Patent Publication Number: US-2021174615-A1

Title: Driving assistance method and driving assistance device

Description:
TECHNICAL FIELD 
     The present invention relates to a driving assistance method and a driving assistance device. 
     BACKGROUND ART 
     A technique is known that calls a driver&#39;s attention to information on malfunctions when caused in a vehicle (Patent Literature 1). The technique disclosed in Patent Literature 1 notifies the driver of the information on malfunctions with regard to a rotation rate of an engine, a remaining amount of fuel, or a temperature of a coolant in the engine. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2015-38894 
     SUMMARY OF INVENTION 
     Technical Problem 
     It is preferable to notify the driver of the information having a higher priority when several malfunctions are caused simultaneously in the vehicle. Patent Literature 1 does not mention the priority of the information, which needs to be dealt with. 
     To solve the conventional problem described above, the present invention provides a driving assistance method and a driving assistance device capable of notifying a driver of information having a higher priority when several malfunctions are caused in a vehicle. 
     Technical Solution 
     A driving assistance method according to a first aspect of the present invention detects a plurality of malfunctions in devices mounted on a vehicle, and selects candidates for a plurality of actions urged on a driver in accordance with the detected plural malfunctions. The driving assistance method chooses a candidate having a higher priority as an action to be urged on the driver from the candidates for the plural actions, and informs the driver of the chosen action so as to be urged on the driver. 
     Advantageous Effects 
     The present invention can notify the driver of the information having a higher priority when several malfunctions are caused in the vehicle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a driving assistance device according to a first embodiment of the present invention. 
         FIG. 2  is a diagram showing examples of actions urged on a driver. 
         FIG. 3  is a diagram showing another example of the actions urged on the driver. 
         FIG. 4A  is a diagram showing examples of traveling restriction states presented to the driver. 
         FIG. 4B  is a diagram showing other examples of the traveling restriction states presented to the driver. 
         FIG. 5  is a flowchart showing an example of operation of the driving assistance device according to the first embodiment of the present invention. 
         FIG. 6  is a schematic configuration diagram of a driving assistance device according to a second embodiment of the present invention. 
         FIG. 7  is a diagram showing examples of actions urged on the driver and traveling restriction states presented to the driver. 
         FIG. 8  is a diagram showing other examples of the actions urged on the driver. 
         FIG. 9  is a diagram illustrating a margin to be set according to the second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments according to the present invention will be described with reference to the drawings. The same elements illustrated with reference to the drawings are indicated by the same reference numerals, and overlapping explanations are not made below. 
     First Embodiment 
     An example of a configuration of a driving assistance device according to a first embodiment is described below with reference to  FIG. 1 . The driving assistance device informs a driver of an action to be urged, depending on a plurality of malfunctions caused in devices mounted on a vehicle. Examples of devices mounted on the vehicle include a generator  10 , a battery  11 , an engine  12 , a drive motor  13 , and auxiliary equipment  14 , as shown in  FIG. 1 . The devices mounted on the vehicle are not limited to these elements, and may further include a radiator and a transmission. 
     As shown in  FIG. 1 , the driving assistance device includes a controller  20 , a speaker  40 , and a display  41 . As used in the first embodiment, the vehicle refers to an automobile that the driver rides on unless otherwise specified. 
     The generator  10  receives power from the engine  12  to charge the battery  11 . The battery  11  supplies electricity to the drive motor  13 . The drive motor  13  drives the wheels with the electricity received from the battery  11 . The drive motor  13  also charges the battery  11  with regenerated electricity. The auxiliary equipment  14  includes an electric motor for driving a compressor of an air conditioner, and a head light, for example. The battery  11  may be any kind of battery, and may be a lithium ion battery. The generator  10 , the battery  11 , the engine  12 , the drive motor  13 , and the auxiliary equipment  14  are herein collectively referred to simply as the generator  10  and the like as necessary for brevity. 
     The controller  20  is connected to the generator  10  and the like, and detects malfunctions in the generator  10  and the like to inform the driver of an action to be urged through the speaker  40  or the display  41 . The way of connection between the controller  20  and the generator  10  and the like may be, but not necessarily, a controller area network (CAN). The controller  20  is a general-purpose microcomputer including a central processing unit (CPU), a memory, and an input-output unit. A computer program is installed on the microcomputer so as to function as the driving assistance device. The microcomputer functions as a plurality of information processing circuits included in the driving assistance device when the computer program is executed. While the present embodiment is illustrated with the case in which the software is installed to fabricate the information processing circuits included in the driving assistance device, dedicated hardware for executing each information processing as described below can be prepared to compose the information processing circuits. The respective information processing circuits may be composed of individual hardware. 
