A downshift control method and system for an automatic transmission vehicle with exhaust brake system

Abstract

The application provides a downshift control method and system of an automatic gear vehicle with an exhaust brake system, and belongs to the technical field of vehicle gear shifting control. The method steps are as follows: when the exhaust brake linkage of the brake is activated, the AMT gearbox judges whether to enter the exhaust brake gear shifting mode; in the exhaust brake gear shifting mode, the gearbox control unit collects the brake signal of the brake pedal to identify the brake intention; the gearbox control unit collects the slope information, the distance from the front vehicle and the brake signal of the brake pedal, and corrects the engine downshift speed in combination with the brake intention, and completes the gear shifting of the AMT gearbox by using the corrected engine downshift speed. The application realizes the reasonable downshift of the vehicle under the exhaust linkage through the exhaust brake downshift mode, plays the engine brake efficiency, accurately identifies the brake demand of the user according to the brake pedal opening interval division, compensates and corrects the downshift point speed through the brake pedal, the slope and the obstacle influence, and realizes the reasonable downshift.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of vehicle gear shifting control, and particularly relates to a downshift control method and system for an automatic gear vehicle with an exhaust brake system. BACKGROUND

[0002] With the increase in the number and types of commercial vehicles, higher requirements are put forward for the performance, safety and efficiency of the vehicles. Since commercial vehicles have large mass, long running distance and complex and changeable driving environment, higher reliability and efficiency are required for the brake system. However, the traditional brake system, such as hydraulic brake, may face problems of heat recession and brake efficiency reduction, and even brake failure in severe cases, thereby causing traffic accidents. Therefore, the auxiliary brake system becomes an important means to improve the performance of commercial vehicles.

[0003] The exhaust brake system is a common auxiliary brake mode for commercial vehicles. The exhaust brake system uses the resistance generated in the compression stroke of the engine to assist braking by closing the engine exhaust valve or adjusting the exhaust back pressure. However, the brake efficiency is significantly affected by the engine speed, and the actual effect of exhaust brake is directly affected by the selection of the gear position of the transmission under different working conditions. At present, the AMT transmission enters the exhaust linkage brake mode, and when the exhaust brake system is integrated, the shift logic of the AMT transmission and the control strategy of the exhaust brake system need to be highly coordinated. The current problems include that when the brake is lightly pressed, the AMT transmission may excessively actively downshift to increase the engine speed, which not only may cause unnecessary fuel consumption, but also may affect the optimal intervention time of the exhaust brake; and under downhill working conditions, the engine speed should be in a high speed range, and the step-down shift strategy of the AMT transmission may not be able to quickly increase the engine speed to the optimal brake range, thereby missing the braking opportunity.

[0004] Therefore, it is necessary to provide a downshift control method and system for an automatic gear vehicle with an exhaust brake system to solve the above technical problems. SUMMARY

[0005] In view of the defects that when the exhaust brake is used as the auxiliary brake for commercial vehicles, the AMT transmission downshifts to increase the engine speed after the brake is lightly pressed, resulting in fuel waste and affecting the optimal intervention time of the exhaust brake, and the step-down shift strategy cannot quickly increase the engine speed to the optimal brake range under downhill working conditions, the present application provides a downshift control method and system for an automatic gear vehicle with an exhaust brake system to solve the above technical problems.

[0006] In a first aspect, the present application provides a downshift control method for an automatic gear vehicle with an exhaust brake system, comprising the following steps:

[0007] S1. When the exhaust brake linkage of the brake is activated, the AMT gearbox determines whether to enter the exhaust brake shift mode;

[0008] S2. In the exhaust brake shift mode, the gearbox control unit TCU collects the brake signal of the brake pedal to identify the braking intention;

[0009] S3. The gearbox control unit TCU collects the slope information of the vehicle, the distance from the front vehicle and the brake signal of the brake pedal, and corrects the engine downshift speed in combination with the braking intention, and completes the AMT gearbox shift using the corrected engine downshift speed.

[0010] Further, the specific steps of step S1 are as follows:

[0011] S11. During vehicle driving, the vehicle controller ECU determines whether to receive the brake signal of the brake pedal;

[0012] If yes, go to step S12;

[0013] If no, wait for a set period of time and return to step S11;

[0014] S12. The vehicle controller ECU informs the AMT gearbox to activate the exhaust brake linkage;

[0015] S13. The AMT gearbox obtains the engine torque signal through the vehicle controller ECU;

[0016] When the engine torque signal is 0, go to step S14;

[0017] When the engine torque signal is not 0, go to step S15;

[0018] S14. The AMT gearbox enters the exhaust brake shift mode, and goes to step S2;

[0019] S15. The AMT gearbox enters the normal shift mode, and ends.

