Control method for braking torque of hybrid vehicle and hybrid vehicle

Abstract

The present invention discloses a method for controlling the braking torque of a hybrid vehicle and a hybrid vehicle, relating to the technical field of hybrid vehicles. The method for controlling the braking torque of a hybrid vehicle includes a method for automatically controlling the braking torque, and the method for automatically controlling the braking torque includes the following steps: calculating the maximum power currently allowed for the motor energy recovery of the vehicle; setting a required target acceleration according to the opening degree of the current brake pedal, and the target acceleration is less than zero; determining whether the maximum power currently allowed for the motor energy recovery of the vehicle can make the acceleration of the vehicle reach the target acceleration; if so, maintaining the electric braking until the acceleration of the vehicle reaches the target acceleration; if not, controlling the combined braking of the electric braking and the engine assisted braking. It realizes the automatic control of the electric braking or the combined braking of the electric braking and the engine assisted braking according to the actual working conditions, effectively improves the braking safety of the vehicle under the ramp working conditions; and the cost is relatively low.

Description

Technical Field

[0001] The present invention relates to the technical field of hybrid vehicles, and particularly to a method for controlling the braking torque of a hybrid vehicle and a hybrid vehicle. Background Art

[0002] During long downhill driving conditions, a hybrid vehicle recovers energy through electric motor braking, converts the recovered energy into electrical energy and stores it in a battery, and further converts it into driving energy. However, when the electric motor braking cannot meet the braking demand, it is necessary to activate the engine assisted braking, and the electric motor braking and the engine assisted braking are used together to meet the braking demand.

[0003] In the control method for braking of a hybrid vehicle in the prior art, when the electric motor braking cannot meet the braking demand, the driver is reminded through a dashboard to manually activate the engine assisted braking, so that the electric motor braking and the engine assisted braking together meet the braking demand. However, the engine assisted braking cannot be automatically controlled, and it is not intelligent enough. Moreover, in the prior art, it is necessary to judge the road condition information ahead through an additional in-vehicle intelligent system, a GPS system and an in-vehicle map system to realize the control of the braking torque, and the cost is relatively high. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for controlling the braking torque of a hybrid vehicle, which can automatically activate the engine assisted braking and jointly provide braking force through the electric motor braking and the engine assisted braking; moreover, the control method is simple and the cost is relatively low.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] The method for controlling the braking torque of a hybrid vehicle includes a method for automatically controlling the braking torque, and the method for automatically controlling the braking torque includes the following steps:

[0007] Calculate the maximum power currently allowed for the electric motor energy recovery of the vehicle;

[0008] Set a target acceleration required according to the opening degree of the current brake pedal, and the target acceleration is less than zero;

[0009] Judge whether the maximum power currently allowed for the electric motor energy recovery of the vehicle can make the acceleration of the vehicle reach the target acceleration;

[0010] If so, maintain the electric motor braking until the acceleration of the vehicle reaches the target acceleration;

[0011] If not, control the electric motor braking and the engine assisted braking to jointly brake.

[0012] As an alternative to the method for controlling the braking torque of a hybrid vehicle, the control method of combined electric motor braking and engine assisted braking includes the following steps:

[0013] First, control the engine to provide all of its braking torque;

[0014] Then, gradually increase the electric motor braking torque until reaching the maximum power currently allowed for the electric motor energy recovery of the vehicle, or until the acceleration of the vehicle reaches the target acceleration.

[0015] As an alternative to the method for controlling the braking torque of a hybrid vehicle, the engine assisted braking includes primary braking and secondary braking. When the engine assisted braking is the primary braking, the engine assisted braking provides a part of all of its braking torque; when the engine assisted braking is the secondary braking, the engine provides all of its braking torque. The control method of combined electric motor braking and engine assisted braking includes the following steps:

[0016] First, control the engine to provide a part of all of its braking torque;

[0017] Then, gradually increase the electric motor braking torque, and determine whether the acceleration of the vehicle is greater than the target acceleration when the electric motor reaches the maximum power currently allowed for the electric motor energy recovery of the vehicle;

[0018] If so, control the engine to provide all of its braking torque;

[0019] After the engine provides all of its braking torque, determine whether the acceleration of the vehicle at this time is greater than the target acceleration; if so, continue to increase the electric motor braking torque until reaching the maximum power currently allowed for the electric motor energy recovery of the vehicle, or until the acceleration of the vehicle reaches the target acceleration.

