MXPA99003814A - Method and device for controlling a capacitative actuator - Google Patents

Abstract

In order to obtain constant travel (ds) of a capacitative actuator, e.g. for a fuel injection valve in an internal combustion engine, over a large temperature range, the actuator is charged by a supply of predetermined energy i.e. a capacitor is discharged in a defined manner. Alternately, the current supplied to the actuator and the voltage released thereto are multiplied, the product is integrated and the integral value is compared with a predetermined set point value. The charging process is interrupted if the integral value reaches or exceeds the set point value.

Description

DEVICE AND PROCEDURE TO CONTROL A MEMBER OF CAPACITIVE ADJUSTMENT FIELD OF THE INVENTION The invention relates to a method and a device for controlling a capacitive adjusting member, in particular a piezoelectrically operated fuel injection valve of an internal combustion engine.

BACKGROUND OF THE INVENTION The piezo-adjustment members consist of a plurality of piezoceramic layers and form a so-called "stack", which when applying a tension modifies its dimensions, in particular its length s by a distance ds, or with pressure or traction Mechanics generates an electrical voltage. Various methods are known for controlling piezo-adjustment members, which behave electrically as capacitors, in which the tension existing in the piezo-adjustment member is monitored. As a criterion for the termination of the load, in all the known methods it is used to reach a certain tension in the piezo-adjustment member, if a costly measurement of the piezo-adjustment member dimension ds reached is not foreseen. An example of this is the old German Patent Application 1932872.1.

The electrical properties of a piezo-battery of this type vary with the temperature at which it is located. With increasing temperature, the capacity increases, but also the route. In the case of temperatures of approximately -40 ° C to + 150 ° C, to be considered for automotive applications, variations of up to a factor of 2 are observed. If, for example, a piezo-adjustment member is loaded on all points of operation at a constant voltage, which at low temperatures provides the necessary travel ds, at high temperatures a path is obtained that is considerably higher than required, which, in the case of fuel injection valves, with fuel pressure constant implies too large a quantity of fuel, or vice versa. Since the piezo-stack capacity is also higher at higher temperatures, much more charge and energy is used (E = 1/2 * C * U) than necessary. From US Pat. No. 5,387,834 a control circuit for a piezoelectric element of a matrix printer is known, in which a temperature sensor senses the temperature of the piezoelectric element. The control of this one takes place with times of load, which are stored in a table depending on the temperature.

From US Pat. No. 5,543,679 a control circuit for a piezoelectric element for operating a fuel valve is known, in which a supposedly constant load is taken from a capacitor and fed to the piezoelectric element by a transmitter- All variations of the circuit due to variations of temperature, humidity, tolerances of the components, aging, etc., are not taken into account. In Patent Abstracts of Japan, Vol. 018, No. 188 (E-1532), of March 31, 1994 and in Japanese Patent JP-A 05 344755, a control circuit for a piezoelectric element for operating a valve is disclosed of fuel, which the piezo-electric element is charged through a first regulated voltage with a constant amount of charge and, through a determination of capacity of the piezoelectric element from the voltage measured at the time of discharge, becomes to discharge completely to a second regulated negative voltage.

