Method and device for detecting and characterizing fuel leakage, and vehicle

Abstract

A method and a device detect and characterize fuel leakage in an injection system of an internal combustion. The injection system has an injection device for injecting fuel into a combustion chamber of the internal combustion engine, a closable high-pressure branch for supplying the injection device with fuel placed under a first fuel pressure, and a closable low-pressure branch for feeding fuel placed under a second, lower fuel pressure from a fuel supply to the high-pressure branch. The high-pressure branch and the low-pressure branch are each closed, wherein in the high-branch branch and in the low-pressure branch an associated curve of fuel pressure over time is sensed at the same time during a measurement time period. On the basis of the sensed curve of fuel pressure of the high-pressure branch, it is checked whether fuel loss occurred in the closed-off high-pressure branch during the measurement time period. By way of the sensed curve of fuel pressure of the low-pressure branch, it is checked whether a flow of fuel into the closed-off low-pressure branch occurred during the measurement time period. If the existence of fuel loss was determined in the first checking step and additionally it was determined in the second checking step that no flow of fuel into the low-pressure branch occurred, a signal is output, which indicates fuel leakage from the high-pressure branch into the combustion chamber.

Claims

1. A method for detecting and characterizing fuel leakage in an injection system of an internal-combustion engine that includes an injection device for injecting fuel into a combustion chamber of the internal-combustion engine, a closable high-pressure branch for supplying the injection device with fuel under a first fuel pressure, and a closable low-pressure branch for supplying fuel under a second, lower fuel pressure to the high-pressure branch from a fuel supply, the method comprising the steps of: capturing at the same time in the high-pressure branch and in the low-pressure branch an associated temporal fuel-pressure profile by way of sensors during a measuring period in which the high-pressure branch and the low-pressure branch have each been closed; a first checking act, in which, on the basis of the captured fuel-pressure profile of the high-pressure branch, it is checked whether a loss of fuel in the sealed high-pressure branch has arisen in the measuring period; a second checking act, in which, on the basis of the captured fuel-pressure profile of the low-pressure branch, it is checked whether an influx of fuel into the sealed low-pressure branch has occurred in the measuring period; and outputting a signal that indicates a fuel leakage running from the high-pressure branch into the combustion chamber if the existence of a loss of fuel was established in the first checking act and additionally it was established in the second checking act that no influx of fuel into the low-pressure branch has occurred.

2. The method according to claim 1, wherein in the first checking act any loss of fuel is quantified on the basis of the fuel-pressure profile in the high-pressure branch, and in the second checking act, any influx of fuel is quantified on the basis of the fuel-pressure profile in the low-pressure branch.

3. The method according to claim 2, wherein the signal that indicates a fuel leakage running from the high-pressure branch into the combustion chamber is output even when the quantified influx of fuel in the low-pressure branch is less than the quantified loss of fuel in the high-pressure branch.

4. The method according to claim 1, wherein in the first checking act, a loss of fuel in the high-pressure branch is established only when the first fuel pressure in the high-pressure branch according to the associated captured fuel-pressure profile has reached or fallen short of a defined high-pressure threshold value in the measuring period.

5. The method according to claim 1, wherein in the second checking act, an influx of fuel into the low-pressure branch is established only when the second fuel pressure in the low-pressure branch according to the associated captured fuel-pressure profile has reached or exceeded a defined low-pressure threshold value in the measuring period.

6. The method according to claim 5, wherein in the first and/or in the second checking acts, a loss of fuel in the high-pressure branch or an influx of fuel into the low-pressure branch is established only when, as an additional condition, a predetermined time-interval has elapsed since the beginning of the measuring period.

7. The method according to claim 1, wherein for the purpose of performing the check occurring in the first checking act, a slope of the fuel-pressure profile in the high-pressure branch is ascertained and it is then established that in the sealed high-pressure branch a loss of fuel has arisen in the measuring period if the ascertained slope of the fuel-pressure profile in the high-pressure branch for an arbitrary instant in the measuring period is less than the slope of a reference fuel-pressure profile, indicating an absence of leakages, in the high-pressure branch at the same instant.

