CN113104100B

CN113104100B - Control method and system for energy-saving intelligent electro-hydraulic steering system

Info

Publication number: CN113104100B
Application number: CN202110582633.8A
Authority: CN
Inventors: 陶书鑫; 姚俊明; 董晴; 刘亚辉
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2021-05-27
Filing date: 2021-05-27
Publication date: 2022-07-19
Anticipated expiration: 2041-05-27
Also published as: CN113104100A

Abstract

The invention relates to a control method and a system for an energy-saving intelligent electro-hydraulic steering system, which comprises the following steps: 1) determining the working mode of the energy-saving intelligent electro-hydraulic steering system based on the acquired steering wheel torque; 2) if the working mode is the power-assisted-free mode, acquiring a short-circuit duty ratio of the motor according to the vehicle speed information, and controlling the motor to generate damping according to the short-circuit duty ratio; 3) if the working mode is the EPS power-assisted mode, calculating to obtain a three-phase duty ratio of a motor in the EPS subsystem by adopting a power-assisted control algorithm, and outputting a corresponding control signal to the EPS subsystem; 4) if the working mode is the EPS + EHPS power-assisted mode, the three-phase duty ratio of the electric pump driving motor in the EHPS subsystem and the opening and closing state of the electromagnetic valve are calculated by adopting a hydraulic power-assisted control method, then the electric pump driving motor is driven to generate corresponding torque, and meanwhile, the opening and closing of the electromagnetic valve are controlled. The invention can be widely applied to the field of steering system design.

Description

Control method and system for energy-saving intelligent electro-hydraulic steering system

Technical Field

The invention belongs to the technical field of steering systems, and particularly relates to a control method and a control system for an energy-saving intelligent electro-hydraulic steering system.

Background

For a large-sized commercial vehicle, the electric power steering system generally applied to a passenger vehicle cannot provide sufficient steering power for the large-sized commercial vehicle due to the large axle load, so that the hydraulic power steering system is still widely applied to the large-sized commercial vehicle (including an engine-driven hydraulic power steering system HPS and an electric power steering system EHPS driven by an electric pump system). Such hydraulic power steering systems have two main problems:

the EHPS system needs to have larger rated power to meet all steering requirements of commercial vehicles, so that on one hand, the selection of key parts such as an electric pump is limited, and on the other hand, the hydraulic pump system usually needs to be powered by a high-voltage electric system of the whole vehicle, high-voltage system resources are consumed, and the EHPS system cannot be applied to fuel vehicles.

2. The steering gear serving as the core of the steering mechanism generally adopts a middle open type circulating ball steering gear, the steering gear still keeps equivalent hydraulic oil flow under the non-steering working condition, great energy waste is caused, and in the steering working condition, most hydraulic oil still does not produce useful work, and the energy efficiency is extremely low.

Therefore, a novel steering system and a control method for the commercial vehicle are developed, the problems are fundamentally solved, and the novel steering system and the control method are a key technology for realizing the electromotion and energy conservation of the commercial vehicle in the future.

At present, some related researches appear, for example, an energy accumulator is used as a hydraulic power source during heavy-load steering, a low-power electric pump is used as a hydraulic power source during light-load steering, the rated power of a steering system can be effectively reduced, the steering system can be in standby state under a non-steering working condition, and a certain energy-saving effect is achieved.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a control method and system for an energy-saving intelligent electro-hydraulic steering system, which utilize the structural advantages of the energy-saving intelligent electro-hydraulic steering system to realize the cooperative coordination of an Electric Power Steering (EPS) subsystem and a Hydraulic Power Steering (HPS) subsystem, and minimize the flow demand of the steering system, i.e., the flow of the system is completely determined by the volume change of a power cylinder caused by the rotation of a steering wheel, and no flow is wasted.

In order to realize the purpose, the invention adopts the following technical scheme:

the invention provides a control method for an energy-saving intelligent electro-hydraulic steering system, which comprises the following steps:

1) determining the working mode of an energy-saving intelligent electro-hydraulic steering system based on the obtained steering wheel torque, wherein the energy-saving intelligent electro-hydraulic steering system comprises: the EPS system comprises a steering system, an EPS subsystem and an EHPS subsystem, wherein the EPS subsystem and the EHPS subsystem are connected with the steering system; the EHPS subsystem comprises an oil tank, an energy accumulator, an electric pump driving motor and an electromagnetic valve group, wherein an oil outlet of the electric pump is sequentially connected with the energy accumulator, the electromagnetic valve group and an oil inlet of a steering gear, an oil outlet of the steering gear is connected with the oil tank, and an oil inlet of the electric pump is connected with the oil tank; the working modes comprise a no-assistance mode, an EPS assistance mode and an EPS + EHPS assistance mode;

2) if the working mode is the no-power mode, the EPS subsystem enters a damping control mode, a motor short-circuit duty ratio is obtained according to the vehicle speed information, and the motor is controlled to generate damping according to the motor short-circuit duty ratio;

3) if the working mode is the EPS power-assisted mode, the EPS subsystem enters the electric power-assisted mode, a power-assisted control algorithm is adopted to calculate and obtain the three-phase duty ratio of a motor in the EPS subsystem, and a corresponding control signal is output to the EPS subsystem to realize EPS power assistance;

4) if the working mode is the EPS + EHPS power-assisted mode, the EPS subsystem is controlled to be in the maximum power-assisted state, meanwhile, the three-phase duty ratio of an electric pump driving motor in the EHPS subsystem and the opening and closing state of an electromagnetic valve are calculated by adopting a hydraulic power-assisted control method, then the electric pump driving motor is driven to generate corresponding torque, and meanwhile, the opening and closing of the electromagnetic valve are controlled, so that the EPS + EHPS power assistance is realized.

Further, in the step 1), the method for determining the working mode of the energy-saving intelligent electro-hydraulic steering system comprises the following steps:

1.1) detecting the torque of a steering wheel in real time through a steering wheel angle torque sensor;

1.2) determining whether the steering wheel torque is within a set dead band range, i.e. greater than a set minimum starting torque T_{min_e}: if the steering wheel torque is within the deadband range, i.e., T ≦ T_{min_e}If the EPS subsystem is in the damping control mode, the power is not generated, and the EHPS subsystem is in a standby state; if the steering wheel torque is not within the deadband range, i.e. T > T_{min_e}Starting the EPS subsystem for assisting power;

1.3) after the EPS subsystem helping hand is opened, whether the EPS subsystem helping hand satisfies the demand is judged according to whether the steering wheel moment of torsion still continuously rises and exceeds the preset threshold: if the EPS subsystem meets the requirement, the electromagnetic valve is completely closed, so that the EHPS subsystem is kept in standby; if the EPS subsystem power assistance does not meet the requirements, the electromagnetic valve is controlled to be gradually opened, the EHPS subsystem starts to work, and the hydraulic power assistance is added.

Further, in the step 2), a calculation formula of the short-circuit duty ratio of the motor is as follows:

in the formula, v_cmin、v_cmaxRespectively a low vehicle speed threshold and a high vehicle speed threshold, D_cIs the short circuit duty cycle; k is a short circuit duty ratio set value; and v is the vehicle speed.

