A method for controlling the speed of a cooling fan of a tracked vehicle using liquid viscosity

Abstract

The application provides a liquid viscosity speed regulation control method for a cooling fan of a tracked vehicle, four working modes of optimal rotating speed control, emergency discharge control, two-gear switch control and external direct control are designed, and specific control methods in each mode are provided, so that the sliding friction speed regulation capacity within the heat load capacity range of the liquid viscosity is fully utilized, the vehicle temperature control precision is further improved, the dynamic impact torque of the fan shaft system is reduced by inhibiting the rotating speed fluctuation amplitude of the fan, and the reliability of the vehicle comprehensive transmission device is improved. In addition, the power occupation of the fan in an emergency condition is released by the emergency discharge control mode, the emergency acceleration performance and the steering maneuvering capacity of the vehicle in the emergency condition are improved, and the control target of the optimal comprehensive performance of the vehicle is achieved.

Description

Technical Field

[0001] This invention belongs to the field of liquid viscosity speed control technology, specifically relating to a liquid viscosity speed control method for a cooling fan of a tracked vehicle. Background Technology

[0002] Tracked vehicles commonly use viscous clutches to regulate the speed of cooling fans. Traditional speed control methods typically employ multi-speed settings, which only aim to keep engine coolant and transmission oil temperatures within a certain range. Because this method is relatively simple, it cannot effectively counteract fluctuations in engine speed, causing drastic fan speed fluctuations and generating large dynamic impact torques, thus reducing the reliability of the fan drive shaft system. Furthermore, traditional methods, due to their singular control objective, cannot comprehensively consider both the vehicle's cooling and mobility requirements, failing to achieve optimal overall vehicle performance. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] This invention proposes a liquid viscous speed control method for cooling fans of tracked vehicles to solve the technical problems of how to improve the temperature control accuracy of the vehicle, suppress the dynamic impact torque of the fan shaft system to improve the reliability of the fan transmission, and release the fan power occupation in emergency situations to improve the vehicle's rapid acceleration performance and steering maneuverability in emergency situations.

[0005] (II) Technical Solution

[0006] To address the aforementioned technical problems, this invention proposes a viscous speed control method for cooling fans in tracked vehicles. This method collects external switch commands, engine speed, fan speed, engine coolant temperature, transmission oil temperature, and engine throttle opening signals. It then executes different operating modes and outputs a control current signal to the viscous clutch, thereby controlling the fan speed. This improves vehicle temperature control accuracy, reduces the dynamic impact torque of the fan shaft system, enhances vehicle maneuverability in emergency situations, and achieves the optimal overall vehicle performance control objective.

[0007] Furthermore, the liquid viscosity speed control method specifically includes the following steps:

[0008] S1. Execute the optimal speed control mode

[0009] Set the external switch in the cockpit to automatic mode to enable the viscous clutch to operate in the optimal speed control mode. Utilize the slippery speed regulation capability of the viscous clutch to resist the interference of engine speed fluctuations on fan speed. With the optimization goal of improving temperature control accuracy and reducing fan speed fluctuations, the optimal control of fan speed is achieved, thereby synergistically improving vehicle temperature control accuracy and transmission reliability.

[0010] S2. Execute two-position switch control mode

[0011] When the single sliding time reaches the maximum allowable sliding time for viscous fluid, the optimal speed control mode is exited, and a two-speed switch control mode is entered. In the two-speed switch control mode, the basic principle of control is to minimize the heat generation intensity of viscous fluid sliding. The viscous fluid can only operate in two working states: fully disengaged and fully engaged, in order to minimize the heat generation of viscous fluid sliding. When operating in fully disengaged viscous fluid mode, the fan idles at its lowest speed. When operating in fully engaged viscous fluid mode, the fan rotates at its highest speed. When the set duration is reached in the two-speed switch control mode, the viscous fluid has achieved sufficient heat dissipation, and the optimal speed control mode is automatically restored. When the oil temperature or water temperature is below the lower limit of the temperature control or above the upper limit of the temperature control, the two-speed switch control mode is entered.