[0020] Further, the specific steps of step S2 are as follows:

[0021] S21. After entering the exhaust brake shift mode, the gearbox control unit TCU calculates the brake pedal depth; S22. The gearbox control unit TCU compares the calculated brake pedal depth with the pre-set first depth threshold and second depth threshold;

[0022] When the brake pedal depth is less than the first depth threshold, go to step S23;

[0023] When the brake pedal depth is greater than or equal to the first proportion threshold and less than or equal to the second proportion threshold, go to step S24;

[0024] When the brake pedal depth is greater than the second proportional threshold value, step S25 is entered;

[0025] S23. Identify as light brake pedal, determine to maintain the current vehicle speed, the required downshift speed is the same as that in the normal shift mode, end;

[0026] S24. Identify as moderate brake pedal, determine to reduce the current vehicle speed, enter step S3;

[0027] S25. Identify as heavy brake pedal, determine to need emergency braking, the transmission control unit TCU sends a command to maintain the current gear to the AMT transmission, and separates the clutch, end.

[0028] Further, the specific steps of step S21 are as follows:

[0029] S211. The transmission control unit TCU pre-acquires the vehicle speed, deceleration and brake pedal depth data of the vehicle to the vehicle controller, and establishes a two-dimensional interpolation module with vehicle speed and deceleration as input and brake pedal depth as output and saves it;

[0030] S212. The transmission control unit TCU obtains the real-time vehicle speed and deceleration of the vehicle from the vehicle controller, and estimates the real-time brake pedal depth through the saved two-dimensional interpolation module.

[0031] Further, the specific steps of step S3 are as follows:

[0032] S31. The transmission control unit TCU obtains the calculated brake pedal depth and duration, and calculates the brake pedal influence factor;

[0033] S32. The transmission control unit TCU obtains the slope information of the current section of the vehicle through GPS, and calculates the slope influence factor;

[0034] S33. The transmission control unit TCU calculates the relative distance between the vehicle and the front obstacle through the radar and optical sensor in the front of the vehicle, and calculates the distance influence factor;

[0035] S34. The transmission control unit TCU uses the brake pedal influence factor, the slope influence factor and the distance influence factor to correct the downshift speed in the normal shift mode, and obtains the required engine speed.

[0036] Further, the specific steps of step S31 are as follows:

[0037] S311. The transmission control unit TCU analyzes the brake pedal depth in the set time period, and identifies the brake pedal depth BrkPedal whose duration exceeds the time threshold value;

[0038] S312. Calculate the brake pedal influence factor Fac using the pre-set proportional gain coefficient KP and integral gain coefficient KI b :

[0039] Fac b = KP * BrkPedal + ∑(KI * BrkPedal), where the brake pedal influence factor Fac b Reset to zero after braking is completed.

[0040] Further, the step S32 is specifically as follows:

[0041] S321. Pre-set the first slope threshold value, the second slope threshold value, and set the slope range of uphill to be greater than 0 and less than the first slope threshold value, set the slope threshold value of flat road to be the distance from 0 less than or equal to the set threshold value, set the slope threshold value of small downhill to be greater than the second slope threshold value and less than 0, set the slope threshold value of large downhill to be greater than or equal to the second slope threshold value and less than 1;

[0042] S322. Pre-establish an empirical table of slope influence factors corresponding to each slope classification;

[0043] S323. The transmission control unit TCU obtains the slope information of the current road section of the vehicle through GPS, compares with each slope range to determine the slope classification, and then looks up the empirical table to obtain the slope influence factor.

[0044] Further, the step S33 is specifically as follows:

[0045] S331. The transmission control unit TCU calculates the relative distance between the vehicle and the front obstacle through the radar and optical sensor at the front of the vehicle, and compares the relative distance with the safety distance;

[0046] When the relative distance is greater than the safety distance, enter step S332;

[0047] When the relative distance is less than or equal to the safety distance, enter step S333;

[0048] S332. Determine that the distance influence factor Fac d is 0, enter step S4;

[0049] S333. Determine that the distance influence factor Fac d is pre-set value.

