Method for restraining automobile pitching through damping switching

Abstract

The invention provides a method for restraining automobile pitching through damping switching. The method comprises the following steps: acquiring automobile driving state parameters in real time and judging whether to enter a pitching suppression working condition; when the working condition is started, damping switching control is started, and the stretching stroke damping coefficient and the compression stroke damping coefficient of the front suspension and the rear suspension are adjusted respectively. The height of a front vehicle body and the height of a rear vehicle body are reversely adjusted by utilizing the vehicle body balance position change characteristic generated by a semi-active suspension under different damping ratios, namely by setting the state which is easy to press and difficult to stretch or easy to stretch and press, and anti-pitching moment is generated to restrain pitching of the vehicle body. In addition, the method further comprises a suspension stroke safety protection step and a front-back cooperative concession strategy based on moment balance, and the stress balance of the whole vehicle is maintained while mechanical breakdown of the suspension is prevented. According to the method, the attitude control effect similar to that of an active suspension is achieved through the semi-active suspension, and the stability of the vehicle during acceleration and deceleration is improved.

Description

Technical Field

[0001] This invention relates to the field of automotive attitude control technology, and in particular to a method for suppressing vehicle pitch using damping switching. Background Technology

[0002] Frequent acceleration and braking in urban traffic conditions cause longitudinal pitch vibrations in the vehicle body. This phenomenon, commonly known as "nose-up" or "nodding," not only reduces passenger comfort but can also lead to motion sickness in severe cases and affect the driver's visibility and tire grip. Currently, the industry's technologies for suppressing vehicle pitch are mainly divided into two categories: active suspension and semi-active suspension. Active suspension, such as air suspension or hydraulic suspension, can directly adjust the vehicle height by injecting energy into the system, controlling the pitch angle within a very small range. However, its system structure is complex, typically including components such as compressors, air tanks, or high-pressure oil pumps. This not only results in high manufacturing costs but also occupies valuable chassis space and has relatively high energy consumption, thus limiting its widespread adoption.

[0003] Semi-active suspension systems, such as continuously damped control shock absorbers, offer advantages such as compact structure, rapid response, and low cost, making them a mainstream high-performance solution. However, current applications of semi-active suspension primarily focus on dissipating vibration energy by altering the damping force, emphasizing the reduction of the rate and amplitude of pitch motion. The engineering community generally believes that semi-active suspensions can only change damping characteristics and cannot actively alter the vehicle's static equilibrium position. Therefore, when dealing with continuous acceleration and deceleration inertial moments, their ability to suppress pitch angles is relatively limited, making it difficult to achieve the completely smooth zero-pitch attitude control found in active suspensions. Summary of the Invention

[0004] The purpose of this invention is to provide a method for suppressing vehicle pitch using damping switching, in order to solve the problems mentioned in the background art.

[0005] This invention provides a method for suppressing vehicle pitch using damping switching, comprising the following steps: The vehicle's driving status parameters are acquired in real time, and the vehicle is judged to have entered pitch suppression mode based on the driving status parameters. When it is determined that the vehicle has entered the pitch suppression condition, the damping switching control is activated to adjust the relationship between the extension stroke damping coefficient and the compression stroke damping coefficient of the front and rear suspensions of the vehicle, respectively. By utilizing the height variation characteristics of the vehicle's balance position caused by the semi-active suspension under different ratios of extension stroke damping coefficient and compression stroke damping coefficient, the heights of the front and rear vehicles are adjusted in opposite directions to generate anti-pitch torque and suppress vehicle pitch.

[0006] Optionally, the method of utilizing the vehicle body balance position height variation characteristics generated by the semi-active suspension under different ratios of extension stroke damping coefficient and compression stroke damping coefficient is based on the following principle: When the extension stroke damping coefficient of the semi-active suspension is greater than the compression stroke damping coefficient, the vehicle balance position at that suspension point is lowered. When the extension stroke damping coefficient of the semi-active suspension is less than the compression stroke damping coefficient, the vehicle body balance position at that suspension point rises.

[0007] Optionally, the pitch suppression condition includes an acceleration condition; when it is determined that the vehicle has entered the acceleration condition, the specific steps of the damping switching control are as follows: The extension stroke damping coefficient of the front suspension is controlled to be greater than the compression stroke damping coefficient, so that the front of the vehicle body drops. At the same time, the extension stroke damping coefficient of the rear suspension is controlled to be less than the compression stroke damping coefficient, so that the rear vehicle body is raised, thereby maintaining the same height between the front and rear vehicle bodies.

[0008] Optionally, the pitch suppression condition includes the braking condition; when it is determined that the vehicle has entered the braking condition, the specific steps of the damping switching control are as follows: The extension stroke damping coefficient of the front suspension is controlled to be less than the compression stroke damping coefficient, thereby raising the front vehicle body. At the same time, the extension stroke damping coefficient of the rear suspension is controlled to be greater than the compression stroke damping coefficient, so that the rear vehicle body is lowered, thereby maintaining the same height between the front and rear vehicle bodies.

[0009] Optionally, determining whether the vehicle has entered pitch suppression mode based on the driving state parameters specifically includes: The vehicle's longitudinal acceleration, pitch angle, and pitch angular velocity are collected as the driving state parameters. Determine whether at least one of the vehicle body longitudinal acceleration, the pitch angle, or the pitch angular velocity exceeds a preset threshold; if so, determine that the vehicle has entered the pitch suppression condition.

