Method and Device to design a Domain Model for Control Systems in Vehicles with respect of the functional Requirements

State of the Art

The invention concerns a method and device to design a domain model for control systems in vehicles with respect of the functional requirements .

The importance of electronic systems in vehicles is constantly increasing due to the demand for more security, economy, comfort, and better environmental protection.

In order to fulfil these partly diametrical demands, the creation of a car wide web including the up to now usually independently working systems in a vehicle seems to be an obvious choice. With the help of standardised interfaces this web combines - from a functional point of view - the system components that form logical units .

Functions and systems of different origin, different automobile manufacturers and suppliers with standardised interfaces can be interconnected to a system compound. Therefore, the system and the function supplier respectively have to guarantee that the function is able to fulfil the required specification also in case of a distribution on several, interconnected control systems .

The development of automotive electronic systems can be divided into three development aspects: function, software and hardware development (Figure 1) . Based on customer requirements the functionality of a system has to be elaborated and implemented in soft- and/or hardware and finally results in the ready to use control unit (product) . Although these different development aspects are strongly linked they are usually carried out concurrently by different development teams. Each team is specialised in one aspect preferring task driven proprietary views of the entire system. To specify the particular subarea suitable description languages and methods are used. Beside the different teams use especially adapted development processes . To ensure that the functional specifications and quality requirements are met and at the same time the development process is cost and time optimised, a structured and constantly co-ordinated handling of the global developing process is necessary.

To cope with the constantly increasing functionality, the control of complex system structures and the demands for an economic vehicle development the structuring concept CARTRONIC⁸ was developed by Robert Bosch GmbH (see Bertram, T., R. Bitzer, R. Mayer and A. Volkart, 1998, CARTRONIC - An open architecture for networking the control systems of an automobile, SAE International Congress and Exposition, Detroit/Michigan U.S.A., SAE 98200, 1-9) . Furthermore the concept also serves to ease the communication between the different developing teams i.e. to have a common language to discuss the different development aspects and to get an adequate documentation. In CARTRONIC⁰ systems, which are supposed to be interconnected, are components with defined tasks, i.e. powertrain management or cruise control but not control units. This open concept can be applied to the very different types of vehicles and control unit configurations and allows the integration of systems of different manufacturers .

The object-based structuring concept that is used in the first phase of a development process, i.e. the analysis phase, allows the interconnection of system components to units under the aspect of a functional, tasks-oriented systematic. The classified functional units are supplied with standardised interfaces. Thus, CARTRONIC^* represents a (meta-) odel for a modularly expandable function architecture used for the networking of independently working individual automotive systems towards a car wide web. Such a function architecture developed by using this concept is a structural decomposition, an object structure with respect to functionality. It can be interpreted as one logical view of the entire system architecture .

The fundamental benefit of this web concept being neutral concerning the automobile manufacturers and suppliers is the logical description of the functional requirements. And this description is comprehensible for all those who take part in the development process even after a short training period.

Control units are the most frequent mechatronic applications and nowadays mostly realised as embedded systems i.e. implemented in software. So their development is closely linked to the software development process (SDP) . Figure 2 displays the SDP over time. Software is specified with respect to functional, time related behaviour, etc. in static (structural) and dynamic (behavioural) architectural views. At the beginning of the development process, in the analysis phase, these aspects are specified roughly on an abstract level. In the progress of the SDP the specifications are put into more concrete terms . This represents the transition from an analysis to a design and finally to an implementation phase.

If the functional structures developed by using CARTRONIC"⁸ shall be integrated into an information technology design of the software development, an increase of the level of formalisation of the modelling becomes inevitable. A formalised description improves the clearness of the model, decreases the contradictions and increases the information density via the extension of the semantic content of elaborated models. Therefore the analysis model is described in such a way that a continuous coupling to a software model of the consecutive design phase can be realised.

In the following a domain model drawn up in CARTRONIC¹⁰ in a standardised object-oriented presentation is described.

