Method for controlling a fuel delivery system

Abstract

A method for controlling a fuel delivery system of an internal combustion engine, having a fuel delivery pump that is driven by an electric motor. The pressure that prevails in the fuel delivery system is determined by a volume difference between the fuel quantity delivered by the fuel delivery pump and the fuel requirement of the internal combustion engine and/or of the fuel delivery system.

Claims

1. A method for controlling a fuel delivery system of an internal combustion engine, having a fuel delivery pump that is driven by an electric motor, comprising: determining a volume difference between a fuel quantity delivered by the fuel delivery pump and a fuel requirement of the internal combustion engine and the fuel delivery system; and determining a pressure that prevails in the fuel delivery system is determined based on the volume difference between the fuel quantity which is delivered by the fuel delivery pump and the fuel requirement of the internal combustion engine and at least one suction jet pump of the fuel delivery system.

2. A method for controlling a fuel delivery system of an internal combustion engine, having a fuel delivery pump that is driven by an electric motor, comprising: determining a volume difference between a fuel quantity delivered by the fuel delivery pump and a fuel requirement of at least one of the internal combustion engine and the fuel delivery system; determining a pressure that prevails in the fuel delivery system is determined based on the volume difference between the fuel quantity which is delivered by the fuel delivery pump and the fuel requirement of at least one of the internal combustion engine and the fuel delivery system; performing a calibration to determine the pressure that prevails in the fuel delivery system; and setting an operating point for calibration purposes at which operating point the fuel requirement of the internal combustion engine is substantially identical to the fuel quantity delivered by the fuel delivery pump, wherein a known pressure prevails in the fuel delivery system at the operating point for calibration.

3. The method as claimed in claim 2, wherein, starting from the calibration point, a change in the pressure is determined in a manner dependent on a fuel quantity delivered by the fuel delivery pump.

4. The method as claimed in claim 2, wherein the pressure in the fuel delivery system is determined within a predefinable operating range of the fuel delivery pump based at least in part on a change in the fuel delivery quantity, starting from the fuel delivery quantity at the calibration point.

5. The method as claimed in claim 2, wherein a characteristic diagram is used to determine the pressure, the characteristic diagram providing a relationship between the fuel quantity delivered by way of the fuel delivery pump, the fuel requirement of the at least one of the internal combustion engine and the fuel delivery system, and the pressure that prevails in the fuel delivery system.

6. The method as claimed in claim 5, wherein curves of the characteristic diagram used to determine the pressure in the fuel delivery system form a straight line with a high ascending gradient for each fuel requirement of the internal combustion engine within a defined pressure range.

7. The method as claimed in claim 2, wherein, starting from the pressure at the calibration point, the pressure in the fuel delivery system rises in a case of an increase in the fuel quantity delivered by way of the fuel delivery pump, at a constant fuel requirement of the internal combustion engine.

8. The method as claimed in claim 2, wherein, starting from the pressure at the calibration point, the pressure in the fuel delivery system drops in a case of a reduction in the fuel quantity delivered by way of the fuel delivery pump, at a constant fuel requirement of the internal combustion engine.

9. The method as claimed in claim 2, wherein a value for the fuel requirement of the internal combustion engine is provided by a control unit of the internal combustion engine.

10. The method as claimed in claim 2, wherein the fuel quantity delivered by the fuel delivery pump is determined via one of: a flow meter, computationally from a rotational speed of the fuel delivery pump, or from a current with which the fuel delivery pump is actuated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following text, the invention will be described in detail using exemplary embodiments, with reference to the drawings, in which:

(2) FIG. 1 is a of fuel consumption by an internal combustion engine plotted against a fuel delivery quantity of the fuel delivery pump;

(3) FIG. 2 is a graph of fuel consumption by the internal combustion engine plotted against rotational speed of the fuel delivery pump; and

(4) FIG. 3 is a block diagram of the method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) FIG. 1 shows a graph 1. In the graph 1, the fuel delivery quantity of a fuel delivery pump in a fuel delivery system is plotted on the X-axis 2. Here, the fuel delivery quantity is plotted for a range from zero liters per hour at the point of intersection with the Y-axis 3 up to 80 liters per hour on the right-hand end region of the X-axis 2. The pressure that prevails in the fuel delivery system is plotted on the Y-axis 3. The curves 4, 5, 6, 7, and 8 represent the respective fuel requirement of an internal combustion engine. The curve 4 corresponds to a fuel requirement of 20 liters per hour, the curve 5 corresponds to a fuel requirement of 30 liters per hour, the curve 6 corresponds to a fuel requirement of 40 liters per hour, the curve 7 corresponds to a fuel requirement of 50 liters per hour, and the curve 8 corresponds to a fuel requirement of 60 liters per hour. The fuel requirements of the graph 1 are by way of example and represent values for a specific fuel delivery system for an internal combustion engine. The respective diagrams will also look similar in terms of the quality, however, for other fuel requirements in differing fuel delivery systems.

