AMT shifting control method in electric truck combined braking constant speed downhill process

Abstract

The present application belongs to the technical field of new energy vehicle transmission shift control, and discloses an AMT shift control method in the process of combined braking constant speed downhill of an electric truck, which comprises judging whether the vehicle enters the combined constant speed control state, and if the vehicle enters the combined constant speed control state, obtaining the AMT optimal gear according to the current vehicle speed and the required regenerative braking torque based on the preset AMT shift rule. The method breaks through the limitation of traditional methods which only consider motor efficiency, synchronously covers the transmission system and the battery charging and discharging efficiency, and innovatively adopts a braking torque cooperative change mechanism. In the shift process, the preset AMT shift rule is used to coordinate the braking force distribution of the motor and the hydraulic retarder, eliminate the vehicle speed fluctuation caused by power interruption, overcome the energy loss and speed control instability risk caused by frequent gear shifting, and ensure the driving comfort through shift hysteresis control and the lowest vehicle speed threshold, forming a safe and energy-saving closed-loop control.

Description

Technical Field

[0001] This invention belongs to the field of new energy vehicle transmission shift control technology, specifically an AMT shift control method for electric trucks during constant speed downhill combined braking. Background Technology

[0002] Driven by the global energy structure transformation, the transportation industry is undergoing an electrification revolution. As a core transport capacity in the logistics system, the electrification of heavy-duty trucks is of strategic significance for achieving carbon reduction across the entire industry. In the current complex geographical environment, mountainous roads account for over 30%, and the safety control of long downhill sections has become a key technological bottleneck restricting the promotion of new energy heavy-duty trucks. These road sections pose severe challenges to vehicle braking systems: traditional friction braking is prone to failure due to heat fade under long downhill conditions, while the regenerative braking system unique to new energy vehicles can achieve energy recovery, but its effectiveness is limited by the overall efficiency optimization of the powertrain system.

[0003] Current research focuses on the coordinated control of regenerative braking and mechanical braking, with the shift pattern design of automated mechanical transmissions (AMTs) being a core component. Existing AMT regenerative braking shift strategies are primarily based on the principle of prioritizing motor efficiency. This involves optimizing the motor's operating point to ensure it operates within its high-efficiency range, while employing a braking demand decomposition model to allocate the ratio of regenerative braking to mechanical braking. The regenerative torque of the motor is controlled by adjusting the gear position. Shift point decisions rely on a fixed threshold strategy, combining vehicle speed and gradient parameters to determine the shift timing, but this approach does not adequately consider the dynamic changes in the transmission efficiency within the gearbox. In the field of constant-speed downhill control, existing technologies often employ proportional-integral-derivative (PID) closed-loop control algorithms to adjust braking pressure and regenerative braking power. However, the shifting process is treated as an independent event, lacking a coordinated mechanism with the braking system.

[0004] However, existing technologies have key flaws: focusing solely on motor efficiency while neglecting differences in transmission efficiency leads to overall energy recovery efficiency losses; the switching between regenerative braking and mechanical braking during gear shifts creates a power vacuum period, which can easily cause speed fluctuations on long downhill sections; and the constant-speed downhill control lacks a joint optimization model for gear selection and braking power distribution, resulting in frequent gear shifts or brake overheating risks when dealing with changes in gradient. These technical shortcomings are particularly pronounced in complex mountainous environments, hindering the large-scale application of new energy heavy-duty trucks in long-haul logistics. Summary of the Invention

[0005] This invention provides an AMT shifting control method for electric trucks during constant-speed downhill combined braking, which solves the problem of frequent shifting or brake overheating risks when the system responds to changes in gradient.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The AMT shifting control method for electric trucks during constant-speed downhill braking includes:

[0008] Determine whether the vehicle has entered a combined constant speed control state;

[0009] If the vehicle enters the joint constant speed control state, the optimal AMT gear is obtained based on the preset AMT shift rules and the regenerative braking torque required according to the current vehicle speed and demand.

[0010] The system determines whether to shift gears by comparing the current AMT gear. If the current AMT gear is the optimal AMT gear, the current AMT gear is maintained; otherwise, the gear is shifted to the optimal AMT gear.

[0011] Preferably, the method for obtaining the preset AMT shift pattern is as follows:

[0012] Obtain the transmission efficiency of each gear in the AMT;

[0013] Based on the transmission efficiency of each gear in the AMT, with the goal of maximizing the recovery of braking energy per unit time, the optimal gear of the AMT under different vehicle speeds and required regenerative braking torque is solved. The initial AMT shifting law is obtained based on the optimal gear of the AMT, and the initial AMT shifting law is corrected to obtain the AMT shifting law.