[0012] S3. Execute emergency exhaust control mode

[0013] The controller monitors the engine throttle opening signal in real time and identifies whether the driver has suddenly pressed the accelerator by calculating the rate of change of the throttle opening. When sudden acceleration is detected, the controller checks whether the engine coolant temperature and transmission oil temperature are below the set thresholds to determine if the fluid viscosity meets the emergency discharge conditions. When sudden acceleration is detected and the fluid viscosity meets the emergency discharge conditions, the controller executes the emergency discharge control mode to control the fluid viscosity to discharge quickly and cut off the fan power flow to ensure that the engine power is used for vehicle maneuvering to the maximum extent. By monitoring the rate of change of engine speed, the controller identifies whether the vehicle has completed the emergency maneuver and monitors whether the engine coolant temperature and transmission oil temperature exceed the temperature control limit. If any of the above conditions are met, the controller exits the emergency discharge control mode and restores the optimal speed control mode.

[0014] S4. Execute external direct control mode

[0015] When control is required according to the driver's intention, the external switch in the cockpit is set to manual mode to execute the external direct control mode. The driver controls the hydraulic pressure to force the viscous clutch to engage, and the fan runs at full speed; or the driver controls the hydraulic pressure to drop to the minimum to disengage the viscous clutch, and the fan idles at the minimum speed.

[0016] Furthermore, in step S1, the optimal speed control method includes executing outer-loop temperature control and inner-loop speed control. The outer-loop temperature control aims to improve vehicle temperature control accuracy and suppress fan speed fluctuations, using fan speed as the optimization variable and employing model predictive control to calculate the optimal fan speed in real time. The inner-loop speed control uses the optimal fan speed calculated from the outer-loop temperature control as input, employing a combination of PID speed feedback control and proportional inverse compensation feedforward control to calculate the control current signal as the feedforward component of the viscous control signal, thereby achieving precise tracking of the optimal fan speed.

[0017] Furthermore, in step S1, when performing outer-loop temperature control, the engine coolant temperature and transmission oil temperature are reduced in dimensionality using a temperature dimensionality reduction model. Specifically, the average value of the engine coolant temperature and transmission oil temperature is taken as the target reference temperature T for control. wo .

[0018] Furthermore, in step S1, the target reference temperature T is simplified and considered using a temperature prediction model. wo It is only related to the engine speed n1 and the fan speed n2, where the engine speed n1 determines the heat generation intensity of the engine compartment and the fan speed n2 determines the heat dissipation capacity of the engine compartment. The target reference temperature T is simplified by superimposing two first-order inertial elements. wo The dynamic transfer characteristics between engine speed n1 and fan speed n2, specifically the transfer function T w Expressed as:

[0019]

[0020] In the formula, t we t wf These represent the dynamic response speeds of temperature to engine speed and fan speed, respectively; k we k wf These represent the proportional relationship between temperature and engine speed and fan speed under thermally stable conditions, respectively; the above four parameters are obtained using a system identification method based on actual sports car data; s is a complex variable in the transfer function.

[0021] Furthermore, in step S1, when performing outer-loop temperature control, an optimization objective function and constraints are defined through an optimization model; among them, the optimization objectives are to achieve the highest temperature control accuracy and the lowest fan speed fluctuation within the prediction interval, and the optimization objective function is defined as follows:

[0022]

[0023] In the formula, t is the single-step prediction time of the model, predicting n steps into the future, with a total prediction interval of nt; T′ wo To control the target temperature, ΔT wo Δn2 is the difference between the model-predicted temperature and the target control temperature in step i; Δn2 is the difference between the model-predicted speed in the current step and the previous step; n′2 is the median value of the fan speed range; k is the weighted adjustment coefficient of the two optimization sub-objectives of temperature control accuracy and fan speed fluctuation.

[0024] Furthermore, in step S1, when performing the inner loop speed control, a combination of PID speed feedback control and proportional inverse feedforward control is used to generate a viscous control signal by weighting the feedback and feedforward control components.

[0025] Furthermore, in step S1, when calculating the feedforward control component based on the proportional inverse compensation feedforward control method, the main loop data model is used. The main loop data model is a set of multiple main loop data under multiple viscous input speeds. Based on the main loop data model, the viscous control oil pressure required to achieve the optimal fan speed is calculated using the proportional inverse compensation feedforward control method. Then, the viscous control signal feedforward component required to achieve the above-mentioned viscous control oil pressure is calculated by combining the valve control characteristic curve.

[0026] Furthermore, in step S2, the average of the measured engine coolant temperature and transmission oil temperature is compared with the set temperature threshold to select a state. When a certain measured temperature is higher than the upper limit of the control target, the system operates in a fully engaged state. When the temperature drops to a certain value, the system operates in a fully disengaged state.

