Abstract:
The purpose is to provide a working vehicle such that, when a reverse switch coupler is detached, or when a wire connecting a reverse switch to a control device is disconnected, driving of a PTO shaft can be reliably prevented and reliability of the reverse switch can be improved. In a tractor, a reverse switch includes a normally closed type first contact, and a normally open type second contact that is switched in association with the first contact. When an input voltage from the first contact is higher than a set voltage, and when the input voltage from the first contact is lower than the set voltage and an input voltage from the second contact is equal to or lower than the set voltage, a control device controls the actuator such that the PTO clutch is disconnected.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is the U.S. national stage of application No. PCT/JP2013/083621, filed on Dec. 16, 2013. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2012-274605, filed Dec. 17, 2012, Japanese Application No. 2012-276140, filed Dec. 18, 2012; and Japanese Application No. 2012-276141, filed Dec. 18, 2012, the disclosures of which are also incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a working vehicle in which a working machine is connected to a vehicle body and the working machine is driven via a PTO shaft. 
       BACKGROUND ART 
       [0003]    Conventionally, a working vehicle is known in which a working machine is connected to a vehicle body and the working machine is driven via a PTO shaft. For example, an agricultural tractor described in the Patent Literature 1 is so. 
         [0004]    In the agricultural tractor described in the Patent Literature 1, the working machine (rotary tilling device) is connected to a rear part of the vehicle body and the working machine can be via the PTO shaft. In the agricultural tractor described in the Patent Literature 1, a vehicle operation instrument (forward/rearward traveling switch lever) which is operated so as to make the vehicle body travel rearward is provided. In a basal end part of the vehicle operation instrument, a reverse switch (back switch) detecting the operation of the vehicle operation instrument to the rearward traveling side is provided. In the tractor configured as the above, for preventing drive of the PTO shaft at the time of rearward traveling of the vehicle body, during the operation of the vehicle operation instrument to the rearward traveling side is detected by the reverse switch, in principle, a control device performs control so as not to transmit power from an engine to the PTO shaft. 
         [0005]    The reverse switch has a circuit in which a contact which is normally opened type is arranged and attached to the vehicle body so that when the vehicle operation instrument is operated to the rearward traveling side, the contact is closed, and when the vehicle operation instrument is not operated to the rearward traveling side, the contact is opened. 
       PRIOR ART REFERENCE 
     Patent Literature 
       [0006]    Patent Literature 1: the Japanese Patent Laid Open Gazette 2010-172197 
       DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
       [0007]    However, in the agricultural tractor described in the Patent Literature 1, an operator may remove a coupler of the reverse switch because of trouble that the PTO shaft cannot be drive at the time of rearward traveling of the vehicle body. Disconnection may occur in the circuit of the reverse switch. When such abnormality occurs in the reverse switch, the circuit in which the contact is arranged is held to be opened. However, in the above configuration, whether the reason of the opening state of the circuit is the abnormality of the reverse switch or the operation of the vehicle operation instrument to a forward traveling side (or a neutral position) cannot be distinguished. Accordingly, when such abnormality occurs in the reverse switch, it is difficult to prevent certainly the drive of the PTO shaft. 
         [0008]    In consideration of the above problem, the purpose of the present invention is to prevent drive of a PTO shaft certainly and improve reliability of a reverse switch when a coupler of the reverse switch is removed or when wiring connecting the reverse switch to a control device is disconnected. 
       Means for Solving the Problems  
       [0009]    According to the present invention, a working vehicle includes an actuator switching transmission and interruption of a PTO clutch, and a reverse switch detecting rearward traveling operation. The reverse switch has a first contact which is normally closed type and a second contact which is normally opened type and switched interlockingly with the first contact, and these contacts are connected to a control device so that the first contact is closed and the second contact is opened while rearward traveling operation is performed and the first contact is opened and the second contact is closed while the rearward traveling operation is not performed. When an input voltage from the first contact is higher than a set voltage, or when the input voltage from the first contact is not higher than the set voltage and an input voltage from the second contact is not higher than the set voltage, the control device controls the actuator so as to shift the PTO clutch to an interruption state. 
