Four-wheel steering automobile side parking minimal space path planning and control method

Abstract

The invention discloses a four-wheel steering automobile side parking minimum space path planning and control method. The method specifically comprises the following steps that firstly, the size of a side parking minimum space is divided into the first situation, the second situation and the third situation; 2, adopting a front and rear wheel out-of-phase steering scheme according to the situation 1; aiming at the second situation, a front and rear wheel in-phase steering scheme is adopted; according to the third situation, a front and rear wheel fused steering scheme is adopted; 3, establishing a cost function based on kinematics transient characteristics of the four-wheel steering automobile, and optimizing a space optimal parameter, a path shortest parameter and a time optimal parameter through the cost function to obtain an optimal turning angle and an optimal driving distance; and 4, the four-wheel steering automobile is controlled to adopt a corresponding steering scheme to complete parking. According to the invention, more accurate and efficient parking operation can be realized in a side parking extremely small space, the parking space can adapt to various parking space forms, and the side parking efficiency of an automobile in a narrow space is improved.

Description

Technical Field

[0001] The present invention belongs to the field of automatic parking technology, and specifically relates to a method for planning and controlling a path in a very small space for side parking of a four-wheel steering vehicle. Background Art

[0002] With the acceleration of urbanization, the problem of difficult parking in cities has become increasingly prominent, especially in some narrow spaces. Traditional front-wheel steering vehicles have limited parking performance in narrow spaces, especially when parking sideways. The vehicle's turning radius is limited, making parking operations not only complicated, but often inefficient. For example, a Chinese invention patent with the authorization publication number CN 115285221A discloses a parking planning method, device, storage medium and vehicle based on four-wheel steering, wherein the method includes: when detecting that the automatic parking function is triggered, obtaining the parking space information of the parking space to be parked by the vehicle, and the obstacle information around the parking space to be parked; determining the parking planning information of the vehicle in two four-wheel steering modes respectively according to the parking space information and the obstacle information; wherein the parking planning information includes the parking path, the number of gear switching times and the length of the parking path, and the two four-wheel steering modes include the front and rear wheel in-phase mode and the front and rear wheel out-of-phase mode; based on the number of gear switching times and / or the length of the parking path in the two parking planning information, determining the target parking path from the two parking paths; and controlling the vehicle to park at the parking space according to the target parking path. The prior art is mainly devoted to the study of planning methods in general parking scenarios, and does not combine the self-kinematic transient characteristics of the four-wheel steering vehicle to improve the parking performance in special scenarios (extremely small space). Summary of the invention

[0003] The purpose of the present invention is to provide a path planning and control method for a four-wheel steering vehicle in a very small space for side parking. The present invention can achieve more accurate and efficient parking operations in a very small space for side parking, and can adapt to a variety of parking space forms, thereby improving the efficiency of side parking of vehicles in a small space.

[0004] The technical solution of the present invention is a method for planning and controlling a path in a very small space for side parking of a four-wheel steering vehicle, which specifically comprises the following steps:

[0005] Step 1: Based on the size of the small parking space and the parameters of the four-wheel steering vehicle, the size of the extremely small parallel parking space is divided into the first case where the length margin is tight but the width margin is ample, the second case where the length margin is ample but the width margin is tight, and the third case where both the length margin and the width margin are tight;

[0006] Step 2: For situation 1, adopt a steering scheme where the front and rear wheels are out of phase; for situation 2, adopt a steering scheme where the front and rear wheels are in phase; for situation 3, adopt a steering scheme where the front and rear wheels are integrated;

[0007] Step 3: Establish a cost function based on the kinematic transient characteristics of the four-wheel steering vehicle, and use the cost function to optimize the optimal spatial parameters, the shortest path parameters, and the optimal time parameters to obtain the optimal turning angle and the optimal driving distance;

[0008] Step 4: Based on the obtained optimal turning angle and optimal driving distance, the four-wheel steering vehicle is controlled to adopt a corresponding steering plan to complete parking.

[0009] In the aforementioned method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking, in step 1, the size of the very small space for side parking is further reduced based on the size of a small parking space, and the size of the small parking space includes a length L P and width W P , respectively expressed as:

[0010]

[0011] In the formula, w c Represents the width of the vehicle, l r Indicates the horizontal distance from the rear end of a four-wheel steering vehicle to the center of the rear axle, l f Indicates the horizontal distance from the front end of a four-wheel steering vehicle to the center of the front axle, l t Indicates wheelbase, R min is the minimum turning radius of a front-wheel steering vehicle, R min It is expressed as:

[0012]

[0013] In the formula, δ fmax Indicates the maximum turning angle of the front wheels.

[0014] In the aforementioned method for planning and controlling the path of the four-wheel steering vehicle in the extremely small space for side parking, the parameters of the four-wheel steering vehicle include: Δl is the difference between the length of the extremely small space for side parking and the length of the vehicle, and Δw is the difference between the width of the extremely small space for side parking and the width of the vehicle, which are respectively expressed as:

[0015]

[0016] Where Δx is the instantaneous center offset of the four-wheel steering vehicle, w t Indicates wheelbase, R t is the vertical distance from the instantaneous center of the four-wheel steering vehicle to the central axis of the four-wheel steering vehicle, and Δx is the instantaneous center offset of the vehicle, which can be expressed as:

[0017]

[0018] In the formula, the counterclockwise rotation of the vehicle tire around the center point of contact with the ground is defined as the positive direction, and the reverse direction is defined as the negative direction; δ fmax(+) Indicates that the front wheel rotates counterclockwise to the maximum angle, δ rmax(-) Indicates that the rear wheels rotate clockwise to the maximum angle.