[0010] Optionally, the damping switching control aims to control the vehicle's pitch angle to 0, and employs the following control strategy: For the suspension at the end where the vehicle body needs to be lowered, its compression stroke damping coefficient is set to a first fixed value, and its extension stroke damping coefficient is calculated by the controller. For the suspension at the end where the vehicle body needs to be raised, its extension stroke damping coefficient is set to a second fixed value, and its compression stroke damping coefficient is calculated by the controller.

[0011] Optionally, under the acceleration condition, the front suspension, as the suspension at the end that needs to lower the vehicle body, has a first fixed value of 10 N for its compression stroke damping coefficient; and the rear suspension, as the suspension at the end that needs to raise the vehicle body, has a second fixed value of 0 N for its extension stroke damping coefficient.

[0012] Optionally, the method further includes a damping recovery step: When the longitudinal acceleration of the vehicle body in the driving state parameters is detected to decrease and fall below the preset threshold, the control system controls the extension stroke damping coefficient and compression stroke damping coefficient of the front suspension and the rear suspension to gradually return to a symmetrical state through time gradual change or state feedback.

[0013] Optionally, the method further includes a suspension travel safety protection step, which specifically includes: During the execution of the damping switching control, the suspension travel of the front suspension and the rear suspension is monitored in real time, and the remaining working travel of each suspension in the current direction of motion is calculated based on the suspension travel; the remaining working travel is compared with a preset travel safety threshold. When the remaining working stroke of any end suspension is less than the stroke safety threshold, it is determined that the end suspension is at risk of breakdown, and a stroke protection command is immediately generated. The control strategy of the suspension at that end is forcibly corrected by the stroke protection command, reducing the difference between its extension stroke damping coefficient and compression stroke damping coefficient, so as to prioritize increasing the effective working stroke of the suspension at that end and prevent mechanical impact of the suspension.

[0014] Optionally, the suspension travel safety protection steps further include a front-to-rear coordinated yielding strategy based on torque balance: When it is determined that only one end of the suspension executes the travel protection command due to the risk of breakdown, the control system calculates in real time the amount of anti-pitch torque lost by the suspension at that end due to damping correction based on the vehicle center of gravity torque balance equation. Based on the lost anti-pitch torque, the suspension at the other end, which is not at risk of breakdown, is simultaneously damped and corrected. This actively weakens the anti-pitch force of the suspension at the other end, ensuring that the anti-pitch torque generated by the front and rear suspensions remains symmetrically balanced around the center of gravity. This avoids additional longitudinal vibration of the vehicle body caused by the triggering of the single-end suspension protection.

[0015] The present invention has achieved the following beneficial effects: This invention controls the extreme difference between the extension and compression damping coefficients, utilizing the physical characteristics of the suspension under asymmetric damping to induce a directional shift in the vehicle's balance position. This allows the vehicle to actively adjust its front and rear vehicle height during acceleration or braking without adding expensive hardware such as hydraulic or air pumps, generating a strong anti-pitch moment, thereby significantly improving the vehicle's acceleration and deceleration stability and ride comfort.

[0016] This invention establishes a comprehensive suspension travel safety protection mechanism, resolving the mechanical risks that may arise from aggressive damping strategies. The system can monitor the remaining suspension travel in real time, and when a breakdown risk is detected, it prioritizes switching to energy absorption protection mode, effectively preventing rigid impacts to the shock absorbers and ensuring the service life of chassis structural components and driving safety.

[0017] This invention solves the problem of vehicle force imbalance when a single-end suspension triggers protection by employing a front-rear coordinated yielding strategy based on torque balance. When one end of the suspension disengages from height control due to road impact, the system can automatically reduce the control force of the other end of the suspension, always maintaining torque balance centered on the center of gravity. This avoids longitudinal vibration of the vehicle body caused by sudden changes in control force, ensuring the linearity and smoothness of the control process.

[0018] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram illustrating the principle of vehicle height change caused by semi-active suspension damping switching in an embodiment of the present invention, showing the offset of the vehicle's balance position under different damping coefficient ratios. Figure 2 This is a simulation curve of the vehicle body balance position changing over time when the suspension extension stroke damping coefficient is greater than the compression stroke damping coefficient in an embodiment of the present invention (vehicle body lowered). Figure 3 This is a simulation curve showing the change of the vehicle's equilibrium position over time (vehicle height) when the suspension extension stroke damping coefficient is less than the compression stroke damping coefficient in an embodiment of the present invention. Detailed Implementation

[0021] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0022] This invention provides a method for suppressing vehicle pitch using damping switching, which is implemented based on a sophisticated vehicle chassis electronic control system.

[0023] In the prevailing understanding of existing technologies, semi-active suspension is generally considered to only control the rate of vibration decay of the vehicle body by changing the magnitude of the damping force; that is, it can only change the speed at which vibration energy is dissipated, and cannot inject energy into the system to directly change the vehicle's height or balance position like active suspension (such as air suspension or hydraulic suspension). However, by utilizing the extreme asymmetry of the damping characteristics of the shock absorber in its rebound and compression strokes, it is possible to induce a directional shift in the average working position of the suspension system under random road surface excitation, thereby achieving a near-active vehicle height adjustment effect.

[0024] Please refer to the instruction manual appendix. Figure 1 , Figure 1 This visually demonstrates the physical mechanism by which the vehicle's height changes due to the switching of damping in a semi-active suspension. (See image.) The damping coefficient represents the suspension's extension stroke. This represents the damping coefficient during the compression stroke.

