Engine start controller for hybrid electric vehicle and method therefor

An engine start controller for a hybrid vehicle and a method thereof are provided. The engine start controller includes a hybrid starter generator (HSG) that is connected to an engine by a belt, a sensor that is configured to measure an HSG speed, and a processor that applies a starting torque to the HSG. When starting the engine, the processor calculates an HSG speed estimated based on the applied starting torque and calculates an amount of slip of the belt using the HSG speed. In addition, the processor calculates a torque change rate correction value based on the calculated amount of slip, and corrects a rate of change rate in the starting torque based on the torque change rate correction value.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean Patent Application No. 10-2020-0175699, filed on Dec. 15, 2020, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an engine start controller for a hybrid electric vehicle and a method therefor.

BACKGROUND

An engine start device may play a role in starting the engine of the vehicle to rotate the engine of the vehicle. Such an engine start device may include a starter motor and a generator. The starter motor may be used to start the engine in the internal combustion engine vehicle. When the starter motor is connected with the engine by the gear, a problem due to the slip does not occur when starting the engine. The generator may play a role in producing electrical energy to charge the battery. The generator is connected to the crankshaft to deliver electric power in the form of being directly connected with the engine.

Furthermore, since the generator and the engine are directly connected with each other, a problem due to the slip does not occur when starting the engine. Herein, as the generator is directly connected with the engine, there is a disadvantage in which a substantial amount of space is required upon packaging. To solve such a disadvantage, a structure of connecting the generator with the engine using a belt is proposed. In the structure of connecting the engine with the generator by the belt, noise and vibration may occur due to the generation of a revolutions per minute (RPM) difference between the engine and the generator, that is, a slip, a slip may excessively occur since the friction of the belt is varied according to environment conditions, and durability of the belt may be degraded.

SUMMARY

The present disclosure has been made to solve the above-mentioned problems occurring in the prior art while advantages achieved by the prior art are maintained intact. An aspect of the present disclosure provides an engine start controller for a hybrid electric vehicle for actively limiting a rate of change in starting torque of a hybrid starter generator (HSG) in a situation where a belt which connects the engine with the HSG is slipped and minimizing the slip of the belt to provide stable starting performance and a method therefor.

According to an aspect of the present disclosure, an apparatus for controlling engine starting of a hybrid electric vehicle may include a hybrid starter generator (HSG) connected to an engine by a belt, a sensor configured to measure an HSG speed, and a processor configured to apply a starting torque to the HSG, when starting the engine, calculate an HSG speed estimated based on the applied starting torque and calculate an amount of slip of the belt using the HSG speed, calculate a torque change rate correction value based on the calculated amount of slip, and correct a rate of change in the starting torque based on the torque change rate correction value.

The processor may be configured to estimate the HSG speed according to the applied starting torque based on a nominal model. The processor may be configured to calculate the estimated HSG speed using a state observer. Additionally, the processor may be configured to calculate the torque change rate correction value in a form where the larger the amount of slip, the more limited the torque rate of change. The processor may be configured to calculate the torque change rate correction value in a form where the smaller the amount of slip, the less limited the torque rate of change. The processor may be configured to limit the rate of change in the starting torque such that the larger the amount of slip, the smaller the change in the starting torque. The processor may also be configured to limit the rate of change in the starting torque such that the smaller the amount of slip, the larger the change in the starting torque.

According to another aspect of the present disclosure, a method for controlling engine starting of a hybrid electric vehicle may include applying a starting torque to an HSG connected with an engine by a belt, when starting the engine, calculating an HSG speed estimated based on the applied starting torque after applying the stating torque to the HSG and calculating an amount of slip of the belt using the HSG speed, calculating a torque change rate correction value based on the amount of the slip, and adjusting a rate of change in the starting torque based on the torque change rate correction value. The calculating of the amount of slip of the belt may include estimating the HSG speed according to the applied starting torque based on a nominal model. The calculating of the amount of slip of the belt may include calculating the estimated HSG speed using a state observer.

