Communication system

A communication system includes a first device and a second device connected to the first device by a single communication line. The first device includes a first transmitting portion which transmits to the second device a pulse signal set to a predetermined cycle that differs according to data, and a first receiving portion which reads data transmitted from the second device based on a voltage value of a transmission signal transmitted over the communication line. The second device includes a second transmitting portion which transmits to the first device a voltage signal set to a predetermined voltage value that differs according to the data, and a second receiving portion which reads data transmitted from the first device based on a pulse signal cycle of the transmission signal transmitted over the communication line.

The disclosure of Japanese Patent Application No. 2005-335260 filed on Nov. 21, 2005 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a communication system which is provided with a first device and a second device that are connected by a single communication line, and which performs two-way simultaneous communication between the two devices.

2. Description of the Related Art

Japanese Patent Application Publication No. JP-A-8-265308, for example, describes a communication system that performs two-way simultaneous communication between two stations using a single communication line. The communication system described in that publication transmits data from a first station to a second station using a pulse signal set at a duty ratio that differs according to the data, and transmits data from the second station to the first station using a pulse signal having an amplitude value that differs according to the data. At the first station, the data transmitted from the second station is classified based on the amplitude value of the pulse signal transmitted over the communication line, while at the second station, the data transmitted from the first station is classified based on the duty ratio of the pulse signal transmitted over the communication line. As a result, even if data is transmitted from the two stations simultaneously over the single communication line, all of the data is able to be read without interference.

In the foregoing communication system, however, the pulse signal transmitted from the first station changes the duty ratio according to the data and its cycle is always fixed. Therefore, the data transmission speed from the first station to the second station ends up being fixed. If that communication method is employed for data communication in a system in a vehicle provided with vehicle state control units for controlling a plurality of vehicle states, in which those control units operate by transmitting and receiving data to and from each other, for example, the data transmission speed when an abnormality is detected ends up being the same as the data transmission speed during normal operation, which is undesirable. That is, when an abnormality is detected, an abnormality processing command is preferably transmitted to the appropriate control unit quicker than data is transmitted during normal operation. This, however, is not possible with the foregoing communication method.

SUMMARY OF THE INVENTION

This invention thus provides a communication system that includes a first device and a second device connected to the first device by a single communication line. The first device includes a first transmitting portion which transmits to the second device a pulse signal set to a predetermined cycle that differs according to data, and a first receiving portion which reads data transmitted from the second device based on a voltage value of a transmission signal transmitted over the communication line. The second device includes a second transmitting portion which transmits to the first device a voltage signal set to a predetermined voltage value that differs according to data, and a second receiving portion which reads data transmitted from the first device based on a pulse signal cycle of the transmission signal transmitted over the communication line.

According to this structure, the first transmitting portion of the first device transmits a pulse signal and the cycle of this pulse signal is set differently depending on the data. As a result, the transmission speed of the data transmitted to the second device also changes depending on the data. For example, a shorter cycle of the pulse signal results in the data being transmitted to the second device at a faster speed. Therefore, good communication control is able to be achieved by setting the cycle of the pulse signal according to the type of data such that a data transmission speed appropriate for that type of data is achieved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, the present invention will be described in more detail in terms of exemplary embodiments.

Hereinafter, a communication system according to one example embodiment of the invention will be described with reference to the accompanying drawings.FIG. 1is a block diagram of a power supply control system of a vehicle provided with a communication system according to this example embodiment.FIG. 2is a block diagram schematically showing that power supply control system. The communication system of this example embodiment performs communication between a hybrid control unit11(i.e., HV-ECU11) and a DC/DC converter20shown inFIG. 1. First the power supply control system of a vehicle to which this communication system may be applied will be described.

