made when a predeterminable load Tthreshold is undershot are advantageous, for which purpose the measures for initiating autoignition are omitted, thus deactivating autoignition.
Embodiments of the method in which, starting from activated autoignition, a switch back to spark ignition is made when a predeterminable engine speed nthreshold is exceeded are advantageous, for which purpose the measures for initiating autoignition are omitted, thus deactivating autoignition.
If at step 512, it is determined that the engine load is greater than the predetermined threshold (YES) auto ignition is maintained and the valve open duration is adjusted to allow exhaust gas from the first cylinder into the exhaust pipe of the adjacent cylinder until the load is not greater than the predetermined threshold. The method then returns.
It should be appreciated that the method may be adapted to accommodate any engine with at least two cylinders. Furthermore, in some circumstances the method may be adapted such that the valve open duration is adjusted to allow exhaust gas from a first cylinder into the adjacent cylinder to supply ignition gas, but spark ignition via the spark plug may still be used. This embodiment, may be used, for example, following a cold start when exhaust gases may not be high enough temperature to serve as ignition gas. Additionally, the valve open duration may be adjustable by degrees such that in some scenarios more or less exhaust gas may be permitted to enter the adjacent cylinder. All of the above method variants are further compatible with a standard EGR system, turbocharging, or additional system or treatment, peripheral to, or located in the exhaust gas system as discussed above.
A system and method are disclosed for operating a spark ignition engine, comprising: discharging exhaust gases from each of at least two cylinders via an exhaust system comprising exhaust pipes from the at least two cylinders coming together to form an exhaust manifold; and initiating autoignition with exhaust gas from a first, exhaust-gas-supplying cylinder, which is discharged from the first cylinder into the exhaust system, the exhaust gas is introduced into an adjacent, exhaust-gas-receiving cylinder via the exhaust system. Exhaust gas from the first cylinder mixes with the air-fuel mixture of an adjacent cylinder raising the temperature therein. Under high loads the higher temperature and density of the aircharge is suitable to undergo autoignition. Furthermore, the method may be adapted to an engine comprising a specially adapted exhaust manifold with an adjustable shutoff element therein to further facilitate crosstalk of exhaust gases between a first and an adjacent cylinder. Additionally, the method of the present disclosure may be adapted such that spark ignition is still active under conditions for autoignition.
The actions in flowcharts and methods described herein may represent code stored in memory of the controller 12.
It will be appreciated that the configurations and methods disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, 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 other features, functions, and/or properties disclosed herein.
The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.

## Claims

1. A method for operating a spark ignition engine, comprising:
discharging exhaust gases from each of at least two cylinders via an exhaust system comprising exhaust pipes from the at least two cylinders coming together to form an exhaust manifold; and
under high loads, initiating autoignition with exhaust gas from a first, exhaust-gas-supplying cylinder, which is discharged from the first cylinder into the exhaust system, the exhaust gas is introduced into an adjacent, exhaust-gas-receiving cylinder via the exhaust system, each of the at least two cylinders having at least two exhaust ports for discharging the exhaust gases from the cylinder, the at least two exhaust ports of each cylinder operated with different timings.

2. The method as claimed in claim 1, wherein high loads are loads greater than half the maximal load at a respective engine speed.

3. The method as claimed in claim 1, wherein high loads are loads greater than 0.65 times the maximal load at a respective engine speed.

4. The method as claimed in claim 1, further comprising deactivating spark ignition in response to a switch being made to autoignition and autoignition being induced by exhaust gas.

5. The method as claimed in claim 1, further comprising maintaining spark ignition when autoignition is induced by means of exhaust gas.

6. The method as claimed in claim 1, wherein each of the at least two cylinders is equipped with a spark plug serving as an ignition device for initiating spark ignition.

7. The method as claimed in claim 1, wherein the first, exhaust-gas-supplying cylinder, succeeds the adjacent, exhaust-gas-receiving cylinder, in firing order.

8. The method as claimed in claim 1, further comprising opening earlier the exhaust port which faces and is nearest to the adjacent cylinder and opening later the exhaust port which faces away and is arranged further away from the adjacent cylinder, the adjacent cylinder firing immediately after the first cylinder.

9. The method as claimed in claim 1, further comprising closing later the exhaust port which faces and is nearest to the first cylinder, and closing earlier the exhaust port which faces away and is arranged further away from the first cylinder.

10. The method as claimed in claim 1, further comprising increasing an opening duration of at least one of the exhaust ports of each cylinder in order to assist the transfer of exhaust gas serving as ignition gas.

11. A method for operating a spark ignition engine, comprising:
discharging exhaust gases from each of at least two cylinders via an exhaust system comprising exhaust pipes from the at least two cylinders coming together to form an exhaust manifold; and
under high loads, initiating autoignition with exhaust gas from a first, exhaust-gas-supplying cylinder, which is discharged from the first cylinder into the exhaust system, the exhaust gas is introduced into an adjacent, exhaust-gas-receiving cylinder via the exhaust system, at least two exhaust ports of the first cylinder and at least two exhaust ports of the adjacent, exhaust-gas-receiving cylinder are operated with different timings.

12. The method as claimed in claim 11, further comprising advancing an opening time of at least one of the exhaust ports of the first cylinder.

13. The method as claimed in claim 11, further comprising retarding closing of at least one of the exhaust ports of the adjacent, exhaust-gas-receiving cylinder.

14. A method, comprising:
under low loads,
maintaining separation of exhaust gas from a first and an adjacent cylinder; and
initiating combustion by spark ignition;

under high loads,
adjusting valve open duration to allow exhaust gas from the first cylinder into the adjacent cylinder; and
discontinuing spark ignition and operating with auto ignition, at least two exhaust ports of the first cylinder and at least two exhaust ports of the adjacent cylinder operated with different timings.

15. The method as claimed in claim 14, wherein high loads are loads greater than half the maximal load at a respective engine speed.

16. The method as claimed in claim 14, wherein high loads are loads greater than 0.65 times the maximal load at a respective engine speed.

17. The method as claimed in claim 14, wherein adjusting valve open duration comprises increasing an open duration of an exhaust port of the first and the adjacent cylinder in order to assist the transfer of exhaust gas into the adjacent cylinder.