OBJECTIVES AND ADVANTAGES OF THE INVENTION The object of the invention is to carry out in such a way the use of the control of a capacitive adjustment member without a temperature sensor, which over the whole temperature range in which the adjustment member operates achieves a journey ds as constant as possible. It is also an object of the invention to provide a device for carrying out said method. This object is achieved according to the invention by means of the features recited in one of claims 1 or 2. Corresponding devices are indicated in claims 3 and 4. Research showed that the energy supplied to a capacitive adjustment member, it is a much more precise measurement of the distance ds than the applied voltage, and that a load with constant energy in the required temperature range, results in a simply more constant travel. The path varies approximately linearly with the voltage applied at a certain temperature. If the temperature varies, the path also varies with the constant voltage. In contrast, the path varies proportionally to the square of the energy supplied (ds ~ e-), but independently of the temperature. In the manufacture in large series of piezo-piles, the layer thickness of the respective piezo-layers is not exactly the same. For example, batteries of constant length s can be manufactured, but a different number of layers. This type of diverse batteries also find application when a defective fuel valve is replaced with another one. When charging this type of different batteries with constant voltage, even with constant temperature, different paths are traveled. An advantage of the control method according to the invention is that when charging an adjustment member with constant energy, this type of different batteries presents an approximately equal, constant travel, not only at a certain temperature, but also throughout the range of above indicated temperature. Another advantage of the control method according to the invention is that when recording the energy supplied to the adjustment member, not the load taken from a supply source or a capacitor, in the measurement or energy allocation are taken into account all circuit variations due to variations in temperature, humidity, component tolerances, aging, etc.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, with the aid of the drawing, two embodiment examples for controlling a capacitive adjusting member (piezo-adjustment member) to drive a fuel injection valve of an internal combustion engine are illustrated in more detail. . They show: Figure 1, a schematic connection plan of a first embodiment.

Figure 2, a schematic connection plan of a second exemplary embodiment. And Figure 3, a flow chart relating to the operation of the circuits according to Figures 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a first embodiment to control a piezo-adjustment member P of a fuel injection valve not shown in an internal combustion engine, by means of a control circuit ST, usually controlled by microprocessor . Between the positive pole + V and the negative pole GND of a power source V, there is a series connection of an electronic switch TI, controlled by the control circuit ST, a current limiting element, for example, a resistance R (or a coil) and a piezo-adjusting member P of the fuel injection valve with the length s. Parallel to the series connection of the piezo-adjustment member P and the resistance R, another electronic switch T2 is provided. The electronic transistor switches TI and T2 are controlled by the control circuit ST, which receives an external control signal st for the duration of the injection, for example, of an engine control apparatus (in which it may also be integrated the control circuit). In addition, with the TI switch in conductive position, the current i flowing to the piezo-adjusting member P, delimited by the resistance R, and the voltage u falling on the piezo-adjustment member P, can be measured and provide this data as other input dimensions to the control circuit ST. In the control circuit, a multiplier member X, an integrator I and a comparator K are arranged in series, indicated by dotted lines around, a multiplier member X being connected to the input of the integrator I, and its output with an input from the comparator K. To the other input of the comparator K a theoretical value G is supplied for the desired amount of energy. Based on the flow diagram shown in Figure 3, a procedure for operating the circuit according to Figure 3 is described, which can be applied on the circuit according to Figure 2, described below, starting from an initial state (state 0), in which both the TI and T2 switches are in a non-conductive position. TI = 0 means non-conductive; TI = 1 means driver. The same is valid for T2. For the st and k signals, it is valid: "1" means present, "0" means absent. With the start of a control signal st, which changes from 0 to 1 (state I), the TI switch passes to the driver. In this way, a current i delimited by the resistor R starts flowing from the positive pole + V of the voltage source, through the switch TI and the piezo-adjusting member P, towards the negative pole GND. In the piezo-adjusting member P the voltage u is produced: the piezo-adjustment member expands along the path ds to the length s + ds and opens the injection valve (state II), so that fuel is injected. Driven by the initial flank st 'of the control signal st, the integrator I is simultaneously discharged. Thus, at the start of each injection process, its output signal e = 0. The dimensions i and y fed to the control circuit ST, are multiply each other in the multiplier member X and the product p that appears in its output is then integrated into the newly downloaded integrator I. The output signal e of the integrator I is proportional to the energy e = J "uidt fed to the piezo-adjustment member P, and is supplied to the comparator K, where it is compared with a theoretical value G. As soon as it reaches or exceeds said value, the comparator emits a digital output signal k = 1 (state III). This output signal from the comparator k = 1 causes the control circuit ST to switch the TI switch to the non-conducting position (state IV), thereby completing the loading process of the piezo-adjusting member P. The adjusting member reached the desired travel ds, and with it, the fuel injection valve the desired opening, whereby, due to the constant fuel pressure, the amount of fuel injected is proportional to the opening duration of the adjustment member. The fuel injection valve, with the path ds assigned to the supplied energy e, remains open until the control signal st, st = 0 (state V) disappears. If the control signal becomes st = 0, the control circuit ST switches the switch T2 to the conducting position (state VI), whereby the piezo-adjusting member is discharged through the resistor R and the valve fuel injection closes. This concludes the injection process. The next and all the other injection processes are carried out in the same way. Figure 2 shows an example of simple embodiment of the circuit according to the invention, with a modification with respect to the circuit according to Figure 1, which consists in that, in the path of the load current of the piezo-adjustment member P is it introduces a constant current source Q, which charges the piezo-adjustment member P with a constant current i = const. Due to the known current intensity, the current measurement can be eliminated and, therefore, also the multiplication u * ia be carried out laboriously, as well as the multiplier member X. The only input dimension besides the control signal st, of the control circuit ST, is fed to the integrator I, whose output signal e is proportional to the power supplied. The other operation of the circuit agrees with that of the circuit according to Figure 1. The resistance, or else, the delimiting element of the current is required in this case only to delimit the discharge current and, therefore, is disposed between the piezo- adjustment member P and switch T2.

