Power generation control device of a hybrid vehicle

Abstract

A power generation control device of a hybrid vehicle (10) having an internal combustion engine (11) and an electric motor (12) with a function of generating electric energy as drive sources, the power generation control device comprising: an inter-vehicle distance detection unit (23) configured to detect an inter-vehicle distance (L) between the vehicle and a preceding vehicle, an inter-vehicle distance change amount detection unit (24) configured to detect an inter-vehicle distance change amount per unit time between the vehicle and a preceding vehicle, and a power generation control unit configured to set a target engine torque of the internal combustion engine (11) to a valuewhich is obtained by adding a negative target engine torque for power generation by the electric motor (12) to the engine torque for traveling transmitted to the drive wheels (17), and limiting a power generation amount according to the inter-vehicle distance (L) to reduce a load on the engine (11) during a power generation travel in which the output torque of the engine (11) is supplied to both the electric motor (12) and the drive wheels (17), wherein the power generation control unit is configured to perform power generation control in a power generation travel mode, comprising: setting a motor torque gain (K) based on the inter-vehicle distance (L) and an inter-vehicle distance change rate (η) to make the motor torque gain (K) smaller as the inter-vehicle distance (L) becomes smaller,and making the motor torque gain (K) smaller as the inter-vehicle distance change rate (η) becomes negatively larger, multiplying the motor torque gain (K) by the target motor torque so that the power generation amount is limited, and canceling the power generation control of the target motor torque when the brake (27) is applied.

Description

The present invention relates to a power generation control device of a hybrid vehicle having an electric motor with an electric power generation function and an internal combustion engine as drive sources.In some hybrid vehicles having an engine and an electric motor as drive sources, the electric motor has a function of generating electric power. Japanese Unexamined Patent Application Publication JP H09-298 802 A discloses a hybrid vehicle having an engine that drives the front wheels and a motor generator that drives the rear wheels. In this hybrid vehicle, electric power generated by regeneratively braking the motor-generator is stored in a battery when the speed of the vehicle is reduced.JP 2007-168 502 A discloses a power split hybrid vehicle having a power train in which an engine and an electric motor are connected to each other via a power split mechanism and a generator to the power split mechanism to store electric power generated in regenerative braking in a battery. JP 2009-189 217 A discloses a power split hybrid vehicle having a three-shaft type power split mechanism connected to a crankshaft of an internal combustion engine, a first motor generator connected to the power split mechanism, and a second motor generator connected to a ring gear shaft of the power split mechanism. In this hybrid vehicle, both motor-generators function as an electric motor and a generator.JP 2009-274 611 A discloses a parallel hybrid vehicle having an internal combustion engine and a power generating electric motor directly connected to the internal combustion engine. In this hybrid vehicle, power generated by both the engine and the motor is transmitted through a transmission for driving the wheels. The electric power generated by the electric motor is stored in a battery during regenerative braking.These hybrid vehicles have the following operation modes: a traveling mode in which the vehicle travels using driving force output from at least one of the engine or the motor generator, a charging mode in which the electric energy of the generator is stored in the battery when the vehicle speed is reduced, and a power generation traveling mode in which the vehicle generates power during traveling.When a vehicle has an inter-vehicle distance detection unit, an inter-vehicle distance from the vehicle to a preceding vehicle and a target such as an obstacle may be detected. The above-described hybrid vehicles have an inter-vehicle distance sensor for detecting the inter-vehicle distance. In JP H09-298 802 A, an increase in vehicle speed is limited by regeneratively braking the motor generator when the vehicle travels and a braking request is detected, and an approach to the obstacle is limited by regeneratively braking the motor generator when an obstacle is detected in the traveling direction.In JP 2007-168 502 A, an inter-vehicle distance between the vehicle and the preceding vehicle is maintained, and a distribution ratio of a driving force shared by the electric motor is set higher with respect to a requested driving force when information requiring a driving force of higher responsiveness is