Electronic control unit

Abstract

To provide an electronic control unit capable of reliably avoiding over-boosting sate of a boosting capacitor, and returning back counter electromotive force to a battery.SOLUTION: A boosting circuit 2 boosts voltage by charging a power supply voltage VB supplied from a battery 3 to a boosting capacitor C1. Transistor SW2, SW3 current drives a coil L2 with boosted output voltage VA of the boosting circuit 2 and the power supply voltage VB of the battery 3, and for transistor SW4, its on / off state is selected for each cylinder of an internal combustion engine. A control part 4 controls the boosting circuit 2 and the transistors SW2 to SW4. A diode D4 returns back current from a connection point of the coil L2 and the transistor SW4 to the boosting capacitor C1 side, and a Zener diode ZD1 is connected between the diode D4 and the battery 3 and clamps the voltage applied to the boosting capacitor C1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electronic control device that boosts a power supply voltage supplied from a battery by a boosting circuit and drives an inductive load with current.

Background Art

[0002] For example, in Patent Document 1, when a current associated with a back electromotive force generated when power supply to an inductive load is stopped is regenerated to the boosting circuit side, if the voltage charged in the boosting capacitor rises excessively, a technique for eliminating the overboost state by discharging the voltage to the battery side is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the configuration of Patent Document 1, when refluxing the back electromotive force generated in the inductive load, it always passes through the boosting circuit. And since the back electromotive force cannot be refluxed to the battery until the boosting switching operation in the boosting circuit ends, it will be refluxed to the boosting capacitor for a certain period, and there is a problem that it cannot be said that the overboost state can be surely eliminated.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide an electronic control device that can surely avoid the boosting capacitor from being in an overboost state and can reflux the back electromotive force to the battery.

Means for Solving the Problems

[0006] According to the electronic control device described in claim 1, the boost circuit (2) charges a boost capacitor (C1) with the power supply voltage supplied from the battery (3) to perform a voltage boost. The high-side switches (SW2, SW3) drive an inductive load (L2) with current based on the output voltage of the boost circuit and the power supply voltage, and the multiple low-side switches (SW4) are selected to be on or off for each cylinder of the internal combustion engine. The control units (4, 4A, 4B) control the boost circuit, the high-side switches and the low-side switches. The diode (D4) returns current from the connection point between the inductive load and the low-side switch to the boost capacitor, and the Zener diode (ZD1) is a diode The cathode is connected to the cathode of the battery, and the anode is connected to the positive terminal of the battery. Connected hand The voltage applied to the boost capacitor is clamped.

[0007] With this configuration, when the power supply to the inductive load is stopped, the current associated with the back electromotive force generated is regenerated to the boost circuit side via the diode. As the voltage of the boost capacitor rises, the Zener diode breaks down, and the anode potential of the diode is clamped to the value obtained by adding the Zener voltage to the battery voltage. Therefore, without stopping the boost operation of the boost circuit, it is possible to reliably prevent the boost capacitor from becoming over-boosted and to recirculate the generated back electromotive force back to the battery.

[0008] According to the electronic control device described in claim 2, the Zener voltage of the Zener diode is set to be greater than the output voltage setting of the boost circuit, and the value added to the power supply voltage is set to be lower than the breakdown voltage of the boost capacitor, thereby providing more reliable protection to the circuit. [Brief explanation of the drawing]

[0009] [Figure 1] This is a first embodiment, and the diagram shows the configuration of the electronic control unit. [Figure 2] Timing chart showing circuit operation when the boosted output voltage is within the normal range. [Figure 3] Timing chart showing circuit operation when the boosted output voltage becomes over-boosted. [Figure 4] A flowchart illustrating the circuit operation for switching the return path. [Figure 5] This is a second embodiment, and the diagram shows the configuration of the electronic control unit. [Figure 6] A flowchart showing the control details of the arithmetic unit. [Figure 7] This is a third embodiment, and the diagram shows the configuration of the electronic control unit. [Figure 8] A flowchart showing the control details of the arithmetic unit. [Modes for carrying out the invention]

[0010] (First Embodiment) As shown in Figure 1, the electronic control unit 1 of this embodiment drives, for example, a fuel injection valve in an internal combustion engine of a vehicle. The electronic control unit 1 includes a boost circuit 2 that generates a voltage VA by boosting the power supply voltage VB of the battery 3. The boost circuit 2 has a series circuit of a coil L1, a diode D1, and a boost capacitor C1 connected between the battery 3 and ground. A transistor SW1, which is a boost control switch, is connected between the anode of diode D1 and ground. The cathode of diode D1 is the output terminal of the boosted output voltage VA, and this output terminal is connected to the input terminal of the control unit 4. The control unit 4 controls the on / off state of transistor SW1 and monitors the boosted output voltage VA.

