METHOD FOR TUNING A CALIBRATION TABLE FOR AN ELECTRIC POWER STEERING SYSTEM

Abstract

A method for tuning a calibration table for an electric power steering system involves connecting the electric power steering system to an actuator machine and communicating a control input from a vehicle simulator to the actuator machine. Input forces and steering angles are applied to the electric power steering system by the actuator machine, based on the control input. The electric power steering system is controlled by a steering controller to input a steering input, i.e., an assist torque. The steering controller uses the calibration table to define the steering input, based on the applied input forces and steering angles. A steering torque generated in the electric power steering system in response to the input steering input is detected and communicated to the vehicle control system, thereby establishing a closed control loop and feedback.The calibration table can then be redefined to set a steering target value based on the detected steering response for the applied input forces.

Description

TECHNICAL AREA

[0001] The disclosure relates to a method for tuning a calibration table for an electric power steering system. BACKGROUND

[0002] A vehicle may be equipped with electric power steering. Electric power steering uses an electric motor to assist the driver in turning the vehicle's steering wheel. Sensors detect the position and torque of the steering column and / or steering wheel, as well as the vehicle's current operating conditions. A steering control unit applies assisting torque to the motor to reduce the amount of torque the driver must apply to turn the steering wheel and thus steer the vehicle.

[0003] The amount of assist torque that the steering control unit applies to the engine varies depending on the vehicle's operating conditions. The vehicle control unit can access a calibration table that maps different vehicle operating conditions to a desired amount of assist torque. This calibration table is stored in the steering control unit's electronic memory. The calibration table must be defined to provide the desired level of assist torque for the various vehicle operating conditions. If the assist torque is too low, the steering wheel requires more torque from the driver, which some drivers may find undesirable. Conversely, if the assist torque is too high, the steering wheel may turn too freely, which some drivers may also find undesirable.Defining the values ​​of the supporting torque in the calibration table can be referred to as tuning the calibration table and is usually done during vehicle development.

[0004] It is difficult to model electric power steering systems electronically. Accordingly, in the past, the calibration table for electric power steering systems was adjusted by installing the electric power steering system in a prototype vehicle, test-driving the prototype vehicle with a defined calibration table, and then adjusting the calibration table based on the subjective perception of the prototype vehicle's driver.

[0005] German patent application DE 20 2011 050 806 U1 discloses a steering test bench for testing a steering control unit, comprising a first steering device, a drive unit, a measuring device, and a test driver unit for a test driver with a second steering device. German patent application DE 10 2011 089 950 A1 discloses a method for evaluating a vehicle's steering system. SUMMARY

[0006] It is an object of the invention to provide a more precise and economical method for tuning a calibration table for an electric power steering system.

[0007] This problem is solved by the features of claim 1. Advantageous further developments are defined in the dependent claims.

[0008] Accordingly, the calibration table tuning procedure uses the calibration system to develop the calibration table without using a physical prototype vehicle. For example, the calibration table for the electric power steering can be tuned in a workshop, independent of ambient temperature, weather, and / or road conditions. Additionally, the calibration table can be tuned according to predefined metrics, ensuring consistency among the engineers involved in the tuning process. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic diagram of a simulator system that includes a vehicle simulator and an actuator machine. Fig. Figure 2 is a schematic, perspective view of the actuator machine that supports an electric power steering system. DETAILED DESCRIPTION

[0009] Experts in the field will recognize that terms such as "above," "below," "upwards," "downwards," "above," "below," etc., are used descriptively for the figures and do not constitute limitations on the scope of the disclosure defined by the accompanying claims. Furthermore, the teachings contained herein may be described in relation to the functional or logical block components or various processing steps. It should be noted that such block components may be composed of any number of hardware, software, and / or firmware components configured to perform the specified functions.