displayed. Further, in JP 2009-189 217 A, during low-speed travel to follow a preceding vehicle, motor regenerative braking is performed within a range of a requested braking torque when the vehicle speed is equal to or greater than a predetermined vehicle speed, and a braking torque of the motor, which is a regenerative torque, is replaced by a braking force by the brake when the vehicle speed is less than the predetermined vehicle speed based on the vehicle speed and the inter-vehicle distance. Further, in JP 2009-274 611 A, an expected regenerative amount is calculated based on a relative speed change calculated from the vehicle speeds of the vehicle and the preceding vehicle, and a target SOC (state of charge) of the energy storage device is changed based on the expected regenerative amount.DE 10 2014 102 896 A1 discloses a system comprising a cruise control module, an engine control module and a brake control module. The cruise control module determines a cruise control torque request based on a following distance of a vehicle and / or a rate at which the vehicle approaches an object. The engine control module determines a negative torque capacity of a powertrain. The powertrain includes an engine and an electric motor. The brake control module applies a friction brake when the cruise torque request is less than the negative torque capacity of the powertrain.DE 197 18 709 A1 discloses a hybrid vehicle, enabling the drive or braking force provided by an internal combustion engine to be supplemented by an independently controlled electric motor generator. The deceleration of the vehicle is detected in the free running operation of the motor by a control device) to prevent an increase in the speed of the vehicle by regenerative braking of the motor-generator. The control device can also be used to control the regenerative braking force of the motor-generator as a function of the detected distance of the vehicle from the vehicle traveling ahead.The above-described known hybrid vehicles have a power running mode. When the vehicle travels in the power generation travel mode, the load of the engine needs to be increased further than the torque transmitted to the drive wheels to generate power, and the fuel consumption increases. The power generation running mode may therefore be a disadvantageous running mode in view of fuel consumption. However, without running in which the electric motor generates power, the state of charge of the battery is reduced and it may be difficult to run when the electric motor outputs torque to the drive wheels.On the other hand, when the brake is operated while driving in the power generation travel mode, the travel mode is switched to the regenerative brake mode and electric power is generated from the motor generator, so that the generator and the like recharges the battery. However, in the power generation travel mode of the conventional hybrid vehicles, the power generation amount is constant. When the power generation amount is constant and power generation is performed from the engine while power of the engine is transmitted to the drive wheels, this instantaneously deteriorates fuel consumption.The present invention is based on the object of improving the fuel consumption of a hybrid vehicle having a power generation running mode.According to an aspect of the present invention, there is provided a power generation control device of a hybrid vehicle having, as drive sources, an internal combustion engine and an electric motor having an electric power generation function, the power generation control device including: an inter-vehicle distance detection unit configured to detect an inter-vehicle distance between the vehicle and a preceding vehicle; and a power generation control unit configured to set a target engine torque of the internal combustion engine to a value obtained by adding a target negative engine torque for power generation by the electric motor to the engine torque for traveling transmitted to the drive wheels and limit a power generation amount corresponding to the inter-vehicle distance corresponding to the inter-vehicle distance to set a load of the internal combustion engine during power generation traveling, wherein the output torque of the internal combustion engine is supplied to both the electric motor and the drive wheels. The power generation control unit is configured to perform power generation control in a power generation travel mode. The power generation control includes setting an engine torque gain based on the inter-vehicle distance and an inter-vehicle distance change rate to make the engine torque gain smaller as the inter-vehicle distance becomes smaller and make the engine torque gain smaller as the inter-vehicle distance change rate becomes negatively larger, multiplying the engine torque gain by the target engine torque so that the power generation amount is limited, and canceling the power generation control of the target engine torque when the brake is operated.Preferred