CN106800020B - Four-wheel drive hybrid power system and control method thereof - Google Patents

Abstract

The invention provides a four-wheel drive hybrid power system and a control method thereof. The four-wheel drive hybrid power system includes: a front axle drive assembly and a rear axle drive assembly. The front axle drive assembly includes a coaxially connected engine, an ISG motor and a The gearbox and the rear axle drive assembly include a coaxially connected rear axle motor and a differential reducer. The ISG motor is electrically connected to the first motor controller, the rear axle motor is electrically connected to the second motor controller, and the first motor controller is electrically connected to the second motor controller. The second motor controllers are all electrically connected to the power battery; the vehicle controller is connected to the first motor controller, the second motor controller, the battery management system and the engine management system signally respectively, and is used to adjust the driving conditions of the vehicle and the vehicle. Sensor value for torque distribution. The embodiment of the present invention has a simple structure and relatively low cost. The front and rear axles of the vehicle can be driven independently, which can improve the vehicle's power acceleration, fuel economy, driving stability and vehicle adaptability to the driving environment.

Description

A four-wheel drive hybrid system and its control method

Technical field

The invention relates to the field of new energy vehicles, and in particular, to a four-wheel drive hybrid power system and a control method thereof.

Background technique

In the field of hybrid electric vehicles, models with various structures can be divided into weak hybrid, medium hybrid and strong hybrid according to the mixing intensity. Among them, weak hybrid mainly refers to the hybrid power of BSG structure, which means adding a starter motor to the engine. The starter motor has functions such as assisting in starting the engine, automatic shutdown and coasting recovery. The fuel saving rate is about 5%; medium hybrid mainly includes adding ISG motor. Or add a low-power rear-drive motor, etc., which can not only realize the weak hybrid function, but also realize the low-speed pure electric function. The above-mentioned hybrids are generally two-wheel drive hybrids. When the front wheel side of the vehicle is slipping through water or ice, the vehicle can easily lose control. Moreover, when a two-wheel drive hybrid vehicle is driving on a muddy road, it is also easy for the driving wheels to get stuck. The vehicle was trapped in the quagmire.

Based on the current situation that general hybrid vehicles are two-wheel drive, slipping will occur when encountering road surfaces with poor adhesion. The FF model will understeer due to wheel spin and deviate from the curve, while the FR model will drift. If a hybrid system with a traditional four-wheel drive structure is used, problems such as a complex structure and high cost will occur due to the presence of structures such as a center differential.

Contents of the invention

The technical problem to be solved by the present invention is to provide a four-wheel drive hybrid system and a control method thereof that can improve the power acceleration, fuel economy, and driving stability of the vehicle and have a simple structure.

In order to solve the above technical problems, the present invention provides a four-wheel drive hybrid system, including:

Front axle drive assembly and rear axle drive assembly. The front axle drive assembly includes a coaxially connected engine, ISG motor and gearbox. The rear axle drive assembly includes a coaxially connected rear axle motor and differential reducer. The ISG motor It is electrically connected to the first motor controller, the rear axle motor is electrically connected to the second motor controller, and both the first motor controller and the second motor controller are electrically connected to the power battery;

The vehicle controller is connected with the signals of the first motor controller, the second motor controller, the battery management system and the engine management system respectively, and is used to control the front axle drive assembly and rear axle according to the vehicle driving conditions and vehicle sensor values. The drive assembly performs torque distribution.

Wherein, the differential reducer coaxially connected to the rear axle motor has a large reduction ratio.

Wherein, the vehicle controller, the first motor controller, the second motor controller, the battery management system and the engine management system all communicate interactively through the CAN bus.

Wherein, the four-wheel drive hybrid system is a four-wheel drive plug-in hybrid system.

Among them, the vehicle controller is also used to select pure electric mode, extended range mode or hybrid mode according to vehicle driving conditions and vehicle sensor values.

The invention also provides a control method for a four-wheel drive hybrid system, including:

The vehicle controller VCU sends a torque request command to the ISG motor, and the ISG motor outputs torque to start the engine;

The VCU controls the engine to stop based on the current SOC value of the power battery, and the rear axle motor starts driving;

The VCU calculates the current vehicle driving torque demand based on the current throttle depth, SOC value and vehicle speed. When the SOC value is higher than a certain threshold and within the power range that the rear axle motor can satisfy, the VCU allocates all the torque to the rear axle motor. The shaft motor performs travel drive.

