阅读说明：本技术 一种轮边驱动电动拖拉机的控制方法 (Control method of wheel-side driving electric tractor ) 是由 谢斌 张胜利 王帅 李家坤 娄秀华 武秀恒 李俊林 于 2021-03-17 设计创作，主要内容包括：本发明属于电动拖拉机的技术领域,具体涉及一种轮边驱动电动拖拉机的控制方法,所述轮边驱动电动拖拉机,包括电控箱(2)、后电池组(6)、驱动总成(8)、驱动轮(10)、轮边减速器(11)、前电池组(12)、车架总成(13)、前桥总成(14)和转向轮(15)；本发明采用轮边电机驱动的形式,取消了传统拖拉机复杂的传动机械结构,驱动电机通过轮边减速器直接将驱动力传递至驱动轮,结构简单紧凑,提高了整机传动效率。此外,采用双电机驱动不同于传统后桥差速器分动,电机的转矩分配具有更大空间,提高了电动拖拉机在各种极端工况下的适应能力。(The invention belongs to the technical field of electric tractors, and particularly relates to a control method of a wheel-side driving electric tractor, which comprises an electric cabinet (2), a rear battery pack (6), a driving assembly (8), a driving wheel (10), a wheel-side reducer (11), a front battery pack (12), a frame assembly (13), a front axle assembly (14) and a steering wheel (15); the invention adopts the form of wheel-side motor driving, cancels the complex transmission mechanical structure of the traditional tractor, directly transmits the driving force to the driving wheel by the driving motor through the wheel-side reducer, has simple and compact structure and improves the transmission efficiency of the whole machine. In addition, the double-motor driving mode is different from the transfer of the traditional rear axle differential, the torque distribution of the motors has larger space, and the adaptability of the electric tractor under various extreme working conditions is improved.)

1. A control method of a wheel-side driven electric tractor comprises an electric cabinet (2), a rear battery pack (6), a driving assembly (8), a driving wheel (10), a wheel-side reducer (11), a front battery pack (12), a frame assembly (13), a front axle assembly (14) and a steering wheel (15);

the frame assembly (13) comprises a front frame and a rear frame, and the front frame and the rear frame are fixed into a whole; the front frame is used for mounting an electric control box (2), a front battery pack (12) and a front axle assembly (14), and the rear frame is used for mounting a driving assembly (8); the left side and the right side of the rear frame are provided with driving assembly mounting holes, and the wheel-side speed reducer (11) is connected with the rear frame through the driving assembly mounting holes; a rear battery pack (6) is arranged on the rear frame, and the rear battery pack (6) is fixed with the rear frame; the front battery pack (12) and the rear battery pack (6) are connected in series to form a power battery pack;

the steering wheel (15) is arranged on a front axle assembly (14); the driving assembly (8) comprises a left driving motor, a right driving motor and a wheel reduction gear (11), wherein the left driving motor and the right driving motor are connected with the wheel reduction gear (11) through spline shafts, one end of the wheel reduction gear (11) is connected with a driving assembly mounting hole on the side surface of the frame through a bolt, the other end of the wheel reduction gear is connected with a hub of the driving wheel (10), power is provided by the left driving motor and the right driving motor, and the power is transmitted to the driving wheel (10) through the wheel reduction gear (11);

the signal acquisition port of the whole machine controller is connected with a wiring terminal through a controller wire harness and then is respectively connected with sensor signal output lines such as a key, a gear, an accelerator pedal, a brake pedal and an operation mode switch, and the whole machine state information and the driver operation information of the electric tractor are acquired;

the driving motor controller controls the left and right driving motors;

the steering controller is connected with a front wheel steering angle sensor to acquire a front wheel steering angle delta in real time; the whole machine controller is connected with the driving controller and the steering controller through a CAN bus;

the complete machine controller and the driving motor controller are arranged in the electric cabinet (2);

the method is characterized in that: the control method comprises the following steps:

step 1: the whole machine controller collects operation information of a driver such as a key/gear signal, an accelerator pedal signal, a brake pedal signal, an operation mode signal and the like to judge the state of the whole machine;

step 2: when the electric tractor is judged to be in a driving state, the complete machine controller calculates the total required torque T of the complete machine by combining the complete machine state information_reqThe complete machine state information comprises the allowable battery use power, the motor rotating speed and torque and the actual vehicle speed;

step 2.1: under the driving state of the electric tractor, the whole machine controller analyzes the collected accelerator pedal signal and filters a pedal interference signal based on a first-order filtering algorithm; the filtered voltage value of the accelerator pedal signal is expressed as

u(k)＝(1-λ)u_filt(k) + λ u (k-1) formula 1

Wherein u (k) is the output voltage of the accelerator pedal at this time, and the unit is V; u (k-1) is the last output voltage of the accelerator pedal and has the unit of V; u. of_filt(k) Is the filtered voltage of the accelerator pedal, in units of V; lambda is a filter coefficient, and the value range of lambda is 0-1;

then setting pedal signal dead zone voltage parameter, adding minimum voltage parameter u₀And a maximum voltage parameter u₁₀₀Then, accelerator pedal opening θ (k):

wherein θ (k) is an accelerator pedal opening; u. of_filt(k) Is the filtered voltage of the accelerator pedal, in units of V; u. of₀Is the minimum voltage parameter in units of V; u. of₁₀₀Is the maximum voltage parameter, with the unit of V;

introducing a pedal opening mapping parameter delta (k) on the basis of formula 2 to realize different pedal output responses, and finally obtaining a used pedal opening theta:

wherein θ is the opening degree of the use pedal; δ (k) is a pedal opening degree mapping parameter; θ (k) is an accelerator pedal opening;

step 2.2: when the electric tractor works in the field, the driving torque control is carried out based on the pedal opening theta to obtain the reference required torque T_bas；

