JP6477454B2 - Load drive device - Google Patents

Description

  The disclosure in this specification relates to a load driving device for driving an inductive load.

  A load driving device that drives an inductive load includes a switch that is provided on a current-carrying path of the inductive load and flows current to the inductive load when turned on. Patent Document 1 discloses a load driving device (abnormality detection device) configured to be able to detect an overcurrent flowing through a MOSFET as a switch.

  In this load driving device, the drain voltage (drain-source voltage) of the MOSFET is detected. When the drain voltage exceeds the threshold voltage, it is determined that an overcurrent has flown through the MOSFET, and the MOSFET is forcibly turned off. Further, the drain voltage change is masked according to the ON / OFF timing of the MOSFET, and the overcurrent is detected except for the mask period.

JP 2013-255304 A

  By the way, when the MOSFET is turned off, the energization path is cut off, the drain voltage rises, and the drain voltage shows a value higher than the threshold voltage, so that an overcurrent is erroneously detected.

  On the other hand, according to the above-described load driving device, for example, a predetermined time can be set as the mask period from the switching timing (rise timing) of switching off the PWM signal for driving the MOSFET. When the mask period ends, detection of overcurrent can be started, and detection of overcurrent can be stopped in accordance with the switching timing (falling) of the PWM signal from on to off.

  The mask period is determined by performing a calculation in advance so that the time is sufficient to prevent erroneous detection of overcurrent. Specifically, it is determined by estimating worst values such as the operation delay of the MOSFET and the operation delay inside the IC for operating the MOSFET, and adding a predetermined margin to the time obtained by adding the values.

  Since the mask period determined in this way is longer than required in the actual average driving state, the threshold value is set at an early timing such as when an overcurrent abnormality occurs at a relatively early timing after the MOSFET is turned on. Even when a large current exceeding the current flows in the MOSFET, it cannot be determined that an overcurrent has occurred until the mask period ends. Meanwhile, the value of the current flowing through the MOSFET continues to rise, and the amount of heat generated in the MOSFET also increases. Therefore, in order to satisfy heat resistance, a large MOSFET must be used.

  The present disclosure has been made in view of such problems, and an object thereof is to provide a load driving device that can accelerate detection start of overcurrent as compared with the related art while suppressing erroneous detection of overcurrent. .

  The present disclosure employs the following technical means to achieve the above object. In addition, the code | symbol in parenthesis shows the corresponding relationship with the specific means as described in embodiment mentioned later as one aspect | mode, Comprising: The technical scope is not limited.

One of the present disclosure is a load driving device that drives an inductive load (100a),
A switch (Q1) that is provided on the energization path of the inductive load and flows current to the inductive load when turned on
A voltage detector (30) for detecting a voltage between terminals, which is a voltage between terminals forming an energization path in the switch;
A calculation unit (32) for differentiating the detected inter-terminal voltage to calculate a voltage differential value;
The overcurrent flowing through the switch is detected based on the voltage between the terminals. After the switch is turned on, the voltage differential value falls below the first threshold, and then the overcurrent is detected when the voltage differential value exceeds the first threshold. And an overcurrent detection unit (34) that stops detection of overcurrent in response to turning off of the switch,
Is provided.

  According to this, the overcurrent detection start timing is determined using the detected voltage differential value of the terminal voltage. Therefore, the overcurrent detection start timing can be advanced compared to the start timing after the mask period set on the safe side in consideration of the switch operation delay and the like. Further, the detection of overcurrent is stopped in response to the switch being turned off, and the detection of overcurrent is not started until the voltage differential value falls below the first threshold and then exceeds the first threshold. Can also be suppressed.

It is a figure which shows schematic structure of the electronic controller which concerns on 1st Embodiment. It is a flowchart which shows the overcurrent detection process which a control circuit performs. It is a timing chart at the time of normal driving in which no overcurrent abnormality has occurred. 6 is a timing chart when an overcurrent abnormality occurs. In a reference example, it is a timing chart at the time of normal driving in which no overcurrent abnormality has occurred. 5 is a timing chart when an overcurrent abnormality occurs in a reference example.

  A plurality of embodiments will be described with reference to the drawings. In several embodiments, functionally and / or structurally corresponding parts are given the same reference numerals.

