JP7323778B2 - Overcurrent protection device - Google Patents

Description

Application of Patent Law Section 30, Paragraph 2 On February 3, 2019, an automobile equipped with the overcurrent protection device of the present application was sold in Australia.

The present invention relates to an overcurrent protection device for vehicles that protects a load from overcurrent.

In order to protect the load and wire harness that can be connected to the power supply via the vehicle's electronic control unit (ECU), etc., from overcurrent caused by a short circuit, etc., the connection between the load and the power supply is mechanically cut off when an overcurrent occurs. Conventionally, an overcurrent protection device using a fuse that

In Patent Document 1, in order to be able to cut off overcurrent from the load without replacing parts, it is determined whether or not overcurrent has flowed through the load based on overcurrent cutoff characteristics equivalent to fuse characteristics. An overcurrent interrupter has been proposed to

Japanese Patent Application Laid-Open No. 2014-2300396

A fuse has a function of melting in a short time when the current is large and melting in a relatively long time when the current is small. Therefore, in an overcurrent protection device using a fuse, if the current value is small and the fuse is not cut easily due to a layer short circuit (partial short circuit), there is a concern that the harness will heat up and lead to a serious accident.

In Patent Document 1, whether or not an overcurrent has flowed to the load is determined based on the overcurrent interrupting characteristics of a shape equivalent to the fuse characteristics, so the overcurrent protection device is complicated, the shape is large, and the price is high. It is thought that

SUMMARY OF THE INVENTION An object of the present invention is to provide an overcurrent protection device that has high accuracy against layer shorts and does not increase in size.

The present invention is an overcurrent protection device that protects a load from overcurrent, comprising an overcurrent protection circuit that cuts off the current to the load when it detects that a load current greater than or equal to a specified current flows for a specified time or longer;
a control element that controls the overcurrent protection circuit to restore the current when the overcurrent protection circuit cuts off the current ;
The return control by the control element includes, after repeating interruption and connection of the current to the load side by the overcurrent protection circuit, when the voltage value on the load side is equal to or higher than a threshold, the current supply is restored, continuing to interrupt the current if below said threshold;
The overcurrent protection circuit cuts off the current to the load not only in the ground fault state but also in the overcurrent state at the time of current inrush,
In the return control by the control element, when the voltage value on the load side exceeds a threshold value after the overcurrent protection circuit repeatedly cuts off and connects the current to the load side, the overcurrent at the time of current inrush. state, interrupting and connecting the current are repeated to charge the capacitor on the load side, and then the supply of current is restored, and if the threshold is below the threshold, it is judged to be a ground fault state and the interrupting of the current is continued. characterized by

The overcurrent protection device of the present invention sets the specified current for detecting overcurrent to not only the ground fault condition, but also the overcurrent condition at the time of current rush, and the current value when partial short circuit (layer short circuit) occurs. can be set. Therefore, even when a partial short circuit occurs, the current can be cut off quickly, and the harness can be heated to prevent a serious accident from occurring. When the current is cut off, the control element controls the cut-off circuit and restores the current. If the current is interrupted due to an overcurrent condition at times, a return operation can be performed to restore the current. Since the specified current for detecting overcurrent can be set to a small current that is equal to or less than the current value when a partial short circuit occurs, the overcurrent protection device can be miniaturized and provided at low cost.

1 is a configuration diagram of an overcurrent protection device according to an embodiment of the present invention; Control Flow of Microcomputer of Overcurrent Protection Device of Embodiment Timing chart of the overcurrent protection device of the embodiment

FIG. 1 is a block diagram showing the configuration of an overcurrent protection device 10 according to an embodiment.
The overcurrent protection device 10 has an overcurrent protection circuit 12 and a microcomputer 18 that constitutes a control element. The overcurrent protection device 10 is arranged inside the ECU 20 . The ECU 20 steps down the voltage of 24V applied to the input terminal 20i to 12V in the step-down circuit 22 and outputs it from the output terminal 20o. A terminal 20b of the ECU 20 is connected to a 12V Battery. The overcurrent protection device 10 is provided between the input terminal 20i and the output terminal 20o of the ECU 20. As shown in FIG. The overcurrent protection device 10 detects an overcurrent when a ground fault occurs on the output terminal 20o side, and protects the load by shutting off the output terminal 20o side. However, not only the ground fault, but also when the battery terminals are connected, when a rush current flows when the fuse is inserted, etc., after the first cutoff, the resetting operation is performed by the control from the microcomputer 18, and the resetting is performed again. . In the overcurrent protection circuit 12 of the embodiment, an FET is used as a load current interrupting element.