Step 2.2.1 when the electric tractor operates in the field, the target rotating speed of the motor and the opening theta of the used pedal are in a linear relation, the target speed of the whole tractor is determined based on the opening theta of the used pedal and the maximum calibration speed of the tractor, and the target rotating speed of the driving motor is further obtained; in order to better track the target rotating speed of the driving motor, the reference required torque T of the driving motor is adjusted by combining the target rotating speed and the actual rotating speed of the driving motor_basMeanwhile, the maximum output power of the power battery is calculated based on battery state parameters such as SOC, temperature, open-circuit voltage, internal resistance and the like of the power battery, and the reference torque T of the driving motor is limited_basTo limit the power demand of the drive motor;

step 2.2.2, if the torque of the driving motor changes too fast and is not controlled, the electric tractor is easy to be impacted, and the service life of the whole transmission system is further influenced; limiting the drive motor reference torque T at step 2.2.1_basFurther reference torque T is added to the driving motor_basCarrying out smoothing treatment to limit the torque variation in each cycle; obtaining a reference required torque T after four stages of motor target rotating speed calculation, motor reference rotating speed calculation, battery maximum power limitation and driving torque smoothing_bas；

Step 2.3: for the reference required torque T_basLimiting, wherein the limiting mainly comprises motor overload protection, system over-temperature and under-voltage protection, and the influence of factors such as motor overload running time, motor and controller temperature, system input voltage and the like on the operation capacity of the tractor is considered, wherein the motor temperature is obtained by a temperature sensor; the reference required torque T is under the working conditions of system overload, over-temperature, under-voltage and the like_basLimiting to obtain total required torque T of the whole machine_req；

And step 3: then, the complete machine controller is communicated with the steering controller in real time through a CAN bus to obtain the steering angle of the steering wheel of the electric tractor, and the theoretical speeds of the left driving wheel and the right driving wheel are calculated based on the Ackerman steering model;

based on the Ackerman steering model, when the tractor steers at low speed, the target rotating speed ratio of the two driving wheels is expressed as

Wherein rho is a target rotation speed ratio; omega_w1Is the actual rotating speed of the left driving wheel and has the unit of rad.s^-1；ω_w2Is the actual rotation speed of the right driving wheel with the unit of rad.s^-1(ii) a L is the wheelbase of the tractor, and the unit is m; b is the rear axle wheel base of the tractor, and the unit is m; delta is the front wheel deflection angle, in degrees;

and 4, step 4: whole machine controller combined with total required torque T of whole machine_reqCalculating the driving torque distribution proportion of the left driving motor and the right driving motor with the theoretical speed of the left driving wheel and the right driving wheel of the tractor steering to ensure that the slip states of the left driving wheel and the right driving wheel are consistent, and finally obtaining the target driving torque of the left driving motor and the target driving torque of the right driving motor;

in order to ensure that the tractor obtains good traction driving performance under field operation, the ratio omega of the rotating speed of the right driving wheel to the rotating speed of the left driving wheel is controlled_w2/ω_w1Approximating the target rotation speed ratio ρ given by equation 4;

design sliding mode function s based on sliding mode control method_δThe following were used:

s_δ＝ω_w2-ρ·ω_w1equation 5

The first derivative of the slip form surface is

And is

To ensureOrder to

In the formula, k₁And k₂The control parameters corresponding to the index approach term and the constant speed approach term in the approach law influence the convergence speed of the actual rotating speed ratio to the target rotating speed ratio;

sgn(s_δ) About the slip form surface s_δThe symbol function of (2) is obtained by simultaneous equations 5, 6, 7 and 8:

according to the combined external moment of the two driving wheels of the tractor in the rotating direction, a dynamic equation of the driving wheels is obtained:

further, the output torques of the left and right driving motors are expressed as

In the formula, J_wIs the moment of inertia of the wheel, in kg.m²；T_w1Is the driving torque of the left driving wheel, and the unit is N.m; t is_w2Is the driving torque of the right driving wheel, and the unit is N.m; f_x1Is the left drive tire longitudinal force in units of N; f_x2Is the right drive tire longitudinal force in units of N; r_rIs the rolling radius of the rear wheel, and the unit is m; t is_f1The unit is N.m, and is the rolling moment of a left driving wheel; t is_f2The unit is N.m, and is the rolling moment of a right driving wheel; t is_m1For the left drive motor output torque, unitIs N.m; t is_m2The unit is N.m, and is the output torque of the right driving motor; i.e. i_gIs the total speed ratio of the transmission system; eta_tFor driveline efficiency; rho is a target rotation speed ratio; t is_reqThe unit is N.m, which is the total required torque of the whole machine; omega_w1Is the actual rotating speed of the left driving wheel and has the unit of rad.s^-1；ω_w2Is the actual rotation speed of the right driving wheel with the unit of rad.s^-1；k₁And k₂The control parameters corresponding to the index approach term and the constant speed approach term in the approach law influence the convergence speed of the actual rotating speed ratio to the target rotating speed ratio;

in equation 11, the left drive wheel speed ω_w1And right driving wheel rotation speed omega_w2The motor rotating speed is obtained through motor rotating speed conversion, and the motor rotating speed is obtained through signals of a Hall rotating speed sensor; total required torque T of whole machine_reqThe driving input information is obtained by analyzing driving input information such as an accelerator pedal; the target rotation speed ratio rho is obtained by measuring the deflection angle delta of the front wheel;

and 5: the complete machine controller calculates the output torque T of the left and right driving motors obtained in the step 4_m1、T_m2And the torque control of the left and right driving motors is realized by the driving motor controller through torque closed-loop vector control.

