Controller for a common-rail injection system

Abstract

A controller for a common-rail injection system includes a plurality of fuel injectors, a common fuel supply line for the fuel injectors, a high-pressure pump for supplying the common fuel supply line with fuel, and a pressure sensor for determining the pressure in the common fuel supply line. A determination unit evaluates data of the pressure sensor and, from the pressure drop caused by an injection in the common fuel supply line, determines the fuel quantity actually injected during this injection or a value derived therefrom. An adaption unit uses the results of the determination unit in order to adapt the actuation of the fuel injectors. The determination unit carries out at least one test injection, and the actually injected fuel quantity or a value derived therefrom is effected by way of the test injection or injections.

Claims

1. A controller for a common-rail injection system, which includes a plurality of fuel injectors, a common fuel supply line for the fuel injectors, a high-pressure pump for supplying the common fuel supply line with fuel, and a pressure sensor for determining the pressure in the common fuel supply line, comprising: a determination unit configured to evaluate data of the pressure sensor during an evaluation interval chosen, depending on an actuation start time or an actuation end time of at least one test injection in the common fuel supply line made in addition to normal injections in the common fuel supply line for engine operation, to start after an attenuated half oscillation of a pressure signal caused by the at least one test injection and to end during a normal injection in the common fuel supply line for engine operation, and, from a pressure drop occurring during the evaluation interval caused by the at least one test injection in the common fuel supply line made in addition to the normal injections, to determine a fuel quantity actually injected during this injection or a value derived therefrom, and an adaption unit configured to use the results of the determination unit in order to adapt the actuation of the fuel injectors, wherein the determination unit is further configured to carry out the at least one test injection by way of which the actually injected fuel quantity or the value derived therefrom is determined.

2. The controller according to claim 1, wherein the determination unit is further configured to determine a reference measurement signal of the pressure sensor without the test injection and a test measurement signal of the pressure sensor when the test injection has been made, and wherein for determining the pressure drop caused by the injection, the determination unit is configured to employ the difference between the reference measurement signal and the test measurement signal.

3. The controller according to claim 2, wherein the determination unit is further configured to determine the reference measurement signal and the test measurement signal in the same time interval with respect to an engine cycle and/or under injection and/or engine operating conditions that are identical except for the test injection.

4. The controller according to claim 1, wherein the determination unit is configured to carry out several test injections and for determining the actually injected fuel quantity or a value derived therefrom forms a mean value, wherein the determination unit is configured to perform the several test injections at least one of in the same time interval with respect to the engine cycle, under identical injection, engine operating conditions, or injection and engine operating conditions, with at least one of identical durations of actuation, injection quantities of the fuel injector, and identical actuation signals, and wherein the determination unit is configured to determine both the test measurement signal and the reference measurement signal several times.

5. The controller according to claim 1, wherein the determination unit is configured to perform the at least one test injection at least one of in a specified time interval, with a specified duration of actuation, and/or injection quantity of the fuel injector, and with a specified actuation signal, and wherein at least one of the specified time interval, the specified duration of actuation, the injection quantity of the fuel injector, and the specified actuation signal is independent of the injection time and/or injection quantity desired for the normal engine operation.

6. The controller according to claim 1, wherein the at least one test injection is a pre-injection or a post-injection effected before or after a main injection.

7. The controller according to claim 1, further comprising a monitoring unit configured to monitor engine operation, which is connected with the determination unit such that determination of the actually injected fuel quantity or a value derived therefrom is carried out by the determination unit at constant pressure and/or constant temperature in the common fuel supply line, constant speed and/or constant fuel injection quantity for the normal engine operation, wherein the determination is effected over several engine cycles or initiation of the determination of the actually injected fuel quantity or a value derived therefrom is effected by the determination unit in response to an inquiry as to whether the speed of the engine operates below a certain speed threshold, and wherein the determination is effected in the idling mode of the internal combustion engine.

