Method for operating an internal combustion engine

Abstract

Method for operating an internal combustion engine, wherein fuel is supplied from a fuel tank (9), via a pre-supply pump (5), via a metering unit (14) and via a high-pressure pump (3) to a high-pressure accumulator (13), wherein the pre-supply pump (5) can be switched on to supply fuel, and wherein a pressure signal (22; 22a-22d) of a pressure in the high-pressure accumulator (13) is determined, characterized in that a fault of the metering unit (14) is determined, that the metering unit (14) is substantially open, that a time period (d(n); d(n+1)) is determined as a function of the determined pressure signal (22; 22a-22d), and that the pre-supply pump (5) is switched on for the time period (d(n); d(n+1)).

Description

State of the art

[0001] The invention relates to a method for operating an internal combustion engine according to the preamble of claim 1.

[0002] In the event of a failure or operational limitation of a component of an internal combustion engine, it is known that so-called "limp home" procedures are used, which maintain the operation of the internal combustion engine under certain limitations, such as reduced torque, and thus increase the overall availability of the vehicle.

[0003] From EP 0 780 559 B1 it is known that in the event of a defect in the area of ​​pressure regulation, the fuel pressure can be controlled and / or regulated by influencing the fuel flow in the low-pressure area in such a way that limited operation of the internal combustion engine can be ensured.

[0004] Furthermore, a metering unit for a high-pressure pump is known that can exhibit an electrical or mechanical fault. Typically, the internal combustion engine shuts down in such a case, making further driving impossible.

[0005] A pre-supply pump for pumping fuel from a fuel tank is also known, which is usually not continuously controllable. Disclosure of the invention

[0006] The problem underlying the invention is solved by a method according to claim 1. Advantageous embodiments are specified in the dependent claims. Further features important to the invention are found in the following description and in the drawings, whereby the features may be important to the invention both individually and in various combinations, without this being explicitly stated again.

[0007] This method allows the fuel pressure in a high-pressure accumulator to be influenced in such a way that controlled injections can be carried out, even if the metering unit is faulty. With moderate driving behavior, the injection quantity can thus be adjusted to such an extent that continued driving is possible even with a faulty metering unit. The faulty metering unit is essentially open in this process. This means that the fuel pressure in the high-pressure accumulator remains within specific limits, neither too high nor too low. Overall, this prevents the internal combustion engine from stalling due to a faulty metering unit and allows continued driving. This increases the availability of the internal combustion engine and the associated vehicle.

[0008] In an advantageous further development of the method, the determined pressure signal falls below a first pressure value at a given time. This first pressure value is lower than a target pressure value. This advantageously ensures that the pre-supply pump is switched on to prevent the pressure from becoming too low.

[0009] In a further advantageous embodiment of the method, the time until the next activation of the fuel pump is increased if the measured pressure signal does not exceed a second pressure value. This second pressure value is higher than the target pressure value. Extending the activation time of the fuel pump advantageously prevents excessively low pressure, thus enabling continuous fuel injection.

[0010] In a further advantageous embodiment of the method, the time until the next activation of the pre-supply pump is reduced when the measured pressure signal exceeds a third pressure value. This third pressure value is greater than the second pressure value. By reducing the activation time of the pre-supply pump, excessively high pressure is advantageously prevented.

[0011] In a further advantageous embodiment of the method, the time for the next activation of the pre-supply pump is not changed if the determined pressure signal exceeds the second pressure value but does not exceed the third pressure value. This embodiment advantageously allows an achieved pressure profile to be maintained.

[0012] In a further advantageous embodiment of the method, an additional time period is started at the same point in time, and the pre-supply pump is switched on at the end of this additional time period. This advantageously eliminates the need to wait for the pressure to fall below the initial value; instead, the pre-supply pump is switched on after the additional time period has elapsed, thus preventing a further drop in pressure.

