Method for controlling the duty cycle of a signal enabling the current control of a conversion module of a converter

Abstract

Disclosed is a method for regulating the duty cycle of a controlled current signal of a conversion module of a voltage converter including a step of measuring, by the microcontroller, the duty cycle of the envelope of the controlled current signal, and when the value of the duty cycle is below a predetermined threshold, a step of controlling, by the microcontroller, the current control module to decrease the amplitude of the control signal and that the duty cycle of the envelope of the controlled current signal thus tends toward a predetermined threshold, or when the value of the duty cycle is higher than the predetermined threshold, a step of controlling, by the microcontroller, the current control module so the current control module increases the amplitude of the controlled current signal and that the duty cycle of the envelope of the controlled current signal thus tends toward the predetermined threshold.

Claims

1. A method for regulating a duty cycle of a controlled current signal (Imes) of a conversion module (310-1) of a DC-to-DC voltage converter (310) of a control computer (30) for controlling a combustion engine (20) of a motor vehicle (1), said combustion engine (20) comprising fuel injectors (210), said control computer (30) comprising a microcontroller (300), the DC-to-DC voltage converter (310) and a control module (320) for controlling the fuel injectors (210), said DC-to-DC voltage converter (310) comprising: the conversion module (310-1), configured to convert a DC voltage delivered by a power supply battery (10) of the motor vehicle (1) into a DC output voltage (Vs) of higher value delivered to the control module (320) for controlling the fuel injectors (210) by generating the controlled current signal (Imes), a current control module (310-2) configured to control said controlled current signal (Imes) of the conversion module (310-1), said controlled current signal (Imes) exhibiting an alternation of phases of peaks of positive amplitude, allowing the conversion module (310-1) to be controlled so that it delivers power allowing a target output voltage of the DC-to-DC voltage converter (310) to be reached, and of phases of rest during which the value of said controlled current signal (Imes) is zero, thus defining the envelope of the controlled current signal (Imes), a peak phase followed by a consecutive rest phase constituting a cycle and the ratio of the duration of a peak phase to the duration of the corresponding cycle constituting the duty cycle of the envelope of the controlled current signal (Imes) at a given time, said method comprising: a step (E1) of measuring, by means of the microcontroller (300), the duty cycle of the envelope of the controlled current signal (Imes), when the value of the duty cycle is lower than a predetermined threshold, a step (E2A) of controlling, by means of the microcontroller (300), the current control module (310-2) so that said current control module (310-2) decreases the amplitude of the controlled current signal (Imes) and that the duty cycle of the envelope of said controlled current signal (Imes) thus tends toward said predetermined threshold, when the value of the duty cycle is higher than said predetermined threshold, a step (E2B) of controlling, by means of the microcontroller (300), the current control module (310-2) so that said current control module (310-2) increases the amplitude of the controlled current signal (Imes) and that the duty cycle of the envelope of said controlled current signal (Imes) thus tends toward said predetermined threshold.

2. The method as claimed in claim 1, wherein the microcontroller (300) provides the current control module (310-2) with a predetermined amplitude value to be reached for the controlled current signal (Imes).

3. The method as claimed in claim 2, wherein the value of the duty cycle is between 70 and 95%.

4. The method as claimed in claim 3, wherein the value of the duty cycle is between 85 and 90%.

5. The method as claimed in claim 1, wherein the value of the duty cycle is between 70 and 95%.

6. The method as claimed in claim 5, wherein the value of the duty cycle is between 85 and 90%.

7. The method as claimed in claim 6, wherein the value of the duty cycle is about 90%.

8. A control computer (30) for controlling a combustion engine (20) of a motor vehicle (1), said combustion engine (20) comprising fuel injectors (210), said control computer (30) comprising a microcontroller (300), a DC-to-DC voltage converter (310) and a control module (320) for controlling the fuel injectors (210), said DC-to-DC voltage converter (310) comprising: a conversion module (310-1), configured to convert a DC voltage delivered by a power supply battery (10) of the motor vehicle (1) into a DC output voltage (Vs) of higher value delivered to the control module (320) for controlling the fuel injectors (210) by generating a current signal (Imes), a current control module (310-2) configured to control said current signal (Imes) of the conversion module (310-1), said “controlled” current signal (Imes) exhibiting an alternation of phases of peaks of positive amplitude, allowing the conversion module (310-1) to be controlled so that it delivers power allowing a target output voltage of the DC-to-DC voltage converter (310) to be reached, and of phases of rest during which the value of said controlled current signal (Imes) is zero, thus defining the envelope of the controlled current signal (Imes), a peak phase followed by a consecutive rest phase constituting a cycle and the ratio of the duration of a peak phase to the duration of the corresponding cycle constituting the duty cycle of the envelope of the controlled current signal (Imes) at a given time, wherein said control computer (30) being characterized in that the microcontroller (300) is configured: to measure the duty cycle of the envelope of the controlled current signal (Imes), when the value of the duty cycle is lower than a predetermined threshold, to control the current control module (310-2) so that said current control module (310-2) decreases the amplitude of the controlled current signal (Imes) and that the duty cycle of the envelope of said controlled current signal thus tends toward said predetermined threshold, when the value of the duty cycle is higher than said predetermined threshold, to control the current control module (310-2) so that said current control module (310-2) increases the amplitude of the controlled current signal (Imes) and that the duty cycle of the envelope of said controlled current signal (Imes) thus tends toward said predetermined threshold.