[0025] like Figure 1 As shown in the intermediate state, when At this time, the suspension damping is symmetrical, and the vehicle body is in the normal initial equilibrium position (marked as I).

[0026] like Figure 1 As shown on the left, when the control system adjusts the damper so that the extension stroke damping coefficient is significantly greater than the compression stroke damping coefficient ( When the suspension exhibits the characteristic of being "easy to compress but difficult to extend", the dynamic balance position shifts downward, and the vehicle height decreases to position II.

[0027] like Figure 1 As shown on the right, when the control system adjusts the damper so that the extension stroke damping coefficient is significantly smaller than the compression stroke damping coefficient ( When the suspension exhibits the characteristic of being "easy to extend but difficult to compress", the dynamic balance position shifts upward, and the vehicle height is raised to position III.

[0028] In this embodiment, the vibration damper is preferably a continuously damped controlled (CDC) vibration damper or a magnetorheological (MR) vibration damper. A key characteristic of these vibration dampers is their ability to independently adjust the tensile damping coefficient and the compressive damping coefficient, or at least to establish a large difference between the two. For example, with a magnetorheological vibration damper, decoupled control of the tensile and compressive resistance characteristics can be achieved by changing the direction or magnitude of the current in the excitation coil, or by controlling the switching of different internal flow channels.

[0029] The specific working principle and physical mechanism are as follows: When a vehicle is driving on a road, regardless of the road's smoothness, the road's micro-textures, seams, or undulations will always be transmitted to the suspension through the tires, causing the suspension to reciprocate and extend.

[0030] When the control system adjusts the shock absorber so that the extension stroke damping coefficient is significantly greater than the compression stroke damping coefficient, the suspension system exhibits a nonlinear mechanical characteristic of "easy to compress, difficult to extend." During the compression half-cycle, due to the smaller compression damping setpoint, the shock absorber valve system opening is large, fluid resistance is low, and the suspension can be smoothly compressed, absorbing road impacts and resulting in low downward resistance of the vehicle body. However, during the subsequent extension half-cycle, due to the large extension damping setpoint, the resistance of the fluid through the valve system is extremely high, and the spring's attempt to release elastic potential energy to push the vehicle body upward is strongly suppressed, making it difficult for the suspension to rebound to its initial position. As vibration continues, this "hydraulic ratchet" effect causes each compression of the suspension to be greater than the subsequent rebound, ultimately causing the average position of the suspension in dynamic equilibrium to shift towards the compression direction, macroscopically manifested as a decrease in vehicle height at that position. The aforementioned "easy to compress, difficult to extend" effect leading to a decrease in vehicle height has been verified through simulation, such as... Figure 2 As shown. Figure 2 The curve showing the change in the vehicle's vertical displacement over time is displayed. From 0 to 20 seconds, the vehicle is under normal damping control, with displacement fluctuating around 0 cm (midpoint). At the 20-second mark, the system switches to control, forcibly setting the extension stroke damping coefficient to be greater than the compression stroke damping coefficient. It is evident that the vehicle's equilibrium position rapidly drops in a step and stabilizes within approximately -5 cm (lower position). This strongly demonstrates that increasing the extension damping ratio can effectively lower the vehicle's height.

[0031] Conversely, when the control system adjusts the shock absorber so that the extension stroke damping coefficient is significantly less than the compression stroke damping coefficient, the suspension system exhibits a "easy to extend, difficult to compress" mechanical characteristic. During the extension half-cycle, the resistance is minimal, the shock absorber hardly hinders the spring release, and the suspension can quickly rebound and extend; however, during the compression half-cycle, the resistance is enormous, and the suspension is difficult to compress. This characteristic causes the suspension to only extend or extend more than it extends during dynamic operation, resulting in the average position of the suspension shifting towards the extension direction, macroscopically manifested as an increase in vehicle height at that position. Similarly, the effect of the "easy to extend, difficult to compress" characteristic leading to an increase in vehicle height has also been verified, such as... Figure 3 As shown. With Figure 2 Conversely, when the control system switches its strategy at the 20-second mark, setting the extension stroke damping coefficient to be less than the compression stroke damping coefficient, the suspension exhibits a strong rebound tendency. Figure 3 As can be seen, the vehicle's balance position rises rapidly, jumping from the midpoint of 0cm and stabilizing in the range of approximately +5cm (high position). This characteristic gives the semi-active suspension a vehicle lifting capability similar to that of an active suspension.

[0032] Based on the detailed physical principles described above, this invention constructs a complete control logic. This control logic operates within the vehicle's electronic control unit (ECU) or domain controller. The ECU is connected to a vehicle attitude sensing sensor array via a high-speed vehicle communication bus (such as CAN-FD or FlexRay). The sensor array includes at least a six-axis inertial measurement unit (IMU) mounted at or near the vehicle's center of gravity, used to acquire high-precision longitudinal acceleration, lateral acceleration, vertical acceleration, yaw rate, pitch rate, and roll rate. In this embodiment, the IMU has a built-in Kalman filter algorithm or complementary filter algorithm module, capable of directly outputting attitude data after temperature compensation and zero-bias correction. Furthermore, the sensor array also includes vehicle height sensors mounted on the four suspension arms for real-time monitoring of the dynamic travel and relative speed of each suspension; and wheel speed sensors to assist in determining the road surface excitation frequency. The ECU also communicates with the engine management system (EMS) and the anti-lock braking system (ESP / ABS) at a low level to obtain the driver's drive torque request signal, accelerator pedal position signal and brake master cylinder pressure signal. These signals will serve as important inputs for feedforward control to compensate for the lag of simple feedback control.

