braking systems with new ima generation - scarlettproject.eu systems-sae... · function needs very...

ABSTRACTFirst generation of Integrated Modular Avionics (IMA),currently onboard in aircraft type Airbus A380, A400M, ordesigned for Airbus A350, and whose principle was initiallyto introduce some common processing resources, had beendeveloped in such a way to reduce the quantity of embeddedequipment part number, and to harmonize the nature of theavionic units by minimizing the specificity of electronicequipment: thus, for instance, the number of processing unitsin the A380 is half that of previous LRU-based avionicgenerations.

This type of architecture had already many interest at aircraftlevel; nevertheless, some of the designed electroniccomponents were not able to support some performancerequirements of the function suppliers, such as Messier-Bugatti-Dowty, which had to limit the deployment of thefunctions to implement in IMA; For this reason, it was stillnecessary to execute the fast control loops, as the antiskidalgorithms, in specific remote electronics (RDC, RBCU),independently from the standardized CPIOM.

Beyond this first generation of avionics architecture, newmore optimised concepts are presently studied, throughresearch programs as SCARLETT (IMA of secondgeneration, “IMA2G”), where Messier-Bugatti-Dowty takespart to the definition and the evaluation of new modularelectronics standard, more powerful and capable to host themost critical and fast control functions, and in such a way toensure that the performance of these defined genericcomponents (middleware, reduced API653 layer), plus thelatency introduced by the fast field bus match well with thehigh time critical performances required, for example, for theexecution of the braking regulation. In particular, the antiskid

function needs very low latency and jitter, and fulldeterministic transmission to operate nominally.

Furthermore, actual research study on braking, landing gearand aircraft on ground control laws requires more and morereal-time power and fast control loops to provide newfunctionalities and higher efficiency, and necessary to beconsidered in the design of these new platforms.

The target is, thus, to reach more standardized and scalableavionics, dedicated to the highest critical aircraft functions asthe braking control, and standard capable to facilitate the highcritical system integration and to harmonize the developmentand test process, regarding the final common objective (ataircraft and system levels) to reduce the development timeand cost, without compromising the trend of more efficientand powerful real time control laws with adaptive behaviour.

INTRODUCTIONThe European Research & Technology program calledSCARLETT (SCAlable & ReconfigurabLe ElectronicsplaTforms and Tools), in which Messier-Bugatti-Dowtycontributes as active partner in the design of the future highlytime critical system architectures, provides the mainopportunity to progress the state of the art of the embeddedavionics beyond the current IMA1G concept, especiallyregarding the following aspects :

• Scalability, portability and adaptability

• Fault tolerance and reconfiguration capabilities

• Minimum number of types of standardized electronicmodules

These new platform generations have to be designed in takinginto account to cover as much as possible the functional andperformance requirements, plus all the technical constraints

Braking Systems with New IMA Generation 2011-01-2662Published

10/18/2011

Stephane Bernard and Jean-Pierre GarciaMessier-Bugatti-Dowty

Copyright © 2011 SAE International

doi:10.4271/2011-01-2662

Gratis copy for Stephane BernardCopyright 2011 SAE International

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http://dx.doi.org/10.4271/2011-01-2662

highlighted by the airframers, and by the time-critical systemsuppliers, such as Messier-Bugatti-Dowty dedicated to theATA32 landing gear system design.

In particular, the antiskid braking control, one of the mosttime-critical aircraft systems, included in the ATA32perimeter, appears as sizing and important to consider for astudy of IMA2G “time critical” platform, especiallyregarding :• Its high criticality level (DALA)• Its high processing rate (dedicated to the antiskid control)and its determinism constraints• Its variety of Input / Output• Its required level of fault tolerance

Thus, the IMA2G platform shall offer sufficient materialresources (in term of CPU capability, memory size, bus,interface processing) in order to maintain high real-timeperformance level especially required for the braking controlfunction.

DESCRIPTION OF NEW BRAKINGCONTROL ARCHITECTUREThis new IMA platform is based on avionic architectureconcept composed of set of Core Processing Module andRemote Data Concentrator generic components drawing,thus, a segregation (partial or total according to the adoptedconfiguration) between computation resource and Input /Output management stage; this design philosophy aims toreach the use of fully standard electronic bricks (coveringmaximum functional and interface needs), consequentlyreducing the development effort and improving the high levelof integration of numerous systems.

On a strict technological viewpoint, the avionic strategy, suchas considered here, reclaims much more powerful andefficient CPU resource, in the main or remote computationcore, in such a way even to be capable to execute fast controlloops, for instance the antiskid braking algorithms with somefast processing phase running up to 400Hz.