9. The control computer (30) as claimed in claim 8, wherein the microcontroller (300) is configured to provide the current control module (310-2) with a predetermined amplitude value to be reached for the controlled current signal (Imes).

10. The control computer (30) as claimed in claim 9, wherein the value of the duty cycle is between 70 and 95%.

11. The control computer (30) as claimed in claim 10, wherein the value of the duty cycle is between 85 and 90%.

12. The control computer (30) as claimed in claim 8, wherein the value of the duty cycle is between 70 and 95%.

13. The control computer (30) as claimed in claim 12, wherein the value of the duty cycle is between 85 and 90%.

14. The control computer (30) as claimed in claim 13, wherein the value of the duty cycle is about 90%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will become apparent from the following description, which is provided with reference to the appended figures, which are given by way of non-limiting examples and in which the same references are given to similar objects.

(2) FIG. 1 shows one example of a vehicle according to the invention.

(3) FIG. 2 illustrates one embodiment of the computer according to the invention.

(4) FIG. 3 is a timing diagram illustrating one exemplary implementation of the computer of FIG. 2.

(5) FIG. 4 schematically illustrates one embodiment of the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) The computer according to the invention is a control computer intended to be installed in a motor vehicle with a combustion engine in order to control the injection of fuel into the cylinders of said engine.

(7) FIG. 1 shows one example of a vehicle 1 according to the invention.

(8) I) Vehicle 1

(9) The vehicle 1 comprises a battery 10, used to supply power to equipment (not shown) of the vehicle 1, an engine 20 and a computer 30 for controlling said engine 20.

(10) A) Battery 10

(11) The battery 10 is an electrical power supply battery on board the vehicle 1 in order to supply power to electrical equipment of said vehicle 1. The battery 10 delivers, for example, a DC voltage whose value may be between 6 and 24 V and that is preferably of the order of 12 V.

(12) B) Engine 20

(13) The engine 20 is a combustion engine comprising a plurality of cylinders on each of which at least one fuel injector 210 is mounted.

(14) C) Computer 30

(15) Still with reference to FIG. 1, the computer 30 comprises a microcontroller 300, a DC-to-DC voltage converter 310 and a control module 320 for controlling the injectors 210.

(16) 1) Control Module 320

(17) The control module 320 (commonly known as a “driver”) is configured to drive the opening of the fuel injectors 210 on the basis of a what is called “injector control” current delivered by the converter 310.

(18) 2) Converter 310

(19) The converter 310 comprises a conversion module 310-1, a current control module 310-2 and a what is called “intermediate” capacitor Cs defining across its terminals an output voltage Vs of the converter 310 used by the control module 320 to control the injectors 210.

(20) i) Conversion Module 310-1

(21) The conversion module 310-1 is configured to convert the DC voltage delivered by the battery 10 into a DC output voltage Vs of higher value, for example of the order of 60 V, delivered to the control module 320 for controlling the injectors 210. The output voltage Vs allows the control module 320 to be provided with a current whose intensity is high enough to control the injectors 210.

(22) ii) Current Control Module 310-2

(23) The current control module 310-2 is configured to generate a controlled current signal I_mes (FIGS. 2 and 3) allowing the conversion module 310-1 to be driven.

(24) This controlled current signal I_mes exhibits an alternation of peak phases and rest phases. The peak phases (or active phases) have peaks of high frequency, for example of a few hundred hertz, of positive amplitude which allow the conversion module 310-1 to be controlled so that it delivers power allowing a target output voltage of the converter 310, for example 60 V, to be reached. The rest phases (or inactive phases) correspond to phases in which the value of the controlled current signal I_mes is zero.

