Vehicle wet clutch pressure control method

Abstract

This invention discloses a wet clutch pressure control method for a vehicle, comprising: acquiring a target pressure of the wet clutch and acquiring the actual pressure of the wet clutch; determining the operating state of the wet clutch based on the target pressure and the actual pressure, wherein the operating state of the wet clutch includes an idle state and a non-idle state; when the operating state of the wet clutch is determined to be an idle state, acquiring the idle control parameters of the wet clutch and performing open-loop control of the wet clutch pressure based on the idle control parameters; when the operating state of the wet clutch is determined to be a non-idle state, acquiring the non-idle control parameters of the wet clutch and performing feedforward pressure plus closed-loop control of the wet clutch pressure based on the non-idle control parameters. The pressure control process is divided into four states, with corresponding control methods and parameters used in each state to improve the robustness of the pressure control.

Description

Technical Field

[0001] This invention relates to the field of clutch control technology, and more particularly to a method for controlling the pressure of a wet clutch in a vehicle. Background Technology

[0002] The wet clutch pressure control system is a non-linear coupling system composed of mechanical, electrical, and hydraulic components. The actual pressure in the clutch chamber, through the clutch's torque characteristics, directly affects the vehicle's torque transmission and thus the actual driving experience. During clutch filling, a mechanical pump provides power, and the oil passes through the pressure control valve to push the clutch piston, overcoming the pressure of the return spring. At this point, the load stiffness of the piston movement is equal to the return spring stiffness, ultimately pressing the friction plates against the pressure plates. At this point, the load stiffness of the piston movement is equal to the return spring stiffness plus the corrugated plate stiffness. As the pressure in the clutch piston chamber further increases, the piston essentially stops moving. The position where the free clearance of the clutch friction plates is completely eliminated is defined as the Volume-Kiss Point (VKP). At this point, the system load stiffness is equal to the return spring stiffness plus the corrugated plate stiffness plus the friction material stiffness. The clutch pressure depends entirely on the outlet pressure of the pressure valve.

[0003] During operation, the physical characteristics of the clutch differ at each stage of motion, resulting in varying actual pressure responses within the clutch chamber. Currently, both open-loop and closed-loop control methods exist. With open-loop control, the initial control effect after calibration may be ideal, but as the vehicle's operating environment changes and hardware system performance degrades, the control accuracy of the actual clutch pressure decreases significantly. While a single closed-loop control method can improve the clutch's applicability and control accuracy to some extent, it suffers from the inability to control the pressure and pressure response differences at each stage of clutch motion due to varying clutch states. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of large differences in the pressure response of the clutch during different motion processes in the prior art, and how to achieve the following control of the clutch oil chamber pressure relative to the target pressure.

[0005] To address the aforementioned problems, one embodiment of the present invention provides a wet clutch pressure control method for a vehicle, comprising the following steps: obtaining a target pressure of the wet clutch and obtaining an actual pressure of the wet clutch; determining the operating state of the wet clutch based on the target pressure and the actual pressure, wherein the operating state of the wet clutch includes an idle state and a non-idle state; when the operating state of the wet clutch is determined to be an idle state, obtaining an idle control parameter of the wet clutch and performing open-loop control on the pressure of the wet clutch based on the idle control parameter; when the operating state of the wet clutch is determined to be a non-idle state, obtaining a non-idle control parameter of the wet clutch and performing feedforward pressure plus closed-loop control on the pressure of the wet clutch based on the non-idle control parameter.

[0006] By adopting the above technical solution, the target pressure and actual pressure of the clutch are obtained, and the working state of the clutch is divided into idle state and non-idle state according to the target pressure and actual pressure. Moreover, different pressure control methods are used in different states. When in the idle state, an open-loop control method is used, and the control pressure of the clutch is determined by determining the idle parameters based on the target pressure of the clutch. When in the non-idle state, a feedforward plus closed-loop control method is used. At this time, the control pressure of the clutch is equal to the feedforward control pressure plus the closed-loop control pressure. The clutch pressure control is divided into multiple states according to the target pressure and the clutch movement stage, and different control methods are adopted in each state to adapt to the influence of the actual pressure during the clutch movement process, improve the control of the actual clutch pressure, and thus improve the robustness of the actual pressure control.

[0007] According to another specific embodiment of the present invention, the wet clutch pressure control method for a vehicle disclosed in the present invention, when it is determined that the working state of the wet clutch is an idle state, acquires a target pressure as an idle control parameter, and performs open-loop control on the pressure of the wet clutch according to the target pressure.

[0008] Using the above technical solution, the working state of the clutch is first determined. If the working state of the clutch is in the idle state, the pressure control method adopted in the idle state is open-loop control. The idle control parameters are obtained based on the target pressure. The control pressure of the clutch in this state is adjusted according to the idle control parameters to achieve better open-loop control pressure.

[0009] According to another specific embodiment of the present invention, the wet clutch pressure control method for a vehicle disclosed in the present invention determines that the working state of the wet clutch is an idle state by: obtaining the minimum torque transmission pressure of the wet clutch and comparing the target pressure with the minimum torque transmission pressure; when the target pressure is less than the minimum torque transmission pressure, it is determined that the working state of the wet clutch is an idle state.

[0010] According to another specific embodiment of the present invention, the wet clutch pressure control method for a vehicle disclosed in the present invention, when it is determined that the working state of the wet clutch is from non-idle state to idle state, obtains the maximum speed of the transmission input shaft within a predetermined time period, and adjusts the idle control parameters according to the maximum speed.

[0011] Using the above technical solution, when the wet clutch is determined to be in an idle state, the speed of the transmission input shaft will not change. However, when the wet clutch transitions from a non-idle state to an idle state, the speed of the transmission input shaft will fluctuate. During open-loop control based on the target pressure, the maximum speed within a predetermined time period is obtained by monitoring the transmission input shaft speed. Adjusting the idle control parameters based on this maximum speed further enhances the open-loop control effect.

