CN114347973B

CN114347973B - Torque control method for heating stage of hybrid electric vehicle catalyst

Info

Publication number: CN114347973B
Application number: CN202210070354.8A
Authority: CN
Inventors: 王建波
Original assignee: Dongfeng Peugeot Citroen Automobile Co Ltd
Current assignee: Dongfeng Peugeot Citroen Automobile Co Ltd
Priority date: 2022-01-21
Filing date: 2022-01-21
Publication date: 2023-05-26
Anticipated expiration: 2042-01-21
Also published as: CN114347973A

Abstract

The invention discloses a torque control method for a heating stage of a hybrid electric vehicle catalyst, which comprises the following steps: in the heating stage of the catalyst, torque control is divided into four control modes according to the SOC of the power battery and the input rotation speed of the gearbox, so that the engine is always ensured to run in an engine optimal rotation speed-torque interval meeting the heating of the catalyst; in the first torque control mode, the rear axle motor and the front axle motor are controlled to sequentially output torque; in the second torque control mode, controlling the engine, the front shaft motor and the rear shaft motor to sequentially output torque; in the third torque control mode, only the output torque of the rear axle motor is controlled, the engine runs at the maximum limit value of the engine power, and the front axle motor is driven to generate power; in the fourth torque control mode, only the engine output torque is controlled, and the front axle motor and the rear axle motor do not output torque. Under the condition of keeping the heating effect of the catalyst preferentially, the invention reasonably controls the distribution of torque, and improves the energy utilization efficiency and ensures the SOC of the power battery.

Description

Torque control method for heating stage of hybrid electric vehicle catalyst

Technical Field

The invention relates to the technical field of automobile torque control, in particular to a torque control method in a heating stage of a hybrid electric vehicle catalyst.

Background

In order to meet the emission regulation requirements, the engine is provided with a catalyst, and the catalyst has better activity when the temperature of the catalyst exceeds 500 ℃ in general, so that the heating program of the catalyst can be started when the automobile is started for the first time, and the temperature of the catalyst can be raised as soon as possible.

The existing heating method of the engine catalyst mainly depends on that thicker fuel oil is sprayed after the engine is started, and the ignition angle is retarded, so that the combustion of the engine is delayed, and partial incompletely combusted fuel flows into a catalyst cavity through an exhaust pipeline to continue to combust, and the temperature of the catalyst is increased. The working principle of the engine is that the combustion expansion of fuel is utilized to push the piston to do work, and if more fuel is used for heating the catalyst, the part used for doing work in the engine cylinder is reduced. Because this process is relatively fuel consuming, resulting in an inefficient engine, the process is controlled to end as soon as possible.

In order to terminate the engine catalyst heating process as soon as possible, it is generally necessary to maintain the engine speed and torque in a control interval. How to control the engine output power well during this period is the key to the engine to improve thermal efficiency. The hybrid electric vehicle is provided with a battery motor system, and how to match the output torque of the engine in the heating stage of the catalyst with the output torque of the motor is also an important technology for research on energy conservation and consumption reduction.

Chinese patents CN201210526797X and CN2020100671815 are both structures of hybrid vehicles based on front axle motor drive, and do not mention the problem of engine torque and front and rear axle motor torque distribution. Different automotive hardware systems are subject to different constraints and therefore different ways of torque distribution.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a torque control method in a heating stage of a hybrid electric vehicle catalyst.

In order to achieve the above object, the present invention provides a torque control method for a heating stage of a catalyst of a hybrid vehicle, comprising: obtaining the temperature of a catalyst, the input rotating speed of a gearbox, the required torque, the maximum output torque of a power battery SOC, a front shaft motor and a rear shaft motor, and the engine rotating speed limit, the engine torque limit and the maximum engine power limit of the catalyst in the heating stage; when the temperature of the catalyst is smaller than the lower limit value of the optimal working temperature of the catalyst, entering a torque control program in a heating stage of the catalyst; when the SOC of the power battery is greater than or equal to the SOC critical value and the input speed of the gearbox is smaller than the minimum limit value or greater than the maximum limit value of the engine speed, entering a first torque control mode; controlling a rear shaft motor and a front shaft motor to sequentially output torque according to the required torque; when the SOC of the power battery is greater than or equal to the SOC critical value, and the input speed of the gearbox is greater than the minimum limit value of the engine speed and less than the maximum limit value of the engine speed, entering a second torque control mode; controlling an engine, a front shaft motor and a rear shaft motor to sequentially output torque according to the required torque; when the SOC of the power battery is smaller than the SOC critical value and the input rotating speed of the gearbox is smaller than the minimum rotating speed limit value or larger than the maximum rotating speed limit value of the engine, entering a third torque control mode; only controlling the output torque of the rear axle motor according to the required torque, running the engine at the maximum limit value of the engine power, and driving the front axle motor to generate electricity; when the SOC of the power battery is smaller than the SOC critical value and the input rotating speed of the gearbox is larger than the minimum limiting value of the rotating speed of the engine and smaller than the maximum limiting value of the rotating speed of the engine, a fourth torque control mode is entered; only the engine output torque is controlled according to the magnitude of the required torque, and the front axle motor and the rear axle motor do not output torque.

