Steer-by-wire system variable ratio control method and system

Abstract

The invention discloses a variable transmission ratio control method for a steer-by-wire system. The variable transmission ratio control method comprises the following steps that 1, data signals of the actual steering control state of a whole vehicle in the running process of the vehicle are collected in real time; step 2, determining a current basic transmission ratio according to a preset rule and calculating a transmission ratio gain according to the vehicle speed, thereby calculating a reference transmission ratio; 3, determining a transmission ratio change gradient gain according to a rack speed or a steering wheel angular speed, and determining a transmission ratio according to a preset formula; and 4, determining the current constant-speed maximum turning rack position according to the vehicle speed and a preset rule, judging whether the current steering control of the vehicle is in a safe area or not according to the maximum turning rack position, and further determining whether the change of the transmission ratio is limited or not. The invention further discloses a variable transmission ratio control system of the steer-by-wire system.

Description

Technical Field

[0001] The present invention relates to the technical field of automotive steering control, and particularly to a control method for variable transmission ratio of a steer-by-wire system. Background Art

[0002] A steer-by-wire system realizes the control of the driver's steering through a feel motor and an assist motor. Compared with the current electric power steering system, it cancels the mechanical connection device between the steering wheel and the steering rack. Therefore, the transmission ratio and the assist characteristics of the steering system can be controlled by software algorithms. Thus, this technology is also one of the core technologies for realizing autonomous driving technology in the future.

[0003] Currently, most steer-by-wire systems calculate the target transmission ratio by weighting the vehicle speed, yaw rate, and lateral acceleration. Although this solution can achieve the design idea of a large transmission ratio at low speed and a small transmission ratio at high speed, the overall vehicle shows that the transmission ratio fluctuates with the vehicle state at all times. When the driver turns the steering wheel, the driver cannot accurately obtain the actual steering control state of the vehicle at present, and it cannot cope with the safety of the vehicle's lateral driving under sudden working conditions. For example, when fine-tuning and correcting the vehicle direction under low-speed conditions, due to the large transmission ratio, the driver needs to control the driving direction more precisely. At high speed, due to the small transmission ratio, the driver needs to turn a larger steering angle when making an emergency avoidance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to design a control system based on large-angle variable transmission ratio control and angular velocity, which can take into account both the controllability and safety of driving.

[0005] To solve the above technical problem, the present invention provides a control method for variable transmission ratio of a steer-by-wire system, including the following steps:

[0006] Step 1: Real-time collect the data signals of the vehicle during driving and the actual steering control state of the vehicle.

[0007] Step 2: Determine the current basic transmission ratio according to a preset rule and calculate the transmission ratio gain according to the vehicle speed, thereby calculating the reference transmission ratio.

[0008] Step 3: Determine the transmission ratio change gradient gain according to the rack speed or the steering wheel angular velocity, and then establish the transmission ratio according to a preset formula.

[0009] Step 4: Determine the current maximum turning rack position at a constant speed according to the vehicle speed and a preset rule, determine whether the current steering control of the vehicle is in a safe area according to the maximum turning rack position, and further determine whether to limit the change of the transmission ratio.

[0010] Preferably, the data signals of the actual steering control state of the whole vehicle at least include: vehicle speed signal, steering wheel angle signal, steering wheel rotation speed signal, rack position signal, cumulative angle signal of the assist motor, yaw rate signal or lateral acceleration signal.

[0011] Preferably, the preset rule in step 2 is the relationship between the rack position and the basic transmission ratio.

[0012] Preferably, the reference transmission ratio in step 2 is equal to the basic transmission ratio multiplied by the transmission ratio gain.

[0013] Preferably, the formula in step 3 is:

[0014] i term =i cur +(i ref -i cur )*x grad

[0015] where x grad is the transmission ratio change gradient gain, i ref is the reference transmission ratio, i cur is the current transmission ratio, i term is the transmission ratio.

[0016] Preferably, the preset rule in step 4 is the rack position when the yaw rate reaches the critical safety value or the rack position when the lateral acceleration reaches the critical safety value by making the whole vehicle perform a constant-speed circular motion.

[0017] Preferably, when the rack position is less than the maximum turning rack position, it is determined that the current steering control of the vehicle is in the safe area; when the rack position is greater than the maximum turning rack position, it is determined that there is a risk in the current steering control of the vehicle, and it is necessary to limit the change of the transmission ratio.

[0018] A variable transmission ratio control system for a steer-by-wire system, comprising:

[0019] Data monitoring and acquisition module: Real-time monitoring and collection of data related to the actual steering control state of the vehicle during driving;

[0020] Data processing and calculation module: Reading the relevant data in the data monitoring and acquisition module, processing and calculating to obtain the current basic transmission ratio, transmission ratio gain, reference transmission ratio, transmission ratio change gradient gain and transmission ratio;

[0021] Target transmission ratio control module: Determining the target transmission ratio or limiting the change of the transmission ratio according to the judgment of whether the current steering control of the vehicle is in the safe area and outputting it to the steering execution.

