Abrupt slope slow descent system based on energy recovery

Abstract

The invention discloses an abrupt slope slow descent system based on energy recovery, and particularly relates to the technical field of vehicle control, and the system comprises a slope estimation module which receives a vehicle speed signal and a vehicle acceleration signal, and estimates the current slope of a vehicle through the vehicle speed signal and the vehicle acceleration signal; the abrupt slope slow descent activation judgment module is used for receiving a slope signal, a vehicle gear signal, a brake pedal signal, an accelerator pedal signal, a driving direction signal and a driving mode signal; when the vehicle is on the slope, a brake pedal and an accelerator pedal are not stepped on, and the vehicle speed is within a vehicle speed threshold interval, the abrupt slope slow descent function is activated, and otherwise, the abrupt slope slow descent function exits; the target vehicle speed calculation module identifies the intention of the driver and gives a target vehicle speed; and the electromechanical braking force distribution module introduces feedforward control through a gradient signal firstly, then gives target braking force by superposing closed-loop control of a target vehicle speed, and then distributes the braking force to electric braking and mechanical braking to realize energy recovery and caliper braking respectively.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle control, and in particular to a steep slope descent system based on energy recovery. Background Art

[0002] Hill Descent Control is primarily used for descending steep or continuous slopes. The driver can release the accelerator and brake pedals, and the braking system actively builds pressure to control the vehicle, maintaining the target speed and allowing it to smoothly negotiate the downhill slope. Once activated, the vehicle's speed can be stabilized without pressing the brake or accelerator pedals, allowing the driver to fully focus on steering, improving driving safety. To reduce the operational complexity of downhill driving in vehicles with active boost systems such as ESC, OneBox, and EMB, numerous researchers and companies have proposed control algorithms and devices for hill descent control.

[0003] Regarding the control method for the hill descent function, publication number CN117755094A proposes determining the activation of the hill descent system by determining whether the hill descent conditions are met. It details the entry and exit conditions of the function, including gear position, slope, vehicle speed, hill descent on / off, and how the target vehicle speed changes based on the accelerator and brake pedals. Publication number CN117400886A mainly explains how to determine the target vehicle speed when the hill descent function is activated. Publication number CN116985770A shortens the pressure buildup time after the hill descent function is activated by establishing a pre-filled brake hydraulic pressure, allowing the vehicle to brake promptly after the hill descent function is activated. However, the calculation of the target vehicle speed is not detailed. None of the above patents provide detailed information on how to control the vehicle's braking force.

[0004] Publication No. CN117533276A describes how to control vehicle braking force using yaw angular acceleration. However, the patent performs closed-loop pressure regulation based on driver demand to control the vehicle speed to reach the target speed smoothly and quickly. It lacks feedforward control and does not describe slope recognition.

[0005] In addition, long-term triggering of the steep slope descent function can easily lead to high temperatures in the brake disc, which in turn reduces braking efficiency and even causes vehicle brake failure, seriously affecting driving safety. Summary of the Invention

[0006] To this end, the present invention provides a steep slope descent system based on energy recovery to solve the problems raised in the background technology.

[0007] In order to achieve the above-mentioned object, the present invention provides the following technical solution: a steep slope descent system based on energy recovery, comprising:

[0008] A slope estimation module receives a vehicle speed signal and a vehicle acceleration signal, and estimates the current slope of the vehicle based on the vehicle speed and vehicle acceleration signals;

[0009] The steep hill descent activation judgment module receives the slope signal, vehicle gear signal, brake pedal signal, accelerator pedal signal, driving direction signal and driving mode signal; when the vehicle is on a slope, the brake pedal and accelerator pedal are not pressed, and the vehicle speed is within the speed threshold range, the steep hill descent function is activated; otherwise, the steep hill descent function is deactivated;

[0010] Target speed calculation module, which identifies the driver's intention and gives the target speed;

[0011] The electromechanical braking force distribution module first introduces feedforward control through the slope signal, then superimposes the closed-loop control of the target vehicle speed to give the target braking force, and then distributes the braking force to the electric brake and mechanical brake to achieve energy recovery and caliper braking respectively.