[0013] In a further advantageous development of the method, the time until the next activation of the pre-supply pump is increased if the measured pressure signal does not rise above the initial pressure value within this extended time period. This ensures the pre-supply pump remains active for a longer period, thus providing additional countermeasures against excessively low pressure.

[0014] In an advantageous further development of the method, the subsequent time period is approximately twice as long as the minimum point period, wherein the minimum point period extends from the time until an expected minimum point of the determined pressure, and wherein the minimum point period is determined from a weighted average. This advantageously selects the subsequent time period such that it can be determined whether the course of the determined pressure signal behaves as desired and increases, or whether the course of the determined pressure remains continuously in a low range. If the determined pressure remains in the low range, corrective action can be advantageously taken and injections can be carried out.

[0015] Further features, applications, and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated features, individually or in any combination, constitute the subject matter of the invention, irrespective of their inclusion in the claims or their cross-references, and irrespective of their formulation or representation in the description or in the drawing. The same reference numerals are used for functionally equivalent quantities in all figures, even in different embodiments.

[0016] Exemplary embodiments of the invention are explained below with reference to the drawing. The drawing shows: Fig. 1 a simplified diagram of a fuel injection system of an internal combustion engine; Fig. 2 a schematic block diagram with a unit for controlling a pre-supply pump; Fig. 3a-3d each show a schematic diagram with a time course of a determined pressure signal and a time course of a control signal for the pre-supply pump; Fig. 3e a schematic diagram for determining a time duration.

[0017] Fig. Figure 1 shows a highly simplified representation of a fuel injection system 1 of an internal combustion engine. A fuel tank 9 is connected to a high-pressure pump 3 (not described in detail) via a suction line 4, a pre-supply pump 5, and a low-pressure line 7. In an embodiment not shown, the pre-supply pump 5 can also be located in the fuel tank 9, in which case the suction line 4 is omitted. The pre-supply pump 5 can, in particular, be an electric fuel pump. A control signal 26 is supplied to the pre-supply pump 5. A high-pressure accumulator 13 ("common rail") is connected to the high-pressure pump 3 via a high-pressure line 11. A metering unit 14 – hereinafter referred to as ZME – with an actuating device 15 is hydraulically arranged in the course of the low-pressure line 7 between the pre-supply pump 5 and the high-pressure pump 3.

[0018] Other elements, such as the valves of high-pressure pump 3, are located in the Fig. 1 not shown. It is understood that the ZME 14 can be configured as a unit together with the high-pressure pump 3. For example, the ZME 14 can be used to forcibly open an inlet valve of the high-pressure pump 3.

[0019] During operation of the fuel injection system 1, the pre-supply pump 5 delivers fuel from the fuel tank 9 into the low-pressure line 7 and the high-pressure pump 3 delivers the fuel into the high-pressure accumulator 13. The ZME 14 determines the amount of fuel supplied to the high-pressure pump 3.

[0020] The pressure within the high-pressure accumulator 13 is measured by a pressure sensor 16 on the high-pressure accumulator 13. A value measured by this pressure sensor 16 is referred to as a pressure signal 22.

[0021] The ZME 14 receives a control signal 28. The opening of the ZME 14 can be influenced via the control signal 28. The ZME 14 generates a fault signal 24. The fault signal 24 can be used to determine whether a fault exists in the ZME 14. Furthermore, it can be used to determine whether the fault is electrical or mechanical. A fault in the ZME 14 can also be determined by a combination of other parameters. An electrical fault occurs, for example, if the ZME 14 is no longer supplied with power, e.g., due to a disconnected plug. In the case of an electrical fault, the ZME 14 typically switches to an open state, allowing fuel to flow freely from the pre-supply pump 5 to the high-pressure pump 3. In the case of a mechanical fault, the ZME 14 can be fully open, fully closed, or partially open.

