Control method for auxiliary braking of hybrid vehicle

Abstract

The present invention discloses a method for controlling auxiliary braking of a hybrid vehicle, and relates to the technical field of vehicle auxiliary braking. The method for controlling auxiliary braking of a hybrid vehicle uses the vehicle speed at the moment of entering auxiliary braking as the target vehicle speed. When controlling the motor and the engine to jointly provide auxiliary braking force, the engine exhaust brake is controlled to provide maximum braking torque, and the motor is controlled to gradually increase the braking torque. The motor gradually increases the braking torque at a first preset step size until the acceleration of the hybrid vehicle is less than zero. When the acceleration of the hybrid vehicle is less than zero, the braking torque jointly provided by the engine and the motor at this moment is maintained, so that the vehicle speed is reduced until the speed of the hybrid vehicle reaches the target vehicle speed. When the motor and the engine jointly provide auxiliary braking force, the control difficulty when the two jointly provide auxiliary braking force is reduced, and accurate response of the auxiliary braking force is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle auxiliary braking, and in particular to a control method for auxiliary braking of a hybrid vehicle. Background Art

[0002] The hybrid parallel system is used in heavy-duty vehicles. When the vehicle is going down a long slope, the engine can provide exhaust braking to assist the vehicle in decelerating, and can also assist the vehicle in decelerating by feeding power through the motor. Compared with traditional models, it can reduce the use of brakes and increase the service life of the brake system.

[0003] Current hybrid vehicle auxiliary braking control methods utilize independent engine exhaust braking and electric motor auxiliary braking. When the battery charge is low, electric motor braking takes precedence, recovering energy fed by the motor to recharge the battery. However, when the auxiliary braking force demand is high, these two methods cannot operate simultaneously to provide greater auxiliary braking force. Existing control methods that combine the engine and electric motor to provide auxiliary braking force are difficult to control in practice and cannot achieve precise response of the auxiliary braking force. Summary of the Invention

[0004] The purpose of the present invention is to provide a control method for auxiliary braking of a hybrid vehicle, which can not only control the engine and motor to provide auxiliary braking force simultaneously when the auxiliary braking force demand is large, thereby reducing the use of brakes; but also reduces the control difficulty and can achieve accurate response of the auxiliary braking force.

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

[0006] A method for controlling auxiliary braking of a hybrid vehicle uses the vehicle speed at the moment of entering auxiliary braking as a target vehicle speed, and controls the motor and the engine to jointly provide auxiliary braking force, including the following steps:

[0007] Control the engine exhaust brake to provide maximum braking torque, and control the motor to gradually increase the braking torque;

[0008] When the motor gradually increases the braking torque, the motor gradually increases the braking torque at a first preset step size until the acceleration of the hybrid vehicle is less than zero;

[0009] The braking torque provided by the engine and the motor at this moment is maintained until the vehicle speed of the hybrid vehicle reaches the target vehicle speed.

[0010] As an optional solution of the auxiliary braking control method of a hybrid vehicle, the process of maintaining the braking torque jointly provided by the engine and the motor until the speed of the hybrid vehicle reaches the target speed further includes the following steps:

[0011] When the speed of the hybrid vehicle differs from the target speed by a preset value, the braking torque of the motor is reduced by a second preset step size until the acceleration of the hybrid vehicle is equal to zero, and the first preset step size is larger than the second preset step size.

[0012] As an optional solution of the auxiliary braking control method of a hybrid vehicle, when the acceleration of the hybrid vehicle is less than zero, the auxiliary braking torque of the first preset step is further increased, and the motor maintains the increased braking torque.

[0013] As an optional solution to the auxiliary braking control method of a hybrid vehicle, during the process in which the engine provides the auxiliary braking force, the transmission is kept in the gear position at the moment of entering the auxiliary braking.

