A feedforward correction method for tire force fluctuation of a distributed drive electric vehicle

Abstract

This invention discloses a feedforward correction method for tire force fluctuations in distributed drive electric vehicles. Based on the calculation formula of the relative damping coefficient of tire torsional vibration, a feedforward correction method is designed to implement notch filtering on a given torque near the natural frequency of wheel torsional vibration, thereby suppressing tire force fluctuations. Addressing the variation of the relative damping coefficient of tire torsional vibration with wheel speed and longitudinal slip stiffness, a real-time calculation method for the relative damping coefficient of tire torsional vibration is designed and implemented. By obtaining wheel speed, vehicle speed, and motor output torque signals in real time, the slip ratio derivative and longitudinal slip stiffness are calculated, and the actual relative damping coefficient of tire torsional vibration is calculated online. The absolute value of the difference between the actual and target relative damping coefficient determines whether the feedforward correction intervenes in the adjustment of the given motor torque, thereby improving the dynamic quality of tire force response and ride comfort during acceleration of the distributed drive vehicle.

Description

Technical Field

[0001] This invention relates to the field of electric vehicles, and in particular to a method for suppressing tire force fluctuations in distributed drive electric vehicles. Background Technology

[0002] Distributed drive electric vehicles (EVs) are characterized by short drive chains, high transmission efficiency, compact structure, and ease of modular chassis design, making them one of the important development directions for electric vehicles. Wheel-side / in-wheel motors are directly connected to the wheels via reduction gears, eliminating the need for complex mechanical transmission devices such as drive shafts, drive axles, and half-shafts. This effectively avoids the risk of torque fluctuations caused by elastic deformation of the transmission structure. However, it also highlights the problem of vehicle vibration caused by fluctuations in tire-road force due to dynamic tire deformation. The high response bandwidth and short latency of the motors allow for instantaneous changes in output torque (e.g., during rapid vehicle startup). Under the excitation of large transient drive torque, the wheels undergo torsional vibration, further leading to underdamped oscillations in the tire-road force. These oscillating tire-road contact forces deteriorate the dynamic quality of the overall vehicle response and reduce the performance and lifespan of the wheel-side / in-wheel motors. Furthermore, the force transmitted through the suspension to the vehicle body causes overall vehicle vibration and reduces ride comfort. Summary of the Invention

[0003] To suppress tire-road force fluctuations caused by dynamic wheel deformation during transient changes in motor output torque, this invention provides a feedforward correction method for tire force fluctuations in distributed drive electric vehicles. This method aims to suppress tire-road force fluctuations, thereby improving the force response quality of distributed drive electric vehicles, enhancing ride comfort, and increasing the performance and lifespan of the motor drive system.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes the following steps:

[0005] The present invention provides a feedforward correction method for tire force fluctuations in a distributed drive electric vehicle, characterized by its application in a distributed scenario consisting of an electronic stability control system (ESC), a CAN bus, a motor controller, and a wheel torsional vibration system, and includes the following steps:

[0006] Step 1: The Electronic Stability Control (ESC) system outputs the vehicle speed signal at time k. The signal is transmitted via the CAN bus to the motor controller, which then determines the speed based on the vehicle speed signal at time k. Subtract the vehicle speed signal at time k-1 Then divide by the sampling time. Thus, the derivative signal of the vehicle speed at time k is obtained. ;

[0007] Step 2: Utilize the motor speed signal at the current time k. and reducer transmission ratio Calculate the wheel speed signal at time k. Then send the wheel speed signal Subtract the wheel speed signal at time k-1 Then, divide by the sampling time. Obtain the derivative signal of the wheel velocity at time k. ;

[0008] Step 3: Calculate the slip ratio signal at time k. ; Calculate the derivative signal of the slip ratio at time k. ;in, Indicates the effective rolling radius of the wheel;

[0009] Step 4: Based on the motor output torque at time k and reducer transmission ratio Calculate the wheel-end torque at time k. This allows for the calculation of the longitudinal tire force at time k. ;in, Let the wheel's rotational inertia be the moment of inertia; let the tire force signal at time k be... Subtract the tire force signal at time k-1 Then, divide by the sampling time. Thus, the derivative signal of the longitudinal tire force at time k is obtained. ;