aspects are defined in the dependent claims.The invention is explained further below on the basis of an exemplary embodiment with reference to the drawings, in which FIG. 1 is a diagram illustrating an embodiment of a system configuration of a hybrid vehicle, FIG. 2A is a time chart illustrating power generation control in a power generation travel mode according to an embodiment of the present invention, and FIG. 2B is a time chart illustrating a known power generation control according to a comparative example, FIG. 3 is a graph showing an engine torque increase to perform a power generation limiting process according to the inter-vehicle distances and the inter-vehicle distance change amounts; and FIG. 4 is a flowchart showing an algorithm of a power generation restriction process of the power generation control device according to the embodiment of the present invention.A hybrid vehicle 10 illustrated in FIG. 1 includes, as drive sources, an engine 11 that is an internal combustion engine such as a gasoline engine or a diesel engine, and a motor generator 12 that is an electric motor having an electric power generation function. An output shaft of the engine 11 is connected to a transmission 13, and the motor generator 12 is connected to an output shaft 14 of the transmission 13. The output shaft 14 is connected to a front wheel axle 16 via a speed reducer 15. The hybrid vehicle 10 uses a parallel system, that is, the hybrid vehicle 10 includes an engine powertrain for transmitting power of the engine 11 to the front wheels 17 serving as driving wheels and an electric motor powertrain for transmitting power of the motor-generator 12 to the engine. The front wheels 17 mounted on the front wheel axle 16 receive power from at least one of the engine 11 and the motor generator according to a running mode. A rear wheel axle 18 is provided with rear wheels 19. In FIG. 1, a differential gear provided on the front wheel axle 16 is not illustrated.In the hybrid vehicle 10 illustrated in FIG. 1, the engine 11 drives the wheels and the motor-generator 12 to generate electric power, while the motor-generator 12 is also used as a drive source to drive. An inverter 21 is connected to a stator of the motor-generator 12. The inverter 21 is connected to a battery 22 as an energy storage device via an energy distribution line. In the hybrid vehicle 10, power from the engine 11 is transmitted to the front wheels 17 as indicated by the arrows E, electric current from the battery 22 flows to the motor generator 12 as indicated by the arrows B, and power from the motor generator 12 is transmitted to the front wheels 17 as indicated by the arrow M. With this configuration, the vehicle can be driven by using, as a drive source, at least one of the engine 11 and the motor generator 12.The motor generator 12 functions as an electric generator when a vehicle speed is reduced, whereby the travel mode is switched to the regenerative braking mode in which braking energy released as thermal energy upon braking is absorbed and stored in the battery 22, as indicated by the broken arrows G. Further, the hybrid vehicle 10 has a power generation running mode in which a load of the engine 11 is raised to transmit a running output to both the drive wheels and the motor generator 12 using the surplus electric power generation output.The hybrid vehicle 10 includes an inter-vehicle distance detection unit 23 for detecting an inter-vehicle distance between the hybrid vehicle 10 and a preceding vehicle. The inter-vehicle distance detection unit 23 is configured with, for example, two CCD cameras for detecting the distance to the preceding vehicle as a target based on left and right parallax images. Alternatively, the inter-vehicle distance detection unit 23 may be configured with a millimeter wave radar for detecting the distance. With respect to a detection sensor signal from the inter-vehicle distance detection unit 23, the inter-vehicle distance between the vehicle and the preceding vehicle and an inter-vehicle distance change amount are detected based on the detection sensor signal in an inter-vehicle distance detection controller 24 serving as the inter-vehicle distance detection unit and the inter-vehicle distance change amount detection unit according to the present invention. The signal of the detected inter-vehicle distance and the inter-vehicle distance change amount is sent to an HEV (hybrid vehicle) controller 25 serving as the power generation control unit according to the present invention. The HEV controller 25 receives an accelerator operation signal from an accelerator pedal 26 and a brake operation signal from a brake 27. As for the brake 27, there are a brake that is operated by being depressed by a driver and an automatic brake when the vehicle is caused to apply a braking force corresponding to an inter-vehicle distance.The HEV controller 25 transmits a control signal to an engine controller 31 that controls the engine 11, and the output torque of the engine 