Further, in the step 3), a method for calculating a three-phase duty ratio of a motor in the EPS subsystem by using a power control algorithm and outputting a corresponding control signal to the EPS subsystem to realize EPS power assistance includes the following steps:

3.1) detecting the torque and the rotation angle of the steering wheel through a steering wheel rotation angle torque sensor, and acquiring the vehicle speed through a vehicle-mounted CAN bus;

and 3.2) calculating a three-phase duty ratio of a motor in the EPS subsystem according to the steering wheel rotation angle, the torque and the vehicle speed and a power-assisted control algorithm, and then driving the motor to generate corresponding torque to realize steering power assistance.

Further, in the step 3.2), the method for calculating the three-phase duty ratio of the motor in the EPS subsystem according to the power-assisted control algorithm includes the following steps:

3.2.1) calculating to obtain the steering wheel torque after filtering correction according to the steering wheel torque acquired in real time;

wherein, the transfer function G(s) of the filtering correction is:

in the formula, K_dIs a differential coefficient, K_iAs an integral coefficient, T₁Is a differential time constant, T₂Is an integration time constant; s is a laplace operator;

3.2.2) calculating to obtain the rotating speed of the steering wheel at the current moment according to the steering wheel rotating angle acquired in real time, wherein the calculating method comprises the following steps:

ω_o[n]＝ω_o[n-1]+ΔTε_o[n-1]+K₂(θ_[n]-θ_o[n])

ε_o[n]＝ε_o[n-1]+K₃(θ_[n]-θ_o[n])

in the formula, theta_oAs an observation of the steering wheel angle, omega_oAs an observation of the speed of rotation of the steering wheel, e_oAs an observed value of the acceleration of the steering wheel,

is an estimate of the steering wheel angle, theta is a measure of the steering wheel angle, subscript n]Indicates the current time, [ n-1 ]]Indicates the last time, K₁、K₂、K₃For estimating the coefficients, Δ T is the calculation period;

3.2.3) calculating to obtain a target motor torque according to the filtered and corrected steering wheel torque and the vehicle speed obtained in the step 3.2.1);

3.2.4) calculating to obtain target motor current according to the target motor torque and the steering wheel rotating speed, and using the target motor current to improve the motor rotating speed;

3.2.5) calculating to obtain target motor voltage by PI algorithm according to the target motor current and the actual motor current;

3.2.6) calculating to obtain the three-phase duty ratio of the motor according to the target motor voltage and the position of the motor rotor, and further driving the motor to generate corresponding torque to perform steering assistance.

Further, in the step 4), the hydraulic assist control method includes:

4.1) an electric pump control method is adopted to control an electric pump driving motor in the EHPS subsystem, so as to supply oil to the energy accumulator and ensure that the pressure of the energy accumulator is within a set range;

the method comprises the following steps:

4.1.1) acquiring the existing pressure of the energy accumulator through a pressure electromagnetic valve inlet sensor, acquiring vehicle speed information through a vehicle-mounted CAN bus, and filtering the acquired existing pressure of the energy accumulator by adopting a sliding average filtering method to reduce noise in a pressure signal;

4.1.2) calculating according to the vehicle speed information to obtain an electric pump opening pressure threshold and an electric pump closing pressure threshold, wherein the calculation formula is as follows:

P_lowset＝P_set-0.5

P_highset＝P_set+0.5

in the formula, P_setIs the accumulator pressure target value, P_lowset、P_highsetRespectively, electric pump opening pressure threshold and electric pump closing pressure threshold, v_L、v_HV is the current vehicle speed, and is a set low vehicle speed threshold value and a set high vehicle speed threshold value;

4.1.3) judging the current on-off state of the electric pump, and if the current state of the electric pump is on, performing the step 4.1.4); if the current electric pump state is off, performing step 4.1.5);

4.1.4) comparing the existing pressure of the energy accumulator with the closing pressure threshold of the electric pump, if the existing pressure of the energy accumulator is higher than the closing pressure threshold of the electric pump, controlling the driving motor of the electric pump to stop working, and if the existing pressure of the energy accumulator is lower than the closing pressure threshold of the electric pump, keeping the driving motor working;

4.1.5) comparing the current pressure of the energy accumulator with the opening pressure threshold of the electric pump, if the current pressure of the energy accumulator is higher than the opening pressure threshold of the electric pump, controlling the electric pump to drive the motor to start working and enter a rotating speed control mode, and if the current pressure of the energy accumulator is lower than the opening pressure threshold of the electric pump, keeping the driving motor in a standby state;

4.2) an electromagnetic valve control method is adopted to control the opening and closing state of an electromagnetic valve in the EHPS subsystem, so that the pressure in the steering gear is ensured to be in a proper range, and the steering power is ensured to be smooth;

the method comprises the following steps:

4.2.1) acquiring the speed, the steering wheel angle, the steering wheel torque, the energy accumulator pressure and the steering gear pressure by each sensor and a finished automobile CAN bus, calculating to obtain the steering wheel rotating speed based on the steering wheel angle, and simultaneously carrying out filtering correction treatment on the acquired energy accumulator pressure, steering gear pressure and steering wheel torque to obtain the energy accumulator pressure, steering gear pressure and steering gear torque T after filtering correction;

4.2.2) calculating to obtain a hydraulic power-assisted opening torque threshold T according to the vehicle speed information_{min_h}；

4.2.3) comparing the steering wheel torque T with a hydraulic power-assisted opening torque threshold T_{min_h}The size of (2):

if T is less than T_{min_h}If the output electromagnetic valve group is in a fully closed state, the EHPS subsystem is in a standby state;

if T > T_{min_h}And then, an electromagnetic valve control algorithm is adopted, the on-off of each electromagnetic valve is controlled in real time according to the input quantity, hydraulic assistance is generated, and the defect of electric assistance is overcome.

Further, in the step 4.1.5), the rotation speed control mode includes the following steps:

4.1.5.1) calculating the target motor speed according to the current pressure of the accumulator and the set pressure. And outputting the expected motor rotating speed according to the difference value between the set pressure of the energy accumulator and the current pressure by relying on a database calibrated by the test, wherein the larger the difference value is, the higher the expected rotating speed is, and the oil supply speed is increased.

4.1.5.2) calculating to obtain the target motor torque by PI algorithm according to the target rotating speed and the actual rotating speed of the electric pump, and performing closed-loop control on the rotating speed of the electric pump.

The calculation formula of the motor target torque is as follows:

T_out＝k_p(ω_ref-ω)+k_i∫ω_ref-ωdt

in the formula, T_outTarget torque (Nm), ω, for output_refIs a target rotational speed (rpm), ω is a current rotational speed (rpm), k_p、k_iProportional coefficients and integral coefficients, respectively.

4.1.5.3) calculating to obtain target motor current according to the target motor torque and the steering wheel rotating speed, and increasing the motor rotating speed;

4.1.5.4) calculating to obtain the target motor voltage by PI algorithm according to the target motor current and the actual motor current;

4.1.5.5) calculating to obtain the three-phase duty ratio of the motor according to the target motor voltage and the position of the motor rotor, and further driving the motor to generate corresponding torque, so that the electric pump reaches an ideal rotating speed, and further supplementing hydraulic oil for the energy accumulator.

