CN118560491A

CN118560491A - Full-time four-wheel drive vehicle fuel-saving control method and device, storage medium and vehicle

Info

Publication number: CN118560491A
Application number: CN202410570720.5A
Authority: CN
Inventors: 丁健; 汪振晓; 谢锡春; 李进伟; 付邦璀
Original assignee: Dongfeng Off Road Vehicle Co Ltd
Current assignee: Dongfeng Off Road Vehicle Co Ltd
Priority date: 2024-05-09
Filing date: 2024-05-09
Publication date: 2024-08-30

Abstract

The invention discloses a fuel-saving control method of a full-time four-wheel drive vehicle, which comprises the following steps: the method comprises the following steps: in the four-wheel drive mode, judging whether the transmission currently meets E gear hanging, whether the transfer case currently meets H gear hanging and whether four wheels in the four-wheel drive mode are not slipped, if at least 1 of the three conditions is not met, keeping the four-wheel drive mode, otherwise, entering a step two; correcting the engine torque, outputting a corrected engine torque command, and sending the corrected engine torque command to an engine controller; the engine controller controls the engine torque to reach a torque command value and is pre-switched into a two-drive mode; judging whether the two-drive driving wheels slip or not; if slipping, reducing the output torque of the engine until no slipping occurs; if not slipping, switching to a two-drive mode; corresponding device, storage medium and vehicle are also disclosed; the method has the advantages of stable switching and improvement of the fuel economy of the vehicle.

Description

Full-time four-wheel drive vehicle fuel-saving control method and device, storage medium and vehicle

Technical Field

The invention belongs to the technical field of vehicle transmission, and particularly relates to a fuel-saving control method and equipment for a full-time four-wheel drive vehicle.

Background

Today, four-wheel drives of automobiles are divided into three types, namely time-sharing four-wheel drives, timely four-wheel drives and full-time four-wheel drives.

The time sharing four-wheel drive allows the driver to manually switch between two drive modes: two-wheel drive and four-wheel drive. Such a system is commonly used for off-road vehicles and SUVs because it is capable of providing additional traction to assist the vehicle in traveling over rough terrain or rough roads. In the time-sharing four-wheel drive system, a driver needs to manually select a drive mode according to road conditions. When the road conditions are good, the vehicle may be operated in a two-wheel drive mode to improve fuel economy. When the vehicle encounters a slippery, muddy or snowy challenging surface, the driver can switch to the four-wheel drive mode, so that all four wheels are powered, and traction and stability of the vehicle are increased. Time-shared four-wheel drive systems are typically relatively simple and robust, but they may not be suitable for all-weather use because long-term use of the four-wheel drive mode on dry road surfaces may result in steering difficulties and uneven tire wear. In addition, time-sharing four-wheel drive systems are typically not provided with a central differential, which means that there is no speed differential between the four wheels when turning, so using four-wheel drive mode on paved roads may cause damage to the steering and tires of the vehicle. Meanwhile, when the vehicle encounters a low-adhesion, soft road surface or climbs a steep slope, the vehicle is required to be stopped first and then manually switched to a four-wheel drive mode, and because the vehicle is not provided with a central differential mechanism, the vehicle cannot run on a hard road surface by four-wheel drive, particularly cannot turn by four-wheel drive, and the vehicle has high technical requirements on drivers.

Timely four-wheel drive is an automatic four-wheel drive system that automatically distributes power to all four wheels when needed to improve traction and stability. Such systems are designed to provide better performance under a variety of road conditions, including wet, muddy, snowy or sandy, etc. The timing four-wheel drive system typically includes a central differential that transfers power from the front axle to the rear axle as needed. This system typically relies on a series of sensors to monitor parameters such as wheel speed, steering angle, acceleration and braking force to determine when power needs to be distributed to the front and rear axles. When the system detects a slip of the front or rear wheels, it automatically transmits power to the wheels with traction to maintain stability and traction of the vehicle. This automatic adjustment makes the timely four-wheel drive system well suited for everyday driving because it provides immediate traction while eliminating the need for the driver to manually switch drive modes. The disadvantages of this system are quite obvious, however, for example: off-road capability limitations (typically not as suitable for extreme off-road conditions as a time-shared four-drive or full-time four-drive system); reaction times are not timely (may not respond instantaneously to wheel slip as in a full-time four-wheel drive system); limited front-rear axle power distribution (which may not be as flexible as a full-time four-drive system); more than 50% of the power cannot be transmitted to the rear axle.

