DE10341279B4 - Method of performing a high-pressure start - Google Patents

Abstract

Method for performing a high-pressure start of an internal combustion engine (1) with direct fuel injection, in which the internal combustion engine (1) comprises at least one piston (2) movable in a cylinder (3), the piston (2) being coupled to a crankshaft (14) and a high-pressure piston pump is controlled by means of the crankshaft (14) or a camshaft connected to the crankshaft (14), the position of the crankshaft (14) and / or the camshaft being determined when the internal combustion engine (1) is switched off and / or before starting in which a piston of the high-pressure piston pump is positioned before the start.

Description

State of the art

The invention relates to a method for carrying out a high pressure start of a direct injection fuel internal combustion engine, wherein the internal combustion engine comprises at least one piston movable in a cylinder, wherein the piston is coupled to a crankshaft and a high pressure piston pump is driven by means of a camshaft or crankshaft.

Internal combustion engines with direct injection of fuel into a combustion chamber are well known. In this case, a so-called stratified charge or stratified operation is distinguished as the first operating mode, and a so-called homogeneous operation as the second operating mode. The shift operation is used in particular for smaller loads, while the homogeneous operation is used for larger, applied to the engine loads. In stratified operation, the fuel is injected during the compression phase of the internal combustion engine into the combustion chamber, specifically there in the immediate vicinity of a spark plug. This has the consequence that no uniform distribution of the fuel in the combustion chamber can be done more. The advantage of the shift operation is that with a very low fuel consumption, the adjacent smaller loads of the internal combustion engine can be performed. However, larger loads can not be met by the shift operation. In addition, the shift operation offers the advantage of a lower exhaust gas production, in particular with regard to hydrocarbons formed. In the homogeneous operation provided for larger loads, the fuel is injected during the intake phase of the internal combustion engine, so that a swirling and thus a distribution of the fuel in the combustion chamber can still take place without further ado.

In both modes, the fuel masses to be injected and the oxygen demand are controlled and / or regulated by a controller in response to a plurality of parameters to an optimum value in terms of fuel economy, exhaust gas reduction, and the like.

For starting such internal combustion engines with direct injection, it is known to set the internal combustion engine with an electric motor starter and then after about one to two revolutions or when reaching an ignition speed of the internal combustion engine, the fuel according to the second mode, ie the homogeneous operation, in inject the combustion chambers and ignite.

From the DE 100 20 104 A1 a method for starting an internal combustion engine is known in which the position of a piston is determined in a cylinder and fuel is injected into a combustion chamber of that cylinder, the piston is in a working phase. In order to allow the most reliable start possible without electromotive starter, the inlet and / or exhaust valves of at least one cylinder, the piston is after a top dead center, brought before the starting process in a working phase corresponding position.

From the DE 198 35 045 C2 For example, a method of starting an internal combustion engine is known in which, before starting, a combustion chamber is identified which keeps combustion air close and in which the crankshaft is in a position corresponding to a working stroke of the associated piston, with a certain amount of fuel supplied to that combustion chamber , which enables an ignitable mixture, which is subsequently ignited, wherein when the engine is switched off, the crankshaft is stopped in an angular position which corresponds to the working stroke of a piston.

From the DE 198 08 472 A1 a method for starting an internal combustion engine is known in which the advancing of the ignition of the engine is brought by a drive at a slow speed in such a position that the piston of a cylinder is at top dead center.

From the DE 600 34 837 T2 For example, there is known a starting apparatus for a spark-ignition direct injection internal combustion engine in which fuel can be injected directly into cylinders, comprising: cylinder identifying means for performing cylinder identification of the internal combustion engine while the engine is turned off; start request determination means for determining whether an engine start request for the internal combustion engine is present; a start control means for injecting fuel into a compression stroke cylinder identified by the cylinder identification means when it is determined by the start request determination means that an engine start request for the internal combustion engine is present; an engine temperature detection device for detecting an engine temperature of the internal combustion engine; piston position detecting means for detecting the position of a piston in the identified compression stroke cylinder; and ignition range detecting means for determining, on the basis of the temperature detected by the engine temperature detecting means and the piston position detecting means detected piston position to determine whether in the identified Kompressionshubzylinder injected fuel is in an ignition range, the start control means the fuel injection for the identified Kompressionshubzylinder so controlled that a quick start operation is performed, if it is determined that injected into the identified Kompressionshubzylinder fuel in is an ignition area, and the start control means controls the fuel injection for an intake stroke cylinder identified by the cylinder identification means during its intake stroke so as to perform a normal startup operation when it is determined that fuel injected into the identified compression stroke cylinder is not in an ignition range.