[0022] Fig. Figure 2 shows a schematic block diagram with a unit 20 for controlling the pre-supply pump 5. The pressure signal 22 and the fault signal 24 are supplied to the unit 20. Other parameters, such as the rotational speed of the internal combustion engine, can be supplied to the unit 20 (not shown). The unit 20 generates the control signal 26. The unit 20 can also generate the control signal 28 (not shown).

[0023] In the event of a fault in the ZME 14, particularly a mechanical fault, the temporal profile of the pressure signal 22 can be analyzed to determine whether the ZME 14 is sufficiently open to supply fuel to the high-pressure pump 3 via the pre-supply pump 5. If the pressure rise is not steep enough when the pre-supply pump 5 is switched on, it can be concluded that the ZME 14 is closed. Similarly, if the pressure drop is not steep enough when the pre-supply pump 5 is switched off, it can also be concluded that the ZME 14 is closed.

[0024] Unit 20 is part of a control unit (not shown). This control unit (not shown) is part of the internal combustion engine, specifically for a motor vehicle.

[0025] The control signal 26 typically has two states. In the first state of the control signal 26, the pre-supply pump 5 is switched on and delivers fuel from the fuel tank 9 to the ZME 14. In the second state of the control signal 26, the pre-supply pump 5 is switched off, so that no fuel is delivered from the fuel tank 9 to the ZME 14 via the pre-supply pump 5.

[0026] The control signal 26 is essentially generated depending on the pressure signal 22 and the error signal 24.

[0027] Fig. Figure 3a shows a schematic diagram 30a with a time course of a determined pressure signal 22a and a time course of a control signal 26a for the pre-supply pump 5. Fig. 1. Pressure signal 22a corresponds to pressure signal 22 from the Fig. 1 and Fig. 2. The control signal 26a corresponds to the control signal 26 from the Fig. 1 and Fig. 2.

[0028] The time axis t represents time points t1, t2, t3, and t4. The pressure axis p represents a first pressure value pL, a target pressure value pS, a second pressure value pH1, and a third pressure value pH2. The pressure values ​​pL, pH1, and pH2 are determined as a function of the target pressure value pS, more precisely with a respective offset from the target pressure value pS. The state axis z represents two states z0 and z1. State z0 corresponds to a switched-off pre-supply pump 5. Fig. 1. State z1 corresponds to a switched-on pre-supply pump 5 off Fig. 1.

[0029] At time t1, the pressure signal 22a falls below the first pressure value pL in area A. After time t2, the pressure signal 22a transitions from a decreasing to an increasing trend. The pressure signal 22a rises above the second pressure value pH1. However, the pressure signal 22a does not exceed the third pressure value pH2. The pressure signal 22a then begins to decrease. At time t3, the pressure signal 22a falls below the first pressure value pL in area B. After time t4, the pressure signal 22a begins to rise again and exceeds the first pressure value pL.

[0030] The control signal 26a remains in state z0 until time t1, rises to state z1 at time t1, remains in state z1 until time t2, and falls back to state z0 at time t2. The control signal 26a remains in state z0 until time t3, rises to state z1 at time t3, remains in state z1 until time t4, and falls back to state z0 at time t4.

[0031] The measured pressure signal 22a falls below the first pressure value pL at times t1 and t3. This drop below the first pressure value pL causes the pressure signal 26a to transition from state z0 to state z1. Therefore, if the measured pressure signal 22a falls below the first pressure value pL, the pre-supply pump 5 is switched off. Fig. 1 switched on.