[0014] Preferably, with the goal of maximizing regenerative braking energy recovery per unit time, the optimal gear ratio of the AMT is obtained under different vehicle speeds and required regenerative braking torques. Then, the optimal AMT gear is obtained based on the optimal gear ratio. The method for solving the optimal gear ratio of the AMT under different vehicle speeds and required regenerative braking torques is as follows:

[0015]

[0016] In the formula, For braking energy recovery per unit time, For the motor output torque, This refers to the motor speed. For motor efficiency, Improve battery charging efficiency. For regenerative braking torque, For the efficiency of the transmission system, This is the optimal gear ratio for the AMT (Automated Manual Transmission). The optimal gear for the AMT is then determined based on this optimal gear ratio. Main reducer transmission ratio, To maximize braking energy recovery per unit time.

[0017] Preferably, the step of correcting the initial AMT shift pattern specifically involves:

[0018] The initial AMT shifting pattern is corrected based on the relationship between vehicle speed and the minimum vehicle speed under joint constant speed control.

[0019] The initial AMT shifting pattern is corrected based on the vehicle speed fluctuation threshold;

[0020] Perform shift hysteresis control to correct the initial AMT shift pattern.

[0021] Preferably, the initial AMT shift pattern is corrected based on the relationship between vehicle speed and the minimum vehicle speed of the joint constant speed control, specifically as follows:

[0022]

[0023] In the formula, Current vehicle speed The minimum speed for combined constant speed control.

[0024] Preferably, the correction of the initial AMT shift pattern based on the vehicle speed fluctuation threshold is specifically as follows:

[0025] The speed fluctuation threshold is 2 km / h. When the speed fluctuation is within 2 km / h, the gear will not be adjusted.

[0026] Preferably, the shift hysteresis control is specifically as follows:

[0027]

[0028] In the formula, and These are the regenerative braking torque threshold values ​​for upshifting and downshifting, respectively. For the shift hysteresis threshold, This is regenerative braking torque.

[0029] Preferably, the steps for obtaining the transmission efficiency of each gear in the AMT are as follows:

[0030] The torque and speed data of the input / output shafts are obtained through AMT bench testing, and the input power and output power are obtained, thereby obtaining the transmission efficiency of each gear of the AMT.

[0031] Preferably, the steps for shifting to the optimal gear in the AMT are as follows:

[0032] The AMT controller takes over control of the drive motor from the vehicle controller, controls the drive motor torque to drop to 0, controls the shift actuator to shift the transmission gear to neutral, controls the drive motor speed to keep the input and output speeds of the shift engagement sleeve synchronized, controls the shift actuator to shift the transmission gear from neutral to the optimal AMT gear, controls the drive motor torque to rise to the target torque, and returns motor control to the vehicle controller, thus ending the shift.

[0033] Preferably, the torque change rates for controlling the drive motor torque to drop to 0 and controlling the drive motor torque to rise to the target torque are set to -3.5 kN·m / s and 4.5 kN·m / s, respectively.

[0034] Compared with existing technologies, this invention has the following advantages: This invention provides an AMT shifting control method for electric trucks during combined braking and constant speed downhill driving. By dynamically matching the optimal gear, it significantly improves braking energy recovery efficiency, breaking through the limitations of traditional methods that only consider motor efficiency. It simultaneously covers the transmission system and battery charging and discharging efficiency. Furthermore, it innovatively adopts a braking torque coordinated change mechanism, coordinating the braking force distribution between the motor and the hydraulic retarder during gear shifting according to a preset AMT shifting pattern, eliminating speed fluctuations caused by power interruption. This dual optimization enables the vehicle to achieve both energy saving and driving stability during long downhill combined constant speed control. It overcomes the energy loss and speed control instability risks caused by frequent gear shifting, while ensuring driving comfort through shift hysteresis control and a minimum speed threshold, forming a safe and energy-saving closed-loop control.