Alternatively, direct start methods have been proposed.

So it is on the one hand especially in so-called start-stop situations of the internal combustion engine, in which this z. B. switched off at red lights and then started to continue, provided to provide a direct start without starter. For example, the DE 197 43 492 A1 a method for starting an internal combustion engine, wherein the internal combustion engine comprises a piston movable in a cylinder, which can undergo a suction phase, a compression phase, a working phase and an ejection phase, and wherein the fuel either in a first mode during a compression phase or a second mode can be injected during a suction directly into a limited by the cylinder and the piston combustion chamber. In order to allow a direct start, it is provided that the fuel is injected directly into a combustion chamber in a first injection, the piston is in the working phase. This ensures that combustion of the fuel in the combustion chamber can take place even during the first revolution of the internal combustion engine. By the injection into that combustion chamber whose piston is in the working phase, it is achieved that the internal combustion engine is started immediately with a correct operation. This has the consequence that the internal combustion engine is driven by its own power already during the first revolution. This makes it possible that no starter is required. The injected in the injection into the combustion chamber fuel is sufficient to move the engine in motion and then accelerate to the idle speed.

However, such direct start methods only function at certain positions of the piston in the cylinder and, moreover, only at certain engine temperature values, such as those in a start-stop mode, for example.

The invention now has the task of providing an alternative starting method with which a safe start can also be achieved with simultaneously improved exhaust emissions.

The invention solves this problem by a method for performing a high-pressure start of an internal combustion engine with direct fuel injection of the generic type, wherein the position of the crankshaft and / or an associated camshaft when parking and / or before the start of the internal combustion engine is determined and in which a positioning of the High-pressure piston pump before starting takes place.

Advantages of the invention

For gasoline engines with direct injection, it is planned to start them in the future by means of a high-pressure or shift start. It is provided in particular that the injection for the first combustion takes place in the compression or compression stroke, as is usually provided in a stratified injection. This leads to a better mixture preparation due to the higher combustion chamber temperature in the compression phase and thus to a higher ignition safety also due to the rich mixture of the spark plug. In this way, the hydrocarbon emissions can be significantly reduced.

Basically, a sufficient fuel pressure is required for a stratified injection. This is constructed by a high-pressure pump, which is designed in particular as a high-pressure piston pump with a cylinder, during the starting process. Depending on the position of the cylinder of the high-pressure piston pump when starting the engine, fuel pressure builds up faster or slower. In this case, a rapid pressure build-up allows an early shift injection and thus an exhaust-optimized, fast engine run-up.

Provided that the fuel pressure during the first injection is not sufficient, it may be provided to first carry out a homogeneous injection and to switch over to stratified injection at the next or a later injection. It is z. B. provided that for a high-pressure start with stratified injection of the injection pressure, which is generated by the high-pressure pump, for example in a common rail, should be ≥ 20 bar. The pressure is monitored for this purpose.

Furthermore, a starter or a starting aid system can be provided, which in addition to its function to assist the start, a Positioning of the high-pressure pump can make and wherein the positioning can also be alternatively via a controlled outlet and an intervention by means of the throttle position or engagement of an engine braking device, the positioning should preferably be such that the high-pressure piston pump before starting in a position in the range of ± 45 ° is brought around the bottom dead center of the piston pump. Preferably, a position of ± 30 °, in particular of ± 20 ° and in particular by ± 10 ° and in particular preferably by ± 5 ° around the bottom dead center be provided.

As a start assist system, a conventional starter may be provided which initially accelerates or anfährt the internal combustion engine to a required firing speed at a start request, in which case a positioning can be carried out at the same time.

It can be provided that, starting from a predetermined defined injection pressure, a first injection takes place in stratified operation, wherein previously an injection is carried out in homogeneous operation.

In addition, it may be provided, since the position of the piston is coupled in the high-pressure cylinder of the pump to the position of the crankshaft to provide this coupling such that at a preferred position, as it exists for most engines, in which the crankshaft together with the piston preferred for Standing comes, then a favorable position of the high-pressure pump is reached. Alternatively, it can be provided to couple the starting position of the piston pump with a favorable starting arrangement of the crankshaft and the piston connected thereto. A favorable starting arrangement of the piston pump is given, if the piston of the piston pump is in the vicinity of the bottom dead center with the internal combustion engine and at the same time the cam for driving the piston pump and for generating a pressure build-up in the piston pump is arranged so that it immediately after starting the internal combustion engine, for example by means of a starter, causes a pressure build-up in the piston pump.