[0014] As an optional scheme for the control method of auxiliary braking of a hybrid vehicle, when the vehicle speed of the hybrid vehicle reaches the target vehicle speed, the sum of the current torque of the engine and the current torque of the motor is calculated, and the sum of the current torque of the engine and the current torque of the motor is limited to be less than the maximum torque allowed by the transmission input shaft.

[0015] As an optional solution of the auxiliary braking control method of a hybrid vehicle, before controlling the motor and the engine to jointly provide the auxiliary braking force, the auxiliary braking control method further includes the following steps:

[0016] monitoring the battery charge ratio, giving priority to controlling motor braking, and simultaneously recovering energy to charge the battery;

[0017] If the vehicle speed of the hybrid vehicle can be maintained at the target vehicle speed, the motor braking can meet the auxiliary braking demand.

[0018] As an optional solution to the auxiliary braking control method of a hybrid vehicle, if the electric motor braking cannot meet the auxiliary braking demand, when the battery is charged to a battery power ratio greater than a first preset power limit and the vehicle speed of the hybrid vehicle is still greater than the target vehicle speed, the electric motor braking is turned off and the engine exhaust braking is controlled;

[0019] When the battery power ratio is less than the second preset power limit, the motor is controlled to brake and the engine exhaust brake is stopped, and the first preset power limit is greater than the second preset power limit;

[0020] This cycle continues until the vehicle speed of the hybrid vehicle reaches the target vehicle speed.

[0021] As an optional solution for the control method of auxiliary braking of a hybrid vehicle, when the braking torque of the motor brake reaches a maximum and the acceleration of the hybrid vehicle is still greater than zero, the motor and the engine are controlled to jointly provide auxiliary braking force.

[0022] As an optional solution of the control method for auxiliary braking of a hybrid vehicle, the first preset power limit value is 85% to 95%, and the second preset power limit value is 55% to 65%.

[0023] As an optional solution of the auxiliary braking control method of a hybrid vehicle, the auxiliary braking control method further includes the following steps:

[0024] The accelerator pedal and brake pedal are used as control conditions;

[0025] When the accelerator pedal is depressed, the current auxiliary braking torque is reduced;

[0026] When the brake pedal is depressed, the current auxiliary braking torque is increased.

[0027] Beneficial effects of the present invention:

[0028] The hybrid vehicle auxiliary braking control method provided by the present invention uses the vehicle speed at the time of initiating auxiliary braking as the target vehicle speed. When controlling the electric motor and the engine to jointly provide auxiliary braking force, the engine exhaust brake is controlled to provide maximum braking torque, while the electric motor is controlled to gradually increase the braking torque. The electric motor gradually increases the braking torque in a first preset step size until the hybrid vehicle's acceleration is less than zero. When the hybrid vehicle's acceleration is less than zero, the braking torque jointly provided by the engine and the electric motor is maintained at that moment, reducing the vehicle speed until the hybrid vehicle's speed reaches the target vehicle speed. Because the engine auxiliary braking force is strongly correlated with the engine speed, controlling it by adjusting the engine's auxiliary braking force is difficult. However, the electric motor can precisely respond to the required torque. Therefore, when controlling the electric motor and the engine to jointly provide auxiliary braking force, the engine serves as the primary power source, providing the majority of the auxiliary braking force, while the electric motor provides the remaining auxiliary braking force. This ensures precise response of the auxiliary braking force and reduces control difficulty. The hybrid vehicle auxiliary braking control method provided by the present invention not only enables the electric motor and the engine to jointly provide auxiliary braking force when the hybrid vehicle's auxiliary braking force demand is high, but also reduces the control difficulty when both jointly provide auxiliary braking force, achieving precise response of the auxiliary braking force.

[0029] When the acceleration of the hybrid vehicle is less than zero, an auxiliary braking torque of a first preset step size is added to speed up the reduction of the vehicle speed, while preventing the slope change from causing the vehicle acceleration to be greater than zero again. Therefore, when it is monitored that the acceleration of the hybrid vehicle is less than zero, an auxiliary braking torque of a preset step size is added to ensure that the acceleration of the hybrid vehicle is in a gradually decreasing state under the braking torque provided by the engine and the motor at this moment.

