WO2010023041A1

WO2010023041A1 - Method for operating a fuel injection device of an internal combustion engine

Info

Publication number: WO2010023041A1
Application number: PCT/EP2009/059433
Authority: WO
Inventors: Hans-Peter Lehr; Erik Tonner
Original assignee: Robert Bosch Gmbh
Priority date: 2008-08-25
Filing date: 2009-07-22
Publication date: 2010-03-04
Also published as: DE102008041527A1

Abstract

The invention relates to a method for operating a fuel injection device of an internal combustion engine comprising an injection valve (1), wherein the injection valve (1) comprises a piezoelectric element (2) and a control valve (15) having a valve member (16) and at least one valve seat (22), wherein an electric potential at the piezoelectric element (2) is detected and analyzed during the charging of the piezoelectric element (2). In this manner it is possible to periodically detect any possibly occurring drift of the piezoelectric element (2) and/or any wear and tear at the control valve (15) during the entire life of the internal combustion engine, and to take the same into consideration accordingly when calculating the actuation times of the fuel injection device (1).

Description

title

Method for operating a fuel injection device of an internal combustion engine

description

State of the art

The invention is based on a method for operating a

Fuel injection device of an internal combustion engine, in particular an internal combustion engine of a motor vehicle, according to the features of the preamble in claim 1. The invention also relates to a corresponding computer program, an electrical memory and a control device.

From DE 10 2006 058 742 a method is known in which the closing of the nozzle needle is detected by a corresponding monitoring of a piezoelectric actuator.

Disclosure of the invention

The invention is based, even for injectors in which the nozzle needle is controlled by a valve, to provide a method which allows the monitoring of the state of the control valve, the task.

This object is achieved by a method for operating a fuel injection device, in particular a motor vehicle with an injection valve, wherein the injection valve comprises a piezoelectric element and a control valve with a valve member and a valve seat, achieved in that the piezoelectric element is charged, and that of the the second time derivative is formed on the piezoelectric element during the charging process and that the time at which the second time derivative of the voltage has a maximum is considered as corresponding to the time of impact of the valve member on the valve seat size.

By monitoring the voltage curve on the piezoelectric element during the charging process according to the invention, it is possible to continuously monitor the state of the injection device and in particular of the control valve and to compensate for changes in the injection device by corresponding changes in the control of the injection device.

The invention is based on the finding that a measure of the state of the injection device or of the control valve can be obtained from the evaluation of the voltage profile. The state of the injector and with it also the switching time of the control valve is subject to aging and wear-related changes over the life of an internal combustion engine. The inventive method determines the time at which a valve member of the control valve impinges on the valve seat. From this, the switching time of the control valve can be determined. Since this switching time for the optimal control or fuel metering in the combustion chamber of the internal combustion engine is of considerable importance, this switching time can be detected periodically using the inventive method over the entire life of the internal combustion engine and in the calculation of the driving time and the driving times of the piezoelectric element of the fuel injection device be considered accordingly. This makes it possible to keep the operating behavior of the fuel injection device controlled according to the method of the invention independent of aging, drift and mechanical wear, over the entire service life of the internal combustion engine to almost constant level. As a result, noise behavior, smoothness and emission behavior of the internal combustion engine remain at a consistently high level.

In order to determine the time of impact of the valve member on the valve seat even more accurately, a delay time constant, which is between the impact of the valve member on the valve seat and the occurrence of the maximum of the second time derivative of the voltage applied to the piezoelectric element taken into account. This delay time ΔT is essentially determined by the mechanical properties, in particular mass inertia and dimensions of the coupler, and therefore almost constant over the entire life of the fuel injector. Therefore, it is possible without significant effort to take into account this size in the calculation of the switching time of the control valve and thereby determine the switching even more accurate even more accurate. In order to perform the inventive method in various operating conditions of the internal combustion engine, in particular injection pressure and driving time, is further provided during the implementation of the method according to the invention to increase the drive voltage and indeed to a value which is so high that the valve member of the control valve reached the valve seat during the charging process. Usually piezoelectric elements are supplied with approximately 160V drive voltage. Since it is not possible in all operating points of the internal combustion engine to achieve with this drive voltage, that the valve member impinges on the valve seat during the charging process, it is provided according to the invention to increase the drive voltage during implementation of the method by about 50%. This ensures that at different injection pressures and small amounts of fuel to be injected, the valve member impinges on the valve seat. Of course, this effect can also be ensured by the fact that the charging process is extended accordingly. A combination of increase from the drive voltage and extension of the charging process may be provided according to the invention.

