A method for diagnosing the failure of the shift fork in a dual-clutch automatic transmission to return to neutral.

Abstract

This invention relates to the field of dual-clutch automatic transmission technology, specifically to a method for diagnosing shift fork return-to-neutral failure in dual-clutch automatic transmissions. By real-time acquisition of signals from the engine, clutch, transmission, and shift forks, the method achieves real-time monitoring of the return-to-neutral process for each shift fork. Based on the expected gear, pre-selected gear, and shift fork position relationship according to the shifting pattern, as well as the relationship between the target shift fork position and the actual shift fork position, the method monitors the shift fork return-to-neutral process in two main aspects: shift fork return-to-neutral and target gear engagement. It promptly diagnoses failures in the target gear return-to-neutral process, helping to achieve smooth shift fork return-to-neutral engagement, improving the deceleration and stopping performance and power response of automatic transmission vehicles, reducing shift fork jerking and noise, lowering fuel consumption, improving vehicle economy, and facilitating rapid identification of the cause of problems by after-sales personnel during vehicle maintenance.

Description

Technical Field

[0001] This invention relates to the field of dual-clutch automatic transmission technology, and specifically to a method for diagnosing the failure of a dual-clutch automatic transmission shift fork to return to neutral. Background Technology

[0002] In automatic transmission vehicles, the shift fork return to neutral in a dual-clutch automatic transmission plays a crucial role. Whether it is decelerating to a stop or automatically shifting gears, the shift fork must be returned to neutral to achieve this.

[0003] When the transmission controller issues the desired gear and pre-selected gear command according to the shift pattern, the shift fork drives the synchronizer to return to neutral. Then, it enters the target gear to be engaged, returning to neutral even when the shift fork is in the neutral position. On a shift fork, the left side is one gear, the right side is another gear, and the middle of the shift fork is neutral. During shifting or returning to neutral, the actual position of the shift fork is usually obtained through a sensor. The sensor value can be positive or negative, with the sign indicating whether it is to the right or left of the shift fork, and the magnitude indicating the distance from the middle position.

[0004] During the operation of automatic transmission vehicles, when shifting the shift fork back to neutral or engaging the target gear, delays or repeated attempts to shift to neutral often occur. If the automatic transmission cannot quickly and accurately grasp the neutral shift status, it cannot complete the shift fork return to neutral or engage the target gear as expected, thus affecting deceleration and stopping performance or the vehicle's rapid power response. In severe cases, it can even affect the overall functionality of the vehicle, posing safety risks or consequences to the vehicle's occupants, surrounding personnel, and the environment. Furthermore, repeated attempts to shift to neutral when the target gear fails not only cause impacts, jerking, and noise from the shift forks, but also increase fuel consumption, severely impacting vehicle economy. To solve these problems in dual-clutch automatic transmissions, a method for diagnosing shift fork return-to-neutral failures is needed. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for diagnosing the failure of the shift fork in a dual-clutch automatic transmission to return to neutral. This method can diagnose the failure of the shift fork to return to neutral in real time, allowing the transmission to receive return status information in a timely manner and make corresponding controls. It effectively solves the problem of slow vehicle power response caused by delayed or repeated return to neutral, and effectively improves the power, economy and comfort of automatic transmission vehicles.

[0006] The objective of this invention is achieved through the following solution: a method for diagnosing the failure of a dual-clutch automatic transmission shift fork to return to neutral, specifically comprising the following steps:

[0007] 1) Set the first position threshold, second position threshold, and third position threshold of the gear shift fork, as well as the first return time threshold and the second return time threshold of the gear shift fork;

[0008] 2) The transmission controller sequentially checks whether the absolute value of the actual position of the shift fork containing the target gear is greater than or equal to the first position threshold, whether the shift fork containing the target gear can move, and whether the activated shift fork is the shift fork containing the target gear. If all three conditions are met, it then checks whether the shift fork control state is either the target gear in neutral or the target gear in gear.

