Method for starting an internal combustion engine

Abstract

A method for starting an internal combustion engine with a fuel tank and a low-pressure pump which pumps gasoline out of the fuel tank at a low-pressure to a high-pressure pump that pumps the gasoline at a high-pressure to injectors of the internal combustion engine. An electronic controller is provided for controlling and/or regulating the low-pressure pump, the high-pressure pump, and the injectors. After a start pulse for the internal combustion engine, the method: checks whether a formation of vapor bubbles in the gasoline is possible on the low-pressure side during a hot start. If not possible, then the normal low-pressure is set. If possible, then a low pressure which is high enough that the formation of vapor bubbles is not possible on the low-pressure side is set, and the normal low-pressure is set after a period of time. The problem of vapor bubble formation is prevented in an inexpensive or cost neutral manner via the method.

Claims

1. A method for starting an internal combustion engine having a fuel tank and a low pressure pump which conveys gasoline at a low pressure from the fuel tank to a high pressure pump, the high pressure pump conveying the gasoline at a high pressure to injectors of the internal combustion engine, wherein an electronic control unit controls and/or regulates the low pressure pump, the high pressure pump, and the injectors, the method comprising the acts of: during a starting event of the internal combustion engine: determining using the electronic control unit whether a temperature of the gasoline on the low pressure side is such that a formation of vapor bubbles in the gasoline is expected, if formation of vapor bubbles is determined to be expected, then setting the low pressure pump to generate a predetermined normal low pressure, or if formation of vapor bubbles is determined to not be expected, then setting the low pressure pump to generate a gasoline pressure at a level sufficient to suppress vapor bubble formation at the temperature of the gasoline, and then setting the predetermined normal low pressure after a defined time period, wherein the act of determining whether formation of bubbles is possible is based at least in part on a temperature of the gasoline estimated by a model or a characteristic diagram stored in the electronic control unit.

2. The method according to claim 1, wherein the act of checking takes place over a defined time window after the internal combustion engine is switched off.

3. The method according to claim 1, further comprising a temperature sensor for a coolant temperature and/or a lubricant temperature of the internal combustion engine, wherein the act of checking takes place via a determination of a coolant temperature and/or a lubricant temperature of the internal combustion engine.

4. A method for starting an internal combustion engine having a fuel tank and a low pressure pump which conveys gasoline at a low pressure from the fuel tank to a high pressure pump, the high pressure pump conveying the gasoline at a high pressure to injectors of the internal combustion engine, and a fuel pressure sensor provided on a high pressure side, wherein an electronic control unit controls and/or regulates the low pressure pump, the high pressure pump, and the injectors, the method comprising the acts of: during a starting event of the internal combustion engine: determining using the electronic control unit whether a temperature of the gasoline on the low pressure side is such that a formation of vapor bubbles in the gasoline is expected, if formation of vapor bubbles is determined to be expected, then setting the low pressure pump to generate a predetermined normal low pressure, or if formation of vapor bubbles is determined to not be expected, then setting the low pressure pump to generate a gasoline pressure at a level sufficient to suppress vapor bubble formation at the temperature of the gasoline, and then setting the predetermined normal low pressure after a defined time period, wherein the act of determining whether formation of bubbles is possible is based at least in part on an actual high pressure measurement via the fuel pressure sensor.

5. A method for starting an internal combustion engine having a fuel tank and a low pressure pump which conveys gasoline at a low pressure from the fuel tank to a high pressure pump, the high pressure pump conveying the gasoline at a high pressure to injectors of the internal combustion engine, and a fuel pressure sensor provided on a high pressure side, wherein an electronic control unit controls and/or regulates the low pressure pump, the high pressure pump, and the injectors, the method comprising the acts of: during a starting event of the internal combustion engine: determining using the electronic control unit whether a temperature of the gasoline on the low pressure side is such that a formation of vapor bubbles in the gasoline is expected, if formation of vapor bubbles is determined to be expected, then setting the low pressure pump to generate a predetermined normal low pressure, or if formation of vapor bubbles is determined to not be expected, then setting the low pressure pump to generate a gasoline pressure at a level sufficient to suppress vapor bubble formation at the temperature of the gasoline, and then setting the predetermined normal low pressure after a defined time period, wherein the act of determining whether formation of bubbles is possible is based at least in part on a temperature of the gasoline estimated by a model or a characteristic diagram stored in the electronic control unit and at least in part on an actual high pressure measurement via the fuel pressure sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram showing a fuel system of the generic type for an internal combustion engine.

