EP1740813B1 - Method for determining the closing time for a closing body and circuit arrangement - Google Patents

Abstract

A method for determining the closure time for a valve, operated by a piezoelectric actuator, is disclosed. In order to record the closing time, the voltage at the piezoelectric actuator is recorded and the time is recorded at which the voltage has a maximum difference value from a comparison curve. The difference curve is generated between a start and an end point for a measured curve, comprising the voltage values applied to the piezoelectric actuator. A precise determination of the closing time can thus be carried out.

Description

The invention relates to a method for determining a closing time of a closing member according to the preamble of patent claim 1 and a circuit arrangement for determining the closing time of a closing member according to the preamble of patent claim 5.

In the field of automotive engineering are hydraulically controlled injection systems, such. B. a pump-nozzle system uses valves that are actuated with a piezoelectric actuator. For the hydraulically controlled injection system, determining the closing time of the valve, which adjusts the hydraulic pressure, is an important parameter that must be precisely detected and controlled.

Out DE 199 30 309 C2 a method and an apparatus for controlling the injection quantity in a fuel injection valve with a piezoelectric actuator is known. The fuel injection valve has a control chamber communicating in a high-pressure accumulator and with a control valve. In the control chamber prevailing pressures act on a movable nozzle body with a nozzle needle for opening and closing of injection holes. To open the injection valve, the control valve is actuated by the piezoelectric actuator. The voltage at the piezoelectric actuator is detected after its initial charging and from the measured voltage, the start of injection and / or the needle opening time of the injection valve is determined.

Out WO 03/104633 A1 Also, a method and apparatus for determining the closing time of a piezoelectric driven valve is known.

The object of the invention is to provide a robust and precise method for determining the closing time of the closing member of the piezoelectrically driven valve. In addition, the object of the invention is a To provide a circuit device with which the closing time of the piezoelectric actuator driven valve can be determined in a simple manner.

The object of the invention is achieved by the method according to claim 1 and by the circuit arrangement according to claim 5.

Further advantageous embodiments of the invention are specified in the dependent claims.

An advantage of the method according to the invention is that the closing time of the valve can be determined precisely. In order to determine the closing time, according to the invention a comparison straight line is laid between a start and an end point of a measuring interval, and the voltage applied to the piezoelectric actuator is detected during the measuring interval. Difference values are determined between the measured voltage values and the comparison straight line and the closing time is recognized at the time at which the difference value has the largest value within the measuring interval.

In a preferred embodiment, the measured voltage values are further processed as squared quantities. As a result, a precise detection of the closing time is possible.

In a further preferred embodiment, a closing time is only recognized if the difference value exceeds a specified comparison value. In this way it is avoided that a closing time is detected for a non-closed valve.

In a further preferred embodiment of the method according to the invention, a closing time is detected only when the sum of the difference values of the measuring interval exceeds a predetermined comparison sum. Also these others Prerequisite is to reliably detect a closing time.

• Figur 1 eine schematische Darstellung eines Einspritzventils, das nach dem Pumpe-Düse-Prinzip ausgebildet ist;
• Figur 2 einen schematischen Programmablauf zur Bestimmung der Schließzeit;
• Figur 3 Messkurve der am Aktor anliegenden Spannung während eines Schließvorganges des Ventils;
• Figur 4 die Messkurze mit einer Referenzkurve;
• Figur 5 eine Differenzkurve, die aus der Messkurve und der Referenzkurve gebildet ist; und
• Figur 6 eine detaillierte Darstellung der Schaltungsanordnung, die zur Erfassung der Schließzeit verwendet wird;

The invention will be explained in more detail below with reference to FIGS. Show it:

• FIG. 1 a schematic representation of an injection valve, which is designed according to the pump-nozzle principle;
• FIG. 2 a schematic program flow for determining the closing time;
• FIG. 3 Measuring curve of the voltage applied to the actuator during a closing operation of the valve;
• FIG. 4 the measuring curves with a reference curve;
• FIG. 5 a difference curve formed from the measurement curve and the reference curve; and
• FIG. 6 a detailed representation of the circuitry used to detect the closing time;