[0033] An embodiment of the present invention provides a method for suppressing vehicle pitch using damping switching, the execution process of which is a closed-loop real-time control cycle. Specifically, it includes: First, perform step one: acquire the vehicle's driving status parameters in real time, and determine whether the vehicle has entered pitch suppression mode based on the driving status parameters.

[0034] The ECU reads raw signals from the sensor array at a preset high sampling frequency (e.g., 1000Hz). Specifically, the driving state parameters mainly include vehicle longitudinal acceleration, vehicle pitch angle, and vehicle pitch rate.

[0035] Because the raw sensor signals inevitably contain high-frequency vibration noise caused by road surface texture, mechanical vibration noise caused by engine idling, and electromagnetic interference noise from the sensors themselves, directly using the raw signals can lead to false triggering of the control strategy or actuator jitter. Therefore, the system first preprocesses the raw signals before making operating condition judgments.

[0036] For longitudinal acceleration of the vehicle body, the system uses a low-pass filter with zero phase offset, with the cutoff frequency set between 5Hz and 15Hz to filter out high-frequency components caused by road impacts and retain low-frequency components that reflect the rigid motion of the vehicle body.

[0037] For the vehicle pitch angle, the system uses sensor fusion technology, combining the angle change obtained by gyroscope integration with the static tilt angle calculated by accelerometer, to obtain an accurate pitch angle data that has both high dynamic response characteristics and no zero-point drift.

[0038] After acquiring the cleaned driving status parameters, the system enters the operating condition identification logic. The core of this logic is to accurately determine whether the vehicle is in a pitch suppression condition that requires intervention.

[0039] Determining whether a vehicle has entered pitch suppression mode based on driving status parameters includes: The system has a preset set of first judgment thresholds, which includes, but is not limited to, longitudinal acceleration threshold, pitch angle threshold, and pitch rate threshold. These thresholds are derived from vehicle dynamic parameters (such as wheelbase, center of gravity height, and suspension stiffness) through real-vehicle calibration. For example, the longitudinal acceleration threshold can be set to 0.2g, the pitch angle threshold can be set to 1.5 degrees, and the pitch rate threshold can be set to 3 degrees / second.

[0040] The system compares the current parameters with thresholds in real time. It determines whether at least one of the vehicle's longitudinal acceleration, pitch angle, or pitch velocity exceeds a preset threshold. The OR logic used here is to improve the system's sensitivity; for example, in the initial stage of rapid acceleration, the acceleration signal changes before the angle signal, triggering the judgment and enabling predictive control.

[0041] If so, the vehicle is determined to have entered pitch suppression mode.

[0042] To further improve the system's intelligence and control targeting, the operating condition determination logic in this embodiment also includes the identification of acceleration and braking conditions: When a positive longitudinal acceleration is detected (defined as forward acceleration), and its absolute value exceeds a threshold, or when the pitch angular velocity shows that the front of the vehicle is rising and exceeds a threshold, the vehicle is determined to enter the acceleration pitch suppression mode. At this time, the vehicle is subjected to inertial forces, exhibiting a tendency for the front suspension to extend (the front of the vehicle rises) and the rear suspension to compress (the rear of the vehicle sinks).

[0043] When a negative longitudinal acceleration is detected and its absolute value exceeds a threshold, or when the pitch angular velocity indicates that the front of the vehicle is sinking and exceeds a threshold, the vehicle is determined to enter the braking pitch suppression mode. At this time, the vehicle exhibits a trend of front suspension compression (front of the vehicle sinking) and rear suspension extension (rear of the vehicle rising).

[0044] It is worth noting that, to avoid control oscillations near the threshold, a hysteresis comparison mechanism is introduced into the judgment logic of this invention. For example, the acceleration threshold for entering the operating condition is 0.2g, while the threshold for exiting the operating condition is set to 0.1g. Only when the acceleration falls below 0.1g does the system determine that the pitch operating condition has ended. This design greatly improves the stability and robustness of the control system.

[0045] Subsequently, step two is executed: when it is determined that the vehicle has entered the pitch suppression condition, the damping switching control is activated to adjust the relationship between the extension stroke damping coefficient and the compression stroke damping coefficient of the front and rear suspensions of the vehicle, respectively.

[0046] Once the result of step one is affirmative, the ECU immediately takes over the damping control of the four wheel shock absorbers, seamlessly switching from the conventional comfort control mode to the asymmetric damping anti-pitch control mode of this invention. This step is the core execution link of this invention, which utilizes semi-active suspension to generate anti-pitch moment. Its specific implementation is designed for two distinctly different operating conditions: acceleration and braking.

[0047] Implementation method of damping switching control for acceleration conditions: When the vehicle is determined to be in an acceleration state, the vehicle body posture exhibits a nose-up behavior. To suppress this tendency, the control objective of this invention is to actively lower the front of the vehicle body and raise the rear of the vehicle body, thereby generating a reverse restoring torque to keep the vehicle body level.

[0048] Based on the aforementioned physical principles, the specific steps of damping switching control are as follows: First, the control system controls the extension stroke damping coefficient of the front suspension to be greater than the compression stroke damping coefficient for the two semi-active suspensions on the left and right sides of the front axle.

