JP4483127B2 - Inductive load drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drive circuit for driving an inductive load such as a relay mounted on an electric vehicle or the like, and more particularly to a technique for reducing the influence of noise on the determination of abnormality of the inductive load.
[0002]
[Prior art]
In hybrid vehicles and electric vehicles, a main relay is used to open and close a connection between a motor drive system such as an inverter and a battery. The main relay is controlled to be opened and closed by a relay control mechanism in an ECU (electronic control unit). Here, the relay has abnormalities such as an open (non-conducting) abnormality and a short (conducting) abnormality, and such an abnormality adversely affects the state of the vehicle. Therefore, the relay control mechanism detects an open abnormality or a close abnormality, and outputs an abnormality detection signal when the abnormality is detected, so that a predetermined abnormal operation is performed. Detection of these abnormalities is performed by monitoring the drive signal output from the relay control mechanism to the main relay. For example, when the drive signal output is at a high (H) level even though the relay control mechanism has not issued a drive command, it is determined that an open abnormality has occurred.
[0003]
Here, a hybrid vehicle or the like is provided with a switching circuit such as an inverter for driving a motor or a DC-DC converter, which is electrically connected to a relay control mechanism via a main relay by electrostatic coupling or the like. Is bound to. A high voltage and a large power for driving the motor are applied to the inverter and the like, and since it is switched at a high speed for PWM control or the like, a considerably high level of high frequency such as 10 MHz is generated. This high frequency acts as noise on the drive signal output of the electrically coupled relay control mechanism. For this reason, conventionally, by providing a low-pass filter component between the drive signal output and the comparator for high / low determination of the signal, the high-frequency noise has an influence on the relay abnormality determination. I am trying not to.
[0004]
As a countermeasure against high frequency noise for controlling an inductive load such as a relay, there is a technique disclosed in JP-A-8-22336. In this document, in a driving device for driving an inductive load such as an electromagnetic actuator or an electromagnetic valve of an automobile, a method for providing a noise removing capacitor in a flyback circuit in order to remove high frequency noise due to switching of a current path. Is disclosed. Japanese Patent Laid-Open No. 11-136801 discloses that in an electric vehicle, in order to avoid switching noise of an inverter for driving a motor from flowing into a low-voltage power line to an auxiliary device such as a radio, A technique for shielding a high-voltage power supply line from a battery is disclosed.
[0005]
[Problems to be solved by the invention]
In a drive circuit such as a relay control mechanism for driving an inductive load such as a relay, the above high frequency noise is reduced to low frequency noise (for example, due to the influence of the inductance of the load and the stray capacitance of the wiring from the drive circuit to the load). Several tens of kHz) may be induced.
[0006]
However, although all the above prior arts give consideration to high-frequency noise, they do not pay attention to low-frequency noise induced therefrom. For example, in the case of the relay control mechanism described above, such low-frequency noise cannot be sufficiently attenuated by the low-pass filter, and may cause erroneous determination of relay abnormality.
[0007]
The present invention has been made in view of such a problem, and in an inductive load drive circuit such as a relay, it is possible to reduce erroneous determination of abnormality determination of the load due to low frequency noise caused by high frequency noise. The purpose is to provide technology.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a drive circuit according to the present invention is a drive circuit for driving an inductive load, and includes an arc extinguishing means for releasing electromagnetic energy of the load at the end of driving the load. In the drive circuit for monitoring the voltage of the wiring for supplying driving power to the load and judging the load abnormality, the output of the driving circuit for the wiring is in parallel with the stray capacitance related to the wiring to the load. A predetermined capacity is connected.
[0009]
Here, the inductive load is, for example, a relay or an actuator. The arc extinguishing means generates a direct current component from external high frequency noise by its detection action. This direct current component vibrates a resonance system composed of an inductive load and a stray capacitance of the wiring corresponding thereto, and thus low frequency noise is generated, which contributes to erroneous determination of load abnormality. In the present invention, by connecting a predetermined capacitor in parallel with the stray capacitance, the level of the high frequency noise induced in the stray capacitance of the wiring to the load is reduced, and the low frequency noise finally induced from this high frequency noise is reduced. Reduce the level of By reducing the level of the low frequency noise, erroneous determination due to the low frequency noise can be prevented or reduced.
