ECU control system and ECU control method

Abstract

This ECU control system comprises a master ECU (10) and slave ECUs (20, 30) that determine the on / off states of a plurality of relays (12, 22, 32). The plurality of relays (12, 22, 32) includes: a relay (12) the on / off state of which is switched by the master ECU (10); and relays (22, 32) the on / off states of which are switched by the slave ECUs (20, 30). Upon reception of an on / off instruction signal from the master ECU (10), the slave ECUs (20, 30) switch the on / off states of the relays (22, 32). The master ECU (10) sets a standby time for synchronizing the on / off state of the relay (12) and the on / off states of the relays (22, 32), and, after the standby time has elapsed, starts processing for switching the on / off state of the relay (12).

Description

ECU control system and ECU control method

[0001] The present invention relates to an ECU control system and an ECU control method.

[0002]

[0003] Conventionally, there have been known vehicle power supply control devices that supply and cut off power to a load by turning on and off semiconductor switching elements. For example, a vehicle power supply control device described in Patent Document 1 supplies power from a power source to a load via a parallel circuit of two electric wires having equal wiring resistance, and measures the passing currents that flow through the semiconductor switching elements on each electric wire using current measuring units of multiple IPDs. In order to match the temperatures of each electric wire estimated by a current temperature estimating unit from the measured currents, the vehicle power supply control device adjusts the target duty ratio of the drive signals of the semiconductor switching elements of the IPDs on the electric wires to synchronize the timing of turning off the semiconductor switching elements and cutting off the power supply.

[0003] JP 2016-208762 A

[0004] However, in the above-mentioned vehicle power supply control device, since the multiple IPDs estimate the temperature of the electric wire independently in each current measurement unit, if the temperature estimation accuracy differs between the current measurement units, there is a problem that the synchronization timing for turning off the semiconductor switching element will be shifted.

[0005] The problem to be solved by the present invention is to provide an ECU control system and an ECU control method that can suppress mis-synchronization of the on / off of a plurality of relays.

[0006] The present invention solves the above problem by comprising a master ECU and a slave ECU, wherein the master ECU determines whether a plurality of relays are on or off, sets a waiting time for synchronizing the on / off of the plurality of relays, and starts the process of switching the relays on and off after the waiting time has elapsed, and the slave ECU switches the relays on and off when it receives an on / off instruction signal from the master ECU.

[0007] According to the present invention, it is possible to suppress the on / off synchronization of a plurality of relays.

[0008] Fig. 1 is a block diagram of an ECU control system according to an embodiment of the present invention. Fig. 2 is a flowchart of a control flow executed by a master ECU. Fig. 3 is a conceptual diagram illustrating the timing from the on / off determination of a relay to the on / off switching. Fig. 4 is a conceptual diagram illustrating the timing from the on / off determination of a relay to the on / off switching. Fig. 5 is a conceptual diagram illustrating the timing from the on / off determination of a relay to the on / off switching. Fig. 6 is a flowchart of a control flow executed by a master ECU.

[0009] FIG. 1 is a schematic diagram of an ECU control system 1 according to this embodiment. The ECU control system 100 is mounted on a vehicle equipped with communication lines 2 and 3 and a battery. The vehicle may be a hybrid vehicle or an electric vehicle equipped with an engine and a motor. The ECU control system 100 may also be mounted on a vehicle powered by an engine (an ICE vehicle). The battery is a low-voltage power source for operating loads 13, 23, and 33 and the ECU. The battery is a battery of 60 volts or less, e.g., a 12V battery, and is a secondary battery such as a lithium-ion battery or a lead battery. The vehicle equipped with the ECU control system 100 also includes a generator (alternator or DC-DC converter) in addition to the battery. The loads 13, 23, and 33, described below, receive power from the generator and / or the battery.

[0010] As shown in Fig. 1, the ECU control system 1 includes communication lines 2 and 3, a master ECU 10, loads 13, 23, and 33, and slave ECUs 20 and 30. In Fig. 1, the thick lines correspond to power lines. The communication lines 2 and 3 are, for example, CAN or LIN communication lines.