[0022] Compared with the prior art, the present invention has the following technical effects:

[0023] 1. When steering at low speed, the driver's intended turning direction can be determined based on the steering wheel angle and angular velocity. That is, when the driver makes a large-angle sharp turn, the target transmission ratio increases, so as to achieve a smaller steering wheel angle and a greater adjustment of the vehicle's direction; when the driver needs to make a small-angle correction, the target transmission ratio decreases to achieve a higher-precision control of the wheel angle.

[0024] 2. During straight driving at medium and high speeds, the target transmission ratio decreases with the vehicle speed, thereby reducing the operation sensitivity and avoiding frequent angle corrections by the driver; when the driver makes an emergency lane change, the target transmission ratio increases with the steering wheel speed, improving the driver's controllability.

[0025] 3. The yaw angular velocity and lateral acceleration are limited to ensure that the target transmission ratio is within a safe range, avoiding unstable phenomena such as vehicle sideslip and loss of control. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments:

[0027] Figure 1 It is a diagram of the rack position and basic transmission ratio of the variable transmission ratio control method and system for the steer-by-wire system of the present invention.

[0028] Figure 2 It is a diagram of the vehicle speed and transmission ratio gain of the variable transmission ratio control method and system for the steer-by-wire system of the present invention.

[0029] Figure 3 It is a diagram of the steering wheel angular velocity and gradient gain of the variable transmission ratio control method and system for the steer-by-wire system of the present invention.

[0030] Figure 4 It is a diagram of the rack speed and gradient gain of the variable transmission ratio control method and system for the steer-by-wire system of the present invention.

[0031] Figure 5 It is a diagram of the vehicle speed and maximum safe rack position of the variable transmission ratio control method and system for the steer-by-wire system of the present invention.

[0032] Figure 6 It is a diagram of the lateral acceleration and transmission ratio gradient of the variable transmission ratio control method and system for the steer-by-wire system of the present invention. Figure 7 It is a schematic diagram of the variable transmission ratio control method and system for the steer-by-wire system of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can fully understand other advantages and technical effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through different specific implementation manners. The details in this specification can also be applied based on different viewpoints, and various modifications or changes can be made without departing from the overall design concept of the invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. The following exemplary embodiments of the present invention can be implemented in many different forms and should not be construed as being limited only to the specific embodiments set forth herein. It should be understood that these embodiments are provided so that the disclosure of the present invention is thorough and complete, and the technical solutions of these exemplary specific embodiments can be fully conveyed to those skilled in the art.

[0034] Embodiment 1

[0035] The present invention discloses a variable transmission ratio control method for a steer-by-wire system, including the following steps:

[0036] Step 1: Real-time collect the data signals of the actual steering control state of the vehicle during driving.

[0037] Specifically, a data acquisition module can be used to obtain sensor data, such as the current hand force torque (m tbt ), vehicle speed (v veh ), steering wheel angle (w str ) and steering wheel rotation speed (v str ) (or motor RPS angle w rps ) and rotation speed v rps ), rack position (I rp ) and rack speed (v rs ), yaw rate (v yaw ), lateral acceleration (Acc lateral ).

[0038] Step 2: Determine the current basic transmission ratio ( Figure 1 ) (i base ) according to the rack position or the steering wheel angle, and calculate the transmission ratio gain (x veh ) according to the vehicle speed, and thus calculate the reference transmission ratio (i ref ):

[0039] i ref = i base * x veh

[0040] For example, when driving at a vehicle speed below 20 km / h and at a steering angle of 0° (rack position is 0 mm), the basic transmission ratio is i base = 50, and the transmission ratio gain is x veh= 1.2, the reference transmission ratio is i ref = 60; while when driving at a speed of 80 km / h and a steering angle of 0° (rack position is 0 mm), the basic transmission ratio is i base = 50, and the transmission ratio gain is x veh = 0.4, the transmission ratio is i ref = 20.

[0041] Step 3: Determine the transmission ratio change gradient gain (x grad ) according to the rack speed or the angular velocity of the steering wheel, and calculate the transmission ratio: i term = i cur +(i ref - i cur ) * x grad .

[0042] For example, when driving at a speed below 20 km / h and turning the steering wheel at an angular velocity of 50° / s, the current transmission ratio i cur = 60, i ref = 64.5, x grad = 0, so i term = 60. That is, when steering at low speed, the value of i term is small, so a larger range of steering wheel angles corresponds to the tire angles, which is convenient for the driver to adjust the driving direction.

[0043] When driving at a speed below 20 km / h and turning the steering wheel at an angular velocity of 300° / s, the current transmission ratio i cur = 60, i ref = 73.4, x grad = 1, so i term = 73.4.

[0044] That is, when steering quickly, the transmission ratio is increased to achieve a smaller steering wheel angle corresponding to a larger turning direction.

