METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE

Abstract

A method for operating an internal combustion engine, in which fuel is supplied to the internal combustion engine by a rotary pump, and the speed of the pump and/or the electrical current for feeding the pump (pump current) is controlled in accordance with a requirement variable, taking into account a determination specification. When in an overrun mode, a calibration is carried out and the speed of the pump is detected and is maintained during the calibration step. Once the triggering pressure for a calibration valve, arranged on the high-pressure side of the pump, has been reached, the pump current is detected and the determined speed and the determined pump current are used to calibrate the determination specification. A calibration in the overrun mode is performed without alteration to the speed of the fuel pump. This prevents a variable behaviour of the fuel pump which might produce undesired operating conditions.

Claims

1. A method for operating an internal combustion engine, in which fuel is supplied to the internal combustion engine, comprising the steps of: providing a rotating pump having a pressure side, the rotating pump having a rotational speed and a pump current; providing a demand variable; providing a calibration valve in fluid communication with the pressure side of the rotating pump; providing a demand specification having a characteristic map; and providing a trigger pressure which actuates the calibration valve; changing the operating mode of the internal combustion engine to an overrun mode of operation; performing a calibration including detecting and maintaining the rotational speed of the rotating pump, and detecting the pump current upon actuation of the calibration valve at the trigger pressure, such that the rotational speed of the rotating pump and the pump current of the rotating pump are part of the determination specification; controlling the rotational speed of the fuel pump and the pump current for feeding the fuel pump based on the demand variable and the determination specification.

2. The method of claim 1, further comprising the steps of: providing a rotational speed threshold for the rotating pump; identifying the change in operating mode of the internal combustion engine to the overrun mode of operation; determining the rotational speed of the rotating pump after identifying the change in operating mode of the internal combustion engine to the overrun mode of operation; performing the calibration only when the rotational speed of the rotating pump has exceeded the rotational speed threshold.

3. The method of claim 2, further comprising the steps of deactivating the rotating pump if, after identifying the change in operating mode of the internal combustion engine to the overrun mode of operation, the rotational speed of the rotating pump is less than the rotational speed threshold.

4. The method of claim 1, further comprising the steps of: providing a predefined set of fixed values representing a plurality of rotational speeds of the rotational pump; before the calibration, changing the rotational speed of the rotational pump to one of the predefined set of fixed values.

5. The method of claim 1, further comprising the steps of: providing a predefined set of fixed values representing a plurality of rotational speeds of the rotating pump; changing the rotational speed of the rotating pump during the calibration, such that that rotational speed of the rotating pump corresponds to one of the predefined set of fixed values.

6. The method of claim 5, further comprising the steps of changing the rotational speed of the rotating pump during the calibration, such that that the rotational speed of the rotating pump corresponds to one of the predefined set of fixed values that has not previously been used during the calibration.

7. The method of claim 5, further comprising the steps of reducing the rotational speed of the rotational pump during the calibration, such that that rotational speed of the rotational pump corresponds to one of the predefined set of fixed values that has not previously been used during the calibration.

8. The method of claim 1, further comprising the steps of: providing a predefined minimum number of calibrations points; determining whether the number of calibrations points has reached the predefined minimum number of calibration points after the determination of the pump current and the triggering of the calibration valve.

9. The method of claim 1, further comprising the steps of deactivating the fuel pump after completion of the calibration.

10. The method of claim 1, further comprising the steps of: providing a plurality of calibration values obtained during the calibration; changing the operation of the internal combustion engine as a result of a change in the demand variable such that the internal combustion engine is no longer in the overrun mode of operation; ending the calibration as a result of the internal combustion engine is no longer being in the overrun mode of operation; determining to what extent the calibration has progressed; assigning a weight to the plurality of calibration values.

11. The method of claim 1, further comprising the steps of: providing a plurality of calibration values obtained during the calibration; changing the operation of the internal combustion engine as a result of a change in the demand variable such that the internal combustion engine is no longer in the overrun mode of operation; ending the calibration as a result of the internal combustion engine no longer being in the overrun mode of operation; determining to what extent the calibration has progressed; ignoring the plurality of calibration values obtained during the calibration

12. The method of claim 1, further comprising the steps of: providing a bus system; and providing a pump controller operable for controlling the fuel pump; communicating the change to the overrun mode of operation of the internal combustion engine to the pump controller using the bus system.