11 is controlled. The HEV controller 25 further outputs a transmission driving signal to a transmission controller 32 that controls the transmission 13, and a driving signal of the output torque of the motor-generator 12 to an inverter controller 33 that controls the inverter 21. The HEV controller 25 has a function of detecting a state of charge (SOC) of the battery 22.FIG. 2A is a time chart showing power generation control in the power generation travel mode according to the embodiment of the present invention, and FIG. 2B is a time chart showing conventional power generation control given as a comparative example. In FIGS. 2A and 2B, the power generation travel mode and the regenerative braking mode are shown. The running mode is switched to the regenerative brake mode when the vehicle approaches a preceding vehicle and the driver operates the brake 27. In such a case where an automatic brake system is installed, when the vehicle approaches the preceding vehicle at a predetermined distance, the automatic brake system is activated and the travel mode is automatically switched to the regenerative brake mode.In the power generation running mode, the output torque of the engine 11 is supplied to both the motor generator 12 and power is generated to the drive wheels and the motor generator 12. As shown in FIG. 2A, while traveling in the power generation traveling mode, the power generation amount in the power generation traveling mode is limited based on the inter-vehicle distance or the inter-vehicle distance and the inter-vehicle distance change amount.As shown in the comparative example in FIG. 2B, usually, until the travel mode is switched to the regenerative braking mode, the power generation amount is set constant in the power generation travel mode. On the other hand, as shown in FIG. 2A, when the power generation amount is limited in the power generation travel mode based on the inter-vehicle distance and the like, the power generation amount is limited before the travel mode is switched to the regenerative braking mode. This results in improving the fuel consumption of the hybrid vehicle 10.FIG. 3 is a map showing gain of engine torque used for performing power generation limiting processing by the power generation control device according to the inter-vehicle distance and the inter-vehicle distance change amount. This map is stored in a memory provided in the inter-vehicle distance detection controller 24 and / or the HEV controller 25.In FIG. 3, the horizontal axis represents the inter-vehicle distances L (m), and the vertical axis represents the inter-vehicle distance change amount (m) per unit time (second) which is the inter-vehicle distance change rate η (m / s). When the inter-vehicle distance L is from 100 to 80 m, the engine torque gain K is set to 0.8 to 1, and when the inter-vehicle distance is from 80 to 60 m, the gain K is set to 0.8 to 0.6. The gain K is set smaller as the inter-vehicle distance L becomes smaller as shown in FIG. 3. In addition, the gain K is set smaller as the inter-vehicle distance change rate (m / s) becomes negatively larger, in other words, the inter-vehicle distance change rate becomes larger in a direction of approaching the preceding vehicle.In the power generation running mode shown in FIG. 2, the target engine torque (Nm) of the engine 11 is set to a value obtained by adding a target negative engine torque (Nm) for power generation by the motor generator 12 to the engine torque for running transmitted to the drive wheels, and the transmission gear ratio is also set to a target transmission gear ratio in the power generation running mode. In this travel mode, the inter-vehicle distance L and the inter-vehicle distance change rate η are calculated by the inter-vehicle distance detection controller 24 based on a detection signal from the inter-vehicle distance detection unit 23. With this configuration, the power generation amount in the power generation travel mode is limited, whereby fuel consumption can be improved.When the negative target engine torque limiting process is performed, the output torque of the drive train for the drive wheels becomes larger than a driver-demanded driving force. Therefore, as shown in FIG. 2A, in order to maintain the output torque of the powertrain to correspond to the driver required driving force, a load of the engine is reduced by subtracting the amount of the target engine torque limit from the target engine torque. To subtract the output torque of the powertrain engine, instead of subtracting the target engine torque to reduce engine load, the transmission gear ratio may be adjusted to reduce engine load as long as the driver demanded drive force is maintained. Further, both of the subtraction of the target engine torque and the adjustment of the transmission may be performed.FIG. 4 is a flowchart showing an algorithm of the power generation restriction process of the power generation control device. When it is determined in step S 1 that the power generation