The Unified Modelling Language UML as an unification of different language approaches of the object-oriented modelling (see OMT by Ru baugh, J., M. Blaha, W. Premerlani, F. Eddy and W. Lorenson, 1991, Object-Oriented Modelling and Design, Prentice Hall, Englewood Cliffs, U.S.A., OOSE by Jacobson, I., M. Chris- terson, P. Jonsson and G. Overgaard, 1992, Object-Oriented Software Engineering: A Use Case Driven Approach, orkingham: Addison Wesley, OOAD by Booch, G., 1994, Object-Oriented Analysis and Design, 2. Edition, Redwood City, CF: Benjamin/Cunnings, etc.) is predestined for the description of the requirements analyses defined according to the structuring concept. It represents an international standard passed by the OMG (see Object Management Group (OMG), 1998, Unified Modelling Language VI.2, OMG Headquarters 1998, http://www.omg.org.) . The UML is not a process model but a standardised notation for the modelling of software systems.

The document offers an overall view over structure elements and the formal structuring as well as the modelling rules of the presented concept . A function architecture of the entire -vehicle with a specification for the component propulsion is presented on a high level of abstraction.

Besides the documentation includes a procedure for the integration of the concept and the developed function structures respectively into the software development process. Proceeding from the description of the used UML notation elements a CAR- TRONIc'-conform modelling in the UML for the representation of the function structure is presented.

In addition the structural modelling as described before is extended to model dynamic aspects. The specification of these behavioural aspects in the formalised UML notation is shown, giving an example of state transition of an simplified gearshift process at an abstract level within the powertrain.

Traction control is an example of a car wide web which has already been developed. Concerning this regulation concept the access of the control unit of the traction slip control to the engine control unit is required in order to initiate a reduction of the motor output torque in case of spinning of the dri"ving wheels during an acceleration manoeuvre. That means that e.g. a spinning of the wheels during the starting phase can be a-voided with the help of this system networking. This example represents a variety of already realised interconnections of systems which have already been developed without a general, systematically structured car wide web. Nevertheless, such a system compound is not appropriate for the constantly increasing integration density of networked electronic systems in the vehicle, so that the development of a systematic for the planned car wide web is inevitable.

CARTRONIC^* is an structuring concept for all control systems in a vehicle. It is used for the structuring of tasks in the phase of the requirement analysis . The concept comprises the structuring and modelling rules and a modular, hierarchic and expandable structure which complies with this rules. During the structuring design patterns are used for similar tasks.

In the following, the structuring systematic (rules) and its transformation into a concrete structure is referred to as 'function architecture'. The function structure consists of components with restricted, independently resolved tasks and exactly defined physical interfaces.

Components and communication relations are the elements of the function architecture. Within the scope of the structuring, a system has to be understood as a combination of components that form a whole. Nevertheless, the term component does not automatically represent a physical unit in the sense of a constructing element or a control unit, but has to be understood as a function unity. The interaction of the components is modelled with the help of the communication relations. The structuring concept distinguishes between three functional types of components :

• components with mainly co-ordinating and distributing tasks,

• components with mainly operative and executing tasks and

• components which exclusively generate and provide information.

Seen from outside, i.e. from the point of view of neighbour components, a component of a function structure has to be interpreted as a system which principally might be subdivided into sub-systems and sub-components respectively. A further refinement might be carried out if necessary, e.g. in case of complex components. Seen from inside, i.e. from the point of view of the sub-systems or the sub-components, the original component is only an enclosure which integrates the entirety of all subsystems .

There are also three different types of communication relations (in order to simplify the terminology, we only use the terms order, inquiry and request if we refer to the communication relations) :

• order (with response) ,

• request and

• inquiry (with notice) .

An order is characterised by the obligation to be executed by the instructed component. If the order is not executed the receiving component has to provide the orderer with a response why the order could not be fulfilled. A request describes the demand of a source component so that the target component initiates an action or realises a function. Nevertheless, in contrast to the order the request is not obliged to be fulfilled. This communication relation is used e.g. for the realisation of competing resource demands (energy or information) . The inquiry is used to get information needed for the fulfilment of an order. If a component is not able to provide the requested information it can notify the inquiring component accordingly.

