A vehicle steering assist method, device and system

Abstract

The application provides a vehicle steering assisting method, device and system. The device comprises a vehicle hydraulic braking system, wherein the vehicle hydraulic braking system comprises a pressure building main path, a pressure building branch path, a liquid storage tank and wheel cylinders. The pressure building main path is communicated with the pressure building branch path, brake fluid can flow from the liquid storage tank to the pressure building branch path through the pressure building main path, and the pressure building branch path is communicated with the wheel cylinders of different wheels from the communication position with the pressure building main path. A pressure building valve is arranged on the path of the pressure building branch path leading to the wheel cylinders of different wheels. The pressure building valves on the paths of different wheel cylinders can cause pressure difference between the wheel cylinders, form wheel speed difference between the wheels and generate steering assisting force. The application can improve the functional safety level of the whole vehicle without setting a redundant electric power steering device, and the safety and economy are considered, the modification of the whole vehicle is small, and the adaptability is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of vehicle steering control, in particular to a vehicle steering assist method, device and system. BACKGROUND

[0002] The vehicle assist steering system is a system that enables the driver to complete the vehicle steering with less force by means of external force. The assist steering system currently configured on the vehicle is roughly divided into three categories: mechanical hydraulic power steering system, electronic hydraulic assist steering system and electric power assist steering system. Among them, the electric power assist steering system relies on the assist motor to provide auxiliary torque for the wheels. When the driver operates the steering wheel, the torque sensor detects the torque (also known as steering wheel hand force) applied by the driver on the steering wheel and generates a corresponding torque voltage signal, the angle sensor detects the steering angle of the steering wheel and generates a corresponding steering voltage signal, and the vehicle speed sensor detects the current vehicle speed signal. The electronic control unit generates a power steering instruction based on the torque voltage signal, the steering voltage signal and the current vehicle speed signal obtained from the torque sensor, the angle sensor and the vehicle speed sensor, respectively, to control the operation of the assist motor, so that the assist motor generates the required steering assist torque. When the assist motor fails, in order to avoid unintended assist to the vehicle, the corresponding control module will directly cut off the steering assist provided by the assist motor. After the steering assist is cut off, if the vehicle is in a low-speed driving state at this time, the road resistance is large and the vehicle urgently needs to turn, it is extremely likely that the steering will not be timely and traffic accidents will occur.

[0003] In order to prevent the occurrence of the above situation, the electric power assist steering system is usually redundantly designed in the related technology, that is, two sets of electric power assist steering devices are configured, including a main electric power assist steering device and an auxiliary electric power assist steering device. Under normal circumstances, the main electric power assist steering device provides 100% steering assist. When the main electric power assist steering device fails, the steering assist of the main electric power assist steering device is cut off, the auxiliary electric power assist steering device is awakened, and the auxiliary electric power assist steering device provides 100% steering assist for the vehicle. Alternatively, under normal circumstances, the main electric power assist steering device provides 50% steering assist, and the auxiliary electric power assist steering device provides the remaining 50% steering assist. When either of the two fails, the remaining one continues to provide steering assist. The disadvantage of this redundant design is that the double electric power assist steering devices will increase the structural complexity of the vehicle and require more layout space. In addition, the double electric power assist steering devices will directly increase the weight, development cost and production cost of the whole vehicle, which is not conducive to the lightweight of the vehicle.