[0010]
In a preferred aspect, the drive circuit determines that the load is abnormal when the voltage level of the wiring deviates from a predetermined allowable range, and the predetermined capacitance connected in parallel to the stray capacitance is electrically connected to the wiring. The low frequency noise level generated by the action of the arc extinguishing means, the inductive load, and the stray capacitance is set to be within the allowable range due to high frequency noise from a noise source to be coupled to each other. Is done.
[0011]
In another preferable aspect, the inductive load is a relay or an actuator mounted on a vehicle, and the stray capacitance is a stray capacitance formed between a wire harness of the vehicle and a vehicle body. .
[0012]
In another preferred aspect, the inductive load is a relay or an actuator mounted on a vehicle, and the noise source is a high power switching circuit mounted on the vehicle.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0013]
In a drive circuit of a main relay for power supply interruption such as a hybrid vehicle or an electric vehicle, a low frequency noise is induced from a high frequency noise generated by a switching circuit such as an inverter, which influences an abnormality determination of the relay in the drive circuit. The mechanism will be described with reference to FIG.
[0014]
FIG. 1 is a diagram showing an equivalent circuit around the drive circuit of such a main relay. In the figure, an ECU (electronic control unit) 10 as a drive circuit performs drive control of an inductive load 20. In this case, the inductive load 20 is a main relay for opening and closing a connection between a motor drive system such as an inverter and a battery. The ECU 10 itself can execute various control functions in addition to the control of the inductive load 20, but only the components related to the control of the inductive load 20 related to the present invention are illustrated here.
[0015]
In the ECU 10, a CPU (central processing unit) 11 is a device that executes processing for various controls. In connection with the present embodiment, the generation of the drive signal IN to the inductive load 20 and the inductive load are performed. Processing such as determination of 20 open abnormalities and short abnormalities and output of an abnormality notification signal according to the determination is performed. The drive signal IN is amplified by the amplifier of the switch element drive stage 13 and supplied to the gate of the drive switch element 15. The drive switch element 15 is an element that controls the supply / cutoff of drive power to the inductive load 20, and is composed of, for example, a MOS transistor. The drive switch element 15 opens the gate when the drive signal IN is high, for example, and supplies a drive current of 12 V, for example, from the power supply 16 to the inductive load 20. The comparator 17 compares the voltage (potential) of the wiring 21 from the output of the drive switch element 15 to the inductive load 20 with a predetermined reference voltage (threshold potential), and outputs the comparison result as the status signal ST. For example, when the drive signal IN is high, the gate of the drive switch element 15 is opened, and drive power is supplied to the inductive load 20, the voltage of the wiring 21 becomes higher than the reference voltage, and the status signal ST goes high. The CPU 11 checks the consistency between the status signal ST and the state of the drive switch control performed by the CPU 11 (for example, whether or not the drive signal IN is high). Determine whether there is an open error or short circuit error. When the driving of the inductive load 20 is finished, the free wheel diode 19 quickly releases the electromagnetic energy accumulated in the inductive load 20 so that the relay can be switched quickly or the switch element can be damaged. It performs functions such as prevention. This function is also called arc extinguishing function.
[0016]
In the case of a hybrid vehicle, the high-frequency noise source 26 is a high-voltage / high-power switching circuit such as an inverter or a DC-DC converter for driving control of a motor / generator. The high frequency noise source 26 is electrically coupled to an inductive load 20 such as a main relay. The stray capacitance 22 is a stray capacitance generated between the load wiring 21 from the ECU 10 to the inductive load 20 and the ground (GND) potential (in the case of a hybrid vehicle, the potential of the vehicle body).
[0017]
In such a circuit, a mechanism in which low frequency noise is generated from high frequency noise generated by the high frequency noise source 26 and causes erroneous determination of load abnormality is as follows.
