Method for controlling mild hybrid vehicle

A method for controlling a mild hybrid vehicle may include determining, by a controller, whether an engine of the mild hybrid vehicle operates based on a demand torque of a driver of the mild hybrid vehicle; determining, by the controller, a torque of a starter-generator of the mild hybrid vehicle that assists a torque of the engine according to the demand torque of the driver based on a temperature of a turbocharger of the mild hybrid vehicle when the engine is operated; and operating, by the controller, the starter-generator to assist the torque of the engine based on the determined torque of the starter-generator.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2017-0174094 filed on Dec. 18, 2017, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a mild hybrid vehicle (or a mild hybrid electric vehicle), and more particularly, to a method for controlling a mild hybrid vehicle.

Description of Related Art

A hybrid electric vehicle utilizes both an internal combustion engine and a battery power source. The hybrid electric vehicle efficiently combines the torque of the internal combustion engine and the torque of a motor.

Hybrid electric vehicles may be categorized as either a hard type or a mild type according to a power sharing ratio between the engine and the motor. In the case of the mild type of hybrid electric vehicle (or a mild hybrid electric vehicle), a mild hybrid starter & generator (MHSG) configured to start the engine or generate electricity according to an output of the engine is used instead of an alternator. In the case of the hard type of hybrid electric vehicle, a driving motor configured for generating driving torque is used in addition to an integrated starter & generator (ISG) configured to start the engine or generate electricity.

The mild hybrid electric vehicle does not provide a driving mode in which torque of the MHSG is used for the main driving torque, but the MHSG may assist the torque of the engine according to the running state of the vehicle and may charge a battery (e.g., a 48 V battery) through regenerative braking. Accordingly, the fuel efficiency of the mild hybrid electric vehicle may be improved.

A vehicle may use a turbocharger to increase output of an engine without increasing volume of the engine. An exhaust gas rotates a turbine wheel of the turbocharger and a wheel of an air compressor connected to a shaft which is connected to the turbine wheel is rotated to provide a compressed air into the combustion chamber so that the turbocharger increases the output of the engine.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing a method for controlling a mild hybrid vehicle which is configured for maintaining or reducing fuel injection and assisting torque of an engine by operating a starter-generator when temperature of a turbocharger exceeds a reference value because of continuous fuel injection for operating the engine.

An exemplary embodiment of the present invention may provide the method for controlling the mild hybrid vehicle, including: determining, by a controller, whether an engine of the mild hybrid vehicle operates based on a demand torque of a driver of the mild hybrid vehicle; determining, by the controller, a torque of a starter-generator of the mild hybrid vehicle that assists a torque of the engine according to the demand torque of the driver based on a temperature of a turbocharger of the mild hybrid vehicle when the engine is operated; and operating, by the controller, the starter-generator to assist the torque of the engine based on the determined torque of the starter-generator.

The torque of the starter-generator may increase when the temperature of the turbocharger is increased.

The determining of the torque of the starter-generator may include: determining, by the controller, whether a state of charge (SOC) value of a battery that supplies electric power to the starter-generator exceeds a reference value after receiving the temperature of the turbocharger. The controller may be configured to determine the torque of the starter-generator when it is determined that the SOC value of the battery exceeds the reference value.

The controller may be configured to determine that the starter-generator does not assist the torque of the engine and may control the engine to generate a torque corresponding to the demand torque of the driver when it is determined that the SOC value of the battery is less than or equal to the reference value.

The controller may prohibit fuel injection for an operation of the engine to stop the operation of the engine when the temperature of the turbocharger exceeds a temperature at which the turbocharger is burned and it is determined that the SOC value of the battery is less than or equal to the reference value.

The method for controlling the mild hybrid vehicle may further include: confirming, by the controller, that a vehicle including the starter-generator is the mild hybrid vehicle when the controller receives a signal corresponding to a first controller area network identification from the starter-generator to which the first controller area network identification is assigned.

The method for controlling the mild hybrid vehicle may further include: confirming, by the controller, that the vehicle including the starter-generator is the mild hybrid vehicle including the turbocharger when the controller receives a signal corresponding to a second controller area network identification from the turbocharger to which the second controller area network identification is assigned.

The method for controlling the mild hybrid vehicle according to the exemplary embodiment of the present invention may not limit demand torque of the driver of the vehicle using the engine torque assist by the starter-generator when temperature of an exhaust gas excessively rises due to the engine operation in the vehicle including the starter-generator.