[0049] Specifically, the system sets the compression stroke damping coefficient of the front suspension to a minimum value (e.g., a first fixed value, corresponding to the softest state of the shock absorber), making the front suspension easily compressed under road excitation. At the same time, based on the severity of pitch, a larger extension stroke damping coefficient is calculated, making it difficult for the front suspension to rebound. This "easy to compress, difficult to extend" characteristic utilizes the axle load transfer and road vibration during vehicle acceleration to bring the front of the vehicle body closer to the ground, achieving active descent of the front body.

[0050] At the same time, the control system controls the extension stroke damping coefficient of the rear suspension to be less than the compression stroke damping coefficient for the left and right semi-active suspensions of the rear axle.

[0051] Specifically, the system sets the extension stroke damping coefficient of the rear suspension to a minimum value (e.g., a second fixed value), making the rear suspension extremely easy to rebound and extend; at the same time, it calculates a larger compression stroke damping coefficient, making the rear suspension difficult to compress. This "easy to extend, difficult to compress" characteristic utilizes the elastic potential energy of the rear suspension and road surface excitation to position the rear vehicle body in a higher position, achieving active lifting of the rear vehicle body.

[0052] By lowering the front of the vehicle and raising the rear, the vehicle generates a posture correction amount that is lower in the front and higher in the rear. This correction amount precisely counteracts the tendency of the front being higher and the rear being lower caused by acceleration, thereby maintaining a consistent height between the front and rear of the vehicle and keeping the vehicle level. This significantly improves the vehicle's acceleration stability and the stability of the driver's field of vision.

[0053] Implementation method of damping switching control for braking conditions: When the vehicle is determined to be in braking condition, the vehicle body exhibits a nose-diving posture. To suppress this tendency, the control objective is to actively raise the front of the vehicle body and lower the rear of the vehicle body.

[0054] At this point, the specific steps of the damping switching control are as follows: The control system targets the semi-active suspension on the front axle, ensuring that the extension stroke damping coefficient of the front suspension is less than the compression stroke damping coefficient. This employs a "easy to extend, difficult to compress" strategy, utilizing road surface excitation to actively extend the front suspension, raising the front of the vehicle to counteract the nose-down caused by braking.

[0055] Meanwhile, the control system controls the semi-active rear suspension, ensuring that the extension stroke damping coefficient is greater than the compression stroke damping coefficient. This employs a "easy to compress, difficult to extend" strategy, utilizing road surface excitation to actively shorten the rear suspension, lowering the rear vehicle body and counteracting the rear-end lift caused by braking.

[0056] Through this series of coordinated actions, the vehicle can maintain stability during emergency braking. This not only improves ride comfort and eliminates the feeling of forward tilting, but more importantly, the stable vehicle posture helps optimize the vertical load distribution of the front and rear wheels, allowing all four wheels to provide maximum braking grip, thereby effectively shortening the braking distance and improving active safety.

[0057] The damping switching control aims to reduce the vehicle's pitch angle to 0 and employs a control strategy combining single-sided clamping and single-sided closed-loop control. Specifically, the strategy is as follows: For suspensions that require lowering the vehicle body (such as the front suspension during acceleration or the rear suspension during braking), in order to maximize their downward tendency, it is necessary to minimize their resistance in the compression direction. Therefore, the system sets its compression stroke damping coefficient to a first fixed value.

[0058] In this preferred embodiment, the first fixed value is set to 10 N (Newtons). Here, 10 N is an engineering calibration value, representing the basic physical minimum damping force of the shock absorber at the current vehicle speed and temperature, corresponding to the state where the solenoid valve is fully open or the control current is 0A (depending on the specific valve body logic).

[0059] The extension stroke damping coefficient of this end suspension is calculated in real time by the controller. The controller uses a PID (Proportional-Integral-Derivative) control algorithm, with the current pitch angle deviation (target value 0 minus actual value) as the input. The calculation formula can be expressed as: the target extension damping force equals the proportional coefficient multiplied by the angle deviation, plus the integral coefficient multiplied by the integral of the angle deviation, plus the derivative coefficient multiplied by the angular velocity. The larger the pitch angle deviation, the larger the calculated target extension damping force, thus producing a stronger pulling effect and preventing suspension rebound.

[0060] For suspensions that require raising the vehicle body (such as the rear suspension during acceleration or the front suspension during braking), in order to maximize their upward tendency, it is necessary to minimize their resistance in the extension direction. Therefore, the system sets its extension stroke damping coefficient to a second fixed value.

[0061] In this preferred embodiment, the second fixed value is set to 0 N. This also represents that the shock absorber is in its softest physical state in the extension direction, allowing the spring to freely release energy and rebound quickly.

[0062] The compression stroke damping coefficient of this end suspension is also calculated using a PID controller. The larger the pitch angle deviation, the greater the calculated target compression damping force, thus providing stronger rigid support and preventing the suspension from being compressed.

[0063] For example, in a specific acceleration scenario, the front suspension, which is the end of the suspension that needs to lower the vehicle body, has a first fixed value of 10 N for its compression stroke damping coefficient; the rear suspension, which is the end of the suspension that needs to raise the vehicle body, has a second fixed value of 0 N for its extension stroke damping coefficient. This extreme setting maximizes the utilization of the shock absorber's physical bandwidth and achieves optimal control performance.