The three communication relations are subject of different restrictions concerning the possible communication partner within the function architecture of the entire vehicle. These restrictions are part of the structuring rules. However, the structuring rules also distinguish between communications being realised on the same level of abstraction or on higher or lower levels. Finally, the rules concerning the structuring also offer procedures which control a forwarding of communication relations from one system into another in the respective refinement.

A main idea of the structuring concept is the hierarchical flow of orders. This is an example for communication restrictions. Always exactly one component exists in a refinement which receives all incoming orders. This so called 'entry component' distributes and forwards these orders.

The modelling rules contain patterns which combine the components and communication relations needed for the solution of special and repeatedly occurring tasks . An example for such a pattern is the energy management which can be reused at different locations within the structure of the vehicle both for electrical and mechanical as well as for thermic energy. Summarising, the following features of a function structure, developed in accordance with the structuring and modelling rules, can be listed:

• defined, consistent structuring and modelling rules on all levels of abstraction,

• hierarchic flows of orders with each component being assigned to only one orderer,

• high level of responsibility of the individual components,

• control elements, sensors and estimators are equal information providers,

• encapsulation so that each component is only as visible as necessary and as invisible as possible for the other components .

Finally, the structuring concept is illustrated with the help of the example given in Figure 3. The vehicle structure, on the highest abstraction layer, contains one co-ordinator (Vehicle coordinator) , four components with operational tasks, and four information providers . By grouping the components according to functions, the general task of the vehicle is partitioned into a number of smaller, manageable tasks. These are the control of the Powertrain, Vehicle motion, Body and interior, and El ectri cal supply system for the operational components. The information providers are partitioned into the groups environment, vehicle, user and driving conditions. The dimensionality of each of these tasks is still relatively high. Therefore each system is structured into a set of yet smaller even more manageable components. Because the components interact, the refined system often needs a co-ordinator to co-ordinate the tasks of these components . Such a refinement is shown in Figure 3 for the powertrain functionality, where a simplified gearshift process is specified on an abstract level by the sub-components Engine, Transmission, Converter/Clutch, Gearshif panel and Powertrain coordina tor.

In addition to the components the communication relationships between the components are specified as follows:

• The order torgue_go (to provide a certain torque at the gear output) , is given by the Vehicle coordinator to the Power- train and forwarded to the 'entry component' Powertrain coordinator,

• the order torgue_eo (to provide a certain torque at the Engine output) from the Powertrain coordinator to the component Engine,

• the orders εhift_gear (to change the transmission gear) and clutch_action (to engage or disengage the clutch) are given by the Powertrain coordinator to the component Transmission and Converter/Clutch respectively,

• the request gear_ratio ! (new gear ratio chosen) from Gearshift panel to the Powertrain coordinator,

• the inquiry air_pressure? (present environment air pressure) from the Engine to the Environment data,

• the inquiries gear_state? (present gear state) and pos± - tive_engaged? (transmission positive engaged) from the Power- train coordinator to Transmission,

• the inquiry torgue_co? (present torque at the clutch output) from the Powertrain coordinator to the Converter/Clutch,

• as well as the inquiry rot_speed? (present rotational speed) to the Powertrain which is transferred to the responsible component Engine. The classical software development process can roughly be divided into three phases: analysis, design and implementation. For practical applications the software development process is not a strictly sequential development process. Development phases - in theory clearly distinguishable - overlap.

An object-oriented model for the software design allows a phase- overlapping procedure with the option to achieve a high level of reusability of already developed or already existing parts and concepts if the respective measurements are applied. This aim can be achieved considerably easier if computer-aided, graphical notations with a high level of formalisation are used. The Unified Modelling Language as an international standardised notation allows a graphical, object oriented software specification. The UML cannot be regarded as a method. It is only a notation based' on a meta-model used for the modelling of software- systems. The most decisive aspects which point to the application of UML models are:

• the use of an international standard,

• a tool-aided procedure which is as far as possible independent from manufacturers,

• the independence - as far-reaching as possible - from the finally used programming language and

• the preservation of the consistency between analysis, design and implementation.