8. The controller according to claim 1, wherein several measurement values are averaged within the evaluation interval, and wherein the test injection is effected at a time which lies after the first attenuated half oscillation of the pressure signal caused by at least one of a main injection and the operation of the pump.

9. The controller according to claim 1, wherein the determination and the adaption are effected individually for each fuel injector.

10. The controller according to claim 1, wherein the determination and the adaption are effected for several different pressures in the common fuel supply line, for several different durations of actuation and/or injection quantities of the fuel injector during test injections, or both.

11. The controller according to claim 1, wherein the determination of the actually injected fuel quantity or a value derived therefrom by the determination unit is coordinated with an actuation circuit of the high-pressure pump, wherein between a start of the test injection and an end of an associated measurement phase, no operation of the high-pressure pump is effected, and wherein on determination of a reference measurement signal of the pressure sensor without test injection, no operation of the high-pressure pump is effected during a corresponding reference period.

12. The controller according to claim 1, wherein operation of the high-pressure pump is, each initiation of the test injection within an engine cycle is, or both the operation and the initiation are effected at specified points in time and/or crankshaft angles, wherein, in an operating phase in which test injections are made, the operation of the high-pressure pump is shifted towards early or towards late, wherein the test injection is effected in a prolonged interval between the operation of the high-pressure pump and a main injection or in a prolonged interval between the main injection and the operation of the high-pressure pump, and wherein in an operating phase in which test injections are made, individual main injections and/or operating phases of the high-pressure pump are omitted.

13. The controller according to claim 8, wherein the evaluation interval is chosen such that it starts after a first attenuated full oscillation of the pressure signal caused by the test injection, and wherein the test injection is effected at a time which lies after the first attenuated full oscillation of the pressure signal caused by at least one of the main injection and the operation of the pump.

14. The controller according to claim 10, wherein the injection quantity of the test injection lies between 2 mg and 80 mg.

15. The controller according to claim 14, wherein the injection quantity of the test injection lies between 5 mg and 50 mg.

16. The controller according to claim 10, wherein the number of the different durations of actuation and/or the number of injection quantities lies between 2 and 20.

17. The controller according to claim 16, wherein the number of the different durations of actuation and/or the number of injection quantities lies between 4 and 10.

18. A common-rail injection system comprising: a plurality of fuel injectors, a common fuel supply line for the fuel injectors, a high-pressure pump for supplying the common fuel supply line with fuel, a pressure sensor for determining a pressure in the common fuel supply line, and a controller having a determination unit configured to evaluate data of the pressure sensor during an evaluation interval chosen, depending on an actuation start time or an actuation end time of at least one test injection in the common fuel supply line made in addition to normal injections in the common fuel supply line for engine operation, to start after an attenuated half oscillation of a pressure signal caused by the at least one test injection and to end during a normal injection in the common fuel supply line for engine operation, and, from a pressure drop occurring during the evaluation interval caused by the at least one test injection in the common fuel supply line in addition to the normal injections, determines a fuel quantity actually injected during this injection or a value derived therefrom, and an adaption unit configured to use the results of the determination unit in order to adapt the actuation of the fuel injectors, wherein the determination unit is further configured to carry out at least one test injection by way of which the actually injected fuel quantity or the value derived therefrom is determined.

19. An engine comprising a common-rail injection system according to claim 18.

20. A method for actuating a common-rail injection system which includes a plurality of fuel injectors, a common fuel supply line for the fuel injectors, a high-pressure pump for supplying the common fuel supply line with fuel, a pressure sensor for determining a pressure in the common fuel supply line using a controller having a determination unit, and an adaption unit, the method comprising: evaluating data of the pressure sensor with the determination unit during an evaluation interval chosen, depending on an actuation start time or an actuation end time of at least one test injection in the common fuel supply line made in addition to normal injections in the common fuel supply line for engine operation, to start after an attenuated half oscillation of a pressure signal caused by the at least one test injection and to end during a normal injection in the common fuel supply line for engine operation, determining, with the determination unit, a fuel quantity actually injected during an injection or a value derived therefrom from a pressure drop occurring during the evaluation interval caused by way of the at least one test injection carried out by the determination unit in the common fuel supply line in addition to the normal injections in the common fuel supply line for engine operation, and adapting, with the adaption unit, actuation of the fuel injectors using results of the data evaluation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an exemplary embodiment of an injection system according to the invention with an exemplary embodiment of an inventive controller.