Among them, if the current SOC value is greater than or equal to the automatic shutdown threshold, the engine enters the automatic shutdown state, and the VCU calculates the driver's torque request based on the driver's throttle depth, and sends the driver's torque request to the second motor controller, which is controlled by the rear axle motor. Start driving and the vehicle enters pure electric mode.

Among them, if the current SOC value is lower than the automatic shutdown threshold, the ISG motor generates electricity, the rear axle motor starts driving, and the vehicle enters the extended range mode.

Among them, if the power of the rear axle motor cannot meet the driver's torque demand, the VCU will start the engine and the vehicle will enter hybrid mode. The engine will use the excess torque to generate electricity. If the torque is still insufficient, the rear axle motor will output the insufficient torque. Provide assistance; if the torque of the engine and rear axle motor cannot meet the driver's torque demand, the ISG motor will output torque for assistance.

Among them, when the VCU receives the forced pure electric signal, it determines whether the current SOC value is greater than the forced pure electric threshold. If so, the VCU allocates torque only to the rear axle motor.

Wherein, the forced pure electric threshold is greater than the automatic shutdown threshold, and the automatic shutdown threshold is a hysteresis loop [the second automatic shutdown threshold, the first automatic shutdown threshold].

Wherein, the first automatic shutdown threshold is set to 25%-30%, and the second automatic shutdown threshold is set to 15%-25%.

Among them, when the vehicle is braking or coasting, the VCU sends negative torque to the rear axle motor according to the vehicle speed and brake pedal depth to recover braking and coasting energy.

The four-wheel drive hybrid system and its control method according to the embodiment of the present invention have a simple structure and relatively low cost. The power distribution of the front and rear axles of the vehicle is intelligently allocated by the vehicle controller VCU according to the current working conditions of the vehicle, and the front and rear axles can be independently distributed. Drive, the vehicle's tracking performance is better, it can improve the vehicle's power acceleration, fuel economy, driving stability and the vehicle's adaptability to the driving environment, and the vehicle's passing performance is better.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic structural diagram of a four-wheel drive hybrid system according to an embodiment of the present invention.

Figure 2 is a schematic diagram of vehicle driving mode selection in the embodiment of the present invention.

Figure 3 is a schematic flowchart of the control method of the four-wheel drive hybrid system in Embodiment 2 of the present invention.

Detailed ways

The following description of the embodiments refers to the accompanying drawings to illustrate specific embodiments in which the invention may be implemented. Direction and position terms mentioned in this invention, such as "up", "down", "front", "back", "left", "right", "inside", "outside", "top", "bottom" ”, “side”, etc. are only for reference to the direction or position in the drawings. Therefore, the directional and positional terms used are used to illustrate and understand the present invention, but not to limit the scope of the present invention.

Referring to Figure 1, an embodiment of the present invention provides a four-wheel drive hybrid system, including:

Front axle drive assembly and rear axle drive assembly. The front axle drive assembly includes a coaxially connected engine, ISG motor and gearbox. The rear axle drive assembly includes a coaxially connected rear axle motor and differential reducer. The ISG motor It is electrically connected to the first motor controller, the rear axle motor is electrically connected to the second motor controller, and both the first motor controller and the second motor controller are electrically connected to the power battery;

The vehicle controller is connected with the signals of the first motor controller, the second motor controller, the battery management system and the engine management system respectively, and is used to control the front axle drive assembly and rear axle according to the vehicle driving conditions and vehicle sensor values. The drive assembly performs torque distribution.

Among them, the differential reducer coaxially connected to the rear axle motor has a large reduction ratio.

The advantages of the above-mentioned hybrid system are simple structure, relatively low cost, high fuel economy, and the front and rear axles can be driven independently, and the torque can be distributed intelligently according to the vehicle's driving conditions. In terms of vehicle control and system integration, More suitable for industrial production.

As shown in Figure 1, the embodiment of the present invention adds a rear axle motor (Electric RearAxle Drive Motor, or ERAD motor) to the ISG (Integrate starter/generator) four-wheel drive hybrid vehicle (E4WD). ), the rear axle motor is connected to the rear axle through a differential reducer with a large reduction ratio. The MCU in the picture is a motor controller (Motor Control Unit). The ISG motor is controlled by the first motor controller MCU1, the rear axle motor is controlled by the second motor controller MCU2, and the power battery is controlled by the battery management system BMS (Battery Management System). , MCU1, MCU2, BMS and engine management system EMS all communicate interactively with the vehicle controller VCU (Vehicle Control System) through the CAN bus. The vehicle controller VCU performs vehicle monitoring, driver torque request calculation and torque distribution to the front and rear axles. wait.

