CN116605286A - Transmission ratio calculation method, application and system for steer-by-wire system - Google Patents

Transmission ratio calculation method, application and system for steer-by-wire system Download PDF

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Publication number
CN116605286A
CN116605286A CN202310526055.5A CN202310526055A CN116605286A CN 116605286 A CN116605286 A CN 116605286A CN 202310526055 A CN202310526055 A CN 202310526055A CN 116605286 A CN116605286 A CN 116605286A
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China
Prior art keywords
transmission ratio
vehicle speed
steering wheel
vehicle
steering
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吴长水
王纪为
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Shanghai University of Engineering Science
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Shanghai University of Engineering Science
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Priority to CN202310526055.5A priority Critical patent/CN116605286A/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D6/00—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits
    • B62D6/002—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits computing target steering angles for front or rear wheels
    • B62D6/003—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits computing target steering angles for front or rear wheels in order to control vehicle yaw movement, i.e. around a vertical axis
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/10—Geometric CAD
    • G06F30/15—Vehicle, aircraft or watercraft design
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation

Abstract

The application relates to a transmission ratio calculating method for a steer-by-wire system, which comprises the following steps of: fixing the value of steady-state yaw rate gain under the input of a steering wheel, and establishing a transmission ratio-vehicle speed change model; adding a speed limiting condition to the transmission ratio-vehicle speed change model; carrying out smooth operation on the transmission ratio-vehicle speed change model after the speed limit condition is increased; in the transmission ratio-vehicle speed change model after the smooth operation, adding a steering wheel angle correction variable; and obtaining the speed and the steering wheel angle, and obtaining the transmission ratio value by using a transmission ratio-speed change model after the steering wheel angle correction variable is added. Compared with the prior art, the application designs the variable-angle transmission algorithm related to the vehicle speed and the steering wheel angle based on the fixed yaw rate gain value, can effectively reduce the yaw rate of the vehicle and improve the safety and the comfort of the vehicle during driving.

Description

Transmission ratio calculation method, application and system for steer-by-wire system
Technical Field
The application relates to the technical field of vehicle steering, in particular to a transmission ratio calculation method, application and system for a steer-by-wire system.
Background
The Steering-By-Wire (SBW) system eliminates the physical connection between the Steering wheel and the tie rod in the conventional Steering system, converts the input of the driver into an electric signal By using the XBW (X-By-Wire) technology, and then transmits the electric signal to the electronic control unit (Electronic Control Unit, ECU), and the controller receives the signals of the sensor and the vehicle-mounted cable and sends a control command to control the Steering actuator, and then performs an appropriate control action, so that the running state of the vehicle finally satisfies the running wish of the driver. The demands of people on the steering stability and the driving safety of vehicles have also driven the development of steer-by-wire systems to a certain extent. Steering-by-wire systems have become the dominant steering control systems in the future.
Conventional steering is limited by the structural characteristics of its mechanism, the transmission ratio of which is essentially a constant value. Meanwhile, since a steering system, tires, suspensions, etc. of an automobile are not ideal linear members, steering characteristics thereof may vary due to changes in vehicle speed and steering wheel angle. In the steer-by-wire system, the transmission ratio algorithm can be controlled by the electronic control unit, the possibility of free design exists, and the problem that the transmission ratio of the mechanical steering system cannot be changed due to physical coupling is solved.
In the SBW system, a steering actuating mechanism drives the steering motion of the vehicle, the direct action of the force of a driver is not needed, and the steering wheel resistance moment in the steering process is simulated by a road feel simulation system, so that the driver can acquire the driving feel again. According to the SBW system theory, the angle transmission characteristic and the steering power transmission characteristic of the automobile steering system from the steering wheel to the wheels allow free design, and the setting of the steering characteristic according to individuation can be realized, so that the wide design space and development prospect of the automobile steer-by-wire system are provided, and the automobile steer-by-wire system has a very large application market. Based on the characteristics of the steer-by-wire system, a reasonable angle-changing transmission ratio control strategy can be designed, and further the steering stability of the vehicle is improved.
