Active robust control method for low-frequency longitudinal vibration under rapid acceleration working condition

Abstract

The invention relates to a low-frequency longitudinal vibration active robust control method under a sudden acceleration working condition, and aims to comprehensively improve the dynamic property and comfort of a vehicle. The method comprises the following steps: firstly, establishing a control-oriented kinetic equation according to an urgent acceleration working condition working principle of a transmission system; then, considering vehicle dynamic property and comfort requirements, designing a rolling time domain linear quadratic tracking method to carry out vehicle longitudinal vibration active control, and carrying out optimization selection of different prediction time domains and control time domains; and finally, designing a fuzzy control algorithm, and carrying out online adaptive updating of a rolling time domain linear quadratic tracking control weight coefficient based on an offline optimization result. According to the method, through fusion of various control algorithms, the good vibration reduction effect and riding comfort of the transmission system under the rapid acceleration working condition are achieved, and the excellent power performance is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of automobile torsional vibration control, and in particular is a low-frequency longitudinal vibration active robust control method for rapid acceleration conditions. Background Art

[0002] During the motor drive process, there is no torque converter, torsional vibration damper or other vibration reduction device between the motor and the wheel. The sudden change of the motor output torque can easily cause torsional vibration in the transmission system, resulting in longitudinal shaking of the vehicle in the driving direction, affecting the vehicle's smoothness. Different from the structural parameter optimization method of passive vibration reduction, active vibration reduction achieves the purpose of vibration reduction by controlling the output of the power source torque without changing the structural parameters of the transmission system. For pure electric vehicles, the motor torque is mostly regulated from the perspective of the excitation source by using a suitable control algorithm to reduce the torsional vibration response of the transmission system.

[0003] Some existing patents, such as the invention patent with publication number CN106541854 A, involve an active control method for electric vehicle starting vibration based on waveform superposition. The motor torque signal is modified and split into multiple torque sub-signals with specific phase differences, and then the torque sub-signals are superimposed to obtain the motor torque given signal. The principle that the superposition of signals with non-cophase will weaken is used to reduce the vibration in the under-damped system. The invention patent with publication number CN109941120 A proposes an improved pole displacement control algorithm for low-frequency torsional vibration of electric vehicle power transmission system. On the basis of a stable torque reference signal, a compensation torque is obtained through the pole displacement control algorithm to compensate for the vibration amount, which has a significant inhibitory effect on torsional vibration.

[0004] However, the torsional vibration control algorithm for rapid acceleration conditions usually pays little attention to the influence of model parameter uncertainty and external disturbance on control performance. The control accuracy is greatly affected by the model error, and even the control fails in severe cases. In addition, the practical performance of the algorithm must also be guaranteed. Therefore, how to develop an active vibration reduction control algorithm for rapid acceleration conditions with strong robustness to achieve the goal of reducing the torsional vibration of the transmission system is a difficult problem that needs to be solved urgently. Summary of the invention

[0005] The present invention proposes an active robust control method for low-frequency longitudinal vibration for rapid acceleration conditions. In order to overcome the problem that the performance of the existing torsional vibration control algorithm for rapid acceleration conditions is affected by model parameter uncertainty and external interference, the method considers the vehicle's dynamics and comfort requirements, designs a rolling time-domain linear quadratic tracking method to calculate the control law, and performs online adaptive update of the rolling time-domain linear quadratic tracking control weight coefficient, so as to achieve a better solution to the vehicle torsional vibration problem.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A transmission system, which is composed of a drive motor, a fixed speed ratio reducer and a final reducer integrated together to form a centralized electric drive system, and also includes components such as left and right half shafts and wheels. The torque output by the drive motor is decelerated and increased by the fixed speed ratio reducer, and then distributed to the left and right half shafts through the final reducer, and transmitted to the wheels to drive the vehicle.