(25) This succession of peak phases and rest phases takes place at low frequency in what is called “on/off” mode. Since a peak phase followed by a consecutive rest phase constitutes a cycle, the ratio of the duration of a peak phase to the duration of the cycle in which said peak phase occurs constitutes the duty cycle of the envelope of the controlled current signal I_mes at a given time (that of said cycle).

(26) 3) Microcontroller 300

(27) The microcontroller 300 performs several functions. First, the microcontroller 300 is configured to measure the duty cycle of the envelope of the controlled current signal I_mes. More precisely, the function of the microcontroller 300 is to measure the duration of the peak phases (duration in which the output voltage Vs measured across the terminals of the intermediate capacitor Cs is lower than the setpoint value (for example 60 V)) and the duration of the rest phases (waiting time before the next injection and after the target voltage has been reached) of the controlled current signal I_mes so as to tend toward a duty cycle as close as possible to the predetermined duty cycle threshold (referenced “reference duty cycle RC_ref” in FIGS. 2 and 3, for example 85%).

(28) Next, the microcontroller 300 is configured to control the current control module 310-2 so that said current control module 310-2 decreases the amplitude of the controlled current signal I_mes when the value of the duty cycle is lower than a predetermined threshold. This allows the duty cycle of the envelope of the controlled current signal I_mes to be increased so that it tends toward said predetermined threshold.

(29) Similarly, the microcontroller 300 is configured to control the current control module 310-2 so that said current control module 310-2 increases the amplitude of the controlled current signal I_mes when the value of the duty cycle is higher than the predetermined threshold. This allows the duty cycle of the envelope of the controlled current signal I_mes to be decreased so that it tends toward said predetermined threshold.

(30) The predetermined duty cycle threshold is between 50% and 100%, and preferably of the order of 85% to 90% in order to increase the efficiency of the conversion module while decreasing the heating of the converter 310.

(31) The microcontroller 300 is also configured to send an injection control signal to the control module 320 for controlling the injectors 210 at predetermined times so that said control module 320 delivers a control current to one or more of the injectors 210 on the basis of the output voltage Vs of the converter 310 so that said injectors 210 inject fuel into the cylinders of the engine 20. Such an injection control signal may for example indicate the fuel injection duration.

Detailed Example of One Embodiment

(32) One detailed embodiment of the computer 30 according to the invention, and more particularly of the microcontroller 300 and of the converter 310, will now be described with reference to FIGS. 2 and 3, without this limiting the scope of the present invention.

(33) In this example, the conversion module 310-1 of the converter 310 comprises an inductor L that is suitable for being connected to the battery 10 of the vehicle 1 at a point P1 and which is connected to a first terminal of a diode D and to a first terminal of a transistor T, for example of MOS type, at a point P2.

(34) The diode D is connected to the intermediate capacitor Cs via its second terminal, the diode D allowing current to flow from its first terminal to its second terminal. A second terminal of the transistor T is connected, at a point P3, to a resistor R which is additionally connected to ground M, the transistor T allowing or preventing the flow of current between its first terminal and its second terminal.

(35) The current control module 310-2 comprises an operational amplifier AO, an off module 310-21 for turning the transistor T off, an on module 310-22 for turning the transistor T on and a latch Q.

(36) The latch Q is a high-frequency latch of SR (set/reset) type that allows the transistor T to be controlled so that it is on or off. To this end, the output of the latch Q is connected to the control terminal of the transistor T, the “SET” input terminal of the latch Q is connected to the on module 310-22 for turning the transistor T on and the “RESET” input terminal of the latch Q is connected to the off module 310-21 for turning the transistor T off.

(37) The negative input terminal of the operational amplifier AO receives the controlled current signal I_mes flowing between the transistor T and the resistor R.

(38) The output of the operational amplifier AO is connected to the input of the off module 310-21 which has the role of switching the transistor T to the off state, via the “Reset” input terminal of the latch Q (which deactivates the latch Q), when the value of the intensity of the controlled current signal I_mes reaches a predetermined current amplitude value, delivered by the microcontroller 300 and denoted I_signal.

(39) The off module 310-21 for turning the transistor T off is also activated when the output voltage Vs of the conversion module 310-1 reaches its target setpoint value (Stop indicator in FIG. 2) by generating a RESET signal on the RESET input of the latch Q.

(40) The on module 310-22 for turning the transistor T on detects the times in which the point P2 of the conversion module 310-1 is at zero potential (called ZVD for zero voltage detection by those skilled in the art) through a capacitor C1 in order to turn the transistor T on by activating the SET input of the latch Q.

(41) The on module 310-22 for turning the transistor T on also activates the SET input of the latch Q when it receives a trigger signal (“Start” in FIG. 2) coming from a management module 301 of the microcontroller 300 corresponding to a start of injection, as will be described below.

