Method and system for controlling charging and discharging for a hybrid vehicle

A method and system for controlling charging and discharging for a hybrid vehicle that may consume regenerative electric power collected by a motor through regenerative braking while coasting the hybrid vehicle when operating an integrated starter-generator (ISG) according to a state of charge (SOC) of a battery. The method of controlling charging and discharging for a hybrid vehicle which includes a motor operated by power of a battery and an ISG configured to start an engine or generate electric power by torque of the engine includes: changing a running mode of the hybrid vehicle to a regenerative braking mode when the hybrid vehicle is coasting, controlling the motor to generate electric power in the regenerative braking mode, determining whether an SOC of the battery is a charge limiting state, and operating the ISG by electric power generated by the motor when the SOC of the battery is the charge limiting state.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0133818 filed in the Korean Intellectual Property Office on Nov. 23, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present disclosure relates generally to a method and a system for controlling charging and discharging for a hybrid vehicle, and more particularly, to a method and system for controlling charging and discharging for a hybrid vehicle that may consume regenerative electric power collected by a motor through regenerative braking during coasting of the hybrid vehicle when operating an integrated starter-generator (ISG) according to a state of charge (SOC) of a battery.

(b) Description of the Related Art

Hybrid vehicles operate through the use of power from an internal combustion engine and power from a battery. In particular, hybrid vehicles are designed to efficiently combine and use power of the internal combustion engine and the motor. For example, as illustrated inFIG. 1, a hybrid vehicle includes: an engine10; a motor20; an engine clutch30which controls power connection between the engine10and the motor20; a transmission40; a differential gear unit50; a battery60; an integrated starter-generator (ISG)70which starts the engine10or generates electric power by output of the engine10; and wheels80.

As further shown, the hybrid vehicle includes: a hybrid control unit (HCU)200for controlling an overall operation of the hybrid vehicle; an engine control unit (ECU)110for controlling an operation of the engine10; a motor control unit (MCU)120for controlling an operation of the motor20; a transmission control unit (TCU)140for controlling an operation of the transmission40; and a battery control unit (BCU)160for managing and controlling the battery60. The BCU160may also be referred to as a battery management system (BMS). The ISG70may also be referred to as a starting/generating motor or a hybrid starter-generator (HSG).

The hybrid electric vehicle may be driven in a driving mode, such as an electric vehicle (EV) mode, which is a mode of a true electric vehicle solely using power of the motor20; a hybrid electric vehicle (HEV) mode using torque of the motor20as auxiliary power while using torque of the engine10as main power; and a regenerative braking (RB) mode collecting braking and inertia energy through power generation of the motor20to charge the battery60during braking or driving using the inertia of the vehicle. The motor20of the hybrid vehicle generally operates as a generator for collecting the inertia energy during the regenerative braking (RB) mode. The running by inertia energy of the hybrid vehicle may be referred to coasting.

As shown inFIG. 2, by setting a minus torque to the motor while coasting, the inertia energy may be collected as regenerative electric power. When the motor operates as a generator, the regenerative electric power generally charges the battery of the hybrid vehicle. However, when the battery is in a fully charged state such that charging is limited or in an over-temperature state, the regenerative electric power from the motor20cannot charge the battery.

When the battery is in the fully charged state during coasting, a conventional method known in the related art performs fuel-cut control instead of the regenerative braking so as to use a friction torque (minus torque) of the engine, as shown inFIG. 3. Because the friction torque of the engine while the fuel is cut is transmitted to an axle through the engine clutch, the same drivability as during the regenerative braking by the motor may be accomplished. However, the friction torque cannot be varied, and when the shift gear of the transmission is changed, drivability may rapidly deteriorate.

Further, in another conventional method known in the related art, when the battery is in the fully charged state during coasting, the regenerative electric power of the motor produced by the regenerative braking is consumed by an air conditioner or heater90. However, due to the unwanted operation of the air conditioner or heater, the temperature in the hybrid vehicle may be changed.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the related art that is already known to a person of ordinary skill in the art.

SUMMARY

The present disclosure has been made in an effort to provide a method and a system for controlling charging and discharging for a hybrid vehicle which is able to protect a battery and to enhance drivability by consuming regenerative electric power collected by a motor through regenerative braking while coasting when operating an integrated starter-generator (ISG) according to a state of charge (SOC) of a battery.

An exemplary embodiment of the present disclosure provides a method of controlling charging and discharging for a hybrid vehicle, wherein the hybrid vehicle includes a motor operated by power of a battery and an ISG configured to start an engine or generate electric power by torque of the engine, the method including: changing a running mode of the hybrid vehicle to a regenerative braking mode when the hybrid vehicle is coasting, controlling the motor to generate electric power in the regenerative braking mode, determining whether an SOC of the battery is a charge limiting state, and operating the ISG by electric power generated by the motor when the SOC of the battery is the charge limiting state.

