CN106800020A - A kind of four-wheel-drive hybrid power system and its control method - Google Patents

Abstract

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

Description

A four-wheel drive hybrid power system and its control method

technical field

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

Background technique

Vehicles with various structures in the field of hybrid vehicles can be divided into mild hybrid, medium hybrid and strong hybrid according to the mixing intensity. Among them, the weak hybrid mainly refers to the hybrid power of the BSG structure, that is, adding a starter motor to the engine. The starter motor has functions such as assisting in starting the engine, automatic shutdown and coasting recovery, and the fuel saving rate is about 5%. The medium hybrid mainly includes the addition of an ISG motor Or add a low-power rear drive motor, etc., in addition to realizing the weak hybrid function, it can also realize the low-speed pure electric function. The above-mentioned hybrids are generally two-wheel drive hybrids. When one side of the front wheel of the vehicle is wading or slipping on ice, the vehicle is prone to lose control, and the two-wheel drive hybrid vehicles are also prone to sinking due to the driving wheels when driving on muddy roads. The quagmire caused the vehicle to become trapped.

Based on the current situation that the general hybrid vehicle is two-wheel drive, it will slip when encountering poorly adhered road surfaces. The FF model will understeer due to wheel spin and go out of the corner, while the FR model will drift. If a hybrid power system with a traditional four-wheel drive structure is adopted, due to the existence of structures such as a center differential, problems such as complex structure and high cost will result.

Contents of the invention

The technical problem to be solved by the present invention is to provide a four-wheel drive hybrid power system and its control method 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 power system, comprising:

Front axle drive assembly and rear axle drive assembly, front axle drive assembly includes coaxially connected engine, ISG motor and gearbox, rear axle drive assembly includes coaxially connected rear axle motor and differential reducer, 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 respectively connected with the first motor controller, the second motor controller, the battery management system and the engine management system, and is used to control the front axle drive assembly and the rear axle according to the vehicle driving conditions and vehicle sensor values. The drive assembly performs torque distribution.

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

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

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

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

The present invention also provides a control method for a four-wheel drive hybrid power 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;

According to the current SOC value of the power battery, the VCU controls the engine to stop and is driven by the rear axle motor;

According to the current throttle depth, SOC value and vehicle speed, the VCU calculates the current driving torque demand of the whole vehicle. When the SOC value is higher than a certain threshold and within the power range that the rear axle motor can meet, all the torque is distributed to the rear axle motor. Shaft motor for travel drive.

Wherein, 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 torque request according to the driver's throttle depth, and sends the driver torque request to the second motor controller, and the rear axle motor Carry out the starting drive, and the vehicle enters the pure electric mode.

Among them, if the current SOC value is lower than the automatic shutdown threshold, the ISG motor will generate power, the rear axle motor will start driving, and the vehicle will enter the range-extending mode.

Among them, if the power of the rear axle motor cannot meet the torque demand of the driver, the VCU will start the engine, the vehicle will enter the hybrid mode, and the engine will use the excess torque for power generation. If the torque is still insufficient, the rear axle motor will output the insufficient torque. 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.

Among them, when the VCU receives the forced pure electric signal, it judges whether the current SOC value is greater than the forced pure electric threshold, and if so, the VCU only distributes the torque 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 at 25%-30%, and the second automatic shutdown threshold is set at 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 the depth of the brake pedal to recover braking and coasting energy.

The four-wheel drive hybrid power system and its control method in 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 distributed by the vehicle controller VCU according to the current working conditions of the vehicle, and the front and rear axles can be independently distributed. Driving, the tracking performance of the vehicle is better, which can improve the vehicle's power acceleration, fuel economy, driving stability and adaptability of the vehicle to the driving environment, and the vehicle's passing performance is better.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

FIG. 1 is a schematic structural diagram of a four-wheel drive hybrid power system according to Embodiment 1 of the present invention.

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

FIG. 3 is a schematic flowchart of a control method for a four-wheel drive hybrid system according to Embodiment 2 of the present invention.

detailed description

The following descriptions of various embodiments refer to the accompanying drawings to illustrate specific embodiments in which the present invention can be implemented. The terms of direction and position mentioned in the present invention, such as "up", "down", "front", "back", "left", "right", "inside", "outside", "top", "bottom" ", "side", etc., are only referring to the direction or position of the drawings. Therefore, the terms used in direction and position are used to illustrate and understand the present invention, but not to limit the protection scope of the present invention.

Please refer to Fig. 1, an embodiment of the present invention provides a four-wheel drive hybrid power system, including:

Front axle drive assembly and rear axle drive assembly, front axle drive assembly includes coaxially connected engine, ISG motor and gearbox, rear axle drive assembly includes coaxially connected rear axle motor and differential reducer, 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 respectively connected with the first motor controller, the second motor controller, the battery management system and the engine management system, and is used to control the front axle drive assembly and the 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 with the rear axle motor has a large reduction ratio.