Further, in the step 4.2.3), the electromagnetic valve control algorithm comprises the following steps:

4.2.3.1) calculating to obtain a percentage form first solenoid valve opening according to the steering wheel torque and the vehicle speed information;

4.2.3.2) calculating to obtain the opening degree of the second electromagnetic valve in a percentage form according to the torque of the steering wheel, the pressure of the energy accumulator and the pressure of the steering gear, wherein the calculation formula is as follows:

D_{out_d}＝(D_L+D_H)f(ΔP)

in the formula D_{out_d}Solenoid valve opening (%) output by the module, D_L、D_HIs D_outOf the low-frequency component and the high-frequency component, T_[n]The current moment steering wheel torque value (Nm), T_[n-1]The steering wheel torque value, T, at the previous moment_[n-2]The torque value of the steering wheel at the first two moments, and so on, K₁、K₂F (delta P) is a function of the pressure difference between the energy accumulator and the steering gear and is used as a correction coefficient between 0 and 1, and the larger the pressure difference is, the more the value of the pressure difference approaches to 0, and the more the pressure difference approaches to 1;

4.2.3.3) calculating to obtain the opening degree of a third electromagnetic valve in a percentage form according to the rotating speed of the steering wheel, the pressure of an energy accumulator, the pressure of a steering gear and the speed of the vehicle; the calculation formula is as follows:

in the formula, D_{out_ω}Is the third solenoid valve opening degree, and Δ P is the accumulator-steering gear pressureForce difference, ω is steering wheel speed, K is gain factor, g (v) is a function of vehicle speed;

4.2.3.4) calculating the opening of the fourth electromagnetic valve in percentage form according to the torque of the steering wheel, the vehicle speed and the pressure of the steering gear, wherein the calculation formula is as follows:

D_{out_p}＝k_p(P_ref(T，v)-P_raw)，D_{out_p}≥0

in the formula, D_{out_p}Is the opening of the fourth solenoid valve, k_pIs a proportionality coefficient, P_ref(T, v) is a steering target pressure that is a function of steering wheel torque T and vehicle speed v;

4.2.3.5) to the fourth solenoid valve opening to obtain a final solenoid valve opening, i.e., a final solenoid valve opening

D＝D_{out_T}+D_{out_d}+D_{out_ω}+D_{out_p}

4.2.3.6) converting the percentage type solenoid valve opening obtained in the step 4.2.3.6) to obtain the opening and closing state of each solenoid valve in the solenoid valve group.

In a second aspect of the present invention, there is provided a control system for an energy-saving intelligent electro-hydraulic steering system, where the control system is connected to the energy-saving intelligent electro-hydraulic steering system, and the control system includes: the device comprises a working mode judging module, a damping control module, an electric power-assisted control module and a hydraulic power-assisted control module; the working mode judging module is used for determining a working mode of the energy-saving intelligent electro-hydraulic steering system based on the acquired steering wheel torque, sending a control signal to the damping control module when the working mode is a no-power mode, sending a control signal to the electric power assisting control module when the working mode is an EPS (electric power steering) power assisting mode, and sending a control signal to the electric power assisting control module and the hydraulic power assisting control module when the working mode is an EPS + EHPS power assisting mode; the damping control module is used for acquiring a short-circuit duty ratio of the motor according to the vehicle speed information and controlling the motor in the EPS subsystem to generate damping based on the short-circuit duty ratio; the electric power-assisted control module is used for calculating a three-phase duty ratio of a motor in the EPS subsystem by adopting a power-assisted control algorithm and outputting a corresponding control signal to the EPS subsystem to realize EPS power assistance; the hydraulic power assisting module is used for calculating the three-phase duty ratio of an electric pump driving motor in the EHPS subsystem and the opening and closing state of the electromagnetic valve by adopting a hydraulic power assisting control method, then driving the electric pump driving motor to generate corresponding torque, and simultaneously controlling the opening and closing of the electromagnetic valve to realize hydraulic power assisting.

Further, the electric power-assisted control module comprises a steering wheel torque filtering correction module, an electric power-assisted characteristic database, a steering wheel rotating speed calculation module, a weak magnetic control module, a motor current closed-loop control module and a space vector pulse width modulation module; the input of the steering wheel torque filtering correction module is steering wheel torque acquired in real time, and the output is the steering wheel torque subjected to filtering correction; the input of the electric power-assisted characteristic database is steering wheel torque and vehicle speed, and the output is target motor torque; the input of the steering wheel rotating speed calculating module is a steering wheel rotating angle acquired in real time, and the output is the steering wheel rotating speed at the current moment; the input of the weak magnetic control module is target motor torque and steering wheel rotating speed, and the output is target motor current; the input of the motor current closed-loop control module is target current and motor current, and the output is motor voltage; the input of the space vector pulse width modulation module is target motor voltage and motor rotor position, and the output is motor three-phase duty ratio;

the hydraulic power-assisted control module comprises an electric pump control module and a hydraulic control module; the electric pump control module is used for controlling an electric pump driving motor in the EHPS subsystem by adopting an electric pump control method, supplying oil to the energy accumulator and ensuring that the pressure of the energy accumulator is within a set range; the hydraulic control module is used for controlling the opening and closing states of the electromagnetic valves in the EHPS subsystem by adopting an electromagnetic valve control method, so that the pressure in the steering gear is ensured to be in a proper range, and the steering assistance is ensured to be smooth.

Due to the adoption of the technical scheme, the invention has the following advantages:

1. the control method of the invention enables the steering system to keep standby in the straight-line driving process, and ensures that no energy loss exists in the straight-line driving process, thereby avoiding the defect that the existing hydraulic power-assisted steering system consumes a large amount of energy in the straight-line driving process, and improving the energy-saving level of the steering system.

2. The control method provided by the invention has the advantages that the EPS subsystem and the EHPS subsystem work cooperatively, corresponding steering power is provided according to actual steering requirements, energy waste caused by mismatching of input power and load is reduced, most steering work is borne by the EPS subsystem particularly under the condition of high-speed driving, the defect of low efficiency of a hydraulic system is completely avoided, and the energy-saving level of the steering system is improved.

3. The control method of the invention ensures that the hydraulic flow of the steering system is completely determined by the volume change of two sides of the hydraulic power cylinder caused by the rotation of the steering wheel, completely avoids the defect that the existing hydraulic power steering system still keeps most of straight-through flow under the steering working condition, thereby generating energy waste, realizes the on-demand supply of the flow of the steering system, and improves the energy-saving level of the steering system.

4. The hydraulic control unit controls 12 electromagnetic valves at the highest frequency of 100Hz according to the measurement results of sensors such as the torque, the rotating speed and the pressure of a steering wheel, accurately controls the pressure of the steering wheel and ensures the smoothness of the power assistance.

Therefore, the invention can be widely applied to the technical field of steering systems.