(First embodiment)
First, a schematic configuration of the electronic control device according to the present embodiment will be described with reference to FIG. An electronic control device 10 shown in FIG. 1 is disposed in an engine room of a vehicle and controls driving of injectors 100 provided in each cylinder of an engine (internal combustion engine). The electronic control device 10 is configured as an engine ECU. The injector 100 is an injector that injects fuel directly into the combustion chamber of a direct injection gasoline engine. In FIG. 1, for convenience, only one of a plurality of injectors 100 corresponding to each cylinder is shown.

  The injector 100 has a solenoid 100a (coil). The solenoid 100a corresponds to an inductive load, and the electronic control device 10 corresponds to a load driving device. The injector 100 is opened by the electromagnetic force generated by the solenoid 100a when the solenoid 100a is energized to inject fuel. Further, when the solenoid 100a is not energized, the solenoid 100a is closed by a biasing force of a spring (not shown) provided in the injector 100. The upstream side of the solenoid 100a is connected to the terminal P1 of the electronic control device 10, and the downstream side is connected to the terminal P2.

  The electronic control device 10 includes a booster circuit 20, a discharge switch Q1, a constant current switch Q2, a low side switch Q3, a current detection resistor R1, diodes D1 and D2, a microcomputer 22, and a drive IC 24.

  The booster circuit 20 boosts the battery voltage VB input via the terminal P3 of the electronic control device 10, and generates a predetermined boosted voltage VBst (for example, 65V). As such a booster circuit 20, for example, a known configuration including a booster coil, a switch for controlling energization of the coil, a backflow prevention diode, and a capacitor can be employed.

  The discharge switch Q1 is arranged upstream of the solenoid 100a and between the booster circuit 20 (capacitor) and the terminal P1. The discharge switch Q1 is a switch that, when turned on, applies the boosted voltage Vbst to the solenoid 100a via the terminal P1. In this embodiment, an n-channel MOSFET is employed as the discharge switch Q1. The drain of the discharge switch Q1 is connected to the booster circuit 20 (the positive electrode of the capacitor).

  The constant current switch Q2 is disposed upstream of the solenoid 100a and between the terminals P1 and P3. The constant current switch Q2 is a switch that, when turned on, supplies the battery voltage VB to the solenoid 100a via the terminal P1. In this embodiment, an n-channel MOSFET is employed as the constant current switch Q2. The drain of the constant current switch Q2 is connected to the terminal P3, and the source is connected to the upstream side of the solenoid 100a via the backflow prevention diode D1 and the terminal P1.

  The anode of the diode D1 is connected to the source of the constant current switch Q2, and the cathode is connected to the source of the discharge switch Q1. Between the connection point of the diode D1 and the discharge switch Q1 and the ground, a reflux diode D2 is arranged with the anode on the ground side.

  The low side switch Q3 is provided corresponding to the solenoid 100a and is disposed on the downstream side of the corresponding solenoid 100a. The low side switch Q3 is turned on to connect the downstream side of the corresponding solenoid 100a to the ground. For this reason, the low side switch is also referred to as a cylinder selection switch. In this embodiment, an n-channel MOSFET is employed as the low-side switch Q3. The source of the low-side switch Q3 is connected to the ground via the current detection resistor R1, and the drain is connected to the downstream side of the solenoid 100a via the terminal P2.

  The microcomputer 22 and the drive IC 24 control the boost operation of the boost circuit 20. Further, it controls on / off of the discharge switch Q1, on / off of the constant current switch Q2, and on / off of the low side switch Q3. In FIG. 1, for the sake of convenience, the connection between the driving IC 24 and the constant current switch Q2 and the low-side switch Q3 is omitted. In a period in which the voltage level of an injection signal TQ, which will be described later, is high, that is, in the energization period, the discharge switch Q1 and the low-side switch Q3 are turned on in the initial discharge period. Then, the drive current flowing through the solenoid 100a is detected by the voltage across the current detection resistor R1, and when the drive current reaches the target peak current value, the discharge switch Q1 is turned off. In the constant current period from when the discharge switch Q1 is turned off until the end of the energization period, for example, on / off of the constant current switch is controlled so that the drive current becomes a predetermined current value lower than the target peak current value.

  The microcomputer 22 is a microcomputer that includes a CPU, a ROM, a RAM, a register, an I / O port, and the like. For example, the microcomputer 22 calculates a target torque that the engine should output. Further, in order to generate the target torque required by the engine, a throttle valve (not shown) is controlled to an appropriate opening degree, and the fuel injection amount and ignition timing of the engine are controlled.