[0011] The master ECU 10 is a higher-level ECU in a network including communication lines 2 and 3 and multiple ECUs, and is a control unit connected at an upstream position on the network. The master ECU 10 includes a microcontroller 11 and multiple relays 12. The master ECU 10 determines the on / off states of the multiple relays 12, 22, and 32. The microcontroller 11 acquires trigger information that triggers the on / off state of the multiple relays 12, 22, and 32. The master ECU 10 incorporates multiple relays 12. The multiple relays 12 are relays that are operated by the master ECU 10. In other words, the master ECU 10 directly controls the multiple relays 12 to switch them on and off. The master ECU 10 also switches the multiple relays 22 and 32 on and off via the slave ECUs 20 and 30. Specifically, the master ECU 10 transmits on / off instruction signals to the slave ECUs 20 and 30 to switch the relays 22 and 32 on and off. When receiving an on / off instruction signal from the master ECU 10, the slave ECUs 20, 30 switch on / off the relays 22, 32. That is, the master ECU 10 switches on / off the relays 22, 32 by indirect control via the slave ECUs 20, 30.

[0012] For example, when a user performs an operation to turn on autonomous driving using an ADAS (Advanced Driver Assistance System), the master ECU 10 acquires trigger information for operating loads 13, 23, and 33 included in the ADAS. Based on the trigger information, the master ECU 10 determines relays 12, 22, and 32 for operating the loads 13, 23, and 33 included in the ADAS. The master ECU 10 then determines whether to turn on or off the multiple relays 12, 22, and 32. If the relays to be turned on include the relay 12 that is the target of operation by the master ECU 10, the microcontroller 11 of the master ECU 10 executes internal processing for switching the relay 12 on and off. Furthermore, if the relays to be turned on include the relays 22 and 32, the microcontroller 11 transmits an on / off instruction signal to the slave ECUs 20 and 30 to which the relays 22 and 32 to be turned on belong.

[0013] The master ECU 10 also sets a standby time for synchronizing the on / off of the relay 12 with the on / off of the relays 22 and 32, and when the standby time has elapsed, transmits an on / off instruction signal to the slave ECUs 20 and 30. The method for setting the standby time will be described later.

[0014] The multiple relays 12 are semiconductor switches built into the master ECU 10. The multiple relays 12 may be semiconductor switching elements such as FEIs or IPDs, or may be mechanical relays having operating contacts and coils. The multiple relays 12 are switched on and off by the master ECU 10. The multiple relays 12 are grouped as switches belonging to the master ECU 10 and connected to a battery. When a relay 12 is turned on, power from the battery is supplied to a load 13. The relay 12 corresponds to the "higher-level relay" of the present invention.

[0015] The slave ECUs 20, 30 are lower-level ECUs in a network including communication lines 2, 3 and multiple ECUs, and are control units connected at downstream positions on the network. The slave ECUs 20, 30 each include a microcontroller 21, 31 and multiple relays 22, 32. The slave ECU 20 is connected to the master ECU 10 via communication line 2. The slave ECU 30 is connected to the master ECU 10 via communication line 3. When the microcontrollers 21, 31 of the slave ECUs 20, 30 receive an on / off instruction signal from the master ECU 10, they execute internal processing for switching the relays 22, 32 on and off, thereby switching the relays 22, 32 on and off.

[0016] The multiple relays 22, 32 are semiconductor switches built into the slave ECUs 20, 30, respectively. The multiple relays 22, 32 may be semiconductor switching elements such as FEIs or IPDs, or may be mechanical relays having operating contacts and coils. The multiple relays 22, 32 are switched on and off by the slave ECUs 20, 30. The multiple relays 22, 32 are grouped as switches belonging to the slave ECUs 20, 20, respectively, and are connected to the battery. When the relays 22, 32 are turned on, battery power is supplied to the loads 23, 33, respectively. The multiple relays 22 and the multiple relays 32 belong to the slave ECUs 20 and 30, respectively, and are divided into different groups by the communication lines 2 and 3. The relays 22, 32 correspond to the "lower relays" of the present invention.

[0017] Next, a control method for the relays 12, 22, and 32 executed by the master ECU 10 will be described with reference to Fig. 2. Fig. 2 is a flowchart of a control flow executed by the master ECU.

[0018] In step S1, the master ECU 10 detects the operating states of the slave ECUs 20, 30 and determines whether the slave ECUs 20, 30 are in sleep mode. The master ECU 10 transmits to the slave ECUs 20, 30 control commands for waking up the slave ECUs 20, 30 and control commands for putting the slave ECUs 20, 30 to sleep. The master ECU 10 can identify the operating states of the slave ECUs 20, 30 from the control commands for waking up or putting the slave ECUs to sleep that have been transmitted to the slave ECUs 20, 30. For example, after transmitting a control command for putting the slave ECU 20 to sleep to the slave ECU 20, the master ECU 10 determines that the slave ECU 20 is in sleep mode.