Embodiments of the present invention are applied to four-wheel drive hybrid vehicles, which can use plug-in hybrids (PHEV) and non-plug-in hybrids (HEV). If a plug-in hybrid is used, its battery capacity and rear axle motor power can be increased, and the rear axle motor can participate more in driving. This type of hybrid system can be classified as a strong hybrid; if a non-plug-in hybrid is used, Its battery capacity and rear axle motor power will be relatively small. The output of the rear axle motor is mainly used in a few working conditions such as vehicle starting, shift assistance, and full-throttle acceleration assistance, and is classified as a medium hybrid. This embodiment is preferably applied to plug-in hybrid power, because it belongs to the strong hybrid series and can effectively ensure the power of the rear axle drive of the vehicle.

The invention uses the vehicle controller VCU to distribute the torque of the front and rear axles according to the vehicle driving conditions and vehicle sensor values. Under various working conditions, such as: vehicle start, vehicle start, vehicle normal driving, brake coasting recovery, driver forced pure electric driving, etc., VCU automatically distributes torque to the front and rear axles. That is to say, VCU can intelligently select the driving mode of the vehicle to achieve the best economy without sacrificing power. The mode selection diagram is shown in Figure 2, which specifically includes the following aspects:

1. Vehicle start

Different from traditional car 12V starter motor to start the engine, this invention uses ISG motor to start the engine. The VCU sends a torque request command to the ISG motor, and the ISG motor outputs torque, raises the engine to a higher speed, and starts fuel injection, thus completing the engine start. Starting the engine through the ISG motor improves the problems of high fuel consumption and poor emissions when starting traditional vehicles, and can effectively improve fuel economy and emissions.

2. Vehicle starts

After the vehicle is started, the engine self-learning and exhaust catalyst heating and other related functions are completed, the VCU determines whether the engine enters the automatic shutdown state based on the current SOC value. If the SOC value is greater than or equal to a certain threshold, the engine enters an automatic shutdown state. The VCU calculates the driver's torque request based on the driver's throttle depth, and sends the driver's torque request to the second motor controller MCU2 to allow the rear axle motor to perform Starting drive, the vehicle enters pure electric mode; if the SOC value is lower than a certain threshold, the rear axle motor is also used for starting drive, but at this time the vehicle is in extended range mode, that is, the ISG motor generates electricity and the rear axle motor drives series hybrid mode. In starting mode, only the rear axle motor works. If the battery SOC value is relatively low, the ISG motor charges the power battery, and the power battery supplies power to the rear axle motor. The engine stops and the vehicle starts purely on electric power, but after the vehicle speed increases, the engine will still start to generate electricity.

3. Vehicle drive

After the vehicle starts and enters normal driving, the VCU calculates the current vehicle driving torque demand based on the current throttle depth, SOC value and vehicle speed, and monitors the torque output capability of the rear axle motor in real time. When the SOC value is high, within the power range that the rear axle motor can satisfy, the VCU allocates all torque to the rear axle motor, allowing the rear axle motor to drive to meet the torque needs of the entire vehicle. The engine is still in a stopped state, and the vehicle In pure electric driving; if the power of the rear axle motor cannot meet the driver's torque demand, the VCU will start the engine and the vehicle will enter hybrid mode. The engine will work in the high-efficiency range and use the excess torque for power generation. If the torque is still If it is insufficient, the rear axle motor will output the insufficient torque to assist.

4. Mandatory pure electric power

The driver can use the EV-On button to achieve forced pure electric driving according to his own preferences. At this time, as long as the SOC is greater than a certain value, the VCU does not limit the driver's accelerator depth and vehicle speed, and the VCU only distributes torque to the rear. shaft motor, the vehicle realizes pure electric driving. Pure electric driving has the advantages of strong starting power, fast power response and low noise. Drivers can fully enjoy the fun of pure electric vehicles. In this embodiment, when a high-power rear axle motor and a high-capacity power battery are used, the pure electric cruising range of the vehicle can reach 50km, and the pure electric maximum speed can reach 130km/h.