Currently, in the prior art, patent CN201810527261.7 discloses an active steering system based on an angular actuator comprising: the driving steering system is based on the angle driver and further comprises: the speed reducing motor, the second input shaft and the double-row planetary gear; one end of the first input shaft is coaxially connected with the steering wheel, and the other end of the first input shaft is coaxially and fixedly connected with the drive bevel gear; the driven bevel gear is meshed with the driving bevel gear and is coaxially and fixedly connected to the planet carrier of the double-row planetary gear; an output shaft of the speed reducing motor is fixedly connected with one sun gear of the double-row planetary gear through a second input shaft, the other sun gear is connected with an electric power steering gear arranged on a connecting rod between two wheels of the automobile through the output shaft, and the driving adjustable of the transmission ratio is realized. However, it employs a mechanical reduction mechanism, which is costly to design and install and is detrimental to smooth transition of the gear ratio.
Patent CN202210038375.1 discloses a 4WID/S electric automobile variable angle transmission ratio control method, which introduces an objective multi-objective evaluation index function of vehicle steering stability, combines 4 evaluation index functions into a comprehensive evaluation index function through weighting, and determines the angle rotation ratio corresponding to the comprehensive evaluation index of the vehicle steering stability under different vehicle speeds in an open loop snake-shaped working condition experiment through the comprehensive evaluation index function; and combining a steering angle transmission ratio corresponding to the fixed yaw rate gain and a steering angle transmission ratio corresponding to the fixed lateral acceleration gain, fitting an angle transmission ratio curve of the vehicle by a vehicle speed interval variable weight fitting method to control the 4WID/S electric vehicle, and improving the steering stability of the vehicle. However, the control method is complex, the weight ratio is not well determined, and a certain risk exists in practical application.
Generally, when a vehicle is driven at a low speed, steering is required to be sensitive, and an angular transmission ratio is required to be relatively small. However, in order to prevent the steering from being too sensitive, the steering angle transmission ratio cannot be too small, otherwise, when a driver applies small-angle steering to the steering wheel, the steering wheel of the automobile rotates greatly, and the wheels easily reach the limit corner position, so that the driving safety and the control stability are not facilitated. Meanwhile, when the vehicle runs at a high speed, steering operation is required to be relatively slow, so that the vehicle is prevented from being out of control due to misoperation of a driver, and the stability of the vehicle is ensured, at the moment, the transmission ratio is designed so that the input response of the vehicle to the steering wheel is slower, and a relatively large transmission ratio design of a steering system is required. But the transmission ratio cannot be designed to be too large, so that the steering is slow, the lane change of a driver is not facilitated, the driver overtakes, and the obstacle is avoided.
Disclosure of Invention
The present application is directed to a gear ratio calculating method, application and system for steer-by-wire systems, which overcomes the above-mentioned drawbacks of the prior art.
The aim of the application can be achieved by the following technical scheme:
according to a first aspect of the present application, there is provided a gear ratio calculation method for a steer-by-wire system, comprising the steps of:
s1, fixing a value of a steady-state yaw rate gain under the input of a steering wheel, and establishing a transmission ratio-vehicle speed change model to obtain the transmission ratio of a steering system under different vehicle speeds;
s2, increasing a speed limit condition for the transmission ratio-vehicle speed change model, setting the value of the transmission ratio of the steering system to be a preset maximum constant transmission ratio when the vehicle speed is higher than a preset high speed threshold value, and setting the value of the transmission ratio of the steering system to be a preset minimum constant transmission ratio when the vehicle speed is lower than a preset low speed threshold value;
s3, carrying out smooth operation on the transmission ratio-vehicle speed change model after the speed limit condition is increased;
s4, adding a steering wheel angle correction variable into the transmission ratio-vehicle speed change model after the smooth operation;
s5, acquiring the vehicle speed and the steering wheel angle, and obtaining a transmission ratio value by using the transmission ratio-vehicle speed change model with the steering wheel angle added and corrected variable.