[0010] Step 5: Calculate the longitudinal slip stiffness at time k. ;

[0011] Step 6: Calculate the relative damping coefficient of the tire torsional vibration system at time k. ,in, Indicates the longitudinal stiffness of the tire body; Let be the nominal inertial parameter, and ; Dynamic loads for distributed drive units;

[0012] Step 7: Calculate the difference at time k. ,in, Indicates the target's relative damping coefficient;

[0013] if Then, after performing a Laplace transform on the given torque, the transfer function of the feedforward compensator... Multiply the products, then perform an inverse Laplace transform on the product to obtain the feedforward corrected torque, which is then output to the wheel end.

[0014] if Then the given torque is directly output to the wheel end, where, Indicates the threshold, and ; For complex variables, Let ω be the natural angular frequency of the wheel's torsional vibration.

[0015] The present invention provides an electronic device, including a memory and a processor, wherein the memory is used to store a program that supports the processor in executing the above-described feedforward correction method, and the processor is configured to execute the program stored in the memory.

[0016] The present invention discloses a computer-readable storage medium on which a computer program is stored, wherein the computer program is executed by a processor to perform the steps of the above-described feedforward correction method.

[0017] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0018] 1. This invention proposes an effective method to suppress tire force fluctuations in distributed drive electric vehicles. Through theoretical analysis, the expression for the relative damping coefficient of wheel torsional vibration is derived. It has the technical feature of accurately and quantitatively describing the dependence of the relative damping coefficient of wheel torsional vibration on system parameters and operating parameters. This overcomes the need for a large number of experiments to identify the dependence of the relative damping coefficient of wheel torsional vibration on parameters in the prior art, thereby saving development time.

[0019] 2. This invention uses a feedforward correction method to suppress tire force fluctuations. It has the technical characteristics of simple structure and easy implementation. It does not require feedback control and complex control algorithms, and overcomes the problems of complex and difficult-to-implement algorithms and poor algorithm stability in the prior art, thus improving the stability of the algorithm.

[0020] 3. This invention designs a feedforward correction transfer function based on the transfer function of the wheel torsional vibration system. It has the technical feature of model-based feedforward correction transfer function design, which enables the given torque to be output accurately according to the expected response characteristics after correction, thereby making tire force fluctuations more accurately suppressed.

[0021] 4. Regarding the variation of the relative damping coefficient of wheel torsional vibration with wheel speed and longitudinal slip stiffness, this invention utilizes the sensor signals standard in distributed drive electric vehicles to achieve online real-time estimation of the relative damping coefficient of wheel torsional vibration, eliminating the need for additional sensors. Furthermore, by comparing the real-time relative damping coefficient of wheel torsional vibration with the target relative damping coefficient, it determines whether to implement feedforward correction for a given torque. The feedforward correction has adaptive characteristics under operating conditions, overcoming the need for extensive offline testing and calibration in existing technologies to determine when the tire force fluctuation suppression algorithm should intervene, thus saving development costs. Attached Figure Description

[0022] Figure 1 This is a simplified schematic diagram of the distributed drive system of the present invention;

[0023] Figure 2 A wheel model diagram considering the torsional deformation of the tire carcass in this invention;

[0024] Figure 3 The diagram shows the tire force response under different operating conditions of the present invention, with the tires showing the uncorrected (solid line) and corrected (dashed line) forces respectively.

[0025] Figure 4 This is a flowchart of the method of the present invention. Detailed Implementation

[0026] The invention will be further described below with reference to the accompanying drawings.

