A road feel planning method for a by-wire electro-hydraulic composite steering

Abstract

The application provides a road feeling planning method for a wire control electro-hydraulic composite steering system, which comprises the following steps: firstly, estimating an equivalent steering resistance moment of the electro-hydraulic composite steering system based on a motor model and a vehicle dynamics model respectively; then, comprehensively estimating a wire control equivalent steering resistance moment by a longitudinal velocity weighting method; then, combining a designed electric power assistance characteristic curve with a hydraulic power assistance characteristic curve to obtain a wire control electro-hydraulic composite steering system power assistance characteristic curve; constructing a relationship between the wire control electro-hydraulic composite steering system power assistance characteristic curve and a simulated hand torque according to the wire control electro-hydraulic composite steering system power assistance characteristic curve; and finally, obtaining a real-time simulated hand torque, i.e., a steering road feeling, according to the wire control electro-hydraulic composite steering system equivalent steering resistance moment estimated in real time. The road feeling planning method provided by the application improves the authenticity, accuracy and applicability of the road feeling simulation of the wire control electro-hydraulic composite steering system, and helps to obtain an accurate and reliable road feeling, thereby improving the driving experience of a driver.

Description

Technical Field

[0001] This invention belongs to the field of vehicle steering systems, and particularly relates to a road feel planning method for steer-by-wire electro-hydraulic composite steering. Background Technology

[0002] The performance of the steering system has a significant impact on vehicle handling stability and driving comfort. With the development of advanced technologies such as autonomous driving, the steering systems of commercial vehicles are also evolving towards greater intelligence and safety. Electro-hydraulic hybrid steering (EHHPS) is a new type of steering system that integrates hydraulic steering (HPS) and electric power steering (EPS), combining the advantages of high assist torque from HPS and strong controllability from EPS. However, EHHPS still suffers from low precision, slow response, and poor adaptability. In contrast, steer-by-wire systems offer rapid response, high precision, and strong adaptability, making them more suitable for the intelligent development needs of commercial vehicles. Because steer-by-wire systems eliminate the mechanical connection between the steering wheel and wheels, the interaction between the road surface and the vehicle's tires—the "road feel"—cannot be directly transmitted to the driver through mechanical structures. Steer-by-wire systems often simulate steering road feel using a road feel motor, and road feel planning is a prerequisite for road feel simulation. However, current research on road feel planning for steer-by-wire electro-hydraulic hybrid steering systems is limited, and the methods for simulation planning are relatively simple and cannot adequately handle various operating conditions. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes a road feel planning method for steer-by-wire electro-hydraulic composite steering. First, the electro-torque provided by the steering motor of the electric steering subsystem in the steer-by-wire electro-hydraulic hybrid steering system is estimated based on the linear expansion state observer. The hydraulic pressure provided by the hydraulic steering subsystem is obtained based on the pressure difference between the left and right chambers of the hydraulic power steering cylinder and the effective area of ​​the hydraulic cylinder piston. The equivalent steering resistance torque estimated based on the motor model is then estimated using the obtained electro-torque of the electric steering subsystem and the hydraulic pressure provided by the hydraulic steering subsystem. Next, based on vehicle dynamic response and road adhesion conditions, the reaction force of the tire on the ground is obtained using the Dugoff tire model, and the equivalent steering resistance torque is calculated using vehicle dynamics. The equivalent steering resistance torque estimated by the motor model and the equivalent steering resistance torque estimated by the vehicle dynamics model are then combined using the longitudinal velocity weighting method to estimate the equivalent steering resistance torque of the steer-by-wire electro-hydraulic hybrid steering system. Then, the designed electric power steering characteristic curve and the hydraulic power steering characteristic curve are combined to obtain the power steering characteristic curve of the electro-hydraulic hybrid steering system. Based on the power steering characteristic curve, the relationship between the equivalent steering resistance torque and the simulated hand torque of the electro-hydraulic hybrid steering system is constructed. Finally, the real-time simulated hand torque, i.e., the steering feel, is obtained based on the real-time estimated equivalent steering resistance torque of the steer-by-wire electro-hydraulic hybrid steering system.

[0004] A road feel planning method for steer-by-wire electro-hydraulic hybrid steering includes the following steps:

[0005] Step S1: Obtain the electrodynamic torque coupled to the steering input shaft of the electric steering subsystem using the linear extended state observer;

[0006] Step S2: Based on the pressure difference of the power steering oil formed in the left and right chambers of the hydraulic power steering cylinder and the effective area of ​​the hydraulic cylinder piston, obtain the hydraulic pressure under the hydraulic steering subsystem;

[0007] Step S3: Combine the electrodynamic torque of the electric steering subsystem obtained in step S1 and the hydraulic pressure of the hydraulic steering subsystem obtained in step S2 to obtain the equivalent steering resistance torque estimated based on the motor model.

[0008] Step S4: Based on information such as vehicle dynamic response and road adhesion conditions, the reaction force of the tire on the ground is obtained using the Dugoff tire model, and then the equivalent steering resistance torque is obtained based on the vehicle dynamics calculation method.

[0009] Step S5: Obtain the equivalent steering resistance torque of the steer-by-wire electro-hydraulic composite steering system according to the longitudinal velocity weighting method;

[0010] Step S6: Construct the relationship between the equivalent steering resistance torque and the simulated hand torque of the electro-hydraulic composite steering system based on the power assist characteristic curve of the electro-hydraulic composite steering system; finally, obtain the real-time simulated hand torque, i.e., steering feel, based on the real-time estimated equivalent steering resistance torque of the steerable electro-hydraulic composite steering system.

