DE102011086956A1 - Method for starting internal combustion engine involves directly introducing fuel into combustion chamber in pre-injection cycle which is prior to ignition cycle during compression stroke - Google Patents

Abstract

A fuel/air mixture is ignited for the initial time in a combustion chamber in an ignition cycle. The fuel is directly introduced into the combustion chamber in a pre-injection cycle which is prior to the ignition cycle during a compression stroke. Independent claims are included for the following: (1) computer program stored in computer readable medium for starting internal combustion engine; and (2) control and regulating device.

Description

State of the art

The invention relates to a method for operating an internal combustion engine. The invention further relates to a computer program, an electrical storage medium and a control and / or regulating device.

Direct-injection gasoline engines operate with injection pressures of up to 200 bar. The pressure is adjusted depending on the operating point in the range 40 ... 200 bar. For example, systems with a piston pump which is mechanically driven by the internal combustion engine, a quantity control valve and a high pressure sensor can be used for high pressure generation. The flow rate of the pump can be changed via the control of the quantity control valve. Together with the measured high-pressure signal, a control and / or regulating device regulates the pressure to the desired level.

The control of the injection valves is based on the measured pressure signal. A cold start of a direct-injection engine takes place either as a low-pressure start or as a high-pressure start. Advantages of a high-pressure start are a lower injected fuel quantity required, less oil dilution and lower requirements for the design of the injection valves (due to a reduction of the static flow rate Q _STAT and thus higher accuracy for small quantities).

The start of the internal combustion engine can be done with different concepts:
It is possible, for example, to discontinue a single, double or triple injection either in an intake tract (360 ° to 180 ° crankshaft angle before ZOT) or in a compression stroke (180 ° to 0 ° crankshaft angle before ZOT).

It is also possible to perform a double or triple injection divided into the suction and the compression stroke, or in the case of triple injection with two injections in the compression stroke.

If the internal combustion engine is designed in such a way that the injection valve has a central installation position, it is also possible in addition to discontinue a short injection near the ignition point.

Further, it is possible to additionally settle one or two pilot injections each without ignition in the relevant cycle partly with low pressure or high pressure in the intake stroke.

In a direct-injection system, a cold start places high demands on the system. For gasoline, this is the case at low temperatures, ethanol is added as fuel, the high requirements depending on the ethanol content already from 10 ° to 20 ° C. Background is that due to the poor mixture preparation at cold temperatures compared to the warm engine injection of a considerable additional fuel is required. This additional quantity can be made possible, for example, by overdimensioning the high-pressure pump and / or by oversizing the fuel rail. Furthermore, in order to improve the mixture preparation and / or to store the necessary amount of fuel into the fuel rail, it is initially possible to build up an excessive system pressure which then dissipates at the beginning of the injection until the high-pressure pump covers the quantity requirement of the engine again. However, such a pressure build-up leads to an extension of the start time, which in the worst case can lead to a start of the internal combustion engine for the driver as uncomfortable noticeable.

From the DE 10 2004 046 628 A1 For example, a method for starting an engine at low and low pressures is known in which fuel pressure is detected and compared to a threshold. If the fuel pressure is below this threshold, it is provided to divide the fuel injection to a plurality of injection pulses.

For applications in which fuel with a high ethanol content is used, such methods are not sufficient. In such special fuels, such. B. E85, z. B. an additional cold start valve can be used, which is complicated and expensive. If E100 is used as fuel, then there is still no technical solution for starting at temperatures> 5 ° C.

Disclosure of the invention

The invention with the features of the independent claims has the advantage that the starting ability of internal combustion engines is reliable even when using fuels with high ethanol content at low temperatures. This makes it possible, for example, interpret the high pressure pump used to a lower maximum flow.

According to the invention, it has been recognized that it is particularly advantageous if fuel is introduced into the combustion chamber in a pre-injection cycle, which is before the ignition cycle, before an ignition cycle in which a fuel / air mixture in a combustion chamber is ignited for the first time.

In this pre-injection cycle is therefore not ignited. The cycle-to-cycle transition may be set in a conventional manner as the e-work from a compression stroke to a stroke in the ignition top dead center (ZOT). The pilot injection cycle then includes, in that order, stroke, exhaust stroke, intake stroke, and compression stroke. The ignition cycle then begins with the power stroke, which immediately follows the compression stroke of the pre-injection stroke. But it is also possible that the ignition cycle begins one, two or more cycles later. If the first-time ignition is not initiated in the compression stroke, another definition of the "cycle" is appropriate: in this case, it is useful to define the cycle-to-cycle transition as the crankshaft angle at which ignition is initiated for the first time.