[0011] A series circuit consisting of transistor SW3 (high-side switch), diode D3, coil L2 (external to the electronic control unit 1), and transistor SW4 (low-side switch) is connected between battery 3 and ground. A series circuit consisting of transistor SW2 (high-side boost output switch) and diode D2 (reverse-direction switch) is connected between the output terminal of boost circuit 2 and ground. The cathode of diode D2 is connected to the cathode of diode D3. A series circuit of reverse-direction diodes D5 and D4 is connected between the output terminal of boost circuit 2 and transistor SW4. The anode of Zener diode ZD1 is connected to battery 3, and the cathode of Zener diode ZD1 is connected to the anode of diode D5.

[0012] The inductive loads, coil L2 and transistor SW4, actually exist in multiple sets depending on the number of cylinders in the internal combustion engine. Transistors SW1 to SW4 are, for example, N-channel MOSFETs. The on / off state of each transistor SW2 to SW4 is also controlled by a control unit 4, which is, for example, a microcomputer.

[0013] Next, the operation of this embodiment will be described. First, before starting to control the energization of coil L2, the control unit 4 charges the boost capacitor C1 by repeatedly switching the transistor SW1 of the boost circuit 2 on and off. Specifically, when transistor SW1 is turned on, current flows through the path including coil L1 and transistor SW1. Subsequently, when transistor SW1 is turned off, a back electromotive force is generated in coil L1, so the capacitor C1 is charged with a voltage equal to or greater than the battery voltage VB. During this time, the control unit 4 keeps transistors SW2 to SW4 turned off.

[0014] As shown in Figure 2, the boosted output voltage VA under normal conditions is set to be lower than the voltage obtained by adding the Zener voltage Vz of the Zener diode ZD1 to the voltage VB of the battery 3, so the diode D5 is on. The control unit 4 energizes and drives the coil L2 that constitutes the injector, and therefore simultaneously turns on transistors SW2 to SW4 at time T1. Transistor SW4 is turned on to correspond to the selected cylinder / fuel injector. At this time, since the boosted output voltage VA is higher than the battery voltage VB, the boosted output voltage VA is applied to the coil L2 and the fuel injector opens. The boosted output voltage VA decreases as the capacitor C1 discharges.

[0015] Next, at time T2, when the control unit 4 turns off transistors SW2 and SW3, it controls the on / off switching of transistor SW3 so that the current IR flowing through coil L2 is within a predetermined target range. As a result, the battery voltage VB is intermittently applied to coil L2, maintaining the fuel injection valve in an open state. The control unit 4 also controls the on / off switching of transistor SW1 until the boosted output voltage VA reaches a predetermined value, thereby charging the boost capacitor C1. Note that Figure 2 illustrates a case where the target range of the current IR flowing through coil L2 decreases in two stages, but it may be one stage or three or more stages.

[0016] Next, at time T3, control unit 4 turns off transistors SW3 and SW4. This reduces the current IR flowing through coil L2, causing the fuel injector to close. At this time, the decrease in current IR through coil L2 generates a back electromotive force in coil L2. This current IB due to the back electromotive force is returned to the output terminal of boost circuit 2 via diodes D4 and D5. This charges the boost capacitor C1, causing the boosted output voltage VA to increase. Diode D5 turns off after the current IB has flowed. Subsequently, at the timing when the fuel injector should be opened next, control unit 4 turns on transistors SW2 to SW4 at the same time as at time T2, and performs the same operation as described above from time T2 onwards.

[0017] On the one hand, as shown in FIG. 3, when the voltage of the boost capacitor C1 rises excessively due to reflux and the boost output voltage VA becomes higher than the value obtained by adding the Zener voltage Vz to the battery voltage VB, the Zener diode ZD1 undergoes Zener breakdown, so the current switches to flow back to the battery 3 through the Zener diode ZD1. Incidentally, the Zener voltage Vz is preferably set to be larger than, for example, the set value of the boost output voltage VA of the boost circuit 2 and such that the voltage (VB + Vz) is lower than the withstand voltage of the boost capacitor C1. FIG. 4 shows the circuit operation for switching the reflux path in a flowchart.

[0018] As described above, according to this embodiment, the boost circuit 2 boosts the power supply voltage VB supplied from the battery 3 by charging the boost capacitor C1. The transistors SW2 and SW3 drive the coil L2 with current according to the boost output voltage VA of the boost circuit 2 and the power supply voltage VB of the battery 3, and the transistor SW4 is selected to be in an on / off state for each cylinder of the internal combustion engine. The control unit 4 controls the boost circuit 2 and the transistors SW2 to SW4. The diode D4 causes the current to flow back to the boost capacitor C1 side from the connection point between the coil L2 and the transistor W4, and the Zener diode ZD1 is connected between the diode D4 and the battery 3 to clamp the voltage applied to the boost capacitor C1.