[0011] Furthermore, the method for obtaining the electric torque of the electric steering subsystem in step S1 is as follows:

[0012] Step S1.1 Obtain the current I of the steering motor based on the motor current sensor. a The output torque of the steering motor is calculated, and then an electro-torque estimation model is established based on the dynamic model of the steering system, as shown below:

[0013] T m =K m I a

[0014]

[0015] In the formula, J c B is the equivalent moment of inertia of the steering gear input shaft. c Let θ be the equivalent damping coefficient of the steering system. c T is the steering input shaft angle. EPS For the electric torque under the electric steering subsystem, i m K is the reduction ratio from the output shaft of the steering motor to the input shaft of the steering gear.m T is the electromagnetic torque coefficient of the steering motor. m For the steering motor to output torque, I a This is the current of the steering motor.

[0016] Step S1.2: Based on the electrodynamic torque estimation model in Step S1.1 above, a linear extended state observer is used to estimate the electrodynamic torque of the electric steering subsystem. The observer model is shown below:

[0017]

[0018] In the formula, x1=θ c , For the system's state variables, State variables x1, x2, and T are respectively. EPS The estimated values ​​are β1, β2, and β3, which are the gain coefficients of the observer, respectively.

[0019] Furthermore, the method for obtaining the hydraulic pressure under the hydraulic steering subsystem in step S2 is as follows:

[0020] Step S2.1: Calculate the hydraulic oil pump output flow rate based on the hydraulic oil pump flow coefficient and the pump motor speed. The calculation formula is as follows:

[0021] Q s =V p n mb

[0022] In the formula, Q s V is the output flow rate of the hydraulic oil pump. p n is the flow coefficient of the hydraulic oil pump. mb This refers to the speed of the oil pump motor.

[0023] Step S2.2: Based on the conservation of flow on the left and right sides of the hydraulic cylinder, determine the flow rate of the rotary valve into the left and right chambers of the hydraulic cylinder. The calculation formula is as follows:

[0024]

[0025] In the formula, Q A Q B These represent the flow rates from the rotary valve into the left and right chambers of the hydraulic cylinder, respectively. p X is the effective working area of ​​the piston. s This represents the piston displacement.

[0026] Step S2.3: The electric torque of the electric steering subsystem is transmitted to the torsion bar in the rotary valve. Based on the torque transmitted by the torsion bar, the rotary valve angle is calculated using the following formula:

[0027]

[0028] In the formula, k s For the torsion bar stiffness of the rotary valve, This refers to the torsion bar deformation angle, which is the valve rotation angle.

[0029] Step S2.4: Calculate the opening area of ​​each valve port of the rotary valve based on the rotation angle of the rotary valve. The calculation formula is shown below:

[0030]

[0031] In the formula, R is the valve core and valve sleeve mating radius, W1 is the short notch width, W2 is the valve port pre-opening clearance width in the neutral position, L1 is the axial length of the short notch, L2 is the axial length of the valve port, and A j (j=1,2,3,4) represents the opening area of ​​each valve port of the rotary valve, where A1=A4, A2=A3.

[0032] Step S2.5: Based on the hydraulic pump output flow rate, the flow rate into the left and right chambers of the hydraulic cylinder from the rotary valve, and the opening area of ​​each valve port of the rotary valve, calculate the pressure difference of the booster oil formed in the left and right chambers of the hydraulic booster cylinder. The calculation formula is as follows:

[0033]

[0034] In the formula, ΔP is the pressure difference of the power steering oil formed in the left and right chambers of the hydraulic power steering cylinder, and P A ,P B These represent the pressures in the left and right chambers of the hydraulic cylinder, respectively.

[0035] Step S2.6: Based on the pressure difference of the power steering oil formed in the left and right chambers of the hydraulic power steering cylinder and the effective area of ​​the hydraulic cylinder piston, the hydraulic pressure under the hydraulic steering subsystem is calculated. The calculation formula is as follows:

[0036] F EHPS =ΔP·A p

[0037] The formula for calculating the effective area of ​​the hydraulic cylinder piston is as follows:

[0038]

[0039] In the formula, F EHPS D1 represents the hydraulic pressure in the hydraulic steering subsystem, D2 represents the piston diameter, and D3 represents the piston push rod diameter.

[0040] Furthermore, the method for estimating the equivalent steering resistance torque based on the motor model in step S3 is as follows:

[0041] Step S3.1: Based on the steering screw-steering nut transmission pair model, calculate the axial force on the nut in the steering screw-steering nut transmission pair. The calculation formula is shown below:

[0042] M l =T EPS

[0043]

[0044] In the formula, M l For the torque transmitted by the screw in the steering screw-steering nut transmission pair, F l η is the axial force on the nut in the steering screw-steering nut transmission pair. l Let P be the transmission efficiency of the steering screw-steering nut transmission pair, and P be the lead of the steering screw-steering nut transmission pair.

[0045] Step S3.2: Calculate the force acting on the rocker arm shaft gear sector. The calculation formula is as follows:

[0046]

[0047] In the formula, M s For the mass of the steering nut, B s X is the damping coefficient of the steering nut. s =θ c P / 2π, F cs This is the force acting on the rocker arm shaft gear sector.

[0048] Step S3.3: Calculate the steering resistance torque equivalent to the gear sector. The calculation formula is shown below:

[0049]

[0050] In the formula, J cs B is the equivalent rotational inertia from the gear sector to the rocker arm. cs θ is the equivalent damping coefficient from the gear sector to the rocker arm. cs Let θ be the rotation angle of the gear sector. cs =X s / R cs T p R is the equivalent steering resistance torque estimated on the gear sector based on the motor model. cs Let be the pitch circle radius of the gear sector.

[0051] Furthermore, the method for calculating the equivalent steering resistance torque based on vehicle dynamics in step S4 is as follows:

[0052] Step S4.1: Calculate the vertical force of each wheel based on the overall vehicle structural parameters. The calculation formula is shown below:

[0053]

[0054] In the formula, F zi (i = 1, 2, 3, 4) represent the vertical forces on each wheel (i = 1 represents the left front wheel, i = 2 represents the right front wheel, i = 3 represents the left rear wheel, and i = 4 represents the right rear wheel), m is the total mass of the vehicle, g is the acceleration due to gravity, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, and a x For longitudinal acceleration, a y denoted as lateral acceleration, h as the vehicle's center of gravity height, and B as the track width between the front and rear axles.

