Method and system for torque control for an all-wheel drive vehicle

Abstract

Method and system for torque control of an all-wheel-drive vehicle. The method for torque control of an all-wheel-drive vehicle comprises the following: Step S1, sensing a coefficient of static friction of a reference wheel and other wheels in response to a vehicle skidding condition; Step S2, sensing a target drive torque to prevent wheel spin of the reference wheel based on the coefficient of static friction of the other wheels; Step S3, sensing a linear wheel speed of the reference wheel in response to the reference wheel not spinning, and using the linear wheel speed as the vehicle's reference speed; and Step S4, adjusting the drive torque of the other wheels based on the vehicle's reference speed.A target drive torque to prevent a reference wheel from spinning is obtained from the coefficient of static friction of other wheels, and a wheel speed of the reference wheel is used as the reference vehicle speed, thereby reducing the loss of drive force and the generation of a yaw moment.

Description

Technical field

[0001] The present invention relates to the technical field of vehicle control, in particular a method and system for torque control for a vehicle with all-wheel drive. Technical background

[0002] As in Fig. Figure 1 shows an all-wheel-drive automobile with a transfer case equipped with four independent motors, each corresponding to one of the four wheels. Therefore, the torque and speed of each of the four wheels can be controlled independently. When the automobile is traveling on a road with a low coefficient of friction, the output torque of each motor can be used to control the torque of the corresponding wheel, thus preventing wheel spin and loss of drive power.

[0003] To prevent wheel spin and loss of drive power, it is therefore an urgent problem to be solved for an all-wheel drive vehicle with a transfer case whether the output torque of the motors can be precisely controlled to maximize the use of road friction. Brief description of the invention

[0004] To overcome the problem existing in the prior art, the present disclosure provides a method and system for torque control for an all-wheel drive vehicle.

[0005] According to a first aspect of embodiments of the present disclosure, the present disclosure provides a method for torque control for an all-wheel-drive vehicle, comprising: Step S1: Detecting a coefficient of static friction of a reference wheel and other wheels in response to a skidding condition of the vehicle; Step S2: Detecting a target drive torque to prevent the reference wheel from spinning based on the coefficient of static friction of the other wheels; Step S3: Detecting a linear wheel speed of the reference wheel in response to the reference wheel not spinning, and using the linear wheel speed as the reference vehicle speed of the vehicle; and Step S4: Adjusting the drive torque of the other wheels based on the reference vehicle speed.

[0006] In some embodiments, step S2 specifically further includes: step S21: sensing a target static friction rate of the reference wheel based on the coefficient of static friction of the other wheels; step S22: sensing a wheel load of the reference wheel; and step S23: sensing a target drive torque to prevent slippage of the reference wheel based on the target static friction rate and the wheel load of the reference wheel.

[0007] In some embodiments, the target static friction rate of the reference wheel in step S21 is a difference between the minimum value of the coefficient of static friction of the other wheels and a calibration value.

[0008] In some embodiments, the target static friction rate of the reference wheel in step S21 is a difference between the coefficient of static friction of the wheel on the same side and a calibration value.

[0009] In some embodiments, adjusting the drive torque of the other wheels based on the reference vehicle speed includes: Step S41: Detecting an actual slip rate of the other wheels based on the reference vehicle speed; and Step S42: Adjusting the drive torque of the other wheels accordingly in response to the difference between the actual slip rate of the other wheels and a target slip rate.

[0010] According to a second aspect of the embodiments of the present disclosure, the present disclosure provides a torque control system for an all-wheel-drive vehicle, comprising: a coefficient of static friction detection module that detects a coefficient of static friction of a reference wheel and other wheels in response to a skidding condition of the vehicle; a drive torque detection module that detects a target drive torque to prevent the reference wheel from spinning based on the coefficient of static friction of the other wheels; a reference vehicle speed detection module that detects a linear wheel speed of the reference wheel in response to the reference wheel not spinning and uses the linear wheel speed as the reference vehicle speed of the vehicle; and an adjustment module for adjusting the drive torque of the other wheels based on the reference vehicle speed.

