Air spring height adjustment method for off-road mode of vehicle

Abstract

The invention relates to the technical field of vehicle active suspension control, in particular to an air spring height adjusting method for a vehicle off-road mode, which comprises the following steps of: dynamically dividing the current state of a vehicle into one of a horizontal state, an inclined state and a dangerous state by setting a plurality of threshold values and combining the current attitude angle of the vehicle and the suspension height; and the height adjustment of the air spring is controlled according to the current state of the vehicle, so that the height adjustment limitation in a complex cross-country environment is relieved on the premise of ensuring safety, and the function of the air spring is fully played.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle active suspension control, and in particular to a method for adjusting the height of an air spring used in an off-road mode of a vehicle. Background Art

[0002] The Electronic Controlled Air Suspension (ECAS) system is a vehicle suspension system that adjusts the vehicle's height by controlling the inflation / deflation of air springs based on the vehicle's real-time driving status and external environmental parameters.

[0003] However, when vehicles equipped with the ECAS system perform height adjustment, the air spring height adjustment is often limited by fixed thresholds (such as static thresholds of a single parameter such as steering wheel angle, vehicle tilt angle, and door status), making it difficult to adapt to complex off-road scenarios. Once the vehicle's attitude angle (pitch angle, roll angle) exceeds the set threshold, the ECAS system will directly prohibit the air spring from adjusting the height. As a result, in scenarios such as steep slopes and rough roads where flexible vehicle height adjustment is required, the air spring cannot adaptively adjust the vehicle height, resulting in poor vehicle passability and even the risk of attitude loss of control.

[0004] To solve the above problems, those skilled in the art have attempted to jointly control the attitude angle and suspension travel, for example, in publications CN109353178A, "An Electronically Controlled Air Suspension Vehicle Attitude Control System and Method," and CN105599558A, "A Method for Jointly Controlling Vehicle Height Adjustment and Attitude of an Electronically Controlled Air Suspension." However, this approach has many drawbacks, such as:

[0005] (1) Lack of dynamic hierarchical control strategy for road conditions: Both are based on fixed attitude angle thresholds (such as a single threshold for roll angle and pitch angle) or suspension travel thresholds to determine adjustment authority, without distinguishing the degree of vehicle tilt (such as slight tilt, medium tilt, dangerous tilt, etc.). When the attitude angle exceeds the threshold, adjustment is directly prohibited or uniformly corrected. This is unable to adapt to the gradual changes in road conditions from flat roads to steep slopes and cross-axles in off-road scenarios. It is easy to over-intervention (limiting adjustment when slightly tilted) or under-intervention (not prohibiting in time when dangerous tilting) resulting in reduced vehicle passability and posture instability.

[0006] (2) There is no attitude angle locking mechanism, which can easily lead to attitude deviation: Both methods only make the vehicle tend to be level by correcting the current attitude angle, without considering the consistency of adjusting the front and rear attitudes. After adjusting on an inclined road surface, if the vehicle is driven to a level road surface, the sudden change in attitude angle may cause the vehicle body to become unbalanced. For example, after raising the vehicle height by correcting the attitude angle on a slope, when returning to flat ground, the vehicle body may tilt more due to the large height difference between the front and rear axles, increasing the risk of rollover;

[0007] (3) The accuracy of wheel suspension detection is insufficient, and it is easy to misjudge the situation by relying on a single threshold: Both rely on a single height sensor or suspension travel to judge the wheel status. On complex off-road surfaces such as cross-axles and potholes, it is easy to misjudge the wheel suspension status due to sensor signal fluctuations or road interference, which may cause the air spring to overcharge / undercharge and cause the vehicle to lose balance.

[0008] Therefore, how to provide an air spring height adjustment control strategy for off-road scenarios that can both ensure vehicle safety and dynamically adapt to the vehicle driving environment has always been an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0009] The purpose of the present invention is to address the corresponding deficiencies in the existing technology and provide an air spring height adjustment method for a vehicle off-road mode. By setting several thresholds and combining the vehicle's current attitude angle and suspension height, the vehicle's current state is dynamically divided into one of three states: horizontal, inclined, and dangerous. The height adjustment of the air spring is controlled according to the vehicle's current state. While ensuring safety, the height adjustment restrictions in complex off-road environments are removed, and the function of the air spring is fully utilized.

[0010] The purpose of the present invention is to adopt the following scheme to achieve:

[0011] A method for adjusting the height of an air spring for an off-road mode of a vehicle comprises the following steps:

[0012] 1) Determine a horizontal state pitch angle calibration threshold, a horizontal state roll angle calibration threshold, an inclined state pitch angle calibration threshold, an inclined state roll angle calibration threshold, and an air spring adjustment height lower limit and an air spring adjustment height upper limit;

[0013] 2) Collect vehicle acceleration, vehicle angular velocity, and vehicle suspension height;

[0014] 3) Calculating the vehicle's attitude angle based on the vehicle's acceleration and angular velocity in combination with an extended Kalman filter, wherein the attitude angle includes the vehicle's pitch angle and the vehicle's roll angle;

[0015] 4) Determine the air spring height adjustment method based on the vehicle's attitude angle and suspension height:

[0016] If |the vehicle's pitch angle| ≤ the horizontal pitch angle calibration threshold, and |the vehicle's roll angle| ≤ the horizontal roll angle calibration threshold, and the air spring adjustment height lower limit ≤ the suspension height ≤ the air spring adjustment height upper limit, then the vehicle is determined to be level and the air spring height is adjusted normally.

[0017] If the horizontal state pitch angle calibration threshold <|vehicle pitch angle| ≤ tilted state pitch angle calibration threshold, or the horizontal state roll angle calibration threshold <|vehicle roll angle| ≤ tilted state roll angle calibration threshold, and there is no suspended wheel, the vehicle is determined to be in a tilted state, and the air spring height is adjusted for attitude angle locking;

[0018] If |Vehicle's pitch angle|>the pitch angle calibration threshold in the tilted state, or |Vehicle's roll angle|>the roll angle calibration threshold in the tilted state, or there is an overhung wheel, height adjustment of the air spring is prohibited.