Further, the transmission ratio-vehicle speed variation model is specifically:
wherein i represents a transmission ratio, u represents a vehicle speed, L represents a vehicle wheelbase, K represents a vehicle stability factor, G s r w Indicating the steady state yaw rate gain at the steering wheel input.
Further, the calculation formula of the vehicle stability factor is:
wherein m represents the vehicle mass, a represents the distance from the centroid to the front axis, b represents the distance from the centroid to the rear axis, k r Represents the total cornering stiffness, k of the front wheel f Indicating the total cornering stiffness of the rear wheel.
Further, the transmission ratio-vehicle speed change model after the speed limit condition is added is specifically as follows:
wherein i is min Representing the minimum constant gear ratio, i max Representing the maximum constant gear ratio, u min Represents a low speed threshold, u max Representing a high speed threshold.
Further, the smoothing operation is specifically: the Savitzky-Golay second order smoothing process is performed in the data processing software.
Further, after the steering wheel angle correction variable is increased, the gear ratio increment is:
wherein Δi represents a gear ratio increment, u represents a vehicle speed, i aim Represents a preset maximum gear ratio increment, theta sw Indicating steering wheel angle, theta aim Indicating the angular position of the preset steering wheel maximum running gear ratio increment, r 1 、r 2 Respectively representing a preset vehicle speed proportional coefficient and a preset steering wheel angle proportional coefficient.
Further, the deduction process of the transmission ratio-vehicle speed change model is as follows:
obtaining steady-state yaw rate gain at front wheel steering angle from vehicle dynamics model
Obtaining the steady-state yaw rate gain under the input of the steering wheel based on the steady-state yaw rate gain under the front wheel rotation angle and the transmission ratio i between the front wheel rotation angle and the steering wheel rotation angle
Steady state yaw rate gain from steering wheel inputBack-pushing to obtain a transmission ratio i:
wherein omega r Represents yaw rate, θ sw Indicating steering wheel angle and delta indicating front wheel angle.
According to a second aspect of the present application, there is provided an application of a gear ratio calculation method for a steer-by-wire system, for use in a vehicle steering control, for obtaining a gear ratio value in the vehicle steering control.
According to a third aspect of the present application, there is provided a gear ratio calculation system for a steer-by-wire system, comprising:
the model building module is used for fixing the value of the steady-state yaw rate gain under the input of the steering wheel, building a transmission ratio-vehicle speed change model and obtaining the transmission ratio of the steering system under different vehicle speeds;
the speed limit setting module is used for increasing speed limit conditions for the transmission ratio-vehicle speed change model, setting the value of the transmission ratio of the steering system to be a preset maximum constant transmission ratio when the vehicle speed is higher than a preset high speed threshold value, and setting the value of the transmission ratio of the steering system to be a preset minimum constant transmission ratio when the vehicle speed is lower than a preset low speed threshold value;
the smoothing operation module is used for carrying out smoothing operation on the transmission ratio-vehicle speed change model after the speed limit condition is increased;
the steering wheel angle correction module is used for adding a steering wheel angle correction variable into the transmission ratio-vehicle speed change model after the smooth operation;
and the calculation module is used for acquiring the vehicle speed and the steering wheel angle, and obtaining a transmission ratio value by using the transmission ratio-vehicle speed change model with the steering wheel angle added and corrected variable.
Further, the transmission ratio-vehicle speed variation model is specifically:
wherein i represents a transmission ratio, u represents a vehicle speed, L represents a vehicle wheelbase, K represents a vehicle stability factor, G s r w Indicating the steady state yaw rate gain at the steering wheel input.
Compared with the prior art, the application has the following beneficial effects:
based on the fixed yaw rate gain value, a variable angle transmission algorithm related to the speed and the steering wheel angle is designed, so that the yaw rate of the vehicle can be effectively reduced, and the safety and the comfort of the vehicle during driving are improved.
Drawings
FIG. 1 is a flow chart of a gear ratio calculation method of the present application;
FIG. 2 is a graphical representation of steering system gear ratio versus vehicle speed;
FIG. 3 is a graph of gear ratio versus vehicle speed after increasing speed limit;
FIG. 4 is a graph of gear ratio versus vehicle speed after smoothing;
FIG. 5 is a MAP of the variable ratio relationship not related to steering wheel angle;
FIG. 6 is a MAP of gear ratio relationships relating vehicle speed to steering wheel angle.