  The microcomputer 22 generates an injection signal TQ corresponding to the injector 100 based on engine operation information detected by various sensors (not shown) such as the engine speed and the accelerator opening, and outputs the injection signal TQ to the drive IC 23. The microcomputer 22 outputs an H level signal as the injection signal TQ during the valve opening instruction period, and outputs an L level signal as the injection signal TQ during the valve closing instruction period.

  The drive IC 23 includes a potential difference detection circuit 30, a differentiation circuit 32, a control circuit 34, and a gate drive circuit 36.

  The potential difference detection circuit 30 detects a potential difference between terminals forming the energization path of the solenoid 100a in the discharge switch Q1, that is, a potential difference between the drain and the source (hereinafter referred to as a drain voltage Vds). The potential difference detection circuit 30 corresponds to a voltage detection unit.

  The differentiating circuit 32 differentiates the drain voltage Vds to calculate a voltage differential value Vds ′. As the differentiating circuit 32, a known configuration having a resistor and a capacitor can be employed. For this reason, the characteristic (time constant) of the differentiation circuit 8 is mainly determined by the resistor and the capacitor. The differentiation circuit 32 corresponds to the calculation unit.

  The control circuit 34 includes a first comparison circuit 40, a second comparison circuit 42, a gate drive timing generation circuit 44, and a gate drive mask circuit 46. The control circuit 34 corresponds to an overcurrent detection unit.

  The first comparison circuit 40 compares the drain voltage Vds with a preset threshold voltage Vth2, and outputs a signal S1 indicating the comparison result (hereinafter referred to as comparison result S1) to the gate drive mask circuit 48. The threshold voltage Vth2 corresponds to the second threshold value. When the drain voltage Vds is equal to or lower than the threshold voltage Vth2, the first comparison circuit 40 outputs a signal having a voltage level of L level as a comparison result. When the drain voltage Vds exceeds the threshold voltage Vth2, the signal having a voltage level of H level as a comparison result. Is output.

  The second comparison circuit 42 compares the voltage differential value Vds' with a preset threshold voltage Vth1. Then, when the discharge switch Q1 is turned on, the voltage differential value Vds' falls below the threshold voltage Vth1, and thereafter exceeds the threshold voltage Vth1, a pulse signal indicating the start of overcurrent detection is output to the gate drive mask circuit 46.

  The gate drive timing generation circuit 44 generates a PWM signal having a predetermined frequency and a predetermined duty based on a clock having a predetermined frequency generated by a clock generation circuit (not shown) and an injection signal TQ input from the microcomputer 22. The gate drive timing generation circuit 44 outputs the generated PWM signal to the gate drive mask circuit 46.

  The gate drive mask circuit 46 detects overcurrent by the drain voltage Vds based on the comparison result S1 output from the first comparison circuit 40, the output signal of the second comparison circuit 42, and the output signal of the gate drive timing generation circuit 44. A period for invalidating (hereinafter referred to as a mask period) is determined, and a control signal for on / off timing is output to the gate drive circuit 36.

  After the timing (rising) at which the PWM signal is switched from OFF to ON, the gate drive mask circuit 46 is used as the mask period until the pulse signal indicating the start of overcurrent detection is input from the second comparison circuit 42. The comparison result S1 of one comparison circuit is invalidated. That is, when the pulse signal is input, detection of overcurrent based on the comparison result S1 is started. When the overcurrent abnormality does not occur, the gate drive mask circuit 46 detects the timing (falling) when the PWM signal switches from on to off, and stops detecting the overcurrent according to the off timing. That is, the mask period is set according to the off timing. In the present embodiment, a period from when the off timing is detected to when the pulse signal is input is a mask period. Therefore, the period from when the pulse signal is input until the PWM signal is turned off is the overcurrent detection period.

  If the comparison result S1 does not become H level in the overcurrent detection period, that is, if no overcurrent is detected, the gate drive mask circuit 46 outputs a PWM signal as a control signal. On the other hand, when an overcurrent is detected, a control signal is output so as to turn off the discharge switch Q1 without waiting for the OFF timing of the PWM signal. Thereby, the turn-off timing of the discharge switch Q1 is earlier than normal. Further, the start timing of the mask period is earlier than the normal time by turning off the discharge switch Q1.

