METHOD FOR OPERATING A FUEL INJECTION SYSTEM FOR SUPPLYING A COMBUSTION ENGINE WITH FUEL, AND ELECTRONIC CONTROL UNIT

Abstract

The invention relates to a method for operating a fuel injection system (1) for supplying a combustion engine of a vehicle with fuel, in which method the fuel is conveyed at high pressure with the aid of a high-pressure pump (2), fed to a high-pressure accumulator (3), and injected into a cylinder of the combustion engine with the aid of at least one injector connected to the high-pressure accumulator (3). In order to detect any damage to the drive of the high-pressure pump (3), according to the invention a) the pressure (P) in the high-pressure accumulator (3) is measured and, on the basis of the measured values, a pressure drop (?P) in the high-pressure accumulator (3) caused by an injection into a cylinder is determined, b) a maximum pressure gradient is determined during a pressure build-up phase following the injection, c) the determined pressure drop (?P) and the determined maximum pressure gradient are put into proportion.

The invention further relates to an electronic control unit for carrying out the method.

Claims

1. A method for operating a fuel injection system (1) for supplying a combustion engine of a vehicle with fuel, in which method the fuel is conveyed at high pressure with the aid of a high-pressure pump (2), fed to a high-pressure accumulator (3), and injected into a cylinder of the combustion engine with the aid of at least one injector (4) connected to the high-pressure accumulator (3), wherein, in order to detect any damage to the drive of the high-pressure pump (3), a) the pressure (P) in the high-pressure accumulator (3) is measured and, on the basis of the measured values, a pressure drop (?P) in the high-pressure accumulator (3) caused by an injection into a cylinder is determined, b) a maximum pressure gradient is determined during a pressure build-up phase following the injection, c) the determined pressure drop (?P) and the determined maximum pressure gradient are put into proportion.

2. The method according to claim 1, wherein in step a) the pressure (P) in the high-pressure accumulator (3) is measured angle-synchronously, in particular continuously, with the aid of a pressure sensor (5) arranged on the high-pressure accumulator (3).

3. The method according to claim 1, wherein in step a), the pressure drop (?P) in the high-pressure accumulator (3) is determined with the aid of discrete Fourier transformation (DFT) on a cylinder-specific basis.

4. The method according to claim 1, wherein in step b) the maximum pressure gradient is determined from the first derivative of the pressure (P) measured in step a).

5. The method according to claim 1, wherein steps a) to c) are carried out repeatedly.

6. The method according to claim 1, wherein at least steps b) and c) are carried out with the aid of an electronic control unit.

7. The method according to claim 1, wherein upon detection of damage to the drive of the high-pressure pump (3), a warning signal is output to the driver of the vehicle and/or to an external control station connected to the vehicle via a communication interface.

8. An electronic control device configured to operate a fuel injection system (1) for supplying a combustion engine of a vehicle with fuel, where the fuel is conveyed at high pressure with the aid of a high-pressure pump (2), fed to a high-pressure accumulator (3), and injected into a cylinder of the combustion engine with the aid of at least one injector (4) connected to the high-pressure accumulator (3), by measuring the pressure (P) in the high-pressure accumulator (3), determining, based on the measured pressure values, a pressure drop (?P) in the high-pressure accumulator (3) caused by an injection into a cylinder, determining a maximum pressure gradient during a pressure build-up phase following the injection, and proportioning the determined pressure drop (?P) and the determined maximum pressure gradient.

9. (canceled)

10. A machine-readable storage medium on which the computer program according to claim 9 is stored.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention will be explained in more detail in the following with reference to the accompanying drawings. The figures show:

[0020] FIG. 1 a schematic view of a fuel injection system having a high-pressure pump having two pump elements,

[0021] FIG. 2 a) and b) a schematic longitudinal section through a drive of a pump element, a) without damage to the drive, and b) with damage to the drive,

[0022] FIG. 3 a graph of the pressure profile in the high-pressure accumulator of a fuel injection system during an injection cycle of a high-pressure pump having two pump elements,

[0023] FIG. 4 a) a diagram for plotting the pressure profile at two different fuel temperatures and b) a graph for plotting the associated pressure gradients,

[0024] FIG. 5 a diagram for graphing the ratio of pressure drop to maximum pressure gradient on the basis of the values of FIG. 4,

[0025] FIG. 6 a further diagram for graphing the ratio of pressure drop to maximum pressure gradient on the basis of values measured at a changed fuel temperature, and

[0026] FIG. 7 a diagram illustrating the ratio of pressure drop to maximum pressure gradient ratio on the basis of values measured in case of damage to the drive.