This power supply control system includes a high voltage battery (main battery)1which is used as a power source for driving a hybrid system10, a low voltage battery (auxiliary battery)2which is used by the general vehicle control system, a DC/DC converter20which reduces (i.e., steps down) the voltage of the high voltage battery1or increases (i.e., steps up) the voltage of the low voltage battery2, and a hybrid control unit (hereinafter simply referred to as “HV-ECU”)11which controls both operations of the hybrid system10and operations of the DC/DC converter20. ECU is an abbreviation of Electronic Control Unit.

First the hybrid system10will be described. The hybrid system10includes a transaxle12that includes a main motor which is an electric actuator for running the vehicle, a generator, a power split mechanism, reduction gears, and a differential gear (these are omitted in the drawing), an engine13which is an internal combustion engine for driving the vehicle, an engine control unit14(hereinafter referred to as “engine ECU14”) which controls the operation of the engine, an inverter15for converting direct current power of the high voltage battery1into three phases and controlling the main motor of the transaxle12on and off, and the HV-ECU11which controls operations within the hybrid system10.

The main portion of the HV-ECU11is a microcomputer. The HV-ECU11calculates motor torque and engine output based on the operating state of the engine according to various signals indicative of, for example, the accelerator opening amount, the shift lever position and the like from various sensors, and outputs required values to the engine ECU14as well as controls the output of the inverter15.

In this example embodiment, the high voltage battery1has a rated voltage of 288 volts (V). A high voltage main power supply line3which serves as the power supply path of the high voltage battery1is connected to the inverter15. A system main relay4(hereinafter referred to as “SMR4”) for allowing and interrupting the supply of power from the high voltage power supply is provided midway in the high voltage main power supply line3. Also, a high voltage power supply branch line5is branch-connected to the high voltage main power supply line3on the side of the SMR4that is closer to the load. Power from the high voltage battery1is supplied to the DC/DC converter20via this high voltage power supply branch line.

Meanwhile in this example embodiment, the low voltage battery2has a general rated voltage of 12 V. A low voltage main power supply line6which serves as the power supply path for the low voltage battery2branches off into an ignition (IG) linked low voltage power supply line8which supplies power and is operatively linked to the on/off operation of an ignition switch7, and a regular supply low voltage power supply line9which supplies power but is not operatively linked to the ignition switch7. These lines8and9both supply low voltage power to the HV-ECU11, the DC/DC converter20, and an electric power steering apparatus30. Although omitted inFIG. 2, there are many more electrical loads to which power is supplied from the low voltage battery2.

Further, a step-down circuit17which serves as the auxiliary assist power supply for stepping down the voltage to 12 V is connected to the high voltage main power supply line3of the high voltage battery1. The output of this step-down circuit17is connected to the low voltage main power supply line6.

The DC/DC converter20includes the step-down circuit21which steps down (i.e., reduces) the 288 V power supplied from the high voltage power supply branch line5to a predetermined voltage (42 V in this example embodiment), a step-up circuit22that steps up (i.e., increases) the 12 V power supplied from the regular supply low voltage power supply line9to a predetermined voltage (33 V in this example embodiment), and a DC/DC control unit23that controls the operations of the step-down circuit21and the step-up circuit22. This DC/DC control unit23is connected to the HV-ECU11by a single communication line16. The DC/DC control unit23and the HV-ECU11are able to communicate two ways simultaneously via this communication line16.

The step-down circuit21for example generates direct current power of a predetermined voltage after once converting input voltage to alternating current voltage by a transistor bridge circuit, stepping it down to a low voltage with a transformer, and then rectifying and smoothing it out. Also, the step-up circuit22for example generates power within a step-up coil provided in series in the power line by running current intermittently to the step-up coil, and then steps up the voltage by outputting that power.

The output terminals of the step-down circuit21and the step-up circuit22are connected to a common DC/DC converter output line24(hereinafter simply referred to as “converter output line24”). The DC/DC control unit23monitors the voltage in this converter output line24and feedback-controls the operation of the step-down circuit21or the step-up circuit22to make the output voltage match a target voltage. The DC/DC control unit also monitors the output current and checks for current surges.