[0019] Preferably, the conventional height adjustment specifically includes:

[0020] S1) setting a target height threshold value, which is used as a basis for adjusting the height of the air spring under conventional height adjustment;

[0021] S2) simultaneously raising the heights of the left rear air spring and the right rear air spring of the rear axle of the vehicle until the heights of the left rear air spring and the right rear air spring of the rear axle of the vehicle both reach a target height threshold;

[0022] S3) simultaneously raising the left front air spring and the right front air spring of the front axle of the vehicle until the heights of the left front air spring and the right front air spring of the front axle of the vehicle both reach a target height threshold;

[0023] S4) Finely adjust the heights of the left front air spring, right front air spring, left rear air spring, and right rear air spring to eliminate overshoot of the air spring height caused by vehicle body rigidity.

[0024] Preferably, the fine adjustment specifically includes:

[0025] S5-1) setting a fine adjustment threshold value, which is used as a basis for fine adjustment of the air spring height under conventional height adjustment;

[0026] S5-2) respectively collecting the real-time heights of the left rear air spring, the right rear air spring, the left front air spring, and the right front air spring;

[0027] S5-3) Determine whether the heights of the corresponding air springs need to be adjusted based on the real-time heights of the left rear air spring, the right rear air spring, the left front air spring, and the right front air spring in the following manner:

[0028] If |real-time height-target height threshold|≤fine adjustment threshold, the air spring maintains the current height and does not make any height adjustments;

[0029] If |real-time height-target height threshold|>fine adjustment threshold, the height of the air spring is adjusted and steps S5-2) to S5-3) are repeated.

[0030] Preferably, the posture angle locking adjustment specifically includes:

[0031] SS1) setting a posture angle deviation threshold to limit the range of change of the vehicle body posture angle during the posture angle locking adjustment process, ensuring that the vehicle body posture after adjustment is consistent with the locked reference posture angle;

[0032] SS2) After the air spring operating mode is switched to off-road mode, the vehicle's attitude angle at this time is calculated and recorded as the reference attitude angle, which serves as the attitude maintenance target during the vehicle suspension height adjustment process;

[0033] SS3) determining an air spring adjustment sequence for a left front air spring and a right front air spring of a front axle of the vehicle and a left rear air spring and a right rear air spring of a rear axle of the vehicle based on the reference attitude angle;

[0034] SS4) adjusting the heights of the left front air spring, the right front air spring, the left rear air spring, and the right rear air spring in sequence according to the adjustment sequence determined in step SS3), and calculating the real-time attitude angle of the vehicle;

[0035] SS5) Based on the reference attitude angle, the real-time attitude angle, and the attitude angle deviation threshold, determine whether to continue adjusting the height of the left front air spring, the right front air spring, the left rear air spring, and the right rear air spring in the following manner:

[0036] If |real-time attitude angle of the vehicle-reference attitude angle|<attitude angle deviation threshold, then stop adjustment;

[0037] If |real-time attitude angle of vehicle-reference attitude angle|≥attitude angle deviation threshold, repeat steps SS4) to SS5) to continue adjusting the heights of the left front air spring, right front air spring, left rear air spring, and right rear air spring.

[0038] Preferably, the process of determining the air spring adjustment sequence specifically includes:

[0039] ① According to the vehicle's pitch angle, determine the height adjustment order of the vehicle's front and rear axle air springs:

[0040] If the vehicle's pitch angle is greater than 0, adjust the height of the air spring on the front axle first, then adjust the height of the air spring on the rear axle;

[0041] If the vehicle's pitch angle is ≤0, first adjust the height of the rear axle air spring on the vehicle's rear axle, then adjust the height of the air spring on the vehicle's front axle;

[0042] ② According to the vehicle's roll angle, determine the height adjustment order of the left and right air springs:

[0043] If the vehicle's roll angle is greater than 0, adjust the height of the air spring on the right side of the vehicle first, then adjust the height of the air spring on the left side of the vehicle within the same axis;

[0044] If the vehicle's roll angle is ≤0, adjust the height of the air spring on the left side of the vehicle first, then adjust the height of the air spring on the right side of the vehicle within the same axle;

[0045] ③ Use the height adjustment sequence determined in steps ① and ② as the air spring adjustment sequence.

[0046] Preferably, the attitude angle is calculated in the following manner:

[0047] 3-1) Define the state variables and state prediction equations of the extended Kalman filter, combine the vehicle's angular velocity and zero bias compensation, perform time-recursive prediction of the attitude angle, and obtain the prior state estimate;

[0048] 3-1) Define the state variables and state prediction equations of the extended Kalman filter, combine the vehicle's angular velocity and zero bias compensation, perform time-recursive prediction of the attitude angle, and obtain the prior state estimate;

[0049] 3-2) Establish a state transfer matrix based on the state variables and state prediction equation, and use the state transfer matrix to perform time domain propagation of the error covariance to obtain the prior estimated covariance;

[0050] 3-3) Establish a vehicle's gravity acceleration component model and generate theoretical observations based on prior state estimates;

[0051] 3-4) Based on the gravity acceleration component model and state variables, construct the observation Jacobian matrix to reflect how the attitude angle changes affect the observed value of the gravity component;

[0052] 3-5) Calculate the Kalman gain matrix based on the prior estimated covariance, the observed Jacobian matrix, and the observed noise covariance, which is used to calculate the confidence weights of the equilibrium state prediction and the observed measurement;

[0053] 3-6) Calculate the difference between the vehicle acceleration and the theoretical observation value, and use the Kalman gain matrix to correct the prior state estimate to obtain the posterior state estimate;

[0054] 3-7) Combining the identity matrix, the Kalman gain matrix, the observation Jacobian matrix and the prior estimated covariance, the posterior covariance is calculated and used as the initial input for the next extended Kalman filter cycle;

[0055] 3-8) Perform angle normalization on the posterior state estimate to obtain the vehicle's attitude angle.

[0056] Preferably, the existence of suspended wheels specifically includes:

[0057] (1) Test the maximum travel of each air spring in the empty spring mode as the base height of the suspension;

[0058] (2) Setting a hysteresis value to prevent misjudgment of the wheel suspension state and avoid unnecessary adjustment restrictions caused by sensor signal fluctuations;

[0059] (3) Collect the height of the vehicle suspension and determine whether there are any suspended wheels in the following manner:

[0060] If any wheel height > suspended base height + hysteresis value, there is a suspended wheel;

[0061] If the height of all wheels is less than or equal to the suspended base height + hysteresis value, there is no suspended wheel.

