CN104047731B - Method for running electric petrolift - Google Patents

Abstract

The invention relates to a method for operating an electric fuel pump, in particular an electric fuel pump of an injection system, wherein a maximum limit value ( 48 ) is preset for the voltage applied to the electric fuel pump, for the flow A preset maximum limit value (62) for the electric current of the fuel pump, wherein the value (62) of the current required by the electric fuel pump is measured, wherein the measured value (62) for the current exceeds the preset maximum limit value ( In the case of 64), the preset maximum limit value (48) for the voltage applied to the electric fuel pump is reduced depending on the measured value (62) of the current.

Description

Method for operating an electric fuel pump

technical field

The invention relates to a method and a control device for operating an electric fuel pump.

Background technique

The function of the injection system for the internal combustion engine can be controlled by the control device. A so-called EDC (Electronic Diesel Control) control device can be used for injecting diesel into the combustion chamber of the internal combustion engine. The output stage of the EDC control device is usually designed in such a way that the current requirements of the regulating components of the injection system can be met without problems even under unfavorable operating boundary conditions. In addition, a monitoring module is provided, with which the output stage can be switched off in the event of a fault, for example in the event of a short circuit or overheating.

The regulating component of the injection system can be designed as an electric fuel pump (EKP), which in normal operation has only a limited current demand taking into account all preset boundary conditions, however this current demand is Cases can be raised for example. In exceptional cases, however, the current demand increases sharply, for example when the pressure drops even more due to particularly heavy fuel contamination or due to partial condensation of the fuel. In FPC (Feed Pump Control) devices, the rail pressure of the injection system is regulated via the electric fuel pump (EKP), whereby the current demand of the electric fuel pump depends largely on the operating point of the injection system .

In such injection systems with a fuel accumulator (common rail), the pressure of the fuel also depends on the quantity of fuel delivered by a fuel pump, for example designed as a high-pressure pump, and on the pressure of the fuel at the input of the fuel pump and the current required to run the electric fuel pump. However, the voltage required for the operating point at the fuel pump varies greatly in different cases and depending on the ambient conditions. The design of the injection system therefore requires a permissible large voltage range of the electric fuel pump, however, in exceptional cases, for example, at the fuel filter, this can result in significantly higher, current at the fuel pump. However, designing the output stage of the electric fuel pump for this maximum possible current within the injection system is relatively more expensive than designing the current that occurs only under normal conditions.

Laid-open document DE 10 2010 030 872 A1 describes a method for determining a corrected characteristic curve for adjusting the characteristic curve of an injection system, wherein the corrected characteristic curve comprises at least one deviation of the measured characteristic curve relative to the theoretical characteristic curve. In this case, the at least one deviation includes an overall tolerance of at least two components of the injection system which influence the characteristic curve.

Contents of the invention

Against this background, a method and a control device are proposed having the features stated in the independent claims. Further configurations of the invention emerge from the subclaims and the description.

The invention makes it possible to limit the current level of the electric fuel pump (EKP), which is designed as part of the injection system, to a maximum permissible value by designing the output stage and thereby protect the output stage.

The fuel quantity is delivered by means of an electric fuel pump into a fuel accumulator (common rail) of the injection system, the quantity also being dependent on the voltage value applied to the fuel pump and/or the current value flowing through the fuel pump. The pressure of the fuel in the fuel accumulator (rail pressure) can also be adjusted via the quantity delivered and the current and/or voltage. The voltage can therefore be used as an adjustment variable for regulating the pressure in the configuration. Alternatively or additionally, the pressure of the fuel can be regulated as a function of at least one other regulator, for example a pressure regulating valve. For the voltage there is a value range which is defined by minimum and maximum limit values for the voltage. The current value of the voltage at the operating point of the fuel pump is limited to this value range in an embodiment by a limiting function.

Furthermore, it is proposed that the current value of the fuel pump can also be influenced by the current value of the fuel pressure. This can lead to: the current value depends on the pressure rise and exceeds the preset maximum limit value for the current. In this case, the value range of the voltage, usually the maximum limit value of the voltage, can be reduced by a closed control loop with a reduction function unit in the embodiment of the method to a corresponding current measured value which can depend on the current value until the current value of the current is less than the preset maximum limit. Furthermore, the maximum limit value of the voltage may depend on a predetermined gradient reduction of the measured voltage over time and thus on a temporal variation of the voltage.