[0018]
First, in the high frequency noise source 26, with switching of an inverter or the like, high frequency ringing noise of, for example, 10 MHz and several tens of Vpp (volt peak to peak) is generated due to stray capacitance and wiring inductance of components such as the inverter. appear. FIG. 2A shows an example of the waveform of this high frequency noise. In this waveform, the repetition frequency of the burst is about 10 kHz, and the noise in each burst is a high frequency of 10 MHz, for example.
[0019]
This high-frequency noise is induced and superimposed on a high-voltage power supply line that connects the main relay (inductive load 20) and the switching circuit (high-frequency noise source), internal wiring in the switching circuit, and the like. The high-frequency noise is caused by the electrostatic coupling capacitance (for example, several tens of pF) between the high-voltage power supply line and the exciting wire (that is, the wiring 21) of the main relay, the low-voltage control signal line such as an inverter, and the relay exemplified wire. Through electrostatic coupling capacitance (in FIG. 1, these are collectively shown as coupling capacitance 24), electrostatic induction is caused to stray capacitance 22 (for example, about 500 pF) between the excitation wire and ground. In this case, the noise induced in the stray capacitance 22 when the ECU 10 is not connected is, for example, a burst wave of about 10 MHz and 10 to 20 Vpp.
[0020]
When the output terminal of the ECU 10 is connected (the switch element 15 is conductive), the switch element 15 and the free wheel diode 19 in the ECU 10 detect the high frequency component of about 10 MHz and generate a DC (direct current) component. This DC component causes resonance at a low frequency (for example, about 30 kHz) by the parallel resonance system of the inductance of the main relay (inductive load 20) and the stray capacitance 22. A low frequency component due to this resonance is superimposed on the wiring 21. This low-frequency noise is induced from a high-level high-frequency noise from a high-voltage / high-power switching circuit for driving a motor or the like, and thus becomes a considerably high-level noise. FIG. 2B is an example of a voltage waveform of the output to the relay excitation line (wiring 21), which is a waveform when the drive switch element 15 is OFF (that is, when the relay is not driven, that is, non-conductive). is there. As shown in this figure, the output voltage to the wiring 21 is superposed with a burst high frequency noise component of about 10 MHz and a low frequency noise component of about 30 kHz. A broken line of 3.6 V level shown in FIG. 2B indicates a reference voltage of the comparator 17.
[0021]
In the ECU 10, the voltage at the output terminal to the wiring 21 is monitored by the comparator 17. A low-pass filter (LPF) component is conventionally provided between the output terminal and the comparator 17. For this reason, the high frequency noise component of about 10 MHz superimposed on the voltage of the output to the wiring 21 is attenuated and does not affect the voltage monitoring.
[0022]
On the other hand, since the low frequency noise component of about 30 kHz induced from this high frequency noise is not attenuated so much by the LPF component, the level exceeds the reference voltage, and the comparator 17 should output the low (L) level. In some cases, a high (H) level is output. For example, in the example of FIG. 2, since the relay is not driven, the voltage of the wiring 21 should be lower than the reference voltage, and the output of the comparator 17 should be L. However, there is a portion where the level of the low frequency noise component exceeds the reference voltage level (broken line) as shown in FIG. 5B, and in this portion, the output of the comparator 17 (status signal ST) becomes H level ( FIG. 2 (c)). In this case, the CPU 11 determines that the relay (inductive load 20) is open abnormally because the place where the status signal ST should be at the L level is actually the H level. At this time, since the relay is actually in a non-driven state, the determination of an open abnormality is an erroneous determination.
[0023]
In the foregoing, the mechanism of occurrence of abnormal determination due to low frequency noise induced by high frequency noise has been described. In order to prevent or reduce such erroneous determination, the circuit of the present embodiment has a sufficient capacity in parallel with the stray capacitance 22 of the wiring 21 between the wiring 21 for exciting output of the ECU 10 and the ground. Provide a capacitor.
[0024]
For example, if the capacitance of this capacitor is equal to or greater than that of the stray capacitance 22, more than half of the current flowing into the stray capacitance 22 when the capacitor is not provided flows into the capacitor, and the amount of current flowing into the stray capacitance 22 is Since it is less than half, the amplitude of burst high frequency (about 10 MHz) noise induced in the stray capacitance 22 is less than half.