(2) FIG. 2 shows a flow diagram of an exemplary embodiment of a method according to the invention as it proceeds in an inventive controller.

(3) FIG. 3 shows two diagrams which illustrate the time profile of a test injection used according to the invention and of the test pressure profile caused thereby in the common fuel supply line as compared to a reference pressure profile without test injection.

(4) FIG. 4 shows a representation of an evaluation interval chosen according to a first alternative for the pressure profiles shown in FIG. 3.

(5) FIG. 5 shows a representation of two alternative measurement times or evaluation intervals for the pressure profiles shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows an exemplary embodiment of an injection system according to the invention with an inventive controller. The common-rail injection system includes a plurality of injectors I1, I2 to Ii, which are supplied with pressurized fuel by a common fuel supply line 1. There is provided a high-pressure pump 2 which supplies the common fuel supply line 1 with high pressure. Furthermore, there is provided a pressure sensor 3 for measuring the pressure in the common fuel supply line 1.

(7) FIG. 1 furthermore shows a block diagram of an engine control unit 4 according to the invention. The same initially contains a conventional control block 12 in which the duration of actuation for the respective injector is determined from the injection quantity requested for the engine operation with reference to maps. The requested injection quantity serving as input for the control block 12 is determined for example on the basis of engine operating conditions and/or control signals generated by the driver, in particular from the desired speed and/or the desired torque of the engine. The control block 12 can comprise either a common map 11 for all injectors or injector-individual maps.

(8) The engine control unit 4 furthermore comprises a controller 5 according to the invention, which in a determination unit 6 determines the actually injected fuel quantity from the fuel pressure determined by the sensor 3 during a test injection. In an adaption unit 7 one or more correction factors are formed from a comparison of the target injection quantity and the actual injection quantity during the test injection, by which the duration of actuation determined by the control block 12 is corrected. The corrected duration of actuation then is supplied to the injector end stage 13, which generates the immediate electrical actuation signals for the injectors, which are transmitted to the same via a control line 8.

(9) The exemplary embodiment of the controller according to the invention as shown in FIG. 1 will now be described in detail below.

(10) The precise dosage of the injected fuel quantity plays an essential role with regard to the subsequent combustion and the exhaust gases generated thereby. Due to production-related component variances of the fuel injectors and aging phenomena during the engine operation, the same must be calibrated while the engine is running.

(11) Fuel injectors are subject to production-related component variances which impair the dosing accuracy. The loading of the fuel system with higher and higher system pressures leads to additional component drifts, which entail negative effects on the emission behavior and the efficiency of the engine. To counteract these deviations, a correction of the injector actuation is necessary, in order to ensure stable running of the engine.

(12) This means that deviations or drifts in the actually injected fuel quantity must be detected, quantified and compensated by a corresponding adaptation of the injector actuation.

(13) For this purpose, the present invention provides a strategy and a controller for the injector diagnosis and calibration. Since an additional expenditure of engine sensors, e.g. additional acceleration or pressure sensors, should be avoided as far as possible, the exemplary embodiment relies on the signal of the common-rail pressure sensor installed as standard in the high-pressure pump. The control hence is based on the evaluation of the pressure sensor signal at the high-pressure pump.

