Patent ID: 12237801

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention, and limitation is not made to an invention that requires a combination of all features described in the embodiments. Two or more of the multiple features described in the embodiments may be combined as appropriate. Furthermore, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted.

In an engine generator100shown inFIG.1, a starter101is connected to a crank shaft of an engine102. When the starter101rotates the crank shaft, the engine102starts. The engine102burns fuel (for example, gasoline, natural gas, or hydrogen) in a cylinder. The crank shaft (output shaft) rotates in synchronism with a piston that reciprocally moves in the cylinder. The rotor of a generator103is connected to the crank shaft. When the rotor rotates, the generator103generates power. The stator of the generator103includes a U winding, a V winding, and a W winding. The U winding, the V winding, and the W winding are connected to a rectification circuit111in an inverter110. The rectification circuit111and a smoothing circuit112serve as a conversion circuit that converts an AC generated by the generator103into a DC. More specifically, the rectification circuit111rectifies an AC generated in the U winding, the V winding, and the W winding, thereby generating a pulsating current. The rectification circuit111may be formed by a bridge circuit including a plurality of rectification elements (for example, diodes, thyristors, or transistors). The smoothing circuit112smooths the pulsating current to generate a DC. The smoothing circuit112can be formed by, for example, an electrolytic capacitor or the like. The smoothed DC voltage may be called a DC link voltage or a DC bus voltage. The DC voltage (DC bus voltage) output from the smoothing circuit112is input to an AC generating circuit113. An AC voltage generated by the AC generating circuit113is supplied from an outlet115to a load109.

An inverter control circuit117controls the AC generating circuit113in accordance with a load current I2detected by a current detection circuit114. The inverter control circuit117may be formed by hardware components such as a CPU (Central Processing Unit), an ASIC (Application-Specific Integrated Circuit), and a memory. The function of the inverter control circuit117to be described below may be implemented when the CPU executes a control program stored in the memory. If the load current I2becomes zero, the inverter control circuit117stops the AC generating circuit113. The AC generating circuit113is formed by, for example, a half-bridge circuit or a full-bridge circuit including a plurality of FETs (Field Effect Transistors). In this case, the inverter control circuit117maintains the AC voltage at a target voltage by controlling the ON period of a control signal (driving signal) supplied to the gate of each FET. The inverter control circuit117may transmit the value of the load current I2to a controller120. A power circuit116converts a voltage supplied from the generator103or a DC DC converter123to generate an operating voltage of the inverter control circuit117. More specifically, during a period in which the engine102rotates, the power circuit116converts an AC generated by the generator103to generate a DC. During a period in which the engine102stops, the power circuit116converts an AC generated in a secondary winding of a transformer125of the DC DC converter123to generate a DC.

The controller120rotates or stops the starter101by switching ON/OFF of a relay105. A battery104is a battery that supplies a DC voltage to the starter101via the relay105. The battery104may be charged by power generated by the generator103. This charging circuit is well known and is thus not illustrated inFIG.1.

The DC DC converter123is a conversion circuit that lowers or raises a battery voltage Vbat supplied from the battery104to generate an operating voltage of each of the power circuit116and a CPU121. The DC DC converter123is a conversion circuit that raises the battery voltage Vbat to generate a pseudo DC bus voltage. In the DC DC converter123, a driving circuit124is a circuit that is connected to the primary winding of the transformer125, and switches a voltage to be applied to the primary winding. The transformer125includes the primary winding and two secondary windings. The power circuit116is connected to one of the secondary windings of the transformer125, and an AC generated in this secondary winding is supplied to the power circuit116. The power supply voltage of the CPU121may be generated by converting the battery voltage Vbat by the DC DC converter123or a DC DC converter (not shown). A rectification smoothing circuit127is connected to the other secondary winding of the transformer125, generates a DC voltage (pseudo DC bus voltage) by rectifying and smoothing an AC generated in this secondary winding, and applies this DC voltage to the input of the AC generating circuit113via a switch130. The level of the DC voltage is a level sufficient for the AC generating circuit113to generate an AC. The CPU121turns on the switch130in a state in which the engine102stops, and turns off the switch130in a state in which the engine102rotates. That is, during the stop period of the engine102, the AC generating circuit113is supplied with a DC voltage from the DC DC converter123. During the operating period of the engine102, the AC generating circuit113is supplied with a DC voltage from the generator103, the rectification circuit111, and the smoothing circuit112. The switch130may be a semiconductor switch (transistor), a relay, or a diode.