2. The control method of a wheel-side drive electric tractor according to claim 1, characterized in that: in step 1, the complete machine state comprises: 7 states of a shutdown state, an awakening state, a starting state, a driving state, a braking state, a charging state and a fault state; wherein the content of the first and second substances,

and (3) awakening state: when the electric tractor works normally or is charged, when a complete machine controller receives a Key opening (Key _ On is 1) instruction of a driver, the complete machine enters an awakening state; in the awakening state, the whole system controller is powered on firstly, the whole system controller starts system initialization after the power-on and self-checking are controlled by the whole machine, and then the power-on and self-checking are carried out on each system controller;

and (3) starting: when the complete machine controller and each subsystem controller are electrified to complete self-checking and initialization and have no fault, after the complete machine controller receives a Key (Key _ Start ═ 1) starting instruction of a driver, the complete machine enters a starting state; in the starting state, firstly, a pre-charging relay is switched on for pre-charging, at the moment, a motor control enable and a high-voltage power distribution enable are switched on, and after the pre-charging is finished, the pre-charging relay is switched off and a main relay is switched on; if the pre-charging fails, the pre-charging relay is disconnected, and the motor control enable and the high-voltage power distribution enable are closed;

a driving state: after the electric tractor finishes precharging and is switched on with high voltage electricity in a starting State, high pedal protection judgment is carried out, and if a gear switch is in a Neutral gear (DNR _ State) and the opening degree of an accelerator pedal is zero (Acc _ Throttle is 0), the whole tractor enters a driving State; under the driving state, the complete machine controller judges a driving mode according to a gear state (DNR) and the opening degree of an accelerator pedal and calculates the required torque of the complete machine;

a braking state: when the electric tractor is in a driving state, when a complete machine controller receives a Brake intention (Brake _ Percent < >0) of a driver, the complete machine enters a Brake state; under the braking state, the whole machine controller calculates the magnitude of braking torque according to the opening degree of a brake pedal and the current vehicle speed, and controls a braking mechanism to realize the braking of the whole machine;

the charging state is as follows: when the electric tractor is in an awakening state, when the whole machine controller receives a charging instruction (Charge _ switch is 1) and the battery management system has no fault, the whole machine enters a charging state; in a charging state, the motor controller enable and the high-voltage distribution enable are closed, the charging relay is opened, and after charging is finished, the whole machine enters an awakening state;

and (3) fault state: the electric tractor is in a normal working or charging state, and when the fault is detected by the fault diagnosis of the controller of the whole tractor or fault information is sent by each subsystem, the whole tractor enters a fault state; under the fault state, the complete machine controller judges the fault grade and processes the fault;

a shutdown state: when the electric tractor is in a normal working state, a charging state or a fault state, after a complete machine controller receives a Key closing (Key _ Off ═ 1) instruction of a driver, the complete machine enters a shutdown state; and in the shutdown state, the complete machine controller clears relevant data of the complete machine, disconnects the main relay and the pre-charging relay, and closes the motor controller enable and the high-voltage power distribution enable.

3. The control method of a wheel-side drive electric tractor according to claim 1, characterized in that: in step 2.2, the field operation of the electric tractor comprises ploughing, rotary tillage and seeding.

4. The control method of a wheel-side drive electric tractor according to claim 1, characterized in that: the wheel-side driving electric tractor further comprises a hood (1), an instrument panel (3), a steering wheel (4), a driving seat (5), an electric suspension (7) and a power output shaft (9); the hood (1) is fixed at the front end of the frame assembly (13) through a hinge; the front frame is used for mounting an instrument panel (3) and a steering wheel (4), and the rear frame is used for mounting a driving seat (5), a rear battery pack (6), an electric suspension (7), a power output shaft (9) and a driving wheel (10); the instrument panel (3) is used for arranging instruments and switches.

5. The control method of a wheel-side drive electric tractor according to claim 1, characterized in that: the front battery pack (12) and the rear battery pack (6) are connected in series by two power battery buses to form a 48V power battery pack, a power source is provided for the electric tractor, and the battery pack is connected with an adaptive charger by using a charging plug to charge the battery pack.

6. The control method of a wheel-side drive electric tractor according to claim 1, characterized in that: the drive motor controller converts the 48V direct current into three-phase alternating current which is connected with U, V, W ports of the left and right drive motors through three wires, and a Hall rotating speed sensor and a temperature sensor which are arranged on the drive motor are connected with a control signal wire of the drive motor controller together.

Technical Field

The invention belongs to the technical field of electric tractors, and particularly relates to a control method of a wheel-side driven electric tractor.

Background

The traditional tractor is easy to generate transverse deviation when in field operation, namely, the single-side adhesion condition of wheels is generated, the slip rate is usually too high, the power of the tractor is poor, even if part of the tractor is provided with a limited slip differential, an electronic clutch and other parts, the torque power adjustment within a certain range can be realized, the full-range degree can not be reached, and a large amount of energy can be additionally consumed in the adjustment process. At present, a centralized driving scheme or a double-motor coupling driving scheme is mostly adopted for an agricultural electric tractor chassis, and the application of a wheel edge driving configuration is very limited.

The wheel-side driving power structure is used as one of special distributed driving structures of the electric tractor, two driving motors are arranged on the inner side of a rear driving wheel, and the two driving motors are connected with the driving wheel through wheel-side speed reducers respectively. In addition, the structure also has the characteristic of high integration level of the motor, the arrangement flexibility of the chassis can be greatly increased, and the arrangement of the battery of the whole machine is easier.

The configuration of the power transmission system of the electric tractor and the driving control strategy thereof have important influence on the dynamic performance and the traction performance of the whole tractor. The wheel-side driving electric tractor can fully exert the self configuration advantage and the control effect of a complete machine controller, realize the distribution of power torque in a large range under the condition of no extra energy consumption, and the driving torque of each driving wheel can be independently controlled and actively regulated according to the running state and the road surface condition of the tractor, so that the potential advantages of the electric chassis in the aspects of improving the traction performance and the operation adaptability of the complete machine can be more easily exerted.

Disclosure of Invention

The invention provides a control method of a wheel-side driven electric tractor, which is used for solving the problem of unreasonable distribution of driving torque caused by large difference of attachment conditions of left and right driving wheels under the field operation condition of the electric tractor.