[0008] A low-frequency longitudinal vibration active robust control method under rapid acceleration conditions, the control method is based on a transmission system, and comprises the following steps:

[0009] S1: Based on the working principle of the transmission system under rapid acceleration conditions and the multi-degree-of-freedom transmission system model, the transmission system dynamics equation is derived;

[0010] S2: Based on the ADMAS multi-body dynamics software, the relationship between motor excitation and vibration is simulated, the influence of different transmission system parameters on the low-frequency longitudinal vibration of the transmission system is analyzed, and the root cause of the low-frequency longitudinal vibration of the power system when the torque of the drive motor changes rapidly is clarified, which serves as the basis for the development of the control algorithm;

[0011] S3: Considering the vehicle dynamics and comfort requirements, a vehicle acceleration preview model is established, and a rolling time-domain linear quadratic tracking method is designed to actively control the vehicle longitudinal vibration. The reference trajectory tracking problem is transformed into a trajectory state adjustment problem, and the active control law is derived;

[0012] S4: Design a fuzzy control algorithm to perform online adaptive update of the rolling time domain linear quadratic tracking control weight coefficient based on the offline optimization results, so as to achieve a comprehensive improvement in the vehicle's dynamic performance and vibration reduction performance under rapid acceleration conditions.

[0013] Furthermore, step S1 is specifically as follows:

[0014] The dynamic equation of the transmission system is shown in formula (1):

[0015]

[0016] In the formula, J e , J w are the rotational inertia of the drive motor and the wheel respectively; They are the angular displacement, speed and angular acceleration of the driving motor respectively; are wheel angular displacement, rotation speed and angular acceleration respectively; T e is the driving motor torque; k s d s are stiffness and damping parameters respectively; i g 、i f are the speed ratios of the fixed speed ratio reducer and the main reducer respectively; m is the vehicle mass; r is the wheel radius.

[0017] Furthermore, step S3 is specifically as follows:

[0018] S31: Based on equation (1), the control-oriented state equation is established as:

[0019]

[0020] In the formula, the state variables are the motor-wheel torsion angle, wheel speed and motor speed, The control variable is the motor compensation torque, u = T com ; System disturbance is the motor command torque, which is determined by the accelerator pedal command and vehicle state in the energy management strategy, d = T cmd ; The system output is the vehicle longitudinal acceleration, A, B, C, and D are coefficient matrices.

[0021] S32: Considering the balance between vehicle impact and dynamic performance, the objective function J is set to:

[0022]

[0023] Where r(k) is the target acceleration of the vehicle; Q and R are weight matrices.

[0024] S33: The linear quadratic optimal control problem is solved by the minimum principle, so the discrete LQT algorithm can be derived. Let:

[0025]

[0026] Among them, the coordination variable is derived from formula (5):

[0027] λ * (k)=P(k)x(k)-g(k)-q(k) (5)

[0028] In the formula, the matrix P(k) is related to the state feedback control, and its sequence P(k0)~P(k f ) is solved iteratively by the differential Riccati equation based on the terminal conditions; the vector g(k) is related to the feedforward control, which will be solved iteratively by the reference difference vector equation; the vector q(k) is related to the disturbance d(k) feedforward control, which will be solved iteratively by the feedback difference vector equation.

[0029] The optimal control law is obtained as shown in formula (6):

[0030] u(k)=-F P x(k)+F gq g(k+1)+F gq q'(k+1) (6)

[0031] In formula (6), each term is calculated as:

[0032]

[0033] q'(k+1)=q(k+1)-P(k+1)D d (k)d(k) (9)

[0034] Furthermore, step S4 is specifically as follows:

[0035] S41: Set the fuzzy input variables to the accelerator pedal acc and its change rate Δacc, and the output variable to the weight coefficient ΔQ; the fuzzy domains of the input variables and the output variables are both set to [-3, 3], the corresponding system input fuzzy subsets and output subsets are both defined as {NS, NB, ZO, PS, PB}, and set the triangle membership function.

[0036] S42: Formulate fuzzy control rules as follows:

[0037]

[0038] S43: Defuzzify the control quantity generated by fuzzy reasoning using the center of gravity method. The output quantity ΔQ of the fuzzy control rule is calculated as shown in formula (11):

[0039]

[0040] In the formula, is the membership function of the fuzzy set.