     The controller  20  includes, as the respective information processing circuits, a malfunction detection unit  21 , a traveling state detection unit  23 , a traveling restriction detection unit  25 , a candidate selection unit  27 , a priority determination unit  29 , and an information unit  31 . 
     The malfunction detection unit  21  detects a plurality of malfunctions caused in the generator  10  and the like based on pieces of information acquired from the generator  10  and the like. The malfunction detection unit  21  outputs the information on the respective detected malfunctions to the traveling state detection unit  23 , the traveling restriction detection unit  25 , and the candidate selection unit  27 . The malfunction detection unit  21  may be a sensor for detecting the malfunctions in the generator  10  and the like. Various kinds of malfunctions can be caused in the generator  10 , the battery  11 , the engine  12 , the drive motor  13 , and the auxiliary equipment  14 . Examples of malfunctions caused in the generator  10  include a malfunction of a temperature sensor, a malfunction of a resolver, or a malfunction of a main circuit element. 
     The traveling state detection unit  23  detects a traveling state of the vehicle. In particular, the traveling state detection unit  23  detects the traveling state of the vehicle based on pieces of information acquired with a velocity sensor (not shown), for example. The traveling state includes a state in which the vehicle is traveling and a state in which the vehicle is stopping. The traveling state may include a state of a shift lever. For example, the traveling state includes a state in which the shift lever is set in the parking gear, and a state in which the shift lever is set in the drive gear. The traveling state detection unit  23  outputs the detected traveling state to the candidate selection unit  27 . 
     The traveling restriction detection unit  25  detects a traveling restriction of the vehicle or calculates a restriction value of the traveling restriction in accordance with the plural malfunctions detected by the malfunction detection unit  21 . For example, the traveling restriction of the vehicle is a restriction on a maximum speed and a maximum drive force (such as a maximum starting acceleration) of the vehicle, or refers to a state in which the vehicle cannot start up next. Examples of restriction parameters upon the execution of the restriction include a maximum drive power and a maximum drive torque. Specific explanations of the traveling restriction will be made below. The traveling restriction detection unit  25  outputs the detected traveling restriction to the candidate selection unit  27 . 
     The candidate selection unit  27  (first selection circuit) selects a plurality of candidates for actions to be urged on the driver in accordance with the plural malfunctions detected by the malfunction detection unit  21 . 
     The priority determination unit  29  (second selection circuit) chooses a candidate having a higher priority as an action to be urged on the driver from the plural candidates selected by the candidate selection unit  27 , in accordance with the pieces of the information output from the malfunction detection unit  21 , the traveling state detection unit  23 , and the traveling restriction detection unit  25 . 
     The information unit  31  (information circuit) informs the driver of the action chosen by the priority determination unit  29 . The information unit  31  may inform the driver of the action with a voice through the speaker  40  or with an image displayed on the display  41 . The display  41  may be, but not necessarily, a liquid crystal display installed in a meter panel or a liquid crystal display used for a car navigation device. 
     The action to be urged on the driver is described below with reference to  FIG. 2 . The action to be urged on the driver described in the first embodiment is an action presumed to be appropriate for the driver to take when malfunctions are caused in the devices (the generator  10  and the like) mounted on the vehicle. 
     When a malfunction A is presumed to be caused in the generator  10 , for example, an action “Please have the vehicle serviced at the dealer” can be presented so as to be urged on the driver. The information unit  31  displays an image  60  shown in  FIG. 2  on the display  41  to inform the driver of the action “Please have the vehicle serviced at the dealer” so as to be urged on the driver. The information unit  31  may inform the driver of the action “Please have the vehicle serviced at the dealer” with a voice through the speaker  40 . The voice information may be presented either once or repeated a predetermined number of times. 
     When a malfunction B, which is different from the malfunction A, is presumed to be caused in the battery  11 , an action “Please make a stop safely” can be presented so as to be urged on the driver. The information unit  31  displays an image  61  shown in  FIG. 2  on the display  41  to inform the driver of the action “Please make a stop safely” so as to be urged on the driver. The information unit  31  may inform the driver of the action “Please make a stop safely” with a voice through the speaker  40 . 
     As described above, the information unit  31  informs the driver of the action to be urged depending on the malfunction caused in the generator  10  or the like, so as to enable the driver to take an appropriate action. 