[0035] The triple correction mechanism synergistically enhances the quality of constant-speed downhill control. The vehicle speed fluctuation threshold is locked to maintain the original gear when the vehicle speed is below the safety threshold, avoiding ineffective shifting and energy loss in inefficient operating conditions and ensuring the stability of basic control. The vehicle speed fluctuation tolerance control freezes gear adjustment with a fluctuation boundary of ±2km / h, effectively filtering out erroneous shifting caused by sensor noise and road disturbances. The shift hysteresis control establishes a buffer zone when the energy recovery benefits of the optimal and suboptimal gears are close by setting up / down torque thresholds and hysteresis intervals. By reducing the frequency of shifting, it reduces energy loss caused by power interruption, achieving a balance between economy and comfort. These correction strategies form a progressive optimization chain: the vehicle speed fluctuation threshold establishes a safety baseline, the vehicle speed fluctuation tolerance improves the system's anti-interference capability, and the hysteresis control achieves a fine balance between energy saving and smoothness. In long downhill verification, a dual breakthrough was achieved in suppressing vehicle speed fluctuations and increasing energy recovery gains. Attached Figure Description

[0036] Figure 1 This is a flowchart of the AMT shift control method for electric freight trucks during constant speed downhill braking in accordance with the present invention.

[0037] Figure 2 This is a transmission efficiency diagram of a six-speed AMT according to an embodiment of the present invention;

[0038] Figure 3 This is an image showing the optimization results of the AMT shifting pattern in an embodiment of the present invention. The image on the right is a magnified view of the area within the red box in the optimization results, where the values ​​represent the unit time.

[0039] Figure 4 This is a diagram showing the correction results of the AMT shifting pattern in an embodiment of the present invention;

[0040] Figure 5 This is a comparison diagram of the shift control results during the combined constant speed downhill process according to an embodiment of the present invention. a is a comparison of vehicle speed under no shift, normal shift, and coordinated shift control proposed in the present invention. b is a comparison of braking torque under normal shift and coordinated shift control proposed in the present invention. c is the motor efficiency and energy recovery before and after shifting. d is the motor operating point before and after shifting. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0042] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0043] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0044] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0045] like Figure 1 As shown, this invention provides an AMT (Automated Manual Transmission) shifting control method for an electric truck during a constant-speed downhill process with combined braking, comprising:

[0046] The AMT shifting control method for electric trucks during constant-speed downhill braking includes:

[0047] S1: Determine whether the vehicle has entered the joint constant speed control state;

[0048] S2: If the vehicle enters the combined constant speed control state, the optimal AMT gear is obtained based on the preset AMT shift rules and the current vehicle speed and required regenerative braking torque.

[0049] S3: Determine whether to perform a gear shift by comparing the current AMT gear. If the current AMT gear is the optimal AMT gear, keep the current AMT gear; otherwise, shift to the optimal AMT gear.

[0050] The specific method for obtaining the preset AMT shift pattern is as follows:

[0051] Obtain the transmission efficiency of each gear in the AMT;

[0052] Based on the transmission efficiency of each gear in the AMT, with the goal of maximizing the recovery of braking energy per unit time, the optimal gear of the AMT under different vehicle speeds and required regenerative braking torque is solved. The initial AMT shifting law is obtained based on the optimal gear of the AMT, and the initial AMT shifting law is corrected to obtain the AMT shifting law.

[0053] By dynamically matching the optimal gear, the efficiency of regenerative braking is significantly improved, breaking through the limitations of traditional methods that only consider motor efficiency. It simultaneously covers the efficiency of the transmission system and battery charging and discharging. At the same time, it innovatively adopts a braking torque coordinated change mechanism, which coordinates the distribution of braking force between the motor and the hydraulic retarder during gear shifts according to the preset AMT shift pattern, eliminating speed fluctuations caused by power interruption. This dual optimization enables the vehicle to achieve both energy saving and driving stability when using combined constant speed control on long downhill slopes. It overcomes the energy loss and speed control instability risks caused by frequent gear shifts, while ensuring driving comfort through shift hysteresis control and minimum vehicle speed threshold, forming a safe and energy-saving closed-loop control.

[0054] The detailed steps are as follows:

[0055] Determine whether the vehicle has entered a combined constant speed control state;

[0056] If the vehicle enters the combined constant speed control state, based on the AMT shifting rules, the optimal AMT gear is obtained according to the current vehicle speed and the required regenerative braking torque. By comparing the current AMT gear, it is determined whether to perform a shift. If the current AMT gear is the optimal AMT gear, the current AMT gear is maintained; otherwise, the gear is shifted to the optimal AMT gear.