In order to achieve the purpose, the invention provides the following technical scheme:

a control method of a wheel-side driving electric tractor comprises an electric cabinet 2, a rear battery pack 6, a driving assembly 8, a driving wheel 10, a wheel-side reducer 11, a front battery pack 12, a frame assembly 13, a front axle assembly 14 and a steering wheel 15;

the frame assembly 13 comprises a front frame and a rear frame, and the front frame and the rear frame are fixed into a whole; the front frame is used for mounting the electric control box 2, the front battery pack 12 and the front axle assembly 14, and the rear frame is used for mounting the driving assembly 8; the left side and the right side of the rear frame are provided with driving assembly mounting holes, and the wheel reduction gear 11 is connected with the rear frame through the driving assembly mounting holes; a rear battery pack 6 is arranged on the rear frame, and the rear battery pack 6 is fixed with the rear frame; the front battery pack 12 and the rear battery pack 6 are connected in series to form a power battery pack;

the steering wheel 15 is mounted on the front axle assembly 14; the driving assembly 8 comprises a left driving motor, a right driving motor and a wheel-side reducer 11, wherein the left driving motor and the right driving motor are connected with the wheel-side reducer 11 through spline shafts, one end of the wheel-side reducer 11 is connected with a driving assembly mounting hole on the side surface of the frame through a bolt, the other end of the wheel-side reducer 11 is connected with a hub of the driving wheel 10, and the left driving motor and the right driving motor provide power and transmit the power to the driving wheel 10 through the wheel-side reducer 11;

the signal acquisition port of the whole machine controller is connected with a wiring terminal through a controller wire harness and then is respectively connected with sensor signal output lines such as a key, a gear, an accelerator pedal, a brake pedal and an operation mode switch, and the whole machine state information and the driver operation information of the electric tractor are acquired;

the driving motor controller controls the left and right driving motors;

the steering controller is connected with a front wheel steering angle sensor to acquire a front wheel steering angle delta in real time; the whole machine controller is connected with the driving controller and the steering controller through a CAN bus;

the complete machine controller and the driving motor controller are arranged in the electric cabinet 2;

the control method comprises the following steps:

step 1: the whole machine controller collects operation information of a driver such as a key/gear signal, an accelerator pedal signal, a brake pedal signal, an operation mode signal and the like to judge the state of the whole machine;

step 2: when the electric tractor is judged to be in a driving state, the complete machine controller calculates the total required torque T of the complete machine by combining the complete machine state information_reqThe complete machine state information comprises the allowable battery use power, the motor rotating speed and torque and the actual vehicle speed;

step 2.1: under the driving state of the electric tractor, the whole machine controller analyzes the collected accelerator pedal signal and filters a pedal interference signal based on a first-order filtering algorithm; the filtered voltage value of the accelerator pedal signal is expressed as

u(k)＝(1-λ)u_filt(k) + λ u (k-1) formula 1

Wherein u (k) is the output voltage of the accelerator pedal at this time, and the unit is V; u (k-1) is the last output voltage of the accelerator pedal and has the unit of V; u. of_filt(k) Is the filtered voltage of the accelerator pedal, in units of V; lambda is a filter coefficient, and the value range of lambda is 0-1;

then setting pedal signal dead zone voltage parameter, adding minimum voltage parameter u₀And a maximum voltage parameter u₁₀₀Then, accelerator pedal opening θ (k):

wherein θ (k) is an accelerator pedal opening; u. of_filt(k) Is the filtered voltage of the accelerator pedal, in units of V; u. of₀Is the minimum voltage parameter in units of V; u. of₁₀₀Is the maximum voltage parameter, with the unit of V;

introducing a pedal opening mapping parameter delta (k) on the basis of formula 2 to realize different pedal output responses, and finally obtaining a used pedal opening theta:

wherein θ is the opening degree of the use pedal; δ (k) is a pedal opening degree mapping parameter; θ (k) is an accelerator pedal opening;

step 2.2: when the electric tractor works in the field, the baseObtaining a reference required torque T for drive torque control using a pedal opening degree theta_bas；

Step 2.2.1 when the electric tractor operates in the field, the target rotating speed of the motor and the opening theta of the used pedal are in a linear relation, the target speed of the whole tractor is determined based on the opening theta of the used pedal and the maximum calibration speed of the tractor, and the target rotating speed of the driving motor is further obtained; in order to better track the target rotating speed of the driving motor, the reference required torque T of the driving motor is adjusted by combining the target rotating speed and the actual rotating speed of the driving motor_basMeanwhile, the maximum output power of the power battery is calculated based on battery state parameters such as SOC, temperature, open-circuit voltage, internal resistance and the like of the power battery, and the reference torque T of the driving motor is limited_basTo limit the power demand of the drive motor;

step 2.2.2, if the torque of the driving motor changes too fast and is not controlled, the electric tractor is easy to be impacted, and the service life of the whole transmission system is further influenced; limiting the drive motor reference torque T at step 2.2.1_basFurther reference torque T is added to the driving motor_basCarrying out smoothing treatment to limit the torque variation in each cycle; obtaining a reference required torque T after four stages of motor target rotating speed calculation, motor reference rotating speed calculation, battery maximum power limitation and driving torque smoothing_bas；

Step 2.3: for the reference required torque T_basLimiting, wherein the limiting mainly comprises motor overload protection, system over-temperature and under-voltage protection, and the influence of factors such as motor overload running time, motor and controller temperature, system input voltage and the like on the operation capacity of the tractor is considered, wherein the motor temperature is obtained by a temperature sensor; the reference required torque T is under the working conditions of system overload, over-temperature, under-voltage and the like_basLimiting to obtain total required torque T of the whole machine_req；