The converter output line24is connected as a motor driving power source to the electric power steering apparatus30as well as to other running control apparatuses60(only one of which is shown in the drawing). These other running control apparatuses60may be, for example, control systems that consume a lot of power and are provided with an electric actuator61and an ECU62for driving the electric actuator61. Some examples include a brake control system, a stabilizer system, and a suspension system.

The electric power steering apparatus30includes a steering assist mechanism31that applies a steering assist force to steered wheels WH, and a steering assist control unit (hereinafter simply referred to as “EPS-ECU”)40for driving an electric motor32provided in the steering assist mechanism31.

The steering assist mechanism31converts rotation around the axis of a steering shaft35which is operatively linked to a rotating operation of a steering wheel34into motion in the axial direction of a rack bar37by a rack and pinion mechanism36, and steers the left and right steered wheels WH according to movement in the axial direction of the rack bar37. The electric motor32is assembled onto the rack bar37. The electric motor32applies an assist force to the rotating operation of the steering wheel34by driving the rack bar37in the axial direction via a ball screw mechanism38according to that rotation. Also, a rotation angle sensor33which outputs a signal indicative of the motor rotation angle is provided on the electric motor32. Further, a steering torque sensor39is assembled onto the steering shaft35.

The EPS-ECU40includes an electronic control unit41which calculates the amount of electricity to needed by the electric motor32to apply a predetermined steering assist force, and a motor drive circuit42which drives the electric motor32in response to a control signal from the electronic control unit41.

The motor drive circuit42is formed of a three-phase inverter which uses six switching elements S1, S2, S3, S4, S5, and S6(a MOSET is used in this example embodiment). Power for driving the motor is supplied by the converter output line24of the DC/DC converter20. The motor drive circuit42also includes a current sensor43that measures the amount of current flowing through each phase of the electric motor32.

The main portion of the electronic control unit41is a microcomputer. This electronic control unit41inputs detection signals from the steering torque sensor39and a vehicle speed sensor45that detects the running speed of the vehicle, and calculates the amount of electricity needed by the electric motor32based on these detection signals. The electronic control unit41also generates the desired steering assist force by controlling the operation of the electric motor32based on a signal from the rotation angle sensor33and the detected value from the current sensor43.

This electronic control unit41is connected to the DC/DC control unit23of the DC/DC converter20via a communication line18so as to be able to receive a gradual change command, to be described later, transmitted from the DC/DC control unit23.

Next, the power supply control by the HV-ECU11and the DC/DC converter20will be described.FIG. 3is a timing chart relating to the power supply control in this example embodiment. Also,FIGS. 4A and 4Bare flowcharts of a command control routine executed by the HV-ECU11andFIG. 5is a flowchart of a voltage conversion control routine executed by the DC/DC control unit23. Both of these routines are stored as control programs in a memory unit, not shown. The command control routine and the voltage conversion control routine are performed in parallel. First, the command control routine executed by the HV-ECU11will be described with reference toFIGS. 3,4A and4B.

This control routine starts when the ignition switch7is turned on. First, the HV-ECU11outputs a prohibit command to the DC/DC control unit23for a predetermined period of time (S10). During this time, an initial check of the hybrid system is performed (S11). Once the initial check is complete, the SMR4is turned on so that power from the high voltage battery1is supplied to the hybrid system10(S12; time t1inFIG. 3). The predetermined period of time for which the prohibit command is output may be an elapsed time measured by a timer or may end when the initial check is complete.

Continuing on, an allow command which allows power from the high voltage battery1to be used is output to the DC/DC control unit23(S13; time t2inFIG. 3), and a flag F is set to F=1 (S14). This flag F is set to F=0 when the SMR4is off and the usage of power from the high voltage battery1is prohibited, and is set to F=1 when the SMR4is on and the usage of power from the high voltage battery1is allowed. When this control routine starts, the flag F is set at F=0. The command signal output by the HV-ECU11to the DC/DC control unit23will hereinafter be referred to as an “HV command”.

