Torque control system and method for drive system of electric vehicle

Abstract

A torque control system for a drive system of an electric vehicle includes: a controller generating a front wheel torque command and a rear wheel torque command having a torque value distributed from a required torque for driving of the vehicle according to a torque distribution mode selected among a plurality of torque distribution modes based on vehicle driving information; and the front-wheel motor and the rear-wheel motor are controlled according to the torque command output by the controller. The controller determines whether switching between the plurality of torque distribution modes occurs; calculating a torque correction amount for reducing a backlash shock based on a backlash estimation value in the drive system of a zero-crossing torque command among the front wheel torque command and the rear wheel torque command during mode switching; and performing torque correction on another torque command that does not cross zero using the calculated torque correction amount.

Description

Technical Field

[0001] This disclosure relates to a torque control method for a drive system of an electric vehicle, and more specifically, to a torque control system and method for a drive system capable of reducing backlash in a drive system of an electric vehicle, reducing backlash vibration, and improving the drivability of the vehicle. Background Technology

[0002] Typically, a vehicle's drive system must generate appropriate torque based on the driver's driving input values ​​(e.g., accelerator position sensor values ​​or brake position sensor values) or torque commands determined by requests from advanced driver assistance systems (ADAS).

[0003] Here, if the torque change rate (i.e., torque gradient) is set too large, problems such as drive shaft torsion, gear backlash, or deterioration of drivability may occur due to rapid torque changes.

[0004] Conversely, if the torque change rate is set too small, additional time is required to deliver the torque requested by the driver or ADAS controller, and the actual vehicle behavior may differ from the driver's intention, resulting in poor responsiveness or dangerous situations.

[0005] Therefore, it can be said that there is a contradiction between the degree of NVH (noise, vibration, and harshness) reduction and the degree of ensuring the vehicle's acceleration and deceleration responsiveness, which is attributable to rapid torque changes in the vehicle.

[0006] In this regard, in mass-produced vehicles, gradient constraints and filters with various conditions as factors are used to generate the optimal drive system torque command that can resolve the above contradictions.

[0007] Furthermore, in electrified vehicles that use an electric motor as a drive source or as part of it, active feedback torque correction control that can use the electric motor to suppress the vibrations that have already been generated can be employed.

[0008] However, no matter how advanced the backlash correction control is, it is difficult to suppress the inevitable reduction in vehicle responsiveness caused by hardware characteristics. Furthermore, in electric vehicles where there are almost no damping elements in the drive system, NVH problems caused by backlash frequently occur.

[0009] As a related technical document, Korean Patent No. 10-1704243 (February 1, 2017) discloses a method that generates a model speed of a drive shaft using a disturbance observer and uses the difference between the model speed and the actual speed of the drive shaft to reduce vibration. This patent document also discloses a method for calculating the model speed based on wheel speed rather than the disturbance observer when determining the model speed.

[0010] In addition, Korean Patent No. 10-1448746 (October 1, 2014) discloses a method that uses an input torque model to generate a model speed of an electric motor and uses the difference between the model speed of the electric motor and the actual speed (measured speed) to reduce vibration.

[0011] Furthermore, Korean Patent No. 10-2022-0096746 (published on July 7, 2022) discloses a method that uses a torque model to estimate the speed of a drive system and uses the difference between the actual speed of the drive system and the estimated speed to determine the gradient of the torque command.

[0012] However, all the aforementioned related technologies only disclose torque post-correction methods for reducing and suppressing vibrations generated in drive systems, without disclosing torque distribution methods capable of suppressing or preventing vibrations, or torque correction methods based on such methods.

[0013] The information disclosed in this background section is only intended to enhance the understanding of the background of this disclosure, and therefore may contain the following information: such information does not constitute prior art known to those skilled in the art within this country. Summary of the Invention

[0014] Therefore, this disclosure is dedicated to solving the aforementioned problems related to the prior art, and the purpose of this disclosure is to provide a torque control system for a drive system of an electric vehicle and a method for using the system, which can reduce backlash in the drive system, reduce backlash vibration, and improve the drivability of the vehicle.

[0015] This disclosure is not limited to the above-described purposes, and other purposes not explicitly mentioned may be understood by those skilled in the art from the following description.

[0016] In one aspect, this disclosure provides a torque control system for a drive system of an electric vehicle, comprising: a controller that generates a front-wheel torque command and a rear-wheel torque command having torque values ​​to be distributed from vehicle driving according to a torque distribution mode selected from among a plurality of preset torque distribution modes based on vehicle driving information; a front-wheel motor that controls the operation of the front-wheel motor according to the front-wheel torque command generated and output by the controller; and a rear-wheel motor that controls the operation of the rear-wheel motor according to the rear-wheel torque command generated and output by the controller; wherein the controller determines whether a switching between the plurality of torque distribution modes occurs; during a switching between torque distribution modes, calculating a torque correction amount for reducing backlash impact based on a backlash estimate in the drive system of a zero-crossing torque command among the front-wheel torque command and the rear-wheel torque command; and performing torque correction on the other torque command that does not cross zero using the calculated torque correction amount.

[0017] In another embodiment, the multiple torque distribution modes may include a same-direction distribution mode and a reverse-direction distribution mode. In the same-direction distribution mode, the allocated front wheel torque command and rear wheel torque command are determined to be torque values ​​in the same direction between the motor regeneration direction and the motor drive direction. In the reverse-direction distribution mode, the allocated front wheel torque command and rear wheel torque command are determined to be torque values ​​in different directions between the motor regeneration direction and the motor drive direction.

[0018] In another embodiment, the controller can select the torque distribution mode corresponding to the current vehicle driving state from among multiple torque distribution modes, based on the accelerator operation state, brake operation state and required torque, which are vehicle driving information.

[0019] In another embodiment, the backlash estimate may correspond to one or both of the backlash velocity estimate of the drive system when the torque command crosses zero and the backlash acceleration estimate of the drive system when the torque command crosses zero.

[0020] In another embodiment, the controller may determine the torque correction amount as a value obtained by applying one or more of weights, filters, rate of change limits, and dead zones to the backlash estimate.

[0021] In yet another embodiment, the controller can adjust the weights applied to the backlash estimate, the time constant or gain of the filter, the rate of change limit for rate of change limitation, and the dead zone based on at least one of the required torque, the current torque estimate, the accelerator position sensor value, the vehicle speed, and the motor speed.

[0022] In another aspect, this disclosure provides a torque control method for a drive system of an electric vehicle, comprising: determining, by a controller, a front wheel torque command and a rear wheel torque command having torque values ​​to be distributed from vehicle driving according to a torque distribution mode selected from among a plurality of preset torque distribution modes based on vehicle driving information; determining whether a switching between the plurality of torque distribution modes has occurred; during the switching between torque distribution modes, determining, by the controller, a backlash estimate for the drive system of the zero-crossing torque command among the front wheel torque command and the rear wheel torque command; calculating, by the controller, a torque correction amount for reducing backlash impact based on the determined backlash estimate; and using the calculated torque correction amount, performing torque correction on the other torque command among the front wheel torque command and the rear wheel torque command that does not cross zero.

[0023] Other aspects and preferred embodiments of this disclosure will be discussed below.

[0024] It should be understood that, as used herein, the term "vehicle" or other similar terms generally include motor vehicles, such as passenger cars including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, water vehicles including various ships, aircraft, etc., and includes hybrid vehicles, electric vehicles, plug-in hybrid vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-petroleum resources). As cited herein, a hybrid vehicle is a vehicle with two or more power sources, such as a vehicle powered by both electricity and gasoline. Attached Figure Description

[0025] The above and other features of this disclosure will be described in detail with reference to certain exemplary embodiments of this disclosure shown in the accompanying drawings, which are given hereinafter by way of illustration only, and therefore the drawings do not limit this disclosure, and wherein:

[0026] Figure 1 This is a block diagram illustrating the configuration of a torque control system for performing a torque control process for a drive system according to an embodiment of the present disclosure;

[0027] Figure 2 This is a diagram illustrating the types of torque control modes of a drive system and the conditions and methods for switching modes according to embodiments of the present disclosure;

[0028] Figure 3 This is a diagram illustrating the torque control state in a unidirectional distribution mode according to an embodiment of the present disclosure;

[0029] Figure 4 This is a diagram illustrating the torque control state in a reverse distribution mode according to an embodiment of the present disclosure;

[0030] Figure 5 , Figure 6 , Figure 7 and Figure 8 This is an illustration showing several examples of corrected backlash estimates to determine corrected backlash estimates according to embodiments of the present disclosure;

[0031] Figure 9 This is a diagram illustrating the torque control state according to an embodiment of the present disclosure; and

[0032] Figure 10 This is a diagram illustrating the front wheel torque command, rear wheel torque command, and backlash estimate for each torque distribution mode according to embodiments of the present disclosure.

[0033] It should be understood that the accompanying drawings are not necessarily drawn to scale, but are simplified representations illustrating various preferred features that illustrate the basic principles of this disclosure. Specific design features of this disclosure, such as those disclosed herein (including, for example, specific dimensions, orientations, locations, and shapes), will be determined in part by the specific intended application and environment of use.

[0034] In the figures, throughout the various figures, reference numerals refer to the same or equivalent parts of this disclosure. Detailed Implementation

[0035] In the following, reference will 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 present disclosure will be described in conjunction with exemplary embodiments, it will be understood that this specification is not intended to limit the present disclosure to the exemplary embodiments. Rather, within the spirit and scope defined by the appended claims, the present disclosure is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments.

[0036] It should be understood that although the terms "first," "second," etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of exemplary embodiments of this disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0037] Furthermore, it can be understood that when an element is "connected" or "coupled" to another element, that element can be directly connected or coupled to another element, or indirectly connected or coupled to another element, with different elements interspersed between them. Conversely, when an element is "directly connected" or "directly coupled" to another element, this means that there are no intermediate elements between them. Other expressions used to describe the relationship between elements should also be interpreted in a similar manner (e.g., "between" and "directly between," "adjacent" and "directly adjacent," etc.).

[0038] Where possible, the same reference numerals will be used throughout the drawings to refer to the same or identical parts. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of this disclosure. As used herein, the singular forms “a,” “an,” and “the” include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the terms “comprising,” “including,” and “having” as used herein specify the presence of the said components, steps, operations, and / or elements, but do not exclude the presence or addition of one or more other components, steps, operations, and / or elements.

[0039] This disclosure provides a method for generating electric motor torque commands and controlling drive system torque, which minimizes the impact of drive system backlash on the drivability of an electric vehicle having two or more individual drive motors.

[0040] Therefore, the torque control method for a drive system according to this disclosure is not a method to alleviate the problem caused by backlash in the drive system, but rather includes a method for reverse torque distribution between the front and rear wheels, which can avoid the backlash band while generating drive system torque in a way that prevents backlash from occurring in the drive system in advance.

[0041] In this disclosure, in order to avoid the backlash band (which is a torque band that may cause backlash in the drive system when generating torque during vehicle operation), a reverse torque distribution method between the front and rear wheels is used to separate the drive torque bands of the front wheel motor and the rear wheel motor.

[0042] Therefore, as a torque control mode of the drive system of the electric vehicle according to this disclosure, in addition to the typical same-direction distribution mode that distributes torque in the same direction to the front and rear wheels, the torque distribution mode also includes a reverse-direction distribution mode that distributes torque in the opposite direction to the front and rear wheels.

[0043] Furthermore, the torque control method for a drive system of an electric vehicle according to this disclosure includes a control method for switching between a same-direction distribution mode and a reverse-direction distribution mode (i.e., distribution mode switching).

[0044] In this specification, backlash can be defined as the torque band in which backlash may occur in the vehicle's drive system. The vehicle's drive system includes a drive unit that drives the vehicle, drive wheels, and drive elements such as drive shafts, reduction gears, differentials, and axles between the drive unit and the drive wheels.

