Calibration method of electric power steering system, electric power steering system and truck

Abstract

The invention discloses a calibration method of an electric power-assisted steering system, the electric power-assisted steering system and a truck, the calibration method of the electric power-assisted steering system comprises the following steps: acquiring a theoretical error value and a calculation error value of the electric power-assisted steering system before calibration, and starting calibration after the calculation error value is smaller than the theoretical error value; a steering wheel is manually rotated, and the electric power steering system is controlled to operate; obtaining the rotating torque of the electric power steering system; when the rotating torque exceeds a torque threshold value corresponding to the set steering stop point position, the current steering angle of the electric power steering system is obtained; and subtracting the theoretical error value from the current steering angle to obtain a dead center position. According to the method, the steering angle of the electric power steering system can be calibrated, the steering angle error is reduced, the steering accuracy is ensured, the steering stop point position is calibrated to prevent damage to a steering mechanical mechanism caused by excessive steering, a steering machine is effectively protected, and the steering safety is improved.

Description

Technical Field

[0001] The invention relates to the field of vehicles, and in particular to a calibration method for an electric power steering system, an electric power steering system and a truck. Background Art

[0002] In the related technology, electric power steering is achieved by an electric motor, which affects the steering gear through the worm gear to achieve power steering, providing the driver with better driving comfort and safety. However, the steering angle calibration error of the existing electric power steering system is large, and the steering accuracy cannot be guaranteed. The steering stop position is not calibrated, and oversteering may cause damage to the steering mechanical mechanism. The steering machine cannot be effectively protected, and the steering safety is low. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one purpose of the present invention is to provide a calibration method for an electric power steering system, which can calibrate the steering angle of the electric power steering system, reduce the steering angle error, ensure the accuracy of steering, calibrate the steering dead point position to prevent damage to the steering mechanical mechanism caused by oversteering, effectively protect the steering machine, and improve the safety of steering.

[0004] A second object of the present invention is to provide an electric power steering system.

[0005] A third object of the present invention is to provide a truck.

[0006] In order to solve the above problems, an embodiment of the first aspect of the present invention provides a calibration method for an electric steering power-assist system, including: obtaining a theoretical error value and a calculated error value of the electric steering power-assist system before calibration, and starting calibration after the calculated error value is less than the theoretical error value; manually rotating the steering wheel to control the operation of the electric steering power-assist system; obtaining the rotational torque of the electric steering power-assist system; when the rotational torque exceeds a torque threshold corresponding to a set steering dead point position, obtaining the current steering angle of the electric steering power-assist system; and obtaining the dead point position by subtracting the theoretical error value from the current steering angle.

[0007] According to the calibration method of the embodiment of the present invention, the steering angle of the electric steering power system can be calibrated to reduce the steering angle error, ensure the accuracy of steering, calibrate the steering stop position to prevent damage to the steering mechanical mechanism caused by oversteering, effectively protect the steering machine, and improve the safety of steering.

[0008] In some embodiments, manually rotating the steering wheel includes turning the steering wheel left and turning the steering wheel right, and the corresponding stop points include a left stop point and a right stop point.

[0009] In some embodiments, the calibration method also includes: calibrating the steering midpoint position of the electric steering assist system according to a first steering angle and a second steering angle, wherein the first steering angle is the current steering angle of the electric steering assist system minus a theoretical error value when the rotational torque exceeds the torque threshold corresponding to the set left stop point, and the second steering angle is the current steering angle of the electric steering assist system minus a theoretical error value when the rotational torque exceeds the torque threshold corresponding to the set right stop point.

[0010] In some embodiments, calibrating the steering midpoint position of the electric steering assist system according to the first steering angle and the second steering angle includes: obtaining an absolute value of a difference between the first steering angle and the second steering angle; When the absolute value of the difference is smaller than the difference between the theoretical error and the calculated error, the midpoint position calibration is successful; Alternatively, when the absolute value of the difference is greater than the difference between the theoretical error and the calculated error, the midpoint position calibration is unsuccessful.