An on-off request port (Enable) 14 and a status report port (Status) 16 are provided between the overcurrent protection circuit 12 and the microcomputer 18 . The on-off request port 14 is an output port of the microcomputer 18 and is connected to the overcurrent protection circuit 12 . A request for an on-off operation to the overcurrent protection circuit 12 is meant. When the on-off request port 14 is high, it is a request for an on (connect) action to the overcurrent protection circuit 12 . When the on-off request port 14 is low, it is a request for an off (interrupt) action to the overcurrent protection circuit 12 .

A status report port (Status) 16 is an input port of the microcomputer 18 and is connected from the overcurrent protection circuit 12 . It means the report of the connection state and cutoff state from the overcurrent protection circuit 12 . When the status report port 16 is high, it is the connection status report from the overcurrent protection circuit 12 . When the status report port 18 is low, it is a shutdown condition report from the overcurrent protection circuit 12 .

The load connected to the output terminal 20o of the ECU 20 includes a capacitive load such as a capacitor for coping with instantaneous power loss of the ECU. A rush current flows when the battery terminals are connected or when a fuse is inserted. This inrush current does not change greatly instantaneously from the current that flows during a ground fault. On the other hand, the current when a partial short circuit (layer short circuit) occurs is smaller than the current which flows when a ground fault occurs. The overcurrent protection circuit 12 of the embodiment protects the current from not only a ground fault but also a current when a rush current flows when a battery terminal is connected, when a fuse is inserted, or when a partial short circuit (layer short circuit) occurs. to cut off the supply current. The overcurrent protection circuit 12 is returned to the connected state by the return control of the microcomputer when the terminals of the battery are connected or when a rush current flows due to insertion of a fuse or the like.

The return operation of the microcomputer 18 turns on/off the overcurrent protection device 10 by duty control that sets the on-off request port (Enable) 14 to low for 1 ms and high for 69 ms, and the load connected to the output terminal 20 o side. charge the side capacitor. After 7 cycles (490 ms), it is determined whether the voltage on the output terminal 20o side is 5 V or more, and if it is 5 V or more, it is determined that it is cut off due to inrush current. After raising, the on-off request port 14 is tied high to reconnect the overcurrent protection circuit 12 . A voltage of 5V corresponds to an example of a "threshold value".

On the other hand, after 7 cycles (490ms), if the voltage at the output terminal 20o side is less than 5V, it is determined that there is a ground fault, the on-off request port 14 is fixed low, and the overcurrent protection circuit 12 is cut off.

The microcomputer 18 is configured to be switched between a power-saving non-operating state (sleep mode) and an operating state. The microcomputer 18 is normally kept in a non-operating state while the ignition is off, and is kept in an operating state while the ignition is on. Then, when the overcurrent protection circuit 12 cuts off the current during operation, the microcomputer 18 immediately performs current recovery control. When the overcurrent protection circuit 12 cuts off the current in the non-operating state, the microcomputer 18 continues the cutoff of the current by the overcurrent protection circuit 12, and after switching to the operating state, performs current recovery control. Therefore, even when the microcomputer 18 is not operating, such as when the ignition is turned off, the overcurrent protection circuit 12 alone can cut off the current. After the microcomputer 18 is switched to an operating state such as when the ignition is turned on, the overcurrent protection circuit 12 can be appropriately controlled.

In the overcurrent protection device 10 of the embodiment, it is possible to suppress heat generation of the interrupting element (FET) and prevent failure by repeating the current operation for the time set so that the interrupting element does not fail. This eliminates the need to set an additional protection circuit, makes it possible to use a breaking element with a current capacity close to that of normal use, and allows the layout to be kept compact.

FIG. 2 is a control flow of the microcomputer.
When the battery is connected (S11), the microcomputer 18 unconditionally executes the above-described overcurrent protection circuit recovery control (S12). That is, the return operation of the microcomputer 18 turns on/off the overcurrent protection circuit 12 by duty control in which the on-off request port (Enable) 14 is set low for 1 ms and high for 69 ms. After 7 cycles (490 ms), the cutoff and connection of the overcurrent protection circuit 12 are continued based on the voltage at the output terminal.

Then, the microcomputer 18 determines whether the ignition is turned on (S14). When the ignition is turned on (S14: Yes), it is determined whether the status report port (Status) 16 is low, that is, whether the overcurrent protection circuit 12 is cut off (S16). While the status report port (Status) 16 is high, that is, the overcurrent protection circuit 12 is in the connected state (S16: No), the state shifts to "1", and the process returns to the judgment in S14.

