JP2015221654A - Electronic control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic control unit including a stable power supply circuit capable of preventing a reduction in the power supply voltage of a microcomputer even if a battery voltage decreases at a time of starting an engine while reducing the capacity of a capacitor.SOLUTION: An electronic control unit comprises: a microcomputer 20; and a power supply circuit 10 that includes a step-up/step-down DCDC circuit 110 and that generates a power supply voltage of the microcomputer 20 using a battery 30, an operation mode of the microcomputer 20 transitioning from a normal operation mode to a power saving mode in which power consumption is relatively lower than that in the normal operation mode if it is determined that the battery voltage decreases at a time of starting an engine.

Description

  The present invention relates to an electronic control unit connected to an in-vehicle battery, and more particularly to an electronic control unit suitable for stabilizing the power supply of a microcomputer even when the voltage of the in-vehicle battery drops sharply.

  For example, in vehicles such as automobiles, it is required to improve the fuel consumption (fuel consumption) of internal combustion engines in response to environmental problems and exhaust gas emission regulations, as well as heightened awareness of energy conservation and concerns about resource depletion. . For this purpose, by increasing the combustion efficiency of the internal combustion engine, combustion is performed with less fuel, and exhaust harmful components are further reduced.

  Further, as an example of stopping unnecessary combustion in an automobile or the like as much as possible, there is an idle stop in which the engine (internal combustion engine) is stopped so as not to perform unnecessary idling when the vehicle is stopped. In idle stop, fuel can be saved and exhaust gas can be reduced by stopping the engine when parking or waiting for traffic lights at intersections.

  On the other hand, when the engine of a car or the like is started (including engine start after idling stop), a rush current (approximately several hundreds A) flows through the starter motor, so that a voltage drop due to the internal resistance of the battery occurs. The battery voltage will drop sharply. Therefore, an in-vehicle electronic control unit that uses a battery voltage as a power supply voltage or an electronic device as an accessory is required to have resistance to voltage drop.

  For example, as an invention that suppresses a voltage drop at the time of starting an engine and prevents a problem with an in-vehicle device, there is one described in Japanese Patent Application Laid-Open No. 2002-38984 (Patent Document 1). This Patent Document 1 describes a method for compensating a battery voltage by providing a voltage compensating means for the purpose of compensating for a voltage drop at the time of starting the engine.

  In addition, ISO 16750-2 “Starting Profile” shows a standard for a device resistance test against battery voltage fluctuation during engine starting.

JP 2002-38984 A

  By the way, in the power supply circuit of the conventional electronic control unit, since the power supply voltage of the microcomputer is generated by stepping down the battery voltage by the step-down DCDC circuit, the microcomputer is reset when the battery voltage falls below the operation voltage of the microcomputer at the time of engine start. There was a phenomenon that it stopped and stopped.

  In order to cope with this phenomenon, in the conventional technique, a method of absorbing a voltage ripple by arranging a large-capacity capacitor is generally used. However, in recent years, there has been a strong demand for resistance to a decrease in battery voltage as well as a reduction in the capacity of the capacitor because of the demand for downsizing the electronic control unit.

  An object of the present invention is to meet such demands by providing an electronic control unit having a stable power supply circuit that does not reduce the power supply voltage of the microcomputer even when the battery voltage drops at the time of starting the engine while reducing the capacity of the capacitor. It is to provide.

  In order to achieve the above object, the present invention includes a microcomputer unit and a power supply unit that has a step-up / step-down DCDC circuit and generates a power supply voltage of the microcomputer unit based on an external power supply. When it is determined that the voltage of the external power supply has decreased at the time of startup, the operation mode of the microcomputer is changed from the normal operation mode to the low power consumption mode in which the power consumption is lower than that of the normal operation mode.

  According to the present invention, when the voltage of the external power supply decreases, the operation mode of the microcomputer unit transitions from the normal operation mode to the low power consumption mode. The power can be suppressed, and the capacitor capacity can be reduced or the capacitor can be reduced.

1 is a configuration diagram of a power supply circuit of an electronic control unit (ECU) 1 according to an embodiment of the present invention. The block diagram at the time of comprising the buck-boost DCDC circuit 110 of the electronic control unit 1 which concerns on embodiment of this invention with the switching element. Explanatory drawing which shows operation | movement at the time of comprising the buck-boost DCDC circuit 110 of the electronic control unit 1 which concerns on embodiment of this invention by a switching element. Explanatory drawing which shows the mode of the time change of the output voltage of the buck-boost DCDC circuit 110 and the regulator 120 at the time of utilizing the test voltage 311 as an external power supply of the electronic control unit 1 which concerns on embodiment of this invention. The main processing flow performed when the power supply to the electronic control unit 1 which concerns on embodiment of this invention is turned on is a trigger. An interrupt processing flow that is executed with a predetermined interrupt as a trigger when the microcomputer 20 is set to permit an interrupt. FIG. 4 is a timing diagram of intermittent operation performed by the electronic control unit 1 as a result of the processing flow of FIGS. 4A and 4B. The block diagram of the electronic control unit 201 of the comparative example provided with the pressure | voltage fall DCDC circuit 210 in the power supply circuit. FIG. 7 is a configuration diagram of a step-down DCDC circuit 210 in the electronic control unit 201 shown in FIG. 6. It is explanatory drawing which shows the output waveform of the power supply circuit in the electronic control unit 201 shown in FIG. Explanatory drawing which showed an example of the DC characteristic of the microcomputer in a reference. Explanatory drawing which showed an example of the AC characteristic of the microcomputer in a reference. Explanatory drawing of the component mounted in the vehicle for engine starting. Explanatory drawing which shows the time change (voltage waveform) of the test voltage as described in ISO16750-2. Explanatory drawing which shows the relationship between the test voltage as described in ISO16750-2, and time. The main process flow performed by using the start signal output at the time of the engine restart from an idle stop in the electronic control unit 1 which concerns on embodiment of this invention as a trigger.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments, and includes various modifications and application examples without departing from the scope of the present invention. It is included in the range. For example, the present invention is not limited to the one having all the configurations described in the following embodiments, and includes a configuration in which a part of the configuration is deleted.

