Motor torque control method in coasting state of hybrid electric vehicle

Abstract

A method of controlling motor torque in coasting of a vehicle includes: acquiring information about a speed of an input shaft of a transmission detected by a detector while the vehicle is running, information about an acceleration of the input shaft of the transmission obtained from the speed of the input shaft of the transmission, and information about a state of an engine clutch; determining whether the vehicle is coasting based on the acquired information; calculating a motor torque instruction based on engine friction torque corresponding to the speed of the input shaft of the transmission, a rotary inertia of an engine, and the acceleration of the input shaft of the transmission, when the vehicle is determined to be coasting with the engine clutch disengaged; and controlling torque of a driving motor for driving the vehicle in accordance with the calculated motor torque instruction.

Claims

1. A method of controlling motor torque during coasting of a vehicle, the method comprising: acquiring, by a controller including a memory and a processor, information about a speed of an input shaft of a transmission detected by a detector while the vehicle is running, information about an acceleration of the input shaft of the transmission obtained from the speed of the input shaft of the transmission, and information about a state of an engine clutch; determining, by the controller, whether the vehicle is coasting based on the acquired information; calculating, by the controller, a motor torque instruction based on engine friction torque corresponding to the speed of the input shaft of the transmission, a rotary inertia of an engine, and the acceleration of the input shaft of the transmission, when the vehicle is determined to be coasting with the engine clutch disengaged; and controlling, by the controller, torque of a driving motor for driving the vehicle in accordance with the calculated motor torque instruction, wherein the motor torque instruction derives from an equation, as follows: motor torque instruction=engine friction torque(rotary inertia of engineacceleration of input shaft of transmission).

2. The method of claim 1, wherein the engine friction torque is determined by the controller as a value corresponding to the speed of the input shaft of the transmission from a map.

3. The method of claim 1, wherein when the vehicle is coasting with the engine clutch engaged, the motor torque instruction is calculated by the controller as zero, and zero-torque control is performed on the driving motor.

4. The method of claim 1, wherein it is determined by the controller whether an accelerator pedal is being operated based on information about operation of the accelerator pedal detected by an accelerator pedal detector, and when the speed of the input shaft of the transmission is greater than a predetermined value, it is determined by the controller that the vehicle is coasting.

5. A method of controlling motor torque during coasting of a vehicle, the method comprising: acquiring, by a controller including a memory and a processor, information about a speed of an input shaft of a transmission detected by a detector while the vehicle is running, information about an acceleration of the input shaft of the transmission obtained from the speed of the input shaft of the transmission, and information about a state of an engine clutch; determining, by the controller, whether the vehicle is coasting based on the acquired information; calculating, by the controller, a motor torque instruction based on a rotary inertia of an engine and the acceleration of the input shaft of the transmission, when the vehicle is determined to be coasting with the engine clutch engaged; and controlling, by the controller, torque of a driving motor for driving the vehicle in accordance with the calculated motor torque instruction, wherein the motor torque instruction derives from an equation, as follows: motor torque instruction=rotary inertia of engineacceleration of input shaft of transmission.

6. The method of claim 5, wherein when the vehicle is coasting with the engine clutch disengaged, the motor torque instruction is calculated by the controller as equal to engine friction torque corresponding to the speed of the input shaft of the transmission.

7. The method of claim 6, wherein the engine friction torque is determined by the controller as a value corresponding to the speed of the input shaft of the transmission from a map.

8. The method of claim 5, wherein it is determined by the controller whether an accelerator pedal is being operated based on information about operation of the accelerator pedal detected by an accelerator pedal detector, and when the speed of the input shaft of the transmission is greater than a predetermined value, it is determined by the controller that the vehicle is coasting.

9. A non-transitory computer readable medium containing program instructions executable by a controller including a memory and a processor for controlling motor torque during coasting of a vehicle, the computer readable medium comprising: program instructions that acquire information about a speed of an input shaft of a transmission detected by a detector while the vehicle is running, information about an acceleration of the input shaft of the transmission obtained from the speed of the input shaft of the transmission, and information about a state of an engine clutch; program instructions that determine whether the vehicle is coasting based on the acquired information; program instructions that calculate a motor torque instruction based on engine friction torque corresponding to the speed of the input shaft of the transmission, a rotary inertia of an engine, and the acceleration of the input shaft of the transmission, when the vehicle is determined to be coasting with the engine clutch disengaged; and program instructions that control torque of a driving motor for driving the vehicle in accordance with the calculated motor torque instruction, wherein the motor torque instruction derives from an equation, as follows: motor torque instruction=engine friction torque(rotary inertia of engineacceleration of input shaft of transmission).