[0045] Since problems caused by backlash in a vehicle's drive system mainly occur only in the torque band close to zero, it can be said that the torque band close to zero is the backlash band where backlash problems may occur.

[0046] In this disclosure, the backlash band may include the backlash band of the front-wheel drive system (which is a torque band in which backlash may occur in the front-wheel drive system) and the backlash band of the rear-wheel drive system (which is a torque band in which backlash may occur in the rear-wheel drive system).

[0047] In this disclosure, the backlash band of the front-wheel drive system and the backlash band of the rear-wheel drive system can be set to torque ranges having a lower threshold value of negative (-) and an upper threshold value of positive (+), respectively.

[0048] That is, the backlash band can be set to a torque range that includes 0, and a backlash state may occur when the input torque applied to the drive system by the motor as the drive unit enters the set backlash band.

[0049] Here, backlash refers to the gap that exists between the meshing teeth of two gears. Between two meshing gears, as the gear teeth collide with each other, backlash can cause vibration or noise, and in the worst case, it can damage the gears.

[0050] When torque is continuously applied in a specific direction, the teeth of the two meshing gears remain aligned and engaged in that specific direction because one of the two meshing gears continues to transmit power in the same direction as the other. Therefore, backlash does not occur.

[0051] However, when the torque direction changes, the power transmission direction changes, and the gear teeth align in the opposite direction after experiencing backlash. Here, after achieving alignment in the opposite direction, since the gear meshing is not released again during power transmission in the same direction, no backlash problem occurs.

[0052] However, at the moment the power transmission direction changes again, the meshing between the gears is released, and then they mesh again after passing through the backlash gap, thus causing a backlash problem.

[0053] Therefore, the key to avoiding backlash problems lies in eliminating or minimizing the release gear engagement, which can be achieved by eliminating or minimizing the directional changes in the torque command of each drive unit (e.g., an electric motor).

[0054] To eliminate or minimize directional changes in torque command, the following approach can be considered: using the front-wheel drive unit and the rear-wheel drive unit (i.e., the front wheel motor and the rear wheel motor) to share their functions, and for this purpose, dividing the torque operation areas of the front wheel motor and the rear wheel motor.

[0055] However, applying this control can limit maximum acceleration performance. To overcome this limitation, it is necessary to switch the drive system torque control mode (i.e., torque distribution mode). This disclosure proposes an efficient method for switching the distribution mode.

[0056] In the following description, torque includes both the torque input from the drive unit to the drive system and transmitted to the drive wheels, and the torque transmitted from the drive wheels through the drive system to the drive unit.

[0057] Furthermore, in the following description, torque includes both the drive torque used to accelerate the vehicle and the braking torque used to decelerate the vehicle. Here, braking torque includes regenerative braking torque obtained from the electric motor and friction braking torque obtained from the friction brake.

[0058] Unless otherwise specified in this specification as drive torque and braking torque, torque may be a drive torque for accelerating the vehicle (acceleration condition) or a braking torque for decelerating the vehicle (deceleration condition), depending on the vehicle's driving conditions. The electric motor torque used to decelerate the vehicle is regenerative braking torque.

[0059] The torque control system and torque control method for a drive system of an electric vehicle according to the present disclosure will be described in detail below.

[0060] Figure 1 This is a block diagram illustrating the configuration of an apparatus for performing a torque control process of a drive system according to the present disclosure.

[0061] This disclosure is applicable to vehicles in which the front wheels 33 and the rear wheels 43 are each driven by an independent drive unit. Specifically, this disclosure is applicable to vehicles equipped with a front-wheel drive unit that applies torque to the front wheels 33 and a rear-wheel drive unit that applies torque to the rear wheels 43. Here, both the front wheels 33 and the rear wheels 43 are drive wheels connected to the drive unit for power transmission.

[0062] Furthermore, this disclosure can also be applied to vehicles in which both the front-wheel drive unit and the rear-wheel drive unit are electric motors. In the following description, the electric motor 31, which is the front-wheel drive unit, is referred to as the "front-wheel electric motor," and the electric motor 41, which is the rear-wheel drive unit, is referred to as the "rear-wheel electric motor."

[0063] Reference Figure 1 The front wheel motor 31 is connected to the front wheel 33 via a reducer and a differential 32 for power transmission; while the rear wheel motor 41 is connected to the rear wheel 43 via a reducer and a differential 42 for power transmission.

[0064] In the following description, the front wheel torque command and the rear wheel torque command are torque (front axle torque and rear axle torque) commands for the corresponding axles, which refer to the torque commands for the corresponding electric motors 31 and 41 that drive the vehicle, that is, the front wheel motor torque command as the torque command for the front wheel motor 31, and the rear wheel motor torque command as the torque command for the rear wheel motor 41.

[0065] Here, in the electric motor torque, the torque in the vehicle acceleration direction and the torque in the electric motor driving direction are defined as positive (+) torque, that is, torque with a positive (+) value. Furthermore, in the electric motor torque, the torque in the vehicle deceleration direction and the torque in the electric motor regeneration direction are defined as negative (-) torque, that is, torque with a negative (-) value.

[0066] When the torque values ​​of the front wheel torque command and the rear wheel torque command are positive (+), these commands are drive torque commands for the relevant electric motors. When the torque values ​​of the front wheel torque command and the rear wheel torque command are negative (-), these commands are regenerative braking torque commands for the relevant electric motors. The torque value of each command becomes the magnitude of the torque that the relevant electric motor is to generate according to the command.

[0067] In this disclosure, the vehicle's drive system includes a front-wheel drive system and a rear-wheel drive system. Each of the front-wheel drive system and the rear-wheel drive system includes an electric motor that drives the vehicle, drive wheels, and drive elements between the electric motor and the drive wheels (e.g., drive shaft, reduction gear, differential, and axle).

[0068] That is, the front-wheel drive system includes a front wheel motor 31, a front wheel 33, a drive shaft (not shown) between the front wheel motor 31 and the front wheel 33, a reducer and a differential 32, and an axle (not shown); while the rear-wheel drive system includes a rear wheel motor 41, a rear wheel 43, a drive shaft (not shown) between the rear wheel motor 41 and the rear wheel 43, a reducer and a differential 42, and an axle (not shown).

[0069] In each drive system, the torque output from the front wheel motor 31 and the rear wheel motor 41 can be transmitted to the front wheel 33 and the rear wheel 43 through drive elements (e.g., drive shaft, reducer and differential 32 and 42 and axle).

[0070] In addition, although Figure 1 Although not shown, the battery is connected to the front wheel motor 31 and the rear wheel motor 41 via an inverter to enable charging and discharging. The inverter may include a front wheel inverter (not shown) for driving and controlling the front wheel motor 31 and a rear wheel inverter (not shown) for driving and controlling the rear wheel motor 41.

[0071] In the electric vehicle, the operation (driving and regenerative braking) of the front wheel motor 31 and the rear wheel motor 41 is controlled according to the torque command generated by the controller 20. The controller 20 determines the required torque for driving the vehicle based on the vehicle driving information obtained by the driving information detection unit 10, and determines the front wheel torque and rear wheel torque distributed to the front and rear wheels from the required torque.

[0072] Then, the controller 20 uses the determined front wheel torque and rear wheel torque as command values ​​to generate and output torque commands for the corresponding motors, namely, front wheel torque commands and rear wheel torque commands, which are torque commands used to generate front wheel torque and rear wheel torque for the corresponding motors.

[0073] Furthermore, the controller 20 controls the operation of the front wheel motor 31 and the rear wheel motor 41 via the inverter based on the front wheel torque command and the rear wheel torque command. As described above, when the torque values ​​of the front wheel torque command and the rear wheel torque command are positive (+) directional torques, the front wheel torque command and the rear wheel torque command can be defined as drive torque commands, which are torque commands in the vehicle's acceleration direction and drive direction; while when the torque values ​​of the front wheel torque command and the rear wheel torque command are negative (-) directional torques, the front wheel torque command and the rear wheel torque command can be defined as regenerative braking torque commands, which are torque commands in the vehicle's deceleration direction and regenerative direction.

[0074] In this embodiment, the controller 20 may include a first controller 21 and a second controller 22. The first controller determines the required torque necessary for vehicle operation based on the vehicle driving information (e.g., the driver's driving input value) detected by the driving information detection unit 10, or receives the required torque from other devices (e.g., ADAS (Advanced Driver Assistance System) controller), and generates and outputs front wheel torque commands and rear wheel torque commands as torque commands for the corresponding motors (corresponding axles) based on the required torque. The second controller controls the operation of the front wheel motor 31 and the rear wheel motor 41 according to the front wheel torque commands and rear wheel torque commands output by the first controller 21.

[0075] The first controller 21 may be a vehicle control unit (VCU), which determines and generates the torque command necessary for vehicle operation in a typical vehicle. Since the methods and processes for determining the required torque for vehicle operation from vehicle driving information and for determining the torque command for controlling the drive system (including the electric motor) are well known in the relevant art, their detailed description will be omitted.

[0076] When the first controller 21 outputs the front wheel torque command and the rear wheel torque command, the second controller 22 receives the front wheel torque command and the rear wheel torque command, and controls the operation of the front wheel motor 31 and the rear wheel motor 41 through the front wheel inverter and the rear wheel inverter.

[0077] Therefore, the torque output by the front wheel motor 31 is applied to the front wheel 33 through the reducer and differential 32 of the front wheel drive system, while the torque output by the rear wheel motor 41 is applied to the rear wheel 43 through the reducer and differential 42 of the rear wheel drive system.

[0078] The second controller 22 can be a typical motor control unit (MCU), which controls the operation of the drive motor via an inverter based on the torque command output from the vehicle control unit (VCU) in the electric vehicle.

[0079] In this embodiment, the vehicle driving information (indicating the vehicle driving status, such as driver driving input values) input to the controller 20 may include sensor detection information, which is detected by the driving information detection unit 10 and input to the controller 20 through the vehicle network.

[0080] Here, the driving information detection unit 10 may include an accelerometer position sensor (APS) that detects the driver's accelerometer position sensor value (APS value, %), a speed sensor that detects the speed of the drive system, and a sensor that detects the vehicle speed.

[0081] Here, the drive system speed can be the rotational speed of the drive elements present in the power transmission path from the front wheel motor 31 or the rear wheel motor 41 to the corresponding wheels 33 and 43 in the front wheel drive system or the rear wheel drive system.

[0082] For example, the drive system speed can be the rotational speed of the front wheel motor 31 or the rear wheel motor 41, which are drive motors, or the rotational speed (wheel speed) of the drive wheels 33 or 43. The speed sensor that detects the drive system speed (the drive system speed measurement described later) can be a sensor that detects the rotational speed of each of the motors 31 and 41, and can be a conventional resolver that detects the rotor position of the motor. Alternatively, the speed sensor can be a conventional wheel speed sensor that detects the rotational speed (wheel speed) of the drive wheels 33 and 43.

[0083] Alternatively, the sensor used to detect vehicle speed can also be a wheel speed sensor. Since methods for obtaining vehicle speed information from signals from wheel speed sensors are well known in the art, their detailed description will be omitted.

[0084] As vehicle driving information used to determine and generate the required torque and torque command in the controller 21, the driver's accelerometer position sensor value (APS value, %), the rotational speed of the motors 31 and 41, the rotational speed of the drive wheels 33 and 43, the vehicle speed, etc., detected by the driving information detection unit 10 can be selectively used.

[0085] In a broad sense, vehicle driving information may include information determined by the controller 20 itself, and may also include information (e.g., required torque information) input to the controller 20 from another controller in the vehicle (e.g., an ADAS controller) via the vehicle network.

[0086] exist Figure 1In the attached drawing, reference numeral "50" indicates a friction brake for the vehicle, which can be a conventional hydraulic brake. The friction brake 50 can be a front wheel friction brake that applies friction braking torque to the front wheels 33, or a rear wheel friction brake that applies friction braking torque to the rear wheels 43.