[0009] 3) If the target gear shift fork is in neutral control mode, determine whether the target gear shift fork has failed to return to neutral by following these steps:

[0010] 3-1) Timing is performed for the target gear returning to neutral;

[0011] 3-2) Control the shift fork of the target gear to return to neutral;

[0012] 3-3) Compare the absolute value of the actual position of the shift fork containing the target gear with the first position threshold. If the absolute value of the actual position of the shift fork containing the target gear is less than the first position threshold, the determination ends. If the absolute value of the actual position of the shift fork containing the target gear is greater than or equal to the first position threshold, compare the duration of the target gear return state with the first return time threshold. If the duration of the target gear return state is greater than the first return time threshold, the shift fork fails to return to the target gear.

[0013] 4) If the target gear shift fork is in the gear engagement control state, determine whether the shift fork failed to return to neutral by following these steps:

[0014] 4-1) The fork movement action sub-state enters the return state, and the return state sub-action is timed;

[0015] 4-2) Control the shift fork of the target gear to return to neutral;

[0016] 4-3) Compare the absolute value of the actual position of the shift fork containing the target gear with the third position threshold. If the absolute value of the actual position of the shift fork containing the target gear is less than or equal to the third position threshold, the judgment ends. If the absolute value of the actual position of the shift fork containing the target gear is greater than the third position threshold, compare the timer of the return motion state with the second return time threshold. If the timer of the return motion state is greater than the second return time threshold, the shift fork fails to return to the target gear.

[0017] Preferably, when the shift fork control state is in the target gear return state, the return control of the shift fork in the target gear position must meet one of the following conditions:

[0018] a. The clutch is in a non-torque shifting state, and the desired gear is neutral;

[0019] b. The clutch is in a non-torque shifting state, and the desired gear is coaxial with the target gear but on a different shift fork;

[0020] c. The clutch is in a non-torque shifting state, and the pre-selected gear is neutral;

[0021] d. The clutch is in a non-torque shifting state, and the pre-selected gear and the target gear are coaxial but on different shift forks.

[0022] Preferably, when the shift fork control state is the target gear engaged, controlling the shift fork to return to neutral requires meeting the following two conditions:

[0023] a. The target gear is at the right end of the shift fork and the actual position of the shift fork where the target gear is located is on the left side of the shift fork; or, the target gear is at the left end of the shift fork and the actual position of the shift fork where the target gear is located is on the right side of the shift fork.

[0024] b. The absolute value of the actual position of the shift fork where the target gear is located is greater than the second position threshold.

[0025] Preferably, whether the shift fork of the target gear can be moved is determined based on the engine status, transmission status, shift fork control status, P and N gear holding conditions, clutch status, actual clutch torque, and actual pressure.

[0026] More preferably, whether the shift fork containing the target gear can be moved is determined according to the following steps:

[0027] A. Set the speed threshold, oil temperature threshold, shutdown time threshold, ignition time threshold, first torque threshold, second torque threshold, and pressure threshold;

[0028] B. Determine whether the engine speed is greater than or equal to the speed threshold and whether there is no engine speed error signal. If both conditions are met, proceed to the next step; otherwise, determine that the shift fork cannot be moved.

[0029] C. Determine whether the shift fork control status is not idle, whether the transmission mode is neither P nor N, whether the transmission oil temperature is lower than the oil temperature threshold or the ignition time is greater than the ignition time threshold when the shutdown time is greater than the shutdown time threshold. If any condition is met, proceed to the next step; otherwise, determine that the shift fork cannot move.

[0030] D. Determine whether the requested torque of the clutch where the shift fork is located is less than or equal to the first torque threshold. If the requested torque of the clutch where the shift fork is located is less than or equal to the first torque threshold, proceed to the next step; otherwise, determine that the shift fork cannot move.

[0031] E. Determine whether the clutch status is torque switching or torque interruption shifting. If the clutch status is not torque switching or torque interruption shifting, proceed directly to the next step. If the clutch status is torque switching, analyze the status and stage of the clutch where the shift fork is located. If the specified conditions are met, proceed to the next step; otherwise, determine that the shift fork cannot move. If the clutch status is torque interruption shifting, analyze the stage and status of the clutch where the shift fork is located. If the specified conditions are met, proceed to the next step; otherwise, determine that the shift fork cannot move.