FIG. 1 shows schematically the structure of a pump-nozzle unit. The pump-nozzle unit is used for supplying fuel into a combustion chamber 1 of an internal combustion engine. The pump-nozzle unit has a pump 2, which compresses via a piston 3, which is guided in a cylinder 4, fuel. The piston 3 is driven directly or indirectly via a camshaft, not shown, of the internal combustion engine. In the cylinder 4, a first pressure chamber 5 is formed adjacent to the piston 3. The first pressure chamber 5 is connected via a fuel line 6 with a valve 7. The valve 7 serves to either close the fuel line 6 or to connect it to a low-pressure region 8. The pressure chamber 5 is also connected via a second fuel line 9 with an injection chamber 10 in connection. In the injection chamber 10, a nozzle needle 11 is arranged, the closing surfaces is associated with a sealing seat 41. The sealing seat 41 is arranged between injection holes 12 and the injection space 10. In the upper region of the injection chamber 10, the nozzle needle 11 has pressure surfaces 13. About the printing surface 13, the nozzle needle 11 is biased by a fuel pressure in the injection chamber 10 against a closing direction of the sealing seat 41 away. The nozzle needle 11 is biased by a spring element 15 on the sealing seat 41 via a pressure pin 14.

The valve 7 has a closing member 16 which is associated with a valve seat 17. The closing member 16 is in operative connection with a piezoelectric actuator 18, which is controlled by a control unit 19.

If the valve 7 is open, the piston 3 sucks in a suction upward fuel over the low pressure region 8, the valve 7 and the fuel line 6 in the pressure chamber 5. The low pressure region 8 is connected to a fuel tank. During a compression movement of the piston 3 downwards, the fuel is pressed back into the low-pressure region 8 when the valve 7 is open. The fuel lines, the injection space 10 and the second fuel line 9 are completely filled with power.

To start an injection, the valve 7 is closed by the control unit 19 and the piezoelectric actuator 18 in a compression stroke in which the piston 3 moves down. Thus, the fuel compressed by the piston 3 can not escape via the low-pressure region 8, but a high pressure is generated in the injection chamber 10. The high pressure lifts the nozzle needle 11 from the associated sealing seat 41. Consequently, fuel is discharged from the injection space 10 via the injection holes 12 into the combustion chamber 1 of the internal combustion engine. If the valve 7 is opened, that is, the closing member 16 lifted from the associated sealing seat 17 by the piezoelectric actuator 18, the fuel pressure in the fuel line 6 and thus also in the injection chamber 10 decreases. Consequently, the nozzle needle 11 is pressed back onto the sealing seat and the connection between the injection space 10 and the injection holes 12 closed. This ends the injection.

For a precise determination of the time at which the valve 7 is pressed with the closing member 16 back to the valve seat 17, the voltage applied to the piezoelectric actuator 18 voltage is evaluated. The piezoelectric actuator 18 is supplied via voltage lines 20 from the controller 19 with voltage. In addition, the control unit 19 detects via the voltage lines 20, the voltage applied to the piezoelectric actuator voltage. The control unit 19 thus has both a voltage source and a voltmeter. In addition, the control unit 19 is connected to a data memory 42.

The valve 7 is formed in such a way that in the de-energized state of the piezoelectric actuator 18, the closing member 16 is lifted from the valve seat 17 and thus the valve 7 is opened.

FIG. 2 shows a schematic program flow for performing the method. At program point 50, the control unit 19 detects various operating conditions, such. As the speed of the engine and the driver's request and then determines the beginning of the injection and the duration of the injection. For this purpose, the control unit 19 accesses corresponding data and characteristics which are stored in the data memory 42. At the following program item 51, the control unit 19 applies a corresponding voltage via the voltage lines 20 to the piezoelectric actuator 18. The piezoelectric actuator 18 then expands and presses the closing member 16 onto the valve sealing seat 17 during a compression stroke of the piston 3. In the following program item 52, the control unit 19 monitors the voltage applied to the piezoelectric actuator 18 in parallel with the application of the voltage to the piezoelectric actuator 18 , For this purpose, the control unit 19 detects at specified intervals the voltage which is at Actuator 18 is present. A diagram with a corresponding trace is in FIG. 3 shown.