[0019] With this configuration, when the current associated with the back electromotive force generated when power supply to coil L2 is stopped is regenerated to the boost circuit 2 side via diodes D4 and D5, if the voltage of boost capacitor C1 rises and Zener diode ZD1 enters the breakdown state, the anode potential of diode D4 is clamped to a value obtained by adding the Zener voltage Vz to the battery voltage VB. Therefore, hardware operation alone can surely avoid the boost capacitor C1 from entering an overvoltage state without stopping the boosting operation by the boost circuit 2, and the generated back electromotive force can be refluxed to battery 3. At that time, the Zener voltage Vz of Zener diode ZD1 is set to be larger than the set value of the boost output voltage VA of boost circuit 2 and the voltage (VB + Vz) is lower than the withstand voltage of boost capacitor C1, so that the circuit can be more surely protected.

[0020] (Second Embodiment) Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted, and different parts will be described. As shown in FIG. 5, the electronic control device 11 of the second embodiment includes an arithmetic unit 12. The input terminal of the arithmetic unit 12 is connected to the cathode of the diode D4, and the output terminal is connected to the control unit 4A. The arithmetic unit 12 monitors the above cathode potential.

[0021] Next, the operation of the second embodiment will be described. As shown in FIG. 6, when the arithmetic unit 12 monitors the cathode potential of the diode D4 and detects that the boost output voltage VA becomes larger than (VB + Vz) and the Zener diode ZD1 has undergone Zener breakdown (S4; YES), the arithmetic unit 12 outputs a control switching request to the control unit 4A (S5). In response to this request, the control unit 4A, for example, stops the switching of the transistor SW1 to stop the operation of the boost circuit 2, or turns off all of the transistors SW2 to SW4 to stop the energization to the coil L2. These correspond to overvoltage elimination control, and both may be performed simultaneously, or only either one may be performed.

[0022] As described above, according to the second embodiment, the control unit 4A monitors the cathode potential of diode D4 monitored by the arithmetic unit 12. to By performing overvoltage elimination control accordingly, the circuit can be protected from overvoltage even more reliably.

[0023] (Third embodiment) As shown in Figure 7, the electronic control device 13 of the third embodiment includes a control unit 4B and a calculation unit 14, replacing the control unit 4A and calculation unit 12. The calculation unit 14 controls the switching of each transistor SW1 to SW4 independently of the control unit 4B. As shown in Figure 8, if (YES) is determined in step S4, the calculation unit 14 outputs a request to the control unit 4B to stop the control of transistors SW1 to SW4. Then, the calculation unit 14 controls the switching of transistors SW1 to SW4 to perform over-boost elimination control in the same manner as in the second embodiment (S6).

[0024] (Other embodiments) The high-side and low-side switches are not limited to N-channel MOSFETs. The Zener voltage Vz can be set appropriately according to individual settings, without departing from the spirit of the invention. This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure. [Explanation of Symbols]

[0025] In the diagram, 1 represents the electronic control unit, 2 the boost circuit, 3 the battery, 4 the control unit, C1 the boost capacitor, L2 the coil, SW1 to SW4 the transistors, D4 and D5 the diodes, and ZD1 the Zener diode.

Claims

1. A boost circuit (2) charges a boost capacitor (C1) with the power supply voltage supplied from the battery (3) to perform a voltage boost, This boost circuit has output voltage and the power supply voltage, which are used to drive an inductive load (L2) with high-side switches (SW2, SW3), Multiple low-side switches (SW4) that allow on / off states to be selected for each cylinder of the internal combustion engine, The system comprises the boost circuit, the high-side switch, and the control units (4, 4A, 4B) that control the low-side switch, A diode (D4) that recirculates current from the connection point between the inductive load and the low-side switch to the boost capacitor side, An electronic control device comprising a Zener diode (ZD1) whose cathode is connected to the cathode of this diode and whose anode is connected to the positive terminal of the battery, thereby clamping the voltage applied to the boost capacitor.

2. The electronic control device according to claim 1, wherein the Zener voltage of the Zener diode is set to be greater than the set value of the output voltage of the boost circuit, and the value added to the power supply voltage is lower than the breakdown voltage of the boost capacitor.

3. The system includes a calculator (12) that monitors the cathode voltage of the Zener diode, The electronic control device according to claim 1 or 2, wherein the control unit (4A) performs over-boost elimination control, which involves stopping the operation of the boost circuit or stopping the supply of power to the inductive load, in accordance with the voltage monitored by the calculator.

4. comprising a calculator (14) for monitoring the cathode voltage of the Zener diode, The electronic control device according to claim 1 or 2, wherein the calculator performs over-boost elimination control, which involves stopping the operation of the boost circuit or stopping the supply of power to the inductive load in accordance with the monitored voltage.

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