The calculating of the torque change rate correction value may include calculating the torque change rate correction value in a form where the larger the amount of slip, the more limited the torque rate of change and calculating the torque change rate correction value in a form where the smaller the amount of slip, the less limited the torque rate of change. The adjusting of the rate of change in the starting torque may include limiting the rate of change rate in the starting torque such that the larger the amount of slip, the smaller the change in the starting torque and limiting the rate of change in the starting torque such that the smaller the amount of slip, the larger the change in the starting torque.

DETAILED DESCRIPTION

FIG.1is a drawing illustrating a configuration of a hybrid electric vehicle associated with the present disclosure. The hybrid electric vehicle (HEV) is a vehicle which uses two or more different driving sources, which generally refers to a vehicle driven by an engine which burn fuel to generate a driving force and a motor which generates a driving force using electrical energy of its battery.

Referring toFIG.1, the HEV may include an engine10, a hybrid starter generator (HSG)20, an engine clutch30, a motor40, a transmission50, and an inverter60. The engine10may burn fuel to generate electric power (an engine torque) necessary to drive the vehicle. Various well-known engines such as a gasoline engine or a diesel engine may be used as the engine10. The engine10may control an output torque (i.e., an engine torque) under a command of an engine management system (EMS).

The HSG20may be connected with the engine10by a belt. The HSG20may crank the engine10to start the engine10. The HSG20may play a role in starting the engine10when an electric vehicle mode switches to a hybrid mode. The HSG20may operate as a generator which generates electrical energy using electric power of the engine10in the state where the engine10is started. The electrical energy generated by the HSG20may be used to charge a battery B. The HSG20and the engine10may be collectively referred to as a plant G. The engine clutch30may be disposed between the engine10and the motor40to turn on/off an electric power (an output torque) of the engine10. The engine clutch30may transmit or block an electric power (an engine torque) generated by the engine10to drive wheels (vehicle wheels) by being engaged or disengaged.

The motor40may be configured to receive power from the inverter60to generate electric power (motor electric power) and transmit the electric power to drive wheels. The motor40may be configured to change a rotation direction and a revolution per minute (RPM) under an instruction of a motor control unit (MCU) to adjust an output torque (a motor torque) of the motor40. The motor40may be used as a generator which generates a back electromotive force when a state of charge (SOC) is insufficient or upon regenerative braking and charges the battery B. The battery B may play a role in supplying power necessary for driving of the vehicle, which may be implemented as a high-voltage battery. The battery B may be charged by regenerative energy generated by the motor40.

The transmission50may be configured to convert the motor torque or the engine torque and the motor torque into a transmission ratio matched to a transmission stage (a gear stage). The transmission50may be configured to change a transmission stage under an instruction of a transmission control unit (TCU). The TCU may be configured to determine an optimum transmission stage based on information such as a driving speed of the vehicle (i.e., a vehicle speed or a wheel speed), a location of an accelerator pedal, an engine RPM, and/or a clutch travel by sensors in the vehicle.

The inverter60may be a power converter disposed between the motor40and the battery B, and configured to convert power output from the battery B into a motor drive power to supply the motor drive power to the motor40. For example, the inverter60may be configured to convert a direct current (DC) voltage output from the battery B into a 3-phase alternating current (AC) voltage necessary to drive the motor40. The inverter60may be configured to adjust power (e.g., an output voltage) supplied to the motor40under an instruction of a motor control unit (MCU) to adjust a motor torque. The present embodiment is exemplified as the inverter60is disposed between the motor40and the battery B, but not limited thereto. When the motor40applied to the vehicle is a DC motor, a converter may be disposed between the motor40and the battery B or the motor40and the battery B may be directly connected to each other without using the power converter.

FIG.2is a block diagram illustrating a configuration of an engine start controller for a hybrid electric vehicle according to embodiments of the present disclosure. Referring toFIG.2, an engine start controller100may include a start and stop (start/stop) button110, a hybrid control unit (HCU)120, a sensor130, a storage140, and a processor150. The processor150may be connected with the start/stop button110, the HCU120, and the sensor130over a vehicle network. The vehicle network may be implemented as a controller area network (CAN), a media oriented systems transport (MOST) network, a local interconnect network (LIN), an Ethernet, an X-by-Wire (Flexray), and/or the like.

