阅读说明：本技术 电动汽车双电机并轴传动系统及其模式切换动态控制策略 (Electric automobile double-motor parallel-shaft transmission system and mode switching dynamic control strategy thereof ) 是由 吴景铼 王兵 于 2020-05-25 设计创作，主要内容包括：本发明涉及一种电动汽车双电机并轴传动系统,包括第一电机,第一电机通过第一轴与第一齿轮连接,第二电机通过第二轴与第二齿轮连接,第一齿轮与第三齿轮的传动比为n<Sub>1</Sub>,第二齿轮与第三齿轮的传动比为n<Sub>2</Sub>,中间轴的两端分别连接第三齿轮和第四齿轮,第四齿轮与第五齿轮的传动比为n<Sub>3</Sub>,第五齿轮通过主减速器轴将扭矩传递给车轮。本发明还公开了一种电动汽车双电机并轴传动系统的模式切换动态控制策略。本发明提出动态控制策略实现双电机并联轴传动系统的理想模式切换,实现跟踪驾驶员所期望的理想车速和能量管理策略提供的理想扭矩,控制两个电动机以实现无动力中断的模式转换。(The invention relates to a double-motor shaft-combining transmission system of an electric automobile, which comprises a first motor, wherein the first motor is connected with a first gear through a first shaft, a second motor is connected with a second gear through a second shaft, and the transmission ratio of the first gear to a third gear is n 1 The transmission ratio of the second gear to the third gear is n 2 The two ends of the intermediate shaft are respectively connected with a third gear and a fourth gear, and the transmission ratio of the fourth gear to the fifth gear is n 3 The fifth gear transmits torque to the wheels through the final drive shaft. The invention also discloses a mode switching dynamic control strategy of the double-motor parallel shaft transmission system of the electric automobile. The invention provides a dynamic control strategy to realize the ideal mode switching of a double-motor parallel shaft transmission system, realize the tracking of the ideal vehicle speed expected by a driver and the ideal torque provided by an energy management strategy, and control two motors to realize the mode switching without power interruption.)

1. The utility model provides an electric automobile bi-motor and axle transmission system which characterized in that: the device comprises a first motor, a second motor, a first gear, a second gear, a third gear, a fourth gear, a fifth gear, a first shaft, a second shaft, an intermediate shaft, a main speed reducer shaft and wheels; the first motor is connected with the first gear through the first shaft, the second motor is connected with the second gear through the second shaft, and the transmission ratio of the first gear to the third gear is n₁The transmission ratio of the second gear to the third gear is n₂The two ends of the intermediate shaft are respectively connected with a third gear and a fourth gear, and the fourth gear and the fifth gearHas a transmission ratio of n₃The fifth gear transmits torque to the wheels through the final drive shaft.

2. The electric automobile double-motor parallel shaft transmission system according to claim 1, characterized in that: the first shaft, the second shaft, the intermediate shaft and the main speed reducer shaft are all connected by elastic shafts, and the elastic shafts are formed by modeling of a torsion spring and a damper: k₁And C₁Representing the spring rate and damping of the first shaft, K₂And C₂Spring rate and damping representing the second axis, K₃And C₃Spring rate and damping, K, of the intermediate shaft₄And C₄Representing the spring rate and damping of the final drive shaft.

3. The dynamic control strategy for mode switching of a dual-motor parallel shaft transmission system of an electric vehicle according to any one of claims 1-2, characterized in that: the strategy comprises the following sequential steps:

(1) establishing a five-degree-of-freedom dynamic model of a double-motor parallel shaft transmission system of the electric automobile;

(2) selecting a driving mode and determining ideal driving torques of the two motors through an energy management strategy, wherein the driving modes are a mode 1, a mode 2 and a mode 3 respectively;

(3) and controlling the driving torques of the first motor and the second motor through a backward dynamic control strategy and a nested forward and backward dynamic control strategy.

4. The mode switching dynamic control strategy of claim 3, wherein: in the step (1), the five degrees of freedom of the five-degree-of-freedom dynamic model are respectively the angular displacement theta of the first motor₁Angular displacement theta of the second motor₂Angular displacement theta of intermediate shaft₃Angular displacement theta of fifth gear₄And angular wheel displacement theta₅(ii) a The equivalent inertia of the first motor is I₁Let the equivalent inertia of the second motor be I₂The equivalent inertia of the first gear, the second gear and the third gear is I_3a，I_3b，I_3cThe equivalent inertia of the fourth gear and the fifth gear is I_4a，I_4bEquivalent inertia of wheel is I₅；K₁And C₁Representing the spring rate and damping of the first shaft, K₂And C₂Spring rate and damping representing the second axis, K₃And C₃Spring rate and damping, K, of the intermediate shaft₄And C₄Representing the spring rate and damping of the final drive shaft; the five degree of freedom kinetic model has three external torque drives, where T₁Representing the output torque of the first electric machine, T₂Representing the output torque of the second electric machine, T₅Represents an equivalent vehicle load torque;