In this case, the voltage applied to the electric fuel pump is limited based on the measured current delivered by the electric fuel pump or the required current flowing through the electric fuel pump. In this case, the voltage end value is usually limited by the limiting function unit to a value range defined by a maximum limit value and a minimum limit value. In this case, the voltage value range predetermined by the limiting function unit can be continuously reduced and based on the closed control loop which checks whether the measured current value is greater than the limit value, it can be set exactly to the currently required value range, wherein usually Reduce the maximum limit of the voltage. As a result, the power of the injection system is kept within the maximum permissible range. Even in the event of an undesirably large pressure drop of the fuel in the low-pressure circuit of the injection system, it is ensured that the injection system of the internal combustion engine and thus the motor vehicle to be driven can be used.

When carrying out the method, the voltage end value in the initial state is set to a maximum limit value by the limiting function unit and is thus limited. Furthermore, the reduction function unit is activated when the current flowing through the electric fuel pump exceeds a predetermined limit value, wherein the maximum limit value can be determined, for example, by the design of the output stage.

The reduction function unit (Reduktionsfunktion) first acquires the current value of the voltage. Furthermore, the reduction of the functional unit is activated and based on a predetermined gradient of the voltage over time, usually based on the measured voltage and/or on the basis of an already reduced maximum voltage limit, from which the maximum voltage is reduced by the reduction of the functional unit Limit values, wherein the gradient can also depend on the measured current value and/or the temporal change of the current.

There is also the possibility that briefly exceeded current limit values, as they occur, for example, during dynamic operation of the injection system and/or the fuel pump, can be tolerated. In this case, after the current exceeds the limit value, a certain period of time is waited, which can be measured and/or monitored, for example, by a timing module, before activating the reducing function unit. If the current measured current value falls below the limit value during this time period, the reduction function unit is not activated, and the timekeeping module is also stopped and reset during this time period.

In order to reduce the voltage value, an integrator is also activated, which is designed to reduce the maximum limit value of the voltage starting from the current voltage value until the value of the current reaches the permissible range below the preset limit value again. . As soon as this occurs, the integrator is switched off, wherein the limitation of the value range of the voltage is set to the maximum limit value reached. If the current value rises at a later time and is outside the permissible range, the integrator is reactivated and the voltage limit is further reduced. In this case, a closed control loop is used, which however is only temporarily activated depending on whether the current value is within or outside the permissible range.

The regulation of the pressure of the fuel in the fuel accumulator (rail) of the injection system continues to work unrestrictedly, with which a set value for the voltage of the electric fuel pump in the injection system can be preset. However, if a reduced limit value for the voltage is provided, the operating range of the injection system and/or the internal combustion engine can be limited, wherein, for example, the injection quantity of the injection system and/or the torque of the internal combustion engine can be reduced. A regulation deviation of the pressure, that is to say a regulation deviation of the fuel pressure in the fuel accumulator of the injection system, can thus be avoided. This can be set as a fault reaction via a fault message, by a reduction function preset within the scope of the method and/or by a voltage limiting function, or independently of this by a special type of monitoring of the rail pressure implement. If the low-pressure range is intervened, for example, by means of an adjustable throttle, a limitation of the voltage of the electric fuel pump of the injection system can occur when implementing the method.

If the fuel pressure in the low-pressure range of the injection system increases due to fuel partial condensation and/or due to clogging of the fuel filter and thus the current demand of the electric fuel pump increases, then there is the possibility when carrying out the method that By adjusting, usually reducing the voltage, the operating point of the electric fuel pump is changed and the current demand is readjusted into the normal operating range. In this case, the delivery rate of the electric fuel pump is reduced and as a result the pressure drop in the low-pressure range of the injection system is reduced, so that the current demand of the electric fuel pump can be reduced and brought back into the permissible value range, The value range is defined by a maximum limit value and possibly a minimum limit value for the current.