[0032] The pre-supply pump 5, which is switched on at time t1, is off Fig. Pump 1 is switched off at time t2 after a time interval d(n). In a subsequent cycle n+1, where n denotes a previous cycle, a time interval d(n+1) is used for the next switching on of the pre-supply pump 5. Fig. Time duration d(n) is chosen to be equal to 1 because the pressure signal 22a exceeds the second pressure value pH1 after time t1 and before time t3, and the pressure signal 22a does not exceed the third pressure value pH2 after time t1 and before time t3. Therefore, times t1, t2, etc., depend on the course of the pressure signal 22a. The range of values ​​for the time durations d(n) and d(n+1) is limited by a minimum and a maximum value. A cycle typically begins when the pressure signal 22, or in this case 22a, falls below the pressure value pL. Fig. Cycle n begins when the pressure value pL is reduced by the pressure signal 22a in area A at time t1 and ends when the pressure value pL is reduced by the pressure signal 22a in area B at time t3. Cycle n+1 begins when the pressure value pL is reduced by the pressure signal 22a in area B at time t3.

[0033] An additional pressure value below the first pressure value pL is provided, though not shown. This additional pressure value is independent of other pressure values, such as the target pressure value pS, and is constant. If the pressure signal 22 or 22a falls below this additional pressure value, the pre-supply pump 5 is switched on, regardless of whether it is switched on or off, i.e., regardless of the state of the control signal 26 or 26a. This corresponds to state z1 of the control signal 26 or 26a. If the pressure signal 22 or 22a exceeds this additional pressure value, the previously deactivated process components or the previously deactivated process are reactivated.

[0034] In a manner not shown, a further pressure value above the first pressure value pL is provided, whereby this further pressure value is independent of the other pressure values, such as the target pressure value pS, and is constant. If the pressure signal 22 or 22a exceeds this further pressure value, the pre-supply pump 5 is switched off, regardless of whether it is switched on or off, i.e., regardless of the state of the control signal 26 or 26a. This corresponds to the state z0 of the control signal 26 or 26a. If the pressure signal 22 or 22a falls below this further pressure value, the previously deactivated process components or the previously deactivated process are reactivated.

[0035] Fig. Figure 3b shows a schematic diagram 30b with a time course of a determined pressure signal 22b and a time course of a control signal 26b for the pre-supply pump 5. Fig. 1. Pressure signal 22b corresponds to pressure signal 22 from the Fig. 1 and Fig. 2. The control signal 26b corresponds to the control signal 26 from the Fig. 1 and Fig. 2.

[0036] The time axis t shows time points t5, t6, t7, t8 and t9.

[0037] At time t5, the pressure signal 22b falls below the first pressure value pL in area A. The pressure signal 22b continues to fall, only to rise again after time t6. The pressure signal 22b reaches a peak between the target pressure value pS and the second pressure value pH1 and then begins to fall again, dropping below the first pressure value pL at time t7 in area B. After time t9, the pressure signal 22b rises above the first pressure value pL again.

[0038] At time t5, the control signal 26b rises from state z0 to state z1. The control signal 26b remains in state z1 and falls back to state z0 at time t6. Until time t7, the control signal 26b remains in state z0 and jumps to state z1 at time t7. The control signal 26b remains in state z1 until time t9 and falls back to state z0 at time t9.

[0039] Since the pressure signal 22b does not rise above the second pressure value pH1 after the previous cycle n, which begins at time t5, and before the control cycle n+1, which begins at time t7, the time duration d(n+1) in the next cycle n+1 is increased by a time duration dinc1 from the time duration d(n) of the previous cycle.

[0040] In the form not shown, the pre-supply pump 5 can be used Fig. The pump can be switched on again at an earlier time, such as time t7, which corresponds to the control signal 26b transitioning from state z0 to state z1. This can occur between the pressure signal 22b reaching its peak and the start of the next cycle, i.e., between times t6 and t7, when the pressure signal 22b falls. The trigger for switching the pre-supply pump 5 back on could, for example, be the elapse of a time period, as explained below, starting from time t5.

[0041] Fig. Figure 3c shows a schematic diagram 30c with a time course of a determined pressure signal 22c and a time course of a control signal 26c for the pre-supply pump 5. Fig. 1. Time points t10, t11, t12, t13 and t14 are plotted on the time axis t.

