Calibration method for controlling output torque of motor based on variable angle transmission ratio

Abstract

The invention relates to the technical field of steering systems, in particular to a calibration method for controlling the output torque of a motor based on a variable angle transmission ratio. The specific method comprises the following steps: calculating a whole vehicle angle transmission ratio through a whole vehicle steering wheel angle and a steering wheel angle; calculating a steering system line angle transmission ratio through a steering wheel angle and a rack moving speed; the trapezoidal mechanism transmission ratio is calculated through the rack moving speed and the steering wheel angular speed; obtaining the relation between the vehicle angular transmission ratio and the motor speed; under the whole vehicle angular transmission ratio, a new torque curve can be fitted according to the torque change coefficient. Compared with the prior art, by means of the calibration method, the calibration process can be simplified, and motor torque output curves of different angular transmission ratios are adjusted according to the initial calibration curve and the change requirements of the angular transmission ratios; the safety risk caused by insufficient assistance in the drive-by-wire power-assisted steering system is avoided, and the steering stability and response of the drive-by-wire power-assisted steering system are improved.

Description

Technical Field

[0001] The invention relates to the technical field of steering systems, and in particular to a calibration method for controlling the output torque of a motor based on a variable angle transmission ratio. Background Art

[0002] In the automotive field, compared with traditional steering systems, the wire-controlled steering system eliminates the permanent mechanical connection between the upper and lower intermediate shafts, and realizes the driver's steering control through the upper and lower redundant control units. Since the mechanical connection is eliminated, the transmission ratio between the steering wheel and the steering wheel angle is no longer subject to mechanical hard connection. Therefore, under the same working conditions, the angular transmission ratio required by different driving modes can be adjusted in a wide range under various working conditions.

[0003] Due to mechanical connection, the current traditional steering system usually has a fixed transmission ratio at the hand-end of the steering system. Therefore, the angular transmission ratio of the vehicle varies very little during the entire steering stroke, generally between 14-20, which is usually manifested as insufficient convenience in low-speed steering, and the number of steering wheel turns in the full stroke is usually 3-4 turns. Currently, vehicles equipped with wire-controlled steering systems usually require a lower angular transmission ratio at low and medium speeds, and the angular transmission ratio is also smaller than that of transmission steering systems at high speeds. For example, in conditions such as low-speed U-turns, the number of steering wheel turns in a traditional steering system generally needs to be turned 2 times in one direction. Under a smaller angular transmission ratio, the number of steering wheel turns can be reduced to 0.5-1, which greatly increases the convenience of steering in low-speed conditions. For conditions such as high-speed emergency avoidance, while taking into account the safety of the entire vehicle, a smaller angular transmission ratio can respond faster and have higher avoidance efficiency. However, under different variable angular transmission ratios, the output capacity boundary of the motor of the wire-controlled steering system is no longer fixed. Generally, the smaller the angular transmission ratio, the higher the motor speed requirement under the same working condition and the same motor torque requirement. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a calibration method for controlling the output torque of a motor based on a variable angle transmission ratio. Through this calibration method, the calibration process can be simplified and the safety risks caused by insufficient power assistance in a wire-controlled power steering system can be avoided.

[0005] In order to achieve the above purpose, a calibration method for controlling the output torque of a motor based on a variable angle transmission ratio is designed, which includes, and is characterized in that: the specific method flow is as follows:

[0006] S1, the vehicle angular transmission ratio i is calculated by the vehicle steering wheel angle and steering wheel angle aa ;

[0007] S2, the steering system linear angle transmission ratio i is calculated by the steering wheel angle and rack moving speed al ;

[0008] S3, the transmission ratio i of the trapezoidal mechanism is calculated by the rack moving speed and the steering wheel angular velocity. la ;

[0009] S4, according to step S1 to step S3, obtain i aa =i al ×i la ;

[0010] S5, for parallel axis power steering system, rack speed V rack The relationship between the power assist motor speed N is: Among them, V rack is the rack speed, N is the motor speed, p is the ball screw pitch, i belt It is a parallel-axis power steering with a gear ratio;

[0011] S6, according to step S1 to step S3, the vehicle angular transmission ratio i is obtained. aa The relationship with the motor speed N is