[0062] The beneficial effects of the present invention are as follows:

[0063] A method for adjusting the height of an air spring for an off-road mode of a vehicle comprises the following steps:

[0064] 1) Determine a horizontal state pitch angle calibration threshold, a horizontal state roll angle calibration threshold, an inclined state pitch angle calibration threshold, an inclined state roll angle calibration threshold, and an air spring adjustment height lower limit and an air spring adjustment height upper limit;

[0065] 2) Collect vehicle acceleration, vehicle angular velocity, and vehicle suspension height;

[0066] 3) Calculating the vehicle's attitude angle based on the vehicle's acceleration and angular velocity in combination with an extended Kalman filter, wherein the attitude angle includes the vehicle's pitch angle and the vehicle's roll angle;

[0067] 4) Determine the air spring height adjustment method based on the vehicle's attitude angle and suspension height:

[0068] If |the vehicle's pitch angle| ≤ the horizontal pitch angle calibration threshold, and |the vehicle's roll angle| ≤ the horizontal roll angle calibration threshold, and the air spring adjustment height lower limit ≤ the suspension height ≤ the air spring adjustment height upper limit, then the vehicle is determined to be level and the air spring height is adjusted normally.

[0069] If the horizontal state pitch angle calibration threshold <|vehicle pitch angle| ≤ tilted state pitch angle calibration threshold, or the horizontal state roll angle calibration threshold <|vehicle roll angle| ≤ tilted state roll angle calibration threshold, and there is no suspended wheel, the vehicle is determined to be in a tilted state, and the air spring height is adjusted for attitude angle locking;

[0070] If |Vehicle's pitch angle|>the pitch angle calibration threshold in the tilted state, or |Vehicle's roll angle|>the roll angle calibration threshold in the tilted state, or there is an overhung wheel, height adjustment of the air spring is prohibited.

[0071] The present invention sets several thresholds and combines the vehicle's current attitude angle and suspension height to dynamically divide the vehicle's current state into one of three states: horizontal, tilted, and dangerous. Conventional adjustment is allowed in the horizontal state, attitude angle locking adjustment is performed in the tilted state, and adjustment is prohibited only in the dangerous state (exceeding the tilt threshold or the wheel is suspended). This grading strategy breaks the traditional crude restriction of air spring adjustment through a single fixed threshold, reduces the functional constraints of air springs in complex off-road environments, and enables the air springs to work safely and fully exert their functions in complex off-road environments.

[0072] Preferably, the posture angle locking adjustment specifically includes:

[0073] SS1) setting a posture angle deviation threshold to limit the range of change of the vehicle body posture angle during the posture angle locking adjustment process, ensuring that the vehicle body posture after adjustment is consistent with the locked reference posture angle;

[0074] SS2) After the air spring operating mode is switched to off-road mode, the vehicle's attitude angle at this time is calculated and recorded as the reference attitude angle, which serves as the attitude maintenance target during the vehicle suspension height adjustment process;

[0075] SS3) determining an air spring adjustment sequence for a left front air spring and a right front air spring of a front axle of the vehicle and a left rear air spring and a right rear air spring of a rear axle of the vehicle based on the reference attitude angle;

[0076] SS4) adjusting the heights of the left front air spring, the right front air spring, the left rear air spring, and the right rear air spring in sequence according to the adjustment sequence determined in step SS3), and calculating the real-time attitude angle of the vehicle;

[0077] SS5) Based on the reference attitude angle, the real-time attitude angle, and the attitude angle deviation threshold, determine whether to continue adjusting the height of the left front air spring, the right front air spring, the left rear air spring, and the right rear air spring in the following manner:

[0078] If |real-time attitude angle of the vehicle-reference attitude angle|<attitude angle deviation threshold, then stop adjustment;

[0079] If |real-time attitude angle of vehicle-reference attitude angle|≥attitude angle deviation threshold, repeat steps SS4) to SS5) to continue adjusting the heights of the left front air spring, right front air spring, left rear air spring, and right rear air spring.

[0080] The present invention solves the problem of posture loss of control caused by adjusting the inclined road surface according to a fixed target in the prior art by setting a posture angle deviation threshold and recording a reference posture angle, ensures that the posture of the vehicle body after adjustment is consistent with the initial tilt state, and significantly reduces the risk of rollover; secondly, the height adjustment sequence of each air spring is determined based on the reference posture angle, which can adapt to the needs of complex inclined road conditions, ensuring that the driver's field of vision is not affected, and breaking through the rigid limitations of the traditional single threshold on the function of the air spring, so that the vehicle can lift the chassis within a safe range to improve passability; at the same time, combined with the closed-loop adjustment mechanism formed by real-time posture angle calculation, relying on the precise data support of the extended Kalman filter, it can ensure that the posture is always stable within the deviation range during the adjustment process, reducing the driving discomfort caused by sudden posture changes, and achieving the unity of full play of the air spring function and driving safety and comfort in complex off-road scenarios.

[0081] Preferably, the process of determining the air spring adjustment sequence specifically includes:

[0082] ① According to the vehicle's pitch angle, determine the height adjustment order of the vehicle's front and rear axle air springs:

[0083] If the vehicle's pitch angle is greater than 0, adjust the height of the air spring on the front axle first, then adjust the height of the air spring on the rear axle;

[0084] If the vehicle's pitch angle is ≤0, first adjust the height of the rear axle air spring on the vehicle's rear axle, then adjust the height of the air spring on the vehicle's front axle;

[0085] ② According to the vehicle's roll angle, determine the height adjustment order of the left and right air springs:

[0086] If the vehicle's roll angle is greater than 0, adjust the height of the air spring on the right side of the vehicle first, then adjust the height of the air spring on the left side of the vehicle within the same axis;

[0087] If the vehicle's roll angle is ≤0, adjust the height of the air spring on the left side of the vehicle first, then adjust the height of the air spring on the right side of the vehicle within the same axle;

[0088] ③ Use the height adjustment sequence determined in steps ① and ② as the air spring adjustment sequence.