[0020] As an alternative to the method for controlling the braking torque of a hybrid vehicle, the step of maintaining the electric motor braking until the acceleration of the vehicle reaches the target acceleration includes:

[0021] The electric motor first brakes with the currently set braking torque;

[0022] If the rotational speed of the electric motor exceeds the maximum set rotational speed allowed by the currently set braking torque, gradually increase the electric motor braking torque until the acceleration of the vehicle reaches the target acceleration.

[0023] As an alternative to the method for controlling the braking torque of a hybrid vehicle, when the opening of the brake pedal is equal to zero, the currently set braking torque is set according to the rotational speed of the electric motor; when the opening of the brake pedal is greater than zero, the currently set braking torque is set according to the opening of the brake pedal.

[0024] As an alternative to the method for controlling the braking torque of a hybrid vehicle, the method for setting the current braking torque according to the motor speed is as follows:

[0025] When the motor speed is less than or equal to the first speed, control the motor to perform energy recovery at the first set torque;

[0026] When the motor speed is greater than the first speed and less than or equal to the warning speed, control the motor to perform energy recovery at the second set torque, and the second set torque is greater than the first set torque;

[0027] When the motor speed is greater than the warning speed, control the motor to perform energy recovery at the maximum allowable torque.

[0028] As an alternative to the method for controlling the braking torque of a hybrid vehicle, the method for setting the current braking torque according to the brake pedal opening is as follows:

[0029] When the brake pedal opening is less than or equal to the first opening, control the motor to perform energy recovery at the third set torque;

[0030] When the brake pedal opening is greater than the first opening and less than or equal to the intermediate opening, control the motor to perform energy recovery at the fourth set torque, and the fourth set torque is greater than the third set torque;

[0031] When the brake pedal opening is greater than the intermediate opening and less than or equal to the maximum opening, control the motor to perform energy recovery at the fifth set torque, and the fifth set torque is greater than the fourth set torque.

[0032] As an alternative to the method for controlling the braking torque of a hybrid vehicle, a manual auxiliary braking switch is provided on the hybrid vehicle. Determine whether the driver presses the manual auxiliary braking switch. If so, execute the control method of jointly braking by electric motor braking and engine auxiliary braking; if not, execute the control method of automatically controlling the braking torque.

[0033] As an alternative to the method for controlling the braking torque of a hybrid vehicle, if the driver does not press the manual auxiliary braking switch, determine whether the driver releases the accelerator pedal; if so, execute the control method of automatically controlling the braking torque.

[0034] A hybrid vehicle that adopts the method for controlling the braking torque of a hybrid vehicle according to any of the above solutions.

[0035] Advantages of the present invention:

[0036] The braking torque control method for a hybrid vehicle provided by the present invention calculates the maximum power currently allowed for the motor to recover energy in the vehicle; then sets the target acceleration required according to the opening degree of the current brake pedal. The target acceleration is less than zero, which can cause the vehicle to decelerate. It is determined whether the maximum power currently allowed for the motor to recover energy can make the acceleration of the vehicle reach the target acceleration, that is, whether the acceleration of the vehicle can reach the target acceleration when the motor provides the maximum braking torque. If so, the vehicle reaches the target acceleration only through electric braking; if not, electric braking and engine assisted braking are controlled to brake together. The braking torque control method for a hybrid vehicle provided by the present invention calculates the maximum power currently allowed for the motor to recover energy in the vehicle and the required target acceleration. If the braking torque provided by the motor can reach the required target acceleration, then only electric braking is used. If electric braking cannot reach the target acceleration, then electric braking and engine assisted braking are controlled to brake together, realizing automatic control of electric braking or electric braking and engine assisted braking together according to the actual working conditions, effectively improving the braking safety of the vehicle under ramp conditions; moreover, the braking method is simple and can be realized by using the vehicle's own control system, with low cost.