[0019] The master ECU 10 may determine whether the slave ECUs 20, 30 are in a sleep state based on a response signal from the slave ECUs 20, 30. When the slave ECUs 20, 30 are in a wake-up state, the slave ECUs 20, 30 transmit a response signal to the master ECU 10. The master ECU 10 may identify the state of the slave ECUs 20, 30 based on the presence or absence of a response signal from the slave ECUs 20, 30 or the reception cycle of the response signal.

[0020] If it is determined that the slave ECUs 20, 30 are not in sleep mode, the master ECU 10 sets a standby time in step S2 according to the communication time between the master ECU 10 and the slave ECUs 20, 30. The standby time corresponds to the time by which the timing of starting the process for switching the relay 12 on and off is delayed relative to the timing of transmitting an on / off instruction signal to the slave ECUs 20, 30. As shown in FIG. 1 , the master ECU 10 and the slave ECUs 20, 30 are connected by communication lines 2, 3. A communication time is required for the on / off instruction signal to be transmitted from the master ECU 10 to the slave ECU 20 through the communication lines 2, 3. Therefore, a delay of at least the communication time occurs between the time when the master ECU 10 transmits the on / off instruction signal to the slave ECUs 20, 30 and the time when the relays 22, 32 switch on and off.

[0021] On the other hand, the relay 12 can be switched on and off under direct control of the master ECU 10, and is a switch that is operated by the master ECU 10. Therefore, when the master ECU 10 switches the relay 12 on and off, there is no delay, unlike the communication time over the communication lines 2 and 3. For example, if the timing at which the master ECU 10 transmits an on / off instruction signal to the slave ECUs 20 and 30 coincides with the timing at which the master ECU 10 starts the process of switching the relay 12 on and off, the relays 22 and 32 will switch on and off later than the relay 12. In other words, the on / off timing of the relay 12 and the on / off timing of the relays 22 and 32 will be out of sync, resulting in a loss of synchronization.

[0022] Therefore, the master ECU 10 sets the standby time to a time equivalent to the communication time of the communication lines 2 and 3, and delays the timing of the master ECU 10's process of switching on and off the relay 12 by the standby time. In other words, the master ECU 10 provides a standby time between the time when it determines to turn on or off the relays 12, 22, and 32 (or the time when it transmits an on / off instruction signal to the slave ECUs 20 and 30) and the time when it starts the process of switching on and off the relay 12. In the control process of step S2, the master ECU 10 sets the standby time to a first standby time equivalent to the communication time.

[0023] If the master ECU 10 determines that the slave ECUs 20 and 30 are in sleep mode, the master ECU 10 sets the standby time to a second standby time in step S3. The second standby time is longer than the first standby time. When the slave ECUs 20 and 30 are in sleep mode, the slave ECUs 20 and 30 must wake up to switch the relays 22 and 32 on and off. That is, the timing of switching the relays 22 and 32 on and off is delayed by the sum of the communication time on the communication lines 2 and 3 and the processing time required to wake up the slave ECUs 20 and 30 (hereinafter also referred to as the "wake-up time"). Therefore, the master ECU 10 sets the standby time to the sum of the communication time on the communication lines 2 and 3 and the processing time of the slave ECUs 20 and 30 (the second standby time). That is, when the slave ECUs 20 and 30 are in sleep mode, the master ECU 10 sets the standby time to be longer than when the slave ECUs 20 and 30 are in wake-up mode. The master ECU 10 knows the processing times of the slave ECUs 20 and 30 in advance.

[0024] In step S4, the master ECU 10 determines the plurality of relays 12, 22, 32 to be switched on and off based on the trigger information. In step S5, the master ECU 10 transmits an on / off instruction signal to the slave ECUs 20, 30. In step S6, the master ECU 10 measures the elapsed time from the time the on / off instruction signal was transmitted to the slave ECUs 20, 30, and determines whether a set standby time has elapsed. If the standby time has not elapsed, the control flow of the master ECU 10 waits in the flow of step S6, waiting for the standby time to elapse.

[0025] When the standby time has elapsed, the master ECU 10 starts the process of switching on and off the relay 12, which is the relay to be operated by the master ECU 10. Then, the master ECU 10 ends the control flow.