Drawings

FIG. 1 is a diagram illustrating the structure and composition of a control method and a controlled system according to the present invention;

FIG. 2 is a schematic diagram of the switching of the operation modes in the control method of the present invention;

FIG. 3 is a control method framework for an electric power steering subsystem of the present invention;

FIG. 4 is a control method framework of the electric pump of the present invention;

FIG. 5 is a control method framework of the hydraulic control unit of the present invention;

the reference numbers in the figures are as follows:

1. an electric pump; 2. a one-way valve; 3. an overflow valve; 4. a filter; 5. an electromagnetic valve group; 6. a steering wheel; 7. a pressure sensor; 8. an accumulator; 9. an EPS assembly; 10. a diverter; 101. an electric power steering system control module; 102. an electro-hydraulic power steering system control module; 103. a hydraulic control unit; 104. an electric pump control unit.

Detailed Description

The invention is described in detail below with reference to the figures and examples.

As shown in fig. 1, for convenience of understanding, the structure of the energy-saving intelligent electro-hydraulic steering system to which the present invention is directed will be briefly described first. The energy-saving intelligent electro-hydraulic steering system 105 to which the present invention is directed should have the following basic features, including: a steering system, an electric power steering subsystem (EPS system), and a hydraulic power steering subsystem (EHPS subsystem). The steering system comprises a steering wheel 6 and a steering gear 10 connected with the steering wheel 6 through a steering shaft; the input end of the electric power steering subsystem is connected with the steering wheel 6, and the output end is connected with the input shaft of the steering gear 10. The hydraulic power-assisted steering subsystem provides hydraulic oil for the steering gear 10, and the hydraulic power-assisted steering subsystem comprises an electric pump 1, an energy accumulator 8, an electromagnetic valve group 5 electric pump driving motor and an oil tank, wherein an oil outlet of the electric pump 1 is connected with an inlet of the energy accumulator 8, an outlet of the energy accumulator 8 is connected with an inlet of the electromagnetic valve group 5, an outlet of the electromagnetic valve group 5 is connected with an oil inlet of the steering gear 10, an oil outlet of the steering gear 10 is connected with the oil tank, an oil inlet of the electric pump 1 is connected with the oil tank, and the electric pump driving motor is connected with a controller and used for driving the electric pump 1.

The invention provides a control system for an energy-saving intelligent electro-hydraulic steering system, which is connected with the energy-saving intelligent electro-hydraulic steering system and comprises a working mode judgment module, a damping control module, an electric power assisting control module and a hydraulic power assisting control module. The working mode judging module is used for determining a working mode of the energy-saving intelligent electro-hydraulic steering system based on the acquired steering wheel torque, sending a control signal to the damping control module when the working mode is a no-power mode, sending a control signal to the electric power assisting control module when the working mode is an EPS (electric power steering) power assisting mode, and sending a control signal to the electric power assisting control module and the hydraulic power assisting control module when the working mode is an EPS + EHPS power assisting mode; the damping control module is used for acquiring a short-circuit duty ratio of the motor according to the vehicle speed information and controlling the motor in the EPS subsystem to generate damping based on the short-circuit duty ratio; the electric power-assisted control module is used for calculating a three-phase duty ratio of a motor in the EPS subsystem by adopting a power-assisted control algorithm and outputting a corresponding control signal to the EPS subsystem to realize EPS power assistance; the hydraulic power assisting module is used for calculating the three-phase duty ratio of an electric pump driving motor in the EHPS subsystem and the opening and closing state of the electromagnetic valve by adopting a hydraulic power assisting control method, then driving the electric pump driving motor to generate corresponding torque, and simultaneously controlling the opening and closing of the electromagnetic valve to realize hydraulic power assisting.

Further, the working mode judging module comprises a steering wheel torque collecting module, a first judging module and a second judging module. The steering wheel torque acquisition module is used for detecting the torque of a steering wheel in real time through a steering wheel corner torque sensor; the first judgment module is used for judging whether the steering wheel torque is in a set dead zone range: if the steering wheel torque is in the dead zone range, the EPS subsystem and the EHPS subsystem both enter a standby state; if the torque of the steering wheel is not in the dead zone range, the EPS subsystem is started to carry out power assistance, and at the moment, a control signal is sent to the electric power assistance control module; the second judging module is used for judging whether the assistance of the EPS subsystem meets the requirement: if the EPS subsystem meets the requirement, the electromagnetic valve is completely closed, so that the EHPS subsystem is kept in standby; if the EPS subsystem power assistance does not meet the requirements, the electromagnetic valve is controlled to be gradually opened, the EHPS subsystem starts to work, and the hydraulic power assistance is added.

Further, the electric power assisting control module 308 includes a steering wheel torque filtering correction module 301, an electric power assisting characteristic database 302, a steering wheel rotating speed calculation module 303, a field weakening control module 304, a motor current closed-loop control module 305, and a Space Vector Pulse Width Modulation (SVPWM) module 306. The input of the steering wheel torque filtering correction module 301 is the steering wheel torque acquired in real time, and the output is the steering wheel torque subjected to filtering correction; the input of the electric power-assisted characteristic database 302 is a steering wheel torque and a vehicle speed, and the output is a target motor torque; the input of the steering wheel rotating speed calculating module 303 is the steering wheel rotating angle acquired in real time, and the output is the steering wheel rotating speed at the current moment; the input of the weak magnetic control module 304 is target motor torque and steering wheel rotating speed, and the output is target motor current; the input of the motor current closed-loop control module 305 is a target current and a motor current, and the output is a motor voltage; the input of the space vector pulse width modulation module 306 is the target motor voltage, the motor rotor position, and the output is the motor three-phase duty ratio.

Further, the hydraulic power-assisted control module comprises an electric pump control module and a hydraulic control module. The electric pump control module is used for controlling an electric pump driving motor in the EHPS subsystem by adopting an electric pump control method, supplying oil to the energy accumulator and ensuring that the pressure of the energy accumulator is within a set range; the hydraulic control module is used for controlling the opening and closing states of the electromagnetic valves in the EHPS subsystem by adopting an electromagnetic valve control method, so that the pressure in the steering gear is ensured to be in a proper range, and the steering assistance is ensured to be smooth.

Further, the electric pump control module includes an accumulator pressure setting module 401, an accumulator pressure filtering module 402, and an electric pump speed control mode 403. The input of the accumulator pressure setting module 401 is a vehicle speed, and the output is an electric pump opening pressure threshold and a closing pressure threshold; the input of the accumulator pressure filtering module 402 is an accumulator existing pressure value acquired in real time, and the output is a filtered accumulator existing pressure; the input of the electric pump rotation speed control mode 403 is the filtered existing pressure of the accumulator, the opening pressure threshold and the closing pressure threshold of the electric pump, and the output is the three-phase duty ratio of the driving motor.

Further, the electric pump speed control mode 403 includes an electric pump speed setting module 404, a speed control module 405, a field weakening control module 406, a current control module 407, and a space vector pulse width modulation module 408. The input of the electric pump rotating speed setting module 404 is the current pressure and the set pressure of the energy accumulator, and the output is the target motor rotating speed; the input of the speed control module 405 is the target rotating speed and the actual rotating speed of the electric pump, and the output is the target torque of the motor; the input of the weak magnetic control module 406 is target motor torque and steering wheel rotating speed, and the output is target motor current; the input of the motor current closed-loop control module 407 is target current and motor current, and the output is motor voltage; the input of the space vector pulse width modulation module 408 is the target motor voltage, the motor rotor position, and the output is the motor three-phase duty ratio.

