METHOD FOR CONTROLLING A DC-TO-DC VOLTAGE CONVERTER

Abstract

Disclosed is a method for controlling a DC-DC voltage converter for driving with current at least one fuel injector of a motor-vehicle internal combustion engine. The method includes, when the transistor is switched from the off state to the on state, triggering a counter for measuring time, and, if at the end of a preset time called the “observation” time, the amplitude of the peak current has not reached its maximum value, steps of commanding that transistor so that the transistor switches from the on state to the off state, of keeping the transistor in the off state for a preset time called the “cooling time”, and of commanding the transistor so that the transistor switches to the on state at the end of the cooling time.

Claims

1. A method for controlling a DC-DC voltage converter (1) for driving with current at least one fuel injector (2) of a motor-vehicle internal combustion engine, said converter (1) comprising a control module (10) and an induction coil (20) that is connected to a field-effect transistor (30) comprising a drain (D), a source (S) and a gate (G), said gate (G) being connected to the control module (10) in order for said control module (10) to command the transistor (30) to an on state in which current passes between the drain (D) and the source (S) or to an off state in which current does not pass between the drain (D) and the source (S), the alternation of the on and off states of the transistor (30) generating a sawtooth current called the peak current (Ipeak), the amplitude of which is bounded by a maximum value, called the “top” value, and that allows the converter (1) to deliver an output voltage (Vout) across the terminals of a capacitor called the “intermediate” capacitor (Cint), the discharge of which is commanded by a computer via a drive module in order to command at least one fuel injector (2), the converter (1) being configured to make said output voltage (Vout) tend toward a target value, the method comprising: when the transistor (30) is switched from the off state to the on state, triggering (E1) a counter (120) for measuring time, if at the end of a preset time called the “observation” time, the amplitude of the peak current (Ipeak) has not reached the maximum value, commanding (E2) the transistor (30) so that said transistor (30) switches from the on state to the off state, keeping (E3) the transistor (30) in the off state for a preset time called the “cooling” time, commanding (E4) the transistor (30) so that said transistor (30) switches to the on state at the end of the cooling time.

2. The method as claimed in claim 1, wherein the preset observation time is comprised between 50 and 100 microseconds.

3. The method as claimed in claim 1, wherein the preset cooling time is comprised between 0 and 2000 microseconds.

4. A DC-DC voltage converter (1) for driving with current at least one fuel injector (2) of a motor-vehicle internal combustion engine, said converter (1) comprising a control module (10) and an induction coil (20) that is connected to a field-effect transistor (30) comprising a drain (D), a source (S) and a gate (G), said gate (G) being connected to the control module (10) in order for said control module (10) to command the transistor (30) to an on state in which current passes between the drain (D) and the source (S) or to an off state in which current does not pass between the drain (D) and the source (S), the alternation of the on and off states of the transistor (30) generating a sawtooth current called the peak current (Ipeak), the amplitude of which is bounded by a maximum value, called the “top” value, and that allows the converter (1) to deliver an output voltage (Vout) across the terminals of a capacitor called the “intermediate” capacitor (Cint), the discharge of which is commanded by a computer via a drive module in order to command at least one fuel injector (2), the converter (1) being configured to make said output voltage (Vout) tend toward a target value, wherein the control module (10) is configured to: switch the transistor (30) from the off state to the on state, trigger a counter (120) for measuring time when the transistor (30) is switched to the on state, if at the end of a preset time called the “observation” time, the amplitude of the peak current (Ipeak) has not reached its maximum value, command the transistor (30) so that said transistor (30) switches from the on state to the off state, keep the transistor (30) in the off state for a preset time called the “cooling” time, command the transistor (30) so that said transistor (30) switches to the on state at the end of the cooling time.

5. The converter (1) as claimed in claim 4, wherein the control module (10) comprises the counter (120) for measuring the time taken for the peak current to reach or not its top value.

6. The converter (1) as claimed in claim 4, wherein the control module (10) comprises a comparator (160) of the voltage defined across the terminals of a current-measuring shunt connected between the source (S) of the transistor (30) and ground (M), and of a reference voltage (Vref) representing the top value of the peak current (Ipeak).

7. The converter (1) as claimed in claim 6, wherein the control module (10) comprises an OR logic gate (130) a first input of which is connected to the output of the counter (120) and a second input of which is connected to the output of the comparator (160).