Due to the changes in the drive voltage and / or the duration of the charging process, the opening time of the nozzle needle changes. As a result, there may also be changes in the amount of fuel injected. These changes can be made by changing the injection durations during the performance of the invention

Fully compensated. As a result, it is possible for the method according to the invention also during normal operation of the internal combustion engine, that is, when the internal combustion engine outputs torque, are performed. As a result of the compensation claimed according to the invention, the torque output by the internal combustion engine does not change, so that the driver of a vehicle who is equipped with a control according to the invention of the internal combustion engine does not have to accept loss of comfort.

In order to obtain comparable and reproducible results, it is further provided to regulate the charging current during the test drive of the piezoelectric element to a predetermined value. Also, no additional effort is required because anyway the charge current must be controlled at each activation of the piezoelectric element.

Since the method according to the invention is above all suitable for detecting the drift of the piezoelectric element, aging and wear phenomena of the fuel injection in general, but in particular of the control valve, and it is only these changes that take effect over many operating hours sufficient to perform the inventive method periodically, that is, for example, after a predetermined number of several hours of operation and by the obtained values for the switching time of the control valve or the time of impact of the valve member on the valve seat to use accordingly in the control of the internal combustion engine.

The aforementioned object is also achieved by a computer program, an electrical memory on which a computer program is stored, and a control device for an internal combustion engine, which is prepared for carrying out a method according to one of claims 1 to 8.

Other features, applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which are illustrated in the figures described below. All described or illustrated features, alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing.

drawing

Show it:

Figure 1 is a suitable for carrying out the method according to the invention fuel injection device;

Figure 2 shows the control of an injector in normal operation; and

Figures 3 and 4 are diagrams, based on which the inventive evaluation of the voltage of the piezoelectric element is shown and explained.

The injection valve 1 according to FIG. 1 has a piezoelectric element 2 which comprises a multiplicity of piezoelectrically active layers 4 connected in series. The piezoelectric element 2 is driven via terminals 7 by a control unit, not shown.

The piezoelectric element 2 is connected on the one hand with a housing wall 6 and on the other hand with a control piston 8 frictionally. The actuating piston 8 terminates with its element 2 facing away from the end face 9 from a hydraulic coupler 10. The hydraulic coupler 10 in turn acts on a guided in a connecting channel 12 actuator piston 14, at its end facing away from the coupler 10 a control valve 15 shown a valve member 16 is arranged. The exemplary control valve 15 shown in Figure 1 is designed as a double-closing control valve. However, the invention is not limited to injection valves with double-closing control valves 15.

In the illustrated position, which corresponds to a rest position of the element 2, the valve member 16 closes a first valve seat 18 of a valve chamber 20. In a second closed position, which corresponds to a maximum actuation of the actuator 2, the valve member 16 closes a second valve seat 22 of the valve chamber 20th

Via an opening in the second valve seat 22, the valve chamber 20 is connected to a guide channel 24, which is connected on the input side via a connecting piece 26 to a pressure channel, not shown, of a common rail fuel supply system of a motor vehicle. Alternatively, the injection valve 1 can also be part of a fuel supply system with individual pressure generation and supply of the injection nozzles.

In the guide channel 24, a nozzle needle 28 is arranged, which releases or closes a fuel outlet 30 of a branched off from the connecting piece 26 fuel passage 32 depending on a voltage applied to the element 2 via the terminals 7 drive voltage. To set functional pressure conditions during operation of the injection valve 1, the connecting piece 26 with an inlet throttle 34 and the guide channel 24 are provided with an outlet throttle 36.

Depending on the voltage applied to the element 2 drive voltage, the element 2 of the injection valve 1 expands in its longitudinal direction, so that the actuating piston 8 moves in the direction of the hydraulic coupler 10. As a result of the pressure increase caused thereby in the coupler 10, the actuating piston 14 with the valve member 16 arranged thereon also moves in the direction of the second valve seat 22.

