EP1828583A1

EP1828583A1 - Method for electronically controlling an ultrasonic piezoelectric actuator

Info

Publication number: EP1828583A1
Application number: EP05824392A
Authority: EP
Inventors: Christophe Ripoll
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2004-12-14
Filing date: 2005-12-07
Publication date: 2007-09-05
Also published as: FR2879255A1; WO2006077295A1; FR2879255B1

Abstract

The invention relates to a method for controlling at least one ultrasonic piezoelectric injector which is electronically controlled by a control calculator and a continuous voltage source (Epsilon) and comprises a first stage (Epsilon 1) for amplifying the voltage in order to generate a high voltage (Vboost), and a second stage (Epsilon 2) which is fed by the high voltage (Vboost) and used to generate a power source for feeding the injectors associated with selection means (Si) that can be controlled by the calculator. Said method is characterised in that it controls the cyclic ratio of the control signal of the second stage (Epsilon 2), in the initial phase, in order to reduce the energy stored in the resonance inductance (Lr) and thus the excitation voltage (Lpi) of the injectors. The aim of the invention is to reduce the transient overvoltages during the starting process.

Description

Process for electronically controlling an ultrasonic piezoelectric actuator

The present invention relates to a method for controlling an electronically controlled ultrasonic piezoelectric actuator, and more particularly to a piezoelectric stage fuel injector controlled by the electronic injection computer of an internal combustion engine in a vehicle. automobile.

More specifically, the problem that the invention aims to solve is the excitation of the piezoelectric cells to vibrate the structure of an ultrasonic injector, as described in the French patent application, filed under the number 99 14548 in the name of the Applicant. This type of injector very finely sprays the fuel into calibrated droplets to ensure an accurate dosage and small enough to ensure complete and homogeneous vaporization of the fuel injected. Such an ultrasonic injector comprises, inter alia, a cylindrical nozzle supplied with fuel and at the end of which is provided an injection orifice, and means for cyclically vibrating the nozzle, such as a transducer, comprising a piezo ceramic stage. -electric across which the voltage is varied to change its thickness between two extreme positions corresponding to the opening and closing of the injector, to a gear ratio. A piezoelectric injector ceramic is first-order equivalent to a capacitance whose charging voltage is high, greater than a hundred volts.

In a motor vehicle, the supply voltage is 12 or 42 volts, which involves increasing this voltage to ensure the charging and discharge of the ceramic.

There are currently transformerless control devices, such as the one shown in FIG. 1, which is powered by a DC voltage source E, the vehicle battery for example, whose terminal (B-) is connected to the ground and the terminal (B +) is connected to a first amplification stage of said DC voltage.

The N injectors Pi of a heat engine, N being an integer generally equal to 4, 6 or 12, are connected in parallel and sequentially controlled by selector switches S ₁ each connected in series with an injector P ₁ . An electronic injection computer sends a control logic signal to each selection switch so that the high voltage output of the voltage booster is applied to the terminals of the selected injector. The steering device comprises:

a first stage εi for amplifying the DC supply voltage E to generate a high voltage Vboost;

a second stage ε ₂ for generating a current source i _r for supplying the injectors Pi and which is powered by the high voltage V _b00st generated by the first stage;

a third stage 3 for selecting the piezoelectric injectors to be driven;

a fourth stage ε ₄ for controlling the excitation voltage V _pi of the injectors, which is not shown in FIG.

The first stage E ₁ for generating a high voltage by amplification of the direct supply voltage E is constituted by a first branch B ₁ comprising a first inductor L ₁ connected to a switching switch I _D i, which can be controlled, with a freewheel diode U ₁ , mounted in anti-parallel in the direction of the discharge current of the injector Pi selected to be controlled. The inductor L ₁ is connected on one side to the terminal (B +) of the voltage source E and on the other side to a terminal of the switch l _D i whose other terminal is connected to the terminal ( B-) of the voltage source E.

A second branch B ₂ is connected in parallel to the switch I ₀₁ switching and comprises a rectifier diode D connected to a capacitor C filtering. Thus, one of the terminals of said diode D is connected to the junction point J ₁ of the inductor L ₁ and the other switch I ₀₁ and its other terminal is connected to a first terminal of the capacitor C whose second terminal is connected to the terminal (B-) of the voltage source E.

The first stage S ₁ of amplification of the battery voltage E delivers a high voltage V _b00St across the filtering capacitor C, which supplies a second stage

Z ₂ consists of a branch mounted between the terminals of said filtering capacitor C and comprising a second inductor L ₁ - connected to a second switching switch I _D2 . controllable, with an O ₂ freewheel diode mounted in antiparallel.