On other hand, for this same braking function, the datacommunication technology, used between the CoreProcessing Module and the Remote Data Concentrator, isrequired to operate with total transmission determinism andlowest possible latency and jitter to reach the expectedprocessing performances, widely reducing the choice of thepossible solution today proposed.

DETAILS OF IMA2G AVIONICSCONCEPTWith these different requirement, two concepts of modularavionics are today imagined and highlighted, dedicated tohost the high critical functions, such as the Messier-Bugatti-Dowty's antiskid braking control, for the future aircraftgeneration.

Both showed architectures deal with dual command strategyin active/passive mode at CPM level, in active/active mode atRDC level (each RDC ensures the braking control for twowheels); these 2 control architectures are dedicated to thehydraulic braking of four-braked- wheels aircraft type.

Control Architecture 1This first concept, as illustrated in Figure 1, proposes asystem cluster composed of 3 types of avionic components:• A COMMAND Core Processing Module This component issized to host a braking COMMAND software partition,capable to compute the high level braking mode, the flightphases, the braking orders on each aircraft hydraulic circuit,and execute the braking activation. The fastest computationalgorithm, within this partition, is executed at 50Hz.• A MONITORING Core Processing Module Thiscomponent is sized to host a braking MONITORINGsoftware partition, capable to determine the system failure forsystem reconfiguration and provide information to othersaircraft systems; The fastest computation algorithm, withinthis partition, is executed at 50Hz.• An Intelligent Remote Data Concentrator This component issized to host a REMOTE braking software partition, capableto determine the corrected pressures, servo valve drift,

Figure 1. IMA2G Braking avionic architecture 1



compute the braking servovalve currents, and manage theantiskid protection. The fastest processing, within thispartition, is executed at 400Hz.

Here, the 3 types of equipment exchange command &monitoring data through an ARINC664 part 7 communicationnetwork (AFDX technology), without additional need of fastnetwork to reduce the communication time, because theantiskid control is locally managed by the iRDC.

Control Architecture 2The second concept, as illustrated in Figure 2, proposes anarchitecture with the 3 same types of avionic components, aspreviously described. However, the difference in this avionicconfiguration is only the COMMAND Core ProcessingModule executes all braking control software functions, evenincluding the fast control loops which manage the wheelantiskid control algorithms. Whereas the Remote DataConcentrator (specific and only dedicated to the brakingfunction) becomes a simple passive equipment (withoutapplicative software) which ensures the network processingand the Input / Output management: the generation of theservovalve command currents - the conditioning of thephysical measurement feedbacks (wheel speed frequentialsignals, hydraulic pressure transducer voltage data).

In other hand, like in the architecture 1 showed above, thepure computation resources (the CPMs) communicate withperipheral Input / Output resources through ARINC664 part 7network. However, a faster field bus is here parallel required:the role of this one, here fulfilled by a communicationtechnology Low Capacity AFDX, is to ensure the exchange ofthe fastest command data between the CPM and the RDC, insuch a way, as the antiskid control is implemented up in theCPM COM, not to compromize significantly the globalsystem reactivity with too much communication latency forthe acquisition of the wheel speed and the transmission of theresulting current command.

PERFORMANCES OF THE BRAKINGIMA2G PLATFORMRegarding the design structure, the distribution principleintroduced by these new generation of avionic platform isleading to consider new timing constraints, especiallydepending on:

• The latency of processing performed by each equipment, atlevel of the middleware and API layers (CPM + iRDC ifremote control application implemented)

• The latency and the jitter of the communication networklinking the computation resources and the Input / Outputmanagement stage

These delays are illustrated for both braking architecturesthrough the Figure 3.

In both showed braking architecture, the network processingtime (applied to AFDX and Low Capacity AFDX) is takeninto account in the network global latency.

In any case, it appears that the management of the antiskidalgorithms by the Core Processing Module, is going tointroduce significantly more delay than the distributedarchitecture concept 1 or a more classic centralized concept,in requiring to forward the wheel speed data at higheravionics level, to compute and retransmit the correct currentreferences to the RDC.

But, whatever the implementation way of the antiskidfunction in the iRDC or in the CPM, the current challengewith this IMA2G is, thus, to optimize sufficiently theprocessing tasks, the software process (services OS 653…)on the different avionic bricks, and the performances of thedigital transmission network, in such a way to reach, as muchas possible, a system reactivity level close to a morecentralized architecture solution.

