A method and system for acquiring front wheel steering load of a steer-by-wire vehicle

Abstract

The present invention discloses a method and system for acquiring the front wheel steering load of a steer-by-wire vehicle. During the driving process of the vehicle, the current speed of the vehicle is detected in real time, and the next reference speed of the speed interval in which the current speed is located and the previous reference speed of the interval are determined; the front wheel reference load at the next reference speed of the interval and the previous reference speed of the interval are determined according to the front wheel steering load at a fixed speed; the front wheel steering load at the current speed is determined according to the front wheel reference load at the next reference speed of the interval and the previous reference speed of the interval. The present invention improves the accuracy, adaptability and efficiency of acquiring the front wheel steering load torque by dividing the speed interval and combining the interpolation method to acquire the instantaneous load of the front wheel when the speed is constantly changing.

Description

Technical Field

[0001] The invention belongs to the technical field of automobiles, and in particular relates to a method and system for acquiring the front wheel steering load of a steer-by-wire automobile. Background Art

[0002] In traditional mechanical steering systems, steering load is the main source of the driver's direct perception of road conditions through the steering wheel. Through the steering wheel, the driver can feel the changes in the road surface during the vehicle's driving in real time and make corresponding control adjustments. However, in cars equipped with wire-controlled steering systems, the mechanical connection is replaced by an electronic control system, and the steering load cannot be directly transmitted to the steering wheel. This poses a new challenge to road feel simulation: how to obtain and process accurate front wheel steering load information and convert it into road feel feedback that the driver can perceive.

[0003] While providing comfort and responsiveness, the steer-by-wire system also needs to address the accuracy of road feel feedback. As the main source of road feel during vehicle driving, the acquisition and processing of front-wheel steering load is crucial to the driver's control experience. Accurate front-wheel steering load information can not only reflect real-time road conditions, but also provide the driver with a reliable basis for control, thereby improving driving safety and control performance.

[0004] At present, the road feel simulation of steer-by-wire vehicles is achieved by constructing a steering load model to obtain the front wheel steering load at a fixed speed, or directly through the sensor front wheel load. However, the vehicle speed will fluctuate and change continuously during actual vehicle operation. When the vehicle speed fluctuates and changes continuously, the steering load model may be distorted, resulting in low accuracy of the obtained front wheel steering load and inability to obtain accurate road feel feedback; there are large errors in sensor measurement. Summary of the invention

[0005] The purpose of the present invention is to solve the deficiencies of the above-mentioned background technology and to provide a method for obtaining the front wheel steering load of a steer-by-wire vehicle with high accuracy and high efficiency.

[0006] The technical solution adopted by the present invention is: a method for obtaining the front wheel steering load of a steer-by-wire vehicle, in which the current vehicle speed is detected in real time during the vehicle driving process, and the next reference speed of the speed interval in which the current vehicle speed is located and the previous reference speed of the speed interval are determined;

[0007] Determine the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval according to the front wheel steering load at the fixed speed;

[0008] The front wheel steering load at the current vehicle speed is determined based on the front wheel reference load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval.

[0009] Furthermore, the speed interval division table is searched according to the current vehicle speed to determine the next reference vehicle speed and the previous reference vehicle speed of the interval where the current vehicle speed is located.

[0010] Furthermore, the process of determining the front wheel steering load at a fixed vehicle speed is as follows:

[0011] Determine the yaw rate, lateral acceleration and lateral velocity based on the two-degree-of-freedom differential equation of the vehicle;

[0012] Determine tire vertical force, tire lateral force, and tire self-aligning moment based on tire model and yaw angular velocity, lateral acceleration, and lateral velocity;

[0013] The front wheel steering load at a fixed vehicle speed is determined based on the tire vertical force, the tire lateral force, and the tire self-aligning torque.

[0014] Furthermore, the process of determining the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval is as follows: replacing the fixed vehicle speed in the front wheel steering load formula at a fixed vehicle speed with the next reference speed in the interval and the previous reference speed in the interval, respectively, and replacing the longitudinal acceleration in the front wheel steering load formula at a fixed vehicle speed with zero, to obtain the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval.

[0015] Furthermore, the front wheel steering load at the current vehicle speed is determined by interpolation method according to the front wheel reference front wheel load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval.

[0016] Furthermore, the front wheel steering load at the current vehicle speed is determined by the following formula:

[0017]

[0018] in, is the front wheel steering load at the current vehicle speed, is the front wheel reference load at the previous reference speed in the interval, is the front wheel reference load at the next reference speed in the interval, is the previous benchmark speed of the section, is the next benchmark speed in the interval, is the current vehicle speed.