  FIG. 1 is a configuration diagram of a power supply circuit of an electronic control unit (ECU) 1 according to an embodiment of the present invention. The electronic control unit 1 shown in this figure is mounted on an automobile including an engine as a prime mover, and includes a power supply circuit 10 and a microcomputer (microcomputer unit) 20 therein. The power supply circuit 10 outputs a step-up / down DCDC circuit 110 that steps up / steps down and outputs an input voltage from a battery 30 that is an external power supply, a voltage detection unit 150 that detects the voltage of the battery 30, and outputs a voltage of a predetermined value. And a regulator 120 for outputting a reset signal to the microcomputer 20 and a control unit 140 for executing various processes related to control of the power supply circuit 10.

  In the power supply circuit 10, for example, 6 V is generated from the voltage of the battery 30 by the step-up / step-down DCDC circuit 110, and for example, 5 V is generated by the regulator 120, which is the subsequent series power supply, and this is used as the power supply voltage of the microcomputer 20. This is supplied to the microcomputer 20 via the line L3. That is, in the power supply circuit 10 according to the present embodiment, the DCDC circuit 110 with high conversion efficiency is arranged in the front stage, and the series power supply (regulator) 120 with a small output voltage ripple is arranged in the rear stage. The capacitor 3 is provided to suppress voltage ripple in the line L3.

  The voltage value of the line L3 is input to the reset circuit 130, and the reset circuit 130 is connected to the microcomputer 20 via the line L4. The reset circuit 130 issues a reset signal to the microcomputer 20 when the power is turned on, and when the voltage of the line L3 decreases to a value lower than the operating voltage of the microcomputer 20 (for example, when the operating voltage of the microcomputer 20 is 5V). The reset signal is issued to restart the microcomputer 20 even when the voltage of L3 drops to 4.5V.

  The positive electrode of the external battery 30 is connected to the terminal Vi and the voltage detection unit 150 of the step-up / step-down DCDC circuit 110 and further to the terminal A / D of the microcomputer 20 via the line L1.

  The microcomputer 20 starts the battery voltage (analog signal is converted into a digital signal by an AD converter (not shown) inside the microcomputer 20) input as an analog signal via the line L1 and the terminal A / D. Sometimes, the battery voltage is determined to be “the voltage of the battery 30 has decreased” by detecting that the battery voltage has reached less than a set value Vm (for example, the operating voltage value (5V) of the microcomputer 20) based on the monitoring voltage. Then, the microcomputer 20 changes its own operation mode from the normal operation mode to the low power consumption mode. Although details will be described later, the low power consumption mode is an operation mode in which power consumption is relatively lower than that in the normal operation mode.

  Although omitted in FIG. 1, in connection with the detection of the battery voltage by the microcomputer 20, a voltage exceeding the operating voltage of the microcomputer 20 is present on the line L <b> 1 connecting the positive electrode of the battery 30 and the terminal A / D of the microcomputer 20. In order to avoid the input from the battery 30, a voltage dividing circuit is provided (the voltage dividing circuit is preferably provided in the vicinity of the terminal A / D of the microcomputer 20). As an example of the voltage dividing circuit, 30 kΩ and 10 kΩ resistors are connected in series to the positive electrode of the battery 30, the 10 kΩ resistor is connected to the terminal GND of the battery 30, and the connection point of the two resistors is the terminal of the microcomputer 20. Some input to A / D. In this case, since the battery voltage is divided into ¼ and inputted to the terminal A / D of the microcomputer 20, 3V is inputted to the microcomputer 20 when the battery voltage is 12V. Therefore, whether or not the battery voltage has decreased to a value less than a predetermined value (for example, the set value Vm (5V)) is determined by whether the voltage input to the terminal A / D of the microcomputer 20 is ¼ of the predetermined value. The determination can be made based on whether or not the value has reached less than the multiplied value (1.25 V when the predetermined value is 5 V).

  As to which operation mode is currently selected in the microcomputer 20, for example, when the operation voltage of the microcomputer 20 is constant as in this embodiment, the current value of the line L3 is measured by a current sensor or the like. Judgment is possible.

  In addition, the configuration for inputting the battery voltage to the microcomputer 20 is not limited to that illustrated and described above, and a known configuration can be used. For example, the microcomputer 20 of the present embodiment directly detects the value of the battery voltage via the line L1, but voltage detection means (voltage detection unit) independent of the microcomputer 20 such as the voltage detection unit 150. May be installed separately, and the output (battery voltage) from there may be input to the terminal A / D. Further, instead of inputting the battery voltage via the terminal A / D as in the present embodiment, an analog voltage comparator is built in the microcomputer, and the voltage is determined based on the battery voltage input via the voltage comparator. It may be determined.