[0027] (III) Beneficial Effects

[0028] This invention proposes a viscous speed control method for cooling fans in tracked vehicles. By designing four operating modes—optimal speed control, emergency de-energization control, two-speed switch control, and direct external operation—and specific control methods for each mode, it fully utilizes the slip-friction speed regulation capability within the viscous heat load capacity range. This not only further improves the vehicle's temperature control accuracy but also reduces the dynamic impact torque of the fan shaft system by suppressing fan speed fluctuations, thereby enhancing the reliability of the vehicle's overall transmission system. Furthermore, the emergency de-energization control mode relieves the fan's power consumption in emergency situations, improving the vehicle's rapid acceleration and steering maneuverability under emergency conditions, achieving the control objective of optimal overall vehicle performance. Attached Figure Description

[0029] Figure 1 Schematic diagram of a liquid viscous fan speed control system;

[0030] Figure 2 This is a schematic diagram of the liquid viscosity speed control method of the present invention;

[0031] Figure 3 This is a schematic diagram of the optimal speed control principle of the present invention;

[0032] Figure 4 This is the main loop data model of the present invention;

[0033] Figure 5 This is a comparison chart of the temperature control effect before and after the implementation of the present invention;

[0034] Figure 6 This is a comparison diagram of the dynamic distortion of the fan before and after the implementation of the present invention. Detailed Implementation

[0035] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0036] The principle of the liquid viscous speed control system for cooling fans of tracked vehicles is as follows: Figure 1 As shown, the viscous speed control system mainly consists of a viscous clutch, a hydraulic cylinder, a proportional valve, and a controller. The input end of the viscous clutch is connected to the engine, and the output end is connected to the cooling fan. The proportional valve receives the control current signal from the controller to change the operating oil pressure in the hydraulic cylinder, thereby altering the viscous transmission ratio by changing the thickness of the lubricating oil film between the friction pairs of the viscous clutch, ultimately controlling the fan speed.

[0037] Regarding the aforementioned viscous speed control system, this embodiment proposes a viscous speed control method for a cooling fan in a tracked vehicle, the main principle of which is as follows: Figure 2 As shown, by collecting external switch commands, engine speed, fan speed, engine coolant temperature, transmission oil temperature, and engine throttle opening signals, different operating modes are executed, and a control current signal for the viscous clutch is output to control the fan speed. This improves vehicle temperature control accuracy, reduces the dynamic impact torque of the fan shaft system, and enhances vehicle maneuverability in emergency situations, thereby achieving the control goal of optimal overall vehicle performance. The viscous speed control method specifically includes the following steps:

[0038] S1. Execute the optimal speed control mode

[0039] Set the external switch in the cockpit to automatic mode to operate the viscous clutch in optimal speed control mode. The goal of optimal speed control mode is to fully utilize the slip-slip speed regulation capability of the viscous clutch to resist the interference of engine speed fluctuations on fan speed, with the optimization objectives of improving temperature control accuracy and reducing fan speed fluctuations. By achieving optimal fan speed control, the vehicle's temperature control accuracy and transmission reliability are improved in tandem.

[0040] The optimal speed control method is as follows Figure 3 As shown, the system comprises two parts: an outer-loop temperature control and an inner-loop speed control. The outer-loop temperature control aims to improve vehicle temperature control accuracy and suppress fan speed fluctuations, using fan speed as the optimization variable. Model predictive control (MPC) is employed to calculate the optimal fan speed in real time. The inner-loop speed control uses the optimal fan speed calculated from the outer-loop temperature control as input. It combines PID speed feedback control and proportional inverse compensation feedforward control to calculate the control current signal as the feedforward component of the viscous fluid control signal. This overcomes the inherent nonlinearity and large hysteresis of viscous fluid, achieving precise tracking of the optimal fan speed.

[0041] When performing outer-loop temperature control, to reduce the computational load of the controller in real-time calculation of the optimal fan speed, a temperature dimensionality reduction model is used to reduce the dimensionality of the engine coolant temperature and transmission oil temperature. Specifically, the average value of the engine coolant temperature and transmission oil temperature is taken as the target reference temperature T for control. wo .