[0089] The present invention determines the adjustment sequence of the air spring heights of the front and rear axles and the left and right sides of the vehicle according to the positive or negative posture angle of the vehicle, and can accurately match the actual tilt state of the vehicle. For example, when the front is low and the rear is high, the front axle is adjusted first to avoid obstruction of the field of vision. When the left is high and the right is low, the right side balance posture is adjusted first, ensuring that the driver always maintains a good field of vision during the adjustment process, thereby improving operational safety.

[0090] The advantages of the present invention include the following:

[0091] ① The present invention breaks through the limitations of existing technologies with a single fixed threshold by establishing a dynamic hierarchical control strategy for three states: horizontal, tilted, and dangerous. It can accurately adapt to gradual changes in road conditions in off-road scenarios, from gentle roads to steep slopes and cross-axle roads. It avoids excessive intervention during slight tilts to ensure passability, while promptly prohibiting adjustments during dangerous tilts to ensure safety, effectively resolving the issue of excessive or insufficient intervention.

[0092] ② In order to solve the posture deviation problem caused by the lack of posture angle locking mechanism in the existing technology, the present invention introduces a posture angle locking mechanism in the tilted state, locks the current pitch angle and roll angle as the reference, and maintains the posture angle deviation within the set threshold in real time during the adjustment process, ensuring that the body posture before and after adjustment is consistent, avoiding body imbalance caused by sudden change of posture angle when the vehicle travels on a horizontal road, and significantly reducing the risk of rollover.

[0093] ③ In order to solve the problem of insufficient accuracy in wheel suspension detection, the present invention adopts a multi-parameter fusion and calibration mechanism. By pre-calibrating the suspension base height when the wheel leaves the ground in maintenance mode, the wheel status is judged in actual driving by combining the real-time reading of the height sensor with the "base height + calibration hysteresis value", which effectively suppresses the misjudgment caused by a single threshold, avoids vehicle imbalance caused by overcharging or undercharging of the air spring, and greatly improves the detection reliability on complex off-road roads.

[0094] Glossary:

[0095] The Kalman filter (KF) is a classic linear optimal estimation algorithm suitable for linear systems with Gaussian noise. By fusing system model predictions with observed data, it can obtain more accurate state estimates (such as position and velocity) than using either the model or observations alone. The extended Kalman filter (EKF) is an extension of the Kalman filter (KF) for nonlinear systems and is primarily used to solve state estimation problems in nonlinear dynamic systems.

[0096] Time step: refers to the time interval between two sensor data acquisitions or filtering iterations (usually represented by Δt).

[0097] Attitude loss of control: refers to the phenomenon that the orientation and attitude angles (such as pitch angle, roll angle, yaw angle, etc.) of an object (usually a system with dynamic attitude requirements) in space cannot remain stable according to the preset target or control instructions, or cannot be adjusted to the expected state through its own control system, causing the attitude to deviate from the normal range. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] Figure 1 A schematic diagram of the system architecture in an embodiment of the present invention;

[0099] Figure 2 Schematic diagram of three-level state transition in an embodiment of the present invention;

[0100] Figure 3 Schematic diagram of the attitude angle locking adjustment process in an embodiment of the present invention;

[0101] Figure 4 This is a logic diagram of wheel suspension detection in an embodiment of the present invention;

[0102] Figure 5 Schematic diagram of the flow chart of the extended Kalman filter (EKF) algorithm in an embodiment of the present invention;

[0103] Figure 6 Schematic diagram of the simulation effect in an embodiment of the present invention. DETAILED DESCRIPTION

[0104] like Figures 1 to 6 As shown, a method for adjusting the height of an air spring for an off-road mode of a vehicle includes the following steps:

[0105] 1) Determine a horizontal state pitch angle calibration threshold, a horizontal state roll angle calibration threshold, an inclined state pitch angle calibration threshold, an inclined state roll angle calibration threshold, and an air spring adjustment height lower limit and an air spring adjustment height upper limit;

[0106] 2) Collect vehicle acceleration, vehicle angular velocity, and vehicle suspension height;

[0107] 3) Calculating the vehicle's attitude angle based on the vehicle's acceleration and angular velocity in combination with an extended Kalman filter, wherein the attitude angle includes the vehicle's pitch angle and the vehicle's roll angle;

[0108] 4) Determine the vehicle's control state based on the vehicle's pitch angle, roll angle, and suspension height:

[0109] If |the vehicle's pitch angle| is less than or equal to the horizontal pitch angle calibration threshold, and |the vehicle's roll angle| is less than or equal to the horizontal roll angle calibration threshold, and the air spring adjustment height lower limit is less than or equal to the suspension height and less than or equal to the air spring adjustment height upper limit, the vehicle is determined to be level and conventional height adjustment is performed.

[0110] If the horizontal state pitch angle calibration threshold < |the vehicle's pitch angle| ≤ the tilted state pitch angle calibration threshold and there are no suspended wheels, or if the horizontal state roll angle calibration threshold < |the vehicle's roll angle| ≤ the tilted state roll angle calibration threshold and there are no suspended wheels, the vehicle is determined to be in a tilted state and attitude angle locking adjustment is performed;

[0111] If |the vehicle's pitch angle|>the pitch angle calibration threshold in the tilted state, or |the vehicle's roll angle|>the roll angle calibration threshold in the tilted state, or there is a suspended wheel, height adjustment is prohibited.

[0112] According to the above method, the following embodiments are made:

[0113] 1) Through simulation experiments, it was determined that the pitch angle calibration threshold value in the horizontal state is 0.8°, the roll angle calibration threshold value in the horizontal state is 0.8°, the pitch angle calibration threshold value in the tilted state is 2°, the roll angle calibration threshold value in the tilted state is 2°, and the lower limit of the air spring adjustment height is 700 mm, and the upper limit of the air spring adjustment height is 800 mm;

[0114] It is worth noting that the horizontal state pitch angle calibration threshold, horizontal state roll angle calibration threshold, tilted state pitch angle calibration threshold, and tilted state roll angle calibration threshold are all empirical values ​​determined through calibration experiments. In order to better fit the actual driving state of the vehicle, a real vehicle can be used to calibrate data in real scenes.