[0012] Preferably, the slope estimation module collects vehicle driving information and current posture through inertial sensors and wheel speed sensors, wherein the inertial sensors obtain the vehicle's lateral acceleration and longitudinal acceleration, and the wheel speed sensors obtain the vehicle's wheel speed and vehicle speed and calculate the current slope;

[0013] When the vehicle is stationary on a slope, the signal obtained by the inertial sensor is equal to the decomposition value of the gravity acceleration along the road surface:

[0014] a xs =gsin(θ) (1.1)

[0015] θ: slope angle; g: acceleration due to gravity;

[0016] The slope value i calculated by the inertial sensor slope method is s for:

[0017]

[0018] a xf : The acceleration value along the x-axis measured by the inertial sensor;

[0019] When the vehicle accelerates or decelerates on a slope, the signals obtained by the inertial sensor include gravity acceleration and inertial acceleration;

[0020] Inertial acceleration is the differential of vehicle speed:

[0021]

[0022] a x_IMU =a i +a xs (1.4)

[0023]

[0024] a i : The differential of the vehicle speed, representing the longitudinal acceleration of the vehicle; a x_IMU Get the x-axis acceleration value for the inertial acceleration sensor; a xs is the acceleration along the ramp generated by the ramp; is the differential of vehicle speed;

[0025] The slope is therefore:

[0026]

[0027] δ is the direction of movement, forward is 1, backward is -1; i s is the slope;

[0028] Preferably,

[0029] When a vehicle accelerates or decelerates on a slope, the signal obtained by the inertial sensor includes gravity acceleration and inertial acceleration; gravity acceleration will include the slope and vehicle pitch angle and add pitch angle correction;

[0030] The pitch angle is calculated from the acceleration due to gravity and inertia, as well as the vehicle's suspension stiffness:

[0031] α=K r (δa i +a xs ) (1.7)K r Represents the strength of the suspension; α is the vehicle pitch angle;

[0032] a xs =gsin(θ+α)

[0033]

[0034] The slope is therefore:

[0035]

[0036] Preferably, the steep slope descent activation determination module determines whether to trigger the steep slope descent instruction according to the vehicle driving information and the current slope, and determines the target speed in response to the steep slope descent instruction;

[0037] The specific operations are as follows:

[0038] When the vehicle is in motion and not stationary, including moving forward or backward, with a speed between 4 and 39 km / h and a slope between 8% and 100%, and no active or passive safety features are engaged, including ADAS, ABS, and AEB; the driver does not control the accelerator or brake pedal, the hill descent control function is activated, and the vehicle is traveling at a low speed using the target speed at the moment the hill descent control function is engaged;

[0039] determining a vehicle brake pressure according to a target speed and a current acceleration, and controlling the vehicle to decelerate according to the vehicle brake pressure when a steep slope descent execution instruction is received;

[0040] When the vehicle speed is higher than the target speed, or the slope is between 0% and 8%, or the active and passive safety functions intervene, the vehicle's steep slope descent function will exit.

[0041] Preferably,

[0042] Target speed calculation:

[0043] Target vehicle speed when hill descent control is activated: The vehicle speed at the moment of hill descent control intervention is the target vehicle speed V Tar =V start ;

[0044] V Tar represents the target vehicle speed, V start The vehicle speed at the moment of intervention for steep slope descent;

[0045] Target vehicle speed when pressing the accelerator: Press the accelerator pedal, the target vehicle speed increases, V tar_k =V tar_k-1 +p k *Acc_Pedal;

[0046] Target vehicle speed when braking: When the brake pedal is pressed, the target vehicle speed decreases, V tar_k =V tar_k-1 -p k *Brk_Pedal;

[0047] V tar_k is the target vehicle speed at the current moment, V tar_k-1 is the target vehicle speed at the next moment; p k is a calibratable coefficient, Acc_Pedal is the accelerator pedal opening, and Brk_Pedal is the brake pedal opening.

