EP1272754A1

EP1272754A1 - Method for the diagnosis of the voltage control for a piezoelectric actuator of an injection valve

Info

Publication number: EP1272754A1
Application number: EP01911413A
Authority: EP
Inventors: Johannes-Joerg Rueger; Matthias Mrosik; Volker Pitzal; Udo Schulz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-04-01
Filing date: 2001-02-02
Publication date: 2003-01-08
Anticipated expiration: 2021-02-02
Also published as: DE10016476A1; US20040008032A1; US6820474B2; EP1272754B1; ES2248289T3; WO2001075289A1; DE50107910D1; JP2003529714A

Abstract

The invention relates to a method for the diagnosis of a control voltage for a piezoelectric actuator of an injection valve. The control voltage is measured for the individual phases of the injection procedure. A corresponding tolerance band (B1 ... B4) is provided for each control phase. Said band is placed above the desired value of the control voltage (Ua). The tolerance regions (B1 ... B4) are determined according to operating and/or environmental conditions. When the corresponding tolerance regions are not obtained for the individual control cycles, said measuring errors are counted in repeated measurements. A permanent error is diagnosed when a predetermined number of the measuring errors is exceeded. The counter is set back when the number has not been exceeded after a while. The error memory can be set back during service by means of a service plug when an error occurs.

Description

Method for diagnosing the voltage control for a piezoelectric actuator of an injection valve

State of the art

The invention relates to a method for diagnosing the control voltage for a piezoelectric actuator of an injection valve according to the preamble of the main claim. It is already known to use piezoelectrically driven injection valves, in particular for a common rail system. To initiate the injection process, the actuator is actuated with a corresponding voltage, so that a valve needle opens or closes the injection channel for the injection process due to its change in length. Since the injection medium, in particular fuel for an internal combustion engine, is under high pressure, an exact opening and closing duration of the injection valve is required for the highly precise metering of the injection quantity. In particular in the case of injection valves with a double-switching control valve, the problem arises that due to the hysteresis behavior of the piezoelectric

Actuators are required for the closed position in the second seat as well as for the two 'open' positions depending on the switching direction. If the intended control voltage of the actuator is not reached, the injection can be interrupted and thus Uneven running of the engine, deterioration of the exhaust gas and deterioration in comfort come.

Advantages of the invention

In contrast, the method according to the invention with the characterizing advantages of the main claim has the advantage that simple monitoring of the activation process is possible for each activation by forming a tolerance band. It is particularly advantageous that the tolerance bands are set taking into account system and injection conditions, so that a plausibility check can easily determine whether the desired control voltage was present for the current injection cycle.

The measures listed in the dependent claims allow advantageous developments and improvements of the method specified in the main claim. It is particularly advantageous that the

Control voltage is measured in the area of the actuator terminals, so that line interruptions up to the actuator are detected at the same time.

In the case of injection systems with multiple injection within a drive cycle, it is advantageous that the desired level of the drive voltage is monitored in each phase of the injection. This ensures that every injection pulse is monitored and errors are easily identified.

The symmetrical position of the tolerance bands around the setpoints ensures that over- or understeer are recognized to the same extent. In the case of an injection valve with a double-switching control valve, there are at least four voltage levels for the individual switching states, which can advantageously be monitored in a simple manner without additional effort.

If one of the specified tolerance bands is not reached, there is an error that can lead to an injection fault, incorrect injection or engine damage.

An error analysis can be carried out in a simple manner, in particular by multiple measurement and counting of the incorrect measured values. For example, if an error occurs only sporadically, this can also be an indication of a harmless malfunction. In this case the counter is automatically reset.

Only when the errors occur continuously can it be concluded that the corresponding actuator or the corresponding injection valve is not working properly. In the event of such an error, if a permanent

Control deviation is present, can be switched from "control voltage control" to "control voltage control" in an alternative embodiment in order to advantageously maintain at least one emergency operation.

However, if the actuator itself is defective, it is switched off so as not to damage the control unit with its output stage.

It is also advantageous to maintain the last selected control voltage if it can be assumed that, for example, the control does not work as desired. An error that has occurred is advantageously stored so that it can be traced, for example, in the workshop and the corresponding component can be replaced.