Furthermore, the exemplary embodiment of the present invention may prevent overheating of the exhaust gas in advance using the engine torque assist by the starter-generator which is performed from a time when a temperature rise in the turbocharger due to the exhaust gas is detected. When a temperature of the turbocharger exceeds a temperature at which the turbocharger is burnt or damaged due to the exhaust gas according to the engine operation, the exemplary embodiment of the present invention may satisfy the driver's demand torque by assisting the engine torque using a maximum output of the starter-generator.

DETAILED DESCRIPTION

In order to sufficiently understand the present invention and the object achieved by embodying the present invention, the accompanying drawings illustrating exemplary embodiments of the present invention and contents described in the accompanying drawings are to be referenced.

Hereinafter, the present invention will be described in detail by describing exemplary embodiments of the present invention with reference to the accompanying drawings. In describing the present invention, well-known configurations or functions will be omitted in detail since they may unnecessarily obscure the gist of the present invention. Throughout the accompanying drawings, the same reference numerals will be used to denote the same components.

Throughout this specification and the claims that follow, when it is described that an element is “coupled” to another element, the element may be “directly coupled” to the other element or “electrically or mechanically coupled” to the other element through a third element.

Unless defined otherwise, it is to be understood that the terms used in specification including technical and scientific terms have the same meanings as those that are generally understood by those skilled in the art. It must be understood that the terms defined by the dictionary are identical with the meanings within the context of the related art, and they should not be ideally or excessively formally defined unless the context clearly dictates otherwise.

A turbocharger is a system that utilizes an exhaust gas to drive a compressor and supercharges air into an intake port or an intake manifold, and is a device that requires high temperature thermal management. The exhaust gas may rotate an internal vane of the turbocharger to supply compressed air to an engine, which is a power source, but the turbocharger hardware may be burned out due to a high temperature exhaust gas.

A related art performs a torque limit of the engine when a temperature of the turbocharger exceeds a temperature upper limit so that an injection amount of fuel is further increased or a fuel amount is reduced to lower a temperature of the turbocharger. Therefore, even though a driver's demand torque is great, additional torque may not be increased to protect the turbocharger. In more detail, the related art may reduce the exhaust gas temperature by restricting the engine output to prevent the hardware burnout of the turbocharger when the temperature of the turbocharger excessively rises.

FIG. 1is a flowchart illustrating a method for controlling a mild hybrid vehicle according to an exemplary embodiment of the present invention.FIG. 2is a view for explaining a step of confirming whether a turbocharger is applied to the vehicle which is shown inFIG. 1.FIG. 3andFIG. 4are views illustrating a step of assisting an engine torque which is shown inFIG. 1.FIG. 5is a block diagram illustrating a mild hybrid vehicle to which the method for controlling the mild hybrid vehicle shown inFIG. 1is applied.

Referring toFIG. 1toFIG. 5, in a confirmation step105, a controller200may confirm or determine whether the vehicle is a mild hybrid vehicle. The controller200may be connected to a starter-generator (e.g., a mild hybrid starter and generator (MHSG))30via a controller area network (CAN) which is a vehicle network. Accordingly, when the controller80receives a signal corresponding to an inherent CAN identification (ID) from the starter-generator30to which the inherent CAN ID which is a first CAN ID is assigned, the controller80may confirm that the vehicle to be controlled is the mild hybrid vehicle.

The controller200may control an overall operation of the mild hybrid vehicle. For example, the controller200such as an engine control unit (ECU) may be one or more microprocessors operated by a program or hardware including the microprocessor. The program may include a series of commands for executing the method for controlling the mild hybrid vehicle according to the exemplary embodiment of the present invention. The commands may be stored in a memory.

The mild hybrid vehicle includes an engine205, a transmission20, the starter-generator (or a mild hybrid starter and generator)30, a battery40, a differential gear device50, wheels60, the controller200, and the turbocharger shown inFIG. 2.

The engine205may convert chemical energy to mechanical energy by combusting fuel and air. Torque of the engine205may be transmitted to an input shaft of the transmission20, and a torque output from an output shaft of the transmission may be transmitted to an axle of the vehicle via the differential gear device50. The axle may rotate the wheels60so that the mild hybrid vehicle may be driven.