The method further includes charging the battery with the electric power generated by the motor up to the charge limiting state when the SOC of the battery is not the charge limiting state of the battery, and then operating the ISG by the electric power generated by the motor when the SOC of the battery is the charge limiting state. The operating of the ISG by the electric power generated by the motor includes setting a speed of the ISG based on speed of the engine and a predetermined friction torque map related to operation of the engine. Further, an engine clutch configured to control power transmission between the engine and the motor is in an open state.

Another exemplary embodiment of the present disclosure provides a system for controlling charging and discharging for a hybrid vehicle, the system including: a motor configured to be operated by power of a battery, an ISG configured to start an engine or generate electric power by torque of the engine, an engine clutch configured to control power transmission between the engine and the motor, and a control unit configured to operate the ISG using electric power generated by the motor in a regenerative braking mode when the hybrid vehicle is coasting and the battery is in a charge limiting state.

The control unit may include: a coasting determination unit configured to determine whether the hybrid vehicle is in a coasting state based on a signal according to manipulation of an accelerator pedal and a brake pedal, a regenerative braking mode changing unit configured to change a running mode to a regenerative braking mode when the hybrid vehicle is in a coasting state, an SOC determination unit configured to determine an SOC of the battery, an ISG speed control unit configured to control speed of the ISG based on speed of the engine and a predetermined friction torque map related to operation of the engine, and a charging/discharging control unit configured to control charging and discharging based on signals from the coasting determination unit, the regenerative braking mode changing unit, the SOC determination unit, and the ISG speed control unit while the hybrid vehicle is coasting.

As described above, according to an exemplary embodiment of the present disclosure, it is possible to protect a battery and to enhance drivability by consuming regenerative electric power collected by a motor through regenerative braking while coasting when operating an ISG according to an SOC of a battery.

Reference numbers refer to the same or equivalent parts of the present disclosure throughout the figures. It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the disclosure. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes, will be determined in part by the particular intended application and use environment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Additionally, it is understood that the below methods are executed by at least one control unit. The term “control unit” refers to a hardware device that includes a memory and a processor. The memory is configured to store program instructions and the processor is specifically configured to execute said program instructions to perform one or more processes which are described further below.

FIG. 1is a diagram illustrating a typical hybrid vehicle to which a system for controlling charging and discharging while coasting according to an exemplary embodiment of the present disclosure may be applied. As shown inFIG. 1, the hybrid vehicle generally includes an engine10, a motor20, an engine clutch30, a transmission40, a differential gear unit50, a battery60, and an integrated starter-generator70. The engine clutch30controls power transmission between the engine10and the motor20, and the integrated starter-generator70starts the engine10or generates electric power by output of the engine10.

The hybrid vehicle to which the system for controlling the charging and the discharging while coasting according to the exemplary embodiment of the present invention can be applied further includes a hybrid control unit (HCU)200configured to control an overall operation of the hybrid electric vehicle, an engine control unit (ECU)110configured to control an operation of the engine10, a motor control unit (MCU)120configured to control an operation of the motor20, a transmission control unit (TCU)140configured to control an operation of the transmission40, and a battery control unit (BCU)160configured to manage and control the battery60.

FIG. 5is a configuration diagram of a system for controlling charging and discharging of a hybrid vehicle while coasting according to an exemplary embodiment of the present disclosure. Operationally, the system consumes regenerative electric power collected by a motor through regenerative braking of a hybrid vehicle while coasting when operating an ISG according to an SOC of a battery.

Illustratively, the system may include a motor20, an integrated starter-generator (ISG)70, an engine clutch30, and a control unit300. The motor20is operated by power of a battery60, the ISG70starts an engine10or generates electric power by torque of the engine10, and the engine clutch30controls connection between the engine10and the motor20. The control unit300controls the ISG70to be operated by electric power generated by the motor20in a regenerative braking mode while coasting according to an SOC of the battery when the hybrid vehicle is coasting and the SOC of the battery60is in a charge limiting state. The engine10, the motor20, the engine clutch30, the battery60, and the integrated starter-generator70are components generally included in the hybrid vehicle, so detailed descriptions thereof will be omitted in the present specification.

The control unit300may be made up of one or more processors or microprocessors and/or hardware operated by a program including a series of commands for executing a method of controlling charging and discharging of a hybrid vehicle while coasting according to an exemplary embodiment of the present disclosure, which will be described below. In the exemplary embodiment of the present disclosure, the control unit300may include an engine control unit (ECU) configured to control operation of the engine10, a motor control unit (MCU) configured to control operation of the motor20, a battery control unit (BCU) configured to manage and control the battery60, and a hybrid control unit (HCU) configured to control overall operation of the hybrid electric vehicle which includes operation of the ISG70.

