METHOD FOR ESTIMATING A TOP DEAD CENTRE FOR A HIGH-PRESSURE PUMP OF A FUEL INJECTION SYSTEM IN AN AUTOMOTIVE VEHICLE ENGINE

Abstract

Disclosed is a method for estimating an angular position of top dead center for a high-pressure fuel injection pump that forms part of a system for injecting fuel into a motor vehicle engine, the pump including at least one piston moving in a chamber between the top and the bottom dead center, the pump being equipped with a digital control valve for controlling a quantity of fuel, an electrical current being applied to the digital valve as it closes then removed in order to open the digital valve, a movement of the digital valve in the direction of opening creating an induced current which makes it possible to detect a position of start-of-opening of the digital valve. An instant at which the pump piston passes through top dead center is estimated as a function of an instant at which the position of start-of-opening of the digital valve appears.

Claims

1. A method for estimating an angular position of top dead center (25) for a high-pressure fuel injection pump (4) that forms part of a system (1) for injecting fuel into a motor vehicle internal combustion engine (12), the pump (4) comprising at least one piston (19) moving in a chamber of the pump (4) between a top dead center (25) for which the volume of the chamber is at its smallest and a bottom dead center for which the volume of the chamber is at its greatest, the pump (4) being equipped with a digital control valve (13) for controlling the quantity of fuel fuel delivery, this valve being commanded electrically between an open position in which a high-pressure part of the injection system is not supplied with fuel and a closed position in which the high-pressure part of the injection system is supplied with the digital valve (13) then being in a fully closed position, an electrical current being applied to the digital valve (13) as it closes then removed in order to open the digital valve (13), a movement of the digital valve (13) toward its open position creating an induced current which, when its profile over time is monitored, makes it possible to detect a position of start-of-opening (23) of the digital valve (13) and the instant at which this occurs, wherein an angular position at an instant at which the pump (4) piston (19) passes through pump (4) top dead center (25) is estimated as a function of an angular position of the instant at which the position of start-of-opening (23) of the digital valve (13) appears, the estimate of the angular position at the instant of passing through top dead center (25) as a function of the angular position at the instant at which the position of start-of-opening (23) of the digital valve (13) appears taking account of at least one of the following parameters: the pressures upstream and downstream of the pump (4), the elastic modulus of the fuel, which is dependent on its temperature and pressure, technical characteristics of the pump (4) such as its dead volume and its swept volume.

2. The method as claimed in claim 1, in which the pressures upstream and downstream of the pump (4) are measured, the elastic modulus of the fuel is data provided by the fuel supplier, whereas the temperature of the fuel is modeled and its pressure measured and the technical characteristics of the pump (4) are data provided by the pump (4) manufacturer.

3. The method as claimed in claim 1, in which the position of start-of-opening (23) of the digital valve (13) is manifested by the appearance of a point of inflection on a curve monitoring the profile of the induced current, the instant of appearance of the point of inflection being considered to be the instant that the position of start-of-opening (23) of the digital valve (13) appears.

4. The method as claimed in claim 1, in which the digital valve (13) comprises a shutter returned to an open position by a return element (22), the digital valve (13) opening as soon as the pressure of the fuel in the chamber drops below the pressure that the return element applies to the shutter of the digital valve (13).

5. The method as claimed in claim 1, in which the digital valve (13) is activated using electric angular control.

6. A method for timing a high-pressure fuel injection pump (4) that forms part of a system (1) for injecting fuel into a motor vehicle internal combustion engine (12), an appearance of pump (4) top dead center (25) being synchronized with the engine (12), wherein it implements such a method for estimating an angular position of pump (4) top dead center (25) as claimed in claim 1.

7. The timing method as claimed in claim 6, in which the appearance of a pump (4) top dead center (25) is in phase with the appearance of a top dead center of a piston of the engine.

8. A system (1) for injecting fuel into a motor vehicle internal combustion engine (12) comprising a high-pressure fuel injection pump (4) and a control unit (5, 6), the pump (4) comprising at least one piston (19) moving in a chamber and equipped with a digital control valve (13) for controlling a delivery of fuel which valve is operated by the control unit (5, 6) via an electrical control element connected to the digital valve (13) by an electric circuit, wherein it implements a method for estimating an angular position of pump (4) top dead center (25) as claimed in claim 1, the control unit (5, 6) comprising an element for monitoring an induced current induced in the electric circuit as the digital valve (13) opens and for detecting a position of start-of-opening (23) of the digital valve (13) and the instant at which it appears, and an element of calculating the instant at which the pump (4) piston (19) passes pump (4) top dead center (25) as a function of the instant at which the position of start-of-opening (23) of the digital valve (13) appears.