[0057] If a gear shift is to be performed, firstly, the AMT controller takes over control of the drive motor from the vehicle controller and reduces the drive motor torque to 0; secondly, it controls the shift actuator to shift the transmission gear to neutral; thirdly, it controls the drive motor speed to keep the input and output speeds of the shift engagement sleeve synchronized; then, it controls the shift actuator to shift the transmission gear from neutral to the optimal AMT gear; finally, it controls the drive motor torque to increase to the target torque and returns control of the drive motor to the vehicle controller, thus ending the gear shift.

[0058] The torque and speed data of the input / output shafts are obtained through AMT bench tests, and the input power and output power are obtained, thereby obtaining the transmission efficiency of each gear of the AMT.

[0059] Based on the transmission efficiency of each gear in the AMT, with the goal of maximizing the recovery of braking energy per unit time, the optimal gear of the AMT under different vehicle speeds and required regenerative braking torque is solved, and the optimal gear of the AMT is corrected according to the principle of reducing the frequency of gear shifting, and finally the AMT shifting law is obtained.

[0060] Unlike existing AMT shift control methods that only consider motor efficiency when designing AMT shift rules, the steps for obtaining AMT shift rules are as follows:

[0061] First, considering the impact of the difference in transmission efficiency under different AMT gears on the energy recovery effect, with the goal of maximizing braking energy recovery, the vehicle speed and the required regenerative braking torque at the wheel ends are used as inputs, and an exhaustive search method is used to solve for the optimal AMT gear.

[0062] Then, considering the impact of frequent gear shifts on the combined constant speed control effect and energy loss, the optimized AMT gear shifting pattern is modified.

[0063] Unlike existing AMT shift control methods that aim to shorten shift time, this method uses the maximum allowable impact to constrain the torque change rate during the unloading and recovery phases of the drive motor to ensure shift quality. It aims to minimize the impact of power interruption during shifting on the combined constant speed control effect by coordinating braking torque control. It also limits the torque change rate during the unloading and recovery phases of the drive motor by combining the dynamic characteristics of the hydraulic retarder's charging and discharging fluid.

[0064] Another embodiment of the present invention provides an AMT shifting control method during a constant-speed downhill process of combined braking for an electric truck, based on bench test results of the transmission efficiency of a certain six-speed AMT, such as... Figure 2 As shown, there are significant differences in transmission efficiency under different gears, torques, and speeds. Figure 2In the diagram, a to f correspond to gears 1 through 6, respectively. During regenerative braking, the higher the efficiency of the transmission system, the less energy is lost during energy transmission due to power losses caused by bearings and gear meshing. Therefore, the overall efficiency of the regenerative braking system should be considered when formulating AMT shifting rules.

[0065] First, taking vehicle speed and wheel-end regenerative braking torque as inputs, an exhaustive search method is used to find the optimal gear for AMT under different conditions, with the goal of maximizing braking energy recovery per unit time, as shown in the following formula:

[0066] (1)

[0067] In the formula, For braking energy recovery per unit time, This represents the absolute value of the motor's output torque. This refers to the motor speed. For motor efficiency, Improve battery charging efficiency. For regenerative braking torque, For the efficiency of the transmission system, The optimal gear ratio for AMT (Automated Manual Transmission). Main reducer transmission ratio, To maximize braking energy recovery per unit time.

[0068] AMT gear optimization results, such as Figure 3 As shown in the figure on the right, it is a magnified view of the area within the red box in the optimization results. The values ​​represent the amount of braking energy recovered per unit time in the optimal gear compared to the second-best gear. The figure shows that because the AMT's 6th gear has higher transmission efficiency than other gears, it accounts for the largest proportion of the optimal gears. When a larger regenerative braking torque is required, the motor output torque is lower and the speed is higher when the AMT is in a lower gear, resulting in higher motor efficiency. In this case, the overall efficiency of the regenerative braking system is higher, thus leading to better energy recovery.

[0069] Then, due to the power interruption characteristic of AMT gear shifting, the braking energy during the shifting process cannot be effectively recovered. Therefore, excessively frequent gear shifting during constant speed downhill braking will cause braking energy loss and affect the vehicle's combined constant speed control effect. Therefore, based on the actual operating characteristics of the vehicle, the optimized AMT shifting pattern is modified according to the following principles.

[0070] (1) When the vehicle speed is low, the motor may not be able to achieve regenerative braking, and shifting gears has a very limited effect on improving the energy recovery efficiency. Therefore, if the current vehicle speed is lower than the minimum speed of the combined constant speed control, the AMT will keep the original gear unchanged, as shown in the following formula:

[0071] (2)

[0072] In the formula, Current vehicle speed The minimum speed for combined constant speed control.