[0011] In some embodiments, the drive torque sensing module specifically further includes: a first sensing module that detects a target static friction rate of the reference wheel based on the coefficient of static friction of the other wheels; a second sensing module that detects a wheel load of the reference wheel; and a third sensing module that detects a target drive torque to prevent wheel spin based on the target static friction rate and the wheel load of the reference wheel.

[0012] In some embodiments, the target static friction rate of the reference wheel in the first detection module is a difference between the minimum value of the coefficient of static friction of the other wheels and a calibration value.

[0013] In some embodiments, the target static friction rate of the reference wheel in the first detection module is a difference between the coefficient of static friction of the wheel on the same side and a calibration value.

[0014] In some embodiments, adjusting the drive torque of the other wheels based on the reference vehicle speed includes: a fourth sensing module that detects an actual slip rate of the other wheels based on the reference vehicle speed; and a first adjustment module that adjusts the drive torque of the other wheels in response to the difference between the actual slip rate of the other wheels and a target slip rate.

[0015] The technical solution provided by the embodiments of the present disclosure may include the following advantageous effects: Compared to a reference vehicle speed obtained by means of integrated acceleration, Kalman filters and the like, the present invention obtains a drive torque to prevent slippage of a reference wheel by a coefficient of static friction of the other wheels and then uses the linear wheel speed of the reference wheel as the reference vehicle speed such that a numerical value of the obtained reference vehicle speed is more accurate and has a smaller error.In addition, the reference vehicle speed according to the present invention, compared to a method with periodic reduction of the driving force of a wheel, does not require excessive waste of driving force from the wheels and also avoids the risk of the vehicle rotating or overturning due to a yaw moment generated by reducing the driving force of a wheel, so that driving behavior and vehicle speed are more stable. Brief description of the drawings

[0016] The accompanying drawings, which are included in the description and form part of it, illustrate embodiments in accordance with the present disclosure and serve to explain the principles of the present disclosure in connection with the description. Fig. Figure 1 is a schematic construction diagram of a chassis design of an all-wheel drive vehicle; Fig. Figure 2 is a schematic side view of an all-wheel drive vehicle; Fig. 3 is a schematic top view of an all-wheel drive vehicle; and Fig. Figure 4 is a schematic flowchart of a method for torque control for an all-wheel drive vehicle, illustrated according to an exemplary embodiment. Detailed description of embodiments

[0017] Exemplary embodiments are described in detail herein; examples are illustrated in the accompanying drawings. Where reference is made to the drawings in the following description, the same reference numerals, unless otherwise specified, refer to the same or similar elements in different drawings. The embodiments described in the following examples do not represent all embodiments within the meaning of this disclosure. Rather, they are merely examples of devices and methods that correspond to some aspects of this disclosure as described in detail in the accompanying claims.In the prior art, the most important prerequisite for controlling drive torque to prevent wheel spin is knowing the current reference vehicle speed (the longitudinal speed of the actual movement of a vehicle's center of gravity relative to the ground). However, when a driver depresses the accelerator pedal hard, all four wheels deliver a high drive torque, potentially causing all four wheels to spin. This means that the linear wheel speed measured by a sensor during wheel spin cannot be used as the reference vehicle speed. Therefore, the reference vehicle speed can only be obtained using other methods, such as an integrated acceleration method, a Kalman filter method, or a method involving periodic reduction of the drive force applied to one of the wheels.

[0018] However, if the integrated acceleration method or the Kalman filter method is used to calculate the reference vehicle speed, one signal in this method originates from an acceleration sensor. Errors in the acceleration sensor itself and deviations caused by changes in road inclination inevitably combine, resulting in a high numerical error and an inaccuracy in the calculated reference vehicle speed.