wherein I is an inertia matrix, C is a damping matrix, K is a stiffness matrix, θ is a state vector, and T is a load vector containing a driving torque and a load torque; n is₁Is the gear ratio of the first gear to the third gear, n₂Is the gear ratio of the second gear to the third gear, n₃The transmission ratio of the fourth gear to the fifth gear; vehicle load torque T₅Represented by the following equation:

wherein, F_VIs the sum of resistance caused by climbing resistance, air resistance and rolling resistance, m_VIs the mass of the vehicle, g is the acceleration of gravity,

5. The mode switching dynamic control strategy of claim 3, wherein: the step (2) specifically comprises the following steps:

the dynamic equation of the double-motor parallel shaft transmission system of the electric automobile is as follows:

wherein ω is₁And ω₂The rotational speeds of the first and second electrical machines, T, respectively₁,T₂The output torques of the first motor and the second motor are respectively, the ideal driving torques of the two motors are output by applying an energy management strategy, and the formula of the energy management strategy is expressed as follows:

s.t.Eqs.(4-5)

P_M(T₁,T₂,ω₁,ω₂)＝T₁ω₁+P_loss₁(T₁,ω₁)+T₂ω₂+P_loss₂(T₂,ω₂)

-ω_max1≤ω₁≤ω_max1；-T_max1(ω₁)≤T₁≤T_max1(ω₁)

-ω_max2≤ω₂≤ω_max2；-T_max2(ω₂)≤T₂≤T_max2(ω₂)

(6)

wherein, P_MIs the instantaneous power consumption of the two drive motors, P _ loss₁And P _ loss₂The power loss, k, of the first and second electrical machines, respectively₃Is a penalty factor for avoiding frequent mode switching operations, Δ ω₁Representing the first motor from time t_i-1To t_iA speed change of (d); the optimization model of the energy management strategy uses the torque of the first motor as a design variable on the principle of selecting the lowest energy loss, because the torque of the second motor is determined by equation (4) and the rotation speeds of the two motors are determined by equation (5), and the ideal driving torque distribution between the two motors is obtained by solving equation (6); when T is₂＝0，T₁When not equal to 0, the working mode is the mode 1; on the contrary, when T is₁＝0，T₂When not equal to 0, the working mode is the mode 2; when T is₁And T₂When the values are all non-zero, the working mode is mode 3;

three driving modes, namely a mode 1, a mode 2 and a mode 3, are provided by switching the working states of the first motor and the second motor; in the mode 1 state, the first motor outputs torque, the torque is transmitted to wheels through the first gear, the third gear, the fourth gear and the fifth gear, and the second motor does not output the torque; in the mode 2 state, the second motor outputs torque, the torque is transmitted to wheels through the second gear, the third gear, the fourth gear and the fifth gear, and the first motor does not output the torque; in the mode 3 state, the first motor and the second motor output torque coupling to drive the vehicle simultaneously.

6. The mode switching dynamic control strategy of claim 3, wherein: the backward dynamic control strategy in the step (3) refers to:

the energy management strategy generates ideal driving torques of the first motor and the second motor on the basis of the principle of lowest energy loss, and because the energy management strategy is based on a backward dynamics model, the torque obtained in the energy management strategy is called backward torque; energy management policy output second per secondThe backward torque of one motor and the second motor is respectively T_1,0(t_i) And T_2,0(t_i) It is shown that increasing the average operation over a one second period after the backward torque signal converts the discrete values output by the energy management strategy into a continuous torque output by equation (7), respectivelyAndthe motor model will continue torqueAnd

the dynamic control strategy before and after nesting in the step (3) is as follows:

driving torque of vehicleThe energy management strategy is used to distribute torque between the two motors, as generated by the PI controller, and the tracking torques of the first and second motors are expressed as equation (8):

n₁is the gear ratio of the first gear to the third gear, n₂Is the gear ratio of the second gear to the third gear, n₃The transmission ratio of the fourth gear to the fifth gear; selecting whether control signals of the two motors are driving torque or tracking by the first switch and the second switchWhen the working mode is the mode 2, the first motor outputs driving torque, and the second motor outputs tracking torque; when the working mode is the mode 1 or the mode 3, the first motor outputs tracking torque, and the second motor outputs driving torque; the mathematical model of the two switches is shown below:

output torque T of intermediate shaft₃Represented by the formula (10):

whatever the driving mode, T₃Always equal to the torque produced by the PI controller; due to the fact thatAnd

Technical Field

The invention relates to the technical field of electric automobile driving, in particular to a double-motor parallel-shaft transmission system of an electric automobile and a mode switching dynamic control strategy thereof.