(14) The controller (5) according to the invention, which can be integrated into the engine control unit (4), substantially consists of two parts, see the exemplary embodiment shown in FIG. 1: A determination unit (6) for estimating the actually injected fuel quantity. This unit consists of a method which estimates the actually injected fuel quantity per injector on the basis of the respective pressure drop in the fuel supply line. The pressure drop is determined from the pressure sensor signal of the fuel supply line. An adaption unit (7), which carries out a target/actual comparison on the basis of the injection quantity estimation and adapts the injector actuation on the basis of the result.

(15) By means of the controller according to the invention, deviations or inaccuracies in the injected fuel quantity can be compensated, which are due to the following reasons: inaccuracies due to manufacturing tolerances aging phenomena or wear nozzle coking

(16) FIG. 2 shows the block circuit diagram of the controller for an individual injector of the common-rail system. The same carries out test injections (10), by which the injected fuel quantity can be estimated for the respective injector.

(17) This is effected in a static operating point of the internal combustion engine, i.e. with constant duration of injector actuation and constant fuel pressure. On the basis of this estimation an injector-individual correction of the duration of actuation is determined, by means of which the actuation map is adapted. The actually injected fuel quantity can be determined in several specified static operating points of the engine, in order to thereupon carry out a target/actual comparison.

(18) The controller operates as follows: A monitoring unit (9) sets an ok_flag to 1, as soon as the engine is in an operating condition favorable for carrying out the injection correction. If this is the case, a test injection (10) is carried out in cylinder 1, 2, . . . in a defined, fixed time interval with a specified duration of actuation at constant fuel pressure. After a data quality check, above all an outlier handling for identifying poor measurements, the signal course is temporarily stored in buffer 1. Directly thereafter, the pressure sensor history is recorded in the same time interval without injection. This signal course serves as reference and is stored in buffer 2. When both buffers are filled, the estimation of the actually injected fuel quantity is carried out and the result is stored temporarily. On the basis of the estimation results for different test injections, an injector-individual correction of the duration of actuation is determined.

(19) Input quantities of the monitoring unit (9) include the injection quantity for the normal engine operation and/or the temperature of the fuel. It is checked whether the variation of these quantities lies below a specified threshold, i.e. whether the engine operation is changed and/or the fuel injection system is in a stable state. The speed of the internal combustion engine serves as further input quantity. It is checked whether the same lies below a specified threshold, since at low speeds the period available for the test injection is longer than at high speeds. Preferably, the test operation therefore is effected in the idle mode of the engine.

(20) The estimation of the injection quantity is based on the determination of the pressure drop obtained in the common rail due to the fuel injection. The same can be determined from the two pressure profiles of buffer 1 and buffer 2.

(21) The set-up for determining the actually injected fuel mass is supplied by equation (1),
Δm=−V.sub.0.Math.β.Math.ρ.Math.Δp  (1)
with
Δp(t)=p.sub.ref(t)−p(t)  (2)

(22) V.sub.0 herein represents the known raw volume of the high-pressure side of the injection system, β the compressibility coefficient and ρ the fuel density at the system pressure p and the temperature T.

(23) The pressure difference Δp can be determined by forming the average from a plurality of measurements. In FIG. 3 the mean of the family of curves of ten (10) measurements of the course of the pressure sensor signal is shown in a continuous line as test signal course (40) with a constant test injection (10), here a pre-injection each with constant duration of actuation. In a broken line, the mean of the family of curves of ten (10) measurements of the signal course is shown as reference signal course (30), at which no test injection (10) was made. From these measurements, the actually injected fuel mass can be determined.

(24) In the exemplary embodiment, the measurement pick-up is triggered by the actuation pulse of the fuel injector for triggering the test injection (10). The same represents triggering by hardware, which triggers the measurement pick-up by the A/D converter provided for measurement pick-up.

(25) FIG. 3 also shows a small deflection in the actuation signal during the generation of the reference measurement signal. This is a very short duration of actuation of the fuel injector, in which no injection occurs. This means that this short excitation is not sufficient to open the injector. This very short actuation pulse is used to trigger the measurement pick-up for determining the reference measurement signal.