[0055] Step S4.2: Based on the tire vertical force, tire slip ratio, and tire slip angle, calculate the lateral force of each tire using the Dugoff tire model. The calculation formula is shown below:

[0056]

[0057] In the formula, F yi k represents the lateral force of each tire. y For tire lateral stiffness, s i For each tire's longitudinal slip ratio, α i The slip angle of each wheel.

[0058] in,

[0059]

[0060]

[0061]

[0062]

[0063] In the formula, δ i Let ω be the wheel turning angle, u be the longitudinal vehicle speed, v be the lateral vehicle speed, and ω be the lateral vehicle speed. r Let μ be the yaw rate, μ be the road adhesion coefficient, and k be the yaw rate. x For the longitudinal stiffness of the tire, u w Let ω be the velocity at the center of the tire. w ω is the tire angular velocity, and r is the tire rolling radius.

[0064] Step S4.3: Calculate the restoring torque related to the tire's vertical force based on the tire's vertical force. The calculation formula is shown below:

[0065]

[0066] In the formula, M zn (n=1,2) represents the steering resistance torque related to the vertical force of the left and right front tires, F. znLet D be the vertical force on the left and right tires, θ be the kingpin inclination angle, and δ be the vertical force on the left and right tires. n The turning angles are for the left and right front wheels.

[0067] Step S4.4: Calculate the self-aligning torque related to the tire lateral force based on the tire lateral force. The calculation formula is as follows:

[0068] M y =(F y1 +F y2 )·(t c +t n )

[0069] Among them, t n =rtanθ cas +r co

[0070] In the formula, M y F is the steering resistance torque related to the lateral force of the tire. y1 F y2 The lateral forces on the left and right front wheels are t, respectively. c For mechanical drag torque, t n The tire drag torque is r, the wheel rolling radius is θ. cas Kingpin caster angle, r co This is the longitudinal offset of the kingpin at the wheel center.

[0071] Step S4.5: Calculate the equivalent steering resistance torque based on the vehicle dynamics calculation method. The calculation formula is as follows:

[0072]

[0073] In the formula, M p For the equivalent steering resistance torque calculated based on vehicle dynamics, i s η is the transmission ratio from the wheel to the rocker arm. s For transmission efficiency.

[0074] Furthermore, the calculation method for the equivalent steering resistance torque of the steer-by-wire electro-hydraulic composite steering system obtained by the longitudinal velocity weighting method in step S5 is as follows:

[0075] M=λT p +(1-λ)M p

[0076] in,

[0077] In the formula, M is the equivalent steering resistance torque of the steer-by-wire electro-hydraulic composite steering system, and λ is the weight.

[0078] Furthermore, in step S6, the relationship between the equivalent steering resistance torque and the simulated hand torque of the electro-hydraulic composite steering system is constructed based on the power assist characteristic curve of the electro-hydraulic composite steering system. Finally, the real-time simulated hand torque, i.e., the steering feel, is obtained based on the real-time estimated equivalent steering resistance torque of the steerable electro-hydraulic composite steering system. The specific method is as follows:

[0079] Step S6.1: Design a piecewise linear power assist characteristic curve to obtain the functional relationship between the electric power assist torque and the hand torque of the electric steering subsystem as follows:

[0080]

[0081] In the formula, T a The electric assist torque provided by the electric steering subsystem, T d T is the torque input to the steering wheel. d0 T is the steering wheel input torque corresponding to when power steering is started. dmax The steering wheel input torque is the maximum assist torque input to the system, and K(v) is a gain function related to vehicle speed. amax This is the maximum assist torque that the electric steering subsystem can output.

[0082] Furthermore, the gain function K(v) related to vehicle speed is obtained by fitting, as shown below:

[0083] K(v) = p1v 3 +p2v 2 +p3v+p4

[0084] In the formula, p1, p2, p3, and p4 are the coefficients of the gain function K(v).

[0085] Furthermore, based on the worm gear transmission ratio and the rated torque provided by the steering motor, the maximum electric assist torque provided by the electric steering subsystem is obtained. The formula for calculating the maximum electric assist torque is as follows:

[0086] T = i T

[0087] amax w mmax

[0088] In the formula, i w T is the worm gear transmission ratio. mmax The rated torque provided to the steering motor.

[0089] Step S6.2: Based on the functional relationship between the hydraulic assist and the hand torque of the hydraulic steering subsystem, obtain the hydraulic assist of the hydraulic steering subsystem under different hand torques, and then obtain the hydraulic assist torque T of the hydraulic steering subsystem. a2 The calculation formula is as follows:

[0090] T a2 =Fh R cs

[0091] In the formula, T a2 R is the hydraulic assist torque of the hydraulic steering subsystem. cs R is the radius of the gear sector.

[0092] Furthermore, the functional relationship between the hydraulic assist and the hand torque of the hydraulic steering subsystem is shown below:

[0093]

[0094] In the formula, p5, p6, p7, a, b, c, d are the coefficients of the function of hydraulic assist and hand torque, respectively, and F hmax Provides maximum assistance to the hydraulic steering subsystem.

[0095] The above F hmax The calculation is based on the maximum axial force generated in the steering gear screw-nut transmission pair and the maximum force acting on the rocker arm shaft gear sector, as shown in the following formula:

[0096] F hmax =F csmax -F Lmax

[0097] In the formula, F Lmax F is the maximum axial force on the nut in the screw-nut transmission pair. csmax This is the maximum force acting on the rocker arm shaft gear sector.

[0098] The formulas for calculating the axial force generated in the steering gear screw-nut transmission pair and the maximum force acting on the rocker arm shaft gear sector are as follows:

[0099]

[0100]

[0101] In the formula, η L η is the transmission efficiency of the screw-nut drive pair. g For the transmission efficiency of the steering linkage, i g This is the angular transmission ratio of the steering linkage.