[0004] Based on this, the inventor finds that in the hydraulic braking system, when the wheel cylinder pressures corresponding to different wheels are different, the forces of the brakes of the hydraulic braking system on the wheels are also different, which causes the wheel speed difference between the wheels, and further causes the vehicle to deflect to one side. When the wheel speed difference can be artificially controlled, the purpose of providing steering assistance for the vehicle is achieved. More specifically, as shown in Figure 1 The hydraulic braking system includes a liquid storage tank 1 storing brake fluid, a pressure building main path A, a pressure releasing main path B, a master cylinder 2, and a wheel cylinder 3. The wheel cylinder 3 corresponds to a wheel 4 one-to-one. Each wheel 4 is provided with a single wheel cylinder 3 corresponding thereto. The wheel cylinder 3 is connected to the pressure building main path A and the pressure releasing main path B, respectively. In the pressure releasing main path B, one end of the pressure releasing main path B is connected to the wheel cylinder 3, and the other end is connected to the liquid storage tank 1. In the pressure building main path A, one end of the pressure building main path A is connected to the wheel cylinder 3, and the other end is connected to the master cylinder 2. The master cylinder 2 is connected to the liquid storage tank 1 in addition to being connected to the pressure building main path A. In addition, the pressure in the master cylinder 2 is generally controlled by a corresponding mechanical device driven by a pressure building motor 5. When the vehicle does not need to brake or the braking is completed, the hydraulic oil in the wheel cylinder 3 enters the pressure releasing main path B under the action of an externally provided delivery pump (not shown in the figure), and flows to the liquid storage tank 1 via the pressure releasing main path B. When the vehicle brakes, the brake fluid in the liquid storage tank 1 flows into the master cylinder 2. The brake fluid in the master cylinder 2 is discharged into the pressure building main path A under the driving of the mechanical device driven by the pressure building motor 5, and flows into the wheel cylinder 3 via the pressure building main path A. The wheel cylinder 3 then applies pressure to the brake to brake the wheel 4, so as to change the acceleration of the wheel 4. When the pressures of the wheel cylinders 3 flowing into different wheels 4 are different, the degrees of braking of the wheels 4 by the wheel cylinders 3 are also different. The acceleration differences between the wheels 4 also appear, and further, the wheel speed difference is generated, which causes the vehicle to deflect to the side where the wheel with higher speed is located. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a vehicle steering assistance method, device and system, which can complete the action of assisting vehicle steering when the electric power steering device of the vehicle fails without setting a double electric power steering device.

[0006] The present application provides a vehicle steering assistance device, which comprises a vehicle hydraulic braking system. The vehicle hydraulic braking system comprises a pressure building main path, a pressure building branch path, a liquid storage tank and a wheel cylinder. The pressure building main path is connected to the pressure building branch path. Brake fluid can flow from the liquid storage tank into the pressure building branch path via the pressure building main path. The pressure building branch path leads to wheel cylinders of different wheels from the connection position with the pressure building main path. A pressure building valve is arranged on the passage of the pressure building branch path leading to the wheel cylinders of different wheels. The pressure building valves on the passages of different wheel cylinders can cause pressure differences between the wheel cylinders, form wheel speed differences between the wheels, and generate steering assistance.

[0007] Optionally, a master cylinder is further included, which is connected with the pressure building main line, and brake fluid in the master cylinder can be discharged into the pressure building main line when the pressure in the master cylinder changes.

[0008] Optionally, the pressure building main line connects the liquid storage tank and the pressure building branch line, the master cylinder is connected with an auxiliary pressure building branch line, one end of the auxiliary pressure building branch line is connected with the master cylinder, and the other end is connected with the pressure building main line, and the connection port of the auxiliary pressure building branch line with the pressure building main line is located between the liquid storage tank and the connection port of the pressure building main line with the pressure building branch line.

[0009] The application further provides a vehicle steering assist method using the vehicle steering assist device as claimed in any one of the above, comprising:

[0010] judging whether the electric power steering device is failed;

[0011] if the electric power steering device is judged to be failed, detecting the steering wheel angle information, the steering wheel hand force information and the vehicle speed;

[0012] calculating the steering assist force to be generated and the speed of building the steering assist force according to the steering wheel angle information, the steering wheel hand force information and the vehicle speed;

[0013] controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the steering assist force to be generated and the speed of building the steering assist force, so as to form the pressure difference between the wheel cylinders and cause the wheel speed difference between the wheels, thereby generating the steering assist force.

[0014] Optionally, the step of controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the steering assist force to be generated and the speed of building the steering assist force, so as to form the pressure difference between the wheel cylinders comprises: judging whether there is a braking demand, and if there is a braking demand, the pressure in the wheel cylinders first meets the requirement of the braking operation.