Detailed Description
The application will now be described in detail with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical solution of the present application, and a detailed implementation manner and a specific operation process are given, and obviously, the described embodiment is only a part of the embodiment of the present application, but not all the embodiments, and the protection scope of the present application is not limited to the following embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present application without making any inventive effort, shall fall within the scope of the present application.
Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic may be included in at least one implementation of the application. In the description of the present application, it should be understood that the terms "first," "second," and "third," etc. in the description and claims of the application and in the above figures are used for distinguishing between different objects and not for describing a particular sequential order. Furthermore, the terms "comprise" and "have," as well as any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those listed steps or elements but may include other steps or elements not listed or inherent to such process, method, article, or apparatus.
The present specification provides method operational steps as an example or flow diagram, but may include more or fewer operational steps based on conventional or non-inventive labor. The order of steps recited in the embodiments is merely one way of performing the order of steps and does not represent a unique order of execution. In actual system or server product execution, the steps may be performed sequentially or in parallel (e.g., in a parallel processor or multi-threaded processing environment) or in an order that is not timing-constrained, as per the methods shown in the embodiments or figures.
The application provides a transmission ratio calculating method for a steer-by-wire system, which is shown in fig. 1 and comprises the following steps:
s1, fixing a value of a steady-state yaw rate gain under the input of a steering wheel, and establishing a transmission ratio-vehicle speed change model to obtain the transmission ratio of a steering system under different vehicle speeds;
first, the derivation of the gear ratio is performed:
(1) Obtaining steady-state yaw rate gain under front wheel steering angle through two-degree-of-freedom vehicle dynamics model in automobile theoryThe steady-state yaw rate is an important parameter for evaluating the running stability of the vehicle.
Wherein omega r The yaw rate, delta, u, vehicle speed (m/s), K, vehicle stability factor, L, vehicle wheelbase, and the vehicle stability factor are calculated by the following formula:
wherein m represents the vehicle mass, a represents the distance from the centroid to the front axis, b represents the distance from the centroid to the rear axis, k r Represents the total cornering stiffness, k of the front wheel f Indicating the total cornering stiffness of the rear wheel.
Thus, for a structurally determined vehicle, the vehicle stability factor K is a fixed value, the steady state yaw rate gain at front wheel steering angle thereofOnly the vehicle speed.
In the embodiment of the application, the parameters of the vehicle are shown in the following table:
TABLE 1 vehicle parameters
Calculated vehicle stability factor k=0.0014 s 2 /m 2 。
(2) Obtaining the steady-state yaw rate gain under the input of the steering wheel based on the steady-state yaw rate gain under the front wheel rotation angle and the transmission ratio i between the front wheel rotation angle and the steering wheel rotation angle
Wherein θ sw Indicating steering wheel angle and i indicating gear ratio.
(3) Steady state yaw rate gain from steering wheel inputBack-pushing to obtain a transmission ratio i:
from this formulaIt is known that the magnitude of the steering system gear ratio is subject to the vehicle speed, stability factor K, and yaw rate gainThe effect of these three dynamic parameters. For a determined vehicle structure, a stability factor is determined. And calculating a steady-state yaw rate gain of the vehicle at the steering wheel input>Usually in the range of 0.16 to 0.33s -1 The application takes the water as a constant value and takes the water as a fixed value of 0.28s -1 . The transmission ratio is affected only by the vehicle speed and changes with the change of the running speed. At this time, the relationship between the variable angle transmission ratio and the vehicle speed is shown in fig. 2.
