CN115130224A - Method for constructing automobile steer-by-wire system based on Modelica model - Google Patents

Abstract

The invention provides a Modelica model-based steer-by-wire system model construction method, which comprises the following steps: step 1: constructing a steer-by-wire system model through a Modelica language based on the structure and the principle of the steer-by-wire system; step 2: planning and controlling steering road feel on the basis of a steer-by-wire system model; and 3, step 3: and setting a simulated fault on the basis of the steer-by-wire system model. The construction method of the invention uses a non-causal mode to carry out physical modeling, uses the mode same as a theoretical equation to establish a model, uses a causal modeling mode to realize logic control, and can reduce the difficulty of model construction; the method constructs a model by a method closest to a theoretical equation.

Description

Method for constructing automobile steer-by-wire system based on Modelica model

Technical Field

The invention relates to the field of design of an automobile steer-by-wire system, in particular to a method for constructing the automobile steer-by-wire system based on a Modelica model.

Background

With the continuous development of automobile electromotion and intellectualization, the design direction of an automobile steering system gradually changes from traditional mechanical steering to Electric Power Steering (EPS) and then to a steer-by-wire system. The drive-by-wire technology converts the operation input of a driver into an electric signal, and an electric wire or the electric signal realizes instruction transmission without a mechanical connecting device so as to operate the automobile.

In contrast to conventional steering systems, steer-by-wire systems enable decoupling of driver operation and vehicle motion. The steer-by-wire system cancels the mechanical connection from the steering wheel to the steering actuator, completely realizes the steering by the electric control system, and can get rid of various limitations of the traditional steering system. Meanwhile, higher requirements are provided for simulation modeling, modeling in the same modeling software is needed in different fields such as control strategies, electric control, machinery and the like, and certain reliability of the model is guaranteed.

Disclosure of Invention

The invention provides a Modelica model-based steer-by-wire system model construction method, which comprises the following steps:

step 1: constructing a steer-by-wire system model through a Modelica language based on the structure and the principle of the steer-by-wire system;

step 2: planning and controlling steering road feel on the basis of a steer-by-wire system model;

and step 3: setting a simulation fault on the basis of the steer-by-wire system model;

in step 2, the method further comprises the following steps:

step 201, planning steering road feel on the basis of a line control steering system model;

and 202, controlling steering road feel on the basis of the line control steering system model.

Further, in step 1, the method further comprises the following steps:

step 101, decomposing a steer-by-wire system into a plurality of elements based on a steer-by-wire system structure;

102, dividing a steer-by-wire system according to a mechanical part, an electrical part and a logic control part based on the steer-by-wire system principle, and constructing a corresponding model through modelica language;

103, constructing corresponding models by the mechanical part, the electrical part and the logic control part through modelica language, and combining the models into a steer-by-wire system model of a corresponding actual component according to the connection relation of the elements;

the elements comprise a steering wheel assembly, a steering axle mechanism assembly, a controller and various sensors;

the mechanical part comprises a friction pair model and a connecting rod model;

the electrical portion comprises a resistance model and an inductance model;

the logic control portion comprises AND, OR, AND, XOR.

Further, in step 3, the method further comprises the following steps:

301, simulating a steering motor fault on the basis of an online control steering system model;

step 302, simulating sensor faults on the basis of a line control steering system model;

and step 303, carrying out fault test on the linear control steering system.

Furthermore, in step 201, a steering resistance model of the current steering system is constructed according to a steering resistance generation mechanism of the steering system, the steering resistance equivalent to the steering column is calculated according to the transmission ratio of the steering system, and the power of the electric power-assisted system is superposed to obtain the current steering feedback moment;

obtaining steering road feel through estimation of rack steering resistance of a steer-by-wire system, wherein the steering road feel which is finally designed comprises steering resistance which is equivalent to steering resistance on a rack by expanding front wheel aligning torque; internal frictional resistance of the steering actuator; the frictional resistance of the steering wheel and the steering column.