[0042] To save on controller computing power, the target reference temperature T is assumed to be simplistically considered using the temperature prediction model. wo It is only related to the engine speed n1 and the fan speed n2, where the engine speed n1 determines the heat generation intensity of the engine compartment and the fan speed n2 determines the heat dissipation capacity of the engine compartment. The target reference temperature T is simplified by superimposing two first-order inertial elements. wo The dynamic transfer characteristics between engine speed n1 and fan speed n2, specifically the transfer function T w Expressed as:

[0043]

[0044] In the formula, t we t wf These represent the dynamic response speeds of temperature to engine speed and fan speed, respectively; k we k wf These represent the proportional relationship between temperature and engine speed and fan speed under thermally stable conditions, respectively; the above four parameters are obtained using a system identification method based on actual sports car data; s is a complex variable in the transfer function.

[0045] When performing outer-loop temperature control, an optimization objective function and constraints are defined through an optimization model. The optimization objectives are to achieve the highest temperature control accuracy and the lowest fan speed fluctuation within the prediction interval. The optimization objective function is defined as follows:

[0046]

[0047] In the formula, t is the single-step prediction time of the model, predicting n steps into the future, with a total prediction interval of nt; T′ wo To control the target temperature, ΔT wo Δn2 is the difference between the model-predicted temperature and the target control temperature in step i; Δn2 is the difference between the model-predicted speed in the current step and the previous step; n′2 is the median value of the fan speed range; k is the weighted adjustment coefficient of the two optimization sub-objectives of temperature control accuracy and fan speed fluctuation.

[0048] Based on the effective speed regulation range of the viscous fluid and combined with the instantaneous speed input constraint of the engine, the fan speed regulation range within the predicted range is determined. Based on the thermal load capacity of the viscous fluid, the maximum duration of a single slip friction and the minimum time interval between two consecutive slip friction states are limited. In other words, the maximum working time of a single optimal speed control mode and the minimum time interval between two consecutive optimal speed control modes are constrained to prevent overheating damage to the viscous fluid friction pair.

[0049] To overcome the inherent nonlinearity and large hysteresis of viscous fluid during inner-loop speed control and achieve precise fan speed control, a combination of PID speed feedback control and proportional inverse feedforward control is employed. The viscous fluid control signal is generated by weighting the feedback and feedforward control components. Specifically, the calculation of the feedforward control components based on the proportional inverse compensation feedforward control method requires the use of the main loop data model. For example... Figure 4 As shown, the main loop data refers to the steady-state relationship curve between the control oil pressure and the actual viscous output speed, measured experimentally under open-loop control mode, given a constant viscous input speed. This curve includes a complete acceleration and deceleration process. Due to the severe nonlinearity and large hysteresis inherent in viscous fluid, the main loop data curve constitutes a large hysteresis loop, making precise fan speed control impossible using only conventional PID feedback control. Furthermore, since the vehicle engine actually operates over a wide speed range, the main loop data model used in this method is a set of multiple main loop data points under multiple viscous input speeds. Based on the main loop data model, the viscous control oil pressure required to achieve the optimal fan speed is calculated using a proportional inverse compensation feedforward control method. Then, the feedforward component of the viscous control signal required to achieve the aforementioned viscous control oil pressure is further calculated by combining the valve control characteristic curve.

[0050] S2. Execute two-position switch control mode

[0051] The optimal speed control mode is the main operating mode of the viscous clutch. However, the optimal speed control mode must operate within the viscous thermal load capacity range. The viscous clutch cannot continuously operate in the optimal speed control mode, otherwise it will cause overheating damage to the viscous friction pair.

[0052] When the single sliding time reaches the maximum allowable sliding duration for viscous fluid, the optimal speed control mode exits and enters the two-speed switch control mode. In the two-speed switch control mode, the basic control principle is to minimize the heat generated by viscous fluid sliding. The viscous fluid can only operate in two states: fully disengaged and fully engaged, to minimize heat generation from viscous fluid sliding. When operating in fully disengaged mode, the fan idles at its lowest speed; when operating in fully engaged mode, the fan rotates at its highest speed. When the set duration is reached in the two-speed switch control mode, the viscous fluid has achieved sufficient heat dissipation, and the optimal speed control mode automatically resumes. The mode is selected by comparing the average measured engine coolant temperature and transmission oil temperature with the set temperature threshold. When a measured temperature exceeds the upper limit of the control target (e.g., 95℃), the fully engaged state is activated. When the temperature drops to a certain value (e.g., 85℃), the fully disengaged state is activated.