One of the terminals of the inductance L _r is connected to the junction point J ₂ of the diode D with the capacitor C and its other terminal is connected to the transistor \ ₀₂ . The inductance L _r is determined so as to provide an oscillating circuit with each driven injector, to which it delivers a feed stream i _r . The injector control method is broken down into at least three sequences, a selection sequence of a piezoelectric actuator P ₁ by the switch S ₁ , an AC voltage supply sequence of the selected actuator, to which adds an electronic control sequence of the excitation voltage V _p , the injectors Pi by regulating the high voltage V _bOost generated by the first stage of the control device.

The computer sends a control signal to control the closing of the selection switch S ₁ , so that the piezoelectric actuator can be powered by this AC voltage, and during a first phase of the power supply sequence. the injector, it sends another control signal which controls the closing of the switching switch _{D2 D2} so that the energy from the high voltage V _boost accumulates in the inductance L _r by circulation of a current i _r in the loop consisting of the filtering capacitor C, the inductance L ₂ and the switch l _D2 . During a second oscillation phase between the capacity of the injector and the inductance L _r , the switch I _D2 switching is controlled at the opening, the current i _r can not pass through the diode d ₂ in non-parallel anti-parallel is forced to flow in the actuator Pi in one direction and then in the other because the inductance L _r and the injector Pj are in electrical resonance. Since the value of the inductance L _r is a function of the acoustic excitation resonance of the piezoelectric actuator, it is determined so that the inductance L _r has the time to charge sufficiently in the first phase so that the excitation voltage V _pι across the injector P ₁ , close to 1200 volts, is reached. In addition, the filtering capacitor C is sized to have a very high reactivity to the rise in voltage Vb _00S t-

Then, since the voltage V _p i across the injector is still zero, the inductance L _r is discharged by energy transfer from the inductance L _r to the filtering capacitor C, creating a negative current i _r in the loop comprising the inductance L _r , the filtering capacitor C and the anti-parallel diode d ₂ .

As shown in Figures 2a and 2b, which are the temporal representations of the voltage V _pi across the injector P ₁ and the current i _r in the inductance L _r , for a high supply voltage V _bO constant _o the first phase of the supply sequence of the injector, corresponding to the accumulation of energy in the inductance L ₁ -, takes place between the times to and U when the current i _r in the inductance L _r increases from 0 to a maximum value i _max . The second phase of the sequence takes place between the instants ti and t ₃ : first between the instants U and t ₂ when the current i _r decreases from i _max to 0 while the voltage V _pι increases from 0 to a maximum value V _pim , close to 1200 Volts, which corresponds to the charge of the injector, and then between the instants t ₂ and t ₃ from 0 to a negative minimum value i _m , _n while the voltage V _pι decreases from the maximum value V _pιm to 0, and which corresponds to its discharge. During the discharge phase of the inductance L _r between the instants t ₃ and U, the voltage V _p ι remains zero and the current i _r increases again from the minimum value i _mιn to 0. Between these instants and U, the piezoelectric actuator is in electrical resonance with the inductance L _r .

The period of electrical resonance between the piezoelectric actuator and the inductance L ₂ corresponding to the second phase of the supply sequence of the actuator, between times t ₁ and t ₃ , is shorter than the resonance period. This acoustic resonance depends on the characteristics of the piezoelectric injector. The actual high-voltage supply phase of the injector P between times t ₁ and t ₃ depends on the value of the inductance L _r , the high voltage V _{t500 St} to be reached and the closing time of the switch P, to obtain the voltage V _p , necessary.

The voltage V _pi at the terminals of a selected injector P has the form of a sinusoidal pulse when the switch ID2 for switching off the second stage of the control device is controlled at the opening, between U and t ₃ . This excitation voltage V _p , of a piezoelectric injector depends on the following parameters:

the input DC continuous voltage E of the control device, the cyclic opening ratios of the two switches _D 1 and I _{O 2} respectively for switching off the first generation stage of a high voltage V _boost and the second generation stage a feed current of the injectors, controlled by the electronic computer,

the characteristics of the inductances Li and L _r of these two stages as well as the charging capacity of the injectors,

- the setpoint of the excitation voltage.

To control this excitation voltage V _pι of an injector, it is necessary to control the cyclic ratios of the two _switching switches l _D i and I _02. As mentioned previously, the control device comprises a fourth control stage of this excitation voltage V _pι which will act as follows: the switch I ₀₂ of the second stage is controlled so that at its closure, the inductance L _r is charged for a certain time, and when it is opened, the voltage at the terminals of the selected injector describes a sinusoidal pulse. The peak value of this voltage V _pι depends on the energy stored in the inductance L _r and the high voltage Vb ₀₀ St generated.