[0019] In the aforementioned method for planning and controlling the path of a four-wheel steering vehicle in a very small side parking space, the first case is as follows: the length L of the very small side parking space is P1 Smaller than the length L of a small parking space P , width W P1 Greater than or equal to the width W of a small parking space P , expressed as l C <L P1 <L P &W P1 ≥W P ;

[0020] Situation 2: Width W of the extremely small parallel parking space P2 Smaller than the width W of a small parking space P , length L P2 Greater than or equal to the length L of a small parking space P , denoted as L P2 ≥L P &w C <W P2 <W P ;

[0021] Situation 3: The length of the extremely small parallel parking space L P3 and width W P3 All are longer than the length of a small parking space L P and width W P Small, represented by l C <L P3 <L P &w C <W P3 <W P ;

[0022]

[0023] In the formula, N represents different situations; L PN Represents the length of the minimum parallel parking space in different situations, l c Represents the vehicle length, Δl N Represents the length margin of the minimum parallel parking space under different circumstances; W PN Represents the width of the minimum parallel parking space in different situations, Δw N Represents the width margin of the extremely small space for parallel parking in different situations;

[0024] The length margin Δl of the minimum parallel parking space in different situations N and width margin Δw N The functional relationship is expressed as:

[0025]

[0026] In the formula, δ f represents the front wheel turning angle, δ r represents the rear wheel turning angle, C represents [l c ,w c ,l t ,w t ,l f ,l r ]; is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the minimal parking space when the car is successfully exiting the parking space from a completely parked position in the minimal parking space; It is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the width margin of the minimal parking space when the car can smoothly leave the parking space from a completely parked position in the minimal parking space.

[0027] In the aforementioned method for planning and controlling the path of a four-wheel steering vehicle for side parking in a very small space, in step 2, the steering scheme of the front and rear wheels being out of phase is expressed as follows:

[0028]

[0029] Where Δl1 represents the length margin of the minimum space for side parking in the case of side parking, δ f represents the front wheel turning angle, δ r Rear wheel turning angle, C represents [l c ,w c ,l t ,w t ,l f ,l r ], l c Represents the vehicle commander, w c Represents the width of the vehicle, l t Indicates wheelbase, w t Indicates wheelbase, l r Indicates the horizontal distance from the rear end of a four-wheel steering vehicle to the center of the rear axle, l f Indicates the horizontal distance from the front end of a four-wheel steering vehicle to the center of the front axle, L P1 represents the length of the minimum space for side parking in the following situation, Δw1 represents the width margin of the minimum space for side parking in the following situation, W P1 Here is the width of the narrow space for parallel parking: is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the parking space under the condition that the car leaves the parking space from the fully parked position in the side parking space under the following situation. is the geometric relationship between the front wheel turning angle, rear turning angle and the width margin of the minimum parking space when the car leaves the parking lot from a completely parked position in the minimum parking space under the following conditions;

[0030] The steering scheme with the front and rear wheels in phase:

[0031]

[0032] Where Δl2 represents the length margin of the extremely small side parking space under situation 2, L P2 represents the length of the minimum side parking space under situation 2, Δw2 represents the width margin of the minimum side parking space under situation 2, W P2 The width of the extremely small parallel parking space in the second representative case is: is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the minimal parking space when the car leaves the parking lot from the fully parked position in the minimal parking space under situation 2. is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the width margin of the minimal parking space under the condition that the car leaves the parking space once from the fully parked position in the minimal parking space in situation 2;

[0033] The steering scheme of the front and rear wheels is as follows:

[0034]

[0035] Where Δl3 represents the length margin of the minimum side parking space under situation 3, L P3 represents the length of the minimum space for side parking in case 3, Δw3 represents the width margin of the minimum space for side parking in case 3, W P3 The width of the minimum parallel parking space in case 3 is: is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the minimal parking space under the condition that the car can smoothly exit the parking space from the fully parked position in the minimal parking space in situation three, It is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the width margin of the minimal parking space under the condition that the car can successfully leave the parking space from a completely parked position in the minimal parking space under situation three.

[0036] In the aforementioned path planning and control method for parallel parking in a very small space for a four-wheel steering vehicle, the front and rear wheel integrated steering scheme makes up for the length margin Δl3 by sacrificing the width margin Δw3 of the parallel parking in a very small space or sacrificing the length margin Δl3 to make up for the width margin Δw3.

[0037] In the aforementioned method for planning and controlling the path of a four-wheel steering vehicle in a very small side parking space, the front and rear wheel integrated steering schemes that sacrifice the width margin Δw3 of the very small side parking space to make up for its length margin Δl3 are, in order, front and rear wheel out-of-phase driving, front and rear wheel forward driving, and front and rear wheel in-phase driving;

[0038] The front and rear wheels driving out of phase is a process in which the vehicle turns from a fully parked position to an initial state at an angle δ1. The turning angle δ1 is expressed as follows:

[0039]

[0040] Where Δw is the width margin of the minimum parallel parking space, and are the turning angle change rates of the front and rear wheels of the four-wheel steering vehicle, v is the vehicle speed, and the calculation formula is as follows:

[0041]

[0042] 0<v1<v2<v3

[0043] Where s1 is the total length of the path during the outbound process; t1 is the total time of the outbound process; ΔX1 is the distance between the vertex of the lower right corner of the car and the right boundary of the parking space when the outbound process is completed;

[0044] The turning angle of a four-wheel steering vehicle with front and rear wheels driving out of phase is:

[0045]

[0046] In the formula, v y is the speed of the vehicle decomposed along the lateral direction, Δl new It is the shortest distance between the right edge of the parking space and the car body;

[0047] The front and rear wheels are in the process of traveling a distance S in a straight line along the central axis from the final position of out-of-phase driving. The travel distance S is expressed as:

[0048] S=f S (S1,S2);

[0049] Where S1 and S2 are the distances between the upper left and lower left vertices and the boundary of the minimum space for side parking when the four-wheel steering vehicle is driving, respectively, and f S Take the minimum function for the boundary distance;

[0050] The minimum space length margin Δl of the front and rear wheels of a four-wheel steering vehicle after driving final It is expressed as:

[0051]

[0052] The front and rear wheels are driven in phase by the final posture of the front and rear wheels moving forward in a phased manner. fmax(+) and δ rmax(+) The process of turning out of a very small parallel parking space.