13. A drive system having an internal combustion engine, comprising: a rotating pump for supplying fuel to an internal combustion engine; a determination specification having one or more operating parameters for controlling the rotating pump; a demand variable, the rotational speed of the rotating pump and the electrical current for feeding the rotating pump (pump current) are controlled in a manner dependent on the demand variable and the determination specification; a calibration valve in fluid communication with the rotating pump; a calibration device for calibrating parameters of the determination specification, the calibration device further comprising: a control device which keeps the rotational speed of the rotating pump at a constant value; a detection device which detects the triggering pressure of the calibration valve; a measurement device which determines the pump current; a correction determining device which determines a correction variable of the determination specification from one or more calibrations.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Below, on the basis of an exemplary embodiment, the invention will be shown in the figures of a drawing and discussed below. The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0040] FIG. 1 schematically shows the construction of an internal combustion engine, of a fuel pump, of a high-pressure pump and of corresponding control and sensor devices,

[0041] FIG. 2 shows a typical characteristic map of a fuel pump, and

[0042] FIG. 3 shows a flow diagram of a process according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0044] FIG. 1 shows an internal combustion engine 1 which is controlled by means of an engine controller (ECU) 40 and which, via a fuel line 2, is supplied with fuel at high pressure by means of the high-pressure pump/injection pump 38, wherein the fuel is injected into individual cylinders (not illustrated) by means of four injection valves 3, 4, 5, 6. For this purpose, fuel is supplied to the high-pressure pump 38 from a tank 8 via a low-pressure circuit 39 by means of the fuel pump 7. It is the intention in the method according to the invention to calibrate the fuel pump 7, which may be arranged in the tank 8. The pump 7 is driven by means of an electric motor integrated therein, and has a rotor 9 for delivering the fuel. The rotor is schematically illustrated, wherein, for example, a positive-displacement pump or some other pump embodiment may be used as the pump.

[0045] The electric motor of the pump 7 is fed with a current (pump current) via an electrical line 10, wherein the current intensity is detected by means of a current sensor 11. The rotational speed of the pump is detected by means of a sensor 12, or the rotational speed is determined on the basis of the current information from 11, and transmitted to a control device 13 of the pump (pump controller). The control device 13 is actuated with the demand variable by means of an accelerator pedal 14, and, in the actuation of the pump 7, takes into consideration both the rotational speed of the pump rotor 9, which is transmitted by the sensor 12, and the current intensity of the pump current. For this purpose, the controller 13 has a data processing part 15 in which corresponding determination algorithms and/or characteristic maps are stored. The remaining part 16 of the control device 13 performs the actuation of the pump 7.

[0046] To the low-pressure circuit 39, which is at an elevated fuel pressure in relation to the tank 8 and situated between the fuel pump 7 at one side and the high-pressure pump 38 and the engine 1 at the other side, there is connected a reference valve 18, which may be arranged in the fuel tank 8 and which, in the event of an exceedance of a reference pressure, opens and discharges fuel via an outlet duct 19. The reference valve 18, which itself may be situated outside the tank, is used in the manner according to the invention for calibrating the controller 13 and/or the data processing part 15. The calibration process may be controlled by means of the engine controller 40 or the pump controller or a software module integrated in some other assembly of the vehicle.

[0047] In addition to the input variables of the load demand from the accelerator pedal 14, the rotational speed of the pump 7, the pump current and possibly other influential variables such as the air humidity and the operating temperature, the control device 13 may also have the rotational speed of the internal combustion engine transmitted thereto from the rotating part 20 of the internal combustion engine. The engine or the engine controller may for example transmit a signal to the control device 13 via a CAN bus 21, 21′, which signal signalizes the rotational speed and possibly the change to overrun operation. For the identification of overrun operation, a signal from the accelerator pedal 14 may also be concomitantly processed. The process of the calibration will be discussed in more detail further below on the basis of FIG. 3.