[0032] F. Sequentially determine whether the transmission does not meet the pre-engagement holding conditions of P or N gear, whether the actual torque of the clutch where the shift fork is located is less than or equal to the second torque threshold, and whether the actual pressure of the clutch where the shift fork is located is less than or equal to the pressure threshold. If all conditions are met, the shift fork is determined to be movable; otherwise, the shift fork is determined to be immovable.

[0033] In a further preferred embodiment, when the clutch is in torque shifting mode, step F is performed if the following two conditions are met in sequence:

[0034] a. The clutch containing the shift fork is a disengagement clutch;

[0035] b. The clutch where the shift fork is located is in the recovery phase or completion phase of torque shifting.

[0036] In a further preferred embodiment, when the clutch is in a torque interruption shift state, step F is performed if the following two conditions are met in sequence:

[0037] a. The clutch where the shift fork is located is in the engagement or recovery phase of torque interruption shifting;

[0038] b. The clutch where the shift fork is located is the idle clutch.

[0039] This invention, during the operation of a dual-clutch automatic transmission, collects real-time operating signals from the engine, clutch, transmission, and shift forks to monitor the return-to-neutral process of each shift fork in real time. Based on the expected gear, pre-selected gear, and shift fork position relationship, as well as the relationship between the target shift fork position and the actual shift fork position, the invention monitors the return-to-neutral process of the shift fork in two main aspects: return-to-neutral and target gear engagement. It also promptly diagnoses failures in the return-to-neutral process, facilitating smooth shift fork return-to-neutral engagement, improving the deceleration and stopping performance and power response of automatic transmission vehicles, reducing shift fork jerking and noise, lowering fuel consumption, improving vehicle economy, and enabling after-sales personnel to quickly pinpoint the cause of problems during vehicle maintenance.

[0040] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0041] Figure 1 This is a flowchart of the present invention;

[0042] Figure 2 This is a flowchart illustrating the process of determining the movement of the shift fork in this invention. Detailed Implementation

[0043] A method for diagnosing a failure of a dual-clutch automatic transmission shift fork to return to neutral includes the following steps:

[0044] 1) Set the first position threshold, second position threshold, and third position threshold of the shift fork, as well as the first return time threshold and second return time threshold of the shift fork; collect and process various signals and information from the engine, clutch, transmission, and shift fork in real time; the first position threshold, second position threshold, third position threshold, and the first return time threshold and second return time threshold of the shift fork are determined through calibration tests;

[0045] 2) The transmission controller sequentially checks whether the absolute value of the actual position of the shift fork containing the target gear is greater than or equal to the first position threshold, whether the shift fork containing the target gear can move, and whether the activated shift fork is the shift fork containing the target gear. If all three conditions are met, it then checks whether the shift fork control state is either the target gear in neutral or the target gear in gear.

[0046] 3) If the target gear shift fork is in neutral control mode, determine whether the target gear shift fork has failed to return to neutral by following these steps:

[0047] 3-1) Timing is performed for the target gear returning to neutral;

[0048] 3-2) Control the shift fork of the target gear to return to neutral:

[0049] When the shift fork control state is in the target gear return-to-neutral position, one of the following conditions must be met to perform return-to-neutral control on the shift fork containing the target gear:

[0050] a. The clutch is in a non-torque shifting state, and the desired gear is neutral;

[0051] b. The clutch is in a non-torque shifting state, and the desired gear is coaxial with the target gear but on a different shift fork;

[0052] c. The clutch is in a non-torque shifting state, and the pre-selected gear is neutral;

[0053] d. The clutch is in a non-torque shifting state, and the pre-selected gear and the target gear are coaxial but on different shift forks.

[0054] 3-3) Compare the absolute value of the actual position of the shift fork containing the target gear with the first position threshold. If the absolute value of the actual position of the shift fork containing the target gear is less than the first position threshold, the determination ends. If the absolute value of the actual position of the shift fork containing the target gear is greater than or equal to the first position threshold, compare the duration of the target gear return state with the first return time threshold. If the duration of the target gear return state is greater than the first return time threshold, the shift fork fails to return to the target gear.