[0053] In the aforementioned method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking, the front and rear wheel integrated steering schemes that sacrifice the length margin Δl3 of the very small space for side parking to make up for the width margin Δw3 are, in sequence, front and rear wheel in-phase driving, front and rear wheel forward driving, and front and rear wheel out-of-phase driving;

[0054] The front and rear wheels driving out of phase is a process in which the vehicle turns from a fully parked position to an initial state at an angle δ1. The turning angle δ1 is expressed as follows:

[0055]

[0056] Where Δl is the length margin of the minimum space for parallel parking;

[0057] The turning angle of a four-wheel steering vehicle when the front and rear wheels are moving in phase is:

[0058]

[0059] In the formula, v x is the speed decomposed along the longitudinal direction, Δw new It is the shortest distance between the lower boundary of the parking space and the car body;

[0060] The front and rear wheels are moving forward from the final position of the same-phase movement to a straight line along the central axis for a distance S;

[0061] The minimum space width margin Δw of the front and rear wheels of a four-wheel steering vehicle after driving final It is expressed as:

[0062]

[0063] In the formula, f w is the width margin conversion function, which is related to the return travel distance;

[0064] The front and rear wheels are out of phase with each other, and the front and rear wheels are in the same phase with each other. fmax(+) and δ rmax(-) The process of turning out of a very small parallel parking space.

[0065] In the aforementioned method for parallel parking of a four-wheel steering vehicle in a very small space, in step 3, the regulation of various parameters of the kinematic transient characteristics of the four-wheel steering vehicle is represented by a function function Γ(t):

[0066]

[0067] The cost function is defined as:

[0068]

[0069] In the formula, X = f (X0, δ1, S) represents the horizontal coordinate of the final position of the lower right vertex of the car, X1 is the horizontal coordinate of the vertex on the right boundary of the parking space, q1, q2, q3, q4 and q5 are weighting coefficients used to balance the weights of each part. Represents the derivative of the angle of rotation of the front and rear wheels of the car when they are out of phase. Represents the derivative of the forward displacement of the front and rear wheels of the car; through the Newton iteration method, the gradient and Hessian matrix are used to find the optimal update amount for each iteration, so as to quickly converge to the optimal solution, that is, output the optimal turning angle δ1 and the optimal driving distance S.

[0070] In the aforementioned method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking, the optimal space parameter ΔX max When 0<X<X1, maximize q1(X-X1) in the cost function 2 part:

[0071] J1(δ1,S)=q1(X-X1) 2 ;

[0072] The shortest path parameter s min When |X-X1|<ε, minimize the cost function part:

[0073]

[0074] The optimal time parameter t min When |X-X1|<ε, minimize the cost function part:

[0075]

[0076] Compared with the prior art, the present invention has the following beneficial effects:

[0077] The present invention divides the size of the extremely small space for parallel parking into three situations, and can formulate corresponding steering schemes for different space situations, making full use of the kinematic transient characteristics of the vehicle, and improving the success rate and adaptability of parking in an extremely small space. The present invention regards the parking process as a multi-stage continuous optimization problem, establishes a cost function, optimizes the optimal parameters of space, the shortest path parameters and the optimal time parameters, and solves to obtain the optimal turning angle and the optimal driving distance, thereby realizing precise control of the vehicle in an extremely small space. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 It is a control strategy diagram of the method of the present invention;

[0079] Figure 2 A schematic diagram of a small parking space for a front-wheel steering vehicle sideways parking according to the present invention;

[0080] Figure 3 A schematic diagram of a very small parallel parking space according to the present invention;

[0081] Figure 4 This is a schematic diagram of the extremely small space for side parking of a four-wheel steering vehicle of the present invention;

[0082] Figure 5 This is a relationship diagram between the parking space length and the wheel turning angle of the present invention;

[0083] Figure 6 This is a relationship diagram between parking space width and wheel turning angle of the present invention;

[0084] Figure 7 This is a schematic diagram of the front and rear wheel integrated steering process of a four-wheel steering vehicle in the first embodiment of the present invention;

[0085] Figure 8 This is the out-of-phase driving process of the front and rear wheels of the four-wheel steering vehicle in the second situation of the present invention;

[0086] Fig. 9 The process of the front and rear wheels of the four-wheel steering vehicle of the present invention running in phase with each other;

[0087] Fig.10 It is a schematic diagram of the Newton method iterative solution principle of the present invention;

[0088] Fig.11 It is a schematic diagram of the same-phase steering process of the front and rear wheels of the four-wheel steering vehicle of the present invention;

[0089] Fig.12 The diagram is a schematic diagram of the out-of-phase steering process of the front and rear wheels of a four-wheel steering vehicle according to the present invention. DETAILED DESCRIPTION

[0090] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0091] Example

[0092] A method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking. Figure 1 shown.

