Abstract:
A method operates an onboard power supply system in a motor vehicle. The onboard power supply system has a master controller and a slave controller, in which the master controller communicates with the slave controller via a subsidiary bus system and a further onboard power supply system component via a main bus system. Present requests are received in the slave controller and in response to the present requests, performing one of: putting the slave controller into an operating mode and switching the master controller to a transmission mode, in which the master controller coordinates communication between the slave controller and the onboard power supply system component; or putting the slave controller into a sleep mode and switching the master controller to an undertaking mode, in which the master controller responds to queries from the onboard power supply system component to the slave controller.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation, under 35 U.S.C. §120, of copending international application No. PCT/EP2011/006020, filed Dec. 1, 2011, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2010 053 803.5, filed Dec. 8, 2010; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a method for operating an onboard power supply system in a motor vehicle, having a master controller and a slave controller, and also to a bus system operating on the basis of the method. 
         [0003]    Within a motor vehicle, a large number of controllers are used, each of which is usually connected to at least one associated actuator and/or sensor. The relevant controller controls the actuator and evaluates the sensor data delivered, with the control being effected using the sensor data for example. Frequently, however, the control is affected on the basis of requests which are retrieved from a further controller. This requires the controllers to be connected by a data line. 
         [0004]    In order to reduce the cabling within the motor vehicle, the controllers are normally connected by a main bus system, for example CAN bus system. In this case, there is a central data line to which a number of controllers are connected. The data line is used to transmit messages. By indicating an addressee or a group of addressees for the message, there is the assurance that the respectively intended controller reacts to the message. 
         [0005]    Usually, a plurality of controllers is combined to form a subsystem, for example door controllers in the motor vehicle. Since the subgroups are normally of homogeneous design in comparison with the whole onboard power supply system, it is possible to use within the subsystem a bus system which, although it does not have the bandwidth and flexibility of the main bus system, is cheaper to produce. One of the controllers in the subsystem then frequently undertakes the control of the subsidiary bus system. The controller is called the master controller. 
         [0006]    Published, European patent application EP 0 829 786 A2 discloses an interconnection of a master controller with at least one further controller, wherein the master controller undertakes the communication with further components of the onboard power supply system. To save power, the master controller puts all of the controllers in the subsystem into a quiescent-current consumption state as soon as there are no present requests to the subsystem. The whole subsystem is put back into a normal consumption state following a request to one of the controllers. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention is based on the object of specifying an energy-efficient method for operating an onboard power supply system and also an energy-efficient bus system. 
         [0008]    Accordingly, a master controller and a slave controller communicate with one another via a subsidiary bus system. The master controller communicates with a further onboard power supply system component of an onboard power supply system in a motor vehicle via a main bus system. If there is a present request to the slave controller, the latter is put into an operating mode and the master controller switches to a transmission mode, in which the master controller coordinates the communication between the slave controller and the onboard power supply system component. 
         [0009]    The present request to the slave controller is a signal from a sensor that is connected to the slave controller or a function request to an actuator that is connected to the slave controller, for example. The function request comes from the sensor, the master controller or the onboard power supply system component, for example. If the function request comes from the onboard power supply system component, the request is first of all sent to the master controller, which forwards the request to the slave controller. In particular, the master controller translates the request, which is formulated using the protocol used within the main bus system, into a request that is compliant with the protocol used within the subsidiary bus system if a different protocol is used within the subsidiary bus system than in the main bus system. An acknowledgment from the slave controller to the onboard power supply system component or the signal from the sensor is first of all sent to the master controller, which forwards the message to the onboard power supply system component in compliance with the main bus system. 
         [0010]    In the operating mode, the slave controller is capable of handling a request that is made to it immediately so long as there are no further requests being handled by it at present, and if the slave controller is configured to handle the request. 
         [0011]    If there are no present requests to the slave controller, the slave controller is put into a sleep mode. By way of example, this is accomplished by virtue of the master controller sending a special command or the slave controller registering that there are no requests and automatically switching to sleep mode. In sleep mode, the slave controller has a lower power consumption than in operating mode. By way of example, functions and/or peripheral modules of the slave controller, such as a flash memory, are at least to some extent disconnected in sleep mode, and/or the clock frequency of a processor which the slave controller contains is lowered, or the processor is disconnected completely. 
