Hydrostatic drive vehicle downhill control method, control system and device

Abstract

The invention discloses a downhill control method, a downhill control system and a downhill control device for a hydrostatic driving vehicle. The downhill control method for the hydrostatic drive vehicle comprises the steps that current driving data of the vehicle are obtained, and whether the vehicle is in a downhill working condition or not is judged according to the driving data; when the vehicle is judged to be in the downhill working condition, power limit grade evaluation is conducted on the vehicle according to the current slope value of the vehicle; and when it is judged that the current vehicle needs to be subjected to anti-stall control according to the power limiting level, one or more of an engine, a closed variable pump and a variable motor of the vehicle are correspondingly controlled to conduct power combined limiting according to the power limiting level. The current working condition of the vehicle is judged according to related signals of the vehicle, different levels of power limitation and self-adaptive adjustment of the limitation value are carried out according to the slope value of the vehicle under the corresponding working condition and the specific working condition, the vehicle is prevented from stalling, on one hand, an operator is protected, and on the other hand, the safety of the vehicle is improved. On the other hand, a variable displacement motor and an engine of the vehicle are protected.

Description

Technical Field

[0001] The present invention belongs to the field of engineering machinery and forestry machinery, and in particular relates to a downhill control method, control system and device for a hydrostatically driven vehicle, which can realize a downhill stall prevention function. Background Art

[0002] Hydrostatic drive technology is one of the core technologies of current agricultural machinery, forestry machinery, and mobile engineering machinery. When hydrostatically driven mobile equipment goes downhill, the speed will increase under the influence of gravity and the power of the entire machine, and it will lose control and stall, which can easily cause damage to the pump and motor. At this time, limiting the power depends on the engine's back-drag braking ability, which can easily cause the engine to overspeed and cause engine damage.

[0003] Existing solutions usually detect the vehicle's driving speed and make a judgment based on the current speed; when the vehicle speed reaches the first overspeed range, the motor displacement is maintained at the current value; when the vehicle speed reaches the second overspeed range, the engine output torque is adjusted on the basis of maintaining the motor speed at the current value, so that the engine output torque is reduced to the minimum torque; when the vehicle speed reaches the third stage, in addition to maintaining the above two controls, the pump displacement is controlled according to the pump's suction and outlet pressures to prevent the reverse driving torque generated by the pump from causing the engine negative torque to exceed the preset threshold; and according to the accelerator pedal signal, the driving anti-speeding control and the parking anti-speeding control are distinguished.

[0004] The above scheme mainly performs speed prevention control based on the vehicle speed during the downhill process. However, in actual driving conditions, the speed prevention thresholds that need to be intervened are different under different slopes. Moreover, for downhill conditions, no further restrictions are made based on the current driving conditions, and it is impossible to provide protection for different driving conditions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a downhill control method, control system and device for a hydrostatically driven vehicle. The method determines the current working condition of the vehicle based on relevant vehicle signals, and performs adaptive adjustment of different levels of power limitation and limitation values according to the slope value and specific working conditions of the vehicle under the corresponding working conditions to prevent the vehicle from stalling. On the one hand, it protects the operator, and on the other hand, it protects the vehicle's variable motor and engine.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for controlling a hydrostatically driven vehicle downhill, comprising: Obtain the vehicle's current driving data and determine whether the vehicle is in a downhill condition based on the driving data; When the vehicle is determined to be in downhill operation, the power limit level is evaluated based on the vehicle's current slope value; When it is determined that the current vehicle needs to perform anti-stall control according to the power limit level, one or more of the vehicle's engine, closed variable pump, and variable motor are controlled accordingly to perform combined power limitation.

[0007] The aforementioned downhill control method for a hydrostatically driven vehicle is characterized in that the power limit level is divided into four levels, namely no power limit, level 1 power limit, level 2 power limit, and level 3 power limit, wherein: Under the first-level power limitation condition, one of the vehicle's engine, closed variable pump, and variable motor is controlled to limit power; Under the secondary power limiting condition, two of the vehicle's engine, closed variable pump, and variable motor are controlled to limit power; Under the third-level power limitation working condition, the engine, closed variable pump and variable motor that control the vehicle are all power limited.