[0010] In the figures, where the components are numbered and shown in several views, 20 of them are... Fig. 1. In general, the calibration system is the focus. The calibration system 20 is used to calibrate a calibration table 38 for an electric power steering system 22. The calibration table 38 assigns various operating conditions of the vehicle to a desired steering input. The steering input can, for example, include an assist torque applied by an electric motor 30 of the electric power steering system 22 to a component of the steering system to assist an operator in turning the vehicle's steering wheel. Accordingly, it is understood that the magnitude of the assist torque applied by the electric motor 30 varies and depends on the current operating conditions of the vehicle. The steering input values, i.e., the assist torque for the various possible operating conditions of the vehicle, are defined by and stored in the calibration table 38.During product development, calibration table 38 is "tuned," i.e., adjusted or modified, to determine the optimal level of assist torque for the various operating conditions of the vehicle. Calibration table 38 is specific to individual vehicle designs and / or individual steering system configurations, so any new vehicle design and / or configuration of the electric power steering 22 that uses a power steering calibration table 38 requires tuning of the calibration table 38 to the specific vehicle design and / or configuration.

[0011] Referring to Fig. The electric power steering system 22 typically includes a rack 24 coupled to a left tie rod 26 and a right tie rod 28, and an electric motor 30, operable to apply a variable torque to the rack 24. The left tie rod 26 and the right tie rod 28 each contain a force sensor for inputting forces into their respective tie rods. The rack 24 is connected to the left tie rod 26 and the right tie rod 28 via the rack. An intermediate shaft 32 is attached to the rack 24 and connects the rack 24 to a steering actuator 34. The steering actuator 34 includes a torque sensor 56 and a steering angle sensor 60. The torque sensor 56 serves to detect steering torque feedback in the intermediate shaft 32.The steering angle sensor 60 is used to detect and / or determine an angular position of the intermediate shaft 32, and is used to input a steering angle into the intermediate shaft 32.

[0012] The electric power steering system 22 further includes a steering control unit 36. The steering control unit 36 ​​and the electric motor 30 are preferably formed as a single unit and connected to the rack 24. The steering control unit 36 ​​may include a control module or a computer that can be operated to control the operation of the electric power steering system 22. The steering control unit 36 ​​may include a processor, as well as all software, hardware, memory, algorithms, connections, sensors, etc., necessary for managing and operating the electric power steering system 22. It is understood that the steering control unit 36 ​​may include any device capable of analyzing data from various sensors or other devices, comparing data, and making the necessary decisions for controlling the electric power steering system 22 and executing the necessary operating steps of the electric power steering system 22.

[0013] The steering control 36 can be embodied by one or more digital or host computers, each having one or more processors, read-only memory (ROM), random access write-read memory (RAM), electrically programmable read-only memory (EPROM), optical drives, magnetic drives, etc., a high-speed clock, analog / digital (A / D) circuits, digital / analog (D / A) circuits and all necessary input / output (I / O) circuits, input / output devices and communication interfaces, as well as signal conditioning and buffer circuits.

[0014] Computer-readable storage can include any physical / durable medium that participates in the provision of data or computer-readable instructions.

[0015] Storage can be non-volatile or volatile. Non-volatile media can include, for example, optical or magnetic disks and other persistent storage devices. Volatile media can include, for example, dynamic random-access memory (DRAM), which can form main memory. Other examples of storage devices include a floppy disk, a flexible disk or hard disk, magnetic tape or other magnetic media, a CD-ROM, DVD or other optical media, and other possible storage elements such as flash memory.

[0016] The steering control unit 36 ​​includes a tangible, non-temporary memory in which computer-executable instructions are recorded, including a power steering selection algorithm. The processor of the steering control unit 36 ​​is configured to execute the power steering selection algorithm. The power steering selection algorithm implements a procedure for selecting a steering input value for the electric power steering system 22. The steering input may include, or otherwise be defined as, an assist torque. The power steering selection algorithm accesses the calibration table 38 to define a steering input value based on the current operating conditions. Accordingly, the calibration table 38 may be stored in a memory device of the steering control unit 36 ​​in the form of a file or the like.

[0017] Referring to Fig.The calibration system 20 comprises an actuator machine 40 and a vehicle simulator 42. The actuator machine 40 can be operated to assist the electric power steering 22 and to apply input forces and steering angles to the electric power steering 22 in response to a control input 44 from the vehicle simulator 42 to simulate the movement of a vehicle. One embodiment of the actuator machine 40 includes a plurality of hydraulic actuators to move the electric power steering 22 in multiple directions for the purpose of simulating the operation of a vehicle. For example, the actuator machine 40 can include five degrees of freedom to simulate vehicle roll, vehicle rebound, steering angle, left turn, and right turn.The control inputs 44 include the steering angle input from the steering actuator 34 and tie rod force input from the force sensors in the left tie rod 26 and the right tie rod 28. The actuator 40 receives the steering torque feedback as output. This steering torque feedback is detected by the torque sensor 56, which is located in the steering actuator 34.