9. The injection system (1) as claimed in claim 8, in which the high-pressure pump (4) is fed by a booster pump (2) and supplies a common rail (7) that forms a high-pressure fuel reservoir, the common rail (7) comprising at least one pressure sensor sensing the pressure of the fuel inside it and supplying fuel to a fuel injector for each cylinder of the internal combustion engine (12), the high-pressure pump (4) being driven by the internal combustion engine (12).

10. The method as claimed in claim 2, in which the position of start-of-opening (23) of the digital valve (13) is manifested by the appearance of a point of inflection on a curve monitoring the profile of the induced current, the instant of appearance of the point of inflection being considered to be the instant that the position of start-of-opening (23) of the digital valve (13) appears.

11. The method as claimed in claim 2, in which the digital valve (13) comprises a shutter returned to an open position by a return element (22), the digital valve (13) opening as soon as the pressure of the fuel in the chamber drops below the pressure that the return element applies to the shutter of the digital valve (13).

12. The method as claimed in claim 3, in which the digital valve (13) comprises a shutter returned to an open position by a return element (22), the digital valve (13) opening as soon as the pressure of the fuel in the chamber drops below the pressure that the return element applies to the shutter of the digital valve (13).

13. The method as claimed in claim 2, in which the digital valve (13) is activated using electric angular control.

14. The method as claimed in claim 3, in which the digital valve (13) is activated using electric angular control.

15. The method as claimed in claim 4, in which the digital valve (13) is activated using electric angular control.

16. A system (1) for injecting fuel into a motor vehicle internal combustion engine (12) comprising a high-pressure fuel injection pump (4) and a control unit (5, 6), the pump (4) comprising at least one piston (19) moving in a chamber and equipped with a digital control valve (13) for controlling a delivery of fuel which valve is operated by the control unit (5, 6) via an electrical control element connected to the digital valve (13) by an electric circuit, wherein it implements a method for estimating an angular position of pump (4) top dead center (25) as claimed in claim 2, the control unit (5, 6) comprising an element for monitoring an induced current induced in the electric circuit as the digital valve (13) opens and for detecting a position of start-of-opening (23) of the digital valve (13) and the instant at which it appears, and an element of calculating the instant at which the pump (4) piston (19) passes pump (4) top dead center (25) as a function of the instant at which the position of start-of-opening (23) of the digital valve (13) appears.

17. A system (1) for injecting fuel into a motor vehicle internal combustion engine (12) comprising a high-pressure fuel injection pump (4) and a control unit (5, 6), the pump (4) comprising at least one piston (19) moving in a chamber and equipped with a digital control valve (13) for controlling a delivery of fuel which valve is operated by the control unit (5, 6) via an electrical control element connected to the digital valve (13) by an electric circuit, wherein it implements a method for estimating an angular position of pump (4) top dead center (25) as claimed in claim 3, the control unit (5, 6) comprising an element for monitoring an induced current induced in the electric circuit as the digital valve (13) opens and for detecting a position of start-of-opening (23) of the digital valve (13) and the instant at which it appears, and an element of calculating the instant at which the pump (4) piston (19) passes pump (4) top dead center (25) as a function of the instant at which the position of start-of-opening (23) of the digital valve (13) appears.

18. A system (1) for injecting fuel into a motor vehicle internal combustion engine (12) comprising a high-pressure fuel injection pump (4) and a control unit (5, 6), the pump (4) comprising at least one piston (19) moving in a chamber and equipped with a digital control valve (13) for controlling a delivery of fuel which valve is operated by the control unit (5, 6) via an electrical control element connected to the digital valve (13) by an electric circuit, wherein it implements a method for estimating an angular position of pump (4) top dead center (25) as claimed in claim 4, the control unit (5, 6) comprising an element for monitoring an induced current induced in the electric circuit as the digital valve (13) opens and for detecting a position of start-of-opening (23) of the digital valve (13) and the instant at which it appears, and an element of calculating the instant at which the pump (4) piston (19) passes pump (4) top dead center (25) as a function of the instant at which the position of start-of-opening (23) of the digital valve (13) appears.

