A calibration method for controlling motor output torque based on variable angle transmission ratio

Abstract

The present application relates to the technical field of steering system, and particularly relates to a calibration method for controlling motor output torque based on variable angle transmission ratio. The specific method process is as follows: the vehicle angle transmission ratio is calculated through the vehicle steering wheel angle and the steering wheel angle; the steering system linear angle transmission ratio is calculated through the steering wheel angle and the rack moving speed; the trapezoidal mechanism transmission ratio is calculated through the rack moving speed and the steering wheel angular velocity; the relationship between the vehicle angle transmission ratio and the motor rotating speed is obtained; under the vehicle angle transmission ratio, the new torque curve can be fitted according to the torque change coefficient. Compared with the prior art, through the calibration method, the calibration process can be simplified, the motor torque output curve of different angle transmission ratios is adjusted according to the starting calibration curve and the change requirement of the angle transmission ratio; the safety risk caused by insufficient power in the online control power steering system is avoided, and the steering stability and response of the online control power steering system are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steering system, in particular to a calibration method for controlling motor output torque based on variable angle transmission ratio. BACKGROUND

[0002] In the field of automobiles, compared with the traditional steering system, the steer-by-wire steering system cancels the mechanical permanent connection of the upper and lower intermediate shafts, and realizes the driver steering control through the upper and lower steering redundant control units. Since the mechanical connection is canceled, the transmission ratio between the steering wheel and the steering wheel angle is not subject to mechanical hard connection, so under the same working condition, the adjustable range of the angle transmission ratio required by different driving modes is very large.

[0003] The current traditional steering system usually has a fixed steering system hand force transmission ratio due to mechanical connection, so the vehicle angle transmission ratio change range in the whole steering stroke is small, generally between 14-20, and the steering wheel usually turns 3-4 turns in the whole stroke. The current vehicle equipped with steer-by-wire steering system usually requires a lower angle transmission ratio at low vehicle speed, and the angle transmission ratio at high vehicle speed is also smaller than that of the traditional steering system. For example, in the low-speed U-turn working condition, the steering wheel of the traditional steering system generally needs to turn 2 turns in one direction, and the steer-by-wire steering system can reduce the steering wheel turns to 0.5-1 turn under a smaller angle transmission ratio, greatly increasing the steering convenience in low-speed working condition. For high-speed emergency avoidance working condition, under the condition of considering vehicle safety, smaller angle transmission ratio can respond faster and have higher avoidance efficiency. However, in the case of different variable angle transmission ratios, the motor output capacity boundary of the steer-by-wire steering system is no longer fixed. Generally, the smaller the angle transmission ratio, the higher the motor speed requirement under the same motor torque demand in the same working condition. SUMMARY

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

[0005] To achieve the above purpose, a calibration method for controlling motor output torque based on variable angle transmission ratio is designed, which comprises the following specific method process.

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

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

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

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

[0010] S5, for parallel axis power-assisted steering system, the relationship between rack speed V rack and power-assisted motor speed N is Wherein, V rack is the rack speed, N is the motor speed, p is the ball screw pitch, i belt is the parallel axis power-assisted steering belt transmission ratio;

[0011] S6, according to steps S1 to S3, the vehicle angle transmission ratio i aa and the motor speed N relationship is

[0012] S7, under the vehicle angle transmission ratio i aa1 , the motor torque boundary is calibrated, a reference point N1, T1 is selected in a certain working condition, when the motor torque is constant, the vehicle angle transmission ratio is changed from i aa1 to i aa2 , then according to the relationship of step S6, i aa2 corresponding motor speed is N2;

[0013] S8, the torque change coefficient k is calculated Then the relationship between motor torque T and motor speed N and motor power P is

[0014] S9, because the inflection point of motor torque curve is in constant power area, therefore, according to steps S6, S8, the torque change coefficient k is calculated

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

[0016] In the step S1, the calculation formula of vehicle angle transmission ratio is Wherein, i aa is the vehicle angle transmission ratio, W hw is the steering wheel angular velocity, unit: ° / s, W w is the steering wheel angular velocity, unit: ° / s.