Further, the input speed of the gearbox is obtained according to the wheel speed and the reduction ratio of the front axle transmission system, and the required torque is obtained according to the opening calibration of the accelerator pedal.

Further, when the gearbox is in a combined state, the gear ratio of the wheel and the front axle is calculated, and when the gearbox is in N gear, the gear is calibrated by the rotation speed of the wheel and a predicted combined gear, wherein the predicted gear is calibrated according to the vehicle speed and the required torque.

Further, the method for determining the engine speed limit, the engine torque limit and the engine power maximum limit in the catalyst heating stage comprises the steps of controlling the engine speed and the engine torque by adjusting the throttle opening and the load in the engine bench test stage, enabling the catalyst heating rate to be larger than the catalyst heating rate critical value and the concentration of engine emissions not to exceed the standard, obtaining an engine optimal speed-torque section meeting the conditions, and obtaining the engine speed limit, the engine torque limit and the engine power maximum limit according to the engine optimal speed-torque section.

Further, in the first torque control mode, when the front axle motor does not output torque, the engine is operated at the minimum limit value of the engine speed, and the front axle motor is driven to generate power through the coupling clutch; when the front axle motor outputs torque, the disconnect clutch freewheels the engine at the engine speed minimum limit.

Further, when the required torque is smaller than the maximum output torque of the rear axle motor, the rear axle motor output torque is equal to the required torque, and when the required torque is larger than the maximum output torque of the rear axle motor and smaller than the sum of the maximum output torques of the rear axle motor and the front axle motor, the rear axle motor output torque is equal to the maximum output torque of the rear axle motor, and the front axle motor output torque is equal to the difference between the required torque and the maximum output torque of the rear axle motor.

Further, in the second torque control mode, when the required torque is smaller than the engine torque maximum limit value, only the engine output torque is controlled to satisfy the required torque; when the required torque is larger than the maximum limit value of the engine torque and smaller than the sum of the maximum limit value of the engine torque and the maximum output torque of the front axle motor, the engine output torque is the maximum limit value of the engine torque, and the residual required torque is met by the front axle motor; when the required torque is larger than the sum of the maximum limit value of the engine torque and the maximum output torque of the front axle motor and smaller than the sum of the maximum limit value of the engine torque, the maximum output torque of the front axle motor and the maximum output torque of the rear axle motor, the engine output torque is the maximum limit value of the engine torque, the front axle motor output torque is the maximum output torque of the front axle motor, and the residual required torque is met by the rear axle motor.

Further, in the second torque control mode, when the required torque is less than the engine torque minimum limit, the engine output torque is the engine torque minimum limit, and the coupling clutch places the front axle motor in a power generation state.

Further, in the third torque control mode, the input rotation speed of the rear axle speed reducer is obtained according to the rotation speed of the wheels and the reduction ratio of the rear axle transmission system, the maximum allowable torque of the rear axle motor is obtained according to the maximum limit value of the engine power and the input rotation speed of the rear axle speed reducer, the maximum allowable torque of the rear axle motor and the maximum output torque of the rear axle motor are reduced to obtain the maximum actual output torque of the rear axle motor, and when the required torque is larger than the maximum actual output torque of the rear axle motor, the output torque of the rear axle motor is the maximum actual output torque of the rear axle motor.

Further, in the fourth torque control mode, an engine torque corresponding value corresponding to the engine power maximum limit value is obtained according to the engine power maximum limit value and the engine characteristic curve, and when the required torque is smaller than the engine torque corresponding value, the engine output torque is the engine torque corresponding value; when the required torque is greater than the engine torque corresponding value and less than the engine torque maximum limit value, the engine output torque is the engine torque maximum limit value.