[0055] 4) If the target gear shift fork is in the gear engagement control state, determine whether the shift fork failed to return to neutral by following these steps:

[0056] 4-1) The fork movement action sub-state enters the return state, and the return state sub-action is timed;

[0057] For the control fork to return to its neutral position, the following two conditions must be met:

[0058] a. The target gear is at the right end of the shift fork and the actual position of the shift fork where the target gear is located is on the left side of the shift fork; or, the target gear is at the left end of the shift fork and the actual position of the shift fork where the target gear is located is on the right side of the shift fork.

[0059] b. The absolute value of the actual position of the shift fork where the target gear is located is greater than the second position threshold.

[0060] 4-2) Control the shift fork of the target gear to return to neutral;

[0061] 4-3) Compare the absolute value of the actual position of the shift fork containing the target gear with the third position threshold. If the absolute value of the actual position of the shift fork containing the target gear is less than or equal to the third position threshold, the judgment ends. If the absolute value of the actual position of the shift fork containing the target gear is greater than the third position threshold, compare the timer of the return motion state with the second return time threshold. If the timer of the return motion state is greater than the second return time threshold, the shift fork fails to return to the target gear.

[0062] like Figure 1 As shown, the specific steps for diagnosing the failure of the shift fork in a dual-clutch automatic transmission to return to neutral are as follows:

[0063] S1, if the absolute value of the actual position of the shift fork where the target gear is located is greater than or equal to the first position threshold, then execute S2; otherwise, end.

[0064] Wherein, the first position threshold is the maximum boundary value of the gap range. In this embodiment, the first position threshold is set to 150 mm.

[0065] S2, if the shift fork of the target gear can be moved, then execute S3; otherwise, end.

[0066] S3: If the activated shift fork is the shift fork of the target gear, then SA4 and SB4 are executed simultaneously; otherwise, the process ends.

[0067] SA4: If the shift fork control status is the target gear return to neutral, then execute SA5; otherwise, end.

[0068] SA5 starts timing the return to neutral in the target gear, and then executes SA6.

[0069] SA6: If the clutch is in a non-torque shifting state, SA7, SA8, SA9 and SA10 will be executed simultaneously; otherwise, the process ends.

[0070] SA7: If the desired gear is neutral, then execute SA11; otherwise, end.

[0071] SA8: If the desired gear is coaxial with the target gear but not on the same shift fork, then execute SA11; otherwise, end.

[0072] SA9: If the pre-selected gear is neutral, then execute SA11; otherwise, end.

[0073] SA10: If the pre-selected gear and the target gear are coaxial but not on the same shift fork, then execute SA11; otherwise, end.

[0074] SA11 controls the shift fork in the target gear to return to neutral, then executes SA12.

[0075] SA12: If the absolute value of the actual position of the shift fork where the target gear is located is greater than or equal to the first position threshold, then execute SA13; otherwise, end.

[0076] SA13: If the duration of the target gear return state is greater than the first return time threshold (in this embodiment, the first return time threshold is set to 3000 milliseconds), then execute S15; otherwise, return to SA5 to continue execution.

[0077] SB4: If the shift fork control status is the target gear engaged, then SB5 and SB7 are executed simultaneously; otherwise, the process ends.

[0078] SB5: If the target gear is at the right end of the shift fork, then execute SB6; otherwise, end.

[0079] SB6: If the target gear is actually located on the left side of the shift fork, then execute SB9; otherwise, end.

[0080] SB7: If the target gear is at the left end of the shift fork, then execute SB8; otherwise, end.

[0081] SB8: If the target gear is actually located on the right side of the shift fork, then execute SB9; otherwise, end.

[0082] SB9: If the absolute value of the actual position of the shift fork where the target gear is located is greater than the second position threshold (in this embodiment, the second position threshold is set to 500 mm), then execute SB10; otherwise, end.

[0083] SB10, the fork movement action sub-state enters the return-to-empty state, and then SB11 is executed.

[0084] SB11, start timing the return to empty state, then execute SB12.

[0085] SB12, return the shift fork containing the target gear to neutral, then execute SB13.