[0087] In the above description, the control body is divided into a first controller 21 and a second controller 22, but the torque control process according to this disclosure can be executed by a single integrated control element, rather than the multiple controllers mentioned above.

[0088] In this specification, the plurality of controllers 21 and 22, as well as a single integrated control element, may be collectively referred to as controller 20, and the torque control process according to this disclosure may be executed by controller 20. In the following description, controller 20 refers to... Figure 1 The first controller 21 and the second controller 22 are shown in the figure.

[0089] The configuration of the system for performing the drive system torque control process according to this disclosure has been described above. The drive system torque control process performed by the described system will be described in detail below.

[0090] In embodiments of this disclosure, the controller 20 determines the required torque for vehicle driving from real-time vehicle driving information detected by the driving information detection unit 10, and then performs front and rear wheel torque distribution to follow the determined required torque.

[0091] During the front and rear wheel torque distribution process, the controller 20 determines the front wheel torque command and the rear wheel torque command such that the sum of the front wheel torque command and the rear wheel torque command (the sum of the distributed front wheel and rear wheel torque values) is the value used to follow the required torque.

[0092] The controller 20 can distribute the desired torque received from another controller (e.g., an ADAS controller) to the front and rear wheel torques (instead of the desired torque determined by the controller 20 based on vehicle driving information).

[0093] Since the method for determining the required torque from vehicle driving information, which indicates the driver's driving input values ​​(e.g., accelerator position sensor values ​​or brake position sensor values) and vehicle speed, is well known, its detailed description will be omitted.

[0094] When the driver depresses the accelerator or releases the accelerator while it is depressed, the required torque may switch from the torque in the vehicle's deceleration direction to the torque in the vehicle's acceleration direction, and vice versa. In this disclosure, the required torque includes both the torque in the vehicle's acceleration direction and the torque in the vehicle's deceleration direction.

[0095] In the same-direction torque distribution mode of this disclosure, when the direction of the required torque is reversed, the directions of the front wheel torque and the rear wheel torque are also reversed. That is, in the same-direction torque distribution mode, when there is a zero-crossing request for the required torque, the controller 20 will change the direction of the front wheel torque (command) and the rear wheel torque (command) to follow the required torque.

[0096] On the other hand, in the reverse torque distribution mode, even if the direction of the required torque is reversed, the directions of the front wheel torque and the rear wheel torque do not change, and the sum of the front wheel torque and the rear wheel torque follows the required torque. Here, the front wheel torque is always determined as the negative (-) direction torque, while the rear wheel torque is always determined as the positive (+) direction torque.

[0097] The torque control modes of the drive system according to this disclosure will be described in more detail. Here, the reverse distribution mode is a mode for generating torque command while avoiding a backlash zone in which backlash of the drive system may occur. Here, avoiding a backlash zone means preventing the torque command from entering and intruding into the backlash zone as much as possible.

[0098] This can be achieved by keeping the front wheel torque and front wheel torque command only at negative (-) torque values, and keeping the rear wheel torque and rear wheel torque command only at positive (+) torque values. This is because the backlash problem arises when the torque direction changes, as described above.

[0099] When the above control strategy is applied, in the rear-wheel drive system, the gears are continuously aligned in the positive (+) torque transmission direction to avoid entering the backlash zone. This can be achieved by continuously generating at least a small amount of positive (+) torque in the rear-wheel drive system.

[0100] In this disclosure, a small amount of positive torque used to continuously align the gears in the positive (+) torque transmission direction is defined as the rear wheel minimum torque threshold (positive value), and during the reverse distribution mode (which is the mode for performing backlash band avoidance control), the value of the rear wheel torque command (positive value) is determined within a range equal to or greater than the preset rear wheel minimum torque threshold.

[0101] Similarly, in a front-wheel drive system, the gears are continuously aligned in the negative (-) torque transmission direction to avoid entering the backlash zone. This can be achieved by continuously generating at least a small amount of negative (-) torque in the front-wheel drive system.

[0102] Here, the small amount of negative torque used to continuously align the gears in the negative (-) torque transmission direction is defined as the front wheel maximum torque threshold (negative value), and during the reverse distribution mode (which is the mode for performing backlash band avoidance control), the value of the front wheel torque command (negative value) is determined within a range equal to or less than the preset front wheel maximum torque threshold. In other words, the absolute value of the front wheel torque command is determined to be equal to or greater than the front wheel maximum torque threshold.

[0103] In this disclosure, the minimum rear wheel torque threshold can be set in the controller 20 as a torque value outside the backlash band, which is the torque band where backlash may occur in the rear-wheel drive system. In other words, the minimum rear wheel torque threshold can be set to a value greater than the upper limit threshold of the backlash band of the rear-wheel drive system.

[0104] Similarly, the maximum torque threshold for the front wheels can be set in controller 20 as a torque value outside the backlash zone, which is the torque band where backlash may occur in the front-wheel drive system. Here, the maximum torque threshold for the front wheels can be set to a value smaller than the lower limit threshold of the backlash zone of the front-wheel drive system.

[0105] However, a potential problem with this approach is that, since only one of the front or rear axle motors is used for acceleration and regenerative braking (deceleration), the maximum generated power may be insufficient compared to when both axle motors are used for all purposes.

[0106] That is, since only one of the front wheel motor 31 and the rear wheel motor 41 is used, the maximum generated power may be insufficient compared to the case where both the front wheel motor 31 and the rear wheel motor 41 are used for acceleration or regenerative braking. This may make it difficult to achieve maximum acceleration performance or maximum regenerative braking.

[0107] However, typically, since load transfer is primarily concentrated on the rear wheel side during acceleration and the driving torque of the rear axle plays a major role, and conversely, load transfer is concentrated on the front wheel side during deceleration and the regenerative braking torque of the front axle plays a major role, the backlash avoidance strategy proposed in this disclosure does not lead to significant performance degradation.

[0108] However, since the maximum performance of using two motors together cannot be achieved when only one motor is used, the following countermeasures can be considered.

[0109] First, a reverse torque distribution mode is set in the controller 20, and this reverse torque distribution mode can be selectively executed by the controller 20. The reverse torque distribution mode can be a responsiveness-priority mode that prioritizes vehicle acceleration / deceleration response, or a backlash avoidance mode that performs backlash avoidance control. In the reverse torque distribution mode, reverse torque distribution control is executed, which is used to distribute torque commands to the front and rear wheels in the opposite direction and to apply torque in the opposite direction.

[0110] Unlike the reverse-direction distribution mode, a same-direction distribution mode is set in controller 20 to generate maximum output. This same-direction distribution mode can be a normal drive system torque control mode applied to a typical vehicle. In the same-direction distribution mode, torque commands in the same direction are distributed to the front and rear wheels, and torque in the same direction is applied during vehicle acceleration and regeneration.

[0111] Therefore, in this disclosure, the torque distribution between the front and rear wheels can be either in the same direction or in opposite directions. In the same-direction distribution, the front wheel motor and the rear wheel motor are controlled to generate torque in the same direction (both positive (+) torque or both negative (-) torque). Here, since the front wheel motor and the rear wheel motor generate torque in the same direction, the front wheel torque and the rear wheel torque are added together to generate the maximum torque.

[0112] However, in the same direction distribution, when the required torque passes through 0 (zero crossing) and the direction and sign ("+" or "-") of the required torque are reversed, the torque direction of the front wheel torque command and the rear wheel torque command must also be reversed.

[0113] Therefore, when passing through the backlash zone, both the front and rear wheel torque commands cross zero, and the rate of change (gradient) of the front and rear wheel torque commands is limited. Due to these control characteristics when passing through the backlash zone, the vehicle's acceleration / deceleration response is delayed.

[0114] On the other hand, in reverse torque distribution, even when the direction of the required torque changes, the front wheel motor and the rear wheel motor always generate torque in different directions. That is, the front wheel torque command used to control the operation of the front wheel motor 31 is determined and generated as a negative (-) torque value, while the rear wheel torque command used to control the operation of the rear wheel motor 41 is determined and generated as a positive (+) torque value.

[0115] Therefore, the rear wheel motor mainly generates drive torque for vehicle acceleration, while the front wheel motor mainly generates regenerative braking torque for vehicle deceleration (regenerative braking).

[0116] In reverse distribution, since the torque command does not need to pass through the backlash band and there is no need to limit the rate of change (gradient) of the torque command in the backlash band, the vehicle's acceleration / deceleration response can be improved.

[0117] In the reverse torque distribution mode according to this disclosure, when the required torque is in the positive (+) direction, a drive torque for vehicle acceleration must be generated, therefore reverse torque distribution control in the acceleration direction is performed. Here, the torque command for the front wheel motor 31, i.e., the front wheel torque command, is determined to be a torque command in the negative (-) direction.

[0118] Specifically, the absolute value of the front wheel torque command is determined to be the minimum value that maintains gear tooth alignment, preventing backlash in the front-wheel drive system. Here, the minimum value is the front wheel maximum torque threshold. In embodiments of this disclosure, the front wheel maximum torque threshold may be a value that varies in real time according to the state of the drive system.

[0119] Meanwhile, the torque command for the rear wheel motor 41 (i.e., the rear wheel torque command) can be determined as a torque command in the positive (+) direction, and the rear wheel torque command can be determined as the value obtained by subtracting the front wheel torque command from the total torque command (as the required torque for distributing the front torque).

[0120] When the required torque is in the negative (-) direction, regenerative braking torque must be generated to decelerate the vehicle; therefore, reverse torque distribution control in the regenerative direction is executed. Here, the rear wheel torque command is determined to be a positive (+) direction torque command.

[0121] Specifically, the magnitude of the rear wheel torque command is determined to be a minimum value that maintains gear tooth alignment, preventing backlash in the rear-wheel drive system. Here, the minimum value is the rear wheel minimum torque threshold. In embodiments of this disclosure, the rear wheel maximum torque threshold can be a value that varies in real time according to the state of the drive system.

[0122] Meanwhile, the torque command for the front wheel motor 31 can be determined as a positive (+) direction torque command, and the front wheel torque command can be determined as the value obtained by subtracting the rear wheel torque command from the total torque command (as the required torque for distributing the front torque).

[0123] The state of the drive system used to determine the maximum torque threshold of the front wheels and the minimum torque threshold of the rear wheels may include the input torque applied to the drive system by the front wheel motor 31 or the rear wheel motor 41.

[0124] The input torque can be one of the following: the total torque command, the estimated motor torque value estimated by the motor controller, the detected motor torque value detected by the torque sensor, the value obtained by applying a filter to the total torque command, the value obtained by applying a filter to the estimated motor torque value, and the value obtained by applying a filter to the detected motor torque value.

[0125] Alternatively, the input torque can be a front-wheel torque command and a rear-wheel torque command, which are determined through a typical front-to-rear-wheel torque distribution process that distributes the total torque command according to the front-to-rear-wheel distribution ratio. Here, the maximum front-wheel torque threshold can be variably determined to correspond to the value of the distributed front-wheel torque command, while the minimum rear-wheel torque threshold can be variably determined to correspond to the value of the distributed rear-wheel torque command.

[0126] Based on the aforementioned reverse distribution pattern, although it is impossible to generate the maximum driving force or maximum regenerative braking force of the electric motor, relatively instantaneous acceleration / deceleration response can be expected under all conditions.

[0127] In this manner, the torque control mode (i.e., torque distribution mode) of the vehicle drive system according to this disclosure may include the following four modes, which take into account the above characteristics and are distinguished according to the vehicle driving state.

[0128] 1) Distribution of acceleration in the opposite direction

[0129] 2) Reverse distribution of regeneration direction

[0130] 3) Distribution of acceleration directions in the same direction

[0131] 4) Distribution in the same direction of regeneration

[0132] This disclosure proposes switching (conversion) conditions and switching methods between modes, which can ensure the driving performance and drivability of electric vehicles when the above four drive system torque control modes are set in the controller 20.