[0050] Further, in step S34, the required engine speed N D is calculated by the following formula:

[0051] N D = N J + N JFac b Fac J Fac d Fac J Fac c

[0052] Wherein, N J is the downshift speed of normal shift mode, Fac b is the brake pedal influence factor, Fac d is the distance influence factor, Fac c is the slope influence factor.

[0053] In the second aspect, the application provides a downshift control system of an automatic shift vehicle with an exhaust brake system, comprising:

[0054] An exhaust brake shift mode entering judging module is used for judging whether the AMT gearbox enters the exhaust brake shift mode when the brake exhaust brake linkage is activated.

[0055] A brake intention recognition module is used for recognizing the brake intention of the brake pedal by the TCU in the exhaust brake shift mode.

[0056] A downshift speed correction module is used for collecting the slope information of the vehicle, the distance from the front vehicle and the brake signal of the brake pedal by the TCU, and correcting the engine downshift speed in combination with the brake intention, and completing the AMT gearbox shift by using the corrected engine downshift speed.

[0057] The downshift control method and system of the automatic shift vehicle with the exhaust brake system provided by the application realize the reasonable downshift of the vehicle under the exhaust linkage by the exhaust brake downshift mode, exert the engine brake efficiency, estimate the brake opening degree by the vehicle speed and the vehicle acceleration, accurately recognize the brake demand of the user according to the brake pedal opening degree interval division, compensate and correct the downshift point speed by the brake pedal influence, the slope and the obstacle influence, and realize the reasonable downshift.

[0058] In addition, the design principle of the application is reliable, the structure is simple, and the application prospect is very wide.

[0059] Therefore, compared with the prior art, the application has outstanding substantial characteristics and significant progress, and the beneficial effects of the implementation are also obvious. BRIEF DESCRIPTION OF DRAWINGS

[0060] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0061] Figure 1 is a flowchart of the downshift control method of the automatic vehicle with the exhaust brake system of the present application.

[0062] Figure 2 is a schematic diagram of the downshift control system of the automatic vehicle with the exhaust brake system of the present application. DETAILED DESCRIPTION

[0063] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort should belong to the protection scope of the present application.

[0064] Please refer to Figure 1 Fig. 1 shows a downshift control method of an automatic vehicle with an exhaust brake system in a specific embodiment, which comprises the following steps:

[0065] S1. When the exhaust brake linkage of the brake is activated, the AMT gearbox judges whether to enter the exhaust brake shift mode;

[0066] S2. In the exhaust brake shift mode, the TCU of the gearbox control unit collects the brake signal of the brake pedal to identify the brake intention;

[0067] S3. The TCU of the gearbox control unit collects the slope information of the vehicle, the distance from the front vehicle and the brake signal of the brake pedal, and corrects the engine downshift speed in combination with the brake intention, and completes the shift of the AMT gearbox using the corrected engine downshift speed.

[0068] In the embodiment, the specific steps of step S1 are as follows:

[0069] S11. During the vehicle driving process, the ECU of the vehicle control unit judges whether to receive the brake signal of the brake pedal;

[0070] If yes, go to step S12;

[0071] If no, wait for a set period of time and return to step S11;

[0072] S12. The ECU of the vehicle control unit informs the AMT gearbox to activate the exhaust brake linkage;

[0073] S13. The AMT gearbox obtains the engine torque signal through the vehicle controller ECU;

[0074] When the engine torque signal is 0, go to step S14;

[0075] When the engine torque signal is not 0, go to step S15;

[0076] S14. The AMT gearbox enters the exhaust brake shift mode, go to step S2;

[0077] S15. The AMT gearbox enters the normal shift mode, end;

[0078] The specific steps of step S2 are as follows:

[0079] S21. After entering the exhaust brake shift mode, the gearbox control unit TCU calculates the brake pedal depth;

[0080] S22. The gearbox control unit TCU compares the calculated brake pedal depth with the pre-set first depth threshold and second depth threshold;

[0081] When the brake pedal depth is less than the first depth threshold, go to step S23;

[0082] When the brake pedal depth is greater than or equal to the first proportion threshold and less than or equal to the second proportion threshold, go to step S24;

[0083] When the brake pedal depth is greater than the second proportion threshold, go to step S25;

[0084] S23. Recognize as light brake, determine to maintain the current vehicle speed, the required downshift speed is the same as that in the normal shift mode, end;

