Method and system for controlling gear shifting process of electric drive transmission for construction machinery

Abstract

Start No No No Yes Yes Yes End FIG. 2

Description

TECHNICAL FIELD The present invention belongs to the technical field of construction machinery, and relates to a method and system for controlling a gear shifting process of an electric drive transmission for construction machinery. BACKGROUND OF THE INVENTION With the increasing development of electric drive of construction machinery, the traditional powershift transmission route of engine + powershift transmission has been replaced by the route represented by motor + powershift transmission (hereinafter referred to as “electric drive transmission”). Due to the wide range of the speed and torque of the motor, the number of gears of the electric drive transmission can be greatly reduced compared to the traditional transmission, leading to a significant increase in the speed ratio difference between the gears of the transmission. Meanwhile, due to the difference in characteristics between the motor and the engine, not installing a hydraulic torque converter in the transmission and other reasons, it is more difficult to control the quality of the gear shifting process of the electric drive transmission, leading to a poor driving experience, which seriously restricts the development of an electric drive in the construction machinery industry. In the prior art, there are drawbacks as follows. In existing patents, the torque of a motor is reduced during gear shifting to facilitate dragging of the motor for speed synchronization after the clutch is filled with oil. However, in a case of gear downshifting, reducing the motor torque goes against the speed increase of the motor (the motor speed should be increased in a case of downshifting), making it more difficult to achieve speed synchronization, resulting in compromised quality during gear shifting. According to the existing literature, the speed of a motor is adjusted by changing the operating mode of the motor during gear shifting to achieve speed synchronization between driving and driven friction plates. This technique is commonly used in gear shifting and speed changing for AMT vehicles, with complicated control over gear shifting and dramatic changes in operating conditions and load of construction machinery. If the load suddenly increases during speed adjustment, a violent power interruption occurs, possibly making it impossible to achieve speed synchronization. BRIEF SUMMARY OF THE INVENTION Object: In view of at least one of the above technical problems, the present invention provides a method and system for controlling a gear shifting process of an electric drive transmission for construction machinery. Technical solution: To solve the technical problems above, the technical solution used in the present invention is as follows. In a first aspect, a method for controlling a gear shifting process of an electric drive transmission for construction machinery is provided. The method includes: acquiring a required gear, a current gear, a motor output torque and a gradient signal in response to a received gear shifting signal; determining a gear shifting load type based on the motor output torque and the gradient signal, wherein the gear shifting load type includes a light / medium-load gear shifting and heavy-load gear shifting; determining a gear shifting requirement type based on the required gear and the current gear, wherein the gear shifting requirement type is a gear upshifting requirement or a gear downshifting requirement; if the gear shifting load type is the light / medium-load gear shifting and the gear shifting requirement type is the gear upshifting requirement, sending an instruction to execute light / medium-load gear upshifting control; and if the gear shifting load type is the light / medium-load gear shifting and the gear shifting requirement type is the gear downshifting requirement, sending an instruction to execute light / medium-load gear downshifting control. In some embodiments, determining the gear shifting load type based on the motor output torque and the gradient signal includes: if the motor output torque is less than a pre-set condition for heavy-load gear shifting and the gradient signal is less than a pre-set condition for steep-gradient gear shifting are satisfied, the gear shifting load type is the light / medium-load gear shifting; and if the motor output torque being less than the pre-set condition for heavy-load gear shifting and the gradient signal being less than the pre-set condition for steep-gradient gear shifting are not satisfied, the gear shifting load type is the heavy-load gear shifting. In some embodiments, determining the gear shifting requirement type based on the required gear and the current gear includes: if the required gear is greater than the current gear, the gear shifting requirement type is the gear upshifting requirement; and if the required gear is less than the current gear, the gear shifting requirement type is the gear downshifting requirement. In some embodiments, prior to executing the light / medium-load gear upshifting control or the light / medium-load gear downshifting control, the method further includes: determining a clutch to be disengaged and a clutch to be engaged that are involved in gear shifting, to be specific: the clutch to be disengaged being a clutch corresponding to the current gear and excluding clutches that correspond to both the current gear and the required gear; and the clutch to be engaged is a clutch corresponding to the required gear and excluding clutches that correspond to both the current gear and the required gear. In some embodiments, the light / medium-load gear upshifting control includes: decreasing at a first slope value, an oil pressure of the clutch to be disengaged, and prefilling oil for the clutch to be engaged to subsequently maintain at a first set oil pressure value, wherein the first set oil pressure value is expressed as a set range value below an oil pressure of a semi-engaged clutch; in response to the oil pressure of the clutch to be disengaged decreasing to 0 and an oil pressure of the clutch to be engaged maintained at the first set oil pressure value, controlling to reduce an output torque of the driving motor to a first set torque value; and in response to a driving / driven speed difference of the clutch to be engaged being less than a first set speed difference value, controlling