In this way, depending on the pressure buildup at engine start, the correct injection strategy can be selected, namely a stratified injection at sufficient pressure and a homogeneous injection at first lower pressure. In addition, it can always be switched to a stratified injection as soon as a sufficient pressure is applied. Furthermore, the invention relates to a computer program for carrying out the method when it is executed on a computer, wherein it is stored in a memory and a control and / or regulating device for operating an internal combustion engine, in particular a motor vehicle with a memory on which a computer program the above type is stored.

Finally, the invention also relates to an internal combustion engine, in particular for a motor vehicle, with at least one cylinder and a piston movable in the cylinder, a crankshaft for transmitting the engine power and a camshaft coupled therewith, wherein means for determining the position of the crank and / or the camshaft is provided, and a device for injecting fuel into a combustion chamber of a cylinder, wherein the means for injection comprises a high-pressure piston pump for carrying out the method of the type described above. The internal combustion engine may have a corresponding control and / or regulating device. Finally, the internal combustion engine may be a gasoline engine. In addition, a device for determining the pressure in a rail may be provided.

Further advantages and features of the invention will become apparent from the remaining documents. The invention will be explained in more detail below with reference to a drawing.

drawings

1 a schematic block diagram of an embodiment of an internal combustion engine according to the invention of a motor vehicle and

2 a schematic representation of the method.

Description of the embodiments

In 1 is an internal combustion engine in its entirety by the reference numeral 1 designated. The internal combustion engine 1 has a piston 2 up in a cylinder 3 is reciprocable. The cylinder 3 is with a combustion chamber 4 provided to the over valves 5 an intake pipe 6 and an exhaust pipe 7 are connected. Furthermore, the combustion chamber 4 a controllable with a signal TI injector 8th and a triggerable with a signal ZW spark plug 9 assigned.

In a first mode, the shift operation of the internal combustion engine 1 , the fuel from the injector 8th while passing through the piston 2 caused compaction phase in the combustion chamber 4 injected, locally in the immediate vicinity of the spark plug 9 as well as just before the top dead center OT of the piston 2 or before the ignition point. Then with the help of the spark plug 9 the fuel ignites, leaving The piston 2 is driven in the now following working phase by the expansion of the ignited fuel.

In a second mode, the homogeneous operation of the internal combustion engine 1 , the fuel from the injector 8th while passing through the piston 2 Induced intake into the combustion chamber 4 injected. By simultaneously sucked air, the injected fuel is swirled and thus in the combustion chamber 4 distributed substantially evenly (homogeneously). Thereafter, the fuel / gas mixture is compressed during the compression phase, then from the spark plug 9 to be ignited. Due to the expansion of the ignited fuel, the piston becomes 2 driven.

In stratified operation as well as in homogeneous operation is by the driven piston 2 a crankshaft 14 offset in a rotational movement over which ultimately the wheels of the motor vehicle are driven. The crankshaft 14 is a speed sensor 15 assigned, in response to the rotational movement of the crankshaft 14 a signal N is generated.

The fuel is in stratified operation and in homogeneous operation under a high pressure in the injection valve 8th in the combustion chamber 4 injected. For this purpose, a high-pressure electric fuel pump is provided, which has one with the crankshaft 14 coupled camshaft (not shown) of the internal combustion engine 1 is driven and generates a so-called rail pressure.

In the shift operation and in the homogeneous operation of the injection valve 8th in the combustion chamber 4 Injected fuel mass is from a controller 16 controlled and / or regulated in particular with regard to low fuel consumption and / or low pollutant emission. For this purpose, the control unit 16 provided with a microprocessor which has stored in a control, in particular a read-only memory, a program which is adapted to perform the control and / or regulation.

The control unit 16 is acted upon by input signals, the operating variables of the internal combustion engine measured by means of sensors 1 represent. For example, the controller 16 with one in the intake pipe 6 arranged air mass sensor 12 , one in the exhaust pipe 7 arranged lambda sensor 13 and / or with the speed sensor 15 connected. Furthermore, the control unit with an accelerator pedal sensor 17 which generates a signal FP indicative of the position of a driver-operated accelerator pedal.