[0019] Furthermore, when using the method of periodically reducing the drive force to one of the wheels, an additional yaw moment is generated, causing instability in the vehicle's handling and speed, which may lead to the risk of the vehicle spinning out or rolling over. To solve the aforementioned technical problem, the present disclosure therefore provides a method for torque control for an all-wheel-drive vehicle, as described in Fig. Figure 4 shows the following steps: Step S1: in response to a vehicle skidding condition, a coefficient of static friction of a reference wheel and other wheels is detected; Step S2: based on the coefficient of static friction of the other wheels, a target drive torque is detected to prevent the reference wheel from spinning; Step S3: in response to the reference wheel not spinning, a linear wheel speed of the reference wheel is detected and the linear wheel speed is used as the vehicle's reference speed; and Step S4: based on the vehicle's reference speed, the drive torque of the other wheels is adjusted.

[0020] The reference wheel is a pre-selected wheel, and its linear speed in a non-spinning state is used as the vehicle's reference speed (i.e., vehicle speed). In this embodiment, a rear wheel can be selected as the reference wheel. When the rear wheels are stable and do not spin, the vehicle will be driven more safely and stably.

[0021] In step S1, the vehicle records the static friction rate of each wheel in real time; more precisely, the vehicle automatically monitors the static friction rate of each wheel according to a cycle period, which is typically a software run cycle, generally 1-10 ms. Whether a wheel is slipping can be determined by measuring its acceleration. If it is detected that the wheel is not slipping, the coefficient of static friction is the maximum value of the static friction rate calculated in the previous cycle and the static friction rate calculated in the current cycle.

[0022] When a vehicle's wheel is detected spinning, the corresponding rate of static friction at that moment is the coefficient of static friction. The rate of static friction is the ratio of the tangential reaction force on the ground, caused by the drive torque acting on the wheel, to the normal wheel reaction force (also called wheel load); more precisely, rate of static friction = wheel drive torque / wheel load. The coefficient of static friction is the ratio of the maximum limit of the tangential reaction force on the ground acting on the wheel to the normal wheel reaction force; more precisely, the maximum value of the rate of static friction.

[0023] The static friction rate of each wheel is obtained by measuring the wheel load of each wheel and the drive torque of each wheel.

[0024] The signals required to detect the wheel load include the following: longitudinal acceleration from a sensor, lateral acceleration from a sensor, road inclination and road gradient. Front axle load GF=G*(b / L*(g2−incline2)0.5 / g−longitudinal acceleration*h / L / g); Rear axle load GR=G*(a / L*(g2−incline2−gradient2)0.5 / g+longitudinal acceleration*h / L / g); Wheel load front left=GF*(0.5−lateral acceleration*h / B / g); Front right wheel load = GF*(0.5+lateral acceleration*h / B / g); Rear left wheel load = GR*(0.5−lateral acceleration*h / B / g); and Rear right wheel load GR*(0.5+lateral acceleration*h / B / g).

[0025] As in Fig. 2 and Fig. Figure 3 shows that G is the gravity of the vehicle, h is the height of the vehicle's center of gravity, L is the distance between a front axle and a rear axle, a is the distance between the front axle and the center of gravity, b is the distance between the rear axle and the center of gravity, B is the width of the axles, and g is the gravitational constant.

[0026] The signals required to detect the drive torque at each wheel include the following: an output torque of a motor corresponding to each wheel from a sensor and a wheel angular acceleration of each wheel from a sensor. Wheel drive torque = (Output torque of the motor − (Wheel angle acceleration) * J) / R where J is the moment of inertia, including the motor, wheel and transmission component, and R is the wheel radius.

[0027] Finally, the static friction rate of each wheel is obtained by static friction rate = wheel drive torque / wheel load.

[0028] In some embodiments, step S2 specifically further includes: step S21: sensing a target static friction rate of the reference wheel based on the coefficient of static friction of the other wheels; step S22: sensing a wheel load of the reference wheel; and step S23: sensing a target drive torque to prevent slippage of the reference wheel based on the target static friction rate and the wheel load of the reference wheel.