to increase the oil pressure of the clutch to be engaged to a target oil pressure value within a first period, and to increase the output torque of the driving motor to a total required motor torque value within a second period, thereby completing gear shifting. In some embodiments, the first set torque value is determined based on the driving / driven speed difference of the clutch to be engaged and the output torque of the driving motor before the gear shifting. In some embodiments, the light / medium-load gear downshifting control includes: decreasing at a first slope value, an oil pressure of the clutch to be disengaged, and prefilling oil for the clutch to be engaged to subsequently maintain at a second set oil pressure value, wherein the second set oil pressure value is expressed as a set range value below an oil pressure of a semi-engaged clutch; in response to the oil pressure of the clutch to be disengaged decreasing to 0 and an oil pressure of the clutch to be engaged maintained at the first set oil pressure value, controlling to increase an output torque of the driving motor to a second set torque value; and in response to a driving / driven speed difference of the clutch to be engaged being less than a second set speed difference value, controlling to increase the oil pressure of the clutch to be engaged to a target oil pressure value within a first period, and to decrease the output torque of the driving motor to a total required motor torque value within a second period, thereby completing gear shifting. In some embodiments, the second set torque value is determined based on the driving / driven speed difference of the clutch to be engaged and the output torque of the driving motor before gear shifting. In some embodiments, in the above-mentioned method for controlling a gear shifting process of an electric drive transmission for construction machinery, at least one of the following is satisfied: the first slope value is an oil pressure decrease rate when an oil inlet passage of the clutch to be disengaged is completely closed and an oil return passage of the clutch to be disengaged is completely opened; increasing the oil pressure of the clutch to be engaged to the target oil pressure value within the first period is expressed as: pre-filling oil to a maximum oil pressure of the clutch to be disengaged, when the oil return passage of the clutch to be engaged is completely closed and the oil inlet passage of the clutch to be engaged is completely opened; the second period is determined based on a difference between an actual torque value of the driving motor and a total required motor torque value; and the total required motor torque value is determined based on a speed of the driving motor and an position of an accelerator pedal. In some embodiments, if a speed decrease rate of an output shaft of the transmission is greater than a set rate value when executing the light / medium-load gear upshifting control or the light / medium-load gear downshifting control, the light / medium-load gear upshifting control or the light / medium-load gear downshifting control is quitted, and an oil pressure of the clutch to be engaged is increased to a target oil pressure value at a second slope value. In some embodiments, the second slope value is calibrated and acquired from a speed change slope of the output shaft of the transmission and a torque of the driving motor. In a second aspect, a device for controlling a gear shifting process of an electric drive transmission for construction machinery is provided. The device includes a memory and a processor, wherein the memory is configured to store an instruction, which is configured to control the processor to operate to perform the method for controlling the gear shifting process of an electric drive transmission for construction machinery according to the first aspect. In a third aspect, a system for controlling a gear shifting process of an electric drive transmission for construction machinery is provided. The system includes the device for controlling a gear shifting process of an electric drive transmission for construction machinery according to the second aspect. In a fourth aspect, a construction machinery is provided. The construction machinery includes the device for controlling a gear shifting process of an electric drive transmission for 6 construction machinery according to the first aspect, or the system for controlling a gear shifting process of an electric drive transmission for construction machinery according to the second aspect. Beneficial effects: According to the method and system for controlling a gear shifting process of an electric drive transmission for construction machinery as provided by the present invention, the synchronization in the speed of the clutch can be achieved quickly by means of the method, such that the slipping friction power of the clutch is reduced, and the method is better adapted to the application requirements of construction machinery with variable loads, which effectively shortens the gear shifting time, and solves the problem of unstable gear shifting caused by improper control over the oil pressure of the clutch during the gear shifting. BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS FIG. 1 is a schematic diagram of a system for controlling a gear shifting process of an electric drive transmission for construction machinery according to an embodiment of the present invention; FIG. 2 is a schematic main flowchart of a method for controlling a gear shifting process of an electric drive transmission for construction machinery according to an embodiment of the present invention; FIG. 3 is a schematic flowchart of light / medium-load gear upshifting control according to an embodiment of the present invention; FIG. 4 is a schematic diagram of parameter variations in a process of light / medium-load gear upshifting control according to an embodiment of the present invention; FIG. 5 is a schematic flowchart of light / medium-load gear downshifting control according to an embodiment of the present invention; FIG. 6 is a schematic diagram of a method for determining a total required motor torque value according to an embodiment of the present invention; and FIG. 7 is a schematic diagram of a torque exchange stage in a heavy-load gear upshifting process according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION The present invention will be further described below in conjunction with the accompanying drawings