Power-generation control device and power-generation control method for hybrid vehicle

Provided is a power-generation control device and a power-generation control method for a hybrid vehicle, which are capable of suppressing a temperature rise of an electric motor while controlling a field-weakening current to flow through the electric motor to protect the electric motor and a battery even when an induced voltage increased by an increase in rpm of the electric motor exceeds an allowable voltage of the battery. Power generation by an electric motor is stopped when a voltage of a battery is equal to or higher than a predetermined first voltage, and an in-vehicle electric load is supplied with power generated by the electric motor and a power-generation amount by the electric motor is controlled so that the voltage of the battery becomes equal to a predetermined second voltage, when the voltage of the battery is lower than the predetermined second voltage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power-generation control device and a power-generation control method for a hybrid vehicle, for controlling an internal combustion engine, an electric motor, a battery, and an in-vehicle electric load which constitute a power-generation system of the hybrid vehicle so that a temperature rise of the electric motor is suppressed.

2. Description of the Related Art

The following hybrid vehicle technology to reduce a fuel consumption amount of an automobile is generally known. Specifically, an electric motor is provided on an output shaft of an internal combustion engine so as to compensate for a low-thermal efficiency portion of the internal combustion engine with a driving force of the electric motor and to recover deceleration energy generated at the time of deceleration of the automobile by the electric motor as regenerative power.

The above-mentioned hybrid vehicle, which is operated by the combination of power of the internal combustion engine and power of the electric motor, additionally requires a battery as compared with a vehicle using only the power of the internal combustion engine. In current general hybrid vehicles, an about 100- to 300-V battery is mounted in order to drive the electric motor. Specifically, a large battery is required to be mounted so as to reduce the fuel consumption amount.

Therefore, in recent years, hybrid vehicles compliant with a 48 V-battery which is smaller than those of conventional hybrid vehicles have been proposed. This proposition is also encouraged by situations in which a 12-V battery mounted in conventional vehicles cannot supply sufficient power to an in-vehicle electric load for an automobile, which requires large power.

However, the electric motor for assisting drive of the internal combustion engine is required to have a high torque. In general, the high-torque electric motor has a large induced voltage constant. Therefore, an induced voltage of the electric motor becomes large when an rpm of the electric motor becomes higher. As a result, there is a problem in that the induced voltage of the electric motor adversely exceeds an allowable voltage of the 48-V battery.

As a technology for reducing the adverse effects of the increase in induced voltage of the electric motor on the battery as described above, there exists a method of suppressing an induced-voltage rise by controlling a field-weakening current to flow through the electric motor (see, for example, Japanese Patent Application Laid-open No. 2000-354305).

However, the related art has the following problem.

Specifically, according to Japanese Patent Application Laid-open No. 2000-354305, in order to protect the battery, the field-weakening current is required to be controlled to flow through the electric motor to suppress the induced-voltage rise. However, there is a fear in that the temperature of the electric motor is disadvantageously increased by the field-weakening current to cause an electric motor failure.

SUMMARY OF THE INVENTION

The present invention has been made to solve the problem described above and therefore has an object to provide a power-generation control device and a power-generation control method for a hybrid vehicle, which are capable of suppressing a temperature rise of an electric motor while controlling a field-weakening current to flow through the electric motor to protect the electric motor and a battery even when an induced voltage increased by an increase in rpm of the electric motor exceeds an allowable voltage of the battery.

According to one embodiment of the present invention, there is provided a power-generation control device for a hybrid vehicle, including: a control section for controlling a power-generation system of the hybrid vehicle, the power-generation system including: an internal combustion engine; an electric motor coupled to an output shaft of the internal combustion engine, which is capable of generating power; a battery for accumulating the power generated by the electric motor; and an in-vehicle electric load to be supplied with the power from the battery; and a battery-state detecting section for detecting a voltage of the battery, in which the control section stops the power generation by the electric motor when the voltage of the battery, which is detected by the battery-state detecting section, is equal to or higher than a predetermined first voltage, and supplies the in-vehicle electric load with the power generated by the electric motor and controls a power-generation amount by the electric motor so that the voltage of the battery becomes equal to a predetermined second voltage, which is lower than the predetermined first voltage, when the voltage of the battery is lower than the predetermined second voltage.