[0102] Step S6.3: Based on the equivalent steering resistance torque M calculated in step S4.5, and the electric assist torque T provided by the electric steering subsystem in S6.1... a And the hydraulic assist torque T of the hydraulic steering subsystem in step S6.2 a2 The simulated hand torque is calculated using the following formula:

[0103]

[0104] in,

[0105] In the formula, T a1 The electric assist torque provided to the electric steering subsystem is equivalent to the torque on the gear sector.

[0106] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0107] This invention combines the equivalent steering resistance torque estimated by the motor model and the equivalent steering resistance torque estimated by the vehicle dynamics model, and uses the longitudinal velocity weighting method to obtain the equivalent steering resistance torque of the steerable electro-hydraulic hybrid steering system. Then, it combines the designed electric power assist characteristic curve and the hydraulic power assist characteristic curve to derive the power assist characteristic curve of the steerable electro-hydraulic hybrid steering system. Next, based on the power assist characteristic curve, it establishes the relationship between the steering resistance torque of the steerable electro-hydraulic hybrid steering system and the simulated hand torque. Finally, it obtains the real-time simulated hand torque based on the real-time estimated steering resistance torque of the steerable electro-hydraulic hybrid steering system. In the road feel planning method proposed in this invention, the combination of the equivalent steering resistance torque estimated by the motor model and the equivalent steering resistance torque estimated by the vehicle dynamics model, along with the longitudinal velocity weighting method, results in a more accurate estimated equivalent steering resistance torque for the steerable electro-hydraulic hybrid steering system, providing the driver with a clearer steering feel. Attached Figure Description

[0108] Figure 1 This is a schematic diagram of the road feel planning principle for steer-by-wire electro-hydraulic composite steering.

[0109] Figure 2 This is a schematic diagram of the principle for estimating the electrodynamic torque of the electric steering subsystem.

[0110] Figure 3 This is a schematic diagram of the rotary valve model in the hydraulic steering subsystem.

[0111] Figure 4 This is a schematic diagram of the steer-by-wire electro-hydraulic composite steering system. Detailed Implementation

[0112] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0113] This invention proposes a road feel simulation and planning method for steer-by-wire electro-hydraulic hybrid steering. The method flow is as follows: Figure 1 As shown, the specific steps are as follows:

[0114] Step S1 uses a linearly extended state observer to obtain the electrodynamic torque coupled to the steering input shaft of the electric steering subsystem;

[0115] Step S1.1 Obtain the current I of the steering motor based on the motor current sensor. a The output torque of the steering motor is calculated, and then an electro-torque estimation model is established based on the dynamic model of the steering system, as shown below:

[0116] T m =K m I a

[0117]

[0118] In the formula, J c B is the equivalent moment of inertia of the steering gear input shaft. c Let θ be the equivalent damping coefficient of the steering system. c T is the steering input shaft angle. EPS For the electric torque under the electric steering subsystem, i m K is the reduction ratio from the output shaft of the steering motor to the input shaft of the steering gear. m T is the electromagnetic torque coefficient of the steering motor. m For the steering motor to output torque, I a This is the current of the steering motor.

[0119] Step S1.2: Based on the electro-torque estimation model in step S1.1 above, a linear extended state observer is used to estimate the electro-torque of the electric steering subsystem. The electro-torque estimation principle diagram is shown below. Figure 2 As shown, the observer model is as follows:

[0120]

[0121] In the formula, x1=θ c , For the system's state variables, State variables x1, x2, and T are respectively. EPS The estimated values ​​are β1, β2, and β3, which are the gain coefficients of the observer, respectively.

[0122] Step S2: Based on the pressure difference of the power steering oil formed in the left and right chambers of the hydraulic power steering cylinder and the effective area of ​​the hydraulic cylinder piston, obtain the hydraulic pressure under the hydraulic steering subsystem;

[0123] Step S2.1: Calculate the hydraulic oil pump output flow rate based on the hydraulic oil pump flow coefficient and the pump motor speed. The calculation formula is as follows:

[0124] Q s =V p n mb

[0125] In the formula, Q s V is the output flow rate of the hydraulic oil pump. p n is the flow coefficient of the hydraulic oil pump. mb This refers to the speed of the oil pump motor.

[0126] Step S2.2: Based on the conservation of flow on the left and right sides of the hydraulic cylinder, determine the flow rate of the rotary valve into the left and right chambers of the hydraulic cylinder. The calculation formula is as follows:

[0127]

[0128] In the formula, Q A Q B These represent the flow rates from the rotary valve into the left and right chambers of the hydraulic cylinder, respectively. p X is the effective working area of ​​the piston. s This represents the piston displacement.

[0129] Step S2.3: The electric torque of the electric steering subsystem is transmitted to the torsion bar in the rotary valve. Based on the torque transmitted by the torsion bar, the rotary valve angle is calculated using the following formula:

[0130]

[0131] In the formula, k s For the torsion bar stiffness of the rotary valve, This refers to the torsion bar deformation angle, which is the valve rotation angle.

[0132] Step S2.4: Calculate the opening area of ​​each valve port of the rotary valve based on the rotation angle. The rotary valve model is as follows: Figure 3 As shown, the calculation formula is as follows:

[0133]

[0134] In the formula, R is the valve core and valve sleeve mating radius, W1 is the short notch width, W2 is the valve port pre-opening clearance width in the neutral position, L1 is the axial length of the short notch, L2 is the axial length of the valve port, and A j (j=1,2,3,4) represents the opening area of ​​each valve port of the rotary valve, where A1=A4, A2=A3.

[0135] Step S2.5: Based on the hydraulic pump output flow rate, the flow rate into the left and right chambers of the hydraulic cylinder from the rotary valve, and the opening area of ​​each valve port of the rotary valve, calculate the pressure difference of the booster oil formed in the left and right chambers of the hydraulic booster cylinder. The calculation formula is as follows:

[0136]

[0137] In the formula, ΔP is the pressure difference of the power steering oil formed in the left and right chambers of the hydraulic power steering cylinder, and P A ,P B These represent the pressures in the left and right chambers of the hydraulic cylinder, respectively.