         [0012]    By way of example, such power saving measures mean that the slave controller is not able to handle a request made to it immediately, since this first of all requires the supply of power to the whole slave controller to be restored and particularly the clock frequency to be raised, for example. As soon as the slave controller is in sleep mode, the master controller switches to an undertaking mode. 
         [0013]    If the onboard power supply system component sends to the slave controller a query which is not a present request to the slave controller while the latter is in sleep mode, the master controller responds to the query and leaves the slave controller in the sleep mode. In particular, the master controller does not forward the query to the slave controller. By way of example, the query is a query concerning the position of the actuator associated with the slave controller. Expediently, the slave controller sends all of the status information from the sensors and actuators associated with the slave controller to the master controller before the latter switches to the sleep mode. 
         [0014]    The method allows the slave controller to be left in the power-saving sleep mode over a comparatively large period of time. In this case, the onboard power supply system component receives responses to queries to the slave controller in a shorter period of time than if the master controller has no undertaking mode, since the slave controller does not need to be woken and the coordination of the communication by the master controller is dispensed with. 
         [0015]    Fittingly, during communication with the onboard power supply system component, the master controller that has been switched to the undertaking mode simulates the slave controller being in the operating mode. In other words, the onboard power supply system component cannot distinguish whether the response to a query to the slave controller comes from the master controller or from the slave controller itself. It is thus possible, in an already existing onboard power supply system, for just a subgroup of controllers to be operated with the method without having to make adjustments to the onboard power supply system component or to further modules of the onboard power supply system. 
         [0016]    By way of example, the slave controller has an input without wakeup capability. An input without wakeup capability denotes an input to which a component, such as a sensor, is connected, the component not being able to terminate the sleep mode of the slave controller, that is to say not being able to put the slave controller into the operating mode. 
         [0017]    Advantageously, after it has been in the sleep mode for a particular period of time, the slave controller polls the input without wakeup capability in order to determine whether there is a present request. This ensures that the slave controller handles all requests to itself. Fittingly, the slave controller repeats the polling whenever the period of time has elapsed for as long as the slave controller is in sleep mode, and for as long as there is no request on the input without wakeup capability. By way of example, the period of time is between 5 ms and 15 ms and particularly 10 ms. This allows energy-efficient operation of the slave controller, with requests thereto being handled without exception. 
         [0018]    Expediently, the master controller switches to the sleep mode as soon as there is no present request to the master controller. By way of example, a present request to the master controller is a signal from a sensor connected to the master controller or a function request to an actuator connected to the master controller. In addition, such a request is particularly coordinating the communication between the slave controller and the onboard power supply system component and also responding to the queries to the slave controller. 
         [0019]    Switching the master controller to the sleep mode allows a further reduction in current consumption to be achieved. By way of example, in the sleep mode, functions and/or peripheral modules of the master controller, such as a flash memory, are at least to some extent disconnected. In particular, the clock frequency of the master controller is reduced in the sleep mode in comparison with transmission mode. The power consumption of the master controller is essentially proportional to the clock frequency, which is why reduction is effective power saving. The clock frequency is particularly reduced to zero. 
         [0020]    In addition, in the undertaking mode, for example, the clock frequency of the master controller is lower than in the transmission mode, since no communication takes place via the subsidiary bus system and hence no computation capacity is required for coordinating the communication of the slave controller. 
         [0021]    By way of example, the master controller and/or the slave controller at least to some extent undertake tasks from a door controller in the motor vehicle. Typical tasks of a door controller are controlling and monitoring a door lock, a window lifter, lighting for a door, a rearview mirror or a seat arranged adjacent to the door, for example. 
         [0022]    The bus system of an onboard power supply system in a motor vehicle, which bus system operates on the basis of the method according to the invention, has a main bus system, a subsidiary bus system, a master controller and also at least one slave controller. 
         [0023]    In one preferred embodiment, the main bus system is a CAN bus system or a Flexray bus system. The subsidiary bus system is particularly a Lin bus system. Expediently, the main bus system is a CAN bus system and the subsidiary bus system is a Lin bus system, since these are in comparatively widespread use in automotive construction and there is no need for special adjustment of the cables for the, in particular, already existing, onboard power supply system or further controllers. 