     A plurality of malfunctions may be simultaneously caused in the generator  10  and the like. For example, when the malfunction A is presumed to be caused in the generator  10 , and the malfunction B is presumed to be caused in the battery  11 , a plurality of actions to be urged on the driver, such as “Please have the vehicle serviced at the dealer” and “Please make a stop safely” as described above, can be presented to the driver. According to the first embodiment, when plural malfunctions are caused in the generator  10  and the like, the candidate selection unit  27  selects candidates for a plurality of actions to be urged on the driver based on the plural malfunctions caused. The candidates for the plural actions selected by the candidate selection unit  27  are herein the two actions of “Please have the vehicle serviced at the dealer” and “Please make a stop safely”. The priority determination unit  29  chooses the candidate having a higher priority as the action to be urged on the driver from the plural actions selected by the candidate selection unit  27 . 
     The order of the priority according to the first embodiment is determined according to at least one of the contents of the respective malfunctions, the traveling state, and the traveling restriction. The order of the priority may be determined by a combination of any of the contents of the plural malfunctions, the traveling state, and the traveling restriction. 
     The priority based only on the contents of the respective malfunctions is described below. For example, the priority determination unit  29  determines that the action based on the malfunction B has a higher priority than the action based on the malfunction A. In particular, when the action “Please have the vehicle serviced at the dealer” and the action “Please make a stop safely” are selected as the candidates for the actions to be urged on the driver, the priority determination unit  29  determines that the action “Please make a stop safely” has a higher priority than the action “Please have the vehicle serviced at the dealer”. The priority determination unit  29  then chooses the action “Please make a stop safely” as the action to be urged on the driver. 
     The order of the priority can be preliminarily determined depending on the importance or urgency of the contents of the respective malfunctions. For example, a malfunction in a 12V-power supply system may be set to have a higher priority than malfunctions in the other devices. 
     The information unit  31  informs the driver of the action chosen by the priority determination unit  29 . The driving assistance device according to the first embodiment thus can choose the candidate with the higher priority as the action to be urged on the driver only based on the contents of the respective malfunctions, when the plural malfunctions are caused in the devices (the generator  10  and the like) mounted on the vehicle, and when the candidates for the plural actions such as the images  60  and  61  as shown in  FIG. 2  are selected. The driving assistance device then informs the driver of the chosen action so as to enable the driver to take an appropriate action. 
     The information unit  31  may indicate an image for calling the driver&#39;s attention, as illustrated with an image  80  shown in  FIG. 2 , when displaying the action urged on the driver on the display  41 . The information unit  31  displays the image  60  indicating the action urged on the driver together with the image  80  for calling the driver&#39;s attention on the display  41 , so as to allow the driver to immediately recognize the occurrence of a malfunction in the vehicle. The information unit  31  may display the image  80  in a lit-up state on the display  41  when the priority of the action is relatively low. This enables the driver to immediately recognize the occurrence of a malfunction in the vehicle. The information unit  31  may display an image for calling the driver&#39;s attention in a blinking state, as illustrated with the image  81  in  FIG. 2 , when the priority of the action is relatively high. This enables the driver to immediately recognize the action with the higher priority. The images  80  and  81  may be used upon the traveling restriction. As described above, since the traveling restriction is the restriction on the maximum speed and the maximum drive force of the vehicle, for example, the information unit  31  may switch the lighting state of the images  80  and  81  depending on the maximum speed and the maximum drive force. For example, when the maximum speed and the maximum drive force are each a predetermined value or greater, the information unit  31  may display the image  80  in the lit-up state on the display  41 , as shown in  FIG. 2 . When the maximum speed and the maximum drive force are each smaller than the predetermined value, the information unit  31  may display the image  81  in the blinking state on the display  41 , as shown in  FIG. 2 . The images  80  and  81  have the same functions in the following explanations from  FIG. 3 , and overlapping explanations may be omitted below. 
     Next, the traveling restriction of the vehicle is described below. 
     The traveling restriction detection unit  25  calculates the restriction value of the traveling restriction in accordance with the plural malfunctions detected by the malfunction detection unit  21 . As used in the first embodiment, the information on the malfunction caused in each device detected by the malfunction detection unit  21  includes a restriction value of the corresponding device. The restriction value of the corresponding device is the maximum torque that the drive motor  13  can output, for example. 