The start/stop button110may be configured to generate a command to turn on the power of the vehicle, a command to start the engine (turn on the engine), a command to stop the engine (turn off the engine), or the like depending on manipulation of the user. For example, the start/stop button110may be configured to generate a vehicle power on signal, when the user pushes or otherwise engages the start/stop button110once, generate an engine start signal, when the user pushes the start/stop button110once again, and generate an engine stop signal, when the user pushes the start/stop button110while adjusting the shift lever into the P stage. The present embodiment is exemplified as the start/stop button110is implemented as a push button, but not limited thereto. The start/stop button110may be implemented as a pull button, a toggle switch, a rotary switch, a touch button, and/or the like.

The HCU120may be configured to recognize or detect a driving environment using sensors (e.g., a speed sensor, a shift lever position sensor, and the like) loaded into the vehicle. The HCU120may be configured to operate an engine10, an HSG20, an engine clutch30, a motor40, a transmission50, an inverter60, and a battery B ofFIG.1based on the driving environment of the vehicle. The HCU120may be configured to transmit a command to start or stop the engine10to the processor150based on the driving environment of the vehicle. When the vehicle meets an engine start condition in an engine stop state, the HCU120may be configured to transmit an engine start command to the processor150. When the vehicle meets an engine stop condition in an engine run state, the HCU120may be configured to transmit an engine stop command to the processor150. For example, the HCU120may be configured to transmit an engine start command, when a vehicle driving mode switches from an electric vehicle (EV) mode to a hybrid electric vehicle (HEV) mode, and may be configured to transmit an engine stop command, when the vehicle driving mode switches from the HEV mode to the EV mode. Such an HCU120may include at least one processor, a memory, and a network interface.

The sensor130may be configured to measure an angular velocity (a rotational velocity) of the HSG20. The sensor130may be implemented as an angular velocity sensor, a rotary angle sensor, and/or the like. The sensor130may be configured to deliver the measured angular velocity (i.e., an HSG speed) to the processor150. The memory140may be a non-transitory storage medium which stores instructions executed by the processor150. The memory140may be implemented as at least one of storage media (recording media) such as a flash memory, a hard disk, a solid state disk (SSD), a secure digital (SD) card, a random access memory (RAM), a static RAM (SRAM), a read only memory (ROM), a programmable ROM (PROM), an electrically erasable and programmable ROM (EEPROM), an erasable and programmable ROM (EPROM), and/or a register.

The processor150may perform the overall control of the engine start controller100. The processor150may be implemented as at least one of processing devices such as an application specific integrated circuit (ASIC), a digital signal processor (DSP), programmable logic devices (PLD), field programmable gate arrays (FPGAs), a central processing unit (CPU), microcontrollers, and/or microprocessors. The processor150may be configured to receive an engine start command or an engine stop command from the start/stop button110or the HCU120. In response to receiving the engine start command, the processor150may be configured to set a target starting torque of the HSG20for increasing an engine speed before engine fuel injection and may command (instruct) the HSG20to generate the target starting torque. The processor150may be configured to compare the set target starting torque with a real output torque of the HSG20and may be configured to adjust a starting torque of the HSG20depending on the compared result. In other words, the processor150may be configured to determine a starting torque of the HSG20(an HSG starting torque) such that the real output torque of the HSG20follows the set target starting torque.

The processor150may be configured to operate a motor of the HSG20based on a reference torque rate of change stored in the memory140, when the engine10starts. The reference torque rate of change may be set as a default in advance by a system designer, which may be defined as a starting torque over time. The processor150may be configured to measure an angular velocity (an HSG speed) of the HSG20using the sensor130after an HSG starting torque command. When applying the starting torque to the HSG20, the processor150may be configured to estimate an HSG speed according to the applied starting torque based on a nominal model.

The processor150may be configured to compare the estimated HSG speed with the HSG speed measured by the sensor130to detect that a slip (disturbance) is generated. The processor150may be configured to calculate a difference between the estimated HSG speed and the measured HSG speed to calculate an amount of slip. Additionally, the processor150may be configured to variably (actively) adjust an increasing rate of change in starting torque based on the calculated amount of slip. The processor150may be configured to calculate a torque change rate correction value of the HSG20based on the calculated amount of slip. The processor150may be configured to calculate a slew rate of the starting torque such that the previously calculated starting torque varies with the torque change rate correction value.

