Regularized modeling method of the hottest bus bod

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The regular modeling method of bus body control system

1. Preface

the electronic devices and equipment installed on the car body are increasing, such as: electric seats, electric doors and windows, open roof, adjustable steering wheel, air conditioning system, etc; There are also various lights, wipers, electric door locks, defrosters, rearview mirrors, horns, various indicator lights and various digital instruments (tachometer, speedometer, water temperature gauge, fuel gauge), etc. The number of vehicle electronic control systems, sensors, actuators and wires is also increasing. The function of vehicle body control system is to realize the convenient and flexible comprehensive control of various devices on the vehicle body

in the traditional body control system, the wiring harness is used to realize the interconnection and direct control of various electronic devices through point-to-point mode. However, with the increase of devices, the car believes that these two driving modes will still coexist at present. The internal harness is becoming more and more complex, and the available space in the car is becoming smaller and smaller. Moreover, due to the complexity of lines and the increase of failure rate, the manufacturing cost of the car is increased, the difficulty of design and maintenance is also increasing, but the reliability is greatly reduced. How to reform the body control system and solve the above problems has attracted more and more attention from people in the automotive industry at home and abroad

second, bus body control system

the harness in the traditional body control system is not only used to transmit signals, but also realizes the control logic between various devices with the help of the harness and the contacts of relays and switches. Because various devices are scattered in various parts of the car body, the car body control system is more suitable to use distributed control system to build

the new body control system uses a bus to replace the complicated point-to-point harness, and introduces intelligent control nodes combining software and hardware to build the body control system. The method is to connect various devices to multiple intelligent control nodes distributed in the car body. Each intelligent control node is an embedded processing unit with certain computing and storage resources. The intelligent control nodes are connected together through the bus, and the software in the intelligent control node can realize the comprehensive control of various devices, that is, using software logic to replace the hardware logic in the traditional body control system, which has better flexibility and maintainability

can is a bus technology widely used in automobiles. The CAN bus technology is used to build the network platform of the body control system, and the serial structure bus is used to replace the parallel structure harness to realize distributed multiplex transmission, which can easily realize the information interaction and sharing between various components; At the same time, it integrates real-time diagnosis, testing, fault alarm and other functions; And it can directly give the fault location through the information screen, which is convenient for maintenance; Increase or decrease functions at will without affecting the work of other parts. Using CAN bus technology to build the network platform of body control system is the future development direction

but how to design and develop the software of body control system, establish convenient and standardized modeling and design methods and the corresponding development platform are the key problems to be solved

III. modeling and analysis of automata model

the state of the body control system is reflected in the state of various devices. The change of device state is driven by discrete events triggered by user operation and sensor detection, which leads to the dynamic evolution of system state. Body control system is a typical discrete event control system, which is usually modeled by finite automata model. A typical finite automaton is represented as a quintuple

a= (s, e, the national composite center has a 1-BODY manufacturing unit for semi-finished fiber-reinforced injection molding inserts η, Y0, SM) (1)

Where s is the state set, e is the event set, η Is the state transition function, Y0 is the initial state, SM is the termination state set

s is a non empty set, Y0 ∈ s, smas2 The dial pointer has poor sensitivity, and η: S × E→S。 Its meaning is: if e ∈ e, S1 ∈ s, S2 ∈ s, when event E occurs, the state of the system changes from S1 to S2, η Map the product of S and e to s

to model the body control system with the finite automata model, we must first determine the s of the system, and then give the s of the system η。 There are many devices involved in the body control system, and the number of states of devices is also large. If the whole system is modeled directly, the state space s of the system will be very large

assuming that the number of devices is 20, the number of states of each device is 3, and the state of the body control system is determined by the state of all devices, the state of the system is the combination of the states of all devices, and the corresponding number of States is 320, so the state space is very large. Reconsider η It can be expressed in the form of state transition matrix, state transition table or state transition diagram. The three are equivalent and can be converted to each other. Taking the state transition matrix as an example, the current state of the state machine is represented by rows, the next state to be reached is listed, and the intersection of rows and columns represents the trigger event, so the result is 320 × 320 matrix, the state space is even larger

from the above analysis, it can be seen that the finite automata model is used to model the body control system, and the state number of the system has the problem of state combination complexity. In addition, modeling with finite automata, only one operation can be performed at any time in each state of the system, that is, only the sequential system can be described, but there is no concurrent description ability, but there are a large number of concurrent events and concurrent behaviors in the body control system

aiming at the problems existing in the modeling of body control system with finite automata model, the author puts forward a new modeling and design method of body control system - regular description method

