Projects:2017s1-185 BMW Autonomous Vehicle Project Implementation of a Steering Angle Controller on a Lab Test Bench

Abstract

Autonomous driving is now becoming a new popular technology in the vehicle industry. To achieve this goal, people need to control the vehicle movements especially the steering performance with corresponding pre-set algorithm. The main part of the steering system is an Electrical Power Steering system(EPS). EPS is a product widely used in the field of vehicle steering to save energy and create a safety, make a comfort performance with high efficiency and low power consumption.

This project focus on designing the steering unit control system of autonomous vehicles and by testing and verifying the performance and reliability to make a vehicle can steer by itself. Since the DC motor of EPS can be re-programmed in order to create different steering performance, people start to research on how to modify it to achieve the autonomous driving technology. The model and the dynamic behaviour of the EPS can be built and simulated on Matlab and Simulink hence designers can implement the simulation to analysis the impact of the steering system and find the method to handle these factors. By establishing PID controllers to adjust the outputs coming from the EPS to control the torque, speed and position of the rack of the system.

Finally, designers will test the steering performance with the help of the MicroAutoBox on the steering rig test bench of the laboratory, compare the tests results and the simulation results to adjust the parameters of the PID controllers to get a more reasonable steering model.

Keywords: Electrical Power Steering, Dynamic Behaviours, Simulation, Reliability and Stability, Self-driving System

Objects

• Development of a steering angle control
• Implementation of the EPS on the testbench
• Complete the communication with EPS using the MicroAutoBox
• Implementation of steering rack controller on the test bench
• Achieve accurate angle controlling

Aims

This project aims to construct a simulation model for the EPS and design three controllers, toque controller, speed controller and position controller for optimizing the dynamic performance of the steering system. A test bench will be implemented on a base associated with two springs on both side. This will be used to test the algorithm, verify the operations of the EPS and measure some important parameters. By completing all those steps, a primary level of autonomous vehicle steering system is developed.

Motivation

Nowadays, city traffic conditions are becoming more and more complex. Traffic jam is one of the most significant problems in the urban planning and administration. Urban constructors need to consider how to manage the vehicles running in the city area. The autonomous driving is an efficient method to control traffic. If all cars on the road can be managed by electronic system, the driving surroundings will be smooth because human mistakes can be limited with the electronic assistance.

The EPS system has been developed for more than 50 years and more and more popular owing to its special aspects. In different driving conditions, this steering system will perform in variable and adjustable working status. The assisted force and torque generated by the internal motor can be adjusted with the changing of the human driver’s operation. If the motor of EPS is able to analyses and modify the required torque and force automatically according to the surrounding driving environment, it will provide the required forces to rotate the steering rack, so it is unnecessary for the driver to act on the steering wheel which makes self-driving technology possible [1]. Many program languages can build some algorithm to control the power steering system, so after optimizing the performance of the algorithm, the automatic steering angle controller will work better on autonomous vehicles. That is what this project wants to complete.

Background

Electrical Power Steering

The vehicle steering system is a specific module in the vehicle which is used to keep the car in the track or change its movements when a car is running on road. It cooperates with the automatic transmission system to ensure the movement stability and used to change driving directions with the driver’s actions. With the development of technology, some power assistance steering equipment are assembled on vehicles to provide extra force for the drivers to easily control the vehicle.

Temporarily, there are two types of steering system used. One is hydraulic steering assist equipment and the other is the electrical power steering equipment [1]. The hydraulic is the old design system which has a hydraulic pump and a system of valves inside. It will activate the pump to generate a hydraulic pressure and pump fluid into the hydraulic lines to create an assistance force to drive the steering wheel. Although, this equipment is quite cheap and easy to product, it still has a lot of drawbacks. The pump of the system is always running during the car motion hence it has a high-power consumption. The hydraulic fluid needs to be maintained periodically and replaced eventually thus users have to spend much money in daily life. For those reasons, the EPS is designed.

EPS is the up-to-date steering system technology across people’s daily life. This steering system is able to control the front wheel direction to control the vehicle movements. It also offers the proper amount of effort to turn the wheels. [1] The steering system is installed on the current steering column and equipped with an electrical motor as well as a torque sensor. The sensor will detect the torque coming from the steering wheel firstly, then the rack and pinion coverts the driver torque to rack force. The electronic torque sensor sends the signal to the Engine Control Unit (ECU) to calculate the on-demand electrical power. Afterwards, the ECU sends the command to the brushless DC motor to generate a required assist torque. Belt and ball nut will transmit the torque to rack screw to assist force. [2] Compared with the old designer device, EPS saves more power and it is more reliable when it is running.

Current State of Autonomous Vehicle

An autonomous vehicle is a car with the capability of moving on the road without human input by detecting its surroundings and controlling itself. It will consist of many subsystems to achieve this goal such as vehicle controlling system, self-steering system, camera detecting system, navigating system and so on. The first autonomous vehicle was developed in 1980s [3] and then, several vehicle companies and organizations started to develop the technical prototypes.

The autonomous vehicle driving levels are classified from 0 to 5. [4]

• Level 0: Basic level, no self-driving system equipped, all controls are coming from human.

• Level 1: Most operations of the vehicle are controlled by the driver; however, some specific terms will be done by the car such as steering and accelerating.

• Level 2: The system provides the driver with assistance in the field of steering/acceleration/deceleration according to the surrounding information automatically.

• Level 3: Drivers do not have to operate the vehicles most of the time. The car can complete almost every basic operation for the driver and the driver only needs to react to the emergency.

• Level 4: Fully autonomous, the vehicle can cover every driving scenario. It can perform not only driving functions but also safety monitor functions for the driver to ensure the security.

• Level 5: The vehicle’s performance is reliable all the time even in some extreme environment. All the vehicles running on the road will be driverless, so the transportation issues will be handle in the future.

Project Team

Team Members

Zeyu Yan
Tianhao Gu

Supervisor

Prof.Nesimi Ertugrul
Dr.Cheng Chew Lim
Robert Dollinger