[0019] A front wheel steering load acquisition system for a steer-by-wire vehicle, characterized in that:

[0020] Vehicle speed detection module, used to detect the current vehicle speed in real time;

[0021] A vehicle speed interval determination module, used to determine the next reference vehicle speed and the previous reference vehicle speed of the vehicle speed interval in which the current vehicle speed is located;

[0022] A reference steering load determination module, used to determine the reference steering load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval according to the front wheel steering load at a fixed vehicle speed;

[0023] The instantaneous steering load determination module is used to determine the front wheel steering load at the current vehicle speed according to the reference steering load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval.

[0024] Furthermore, the vehicle speed interval determination module searches the vehicle speed interval division table according to the current vehicle speed to determine the next reference vehicle speed and the previous reference vehicle speed of the interval where the current vehicle speed is located.

[0025] Furthermore, the process of determining the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval is as follows: replacing the fixed vehicle speed in the front wheel steering load formula at a fixed vehicle speed with the next reference speed in the interval and the previous reference speed in the interval, respectively, and replacing the longitudinal acceleration in the front wheel steering load formula at a fixed vehicle speed with zero, to obtain the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval.

[0026] Furthermore, the front wheel steering load at the current vehicle speed is determined by the following formula:

[0027]

[0028] in, is the front wheel steering load at the current vehicle speed, is the front wheel reference load at the previous reference speed in the interval, is the front wheel reference load at the next reference speed in the interval, is the previous benchmark speed of the section, is the next benchmark speed in the interval, is the current vehicle speed.

[0029] The beneficial effects of the present invention are:

[0030] 1. The present invention improves the accuracy of front wheel steering load torque acquisition: by setting a reference speed to divide the speed interval in detail, and combining the interpolation method to obtain the instantaneous load of the front wheel when the speed is constantly changing, the accuracy of the load torque acquisition method is improved. Compared with using sensors to directly measure the front wheel load, the algorithm method of the present invention avoids the influence of sensor measurement errors and noise, and also reduces the complexity and cost of the system.

[0031] 2. The present invention improves the applicability of obtaining the front wheel steering load torque: the scheme of the present invention has good applicability under low vehicle speed conditions. By dividing the vehicle speed range in detail, the method can accurately capture the changes in the front wheel load under low vehicle speed conditions, thereby solving the problem of poor applicability of the prior art under low vehicle speed conditions; at the same time, the interpolation method of the present invention calculates the formula for the current instantaneous load, so that during the vehicle speed switching process, the acquisition of the load torque is more continuous and accurate, avoiding distortion problems, thereby improving the driver's control experience.

[0032] 3. The present invention improves the efficiency of obtaining high-load torque of front-wheel steering: The present invention establishes a two-degree-of-freedom differential equation of the vehicle and a tire model, as well as a front-wheel load calculation model, and uses these models for calculation, so as to quickly and efficiently obtain the changes in the front-wheel load, which is of great significance for real-time simulation of road feel feedback. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Example 1

[0036] like Figure 1 As shown, the present invention provides a method for obtaining the front wheel steering load of a steer-by-wire vehicle, comprising the following steps:

[0037] Step 1: Get the current data of the vehicle.

[0038] The vehicle's current data includes the current speed , steering wheel angle , Current transmission ratio of the steering system .

[0039] The vehicle's current front wheel angle Calculated by the following formula: .

[0040] Step 2: Determine the current vehicle speed range.

[0041] According to the current speed Determine the current speed interval by looking up the speed interval table, and record the next benchmark speed of the interval where the current speed is located and the previous benchmark speed of the section .

[0042] The vehicle speed interval division table is shown in Table 1.

[0043] Table 1 Speed ​​range division table

[0044]

[0045] In Table 1, V0-V8 are reference vehicle speeds, which can be obtained by actual vehicle calibration or divided according to experimental parameters.

[0046] Step 3, calculate the front wheel reference load at the reference vehicle speed.

[0047] The front wheel reference load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval are determined according to the front wheel steering load at a fixed vehicle speed.

[0048] The steps for calculating the front wheel steering load at a fixed vehicle speed are as follows:

[0049] 3.1. Establish the two-degree-of-freedom differential equation of the front-wheel steering vehicle, and obtain , lateral acceleration , lateral speed .

[0050] Among them, the two-degree-of-freedom differential equation of the front-wheel steering car is as follows:

[0051]

[0052] Where: , is the equivalent cornering stiffness of the front and rear wheels; is the sideslip angle of the center of mass; , is the longitudinal speed and lateral speed of the car; is the rate of change of lateral velocity with time; a and b are the distances from the center of mass of the vehicle to the front and rear axles; is the yaw angular velocity; is the rate of change of yaw angular velocity with time; is the front wheel turning angle; m is the vehicle mass; is the moment of inertia of the car around the z-axis.