8. The method according to claim 1, wherein for the purpose of performing the check occurring in the second checking act, a slope of the fuel-pressure profile in the low-pressure branch is ascertained and it is then established that a loss of fuel has arisen in the sealed low-pressure branch in the measuring period if the ascertained slope of the fuel-pressure profile in the low-pressure branch for an arbitrary instant in the measuring period is higher than the slope of a reference fuel-pressure profile, indicating an absence of leakages, in the low-pressure branch at the same instant.

9. The method according to claim 7, further comprising: a reference act, taking place before the capturing, in which the reference fuel-pressure profile in the high-pressure branch and/or the reference fuel-pressure profile in the low-pressure branch are ascertained.

10. The method according to claim 8, further comprising: a reference act, taking place before the capturing, in which the reference fuel-pressure profile in the high-pressure branch and/or the reference fuel-pressure profile in the low-pressure branch are ascertained.

11. The method according to claim 8, wherein the ascertaining of the reference fuel-pressure profile in the high-pressure and/or low-pressure branch is carried out on the basis of a physical model, into which at least one of the following quantities is entered: a measured first fuel pressure in the high-pressure branch and/or a measured second fuel pressure in the low-pressure branch; an engine speed; a temperature of the internal-combustion engine; an arrangement and/or geometrical property of one or more components of the internal-combustion engine; and a thermal conductivity of one or more components of the internal-combustion engine.

12. The method according to claim 9, wherein the ascertaining of the reference fuel-pressure profile in the high-pressure and/or low-pressure branch is carried out on the basis of a physical model, into which at least one of the following quantities is entered: a measured first fuel pressure in the high-pressure branch and/or a measured second fuel pressure in the low-pressure branch; an engine speed; a temperature of the internal-combustion engine; an arrangement and/or geometrical property of one or more components of the internal-combustion engine; and a thermal conductivity of one or more components of the internal-combustion engine.

13. A device for detecting and characterizing a fuel leakage in an injection system of an internal-combustion engine having an injection device for injecting fuel into a combustion chamber of the internal-combustion engine, a closable high-pressure branch for supplying the injection device with fuel under a first fuel pressure, and a closable low-pressure branch for supplying fuel under a second, lower fuel pressure to the high-pressure branch from a fuel supply, wherein said device is configured to execute the method according to claim 1.

14. The device according to claim 13, wherein for the high-pressure branch and the low-pressure branch, in each instance a pump for pressurizing the fuel located in the respective branch at the first and the second fuel pressure, respectively, is provided, said pumps having been set up at the same time to form, respectively, a closure for at least one of the two branches in their switched-off state, in order to close said branch or branches.

15. An injection system for an internal-combustion engine, comprising: an injection device for injecting fuel into a combustion chamber of the internal-combustion engine; a closable high-pressure branch for supplying the injection device with fuel at a first fuel pressure; a closable low-pressure branch for supplying fuel under a second, lower fuel pressure to the high-pressure branch from a fuel supply; and a device for detecting and characterizing fuel leakages in the injection system, said device being configured to execute the method of claim 1.

16. A vehicle comprising an injection system according to claim 15.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of an embodiment of a device according to the invention.

(2) FIG. 2 is a first example of pressure profiles in a high-pressure and low-pressure branch.

(3) FIG. 3 is a second example of pressure profiles in a high-pressure and low-pressure branch.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 shows a device 1 for detecting and characterizing a fuel leakage in an injection system 2 of an internal-combustion engine 3. The injection system 2 has a low-pressure pump 4, by means of which fuel is taken from a fuel tank 5 and supplied to a low-pressure branch 6, for instance a low-pressure line, at a second fuel pressure p.sub.2. The low-pressure branch 6 is adjoined by a high-pressure branch 7, for instance a high-pressure line, in particular a central manifold (common rail), which makes fuel available to several injection devices 8 at a first fuel pressure p.sub.1. In this connection, the second fuel pressure p.sub.2 is lower than the first fuel pressure p.sub.1 which, in turn, is generated by a high-pressure pump 9 which connects the low-pressure branch 6 to the high-pressure branch 7 and pumps fuel from the low-pressure branch 6 into the high-pressure branch 7.