Further, the hydraulic control module includes: a hydraulic power assist opening torque threshold setting module 501, a steering wheel torque filtering correction module 502, and a solenoid valve control module 503. The input of the hydraulic power-assisted starting torque threshold setting module 501 is vehicle speed information, and the output is a hydraulic power-assisted starting torque threshold; the input of the steering wheel torque filtering correction module 502 is the steering wheel torque acquired in real time, and the output is the steering wheel torque after filtering correction; the input of the solenoid valve control module 503 is the steering wheel torque, the steering wheel rotation speed, the hydraulic power-assisted opening torque threshold, the vehicle speed information, the accumulator pressure and the steering gear pressure, and the output is the open-close state of the solenoid valve set.

Further, the solenoid valve control module 503 includes a torque-solenoid valve opening database 504, a torque differential compensation module 505, a steering wheel speed compensation module 506, a minimum pressure control module 507, and a solenoid valve encoding module 508. Wherein, the input of the torque-electromagnetic valve opening database 504 is the steering wheel torque and the vehicle speed, and the output is the electromagnetic valve opening (%); the input of the torque differential compensation module 505 is steering wheel torque, accumulator pressure and steering gear pressure, and the output is solenoid valve opening (%); the inputs of the steering wheel speed compensation module 506 are steering wheel rotation speed, accumulator pressure, steering gear pressure, vehicle speed, and the output is solenoid valve opening (%); the input of the minimum pressure control module 507 is steering wheel torque, vehicle speed and steering gear pressure, and the output is solenoid valve opening (%); the input of the solenoid valve coding module 508 is the percentage form of the solenoid valve opening of the output of the torque-solenoid valve opening database 504, the torque differential compensation module 505, the steering wheel speed compensation module 506 and the minimum pressure control module 507, and the output is the open-close state of the solenoid valve.

Based on the energy-saving intelligent electro-hydraulic steering system, the invention provides a control method for the energy-saving intelligent electro-hydraulic steering system, and the logic of the control method is as follows: 1. the EHPS subsystem is completely closed under the non-steering working condition (namely the torque of the steering wheel is in the dead zone range), only the electric pump supplies oil to the energy accumulator under the condition that the pressure of the energy accumulator is lower than a set value, and the electric pump stops working under the condition that the pressure of the energy accumulator is higher than the set value; the EPS subsystem is in a standby state, and a certain neutral position damping is provided for the system only by short-circuiting the motor at a certain duty ratio, so that the neutral position road feeling performance is improved. Therefore, the energy consumption of the system is only the standby power of the controller under the non-steering working condition, and almost no energy waste exists. 2. In the initial stage of power assistance, an EPS subsystem is adopted to provide steering power assistance, when the EPS subsystem can not meet the steering requirement, the EHPS subsystem is gradually started to supplement the power assistance by controlling an electromagnetic valve, the EPS subsystem operates a middle open type steering control valve to a limit position at the moment, the through opening of a rotary valve is close to 0 at the moment, the hydraulic oil flow of the system is completely determined by the volume change of a steering power-assisted oil cylinder caused by the rotation of a steering wheel, theoretically, all high-pressure oil participates in acting, the waste of the high-pressure oil is avoided, and the hydraulic energy loss is lowest.

Specifically, the control method for the energy-saving intelligent electro-hydraulic steering system provided by the invention comprises the following steps:

1) determining the working mode of the energy-saving intelligent electro-hydraulic steering system based on the obtained steering wheel torque, wherein the working mode of the energy-saving intelligent electro-hydraulic steering system comprises a no-power mode, an EPS power-assisted mode and an EPS + EHPS power-assisted mode.

As shown in fig. 2, in particular, the method for determining the working mode of the energy-saving intelligent electro-hydraulic steering system includes the following steps:

1.1) detecting the steering wheel torque T in real time through a steering wheel corner torque sensor;

1.2) determining whether the steering wheel torque T is within a set dead band range, i.e. greater than a set minimum starting torque T_{min_e}: if the steering wheel torque is within the deadband range, i.e., T ≦ T_{min_e}If the current state of the EHPS subsystem is the standby state, the EPS subsystem enters the damping control state and does not provide steering assistance; if the steering wheel torque is not in the deadband range, i.e. T > T_{min_e}And the EPS subsystem starts to assist.

1.3) after EPS helping hand is opened, whether the EPS subsystem helping hand satisfies the demand according to whether the steering wheel moment of torsion still continuously rises and exceeds the preset threshold: if the torque of the steering wheel does not continuously rise, judging that the power assisting of the EPS subsystem meets the requirement, and completely closing the electromagnetic valve to enable the EHPS subsystem to keep standby; if the torque of the steering wheel still continuously rises and exceeds a set threshold value, the EPS subsystem power assisting does not meet the requirement, the electromagnetic valve is controlled to be gradually opened, the EHPS subsystem starts to work, hydraulic power assisting is added, and an EPS and EHPS power assisting mode is entered.

It can be seen that under the control of the control method of the invention, the EPS subsystem will firstly work in the boosting process, on one hand, a certain steering boosting is provided, on the other hand, the rotary valve of the middle open type circulating ball steering gear is positioned at the limit position, at this time, the through opening of the rotary valve is close to 0, and in the process of hydraulic boosting intervention, flow waste caused by through the rotary valve hardly exists, so that a good energy-saving effect is generated.

2) And if the working mode is the no-power mode, the EPS subsystem enters a damping control state, namely the motor short-circuit duty ratio is obtained according to the vehicle speed information, and the motor in the EPS subsystem is controlled to generate corresponding damping according to the motor short-circuit duty ratio.

When the vehicle speed is between the low vehicle speed threshold and the high vehicle speed threshold, the short-circuit duty ratio is linearly increased along with the vehicle speed, when the vehicle speed is below the low vehicle speed threshold, the short-circuit duty ratio is 0, and when the vehicle speed is above the high vehicle speed threshold, the short-circuit duty ratio is a set value k. Namely, the calculation formula of the short-circuit duty ratio of the motor is as follows:

in the formula, v_cmin、v_cmaxLow and high vehicle speed thresholds (km/h), D, respectively_cIs the short circuit duty cycle of the motor; k is a short circuit duty ratio set value; and v is the vehicle speed.

3) If the working mode is the EPS power-assisted mode, the EPS subsystem enters the electric power-assisted mode, namely a power-assisted control algorithm is adopted to calculate the three-phase duty ratio of a motor in the EPS subsystem, and a corresponding control signal is output to the EPS subsystem to realize EPS power assistance.

Specifically, the method comprises the following steps:

and 3.1) detecting the torque and the steering angle of the steering wheel through a steering wheel angle torque sensor, and acquiring the vehicle speed through a vehicle-mounted CAN bus.

And 3.2) calculating to obtain the three-phase duty ratio of the motor in the EPS subsystem according to the acquired steering wheel rotation angle, torque and vehicle speed and a power-assisted control algorithm, and then driving the motor to generate corresponding torque to realize EPS steering power assistance.

As shown in fig. 3, the assist control algorithm includes the following steps:

3.2.1) calculating to obtain the steering wheel torque corrected by filtering according to the steering wheel torque acquired in real time.

