Determination of the quantity of fuel flowing through a fuel injector based on the heating of the fuel by means of an electric heating device

Abstract

A method for determining the quantity of fuel flowing through a fuel injector. The fuel injector has an electric heating device for heating the fuel and a temperature-measuring device for measuring the temperature of the heated fuel. The method includes (a) applying a predetermined electrical heating power to the electric heating device, (b) measuring an increase in the temperature of the fuel as a consequence of the heating power, and (c) determining the quantity of fuel flowing through the fuel injector on the basis of the applied electrical heating power and the measured increase in the temperature. A method for equalizing the fuel feed at at least two cylinders of an internal combustion engine utilizes the method for determining the quantity of fuel flowing through a fuel injector. An engine controller and a computer program carry out the specified methods.

Claims

1. A method for determining a quantity of fuel flowing through a fuel injector, the fuel injector having an electric heating device for heating the fuel and a temperature-measuring device for measuring a temperature of the heated fuel, the method comprising: closing the fuel injector; measuring, with the temperature-measuring device, the temperature of the fuel located in the fuel injector; feeding in, with the fuel injector closed, a predefined test heating power until the measured temperature of the fuel located in the fuel injector has reached a predefined setpoint temperature; measuring a time period that is required to reach the predefined setpoint temperature at the predefined test heating power; and determining an electrical heating power for a fuel injector of the internal combustion engine on the basis of the measured time period, where said electrical heating power is determined to be higher or lower based on longer or shorter measured time periods; applying the electrical heating power to the electric heating device; measuring an increase in the temperature of the fuel caused by the heating power; and determining the quantity of fuel flowing through the fuel injector from the electrical heating power applied to the electric heating device and the measured increase in the temperature of the fuel and adjusting the quantity of fuel flowing through the fuel injector based on the previously determined quantity of fuel.

2. The method according to claim 1, which comprises measuring the increase in the temperature of the fuel by way of the electric heating device.

3. A method for equalizing a feeding of fuel in at least two cylinders of an internal combustion engine, the method comprising: carrying out the method according to claim 1 for each fuel injector respectively assigned to a cylinder of the internal combustion engine; and balancing the feeding of fuel based on the quantities of fuel determined by the method.

4. The method according to claim 3, wherein the step of balancing the feeding of fuel comprises adapting opening times and/or closing times of the respective fuel injector.

5. The method according to claim 3, also comprising: determining the electrical heating power for each fuel injector of the internal combustion engine, so as to cause a thermal heating power that is transferred to the fuel in case of a specific fuel mass flow through the respective fuel injector, to be equal for all the fuel injectors.

6. The method according to claim 5, which comprises determining the electrical heating power for each fuel injector of the internal combustion engine at a time after the internal combustion engine was not operational for at least one specific rest time period.

7. The method according to claim 5, which comprises adjusting the predefined test heating power to a specific value.

8. An engine controller for an internal combustion engine, the engine controller being configured to execute the method according to claim 1 for determining a quantity of fuel flowing through a fuel injector of an internal combustion engine.

9. An engine controller for an internal combustion engine, the engine controller being configured to execute the method according to claim 3 for equalizing a fuel feed into two or more cylinders of an internal combustion engine.

10. A non-transitory computer program product comprising a computer program for determining a quantity of fuel flowing through a fuel injector, wherein the computer program, when executed by a processor, is configured to carry out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Further advantages and features of the present invention can be found in the following exemplary description of currently preferred embodiments. In the drawing:

(2) FIG. 1 illustrates, according to an exemplary embodiment of the invention, a method for determining the quantity of fuel flowing through a fuel injector,

(3) FIG. 2 illustrates, in the form of a flowchart for a four-cylinder engine, a procedure for standardizing the predetermined electrical heating power for four electric heating devices which are each assigned to a fuel injector, and

(4) FIG. 3 illustrates, in the form of a flowchart for a four-cylinder engine, a method for determining the correction values, necessary for cylinder equalization, for the metering of fuel for each individual cylinder.

DESCRIPTION OF THE INVENTION

(5) It is to be noted that the embodiments described below merely represent a restricted selection of possible embodiment variants of the invention. In particular, it is possible to combine the features of individual embodiments with one another in a suitable way, with the result that the embodiment variants which are presented explicitly here are to be considered as disclosing a multiplicity of various embodiments in an obvious way to a person skilled in the art.