Other advantages and configurations of the present invention emerge from the description and drawings.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or on their own without departing from the scope of the present invention.

Description of drawings

Figure 1 shows a diagram for a first embodiment of the proposed method;

Figure 2 shows a diagram for a second embodiment of the method;

FIG. 3 shows a schematic diagram of an example of an injection system with an electric fuel pump and an embodiment of the proposed control device.

Detailed ways

The invention is shown schematically on the basis of an embodiment in the drawing and is described in detail below with reference to the drawing.

The drawings are generally and collectively described, like reference numerals referring to like parts.

Figure 1 generally comprises five graphs, namely a first pressure-time graph 2 and a second pressure-time graph 4, wherein the time in milliseconds is recorded each along the abscissa 6 and the time in bar is each recorded along the ordinate 8 Unit of fuel pressure in injection equipment. Furthermore, FIG. 1 shows a first current-time diagram 10 and a second current-time diagram 12 , which likewise each have an abscissa 6 along which the time in milliseconds is plotted. Furthermore, the two current-time diagrams 10 , 12 each include an ordinate 14 along which the current flowing through the electric fuel pump of the injection system is recorded in amperes. In the middle between the first pressure-time diagram 2 and the first current-time diagram 10 on the left and the second pressure-time diagram 4 and the second current-time diagram 12 on the right, another diagram is shown in FIG. 1 15. The graph includes an abscissa 16 along which the fuel pressure in bar is recorded. Along a first ordinate 18 of the graph 15 the fuel delivery rate in liters per hour is recorded and along a second ordinate 20 the current flowing through the fuel pump in amperes is recorded.

In the proposed first embodiment of the method it is envisaged that, due to clogging of the fuel filter in the injection system, as indicated by the first pressure-time diagram 2, the pressure value starts from the first operating point 22 within 50 ms. It rises during the time period 24 and reaches a raised value at the second operating point 26 , at which the pressure is 4.2 bar. It follows from this that, as shown in the first current-time diagram 10 , the current flowing through the electric fuel pump rises within a period 24 of 50 ms from the first operating point 22 to a significant increase in the second operating point 26 . For a high value, a current of 7.5 A flows here for the first operating point, it being provided that the current value in the second operating point 26 is greater than the limit value specified for this. The voltage applied to the electric fuel pump has a first duty factor 27 of 95% in both operating points 22 , 26 .

As a countermeasure for increasing the current value above a predetermined limit value, the permissible maximum limit value of the voltage applied to the electric fuel pump is reduced. Furthermore, the first duty cycle of 95% of the voltage is reduced to a second duty cycle of 85%. In this regard, reference is made to diagram 15 which shows the pressure-dependent first current curve 28 at a first duty cycle 27 of 95% and the pressure-dependent first current curve 28 at a second duty cycle 29 of 85%. Two current curves 30 . For comparison, graph 15 also shows curve 32 for a constant current of 7.5 A. The current level is also reduced due to the reduction of the maximum limit of the voltage, which also results from the reduction of the first duty cycle 27 of 95% to the second duty cycle 29 of 85%. This also reduces the fuel pressure for the fuel delivery quantity delivered by the electric fuel pump. Graph 15 shows here a first pressure-dependent curve 34 of the delivery rate at a first duty factor 27 of 95% and a second pressure-dependent curve of the delivery rate at a second duty factor 29 of 85%. 36 , wherein the second pressure-dependent curve 36 of the delivery volume is lower than the first pressure-dependent curve for the first duty cycle 27 of 95% at a lower second duty factor 29 of 85% 34.

The reduction of the duty cycle 27, 29 of the voltage from 95% to 85% during the voltage regulation carried out within the scope of the method also has an effect on the pressure and the current in the third operating point 38, in which the A second duty cycle of 85%. By reducing the duty cycle 27 , 29 and thus the voltage, the prevailing pressure in the second operating point 26 is reduced to a lower value in the third operating point 38 , as shown in the second pressure-time diagram 4 . Furthermore, the increased current in the second operating point 26 is reduced again to a comparatively small value of 7.5 A in the third operating point 38 .