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

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

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

[0020] In the step S6, for the same working condition of the whole vehicle, the steering wheel speed W hw and the trapezoidal mechanism transmission ratio i la require the same, the parallel shaft type power steering belt transmission ratio i belt and the ball screw pitch p are the design values of the steering system, so under the same working condition, when the whole vehicle angular transmission ratio i aa changes, the required motor speed N and the whole vehicle angular transmission ratio i aa under the corresponding working condition are in inverse proportion.

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

[0022] Compared with the prior art, the present application provides a kind of calibration method of motor output torque based on variable angular transmission ratio, by the calibration method, the calibration process can be simplified, and the motor torque output curve of different angular transmission ratio is adjusted according to the starting calibration curve and the change requirement of angular transmission ratio;Avoid the safety risk caused by insufficient power in the online control power steering system, improve the steering stability and response of the online control power steering system. BRIEF DESCRIPTION OF DRAWINGS

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

[0024] Figure 2 It is the motor torque curve schematic diagram.

[0025] Figure 3 It is the motor torque curve calibration schematic diagram. DETAILED DESCRIPTION

[0026] The application will be further described in the light of the accompanying drawings.

[0027] The application provides a calibration method for controlling motor output torque based on variable angle transmission ratio under the same working condition and different angle transmission ratio requirements, and the purpose is to calibrate the maximum torque curve of the motor according to the requirements of different angle transmission ratios under each working condition. In the early development stage, only the motor torque curve under a certain fixed transmission ratio needs to be set, and the motor output capacity can be calibrated according to the requirements of different variable angle transmission ratios, so as to ensure that the motor output capacity can meet the requirements of the steer-by-wire under different variable ratio requirements.

[0028] The specific implementation steps are as follows:

[0029] (1) The vehicle angle transmission ratio can be calculated by the steering wheel rotation angle and the steering wheel rotation angle: Wherein, i aa is the vehicle angle transmission ratio, W hw is the steering wheel angular velocity, unit: ° / s, W w is the steering wheel angular velocity, unit: ° / s.

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

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

[0032] Therefore: i aa = i al × i la .

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

[0034] (5) Through the above calculation formula, the relationship between the vehicle angle transmission ratio i aa and the motor speed N is:

[0035] For the same vehicle conditions, steering wheel speed W hw With trapezoidal mechanism transmission ratio i la The same demand, parallel axis type power steering belt transmission ratio i belt With ball screw pitch p is the steering system design value, so the same conditions, when the vehicle angle transmission ratio i aa Demand changes, the corresponding conditions under the demand motor speed N and vehicle angle transmission ratio i aa Inverse relationship, as shown in Figure 2 .

[0036] As shown in Figure 2 , first in the vehicle angle transmission ratio i aa1 , you can calibrate the motor torque boundary, select a reference point N1, T1 when a condition. When the steering wheel speed, motor torque demand does not change, only the angle transmission ratio from i aa1 To i aa2 (i aa1 >i aa2 ), by the vehicle angle transmission ratio i aa And the motor speed N calculation formula can be obtained, i aa2 The corresponding motor speed demand is N2, torque demand remains T1, if in the original calibration torque curve output, the speed N2 corresponding to the torque T2, therefore, N2 speed corresponding to T2 to T1, in order to meet the new output demand, torque change coefficient k formula:

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

[0038] Because the inflection point of the motor torque curve is in the constant power area, so by the above formula can be obtained

[0039] Therefore, the torque change coefficient k can be calculated by the angle transmission ratio, so for the torque curve A1 has been calibrated, when the angle transmission ratio demand changes, you can calculate the torque curve A2 according to the coefficient k, through the 6-10 points on the curve A1 according to the coefficient k to calculate the new points corresponding to it, through the interpolation algorithm can be fitted new torque curve A2, as shown in Figure 3 .

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

[0041] As shown in Figure 3 When the angular transmission ratio demand 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 application fits a new variable ratio demand by calculating and extrapolating a new torque curve, greatly reduces the calibration workload by calibrating only one set of reference torque boundary at the beginning, multiplies the requested torque by the change coefficient before calling the software app layer, improves the motor assist performance, ensures that the motor torque output adapts to each working condition, avoids insufficient assist, and is beneficial to improving the steering stability and response of the steer-by-wire assist steering system.