[0138] Step S2.6: Based on the pressure difference of the power steering oil formed in the left and right chambers of the hydraulic power steering cylinder and the effective area of ​​the hydraulic cylinder piston, the hydraulic pressure under the hydraulic steering subsystem is calculated. The calculation formula is as follows:

[0139] F EHPS =ΔP·A p

[0140] The formula for calculating the effective area of ​​the hydraulic cylinder piston is as follows:

[0141]

[0142] In the formula, F EHPS D1 represents the hydraulic pressure in the hydraulic steering subsystem, D2 represents the piston diameter, and D3 represents the piston push rod diameter.

[0143] Step S3: Combine the electrodynamic torque of the electric steering subsystem obtained in step S1 and the hydraulic pressure of the hydraulic steering subsystem obtained in step S2 to obtain the equivalent steering resistance torque estimated based on the motor model.

[0144] Step S3.1: Based on the steering screw-steering nut transmission pair model, calculate the axial force on the nut in the steering screw-steering nut transmission pair. The calculation formula is shown below:

[0145] M l =T EPS

[0146]

[0147] In the formula, M l For the torque transmitted by the screw in the steering screw-steering nut transmission pair, F l η is the axial force on the nut in the steering screw-steering nut transmission pair. l Let P be the transmission efficiency of the steering screw-steering nut transmission pair, and P be the lead of the steering screw-steering nut transmission pair.

[0148] Step S3.2: Calculate the force acting on the rocker arm shaft gear sector. The calculation formula is as follows:

[0149]

[0150] In the formula, M s For the mass of the steering nut, X s =θ c P / 2π, B s F is the damping coefficient of the steering nut. cs This is the force acting on the rocker arm shaft gear sector.

[0151] Step S3.3: Calculate the steering resistance torque equivalent to the gear sector. The calculation formula is shown below:

[0152]

[0153] In the formula, J cs B is the equivalent rotational inertia from the gear sector to the rocker arm. cs θ is the equivalent damping coefficient from the gear sector to the rocker arm. cs Let θ be the rotation angle of the gear sector. cs =X s / R cs T p R is the equivalent steering resistance torque estimated on the gear sector based on the motor model. cs Let be the pitch circle radius of the gear sector.

[0154] Step S4: Based on information such as vehicle dynamic response and road adhesion conditions, the reaction force of the tire on the ground is obtained using the Dugoff tire model, and then the equivalent steering resistance torque is obtained based on the vehicle dynamics calculation method.

[0155] Step S4.1: Calculate the vertical force of each wheel based on the overall vehicle structural parameters. The calculation formula is shown below:

[0156]

[0157] In the formula, F zi (i = 1, 2, 3, 4) represent the vertical forces on each wheel (i = 1 represents the left front wheel, i = 2 represents the right front wheel, i = 3 represents the left rear wheel, and i = 4 represents the right rear wheel), m is the total mass of the vehicle, g is the acceleration due to gravity, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, and a x For longitudinal acceleration, a y denoted as lateral acceleration, h as the vehicle's center of gravity height, and B as the track width between the front and rear axles.

[0158] Step S4.2: Based on the tire vertical force, tire slip ratio, and tire slip angle, calculate the lateral force of each tire using the Dugoff tire model. The calculation formula is shown below:

[0159]

[0160] In the formula, F yi k represents the lateral force of each tire. y For tire lateral stiffness, s i For each tire's longitudinal slip ratio, α i The slip angle of each wheel.

[0161] in,

[0162]

[0163]

[0164]

[0165]

[0166] In the formula, δ i Let ω be the wheel turning angle, u be the longitudinal vehicle speed, v be the lateral vehicle speed, and ω be the lateral vehicle speed. r Let μ be the yaw rate, μ be the road adhesion coefficient, and k be the yaw rate. x For the longitudinal stiffness of the tire, u w Let ω be the velocity at the center of the tire. w ω is the tire angular velocity, and r is the tire rolling radius.

[0167] Step S4.3: Calculate the restoring torque related to the tire's vertical force based on the tire's vertical force. The calculation formula is shown below:

[0168]

[0169] In the formula, M zn (n=1,2) represents the steering resistance torque related to the vertical force of the left and right front tires, F. zn Let D be the vertical force on the left and right tires, θ be the kingpin inclination angle, and δ be the vertical force on the left and right tires. n The turning angles are for the left and right front wheels.

[0170] Step S4.4: Calculate the self-aligning torque related to the tire lateral force based on the tire lateral force. The calculation formula is as follows:

[0171] M y =(F y1 +F y2 )·(t c +t n )

[0172] Among them, t n =rtanθ cas +r co

[0173] In the formula, M y F is the steering resistance torque related to the lateral force of the tire. y1 F y2 The lateral forces on the left and right front wheels are t, respectively. c For mechanical drag torque, t n The tire drag torque is r, the wheel rolling radius is θ. cas Kingpin caster angle, r co This is the longitudinal offset of the kingpin at the wheel center.

[0174] Step S4.5: Calculate the equivalent steering resistance torque based on the vehicle dynamics calculation method. The calculation formula is as follows:

[0175]

[0176] In the formula, M p For the equivalent steering resistance torque calculated based on vehicle dynamics, i s η is the transmission ratio from the wheel to the rocker arm. s For transmission efficiency.

[0177] Step S5: Obtain the equivalent steering resistance torque of the steer-by-wire electro-hydraulic composite steering system according to the longitudinal velocity weighting method;

[0178] The longitudinal velocity weighting method yields the following calculation method for the equivalent steering resistance torque of the steer-by-wire electro-hydraulic hybrid steering system:

[0179] M=λT p +(1-λ)M p

[0180] in,

[0181] In the formula, M is the equivalent steering resistance torque of the steer-by-wire electro-hydraulic composite steering system, and λ is the weight.