[0093] It should be noted that, in this embodiment, in order to facilitate the analysis of the parallel parking process of a four-wheel steering vehicle, the following assumptions are made:

[0094] (1) Assume that the parallel parking space is the parking space on the right side of the road;

[0095] (2) The cars and parking spaces involved in the parallel parking task are defined as rectangular shapes with regular shapes;

[0096] (3) Reverse the process of parallel parking, that is, regard parallel parking as the process of the car moving out of the parking space from a completely parked position along the desired path;

[0097] (4) A four-wheel steering vehicle is a four-wheel drive vehicle;

[0098] (5) Define the parameters related to four-wheel steering vehicles and parking spaces, as shown in Table 1.

[0099] Table 1 Parameters related to four-wheel steering vehicles and small parking spaces

[0100]

[0101]

[0102] Step 1: Based on the size of the small parking space and the parameters of the four-wheel steering vehicle, the size of the extremely small parallel parking space is divided into the first case where the length margin is tight but the width margin is ample, the second case where the length margin is ample but the width margin is tight, and the third case where both the length margin and the width margin are tight;

[0103] In this embodiment, the small parking space for the front-wheel steering vehicle side parking (hereinafter referred to as the small parking space) is defined based on the minimum turning radius of the vehicle, such as Figure 2 The minimum turning radius R of a front-wheel steering vehicle min , the formula is as follows:

[0104]

[0105] In the formula, l t Indicates wheelbase, δ fmax Indicates the maximum turning angle of the front wheels.

[0106] The size of the side parking space is further reduced based on the size of the small parking space. The size of the small parking space includes the length L P and width W P , respectively expressed as:

[0107]

[0108] In the formula, w c Represents the width of the vehicle, l r Indicates the horizontal distance from the rear end of a four-wheel steering vehicle to the center of the rear axle, l f Indicates the horizontal distance from the front end of a four-wheel steering vehicle to the center of the front axle.

[0109] The parameters of the four-wheel steering vehicle include: Δl is the difference between the length of the minimum side parking space and the vehicle length, Δw is the difference between the width of the minimum side parking space and the vehicle width, which are respectively expressed as:

[0110]

[0111] Where Δx is the instantaneous center offset of the four-wheel steering vehicle, l t Indicates wheelbase, w t Indicates wheelbase, l f Indicates the horizontal distance from the front end of a four-wheel steering vehicle to the center of the front axle, w c Represents the width of the vehicle, l r Indicates the horizontal distance from the rear end of a four-wheel steering vehicle to the center of the rear axle, R t is the vertical distance from the instantaneous center of the four-wheel steering vehicle to the central axis of the four-wheel steering vehicle, and Δx is the instantaneous center offset of the vehicle, which can be expressed as:

[0112]

[0113] In the formula, δ fmax(+) Indicates that the front wheel rotates counterclockwise to the maximum angle, δ rmax(-) Indicates that the rear wheels rotate clockwise to the maximum angle.

[0114] The minimum parallel parking space for a four-wheel steering vehicle is based on the further reduction of the size of a small parking space, that is, at least one of the following three conditions is met: Figure 3 shown.

[0115] Situation 1: The length of the extremely small parallel parking space L P1 Smaller than the length L of a small parking space P , width W P1 Greater than or equal to the width W of a small parking space P , expressed as l C <L P1 <L P &W P1 ≥W P ;

[0116] Situation 2: Width W of the extremely small parallel parking space P2 Smaller than the width W of a small parking space P , length L P2 Greater than or equal to the length L of a small parking space P , denoted as L P2 ≥L P &w C <W P2 <W P ;

[0117] Situation 3: The length of the extremely small parallel parking space L P3 and width W P3 All are longer than the length of a small parking space L P and width W P Small, represented by l C <L P3 <L P &w C <W P3 <W P ;

[0118] Figure 4 This is a schematic diagram of a four-wheel steering vehicle parking in a very small space. The formulas for Case 1, Case 2 and Case 3 are as follows:

[0119]

[0120] In the formula, N represents different situations; L PN Represents the length of the minimum parallel parking space in different situations, l c Represents the vehicle length, Δl N Represents the length margin of the minimum parallel parking space under different circumstances; W PN Represents the width of the minimum parallel parking space in different situations, Δw N Represents the width margin of the extremely small space for parallel parking in different situations;

[0121] The length margin Δl of the minimum parallel parking space in different situations N and width margin Δw N The functional relationship is expressed as:

[0122]

[0123] In the formula, δ f represents the front wheel turning angle, δ r represents the rear wheel turning angle, C represents [l c ,w c ,l t ,w t ,l f ,l r ]; is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the minimal parking space when the car is successfully exiting the parking space from a completely parked position in the minimal parking space; It is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the width margin of the minimal parking space when the car can smoothly leave the parking space from a completely parked position in the minimal parking space.

[0124] Step 2: For situation 1, adopt a steering scheme where the front and rear wheels are out of phase; for situation 2, adopt a steering scheme where the front and rear wheels are in phase; for situation 3, adopt a steering scheme where the front and rear wheels are integrated;

[0125] In this embodiment, the maximum turning angle of the front wheels of the four-wheel steering vehicle is taken as δ fmax(+) =35°, the maximum turning angle of the rear wheel is δ rmax(-) = 8°, decoupling analysis is performed to determine the influence of the front and rear wheel turning angles on the length and width of the extremely small side parking space, such as Figure 5 and Figure 6 shown.