[0012] S7, in the vehicle angular transmission ratio i aa1 Under this condition, the motor torque boundary is calibrated, and a reference point N1 and T1 are selected under a certain working condition. When the motor torque remains unchanged, the vehicle angular transmission ratio is changed from i to aa1 becomes i aa2 , then according to the relationship in step S6, we can get i aa2 The corresponding motor speed is N2;

[0013] S8, calculate the torque variation coefficient Then the relationship between the motor torque T and the motor speed N and the motor power P is:

[0014] S9, because the motor torque curve is in the constant power area after the inflection point, therefore, according to step S6 and step 8, it is calculated that

[0015] S10, according to the calculation formula of the torque variation coefficient k obtained in step S9, when the vehicle angular transmission ratio i aa When the demand changes, the torque curve A2 can be calculated from the torque curve A1 according to the torque change coefficient k.

[0016] In step S1, the calculation formula of the vehicle angular transmission ratio is: Among them, i aa is the vehicle angular transmission ratio, W hw is the steering wheel angular velocity in degrees / s, W w is the steering wheel angular velocity, in degrees / s.

[0017] In step S2, the calculation formula of the steering system line angle transmission ratio is: Among them, i al is the steering system line angle transmission ratio, W hw is the steering wheel angular velocity in ° / s, V rack is the rack speed in mm / s.

[0018] In step S3, the calculation formula of the transmission ratio of the trapezoidal mechanism is: Among them, i la is the transmission ratio of the trapezoidal mechanism, V rack is the rack speed in mm / s, W w is the steering wheel angular velocity, in degrees / s.

[0019] The transmission ratio of the trapezoidal mechanism is the ratio of the steering system rack speed to the steering wheel angular velocity, and the unit is mm / °.

[0020] In step S6, for the same working condition of the whole vehicle, the steering wheel speed W hw Transmission ratio with trapezoidal mechanism i la Same requirements, parallel axis power steering with transmission ratio i belt The ball screw pitch p is the design constant of the steering system. Therefore, under the same working condition, when the vehicle angular transmission ratio i aa When the demand changes, the required motor speed N and the vehicle angular transmission ratio i under the corresponding working conditions aa Inversely proportional relationship.

[0021] In the step S10, when the calculated torque variation coefficient k is less than 1, the torque curve does not need to be adjusted; when the calculated torque variation coefficient k is greater than 1, the torque curve is fitted according to the torque variation coefficient k.

[0022] Compared with the prior art, the present invention provides a calibration method for controlling the output torque of a motor based on a variable angular transmission ratio. Through this calibration method, the calibration process can be simplified, and the motor torque output curves of different angular transmission ratios can be adjusted according to the initial calibration curve and the change requirements of the angular transmission ratio; the safety risks caused by insufficient power assistance in the wire-controlled power steering system can be avoided, and the steering stability and response of the wire-controlled power steering system can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a logic flow chart of torque calibration of the present invention.

[0024] Figure 2 Schematic diagram of motor torque curve.

[0025] Figure 3 This is a schematic diagram of motor torque curve calibration. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings.

[0027] The present invention provides a calibration method for controlling the output torque of a motor based on a variable angular transmission ratio under the requirements of different angular transmission ratios under the same working condition. The purpose of the present invention is to calibrate the maximum torque curve of the motor according to the requirements of different angular transmission ratios under various working conditions. In the early stage of development, it is usually only necessary to set the motor torque curve under a certain fixed transmission ratio. The motor output capacity can be calibrated according to the requirements of different variable angular transmission ratios to ensure that the motor output capacity can meet the requirements of wire-controlled steering under different ratio requirements.

[0028] The specific implementation steps are as follows:

[0029] (1) The vehicle angular transmission ratio can be calculated from the steering wheel angle and the steering wheel angle: Among them, i aa is the vehicle angular transmission ratio, W hw is the steering wheel angular velocity in degrees / s, W w is the steering wheel angular velocity, in degrees / s.

[0030] (2) The steering system linear angle transmission ratio can be calculated from the steering wheel angle and rack moving speed: Among them, i al is the steering system line angle transmission ratio, W hw is the steering wheel angular velocity in ° / s, V rack is the rack speed in mm / s.