[0064] Furthermore, this invention also fully considers the smoothness of control exit. The method further includes a damping recovery step: When the longitudinal acceleration of the vehicle body in the driving status parameters is detected to decrease and fall below the preset threshold (for example, when the vehicle ends acceleration and enters a constant speed cruise state), the control system does not immediately cut off control. Instead, it controls the extension stroke damping coefficient and compression stroke damping coefficient of the front suspension and the rear suspension to gradually return to a symmetrical state through time-varying or state feedback.

[0065] Specifically, the controller generates a decay coefficient that linearly decreases from 1 to 0 within a preset time window (e.g., 500 milliseconds). This coefficient is applied to the calculated asymmetric damping force, allowing the damping force to smoothly transition to the conventional roof control damping force. This step effectively avoids vehicle body rebound or impact caused by sudden changes in control force.

[0066] Furthermore, in order to ensure the engineering feasibility and safety of the technical solution of the present invention under actual complex working conditions, especially to solve the mechanical impact risk that semi-active suspension may face when performing extreme asymmetric damping control and the resulting vehicle attitude imbalance problem, this embodiment also includes a suspension travel safety protection step and a front and rear coordinated yielding strategy based on torque balance.

[0067] In the damping switching control process of this invention, the system forces the suspension to move unidirectionally towards a certain extreme position (compression limit or extension limit) under road excitation by forcibly setting a large difference between extension and compression damping (e.g., "easy to compress, difficult to extend" or "easy to extend, difficult to compress"), thereby achieving a reduction or increase in vehicle height. The essence of this control strategy is to artificially compress the remaining effective travel of the suspension. For example, under acceleration conditions, the front suspension is actively controlled to a low compression position, meaning that the remaining compression buffer space of the front suspension is significantly reduced. At this time, if the vehicle happens to pass over a road protrusion (such as a speed bump, manhole cover, or bridge expansion joint) at medium to high speed, because the front suspension is already in a pre-compression state, its remaining travel may not be sufficient to absorb the impact energy from the obstacle, causing the shock absorber piston rod to move rapidly to the bottom, resulting in a violent rigid impact with the built-in polyurethane buffer block or even the bottom valve mechanism. This phenomenon is known in engineering as "suspension breakdown" or "bottoming out." Suspension breakdown not only generates significant impact noise (NVH deterioration), resulting in extremely poor ride comfort, but also directly transmits impact forces several times greater than normal road loads to the vehicle struts, suspension arms, and bushings. Over time, this can easily lead to fatigue fracture of structural components, seriously threatening driving safety.

[0068] Therefore, this invention constructs a set of safety monitoring logic with the highest priority at the bottom layer of the control algorithm. The suspension travel safety protection steps specifically include the following sub-steps: Throughout the entire process of damping switching control (i.e., every millisecond from the triggering of the operating condition to its exit), the chassis domain controller (ECU) reads the raw signals from the vehicle height sensors mounted on the four wheel suspension arms in real time via a high-speed onboard communication bus (such as FlexRay or CAN-FD). To accurately capture transient road impacts, the sampling frequency of these sensors is set to no less than 1000Hz.

[0069] Since height sensors are typically rotary Hall effect sensors, their output is the rotation angle signal of the control arm relative to the subframe. The ECU stores a kinematics model of the vehicle's suspension system. Through real-time calculation or table lookup interpolation, it converts the sensor's angle signal into the axial displacement of the shock absorber piston rod relative to the cylinder, i.e., the suspension travel. The system performs Kalman filtering on the signal to remove high-frequency noise caused by road surface texture while retaining the true characteristics of abrupt changes in the travel path.

[0070] The system dynamically locks the monitoring direction based on the current control status.

[0071] When a suspension at one end (such as the front suspension during acceleration) is employing a strategy of lowering the vehicle body, the system focuses on monitoring the risk in its compression direction. At this time, the system calls upon pre-stored damper physical parameters to obtain the maximum physical compression stroke under the current suspension geometry. ), and calculate the remaining compression stroke in real time ( ): ; When a suspension element (such as the rear suspension during acceleration) is employing a strategy of raising the vehicle body, the system focuses on monitoring the risk in its extension direction. The system obtains the maximum physical extension stroke ( ), and calculate the remaining extension stroke in real time ( ): ; To achieve the best balance between attitude control effectiveness and absolute mechanical safety, the system sets a stroke safety threshold ( ) is based on the current vehicle speed ( ) and road surface roughness level ( (Multidimensional map)

[0072] At low speeds (e.g., <30km / h) and on smooth roads, the energy input from the road surface is small, and the system sets a small threshold (e.g., 10mm), allowing the control strategy to "eat up" the suspension travel to the maximum extent to suppress pitch and provide a magnetic feel.

[0073] In situations involving high speeds (e.g., >80km / h) or poor road surface roughness (e.g., Class C road surface), considering that road impact energy is proportional to the square of vehicle speed, the system will automatically increase the safety threshold (e.g., increase it to 30mm) to prevent destructive penetration at high speeds and reserve sufficient hydraulic buffer distance in advance.

[0074] The system will calculate in real time or With the current A comparison is performed. When the remaining working stroke of any suspension end is less than the travel safety threshold, the system immediately determines that the suspension end is at risk of breakdown.

[0075] At this moment, the safety logic instantly takes over control of the shock absorber at this end, generates a travel protection command, and forcibly corrects the control strategy.