[0025]
Here, the level of the DC component generated when the high frequency noise is detected by the switch element 15 and the free wheel diode 19 of the ECU 10 is substantially proportional to the amplitude of the high frequency noise. Further, from this DC component, the amplitude of the low frequency noise generated by the parallel resonance system of the inductive load 20 and the stray capacitance 22 is substantially proportional to the DC component.
[0026]
Therefore, if the amplitude of the high frequency noise is reduced to half or less by the capacitor added in parallel to the stray capacitance 22, the finally induced low frequency noise amplitude can also be reduced to half or less. For example, in the example shown in FIG. 2, if the level of the low-frequency noise is halved, the reference voltage of the comparator 17 is not exceeded, so that erroneous detection of abnormality is prevented.
[0027]
In addition, as an example of the capacity of the capacitor added in parallel to the stray capacitance 22, a case where the capacitance is equal to or greater than that of the stray capacitance 22 is illustrated, but of course this is only an example. In principle, it should be a capacity that can divert the current to the stray capacitance 22 so that the level of the induced low frequency noise is below the reference voltage of the means (comparator 17) for monitoring the output voltage to the wiring 21. That's fine. The capacity required for preventing erroneous determination is to perform experiments as necessary in consideration of the high-frequency noise level of the noise source 26, the capacity of the stray capacitance 22, the reference voltage of the comparator 17, and the like. Can be determined appropriately.
[0028]
FIG. 3 is a diagram showing a correlation between the level of high-frequency noise and the level of low-frequency noise induced therefrom. This correlation is obtained by experiment, and it can be seen that when the level of the high frequency noise decreases, the level of the low frequency noise decreases in proportion to it. From this, it can be seen that by reducing the level of the high-frequency noise component induced in the stray capacitance 22 that is the source of the DC component, the low-frequency noise can be reduced accordingly.
[0029]
As explained above, with respect to the output to the load wiring to the inductive load such as the main relay, in parallel with the stray capacitance around the load wiring, sufficient capacity to make the low frequency noise level below the reference voltage. By connecting, it is possible to prevent or reduce errors in the abnormality determination of the inductive load.
[0030]
In addition, although error prevention of abnormality determination can also be realized by providing a low-pass filter between the output of the comparator 17 and the CPU 11, in this method, when abnormality actually occurs, timing of abnormality detection Will cause a delay, leading to a decrease in anomaly detection performance. On the other hand, according to the system of the present embodiment, it is possible to prevent or reduce abnormal detection of an abnormality without causing a decrease in the abnormality detection performance.
[0031]
Further, in the above, the case where the free wheel diode 19 is provided is taken as an example, but the system of the present embodiment can be applied even when arc extinguishing means other than the free wheel diode is provided instead. It will be clear.
[0032]
Next, an example of a circuit of a motor drive system of a hybrid vehicle to which the above-described method is applied will be described with reference to FIG.
[0033]
In the circuit configuration shown in FIG. 4, the SMR assembly 200 includes three system main relays SMR 1 to 3 for connecting / disconnecting a high-voltage power supply line connecting the main battery 210 and the motor / generator 240 side. SMR). SMR3 is a negative side relay, and SMR2 is a positive side relay. In the power line connection state, these relays are in a connected state. However, if both of these relays are connected from the power line cut-off state, a large current may flow instantaneously and the fuse may melt. Therefore, before connecting SMR2, first connect SMR1 provided in series with the resistor. Thus, a procedure is adopted in which a large current is prevented, and then SMR2 is connected and SMR1 is cut off. Main battery 210 is controlled by battery ECU 215. The DC-DC converter 220 reduces the voltage of the main battery 210 to obtain a 12V auxiliary power supply. The inverter unit 230 switches the supplied high-voltage direct current power to generate a three-phase alternating current and supplies it to the motor / generator 240, or vice versa, converts the electric power generated by the motor / generator 240 into direct current and converts it into a main battery. Or supply to the 210 side. Since such a circuit configuration is well known, the description will be limited to the above.