S2, adding a speed limiting condition to the transmission ratio-vehicle speed change model, setting the value of the transmission ratio of the steering system to be a preset maximum constant transmission ratio when the vehicle speed is higher than a preset high speed threshold value, and setting the value of the transmission ratio of the steering system to be a preset minimum constant transmission ratio when the vehicle speed is lower than a preset low speed threshold value;
during actual driving, the angular transmission ratio of the steering system of the vehicle cannot be continuously increased or decreased, and a limiting algorithm is designed. The running speed of the vehicle is divided into a low-speed working condition, a medium-high-speed working condition and a high-speed working condition. The minimum constant transmission ratio of the steer-by-wire system is designed under the low-speed working condition, and the maximum constant transmission ratio of the steer-by-wire system is designed under the high-speed working condition.
The transmission ratio-vehicle speed change model after the speed limit condition is added is specifically as follows:
wherein i is min Representing the minimum constant gear ratio, i max Representing the maximum constant gear ratio, u min Represents a low speed threshold, u max Representing a high speed threshold. The minimum constant transmission ratio and the maximum constant transmission ratio are related to the design of the steering system of the car,assuming that the front wheel turning angle of the vehicle is +/-30 degrees, and ensuring stability and safety at high speed, the maximum turning angle of the steering wheel is +/-240 degrees, and the minimum transmission ratio is 8; assuming that the front wheel rotation angle of the vehicle is + -30 DEG, and the maximum rotation angle of the steering wheel is + -600 DEG at low speed, the maximum transmission ratio is 20. Specifically, the person skilled in the art can take the value according to the actual situation.
In the embodiment of the application, 25km/h and 95km/h are used as a low speed threshold and a high speed threshold, so that a transmission ratio-vehicle speed change model after speed limit is specifically:
at this time, the relationship between the obtained variable angle transmission ratio and the vehicle speed is shown in fig. 3. In other embodiments, different speed thresholds may be used as desired.
S3, carrying out smooth operation on the transmission ratio-vehicle speed change model after the speed limit condition is increased;
abrupt changes in gear ratio occur when the vehicle speed is at a low speed threshold and a high speed threshold. Specifically, in the embodiment of the application, when the vehicle speed is 25km/h, the set minimum transmission ratio is slightly smaller than the transmission ratio calculated based on yaw steady-state yaw rate gain, and abrupt change of the transmission ratio is generated. At 95km/h, a small abrupt change in the transmission ratio is likewise produced. If these gear ratio jumps are not handled, the handling comfort of the driver will be greatly affected.
Therefore, the present application performs smoothing operation, specifically: the Savitzky-Golay second order smoothing process is performed in the data processing software. The smoothed gear ratio curve is shown in fig. 4.
S4, adding a steering wheel angle correction variable into the transmission ratio-vehicle speed change model after the smooth operation;
in the steps S1 to S3, the obtained transmission ratio-vehicle speed change model is converted into a three-dimensional perspective view as shown in fig. 5 without considering the influence of the steering wheel angle, and at this time, the change of the steering wheel angle cannot cause the change of the transmission ratio as shown in fig. 5. However, the ideal drive-by-wire steering system transmission ratio should take into account both the effects of vehicle speed and steering wheel angle changes, and the variable angle transmission ratio design should follow the law of change of the steering wheel with a large transmission ratio in the middle position and a low transmission ratio on both sides.
Therefore, the application designs a variable angle transmission ratio algorithm based on cosine by considering the influence of the speed and the steering wheel on the transmission ratio. After the steering wheel angle correction variable is increased, the transmission ratio increment is as follows:
wherein Δi represents a gear ratio increment, u represents a vehicle speed (km/h), i aim Represents a preset maximum gear ratio increase (20 according to the designed maximum gear ratio), θ sw Indicating steering wheel angle (deg), θ aim An angular position (deg, where the steering wheel angle range is + -100) representing a preset maximum steering wheel ratio increment, r 1 、r 2 Respectively representing a preset vehicle speed proportional coefficient and a preset steering wheel angle proportional coefficient, and representing the position of the steering wheel with an incremental variable transmission ratio 1 、r 2 33.3 and 100 were taken respectively.
To this end, the steer-by-wire system variable angle transmission ratio MAP that considers both the steering wheel angle and the vehicle running speed is shown in fig. 6.