(2) FIG. 2 is a graphical diagram of the relationship between the formation of vapor bubbles and the fuel system pressure.

(3) FIG. 3 is a flow diagram of the procedural logic.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 diagrammatically shows a fuel system 1 of the generic type for a gasoline internal combustion engine (not shown), by way of which internal combustion engine the method according to the invention for starting the internal combustion engine can be carried out. Fuel is conveyed with the aid of a low pressure pump 2 out of a fuel tank 1 through a fuel line 7 to a high pressure pump 3. From the high pressure pump 3, the gasoline is conveyed further through the fuel line 7 into a rail 10. Four injectors 4 for injecting the gasoline into combustion chambers of the internal combustion engine are arranged on the rail 10. A fuel pressure sensor 5 is provided in the rail 10 for monitoring the high pressure of the fuel. A control unit 6 (DME) is connected via electrical connections 11 to the injectors 4, to the fuel pressure sensor 5, and to the low pressure pump 2 and the high pressure pump 3. The fuel system is divided into a low pressure region 8 and a high pressure region 9, represented by two arrows.

(5) A fuel supply system of this type for an internal combustion engine can be used to provide a method for starting an internal combustion engine having a fuel tank 1 and a low pressure pump 2 which conveys the gasoline out of the fuel tank 1 at a low pressure to a high pressure pump 3 which conveys the gasoline at a high pressure to injectors 4 of the internal combustion engine. An electronic control unit 6 is provided for controlling and/or regulating the low pressure pump 2, the high pressure pump 3 and the injectors 4. After a start pulse for the internal combustion engine, the method:

(6) checks whether a formation of vapor bubbles of the gasoline is possible on the low pressure side during a hot start,

(7) if not, then set the normal low pressure,

(8) if possible, then set a low pressure which is sufficiently high that a formation of vapor bubbles is not possible on the low pressure side, and set the normal low pressure after a defined time period.

(9) In one aspect of the invention, the check takes place over a time window after switching off the internal combustion engine. It is to be noted that the maximum temperatures in reheating occur only after a certain switched-off time.

(10) Furthermore, the check can take place via the determination of the coolant temperature and/or a lubricant temperature of the internal combustion engine by way of a temperature sensor.

(11) A further option for checking consists in a calculation model or a characteristic diagram for determining the gasoline temperature being provided in the control unit 6. In the first case, the check can be calculated via the calculation model. In the second case, the check can be calculated by way of stored data being read out from a characteristic diagram.

(12) A further option is to check via an actual high pressure measurement by way of the fuel pressure sensor 5. If the high pressure collapses during, or briefly after, a hot start (actual pressure<setpoint pressure), a formation of vapor bubbles in the fuel low pressure region 8 upstream of the high pressure pump 3 can be assumed. In this case, the fuel low pressure is likewise raised briefly as required, with the result that a further formation of vapor bubbles is avoided and the high pressure pump 3 can convey the liquid fuel for the build-up of high pressure.

(13) FIG. 2 is a diagram with a vapor pressure curve 12 showing the relationship between the formation of vapor bubbles and a fuel system pressure of a fuel. The fuel pressure [bar] is plotted against the Y-axis, and the fuel temperature [ C.] is plotted against the X-axis. Dashed line 13 denotes a defined fuel temperature in the low pressure region 8 of the fuel system. A triangle shows an operating point (pressure-temperature combination) below the vapor pressure curve 12. A formation of vapor bubbles is possible at said temperature in conjunction with the prevailing pressure. A reliable hot start is therefore not ensured. The operating point is shifted above the vapor pressure curve 12 by way of the operating pressure being raised in a region which is shown by way of a circle. Therefore, a formation of vapor bubbles is no longer possible and a reliable hot start is ensured according to the invention.

(14) FIG. 3 is a flow diagram showing the procedural logic for the method according to the invention for starting an internal combustion engine. After the start of the internal combustion engine, a check is made as to whether a formation of vapor bubbles of the gasoline is possible on the low pressure side during a hot start:

(15) (i) if not, then the normal low pressure is set,

(16) (ii) if possible, then a low pressure is set which is sufficiently high that a formation of vapor bubbles is not possible on the low pressure side, and the normal low pressure is set after a time period.

LIST OF DESIGNATIONS:

(17) 1 Fuel (gasoline) tank 2 Low pressure pump 3 High pressure pump 4 Injector 5 Fuel pressure sensor 6 Control unit 7 Fuel line 8 Low pressure region 9 High pressure region 10 Rail 11 Electric connection 12 Vapor pressure curve 13 Operating temperature

(18) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.