[0030] When the speed of the hybrid vehicle approaches the target speed, specifically when the speed differs from the target speed by a preset value, the braking torque is reduced with a second preset step size that is smaller than the first preset step size, so that the acceleration of the hybrid vehicle increases to zero until the target speed is reached, to prevent the speed of the hybrid vehicle from changing too much when it approaches the target speed, thereby reducing the driver's driving experience.

[0031] To prevent the transmission input shaft from breaking due to excessive auxiliary braking torque when the engine and motor jointly provide auxiliary braking force, the system calculates the sum of the engine's current torque and the motor's current torque when the hybrid vehicle reaches the target speed. This sum is then limited to less than the maximum allowable torque of the transmission input shaft. This limits the sum of the engine's current torque and the motor's current torque to less than the maximum allowable torque of the transmission input shaft when the hybrid vehicle reaches the target speed to prevent the transmission input shaft from breaking.

[0032] During the engine exhaust braking process, downshifting is not allowed to ensure full utilization of the engine friction torque, because downshifting will increase the transmission speed ratio, resulting in a decrease in the engine friction torque. By maintaining the transmission speed ratio, the vehicle's braking torque is increased so that the engine can provide more auxiliary braking force.

[0033] During the assisted braking process, the accelerator pedal and brake pedal are introduced as inputs for the driver to adjust the target vehicle speed, so that the vehicle speed after assisted braking can be controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of a method for controlling auxiliary braking of a hybrid vehicle provided by an embodiment of the present invention;

[0035] Figure 2 This is a flow chart of a control method for jointly providing auxiliary braking force by a motor and an engine provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but are not to be construed as limiting the present invention.

[0037] In the description of the present invention, it should be noted that the terms "center," "up," "down," "left," "right," "vertical," "horizontal," "inside," and "outside" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions.

[0038] Unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," and "fixed" should be interpreted broadly. For example, they may refer to fixed or removable connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0039] Unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first feature being in direct contact with the second feature, or may include the first feature being in contact with the second feature through another feature between them instead of being in direct contact. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0041] When the driver has an auxiliary braking demand, such as a hybrid heavy-duty vehicle, when the vehicle is going downhill, the driver presses the auxiliary braking switch in the cab, and the vehicle controller receives the signal that the driver has an auxiliary braking demand and controls the vehicle to enter the auxiliary braking mode.

[0042] The vehicle controller obtains operating parameters related to vehicle braking, which include at least one of brake pedal opening, vehicle speed, battery power ratio and vehicle acceleration. The battery power ratio is the ratio of the remaining battery power to the total battery power.

[0043] When the auxiliary braking system is activated, the target speed is used as the vehicle speed at the time of activation. This prevents the vehicle from accelerating too quickly when descending a long slope, which could lead to loss of control and a dangerous situation. Therefore, the target speed is usually set as the vehicle speed at the time of activation, ensuring that the vehicle reaches the target speed under the control of the auxiliary braking force.

[0044] like Figure 1 As shown, in order to improve vehicle fuel economy, before controlling the motor and the engine to jointly provide auxiliary braking force, the auxiliary braking control method includes the following steps:

[0045] S10, monitor the battery charge ratio, give priority to controlling motor braking, and recover energy to charge the battery.

[0046] When the vehicle decelerates, the wheels drive the motor to rotate, and the motor becomes an AC generator to generate current. The motor controller rectifies the AC power into DC power to charge the battery. This can fully utilize braking energy, avoid energy waste, and improve vehicle fuel economy.

[0047] It should be noted that during the energy recovery process, it is necessary to monitor the battery charge ratio to avoid continuing to recover energy to charge the battery when the battery charge is saturated, which may cause overcharging and damage to the battery.