In this way, power from the high voltage battery1is supplied to the DC/DC converter20, and the DC/DC control unit23operates the step-down circuit21and outputs 42 V power in response to an allow command from the HV-ECU11(time t2inFIG. 3). Although the control on the DC/DC converter20side will be described later with reference toFIG. 5, the points in that control which are related toFIG. 3will be described here.

Once 42 V power is output from the secondary side of the DC/DC converter20, the HV-ECU11repeatedly checks the state of the ignition switch7, checks for abnormalities, and checks the state of the flag F (S15, S16, and S17). The abnormality check in step S16is performed by checking for abnormalities in the hybrid system10and abnormalities (such as a ground-fault abnormality or a voltage abnormality) in the high voltage battery1. Also, the determination in step S17is “NO” because the flag F was set to F=1 in step S14.

Accordingly, this state continues as long as the ignition switch7is turned on and no abnormalities are detected. That is, the SMR4remains on and the allow command continues to be output to the DC/DC control unit23. Therefore, during this time, power from the high voltage battery1that has been stepped down to 42 V is supplied from the converter output line24to the electric power steering apparatus30and the other running control apparatuses60.

When the ignition switch7is turned off (time t7inFIG. 3), the determination in step S15changes to “YES” and the process proceeds on to step S18where the state of the flag F is checked. In this case, because the flag F is set to F=1, the process proceeds on to step S19where a gradual change command is output to the DC/DC control unit23(time t8inFIG. 3). This gradual change command is a command which gives advance notice that the supply of power will stop so that when the supply of power from the converter output line24is stopped, the load of the electric power steering apparatus30and the like will not be cut off suddenly.

Continuing on, the HV-ECU11then checks whether a predetermined period of time has passed after the gradual change command was output (S20), and if so (i.e., YES in step S20), then outputs a prohibit command to the DC/DC control unit23(S21; time t10inFIG. 3). In this case, after the predetermined time has passed after receiving the gradual change command, the DC/DC control unit23stops the step-down operation of the step-down circuit21(time t9inFIG. 3). The HV-ECU11then checks whether a predetermined period of time has passed after the prohibit command was output (S22), and if so (i.e., YES in step S22), then outputs an interrupt signal to the SMR4to interrupt the supply of high voltage power to the hybrid system10. The control routine then ends (S23).

If, on the other hand, the ignition switch7is turned on (i.e., NO in step S15) and an abnormality is detected when the step-down circuit21is performing a step-down operation (i.e., YES in step S16), the process proceeds on to step S24where the state of the flag F is checked. In this case, because the flag F is set to F=1, the process proceeds on to step S25where a prohibit command is output to the DC/DC control unit23(time t4inFIG. 3). A usage state signal from the DC/DC control unit23is read (S26) and once a high-voltage-not-used signal is received (time t5inFIG. 3), the SMR4is turned off (S27; time t6inFIG. 3). The flag F is then set to F=0 (S28) after which this state continues.

In this way, when an abnormality is detected, the SMR4is turned off so that the supply of power from the high voltage battery1is interrupted. For example, if the voltage of the power from the high voltage battery1falls equal to or below a predetermined voltage, this is detected as a battery abnormality. Turning off the SMR4thus prevents an abnormality from occurring in the hybrid system10as well as prevents an unstable supply of power to the control apparatuses that receive power via the converter output line24, such as the electric power steering apparatus30, thereby improving safety.

Further, when, after an abnormality was detected and the SMR4was turned off to interrupt the supply of power from the high voltage battery1, the abnormality check determination then changes to “no abnormality” (i.e., NO in step S16), the process then proceeds on to step S17. In this case, because the flag F is set to F=0, the determination in step S17is “YES”. Accordingly, the process proceeds on to step S29where the SMR4is turned on thus allowing power from the high voltage battery1to be used, an allow command is output to the DC/DC control unit23(S30), and the flag F is set to F=1 (S31). For example, when the voltage of the power from the high voltage battery1returns to the reference voltage after falling, the determination in step S16switches from “abnormality” to “no abnormality”. Once the voltage returns to normal, the SMR4is turned on and an allow command is output to the DC/DC control unit23.