The CPU121is a central processing unit (processor circuit) that controls the relay105and the switch130by executing a control program. The CPU121may be formed by a single processor circuit, a plurality of processor circuits, an ASIC (Application-Specific Integrated Circuit), or an FPGA (Field Programmable Gate Array). The engine generator100has a generating mode (operating mode) in which the engine102rotates and the generator103generates power, and a stop mode in which the engine102stops and the generator103generates no power. If a stop condition is met, the CPU121stops the engine102. For example, the engine102stops by cutting power supplied to a fuel pump (not shown). The stop condition may be that, for example, the load current I2is smaller than a predetermined threshold. Alternatively, the stop condition may be that, for example, the load current I2is smaller than the predetermined threshold and the battery voltage Vbat is equal to or higher than a predetermined threshold. If the battery voltage Vbat is lower than the predetermined threshold (if charging is insufficient), the CPU121may not be able to detect the load109during the stop period (stop mode) in which the engine102stops or to start the engine102by the starter101. Therefore, after the battery104is sufficiently charged by the generator103, the CPU121may stop the engine102.

Load Detection Method I

Referring toFIG.1, if a restart condition of the engine102is met, the CPU121operates the starter101by switching the switch130from ON to OFF and also switching the relay105from OFF to ON, thereby restarting the engine102. Note that the timing of switching the switch130from ON to OFF may be after a DC bus voltage Vdc output from the smoothing circuit112reaches a target voltage and is thus stable. The restart condition may be that the battery voltage Vbat is lower than the predetermined threshold. As shown inFIG.1, while the engine102stops, the rectification smoothing circuit127generates a DC voltage and supplies it to the AC generating circuit113, and the AC generating circuit113generates an AC and supplies it to the load109. Therefore, if the load109is connected to the outlet115while the engine102stops, a load current flows into the load109, thereby lowering the battery voltage Vbat. To cope with this, by monitoring the battery voltage Vbat while the engine102stops, the CPU121can detect or recognize that the load109is connected to the outlet115.

Load Detection Method II

FIG.2shows a state in which the load109is detected based on a change in the pseudo DC bus voltage Vdc supplied from the DC DC converter123to the AC generating circuit113. InFIG.2, the same reference numerals as inFIG.1denote common components and the above description thereof will be referred to. If the load109is connected to the outlet115while the engine102stops, a load current flows into the load109, thereby lowering the DC bus voltage Vdc. By monitoring the DC bus voltage Vdc while the engine102stops, the CPU121can detect or recognize that the load109is connected to the outlet115. As shown inFIG.2, a voltage detection circuit128is connected between the output terminal of the rectification smoothing circuit127and the input terminal of the AC generating circuit113. Therefore, the voltage detection circuit128detects the pseudo DC bus voltage Vdc supplied from the rectification smoothing circuit127to the AC generating circuit113, and reports the DC bus voltage Vdc to the CPU121. In fact, a detected voltage proportional to the DC bus voltage Vdc is applied to the port of the CPU121via a photocoupler or the like. If the DC bus voltage Vdc is lower than the predetermined threshold, the CPU121determines that the restart condition is met, and switches the relay105from OFF to ON. If the DC bus voltage Vdc is equal to higher than predetermined threshold, the CPU121determines that the restart condition is not met, and maintains the relay105in the OFF state.

Load Detection Method III

FIG.3shows a state in which the load109is detected by inputting the pseudo DC bus voltage Vdc to the AC generating circuit113while the engine102stops and monitoring a current flowing to the input side of the AC generating circuit113. InFIG.3, the same reference numerals as inFIG.1or2denote common components and the above description thereof will be referred to. If the load109is connected to the outlet115while the engine102stops, the load current I2flows into the load109. If the load current I2flows into the load109, a current (input-side current I1) flowing from the DC DC converter123to the input of the AC generating circuit113also increases. Thus, the CPU121detects the input-side current I1by a current detection circuit129, and detects or recognize, based on a change in the input-side current I1, that the load109is connected to the outlet115while the engine102stops. For example, the restart requirement may be that the input-side current I1is equal to or larger than a predetermined threshold.

Load Detection Method IV

FIG.4shows a state in which the load109is detected by inputting the pseudo DC bus voltage Vdc to the AC generating circuit113while the engine102stops and monitoring the load current I2flowing from the AC generating circuit113to the load109. InFIG.4, the same reference numerals as in each ofFIGS.1to3denote common components and the above description thereof will be referred to. If the load109is connected to the outlet115while the engine102stops, the load current I2flows into the load109. The current detection circuit114is connected between the AC generating circuit113and the load109, and can detect the load current I2. The inverter control circuit117and the CPU121are connected via an insulated communication circuit (for example, a photocoupler or the like). The inverter control circuit117notifies the CPU121of the value of the load current I2via the insulated communication circuit. The CPU121detects or recognizes, based on a change in the load current I2, that the load109is connected to the outlet115while the engine102stops. For example, the restart requirement may be that the load current I2is equal to or larger than a predetermined threshold.