[0037] The hybrid vehicle provided by the present invention adopts the above braking torque control method for a hybrid vehicle, which can not only ensure the braking requirements of the vehicle and increase energy recovery; but also can realize automatic control by using the vehicle's own control system, improving safety and economy. Description of the Drawings

[0038] Figure 1 is a flowchart of the braking torque control method for a hybrid vehicle provided by an embodiment of the present invention;

[0039] Figure 2 is a flowchart of the control method for automatically controlling the braking torque provided by an embodiment of the present invention;

[0040] Figure 3 is the flow of the control method for controlling electric braking and engine assisted braking to brake together provided by an embodiment of the present invention Figure 1 ;

[0041] Figure 4 is the flow of the control method for controlling electric braking and engine assisted braking to brake together provided by an embodiment of the present invention Figure 2 。 Detailed Embodiments

[0042] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0043] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions.

[0044] Unless otherwise clearly defined and limited, the terms "installed", "connected", "connected to", "fixed" shall be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. It can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] Unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the first feature and the second feature being in direct contact, or may include the first feature and the second feature not being in direct contact but being in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "below", "under" and "beneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

[0046] The technical solution of the present invention will be further described below with reference to the drawings and through specific embodiments.

[0047] This embodiment provides a hybrid vehicle, which includes a vehicle controller. The vehicle controller can detect in real time the vehicle speed, output shaft speed, relevant information of the driver's operation, relevant information of the power battery, relevant information of the motor, relevant information of the engine, and other relevant information. The relevant information of the driver's operation includes whether the driver steps on the accelerator, whether the driver steps on the brake pedal, and whether the manual auxiliary brake switch is pressed. The manual auxiliary brake switch is arranged in the cab and is electrically connected to the vehicle controller. The vehicle controller can also obtain the opening degrees of the accelerator and the brake pedal through sensors. The relevant information of the power battery includes the real-time power, current, power limit value, and current limit value of the power battery, as well as the current battery charge. The relevant information of the motor includes information such as the real-time torque, temperature, and faults of the motor. The relevant information of the engine includes information such as the real-time speed and torque of the engine. The vehicle controller can also obtain the current driving torque and transmission ratio of the vehicle, then calculate the driving force according to the driving force calculation formula, calculate the driving resistance according to the current vehicle speed, slope signal, and driving resistance formula, and then calculate the current acceleration of the vehicle according to the force calculation formula F = Ma, where F is equal to the driving force minus the driving resistance and the mass M of the vehicle is known.

[0048] As Figure 1 shown, this embodiment also discloses a control method for the braking torque of a hybrid vehicle, which is applied to the above hybrid vehicle. The control method for the braking torque of the hybrid vehicle includes a control method for automatically controlling the braking torque. The control method for automatically controlling the braking torque is as follows: The vehicle controller analyzes the current working condition of the vehicle based on the information obtained and calculated, and automatically controls the braking method of the motor or the combined braking of the motor and the engine auxiliary braking according to the current working condition of the vehicle.

[0049] The control method for the braking torque of the hybrid vehicle includes the following steps:

[0050] S10. Determine whether the driver presses the manual auxiliary brake switch. If so, execute S30; if not, execute S20.

[0051] In the case of special working conditions such as a long downhill, when the driver believes that the engine auxiliary braking must be turned on in advance, the driver presses the manual auxiliary brake switch. After the vehicle controller receives the signal that the driver presses the manual auxiliary brake switch, it directly controls the vehicle to execute the combined braking method of the motor and the engine auxiliary braking. If the driver does not press the manual auxiliary brake switch, the vehicle controller executes the control method for automatically controlling the braking torque according to the current working condition of the vehicle.

[0052] S20. The control method for automatically controlling the braking torque.

[0053] If the driver does not press the manual auxiliary brake switch, it is determined whether the driver releases the accelerator pedal; if so, the control method for automatically controlling the braking torque is executed. If not, the vehicle is controlled to run normally.