Further, according to one embodiment of the present invention, there is provided a power-generation control method for a hybrid vehicle for use in a power-generation system of the hybrid vehicle, the power-generation system including: an internal combustion engine; an electric motor coupled to the internal combustion engine, which is capable of generating power; a battery for accumulating the power generated by the electric motor; and an in-vehicle electric load to be supplied with the power from the battery, the power-generation control method including: detecting a voltage of the battery; and stopping the power generation by the electric motor when the voltage of the battery is equal to or higher than a predetermined first voltage, and supplying the in-vehicle electric load with the power generated by the electric motor and controlling a power-generation amount by the electric motor so that the voltage of the battery becomes equal to a predetermined second voltage, which is lower than the predetermined first voltage, when the voltage of the battery is lower than the predetermined second voltage.

In the present invention, in order to suppress the temperature rise of the electric motor, the power generation by the electric motor is stopped when the voltage of the battery, which is detected by the battery-state detecting section, is equal to or higher than the predetermined first voltage, and the in-vehicle electric load is supplied with the power generated by the electric motor and a power-generation amount by the electric motor is controlled so that the voltage of the battery becomes equal to the predetermined second voltage, which is lower than the predetermined first voltage, when the voltage of the battery is lower than the predetermined second voltage. As a result, it is possible to provide the power-generation control device and the power-generation control method for a hybrid vehicle, which are capable of suppressing the temperature rise of the electric motor while controlling the field-weakening current to flow through the electric motor to protect the electric motor and the battery even when the induced voltage increased by the increase in rpm of the electric motor exceeds the allowable voltage of the battery.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, a power-generation control device for a hybrid vehicle and a power-generation control method for a hybrid vehicle according to a preferred embodiment of the present invention is described referring to the accompanying drawings. In the drawings, the same or corresponding parts are denoted by the same reference symbols for description.

First Embodiment

FIG. 1is an exemplary view of a configuration of a power-generation system of a hybrid vehicle according to a first embodiment of the present invention. The power-generation system of the hybrid vehicle according to the first embodiment includes an internal combustion engine101, an electric motor102, a battery106, and an in-vehicle electric load107. The electric motor102is coupled to the internal combustion engine101and is capable of generating electric power. The battery106accumulates the electric power generated by the electric motor102. The in-vehicle electric load107is supplied with the electric power from the battery106.

The internal combustion engine101is controlled based on a control signal output from an HEV control unit108. In this case, the internal combustion engine101is, for example, a gasoline engine or a diesel engine, which is capable of generating power for an automobile based on a fossil fuel.

The electric motor102is provided on an output shaft of the internal combustion engine101. The electric motor102starts the internal combustion engine101and assists drive of the internal combustion engine101while the vehicle is running. Moreover, when the vehicle decelerates, the electric motor102performs regenerative power generation by a torque transmitted from tires104through an intermediation of a transmission103. After an induced voltage generated by the regenerative power generation is converted into electric power by an electric-motor control unit105, which is an inverter for controlling the electric motor102, the electric power obtained by the conversion is supplied to the battery106or the in-vehicle electric load107.

As the in-vehicle electric load107, there are, for example, a DC-DC converter for supplying electric power from the battery106to a 12-V in-vehicle load (not shown) and an electric water pump for supplying cooling water to the internal combustion engine101. However, the details of the in-vehicle electric load107do not closely relate to technical characteristics of the present invention, and therefore the detailed description thereof is herein omitted.

FIG. 2is a block diagram of a power-generation control device for a hybrid vehicle according to the first embodiment of the present invention. The power-generation control device for a hybrid vehicle according to the first embodiment of the present invention includes the HEV control unit (control section)108, an electric-motor temperature detecting section201, a battery-state detecting section202, an electric-load detecting section203, and an internal-combustion-engine rpm detecting section204.