[0085] S24. Recognize as moderate brake, determine to reduce the current vehicle speed, go to step S3;

[0086] S25. Recognize as heavy brake, determine to need emergency braking, the gearbox control unit TCU sends a current gear maintenance instruction to the AMT gearbox and separates the clutch, end;

[0087] The specific steps of step S3 are as follows:

[0088] S31. The gearbox control unit TCU obtains the calculated brake pedal depth and duration, and calculates the brake pedal influence factor;

[0089] S32. The gearbox control unit TCU obtains the slope information of the current road section of the vehicle through GPS, and calculates the slope influence factor;

[0090] S33. The transmission control unit TCU calculates the relative distance between the vehicle and the front obstacle by the radar and optical sensors in the front of the vehicle, and calculates the distance influence factor;

[0091] S34. The transmission control unit TCU corrects the downshift speed in the normal shift pattern by using the brake pedal influence factor, the slope influence factor and the distance influence factor, and obtains the required engine speed.

[0092] In some embodiments, step S21 has the following specific steps:

[0093] S211. The transmission control unit TCU collects the vehicle speed, deceleration and brake pedal depth data of the vehicle in advance to the vehicle control unit, and establishes a two-dimensional interpolation module with the vehicle speed and deceleration as inputs and the brake pedal depth as output and saves it;

[0094] S212. The transmission control unit TCU obtains the real-time vehicle speed and deceleration of the vehicle from the vehicle control unit, and estimates the real-time brake pedal depth through the saved two-dimensional interpolation module.

[0095] In some embodiments, step S31 has the following specific steps:

[0096] S311. The transmission control unit TCU analyzes the brake pedal depth in the set time period, and identifies the brake pedal depth BrkPedal whose duration exceeds the time threshold value;

[0097] S312. The brake pedal influence factor Fac is calculated using the pre-set proportional gain coefficient KP and integral gain coefficient KI b :

[0098] Fac b = KP*BrkPedal + ∑(KI*BrkPedal), wherein the brake pedal influence factor Fac b is reset to zero after braking is completed;

[0099] Step S32 has the following specific steps:

[0100] S321. The first slope threshold value and the second slope threshold value are pre-set, and the slope range of uphill is greater than 0 and less than the first slope threshold value, the slope threshold value of flat road is the distance from 0 less than or equal to the set threshold value, the slope threshold value of small downhill is greater than the second slope threshold value and less than 0, and the slope threshold value of large downhill is greater than or equal to the second slope threshold value and less than 1;

[0101] S322. An empirical table of slope classification corresponding to slope influence factor is pre-established;

[0102] S323. The transmission control unit TCU acquires the slope information of the current road section of the vehicle through GPS, compares with each slope range to determine the slope classification, and then looks up the experience table to obtain the slope influence factor;

[0103] Step S33 is specifically as follows:

[0104] S331. The transmission control unit TCU calculates the relative distance between the vehicle and the front obstacle through the radar and optical sensor at the front of the vehicle, and compares the relative distance with the safety distance;

[0105] When the relative distance is greater than the safety distance, step S332 is entered;

[0106] When the relative distance is less than or equal to the safety distance, step S333 is entered;

[0107] S332. Determine the distance influence factor Fac d = 0, step S4 is entered;

[0108] S333. Determine the distance influence factor Fac d = a preset value;

[0109] In step S34, the required engine speed N D is calculated by the following formula:

[0110] N D = N J + N J × Fac b + N J × Fac d + N J × Fac c

[0111] Wherein, N J is the downshift speed in normal shift mode, Fac b is the brake pedal influence factor, Fac d is the distance influence factor, and Fac c is the slope influence factor.

[0112] It should be understood that the size of the serial number of each step in the above embodiment does not mean the order of execution. The execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0113] The following is an embodiment of the automatic gear vehicle with exhaust brake system provided by the embodiment of the present disclosure, which belongs to the same inventive concept as the above-mentioned embodiments of the downshift control method of the automatic gear vehicle with exhaust brake system. Details not described in the embodiment of the downshift control system of the automatic gear vehicle with exhaust brake system can be referred to the above-mentioned embodiments of the downshift control method of the automatic gear vehicle with exhaust brake system.

[0114] As shown in Figure 2 The system comprises:

[0115] An exhaust brake shift mode entering judging module is configured to judge whether the AMT gearbox enters the exhaust brake shift mode when the exhaust brake linkage of the brake is activated.