     The traveling restriction detection unit  25  calculates the maximum speed and the maximum drive force of the vehicle as the restriction value of the traveling restriction in accordance with the restriction value of each device. The priority determination unit  29  chooses the candidate with the higher priority as the action to be urged on the driver in accordance with the maximum speed and the maximum drive force calculated by the traveling restriction detection unit  25 . 
     As in the case described above, when the malfunction A is caused in the generator  10 , and the malfunction B is caused in the battery  11 , the candidate selection unit  27  selects the candidates for the plural actions to be urged on the driver based on the plural malfunctions caused. The candidates for the plural actions to be urged on the driver are herein the two actions of “Please have the vehicle serviced at the dealer” and “Please make a stop safely”. 
     The traveling restriction detection unit  25  first calculates the maximum speed and the maximum drive force derived from the malfunction A. The traveling restriction detection unit  25  also calculates the maximum speed and the maximum drive force derived from the malfunction B. The calculation order may, be inverted. The priority determination unit  29  chooses, as the candidate with the higher priority, the action corresponding to the malfunction having a lower maximum speed and a lower maximum drive force than the other malfunction calculated by the traveling restriction determination unit  25 . For example, when the maximum speed and the maximum drive force derived from the malfunction B are smaller than the maximum speed and the maximum drive force derived from the malfunction A, the priority determination unit  29  chooses the action “Please make a stop safely” as the action to be urged on the driver. The priority determination unit  29  thus can choose the candidate with the higher priority as the action to be urged on the driver only based on the traveling restriction. 
     According to the first embodiment, the plural actions to be urged on the driver include at least an action regarding parking, an action regarding stopping, and an action regarding servicing. The action regarding stopping corresponds to the action “Please make a stop safely” described above. The action regarding servicing corresponds to the action “Please have the vehicle serviced at the dealer” described above. The action regarding parking is an action “Please put the parking brake on”, as shown in  FIG. 3 . According to the first embodiment, the priority is lower for the action regarding servicing than for the action regarding parking and the action regarding stopping. The action regarding stopping is informed when the vehicle is traveling, while the action regarding parking is informed when the vehicle is stopping. The more specific explanations are as follows. As used in the first embodiment, the stop of the vehicle refers to a state in which the speed of the vehicle is zero, and the shift lever is set in the parking gear. 
     As in the case described above, when the malfunction A is caused in the generator  10 , and the malfunction B is caused in the battery  11 , the candidate selection unit  27  selects the candidates for the plural actions to be urged on the driver based on the plural malfunctions caused. The candidates for the plural actions to be urged on the driver are herein the three actions of “Please have the vehicle serviced at the dealer”, “Please make a stop safely”, and “Please put the parking brake on”. The priority determination unit  29  chooses the candidate with the higher priority as the action to be urged on the driver from the candidates for the three actions selected by the candidate selection unit  27 . First, the priority determination unit  29  determines that the priority is higher for the action “Please make a stop safely” and the action “Please put the parking brake on” than for the action “Please have the vehicle serviced at the dealer”. The priority determination unit  29  chooses the action “Please make a stop safely” when the vehicle is traveling, and chooses the action “Please put the parking brake on” when the vehicle is stopping. The priority determination unit  29  thus can choose the candidate with the higher priority as the action to be urged on the driver only based on the traveling state. The information unit  31  may inform the driver of the action “Please put the parking brake on” with a voice, or may display an image  62  shown in  FIG. 3  on the display  41 . The information unit  31  may display the image  81  for calling the driver&#39;s attention in a lit-up state when the image  62  is displayed on the display  41 . 
     Next, traveling restriction states are described below with reference to  FIG. 4A  and  FIG. 4B . The traveling restriction detection unit  25  detects a plurality of traveling restriction states in accordance with the plural malfunctions detected by the malfunction detection unit  21 . Examples of traveling restriction states detected by the traveling restriction detection unit  25  include a state “under traveling restrictions” and a state “unable to start up next”, as indicated by images  63  and  64  shown in  FIG. 4 . As used in the first embodiment, the state “under traveling restrictions” refers to a state in which the vehicle&#39;s traveling is restricted, and the state “unable to start up next” refers to a state in which the vehicle cannot start up next. While the present embodiment uses the different terms for the traveling restriction and the traveling restriction states for illustration purposes, the term of the traveling restriction encompasses the traveling restriction states. 
     The priority determination unit  29  chooses a candidate having a higher priority as a traveling restriction state to be presented to the driver, from the candidates for the traveling restriction states selected by the traveling restriction determination unit  25 . 