[0008] The aforementioned method for controlling a hydrostatically driven vehicle downhill is characterized in that the power limit levels are divided according to the threshold range of the current slope value, and the specific steps are as follows: According to the vehicle's driving conditions, multiple slope values are set and anti-stall control tests are performed at each slope value; If, at a certain slope value, speed control can be achieved without limiting any of the engine, closed variable pump, and variable motor, and if speed control is achieved beyond this slope, limiting one of the engine, closed variable pump, and variable motor is required, then this slope value is defined as the first slope threshold; If, at a certain slope value, speed control cannot be achieved by only one of the engine, closed variable pump, or variable motor, the slope value is defined as the second slope threshold; If, at a certain slope value, speed control cannot be achieved using only two devices among the engine, the closed variable pump, and the variable motor, the slope value is defined as the third slope threshold; When the vehicle's current slope value is less than the first slope threshold, it is defined as no power restriction; when the vehicle's current slope value is greater than the first slope threshold and less than the second slope threshold, it is defined as level one power restriction; when the vehicle's current slope value is greater than the second slope threshold and less than the third slope threshold, it is defined as level two power restriction; when the vehicle's current slope value is greater than the third slope threshold, it is defined as level three power restriction.

[0009] The aforementioned method for controlling a downhill slope of a hydrostatically driven vehicle is characterized in that, when determining an interpolation curve between the limit values of the engine, the closed variable pump, and the variable motor at each slope and the slope value, the specific steps are as follows: Set multiple slope values according to the vehicle's driving conditions; Randomly select one of the engine, closed variable pump, and variable motor to perform anti-stall test according to the slope from low to high; Obtaining a limit value of the device that can ensure that the vehicle does not stall at each slope until the limit value of the device reaches its maximum limit value, and obtaining a limit interpolation curve between the device and the slope; While the first device maintains its maximum limit value, the test slope value is continuously increased. The second device intervenes in the anti-stall test to obtain the limit value of the second device that can ensure that the vehicle does not stall at each slope. This is done until the limit value of the second device reaches its maximum limit value, thereby obtaining a limit interpolation curve between the second device and the slope. While the first and second devices maintain their maximum limit values, the test slope value is continuously increased, and the third device is used in the anti-stall test to obtain the limit value of the third device that can ensure that the vehicle does not stall at each slope. This is done until the limit value of the third device reaches its maximum limit value, thereby obtaining a limit interpolation curve between the third device and the slope. In this way, the correlation between the slope at each level of power limitation and the corresponding limit value of each device is obtained.

[0010] The aforementioned method for controlling downhill slope of a hydrostatically driven vehicle is characterized in that the current driving data of the vehicle is obtained and also includes transmission gear information. When it is detected that the transmission is in a high-speed gear, the power limit value of one or more of the vehicle's engine, closed variable pump and variable motor is set based on a linear relationship with the slope value and multiplied by a first coefficient.

[0011] The aforementioned downhill control method for a hydrostatically driven vehicle is characterized in that the current driving data of the vehicle is obtained, including: a seat orientation signal, a gear switch signal and a slope value.

[0012] The aforementioned method for controlling a downhill slope of a hydrostatically driven vehicle is characterized in that: when performing anti-stall control, if the detected gear switch signal is a reverse gear, the power limit value of one or more of the vehicle's engine, closed variable pump and variable motor is set based on a linear relationship with the slope value and multiplied by a second coefficient.

[0013] The aforementioned downhill control method for a hydrostatically driven vehicle is characterized in that: the current driving data of the vehicle is obtained, including the vehicle driving pressure value, and the current vehicle driving condition is determined to be a heavy-load driving condition or a light-load driving condition based on the driving pressure value. When performing anti-stall control under the heavy-load driving condition, the power limit value of one or more of the vehicle's engine, closed variable pump and variable motor is set based on a linear relationship with the slope value and multiplied by a third coefficient.

[0014] The aforementioned method for controlling a hydrostatically driven vehicle downhill is characterized in that, when performing anti-stall control on the vehicle, the engine speed signal is obtained in real time, and when the engine speed exceeds a set threshold, intervention of the closed variable pump displacement limit is prohibited.