[0048] Preferably, the electromechanical braking force distribution module takes the driving and braking forces as inputs, ignoring wind resistance and rolling resistance, and outputs the vehicle speed. According to Newton's second law:

[0049]

[0050] F xIt is the comprehensive sum of the longitudinal forces acting on the vehicle, i.e. the sum of the electric braking force and the mechanical braking force;

[0051] Then the differential equation of the whole vehicle is:

[0052]

[0053] m is the vehicle mass;

[0054] Using Laplace transform, we can get the longitudinal speed control system of the vehicle:

[0055]

[0056] Where,

[0057] The gravity component caused by wind resistance, rolling resistance, and ramp is equivalent to external disturbance;

[0058] After adding external perturbation:

[0059]

[0060] F i It is external disturbances such as wind resistance, rolling resistance, and gravity component caused by ramps;

[0061] For the system after adding external disturbance to the longitudinal vehicle speed control system, the steady-state error caused is:

[0062]

[0063] F i (s) is the external disturbance input, H(s) is the control input;

[0064] For input disturbances, rolling resistance and wind resistance can be ignored, and a feedforward control of N(s) is added;

[0065] Then the closed-loop transfer function for interference is formed:

[0066]

[0067] N(s) is a feedforward control input; Represents the response of vehicle speed to external disturbance input;

[0068] Therefore, let G(s)+G(s)N(s)=0 to eliminate the steady-state error; H(s) selects PI control.

[0069] Preferably,

[0070] Feedforward control:

[0071] F b1=mgsin(θ) (1.16)

[0072] F b1 is the braking force calculated from the slope, θ is the slope;

[0073] Feedback control:

[0074] F b2 =K p V err +K i ∫V err (1.17)

[0075] V err =V Tar -V real (1.18)

[0076] F b2 is the braking force part of the closed-loop speed control, K p , K i is the coefficient of PI, V err is the difference between the target speed and the actual speed, V real is the real vehicle speed;

[0077] Anti-pitch control:

[0078] F b3 =K p a τ +K i ∫a τ (1.19)

[0079] a τ =gsin(α) (1.20)

[0080] F b3 is the braking force against pitching, a τ is the acceleration caused by pitching, and α is the pitch angle.

[0081] Combining the three controls, the output is:

[0082] F b =F b1 +F b2 +F b3 (1.21)

[0083] F b braking force for the overall goal;

[0084] After obtaining the total target braking force, the electric braking and mechanical braking forces are distributed according to the following principles:

[0085] When the target braking force is less than the maximum force provided by the electric brake, the electric brake is equal to the target braking force and the mechanical braking force is 0; when the target braking force is greater than the maximum force provided by the electric brake, the electric brake takes the maximum force that the electric brake can provide, and the mechanical brake = target braking force - electric brake force;

[0086]

[0087] F emax F is the maximum braking force that the motor can provide. m is the mechanical braking force, F e For electric braking force.

[0088] The present invention has the following advantages:

[0089] 1. Even without a slope sensor, the system of the present invention can accurately estimate the slope of a downhill slope. Vehicle speed information is derived from the wheel speeds, and the inertial acceleration is derived from the differential of the speed, disabling the hill descent control function. The vehicle's pitch angle is estimated from the acceleration due to gravity, inertia, and suspension stiffness. The slope value is then calculated by subtracting the inertial acceleration and the acceleration at the pitch angle from the signal obtained by the IMU.

[0090] 2. The present invention optimizes the target vehicle speed and associates it with the accelerator and brake pedals. When the driver steps on the accelerator pedal, the target vehicle speed gradually increases. When the target vehicle speed exceeds the upper speed limit, the steep hill descent system is exited; when the driver steps on the brake pedal, the target vehicle speed gradually decreases. When the target vehicle speed falls below the lower speed limit, the steep hill descent system is exited; when the slope disappears or active and passive safety functions such as ADAS, ABS, and AEB intervene, the vehicle's steep hill descent function is exited.