[0029] In particular, in some embodiments, the target static friction rate of the reference wheel in step S21 is the difference between the minimum value of the coefficient of static friction (µ1, µ2, µ3) of the other wheels and a calibration value. More precisely, target static friction rate of the reference wheel = min(µ1, µ2, µ3) - calibration value, where the calibration value can be in a range of 0.02 to 0.05. In this way, the resulting target static friction rate of the reference wheel is only slightly lower than the static friction rate of the other three wheels, without wasting too much of the motor's drive torque.

[0030] In some other embodiments, the target static friction rate of the reference wheel in step S21 is a difference between a static friction coefficient of a wheel on the same side and a calibration value. For example, if the left rear wheel is the reference wheel, the target static friction rate of the reference wheel can be a difference between a static friction coefficient of the left front wheel and the calibration value. This can also reduce the calculated quantity of a system.

[0031] Furthermore, the wheel load of the reference wheel was described in detail in step S22 in the aforementioned step of recording the wheel load and is not repeated here.

[0032] In step S23, the target drive torque of the wheel is obtained using the target static friction rate of the reference wheel obtained in step S21 and the wheel load of the reference wheel obtained in step S22, using the formula above: Static friction rate = Wheel drive torque / Wheel load.

[0033] According to the above formula: Wheel drive torque = (Motor output torque - (Wheel angle acceleration)*J) / R, a motor output torque corresponding to the reference wheel is obtained, and the motor output torque is the maximum torque to prevent the reference wheel from spinning.

[0034] Furthermore, in step S3, the output of the corresponding motor is controlled based on the received output torque of the reference wheel's motor in such a way that the reference wheel does not spin under the input torque. As a result of the reference wheel not spinning, its linear speed is detected by a sensor and used as the vehicle's reference speed; more precisely, the linear speed of the reference wheel is used as the vehicle's speed.

[0035] As can be seen from step S21, as long as the target coefficient of static friction of the reference wheel is only slightly below the minimum value of the coefficient of static friction of the other three wheels, or only slightly below the coefficient of static friction of the wheel on the same side, an accurate reference vehicle speed can be obtained, the loss of the drive torque of the motor of the reference wheel is minimal, and any additional yaw moment generated is also very small, so that the vehicle speed is more stable without compromising the driving stability and safety of the vehicle.

[0036] Furthermore, adjusting the drive torque of the other wheels based on the reference vehicle speed includes the following: Step S41: based on the reference vehicle speed, an actual slip rate of the other wheels is detected; and Step S42: in response to the difference between the actual slip rate of the respective other wheels and a target slip rate, the drive torque of the other wheels is adjusted.

[0037] In particular, the wheel slip rate (also known as slip rate) is the proportion of a spinning component of the wheel's movement.

[0038] The linear wheel speed of each wheel can be measured by a sensor. The vehicle speed is the reference vehicle speed in the non-slip state of the reference wheel obtained in step S3. Using the formula: Wheel Slip Rate (Wheel Slip) = (Linear Wheel Speed ​​- Vehicle Speed) / Linear Wheel Speed, the actual slip rate of the other three wheels at the reference vehicle speed can be obtained. The output torque of the motor of the other three wheels (or the input torque of the wheels) is adjusted to match the linear wheel speed of each wheel until the actual slip rate of the other three wheels falls within a preset required range or is close to a target slip rate corresponding to each wheel, and the vehicle no longer skids. Each wheel has a target slip rate that is pre-calibrated based on the vehicle and tire characteristics.The target slip rate is not a fixed numerical value, but the system can automatically generate a corresponding target slip rate under several input conditions, such as different vehicle speeds and drive torques.

[0039] In summary, compared to the reference vehicle speed determined by means of integrated acceleration, Kalman filters and the like, the present invention obtains the drive torque to prevent the reference wheel from slipping by a coefficient of static friction of the other wheels and then uses the linear wheel speed of the reference wheel as the reference vehicle speed in such a way that the numerical value of the obtained reference vehicle speed is more accurate and has a smaller error.In addition, the reference vehicle speed according to the present invention, compared to a method with periodic reduction of the driving force of one of the wheels, does not require excessive waste of driving force from the wheels and also avoids the risk of the vehicle rotating or overturning due to a yaw moment generated by reducing the driving force of one wheel, thus resulting in more stable handling and vehicle speed.