[0015] A hydrostatically driven vehicle downhill control system includes a hydrostatic controller, an engine controller, an engine, a closed variable pump, a closed variable pump electric proportional displacement control valve, a variable motor, and a variable motor electric proportional displacement control valve, wherein: The signal output end of the hydrostatic controller is connected to the signal input end of the engine controller, the closed variable pump electric proportional displacement control valve and the variable motor electric proportional displacement control valve; The signal input end of the hydrostatic controller is connected to the signal output end of the engine controller, the gearbox, the slope detection sensor and the FNR gear switch; The signal input end of the hydrostatic controller is further connected to a vehicle speed sensor and / or a motor speed sensor; There are two closed variable pump electric proportional displacement control valves, both connected to the closed variable pump, and the variable motor electric proportional displacement control valve is connected to the variable motor; The input end of the engine is connected to the output end of the engine controller, and the output shaft end of the engine is connected to the input shaft end of the closed-type charge pump; The two oil ports of the closed variable pump and the two oil ports of the electronically controlled variable motor are connected by pipelines to form a closed loop, and the output shaft end of the electronically controlled variable motor is connected to the gearbox.

[0016] The aforementioned downhill control system for a hydrostatically driven vehicle is characterized in that a seat orientation detection sensor is further connected to the signal input end of the hydrostatic controller.

[0017] The aforementioned hydrostatic drive vehicle downhill control system is characterized in that the signal input end of the hydrostatic controller is also connected to a pressure sensor installed at the oil inlet and outlet of the closed variable pump or the oil inlet and outlet of the variable motor.

[0018] A downhill control device for a hydrostatically driven vehicle includes the aforementioned control system, wherein the control system is used to execute the aforementioned control method.

[0019] The beneficial effects of the present invention are: 1. By collecting multiple relevant driving signals during vehicle operation, the system identifies the current driving condition. When a downhill condition is detected, it applies corresponding limit control to the closed variable pump, variable motor, and engine at different slopes to achieve anti-stall control in multiple operating conditions. 2. Based on the detected driving signals, the corresponding closed variable pump, variable motor and engine limit values are precisely controlled in dangerous or overloaded conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic flow chart of a downhill control method for a hydrostatically driven vehicle according to the present invention; Figure 2 This is a schematic structural diagram of a downhill control system for a hydrostatically driven vehicle according to the present invention; Figure 2 Among them, 1. Engine controller; 2. Engine; 3. Closed variable pump; 4. Variable motor; 5. Speed sensor; 6. Gearbox; 7. Motor electric proportional displacement control valve; 8. Pressure sensor; 9. First closed pump electric proportional displacement control valve; 10. Second closed pump electric proportional displacement control valve; 11. Hydrostatic controller; 12. Seat orientation detection sensor; 13. Slope detection sensor; 14. FNR gear switch; 15. Vehicle speed sensor. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0022] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. Example 1

[0023] like Figure 1 As shown, a method for controlling a hydrostatically driven vehicle downhill comprises: First: obtain the current driving data of the vehicle, and determine whether the vehicle is in a downhill condition based on the driving data; in this embodiment, the current driving data of the vehicle that needs to be obtained mainly include: a seat orientation signal, a gear switch signal and a slope value. First, identify the current seat orientation based on the seat orientation signal, and then determine the vehicle's driving direction based on the gear switch signal (hereinafter, the vehicle is driving in the direction of the front of the vehicle as the forward direction, and the vehicle is driving in the direction of the rear of the vehicle as the reverse direction), and then determine the actual driving condition based on the slope value (hereinafter, a positive slope value is described as an uphill slope).

[0024] When the seat is facing forward and the vehicle is in gear F, the driver is facing the front of the vehicle and the vehicle is moving forward. At this time, if the slope detection is a positive value, it is a climbing condition; if the slope detection is a negative value, it is a downhill condition; When the seat is facing forward and the vehicle is in gear R, the driver is facing the front of the vehicle and the vehicle is traveling in the reverse direction. At this time, if the slope detection is a positive value, it is a downhill condition; if the slope detection is a negative value, it is a climbing condition; When the seat is facing backward and the vehicle is in gear F, the driver is facing the rear of the vehicle and the vehicle is moving in the opposite direction. If the slope detection is a positive value, it is a downhill condition; if the slope detection is a negative value, it is a climbing condition; When the seat is facing backward and the vehicle is driving in R gear, the driver is facing the rear of the vehicle and the vehicle is traveling forward. If the slope detection is a positive value, it is a climbing condition; if the slope detection is a negative value, it is a downhill condition.

[0025] Secondly: When the vehicle is determined to be in a downhill condition based on the corresponding driving data, the power limit level is evaluated according to the vehicle's current slope value.