Further, in step 301, simulating a steering motor fault includes simulating a stuck-at fault, simulating a partial failure, and simulating a complete failure;

simulating a jamming fault, adding a random timing module to a steering motor part in the original step one, and switching the original motor output into constant output with a constant rotating angle unchanged when a certain time point is reached;

if the simulation part fails, adding a random timing module to the steering motor part in the original step one, and limiting the original maximum output value of the motor when a certain time point is reached;

and (4) simulating complete failure, and directly switching the original motor into a constant of 0 output.

Further, in step 302, the sensor faults include noise distortion and failure;

noise distortion, wherein a noise signal similar to the noise signal is additionally established by considering noise forms generated by different sensors in a working environment, and the noise signal and an original sensor signal are superposed and output to be used as a simulated distortion signal;

and (4) failing, randomly using a random number for a time, and switching the original sensor signal into a constant or return-to-zero output for keeping the value of the previous calculation time when the random time point is reached.

The invention achieves the following beneficial effects:

the construction method of the invention uses a non-causal mode to carry out physical modeling, uses the mode same as a theoretical equation to establish a model, uses a causal modeling mode to realize logic control, and can reduce the difficulty of model construction; the method constructs a model by using a method closest to a theoretical equation.

Drawings

FIG. 1 is a schematic flow chart of a construction method of a Modelica model-based automobile steer-by-wire system;

FIG. 2 is a model construction diagram of a Modelica model-based automobile steer-by-wire system;

fig. 3 is a schematic diagram of a model steering wheel assembly of a Modelica model-based automotive steer-by-wire system.

Detailed Description

The technical solution of the present invention will be described in more detail with reference to the accompanying drawings, and the present invention includes, but is not limited to, the following embodiments.

As shown in fig. 1, the invention provides a model construction method of a steer-by-wire system based on a Modelica model, which comprises the following steps:

step 1: constructing a steer-by-wire system model through a Modelica language based on the structure and the principle of the steer-by-wire system;

step 2: planning and controlling steering road feel on the basis of a steer-by-wire system model;

and step 3: and setting a simulation fault on the basis of the steer-by-wire system model.

The method also comprises the following steps in the step 1:

step 101, decomposing the steer-by-wire system into a plurality of elements based on the steer-by-wire system structure, wherein the elements comprise a steering wheel assembly, a steering axle mechanism assembly, a controller and various sensors.

As shown in fig. 2-3, in particular, the common components can be subdivided into the following categories:

the steering wheel assembly includes a steering wheel assembly and a aligning torque motor.

The steering actuating mechanism assembly comprises a front wheel steering component, a steering wheel steering motor and a control motor thereof.

The controller includes a base controller and a fault handling controller.

The sensor comprises a steering wheel angle sensor, a torque sensor and a front wheel steering angle sensor.

And 102, dividing the steer-by-wire system according to a mechanical part, an electrical part and a logic control part based on the steer-by-wire system principle, and constructing a corresponding model through a modelica language.

The mechanical part, the electrical part and the logic control part are modeled by a modelica language. Constructing mechanical models such as a friction pair model, a connecting rod model and the like; resistance models, inductance models, etc. in electricity; and, or, and, xor in the logic control, such as a series of basic model elements. And combining the specific functions and structures of the components in the actual analysis process, and combining the basic models related to the components in the modeling process to construct a simulation model of the actual physical part meeting the simulation requirements.

And 103, constructing corresponding models by the mechanical part, the electrical part and the logic control part through modelica language, and combining the models into a steer-by-wire system model of a corresponding actual component according to the connection relation of the elements.