     As in the case described above, when the malfunction A is caused in the generator  10 , and the malfunction B is caused in the battery  11 , the traveling restriction state derived from the malfunction A caused in the generator  10  is presumed to correspond to the state “unable to start up next”, and the traveling restriction state derived from the malfunction B caused in the battery  11  is presumed to correspond to the state “under traveling restrictions”. The candidates for the plural traveling restriction states selected by the candidate selection unit  27  are the two states “under traveling restrictions” and “unable to start up next”. The priority of the respective traveling restriction states is preliminarily determined. For example, when the state “under traveling restrictions” is set to have a higher priority than the state “unable to start up next”, the priority determination unit  29  determines that the priority is higher for the traveling restriction state derived from the malfunction B than for the traveling restriction state derived from the malfunction A. The priority determination unit  29  chooses the state “under traveling restrictions” as the traveling restriction state to be presented to the driver. The information unit  31  then informs the driver of the traveling restriction state chosen by the priority determination unit  29 . The information unit  31  may inform the driver of the state with the image  63  displayed on the display  41 , or may inform the driver of the state while providing the voice stating “Traveling is being restricted”. 
     The information unit  31  may inform the driver of both the traveling restriction state and the action to be urged on the driver, as illustrated with images  65  and  66  shown in  FIG. 4B . When the candidate selection unit  27  selects the plural traveling restriction states and the plural actions to be urged on the driver, the priority determination unit  29  can choose the traveling restriction state with the higher priority and the action with the higher priority. The following is a presumed case in which the plural traveling restriction states to be selected are the state “under traveling restrictions” and the state “unable to start up next”, and the state “under traveling restrictions” has a higher priority than the state “unable to start up next”. The following is also a presumed case in which the candidates for the actions to be selected are the action “Please have the vehicle serviced at the dealer” and the action “Please make a stop safely”, and the action “Please make a stop safely” has a higher priority than the action “Please have the vehicle serviced at the dealer”. While the image  65  and the image  66  shown in  FIG. 4B  are the options to choose, the information unit  31  displays, on the display  41 , the image  65  having a higher priority than the image  66 . The information unit  31  thus can inform the driver of both the traveling restriction state and the action urged on the driver. The information unit  31  may inform the driver while alternately presenting the phrase “Traveling is being restricted” and the phrase “Please make a stop safely” with a voice. 
     The information unit  31  may inform the driver only of the traveling restriction state, as shown in  FIG. 4A , without the action to be urged on the driver. 
     The priority determination unit  29  can choose the candidate for the action to be urged on the driver having a higher priority only in accordance with the traveling restriction state. For example, as in the case described above, when the traveling restriction state derived from the malfunction A is the state “unable to start up next”, the action “Please have the vehicle serviced at the dealer” is chosen to be urged on the driver. When the traveling restriction state derived from the malfunction B is the state “under traveling restrictions”, the action “Please make a stop safely” is chosen to be urged on the driver. As described above, the action “Please make a stop safely” has a higher priority than the action “Please have the vehicle serviced at the dealer”, so that the priority determination unit  29  can choose the action “Please make a stop safely” to be urged on the driver. The priority determination unit  29  thus can choose the action with the higher priority to be urged on the driver only based on the traveling restriction state. 
     Next, an example of operation of the driving assistance device according to the first embodiment is described below with reference to  FIG. 5 . 
     In step S 101 , the malfunction detection unit  21  detects a malfunction in the generator  10  or the like. When the malfunction detection unit  21  detects plural malfunctions, the process proceeds to step S 102 , and the traveling restriction detection unit  25  detects traveling restriction states of the vehicle based on the plural malfunctions detected by the malfunction detection unit  21 . When the malfunction detection unit  21  does not detect more than one malfunction in step S 101 , the process is on standby. 
     The process proceeds to step S 103 , and the traveling restriction detection unit  25  detects a traveling restriction based on the plural malfunctions detected by the malfunction detection unit  21 . The process proceeds to step S 104 , and the traveling state detection unit  23  detects a traveling state of the vehicle. The process proceeds to step S 105 , and the candidate selection unit  27  selects candidates for plural actions to be urged on the driver based on the plural malfunctions detected by the malfunction detection unit  21 . The process proceeds to step S 106 , and the priority determination unit  29  chooses a candidate having a higher priority as the action to be urged on the driver from the candidates selected by the candidate selection unit  27 . The priority determination unit  29  chooses the candidate with the higher priority as the action to be urged on the driver according to at least one of the contents of the respective malfunctions, the traveling state, the traveling restriction states, and the traveling restriction. The process proceeds to step S 107 , and the information unit  31  informs the driver of the action chosen by the priority determination unit  29 . 