         [0010]    According to the present invention, the working vehicle according to claim  1 , further includes a PTO switch selecting a transmission state or the interruption state of the PTO clutch, and an overriding switch turned ON so as to enable drive of the PTO shaft at the time of rearward traveling. When the input voltage from the first contact is higher than the set voltage and both the PTO switch and the overriding switch are turned ON, the control device controls the actuator so as to shift the PTO clutch to the transmission state. 
         [0011]    According to the present invention, in the working vehicle according to claim  1  or  2 , when the input voltage from the first contact is not detected to be not higher than the set voltage until a predetermined abnormality detection time from turning ON of a power switch, or when the input voltage from the second contact is not detected to be higher than the set voltage until the predetermined abnormality detection time from turning ON of the power switch, the control device judges that abnormality occurs in the reverse switch, and controls the actuator so as to shift the PTO clutch to the interruption state. 
         [0012]    According to the present invention, in the working vehicle according to claim  3 , when the abnormality is judged to occur in the reverse switch, the power switch is turned OFF once and turned ON again, and after the turning ON of the power switch for the predetermined abnormality detection time, only when the input voltage from the first contact is detected to be not higher than the set voltage and the input voltage from the second contact is detected to be higher than the set voltage, the PTO clutch can be shifted to the transmission state after the predetermined abnormality detection time. 
       Effect of the Invention  
       [0013]    The present invention brings the following effects. 
         [0014]    According to the present invention, when the operation of the vehicle operation instrument to the rearward traveling side is detected, when the coupler of the reverse switch removed, or when the wiring connecting the reverse switch to the control device is broken, the PTO clutch is not shifted to the transmission state. Accordingly, at the time of rearward traveling of the vehicle body, or at the time of abnormality of the reverse switch, the drive of the PTO shaft can be prevented certainly, whereby reliability of the reverse switch can be improved. Safety can be improved. 
         [0015]    According to the present invention, only when the PTO switch is turned ON and the overriding switch is turned ON, the PTO shaft can be driven at the time of rearward traveling of the vehicle body, whereby safety can be improved. 
         [0016]    According to the present invention, when a user drops the reverse switch from the attachment frame or removes the coupler of the reverse switch so as to avoid intentionally detection of the rearward traveling by the reverse switch, the PTO clutch cannot be shifted to the transmission state. Accordingly, when abnormality occurs in the reverse switch, the drive of the PTO shaft can be prevented certainly, whereby reliability of the reverse switch can be improved. 
         [0017]    Concretely, when a user turns the power switch ON while the coupler of the reverse switch is not removed and the reverse switch is dropped from the attachment frame for attachment to the vehicle frame, the detection voltage of the first connection part is held to be higher than the predetermined voltage and the detection voltage of the second connection part is held to be not higher than the predetermined voltage, whereby the PTO clutch is shifted to the interruption state. 
         [0018]    When a user turns the power switch ON while the coupler of the reverse switch is removed, the detection voltage of the second connection part is held to be not higher than the predetermined voltage, whereby the PTO clutch is shifted to the interruption state. 
         [0019]    Accordingly, when abnormality occurs in the reverse switch, the drive of the PTO shaft can be prevented certainly, whereby reliability of the reverse switch can be improved. 
         [0020]    According to the present invention, when abnormality occurs in the reverse switch, a user can be urged to stop the engine once so as to correct the abnormality of the reverse switch. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1  is a left side view of an agricultural tractor. 
           [0022]      FIG. 2  is a block diagram of a control mechanism of the tractor. 
           [0023]      FIGS. 3A-3C  are drawing showing three positions of a mid PTO switch which also serves as an overriding switch.  FIG. 3A  shows a position at which a projection amount is the minimum,  FIG. 3B  shows a position at which the projection amount is in the middle of the minimum and the maximum, and  FIG. 3C  shows a position at which the projection amount is the maximum. 
