METHOD FOR OPERATING A DIESEL ENGINE

Abstract

A method for operating an engine in which fuel is supplied to the engine by a fuel pump and by a high-pressure fuel pump, and in which the speed of the fuel pump and/or the electrical current for feeding the fuel pump is controlled in accordance with a requirement variable, taking into account a determination specification. When the engine has changed to an overrun mode of operation, a calibration is performed and the speed of the fuel pump is detected and is maintained. Once the triggering pressure for a calibration valve has been reached, the pump current is detected, a bypass volumetric flow rate of the high-pressure fuel pump is determined during calibration using operating parameters and the triggering pressure for the calibration valve, the determined speed, the bypass volumetric flow rate and the determined pump current are used to calibrate the determination specification.

Claims

1. A method for operating an internal combustion engine, where fuel is supplied to the internal combustion engine, comprising the steps of: providing a fuel pump, the fuel pump having a pressure side, and the fuel pump having a rotational speed and a pump current; providing a high-pressure pump arranged between the fuel pump and the internal combustion engine; providing a demand variable; providing a calibration valve in fluid communication with the pressure side of the fuel pump, the calibration valve having a triggering pressure; and providing a determination specification which includes the triggering pressure of the calibration valve, the determined rotational speed of the fuel pump, the bypass volume flow, and the determined pump current of the fuel pump; controlling the rotational speed of the fuel pump and the pump current for feeding the fuel pump based on the demand variable; changing the operating mode of the internal combustion engine to an overrun mode of operation; performing a calibration which includes actuating the fuel pump during the calibration such that the pressure on the pressure side of the fuel pump increases, while detecting and maintaining the rotational speed of the fuel pump, and detecting the pump current and the bypass volume flow after the calibration valve has reached the trigger pressure.

2. The method of claim 1, further comprising the steps of: providing an estimated pressure value on the pressure side of the fuel pump; determining the bypass volume flow of the high-pressure pump based on the estimated pressure value and the rotational speed of the fuel pump after the triggering pressure of the calibration valve is reached during the calibration.

3. The method of claim 1, providing the steps of: providing a temperature of the internal combustion engine; and providing a rotational speed of the internal combustion engine; determining the bypass volume flow of the high-pressure pump based on the temperature and the rotational speed of the internal combustion engine.

4. The method of claim 1, further comprising the steps of determining the triggering pressure of the calibration valve based on the rotational speed of the fuel pump.

5. The method of claim 1, further comprising the steps of determining the triggering pressure of the calibration valve based on the bypass volume flow of the high-pressure pump.

6. The method of claims 1, further comprising the steps of maintaining constant pressure on the high-pressure side of the high-pressure pump during the calibration process.

7. The method of claim 1, further comprising the steps of: providing a defined rotational speed threshold for the fuel pump; determining the rotational speed of the fuel pump after the internal combustion engine has changed to the overrun mode of operation; performing the calibration only when the defined rotational speed threshold has been exceeded.

8. The method of claim 7, further comprising the steps of deactivating the fuel pump and if the rotational speed of the fuel pump is less than the defined rotational speed threshold.

9. 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 fuel pump; changing the rotational speed of the fuel pump during the calibration, such that that rotational speed of the fuel pump corresponds to one of the predefined set of fixed values.

10. The method of claim 9, further comprising the steps of changing the rotational speed of the fuel pump during the calibration, such that that the rotational speed of the fuel pump corresponds to one of the predefined set of fixed values that has not been used during the calibration.

11. The method of claim 10, further comprising the steps of reducing the rotational speed of the fuel pump during the calibration, such that that rotational speed of the fuel pump corresponds to one of the predefined set of fixed values that has not been used during the calibration.

12. The method of claim 1 or one of the following claims, 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.

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

14. 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; assigning a weight to the plurality of calibration values.

15. 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.

16. 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.