In order to increase the efficiency of the software development using the presented concept it is necessary to integrate the results of the requirements analysis according to the structuring concept, which are available e.g. in form of function structures (Figure 4) and interface tables. The aim is the creation of consistent processes. The variety of hardware components, operating systems, bus-systems, real-time demands, tools etc. does not permit a complete unification of the sof ware development . Only at the beginning of a process, in the analysis phase, a standardisation seems to be appropriate, proceeding from the assumption that already in this phase a restriction concerning the specification language and the possibly used tools for CAR- TRONIC¹⁸ is determined. In this context, Figure 4 describes a possible procedure of the software development using the structuring concept elaborated by Robert Bosch GmbH.

Figure

The invention is illustrated by means of the Figures 1 to 11.

Description of an examples

In the following the mapping of the structuring elements, which are presented before, in UML is illustrated using the example given in Figure 3. The focus here is to create a CARTRONIC^I'-UML- Model as a domain model of the entire system (Figure 4) . The aim of the realisation of a modelling of the structuring concept in elements of the UML notation is:

• the complete modelling of the structuring and modelling rules,

• the preservation of the basic idea of an object-oriented approach,

• the intuitive comprehensibility as well as a sufficient transparency for the modelling designers and

• the integration of all required information of the domain specification and a distinct presentation. Within the object-oriented terminology the term class usually refers to the generalisation of same structured objects. Objects are instances of classes with features and behaviour. Concerning the object-oriented modelling a first step often used when looking for classes is the search for nouns since these nouns usually create the generalisation of object groups within the language .

Therefore, in the UML model the CARTRONIC⁰ components are generally presented by UML classes. In order to illustrate the visibility of the these components concerning the communication restrictions (see Bertram, T., R. Bitzer, R. Mayer and A. Volkart, 1998, CARTRONIC - An open architecture for networking the control systems of an automobile, SAE International Congress and Exposition, Detroit/Michigan U.S.A., SAE 98200, 1-9) and to separate the realisation of a component (internal behaviour) from the extern visible behaviour a component is modelled by an object instantiation of an UML class with an appropriate interface. E.g. the component Engine is represented by the interface Engine and the realisation EngineRl . An interface is a collection of operations which are used to specify a service of a certain class. The interface capsulate the functionality which can be realised in different ways e.g. EngineRl and EngineR2 may be possible realisations of the interface Engine. The relation between an interface and a class can either be modelled by the realisation relationship (Figure la) or the interface lollipop notation (Figure lb) (see Booch, G., 1994, Object-Oriented Analysis and Design, 2. Edition, Redwood City, CF: Benjamin/Cunnings) . Components of the structuring concept communicate via orders, requests, and inquiries. The target component of a communication offers a service to the source component in order to comply with the entering communication. This service corresponds to the tasks and the content of a CARTRONIC^β communication relation which the source component uses to access the target component.

In order to rebuild these aspects in an UML model UML operations

(often synonymical called methods) are assigned to the UML classes representing the CARTRONIC° components. As mentioned above these operations are specified in the interfaces of the classes .

In order to illustrate which type of a communication claims access to an UML operation the type is specified by the stereotypes <<Order>>, <<Request>> and <<Inguiry>> . If an UML operation is used to fulfil an order it receives the stereotype <<0r- der>>. If an UML operation is addressed by a request the stereotype <<Request>> has to be chosen. In case of an inquiry to an information provider the respective UML operation of the provider is specified by <<Inquiry>> (Figure 2) . To improve the clarity of the presented figures possible operation arguments are omitted.

The UML composition relations are appropriate for the modelling of these function structures concerning the aspect of the hierarchic assignment of sub-components to a superior component. Thus the UML composition defined as a link between the UML class and its superior class (it represents the enclosure of the CAR- TRONIC⁶ component modelling an UML class) models the so-called part-of-relation of the function structure as shown in Figure 3. Components of Figure 3 without communication links are omitted. As shown a composition always connects a realisation class with the interface of one refinement. The classes Vehicle_coordina- torRl , Vehicle_motionRl , PowertrainRl and Environment_data.Rl compose the Vehicle_layer. The class PowertrainRl is refined further by part-of-relations corresponding to the structure in

Figure 3.