[0115] In this embodiment, a simulation experiment is conducted to simulate a vehicle equipped with air springs driving on a level road, an inclined road, and a special driving environment. After the air spring operating mode is switched from standard mode to off-road mode, the ECAS system receives signals from the IMU and estimates the vehicle's pitch and roll angles through the EKF. Combined with the vehicle's current suspension height, the system performs three-level attitude adjustments, as follows:

[0116] 2) The IMU's gyroscope collects the vehicle's acceleration, the IMU's accelerometer collects the vehicle's angular velocity, and four height sensors collect the vehicle's suspension height;

[0117] 3) Calculate the vehicle's attitude angle based on the vehicle's acceleration and angular velocity, combined with the extended Kalman filter, including the vehicle's pitch angle θ pitch and the vehicle's roll angle θ roll , the calculation process of the attitude angle specifically includes:

[0118] 3-1) Define the state variables of the extended Kalman filter and implement time-recursive prediction of attitude angles using gyroscope angular velocity measurements and bias compensation.

[0119] Definition of state variables:

[0120]

[0121] Where θ is the pitch angle, φ is the roll angle, and b gx is the x-axis gyroscope zero bias, b gy is the y-axis gyroscope bias.

[0122] State prediction equation:

[0123]

[0124] Where, is the prior state estimate at time k, x k-1 is the optimal state estimate at time k-1, u k is the control vector, which represents the measurement value of the IMU gyroscope, i.e. u k =[ω x ,ω y ]. Substituting the state vector into the above formula, we get:

[0125]

[0126] Where, is the prior pitch angle at time k, is the prior roll angle at time k, is the prior X-axis gyro bias at time k, is the prior Y-axis gyro bias at time k, ω y is the prior Y-axis gyro bias at time k, ω x is the X-axis gyroscope angular velocity measurement value, and Δt is the discrete system sampling step.

[0127] 3-2) Using the state transfer matrix to realize the time domain propagation of error covariance

[0128] Covariance prediction equation:

[0129]

[0130] Where, is the a priori estimated covariance, is the posterior estimated covariance, and Q is the process noise covariance. k is the state transfer matrix:

[0131]

[0132] 3-3) Generate theoretical observation values ​​based on the gravity acceleration component model

[0133] Observation model equation:

[0134]

[0135] Where, is the accelerometer observation prediction vector, is the predicted value of the X-axis gravity component, is the predicted value of the Y-axis gravity component, The predicted value of the Z-axis gravity component.

[0136] 3-4) Establish a sensitivity model for attitude angle changes to gravity components

[0137] Observation Jacobian matrix H k for:

[0138]

[0139] 3-5) Confidence weights for prediction and observation of dynamic equilibrium states

[0140]

[0141] H k is the Kalman gain matrix, is the prior estimate of covariance, H k is the observation Jacobian matrix, and R is the observation noise covariance.

[0142] 3-6) Fusion of accelerometer measured values ​​to correct attitude angle estimation

[0143]

[0144] in, is the posterior state estimate at time k, is the prior state estimate at time k, z m is the measured vector of the accelerometer, that is is the observation prediction vector, K k is the Kalman gain matrix. m and Substituting into the above formula we get:

[0145]

[0146] 3-7) Uncertainty measurement for real-time state estimation

[0147]

[0148] in is the posterior covariance estimate at time k, I is the identity matrix, K k is the Kalman gain matrix, H k is the Jacobian matrix of the observation model, Prior state estimate covariance matrix.

[0149] 3-8) Angle normalization eliminates periodic jumps during angle integration

[0150]

[0151] In this embodiment, the vehicle's attitude angle is calculated using the IMU sensor built into the controller (a 6-axis sensor consisting of three accelerometers that measure acceleration in the x, y, and z axes, and three gyroscopes that measure angular velocity around the x, y, and z axes). The EKF fuses the accelerometer and gyroscope measurements to estimate the attitude angle.

[0152] 4) Determine the vehicle's control state based on the vehicle's pitch angle, roll angle, and suspension height:

[0153] If |the vehicle's pitch angle| is less than or equal to the horizontal pitch angle calibration threshold, and |the vehicle's roll angle| is less than or equal to the horizontal roll angle calibration threshold, and the air spring adjustment height lower limit is less than or equal to the suspension height and less than or equal to the air spring adjustment height upper limit, the vehicle is determined to be level, and the ECAS control system controls the air springs to perform conventional height adjustment, including:

[0154] S1) setting a conventional adjustment target height, which serves as a basis for adjusting the air spring height in conventional height adjustment, wherein the target height is a height set in off-road mode, and a value range of the conventional adjustment target height is 790±5 mm (700-800 mm in non-off-road mode);

[0155] S2) simultaneously raising the heights of the left rear air spring and the right rear air spring of the rear axle of the vehicle until the heights of the left rear air spring and the right rear air spring of the rear axle of the vehicle both reach a target height threshold;

[0156] S3) simultaneously raising the left front air spring and the right front air spring of the front axle of the vehicle until the heights of the left front air spring and the right front air spring of the front axle of the vehicle both reach a target height threshold;

[0157] S4) After the front axle air spring height is adjusted to the target height, in order to eliminate the overshoot of some air spring heights caused by vehicle body rigidity, the height of each air spring is finely adjusted to within the target height error range.

[0158] The so-called fine adjustment refers to the fact that after the system completes the front and rear axle adjustment (i.e., first raise the rear axle, then raise the front axle), the height of an air spring may exceed the error range (generally ±5mm) due to the influence of vehicle body rigidity. In this embodiment, the fine adjustment is applied to all air springs. The purpose is to eliminate the possibility that the height of one or more air springs exceeds the target height error range due to the mutual influence of the front and rear axles during the vehicle height adjustment process. Specifically, it includes:

[0159] S5-1) setting a fine adjustment threshold value, which is used as a basis for fine adjustment of the air spring height under conventional height adjustment, wherein the fine adjustment threshold value is set to 5 mm;

[0160] S5-2) respectively collecting the real-time heights of the left rear air spring, the right rear air spring, the left front air spring, and the right front air spring;

[0161] S5-3) Check the heights of the four air springs, front left, front right, rear left, and rear right, in turn to see if they meet the adjustment target. If so, maintain the heights. Otherwise, adjust the heights based on the target heights and real-time sensor readings to ensure that the height of each air spring meets the following formula, including:

[0162] Use the following method to determine whether the height of the corresponding air spring needs to be adjusted based on the real-time height of the left rear air spring, right rear air spring, left front air spring, and right front air spring:

[0163] If |real-time height-target height threshold|≤fine adjustment threshold, the air spring maintains the current height and does not make any height adjustments;

[0164] If |real-time height-target height threshold|>fine adjustment threshold, the height of the air spring is adjusted and steps S5-2) to S5-3) are repeated.

