Volkswagen AG Business Unit Braunschweig

WERK Braunschweig

Volkswagen AG Business Unit BraunschweigSoftware Timing Analysis for Steering Components

Dr. Fabian Wolf, Dieter Brinkema

H – Dieter Brinkema – Tel.: 39312 – Stand: 18.09.2008 – 2WERK Braunschweig

Agenda

1 Introduction of the Electronics Development

2 The Architecture of APA-BS

3 Scenarios for Timing Analysis (Tool Usage)

4 Summary and Outlook


Introduction of the Electronics Development

•Development of electromechanical steering (e.g. Volkswagen and Audi)

•APA-BS (Axially Parallel Actuation BraunSchweig) is being used for Tiguan and Passat

•The Safety Concept was developed according to ICE 61508 regulations

•Safety Concept ensures that the electromechanical steering acts safely at any time and provides maximum availability

•Conflict of objectives: maximum safety AND maximum availability


APA-BS (Axially Parallel Actuation BraunSchweig)

Steering column

Steering Moment Sensor

Steering Pinion

Control Unit

Control Shaft

Synchronous Engine

Ballscrew

Belt


Architecture Overview: Hardware

Two-computer system of the steering control unit

•Steering functions, motor control, and I/O handling are implemented on the main computer

•The second computer monitors the main computer

•Communication via digital interface

•Exchange of high-frequency question-answer-sequences

•Both computers have an independent clock and energy supply


Architecture Overview: Hardware

Main Computer- 16 bit DSP- 60 MIPS- 60 MHz

Sensor

Engine

Steering functions

Monitoring Computer

- 8 bit µC

Monitoring functions

Question-answer-sequences

Clock1

Energy supply1

Clock2

Energy supply2


Architecture Overview: Software

Considering the wide range of possible driving situations, the objectives are:

•Optimal adaption to the respective driving situation

•Maximum driving and steering comfort

•Standard equipment functions:

- Steering power support, speed dependent

- Active centering and dampening

- Straight-running function …

•Upgrade equipment functions (optional)

- Park assist

- Lane-keeping assist

- Customizable adaptivity - from sportive to an emphasis on comfort…


Architecture Overview: Safety Concept

Basic elements of the safety concept:

•Redundant sensor signals for steering moment / motor position

•Two-computer concept

•Thermal protection for motor, electronic amplifier, and computer

•Voltage control for logic-module / power-module

•Validation of all system sensors and signals

•Cyclic memory test: RAM, ROM, EEPROM

•Isolated function deactivation

•Appropriate substitute measures

•Ensured dry-running operation in case of failure


Monitoring the Real Time Correctness

Monitoring the real time correctness is part of the nominal/actual comparison; this means it is monitored whether the required software algorithms are calculated within their respective time intervals

Missed deadlines are interpreted as exceptions

The system has to be kept in a safe state

Reasons:

•Real error (e.g. defective component)

•Insufficient computing performance


Verifying the Availability with Scheduling AnalysisRequirements

•The OEM requires analytical proof that functions are not deactivated due to insufficient computing performance at maximum load

•ICE 61508 requires meeting the reaction times in case of error

Solution

•Through SymTA/S scheduling analysis, the Electronics Development of VW Braunschweig can assure that no timing problems occur


Availability verification through Scheduling Analysis

Designated hardware

SymTA/SSymTA/S

Scheduling Analysis

Test, measurement

Core execution times

System model

Environment model

Import

Time requirements Comparison ReportExport

Response times

Input

Input


Selection of new Hardware

Conflicting objectives

•Sufficient resource availability at any time

•Avoid unnecessary over-dimensioning of computing resources

Easy: Determination of the required memory

Difficult: Determination of the required computing performance under worst-case conditions


Selection of new Hardware for Tiguan

Starting basis

•Available SymTA/S model from predecessor

Approach

•Reusability of the model (ensured via analysis)

•Adoption of the model without major changes

•Calculation of computing time for new functions based on prototypes

Result

•Verification of availability and optimum dimensioning on virtual level

•Sensitivity analysis for the determination of reserves


Extension of Software

Challenge: in case of new system requirements – e.g. for model upgrading – it has to be analyzed if the available computing performance is sufficient to fulfill the new AND the already existing requirements

Solution:

•Display of the available execution time per task via sensitivity analysis

•Analysis of alternatives in case modifications are necessary (e.g. moving routines into other tasks)

Advantages: the analysis results can be displayed and traced transparently and plausibly.


Usage of SymTA/S

2. Auswahl neuer Hardware

3. Bewertung der Erweiterbarkeit der Software

1. Absicherung der Verf ügbarkeit2. Selecting new hardware

3. Validating the expandability of the software

1. Availability verification

Reuse of the first generation model

Sensitivity analysis

(What if?)

2. Auswahl neuer Hardware

3. Bewertung der Erweiterbarkeit der Software

1. Absicherung der Verf ügbarkeit2. Selecting new hardware

3. Validating the expandability of the software

1. Availability verification

Reuse of the first generation model

Sensitivity analysis

(What if?)


Summary

The Electronics Development uses SymTA/S to verify the availability of steering functions for the OEM

Further applications are the selection and dimensioning of new hardware as well as the estimation of extensibility for new functions

Advantages of SymTA/S:

•Easy to use

•Fast calculation of results

•Results and approach are well-established at OEM


Outlook

Model optimization through new SymTA/S features

•Task chaining

•FlexRay library

Model-based run-time maintenance

Application in further projects of the Electronics Development at Business Unit Braunschweig

Volkswagen AG Business Unit Braunschweig

Documents

Transcript of Volkswagen AG Business Unit Braunschweig