[0011] In some embodiments, the calibration method further includes: before calibrating the dead point position, obtaining a calculated error value, the calculated error value including a calibration software error, a hardware error of the electric steering assist system and a correction value; when the calculated error value is within a theoretical error value range, calibrating the dead point position.

[0012] In some embodiments, the calculated error value = the calibrated software error + the hardware error of the electric steering power system + the correction value; wherein, the calibrated software error = |software set steering value-actual steering value|, the hardware error of the electric steering power system and the correction value are known values.

[0013] In some embodiments, the stop point angle corresponding to the steering stop point position is 48 degrees to the left and right of the midpoint.

[0014] In some embodiments, the theoretical error value range is 2 degrees. If the calculated error value is smaller than the theoretical error value, the steering wheel cannot touch the actual dead point no matter how it is rotated, thereby damaging the steering machine.

[0015] A second aspect of the present invention provides an electric power steering system, comprising a motor, a controller, a gearbox, a steering and torque sensor, wherein the motor is connected to the controller for converting a control signal into a rotational motion, the gearbox is connected to the motor for transmitting the rotational motion, the controller is also connected to the steering and torque sensor, and the controller is configured with calibration software for executing the calibration method of the electric power steering system described in the above embodiment.

[0016] According to the electric power steering system of the embodiment of the present invention, the theoretical error value and calculated error value of the electric power steering system are obtained before calibration, and calibration can be started after confirming that the calculated error value is less than the theoretical error value; the steering wheel is manually rotated to obtain the rotational torque of the electric power steering system; when the rotational torque exceeds the torque threshold corresponding to the set steering stop position, the current steering angle of the electric power steering system is obtained, and the theoretical error value is subtracted from this angle to obtain the stop point. At the same time, a 2.5 times theoretical error value interval is set, and a reverse force is applied within this interval to ensure that the steering wheel does not touch the actual stop point. Calibration of the steering stop point position prevents damage to the steering mechanical mechanism caused by oversteering, effectively protects the steering machine, and improves the safety of steering.

[0017] A third aspect of the present invention provides a truck, comprising the electric power steering system of the above embodiment.

[0018] According to the truck of the embodiment of the present invention, the theoretical error value and the calculated error value of the electric steering power-assist system are obtained before calibration, and the calibration can be started after confirming that the calculated error value is less than the theoretical error value; the steering wheel is manually rotated to obtain the rotational torque of the electric steering power-assist system; when the rotational torque exceeds the torque threshold corresponding to the set steering stop position, the current steering angle of the electric steering power-assist system is obtained, and the theoretical error value is subtracted from this angle, that is, the steering stop position is calibrated to the stop point to prevent damage to the steering mechanical mechanism caused by oversteering, effectively protect the steering machine, and improve the safety of steering.

[0019] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 is a flow chart of a calibration method of an electric power steering system according to an embodiment of the present invention; Figure 2 is a schematic diagram of the working range of a parking steering machine according to an embodiment of the present invention; Figure 3 is a schematic diagram of steering torque at different vehicle speeds according to an embodiment of the present invention; Figure 4 is a structural block diagram of an electric power steering system according to an embodiment of the present invention; Figure 5 is a structural block diagram of a truck according to an embodiment of the present invention.

[0021] Reference numerals: Truck 200; Electric power steering system 100; Electric motor 101; controller 102; gear box 103; steering 104; torque sensor 105. DETAILED DESCRIPTION

[0022] Embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. Embodiments of the present invention are described in detail below.

[0023] The first aspect of the embodiment of the present invention provides a calibration method for an electric power steering system, which can calibrate the steering angle of the electric power steering system, reduce the steering angle error, ensure the accuracy of steering, calibrate the steering stop position to prevent damage to the steering mechanical mechanism caused by oversteering, effectively protect the steering machine, and improve the safety of steering.