Claims (5)

NOVELTY OF THE INVENTION Having described the above invention, it is considered as a novelty, and therefore, the content of the following is claimed as property: CLAIMS

1. A method for controlling a capacitive adjusting member, in particular a piezoelectrically operated fuel injection valve, of an internal combustion engine, with a predetermined amount of energy, assigned to a particular adjustment member path, characterized in that during the process of load of the adjusting member from a power source, the voltage flowing to the adjusting member and the voltage measured therein multiply together; because the product of current and voltage is integrated over time, and because the charging process ends when the value of the integral reaches or exceeds a predetermined theoretical value.

2. A method for controlling a capacitive adjusting member, in particular a piezoelectrically operated fuel injection valve, of an internal combustion engine, with a predetermined amount of energy, assigned to a particular adjustment member stroke, characterized in that the Adjustment member is charged with a predetermined constant current; because the voltage that is measured in the adjustment member during the charging process is integrated over time, and because the charging process ends when the value of the integral reaches or exceeds a predetermined theoretical value.

3. A device for performing the method according to claim 1, with a series connection arranged between the positive pole and the negative pole of a voltage source, which consists of the adjustment member, an element that it delimits the current and an electronic switch, characterized in that a control circuit is provided, which receives as input dimensions a control signal for the start, duration and termination of a control process, and the measured values of the current fed to the adjustment member and of the voltage that can be registered in the adjustment member, and which switches the switch to the driver with the start of a control signal; because the control circuit contains a multiplier member, in which the measured values of current and voltage are multiplied together, an integrator, which integrates the product, a comparator, which compares the value of the integral with a value default, and switches the switch to non-conductive, when the value of the integral reaches or exceeds the theoretical value.

4. A device for performing the method according to claim 2, with a series connection arranged between the positive pole and the negative pole of a voltage source, which consists of the adjustment member and an electronic switch , characterized in that a constant current source is provided in the charging circuit of the adjusting member; because a control circuit is provided, which receives as input dimensions a control signal for the start, duration and termination of a control process, and the measured value of the voltage that can be recorded in the adjustment member , and which switches the switch to the driver with the start of a control signal; because the control circuit contains an integrator, which integrates the measured value, a comparator, which compares the value of the integral with a predetermined theoretical value, and switches the switch to non-conductive, when the value of the integral reaches or exceeds the theoretical value.

5. A device for carrying out the method according to claim 3 or 4, characterized in that the integrator is discharged by the starting edge of each control signal. SUMMARY OF THE INVENTION To achieve a constant travel of a capacitive adjusting member, for example, for a fuel injection valve, over a wide temperature range, the adjustment member is charged, multiplying the current fed to the adjustment member and the voltage that it is recorded in it, integrating the product and comparing the value of the integral with a predetermined theoretical value. The charging process is interrupted when the value of the integral reached or exceeded the theoretical value. START J = IG. 3