the rule-based description method introduces the hierarchical modeling mechanism, decomposes the objects of the system into multiple layers, establishes the tree hierarchical model of the system objects, describes the logical control relationship between the system objects with logical rule expressions, and transmits the control relationship with messages. The control task of the system is divided into several sub tasks, which are distributed to the objects of each layer of the system, so as to effectively reduce the complexity of system control. The message mechanism can be used to deal with concurrent events and behaviors conveniently

fourth, hierarchical modeling mechanism

the body control system is modeled by the rule-based description method. In order to reduce the complexity of system design, the system object is divided into two layers: component and interface. The objects of the system are divided into several subspaces according to the composition relationship. The division of the system follows the principle of "high cohesion and low coupling", so as to effectively reduce the complexity of control. The control task of the system is divided into several sub tasks, which are distributed to the objects of each layer of the system. The high-level object acts as a manager to coordinate the control tasks between the various components of the system; The lower layer is the sensor and actuator, which interact directly with the outside world. The sensor senses the environmental information in real time and submits it to the higher object. The actuator is mainly used to transform the instructions of the controller into actual physical actions and act on the environment. There is a logical control relationship between objects at all levels of the system. The logical control relationship between objects is transmitted through messages. Notification messages are sent from the low level to the high level, and control (command) messages are sent from the high level to the low level

the body control system is composed of multiple components, each of which contains one or more interfaces, forming a tree hierarchical model as shown in Figure 1

among them, the component is the logical abstraction of each device in the system that is relatively independent in function, and the interface is the abstraction of the i/o port of the control unit. For example, the headlights of a car are composed of two left and right headlights, which are always on and off under non fault conditions, so they can be logically defined as a component of "headlights"; The headlamp has normal states such as high beam, low beam and switch, and fault states such as open circuit and short circuit. There are logical control relationships between components and interfaces, including those between components, between components and interfaces, and between interfaces. This logical relationship is described by formal logical rule expressions

v. rule description of logical control relationship

the state of the body control system is determined by the set of the states of all components and interfaces that make up the system. Events cause changes in the state of the system, that is, they lead to changes in the state of components and interfaces. How to change and change the process is determined by the logical control relationship of components and interfaces. The logic control relationship is described by the logic rule expression, and the change of system state is reflected in that the logic control relationship is transmitted between components and interfaces in the form of messages (when the two components involved in the logic control relationship are located in different control units, the control message is transmitted through can), and the state change of corresponding components and interfaces is triggered

logical rule expression, abbreviated as rule expression, is a formal representation of the logical relationship between components and interfaces. Logical rule expressions can be seen as a simplification of ECA rules. An ECA rule can be expressed as

, where e, C and a are the events, conditions and actions of the rule respectively; P is an additional property that describes the behavior or state of a rule

the function of ECA rules is: when rule events occur, the system checks the conditions of the rules in real time or at a specified time, and executes the actions of the rules if they are met

events in the body control system are triggered by user operation or sensor detection, and cause changes in the state of corresponding devices. Therefore, events can also be treated as conditions in the expression, which can simplify the expression

the formal definition of logical rule expression is given as follows by using Backus Naur normal form syntax representation method

definition 1 (logical rule expression)

logical rule expression:: = left piece → right piece

left piece:: = factor | factor & left piece

right piece:: = factor | factor & right piece

that is, the general form of logical rule expression is

factor & factor → factor & factor

the part to the left of the symbol "→" in the expression is called the left piece of logical rule expression, The right part is called the right part of the logical rule expression. Both the left part and the right part are composed of factors. When there are more than one factor, the middle is connected with "&", indicating "logical and". The left factor is the condition factor and the right factor is the response factor

definition 1 gives the syntax form of the logical rule expression. The semantics are: if the left part is true, that is, all the condition factors in the left part are true, that is, if the conditions are met, the right part is executed, that is, each response factor is executed

Backus Naur normal form syntax is used to express the factor, and the formal definition is given as follows

definition 2 (factor)

factor:: = (factor name = factor value)

factor is the basic unit of logical rule expression. Factor is composed of factor name and factor value, which represent component/interface and its status value respectively

the control behavior in the body control system and the logical control relationship between various components can be easily described by logical rule expressions

for example, for the following logic control relationship

if the dimmer switch is in the "low beam" gear

the light switch is in the "headlamp" gear

the ignition switch is in the "on" state

then the car headlamp is on the low beam

the logic control relationship can be formally expressed as the regular form

(dimmer switch = low beam) & (light switch = headlamp)&

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