Further, when the engine output torque is greater than the demand torque, the clutch coupling places the front axle motor in a power generation state.

The invention has the beneficial effects that: in the invention, torque control is divided into four control modes according to the SOC of a power battery and the input rotation speed of a gearbox in a catalyst heating stage, and in the four control modes, the engine is always ensured to run in an engine optimal rotation speed-torque interval meeting the heating of the catalyst; in the first torque control mode, the rear axle motor and the front axle motor are controlled to sequentially output torque; in the second torque control mode, controlling the engine, the front shaft motor and the rear shaft motor to sequentially output torque; in the third torque control mode, only the output torque of the rear axle motor is controlled, the engine runs at the maximum limit value of the engine power, and the front axle motor is driven to generate power; in the fourth torque control mode, only the engine output torque is controlled, and the front axle motor and the rear axle motor do not output torque. The torque distribution can be reasonably controlled under the condition of keeping the heating effect of the catalyst preferentially, and the energy utilization efficiency is improved and the SOC of the power battery is ensured.

Drawings

FIG. 1 is a flow chart of a torque control method for a catalyst heating stage according to the present invention.

Fig. 2 is a schematic diagram of a power configuration structure of a hybrid electric vehicle according to the present invention.

The reference numerals of the components in the drawings are as follows: the engine 1, the clutch 2, the front axle motor 3, the gearbox 4, the front axle differential 5, the front axle 6, the front wheels 7, the power battery 8, the high-voltage distribution box 9, the rear axle motor 10, the speed reducer 11, the rear axle differential 12, the rear axle 13 and the rear wheels 14.

Detailed Description

The following detailed description is presented to provide further details in the context of the claimed subject matter, as will be apparent to those skilled in the art. The scope of the invention is not limited to the specific examples below. It is also within the scope of the invention to include the claims of the present invention as made by those skilled in the art, rather than the following detailed description.

As shown in fig. 2, a hybrid electric vehicle power configuration structure comprises a front axle power system and a rear axle power system, wherein the front axle power system comprises an engine 1, a clutch 2, a front axle motor 3, a gearbox 4 and a front axle differential 5 which are sequentially connected; the rear axle power system comprises a rear axle motor 10, a speed reducer 11 and a rear axle differential 12 which are sequentially connected, wherein the front axle motor 3 and the rear axle motor 10 are both connected to a power battery 8 through a high-voltage distribution box 9, and when a clutch is coupled, an engine runs and drives the front axle motor 3 to generate power, and torque can be output together with the front axle motor to drive front wheels to rotate; when the clutch is separated, the engine can only idle, the front axle motor can not generate electricity, and only torque can be output to drive the front wheels to rotate; the rear axle motor cannot generate electricity, either does not output torque or outputs torque to drive the rear wheels to rotate.

As shown in fig. 1, the torque control method in the catalyst heating stage of the hybrid vehicle is as follows.

1. And acquiring the temperature of the catalyst, the rotation speed of the wheels, the opening degree of the accelerator pedal, the SOC of the power battery, the maximum output torque of the front shaft motor and the rear shaft motor, the engine rotation speed limit value, the engine torque limit value and the maximum engine power limit value of the catalyst in the heating stage in real time. And then, multiplying the wheel rotation speed by the reduction ratio of the front axle transmission system to obtain the input rotation speed of the gearbox, and calibrating according to the opening degree of the accelerator pedal to obtain the required torque, wherein the calibration relation between the opening degree of the accelerator pedal and the required torque is the same no matter the torque output mode is that the engine is independently output, the motor is independently output or the engine and the motor are jointly output.

The method for determining the engine speed limit value, the engine torque limit value and the engine power maximum limit value in the catalyst heating stage comprises the steps of controlling the engine speed and the engine torque by adjusting the throttle opening and the load in the engine bench test stage, enabling the catalyst heating rate to be larger than the catalyst heating rate threshold value and enabling the concentration of engine emissions not to exceed the standard, indicating that the heating effect and the catalysis effect of the catalyst reach the design requirements, obtaining an engine optimal speed-torque section meeting the conditions, obtaining an engine speed minimum limit value, an engine speed maximum limit value, an engine torque minimum limit value, an engine torque maximum limit value and an engine power maximum limit value according to the engine optimal speed-torque section, and determining the engine torque corresponding to the engine power maximum limit value, namely an engine torque corresponding value.

2. And when the temperature of the catalyst is less than the lower limit value of the optimal working temperature of the catalyst by 500 ℃, entering a torque control program in a heating stage of the catalyst.