  The terminal Vo of the step-up / step-down DCDC circuit 110 is connected to the terminal Vi of the regulator 120 and the control unit 140 via a line L2. The terminal Vo of the regulator 120 is connected to the terminal VCC of the microcomputer 20 and the reset circuit 130 via a line L3. The reset signal is connected to the terminal RES of the microcomputer 20 via the line L4. The line L5 is connected to a terminal DIO (digital input / output terminal) of the microcomputer 20. Connected to the other end of the line L5 are various sensors for detecting the state quantity of the engine and the vehicle and various actuators in the engine and the vehicle. For example, the crank angle for detecting the rotation angle of the crankshaft of the engine. The outputs of various sensors that detect the state quantity of the engine, including a sensor 90 (see FIG. 10) and a water temperature sensor (not shown) that detects the engine coolant temperature, are input to the microcomputer 20 via the terminal DIO.

  The control unit 140 is connected to the step-up / step-down DCDC circuit 110 via the line L6, and the control unit 140 sends a control signal for switching between the PWM switching operation and the step-up / step-down operation via the line L6. Output to. The control unit 140 is connected to the voltage detection unit 150 via the line L7, and the battery voltage detection signal output from the voltage detection unit 150 is sent to the control unit 140 via the line L7.

  The control unit 140 according to the present embodiment determines that the voltage of the battery 30 has decreased when the battery voltage input from the voltage detection unit 150 via the line L7 is less than the set value Vb, and the step-up / step-down DCDC circuit 110 outputs a control signal for instructing a boosting operation via line L6. On the other hand, when the battery voltage input from voltage detector 150 is equal to or higher than set value Vb, it is determined that the voltage of battery 30 is normal or recovered. Then, a control signal for instructing the step-down operation to the step-up / step-down DCDC circuit 110 is output. The set value Vb is a value used when the power supply unit 10 (control unit 140) determines that the voltage of the battery (external power supply) 30 has dropped or recovered. For example, the set value Vb is an output voltage value of the step-up / down DCDC circuit 110 ( 6V) or more, and is included in the range below the normal operating voltage of the battery 30 (generally about 12 to 14V, which corresponds to the test voltage UB = 12V in the example of FIG. 11A described later). Here, Vb = 8V. In addition, since the ripple voltage in the test period t8 in FIG. 11A described later becomes 5 to 7V, Vb = 8V is preferable, but Vb is not limited to this value.

  FIG. 2 shows the configuration of the step-up / step-down DCDC circuit 110. 2A is a configuration diagram when the step-up / step-down DCDC circuit 110 of the electronic control unit 1 of the present invention is configured by a switching element, and FIG. 2B is a configuration diagram of the step-up / step-down DCDC circuit 110 of the electronic control unit 1 of the present invention by a switching element. It is explanatory drawing which shows the operation | movement at the time of comprising.

  As shown in FIG. 2A, the step-up / step-down DCDC circuit 110 has a configuration in which a step-down DCDC circuit and a step-up DCDC circuit having a typical topology are connected in series, and uses a switching element (such as a MOSFET), and includes an inductor. 113 and the capacitor 117 are shared by the step-down DCDC circuit and the step-up DCDC circuit. In the example of FIG. 2A, the step-down DCDC circuit is arranged on the input terminal Vi side (left side in the figure), and the step-up DCDC circuit is arranged on the output terminal side Vo side (right side in the figure).

  First, the step-down operation will be described. The step-down DCDC circuit includes a switching element 111, a switching element 112, and an inductor 113. As shown in FIG. 2B, during the step-down operation, the switching element 115 is set to the OFF state by the control signal CTRL3, and the switching element 116 is set to the ON state by the control signal CTRL4. A voltage lower than the voltage input from the terminal Vi can be output to the terminal Vo by PWM-controlling the switching element 111 and the switching element 112 with the control signal CTRL1 and the control signal CTRL2.

  Next, the boosting operation will be described. The step-up DCDC circuit includes an inductor 113, a switching element 115, and a switching element 116. As shown in FIG. 2B, during the step-up operation, the switching element 112 is set to the OFF state by the control signal CTRL2, and the switching element 111 is set to the ON state by the control signal CTRL1. A voltage higher than the voltage input from the terminal Vi can be output to the terminal Vo by PWM control of the switching element 115 and the switching element 116 using the control signal CTRL3 and the control signal CTRL4.

  As described above, the step-up / step-down DCDC circuit 110 can switch between the step-up operation and the step-down operation by the control signals CTRL1 to CTRL4.

  FIG. 3 is an explanatory diagram showing how the output voltages of the step-up / step-down DCDC circuit 110 and the regulator 120 change with time when the test voltage 311 is used as the external power source of the electronic control unit 1 according to the embodiment of the present invention. The test voltage 311 in the figure is determined by ISO 16750-2, and details of the test voltage 311 will be described later with reference to FIG.