[0091] 3. The present invention uses control theory to analyze the presence of disturbances and steady-state errors in the hill descent control system. By introducing a feedforward term, the system can reach a stable state more quickly, eliminating the steady-state error. By analyzing the vehicle's dynamic characteristics on steep slopes and deriving a differential equation for the entire vehicle, it is determined that the steady-state error is real. Therefore, feedforward control is introduced to eliminate the steady-state error. This feedforward control is based entirely on slope information. Compared to traditional closed-loop speed-only control, it achieves faster and more accurate braking control, smoothly implementing the vehicle's hill descent function.

[0092] 4. The present invention combines energy recovery and allocates it to electric braking first after obtaining the target braking force. When the electric braking is insufficient, it is allocated to mechanical braking, thereby avoiding the problem of thermal failure caused by overheating of the brake disc during long downhill slopes. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 A schematic diagram of the external disturbance structure provided by the present invention;

[0094] Figure 2 A schematic diagram of the feedforward control structure provided by the present invention;

[0095] Figure 3 This is a schematic diagram of the logical architecture of the energy recovery steep slope descent system provided by the present invention. DETAILED DESCRIPTION

[0096] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0097] The present invention discloses a steep slope descent system based on energy recovery, comprising:

[0098] A slope estimation module receives a vehicle speed signal and a vehicle acceleration signal, and estimates the current slope of the vehicle based on the vehicle speed and vehicle acceleration signals;

[0099] The steep hill descent activation judgment module receives the slope signal, vehicle gear signal, brake pedal signal, accelerator pedal signal, driving direction signal and driving mode signal; when the vehicle is on a slope, the brake pedal and accelerator pedal are not pressed, and the vehicle speed is within the speed threshold range, the steep hill descent function is activated; otherwise, the steep hill descent function is deactivated;

[0100] Target speed calculation module, which identifies the driver's intention and gives the target speed;

[0101] The electromechanical braking force distribution module first introduces feedforward control through the slope signal, then superimposes the closed-loop control of the target vehicle speed to give the target braking force, and then distributes the braking force to the electric brake and mechanical brake to achieve energy recovery and caliper braking respectively.

[0102] Preferably, the slope estimation module collects vehicle driving information and current posture through inertial sensors and wheel speed sensors, wherein the inertial sensors obtain the vehicle's lateral acceleration and longitudinal acceleration, and the wheel speed sensors obtain the vehicle's wheel speed and vehicle speed and calculate the current slope;

[0103] When the vehicle is stationary on a slope, the signal obtained by the inertial sensor is equal to the decomposition value of the gravity acceleration along the road surface:

[0104] a xs =gsin(θ) (1.1)

[0105] θ: slope angle; g: acceleration due to gravity;

[0106] The slope value i calculated by the inertial sensor slope method is s for:

[0107]

[0108] a xf : The acceleration value along the x-axis measured by the inertial sensor;

[0109] When the vehicle accelerates or decelerates on a slope, the signals obtained by the inertial sensor include gravity acceleration and inertial acceleration;

[0110] Inertial acceleration is the differential of vehicle speed:

[0111]

[0112] a x_IMU =a i +a xs (1.4)

[0113]

[0114] a i : The differential of the vehicle speed, representing the longitudinal acceleration of the vehicle; a x_IMU Get the x-axis acceleration value for the inertial acceleration sensor; a xs is the acceleration along the ramp generated by the ramp; is the differential of vehicle speed;

[0115] The slope is therefore:

[0116]

[0117] δ is the direction of movement, forward is 1, backward is -1; i s is the slope;

