Method for starting a direct-injection internal combustion engine by adapting the quantity of fuel injected

1. A method for starting a direct-injection internal combustion engine of a vehicle, such that a starting phase is accelerated by adapting a quantity of fuel injected during said starting phase, before the engine reaches a steady operating speed, by means of an injection system containing a high-pressure fuel injection pump, means of measuring a pressure delivered by the high-pressure fuel injection pump, and an engine control unit, wherein said method comprises the following steps:

rotating the high-pressure injection pump by means of a starter;

measuring the pressure of the fuel delivered by said high-pressure injection pump, taken at least at two successive compression top dead centers of the pump operating in a maximum output mode;

establishing a pressure gradient, on an angular reference system, of the fuel delivered by said high-pressure injection pump, based on the pressure measured at said at least two successive compression top dead centers of the high-pressure injection pump characterized by their angular positions;

comparing said established pressure gradient with at least one predefined bijective table that respectively matches a plurality of quantities of fuel to be injected and a plurality of said pressure gradients for a given temperature or a given range of temperatures of the engine, said at least one predefined bijective table being implemented in the engine control unit; and

adapting the quantity of fuel injected during the starting phase before the engine reaches a steady operating speed, depending on a result of the comparison, in order to inject a quantity of fuel that corresponds, in the predefined bijective table, to the established pressure gradient, upon authorization of the first injection given by the engine control unit.

2. The method as claimed in claim 1 , wherein:

said at least one bijective table that respectively matches a plurality of quantities of fuel to be injected and a plurality of pressure gradients is predefined for a given range of engine temperatures,

a plurality of said predefined bijective tables are implemented in the engine control unit, covering a plurality of ranges of engine temperatures, respectively, including at least one range of cold-starting temperatures, and

said method in addition consisting of measuring the engine temperature before comparing said established gradient with said at least one predefined bijective table.

3. The method as claimed in claim 1 , wherein the position of said at least two successive compression top dead centers of the fuel injection pump is defined by means of a sensor for the position of the engine crankshaft, by a rule linking the angular positions between the crankshaft and the high-pressure fuel injection pump, and by the engine control unit.

4. The method as claimed in claim 1 , wherein the pressure gradient is established in relation to a variation in the angular position of the high-pressure injection pump, in the form dp/dα, where:

dp is the variation in pressure between said at least two successive compression top dead centers of the pump,

dα is the angular variation of the crankshaft between said at least two successive compression top dead centers of the pump.

5. The method as claimed in claim 1 , wherein the pressure gradient of the fuel delivered by said high-pressure injection pump is established with three compression top dead centers of the high-pressure injection pump, or more.

6. A device for starting a direct-injection internal combustion engine, such that a starting phase is accelerated by adapting a quantity of fuel injected during said starting phase before the engine reaches a steady operating speed, by an injection system containing a high-pressure fuel injection pump, means of measuring the pressure delivered by the fuel injection pump, an engine control unit, a starter, means of authorization of the first injection given by the engine control unit, comprising means for the implementation of a method as claimed in claim 1 .

7. The method as claimed in claim 2 , wherein the position of said at least two successive compression top dead centers of the fuel injection pump is defined by means of a sensor for the position of the engine crankshaft, by a rule linking the angular positions between the crankshaft and the high-pressure fuel injection pump, and by the engine control unit.

8. The method as claimed in claim 2 , wherein the pressure gradient is established in relation to a variation in the angular position of the high-pressure injection pump, in the form dp/dα, where:

dp is the variation in pressure between said at least two successive compression top dead centers of the pump,

dα is the angular variation of the crankshaft between said at least two successive compression top dead centers of the pump.

9. The method as claimed in claim 3 , wherein the pressure gradient is established in relation to a variation in the angular position of the high-pressure injection pump, in the form dp/dα, where:

dp is the variation in pressure between said at least two successive compression top dead centers of the pump,

dα is the angular variation of the crankshaft between said at least two successive compression top dead centers of the pump.

10. The method as claimed in claim 2 , wherein the pressure gradient of the fuel delivered by said high-pressure injection pump is established with three compression top dead centers of the high-pressure injection pump, or more.

11. The method as claimed in claim 3 , wherein the pressure gradient of the fuel delivered by said high-pressure injection pump is established with three compression top dead centers of the high-pressure injection pump, or more.

12. The method as claimed in claim 4 , wherein the pressure gradient of the fuel delivered by said high-pressure injection pump is established with three compression top dead centers of the high-pressure injection pump, or more.

13. A device for starting a direct-injection internal combustion engine, such that a starting phase is accelerated by adapting a quantity of fuel injected during said starting phase before the engine reaches a steady operating speed, by an injection system containing a high-pressure fuel injection pump, means of measuring the pressure delivered by the fuel injection pump, an engine control unit, a starter, means of authorization of the first injection given by the engine control unit, comprising means for the implementation of a method as claimed in claim 2 .

14. A device for starting a direct-injection internal combustion engine, such that a starting phase is accelerated by adapting a quantity of fuel injected during said starting phase before the engine reaches a steady operating speed, by an injection system containing a high-pressure fuel injection pump, means of measuring the pressure delivered by the fuel injection pump, an engine control unit, a starter, means of authorization of the first injection given by the engine control unit, comprising means for the implementation of a method as claimed in claim 3 .

15. A device for starting a direct-injection internal combustion engine, such that a starting phase is accelerated by adapting a quantity of fuel injected during said starting phase before the engine reaches a steady operating speed, by an injection system containing a high-pressure fuel injection pump, means of measuring the pressure delivered by the fuel injection pump, an engine control unit, a starter, means of authorization of the first injection given by the engine control unit, comprising means for the implementation of a method as claimed in claim 4 .

16. A device for starting a direct-injection internal combustion engine, such that a starting phase is accelerated by adapting a quantity of fuel injected during said starting phase before the engine reaches a steady operating speed, by an injection system containing a high-pressure fuel injection pump, means of measuring the pressure delivered by the fuel injection pump, an engine control unit, a starter, means of authorization of the first injection given by the engine control unit, comprising means for the implementation of a method as claimed in claim 5 .

17. The method as claimed in claim 7 , wherein the pressure gradient is established in relation to a variation in the angular position of the high-pressure injection pump, in the form dp/dα, where:

dp is the variation in pressure between said at least two successive compression top dead centers of the pump,

dα is the angular variation of the crankshaft between said at least two successive compression top dead centers of the pump.

18. The method as claimed in claim 7 , wherein the pressure gradient of the fuel delivered by said high-pressure injection pump is established with three compression top dead centers of the high-pressure injection pump, or more.

19. The method as claimed in claim 8 , wherein the pressure gradient of the fuel delivered by said high-pressure injection pump is established with three compression top dead centers of the high-pressure injection pump, or more.

20. The method as claimed in claim 9 , wherein the pressure gradient of the fuel delivered by said high-pressure injection pump is established with three compression top dead centers of the high-pressure injection pump, or more.