The structure of a second embodiment of the proposed method is shown by the diagram according to FIG. 2 . The method structure shown in the diagram can be realized as software in a control device for carrying out the method.

The proposed structure for carrying out the second specific embodiment of the method comprises a limiting function unit 56 controlled by the control device, which limits the feed-in (eingehend) value 42 of the voltage applied to the electric fuel pump The value range between the smallest lower limit value 46 and the largest upper limit value 48 of the voltage is limited. Both limit values 46 , 48 of the value range of the voltage can be predetermined in the design by a voltage-dependent regulation of the fuel pressure (rail pressure regulation) in the fuel accumulator (rail) of the injection system. The pressure of the fuel in the fuel accumulator also depends on the quantity of fuel which is delivered from the electric fuel pump to the fuel accumulator by the electric fuel pump as a function of the voltage applied to the electric fuel pump and as a function of the current flowing through the electric fuel pump.

The fed-in, currently measured voltage value 42 is supplied to a limiting function unit 56 via an input signal. Furthermore, the final resultant value 44 for the voltage is provided by the limiting function unit 56 via an output signal. In this case, the end value 44 of the voltage corresponds to the fed-in value 42 of the voltage as long as the fed-in value 42 of the voltage lies within the predetermined limit values 46 , 48 of the value range of the voltage. The voltage end value 44 provided by the limiting function unit 56 via the output signal then corresponds to the minimum limit value 46 as long as the fed-in value 42 of the voltage is smaller than the minimum limit value 46 . If, on the other hand, the fed-in value 42 of the voltage is greater than the maximum limit value 48 , the voltage end value 44 is limited by the limiting function unit 56 to the maximum limit value 48 .

As long as the reduction function unit is not activated, the first switch 59 for switching on the voltage is in the first position shown here. In this case, a predetermined maximum value 47 of the voltage is used as maximum limit value 48 for limiting functional unit 56 . The measured value 62 of the current of the electric fuel pump is compared with a limit value 64 of the current in a module 70 designed for comparison. If the measured value 62 of the current exceeds the limit value 64, the second switch 52 is switched for switching on the current and a timer module 72 (Timer) is started, wherein, with the timer module 72, the measured value of the current 62 how long is greater than the limit 64 preset for this. It is monitored here whether the measured value 62 of the current is greater than a limit value 64 for longer than a defined time interval.

Furthermore, the difference 68 formed in a module 78 for calculating the difference 68 between the measured value 62 of the current and the preset limit value 64 is transmitted to the integrator 54 by the second switch 52 for switching on the current. . As long as the measured value 62 is greater than the limit value 64 of the current, a negative difference 68 results. When there is a negative difference 68, the value 49 output from the integrator 54 is continuously reduced by a value in order to specify the maximum limit value 48 of the voltage, which value depends on the difference 68 and thus on the measured value 62 of the current, which in This is greater than the preset maximum limit of 64. The amount by which the maximum limit value 48 of the voltage is reduced can also depend on the gradient of the voltage reduction over time. In this case, the predetermined gradient can be used to take into account the time curve of the measured value of the voltage and/or the time curve of the maximum limit value of the voltage which has been reduced during the method.

If the measured value 62 of the current is greater than the limit value 64 after the time period preset by the timer module 72 has expired, a trigger 74 (Trigger) is set and thus switches the third switch 58 for switching on the integrator 54 and set the start end of the trigger circuit module 76 (Ausgang). By switching the switch 58 , the integrator 54 is initialized once with the end value 44 of the voltage currently provided by the limiting function unit 56 . The start of the trigger circuit module 76 switches the first switch 59 into the second position and holds the first switch 59 in this position, wherein the end value 49 provided by the integrator 54 is continuously transmitted to the limiting function unit 56 to a maximum limit of 48 for updating the voltage. Since the integrator 54 continuously reduces its end value 49 as already described, the maximum limit value 48 of the value range of the voltage and thus also the end value 44 of the voltage is continuously reduced.