(5) The fuel located in the high-pressure branch 7 is injected in an atomizing manner by the injection devices 8 into corresponding combustion chambers 10 of the internal-combustion engine 3 and is burned cleanly, with high power output.

(6) An escape of the fuel from the high-pressure branch 7 into one of the combustion chambers 10 via at least one injection device 8 after the internal-combustion engine 3 has been switched off has an adverse effect on the exhaust emissions of the internal-combustion engine 3, in particular in the course of restarting the internal-combustion engine 3. In this connection, just a few droplets of fuel can distinctly increase exhaust emissions.

(7) Therefore it is advantageous to detect and/or to display such a fuel leakage into the combustion chambers 10 of the internal-combustion engine 3 as early as possible, in order to be able to adopt countermeasures, or cause them to be executed, quickly and effectively, for instance by repair or replacement of defective, in particular leaky, injection devices 8.

(8) For this purpose, the device 1 has a control unit 11 which is in communication, on the one hand, with a low-pressure sensor unit 12 and, on the other hand, with a high-pressure sensor unit 13, and has been set up to process sensor data, in particular with respect to the fuel-pressure profiles in the low-pressure branch 6 and in the high-pressure branch 7, made available by the pressure sensor units 12, 13.

(9) For the purpose of generating these sensor data, the low-pressure sensor unit 12 has preferentially been arranged in the low-pressure branch 6 and is preferably in fluid-conducting communication with a low-pressure line of the low-pressure branch 6. The high-pressure sensor unit 13 has correspondingly preferentially been arranged in the high-pressure branch 7 and is preferably in fluid-conducting communication with a high-pressure line of the high-pressure branch 7, so that the fuel-pressure profiles, in particular the slopes thereof, in the low-pressure branch 6 and in the high-pressure branch 7 can be evaluated, preferentially related to one another, in particular compared with one another, by the control unit 11 on the basis of the sensor data generated by the pressure sensor units 12, 13.

(10) The control unit 11 has, in particular, been set up to establish, and where appropriate to quantify, an influx of fuel into the low-pressure branch 6 on the basis of the fuel-pressure profile in the low-pressure branch 6. In particular, said control unit has also been set up to establish, and where appropriate to quantify, a fuel leakage out of the high-pressure branch 7 on the basis of the fuel-pressure profile in the high-pressure branch 7.

(11) If the first fuel pressure p.sub.1 in the high-pressure branch 7 falls more quickly or more intensely than is to be expected, for instance by reason of thermodynamic effects, after the internal-combustion engine 3 has been shut down, a fuel leakage in the high-pressure branch 7 is present. In order to determine whether fuel is escaping into the combustion chamber(s) 10 via one or more injection devices 8, or into the low-pressure branch 6 via the high-pressure pump 9, the first fuel pressure p.sub.1 is related to the second fuel pressure p.sub.2 in the low-pressure branch 6. If the second fuel pressure p.sub.2 rises in relation to an expected fuel pressure in the low-pressure branch 6, or falls at least more slowly than is to be expected, for instance by reason of thermodynamic effects, a fuel leakage from the high-pressure branch 7 into the low-pressure branch 6, in particular via the high-pressure pump 9, can be inferred. However, if the second fuel pressure p.sub.2 corresponds to an expected pressure, a leakage from the high-pressure branch 7 into the combustion chambers 10 of the internal-combustion engine 3 via the injection devices 8 can be inferred, and a corresponding signal can be output by the control unit 11.

(12) In FIG. 2, a first exemplary fuel-pressure profile p.sub.H(t) in a high-pressure branch of an injection system of an internal-combustion engine and a first exemplary fuel-pressure profile p.sub.N(t) in a low-pressure branch of the injection system of the internal-combustion engine are represented. An operating state of the internal-combustion engine is indicated by the curve with the reference symbol 14. At a reference instant t.sub.Ref the engine is shut down and a measuring period 15 begins, so that the curve with the reference symbol 14 exhibits a corresponding step at this point.