[0053] because It is usually very small and can be approximated as , , is the rate of change of the sideslip angle of the center of mass over time. The above differential equation can be transformed into:

[0054]

[0055] The lateral velocity and lateral acceleration can be calculated by the following equations:

[0056]

[0057] The above two-degree-of-freedom model of the vehicle can be based on the input front wheel angle With longitudinal speed The yaw rate is obtained , lateral acceleration , lateral speed , which is used in the subsequent tire model to calculate the lateral force and sideslip angle. , lateral acceleration , lateral speed All about longitudinal speed and front wheel angle Function:

[0058] , It is the formula obtained by transforming the two-degree-of-freedom differential equation of the car, where is the longitudinal velocity, which is approximated by the corresponding fixed vehicle speed.

[0059] , This is the formula obtained by transforming the two-degree-of-freedom differential equation of a car.

[0060] , This is the formula obtained by transforming the two-degree-of-freedom differential equation of a car.

[0061] 3.2. Establish tire model and obtain tire slip angle , Tire vertical force , tire lateral force , Tire self-aligning torque .

[0062] This embodiment uses the magic tire model to model the lateral force and self-aligning torque of the tire. The magic tire model usually uses the following formula to describe the tire characteristics:

[0063]

[0064] when When is the slip angle, It can be lateral force or self-righting torque. B, C, D, and E are the first coefficient, second coefficient, third coefficient, and fourth coefficient related to the tire model, vertical load, and camber angle. They are usually given when the tire leaves the factory or measured experimentally.

[0065] According to the experimental data of a certain test vehicle on the KC test bench, the magic tire formula for lateral force and the magic tire formula for self-aligning torque are fitted as follows:

[0066]

[0067]

[0068] In the formula is the lateral force of a single tire; is the self-aligning torque of a single tire; , , , They are the first lateral force coefficient, the second lateral force coefficient, the third lateral force coefficient, and the fourth lateral force coefficient. , , , They are the first coefficient of self-aligning torque, the second coefficient of self-aligning torque, the third coefficient of self-aligning torque, and the fourth coefficient of self-aligning torque respectively; is the vertical force of a single tire; is the side slip angle.

[0069] and The calculation formula is as follows:

[0070]

[0071]

[0072] In the formula , are the vertical forces of the left front wheel and the left rear wheel respectively; , They are the left front wheel and left rear wheel side slip angles respectively; is the acceleration due to gravity; , are longitudinal acceleration and lateral acceleration respectively; is the height of the vehicle's center of mass; Front axle track.

[0073] From the above, it can be seen that the tire vertical force For the lateral acceleration , longitudinal acceleration The tire lateral force is a function of , the tire self-aligning torque is about the longitudinal speed and front wheel angle function.

[0074] , is the formula derived from the tire model.

[0075] , The formula is derived from the force analysis of tire forces combined with vehicle parameters.

[0076] .

[0077] .

[0078] 3.3. Establish a front wheel load calculation model to obtain the front wheel steering load at a fixed vehicle speed.

[0079] When analyzing the forces acting on the tires, longitudinal force, lateral force, and vertical force will all generate self-aligning loads. Since the left and right wheels are symmetrical, the self-aligning moments generated by the longitudinal forces on both sides cancel each other out. The effect of the longitudinal force on the front wheel load is ignored here.

[0080] Right now

[0081] It is the self-aligning load generated by the vertical force on a single tire, and the calculation formula is as follows:

[0082]

[0083] In the formula is the lateral offset of the kingpin, is the kingpin inclination angle;

[0084] It is the self-aligning load generated by the lateral force on a single tire, which is generated by the interaction between the lateral force and the tire drag moment. The tire drag moment includes the caster drag moment. Pneumatic tire drag torque caused by tire characteristics . The calculation formula is as follows:

[0085]

[0086] in, is the self-aligning torque generated by the caster torque of a single wheel, R is the effective radius of the vehicle, is the caster angle, Longitudinal offset of the kingpin

[0087] Pneumatic tire drag Related to tire characteristics and stress conditions, The tire self-aligning torque generated It has been expressed in the tire model in the form of the magic tire formula.

[0088] The front wheel steering load at a fixed vehicle speed is obtained for , In order to analyze the force on the front wheels during steering, a formula is derived from the front wheel load calculation model.

