Patent Application
20200398629
This disclosure relates to an active suspension system and a control method thereof, in particular to an active suspension system, in which a vehicle based on an active suspension vehicle performs inertia regulation on an active suspension mechanism by measuring a posture deviation of the vehicle, and a control method thereof. The present disclosure pertains to the technical field of vehicle control.
A suspension system is an important composition of a vehicle chassis. Ride comfort, handling stability and traveling safety of a vehicle can be determined directly depending on performance of the suspension system. Traditional vehicles adopt passive suspensions, which have suspension parameters designed according to specific road conditions. Once the suspension parameters are selected, it is difficult to be changed along with the road conditions and vehicle speed, so that the further improvement of driving performance of the vehicle is restricted.
With the development of electronic information technology and the progress in hydraulic and electrical drive technology, it is possible to use a controllable suspension in vehicle field. It is generally considered now that the controllable suspension technology is of an effective way to improve suspension performance. If rigidity and damping characteristics of the suspension system can be dynamically and adaptively adjusted according to driving conditions of the vehicle (including motion state of the vehicle and the road surface condition, etc.), such that the suspension system is always at the best vibration reduction state, which is called as an active suspension. The active suspension has many advantages, such as controlling a height of the vehicle body, improving trafficability, and taking the ride comfort and handling stability of the vehicle into account.
The active suspension technology mainly includes a control mechanism and a control strategy. Since control mechanism outputs an active force according to the requirement of the control strategy, a key point of designing the active suspension is to select the control strategy capable of providing better performance for the vehicle. Various suspension characteristics and damping effects can be generated according to different control strategies.
The control strategies of active suspension in the prior art mainly include: optimal control, preview control, adaptive control, fuzzy control, neural network control, ceiling damping control, sliding mode control, immune evolutionary control and the like. According to disclosure of the documents, no matter any of the afore-mentioned control methods is adopted, the performance of vehicles can be improved to some extents. However, there are still some problems that are existed in the control methods and have not been well solved yet, in particular, the vehicle suspension system is a typical complex system with multiple inputs and multiple outputs. One of the important issues is decoupling control, by which such complex systems can be controlled, while the control strategy in the prior art cannot provide a better solution for the decoupling control of the suspension system of the vehicle.
The posture adjustment and the ride comfort control of the vehicle are two important aspects to be considered in the suspension design. According to the existing research achievements, various mathematical models are established as desired and respective designs are accomplished independently, and it is considered that the overall performance of the vehicle is a sum of the performances of the subsystems; or the mathematical models are decompostured and then combined for control. The posture control and the ride comfort are not taken into account when the mathematical model is established, so that the design process is complicated.
A technical problem to be solved by the present disclosure is to provide an inertia regulation active suspension system based on posture deviation of a vehicle and a control method thereof. As extension and retraction of suspension is actively controlled, a centroid of the vehicle is movable approximately along a straight line or an arc line when the vehicle travels on uneven roads, and the posture of a vehicle body remains approximately unchanged, thereby reducing vibration of the vehicle body when is traveling, and improving travel speed, handling stability and ride comfort of the vehicle when driving on a rough road.
To solve the above technical problem, a technical solution is employed in the present disclosure.
An inertial regulation active suspension system based on posture deviation of a vehicle includes a vehicle body and a plurality of wheels, an inertial measurement unit, an electronic control unit, a servo controller group, suspension servo actuating cylinders corresponding to the wheels one by one, and displacement sensors, wherein the inertial measurement unit, the electronic control unit and the servo controller group are secured to the vehicle body; the wheels are connected to a lower part of the vehicle body through the suspension servo actuating cylinders; the displacement sensors are used for measuring strokes of the suspension servo actuating cylinders; the electronic control unit is communicated with the inertial measurement unit and the servo controller group, respectively; the servo controller group is communicated with the displacement sensors; the electronic control unit reads vehicle posture parameters measured by the inertial measurement unit, and calculates a posture deviation of the vehicle at a current moment from at a previous moment, and then outputs the posture control parameters to the servo controller group; and the servo controller group controls each of the suspension servo actuating cylinders according to the position and posture control parameters output by the electronic control unit and displacement feedback values of the displacement sensors, so that a centroid of the vehicle moves approximately along a straight line or an arc line to permit the posture of the vehicle body to remain unchanged.