[0086] SB13: If the absolute value of the actual position of the shift fork where the target gear is located is greater than the third position threshold (in this embodiment, the third position threshold is set to 70 mm), then execute SB14; otherwise, end.

[0087] SB14: If the timeout period for the return-to-empty state is greater than the second time threshold (in this embodiment, the second time threshold is calculated from the automatic transmission oil temperature and the number of secondary gear shifts by looking up a table), then execute S15; otherwise, return to step SB11 to continue execution.

[0088] S15 indicates that the shift fork failed to return to neutral.

[0089] Whether the shift fork of the target gear can move is determined based on the engine status, transmission status, shift fork control status, P and N gear holding conditions, clutch status, actual clutch torque, and actual clutch pressure. The determination of whether the shift fork of the target gear can move is based on the following steps:

[0090] A. Set speed threshold, oil temperature threshold, shutdown time threshold, ignition time threshold, first torque threshold, second torque threshold, and pressure threshold; the speed threshold, oil temperature threshold, shutdown time threshold, ignition time threshold, first torque threshold, second torque threshold, and pressure threshold are determined through calibration tests;

[0091] B. Determine whether the engine speed is greater than or equal to the speed threshold and whether there is no engine speed error signal. If both conditions are met, proceed to the next step; otherwise, determine that the shift fork cannot be moved.

[0092] C. Determine whether the shift fork control status is not idle, whether the transmission mode is neither P nor N, whether the transmission oil temperature is lower than the oil temperature threshold or the ignition time is greater than the ignition time threshold when the shutdown time is greater than the shutdown time threshold. If any condition is met, proceed to the next step; otherwise, determine that the shift fork cannot move.

[0093] D. Determine whether the requested torque of the clutch where the shift fork is located is less than or equal to the first torque threshold. If the requested torque of the clutch where the shift fork is located is less than or equal to the first torque threshold, proceed to the next step; otherwise, determine that the shift fork cannot move.

[0094] E. Determine whether the clutch status is torque switching or torque interruption shifting. If the clutch status is not torque switching or torque interruption shifting, proceed directly to the next step. If the clutch status is torque switching, analyze the status and stage of the clutch where the shift fork is located. If the specified conditions are met, proceed to the next step; otherwise, determine that the shift fork cannot move. If the clutch status is torque interruption shifting, analyze the stage and status of the clutch where the shift fork is located. If the specified conditions are met, proceed to the next step; otherwise, determine that the shift fork cannot move.

[0095] When the clutch is in torque shift mode, step F is performed if the following two conditions are met in sequence:

[0096] a. The clutch containing the shift fork is a disengagement clutch;

[0097] b. The clutch where the shift fork is located is in the recovery phase or completion phase of torque shifting.

[0098] When the clutch is in a torque interruption shift state, step F is performed if the following two conditions are met in sequence:

[0099] a. The clutch where the shift fork is located is in the engagement or recovery phase of torque interruption shifting;

[0100] b. The clutch where the shift fork is located is the idle clutch.

[0101] F. Sequentially determine whether the transmission does not meet the pre-engagement holding conditions of P or N gear, whether the actual torque of the clutch where the shift fork is located is less than or equal to the second torque threshold, and whether the actual pressure of the clutch where the shift fork is located is less than or equal to the pressure threshold. If all conditions are met, the shift fork is determined to be movable; otherwise, the shift fork is determined to be immovable.

[0102] like Figure 2 As shown, the specific steps for determining whether the shift fork can move are as follows:

[0103] S201, If ​​the engine speed is greater than or equal to the speed threshold (in this embodiment, the speed threshold is set to 500 rpm), then execute S202; otherwise execute S217.

[0104] S202, if the engine speed error signal is not an error, then execute S203, S204 and S205 simultaneously; otherwise execute S217.

[0105] S203, if the fork control state is not equal to the idle state, then execute S206; otherwise execute S217.

[0106] S204. If the transmission mode is neither P nor N, then execute S206; otherwise, execute S217.