Aiming at the problems that in the prior art, due to the sensitivity change when a vehicle turns, a driver needs to continuously compensate the steering wheel angle, the driving load is increased and the like, the application designs a variable angle transmission algorithm related to the vehicle speed and the steering wheel angle based on a fixed yaw rate gain value, can effectively reduce the yaw rate of the vehicle, improves the safety and the comfort when the vehicle is driven, and simultaneously has the advantages of improving the running safety, the running stability and the like of the vehicle. The application is not only suitable for low-speed driving conditions, but also can be used for high-speed driving conditions, and can reduce the busyness of a driver.
In order to design stable and reliable variable-angle transmission ratio, smoothing is carried out on a variable-angle transmission ratio algorithm; secondly, in order to prevent the added variable angle transmission ratio from being too small or too large, limiting value processing is carried out on the variable angle transmission ratio; analyzing the influence of the steering wheel angle on the variable-angle transmission ratio, and adding a variable-angle transmission ratio increment algorithm in the middle position of the steering wheel; and further obtaining an angle-variable transmission ratio algorithm under the influence of the vehicle speed and the steering wheel angle.
S5, acquiring the vehicle speed and the steering wheel angle, and obtaining a transmission ratio value by using a transmission ratio-vehicle speed change model with the steering wheel angle added to correct the variable.
The derivation process of the transmission ratio-vehicle speed variation model is as follows:
the application of the transmission ratio calculation method for the steer-by-wire system can be applied to vehicle steering control and used for obtaining the value of the transmission ratio in the vehicle steering control.
The present application also provides a gear ratio calculation system for a steer-by-wire system, comprising:
the model building module is used for fixing the value of the steady-state yaw rate gain under the input of the steering wheel, building a transmission ratio-vehicle speed change model and obtaining the transmission ratio of the steering system under different vehicle speeds;
the speed limiting setting module is used for increasing speed limiting conditions for the transmission ratio-vehicle speed change model, setting the value of the transmission ratio of the steering system to be a preset maximum constant transmission ratio when the vehicle speed is higher than a preset high speed threshold value, and setting the value of the transmission ratio of the steering system to be a preset minimum constant transmission ratio when the vehicle speed is lower than a preset low speed threshold value;
the smooth operation module is used for carrying out smooth operation on the transmission ratio-vehicle speed change model after the speed limit condition is increased;
the steering wheel angle correction module is used for adding a steering wheel angle correction variable into the transmission ratio-vehicle speed change model after the smooth operation;
and the calculation module is used for acquiring the vehicle speed and the steering wheel angle, and obtaining the transmission ratio value by using a transmission ratio-vehicle speed change model with the steering wheel angle added to correct the variable.
It will be clear to those skilled in the art that, for convenience and brevity of description, specific working procedures of the described modules may refer to corresponding procedures in the foregoing method embodiments, which are not described herein again.
The foregoing describes in detail preferred embodiments of the present application. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the application by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.

Claims (10)

1. A gear ratio calculation method for a steer-by-wire system, comprising the steps of:
s1, fixing a value of a steady-state yaw rate gain under the input of a steering wheel, and establishing a transmission ratio-vehicle speed change model to obtain the transmission ratio of a steering system under different vehicle speeds;
s2, increasing a speed limit condition for the transmission ratio-vehicle speed change model, setting the value of the transmission ratio of the steering system to be a preset maximum constant transmission ratio when the vehicle speed is higher than a preset high speed threshold value, and setting the value of the transmission ratio of the steering system to be a preset minimum constant transmission ratio when the vehicle speed is lower than a preset low speed threshold value;
s3, carrying out smooth operation on the transmission ratio-vehicle speed change model after the speed limit condition is increased;
s4, adding a steering wheel angle correction variable into the transmission ratio-vehicle speed change model after the smooth operation;
s5, acquiring the vehicle speed and the steering wheel angle, and obtaining a transmission ratio value by using the transmission ratio-vehicle speed change model with the steering wheel angle added and corrected variable.