Background

The mileage limitation of electric vehicles is the biggest obstacle to its popularization. The electric automobile can effectively improve the overall efficiency by matching with a multi-speed transmission or applying a multi-power source driving system, so that the driving mileage is increased, and the multi-mode driving system of the electric automobile is a research hotspot in recent years. At present, the transmission system of the electric automobile on the market mostly adopts a form of matching a single motor with a single-stage speed reducer, and the configuration is an economic and effective solution. However, the performance requirement of the driving motor is high, and the motor is required to provide a high rotating speed in a constant torque area and output a large torque in a constant power area to meet the dynamic requirement of automobile driving, so that the power of the motor needs to be selected to be large enough. The electric motor, which is matched to the single reduction gear, is normally operated in a low efficiency region, thereby increasing the power consumption.

The multi-speed transmission replaces a single-stage speed reducer, so that the motor can work in a higher efficiency area, and the dynamic property and the economical efficiency of the power assembly are improved. The system energy consumption of the matching of the electric automobile and a single-stage speed reducer transmission, the two-stage speed transmission and the four-stage speed transmission based on different driving cycles is compared, and the result shows that for a common passenger car, the two-stage speed transmission obviously improves the system efficiency of the single-stage speed transmission, the advantages of a power transmission system are optimally balanced in a multi-speed transmission system, and the balance between the performance and the cost of the electric passenger car is good. Therefore, electric vehicle transmission systems equipped with two-speed transmissions, such as AMT, AT, and DCT, have been studied. Mechanical two-speed automatic transmissions have good performance advantages, but power interruption during gear shifting can affect driving comfort. In order to avoid power interruption, a novel two-gear AMT is proposed, and since the clutch is located at the rear part of the transmission with the new layout of the two-gear AMT, unpowered gear shifting can be realized by properly controlling the driving of the driving motor and the clutch. Two-speed ATs are also used for matching electric vehicles by using two planetary gear sets, wherein the gear position is determined by braking different ring gears in the two planetary gear sets. The proposed two-speed AT has higher efficiency than a conventional hydraulic AT due to elimination of viscosity and pumping losses in the torque converter. There have been studies to develop a shift control scheme for a two-speed AT in an electric vehicle that proposes a two-phase control for shifting between every two gear ratios, which ensures smooth and fast shifting. The DCT has the capability of avoiding power interruption during a shift in addition to AT, a series of power-up and power-down transition control strategies have been developed for two-gear DCT-based electric vehicles, power interruption and jerk can be reduced by controlling clutch torque and motor torque in a torque phase and an inertia phase, a smooth shift control structure of the DCT is developed, the control structure is divided into two levels, wherein an upper level controls the process to determine the most appropriate torque trajectory for the clutch and power source, and a lower level controls the strategy of each actuator controller to track a given torque trajectory.

The power system mostly adopts a clutch, a brake or a synchronizer structure to realize the switching of working modes, the control content relates to the control of a motor, the control of the clutch, the control of the brake and the control of the synchronizer, and the control method is more complex. The application of clutches and brakes, while improving comfort during mode switching, increases energy consumption and thus reduces transmission efficiency. The use of synchronizers can present a problem of power interruption during the mode switching process, thereby affecting comfort.

Disclosure of Invention

The invention aims to provide a double-motor parallel shaft transmission system of an electric automobile, which has a simple and compact structure, omits complex mechanical structures such as a clutch and a synchronizer, realizes the output of three driving modes by adjusting the driving states of two motors, and meets the requirements of the dynamic property and the economical efficiency of the automobile under the multi-driving working condition.

In order to achieve the purpose, the invention adopts the following technical scheme: a double-motor shaft-combining transmission system of an electric automobile comprises a first motor, a second motor, a first gear, a second gear, a third gear, a fourth gear and a fourth gearThe five gears, the first shaft, the second shaft, the intermediate shaft, the main speed reducer shaft and the wheels; the first motor is connected with the first gear through the first shaft, the second motor is connected with the second gear through the second shaft, and the transmission ratio of the first gear to the third gear is n₁The transmission ratio of the second gear to the third gear is n₂The two ends of the intermediate shaft are respectively connected with a third gear and a fourth gear, and the transmission ratio of the fourth gear to the fifth gear is n₃The fifth gear transmits torque to the wheels through the final drive shaft.