[0015] Optionally, the step of judging whether the electric power steering device is failed comprises:

[0016] collecting a fault signal;

[0017] if at least one of the following faults occurs in the electric power steering device: the assist motor driving chip fault, the assist motor driving bridge fault, the assist motor winding fault, the assist motor rotor position sensor fault and the assist motor current sensor fault, the electric power steering device is judged to be failed.

[0018] Optionally, the step of controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the steering assist force to be generated and the speed of building the steering assist force, so as to form the pressure difference between the wheel cylinders comprises:

[0019] If the steering wheel angle is greater than 0° and less than 180°, the pressure difference between the wheel cylinders is selected from the first pressure difference selection range; if the steering wheel angle is greater than 180° and less than 360°, the pressure difference between the wheel cylinders is selected from the second pressure difference selection range; if the steering wheel angle is greater than 360° and less than 540°, the pressure difference between the wheel cylinders is selected from the third pressure difference selection range; if the steering wheel angle is greater than 540°, the pressure difference between the wheel cylinders is selected from the fourth pressure difference selection range, and the upper and lower limits of the first pressure difference selection range, the second pressure difference selection range, the third pressure difference selection range and the fourth pressure difference selection range increase in turn.

[0020] Optionally, the step of controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the steering assist force to be generated and the speed of building the steering assist force to form the pressure difference between the wheel cylinders comprises:

[0021] If the steering wheel angle is in the first angle range, the wheel cylinders build pressure at a first speed; if the steering wheel angle is in the second angle range, the wheel cylinders build pressure at a second speed; if the steering wheel angle is in the third angle range, the wheel cylinders build pressure at a third speed; if the steering wheel angle is in the third angle range, the pressure building speed of the wheel cylinders is not greater than the third speed, and the upper and lower limits of the first angle range, the second angle range and the third angle range increase in turn, and the first speed, the second speed and the third speed decrease in turn.

[0022] Optionally, the step of controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the steering assist force to be generated and the speed of building the steering assist force to form the pressure difference between the wheel cylinders comprises: if the vehicle speed is in the first vehicle speed range, the wheel cylinders build pressure at a fifth speed; if the vehicle speed is in the second vehicle speed range, the wheel cylinders build pressure at a sixth speed; if the vehicle speed is in the third vehicle speed range, the wheel cylinders build pressure at a seventh speed, and the upper and lower limits of the first vehicle speed range, the second vehicle speed range, the third vehicle speed range and the fourth vehicle speed range increase in turn, and the upper and lower limits of the fifth speed, the sixth speed and the seventh speed decrease in turn.

[0023] The application also provides a vehicle steering assist system using the vehicle steering assist device according to any one of the above, comprising:

[0024] An electric power steering system for providing steering assist for vehicle steering and sending a steering system failure signal and a current steering wheel angle signal to a braking system when the electric power steering system fails;

[0025] A braking system for activating a steering assist function according to the steering system failure signal and commanding the above vehicle steering assist device to work according to the vehicle steering assist method according to any one of the above according to the steering wheel angle information, the steering wheel hand force information and the vehicle speed to build the pressure difference between the wheel cylinders corresponding to the steering wheels to complete the steering assist action.

[0026] In summary, the present application has the following beneficial effects:

[0027] 1、The present application can improve the functional safety level of the whole vehicle without setting a redundant electric power steering device, and takes into account safety and economy;

[0028] 2、The vehicle steering assist device provided by the present application is improved on the basis of the standard braking control system of the whole vehicle, and compared with the standard vehicle braking control system, only a pressure building valve (such as a first pressure building valve) is newly added on the corresponding steering wheel side for controlling pressure building, and the control logic between each electronic module is correspondingly modified, so that the modification of the whole vehicle is small and the adaptability is high.

[0029] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, and to be implemented in accordance with the content of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following preferred embodiments are described in detail, and the accompanying drawings are described as follows. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a schematic diagram of the hydraulic braking system corresponding to a single wheel in the related art.