[0026] Finally, when it is determined that the current vehicle requires anti-stall control based on the power limit level, one or more of the vehicle's engine, closed variable pump, and variable motor are controlled accordingly to perform combined power limitation.

[0027] Specifically, in this embodiment, the power limit levels are divided into four levels, namely no power limit, level 1 power limit, level 2 power limit, and level 3 power limit, where: Under the first-level power limitation condition, one of the vehicle's engine, closed variable pump, and variable motor is controlled to limit power; Under the secondary power limiting condition, two of the vehicle's engine, closed variable pump, and variable motor are controlled to limit power; Under the third-level power limitation working condition, the engine, closed variable pump and variable motor that control the vehicle are all power limited.

[0028] The power limit levels are divided according to the threshold range of the current slope value, and the specific division steps are as follows: According to the vehicle's driving conditions, multiple slope values are set and anti-stall control tests are performed at each slope value; If, at a certain slope value, speed control can be achieved without limiting any of the engine, closed variable pump, and variable motor, and if speed control is achieved beyond this slope, limiting one of the engine, closed variable pump, and variable motor is required, then this slope value is defined as the first slope threshold; If, at a certain slope value, speed control cannot be achieved by only one of the engine, closed variable pump, or variable motor, the slope value is defined as the second slope threshold; If, at a certain slope value, speed control cannot be achieved using only two devices among the engine, the closed variable pump, and the variable motor, the slope value is defined as the third slope threshold; When the vehicle's current slope value is less than the first slope threshold, it is defined as no power restriction; when the vehicle's current slope value is greater than the first slope threshold and less than the second slope threshold, it is defined as level one power restriction; when the vehicle's current slope value is greater than the second slope threshold and less than the third slope threshold, it is defined as level two power restriction; when the vehicle's current slope value is greater than the third slope threshold, it is defined as level three power restriction.

[0029] It should be noted that under various levels of power limitation conditions, the degree of limitation of the engine, closed variable pump, and variable motor forms a limitation difference curve with the slope value of the vehicle.

[0030] The specific steps for obtaining the interpolation curve between the limit values of the engine, closed variable pump, and variable motor and the slope value at each slope are as follows: Set multiple slope values according to the vehicle's driving conditions; Randomly select one of the engine, closed variable pump, and variable motor to perform anti-stall test according to the slope from low to high; Obtaining a limit value of the device that can ensure that the vehicle does not stall at each slope until the limit value of the device reaches its maximum limit value, and obtaining a limit interpolation curve between the device and the slope; While the first device maintains its maximum limit value, the test slope value is continuously increased. The second device intervenes in the anti-stall test to obtain the limit value of the second device that can ensure that the vehicle does not stall at each slope. This is done until the limit value of the second device reaches its maximum limit value, thereby obtaining a limit interpolation curve between the second device and the slope. While the first and second devices maintain their maximum limit values, the test slope value is continuously increased, and the third device is used in the anti-stall test to obtain the limit value of the third device that can ensure that the vehicle does not stall at each slope. This is done until the limit value of the third device reaches its maximum limit value, thereby obtaining a limit interpolation curve between the third device and the slope. In this way, the correlation between the slope at each level of power limitation and the corresponding limit value of each device is obtained.

[0031] The following examples illustrate how to determine the relationship between the limit value of each device and the slope value at each slope, using the following scenarios: a variable motor as the limiting device for level one power limitation, a variable motor and a closed variable pump as the limiting device for level two power limitation, and a variable motor, a closed variable pump, and an engine as the limiting device for level three power limitation: First, the main slope is divided into several slope test values according to the vehicle's driving conditions and test conditions, and then tests are performed from low to high slopes. The critical value of the variable motor displacement that can ensure the vehicle does not stall is obtained at each slope until the variable motor limit value reaches the maximum, thereby obtaining a slope-variable motor displacement limit interpolation curve. At this time, if the slope increases further, it is no longer possible to limit the speed by adjusting the variable motor displacement. At this time, the secondary power limit intervenes to limit the displacement of the closed variable pump until the closed variable pump limit value reaches the maximum, thereby obtaining a slope-closed variable pump displacement limit interpolation curve. Finally, the engine speed is limited to obtain a slope-engine speed limit interpolation curve. This method obtains the correlation between the slope and the limit value at each level of power limit, ensuring that stalling does not occur under various operating conditions.