Wherein, the transfer function G(s) of the filtering correction is:

in the formula, K_dIs a differential coefficient, K_iAs an integral coefficient, T₁Is a differential time constant, T₂Is the integration time constant.

ω_o[n]＝ω_o[n-1]+ΔTε_o[n-1]+K₂(θ_[n]-θ_o[n])

ε_o[n]＝ε_o[n-1]+K₃(θ_[n]-θ_o[n])

in the formula, theta_oFor turning the steering wheelObserved value, ω_oIs an observed value of the steering wheel speed, epsilon_oAs an observed value of the acceleration of the steering wheel,

is an estimate of the steering wheel angle, theta is a measure of the steering wheel angle, subscript n]Indicates the current time, [ n-1 ]]Indicates the last time, K₁、K₂、K₃To estimate the coefficients, Δ T is the calculation period. The algorithm can effectively observe the rotating speed of the steering wheel, and has small burrs and high real-time performance.

3.2.3) calculating to obtain the target motor torque according to the filtered and corrected steering wheel torque and the vehicle speed obtained in the step 3.2.1).

3.2.4) weak magnetic control is applied, namely, the target motor current is obtained through calculation according to the target motor torque and the steering wheel rotating speed.

3.2.5) calculating the target motor voltage by PI algorithm according to the target motor current and the actual motor current.

4) If the working mode is the EPS + EHPS power-assisted mode, the EPS subsystem is controlled to be in the maximum power-assisted state, meanwhile, the three-phase duty ratio of an electric pump driving motor in the EHPS subsystem and the opening and closing states of all electromagnetic valves in the electromagnetic valve bank are calculated by adopting a hydraulic power-assisted control method, then the electric pump driving motor is driven to generate corresponding torque, meanwhile, the opening and closing of the electromagnetic valve bank are controlled, and the EPS + EHPS power assistance is realized.

Specifically, the method comprises the following steps:

4.1) an electric pump control method is adopted to control an electric pump driving motor in the EHPS subsystem, so as to supply oil to the energy accumulator and ensure that the pressure of the energy accumulator is within a set range.

As shown in fig. 4, the electric pump control method includes the steps of:

4.1.1) acquiring the existing pressure of the energy accumulator through a pressure electromagnetic valve inlet sensor, acquiring vehicle speed information through a vehicle-mounted CAN bus, and filtering the acquired existing pressure of the energy accumulator by adopting a sliding average filtering method to reduce noise in a pressure signal. Wherein, when filtering, the time window length is 20.

P_lowset＝P_set-0.5

P_highset＝P_set+0.5

in the formula, P_setIs the target value (MPa), P, of the accumulator pressure_lowset、P_highsetRespectively, an electric pump opening pressure threshold and an electric pump closing pressure threshold (MPa), v_L、v_HV is the current vehicle speed for the set low vehicle speed threshold and the set high vehicle speed threshold.

4.1.3) judging the current on-off state of the electric pump, and if the current state of the electric pump is on, performing the step 4.1.4); if the current electric pump status is off, step 4.1.5) is performed.

4.1.4) comparing the existing pressure of the energy accumulator with the closing pressure threshold value of the electric pump, if the existing pressure of the energy accumulator is higher than the closing pressure threshold value of the electric pump, controlling the driving motor of the electric pump to stop working, and if the existing pressure of the energy accumulator is lower than the closing pressure threshold value of the electric pump, keeping the driving motor working.

4.1.5) comparing the current pressure of the energy accumulator with the opening pressure threshold of the electric pump, if the current pressure of the energy accumulator is higher than the opening pressure threshold of the electric pump, controlling the driving motor of the electric pump to start working and entering a rotating speed control mode, and if the current pressure of the energy accumulator is lower than the opening pressure threshold of the electric pump, keeping the driving motor in a standby state.

Wherein the rotation speed control mode comprises the following steps:

4.1.5.2) calculating the target motor torque by PI algorithm according to the target rotating speed and the actual rotating speed of the electric pump, and carrying out closed-loop control on the rotating speed of the electric pump.

The calculation formula of the motor target torque is as follows:

T_out＝k_p(ω_ref-ω)+k_i∫ω_ref-ωdt

in the formula, T_outTarget torque (Nm), ω, for output_refIs a target rotational speed (rpm), ω is a current rotational speed (rpm), k_p、k_iProportional and integral coefficients, respectively.

4.1.5.3) calculating the target motor current according to the target motor torque and the steering wheel rotating speed.

4.1.5.4) calculating the target motor voltage by PI algorithm according to the target motor current and the actual motor current.

4.1.5.5) calculating to obtain the three-phase duty ratio of the motor according to the target motor voltage and the position of the motor rotor, and further driving the motor to generate corresponding torque, so that the electric pump reaches corresponding rotating speed, and the accumulator is supplemented with hydraulic oil.

And 4.2) controlling the opening and closing states of the electromagnetic valve in the EHPS subsystem by adopting an electromagnetic valve control method, ensuring that the pressure in the steering gear is in a proper range, and ensuring the steering assistance to be smooth.

Specifically, the method comprises the following steps:

4.2.1) acquiring the vehicle speed, the steering wheel angle, the steering wheel torque, the energy accumulator pressure and the steering gear pressure by each sensor and a whole vehicle CAN bus, calculating based on the steering wheel angle to obtain the steering wheel rotating speed, and simultaneously carrying out filtering correction treatment on the acquired energy accumulator pressure, steering gear pressure and steering wheel torque to obtain the energy accumulator pressure, steering gear pressure and steering wheel torque T after filtering correction.

4.2.2) calculating to obtain a hydraulic power-assisted opening torque threshold T according to the vehicle speed information_{min_h}。

if T is less than T_{min_h}If the state of 12 electromagnetic valves is completely closed, the EHPS subsystem is in a standby state;

if T > T_{min_h}And the electromagnetic valve control algorithm is adopted to control the on-off of each electromagnetic valve in real time according to the input quantity, so that hydraulic power assistance is generated, and the defect of electric power assistance is overcome.

As shown in FIG. 5, the solenoid control algorithm includes the steps of:

4.2.3.1) calculating a first solenoid valve opening (%) according to the steering wheel torque and the vehicle speed information, and providing a basic solenoid valve opening according to the torque and a steering assisting force increasing with the steering wheel torque.

The implementation method comprises the steps of calibrating a steering wheel torque, a vehicle speed and a solenoid valve opening database by means of tests according to different target vehicles and hand feelings, and then looking up a table according to the calibrated database to obtain a first solenoid valve opening D corresponding to the actual steering wheel torque and the actual vehicle speed_{out_T}(％)。

4.2.3.2) according to the steering wheel torque, the energy accumulator pressure and the steering gear pressure, calculating to obtain a second electromagnetic valve opening (%), aiming at providing corresponding power assistance according to the change condition of the steering wheel torque, providing larger steering power assistance when the steering wheel torque is in the rising process, and otherwise providing smaller steering power assistance to ensure the stability of the steering wheel torque.