Different from the initial stage, pure electric driving has relatively high requirements for SOC value. Generally, a SOC value of more than 30% is required to meet the requirements of pure electric driving; while in the initial stage, the SOC value generally only needs to be greater than 20% to achieve it.

5. Braking and coasting recovery

When the vehicle is braking or coasting, the VCU will send negative torque to the rear axle motor according to the vehicle speed and brake pedal depth to recover braking and coasting energy. Fuel economy can be effectively improved by recovering energy.

Please refer to FIG. 3 again. Embodiment 2 of the present invention provides a control method for a four-wheel drive hybrid system as described in Embodiment 1 of the present invention, including:

The vehicle controller VCU sends a torque request command to the ISG motor, and the ISG motor outputs torque to start the engine;

The VCU controls the engine to stop based on the current SOC value of the power battery, and the rear axle motor starts driving;

The VCU calculates the current vehicle driving torque demand based on the current throttle depth, SOC value and vehicle speed. When the SOC value is higher than a certain threshold and within the power range that the rear axle motor can satisfy, the VCU allocates all the torque to the rear axle motor. The shaft motor performs travel drive.

As mentioned before, starting driving by the rear axle motor includes two situations: if the SOC value is greater than or equal to the automatic shutdown threshold, the engine enters the automatic shutdown state, and the VCU calculates the driver's torque request based on the driver's throttle depth and sends the driver The torque request is sent to the second motor controller MCU2, which is driven by the rear axle motor, and the vehicle enters pure electric mode; if the SOC value is lower than the automatic shutdown threshold, the rear axle motor is also used for starting drive, but at this time the vehicle is increasing. The range mode is a series hybrid mode in which the ISG motor generates electricity and the rear axle motor drives the vehicle. It should be noted that in this embodiment, the automatic shutdown threshold is a hysteresis loop [the second automatic shutdown threshold, the first automatic shutdown threshold], where the first automatic shutdown threshold is set to 25%-30%, and the second automatic shutdown threshold is set to 25%-30%. The automatic shutdown threshold is set to 15%-25%. The purpose of setting the automatic shutdown threshold as a hysteresis loop is to prevent the engine from starting and stopping all the time. For simplicity of description, take the first automatic shutdown threshold as 25% and the second automatic shutdown threshold as 20%, that is, the hysteresis loop is [20%, 25%] as an example. When the SOC value is above 25% (greater than the first When the automatic shutdown threshold is reached (the second automatic shutdown threshold), the engine is stopped and the SOC value enters the hysteresis loop, for example, when it becomes 23%, the engine will still remain in the shutdown state; when it is lower than 20% (the second automatic shutdown threshold), the engine is started and the SOC value enters the hysteresis loop. , for example, the SOC value rises back to 23%, and the engine still remains started. If there is no hysteresis loop control, for example, if 25% is directly used as the engine automatic shutdown threshold, then when the SOC value is above 25%, the engine will stop. When the SOC value drops below 25%, the engine will start again to generate electricity; after generating electricity The SOC value rose back to above 25%, and the engine stopped again, which caused the engine to keep starting and stopping.

After the vehicle starts and enters normal driving, the VCU allocates all the torque to the rear axle motor and allows the rear axle motor to drive to meet the torque needs of the entire vehicle. The engine is still shut down and the vehicle is driving purely electric. If the power of the rear axle motor cannot meet the driver's torque demand, the VCU will start the engine and the vehicle will enter hybrid mode. The engine will work in the high-efficiency range and use the excess torque for power generation. If the torque is still insufficient, the rear axle will The motor outputs insufficient torque to assist. If the torque of the engine and the rear axle motor cannot meet the driver's torque demand, the ISG motor will output torque for assistance.

If the driver wishes to force pure electric driving, this can be achieved by pressing the EV-On button. The VCU receives the signal from the EV-On button and determines whether the current SOC value is greater than the mandatory pure electric threshold. If so, the VCU will not limit the driver's accelerator depth and vehicle speed, and allocate torque only to the rear axle motor, making the vehicle purely electric. travel. As mentioned before, since pure electric driving has relatively high requirements for SOC value, in this embodiment, the forced pure electric threshold is greater than the automatic shutdown threshold in the starting stage. In addition, when the vehicle is braking or coasting, the VCU will send negative torque to the rear axle motor according to the vehicle speed and brake pedal depth to recover braking and coasting energy. Fuel economy can be effectively improved by recovering energy.