[0031] Figure 2 It is a schematic diagram of the device for vehicle steering assist failure in the embodiment of the present application.

[0032] MARKED FOR EXPLANATION

[0033] A-Pressure building main road, B-Pressure relief main road, C-Pressure building branch, D-Assisted pressure building branch;

[0034] 1-Reservoir, 2-Master cylinder, 3-Wheel cylinder, 31-First wheel cylinder, 32-Second wheel cylinder, 4-Wheel, 41-First wheel, 42-Second wheel, 5-Pressure building motor, 6-First pressure building valve, 7-Second pressure building valve, 8-First pressure relief valve, 9-Second pressure relief valve. DETAILED DESCRIPTION

[0035] The specific embodiments of the present application will be further described in detail below in combination with the drawings and examples. The following examples are used to illustrate the present application, but not to limit the scope of the present application.

[0036] The terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence.

[0037] As Figure 2As shown, the embodiment provides a vehicle steering assist device, which comprises an electric power steering system and a brake system, the electric power steering system is used to send signals (including current steering wheel angle signal and steering system failure signal) to the brake system when it fails, so that the brake system can be in an auxiliary steering state in response to the steering system failure signal, and a pressure difference between left and right wheel cylinders is generated to provide steering assist for the vehicle and drive the vehicle to steer to the low speed wheel side.

[0038] In the embodiment, the brake system is applied to the left front wheel and the right front wheel of a vehicle using disc brakes, which comprises a liquid storage tank 1 containing brake fluid, a pressure building main line A, a pressure building branch line C, a pressure relief main line B, a master cylinder 2 and a wheel cylinder 3, wherein the wheel cylinder 3 comprises a first wheel cylinder 31 and a second wheel cylinder 32, the left front wheel is the first wheel 41, and the right front wheel is the second wheel 42, the first wheel cylinder 31 is arranged on the first wheel 41, and the second wheel cylinder 32 is arranged on the second wheel 42, on the pressure building main line A, one end of the pressure building main line A is communicated with the liquid storage tank 1, and the other end is communicated with the pressure building branch line C, the pressure building branch line C divides into two branches from the communication position with the pressure building main line A, and the two branches are communicated with the first wheel cylinder 31 and the second wheel cylinder 32 respectively, on the channel of the pressure building branch line C leading to each wheel cylinder, a pressure building valve is arranged, the pressure building valve comprises a first pressure building valve 6 and a second pressure building valve 7, the first pressure building valve 6 is arranged on the channel of the pressure building branch line C leading to the first wheel cylinder 31, and the second pressure building valve 7 is arranged on the channel of the pressure building branch line C leading to the second wheel cylinder 32, in addition, the pressure building main line A is also communicated with an auxiliary pressure building branch line D, the communication port of the auxiliary pressure building branch line D with the pressure building main line A is located between the liquid storage tank 1 and the communication port of the pressure building main line A with the pressure building branch line C, one end of the auxiliary pressure building branch line D is communicated with the pressure building main line A, and the other end is communicated with the master cylinder 2, the master cylinder 2 is filled with brake fluid, the pressure of the outlet of the master cylinder 2 is controlled by a corresponding mechanical device, and the mechanical device is driven by a pressure building motor 5.