A control method of the inertial regulation active suspension system based on the posture deviation of the vehicle is provided, wherein a coordinate system OXYZ in which a center point O of the inertial measurement unit is taken as a coordinate origin is established, a right forward direction in which the vehicle travels is defined as a Y-axis positive direction, a right side direction in which the vehicle travels is defined as a X-axis positive direction, and an upward direction perpendicular to a XOY plane is defined as a Z-axis positive direction; a centroid of the vehicle body is defined as W; scanning periods are preset in the electronic control unit; and the control method comprises steps of:
1) in some scanning period, a vertical displacement wO, a pitch angle αO and a roll angle βO of the coordinate origin O are measured by the inertial measurement unit and output to the electronic control unit;
2) the electronic control unit calculates a vertical displacement ww, a pitch angle αw and a roll angle βw at the centroid W of the vehicle according to a geometric relationship of the centroid W relative to the coordinate origin O and the vertical displacement wO, the pitch angle αO and the roll angle βO of the coordinate origin O;
3) the electronic control unit performs a high-pass filter with a cutoff frequency ωH on the vertical displacement ww, the pitch angle αw and the roll angle βw, and after being filtered, the vertical displacement is wH, the pitch angle is αH and the roll angle is βH; 4) the vertical displacement wH, the pitch angle αH and the roll angle βH obtained in step 3) are compared with values of the previous scanning period, to calculate variations Δw, Δα, Δβ of the vertical displacement, the pitch angle and the roll angle; and −Δw, Δα, Δβ are taken as posture relative correction quantities; a target value of the extension and retraction of each of the suspension servo actuating cylinders of the vehicle is calculated through an inverse kinematics algorithm of a vehicle suspension mechanism, and the target value is transmitted to the servo controller group such that displacement servo control is performed on each of the suspension servo actuating cylinders, thereby realizing the control of the vehicle body posture target, maintaining the vertical displacement wH, the pitch angle αH and the roll angle βH as stable as possible, and making a motion trajectory of the centroid of the vehicle in a straight line or in an arc line while keeping the posture of the vehicle body approximately unchanged.
Preferably, a calculation formula of the vertical displacement ww, the pitch angle αw and the roll angle βw at the centroid W of the vehicle is as follows:
wherein the centroid W has coordinates xW, yW and zW in coordinate system OXYZ.
Preferably, the cut-off frequency wH is determined by following processes: S1, the vertical displacement wH, the pitch angle αH and the roll angle βH output after the high-pass filter all converge to 0 when the vehicle is stationary on a horizontal plane;
S2, the vertical displacement wH, the pitch angle αH and the roll angle βH output after the high-pass filter converge to a smaller value that is in an error range necessary for stable control of the system, when the vehicle stops at a transverse slope and a longitudinal slope for which a limit is allowed; and
S3, a low value is selected by the cut-off frequency wH when conditions of S1 and S2 are satisfied.
Due to the technical scheme employed above, the technical progress can be achieved by the present disclosure as follows:
Compared with the traditional active suspension system and the control method thereof, the active suspension system based on the inertia regulation principle and the control method thereof as proposed by the present disclosure controls the posture of the vehicle body during the vehicle travels by controlling the extension and retraction of each of the servo actuating cylinders, to enable it to maintain approximately unchanged, so as to reduce the vibration of the vehicle body as traveling and improve the travel speed, handling stability and ride comfort of the vehicle which is traveling on the rough roads.
The active suspension system and the control method according to the present disclosure are employed such that adjustment of the vehicle posture and control of the ride comfort can be taken into account simultaneously, and the wheels of the vehicle as traveling are adjustable to adapt to the uneven road conditions such that influence of the road conditions on the posture of the vehicle body can be reduced to a lower level, that is, such complex system as the active suspension system with multiple inputs and multiple outputs can be well decoupled.
Integral errors that have change frequency slower in ww, αw and βw and the portion changed slowly in ww, αw and βw caused when the vehicle crosses a gentle slope are removed by the high-pass filter. The removal of the latter enables the vehicle to travel along an envelope surface of valleys without allowing the suspension stroke to reach a limit, and trafficability of the vehicle can be improved.
Hereinafter, the present disclosure will be further described in detail with reference to embodiments below.
The present disclosure provides an inertial regulation active suspension system based on posture deviation, which is suitable for a vehicle active suspension system with three or more wheels.
The conventional three-wheeled vehicles and four-wheeled vehicles are taken as an example to make explanation. A vehicle with more than four wheels can be constructed according to a construction principle and method of the four-wheeled vehicle.
According to the first embodiment, a three-wheeled vehicle inertial regulation active suspension system and a control method thereof are provided.
As shown in
As an example of a three-wheeled vehicle in this embodiment, the wheels and the suspension servo actuating cylinders thereof can form supporting points for the vehicle body, so that the posture of the vehicle body may be controlled in a manner that a plane can be determined by three points.
The inertial measurement unit 1 of the present disclosure may also be a gyroscope and other components capable of measuring inertial parameters.