[0133] The mode determination and mode switching control are executed by the controller 20 based on vehicle driving information, which includes pedal input values, which are the driver's driving input information, and the pedal input values ​​include accelerometer position sensor values ​​and brake position sensor values. The accelerometer position sensor values ​​and brake position sensor values ​​can be obtained from the signals of the accelerometer position sensor (APS) and brake position sensor (BPS) in the driving information detection unit 10.

[0134] Figure 2This is a diagram illustrating the types of torque control modes of the drive system in this disclosure, as well as the conditions and methods for switching modes. In the following description, "accelerator on" and "brake on" are defined as states with pedal input, in which the driver depresses the corresponding pedal and applies pressure to it, i.e., the pressure application state or depressing state of the accelerator and brake.

[0135] In addition, "accelerator off" and "brake off" are defined as a state without pedal input, in which the driver does not press the pedal, that is, the accelerator and brake pressure is released or released.

[0136] In this disclosure, the accelerator on and off states and the brake on and off states can be identified in real time by the controller 20 from the signals of the accelerator position sensor and the brake position sensor in the driving information detection unit 10.

[0137] In this disclosure, the controller 20 can select a reverse distribution mode when the driver releases both the accelerator and the brake (off), and when the driver depresses the accelerator (on) and the required torque (command) based on the accelerator position sensor value is lower than a preset mode switching threshold.

[0138] Here, the required torque is the torque required before distribution, and it can be the sum of the front wheel torque and the rear wheel torque. In this specification, the required torque (command) necessary for vehicle operation, the total torque command, and the total torque command have the same meaning.

[0139] With both the accelerator and brake closed, the controller 20 selects the reverse direction distribution mode of the regeneration direction. Figure 2 In "Mode 2", when the driver depresses the accelerator (accelerator activated) and the required torque is below the mode switching threshold, the controller 20 selects the opposite acceleration direction distribution mode. Figure 2 (Mode 1 in the text).

[0140] Furthermore, when the driver depresses the accelerator (accelerator on) while the reverse direction distribution mode of regeneration is selected, the mode is switched to the reverse direction distribution mode of acceleration. Conversely, when the driver releases the accelerator (accelerator off) while the reverse direction distribution mode of acceleration is selected, the mode is switched to the reverse direction distribution mode of regeneration.

[0141] Furthermore, after switching from the reverse distribution mode in the regeneration direction to the reverse distribution mode in the acceleration direction, since the reverse distribution mode in the acceleration direction is maintained until the required torque corresponding to the accelerator position sensor value (APS value) reaches the mode switching threshold, the zero crossing of the front wheel torque and the rear wheel torque is not necessary.

[0142] Here, the mode switching threshold can be set to a positive (+) torque value. Furthermore, the mode switching threshold can be a preset value within the range of required torque values ​​that can only be satisfied by the torque of the rear wheel motor.

[0143] Furthermore, regarding the mode switching threshold, the mode used for assigning modes from the reverse direction can be... Figure 2 Switch from "Mode 1" to same-direction allocation mode. Figure 2 The mode switching threshold for "Mode 3" and the mode switching threshold for switching from the same direction allocation mode and re-entering the opposite direction allocation mode are set to different values.

[0144] Furthermore, if the required torque for vehicle operation (i.e., the required torque corresponding to the accelerator position sensor value) exceeds the mode switching threshold, or if the driver depresses the brake (brake is engaged), the controller 20 terminates the reverse direction distribution mode and switches to the same direction distribution mode.

[0145] In this disclosure, in the opposite direction of acceleration distribution mode, if the required torque for driving the vehicle (i.e., the required torque corresponding to the accelerator position sensor value) exceeds the mode switching threshold, the controller 20 switches the mode to the same direction of acceleration distribution mode. Figure 2 (Mode 3 in the text).

[0146] Furthermore, in the reverse direction distribution mode of the regeneration direction, when the driver depresses the brake (brake open), the controller 20 switches the reverse direction distribution mode of the regeneration direction to the same direction distribution mode of the regeneration direction. Figure 2 (Mode 4 in the text).

[0147] Furthermore, in the same-direction distribution mode in the acceleration direction, if the required torque is reduced to below the mode switching threshold, or in the same-direction distribution mode in the regeneration direction, if the driver releases the brake (brake closed), the controller 20 terminates the same-direction distribution mode and returns to the opposite-direction distribution mode.

[0148] As mentioned above, a zero crossing occurs when switching from a same-direction distribution mode to a opposite-direction distribution mode, or vice versa. This can make it difficult to immediately execute the mode switch to address areas where backlash impacts may occur. However, this time delay, combined with the time interval from the driver releasing the brake to the accelerator position sensor input, can provide a natural driving experience.

[0149] Furthermore, in the mode switching strategy according to this disclosure, since only the zero crossing of one of the front wheel motor torque and the rear wheel motor torque occurs when switching between the same-direction distribution mode and the opposite-direction distribution mode, the response delay caused by the zero crossing of the front wheel motor torque and the rear wheel motor torque can be significantly compensated by using another motor.

[0150] In the following text, reference will be made to Figure 3 and Figure 4 The control states of the same-direction allocation mode and the opposite-direction allocation mode are described in more detail. Figure 3 This is a diagram illustrating the torque control state under the same-direction distribution mode, and Figure 4 This is a diagram illustrating the torque control state in the reverse direction distribution mode.

[0151] In this disclosure, when the desired torque changes direction and increases or decreases, the desired torque is executed according to the desired torque. Figure 3 Same direction allocation mode and Figure 4 Switching between reverse allocation modes in the system.

[0152] Figure 3 and Figure 4 Examples are shown where the same-direction distribution mode and the opposite-direction distribution mode are executed independently only, without switching between the aforementioned torque distribution modes throughout the entire range of the required torque and throughout the entire time period of the required torque variation.

[0153] Figure 3 and Figure 4 This diagram illustrates the front and rear wheel torque distribution state and front and rear wheel torque command determination method performed by the controller 20 in same-direction distribution mode control and opposite-direction distribution mode control when the accelerometer position sensor value (APS value) is detected by the accelerometer position sensor of the driving information detection unit 10.

[0154] In the same-direction torque distribution mode, the front and rear wheel torques are determined to be torques in the same direction, and the sum of the distributed front and rear wheel torques meets the required torque. Figure 3 In the middle, the direction of the required torque switches to the positive (+) direction when the accelerator is pressed, that is, the direction of vehicle acceleration.

[0155] In the same direction distribution mode, when the direction of the required torque changes due to the zero crossing of the required torque, the directions of the front wheel torque and the rear wheel torque also change, thereby causing the zero crossing of the back clearance zone. Therefore, when the front wheel torque and the rear wheel torque pass through the back clearance zone, the gradient of the torque value change is limited.

[0156] In the same-direction distribution mode, the front wheel torque command and the rear wheel torque command are determined based on the total torque command (sum torque command) (which is the required torque command before distribution) across the entire range of positive (+) and negative (-) torque values.

[0157] That is, in the same direction distribution mode, when the required torque is in the positive (+) direction of vehicle acceleration, the torque of the front wheel and the torque of the rear wheel are both determined to be the torque value in the positive (+) direction (i.e., the driving direction), while when the required torque is in the negative (-) direction of vehicle deceleration, the torque of the front wheel and the torque of the rear wheel are both determined to be the torque in the negative (-) direction (i.e., the regeneration direction).

[0158] For example, in the absence of accelerometer position sensor values ​​from the driver (such as...) Figure 3 In other words, when the vehicle decelerates without the driver pressing the accelerator, both the front wheel torque command and the rear wheel torque command can be determined as negative (-) torque values.

[0159] Then, when the driver depresses the accelerator to accelerate the vehicle, in the same-direction torque distribution mode, both the front wheel torque command and the rear wheel torque command change from negative (-) torque values ​​to positive (+) torque values. Thus, when the torque direction changes, both the front wheel torque command and the rear wheel torque command inevitably pass through the backlash band.

[0160] Furthermore, when the driver depresses the accelerator, the sum of the front wheel torque command and the rear wheel torque command must follow the total torque command (required torque), and in this case, the front wheel torque command and the rear wheel torque command are determined by the usual front and rear wheel torque distribution process of distributing the total torque command according to the front and rear wheel distribution ratio.

[0161] However, during the backlash zone when the front and rear wheel torque commands pass through the backlash zone, even if the driver depresses the accelerator, the direction of the torque applied to the drive system by the electric motor does not change rapidly, thus minimizing the backlash problem.

[0162] That is, such as Figure 3 It can be seen that in the same direction distribution mode, when the driver depresses the accelerator, the front wheel torque command and the rear wheel torque command do not immediately change from negative (-) torque to positive (+) torque. Instead, the front wheel torque command and the rear wheel torque command are determined such that the torque applied to the drive system by the electric motor can change direction while passing through the back clearance zone during a predetermined time period after the accelerator is depressed.

[0163] Specifically, during the passage through the backlash zone, rate-of-change control is implemented to limit the rate of change (gradient) of the front and rear wheel torque commands, thereby preventing a rapid increase in torque commands. In the same-direction distribution mode, backlash control is applied to both the front and rear wheel torque commands, resulting in a smooth torque change within the backlash zone.

[0164] Therefore, in the controller 20, the maximum permissible rate of change (maximum permissible gradient) of the backlash band for the front wheel torque command and the rear wheel torque command can be set to a small value that does not cause backlash impact.

[0165] During the increase of the front wheel torque command and the rear wheel torque command and as they pass through the back clearance zone, in the controller 20, the front wheel torque command and the rear wheel torque command are determined to be values ​​that change slowly according to the maximum permissible rate of change of the smaller value.

[0166] Furthermore, the magnitudes of the front and rear wheel torque commands after passing the backlash zone can satisfy the necessary drive torque for acceleration through the normal front and rear wheel torque distribution process.

[0167] With the front wheel torque command and rear wheel torque command determined as described above, the controller 20 controls the front wheel motor 31 and the rear wheel motor 41 according to the determined final front wheel torque command and rear wheel torque command.

[0168] The reverse distribution mode is used to separate the torque operating areas of the front and rear wheel motors to avoid zero crossing, while preventing the front wheel torque and rear wheel torque from entering the backlash zone.

[0169] As described above, in the reverse distribution mode, the front wheel torque and the rear wheel torque can be determined as torques in opposite directions, and can be determined as the sum of the two distributed torques to meet the required torque.

[0170] like Figure 4 As can be seen, in the reverse direction distribution mode, regardless of whether the required torque is the positive (+) torque in the vehicle acceleration direction or the negative (-) torque in the vehicle deceleration direction, the front wheel torque is determined to be the negative (-) torque in the regeneration direction, while the rear wheel torque is determined to be the positive (+) torque in the driving direction.

[0171] Therefore, in the reverse distribution mode, the controller 20 performs backlash avoidance control, which limits the front wheel torque command to a value equal to or lower than the front wheel maximum torque threshold, or limits the rear wheel torque command to a value equal to or greater than the rear wheel minimum torque threshold.

[0172] However, in the reverse-direction distribution mode, the front wheel motor 31 and the rear wheel motor 41 do not generate driving force or regenerative braking force in the same direction, and the front wheel motor 31 only performs regenerative braking, while the rear wheel motor 41 only performs driving. Therefore, it is difficult to drive the vehicle and perform regenerative braking at maximum output.

[0173] However, in the reverse torque distribution mode, unlike the same torque distribution mode (i.e., the typical drive system torque control mode), responsiveness can be ensured because zero crossing of the front wheel torque command or the rear wheel torque command (passing through 0 torque within the backlash band) is not necessary.

[0174] On the other hand, when the reverse distribution mode is deactivated and the same-direction distribution mode is entered, the vehicle can be driven and regenerated at maximum output because the front wheel motor 31 and the rear wheel motor 41 work together to drive and regenerate.

[0175] However, in the same-direction torque distribution mode, the directions of the front-wheel torque command and the rear-wheel torque command change when the direction of the desired torque changes. Here, since the zero-crossing of torque inevitably limits the rate of change of each torque command, a responsive delay inevitably occurs.