The first shaft, the second shaft, the intermediate shaft and the main speed reducer shaft are all connected by elastic shafts, and the elastic shafts are formed by modeling of a torsion spring and a damper: k₁And C₁Representing the spring rate and damping of the first shaft, K₂And C₂Spring rate and damping representing the second axis, K₃And C₃Spring rate and damping, K, of the intermediate shaft₄And C₄Representing the spring rate and damping of the final drive shaft.

Another object of the present invention is to provide a dynamic control strategy for mode switching of a dual-motor parallel-shaft transmission system of an electric vehicle, which comprises the following sequential steps:

(1) establishing a five-degree-of-freedom dynamic model of a double-motor parallel shaft transmission system of the electric automobile;

(2) selecting a driving mode and determining ideal driving torques of the two motors through an energy management strategy, wherein the driving modes are a mode 1, a mode 2 and a mode 3 respectively;

(3) and controlling the driving torques of the first motor and the second motor through a backward dynamic control strategy and a nested forward and backward dynamic control strategy.

In the step (1), the five degrees of freedom of the five-degree-of-freedom dynamic model are respectively the angular displacement theta of the first motor₁Angular displacement theta of the second motor₂Angular displacement theta of intermediate shaft₃Angular displacement theta of fifth gear₄And angular wheel displacement theta₅(ii) a The equivalent inertia of the first motor is I₁Let the equivalent inertia of the second motor be I₂Equivalent inertia fractions of the first gear, the second gear, and the third gearIs other than I_3a，I_3b，I_3cThe equivalent inertia of the fourth gear and the fifth gear is I_4a，I_4bEquivalent inertia of wheel is I₅；K₁And C₁Representing the spring rate and damping of the first shaft, K₂And C₂Spring rate and damping representing the second axis, K₃And C₃Spring rate and damping, K, of the intermediate shaft₄And C₄Representing the spring rate and damping of the final drive shaft; the five degree of freedom kinetic model has three external torque drives, where T₁Representing the output torque of the first electric machine, T₂Representing the output torque of the second electric machine, T₅Represents an equivalent vehicle load torque;

wherein I is an inertia matrix, C is a damping matrix, K is a stiffness matrix, θ is a state vector, and T is a load vector containing a driving torque and a load torque; n is₁Is the gear ratio of the first gear to the third gear, n₂Is the gear ratio of the second gear to the third gear, n₃The transmission ratio of the fourth gear to the fifth gear; vehicle load torque T₅Represented by the following equation:

wherein, F_VIs the sum of resistance caused by climbing resistance, air resistance and rolling resistance, m_VIs the mass of the vehicle, g is the acceleration of gravity,is the angle of inclination of the road, p is the air density, A_VIs the frontal area, C_dDenotes the coefficient of drag, C_tRepresenting the coefficient of rolling friction, R, of the tire_WIs the tire radius, and v is the vehicle speed.

The step (2) specifically comprises the following steps:

the dynamic equation of the double-motor parallel shaft transmission system of the electric automobile is as follows:

wherein ω is₁And ω₂The rotational speeds of the first and second electrical machines, T, respectively₁,T₂The output torques of the first motor and the second motor are respectively, the ideal driving torques of the two motors are output by applying an energy management strategy, and the formula of the energy management strategy is expressed as follows:

wherein, P_MIs the instantaneous power consumption of the two drive motors, P _ loss₁And P _ loss₂The power loss, k, of the first and second electrical machines, respectively₃Is a penalty factor for avoiding frequent mode switching operations, Δ ω₁Representing the first motor from time t_i-1To t_iA speed change of (d); the optimization model of the energy management strategy uses the torque of the first motor as a design variable on the principle of selecting the lowest energy loss, because the torque of the second motor is determined by equation (4) and the rotation speeds of the two motors are determined by equation (5), and the ideal driving torque distribution between the two motors is obtained by solving equation (6); when T is₂＝0，T₁When not equal to 0, the working mode is the mode 1; on the contrary, when T is₁＝0，T₂When not equal to 0, the working mode is the mode 2; when T is₁And T₂All are non-zero, workThe mode is mode 3;

three driving modes, namely a mode 1, a mode 2 and a mode 3, are provided by switching the working states of the first motor and the second motor; in the mode 1 state, the first motor outputs torque, the torque is transmitted to wheels through the first gear, the third gear, the fourth gear and the fifth gear, and the second motor does not output the torque; in the mode 2 state, the second motor outputs torque, the torque is transmitted to wheels through the second gear, the third gear, the fourth gear and the fifth gear, and the first motor does not output the torque; in the mode 3 state, the first motor and the second motor output torque coupling to drive the vehicle simultaneously.