[0182] Step S6 establishes the relationship between the equivalent steering resistance torque and the simulated hand torque of the electro-hydraulic composite steering system based on the power assist characteristic curve of the electro-hydraulic composite steering system; finally, the real-time simulated hand torque, i.e., steering feel, is obtained based on the real-time estimated equivalent steering resistance torque of the steerable electro-hydraulic composite steering system.

[0183] Step S6.1: Design a piecewise linear power assist characteristic curve to obtain the functional relationship between the electric power assist torque and the hand torque of the electric steering subsystem as follows:

[0184]

[0185] In the formula, T a The electric assist torque provided by the electric steering subsystem, T d T is the torque input to the steering wheel. d0 T is the steering wheel input torque corresponding to when power steering is started. dmax The steering wheel input torque is the maximum assist torque input to the system, and K(v) is a gain function related to vehicle speed. amax This is the maximum assist torque that the electric steering subsystem can output.

[0186] Furthermore, the gain function K(v) related to vehicle speed is obtained by fitting, as shown below:

[0187] K(v) = p1v 3 +p2v2 +p3v+p4

[0188] In the formula, p1, p2, p3, and p4 are the coefficients of the gain function K(v).

[0189] Furthermore, based on the worm gear transmission ratio and the rated torque provided by the steering motor, the maximum electric assist torque provided by the electric steering subsystem is obtained. The formula for calculating the maximum electric assist torque is as follows:

[0190] T = i T

[0191] amax w mmax

[0192] In the formula, i w T is the worm gear transmission ratio. mmax The rated torque provided to the steering motor.

[0193] Step S6.2: Based on the functional relationship between the hydraulic assist and the hand torque of the hydraulic steering subsystem, obtain the hydraulic assist of the hydraulic steering subsystem under different hand torques, and then obtain the hydraulic assist torque T of the hydraulic steering subsystem. a2 The calculation formula is as follows:

[0194] T a2 =F h R cs

[0195] In the formula, T a2 R is the hydraulic assist torque of the hydraulic steering subsystem. cs R is the radius of the gear sector.

[0196] Furthermore, the functional relationship between the hydraulic assist and the hand torque of the hydraulic steering subsystem is shown below:

[0197]

[0198] In the formula, p5, p6, p7, a, b, c, d are the coefficients of the function of hydraulic assist and hand torque, respectively, and F hmax Provides maximum assistance to the hydraulic steering subsystem.

[0199] The above F hmax The calculation is based on the maximum axial force generated in the steering gear screw-nut transmission pair and the maximum force acting on the rocker arm shaft gear sector, as shown in the following formula:

[0200] F hmax =F csmax -F Lmax

[0201] In the formula, F Lmax F is the maximum axial force on the nut in the screw-nut transmission pair. csmaxThis is the maximum force acting on the rocker arm shaft gear sector.

[0202] The formulas for calculating the axial force generated in the steering gear screw-nut transmission pair and the maximum force acting on the rocker arm shaft gear sector are as follows:

[0203]

[0204]

[0205] In the formula, η L η is the transmission efficiency of the screw-nut drive pair. g For the transmission efficiency of the steering linkage, i g This is the angular transmission ratio of the steering linkage.

[0206] Step S6.3: Based on the equivalent steering resistance torque M calculated in S4.5, the electric assist torque T provided by the electric steering subsystem in step S6.1... a And the hydraulic assist torque T of the hydraulic steering subsystem in step S6.2 a2 The simulated hand torque is calculated using the following formula:

[0207]

[0208] in,

[0209] In the formula, T a1 The electric assist torque provided to the electric steering subsystem is equivalent to the torque on the gear sector.

[0210] A schematic diagram of the steer-by-wire electro-hydraulic hybrid steering system is shown below. Figure 4 As shown, the system includes a road feel simulation assembly, an electric steering subsystem, and a hydraulic steering subsystem. The road feel simulation assembly includes a steering wheel, a road feel motor, and a reduction gear 1; its main function is to execute the planned steering torque, providing the driver with simulated steering hand torque. The electric steering subsystem includes a steering motor, a reduction gear 2, and a steering angle sensor; the hydraulic steering subsystem consists of a recirculating ball steering gear assembly, a hydraulic pump, and an oil pump motor. The electric steering subsystem and the hydraulic steering subsystem are connected via the steering gear input shaft, working together to overcome steering resistance torque and achieve angular following of the steering wheel.

[0211] The above embodiments are only used to illustrate the design concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A road feel planning method for steer-by-wire electro-hydraulic hybrid steering, characterized in that, The steps include the following: Step S1: Obtain the electrodynamic torque coupled to the steering input shaft of the electric steering subsystem using the linear extended state observer; Step S2: Based on the pressure difference of the power steering oil formed in the left and right chambers of the hydraulic power steering cylinder and the effective area of ​​the hydraulic cylinder piston, obtain the hydraulic pressure under the hydraulic steering subsystem; Step S3: Based on the combination of the electrodynamic torque obtained in step S1 under the electric steering subsystem and the hydraulic pressure obtained in step S2 under the hydraulic steering subsystem, the equivalent steering resistance torque estimated based on the motor model is obtained. Step S4: Based on the vehicle dynamic response and road adhesion condition information, the reaction force of the tire on the ground is obtained using the Dugoff tire model, and then the equivalent steering resistance torque is obtained based on the vehicle dynamics calculation method. Step S5: Obtain the equivalent steering resistance torque of the steer-by-wire electro-hydraulic composite steering system according to the longitudinal velocity weighting method; Step S6: Construct the relationship between the steering resistance torque and the simulated hand torque of the electro-hydraulic composite steering system based on the power assist characteristic curve of the electro-hydraulic composite steering system. Finally, obtain the real-time simulated hand torque, i.e., steering feel, based on the real-time estimated equivalent steering resistance torque of the steerable electro-hydraulic composite steering system.