Full-time four-wheel drive is a four-wheel drive system that is capable of distributing power to all four wheels at all times to improve traction, stability, and handling of the vehicle. Such a system is suitable for use in a variety of road conditions, including slippery, muddy, snowy or sandy, and particularly suitable for vehicles that are required to travel in harsh environments. The system generally includes a central differential that allows the front and rear axles to rotate at different speeds, which is particularly important in cornering, as it reduces tire wear and improves vehicle handling. Because the central differential mechanism is arranged between the front driving shaft and the rear driving shaft, the defects of the time-sharing four-wheel drive and the timely four-wheel drive are overcome, and meanwhile, the vehicle has better running safety, trafficability, dynamic performance and extreme off-road performance, and the user range is wider and wider. However, the four-wheel drive system of the full-time four-wheel drive vehicle has the remarkable defects that large mechanical loss and stirring oil loss in a drive axle exist, so that the fuel economy of the vehicle is poor, and compared with the two-wheel drive vehicle with the same grade, the fuel consumption is increased by about 5-10%. Therefore, how to improve the fuel economy of the full-time four-wheel drive vehicle while ensuring the advantages of the full-time four-wheel drive vehicle becomes a technical problem to be solved urgently.

Disclosure of Invention

The invention provides a fuel-saving control method and equipment for a full-time four-wheel drive vehicle, which are used for reducing mechanical loss of a transmission system and oil stirring loss in a drive axle and improving the fuel economy of the vehicle by switching four-wheel drive into two-wheel drive under the working condition that the four-wheel drive is not needed according to the intention of a driver.

The scheme of the invention is as follows: a fuel-saving control method for a full-time four-wheel drive vehicle comprises the following steps: the method comprises the following steps:

step one, in a four-wheel drive mode, judging whether the transmission currently meets E gear hanging, whether the transfer case currently meets H gear hanging and whether four wheels in the four-wheel drive mode are all not slipped, if at least 1 of the three conditions is not met, keeping the four-wheel drive mode, otherwise, entering a step two;

Correcting the engine torque, outputting a corrected engine torque command, and sending the corrected engine torque command to an engine controller;

step three, an engine controller controls the engine torque to reach a torque command value and is pre-switched into a two-drive mode;

Judging whether the two-drive driving wheel slips or not; if slipping, reducing the output torque of the engine until no slipping occurs; if the vehicle does not slip, the vehicle is switched to a two-drive mode, so that the fuel economy is improved.

Further, the method for correcting the engine torque in the second step comprises the following steps:

If T _s<T_sl and T _a<T_al, the engine correction torque T _tq0 is as follows Calculating to obtain; otherwise, the engine correction torque T _tq0 is calculated according to the formula And (5) calculating to obtain the product.

Wherein, T _sl is the maximum transmission torque allowed by the transmission shaft, T _al is the maximum output torque allowed by the driving axle, T _s is the transmission torque transmitted by the transmission shaft during two-drive, T _a is the output torque of the driving axle during two-drive, and F _w is the total driving force of the wheel end.

Further, the T _s、T_a and F _w are calculated according to the following formulas:

T_a＝F_w×r

Wherein r is the wheel rolling radius, T _tq is the engine output torque, i _a is the drive axle speed ratio when two drives, eta _a is the drive axle transmission efficiency when two drives, i _g is the transmission speed ratio, eta _g is the transmission efficiency, i _d is the transfer case high gear speed ratio, eta _d is the transfer case transmission efficiency, i _fa is the front drive axle speed ratio, eta _fa is the front drive axle transmission efficiency, k is the transfer case front-rear output torque distribution ratio, i _ra is the rear drive axle speed ratio, eta _ra is the rear drive axle transmission efficiency.

Further, the method for pre-switching to the two-drive mode in the third step comprises the following steps: firstly, sending a command to a central differential controller to lock the central differential; transmitting an instruction to a clutch device controller between the output end of the transfer case and the transmission shaft to disconnect the clutch device; and then sending a command to a clutch device controller between the drive axle and the left wheel and the right wheel respectively, so that the clutch device is disconnected, and the default four-wheel drive mode is switched into the two-wheel drive mode.