(13) The dotted curves represent a reference fuel-pressure profile p.sub.H,Ref(t) in the high-pressure branch and a reference fuel-pressure profile p.sub.N,Ref(t) in the low-pressure branch. The reference fuel-pressure profiles p.sub.H,Ref(t), p.sub.N,Ref(t) correspond to the profiles to be expected of the first and second fuel pressures p.sub.1, p.sub.2 in the high-pressure and low-pressure branches after the shutdown of the internal-combustion engine at the reference instant t.sub.Ref, in which connection the two pumps and the injection devices then close the low-pressure branch and the high-pressure branch, respectively, in such a way that no fuel can escape from the two branches in the absence of undesirable leakages. The reference fuel-pressure profiles p.sub.H,Ref(t), p.sub.N,Ref(t) can be calculated or simulated, in particular on the basis of a physical model.

(14) The reference fuel-pressure profile p.sub.N,Ref(t) in the low-pressure branch remains substantially constant after the shutdown of the internal-combustion engine at the reference instant t.sub.Ref and substantially corresponds to an operating pressure in the low-pressure branch in the course of operation of the internal-combustion engine.

(15) On the other hand, the reference fuel-pressure profile p.sub.H,Ref(t) in the high-pressure branch falls after the reference instant t.sub.Ref in relation to an operating pressure in the high-pressure branch in the course of operation of the internal-combustion engine. This fall in pressure is brought about, in particular, by thermodynamic effects, for instance by a cooling of the fuel in the high-pressure branch.

(16) In the case of a leakage from the high-pressure branch, the fuel-pressure profile p.sub.H(t) in the high-pressure branch after the reference instant t.sub.Ref falls more intensely than the corresponding reference fuel-pressure profile p.sub.H,Ref(t), this being manifested in the fact that the slope of the fuel-pressure profile p.sub.H(t) within the measuring period 15 is less than the slope of the reference fuel-pressure profile p.sub.H,Ref(t). In particular, the absolute value of the slope of the fuel-pressure profile p.sub.H(t) within the measuring period 15 is higher than the absolute value of the slope of the reference fuel-pressure profile p.sub.H,Ref(t). From this it can be inferred that there is a fuel leakage in the high-pressure branch.

(17) On the other hand, the corresponding fuel-pressure profile p.sub.N(t) in the low-pressure branch in the present example shown in FIG. 2 rises after the reference instant t.sub.Ref in relation to the corresponding reference fuel-pressure profile p.sub.N,Ref(t), this being manifested in the fact that the slope of the fuel-pressure profile p.sub.N(t) within the measuring period 15 is higher than the slope of the reference fuel-pressure profile p.sub.N,Ref(t). In particular, the absolute value of the slope of the fuel-pressure profile p.sub.N(t) within the measuring period 15 is higher than the absolute value of the slope of the reference fuel-pressure profile p.sub.H,Ref(t). From this it can be inferred that there is an influx of fuel into the low-pressure branch.

(18) The fuel leakage in the high-pressure branch is preferentially quantified on the basis of a difference Δp.sub.H between the reference fuel-pressure profile p.sub.H,Ref(t) and the fuel-pressure profile p.sub.H(t) at a predetermined instant t.sub.test, for instance by the amount of escaping fuel—which causes the pressure difference Δp.sub.H—being calculated thermodynamically. The predetermined instant t.sub.test may lie within the measuring period 15, as represented in the present example. But alternatively the predetermined instant t.sub.test may also lie at the end of the measuring period 15 (not represented). In particular, the predetermined instant t.sub.test may also lie after an instant at which the fuel-pressure profile p.sub.H(t) reaches or falls short of a high-pressure threshold value 16. This is particularly advantageous if a loss of fuel in the high-pressure branch is established only when the fuel-pressure profile p.sub.H(t) in the high-pressure branch reaches or falls short of the high-pressure threshold value 16.