[0018] The vehicle simulator 42 is electrically connected to the actuator 40. The vehicle simulator 42 transmits the control inputs 44 to the hydraulic machine and receives the steering torque feedback, hereinafter referred to as steering response 46, from the electric power steering 22. In particular, the steering actuator 34 detects the steering response 46 from the electric power steering 22 and communicates it to the vehicle simulator 42, as described in more detail below. The vehicle simulator 42 and the actuator 40 can communicate in any suitable manner, for example, by means of a high-speed communication protocol.

[0019] The vehicle simulator 42 may include a computer or other similar device capable of controlling the operation of the actuator 40. The vehicle simulator 42 may include a processor and all software, hardware, memory, algorithms, connections, sensors, CAN communication modules, etc., necessary for managing and operating the actuator 40. Such a method for adjusting the calibration table 38, as described below, may be implemented, at least in part, as a program executable on the vehicle simulator 42. It is understood that the vehicle simulator 42 may include any device capable of analyzing data from various sensors or other devices, comparing data, and making the necessary decisions for controlling the actuator 40 and executing the necessary operating steps of the actuator 40.

[0020] The Vehicle Simulator 42 can be embodied by one or more digital or host computers, each containing one or more processors, read-only memory (ROM), random access read / write memory (RAM), electrically programmable read-only memory (EPROM), optical drives, magnetic drives, etc., a high-speed clock, analog / digital (A / D) circuits, digital / analog (D / A) circuits, and all necessary input / output (I / O) circuits, input / output devices and communication interfaces, as well as signal conditioning and buffer circuits.

[0021] Computer-readable memory can include any physical / durable medium that participates in providing data or computer-readable instructions. Memory can be non-volatile or volatile. Non-volatile media can include, for example, optical or magnetic disks and other persistent storage devices. Volatile media can include, for example, dynamic random-access memory (DRAM), which can form main memory. Other examples of memory configurations include a floppy disk, a flexible disk or hard disk, magnetic tape or other magnetic media, a CD-ROM, DVD or other optical media, and other possible storage elements such as flash memory.

[0022] The vehicle simulator 42 can include tangible, non-temporary memory in which computer-executable instructions are recorded, including, but not limited to, a simulator algorithm 48, a vehicle dynamics mathematical model 50, and an animation algorithm 52. The processor of the vehicle simulator 42 is configured to execute the simulator algorithm 48, the vehicle dynamics mathematical model 50, and the animation algorithm 52.

[0023] The vehicle dynamics mathematical model 50 is a mathematical model of the specific vehicle to which the calibration table 38 is to be aligned. The vehicle dynamics mathematical model 50 describes the physical structure and operating characteristics of the specific vehicle. The vehicle dynamics mathematical model 50 can be stored as a program or file set in the memory of the vehicle simulator 42. The vehicle dynamics mathematical model 50 describes the vehicle mass and loads, vehicle kinematics and compliance, center of gravity, tire characteristics, vehicle orientation and geometry, etc. The vehicle dynamics mathematical model 50 can describe any physical attributes of the vehicle that are simulated, both those mentioned herein and those not mentioned.

[0024] The simulator algorithm 48 simulates the operation of one or more control modules of the specific vehicle to which the calibration table 38 is to be adapted. Accordingly, the simulator algorithm 48 must be programmed for each specific vehicle. The simulator algorithm 48 accesses and / or interacts with the vehicle dynamics mathematical model 50 to generate the control inputs 44, which are used to control the actuator machine 40 for the purpose of simulating the motion and operation of the specific vehicle. It is understood that the control inputs 44 can contain more than a single command and typically include multiple commands, for example, but not limited to, a steering angle, a left tie rod force, and / or a right tie rod force. The simulator algorithm 48 encompasses all input / output signals and communication protocols between real and virtual control units.The simulator algorithm 48 can also include mathematical correctives and mathematical equivalents of subsystem components.