[0032] Furthermore, in addition to determining the motor displacement limit, pump displacement limit, and engine speed limit based on the slope-limit curve, a limit coefficient is also determined based on the driving condition. For example, further limits may be imposed based on high and low speed gears, hazardous driving conditions, and heavy and light load driving conditions. Ultimately, limit values are obtained for different slopes and driving conditions. Specifically, the vehicle's current driving data, including transmission gear information, is obtained. When the transmission is detected to be in high gear, the power limit for one or more of the vehicle's engine, closed variable pump, and variable motor is multiplied by a first coefficient based on a linear relationship with the slope value.

[0033] When anti-stall control is in effect, if the detected gear switch signal indicates reverse gear (R gear), a power limit value of one or more of the vehicle's engine, closed variable displacement pump, and variable displacement motor is multiplied by a second coefficient based on a linear relationship with the slope value.

[0034] The current driving data of the vehicle is also obtained, including the driving pressure value of the vehicle. The current vehicle is determined to be in a heavy-load driving condition or a light-load driving condition based on the driving pressure value. When anti-stall control is performed under the heavy-load driving condition, the power limit value of one or more of the vehicle's engine, closed variable pump and variable motor is set to be multiplied by a third coefficient based on a linear relationship with the slope value.

[0035] The first and third coefficients for anti-stall control in high-speed transmissions and under heavy-load driving conditions are determined through testing under extreme operating conditions. The specific testing process is similar to that used for limiting interpolation curves. For anti-stall control in reverse, the conditions are considered dangerous, and the second coefficient is manually set based on the driver's actual experience.

[0036] When performing anti-stall control on the vehicle, it is necessary to obtain the engine speed signal in real time. When the engine speed exceeds the set threshold, it is prohibited to intervene in the closed variable pump displacement limit. Because when the engine speed is high, if the closed variable pump displacement limit is suddenly triggered due to the slope, the closed variable pump displacement will be reduced. During the downhill process, the closed variable pump speed will increase, thereby driving the engine speed to increase, resulting in overspeed. Therefore, it is necessary to judge the engine speed. Example 2

[0037] like Figure 2 As shown, a hydrostatic drive vehicle downhill control system includes a hydrostatic controller 11, an engine controller 1, an engine 2, a closed variable pump 3, a closed variable pump electric proportional displacement control valve, a variable motor 4 and a variable motor electric proportional displacement control valve 7, wherein: The signal output end of the hydrostatic controller 11 is connected to the signal input end of the engine controller 1, the closed variable pump electric proportional displacement control valve and the variable motor electric proportional displacement control valve 7; The signal input end of the hydrostatic controller 11 is connected to the signal output end of the engine controller 1, the gearbox 6, the slope detection sensor 13 and the FNR gear switch 14; The signal input end of the hydrostatic controller 11 is also connected to a vehicle speed sensor 15 and / or a motor speed sensor 5; There are two closed variable pump electric proportional displacement control valves, namely a first closed variable pump electric proportional displacement control valve 9 and a second closed variable pump electric proportional displacement control valve 10, both of which are connected to the closed variable pump to achieve stepless conversion of the closed variable pump displacement between the maximum forward displacement and the maximum reverse displacement; The variable motor electric proportional displacement control valve 7 is connected to the variable motor 4; the input end of the engine 2 is connected to the output end of the engine controller 1, and the output shaft end of the engine 2 is connected to the input shaft end of the closed charge pump 3; the two oil ports of the closed variable pump 3 and the two oil ports of the electronically controlled variable motor 4 are respectively connected by pipelines to form a closed loop, and the output shaft end of the electronically controlled variable motor 4 is connected to the gearbox.

[0038] Among them, the engine controller 1 is used to receive the request speed signal to control the engine 2 and feedback the actual speed signal, the motor speed sensor 5 is used to detect the motor speed signal, and the vehicle speed sensor 15 is used to detect the vehicle speed. In this embodiment, the vehicle speed sensor 15 and the motor speed sensor 5 are redundantly controlled. The driving speed can be obtained by calculating the motor speed, and the motor speed can also be calculated by the vehicle speed, thereby preventing driving problems caused by the loss of a sensor signal.

[0039] The transmission 6 is used to change the transmission ratio to achieve high and low speed driving. The transmission also provides feedback on the current high and low speed gear position, providing a basis for determining the vehicle's driving condition. The motor electric proportional displacement control valve 7 controls the variable motor displacement by controlling the current. The hydrostatic controller 11 is the system's main controller and has a built-in downhill anti-stall control method. It receives signals from multiple sensors and performs logical judgment and control based on the downhill anti-stall control method. It ultimately outputs the requested engine speed to the engine controller, the closed variable pump control current to the closed variable pump electric proportional displacement control valve, and the variable motor control current to the motor electric proportional displacement control valve 7.