[0031] (3) The transmission ratio of the trapezoidal mechanism can be calculated by the rack moving speed and the steering wheel angular velocity: Among them, i la is the transmission ratio of the trapezoidal mechanism, V rack is the rack speed in mm / s, W w is the steering wheel angular velocity, in degrees / s.

[0032] Therefore: i aa =i al ×i la .

[0033] (4) For parallel axis power steering system, the relationship between rack speed and power steering motor speed is: Among them, V rack is the rack speed, N is the motor speed, p is the ball screw pitch, i belt It is a parallel axis power steering with transmission ratio.

[0034] (5) According to the above calculation formula, the vehicle angular transmission ratio i aa Relationship with motor speed N:

[0035] For the same working condition of the whole vehicle, the steering wheel speed W hw Transmission ratio with trapezoidal mechanism i la Same requirements, parallel axis power steering with transmission ratio i belt The ball screw pitch p is the design constant of the steering system. Therefore, under the same working condition, when the vehicle angular transmission ratio i aa When the demand changes, the required motor speed N and the vehicle angular transmission ratio i under the corresponding working conditions aa Inversely proportional relationship, such as Figure 2 shown.

[0036] like Figure 2 As shown, first, the vehicle angular transmission ratio i aa1 Under this condition, the motor torque boundary can be calibrated, and a reference point N1 and T1 can be selected for a certain working condition. When the steering wheel speed and motor torque demand remain unchanged under this working condition, only the angular transmission ratio is changed by i aa1 becomes i aa2 (i aa1 >i aa2 ), then the vehicle angular transmission ratio i aa The calculation formula of motor speed N can be obtained, i aa2 The corresponding motor speed requirement is N2, and the torque requirement remains unchanged at T1. If the speed N2 corresponds to the torque T2 under the original calibrated torque curve output, the T2 corresponding to the N2 speed needs to be enlarged to T1 to meet the new output requirement. The calculation formula of the torque change coefficient k is:

[0037] The relationship between motor torque T and motor speed N and motor power P is:

[0038] Since the motor torque curve is in the constant power region after the inflection point, the above formula can be used to calculate:

[0039] Therefore, the torque change coefficient k can be calculated from the angular transmission ratio. So for the calibrated torque curve A1, when the angular transmission ratio requirement changes, the torque curve A2 can be calculated based on the coefficient k. New points corresponding to the 6 to 10 points on the A1 curve can be calculated based on the coefficient k. The new torque curve A2 can be fitted through the interpolation algorithm, as shown in the following example: Figure 3 shown.

[0040] For example, at a vehicle speed of 30km / h, the steering wheel angular velocity is 300° / s in the middle position, the steering motor speed is 2000rpm, the output torque demand is 5Nm, and the angular transmission ratio is 20. When the angular transmission ratio demand changes to 10, the change coefficient k=2 can be obtained, corresponding to a motor speed of 4000rpm. Under the original torque curve, the corresponding output torque is 2.5Nm. At this speed, the torque output cannot meet the demand and needs to be amplified to 5Nm according to the coefficient k. At this time, the motor torque demand boundary changes.

[0041] like Figure 3 As shown, when the angular transmission ratio requirement changes, a, b, c, d, e, and f can correspond to a1, b1, c1, d1, e1, and f1 according to the torque change coefficient, and a new torque curve A2 can be fitted by interpolation calculation.

[0042] The present invention adapts to new ratio requirements by calculating and extrapolating the fitted new torque curve. In the initial stage, only one set of reference torque boundaries is calibrated, which greatly reduces the calibration workload. The requested torque is multiplied by the variation coefficient before the software app layer calls it, thereby improving the motor assist performance and ensuring the motor torque output adaptation under various working conditions to avoid insufficient assist, which is beneficial to improving the steering stability and response of the wire-controlled power steering system.

[0043] according to Figure 1 As shown, the initial torque boundary is set according to a single demand. When the angular transmission ratio demand changes, the torque adjustment coefficient k needs to be checked to determine whether the boundary needs to be adjusted. If k < 1, no adjustment is required. If k > 1, the adjustment coefficient k needs to be extrapolated to the motor control layer, and the coefficient k is multiplied on the original motor torque output to ensure that the new motor torque curve can meet the power assistance demand after the demand changes.