[0039] As described above, one end of the pressure relief main line B is connected to the liquid storage tank 1, and the other end is divided into two pressure relief branches, which are respectively connected to the first wheel cylinder 31 and the second wheel cylinder 32. On the pressure relief branch leading to the first wheel cylinder 31, the first pressure relief valve 8 is arranged, and on the pressure relief branch leading to the second wheel cylinder 32, the second pressure relief valve 9 is arranged. When only braking is needed, the first pressure building valve 6 and the second pressure building valve 7 are controlled to be fully open, and the pressure building motor 5 is controlled to drive the mechanical device to change the flow of brake fluid from the master cylinder 2 into the pressure building main line A, so that the brake fluid flows into the first wheel cylinder 31 and the second wheel cylinder 32, respectively, thereby normally braking the first wheel 41 and the second wheel 42. After braking, the first pressure relief valve 8 and the second pressure relief valve 9 are controlled to be fully open, so that the brake fluid flows back into the liquid storage tank 1 under the action of the pressure difference, thereby completing the entire vehicle braking process. When steering is needed, it is determined whether the pressure building motor 5 needs to work according to the requirement, and the working parameters (such as opening time or opening degree) of the first pressure building valve 6 and the second pressure building valve 7 are controlled, respectively, so that a pressure difference is generated between the first wheel cylinder 31 and the second wheel cylinder 32, thereby causing the first wheel 41 and the second wheel 42 to be clamped by the corresponding disc brake calipers, resulting in a wheel speed difference between the first wheel 41 and the second wheel 42, and thereby assisting the vehicle steering.

[0040] As described above, the vehicle steering assist device can assist the vehicle steering when the electric power steering assist device fails. In the device, the pressure building main line A is directly connected to the liquid storage tank 1, the master cylinder 2 is connected to the auxiliary pressure building branch D, and the auxiliary pressure building branch D is designed as a branch connected to the pressure building main line A, which can reduce the number of times the corresponding pressure building motor 5 of the master cylinder 2 is awakened and save energy. Based on the device, the embodiment further provides a vehicle steering assist method, which includes the following steps:

[0041] S1: Determine whether the electric power steering assist device fails, and if the electric power steering assist device fails, send a steering system failure signal and a current steering wheel angle signal to the braking system. More specifically, when the electric power steering assist device fails due to any of the following faults, such as a power steering motor drive chip fault, a power steering motor drive bridge fault, a power steering motor winding fault, a power steering motor rotor position sensor fault, and a power steering motor current sensor fault, it is determined that the electric power steering assist device fails and cannot normally provide steering assist, and a steering system failure signal and a current steering wheel angle signal are sent to the braking system, and a steering failure light on the vehicle instrument panel is turned on to remind the driver that the steering device has failed.

[0042] S2: The braking system activates the steering assist function according to the steering system failure signal, detects the steering wheel hand force information and the vehicle speed, and then enters step S3.

[0043] S3: According to the steering wheel angle information and the steering wheel hand force information, the required steering assist force and the building speed of the steering assist force are confirmed (the steering wheel hand force information is mainly collected to determine the degree of impatience of the driver's expected steering), and the working parameters (opening time or opening degree) of the first pressure building valve 6 and the second pressure building valve 7 are determined according to the required steering assist force and the building speed of the steering assist force, so as to realize the pressure difference between the first wheel cylinder 31 and the second wheel cylinder 32 by controlling the working parameters of the first pressure building valve 6 and the second pressure building valve 7, provide steering assist force for the vehicle, and drive the vehicle to steer to the low speed wheel side. In other embodiments of the present application, if the driver needs to steer when the electric power steering device fails, the brake pedal is pressed at the same time, the working parameters of the first pressure building valve 6 and the second pressure building valve 7 need to be further determined in combination with the braking demand (braking torque) to make the corresponding first wheel cylinder 31 and second wheel cylinder 32 can provide sufficient braking force to complete the braking of the vehicle. It should be noted that if the driver presses the brake pedal while steering, the device will first make the pressure in the first wheel cylinder 31 and the second wheel cylinder 32 meet the requirements of the brake operation, and then increase the pressure in the wheel cylinder 3 on the side of the steering direction of the steering wheel, and maintain the pressure in the other side of the wheel cylinder 3, drive the vehicle to steer to the low speed wheel side, to complete the steering assist action.

[0044] It should be further noted that the calculation of the required steering assist force and the building speed of the steering assist force according to the steering wheel angle information and the steering wheel hand force information belongs to the common knowledge of those skilled in the art, and this embodiment will not be repeated here. The corresponding relationship between the required steering assist force, the working parameters of the first pressure building valve 6 and the second pressure building valve 7, the pressure difference between the first wheel cylinder 31 and the second wheel cylinder 32, and the building speed of the steering assist force, and the corresponding relationship between the braking demand assist force and these parameters when there is a braking demand, etc. are all calibrated in advance and pre-stored in the corresponding system control module.