[0024] Reference below Figure 1 A calibration method for an electric power steering system according to an embodiment of the first aspect of the present invention is described. Figure 1 As shown, the method at least includes steps S1 to S4.

[0025] Step S1, obtaining a theoretical error value and a calculated error value of the electric power steering system before calibration, and starting calibration after the calculated error value is smaller than the theoretical error value.

[0026] Specifically, before calibration, the theoretical error value and calculated error value of the electric power steering system are obtained. The theoretical error value is a set value, and the calculated error value is an error value obtained by calculation before calibration. Calibration can be started after confirming that the calculated error value is less than the theoretical error value.

[0027] Step S2, manually rotating the steering wheel to control the operation of the electric power steering system.

[0028] Specifically, manually rotate the steering wheel to control the operation of the electric power steering system and obtain the rotational torque of the electric power steering system; when the rotational torque exceeds the torque threshold corresponding to the set steering dead point position, obtain the current steering angle of the electric power steering system, and subtract the theoretical error value from this angle to obtain the dead point. At the same time, set a 2.5 times theoretical error value interval, and apply a reverse force within this interval to ensure that the steering wheel does not touch the actual dead point. Rotate the steering wheel in the opposite direction and obtain another dead point using the same method. Calculate the midpoint of the steering wheel based on the left and right dead points and calibrate it.

[0029] Step S3, obtaining the rotation torque of the electric power steering system.

[0030] Specifically, the electric power steering system detects the rotational torque in real time through the torque sensor and transmits the signal to the controller for calculation and processing. To prevent oversteering from damaging the steering gear, the electric power steering system sets a buffer zone before the steering dead center position. In the buffer zone, the power steering system will apply a reverse force to avoid damage to the steering mechanism. When the steering angle of the steering gear is within the buffer zone, the electric power steering system applies a reverse torque and detects the rotational torque in real time through the torque sensor.

[0031] Step S4, when the rotational torque exceeds the torque threshold corresponding to the set steering dead center position, obtaining the current steering angle of the electric steering system.

[0032] Specifically, when the steering angle of the steering gear is within the buffer zone, the electric steering power system applies a rotational torque. The greater the steering angle of the steering gear, the greater the rotational torque applied by the electric steering power system. When the torque sensor detects that the current rotational torque exceeds the torque threshold corresponding to the set steering stop position, the electric steering power system obtains the current steering angle through the angle sensor. The current steering angle can be understood as the steering angle of the steering gear at the current moment; the torque threshold corresponding to the steering stop position can be understood as the maximum rotational torque of the electric steering power system when the steering gear reaches the stop position. The torque threshold corresponding to the steering stop position can be set to 10Nm. When the torque sensor detects that the current rotational torque is 10Nm, the electric steering power system obtains the current steering angle through the angle sensor.

[0033] Step S5: The dead point position is obtained by subtracting the theoretical error value from the current steering angle.

[0034] Specifically, the calculated error value of the electric steering assist system can be 1.5 degrees, and the theoretical error value range is 2 degrees, which can meet the calibration conditions. The steering angle is 100 degrees. In order to prevent oversteering from damaging the steering gear, the stop angle of the steering stop position should be smaller than the theoretical rotation angle. For example, the theoretical rotation angle of the steering gear can be set to 48 degrees left and right (steering angle 50 degrees minus theoretical error 2 degrees), and the actual working range of the steering gear is 96 degrees. At this time, the stop angle of the steering stop position should be smaller than the theoretical rotation angle. At the same time, a theoretical error value interval of 2.5 times is set, and a reverse force is applied within this interval to ensure that the steering wheel does not touch the actual stop point.

[0035] The steering angle of the electric power steering system is calibrated to reduce the steering angle error and ensure the accuracy of steering. The steering stop position is calibrated to prevent damage to the steering mechanism caused by oversteering, effectively protect the steering machine, improve the safety of steering, and meet the functional requirements of automatic steering wheel return during automatic driving.