[0026] The timing of switching on and off the relay 12 by the master ECU 10 and the timing of switching on and off the relays 22 and 32 by the slave ECUs 20 and 30 will be described with reference to Figure 3. In Figure 3, "ON / OFF decision" refers to the timing at which the master ECU 10 decides to turn on and off the multiple relays 12, 22, and 32. Note that Figure 3 shows the relay on / off timing when the operating state of the slave ECUs 20 and 30 is the wake-up state.

[0027] As shown in "Slave ECU" in FIG. 3 , the relays 22 and 32 are switched on and off after the communication time has elapsed since the master ECU 10 made the on / off decision, and after the processing time (processing time by the microcontrollers 21 and 31) within the slave ECUs 20 and 30 has elapsed (corresponding to "ON / OFF switching" in FIG. 3 ). Also, as shown in "Master ECU" in FIG. 3 , the relay 12 is switched on and off after the first standby time has elapsed since the master ECU 10 made the on / off decision, and after the processing time (processing time by the microcontroller 11) within the master ECU 10 has elapsed (corresponding to "ON / OFF switching" in FIG. 3 ). The first standby time is the same length as the communication time. The processing time within the master ECU 10 is the same length as the processing time within the slave ECUs 20 and 30. Therefore, the on / off switching timing of the relays 22 and 32 corresponds to the off switching timing of the relays 22 and 32, and the on / off of the relay 10 is synchronized with the on / off of the relays 22 and 32.

[0028] 4, the timing of switching on and off the relay 12 by the master ECU 10 and the timing of switching on and off the relays 22 and 32 by the slave ECUs 20 and 30 will be described. Note that Fig. 4 shows the timing of switching on and off the relays when the operating state of the slave ECUs 20 and 30 is the sleep state.

[0029] As shown in "Slave ECU" in FIG. 4 , relays 22 and 32 are switched on and off after the wake-up time, communication time, and processing time within slave ECUs 20 and 30 (processing time by microcontrollers 21 and 31) have elapsed since the master ECU 10 made the on / off decision (corresponding to "ON / OFF switching" in FIG. 4 ). Also, as shown in "Master ECU" in FIG. 4 , relay 12 is switched on and off after the second standby time and processing time within master ECU 10 (processing time by microcontroller 11) have elapsed since the master ECU 10 made the on / off decision (corresponding to "ON / OFF switching" in FIG. 4 ). The second standby time is the same length as the communication time plus the wake-up time. The processing time within master ECU 10 is the same length as the processing time within slave ECUs 20 and 30. Therefore, the timing of switching on and off the relay 10 corresponds to the timing of switching off the relays 22 and 32, and the on and off of the relay 10 and the on and off of the relays 22 and 32 are synchronized.

[0030] As described above, the ECU control system according to this embodiment includes the master ECU 10 and the slave ECUs 20 and 30 that determine the on / off states of the multiple relays 12, 22, and 32. The multiple relays 12, 22, and 32 include the relay 12 that is switched on and off by the master ECU 10, and the relays 22 and 32 that are switched on and off by the slave ECUs 20 and 30. The slave ECUs 20 and 30 switch the relays 22 and 32 on and off when they receive an on / off instruction signal from the master ECU 10. The master ECU 10 sets a waiting time for synchronizing the on / off states of the relay 12 with the on / off states of the relays 22 and 32, and starts the process of switching the relay 12 on and off after the waiting time has elapsed. This makes it possible to prevent the on / off states of the multiple relays 12, 22, and 32 from becoming out of sync.

[0031] In this embodiment, the master ECU 10 sets the standby time in accordance with the communication time between the master ECU 10 and the slave ECUs 20 and 30. This delays the timing of the on / off switching process of the relay 12 by the communication time of the communication lines 2 and 3, thereby synchronizing the on / off of the relay 10 with the on / off of the relays 22 and 32.

[0032] Furthermore, in this embodiment, when the slave ECUs 20, 30 receive an on / off instruction signal, they execute internal processing for switching the relays 22, 32 on and off, and the master ECU 10 sets a standby time in accordance with the processing time of the internal processing of the slave ECUs 20, 30. This delays the timing of the on / off switching process of the relay 12 by the processing time of the internal processing of the slave ECUs 20, 30, thereby enabling the on / off of the relay 10 to be synchronized with the on / off of the relays 22, 32.