[0118] Preferably,

[0119] When a vehicle accelerates or decelerates on a slope, the signal obtained by the inertial sensor includes gravity acceleration and inertial acceleration; gravity acceleration will include the slope and vehicle pitch angle and add pitch angle correction;

[0120] The pitch angle is calculated from the acceleration due to gravity and inertia, as well as the vehicle's suspension stiffness:

[0121] α=K r (δa i +a xs ) (1.7)

[0122] K r Represents the strength of the suspension; α is the vehicle pitch angle;

[0123] a xs =gsin(θ+α)

[0124]

[0125] The slope is therefore:

[0126]

[0127] Preferably, the steep slope descent activation determination module determines whether to trigger the steep slope descent instruction according to the vehicle driving information and the current slope, and determines the target speed in response to the steep slope descent instruction;

[0128] The specific operations are as follows:

[0129] When the vehicle is in motion and not stationary, including moving forward or backward, with a speed between 4 and 39 km / h and a slope between 8% and 100%, and no active or passive safety features are engaged, including ADAS, ABS, and AEB; the driver does not control the accelerator or brake pedal, the hill descent control function is activated, and the vehicle is traveling at a low speed using the target speed at the moment the hill descent control function is engaged;

[0130] determining a vehicle brake pressure according to a target speed and a current acceleration, and controlling the vehicle to decelerate according to the vehicle brake pressure when a steep slope descent execution instruction is received;

[0131] When the vehicle speed is higher than the target speed, or the slope is between 0% and 8%, or the active and passive safety functions intervene, the vehicle's steep slope descent function will exit.

[0132] Preferably,

[0133] Target speed calculation:

[0134] Target vehicle speed when hill descent control is activated: The vehicle speed at the moment of hill descent control intervention is the target vehicle speed V Tar =V start ;

[0135] V Tar represents the target vehicle speed, V start The vehicle speed at the moment of intervention for steep slope descent;

[0136] Target vehicle speed when pressing the accelerator: Press the accelerator pedal, the target vehicle speed increases, V tar_k =V tar_k-1 +p k *Acc_Pedal;

[0137] Target vehicle speed when braking: When the brake pedal is pressed, the target vehicle speed decreases, V tar_k =V tar_k-1 -p k *Brk_Pedal;

[0138] V tar_k is the target vehicle speed at the current moment, V tar_k-1 is the target vehicle speed at the next moment; p k is a calibratable coefficient, Acc_Pedal is the accelerator pedal opening, and Brk_Pedal is the brake pedal opening.

[0139] Preferably, the electromechanical braking force distribution module takes the driving and braking forces as inputs, ignoring wind resistance and rolling resistance, and outputs the vehicle speed. According to Newton's second law:

[0140]

[0141] F x It is the comprehensive sum of the longitudinal forces acting on the vehicle, i.e. the sum of the electric braking force and the mechanical braking force;

[0142] Then the differential equation of the whole vehicle is:

[0143]

[0144] m is the vehicle mass;

[0145] Using Laplace transform, we can get the longitudinal speed control system of the vehicle:

[0146]

[0147] Where, The gravity component caused by wind resistance, rolling resistance, and ramp is equivalent to external disturbance;

[0148] After adding external disturbance, such as Figure 1 As shown:

[0149]

[0150] F i It is external disturbances such as wind resistance, rolling resistance, and gravity component caused by ramps;

[0151] For the system after adding external disturbance to the longitudinal vehicle speed control system, the steady-state error caused is:

[0152]

[0153] F i (s) is the external disturbance input, H(s) is the control input;

[0154] For input disturbances, rolling resistance and wind resistance can be ignored, and a feedforward control of N(s) is added;

[0155] like Figure 2As shown, the closed-loop transfer function to the disturbance is formed:

[0156]

[0157] N(s) is a feedforward control input; Represents the response of vehicle speed to external disturbance input;

[0158] Therefore, let G(s)+G(s)N(s)=0 to eliminate the steady-state error; H(s) selects PI control.