[0027] In this embodiment, to suppress tire-road force fluctuations caused by wheel dynamic deformation during transient torque changes in a distributed drive vehicle, and to improve the overall vehicle force response quality while suppressing fluctuations, a feedforward correction method for tire force fluctuations in a distributed drive electric vehicle is proposed. This method features a model-based feedforward corrector design and online identification of the relative damping coefficient of wheel torsional vibration to ensure effective suppression of tire force fluctuations under different operating conditions. This invention relates to Electronic Stability Control (ESC), CAN bus, motor controller, and wheel torsional vibration system, specifically, as... Figure 4 As shown, the method includes:

[0028] Step 1: The Electronic Stability Control (ESC) system outputs the vehicle speed signal at time k. The signal is transmitted via the CAN bus to the motor controller, which then determines the speed based on the vehicle speed signal at time k. Subtract the vehicle speed signal at time k-1 Then divide by the sampling time. Thus, the derivative signal of the vehicle speed at time k is obtained. ;

[0029] Step 2: Utilize the motor speed signal at the current time k. and reducer transmission ratio Calculate the wheel speed signal at time k. Then send the wheel speed signal Subtract the wheel speed signal at time k-1 Then, divide by the sampling time. Obtain the derivative signal of the wheel velocity at time k. ;

[0030] Step 3: Calculate the slip ratio signal at time k. ; Calculate the derivative signal of the slip ratio at time k. ;in, Indicates the effective rolling radius of the wheel;

[0031] Step 4: Based on the motor output torque at time k and reducer transmission ratio Calculate the wheel-end torque at time k. This allows for the calculation of the longitudinal tire force at time k. ;in, Let the wheel's rotational inertia be the moment of inertia; let the tire force signal at time k be... Subtract the tire force signal at time k-1 Then, divide by the sampling time. Thus, the derivative signal of the longitudinal tire force at time k is obtained. ;

[0032] Step 5: Calculate the longitudinal slip stiffness at time k. ;

[0033] Step 6: Calculate the relative damping coefficient of tire torsional vibration at time k. ,in, Indicates the longitudinal stiffness of the tire body; Let be the nominal inertial parameter, and ; Dynamic loads for distributed drive units;

[0034] Step 7: Calculate the difference at time k. ,in, Indicates the target's relative damping coefficient;

[0035] if Then, the given torque, after undergoing a Laplace transform, is compared with the transfer function of the feedforward compensator. After multiplication and inverse Laplace transform, the feedforward corrected torque is obtained and output to the wheel end;

[0036] if Then the given torque is directly output to the wheel end, where, To represent the threshold, generally take and ; For complex variables, Let ω be the natural angular frequency of the wheel's torsional vibration.

[0037] In this embodiment, the formula for calculating the relative damping coefficient is derived as follows:

[0038] First, the drive unit in a real distributed electric vehicle is simplified as follows: Figure 1 As shown, the wheel is then simplified to the following shape, considering the torsional deformation of the elastic wheel: Figure 2The structural diagram is shown below. Combined with... Figure 2 And according to Newton's second law, the dynamic equations can be written as follows:

[0039] (1) (2)

[0040] (3)

[0041] in, and The moments of inertia of the wheel rim and the rigid ring are respectively. and These are distributed drive units and rigid ring mass, respectively. and These are the torsional stiffness and torsional damping of the tire body, respectively. and These are the angular displacements of the rim and the rigid ring, respectively. For the longitudinal displacement of the distributed drive unit.

[0042] Equation (2) can be rearranged into the following expression:

[0043] (4)

[0044] And order , which is the longitudinal stiffness of the tire body, let , which is the longitudinal damping of the tire body.

[0045] make This refers to longitudinal deformation of the tire body.

[0046] Equation (4) can be further written as:

[0047] (5)

[0048] Higher-order inertial terms can be reasonably ignored, resulting in dynamic tire forces expressed based on tire carcass deformation:

[0049] (6)

[0050] Further, based on the tread deformation expression and retaining the first-order term according to Taylor expansion, another expression for dynamic tire force is obtained:

[0051]

[0052] in, The relative sliding velocity between the rigid ring and the road surface. The relative sliding speed between the wheel rim and the road surface. This represents the steady-state tire force.

[0053] Based on equations (6) and (7), the expression for the transient characteristics of the tire can be written as follows:

[0054] (8)

[0055] According to Newton's second law, the equation of motion for a wheel rotor, neglecting tire torsional deformation, is:

[0056] (9)

[0057] (10)

[0058] Based on equations (8)-(10) and combined with the local linearization method and Laplace transform, the longitudinal tire force transmission function under small-range variation of driving torque can be obtained:

[0059] (11)

[0060] in, , .