[0076] Specifically, the corrected logic is damping unloading and energy absorption: If there is a risk of compression breakdown (the front suspension is too low and encounters a bulge), the system immediately discards the original minimal compression damping setting (10 N) and instantly adjusts the compression stroke damping coefficient to a very high safe damping value (e.g., 2500 N). Utilizing the high-speed throttling effect of the shock absorber fluid flowing through the bottom valve, a huge hydraulic damping force is generated to dissipate the kinetic energy of the suspension's high-speed compression, flexibly catching the falling vehicle body and avoiding a rigid metal-on-metal impact. At the same time, the system will appropriately reduce the extension stroke damping coefficient, allowing the suspension to quickly extend during the subsequent rebound stroke, pulling the piston rod back to the safe operating range (i.e., the suspension center position).

[0077] If there is a risk of tension failure (the rear suspension is too high and encounters a dent), the system will perform the opposite operation, increasing the tension damping to prevent the suspension from flying out of its limit.

[0078] Through this mechanism, the system can prioritize the protection of the suspension mechanical structure, ensuring the integrity and lifespan of chassis components under any extreme road conditions.

[0079] While the aforementioned travel protection mechanism solves the mechanical safety problem of a single wheel, if it operates in isolation, it will have a negative impact on the attitude dynamics of the entire vehicle.

[0080] During emergency braking, the vehicle is under strong anti-dive control with the front suspension raised and the rear suspension lowered. The entire vehicle is subjected to a pair of opposing vertical forces (upward in front, downward in rear), forming a couple that counteracts the braking inertial torque. At this time, if a sudden change in road surface causes the front suspension to trigger its travel protection, the front suspension has to abandon its raising strategy (or even stiffen to absorb energy), and the upward support it provides disappears instantly or is greatly weakened; while the rear suspension has not triggered its protection and continues to strongly execute its lowering strategy, generating a huge downward pull.

[0081] This will cause the vehicle's force balance to be instantly disrupted. The force couple that was originally used to counteract nose-nodding becomes asymmetrical, and the vehicle's center of gravity will be subjected to a net net torque and a net vertical force. This will cause a sharp change in longitudinal angular acceleration and vertical coupled vibration in the vehicle body. The driver will feel a sudden drop in the front of the car or a twisting sensation in the body, which will seriously affect driving confidence and ride quality.

[0082] To address this problem, this invention introduces a forward and backward coordinated yielding strategy based on torque balance. The specific implementation is as follows: When the control system determines that only one suspension (set as the trigger end, such as the front suspension) is at risk of breakdown and executes the travel protection command, the observer module inside the system will be activated immediately.

[0083] Based on vehicle dynamic parameters (wheelbase) Location of the center of mass The system utilizes the inverse damper model to estimate in real time the actual vertical force output by the suspension at the trigger end due to damping correction. , and compare it with the original planned target control ( The difference is calculated to obtain the vertical control force of the suspension loss at that end. ).

[0084] Furthermore, the anti-pitch moment of the suspension loss at this end is calculated. ): ; in, It is the longitudinal horizontal distance from the center of the suspension wheel at the trigger end to the center of gravity of the vehicle.

[0085] Based on the lost pitching moment, the system simultaneously performs damping correction on the suspension at the other end (set as the cooperating end, such as the rear suspension) that is not at risk of breakdown.

[0086] Although the suspension at the collaborative end is not facing any travel risk at this time and is fully capable of continuing to perform strong anti-pitch control, in order to maintain the torque balance of the whole vehicle, the system will actively weaken its anti-pitch force.

[0087] The system is based on the torque balance equation ( Calculate the pitching moment that needs to be reduced at the coordinating end, and then calculate the target damping force correction value at the coordinating end. Under normal circumstances, in order to maintain the stability of the center of gravity position, the reduction in torque at the coordinating end should maintain a specific proportional relationship with the loss at the triggering end (related to the front and rear axle load ratio).

[0088] Based on the corrected target force, the controller adjusts the control current of the damper at the cooperating end, actively reducing its pull-down or lift amplitude to match the current state of the trigger end.

[0089] Through this coordinated yielding, the anti-pitch moments generated by the front and rear suspensions always maintain a symmetrical balance centered on the center of mass.

[0090] While this strategy sacrifices some anti-pitch range in the short term (the pitch angle may temporarily fluctuate slightly), it effectively eliminates additional longitudinal vibrations and vertical jolts caused by mismatched front and rear control forces. This ensures that the vehicle's attitude changes under extreme conditions are linear, smooth, and predictable, avoiding the impact of abrupt attitude changes on the driver and improving the driving experience.

[0091] The control system of this invention relies on a high-performance automotive-grade microcontroller (MCU), such as the Infineon Aurix or NXP S32G series, which has a floating-point unit (FPU) to handle complex PID algorithms and matrix operations.

[0092] To address the risk of sensor failure, the system is designed with multiple verification mechanisms. For example, if the longitudinal acceleration measured by the IMU deviates too much from the acceleration obtained by the derivative of the wheel speed, the system will determine that the sensor signal is unreliable, immediately exit active attitude control, and lock the shock absorber in a safe mode with medium damping to ensure the basic driving safety of the vehicle.

[0093] To address the risk of overheating in the shock absorbers, the system has established a thermal model to estimate the internal oil temperature of the shock absorbers in real time. When the oil temperature exceeds a critical value (such as 110℃), the system will automatically implement a thermal attenuation strategy to gradually reduce the control amplitude of the damping force, preventing hardware damage caused by oil vaporization or seal failure.