The control method according to the present disclosure is that a coordinate system OXYZ is established for the whole vehicle and a centroid of the vehicle body is defined as W; a coordinate origin of the coordinate system is a center point O of the inertial measurement unit, and a right forward direction in which the vehicle travels is defined as a Y-axis positive direction, a right side direction in which the vehicle travels is defined as a X-axis positive direction, and an upward direction perpendicular to a XOY plane is defined as a Z-axis positive direction; and at the same time, scanning periods are preset in the electronic control unit. The control method according to the present disclosure comprises steps of:
In the first step, the coordinate origin O is taken as a measuring point. In some scanning period, a vertical displacement wO, a pitch angle αO and a roll angle βO of the coordinate origin O are measured by the inertial measurement unit and output to the electronic control unit. The wO is a vertical displacement of the vehicle body in a Z-axis direction at the coordinate origin O, αO is a pitch angle of the vehicle body rotating around a X axis, and the βO is a roll angle of the vehicle body rotating around a Y axis.
In the second step, the posture parameters at the centroid W of the vehicle are calculated. The centroid of the vehicle body is defined as W. The electronic control unit calculates a vertical displacement ww, a pitch angle αw and a roll angle βw at the centroid W of the vehicle according to a geometric relationship of the centroid W relative to the coordinate origin O and the vertical displacement wO, the pitch angle αO and the roll angle βO of the coordinate origin O. The centroid W of the vehicle body has coordinates xW, yW and zW in the coordinate system OXYZ. The ww is a vertical displacement of the centroid W of the vehicle in a Z-axis direction, the αO is a pitch angle when the vehicle rotates in an axis parallel to the X-axis around the centroid W, and the βw is a roll angle when the vehicle rotates in an axis parallel to the Y-axis around the centroid W. A formula of the centroid W is as follows:
In the third step, the electronic control unit performs a high-pass filter with a cutoff frequency ωH on the vertical displacement ww, the pitch angle αw and the roll angle βw, and after being filtered, the vertical displacement wH, the pitch angle αH and the roll angle βH can be obtained. Integral errors that have change frequency slower in ww, αw and βw and the portion changed slowly in ww, αw and βw caused when the vehicle crosses a gentle slope are removed by the high-pass filter. The removal of the latter enables the vehicle to travel along an envelope surface of valleys without allowing the suspension stroke to reach a limit, and trafficability of the vehicle can be improved. The cutoff frequency ωH can be determined by following experimental processes:
S1, the vertical displacement wH, the pitch angle αH and the roll angle βH output after the high-pass filter all converge to 0 when the vehicle is stationary on a horizontal plane;
S2, the vertical displacement wH, the pitch angle αH and the roll angle βH output after the high-pass filter converge to a smaller value that is in an error range necessary for stable control of the system, when the vehicle stops at a transverse slope and a longitudinal slope for which a limit is allowed; and
S3, a low value is selected by the cut-off frequency wH when conditions of S1 and S2 are satisfied.
In the fourth step, the vertical displacement wH, the pitch angle αH and the roll angle βH are kept as stable as possible by controlling the extension and retraction of each of the suspension servo actuating cylinders, such that a motion trajectory of the centroid of the vehicle is in a straight line or an arc line and the posture of the vehicle body remains approximately unchanged. Specifically, the vertical displacement wH, the pitch angle αH and the roll angle βH obtained in the third step are compared with the same values in the previous scanning period, to calculate variations Δw, Δα, Δβ of the vertical displacement, the pitch angle and the roll angle; and −Δw, Δα, Δβ are taken as posture relative correction quantities; target values of the extension and retraction amount l5, l6 and l7 of the suspension servo actuating cylinders 5, 6 and 7 of the vehicle are calculated and are transmitted to the servo controller group 12, such that displacement servo control is performed on each of the suspension servo actuating cylinders, thereby realizing the control of the vehicle body posture target, maintaining the vertical displacement wH, the pitch angle αH and the roll angle βH as stable as possible, and making a motion trajectory of the centroid of the vehicle in a straight line or in an arc line while keeping the posture of the vehicle body approximately unchanged. The target values of the extension and retraction amount of the suspension servo actuating cylinders can be calculated through an inverse kinematics algorithm of a vehicle suspension mechanism.
According to the second embodiment, a four-wheeled vehicle inertial regulation active suspension system based on posture deviation and a control method thereof are provided.