[0165] If the horizontal state pitch angle calibration threshold <|vehicle pitch angle| ≤ tilted state pitch angle calibration threshold and there is no suspended wheel, or the horizontal state roll angle calibration threshold <|vehicle roll angle| ≤ tilted state roll angle calibration threshold and there is no suspended wheel, the vehicle is determined to be in a tilted state and attitude angle locking adjustment is performed, specifically including:

[0166] SS1) setting a posture angle deviation threshold to limit the range of change of the vehicle body posture angle during the posture angle locking adjustment process to ensure that the adjusted vehicle body posture remains consistent with the locked reference posture angle. The posture angle deviation threshold is set to 0.8° when the vehicle is in a horizontal state and 2.0° when the vehicle is in a tilted state;

[0167] SS2) After the air spring operating mode is switched to off-road mode, the ECAS system first calculates the vehicle's current attitude angle and stores it in the NVM. This is recorded as the reference attitude angle, which serves as the attitude maintenance target during the vehicle's suspension height adjustment process.

[0168] SS3) Determine the air spring adjustment sequence of the left front air spring and the right front air spring of the front axle of the vehicle and the left rear air spring and the right rear air spring of the rear axle of the vehicle based on the reference attitude angle, specifically including:

[0169] ① According to the vehicle's pitch angle, determine the height adjustment order of the vehicle's front and rear axle air springs:

[0170] If the vehicle's pitch angle is greater than 0, indicating that the vehicle's current state is that the front is lower and the rear is higher, first adjust the height of the air spring on the front axle of the vehicle, then adjust the height of the air spring on the rear axle of the vehicle;

[0171] If the vehicle's pitch angle is ≤0, indicating that the vehicle's current state is that the front is higher and the rear is lower, first adjust the height of the rear axle air spring of the vehicle, and then adjust the height of the front axle air spring of the vehicle;

[0172] The adjustment order of the left and right air springs on the same axle of the vehicle is determined by the vehicle's roll angle, as follows:

[0173] ② According to the vehicle's roll angle, determine the height adjustment order of the left and right air springs:

[0174] If the vehicle's roll angle is greater than 0, indicating that the vehicle's current state is that the left side is higher than the right side, first adjust the height of the right side air spring of the vehicle within the same axle, and then adjust the height of the left side air spring of the vehicle;

[0175] If the vehicle's roll angle is ≤0, indicating that the vehicle's current state is that the right side is higher than the left side, first adjust the height of the air spring on the left side of the vehicle, then adjust the height of the air spring on the right side of the vehicle within the same axle;

[0176] ③ Use the height adjustment sequence determined in steps ① and ② as the air spring adjustment sequence.

[0177] SS4) adjusting the heights of the left front air spring, the right front air spring, the left rear air spring, and the right rear air spring in sequence according to the adjustment sequence determined in step SS3), and calculating the real-time attitude angle of the vehicle;

[0178] In this embodiment, the process of obtaining the real-time attitude angle of the vehicle is as follows:

[0179] (1) Real-time acquisition of gyroscope and accelerometer measurement data through the vehicle-mounted inertial measurement unit;

[0180] (2) Establishing the state equation and observation equation of the extended Kalman filter, where the state variables include pitch angle, roll angle, gyroscope x-axis zero bias, and gyroscope y-axis zero bias;

[0181] (3) State prediction: Use the gyroscope measurement value to subtract the zero bias estimate in the state variable to obtain the angular velocity, combine the time step to predict the attitude angle, and update the state covariance matrix;

[0182] (4) Observation update: The three axial components of gravity acceleration in the vehicle coordinate system are calculated using the current attitude angle prediction value as the observation prediction value, and the accelerometer measurement value is used as the actual observation value to calculate the Kalman gain. The state variables and covariance matrix are updated according to the difference between the observation prediction value and the actual observation value.

[0183] (5) Output the updated pitch angle and roll angle as the attitude angle estimate at the current moment.

[0184] SS5) Based on the reference attitude angle, the real-time attitude angle, and the attitude angle deviation threshold, determine whether to continue adjusting the height of the left front air spring, the right front air spring, the left rear air spring, and the right rear air spring in the following manner:

[0185] If |real-time attitude angle of the vehicle-reference attitude angle|<attitude angle deviation threshold, then stop adjustment;

[0186] If |real-time attitude angle of vehicle-reference attitude angle|≥attitude angle deviation threshold, repeat steps SS4) to SS5) to continue adjusting the heights of the left front air spring, right front air spring, left rear air spring, and right rear air spring.

[0187] In this embodiment, by setting the attitude angle deviation threshold, the vehicle is subjected to real-time and dynamic attitude constraints, so that the vehicle body attitude is always stable within the safety deviation range of the initial reference attitude during the adjustment process, which can ensure the stability of the vehicle body attitude during the adjustment process, avoid the sudden increase of the pitch angle and roll angle due to excessive lifting or lowering of one side when adjusting a certain air spring, and reduce the discomfort of the driver and passengers caused by sudden changes in attitude.

[0188] It is worth noting that the above-mentioned attitude angle locking adjustment is before the vehicle passes through the off-road surface, when the driver or the vehicle's pre-aiming system senses that there are obstacles such as potholes or raised roads on the road ahead. If the current vehicle air spring mode is not off-road mode (the air spring height corresponding to the off-road mode is the highest), the driver usually stops the car first, switches to the air spring mode, lifts the vehicle up, and then tries to pass. When the driver switches the ECAS mode to off-road mode, the attitude angle at this time is first calculated and locked, and then the air spring height is adjusted according to the attitude angle. After the adjustment is completed, the attitude angle remains the same. This process is completed when the vehicle is stationary, that is, the adjustment is completed before passing the off-road surface.

[0189] In this embodiment, when the vehicle returns from an inclined road (off-road) to a level surface, all four suspension heights are at off-road height, and the vehicle's attitude angle is near horizontal. At this point, the driver manually switches the vehicle's suspension height to Comfort or Sport mode for adjustment. Alternatively, when the vehicle speed exceeds a calibrated threshold, the driver enters Speed-Following mode, followed by Comfort or Off-Road mode. Otherwise, the suspension height remains in Off-Road mode.