           [0024]      FIGS. 4A-4B  is a schematic drawing of a reverse switch.  FIG. 4A  shows a state at which a vehicle operation instrument is not operated to a rearward traveling side, and  FIG. 4B  shows a state at which the vehicle operation instrument is operated to the rearward traveling side. 
           [0025]      FIG. 5  is a flow chart of a control flow. 
           [0026]      FIG. 6A  is a drawing of a state at which a coupler of the reverse switch is removed, and  FIG. 6B  is a drawing of a state at which the reverse switch is fallen out from an attachment frame. 
           [0027]      FIG. 7  is a left side view of the agricultural tractor which is equipped with a front working machine. 
           [0028]      FIG. 8  is a flow chart of a control flow. 
           [0029]      FIG. 9  is a flow chart of a control flow. 
           [0030]      FIG. 10  is a flow chart of a control flow. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    Firstly, a first embodiment of an agricultural tractor  1  which is an example of a working vehicle is explained. 
         [0032]    As shown in  FIG. 1 , the tractor  1  is a working vehicle which can transmit power via a PTO shaft to a working machine connected to a vehicle body. Front wheels  3  and rear wheels  4  are arranged respectively at front and rear parts of the vehicle body  2  of the tractor  1 . In the front part of the vehicle body  2 , an engine  5  which is a power source of the tractor  1  is mounted, and the engine  5  is covered by a bonnet  6 . As shown in  FIG. 2 , an engine starting/stopping means  7  is provided in the engine  5  so as to start and stop the engine  5 . Concretely, the engine starting/stopping means  7  is configured by a solenoid, which is an actuator for opening and closing a fuel supply valve provided in a fuel supply passage to the engine  5 , or the like. The engine starting/stopping means  7  is connected electrically to a control device  40 . 
         [0033]    As shown in  FIG. 1 , in the rear part of the vehicle body  2 , an operation part  8  is provided. In the operation part  8 , a steering wheel  9  is provided, and behind the steering wheel  9 , a seat  10  on which a user (operator) sits is provided. Near the steering wheel  9 , a power switch  11 , a mid PTO switch  12 , a rear PTO switch  13 , a boss PTO switch  26 , an overriding switch  14  and the like are provided (see  FIG. 2 ). Below the steering wheel  9 , a vehicle operation instrument  15  (see  FIG. 1 ) and a reverse switch  16  are provided. 
         [0034]    A clutch housing is disposed behind the engine  5 , and a transmission casing  17  is disposed behind the clutch housing. Power of the engine  5  is transmitted via a main clutch housed in the clutch housing and a speed change device housed in the transmission casing  17  to the rear wheels  4 , and transmitted via a four-wheel drive/front wheel acceleration drive switching mechanism to the front wheels  3 . 
         [0035]    In a rear surface of the transmission casing  17 , a rear PTO shaft  21  is provided so as to project rearward. In a bottom of the transmission casing  17 , a mid PTO shaft  22  projecting forward is disposed. The rear PTO shaft  21  transmits the power from the engine  5  to a working machine (not shown) connected to the rear part of the vehicle body  2  such as crushing working machine or a rotary working machine. The mid PTO shaft  22  transmits the power from the engine  5  to the working machine such as a mower working machine  23  for grass cutting provided below a center of the vehicle body  2 . Then, the power from the engine  5  is transmitted via a main driving shaft housed in the clutch housing and the like to the rear PTO shaft  21  and the mid PTO shaft  22 . 
         [0036]    In a middle part of a power transmission route from the main driving shaft to the mid PTO shaft  22 , that is, between the engine  5  and the mid PTO shaft  22 , a mid PTO clutch  24  is arranged (see  FIG. 2 ). The mid PTO clutch  24  is configured by an electromagnetic clutch for example, and transmission and interruption of the power to the mid PTO shaft  22  is switched by a PTO solenoid  25 . Namely, by supplying electric power to the PTO solenoid  25 , the mid PTO clutch  24  is shifted to a transmission state (“engagement”), and by stopping supply of electric power to the PTO solenoid  25 , the mid PTO clutch  24  is shifted to an interruption state (“disengagement”). The mid PTO shaft  22  is an embodiment of a “PTO shaft” according to the present invention, the mid PTO clutch  24  is an embodiment of a “PTO clutch” according to the present invention, and the PTO solenoid  25  is an embodiment of an “actuator” according to the present invention. The PTO solenoid  25  is connected electrically to the control device  40 . 