and embodiments. The embodiments below are mainly for the purpose of more clearly illustrating the technical solutions of the present invention, and are not intended to limit the protection scope of the present invention. In the description of the present invention, “several” means more than one, “a plurality of” means more than two, “greater than,” “smaller than,” “more than” and the like should be understood as excluding the indicated figure, and “above,” “below,” “within” and the like should be understood as including the indicated figure. “First” and “second”, if described, are only for the purpose of distinguishing the technical features, and should not be understood as indicating or implying relative importance, or implicitly specifying the number of the indicated technical features, or implicitly specifying the precedence relationship between the indicated technical features. In the description of the present description, the description made with reference to terms such as “one embodiment,” “some embodiments,” “exemplary embodiment,” “example”, “specific example” or “some examples” means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In the specifications, the schematic expressions of the above terms do not necessarily pertain to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics as described can be combined in an appropriate manner in any one or more embodiments or examples. Embodiment 1: In a first aspect, this embodiment provides a method for controlling a gear shifting process of an electric drive transmission for construction machinery. The method includes the steps as follows. In step S1, a required gear GearReq, a current gear GearCurr, a motor output torque TMotor and a gradient signal a are acquired in response to a received gear shifting signal. In step S2, a gear shifting load type is determined based on the motor output torque TMotor and the gradient signal a, where the gear shifting load type includes a light / medium-load gear shifting and heavy-load gear shifting. In some embodiments, the gear shifting load type being determined based on the motor output torque and the gradient signal includes: if the motor output torque TMotor being less than a preset condition Tt for heavy-load gear shifting and the gradient signal a being less than a preset condition at for steep-gradient gear shifting are satisfied, the gear shifting load type is the light / medium-load gear shifting; and if the motor output torque TMotor being less than the pre-set condition Tt for heavy-load gear shifting and the gradient signal being less than the pre-set condition for steep-gradient gear shifting are not satisfied, the gear shifting load type is the heavy-load gear shifting. In step S3, a gear shifting requirement type is determined based on the required gear GearReq and the current gear GearCurr, where the gear shifting requirement type is a gear upshifting requirement or a gear downshifting requirement. In some embodiments, the gear shifting requirement type being determined based on the required gear GearReq and the current gear GearCurr includes: if the required gear GearReq is greater than the current gear GearCurr, the gear shifting requirement type is the gear upshifting requirement; and if the required gear GearReq is less than the current gear GearCurr, the gear shifting requirement type is the gear downshifting requirement. In step S4, if the gear shifting load type is the light / medium-load gear shifting and the gear shifting requirement type is the gear upshifting requirement, an instruction is sent to execute light / medium-load gear upshifting control; and if the gear shifting load type is the light / medium-load gear shifting and the gear shifting requirement type is the gear downshifting requirement, an instruction is sent to execute light / medium-load gear downshifting control. In some embodiments, prior to executing the light / medium-load gear upshifting control or the light / medium-load gear downshifting control, the method further includes: determining a clutch to be disengaged and a clutch to be engaged that are involved in gear shifting, to be specific: the clutch to be disengaged is a clutch corresponding to the current gear and excluding clutches that correspond to both the current gear and the required gear; and the clutch to be engaged being a clutch corresponding to the required gear and excluding clutches that correspond to both the current gear and the required gear. In some embodiments, the light / medium-load gear upshifting control includes: decreasing at a first slope value, an oil pressure of the clutch to be disengaged, and prefilling oil for the clutch to be engaged to subsequently maintain at a first set oil pressure value, where the first set oil pressure value is expressed as a set range value below an oil pressure of a semi-engaged clutch; in response to the oil pressure of the clutch to be disengaged decreasing to 0 and an oil pressure of the clutch to be engaged maintaining at the first set oil pressure value, controlling to reduce an output torque of the driving motor to a first set torque value T1; and in response to a driving / driven speed difference of the clutch to be engaged being less than a first set speed difference value Dn1, controlling to increase the oil pressure of the clutch to be engaged to a target oil pressure value within a first period, and to increase the output torque of the driving motor to a total required motor torque value within a second period, thereby completing gear shifting. Here, the first set torque value T1 is determined based on the driving / driven speed difference of the clutch to be engaged and the output torque of the driving motor before the gear shifting. In some embodiments, the light / medium-load gear downshifting control includes: decreasing at a first slope value, an oil pressure of the clutch to be disengaged, and prefilling oil for the clutch to be engaged to be subsequently maintained at a second set oil pressure value, wherein the second set oil pressure value is expressed as a set range value below an oil pressure of a semi-engaged clutch; in response to the oil pressure of the clutch to be disengaged decreasing to 0 and an oil pressure of the clutch to be engaged maintained at the first set oil pressure value, controlling to increase an output torque of the driving motor to a second set torque value T2; and in response to a driving / driven speed difference of the clutch to be engaged being less than a second