Flowchart

FIG.5is a flowchart illustrating the operating mode.

In step S501, the CPU121starts the engine102. For example, the CPU121turns on the relay105to connect the battery104to the starter101, and rotates the starter101. This causes the engine102to start rotating.

In step S502, the CPU121detects the load current I2and the battery voltage Vbat. The load current I2is detected by the current detection circuit114, and input to the CPU121via the inverter control circuit117.

In step S503, based on the load current I2and the battery voltage Vbat, the CPU121determines whether the stop condition is met. For example, if the load current I2is smaller than a threshold Ith1and the battery voltage Vbat is equal to or higher than Vth1, the CPU121determines that the stop condition is met. If the load109is disconnected from the outlet115or the load109stops, the load current I2is smaller than the threshold Ith1. If the load current I2is equal to or larger than the threshold Ith1, the CPU121determines that the stop condition is not met. If the battery voltage Vbat is lower than Vth1, the CPU121also determines that the stop condition is not met. If the stop condition is not met, the CPU121returns to step S502. If the stop condition is met, the CPU121advances to step S504.

In step S504, the CPU121transits from the operating mode (generating mode) to the stop mode.

FIG.6is a flowchart illustrating the stop mode.

In step S601, the CPU121stops the engine102. For example, the CPU121switches the relay105from ON to OFF. Furthermore, the CPU121stops the engine102by stopping fuel supply to the engine102.

In step S602, the CPU121supplies a DC voltage to the inverter110, thereby starting detection of the load109. For example, the CPU121turns on the switch130to apply the pseudo DC bus voltage generated by the DC DC converter123to the input bus of the AC generating circuit113. This causes the AC generating circuit113to start generation of an AC based on the pseudo DC bus voltage. Furthermore, to detect that the load109is connected to the outlet115, the CPU121periodically monitors the battery voltage Vbat, a DC bus voltage Vbus, the input-side current I1, or the load current I2. A state in which the load109is electrically connected to the outlet115is equivalent to a state in which the load109physically connected to the outlet115is switched from the stop state to the operating state. That is, even in a case where the load109is physically connected to the outlet115, the load109may not electrically be connected to the engine generator100. For example, there is a case where the power plug of the load109is connected to the outlet115but the power switch of the load109is OFF. Therefore, a state in which the load109is connected to the engine generator100(outlet115) generally indicates a state in which the load109is electrically connected to the outlet115.

In step S603, the CPU121determines whether the restart condition is met. For example, if the battery voltage Vbat is lower than a predetermined threshold Vth2, the CPU121may determine that the restart condition is met. Alternatively, if the DC bus voltage Vbus is lower than a predetermined threshold Vth3, the CPU121may determine that the restart condition is met.

Alternatively, if the input-side current I1is equal to or larger than a predetermined threshold Ith2, the CPU121may determine that the restart condition is met. Alternatively, if the load current I2is equal to or larger than a predetermined threshold Ith3, the CPU121may determine that the restart condition is met. Alternatively, the restart condition may be that two of the four conditions are met, three of the four conditions are met, or all the four conditions are met. If the restart condition is not met, the CPU121returns to step S602. If the restart condition is met, the CPU121advances to step S604.

In step S604, the CPU121transits to the operating mode. That is, the CPU121advances to step S501, and restarts the engine102.

According to the present invention, it is possible to accurately restart an engine by making it possible to detect even a load with a high impedance.

Summary

[Aspect 1]