[0012] According to another specific embodiment of the present invention, the wet clutch pressure control method for a vehicle disclosed in the present invention, when it is determined that the working state of the wet clutch is a non-idle state, acquires the oil temperature of the wet clutch and the pressure difference between the target pressure and the actual pressure as non-idle control parameters, and performs feedforward pressure plus closed-loop control on the pressure of the wet clutch according to the non-idle control parameters.

[0013] By adopting the above technical solution, when the working state of the wet clutch enters the non-idle state, the non-idle control parameters are obtained by the oil temperature of the wet clutch and the pressure difference between the target pressure and the actual pressure. Then, the pressure of the wet clutch is controlled by feedforward and closed loop according to the non-idle control parameters. The control effect is better and the actual pressure response effect of the wet clutch is improved.

[0014] According to another specific embodiment of the present invention, the wet clutch pressure control method for a vehicle disclosed in the present invention includes a non-idle state, a ready state, and a linear state; wherein determining the wet clutch to be in the ready state includes: if the target pressure jumps from below the minimum torque transmission pressure to the minimum torque transmission pressure, then the working state of the wet clutch is determined to be in the ready state; and determining the wet clutch to be in the non-linear state or the linear state includes: acquiring the pressure of the wet clutch from the start of torque transmission to the position where the friction plate gap is completely eliminated, and comparing it with the target pressure and the actual pressure respectively; if the target pressure or the actual pressure is less than the pressure of the wet clutch from the start of torque transmission to the position where the friction plate gap is completely eliminated, then the working state of the wet clutch is determined to be in the non-linear state; if the target pressure or the actual pressure is greater than or equal to the pressure of the wet clutch from the start of torque transmission to the position where the friction plate gap is completely eliminated, then the working state of the wet clutch is determined to be in the linear state.

[0015] By adopting the above technical solution, the non-idle state is further divided into a ready state, a linear state, and a nonlinear state. Moreover, the control parameters obtained in each state are different, which improves the actual pressure control accuracy of the clutch and covers the pressure response problem of the clutch in different motion stages through different control states, so that the actual pressure of the wet clutch can accurately respond to the target pressure.

[0016] According to another specific embodiment of the present invention, the wet clutch pressure control method for vehicles disclosed in the present invention is a feedforward pressure control plus closed-loop control, which is a feedforward pressure control plus closed-loop proportional-integral-derivative pressure control.

[0017] The above technical solution uses a closed-loop proportional-integral-derivative (PID) pressure control method to control pressure. This means that the proportional term controls the pressure, the integral term controls the pressure, and the derivative term controls the pressure. This is called closed-loop proportional-integral-derivative (PID) pressure control. The PID closed-loop control method provides feedback correction for the pressure. The basis of PID closed-loop pressure control is proportional control. Integral control can eliminate errors in each pressure, and derivative control can reduce overshoot tendency. The PID closed-loop pressure control method is simple to operate, and the control parameters of the closed-loop pressure control are relatively easy to determine.

[0018] According to another specific embodiment of the present invention, the wet clutch pressure control method for a vehicle disclosed in the present invention obtains the response time and overshoot of the wet clutch based on the pressure difference between the target pressure and the actual pressure, and adjusts and determines the control coefficients of feedforward pressure control plus closed-loop proportional-integral-derivative pressure control in the preparation state based on the response time and overshoot.

[0019] Using the above technical solution, when the wet clutch is in the preparation state, a feedforward plus PID closed-loop control method is adopted. During the control process, the response time and overshoot of the wet clutch are obtained according to the pressure difference between the target pressure and the actual pressure. Then, the integral term coefficient, derivative term coefficient and proportional term coefficient are adjusted according to the overshoot and response time, so that the control coefficients are adjusted in the preparation state, thereby improving the control effect in the preparation state.

[0020] According to another specific embodiment of the present invention, the wet clutch pressure control method for a vehicle disclosed in the present invention obtains the maximum delay, maximum error, and linearity of the wet clutch based on the pressure difference between the target pressure and the actual pressure, and adjusts and determines the control coefficients of feedforward pressure control plus PID closed-loop control in nonlinear and linear states based on the maximum delay, maximum error, and linearity.

[0021] Using the above technical solution, when the wet clutch is in a linear / nonlinear state, a feedforward plus PID closed-loop control method is adopted. During the control process, the maximum delay, maximum error and linearity of the wet clutch are obtained according to the pressure difference between the target pressure and the actual pressure. Then, the integral term coefficient, derivative term coefficient and proportional term coefficient of the PID closed-loop control are adjusted according to the maximum delay, maximum error and linearity, so that the control coefficients are adjusted in the linear / nonlinear state, thereby improving the control effect in the linear / nonlinear state.

[0022] The beneficial effects of this invention are:

[0023] The wet clutch pressure control method proposed in this invention divides the pressure control into idle and non-idle states based on the movement stage of the wet clutch during operation. Each state employs a corresponding control method and control parameters. The target and actual pressures of the wet clutch are obtained experimentally. The idle state is determined by comparing the target pressure with the minimum torque transmission pressure, and open-loop control is used in the idle state. The non-idle state is determined by combining the actual and target pressures, and a feedforward plus closed-loop control method is used in the non-idle state. Furthermore, the non-idle state is further divided into a preparation state, a nonlinear state, and a linear state, all of which employ a feedforward plus closed-loop control method. In addition, the closed-loop control method provides feedback correction for the pressure during the control process. The closed-loop proportional-integral-derivative pressure control is based on proportional control. Integral control can eliminate errors in various pressures, and derivative control can reduce overshoot tendencies. The PID closed-loop pressure control method is simple to operate, and its control parameters are relatively easy to determine. Furthermore, by adjusting the coefficients of the control parameters, namely the proportional, integral, and derivative terms, through evaluation indicators, the robustness of pressure control is improved, covering the pressure response differences in each motion stage of the wet clutch, so that the actual pressure can accurately respond to the target pressure. Attached Figure Description

[0024] Figure 1 A schematic diagram of the clutch oil filling process in the wet clutch pressure control method for a vehicle provided in an embodiment of the present invention;

[0025] Figure 2 A schematic flowchart of a wet clutch pressure control method for a vehicle provided in an embodiment of the present invention;

[0026] Figure 3 A schematic diagram illustrating the change of the transmission input shaft in the idle state in the wet clutch pressure control method for a vehicle provided in an embodiment of the present invention;

[0027] Figure 4 A schematic diagram illustrating the pressure control state division in the wet clutch pressure control method for a vehicle provided in an embodiment of the present invention;

[0028] Figure 5 This is a schematic diagram of each mode when the control state is in the ready state in the wet clutch pressure control method for a vehicle provided in an embodiment of the present invention.