Hereinafter, a description will be given of a slip detection process and a control torque calculation process with reference toFIGS.3to6B.

FIG.3is a functional block diagram illustrating an engine start controller according to embodiments of the present disclosure.FIG.4is a drawing illustrating an equivalent circuit of an engine and an HSG according to embodiments of the present disclosure.FIG.5is a drawing illustrating a configuration of a state observer according to embodiments of the present disclosure.FIG.6Ais a graph illustrating an increasing rate of change according to an amount of slip associated with the present disclosure.FIG.6Bis a graph illustrating a change in starting torque according to an amount of slip associated with the present disclosure.

An engine start controller100may include a plant (G)115, a slip sensor310, a compensator320, and a limiter330. The plant (G)115may be represented as an engine10and an HSG20which are connected by a belt. When the engine10starts, the HSG20may be configured to generate a torque under a command of the engine start controller100to increase revolutions per minute (RPM) of the engine10. The engine start controller100may be configured to generally apply a maximum torque to the HSG20to increase the RPM of the engine10to specific RPM.

The slip sensor310may be configured to detect a slip of the belt which connects the engine10with the HSG20using a starting torque (a final starting torque) and an angular velocity (an HSG speed) of the HSG20, which are input to the plant (G)115. The slip sensor310may be configured to calculate an amount of slip of the belt based on a nominal model Gn. To calculate the amount of slip, the slip sensor310may be configured to derive the nominal model Gn indicating a target behavior (a reference behavior) of the plant (G)115. An equivalent circuit of the plant (G)115may be represented asFIG.3. K in the equivalent circuit shown inFIG.4is a spring constant in a mass damper spring model, which may be used to derive a nominal model using a system which has only inertia assuming that it is infinite. In the equivalent circuit, Th, dh, and θhrespectively denote the output torque (HSG torque), the disturbance, and the rotary angle of the HST20, Te, de, and θerespectively denote the output torque (engine torque), the disturbance, and the rotary angle of the engine10, and R denotes the ratio of the RPM Nhof the pulley at the HSG20to the RPM Neof the pulley at the engine10, that is, the pulley ratio between the engine10and the HSG20.

An inertia moment of the nominal model may be represented as Equation 1 below.
eq=h+e/R2(1−λ)  Equation 1

Herein, Jhdenotes the inertia moment of the HSG20, Jedenotes the inertial moment of the engine10, and λ denotes the slip ratio.

Since the slip ratio λ should be minimized, when substituting λ=0 into Equation 1 above, the inertia moment Jeqof the nominal model may be represented as Equation 2 below.
eq=h+e/R2Equation 2

The slip sensor310may be configured to estimate an angular velocity (an HSG speed) of the HSG20using the nominal model. In other words, the slip sensor310may be configured to calculate an HSG speed according to a starting torque u of the HSG20, that is, a nominal model speed {circumflex over (ω)} based on the nominal model. In particular, the slip sensor310may be configured to calculate a nominal model speed using a state observer shown inFIG.5.

The state observer may be configured to receive the starting torque u and the HSG speed ω measured by the sensor130. The state observer may be configured to calculate the angular velocity Jeq{dot over (ω)} of the HSG20according to the starting torque u (=Jeq{dot over (ω)}) of the HSG20using the nominal model. In other words, the state observer may be configured to obtain the angular velocity Jeq{dot over (ω)} by multiplying the starting torque u by 1/Jeq.

The state observer may be configured to calculate a difference between the measured HSG speed ω and the estimated HSG speed {circumflex over (ω)}, that is, the amount of slip e(=ω−{circumflex over (ω)}). The state observer may be configured to correct the amount of slip e by reflecting the correction gain L in the amount of slip e. The state observer may be configured to calculate the angular speed Jeq{dot over (ω)} and the corrected amount of slip to calculate the angular velocity {circumflex over ({dot over (ω)})} in which the corrected amount of slip is reflected. In other words, the state observer may be configured to estimate the angular velocity of the HSG20according to the starting torque u. The state observer may be configured to integrate the estimated angular velocity to calculate the HSG speed {circumflex over (ω)}.