[0190] If |the vehicle's pitch angle|>the pitch angle calibration threshold in the tilted state, or |the vehicle's roll angle|>the roll angle calibration threshold in the tilted state, or there is a suspended wheel, it is determined that the vehicle is driving in a special road environment (such as a cross-axle road surface, or a large-angle climbing state in off-road conditions). In order to avoid vehicle rollover or vehicle imbalance due to height adjustment, the ECAS system will enter the height adjustment prohibited state, and the control system will not respond even if the air spring mode switching request is currently made.

[0191] In this embodiment, the specific process of determining whether there is a suspended wheel includes:

[0192] (1) When the vehicle is stationary, with the air spring adjustment disabled, test the maximum travel of each air spring in the air spring mode, which is used as the base height of the suspension (i.e., the base height of the wheel suspension travel);

[0193] (2) Setting a hysteresis value to prevent misjudgment of the wheel suspension state and avoid unnecessary adjustment restrictions due to sensor signal fluctuations. The hysteresis value is set to 5 to 10 mm;

[0194] (3) During actual driving, the height sensors installed at each corner of the vehicle body can be used to monitor the height readings in real time, collect the height of the vehicle suspension, and determine whether there are suspended wheels in the following manner:

[0195] If any wheel height > suspended base height + hysteresis value, there is a suspended wheel;

[0196] If the height of all wheels is less than or equal to the suspended base height + hysteresis value, there is no suspended wheel.

[0197] In this embodiment, the normal adjustment range of the suspension, determined through simulation experiments, is 700-800 mm. The target height in off-road mode is 790 mm. The vehicle is then lifted using a lift. Before lifting, the ECAS control system is placed into maintenance mode through the central control panel's human-machine interface. When the four wheels leave the ground, gravity pulls the air springs downward, extending the suspension travel to its maximum. The current suspension height is recorded. For example, in this example, the corresponding suspended base height in off-road mode is 900 mm. To prevent misjudgment, a hysteresis value of 5 to 10 mm is added.

[0198] In this embodiment, when the vehicle air spring operating mode is switched to non-off-road mode or the vehicle speed is greater than the calibrated threshold of the speed-dependent vehicle speed (80 kph), the ECAS system will control the air spring to lower. The lowering process is the opposite of the raising process, generally lowering the front axle first and then the rear axle.

[0199] Through simulation tests, the results of vehicle height adjustment in different road environments are as follows: Figure 6 As shown, in the horizontal state, when the air spring operating mode is switched from standard mode to off-road mode, the ECAS system will first raise the rear axle and then the front axle. During the lifting process, the left and right air springs of the rear axle are first raised simultaneously to near the target value, and then the height of the left and right rear air springs are finely adjusted respectively. When switching from off-road mode to standard mode, the front axle is lowered first and then the rear axle. Similarly, during the adjustment process, the air spring height of each axle is first lowered to near the target height simultaneously, and then fine-tuned to within the error range. Except for the change in attitude angle during the adjustment, the entire process remains in a nearly horizontal state, that is, the pitch angle is <0.8° and the roll angle is <0.8°.

[0200] When the vehicle's pitch angle is 0.8° < ≤ 2° and the roll angle is 0.8° < ≤ 2° and the four sensors read normal, the ECAS system will determine that it is in a tilted state. For example, the simulation data shows a pitch angle of 0.91° and a roll angle of 0.85°. The four suspension heights are within [700-800mm]. When the air spring mode is switched from standard mode to off-road mode, the pitch angle and roll angle are both greater than zero. Therefore, the adjustment sequence should be right front --> left front --> right rear --> left rear. The simulation data satisfies the above adjustment sequence. The body posture angle after the adjustment is the same as before the adjustment. The next step is to simulate the vehicle returning to a horizontal road. The vehicle should have maintained the posture angle before the adjustment, and the body posture angle also returns to a horizontal state.

[0201] The ECAS system deems a dangerous state if the vehicle's pitch angle exceeds 2°, the roll angle exceeds 2°, or a wheel is in the air. Simulation data simulates a re-crossing axle condition, where the attitude angle exceeds the tilt threshold. This data shows that even if the air spring mode is requested to switch from standard to off-road mode, the system will not respond, maintaining the state it was in before the cross-axle condition. Finally, when the vehicle returns to a level surface, the attitude angle returns to the horizontal range.

[0202] It is worth noting that the multiple thresholds set in this embodiment are all empirical values ​​determined by calibration experiments for specific vehicles. Different vehicles need to calculate specific thresholds based on vehicle geometric parameters.

[0203] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for adjusting the height of an air spring in an off-road mode of a vehicle, characterized in that: The following steps are involved: 1) Determine a horizontal state pitch angle calibration threshold, a horizontal state roll angle calibration threshold, an inclined state pitch angle calibration threshold, an inclined state roll angle calibration threshold, and an air spring adjustment height lower limit and an air spring adjustment height upper limit; 2) Collect vehicle acceleration, vehicle angular velocity, and vehicle suspension height; 3) Calculating the vehicle's attitude angle based on the vehicle's acceleration and angular velocity in combination with an extended Kalman filter, wherein the attitude angle includes the vehicle's pitch angle and the vehicle's roll angle; 4) Determine the air spring height adjustment method based on the vehicle's attitude angle and suspension height: If |the vehicle's pitch angle| ≤ the horizontal pitch angle calibration threshold, and |the vehicle's roll angle| ≤ the horizontal roll angle calibration threshold, and the air spring adjustment height lower limit ≤ the suspension height ≤ the air spring adjustment height upper limit, then the vehicle is determined to be level and the air spring height is adjusted normally. If the horizontal state pitch angle calibration threshold <|vehicle pitch angle| ≤ tilted state pitch angle calibration threshold, or the horizontal state roll angle calibration threshold <|vehicle roll angle| ≤ tilted state roll angle calibration threshold, and there is no suspended wheel, the vehicle is determined to be in a tilted state, and the air spring height is adjusted for attitude angle locking; If |Vehicle's pitch angle|>the pitch angle calibration threshold in the tilted state, or |Vehicle's roll angle|>the roll angle calibration threshold in the tilted state, or there is an overhung wheel, height adjustment of the air spring is prohibited.