[0029] Figure 6 A block diagram of the feedforward + closed-loop pressure control method in the wet clutch pressure control method for vehicles provided in the embodiments of the present invention;

[0030] Figure 7 A block diagram of the PID closed-loop control method in the wet clutch pressure control method for a vehicle provided in an embodiment of the present invention;

[0031] Figure 8 A schematic diagram illustrating the delay time variation in the linear / nonlinear states of the wet clutch pressure control method for a vehicle provided in an embodiment of the present invention;

[0032] Figure 9 A schematic diagram of linearity in the linear / nonlinear state of the wet clutch pressure control method for a vehicle provided in an embodiment of the present invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] 10: Piston chamber;

[0035] 20: Spring;

[0036] 30: Oil passage;

[0037] 40: Friction plate. Detailed Implementation

[0038] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0039] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0040] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0042] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0043] In the description of this embodiment, it should be noted that the terms "upper", "lower", "inner", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship that the product of the invention is usually placed in during use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0044] In the description of this embodiment, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this embodiment based on the specific circumstances.

[0045] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0046] The wet clutch pressure control system is a non-linear coupling system composed of mechanical, electrical, and hydraulic components. The actual pressure in the clutch chamber, through the clutch torque characteristics, can directly affect the torque transmission of the vehicle and thus influence the actual driving experience.

[0047] The oil filling process of a wet clutch can be divided into the following steps:

[0048] like Figure 1As shown, during the oil filling process of a wet clutch, the components include the clutch piston chamber 10, spring 20, oil passage 30, and friction plates 40. The working process is represented by numbers ①②③④ in sequence. More specifically, process ① represents: oil is filled into the clutch piston chamber 10, including the oil passage 30, and the clutch piston does not move. After the oil passage 30 is filled with oil, the return preload of the clutch spring 20 is overcome, i.e., process ②. This causes the clutch piston to gradually move, eliminating the free travel between the piston and the clutch, i.e., process ③. At this time, the load stiffness of the piston movement is equal to the return stiffness of the spring 20. It should be noted that the piston itself can be approximated as a rigid body, and its deformation can be ignored. After the free travel between the piston and the clutch has been eliminated and the spring 20 has been overcome to return, the piston continues to move until the gap between the clutch friction plates 40 is completely eliminated, and the friction plates 40 are flattened by the wave plate, i.e., process ④. At this time, the load stiffness of the piston movement is equal to the return stiffness of the spring 20 plus the stiffness of the wave plate. Furthermore, as the pressure in the clutch piston chamber 10 increases further, the piston essentially stops moving. The position where the free clearance of the clutch friction plate 40 is completely eliminated is defined as the volume-kiss point (VKP). At this point, the system load stiffness is equal to the return stiffness of the spring 20 + the stiffness of the wave plate + the stiffness of the friction material. The clutch pressure depends entirely on the outlet pressure of the pressure valve.

[0049] During clutch operation, due to differences in physical characteristics, the actual pressure response within the clutch oil chamber varies. Generally, clutch control employs either open-loop or closed-loop control. With open-loop control, the clutch is calibrated using a target pressure, potentially resulting in ideal initial control. However, as the vehicle's operating environment changes and hardware performance degrades—specifically, under high or low temperature conditions, or due to continuous clutch operation causing gradual performance degradation of the clutch hydraulic system—the accuracy of actual clutch pressure control significantly decreases. While closed-loop control can broaden the applicability and accuracy of the strategy, it cannot control the different stages of clutch movement, making it highly susceptible to the influence of actual clutch pressure and unable to cover the pressure response differences across various clutch stages.

[0050] To solve the above technical problems, refer to Figures 2-9 As shown, the wet clutch pressure control method for a vehicle provided by the embodiments of the present invention is described in detail.

[0051] like Figure 2As shown, the wet clutch pressure control method for a vehicle provided by this invention includes the following steps: obtaining a target pressure of the wet clutch and obtaining the actual pressure of the wet clutch. The operating state of the wet clutch is determined based on the target pressure and the actual pressure, wherein the operating state of the wet clutch includes an idle state and a non-idle state. When the operating state of the wet clutch is determined to be an idle state, an idle control parameter of the wet clutch is obtained, and the pressure of the wet clutch is subjected to open-loop control based on the idle control parameter. When the operating state of the wet clutch is determined to be a non-idle state, a non-idle control parameter of the wet clutch is obtained, and the pressure of the wet clutch is subjected to feedforward pressure plus closed-loop control based on the non-idle control parameter.

[0052] In this embodiment, the method for obtaining closed-loop pressure control can be a closed-loop proportional-integral-differential (PID) pressure control method, a closed-loop proportional-integral (PI) pressure control method, or a closed-loop proportional-differential (PD) pressure control method. Those skilled in the art can choose according to actual needs, and this embodiment does not impose specific limitations on this.

[0053] The target torque of the wet clutch is obtained based on the vehicle's driving parameters. Then, the target pressure of the wet clutch is obtained by referring to the torque characteristic curve of the wet clutch. The torque characteristic curve of the wet clutch represents the relationship between the clutch's target pressure and its transmitted torque. The vehicle's driving parameters include the engine torque, engine torque change rate, engine speed, accelerator pedal depressor, transmission output shaft speed, and transmission input shaft speed. The actual clutch pressure is obtained by installing a pressure sensor at the clutch oil chamber inlet. Based on the obtained target pressure and actual pressure, the working state of the wet clutch is divided into idle and non-idle states.