Further, in the third step, the engine controller controls the engine torque to reach the torque command value, and after the pre-switching to the two-drive mode, the method further includes: if the transmission is not engaged with E gear, switching to a four-wheel drive mode; if the transmission is engaged in the E gear, judging whether the two driving wheels slip or not to enter the fourth step; one of the preconditions for both drives is to engage E-gear in order to confirm again that the driver is not out of E-gear during this period, and in extreme cases, such as when the vehicle is fully loaded and climbing a hill, if the vehicle is switched to the two-drive mode, it is possible to reduce the engine output torque in order to prevent overload of the transmission system, at this time, the driver may feel that the vehicle is under-powered, and may manually disengage from E-gear, engage into power mode D-gear, which corresponds to exiting the fuel-saving mode.

Further, if the transmission is not engaged in the E gear, the switching to the four-wheel drive mode includes: firstly, sending a command to a clutch device controller between the output end of the transfer case and the transmission shaft to combine the clutch device; transmitting a command to a clutch device controller between the drive axle and the left wheel and the right wheel respectively to combine the clutch devices; and then sending a command to the central differential controller to enable the central differential lock not to be locked, and switching the pre-two-drive mode into the four-drive mode.

Further, in the fourth step, whether the two-wheel drive wheel slips or not is judged; if slipping, reducing the engine output torque until no slipping is followed by: if the transmission is not engaged with E gear, switching to a four-wheel drive mode; if the transmission is engaged in E gear, a two-drive mode is maintained; here again in order to confirm again that the driver is not exiting the transmission E-stage during this period.

As another aspect of the present invention, there is also provided a fuel saving control device for a full-time four-wheel drive vehicle, comprising:

The first main module is used for judging whether the transmission currently meets E gear hanging, whether the transfer case currently meets H gear hanging and whether four wheels in the four-wheel driving mode are all not slipped or not in the four-wheel driving mode, if at least 1 of the three conditions is not met, the four-wheel driving mode is maintained, and if not, the second main module is started;

The second main module is used for correcting the engine torque, outputting a corrected engine torque command and sending the corrected engine torque command to the engine controller;

the third main module is used for enabling the engine controller to control the engine torque to reach a torque command value and pre-switching into a two-drive mode;

A fourth main module for judging whether the two-drive driving wheels slip; if slipping, reducing the output torque of the engine until no slipping occurs; if the vehicle does not slip, the vehicle is switched to a two-drive mode, so that the fuel economy is improved.

As another aspect of the present invention, there is also provided a computer storage medium having stored thereon a computer program which, when executed by a processor, implements the above-described full-time four-wheel drive vehicle fuel saving control method.

As another aspect of the present invention, there is also provided a vehicle equipped with the above-described full-time four-wheel drive vehicle fuel saving control device.

Compared with the prior art, the invention has the following effects:

(1) The full-time four-wheel drive vehicle fuel-saving control method provided by the invention judges that the transmission is in an economy gear, the transfer case is in a high gear and all four wheels are not slipped as starting conditions for switching to a two-wheel drive mode. The condition judgment can ensure that the fuel-saving control is only executed under proper working conditions, avoid influencing the normal running performance of the vehicle, improve the fuel economy of the vehicle and reduce the fuel consumption of the vehicle.

(2) The invention relates to a full-time four-wheel drive vehicle fuel-saving control method, which adopts a method for calculating and correcting an engine torque command according to the load capacity of a transmission system and the total driving force requirement. This ensures that the drive train is not overloaded in the two-drive mode, and the vehicle drive force is not significantly reduced, ensuring driving safety and dynamic performance.

(3) The full-time four-wheel drive vehicle fuel-saving control method adopts a switching mode of locking the central differential, disconnecting the transfer case from the transmission shaft clutch and disconnecting the drive axle from the wheel clutch, realizes stable switching from a four-wheel drive mode to a two-wheel drive mode, and avoids power interruption.

Drawings

FIG. 1 is a flow chart of a fuel-saving control method for a full-time four-wheel drive vehicle according to a preferred embodiment of the present invention;

FIG. 2 is a main logic flow diagram of a fuel-saving control method for a full-time four-wheel drive vehicle according to a preferred embodiment of the present invention;

FIG. 3 is a schematic diagram of a fuel-saving control device for a full-time four-wheel drive vehicle according to a preferred embodiment of the present invention; a figure;

fig. 4 is a schematic diagram of an entity structure of an electronic device according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.