set speed difference value Dn2, controlling to increase the oil pressure of the clutch to be engaged to a target oil pressure value within a first period, and to decrease the output torque of the driving motor to a total required motor torque value within a second period, thereby completing gear shifting. Here, the second set torque value T2 is determined based on the driving / driven speed difference of the clutch to be engaged and the output torque of the driving motor before the gear shifting. In some embodiments, in the light / medium-load gear upshifting control or the light / medium-load gear downshifting control, the first slope value is an oil pressure decrease rate when an oil inlet passage of the clutch to be disengaged is completely closed and an oil return passage of the clutch to be disengaged is completely opened; increasing the oil pressure of the clutch to be engaged to the target oil pressure value within the first period is expressed as: pre-filling oil to a maximum oil pressure of the clutch to be disengaged, when the oil return passage of the clutch to be engaged is completely closed and the oil inlet passage of the clutch to be engaged is completely opened; the second period is determined based on a difference between an actual torque value of the driving motor and a total required motor torque value; and the total required motor torque value is determined based on a speed of the driving motor and a position of an accelerator pedal. It should be specially noted that if a speed decrease rate of an output shaft of the transmission is greater than a set rate value Av during executing of the light / medium-load gear upshifting control or the light / medium-load gear downshifting control, the light / medium-load gear upshifting control or the light / medium-load gear downshifting control is quitted, and an oil pressure of the clutch to be engaged is increased to a target oil pressure value at a second slope value to restore power transmission quickly. Here, the second slope value is calibrated and acquired from a speed change slope of the output shaft of the transmission and a torque of the driving motor. Embodiment 2: In a second aspect, this embodiment provides a device for controlling a gear shifting process of an electric drive transmission for construction machinery. The device includes a memory and a processor, wherein the memory is configured to store an instruction, which is configured to control the processor to operate to perform the method for controlling a gear shifting process of an electric drive transmission for construction machinery according to the first aspect. In some embodiments, the mentioned device for controlling a gear shifting process of an electric drive transmission for construction machinery is a transmission control unit as shown in FIG. 1. Embodiment 3: In third aspect, this embodiment provides a system for controlling a gear shifting process of an electric drive transmission for construction machinery. The system includes the device for controlling a gear shifting process of an electric drive transmission for construction machinery according to the second aspect. In some embodiments, as shown in FIG. 1, a system for controlling a gear shifting process of an electric drive transmission for construction machinery includes: a gear shifting handle, a transmission control unit, a motor control unit, a vehicle control unit, a solenoid valve, a speed sensor and a gradient sensor. The gear shifting handle is configured to shift the gear of a transmission. The solenoid valve is configured to control the engagement and disengagement oil pressure of a clutch. The speed sensor is configured to acquire a speed of an output shaft of the transmission. The gradient sensor is configured to acquire an angle of inclination of a vehicle to determine a type of road on which the vehicle runs. The transmission control unit is configured to acquire a speed sensor signal to acquire a speed state of the transmission; to control the solenoid valve based on a gear shifting request to control the oil pressure of the clutch during gear shifting; and to conduct override control on the motor output torque and speed during the gear shifting based on the gear shifting requirement. The motor control unit is configured to receive control modes of an vehicle control unit and the transmission control unit as well as speed and torque requests, and to respond to a corresponding requirement. The vehicle control unit is configured to acquire an operation signal of the gear shifting handle, determine whether or not gear shifting is allowed, and send a gear request signal to the transmission control unit; and to analyze the speed and torque requests of a driver and send the requests to the motor control unit, so as to achieve motor control. According to an embodiment of the present invention, a flow process of controlling a gear shifting process of a transmission is as shown in FIG. 2, with the specific steps as follows. The gear change request of the gear shifting handle, the motor output torque and the road gradient are monitored in real time. When a gear requires to be changed, determination is made for the following conditions. The relationship between the required gear GearReq and the current gear GearCurr is determined, to be specific: if GearReq > GearCurr, there is a gear upshifting requirement for the transmission; and if GearReq < GearCurr, there is a gear downshifting requirement for the transmission. The clutch involved in gear shifting is determined, to be specific: a clutch corresponding to the current gear is a clutch to be disengaged, a clutch corresponding to the required gear is the clutch to be disengaged, and if the current gear and the required gear include a clutch at the same time, this clutch may not be involved in disengagement and engagement during gear shifting according to the clutch control strategy. The transmission gear shifting type is determined based on the motor output torque TMotor and the gradient signal a, to be specific: if TMotor is less than a preset condition Tt of heavy-load gear shifting and a is less than a preset condition a of steep-gradient gear shifting, the gear shifting type is light / medium-load gear shifting; or else, the gear shifting type is heavyload gear shifting. (1) When the gear shifting type is determined to be light / medium-load gear upshifting, a light / medium-load gear upshifting process according to an embodiment of the present invention is as