[0054] Before executing the control method for automatically controlling the braking torque, it is also necessary to determine whether braking torque needs to be provided based on the driver's operation information. When the driver does not release the accelerator pedal, it means that the vehicle does not need to provide braking torque, and the vehicle is controlled to run normally. When the driver releases the accelerator pedal, it indicates that the driver needs the vehicle to decelerate.

[0055] After the driver releases the accelerator pedal, it is necessary to determine whether the driver steps on the brake pedal. The vehicle controller collects the opening of the brake pedal. If the opening of the brake pedal is zero, it means that the driver does not step on the brake pedal; if the opening of the brake pedal is greater than zero, it means that the driver steps on the brake pedal.

[0056] Generally, when the driver releases the accelerator pedal, if the driver does not step on the brake pedal, it means that the driver believes that the vehicle can reach the required vehicle speed by coasting. When the vehicle is coasting, the motor provides braking torque by monitoring the motor speed. The motor speed is divided into different stages from low to high in advance, and different motor braking torques are set for each stage. According to the real-time speed of the motor, the braking torque of the motor is gradually increased in stages. The higher the motor speed, the greater the required motor braking torque, ensuring the smoothness of the hybrid vehicle during braking.

[0057] If the driver steps on the brake pedal, it means that the driver believes that the vehicle can reach the required vehicle speed by braking. When the vehicle is braking, the braking torque is provided by monitoring the opening of the brake pedal. The opening of the brake pedal is divided into different stages from small to large, and different motor braking torques are set for each stage. According to the real-time opening of the brake pedal, the braking torque of the motor is gradually increased in stages. The greater the opening of the brake pedal, the greater the required motor braking torque, which can also ensure the smoothness of the hybrid vehicle during braking.

[0058] As Figure 2 shown, the control method for automatically controlling the braking torque includes the following steps:

[0059] S21. Calculate the maximum power that the vehicle currently allows the motor to recover energy.

[0060] Judge the maximum braking torque that the motor braking can provide by calculating the maximum power that the vehicle currently allows the motor to recover energy.

[0061] The method for calculating the maximum power that the vehicle currently allows the motor to recover energy is:

[0062] The vehicle controller calculates the allowable energy recovery power limit of the power battery system based on parameters such as the current battery level, power limit, and current limit of the power battery. Specifically, based on the currently allowed instantaneous charging maximum power, continuous charging maximum power, instantaneous charging maximum current, and continuous charging maximum current collected by the battery management system, the smaller value between the power calculated according to the continuous charging maximum power, continuous charging maximum current, and real-time voltage is taken to obtain the allowable energy recovery power limit of the power battery system. The allowable energy recovery power limit of the motor system is calculated based on parameters such as the temperature of the motor system (including the motor and the motor controller), the external characteristics of the motor, and motor faults. The motor controller collects the currently allowed maximum torque limit and calculates the allowable energy recovery power limit of the motor system according to the power-torque formula P = Tn / 9.55, where Tn is the currently allowed maximum torque limit. The allowable energy recovery power limit of the vehicle is obtained based on the states of the vehicle and other components of the high-voltage system. The vehicle controller, according to vehicle faults or driver operations, such as a high-voltage fault occurring, requires a 50% torque limit; or when the driver activates the snow mode, energy recovery is not allowed. Then, the minimum value among the allowable energy recovery power limit of the power battery system, the allowable energy recovery power limit of the motor system, and the allowable energy recovery power limit of the vehicle is taken to obtain the maximum power currently allowed for the vehicle's motor energy recovery. Through the power-torque formula, the maximum braking torque that the motor can provide during braking at the current vehicle speed is obtained.

[0063] S22. Set the target acceleration required according to the opening of the current brake pedal, and the target acceleration is less than zero.

[0064] When the driver steps on the brake pedal, the target acceleration required is set according to the opening of the brake pedal. The larger the opening of the brake pedal, the smaller the target acceleration. Regarding the method of setting the target acceleration required according to the opening of the current brake pedal, the vehicle controller draws a mapping relationship table between the opening of the brake pedal and the target acceleration required for the vehicle to reach according to the driver's demand corresponding to the size of the opening of the brake pedal obtained. The drawn mapping relationship table between the opening of the brake pedal and the target acceleration required is stored in the vehicle controller. The vehicle controller queries the mapping relationship table between the opening of the brake pedal and the target acceleration required according to the obtained current opening of the brake pedal to obtain the target acceleration.