The implementation method can be described by the following formula:

D_{out_d}＝(D_L+D_H) f (. DELTA.P) formula, D_{out_d}Is a secondSolenoid valve opening (%), D_L、D_HIs D_outOf the low-frequency component and the high-frequency component, T_[n]The current moment steering wheel torque value (Nm), T_[n-1]Is the steering wheel torque value, T, of the previous moment_[n-2]The torque value of the steering wheel at the first two moments, and so on, K₁、K₂For the gain factor, f (Δ P) is a function of the pressure difference between the accumulator and the steering gear, and as a correction factor, between 0 and 1, the larger the pressure difference, the closer the value to 0, and vice versa, the closer to 1.

4.2.3.3) calculating to obtain a third electromagnetic valve opening (%) according to the rotating speed of the steering wheel, the pressure of the energy accumulator, the pressure of the steering gear and the vehicle speed.

When the energy-saving intelligent electro-hydraulic steering system performs hydraulic power assistance, the required flow is completely determined by the rotating speed of the steering wheel, so that the step aims to provide corresponding opening of the electromagnetic valve according to the rotating speed of the steering wheel, and the system is ensured to have enough flow. According to the orifice flow formula:

in the formula, A₀Is the area of the small hole (m)²)，C_dThe typical value is 0.60, rho is the liquid density, and deltap is the pressure difference (MPa) between two sides of the small hole. The flow through the orifice is proportional to the area of the orifice and proportional to the square root of the pressure differential across the orifice. Thus, the design solenoid valve opening is proportional to the steering wheel speed and inversely proportional to the square root of the accumulator-steering differential pressure, and the implementation method can be described by the following formula:

in the formula, D_{out_ω}Is the third electromagnetic valve opening (%), delta P is the pressure difference (MPa) between the energy accumulator and the steering gear, omega is the rotating speed (DEG/s) of the steering wheel, K is the gain coefficient, g (v) is the function of the vehicle speed (km/h), is used for correcting the opening of the output electromagnetic valve according to the vehicle speed to ensure the system damping, and is between 0 and 1The larger the vehicle speed, the closer the value to 0, and vice versa, the closer to 1.

4.2.3.4) calculating to obtain a fourth electromagnetic valve opening (%) according to the steering wheel torque, the vehicle speed and the steering gear pressure.

When the EPS assistance can not meet the actual requirement, and the hydraulic assistance is just started to intervene, the establishment of the pressure in the steering gear has certain delay, and the step aims to reduce the delay and improve the response of the system. The implementation method comprises the following steps: when the torque of the steering wheel is detected to be within a certain range, the pressure of the steering gear is controlled in a closed loop mode through P control, the pressure is controlled within a small range within 2MPa, and the subsequent pressure response is improved, wherein the calculation method of the opening degree of the electromagnetic valve comprises the following steps:

D_out-p＝k_p(P_ref(T，v)-P_raw)，D_{out_p}≥0

in the formula D_{out_p}Is the fourth solenoid valve opening (%), k_pIs a proportionality coefficient, P_ref(T, v) is the steering target pressure (MPa) which is a function of steering wheel torque T (Nm) and vehicle speed v (km/h), with a positive correlation with T and a negative correlation with v, up to 2MPa, P_rawThe steering gear pressure value (MPa) is acquired in real time.

D＝D_{out_T}+D_{out_d}+D_{out_ω}+D_{out_p}

The value is between 0 and 100%.

Because the solenoid valve that this system adopted is the solenoid valve group that 12 two-state normally closed solenoid valves constitute, wherein 0.4mm diameter valve port 4, 0.7mm diameter valve port 8, each solenoid valve only has two kinds of states of opening and closing, consequently can only realize limited solenoid valve opening. By switching the opening of the solenoid valve, specifically, the encoding manner is as follows: the method comprises the steps of taking 12 solenoid valves as 100% opening degree, combining all effective opening degrees generated by the combination of the 12 solenoid valves and corresponding opening and closing states to form a database, taking 12 solenoid valve opening degrees corresponding to the closest effective opening degree in the database as module output for any solenoid valve opening degree obtained through calculation, and delivering the module output to a driver for execution.

Further, in order to ensure the energy-saving effect of the system, the following requirements are met:

T_{min_e}≤T_{min_h}

T_eps|T＝T_{min_h}＞T_close

wherein, T_{min_e}Torque dead zone for electric power assistance, T_{min_h}Opening a threshold torque for hydraulic power assistance, T_closeThe torque corresponding to the middle open type steering control valve reaching the limit position is T, and T is the torque of the steering wheel.

The above embodiments are only used for illustrating the present invention, and the structure, connection mode, manufacturing process, etc. of the components may be changed, and all equivalent changes and modifications performed on the basis of the technical solution of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A control method for an energy-saving intelligent electro-hydraulic steering system is characterized by comprising the following steps:

1) determining the working mode of an energy-saving intelligent electro-hydraulic steering system based on the obtained steering wheel torque, wherein the energy-saving intelligent electro-hydraulic steering system comprises: the EPS system comprises a motor and a controller, wherein the controller is connected with the motor, and the motor is connected with the steering gear; the EHPS subsystem comprises an oil tank, an energy accumulator, an electric pump driving motor and an electromagnetic valve group, wherein an oil outlet of the electric pump is sequentially connected with the energy accumulator, the electromagnetic valve group and an oil inlet of a steering gear, an oil outlet of the steering gear is connected with the oil tank, and an oil inlet of the electric pump is connected with the oil tank; the working modes comprise a no-assistance mode, an EPS assistance mode and an EPS + EHPS assistance mode;

in the step 3), a method for calculating a three-phase duty ratio of a motor in the EPS subsystem by using a power control algorithm and outputting a corresponding control signal to the EPS subsystem to realize EPS power assistance comprises the following steps:

3.1) detecting the torque and the steering angle of the steering wheel through a steering wheel corner torque sensor, and acquiring the vehicle speed through a vehicle-mounted CAN bus;

3.2) calculating a three-phase duty ratio of a motor in the EPS subsystem according to a steering wheel rotation angle, torque and a vehicle speed and a power-assisted control algorithm, and then driving the motor to generate corresponding torque to realize steering power assistance;

in the step 3.2), the method for calculating the three-phase duty ratio of the motor in the EPS subsystem according to the power-assisted control algorithm comprises the following steps:

3.2.1) calculating to obtain the steering wheel torque which is corrected by filtering according to the steering wheel torque which is collected in real time;

wherein, the transfer function C(s) of the filtering correction is:

ω_o[n]＝ω_o[n-1]+ΔTε_o[n-1]+K₂(θ_[n]-θ_o[n])

ε_o[n]＝ε_o[n-1]+K₃(θ_[n]-θ_o[n])

is an estimate of the steering wheel angle, theta is a measure of the steering wheel angle, subscript n]Indicates the current time, [ n-1 ]]Indicates the last time, K₁、K₂、K₃To estimate the coefficients, Δ T is the calculation period;

3.2.6) calculating to obtain the three-phase duty ratio of the motor according to the target motor voltage and the position of the motor rotor, and further driving the motor to generate corresponding torque to perform steering assistance;

2. The control method for the energy-saving intelligent electro-hydraulic steering system as claimed in claim 1, wherein: in the step 1), the method for determining the working mode of the energy-saving intelligent electro-hydraulic steering system comprises the following steps:

1.1) detecting the torque of a steering wheel in real time through a steering wheel corner torque sensor;

1.2) determining whether the steering wheel torque is within a set dead band range, i.e. greater than a set minimum starting torque T_{min_e}: if the steering wheel torque is within the dead band range, i.e., T ≦ T_{min_e}If the EPS subsystem enters a damping control mode, no power assistance is generated, and the EHPS subsystem enters a standby state; if the steering wheel torque is not in the deadband range, i.e. T > T_{min_e}Starting the EPS subsystem for assisting power;

3. The control method for the energy-saving intelligent electro-hydraulic steering system as claimed in claim 1, wherein: in the step 2), a calculation formula of the short-circuit duty ratio of the motor is as follows:

in the formula, v_cmin、v_cmaxA low vehicle speed threshold and a high vehicle speed threshold respectively, and Dc is a short-circuit duty ratio; k is a short circuit duty ratio set value; and v is the vehicle speed.