[0048] FIG. 2 illustrates a diagram in which the fuel pressure p in bar is plotted on the y axis versus the rotational speed on the x axis, measured in revolutions per minute. Multiple curves/characteristic curves 22, 23, 24 are shown, each of which represents a fixed current intensity value of the pump current, that is to say of the current which is fed to the electric motor which drives the pump. For each individual one of the characteristic curves 22, 23, 24, the relationship between the fuel pressure and the rotational speed of the pump is illustrated. The upper boundary line 25 of the diagram denotes, in simplified form and disregarding any hysteresis (see below), the triggering pressure of the reference valve, that is to say, as soon as the fuel pressure crosses the boundary in the direction of higher pressures, the reference valve opens, and the pump cannot generate any higher pressure. The two dashed lines 25a and 25b are illustrated merely schematically and not to scale, and indicate triggering pressure values of the reference/calibration valve, with more detailed consideration being given to a hysteresis, that is to say, in the event of an increase of the pressure, the valve opens only in the presence of the higher of the two pressure values (lying on the line 25a), whereas in the event of a decrease of the pressure, the valve closes again in the presence of the relatively low pressure value (lying on the line 25b).

[0049] To expand the calibration possibilities, it is possible, in an overshoot process during overrun operation, to detect not only the triggering of the reference valve in the event of the pressure increase but also the switching pressure of the valve in the event of the pressure decrease, and thus, in a single process, to record two reference points in each case with pump rotational speed/pump volume flow and pump current.

[0050] The boundary line 26 denotes the maximum rotational speed that may be achieved by the fuel pump, and the boundary line 27 denotes the values of the maximum delivery quantity that is achieved by means of the pump, and the line 28 denotes the limit of the delivery quantity of the pump that cannot be undershot, for example if the pump is a positive displacement pump.

[0051] Corresponding characteristic maps in another representation but with the same information content also exist for lines of constant rotational speed of the pump, wherein, in this case, the current intensity is variable.

[0052] If, in the presence of constant rotational speed, the current intensity is increased, the pressure increases up to the line 25, or more specifically the line 25a, and when the triggering pressure of the reference pump is reached, the set rotational speed of the pump, and the current intensity of the pump current attained at this point, are present, such that a data triplet composed of the three values pump current, rotational speed and pressure are stored as a reference. For this purpose, it must furthermore be considered that the triggering pressure of the pump, illustrated by the line 25, is not independent of the rotational speed of the pump, such that the triggering pressure may be corrected on the basis of the rotational speed and the pump current.

[0053] Measurements of different data triplets, that is to say different current intensities at different rotational speeds of the pump in each case upon the attainment of the triggering pressure of the reference valve (according to the invention, in the presence of a constant rotational speed of the pump) make it possible for the entire characteristic map to be calibrated. The method according to the invention will be discussed by way of example for one possible embodiment on the basis of FIG. 3.

[0054] In a first step 29, the pump controller 13 or some other responsible module in an assembly of the vehicle signals that a change to overrun operation is presently taking place or has taken place. In the second step 30, it is checked whether the present rotational speed of the pump 7 lies above a minimum rotational speed required for the calibration.

[0055] If this is not the case, the calibration method is stopped by means of a transition to a termination step 31, and it is for example possible for the fuel pump to be run down to a rotational speed of zero or to a low rotational speed. If the rotational speed of the pump lies above the threshold value, then in the next method step 32, it is checked whether the present rotational speed of the pump is suitable for a calibration, and whether a calibration point already exists for the rotational speed. If the rotational speed is suitable for a calibration and if it is the case that no calibration measurement has yet been performed at the rotational speed, then a transition is made directly to step 34. If this is not the case, then in a method step 33, the rotational speed of the pump is changed slightly, is reduced to a preselected value and/or to a “round” value.

[0056] In the next method step 34, the electric pump current is then checked; as a result of the increasing pressure, the pump current also increases. This may be performed in small discrete steps or continuously. After every measured increase, it may be checked in the method step 35 whether a current increase has led to a sufficient pressure increase, or whether the reference valve has been triggered. If this is not determined directly by observing the load of the pump, then it may also be signaled by means of a sensor arranged at the calibration valve/reference valve.

[0057] If the current does not increase, or if a triggering of the reference valve is directly signaled, then a transition is made from the step 35 to a step 36, in which the data triplet composed of the current intensity of the pump current, the rotational speed and the triggering pressure of the reference valve, or a corrected value of the triggering pressure taking into consideration rotational speed and pump current, is stored. The calibration measurement point is thereupon detected, and the rotational speed of the pump may, in the final method step 37, be reduced, for example to zero. The calibration measurement may be repeated later such as at other starting rotational speeds of the pump in order to collect a multiplicity of data triplets, which can together be used to correct a characteristic map which is stored in the region 15 of the control device 13.

[0058] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.