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

As shown in Figure 1, the embodiment of the present invention adds an Electric Rear Axle Drive Motor (Electric Rear Axle Drive Motor, or ERAD electric motor), the rear axle motor is connected to the rear axle through a differential reducer with a large reduction ratio. The MCU in the figure is the Motor Control Unit, where 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) control, MCU1, MCU2, BMS and engine management system EMS all communicate with the vehicle controller VCU (Vehicle Control System) through the CAN bus, and the vehicle controller VCU performs vehicle monitoring, driver torque request calculation and Torque front and rear axle distribution, etc.

The embodiment of the present invention is applied to a four-wheel-drive hybrid electric vehicle, which can adopt plug-in hybrid electric power (PHEV) and non-plug-in hybrid electric power (HEV). If plug-in hybrid power is used, the battery capacity and rear axle motor power can be increased, and the rear axle motor can be more involved in driving. This type of hybrid power system can be classified as strong hybrid; if non-plug-in hybrid power is used, Its battery capacity and rear axle motor power will be relatively small, and the output of the rear axle motor is mainly used for a few working conditions such as vehicle start, gear shift assistance, and full throttle acceleration assistance, and it is classified as a mid-mix. This embodiment is preferably applied to plug-in hybrid power, and because it belongs to the strong hybrid series, it can effectively ensure the dynamic performance of the rear axle drive of the vehicle.

In the present invention, the torque distribution of the front and rear axles is carried out through the vehicle controller VCU according to the vehicle running conditions and vehicle sensor values. Under various working conditions, such as: vehicle startup, vehicle starting, vehicle normal driving, brake coast recovery, driver forced pure electric power, etc., the VCU will automatically distribute the torque to the front and rear axles. That is to say, the VCU can intelligently select the driving mode of the vehicle to achieve the best economy without sacrificing power. The schematic diagram of the mode selection is shown in Figure 2, including the following aspects:

1. Start the vehicle

Different from the 12V starter motor of the traditional car to start the engine, the present invention adopts the ISG motor to start the engine. The VCU sends a torque request command to the ISG motor, and the ISG motor outputs torque to pull the engine up to a higher speed and start fuel injection, thus completing the engine start. The engine is started by the ISG motor, which solves the problems of high fuel consumption and poor emission when the traditional car is started, and can effectively improve fuel economy and emission.

2. The 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 according to the current SOC value. If the SOC value is greater than or equal to a certain threshold value, the engine enters the automatic shutdown state, and the VCU calculates the driver torque request according to the driver's throttle depth, and sends the driver torque request to the second motor controller MCU2, so that the rear axle motor Start 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 start drive, but at this time the vehicle is in the extended range mode, that is, the ISG motor generates power and the rear axle motor drives series hybrid mode. In the starting mode, only the rear axle motor works. If the battery SOC value is relatively low, the ISG motor will charge the power battery, and the power battery will supply power to the rear axle motor. The engine is stopped and started purely electric, but after the vehicle speed comes up, the engine will still start to generate electricity.

3. Vehicle drive

After the vehicle has started and enters normal driving, the VCU calculates the current driving torque demand of the vehicle based on the current accelerator 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 distributes all the torque to the rear axle motor to drive the rear axle motor to meet the torque requirements of the 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 torque demand of the driver, the VCU will start the engine, the vehicle will enter the hybrid mode, the engine will work in the high efficiency range, and use the excess torque for power generation. Insufficient, it is assisted by the torque of the insufficient output part of the rear axle motor.

4. Mandatory pure electric

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

Different from the initial stage, pure electric driving has relatively high requirements on the SOC value. Generally, an 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%.

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 the depth of the brake pedal to recover braking and coasting energy, which can effectively improve fuel economy through energy recovery.

Please refer to FIG. 3 again, Embodiment 2 of the present invention provides a control method for a four-wheel drive hybrid power 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;

According to the current SOC value of the power battery, the VCU controls the engine to stop and is driven by the rear axle motor;

According to the current throttle depth, SOC value and vehicle speed, the VCU calculates the current driving torque demand of the whole vehicle. When the SOC value is higher than a certain threshold and within the power range that the rear axle motor can meet, all the torque is distributed to the rear axle motor. Shaft motor for travel drive.

As mentioned above, the starting drive 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 according to the driver’s throttle depth, and 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 the pure electric mode; if the SOC value is lower than the automatic shutdown threshold, it is also driven by the rear axle motor, but at this time the vehicle Range mode, that is, the series hybrid mode in which the ISG motor generates power and the rear axle motor drives. 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], wherein the first automatic shutdown threshold is set to 25%-30%, and the second The automatic shutdown threshold is set at 15%-25%. The purpose of setting the auto-shutdown threshold as a hysteresis loop is to avoid the engine starting and stopping all the time. To simplify the description, take the first automatic shutdown threshold as 25%, 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 Automatic shutdown threshold), the engine stops, and the SOC value enters the hysteresis loop. , For example, the SOC value rises to 23%, and the engine remains on. 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, and when the SOC value drops below 25%, the engine will start again to generate electricity; The SOC value rises back to more than 25%, and the engine shuts down again, which will cause the engine to start and stop working back and forth all the time.

After the vehicle has started and enters normal driving, the VCU distributes all the torque to the rear axle motor to drive the rear axle motor to meet the torque requirements of the vehicle. The engine is still in a stopped state, and the vehicle is in pure electric driving. If the power of the rear axle motor cannot meet the torque demand of the driver, the VCU will start the engine, the vehicle will enter the 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 for assistance. 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.