  Based on the control signal output from the gate drive mask circuit 46, the gate drive circuit 36 outputs a gate drive signal S2 to the gate of the discharge switch Q1. The gate drive circuit 36 corresponds to a drive unit.

  In addition to the above, the drive IC 24 controls the operation of the booster circuit 20 so that the booster circuit 20 boosts the battery voltage VB to the target voltage (65V).

  Next, overcurrent detection processing executed by the control circuit 34 will be described with reference to FIG. The control circuit 34 repeatedly executes the process shown in FIG. 2 while the electronic control device 10 is powered on. When the electronic control device 10 is turned on, the control circuit 34 initially sets a mask period.

  First, in step S10, it is determined whether or not it is the energization start timing of the discharge switch Q1, and if it is determined that it is the energization start timing, the process of step S20 is executed. In step S20, a control signal is output to the gate drive circuit 36 to turn on the discharge switch Q1. As a result, an H level signal is output from the gate drive circuit 36 as a gate drive signal, and the discharge switch Q1 is turned on. When the process of step S20 ends, the process of step S30 is executed.

  In step S30, the drain voltage Vds is detected. In subsequent step S40, the detected drain voltage Vds is differentiated to calculate a voltage differential value Vds'. After the calculation, the process of step S50 is executed. In step S50, the calculated voltage differential value Vds 'is compared with the threshold voltage Vth1, and it is determined whether or not the voltage differential value Vds' is less than the threshold voltage Vth1. When the voltage differential value Vds ′ is less than the threshold voltage Vth1, the process proceeds to step S60, and when it is equal to or higher than the threshold voltage Vth1, the process returns to step S30.

  In step S60, the drain voltage Vds is detected again, and in the subsequent step S70, a voltage differential value Vds' is calculated. When step S70 ends, in step S80, the calculated voltage differential value Vds 'is compared with the threshold voltage Vth1, and it is determined whether or not the voltage differential value Vds' is larger than the threshold voltage Vth1. When the voltage differential value Vds ′ is larger than the threshold voltage Vth1, the process proceeds to step S90, and when it is equal to or lower than the threshold voltage Vth1, the process returns to step S60.

  After the voltage differential value Vds' has fallen below the threshold voltage Vth1, it has exceeded the threshold voltage Vth1, so in step S90, detection of an overcurrent is started. That is, the mask period ends (mask off).

  Next, in step S100, the drain voltage Vds is detected, and in step S110, the detected drain voltage Vds is compared with the threshold voltage Vth2, and whether or not the drain voltage Vds is larger than the threshold voltage Vth2, that is, the drain voltage Vds is It is determined whether or not the threshold voltage Vth2 has been exceeded. When the drain voltage Vds is larger than the threshold voltage Vth2, the process proceeds to step S120, and when the drain voltage Vds is less than or equal to the threshold voltage Vth2, the process proceeds to step S130.

  Since an overcurrent is detected in step S110, in step S120, a control signal is output to the gate drive circuit 36 in order to forcibly turn off the discharge switch Q1 without waiting for the OFF timing of the PWM signal. Thereby, an L level signal is output as a gate drive signal from the gate drive circuit 36, and the discharge switch Q1 is turned off. Therefore, the discharge switch Q1 is turned off earlier than usual. When the process of step S120 ends, the process proceeds to step S150.

  In step S130 executed when no overcurrent is detected in step S110, it is determined whether or not the energization period of the discharge switch Q1 has ended. In the present embodiment, when the drive current flowing through the solenoid 100a reaches the target peak current value, the energization period of the discharge switch Q1 ends. When boosted voltage Vbst is 65V, the energization period of discharge switch Q1 is, for example, about 300 μs to 350 μs. If the energization period has ended, the process proceeds to step S140. If the energization period has not ended, the process returns to step S100.

  In step S140, a control signal is output to the gate drive circuit 36 to turn off the discharge switch Q1. Then, the process proceeds to step S150. In step S150, the overcurrent detection is stopped. That is, the mask period is started (mask on). As described above, when the overcurrent abnormality occurs and the discharge switch Q1 is forcibly turned off in step S120, the discharge switch Q1 is turned off in both cases where the energization period ends and the discharge switch Q1 is turned off in step S140. In response, overcurrent detection is stopped. Then, a series of processing ends.

  In steps S120 and S140, the low-side switch Q3 may be turned off together with the discharge switch Q1.