[0053] In addition, when the oil temperature or water temperature is below the lower limit of the temperature control or above the upper limit of the temperature control, it enters a two-speed switch control mode to ensure that the fan can idle at the lowest cooling capacity or run at full speed at the highest cooling capacity to adjust the temperature to the target range as quickly as possible.

[0054] S3. Execute emergency exhaust control mode

[0055] The controller monitors the engine throttle opening signal in real time and identifies whether the driver has engaged in sudden acceleration by calculating the rate of change of throttle opening. When sudden acceleration is detected, the controller checks whether the engine coolant temperature and transmission oil temperature are below set thresholds to determine if the fluid viscosity meets the emergency discharge conditions. If sudden acceleration is detected and the fluid viscosity meets the emergency discharge conditions, the emergency discharge control mode is executed to control rapid fluid discharge and cut off fan power flow to ensure that the engine power is used for maximum vehicle maneuverability. By monitoring the rate of change of engine speed, the controller identifies whether the vehicle has completed the emergency maneuver and whether the engine coolant temperature and transmission oil temperature exceed the temperature control limits. If either condition is met, the emergency discharge control mode is exited, and the optimal speed control mode is restored.

[0056] S4. Execute external direct control mode

[0057] When control is required according to the driver's intention, the external switch in the cockpit is set to manual mode to execute the external direct control mode. The driver controls the hydraulic pressure to force the viscous clutch to engage, and the fan runs at full speed; or the driver controls the hydraulic pressure to drop to the minimum to disengage the viscous clutch, and the fan idles at the minimum speed.

[0058] like Figure 5 and 6As shown, the control method proposed in this invention is verified using real vehicle data. The results show that, compared with previous control methods, the temperature control accuracy is significantly improved and the dynamic torque of the shaft system is significantly reduced after implementing this control method. This invention, while improving temperature control accuracy, can further enhance the reliability of the fan shaft system. Furthermore, because the liquid viscous emergency desiccation control mode proposed in this invention can briefly cut off the fan power flow in emergency situations compared to previous methods, it can effectively improve the vehicle's rapid acceleration and steering maneuverability in emergency situations, thereby achieving the control goal of optimal overall vehicle performance.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the speed of a cooling fan in a tracked vehicle using viscous fluid, characterized in that, The described viscous speed control method acquires external switch commands, engine speed, fan speed, engine coolant temperature, transmission oil temperature, and engine throttle opening signals. It then executes different operating modes and outputs a control current signal to the viscous clutch to control the fan speed. This improves vehicle temperature control accuracy, reduces dynamic impact torque on the fan shaft system, enhances vehicle maneuverability in emergency situations, and achieves the optimal overall vehicle performance control objective. The liquid viscosity speed control method specifically includes the following steps: S1. Execute the optimal speed control mode Set the external switch in the cockpit to automatic mode to enable the viscous clutch to operate in the optimal speed control mode. Utilize the slippery speed regulation capability of the viscous clutch to resist the interference of engine speed fluctuations on fan speed. With the optimization goal of improving temperature control accuracy and reducing fan speed fluctuations, the optimal control of fan speed is achieved, thereby synergistically improving vehicle temperature control accuracy and transmission reliability. S2. Execute two-position switch control mode When the single sliding time reaches the maximum allowable sliding time for viscous fluid, the optimal speed control mode is exited, and a two-speed switch control mode is entered. In the two-speed switch control mode, the basic principle of control is to minimize the heat generation intensity of viscous fluid sliding. The viscous fluid can only operate in two working states: fully disengaged and fully engaged, in order to minimize the heat generation of viscous fluid sliding. When operating in fully disengaged viscous fluid mode, the fan idles at its lowest speed. When operating in fully engaged viscous fluid mode, the fan rotates at its highest speed. When the set duration is reached in the two-speed switch control mode, the viscous fluid has achieved sufficient heat dissipation, and the optimal speed control mode is automatically restored. When the oil temperature or water temperature is below the lower limit of the temperature control or above the upper limit of the temperature control, the two-speed switch control mode is entered. S3. Execute emergency exhaust control mode The controller monitors the engine throttle opening signal in real time and identifies whether the driver has suddenly pressed the accelerator by calculating the rate of change of the throttle opening. When sudden acceleration is detected, the controller checks whether the engine coolant temperature and transmission oil temperature are below the set thresholds to determine if the fluid viscosity meets the emergency discharge conditions. When sudden acceleration is detected and the fluid viscosity meets the emergency discharge conditions, the controller executes the emergency discharge control mode to control the fluid viscosity to discharge quickly and cut off the fan power flow to ensure that the engine power is used for vehicle maneuvering to the maximum extent. By monitoring the rate of change of engine speed, the controller identifies whether the vehicle has completed the emergency maneuver and monitors whether the engine coolant temperature and transmission oil temperature exceed the temperature control limit. If any of the above conditions are met, the controller exits the emergency discharge control mode and restores the optimal speed control mode. S4. Execute external direct control mode When control is required according to the driver's intention, the external switch in the cockpit is set to manual mode to execute the external direct control mode. The driver controls the hydraulic pressure to force the viscous clutch to engage, and the fan runs at full speed; or the driver controls the hydraulic pressure to drop to the minimum to disengage the viscous clutch, and the fan idles at the minimum speed.