4. The control method for the energy-saving intelligent electro-hydraulic steering system as claimed in claim 1, wherein: in the step 4), the hydraulic assist control method includes the steps of:

the method comprises the following steps:

P_lowset＝P_set-0.5

P_highset＝P_set+0.5

in the formula, P_setFor the accumulator pressure target value, P_lowset、P_highsetRespectively electric pump opening pressure threshold and electric pump closing pressure threshold, v_L、v_HSetting a low vehicle speed threshold value and a high vehicle speed threshold value, wherein v is the current vehicle speed;

4.1.4) comparing the existing pressure of the energy accumulator with the closing pressure threshold value of the electric pump, if the existing pressure of the energy accumulator is higher than the closing pressure threshold value of the electric pump, controlling the driving motor of the electric pump to stop working, and if the existing pressure of the energy accumulator is lower than the closing pressure threshold value of the electric pump, keeping the driving motor working;

the method comprises the following steps:

5. The control method for the energy-saving intelligent electro-hydraulic steering system as claimed in claim 4, wherein the control method comprises the following steps: in the step 4.1.5), the rotation speed control mode comprises the following steps:

4.1.5.1) calculating to obtain the target motor speed according to the current pressure and the set pressure of the energy accumulator; outputting an expected motor rotating speed according to the difference value between the set pressure of the energy accumulator and the current pressure by relying on a database calibrated by a test, wherein the larger the difference value is, the higher the expected rotating speed is, and the oil supply speed is increased;

4.1.5.2) calculating to obtain target motor torque by adopting PI algorithm according to the target rotating speed and the actual rotating speed of the electric pump, and performing closed-loop control on the rotating speed of the electric pump;

the calculation formula of the motor target torque is as follows:

T_out＝k_p(ω_ref-ω)+k_i∫ω_ref-ωdt

in the formula, T_outTarget torque (Nm), ω, for output_refIs a target rotational speed (rpm), ω is a current rotational speed (rpm), k_p、k_iProportional coefficient and integral coefficient respectively;

4.1.5.4) calculating to obtain target motor voltage by PI algorithm according to the target motor current and the actual motor current;

6. The control method for the energy-saving intelligent electro-hydraulic steering system as claimed in claim 4, wherein the control method comprises the following steps: in the step 4.2.3), the electromagnetic valve control algorithm comprises the following steps:

D_{out_d}＝(D_L+D_H)f(ΔP)

in the formula D_{out_d}Solenoid valve opening (%) for output, D_L、D_HIs D_outOf the low-frequency component and the high-frequency component, T_[n]The current moment steering wheel torque value (Nm), T_[n-1]The steering wheel torque value, T, at the previous moment_[n-2]The torque value of the steering wheel at the first two moments, and so on, K₁、K₂F (delta P) is a function of the pressure difference between the energy accumulator and the steering gear and is used as a correction coefficient between 0 and 1, and the larger the pressure difference is, the more the value of the pressure difference approaches to 0, and the more the pressure difference approaches to 1;

4.2.3.3) calculating the opening of the third electromagnetic valve in percentage form according to the rotating speed of the steering wheel, the pressure of the energy accumulator, the pressure of the steering gear and the vehicle speed; the calculation formula is as follows:

in the formula D_{out_ω}Δ P is the accumulator-steering pressure difference, ω is the steering wheel speed, K is the gain factor, g (v) is a function of vehicle speed for the third solenoid opening;

4.2.3.4) calculating the opening degree of the fourth electromagnetic valve in a percentage form according to the torque of the steering wheel, the vehicle speed and the pressure of the steering gear, wherein the calculation formula is as follows:

D_{out_p}＝k_p(P_ref(T，v)-P_raw)，D_{out_p}≥0

in the formula D_{out_p}Is the opening of the fourth solenoid valve, k_pIs a proportionality coefficient, P_ref(T, v) is a steering target pressure that is a function of steering wheel torque T and vehicle speed v;

D＝D_{out_T}+D_{out_d}+D_{out_ω}+D_{out_p}

7. A control system for an energy-saving intelligent electro-hydraulic steering system by adopting the method of any one of claims 1 to 6, wherein the control system is connected with the energy-saving intelligent electro-hydraulic steering system and comprises: the device comprises a working mode judging module, a damping control module, an electric power-assisted control module and a hydraulic power-assisted control module; the working mode judging module is used for determining a working mode of the energy-saving intelligent electro-hydraulic steering system based on the acquired steering wheel torque, sending a control signal to the damping control module when the working mode is a no-power mode, sending a control signal to the electric power assisting control module when the working mode is an EPS (electric power steering) power assisting mode, and sending a control signal to the electric power assisting control module and the hydraulic power assisting control module when the working mode is an EPS + EHPS power assisting mode; the damping control module is used for acquiring a short-circuit duty ratio of the motor according to the vehicle speed information and controlling the motor in the EPS subsystem to generate damping based on the short-circuit duty ratio; the electric power-assisted control module is used for calculating the three-phase duty ratio of a motor in the EPS subsystem by adopting a power-assisted control algorithm and outputting a corresponding control signal to the EPS subsystem to realize EPS power assistance; the hydraulic power assisting module is used for calculating the three-phase duty ratio of an electric pump driving motor in the EHPS subsystem and the opening and closing state of the electromagnetic valve by adopting a hydraulic power assisting control method, then driving the electric pump driving motor to generate corresponding torque, and simultaneously controlling the opening and closing of the electromagnetic valve to realize hydraulic power assisting.

8. The control system for the energy-saving intelligent electro-hydraulic steering system according to claim 7, wherein: the electric power-assisted control module comprises a steering wheel torque filtering correction module, an electric power-assisted characteristic database, a steering wheel rotating speed calculation module, a weak magnetic control module, a motor current closed-loop control module and a space vector pulse width modulation module; the input of the steering wheel torque filtering correction module is steering wheel torque acquired in real time, and the output is the steering wheel torque subjected to filtering correction; the input of the electric power-assisted characteristic database is steering wheel torque and vehicle speed, and the output is target motor torque; the input of the steering wheel rotating speed calculating module is a steering wheel rotating angle acquired in real time, and the output is the steering wheel rotating speed at the current moment; the input of the weak magnetic control module is target motor torque and steering wheel rotating speed, and the output is target motor current; the input of the motor current closed-loop control module is target current and motor current, and the output is motor voltage; the input of the space vector pulse width modulation module is target motor voltage and motor rotor position, and the output is motor three-phase duty ratio;