DE10333261B4 - Method for operating a direct injection gasoline engine and directly injecting gasoline engine - Google Patents

Abstract

Method for operating a direct-injection spark-ignited internal combustion engine in a medium load range with a device for fuel injection by means of an injector into the combustion chamber of at least one cylinder provided with an inlet valve of the engine, wherein at least two injection events per injection operation are discontinued, the beginning of the injection process at the earliest at 400 ° KW is positioned before the top dead center (ZOT) and the end of the injection process at 180 ° CA before ZOT at the latest, characterized in that 70% of the total amount of fuel injected per injection operation is injected before time 270 ° CA before ZOT, wherein 70% of injected fuel quantity injected in the first injection event per injection process.

Description

The invention relates to a method for operating a direct injection gasoline engine and a direct injection gasoline engine according to the preambles of the respective independent claims.

Direct injection in a spark-ignited gasoline engine is a suitable measure, in addition to fuel consumption, to increase the torque and the power of the engine.

• – bei Teillast ein Betrieb mit geschichteter Zylinderladung mit Abgasrückführung;
• – im Leerlauf und bei sehr niedriger Last üblicherweise ein Betrieb mit geschichteter Zylinderladung und Abgasrückführung bei Teilandrosselung;
• – bei höheren Lasten homogener Betrieb, insbesondere zur Vermeidung von Zonen im Brennraum mit geschichteter Zylinderladung und Abgasrückführung bei Teilandrosselung;
• – bei höheren Lasten homogener Betrieb, insbesondere zur Vermeidung von Zonen im Brennraum mit überfettetem Gemisch;
• – in einem Übergangsbereich homogener, magerer Betrieb zwischen Schichtladebetrieb und Homogen-Lambda = 1-Betrieb

The following operating strategies are common in a direct injection gasoline engine:

• - At partial load, an operation with stratified cylinder charge with exhaust gas recirculation;
• In idling and at very low load, usually an operation with stratified cylinder charge and exhaust gas recirculation with partial throttling;
• - At higher loads homogeneous operation, in particular to avoid zones in the combustion chamber with stratified cylinder charge and exhaust gas recirculation at Teilandrosselung;
• - At higher loads homogeneous operation, especially to avoid zones in the combustion chamber with super-rich mixture;
• - In a transition region homogeneous, lean operation between stratified charge mode and homogeneous lambda = 1 operation

Homogeneous operation is typically injected in the intake phase, leaving enough time for homogeneous mixture formation. The flow characteristic of the injection valves is determined inter alia by the fact that it can be injected at rated speed within the intake phase. At rated speed, the absolute injection rate per cycle is typically maximum. It follows that the intake phase lasts longer at lower speeds than the injection time. During the intake phase, therefore, only a portion of the intake air is supplied with fuel. If the charge motion is low, especially at low speeds, sufficient homogenization of fuel and air may occur in the remainder of the time to ignition. It then lean and rich zones in the combustion chamber, which prevents optimal torque yield and smoothness.

From the DE 100 14 553 A1 is addressed in the case of late fuel injection, especially in spark-ignition internal combustion engine, occurring problem of black smoke emissions, which are due, inter alia, to rich mixture zones in the compact mixture cloud. Such rich mixture zones with undesirably high fuel concentration arise due to the low penetration depth of the injected fuel into the combustion chamber against high cylinder pressure. An increase in the injection pressure can not provide a remedy. In addition, no uniform distribution of fuel is achieved in the combustion chamber in full load operation under approximately homogeneous mixture formation, resulting in high pollutant emissions, especially hydrocarbons and carbon monoxide, and low engine performance. In order to reduce the exhaust emission of the internal combustion engine, it is proposed in the cited document to open and close the injector many times during an injection process in a predetermined cycle sequence. In particular, an extension of the entire injection process is proposed to have a longer time for the mixture preparation available.

