Precise determining of the injection quantity of fuel injectors

Abstract

A method for determining an injection quantity of a fuel injector determines a first time at which an injection process of the fuel injector starts, a second time at which the injection process of the fuel injector ends, calculates a model on the basis of the first time and the second time, which model represents the position of a nozzle needle of the fuel injector as a function of the time, and calculates the quantity of fuel to inject.

Claims

1. A method for determining an injection quantity of a fuel injector having a solenoid drive, for an internal combustion engine of a motor vehicle, the method comprising: determining a first time at which an injection process of the fuel injector starts; determining a second time at which the injection process of the fuel injector ends; calculating a model on the basis of the first time and the second time, which model represents a position of a nozzle needle of the fuel injector as a function of the time; calculating the injection quantity on the basis of the model and a relationship between the position of the nozzle needle and a through flow rate through the fuel injector; and injecting the calculated injection quantity of fuel into the engine.

2. The method as claimed in claim 1, wherein the model has a first parameter and a second parameter, wherein the first parameter is assigned to a linear part of the function, and the second parameter is assigned to a quadratic part of the function.

3. The method as claimed in claim 2, wherein the first parameter of the model is calculated on the basis of predetermined data and the first time.

4. The method as claimed in claim 3, wherein the second parameter is calculated on the basis of the first parameter and at least one of the first time and the second time.

5. The method as claimed in claim 4, wherein the model has the function $y\left(t\right)=v_{y0}.Math.t-\frac{1}{2}.Math.g.Math.t^2,$ wherein y(t) denotes the position of the nozzle needle, v.sub.y0 denotes the first parameter, g the second parameter and t the time.

6. The method as claimed in claim 5, wherein the movement of the nozzle needle during the injection process constitutes essentially a ballistic trajectory.

7. A method for actuating a fuel injector having a solenoid drive, the method comprising: carrying out a method for calculating the injection quantity of the fuel injector as claimed in claim 1, and actuating the fuel injector on the basis of the calculated injection quantity, wherein a duration between the application of a boost voltage for opening the fuel injector and application of a voltage for closing the fuel injector is reduced or increased, if it is determined that the injection quantity is larger or smaller than a reference injection quantity.

8. The method of claim 5, wherein the predetermined data comprises a table stored in memory of a value of the first parameter for each of a plurality of time values corresponding to the first time, and calculating the model comprises calculating the first parameter by using the table to identify the value of the first parameter corresponding to the determined first time.

9. The method of claim 8, wherein calculating the model comprises calculating the second parameter by using the function y(t), the calculated first parameter, the determined second time and the determined first time.

10. The method of claim 4, wherein the predetermined data comprises a table stored in memory of a value of the first parameter for each of a plurality of time values corresponding to the first time, and calculating the model comprises calculating the first parameter by using the table to identify the value of the first parameter corresponding to the determined first time.

11. The method of claim 10, wherein calculating the model comprises calculating the second parameter by using the function, the calculated first parameter, the determined second time and the determined first time.

12. A computer program for actuating a fluid injector having a solenoid drive, the computer program stored in non-transitory memory and having instructions, which when executed by a processor, performs determining a first time at which an injection process of the fluid injector starts; determining a second time at which the injection process of the fluid injector ends; calculating a model on the basis of the first time and the second time, which model represents a position of a nozzle needle of the fluid injector as a function of the time; calculating an injection quantity on the basis of the model and a relationship between the position of the nozzle needle and a through flow rate through the fluid injector; and injecting the calculated injection quantity of fluid from the fluid injector.

13. The computer program of claim 12, wherein the model has a first parameter and a second parameter, wherein the first parameter is assigned to a linear part of the function, and the second parameter is assigned to a quadratic part of the function.

14. The computer program of claim 13, wherein the first parameter of the model is calculated on the basis of predetermined data and the first time.

15. The computer program of claim 14, wherein the second parameter is calculated on the basis of the first parameter and at least one of the first time and the second time.

16. The computer program of claim 15, wherein the predetermined data comprises a stored table of a value of the first parameter for each of a plurality of time values corresponding to the first time, and the first parameter is calculated by the computer program by using the table to identify the value of the first parameter corresponding to the determined first time.

17. The computer program of claim 16, wherein the second parameter is calculated by the computer program by using the function, the calculated first parameter, the determined second time and the determined first time.

18. The computer program of claim 15, wherein the model has the function $y\left(t\right)=v_{y0}.Math.t-\frac{1}{2}.Math.g.Math.t^2,$ wherein y(t) denotes the position of the nozzle needle, v.sub.y0 denotes the first parameter, g the second parameter and t the time.

19. The computer program of claim 18, wherein the predetermined data comprises a stored table of a value of the first parameter for each of a plurality of time values corresponding to the first time, and the first parameter is calculated by the computer program by using the table to identify the value of the first parameter corresponding to the determined first time.

20. The computer program of claim 19, wherein the second parameter is calculated by the computer program by using the function, the calculated first parameter, the determined second time and the determined first time.

21. The method of claim 2, wherein the first parameter of the model is calculated on the basis of predetermined simulation data and the first time.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a sectional view of a fuel injector with a solenoid drive.

(2) FIG. 2 shows an illustration of the needle position as a function of the time in the case of ballistic operation of a fuel injector.

(3) FIG. 3 shows an illustration of the relationship between the start of injection (OPP1) and a model parameter.

(4) FIG. 4 shows an illustration of the relationship between the needle position and injector through flow rate.