[0094] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for suppressing vehicle pitch using damping switching, characterized in that, The method comprises the following steps: acquiring real-time driving state parameters of the vehicle, and determining whether the vehicle enters a pitch suppression working condition according to the driving state parameters; when it is determined that the vehicle enters the pitch suppression working condition, starting a damping switching control, and adjusting the size relationship between the extension stroke damping coefficient and the compression stroke damping coefficient of the front suspension and the rear suspension of the vehicle respectively; using the height variation characteristics of the body balance position generated by the semi-active suspension under different extension stroke damping coefficient and compression stroke damping coefficient ratios to reversely adjust the height of the front body and the rear body to generate an anti-pitch torque to suppress the body pitch.

2. The method of claim 1, wherein the method further comprises: The height variation characteristics of the body balance position generated by the semi-active suspension under different extension stroke damping coefficient and compression stroke damping coefficient ratios are based on the following principles: when the extension stroke damping coefficient of the semi-active suspension is greater than the compression stroke damping coefficient, the body balance position at the suspension is lowered; when the extension stroke damping coefficient of the semi-active suspension is less than the compression stroke damping coefficient, the body balance position at the suspension is raised.

3. The method of claim 2, wherein the damping switch is a hydraulic cylinder. The pitch suppression working condition includes an acceleration working condition; when it is determined that the vehicle enters the acceleration working condition, the specific steps of the damping switching control are as follows: controlling the extension stroke damping coefficient of the front suspension to be greater than the compression stroke damping coefficient to lower the front body; at the same time, controlling the extension stroke damping coefficient of the rear suspension to be less than the compression stroke damping coefficient to raise the rear body, so as to keep the front and rear body heights consistent.

4. The method of claim 2, wherein the damping switch is a hydraulic cylinder. The pitch suppression working condition includes a braking working condition; when it is determined that the vehicle enters the braking working condition, the specific steps of the damping switching control are as follows: controlling the extension stroke damping coefficient of the front suspension to be less than the compression stroke damping coefficient to raise the front body; at the same time, controlling the extension stroke damping coefficient of the rear suspension to be greater than the compression stroke damping coefficient to lower the rear body, so as to keep the front and rear body heights consistent.

5. The method of claim 1, wherein the method further comprises: The determination of whether the vehicle enters the pitch suppression working condition according to the driving state parameters specifically comprises: collecting the body longitudinal acceleration, the pitch angle and the pitch angular velocity as the driving state parameters; determining whether at least one of the body longitudinal acceleration, the pitch angle or the pitch angular velocity exceeds a preset threshold value; if yes, it is determined that the vehicle enters the pitch suppression working condition.

6. The method of claim 3, wherein the damping switch is a hydraulic cylinder. The damping switching control takes the control of the pitch angle of the vehicle to 0 as a control target, and adopts the following control strategy: for the suspension at one end of the body that needs to be lowered, the compression stroke damping coefficient thereof is set to a first fixed value, and the extension stroke damping coefficient thereof is calculated by a controller; for the suspension at one end of the body that needs to be raised, the extension stroke damping coefficient thereof is set to a second fixed value, and the compression stroke damping coefficient thereof is calculated by the controller.

7. The method of claim 6, wherein the method further comprises: In the acceleration working condition, the front suspension serves as the suspension at one end of the body that needs to be lowered, and the first fixed value of the compression stroke damping coefficient set for the front suspension is 10 N; the rear suspension serves as the suspension at one end of the body that needs to be raised, and the second fixed value of the extension stroke damping coefficient set for the rear suspension is 0 N.

8. The method of claim 5, wherein the method further comprises: The method further comprises a damping recovery step: When detecting that the vehicle body longitudinal acceleration in the driving state parameter decreases and is lower than the preset threshold value, the control system controls the extension stroke damping coefficient and the compression stroke damping coefficient of the front suspension and the rear suspension to gradually recover to the symmetric state through time gradual change or state feedback.

9. The method of claim 1, wherein the method further comprises: determining a pitch angle of the vehicle; and determining a pitch rate of the vehicle. The method further comprises a suspension stroke safety protection step, which specifically comprises: During the execution of the damping switching control, the suspension dynamic stroke of the front suspension and the rear suspension is monitored in real time, and the remaining working stroke of each suspension in the current motion direction is calculated according to the suspension dynamic stroke; the remaining working stroke is compared with a preset stroke safety threshold value; When the remaining working stroke of any one end suspension is less than the stroke safety threshold value, it is determined that the one end suspension has a risk of breakdown, and a stroke protection instruction is immediately generated; The stroke protection instruction is used to forcibly correct the control strategy of the one end suspension, to reduce the difference between the extension stroke damping coefficient and the compression stroke damping coefficient of the one end suspension, so as to preferentially increase the effective working stroke of the one end suspension and prevent mechanical impact of the suspension.

10. The method of claim 9, wherein the damping switch is a hydraulic cylinder. The suspension stroke safety protection step further comprises a front-rear collaborative retreat strategy based on torque balance: When it is determined that only one end suspension executes the stroke protection instruction due to the risk of breakdown, the control system calculates the amount of anti-pitching torque lost by the one end suspension due to damping correction in real time based on the vehicle center of mass torque balance equation; Based on the amount of anti-pitching torque lost, the damping of the other end suspension without the risk of breakdown is simultaneously corrected, and the anti-pitching strength of the other end suspension is actively weakened, so that the anti-pitching torques generated by the front suspension and the rear suspension always remain symmetrically balanced around the center of mass, thereby avoiding additional longitudinal vibration of the vehicle body caused by single-end suspension protection triggering.

Images