[0045] The corresponding relationship between the steering wheel angle and the steering assist force, and the corresponding relationship between the steering assist force and the required pressure difference between the wheel cylinders, and the preferred corresponding relationship between the steering wheel angle and the pressure difference are as follows:

[0046] For example, when the steering wheel angle is greater than 0° and less than 180°, the pressure difference between the first wheel cylinder 31 and the second wheel cylinder 32 is selected from a first pressure difference selection range (for example, greater than 3 MPa and less than 5 MPa); when the steering wheel angle is greater than 180° and less than 360°, the pressure difference between the first wheel cylinder 31 and the second wheel cylinder 32 is selected from a second pressure difference selection range (for example, greater than 5 MPa and less than 8 MPa); when the steering wheel angle is greater than 360° and less than 540°, the pressure difference between the first wheel cylinder 31 and the second wheel cylinder 32 is selected from a third pressure difference selection range (for example, greater than 8 MPa and less than 9 MPa); when the steering wheel angle is greater than 540°, the pressure difference between the first wheel cylinder 31 and the second wheel cylinder 32 is selected from a fourth pressure difference selection range (for example, greater than 9 MPa and less than 11 MPa), and the upper and lower limits of the first pressure difference selection range, the second pressure difference selection range, the third pressure difference selection range and the fourth pressure difference selection range increase in turn. It should be noted that as the steering wheel angle increases to a certain extent (such as greater than 360°), the pressure difference between the first wheel cylinder 31 and the second wheel cylinder 32 will reach saturation, in order to prevent the pressure difference between the first wheel cylinder 31 and the second wheel cylinder 32 from affecting the normal braking operation of the vehicle of the braking system, therefore, after the steering wheel angle increases to a certain extent, the degree of change of the pressure difference between the first wheel cylinder 31 and the second wheel cylinder 32 should gradually decrease, therefore, the pressure difference curve gradually becomes flat after the steering wheel angle reaches a certain range. Further, when determining the speed at which the steering assist needs to be constructed, the steering wheel angle and / or vehicle speed factors also need to be considered, for example:

[0047] Assuming that in the first round of the first cylinder 31 and the second cylinder 32 pressure building process, the steering wheel angle is in the first corner range (for example, greater than 0° less than 40°) when the first cylinder 31 and the second cylinder 32 with the first speed build pressure, the steering wheel angle is in the second corner range (for example, 40° or more and less than 360°) when the first cylinder 31 and the second cylinder 32 with the second speed build pressure, the steering wheel angle is in the third corner range (for example, 360° or more and less than 540°) when the first cylinder 31 and the second cylinder 32 with the third speed build pressure, the steering wheel angle is in the fourth corner range (for example, 540° or more and less than 900°) when the first cylinder 31 and the second cylinder 32 with the fourth speed build pressure, and the upper and lower limits of the first corner range, the second corner range, the third corner range, the fourth corner range are sequentially increased, the first speed, the second speed, the third speed, the fourth speed are sequentially decreased, the first corner range, the second corner range, the third corner range, the fourth corner range, the first speed, the second speed, the third speed and the fourth speed can be flexibly set by those skilled in the art under the premise of meeting the above size relationship; The reason for such setting is that the hydraulic circuit needs a certain time to fill the brake fluid in the entire pipeline during the initial pressure building process, which will cause a certain delay, so a larger pressure building speed is needed when the steering wheel is in a small corner range (such as 0-40°) to quickly fill the brake fluid in the entire pipeline and increase the response speed in the small corner range.