         [0037]    Similarly, in a middle part of a power transmission route from the main driving shaft to the rear PTO shaft  21 , that is, between the engine  5  and the rear PTO shaft  21 , a rear PTO clutch (not shown) is arranged. 
         [0038]    The “PTO clutch” is not limited to an electromagnetic clutch like this embodiment and may alternatively be a multiplate clutch or a hydraulic clutch for example. The “actuator” is not limited to a solenoid like this embodiment and may alternatively be another electric actuator or the like. 
         [0039]    The power switch  11  is a power switch of the tractor and configured by a key switch or the like. The power switch  11  is connected electrically to the control device  40 . 
         [0040]    The mid PTO switch  12  is an embodiment of a “PTO switch” according to the present invention, and is an operation instrument for selecting artificially one of the transmission state or the interruption state of the mid PTO clutch  24 . The mid PTO switch  12  is connected electrically to the control device  40 . An ON state of the mid PTO switch  12  corresponds to the transmission state (“engagement”) of the mid PTO clutch  24 , and an OFF state of the mid PTO switch  12  corresponds to the interruption state (“disengagement”) of the mid PTO clutch  24 . 
         [0041]    As shown in  FIGS. 3A ,  3 B, and  3 C the mid PTO switch  12  and the overriding switch  14  of this embodiment can be turned ON/OFF with one operation instrument  12   a . A user turns ON the overriding switch  14  for enabling drive of the mid PTO shaft  22  at the time of rearward traveling of the vehicle body  2 . 
         [0042]    Concretely, as shown in  FIGS. 3A-3C , a projection amount of the operation instrument  12   a  of the mid PTO switch  12  and the overriding switch  14  of this embodiment can be switched to three stages (x&lt;y&lt;z). Namely, the operation instrument  12   a  can be switched to three positions. At a position at which the projection amount is the minimum (x) (see  FIG. 3A ), the mid PTO switch  12  is turned OFF and the overriding switch  14  is turned OFF. At a position at which the projection amount is the maximum (z) (see  FIG. 3C ), the mid PTO switch  12  is turned ON and the overriding switch  14  is turned ON. At a position at which the projection amount is a middle between the minimum and the maximum (y) (see  FIG. 3B ), the mid PTO switch  12  is turned ON and the overriding switch  14  is turned OFF. The “overriding switch” according to the present invention may alternatively be provided separately from the mid PTO switch  12  so as to operate the switches separately. 
         [0043]    An overriding lamp  18  is switched on until the overriding switch  14  is turned ON. The overriding lamp  18  is connected electrically to the control device  40 . 
         [0044]    The rear PTO switch  13  is an operation instrument for selecting artificially one of the transmission state or the interruption state of the rear PTO clutch. The rear PTO switch  13  is connected electrically to the control device  40 . An ON state of the rear PTO switch  13  corresponds to the transmission state (“engagement”) of the rear PTO clutch, and an OFF state of the rear PTO switch  13  corresponds to the interruption state (“disengagement”) of the rear PTO clutch. 
         [0045]    The vehicle operation instrument  15  shown in  FIG. 1  is an operation instrument which is operated artificially by an operator at the time of making the vehicle body  2  travel. The vehicle operation instrument  15  of this embodiment is configured by a pedal. In the tractor  1 , the vehicle body  2  can be made travel forward and rearward with the vehicle operation instrument  15 . The vehicle body  2  travels forward by operating the vehicle operation instrument  15  to a forward traveling side, the vehicle body  2  travels rearward by operating the vehicle operation instrument  15  to a rearward traveling side, and the vehicle body  2  is stopped by operating the vehicle operation instrument  15  to a neutral position. The “vehicle operation instrument” is not limited to a member like a pedal and may alternatively be configured by a lever or the like. A potentiometer  38  detecting a rotation angle of the vehicle operation instrument  15  is connected to the vehicle operation instrument  15 . 