[0045] Step 4: Determine the current maximum turning rack position (l max ) according to the vehicle speed by looking up the table. For example, Figure 5 The maximum safe rack position data is determined by making the vehicle perform a constant-speed circular motion. It is the rack position when the yaw angular velocity reaches the critical safety value; or the rack position when the lateral acceleration reaches the critical safety value.

[0046] When l rack is less than l max , it can be judged that the current steering control of the vehicle is in the safe area, that is, the target transmission ratio is i tag = i term ; when l rack is greater than l maxWhen it is determined that there is a certain risk in the current steering control of the vehicle, and the risk will increase if the steering wheel angle continues to increase, it is necessary to limit the change of the transmission ratio.

[0047] Calculate the transmission ratio change gradient g according to the lateral acceleration acc , at l rack greater than l max , and when the steering wheel angle continues to increase, the change gradient limit of the target transmission ratio is within g acc :

[0048] i tag = i term , i term - i cur ≤ g acc

[0049] i tag = i cur + g acc , i term - i cur > g acc .

[0050] Specifically, the gradient can be calculated according to Figure 6 . If the current vehicle speed is less than 20 km / h, the full stroke is the safe position, that is, the safe rack position is the maximum rack position. At this time, the target transmission ratio i tag = i term . When the vehicle speed is high and an emergency lane change is made, for example, an emergency lane change at a vehicle speed of 60 km / h, the rack position is greater than 7 mm, the lateral acceleration is 1 m / s^2, and the transmission ratio gradient is 10 mm / rev / s. That is, when i cur = 60, i term = 73.4, i tag = 70.

[0051] The above has described the present invention in detail through specific embodiments and examples, but these do not constitute a limitation to the present invention. Without departing from the principle of the present invention, those skilled in the art can also make many deformations and improvements, which should also be regarded as the protection scope of the present invention.

Claims

1. A variable transmission ratio control method for a steer-by-wire system, characterized in that: The following steps are involved: Step 1: Real-time acquisition of data signals of the vehicle's driving and the actual steering control state of the vehicle; Step 2: Determine the current basic transmission ratio according to a preset rule and calculate the transmission ratio gain according to the vehicle speed, thereby calculating the reference transmission ratio; Step 3, determining the transmission ratio change gradient gain according to the rack speed or the steering wheel angular velocity, and then establishing the transmission ratio according to a preset formula; Step 4: Determine the current maximum uniform turning rack position according to the vehicle speed and preset rules, and judge whether the current steering control of the vehicle is in a safe area according to the maximum turning rack position, and then determine whether to limit the change of the transmission ratio.

2. The variable transmission ratio control method of a steer-by-wire system according to claim 1, characterized in that: The data signal of the actual steering control state of the whole vehicle includes at least: a vehicle speed signal, a steering wheel angle signal, a steering wheel speed signal, a rack position signal, a power assist motor accumulated angle signal, a yaw angular velocity signal or a lateral acceleration signal.

3. The variable transmission ratio control method of a steer-by-wire system according to claim 1, characterized in that: The preset rule in step 2 is the relationship between the rack position and the basic transmission ratio.

4. The variable transmission ratio control method of a steer-by-wire system according to claim 1, characterized in that: In step 2, the reference transmission ratio is equal to the basic transmission ratio multiplied by the transmission ratio gain.

5. The variable transmission ratio control method of a steer-by-wire system according to claim 1, characterized in that: The formula in step 3 is: i term =i cur +(i ref -i cur )*x grad where x grad is the transmission ratio change gradient gain, i ref is the reference transmission ratio, i cur is the current transmission ratio, i term is the transmission ratio.

6. The variable transmission ratio control method of a steer-by-wire system according to claim 1, characterized in that: The preset rule in step 4 is to determine the rack position when the yaw angular velocity reaches a critical safety value by performing a constant speed circular motion of the entire vehicle; or the rack position when the lateral acceleration reaches a critical safety value.

7. The variable transmission ratio control method of a steer-by-wire system according to claim 1, characterized in that: When the rack position is less than the maximum turning rack position, the current steering control of the vehicle is judged to be in a safe area; when the rack position is greater than the maximum turning rack position, the current steering control of the vehicle is judged to be risky and the change of the transmission ratio needs to be limited.

8. A variable transmission ratio control system for a steer-by-wire system, characterized in that: The variable transmission ratio control method of the steer-by-wire system according to any one of claims 1 to 7 is used, wherein the variable transmission ratio control system of the steer-by-wire system comprises: Data monitoring and acquisition module: real-time monitoring and collection of data related to the actual steering control status of the vehicle during driving; Data processing and calculation module: reads relevant data from the data monitoring and acquisition module, processes and calculates to obtain the current basic transmission ratio, transmission ratio gain, reference transmission ratio, transmission ratio change gradient gain and transmission ratio; Target transmission ratio control module: Determines the target transmission ratio or sets a limit on the change in transmission ratio and outputs it to the steering execution based on whether the vehicle's current steering control is in a safe area.

Images