Moreover, the HEV control unit108includes an electric-motor operation determining section205, a target-power determining section206, and a target-rpm determining section207. The target-power determining section206and the target-rpm determining section207refer to an output from the electric-motor operation determining section205.

The HEV control unit108controls the power-generation system of the hybrid vehicle based on a coil temperature of the electric motor102, which is detected by the electric-motor temperature detecting section201, a voltage of the battery106, which is detected by the battery-state detecting section202, a load of the in-vehicle electric load107, which is detected by the electric-load detecting section203, and an rpm of the internal combustion engine101, which is detected by the internal-combustion-engine rpm detecting section204, so that a temperature rise of the electric motor102is suppressed.

FIG. 3is an exemplary map which defines a relationship between a temperature of the electric motor102of the hybrid vehicle and each of a first voltage V1and a second voltage V2according to the first embodiment of the present invention.

As shown inFIG. 3, when the voltage of the battery106is equal to or higher than the predetermined first voltage V1, the electric-motor operation determining section205of the HEV control unit108determines that a charge amount of the battery106is sufficient and therefore stops the power generation by the electric motor102. As a result, the electric motor102comes into a no-load state where the power is not generated. Thus, a temperature rise of the electric motor102is suppressed. Alternatively, fuel efficiency performance can also be improved by reducing a load of the internal combustion engine101.

On the other hand, when the voltage of the battery106is lower than the predetermined second voltage V2, which is lower than the first voltage V1, the electric-motor operation determining section205controls a power-generation amount by the electric motor102to supply the generated power to the in-vehicle electric load107. Moreover, the battery106is charged so that the voltage of the battery106becomes equal to the second voltage V2. In this manner, by intensively charging the battery106in a state in which the charge amount of the battery106is small, the temperature rise of the electric motor102can be suppressed by the combination with a method of limiting power consumption by the in-vehicle electric motor107or limiting the rpm of the internal combustion engine101as described below.

Specifically, when the temperature of the electric motor102, which is detected by the electric-motor temperature detecting section201, is equal to or higher than a predetermined first temperature T1in the same state as described above in which the voltage of the battery106is lower than the predetermined second voltage V2, the target-power determining section206of the HEV control unit108limits the power consumed by the in-vehicle electric load107. For example, the power consumed by the in-vehicle electric load107is reduced by 50%. However, a specific value thereof depends on a configuration of the hybrid vehicle. As a result, a power-generation load on the electric motor102can be reduced to prevent a further increase in temperature of the electric motor102. It is preferred that the first voltage V1and the second voltage V2be respectively set to, for example, 90% and 50% of an allowable voltage of the battery106. However, characteristics change depending on a vehicle to be realized. Thus, the first voltage V1and the second voltage V2are to be adjusted for each vehicle.

In this case, the target-power determining section206can also limit the power consumed by the in-vehicle electric load107in accordance with a load (such as a current, a voltage, or power) of the in-vehicle electric load107, which is detected by the electric-load detecting section203. In this case, for example, the order of priority of stopping the supply of power only needs to be determined in accordance with the degree of effects on running of the vehicle so that the power supply is stopped in ascending order of the priority.

Moreover, when the temperature of the electric motor102, which is detected by the electric-motor temperature detecting section201, is equal to or higher than the predetermined first temperature T1in the same state as that described above where the voltage of the battery106is lower than the second voltage V2, the target-rpm determining section207of the HEV control unit108controls the internal combustion engine101so that the rpm of the internal combustion engine101, which is detected by the internal-combustion-engine rpm detecting section204, becomes lower than a predetermined rpm (for example, 4,000 rpm; however, a specific value thereof depends on the design of the electric motor).

This is because, as described above, the induced voltage of the electric motor102becomes higher in the hybrid vehicle including the electric motor102having a large induced voltage constant when the rpm of the electric motor102increases, thereby adversely affecting the battery106. In this manner, by reducing the rpm of the internal combustion engine101, a field-weakening current for suppressing an increase in induced voltage of the electric motor102is reduced so as to prevent the temperature of the electric motor102from further increasing.

