Circuit arrangement for inductively heating at least one fuel injector valve, and fuel injector arrangement comprising such a circuit arrangement

Abstract

A circuit configuration for inductively heating at least one fuel injection valve includes a power-transistor full-bridge circuit which acts as a driver for operating a series resonant circuit at an alternating voltage at or near the resonant frequency. The series resonant circuit includes a heater coil on which the resulting voltage can be significantly higher than the supply voltage. The power that can be fed to the heater coil can be modified or controlled by changing the frequency or the duty factor of the control signals of the switching elements of the bridge circuit. A fuel injection valve and methods for operating the circuit configuration are also provided.

Claims

1. A circuit configuration for inductively heating at least one fuel injection valve, the circuit configuration comprising: first and second nodes; a first controllable switching element connected between a positive terminal of a supply voltage and said first node; a second controllable switching element connected between said first node and a negative terminal of the supply voltage; a third controllable switching element connected between the positive terminal of the supply voltage and said second node; a fourth controllable switching element connected between said second node and the negative terminal of the supply voltage; a first heater coil for the at least one injection valve, said first heater coil being electrically connected between said first node and said second node; a first capacitor connected in a first series circuit with said first heater coil between said first and second nodes; a third node and a fourth node; a fifth controllable switching element connected electrically between the positive terminal of the supply voltage and said third node; a sixth controllable switching element connected electrically between said third node and the negative terminal of the supply voltage; a seventh controllable switching element connected electrically between the positive terminal of the supply voltage and said fourth node; an eighth controllable switching element connected electrically between said fourth node and the negative terminal of the supply voltage; a second series circuit including a second heater coil for a second injection valve and a second capacitor connected electrically between said second node and said third node; a third series circuit including a third heater coil for a third injection valve and a third capacitor connected electrically between said third node and said fourth node; and a fourth series circuit including a fourth heater coil for a fourth injection valve and a fourth capacitor connected electrically between said fourth node and said first node.

2. The circuit configuration according to claim 1, which further comprises diodes each being connected in parallel with a respective one of said switching elements, said diodes each being polarized in the reverse direction with respect to the supply voltage.

3. The circuit configuration according to claim 1, wherein said first, said second, said third, said fourth, said fifth, said sixth, said seventh, and said eighth controllable switching elements are the only controllable switching elements that control said first, said second, said third, and said fourth heater coils.

4. A fuel injection valve configuration, comprising: a circuit configuration according to claim 1; fuel injection valves; said heater coil and said capacitor of each of said series circuits being disposed in a respective one of said fuel injection valves; and said series circuits including said heater coils and said capacitors being connected in series with one another.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention will be explained in more detail below with reference to exemplary embodiments with the aid of figures, in which:

(2) FIG. 1 shows a circuit arrangement according to the invention comprising a series resonant circuit comprising a heater coil and driven by an H bridge,

(3) FIG. 2 shows the voltage waveforms between the nodes and at the heater coil,

(4) FIG. 3 shows the voltage waveforms at the nodes with respect to reference potential and the common-mode component of the voltage at the heater coil,

(5) FIG. 4 shows a further circuit arrangement according to the invention comprising series resonant circuits comprising respective heater coils and driven by linked H bridges,

(6) FIG. 5 shows a fuel injection valve arrangement according to the invention comprising resonant circuits arranged in the fuel injection valves.

DESCRIPTION OF THE INVENTION

(7) In the circuit arrangement shown in FIG. 1, a first series circuit comprising a first controllable switching element T1 in the form of a field-effect transistor having a substrate diode D1 and comprising a second controllable switching element T2 likewise in the form of a field-effect transistor having a substrate diode D2 is connected electrically between the positive terminal Vbat and the negative terminal GND of a voltage supply. The node between the two switching elements T1, T2 forms a first node A.

(8) In the same way, a second series circuit comprising a third controllable switching element T3 in the form of a field-effect transistor having a substrate diode D3 and a fourth controllable switching element T4 in the form of a field-effect transistor having a substrate diode D4 is connected electrically between the positive terminal Vbat and the negative terminal GND of the voltage supply. The node between the two switching elements T3, T4 forms a second node B.