The backward dynamic control strategy in the step (3) refers to:

the energy management strategy generates ideal driving torques of the first motor and the second motor on the basis of the principle of lowest energy loss, and because the energy management strategy is based on a backward dynamics model, the torque obtained in the energy management strategy is called backward torque; the energy management strategy outputs the backward torque of the first motor and the backward torque of the second motor per second, which are respectively T_1,0(t_i) And T_2,0(t_i) It is shown that increasing the average operation over a one second period after the backward torque signal converts the discrete values output by the energy management strategy into a continuous torque output by equation (7), respectively

And

the motor model will continue torqueAndtransmitted to the transmission and vehicle model, equation (7) is as follows:

the dynamic control strategy before and after nesting in the step (3) is as follows:

driving torque of vehicleThe energy management strategy is used to distribute torque between the two motors, as generated by the PI controller, and the tracking torques of the first and second motors are expressed as equation (8):

n₁is the gear ratio of the first gear to the third gear, n₂Is the gear ratio of the second gear to the third gear, n₃The transmission ratio of the fourth gear to the fifth gear; the control signals of the two motors are selected to be driving torque or tracking torque by the first switch and the second switch, when the working mode is the mode 2, the first motor outputs the driving torque, and the second motor outputs the tracking torque; when the working mode is the mode 1 or the mode 3, the first motor outputs tracking torque, and the second motor outputs driving torque; the mathematical model of the two switches is shown below:

output torque T of intermediate shaft₃Represented by the formula (10):

whatever the driving mode, T₃Always equal to the torque produced by the PI controller; due to the fact that

Andstill contain step changes; adding a transition procedure between mode 1 and mode 2 switchingThe duration of the shift process is set to 1s, the torque of the first motor varies linearly, and the torque of the second motor is used to compensate for the variation in the torque of the first motor, using the following equation to implement the transition process:

representing the corrected output value at the time of the step change in torque of the first electric machine,representing the first electric machine at t₀The torque before the change in the moment of time,

is the first motor at t₀Target torque after time change, time t from t₀Time begins to t₀The torque of the first motor is changed from the torque before the change in the time of one second until the time of +1Linear change to target torque

Representing the corrected output value when the torque of the second motor has step change;representing the second motor at t₀The torque before the change in the moment of time,is the first motor at t₀Target torque after time change, time t from t₀Time begins to t₀The torque of the second motor is changed from the torque before the change in the time of one second until the time of +1Linear change to target torque

According to the technical scheme, the beneficial effects of the invention are as follows: firstly, under the condition of not using any speed change mechanism, the invention realizes three driving modes only by controlling the torques of two driving motors, thereby meeting the driving requirements of vehicles; secondly, the invention provides a dynamic control strategy to realize the ideal mode switching of the dual-motor parallel shaft transmission system, realize the tracking of the ideal vehicle speed expected by a driver and the ideal torque provided by an energy management strategy, and control two motors to realize the mode switching without power interruption.

Drawings

FIG. 1 is a five-degree-of-freedom model diagram of a dual-motor parallel shaft transmission system;

FIG. 2 is a schematic diagram of a backward dynamic control strategy;

FIG. 3 is a schematic diagram of a nested forward-backward dynamic control strategy;

FIG. 4 is a diagram illustrating nested forward-backward dynamic control policy mode switching;

FIG. 5 is a vehicle speed tracking curve;

FIG. 6 is a schematic view of a driving mode;

FIG. 7 is a schematic illustration of drive torques for the first and second electric machines;

FIG. 8 is a schematic of total output torque;

FIG. 9 is a schematic view of vehicle impact.

Detailed Description

As shown in fig. 1, a dual-motor parallel shaft transmission system for an electric vehicle comprises a first motor 6, a second motor 7, a first gear 1, a second gear 2, a third gear 3, a fourth gear 4, a fifth gear 5, a first shaft 8, a second shaft 9, an intermediate shaft 10, a main reducer shaft 11 and wheels 12; the first motor is 6-wayThe first shaft 8 is connected with the first gear 1, the second motor 7 is connected with the second gear 2 through the second shaft 9, and the transmission ratio of the first gear 1 to the third gear 3 is n₁The transmission ratio of the second gear 2 to the third gear 3 is n₂The two ends of the intermediate shaft 10 are respectively connected with a third gear 3 and a fourth gear 4, and the transmission ratio of the fourth gear 4 to the fifth gear 5 is n₃The fifth gear 5 transmits torque to the wheels through the final drive shaft 11. The first shaft 8, the second shaft 9, the intermediate shaft 10 and the main speed reducer shaft 11 are all connected by elastic shafts, and the elastic shafts are formed by modeling of a torsion spring and a damper: k₁And C₁Representing the spring rate and damping of the first shaft 8, K₂And C₂Spring rate and damping, K, of the second shaft 9₃And C₃Representing spring rate and damping of the intermediate shaft 10, K₄And C₄Representing the spring rate and damping of the final drive shaft 11.