  FIG. 3 shows a timing chart during normal driving in which no overcurrent abnormality has occurred. FIG. 4 shows a timing chart when an overcurrent abnormality occurs. 5 and 6 are reference examples when the conventional mask processing is performed. FIG. 5 shows a timing chart during normal driving in which no overcurrent abnormality has occurred, and FIG. 6 shows a timing chart when an overcurrent abnormality has occurred. In FIGS. 3 to 6, the heat generation amount of the discharge switch Q1 is hatched for the sake of clarity.

  First, the normal driving of this embodiment will be described. As shown in FIG. 3, when the injection signal TQ rises from the L level to the H level, the gate drive signal S2 output from the gate drive circuit also rises at time t1 with a slight delay.

  When the gate drive signal S2 rises, the discharge switch Q1 is turned on with a slight delay, and the drain voltage Vds decreases sharply. For this reason, the voltage differential value Vds ′ also decreases sharply. The threshold voltage Vth1 is set between a value that the voltage differential value Vds ′ can initially take immediately after the discharge switch Q1 is turned on (a value in the vicinity of 0 V) and a minimum value that can be taken as the drain voltage Vds drops sharply. ing. For this reason, as the drain voltage Vds decreases, the voltage differential value Vds ′ falls below the threshold voltage Vth1.

  The drain voltage Vds falls below the threshold voltage Vth2 at time t2. That is, the comparison result S1 indicates the H level until time t2. However, because of the mask period, the detection of overcurrent until time t2 is invalid. After the time t2, the drain voltage Vds becomes a minimum value (a value near 0V), and thereafter monotonously increases like the drain current Id during the energization period. For this reason, when the voltage differential value Vds 'becomes lower than the threshold voltage Vth1 and becomes the minimum value, the voltage differential value Vds' starts to increase. At this time, it increases with a time constant determined mainly by a resistor and a capacitor. Then, it exceeds the threshold voltage Vth1 at time t3. Therefore, the mask period ends at time t3 and overcurrent detection starts. The voltage differential value Vds' finally settles around 0V.

  In the case of normal driving, as shown in FIG. 3, the drain voltage Vds does not exceed the threshold voltage Vth2 after the start of overcurrent detection. When the drive current flowing through the solenoid 100a reaches the target peak current value, the control circuit 34 determines that it is time to turn off the discharge switch Q1, and causes the gate drive signal S2 to fall at time t4. As a result, the discharge switch Q1 is also turned off. Further, at time t4 when the discharge switch Q1 is turned off, the detection of overcurrent is stopped and the mask period is started.

  When the discharge switch Q1 is turned off, the drain voltage Vds increases sharply. During the increase process, the drain voltage Vds exceeds the threshold voltage Vth2 at time t5. However, since the overcurrent detection period ends and the mask period is reached, the overcurrent detection becomes invalid.

  In the discharge switch Q1, heat proportional to the product of the drain voltage Vds and the drain current Id flowing through the discharge switch Q1 is generated. In particular, when the discharge switch Q1 is turned off (turned off), a larger amount of heat is generated than during driving. The hatched portion (area) in FIG. 3 corresponds to the total calorific value.

  FIG. 4 is the same as FIG. 3 until time t3. When an overcurrent abnormality occurs, a large current flows as the drain current Id as shown in FIG. 4, so that the drain voltage Vds exceeds the threshold voltage Vth2 at a time t6 when a predetermined time has elapsed from the time t3.

  As described above, when the drain voltage Vds exceeds the threshold voltage Vth2 at time t6, the comparison result S1 is switched from the H level to the L level. Since overcurrent detection has already started at time t3, it is detected that an overcurrent abnormality has occurred when the comparison result S1 switches to the L level. When the overcurrent abnormality is detected, the control circuit 34 outputs a control signal so as to turn off the discharge switch Q1 without waiting for time t4. Thereby, the gate drive signal S2 falls at time t7. Then, the discharge switch Q1 is turned off. Further, the overcurrent detection period ends and a mask period starts. In the example shown in FIG. 4, the time from time t3 to t7 is about 2 μs.

  As shown in FIG. 4, when an overcurrent abnormality occurs, the amount of current when the discharge switch Q1 is turned off is greater than that during normal driving, and thus the amount of heat generated is greater than during normal driving. However, in this embodiment, since the overcurrent detection start timing can be made earlier than before, the amount of heat generation can be reduced as compared with a comparative example described later.