From the DE 196 02 065 A1 a method for operating an internal combustion engine is known, which is divided to achieve a stable ignition with good fuel treatment, the total amount of fuel to be injected into a main amount of fuel and a later to be injected Zündkraftstoffmenge.

In the DE 197 07 811 A1 In a first early injection, it is proposed to inject a first quantity of fuel for generating hydrocarbon radicals and to start at the same distance after the end of the early injection with the main injection of the fuel quantity necessary for the combustion.

From the US 6,116,208 A In particular, an engine control system for a direct-injection engine is known in which, within certain operating ranges, the amount of fuel injected during an injection process is divided into at least two subsets, one early and one late.

From the AT 006 104 U1 It is also known for an idling operation of a direct-injection engine to divide the amount of fuel injected in an injection process into at least two subsets, an early and a late one.

The object of the present invention is to eliminate disadvantages in the combustion process with subsequent injection in a direct injection gasoline engine and to achieve an improvement of the torque and emission behavior.

This object is achieved by the features of the independent claims.

According to the invention it is provided that at least 70% of the total per injection injected amount of fuel until the time 270 ° CA before ZOT be injected, wherein at least 70% of the total amount of fuel injected are injected by the time 270 ° CA before ZOT, with 70% of the fuel injected per injection fuel quantity are injected in the first injection event, since thus a particularly pronounced combustion improvement can be achieved.

It is also particularly favorable to operate the internal combustion engine in a homogeneous lambda 1 operation since this can effectively avoid the otherwise observable formation of lean and rich zones in the combustion chamber.

The method also allows in lean operation, especially in homogeneous lean operation with 70-80% full load, an increase in efficiency and emission improvement.

Preferably, the number of injection events emitted within an injection event is to be selected as a function of the load and rpm range in which the engine is operated.

With increasing load, it is advantageous to increase the number of remote injection events. With increasing speed, it makes sense to reduce the number of set injection events. It is preferred that for rotational speeds greater than 3000 1 / min a maximum of six different injection events are sold.

To increase the turbulence in the internal mixture formation, it is advantageous if an adjustment between a valve lift curve of the intake valve and the injection process takes place. It is preferable to position the maximum of the valve lift curve centrally in a time window formed by the beginning and the end.

The direct-injection gasoline engine according to the invention has a control module for determining the beginning of the injection process and the end of the injection process in at least two injection events per injection process in accordance with the method described above.

Further advantages and aspects of the invention are given in the following description of exemplary embodiments with the aid of drawings, independently of their summary in the patent claims.

Showing:

1 in a schematic representation of a gasoline engine with direct injection

2 an injection process with three injection events and a valve lift curve of the intake valve according to the invention

3 a speed diagram illustrating an operating strategy for multiple injections.

1 shows a schematic representation of a spark-ignited, preferably stratified charge direct injection internal combustion engine 1 , In a combustion chamber 10 a cylinder 11 can by means of a fuel injection device 12 Fuel injected directly. In 1 If a common rail injection system is shown, however, the invention can also be carried out with conventional injection systems. For injection and metering of fuel is to each cylinder 11 an injector 14 and for controlling the air supply, an inlet valve 16 assigned. About an electronic accelerator 18 an assessment of combustion air in the cylinder 11 , The invention also includes embodiments in which details of the air supply and dimensioning other than in 1 are formed.

The internal combustion engine 1 is also an exhaust system 20 with a close to the engine pre-catalyst 22 and a main catalyst 24 assigned. The invention is also effective for DI gasoline engines without precatalyst with close to the engine main catalyst. Preferably, the precatalyst is designed as a 3-way catalyst and the main catalyst as a NOx storage catalyst (Denox catalyst) to ensure safe emission control even in the most fuel-efficient stratified charge. Via an exhaust gas recirculation valve 26 can from the exhaust system 20 Exhaust gas to be influenced to influence the combustion behavior of the combustion air.