When the temperature of the electric motor102is T′ (>T), the HEV control unit108refers to the map as shown inFIG. 3, which is presorted in a memory section (not shown), to correct the first voltage V1and the second voltage V2. Then, when the voltage of the battery106becomes equal to a corrected first voltage V1′ (>V1), the power generation by the electric motor102is stopped. Similarly, when the voltage of the battery106becomes equal to a corrected second voltage V2′ (>V2), the battery106is charged. In this manner, the optimal first voltage V1′ and second voltage V2′ can be selected in accordance with the temperature of the electric motor102. Therefore, the battery106and the electric motor102can be optimally controlled so as to further suppress a temperature rise of the electric motor102.

Regarding processing in the case where the voltage of the battery106is between the first voltage V1and the second voltage V2, for example, it is preferred that the amount of power generation by the electric motor102be increased little by little after the voltage of the battery106becomes lower than the first voltage V1so that the amount of power generation becomes maximum when the voltage of the battery106becomes equal to the second voltage V2. However, the amount of power generation by the electric motor102greatly relates to operation performance while the vehicle is running. Therefore, the amount of power generation is required to be adjusted for each vehicle.

Moreover, for a boundary of the first voltage V1, hysteresis is provided in the case where the voltage of the battery106is lower than the first voltage V1and the case where the voltage of the battery106is higher than the first voltage V1so as to prevent ON/OFF hunting of a power-generating operation of the electric motor102. For example, in the case where the temperature of the electric motor102is 150° C., when the voltage of the battery106becomes larger to turn OFF the power-generating operation of the electric motor102, the first voltage V1is set to 50 V. When the voltage of the battery106becomes lower to turn ON the power-generating operation of the electric motor102, the first voltage V1is set to 48 V. The above-mentioned values are also adjusted for each vehicle because the characteristics change in accordance with the vehicle to be realized.

FIG. 4is a flowchart of a power-generation control method for a hybrid vehicle according to the first embodiment of the present invention. Now, specific processing of the power-generation control method for a hybrid vehicle is described referring toFIG. 4.

The electric-motor operation determining section205stores the temperature of the electric motor102, which is detected by the electric-motor temperature detecting section201, in the memory section (not shown) (Step S1). The temperature of the electric motor102can be, for example, detected by a thermistor mounted to a coil and can also be estimated from a current flowing through the electric motor102or the like.

Next, the electric-motor operation determining section205stores the voltage of the battery106, which is detected by the battery-state detecting section202, in the memory section (Step S2). The voltage of the battery106can be generally obtained from a unit (not shown) for controlling the battery106through a vehicle communication line such as a controller area network (CAN).

Next, the target-power determining section206stores the load of the in-vehicle electric load107, which is detected by the electric-load detecting section203, in the memory section (Step S3). The load of the in-vehicle electric load107can be calculated from, for example, output power from the battery106and power or regenerative power necessary for the electric motor102.

Next, the target-rpm determining section207stores the rpm of the internal combustion engine101, which is detected by the internal-combustion-engine rpm detecting section204, in the memory section (Step S4). The rpm of the internal combustion engine101can be obtained from a crank-sensor signal input to the HEV control unit108or the like.

Next, the HEV control unit108refers to the map shown inFIG. 3, which is stored in advance in the memory section (not shown), to determine the first voltage V1and the second voltage V2in accordance with the temperature of the electric motor102.

The HEV control unit108compares the voltage of the battery106and the first voltage V1with each other (Step S5). When the voltage of the battery106is equal to or higher than the first voltage V1(Step S5: YES), the HEV control unit108stops the power generation by the electric motor102(Step S6).

On the other hand, when the voltage of the battery106is lower than the first voltage (Step S5: NO), the HEV control unit108compares the voltage of the battery106and the second voltage V2with each other (Step S7).

When the voltage of the battery106is equal to or higher than the second voltage V2(Step S7: YES), the HEV control unit108controls the electric motor102so as to generate a preset power-generation amount to supply power consumed by the in-vehicle electric load107. Alternatively, as described above, the electric motor102may be controlled so as to continuously change the power-generation amount when the voltage of the battery106is between the first voltage V1and the second voltage V2(Step S8).