[0040] For vehicles with switchable seat orientations, the hydrostatic controller's signal input is also connected to a seat orientation sensor 12 to detect the current seat orientation and, in conjunction with the signal from the FNR position switch 14, determine the vehicle's direction of travel. A single seat orientation sensor 12 can be installed for automatic determination, or two can be installed to determine the direction by detecting the seat's working angle. Manual signals can also be provided, controlled by the operator and ultimately transmitted to the controller. For vehicles with fixed seats, this sensor is not required.

[0041] The signal input end of the hydrostatic controller is also connected to a pressure sensor 8 installed at the oil inlet and outlet of the closed variable pump or the oil inlet and outlet of the variable motor. The pressure sensor 8 detects the real-time load pressure value of the vehicle under various working conditions. Combined with other detected vehicle signals, the vehicle climbing and downhill conditions are divided into heavy-load climbing, heavy-load downhill, light-load climbing, and light-load downhill conditions to achieve more precise control. Example 3

[0042] A downhill control device for a hydrostatically driven vehicle includes the aforementioned control system, wherein the control system is used to execute the aforementioned control method.

[0043] In summary, the present invention provides a method, control system, and device for controlling a downhill slope of a hydrostatically driven vehicle. By determining the current operating condition of the vehicle based on relevant vehicle signals, the method performs adaptive adjustment of power limits and limit values at different levels according to the slope value and specific operating conditions of the vehicle under the corresponding operating conditions, thereby preventing the vehicle from stalling. This protects the operator on the one hand, and the variable speed motor and engine of the vehicle on the other.

[0044] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling a hydrostatically driven vehicle downhill, characterized in that: include: Obtain the vehicle's current driving data and determine whether the vehicle is in a downhill condition based on the driving data; When the vehicle is determined to be in downhill operation, the power limit level is evaluated based on the vehicle's current slope value; When it is determined that the current vehicle needs to perform anti-stall control according to the power limit level, one or more of the vehicle's engine, closed variable pump, and variable motor are controlled accordingly to perform combined power limitation.

2. A method for controlling a hydrostatically driven vehicle downhill according to claim 1, characterized in that: There are four levels of power limit: no power limit, level 1 power limit, level 2 power limit, and level 3 power limit. Under the first-level power limitation condition, one of the vehicle's engine, closed variable pump, and variable motor is controlled to limit power; Under the secondary power limiting condition, two of the vehicle's engine, closed variable pump, and variable motor are controlled to limit power; Under the third-level power limitation working condition, the engine, closed variable pump and variable motor that control the vehicle are all power limited.

3. The downhill control method for a hydrostatically driven vehicle according to claim 2, characterized in that: The power limit level is divided according to the threshold range of the current slope value, and the specific steps are as follows: According to the vehicle's driving conditions, multiple slope values are set and anti-stall control tests are performed at each slope value; If, at a certain slope value, speed control can be achieved without limiting any of the engine, closed variable pump, and variable motor, and if speed control is achieved beyond this slope, limiting one of the engine, closed variable pump, and variable motor is required, then this slope value is defined as the first slope threshold; If, at a certain slope value, speed control cannot be achieved by only one of the engine, closed variable pump, or variable motor, the slope value is defined as the second slope threshold; If, at a certain slope value, speed control cannot be achieved using only two devices among the engine, the closed variable pump, and the variable motor, the slope value is defined as the third slope threshold; When the vehicle's current slope value is less than the first slope threshold, it is defined as no power restriction; when the vehicle's current slope value is greater than the first slope threshold and less than the second slope threshold, it is defined as level one power restriction; when the vehicle's current slope value is greater than the second slope threshold and less than the third slope threshold, it is defined as level two power restriction; when the vehicle's current slope value is greater than the third slope threshold, it is defined as level three power restriction.