(6) It can be seen from the curves 4 to 8 that a pressure, which is constant across the fuel requirements 4 to 8, prevails in the fuel delivery system in each case in the case of a match of the fuel requirement 4 to 8 and the fuel delivery quantity on the X-axis 2. The pressure is set when, for example, 20 liters per hour are delivered by the fuel delivery pump and the fuel requirement of the internal combustion engine is likewise 20 s per hour. The substantially constant pressure is dependent on the respective fuel delivery system and can correspondingly be somewhat higher or lower. In the example of FIG. 1, the constant pressure for a fuel delivery system that forms the basis for the curves 4 to 8 is approximately 4 bar.

(7) In the case of a fuel requirement that lies considerably above the fuel delivery quantity, the pressure in the fuel delivery system drops greatly. This can be seen in the region 9 of FIG. 1. In the case of a fuel requirement below the fuel delivery quantity, in contrast, the pressure rises. This can be seen in the region 10.

(8) The curves 4 to 8 result from a simulation and show values for a defined fuel delivery system. Here, this is, in particular, a fuel delivery system that does not act as a hydraulic orifice. Therefore, the fuel consumption quantity of the internal combustion engine is not proportional to the hydraulic orifice formed by way of the fuel delivery system. Depending on the operating mode, the high pressure pump connected downstream of the fuel delivery system and delivers the fuel to the internal combustion engine can contribute to a different appearance of the characteristic diagrams. The basic statement that a constant pressure is set in the fuel delivery system if the fuel consumption quantity coincides with the fuel quantity delivered by way of the fuel delivery system remains unaffected by this, however.

(9) FIG. 2 shows an alternative illustration of the graph 1 from FIG. 1, the fuel requirements 14, 15, 16, 17 and 18 of the internal combustion engine being plotted against the rotational speed of the fuel delivery pump plotted along the X-axis 12. The pressure in the fuel delivery system is plotted on the Y-axis 13 of the diagram 11. Since the rotational speed of the fuel delivery pump is directly linked to the delivery quantity of the fuel delivery pump, the two diagrams 1, are directly dependent on one another and differ substantially merely by way of a different illustration.

(10) It can be derived from the graphs 1 and 11 of FIGS. 1 and 2 that in each case the change in the delivered fuel quantity in the case of a constant fuel consumption by way of the internal combustion engine leads to a change in the pressure in the fuel delivery system. Via the characteristic diagrams, which are formed by way of the diagrams 1 and 11, therefore, the increase and the decrease in the pressure can be determined in a manner dependent on the respectively delivered fuel quantity and the respective fuel requirement of the internal combustion engine. In order to also obtain a statement about an absolute pressure value, a calibration of the fuel delivery system has to take place. Said calibration takes place by way of a defined calibration point being set that is distinguished by the fact that the delivered fuel quantity coincides with the fuel quantity consumed by the internal combustion engine. A defined pressure prevails in the fuel delivery system at said calibration point, which defined pressure can be used as an initial value for the pressure. The changes in the pressure which can be detected by the characteristic diagrams can therefore be translated at any time into an absolute pressure.

(11) A substantially constant pressure value can be determined for every fuel delivery system by way of a calibration, which pressure value is used as a starting basis for the pressure determination. Furthermore, the pressure can also be calculated using what is known as a gradient function in the case of a defined consumption quantity in the fuel delivery system. This can take place, for example, by way of a consideration of the different gradients in the case of different fuel volumes that are delivered. The calibrated base value can be stored in a control unit of the fuel delivery system, with the result that a precise determination of the pressure which prevails in the fuel delivery system is possible at every operating time.

(12) A reliable starting basis for volume-based calculations, such as the throughflow control or the throughflow monitoring, is obtained as a by-product of the setting of an operating point, at which the fuel consumption by way of the internal combustion engine and the fuel delivery quantity of the fuel delivery pump coincide. Furthermore, the aging of the fuel delivery pump and the therefore slowly dropping fuel delivery volume can also be compensated for in this way.

(13) FIG. 3 shows a block diagram 20, the block diagram 20 depicting the method according to the invention by way of example. A calibration of the fuel delivery system takes place in the block 21, by a defined operating point being set, which is distinguished by the fact that the fuel consumption by way of the internal combustion engine and the fuel delivery quantity of the fuel delivery pump correspond to one another. The step can also take place for a specific fuel delivery system empirically in advance or on the basis of a calculation. The pressure that prevails at the calibration point is read into a control unit of the fuel delivery system and is stored as a base value. Starting from said base value, a pressure change can be detected in the block 22 with the observation of the change in the fuel delivery quantity and/or the fuel consumption by way of the internal combustion engine. In the block 23, the respectively prevailing pressure in the fuel delivery system is determined by way of the combination of the initial value for the pressure in the fuel delivery system and the pressure change.

(14) The exemplary embodiments of FIGS. 1 to 3 do not have a restrictive character, in particular, and serve to illustrate the concept of the invention.

(15) Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.