And step 3: then, the complete machine controller is communicated with the steering controller in real time through a CAN bus to obtain the steering angle of the steering wheel of the electric tractor, and the theoretical speeds of the left driving wheel and the right driving wheel are calculated based on the Ackerman steering model;

based on the Ackerman steering model, when the tractor steers at low speed, the target rotating speed ratio of the two driving wheels is expressed as

Wherein rho is a target rotation speed ratio; omega_w1Is the actual rotating speed of the left driving wheel and has the unit of rad.s^-1；ω_w2Is the actual rotation speed of the right driving wheel with the unit of rad.s^-1(ii) a L is the wheelbase of the tractor, and the unit is m; b is the rear axle wheel base of the tractor, and the unit is m; delta is the front wheel deflection angle, in degrees;

and 4, step 4: whole machine controller combined with total required torque T of whole machine_reqCalculating the driving torque distribution proportion of the left driving motor and the right driving motor with the theoretical speed of the left driving wheel and the right driving wheel of the tractor steering to ensure that the slip states of the left driving wheel and the right driving wheel are consistent, and finally obtaining the target driving torque of the left driving motor and the target driving torque of the right driving motor;

in order to ensure that the tractor obtains good traction driving performance under field operation, the ratio omega of the rotating speed of the right driving wheel to the rotating speed of the left driving wheel is controlled_w2/ω_w1Approximating the target rotation speed ratio ρ given by equation 4;

design sliding mode function s based on sliding mode control method_δThe following were used:

s_δ＝ω_w2-ρ·ω_w1equation 5

The first derivative of the slip form surface is

And is

To ensureOrder to

In the formula, k₁And k₂The control parameters corresponding to the index approach term and the constant speed approach term in the approach law influence the convergence speed of the actual rotating speed ratio to the target rotating speed ratio;

sgn(s_δ) About the slip form surface s_δThe symbol function of (2) is obtained by simultaneous equations 5, 6, 7 and 8:

according to the combined external moment of the two driving wheels of the tractor in the rotating direction, a dynamic equation of the driving wheels is obtained:

further, the output torques of the left and right driving motors are expressed as

In the formula, J_wIs the moment of inertia of the wheel, in kg.m²；T_w1Is the driving torque of the left driving wheel, and the unit is N.m; t is_w2Is the driving torque of the right driving wheel, and the unit is N.m; f_x1Is the left drive tire longitudinal force in units of N; f_x2Is the right drive tire longitudinal force in units of N; r_rIs the rolling radius of the rear wheel, and the unit is m; t is_f1The unit is N.m, and is the rolling moment of a left driving wheel; t is_f2The unit is N.m, and is the rolling moment of a right driving wheel; t is_m1The unit is N.m, and is the output torque of the left driving motor; t is_m2The unit is N.m, and is the output torque of the right driving motor; i.e. i_gIs the total speed ratio of the transmission system; eta_tFor driveline efficiency; rho is a target rotation speed ratio; t is_reqIs the total requirement of the whole machineTorque, in units of N · m; omega_w1Is the actual rotating speed of the left driving wheel and has the unit of rad.s^-1；ω_w2Is the actual rotation speed of the right driving wheel with the unit of rad.s^-1；k₁And k₂The control parameters corresponding to the index approach term and the constant speed approach term in the approach law influence the convergence speed of the actual rotating speed ratio to the target rotating speed ratio;

in equation 11, the left drive wheel speed ω_w1And right driving wheel rotation speed omega_w2The motor rotating speed is obtained through motor rotating speed conversion, and the motor rotating speed is obtained through signals of a Hall rotating speed sensor; total required torque T of whole machine_reqThe driving input information is obtained by analyzing driving input information such as an accelerator pedal; the target rotation speed ratio rho is obtained by measuring the deflection angle delta of the front wheel;

and 5: the complete machine controller calculates the output torque T of the left and right driving motors obtained in the step 4_m1、T_m2And the torque control of the left and right driving motors is realized by the driving motor controller through torque closed-loop vector control.

In step 1, the complete machine state comprises: 7 states of a shutdown state, an awakening state, a starting state, a driving state, a braking state, a charging state and a fault state; wherein the content of the first and second substances,

and (3) awakening state: when the electric tractor works normally or is charged, when a complete machine controller receives a Key opening (Key _ On is 1) instruction of a driver, the complete machine enters an awakening state; in the awakening state, the whole system controller is powered on firstly, the whole system controller starts system initialization after the power-on and self-checking are controlled by the whole machine, and then the power-on and self-checking are carried out on each system controller;

and (3) starting: when the complete machine controller and each subsystem controller are electrified to complete self-checking and initialization and have no fault, after the complete machine controller receives a Key (Key _ Start ═ 1) starting instruction of a driver, the complete machine enters a starting state; in the starting state, firstly, a pre-charging relay is switched on for pre-charging, at the moment, a motor control enable and a high-voltage power distribution enable are switched on, and after the pre-charging is finished, the pre-charging relay is switched off and a main relay is switched on; if the pre-charging fails, the pre-charging relay is disconnected, and the motor control enable and the high-voltage power distribution enable are closed;

a driving state: after the electric tractor finishes precharging and is switched on with high voltage electricity in a starting State, high pedal protection judgment is carried out, and if a gear switch is in a Neutral gear (DNR _ State) and the opening degree of an accelerator pedal is zero (Acc _ Throttle is 0), the whole tractor enters a driving State; under the driving state, the complete machine controller judges a driving mode according to a gear state (DNR) and the opening degree of an accelerator pedal and calculates the required torque of the complete machine;

a braking state: when the electric tractor is in a driving state, when a complete machine controller receives a Brake intention (Brake _ Percent < >0) of a driver, the complete machine enters a Brake state; under the braking state, the whole machine controller calculates the magnitude of braking torque according to the opening degree of a brake pedal and the current vehicle speed, and controls a braking mechanism to realize the braking of the whole machine;