Example 1:

Referring to fig. 1-2, an embodiment of the present invention provides a fuel-saving control method for a full-time four-wheel-drive vehicle, which includes:

(1) If the transmission is currently engaged with the E gear, the transfer case is currently engaged with the H gear and the four wheels of the four-wheel drive are not slipped, the fuel economy is improved;

(2) Outputting a corrected engine torque command, and sending the corrected engine torque command to an engine controller;

(3) The engine controller controls the engine torque to reach a torque command value and is pre-switched into a two-drive mode;

(4) Judging whether the two-drive driving wheels slip or not. If slipping, reducing the output torque of the engine until no slipping occurs; if the vehicle does not slip, the vehicle is switched to a two-drive mode, so that the fuel economy is improved.

In particular, the method comprises the steps of,

The first step: firstly, the vehicle control system self-checks that all components can work normally, the vehicle is in a key on state, and the vehicle defaults to a four-wheel drive mode.

And the second step is to judge whether the current gear of the transmission is in E gear. If the transmission is currently engaged in E gear, entering the next step: judging whether the current gear of the transfer case is in an H gear or not; if the current E gear is not engaged, the driver is considered to want to be in an economic mode, and the fuel-saving control method is exited. (E gear is an economy gear of the transmission, and real-time gear information of the transmission is received by the fuel-saving control module as an input parameter through the CAN bus and is sourced from the transmission control system.)

And the third step is to judge whether the current gear of the transfer case is in H gear. If the current hanging H gear of the transfer case is established, entering the following steps: judging whether the four-wheel drive wheel slips or not; if the current gear H of the transfer case is not established, the vehicle is considered to be in an off-road mode, the wheel-side large torque output is required, the transfer case is forbidden to be switched into a two-drive mode, and the fuel-saving control method is exited. (H gear is the high gear of the transfer case, also called as a direct gear, the speed ratio is low, the real-time gear information of the transfer case is derived from a transfer case control system and is received by an oil-saving control module through a CAN bus as an input parameter.)

And the fourth step is to judge whether the four-wheel drive wheel slips or not. If the four-wheel drive wheel slips, the vehicle is considered to have safety risk, and switching to the two-wheel drive mode is forbidden; if the four-wheel drive wheel does not slip, the following steps are carried out: and judging whether the two driving force transmission systems are overloaded. Specifically, if λ _fl<λ₀, λ _fr<λ₀, λ _rl<λ₀, and λ _rr<λ₀, it is determined that the four-wheel drive wheel is not slipping, otherwise it is determined that the four-wheel drive wheel is slipping. Here, λ ₀ is a preset threshold, for example, set to 0.18-0.3 in this embodiment, and λ _fl、λ_fr、λ_rl、λ_rl is the slip ratio of the front left wheel, the front right wheel, the rear left wheel and the rear right wheel, respectively, and is calculated according to the formula (1):

Wherein lambda is the wheel slip ratio, omega is the wheel speed, r is the wheel rolling radius, and v is the vehicle speed. The speed v is a common whole vehicle parameter, and is received by the fuel-saving control module through the CAN bus. The four wheel speed information is measured by the wheel speed sensor on each wheel and is received by the fuel-saving control module. The wheel rolling radius r is preset into the fuel-saving control module.

And fifthly, judging whether the two driving force transmission systems are overloaded. If overload occurs, correcting the engine torque according to the torque limit value of the transmission system; if not, the engine torque is corrected with the total driving force unchanged. And controlling the output torque of the engine according to the corrected engine torque, and simultaneously pre-switching to a two-drive mode.

In the above determination of whether the two driving force transmission systems are overloaded, specifically, if T _s<T_sl and T _a<T_al, it is determined that the two driving force transmission systems are not overloaded, otherwise, it is determined that the two driving force transmission systems are overloaded. T _sl is the maximum transmission torque allowed by the transmission shaft, T _al is the maximum output torque allowed by the drive axle, and the maximum output torque is preset in the fuel-saving control module and is set according to the actual conditions of the transmission shaft and the drive axle. T _s is the transmission shaft transmission torque in two drives, and T _a is the drive axle output torque in two drives. T _s and T _a are calculated according to formulas (2) and (3), respectively.

T_a＝F_w×r (3)

Wherein F _w is the total driving force of the wheel end and is a calculated variable in the fuel-saving control module. T _tq is the engine output torque, which is received by the fuel saving control module via CA bus from the engine controller. i _a is the drive axle speed ratio, eta _a is the drive axle transmission efficiency, i _g is the transmission speed ratio, eta _g is the transmission efficiency, i _d is the transfer case high gear speed ratio, eta _d is the transfer case transmission efficiency, i _fa is the front drive axle speed ratio, eta _fa is the front drive axle transmission efficiency, k is the transfer case front-rear output torque distribution ratio, i _ra is the rear drive axle speed ratio, eta _ra is the rear drive axle transmission efficiency, and all are preset values and are preset in the fuel-saving control module.