[0048] Furthermore, assuming that during the pressure build-up process, when the vehicle speed is within a first speed range (e.g., greater than 0 km / h and less than 20 km / h), the first wheel cylinder 31 and the second wheel cylinder 32 build pressure at a fifth speed (preferably a value below 60 MPa / s); when the vehicle speed is within a second speed range (e.g., above 20 km / h and less than 40 km / h), the first wheel cylinder 31 and the second wheel cylinder 32 build pressure at a sixth speed (preferably a value range greater than 50 MPa / s and less than 60 MPa / s); and when the vehicle speed is within a third speed range (e.g., above 40 km / h)... At this time, the first wheel cylinder 31 and the second wheel cylinder 32 build up pressure at a seventh speed (preferably within a range of 45 MPa / s or less). Furthermore, the upper and lower limits of the first, second, and third vehicle speed ranges increase sequentially, while the upper and lower limits of the fifth, sixth, and seventh speeds decrease sequentially. This is because at low vehicle speeds, the pressure-building speed of the first wheel cylinder 31 and the second wheel cylinder 32 can be set faster according to actual needs, providing the driver with quicker steering response. However, at high vehicle speeds, the pressure-building speed needs to be reduced to prevent excessive pressure build-up from causing a rollover accident. When the vehicle simultaneously has steering wheel angle and vehicle speed, one possible method for determining the final pressure-building speed is to first determine the preferred range of pressure-building speed based on the vehicle speed, then determine the aforementioned first, second, third, and fourth speeds, which decrease sequentially within this preferred range, and finally obtain the corresponding pressure-building speed based on the current steering wheel angle.

[0049] Based on the above-described vehicle steering assist device and vehicle steering assist method, this embodiment also provides a vehicle steering assist system, which includes:

[0050] The electric power steering system is used to provide steering assistance for vehicle steering and, in the event of its failure, sends a steering system failure signal and the current steering wheel angle signal to the braking system.

[0051] The braking system is used to activate the power steering function based on the steering system failure signal, and to command the vehicle power steering device to work according to the vehicle power steering method based on the steering wheel angle information, steering wheel force information and vehicle speed, so as to establish the pressure difference between each wheel cylinder 3 corresponding to the steering wheel and complete the power steering action.

[0052] In summary, by defining a vehicle steering assist method, device, and system, this invention enables the vehicle to provide steering assistance by creating a pressure difference between the corresponding wheel cylinders 3 when the electric power steering device fails. This invention has the following beneficial effects:

[0053] 1. This invention can improve the functional safety level of the whole vehicle without setting redundant electric power steering devices, thus balancing safety and economy.

[0054] 2. The vehicle steering assist device provided by the application is improved on the basis of the brake control system of the whole vehicle, and compared with the original vehicle brake control system, only a pressure building valve (such as the first pressure building valve 6) is additionally arranged on the corresponding steering wheel side for controlling pressure building, and the control logic among the electronic modules is correspondingly modified, so that the whole vehicle is less changed and has high adaptability.

[0055] The above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the application, which should be covered within the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A vehicle steering assist device characterized by comprising: The hydraulic brake system of the vehicle comprises a pressure building main line, a pressure building branch line, a liquid storage tank and wheel cylinders, the pressure building main line is communicated with the pressure building branch line, brake fluid can flow from the liquid storage tank into the pressure building branch line through the pressure building main line, the pressure building branch line leads to the wheel cylinders of different wheels respectively from the communication position with the pressure building main line, pressure building valves are arranged on the passages of the pressure building branch line leading to the wheel cylinders of different wheels, the pressure building valves on the passages of different wheel cylinders can cause pressure difference between the wheel cylinders, form wheel speed difference between the wheels and generate steering assist; the hydraulic brake system further comprises a master cylinder, the master cylinder is communicated with the pressure building main line, brake fluid in the master cylinder can be discharged into the pressure building main line when the pressure in the master cylinder changes, the pressure building main line connects the liquid storage tank and the pressure building branch line, the master cylinder is communicated with an auxiliary pressure building branch line, one end of the auxiliary pressure building branch line is communicated with the master cylinder, and the other end is communicated with the pressure building main line, the communication port of the auxiliary pressure building branch line with the pressure building main line is located between the liquid storage tank and the communication port of the pressure building main line with the pressure building branch line.