When a component is refined it's tasks have to be delegated to the sub-components . This delegation mechanism is realised by the composition relationship which propagates e.g. method calls to it's sub-ordinated class.

To specify exactly which operation is delegated to a subordinated class the UML composition is itemised by a constraint, e.g. PowertrainRl calls the method rot_speed of Engine . This delegation may be specified more detailed by using the Object Constraint Language (OCL) (see Booch, G., J. Rumbaugh and I. Jacobson, 1999, The Unified Modelling Language User Guide, Addison-Wesley, Reading/Massachusetts, U.S.A.) .

During the refinement there is exactly one component which is the target component for forwarded orders. This component is called entry component in the function structure. To model this property the UML composition is specified by the role ÷EntryOrder (Figure 7) .

Components of the function structure communicate via order, request or inquiry. The service, which the target component of a communication offers to the source component in case of a communication relation, is modelled by an explicit UML operation. An UML association is used in order to illustrate the feature of a CARTRONIC^* communication that a specific source component e.g. Gearschift_panelRl (Figure 3) communicates with a target component e.g. Powertrain_coordinator . I.e. in the CARTRONIC^{^}-UML-Model we find a communication between a sender class representing the source component and a receiver class representing the target component, so that the sender class can address the methods of the receiver class.

The UML association is indicated by an arrow pointing from the calling class to the supplier of a service, e.g. in Figure 1 the operation gear_ratio () of Powertrain_coordina or- is called by Gearshift panelRl . To specify exactly which operation is called the association can be itemised by a constraint. This constraint specifies which operations are called. As shown in Figure 1 a communication is always directed from a realisation class to an interface class resulting in a reasonable encapsulation and a high degree of information hiding.

The notation elements presented before are now used to map the structure of Figure 3 to an corresponding CARTRONIC'"- UML-Model. Figure 9 displays the entire UML model referring to this example (only the communicating components are mapped to UML) .

Therefore in the composition model of Figure 7 the communication relationships have to be added, i.e. the orders, requests and inquiries of the function structure depicted in Figure 3 have to be modelled using the association relationship itemised with constraints. A communication according to the structuring concept can only be realised with those target components which are visible for the source component and thus are existent. In case of an access to the service of a target component the source component is not interested in the fact whether this service is directly realised by the offering component itself or if a sub-component is responsible for the realisation. The target component which is refined has to propagate the services to the sub-components which take over the services from the superior component. This aspect is realised by the delegation mechanism of composition relationship.

The UML model in Figure 9 is a structural view of the functionality and can be utilised as a domain model of the system with respect to the functional requirements. Although all components and communications are modelled the behaviour is not specified, i.e. the sequences, repetitions, timing marks and restraints are not addressed.

For automotive applications it is essential to meet real time requirements to ensure the safety and reliability of the vehicle. Therefore the dynamic aspects have to be taken into account already in early developing steps. So the structuring concept CAR-TRONIC^® and the software developing process which up to now consider structural modelling as described above is extended to model behavioural aspects.

Besides numerous continuous and discrete control units also event orientated sequences, repetitions, sampling, priority management tasks, etc. can be found in automotive electronic systems. In the following the modelling of these dynamic aspects in the analysis phase are discussed using the example introduced before dealing with a simplified gearshift process at an abstract level.

Although all the components and communications relationships necessary for the simplified gearshift process are stated in Figure 3 more specification are necessary to implement the function into a control unit . For example it is necessary to specify the sequence and the repetition of the communication links. Furthermore time restriction have to be met to ensure a reliable and comfortable gear switching. These specifications can be modelled using behavioural diagrams of the UML (see Booch, G. , J. Ru baugh and I. Jacobson, 1999, The Unified Modelling Language User Guide, Addison-Wesley, Reading/Massachusetts, U.S.A.). E.g. UML state or sequence diagram on the same formalisation level as the static aspects discussed before.