[0025] The vehicle simulator 42 can further include the animation algorithm 52. The animation algorithm 52 can be used to generate a visual representation on a display device 54. The visual representation can, for example, include a view of the vehicle moving along a path corresponding to the control input 44. If the control input 44 is defined, for example, to simulate a left turn, the visual representation can show that the vehicle is making a left turn. The visual representation shows the estimated movement of the vehicle while the actuator machine manipulates the electric power steering 22, based on the control input 44 from the vehicle simulator 42. The display device 54 can include any device suitable for displaying a moving image, for example, but not limited to, a computer monitor or other similar device.

[0026] The procedure for tuning the calibration table 38 for the electric power steering 22 is described below. To tune the calibration table 38, the vehicle dynamics mathematical model 50 must be defined. As mentioned above, the vehicle dynamics mathematical model 50 is used to model the operating characteristics of the specific vehicle to which the power steering calibration table 38 is to be tuned. Once the vehicle dynamics mathematical model 50 is defined, it is stored in the memory of the vehicle simulator 42 or another suitable device with which it is linked or otherwise connected and can simulate with the vehicle simulator 42.

[0027] The simulator algorithm 48 must also be defined and stored in the memory of the vehicle simulator 42. As already stated, the simulator algorithm 48 simulates the operation of the control modules of the specific vehicle to which the power steering calibration table 38 is to be matched. The simulator algorithm 48 accesses and / or interacts with the vehicle dynamics mathematical model 50 to generate a mathematical equivalent of a simulated vehicle, which is used to generate the control inputs 44 for controlling the actuator machine 40.

[0028] The electric power steering system 22 is then connected to the actuator 40. As previously stated, the actuator 40 can be operated to simulate vehicle movement in response to the control inputs 44 from the vehicle simulator 42. Once the electric power steering system 22 is connected to the actuator 40, the electric power steering system 22 and the actuator 40 must be adjusted so that the steering torque of the electric power steering system 22 is approximately zero. Accordingly, the system is zeroed to start the test procedure. The steering torque in the electric power steering system 22 is set to zero before the control input 44 is communicated to the actuator 40, allowing for an accurate measurement of the steering torque generated solely in response to the control inputs 44.

[0029] Adjusting the electric power steering 22 and the actuator 40 so that the steering torque is approximately zero involves sensing the steering torque in the electric power steering 22 and electronically communicating the sensed steering torque to the vehicle simulator 42. In this form, the calibration system 20 is a closed control loop that provides feedback from the actuator 40 to the vehicle simulator 42. The steering torque in the electric power steering 22 can be sensed in any suitable manner. For example, the steering actuator 34 can include the torque sensor 56, which is suitable for measuring the torque feedback in the intermediate shaft 32 in response to the applied control inputs 44.The vehicle simulator 42 then automatically adjusts the actuator machine 40 accordingly until the detected steering torque is essentially zero and the actuator machine 40 is positioned to simulate a forward, straight-line movement.

[0030] Once the electric power steering 22 and the actuator 40 have been set to zero, the control inputs 44 from the vehicle simulator 42 are communicated to the actuator 40. As mentioned previously, the control inputs 44 contain the output of one or more commands to the actuator 40 to simulate specific driving behavior, for example, a specific cornering rate at a specific vehicle speed. The actuator 40 then applies a variety of input forces to the electric power steering 22, based on the control input 44 from the vehicle simulator 42. The control inputs 44 can, for example, include a steering angle, a left tie rod force, and a right tie rod force.Accordingly, the actuator machine 40 operates to apply the forces requested by the control inputs 44, and to actuate the steering actuator 34 to provide the intermediate shaft 32 with the steering angle requested by the control input 44.

[0031] The electric power steering 22 is then controlled by the steering control unit 36 ​​to apply the steering input. The steering control unit 36 ​​uses the calibration table 38 to define the steering input based on the applied input forces and steering angles and the simulated operating conditions of the vehicle. The steering input can include, or otherwise be defined as, an assist torque, and the torque magnitude is supplied to the power steering 22 by the electric auxiliary motor to assist the operator in turning the steering wheel.