In step 2, the method further comprises the following steps:

step 201, planning steering road feel on the basis of a line control steering system model;

according to a steering resistance generation mechanism of a traditional steering system, a steering resistance model of the current steering system is constructed, the steering resistance equivalent to a steering column is calculated according to the transmission ratio of the steering system, and the power assistance of the electric power-assisted system is superposed to obtain the current steering feedback moment. The steering road feel is obtained by estimating the steering resistance of the rack of the steer-by-wire system, and the finally designed steering road feel comprises 3 parts:

the front wheel aligning moment is equivalent to the steering resistance on the rack;

internal friction resistance of the steering actuator;

the frictional resistance of the steering wheel and the steering column.

On the basis of completing modeling and connection of each part of a vehicle, a submodel for calculating the aligning moment exists on a tire model or the aligning moment is provided by input, and the equivalent resistance of the aligning moment of a front wheel equivalent to the steering resistance on a rack is calculated separately by additionally adding a model for calculating the force of the aligning moment transmitted to a rack and a pinion under an ideal frictionless condition in a logic control model; the calculation of the frictional resistance is to use a friction item in each actually existing physical model corresponding to the interior of the steering actuating mechanism, the steering wheel and the steering column to separately increase an interface for totaling the frictional resistance generated by the whole system.

The real-time steering resistance of the vehicle can be accurately represented by using the planning, and meanwhile, the model in the step one can be utilized to the maximum extent during calculation without constructing other complex algorithm models.

And a logic control module can be directly constructed in logic control by testing the aligning torque of the same type of vehicles on different road surfaces and in different running states, so that the road feel meeting the requirements of drivers can be designed. The same way as acquiring the friction force can be used in the design process to acquire the vehicle parameters required to be referred to in the design of the road feel.

202, controlling steering road feel on the basis of a line control steering system model;

firstly, tracking control is carried out on road feel, namely, a targeted control strategy model is designed, and a steering road feel actuating mechanism (usually a road feel motor) is controlled by adopting a proper control algorithm to output corresponding torque, so that a steering column generates steering wheel feedback torque corresponding to ideal road feel feedback torque obtained by planning, and the problem is substantially the torque tracking problem of the motor.

And constructing a PID control model to calculate the required control current according to the ideal feedback torque and the torque difference value obtained by a torque sensor model on the steering column, and controlling the output torque of the road sensing motor to eliminate the tracking error.

In step 3, the method further comprises the following steps:

structurally, the failure types of the steer-by-wire system can be classified into actuator failure, sensor failure, controller failure, and communication failure. The actuator faults specifically refer to faults of a steering motor and a road sensing motor, the sensor faults are generally divided into 2 types, and signal distortion caused by noise and failure caused by faults are avoided. The controller fault related to the steer-by-wire system comprises 2 aspects, one is a hardware fault of the controller, the other is an algorithm logic fault of the controller, internal hardware contained in the controller is complex and difficult to simulate in modelica, and the algorithm logic fault can be reflected when the whole modelica model is operated.

301, simulating a steering motor fault on the basis of an online control steering system model;

the most intuitive way to achieve fault tolerance control is the redundant backup of important components. As various parts are modeled in the step one, a model is built according to the actually designed structure and scheme in the simulation process. The following simulation scheme can be performed when the following three faults occur in the simulated steering motor at a certain time:

and (3) simulating a jamming fault, adding a random timing module to the steering motor part in the original step one, and switching the original motor output into constant output with a constant rotation angle when a certain time point is reached.

And (3) simulating partial failure, adding a random timing module to the steering motor part in the original step one, and limiting the original maximum output value of the motor when a certain time point is reached.

And (4) simulating complete failure, and directly switching the original motor into a constant of 0 output.

Step 302, simulating sensor faults on the basis of a line control steering system model;

for the implementation in modelica of 2 types of faults occurring at the sensor, the following implementations are provided:

and noise distortion, namely additionally establishing a noise signal similar to the noise distortion by considering noise forms generated by different sensors in a working environment, and superposing and outputting the noise signal and the original sensor signal to serve as a simulated distortion signal.

And (4) failing, randomly using a random number for a time, and switching the original sensor signal into a constant or return-to-zero output for keeping the value of the previous calculation time when the random time point is reached.