17. A drive system having an internal combustion engine, comprising: a rotating fuel pump; a high-pressure pump in fluid communication with the rotating fuel pump and an internal combustion engine; a fuel return line in fluid communication with the high-pressure pump; a determination specification having one or more operating parameters for controlling the rotating fuel pump; a demand variable, the rotational speed of the fuel pump and the electrical current for feeding the fuel 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 fuel pump; a calibration device for calibrating one or more parameters of the determination specification, the calibration device further comprising: an actuation device which maintains the rotational speed of the fuel pump at a constant value, a detection device which detects the triggering pressure of the calibration valve, a determination device which determines a bypass volume flow of the high-pressure pump on the basis of operating parameters, a measurement device which determines the pump flow, and a correction determining device which determines a correction variable of the determination specification from one or more calibrations.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0049] FIG. 1 schematically shows the construction of a diesel internal combustion engine, of a fuel pump and of corresponding control and sensor devices;

[0050] FIG. 2 shows a typical characteristic map of a fuel pump in conjunction with a diesel engine; and

[0051] FIG. 3 shows a flow diagram of a process according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] 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.

[0053] 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 rotor pump may be used as the pump.

[0054] 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 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 flow. The rotational speed of the pump rotor 9, the current intensity of the pump current and the pressure in the low-pressure circuit between the fuel pump 7 and the high-pressure pump 38 are linked to one another by a characteristic map. 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 direct actuation of the pump 7.

[0055] 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 or else outside the tank 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 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.

[0056] Since the high-pressure pump 38, as a constituent part of a diesel common-rail injection system, normally permits a bypass volume flow, the high-pressure pump 38 is equipped with a return line, that is to say with a return duct 41 to the tank 8, via which return duct excess fuel flows back. The corresponding bypass volume flow, which is delivered through the fuel pump 7 on the path to the high-pressure pump 38 and flows through the low-pressure circuit 39, influences the triggering pressure of the calibration valve 18 and is thus, according to the invention, firstly determined and then taken into consideration in the calibration.

[0057] 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 stator or from the rotor 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 identifying the overrun operation, it is additionally also possible to concomitantly process a signal from the accelerator pedal 14. The process of the calibration, which may take place both in normal operation and in overrun operation, will be discussed in more detail further below on the basis of FIG. 3.

[0058] 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 18, 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.

[0059] 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).

[0060] 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 flow. The boundary line 26 denotes the maximum rotational speed that may be achieved by the pump, and the boundary line 27 denotes the values of the maximum delivery quantity that may be achieved by means of the pump, and the line 28 denotes the limit of the delivery quantity of the pump that cannot be undershot.

[0061] 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.

[0062] If, in the presence of constant rotational speed, the pressure is increased, the current intensity increases until the pressure reaches the line 25, or more specifically the line 25a. 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 may be stored as a reference. For this purpose, it must furthermore be considered that the triggering pressure of the pump, illustrated by the lines 25, 25a and 25b, is dependent on the volume flow in the low-pressure circuit 39, that is to say also on 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. However, it is initially necessary, as described above, for the volume flow, which is determined substantially by the bypass volume flow of the high-pressure pump 38, to be determined, which occurs in the course of the method according to the invention.

[0063] 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.

[0064] The method according to the invention will be discussed by way of example for one possible embodiment on the basis of FIG. 3.

[0065] In an optional first step 29, it is signaled to the pump controller 13 or some other responsible module in an assembly of the vehicle 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.

[0066] 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 low rotational speed which still provides the bypass volume of the high-pressure pump. 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.

[0067] In the next method step 34, the electric pump current is then detected. This may be performed in small discrete steps or continuously. After every increase, it may be checked in the method step 35 whether a current increase has led to a pressure increase, or whether the reference valve has been triggered (significantly smaller current increase). 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.

[0068] 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 variable required for the correction of the triggering pressure is the volume flow, which may be determined from the pump rotational speed, and which in turn influences the opening pressure of the calibration valve. Since the triggering/opening pressure of the calibration valve is dependent on the volume flow, the volume flow determined after attainment of the opening pressure may be used to correct the opening pressure of the calibration valve by means of an estimation.

[0069] The calibration measurement point is thereupon detected, and the rotational speed of the pump may, in the final method step 37, be reduced, to zero. The calibration measurement may be repeated later at other starting rotational speeds of the pump in order to collect a multiplicity of data triplets, which may together be used to correct a characteristic map which is stored in the region 15 of the control device 13.

[0070] In the method step 37, a data tuple, such as a data triplet, which comprises the rotational speed of the pump, the pump current and the triggering pressure, is additionally stored. The data form one of possibly several datasets, with the aid of which it is for example possible for a characteristic map of the fuel pump or a corresponding determination specification to be calibrated.

[0071] 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.