The starter-generator30may convert electrical energy to mechanical energy or mechanical energy to electrical energy. In other words, the starter-generator30may start the engine205or generate electricity according to an output of the engine205. Furthermore, the starter-generator30may assist the torque of the engine205. The mild hybrid vehicle may use the torque of the starter-generator30as an auxiliary power while combustion torque of the engine205is a main power. The engine205and the starter-generator30may be connected via the belt32(or a pulley and a belt).

In the mild hybrid vehicle, the starter-generator30may be a portion performing functions of an alternator, the engine torque assist, or regenerative braking.

The starter-generator30may drive the engine205of the vehicle in a cranking and a torque control mode of the vehicle (or the engine) and may generate electricity according to an output of the engine to charge the 48 V battery40using an inverter in an electricity generation mode of the vehicle. The starter-generator30may operate in an operating mode in accordance with a driving state of the vehicle. The operating mode may include an engine starting mode, an engine torque assist mode for assisting torque of the engine by operating as a motor, a mode for charging the 48 V battery charging the 12 V battery which is connected to the 48 V battery via the LDC, a regenerative braking mode for charging the 48 V battery, or an inertial driving mode for extending a mileage of the vehicle. The starter-generator30may be optimally controlled according to the driving state of the vehicle to increase fuel efficiency of the vehicle.

The battery40may supply electricity to the starter-generator30or may be charged by electricity collected through the starter-generator30in a regenerative braking mode of the vehicle. The battery40may be a 48 V battery. The mild hybrid vehicle may further include a low voltage DC-DC converter (LDC) that converts voltage supplied from the battery40to a low voltage and a 12 V battery that supplies the low voltage to an electric load of the vehicle.

According to a confirmation step110, the controller200may confirm or determine whether the turbocharger shown inFIG. 2is disposed in the vehicle. InFIG. 2, a reference numeral34indicates a camshaft included in an auxiliary machinery of the engine205and a reference numeral36indicates a crankshaft included in the auxiliary machinery of the engine.

The controller200may be connected to the turbocharger via the CAN. Accordingly, when the controller80receives a signal corresponding to an inherent CAN ID from the turbocharger to which the inherent CAN ID which is a second CAN ID is assigned, the controller80may confirm that the vehicle to be controlled is the mild hybrid vehicle including the turbocharger.

In another exemplary embodiment of the present invention, the confirmation step105and the confirmation step110may be omitted.

According to a determination step115, the controller200may determine whether the engine205of the mild hybrid vehicle operates or runs according to a demand torque of a driver of the mild hybrid vehicle. For example, whether the engine205is operated may be detected by an engine operation sensor disposed in the engine and may be provided to the controller200.

According to a step120, the controller200may recognize or receive a temperature of the turbocharger when it is determined that the engine205is operated in the determination step115. For example, the temperature of the turbocharger may be detected by a temperature sensor disposed in the turbocharger and may be provided to the controller200.

According to a step125, the controller200may confirm that the temperature of the turbocharger is equal to or greater than a first temperature Temp1and equal to or less than a second temperature Temp2due to an exhaust gas according to the engine operation. For example, as shown inFIG. 3andFIG. 4, a range between the first temperature Temp1and the second temperature Temp2may correspond to a temperature range when the engine205takes charge of 90% of the driver's demand torque and the starter-generator30takes charge of 10% of the driver's demand torque. The range between the first temperature Temp1and the second temperature Temp2may be determined by a test to be stored in a memory.

According to a determination step145, the controller200may determine whether a state of charge (SOC) value of the battery40that supplies electric power to the starter-generator30exceeds a reference value after receiving the temperature of the turbocharger.

According to a step150, when it is determined that the SOC value of the battery40is equal to or less than the reference value, the controller200may determine that the starter-generator30does not assist a torque of the engine205and may control or adjust the torque of the engine to satisfy the required torque of the driver.

According to a step155, when it is determined that the SOC value of the battery40exceeds the reference value, the controller200may determine a torque of the starter-generator30for assisting a torque of the engine205according to the driver's demand torque, and the controller200may operate the starter-generator30to assist the torque of the engine205based on the determined torque of the starter-generator.

According to a step130, the controller200may confirm that the temperature of the turbocharger is equal to or greater than the second temperature Temp2and equal to or less than a third temperature Temp3due to an exhaust gas according to the engine operation. For example, as shown inFIG. 3andFIG. 4, a range between the second temperature Temp2and the third temperature Temp3may correspond to a temperature range when the engine205takes charge of 70% to 90% of the driver's demand torque and the starter-generator30takes charge of 10% to 30% of the driver's demand torque. The range between the second temperature Temp2and the third temperature Temp3may be determined by a test to be stored in the memory.