[0176] Reference Figure 4 In the reverse distribution mode, during the deceleration range when the driver does not press the accelerator and the vehicle is decelerating, the total torque command ultimately determined from the required torque has a negative (-) torque value as a regenerative braking torque command.

[0177] In the reverse torque distribution mode, even in the deceleration range where the vehicle is decelerating, the rear wheel torque command is determined to be equal to or greater than the minimum rear wheel torque threshold value set as a positive (+) torque value, while the front wheel torque command is determined to be the value obtained by subtracting the determined rear wheel torque command (positive torque) from the total torque command (negative torque) (negative value).

[0178] Here, as a comparison result between the total torque command and the rear wheel minimum torque threshold, if the total torque command is equal to or lower than the rear wheel minimum torque threshold, the controller 20 determines the rear wheel torque command as the rear wheel minimum torque threshold, and determines the remaining torque obtained by subtracting the rear wheel minimum torque threshold from the total torque command as the front wheel torque command, so as to follow the total torque command.

[0179] The front wheel torque command determined in this way has a negative (-) torque value. Accordingly, the rear wheel motor 41 outputs a drive torque (which is a positive torque) and applies the output torque to the drive system, while the front wheel motor 31 outputs a regenerative braking torque (which is a negative torque) and applies the output torque to the drive system.

[0180] Then, when the driver depresses the accelerator, immediately after depressing the accelerator, the front wheel torque command can be determined as the front wheel maximum torque threshold set as a negative (-) torque value, and the rear wheel torque command can be determined as a positive (+) torque value obtained by subtracting the determined front wheel torque command (negative torque) from the total torque command (positive torque) corresponding to the accelerator position sensor value.

[0181] Here, as a comparison between the total torque command and the maximum torque threshold of the front wheels, if the total torque command is equal to or greater than the maximum torque threshold of the front wheels, the controller 20 determines the front wheel torque command as the maximum torque threshold of the front wheels, and determines the remaining torque obtained by subtracting the maximum torque threshold of the front wheels from the total torque command as the rear wheel torque command, so as to follow the total torque command.

[0182] While the driver is pressing the accelerator, the front wheel motor 31 can output a negative (-) torque corresponding to the maximum torque threshold of the front wheel, while the rear wheel motor 41 can output a positive (+) torque obtained by subtracting the front wheel motor command (negative torque) from the total torque command (positive torque).

[0183] Then, when the driver lifts (releases) his foot off the accelerator, the rear wheel torque command can be redefined as the rear wheel minimum torque threshold, and the front wheel torque command can be defined as a negative (-) torque value obtained by subtracting the rear wheel torque command (positive torque) from the total torque command (negative torque) which is the regenerative braking torque.

[0184] When the front wheel torque command and the rear wheel torque command are determined in this way, the controller 20 controls the operation of the front wheel motor 31 and the rear wheel motor 41 according to the front wheel torque command and the rear wheel torque command.

[0185] The torque control method for a drive system of an electric vehicle according to this disclosure includes a control method for switching torque control modes of the drive system, and more specifically, includes a torque correction method for mitigating backlash impact when switching between torque control modes of the drive system.

[0186] Here, switching the torque control mode of the drive system refers to switching the torque distribution mode, and more specifically, it includes switching between the same-direction distribution mode and the opposite-direction distribution mode.

[0187] The above has described a torque correction method for limiting the rate of change of the front wheel torque command or the rear wheel torque command during the period of passing through the back clearance zone and thus crossing zero.

[0188] In this disclosure, the zero-crossing of the front wheel torque command and the rear wheel torque command are executed sequentially based on the required torque, and when zero-crossing correction is performed on one of the front wheel torque command and the rear wheel torque command, for the other torque command, a torque correction amount determined based on the backlash estimate of the drive system in which the zero-crossing occurs can be used to perform correction.

[0189] In the torque control mode (i.e., torque distribution mode) of the drive system of electric vehicles, when there are two different torque distribution methods for the front and rear wheels, namely, the same-direction distribution mode and the opposite-direction distribution mode, the switching between the distribution modes occurs when the vehicle driving state changes and the direction of the required torque changes.

[0190] Considering the fundamental characteristics of the distribution modes, the following property exists: traversing the backlash band only occurs when there is a change in torque command between distribution modes. Therefore, a reliable backlash band determination can be achieved by using a method that determines whether torque correction is performed in the backlash band based on whether a switch between distribution modes is executed.

[0191] In embodiments of this disclosure, a backlash value for the drive system is estimated for torque correction to reduce backlash impact. However, since vehicle speed or motor speed information includes noise, the backlash estimate may also contain noise. Therefore, an accurate backlash band identification strategy is effective when removing noise in areas that are not backlash bands.

[0192] By enabling the backlash estimate partially, the conflict between noise removal and effective signal amplification can be eliminated. In other words, the backlash estimate can be disabled without a distribution mode switch, but can be enabled only when a distribution mode switch is present, allowing the backlash estimate in its active state to be used for corrective control.

[0193] As described above, in embodiments of this disclosure, torque correction can be performed when one of the front wheel torque command and the rear wheel torque command crosses zero, in order to limit the rate of change of the zero-crossing torque command to a set rate of change.

[0194] At this point, the torque correction amount for reducing backlash impact can be calculated based on the backlash estimate of the drive system when the torque command crosses zero, and the calculated torque correction amount can be used to perform torque correction on another torque command that does not cross zero.

[0195] Specifically, the backlash estimate of the front-wheel drive system can be used to calculate the torque correction amount to reduce backlash impact when the front wheels cross zero, while the backlash estimate of the rear-wheel drive system can be used to calculate the torque correction amount to reduce backlash impact when the rear wheels cross zero.

[0196] While the torque correction calculated above can be used, when calculating the torque correction from the backlash estimate, another weight, filter, rate of change (gradient) limit, or dead zone can be applied to the calculated torque correction, similar to... Figures 5 to 8 For example, the result can then be used as the final torque correction amount.

[0197] Furthermore, in this disclosure, methods can be applied to disable the dead zone estimated by backlash in torque ranges where correction is unnecessary, to filter the dead zone, or to extend the dead zone, so that the backlash estimate can be used effectively only in finite ranges where torque correction is necessary.

[0198] Typically, backspace estimates include noise. While the characteristics of the noise can vary depending on the backspace estimation method or the specifications of the sensor generally used, techniques for handling noise are essential due to the need for rapid correction of the backspace band.

[0199] However, as noise is cleanly removed, the backlash estimate, which must be monitored to accurately calculate the torque correction, is also partially deleted, leading to insufficient or delayed torque correction. To overcome these limitations, selectively adjusting the noise processing sensitivity or width as needed is effective.

[0200] In this disclosure, controller 20 can determine the torque correction amount as a value obtained by selectively applying one or more of weights, filters, rate of change (gradient) limits, and dead zones to the backlash estimate.

[0201] At this point, the torque range in which backlash may occur (i.e., the backlash band) can be set as the torque range in which correction is necessary, and the following methods can be applied: the weights applied to the backlash estimate, the time constant of the filter applied to the backlash estimate, the rate of change (gradient) limit applied to the backlash estimate, and the dead zone applied to the backlash estimate.

[0202] In addition, a method can be applied that references a zero-crossing starting point and variably adjusts the aforementioned weights, filter time constants, rate of change limits, and dead zones.

[0203] In addition, the following method can be used: based on the torque command mode conversion information between the same-direction distribution mode and the opposite-direction distribution mode, the above-mentioned weights, filter time constants, rate of change limits and dead zones can be variably adjusted according to whether the mode conversion is in progress.

[0204] In the region where torque correction is necessary to reduce backlash impact, the following steps can be performed:

[0205] 1) Increase the weight applied to the backspace estimate;

[0206] 2) Reduce the time constant of the filter applied to the backslot estimation or increase the filter gain;

[0207] 3) Increase the rate of change (gradient) constraint applied to the back gap estimate (i.e., relax the rate of change constraint); and

[0208] 4) Reduce the dead zone applied to back gap estimation.

[0209] Regarding the adjustments to the weights, filter time constants or gains, rate of change limits, and dead zones as described above, the backlash estimates in this disclosure should be corrected in real time as needed, particularly based on whether the current torque has crossed zero.

[0210] However, since whether the current torque crosses zero depends on the required torque, it is possible to determine in real time whether to perform correction using the required torque value.

[0211] Here, the method of determining whether to perform correction to diversify the correction range can be used as the adjustment method described above using parameters such as weights, filter time constants or gains, rate of change limits, and dead zones.

[0212] In this way, it can be determined whether the desired torque value is used to perform the correction, and the weights, filter time constant or gain, rate of change limit, and dead zone can be adjusted as variables of the desired torque value.

[0213] Furthermore, after constructing a mapping that uses one or more information values ​​such as the current torque estimate, accelerator position sensor value, vehicle speed, and electric motor speed, as well as the aforementioned desired torque value as input, the values ​​of weights, filter time constants or gains, rate of change limits, and dead zones can be determined and adjusted from the mapping.

[0214] In this disclosure, during the switching between the same-direction distribution mode and the opposite-direction distribution mode, the backlash estimate of the drive system that has crossed zero is calculated, the torque correction amount is determined based on the calculated backlash estimate, and then the torque command of the drive system that has not crossed zero is corrected using the determined torque correction amount.

[0215] Figures 5 to 8 The figure shows several examples of corrected backlash estimates to determine corrected backlash estimates, wherein the corrected backlash estimates in the figure correspond to the torque correction amounts mentioned above.

[0216] Reference to the description Figures 5 to 8 The process of calculating the backlash estimate and then determining the torque correction amount (the corrected backlash estimate).

[0217] First, in calculating the backlash estimate of the drive system that has crossed zero, the torque correction amount can be determined by applying weights to the initially calculated but unprocessed raw backlash estimate (hereinafter referred to as the "raw backlash estimate"). Here, the weights can be as follows: Figure 5 The value shown is adjusted by controller 20 and can be a variable value determined based on the required torque.

[0218] Figure 5 The graph on the right side shows an example of correcting the backlash estimate by increasing the weight compared to the left side, and the corrected backlash estimate can be used as a torque correction amount.

[0219] In this disclosure, when the front wheel torque command crosses zero, a backlash estimate for the front wheel drive system is calculated, and then the torque correction amount can be determined as a value obtained by multiplying the calculated backlash estimate by a weight determined according to the required torque.

[0220] Here, the backlash estimate can be one or both of the backlash velocity estimate and the backlash acceleration estimate, and the backlash acceleration estimate can be obtained by differentiating the backlash velocity.

[0221] When the backlash speed estimate or backlash acceleration estimate of the front-wheel drive system is calculated as the backlash estimate of the front-wheel drive system, the torque correction amount for the rear-wheel torque command can be determined as a value obtained by multiplying the backlash speed estimate or backlash acceleration estimate of the front-wheel drive system by a weight.

[0222] Alternatively, the torque correction amount for the rear wheel torque command can be determined as the sum of the backlash speed estimate of the front wheel drive system multiplied by a first weight according to the desired torque and the backlash acceleration estimate of the front wheel drive system multiplied by a second weight according to the desired torque, and a filter and rate of change (gradient) limit are applied to this sum.

[0223] Similarly, when the rear wheel torque command crosses zero, the controller 20 calculates the backlash estimate for the rear wheel drive system, and based on the calculated backlash estimate for the rear wheel drive system, calculates the torque correction amount for the front wheel torque command, and then uses the calculated torque correction amount to compensate the front wheel torque command.

[0224] At this point, the value obtained by multiplying the backlash speed estimate or the backlash acceleration estimate of the rear-wheel drive system by the weight value can be determined as the torque correction amount for the front-wheel torque command.