The introduced by the pilot injection fuel / air mixture thus goes through without ignition a Ausschiebetakt. According to the invention, it has been recognized that the fuel thus injected leads to the formation of a wall film on the piston and on the walls of the combustion chamber. Furthermore, depending on the geometry of the combustion chamber, it is possible that the fuel / air mixture is not completely ejected in the exhaust stroke. In addition, it may come in the intake stroke to a sucking back of parts of the fuel / air mixture from the intake or exhaust tract. As a result, the pre-injection causes the amount of fuel to be introduced during the ignition cycle to safely start the engine can be reduced. If, for example, the amount of pilot injection, ie the amount of fuel introduced with the pilot injection, is so great that a saturated wall film has formed in the combustion chamber, then the fuel quantity to be introduced in the ignition cycle for a safe start of the internal combustion engine can be reduced by this fuel contribution required for wall film formation become.

If fuel is injected directly into the combustion chamber in the pre-injection cycle, the pre-injection can be adjusted particularly finely and flexibly. For example, it is possible for fuel to be directly injected during a compression stroke in the pilot injection cycle. This has the advantage that the heat of compression, the compressed in the piston air filling supports the preparation of the fuel / air mixture. This is special for poorly evaporating fuels such. B. E100 advantage.

In particular, it is also possible to directly inject fuel in the pilot injection cycle during the compression stroke with a multi-injection. Multi-injection is an injection in which fuel is injected in many small split injections, e.g. B. two partial injections. But it is also possible that a multi-injection comprises a larger number of partial injections, for example 3 to 20. Such a multi-injection has a positive effect on the mixture formation.

Moreover, it is also possible for fuel to be introduced into the combustion chamber during the intake stroke during the pre-injection cycle. This has the advantage that the fuel quantity to be injected in the pilot injection cycle is distributed over two cycles. This simplifies the design of the fuel system at startup. In addition, the pilot injection in the intake stroke has a positive effect on the mixture preparation.

If fuel is injected into the combustion chamber during the intake stroke with a multi-injection in the pilot injection cycle, this leads to a further improved mixture preparation.

In order to have the best possible mixture preparation in the combustion chamber for the actual starting of the internal combustion engine, it is furthermore advantageous for the fuel to be injected directly in the ignition cycle during an intake stroke and during a compression stroke.

Exemplary embodiments are illustrated in the following figures. In detail show:

1 schematically the construction of a high-pressure injection system;

2 schematically the injection or ignition times;

Description of the embodiments

1 shows an injection system. Fuel comes with an electric fuel pump 10 from a fuel tank 20 via a fuel filter 30 a low pressure damper 40 and a quantity control valve 50 promoted to a high pressure pump. Electric fuel pump 10 , Filters 30 , Low pressure damper 40 and quantity control valve 50 form a low pressure side of the injection system. The electric fuel pump generates a pressure of a few bar, the low pressure damper 40 dampens pressure pulsations in a fuel line in which the fuel is carried, and the quantity control valve 50 is controlled by a control and / or regulating device 70 which can also carry out the method according to the invention, controlled in such a way that it measures the desired or required fuel quantity.

The high pressure pump 60 carries fuel via a check valve 80 to a fuel rail 90 , The high pressure pump 60 produces a pressure of up to a few 100 Bar. The pressure in the high-pressure rail 90 is from a rail pressure sensor 100 recorded, and returned to the tax and / or regulator 70 transmitted. The control and / or regulating device controls the quantity control valve depending on this determined pressure 50 accordingly, so as to set the desired pressure. For safety reasons, a pressure relief valve 110 provided to limit the pressure in the high-pressure rail.

Fuel from the high pressure rail 90 is via high pressure injectors 120a . 120b . 120c and 120d who is also from the control and / or regulating device 70 be controlled in 1 injected combustion chambers not shown. In a cycle / cycle, each of these cylinders passes in a known manner, the four strokes intake stroke, compression or compression stroke, power stroke and Ausschiebetakt. The mechanical work generated is transmitted to a crankshaft and a camshaft, which is the high-pressure pump 60 can drive. But it is also conceivable, the high-pressure pump 60 to be towed by an electric machine.