19. A system (1) for injecting fuel into a motor vehicle internal combustion engine (12) comprising a high-pressure fuel injection pump (4) and a control unit (5, 6), the pump (4) comprising at least one piston (19) moving in a chamber and equipped with a digital control valve (13) for controlling a delivery of fuel which valve is operated by the control unit (5, 6) via an electrical control element connected to the digital valve (13) by an electric circuit, wherein it implements a method for estimating an angular position of pump (4) top dead center (25) as claimed in claim 5, the control unit (5, 6) comprising an element for monitoring an induced current induced in the electric circuit as the digital valve (13) opens and for detecting a position of start-of-opening (23) of the digital valve (13) and the instant at which it appears, and an element of calculating the instant at which the pump (4) piston (19) passes pump (4) top dead center (25) as a function of the instant at which the position of start-of-opening (23) of the digital valve (13) appears.

20. A system (1) for injecting fuel into a motor vehicle internal combustion engine (12) comprising a high-pressure fuel injection pump (4) and a control unit (5, 6), the pump (4) comprising at least one piston (19) moving in a chamber and equipped with a digital control valve (13) for controlling a delivery of fuel which valve is operated by the control unit (5, 6) via an electrical control element connected to the digital valve (13) by an electric circuit, wherein it implements a timing method as claimed in claim 6, the control unit (5, 6) comprising an element for monitoring an induced current induced in the electric circuit as the digital valve (13) opens and for detecting a position of start-of-opening (23) of the digital valve (13) and the instant at which it appears, and an element of calculating the instant at which the pump (4) piston (19) passes pump (4) top dead center (25) as a function of the instant at which the position of start-of-opening (23) of the digital valve (13) appears.

Description

[0036] Other features, objects and advantages of the present invention will become apparent upon reading the detailed description that will follow and upon examining the appended drawings, given by way of nonlimiting example and in which:

[0037] FIG. 1 is a schematic depiction of one view of one embodiment of a high-pressure fuel supply system of an internal combustion engine, this system being equipped with a high-pressure fuel injection pump an angular position of top dead center of which can be estimated according to an estimating method according to the present invention,

[0038] FIG. 2 is a schematic depiction of a view in cross section of a high-pressure fuel injection pump able to implement the method for estimating an angular position of top dead center for the pump according to the present invention,

[0039] FIG. 3 shows two curves, of the current at the digital valve and of the pressure in the common rail of the high-pressure part of the injection system, respectively, identifying an angular position of top dead center for the pump and of start-of-opening of the digital valve, detection of an angular position of top dead center for the pump according to the position of start-of-opening of the digital valve being implemented according to the estimating method according to the present invention,

[0040] FIG. 4 shows two electrical-current curves, respectively relating to one of two digital valves exhibiting a phase shift between them, the two curves having coinciding positions of start-of-opening, the two digital valves having the same angular positions for top dead center estimated according to the method according to the present invention,

[0041] FIG. 5 shows an enlargement of the pump of FIG. 2 considered at the digital valve, showing the balance of forces on this valve,

[0042] FIGS. 6A and 6B correspond to two schematic depictions of a view in cross section of the high-pressure fuel injection pump according to FIG. 2, enlarged in the region of the digital valve, so as respectively to depict two particular operating points of the pump, accompanied by the corresponding synchronized curves of the position of the piston of the pump and of the electrical-current signal for the applied current and the current induced by the movement of the digital valve, for each operating point.

[0043] With more particular reference to FIG. 1, an internal combustion engine high-pressure fuel injection system 1 comprises a booster pump 2 which picks up low-pressure fuel from a low-pressure fuel tank 3, a high-pressure fuel injection pump 4 being fed by the booster pump 2. This high-pressure pump 4 comprises an actuator for a digital valve, which actuator is not depicted in FIG. 1 but is depicted in FIG. 2 and which will be discussed in detail later.

[0044] The injection system 1 also comprises a controller 5 for the high-pressure fuel injection pump 4 and, more particularly, for the digital valve actuator and means for activating the high-pressure injection pump 4 by time-based control or angular control using the high-pressure fuel injection pump 4 controller 5 and an engine control unit 6, time-based control being mainly used just after the starting of the motor vehicle.