[0043] According to Figure 1 An 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 needed, if k>1, the adjustment coefficient k needs to be extrapolated to the motor control layer, and the original motor torque output is multiplied by the coefficient k, to ensure that the new motor torque curve can meet the assist demand after the demand changes.

[0044] The application can simplify the calibration process, adjust the motor torque output curve of different angular transmission ratios according to the initial calibration curve and the change demand of the angular transmission ratio, is beneficial to the motor assist performance adaptation, avoids the safety risk caused by insufficient assist in the steer-by-wire assist steering system, and improves the steering stability and response of the steer-by-wire assist steering system.

Claims

1. A calibration method for controlling motor output torque based on variable angle transmission ratio, comprising, characterized by: The specific method flow is as follows: S1, the vehicle angle transmission ratio i is calculated by the vehicle steering wheel angle and the steering wheel angle aa ; S2, the steering system line angle transmission ratio i is calculated by the steering wheel corner and the rack moving speed al ; S3, the trapezoidal mechanism transmission ratio i is calculated by the rack moving speed and the steering wheel angular velocity la ; S4, according to steps S1 to S3, derive i aa = i al x i la ; S5, for parallel axis type power steering system, rack speed V rack The relationship with the power motor speed N is Wherein, V rack is the rack speed, N is the motor speed, p is the ball screw pitch, i belt is the parallel axis type power steering belt transmission ratio; S6, according to steps S1 to S3, the whole vehicle angle transmission ratio i is obtained aa The relationship with the motor speed N is S7, in the vehicle angle transmission ratio i aa1 Next, the motor torque boundary is calibrated, a reference point N1, T1 is selected in a certain working condition, when the motor torque is unchanged, the vehicle angle transmission ratio is changed from i aa1 aa2 , then according to the relationship of step S6, i aa2 The corresponding motor speed is N2, if the motor speed N2 corresponds to the motor torque T2 under the original calibrated torque curve output, so that T2 corresponding to N2 is amplified to T1;​ S8, the torque change coefficient is calculated The relationship between the motor torque T and the motor speed N and the motor power P is then S9, because the motor torque curve inflection point is in the constant power zone, therefore, according to step S6, step 8, calculated S10, according to the formula for calculating the torque change coefficient k derived from step S9, when the vehicle angle 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. The method of claim 1, wherein the method further comprises: The calculation formula of the whole vehicle angle transmission ratio in the step S1 is Wherein, i aa is the whole vehicle angle transmission ratio, W hw is the steering wheel angular velocity, unit is ° / s, W w is the steering wheel angular velocity, unit is ° / s.

3. The method of claim 1, wherein the method further comprises: The calculation formula of the line-angle transmission ratio of the steering system in step S2 is Wherein, i al is the line-angle transmission ratio of the steering system, W hw is the steering wheel angular velocity, in ° / s, V rack is the rack speed, in mm / s.

4. The method of claim 1, wherein the method further comprises: The calculation formula of the trapezoidal mechanism transmission ratio in the step S3 is Wherein, i la is the trapezoidal mechanism transmission ratio, V rack is the rack speed, unit: mm / s, W w is the steering wheel angular velocity, unit: ° / s.

5. The method of claim 4, wherein the method further comprises: The trapezoidal mechanism transmission ratio is the ratio of the rack speed of the steering system to the rotation angle speed of the steering wheel, and the unit is mm / °.

6. The method of claim 1, wherein: The step S6, for the same vehicle conditions, steering wheel speed W hw The same demand, parallel axis type power steering belt transmission ratio i la The same demand, parallel axis type power steering belt transmission ratio i belt The same demand, parallel axis type power steering belt transmission ratio i aa The same demand, parallel axis type power steering belt transmission ratio i aa The same demand, parallel axis type power steering belt transmission ratio i 7. The method of claim 1, wherein the method further comprises: In the step S10, when the calculated torque change coefficient k value is less than 1, the torque curve does not need to be adjusted; when the calculated torque change coefficient k value is greater than 1, then the torque curve is fitted according to the torque change coefficient k.

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