[0126] Depend on Figure 5 and Figure 6 It can be seen that the front wheel turning angle of the vehicle is the main influencing factor of the length of the minimum space for parallel parking, that is, as the front wheel turning angle increases, the length of the minimum space decreases significantly; the rear wheel turning angle of the vehicle is the main influencing factor of the width of the minimum space for parallel parking, that is, as the rear wheel turning angle increases, the width of the minimum space decreases significantly.

[0127] Based on Figure 5 and Figure 6 Based on the analysis, three steering schemes are proposed for the three situations of parallel parking in extremely small spaces, as shown in Table 1-2.

[0128] Table 1-2 Three steering schemes for four-wheel steering vehicles

[0129] Steering solution symbol Front and rear wheels out of phase <![CDATA[δ fi (+),δ ri (-),Δx(-)i=l,r]]> Front and rear wheels in phase <![CDATA[δ fi (+),δ ri (+),Δx(+)i=l,r]]> Front and rear wheels integrated <![CDATA[δ fi (D),d ri (Δ),Δx(Δ)i=l,r]]>

[0130] If the minimum parallel parking space length is L P1 and width W P1 This belongs to the first case, that is, the length margin Δl1 of the extremely small space for parallel parking is tight, and the width margin Δw1 is sufficient. Therefore, the front and rear wheel out-of-phase steering scheme can be adopted. The front and rear wheel out-of-phase refers to a driving state in which the front and rear wheels of the car turn in opposite directions during the parallel parking process. The functional relationship is as follows:

[0131]

[0132] Where Δl1 represents the length margin of the minimum space for side parking in the case of side parking, δ f represents the front wheel turning angle, δ r Rear wheel turning angle, C represents [l c ,w c ,l t ,w t ,l f ,l r ], l c Represents the vehicle commander, w c Represents the width of the vehicle, l t Indicates wheelbase, wt Indicates wheelbase, l r Indicates the horizontal distance from the rear end of a four-wheel steering vehicle to the center of the rear axle, l f Indicates the horizontal distance from the front end of a four-wheel steering vehicle to the center of the front axle, L P1 represents the length of the minimum space for side parking in the following situation, Δw1 represents the width margin of the minimum space for side parking in the following situation, W P1 Here is the width of the narrow space for parallel parking: is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the parking space under the condition that the car leaves the parking space from the fully parked position in the side parking space under the following situation. is the geometric relationship between the front wheel turning angle, rear turning angle and the width margin of the minimum parking space when the car leaves the parking lot from a completely parked position in the minimum parking space under the following conditions;

[0133] If the minimum parallel parking space length is L P2 and width W P2 This belongs to the second situation, that is, the length margin Δl2 of the extremely small space for parallel parking is sufficient, and the width margin Δw2 is tight. Therefore, the front and rear wheels can be turned in the same phase. The front and rear wheels in the same phase refers to a driving state in which the front and rear wheels of the car are turned in the same direction during the parallel parking process. The function expression is as follows:

[0134]

[0135] Where Δl2 represents the length margin of the extremely small side parking space under situation 2, L P2 represents the length of the minimum side parking space under situation 2, Δw2 represents the width margin of the minimum side parking space under situation 2, W P2 The width of the extremely small parallel parking space in the second representative case is: is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the minimal parking space when the car leaves the parking lot from the fully parked position in the minimal parking space under situation 2. is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the width margin of the minimal parking space under the condition that the car leaves the parking space once from the fully parked position in the minimal parking space in situation 2;

[0136] If the minimum parallel parking space length is L P3 and width W P3 This is the third case, that is, the length margin Δl3 and width margin Δw3 of the extremely small parallel parking space are both tight, so a steering scheme that integrates the front and rear wheels must be adopted:

[0137]

[0138] Where Δl3 represents the length margin of the minimum side parking space under situation 3, L P3 represents the length of the minimum space for side parking in case 3, Δw3 represents the width margin of the minimum space for side parking in case 3, W P3 The width of the minimum parallel parking space in case 3 is: is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the minimal parking space under the condition that the car can smoothly exit the parking space from the fully parked position in the minimal parking space in situation three, It is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the width margin of the minimal parking space under the condition that the car can successfully leave the parking space from a completely parked position in the minimal parking space under situation three.

[0139] The front and rear wheel integrated steering scheme makes up for the length margin Δl3 by sacrificing the width margin Δw3 of the extremely small side parking space, or makes up for the width margin Δw3 by sacrificing the length margin Δl3.

[0140] like Figure 7 As shown, the front and rear wheel integrated steering schemes that sacrifice the width margin Δw3 of the extremely small side parking space to make up for its length margin Δl3 are front and rear wheel out-of-phase driving, front and rear wheel forward driving, and front and rear wheel in-phase driving.

[0141] like Figure 8 As shown, the front and rear wheels driving out of phase is a process in which the car turns an angle δ1 from a completely parked position with an initial state (initial velocity, front and rear wheel turning angles and turning angle change rate, etc.), and the turning angle δ1 is expressed as follows:

[0142]

[0143] Where Δw is the width margin of the minimum parallel parking space, and are the rates of change of the turning angles of the front and rear wheels of the four-wheel steering vehicle, respectively; v is the vehicle speed (considered as a uniform speed throughout the entire process) and is related to the driving mode. The calculation formula is as follows:

[0144]

[0145] 0<v1<v2<v3

[0146] Where s1 is the total length of the path during the outbound process; t1 is the total time of the outbound process; ΔX1 is the distance between the vertex of the lower right corner of the car and the right boundary of the parking space when the outbound process is completed;

[0147] The turning angle of a four-wheel steering vehicle with front and rear wheels driving out of phase is:

[0148]