8. The converter (1) as claimed in claim 4, wherein the control module (10) comprises a logic unit (110) configured to send signals for commanding the gate (G) of the transistor (30) in order to get said transistor (30) to switch to an on state.

9. The converter (1) as claimed in claim 8, wherein the control module (10) comprises a latch (140) that receives, on a first input, the control signals sent by the logic unit (110) in order to switch the transistor (30) to the on state and, on a second input, the output of the logic gate (130) in order to switch the transistor (30) to the off state.

10. A motor vehicle comprising a converter (1) as claimed in claim 4.

11. The method as claimed in claim 2, wherein the preset cooling time is comprised between 0 and 2000 microseconds.

12. The converter (1) as claimed in claim 5, wherein the control module (10) comprises a comparator (160) of the voltage defined across the terminals of a current-measuring shunt connected between the source (S) of the transistor (30) and ground (M), and of a reference voltage (Vref) representing the top value of the peak current (Ipeak).

13. The converter (1) as claimed in claim 5, wherein the control module (10) comprises a logic unit (110) configured to send signals for commanding the gate (G) of the transistor (30) in order to get said transistor (30) to switch to an on state.

14. The converter (1) as claimed in claim 6, wherein the control module (10) comprises a logic unit (110) configured to send signals for commanding the gate (G) of the transistor (30) in order to get said transistor (30) to switch to an on state.

15. The converter (1) as claimed in claim 7, wherein the control module (10) comprises a logic unit (110) configured to send signals for commanding the gate (G) of the transistor (30) in order to get said transistor (30) to switch to an on state.

16. A motor vehicle comprising a converter (1) as claimed in claim 5.

17. A motor vehicle comprising a converter (1) as claimed in claim 6.

18. A motor vehicle comprising a converter (1) as claimed in claim 7.

19. A motor vehicle comprising a converter (1) as claimed in claim 8.

20. A motor vehicle comprising a converter (1) as claimed in claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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 nonlimiting examples and in which the same references are given to similar objects.

[0033] FIG. 1 illustrates one embodiment of the converter according to the invention.

[0034] FIG. 2 illustrates a partial view of the converter of FIG. 1, in which view an exemplary control module is detailed.

[0035] FIG. 3 illustrates one embodiment of the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] FIG. 1 shows one example of a converter 1 according to the invention. The converter 1 is intended to be installed in a motor vehicle, for example in order to deliver an output voltage Vout allowing fuel injectors 2 to be controlled. The converter 1 is a quasi-resonant DC-DC voltage converter.

[0037] In the example described below, but non-limitingly, the converter 1 is a boost converter 1 allowing a capacitor called an “intermediate” capacitor Cint, which supplies the energy required to activate the fuel injectors 2, to be recharged.

[0038] The converter 1 transforms an input voltage Vin (input current I.sub.L) supplied by the battery of the vehicle into an output voltage Vout applied across the terminals of the intermediate capacitor Cint, the voltages being measured with respect to ground M.

[0039] The converter 1 comprises a control module 10, an induction coil 20, a field-effect transistor 30 and a voltage comparator 50.

[0040] The induction coil 20 is installed at the input of the circuit so as to be charged when it is passed through by the input current I.sub.L.

[0041] A diode DI is installed between the induction coil 20 and the high terminal of the intermediate capacitor Cint, which terminal corresponds to the output of the converter 1, i.e. the terminal connected to the injectors 2.

[0042] The diode DI lets current pass from the induction coil 20 to the intermediate capacitor Cint but prevents current from flowing from the intermediate capacitor Cint to the induction coil 20 in order to prevent the intermediate capacitor Cint from discharging into the converter 1.

[0043] The transistor 30 comprises a drain D, a source S and a gate G, said gate G being connected to the control module 10 in order for said control module 10 to command the transistor 30 to an on state in which current passes between the drain D and the source S or to an off state in which current does not pass between the drain D and the source S. The source S is connected to ground M via a shunt resistor Rs.

[0044] The gate G is connected to the control module 10 via a control resistor Rc. In this nonlimiting example, a capacitor Cres is connected in parallel with the transistor 30, between the drain D and the source S, in order to make the converter 1 quasi-resonant.