[0034]
The hybrid ECU 100 includes intelligent MOSs 120 and 140 for driving control of the SMRs 1 to 3. The intelligent MOSs 120 and 140 are devices including a drive switch element 124, a switch element drive stage 122, and a comparator 126, which correspond to the drive switch element 15, the switch element drive stage 13 and the comparator 17 in the equivalent circuit of FIG. ing. The intelligent MOS 120 is for controlling the SMR 2, and the load wiring 250 output therefrom is connected to the solenoid of the SMR 2. On the other hand, the intelligent MOS 140 is for controlling the SMRs 1 and 3, and the load wiring 260 connected to the output terminal is connected to the SMRs 1 and 3 (the wiring is not shown in the figure). Each of these intelligent MOSs 120 and 140 is connected to the CPU 110 and receives a drive signal IN from the CPU 110 or supplies a status signal ST to the CPU 110. The CPU 110 corresponds to the CPU 11 in FIG.
[0035]
A free wheel diode 150 is provided between the load wiring 260 from the intelligent MOS 140 to the SMRs 1 and 3 and the ground potential (vehicle body), and clamps the potential of the output terminal OUT of the MOS 140 to about −1V. Therefore, when the supply of the excitation current to the SMRs 1 and 3 is cut off, the electromagnetic energy stored in the SMRs 1 and 3 is released by the free wheel diode 150 with a voltage drop of about 1V.
[0036]
The load wiring 250 connected to the output terminal of the intelligent MOS 120 is provided with an early-cut circuit 130 between the ground (in this case, the vehicle body). This fast-cut circuit 130 is basically for performing an arc extinguishing function when the exciting current supply to the SMR 2 is cut off, like the free wheel diode 150. However, the early cut circuit 130 realizes a much quicker electromagnetic energy release than the free wheel diode 150 by setting a large clamp voltage such as about −10 to −20 V to the load wiring 250. The SMR2 is provided with the quick disconnect circuit 130 in the load wiring 250 to the SMR2 when the SMR2 is a main relay (compared to the SMR1), and when the ignition switch is turned off, the SMR2 is disconnected and only the SMR3 is connected. This is because control for driving the inverter unit 230 is performed to extract the electric charge of the electrolytic capacitor in the inverter unit 230, and at this time, it is necessary to quickly release a large amount of electromagnetic energy from the SMR2. A Zener diode 132 having a breakdown voltage corresponding to the clamp voltage is used. During normal operation (for example, when driving SMR2), the PNP switch 134 of the early cut-off circuit 130 is in an OFF state. However, when the switch element 124 of the intelligent MOS 120 is turned off, the ground terminal and the load wiring side terminal of the early cut-off circuit 130 are turned off. The Zener diode 132 breaks down and a current flows. As a result, the switch 134 is turned on, so that a relatively large current flows through the circuit 130, thereby quickly increasing the electromagnetic energy of the SMR2 solenoid. Released.
[0037]
In the operation mode when the ignition switch is off, the SMR 2 is controlled so as to be in a cut-off (non-conduction) state, and therefore the voltage of the load wiring 250 should be lower than the reference voltage for voltage monitoring of the intelligent MOS 120. However, since the inverter unit 230 is operated at this time, low frequency noise is induced in the load wiring 250 by the above-described mechanism from high frequency noise due to the high speed switching. That is, the switching element portion A of the inverter unit 230 is a source of high-frequency noise of about 10 MHz. This noise is filtered by the high-voltage power supply line or the portion B in the DC-DC converter 220, and the high-voltage power supply line near the SMR2. High-frequency noise is induced in the stray capacitance 255 of the load wiring 250 by crosstalk or the like due to stray capacitance between the load wiring 250 and the load wiring 250 (excitation line). From this high-frequency noise, a DC component is generated by the detection operation of the early cut-off circuit 130 and the switching element 124, which vibrates the parallel resonance system due to the stray capacitance 255 and the inductance of the SMR 2, thereby causing the load wiring 250 to generate low-frequency noise. Induces. The low-frequency noise may cause the intelligent MOS 120 and the CPU 110 to erroneously determine that the SMR2 is open abnormally.