[0061] According to equation (11), the tire torsional vibration system is a second-order system, and its relative damping coefficient is... for:

[0062] (12)

[0063] Figure 3 Simulations show that, under different operating conditions, the feedforward compensator designed according to the above formula has a good suppression effect on the fluctuation of the motor torque and tire force under a step input.

[0064] In this embodiment, an electronic device includes a memory and a processor. The memory stores a program that supports the processor in executing the above-described method, and the processor is configured to execute the program stored in the memory.

[0065] In this embodiment, a computer-readable storage medium stores a computer program, which is executed by a processor to perform the steps of the above method.

[0066] In summary, this invention designs a feedforward corrector based on the formula for calculating the relative damping coefficient of tire torsional vibration. This corrector applies a notch filter to a given torque near the natural frequency of wheel torsional vibration, thereby suppressing tire force fluctuations. Addressing the variation of the relative damping coefficient of tire torsional vibration with wheel speed, slip ratio, and longitudinal slip stiffness, this invention designs a real-time calculation method for the relative damping coefficient of tire torsional vibration. By obtaining wheel speed, vehicle speed, and motor output torque signals in real time, the derivative of the slip ratio and the longitudinal slip stiffness are calculated, thus estimating the actual relative damping coefficient of tire torsional vibration online. The absolute value of the difference between the actual and target relative damping coefficient determines whether the feedforward corrector intervenes in adjusting the given motor torque, thereby improving the dynamic quality and ride comfort of distributed drive vehicles during acceleration under different operating conditions.

Claims

1. A feedforward correction method for tire force fluctuations in a distributed drive electric vehicle, characterized in that, It is applied in a distributed scenario consisting of an Electronic Stability Control (ESC) system, a CAN bus, a motor controller, and a wheel torsional vibration system, and includes the following steps: Step 1: The Electronic Stability Control (ESC) system outputs the vehicle speed signal at time k. The signal is transmitted via the CAN bus to the motor controller, which then determines the speed based on the vehicle speed signal at time k. Subtract the vehicle speed signal at time k-1 Then, divide by the sampling time T1 to obtain the derivative signal of the vehicle speed at the current time k. Step 2: Utilize the motor speed signal at the current time k. Calculate the wheel speed signal ω at time k using the gear ratio i of the reducer. k Then the wheel speed signal ω k Subtract the wheel speed signal ω at time k-1 k-1 Then, divide by the sampling time T2 to obtain the wheel velocity derivative signal at the current time k. Step 3: Calculate the slip ratio signal at time k. Calculate the derivative signal of the slip ratio at time k. Where, r e Indicates the effective rolling radius of the wheel; Step 4: Based on the motor output torque at time k Given the gear ratio i of the reducer, calculate the wheel-end torque at time k. Therefore, the longitudinal tire force at time k can be calculated. Where J is the wheel's moment of inertia; the tire force signal at time k is... Subtract the tire force signal at time k-1 Then, divide by the sampling time T3 to obtain the derivative signal of the longitudinal tire force at the current time k. Step 5: Calculate the longitudinal slip stiffness at time k. Step 6: Calculate the relative damping coefficient of the tire torsional vibration system at time k. Among them, C Fx Indicates the longitudinal stiffness of the tire body; Let be the nominal inertial parameter, and m represents the dynamic load of the distributed drive unit; Step 7: Calculate the difference at time k. Where, ξ a Indicates the target's relative damping coefficient; If Δ ≥ ε, then after performing a Laplace transform on the given torque, the transfer function with the feedforward compensator... Multiply the products, then perform an inverse Laplace transform on the product to obtain the feedforward corrected torque, which is then output to the wheel end. If Δ < ε, then the given torque is directly output to the wheel end, where ε represents the threshold and ε ∈ (0, 0.3); s is a complex variable, ω n Let ω be the natural angular frequency of the wheel's torsional vibration.

2. An electronic device, comprising a memory and a processor, characterized in that, The memory is used to store a program that supports the processor in executing the feedforward correction method of claim 1, the processor being configured to execute the program stored in the memory.

3. A computer-readable storage medium storing a computer program, characterized in that, The computer program is executed by the processor to perform the steps of the feedforward correction method of claim 1.

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