If the driver wishes to force purely electric driving, he can do so by pressing the EV-On button. The VCU receives the signal from the EV-On button and judges whether the current SOC value is greater than the mandatory pure electric threshold. If so, the VCU will not limit the driver's throttle depth and vehicle speed, and only distribute the torque to the rear axle motor, so that the vehicle is fully electric. drive. As mentioned above, since pure electric driving has relatively high requirements on the SOC value, the mandatory pure electric threshold in this embodiment is greater than the automatic shutdown threshold at the start 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 the depth of the brake pedal to recover braking and coasting energy, which can effectively improve fuel economy through energy recovery.

The four-wheel drive hybrid power system and its control method in 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 distributed by the vehicle controller VCU according to the current working conditions of the vehicle, and the front and rear axles can be independently distributed. Driving, the tracking performance of the vehicle is better, which can improve the vehicle's power acceleration, fuel economy, driving stability and adaptability of the vehicle to the driving environment, and the vehicle's passing performance is better.

The above disclosures are only preferred embodiments of the present invention, and certainly cannot limit the scope of rights 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 (13)

1. a kind of four-wheel-drive hybrid power system, it is characterised in that including：

Front axle drive assembly and rear axle drive assembly, front axle drive assembly includes coaxial connected engine, ISG motors and gearbox, rear axle drive assembly includes coaxial connected rear spindle motor and difference speed reducer, ISG motors are electrically connected with the first electric machine controller, spindle motor is electrically connected with the second electric machine controller afterwards, and the first electric machine controller and the second electric machine controller are electrically connected with electrokinetic cell；

Entire car controller, it is connected with the first electric machine controller, the second electric machine controller, battery management system and engine management system signal respectively, for according to vehicle driving-cycle and vehicle sensors numerical value, moment of torsion distribution being carried out to front axle drive assembly and rear axle drive assembly.

2. four-wheel-drive hybrid power system according to claim 1, it is characterised in that the difference speed reducer being connected with rear axle motor coaxle has big retarding ratio.

3. four-wheel-drive hybrid power system according to claim 1, it is characterised in that the entire car controller and the first electric machine controller, the second electric machine controller, battery management system and engine management system pass through CAN interactive correspondence.

4. four-wheel-drive hybrid power system according to claim 1, it is characterised in that the four-wheel-drive hybrid power system is 4 wheel driven plug-in hybrid system.

5. four-wheel-drive hybrid power system according to claim 1, it is characterised in that the entire car controller is additionally operable to according to vehicle driving-cycle and vehicle sensors numerical value selection electric-only mode, increases journey pattern or mixed dynamic model formula.

6. the control method of a kind of four-wheel-drive hybrid power system as described in claim any one of 1-5, including：

Entire car controller VCU sends torque request and instructs to ISG motors, and ISG motor output torques start engine；

VCU is shut down according to the current SOC value of electrokinetic cell, control engine, and starting driving is carried out by rear spindle motor；

VCU calculates current vehicle driving torque demand according to current throttle depth, SOC value and speed, in SOC value higher than a certain threshold value and in the power bracket that rear spindle motor disclosure satisfy that, moment of torsion is fully allocated into rear spindle motor, and traveling driving is carried out by rear spindle motor.

7. control method according to claim 6; it is characterized in that; if current SOC value is more than or equal to autostop threshold value; engine enters autostop state; throttle depth calculation driver torque requests of the VCU according to driver; driver torque request is sent to the second electric machine controller, starting driving is carried out by rear spindle motor, vehicle enters electric-only mode.

8. control method according to claim 6, it is characterised in that if current SOC value is less than autostop threshold value, generated electricity by ISG motors, rear spindle motor carries out starting driving, and vehicle enters and increases journey pattern.

9. the control method according to claim any one of 6-8, it is characterized in that, if the power of rear spindle motor can not meet the torque demand of driver, VCU will start engine, vehicle enters mixed dynamic model formula, be used for for unnecessary moment of torsion to generate electricity by engine, if moment of torsion is still not enough, is aided in by the moment of torsion of rear spindle motor output insufficient section；If the moment of torsion of engine and rear spindle motor can not all meet operator torque demands, aided in by ISG motor output torques.

10. whether control method according to claim 9, it is characterised in that when VCU receives pressure pure electromotive signal, judge current SOC value more than the pure electronic threshold value of pressure, if it is, moment of torsion is assigned to only rear spindle motor by VCU.

11. control methods according to claim 10, it is characterised in that the pure electronic threshold value of pressure is more than the autostop threshold value, the autostop threshold value is a hysteresis loop [the second autostop threshold value, the first autostop threshold value].

12. control methods according to claim 11, it is characterised in that the first autostop threshold value is set to 25%-30%, the second autostop threshold value is set to 15%-25%.

13. control method according to claim any one of 6-8, it is characterised in that when being braked or being slided, VCU sends negative torque to vehicle according to speed and brake pedal depth to rear spindle motor, is braked and slided energy regenerating.