  As shown in FIG. 3, since the test voltage 311 (thin line in FIG. 3) immediately after the start of application is equal to or higher than the set value Vb (8 V), the step-up / step-down DCDC circuit 110 performs a step-down operation. Thereafter, the power supply circuit 10 determines that “the voltage of the external power supply (test voltage 311) has decreased” by detecting that the test voltage 311 corresponding to the battery voltage has reached less than the set value Vb. Then, switching from the current step-down operation to the step-up operation is performed (timing t3 in FIG. 3). As a result, even if the test voltage 311 further decreases and reaches 3V as shown in the figure, the output voltage 312 (thick line in FIG. 3) of the step-up / step-down DCDC circuit 110 is boosted, and the step-up / step-down DCDC circuit 110 is stably It can be seen that the target voltage of 6V is output. In the present embodiment, the target voltage is a value smaller than the set value Vb (8V) and is set to a value higher than the microcomputer operating voltage (5V).

  The step-up / step-down DCDC circuit 110 during the boosting operation outputs the target voltage (6V) when the input voltage is less than the target voltage (6V), and the same voltage as the input voltage when the input voltage exceeds the target voltage (6V). (That is, a voltage exceeding the target voltage) is output. Further, the step-up / step-down DCDC circuit 110 is switched from the step-up operation to the step-down operation when the test voltage 311 recovers to the set value Vb or more (timing t4 in FIG. 3), and the DCDC circuit output voltage 312 is stepped down to 6V. Return.

  As shown in FIG. 3, the step-up / step-down DCDC circuit 110 according to the present invention appropriately switches between the step-down operation and the step-up operation according to the time change of the test voltage 311, so that the DCDC circuit output voltage 312 is ensured to be 6V or more. As a result, the regulator output voltage 313 (thick dotted line in the figure) is continuously stable at 5V. Therefore, even when the battery voltage drops sharply and falls below the operating voltage (5 V) of the microcomputer 20 (between timing t1 and timing t2 in FIG. 3), the power supply voltage of the microcomputer 20 can be maintained at the operating voltage. The electronic control unit is not disturbed at all.

  Although it has been described that the switching between the step-down operation and the step-up operation and the switching from the step-up operation to the step-down operation are performed based on whether or not the battery voltage is less than 8 V (set value Vb), the voltage value used for the determination is as follows. It is not limited to 8V. In order to prevent 6V of the DCDC circuit output voltage 312 from dropping, the voltage may be switched to the boosting operation immediately before the battery voltage drops below 8V (for example, 9V), and in order to suppress the loss of the regulator 120, It goes without saying that a voltage value that does not increase the potential difference between the input Vi and the output Vo of the DCDC circuit 110 is desirable.

  By the way, when the microcomputer 20 detects that the test voltage 311 has reached less than the set value Vm (the operation voltage of the microcomputer 20 is 5V) (between timing t1 and timing t2 in FIG. 3), the microcomputer 20 changes its operation mode. Switch from normal operation mode to low power consumption mode. Since the set value Vm is set to a value smaller than the set value Vb, the test mode 311 switches the operation mode of the microcomputer 20 to the low power consumption mode after the step-up operation of the step-up / step-down DCDC circuit 110 is started. After the 20 operation modes return to the normal mode, the step-up / step-down DCDC circuit 110 performs the step-down operation again.

  According to the electronic control unit 1 configured as described above, since the power supply circuit 10 includes the step-up / step-down DCDC circuit 110, when the battery voltage drops below the set value Vb, the step-up / step-down DCDC circuit 110 is switched from the step-down operation. By switching to the boosting operation, it is possible to prevent a decrease in the power supply voltage of the microcomputer 20. As a result, it is not necessary to increase the capacity of the capacitor in preparation for a temporary steep drop in battery voltage when the engine is started, and the electronic control unit can be downsized. Furthermore, in the present embodiment, when the microcomputer 20 determines that the battery voltage has dropped below the set value Vm during the step-up operation of the step-up / step-down DCDC circuit 110, the operation mode of the microcomputer 20 itself is lower than the normal operation mode. Since the mode is changed to the power consumption mode, the load current during the step-up / step-down DCDC circuit 110 during the boosting operation can be reduced. Therefore, according to the electronic control unit 1 according to the present embodiment, it is possible to suppress power consumption while stably operating the microcomputer 20 even when the battery voltage is lowered, and the power supply unit 10 is installed to absorb voltage ripple. The capacity of the capacitor to be reduced or the power supply unit 10 can be reduced.

  When the microcomputer 20 determines that the battery voltage has recovered to the set value Vm or higher during the step-up operation of the step-up / step-down DCDC circuit 110, the microcomputer 20 quickly shifts to the normal mode, so the CPU stop time of the microcomputer 20 is minimized. it can.

  By the way, when the operation mode of the microcomputer 20 is the low power consumption mode, the operation temporarily changes to the normal mode, and after performing various in-vehicle sensor output inputs and predetermined processing, the intermittent operation returns to the low power consumption mode again. It is preferable to carry out.

  4A and 4B are explanatory diagrams of an operation flow performed by the microcomputer 20 when the engine is started in the electronic control unit 1 according to the embodiment of the present invention. FIG. 4A shows a main processing flow executed when the power to the electronic control unit 1 is turned on. FIG. 4B shows a setting for permitting an interrupt to the microcomputer 20 (hereinafter sometimes referred to as “interrupt setting”). 5 shows an interrupt processing flow executed when a predetermined interrupt (here, a hardware interrupt request (IRQ based on the output of the crank angle sensor 90)) is used as a trigger. Details of the configuration for starting the engine including the starter motor 70 and the start switch 60 referred to in the following description will be described later with reference to FIG.