the charging state is as follows: when the electric tractor is in an awakening state, when the whole machine controller receives a charging instruction (Charge _ switch is 1) and the battery management system has no fault, the whole machine enters a charging state; in a charging state, the motor controller enable and the high-voltage distribution enable are closed, the charging relay is opened, and after charging is finished, the whole machine enters an awakening state;

and (3) fault state: the electric tractor is in a normal working or charging state, and when the fault is detected by the fault diagnosis of the controller of the whole tractor or fault information is sent by each subsystem, the whole tractor enters a fault state; under the fault state, the complete machine controller judges the fault grade and processes the fault;

a shutdown state: when the electric tractor is in a normal working state, a charging state or a fault state, after a complete machine controller receives a Key closing (Key _ Off ═ 1) instruction of a driver, the complete machine enters a shutdown state; and in the shutdown state, the complete machine controller clears relevant data of the complete machine, disconnects the main relay and the pre-charging relay, and closes the motor controller enable and the high-voltage power distribution enable.

In step 2.2, the field operation of the electric tractor comprises ploughing, rotary tillage and seeding.

The wheel-side driving electric tractor further comprises a hood 1, an instrument panel 3, a steering wheel 4, a driving seat 5, an electric suspension 7 and a power output shaft 9; the hood 1 is fixed at the front end of the frame assembly 13 through a hinge; the front frame is used for mounting an instrument panel 3 and a steering wheel 4, and the rear frame is used for mounting a driving seat 5, a rear battery pack 6, an electric suspension 7, a power output shaft 9 and a driving wheel 10; the meter panel 3 is used to arrange meters and switches.

The front battery pack 12 and the rear battery pack 6 are formed by connecting two power battery buses in series to form a 48V power battery pack, so as to provide a power source for the electric tractor, and the battery pack is connected with an adaptive charger by using a charging plug to realize charging of the battery pack.

The drive motor controller converts the 48V direct current into three-phase alternating current which is connected with U, V, W ports of the left and right drive motors through three wires, and a Hall rotating speed sensor and a temperature sensor which are arranged on the drive motor are connected with a control signal wire of the drive motor controller together.

Compared with the prior art, the invention has the beneficial effects that:

the invention adopts the form of wheel-side motor driving, cancels the complex transmission mechanical structure of the traditional tractor, directly transmits the driving force to the driving wheel by the driving motor through the wheel-side reducer, has simple and compact structure and improves the transmission efficiency of the whole machine. In addition, the double-motor driving mode is different from the transfer of the traditional rear axle differential, the torque distribution of the motors has larger space, and the adaptability of the electric tractor under various extreme working conditions is improved.

In order to fully exert the driving force of the tractor, when the left and right driving wheels are subjected to differential speed control, it is more desirable to control the slip ratios of the driving wheels on both sides to the same level, that is, to sufficiently exert the driving force of the wheel on the well-adhered side while avoiding excessive slip of the wheel on one side while satisfying the differential speed requirement of the wheels on both sides, rather than simply controlling the rotation speed of each wheel to a certain target rotation speed.

Drawings

Fig. 1 is an overall perspective view of a wheel-side drive electric tractor according to the present invention;

FIG. 2 is a flow chart of the drive slip control of the wheel-side drive electric tractor according to the present invention;

FIG. 3 is the logic diagram of the state control of the whole wheel-side driven electric tractor.

Wherein the reference numerals are:

1. aircraft bonnet 2, electric cabinet

3. Instrument panel 4 and steering wheel

5. Driving seat 6 and rear battery pack

7. Electric suspension 8 and driving assembly

9. Power output shaft 10 and drive wheel

11. Hub reduction gear 12 and front battery pack

13. Frame assembly 14 and front axle assembly

15. Steering wheel

Detailed Description

The following further describes embodiments of the present invention with reference to the drawings.

As shown in fig. 1, a wheel-side drive electric tractor comprises a hood 1, an electric cabinet 2, an instrument panel 3, a steering wheel 4, a driving seat 5, a rear battery pack 6, an electric suspension 7, a driving assembly 8, a power output shaft 9, a driving wheel 10, a wheel-side reducer 11, a front battery pack 12, a frame assembly 13, a front axle assembly 14 and a steering wheel 15.

The hood 1 is fixed at the front end of the frame assembly 13 through hinges. The frame assembly 13 comprises a front frame and a rear frame, and the front frame and the rear frame are fixed into a whole. The front frame is used for mounting an electric control box 2, an instrument panel 3, a steering wheel 4, a front battery pack 12 and a front axle assembly 14, and the rear frame is used for mounting a driving seat 5, a rear battery pack 6, an electric suspension 7, a driving assembly 8, a power output shaft 9 and a driving wheel 10; and driving assembly mounting holes are formed in the left side and the right side of the rear frame, and the wheel reduction gear 11 is connected with the rear frame through the driving assembly mounting holes through bolts. The rear battery pack 6 is arranged on the rear frame, and the rear battery pack 6 and the rear frame are fixed through bolts.

The meter panel 3 is used to arrange meters and switches. The steering wheel 15 is mounted on the front axle assembly 14. The driving assembly 8 comprises a left driving motor, a right driving motor and a wheel reduction gear 11, wherein the left driving motor and the right driving motor are connected with the wheel reduction gear 11 through spline shafts, one end of the wheel reduction gear 11 is connected with a mounting hole of the driving assembly on the side surface of the frame through a bolt, the other end of the wheel reduction gear is connected with a hub of the driving wheel 10, and the left driving motor and the right driving motor provide power and transmit the power to the driving wheel 10 through the wheel reduction gear 11. The front battery pack 12 and the rear battery pack 6 are formed by connecting two power battery buses in series to form a 48V power battery pack, so as to provide a power source for the electric tractor, and the battery pack is connected with an adaptive charger by using a charging plug to realize charging of the battery pack.