The engine torque is then corrected according to the driveline torque limit, specifically, the engine corrected torque T _tq0 is calculated according to equation (4).

The above-described engine torque is corrected as the total driving force is unchanged, specifically, the engine correction torque T _tq0 is calculated as formula (5).

And controlling the output torque of the engine according to the corrected engine torque, and simultaneously, pre-switching into a two-drive mode. Specifically, the corrected engine torque T _tq0 is first sent as a command to the engine controller, which controls the engine torque to reach the command value. Then, an instruction is sent to a central differential controller to lock the central differential, then the instruction is sent to a clutch device controller between the output end of the transfer case and the transmission shaft to disconnect the clutch device, the instruction is sent to the clutch device controller between the drive axle and the left wheel and the right wheel respectively to disconnect the clutch device, and the default four-wheel drive mode is switched to the two-wheel drive mode.

Then, the next step is entered: it is determined whether the current gear of the transmission is in E-range. If the transmission is currently engaged in E gear, entering the next step: judging whether the two driving wheels slip or not; if the transmission is currently engaged in E-gear is not established, a four-drive mode is shifted, where the driver is deemed to be dissatisfied with the current vehicle power reduction.

The above-mentioned switching to the four-wheel drive mode, specifically, send the order to the clutch device controller between transfer case output end and drive shaft first, make the clutch device combine, send the order to the clutch device controller between drive axle and left, right wheel respectively, make the clutch device combine, send the order to the central differential mechanism controller again, make the central differential lock not locked, switch over the two-wheel drive mode into the four-wheel drive mode in advance.

Judging whether the two driving wheels slip or not, and if the two driving wheels slip, reducing the output torque of the engine until the driving wheels do not slip; if the two-drive driving wheels do not slip, the current two-drive mode is maintained. Specifically, if lambda _l<λ₀ and lambda _r<λ₀ are found, the two-wheel drive wheel is determined to slip; otherwise, judging that the two-wheel drive wheel slips.

The above-described reduction of the engine output torque to the drive wheels without slipping, specifically, the reduction of the torque value based on the current engine torque, and the transmission of the engine torque command to the engine controller, the engine controller controlling the engine torque to the command value. The change in the value of the two drive wheel slip rate lambda _l、λ_r is monitored simultaneously until lambda _l<λ₀ and lambda _r<λ₀ are met. Then enter the next step: and judging whether the current gear of the transmission is in E gear or not, wherein the method is the same as that described above.

According to the full-time four-wheel drive vehicle fuel-saving control method and equipment provided by the embodiment of the invention, if the fact that the transmission is currently engaged in E gear and the transfer case is currently engaged in H gear and four wheels of the four-wheel drive are not slipped is monitored, the output torque of the engine is corrected, so that the following steps are realized: (1) The two driving force transmission systems are not overloaded so as to protect the transmission systems; (2) the two-drive driving wheels do not slip so as to ensure driving safety; (3) The total driving force of the vehicle is unchanged or changed to the minimum to maintain the dynamic property. Finally, the four-wheel drive is switched into two-wheel drive, so that the mechanical loss of a transmission system and the oil stirring loss in a drive axle are reduced, and the fuel economy of the vehicle is improved.

Referring to fig. 3, as another aspect of the present invention, there is also provided a fuel-saving control device for a full-time four-wheel drive vehicle, including:

Referring to fig. 4, the method of the embodiment of the present invention may be implemented by an electronic device, and for this purpose, the embodiment of the present invention provides an electronic device, which includes: at least one processor (processor), a communication interface (Communications Interface), at least one memory (memory), and a communication bus.

The at least one processor, the communication interface and the at least one memory are in communication with each other through a communication bus. The at least one processor may invoke logic instructions in the at least one memory to perform all or part of the steps of the methods provided by the various method embodiments described above.

Further, the logic instructions in at least one of the memories described above may be implemented in the form of a software functional unit and may be stored in a computer-readable storage medium when sold or used as a stand-alone product.