travel mode is being executed, the inter-vehicle distance L and the inter-vehicle distance change rate η are detected based on the detection signal from the inter-vehicle distance detection unit 23 (steps S 2 and S 3). As shown in FIG. 3, when the inter-vehicle distance L becomes equal to or less than 100 m, the engine torque gain K is set to be equal to or less than 1, and the target engine torque limiting process is executed in step S 4. The limiting process may be executed based on only the inter-vehicle distance L. However, the limiting process may further improve fuel consumption using both the inter-vehicle distance L and the inter-vehicle distance change rate η. Note that even when the power generation travel mode is executed, the target motor torque limiting process is not performed when the state of charge (SOC) of the battery 22 is equal to or lower than a predetermined value.When the target engine torque limiting process is executed, a subtraction process of the output torque of the power train is executed in step S 5. In this subtraction process in step S 5, as described above, a method of extracting the target engine torque, a method of setting the transmission gear ratio, or a method of performing both the target engine torque extraction and the transmission setting are performed to maintain the driver required driving force. When the driver applies the brake or activates auto braking, the mode is switched to the regenerative brake mode and the torque limiting process is canceled (steps S 6 and S 7).According to the above embodiment, the engine load for generating power is reduced by limiting the amount of power generation corresponding to the inter-vehicle distance between the vehicle and a preceding vehicle when traveling in the power generation traveling mode, whereby the fuel consumption of the hybrid vehicle can be improved.The present invention is not limited to the above-explained embodiment, and various modifications are possible without departing from the scope of the present invention. For example, while the hybrid vehicle 10 in FIG. 1 uses a parallel system, the present invention is not limited thereto and may be applied to a power split hybrid vehicle (power split).

Claims

A power generation control device of a hybrid vehicle (10) having, as drive sources, an engine (11) and an electric motor (12) having an electric power generation function, the power generation control device comprising: an inter-vehicle distance detection unit (23) configured to detect an inter-vehicle distance (L) between the vehicle and a preceding vehicle; an inter-vehicle distance change amount detection unit (24) configured to detect an inter-vehicle distance change amount per unit time between the vehicle and a preceding vehicle; and a power generation control unit configured to determine a target motor torque of the engine (11) to a value obtained by adding a target negative motor torque for power generation by the electric motor (12) to the engine torque for driving, setting a power generation amount corresponding to the inter-vehicle distance (L) to reduce a load of the engine (11) during power generation running in which the output torque of the engine (11) is supplied to both the motor (12) and the drive wheels (17), wherein the power generation control unit is configured to perform power generation control in a power generation running mode, comprising: setting an engine torque gain (K) based on the inter-vehicle distance (L) and an inter-vehicle distance change rate (η) to make the engine torque gain (K) smaller as the inter-vehicle distance (L) becomes smaller and to make the engine torque gain (K) smaller as the inter-vehicle distance change rate (η) becomes negatively larger, multiplying the motor torque gain (K) by the target motor torque so as to limit the power generation amount, and canceling the power generation control of the target motor torque when the brake (27) is operated.The power generation control device of a hybrid vehicle (10) according to claim 1, wherein the power generation control unit is configured to maintain the engine torque transmitted to the drive wheels (17) to reduce the engine load.The power generation control device of a hybrid vehicle (10) according to any one of claims 1 or 2, wherein the load of the engine (11) is reduced by reducing the torque of the engine (11).The power generation control device of a hybrid vehicle (10) according to any one of claims 1 or 2, wherein the load of the internal combustion engine is reduced by adjusting a transmission gear ratio.The power generation control device of a hybrid vehicle (10) according to any one of claims 1 or 2, wherein the load of the engine (11) is reduced by reducing the torque of the engine (11) and setting a transmission gear ratio.The power generation control device of the hybrid vehicle (10) according to any one of claims 1 or 5, wherein the power generation control unit controls the motor torque gain (K) to be in a range between 0 and 1.

Images