FIG. 3 shows the measurement curve, which results from the detected voltage values, and which is stored by the control unit 19 in the data memory 42.

In the following program point 53, the control unit 19 determines a starting point TS and an end point TE of a measuring interval in the measuring curve. The starting point TS is preferably preset and is a fixed time after the beginning of the energization of the piezoelectric actuator. The end point is also preferably preset and is a fixed second time after the start of the energization of the piezoelectric actuator. In addition, the control unit 19 calculates in a following program point 54 a comparison straight line between the measured value of the starting point and the measured value of the end point. In a following program point 55, the control unit 19 determines, for each measured voltage value in the measuring interval between the starting point and the end point, the difference value to the corresponding value of the reference curve. For this purpose, the measured voltage value and value of the reference curve belonging to the same time are deducted from each other. The difference values are stored by the control unit 19 in the memory 21.

FIG. 4 shows a corresponding measurement diagram in which the starting point TS and the end point TE are drawn. In addition, the comparison line VG is shown in the form of a line with asterisks. The measured values of the voltage of the piezoelectric actuator detected by the control unit 19 are shown in the form of crosses and an approximated line MW.

Instead of the measured voltage values, the control unit 19 preferably uses squared voltage values, since thereby the determination of the closing time is possible in a more precise manner.

In the following program point 56, the control unit 19 determines the largest difference value between a measured voltage value and the simultaneous value of the reference curve within the measurement interval and assigns the time at which the largest difference value occurred, the closing time of the valve 7. In the presentation of the FIG. 4 If the closing time TF is also drawn.

In FIG. 5 the difference values between the measured voltage values and the time values of the comparison straight line are shown, wherein the difference values were determined on the basis of squared voltage values.

In a preferred embodiment, after the program point 56, it is additionally checked at the following program point 57 whether the calculated maximum difference value lies above a defined comparison value. If the comparison reveals that the maximum difference value is not above the comparison value, then no closing time of the valve 7 is detected. The specified comparison value was previously determined experimentally, for example. In this way, a malfunction of the valve 7 in the determination of the closing time can be filtered out.

In a further preferred embodiment of the invention, either in addition to the program point 57 or instead of the program point 57 at a following program point 58 from the control unit 19, the sum of the difference values is formed and compared with a comparison sum. If the comparison shows that the sum of the difference values is smaller than the comparison sum, then likewise no closing time of the valve is recognized. The comparison sum is also preferably determined experimentally and serves to filter out malfunctions of the valve, in which no closing of the valve takes place, when determining the closing time. The comparison of the sum of the difference values with the comparison sum makes it possible to obtain negative difference values in which the measured values Voltages above the comparison straight line, which however do not correspond to a closing of the valve, filter out. The comparison sum is preferably determined experimentally for the respective pump-nozzle unit.

FIG. 6 shows a detailed illustration of the circuit arrangement, which is preferably formed in the control unit 19.

The voltage detected at the piezoelectric actuator 18 is fed via an input 21 and a linearization device 22 to a second input of a switch 23. In the linearization module 22, the detected voltage value is squared and fed via an output to a second input of the switch 23. An output of the switch 23 is connected to a first calculation block 24 in connection. The first calculation block 24 limits the detection range in which the voltage is detected. Furthermore, a start block 25 and an end block 26 are provided which are each connected to a signal line to an input of the first calculation block 24. The start block 25 contains a start time for the measurement, which is determined by the control unit 19. The start time is passed to the first calculation block 24. The end block 26 includes an end time for the measurement, which is also set by the controller 19. The end time is passed on to the first calculation block 24. When acquiring the measurement curve, an entire injection process is recorded with a multiplicity of measured values, ie voltage values. For example, 40 measured values are recorded which have a defined time interval and are numbered consecutively with a continuous index. The time of the measurement can be determined from the start time, the defined time interval and the index. The first calculation block 24 gives the voltage values supplied by the switch 23, which is an entire measurement curve, as in FIG Fig. 4 represented, via a first output 27 to a second calculation block 29 on. The second calculation block 29 determines on the basis of the supplied voltage values within the measuring interval voltage reference values corresponding to the comparison line Fig. 4 represent. The second calculation block 29 forwards the voltage reference values to an adder unit 30 via an output. In addition, the linearized or nonlinearized voltage values of a measurement curve with a negative sign are fed to the adder unit 30 by the switch 23. In the adder unit 30, difference values for simultaneous voltage values and reference voltage values of the measurement curve are formed which are fed via an output of the adder unit 30 to an input of a third and a fourth calculation block 31, 32.