shown in FIG. 3 and FIG. 4, with the steps of controlling the gear shifting process as follows: (1-1) the clutch to be disengaged is controlled to decrease at a first slope value to an oil pressure of 0 bar to complete gear resetting; (1-2) after the clutch to be engaged is controlled to be pre-filled with oil, the oil pressure is maintained below the semi-engagement point to prevent speed fluctuations due to early slipping friction of the clutch. (1-3) the transmission control unit overrides to request the motor to output a negative torque T1 to control the speed of the motor to decrease, gradually reducing the speed difference between the driving and driven ends of the clutch to be engaged; (1-4) when the speed different is less than Dn1, the oil pressure of the clutch to be engaged is controlled to increase to a target oil pressure within a first period; and (1-5) the transmission control unit controls to restore the motor torque to the total required motor torque value within a second period, and quits override control to complete gear shifting. (2) When the gear shifting type is determined to be light / medium-load gear downshifting, a light / medium-load gear downshifting process according to an embodiment of the present invention is as shown in FIG. 5, with the steps of controlling the gear shifting process as follows: (2-1) the clutch to be disengaged is controlled to decrease at a first slope value to an oil pressure of 0 bar to complete gear re-setting; (2-2) after the clutch to be engaged is controlled to be pre-filled with oil, the oil pressure is maintained below the semi-engagement point, so as to prevent speed fluctuations due to early slipping friction of the clutch. (2-3) the transmission control unit overrides to request the motor to output a positive torque T2 to control the speed of the motor to increase, gradually reducing the speed difference between the driving and driven ends of the clutch to be engaged; (2-4) when the speed difference is less than Dn2, the oil pressure of the clutch to be engaged is controlled to increase to a target oil pressure within a first period; and (2-5) the transmission control unit controls to restore the motor torque to the vehicle required motor torque value within a second period, and quits override control to complete gear shifting. As shown in FIG. 6, the above-mentioned vehicle required motor torque value is determined based on a speed of the driving motor and a position of an accelerator pedal. In particular, if the speed decrease rate of the output shaft of the transmission is greater than Av in the light / medium-load gear upshifting / downshifting process, it is determined that a sudden change has occurred to the vehicle operating condition, the clutch to be engaged is no longer maintained below the oil pressure under semi-engagement, but is increased at a second slope value to a target oil pressure, thereby restoring the power transmission quickly. (3) When the gear shifting type is determined to be heavy-load gear upshifting / downshifting, in order to prevent vehicle power interruption, as shown in FIG. 7, it is necessary to control the clutch to be engaged and the clutch to be disengaged for an intersection between oil pressure curves to a certain extent, so as to ensure avoid power interruption in the gear shifting process. The oil pressure control strategy of the gear shifting process is kept in line with the gear shifting of the traditional engine-driven transmission, the details of which will not be repeated in the present application. With the system and method described above, the present application reduces the slipping friction work of the clutch in the gear shifting process of the electric drive transmission, shortens the gear shifting time, and solves the problem of unsmooth gear shifting caused by improper oil pressure control of the clutch in the gear shifting and synchronization process of the electric drive transmission. Embodiment 4: In a fourth aspect, a construction machinery is provided. The construction machinery includes the above-mentioned device for controlling a gear shifting process of an electric drive transmission for construction machinery, or the above-mentioned system for controlling a gear shifting process of an electric drive transmission for construction machinery. The present application is described with reference to the flowchart and / or block diagram of the method, apparatus (system), and computer program product according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram and a combination of the processes and / or blocks in the flowchart and / or block diagram may be implemented by computer program instructions. These computer program instructions may be provided to a general-purpose computer, a specialpurpose computer, an embedded processor, or a processor of an additional programmable data processing apparatus to produce a machine, such that a device for implementing the function(s) 5 specified in one or more processors in the flowchart and / or in one or more blocks in the block diagram is produced by means of the instructions executed by the computer or the processor of another programmable data processing device. These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or an additional programmable data processing apparatus to 10 work in a particular fashion, such that the instructions stored in the computer-readable memory produce a manufactured product including an instruction device, which implements the function(s) specified in one or more processors in the flowchart and / or in one or more blocks in the block diagram. These computer program instructions may also be loaded into a computer or an additional 15 programmable data processing apparatus, such that a series of operational steps are performed on the computer or the additional programmable apparatus to achieve computer-implemented processing, thereby executing the instructions on the computer or the additional programmable apparatus to provide the steps for implementing the function(s) specified in one or more processors in the flowchart and / or in one or more blocks in the block diagram. 20        The description above only provides preferred embodiments of the present invention. It should be noted that for those of ordinary skills in the art, various improvements and modifications that can be made without departing from the principle of the present invention shall be construed as falling within the protection scope of the present invention.