10. A non-transitory computer readable medium containing program instructions executable by a controller including a memory and a processor for controlling motor torque during coasting of a vehicle, the computer readable medium comprising: program instructions that acquire information about a speed of an input shaft of a transmission detected by a detector while the vehicle is running, information about an acceleration of the input shaft of the transmission obtained from the speed of the input shaft of the transmission, and information about a state of an engine clutch; program instructions that determine whether the vehicle is coasting based on the acquired information; program instructions that calculate a motor torque instruction based on a rotary inertia of an engine and the acceleration of the input shaft of the transmission, when the vehicle is determined to be coasting with the engine clutch engaged; and program instructions that control torque of a driving motor for driving the vehicle in accordance with the calculated motor torque instruction, wherein the motor torque instruction derives from an equation, as follows: motor torque instruction=rotary inertia of engineacceleration of input shaft of transmission.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present disclosure will now be described in detail with reference to embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present disclosure, wherein:

(2) FIG. 1 is a schematic diagram showing the configuration of a power train of a common hybrid electric vehicle using an engine and a motor as driving sources;

(3) FIG. 2 is a diagram showing characteristics of creep torque and coasting torque of a common hybrid electric vehicle;

(4) FIG. 3 is a diagram showing a state when a coasting torque is obtained by a regenerative force of a driving motor with an engine clutch disengaged in a common hybrid electric vehicle;

(5) FIG. 4 is a diagram showing a state when a coasting torque is obtained by an engine friction force with an engine clutch engaged in a common hybrid electric vehicle;

(6) FIG. 5 is a flowchart illustrating a method of controlling motor torque according to embodiments of the present disclosure;

(7) FIG. 6 is a block diagram illustrating a method of determining motor torque when the engine clutch is disengaged in the embodiment of FIG. 5;

(8) FIG. 7 is a flowchart illustrating a method of controlling motor torque according to embodiments of the present disclosure; and

(9) FIG. 8 is a block diagram illustrating a method of determining motor torque when the engine clutch is engaged in the embodiment of FIG. 7.

(10) 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. In the figures, reference numbers refer to the same or equivalent parts of the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

(11) Hereinafter reference will now be made in detail to various embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings and described below. While the disclosure will be described in conjunction with embodiments, it will be understood that present description is not intended to limit the disclosure to those embodiments. On the contrary, the disclosure is intended to cover not only the disclosed embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the disclosure as defined by the appended claims.

(12) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms a, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprises and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.

(13) It is understood that the term vehicle or vehicular or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

(14) Additionally, it is understood that one or more of the below methods, or aspects thereof, may be executed by at least one control unit and/or controller. The terms control unit or controller may refer to a hardware device that includes a memory and a processor. The memory is configured to store program instructions, and the processor is configured to execute the program instructions to perform one or more processes which are described further below. Moreover, it is understood that the below methods may be executed by an apparatus comprising the control unit and/or controller, whereby the apparatus is known in the art to be suitable for controlling torque of a driving motor in a coasting state of a vehicle.

(15) Furthermore, the control unit and/or controller of the present disclosure may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller or the like. Examples of the computer readable mediums include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN).

(16) The present disclosure provides a method of controlling motor torque which can improve drivability in change of modes (EV modeHEV mode) without a difference in deceleration of a vehicle between a mode before an engine clutch is engaged (EV mode) and a mode after the engine clutch is engaged (HEV mode), when controlling torque of a driving motor when a vehicle (e.g., a hybrid vehicle) coasts.

(17) FIG. 5 is a flowchart illustrating a method of controlling motor torque according to embodiments of the present disclosure and shows a process of controlling torque (i.e., coasting torque) of a driving motor in accordance with whether an engine clutch is engaged, when a hybrid electric vehicle coasts.

(18) In the following description, the main part in the process of controlling motor torque according to the disclosed embodiments may be a control unit, or a plurality of control units may perform the process of controlling a motor under control of each other. For example, a hybrid electric vehicle can be equipped with a Hybrid Control Unit (HCU) that is the highest-class control unit generally controlling the vehicle and a motor control unit controlling operation of a driving motor through an inverter, in which the HCU may determine a motor torque instruction and then the motor control unit may control torque of the driving motor in accordance with the motor torque instruction from the HCU.

(19) First, a control unit acquires information about operation of an accelerator pedal detected by an accelerator pedal detector and information about the speed of an input shaft of a transmission (i.e., motor speed) detected by a detector in a vehicle, the acceleration of the input shaft of the transmission determined by the speed of the input shaft of the transmission, and the state of an engine clutch (S11). The accelerator pedal detector may be an accelerator pedal position sensor (APS) that detects the position of an accelerator pedal operated by a driver, for example.