Based on such an understanding, the technical solution of the invention, in essence, or the part contributing to the prior art or the part of the technical solution, can be embodied in the form of a software product. In particular, the computer software product is stored in a storage medium, comprising instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in the various method embodiments of the invention. And the aforementioned storage medium includes: a usb disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), a magnetic disk, or an optical disk, or other various media capable of storing program codes.

The apparatus embodiments described above are merely illustrative, wherein the elements illustrated as separate elements may or may not be physically separate, and the elements shown as elements may or may not be physical elements, may be located in one place, or may be distributed over a plurality of network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art will understand and implement the present invention without undue burden.

From the above description of the embodiments, it will be apparent to those skilled in the art that the embodiments may be implemented by means of software plus necessary general hardware platforms, or of course may be implemented by means of hardware. Based on this understanding, the foregoing technical solution may be embodied essentially or in a part contributing to the prior art in the form of a software product, which may be stored in a computer readable storage medium, such as ROM/RAM, a magnetic disk, an optical disk, etc., including several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the method described in the respective embodiments or some parts of the embodiments.

The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. Based on this knowledge, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims

1. The fuel-saving control method for the full-time four-wheel drive vehicle is characterized by comprising the following steps of: the method comprises the following steps:

2. The fuel saving control method for the full-time four-wheel drive vehicle according to claim 1, wherein: the method for correcting the engine torque in the second step comprises the following steps:

If Ts < Tsl and Ta < Tal, then the engine correction torque Ttq ₀ is formulated Calculating to obtain; otherwise, the engine correction torque Ttq ₀ is formulated And (5) calculating to obtain the product.

Wherein, ts _l is the maximum transmission torque allowed by the transmission shaft, ta _l is the maximum output torque allowed by the drive axle, T _s is the transmission torque transmitted by the transmission shaft when driving two, T _a is the output torque of the drive axle when driving two, and F _w is the total driving force of the wheel end.

3. The fuel saving control method for the full-time four-wheel drive vehicle according to claim 2, wherein T _s、T_a and F _w are calculated according to the following formulas:

，＝Fw×r

4. The fuel saving control method for full-time four-wheel drive vehicles according to claim 1, wherein the method of pre-switching to the two-wheel drive mode in the third step is as follows: firstly, sending a command to a central differential controller to lock the central differential; transmitting an instruction to a clutch device controller between the output end of the transfer case and the transmission shaft to disconnect the clutch device; and then sending a command to a clutch device controller between the drive axle and the left wheel and the right wheel respectively, so that the clutch device is disconnected, and the default four-wheel drive mode is switched into the two-wheel drive mode.

5. The fuel saving control method of full-time four-wheel drive vehicle according to claim 1, wherein in the third step, the engine controller controls the engine torque to reach the torque command value, and after the pre-switching to the two-wheel drive mode, further comprising: if the transmission is not engaged with E gear, switching to a four-wheel drive mode; if the transmission is engaged in E gear, judging whether the two driving wheels slip or not, and entering a step four.

6. The full-time four-wheel drive vehicle fuel saving control method according to claim 1, wherein the switching to the four-wheel drive mode if the transmission is not engaged in E-range includes: firstly, sending a command to a clutch device controller between the output end of the transfer case and the transmission shaft to combine the clutch device; transmitting a command to a clutch device controller between the drive axle and the left wheel and the right wheel respectively to combine the clutch devices; and then sending a command to the central differential controller to enable the central differential lock not to be locked, and switching the pre-two-drive mode into the four-drive mode.

7. The fuel saving control method of the full-time four-wheel drive vehicle according to claim 1, wherein: judging whether the two-drive driving wheel slips or not in the fourth step; if slipping, reducing the engine output torque until no slipping is followed by: if the transmission is not engaged with E gear, switching to a four-wheel drive mode; if the transmission is engaged in E, the two-drive mode is maintained.

8. The fuel-saving control device for full-time four-wheel drive vehicle is characterized by comprising

The first main module is used for judging whether the transmission currently meets E gear hanging, whether the transfer case currently meets H gear hanging and whether the four wheels in the four-wheel driving mode are all not slipped or not in the four-wheel driving mode, if at least 1 of the three conditions is not met, the four-wheel driving mode is maintained, and if not, the second step is entered;

9. A computer storage medium having a computer program stored thereon, which, when executed by a processor, implements the full-time four-wheel drive vehicle fuel saving control method as claimed in any one of claims 1 to 7.

10. A vehicle equipped with the full-time four-wheel drive vehicle fuel saving control apparatus according to claim 8.