On the other hand, if the status report port (Status) 16 is low, that is, if the overcurrent protection circuit 12 is in the interrupted state (S16: Yes), the above-described overcurrent protection circuit recovery control is executed (S18). That is, the return operation of the microcomputer 18 turns on/off the overcurrent protection circuit 12 by duty control in which the on-off request port (Enable) 14 is set low for 1 ms and high for 69 ms. Seven cycles (490 ms) before the return control is completed (S20: No), the process returns to S18 to continue the return control. After seven cycles (490 ms) after the return control is completed (S20: Yes), it is determined whether the voltage on the output terminal 20o side is 5 V or higher (S22). Yes), the ON-OFF request port (Enable) 14 is set to high (S24), the overcurrent protection circuit 12 is set to the connected state, the state is changed to "1", and the process returns to the judgment in S14.

On the other hand, if the voltage on the output terminal 20o side is less than 5 V (S22: No), a ground fault is determined, the ON-OFF request port (Enable) 14 is set to low (S26), and the overcurrent protection circuit 12 is cut off. Then, the ground fault is recorded (S28), and the process ends. This continues until a reset is made.

When it is determined whether the ignition is turned on (S14) and the ignition is turned off 5 seconds after the battery is connected (S14: No), the process proceeds to "2" and the sleep process is executed. is executed (S30). The ECU 20 is put into sleep mode (S32). Along with this, the microcomputer 18 is switched to a power-saving non-operating state (sleep mode). Then, it is determined whether CAN (a communication protocol used for communication between ECUs (Electronic Control Units)) has been received from a unit connected to the bus (S34). Unless CAN is received (S34: No), the process proceeds to "2" and the sleep process in S30 is continued.

On the other hand, when CAN is received (S34: Yes), the ECU 20 is activated (S36), and it is determined whether a specific signal has been received from the PCM (S38). When the specific signal is received from the PCM (S38: Yes), the process shifts to "1" and returns to the judgment in S14. When the specific signal is not received from the PCM (S38: No), the state report port (Status) 16 falls, ie, it is determined whether the overcurrent protection circuit 12 has transitioned to the shutdown state (S40). While the state report port 16 is not turned off (S40: No), the sleep processing is returned to in S30.

On the other hand, when the state report port (Status) 16 falls, that is, when the overcurrent protection circuit 12 transitions to the cutoff state (S40: Yes), the above-described overcurrent protection circuit recovery control is executed (S42). That is, the return operation of the microcomputer 18 turns on/off the overcurrent protection circuit 12 by duty control in which the on-off request port (Enable) 14 is set low for 1 ms and high for 69 ms. Until 7 cycles (490 ms) after the return control is completed (S44: No), it is determined whether the ignition is turned on (S46). Back to judgment. After seven cycles (490 ms) after the return control is completed (S44: Yes), the microcomputer 18 determines whether the voltage on the output terminal 20o side is 5 V or more (S48). S22: Yes), the on-off request port (Enable) 14 is set high (S50), the overcurrent protection circuit 12 is connected, the process shifts to "2", and the sleep process returns to S30.

On the other hand, if the voltage on the output terminal 20o side is less than 5 V (S48: No), the microcomputer 18 sets the on-off request port (Enable) 14 to low (S60), and cuts off the overcurrent protection circuit 12. , "2", and returns to the sleep process in S30. However, the recovery process is not re-executed while the ignition is off.

FIG. 3 is a timing chart of the overcurrent protection device of the embodiment.
(A) in the figure indicates ON/OFF of the battery. (B) shows ignition ON/OFF. (C) indicates reception/non-reception of CAN used for communication between ECUs (Electronic Control Units). (D) indicates WakeUP (activation)/Sleep (sleep)/ShutDown (stop) of the ECU. (E) indicates ground fault/rush/normality of the overcurrent protection circuit. (F) indicates operation/non-operation of return control. (G) indicates high/low of the status report port (Status). (H) indicates a ground fault/normal flag used in the microcomputer.

In the timing chart, [1] to [8] indicate the following states.
In [1], while the ignition is on (S14: Yes), when the state reporting port (Status) 16 of the overcurrent protection circuit 12 falls at timing t1 (S16: Yes), return control is executed ( S18).
In [2], when the battery is reset at timing t2 (S11), recovery control is executed regardless of whether or not there is a ground fault (S12).
In [3], when the state reporting port (Status) 16 of the overcurrent protection circuit 12 falls at timing t3 while the ignition is off (S40: Yes), recovery control is executed (S42).
In [4], when the state reporting port (Status) 16 of the overcurrent protection circuit 12 falls at timing t4 during sleep (S40: Yes), return control is executed at the next activation (timing t4B). (S42). Moreover, it does not sleep until the return processing is completed (S46: No).