[0065] S23. Determine whether the maximum power currently allowed for the vehicle's motor energy recovery can make the vehicle's acceleration reach the target acceleration. If so, execute S24; if not, control the motor braking and the engine auxiliary braking to brake together.

[0066] According to the calculated maximum power currently allowed for the vehicle's motor energy recovery, the maximum braking torque that the motor braking can provide at the current vehicle speed is obtained through the power-to-torque formula. Then, according to the conversion formula between torque and acceleration, it is determined whether the acceleration of the vehicle that the motor braking torque can reach is less than or equal to the target acceleration. If so, it means that the motor braking torque can make the vehicle reach the required vehicle speed. If not, both motor braking and engine assisted braking are required for braking.

[0067] The conversion formula between torque and acceleration is T = Jα, where J is the moment of inertia and α is the angular acceleration. First, the torque is calculated, and then the current driving force is calculated according to the conversion formula between torque and the current driving force F = Tr, where r is the tire rolling radius. Then, according to the conversion formula between the current driving force and the vehicle acceleration F = ma, the vehicle acceleration is calculated, where m is the vehicle weight and a is the vehicle acceleration.

[0068] S24. Keep the motor braking until the acceleration of the vehicle reaches the target acceleration.

[0069] Specifically, the steps of keeping the motor braking until the acceleration of the vehicle reaches the target acceleration include:

[0070] S241. The motor first brakes with the current set braking torque.

[0071] When providing braking torque through motor braking to decelerate the vehicle, gradually increase the motor braking torque to prevent sudden changes in the braking torque of the vehicle, make it transition smoothly, and ensure the smoothness of the vehicle.

[0072] When the opening of the brake pedal is equal to zero, the current set braking torque is set according to the motor speed; when the opening of the brake pedal is greater than zero, the current set braking torque is set according to the brake pedal opening.

[0073] Specifically, the method of setting the current set braking torque according to the motor speed is:

[0074] When the motor speed is less than or equal to the first speed, control the motor to perform energy recovery with the first set torque;

[0075] When the motor speed is greater than the first speed and less than or equal to the warning speed, control the motor to perform energy recovery with the second set torque, and the second set torque is greater than the first set torque;

[0076] When the motor speed is greater than the warning speed, control the motor to perform energy recovery with the maximum allowed torque.

[0077] The first rotational speed is greater than the minimum rotational speed of the motor. The specific values of the first rotational speed and the warning rotational speed can be specifically set according to parameters such as the model of the motor. Those skilled in the art can obtain the first set torque and the second set torque based on experience. The maximum torque allowed by the motor is the maximum braking torque provided by the maximum power currently allowed for motor energy recovery.

[0078] The method for setting the current set braking torque according to the brake pedal opening is as follows:

[0079] When the brake pedal opening is less than or equal to the first opening, control the motor to perform energy recovery with the third set torque;

[0080] When the brake pedal opening is greater than the first opening and less than or equal to the intermediate opening, control the motor to perform energy recovery with the fourth set torque, and the fourth set torque is greater than the third set torque;

[0081] When the brake pedal opening is greater than the intermediate opening and less than or equal to the maximum opening, control the motor to perform energy recovery with the fifth set torque, and the fifth set torque is greater than the fourth set torque.

[0082] The first opening is greater than zero, and the intermediate opening is an intermediate value greater than the first opening and less than the maximum opening, which can be set by those skilled in the art according to the actual situation. Those skilled in the art can obtain the third set torque, the fourth set torque, and the fifth set torque based on experience.

[0083] S242: If the rotational speed of the motor exceeds the maximum set rotational speed allowed by the current set braking torque, increase the braking torque of the motor until the acceleration of the vehicle reaches the target acceleration.

[0084] Exemplarily, when the brake pedal opening is zero, if the current set braking torque of the motor is the first set torque, when the rotational speed of the motor reaches the first rotational speed, increase the braking torque of the motor to the second set torque.