  The normal driving of the reference example shown in FIG. 5 is the same as that in FIG. 3 until time t2. The timings at times t1, t2, t4, and t5 are the same as those in FIG. The timing at time t3 is different.

  As shown in FIG. 5, in the conventional mask process, the mask period is from the time t1 until a predetermined time T elapses. The predetermined time T is determined by performing a calculation in advance so that the time is sufficient to prevent erroneous detection of overcurrent. Specifically, it is determined by estimating the worst value of each delay such as the operation delay of the discharge switch Q1 and the operation delay inside the driving IC, and adding a predetermined margin to the time obtained by adding the values. For this reason, the predetermined time T is, for example, about 8 μs.

  In FIG. 5, when the predetermined time T elapses, the mask period ends and the time t3 at which overcurrent detection starts is reached. In the case of normal driving, the drain voltage Vds does not exceed the threshold voltage Vth2 after the start of overcurrent detection, as in FIG. When the gate drive signal S2 falls at time t4, the discharge switch Q1 is also turned off. Further, at time t4 when the discharge switch Q1 is turned off, the detection of overcurrent is stopped and the mask period is started.

6 is also the same as that in FIG. 4 until time t2. The timings at times t1, t2, and t6 are the same as those in FIG. The timings at times t3 and t7 are different.

  As in FIG. 5, in FIG. 6, the time t3 after the predetermined time T has elapsed from time t1 is the time t3 when the mask period ends. Therefore, as in FIG. 4, even at the time t6, even if the drain voltage Vds exceeds the threshold voltage Vth2, it is during the mask period and the detection of the overcurrent becomes invalid. In other words, the control circuit 34 outputs a control signal to the gate drive circuit 36 so as to keep the discharge switch Q1 on.

  At time t3, the mask period ends and overcurrent can be detected. Therefore, when the comparison result S1 indicates the H level, the control circuit 34 detects that an overcurrent abnormality has occurred. When the overcurrent abnormality is detected, the control circuit 34 outputs a control signal so as to turn off the discharge switch Q1 without waiting for time t4. Thereby, the gate drive signal S2 falls at time t7. Then, the discharge switch Q1 is turned off. Further, the overcurrent detection period ends and a mask period starts.

  As described above, the amount of current when the discharge switch Q1 is turned off increases as the overcurrent detection timing is delayed as compared with FIG. Therefore, as shown in FIG. 6, the amount of generated heat is larger than that of the present embodiment.

  Next, effects of the electronic control device 10 according to the present embodiment will be described.

  In the present embodiment, an overcurrent can be detected by comparing the drain voltage Vds of the discharge switch Q1 and the threshold voltage Vth2.

  Also, the overcurrent detection start timing is determined using the voltage differential value Vds ′ of the drain voltage Vds. The drain voltage Vds decreases sharply when the discharge switch Q1 is turned on, decreases below the threshold voltage Vth2, reaches a minimum value, and then increases monotonously. For this reason, the voltage differential value Vds ′ also sharply decreases and falls below the threshold voltage Vth1, and reaches the minimum value slightly after the timing at which the drain voltage Vds becomes the minimum value. After that, it increases with a predetermined time constant.

  Thus, the voltage differential value Vds ′ exceeds the threshold voltage Vth1 without significantly delaying from the time t2 when the drain voltage Vds falls below the threshold voltage Vth2. Therefore, the end timing of the mask period, that is, the overcurrent detection start timing is not greatly delayed from the time t2. On the other hand, in the conventional mask process, the mask period is set on the safe side in consideration of the operation delay of the discharge switch Q1, etc., so the end timing of the mask period is relatively delayed from the time t2. Therefore, according to the present embodiment, the overcurrent detection start timing can be advanced while reliably detecting that the drain voltage Vds is lower than the threshold voltage Vth2. That is, the overcurrent detection start timing can be advanced while suppressing erroneous detection of the overcurrent caused by turning off the discharge switch Q1.

  Since the overcurrent detection start timing can be advanced, as shown in FIGS. 4 and 6, the overcurrent generated at the timing of the conventional mask period is detected early, thereby turning off the discharge switch Q1 early. The amount of heat generated by the discharge switch Q1 can be suppressed. That is, the discharge switch Q1 can be protected from overcurrent.