Figure 2. IMA2G Braking avionic architecture 2



EVOLUTION TOWARDS ATA32ELECTRICAL SYSTEMSRegarding the current trend, especially followed by Messier-Bugatti-Dowty, to develop and evolute towards new electrictechnology, for instance dedicated to the braking function,with multiple possible advantage in term of maintenanceoperation simplification, reduction of operating costs and,furthermore, proposing new functionalities such as the real-time measurement of heat-sink wear or the smartmanagement of loads affecting each brake (actuallyimplemented to the braking of the Boeing 787 Dreamliner),these new control principles mean also, either an evolution ofthe present control algorithms, either the introduction of newprocessing logics, with significant material constraints toconsider, as soon as possible, in the design of the generic hostavionic platform, in term of :

• Growth of computation load and memory capabilityrequiring the use of new digital technology

• Interface capabilities to acquire and condition data comingfrom new generation of sensor technology: tachometer, wearsensor, torque sensor, or others.

Moreover, within an electric braking solution, the controlprinciple differs significantly from a hydraulic braking mode,with a certain quantity of specificities dedicated to theelectric actuator control. These specificities could be coveredby the introduction of additional electronic equipment typeEMAC, provided by the brake supplier, unit especially incharge of the execution of the motor control & monitoringfast loops. This control unit would communicate with theIMA platform via a fast field bus at low latency and jitter.

Figure 4. Electric braking control architecture

The target is, thus, to reach the design of an IMA2G genericplatform, capable to respond, indifferently for a samefunction, to a need of hydraulic or electric control nature,sometimes with variable real time power constraints or owninterface requirements.

SMART SENSOR CONCEPTIn any case, within these new control architectures, and inaddition of the IMA2G, Messier-Bugatti-Dowty studies alsothe concept of smart sensor (as illustrated in Figure 4),specific component which could be located in aircraft mainlanding gear bottom, with high reliability level on electronicand mechanical components in harsh environment, and whosemain functional role is to acquire and condition locally thebrake parameters, such as the wheel speeds, afterwardsprovided in the fast local network, towards the ATA32computation units (generic or not), data too used by otheraircraft systems like the flight control.

This technology is today strongly highlighted, regarding itsmain interest to be capable to digitalize locally the data, thusto reduce the number of wires along the main landing gear(significant weight gain), and to optimize the noise level inthe transmission line.

Figure 3. IMA2G avionic performances



However, about the real-time performance aspect, specificcare is required to take into account and optimize theadditional latency time on the local processing made by thesmart sensor and the data transmission time in the local fieldnetwork.

IMA PLATFORM, FULL OPENNESSAND GENERICITYIMA2G time-critical platform, as studied in SCARLETT, isaccessible through standardized Application ProgrammingInterface; this API layer is following an ARINC653 part 1specification standard, equipped with a “reduced” processmanagement (limited to up to one periodic process) in such away to optimize the compatible Operating Softwareperformances and determinism.

Regarding this interface context, the braking application isadapted and optimized to satisfy the requirements of thisreduced API653, limited in term of proposed softwareservices; in particular, all the functional tasks of each brakingcontrol application are rescheduled around only one periodicprocess, executed per partition.

Figure 5. Braking Control SW adaptation to “Reduced”API A653 standard

These braking control software bricks are developed in a totalgeneric matter, capable to be interfaced with any type ofelectronic equipment, offering the same API653 standard,and obviously sized to support the real time performancescharacterized by this aircraft system type.

SUMMARY / CONCLUSIONSRegarding the growth of the embedded electronic functions,furthermore required to be always more optimized andefficient, the increase of safety constraints meaning morestronger process of design, validation and certification,sharing of new avionics platform standard appears today asessential for the airframer and the system integrator in such away to facilitate the design effort, reduce the developmentcycle and the resulting costs.

However, this IMA2G standard, to be successful, will have tobe sufficiently sized, optimized, and performant to absorbmore and more computation power and real-time constraints,especially within the future generation of “more electrical”

aircraft, and in order to keep equivalent system performancelevels.

This challenge is widely considered and is presently as thecommon care of any actors of the aeronautical world, such asMessier- Bugatti-Dowty which contributes actively to theIMA2G study in such a way to adapt and optimize its futurecontrol systems with this new generation of avioniccomponents, fully generic and scalable

DEFINITIONS/ABBREVIATIONSAFDX

Avionics Full-DupleX switched ethernet

APIApplication Programming Interface

ARINCAircraft Radio INCorporated

ASApplication Software

ATAAir Transport Association

BCSBraking Control System

CPMCore Processing Module

CPUCore Processing Unit

IMAIntegrated Modular Avionics

LC AFDXLow Capacity Avionics Full-DupleX switchedethernet

RBCURemote Braking Control Unit

RDCRemote Data Concentrator



REURemote Electronics Unit

SELVSelector Valve

SCARLETTScalable & ReconfigurabLe Electronics plaTformsand Tools

SVServo Valve

SWSoftware

TCTime-Critical

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