[0149] In the formula, v y is the speed of the vehicle decomposed along the lateral direction, Δl new It is the shortest distance between the right edge of the parking space and the car body;

[0150] like Fig. 9 As shown, the front and rear wheels are driving forward from the final position of out-of-phase driving along the central axis in a straight line for a distance S, and the driving distance S is expressed as:

[0151] S=f S (S1,S2);

[0152] Where S1 and S2 are the distances between the upper left and lower left vertices and the boundary of the minimum space for side parking when the four-wheel steering vehicle is driving, respectively, and f S Take the minimum function for the boundary distance;

[0153] The front and rear wheel forward driving means that the vehicle drives backward at a constant speed until the width margin and the front and rear wheel turning angle values ​​are all 0;

[0154] The minimum space length margin Δl of the front and rear wheels of a four-wheel steering vehicle after driving final It is expressed as:

[0155]

[0156] The front and rear wheels are driven in phase by the final posture of the front and rear wheels moving forward in a phased manner. fmax(+) and δ rmax(+) The process of turning out of a very small parallel parking space.

[0157] The front and rear wheel integrated steering schemes that sacrifice the length margin Δl3 of the extremely small side parking space to make up for the width margin Δw3 are, in order, the front and rear wheels driving in phase, the front and rear wheels driving in the same direction, and the front and rear wheels driving out of phase;

[0158] The front and rear wheels driving out of phase is a process in which the vehicle turns from a fully parked position to an initial state at an angle δ1. The turning angle δ1 is expressed as follows:

[0159]

[0160] Where Δl is the length margin of the minimum space for parallel parking;

[0161] The turning angle of a four-wheel steering vehicle when the front and rear wheels are moving in phase is:

[0162]

[0163] In the formula, v x is the speed decomposed along the longitudinal direction, Δw new It is the shortest distance between the lower boundary of the parking space and the car body;

[0164] The front and rear wheels are moving forward from the final position of the same-phase movement to a straight line along the central axis for a distance S;

[0165] The minimum space width margin Δw of the front and rear wheels of a four-wheel steering vehicle after driving final It is expressed as:

[0166]

[0167] In the formula, f w is the width margin conversion function, which is related to the return travel distance;

[0168] The front and rear wheels are out of phase with each other, and the front and rear wheels are in the same phase with each other. fmax(+) and δ rmax(-) The process of turning out of a very small parallel parking space.

[0169] Step 3: Based on the kinematic transient characteristics of the four-wheel steering vehicle, a cost function is established to optimize the optimal spatial parameters, the shortest path parameters and the optimal time parameters. According to the obtained optimal spatial parameters, the shortest path parameters and the optimal time parameters, the optimal turning angle and the optimal driving distance are obtained;

[0170] In step 3, the regulation of various parameters of the kinematic transient characteristics of the four-wheel steering vehicle is represented by a function Γ(t):

[0171]

[0172] The cost function is defined as:

[0173]

[0174] In the formula, X = f (X0, δ1, S) represents the horizontal coordinate of the final position of the lower right vertex of the car, X1 is the horizontal coordinate of the vertex on the right boundary of the parking space, q1, q2, q3, q4 and q5 are weighting coefficients used to balance the weights of each part. Represents the derivative of the angle of rotation of the front and rear wheels of the car when they are out of phase. Represents the derivative of the forward displacement of the front and rear wheels of the car; through the Newton iteration method, the gradient and Hessian matrix are used to find the optimal update amount for each iteration, so as to quickly converge to the optimal solution and output the optimal turning angle δ1 and the optimal driving distance S, as shown in Fig.10 shown.

[0175] The spatial optimal parameter ΔX max When 0<X<X1, maximize q1(X-X1) in the cost function 2 part:

[0176] J1(δ1,S)=q1(X-X1) 2 ;

[0177] The shortest path parameter s min When |X-X1|<ε, minimize the cost function part:

[0178]

[0179] The optimal time parameter t min When |X-X1|<ε, minimize the cost function part:

[0180]

[0181] Step 4: Based on the size of the extremely small space for parallel parking, according to the obtained optimal turning angle and optimal driving distance, the four-wheel steering vehicle is controlled to adopt a corresponding steering plan to complete parking.

[0182] For the above-mentioned cases 1 and 2 of the extremely small space for parallel parking, the fsolve function of the MATLAB software is used to solve the nonlinear equations to obtain the optimal turning angle and optimal driving distance, as well as the corresponding front and rear wheel turning angle values, and the appropriate vehicle speed v is used to exit the garage at one time. The process is as follows Fig.11 and Fig.12 shown.

[0183] For the above situation 3 of the extremely small space for parallel parking, the fsolve function of Matlab software is used to solve the nonlinear equations to obtain the optimal turning angles and optimal driving distances in the three stages of the steering scheme for the integration of the front and rear wheels, as well as the corresponding front and rear wheel turning angle values, and the corresponding vehicle speed v for leaving the garage, such as Figure 7-8 shown.

[0184] Since the present invention has high requirements on the accuracy of the vehicle speed v, a PID controller is built to track the target vehicle speed. The difference between the actual vehicle speed and the target vehicle speed is used as the input of the PID controller, and the opening signal of the acceleration / brake pedal is used as the output. The signal is sent to the motor controller to adjust the longitudinal vehicle speed v of the vehicle. The specific process is as follows:

[0185]

[0186] Where e(t) is the vehicle speed error signal, v d is the target vehicle speed, v t is the current vehicle speed, T is the motor output torque, K p is the proportionality coefficient, K i is the integration coefficient, K d is the differential coefficient and t is the time.