2.1 when the SOC of the power battery is more than or equal to 20 percent, and the input rotating speed r of the gearbox _f Less than the minimum limit value r of the engine speed _min Or greater than the maximum limit r of the engine speed _max When the engine speed cannot be matched with the wheel speed and the electric quantity of the power battery is sufficient, the first torque control mode is entered; the engine runs but cannot output torque to drive wheels, and the rear axle motor and the front axle motor are controlled to sequentially output torque according to the required torque.

Specifically, when the required torque is smaller than the maximum output torque of the rear axle motor, the output torque of the rear axle motor is equal to the required torque, and at the moment, the front axle motor does not output torque, so that the engine runs at the minimum limit value of the engine speed, and the front axle motor is driven to generate power through the coupling clutch, thus the fuel consumption can be reduced as much as possible under the conditions that the engine does not output torque and the charging requirement of a power battery is not large, and the energy of the engine is fully utilized; when the required torque is larger than the maximum output torque of the rear axle motor and smaller than the sum of the maximum output torques of the rear axle motor and the front axle motor, the output torque of the rear axle motor is equal to the maximum output torque of the rear axle motor, and the output torque of the front axle motor is equal to the difference between the required torque and the maximum output torque of the rear axle motor; when the required torque is greater than the sum of the maximum output torques of the rear-axle motor and the front-axle motor, both the front-axle motor and the rear-axle motor are driven at the maximum output torque. When the front axle motor outputs torque, the disconnect clutch freewheels the engine at the engine speed minimum limit.

2.2 when the SOC of the power battery is more than or equal to 20 percent, and the input rotating speed r of the gearbox _f Greater than the engine speed minimum limit r _min And is less than the engine speedMaximum limit r _max When the engine speed can be matched with the wheel speed and the electric quantity of the power battery is sufficient, the engine enters a second torque control mode; and controlling the engine, the front shaft motor and the rear shaft motor to sequentially output torque according to the required torque.

In the second torque control mode, when the required torque is smaller than the engine torque minimum limit value, the engine output torque is the engine torque minimum limit value, the coupling clutch enables the front axle motor to be in a power generation state, at the moment, the heating effect of the catalyst must be ensured preferentially, and then the redundant torque of the engine is fully utilized to generate power to charge the power battery, so that the energy utilization efficiency is improved; when the required torque is larger than the minimum limit value of the engine torque and smaller than the maximum limit value of the engine torque, only controlling the output torque of the engine to meet the required torque; when the required torque is larger than the maximum limit value of the engine torque and smaller than the sum of the maximum limit value of the engine torque and the maximum output torque of the front axle motor, the engine output torque is the maximum limit value of the engine torque, and the rest required torque is met by the front axle motor, so that the efficiency of the engine and the front axle motor in coaxial output torque is considered to be higher; when the required torque is larger than the sum of the maximum limit value of the engine torque and the maximum output torque of the front axle motor and smaller than the sum of the maximum limit value of the engine torque, the maximum output torque of the front axle motor and the maximum output torque of the rear axle motor, the engine output torque is the maximum limit value of the engine torque, the front axle motor output torque is the maximum output torque of the front axle motor, and the residual required torque is met by the rear axle motor.

2.3 when the SOC of the power battery is less than 20%, and the input rotation speed r of the gearbox _f Less than the minimum limit value r of the engine speed _min Or greater than the maximum limit r of the engine speed _max When the engine speed cannot be matched with the wheel speed and the power battery is insufficient in electric quantity and needs to be charged, entering a third torque control mode; the engine runs but cannot output torque to drive wheels, only the rear axle motor is controlled to output torque according to the required torque, the engine runs at the maximum limit value of engine power, and the front axle motor is driven to generate electricity. Because it is most critical to ensure priority on the basis of satisfying the heating effect of the catalyst again at this timeThe power battery is charged, so the front axle motor must be in a charging mode, the engine cannot output torque, torque can only be output by the rear axle motor, and the engine must be operated at the maximum limit of engine power in order to raise SOC more quickly.