As shown inFIG.1and the like, the battery104is an example of a power supply (for example, a DC power supply or secondary battery) for supplying power to the starter101that starts the engine. The generator103is an example of a generator that is driven by the engine102to generate power. The inverter110is an example of an inverter including a first conversion circuit (for example, the rectification circuit111and the smoothing circuit112) that converts an AC generated by the generator103into a DC, and a second conversion circuit (for example, the AC generating circuit113) that converts a DC into an AC and supplies it to the load. The outlet115is an example of an outlet that outputs an AC from the inverter110to the load109. The current detection circuits114and129, a voltage detection circuit122, and the voltage detection circuit128are examples of a detection circuit that detects the load109connected to the outlet115. The controller120and the CPU121are examples of a control circuit that stops or starts the engine102in accordance with the load detected by the detection circuit. The control circuit (for example, the CPU121) is configured to cause the second conversion circuit to generate an AC by applying a DC voltage from the power supply to the second conversion circuit during a period in which the engine102stops. Furthermore, the control circuit (for example, the CPU121) is configured to decide, based on whether the detection circuit detects the load, whether to continuously stop the engine102or to start the engine102. According to this embodiment, the CPU121can detect not only the load109with a low impedance but also the load109with a high impedance by outputting an AC from the outlet115during the stop period of the engine102. This enables the CPU121to accurately detect that the load109is connected during the stop period of the engine102, thereby accurately restarting the engine102. Furthermore, the detection accuracy of the load109is improved, and thus the stop state of the engine102can be maintained accurately. This can reduce fuel consumption by the engine102.

[Aspect 2]

The voltage detection circuit128is an example of a voltage detection circuit that detects a voltage input to the second conversion circuit. The control circuit (for example, the CPU121) may be configured to decide, based on a change in the input voltage to the second conversion circuit, which is detected by the voltage detection circuit, whether to continuously stop the engine102or to start the engine102during the stop period of the engine102. If the load109is connected to the outlet115, a current flows from the second conversion circuit to the load109, and thus the input voltage to the second conversion circuit lowers. That is, by monitoring a change in the input voltage to the second conversion circuit, it is possible to accurately detect connection of the load109to the outlet115.

[Aspect 3]

The voltage detection circuit122is an example of a voltage detection circuit that detects the power supply voltage (for example, Vbat) of the power supply. The control circuit (for example, the CPU121) may decide, based on a change in the power supply voltage detected by the voltage detection circuit, whether to continuously stop the engine or to start the engine during the stop period of the engine102. If the load109is connected to the outlet115, a current flows from the second conversion circuit to the load109, and thus the voltage (power supply voltage) between the terminals of the battery104lowers. That is, by monitoring a change in the power supply voltage of the battery104, it is possible to accurately detect connection of the load109to the outlet115.

[Aspect 4]

The current detection circuit129is an example of a current detection circuit that detects a current flowing from the power supply to the second conversion circuit. The control circuit (for example, the CPU121) applies a DC voltage from the power supply to the second conversion circuit to cause the second conversion circuit to generate an AC during a period in which the engine102stops. The control circuit (for example, the CPU121) may decide, based on a change in the current detected by the current detection circuit, whether to continuously stop the engine102or to start the engine102. If the load109is connected to the outlet115by applying an AC voltage to the outlet115, a current flows from the power supply (for example, the battery104and the DC DC converter123) to the second conversion circuit. Therefore, by monitoring this current, the CPU121can accurately detect that the load109is connected to the outlet115during the stop period of the engine102.

[Aspect 5]

The current detection circuit114is an example of a current detection circuit that detects a current flowing from the second conversion circuit to the load109. The control circuit (for example, the CPU121) applies a DC voltage from the power supply to the second conversion circuit to cause the second conversion circuit to generate an AC during a period in which the engine102stops. The control circuit (for example, the CPU121) may decide, based on a change in the current detected by the current detection circuit, whether to continuously stop the engine102or to start the engine102. If the load109is connected to the outlet115by applying an AC voltage to the outlet115, a current flows from the second conversion circuit to the load109. Therefore, by monitoring this current, the CPU121can accurately detect that the load109is connected to the outlet115during the stop period of the engine102.

[Aspect 6]

The DC DC converter123is an example of a third conversion circuit that is provided between the power supply and the second conversion circuit, and converts a DC power supply voltage supplied from the power supply into a DC input voltage to the second conversion circuit. The DC input voltage to the second conversion circuit (for example, the AC generating circuit113) is such DC voltage that the second conversion circuit can generate an AC by that the second conversion circuit is inputted or supplied with the DC input voltage. There may be a lower limit voltage with respect to the input voltage to the third conversion circuit, which is necessary for the third conversion circuit to output an AC voltage. In this case, the DC input voltage input to the second conversion circuit is required to be equal to or higher than the lower limit voltage.

[Aspect 7]

If the engine102transits from the stop state to the operating state, the control circuit (for example, the CPU121) stops supply of power from the power supply to the second conversion circuit. This is because if the engine102rotates, the generator103supplies power to the second conversion circuit. On the other hand, if the engine102transits from the operating state to the stop state, the control circuit (for example, the CPU121) is configured to start supply of power from the power supply to the second conversion circuit.

The invention is not limited to the foregoing embodiments, and various variations/changes are possible within the spirit of the invention.