The strategy comprises the following sequential steps:

(1) establishing a five-degree-of-freedom dynamic model of a double-motor parallel shaft transmission system of the electric automobile;

(2) selecting a driving mode and determining ideal driving torques of the two motors through an energy management strategy, wherein the driving modes are a mode 1, a mode 2 and a mode 3 respectively;

(3) the drive torques of the first and second electric machines 6 and 7 are controlled by a backward dynamic control strategy and a nested forward-backward dynamic control strategy.

As shown in fig. 1, a five-degree-of-freedom model of a dual-motor parallel shaft transmission assembly is established for simulating the dynamic response of an electric vehicle. In the step (1), the five degrees of freedom of the five-degree-of-freedom dynamic model are respectively the angular displacement theta of the first motor₁Angular displacement theta of the second motor₂Angular displacement theta of intermediate shaft₃Angular displacement theta of fifth gear₄And angular wheel displacement theta₅(ii) a The equivalent inertia of the first motor is I₁Let the equivalent inertia of the second motor be I₂The equivalent inertia of the first gear, the second gear and the third gear is I_3a，I_3b，I_3cEquivalent inertia of the fourth gear and the fifth gearAre respectively I_4a，I_4bEquivalent inertia of wheel is I₅；K₁And C₁Representing the spring rate and damping of the first shaft, K₂And C₂Spring rate and damping representing the second axis, K₃And C₃Spring rate and damping, K, of the intermediate shaft₄And C₄Representing the spring rate and damping of the final drive shaft; the five degree of freedom kinetic model has three external torque drives, where T₁Representing the output torque of the first electric machine, T₂Representing the output torque of the second electric machine, T₅Represents an equivalent vehicle load torque;

wherein I is an inertia matrix, C is a damping matrix, K is a stiffness matrix, θ is a state vector, and T is a load vector containing a driving torque and a load torque; n is₁Is the gear ratio of the first gear 1 to the third gear 3, n₂Is the gear ratio of the second gear 2 to the third gear 3, n₃The transmission ratio of the fourth gear 4 to the fifth gear 5; vehicle load torque T₅Represented by the following equation:

wherein, F_VIs the sum of resistance caused by climbing resistance, air resistance and rolling resistance, m_VIs the mass of the vehicle, g is the acceleration of gravity,is the angle of inclination of the road, p is the air density, A_VIs frontal area，C_dDenotes the coefficient of drag, C_tRepresenting the coefficient of rolling friction, R, of the tire_WIs the tire radius, and v is the vehicle speed.

The energy management strategy designed in said step (2) optimizes the energy efficiency of the dynamic system to produce the desired driving torque of the two electric motors after a given driving cycle, for example by providing vehicle speed and acceleration. To ensure real-time control, energy management strategies are developed using a backward dynamic model with less computational cost. In the backward dynamics model, the axis is considered as a rigid body, and thus has only 1 degree of freedom.

The step (2) specifically comprises the following steps:

after neglecting the elastic force, the dynamic equation of the electric automobile dual-motor parallel shaft transmission system is as follows:

wherein ω is₁And ω₂The rotational speeds, T, of the first and second electric machines 6 and 7, respectively₁,T₂Respectively, a first electric machine 6

And the output torque of the second motor 7, and an energy management strategy is applied to output the ideal driving torque of the two motors, namely an energy pipe

The formula of the physical strategy is expressed as follows:

wherein, P_MIs the instantaneous power consumption of the two drive motors, P _ loss₁And P _ loss₂The power loss, k, of the first and second electrical machines, respectively₃Is a penalty factor for avoiding frequent mode switching operations, Δ ω₁Representing the first motor from time t_i-1To t_iA speed change of (d); the optimization model of the energy management strategy is based on selecting the lowest energy loss,using the torque of the first motor as a design variable, since the torque of the second motor is determined by equation (4) and the rotational speeds of the two motors are determined by equation (5), an ideal driving torque distribution between the two motors is obtained by solving equation (6); when T is₂＝0，T₁When not equal to 0, the working mode is the mode 1; on the contrary, when T is₁＝0，T₂When not equal to 0, the working mode is the mode 2; when T is₁And T₂When the values are all non-zero, the working mode is mode 3; as shown in fig. 6.

Three driving modes, namely a mode 1, a mode 2 and a mode 3, are provided by switching the working states of the first motor 6 and the second motor 7; in the mode 1 state, the first motor 6 outputs torque, the torque is transmitted to wheels through the first gear 1, the third gear 3, the fourth gear 4 and the fifth gear 5, and the second motor 7 does not output torque; in the mode 2 state, the second motor 7 outputs torque, the torque is transmitted to wheels through the second gear 2, the third gear 3, the fourth gear 4 and the fifth gear 5, and the first motor 6 does not output torque; in the mode 3 state, the first electric machine 6 and the second electric machine 7 simultaneously output torque coupling to drive the vehicle.