         [0046]    The vehicle operation instrument  15  is interlocked via a link mechanism with a plate  19  shown in  FIGS. 4A and 4B . The plate  19  is arranged near an operation projection part  16   a  of the reverse switch  16 . 
         [0047]    The reverse switch  16  detects the rearward traveling operation of the vehicle operation instrument  15 . The reverse switch  16  is explained concretely referring to  FIGS. 4A and 4B . Entirely, the reverse switch  16  is a push-type switch, and inside thereof, a first contact  31  which is normally closed type and a second contact  32  which is normally opened type are provided. The first contact  31  and the second contact  32  are arranged in parallel and switched interlockingly. One of sides (output side) of each of the first contact  31  and the second contact  32  is connected electrically via a coupler  35  to the control device  40  (see  FIG. 2 ). In more detail, one of sides of the first contact  31  is connected to a first connection part  33  of the control device  40 . One of sides of the second contact  32  is connected to a second connection part  34  of the control device  40 . The other side (input side) of each of the first contact  31  and the second contact  32  is connected to a power circuit and applied thereto with a predetermined voltage. The other side may alternatively be connected to a ground. 
         [0048]    The reverse switch  16  is attached to an attachment frame (not shown) to the vehicle body  2 . While being attached to the attachment frame, the operation projection part  16   a  projected from a body part  16   b  of the reverse switch  16  can be pushed in and projected by rotating the plate  19 . Namely, when the vehicle operation instrument  15  is not operated to the rearward traveling side (at the time of forward traveling or neutral), the operation projection part  16   a  of the reverse switch  16  is pushed into the body part  16   b  by the plate  19  so that the first contact  31  is opened and the second contact  32  is closed (see  FIG. 4A ). On the other hand, when the vehicle operation instrument  15  is operated to the rearward traveling side (at the time of rearward traveling), the plate  19  is separated from the operation projection part  16   a  and the operation projection part  16   a  is pushed out by a biasing member  16   c  provided inside the body part  16   b  so that the operation projection part  16   a  is at the state of not pushed into the body part  16   b , whereby the first contact  31  is closed and the second contact  32  is opened (see  FIG. 4B ). The first connection part  33  and the second connection part  34  of the control device  40  can detect voltages applied thereto respectively. 
         [0049]    The control device  40  is mounted on the tractor  1 . The control device  40  controls the engine starting/stopping means  7  and controls the PTO solenoid  25  as the actuator. The control device  40  is connected electrically to the engine starting/stopping means  7 , the PTO solenoid  25 , the overriding lamp  18 , the power switch  11 , the mid PTO switch  12 , the overriding switch  14 , the rear PTO switch  13 , the reverse switch  16  and the potentiometer  38 . 
         [0050]    A control flow  100  executed by the control device  40  is explained referring to  FIG. 5 . As shown in  FIG. 5 , the control flow  100  is configured by steps S 101  to S 115 . 
         [0051]    When the power switch  11  is turned ON and the engine  5  is started, the control device  40  starts the control flow  100  (START). Firstly, the control device  40  judges whether an input voltage from the first contact  31  is not higher than a set voltage or not, that is, a detection voltage of the first connection part  33  is detected to be 0V for example or not until a predetermined abnormality detection time from turning ON of the power switch  11  (step S 101 ). The “predetermined abnormality detection time” may be 20 seconds for example, but not limited thereto and can be set optionally. Until the predetermined abnormality detection time, when the detection voltage of the first connection part  33  is continuously a predetermined voltage (for example, 12V), the control device  40  judges that abnormality occurs in the reverse switch  16 , and controls the engine starting/stopping means  7  so as to hold the engine  5  at a drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 109 ). Namely, the mid PTO clutch  24  is shifted to “disengagement” while the engine  5  is not stopped. 