[0085] When the brake pedal opening is greater than zero, if the current set braking torque of the motor is the third set torque, when the motor brakes with the third set torque, the opening of the brake pedal continues to increase, and while the opening of the brake pedal increases, the rotational speed of the motor increases to the first set rotational speed. At this time, increase the braking torque of the motor to the fourth set torque.

[0086] S30: The control method for the combined braking of the motor braking and the engine auxiliary braking.

[0087] Before entering the control method of combined braking of motor braking and engine auxiliary braking, the vehicle controller needs to confirm whether the hybrid vehicle enters the hybrid mode from the pure electric mode. If so, execute the control method of combined braking of motor braking and engine auxiliary braking. If not, switch the hybrid vehicle to the hybrid mode and then execute the control method of combined braking of motor braking and engine auxiliary braking. When performing combined braking of motor braking and engine auxiliary braking, the engine auxiliary braking is preferentially used to provide braking torque, and through motor braking compensation, precise regulation of braking force can be achieved.

[0088] In hybrid vehicles, the engines of some vehicles do not support two-stage auxiliary braking and only have two states: on and off. The engines of some vehicles support two-stage auxiliary braking, and there is a second-stage braking button in the cab. When the engine is in auxiliary braking, if the second-stage braking button is not pressed, the engine provides a part of its total braking torque; if the second-stage braking button is pressed, the engine provides its total braking torque. During automatic control, if the engine does not support two-stage auxiliary braking, the engine auxiliary braking is controlled according to first-stage braking. If the engine supports two-stage auxiliary braking, the engine auxiliary braking is controlled according to two-stage braking.

[0089] When the engine auxiliary braking is only first-stage braking, as Figure 3 shown, controlling the combined braking of motor braking and engine auxiliary braking includes the following steps:

[0090] S311. First, control the engine to provide its total braking torque.

[0091] When the engine auxiliary braking is only first-stage braking, the engine auxiliary braking directly provides the maximum braking torque, that is, provides its total braking torque.

[0092] S312. Then gradually increase the motor braking torque until it reaches the maximum power allowed for the vehicle's current motor energy recovery, or the vehicle's acceleration reaches the target acceleration.

[0093] Since the motor braking torque is adjustable, by gradually increasing the motor braking torque, the sudden change of braking torque affecting the vehicle braking smoothness can be avoided; moreover, the braking torque can be accurately regulated in real time to achieve precise control of the vehicle's braking force.

[0094] When performing combined braking of motor braking and engine auxiliary braking, the engine auxiliary braking is prioritized and the motor braking compensates until the vehicle's acceleration reaches the target acceleration. Or, when the motor reaches the maximum power allowed for the vehicle's current motor energy recovery, that is, when the motor braking torque reaches the maximum braking torque, if the target acceleration still cannot be achieved, the motor braking torque still needs to be gradually increased until it reaches the maximum braking torque of the motor to maintain the smoothness of vehicle braking.

[0095] When the engine auxiliary brake is a two-stage brake, as Figure 4 shown, jointly controlling the electric motor brake and the engine auxiliary brake for braking includes the following steps:

[0096] S311ˊ. First, control the engine to provide a part of its full braking torque.

[0097] When the engine is a two-stage brake, first control the engine to be in the first-stage brake and provide a part of its full braking torque.

[0098] In this embodiment, when controlling the engine to be in the first-stage brake, the engine provides half of its full braking torque. Of course, in other embodiments, it can also provide 20%, 30%, or 70% etc. of its full braking torque.

[0099] S312ˊ. Then gradually increase the electric motor braking torque, and when it is judged that when the electric motor reaches the maximum power allowed for the vehicle's current electric motor energy recovery, whether the vehicle's acceleration is greater than the target acceleration;

[0100] If so, execute S313ˊ; if not, gradually increase the electric motor braking torque until the vehicle's acceleration reaches the target acceleration.