In particular to meet consumption and

The use of the method in a common rail injection system appears to be advantageous for exhaust gas requirements.

drawing

An embodiment of the invention is shown in the drawing and explained in more detail in the following description. Figure 1 shows an injection valve with a double-switching control valve, Figure 2 shows a diagram with a control characteristic, Figure 3 shows three

Function diagrams, FIG. 4 shows a voltage diagram, FIG. 5 shows a block diagram for voltage regulation and FIG. 6 shows a block diagram for gradient regulation.

Description of the embodiment;

Figure 1 shows a schematic representation of an injection valve 1 with a central bore. An actuating piston 3 with a piezoelectric actuator 2 is introduced in the upper part, the actuating piston 3 being firmly connected to the actuator 2. The actuating piston 3 closes off a hydraulic coupler 4 at the top, while at the bottom there is an opening with a connecting channel to a first seat 6 in which a piston 5 with a

Closure member 12 is arranged. The closing member 12 is designed as a double closing control valve. It closes the first seat 6 when the actuator 2 is at rest. When actuator 2 is actuated, ie when a control voltage Ua is applied to terminals +, -, actuator 2 actuates the actuating piston 3 and, via the hydraulic coupler 4, presses the piston 5 with the closing member 12 m in the direction of a second seat 7. Below the second seat, a nozzle needle 11 is attached in a corresponding channel, which outlet in the high pressure channel (common rail pressure) 13 closes or opens, depending on which control voltage Ua is present. The high pressure is supplied through the medium to be injected, for example fuel for an internal combustion engine, via an inlet 9. Via an inlet throttle 8 and an outlet throttle 10, the

Flow rate of the medium in the direction of the nozzle needle 11 and the hydraulic coupler 4 controlled. The hydraulic coupler 4 has the task, on the one hand, of increasing the stroke of the piston 5 and, on the other hand, of decoupling the control valve from the static temperature expansion of the actuator 2.

The mode of operation of this injection valve is explained in more detail below. Each time the actuator 2 is actuated, the actuating piston is moved 3 m in the direction of the hydraulic coupler 4. The piston 5 with the closing member 12 also moves in the direction of the second seat 7. Part of the medium located in the hydraulic coupler 4, for example the fuel, is thereby printed out via leakage gaps. The hydraulic coupler 4 must therefore be refilled between two injections in order to maintain its functional safety.

A high pressure prevails over the inlet channel 9, which in the common rail system can be, for example, between 200 and 1600 bar. This pressure acts against the nozzle needle 11 and keeps it closed against the pressure of a spring, not shown, so that no fuel can escape. If the actuator 2 is now actuated in the sequence of the control voltage Ua and thus the closure member 12 m in the direction of the second Seat moves, then the pressure in the high pressure area decreases and the nozzle needle 11 releases the injection channel. Since the hydraulic coupler 4 has a much lower pressure, for example only 10% of the high pressure, the hydraulic coupler 4 becomes again after the control voltage Ua is reduced befullt

The diagram in FIG. 2 shows a control characteristic for the actuator 2. Depending on the control voltage Ua, the stroke, i.e. the change in length of the actuator 2 is plotted. Because of the double-closing control valve 12, the actuator 2 has two closed positions. In the end position 1, the closing member 12 is in contact with the first seat 6 when there is no drive voltage Ua in the actuator 2. This position is marked with 'bottom closed' or 'bottom'. The second closed position in position 2 is reached when the closing member rests on the second seat 7. In this case, the highest control voltage Ua has to be applied. This position is called 'top closed' or 'top'. Between these two positions 1, 2 are the

Hysteresis characteristics a and b, which are traversed depending on the direction of movement. For example, if the closing member 12 moves along the characteristic a from position 1 m towards position 2, then the control voltage Ua must be increased accordingly. The position

'Open' or 'up' is then reached in position 3. This position represents an intermediate position of the closure member 12 between the two seats 6 and 7. In the opposite case, when the closure member 12 moves from position 2 m towards position 1, the characteristic curve b is traversed. The 'open' position is reached in point 4. This point is labeled 'down' or 'open'. The two voltages 'down' or 'up' are therefore possible for the open position 'open'. In practice it has been shown that these voltages in addition to the hysteresis property of the actuator 2 is influenced by the different force ratios of the respective switching direction.

