Abstract:
A method for determining whether an error is present or not in a motor vehicle, a discrete state, in which the motor vehicle is presently in, being ascertained with the aid of a state machine, a decision being made, depending on the ascertained discrete state, whether an error is present or not, whereby the states of the state machine include acceptable states and unacceptable states, then, if the ascertained discrete state is an unacceptable state, the motor vehicle is transferred into an acceptable state.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    The present application claims priority to and the benefit of German patent application no. 10 2015 215 546.3, which was filed in Germany on Aug. 14, 2015, the disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for determining whether an error condition is present or not in a motor vehicle, in particular in the drive system of the motor vehicle. The present invention furthermore relates to a device, in particular a control unit, which is configured to carry out this method. 
       BACKGROUND INFORMATION 
       [0003]    A method for controlling the drive output of a vehicle is discussed in DE 44 38 714 A1, in which a microcomputer is provided to carry out control functions and monitoring functions. At least two levels independent from one another are thereby established in the microcomputer, a first level carrying out the control function and a second level carrying out the monitoring function. 
       SUMMARY OF THE INVENTION 
       [0004]    A continuous monitoring of the torque may be implemented in that an actually set torque in an internal combustion engine is inferred from the fuel injection times with the aid of a back-calculation, and this torque is compared with an intended torque by the driver derived from the gas pedal position. Such a concept is, however, complex, since a change in the control software of the drivetrain or in the application entails a change in the monitoring software. 
         [0005]    Such monitoring is primarily used to secure the safety objective of “preventing unintentional acceleration of the motor vehicle,” which is the single safety objective to be covered in motor vehicles driven exclusively by internal combustion engines. Due to the electrification of the vehicle drivetrains, the drivetrain variance, the number of safety objectives, and thus also has the development complexity of the corresponding monitoring functions strongly increased. This development complexity is often traced back to the limited reusability of existing error mechanisms in new drivetrain variants. 
         [0006]    According to a first aspect, the present invention relates to a method for determining whether an error is present or not in a motor vehicle or in a subsystem of the motor vehicle, in particular the drive system of the motor vehicle, a discrete state, in which the motor vehicle or the subsystem is presently in, being ascertained with the aid of a state machine, a decision being made, depending on the ascertained discrete state, whether an error is present or not, the motor vehicle then being transferred into an acceptable or safe state if the ascertained discrete state is an unacceptable state. This means, that the motor vehicle is controlled in such a way that the discrete state, in which the motor vehicle is in, and which is ascertained in particular after the controlling, is an acceptable or safe state. Thus, the state machine is transferred into a new discrete state which corresponds to an acceptable state. In particular, it may hereby be provided that every state of the state machine is either acceptable or unacceptable. 
         [0007]    The designation “discrete state” is used here in contrast to the term “continuous variable” introduced later. A continuous variable may, during variation between two values, assume arbitrary intermediate values, and is discretized merely for the purposes of its processing in digital technology. Continuous variables are distinguished in that an equality operator, i.e., a comparison whether a first continuous variable is equal to a second continuous variable, makes sense only to a very limited degree because an exact equality of two continuous variables represented in digital technology only occurs if both continuous variables lie close together within the resolution accuracy of the digital representation of the two continuous variables. 
         [0008]    By using the provided method, errors may be identified particularly easily by the presence of an unacceptable state and counter measures may be initiated. 
         [0009]    The provided method has the advantage that it is particularly easily reusable and scalable, i.e., that it may be expanded particularly easily to other motor vehicle topologies, such as, for example, a hybridized drivetrain. By transferring the operating state into an acceptable state, the method is particularly reliable. 
         [0010]    In another aspect, it may be provided that, depending on the ascertained discrete state, a continuous actual operating parameter, which describes an operating state of the motor vehicle, is ascertained or not. Due to this ascertainment, it is possible that additional information is ascertained about the operating state of the motor vehicle, and thus the method is even more reliable. 
         [0011]    Ascertaining the continuous actual operating parameter may be hereby understood in particular that this continuous actual operating parameter is actually used in the provided monitoring method. The mere detection of the continuous actual operating parameter generally proceeds permanently, for example, using a sensor. 
         [0012]    It may be provided in particular that the continuous actual operating parameter is only ascertained at certain states, for example, only when the ascertained discrete state is acceptable. 
         [0013]    The ascertainment of the continuous actual operating parameter may thereby be ascertained with the aid of a characteristic diagram or a mathematical function. Both are methods in which no solver is required for their use. Dispensing with solvers offers a substantial problem solver with regard to modulation capability and scalability. This is due to the fact that the development and calibration of a solver is complex since this must be individually configured for the system of equations to be solved. 
         [0014]    In another aspect, it may be provided that, depending on the ascertained continuous actual operating parameter, a discrete unacceptable state is recommended, into which the state machine is to be transferred. 