The voltage boost converter generates a periodic high voltage V _pι , greater than a hundred volts, with a high frequency F _pι , greater than ten kHz, for exciting P injectors, ultrasound.

FIG. 2a is a representation of this electrical resonance in the case where it is theoretical. But in reality, at the start of the control of the piezoelectric actuators, the excitation voltage V _p1 passes through an initial transient phase during which its peak value Vp, _c can exceed the maximum value V _P i _m , of 30 at 50%, (FIG. 3) so that, in order not to be damaged, the switches must be sized to withstand this maximum value V _plm . Thus they are oversized for a transient voltage withstand greater than the voltage required for the excitation of the piezoelectric injectors, which induces a significant cost factor on the switches.

The object of the invention is to overcome this disadvantage, by proposing several injector control methods for reducing this transient overvoltage at startup.

For this purpose, the object of the invention is a method for controlling at least one ultrasonic piezoelectric actuator, electronically controlled from a control computer and a DC voltage source, comprising a first stage of amplification of said voltage for generating a high voltage and a second stage, powered by said high voltage, for generating a current source for supplying the injectors associated with selection means controllable by said computer, characterized in that consists in controlling the duty cycle of the control signal of the second feed stage of the injectors, in the initial phase, in order to reduce the energy stored in the resonance inductance of this second stage and consequently the excitation voltage of the injectors .

According to a first variant, the control method consists in reducing the duty ratio of the control signal of the second feed stage of the injectors, in the initial phase, in order to reduce the energy stored in the inductor. resonance of this second stage and therefore the excitation voltage of the injectors.

According to a second variant, the control method consists in imposing, as soon as the first pulse of the initial phase, a cyclic ratio of the control signal of the charge of the inductance, which is equal to the steady-state duty cycle to obtain the voltage peak excitation desired at the terminals of the injectors, so a closing time of the switching switch of the second stage of the injector control device, equal to the duration in steady state.

According to a third variant, the control method consists of increasing the duty ratio of the control signal of the first stage of generation of a high voltage, during the initial phase, from a determined minimum value to a maximum value necessary for to obtain, in the steady state, a high supply voltage necessary for excitation of the injectors, and thus to vary the high supply voltage, during the initial phase, by a value lower than that required at the steady state until the latter, to control the charging current of the resonance inductance and the peak value of the excitation voltage, in the initial phase, which does not exceed the value required in steady state.

According to a fourth variant, the control method consists in applying an initial voltage across each selected injector, in the initial driving phase, obtained by precharging the capacity of said injectors, either by controlling the switching switch or by controlling the switches of said injectors.

Other characteristics and advantages of the invention will appear on reading the description, illustrated by the following figures which are, in addition to FIGS. 1, 2 and 3 already described:

FIGS. 4a, 5a, 6a and 7a: the temporal variations of the excitation voltage resulting respectively from the four methods according to the invention; FIGS. 4b, 5b, 6b and 7b: the temporal variations of the control signal of the second stage of the injector control device, respectively following the four methods according to the invention; FIGS. 4c, 5c, 6c and 7c show the temporal variations of the high voltage delivered by the injector control device, respectively following the four methods according to the invention; FIGS. 4d, 5d, 6d and 7d: the temporal variations of the excitation current delivered by the injector control device, respectively following the four methods according to the invention.

The elements bearing the same references in the different figures perform the same functions in view of the same results.

According to a first variant, the control method of the piezoelectric actuators consists, in order to control this excitation voltage V _p , of an injector, to control the duty cycle of the control signal V _C2 of the injector supply stage, either of the switching switch I _D2 , the duty cycle being equal to the conduction time divided by the period T of the signal. The method consists in particular in reducing its conduction time, or closing time, in the initial phase so that, during this closing, the inductance L ₁ - is charged for a shorter time, thus stores less energy and that when it is opened, the excitation voltage V _pi at the terminals of the selected injector describes a sinusoidal pulse of peak value V _p , _c less than or equal to that of the maximum value V _pιm of the excitation voltage in the steady state.

As shown in FIG. 4b, this first method consists in reducing the closing time D _f of the switching switch I _D 2 of this second stage, powered by a high DC voltage V _b00S t (FIG. 4c), causing less current i _r flowing in inductance L _r (Figure 4d), which is thus less charged, so that at the opening of said switch I _D2 , the excitation voltage V _pi will be lower than steady state. As shown in Figure 4a, the first pulses of the excitation voltage V _P V _P i have a peak value determined ι _c, less than the maximum peak value _m i V _p supported by the switches. In the initial regime, the closing time _{D.sub.i of} said switch I _D2 is thus determined to be less than the closing time _D.sub.F necessary, in steady state, to excite the ultrasonic piezoelectric injectors. During this initial transient phase, the closing time is gradually increased to the established speed, the frequency F _kl of the excitation voltage signal remains constant except for the first pulses.