(26) The pressure difference Δp then is obtained as difference between the test pressure signal 40 and the reference pressure signal 30, wherein this difference is determined in a previously defined evaluation interval 50 which depends on the start of actuation, i.e. the start of energization of the injector.

(27) The determination of the measurement values is effected in a fixed time interval [t.sub.1,t.sub.2] (evaluation interval), which is shown in FIG. 4. The evaluation interval (50) depends on the actuation time, e.g. on the actuation start or end of the test injection (10) and accounts for the time delay (60) between this actuation time and the pressure drop triggered by the test injection. Furthermore, the evaluation interval should be chosen such that the pressure signal within the evaluation interval (50) does not depend on the starting of the high-pressure pump or other injections such as e.g. the main injection (20). Alternatively or in addition, a test injection also might be effected after the main injection (20).

(28) The evaluation interval can depend on the injection duration and/or quantity of the test injection (10). In the exemplary embodiment, the evaluation interval has been chosen such that it will start only after the first attenuated half-oscillation of the pressure signal (40) and preferably after the first full oscillation of the pressure signal (40), in order to measure only the static part of the pressure drop, as far as possible.

(29) The pressure signal represents a superposition of the signals generated by the main injections, the operation of the high-pressure pump and the test injections. A certain temporal distance between the test injection and the preceding operation of the high-pressure pump or the preceding main injection therefore is necessary. Preferably, the test injection should be effected only after one or two attenuated full oscillations caused by a main injection and/or the operation of the high-pressure pump.

(30) In the exemplary embodiment, the operation of the high-pressure pump (2), the main injection (20) and the initiation of the test injection (10) each are effected at specified points in time and/or crankshaft angles within the engine cycle. It can thereby be ensured that the test injection is effected with a sufficient temporal distance to the preceding and the succeeding events.

(31) To avoid too short and too long injection times, which would lead to a high inaccuracy in the measurement or too large a temporal proximity between main and test injection, the injection quantities of the test injections in the exemplary embodiment are chosen between 4 mg and 5 mg, furthermore preferably below 50 mg.

(32) In the case of too high speeds and/or an engine with many cylinders only a very short time window between the operation of the high-pressure pump and the main injection is available for the test injection and the succeeding measurement phase. To increase this time interval, the operation of the high-pressure pump can be shifted towards early, when the test injection is effected as pre-injection, or towards late, when the test injection is effected as post-injection. Such shifting can be made either only in those operating phases in which test injections are made or generally. Possibly, the operation of the high-pressure pump and the main injection even can be effected at the same time, so that the time window for the test injection becomes maximal.

(33) Alternatively or in addition, in an operating phase in which test injections are made, individual main injections and/or operating phases of the high-pressure pump can be omitted. The period available for the test injection also is expanded thereby.

(34) According to the present invention, the actual injection quantity now is calculated from the pressure difference caused by the test injection. In the exemplary embodiment, the calculation of the pressure difference Δp is effected from a time-discrete pressure profile p(n) and the reference pressure profile p.sub.ref(n), with n as discrete time index, by calculation of the arithmetic mean value in a previously defined discrete time interval [n.sub.1,n.sub.2] which depends on the start of actuation, i.e. the start of energization of the injector.

(35) The signal evaluation corresponds to the calculation of the pressure drop according to equation (3).

(36) $\begin{array}{cc}\Delta p=\frac{1}{n_2-n_1+1}.Math.\underset{n=n_1}{\overset{n_2}{.Math.}}\left(p_{\mathrm{ref}}\left(n\right)-p\left(n\right)\right)& \left(3\right)\end{array}$

(37) On the basis of the determined pressure drop from equation (3), the actually injected fuel mass is determined by means of equation (1).