         [0015]    This may occur in an embodiment which is particularly easy to implement, in that the ascertained continuous actual operating parameter is compared to an ascertained setpoint operating parameter, and the discrete unacceptable state is recommended depending on the result of this comparison. 
         [0016]    It may then be particularly provided that the state machine is transferred into the recommended discrete unacceptable state, if necessary under the premise that the recommended discrete unacceptable state is checked for plausibility and, depending on the result of this check, the state machine is transferred into the recommended discrete unacceptable state. 
         [0017]    In this way, it is possible in a particularly easy way to expand the monitoring of the operating state of the motor vehicle to continuous variables. From the interplay of the state machine and the use of the continuous actual operating parameters, the result arises that the system is intact or that a defect is present, and this defect has been detected by the presence of an unacceptable state in the state machine, or that the defect has been detected as a function of the continuous actual operating parameter. The error coverage ratio is significantly increased by the latter measure. 
         [0018]    Depending on the ascertained actual operating parameter, the discrete unacceptable state, into which the state machine is to be transferred, is only recommended, thus, it is possible in a particularly easy way to provide a plausibility check of this error detection mechanism. If the state machine is then transferred into the thus recommended unacceptable state, then the monitoring on the basis of the continuous actual operating parameter is integrated in a particularly easy way into the recommended monitoring on the basis of the state machine. 
         [0019]    A method for engine control or a method for brake control, which is monitored using one of the provided methods, is particularly advantageous. 
         [0020]    In additional aspects, the present invention relates to a computer program, which is configured to carry out all steps of one of the methods according to one of the previously mentioned aspects, an electronic storage medium, on which the computer program is stored, and a control unit, which is configured to carry out all steps of one of the methods according to one of the previously mentioned aspects. 
         [0021]    The figures show particularly advantageous specific embodiments of the present invention by way of example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  schematically shows a motor vehicle. 
           [0023]      FIG. 2  shows a structure diagram according to a first aspect of the present invention. 
           [0024]      FIG. 3  shows signal curves according to a second aspect of the present invention. 
           [0025]      FIG. 4  shows a flow chart of the possible sequence of a specific embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows a motor vehicle  97  in which the present invention may be used. The method may, for example, be carried out by a control unit  98 , in particular carried out by a computer program which is stored on a machine-readable storage medium  99  which is contained in control unit  98 . Control unit  98  hereby receives signals from sensors  50  . . .  59  in a known way and controls actuators  60  . . .  69  on the basis of these sensor signals. 
         [0027]      FIG. 2  shows a structure diagram which illustrates how the method according to the present invention may progress according to one aspect of the present invention. State machine  1 , which includes states  10 ,  20 ,  30 , is provided. Depending on the ascertained sensor values of sensors  50  . . .  59 , state transitions are defined, which transfer state machine  1  from the present state, for example, state  20 , into another state, for example, state  10 . These states  10 ,  20 ,  30  are either acceptable or unacceptable. If the present state, for example state  20 , is unacceptable, an error response function  411  is initiated. This causes state  20  to be transferred into another state, for example, into state  10 . 
         [0028]    The quantity of error response functions  411 ,  412 ,  413  is designated as error response block  4 . Likewise, monitoring functions  211 ,  212 ,  213  are provided in a monitoring block  2 , and plausibility check functions  311 ,  312 ,  313  in a plausibility check block  3 . 
         [0029]    State  10  is, for example, an acceptable state. Depending on which state state machine  1  is in, a monitoring function is called up from monitoring block  2 , for example, monitoring function  211 . This function detects a sensor value, for example, and a speed signal, and compares the value of this signal with a threshold value. Depending on this comparison, a plausibility check function  311  is called up, which ascertains whether the result of this comparison is compatible with the fact that the state machine is in state  10 . 
         [0030]    If the result is not compatible with the state, the state machine is transferred into unacceptable state  40 . Thus, because the state machine is then in unacceptable state  40 , error response function  413  is actuated. 
         [0031]      FIG. 3  shows, by way of example, signal curves which lead to an error detection by monitoring block  211 . Signal curves actually ascertained in control unit  98  are represented as dashed lines; states recognized in state machine  1  are represented with a solid line.  FIG. 3 a   ) shows a gear selection;  FIG. 3 b   ) shows a gas pedal position;  FIG. 3 c   ) shows a speed of motor vehicle  97 ;  FIG. 3 d   ) shows a speed of an internal combustion engine of motor vehicle  97 ;  FIG. 3 e   ) shows a torque generated by the internal combustion engine; and  FIG. 3 f   ) shows a signal of an idle speed controller. The discrete state of the motor vehicle recognized in state machine  1  is, in this example, a tuple of substates, which includes these six states as separate dimensions. 