In the connecting piece 26 of the injection valve 1, there is a high pressure, which may be for example between 200 and 1800 bar in a common rail system. This pressure acts against the nozzle needle 28 and keeps it closed, so that no fuel can escape through the fuel outlet 30. However, if the valve member 16 is now moved from the first valve seat 18 to the second valve seat 22 or vice versa due to the voltage applied to the element 2, then the pressure in the high pressure region of the guide channel 24 decreases, so that the nozzle needle 28 in the direction of the valve chamber 20th recedes and releases the fuel outlet 30. In this case, fuel injection takes place in an associated cylinder. The method described below for detecting the impingement of the valve member 16 on the second valve seat 22 is otherwise limited in any way to the injector 1 described above, but rather can also be used in alternatively designed injection valves.

In Figure 2, the drive voltage U is plotted in volts over time t. A first line 40 shows the time profile of the current I, which is used for loading and unloading the piezoelectric element 2 (see FIG. 1). For the process of the invention, especially the loading process is of importance. In the operating point shown in Figure 2, the loading of the piezoelectric element 2 begins at the time ti = 0.2 ms (ms = millisecond) and ends at about tι accordingly t = 0.3 ms. This means that the entire charging process took about 0.1 ms. This charging time is indicated in FIG. 2 by LZ.

A second line 42 shows the course of the voltage applied to the piezoelectric element 2 electrical voltage U. It can be seen that during the loading process in the period ti to tι the voltage U increases sharply. The voltage curve is also characterized during the loading process in that the slope of the voltage is continuously decreasing from a very high level. Kinks or other discontinuities can not be detected in the course of the tension during the loading process.

As soon as the piezo actuator is loaded, the charge state remains throughout

Injection process received. At a time t = 1 s, the injection process is terminated by discharging the piezoelectric element 2. This discharging process can be recognized by the fact that the current (see line 40) assumes negative values. At time t = about 1.075 ms, the piezoelectric element 2 is fully discharged again and the voltage has dropped to the value U = 0 volts. This driving operation of the piezoelectric element 2 corresponds to the prior art and is carried out in normal operation of the internal combustion engine.

In order to now recognize the switching time of the double-closing control valve 15 (see Figure 1), a possible aging of the piezoelectric element 2 and mechanical wear or malfunction of the double-closing control valve 15 and to take into account accordingly in the control of the fuel injection device 1, is at periodic intervals the Inventive method according to FIG. 3 is carried out. Again, the loading process starts at a time ti = about 0.1 sec (see the line 40 in Figure 3). Completed is the charging at the time t = tι, where tι = 0.25 s. In other words, in the control according to the invention, the charging process takes about 0.15 s.

A third line 44 shows the stroke of the piezoelectric element 2 in FIG. The stroke of the valve member 16 of the control valve 15 is represented by a fourth line 46. A fifth line 48 indicates the pressure in the coupler compartment 10. With another line 50, the stroke of the nozzle needle 28 is plotted over time.

It can be clearly seen from FIG. 3 that the drive voltage at the end of the charging process has been raised to approximately 230 V, whereas in normal operation (see FIG. 2) the voltage at the piezoelectric element is only approximately 160 V.

FIG. 4 shows a detail of FIG. 3 enlarged in order to better recognize the highly dynamic processes during the charging process. The numbering of the different lines in Figures 2, 3 and 4 are the same.

When the piezoelectric element 2 is charged, it performs a lifting movement (see the line 44). As a result, the valve member 16 of the double-closing control valve 15 also performs a stroke (see the line 46). It moves from its rest position and moves to the valve seat 22. The stroke of the valve member 16 is slightly delayed relative to the stroke of the piezoelectric element 2.

At time t ₂ , this state is reached and the valve member 16 of the control valve 15 rests on the valve seat 22. This is also expressed in FIGS. 3 and 4 by a horizontal course of the line 46 for times t> t ₂ .

With a slight time delay, the limitation of the stroke of the valve member 16 causes the piezoelectric element 2 to become blocked since the movements of the valve member 16 and the piezoelectric element 2 are coupled to each other via the hydraulic coupler.

At the same time there is also a strong increase in the pressure in the coupler space 10. The pressure increase can be, for example, 150 bar. This increased pressure in the coupler space 10 leads to a corresponding hydraulic force which acts on the piezoelectric element 2. This force leads to a change in length of the piezoelectric element 2. In FIG. 4, a first local maximum 52 in the line 44 is shown by way of example for such a pressure-induced change in length of the piezoelectric element 2. Due to the piezoelectric effect, the compression of the piezoelectric leads Element 2 also to a kink in the voltage curve at the piezoelectric element 2 (see reference numeral 54 in Figure 4).