In FIG. 3, the injection parameters Vent, Ua and TR for one are for three function diagrams

Quadruple injection applied to an injection valve 1 over time t. The upper diagram shows the injection duration for the injections E _lr E ₂ , E ₃ and E ₄ . The designation 1 means that the valve vent is open. At 0 the valve Vent is closed. The

Injections can be pre, main and post injections for a single injection cycle on an injector. In a further embodiment of the invention, injection cycles with different designs can alternatively be provided

The middle diagram shows the control voltage Ua for the actuator 2 for the individual injections, so that the injections E ₁ ... E ₄ can take place. The lower diagram shows the trigger TR for the control of the control voltage Ua at the corresponding times t _x , t ₂ for the first injection, t ₃ , t ₄ for the second injection, t ₅ , t ₆ for the third injection and t ₇ , t ₈ for the fourth injection. It is noteworthy that the control voltage Ua m varies depending on the switching direction and the position of the closing element 12. For example, the control voltage Ua is highest between times t ₄ t _5. Here, the closing member 12 is in contact with the second seat 7, so that no injection can take place. Likewise, at voltage Ua = 0 there is no injection.

The function of the monitoring voltages according to the invention, as explained for FIG. 3, will now be explained in more detail with reference to FIG. For each voltage level for the individual positions of the Closing member 12, a tolerance band B ₁ , B ₂ , B ₃ , B _{4 is} formed. This tolerance band is formed on the basis of operating parameters of the injection system, the internal combustion engine or environmental conditions. In the case of a common rail system, it is, for example, the pressure (rail pressure), the temperature, engine speed, etc. Corresponding control circuits are proposed in FIGS. 5 and 6 and will be explained in more detail later.

The control circuit specifies a setpoint control voltage for the control voltage Ua, which is necessary to control the actuator 2, taking into account the individual parameters. Corresponding tolerance bands B ₁ to B _{4 are} preferably placed symmetrically around these target values for the control voltage Ua. FIG. 4 again shows a multiple injection for an injection cycle, which proceeds as follows. Up to time t _x , the control voltage Ua is in the range of 0 V. Here, the tolerance _band B _{x is set} accordingly for the voltage U _BoCtom . This voltage corresponds to position 1 according to FIG. 2. The tolerance band B _{3 is} provided for the 'open' position according to voltage U _up . Correspondingly, the tolerance band B ₄ for the voltage Uτ _{oP is} provided for the second end position m position 2 (FIG. 2). When the closing member 12 moves towards the first seat 6, the tolerance _band B ₂ corresponding to the voltage U _{dowπ is also} provided. The times t to t ₆ represent the trigger points at which the voltage rises or falls. Before and after these times, the output voltage Ua is measured with an existing measuring device, which is preferably connected to the connecting terminals of the actuator 2, and a fault device is used to check whether the setpoints for the control voltages Ua have been reached. If the target values were not reached for one or more tolerance bands in repeated cycles, the number of incorrect measurements is counted and saved. If the number of errors or incorrect measurements exceeds a predetermined threshold value, it can be assumed that there is a defect. For example, the control circuit may be faulty or there may be a fault in the wire harness. In the other case, if the predetermined threshold is not exceeded, there may have been faults that are not critical for further operation. In this case, the error memory is deleted again because only a 'temporary defect' was detected.

In the event of a final defect, the actuator can advantageously only be reset via a diagnostic interface as part of a service. In an alternative embodiment, the error is identified anew with each driving cycle. Both cases can be provided depending on the application.

As a further alternative, it is provided to go from the control mode to the control mode when control of the control voltage no longer appears possible. In this case, it is advantageous, as it were, to freeze the control voltage Ua last set or the controller outputs, as described for FIGS. 5 and 6, and to continue using them.

Two alternative exemplary embodiments for regulating the control voltage or its gradients are explained in more detail below.

FIG. 5 shows a block diagram for regulating the voltage level Ua in a schematic embodiment. First, a subtractor 51 from the inputs a and b supplied setpoints and actual values for the control voltage Ua form a difference value. This is compared in a downstream comparator 52 with the voltage level in the assigned tolerance band BI ..B4 (eg lower threshold S11, upper threshold S12). The output is connected to an error debouncer 58. If the measured value is in the range 0, then there is no error. If the value is 1, then there is an error and a corresponding control signal is given to the changeover switch 56. At the same time, the difference value is fed to a downstream controller 53 and fed to the changeover switch 56 via a limit value transmitter The output value is supplied to a limiter 57, which outputs the control voltage Ua at an output cde for the actuator 2. According to the invention, the switchover takes place when the difference value for a predetermined number of measured values lies outside the respective tolerance band.