         [0032]    At starting point in time to, the vehicle is standing. The gear selection state signal shown in  FIG. 3 a   ) is in the “park-neutral” state; the gas pedal state signal shown in  FIG. 3 b   ) is in the “gas pedal not actuated” state; the speed state signal shown in  FIG. 3 c   ) is in the “stopped” state; the rpm state signal shown in  FIG. 3 d   ) is in the “idle speed” state; the torque state signal shown in  FIG. 3 e   ) is in the “constant torque” state; and the idle speed controller state signal shown in  FIG. 3 f   ) is in the “ISC active” state. The recognized discrete state of motor vehicle  97  in state machine  1  thus corresponds to the state (“park-neutral,” “gas pedal not actuated,” “stopped,” “idle speed,” “constant torque,” “ISC active”). This state corresponds to state  30  in  FIG. 2 . 
         [0033]    At a point in time t 1 , a gear is engaged and the gear selection state signal ( FIG. 3 a   ) jumps into the “drive” substate, since it has been recognized that the gear selection signal is changed to “1 st  gear.” The gas pedal state signal ( FIG. 3 b   ) remains in the “gas pedal not actuated” substate, since it has been recognized that the gas pedal signal remains at the value “0%.” The speed state signal ( FIG. 3 c   ) jumps to the “in motion” substate, since it has been recognized that the speed signal has exceeded a predefinable minimum speed. The rpm state signal ( FIG. 3 d   ) remains in the “idle speed” substate, since it has been recognized that the rpm signal is not greater than a predefinable minimum rpm. The torque state signal ( FIG. 3 e   ) remains in the “constant torque” substate, since it has been recognized that the torque signal has changed by not more than a predefinable minimum torque change. The idle speed controller state signal ( FIG. 3 f   ) remains in the “ISC active” substate. From point in time t 1 , the recognized discrete state of motor vehicle  97  in state machine  1  thus corresponds to the state (“drive,” “gas pedal not actuated,” “in motion,” “idle speed,” “constant torque,” “ISC active”). This state corresponds to state  10  from  FIG. 2 . In this state, monitoring function  211  is actuated for monitoring the rpm of the internal combustion engine and for monitoring the torque signal. 
         [0034]    At another point in time t 2 , the gear selection state signal ( FIG. 3 a   ), the gas pedal state signal ( FIG. 3 b   ), and the speed state signal ( FIG. 3 c   ) remain unchanged with respect to point in time t 1 . The rpm signal ( FIG. 3 d   ) increases, and monitoring function  211  recognizes that the rpm exceeds the idle speed. Monitoring function  211  therefore recommends to transfer the rpm state signal into the “rpm greater than idle speed” substate, since it has been recognized that the rpm signal is greater than the predefinable minimum rpm. Monitoring function  211  also recommends to transfer the torque state signal into the “increasing torque” state, since an increase of the torque signal has been recognized. Monitoring function  211  also recommends to transfer the idle speed controller state signal ( FIG. 3 f   ) into the “ISC not active” state, since it has been recognized that the idle speed controller signal fell below a predefinable idle speed controller activation degree. Monitoring function  211  thus recommends to transfer the recognized discrete state of motor vehicle  97  in state machine  1  into the state (“drive,” “gas pedal not actuated,” “in motion,” “rpm greater than idle speed,” “increasing torque,” “ISC not active”). 
         [0035]    Plausibility check block  311  permits this transfer. From point in time t 2 , the recognized discrete state of motor vehicle  97  in state machine  1  therefore corresponds to the state (“drive,” “gas pedal not actuated,” “in motion,” “rpm greater than idle speed,” “increasing torque,” “ISC not active”). This state corresponds to state  40  in  FIG. 2 . As a reaction to the state machine transferring into state  40 , error response function  413  is called up, which turns off the internal combustion engine. 
         [0036]    Consequently, state machine  1  recognizes that the motor vehicle has been transferred into a safe state (not shown in  FIG. 2 ), and the method begins again. 
         [0037]      FIG. 4  illustrates the sequence of the method. The method starts in step  1000 . In step  1010 , the state is ascertained, in which motor vehicle  97  is in, and state machine  1  is transferred into this state. 
         [0038]    In subsequent step  1020 , it is checked whether this state is an acceptable state. If this is the case, it branches back to step  1010 , where the state is updated. If this is not the case, step  1030  follows, in which a monitoring function is actuated. A continuous actual operating parameter, for example the rpm of the internal combustion engine, is detected and compared with a setpoint operating parameter, for example, the nominal idle speed. Additional variables may also be detected and compared in parallel. 
         [0039]    Depending on the results of these comparisons, a discrete unacceptable state, into which state machine  1  is to be transferred, is recommended in following step  1040 . 
         [0040]    Step  1050  follows, in which a plausibility check function ascertains whether this recommended state is plausible with the actual state of state machine  1 , for example, whether a transition from the actual state into the recommended state is stored as a possibility in a list in control unit  99 . If this is not the case, the method branches back to step  1010 . 
         [0041]    If, in contrast, this is the case, state machine  1  is transferred into this recommended, discrete, unacceptable state in step  1060 . 
         [0042]    Step  1070  follows, in which an error response function is called up. The method ends here.