[0041] Compared with the prior art, the advantages of the present invention are:

[0042] 1. The active robust control method for low-frequency longitudinal vibration under rapid acceleration conditions described in the present invention solves the uncertainty problems such as parameter perturbation and external interference in the motor driving process, ensures the robust performance of the algorithm, and has important theoretical reference for solving the problem of low-frequency longitudinal vibration of vehicles under rapid acceleration conditions;

[0043] 2. The rolling time domain linear quadratic tracking algorithm designed for the active robust control method of low-frequency longitudinal vibration under rapid acceleration conditions described in the present invention has good advantages in dealing with external interference problems, and achieves good vibration reduction effect through reference trajectory setting, finite time optimization and torque compensation;

[0044] 3. The active robust control method for low-frequency longitudinal vibration under rapid acceleration conditions described in the present invention adopts a fuzzy control algorithm to adaptively update the weight coefficient of the rolling time domain linear quadratic tracking algorithm, thereby achieving a comprehensive improvement in the vehicle's starting performance and vibration reduction performance, and providing a new way to solve the problem of low-frequency longitudinal vibration of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A schematic diagram of the electric vehicle transmission system structure used in the embodiment;

[0046] Figure 2 A flow chart of a method for active robust control of low-frequency longitudinal vibration under rapid acceleration conditions used in the embodiment;

[0047] Figure 3 The electric vehicle multi-degree-of-freedom transmission system model used in the embodiment;

[0048] Figure 4 A flow chart of a rolling-horizon linear quadratic tracking control algorithm used in the embodiment;

[0049] Labels in the figure: 1. Drive motor, 2. Fixed speed ratio reducer, 3. Main reducer, 4. Left and right half shafts, 5. Wheels. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described examples are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Example 1

[0052] A transmission system, wherein the transmission system is integrated with a drive motor 1, a fixed speed ratio reducer 2 and a main reducer 3 to form a centralized electric drive system, such as Figure 1 As shown; in addition, it also includes left and right half shafts 4 and wheels 5. The torque output by the drive motor 1 is decelerated and torque-increased by the fixed speed ratio reducer 2, and then distributed to the left and right half shafts 4 through the main reducer 3, and then transmitted to the wheels 5 to drive the vehicle to travel. The drive motor 1 is both the power source of the whole vehicle and the main excitation source of the torsional vibration of the transmission system.

[0053] Example 2

[0054] A method for active robust control of low-frequency longitudinal vibration under rapid acceleration conditions, the flow chart is as follows: Figure 2 As shown. First, according to the working principle of the transmission system under rapid acceleration conditions, the control-oriented dynamic equation is established; then, considering the vehicle dynamics and comfort requirements, a rolling time domain linear quadratic tracking method is designed to actively control the vehicle longitudinal vibration, and the optimization selection of different prediction time domains and control time domains is performed; finally, a fuzzy control algorithm is designed to perform online adaptive update of the rolling time domain linear quadratic tracking control weight coefficient based on the offline optimization results. The low-frequency longitudinal vibration active robust control method specifically includes:

[0055] S1: According to the working principle of the transmission system under rapid acceleration conditions and the multi-degree-of-freedom transmission system model ( Figure 3 ), the dynamic equation of the transmission system is derived;

[0056] The dynamic equation of the transmission system is shown in formula (1):

[0057]

[0058] In the formula, J e , J w are the rotational inertia of the driving motor 1 and the wheel 5 respectively; are the angular displacement, speed and angular acceleration of the driving motor 1 respectively; are the angular displacement, rotation speed and angular acceleration of wheel 5 respectively; T e is the torque of driving motor 1; k s d s are stiffness and damping parameters respectively; i g 、i f are the speed ratios of fixed speed ratio reducer 2 and main reducer 3 respectively; m is the vehicle mass; r is the radius of wheel 5.

[0059] S2: Based on the ADMAS multi-body dynamics software, the relationship between motor excitation and vibration is simulated, the influence of different transmission system parameters on the low-frequency longitudinal vibration of the transmission system is analyzed, and the root cause of the low-frequency longitudinal vibration of the power system when the torque of the drive motor 1 changes rapidly is clarified, which serves as the basis for the development of the control algorithm;

[0060] S3: Considering the vehicle dynamics and comfort requirements, a vehicle acceleration preview model is established, and a rolling time-domain linear quadratic tracking method is designed to actively control the vehicle longitudinal vibration. The reference trajectory tracking problem is transformed into a trajectory state adjustment problem, and the active control law is derived;

[0061] like Figure 4 The specific calculation method is:

[0062] S31: Based on equation (1), the control-oriented state equation is established as:

[0063]

[0064] In the formula, the state variables are the motor-wheel torsion angle, wheel speed and motor speed, The control variable is the motor compensation torque, u = T com ; System disturbance is the motor command torque, which is determined by the accelerator pedal command and vehicle state in the energy management strategy, d = T cmd ; The system output is the vehicle longitudinal acceleration, A, B, C, and D are coefficient matrices.

