DEVELOPMENT OF STEER-BY-WIRE CONTROL SYSTEM FOR GM SEQUEL

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Presented BY
S.MUTHU SARAVANAN
07MAE023

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VEHICLE STEER BY WIRE
Fully integrated vehicle dynamics.
Relatively new steering system compared to mech, hydraulic & electric steering sys.
No mech coupling between S.W & Steering mechanism.
Different steering function requirements are converted into control design problems, and are solved by using a control system with novel control structures.
system provides adjustable steering feel with realistic tire/road feedback, active steering wheel return with adjustable wheel rate, quick and accurate road wheel angle tracking based on the driverâ„¢s input and variable steering ratio.

Steer Function Requirements for Steer-by-wire
Directional ctrl & wheel synchronization:
Road wheels follow drivers i/p from S.W & possible i/p commands from supervisory vehicle ctrl sys
Road wheels contact synchronization with S.W in real time ie without time delay
Adjustable variable Steer Feel:
should provide feel to drivers while driving ie. Force/torque @ road wheel, tire roadsurface contact should maintain stability
Adjustable S.W Return capability:
should automatically makes the S.W returns to its center when the driver leaves driving S.W (Since it depends on vehicle speed)
Variable steering Ratio:
varying steering ratio enables improved handling performance and vehicle dynamics

SEQUEL STEER “ BY -WIRE
It is based on Next Generation fuel cell demonstration vehicle.
Consists of :
a) Front and rear electro mechanical actuator
b) Torque Feedback emulator for S/w
c) DES (Distributed Electronic Sys)

In this sys, redundancy of sensors, actuators, controllers & Power allows systems to be fault tolerance.

Depends on the influence on H/w, S/w and Communication Design.

OBJECTIVE:
Level of security is high comparable to mech steering sys, ie. Maintains near Normal Performance after 1st failure (provides mech sys back up when electronic fails)


SYSTEM CONFIG
Consists of 3 main Electromechanical sub systems
a) Front steer Actuator
b) DIS “ Driver Interface system ( with mech back up)
c) Independent rear steer




Front steer Actuator
Driver Interface System
42 V Brushless motor provides feedback torque to driver ( 4:1) ie Belt Ratio
Magnetorheological (MR) Brakes provides up to 10 Nm of torque which gives feedback torque and prevents hand wheel from spinning.
3 steering position sensors measures S.W Angle
Mechanical Backup device- Solenoid driven slides over the clutch.
2 types of Clutch used for Engaging & Disengaging
Intermediate shaft attaches to mech backup & spins freely with from steering actuators primary pinion when clutch is disengaged.
Independent Rear Steer Actuators
GM Sequel contains rear steering to reduce turn circle & improve vehicle handling behaviour
Provides +/- 5.7 deg of road wheel angle
Motor drives worm shaft & sector gear to move pitman arm.
Each actuators has 2 abs. position sensors & 1 motion resolver to provide proper level of redundancy
Thus SBW is designed to shutdown rear steering when single point faults are detected

POWER CONFIGURATION
42 V power is distributed between two buses (if one bus fails another operates.
36 V battery provides 2 min backup power if both power modules fails
SBW Ctrl uses DSpace micro-auto boxes which receive power from 4 V Bussed Electrical Center (BEC)
In case of fuel cell failure 14V power supply, 14V BEC communicates with diode battery switch assy to switch on 42 V TO 14 V DC/DC Converter and provides power to micro auto buses.


Performance Objectives
Front steer actuator sub-system:
a) to activate variable steering ratio and improve steer response
b) front steer sys provides overall S.R ( 10:1 to 18:1) range
c) At low speed steer ratio is at lower range
d) At high speed with steer sensitivity reduced with upper range
e) Front steer actuator sub-sys also designed to support aggressive hand wheel velocities.



Control System Design
Feature Expansion
The SBW system was designed to allow it to be integrated with other by-wire chassis systems that are included in the Sequel vehicle.
To accommodate future integration plans, the SBW software includes an interface for a Supervisory Control Module (SCM).
This interface provides the capability to augment steering control. The SBW control system will provide the base steering control.
The SCM will be able to modify the front and rear wheel angles and DIS feedback torque that is commanded by the SBW system
The SCM interface will facilitate integration of by wire systems to enable future vehicle control technologies (i.e. lane keeping, semi- autonomous parking, stability control) and driving dynamics
Conclusion
An acceptable level of security and functional availability was achieved through a use of fault-tolerant and fail-safe architectures

Substantial redundancies are required to achieve fault tolerant operation. Even with electrical redundancy, mechanical backup may be needed to protect against possible loss of function in the event that the vehicle experiences a significant electrical disruption

The redundancies required to achieve an acceptable level of steer-by-wire fault-tolerant operation result in a significant cost penalty compared to current mechanical systems. This extra expense will restrict the application of steer-by-wire technology to unique vehicle designs which draw significant benefits from this technology