In the exemplary method of controlling charging and discharging of a hybrid vehicle while coasting according to an exemplary embodiment of the present disclosure which will be described below, some processes may be performed by the ECU, other processes may be performed by the MCU, and yet further processes may be performed by the BCU or the HCU. However, it should be understood that the scope of the present disclosure is not limited to the exemplary embodiment to be described below. The control unit may be implemented with a different combination from that described in the exemplary embodiment of the present disclosure. Therefore, the ECU, the MCU, the BCU, and the HCU may perform a different combination of processes from that described in the exemplary embodiment of the present disclosure.

The control unit300may be made up of detailed constituent elements as shown inFIG. 6. The detailed constituent elements illustrated inFIG. 6may be configured with one or more modules implemented as hardware and/or software. The hardware may include electric/electronic components and/or microprocessors and/or microcomputers and the like.

Illustratively, the control unit300may include: a coasting determination unit320, a regenerative braking mode changing unit330, an SOC determination unit340, an ISG speed control unit350, and a charging/discharging control unit310. The coasting determination unit320determines whether the hybrid vehicle is in a coasting state, based on a signal according to manipulation of an accelerator pedal and a brake pedal. The regenerative braking mode changing unit330changes to a regenerative braking mode when the hybrid vehicle is in a coasting state. The SOC determination unit340determines an SOC of the battery60, and the ISG speed control unit350controls speed of the ISG based on speed of the engine10and a predetermined friction torque map related to operation of the engine10. The charging/discharging control unit310controls charging and discharging based on signals from the coasting determination unit320, the regenerative braking mode changing unit330, the SOC determination unit340, and the ISG speed control unit350while the hybrid vehicle is coasting.

In an exemplary embodiment of the present disclosure, for example, the coasting determination unit320may determine when both an accelerator pedal and a brake pedal are not manipulated by a driver, and thus conclude that the vehicle is coasting, but it should be understood that the present disclosure is not limited thereto. If the hybrid vehicle is substantially running by inertia, a technical spirit of the present disclosure is applicable thereto.

Hereinafter, a method of controlling charging and discharging of a hybrid vehicle while coasting according to an exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

In this regard,FIG. 7is an exemplary flowchart of a method of controlling charging and discharging of a hybrid vehicle while coasting according to an exemplary embodiment of the present disclosure. As illustrated inFIG. 7, the coasting determination unit320of the control unit300determines whether the hybrid vehicle is in coasting state (S110). The coasting, for example, may be when both an accelerator pedal and a brake pedal are not manipulated by a driver. When both the accelerator pedal and the brake pedal are not manipulated by the driver, the signal according to manipulation of the accelerator pedal and the brake pedal may not be generated. In step S110, when the hybrid vehicle is in the coasting state, the regenerative braking mode changing unit330of the control unit300changes the running mode to a regenerative braking mode (S120).

After changing to the regenerative braking mode, the control unit300may control the engine clutch30to be in an open state so that the regenerative braking may be properly implemented. In step130, after changing to the regenerative braking mode, the motor20starts to generate electric power according to the regenerative braking mode (S130).

Subsequently, the control unit300determines whether an SOC of the battery60is a charge limiting state before charging the battery60with the electric power generated by the motor (S140). The charge limiting state, for example, may be when the SOC of the battery60is 90% or above. In general, an SOC of 100% means that the battery is fully charged, and an SOC of 0% means that the battery is fully discharged. A process of determining whether the SOC of the battery60is the charge limiting state may depend on the process in which the BCU160, according to the related art, determines whether an SOC of a battery is a charge limiting state.

In step S140, when the SOC of the battery60is not in the state of limiting the charging of the battery60, the control unit300charges the battery60with the electric power generated by the motor20(S150). As the control unit300charges the battery60with the electric power generated by the motor20, the control unit300continuously monitors and determines whether the SOC of the battery60reaches the charge limiting state.

When the SOC of the battery60has reached the charge limiting state, the charging/discharging control unit310of the control unit300operates and controls the ISG70by electric power generated by the motor20so that the electric power generated by the motor20is consumed in the ISG70(S160). When the charging/discharging control unit310operates and controls the ISG70, the ISG speed control unit350of the control unit300controls a speed and/or torque of the ISG70so that the electric power generated by the motor20may be totally consumed in the ISG70.

The ISG speed control unit350may control the speed of the ISG70based on speed of the engine10and a predetermined friction torque map of the engine10stored in the ECU110. For example, when an SOC of the battery60is a charge limiting state and electric power generated by the motor20is 5 kW, the ISG speed control unit350controls speed of the ISG70so that 5 kW is totally consumed in the ISG70.

Accordingly, the method according to the exemplary embodiment of the present disclosure may consume regenerative electric power collected by the motor through regenerative braking while coasting when operating an ISG according to an SOC of a battery.

While this disclosure has been in connection with what is presently considered to be exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the accompanying claims.