This process is repeated until the ignition switch7is turned off, at which time the gradual change command and prohibit command are output such that the SMR4is turned off, as described above, after which the control routine ends. Incidentally, if the ignition switch7is turned off while a prohibit command is being output, the determination in step S18changes to “YES” and the control routine directly ends.

Next, a voltage conversion control routine performed on the DC/DC control unit23side will be described with reference to the flowchart inFIG. 5and the timing chart inFIG. 3. This control routine is performed in parallel with the command control routine executed by the HV-ECU11described above and starts when the ignition switch7is turned on.

First, a command from the HV-ECU11is read (S50) and the type of that command is determined (S51). When this control routine starts, the HV-ECU11outputs a prohibit command. The process in this case therefore proceeds on to step S52where the setting of a flag F is checked. This flag F is different from the flag F used in the command control routine described above. That is, this flag F indicates the operating state of the DC/DC converter20. When neither the step-down circuit21nor the step-up circuit22are operating, the flag F is set to F=0. When the step-down circuit21is operating, the flag F is set to F=1, and when the step-up circuit22is operating, the flag F is set to F=2. When this control routine starts the flag F is set to F=0. Therefore, when the vehicle is started, the determination in step S52is “F=0” so the process proceeds on to step S53where a high-voltage-not-used signal is output to the HV-ECU11.

The DC/DC control unit23regularly outputs a usage state signal to the HV-ECU11which indicates whether power from the high voltage battery is being used. The high-voltage-not-used signal is output when the step-down circuit21is not operating. The process then returns to step S50where the command signal from the HV-ECU11is read. This command signal (i.e., HV command) is read repeatedly and when an allow signal is received from the HV-ECU11(S51; time t2inFIG. 3), the setting of the flag F is checked (S54). In this case, the flag F was set at F=0 the last time so the determination in step S54is “F=0”. Accordingly, the process proceeds on to step S55where the step-down circuit21starts to be operated. The flag F is then set to F=1 (S56) and a high-voltage-used signal is output to the HV-ECU11(S57; time t3inFIG. 3).

Once the DC/DC control unit23starts to operate the step-down circuit21, it monitors the output voltage and adjusts it to match a target voltage (42 V in this example embodiment). Moreover, the DC/DC control unit23also monitors the output current. If a current surge is detected, the DC/DC control unit23outputs current surge information to the electronic control unit41of the EPS-ECU40via the communication line18. As a result, the electronic control unit41adjusts the motor drive circuit42and reduces the upper limit value of electricity supplied to the electric motor32to prevent the step-down circuit21from overheating.

In this way, once the step-down circuit21starts to operate and power is supplied from the high voltage battery1to the electric power steering apparatus30and the other running control apparatuses60, this state is continued until the command from the HV-ECU11changes (S54; F=1). The DC/DC control unit23starts to operate the step-down circuit21while transmitting to the electronic control unit41of the EPS-ECU40via the communication line18information indicating that power has started to be supplied from the high voltage battery1. The EPS-ECU40starts assist control at 100% capacity based on this transmission. Accordingly, the electric power steering apparatus30receives the supply of high voltage power and is thus able to obtain sufficient steering assist torque.

If the ignition switch7is turned off (time t7inFIG. 3) in this state, the HV-ECU11transmits a gradual change command to the DC/DC control unit23, as described above (time t8inFIG. 3). Upon receiving this gradual change command from the HV-ECU11(S51; gradual change), the DC/DC control unit23outputs a gradual change command to the electronic control unit41of the EPS-ECU40(S58). This gradual change command gives advance notice that power will stop being supplied from the high voltage battery1.