The present invention proposes two dynamic control strategies for controlling the drive torque of the first electric machine 6 and the second electric machine 7. The first control strategy is to directly control the two motors using the torque signals provided by the energy management strategy described above, which is referred to as a backward dynamic control strategy, as shown in fig. 2. The second control strategy uses a nested control configuration, where the first stage is a PI controller to control the total torque driven on the vehicle and the second stage is an energy management strategy for distributing torque between the two electric machines, so it is referred to as a nested front-to-back dynamic control strategy, as shown in FIG. 3.

The backward dynamic control strategy in the step (3) refers to:

the energy management strategy generates ideal driving torques of the first electric machine 6 and the second electric machine 7 on the principle of lowest energy loss, and the torque obtained in the energy management strategy is called backward torque because the energy management strategy is based on a backward dynamics model; the energy management strategy outputs the rearward torque of the first and second electric machines 6 and 7 per second,respectively formed by T_1,0(t_i) And T_2,0(t_i) It is shown that increasing the average operation over a one second period after the backward torque signal converts the discrete values output by the energy management strategy into a continuous torque output by equation (7), respectively

Andthe motor model will continue torque

Andtransmitted to the transmission and vehicle model, equation (7) is as follows:

to avoid a step change in the drive torque, the average operation with a period of one second is increased after the reverse torque signal so that the reverse torque is continuous. The electric machine model transmits a continuous reverse torque control signal to the actual torque of the transmission and the vehicle model.

The dynamic control strategy before and after nesting in the step (3) is as follows:

the NFBDCS strategy is simpler, but it does not contain any speed feedback control signal, which delays the actual speed of the vehicle compared to the ideal vehicle speed. To overcome this drawback, a new control scheme is proposed in fig. 3, in which a PI controller is added to the control system, which adjusts the motor torque according to the difference between the desired vehicle speed and the actual speed. The PI controller is used for forward dynamic control, and thus the control strategy is referred to as a nested forward-backward dynamic control strategy. The total driving torque of the vehicle drive is controlled by the PI controller, so that the step change of the output torque can be avoided, and the larger impact generated in the mode gear shifting process can be avoided. After the PI controller generates the total torque, the energy management strategy EMS is used to distribute the torque between the two electric machines.

Driving torque of vehicleGenerated by the PI controller, the energy management strategy is used to distribute the torque between the two motors, and the tracking torques of the first motor 6 and the second motor 7 are expressed as equation (8):

n₁is the gear ratio of the first gear 1 to the third gear 3, n₂Is the gear ratio of the second gear 2 to the third gear 3, n₃The transmission ratio of the fourth gear 4 to the fifth gear 5; the control signals of the two motors are selected to be driving torque or tracking torque by the first switch and the second switch, when the working mode is the mode 2, the first motor 6 outputs the driving torque, and the second motor 7 outputs the tracking torque; when the working mode is the mode 1 or the mode 3, the first motor 6 outputs a tracking torque, and the second motor 7 outputs a driving torque; the mathematical model of the two switches is shown below:

output torque T of intermediate shaft 10₃Represented by the formula (10):

whatever the driving mode, T₃Always equal to the torque produced by the PI controller, which avoids large shocks during mode transitions. Due to the fact thatAndstill involving step changes, steps to be avoidedThe influence of the jump change on the two motors, so that a conversion process is added between the two mode switching. A transition process is added between the mode 1 and mode 2 switching, the duration of the transition process is set to 1s, the torque of the first electric machine 6 varies linearly, while the torque of the second electric machine 7 is used to compensate for the variation in torque of the first electric machine 6, using the following equation to achieve the transition process, the torque variation of the mode transition being as shown in fig. 5.

Representing the corrected output value at the time of the step change in torque of the first electric machine 6,representing the first electric machine 6 at t₀The torque before the change in the moment of time,is the first electric machine 6 at t₀Target torque after time change, time t from t₀Time begins to t₀The torque of the first motor 6 is changed from the torque before the change in the torque during one second until the time +1Linear change to target torque

Represents the corrected output value when the torque of the second motor 7 changes in steps;

represents the second electric machine 7 at t₀The torque before the change in the moment of time,is the first electric machine 6 at t₀Target torque after time change, time t from t₀Time begins to t₀The torque of the second motor 7 is changed from the torque before the change in the torque during one second until the time +1

Linear change to target torque

Vehicle speed tracking under different dynamic control strategies as shown in fig. 5, the delay time of the actual speed changes with the change of the driving mode and the vehicle speed. However, regardless of the operation mode, the backward dynamic control strategy BDCS has the longest delay time of about 0.9s, and the nested forward-backward dynamic control strategy has a delay time of less than 0.1s, so the nested forward-backward dynamic control strategy is superior to the backward dynamic control strategy BDCS in speed tracking.