[0048] S20: If the speed of the hybrid vehicle can be maintained at the target speed, the motor braking can meet the auxiliary braking requirement.

[0049] S30. If the motor braking cannot meet the auxiliary braking demand, when the battery is charged to a battery power ratio greater than a first preset power limit and the speed of the hybrid vehicle is still greater than the target speed, the motor braking is turned off and the engine exhaust braking is controlled.

[0050] If the hybrid vehicle can maintain the target speed after motor braking when the battery power does not reach the first preset power limit, it means that the motor braking can meet the auxiliary braking force required by the vehicle, and the engine does not need to provide auxiliary braking force.

[0051] If the speed of the hybrid vehicle does not reach the target speed and the battery power reaches a first preset power limit, the motor braking is stopped and the engine exhaust braking is controlled to prevent damage to the battery.

[0052] Optionally, the first preset power limit is 85% to 95%.

[0053] In this embodiment, the first preset power limit is 90%. Of course, in other embodiments, those skilled in the art can set the first preset power limit according to actual conditions, and can also be set to 85% or 95%.

[0054] S40: When the battery power ratio is less than the second preset power limit, the motor is controlled to brake and the engine exhaust brake is stopped. The first preset power limit is greater than the second preset power limit.

[0055] When the battery charge ratio is less than the second preset charge limit, braking energy can be recovered to charge the battery to meet vehicle fuel economy. Therefore, braking torque is again provided by the motor.

[0056] Optionally, the second preset power limit is 55% to 65%. That is, as long as the battery power accounts for about half of the total power, braking energy can be recovered. In this embodiment, the second preset power limit is 60%.

[0057] S50: Repeat this process until the speed of the hybrid vehicle reaches the target speed.

[0058] In the above auxiliary braking control method, the motor and the engine independently provide auxiliary braking force, which is easy to control and can also recover braking energy.

[0059] However, when the auxiliary braking force required by the hybrid vehicle is relatively large, the control method in which the motor and the engine alone provide the auxiliary braking force cannot provide a larger auxiliary braking force.

[0060] In order to provide greater auxiliary braking force, the auxiliary braking control method of the hybrid vehicle provided in this embodiment proposes a control method for controlling the motor and the engine to jointly provide the auxiliary braking force.

[0061] S60: When the braking torque of the motor brake reaches a maximum and the acceleration of the hybrid vehicle is still greater than zero, the motor and the engine are controlled to jointly provide auxiliary braking force.

[0062] like Figure 2 As shown, controlling the motor and the engine to jointly provide auxiliary braking force specifically includes the following steps:

[0063] S61. Control the engine exhaust brake to provide maximum braking torque, and control the motor to gradually increase the braking torque.

[0064] When the motor and engine jointly provide auxiliary braking force, the engine exhaust brake is the primary power source, providing the majority of the auxiliary braking force, while the motor brake compensates for the remaining auxiliary braking force. This control method can reduce the control difficulty and achieve precise response of the auxiliary braking. Because the engine auxiliary braking force is strongly correlated with the engine speed, if the engine exhaust brake is used to compensate for the remaining auxiliary braking force, the engine speed will also change during the process of increasing the engine auxiliary braking force. The change in engine speed will affect the engine auxiliary braking torque, making it difficult to accurately adjust the auxiliary braking force and increasing the control difficulty. However, the motor auxiliary braking force can precisely respond to the required auxiliary braking torque, significantly reducing the control difficulty in actual application.

[0065] S62. When the motor gradually increases the braking torque, the motor gradually increases the braking torque at a first preset step size until the acceleration of the hybrid vehicle is less than zero.

[0066] By gradually increasing the motor braking torque, the vehicle speed of the hybrid vehicle is gradually controlled to meet the precise response of the remaining auxiliary braking torque.

[0067] The first preset step size refers to gradually increasing the torque at a fixed rate over a period of time, for example, increasing by 10 N·m each time.