This kink 54 (t = 1 ^) in the voltage curve of the piezoelectric element 2 acts in the form of a maximum of the second time derivative of the voltage curve. Since the voltage of the piezoelectric element 2 can be detected and evaluated by a control unit of the internal combustion engine very easily and without additional equipment, it is possible without additional hardware complexity and with little computational time to determine the second time derivative of the voltage curve in the control unit and evaluate.

The kink 54 takes place at the time t = ^{^} t ₃ . Because a maximum of the second temporal

Derivation of the voltage curve can also be easily determined internally by the control unit, can easily and accurately determine the time ^ in the manner just described invention.

Since the kink 54 in the course of the voltage of the piezoelectric element 2 is directly related to the seating of the valve member 16 on the valve seat 22, it is possible from the time t = t3 a statement about the time of impact of the valve member 16 on the To make valve seat 22.

This can be done in a simple manner by subtracting a delay time ΔT from the time t = t _{3 in} order to calculate the time at which the valve member 16 rests on the valve seat 22. In the present case, the amount of the

Delay time ΔT = ^{^} t ₃ - X ₂ . Since this delay time .DELTA.T is a constant quantity, it is sufficient to detect this once in a pattern in series manufactured injector and deposit as a constant value in the control unit. Then it is possible, after the determination of the time t _3, also to calculate the time t ₂ with the following equation:

t ₂ = t ₃ - ΔT

The switching time of the control valve 15 is determined by the time difference t ₂ - ti. The knowledge of this switching time SZ is essential for the precise control of a fuel injection device, since only then the fuel metering can be done with the required precision. However, since the switching time SZ can change in the course of one of many thousands of operating hours due to wear, drift of the piezoelectric element 2 or other external influences, it is possible with the aid of the inventive method, the switching time SZ or the time t ₂ periodically during the entire To record life of the internal combustion engine and store any changes occurring in the switching time or the time T2 in the control unit. These changed values can then be used as the basis for the subsequent calculations of the control or injection of the control of the fuel injection device, so that the quality of the control is independent of the drift and the wear within the fuel injection device.

Since the method of the invention requires no additional hardware, it is also very inexpensive to carry out.

Claims

claims

Method for operating a fuel injection device, in particular of a motor vehicle, having an injection valve (1), wherein the injection valve (1) comprises a piezoelectric element (2) and a control valve (15) with a valve member (16) and at least one valve seat (22), characterized in that the piezoelectric element (2) is charged to open the injection valve (1) such that the time course of the electrical voltage (U) across the piezoelectric element (2) during a charging process (t ₂ <t <t 0 of the detected from the time course of the voltage (U (t)) to the time of impact of the valve member (16) on the valve seat (22) and / or the switching time (SZ) of the control valve (15). is closed.

2. The method according to at least one of the preceding claims, characterized in that of the on the piezoelectric element (2) during the

Charging voltage applied (U), the second time derivative is formed, and that the time (t = ^) to which the second time derivative of the voltage (U) has a maximum than with the impact of the valve member (16) on the valve seat (22 ) corresponding size is considered.

3. The method according to claim 2, characterized in that the time of impact of the valve member (16) on the valve seat (22) from the time (t = ^) to the second time derivative of the voltage (U) has a maximum minus a delay time constant (ΔT) is determined.

4. The method according to any one of the preceding claims, characterized in that for carrying out the method, the electrical voltage (U _on Steue _r ) with which the piezoelectric element (2) is loaded compared to the normal operation is increased.

5. The method according to any one of the preceding claims, characterized in that the current (I) is regulated during the charging process.

6. The method according to any one of the preceding claims, characterized in that changes in the injected amount of fuel by the implementation of the

Be compensated by changes in the opening time of the fuel injection device.

7. The method according to any one of the preceding claims, characterized in that the switching time (SZ) of the control valve (15) is periodically determined and taken into account in the control of the fuel injection device.

8. Computer program, characterized in that it is programmed to carry out a method according to one of claims 1 to 7.

9. Electrical memory on which a computer program is stored, which is programmed for carrying out a method according to one of claims 1 to 7.

10. Control device, in particular for a motor vehicle, characterized in that it is prepared for carrying out a method according to one of claims 1 to 7.