  First, the main processing flow of FIG. 4A will be described. When the electronic control unit 1 is powered on, the processing flow of FIG. 4A is started, a reset signal is issued from the reset circuit 130 to the microcomputer 20, the microcomputer 20 is initialized by the reset signal, and starts up in a normal mode (processing S1). .

  In process S2, it is determined whether or not the start switch 60 (see FIG. 10) is in an on state. If it is detected that the start switch 60 is in an on state, the process proceeds to process S3. If it is detected in step S2 that the start switch 60 is off, step S2 is executed again. That is, in this case, execution of the next process is interrupted until the start switch 60 is turned on.

  When the start switch 60 is turned on, the starter motor 70 starts rotating, whereby the voltage of the battery 30 at the time of starting the engine sharply decreases. In process S3, the microcomputer 20 reads the voltage of the battery 30 at the time of engine start via the terminal A / D.

  In process S4, the microcomputer 20 determines whether or not the battery voltage has decreased to less than the set value Vm. If it is determined that the battery voltage has decreased to less than the set value Vm, the process proceeds to process S5. On the other hand, if it is determined in process S4 that the battery voltage is equal to or higher than the set value Vm, the process returns to process S2.

  In process S5, the microcomputer 20 sets an interrupt, issues a “sleep instruction” in process S6, and transitions from the program execution state (normal mode) to the low power consumption mode (sleep mode). Note that the CPU of the microcomputer 20 stops after executing the “sleep instruction”, but the register contents of the CPU are retained.

  Next, the interrupt processing flow of FIG. 4B will be described. In the following description, it is assumed that an input (interrupt request) from the crank angle sensor 90 (see FIG. 10) to the microcomputer 20 is a trigger for starting the process in FIG. 4B.

  When an interrupt request is input during interrupt setting, the microcomputer 20 checks whether the interrupt request is input from the crank angle sensor 90, and the interrupt request is input from the crank angle sensor 90 (sensor data). If it can be confirmed, the operation mode is returned to the normal mode, the processing of FIG. 4B is started, and the sensor data is read (processing S11).

  In process S12, the microcomputer 20 determines whether sensor data such as a battery voltage or a water temperature sensor has been updated. If it is determined that the data has been updated, the process proceeds to process S13, and if it has not been updated, process 14 is performed. Proceed to In addition, the presence or absence of the update of the sensor data in process S12 can be confirmed by referring each sensor data stored in the memory of the electronic control unit 1, for example.

  In process S13, sensor data (for example, battery voltage or water temperature sensor data) determined to have been updated in process S12 is read. In process S14, based on the data of the crank angle sensor and other sensors (for example, a water temperature sensor) read in process S11 and process S13, a cylinder discrimination process necessary for starting the engine and other predetermined processes are performed.

  In process S15, the microcomputer 20 determines whether or not the battery voltage has recovered to the set value Vm or more based on the input from the terminal A / D. If it is determined that the battery voltage has recovered, the process proceeds to process S18 to cancel the interrupt setting. (Process S18), the operation mode is returned to the normal mode (Process S19).

  On the other hand, if it is not determined in step S15 that the microcomputer voltage has been recovered, interrupt setting is performed in the same manner as in step S11 (step S16), a “sleep instruction” is issued in step S17, and the low power consumption mode ( (Sleep mode) is continued.

  In the above description, the input from the crank angle sensor is used as a trigger for performing an intermittent operation. However, this is only an example, and another interrupt may be used as a trigger. In addition, the types of sensor data read in the processes S11 and S13 described above and the predetermined process performed in S14 are merely examples, and are data and processes necessary for vehicle operation including engine start, and temporarily enter the normal mode. As long as it can be acquired or executed at the time of a general return, it is not limited to the above. Further, in the above description, whether or not the battery voltage has decreased below the set value Vm (process S4) and whether or not the battery voltage has recovered to the set value Vm or more (process S15) is the microcomputer 20, The main body may be a part other than the microcomputer 20, and the operation mode of the microcomputer 20 may be switched based on the determination.

  FIG. 5 is a timing chart of the intermittent operation performed by the electronic control unit 1 as a result of the processing flow of FIGS. 4A and 4B. The operation will be described below.

  As shown in the first row of FIG. 5, when the start switch (START switch in FIG. 5) 60 is turned on, the starter motor 70 starts to rotate, and this causes a decrease in battery voltage (less than the set value Vm (5 V)). Is detected (see the second row in FIG. 5).

  When the battery voltage drops below the set value Vm (5 V), the microcomputer 20 transitions from the normal mode to the low power consumption mode (sleep mode) as shown in the fifth row of FIG. 5 (timing t1).

  When the starter motor 70 rotates after the transition to the low power consumption mode (after timing t1), a sensor signal is output from the crank angle sensor 90 to the microcomputer 20 at a predetermined interval (for example, every 5 milliseconds) (see FIG. 5). This is accepted as an interrupt request by the microcomputer 20 and the microcomputer 20 temporarily returns to the normal mode each time.

  On the other hand, sensor data such as battery voltage and water temperature sensor other than the crank angle sensor 90 are also updated at a predetermined interval (for example, every 10 milliseconds) ((d1) to (dm + 1 in the third row in FIG. 5). )reference).