(19) Likewise, the influx of fuel into the low-pressure branch is preferentially quantified on the basis of the difference Δp.sub.N between the reference fuel-pressure profile p.sub.N,Ref(t) and the fuel profile p.sub.N(t) at the predetermined instant t.sub.test, for instance by the amount of fuel flowing in, which causes the pressure difference Δp.sub.N, being calculated thermodynamically. In particular, the predetermined instant t.sub.test may also in this case lie after an instant at which the fuel-pressure profile p.sub.N(t) reaches or exceeds a low-pressure threshold value 17. This is particularly advantageous if an influx of fuel into the low-pressure branch is established only when the fuel-pressure profile p.sub.N(t) into the low-pressure branch reaches or exceeds the low-pressure threshold value 17.

(20) If the amount of fuel that has flowed away out of the high-pressure branch at the predetermined instant t.sub.test corresponds to the amount of fuel that has flowed into the low-pressure branch at the predetermined instant t.sub.test, a fuel leakage out of the high-pressure branch into a combustion chamber of the internal-combustion engine via at least one injection device can be ruled out.

(21) However, if the amount of fuel that has flowed away out of the high-pressure branch at the predetermined instant t is greater than the amount of fuel that has flowed into the low-pressure branch at the predetermined instant t.sub.test, a fuel leakage out of the high-pressure branch into a combustion chamber of the internal-combustion engine via at least one injection device can be inferred, and a corresponding signal, which indicates the fuel leakage out of the high-pressure branch into a combustion chamber of the internal-combustion engine via the injection devices, can be output.

(22) FIG. 3 shows a second exemplary fuel-pressure profile p.sub.H(t) of a fuel pressure p.sub.1 in a high-pressure branch and also a second exemplary pressure profile p.sub.N(t) of a fuel pressure p.sub.2 in a low-pressure branch. Analogously to the comments in FIG. 2, the fuel-pressure profile p.sub.H(t) falls more quickly than a corresponding reference fuel-pressure profile p.sub.H,Ref(t). Therefore, and also by reason of the fact that the fuel-pressure profile p.sub.H(t) reaches or falls short of a high-pressure threshold value 16 within the measuring period 15, a loss of fuel from the high-pressure branch can be inferred.

(23) In contrast to the case represented in FIG. 2, however, the fuel-pressure profile p.sub.N(t) in the low-pressure branch does not rise within the measuring period 15 but proceeds in accordance with a reference fuel-pressure profile p.sub.N,Ref(t) in the low-pressure branch, so that the fuel-pressure profile p.sub.N(t) does not reach or exceed a low-pressure threshold value 17 within the measuring period 15. In particular, the fuel pressure p.sub.2 in the low-pressure branch remains substantially constant even after a shutdown of the internal-combustion engine at the instant t.sub.Ref at which the high-pressure and low-pressure branches are closed.

(24) It can correspondingly be inferred from the represented fuel-pressure profiles p.sub.N(t), p.sub.H(t) that the fuel escaping from the high-pressure branch does not enter the low-pressure branch but enters a combustion chamber of the internal-combustion engine via at least one of the injection devices. Therefore, also in the example shown in FIG. 3, a signal is output that indicates the fuel leakage out of the high-pressure branch into a combustion chamber of the internal-combustion engine via an injection devices.

LIST OF REFERENCE SYMBOLS

(25) 1 device for detecting and characterizing fuel leakage 2 injection system 3 internal-combustion engine 4 low-pressure pump 5 fuel tank 6 low-pressure branch 7 high-pressure branch 8 injection device 9 high-pressure pump 10 combustion chamber 11 control unit 12 low-pressure sensor 13 high-pressure sensor 14 operating state of an internal-combustion engine 15 measuring period 16 high-pressure threshold value 17 low-pressure threshold value p.sub.1 operating pressure in the low-pressure branch p.sub.2 operating pressure in the high-pressure branch t.sub.Ref reference instant t.sub.test predetermined instant p.sub.H,Ref(t) reference fuel-pressure profile in the high-pressure branch p.sub.H(t) fuel-pressure profile in the high-pressure branch p.sub.N,Ref(t) reference fuel-pressure profile in the low-pressure branch p.sub.N(t) fuel-pressure profile in the low-pressure branch

(26) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.