The signal acquisition port of the whole machine controller is connected with the wiring terminal through a controller wire harness and then is respectively connected with sensor signal output lines such as a key, a gear, an accelerator pedal, a brake pedal and an operation mode switch, and the whole machine controller acquires the whole machine state information of the electric tractor and the operation information of a driver.

The driving motor controller controls the left and right driving motors, the driving motor controller converts the 48V direct current into three-phase alternating current, the three-phase alternating current is connected with U, V, W ports of the left and right driving motors through three wires, and a Hall rotating speed sensor and a temperature sensor which are arranged on the driving motor are connected to a control port of the driving motor controller together with a control signal wire of the driving motor.

The steering controller is connected with a front wheel steering angle sensor to acquire a front wheel steering angle delta in real time; the whole machine controller is connected with the driving controller and the steering controller through a CAN bus.

The whole machine controller and the driving motor controller are installed in the electric cabinet 2, the whole machine controller calculates the required torque of the whole machine and sends a torque command to the driving motor controller through a CAN bus by collecting input signals of a driver, and the driving motor controller controls the left driving motor and the right driving motor to realize the operation driving control of the electric tractor.

A control method of a wheel-side driven electric tractor comprises the following steps:

step 1: the whole machine controller collects operation information of a driver such as a key/gear signal, an accelerator pedal signal, a brake pedal signal and an operation mode signal to judge the state of the whole machine.

As shown in fig. 3, the overall state includes: the system comprises 7 states of a shutdown state, a wake-up state, a start-up state, a driving state, a braking state, a charging state and a fault state.

And (3) awakening state: when the electric tractor works normally or is charged, when the complete machine controller receives a Key opening (Key _ On is 1) instruction of a driver, the complete machine enters an awakening state. In the awakening state, the whole system controller is firstly electrified, the whole system controller starts system initialization after the electrification and self-checking are controlled by the whole system controller, and then the electrification and self-checking are carried out on each system controller.

And (3) starting: when the complete machine controller and each subsystem controller are electrified to complete self-checking and initialization and have no fault, and the complete machine controller receives a Key (Key _ Start ═ 1) starting instruction of a driver, the complete machine enters a starting state. In the starting state, firstly, a pre-charging relay is switched on for pre-charging, at the moment, a motor control enable and a high-voltage power distribution enable are switched on, and after the pre-charging is finished, the pre-charging relay is switched off and a main relay is switched on; and if the pre-charging fails, the pre-charging relay is disconnected, and the motor control enable and the high-voltage power distribution enable are closed.

A driving state: after the electric tractor finishes precharging and is switched on high voltage electricity in the starting State, high pedal protection judgment is carried out, and if the gear switch is in a Neutral gear (DNR _ State) and the opening degree of an accelerator pedal is zero (Acc _ Throttle is 0), the whole tractor enters a driving State. Under the driving state, the complete machine controller judges a driving mode according to a gear state (DNR) and the opening degree of an accelerator pedal and calculates the required torque of the complete machine.

A braking state: when the electric tractor is in a driving state, when the complete machine controller receives that a driver has a braking intention (Brake _ Percent < >0), the complete machine enters a braking state. Under the braking state, the whole machine controller calculates the magnitude of the braking torque according to the opening degree of a brake pedal and the current vehicle speed, and controls the braking mechanism to realize the braking of the whole machine.

The charging state is as follows: when the electric tractor is in the wake-up state, and the whole machine controller receives a charging instruction (Charge _ switch is 1) and the battery management system has no fault, the whole machine enters the charging state. And in the charging state, the motor controller enable and the high-voltage power distribution enable are closed, the charging relay is opened, and after charging is finished, the whole machine enters the awakening state.

And (3) fault state: the electric tractor is in a normal working or charging state, and when the fault is detected by the fault diagnosis of the controller of the whole tractor or fault information is sent by each subsystem, the whole tractor enters a fault state. And under the fault state, the complete machine controller judges the fault level and processes the fault.

A shutdown state: when the electric tractor is in a normal working state, a charging state or a fault state, after a complete machine controller receives a Key Off (Key _ Off ═ 1) instruction of a driver, the complete machine enters a shutdown state. And in the shutdown state, the complete machine controller clears relevant data of the complete machine, disconnects the main relay and the pre-charging relay, and closes the motor controller enable and the high-voltage power distribution enable.

Step 2: when the electric tractor is judged to be in a driving state, the complete machine controller calculates the total required torque T of the complete machine by combining the complete machine state information_reqAnd the complete machine state information comprises the allowable battery use power, the motor rotating speed and torque and the actual vehicle speed.

Step 2.1: under the driving state of the electric tractor, the whole machine controller analyzes the collected accelerator pedal signal and filters the pedal interference signal based on a first-order filtering algorithm. The filtered voltage value of the accelerator pedal signal is expressed as

u(k)＝(1-λ)u_filt(k) + λ u (k-1) formula 1

Wherein u (k) is the output voltage of the accelerator pedal at this time, and the unit is V; u (k-1) is the last output voltage of the accelerator pedal and has the unit of V; u. of_filt(k) Is the filtered voltage of the accelerator pedal, in units of V; and lambda is a filter coefficient and has a value range of 0-1.

Then setting pedal signal dead zone voltage parameter, adding minimum voltage parameter u₀And a maximum voltage parameter u₁₀₀Then, accelerator pedal opening θ (k):

wherein θ (k) is an accelerator pedal opening; u. of_filt(k) Is the filtered voltage of the accelerator pedal, in units of V; u. of₀Is the minimum voltage parameter in units of V; u. of₁₀₀Is the maximum voltage parameter in units of V.

Introducing a pedal opening mapping parameter delta (k) on the basis of formula 2 to realize different pedal output responses, and finally obtaining a used pedal opening theta:

wherein θ is the opening degree of the use pedal; δ (k) is a pedal opening degree mapping parameter; θ (k) is an accelerator pedal opening.