In the third calculation block 31, the maximum difference value is determined within the measurement interval defined by the start time and the end time and fed via an output to a fifth calculation block 34. In the fifth calculation block 34, the time of the maximum difference value and thus the closing time of the valve is calculated on the basis of the index of the maximum difference value and forwarded to the control unit 19 via an output. For this purpose, each index is assigned a time value in an allocation table. A second output 35 of the third calculation block 31 outputs the maximum difference value to a comparison device 36. Furthermore, a first memory field 37 is provided, in which a minimum comparison value is determined. The minimum comparison value has been determined experimentally. The first memory field 37 specifies a minimum voltage difference value, which is supplied to a second input of the comparator 36. The comparator 36 compares whether the maximum difference value is greater than or equal to the minimum difference value, and passes a signal via an output to a second comparator 38 when this condition is met.

The fourth calculation block 32 sums the difference values of the individual measurement points within the measurement interval of Trace on and outputs a sum difference value via an output to a third comparator 39 on. The third comparator 39 is connected to a second input to an output of a second memory array 40 in connection. In the second memory field 40, a minimum sum is stored, which is the third comparator 39 is supplied. The third comparator 39 compares the difference sum calculated by the fourth calculation block 32 with the minimum sum stored in the memory array 40. If the comparison of the third comparison device 39 reveals that the difference sum is greater than or equal to the minimum sum, then a signal is output to the second comparison device 38. If the comparison device 38 recognizes two signals at the two inputs, then the second comparison device 38 outputs an enable signal to the control signal 19, which confirms the validity of the detected closing time.

Depending on the selected embodiment, it is also possible to dispense with individual or all comparison devices 36, 39, 38 that carry out a plausibility check of the measured values.

Claims (5)

1. Method for determining a closing time of a valve which has a closing member which is actuated by a piezoelectric actuator, the electric voltage at the actuator being detected during a closing operation of the valve, the voltage being evaluated in order to determine the closing time,
   characterized in that voltage values for the voltage are detected in a measurement interval having a start point and an end point, in that a comparison curve is designated between the voltage values of the start point and the end point, in that difference values are determined between the measured voltage values and the contemporaneous values of the comparison curve for a plurality of measured voltage values, and in that the instant identified as closing time is that at which the difference value is greatest.
2. Method according to Claim 1, characterized in that the voltage values are used as squared magnitudes.
3. Method according to either of Claims 1 and 2, characterized in that a closing time is identified only when the difference value overshoots a designated comparison value.
4. Method according to one of Claims 1 to 3, characterized in that a closing time is identified on the condition that the sum of the difference values overshoots a designated comparison sum.
5. Circuit arrangement for determining a closing time of a closing member (16) of a valve (7) which is pressed by a piezoelectric actuator (18) against a valve seat (17) or raised from the valve seat (17), having a first means (19) for detecting the voltage, which detects the electric voltage at the actuator (18) during a closing operation of the valve (7), and having a second means (24, 29, 31, 34) which evaluates the voltage in order to determine the closing time,
   characterized in that a third means (24, 29) is provided which designates a measurement interval having a start point and an end point, in that a fourth means (29) is provided which designates a comparison curve between a measured voltage value of the start point and of the end point, in that a fifth means (30) is provided which determines difference values between the detected voltage values and the contemporaneous values of the comparison curve for a plurality of instants inside the measurement interval, and in that a sixth means (31) is provided which designates as closing time an instant at which the greatest difference value is present.

Images