     Advantageous Effects 
     As described above, the driving assistance device according to the first embodiment can achieve the following advantageous effects. 
     The driving assistance device detects a plurality of malfunctions in the generator  10  and the like mounted on the vehicle, and selects candidates for a plurality of actions to be urged on the driver based on the detected plural malfunctions. The driving assistance device chooses a candidate having a higher priority as the action urged on the driver from the candidates for the plural actions, and informs the driver of the chosen action to be urged. The driving assistance device thus can inform the driver of the information with the higher priority when the plural malfunctions are caused in the vehicle. This enables the driver to take an appropriate action accordingly. 
     The driving assistance device also detects a traveling restriction of the vehicle in accordance with the detected plural malfunctions. The driving assistance device chooses a candidate having a higher priority as the action urged on the driver according to at least one of the contents of the respective malfunctions, the traveling state, and the traveling restriction. The driving assistance device thus can choose the candidate with the higher priority based on a small amount of information. 
     According to the first embodiment, the candidates for the plural actions to be urged on the driver include at least the action regarding parking, the action regarding stopping, and the action regarding servicing. The priority is set to be lower for the action regarding servicing than for the action regarding parking and the action regarding stopping. When the action regarding servicing and the action regarding stopping or parking are selected as the candidates for the plural actions to be urged on the driver, the driving assistance device can inform the driver of the action regarding stopping or parking prior to the action regarding servicing. 
     When the action regarding stopping and the action regarding parking are selected as the candidates for the plural actions to be urged on the driver, the driving assistance device chooses the action regarding stopping when the vehicle is traveling, and chooses the action regarding parking when the vehicle is stopping. The driving assistance device thus can present appropriate information to the driver in accordance with the plural malfunctions and the traveling state. 
     A plurality of traveling restriction states based on the plural malfunctions may be detected. The plural traveling restriction states are herein the state “under traveling restrictions” and the state “unable to start up next”. The driving assistance device then informs the driver of the traveling restriction state having a higher priority. The driving assistance device informs the driver of the state “under traveling restrictions” when the priority is set to be higher for the state “under traveling restrictions” than for the state “unable to start up next”. The driving assistance device thus can inform the driver of both the traveling restriction state with the higher priority and the action with the higher priority. 
     The driving assistance device may inform the driver of the traveling restriction state instead of the action urged on the driver. Informing the driver of both the traveling restriction state with the higher priority and the action with the higher priority may bother the driver, depending on the person. Only informing the driver of the traveling restriction state instead of the action urged on the driver can reduce the driver&#39;s discomfort. 
     The driving assistance device displays the image for presenting the information on the display  41  simultaneously with the image  80  or  81  for calling the driver&#39;s attention, as shown in  FIG. 2 . This enables the driver to immediately recognize the occurrence of a malfunction in the vehicle. The images  80  and  81  shown in  FIG. 2  are used upon the traveling restriction, and the driving assistance device switches between the lit-up state and the blinking state of the images  80  and  81  depending on the traveling restriction (the maximum speed and the maximum drive force). For example, when the maximum speed and the maximum drive force are each a predetermined value or greater, the driving assistance device displays the image  80  in the lit-up state on the display  41  as shown in  FIG. 2 . When the maximum speed and the maximum drive force are each smaller than the predetermined value, the driving assistance device displays the image  81  in the blinking state on the display  41 , as shown in  FIG. 2 . This enables the driver to immediately recognize a degradation. 
     The driving assistance device calculates the restriction value of the traveling restriction based on the plural malfunctions. In particular, the driving assistance device calculates the maximum speed and the maximum drive force of the vehicle as the restriction value of the traveling restriction based on the restriction values of the respective devices (the generator  10  and the like). The driving assistance device then chooses a candidate having a higher priority as the action to be urged on the driver in accordance with the maximum speed and the maximum drive force. The driving assistance device thus can choose the candidate for the action to be urged on the driver with the higher priority only based on the traveling restriction. 
     Second Embodiment 
     A driving assistance device according to a second embodiment is described below with reference to  FIG. 6 . The second embodiment differs from the first embodiment in including an information switch unit  35  and a margin setting unit  33 , instead of the information unit  31 . The same elements as in the first embodiment are indicated by the same reference numerals, and overlapping explanations are not repeated below. The main differences are as follows. 