[0116] A brake intention identifying module is configured to identify the brake intention by the TCU collecting the brake signal of the brake pedal in the exhaust brake shift mode.

[0117] A downshift speed correcting module is configured to collect the slope information of the vehicle, the distance from the front vehicle and the brake signal of the brake pedal by the TCU, and correct the engine downshift speed in combination with the brake intention, and complete the shift of the AMT gearbox by using the corrected engine downshift speed.

[0118] Although the present application has been described in detail by referring to the preferred embodiments thereof, it is to be understood that the present application is not limited to the embodiments described herein. Various modifications and equivalents can be made thereto without departing from the spirit and scope of the present application. Any skilled person in the art can easily make various modifications or replacements to the embodiments of the present application without departing from the spirit and scope of the present application, and such modifications or replacements should be covered within the scope of the present application.

Claims

1. A downshift control method for an automatic transmission vehicle with an exhaust brake system, characterized by, Comprising the following steps: S1. When the exhaust brake linkage of the brake is activated, the AMT gearbox determines whether to enter the exhaust brake shift mode; S2. In the exhaust brake shift mode, the gearbox control unit TCU collects the brake signal of the brake pedal to identify the braking intention; S3. The gearbox control unit TCU collects the slope information of the vehicle, the distance from the front vehicle and the brake signal of the brake pedal, and corrects the engine downshift speed in combination with the braking intention, and uses the corrected engine downshift speed to complete the AMT gearbox shift; The specific steps of step S2 are as follows: S21. After entering the exhaust brake shift mode, the gearbox control unit TCU calculates the brake pedal depth; S22. The gearbox control unit TCU compares the calculated brake pedal depth with the pre-set first depth threshold and second depth threshold; When the brake pedal depth is less than the first depth threshold, step S23 is entered; When the brake pedal depth is greater than or equal to the first depth threshold and less than or equal to the second depth threshold, step S24 is entered; When the brake pedal depth is greater than the second depth threshold, step S25 is entered; S23. Identify as light brake, determine to maintain the current vehicle speed, the required engine downshift speed is the same as that in the normal shift mode, and the process ends; S24. Identify as moderate brake, determine to reduce the current vehicle speed, and enter step S3; S25. Identify as heavy brake, determine to need emergency braking, the gearbox control unit TCU sends a current gear maintenance instruction to the AMT gearbox, and the clutch is separated, and the process ends; The specific steps of step S3 are as follows: S31. The gearbox control unit TCU obtains the calculated brake pedal depth and duration, and calculates the brake pedal influence factor; S32. The gearbox control unit TCU obtains the slope information of the road section where the vehicle is currently located through GPS, and calculates the slope influence factor; S33. The gearbox control unit TCU calculates the relative distance between the vehicle and the front obstacle through the radar and optical sensor at the front of the vehicle, and calculates the distance influence factor; S34. The gearbox control unit TCU corrects the engine downshift speed in the normal shift mode using the brake pedal influence factor, the slope influence factor and the distance influence factor, and obtains the required corrected engine downshift speed.

2. The downshift control method of an automatic transmission vehicle with an exhaust brake system according to claim 1, characterized by, The specific steps of step S1 are as follows: S11. During vehicle driving, the vehicle control unit ECU determines whether to receive the brake signal of the brake pedal; If yes, step S12 is entered; If no, wait for a set period of time, and return to step S11; S12. The vehicle control unit ECU informs the AMT gearbox to activate the exhaust brake linkage; S13. The AMT gearbox obtains the engine torque signal through the vehicle control unit ECU; When the engine torque signal is 0, step S14 is entered; When the engine torque signal is not 0, step S15 is entered; S14. The AMT gearbox enters the exhaust brake shift mode, and step S2 is entered; S15. The AMT gearbox enters the normal shift mode, and the process ends.

3. The downshift control method of an automatic transmission vehicle with an exhaust brake system according to claim 1, characterized by, The specific steps of step S21 are as follows: S211. The transmission control unit TCU pre-collects the vehicle speed, deceleration and brake pedal depth data of the vehicle to the vehicle control unit, and establishes a two-dimensional interpolation module with the vehicle speed and deceleration as input and the brake pedal depth as output, and saves it; S212. The transmission control unit TCU obtains the real-time vehicle speed and deceleration of the vehicle to the vehicle control unit, and estimates the real-time brake pedal depth through the saved two-dimensional interpolation module.