(6) FIG. 1 illustrates, according to an exemplary embodiment of the invention, a method for determining the quantity of fuel flowing through a fuel injector. In this context, a fuel injector is used which has an electric heating device for heating the fuel and a temperature-measuring device for measuring the temperature of the heated fuel.

(7) In a first step 110 of the method described here, a predetermined electrical heating power is applied to the electric heating device. As a result of this, the electric heating device outputs heat to the mass flow of fuel flowing through the fuel injector.

(8) In a second step 120, the increase in temperature, based on the electrical heating power, of the fuel mass flow is measured.

(9) In a third step 130, the quantity of fuel flowing through the fuel injector or the mass flow of fuel is determined on the basis of the applied electrical heating power and the measured increase in the temperature. For this purpose, according to the exemplary embodiment represented here, the formula (1) already specified above is used:
P=c.sub.p.Math.T.Math.{dot over (m)}(1)
Where: P[W] is the heating power of for example 200 Watt

(10) $c_p\left[\frac{\mathrm{Ws}}{\mathrm{kg}.Math.K}\right]$ is the specific thermal capacity of the fuel T [K] is the temperature difference in the fuel between the forward run and the outflow of the electric heating device or of the electric heater (for example 75 K) and

(11) $\stackrel{.}{m}\left[\frac{\mathrm{kg}}{s}\right]$ is the mass flow of the fuel (for example 0.001 kg/s or 1 g/s)

(12) The differences in the mass/volume flow which are observed for each fuel injector with respect to the other fuel injectors can subsequently be used to improve the accuracy of the metering by adapting the individual actuation times of a solenoid valve of the fuel injector.

(13) It can be observed that the temperature of the heater and the power of the heater are still not a direct measure of the mass flow through the respective fuel injector. In order to determine said mass flow, additional information is required, for example the fuel-forward run temperature, statistical and dynamic properties of the energy transfer from the heater to the fuel as well as losses as a result of outputting of energy to the surroundings, which can never be entirely avoided. However, this does not require any additional expenditure whatsoever.

(14) After a relatively long stationary time of the internal combustion engine or of the associated vehicle, the oil temperature and the fuel temperature become equalized to such an extent that the value of the oil temperature can be used as a fuel forward run temperature.

(15) The mechanism of the energy transfer from the heater to the fuel is very stable, with the result that in practice one determination during a development phase is sufficient to generate a sufficiently accurate behavior model of the thermal energy transfer from the heater or the heating device to the fuel flowing through the fuel injector. This model, which is also referred to for short as the heater model in this document, can then be used in the vehicle for precisely determining the fuel temperature and the heating power which is input.

(16) Furthermore, after a relatively long stationary time of the internal combustion engine, the first heating phase can be used to adjust the various heaters which are respectively assigned to a fuel injector.

(17) According to the exemplary embodiment explained here, in this heating phase a predefined, regulated heating power P.sub.manip1 . . . 4 is fed in to the heater with the fuel injector closed, until a setpoint temperature is reached. Observing the individual time periods until the setpoint temperature is reached permits a comparison between the various heaters.
E.sub.manip1 . . . 4=t.sub.1 . . . 4.Math.P.sub.manip1 . . . 4(2)

(18) In the equation (2) the following applies: E.sub.manip1 . . . 4 [Ws]=manipulated value of the energy of the heaters 1 . . . 4 t.sub.1 . . . 4 [s]=heating time period of the heaters 1 . . . 4 P.sub.manip1 . . . 4 [W]=manipulated value of the power of the heaters 1 . . . 4

(19) The (thermal) masses of the heater/fuel injector and the fuel located in the fuel injector fluctuate only to a minimum degree. Likewise, the change in temperature in all the heaters is detected by similar observation paths, with the result that hardly any differences can be observed here either.
E.sub.calc1 . . . 4=T.sub.1.Math.(c.sub.p1.Math.m.sub.1+c.sub.p2.Math.m.sub.2)=const(3)

(20) In the equation (3) the following applies: E.sub.calc1 . . . 4 [Ws]=computational actual value of the energy of the heaters 1 . . . 4