4. A method for controlling a hydrostatically driven vehicle downhill according to claim 3, characterized in that: When determining the interpolation curve between the limit values of the engine, closed variable pump, and variable motor and the slope value at each slope, the specific steps are as follows: Set multiple slope values according to the vehicle's driving conditions; Randomly select one of the engine, closed variable pump, and variable motor to perform anti-stall test according to the slope from low to high; Obtaining a limit value of the device that can ensure that the vehicle does not stall at each slope until the limit value of the device reaches its maximum limit value, and obtaining a limit interpolation curve between the device and the slope; While the first device maintains its maximum limit value, the test slope value is continuously increased. The second device intervenes in the anti-stall test to obtain the limit value of the second device that can ensure that the vehicle does not stall at each slope. This is done until the limit value of the second device reaches its maximum limit value, and a limit interpolation curve between the second device and the slope is obtained. While the first and second devices maintain their maximum limit values, the test slope value is continuously increased, and the third device is used in the anti-stall test to obtain the limit value of the third device that can ensure that the vehicle does not stall at each slope. This is done until the limit value of the third device reaches its maximum limit value, thereby obtaining a limit interpolation curve between the third device and the slope. In this way, the correlation between the slope at each level of power limitation and the corresponding limit value of each device is obtained.

5. The downhill control method for a hydrostatically driven vehicle according to claim 4, characterized in that: The current driving data of the vehicle is obtained, including the transmission gear information. When it is detected that the transmission is in a high-speed gear, the power limit value of one or more of the vehicle's engine, closed variable pump and variable motor is set to be multiplied by a first coefficient based on a linear relationship with the slope value.

6. The downhill control method for a hydrostatically driven vehicle according to claim 4, characterized in that: The current driving data of the vehicle also includes: seat orientation signal, gear switch signal and slope value.

7. The downhill control method for a hydrostatically driven vehicle according to claim 6, characterized in that: When anti-stall control is being performed, if the detected gear switch signal is a reverse gear, a power limit value of one or more of the vehicle's engine, closed variable pump and variable motor is set to be multiplied by a second coefficient based on a linear relationship with the slope value.

8. The downhill control method for a hydrostatically driven vehicle according to claim 4, characterized in that: The current driving data of the vehicle is also obtained, including the driving pressure value of the vehicle. The current vehicle is determined to be in a heavy-load driving condition or a light-load driving condition based on the driving pressure value. When anti-stall control is performed under the heavy-load driving condition, the power limit value of one or more of the vehicle's engine, closed variable pump and variable motor is set to be multiplied by a third coefficient based on a linear relationship with the slope value.

9. The downhill control method for a hydrostatically driven vehicle according to claim 2, characterized in that: When performing anti-stall control on the vehicle, the engine speed signal is obtained in real time. When the engine speed exceeds the set threshold, intervention of the closed variable pump displacement limit is prohibited.

10. A downhill control system for a hydrostatically driven vehicle, characterized by: It includes a hydrostatic controller, an engine controller, an engine, a closed variable pump, a closed variable pump electric proportional displacement control valve, a variable motor and a variable motor electric proportional displacement control valve, wherein: The signal output end of the hydrostatic controller is connected to the signal input end of the engine controller, the closed variable pump electric proportional displacement control valve and the variable motor electric proportional displacement control valve; The signal input end of the hydrostatic controller is connected to the signal output end of the engine controller, the gearbox, the slope detection sensor and the FNR gear switch; The signal input end of the hydrostatic controller is further connected to a vehicle speed sensor and / or a motor speed sensor; There are two closed variable pump electric proportional displacement control valves, both connected to the closed variable pump, and the variable motor electric proportional displacement control valve is connected to the variable motor; The input end of the engine is connected to the output end of the engine controller, and the output shaft end of the engine is connected to the input shaft end of the closed-type charge pump; The two oil ports of the closed variable pump and the two oil ports of the electronically controlled variable motor are connected by pipelines to form a closed loop, and the output shaft end of the electronically controlled variable motor is connected to the gearbox.

11. The downhill control system for a hydrostatically driven vehicle according to claim 10, characterized in that: The signal input end of the hydrostatic controller is also connected to a seat orientation detection sensor.

12. The downhill control system for a hydrostatically driven vehicle according to claim 10, characterized in that: The signal input end of the hydrostatic controller is further connected to a pressure sensor installed at the oil inlet and outlet of the closed variable displacement pump or the oil inlet and outlet of the variable displacement motor.

13. A downhill control device for a hydrostatically driven vehicle, characterized in that: The system comprises the control system according to any one of claims 10 to 12, wherein the control system is used to execute the control method according to any one of claims 1 to 9.

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