[0042] The pressure signal 22c falls below the first pressure value pL at time t10 in area A. After time t11, the pressure signal 22c begins to rise again and reaches a peak above the third pressure value pH2. The pressure signal 22c then falls below the first pressure value pL at time t12 in area B. After time t14, the pressure signal 22c again exceeds the first pressure value pL.

[0043] The control signal 26c jumps from state z0 to state z1 at time t10. At time t11, the control signal 26c jumps from state z1 to state z0. At time t12, the control signal 26c jumps from state z0 to state z1. At time t13, the control signal 26c jumps from state z1 to state z0.

[0044] Since the pressure signal 22c rises above the third pressure value pH2 between times t10 and t12, the duration d(n+1) for the next cycle n+1 is reduced by one duration dred from the duration d(n) of the previous cycle n.

[0045] Additionally, the time duration d(n+1) cannot be reduced (as shown) if the pressure signal 22c exceeds the third pressure value pH2 for the first time and then falls below it again. If the time duration d(n+1) was not reduced during this first exceedance, the procedure described above is followed for a subsequent second exceedance of the third pressure value pH2.

[0046] In another form not shown, exceeding the third pressure value pH2 with the pre-supply pump switched on results in 5 Fig. 1 to switch off the pre-supply pump 5.

[0047] Fig. Figure 3d shows a schematic diagram 30d with a time course of a determined pressure signal 22d and a time course of a control signal 26d for the pre-supply pump 5. Fig. 1. The time axis t shows time points t15, t16, t17, t18, t19, t20, t21, t22, t23, and t24. Time point t18 is generally referred to as an additional time point.

[0048] At time t15, the pressure signal 22d falls below the first pressure value pL in area A. At the additional time t18, the pressure signal 22d remains below the first pressure value pL in area C. After time t19, the pressure signal 22d rises, reaches a peak after time t21 and before time t22, and then falls before rising again after time t24.

[0049] The control signal 26d rises from state z0 to state z1 at time t15. At time t16, the control signal 26d falls back from state z1 to state z0. At the additional time t18, the control signal 26d rises from state z0 to state z1. At time t19, the control signal 26d falls back from state z1 to state z0. At time t22, the control signal 26d rises from state z0 to state z1. At time t24, the control signal 26d falls back from state z1 to state z0.

[0050] At time t15, a second time period del2 and a third time period del1 begin to run. The second time period del2 is, for example, essentially twice the third time period del1. The determination of the third time period del1 is described below. Fig. 3e explained. If the pressure signal 22d does not reach the first pressure value pL by the end of the second time period del2, i.e., by the time the additional time t18 is reached, then, firstly, the control signal 26d is switched from state z0 to state z1, i.e., the pre-supply pump 5 is switched on for the time period d(n), and secondly, the time period d(n+1) for the next cycle n+1 to be executed is increased by a time period dinc2 from the time period d(n) of the previous cycle n. In a form not shown, the third time period del1 and the second time period del2 also begin to run at time t22 with the following subsequent steps described above.

[0051] Fig. Figure 3e shows a schematic diagram 30e for determining the third time duration del1. Time points t25, t26, t27 and t28 are plotted on the time axis t.

[0052] The pressure signal 22e falls below the first pressure value pL at time t25 in region A. The pressure signal 22e continues to fall, only to rise again after time t26. At time t26, the pressure signal 22e is at a minimum and then begins to rise again. The pressure signal 22e reaches a maximum between the first pressure value pH2 and the second pressure value pH1 and then begins to fall again, dropping below the first pressure value pL at time t27 in region B. After time t28, the pressure signal 22e rises above the first pressure value pL again. At time t28, the pressure signal 22e is at a minimum. A time period del1(n) begins at time t25 and ends at time t26. A time period del1(n+1) begins at time t27 and ends at time t28.