         [0024]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0025]    Although the invention is illustrated and described herein as embodied in a method for operating an electrical system of a motor vehicle and a bus system operating in accordance with the method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0026]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0027]    The single FIGURE of the drawing schematically shows an onboard power supply system in a motor vehicle, which onboard power supply system operates on the basis of the method according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Referring now to the single FIGURE of the drawing in detail, there is shown an onboard power supply system  1  in a motor vehicle having an onboard power supply system component  2  and a master controller  3  which communicate with one another via a main bus system  4 . By way of example, the main bus system  4  is a CAN bus system and the onboard power supply system component  2  is a combined controller. In particular, the master controller  3  is a door controller and, by way of example, uses an actuator  5  to control lighting for a driver&#39;s door of the motor vehicle and an electric window opener that is provided in the driver&#39;s door and also uses an actuator  6  to control a lock that is integrated in the driver&#39;s door. The master controller  3  has a sensor  7  and a sensor  8  connected to it, the latter sensor monitoring the status of the lock, or opening of the driver&#39;s door. 
         [0029]    Connected to the master controller  3 , which has a transmission mode, an undertaking mode and a sleep mode, via a subsidiary bus system  10 , which is particularly a LIN bus system, is a slave controller  12 , which has an operating mode and a sleep mode. The slave controller  12  is associated with a further door of the motor vehicle. In particular the slave controller  12  controls a lock that is integrated in the door and also an electric window lifter associated with the door and lighting for the door. The lighting and the lock are controlled by an actuator  13  and by an actuator  14 , respectively, which are each connected to the slave controller  12 . A sensor  18  is connected to the slave controller  12  at an input  16  without wakeup capability which checks the status of the lock. A sensor  22  is connected to the slave controller  12  at a connection  20  with wakeup capability which monitors the opening of the door. 
         [0030]    Activities which are controlled by the slave controller  12 , and also sensor data which are captured and processed by the slave controller  12 , and also the communication via the subsidiary bus system  10  that relates to the slave controller  12 , are called present requests to the slave controller  12 . The processing of the present requests to the slave controller  12  takes place in the operating mode of the slave controller  12 . This means that, without exception, all of the functions and components of the slave controller  12  that are necessary for processing the present requests are activated and supplied with power, the components and functions being configured such that time-saving processing is assured. 
         [0031]    As soon as there are no present requests to the slave controller  12 , the master controller  3  sends a sleep request to the slave controller  12 , whereupon the slave controller  12  sends the present status information from the sensors  18 ,  22  that are connected to the slave controller  12  and also from the actuators  13 ,  14  to the master controller  3  via the subsidiary bus system  10 . The slave controller  12  then switches to the sleep mode, while the master controller  3  switches to the undertaking mode. 
         [0032]    In the sleep mode, functions and peripheral modules, such as a flash memory, of the slave controller  12  are disconnected and a main processor that the slave controller  12  contains is disconnected or at least the clock frequency thereof is lowered. The use of this approach means that the slave controller  12  consumes less power in the sleep mode than in the operating mode. 
         [0033]    The slave controller  12  is put into operating mode again by a wakeup or activity request that is sent via the subsidiary bus system  10  or by a sensor value from the sensor  22  that is connected to the input  20  with the wakeup capability on the slave controller  12 , for example. In order to check whether there is a present request to the slave controller  12  on the sensor  18  that is connected to the input  22  without wakeup capability on the slave controller  12 , the slave controller  12  automatically polls the status of the sensor  18 . If the status of the sensor  18  has altered, the slave controller  12  changes to operating mode and communicates this to the master controller  3 . If there is no alteration, the slave controller  12  remains in sleep mode. Whenever the period of time has elapsed, the slave controller  12  repeats the polling. This check on the sensor  18  takes place every 10 ms, for example. 
         [0034]    If the slave controller  12  is in the sleep mode and the master controller  3  is in the undertaking mode and if there are also no present queries to the master controller  3 , the master controller  3  switches to the sleep mode. Activities which are controlled by the master controller  3 , and also sensor data which are captured and processed by the master controller  3 , and also the communication via the subsidiary bus system  10  and the communication via the main bus system  4  that relates to the master controller  3  or to the slave controller  12 , are called present requests to the master controller  3 . 
         [0035]    In the sleep mode, functions and peripheral modules, such as a flash memory, of the master controller  3  are disconnected and the clock frequency of a main processor that the master controller  3  contains is reduced. The use of this approach means that the master controller  3  consumes less power in the sleep mode than in the transmission or undertaking mode. 