If the measured value 62 of the current is now below the limit value 64 , the starting point of the module 70 provided for the comparison is set back, whereby the second switch 52 is set back into its starting position in order to switch on the current. The input of the integrator 54 is thus set to zero, so that the current end value 49 of the integrator 54 is maintained and not changed any more. The maximum limit value 48 of the limit value function unit 56 is therefore determined to the reduced value 49 provided by the integrator 54 and held there. If the measured value 62 of the current exceeds the limit value 64 again, the second switch 52 for switching on the current is switched again and the negative value 68 between the measured value 62 and the limit value 64 of the current is transmitted to the integrator 54, wherein the value 49 from the integrator 54 is further reduced for the limit value 48 of the set voltage.

For the end value 44 of the voltage, in the described embodiment of the method it follows that the maximum voltage limit value 48 updated and/or initialized by the integrator 54 with its end value 49 is set to the current maximum limit value 48 by activating the reduction function unit. The end value is 44. The maximum limit value 48 is then continuously reduced and the end value 44 is therefore concomitantly reduced as long as the measured value 62 of the current is greater than the limit value 64 preset for this purpose.

It usually follows independently of this that the voltage end value 44 corresponds to the preset and/or fed-in voltage value 42 , wherein the fed-in value 42 can be determined from the pressure of the fuel in the fuel accumulator of the injection system. The regulation (rail pressure regulation) is predetermined and/or dependent on the operating point of the injection system, as long as the fed-in value 42 is within a value range between a minimum limit value 46 and a maximum limit value 48 .

FIG. 2 also shows a counter 80 which calculates the maximum limit value 48 of the voltage depending on the measured value 62 of the current, on the difference 68 between the measured value 62 and the preset maximum limit value 64 of the current and / or depending on how often the time gradient of the voltage decreases. At least some of the modules described with reference to FIG. 2 that are designed to carry out the method can be implemented by the proposed control device and/or can be designed as components of the control device. This also involves switches 52 , 58 , 59 , a module 70 designed for comparison, a timer module 72 , a module 78 for calculating the difference 68 , an integrator 54 , a flip-flop 74 , a flip-flop module 76 and a counter 80 . The control device can also have at least one component for realizing the limiting function unit 56 and the reducing function unit.

An example of an injection system 100 of an internal combustion engine of a motor vehicle is shown schematically in FIG. 3 . Injection system 100 includes as part an electric fuel pump 102 which is designed to deliver fuel to a fuel accumulator 104 (common rail) of injection system 100 . FIG. 3 also schematically shows an embodiment of a control device 106 , which is designed to regulate the function of at least one component of injection system 100 , ie at least electric fuel pump 102 , and thus to control and control this function. / or adjust. In this case, control device 106 also regulates operating parameters of electric fuel pump 102 , such as the voltage applied to electric injection pump 102 and the current flowing through fuel pump 102 , usually monitors and sets them. Furthermore, control device 106 is designed to carry out at least one step of at least one embodiment of the method proposed according to FIGS. 1 and 2 .

In the method carried out by the control unit 106 for operating the electric fuel pump 102 of the injection system 100 , a maximum limit value is preset for the voltage present at the electric fuel pump 102 , a preset value for the current flowing through the electric fuel pump 102 Set a maximum limit. Furthermore, the value of the current required by the electric fuel pump is measured. The predetermined maximum limit value for the voltage applied to electric fuel pump 102 is based on the measured value of the current and/or is reduced accordingly for the measured value of the current exceeding the predetermined maximum limit value.

Within the scope of the proposed method, the preset maximum limit value of the voltage applied to the electric fuel pump can be reduced over time as a function of a predetermined gradient of the voltage. In this case, the gradient of the voltage or the change in time of the voltage can relate to the change in time of the measured voltage and/or the change in time of the maximum limit value of the voltage, which has been reduced or has been reduced over time when the method is carried out. .

The amount by which the voltage maximum limit is reduced may depend on the difference between the measured value of the current and the current maximum limit. In one configuration it is possible that the value by which the maximum limit value of the voltage is to be reduced is determined by the function unit for the value of the voltage, which depends on the difference between the measured value and the preset maximum value and/or the voltage The predetermined gradient.

Furthermore, it is possible for a predetermined maximum limit value of the voltage applied to the electric fuel pump to be continuously or gradually reduced, for example by means of a reduction function unit, until the current falls below or falls below the predetermined maximum limit value again.