[0040] Based on the same inventive concept, the present disclosure provides a torque control system for an all-wheel-drive vehicle, comprising: a coefficient of static friction detection module that detects the coefficient of static friction of a reference wheel and other wheels in response to a skidding condition of the vehicle; a drive torque detection module that detects a target drive torque to prevent the reference wheel from spinning based on the coefficient of static friction of the other wheels; a reference vehicle speed detection module that detects a linear wheel speed of the reference wheel in response to the reference wheel not spinning and uses the linear wheel speed as the reference vehicle speed of the vehicle; and an adjustment module for adjusting the drive torque of the other wheels based on the reference vehicle speed.

[0041] In some embodiments, the drive torque sensing module specifically further includes: a first sensing module that detects a target static friction rate of the reference wheel based on the coefficient of static friction of the other wheels; a second sensing module that detects a wheel load of the reference wheel; and a third sensing module that detects a target drive torque to prevent wheel spin based on the target static friction rate and the wheel load of the reference wheel.

[0042] In some embodiments, the target static friction rate of the reference wheel in the first detection module is a difference between the minimum value of the coefficient of static friction of the other wheels and a calibration value.

[0043] In some embodiments, the target static friction rate of the reference wheel in the first detection module is a difference between the coefficient of static friction of the wheel on the same side and a calibration value.

[0044] In some embodiments, adjusting the drive torque of the other wheels based on the reference vehicle speed includes: a fourth sensing module that detects an actual slip rate of the other wheels based on the reference vehicle speed; and a first adjustment module that adjusts the drive torque of the respective other wheels in response to the difference between the actual slip rate of the other wheels and a target slip rate.

[0045] The specific implementation of the torque control system for an all-wheel drive vehicle in the above embodiments has been described in detail in the embodiments of the torque control method for an all-wheel drive vehicle, and a detailed description thereof is omitted here.

[0046] It is understood that in the present revelation, the phrase "a multitude of" refers to two or more, and other quantitative expressions are to be understood similarly. The phrase "and / or" describes the relationship between associated objects and indicates that three possible relationships exist. For example, "A and / or B" can mean: A occurs alone, A and B occur simultaneously, and B occurs alone. The sign " / " generally indicates that the associated objects are in an "or" relationship to each other. The singular forms "a," "an," and "the" are also to include the plural forms unless the context clearly indicates otherwise. It is further understood that the terms "first," "second," and the like are used to describe various constructions, but these constructions are not limited to these terms.These terms serve solely to distinguish constructions of the same type from one another and do not indicate any particular order or ranking. In fact, the terms "first," "second," and the like are completely interchangeable. For example, a first construction may be referred to as a second construction, and similarly, a second construction may be referred to as a first construction, without altering the scope of protection afforded by the present disclosure.

[0047] It is further understood that orientations or positional relationships indicated by terms such as "central", "longitudinal", "transverse", "front", "rear", "upper", "lower", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" and the like are based on the orientations or positional relationships shown in the accompanying drawings and serve solely to facilitate and simplify the description of the embodiments, rather than indicating or implying that said devices or elements must have a particular orientation or must be designed and operated in a particular orientation.

[0048] It is further understood that, unless otherwise specified, "connection" includes both a direct connection between two elements without any further components and an indirect connection with other elements between two elements.

[0049] It is further understood that, although the processes described in the drawings of the embodiments of this disclosure are presented in a specific sequence, this should not be interpreted to mean that these processes must be carried out in the illustrated specific sequence or in a serial sequence, or that all illustrated processes must be carried out to achieve the desired results. Multitasking and parallel processing may be advantageous under certain circumstances.