[0036] According to the calibration method of the electric power steering system of the embodiment of the present invention, when the electric power steering system is running, the rotational torque exceeds the torque threshold corresponding to the set steering stop position, the current steering angle is obtained and compared with the stop angle of the corresponding steering stop position, and the stop position of the electric power steering system is calibrated when the calculated error value is less than the theoretical error range, so as to reduce the steering angle error and ensure the steering accuracy. The steering stop position is calibrated to prevent damage to the steering mechanical mechanism caused by oversteering, effectively protect the steering machine, and improve the safety of steering.

[0037] In some embodiments, manually rotating the steering wheel includes turning the steering wheel left and turning the steering wheel right, and the corresponding stop positions include a left stop and a right stop.

[0038] Specifically, Figure 2 As shown in the figure, the steering stop position of the steering gear includes the left stop or the right stop. The theoretical rotation angle of the electric power steering system steering gear is 100°. At this time, the actual left stop and right stop are both 50°. In order to prevent oversteering from damaging the steering gear, the stop angle of the calibrated steering stop position is subtracted from the theoretical error value of 2°. Therefore, the steering stop position can be set to 96°. The actual working range of the steering gear is 96°. At this time, the left stop and the right stop are both 48°, and the left stop and the right stop are reduced by 2° respectively; when the steering angle of the steering gear in the left and right directions reaches 43°, control The controller controls the motor to start running and generate a rotational torque, which gradually increases between steering angles of 43° and 48°. The rotational torque reaches a maximum value at a steering angle of 48°, which is the torque threshold corresponding to the steering stop position. At this time, the current rotational torque is 10Nm; the rotational torque gradually increases between steering angles of 43° and 48°, 5° in each direction, and an overall range of 10°. In this interval, the controller controls the motor to apply a reverse force, and the actual normal rotation of the steering gear, that is, the working range not subject to a reverse force, is 86 degrees.

[0039] In some embodiments, the calibration method further includes: calibrating a steering midpoint position of the electric steering assist system according to the first steering angle and the second steering angle.

[0040] Among them, the first steering angle is the current steering angle of the electric steering assist system when the rotational torque exceeds the torque threshold corresponding to the set left stop point minus the theoretical error value, and the second steering angle is the current steering angle of the electric steering assist system when the rotational torque exceeds the torque threshold corresponding to the set right stop point minus the theoretical error value.

[0041] Specifically, when the steering gear turns left and the torque sensor detects that the current rotational torque exceeds the torque threshold corresponding to the set steering stop position, the electric steering assist system obtains the current steering angle minus the theoretical error value through the angle sensor. The angle obtained at this time is the first steering angle; when the steering gear turns right and the torque sensor detects that the current rotational torque exceeds the torque threshold corresponding to the set steering stop position, the electric steering assist system obtains the current steering angle minus the theoretical error value through the angle sensor. The angle obtained at this time is the second steering angle. After obtaining the first steering angle and the second steering angle, the steering midpoint position is calibrated by calculating the average value. The steering midpoint position can be understood as the angle when the steering gear is not turning. At this time, the steering angle of the steering gear is 0°.

[0042] In some embodiments, calibrating the steering midpoint position of the electric steering assist system according to the first steering angle and the second steering angle includes: obtaining an absolute value of a difference between the first steering angle and the second steering angle; When the absolute value of the difference is smaller than the difference between the theoretical error and the calculated error, the midpoint position calibration is successful; Alternatively, when the absolute value of the difference is greater than the difference between the theoretical error and the calculated error, the midpoint position calibration is unsuccessful.