In the third torque control mode, since the power battery outputs electric power to both the rear-axle motor and the front-axle motor, in order to ensure that the power battery increases in total, the output power of the rear-axle motor must be made smaller than the charging power of the front-axle motor. Therefore, the input rotating speed of the rear axle speed reducer is obtained according to the rotating speed of the wheels and the reduction ratio of the rear axle transmission system, the maximum allowable torque of the rear axle motor is obtained according to the maximum limit value of the engine power and the input rotating speed of the rear axle speed reducer, the maximum allowable torque of the rear axle motor and the maximum output torque of the rear axle motor are reduced to obtain the maximum actual output torque of the rear axle motor, and when the required torque is larger than the maximum actual output torque of the rear axle motor, the output torque of the rear axle motor is the maximum actual output torque of the rear axle motor.

2.4 when the SOC of the power battery is less than 20%, and the input speed r of the gearbox is higher than the input speed r _f Greater than the engine speed minimum limit r _min And is smaller than the maximum limit value r of the engine speed _max When the engine speed can be matched with the wheel speed and the power battery is insufficient in electric quantity and needs to be charged, the fourth torque control mode is entered; only the engine output torque is controlled according to the magnitude of the required torque, and the front axle motor and the rear axle motor do not output torque. Therefore, the power battery is not discharged but only charged, and the speed of raising the SOC is increased.

In the fourth torque control mode, an engine torque corresponding value corresponding to the engine power maximum limit value is obtained according to the engine power maximum limit value and an engine characteristic curve, when the required torque is smaller than the engine torque corresponding value, the engine output torque is the engine torque corresponding value, and the clutch is coupled to enable the front axle motor to be in a power generation state, so that the engine is ensured to output with the engine power, and under the condition that the required torque is fixed, the power generation power obtained by the front axle motor is maximum; when the required torque is larger than the corresponding value of the engine torque and smaller than the maximum limit value of the engine torque, the engine output torque is the maximum limit value of the engine torque, and the clutch is coupled to enable the front axle motor to be in a power generation state, so that the power generation power of the front axle motor is maximized under the condition that the required torque is preferentially met; when the required torque is larger than the maximum limit value of the engine torque, the engine can only output the maximum limit value of the engine torque, and the front axle motor does not generate electricity.

3. When the power battery SOC increases to more than 25% in the third torque control mode and the fourth torque control mode, if the catalyst heating stage has not been completed, the first torque control mode or the second torque control mode is entered again. Setting the power battery SOC threshold value to 25% instead of 20% here takes into account: if the power battery SOC is set to be 20%, after the power battery SOC exceeds 20%, the front shaft motor or the rear shaft motor outputs torque, and the output power value is smaller than the power obtained by power generation, so that the power battery SOC is immediately reduced to be below 20%, and the power battery SOC is easy to frequently jump at a critical value of 20%, so that the torque control mode is frequently switched, and the running state of a vehicle is unstable; when the SOC critical value of the power battery in the third and fourth torque control modes is set to 25%, the power battery can be continuously charged to 25% in the third and fourth torque control modes and then switched to the first and second torque control modes, even if the motor outputs torque, the maintenance time is longer, the SOC value cannot be immediately reduced to below 20%, and frequent switching of the torque control modes is avoided.

Claims

1. A method for controlling torque in a heating stage of a catalyst of a hybrid vehicle, comprising:

obtaining the temperature of a catalyst, the input rotating speed of a gearbox, the required torque, the maximum output torque of a power battery SOC, a front shaft motor and a rear shaft motor, and the engine rotating speed limit, the engine torque limit and the maximum engine power limit of the catalyst in the heating stage;

when the temperature of the catalyst is smaller than the lower limit value of the optimal working temperature of the catalyst, entering a torque control program in a heating stage of the catalyst:

when the SOC of the power battery is greater than or equal to the SOC critical value and the input speed of the gearbox is smaller than the minimum limit value or greater than the maximum limit value of the engine speed, entering a first torque control mode; controlling a rear shaft motor and a front shaft motor to sequentially output torque according to the required torque;

when the SOC of the power battery is greater than or equal to the SOC critical value, and the input speed of the gearbox is greater than the minimum limit value of the engine speed and less than the maximum limit value of the engine speed, entering a second torque control mode; controlling an engine, a front shaft motor and a rear shaft motor to sequentially output torque according to the required torque;

when the SOC of the power battery is smaller than the SOC critical value and the input rotating speed of the gearbox is smaller than the minimum rotating speed limit value or larger than the maximum rotating speed limit value of the engine, entering a third torque control mode; only controlling the output torque of the rear axle motor according to the required torque, running the engine at the maximum limit value of the engine power, and driving the front axle motor to generate electricity;