[0107] S205: If the transmission oil temperature is lower than the oil temperature threshold or the shutdown time is greater than the shutdown time threshold, and the ignition duration is greater than the threshold, then execute S206; otherwise, execute S217. In this embodiment, the oil temperature threshold is set to -10℃, the shutdown time threshold is set to 480 minutes, and the ignition time threshold is set to 1 minute.

[0108] S206, if the requested torque of the clutch where the shift fork is located is less than or equal to the first torque threshold, then execute S207; otherwise execute S217. The first torque threshold is a constant value near the torque at the half-engagement point of the clutch where the shift fork is located.

[0109] S207 If the clutch status is torque switching or torque interruption shifting, then execute S208; otherwise execute S213.

[0110] S208 If the clutch status is torque shifting, then execute S209; otherwise execute S211.

[0111] S209, if the clutch where the shift fork is located is a disengaged clutch, then execute S210; otherwise execute S217.

[0112] S210: If the process is in the recovery or completion phase of torque shifting, then execute S213; otherwise, execute S217.

[0113] S211 If it is in the engagement or recovery phase of torque interruption shifting, then execute S212; otherwise execute S213.

[0114] S212, if the clutch where the shift fork is located is an idle clutch, then execute S213; otherwise execute S217.

[0115] S213 If the PN gear pre-engagement and holding gear conditions are not met, then execute S214; otherwise execute S217.

[0116] S214, if the actual torque of the clutch where the shift fork is located is less than or equal to the second torque threshold, then execute S215; otherwise, execute S217. The second torque threshold is a constant value near the torque at the half-engagement point of the clutch where the shift fork is located.

[0117] S215, if the actual pressure of the clutch where the shift fork is located is less than or equal to the pressure threshold, then execute S216; otherwise, execute S217. The pressure threshold is calculated from the pressure at the half-engagement point of the clutch where the shift fork is located and the correction value obtained by looking up the automatic transmission oil temperature from a table.

[0118] S216, determine that the fork can move, then end.

[0119] S217, determine that the fork cannot be moved, then end.

[0120] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for diagnosing the failure of a dual-clutch automatic transmission shift fork to return to neutral, characterized in that, Specifically, the following steps are included: 1) Set the first position threshold, second position threshold, and third position threshold of the gear shift fork, as well as the first return time threshold and the second return time threshold of the gear shift fork; 2) The transmission controller sequentially checks whether the absolute value of the actual position of the shift fork containing the target gear is greater than or equal to the first position threshold, whether the shift fork containing the target gear can move, and whether the activated shift fork is the shift fork containing the target gear. If all three conditions are met, it then checks whether the shift fork control state is either the target gear in neutral or the target gear in gear. 3) If the target gear shift fork is in neutral control mode, determine whether the target gear shift fork has failed to return to neutral by following these steps: 3-1) Timing is performed for the target gear returning to neutral; 3-2) Control the shift fork of the target gear to return to neutral; 3-3) Compare the absolute value of the actual position of the shift fork containing the target gear with the first position threshold. If the absolute value of the actual position of the shift fork containing the target gear is less than the first position threshold, the determination ends. If the absolute value of the actual position of the shift fork containing the target gear is greater than or equal to the first position threshold, compare the duration of the target gear return state with the first return time threshold. If the duration of the target gear return state is greater than the first return time threshold, the shift fork fails to return to the target gear. 4) If the target gear shift fork is in the gear engagement control state, determine whether the shift fork failed to return to neutral by following these steps: 4-1) The fork movement action sub-state enters the return state, and the return state sub-action is timed; 4-2) Control the shift fork of the target gear to return to neutral; 4-3) Compare the absolute value of the actual position of the shift fork containing the target gear with the third position threshold. If the absolute value of the actual position of the shift fork containing the target gear is less than or equal to the third position threshold, the judgment ends. If the absolute value of the actual position of the shift fork containing the target gear is greater than the third position threshold, compare the timer of the return motion state with the second return time threshold. If the timer of the return motion state is greater than the second return time threshold, the shift fork fails to return to the target gear.