(42) The on module 310-22 therefore makes it possible to control, via the latch Q, the current signal flowing through the transistor T so that said controlled current signal I_mes exhibits either peaks in the active phase of the converter, or a zero value when the output voltage Vs of the converter 310 is equal to the target voltage.

(43) In order to regulate the duty cycle of the envelope of the controlled current signal I_mes flowing through the transistor T of the conversion module 310-1, the microcontroller 300 comprises, in this example, a management module 301 that decides the fuel injection start times via the sending of a trigger signal (Start), a measurement module 302 for measuring the duration of a peak phase of the controlled current signal I_mes, a measurement module 303 for measuring the duration of a rest phase of the controlled current signal I_mes, a calculation module for calculating the duty cycle 304 of the active phases on the basis of the measurements taken by the measurement modules 302 and 303 and a selection module 305 comprising the memory region in which a table is stored that comprises a list of predetermined discrete current amplitude values that the controlled current signal I_mes must reach in order to converge toward the predetermined duty cycle threshold RC_ref. After analog conversion, the output of the table is connected to the positive terminal of the operational amplifier AO.

(44) The management module 301 manages the start times of the peak phases of the controlled current signal I_mes by sending trigger signals (Start). The trigger signals (Start) correspond both to the triggering of the injectors 210 controlled by the microcontroller 300 via the control module 320 for controlling the injectors 210 and to the starts of the peak phases triggering the activation of the conversion module 310-1 so that it delivers the power required to reach an output voltage value Vs equal to the target value. The stop signals (Stop) correspond to the precise times when the output voltage Vs of the conversion module 310-1 reaches the setpoint value (end of the peak phase and start of a rest phase).

(45) The internal modules (301, 302, 303, 304, 305) of the microcontroller 300 make it possible to regulate the duty cycle of the envelope of the controlled current signal I_mes to the predetermined duty cycle threshold RC_ref. To achieve this, the calculation module for calculating the duty cycle 304 calculates, at each time, the duty cycle of the envelope of the controlled current signal I_mes on the basis of the signals delivered by the measurement modules 302 and 303.

(46) The selection module 305 compares the calculated duty cycle with the reference duty cycle and then selects from the table, stored in the memory region of the selection module 305, a predetermined current amplitude value I_signal that it delivers as input to the operational amplifier AO of the current control module 310-2 such that the next duty cycle of the envelope of the controlled current signal I_mes calculated corresponds to the reference duty cycle.

(47) Thus, a peak phase is characterized by the delivery of the admissible instantaneous power corresponding to the predetermined current amplitude value I_signal and the inactive phase is characterized by a zero instantaneous power, such that the average power delivered over a cycle of the controlled current signal I_mes corresponds to the instantaneous power over said cycle multiplied by the duty cycle of the envelope of said signal. It follows that the predetermined current amplitude value I_signal is inversely proportional to the duty cycle for the delivery of the same average power over a cycle. For a given cycle, a low duty cycle will exhibit a large current amplitude. Likewise, for a given cycle, a high duty cycle will exhibit a small current amplitude.

(48) The microcontroller 300 is configured to measure the duty cycle of the active phases of the converter 310 and, when the value of the duty cycle is lower than a predetermined duty cycle threshold RC_ref, to decrease the amplitude value I_signal such that the duty cycle of the peak phases of the controlled current signal I_mes tends toward the predetermined duty cycle threshold RC_ref, or, when the value of the duty cycle is higher than the predetermined duty cycle threshold RC_ref, to increase the amplitude value I_signal such that the duty cycle of the envelope of the controlled current signal I_mes tends toward the predetermined duty cycle threshold RC_ref.

(49) It should be noted that, when the value of the duty cycle is equal to the predetermined duty cycle threshold RC_ref, then the microcontroller 300 neither increases nor decreases the amplitude value I_Signal. Specifically, the higher the value of the duty cycle, the lower the amplitude value I_Signal, and the lower the heat losses from the converter 310 and the higher the efficiency of the conversion module 310-1.

(50) However, it may be advantageous to choose a value for the predetermined duty cycle threshold RC_ref that is away from the value of 100%, for example by a few %, preferably by at least 10% in order to avoid the risks associated with a sudden change in the frequency of the injection control signals (and therefore of the injections themselves). Specifically, during a sudden change in speed of the engine 20, for example during a substantial acceleration which requires a higher injection frequency, the frequency of the injection control signals will increase significantly, which will decrease the duration of the cycles of the controlled current signal I_mes. A sudden increase in the frequency of the injections will also lead to a rapid decease in the duration of the rest phase which could be canceled out if the duty cycle of the envelope of the regulation signal is too close to 100%.