[0068] Preferably, when the acceleration of the hybrid vehicle is less than zero, an auxiliary braking torque of a first preset step size is added to speed up the reduction of the vehicle speed, while preventing the slope change from causing the vehicle acceleration to be greater than zero again. Therefore, when it is monitored that the acceleration of the hybrid vehicle is less than zero, an auxiliary braking torque of a preset step size is added to ensure that the acceleration of the hybrid vehicle is in a gradually decreasing state under the braking torque provided by the engine and the motor at this moment.

[0069] S63: Maintain the braking torque provided by the engine and the motor at this moment until the speed of the hybrid vehicle reaches the target speed.

[0070] The process of maintaining the braking torque provided by the engine and the motor at this moment until the speed of the hybrid vehicle reaches the target speed also includes the following steps:

[0071] When the speed of the hybrid vehicle differs from the target speed by a preset value, the braking torque of the motor is reduced by a second preset step length until the acceleration of the hybrid vehicle is equal to zero, and the first preset step length is greater than the second preset step length.

[0072] The above control ensures that the first preset step length is greater than the second preset step length. For example, the second preset step length is 5 N·m.

[0073] When the hybrid vehicle's speed approaches the target speed, specifically when the speed differs from the target speed by a preset value, the braking torque is further reduced by a second preset step size, which is smaller than the first preset step size, so that the hybrid vehicle's acceleration increases to zero until the target speed is reached. This prevents excessive speed fluctuations as the hybrid vehicle approaches the target speed, which could degrade the driver's driving experience. In this embodiment, the preset value is not specifically limited and can be set or calibrated based on experience by those skilled in the art.

[0074] The above-mentioned motor braking control method adjusts the motor braking torque according to the real-time changes of the hybrid vehicle's speed and acceleration during the control process, calculates the motor braking torque through the speed and acceleration, and performs PID adjustment. The use of the motor to adjust the torque is conducive to control and can respond quickly, quickly achieve vehicle speed stabilization, realize accurate response of auxiliary braking, and at the same time improve the driver's driving experience.

[0075] As an optional control method for assistive braking in hybrid vehicles, the transmission maintains the gear it was in when assistive braking began while the engine is providing assistive braking force. Downshifting is not permitted during engine exhaust braking to ensure full utilization of engine friction torque. Downshifting increases the transmission ratio, reducing engine friction torque. Maintaining the transmission ratio increases the vehicle's braking torque, allowing the engine to provide more assistive braking force.

[0076] To prevent the transmission input shaft from breaking due to excessive auxiliary braking torque when the engine and motor jointly provide auxiliary braking force, the system calculates the sum of the engine's current torque and the motor's current torque when the hybrid vehicle reaches the target speed. This sum is then limited to less than the maximum allowable torque of the transmission input shaft. This limits the sum of the engine's current torque and the motor's current torque to less than the maximum allowable torque of the transmission input shaft when the hybrid vehicle reaches the target speed to prevent the transmission input shaft from breaking.

[0077] As an optional scheme for the control method of auxiliary braking of a hybrid vehicle, the control method of auxiliary braking also includes the following steps: using the accelerator pedal and the brake pedal as control conditions; when the accelerator pedal is pressed, the current auxiliary braking torque is reduced; when the brake pedal is pressed, the current auxiliary braking torque is increased.

[0078] When a hybrid vehicle enters assisted braking while descending a long slope, the driver will press the accelerator or brake pedal depending on the actual slope and unexpected situations. The vehicle controller receives the accelerator and brake pedal operation signals. When the vehicle controller detects that the driver has pressed the accelerator pedal, it determines that the driver needs to increase vehicle speed and controls the reduction of auxiliary braking force by reducing the engine braking torque or the motor braking torque. When the vehicle controller detects that the driver has pressed the brake pedal, it determines that the driver needs to slow down the vehicle and controls the increase of auxiliary braking force by reducing the engine braking torque or the motor braking torque. When the brake pedal is released, the above control continues, using the decelerated vehicle speed as the target speed.