[0045] The alternation of the on and off states of the transistor 30 generates a sawtooth current called the peak current Ipeak, the amplitude of which is bounded by a maximum value, and that allows the converter 1 to deliver the output voltage Vout, which is defined across the terminals of the capacitor Cint, which is called the “intermediate” capacitor, the discharge of this capacitor being commanded by a computer (not shown and known per se) via a drive module (not shown and known per se) in order to command the fuel injectors 2. The converter 1 is configured to make the output voltage Vout tend to a target value, 65 V for example.

[0046] The control module 10 is configured to switch the transistor 30 from the off state to the on state and to count the time passed since said switch. If at the end of a preset time called the “observation” time, the amplitude of the peak current Ipeak has not reached its maximum value, the control module 10 is configured to command the transistor 30 so that said transistor 30 switches from the on state to the off state. Preferably, but nonlimitingly, the preset observation time is comprised between 50 and 100 microseconds.

[0047] The control module 10 is also configured to keep the transistor 30 in the off state for a preset time called the “cooling” time and to command the transistor 30 so that said transistor 30 switches to the on state at the end of the cooling time. Preferably, but nonlimitingly, the preset cooling time is comprised between 0 and 2000 microseconds (time of zero if the observation time is enough to protect the converter).

[0048] FIG. 2 illustrates an exemplary control module 10 allowing these functions to be performed. In this example, the control module 10 firstly comprises a logic unit 110, a counter 120, an OR logic gate 130 (OR/+), an SR-Q latch 140, a driver 150, a comparator 160 and a generator 117 that delivers a reference voltage Vref.

[0049] The logic unit 110 for example takes the form of an integrated circuit and allows a command for switching the transistor 30 to its on state to be sent via the input S and the output Q of the latch 140 and via the driver 150.

[0050] With reference to FIGS. 2 and 3, when it commands the passage of the transistor 30 from the off state to the on state, the logic unit 110 sends a control pulse to the input S of the latch 140 so that said latch 140 commands, via the driver 150, the gate G of the transistor 30 in order to get said transistor 30 to turn on.

[0051] In so doing, the output signal of the latch 140 is also sent to the counter 120 in order to trigger said counter 120 in a step E1. The time measurement taken by the counter 120 is sent to the logic gate 130 in order to simulate an achievement of the top current, and to the logic unit 110 which suspends the commands of the transistor 30 during the preset cooling time.

[0052] In parallel, the comparator 160 compares the voltage defined across the terminals of the shunt resistor Rs with the reference voltage Vref delivered by the generator 170 (for example 0.3 V) and resets to zero the counter 120 when the voltage defined across the terminals of the shunt resistor Rs becomes equal to the reference voltage Vref.

[0053] If the voltage defined across the terminals of the shunt resistor Rs becomes equal to the reference voltage Vref before the time measurement taken by the counter 120 reaches the preset observation time, the comparator 160 generates an output signal that, on the one hand, resets the counter 120 to zero and, on the other hand, commands stoppage of the transistor 30 via, in succession, the logic gate 130, the input R of the latch 140 and the driver 150.

[0054] In contrast, if the time measurement taken by the counter 120 reaches the preset observation time while the voltage defined across the terminals of the shunt resistor Rs has not equaled the reference voltage Vref, this means that the amplitude of the peak current Ipeak has not reached its top value because the input voltage Vin of the converter 1 (i.e. the voltage delivered by the supply battery of the vehicle) is too low.

[0055] In this case, the counter 120 commands, in a step E2, the transistor 30, via the logic gate 130, the latch 140 and the driver 150, in order to get said transistor 30 to switch from the on state to the off state. The counter 120 also commands the logic unit 110 in order to get the latter to suspend the command of the transistor 30 for the provided cooling time.

[0056] Next, the logic unit 110 keeps, in a step E3, the transistor 30 in the off state for the preset cooling time, for example for 1000 microseconds, in order to leave the electronic components of the converter 1 the time to cool, thus decreasing the losses and a decrease in the efficiency of the converter 1.

[0057] Lastly, when the cooling time has passed, the logic unit 110 again commands, in a step E4, the transistor 30 to its on state in order to get it once again to convert the input voltage Vin into the output voltage Vout, thus allowing the intermediate capacitor Cint to be recharged.

[0058] The method according to the invention thus allows the operation of the converter 1 to be suspended in order to limit overheating thereof, and to leave it to cool for a given time, when the peak current Ipeak has not reached its top value sufficiently rapidly.