[0101] Continue to adjust the braking force by increasing the electric motor braking torque, and judge whether the vehicle's acceleration is greater than the target acceleration when the electric motor reaches the maximum braking torque. If so, it means that providing a part of the engine's full braking torque and the maximum braking force of the electric motor still cannot meet the braking requirement, and then increase the engine's auxiliary braking force to the maximum. If not, it means that providing a part of the engine's full braking torque and then gradually increasing the braking force by the electric motor can meet the braking requirement. Such a setting can ensure that the electric motor provides more braking force, thereby realizing more energy recovery.

[0102] S313ˊ. Control the engine to provide its full braking torque.

[0103] Increase the engine's auxiliary braking force to the maximum, that is, the engine provides the maximum braking torque.

[0104] S314ˊ. After the engine provides its full braking torque, judge whether the vehicle's acceleration at this time is greater than the target acceleration; if so, execute S315ˊ; if not, end.

[0105] After the engine provides its full braking torque, if the vehicle's acceleration at this time is greater than the target acceleration, it means that the full braking torque provided by the engine at this time and the braking torque provided by the electric motor still cannot meet the braking requirement. If the vehicle's acceleration at this time is less than or equal to the target acceleration, it means that the braking force at this time has met the braking requirement and there is no need to continue increasing the braking force.

[0106] S315ˊ. Continue to increase the motor braking torque until the maximum power of the motor energy recovery allowed by the vehicle currently is reached, or the vehicle acceleration reaches the target acceleration.

[0107] When the engine provides all the braking torque and still cannot meet the braking demand, at this time, continue to increase the motor braking torque while monitoring the vehicle acceleration in real time. If the vehicle acceleration can reach the target acceleration, stop increasing the motor braking force. If the vehicle acceleration still cannot reach the target acceleration when the motor braking torque increases to the maximum motor braking torque, it means that neither the engine nor the motor can meet the braking demand by providing their respective maximum braking forces.

[0108] The control method of the braking torque of the hybrid vehicle provided in this embodiment calculates the maximum power of the motor energy recovery allowed by the vehicle currently; then sets the target acceleration required according to the opening of the current brake pedal. This target acceleration is less than zero and can make the vehicle decelerate. It is judged whether the maximum power of the motor energy recovery allowed by the vehicle currently can make the vehicle acceleration reach the target acceleration, that is, it is judged whether the maximum braking torque that the current motor can provide can make the vehicle acceleration reach the target acceleration. If so, only the motor braking is used to reach the target acceleration of the vehicle; if not, the motor braking and the engine auxiliary braking are controlled to brake together. The control method of the braking torque of the hybrid vehicle provided by the present invention calculates the maximum power of the motor energy recovery allowed by the vehicle currently and the required target acceleration. If the braking torque provided by the motor can reach the required target acceleration, only the motor braking is used. If the motor braking cannot reach the target acceleration, the motor braking and the engine auxiliary braking are controlled to brake together, realizing the automatic control of the motor braking or the joint braking of the motor braking and the engine auxiliary braking according to the actual working conditions, effectively improving the braking safety of the vehicle under the ramp working conditions; and the braking method is simple, and it can be realized by using the vehicle's own control system, with low cost.

[0109] When entering the joint braking of the motor braking and the engine auxiliary braking, the engine auxiliary braking is preferentially used, and the motor braking is compensated. Since the motor braking torque is adjustable, by gradually increasing the motor braking torque, the sudden change of the braking torque affecting the braking smoothness of the vehicle can be avoided; and the braking torque can be accurately adjusted in real time to realize the precise control of the vehicle braking force.

[0110] This embodiment also provides a hybrid vehicle, which adopts the above control method of the braking torque of the hybrid vehicle, can not only ensure the braking demand of the vehicle and increase the energy recovery; but also can realize automatic control by using the vehicle's own control system, improving the safety and economy.

[0111] The above content is only a preferred embodiment of the present invention. For those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. The content of this specification should not be construed as a limitation on the present invention.