[0065] S32: Considering the balance between vehicle impact and dynamic performance, the objective function J is set to:

[0066]

[0067] Where r(k) is the target acceleration of the vehicle; Q and R are weight matrices.

[0068] S33: The linear quadratic optimal control problem is solved by the minimum principle, so the discrete LQT algorithm can be derived. Let:

[0069]

[0070] Among them, the coordination variable is derived from formula (5):

[0071] λ * (k)=P(k)x(k)-g(k)-q(k) (5)

[0072] In the formula, the matrix P(k) is related to the state feedback control, and its sequence P(k0)~P(k f ) is solved iteratively by the differential Riccati equation based on the terminal conditions; the vector g(k) is related to the feedforward control, which will be solved iteratively by the reference difference vector equation; the vector q(k) is related to the disturbance d(k) feedforward control, which will be solved iteratively by the feedback difference vector equation.

[0073] The optimal control law is obtained as shown in formula (6):

[0074] u(k)=-F P x(k)+F gq g(k+1)+F gq q'(k+1) (6)

[0075] In formula (6), each term is calculated as:

[0076]

[0077] q'(k+1)=q(k+1)-P(k+1)D d (k)d(k) (9)

[0078] S4: Design a fuzzy control algorithm to perform online adaptive update of the rolling time domain linear quadratic tracking control weight coefficient based on the offline optimization results, so as to achieve a comprehensive improvement in the vehicle's dynamic performance and vibration reduction performance under rapid acceleration conditions.

[0079] The specific calculation process is:

[0080] S41: Set the fuzzy input variables to the accelerator pedal acc and its change rate Δacc, and the output variable to the weight coefficient ΔQ; the fuzzy domains of the input variables and the output variables are both set to [-3, 3], the corresponding system input fuzzy subsets and output subsets are both defined as {NS, NB, ZO, PS, PB}, and set the triangle membership function.

[0081] S42: Formulate fuzzy control rules as follows:

[0082]

[0083] S43: Defuzzify the control quantity generated by fuzzy reasoning using the center of gravity method. The output quantity ΔQ of the fuzzy control rule is calculated as shown in formula (11):

[0084]

[0085] In the formula, is the membership function of the fuzzy set.

[0086] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A transmission system, characterized in that: The transmission system is composed of a drive motor (1), a fixed speed ratio reducer (2) and a main reducer (3) integrated together to form a centralized electric drive system, and also includes left and right half shafts (4) and wheels (5). The torque output by the drive motor (1) is decelerated and torque-increased by the fixed speed ratio reducer (2), and then distributed to the left and right half shafts (4) through the main reducer (3), and then transmitted to the wheels (5) to drive the vehicle to travel.

2. A method for active robust control of low-frequency longitudinal vibration under rapid acceleration conditions, the control method is based on a transmission system according to claim 1, characterized in that: The steps include: S1: Based on the working principle of the transmission system under rapid acceleration conditions and the multi-degree-of-freedom transmission system model, the transmission system dynamics equation is derived; S2: Based on the ADMAS multi-body dynamics software, the relationship between motor excitation and vibration is simulated, the influence of different transmission system parameters on the low-frequency longitudinal vibration of the transmission system is analyzed, and the root cause of the low-frequency longitudinal vibration of the power system when the torque of the drive motor 1 changes rapidly is clarified, which serves as the basis for the development of the control algorithm; S3: Considering the vehicle dynamics and comfort requirements, a vehicle acceleration preview model is established, and a rolling time-domain linear quadratic tracking method is designed to actively control the vehicle longitudinal vibration. The reference trajectory tracking problem is transformed into a trajectory state adjustment problem, and the active control law is derived; S4: Design a fuzzy control algorithm to perform online adaptive update of the rolling time domain linear quadratic tracking control weight coefficient based on the offline optimization results, so as to achieve a comprehensive improvement in the vehicle's dynamic performance and vibration reduction performance under rapid acceleration conditions.

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