The EPS-ECU40that receives this gradual change command then gradually reduces the upper limit current value supplied to the electric motor32so that steering assist torque is gradually reduced. That is, the EPS-ECU40gradually reduces the steering assist torque able to be output so that the steering operation feel does not suddenly change due to the steering assist torque suddenly being cancelled by a sudden stop in the supply of power.

After the command is output in step S58, operation of the step-down circuit21stops (S60, time t9inFIG. 3) after a predetermined period of time has passed. The timing at which the step-down operation is stopped is after a set period of time, which is measured by a timer, has passed (S59) and takes into account the time required by the EPS-ECU40for the gradual change operation. Also, at the same time as the step-down circuit21stops operating, a high-voltage-not-used signal is output to the HV-ECU11(S61). The control routine then ends. The HV-ECU11interrupts the supply of power from the high voltage battery1by turning off the SMR4based on a high-voltage-not-used signal output from the DC/DC control unit23.

When the HV-ECU11transmits a prohibit command (time t4inFIG. 3) while the step-down circuit21is operating, the determination in step S51changes from “allowed” to “prohibited”, after which the state of the flag F is checked in step S52. Immediately after the command from the HV-ECU11changes from “allowed” to “prohibited”, the determination in step S52is “F=1” because the flag F is set at F=1. Operation of the step-down circuit21is then stopped in step S62while operation of the step-up circuit22is started in step S63(time t5inFIG. 3). Then the flag F is set to F=2 and a high-voltage-not-used signal is output to the HV-ECU11(S53).

Accordingly, the supply of power between the high voltage battery1and the electric power steering apparatus30or the other running control apparatuses60is interrupted by stopping operation of the step-down circuit21, while stepped-up power from the low voltage battery2starts to be supplied to the electric power steering apparatus30or the other running control apparatuses60by starting operation of the step-up circuit22. In this case, the DC/DC control unit23starts to operate this step-up circuit22and transmits information that indicates that power has started to be supplied from the low voltage battery2to the electronic control unit41of the EPS-ECU40via the communication wire18. The EPS-ECU40then performs assist control in a save mode, operating at or below a predetermined power based on this transmission.

This step-up operation of the low voltage battery2continues unless the command from the HV-ECU11changes. When this step-up operation of the low voltage battery2is being performed and the command from the HV-ECU11changes from “prohibited” to “allowed”, the determination in step S51changes to “allowed” and the state of the flag F is checked in step S54. In this case, the flag F is set to F=2 so the process proceeds on to step S65where the step-up operation of the step-up circuit22is stopped. Then the process proceeds on to step S55where the step-down circuit21starts to be operated again. The flag F is then set to F=1 (S56) and a high-voltage-used signal is output to the HV-ECU11(S57).

In this way, the control routine changes the operation of the DC/DC converter20according to the command from the HV-ECU11. Therefore, the operation of the DC/DC converter20is not controlled by the EPS-ECU4as is in the related art so output from the DC/DC converter20can be stably used in the other running control apparatuses60as well. That is, the DC/DC converter20is controlled by the HV-ECU11so the output from the DC/DC converter20is not only able to be used by the electric power steering apparatus30, but also by the various running control apparatuses60. As a result, its range of use broadens which increases its general applicability as a power supply apparatus.

Also, because a voltage conversion command is not transmitted using a CAN communication system, as it is in the related art, the amount of data transmitted in the CAN is able to be reduced, thus reducing the load on the CAN communication system a corresponding amount. Furthermore, the wiring cost for the communication lines can also be reduced compared with the conventional system. Also, if an abnormality such as a voltage shortage in the battery occurs, the use of power from the high voltage battery1is prohibited to prevent an unstable supply of power to the electric power steering apparatus30and the other running control apparatuses60. Moreover, even if the use of power from the high voltage battery1is prohibited, power from the low voltage battery2is supplied after being stepped up, thereby enabling good operation of the electric power steering apparatus30and the actuators61of the other running control apparatuses60, which improves safety, reliability, and vehicle performance.