[0054] Furthermore, when the wet clutch is determined to be in an idle state, the target pressure of the wet clutch is obtained as the idle control parameter. Then, open-loop control of the wet clutch pressure is performed based on the target pressure. Open-loop control means that the actual pressure of the clutch oil chamber is not considered during the pressure control process; the control pressure of the pressure valve directly references the target pressure of the wet clutch. When the wet clutch transitions from a non-idle state to an idle state, the control pressure decreases from the target pressure at the end of the non-idle state to 0 in fixed steps. That is, in the idle state, the target pressure range of the clutch is less than the minimum torque transmission pressure.

[0055] Furthermore, when the wet clutch is determined to be in a non-idle state, the non-idle control parameters can be obtained based on the oil temperature in the oil chamber, or based on the pressure difference between the actual and target pressures of the clutch. Then, the wet clutch pressure is controlled by a combination of feedforward and closed-loop pressure based on these non-idle control parameters. That is, in the non-idle state, the control pressure of the wet clutch equals the sum of the feedforward control pressure and the closed-loop control pressure. The feedforward pressure of the wet clutch is calculated by multiplying the target pressure by a feedforward coefficient.

[0056] By adopting the above technical solution, the pressure control process of the wet clutch is divided into two states: idle and non-idle. In the idle state, open-loop control is used, and the control pressure of the wet clutch references the target pressure. In the non-idle state, feedforward and closed-loop control are used, and the control pressure of the wet clutch equals the feedforward control pressure plus the closed-loop control pressure. By dividing the clutch into different control states according to its movement stages, different control methods are applied to the control pressure in different control states. This ensures that the actual pressure in the clutch oil chamber is close to the target pressure, resulting in a faster rate of change of the target pressure during gear shifting in both high and low temperature environments. In other words, regardless of whether the oil temperature in the wet clutch oil chamber is low or high, the control effect of the actual pressure in the wet clutch oil chamber following the target pressure can meet the requirements of actual vehicle driving performance.

[0057] According to another specific embodiment of the present invention, when the working state of the wet clutch is determined to be an idle state, the target pressure is obtained as an idle control parameter, and the pressure of the wet clutch is controlled in an open loop according to the target pressure.

[0058] Using the above technical solution, the working state of the clutch is first determined. If the working state of the clutch is in the idle state, the pressure control method adopted in the idle state is open-loop control. The idle control parameters are obtained based on the target pressure. The control pressure in this state is adjusted according to the control parameters to achieve better adjustment of the control pressure in the idle state and improve the open-loop control effect.

[0059] According to another specific embodiment of the present invention, determining that the working state of the wet clutch is an idle state includes: obtaining the minimum torque transmission pressure of the wet clutch and comparing the target pressure with the minimum torque transmission pressure; when the target pressure is less than the minimum torque transmission pressure, it is determined that the working state of the wet clutch is an idle state.

[0060] like Figure 2As shown, the minimum torque transmission pressure of the wet clutch is obtained, and the minimum torque transmission pressure is compared with the target pressure. If the target pressure is less than the minimum torque transmission pressure or there is no target pressure request, the clutch pressure control is determined to be in an idle state. In a dual-clutch transmission, when the odd-numbered clutch gears are driving stably and there is no need to shift gears, the even-numbered clutch gears generally have no engagement requirement; that is, there is no target pressure request when the clutch has no engagement requirement. It should be noted that the minimum torque transmission pressure is the pressure in the piston chamber corresponding to when the clutch just transmits torque, that is, the clutch pressure corresponding to a clutch torque of 0 Nm.

[0061] Furthermore, the automotive transmission system is a complex nonlinear elastic system composed of an engine, clutch, gearbox, drive shaft, rear axle, etc., with certain clearances between these components. When the actual clutch pressure rises or falls rapidly, the transmission system also experiences a sudden increase or decrease in torque transmission within a short period. However, the existence of these clearances causes significant torque impacts in the transmission system, resulting in low-frequency torsional vibrations that impact the gear meshing pairs and spline contact surfaces, generating noise. When the clutch pressure control transitions from a non-idle state to an idle state, if the control objective is to directly disengage the clutch, the target control pressure of the pressure valve should reference the clutch's target pressure. Otherwise, if transmission noise is generated during this process, the rate of decrease in the pressure valve's control pressure needs to be limited to reduce transmission noise. For example, the clutch's target pressure may jump directly from a certain value to 0, but the output pressure of the control valve needs to decrease from that value to 0 at a certain slope. The rate of decrease is mainly based on experimental results to ensure that the transmission noise and vibration when the clutch is disengaged are within an acceptable range, such as a decrease rate of 50 kPa / 5 ms.

[0062] According to another specific embodiment of the present invention, when it is determined that the working state of the wet clutch is from non-idle to idle, the maximum speed of the gearbox input shaft within a predetermined time period is obtained, and the idle control parameters are adjusted according to the maximum speed.

[0063] Specifically, when the wet clutch is in an idle state, the speed of the transmission input shaft remains unchanged. However, when the wet clutch transitions from a non-idle state to an idle state, the speed of the transmission input shaft fluctuates. During this fluctuation, the maximum speed of the transmission input shaft within a predetermined time period is obtained, and the idle control parameters are adjusted based on this maximum speed.

[0064] like Figure 3As shown, the maximum shaft speed when entering idle control represents the maximum rotational speed (in rpm) of the odd and even input shafts within 1 second after the start of idle control pressure. Excessive shaft speed may cause shocks; ideally, the maximum shaft speed should be zero. Here, shaft 1 is the odd-numbered shaft, shaft 2 is the even-numbered shaft, and the disturbance duration is defined as 1 second.

[0065] By adopting the above technical solution, when the working state of the wet clutch is determined to be idle, and during the open-loop control process based on the target pressure, when the working state of the wet clutch is determined to be non-idle and enters the idle state, the maximum speed within a predetermined time period is obtained by measuring the speed of the gearbox input shaft, and the control pressure is adjusted based on the obtained maximum speed, thereby further improving the control effect of the open-loop control pressure.