In order to reduce the voltage limit, the duty cycle of the voltage applied to electric fuel pump 102 can also be reduced.

In another configuration, the predetermined maximum voltage limit for the voltage applied to the electric fuel pump 102 can be controlled when the predetermined maximum current limit is at least within a predetermined and/or definable time period. Reduced when exceeded.

In addition, the maximum limit value of the voltage applied to electric fuel pump 102 can be reduced to a minimum value when the current falls below the limit value, wherein the minimum value of the voltage is maintained.

Control device 106 for operating and thus for regulating the operation of electric fuel pump 102 and/or injection system 100 is designed to measure the current required by electric fuel pump 102 with an ammeter provided for this purpose of control device 106 and to For a current exceeding a predetermined maximum limit value, the reduction of the predetermined maximum limit value for the voltage applied to electric fuel pump 102 is based on and therefore depends on the currently measured current and/or voltage gradient.

The control device 106 can have an integrator and/or implement an integrator designed to reduce the maximum limit value of the voltage by as long as the difference between the measured value of the current and the preset maximum limit value of the current , until the current falls below the maximum allowable limit.

Claims (9)

1. A method for operating an electric fuel pump (102) of an injection system (100), wherein a maximum voltage limit value (48) is preset for a voltage applied to the electric fuel pump (102) , and a maximum current limit value (64) is preset for the current flowing through the electric fuel pump (102), wherein the value (62) of the current required by the electric fuel pump (102) is measured, And wherein, for the case where the measured value (62) of the current exceeds a preset maximum current limit value (64), such that the preset maximum voltage for the voltage applied to the electric fuel pump (102) The limit value ( 48 ) is reduced as a function of the measured value ( 62 ) of the current, wherein a predetermined maximum voltage limit value ( 48 ) for the voltage applied to the electric fuel pump ( 102 ) is reduced until The measured value of the current ( 62 ) is lower than the preset maximum current limit value ( 64 ). 2 . The method as claimed in claim 1 , wherein a preset maximum voltage limit value ( 48 ) for the voltage applied to the electric fuel pump ( 102 ) is made to depend on a predetermined gradient of the voltage over time. reduce. 3. The method as claimed in claim 1 or 2, wherein a preset maximum voltage limit value (48) for the voltage applied to the electric fuel pump (102) is continuously reduced. 4. The method as claimed in claim 1 or 2, wherein a predetermined maximum limit value for the voltage applied to the electric fuel pump (102) is reduced by means of a reduction function unit. 5. The method according to claim 1 or 2, wherein the duty cycle for the voltage applied across the electric fuel pump (102) is reduced. 6. A method according to claim 1 or 2, wherein if the measured value (62) of the current exceeds a preset maximum current limit value (64) for at least a preset period of time, then for A maximum voltage limit value ( 48 ) of the voltage applied to the electric fuel pump ( 102 ) is reduced. 7. The method according to claim 1 or 2, wherein, if the measured value (62) of current is lower than a maximum current limit value (64), for applying The maximum voltage limit value (48) of the voltage is reduced to a minimum value, wherein the minimum value of the voltage is maintained. 8. A control device for operating an electric fuel pump (102) of an injection system (100), wherein a maximum voltage limit value (48) is preset for a voltage applied to the electric fuel pump (102) ), and a maximum current limit value (64) is preset for the current flowing through the electric fuel pump (102), wherein the control device (106) is designed to measure required current, and wherein said control device (106) is designed to, for the case where the measured value of current (62) exceeds a preset maximum current limit value (64), such that for A preset maximum voltage limit value (48) of the voltage applied to the fuel pump (102) is reduced as a function of the measured value (62) of the current, wherein the reduction is necessary for the voltage applied to the electric fuel pump (102) The preset maximum voltage limit value (48) of the voltage until the measured current value (62) is lower than the preset maximum current limit value (64). 9 . The control device as claimed in claim 8 , which has an integrator ( 54 ) designed to reduce the maximum voltage limit value ( 48 ) for the voltage by as long as the The measured value of the current ( 62 ) falls below the maximum permissible current limit value ( 64 ).