The corresponding driving mode over time is determined by the energy management strategy, as shown in fig. 6, and the vertical axis represents three operating modes: 1 represents a single drive mode by the first motor 6, 2 represents a single drive mode by the second motor 7, and 3 represents two motor-coupled drive modes. The torque of the two motors over time during a given drive cycle is shown in figure 7.

At 105 seconds, the driving mode is switched from mode 2 to mode 1, during which T is₂From an initial value to zero, T₁Changing from zero to the target torque. For the backward dynamic control strategy, T₁And T₂Follows a linear trajectory generated by the energy management strategy. The torque variation trend of the nested forward and backward dynamic control strategy is similar to that of the backward dynamic control strategy, but T₂Is different from the initial value of (T)₁The track of the motor is controlled by the PI controller, so that the stability of the total driving torque is ensured.

At 108 seconds, the driving mode is switched from mode 1 to mode 2, as compared with the case where mode 2 is switched to mode 1, T₂Change from zero to target T₁The value increase is from a negative initial value to zero. For the backward dynamic control strategy, T₁Increases linearly from the initial value to zero, T, during 108s and 109s₂Linearly decreasing to the target value during 108s and 109 s. For nested front-to-back dynamic control strategies, T₁Also increases linearly from the initial value to zero, T₂Controlled by PI controller to compensate for T₁A change in (c).

At 113 seconds, the driving mode is switched from mode 2 to mode 3. The process of mode 2 transition to mode 3 is almost equivalent to mode 2 transition to mode 1. The only difference is T of mode 1₂Target value is zero and mode 3, T₂The target value is non-zero.

The process of mode 3 to mode 2 is equivalent to the process of mode 1 to mode 2, the only difference being the T of mode 3₂Is non-zero and the initial value of mode 1 is zero. The backward dynamic control strategy and the nested forward and backward dynamic control strategy both change T continuously₁And T₂。

FIG. 8 plots output torque T₃This indicates the total torque on the vehicle as a function of the driving cycle. The backward dynamic control strategy and the nested forward and backward dynamic control strategy provide a very smooth total driving torque for the vehicle, but the torque variation of the backward dynamic control strategy always lags behind the nested forward and backward dynamic control strategy, resulting in a long vehicle speed tracking delay time, as shown in fig. 5.

Vehicle jerk under different dynamic control strategies is shown in FIG. 9. The large vehicle jerk is ignored during the initial dynamic balancing phase and both the backward dynamic control strategy and the nested forward and backward dynamic control strategy have a smaller vehicle jerk because their total drive torque varies continuously. It is worth noting that the backward dynamic control strategy has a lot of high-frequency fluctuation, but the impact of the nested forward and backward dynamic control strategy is very smooth. This phenomenon is caused by the unsmooth variation of the driving torque of the backward dynamic control strategy, since its torque is controlled by the EMS. The total driving torque of the nested front-rear dynamic control strategy is controlled by the PI controller, so that the torque is stably changed, and the stable vehicle impact degree is generated.

Vehicle acceleration also demonstrates the dynamic performance of both control strategies, both the backward dynamic control strategy and the nested forward-backward dynamic control strategy having very smooth vehicle acceleration during mode transitions. However, the backward dynamic control strategy still generates many high-frequency vibrations, albeit of very small amplitude. The nested forward and backward dynamic control strategy provides very stable vehicle acceleration throughout the entire driving cycle, enabling unpowered interrupt mode transitions.

In summary, the invention provides a dynamic control strategy for an electric vehicle with a dual-motor parallel shaft transmission system, and provides two single-motor driving modes and a driving mode combining the dual-motor driving modes. The invention establishes a forward dynamic model of a power assembly to simulate the dynamic response of an electric automobile, and provides two dynamic control strategies to track the speed of the automobile and realize mode conversion, wherein the backward dynamic control strategy is a simple control strategy, but generates a long delay time when tracking the speed of the automobile, the other nested front-back dynamic control strategy can track the speed of the automobile in a very short delay time and generates a very small and stable impact degree of the automobile when the mode is converted, the acceleration of the automobile is stably changed in the mode conversion by using the nested front-back dynamic control strategy, and then some high-frequency vibration of the acceleration of the automobile is brought to the dynamic control strategy, so the proposed nested front-back dynamic control strategy can well track the speed of the automobile and realize the mode conversion of interruption.