According to a determination step160, the controller200may determine whether a state of charge (SOC) value of the battery40that supplies electric power to the starter-generator30exceeds the reference value after receiving the temperature of the turbocharger.

According to a step165, when it is determined that the SOC value of the battery40is equal to or less than the reference value, the controller200may determine that the starter-generator30does not assist a torque of the engine205and may control or adjust the torque of the engine to satisfy the required torque of the driver.

According to a step170, when it is determined that the SOC value of the battery40exceeds the reference value, the controller200may determine a torque of the starter-generator30for assisting a torque of the engine205according to the driver's demand torque, and the controller200may operate the starter-generator30to assist the torque of the engine205based on the determined torque of the starter-generator.

According to a step135, the controller200may confirm that the temperature of the turbocharger is equal to or greater than the third temperature Temp3and equal to or less than a turbocharger hardware protection temperature Tmax due to an exhaust gas according to the engine operation. The turbocharger hardware protection temperature Tmax may refer to a temperature at which the turbocharger is overheated by an exhaust gas according to the engine operation so that the turbocharger is be burned (or damaged). For example, as shown inFIG. 3andFIG. 4, a range between the third temperature Temp3and the turbocharger hardware protection temperature Tmax may correspond to a temperature range when the engine205takes charge of 40% to 70% of the driver's demand torque and the starter-generator30takes charge of 30% to 60% of the driver's demand torque. The range between the third temperature Temp3and the turbocharger hardware protection temperature Tmax may be determined by a test to be stored in the memory.

According to a determination step175, the controller200may determine whether a state of charge (SOC) value of the battery40exceeds the reference value after receiving the temperature of the turbocharger.

According to a step180, when it is determined that the SOC value of the battery40is equal to or less than the reference value, the controller200may determine that the starter-generator30does not assist a torque of the engine205and may control or adjust the torque of the engine to satisfy the required torque of the driver.

According to a step185, when it is determined that the SOC value of the battery40exceeds the reference value, the controller200may determine a torque of the starter-generator30for assisting a torque of the engine205according to the driver's demand torque, and the controller200may operate the starter-generator30to assist the torque of the engine205based on the determined torque of the starter-generator.

According to a step140, the controller200may confirm that the temperature of the turbocharger exceeds the turbocharger hardware protection temperature Tmax due to an exhaust gas according to the engine operation. For example, as shown inFIG. 3andFIG. 4, a range of temperatures exceeding the turbocharger hardware protection temperature Tmax may correspond to a temperature range when the engine205takes charge of 0% of the driver's demand torque (i.e., the engine205is not responsible for the driver's demand torque) and the starter-generator30takes charge of 100% of the driver's demand torque. The range of temperatures exceeding the turbocharger hardware protection temperature Tmax may be determined by a test to be stored in the memory.

According to a determination step190, the controller200may determine whether a state of charge (SOC) value of the battery40exceeds the reference value after receiving the temperature of the turbocharger.

According to a step192, when it is determined that the SOC value of the battery40is less than or equal to the reference value, the controller200may determine that the starter-generator30does not assist the torque of the engine205so that the controller is configured to prohibit fuel injection for operating the engine to stop an operation of the engine.

In another exemplary embodiment of the step192, the controller200may determine that the starter-generator30does not assist a torque of the engine205so that the controller limits an injection amount of fuel for operation of the engine to prevent temperature rise of the turbocharger.

According to a step194, when it is determined that the SOC value of the battery40exceeds the reference value, the controller200may determine a torque (e.g., a maximum torque) of the starter-generator30for assisting a torque of the engine205according to the driver's demand torque, and the controller200may operate the starter-generator30to assist the torque of the engine205based on the determined torque of the starter-generator.

Referring toFIG. 3andFIG. 4, when a temperature of the turbocharger is increased, a torque of the starter-generator30may increase.

The components, “˜unit”, block, or module which are used in the present exemplary embodiment of the present invention may be implemented in software such as a task, a class, a subroutine, a process, an object, an execution thread, or a program which is performed in a predetermined region in the memory, or hardware such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), and may be performed with a combination of the software and the hardware. The components, ‘˜part’, or the like may be embedded in a computer-readable storage medium, and some part thereof may be dispersedly distributed in a plurality of computers.