[0033] In this embodiment, the master ECU 10 identifies the operating states of the slave ECUs 20 and 30, and when the slave ECUs 20 and 30 are in a sleep state, the master ECU 10 sets a longer standby time than when the slave ECUs 20 and 30 are in a wake-up state. This delays the timing of the on / off switching process of the relay 12 by the wake-up time, thereby synchronizing the on / off of the relay 10 with the on / off of the relays 22 and 32.

[0034] In the ECU control method of this embodiment, the master ECU 10 determines whether the relays 12, 22, and 32 are turned on or off, sets a waiting time for synchronizing the on / off of the relay 12 with the on / off of the relays 22 and 32, and starts the process of switching the on / off of the relay 12 after the waiting time has elapsed. Furthermore, the slave ECUs 20 and 30 switch the on / off of the relays 22 and 32 when receiving an on / off instruction signal from the master ECU 10. This makes it possible to prevent the on / off of the relays 12, 22, and 32 from becoming out of synchronization.

[0035] In the first modification of this embodiment, if the first communication time between the master ECU 10 and the slave ECU 20 is different from the second communication time between the master ECU 10 and the slave ECU 30, a standby time (hereinafter also referred to as a "communication standby time") for waiting to transmit an on / off instruction signal may be set. The timing of switching the relay 12 on and off by the master ECU 10 and the timing of switching the relays 22 and 32 on and off by the slave ECUs 20 and 30 will be described with reference to Fig. 5. Fig. 5 shows the relay on / off timing when the slave ECUs 20 and 30 are in a sleep state.

[0036] In the example of Figure 5, the first communication time is longer than the second communication time. The master ECU 10 sets a processing standby time for waiting for the process of switching on and off the relay 12 (internal processing of the microcontroller 11). The processing standby time is set according to the first communication time. Note that, when the slave ECU 30 is in sleep mode, the master ECU 10 may set the processing standby time to the time obtained by adding the first communication time to the wake-up time of the slave ECU 30. The master ECU 10 also sets a communication standby time for waiting for transmission of an on / off instruction signal to the slave ECU 20. The communication standby time corresponds to the difference between the first communication time and the second communication time and is shorter than the processing standby time.

[0037] As shown by "slave ECU 30" in FIG. 5 , when the first communication time has elapsed since the on / off determination timing by the master ECU 10 and the processing time within the slave ECU 30 (the processing time by the microcontroller 31) has also elapsed, the relay 32 switches on and off (corresponding to "ON / OFF switching" in FIG. 5 ). As shown by "slave ECU 20" in FIG. 4 , when the communication standby time has elapsed since the on / off determination timing by the master ECU 10 and the second communication time has elapsed and the processing time within the slave ECU 20 (the processing time by the microcontroller 21) has also elapsed, the relay 22 switches on and off (corresponding to "ON / OFF switching" in FIG. 5 ). As shown by "master ECU 10" in FIG. 5 , when the processing standby time has elapsed since the on / off determination timing by the master ECU 10 and the processing time within the master ECU 10 (the processing time by the microcontroller 11) has also elapsed, the relay 12 switches on and off (corresponding to "ON / OFF switching" in FIG. 5 ).

[0038] The first communication time, the time obtained by adding the second communication time to the communication standby time, and the processing standby time are all the same length. The processing time in the master ECU 10 is the same length as the processing time in the slave ECUs 20 and 30. Therefore, the on / off switching timing of the relay 10 corresponds to the off switching timing of the relays 22 and 32, and the on / off switching of the relay 10 is synchronized with the on / off switching of the relays 22 and 32. Note that in the examples of Figures 3 to 5, the processing time in the master ECU 10 and the processing time in the slave ECUs 20 and 30 are the same length, but if the processing times differ, the master ECU 10 may adjust the waiting time by a time equivalent to the difference in the processing times.

[0039] In Modification 1 of this embodiment, the master ECU 10 starts the process of switching the master ECU 10 on and off after a processing standby time (corresponding to the "first standby time" of the present invention) has elapsed, and transmits an on / off instruction signal to the slave ECU 20 after a communication standby time (corresponding to the "second standby time" of the present invention) has elapsed. If the first communication time is longer than the second communication time, the processing standby time is made longer than the communication standby time. This allows the on / off of the relay 10 to be synchronized with the on / off of the relays 22 and 32. Note that the relay 32 corresponds to the "first subordinate relay" of the present invention, and the relay 22 corresponds to the "second subordinate relay" of the present invention.