2. The method for diagnosing the failure of a dual-clutch automatic transmission shift fork to return to neutral as described in claim 1, characterized in that, When the shift fork control state is in the target gear return-to-neutral position, one of the following conditions must be met to perform return-to-neutral control on the shift fork containing the target gear: a. The clutch is in a non-torque shifting state, and the desired gear is neutral; b. The clutch is in a non-torque shifting state, and the desired gear is coaxial with the target gear but on a different shift fork; c. The clutch is in a non-torque shifting state, and the pre-selected gear is neutral; d. The clutch is in a non-torque shifting state, and the pre-selected gear and the target gear are coaxial but on different shift forks.

3. The method for diagnosing the failure of a dual-clutch automatic transmission shift fork to return to neutral as described in claim 1, characterized in that, When the shift fork control state is in the target gear position, the following two conditions must be met to control the shift fork to return to neutral: a. The target gear is at the right end of the shift fork and the actual position of the shift fork where the target gear is located is on the left side of the shift fork; or, the target gear is at the left end of the shift fork and the actual position of the shift fork where the target gear is located is on the right side of the shift fork. b. The absolute value of the actual position of the shift fork where the target gear is located is greater than the second position threshold.

4. The method for diagnosing the failure of a dual-clutch automatic transmission shift fork to return to neutral as described in claim 1, characterized in that, Whether the shift fork of the target gear can be moved is determined based on the engine status, transmission status, shift fork control status, P and N gear holding conditions, clutch status, actual clutch torque, and actual pressure.

5. The method for diagnosing the failure of a dual-clutch automatic transmission shift fork to return to neutral as described in claim 4, characterized in that, Whether the shift fork containing the target gear can be moved is determined by the following steps: A. Set the speed threshold, oil temperature threshold, shutdown time threshold, ignition time threshold, first torque threshold, second torque threshold, and pressure threshold; B. Determine whether the engine speed is greater than or equal to the speed threshold and whether there is no engine speed error signal. If both conditions are met, proceed to the next step; otherwise, determine that the shift fork cannot be moved. C. Determine whether the shift fork control status is not idle, whether the transmission mode is neither P nor N, whether the transmission oil temperature is lower than the oil temperature threshold or the ignition time is greater than the ignition time threshold when the shutdown time is greater than the shutdown time threshold. If any condition is met, proceed to the next step; otherwise, determine that the shift fork cannot move. D. Determine whether the requested torque of the clutch where the shift fork is located is less than or equal to the first torque threshold. If the requested torque of the clutch where the shift fork is located is less than or equal to the first torque threshold, proceed to the next step; otherwise, determine that the shift fork cannot move. E. Determine whether the clutch status is torque switching or torque interruption shifting. If the clutch status is not torque switching or torque interruption shifting, proceed directly to the next step. If the clutch status is torque switching, analyze the status and stage of the clutch where the shift fork is located. If the specified conditions are met, proceed to the next step; otherwise, determine that the shift fork cannot move. If the clutch status is torque interruption shifting, analyze the stage and status of the clutch where the shift fork is located. If the specified conditions are met, proceed to the next step; otherwise, determine that the shift fork cannot move. F. Sequentially determine whether the transmission does not meet the pre-engagement holding conditions of P or N gear, whether the actual torque of the clutch where the shift fork is located is less than or equal to the second torque threshold, and whether the actual pressure of the clutch where the shift fork is located is less than or equal to the pressure threshold. If all conditions are met, the shift fork is determined to be movable; otherwise, the shift fork is determined to be immovable.

6. The method for diagnosing the failure of a dual-clutch automatic transmission shift fork to return to neutral as described in claim 5, characterized in that, When the clutch is in torque shift mode, step F is performed if the following two conditions are met in sequence: a. The clutch containing the shift fork is a disengagement clutch; b. The clutch where the shift fork is located is in the recovery phase or completion phase of torque shifting.

7. The method for diagnosing the failure of a dual-clutch automatic transmission shift fork to return to neutral as described in claim 5, characterized in that, When the clutch is in a torque interruption shift state, step F is performed if the following two conditions are met in sequence: a. The clutch where the shift fork is located is in the engagement or recovery phase of torque interruption shifting; b. The clutch where the shift fork is located is the idle clutch.

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