Claims

1. A method for controlling the braking torque of a hybrid vehicle, characterized in that, The control method of the braking torque of the hybrid vehicle includes a control method for automatically controlling the braking torque, and the control method for automatically controlling the braking torque includes the following steps: Calculate the maximum power currently allowed for motor energy recovery of the vehicle; Set a target acceleration according to the opening of the current brake pedal, and the target acceleration is less than zero; Judge whether the maximum power currently allowed for motor energy recovery of the vehicle can make the acceleration of the vehicle reach the target acceleration; If so, maintain electric braking until the acceleration of the vehicle reaches the target acceleration; If not, control the combined braking of electric braking and engine auxiliary braking; The control method for the combined braking of electric braking and engine auxiliary braking includes the following steps: When the engine auxiliary braking is only the first-stage braking, first control the engine to provide all of its braking torque; Then gradually increase the electric braking torque until the maximum power currently allowed for motor energy recovery of the vehicle is reached, or the acceleration of the vehicle reaches the target acceleration; When the engine auxiliary braking is two-stage braking, the engine auxiliary braking includes first-stage braking and second-stage braking. When the engine auxiliary braking is the first-stage braking, the engine provides a part of all of its braking torque; when the engine auxiliary braking is the second-stage braking, the engine provides all of its braking torque. The control method for the combined braking of electric braking and engine auxiliary braking includes the following steps: First control the engine to provide a part of all of its braking torque; Then gradually increase the electric braking torque, and judge whether the acceleration of the vehicle is greater than the target acceleration when the motor reaches the maximum power currently allowed for motor energy recovery of the vehicle; If so, control the engine to provide all of its braking torque; After the engine provides all of its braking torque, judge whether the acceleration of the vehicle is greater than the target acceleration at this time; if so, continue to increase the electric braking torque until the maximum power currently allowed for motor energy recovery of the vehicle is reached, or the vehicle acceleration reaches the target acceleration.

2. The control method of the braking torque of a hybrid vehicle according to claim 1, characterized in that, The step of maintaining electric braking until the acceleration of the vehicle reaches the target acceleration includes: The motor first brakes with the currently set braking torque; If the motor speed exceeds the maximum set speed allowed by the currently set braking torque, gradually increase the electric braking torque until the acceleration of the vehicle reaches the target acceleration.

3. The control method of the braking torque of a hybrid vehicle according to claim 2, characterized in that, When the opening of the brake pedal is equal to zero, the currently set braking torque is set according to the motor speed; when the opening of the brake pedal is greater than zero, the currently set braking torque is set according to the opening of the brake pedal.

4. The method for controlling the braking torque of a hybrid vehicle according to claim 3, wherein The method for setting the currently set braking torque according to the motor speed is: When the motor speed is less than or equal to the first speed, control the motor to perform energy recovery with the first set torque; When the motor speed is greater than the first speed and less than or equal to the warning speed, control the motor to perform energy recovery with the second set torque, and the second set torque is greater than the first set torque; When the motor speed is greater than the warning speed, control the motor to perform energy recovery with the maximum allowed torque.

5. The control method of the braking torque of a hybrid vehicle according to claim 3, characterized in that, The method for setting the current set braking torque according to the brake pedal opening is as follows: When the brake pedal opening is less than or equal to the first opening, control the motor to perform energy recovery at the third set torque; When the brake pedal opening is greater than the first opening and less than or equal to the intermediate opening, control the motor to perform energy recovery at the fourth set torque, and the fourth set torque is greater than the third set torque; When the brake pedal opening is greater than the intermediate opening and less than or equal to the maximum opening, control the motor to perform energy recovery at the fifth set torque, and the fifth set torque is greater than the fourth set torque.

6. The method for controlling the braking torque of a hybrid vehicle according to any one of claims 1-5, characterized in that, A manual auxiliary braking switch is provided on the hybrid vehicle. Determine whether the driver presses the manual auxiliary braking switch. If so, execute the control method of jointly braking by electric motor braking and engine auxiliary braking; if not, execute the control method of automatically controlling the braking torque.

7. The control method of the braking torque of a hybrid vehicle according to claim 6, characterized in that, If the driver does not press the manual auxiliary braking switch, determine whether the driver releases the accelerator pedal; if so, execute the control method of automatically controlling the braking torque.

8. A hybrid vehicle, characterized in that, Adopt the control method of the braking torque of the hybrid vehicle according to any one of claims 1-7.

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