[0073] (2) The speed fluctuation threshold during constant speed downhill control is 2 km / h. Figure 3 The speed interval on the horizontal axis is 2 km / h. To avoid unnecessary gear shifting, the number of gear changes within the speed fluctuation threshold range (i.e., the same column of data in the figure) should be minimized as much as possible.

[0074] (3) By Figure 3 As shown in the right-hand figure, at the boundary of the gear optimization results, the difference in braking energy recovered per unit time between the optimal and suboptimal gears is not significant. At this point, the energy gain from gear shifting is minimal, and it may even lead to frequent gear changes, affecting braking comfort and energy recovery efficiency. Therefore, a shift hysteresis loop is added, as shown in the following equation:

[0075] (3)

[0076] In the formula, and These are the regenerative braking torque threshold values ​​for upshifting and downshifting, respectively. This is the shift hysteresis threshold value.

[0077] AMT shift pattern correction results, such as Figure 4 As shown, during combined braking and constant-speed downhill driving, the AMT shifts gears based on the regenerative braking torque and vehicle speed, maintaining the original gear when in the upshift / downshift lag zone. This improves the vehicle's braking energy recovery efficiency, reduces unnecessary gear shifts, and ensures driving comfort.

[0078] In previous AMT shift control strategies, to ensure shift quality, the maximum allowable impact was utilized. The torque change rate during the motor torque unloading and recovery phases is constrained, as shown in equation (4). Meanwhile, to shorten the shift time, the motor is typically controlled to complete torque unloading and recovery at its maximum torque change rate (approximately 7 kN·m / s).

[0079] (4)

[0080] in, For the motor output torque, The optimal gear ratio for AMT (Automated Manual Transmission). Main reducer transmission ratio, For the rate of change of the motor, For time, This is the conversion factor for the rotational mass of a vehicle. For the quality of the car, The transmission efficiency of the transmission system. This represents the maximum shift shock.

[0081] Under constant speed downhill control, if the regenerative braking torque changes too rapidly during gear shifting, the hydraulic retarder's output torque cannot respond and adjust in time, inevitably leading to significant vehicle speed fluctuations. To ensure the effectiveness of combined constant speed control during gear shifting, the rate of motor torque unloading and recovery is appropriately slowed down, allowing the retarder's output torque to compensate for the loss of regenerative braking torque during gear shifting. Based on the dynamic characteristics of the hydraulic retarder's fluid charging and discharging, the torque change rates during the motor torque unloading and recovery phases are set to -3.5 kN·m / s and 4.5 kN·m / s, respectively.

[0082] Finally, to verify the superiority of the invention, the proposed shift control method is compared with that of no shift and normal shift (based on maximum impact). A comparison was made between control methods that limit the rate of change of torque during motor torque unloading and recovery.

[0083] A long downhill road with varying gradient (sinusoidal change, ranging from 4% to 6%) was selected as the verification condition. The target vehicle speed was 40 km / h. After the actual vehicle speed stabilized, AMT shift control was activated at approximately 2 seconds, shifting from 6th gear to the optimal AMT gear—4th gear. The comparison results are as follows. Figure 5 As shown.

[0084] Figure a compares the vehicle speed under no shift, normal shift, and the coordinated shift control proposed in this invention. As shown in the figure, the motor torque is cleared and recovered more quickly under normal shift control, and the retarder output torque cannot respond in time, resulting in uncoordinated torque control and causing large fluctuations in vehicle speed between 2 and 3.2 seconds.

[0085] Figure b compares the braking torque under normal shifting and the coordinated shifting control proposed in this invention. As shown in the figure, during the coordinated shifting control, the rates of change of regenerative braking and retarder braking torque are similar during the motor torque unloading and recovery phases. Although the shifting time is slightly increased, it can better avoid the problem of torque control incoordination, resulting in no significant change in vehicle speed during shifting.

[0086] Figure c shows the motor's working efficiency and braking energy recovery before and after gear shifting. It can be seen that the motor is in a more efficient range after gear shifting, and the motor efficiency is significantly improved. The power interruption during gear shifting causes the initial energy recovery to lag behind. As the braking duration increases, the advantage of braking energy recovery gradually becomes apparent.

[0087] Figure d shows the motor operating point before and after shifting gears. As can be seen from the figure, the motor torque and speed change after shifting gears, and the motor operating point shifts from a lower efficiency region to a higher efficiency region.

[0088] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art, guided by the specification, can make many other modifications without departing from the scope of the claims of the present invention, and all of these modifications are within the scope of protection of the present invention.