[0045] The injection system 1 also comprises a high-pressure fuel reservoir or common rail 7 fed by the high-pressure fuel injection pump 4, the common rail 7 being provided with means 8 for measuring pressure. Injectors 9 are fed with fuel by the common rail 7 and controlled by the engine control unit 6 to inject fuel into the cylinders 11 of the internal combustion engine 12.

[0046] The high-pressure fuel injection pump 4 may be able to be driven in a known way by a drive means, not depicted in FIG. 1, using the internal combustion engine 12, for example using a mechanical transmission linking mechanism of the chain, gears, belt or similar type.

[0047] FIG. 2 shows a high-pressure fuel injection pump 4 for the injection system shown in FIG. 1. This pump 4 comprises a pump housing 14. The housing 14 of the pump 4 houses within it a piston 19 returned by a spring 20, the piston 19 being driven by a cam drive mechanism 21.

[0048] The pump housing 14 at its upper end has a displacement unit 15 housing a digital valve 13 or DIV valve. The unit 15 comprises a supply and return pipe 18 from and to the booster pump and an outlet pipe 17 leading toward the common rail, this outlet pipe comprising a nonreturn valve 16.

[0049] When the digital valve 13 is in the open position, the piston 19 draws fuel from the supply pipe 18 into a cylinder while the nonreturn valve 16 of the outlet pipe 17 is closed.

[0050] At the end of the filling phase, the digital valve 13 is still in the open position, the piston 19 drives the fuel in the supply pipe 18 toward the booster pump, namely the low-pressure part of the injection system, while the nonreturn outlet valve 16 of the outlet pipe 17 remains closed. That allows excess fuel to be carried back into the low-pressure part of the injection system.

[0051] Next, the digital valve 13 is electrically commanded to close, the supply pipe 18 then being closed, the piston 19 drives the fuel in the outlet pipe 17 toward the common rail, namely toward the high-pressure part of the injection system, the nonreturn valve 16 of the outlet pipe 17 then being open.

[0052] FIG. 3 illustrates two curves as a function of time. The first curve 26 illustrates the current supplied to the digital valve and the second curve 27 illustrates the pressure in the common rail, namely in the high-pressure part of the injection system. The framed part 28 represents a window for measuring the position of start-of-opening 23 of the digital valve and a wide open position 24 of this digital valve, showing the fluctuations in current as the digital valve opens.

[0053] Pump top dead center 25 can be recognised at the end of the increase in pressure in the common rail, whereas the start-of-opening of the digital valve can be recognised by a point of inflection in the fluctuating current curve.

[0054] As mentioned previously, in order to be controlled with precision, the timing of a high-pressure pump that forms part of a high-pressure fuel injection system needs to be precisely known. The timing is generally achieved by mechanical means in association with the engine, but uncertainties associated with the tolerances on all these components still remain. It is therefore necessary to estimate an angular position of top dead center for the the high-pressure pump quickly and precisely.

[0055] The present invention makes it possible to perform more rapid adaptation of the timing right from the first few revolutions of the engine by using a back check on the current induced by the digital valve that controls the delivery of fuel to the high-pressure part of the injection system. This is achieved by detecting the start-of-opening of the digital valve and deducing the position of an angular position of top dead center for the pump right from the first few revolutions of the engine.

[0056] FIG. 4 shows two more or less superposed curbs of current supplied respectively to a correctly-timed digital valve and to a digital valve the timing of which is phase-shifted. FIG. 4 therefore makes it possible to establish a comparison between the current supplied to a digital valve of a high-pressure pump that is correctly timed and that of a pump the reference angle of which is skewed, in this figure by 10, this figure being nonlimiting.

[0057] During this comparison, it is found that the current profile generated by the control unit is different. By contrast, the instant of start-of-opening 23 of the digital valve that is correctly timed or that is phase-shifted lies at the same point in both instances because it corresponds to a physical phenomenon: the reopening of the digital valve as the piston re-descends just after top dead center for the pump.

[0058] The position of start-of-opening 23 of the digital valve is therefore independent of the reference angle of the digital valve. This then makes it possible reliably and for the one same type of digital valve to estimate an angular position of top dead center for the high-pressure pump housing it, independently of the phase shifting of this digital valve and whatever its programmed angle. Wth reference to all of the figures, the present invention relates to a method for estimating an angular position of top dead center 25 for a high-pressure fuel injection pump 4 that forms part of a system 1 for injecting fuel into a motor vehicle internal combustion engine 12. The pump 4 comprises at least one piston 19 moving in a chamber of the pump 4 between a top dead center 25 for which a volume of the chamber is at its smallest and a bottom dead center for which the volume of the chamber is at its greatest.