     The information switch unit  35  alternately informs the driver of a plurality of actions to be urged when the candidates for the plural actions have the same priority. The information switch unit  35  also alternately informs the driver of a plurality of traveling restriction states when the traveling restriction states have the same priority. When the priority determination unit  29  chooses the action regarding parking or the action regarding stopping after choosing the action regarding servicing, the information switch unit  35  immediately informs the driver of the action regarding parking or the action regarding stopping. When the priority determination unit  29  chooses the action regarding servicing after choosing the action regarding parking or the action regarding stopping, the information switch unit  35  informs the driver of the action regarding servicing by use of a margin set by the margin setting unit  33 . 
     The margin setting unit  33  sets a margin for a threshold used when the information switch unit  35  switches the pieces of the information. When the priority determination unit  29  chooses the action regarding servicing after choosing the action regarding parking or the action regarding stopping, the margin setting unit  33  sets the margin for the threshold used when switching to the state of informing the driver of the action regarding servicing. 
     The functions of the information switch unit  35  and the margin setting unit  33  are described in detail below with reference to  FIG. 7  to  FIG. 9 . 
     The following is a presumed case in which the plural malfunctions are caused in the generator  10  and the like, and the plural traveling restriction states detected by the traveling restriction detection unit  25  correspond to the state “under traveling restrictions” and the state “unable to start up next”. When the state “under traveling restrictions” and the state “unable to start up next” have the same priority, the information switch unit  35  alternately displays an image  63  and an image  67  shown in  FIG. 7  on the display  41  to inform the driver of the respective traveling restriction states. The information switch unit  35  may inform the driver while alternately presenting the phrase “Traveling is being restricted” and the state “unable to start up next” with a voice. 
     The following is a presumed case in which the plural malfunctions are caused in the generator  10  and the like, and the candidates for the plural actions to be urged on the driver selected by the candidate selection unit  27  are the action “Please turn the ignition switch off” and the action “Please put the parking brake on”. When the action “Please turn the ignition switch off” and the action “Please put the parking brake on” have the same priority, the information switch unit  35  alternately displays an image  68  and the image  62  shown in  FIG. 7  on the display  41  to inform the driver of the respective actions. The information switch unit  35  may inform the driver while alternately presenting the phrase “Please turn the ignition switch off” and the phrase “Please put the parking brake on” with a voice. 
     When the plural malfunctions are detected in the generator  10  and the like, and the plural actions to be urged on the driver or the plural traveling restriction states to be informed are thus selected, the driving assistance device informs the driver of the action or the traveling restriction state with the higher priority. After the driving assistance device presents the respective information to the driver, still another malfunction can sometimes be detected. 
     For example, when the priority determination unit  29  chooses the action regarding servicing and the state “under traveling restrictions”, an image  69  shown in  FIG. 8  is displayed on the display  41 . The information can be provided with a voice instead of the image  69 . The following is a presumed case in which still another malfunction is detected after the image  69  is displayed on the display  41 , and the candidate selection unit  27  selects the action “Please have the vehicle serviced at the dealer” and the action “Please make a stop safely”. As described above, the priority determination unit  29  chooses the action “Please make a stop safely” as the action urged on the driver. The information switch unit  35  switches from the image  69  to the image  63 , as shown in  FIG. 8 , in accordance with the choice result by the priority determination unit  29 . The information switch unit  35  immediately switches from the image  69  to the image  63  so as to immediately allow the driver to recognize the action with the higher priority. The information switch unit  35  also immediately switches the pieces of the voice information. While the above case is illustrated with the action regarding stopping while stating “Please make a stop safely”, the action to be urged may be the action regarding parking. 
     One or more of the plural malfunctions detected in the generator  10  and the like are sometimes cleared out. The information switch unit  35  then may switch from the image  63  to the image  69 . The specific explanations are as follows. When the priority determination unit  29  chooses the action regarding stopping and the state “under traveling restrictions”, the image  63  shown in  FIG. 8  is displayed on the display  41 . The information, of course, can be presented with a voice, instead of the image  63 . When one or more of the plural malfunctions are presumed to be cleared out after the image  63  is displayed on the display  41 , and the candidate selection unit  27  then selects only the action “Please have the vehicle serviced at the dealer”, the priority determination unit  29  chooses the action “Please have the vehicle serviced at the dealer” to be urged on the driver. The information switch unit  35  then switches from the image  63  to the image  69  shown in  FIG. 8  in accordance with the choice result by the priority determination unit  29 . The information switch unit  35  makes a switch from the image  63  to the image  69  after a predetermined lapse of time. The reason for this is that a frequent switch between the images may cause the driver to feel uncomfortable. The information switch unit  35  also makes a switch between the pieces of the voice information after a predetermined lapse of time. 