2. The road feel planning method for steer-by-wire electro-hydraulic composite steering according to claim 1, characterized in that, The calculation method for the electrodynamic torque in step S1 is as follows: Step S1.1: Obtain the current I of the steering motor from the motor current sensor. a The output torque of the steering motor is calculated, and then an electro-torque estimation model is established based on the dynamic model of the steering system, as shown below: T m =K m I a In the formula, J c B is the equivalent moment of inertia of the steering gear input shaft. c Let θ be the equivalent damping coefficient of the steering system. c T is the steering input shaft angle. EPS For the electric torque under the electric steering subsystem, i m K is the reduction ratio from the output shaft of the steering motor to the input shaft of the steering gear. m T is the electromagnetic torque coefficient of the steering motor. m For the steering motor to output torque, I a This refers to the current of the steering motor; Step S1.2: Based on the electrodynamic torque estimation model in S1.1 above, a linear extended state observer is used to estimate the electrodynamic torque of the electric steering subsystem. The observer model is shown below: In the formula, x1=θ c , For the system's state variables, State variables x1, x2, and T are respectively. EPS The estimated values ​​are β1, β2, and β3, which are the gain coefficients of the observer, respectively.

3. The road feel planning method for steer-by-wire electro-hydraulic composite steering according to claim 1, characterized in that, The method for calculating hydraulic pressure in step S2 is as follows: Step S2.1: Calculate the hydraulic oil pump output flow rate based on the hydraulic oil pump flow coefficient and the pump motor speed. The calculation formula is as follows: Q s =V p n mb In the formula, Q s V is the output flow rate of the hydraulic oil pump. p n is the flow coefficient of the hydraulic oil pump. mb This refers to the oil pump motor speed. Step S2.2: Based on the conservation of flow on the left and right sides of the hydraulic cylinder, determine the flow rate of the rotary valve into the left and right chambers of the hydraulic cylinder. The calculation formula is as follows: In the formula, Q A Q B These represent the flow rates from the rotary valve into the left and right chambers of the hydraulic cylinder, respectively. p X is the effective working area of ​​the piston. s This represents piston displacement; Step S2.3: The electric torque of the electric steering subsystem is transmitted to the torsion bar in the rotary valve. Based on the torque transmitted by the torsion bar, the rotary valve angle is calculated using the following formula: In the formula, k s For the torsion bar stiffness of the rotary valve, This refers to the torsion bar deformation angle, which is the valve rotation angle. Step S2.4: Calculate the opening area of ​​each valve port of the rotary valve based on the rotation angle of the rotary valve. The calculation formula is shown below: In the formula, R is the valve core and valve sleeve mating radius, W1 is the short notch width, W2 is the valve port pre-opening clearance width in the neutral position, L1 is the axial length of the short notch, L2 is the axial length of the valve port, and A j (j=1,2,3,4) represents the opening area of ​​each valve port of the rotary valve, where A1=A4, A2=A3. Step S2.5: Based on the hydraulic pump output flow rate, the flow rate into the left and right chambers of the hydraulic cylinder from the rotary valve, and the opening area of ​​each valve port of the rotary valve, calculate the pressure difference of the booster oil formed in the left and right chambers of the hydraulic booster cylinder. The calculation formula is as follows: In the formula, ΔP is the pressure difference of the power steering oil formed in the left and right chambers of the hydraulic power steering cylinder, and P A ,P B These are the pressures in the left and right chambers of the hydraulic cylinder, respectively. Step S2.6: Based on the pressure difference of the power steering oil formed in the left and right chambers of the hydraulic power steering cylinder and the effective area of ​​the hydraulic cylinder piston, the hydraulic pressure under the hydraulic steering subsystem is calculated. The calculation formula is as follows: F EHPS =ΔP·A p The formula for calculating the effective area of ​​the hydraulic cylinder piston is as follows: In the formula, F EHPS D1 represents the hydraulic pressure in the hydraulic steering subsystem, D2 represents the piston diameter, and D3 represents the piston push rod diameter.

4. The road feel planning method for steer-by-wire electro-hydraulic composite steering according to claim 1, characterized in that, The method for calculating the equivalent steering resistance torque based on the motor model in step S3 is as follows: Step S3.1: Based on the steering screw-steering nut transmission pair model, calculate the axial force on the nut in the steering screw-steering nut transmission pair. The calculation formula is shown below: M l =T EPS In the formula, M l For the torque transmitted by the screw in the steering screw-steering nut transmission pair, F l η is the axial force on the nut in the steering screw-steering nut transmission pair. l Let P be the transmission efficiency of the steering screw-steering nut transmission pair, and let P be the lead of the steering screw-steering nut transmission pair. Step S3.2: Calculate the force acting on the rocker arm shaft gear sector. The calculation formula is as follows: In the formula, M s For the mass of the steering nut, B s X is the damping coefficient of the steering nut. s =θ c P / 2π, F cs This refers to the force acting on the rocker arm shaft gear sector; Step S3.3: Calculate the steering resistance torque equivalent to the gear sector. The calculation formula is shown below: In the formula, J cs B is the equivalent rotational inertia from the gear sector to the rocker arm. cs θ is the equivalent damping coefficient from the gear sector to the rocker arm. cs Let θ be the rotation angle of the gear sector. cs =X s / R cs T p R is the equivalent steering resistance torque estimated on the gear sector based on the motor model. cs Let be the pitch circle radius of the gear sector.