On the other hand, when the voltage of the battery106is lower than the second voltage V2(Step S7: NO), the HEV control unit108controls the power-generation amount by the electric motor102to supply the generated power to the in-vehicle electric load107and charge the battery106so that the voltage of the battery106becomes equal to the second voltage V2(Step S9).

When the temperature of the electric motor102is equal to or higher than the predetermined first temperature T1, the power consumed by the in-vehicle electric load107is limited in accordance with the load of the in-vehicle electric load107, which is detected by the electric-load detecting section203. Moreover, the internal combustion engine101is controlled so that the rpm of the internal combustion engine101, which is detected by the internal-combustion-engine rpm detecting section204, becomes lower than a predetermined rpm (Step S9).

By limiting the rpm of the internal combustion engine101as described above, the rpm of the electric motor102, which is directly coupled to the internal combustion engine101, can be limited. By reducing the rpm of the electric motor102, the field-weakening current for suppressing the induced voltage can be reduced. Moreover, the load of the electric-load detecting section203is reduced to accelerate charging of the battery106. As a result, the voltage of the battery106can be increased.

As described above, according to the first embodiment, in order to suppress the temperature rise of the electric motor, the power-generation amount by the electric motor is controlled so as to stop the power generation by the electric motor when the voltage of the battery, which is detected by the battery-state detecting section, is equal to or higher than the predetermined first voltage, and to supply the power to the in-vehicle electric load by the power generation by the electric motor so that the voltage of the battery becomes equal to the second voltage when the voltage of the battery is lower than the predetermined second voltage, which is lower than the first voltage. As a result, it is possible to provide the power-generation control device and the power-generation control method for a hybrid vehicle, which are capable of suppressing the temperature rise of the electric motor to protect the electric motor and the battery while controlling the field-weakening current to flow through the electric motor, even when the induced voltage increased with an increase in rpm of the electric motor exceeds the allowable voltage of the battery.

Further, the voltage of the battery is monitored so as to control the power generation by the electric motor in accordance with the map of the first voltage and the second voltage in accordance with the temperature of the electric motor. In this manner, by controlling a large field-weakening current for suppressing the induced voltage of the electric motor to flow when the voltage of the battery drops, the electric motor can be prevented from generating heat to result in a failure.

If there is a possibility that the voltage of the battery106does not increase to increase the temperature of the electric motor102higher than a second temperature T2, which is a fail temperature, to result in a failure even though the power-generation control as described in the first embodiment is carried out, the electric-motor control unit105, which is an inverter for controlling the electric motor102, is set in a short-circuit mode. In this manner, the current generated in the electric motor102can be lowered. Further, when the rpm of the internal combustion engine101becomes equal to or lower than a given rpm (when a corresponding induced-voltage value becomes equal to or smaller than a given value), it is preferred that the electric-motor control unit105be set in an open mode. As described above, by switching the mode of the electric-motor control unit105to any one of the short-circuit mode and the open mode in accordance with the voltage of the battery106and the rpm of the internal combustion engine101, a failure of the electric motor102can be prevented from occurring.

Further, although the method of limiting the power consumption by the in-vehicle electric load107, the method of limiting the rpm of the internal combustion engine101, and the like are described in the first embodiment as the method of suppressing the temperature rise of the electric motor102, the above-mentioned methods may be used in combination or any one thereof may be carried out. For example, in the case where the stability of the power-generation system of the hybrid vehicle can be maintained by using any one of the above-mentioned methods to suppress the temperature rise of the electric motor102, the same effects can be obtained with a simpler configuration.

Although not mentioned in the first embodiment, the vehicle is generally equipped with a water-cooling system for cooling the electric motor102. Therefore, when the temperature of the electric motor102is equal to or higher than the second temperature T2in a state where the voltage of the battery106is lower than the second voltage V2, the electric motor102is cooled by using the water-cooling system. As a result, the possibility of a failure of the electric motor102can be further lowered.