Next, the system by which two-way simultaneous communication is performed between the HV-ECU11and the DC/DC control unit23, i.e., the communication system of this example embodiment, will be described.FIG. 6shows the configuration of communication portions in the HV-ECU11and the DC/DC control unit23. The left side in the drawing represents a communication portion23A of the DC/DC control unit23and the right side in the drawing represents a communication portion11A of the HV-ECU11.

The communication portion23A of the DC/DC control unit23includes resistance elements R1, R2, R3, and R4, a transistor Q1, a transmission control portion23A1, and a receiving portion23A2. The communication line16is connected between the resistance element R1and the resistance element R2provided in series between a ground and a predetermined voltage power source V in the circuit. The transmission control portion23A1outputs a control signal to a base of the transistor Q1which serves as a switch element provided in series with these resistance elements R1and R2, by which it switches the transistor Q1on and off. Accordingly, by switching the transistor Q1on and off, the transmission control portion23A1changes the voltage output to the communication line16, thereby transmits a signal indicating the operating state (i.e., operating state data) of the DC/DC converter20to the HV-ECU11. That is, when the step-down circuit21of the DC/DC converter20is operating, a “high-voltage-used” signal is output, and when the step-down circuit21is not operating, a “high-voltage-not-used” signal is output.

In this case, as shown in the middle ofFIG. 7, for a “high-voltage-used” signal, the transmission control portion23A1turns the transistor Q1on and sets the operating state signal to a predetermined first voltage V1. For a “high-voltage-not-used” signal, the transmission control portion23A1turns the transistor Q1off and sets the operating state signal to a predetermined second voltage V2(V2>V1). That is, this communication portion23A employs a voltage amplitude modulation method which changes the transmission signal (i.e., transmission data) by changing the magnitude of the output voltage. The waveform of the operating state signal inFIG. 7is the waveform of the output terminal voltage when the communication line16is open.

Further, the receiving portion23A2which reads the signal transmitted from the communication portion11A of the HV-ECU11is provided in the communication portion23A in a position where the communication line16and the resistance element R4provided in series are connected.

Meanwhile, the communication portion11A of the HV-ECU11includes resistance elements R1, R12, and R13, a zener diode ZD, a transistor Q2, a condenser C, a transmission control portion11A1, and a receiving portion11A2. The resistance element R13, the zener diode ZD, and the transistor Q2are provided in series between the communication line16and the ground, while the resistance elements R11and R12, which are provided in series, and the condenser C which serves as a noise filter are provided in parallel with those.

The transmission control portion11A1switches the transistor Q2on and off by outputting a pulse signal to a base of the transistor Q2that serves as a switch element. In this case, the transmission control portion11A1outputs a pulse signal of a predetermined duty ratio (50% in this example embodiment) to the base of the transistor Q2, and switches the HV command signal transmitted over the communication line16by switching the cycle of this pulse signal. That is, the HV-ECU11transmits an HV command signal (i.e., HV command data) indicating “allowed”, “prohibited”, or “gradual change” to the DC/DC control unit23, and employs a pulse cycle modulation method that switches between these three types of command signals by changing the cycle of the pulse signal input to the transistor Q2.

In this example, the HV command signal is such that the “prohibited” command signal is set at the shortest cycle T1, and the “allowed” command signal is set at the longest cycle T3, as shown in the top portion ofFIG. 7. Also, the “gradual change” command signal is set at a cycle T2that is in between the shortest cycle T1and the longest cycle T3(i.e., T1<T2<T3).

Also, the receiving portion11A2is provided at a connecting portion between the resistance elements R11and R12. This receiving portion11A2reads the signal transmitted from the communication portion23A of the DC/DC control unit23by reading the voltage value at that connecting portion. The zener diode ZD keeps the HV command signal at or above a predetermined voltage with respect to the ground and is able to detect an on failure (i.e., a ground-fault failure) in the circuit if one occurs.