[0032] The steering response 46 in the electric power steering system 22, in reaction to the applied steering input, i.e., the assist torque, is detected by the torque sensor 56. The detected steering response 46 can include at least lateral acceleration, steering torque feedback, or roll angle, the aforementioned list being non-limiting. The detected steering response 46, generated in response to the applied input forces, is communicated to the vehicle simulator 42 and stored in a file on a storage device of the vehicle simulator 42.

[0033] The detected steering response 46 represents the operation of the electric power steering 22 for the specific control input 44 for the specific vehicle for which the electric power steering calibration table 38 is developed. If, for example, the steering response 46 to be detected is the steering torque, i.e., the torque required for the steering actuator 34 to rotate the intermediate shaft 32, then it is understood that the detected steering response 46 would represent the amount of torque required by an operator to turn the steering wheel for that specific control input 44, based on the specific steering input, i.e., assist torque, currently defined by the calibration table 38.If this value lies outside of acceptable or desirable parameters, the designer can redefine calibration table 38 to set a steering target value for this specific control input 44, based on the detected steering response 46. The redefined calibration table 38 can then be saved as an electronic file on an electronic storage device or in the vehicle control unit's memory and reused and / or retested until the steering response 46 for this specific control input 44, which represents a specific operating condition, meets the designer's expectations.

[0034] As mentioned previously, calibration table 38 provides a variety of different steering input values, i.e., assist torque values, based on different specific operating conditions. Accordingly, it is understood that the procedure described above can be repeated for different simulated operating conditions, each simulated operating condition having its own control input 44 to simulate the operation of the vehicle under those conditions. The procedure described above can be repeated multiple times for several different operating conditions, i.e., with several different control inputs 44, in order to fully calibrate the power steering calibration table 38.

Claims

[1] Method for tuning a calibration table (38) for an electric power steering system (22), the method comprising: Defining a vehicle dynamics mathematical model (50) that models the physical properties and operational characteristics of a specific vehicle; storing the vehicle dynamics mathematical model (50) in an electronic storage device of a vehicle simulator (42); defining a simulator algorithm (48) that simulates the operation of one or more control modules of the specific vehicle to which the calibration table (38) is to be matched; storing the simulator algorithm (48) in the electronic storage device of the vehicle simulator (42); the generation of a mathematical equivalent of a simulated vehicle used to generate a control input (44) for the control of an actuator machine (40), wherein the simulator algorithm (48) interacts with and / or references the vehicle dynamics mathematical model (50) to generate the mathematical equivalent of the simulated vehicle; the connection of the electric power steering (22) to the actuator machine (40), wherein the actuator machine (40) is operable to simulate a movement of the specific vehicle; adjusting the electric power steering (22) and the actuator (40) so that the steering torque is approximately zero, wherein adjusting the electric power steering (22) and the actuator (40) so that the steering torque is approximately zero comprises the following: the detection of the steering torque in the electric power steering system (22) and the electronic communication of the detected steering torque to the vehicle simulator (42), and the automatic adjustment of the actuator machine (40) with the vehicle simulator (42) until the detected steering torque is essentially zero and the actuator machine (40) is positioned to simulate straight-line forward movement; the communication of the control input (44) from the vehicle simulator (42) to the actuator machine (40); the application of a variety of input forces and steering angles to the electric power steering (22) with the actuator machine (40), based on the control input (44) of the vehicle simulator (42); controlling the electric power steering (22) with a steering control (36) to input a steering input, wherein the steering control (36) uses the calibration table (38) to define the steering input based on the applied input forces and steering angles; the detection of a steering response (46) in the electric power steering (22) with a torque sensor (56) in response to the applied steering input; and redefining the calibration table (38) to set a steering input value based on the detected steering response (46). [2] Method according to claim 1, further comprising storing and redefining the calibration table (38) as an electronic file on an electronic storage device. [3] Method according to claim 1, further comprising communicating the detected steering response (46) generated in response to the applied input forces to the vehicle simulator (42). [4] Method according to claim 3, further comprising storing the detected steering response (46) in a file of an electronic storage device of the vehicle simulator (42). [5] Method according to claim 1, wherein the detected steering response (46) comprises at least a lateral acceleration, a steering torque or a roll angle.

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