[0159] Preferably,

[0160] Feedforward control:

[0161] F b1 =mgsin(θ) (1.16)

[0162] F b1 is the braking force calculated from the slope, θ is the slope;

[0163] Feedback control:

[0164] F b2 =K p V err +K i ∫V err (1.17)

[0165] V err =V Tar -V real (1.18)

[0166] F b2 is the braking force part of the closed-loop speed control, K p , K i is the coefficient of PI, V err is the difference between the target speed and the actual speed, V real is the real vehicle speed;

[0167] Anti-pitch control:

[0168] F b3 =K p a τ +K i ∫a τ (1.19)

[0169] a τ =gsin(α) (1.20)

[0170] F b3 is the braking force against pitching, a τ is the acceleration caused by pitching, and α is the pitch angle.

[0171] Combining the three controls, the output is:

[0172] F b =F b1 +F b2 +F b3 (1.21)

[0173] F b braking force for the overall goal;

[0174] After obtaining the total target braking force, the electric braking and mechanical braking forces are distributed according to the following principles:

[0175] When the target braking force is less than the maximum force provided by the electric brake, the electric brake is equal to the target braking force and the mechanical braking force is 0; when the target braking force is greater than the maximum force provided by the electric brake, the electric brake takes the maximum force that the electric brake can provide, and the mechanical brake = target braking force - electric brake force;

[0176]

[0177] F emax F is the maximum braking force that the motor can provide. m is the mechanical braking force, F e For electric braking force.

[0178] like Figure 3 As shown, based on the technical solution of the present invention described above, this embodiment provides a specific implementation method, which is as follows:

[0179] 1. Slope Calculation: Vehicle speed is derived from the wheel speeds, and the inertial acceleration is derived from the differential of the speed. The hill descent control function is disabled. The vehicle pitch angle is estimated from the acceleration due to gravity, inertia, and suspension stiffness. The slope value is calculated by subtracting the inertial acceleration and the acceleration at the pitch angle from the signal obtained by the IMU.

[0180] 2. Function activation conditions: Determine whether to trigger the steep slope descent command based on vehicle driving information and current slope, and determine the target speed in response to the steep slope descent command.

[0181] (1) The vehicle is in the starting state and is not stationary (including moving forward or backward), and the speed is between 4-39 km / h.

[0182] (2) The slope is above 8%.

[0183] (3) No active and passive safety functions such as ADAS, ABS, and AEB are involved.

[0184] (4) The driver fails to control the accelerator pedal or brake pedal.

[0185] When the above conditions are met, the hill descent control function is activated, and the vehicle travels at a target speed, using the speed at the moment the hill descent control is engaged. The vehicle's brake pressure is determined based on the target speed and the current acceleration. When a hill descent control execution command is received, the vehicle's speed is controlled based on the brake pressure.

[0186] 3. Function exit conditions: Exit steep slope descent when the vehicle status and road conditions meet the following conditions.

[0187] (1) When the vehicle speed is higher than the target speed or lower than the target speed,

[0188] (2) or the slope is within 8%,

[0189] (3) When active and passive safety functions such as ADAS, ABS, and AEB intervene, the vehicle's steep slope descent function will be exited.

[0190] 4. Update of target speed

[0191] When the driver steps on the accelerator pedal, the target vehicle speed gradually increases. When the target vehicle speed exceeds the upper speed limit, the steep hill descent system is exited. When the driver steps on the brake pedal, the target vehicle speed gradually decreases. When the target vehicle speed falls below the lower speed limit, the steep hill descent system is exited.

[0192] 5. Braking force control part 1: feedforward control, i.e. F b1 =Mgsin(θ), by introducing feedforward control, the system can eliminate steady-state errors. Compared with feedback control, it can eliminate phenomena such as oscillation and overshoot, and control the vehicle speed more smoothly.