[0089] Step 3.4, after the front wheel steering load at a fixed speed is determined, when determining the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval, the fixed speed in the front wheel steering load formula at a fixed speed is replaced with the next reference speed in the interval and the previous reference speed in the interval, and the longitudinal acceleration in the front wheel steering load formula at a fixed speed is replaced with zero, and the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval is obtained. That is, the next reference speed in the interval where the current speed is located is replaced by and the previous benchmark speed Substitute the above The calculation formula can be obtained:

[0090] , It is the front wheel reference load at the next reference speed in the interval.

[0091] , It is the front wheel reference load at the previous reference speed in the interval.

[0092] Step 4: Calculate the front wheel steering load (instantaneous load) at the current vehicle speed.

[0093] According to the front wheel reference load at the previous reference speed in the interval and the front wheel reference load at the next reference speed in the interval in step 3, the front wheel steering load at the current speed is calculated by interpolation method.

[0094] The interpolation method is used to calculate the front wheel steering load at the current vehicle speed as follows:

[0095]

[0096] In the formula, is the front wheel steering load at the current vehicle speed; is the current vehicle speed.

[0097] The front wheels of the vehicle include the left front wheel and the right front wheel, so the total front wheel load finally calculated is the sum of the left front wheel steering load and the right front wheel steering load.

[0098] Example 2

[0099] This embodiment provides a front wheel steering load acquisition system for a steer-by-wire vehicle, comprising:

[0100] Vehicle speed detection module, used to detect the current vehicle speed in real time;

[0101] A vehicle speed interval determination module, used to determine the next reference vehicle speed and the previous reference vehicle speed of the vehicle speed interval in which the current vehicle speed is located;

[0102] A reference steering load determination module, used to determine the reference steering load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval according to the front wheel steering load at a fixed vehicle speed;

[0103] The instantaneous steering load determination module is used to determine the front wheel steering load at the current vehicle speed according to the reference steering load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval.

[0104] In the above scheme, the speed interval determination module searches the speed interval division table according to the current speed to determine the next reference speed and the previous reference speed of the interval where the current speed is located. The speed interval division table has been described in Example 1 and will not be described in detail here.

[0105] In the above scheme, the process of determining the front wheel steering load at a fixed vehicle speed is as follows:

[0106] Determine the yaw rate, lateral acceleration and lateral velocity based on the two-degree-of-freedom differential equation of the vehicle;

[0107] Determine tire vertical force, tire lateral force, and tire self-aligning moment based on tire model and yaw angular velocity, lateral acceleration, and lateral velocity;

[0108] The front wheel steering load at a fixed vehicle speed is determined based on the tire vertical force, the tire lateral force, and the tire self-aligning torque.

[0109] The above equations, models and calculation methods of various parameters have been described in Example 1 and will not be described in detail here.

[0110] In the above scheme, the process of determining the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval is: replacing the fixed vehicle speed in the front wheel steering load formula at a fixed vehicle speed with the next reference speed in the interval and the previous reference speed in the interval, respectively, and replacing the longitudinal acceleration in the front wheel steering load formula at a fixed vehicle speed with zero, to obtain the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval.

[0111] In the above scheme, the front wheel steering load at the current vehicle speed is determined by interpolation method based on the front wheel reference front wheel load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval. The front wheel steering load at the current vehicle speed is determined by the following formula:

[0112]

[0113] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The attached method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0114] In order to make the description of the present disclosure more detailed and complete, the above description is provided for the implementation and specific embodiments of the present invention; however, this is not the only form of implementing or using the specific embodiments of the present invention. The implementation covers the features of multiple specific embodiments and the method steps and sequences used to construct and operate these specific embodiments. However, other specific embodiments can also be used to achieve the same or equivalent functions and step sequences.

[0115] It should be noted that, although several modules or units of the equipment for action execution are mentioned in the above detailed description, this division is not mandatory. In fact, according to the embodiments of the present application, the features and functions of two or more modules or units described above can be embodied in one module or unit. On the contrary, the features and functions of one module or unit described above can be further divided into being embodied by multiple modules or units.

[0116] Those skilled in the art may also understand that the various illustrative logical blocks, units, and steps listed in the embodiments of the present invention may be implemented by electronic hardware, computer software, or a combination of the two. In order to clearly demonstrate the interchangeability of hardware and software, the various illustrative components, units, and steps mentioned above have generally described their functions. Whether such functions are implemented by hardware or software depends on the specific application and the design requirements of the entire system. Those skilled in the art may use various methods to implement the described functions for each specific application, but such implementation should not be understood as exceeding the scope of protection of the embodiments of the present invention.