[0043] Specifically, after obtaining the first steering angle and the second steering angle, the first steering angle and the second steering angle are calculated. The absolute value of the difference; When the absolute value of the difference is smaller than the difference between the theoretical error and the calculated error, the midpoint position calibration is successful; Alternatively, when the absolute value of the difference is greater than the difference between the theoretical error and the calculated error, the midpoint position calibration is unsuccessful. This indicates that the first steering angle and the second steering angle are not the left and right stop points, and the left and right stop points are not calibrated successfully. After the midpoint position calibration is successful, the automatic self-centering function can be implemented according to the midpoint position when the vehicle realizes the automatic driving function.

[0044] In some embodiments, the calibration method also includes: before calibrating the dead point position, obtaining a calculated error value, the calculated error value includes a calibration software error, a hardware error of the electric steering assist system, and a correction value; when the calculated error value is within a theoretical error value range, starting to calibrate the dead point position.

[0045] Specifically, the hardware errors and correction values ​​of different components in the electric power steering system are different. Before the dead center position is calibrated, the hardware errors and correction values ​​are stored in the controller, and the software error value is obtained by calculation, and the software set steering value and the actual steering value are calculated by comparison; before the dead center position is calibrated, the calculated error value is first obtained, and the calculated error value is calculated by a formula. The theoretical error value is the set value. When the calculated error value is within the theoretical error value range, the dead center position is calibrated.

[0046] For example, after obtaining the calculated error value, the dead center position is calibrated. When calibrating the left dead center, the torque sensor detects that the current rotational torque is 10Nm, and the electric steering assist system obtains the current steering angle through the angle sensor, subtracts the theoretical error value, and the left dead center position is calibrated successfully; when calibrating the right dead center, the torque sensor detects that the current rotational torque is 10Nm, and the electric steering assist system obtains the current steering angle through the angle sensor, subtracts the theoretical error value, and the right dead center position is calibrated successfully.

[0047] At different vehicle speeds, the auxiliary steering torque provided by the power steering system is different. The greater the vehicle speed, the smaller the torque required for the power steering. Figure 3 As shown in the figure, the auxiliary steering torque provided by the power-assist system is different at vehicle speeds of 0km / h, 6km / h, 12km / h, 30km / h, 50km / h, and 80km / h. The horizontal axis is the steering assist perceived by the driver, and the vertical axis is the torque output by the steering motor. The faster the speed, the smaller the assist output under the same steering assist perceived by the driver. Small assist at high speed ensures safety; large assist at low speed ensures comfort.

[0048] In some embodiments, the calculated error value=calibrated software error+electric power steering system hardware error+correction value; Among them, the calibration software error = |software set steering value-actual steering value|, the hardware error and correction value of the electric steering system are known values.

[0049] Specifically, the hardware errors and correction values ​​of different components in the electric power steering system are different. The hardware errors and correction values ​​are stored in the controller before the dead center position is calibrated. The hardware errors and correction values ​​are known values ​​when obtaining the calculated error value; the steering value of the steering machine is stored through software settings. When calibrating the software error, the software set steering value and the actual steering value are subtracted, and the absolute value of the result is obtained.

[0050] In some embodiments, the dead point angle corresponding to the steering dead point position is 48 degrees to the left and right of the midpoint.

[0051] Specifically, Figure 2As shown, in order to prevent oversteering from damaging the steering gear, the stop angle of the steering stop position should be smaller than the theoretical rotation angle. Therefore, the steering stop position can be set to 96 degrees, and the actual working range of the steering gear is 96 degrees. At this time, the stop angle of the steering stop position is 48 degrees to the left and right of the midpoint, and the left and right stop points are each reduced by 2 degrees.

[0052] In some embodiments, the theoretical error value range is 2 degrees, and the calculated error value is smaller than the theoretical error value.

[0053] Specifically, the calculated error value = calibration software error + hardware error of the electric steering assist system + correction value. The calculated error value is obtained through the formula. For example, the calculated error value is 1.5 degrees. The calculated error value is smaller than the theoretical error value, and the dead point position is calibrated.

[0054] A second aspect of the present invention provides an electric power steering system, such as Figure 3 As shown, the electric power steering system 100 includes: an electric motor 101 , a controller 102 , a gear box 103 , a steering wheel 104 and a torque sensor 105 .