         [0052]    When it can be detected at least once that the input voltage from the first contact  31  is not higher than the set voltage, that is, the detection voltage of the first connection part  33  is 0V for example (step S 101 , Yes), the control device  40  judges subsequently whether an input voltage from the second contact  32  is not higher than a set voltage or not, that is, a detection voltage of the second connection part  34  is detected to be a predetermined voltage (for example, 12V) or not until the predetermined abnormality detection time from turning ON of the power switch  11  (step S 102 ). Until the predetermined abnormality detection time, when the detection voltage of the second connection part  34  is continuously 0V for example, the control device  40  judges that abnormality occurs in the reverse switch  16 , and controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 109 ). Namely, the mid PTO clutch  24  is shifted to “disengagement” while the engine  5  is not stopped. 
         [0053]    When the abnormality of the reverse switch  16  is not detected until the predetermined abnormality detection time (step S 102 , Yes), the control device  40  subsequently judges whether the vehicle operation instrument  15  is operated to the rearward traveling side or not. Concretely, when the input voltage from the first contact  31  is higher than the set voltage, that is, the detection voltage of the first connection part  33  is the predetermined voltage, the control device  40  judges that the vehicle operation instrument  15  is operated and shifts to the step S 104 . On the other hand, when the input voltage from the first contact  31  is not higher than the set voltage, that is, any voltage is not applied to the first connection part  33 , the control device  40  shifts to the step S 107 . 
         [0054]    When the vehicle operation instrument  15  is operated to the rearward traveling side (step S 103 , Yes), the control device  40  subsequently judges whether the mid PTO switch  12  and the overriding switch  14  are respectively turned ON or not (steps S 104 , S 105 ). When the mid PTO switch  12  is turned OFF (step S 104 , No), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 110 ). Namely, when operation of the vehicle operation instrument  15  to the rearward traveling side is detected, in principle, the mid PTO clutch  24  is shifted to “disengagement” while the engine  5  is not stopped so as to prevent drive of the mid PTO shaft  22  at the time of rearward traveling. 
         [0055]    When the mid PTO switch  12  is turned ON and the overriding switch  14  is turned OFF (step S 105 , No), the control device  40  subsequently judges whether the rear PTO switch  13  is turned OFF or not (step S 106 ). 
         [0056]    When the rear PTO switch  13  is turned ON (step S 106 , No), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 111 ). Namely, it is judged that a user desires to drive the rear PTO shaft  21  at the time of rearward traveling of the vehicle body  2 , and the drive state of the engine  5  is held and the mid PTO clutch  24  is shifted to “disengagement” so as not to drive the mid PTO shaft  22 . 
         [0057]    When the rear PTO switch  13  is turned OFF (step S 106 , Yes), the control device  40  controls the engine starting/stopping means  7  so as to stop the engine  5  and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 112 ). Namely, it is judged to stop the work because the mid PTO switch  12  is turned ON though a user does not desire to drive the rear PTO shaft  21  at the time of rearward traveling of the vehicle body  2 , whereby the engine  5  is stopped. 
         [0058]    When the mid PTO switch  12  is turned ON and the overriding switch  14  is turned ON (step S 105 , Yes), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the transmission state (step S 113 ). Namely, it is judged that a user desires to drive the mid PTO shaft  22  at the time of rearward traveling of the vehicle body  2 , and the drive state of the engine  5  is held and the mid PTO clutch  24  is shifted to “engagement” so as to drive exceptionally the mid PTO shaft  22  at the time of rearward traveling and the overriding lamp  18  is switched on. 
         [0059]    At the step S 107 , the control device  40  judges whether the input voltage from the second contact  32  is higher than the set voltage or not, that is, the detection voltage of the second connection part  34  is the predetermined voltage or not. When the input voltage from the second contact  32  is not higher than the set voltage, that is, when any voltage is not applied to the second connection part  34  (step S 107 , No), the control device  40  judges that the coupler  35  of the reverse switch  16  is removed or wiring connecting the reverse switch  16  to the control device  40  is broken, and controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 114 ). Namely, the mid PTO clutch  24  is shifted to “disengagement” while the engine  5  is not stopped. 