[0038]
Therefore, in this embodiment, in order to prevent such an erroneous determination, the low-frequency noise reduction capacitor 160 is provided in parallel with the stray capacitance 255 between the load wiring 250 and the ground. It was. With this capacitor 160, the level of low-frequency noise is reduced by the mechanism described above, and errors in SMR2 abnormality determination can be reduced. If the capacitor 160 has a capacity sufficient to make the low-frequency noise level smaller than the reference voltage for load voltage level determination by the comparator 126, erroneous determination can be prevented.
[0039]
In the example of FIG. 4, the low-frequency noise reducing capacitor 160 is provided only for the load wiring 250 to the SMR 2, but this is based on the way of wiring and the relationship of the relay connection mode. This is because high-level low-frequency noise that causes a problem is not induced in the load wiring 260. Accordingly, when high-level low-frequency noise appears also in the load wiring 260 to the SMRs 1 and 3, it is also preferable to provide a similar low-frequency noise reducing capacitor for the load wiring 260. .
[0040]
In the above example, a relay drive circuit that turns on and off a high-voltage power supply line for driving a motor (and / or generator) such as a hybrid vehicle or an electric vehicle has been described as an example. It can be applied to a drive circuit of an inductive load other than the relay. In other words, in a circuit that determines abnormalities such as open abnormalities and short circuit abnormalities of the inductive load based on whether or not the voltage of the wiring that supplies power to the load is within a predetermined allowable range, If low frequency noise is induced from the noise in the load capacity of the wiring, erroneous determination can be prevented or reduced by using the method of this embodiment. For example, an actuator drive circuit that drives an injector solenoid of a vehicle engine is also provided with an arc extinguishing circuit for releasing electromagnetic energy of the solenoid at the end of driving (for example, JP-A-10-311238). Even in such a drive circuit, as in the above embodiment, if high-frequency noise is induced from the vicinity, a DC component is generated due to the detection action of the arc-extinguishing circuit, and this is caused by the resonance system of the floating capacitance of the load wiring and the solenoid. It may be effective to apply the method of this embodiment because noise may be induced to cause erroneous determination.
[Brief description of the drawings]
FIG. 1 is a diagram showing an equivalent circuit composed of a drive circuit and a group of elements related to the target of the method of the embodiment.
FIG. 2 is a diagram illustrating examples of waveforms of high-frequency noise from a noise source, induced low-frequency noise, and a relay status signal when abnormality / error determination occurs.
FIG. 3 is a diagram showing the correlation between the level of high-frequency noise and the level of low-frequency noise induced from now on.
FIG. 4 is a diagram schematically showing a circuit of a motor drive system of a hybrid vehicle to which the present invention is applied.
[Explanation of symbols]
100 Hybrid ECU, 110 CPU, 120 Intelligent MOS, 124 Drive switching element, 126 Comparator, 130 Early cut circuit, 160 Low frequency noise reduction capacitor, 200 SMR (system main relay) assembly, 210 Main battery, 230 Inverter Part, 240 motor generator.

Claims (4)

A drive circuit for driving an inductive load, comprising an arc extinguishing means for releasing electromagnetic energy of the load at the end of driving of the load, and monitoring a voltage of a wiring for supplying driving power to the load In the drive circuit for determining the load abnormality,
A drive circuit for an inductive load, wherein a predetermined capacitance is connected in parallel with a stray capacitance related to the wiring to the load with respect to an output of the driving circuit to the wiring. The drive circuit determines a load abnormality when the voltage level of the wiring deviates from a predetermined allowable range,
The predetermined capacitance connected in parallel to the stray capacitance is caused by high-frequency noise from a noise source electrically coupled to the wiring, and the action of the arc extinguishing means, the inductive load, and the stray capacitance. Is set so that the level of low-frequency noise generated by is within the allowable range,
The drive circuit according to claim 1. The inductive load is a relay or an actuator installed in a vehicle, and the stray capacitance is a stray capacitance formed between a wire harness of the vehicle and a vehicle body. Driving circuit. 3. The drive circuit according to claim 1, wherein the inductive load is a relay or an actuator mounted on a vehicle, and the noise source is a high power switching circuit mounted on the vehicle.

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