[0225] Alternatively, the torque correction amount for the front wheel torque command can be determined as the sum of the backlash speed estimate of the rear wheel drive system multiplied by a first weight based on the desired torque and the backlash acceleration estimate of the rear wheel drive system multiplied by a second weight based on the desired torque, with a filter and a rate of change (gradient) limit applied to this sum.

[0226] Korean Patent No. 10-2021-0020189 (published February 24, 2021, US Patent No. 11,625,959) disclosed by the inventors discloses a method for calculating and estimating backlash velocity, and the backlash velocity estimate of this disclosure can be determined by the method disclosed in the aforementioned patent document.

[0227] According to the aforementioned patent documents, the backlash speed of the front-wheel drive system can be determined from the rotational speed difference between the front wheel motor and the front wheel and the front wheel torque command, which serves as the torque command for the front wheel motor. Similarly, the backlash speed of the rear-wheel drive system can be determined from the rotational speed difference between the rear wheel motor and the rear wheel and the rear wheel torque command, which serves as the torque command for the rear wheel motor.

[0228] Furthermore, by applying a rate-of-change limit to the original backlash estimate, the torque correction amount can be determined as the rate-of-change limit. Here, the rate-of-change limit can be a variable value adjusted according to the desired torque, such as... Figure 6 As shown.

[0229] Figure 6 The graph on the right side shows an example of correcting the backlash estimate by increasing the rate of change limit compared to the left side, where the corrected backlash estimate can be used as a torque correction amount.

[0230] Furthermore, the torque correction amount can be determined as a value obtained by applying the filter to the original backlash estimate. Here, the filter's time constant or gain can be a variable value adjusted based on the desired torque, such as... Figure 7 As shown.

[0231] Figure 7 The graph on the right shows an example of correcting the backlash estimate by decreasing the filter's time constant or increasing the filter's gain compared to the left side, where the corrected backlash estimate can be used as a torque correction amount.

[0232] In addition, such as Figure 8 As shown, the torque correction amount can be determined by applying the dead zone to the original backlash estimate, where the dead zone can expand or shrink according to the desired torque.

[0233] Figure 8The graph on the right side shows an example of correcting the backlash estimate by reducing the dead zone compared to the left side, where the corrected backlash estimate can be used as a torque correction amount.

[0234] Figure 9 This is a diagram illustrating the torque control state according to an embodiment of the present disclosure. Referring below... Figure 2 and Figure 9 The torque control method according to embodiments of the present disclosure will be described in more detail.

[0235] The torque control method according to an embodiment of the present disclosure is executed by a controller 20 and includes: determining a required torque for vehicle driving; determining a torque control mode corresponding to the current vehicle driving state among a plurality of preset torque control modes and switching to the determined torque control mode; determining a front wheel torque command and a rear wheel torque command based on the determined required torque and the switched torque control mode; and controlling the front wheel motor and the rear wheel motor based on the determined front wheel torque command and the rear wheel torque command.

[0236] Here, multiple torque control modes may include: a reverse distribution mode in the acceleration direction, wherein the front wheel torque command is determined to be the maximum torque threshold of the front wheels and the rear wheel torque command is determined to be a positive (+) torque value; and a reverse distribution mode in the regeneration direction, wherein the rear wheel torque command is determined to be the minimum torque threshold of the rear wheels and the front wheel torque command is determined to be a negative (-) torque value.

[0237] Multiple torque control modes may also include a same-direction distribution mode for acceleration, in which the front wheel torque command and the rear wheel torque command are both determined to be positive (+) torque values.

[0238] In addition, multiple torque control modes may include a same-direction distribution mode for regeneration, in which the front wheel torque command and the rear wheel torque command are both determined to be negative (-) torque values.

[0239] Reference Figure 9 This disclosure does not consistently use either reverse or same-direction allocation, but rather uses both reverse and same-direction allocation patterns. Figure 9 In the diagram, dashed circles indicate the switching between the opposite direction distribution mode and the same direction distribution mode.

[0240] Furthermore, in this disclosure, the controller 20 performs mode selection and switching appropriate to the situation in both the reverse distribution mode and the same-direction distribution mode. Therefore, as... Figure 2 As shown, depending on the situation, the front wheel torque command and the rear wheel torque command can have opposite symbols or the same symbol.

[0241] In the driver Figure 9At time point (A), when the accelerator is pressed (accelerator activated), the required torque (= total torque command, total torque command) before pressing the accelerator is negative (-) value, but the required torque increases to a positive (+) value after pressing the accelerator (torque direction changes, "required torque ≤ mode switching threshold").

[0242] Therefore, according to the above mode switching method, at the time point (A) when the driver depresses the accelerator, the vehicle's torque control mode changes from the regeneration direction to the opposite direction distribution mode. Figure 2 Switching to "Mode 2" in the middle of the acceleration direction will result in a reverse direction distribution mode. Figure 2 (Mode 1 in the text).

[0243] Even in this case, since the mode switching occurs between opposing torque distribution modes, the opposing torque distribution method is maintained, eliminating the need for both front-wheel and rear-wheel torque commands to cross zero. As a result, the desired vehicle acceleration responsiveness can be achieved without concern about backlash, as there is no zero-crossing of the front-wheel and rear-wheel torque commands.

[0244] Furthermore, starting from time point (A), when acceleration torque is necessary for vehicle acceleration, the front wheel torque command with a negative (-) torque value in the regeneration direction reverse distribution mode increases to the front wheel maximum torque threshold when the accelerator is depressed and the system switches to the acceleration direction reverse distribution mode. This threshold is not a positive (+) torque value, but a negative (-) torque value.

[0245] Under rear wheel torque command, the minimum rear wheel torque threshold (which is a positive (+) torque value) is maintained during the reverse distribution mode in the regeneration direction before the accelerator is depressed, and then increased when switching to the reverse distribution mode in the acceleration direction after the accelerator is depressed to achieve the desired vehicle acceleration.

[0246] Thus, because the torque distribution mode is maintained in opposite directions before and after the accelerator is depressed, the front wheel torque command is determined to be negative (-) torque, while the rear wheel torque command is determined to be positive (+) torque, so that the front wheel torque command and the rear wheel torque command have torque values ​​with opposite signs and opposite directions.

[0247] Furthermore, in the reverse distribution modes (“Mode 1” and “Mode 2”), the front wheel torque command is restricted to a torque value equal to or less than the front wheel maximum torque threshold (which is a negative (-) value), while the rear wheel torque command is restricted to a torque value equal to or greater than the rear wheel minimum torque threshold (which is a positive (+) value).

[0248] Therefore, the front wheel torque command and the rear wheel torque command can be determined to be values ​​outside the backlash band without intruding into the backlash band that may occur in each drive system, thus enabling the implementation and realization of backlash band avoidance control.

[0249] However, in the mode prior to time point (A), i.e., in the reverse distribution mode of the regeneration direction (mode 2), since the rear wheel torque command is determined as the rear wheel minimum torque threshold (which is a positive (+) value), the front wheel torque needs to be compensated according to the rear wheel torque limit.

[0250] In other words, the torque command compensation for the front wheels needs to be matched with the torque limit of the rear wheels. To this end, the torque value obtained by subtracting the minimum torque threshold of the rear wheels from the required torque is determined as the front wheel torque command, and the sum of the front wheel torque command and the rear wheel torque command is always set to the required torque value.

[0251] Furthermore, in the mode after time point (A), that is, in the opposite direction distribution mode of acceleration (mode 1), since the front wheel torque command is determined to be the front wheel maximum torque threshold (which is negative (-)), the rear wheel torque needs to be compensated according to the front wheel torque limit.

[0252] That is, the rear wheel torque command needs to compensate for the amount of torque corresponding to the front wheel torque limit. To this end, the torque value obtained by subtracting the maximum front wheel torque threshold from the required torque is determined as the rear wheel torque command, and the sum of the front wheel torque command and the rear wheel torque command is always set to the required torque value.

[0253] At point (B), the driver depresses the accelerator (accelerator activated) and increases the required torque (= total torque command, total torque command) based on the accelerator position sensor value to exceed the preset mode switching threshold ("required torque > mode switching threshold").

[0254] According to the above mode switching method, the controller 20 switches the vehicle's torque control mode from mode 1 (which is the opposite direction distribution mode of acceleration) to mode 3 (which is the same direction distribution mode of acceleration).

[0255] At this point, only the front wheel torque command crosses zero and passes through the backlash zone, while the rear wheel torque command continues to maintain a positive (+) torque value. As described above regarding the front wheel torque command, during the period when the front wheel torque command passes through the backlash zone, the controller 20 performs correction control (backlash control) to limit the rate of torque change (gradient).

[0256] In other words, when the front wheel torque command crosses zero, backlash control is executed to limit the rate of change (gradient) of the front wheel torque command, thereby preventing the front wheel torque command from increasing rapidly. For backlash control, the controller 20 sets the maximum permissible rate of change in the backlash band used for the front wheel torque command to a small value that does not cause backlash shock.

[0257] Therefore, as the front wheel torque command increases and crosses the back clearance band, the controller 20 determines the front wheel torque command to be a value that changes slowly along the maximum permissible rate of change of that small value.

[0258] When the rate of change of the front wheel torque command is limited in this way, a delay in vehicle acceleration response (lack of acceleration torque) may occur. However, to prevent this delay in acceleration response, rear wheel torque compensation is performed using the rear wheel electric motor 41, which still has a surplus torque up to the torque limit. That is, the controller 20 performs torque compensation of the rear wheel torque command while limiting the rate of change of the front wheel torque command.

[0259] At this time, the controller 20 calculates the backlash estimate of the drive system that has crossed zero, determines the torque correction amount based on the calculated backlash estimate, and then uses the determined torque correction amount to compensate the torque command of the drive system that has not crossed zero.

[0260] In other words, Figure 9 In the example, the backlash estimate of the front-wheel drive system that crosses zero is calculated, the torque correction amount is determined based on the calculated backlash estimate, and then the determined torque correction amount is used to compensate for the rear-wheel torque command that does not cross zero.

[0261] Therefore, even when the front wheel torque command crosses zero, the torque compensation of the rear wheel torque command prevents the vehicle's acceleration responsiveness from decreasing.

[0262] When the additional accelerometer position sensor value is input more quickly, or when the torque margin of the upper limit of the rear wheel motor 41 is small, rear wheel torque compensation is only performed in the region equal to or below the upper limit of the torque of the rear wheel motor 41.

[0263] Therefore, the controller 20 can determine the minimum value between the rear wheel torque command compensated by the above-mentioned torque correction amount and the upper limit value of the torque of the rear wheel motor 41 as the rear wheel torque command.

[0264] Then, when the front wheel torque command has completely passed the back clearance zone and is distributed in the same direction in the acceleration direction, the front wheel torque command and the rear wheel torque command are determined by the usual front and rear wheel torque distribution process of distributing the required torque according to the front and rear wheel distribution ratio, so that the sum of the front wheel torque command and the rear wheel torque command follows the required torque.

[0265] Subsequently, the accelerator position sensor value decreases (accelerator turns on), and at time point (C), the required torque (= total torque command, total torque command) corresponding to the accelerator position sensor value becomes equal to or lower than the preset mode switching threshold ("required torque ≤ mode switching threshold").

[0266] Therefore, according to the above mode switching method, the vehicle's torque control mode is switched from mode 3 (which is the same direction distribution mode in the acceleration direction) to mode 1 (which is the opposite direction distribution mode in the acceleration direction).

[0267] Then, when the accelerator is released (the accelerator position sensor value becomes 0), the mode switches from mode 1 (which is the opposite direction of the acceleration direction) to mode 2 (which is the opposite direction of the regeneration direction). Figure 9 The example shows the case where the acceleration position sensor value and the corresponding required torque continue to decrease, and the front wheel torque command switches from the reverse distribution mode in the acceleration direction (mode 1) to the reverse distribution mode in the regeneration direction (mode 2) before passing the back gap strip.