The communication portions11A and23A structured in this way are connected together by the single communication line16. Accordingly, the output waveform of the transmission signal transmitted over this communication line16is one in which the HV command signal and the operating state signal have been synthesized, as shown in the lower portion ofFIG. 7.

At the receiving portion11A2in the communication portion11A of the HV-ECU11, the type of signal (i.e., “high-voltage-used” or “high-voltage-not-used”) transmitted from the DC/DC control unit23is determined by converting the voltage between the resistance elements R11and R12into a digital signal using an A/D converter, not shown, and reading the voltage of the transmission signal, i.e., the voltage amplitude (i.e., swing) of the pulse signal.

Meanwhile, at the receiving portion23A2in the communication portion23A of the DC/DC control unit23, the cycle of the pulse signal is obtained by detecting an edge of that signal (i.e., the rise or fall of the pulse signal) from the change in the voltage at the point where the resistance element R3and the resistance element R4are connected. In this way, the type of HV command signal (i.e., “prohibited”, “allowed”, or “gradual change”) output from the HV-ECU11is determined.

According to the communication system between the HV-ECU11and the DC/DC control unit23described above, the HV command signal output from the HV-ECU11is classified according to the pulse cycle. Furthermore, the transmission speed of the signal for the prohibit command, which is an important signal, is increased by shortening its cycle. Therefore, a prohibit command can be recognized earlier in the DC/DC control unit23so that the supply of power from the high voltage battery1is able to be stopped earlier in the event that an abnormality is detected, which improves both safety and vehicle reliability. Moreover, when two-way communication is performed using only the voltage modulation method, the setting range of the threshold value ends up becoming quite narrow when tolerance is included. In this example embodiment, however, this problem is eliminated by combining the voltage modulation method with the pulse cycle modulation method.

The HV-ECU11having the communication portion11A of this example embodiment corresponds to a first device of the invention. The DC/DC control unit23having the communication portion23A in this example embodiment corresponds to a second device of the invention. The transmission control portion11A1in this example embodiment corresponds to a first transmitting portion of the invention. The receiving portion11A2in this example embodiment corresponds to a first receiving portion of the invention. The transmission control portion23A1in this example embodiment corresponds to a second transmitting portion of the invention. The receiving portion23A2in this example embodiment corresponds to a second receiving portion of the invention. The DC/DC converter20in this example embodiment corresponds to an operating apparatus (i.e., voltage converting apparatus) provided with the second device of the invention. Also, the functioning portion (i.e., the process in step S16inFIG. 4A) of the HV-ECU11that detects a voltage abnormality in the high voltage battery1in this example embodiment corresponds to an abnormality detecting portion of the invention. Further, the operating state signal and the HV command signal in this example embodiment correspond to data of this invention. In particular, the HV command signal corresponds to command data of this invention.

While a power supply control system having the communication system has been described with reference to an example embodiment, the invention is not limited to the example embodiment. To the contrary, various modifications are also possible within the scope of the invention.

For example, in the foregoing example embodiment, the invention is applied to a communication system between devices provided in a vehicle. The invention may also be applied to something other than a vehicle. Also, when the invention is applied to a vehicle, it is not limited to communication between the HV-ECU11and the DC/DC control unit23, but may be applied to communication between various vehicle state control units. Moreover, in the foregoing example embodiment, the cycle of a pulse signal is set to be the shortest for data transmitted when an abnormality is detected, but the invention is not necessarily limited to this as long as the cycle of the pulse signal for information that needs to be transmitted the fastest in the system to which the communication system is applied is shortened. Also, the settings of the numerical values (of the battery voltage, the step-down voltage, and the step-up voltage) and the like in the foregoing example embodiment are only examples and may be set as appropriate.