[0079] During assisted braking, the driver can perform the above operations both before and after the hybrid vehicle reaches the target speed. By using the accelerator and brake pedals as inputs for the driver to adjust the target speed, the vehicle speed after assisted braking can be controlled.

[0080] The hybrid vehicle auxiliary braking control method provided in this embodiment can rationally distribute engine and motor torque, improving vehicle fuel economy. When auxiliary braking force is required, it controls both the engine and motor to provide auxiliary braking force simultaneously, reducing brake usage and extending the life of the brake system. Furthermore, the control difficulty when both provide auxiliary braking force is reduced, achieving precise response of the auxiliary braking force.

[0081] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, according to the concept of the present invention, there may be changes in the specific implementation methods and application scopes. The contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for controlling auxiliary braking of a hybrid vehicle, characterized in that: The vehicle speed at the moment of entering auxiliary braking is used as the target vehicle speed, and the motor and engine are controlled to jointly provide auxiliary braking force, including the following steps: Control the engine exhaust brake to provide maximum braking torque, and control the motor to gradually increase the braking torque; When the motor gradually increases the braking torque, the motor gradually increases the braking torque at a first preset step size until the acceleration of the hybrid vehicle is less than zero; maintaining the braking torque provided by the engine and the motor at this moment until the speed of the hybrid vehicle reaches the target speed; Before controlling the motor and the engine to jointly provide the auxiliary braking force, the auxiliary braking control method further includes the following steps: Monitor the battery charge ratio, prioritize motor braking, and recover energy to charge the battery; If the speed of the hybrid vehicle can be maintained at the target speed, the motor braking can meet the auxiliary braking requirement; If the motor brake cannot meet the auxiliary braking demand, when the battery is charged to a battery power ratio greater than a first preset power limit and the speed of the hybrid vehicle is still greater than the target speed, the motor brake is turned off and the engine exhaust brake is controlled; When the battery power ratio is less than a second preset power limit, the motor is controlled to brake and the engine exhaust brake is stopped, and the first preset power limit is greater than the second preset power limit; This cycle is repeated until the speed of the hybrid vehicle reaches the target speed. When the braking torque of the motor brake reaches a maximum and the acceleration of the hybrid vehicle is still greater than zero, the motor and the engine are controlled to jointly provide auxiliary braking force.

2. The control method for auxiliary braking of a hybrid vehicle according to claim 1, characterized in that: The process of maintaining the braking torque provided by the engine and the motor at this moment until the speed of the hybrid vehicle reaches the target speed further includes the following steps: When the speed of the hybrid vehicle differs from the target speed by a preset value, the braking torque of the motor is reduced by a second preset step size until the acceleration of the hybrid vehicle is equal to zero, and the first preset step size is larger than the second preset step size.

3. The control method for auxiliary braking of a hybrid vehicle according to claim 1 or 2, characterized in that: When the acceleration of the hybrid vehicle is less than zero, the auxiliary braking torque is increased by the first preset step size, and the motor maintains the increased braking torque.

4. The control method for auxiliary braking of a hybrid vehicle according to claim 1, characterized in that: During the process of the engine providing auxiliary braking force, the transmission maintains the gear position at the moment of entering the auxiliary braking.

5. The control method for auxiliary braking of a hybrid vehicle according to claim 1, characterized in that: When the vehicle speed of the hybrid vehicle reaches the target vehicle speed, the sum of the current torque of the engine and the current torque of the motor is calculated, and the sum of the current torque of the engine and the current torque of the motor is limited to be less than the maximum torque allowed by the transmission input shaft.

6. The control method for auxiliary braking of a hybrid vehicle according to claim 1, characterized in that: The auxiliary braking control method further comprises the following steps: The accelerator pedal and brake pedal are used as control conditions; When the accelerator pedal is depressed, the current auxiliary braking torque is reduced; When the brake pedal is depressed, the current auxiliary braking torque is increased.

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