Step 303, carrying out fault test on the line control steering system;

after the first two steps are completed, the new model containing the fault is replaced with the model in the original system, and the test is carried out according to the normal test condition. And after the whole steering model is operated, comparing the vehicle data before and after replacement, and detecting whether the design model can pass the fault test.

The present invention is not limited to the above embodiments, and those skilled in the art can implement the present invention in other various embodiments according to the disclosure of the embodiments and the drawings, and therefore, all the designs and ideas of the present invention, which are made by some simple changes or modifications, fall into the protection scope of the present invention.

Claims (6)

1. A Modelica model-based steer-by-wire system model construction method is characterized by comprising the following steps:

step 1: constructing a steer-by-wire system model through a Modelica language based on the structure and the principle of the steer-by-wire system;

and 2, step: planning and controlling steering road feel on the basis of a steer-by-wire system model;

and 3, step 3: setting a simulation fault on the basis of the steer-by-wire system model;

in step 2, the method further comprises the following steps:

step 201, planning steering road feel on the basis of a line control steering system model;

and 202, controlling steering road feel on the basis of the line control steering system model.

2. The steer-by-wire system model building method according to claim 1, further comprising, in step 1, the steps of:

step 101, decomposing a steer-by-wire system into a plurality of elements based on a steer-by-wire system structure;

102, dividing a steer-by-wire system according to a mechanical part, an electrical part and a logic control part based on the steer-by-wire system principle, and constructing a corresponding model through modelica language;

103, constructing corresponding models by the mechanical part, the electrical part and the logic control part through modelica language, and combining the models into a steer-by-wire system model of a corresponding actual component according to the connection relation of the elements;

the elements comprise a steering wheel assembly, a steering axle mechanism assembly, a controller and various sensors;

the mechanical part comprises a friction pair model and a connecting rod model;

the electrical portion comprises a resistance model and an inductance model;

the logic control portion comprises AND, OR, AND, XOR.

3. The steer-by-wire system model building method according to claim 1, further comprising, in step 3, the steps of:

301, simulating a steering motor fault on the basis of an online control steering system model;

step 302, simulating sensor faults on the basis of an online control steering system model;

and step 303, carrying out fault test on the linear control steering system.

4. The method for constructing a steer-by-wire system model according to claim 1, wherein in step 201, a steering resistance model of a current steering system is constructed according to a steering resistance generation mechanism of the steering system, the steering resistance equivalent to a steering column is calculated according to a transmission ratio of the steering system, and the power of the electric power-assisted system is superimposed to obtain a current steering feedback moment;

the steering road feel is obtained through estimation of the steering resistance of a rack of the steer-by-wire system, and the steering road feel which is finally designed is equivalent to the steering resistance on the rack by expanding the front-wheel aligning torque; internal friction resistance of the steering actuator; the frictional resistance of the steering wheel and the steering column.

5. The method for constructing a steer-by-wire model according to claim 3, wherein, in step 301, simulating a steering motor failure comprises simulating a stuck-at failure, simulating a partial failure, and simulating a complete failure;

simulating a jamming fault, adding a random timing module to a steering motor part in the original step one, and switching the original motor output into constant output with a constant rotating angle unchanged when a certain time point is reached;

the simulation part is invalid, a random timing module is added to a steering motor part in the original step one, and when a certain time point is reached, the original motor output maximum value is limited;

and (4) simulating complete failure, and directly switching the original motor into a constant of 0 output.

6. The steer-by-wire system model building method of claim 3, wherein in step 302, said sensor fault comprises noise distortion and failure;

noise distortion, wherein a noise signal similar to the noise signal is additionally established by considering noise forms generated by different sensors in a working environment, and the noise signal and an original sensor signal are superposed and output to be used as a simulated distortion signal;

and when the time reaches the random time point, the original sensor signal is switched to a constant keeping the value of the previous calculation time or is output to zero.

Images