  When the microcomputer 20 temporarily returns to the normal mode, the microcomputer 20 reads the data of the crank angle sensor, and the updated sensor only when other sensor data (battery voltage data or water temperature sensor data) is updated. After the data is read and a predetermined process is executed based on the read sensor data, the mode is again shifted to the low power consumption mode.

  When the battery voltage exceeds the set value Vm (5 V) at timing t2, the microcomputer 20 returns from the low power consumption mode to the normal mode.

  As can be seen from FIG. 5, during the intermittent operation, a normal current waveform with a large current consumption and a low power consumption mode with a small current consumption are repeated, so that the current waveform has a rectangular tooth shape. .

  As described above, according to the above-described series of operation flows, the microcomputer 20 reduces the load on the power supply circuit 10 by shifting to the low power consumption mode when the battery voltage is low, and further performs intermittent operation by performing intermittent operation. Low power consumption operation is possible.

Next, an example of the effect of reducing the current consumption by the intermittent operation is shown (for an example of the DC characteristic and the AC characteristic of the microcomputer 20, refer to the description of FIG. 9 described later). For example, the current, operation time, and operation cycle of each operation mode are assumed as in the following conditions A to E.
A: Normal mode current = 60 mA
B: Low power consumption mode current = 44 mA
C: Normal mode operation time = 0.5 ms
D: Low power consumption mode operation time = 4.5 ms
E: Operation cycle = 5 ms
Under this assumption, the operating current in the case of “no intermittent operation” is equal to the normal mode current as shown in the following equation, and is 60 mA. On the other hand, in the case of “with intermittent operation”, the average current is set to 45.6 mA when the following equation is set.

  Therefore, as is clear from these two results, if the intermittent operation for temporarily returning to the normal mode is performed during the low power consumption mode, only various arithmetic processes necessary for sensing and engine control during the low power consumption mode are performed. In addition, the current consumption can be further reduced.

  Hereinafter, the present embodiment described in a series will be compared with a comparative example. 6 shows a configuration of a comparative electronic control unit 201 provided with a step-down DCDC circuit 210 in the power supply circuit, FIG. 7 shows a configuration of the step-down DCDC circuit 210 in the electronic control unit 201 shown in FIG. 6, and FIG. The output waveform of the power supply circuit in the electronic control unit 201 shown in FIG.

  As can be seen from a comparison between FIG. 6 and FIG. 1, the electronic control unit 201 shown in FIG. 6 differs from the present embodiment in a step-down DCDC circuit 210 and a microcomputer 220 (details of other components) Will be omitted). The microcomputer 220 does not have the transition function from the normal mode to the low power consumption mode and the intermittent operation function in the low power consumption mode, unlike the microcomputer 20 shown in FIG.

  FIG. 7 shows a step-down DCDC circuit 210. The step-down DCDC circuit 210 includes a MOSFET 211, a diode 212, an inductor 213 and a capacitor 214. (Description is omitted). This is a circuit capable of outputting from the Vo terminal a voltage lower than the voltage inputted from the Vi terminal by PWM control of the MOSFET 211. By monitoring the voltage at the Vo terminal and variably controlling the duty of the MOSFET 211, the output voltage can be maintained at the target voltage (6V). The step-down DCDC circuit 210 does not have a step-up function, and therefore cannot output a voltage exceeding the input voltage. Further, when the input voltage falls below the target voltage (6V), the output voltage also falls simultaneously.

  FIG. 8 shows output voltages of the step-down DCDC circuit 210 and the regulator 120 of the electronic control unit 201 of FIG. 6 in the case of the starting profile test waveform. When the test voltage 301 (thin line in the figure) is UB (12 V), the step-down DCDC circuit output voltage 302 (thick line in the figure) is 6 V (target voltage) and the output voltage of the regulator 303 (thick dotted line in the figure) Is 5V. When the test voltage 301 falls below the target voltage (6V) of the step-down DCDC circuit 210, the output of the step-down DCDC circuit 210 also decreases simultaneously, and when the output of the step-down DCDC circuit 210 falls below 5V, the power supply voltage of the microcomputer 220 is also the same period (see FIG. 8 (between timings t1 and t2). Thereafter, when the test voltage 301 recovers to 5V or higher, the output voltage 303 of the regulator 120 recovers to 5V. As described above, in the electronic control unit 201 including the step-down DCDC circuit 210, the power supply voltage of the microcomputer 220 also becomes 5 V or less during the timing t1 to t2 when the test voltage 301 becomes 5 V or less.

  As described above, the electronic control unit 201 according to the comparative example shown in FIG. 6 has a configuration including the step-down DCDC circuit 210, and the power supply voltage of the microcomputer 220 is reduced due to a sharp drop in the voltage of the battery 30 generated when the engine is started. There was a problem that could not be secured.

  On the other hand, according to the present embodiment described above, the power supply voltage of the microcomputer 20 can be secured stably by using the configuration including the step-up / step-down DCDC circuit 110. In addition, by shifting the microcomputer 20 to the low power consumption mode when the battery voltage drops, the load on the step-up / step-down DCDC circuit 110 can be reduced, so that the capacitor capacity can be reduced, and the electronic control unit 1 can be reduced in size. Can be

  The contents referred to above will be described below. First, the low power consumption mode of the microcomputer will be described with reference to FIG. As an example of a microcomputer having a low power consumption mode that can be applied to the electronic control unit according to the present embodiment, “Renesas 32-bit RISC microcomputer SH72531 User's Manual: Hardware” (hereinafter referred to as a reference) There is a description. Here, the low power consumption mode will be described by taking the microcomputer described in the reference as an example.