[0066] According to another specific embodiment of the present invention, when the working state of the wet clutch is determined to be non-idle, the oil temperature of the wet clutch and the pressure difference between the target pressure and the actual pressure are obtained as non-idle control parameters, and the pressure of the wet clutch is subjected to feedforward pressure plus closed-loop control based on the non-idle control parameters.

[0067] Specifically, due to the different temperatures of the oil in the clutch oil chamber, the viscosity, density, elastic modulus and other characteristic parameters of the oil are different, which leads to differences in the actual response process of clutch pressure control. Therefore, the non-idle control parameters should be determined based on the oil temperature and the pressure difference between the actual clutch pressure and the target pressure. Based on the non-idle control parameters, the pressure control in the non-idle state is controlled by a feedforward pressure plus closed-loop pressure control method.

[0068] By employing the above technical solution, when the wet clutch enters the non-idle state, non-idle control parameters are obtained by measuring the oil temperature of the wet clutch and the pressure difference between the target pressure and the actual pressure. Then, feedforward and closed-loop control is applied to the pressure of the wet clutch based on these non-idle control parameters. This combination of obtaining non-idle parameters and applying feedforward and closed-loop control results in better control performance and improves the actual pressure response of the wet clutch.

[0069] According to another specific embodiment of the present invention, the non-idle state includes a ready state, a nonlinear state, and a linear state. Determining the wet clutch to be in the ready state includes: if the target pressure jumps from below the minimum torque transmission pressure to the minimum torque transmission pressure, then the wet clutch is determined to be in the ready state. Determining the wet clutch to be in the nonlinear or linear state includes: acquiring the pressure of the wet clutch from the start of torque transmission to the point where the friction plate clearance is completely eliminated, and comparing it with the target pressure and the actual pressure, respectively. If the target pressure or the actual pressure is less than the pressure of the wet clutch from the start of torque transmission to the point where the friction plate clearance is completely eliminated, then the wet clutch is determined to be in the nonlinear state. If both the target pressure and the actual pressure are greater than or equal to the pressure of the wet clutch from the start of torque transmission to the point where the friction plate clearance is completely eliminated, then the wet clutch is determined to be in the linear state.

[0070] Specifically, such as Figure 4 Show, Figure 4 This is a state curve diagram displayed by the same software, divided according to the actual and target pressures of the clutch. The half-engagement point (KissPoint, KP) indicates the position where the clutch begins to transmit torque. The volume contact point (Volume-KissPoint, VKP) indicates the position where the clutch friction plate clearance is eliminated. ClchPresCmnd represents the clutch target pressure. HydrCtrlState represents the clutch hydraulic control state. kisspoint+offset represents the clutch starting to transmit torque plus the offset torque; offset can be positive or negative, and its specific value is determined based on the actual vehicle conditions. MaxTorqPress represents the maximum torque transmitted by the clutch. Idle represents the idle state, Prepare represents the ready state, Non-Linear represents the non-linear state, and Linear represents the linear state.

[0071] Non-idle states include ready state, nonlinear state, and linear state. Specifically, when the clutch target pressure jumps from below the minimum torque transmission pressure to the minimum torque transmission pressure, that is, when the clutch target pressure jumps from 0 to point KP or from below the minimum torque transmission pressure to point KP, it is determined that the clutch pressure control has entered the ready state.

[0072] Furthermore, when determining whether the clutch pressure control is ready to enter the preparation state, four modes are used as the judgment criteria. Among them, the position of the lever is used to determine whether to enter the static shift mode (GarageShift).

[0073] If the lever is detected to shift from P or N to D or R, or to switch between D and R, the conditions for entering static shift mode are met, and the clutch pressure control enters the ready state.

[0074] like Figure 5 As shown in Figure 'a', the solid line represents the clutch target pressure, and the dashed line represents the clutch actual pressure. The horizontal axis represents time. Based on the trend of the actual clutch pressure change, it is determined whether to enter the Full Step mode. If the lever position does not change, when a change in the clutch target pressure is detected, the actual clutch pressure is less than the preset pressure threshold 1. If threshold 1 is met, the conditions for entering the Full Step mode are met, and the clutch pressure control enters the preparation state.

[0075] Corresponding to Figure 5 As shown in b, the system determines whether to enter the Limited Step mode based on the actual clutch pressure change trend. If the lever position remains unchanged, and a change in the clutch target pressure is detected, and the actual clutch pressure is greater than threshold 1 and less than the preset pressure threshold 2, then the conditions for entering the Limited Step mode are met, and the clutch pressure control enters the preparation state.

[0076] Corresponding to Figure 5 As shown in c, the actual clutch pressure change trend determines whether to enter the non-step mode. If the lever position remains unchanged, and a sudden change in the clutch target pressure is detected, and the actual clutch pressure is greater than threshold 2, then the conditions for entering the non-step mode are met. Furthermore, the clutch pressure control does not enter the preparation state, and the next step of judgment is performed, i.e., further determining whether the clutch pressure control has entered a non-linear state. It should be noted that, according to experimental data, the value range of pressure threshold 1 is 50 kPa, and the value range of pressure threshold 2 is the target pressure - 50 kPa. The values ​​of pressure threshold 1 and pressure threshold 2 are calibrated through bench testing, and the value of pressure threshold 1 is less than the value of pressure threshold 2. Those skilled in the art can calibrate these values ​​based on experimental data.

[0077] Furthermore, such as Figure 2 and Figure 4 As shown, when the clutch target pressure is detected to rise at a certain slope from point KP, and the clutch target pressure is less than point VKP or the actual clutch pressure is less than point VKP, the clutch pressure control enters a nonlinear state. When the clutch pressure control is in a nonlinear state, because the free clearance between the clutch friction plates has not been completely eliminated, the oil chamber volume changes significantly when the clutch piston moves, greatly affecting the actual clutch pressure response. The actual clutch pressure response, in turn, leads to a slower pressure build-up in the clutch piston chamber during this process. Therefore, in the nonlinear state, it is necessary to increase feedforward pressure compensation and closed-loop pressure regulation to compensate for the pressure drop in the oil chamber caused by the clutch piston movement and ensure sufficient oil pressure. Increasing feedforward pressure compensation is achieved by increasing the feedforward coefficient, and closed-loop pressure regulation is performed by adjusting the control parameters.