[0187] In summary, the present invention can achieve more accurate and efficient parking operations in a very small space for parallel parking, and can adapt to various parking space forms, thereby improving the efficiency of parallel parking of cars in a small space.

Claims

1. A method for planning and controlling a path in a very small space for side parking of a four-wheel steering vehicle, characterized in that: The specific steps include: Step 1: Based on the size of the small parking space and the parameters of the four-wheel steering vehicle, the size of the extremely small parallel parking space is divided into the first case where the length margin is tight but the width margin is ample, the second case where the length margin is ample but the width margin is tight, and the third case where both the length margin and the width margin are tight; Step 2: For situation 1, adopt a steering scheme where the front and rear wheels are out of phase; for situation 2, adopt a steering scheme where the front and rear wheels are in phase; for situation 3, adopt a steering scheme where the front and rear wheels are integrated; Step 3: Establish a cost function based on the kinematic transient characteristics of the four-wheel steering vehicle, and use the cost function to optimize the optimal spatial parameters, the shortest path parameters, and the optimal time parameters to obtain the optimal turning angle and the optimal driving distance; Step 4: Based on the obtained optimal turning angle and optimal driving distance, the four-wheel steering vehicle is controlled to adopt a corresponding steering plan to complete parking.

2. The method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking according to claim 1, characterized in that: In step 1, the size of the parallel parking space is further reduced based on the size of the small parking space, and the size of the small parking space includes the length L P and width W P , respectively expressed as: In the formula, w c Represents the width of the vehicle, l r Indicates the horizontal distance from the rear end of a four-wheel steering vehicle to the center of the rear axle, l f Indicates the horizontal distance from the front end of a four-wheel steering vehicle to the center of the front axle, l t Indicates wheelbase, R min is the minimum turning radius of a front-wheel steering vehicle, R min It is expressed as: In the formula, δ fmax Indicates the maximum turning angle of the front wheels.

3. The method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking according to claim 2, characterized in that: The parameters of the four-wheel steering vehicle include: Δl is the difference between the length of the minimum side parking space and the vehicle length, Δw is the difference between the width of the minimum side parking space and the vehicle width, which are respectively expressed as: Where Δx is the instantaneous center offset of the four-wheel steering vehicle, w t Indicates wheelbase, R t is the vertical distance from the instantaneous center of the four-wheel steering vehicle to the central axis of the four-wheel steering vehicle, and Δx is the instantaneous center offset of the vehicle, which can be expressed as: In the formula, the counterclockwise rotation of the vehicle tire around the center point of contact with the ground is defined as the positive direction, and the reverse direction is defined as the negative direction; δ fmax(+) Indicates that the front wheel rotates counterclockwise to the maximum angle, δ rmax(-) Indicates that the rear wheels rotate clockwise to the maximum angle.

4. The method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking according to claim 3, characterized in that: Situation 1: The length of the extremely small parallel parking space L P1 Smaller than the length L of a small parking space P , width W P1 Greater than or equal to the width W of a small parking space P , expressed as l C <L P1 <L P &W P1 ≥W P ; Situation 2: Width W of the extremely small parallel parking space P2 Smaller than the width W of a small parking space P , length L P2 Greater than or equal to the length L of a small parking space P , denoted as L P2 ≥L P &w C <W P2 <W P ; Situation 3: The length of the extremely small parallel parking space L P3 and width W P3 All are longer than the length of a small parking space L P and width W P Small, represented by l C <L P3 <L P &w C <W P3 <W P ; The formulas for Case 1, Case 2 and Case 3 are as follows: In the formula, N represents different situations; L PN Represents the length of the minimum parallel parking space in different situations, l c Represents the vehicle length, Δl N Represents the length margin of the minimum parallel parking space under different circumstances; W PN Represents the width of the minimum parallel parking space in different situations, Δw N Represents the width margin of the extremely small space for parallel parking in different situations; The length margin Δl of the minimum parallel parking space in different situations N and width margin Δw N The functional relationship is expressed as: In the formula, δ f represents the front wheel turning angle, δ r represents the rear wheel turning angle, C represents [l c ,w c ,l t ,w t ,l f ,l r ]; is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the minimal parking space when the car is successfully parked in the minimal parking space; ΔwN It is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the width margin of the minimal parking space when the car can smoothly leave the parking space from a completely parked position in the minimal parking space.

5. The method for parallel parking of a four-wheel steering vehicle in a very small space according to claim 1, characterized in that: In step 2, the steering scheme of the front and rear wheels being out of phase is expressed as follows: Where Δl1 represents the length margin of the minimum space for side parking in the case of side parking, δ f represents the front wheel turning angle, δ r Rear wheel turning angle, C represents [l c ,w c ,l t ,w t ,l f ,l r ], l c Represents the vehicle commander, w c Represents the width of the vehicle, l t Indicates wheelbase, w t Indicates wheelbase, l r Indicates the horizontal distance from the rear end of a four-wheel steering vehicle to the center of the rear axle, l f Indicates the horizontal distance from the front end of a four-wheel steering vehicle to the center of the front axle, L P1 represents the length of the minimum space for side parking in the following situation, Δw1 represents the width margin of the minimum space for side parking in the following situation, W P1 Here is the width of the narrow space for parallel parking: is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the parking space under the condition that the car leaves the parking space from the fully parked position in the side parking space under the following situation. is the geometric relationship between the front wheel turning angle, rear turning angle and the width margin of the minimum parking space when the car leaves the parking lot from a completely parked position in the minimum parking space under the following conditions; The steering scheme with the front and rear wheels in phase: Where Δl2 represents the length margin of the extremely small side parking space under situation 2, L P2 represents the length of the minimum side parking space under situation 2, Δw2 represents the width margin of the minimum side parking space under situation 2, W P2 The width of the extremely small parallel parking space in the second representative case is: is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the minimal parking space when the car leaves the parking lot from the fully parked position in the minimal parking space under situation 2. is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the width margin of the minimal parking space under the condition that the car leaves the parking space once from the fully parked position in the minimal parking space in situation 2; The steering scheme of the front and rear wheels is as follows: Where Δl3 represents the length margin of the minimum side parking space under situation 3, L P3 represents the length of the minimum space for side parking in case 3, Δw3 represents the width margin of the minimum space for side parking in case 3, W P3 The width of the minimum parallel parking space in case 3 is: is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the length margin of the parking space under the condition that the car can smoothly exit the parking space from the fully parked position in the side parking space under situation 3, f Δw3 It is the geometric relationship between the front wheel turning angle, rear wheel turning angle and the width margin of the minimal parking space under the condition that the car can successfully leave the parking space from a completely parked position in the minimal parking space under situation three.