[0268] As described above, during the period when the acceleration position sensor value decreases, only the front wheel torque command must pass through the zero-crossing and backlash bands. For this purpose, the controller 20 performs correction control (backlash control) to limit the rate of change of torque in the front wheel torque command.

[0269] In other words, when the front wheel torque command crosses zero, backlash control is executed to limit the rate of change (gradient) of the front wheel torque command, so that the front wheel torque command does not decrease rapidly, and the controller 20 determines the front wheel torque command as a value that changes slowly along the maximum permissible rate of change.

[0270] Thus, although a vehicle deceleration response delay may occur during backlash control used to limit the rate of change of the front wheel torque command (deceleration delay due to excessive torque), torque compensation for the rear wheel torque command can be performed during the period of limiting the rate of change of the front wheel torque command, so that the deceleration response delay problem can be solved using the rear wheel motor 41.

[0271] At this time, the controller 20 calculates the backlash estimate of the drive system that has crossed zero, determines the torque correction amount based on the calculated backlash estimate, and then uses the determined torque correction amount to compensate the torque command of the drive system that has not crossed zero.

[0272] In other words, Figure 9 In the example, the backlash estimate of the front-wheel drive system that crosses zero is calculated, the torque correction amount is determined based on the calculated backlash estimate, and then the determined torque correction amount is used to compensate for the rear-wheel torque command that does not cross zero.

[0273] However, since the rear wheel torque command is limited to the rear wheel minimum torque threshold with a positive (+) value, the rear wheel torque command cannot be compensated to a value less than the rear wheel minimum torque threshold during the compensation process, and in this case, the rear wheel torque command is determined to be the rear wheel minimum torque threshold.

[0274] At this point, since it is impossible to provide additional compensation for the rear wheel torque command to address the deceleration response delay, brake hydraulic pressure corresponding to the additional torque correction amount required relative to the minimum rear wheel torque threshold is generated, thereby generating the necessary frictional braking torque for compensation. Therefore, the problem of deceleration response delay can be resolved.

[0275] In other words, when the rear wheel torque command is limited to the rear wheel minimum torque threshold, during the period when the rate of change of the front wheel torque command is limited, the insufficient deceleration torque is compensated by friction braking torque.

[0276] During this deceleration torque compensation period, the torque value, which is the sum of the front wheel torque command with a limited rate of change, the rear wheel torque command determined by the rear wheel minimum torque threshold, and the friction braking torque command, follows the required torque. At this time, the friction braking torque command is determined as the value obtained by subtracting the front wheel torque command with a limited rate of change and the rear wheel minimum torque threshold from the required torque.

[0277] Therefore, the controller 20 controls the operation of the front wheel motor 31 and the rear wheel motor 41 according to the front wheel torque command and the rear wheel torque command. At the same time, it generates brake hydraulic pressure according to the friction braking torque command to control the operation of the friction brake 50, thereby generating the torque required in the vehicle.

[0278] Reference Figure 9 It can be seen that after time point (C), the rear wheel torque command is determined as the rear wheel minimum torque threshold, and the torque change rate limit of the front wheel torque command is executed during the zero crossing of the front wheel torque command.

[0279] Furthermore, during torque change rate control, brake hydraulic fluid is generated to generate frictional braking torque, thereby compensating for insufficient deceleration torque. Then, after the front wheel torque command passes the back clearance band, the brake hydraulic fluid and frictional braking torque are reduced, and the required torque is met by the sum of the front wheel torque command and the rear wheel torque command.

[0280] After the front wheel torque command passes through the backlash zone, with the accelerator off, the vehicle's torque control mode switches to "Mode 2," which is a reverse distribution mode in the regeneration direction. Therefore, in Mode 2, the rear wheel torque command is maintained and limited to the minimum rear wheel torque threshold as a positive (+) value, and the front wheel torque command compensates for the torque limit amount based on the rear wheel torque limit.

[0281] At this point, the front wheel torque command is determined to be the value obtained by subtracting the rear wheel torque command from the required torque, and the sum of the front wheel torque command and the rear wheel torque command always satisfies the value of the required torque.

[0282] Reference Figure 9The vehicle acceleration graph shown at the bottom of the graph shows that even though the front wheel torque command crosses zero and passes through the backlash band at time points (B) and (C), there is no acceleration or deceleration delay of the vehicle.

[0283] At time point (D), the driver depresses the brake, the required torque switches to the deceleration torque as a negative torque, and according to the above mode switching method, the vehicle's torque control mode switches from mode 2 (which is the opposite direction distribution mode of the regeneration direction) to mode 4 (which is the same direction distribution mode of the regeneration direction).

[0284] At this point, since the torque control mode switches from the reverse distribution mode to the same-direction distribution mode for regeneration, the rear wheel torque command that is kept positive (+) must be reduced to negative (-) after passing through the back clearance zone while crossing zero.

[0285] Thus, during the period when the rear wheel torque command passes through the backlash zone, the controller 20 performs backlash control to limit the rate of change of the rear wheel torque command, similar to the rate of change (gradient) limit of the front wheel torque command. During backlash control, the rate of change of the rear wheel torque command is controlled within the maximum permissible rate of change, which is set to a small value that does not cause backlash impact.

[0286] Furthermore, the zero-crossing and backlash band of the rear wheel torque command can cause a delay in vehicle deceleration response (torque excess), and the front wheel torque command is reduced to compensate for this deceleration response delay. Here, reducing the front wheel torque command means changing the front wheel torque command in the direction that the absolute value of the front wheel torque command with a negative value (-) increases.

[0287] To compensate for the deceleration response delay as described above, during the rate of change of the rear wheel torque command limit, the controller 20 calculates the backlash estimate of the drive system that has crossed zero, determines the torque correction amount based on the calculated backlash estimate, and then uses the determined torque correction amount to compensate for the torque command of the drive system that has not crossed zero.

[0288] In other words, Figure 9 In the example, the backlash estimate of the rear-wheel drive system that crosses zero is calculated, and the torque correction amount is determined based on the calculated backlash estimate. Then, the determined torque correction amount is used to compensate for the front-wheel torque command that does not cross zero.

[0289] However, if the torque of the front wheel motor 31 is not fully sufficient to meet the torque correction required to meet the required torque due to insufficient lower limit of the front wheel torque command, the controller 20 allows friction braking torque to meet the remaining compensation.

[0290] In other words, if the value obtained by subtracting the rear wheel torque command (negative value) from the required torque is less than the preset lower limit of the front wheel motor 31 torque (negative value), in order to compensate for the insufficient torque in the required torque during the rate of change control of the rear wheel torque command, the compensation is partially performed by the front wheel torque until the lower limit of the front wheel motor 31 torque is reached, and the remaining part is compensated by friction braking torque by generating brake hydraulic fluid.

[0291] Therefore, the front wheel torque command using torque correction compensation and the lower limit of the torque of the front wheel motor 31 can be compared, and the maximum value of the two values ​​can be determined as the front wheel torque command.

[0292] In other words, since both compared values ​​are negative (-), the smaller absolute value between the compensated front wheel torque command and the lower limit of the torque of the front wheel motor 31 is determined as the front wheel torque command.

[0293] When the front wheel torque command using torque correction compensation is less than the lower limit of the torque of the front wheel motor 31, and the front wheel torque command is determined to be the lower limit, the controller 20 supplements the insufficient deceleration torque through friction braking torque. In this case, the friction braking torque command can be determined as the torque value obtained by subtracting the rear wheel torque command and the front wheel torque command (torque lower limit) which have a rate of change limit from the required torque.

[0294] With the friction braking torque command determined in this manner, the controller 20 controls the operation of the front wheel motor 31 according to the front wheel torque command, and controls the operation of the rear wheel motor 41 according to the rear wheel torque command. Simultaneously, based on the determined friction braking torque command, the controller controls the operation of the friction brake 50 to generate the necessary braking hydraulic pressure and friction braking torque, enabling full torque compensation to meet the required torque.

[0295] After the rear wheel torque command has completely passed the back clearance zone, during the same-direction distribution in the regeneration direction, the front wheel torque command and the rear wheel torque command are determined by the usual front and rear wheel torque distribution process of distributing the required torque according to the front and rear wheel distribution ratio, and the required torque is followed by the sum of the front wheel torque command and the rear wheel torque command.

[0296] If the sum of the front wheel torque command and the rear wheel torque command does not meet the required torque due to the lower limit of the torque of the front wheel motor 31 or the rear wheel motor 41, the required residual braking torque is met by generating friction braking torque. At this time, the sum of the rear wheel torque command (regenerative torque command), the front wheel torque command (regenerative torque command), and the friction braking torque command follows the required torque.

[0297] At time point (E), the driver releases the brake and switches the torque control mode from "Mode 4" (which is the same direction distribution as the regeneration direction) to "Mode 2" (which is the opposite direction distribution of the regeneration direction) by means of the above mode switching method.

[0298] At this point, the rear wheel torque command, which maintains a negative (-) torque, is increased again to the rear wheel minimum torque threshold, which is a positive (+) torque value. Therefore, the rear wheel torque command must cross the backlash band simultaneously with crossing zero.

[0299] After time point (E), during the period when the rear wheel torque command crosses zero and passes through the backlash zone, the controller 20 performs backlash control to limit the rate of change of the rear wheel torque command, and during the backlash control, the rate of change of the rear wheel torque command is controlled to the maximum permissible rate of change, which is set to a small value that does not cause backlash impact.

[0300] Additionally, the zero-crossing and backlash band of the rear wheel torque command may cause a delay in the vehicle's deceleration response (excess torque), so the front wheel torque command is increased to compensate for this delay in deceleration response.

[0301] Here, increasing the front wheel torque command means changing the front wheel torque command in the direction that the absolute value of the front wheel torque command with a negative (-) value decreases.

[0302] In the process of compensating for deceleration response delay as described above, the controller 20 calculates the backlash estimate of the drive system that has crossed zero, determines the torque correction amount based on the calculated backlash estimate, and then uses the determined torque correction amount to compensate for the torque command of the drive system that has not crossed zero.

[0303] In other words, Figure 9 In the example, the backlash estimate of the rear-wheel drive system that crosses zero is calculated, the torque correction amount is determined based on the calculated backlash estimate, and then the determined torque correction amount is used to compensate for the front-wheel torque command that does not cross zero.

[0304] As mentioned above, Figure 9 An example of mode switching and torque control based on time points (D) and (E) is described, and it can be seen that, as Figure 9 As shown in the vehicle acceleration graph at the bottom, no vehicle responsiveness delay occurred despite the rear wheel torque command crossing zero and passing through the backlash band at times (D) and (E).

[0305] Figure 10 This is a diagram illustrating the front wheel torque command, rear wheel torque command, and backlash estimate for each torque distribution mode according to this disclosure. Figure 10In this context, the total torque command refers to the command that sums the torque values ​​of the front wheel torque command and the rear wheel torque command. The torque value of the total torque command corresponds to the required torque value before the front and rear wheel torque distribution.

[0306] Figure 10 An example is shown where the direction of the torque required for vehicle movement changes from a negative (-) torque direction (vehicle deceleration direction) to a positive (+) torque direction (vehicle acceleration direction), and then back to a negative (-) torque direction (vehicle deceleration direction).

[0307] exist Figure 10 The "Same-direction front wheel torque distribution command" and "Same-direction rear wheel torque distribution command," indicated by dashed lines, correspond to the entire range of required torque, according to the reference... Figure 3 The torque control mode of the drive system (i.e., the same-direction distribution mode) distributes the required torque (total torque command) as a result of the front wheel torque command and the rear wheel torque command.

[0308] In the same-direction torque distribution mode, when there is a request for a change in the direction of the required torque, the directions of the front wheel torque command and the rear wheel torque command also change simultaneously. During this change in direction, each torque command crosses zero while passing through the backlash zone.

[0309] In addition, by Figure 10 The dashed lines indicating "reverse front wheel torque distribution command" and "reverse rear wheel torque distribution command" correspond to the entire range of required torque, according to reference... Figure 4 The aforementioned drive system torque control mode (i.e., reverse distribution mode) distributes the required torque (total torque command) as a result of front wheel torque command and rear wheel torque command.