[0055] Among them, the motor 101 is connected to the controller 102 for converting the control signal into rotational motion, the gearbox 103 is connected to the motor 1 for transmitting the rotational motion, the controller 102 is also connected to the steering 104 and the torque sensor 105, and the controller 101 is configured with calibration software for executing the calibration method of the electric steering power system.

[0056] Specifically, the controller 102 evaluates all steering requests from the driver and the auxiliary interface and controls the motor 101. The actual steering angle and torque readings on the torque sensor 105 are the direction of the steering request of the controller 102 being executed. This information is also sent to the vision and radar control module through the external CAN (Controller Area Network) bus to calculate the assisted driving. The distributor provides voltage to the controller 102. The motor 101 is controlled by the controller 102 and converts the control signal into rotational motion. The gear ratio of the motor 101 is 21. The motor rotates 21 times and the steering wheel rotates 1 time. The role of the gearbox 103 is to transfer the rotational motion from the motor 101 through the gearbox 103 to the steering gearbox. Through the gearshift gearbox, the torque is amplified to 84Nm. The task of the steering 104 is to capture the current steering angle. The torque sensor 105 also measures the steering torque applied by the driver on the steering wheel. The device has a bogie, through which the rotational motion of the motor 101 is transmitted to the steering device.

[0057] To illustrate, Adaptive Power Steering is a comfort-oriented electrohydraulic steering system whose main task is to transmit the driver's steering desire to the wheels. In this case, the steering force support is adapted depending on the speed. At low speeds, the driver's support is stronger than at high speeds. This leads to better driving comfort and greater safety on the straight. Adaptive Steering Force Support is achieved by means of an electric motor, which influences the steering gear via a worm gear. The system has a steering and torque sensor. This determines the current steering angle and the influence of the forces on the steering wheel. With Adaptive Power Steering, speed-dependent steering assistance is provided, with high steering assistance (comfort) at low vehicle speeds and low steering assistance (safety) at high vehicle speeds.

[0058] Before the mechanical end of the steering stops, the adaptive steering system generates a progressive counter-torque on the electric motor, which forms a software stop. The driver can overcome this counter-torque by steering and will protect the mechanical device. The adaptive steering system uses the electric motor to generate a rising counter-torque outside the working area, just before the mechanical counter-torque. The maximum counter-torque of the adaptive steering system is 42Nm, which ensures that the hydraulic pressure will not cause damage to the steering shaft.

[0059] After turning, the adaptive steering assist system helps the driver return the wheel / steering to the neutral position.

[0060] The adaptive steering system provides an interface that allows active steering interventions by the assistance system. The desired wheel angle is transmitted to the control unit via the CAN bus, and the steering movement is then carried out on the electric motor. The driver can eliminate this interference at any time by controlling the direction with the steering wheel. The adaptive steering system detects the steering intervention via the steering and torque sensors.

[0061] The steering angle sensor is a rotation angle and torque sensor that determines the angle position and steering torque. By turning the steering wheel, torque is generated in the handlebars, which is read by the torque sensor into the handlebars, and the voltage signal is converted and transmitted to the controller by the electric servo steering. According to the electric power steering system of the embodiment of the present invention, the theoretical error value and calculated error value of the electric power steering system are obtained before calibration, and calibration can be started after confirming that the calculated error value is less than the theoretical error value; the steering wheel is manually rotated to obtain the rotational torque of the electric power steering system; when the rotational torque exceeds the torque threshold corresponding to the set steering stop position, the current steering angle of the electric power steering system is obtained, and the theoretical error value is subtracted from this angle to obtain the stop point. At the same time, a 2.5 times theoretical error value interval is set, and a reverse force is applied within this interval to ensure that the steering wheel does not touch the actual stop point. Calibration of the steering stop point position prevents damage to the steering mechanical mechanism caused by oversteering, effectively protects the steering machine, and improves the safety of steering.