     When the state “under traveling restrictions” shown in  FIG. 8  is cleared up, the information switch unit  35  can switch from the image  69  to the image  60 . The information switch unit  35  may switch from the image  69  to the image  60  after a predetermined lapse of time. The pieces of the voice information are switched in the same manner. 
     A threshold for switching the images may be set when the information switch unit  35  switches from the image  63  to the image  69 . The threshold is determined depending on a value obtained such that the plural malfunctions are normalized, for example. As shown in  FIG. 9 , when the value obtained by the normalization of the plural malfunctions exceeds a threshold A, for example, the information switch unit  35  can switch from the image  63  to the image  69 . This threshold A, however, may lead to a frequent switch between the images, as shown in  FIG. 9 . The frequent switch between the images may cause the driver to feel uncomfortable. The margin setting unit  33  then sets a margin for the threshold A so as to use a new threshold B shown in  FIG. 9 . Setting the margin can avoid switching between the images unless the value obtained by the normalization of the plural malfunctions exceeds the threshold B, as shown in  FIG. 9 , so as to reduce the driver&#39;s discomfort. The margin setting unit  33  may set a margin for a threshold used when switching from the image  69  to the image  60  shown in  FIG. 8 . When the margin is set for the threshold used when switching from the image  69  to the image  60  shown in  FIG. 8 , the information switch unit  35  may make a switch from the image  69  to the image  60  after a predetermined lapse of time after the value obtained by the normalization of the plural malfunctions exceeds the threshold obtained after setting the margin. 
     As described above, the driving assistance device according to the second embodiment can achieve the following advantageous effects. 
     The driving assistance device alternately informs the driver of a plurality of actions to be urged on the driver when the candidates for the plural actions have the same priority. The driving assistance device also alternately informs the driver of a plurality of traveling restriction states when the traveling restriction states have the same priority. The driving assistance device thus can present appropriate information to the driver. 
     The driving assistance device, when choosing the action regarding parking or the action regarding stopping after choosing the action regarding servicing, immediately informs the driver of the action regarding parking or the action regarding stopping. The driving assistance device thus can immediately inform the driver of the action having a higher priority. The driving assistance device, when choosing the action regarding servicing after choosing the action regarding parking or the action regarding stopping, informs the driver of the action regarding servicing after a predetermined lapse of time. This decreases the frequency of switching between the images, so as to reduce the driver&#39;s discomfort. 
     The driving assistance device sets a margin for a threshold used when the state in which the vehicle is under traveling restrictions and the state of presenting the action regarding parking or the action regarding stopping are switched to the state in which the vehicle is under traveling restrictions and the state of presenting the action regarding servicing. This decreases the frequency of switching between the images, so as to reduce the driver&#39;s discomfort. 
     The respective functions described in the above embodiments can be implemented in single or plural processing circuits. The respective processing circuits include a programmed processing device, such as a processing device including an electric circuit. The respective processing circuits include an application-specific integrated circuit (ASIC) configured to execute the functions described above or a device including circuit components. 
     While the present invention has been described above by reference to the embodiments, it should be understood that the present invention is not intended to be limited to the descriptions and the drawings composing part of this disclosure. Various alternative embodiments, examples, and technical applications will be apparent to those skilled in the art according to this disclosure. 
     While the first embodiment and the second embodiment have been illustrated with the case in which the plural malfunctions are detected in the plural devices, the present invention may be applied to a case in which the plural malfunctions are detected in a single device. The traveling restriction may include a state of charge (SOC) of the battery  11 . 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  GENERATOR 
               11  BATTERY 
               12  ENGINE 
               13  DRIVE MOTOR 
               14  AUXILIARY EQUIPMENT 
               20  CONTROLLER 
               21  MALFUNCTION DETECTION UNIT 
               23  TRAVELING STATE DETECTION UNIT 
               25  TRAVELING RESTRICTION DETECTION UNIT 
               27  CANDIDATE SELECTION UNIT 
               29  PRIORITY DETERMINATION UNIT 
               31  INFORMATION UNIT 
               33  MARGIN SETTING UNIT 
               35  INFORMATION SWITCH UNIT 
               40  SPEAKER 
               41  DISPLAY 
               60  to  69 ,  80 ,  81  IMAGE