[0059] Such a pump 4 is equipped with a digital control valve 13 for controlling the quantity of fuel, this valve being commanded electrically between an open position in which a high-pressure part of the injection system 1 is not supplied with fuel and a closed position in which the high-pressure part of the injection system 1 is supplied with the digital valve 13 then being in a fully closed position.

[0060] In order to achieve this, an electrical current is applied to the digital valve 13 as it closes then removed in order to open the digital valve 13, a movement of the digital valve 13 between its closed position and its open position creating an induced current which, when its profile over time is monitored, makes it possible to detect a position of start-of-opening 23 of the digital valve 13 and the instant at which this occurs.

[0061] According to the invention, an angular position at an instant at which the piston 19 of the pump 4 passes through top dead center 25 for the pump 4 is estimated as a function of an angular position of the instant at which the position of start-of-opening 23 of the digital valve 13 appears.

[0062] The engine control unit 6 applies a current to the digital valve 13 in order to close it at the moment between bottom dead center and top dead center 25 of the pump 4 during the phase for which it is desired to compress the fuel in the pump 4. This current is removed shortly before top dead center 25, as shown in FIGS. 3 and 4. The compression of the fuel keeps the digital valve 13 closed.

[0063] Once the angular position of top dead center 25 of the pump 4 has been passed, the digital valve 13 will open naturally as soon as the pressure in the cylinder of the pump 4 drops below the force applied by a return element 22 of the digital valve 13.

[0064] In particular, during the first few strokes of the piston 19, as the pressure in the common rail 7 is low, the offset between the instants of crossing top dead center 25 and of start-of-opening 23 of the digital valve 13 is very small also, and so the uncertainty is correspondingly smaller making this a preferred instant at which to estimate an angular position of top dead center 25.

[0065] If a current of predetermined strength is applied, it is possible, via the current induced by the movement of the digital valve 13, to determine the moment at which the digital valve 13 will begin to open, which means to say the start-of-opening 23 of the digital valve 13 and the wide open position 24 of the digital valve 13.

[0066] The estimate of an angular position of the instant of passing through top dead center 25 as a function of an angular position of the instant at which the position of start-of-opening 23 of the digital valve 13 appears may take account of at least one of the following parameters: the pressures upstream and downstream of the pump 4, the elastic modulus of the fuel, which is dependent on its temperature and pressure, technical characteristics of the pump 4 such as its dead volume and its swept volume.

[0067] The pressures upstream and downstream of the pump 4 may be measured respectively in the booster pump 2 and in the common rail 7. The elastic modulus of the fuel is data provided by the fuel supplier, whereas the temperature of the fuel can be modeled and its pressure measured. The technical characteristics of the pump 4 are known as these are data provided by the manufacturer of the pump 4.

[0068] As can be seen in FIGS. 3 and 4, making reference to all of the figures for the numerical references, the position of start-of-opening 23 of the digital valve 13 may be manifested by the appearance of a point of inflection in the curve monitoring the profile of the induced current. It is this instant of appearance of the point of inflection that is considered to be the instant of appearance of the position of start-of-opening 23 of the digital valve 13. The induced current passes through a point of inflection, for example dropping significantly as it passes through a point of inflection, signaling the position of start-of-opening 23, then rising again to pass through a maximum which signals the wide open position 24 of the digital valve 13.

[0069] The digital valve 13 may comprise a shutter 30 returned to the open position by a return element or spring 22. Simplistically, the digital valve 13 or, more specifically, the shutter 30, opens as soon as the pressure of the fuel in the chamber drops below the pressure exerted by the return element on the shutter 30 of the digital valve 13. This is what causes a delay between the angular positions of top dead center 25 and of the position of start-of-opening 23 of the digital valve.

[0070] More specifically, as depicted in FIG. 5 in an enlargement in order to show the structural details of one example of a digital valve 13, the shutter 30 of the digital valve 13 is subjected to a set of four forces F1, F2, F3, and F4, as follows: [0071] F1: force applied to the shutter 30 by the spring 22, [0072] F2: force applied to the shutter 30 by the low-pressure fuel, [0073] F3: force applied to the shutter 30 by the high-pressure fuel, [0074] F4: electromagnetic force applied to the shutter 30 by the digital valve actuator.