[0050] After considering the description and practical implementation of the invention disclosed herein, a person skilled in the art will readily recognize other embodiments of the present disclosure. This application is intended to cover all modifications, uses, or adaptations of the present disclosure that arise from the general principles of the present disclosure and include common general knowledge or established techniques in the field not disclosed herein. The description and embodiments are to be considered merely as examples, the true scope of protection and the fundamental concept of the present disclosure being specified by the following claims.

[0051] It is understood that the present disclosure is not limited to the precise configuration described above and illustrated in the accompanying drawings, and that various modifications and variations may be made without altering its scope of protection. The scope of protection of the present disclosure is limited exclusively by the accompanying claims.

Claims

[1] Method for torque control for an all-wheel-drive vehicle, comprising: Step S1: Determining the coefficient of static friction of a reference wheel and other wheels in response to a vehicle skidding condition; Step S2: Determining a target drive torque to prevent the reference wheel from spinning based on the coefficient of static friction of the other wheels; Step S3: Determining a linear wheel speed of the reference wheel in response to the reference wheel not spinning, and using the linear wheel speed as the vehicle's reference speed; and Step S4: Adjusting the drive torque of the other wheels based on the reference vehicle speed. [2] Method for torque control for an all-wheel drive vehicle according to claim 1, wherein step S2 further comprises in particular the following: Step S21: Determining a target static friction rate of the reference wheel based on the static friction coefficient of the other wheels; Step S22: Recording a wheel load of the reference wheel; and Step S23: Determining a target drive torque to prevent the reference wheel from slipping based on the target static friction rate and the wheel load of the reference wheel. [3] Method for torque control for an all-wheel drive vehicle according to claim 2, wherein the target static friction rate of the reference wheel in step S21 is a difference between the minimum value of the coefficient of static friction of the other wheels and a calibration value. [4] Method for torque control for an all-wheel drive vehicle according to claim 2, wherein the target static friction rate of the reference wheel in step S21 is a difference between a coefficient of static friction of a wheel on the same side and a calibration value. [5] A method for torque control for an all-wheel drive vehicle according to claim 1, wherein adjusting the drive torque of the other wheels based on the reference vehicle speed comprises: Step S41: Determining the actual slip rate of the other wheels based on the reference vehicle speed; and Step S42: Adjusting the drive torque of each of the other wheels in response to the difference between the actual slip rate of the other wheels and a target slip rate. [6] Torque control system for an all-wheel drive vehicle, comprising: a coefficient of static friction detection module that detects the coefficient of static friction of a reference wheel and other wheels in response to a wheel spin condition of a vehicle; a drive torque detection module that detects a target drive torque to prevent the reference wheel from spinning, based on the coefficient of static friction of the other wheels; a reference vehicle speed detection module that, in response to the reference wheel not spinning, detects a linear wheel speed of the reference wheel and uses the linear wheel speed as the vehicle's reference vehicle speed; and An adaptation module for adjusting the drive torque of the other wheels based on the reference vehicle speed. [7] Torque control system for an all-wheel drive vehicle according to claim 6, wherein the drive torque sensing module specifically further comprises: a first detection module that determines a target static friction rate of the reference wheel based on the coefficient of static friction of the other wheels; a second detection module that detects a wheel load of the reference wheel; and a third detection module that, based on the target static friction rate and the wheel load of the reference wheel, detects a target drive torque to prevent the reference wheel from spinning. [8] Torque control system for an all-wheel drive vehicle according to claim 7, wherein the target static friction rate of the reference wheel in the first detection module is a difference between the minimum value of the coefficient of static friction of the other wheels and a calibration value. [9] Torque control system for an all-wheel drive vehicle according to claim 7, wherein the target static friction rate of the reference wheel in the first detection module is a difference between a coefficient of static friction of the wheel on the same side and a calibration value. [10] Torque control system for an all-wheel drive vehicle according to claim 6, wherein adjusting the drive torque of the other wheels based on the reference vehicle speed comprises: a fourth detection module that detects the actual slip rate of the other wheels based on the reference vehicle speed; and a first adaptation module that adjusts the drive torque of the other wheels in response to the difference between the actual slip rate of the other wheels and a target slip rate.

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