[0193] 6. Braking force control part 2: Feedback control, that is, the target vehicle speed minus the actual vehicle speed is used as the error, and PI control is used, that is, the error term is multiplied by the parameter Kp, and then the error term is integrated and multiplied by the parameter Ki to obtain the target braking force.

[0194] 7. The result of feedforward control and the result of feedback control are added together to form the target braking force.

[0195] 8. Target braking force distribution: When the target braking force is less than the maximum force provided by the electric brake, the electric brake is equal to the target braking force and the mechanical braking force is 0. When the target braking force is greater than the maximum force provided by the electric brake, the electric brake uses the maximum force that the electric brake can provide. Mechanical braking = target braking force - electric braking force, achieving control of steep slope descent.

[0196] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A steep slope descent system based on energy recovery, characterized by: include: A slope estimation module receives a vehicle speed signal and a vehicle acceleration signal, and estimates the current slope of the vehicle based on the vehicle speed and vehicle acceleration signals; A steep slope descent activation judgment module receives a slope signal, a vehicle gear position signal, a brake pedal signal, an accelerator pedal signal, a driving direction signal, and a driving mode signal; When the vehicle is on a slope, the brake pedal and the accelerator pedal are not pressed, and the vehicle speed is within the speed threshold range, the steep hill descent function is activated, otherwise the steep hill descent function is exited; Target speed calculation module, which identifies the driver's intention and gives the target speed; The electromechanical braking force distribution module first introduces feedforward control through the slope signal, then superimposes the closed-loop control of the target vehicle speed to give the target braking force, and then distributes the braking force to the electric brake and mechanical brake to achieve energy recovery and caliper braking respectively.

2. The energy recovery-based steep slope descent system according to claim 1, characterized in that: The slope estimation module collects vehicle driving information and current posture through inertial sensors and wheel speed sensors. The inertial sensors obtain the vehicle's lateral acceleration and longitudinal acceleration, and the wheel speed sensors obtain the vehicle's wheel speed and vehicle speed and calculate the current slope. When the vehicle is stationary on a slope, the signal obtained by the inertial sensor is equal to the decomposition value of the gravity acceleration along the road surface: a xs =gsin(θ)(1.1) θ: slope angle; g: acceleration due to gravity; The slope value i calculated by the inertial sensor slope method is s for: a xf : The acceleration value along the x-axis measured by the inertial sensor; When the vehicle accelerates or decelerates on a slope, the signals obtained by the inertial sensor include gravity acceleration and inertial acceleration; Inertial acceleration is the differential of vehicle speed: a x_IMU =a i +a xs (1.4) a i : The differential of the vehicle speed, representing the longitudinal acceleration of the vehicle; a x_IMU Get the x-axis acceleration value for the inertial acceleration sensor; a xs is the acceleration along the ramp generated by the ramp; is the differential of vehicle speed; The slope is therefore: δ is the direction of movement, forward is 1, backward is -1; i s For the slope.

3. The energy recovery-based steep slope descent system according to claim 2, characterized in that: When a vehicle accelerates or decelerates on a slope, the signal obtained by the inertial sensor includes gravity acceleration and inertial acceleration; gravity acceleration will include the slope and vehicle pitch angle and add pitch angle correction; The pitch angle is calculated from the acceleration due to gravity and inertia, as well as the vehicle's suspension stiffness: α=K r (da) i +a xs (1.7) K r Represents the strength of the suspension; α is the vehicle pitch angle; a xs =gsin(θ+α) The slope is therefore:

4. The energy recovery-based steep slope descent system according to claim 1, characterized in that: The steep slope descent activation determination module determines whether to trigger a steep slope descent instruction based on vehicle driving information and the current slope, and determines a target speed in response to the steep slope descent instruction; The specific operations are as follows: When the vehicle is in motion and not stationary, including moving forward or backward, with a speed between 4 and 39 km / h and a slope between 8% and 100%, and no active or passive safety features are engaged, including ADAS, ABS, and AEB; the driver does not control the accelerator or brake pedal, the hill descent control function is activated, and the vehicle is traveling at a low speed using the target speed at the moment the hill descent control function is engaged; determining a vehicle brake pressure according to a target speed and a current acceleration, and controlling the vehicle to decelerate according to the vehicle brake pressure when a steep slope descent execution instruction is received; When the vehicle speed is higher than the target speed, or the slope is between 0% and 8%, or the active and passive safety functions intervene, the vehicle's steep slope descent function will exit.