Claims

1. An AMT shifting control method for electric freight trucks during constant-speed downhill braking, characterized in that, include: Determine whether the vehicle has entered a combined constant speed control state; If the vehicle enters the joint constant speed control state, the optimal AMT gear is obtained based on the preset AMT shift rules and the regenerative braking torque required according to the current vehicle speed and demand. The system determines whether to shift gears by comparing the current AMT gear. If the current AMT gear is the optimal AMT gear, the current AMT gear is maintained; otherwise, the gear is shifted to the optimal AMT gear. The specific method for obtaining the preset AMT shift pattern is as follows: Obtain the transmission efficiency of each gear in the AMT; Based on the transmission efficiency of each gear in the AMT, with the goal of maximizing the recovery of braking energy per unit time, the optimal gear of the AMT under different vehicle speeds and required regenerative braking torque is solved. The initial AMT shifting rule is obtained based on the optimal gear of the AMT, and the initial AMT shifting rule is corrected to obtain the AMT shifting rule. The method for finding the optimal gear of AMT under different vehicle speeds and regenerative braking torque is as follows: with the goal of maximizing the recovery of braking energy per unit time, obtain the transmission ratio of the optimal gear of AMT under different vehicle speeds and regenerative braking torque, and then obtain the optimal gear of AMT based on the transmission ratio of the optimal gear of AMT. The method for determining the optimal gear ratio of an AMT under different vehicle speeds and required regenerative braking torque is as follows: In the formula, For braking energy recovery per unit time, For the motor output torque, This refers to the motor speed. For motor efficiency, Improve battery charging efficiency. For regenerative braking torque, For the efficiency of the transmission system, The optimal gear ratio for AMT (Automated Manual Transmission). Main reducer transmission ratio, To maximize braking energy recovery per unit time; The specific steps for correcting the initial AMT shift pattern are as follows: The initial AMT shifting pattern is corrected based on the relationship between vehicle speed and the minimum vehicle speed under joint constant speed control. The initial AMT shifting pattern is corrected based on the vehicle speed fluctuation threshold; Perform shift hysteresis control to correct the initial AMT shift pattern.

2. The AMT shifting control method for electric freight trucks during constant-speed downhill combined braking as described in claim 1, characterized in that, The initial AMT shift pattern is corrected based on the relationship between vehicle speed and the minimum vehicle speed under combined constant speed control, specifically as follows: In the formula, Current vehicle speed The minimum speed for combined constant speed control.

3. The AMT shifting control method for electric freight trucks during constant-speed downhill combined braking as described in claim 1, characterized in that, The initial AMT shift pattern is corrected based on the vehicle speed fluctuation threshold as follows: The speed fluctuation threshold is 2 km / h. When the speed fluctuation is within 2 km / h, the gear will not be adjusted.

4. The AMT shifting control method for electric freight trucks during constant-speed downhill combined braking as described in claim 1, characterized in that, The shift hysteresis control is specifically as follows: In the formula, and These are the regenerative braking torque threshold values ​​for upshifting and downshifting, respectively. For the shift hysteresis threshold, This is regenerative braking torque.

5. The AMT shifting control method for electric freight trucks during constant-speed downhill combined braking as described in claim 1, characterized in that, The specific steps to obtain the transmission efficiency of each gear in an AMT are as follows: The torque and speed data of the input / output shafts are obtained through AMT bench testing, and the input power and output power are obtained, thereby obtaining the transmission efficiency of each gear of the AMT.

6. The AMT shifting control method for electric freight trucks during constant-speed downhill combined braking as described in claim 1, characterized in that, The steps to shift to the optimal gear in an AMT (Automated Manual Transmission) are as follows: The AMT controller takes over control of the drive motor from the vehicle controller, controls the drive motor torque to drop to 0, controls the shift actuator to shift the transmission gear to neutral, controls the drive motor speed to keep the input and output speeds of the shift engagement sleeve synchronized, controls the shift actuator to shift the transmission gear from neutral to the optimal AMT gear, controls the drive motor torque to rise to the target torque, and then returns control of the drive motor to the vehicle controller, ending the shift.

7. The AMT shifting control method for electric freight trucks during constant-speed downhill combined braking as described in claim 6, characterized in that, The torque change rates for controlling the drive motor torque to drop to 0 and controlling the drive motor torque to rise to the target torque are set to -3.5 kN·m / s and 4.5 kN·m / s, respectively.

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