[0044] The present invention can simplify the calibration process and adjust the motor torque output curves of different angular transmission ratios according to the initial calibration curve and the change requirements of the angular transmission ratio; it is beneficial to the adaptability of the motor power-assisting performance, avoids the safety risks caused by insufficient power assistance in the wire-controlled power-steering system, and improves the steering stability and response of the wire-controlled power-steering system.

Claims

1. A method for calibrating the output torque of a motor based on variable angle transmission ratio control, comprising: The specific method flow is as follows: S1, the vehicle angular transmission ratio i is calculated by the vehicle steering wheel angle and steering wheel angle aa ; S2, the steering system linear angle transmission ratio i is calculated by the steering wheel angle and rack moving speed al ; S3, the transmission ratio i of the trapezoidal mechanism is calculated by the rack moving speed and the steering wheel angular velocity. la ; S4, according to step S1 to step S3, obtain i aa =i al ×i la ; S5, for parallel axis power steering system, rack speed V rack The relationship between the power assist motor speed N is: Among them, V rack is the rack speed, N is the motor speed, p is the ball screw pitch, i belt It is a parallel-axis power steering with a gear ratio; S6, according to step S1 to step S3, the vehicle angular transmission ratio i is obtained. aa The relationship with the motor speed N is S7, in the vehicle angular transmission ratio i aa1 Under this condition, the motor torque boundary is calibrated, and a reference point N1 and T1 are selected under a certain working condition. When the motor torque remains unchanged, the vehicle angular transmission ratio is changed from i to aa1 becomes i aa2 , then according to the relationship in step S6, we can get i aa2 The corresponding motor speed is N2; S8, calculate the torque variation coefficient Then the relationship between the motor torque T and the motor speed N and the motor power P is: S9, because the motor torque curve is in the constant power area after the inflection point, therefore, according to step S6 and step 8, it is calculated that S10, according to the calculation formula of the torque variation coefficient k obtained in step S9, when the vehicle angular transmission ratio i aa When the demand changes, the torque curve A2 can be calculated from the torque curve A1 according to the torque change coefficient k.

2. A calibration method for controlling the output torque of a motor based on a variable angle transmission ratio according to claim 1, characterized in that: In step S1, the calculation formula of the vehicle angular transmission ratio is: Among them, i aa is the vehicle angular transmission ratio, W hw is the steering wheel angular velocity in ° / s, W w is the steering wheel angular velocity, in degrees / s.

3. The method for calibrating the output torque of a motor based on variable angle transmission ratio control according to claim 1, characterized in that: In step S2, the calculation formula of the steering system line angle transmission ratio is: Among them, i al is the steering system line angle transmission ratio, W hw is the steering wheel angular velocity in ° / s, V rack is the rack speed in mm / s.

4. The method for calibrating the output torque of a motor based on variable angle transmission ratio control according to claim 1, characterized in that: In step S3, the calculation formula of the transmission ratio of the trapezoidal mechanism is: Among them, i la is the transmission ratio of the trapezoidal mechanism, V rack is the rack speed in mm / s, W w is the steering wheel angular velocity, in degrees / s.

5. The method for calibrating the output torque of a motor based on variable angle transmission ratio control according to claim 4, characterized in that: The transmission ratio of the trapezoidal mechanism is the ratio of the steering system rack speed to the steering wheel angular velocity, and the unit is mm / °.

6. The method for calibrating the output torque of a motor based on variable angle transmission ratio control according to claim 1, characterized in that: In step S6, for the same working condition of the whole vehicle, the steering wheel speed W hw Transmission ratio with trapezoidal mechanism i la Same requirements, parallel axis power steering with transmission ratio i belt The ball screw pitch p is the design constant of the steering system. Therefore, under the same working condition, when the vehicle angular transmission ratio i aa When the demand changes, the required motor speed N and the vehicle angular transmission ratio i under the corresponding working conditions aa Inversely proportional relationship.

7. The method for calibrating the output torque of a motor based on variable angle transmission ratio control according to claim 1, characterized in that: In the step S10, when the calculated torque variation coefficient k is less than 1, the torque curve does not need to be adjusted; when the calculated torque variation coefficient k is greater than 1, the torque curve is fitted according to the torque variation coefficient k.

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