[0075] The forces F1, F2, F3, and F4 have the following effects on the shutter 30: the forces F1 and F2 seek to open the shutter 30, and the forces F3 and F4 keep it closed. The digital valve 13 therefore opens as soon as the set of forces present are such that F1+F2>F3+F4.

[0076] Definition of the forces:

F1=K*(xx0)

[0077] Where:

[0078] K: spring rate (constant)

[0079] x: compressed length of the spring

[0080] x0: free length of the spring

[0081] The force F1, which is therefore equal to the product of the spring rate constant times the difference between the free and compressed lengths of the spring 22, is constant and known when the digital valve 13 is closed.

F2=supply pressure*contact area of the valve shutter

[0082] Where: [0083] the supply pressure is the measured supply pressure of the low-pressure fuel, and [0084] the contact area of the valve shutter is the area via which the shutter 30 makes contact with its valve 13 seat, which is known by construction.

[0085] The force F2, which is therefore equal to the product of the measured low-pressure fuel supply pressure times the area of contact of the shutter of the digital valve on its seat, is constant and known when the digital valve 13 is closed.

F3=pressure in the cylinder*area of contact of the shutter

[0086] Where:

[0087] The pressure in the cylinder is the pressure of the fuel in the cylinder of the pump 4, and

[0088] The contact area of the shutter is, as defined above, the area via which the shutter of the digital valve makes contact with its seat, which is known by construction.

[0089] As regards the force F3, the pressure in the cylinder starts from a maximum which is the pressure in the common rail when the piston 19 is at top dead center, and decreases as the piston descends.

[0090] The force F4 is characterized by the current passing through the digital valve actuator, for example the coil of a solenoid acting on the shutter 30. This current is measured by the fuel injection system 1 and is known.

[0091] FIG. 6A depicts the digital valve 13 with the piston 19 of the pump 4 depicted at its operational top dead center, referenced point 0. FIG. 6A also depicts two diagrams with the abscissa axis indicating the position of the crankshaft CRK and the ordinate axis indicating, in the top diagram, the travel of the pump piston Pump, and, in the bottom diagram, the current DIV_CUR applied to and induced by the valve 13. The abscissa axis of the two diagrams are synchronized. In the top diagram, curve 31 shows the position of the piston 19 of the pump as a function of the position of the crankshaft, and in the bottom diagram, the signal 26 of the current applied to and induced by the valve 13.

[0092] FIG. 6B depicts the digital valve 13 with the piston 19 of the pump 4 depicted at its operational position of start-of-opening of the digital valve 13, referenced point 1. FIG. 6B also depicts two diagrams with the abscissa axis indicating the position of the crankshaft CRK and the ordinate axis indicating, in the top diagram, the travel of the pump piston Pump, and, in the bottom diagram, the current DIV_CUR applied to and induced by the valve 13. The abscissa axis of the two diagrams are synchronized. In the top diagram, curve 31 shows the position of the piston 19 of the pump as a function of the position of the crankshaft, and in the bottom diagram, the signal 26 of the current applied to and induced by the valve 13. FIG. 6B also shows the expansion of the piston 19 of the pump, between the two respective positions of the piston of FIGS. 6A and 6B, which is referenced by the term Expansion in FIG. 6B.

[0093] Therefore let the two particular operating points, according to FIGS. 6A and 6B, be: [0094] Point 0: top dead center 25 or TDC 25 of the piston 19, characterized by a pressure P0 equal to the pressure in the common rail, the corresponding volume V0 of the chamber of the pump 4 being equal to the dead volume of the pump 4, and the angular position of top dead center 25 for the pump 4, referenced Alpha_0 in FIG. 6A, which is the unknown. [0095] Point 1: position of start-of-opening of the digital valve 13, characterized by a pressure P1, the corresponding volume V1 of the pump 4 chamber and the angular position of start-of-opening 23 of the digital valve 13 referenced Alpha_1 in FIG. 6B.

[0096] The pressure P1 is determined at the point 1 from the following balance of forces: F3=F1+F2F4. The law governing the elasticity of fuels enables V1 to be calculated using the elastic modulus of the fuel and the pressures P0 and P1, as follows.