For controlling the various engine functions is also an engine control unit 30 provided the signals from sensors 34 for engine speed, engine temperature, catalyst temperature, throttle position, and load or power demand, and via the facility 12 Can dose fuel accordingly. The control unit 30 includes a control module 32 , with which the injection of fuel into the combustion chamber 10 can be controlled.

According to the invention, the beginning of the injection process with at least two injection events is positioned at the earliest at 400 ° CA and the end of the injection process at 180 ° CA in each case before the top dead center (ZOT). Preferably, the beginning or end of the injection process is at 280 ° CA or 100 ° CA before ZOT.

According to the invention, an injector with high atomization quality is used. As a measure of the atomization quality, the droplet size is used in Sauter Mean Diameter (SMD). Surprisingly, it has been shown that a deterioration of the combustion process, which is usually associated with a shift of the injection start late into the region around a maximum of the delivery level, can be eliminated by choosing an injector with an atomization quality of 12 μm SMD droplet size or better.

For a typical injector, there is an association between injection pressure and droplet size, which makes it possible to set a desired atomization quality, as expressed in the droplet size, via a suitable injection pressure. An injection pressure of more than 12 MPa is preferred.

In order to enable a sufficiently fast sequence of injection events, a piezo injector is preferably used. Such an injector is for example from the DE 195 48 526 A1 known.

In 2 is shown schematically for an injection process with three injection events, the time sequence of the injection events in dependence on the crank angle KW. The ignition timing is at top dead center (ZOT) at 360 ° KW. In 2 is also shown schematically the movement of the piston. At 0 ° KW, the intake stroke begins, at 180 ° CA, the bottom dead center of the compression stroke. After the start of the charge cycle at 0 ° CW at top dead center, three injection events are initiated during the intake stroke. The first injection event is positioned at 300 ° CA before ZOT, the second at 240 ° CA before ZOT and the third at 180 ° KW before ZOT. A particularly effective combustion can be achieved if at least 70% of the total amount of fuel to be injected is injected before the time of 270 ° CA before ZOT.

According to a further aspect of the invention, at least 80%, preferably at least 90% of the total amount of fuel is injected in a time window of 180 ° CA. With the mentioned measures, it is achieved to take advantage of an intake stroke time optimally for injection. It is particularly preferable if, in the case of a double injection, a main injection takes place at the beginning of the intake phase and a second injection with approximately 20% of the total fuel quantity at the end of the intake phase.

The internal combustion engine may be operated according to the method in a homogeneous lambda-1 operation or in a lean operation. In lean operation, a lambda value of max. 1.6 and a range of max. 80% full load preferred. It is thus achieved more torque, better smoothness and oxygen utilization.

In 2 Furthermore, a valve lift curve of the intake valve is shown. According to the invention, the valve lift is adapted to the remote injection events so that the internal mixture formation is improved by turbulence. This also allows a higher degree of delivery and thus an increase in torque. Particularly preferred is the injection with the valve open.

A particularly homogeneous internal mixture formation is achieved when the maximum of the valve lift curve is in a range of plus / minus 10% of the center of the time window formed by the injection start and end of injection. In this case, at least 50%, particularly preferably 80%, particularly preferably 90% of the injection quantity can be discontinued in a region in which the inlet valve has a stroke of 20% or more of its maximum value.

The number of remote injection events per injection event is selected depending on the load and speed range in which the engine is operating.

In full-load operation of the internal combustion engine, an improvement in the homogeneity of the mixture is achieved in particular in a rotational speed range below 3000 1 / min by the displacement of the injection process and the distribution of the fuel quantity to at least 2 injection events.

In 3 an illustration of a preferred operating strategy using the method according to the invention is shown. Thereafter, an optimum range for the described multiple injection is hatched.

It is particularly favorable to operate the internal combustion engine in a load range of at least 50% of the maximum torque. It is also favorable to operate with at least 70% of the maximum torque.

For loads <50% of the maximum torque, max. five different injection events, preferably three provided. For loads <30%, three, preferably two and for loads <20% max. two injection events discontinued.