(9) In a manner in accordance with the invention, a series resonant circuit comprising a heater coil LH, RL and a first capacitor C is connected between the nodes A, B, wherein the heater coil is represented by its winding inductance LH and its effective resistance RL. The switching elements T1, T2, T3, T4 have control inputs 1, 2, 3, 4. In order to measure the current through the resonant circuit C, LH, RL, a shunt R1 is arranged between the node between the second and third switching elements T2, T3 and the negative terminal GND of the voltage supply.

(10) In order to simulate this circuit arrangement, an inductance of approximately 5 H which is easy to manufacture has been selected, and the resonant capacitor has a value of 2 F. The inductance of the feedlines is negligible with respect to the heater inductance LH. The observed voltages and currents are represented in FIG. 2 and show values which can be managed easily technically and enable cost-effective production of the overall system. As can be seen, a peak voltage of 56.5V is present at the series resonant circuit although the supply voltage only has a value of 11V. As a result, it is possible to transmit sufficient power into the heater coil with acceptable current values.

(11) In order to generate the electromagnetic interference signal, the spectral energy density of the common-mode signal on the feedlines to the heater is of critical importance since these lines act as emission antenna. The low-frequency range is also of importance here since even above 100 kHz, maximum permissible interference signal levels are established.

(12) In principle, the H bridge has the advantage that its two output signals have opposite phase angles and the signal voltages cancel one another out during switchover, apart from differences in amplitude waveform and time. The signal waveforms at the nodes A and B, wherein the node B is the node between the capacitor C and the heater coil LH, RL, are very different, as can be seen from FIG. 3, which makes it possible to assume a high interference emission. There, the square-wave voltage in the illustration at the top is the voltage at the node A with respect to the reference potential GND and the sinusoidal voltage with sudden changes in voltage is the voltage at the node B with respect to the reference potential GND. However, consideration of the common-mode signal demonstrates that the additional amplitude generated by the resonant circuit is a sinusoidal oscillation with a very low harmonic content and therefore does not effect any notable interference emission in the assessed frequency range above 100 kHz.

(13) Control of the heater power can be performed in two ways. A first method according to the invention envisages changing the frequency of the drive signals at the control inputs 1 to 4 of the switching elements T1 to T4. If the resonant circuit is tuned to 50 kHz, a switch-on period of 10 s results, followed by a switch-off period of 10 s, i.e. a duty factor of 50%. If the switching periods are shortened, with the same duty factor, the frequency increases and the resonant circuit is operated above its resonant frequency.

(14) Correspondingly, the magnification factor of the voltage decreases, which in turn reduces the heater power.

(15) Therefore, the heating power can be reduced continuously, starting from a maximum value. A slight mistuning from 50 kHz to 59 kHz already halves the heating power. With the aid of this power control, it is possible to keep the heating power constant within a wide range, in the case of a varying supply voltage. The heating power can also be reduced when a preset set point temperature is reached in the heater in order to keep this temperature stable.

(16) In order to keep the temperature stable, it is necessary to regulate the temperature to a preset set point value. For this purpose, the actual temperature needs to be determined. In a manner in accordance with the invention, the determination of the heater temperature is performed by determining the resonant frequency.

(17) When using a magnet material for the heater of the fuel injection valve with a particularly low Curie temperature, the value of the heater inductance is reduced as this temperature is approached, which results in a temperature-dependent increase in the resonant frequency of the resonant circuit. There are now several possibilities for determining the resonant frequency.

(18) The frequency of the control signals at the control inputs 1 to 4 of the switching elements T1 to T4 is varied (tuned) periodically such that, in the process, the resonant frequency is safely met (sweep). The resonant frequency can be identified very easily from the maximum of the heater current. In this case, the ratio of the repetition rate and the sweep duration is selected such that the increased heating power occurring at the resonant frequency does not substantially change the average heating power.

(19) There is also a systematic (quadratic) relationship between the supply voltage and the heating power. If the resonant frequency is determined once when the heater is cold and the present supply voltage and the heating power generated in this case are also determined, a reference point is obtained. Starting from this reference point and a measurement of the present supply voltage and the heating power, it is possible to draw a conclusion in respect of the heater temperature. Instead of the heater power, the heater current which can be observed at the shunt R1 (FIG. 1) can also be used as measured variable. The heater temperature thus determined can then be used as actual variable for heater temperature regulation.