[0040] In the second modification of this embodiment, the master ECU 10 may set the waiting time depending on the operating states of the slave ECUs 20 and 30. A control method for the relays 12, 22, and 32 executed by the master ECU 10 will be described with reference to Fig. 6. Note that some of the control flow is similar to the control flow of steps S1 to S7 of this embodiment, and the above description will be used as appropriate.

[0041] The control flow of step S11 is the same as step S1. If it is determined that the slave ECUs 20, 30 are not in sleep mode, the master ECU 10 determines in step S12 whether the slave ECUs 20, 30 are experiencing a processing delay. If the slave ECUs 20, 30 are not experiencing a processing delay, the control flow proceeds to step S13. If the slave ECUs 20, 30 are experiencing a processing delay, the control flow proceeds to step S14.

[0042] For example, if the temperature of the slave ECUs 20, 30 exceeds a predetermined threshold, the slave ECUs 20, 30 will lower their clocks to prevent temperature rise and protect their internal circuit elements. Lowering the clock slows down the processing speed of the microcontrollers 21, 31, which in turn slows down the internal processing time of the slave ECUs 20, 30 when they receive an on / off command signal. Therefore, the master ECU 10 adds the processing time delay associated with the clock reduction to the standby time. In other words, if the processing of the slave ECUs 20, 30 is delayed, in step S14, the master ECU 10 sets the standby time to the communication time of the communication lines 2, 3 plus the processing time of the slave ECUs 20, 30 (third standby time). The processing time of the slave ECUs 20, 30 is longer than the normal processing time.

[0043] The control flow from step S15 to step S19 is the same as that from step S3 to 7. As a result, in the second modification, it is possible to suppress the mis-synchronization of the on / off of the plurality of relays 12, 22, and 32.

[0044] REFERENCE SIGNS LIST 1 ECU control system 2, 3 communication line 10 master ECU 11 microcontroller 12 relay 13 load 20 slave ECU 21 microcontroller 22 relay 23 load 30 slave ECU 31 microcontroller 32 relay 33 load

Claims

1. An ECU control system for switching relays on and off, comprising: a host ECU that determines the on / off states of multiple relays; and a lower ECU connected to the host ECU via a communication line, wherein the multiple relays include upper relays that are switched on and off by the host ECU and lower relays that are switched on and off by the lower ECU, wherein the lower ECU switches the lower relays on and off when it receives an on / off instruction signal from the host ECU that switches the relays on and off, and the host ECU sets a waiting time to synchronize the on / off of the upper relay and the on / off of the lower relay, and after the waiting time has elapsed, starts the process of switching the upper relay on and off.

2. An ECU control system according to claim 1, wherein the host ECU sets the standby time in accordance with a communication time between the host ECU and the subordinate ECU.

3. An ECU control system according to claim 1 or 2, wherein the lower ECU, when receiving the on / off instruction signal, executes internal processing to switch the lower relay on / off, and the upper ECU sets the standby time according to the processing time of the internal processing.

4. An ECU control system according to any one of claims 1 to 3, wherein the upper ECU identifies the operating state of the lower ECU, and when the lower ECU is in a sleep state, the standby time is made longer than when the lower ECU is in a wake-up state.

5. An ECU control system according to any one of claims 1 to 3, wherein the host ECU identifies the operating state of the subordinate ECU and sets the standby time in accordance with the operating state.

6. An ECU control system according to any one of claims 1 to 5, wherein the lower ECU includes a first lower ECU and a second lower ECU, the lower relays include a first lower relay that is switched on and off by the first lower ECU and a second lower relay that is switched on and off by the second lower ECU, the upper ECU starts a process of switching on and off the upper relay after a first waiting time has elapsed, and transmits the on / off instruction signal to the second lower ECU after a second waiting time has elapsed, and when a first communication time between the upper ECU and the first lower ECU is longer than a second communication time between the upper ECU and the second lower ECU, the ECU control system makes the first waiting time longer than the second waiting time.

7. An ECU control method executed by an ECU control system that switches multiple relays on and off, wherein the multiple relays include upper relays that are switched on and off by an upper ECU, and lower relays that are switched on and off by a lower ECU connected to the upper ECU via a communication line, the upper ECU determines whether the multiple relays are on or off, sets a waiting time for synchronizing the on-state of the upper relays with the on-state and off-state of the lower relays, and starts processing to switch the on-state and off of the upper relays after the waiting time has elapsed, and the lower ECU switches the on-state and off of the lower relays when it receives an on-off instruction signal from the upper ECU to switch the on-state and off-state of the lower relays.

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