5. The energy recovery-based steep slope descent system according to claim 1, characterized in that: Target speed calculation: Target vehicle speed when hill descent control is activated: The vehicle speed at the moment of hill descent control intervention is the target vehicle speed V Tar =V start ; V Tar represents the target vehicle speed, V start The vehicle speed at the moment of intervention for steep slope descent; Target vehicle speed when pressing the accelerator: Press the accelerator pedal, the target vehicle speed increases, V tar_k =V tar_k-1 +p k *Acc_Pedal; Target vehicle speed when braking: When the brake pedal is pressed, the target vehicle speed decreases, V tar_k =V tar_k-1 -p k *Brk_Pedal; V tar_k is the target vehicle speed at the current moment, V tar_k-1 is the target vehicle speed at the next moment; p k is a calibratable coefficient, Acc_Pedal is the accelerator pedal opening, and Brk_Pedal is the brake pedal opening.

6. The energy recovery-based steep slope descent system according to claim 1, characterized in that: The electromechanical brake force distribution module takes the driving and braking forces as inputs, ignoring wind resistance and rolling resistance, and outputs the vehicle speed. According to Newton's second law: F x It is the comprehensive sum of the longitudinal forces acting on the vehicle, i.e. the sum of the electric braking force and the mechanical braking force; Then the differential equation of the whole vehicle is: m is the vehicle mass; Using Laplace transform, we can get the longitudinal speed control system of the vehicle: Where, The gravity component caused by wind resistance, rolling resistance, and ramp is equivalent to external disturbance; After adding external perturbation: F i It is external disturbances such as wind resistance, rolling resistance, and gravity component caused by ramps; For the system after adding external disturbance to the longitudinal vehicle speed control system, the steady-state error caused is: F i (s) is the external disturbance input, H(s) is the control input; For input disturbances, rolling resistance and wind resistance can be ignored, and a feedforward control of N(s) is added; Then the closed-loop transfer function for interference is formed: N(s) is a feedforward control input; Represents the response of vehicle speed to external disturbance input; Therefore, let G(s)+G(s)N(s)=0 to eliminate the steady-state error; H(s) selects PI control.

7. The energy recovery-based steep slope descent system according to claim 1, characterized in that: Feedforward control: F b1 =mgsin(θ) (1.16) F b1 is the braking force calculated from the slope, θ is the slope; Feedback control: F b2 =K p V err +K i ∫V err (1.17) V err =V Tar -V real (1.18) F b2 is the braking force part of the closed-loop speed control, K p , K i is the coefficient of PI, V err is the difference between the target speed and the actual speed, V real is the real vehicle speed; Anti-pitch control: F b3 =K p a τ +K i ∫a τ (1.19) a τ =gsin(α)(1.20) F b3 is the braking force against pitching, a τ is the acceleration caused by pitching, α is the pitch angle; Combining the three controls, the output is: F b =F b1 +F b2 +F b3 (1.21) F b braking force for the overall goal; After obtaining the total target braking force, the electric braking and mechanical braking forces are distributed according to the following principles: When the target braking force is less than the maximum force provided by the electric brake, the electric brake is equal to the target braking force and the mechanical braking force is 0; when the target braking force is greater than the maximum force provided by the electric brake, the electric brake takes the maximum force that the electric brake can provide, and the mechanical brake = target braking force - electric brake force; F emax F is the maximum braking force that the motor can provide. m is the mechanical braking force, F e For electric braking force.

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