(38) The process of the estimation of the actually injected fuel mass by means of the indicated procedure is repeated for several durations of actuation at a specified constant fuel pressure.

(39) The estimated fuel quantities are stored temporarily for each injector, see FIG. 2. From these data, the injector-individual correction values α for the duration of actuation thereupon are determined by means of a comparison with the target fuel quantities.

(40) As an alternative to averaging as indicated in equation (3), the integral of the pressure drop A can be determined, which in the time-discrete case corresponds to the sum
A=Σ.sub.n=n.sub.1.sup.n.sup.2Δp(n)  (5)
and hence the area between the two curves, see FIG. 5.

(41) Furthermore, the maximum Δp.sub.max of the pressure drop also can be determined, which likewise is shown in FIG. 5.

(42) In the two last-mentioned cases, the characterization of the actual state of the respective injector is not effected by means of the injection quantity, but by means of the auxiliary quantities A or Δp.sub.max by which the injector drift is detected and compensated via injector-individual correction values α for the duration of actuation.

(43) The corrected duration of actuation corresponds to a function of the respective duration of actuation TOC and the injector-individual correction α.
TOC.sub.corrected=f(TOC,α)  (4)

(44) When the injector-individual correction values α as shown above are determined for several different durations of actuation of the test injection, α can be a function of the duration of actuation α(TOC).

(45) Furthermore, the injector-individual correction values α can be determined in several specified static operating points of the engine, in particular at different system pressures p. In this case, the injector-individual correction values α are represented as a map. Alternatively, a determination is possible at only one static operating point of the engine, in particular at a system pressure p, wherein the correction values for other static operating points of the engine, in particular other system pressures p, are extrapolated from the correction values thus determined.

(46) Alternatively, the correction values also can be utilized to correct the injector-individual maps (11) stored in the controller for determining the duration of actuation TOC from the desired injection quantity.

(47) The essential aspects of the inventive controller for compensating deviations and drifts in the injection quantity for direct injection systems on the basis of the injection-related pressure drop in the fuel supply line will again be represented below independent of the exemplary embodiment shown above: i. The controller according to the invention determines the actually injected fuel quantity from the pressure drop in the fuel supply line in a fixed time interval [t.sub.1,t.sub.2] (evaluation interval). ii. According to the invention, a test injection is carried out, if the unit is in a favorable operating point (for this purpose, the engine operation can be monitored). iii. The pressure profiles for M test injections with constant duration of actuation and specified constant fuel pressure are recorded and averaged. iv. By comparison with the reference recording (M pressure profiles without test injection), the effective pressure drop Δp is determined. v. By means of equations (1) and (2), the actually injected fuel mass is determined from the recorded pressure profiles (no auxiliary quantity, but the fuel mass which can be interpreted directly). vi. For recording the pressure sensor signals no additional sensor is necessary, i.e. no constructive change to the injection system. No additional sensors, throttles or hydraulic accumulators are necessary for realizing the injection quantity estimation. The injection quantity purely is determined from the sensor signal which is supplied by the pressure sensor installed as standard. vii. By means of the determined actual injection quantities in various operating points, an injector-individual actuation correction is determined, which is applied for future injections. viii. The injection quantity is determined for each of the installed injectors individually and independently. ix. The injection quantity estimation is carried out on the basis of a test injection, i.e. a pre- or post-injection, and can be carried out in normal engine operation. x. The controller according to the invention can be integrated on an engine control unit. As an alternative to iv., the integral of the pressure drop A can be determined, and/or the maximum Δp.sub.max of the pressure drop. xi. If the proceeding is as in item ix., the characterization of the actual state of the respective injector is not effected by means of the injection quantity, but by means of the auxiliary quantities A or Δpmax by which the injector drift is detected and compensated.

(48) Particularly preferably, the essential aspects set forth above are realized such as has been described in general in the beginning and more detailed above in the exemplary embodiment.

(49) 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.