According to a second variant, the piloting method of the piezoelectric actuators consists in imposing, from the first pulse of the initial phase (FIG.

5b), a duty cycle ratio of the inductance load control signal L _r , which equals the steady-state duty cycle to obtain the peak excitation voltage intended to the terminals of the injectors, in other words a closing time D _f , of the switching switch I ₀₂ of the second feed stage of the injectors which is equal to the duration D _f8 in steady state. This charge duration of the inductance by the current i _r is obtained by knowing the instant of the zero crossing of this current i _r in the inductance L ₁ - (FIG. 5d), this duration being determined by calibration or established by knowledge of the system. As shown in FIG. 5a, the first pulses of this excitation voltage V _pι have a peak value V _peak determined, lower than the maximum peak value V _pι supported by the switches in steady state, for a high supply voltage Vb. _00S t constant (Figure 5c).

According to a third variant, the driving method of the piezoelectric actuators consists in increasing the duty ratio of the control signal of the first generation stage of a high voltage, during the initial phase, from a minimum value determined to a value the maximum necessary to obtain, in steady state, a high supply voltage V _boO st necessary for the excitation of the injectors. Thus the method varies the high supply voltage V _bO o _s t. during the initial phase, by a value lower than that required at the steady state up to the latter, as shown in FIG. 6c, which makes it possible to control the charging current i _r of the resonance inductor L _r (FIG. 6d). The instant of closing of the switch I _D2 must occur when the current i _r increases from the minimum value i _mlπ to zero, that is to say when the diode d ₂ leads. Thus the peak value V _pιc of the excitation voltage V _p1 , in the initial phase, does not exceed the value V _pιm necessary in the steady state (FIG. 6a).

According to a fourth variant, the control method consists in applying an initial voltage V _pii across the terminals of each selected injector, in the initial driving phase, as shown in FIG. 7a, without varying the duty cycle of the control signals of the first two so stages of the switching switch I _D2 , as shown in Figure 6b. This initial voltage V _pll across the injectors is obtained by precharging the capacity of each of them, either by controlling the _switching switch ID ₂ or by controlling the switches S ₁ of the injectors.

Finally, the control method can combine these different variants simultaneously.

Claims

A method for controlling at least one ultrasonic piezoelectric actuator, electronically controlled from a control computer and a DC voltage source, made from a device comprising a first amplification stage of said voltage for generating a high voltage and a second stage, powered by said high voltage, for generating a current source, by charging a resonance inductor, for supplying the actuators associated with selection means that can be controlled by said calculator, a method of controlling the duty cycle ratio of the control signal of the second injector supply stage, characterized in that said duty cycle control is intended to reduce the energy stored in said resonance inductance (U) of said second stage to obtain an excitation voltage (V, *) of the injectors (P ₁ ) whose transient initial phase value of the control of the actuator s is less than or equal to its steady state value.

2. A method of controlling at least one ultrasonic piezoelectric actuator according to claim 1, characterized in that it consists in imposing, as soon as the first pulse of the initial phase, a duty cycle of the control signal of the load of the inductance (L _r ), which is equal to the steady-state duty cycle to obtain the desired peak excitation voltage across the actuators, therefore a closing time (D _fl ) of the switching switch (\ _DZ ) the second stage of the actuator control device, equal to the duration (D _fe ) in steady state.

3. A method of driving at least one ultrasonic piezoelectric actuator, according to claim 2, characterized in that said charge duration of the inductance (L _r ) by the current (i _r ) is obtained by knowing the instant of the zero crossing of this current (i _r ) in the inductance (U), this duration being determined by calibration or established by knowledge of the system.

4. A method of driving at least one ultrasonic piezoelectric actuator according to claim 1, characterized in that it consists in increasing the duty ratio of the control signal of the first generation stage of a high voltage, during the initial phase, from a minimum value determined to a maximum value necessary to obtain, in steady state, a high power supply voltage (Vboost) necessary for the excitation of the injectors and thus to vary the high supply voltage ( Vb ₀₀ St), during the initial phase, of a lower value than necessary to the regime established up to the latter, to control the current (i _r ) of the resonance inductance (l_ _r ) as well as the peak value of the excitation voltage (V _p O, in the initial phase , which does not exceed the value required in steady state.

5. A method of driving at least one ultrasonic piezoelectric actionπeur according to claim 1, characterized in that it consists in applying an initial voltage (V _p j,) across each selected actuator (Pj), in the initial phase of control, obtained by precharging the capacity of said actuators, either by controlling the switching switch (ta) or by controlling the switches (S ₁ ) of said actuators (Pj).