         [0060]    When the input voltage from the second contact  32  is higher than the set voltage, that is, when the detection voltage of the second connection part  34  is the predetermined voltage (for example, 12V) (step S 107 , Yes), the control device  40  judges subsequently whether the mid PTO switch  12  is turned ON or not (step S 108 ). When the mid PTO switch  12  is turned ON (step S 108 , Yes), the control device  40  judges that a user desires to drive the mid PTO shaft  22  at the time of forward traveling of the vehicle body  2 , and controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the transmission state (step S 115 ). On the other hand, when the mid PTO switch  12  is turned OFF (step S 108 , No), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 114 ). 
         [0061]    As explained above, the tractor  1  according to this embodiment has the PTO solenoid  25  switching transmission and interruption of the mid PTO clutch  24  and the reverse switch  16  detecting the rearward traveling operation. The reverse switch  16  has the first contact  31  which is normally closed type and the second contact  32  which is normally opened type and switched interlockingly with the first contact  31 . These contacts are connected to the control device  40  so that the first contact  31  is closed and the second contact  32  is opened while the vehicle operation instrument  15  is operated to the rearward traveling side (see  FIG. 4B ) and the first contact  31  is opened and the second contact  32  is closed while the vehicle operation instrument  15  is not operated to the rearward traveling side (see  FIG. 4B ). When the input voltage from the first contact  31  is higher than the set voltage (see  FIG. 4B ), or when the input voltage from the first contact  31  is not higher than the set voltage and the input voltage from the second contact  32  is not higher than the set voltage (see  FIG. 6A ), the control device  40  controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (see steps S 110  and S 114  in  FIG. 5 ). 
         [0062]    According to the configuration, when the operation of the vehicle operation instrument  15  to the rearward traveling side is detected (see  FIG. 4B ), when the coupler  35  connecting the reverse switch  16  to the control device  40  is removed (see  FIG. 6A ), or when the wiring connecting the reverse switch  16  to the control device  40  is broken, the mid PTO clutch  24  can be shifted to the interruption state (see steps S 110  and S 114  in  FIG. 5 ). Accordingly, at the time of rearward traveling of the vehicle body  2 , or at the time of abnormality of the reverse switch  16 , the drive of the mid PTO shaft  22  can be prevented certainly, whereby reliability of the reverse switch  16  can be improved. Safety can be improved. 
         [0063]    The tractor  1  according to this embodiment further has the mid PTO switch  12  selecting the transmission state or the interruption state of the mid PTO clutch  24 , and the overriding switch  14  turned ON by a user for enabling drive of the mid PTO shaft  22  at the time of rearward traveling. When the input voltage from the first contact  31  is higher than the set voltage and both the mid PTO switch  12  and the overriding switch  14  are turned ON (see  FIG. 3C ), the control device  40  controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the transmission state (see step S 113  in  FIG. 5 ). 
         [0064]    According to the configuration, only when the mid PTO switch  12  is turned ON and the overriding switch  14  is turned ON, the mid PTO shaft  22  can be driven at the time of rearward traveling of the vehicle body  2 , whereby safety can be improved. 
         [0065]    Furthermore, in the tractor  1  according to this embodiment, the mid PTO switch  12  and the overriding switch  14  are configured integrally. According to the configuration, number of parts can be reduced and operation of a user can be simplified. 
         [0066]    In the tractor  1  according to this embodiment, when the input voltage from the first contact  31  is not detected to be not higher than the set voltage until the predetermined abnormality detection time (in this embodiment, 20 seconds) from turning ON of the power switch  11 , or when the input voltage from the second contact  32  is not detected to be higher than the set voltage until the predetermined abnormality detection time from turning ON of the power switch  11 , the control device  40  judges that abnormality occurs in the reverse switch  16 , and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (see step S 109  in  FIG. 5 ). 