(51) II) Implementation

(52) With reference to FIGS. 2 and 3, at each start of fuel injection control (Start (INJ) in FIG. 3), the management module 301 simultaneously controls: the on module 310-22 for turning the transistor T on so that it starts the peak phase of the conversion module 310-1 by activating the latch Q so that it controls the transistor T so as to be in the active state (i.e. on), the measurement module 302 for measuring the peak phase, so that it starts measuring the duration of the peak phase which is starting, the measurement module 303 for measuring the rest phase so that it stops measuring the duration of the rest phase which is ending.

(53) Each time the output voltage Vs reaches the setpoint value, the management module 301 simultaneously controls: the off module 310-21 for turning the transistor T off so that it definitively stops the current peak phase until the next triggering of a peak phase (corresponding to a new injection), the measurement module 302 for measuring the peak phase so that it stops measuring the current peak phase, the measurement module 303 for measuring the rest phase so that it starts measuring the duration of the rest phase which is starting.

(54) It should be noted that, in another embodiment, these measurements could be taken by counters triggered by start commands and interrupted by interrupt commands depending on the output voltage Vs of the conversion module 310-1 (for example when the output voltage Vs is higher than the target voltage value).

(55) The duration measured for the last peak phase and the duration measured for the last rest phase are delivered in real time to the duty cycle measurement module 304 so that it calculates the value of the duty cycle, referenced RC_mes in FIGS. 2 and 3.

(56) The selection module 305 calculates the difference in real time between the predetermined duty cycle threshold RC_ref and the calculated duty cycle RC_mes. Depending on the value of the difference, an increase or decrease calculation is performed by the selection module 305. The result of this calculation is associated with the closest of the predetermined (discrete) current amplitude values I_signal from the table stored in the memory region of the selection module 305 (value higher than, lower than or equal to the result of the calculation performed in order to determine the duty cycle).

(57) Thus, the current control (or regulation) performed by the current control module 310-2 makes the controlled current signal I_mes strictly follow the value I_Signal coming from the microcontroller 300. In other words, for as long as the calculated duty cycle value is higher than the predetermined duty cycle threshold RC_ref, the selected amplitude value I_signal will increase in order to raise the power in the peak phases with a view to lowering the duty cycle of the next cycle. Conversely, for as long as the calculated duty cycle value is lower than the predetermined duty cycle threshold RC_ref, the selected amplitude value I_signal from the table will decrease in order to lower the power in the peak phases with a view to increasing the duty cycle of the next cycle.

(58) In the example of FIG. 3, a measured duty cycle RC_mes of 95% (where it was previously 85%) leads to an increase in the amplitude value I_signal by two which corresponds to a new amplitude value I_signal allowing the intensity of the controlled current signal I_mes (which thus follows the new amplitude I_signal) to be increased in an optimized manner. Next, a decrease in the measured duty cycle RC_mes from 95% to 90% leads to a decrease in the amplitude value I_signal by one which corresponds to a new amplitude value I_signal allowing the intensity of the controlled current signal I_mes (which thus follows the new amplitude I_signal) to be decreased in an optimized manner.

(59) With reference to FIG. 4 describing the method according to the invention in general, the microcontroller 300 measures the duty cycle of the peak phases in a step E1. Next, when the value of the measured duty cycle is lower than the predetermined duty cycle threshold RC_ref, the microcontroller 300 controls the amplitude of the controlled current signal I_mes so that it decreases (by choosing a lower predetermined amplitude value) such that the next duty cycles of the controlled current signal I_mes increase and tend toward said predetermined duty cycle threshold in a step E2A or, when the value of the duty cycle is higher than the predetermined duty cycle threshold, the microcontroller 300 controls the amplitude of the controlled current signal I_mes so that it increases (by choosing a higher predetermined amplitude value) such that the next duty cycles of the controlled current signal I_mes decrease and tend toward said predetermined threshold in a step E2B.

(60) In the present example, the microcontroller 300 measures, for a given cycle, the duration of the peak phase and the duration of the rest phase, then deduces therefrom the duration of the cycle (which is the sum of these two durations) and the duty cycle. However, as a variant, the microcontroller 300 could measure the duration of a peak phase and directly the duration of the cycle in which said peak phase occurs in order to deduce the duty cycle therefrom by straightforward division.

(61) The invention therefore advantageously makes it possible to drive the current converter in an optimized manner so as to keep the duty cycle close to a threshold value which makes it possible to optimize its efficiency while limiting its heating.