DETAILED DESCRIPTION

[0027] FIG. 1 shows an exemplary fuel injection system 1 suitable for carrying out a method according to the invention. It comprises a high-pressure pump 2 having two pump elements A and B that are driven by a camshaft (not shown) of the high-pressure pump 2. The pump elements A, B convey fuel at high pressure. The high-pressure fuel is fed to a high-pressure accumulator 3, to which a plurality of injectors 4 are connected for injecting fuel into a cylinder of a combustion engine (not shown). To monitor the pressure in the high-pressure accumulator 3, a pressure sensor 5 is integrated into the high-pressure accumulator 3 at one end.

[0028] FIGS. 2a) and 2b) show by way of example a drive for a pump element of a high-pressure pump 2. The drive comprises a camshaft having a cam 6 or 6, on which a liftable pump piston 9 or 9 is supported via a respective roller plunger 8 or 8. Upon a rotation of the camshaft, a roller 7 or 7 of the roller plunger 8 or 8 runs off circumferentially on the cam 6 or 6, respectively. Depending on the angular position of the cam 6 or 6, the pump piston 9 or 9 moves from a bottom dead center point to a top dead center point or vice versa and carries out a stroke h. In FIG. 2a), the cam 6 does not yet have any wear. In FIG. 2b), the cam 6 has a clear wear, which can be due for example to the roller 7 not being correctly aligned with respect to the cam 6. The wear results in the stroke h of the pump piston 9 being smaller by the difference ?h. Accordingly, the conveyance rate of the pump element decreases, so that the pressure build-up required after an injection in the high-pressure accumulator 3 is delayed. The damage to the drive of the high-pressure pump 2 accordingly affects the pressure in the high-pressure accumulator 3.

[0029] FIG. 3 shows by way of example a pressure profile in a high-pressure accumulator 3 of a fuel injection system 1, which is constructed analogously to that of FIG. 1, during an injection cycle. That is to say, fuel is withdrawn one time from the high-pressure accumulator 3, so that the pressure in the high-pressure accumulator 3 drops. Then, the pressure is rebuilt with the aid of the two pump elements A, B. The pressure build-up by the pump element A is superposed in part by the injection event, so that the pressure build-up with the aid of the second pump element B is more prevalent. If there is any damage to the drive, the profile changes (see dashed line) for the aforementioned reasons. The pressure drop during injection, on the other hand, remains unchanged.

[0030] Other factors that can affect the pressure in the high-pressure accumulator 3 are, for example, the fuel quality and fuel temperature, because these factors change the compressibility of the fuel. A change of these factors affects both the pressure drop and the subsequent pressure build-up in the high-pressure accumulator 3. This is illustrated by way of example in FIG. 4a), which shows a reference curve as well as a further curve (dashed line) which results in a change of an influencing factor, for example the fuel temperature, by 10%. The bottom part of FIG. 4b) shows the first respective derivative for determining the associated pressure gradient.

[0031] As shown in FIG. 5, if the pressure drop (?P) and the maximum pressure gradient are put into proportion, substantially no change in the profile of the graphs can be determined, because the change by 10% affects both the value of the x-axis and the value of the y-axis.

[0032] A similar graph showing the ratio of pressure drop to maximum pressure gradient can be seen in FIG. 6. Reference values as well as values with a changed fuel temperature are shown. The graph shows that all values move within a certain tolerance window and thus lie essentially on a line or in a direction (see arrow).

[0033] The result is different when the high-pressure pump 3 has damage to the drive. This is shown in FIG. 7 for comparison. This is because, in this case, the values no longer lie on a line, in particular no longer within the tolerance window, but rather move downwards (see arrow) out of the tolerance window. The line thus has a flatter profile, which indicates damage to the drive.

[0034] Independently of FIGS. 1 to 7, the method according to the invention is not limited to the application of a high-pressure pump 2 with two pump elements A, B. Furthermore, the method can be carried out in multiple injections. These should preferably closely follow one another.