The control unit generates output signals with which the behavior of the internal combustion engine via actuators 1 can be influenced according to the desired control and / or regulation. For example, the controller 16 with the injector 8th and the spark plug 9 connected and generates the signals required for their control TI, ZW.

2 shows a schematic diagram in which the engine speed n _mot and the crankshaft angle KW are plotted over time t and on the second axis of the rail pressure p _rail of the injectors of the internal combustion engine upstream common _rail from which then introduced into the valves and fuel there is injected into the combustion chambers. With the line 100 is the sum ° KW of the internal combustion engine shown. With the line 20 is the speed of the engine of the internal combustion engine designated by the dashed vertical line 30 the time of the engine run-up is marked, which is due to the increase of the line 20 can be seen. The line 40 refers to the number of revolutions, which may be referred to as the starting speed generated by a starter or a starting aid system, which initially allows the engine to spin up to a starting speed.

The line 50 shows how the pressure increase in a rail runs due to the pressure generated in a high-pressure piston pump, provided that the pump was at the start in the area of bottom dead center UT (best case). With the line 60 On the other hand, the pressure curve is shown if the pump was located at the start in the region of top dead center (worst case). In the best case, an increase in pressure in the rail initially occurs through the insertion of additional fuel, in which case a check valve between the rail and the pump is closed and the pump is refilled while the pressure in the rail remains constant. In contrast, in the worst case, the rail pressure remains after the start for the first 0.2 sec. initially the same, until the pump is at UT.

It can be seen that at a favorable starting position, as the line 50 clarifies, always about a piston stroke of the high-pressure piston pump is less required to produce the same pressure in the rail. Therefore, it is possible, for example, in a pressure curve according to the line 50 , already at the time of 0.3 sec. make a shift injection, with an unfavorable pressure curve to about 0.5 sec. must be serviced. In this case, it may be necessary to carry out the first injection as homogeneous injection and only to provide the second injection as stratified injection.

In this respect, it is provided to provide a corresponding outlet position of the high-pressure pump when stopping or before starting a motor vehicle with a corresponding internal combustion engine to perform from the beginning to the cheaper shift start with stratified injection, and thus a reduction of the starting time and an improvement of exhaust emissions at the same time to achieve a safe start.

Claims (10)

Method for carrying out a high-pressure start of an internal combustion engine ( 1 ) with direct fuel injection, in which the internal combustion engine ( 1 ) at least one in a cylinder ( 3 ) movable piston ( 2 ), wherein the piston ( 2 ) with a crankshaft ( 14 ) is coupled and a high-pressure piston pump by means of the crankshaft ( 14 ) or one with the crankshaft ( 14 ) connected camshaft, wherein the position of the crankshaft ( 14 ) and / or the camshaft when parking and / or before the start of the internal combustion engine ( 1 ) is determined, in which a positioning of a piston of the high-pressure piston pump takes place before the start. The method of claim 1, wherein the piston of the high-pressure piston pump occupies a position in the range of ± 45 °, in particular ± 30 °, in particular ± 20 °, preferably ± 10 ° and in particular preferably ± 5 ° around the bottom dead center. The method of claim 1 to 2, wherein the positioning is carried out by means of a jump start system. The method of claim 1 to 2, wherein the positioning is carried out by means of a controlled outlet of the internal combustion engine. Method according to one of the preceding claims, wherein the outlet control via the throttle position or via an engine brake device. Method according to one of the preceding claims, in which an injection pressure is monitored in the internal combustion engine and injection takes place in stratified operation from a predetermined defined injection pressure, wherein injected below the defined pressure in the homogeneous operation. Computer program for carrying out the method according to one of the preceding claims, when executed on a computer, wherein it is stored in a memory. Control and / or regulating device for operating an internal combustion engine, in particular a motor vehicle with a memory, on which a computer program according to claim 7 is stored. Internal combustion engine, in particular for a motor vehicle, with at least one cylinder ( 3 ) as well as one in the cylinder ( 3 ) movable piston ( 2 ), a crankshaft ( 14 ) for transmitting the engine power and a camshaft coupled thereto, wherein means for determining the position of the crank ( 14 ) and / or the camshaft is provided and means for injecting fuel ( 8th ) in a combustion chamber ( 4 ) of a cylinder ( 3 ), wherein the device comprises a high-pressure piston pump for carrying out the method according to one of claims 1 to 6. Internal combustion engine according to claim 9 with a control and / or regulating device ( 16 ) according to claim 8.

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