  FIG. 9A is an explanatory diagram showing an example of the DC characteristic of the microcomputer in the reference document, and FIG. 9B is an explanatory diagram showing an example of the AC characteristic of the microcomputer in the reference document. According to FIG. 9A, the current during normal operation (normal mode) of the microcomputer is 60 mA (Typ value) when the clock frequency is 120 MHz. The low power consumption mode has two modes: a sleep mode in which the clock frequency is the same as in normal operation and a transition by a software instruction (Sleep instruction from the CPU of the microcomputer) and a standby mode in which the clock supply is stopped and a transition is made by a hardware signal is there. In the sleep mode, the built-in peripheral modules other than the CPU operate, but in the standby mode, not only the CPU but also the built-in peripheral modules are stopped.

  The current in the sleep mode is 44 mA (Typ value), and the current in the standby mode is 0.3 mA (Max value). Although the sleep mode has a slightly larger current consumption than the standby mode, the clock frequency is the same as that during normal operation, so the recovery time is as short as several μs. The standby mode has a smaller current consumption than the sleep mode, Since the clock is stopped, it takes 10 ms to recover (FIG. 9B).

  When performing an intermittent operation for returning from the low power consumption mode to the normal mode at 5 ms intervals (see FIG. 4) using the microcomputer having the characteristics shown in FIG. 9A and FIG. 9B, It is preferable to use the sleep mode in which the return time is less than 5 ms as the low power consumption mode instead of the standby mode in which the return time exceeds 5 ms. Therefore, in this embodiment, the sleep mode is used as the low power consumption mode. However, this does not limit the low power consumption mode used in the present invention to the sleep mode of FIG. 9, and the present invention is not limited to the low power consumption mode having a shorter recovery time than the return interval to the normal mode in intermittent operation. It is applicable to. Moreover, the individual microcomputers applicable to the present invention are not limited.

  FIG. 10 shows components mounted on the vehicle for starting the engine. One end of the ignition switch 40 and one contact of the relay 50 are connected to the positive electrode of the battery 30 via a line L11. The other end of the ignition switch 40 is connected to the power supply circuit 10 of the electronic control unit 1 and one end of the coil terminal of the relay 50 via a line L12. The other end of the coil terminal of the relay 50 is connected to one end of the start switch 60 via a line L13. The other contact of relay 50 is connected to starter motor 70 via line L14. The negative electrode of the battery 30 is connected to the motor 70, the other end of the start switch 60, and the electronic control unit 1 (the power supply unit 10 and the microcomputer 20) via a line L15.

  Next, the operation will be described. When the start switch 60 is turned on when the ignition switch 40 is in the on state, the coil of the relay 50 is excited and the contact of the relay 50 comes into contact to form a closed circuit, so that the starter motor 70 starts rotating. At the same time, the pinion gear 71 of the starter motor 70 meshes with the ring gear 81 attached to the crankshaft 80 of the engine (not shown), so that the engine starts rotating.

  The rotation of the ring gear 81 is detected by the crank angle sensor 90, and is processed by the microcomputer 20 together with other information (for example, a water temperature sensor) to detect the rotational speed and discriminate the cylinder to determine the fuel injection and ignition timing. .

  For example, when the ring gear is output every 6 ° and the starter motor 70 rotates at 200 rpm, the number of pulses per second is 200 (number of pulses = (200 rpm / 60 s). X (360 ° / 6 °) = 200 pulses), and the interval is 5 ms (1/200 = 5 ms).

  Next, the standard of the durability test described in ISO 16750-2 “Starting Profile” will be described with reference to FIG. FIG. 11A is an explanatory diagram showing a time change (voltage waveform) of the test voltage described in ISO 16750-2 (corresponding to the test voltage 301 in the description of the above embodiment), and FIG. 11B shows the test voltage described in ISO 16750-2. It is explanatory drawing which shows the relationship of time. Us, Ua, and f in FIG. 11B correspond to the two voltages and periods shown in FIG. 11A, respectively.

  Hereinafter, the test voltage 300 shown in FIG. 11A will be described in the case of the test item (III) in FIG. 11B.

  (1) The test voltage 300 starts from a steady state of 12V (UB), but then suddenly drops to 3V (Us) during a time tf (5ms) and maintains 3V for a time t6 (15ms). After the elapse of time t7 (50 ms), the voltage recovers to 6V. The voltage change so far corresponds to the voltage drop of the battery due to the rush current at the start of the starter motor.

  (2) Subsequently, the test voltage 300 fluctuates at a period of 2 Hz and an amplitude of 2 V during the time t8 (1 s). This corresponds to a cranking operation in which the engine rotates.

  (3) Thereafter, the test voltage 300 recovers to a steady state of 12 V after elapse of time tr (100 ms). This corresponds to a reduction in the load on the starter motor due to the start of the engine and the alternator starting to generate power.

  In the above description of the present embodiment, the microcomputer 20 exemplifies the case where the operating voltage is 5V, but the battery voltage in the period t6 in the test item (III) in FIG. 11B is 3V which is less than the operating voltage. In addition, resistance to voltage drop during the period t6 is essential.