2. The air spring height adjustment method according to claim 1, characterized in that: The conventional height adjustment specifically includes: S1) setting a target height threshold value, which is used as a basis for adjusting the height of the air spring under conventional height adjustment; S2) simultaneously raising the heights of the left rear air spring and the right rear air spring of the rear axle of the vehicle until the heights of the left rear air spring and the right rear air spring of the rear axle of the vehicle both reach a target height threshold; S3) simultaneously raising the left front air spring and the right front air spring of the front axle of the vehicle until the heights of the left front air spring and the right front air spring of the front axle of the vehicle both reach a target height threshold; S4) Finely adjust the heights of the left front air spring, right front air spring, left rear air spring, and right rear air spring to eliminate overshoot of the air spring height caused by vehicle body rigidity.

3. The air spring height adjustment method according to claim 2, characterized in that: The refined adjustment specifically includes: S5-1) setting a fine adjustment threshold value, which is used as a basis for fine adjustment of the air spring height under conventional height adjustment; S5-2) respectively collecting the real-time heights of the left rear air spring, the right rear air spring, the left front air spring, and the right front air spring; S5-3) Determine whether the heights of the corresponding air springs need to be adjusted based on the real-time heights of the left rear air spring, the right rear air spring, the left front air spring, and the right front air spring in the following manner: If |real-time height-target height threshold|≤fine adjustment threshold, the air spring maintains the current height and does not make any height adjustments; If |real-time height-target height threshold|>fine adjustment threshold, the height of the air spring is adjusted and steps S5-2) to S5-3) are repeated.

4. The air spring height adjustment method according to claim 1, characterized in that: The attitude angle locking adjustment specifically includes: SS1) setting a posture angle deviation threshold value to limit the range of change of the vehicle body posture angle during the posture angle locking adjustment process, ensuring that the vehicle body posture after adjustment is consistent with the locked reference posture angle; SS2) After the air spring operating mode is switched to off-road mode, the vehicle's attitude angle at this time is calculated and recorded as the reference attitude angle, which serves as the attitude maintenance target during the vehicle suspension height adjustment process; SS3) determining an air spring adjustment sequence for a left front air spring and a right front air spring of a front axle of the vehicle and a left rear air spring and a right rear air spring of a rear axle of the vehicle based on the reference attitude angle; SS4) adjusting the heights of the left front air spring, the right front air spring, the left rear air spring, and the right rear air spring in sequence according to the adjustment sequence determined in step SS3), and calculating a real-time attitude angle of the vehicle; SS5) Based on the reference attitude angle, the real-time attitude angle, and the attitude angle deviation threshold, determine whether to continue adjusting the height of the left front air spring, the right front air spring, the left rear air spring, and the right rear air spring in the following manner: If |real-time attitude angle of the vehicle-reference attitude angle|<attitude angle deviation threshold, then stop adjustment; If |real-time attitude angle of vehicle-reference attitude angle|≥attitude angle deviation threshold, repeat steps SS4) to SS5) to continue adjusting the heights of the left front air spring, right front air spring, left rear air spring, and right rear air spring.

5. The air spring height adjustment method according to claim 4, characterized in that: In step SS3), the process of determining the air spring adjustment sequence specifically includes: ① According to the vehicle's pitch angle, determine the height adjustment order of the vehicle's front and rear axle air springs: If the vehicle's pitch angle is greater than 0, adjust the height of the air spring on the front axle first, then adjust the height of the air spring on the rear axle; If the vehicle's pitch angle is ≤0, first adjust the height of the rear axle air spring on the vehicle's rear axle, then adjust the height of the air spring on the vehicle's front axle; ② According to the vehicle's roll angle, determine the height adjustment order of the left and right air springs: If the vehicle's roll angle is greater than 0, adjust the height of the air spring on the right side of the vehicle first, then adjust the height of the air spring on the left side of the vehicle within the same axis; If the vehicle's roll angle is ≤0, adjust the height of the air spring on the left side of the vehicle first, then adjust the height of the air spring on the right side of the vehicle within the same axle; ③ Use the height adjustment sequence determined in steps ① and ② as the air spring adjustment sequence.

6. The air spring height adjustment method according to claim 1, characterized in that: The attitude angle is calculated as follows: 3-1) Define the state variables and state prediction equations of the extended Kalman filter, combine the vehicle's angular velocity and zero bias compensation, perform time-recursive prediction of the attitude angle, and obtain the prior state estimate; 3-2) Establish a state transfer matrix based on the state variables and state prediction equation, and use the state transfer matrix to perform time domain propagation of the error covariance to obtain the prior estimated covariance; 3-3) Establish a vehicle's gravity acceleration component model and generate theoretical observations based on prior state estimates; 3-4) Based on the gravity acceleration component model and state variables, construct the observation Jacobian matrix to reflect how the attitude angle changes affect the observed value of the gravity component; 3-5) Calculate the Kalman gain matrix based on the prior estimated covariance, the observed Jacobian matrix, and the observed noise covariance, which is used to calculate the confidence weights of the equilibrium state prediction and the observed measurement; 3-6) Calculate the difference between the vehicle acceleration and the theoretical observation value, and use the Kalman gain matrix to correct the prior state estimate to obtain the posterior state estimate; 3-7) Combining the identity matrix, the Kalman gain matrix, the observation Jacobian matrix and the prior estimated covariance, the posterior covariance is calculated and used as the initial input for the next extended Kalman filter cycle; 3-8) Perform angle normalization on the posterior state estimate to obtain the vehicle's attitude angle.

7. The air spring height adjustment method according to claim 1, characterized in that: The existence of suspended wheels specifically includes: (1) Test the maximum travel of each air spring in the empty spring mode as the base height of the suspension; (2) Setting a hysteresis value to prevent misjudgment of the wheel suspension state and avoid unnecessary adjustment restrictions caused by sensor signal fluctuations; (3) Collect the height of the vehicle suspension and determine whether there are any suspended wheels in the following manner: If any wheel height > suspended base height + hysteresis value, there is a suspended wheel; If the height of all wheels is less than or equal to the suspended base height + hysteresis value, there is no suspended wheel.

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