(21) $c_{p1}\left[\frac{\mathrm{Ws}}{\mathrm{kg}.Math.K}\right]=\mathrm{specific}\mathrm{thermal}\mathrm{capacity}\mathrm{of}\mathrm{the}\mathrm{fuel}\left(\mathrm{for}\mathrm{example}\mathrm{ethanol}\right)$$c_{p2}\left[\frac{\mathrm{Ws}}{\mathrm{kg}.Math.K}\right]=\mathrm{specific}\mathrm{thermal}\mathrm{capacity}\mathrm{of}\mathrm{the}\mathrm{fuel}\mathrm{injector}\left(\mathrm{substantially}\mathrm{steel}\right)$ T.sub.1 [K]=temperature difference during the heating process m.sub.1 [kg]=mass of the fuel in the fuel injector m.sub.2 [kg]=mass of the body of the fuel injector

(22) Correspondingly, the heating time periods t.sub.1, t.sub.2, t.sub.3 and t.sub.4, of the individual fuel injectors are actually intended to be identical. However, in fact in practice these heating time periods t.sub.1 . . . 4 actually differ, which is essentially due to differences in the heating power which is actually present at the heater.

(23) A mean value t.sub.avg of the individual heating time periods t.sub.1 . . . 4 can be determined from the measured heating time periods t.sub.1 . . . 4. The deviations from the mean value t.sub.avg then permit the actual heating power of the heaters of the individual fuel injectors to be determinedreferred to a mean valuewithin the scope of a standardization process.

(24) $\begin{array}{cc}{t}_{\mathrm{avg}}=.Math.t_{1\mathrm{.Math.}4}4& \left(4\right)\\ P_{\mathrm{stand}1\mathrm{.Math.}4}=\frac{t_{\mathrm{avg}}}{t_{1\mathrm{.Math.}4}}.Math.P_{\mathrm{manip}1\mathrm{.Math.}4}& \left(5\right)\end{array}$

(25) These standardized heating powers can then be used for more precise determination of the various fuel mass flows (and therefore of the volume flows) by the fuel injector.
P.sub.stand1 . . . 4=c.sub.p.Math.T.Math.{dot over (m)}.sub.1 . . . 4(6)

(26) FIG. 2 illustrates, in the form of a flowchart for a four-cylinder engine, a procedure for standardizing the predetermined electrical heating power for four electric heating devices which are respectively assigned to a fuel injector. During this standardization procedure, the corresponding heater with a predefined test heating power is operated for each fuel injector with the fuel injector closed before the start of the internal combustion engine (BKM) and that time period (heating time) until a predefined setpoint temperature is reached is determined. An average heating time period t.sub.avg is determined from the specific heating time periods. Then, the standardized heating power P.sub.1 . . . 4stand is calculated for each heater using equation (5), on the basis of the average heating time period t.sub.avg, the previously measured heating time period and the predefined, regulated heating power P.sub.manip1 . . . 4 which is used during the heating process.

(27) It is to be noted that the bottom line of the flowchart illustrated in FIG. 2 can in practice be run through repeatedly in the form of an iterative optimization.

(28) FIG. 3 illustrates, in the form of a flowchart for a four-cylinder engine, a method for determining the correction values, necessary for cylinder equalization, for the metering of fuel for each individual cylinder. In this context, after the start of the internal combustion engine (BKM) the heater of each of the fuel injectors is operated with the previously calculated standardized heating power P.sub.1 . . . 4stand. On the basis of knowledge of the fuel forward run temperature T.sub.in, the temperature-measuring functionality of the respective heater determines the increase in temperature T, brought about by the heating process, of the fuel flowing through the fuel injector. On the basis of this increase in temperature T which is determined individually for each fuel injector, the mass flow dm/dt of fuel which flows through the respective fuel injector is determined taking into account equation (6).

(29) Then, an average fuel mass flow dm.sub.1 . . . 4avg/dt is calculated from the individual fuel mass flows dm.sub.1 . . . 4/dt. On the basis of the individual fuel mass flows dm.sub.1 . . . 4/dt and the calculated average fuel mass flow dm.sub.1 . . . 4avg/dt, a correction value dm.sub.1 . . . 4.sub._.sub.corr/dt is then determined for each fuel injector. This correction value dm.sub.1 . . . 4.sub._.sub.corr/dt is then used to actuate the individual fuel injectors in a modified fashion (in particular by adapting the opening times and/or closing times of the respective fuel injector), with the result that the individual cylinders of the internal combustion engine are at least approximately equalized with respect to their fuel mass fed in.

(30) At this point, it is to be noted that the quantity correction illustrated in FIG. 3 can in practice preferably take place in the form of a control loop which is repeated continuously.