Further, the compensator320may be configured to limit a rate of change in starting torque to limit the amount of slip (disturbance) detected by the slip sensor310. The compensator320may be configured to calculate a change rate correction value of the starting torque (e.g., a torque change rate correction value) based on the amount of slip calculated by the slip sensor310. In other words, the compensator320may be configured to correct a predetermined starting torque change rate based on the amount of slip to obtain the torque change rate correction value. At this time, the compensator320may be configured to calculate the torque change rate correction value in a form where the larger the amount of slip, the more limited the rate of change in starting torque. Furthermore, the compensator320may be configured to calculate the torque change rate correction value in a form where the smaller the amount of slip, the less limited the rate of change in starting torque. For example, as shown inFIG.6A, the larger the amount of slip, the smaller the compensator320may set an increasing rate of change in starting torque to be, and the smaller the amount of slip, the larger the compensator320may set the increasing rate of change in starting torque to be.

The limiter330may be configured to limit a slew rate such that the previously calculated starting torque varies with the torque change rate correction value. The limiter330may be configured to limit an increasing rate of change in starting torque based on the torque change rate correction value. Referring toFIG.6B, the limiter330may be configured to determine a starting torque such that the larger the amount of slip, the smaller the change in starting torque, and may be configured to determine a starting torque such that the smaller the amount of slip, the larger the change in starting torque.

FIG.7is a flowchart illustrating an engine start method according to embodiments of the present disclosure. Referring toFIG.7, in S110, a processor150ofFIG.2may apply a starting torque to an HSG20ofFIG.1to start an engine10ofFIG.1. The processor150may determine an HSG starting torque to increase RPM of the engine10.

After applying the starting torque, in S120, the processor150may be configured to calculate an amount of slip based on a nominal model. The processor150may be configured to obtain RPM (an HSG speed) of the HSG20using a sensor130ofFIG.2. The processor150may be configured to estimate an HSG speed according to the starting torque based on the nominal model. The processor150may be configured to calculate a difference between a real HSG speed and the estimated HSG speed to calculate the amount of slip.

In S130, the processor150may be configured to calculate a torque change rate correction value based on the calculated amount of slip. The processor150may be configured to calculate the torque change rate correction value in a form where the larger the amount of slip, the more limited the rate of change in starting torque, and calculate the torque change rate correction value in a form where the smaller the amount of slip, the less limited the rate of change in starting torque.

In S140, the processor150may be configured to adjust the starting torque based on the torque change rate correction value. The processor150may be configured to limit a rate of change in starting torque based on the torque change rate correction value. The processor150may be configured to calculate a starting torque (e.g., an HSG starting torque), the torque rate of change of which is limited based on the torque change rate correction value. The processor150may be configured to command the HSG20to generate the HSG starting torque. The HSG20may be configured to adjust an HSG torque under a command of the processor150.

FIG.8is a drawing illustrating a change in belt slip according to a limit to a rate of change in HSG starting torque according to embodiments of the present disclosure. Referring toFIG.8, since the amount of slip is calculated in a situation where a slip of a belt which connects an engine10ofFIG.1with an HSG20ofFIG.1may be detected and since a rate of change in starting torque of the HSG20is limited based on the calculated amount of slip, the slip of the belt may be reduced. Thus, as the slip of the belt is reduced, performance of controlling the engine10and the HSG20may be improved in terms of noise, vibration, harshness (NVH), belt durability, and energy reduction.

Embodiments of the present disclosure may actively limit a rate of change in starting torque of the HSG in a situation where the belt which connects the engine with the HSG is slipped to minimize the slip of the belt, thus providing stable starting performance. Furthermore, embodiments of the present disclosure may variably control a rate of change in starting torque of the HSG based on the amount of slip of the belt to reduce the slip of the belt, thus reducing noise and vibration generated due to the slip of the belt and ensuring durability of the belt.

Hereinabove, although the present disclosure has been described with reference to exemplary embodiments and the accompanying drawings, the present disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present disclosure pertains without departing from the spirit and scope of the present disclosure claimed in the following claims. Therefore, the exemplary embodiments of the present disclosure are provided to explain the spirit and scope of the present disclosure, but not to limit them, so that the spirit and scope of the present disclosure is not limited by the embodiments. The scope of the present disclosure should be construed on the basis of the accompanying claims, and all the technical ideas within the scope equivalent to the claims should be included in the scope of the present disclosure.