4. The downshift control method of an automatic transmission vehicle with an exhaust brake system according to claim 1, characterized by, The specific steps of step S31 are as follows: S311. The transmission control unit TCU analyzes the brake pedal depth over the set time period and identifies brake pedal depths whose duration exceeds a time threshold ; S312. using a pre-set proportional gain coefficient and an integral gain coefficient calculating a brake pedal influence factor : where the brake pedal influence factor Reset clear after brake end.

5. The downshift control method of an automatic transmission vehicle with an exhaust brake system according to claim 1, characterized by, The specific steps of step S32 are as follows: S321. The first slope threshold value, the second slope threshold value are set in advance, and the slope range of uphill is greater than 0 and less than the first slope threshold value, the slope range of flat road is the distance from 0 less than or equal to the set threshold value, the slope range of small downhill is greater than the second slope threshold value and less than 0, and the slope range of large downhill is less than or equal to the second slope threshold value; S322. An empirical table of slope classification corresponding to slope influence factor is established in advance; S323. The transmission control unit TCU obtains the slope information of the current section of the vehicle through GPS, compares it with each slope range to determine the slope classification, and then looks up the empirical table to obtain the slope influence factor.

6. The downshift control method of an automatic transmission vehicle with an exhaust brake system according to claim 1, characterized by, The specific steps of step S33 are as follows: S331. The transmission control unit TCU calculates the relative distance between the vehicle and the front obstacle through the radar and optical sensor at the front of the vehicle, and compares the relative distance with the safety distance; When the relative distance is greater than the safety distance, step S332 is entered; When the relative distance is less than or equal to the safety distance, step S333 is entered; S332. Determine distance influence factor If the distance influence factor is 0, proceed to step S34. S333. Determine distance influence factor is a pre-set value.

7. The downshift control method of an automatic transmission vehicle with an exhaust brake system according to claim 1, characterized by, The required corrected engine downshift speed in step S34 is calculated by the following equation : wherein, nengdengjia is the engine downshift speed for normal shift mode, chepiaotia is the brake pedal influence factor, juliangjia is the distance influence factor, poguda is the slope influence factor.

8. A downshift control system for an automatic transmission vehicle with an exhaust brake system, characterized by, It includes: An exhaust brake shift mode entering judgment module for the AMT transmission to judge whether to enter the exhaust brake shift mode when the brake exhaust brake linkage is activated; A brake intention recognition module for the transmission control unit TCU to collect the brake signal of the brake pedal to recognize the brake intention in the exhaust brake shift mode; A downshift speed correction module for the transmission control unit TCU to collect the slope information of the vehicle, the distance from the front vehicle and the brake signal of the brake pedal, and to correct the engine downshift speed in combination with the brake intention, and to complete the AMT transmission shift using the corrected engine downshift speed; The specific steps of the brake intention recognition module for the transmission control unit TCU to collect the brake signal of the brake pedal to recognize the brake intention in the exhaust brake shift mode are as follows: After entering the exhaust brake shift mode, the transmission control unit TCU calculates the brake pedal depth; The transmission control unit TCU compares the calculated brake pedal depth with the first depth threshold value and the second depth threshold value set in advance; When the brake pedal depth is less than the first depth threshold value, it is recognized as light braking, and it is determined that the current vehicle speed needs to be maintained, and the required engine downshift speed is the same as that in the normal shift mode; When the brake pedal depth is greater than or equal to the first depth threshold value and less than or equal to the second depth threshold value, it is recognized as moderate braking, and it is determined that the current vehicle speed needs to be reduced; The transmission control unit TCU acquires the calculated brake pedal depth and duration, calculates a brake pedal influence factor; the transmission control unit TCU acquires the slope information of the road section where the vehicle is currently located through GPS, calculates a slope influence factor; the transmission control unit TCU calculates the relative distance between the vehicle and the front obstacle through the radar and optical sensor at the front of the vehicle, calculates a distance influence factor; The transmission control unit TCU corrects the engine downshift speed in the normal shift mode by using the brake pedal influence factor, the slope influence factor and the distance influence factor, to obtain the required corrected engine downshift speed; When the brake pedal depth is greater than the second depth threshold, it is identified as heavy braking, it is determined that emergency braking is needed, the transmission control unit TCU sends a current gear maintenance instruction to the AMT transmission, and the clutch is separated.

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