Figure 10 illustrates behaviour of the Powertrain_coordina.- torRl by a state diagram with respect to a simplified gearshift process. Each possible state is indicated by a rectangle where the name of the state is indicated above and the actions which are executed during this state indicated below a horizontal line. The transitions between the stages are indicated by arrows .

After the initialisation the state control unit remains in the state no_shifting until the present gear_state and the gear_ratio demanded by the Gearshift_panel differ. Therefore the Powertrain_coordinator inquires about the present grear_state at the component Transmission . When a difference occurs a gear_switch is initialised by a transition to the torgue_adaptation state. After the engine output torque is changed to torque_eo the order clutch_action is performed i.e. the clutch is disengaged. This results in a reduction of the clutch output torque torgue_co. If this torque is approximately zero, a state transition disengage_clutch to gear_shifting takes place. Right now the actual gear shift ( shift_gear) is done. If the gear is posi tive_engaged another state transition { engage_gear) happens. In this state torqrue_jbui!d-up the engine output torque is adapted to torςrue_eo and the clutch is engaged again. If the clutch output torque torque_co is equal to the output of the engine torqrue_eo the gearshift process is finished and the no_shifting state is reached again. On each further request of the gearshift panel the described process is performed again. A final state is not specified since in principle the state flow can be interrupted arbitrary by shutting of the engine. Therefore on starting the engine an initialisation process takes place which leads to the no_shifting state. To model the behaviour of the interactions between the CAR- TRONIC^* components the sequence diagram can be used. Figure 11 displays the sequence diagram of a simplified gearshift process. On the horizontal axis objects of the interacting UML classes which are involved in the gearshift process are arranged. On the negative vertical axis the time is indicated. In contrast to the state diagram the chronological sequence of the actions is specified by a sequence of operation calls. So the method gear_state of the object . - TransmissionRl is called by : Power tr in_coordina ori?! . This is indicated by the horizontal arrow 1. The rectangles along the time vertical axis indicate which objects have the focus of action. (Due to tool restrictions the sequence diagram of Figure 11 partly deviates from the standard UML notation accordingly to Booch, G., J. Rumbaugh and I. Jacobson, 1999, The Unified Modelling Language User Guide, Addison-Wesley,

Reading/Massachusetts, U.S.A.).

Once more conditions can be specified in which cases method calls are executed. So the method torgue_eo indicated by arrow 3 is only called if the gear_ratio and the gear_state differ.

Further more UML provides a graphic representation of time marks e.g. for time constraints in sequence diagrams. E.g. in Figure the maximum time interval between the actual gear shift (a) and the positive engagement (b) of the gear is Indicated by the time constraint h - a < 300 s .

These examples show that the UML provides a graphical notation which is able to specify the dynamic aspects of a system and therefore can be used to model requirements to ensure that these requirements are taken into account already during the analysis and the design stage of the software development process. So it is possible to trace these requirements throughout the system development process in general.

The described invention concerns a method and device to design a domain model for control systems in vehicles with respect of the functional requirements. The present document illustrates a model of the object-based structuring concept CARTRONIC^® transferred into the Unified Modelling Language (UML) . The UML is used as a link between the system analysis with respect to functionality and the analysis phase of an object-oriented software development process. Based on an example the elements of the structuring concept which are divided into structuring objects called components as well as orders (with response) , inquiries (with notice) , and re- quests defined as the communication relations are introduced together with the most essential structuring rules. Rules for mapping these elements to UML were presented, which permit the modelling of the function structure in UML. Each CAR- TRONIC^* component is modelled by an UML class and an inter-face. The hierarchy of the structure is realised by UML compositions. The modelling of the communication relations order, inquiry and request are UML operations within classes. They are specified by the stereotypes <<Order>>, <<Request>> and <<Inquiry>>. UML associations between classes ensure that operations are known by the caller. In addition to these structural description also behavioural aspects were discussed. For a simplified gearshift process the modelling of the internal dynamic behaviour of classes as well as the external behaviour, i.e. the communication between classes, are presented. Exemplarily a description of this process by a state and a sequence diagram respect ively were given.