[0097] Let Point 0 (TDC) be defined by: [0098] P0=pressure of the common rail 7, [0099] V0=dead volume, known by design, [0100] Alpha_0=TDC position=unknown

[0101] Let Point 1 (point of start-of-opening of the valve) be defined by P1, V1, and Alpha_1=known position, measured by the system.

[0102] At the Point 1, there is the following balance of forces: F3=F1+F2F4; since the forces F1, F2 and F4 are known, F3 is determined in the knowledge that since F4 is dependent on the current, it will be characterized by measurements taken by the fuel injection system 1:

F3=P1*area of contact of the valve.

There is determined:

P1=(F1+F2F4)/area of contact of the valve.

[0103] Next, V1 is determined using the fuel elasticity equation:

[00001]$\mathrm{dP}=-E*\left(\frac{\mathrm{dV}}{V}\right)$

[0104] Where:

[0105] dP: variation in pressure, in Pa,

[0106] E: cubic elastic modulus, in Pa,

[0107] dV: variation in volume,

[0108] V: volume.

[0109] This gives the following relationship: dP=E * dV/V0, namely (P0-P1)=E * (V0-V1)/V0, where the elastic modulus E is a characteristic of the fuel dependent on its pressure and temperature. The volume V1=V0+(P0-P1) * V0/E is determined.

[0110] Furthermore, V1 is equal to V0 increased by the volume freed by the piston 19, namely the volume equal to the surface area of the piston 19 multiplied by the stroke of the piston 19. Because the surface area of the piston 19 is known, the stroke of the piston 19 is deduced as follows:

Piston stroke=(V1V0)/piston surface area

[0111] Since the cam profile (the lift of the piston 19 as a function of the angle) is known, the stroke of the piston 19 can be expressed in terms of the difference (alpha_1-alpha_0). And since Alpha_1 is measured by the system as being the angle at which the inflection in the current is seen, it can be used to deduce Alpha_0 which is the sought-after TDC of the pump.

[0112] The digital valve 13 can be activated with electric angular control. Electrical angular control requires synchronizing the pump 4 to the internal combustion engine 12. The angular control may follow a crank angle of the internal combustion engine 12.

[0113] Angular control of the high-pressure fuel injection pump 4 may be achieved in the known way using a plurality of electrical pulses, for example of what is known as the Peak and Hold, over a determined number of segments.

[0114] The determination of the top dead center 25 for the pump 4 is used for setting the timing of the high-pressure pump 4 with respect to the internal combustion engine 12, advantageously although not exclusively, by correspondence between top dead center 25 of the pump 4 and top dead center of one piston of the engine 12.

[0115] The invention therefore relates to a method for setting the timing of a high-pressure fuel injection pump 4 that forms part of a system 1 for injecting fuel into a motor vehicle internal combustion engine 12. In this timing method, an appearance of top dead center 25 for the pump 4 is synchronous with the engine 12 and advantageously in phase with the appearance of a top dead center of a piston of the engine 12. This method of setting the pump timing uses a method for estimating an angular position of top dead center 25 for the pump 4 as described hereinabove.

[0116] The invention finally relates to a system 1 for injecting fuel into a motor vehicle internal combustion engine 12, comprising a high-pressure fuel injection pump 4 and a control unit 5, 6. The control unit may comprise a controller 5 specific to the high-pressure fuel injection pump 4 and an engine control unit 6 with broader attributions regarding the operation of the combustion engine 12 and notably the injection of fuel into the engine 12.

[0117] The pump 4 comprises at least one piston 19 moving in a chamber and is equipped with a digital valve 13 for controlling a delivery of fuel this valve being operated by the control unit 5, 6 via an electric control element connected to the digital valve 13 by an electric circuit.

[0118] According to the invention, the injection system 1 employs a method for estimating an angular position of top dead center 25 for the pump 4 or a timing method, each as described hereinabove. The control unit 5, 6, and more particularly the controller 5 specific to the pump, comprises an element for monitoring a current induced in the electric circuit as the digital valve 13 opens and for detecting a position of start-of-opening 23 of the digital valve 13 and the instant at which it appears.

[0119] The control unit 5, 6 also comprises an element for calculating the instant at which the piston 19 of the pump 4 passes through top dead center 25 for the pump 4, as a function of the instant at which the position of start-of-opening 23 of the digital valve 13 appears.