(20) The control unit checks operation of the accelerator pedal based on a signal from the accelerator pedal detector while a vehicle is running (S12). That is, it determines whether a driver has taken a foot off the accelerator pedal on the basis of a signal from the accelerator pedal detector. When it is determined whether the accelerator pedal is operated, the depressed distance of the accelerator pedal obtained from an APS signal is compared with a predetermined first critical value (S12), and then, when the depressed distance of the accelerator pedal is less than the first critical value, it is determined that a driver has taken a foot off the accelerator pedal (i.e., pedal-off).

(21) If a driver operates the accelerator pedal to accelerate the vehicle, i.e., when the depressed distance of the accelerator pedal obtained from an APS signal is greater than the first critical value, it means the driver has operated the accelerator pedal to accelerate the vehicle, so common vehicle acceleration control with an accelerator pedal operated is performed. Conversely, when it is determined that the accelerator pedal is not depressed in step S12, the controller compares the speed of the input shaft of a transmission to a predetermined second critical value (S13), and when the speed of the input shaft of a transmission is greater than the second critical value, it determines that the vehicle is coasting.

(22) If the speed of the input shaft of a transmission is less than the second critical value in step S13, the controller performs common creeping control. Further, when it is determined that the vehicle is coasting in step S13, the state of the engine clutch is checked (S14) and coasting control according to the state of the engine clutch is performed, in which a motor torque instruction depends of whether the engine clutch is engaged. When the engine clutch has been engaged, a motor torque instruction is calculated as zero, zero-torque control is performed on the driving motor (15) so that the engine in a fuel-cut state directly provides a friction load and an inertial load. That is, a braking force is generated by the friction force of the engine, and as a result, the vehicle is braked by the engine friction torque (i.e., braking torque of the engine) such as engine brake.

(23) In contrast, when the engine clutch has been disengaged, a motor torque instruction is calculated on the basis of the engine friction torque, the rotary inertia of the engine, and the acceleration of the input shaft of the transmission (S16) and the torque (i.e., coasting torque) of the driving motor is controlled in accordance with the calculated motor torque instruction. The engine friction torque can be obtained based on the speed of the input shaft of the transmission in a map that is set and input in advance in the controller, and the rotary inertia of the engine is set and input in advance in the controller as an eigen value of the engine.

(24) Further, the acceleration of the input shaft of the transmission, a value determined based on the speed of the input shaft of the transmission, may be determined by differentiating the speed of the input shaft of the transmission, or as shown in FIG. 6, it may be determined based on the difference between the speed of the input shaft of the transmission at the previous sampling time and the speed of the input shaft of the transmission at the current sampling time and the value z of the sampling period.

(25) The motor torque instruction in coasting in step S16 may be calculated by the following Equation (6).
motor torque instruction=engine friction torquerotary inertia of engineacceleration of input shaft of transmission (6)

(26) FIG. 7 is a flowchart illustrating a method of controlling motor torque according to embodiments of the present disclosure, and steps S11 to S14 are the same as those of the embodiments described with reference to FIG. 5, so they are not described.

(27) In the embodiments shown in FIG. 7 as well, a motor torque instruction depends on whether an engine clutch is engaged while a vehicle coasts. That is, when an engine clutch has been engaged, a motor torque instruction can be calculated on the basis of the rotary inertia of the engine and the acceleration of the input shaft of the transmission (S15), by the following Equation (7), as in FIG. 8.
motor torque instruction=rotary inertia of engineacceleration of input shaft of transmission (7)

(28) The controller recognizes the rotary inertia of the engine as the eigen value of the engine, and the acceleration of the input shaft of the engine can be found in the same way as described above.

(29) With the engine clutch engaged, as described above, a friction load and an inertia load may be generated by the transmission in a fuel-cut state, but the inertia load is offset by the motor torque. On the contrary, when the engine clutch is not engaged, the motor torque instruction may be calculated as equal to the engine friction torque that is determined on the basis of the speed of the input shaft of the transmission, as in the following Equation (8) (S16), and the engine friction torque may be obtained on the basis of the speed of the input shaft of the transmission from a map that is set and input in advance in the controller.
motor torque instruction=engine friction torque (8)

(30) Therefore, the torque (i.e., coasting torque) of the driving motor is controlled on the basis of the motor torque instruction calculated from the Equation (7) or (8), in accordance with whether the engine clutch is engaged.

(31) The contents of the disclosure have been described in detail with reference to embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims and their equivalents.