[0062] A third aspect of the present invention provides a truck, such as Figure 4 As shown, the truck 200 includes an electric power steering system 100 .

[0063] According to the truck of the embodiment of the present invention, the theoretical error value and the calculated error value of the electric steering power-assist system are obtained before calibration, and the calibration can be started after confirming that the calculated error value is less than the theoretical error value; the steering wheel is manually rotated to obtain the rotational torque of the electric steering power-assist system; when the rotational torque exceeds the torque threshold corresponding to the set steering stop position, the current steering angle of the electric steering power-assist system is obtained, and the theoretical error value is subtracted from this angle, that is, the steering stop position is calibrated to the stop point to prevent damage to the steering mechanical mechanism caused by oversteering, effectively protect the steering machine, and improve the safety of steering.

[0064] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0065] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A calibration method for an electric power steering system, characterized in that: include: Before calibration, the theoretical error value and calculated error value of the electric power steering system are obtained, and calibration is started after the calculated error value is less than the theoretical error value; Manually rotating the steering wheel to control the operation of the electric power steering system; Obtaining the rotational torque of the electric power steering system; When the rotation torque exceeds a torque threshold corresponding to a set steering dead center position, obtaining a current steering angle of the electric steering assist system; The dead center position is obtained by subtracting the theoretical error value from the current steering angle.

2. The calibration method according to claim 1, characterized in that: Manually rotating the steering wheel includes turning the steering wheel left and turning the steering wheel right, and the corresponding stop point positions include a left stop point and a right stop point.

3. The calibration method according to claim 2, characterized in that: The calibration method further comprises: The steering midpoint position of the electric power steering system is calibrated according to the first steering angle and the second steering angle, wherein the first steering angle is the current steering angle of the electric power steering system minus a theoretical error value when the rotational torque exceeds the torque threshold corresponding to the set left dead center, and the second steering angle is the current steering angle of the electric power steering system minus a theoretical error value when the rotational torque exceeds the torque threshold corresponding to the set right dead center.

4. The calibration method according to claim 3, characterized in that: The method of calibrating a steering midpoint position of the electric power steering system according to a first steering angle and a second steering angle includes: Obtaining an absolute value of a difference between the first steering angle and the second steering angle; When the absolute value of the difference is smaller than the difference between the theoretical error and the calculated error, the midpoint position calibration is successful; Alternatively, when the absolute value of the difference is greater than the difference between the theoretical error and the calculated error, the midpoint position calibration is unsuccessful.

5. The calibration method according to claim 1, characterized in that: The calibration method further comprises: Before calibrating the dead center position, obtaining a calculated error value, the calculated error value including a calibration software error, a hardware error of the electric power steering system and a correction value; When the calculated error value is within the theoretical error value range, the dead point position is calibrated.

6. The calibration method according to claim 5, characterized in that: The calculated error value=the calibration software error+the hardware error of the electric power steering system+the correction value; Among them, the calibrated software error=|software set steering value-actual steering value|, and the hardware error of the electric steering power system and the correction value are known values.

7. The calibration method according to claim 1, characterized in that: The dead point angle corresponding to the steering dead point position is 48 degrees to the left and right of the midpoint.

8. The calibration method according to claim 5, characterized in that: The theoretical error value range is 2 degrees, and the calculated error value is smaller than the theoretical error value.

9. An electric power steering system, characterized in that: The invention comprises an electric motor, a controller, a gearbox, a steering and torque sensor, wherein the electric motor is connected to the controller for converting a control signal into a rotational motion, the gearbox is connected to the electric motor for transmitting the rotational motion, the controller is also connected to the steering and torque sensor, and the controller is configured with calibration software for executing the calibration method of the electric steering assist system according to any one of claims 1 to 8.

10. A truck, characterized in that: Including the electric power steering system as claimed in claim 9.

Images