The mode of operation of FIG. 6 is described below. While the setpoint Ua is essentially determined by the rail pressure and the actuator temperature for the voltage control, the actuator voltages are decisive for the calculation of the gradient setpoints dU / dt. This can be seen from the block diagram in FIG. 6. The cylinder-specific voltage value is fed via an input b to a differential element 61 in order to form the desired gradient characteristics. This is subtracted in a subtractor 62 from an actual gradient value, which was also fed to the subtractor via an input a. The gradient difference is fed to a comparator 63, which compares it with the predetermined tolerance band B1 ... B4 (for example lower tolerance value S13, upper tolerance value S14). The output signal arrives via an error debouncing 70 to the control input of the switch 66.

Furthermore, the differential signal from the differentiating element 62 reaches a controller 64 and then via one

Limit transmitter 65 to the changeover switch 66. Similar to FIG. 5, the signal can be frozen or, after linking in positions 67 and 68, fed to a limiter 69 to limit the current value for the actuator 2. In addition, the cylinder-specific gradient setpoint is added in position 67. In position 68, a capacitance value for the actuator 2 can be entered via an input c. Furthermore, inputs f and g are provided for the minimum / maximum of the current limitation 69. The current value is available at output h.

The calculations are preferably always carried out individually for each cylinder of the internal combustion engine in order to obtain an optimal injection.

Claims

Expectations

1. Method for diagnosing the control for a piezoelectric actuator of an injection valve, wherein the actuator brings a nozzle needle to an 'open' or a 'closed' position and the control voltage (Ua) of the actuator (2) is used to measure the individual control phases by means of a measuring device is measured, characterized in that a tolerance band (Bi, ... B ₄ ) for the control voltage (Ua) and / or the voltage gradient is defined for each control phase, the tolerance band (B ₁ ... B ₄ ) taking into account System and injection conditions, for example the pressure, the temperature, and that a diagnostic test is carried out in such a way that if the voltage level is not reached with the specified tolerance bands CB ₁ ... B ₄ ), an error message is output and / or saved.

2. The method according to claim 1, characterized in that the control voltage (Ua) is measured in the region of the actuator terminals (+, -).

3. The method according to claim 1 or 2, characterized in that in a multiple injection with a Driving course cycle the driving voltage (Ua) is measured in each phase of the driving course cycle.

4. The method according to claim 3, characterized in that the target value for the control voltage (Ua) is determined as a function of the line pressure in the high pressure system and that the tolerance bands (B ₁ ... B) are preferably placed symmetrically around the target values.

5. The method according to any one of the preceding claims, characterized in that the injection valve (1) is designed with a double-switching control valve (5) and that the tolerance bands (B ... B ₄ ) for the voltage levels 'bottom', 'up' , 'Top' and / or 'down' are formed.

6. The method according to any one of the preceding claims, characterized in that when one of the predetermined tolerance bands (B1 ... B4) is not reached, the actuator (2) is discharged in order to go into a safe state.

7. The method according to any one of the preceding claims, characterized in that when the predetermined tolerance band (B1 ... B4) is not reached, the measured values are not used for further calculations.

8. The method according to any one of the preceding claims, characterized in that it is checked for a predetermined number of measuring cycles how often the drive voltage

(Ua) has not reached the expected tolerance band (B ₁ ... B ₄₎ .

9. The method according to claim 8, characterized in that when the predetermined number of measuring cycles of "Control drive voltage" is switched to "Control drive voltage".

10. The method according to claim 8 or 9, characterized in that at least the relevant actuator (2) is switched off when the predetermined number of measuring cycles is reached.

11. The method according to claim 8 or 9, characterized in that when the predetermined number of measuring cycles is reached, the last determined output variable of the regulator for the voltage level and / or for the gradient is maintained.

12. The method according to claim 8, characterized in that when falling below a predetermined limit for the number of measured errors, the actuator (2) is recognized as functional.

13. The method according to claim 12, characterized in that the error memory is reset.

14. Use of the method according to one of the preceding claims for an injection valve (1) a common rail system of a motor vehicle engine.