5. The road feel planning method for steer-by-wire electro-hydraulic composite steering according to claim 1, characterized in that, The method for calculating the equivalent steering resistance torque based on dynamics in step S4 is as follows: Step S4.1: Calculate the vertical force of each wheel based on the overall vehicle structural parameters. The calculation formula is shown below: In the formula, F zi (i = 1, 2, 3, 4) represent the vertical forces on each wheel (i = 1 represents the left front wheel, i = 2 represents the right front wheel, i = 3 represents the left rear wheel, and i = 4 represents the right rear wheel), m is the total mass of the vehicle, g is the acceleration due to gravity, a is the distance from the center of mass to the front axle, b is the distance from the center of mass to the rear axle, and a x For longitudinal acceleration, a y denoted as lateral acceleration, h as the vehicle's center of gravity height, and B as the track width between the front and rear axles; Step S4.2: Based on the tire vertical force, tire slip ratio, and tire slip angle, calculate the lateral force of each tire using the Dugoff tire model. The calculation formula is shown below: In the formula, F yi k represents the lateral force of each tire. y For tire lateral stiffness, s i For each tire's longitudinal slip ratio, α i For each wheel slip angle, in, In the formula, δ i Let ω be the wheel turning angle, u be the longitudinal vehicle speed, v be the lateral vehicle speed, and ω be the lateral vehicle speed. r Let μ be the yaw rate, μ be the road adhesion coefficient, and k be the yaw rate. x For the longitudinal stiffness of the tire, u w Let ω be the velocity at the center of the tire. w ω is the tire angular velocity, and r is the tire rolling radius; Step S4.3: Calculate the restoring torque related to the tire's vertical force based on the tire's vertical force. The calculation formula is shown below: In the formula, M zn (n=1,2) represents the steering resistance torque related to the vertical force of the left and right front tires, F. zn Let D be the vertical force on the left and right tires, θ be the kingpin inclination angle, and δ be the vertical force on the left and right tires. n The turning angle of the left and right front wheels; Step S4.4: Calculate the self-aligning torque related to the tire lateral force based on the tire lateral force. The calculation formula is as follows: M y =(F y1 +F y2 )·(t c +t n ) Among them, t n =rtanθ cas +r co , In the formula, M y F is the steering resistance torque related to the lateral force of the tire. y1 F y2 The lateral forces on the left and right front wheels are t, respectively. c For mechanical drag torque, t n The tire drag torque is r, the wheel rolling radius is θ. cas Kingpin caster angle, r co This refers to the longitudinal offset of the kingpin at the wheel center. Step S4.5: Calculate the equivalent steering resistance torque based on the vehicle dynamics calculation method. The calculation formula is as follows: In the formula, M p For the equivalent steering resistance torque calculated based on vehicle dynamics, i s η is the transmission ratio from the wheel to the rocker arm. s For transmission efficiency.

6. The road feel planning method for steer-by-wire electro-hydraulic composite steering according to claim 1, characterized in that, The calculation method for the equivalent steering resistance torque of the steer-by-wire electro-hydraulic composite steering system obtained by the longitudinal velocity weighting method in step S5 is as follows: M=λT p +(1-λ)M p , in, , In the formula, M is the equivalent steering resistance torque of the steer-by-wire electro-hydraulic composite steering system, and λ is the weight.

7. The road feel planning method for steer-by-wire electro-hydraulic composite steering according to claim 1, characterized in that, Step S6 establishes the relationship between the steering resistance torque and simulated hand torque of the electro-hydraulic composite steering system based on the power assist characteristic curve of the electro-hydraulic composite steering system; finally, it obtains the real-time simulated hand torque, i.e., steering feel, based on the real-time estimated equivalent steering resistance torque of the steerable electro-hydraulic composite steering system. The specific method is as follows: Step S6.1: Design a piecewise linear power assist characteristic curve to obtain the functional relationship between the electric power assist torque and the hand torque of the electric steering subsystem as follows: ， In the formula, T a The electric assist torque provided by the electric steering subsystem, T d T is the torque input to the steering wheel. d0 T is the steering wheel input torque corresponding to when power steering is started. dmax The steering wheel input torque is the maximum assist torque input to the system, K(v) is the gain function related to vehicle speed, and T is the steering wheel input torque. amax This is the maximum assist torque that the electric steering subsystem can output. Furthermore, the gain function K(v) related to vehicle speed is obtained by fitting, as shown below: K(v)=p1v 3 +p2v 2 +p3v+p4 In the formula, p1, p2, p3, and p4 are the coefficients of the gain function K(v), respectively. Furthermore, based on the worm gear transmission ratio and the rated torque provided by the steering motor, the maximum electric assist torque provided by the electric steering subsystem is obtained. The formula for calculating the maximum electric assist torque is as follows: T amax =i w T mmax In the formula, i w T is the worm gear transmission ratio. mmax Rated torque provided to the steering motor; Step S6.2: Based on the functional relationship between the hydraulic assist and the hand torque of the hydraulic steering subsystem, obtain the hydraulic assist of the hydraulic steering subsystem under different hand torques, and then obtain the hydraulic assist torque T of the hydraulic steering subsystem. a2 The calculation formula is as follows: T a2 =F h R cs , In the formula, T a2 R is the hydraulic assist torque of the hydraulic steering subsystem. cs Where is the radius of the gear sector. Furthermore, the functional relationship between the hydraulic assist and the hand torque of the hydraulic steering subsystem is shown below: In the formula, p5, p6, p7, a, b, c, d are the coefficients of the function of hydraulic assist and hand torque, respectively, and F hmax The maximum assistance provided to the hydraulic steering subsystem The above F hmax The calculation is based on the maximum axial force generated in the steering gear screw-nut transmission pair and the maximum force acting on the rocker arm shaft gear sector, as shown in the following formula: F hmax =F csmax -F Lmax , In the formula, F Lmax F is the maximum axial force on the nut in the screw-nut transmission pair. csmax The maximum force acting on the rocker arm shaft gear sector, The formulas for calculating the axial force generated in the steering gear screw-nut transmission pair and the maximum force acting on the rocker arm shaft gear sector are as follows: In the formula, η L η is the transmission efficiency of the screw-nut drive pair. g For the transmission efficiency of the steering linkage, i g The angular transmission ratio of the steering linkage; Step S6.3: Based on the equivalent steering resistance torque M calculated in S4.5, and the electric assist torque T provided by the electric steering subsystem in S6.1... a And the hydraulic assist torque T of the hydraulic steering subsystem in S6.2 a2 The simulated hand torque is calculated using the following formula: in, , In the formula, T a1 The electric assist torque provided to the electric steering subsystem is equivalent to the torque on the gear sector.

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