when the SOC of the power battery is smaller than the SOC critical value and the input rotating speed of the gearbox is larger than the minimum limiting value of the rotating speed of the engine and smaller than the maximum limiting value of the rotating speed of the engine, a fourth torque control mode is entered; only controlling the output torque of the engine according to the magnitude of the required torque, wherein the front shaft motor and the rear shaft motor do not output torque;

the method for determining the engine speed limit value, the engine torque limit value and the engine power maximum limit value in the catalyst heating stage comprises the steps of controlling the engine speed and the engine torque by adjusting the throttle opening and the load in the engine bench test stage, enabling the catalyst heating rate to be larger than the catalyst heating rate critical value and enabling the concentration of engine emissions not to exceed the standard, obtaining an engine optimal speed-torque section meeting the conditions, and obtaining the engine speed limit value, the engine torque limit value and the engine power maximum limit value according to the engine optimal speed-torque section;

in the fourth torque control mode, an engine torque corresponding value corresponding to the engine power maximum limit value is obtained according to the engine power maximum limit value and the engine characteristic curve, and when the required torque is smaller than the engine torque corresponding value, the engine output torque is the engine torque corresponding value; when the required torque is greater than the engine torque corresponding value and less than the engine torque maximum limit value, the engine output torque is the engine torque maximum limit value.

2. The method for controlling torque in a catalyst heating phase of a hybrid vehicle according to claim 1, wherein: and obtaining the input rotation speed of the gearbox according to the rotation speed of the wheels and the reduction ratio of the front axle transmission system, and obtaining the required torque according to the opening calibration of the accelerator pedal.

3. The method for controlling torque in a catalyst heating phase of a hybrid vehicle according to claim 1, wherein: in the first torque control mode, when the front axle motor does not output torque, the engine runs at the minimum limit value of the engine speed, and the front axle motor is driven to generate power through the coupling clutch; when the front axle motor outputs torque, the disconnect clutch freewheels the engine at the engine speed minimum limit.

4. The method for controlling torque in a catalyst heating phase of a hybrid vehicle according to claim 3, wherein: in the first torque control mode, the rear axle motor output torque is equal to the demand torque when the demand torque is less than the rear axle motor maximum output torque, and is equal to the rear axle motor maximum output torque when the demand torque is greater than the rear axle motor maximum output torque and less than the sum of the rear axle motor and the front axle motor maximum output torque, the front axle motor output torque being equal to the difference between the demand torque and the rear axle motor maximum output torque.

5. The method for controlling torque in a catalyst heating phase of a hybrid vehicle according to claim 1, wherein: in the second torque control mode, when the required torque is smaller than the engine torque maximum limit value, only the engine output torque is controlled to satisfy the required torque; when the required torque is larger than the maximum limit value of the engine torque and smaller than the sum of the maximum limit value of the engine torque and the maximum output torque of the front axle motor, the engine output torque is the maximum limit value of the engine torque, and the residual required torque is met by the front axle motor; when the required torque is larger than the sum of the maximum limit value of the engine torque and the maximum output torque of the front axle motor and smaller than the sum of the maximum limit value of the engine torque, the maximum output torque of the front axle motor and the maximum output torque of the rear axle motor, the engine output torque is the maximum limit value of the engine torque, the front axle motor output torque is the maximum output torque of the front axle motor, and the residual required torque is met by the rear axle motor.

6. The method for controlling torque in the catalyst heating phase of a hybrid vehicle according to claim 5, wherein: in the second torque control mode, when the required torque is less than the engine torque minimum limit, the engine output torque is the engine torque minimum limit, and the coupling clutch places the front axle motor in a power generation state.

7. The method for controlling torque in a catalyst heating phase of a hybrid vehicle according to claim 1, wherein: in the third torque control mode, the input rotation speed of the rear axle speed reducer is obtained according to the rotation speed of the wheels and the reduction ratio of the rear axle transmission system, the maximum allowable torque of the rear axle motor is obtained according to the maximum limit value of the engine power and the input rotation speed of the rear axle speed reducer, the maximum allowable torque of the rear axle motor and the maximum output torque of the rear axle motor are reduced to obtain the maximum actual output torque of the rear axle motor, and when the required torque is larger than the maximum actual output torque of the rear axle motor, the output torque of the rear axle motor is the maximum actual output torque of the rear axle motor.

8. The method for controlling torque in a catalyst heating phase of a hybrid vehicle according to claim 1, wherein: in the fourth torque control mode, the clutch is coupled to place the front axle motor in a generating state when the engine output torque is greater than the demand torque.