  It is also conceivable to start overcurrent detection when the drain voltage Vds falls below the threshold voltage Vth2 after the discharge switch Q1 is turned on. However, in this case, if an overcurrent abnormality occurs before the drain voltage Vds falls below the threshold voltage Vth2, the drain voltage Vds increases without falling below the threshold voltage Vth2, so the mask period is not released and an overcurrent is detected. I can't. On the other hand, according to the present embodiment, even in such a case, the voltage differential value Vds ′ exceeds the threshold voltage Vth1 after being lower than the threshold voltage Vth1, and therefore the overcurrent detection start timing can be advanced. .

  The disclosure of this specification is not limited to the illustrated embodiments. The disclosure encompasses the illustrated embodiments and variations by those skilled in the art based thereon. For example, the disclosure is not limited to the combination of elements shown in the embodiments. The disclosure can be implemented in various combinations. The technical scope disclosed is not limited to the description of the embodiments. The several technical scopes disclosed are indicated by the description of the claims, and should be understood to include all modifications within the meaning and scope equivalent to the description of the claims. .

  Although the example in which the electronic control device 10 is applied to a direct injection type gasoline engine has been shown, it can also be applied to a diesel engine. The number of engine cylinders is not limited.

  Although not particularly mentioned, the electronic control device 10 may further include a recovery unit that recovers energy stored in the corresponding solenoid 100a to the capacitor of the capacitor booster circuit 20 when the low-side switch Q3 is turned off. . A switch such as a diode or MOSFET can be employed as the recovery unit.

  The inductive load is not limited to the solenoid 100a of the injector 100 that injects fuel directly into the combustion chamber of the engine.

  Although the overcurrent detection of the discharge switch Q1 is mentioned, it can be applied to the constant current switch Q2 and the low side switch Q3.

  When the control circuit 34 detects an overcurrent, it may be fed back to the microcomputer 22. When an overcurrent occurs, for example, the injection signal TQ can be set to L level for one injection. The control signal may be fed back from the gate drive mask circuit 46, or the gate drive signal S2 may be fed back from the gate drive circuit 36.

  As described above, the threshold voltage Vth1 is a value that the voltage differential value Vds ′ can initially take immediately after the discharge switch Q1 is turned on (a value in the vicinity of 0 V), and a minimum value that can be taken as the drain voltage Vds drops sharply. It may be set between. For example, when a value close to the minimum value is set to the threshold voltage Vth1, the detection of overcurrent can be started immediately after the voltage differential value Vds' starts to increase.

DESCRIPTION OF SYMBOLS 10 ... Electronic control device, 20 ... Boosting circuit, 22 ... Microcomputer, 24 ... Drive IC, 30 ... Potential difference detection circuit, 32 ... Differentiation circuit, 34 ... Control circuit, 36 ... Gate drive circuit, 40 ... First comparison circuit, 42 ... Second comparison circuit, 44 ... Gate drive timing generation circuit, 46 ... Gate drive mask circuit, 100 ... Injector, 100a ... Solenoid, P1, P2, P3 ... Terminal, Q1 ... Discharge switch, Q2 ... Constant current switch, Q3 ... Low-side switch, R1 ... Current detection resistor

Claims (4)

A load driving device for driving an inductive load (100a),
A switch (Q1) that is provided on the energization path of the inductive load and that is turned on to flow current to the inductive load;
A voltage detection unit (30) for detecting a voltage between terminals which is a voltage between terminals forming the energization path in the switch;
A calculation unit (32) for differentiating the detected inter-terminal voltage to calculate a voltage differential value;
An overcurrent flowing through the switch is detected based on the voltage between the terminals, and the voltage differential value falls below a first threshold value after the switch is turned on, and then the voltage differential value falls below the first threshold value. An overcurrent detection unit (34) that starts detection of an overcurrent when exceeding, and stops detection of an overcurrent in response to turning off of the switch;
A load driving device comprising:   2. The load driving device according to claim 1, wherein the overcurrent detection unit determines that an overcurrent flows through the switch when the voltage between the terminals exceeds a second threshold after the start of overcurrent detection. A drive unit (36) for turning on and off the switch;
The load driving device according to claim 2, wherein when the overcurrent detection unit determines that an overcurrent is flowing, the drive unit turns off the switch. The load driving device according to any one of claims 1 to 3, wherein the inductive load is a solenoid of a direct injection injector that injects fuel into a combustion chamber of an internal combustion engine.
The switch is a discharge drive device that is a discharge switch that boosts a power supply voltage to generate a boosted voltage, and turns on to apply the boosted voltage to the solenoid.

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