Claims

1. A method for controlling a gear shifting process of an electric drive transmission for construction machinery, comprising:acquiring a required gear, a current gear, a motor output torque and a gradient signal in response to a received gear shifting signal;determining a gear shifting load type based on the motor output torque and the gradient signal, wherein the gear shifting load type comprises a light / medium-load gear shifting and heavy-load gear shifting;determining a gear shifting requirement type based on the required gear and the current gear, wherein the gear shifting requirement type is a gear upshifting requirement or a gear downshifting requirement;if the gear shifting load type is the light / medium-load gear shifting and the gear shifting requirement type is the gear upshifting requirement, sending an instruction to execute light / medium-load gear upshifting control; andif the gear shifting load type is the light / medium-load gear shifting and the gear shifting requirement type is the gear downshifting requirement, sending an instruction to execute light / medium-load gear downshifting control.

2. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 1, wherein determining the gear shifting load type based on the motor output torque and the gradient signal comprises:if the motor output torque being less than a preset condition for heavy-load gear shifting and the gradient signal being less than a preset condition for steep-gradient gear shifting are satisfied, the gear shifting load type is the light / medium-load gear shifting; andif the motor output torque being less than the pre-set condition for heavy-load gear shifting and the gradient signal being less than the pre-set condition for steep-gradient gear shifting are not satisfied, the gear shifting load type is the heavy-load gear shifting.

3. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 1 or 2, wherein determining the gear shifting requirement type based on the required gear and the current gear comprises:if the required gear is greater than the current gear, the gear shifting requirement type is the gear upshifting requirement; andif the required gear is less than the current gear, the gear shifting requirement type is the gear downshifting requirement.

4. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 1, wherein prior to executing the light / medium-load gear upshifting control or the light / medium-load gear downshifting control, the method further comprises: determining a clutch to be disengaged and a clutch to be engaged that are involved in gear shifting, to be specific:the clutch to be disengaged being a clutch corresponding to the current gear and excluding clutches that correspond to both the current gear and the required gear; andthe clutch to be engaged being a clutch corresponding to the required gear and excluding clutches that correspond to both the current gear and the required gear.

5. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 4, wherein the light / medium-load gear upshifting control comprises:decreasing, at a first slope value, an oil pressure of the clutch to be disengaged, and prefilling oil for the clutch to be engaged to subsequently maintain at a first set oil pressure value, wherein the first set oil pressure value is expressed as a set range value below an oil pressure of a semi-engaged clutch;in response to the oil pressure of the clutch to be disengaged decreasing to 0 and an oil pressure of the clutch to be engaged maintaining at the first set oil pressure value, controlling to reduce an output torque of the driving motor to a first set torque value; andin response to a driving / driven speed difference of the clutch to be engaged being less than a first set speed difference value, controlling to increase the oil pressure of the clutch to beengaged to a target oil pressure value within a first period, and to increase the output torque of the driving motor to a total required motor torque value within a second period, thereby completing gear shifting.

6. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 5, wherein the first set torque value is determined based on the driving / driven speed difference of the clutch to be engaged and the output torque of the driving motor before the gear shifting.

7. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 4, wherein the light / medium-load gear downshifting control comprises:decreasing, at a first slope value, an oil pressure of the clutch to be disengaged, and prefilling oil for the clutch to be engaged to subsequently maintain at a second set oil pressure value, wherein the second set oil pressure value is expressed as a set range value below an oil pressure of a semi-engaged clutch;in response to the oil pressure of the clutch to be disengaged decreasing to 0 and an oil pressure of the clutch to be engaged maintaining at the first set oil pressure value, controlling to increase an output torque of the driving motor to a second set torque value; andin response to a driving / driven speed difference of the clutch to be engaged being less than a second set speed difference value, controlling to increase the oil pressure of the clutch to be engaged to a target oil pressure value within a first period, and to decrease the output torque of the driving motor to a total required motor torque value within a second period, thereby completing gear shifting.

8. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 7, wherein the second set torque value is determined based on the driving / driven speed difference of the clutch to be engaged and the output torque of the driving motor before the gear shifting.

9. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 5 or 7, wherein at least one of the following is satisfied:the first slope value is an oil pressure decrease rate when an oil inlet passage of the clutch to be disengaged is completely closed and an oil return passage of the clutch to be disengaged is completely opened;increasing the oil pressure of the clutch to be engaged to the target oil pressure value within the first period is expressed as: prefilling oil to a maximum oil pressure of the clutch to be disengaged, when the oil return passage of the clutch to be engaged is completely closed and the oil inlet passage of the clutch to be engaged is completely opened;the second period is determined based on a difference between an actual torque value of the driving motor and a total required motor torque value; andthe total required motor torque value is determined based on a speed of the driving motor and a position of an accelerator pedal.

10. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 1, wherein if a speed decrease rate of an output shaft of the transmission is greater than a set rate value during executing of the light / medium-load gear upshifting control or the light / medium-load gear downshifting control, the light / medium-load gear upshifting control or the light / medium-load gear downshifting control is quitted, and an oil pressure of the clutch to be engaged is increased to a target oil pressure value at a second slope value.

11. The method for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 10, wherein the second slope value is calibrated and acquired from a speed change slope of the output shaft of the transmission and a torque of the driving motor.

12. A device for controlling a gear shifting process of an electric drive transmission for construction machinery, comprising a memory and a processor, wherein the memory is configured to store an instruction, which is configured to control the processor to operate, so as to perform the method for controlling a gear shifting process of an electric drive transmission for construction machinery according to any of claims 1 to 11.

13. A system for controlling a gear shifting process of an electric drive transmission for construction machinery, comprising the device for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 12.

14. A construction machinery, comprising the device for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 12 and the system for controlling a gear shifting process of an electric drive transmission for construction machinery according to claim 13.

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