2. A vehicle steering assist method characterized by, The vehicle steering assist device comprises: determining whether the electric power steering device is failed; if the electric power steering device is determined to be failed, detecting the steering wheel angle information, steering wheel hand force information and vehicle speed; calculating the required steering assist force and the speed of building the steering assist force according to the steering wheel angle information, steering wheel hand force information and vehicle speed; controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the required steering assist force and the speed of building the steering assist force, so as to form pressure difference between the wheel cylinders, cause wheel speed difference between the wheels and generate steering assist.

3. The vehicle steering assist method of claim 2 wherein, The step of controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the required steering assist force and the speed of building the steering assist force, so as to form pressure difference between the wheel cylinders, comprises:

4. The vehicle steering assist method of claim 2, wherein if there is a braking demand, the pressure in each wheel cylinder first meets the requirement of the braking operation. The step of determining whether the electric power steering device is failed, comprises: collecting fault signals; 5. The vehicle steering assist method of claim 2 wherein, if at least one of the following faults occurs in the electric power steering device, the electric power steering device is determined to be failed: assist motor driving chip fault, assist motor driving bridge fault, assist motor winding fault, assist motor rotor position sensor fault and assist motor current sensor fault. The step of controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the required steering assist force and the speed of building the steering assist force, so as to form pressure difference between the wheel cylinders, comprises: If the steering wheel angle is greater than 0° and less than 180°, the pressure difference between the wheel cylinders is selected from a first pressure difference selection range; if the steering wheel angle is greater than 180° and less than 360°, the pressure difference between the wheel cylinders is selected from a second pressure difference selection range; if the steering wheel angle is greater than 360° and less than 540°, the pressure difference between the wheel cylinders is selected from a third pressure difference selection range; if the steering wheel angle is greater than 540°, the pressure difference between the wheel cylinders is selected from a fourth pressure difference selection range, and the upper and lower limits of the first, second, third and fourth pressure difference selection ranges are increased in turn.

6. The vehicle steering assist method of claim 2 wherein, The step of controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the required steering assist force and the speed of building the steering assist force to form the pressure difference between the wheel cylinders comprises: If the steering wheel angle is in a first steering angle range, the wheel cylinders build pressure at a first speed; if the steering wheel angle is in a second steering angle range, the wheel cylinders build pressure at a second speed; if the steering wheel angle is in a third steering angle range, the wheel cylinders build pressure at a third speed, and the upper and lower limits of the first, second and third steering angle ranges are increased in turn, and the first, second and third speeds are decreased in turn.

7. The vehicle steering assist method of claim 2 wherein, The step of controlling the working parameters of the pressure building valves corresponding to the wheel cylinders according to the required steering assist force and the speed of building the steering assist force to form the pressure difference between the wheel cylinders comprises: if the vehicle speed is in a first vehicle speed range, the wheel cylinders build pressure at a fifth speed; if the vehicle speed is in a second vehicle speed range, the wheel cylinders build pressure at a sixth speed; if the vehicle speed is in a third vehicle speed range, the wheel cylinders build pressure at a seventh speed, and the upper and lower limits of the first, second and third vehicle speed ranges are increased in turn, and the upper and lower limits of the fifth, sixth and seventh speeds are decreased in turn.

8. A vehicle steering assist system characterized by comprising: The vehicle steering assist device according to claim 1, comprising: An electric power steering system for providing steering assist force for vehicle steering and sending a steering system failure signal and a current steering wheel angle signal to a braking system when the electric power steering system fails; The braking system is used to activate the steering assist function according to the steering system failure signal, and according to the steering wheel angle information, the steering wheel hand force information and the vehicle speed, the above-mentioned vehicle steering assist device is controlled to work according to the vehicle steering assist method of any one of claims 2-7 to establish the pressure difference between the wheel cylinders corresponding to the steering wheels, and complete the steering assist action.

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