[0310] In the reverse torque distribution mode, even if the direction of the required torque changes, the rear wheel torque command remains in the positive (+) direction (which is the direction of electric motor drive) during the change of the required torque. Specifically, even if the required torque is in the direction of vehicle deceleration (i.e., the negative (-) direction), the rear wheel torque command is determined to be the minimum rear wheel torque threshold, which is a positive (+) direction torque value, without any change in direction.

[0311] When a front wheel torque command is in effect, even if the direction of the required torque changes, the torque remains in the negative (-) direction (which is the direction of electric motor regeneration) during the change of the required torque. Specifically, even when the required torque is the torque in the direction of vehicle acceleration (i.e., the torque in the positive (+) direction), the front wheel torque command is determined to be the maximum front wheel torque threshold, which is a negative (-) direction torque value without any change in direction.

[0312] In this disclosure, during the switching between the same-direction distribution mode and the opposite-direction distribution mode, that is, during the distribution mode switching period, when one of the front wheel torque command and the rear wheel torque command crosses zero, torque correction is performed on the other that does not cross zero.

[0313] Figure 10 This shows an example where the torque command for the rear wheels did not cross zero, but the torque command for the front wheels did. Additionally, in... Figure 10 In the example, when the required torque is in the positive (+) direction (i.e., the direction of vehicle acceleration), a switch is made between the same-direction distribution mode and the opposite-direction distribution mode.

[0314] In other words, Figure 10 In the example, during the period when the required torque increases linearly, a switch is first performed from the reverse distribution mode to the same direction distribution mode ("switch from reverse distribution mode to same direction distribution mode"), and then during the period when the required torque decreases linearly, a switch is performed from the same direction distribution mode to the reverse distribution mode ("switch from same direction distribution mode to reverse distribution mode").

[0315] Figure 10 The "front wheel torque command" and "rear wheel torque command" shown by solid lines correspond to the torque commands allocated from the desired torque according to this disclosure. Based on the exemplary front wheel torque commands and rear wheel torque commands, it can be seen that during the allocation mode switching, the rate of change of the front wheel torque command is limited to reduce backlash impact, and torque correction of the rear wheel torque command is performed.

[0316] For more details, please refer to Figure 10 For example, when the required torque (the torque of the total torque command) is in the torque band in the negative (-) direction of the vehicle deceleration direction, the mode is controlled to be the reverse direction distribution mode of the regeneration direction.

[0317] In the reverse distribution mode of the regeneration direction, the rear wheel torque command is determined as the minimum torque threshold of the rear wheel as the positive (+) torque value, while the front wheel torque command is determined as the torque in the negative (-) direction (which is the regeneration direction of the motor).

[0318] Then, when the direction of the required torque changes and the required torque becomes the positive (+) direction torque in the vehicle's acceleration direction, the distribution mode is switched from the regeneration direction to the reverse acceleration direction distribution mode. In the reverse acceleration direction distribution mode, the front wheel torque command is determined as the front wheel maximum torque threshold as a negative (-) torque value, while the rear wheel torque command is determined as the positive (+) direction torque (which is the electric motor drive direction).

[0319] Then, as the required torque increases, the torque distribution mode switches from the opposite direction of acceleration to the same direction of acceleration, and during the distribution mode switch, the front wheel torque command crosses zero while passing through the back clearance zone.

[0320] Furthermore, during the distribution mode switching, a backlash estimate is calculated for the front-wheel drive system passing through the backlash zone, and the backlash estimate calculated during the distribution mode switching can be used as an effective value for correcting the rear wheel torque command.

[0321] More specifically, during the distribution mode switching, when the front wheel torque command crosses zero, the rate of change (gradient) of the front wheel torque command is limited to a predetermined rate of change in order to reduce backlash impact. At the same time, the backlash estimate in the front wheel drive system is calculated, and then based on the calculated backlash estimate in the front wheel drive system, the torque correction amount used to correct the rear wheel torque command is calculated.

[0322] Additionally, during the distribution mode switch, torque correction is performed on the rear wheel torque command using a torque correction amount determined based on the backlash estimate of the front-wheel drive system, to compensate for the original torque command from the desired torque distribution.

[0323] Then, the required torque decreases in the same-direction distribution mode in the acceleration direction and switches to the opposite-direction distribution mode in the acceleration direction. During the distribution mode switching, the front wheel torque command crosses zero while passing through the backlash zone.

[0324] Similarly, during the switch to the reverse distribution mode, a backlash estimate is calculated for the front-wheel drive system passing through the backlash band, and the backlash estimate calculated during the distribution mode switch can be used as an effective value for correcting the rear wheel torque command.

[0325] More specifically, during the switch to the reverse distribution mode, when the front wheel torque command crosses zero, the rate of change (gradient) of the front wheel torque command is limited to a predetermined rate of change to reduce backlash impact. At the same time, the backlash estimate in the front wheel drive system is calculated, and then based on the calculated backlash estimate of the front wheel drive system, the torque correction amount used to compensate for the rear wheel torque command is calculated.

[0326] Additionally, during the switch to reverse torque distribution mode, torque correction is performed using a torque correction amount determined based on the backlash estimate of the front-wheel drive system to compensate for the original torque command from the desired torque distribution for the rear-wheel torque command.

[0327] After the distribution mode switch is completed, in the distribution mode in the opposite direction of acceleration, the front wheel torque command is determined as the front wheel maximum torque threshold. Then, the direction of the required torque is changed so that the required torque becomes the torque in the negative (-) direction of the vehicle deceleration direction, so that the mode is switched from the acceleration direction to the regeneration direction.

[0328] In the reverse distribution mode of the regeneration direction, the rear wheel torque command is determined as the minimum rear wheel torque threshold as a positive (+) torque value, and the front wheel torque command is determined as the torque in the negative (-) direction (which is the regeneration direction of the motor).

[0329] exist Figure 10 At the bottom shown, the backlash speed is exemplified as a backlash estimate calculated for the front-wheel drive system, and the calculated backlash estimate is only valid during the switch from reverse distribution mode to same-direction distribution mode ("switch from reverse distribution to same-direction distribution").

[0330] Therefore, when compensating the rear wheel torque command only during the distribution mode switch, the torque correction amount is determined based on the calculated backlash estimate, and then the determined torque correction amount is used to perform torque correction to compensate the rear wheel torque command.

[0331] The torque control system and method for the drive system of an electric vehicle according to embodiments of the present disclosure have been described in detail above. According to the present disclosure, by applying a method of sequentially switching the direction of front wheel torque and rear wheel torque, backlash in the drive system of an electric vehicle can be reduced, and backlash vibration can be decreased, thereby improving the drivability of the vehicle.

[0332] Furthermore, according to this disclosure, since the backlash impact problem is solved, the vehicle's acceleration / deceleration responsiveness and longitudinal driving performance can be improved.

[0333] Specifically, in this disclosure, during the period when one of the front wheel torque command and the rear wheel torque command passes through the corresponding drive system backlash zone, a backlash estimate is calculated. Based on the calculated backlash estimate, a torque correction amount is determined, and the determined torque correction amount is used to compensate for the other torque command. Therefore, drive system torque that does not pass through the backlash zone can be used to compensate for vehicle acceleration discontinuities that occur during the period when one of the torque commands passes through the backlash zone.

[0334] Therefore, it can significantly solve the discontinuity and impact in vehicle acceleration and two-stage acceleration / deceleration.

[0335] This disclosure has been described in detail with reference to preferred embodiments thereof. However, those skilled in the art will understand that variations may be made in these embodiments without departing from the principles and spirit of this disclosure, the scope of which is defined in the appended claims and their equivalents.

Claims

1. A torque control system for a drive system of an electric vehicle, comprising: The controller generates front wheel torque commands and rear wheel torque commands with the torque values ​​required for the vehicle's driving, based on the torque distribution mode selected from multiple preset torque distribution modes according to the vehicle's driving information. The front wheel motor controls the front wheel motor according to the front wheel torque command generated and output by the controller; and The rear wheel motor controls the rear wheel motor according to the rear wheel torque command generated and output by the controller; The controller is configured as follows: Determine whether a switch between the multiple torque distribution modes has occurred; During the switching between the multiple torque distribution modes, based on the backlash estimate in the drive system of the first torque command that crosses zero among the front wheel torque command and the rear wheel torque command, a torque correction amount for reducing backlash impact is calculated; and Using the calculated torque correction amount, torque correction is performed on the second torque command that does not reach zero.

2. The torque control system according to claim 1, wherein, The multiple torque distribution modes include: In a unidirectional torque distribution mode, the front wheel torque command and the rear wheel torque command are determined to be torque values ​​in the same direction between the motor regeneration direction and the motor drive direction; and In the reverse direction distribution mode, the front wheel torque command and the rear wheel torque command are determined as torque values ​​in different directions between the motor regeneration direction and the motor drive direction.

3. The torque control system according to claim 1, wherein, The controller is configured to: Based on the accelerator operation state, brake operation state, and required torque, which are the vehicle driving information, the torque distribution mode corresponding to the current vehicle driving state is selected from the multiple torque distribution modes.

4. The torque control system according to claim 1, wherein, The backlash estimate corresponds to one or both of the backlash velocity estimate of the drive system when the torque command crosses zero and the backlash acceleration estimate of the drive system when the torque command crosses zero.

5. The torque control system according to claim 1, wherein, The controller is configured to: The torque correction amount is determined as a value obtained by applying one or more of the following to the backlash estimate: weight, filter, rate of change limit, and dead zone.

6. The torque control system according to claim 5, wherein, The controller is configured to: Based on at least one of the required torque, current torque estimate, accelerator position sensor value, vehicle speed, and motor speed, adjust the weights applied to the backlash estimate, the time constant or gain of the filter, the rate of change limit for rate of change constraint, and the dead zone.

7. A torque control method for a drive system of an electric vehicle, comprising the following steps: Based on the torque distribution mode selected from multiple preset torque distribution modes based on vehicle driving information, determine the front wheel torque command and rear wheel torque command with the torque value to be distributed from the vehicle's driving requirements. Determine whether a switch between the multiple torque distribution modes has occurred; During the switching between the plurality of torque distribution modes, a backlash estimate for the drive system is determined for the zero-crossing torque command among the front wheel torque command and the rear wheel torque command. Based on the determined backlash estimate, the torque correction amount used to reduce backlash impact is calculated; and Using the calculated torque correction amount, torque correction is performed on the other torque command among the front wheel torque command and the rear wheel torque command that is not zero.

8. The method according to claim 7, wherein, The multiple torque distribution modes include: In a unidirectional torque distribution mode, the front wheel torque command and the rear wheel torque command are determined to be torque values ​​in the same direction between the motor regeneration direction and the motor drive direction; and In the reverse direction distribution mode, the front wheel torque command and the rear wheel torque command are determined as torque values ​​in different directions between the motor regeneration direction and the motor drive direction.

9. The method according to claim 7, further comprising the following step: Based on the accelerator operation state, brake operation state, and required torque, which are the vehicle driving information, the torque distribution mode corresponding to the current vehicle driving state is selected from the multiple torque distribution modes.

10. The method according to claim 7, wherein, The backlash estimate corresponds to one or both of the backlash velocity estimate of the drive system when the torque command crosses zero and the backlash acceleration estimate of the drive system when the torque command crosses zero.

11. The method of claim 7, further comprising the step of: The torque correction amount is determined as a value obtained by selectively applying one or more of weights, filters, rate of change limits, and dead zones to the backlash estimate.

12. The method of claim 11, further comprising the step of: Based on at least one of the required torque, current torque estimate, accelerator position sensor value, vehicle speed, and motor speed, adjust the weights applied to the backlash estimate, the time constant or gain of the filter, the rate of change limit for rate of change constraint, and the dead zone.

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