The four-wheel drive hybrid system and its control method according to the embodiment of the present invention have a simple structure and relatively low cost. The power distribution of the front and rear axles of the vehicle is intelligently allocated by the vehicle controller VCU according to the current working conditions of the vehicle, and the front and rear axles can be independently distributed. Drive, the vehicle's tracking performance is better, it can improve the vehicle's power acceleration, fuel economy, driving stability and the vehicle's adaptability to the driving environment, and the vehicle's passing performance is better.

What is disclosed above is only the preferred embodiment of the present invention. Of course, it cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (10)

1. A four-wheel drive hybrid system, characterized by including: Front axle drive assembly and rear axle drive assembly. The front axle drive assembly includes a coaxially connected engine, ISG motor and gearbox. The rear axle drive assembly includes a coaxially connected rear axle motor and differential reducer. The ISG motor It is electrically connected to the first motor controller, the rear axle motor is electrically connected to the second motor controller, and both the first motor controller and the second motor controller are electrically connected to the power battery; The vehicle controller is connected with the signals of the first motor controller, the second motor controller, the battery management system and the engine management system respectively, and is used to control the front axle drive assembly and rear axle according to the vehicle driving conditions and vehicle sensor values. The drive assembly performs torque distribution; The vehicle controller is also used to determine whether the current SOC value is greater than the forced pure electric threshold when receiving the forced pure electric signal. If so, allocate torque only to the rear axle motor; the forced pure electric threshold is greater than the automatic shutdown. Threshold, the automatic shutdown threshold is a hysteresis loop [second automatic shutdown threshold, first automatic shutdown threshold]; if the current SOC value is greater than or equal to the automatic shutdown threshold, the engine enters the automatic shutdown state. 2. The four-wheel drive hybrid system according to claim 1, wherein the vehicle controller interacts with the first motor controller, the second motor controller, the battery management system and the engine management system through a CAN bus. communication. 3. The four-wheel drive hybrid system according to claim 1, wherein the four-wheel drive hybrid system is a four-wheel drive plug-in hybrid system. 4. The four-wheel drive hybrid system according to claim 1, characterized in that the vehicle controller is also used to select pure electric mode, extended range mode or hybrid mode according to vehicle driving conditions and vehicle sensor values. 5. A control method for a four-wheel drive hybrid system according to any one of claims 1 to 4, comprising: The vehicle controller VCU sends a torque request command to the ISG motor, and the ISG motor outputs torque to start the engine; The VCU controls the engine to stop based on the current SOC value of the power battery, and the rear axle motor starts driving; specifically: if the current SOC value is greater than or equal to the automatic shutdown threshold, the engine is controlled to enter the automatic shutdown state; The VCU calculates the current vehicle driving torque demand based on the current throttle depth, SOC value and vehicle speed. When the SOC value is higher than a certain threshold and within the power range that the rear axle motor can satisfy, the VCU allocates all the torque to the rear axle motor. The shaft motor performs travel drive. 6. The control method according to claim 5, characterized in that when the engine enters the automatic shutdown state, the VCU calculates the driver's torque request according to the driver's throttle depth, and sends the driver's torque request to the second motor controller. The rear axle motor starts driving and the vehicle enters pure electric mode. 7. The control method according to claim 5, characterized in that if the current SOC value is lower than the automatic shutdown threshold, the ISG motor generates electricity, the rear axle motor performs starting driving, and the vehicle enters the extended range mode. 8. The control method according to any one of claims 5-7, characterized in that if the power of the rear axle motor cannot meet the driver's torque demand, the VCU will start the engine, the vehicle will enter the hybrid mode, and the engine will The torque is used to generate electricity. If the torque is still insufficient, the rear axle motor will output the insufficient torque to assist; if the torque of the engine and the rear axle motor cannot meet the driver's torque demand, the ISG motor will output torque to assist. 9. The control method according to claim 5, characterized in that the first automatic shutdown threshold is set to 25%-30%, and the second automatic shutdown threshold is set to 15%-25%. 10. The control method according to any one of claims 5-7, characterized in that when the vehicle is braking or coasting, the VCU sends negative torque to the rear axle motor according to the vehicle speed and brake pedal depth to brake. and coasting energy recovery.