  By the way, in a vehicle equipped with an idle stop mechanism that automatically stops the engine when a decrease in vehicle speed is detected, the driver's start operation after the engine stops (for example, the driver removes his foot from the brake pedal or operates the steering wheel) When the engine is restarted, the starter motor is used in the same way as when the engine is started normally, so that the battery voltage sharply decreases as described above. Therefore, the present invention can be applied not only at the time of normal engine start but also at the time of engine restart after idle stop. Therefore, “at the time of engine start” in this paper includes not only the normal time but also the time of engine restart from idle stop. Here, an operation flow performed by the microcomputer 20 when the engine is restarted (returned) from the idle stop in the electronic control unit 1 will be described.

  FIG. 12 shows the operation flow performed by the microcomputer 20 when the engine is restarted (returned) from the idle stop in the electronic control unit 1. The microcomputer 20 is triggered by a start signal (described later) output when the engine is restarted. The main processing flow to be executed is shown. That is, FIG. 12 corresponds to FIG. 4A which has already been described, and the other processes except the process S21 are the same as those in FIG. The interrupt process flow executed when the interrupt setting is set in the microcomputer 20 is the same as that in FIG.

  When a decrease in vehicle speed is detected and idling stop (engine stop) is executed, the microcomputer 20 starts the processing flow shown in FIG. 12, and determines whether or not the start signal is on (whether or not the start signal is output). (Process S21). A start signal is a signal that is output when a driver's start operation (for example, an operation in which the driver lifts his or her foot from a brake pedal or operates a steering wheel) is detected in a vehicle in an idle stop state. This is a signal that triggers the start of rotation of the motor 70 (that is, engine restart).

  If the microcomputer 20 detects in step S21 that the start signal is on, the process proceeds to step S3. When the start signal is turned on, the starter motor 70 starts to rotate, and thereby the voltage of the battery 30 sharply decreases. In process S3, the microcomputer 20 reads the voltage of the battery 30 at the time of engine start via the terminal A / D. When detecting a decrease in battery voltage in process S4, the microcomputer 20 sets an interrupt, issues a Sleep command, and transitions to the sleep mode (processes S5 and S6).

  Thus, the present invention can also be applied when the engine is restarted from an idle stop.

  DESCRIPTION OF SYMBOLS 1,201 ... Electronic control unit (ECU), 3 ... Capacitor, 10, 11 ... Power supply circuit (PS), 20, 220 ... Microcomputer (MPU), 30 ... Battery, 40 ... IGN switch, 50 ... Relay, 60 ... Start Switch, 70 ... Starter motor, 71 ... Pinion gear, 80 ... Crankshaft, 81 ... Ring gear, 90 ... Crank angle sensor, 110 ... Buck-boost DCDC circuit, 111, 112, 115, 116 ... Switching element, 113 ... Inductor, DESCRIPTION OF SYMBOLS 117 ... Capacitor, 120 ... Regulator, 130 ... Reset circuit, 140 ... Control part, 150 ... Voltage detection part, 210 ... Step-down DCDC circuit, 211 ... MOSFET, 212 ... Diode, 213 ... Inductor, 214 ... Capacitor, L1-L7, L11 to L16 ... connection line, 300, 301, 311 Test voltage, 302,312 ... DCDC circuit output voltage, 303, 313 ... regulator output voltage

Claims (7)

A microcomputer section;
A step-up / step-down DCDC circuit, and a power supply unit that generates a power supply voltage of the microcomputer unit based on an external power supply
When the microcomputer unit determines that the voltage of the external power supply has decreased when the engine is started, the microcomputer unit changes the operation mode of the microcomputer from the normal operation mode to a low power consumption mode that consumes less power than the normal operation mode. Electronic control unit characterized by The electronic control unit according to claim 1,
The microcomputer unit changes the operation mode of the microcomputer unit from the low power consumption mode to the normal operation mode when it is determined that the voltage of the external power source has recovered after it is determined that the voltage of the external power source has decreased. An electronic control unit characterized by being restored. The electronic control unit according to claim 1,
The microcomputer unit temporarily shifts to the normal mode during the low power consumption mode, performs various sensor output inputs and performs predetermined processing, and then performs an intermittent operation to return to the low power consumption mode again. Electronic control unit. In the electronic control unit according to claim 1 or 2,
The electronic control unit according to claim 1, wherein the voltage value at which the voltage of the external power source is determined to have decreased or recovered is the operating voltage value of the microcomputer unit. The electronic control unit according to claim 1,
The power supply unit further includes a voltage detection unit that detects a voltage of the external power supply,
The electronic control unit according to claim 1, wherein the power supply unit switches the step-up / step-down DCDC circuit from a step-down operation to a step-up operation when determining that the voltage of the external power supply has dropped based on the output of the voltage detection unit. The electronic control unit according to claim 5,
When the power supply unit determines that the voltage of the external power supply has recovered based on the output of the voltage detection unit after determining that the voltage of the external power supply has decreased, the step-down / step-down DCDC circuit is reduced from the step-up operation. Electronic control unit characterized by switching to In the electronic control unit according to claim 5 or 6,
The voltage value at which the power supply unit determines that the voltage of the external power supply has dropped or recovered is in a range that is not less than the output voltage value of the step-up / step-down DCDC circuit and not more than the normal operation voltage of the external power supply. A featured electronic control unit.

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