[0117] The various illustrative logic blocks or units described in the embodiments of the present invention can be implemented or operated by a general-purpose processor, a digital signal processor, an application-specific integrated circuit (ASIC), a field programmable gate array or other programmable logic device, a discrete gate or transistor logic, a discrete hardware component, or any combination of the above. The general-purpose processor can be a microprocessor, and optionally, the general-purpose processor can also be any conventional processor, controller, microcontroller or state machine. The processor can also be implemented by a combination of computing devices, such as a digital signal processor and a microprocessor, a plurality of microprocessors, one or more microprocessors combined with a digital signal processor core, or any other similar configuration.

[0118] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in the field.

Claims

1. A method for acquiring the front wheel steering load of a steer-by-wire vehicle, characterized in that: During the driving process of the vehicle, the current speed of the vehicle is detected in real time, and the next reference speed of the speed interval in which the current speed is located and the previous reference speed of the speed interval are determined; Determine the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval according to the front wheel steering load at the fixed speed; Determine the front wheel steering load at the current vehicle speed according to the front wheel reference load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval; The process of determining the front wheel steering load at a fixed vehicle speed is as follows: determining the yaw rate, lateral acceleration, and lateral velocity according to the two-degree-of-freedom differential equation of the vehicle; determining the tire vertical force, tire lateral force, and tire self-aligning torque according to the tire model and the yaw rate, lateral acceleration, and lateral velocity; determining the front wheel steering load at a fixed vehicle speed based on the tire vertical force, tire lateral force, and tire self-aligning torque; The process of determining the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval is as follows: the fixed vehicle speed in the front wheel steering load formula at a fixed vehicle speed is replaced by the next reference speed in the interval and the previous reference speed in the interval, and the longitudinal acceleration in the front wheel steering load formula at a fixed vehicle speed is replaced by zero, so as to obtain the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval; The front wheel steering load at the current vehicle speed is determined by the following formula: Where T is the front wheel steering load at the current vehicle speed, T u is the front wheel reference load at the previous reference speed in the interval, T l is the front wheel reference load at the next reference speed in the interval, v u is the previous benchmark speed of the interval, v l is the next benchmark speed in the interval, and v is the current speed.

2. The method for acquiring the front wheel steering load of a steer-by-wire vehicle according to claim 1, characterized in that: According to the current vehicle speed, the speed interval division table is searched to determine the next benchmark speed of the interval and the previous benchmark speed of the interval where the current vehicle speed is located.

3. The method for acquiring the front wheel steering load of a steer-by-wire vehicle according to claim 1, characterized in that: The front wheel steering load at the current vehicle speed is determined by interpolation method based on the front wheel reference front wheel load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval.

4. A front wheel steering load acquisition system for a steer-by-wire vehicle, characterized in that: include Vehicle speed detection module, used to detect the current vehicle speed in real time; A vehicle speed interval determination module, used to determine the next reference vehicle speed and the previous reference vehicle speed of the vehicle speed interval in which the current vehicle speed is located; A reference steering load determination module, used to determine the reference steering load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval according to the front wheel steering load at a fixed vehicle speed; The process of determining the front wheel steering load at a fixed vehicle speed is as follows: determining the yaw rate, lateral acceleration, and lateral velocity according to the two-degree-of-freedom differential equation of the vehicle; determining the tire vertical force, tire lateral force, and tire self-aligning torque according to the tire model and the yaw rate, lateral acceleration, and lateral velocity; determining the front wheel steering load at a fixed vehicle speed based on the tire vertical force, tire lateral force, and tire self-aligning torque; The process of determining the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval is as follows: the fixed vehicle speed in the front wheel steering load formula at a fixed vehicle speed is replaced by the next reference speed in the interval and the previous reference speed in the interval, and the longitudinal acceleration in the front wheel steering load formula at a fixed vehicle speed is replaced by zero, so as to obtain the front wheel reference load at the next reference speed in the interval and the previous reference speed in the interval; An instantaneous steering load determination module is used to determine the front wheel steering load at the current vehicle speed according to the reference steering load at the next reference vehicle speed in the interval and the previous reference vehicle speed in the interval; The front wheel steering load at the current vehicle speed is determined by the following formula: Where T is the front wheel steering load at the current vehicle speed, T u is the front wheel reference load at the previous reference speed in the interval, T l is the front wheel reference load at the next reference speed in the interval, v u is the previous benchmark speed of the interval, v l is the next benchmark speed in the interval, and v is the current speed.

5. The front wheel steering load acquisition system for steer-by-wire vehicles according to claim 4, characterized in that: The vehicle speed interval determination module searches the vehicle speed interval division table according to the current vehicle speed to determine the next reference vehicle speed and the previous reference vehicle speed of the interval where the current vehicle speed is located.

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