Continental: Brake-By-Wire Gathers Momentum

PAGE 14 BRAKE-BY-WIRE SYSTEMS

Brake-by-Wire Gathers Momentu HIL Test System for Developing a 12-V Brake-by-Wire System

dSPACE Magazine 1/2008 · © dSPACE GmbH, Paderborn, Germany · [email protected] · www.dspace.com PAGE 15

m The future of the brake is electric (brake-by- wire system). An electric motor (in the foreground) replaces the hydraulic cylinders which press against the brake disc.

Continental is currently developing brake-by-wire systems that can use a new brake technology based on a 12-V electrical system. For Continental to perform function optimization and concept validation for this innovative brake-by-wire system, IABG developed a test system with an interface to a real-time vehicle model based on dSPACE technology.

dSPACE Magazine 1/2008 · © dSPACE GmbH, Paderborn, Germany · [email protected] · www.dspace.com PAGE 16 BRAKE-BY-WIRE SYSTEMS

system interacts with the simulated vehicle electrical system. To create a complete HIL test system, it is supplemented by an application- specifi c, adapted, extended simulation environment based on the dSPACE Automotive Simulation Models (ASM). This simulates the vehicle dynamics’ behavior in a virtual vehicle in real time. The physical vehicle variables and mean value variables calculated for the braking This hardware-in-the-loop (HIL) test The main technical point is that this system are used to control the system has proven to be an effi cient braking principle consumes less dynamic restbus simulation and the development and testing tool energy than other systems. For the test system actuators. within the development process. fi rst time ever, very high clamping The applications focus on putting Its main tasks are putting the system energies and excellent control the system into operation, testing network into operation, function dynamics can be achieved with the communication between system verifi cation, fail-safe trials and 12-V vehicle electrical systems components, and studying error investigating the energy manage- currently in widespread use. behavior when individual components ment functions of the braking The system also has an integrated fail. The integrated vehicle dynamics system. HIL test procedures have parking brake function. simulation makes it possible to numerous advantages over test systematically test different driving drives in laboratory vehicles – repro- HIL Test System: Integral Part of maneuvers including specifi c vehicle ducibility, effi ciency, cost effi ciency, the Development Process for the dynamics situations. The results are etc., – and all these are fully utilized. Electrical Braking System used to validate the system network The HIL test system was designed to and its functional properties, taking Development Approach to verify the networked system func- into account the effects of failures Complete Brake-by-Wire Systems tions and system communication on driving behavior. The completely new braking technol- and to perform further investigations ogy in the electronic braking system during the development process. Set-up and System Architecture utilizes a principle that is as simple as It acts as a system test bench for Since the generation of clamping it is effective. Based on conventional putting the system network into forces depends on (load) torques friction braking, it involves no operation and for testing system being transmitted via the brake hydraulics whatsoever: the actuators functionality. Other purposes include disks, the task at actuator level is to are operated entirely by electronically investigating and optimizing basic implement a suitable load for the test controlled electric drives. Each wheel functions and energy management bench under cost-effi ciency con- has its own control unit. When the in the back-up level of the braking straints, i.e., to avoid using actuators car driver presses the braking pedal, system, and testing how the braking operated via a real gyrating mass like an electronic signal is sent to the wheel brake. Sophisticated sensors Set-up of the HIL test bench. and software optimally adjust the braking power on the wheel to a wide variety of road conditions. During braking, the friction arising between the brake pad and the brake disk generates torque on the pad. This is fed back into clamping force generation. Thus, much of the brake caliper’s clamping energy is obtained from the vehicle’s kinetic energy, so it does not have to be mainly fed in externally as electrical power.

dSPACE Magazine 1/2008 · © dSPACE GmbH, Paderborn, Germany · [email protected] · www.dspace.com PAGE 17

with fl ywheel mass test benches. The core of the test bench automa- side, the HIL platform provides inte- This is done by means of a device tion system (AT) is a DS1005 PPC grated vehicle dynamics behavior that emulates loads. Board networked with several based on the dSPACE Automotive On the test bench, the motors of the dSPACE I/O boards. The test bench Simulation Models (ASM). The major actuators form the interface to the therefore has a complex FlexRay components of this simulation envi- simulated braking actuators. Highly network with a total of two inde- ronment are models for the vehicle, dynamic load equipment consisting pendent networks in addition to driver, and environment, the associ- of servo drives is applied to the CAN communication with the ECUs. ated model control, and model motors to ensure dynamic simulation To connect the test system to the parameterization functions. One of the real loads that would occur FlexRay bus, the FlexRay Confi gura- point particularly worth noting is in the vehicle. The electrical and tion Tool from dSPACE is used with a that integrated simulation is per- mechanical components are network description in a FIBEX (fi eld formed for any system components designed so that prototypes can be bus exchange format) fi le. that are not installed as real parts. installed and assembled fl exibly in The vehicle model is calculated on Because the model structure is open various test confi gurations. an additional DS1005 that is down to the Simulink block level, it did not take long to make optimum modifi cations to the model components of the ASM Vehicle Dynamics “ The seamlessly integrated development Simulation Package. The automation software builds on environment from dSPACE lets us carry out the MATLAB®/Simulink®/Statefl ow® projects effi ciently. The help given by dSPACE development environment and the ControlDesk experiment software Support was exemplary.“ from dSPACE. Some of the functions that have to be executed on the AT Franz Hangl, IABG real-time system are:

■ Event-discrete sequence control The complete communication connected to the test bench auto- for the test system control and network of the electrical braking mation system in real time via the implemented single tests system, with the pedal unit and the dSPACE Gigalink (a high-speed ■ Communication with the ECUs additional function of the electronic optical connection). The processes via FlexRay and CAN protocols parking brake, is represented in on the automation platform and ■ Communication with the HIL hardware form in the test system. the model platform communicate at real-time board via Gigalink In addition to CAN communication intervals of 1 ms. On the software interface with the braking system’s central ECU, a ﬂ exible FlexRay communication architecture was also set up. HIL Real-Time Platform This enables all four wheel units of Virtual Vehicle Environment, ... the brake-by-wire system to be whl spd µ_disc brake torque simulated as required. Switching Actuator Model between the wheel units is per- T_load F_caliper position actuator 1 position actuator 2 position formed by software, right through solenoid to the model. I/O The mechanical, electrical, and com- forces whl spd T_Load munication variables of the system M M network are captured at various Shaft measurement points and archived in load motor 1 actuator 1 T_Load the automation system for subse- Wheel Control Unit M M of Actuators quent evaluation. Shaft load motor 2 actuator 2

Sensor solenoid for failsafe mechanism Load representation at the actuator.

dSPACE Magazine 1/2008 · © dSPACE GmbH, Paderborn, Germany · [email protected] · www.dspace.com PAGE 18 BRAKE-BY-WIRE SYSTEMS

Actuators/Sens. Wheel Speed Wheel Speed Actuators/Sens. Driver Driver MuCWU SuC MuCWU SuC FR RR WU WU EM EM

VEHICLE CAN BOOT_CAN_ENABLE SAFE POWER PU ECCU_CAN PU BUB PU ECCU TO_DASHBOARD S1 BUB1_FR SPWM_A SCA uC1 BuB BuB 1 BUB1_RL S2 SPWM_B Monito- SCB ring SENSOR_CAN VDS S3 BUB2_RR uC3 BUB2_FL BuB BuB 2 BUB_EPB Monito- uC2 ring SPWM_A SPWM_B PRIVATE_CAN PRIVATE_CAN WL1 TO_DISPLAY EPB WL2 WL3

KL 15 KL 30

OPN + –

WU WU EM FL RL EM

MuC WU SuC MuC WU SuC Driver Wheel Speed Wheel Speed Driver Actuators/Sens. Actuators/Sens.

System architecture and communication structure of the electrical brake based on a 12-V vehicle electrical system.

In addition to basic automation, Test Automation and up now contains approx. 800 single the user can also use functionalities Failure Simulation tests of varying complexity and is such as: The task of test automation is to de- constantly being added to. fi ne single tests individually, execute The automated environment ■ Implementation of the graphical them sequentially in a coordinated provides access to the requirements, user interface to handle and manner, and abort test execution in test specifi cations, and test results confi gure the test system the event of a failure. A test report via a direct connection to the test ■ Event-controlled layout and and test run documentation are au- confi guration and management tool experiment management tomatically generated for each test. that is used in the development and ■ Test automation and test manage- The user can confi gure the form and test process. ment with IABG software modules contents of the test report. One of the applications for the test in conjunction with Automation- automation system is inserting fault Desk to confi gure and generate Test automation based on Automa- scenarios to analyze system behav- test sequences tionDesk was developed on the HIL ior. The following fault types can be ■ Automatic evaluation and test system. AutomationDesk lets implemented on the test bench: generation of test reports the user freely defi ne test sequences ■ Access to ECU operating states, that are executed by the test bench ■ Cable harness faults variables and parameters via a automation system. This gives the ■ Signal faults diagnostic interface user the greatest possible fl exibility ■ Communication faults in CAN ■ Evaluation software to display when specifying and implementing and FlexRay measurement data graphically tests. The test database that was set

“ The test system that IABG set up for us, based on dSPACE components, enables us to reliably develop innovative brake-by-wire products up to production level.“

Stephan Lehrl, Continental AG

Cable harness faults are implemented The connection to the test conﬁ gu- by a failure simulation unit with ration and management tool ensures Summary currents of up to 50 A. The automa- a seamlessly integrated process from tion system controls the unit in real the requirements sheet for the over- ■ IABG relies on dSPACE technology time via a CAN interface. Signal all system to single tests on signal for complex test system solutions faults (sensitivity changes, offset software functions. Thanks to drift) and communication faults constant further development of the ■ Function optimization and veriﬁ ca- (message interruptions, checksums) implemented test cases, the system tion for networked vehicle control are switched to physical signals by network can largely be validated systems focusing on brake-by-wire the real-time system. at an early stage on the HIL test ■ Extensive test automation solution system. implemented with ControlDesk and Extending the Test Features Franz Hangl, Automotive Test Systems, AutomationDesk, including a connec- The test system described here is IABG Ottobrunn, Germany tion to a test management tool completely integrated into Conti- Stephan Lehrl, Electronic Brake Systems, nental’s development and testing Chassis & Safety, Continental AG, Regensburg, Germany process. Individual test sequences can be programmed graphically, which supports extensive testing of the system network and of single components.

ControlDesk layout for controlling the test system.