As shown in
One of the control methods of the four-wheeled vehicle according to the present disclosure is the same as that in the first embodiment, that is, scanning periods are preset inside the electronic control unit. In some scanning period, the electronic control unit 11 reads the vehicle posture parameters measured by the inertial measurement unit 1, calculates the posture deviation of the vehicle at a current moment from the previous moment, and then outputs posture control parameters to the servo controller group 12. The servo controller group 12 controls action of each of the suspension servo actuating cylinders 5, 6, 7.1 and 7.2 according to the posture control parameters output by the electronic control unit and the displacement feedback values of the displacement sensors, so as to allow the centroid of the vehicle to be movable approximately along a straight line or an arc line and keep the posture of the vehicle body unchanged.
According to the four-wheeled vehicle in this embodiment, upper chambers and lower chambers of the suspension servo actuating cylinders 7.1 and 7.2 corresponding to the wheels 4.1 and 4.2 are individually communicated; that is, the upper chambers of the suspension servo actuating cylinders 7.1 and 7.2 are connected with each other through an upper chamber connecting pipeline 14; the lower chambers of the suspension servo actuating cylinders 7.1 and 7.2 are connected with each other through a lower chamber connecting pipeline 15. As such, function of the wheels 4.1 and 4.2 and the suspension servo actuating cylinders thereof supporting the vehicle body is equivalent to that of the supporting point, while the other two wheels 2 and 3 and the suspension servo actuating cylinders thereof respectively form supporting points for the vehicle body. As for the conventional vehicle, two rear wheels and the suspension servo actuating cylinders thereof have the same structure, so that the equivalent supporting point is considered as a midpoint of an upper hinge point on the suspension servo actuating cylinders 7.1 and 7.2 corresponding to the wheels 4.1 and 4.2. A height of the equivalent supporting point is controlled by controlling an average value (shown by l7 in
A vehicle with four or more wheels may refer to the method of the second embodiment, that is, the vehicle with four or more wheels can be divided into three wheel groups, each of which is provided with one or more wheels. When the number of wheels of the wheel group is more than one, the upper chambers of the suspension servo actuating cylinders in the wheel group are communicated with one another and the lower chambers of the suspension servo actuating cylinders in the wheel group are communicated with one another, so that the wheel group constitutes a supporting point for supporting the vehicle body, and the three wheel groups constitute three supporting points of the vehicle body. The posture of the vehicle body can be controlled by controlling supporting heights of the three supporting points. The present disclosure provides a control method for the vehicle with four or more wheels, which arranges all wheels of the vehicle with more than three wheels into three wheel groups and controls the posture of the vehicle body based on a principle that a plane is determined by three points, thus the control method is suitable for all vehicles with more than three wheels. At the same time, the wheels that are close to each other in position are selected to form the wheel group in order to facilitate for the communication of the upper chambers and the lower chambers of the suspension servo actuating cylinders in the wheel group. The structure and the size of the wheels in the wheel group and the suspension servo actuating cylinders are the same as that of the displacement sensors as possible when being grouped, in order to determine the supporting points of the wheel group. According to the present disclosure, the interference of integral accumulated error signals in signals is reduced by real-time scanning and monitoring the vertical displacement, the pitch angle and the roll angle of the vehicle coordinate origin in each of the periods, and performing the high-pass filter on the scanning values, and then the extension and retraction of the suspension servo actuating cylinder of each of the wheel groups is calculated through the inverse kinematics algorithm of the vehicle suspension mechanism according to the vertical displacement, the pitch angle and the roll angle after being filtered, so as to allow the motion of the vehicle centroid approximately along a straight line or an arc line and keep the posture of the vehicle body approximately unchanged, thus greatly reducing the vibration of the vehicle body.
As development of the present disclosure is proceeded, a comparison test between a posture that a three-axle vehicle equipped with an inertial regulation active suspension system based on posture deviation crosses a triangle obstacle and a posture that a three-axle vehicle equipped with a passive oleo-preumatic suspension system crosses the triangle obstacle is carried out. The three-axle vehicle used in the test is shown in
All triangle obstacles used in the test are shown in
As can be seen from the above comparison test, the inertial regulation active suspension system based on posture deviation as proposed by the present disclosure can effectively reduce the vibration of the vehicle body and improve the handling stability and ride comfort of the vehicle.
Ultimately, it should be noted that the above-mentioned embodiments are only used to illustrate the technical solution of the present disclosure, rather than limit the present disclosure. Although the present disclosure has been described in detail with reference to the foregoing embodiments, it should be understood by the person skilled in the art that it is allowable to modify the technical solution described in the foregoing embodiments or equivalently substituting some or all of the technical features; however, these modifications or substitutions do not cause the corresponding technical solutions to substantively depart from the scope of the technical solutions of various embodiments of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201811051382.5 | Sep 2018 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2019/098908 | 8/1/2019 | WO | 00 |