2. A transmission ratio calculation method for a steer-by-wire system according to claim 1, characterized in that the transmission ratio-vehicle speed variation model is specifically:
wherein i denotes a transmission ratio, u denotes a vehicle speed, L denotes a vehicle wheelbase, K denotes a vehicle stability factor,indicating the steady state yaw rate gain at the steering wheel input.
3. A transmission ratio calculation method for a steer-by-wire system according to claim 1, wherein the calculation formula of the vehicle stability factor is:
wherein m represents the vehicle mass, a represents the distance from the centroid to the front axis, b represents the distance from the centroid to the rear axis, k r Represents the total cornering stiffness, k of the front wheel f Indicating the total cornering stiffness of the rear wheel.
4. The transmission ratio calculating method for a steer-by-wire system according to claim 2, wherein the transmission ratio-vehicle speed variation model after increasing the speed limit condition is specifically:
wherein i is min Representing the minimum constant gear ratio, i max Representing the maximum constant gear ratio, u min Represents a low speed threshold, u max Representing a high speed threshold.
5. A transmission ratio calculation method for a steer-by-wire system according to claim 1, characterized in that the smoothing operation is specifically: the Savitzky-Golay second order smoothing process is performed in the data processing software.
6. The transmission ratio calculation method for a steer-by-wire system of claim 1, wherein after increasing the steering wheel angle correction variable, the transmission ratio increment is:
wherein Δi represents a gear ratio increment, u represents a vehicle speed, i aim Represents a preset maximum gear ratio increment, theta sw Indicating steering wheel angle, theta aim Indicating the angular position of the preset steering wheel maximum running gear ratio increment, r 1 、r 2 Respectively representing a preset vehicle speed proportional coefficient and a preset steering wheel angle proportional coefficient.
7. A transmission ratio calculation method for a steer-by-wire system according to claim 2, characterized in that the transmission ratio-vehicle speed variation model is derived as follows:
obtaining steady-state yaw rate gain at front wheel steering angle from vehicle dynamics model
Obtaining the steady-state yaw rate gain under the input of the steering wheel based on the steady-state yaw rate gain under the front wheel rotation angle and the transmission ratio i between the front wheel rotation angle and the steering wheel rotation angle
Steady state yaw rate gain from steering wheel inputBack-pushing to obtain a transmission ratio i:
wherein omega r Represents yaw rate, θ sw Indicating steering wheel angle and delta indicating front wheel angle.
8. The application of the transmission ratio calculation method for the steer-by-wire system is characterized by being applied to vehicle steering control and used for acquiring the value of the transmission ratio in the vehicle steering control.
9. A gear ratio calculation system for a steer-by-wire system, comprising:
the model building module is used for fixing the value of the steady-state yaw rate gain under the input of the steering wheel, building a transmission ratio-vehicle speed change model and obtaining the transmission ratio of the steering system under different vehicle speeds;
the speed limit setting module is used for increasing speed limit conditions for the transmission ratio-vehicle speed change model, setting the value of the transmission ratio of the steering system to be a preset maximum constant transmission ratio when the vehicle speed is higher than a preset high speed threshold value, and setting the value of the transmission ratio of the steering system to be a preset minimum constant transmission ratio when the vehicle speed is lower than a preset low speed threshold value;
the smoothing operation module is used for carrying out smoothing operation on the transmission ratio-vehicle speed change model after the speed limit condition is increased;
the steering wheel angle correction module is used for adding a steering wheel angle correction variable into the transmission ratio-vehicle speed change model after the smooth operation;
and the calculation module is used for acquiring the vehicle speed and the steering wheel angle, and obtaining a transmission ratio value by using the transmission ratio-vehicle speed change model with the steering wheel angle added and corrected variable.
10. A gear ratio calculation system for a steer-by-wire system according to claim 9, characterized in that the gear ratio-vehicle speed variation model is specifically:
wherein i denotes a transmission ratio, u denotes a vehicle speed, L denotes a vehicle wheelbase, K denotes a vehicle stability factor,indicating the steady state yaw rate gain at the steering wheel input. />
CN202310526055.5A 2023-05-10 2023-05-10 Transmission ratio calculation method, application and system for steer-by-wire system Pending CN116605286A (en)

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