[0078] Specifically, the pressure build-up process is represented by the following equation:

[0079]

[0080] In the formula, B represents the rate of pressure change within the clutch oil chamber. eff To comprehensively consider the equivalent bulk modulus of elasticity of the gas-containing hydraulic oil and the oil passage arm; x csc V is the displacement of the clutch piston caused by hydraulic pressure. csc0 A represents the initial cavity volume; csc q represents the area of ​​the clutch piston oil chamber. pa q is the flow rate into the CSC oil chamber via the pressure valve; at x is the flow rate of the oil flowing out of the CSC chamber through the pressure valve; sm A represents the displacement of the pressure valve spool relative to its initial position. fb This represents the area of ​​the pressure valve feedback chamber.

[0081] When the clutch target pressure is detected to rise at a certain slope from point KP, and both the clutch target pressure and the actual clutch pressure are greater than point VKP, then the clutch pressure control enters a linear state. In this state, the clutch pressure depends entirely on the outlet pressure of the pressure valve, which is the outlet pressure of the clutch pressure control valve, i.e., p in the following formula. fb The specific formula is as follows:

[0082]

[0083] In the above formula, D sm x is the damping coefficient between the valve core and the valve sleeve of the solenoid valve; sm k is the displacement of the valve core relative to its initial position. sm For the solenoid valve spring stiffness; x sm0 p represents the initial spring compression. fb The pressure in the feedback chamber of the solenoid valve is approximately equal to the output pressure p. a A fb For the feedback area; m sm For valve core mass; F jet (t) represents the steady-state hydrodynamic force, the direction of which is related to the direction of valve core movement and can be controlled by the electromagnetic force F. se To adjust. In the linear state, p fb =p a .

[0084] By adopting the above technical solution, the non-idle state is further divided into a ready state, a linear state, and a nonlinear state. Moreover, the control parameters obtained in each state are different, which improves the actual pressure control accuracy of the clutch and covers the different control states of the clutch in different motion stages, so that the actual pressure of the wet clutch can accurately respond to the target pressure.

[0085] According to another specific embodiment of the present invention, the feedforward pressure plus closed-loop control is feedforward pressure control plus closed-loop proportional-integral-derivative pressure control.

[0086] Specifically, closed-loop control can be PID closed-loop control, which is PID closed-loop pressure control with the target clutch pressure as the objective. The closed-loop pressure refers to the sum of the adjustment pressures of the P term (proportional term), I term (integral term), and D term (derivative term). The actual pressure of the wet clutch is controlled to follow the target pressure based on the coefficients of the P term, I term, and D term.

[0087] like Figure 6 As shown, in the clutch hydraulic system, the actual clutch pressure is obtained by installing a pressure sensor at the clutch oil chamber inlet. The actual clutch pressure is combined with the target pressure to determine the clutch control pressure, employing a feedforward and closed-loop control method. The clutch target pressure determines the clutch feedforward pressure control, and the clutch target pressure and actual pressure together determine the clutch closed-loop control pressure. The feedforward control pressure plus the closed-loop control pressure equals the pressure valve target control pressure, which is finally controlled by a solenoid valve and enters the clutch hydraulic system. Feedforward pressure control is achieved through the clutch target pressure, and then the actual pressure follows the target pressure control through feedforward pressure control plus PID closed-loop control. It should be noted that the control target is determined based on the clutch target pressure; if the clutch target pressure is 0, the control target is determined to be directly disengaging the clutch.

[0088] The closed-loop control in this embodiment adopts PID closed-loop control, such as... Figure 7 As shown, the proportional term coefficient Kp is determined by the oil temperature and the pressure difference between the target and actual clutch pressure. The integral term coefficient Ki and the derivative term coefficient Kd are determined by the oil temperature. It should be noted that different oil temperatures result in different viscosity, density, elastic modulus, and other characteristic parameters of the oil, leading to differences in the actual response process of the clutch pressure control. Therefore, the PID closed-loop control parameters must consider the differences in oil temperature. The PID closed-loop control parameters Kp, Ki, and Kd are calibrated using a hydraulic test bench.

[0089] Furthermore, the formula for calculating the proportional control pressure is as follows:

[0090] P prop =K p ×P error

[0091] P error =P cmnd -P actl

[0092] Among them, P error The pressure difference between the target pressure and the actual pressure in the oil cavity; P actl K represents the actual pressure in the oil cavity. p This is a proportional parameter.

[0093] The formula for calculating the integral term control pressure is as follows:

[0094] P integral =∑K i ×P error

[0095] Among them, K i For integration parameters.

[0096] In this embodiment, the anti-saturation integral method is used to calculate the integral term control pressure; when the integral term control pressure is greater than or equal to the upper limit threshold of the integral term, or 0 <P error When the integral term control pressure is less than or equal to the lower limit threshold, only negative integral pressure is accumulated; when the integral term control pressure is less than or equal to the lower limit threshold, or the lower limit threshold is less than or equal to the upper limit threshold, only negative integral pressure is accumulated. <P error When <0, only positive integral pressure is accumulated.

[0097] It should be noted that prolonged use of integral term control for pressure can lead to pressure overflow, causing the integral term control pressure to remain in place for an extended period when the target pressure direction changes. The anti-saturation integral method can resolve this pressure overflow issue. The control objective of the clutch pressure control system studied in this scheme is to control the steady-state deviation between the target pressure and the actual pressure within ±20 kPa. Therefore, the upper threshold is defined as 20 kPa, and the lower threshold is defined as -20 kPa.

[0098] Furthermore, in PID closed-loop control, the main function of the integral term is to eliminate steady-state error. When the clutch pressure difference is too large or a sudden change occurs, the integral term calculation is stopped to reduce control error. When dP error / dt>threshold or P error When the threshold is reached, the integral term retains the value of the previous cycle.