[0053] To determine the third time duration del1, the first determination, i.e., the time duration del1(n), is set equal to the third time duration del1. The time duration del1(n+1) from the following cycle n+1 is weighted and factored into the third time duration del1. A determined time duration del1(n+z) from a subsequent cycle n+z is weighted and factored into the third time duration del1 as described above. However, a first determination of the third time duration del1 can also be carried out by averaging two or more time durations del1(n), del1(n+1), etc.

Claims

[1] Method for operating an internal combustion engine, wherein fuel is supplied from a fuel tank (9), via a pre-feed pump (5), via a metering unit (14) and via a high-pressure pump (3) to a high-pressure accumulator (13), wherein the pre-feed pump (5) can be switched on to feed fuel, and wherein a pressure signal (22; 22a-22d) of a pressure in the high-pressure accumulator (13) is determined, characterized by that a fault of the metering unit (14) is detected, that the metering unit (14) is substantially open, that a time period (d(n); d(n+1)) is determined as a function of the determined pressure signal (22; 22a-22d), and that the pre-feed pump (5) is switched on for the time period (d(n); d(n+1)). [2] Method according to claim 1, wherein a time (t1; t3; t5; t7; t10; t12; t15; t22) is determined as a function of the determined pressure signal (22; 22a-22d), and wherein the pre-feed pump (5) is switched on at the time (t1; t3; t5; t7; t10; t12; t15; t22) for the time period (d(n); d(n+1)). [3] Method according to claim 1 or 2, wherein the determined pressure signal (22; 22a-22d) at the time (t1; t3; t5; t7; t10; t12; t15; t22) falls below a first pressure value (pL), wherein the first pressure value (pL) is smaller than a target pressure value (pS). [4] Method according to one of the preceding claims, wherein the time period (d(n+1)) for the next switching on of the pre-feed pump (5) is increased if the determined pressure signal (22b) does not exceed a second pressure value (pH1), wherein the second pressure value (pH1) is greater than the desired pressure value (pS). [5] Method according to one of the preceding claims, wherein the time period (d(n+1)) for the next switching on of the pre-feed pump (5) is reduced if the determined pressure signal (22c) exceeds a third pressure value (pH2), wherein the third pressure value (pH2) is greater than the second pressure value (pH1). [6] Method according to one of the preceding claims, wherein the time period (d(n+1)) for the next switching on of the pre-feed pump (5) is not changed if the determined pressure signal (22a) exceeds the second pressure value (pH1) and does not exceed the third pressure value (pH2). [7] Method according to one of the preceding claims, wherein a second time period (del2) is started at the time (t1; t3; t5; t7; t10; t12; t15; t22), wherein the pre-feed pump (5) is switched on at the time (t1; t3; t5; t7; t10; t12; t15; t22) for the time period (d(n); d(n+1)), and wherein the pre-feed pump (5) is switched on at an additional time (t18) for the time period (d(n)) at the end of the second time period (del2) if the determined pressure signal (22d) does not rise above the first pressure value (pL) within the second time period (del2). [8] Method according to claim 7, wherein the time period (d(n+1)) for the next switching on of the pre-feed pump (5) is increased after the expiry of the second time period (del2) if the determined pressure signal (22d) does not rise above the first pressure value (pL) within the second time period (del2), and wherein the pre-feed pump (5) is switched on for the time period (d(n+1)) for the next switching on of the pre-feed pump (5) if the determined pressure signal (22d) falls below the first pressure value (pL). [9] Method according to one of claims 7 or 8, wherein the second time period (del2) is predetermined to be substantially twice as long as a third time period (del1), wherein the third time period (del1) extends from the time (t1; t3; t5; t7; t10; t12; t15; t22) to another time (t26, t28) of an expected low point of the determined pressure signal (22e) after the time (t1; t3; t5; t7; t10; t12; t15; t22), after which the pressure signal (22e) rises again. [10] Control device on which a method according to one of claims 1 to 9 can be carried out. [11] Internal combustion engine, in particular for a motor vehicle, with a control unit according to claim 10.

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