Method and control unit for starting an otto engine

Abstract

A method and control unit for a start of an Otto engine operated at low temperatures, using ethanol and/or gasoline, having direct injection. The method includes generating by a high pressure pump a fuel pressure in a high pressure system connected to a high pressure reservoir; a sensor monitoring the fuel pressure in the reservoir and the system; injecting the fuel, by an injector, from the reservoir into a cylinder of the engine, the fuel pressure, an injection quantity and a fuel quantity being specified by a control unit based on, sensor the fuel pressure being specified based on the operating point of the engine up to an upper pressure which is below a starting pressure to which the fuel is increased before the fuel injection, and the fuel pressure in the reservoir and the system being limited to a maximum by an opening pressure of a limiting valve.

Claims

1. A method for carrying out a high-pressure start of an Otto engine having direct injection, the method comprising: increasing, at a start of the Otto engine, before a release of an injection of fuel into at least one cylinder of the Otto engine, the fuel pressure in the high-pressure system to a starting pressure, which lies between an upper system pressure and a maximum pressure; wherein a fuel pressure in a high-pressure reservoir of a high pressure system is generated by a high-pressure pump, wherein the fuel pressure in the high-pressure reservoir of the high-pressure system are measured using a high-pressure sensor, wherein the fuel is injected from the high pressure reservoir via at least one fuel injector into at least one cylinder of the Otto engine, wherein the fuel pressure, an injection quantity and a conveyed fuel quantity are specified by a control unit as a function of a signal of the high pressure sensor supplied to the control unit, wherein the fuel pressure is specified as a function of an operating point of the Otto engine up to an upper system pressure, wherein the fuel pressure in the high-pressure reservoir and in the high-pressure system is limited to a maximum pressure by an opening pressure of a pressure limiting valve, wherein the starting pressure is at least about 85% of the maximum pressure, and wherein a starting pressure between the upper system pressure and the maximum pressure is provided if the temperature of the fuel or of the Otto engine or of the cooling arrangement of the Otto engine lies below a specified temperature threshold, and a starting pressure below the upper system pressure is provided if the temperature lies above the specified temperature threshold.

2. The method of claim 1, wherein during a buildup of the fuel pressure by a preinjection, a predetermined quantity of fuel is injected into the at least one cylinder.

3. The method of claim 1, wherein at least one of the temperature threshold and the starting pressure is specified as a function of a composition of a fuel mixture used as fuel.

4. A control unit for controlling an Otto engine having direct injection, comprising: a control unit arrangement connected to a high-pressure pump to generate a fuel pressure in a high-pressure system having a high-pressure reservoir, having a high-pressure sensor for determining the fuel pressure in the high-pressure system and having at least one fuel injector for dosing a fuel quantity injected into at least one cylinder of the Otto engine, wherein the control unit arrangement is configured for setting the fuel pressure in a range up to an upper system pressure, and wherein the high-pressure system has a pressure-limiting valve having an opening pressure for limiting the fuel pressure to a maximum pressure; wherein the control unit arrangement is configured to increase, at a start of the Otto engine, before a release of an injection of fuel into at least one cylinder of the Otto engine, the fuel pressure in the high-pressure system to a starting pressure, wherein the control unit arrangement includes, for a cold start, a program routine for increasing the fuel pressure above the upper system pressure and below the maximum pressure, wherein the starting pressure of the is at least about 85% of the maximum pressure, and wherein a starting pressure between the upper system pressure and the maximum pressure is provided if the temperature of the fuel or of the Otto engine or of the cooling arrangement of the Otto engine lies below a specified temperature threshold, and a starting pressure below the upper system pressure is provided if the temperature lies above the specified temperature threshold.

5. The control unit of claim 4, wherein, in the control unit, there are present data on the composition of a fuel mixture used as fuel, wherein the control unit has available the temperature of at least one of the fuel, the Otto engine, and a cooling arrangement of the Otto engine, and wherein in the control unit there are stored specified values for the fuel pressure to be set, as a function of the composition of at least one of the fuel mixture and the temperature.

6. The control unit of claim 4, wherein the Otto engine is operated using one of alcohol and a mixture of alcohol and gasoline.

7. The method of claim 1, wherein the Otto engine is operated using one of alcohol and a mixture of alcohol and gasoline.

8. The method of claim 1, wherein the upper system pressure is in a range between 20 bar and 80 bar.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a system for a direct injection device for an Otto engine.

(2) FIG. 2 shows a pressure curve for a high-pressure start of an Otto engine.

DETAILED DESCRIPTION

(3) FIG. 1 shows a direct injection device 10 for an Otto engine. A fuel mixture of gasoline and alcohol is supplied from a fuel container 18 via a filter 20 using a pump 19 to a quantity control valve 12. A damper 11 minimizes pressure fluctuations in the system. Quantity control valve 12 is actuated by a control unit 16 according to requirements, so that the pressure provided via a high-pressure pump 13 is sufficient for the operating conditions of the Otto engine. High-pressure pump 13, via a check valve 15, supplies a high-pressure reservoir 21 (common rail) with fuel which is dosed via fuel injectors 22 using a nozzle in the cylinder of the Otto engine, in the form of a fuel-spray fog 23. The fuel pressure in high-pressure reservoir 21 is monitored by a high-pressure sensor 17, whose output signal is supplied to control unit 16. A program routine in control unit 16 may thus, for instance, be based on the signal of high-pressure sensor 17, using quantity control valve 12, set the pressure in high-pressure reservoir 21 and also release the injection at the start. In normal operation, as a function of the operating point, the fuel pressure is thus set in a range of 40 to 200 bar. The pressure in the high-pressure system, to which high-pressure reservoir 21 also belongs, is additionally monitored and limited by a pressure-limiting valve 14. The latter takes care that, in the case of a malfunction, the pressure in the system does not rise above the maximum admissible value of 250 bar, for example.

(4) According to the exemplary embodiments and/or exemplary methods of the present invention, a program routine is provided in control unit 16 which, at the start of the Otto engine, at a low temperature, is able to set, via quantity control valve 12 and high-pressure pump 13, a pressure in high-pressure reservoir 21 above the pressure range in normal operation, but below the maximum admissible value.

(5) FIG. 2 shows a pressure diagram 30 at the start of an Otto engine having direct injection, at a low system temperature. In pressure diagram 30, along a time axis 35 and a pressure axis 31 a pressure curve 34 is drawn in, as is measured at the start in high-pressure reservoir 21 of FIG. 1 using high-pressure sensor 17. After the start, pressure curve 34 exceeds a system pressure 33, which lies typically in a range below 200 bar, but remains below an opening pressure 32 for pressure limiting valve 14. At the highest value of pressure curve 34, an injection is released and the Otto engine is started. After that, pressure curve 34 is regulated to a range about system pressure 33.