[0099] In the cumulative value of the integral term and P error When the direction is opposite or the cumulative value of the integral term is opposite to the direction of the clutch target pressure change, the accumulation rate of the integral term should be accelerated to make the integral term conform to the control intention as soon as possible. When the cumulative value of the integral term < 0 and P error >0∥dP cmnd / dt>0 or the cumulative value of the integral term>0 and Perror <0∥dP cmnd When / dt<0, the integral term equals the current cumulative integral value multiplied by the coefficient DecayF. x DecayF x =1-K decay ×|dP cmnd / dt|.

[0100] The formula for calculating the differential term control pressure is as follows:

[0101]

[0102] Among them, K d is the differential parameter.

[0103] Specifically, steady-state error refers to the deviation between the target pressure and the actual pressure when the clutch pressure control system tends to stabilize. The clutch target pressure generally depends on the output torque of the power source (engine or motor). When the output torque of the power source changes abruptly, it will cause a change in the clutch target pressure, resulting in a sudden change in the clutch pressure difference. In addition, when the target pressure rises or falls rapidly from one stable value to another, the actual clutch pressure adjustment takes time, so the deviation between the target pressure and the time pressure is large during the adjustment process, resulting in an excessively large clutch pressure difference.

[0104] Using the above technical solution, the proportional control pressure controls the clutch pressure proportionally. When a deviation occurs between the target pressure and the actual pressure in the clutch oil chamber, proportional control pressure can accelerate the pressure adjustment of the pressure valve, thereby quickly reducing the pressure difference between the target and actual pressures in the clutch oil chamber. Integral control pressure can eliminate the steady-state error of the clutch pressure control system based on this wet clutch pressure control method. As long as a pressure difference exists between the target pressure and the actual pressure in the clutch oil chamber, integral control pressure will be used to reduce this difference. Derivative control pressure can reflect the pressure change trend in the clutch oil chamber, avoiding situations where the pressure difference is too large. Introducing derivative control pressure to adjust the pressure before such a situation occurs provides predictability and allows for proactive pressure control. If a large pressure difference is anticipated, derivative adjustment can eliminate it. With appropriate selection of the derivative control pressure adjustment time, overshoot can be performed to reduce adjustment time.

[0105] According to another specific embodiment of the present invention, the response time and overshoot of the wet clutch are obtained based on the pressure difference between the target pressure and the actual pressure, and the control coefficients of the feedforward pressure control plus closed-loop proportional-integral-derivative pressure control in the preparation state are adjusted and determined based on the response time and overshoot.

[0106] Specifically, the response time and overshoot of the wet clutch are obtained based on the pressure difference between the target pressure and the actual pressure. Then, the obtained control parameters, i.e., various control coefficients, are adjusted based on the response time and overshoot.

[0107] Response time represents the time elapsed from the actual clutch pressure reaching the clutch's target pressure for the first time. Response time is generally less than a certain threshold, typically within 150ms. If the actual clutch pressure does not reach the target pressure during the entire gear engagement phase, the response time for that engagement is not counted.

[0108] Overshoot represents the maximum deviation between the actual pressure and the target pressure during the clutch's movement phase. If no overshoot occurs during the entire clutch movement, the overshoot = Max(actual pressure - target pressure). If the overshoot > 0, it indicates that overshoot has occurred; if the overshoot ≤ 0, it indicates that no overshoot has occurred. The overshoot should be less than a certain threshold, which is generally controlled within 2% of the target pressure.

[0109] By adopting the above technical solution, the integral term coefficient, derivative term coefficient, and proportional term coefficient are adjusted according to the overshoot and response time, so as to improve the control effect in real time during the preparation state, thereby adjusting and correcting each control coefficient and improving the control effect in the preparation state.

[0110] According to another specific embodiment of the present invention, the maximum delay, maximum error, and linearity of the wet clutch are obtained based on the pressure difference between the target pressure and the actual pressure, and the control coefficients of the feedforward pressure control plus closed-loop proportional-integral-derivative pressure control in the nonlinear state and the linear state are adjusted and determined based on the maximum delay, maximum error, and linearity.

[0111] Specifically, the maximum delay, maximum error, and linearity of the wet clutch are obtained based on the pressure difference between the target pressure and the actual pressure. Then, the obtained control parameters, i.e., various control coefficients, are adjusted based on the maximum delay, maximum error, and linearity.

[0112] Maximum delay represents the lag or lead of the actual signal relative to the target signal, with the target signal's time point as a reference. If it lags, the delay time is greater than 0; if it leads, the delay time is less than 0. The entire process is divided into 10 equal pressure points based on the stages of the target pressure rising or falling at a certain slope. The delay time for each pressure point is then calculated. Figure 8 As shown, the maximum single delay should be less than 60ms, while the average delay should be greater than 20ms and less than 60ms.

[0113] Error represents the deviation between the actual pressure signal and the target pressure signal of the clutch. During the entire stage of rising or falling at a certain slope, the minimum error should be greater than 10 cbar, the maximum error should not exceed 250 cbar, and the average error should be between greater than 10 cbar and less than 80 cbar.

[0114] Linearity represents the maximum percentage deviation between the actual clutch pressure signal and the fitted straight line. For example... Figure 9 As shown, the horizontal axis represents time, and the vertical axis represents the actual clutch pressure. Furthermore, the graph shows y... max y represents the maximum value of the actual clutch pressure signal. min Let Δy be the minimum value of the actual clutch pressure signal, and Δy be the deviation between the actual clutch pressure signal and the fitted straight line at the same moment. The least squares method is used for fitting. The formula for calculating linearity is:

[0115]

[0116] The smaller δ is, the better the linearity, and the closer the actual pressure signal is to a straight line. The linearity should be less than 4% during the phase of movement at a certain slope.

[0117] By adopting the above technical solution, the integral term coefficient, derivative term coefficient, and proportional term coefficient of PID closed-loop control are adjusted according to the maximum delay, maximum error, and linearity, so as to adjust and correct the control coefficients under both online and nonlinear states, thereby improving the control effect under both online and nonlinear states.