         [0036]    When the onboard power supply system component  2  polls to determine whether the door associated with the slave controller  12  is open or closed, the master controller  3  terminates the sleep mode and changes to the undertaking mode. Since the query is not a present request to the slave controller  12 , the master controller  3  does not forward the query to the slave controller  12 , but rather leaves the latter in the sleep mode. The master controller  3  sends to the onboard power supply system component  2  the status of the door opening sensor  22 , which the slave controller  12  communicated before the slave controller  12  changed to the sleep mode. In this case, the master controller  3  signs the response using the identifier of the slave controller  12  such that the onboard power supply system component  2  cannot distinguish whether the slave controller  12  is in operating mode or in sleep mode. Subsequent to the response being sent, the master controller  3  switches to the sleep mode again. 
         [0037]    Since no communication takes place via the subsidiary bus system  10  when the master controller  3  is in undertaking mode, it is not necessary for functions and peripheral modules of the master controller  3  which are responsible for the communication to be supplied with power. Therefore, these functions and modules are disconnected in undertaking mode, for example, and optionally the clock frequency of the main processor that the master controller  3  contains is reduced in comparison with transmission mode. 
         [0038]    When the onboard power supply system component  2  sends the cue for the two doors controlled by the master controller  3  and the slave controller  12  to be unlocked, the master controller  3  switches to transmission mode, since the cue is also a present request to the slave controller  12 . The master controller  3  uses the actuator  6  to unlock the lock integrated in the driver&#39;s door and checks execution by means of the sensor  7 . Optionally, the master controller  3  sends confirmation of the execution to the onboard power supply system component  2  via the main bus system  4 . 
         [0039]    In addition, the master controller  3  reformulates the cue from the onboard power supply system component  2 , which is formulated in compliance with the main bus system  4 , into a cue to the slave controller  12  which is compliant with the subsidiary bus system  10 , and sends the latter cue and also optionally the wakeup request to the slave controller  12 . On the basis of the cues, the slave controller  12  changes to the operating mode and operates the actuator  14 , which unlocks the door that is associated with the slave controller  12 . The slave controller  12  uses the sensor  18  to check whether the lock is unlocked. When the door has been unlocked, the slave controller  12  sends confirmation of the unlocking to the onboard power supply system component  2 . For this, the slave controller  12  sends the confirmation to the master controller  3  via the subsidiary bus system  10 . The master controller  3  reformulates the confirmation in compliance with the main bus system  4  and forwards it to the onboard power supply system component  2 . 
         [0040]    Next, the master controller  3  sends the sleep request to the slave controller  12 , with the slave controller  12  in turn first of all transmitting to the master controller  3  the status of the sensors  18 ,  22  connected thereto and of the actuators  13 ,  14  before it switches to the sleep mode and the master controller  3  switches to the undertaking mode. If there is no present request to the master controller  3 , the latter likewise switches to sleep mode. 
         [0041]    When the door associated with the slave controller  12  is opened, the sensor  22  registers this and wakes up the slave controller  12 . The slave controller  12  activates the lighting for the door, for example, by means of the actuator  13  and sends the status of the sensor  22  to the master controller  3  and communicates that the slave controller  12  has activated the actuator  13 . The master controller  3  switches to transmission mode. 
         [0042]    By way of example, the master controller  3  activates the lighting for the driver&#39;s door, which is associated with the master controller  3 , by the actuator  5  and sends information to the onboard power supply system component  2  to the effect that the door which is associated with the slave controller  12  has been opened and that the lighting for both doors has been activated. As soon as the door is closed, the slave controller  12  sends information about this to the master controller  3 . 
         [0043]    Subsequent to a prescribed period of time, for example after 5 s, the master controller  3  terminates the lighting for the driver&#39;s door and sends information to the slave controller  12  to the effect that it likewise needs to terminate the lighting. In addition, the master controller  3  puts the slave controller  12  into sleep mode when there are no further requests to the slave controller  12 , the slave controller  12  in turn communicating the status of the sensors  18 ,  22  associated with the slave controller  12  and of the actuators  13 ,  14  to the master controller  3  before the slave controller switches to the sleep mode and the master controller  3  switches to undertaking mode. 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           1  Onboard power supply system 
           2  Onboard power supply system component 
           3  Master controller 
           4  Main bus system 
           5  Actuator 
           6  Actuator 
           7  Sensor 
           8  Sensor 
           10  Subsidiary bus system 
           12  Slave controller 
           13  Actuator 
           14  Actuator 
           16  Input without wakeup capability 
           18  Sensor 
           20  Input with wakeup capability 
           22  Sensor