(20) In a further driving method, the drive signals at the control inputs 1 to 4 of the switching elements T1 to T4 can be operated at a lower duty factor than 50%. This means that all of the transistors in the H bridge are switched off for a short period of time. Correspondingly, during this period of time, no energy is supplied to the resonant circuit, which in turn results in a reduction in the heating power.

(21) Advantageously, the duration of the switch-off period is 10 s for the values of the simulation, which corresponds to the polarity-reversal duration of the resonant circuit. An advantage of this method consists in that the polarity-reversal process of the resonant circuit can be detected easily.

(22) In this case, too, this signal can be used for determining the heater temperature and can therefore act as actual value for heater temperature regulation.

(23) A typical motor vehicle engine has a plurality of cylinders, for example four or six. Since each cylinder is provided with a fuel injection valve, correspondingly four or six heaters are required. This necessitates the use of four or six H bridges for operating the heaters. By a suitable connection of output stages and heaters and suitable driving of the output stages, it is possible to dispense with half the output stages in the case of a four-cylinder engine and to reduce costs in this way.

(24) As shown in FIG. 4, starting from a circuit arrangement as shown in FIG. 1, a fifth controllable switching element T5 is connected electrically between the positive terminal of the supply voltage Vbat and a third node C, and a sixth controllable switching element T6 is connected electrically between the third node C and the negative terminal of the supply voltage GND. In addition, a seventh controllable switching element T7 is connected electrically between the positive terminal of the supply voltage Vbat and a fourth node D, and an eighth controllable switching element T8 is connected electrically between the fourth node D and the negative terminal for the supply voltage GND.

(25) A second series circuit comprising a second heater coil LH2 of a second injection valve EV2 and a second capacitor C2 is connected electrically between the second node B and the third node C. A third series circuit comprising a third heater coil LH3 of a third injection valve EV3 and a third capacitor C3 and a fourth series circuit comprising a fourth heater coil LH4 of a fourth injection valve EV4 and a fourth capacitor C4 are connected electrically between the third node C and the fourth node D and between the fourth node D and the first node A, respectively.

(26) The first heater coil LH1 is connected to the nodes A and B, i.e. it is fed by the switching elements T1, T2, T3, T4.

(27) The second heater coil LH2 is connected to the nodes B and C, i.e. it is fed by the switching elements T3, T4, T5, T6.

(28) The third heater coil LH3 is connected to the nodes C and D, i.e. it is fed by the switching elements T5, T6, T7, T8.

(29) The fourth heater coil LH4 is connected to the nodes D and A, i.e. it is fed by the switching elements T7, T8, T1, T2.

(30) The driving of the switching elements T1 to T8 takes place by virtue of the control signals at the control inputs 1 to 8. In this case, the signals at the control inputs 1, 4, 5, 8 always have the same level, and the signals at the control inputs 2, 3, 6, 7 always have the same, opposite level. That is to say that if the signals at the control inputs 1, 4, 5, 8 have a high level, the signals at the control inputs 2, 3, 6, 7 have a low level. Correspondingly, the voltages at the heater coils LH1 and LH4 have a positive value in a first phase and the voltages at the heater coils LH2 and LH3 have at the same time a negative value. The switching elements T1 to T8 should in this case be designed for twice the current-carrying capacity.

(31) If, as shown in FIG. 5, the resonant capacitors C1 to C4 are installed in the heaters of the fuel injection valves EV1 to EV4, the number of feedlines can also be halved.

(32) Although additional connections are now required between the fuel injection valves EV1 to EV4, this can be resolved in design terms by installing all of the heaters together in one valve module with integrated heaters, capacitors and connecting lines. This then results in a particularly compact, inexpensive design. It is also advantageous that half of the very expensive (heavy-duty) plugs are no longer required as a result of this arrangement.

(33) The behavior and the driving of the configuration shown in FIG. 5 do not differ from the embodiment illustrated in FIG. 4.