[0118] Using the above technical solution, this invention proposes a wet clutch pressure control method for vehicles. During the operation of the wet clutch, the clutch pressure control is divided into idle state, ready state, nonlinear state, and linear state based on the clutch's movement stage and the target pressure and actual pressure. Each state employs a corresponding control method and applicable control parameters. The target pressure and actual pressure of the wet clutch are obtained experimentally. Based on the target pressure, the clutch control pressure is determined to enter the idle state, where open-loop control is used. Based on the combination of the actual and target pressures, the clutch control pressure is determined to enter the ready state, nonlinear state, and linear state, respectively. In these three states, a feedforward plus PID closed-loop control method is used. The PID closed-loop pressure control method allows for feedback correction of the actual clutch pressure during clutch control. Furthermore, PID control is based on proportional control, integral control can eliminate errors in various pressures, and derivative control can reduce overshoot tendencies. The PID closed-loop pressure control method is simple to operate, and its control parameters are relatively easy to determine. Further, when the clutch is under pressure control in these four states, the control parameters for each control state can be adjusted using evaluation indicators. Specifically, when the wet clutch transitions from a non-idle state to an idle state, the idle control parameters (i.e., the control pressure) are adjusted by controlling the speed of the gearbox input shaft. The control parameters (PID coefficients) for the ready state are adjusted by controlling the response time and overshoot. The coefficients of the proportional, integral, and derivative terms are adjusted by controlling the maximum delay, maximum error, and linearity for both linear and nonlinear states. By dividing clutch pressure control into four states, employing different control methods and corresponding control parameters for each state, and adjusting these parameters using evaluation indicators, the system effectively covers the pressure response differences across various stages of the wet clutch's operation. This ensures that the actual clutch pressure accurately responds to the target pressure, thereby improving the robustness of clutch pressure control.

[0119] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A method for controlling the pressure of a wet clutch in a vehicle, characterized in that, Includes the following steps: The target torque of the wet clutch is obtained based on the vehicle's driving parameters. The target pressure of the wet clutch is then obtained by referring to its torque characteristic curve. The torque characteristic curve represents the relationship between the target pressure and the transmitted torque of the wet clutch. The actual pressure of the wet clutch is obtained by a pressure sensor installed at the clutch oil chamber inlet of the wet clutch; The operating state of the wet clutch is determined based on the target pressure and the actual pressure of the wet clutch, wherein the operating state of the wet clutch includes an idle state and a non-idle state; When the working state of the wet clutch is determined to be the idle state, the idle control parameters of the wet clutch are obtained, and the pressure of the wet clutch is controlled in an open loop according to the idle control parameters. When the working state of the wet clutch is determined to be the non-idle state, the non-idle control parameters of the wet clutch are obtained, and the pressure of the wet clutch is subjected to feedforward pressure plus closed-loop control according to the non-idle control parameters.

2. The wet clutch pressure control method for a vehicle as described in claim 1, characterized in that, When the working state of the wet clutch is determined to be the idle state, the target pressure is obtained as the idle control parameter, and the pressure of the wet clutch is controlled in an open loop according to the target pressure.

3. The wet clutch pressure control method for a vehicle as described in claim 2, characterized in that, Determining the working state of the wet clutch as the idle state includes: Obtain the minimum torque transmission pressure of the wet clutch, and compare the target pressure with the minimum torque transmission pressure; When the target pressure is less than the minimum torque transmission pressure, the working state of the wet clutch is determined to be the idle state.

4. The wet clutch pressure control method for a vehicle as described in claim 3, characterized in that, When the working state of the wet clutch is determined to be from the non-idle state to the idle state, the maximum speed of the gearbox input shaft within a predetermined time period is obtained, and the idle control parameters are adjusted according to the maximum speed.

5. The wet clutch pressure control method for a vehicle as described in any one of claims 1 to 4, characterized in that, When the working state of the wet clutch is determined to be the non-idle state, the oil temperature of the wet clutch and the pressure difference between the target pressure and the actual pressure are obtained as the non-idle control parameters, and the pressure of the wet clutch is subjected to feedforward pressure plus closed-loop control according to the non-idle control parameters.

6. The wet clutch pressure control method for a vehicle as described in claim 5, characterized in that, The non-idle state includes a ready state, a non-linear state, and a linear state; in Determining the wet clutch to be in the ready state includes: If the target pressure jumps from below the minimum torque transmission pressure to the minimum torque transmission pressure, then the working state of the wet clutch is determined to be the ready state; and Determining whether the wet clutch is in the nonlinear state or the linear state includes: The pressure from the start of torque transmission of the wet clutch to the point where the friction plate gap is completely eliminated is obtained, and compared with the target pressure and the actual pressure, respectively. If the target pressure or the actual pressure is less than the pressure when the wet clutch starts transmitting torque until the friction plate gap is completely eliminated, then the working state of the wet clutch is determined to be the nonlinear state. If the target pressure or the actual pressure is greater than or equal to the pressure from the start of torque transmission of the wet clutch to the point where the friction plate gap is completely eliminated, then the working state of the wet clutch is determined to be the linear state.

7. The wet clutch pressure control method for a vehicle as described in claim 6, characterized in that, The feedforward pressure plus closed-loop control is feedforward pressure control plus closed-loop proportional-integral-derivative pressure control.

8. The wet clutch pressure control method for a vehicle as described in claim 7, characterized in that, The response time and overshoot of the wet clutch are obtained based on the pressure difference between the target pressure and the actual pressure, and the control coefficients of the feedforward pressure control plus closed-loop proportional-integral-derivative pressure control in the preparation state are adjusted and determined based on the response time and the overshoot.

9. The wet clutch pressure control method for a vehicle as described in claim 8, characterized in that, The maximum delay, maximum error, and linearity of the wet clutch are obtained based on the pressure difference between the target pressure and the actual pressure. The control coefficients of the feedforward pressure control plus closed-loop proportional-integral-derivative pressure control in the nonlinear state and the linear state are adjusted and determined based on the maximum delay, maximum error, and linearity.

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