(5) FIG. 5 shows a flowchart of a method according to the invention.

DETAILED DESCRIPTION

(6) It should be noted that the embodiments described below are merely a limited selection of possible variant embodiments of the invention.

(7) FIG. 1 shows a sectional view through a fuel injector 100 with a solenoid drive (solenoid injector). The injector 100 has, in particular, a solenoid drive with coil 102 and armature 104. If a voltage pulse is applied to the coil 102, the magnetic armature 104 moves in the direction of the wide part of the nozzle needle 106 and then forces it upward, after overcoming the idle stroke 114 (counter to the force of the spring 110), counter to the spring forces applied by the springs 110 and 132 until the armature 104 strikes against the pole shoe 112. After the end of the voltage pulse, the armature 104 and nozzle needle 106 move downward again to the initial position at the hydro-disk 108.

(8) The solenoid injector 100 which is shown in FIG. 1 has a plurality of features which are known as such and are only of minor significance for the present invention, and are therefore not described in detail. These features comprise, in particular, valve bodies 116, an integrated seat guiding means 118, ball 120, seal 122, housing 124, plastic 126, disk 128, metal filter 130 and calibration spring 132.

(9) The present invention is based on the idea of calculating the movement of the nozzle needle of a fuel injector, for example of the fuel injector 100 described above, during the injection process using a model, in order to calculate the actual injection quantity with high precision, and, if appropriate, to correct it during subsequent actuation processes. The model-based calculation of the needle movement, that is to say the needle position as a function of the time, is described below for injections which are so short that the armature 104 and nozzle needle 106 do not strike against the pole shoe. In this case, the needle movement essentially describes a ballistic trajectory. That is to say the needle position is represented as a function of the time, as in the illustration 210 in FIG. 2, follows a parabolic curve 212 and can consequently be modelled with a polynomial of the 2nd order:

(10) $y\left(t\right)=v_{y0}.Math.t-\frac{1}{2}.Math.g.Math.t^2.$

(11) Here, y(t) denotes the position of the nozzle needle, v.sub.y0 denotes a first parameter of the model, g a second parameter of the model and t the time.

(12) According to the invention, the first and the second parameter is determined on the basis of the times t_OPP1 and t_OPP4, wherein the first time t_OPP1 corresponds to the start of the needle movement (and therefore to the start of the actual injection process), and the second time t_OPP4 corresponds to the end of the needle movement (and therefore the end of the actual injection process). These two times are preferably determined with suitable methods from the prior art.

(13) In particular, the first parameter v.sub.y0 is determined on the basis of a relationship with the first time t_OPP1. This relationship is preferably determined by simulation by means of finite element methods (FEM), and is stored in a dataset, for example as a table, in the memory of the engine control unit. FIG. 3 shows an illustration 310 of such a relationship which is determined by simulation and is illustrated as a curve 312.

(14) The second parameter g can then be determined by making use of the fact that the needle position at the end of the injection process (that is to say at the time t_OPP4) must be equal to zero (position of rest of the needle):

(15) $g=\frac{2.Math.v_{y0}}{\mathrm{t\_OPP}4-\mathrm{t\_OPP}1}.$

(16) If the time axis is defined such that t_OPP1=0, then t_OPP1 is omitted in the above formula.

(17) The model, which is now determined for the needle movement is then used together with the through flow characteristic (that is to say the relationship between the through flow rate and the needle position) of the fuel injector, in order to calculate the actual injection quantity by integrating the through flow rate over the injection period (from t_OPP1 to t_OPP4). FIG. 4 shows an illustration 410 of such a relationship 412 between the needle position and the injector through flow rate.

(18) If the calculated injection quantity deviates from the set point quantity or reference quantity, the actuation for the subsequent injection process is correspondingly adapted. If the calculated injection quantity exceeds the set point quantity, the duration of the boost phase can, for example, be correspondingly shortened.

(19) FIG. 5 shows a flowchart which compiles the method according to the invention as described above for determining an injection quantity of a fuel injector 100, having a solenoid drive, for an internal combustion engine of a motor vehicle.

(20) In step 510, the time t_OPP1 (first time) at which an injection process of the fuel injector starts is determined. Then, in step 520, the time t_OPP4 (second time) at which the injection process of the fuel injector ends is determined.

(21) In step 530, a model (for example with the above-mentioned parameters v.sub.y0 and g), which represents the position y(t) of the nozzle needle 106 of the fuel injector 100 as a function of the time, is calculated.

(22) On the basis of the calculated model and a characteristic relationship between the position of the nozzle needle and the through flow rate of the fuel injector, the precise injection quantity is then calculated in step 540.

(23) The method described above is preferably carried out by means of software in an engine control unit. The actual injection quantity of a fuel injector can then be determined precisely and, if appropriate, used to correct the actuation, without employing additional hardware.

LIST OF REFERENCE NUMBERS

(24) 100 Fuel injector 102 Coil 104 Armature 106 Nozzle needle 108 Hydro-disk 110 Spring 112 Pole shoe 114 Idle stroke 116 Valve body 118 Integrated seat guiding means 120 Ball 122 Seal 124 Housing 126 Plastic 128 Disk 130 Metal filter 132 Calibration spring 210 Illustration 212 Curve t_OPP1 Time t_OPP4 Time 310 Illustration 312 Curve v.sub.y0 Model parameter 410 Illustration 412 Curve 510 Method step 520 Method step 530 Method step 540 Method step