2. The liquid viscosity speed control method as described in claim 1, characterized in that, In step S1, the optimal speed control method includes executing temperature outer loop control and speed inner loop control. The temperature outer loop control aims to improve vehicle temperature control accuracy and suppress fan speed fluctuations, using fan speed as the optimization variable and employing model predictive control to calculate the optimal fan speed in real time. The speed inner loop control uses the optimal fan speed calculated from the temperature outer loop control as input, employing a combination of PID speed feedback control and proportional inverse compensation feedforward control to calculate the control current signal as the feedforward component of the viscous control signal, thereby achieving precise tracking of the optimal fan speed.

3. The liquid viscosity speed control method as described in claim 2, characterized in that, In step S1, when performing outer-loop temperature control, the engine coolant temperature and transmission oil temperature are reduced in dimensionality using a temperature dimensionality reduction model. Specifically, the average value of the engine coolant temperature and transmission oil temperature is taken as the target reference temperature for control. .

4. The liquid viscosity speed control method as described in claim 3, characterized in that, In step S1, the target reference temperature is simplified and assumed using a temperature prediction model. Only related to engine speed and fan speed Related, including engine speed The fan speed determines the heat generation intensity of the engine compartment. The target reference temperature is simplified by superimposing two first-order inertial elements to determine the heat dissipation capacity of the engine compartment. With engine speed and fan speed Dynamic transfer characteristics between them, specific transfer functions Expressed as: In the formula, , These represent the dynamic response speeds of temperature to engine speed and fan speed, respectively. , These represent the proportional relationship between temperature and engine speed and fan speed under thermally stable conditions, respectively; the above four parameters are obtained using a system identification method based on actual sports car data; s For complex variables in the transfer function.

5. The liquid viscosity speed control method as described in claim 4, characterized in that, In step S1, when performing outer-loop temperature control, the optimization objective function and constraints are defined through an optimization model; among them, the optimization objectives are to achieve the highest temperature control accuracy and the lowest fan speed fluctuation within the prediction interval, and the optimization objective function is defined as follows: In the formula, To predict the duration of a single step for the model, and to predict the future. Step, the total duration of the predicted interval is ; To control the temperature to the target, For the first The difference between the temperature predicted by the step model and the target control temperature; This represents the difference in rotational speed predicted by the model between the current step and the previous step. To take the median value of the fan speed range; The weighted adjustment coefficients are used for the two optimization sub-objectives of temperature control accuracy and fan speed fluctuation.

6. The liquid viscosity speed control method as described in claim 2, characterized in that, In step S1, when performing the inner loop speed control, a combination of PID speed feedback control and proportional inverse feedforward control is used to generate a viscous control signal by weighting the feedback and feedforward control components.

7. The liquid viscosity speed control method as described in claim 6, characterized in that, In step S1, when calculating the feedforward control component based on the proportional inverse compensation feedforward control method, the main loop data model is used. The main loop data model is a set of multiple main loop data under multiple viscous input speeds. Based on the main loop data model, the viscous control oil pressure required to achieve the optimal fan speed is calculated using the proportional inverse compensation feedforward control method. Then, the feedforward component of the viscous control signal required to achieve the above-mentioned viscous control oil pressure is calculated by combining the valve control characteristic curve.

8. The liquid viscosity speed control method as described in claim 1, characterized in that, In step S2, the state is selected by comparing the average of the measured engine coolant temperature and transmission oil temperature with the set temperature threshold. When a certain measured temperature is higher than the upper limit of the control target, it operates in the fully engaged state. When the temperature drops to a certain value, it operates in the fully disengaged state.

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