In 2 are injection and ignition timing of the inventive method for starting an internal combustion engine with an injection system according to 1 shown. The transition from Ausschiebetakt to intake stroke is as usual as LWOT (load change top dead center), the transition from compression stroke to power stroke referred to as ZOT (ignition top dead center). The intake stroke is in 2 marked with the letter "N", the compression stroke with "K", the stroke with "A" and the Ausschiebetakt with "U". The transition from cycle to cycle is set in the exemplary embodiment at ZOT. One cycle thus includes the cycles "A", "U", "N" and "K" one after the other.

In the exemplary embodiment, the ignition cycle ZZ connects directly to the pre-injection cycle VZ. In the 2a . 2 B . 2c . 2d and 2e Embodiments of the method according to the invention with different injection strategies in the pre-injection cycle VZ and ignition cycle ZZ are shown. The various injection strategies and pre-injection cycle VZ and ignition cycle ZZ can be combined with one another as desired.

It is also possible to perform each of these injections as a multi-injection.

2a shows a first injection strategy. In a designated "pressure build-up" phase is in the high-pressure rail 90 with the high pressure pump 60 built a high pressure. This can be done, for example, in which the internal combustion engine, the camshaft with the high-pressure pump 60 is attracted by an electric machine. However, it is also conceivable to carry out the method according to the invention as a direct start method, in which the internal combustion engine is started without the use of a starter. In this case it is necessary to build up the high pressure in the high pressure rail 90 the high pressure pump 60 to drive elsewhere, for example, in a directly coupled with her electric machine. This phase of pressure buildup is in 2 marked as "pressure build-up".

In the designated "Pre-injection and injection" phase is in the embodiment of 2a In the compression stroke K, a first pre-injection V1 is discontinued. In ignition cycle ZZ, a first injection E1 is carried out in the intake stroke N. In the compression stroke K, a second injection E2 and a third injection E3 is performed and then ignited shortly before ZOT the fuel / air mixture with an ignition Z. The internal combustion engine now starts to rotate on its own, and in the following cycles, the starting procedure, which is continued at a conventional start.

2 B shows a second embodiment of the method according to the invention, which analogous to that in 2a shown method runs, in which, however, in addition to the pre-injection cycle VZ during the intake stroke N, a second pilot injection V2 is discontinued.

2c shows a third embodiment of the method according to the invention, analogous to in 2a However, in contrast to the method shown in FIG 2a shown method during the ignition cycle ZZ only in the intake stroke N, a first injection E1 and the compression stroke K, a third injection E3 is performed.

2d shows a fourth embodiment of the method according to the invention, which analogous to the in 2a embodiment shown, but in the ignition cycle ZZ only during the compression stroke K, a third injection E3 is performed.

2e shows a fifth embodiment of the method according to the invention, analogous to that in 2 B However, in the ignition cycle ZZ only during the intake stroke N, a first injection E1 is performed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102004046628 A1 [0009]

Claims (11)

Method for starting an internal combustion engine, in which in an ignition cycle (ZZ) a fuel / air mixture is ignited in a combustion chamber for the first time, characterized in that in a pre-injection cycle (VZ), which is before the ignition cycle (ZZ), fuel in the combustion chamber is introduced. A method according to claim 1, characterized in that in the pre-injection cycle (VZ) fuel is injected directly into the combustion chamber. A method according to claim 2, characterized in that in the pre-injection cycle (VZ) fuel is injected directly during a compression stroke. A method according to claim 3, characterized in that in the pre-injection cycle (VZ) fuel is injected directly during the compression stroke with a multi-injection. A method according to claim 2 or 3, characterized in that in the pre-injection cycle (VZ) fuel is introduced during an intake stroke into the combustion chamber. A method according to claim 5, characterized in that in the pre-injection cycle (VZ) fuel is injected during the intake stroke with a multi-injection into the combustion chamber. Method according to one of the preceding claims, characterized in that fuel is injected directly in the ignition cycle (ZZ) during an intake stroke and during a compression stroke A method according to claim 7, characterized in that the injection in the ignition cycle during the power stroke is performed as a multi-injection and / or that the injection is performed in the ignition cycle during the compression stroke as a multi-injection. Computer program, characterized in that it is designed to perform all steps according to a method of claims 1 to 8. Electrical storage medium for a control and / or regulating device of an internal combustion engine, characterized in that a computer program according to claim 9 is stored on it. Control and / or regulating device of an internal combustion engine, characterized in that it is programmed so that it can perform all the steps of a method according to one of claims 1 to 8.

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