Particularly favorable is the use of the method at speeds <3000 1 / min. For speeds> 3000 rpm, max. six different injection events can be discontinued.

In a particularly preferred embodiment of the invention, the engine control unit 30 implemented a torque model in which all engine interventions are expressed as torque requests. To model this model, the torque of the engine 1 depending on the ignition angle with variation of parameters such as speed, lambda value, filling, optionally an exhaust gas recirculation rate and other operating parameters set. The torque model can be used as a map in a data memory of the engine control unit 30 be filed. In a preferred embodiment of the invention, the data model also includes a definition of the dependence of the degree of delivery from the start of injection. In addition, the influence of a variation of the injection duration can be taken into account.

The invention enables an improvement of the combustion process, especially at high loads. Thus, a higher torque, a reduced tendency to knock is easily achieved. The improved homogenization is of particular importance for the operation of stratified charge engines to ensure lower exothermicity with respect to thermal protection of the sensitive catalyst components.

Claims (17)

Method for operating a direct-injection spark-ignited internal combustion engine in a medium load range with a device for fuel injection by means of an injector into the combustion chamber of at least one provided with an intake valve cylinder of the engine, wherein at least two injection events per injection operation are discontinued, the beginning of the injection process at the earliest at 400 ° KW is positioned before the top dead center (ZOT) and the end of the injection process at 180 ° CA before ZOT at the latest, characterized in that 70% of the total amount of fuel injected per injection process is injected before the time 270 ° CA before ZOT, wherein 70% of injected fuel quantity injected in the first injection event per injection process. A method according to claim 1, characterized in that within a time window of 180 ° KW at least 80% of the total amount of fuel injected per injection process are injected. A method according to claim 1 or 2, characterized in that the internal combustion engine is operated in a homogeneous lambda-1 operation. Method according to at least one of the preceding claims 1-3, characterized in that the internal combustion engine in a lean operation, preferably with a lambda value of max. 1.6 is operated. A method according to claim 4, characterized in that a homogeneous lean operation in a range of max. 80% full load is operated. Method according to at least one of the preceding claims, characterized in that the number of remote injection events per injection process is selected as a function of the load and speed range in which the internal combustion engine is operated. Method according to at least one of the preceding claims 1-6, characterized in that the internal combustion engine in a load range of min. 50% of the maximum torque achievable for the respective speed is operated. Method according to at least one of the preceding claims, characterized in that for loads <50% of the maximum torque achievable for the respective rotational speed, a maximum of 5 different injection events, preferably three, are discontinued. Method according to at least one of the preceding claims, characterized in that for loads <30% of the maximum torque achievable for the respective rotational speed, a maximum of three different injection events, preferably two, are discontinued. Method according to at least one of the preceding claims, characterized in that for loads <20% of the maximum torque achievable for the speed max. two different injection events are discontinued. Method according to at least one of the preceding claims, characterized in that in a speed range greater than 3000 1 / min a maximum of six different injection events are sold. Method according to at least one of the preceding claims, characterized in that a distribution of the fuel quantity injected per injection event is provided as a function of the time priority of the injection event. Method according to at least one of the preceding claims, characterized in that at least 20% of the total amount of fuel injected per injection process is injected in the last injection event. Method according to at least one of the preceding claims, characterized in that the injection is carried out in response to a valve lift curve of the intake valve. A method according to claim 14, characterized in that the maximum of the valve lift curve is in a range of +/- 10% of the center of the time window formed by the injection start and end of injection. Method according to at least one of the preceding claims, characterized in that at least 50% of the injection quantity per injection process are injected in a region in which the inlet valve has a stroke of 20% or more of the maximum value of the stroke. Direct injection spark-ignited internal combustion engine with a device for fuel injection by means of an injector into the combustion chamber of at least one cylinder provided with an intake valve of the engine, wherein at least two injection events per injection operation are discontinued, characterized in that a control module for performing the method according to at least one of the preceding claims is provided.

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