6. The method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking according to claim 5, characterized in that: The front and rear wheel integrated steering scheme makes up for the length margin Δl3 by sacrificing the width margin Δw3 of the extremely small side parking space, or makes up for the width margin Δw3 by sacrificing the length margin Δl3.

7. The method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking according to claim 6, characterized in that: The front and rear wheel integrated steering schemes that sacrifice the width margin Δw3 of the extremely small side parking space to make up for its length margin Δl3 are front and rear wheel out-of-phase driving, front and rear wheel forward driving, and front and rear wheel in-phase driving. The front and rear wheels driving out of phase is a process in which the vehicle turns from a fully parked position to an initial state at an angle δ1. The turning angle δ1 is expressed as follows: Where Δw is the width margin of the minimum parallel parking space, and are the turning angle change rates of the front and rear wheels of the four-wheel steering vehicle, v is the vehicle speed, and the calculation formula is as follows: Where s1 is the total length of the path during the outbound process; t1 is the total time of the outbound process; ΔX1 is the distance between the vertex of the lower right corner of the car and the right boundary of the parking space when the outbound process is completed; The turning angle of a four-wheel steering vehicle with front and rear wheels driving out of phase is: In the formula, v y is the speed of the vehicle decomposed along the lateral direction, Δl new It is the shortest distance between the right edge of the parking space and the car body; The front and rear wheels are in the process of traveling a distance S in a straight line along the central axis from the final position of out-of-phase driving. The travel distance S is expressed as: S=f S (S1,S2); Where S1 and S2 are the boundary distances between the upper left and lower left vertices and the minimum side parking space when the four-wheel steering vehicle is driving, and f S Take the minimum function for the boundary distance; The minimum space length margin Δl of the front and rear wheels of a four-wheel steering vehicle after driving final It is expressed as: The front and rear wheels are driven in phase by the final posture of the front and rear wheels moving forward in a phased manner. fmax(+) and δ rmax(+) The process of turning out of a very small parallel parking space.

8. The method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking according to claim 6, characterized in that: The front and rear wheel integrated steering schemes that sacrifice the length margin Δl3 of the extremely small side parking space to make up for the width margin Δw3 are, in order, the front and rear wheels driving in phase, the front and rear wheels driving in the same direction, and the front and rear wheels driving out of phase; The front and rear wheels driving out of phase is a process in which the vehicle turns from a fully parked position to an initial state at an angle δ1. The turning angle δ1 is expressed as follows: Where Δl is the length margin of the minimum space for parallel parking; The turning angle of a four-wheel steering vehicle when the front and rear wheels are moving in phase is: In the formula, v x is the speed decomposed along the longitudinal direction, Δw new It is the shortest distance between the lower boundary of the parking space and the car body; The front and rear wheels are moving forward from the final position of the same-phase movement to a straight line along the central axis for a distance S; The minimum space width margin Δw of the front and rear wheels of a four-wheel steering vehicle after driving final It is expressed as: In the formula, f w is the width margin conversion function, which is related to the return travel distance; The front and rear wheels are out of phase with each other, and the front and rear wheels are in the same phase with each other. fmax(+) and δ rmax(-) The process of turning out of a very small parallel parking space.

9. The method for planning and controlling the path of a four-wheel steering vehicle in a very small space for side parking according to claim 1, characterized in that: In step 3, the regulation of various parameters of the kinematic transient characteristics of the four-wheel steering vehicle is represented by a function Γ(t): The cost function is defined as: In the formula, X = f (X0, δ1, S) represents the horizontal coordinate of the final position of the lower right vertex of the car, X1 is the horizontal coordinate of the vertex on the right boundary of the parking space, q1, q2, q3, q4 and q5 are weighting coefficients used to balance the weights of each part. Represents the derivative of the angle of rotation of the front and rear wheels of the car when they are out of phase. Represents the derivative of the forward displacement of the front and rear wheels of the car; through the Newton iteration method, the gradient and Hessian matrix are used to find the optimal update amount for each iteration, so as to quickly converge to the optimal solution, that is, output the optimal turning angle δ1 and the optimal driving distance S.

10. The method for planning and controlling the path of a four-wheel steering vehicle for side parking in a very small space according to claim 9, characterized in that: The spatial optimal parameter ΔX max When 0<X<X1, maximize q1(X-X1) in the cost function 2 part: J1(δ1,S)=q1(X-X1) 2 ; The shortest path parameter s min When |X-X1|<ε, minimize q2δ1 in the cost function 2 +q3S 2 part: The optimal time parameter t min When |X-X1|<ε, minimize the cost function part:

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