Step 2.2:

when the electric tractor is operated in the field (such as ploughing, rotary tillage and seeding), the driving torque is controlled by using the pedal opening theta to obtain the reference required torque T_bas。

And 2.2.1 when the electric tractor operates in the field, the target rotating speed of the motor and the opening theta of the used pedal are in a linear relation, and the target speed of the whole tractor is determined based on the opening theta of the used pedal and the maximum calibrated speed of the tractor, so that the target rotating speed of the driving motor is obtained. In order to better track the target rotating speed of the driving motor, the reference required torque T of the driving motor is adjusted by combining the target rotating speed and the actual rotating speed of the driving motor_basMeanwhile, the maximum output power of the power battery is calculated based on battery state parameters such as the state of charge (SOC), the temperature, the open-circuit voltage and the internal resistance of the power battery, and the reference torque T of the driving motor is limited_basTo limit the power required by the drive motor.

Step 2.2.2 if the torque of the driving motor is changed too fast and is not controlled, the electric tractor is easy to be impacted, and the service life of the whole transmission system is further influenced. Limiting the drive motor reference torque T at step 2.2.1_basFurther reference torque T is added to the driving motor_basSmoothing is performed to limit the amount of torque change per cycle. Through calculation of target rotating speed of motor, calculation of reference rotating speed of motor, limitation of maximum power of battery and driving of rotorObtaining the reference required torque T after four stages of torque smoothing_bas。

Step 2.3: for the reference required torque T_basAnd limiting, wherein the limiting mainly comprises motor overload protection, system over-temperature and under-voltage protection, and considering the influence of factors such as motor overload running time, motor and controller temperature, system input voltage and the like on the operation capacity of the tractor, wherein the motor temperature is obtained by a temperature sensor. The reference required torque T is under the working conditions of system overload, over-temperature, under-voltage and the like_basLimiting to obtain total required torque T of the whole machine_req。

And step 3: and then, the complete machine controller is communicated with the steering controller in real time through the CAN bus to obtain the steering angle of the steering wheel of the electric tractor, and the theoretical speeds of the left driving wheel and the right driving wheel are calculated based on the Ackerman steering model.

Based on the Ackerman steering model, when the tractor steers at low speed, the target rotating speed ratio of the two driving wheels can be expressed as

Where ρ is a target rotation speed ratio (ω)_w2/ω_w1)*；ω_w1Is the actual rotating speed of the left driving wheel and has the unit of rad.s^-1；ω_w2Is the actual rotation speed of the right driving wheel with the unit of rad.s^-1(ii) a L is the wheelbase of the tractor, and the unit is m; b is the rear axle wheel base of the tractor, and the unit is m; δ is the front wheel yaw angle in units.

And 4, step 4: whole machine controller combined with total required torque T of whole machine_reqAnd calculating the driving torque distribution proportion of the left driving motor and the right driving motor according to the theoretical speed of the left driving wheel and the right driving wheel of the tractor, so that the slip states of the left driving wheel and the right driving wheel are consistent, and finally obtaining the target driving torque of the left driving motor and the target driving torque of the right driving motor.

In order to ensure that the tractor obtains good traction driving performance under field operation, the ratio omega of the rotating speed of the right driving wheel to the rotating speed of the left driving wheel is controlled_w2/ω_w1The target rotation speed ratio ρ given by equation 4 is approximated.

Design sliding mode function s based on sliding mode control method_δThe following were used:

s_δ＝ω_w2-ρ·ω_w1equation 5

The first derivative of the slip form surface is

And is

To ensureOrder to

In the formula, k₁And k₂The control parameters corresponding to the exponential approximation term and the constant speed approximation term in the approximation law influence the convergence speed of the actual rotating speed ratio to the target rotating speed ratio.

sgn(s_δ) About the slip form surface s_δThe symbol function of (2) is obtained by simultaneous equations 5, 6, 7 and 8:

according to the combined external moment of the two driving wheels of the tractor in the rotating direction, a dynamic equation of the driving wheels is obtained:

further, the left and right drive motor output torques may be expressed as

In the formula, J_wIs the moment of inertia of the wheel, in kg.m²；T_w1Is the driving torque of the left driving wheel, and the unit is N.m; t is_w2Is the driving torque of the right driving wheel, and the unit is N.m; f_x1Is the left drive tire longitudinal force in units of N; f_x2Is the right drive tire longitudinal force in units of N; r_rIs the rolling radius of the rear wheel, and the unit is m; t is_f1The unit is N.m, and is the rolling moment of a left driving wheel; t is_f2The unit is N.m, and is the rolling moment of a right driving wheel; t is_m1The unit is N.m, and is the output torque of the left driving motor; t is_m2The unit is N.m, and is the output torque of the right driving motor; i.e. i_gIs the total speed ratio of the transmission system; eta_tFor driveline efficiency; rho is a target rotation speed ratio; t is_reqThe unit is N.m, which is the total required torque of the whole machine; omega_w1Is the actual rotating speed of the left driving wheel and has the unit of rad.s^-1；ω_w2Is the actual rotation speed of the right driving wheel with the unit of rad.s^-1；k₁And k₂The control parameters corresponding to the exponential approximation term and the constant speed approximation term in the approximation law influence the convergence speed of the actual rotating speed ratio to the target rotating speed ratio.

In the above-described torque distribution control law, the driving wheel rotation speed ω_w1And ω_w2The motor rotating speed is obtained through motor rotating speed conversion, and the motor rotating speed is obtained through signals of a Hall rotating speed sensor; total required torque T of whole machine_reqThe driving input information is obtained by analyzing driving input information such as an accelerator pedal; the target rotation speed ratio ρ is calculated by measuring the front wheel deflection angle δ.

And 5: the complete machine controller calculates the output torque T of the left and right driving motors obtained in the step 4_m1、T_m2And the torque control of the left and right driving motors is realized by the driving motor controller through torque closed-loop vector control.