In [5], when WakeUP (activation) in CAN, if the status report port (Status) 16 of the overcurrent protection circuit 12 falls at timing t5 (S40: Yes), immediate return control is executed ( S42). Sleep is not performed until the recovery process is completed (S46: No).
In [6], when the return control is executed due to the ground fault during sleep, the return control is not performed until the ignition is turned on again (S48-S30).
At [7], if the state report port (Status) 16 of the overcurrent protection device 10 is low (S16: Yes) when the ignition is turned on at timing t7, return control is executed (S18).
In [8], when the ignition is turned on at timing t8 during the return operation, the return control is executed again (S44, S46).

When forming an overcurrent protection device with an electronic circuit instead of a fuse, it is necessary to allow a large current to flow in a short period of time when a rush current flows to charge the capacity of an electrical component. When used, it is necessary to secure a large capacity, so it is necessary to increase the number of elements and secure the layout. On the other hand, in the overcurrent protection device 10 of the embodiment, the microcomputer 18 repeats disconnection-connection-disconnection of the overcurrent protection circuit 12 to charge the capacitive load of the electrical component, thereby dividing the charge while suppressing heat generation. do it purposefully. Also, the current can be set to a value that does not cause the harness to heat up. Since the overcurrent protection device 10 of the embodiment can appropriately set the current, it is possible to suppress the heat generation of the harness and protect the harness.

The overcurrent protection device 10 of the embodiment sets the specified current for detecting overcurrent to not only the ground fault condition, but also the overcurrent condition at the time of current rush, and the current value at the time when partial short circuit (layer short circuit) occurs. can be set to Therefore, even when a partial short circuit occurs, the current can be cut off quickly, the harness can be protected, and heat generation of the harness can prevent a serious accident from occurring. When the current is cut off, the control element controls the cut-off circuit and restores the current. When the current is cut off in an overcurrent state at the time of rushing into the circuit, the current can be restored by carrying out a restoration operation. Since the specified current for detecting overcurrent can be set to a small current that is equal to or less than the current value when a partial short circuit occurs, the overcurrent protection device can be miniaturized and provided at low cost. Moreover, even if the fuse is removed and inserted for repair or failure investigation, the overcurrent protection device 10 does not make an erroneous judgment, and noise-resistant characteristics can be realized. For example, in order for an overcurrent protection device to have overcurrent cutoff characteristics similar to fuse characteristics, a switching element such as a large-capacity FET is required to allow a large current to flow. An overcurrent protection device can cut off current with a small-capacity FET.

10 Overcurrent protection device 12 Overcurrent protection circuit 14 On-off request port 16 Status report port 18 Microcomputer

Claims (3)

An overcurrent protection device that protects a load from overcurrent,
an overcurrent protection circuit that cuts off the current to the load when it detects that a load current greater than or equal to a specified current flows for a specified time or longer;
a control element that controls the overcurrent protection circuit to restore the current when the overcurrent protection circuit cuts off the current ;
The return control by the control element includes, after repeating interruption and connection of the current to the load side by the overcurrent protection circuit, when the voltage value on the load side is equal to or higher than a threshold, the current supply is restored, continuing to interrupt the current if below said threshold;
The overcurrent protection circuit cuts off the current to the load not only in the ground fault state but also in the overcurrent state at the time of current inrush,
In the return control by the control element, when the voltage value on the load side exceeds a threshold value after the overcurrent protection circuit repeatedly cuts off and connects the current to the load side, the overcurrent at the time of current inrush. state, interrupting and connecting the current are repeated to charge the capacitor on the load side, and then the supply of current is restored, and if the threshold is below the threshold, it is judged to be a ground fault state and the interrupting of the current is continued. characterized by The overcurrent protection device of claim 1 ,
It is characterized in that the specified current for detecting the overcurrent is set below the current value when the partial short circuit occurs. The overcurrent protection device according to claim 1 or claim 2 ,
the control element is switched between an operative state and a non-operative state;
When the overcurrent protection circuit cuts off the current during an operating state, the control element immediately performs current restoration control,
When the overcurrent protection circuit cuts off the current in the non-operating state, the control element continues to cut off the current by the overcurrent protection circuit, and after switching to the operating state, performs current recovery control.

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