         [0067]    According to the configuration, when a user drops the reverse switch  16  from the attachment frame (see  FIG. 6B ) or removes the coupler  35  connecting the reverse switch  16  to the control device  40  (see  FIG. 6A ) so as to avoid intentionally detection of the rearward traveling by the reverse switch  16 , the mid PTO clutch  24  is shifted to the interruption state. Accordingly, when abnormality occurs in the reverse switch  16 , the drive of the mid PTO shaft  22  can be prevented certainly, whereby reliability of the reverse switch  16  can be improved. 
         [0068]    Concretely, when a user turns the power switch  11  ON while the coupler  35  of the reverse switch  16  is not removed and the reverse switch  16  is dropped from the attachment frame (see  FIG. 6B ), for example, the detection voltage of the first connection part  33  is held to be the predetermined voltage and the detection voltage of the second connection part  34  is held to be 0V, whereby the mid PTO clutch  24  is shifted to the interruption state (see step S 109  in  FIG. 5 ). 
         [0069]    When a user turns the power switch  11  ON while the coupler  35  of the reverse switch  16  is removed (see  FIG. 6A ), for example, the detection voltage of the second connection part  34  is held to be 0V(step S 102  in  FIG. 5 , Yes), whereby the mid PTO clutch  24  is shifted to the interruption state (see step S 109  in  FIG. 5 ). 
         [0070]    Accordingly, when abnormality occurs in the reverse switch  16 , the drive of the mid PTO shaft  22  can be prevented certainly, whereby reliability of the reverse switch  16  can be improved. 
         [0071]    In the tractor  1  according to this embodiment, when abnormality is judged to occur in the reverse switch  16 , the power switch  11  is turned OFF once and turned ON again. After the turning ON of the power switch  11  for the predetermined abnormality detection time, only when the input voltage from the first contact  31  is detected to be not higher than the set voltage and the input voltage from the second contact  32  is detected to be higher than the set voltage, the mid PTO clutch  24  can be shifted to the interruption state after the predetermined abnormality detection time. Namely, without turning off once and restarting the power switch  11 , the interruption state of the mid PTO clutch  24  cannot be canceled. 
         [0072]    According to the configuration, when abnormality occurs in the reverse switch  16 , a user can be urged to stop the engine  5  once so as to correct the abnormality of the reverse switch  16 . 
         [0073]    Though the “PTO shaft” is the mid PTO shaft  22  in this embodiment, the present invention is not limited thereto and the “PTO shaft” may alternatively be the rear PTO shaft  21 . The “PTO shaft” may alternatively be a front PTO shaft. 
         [0074]    Though the “working vehicle” is the agricultural tractor  1  in this embodiment, the present invention is not limited thereto and another working vehicle having a PTO shaft such as a construction tractor may alternatively be used. 
         [0075]    Next, a second embodiment of the agricultural tractor  1  which is the example of the working vehicle is explained. 
         [0076]    As shown in  FIG. 1  or  7 , a mid working machine (for example, the mower working machine  23 ) can be attached between the front wheels  3  and the rear wheels  4 , and a front working machine (for example, a snowplow  29 ) can be attached to the front part of the vehicle body  2 . 
         [0077]    As shown in  FIG. 1 , a gearbox  27  is arranged in an upper part of the mower working machine  23 . The mower working machine  23  is connected via a transmission shaft  28  to the mid PTO shaft  22 . By connecting the transmission shaft  28  to the gearbox  27 , the mower working machine  23  is connected to the mid PTO shaft  22 . 
         [0078]    As shown in  FIG. 7 , a gearbox  30  is arranged in a rear part of the snowplow  29 . The snowplow  29  is connected via a shaft (hexagonal shaft)  36  to the mid PTO shaft  22 . By connecting the shaft  36  to the gearbox  30 , the snowplow  29  is connected to the mid PTO shaft  22 . 
         [0079]    The front working machine (the snowplow  29 ) or the mid working machine (the mower working machine  23 ) can be connected alternatively to the mid PTO shaft  22  (the gearbox  27 ). 
         [0080]    As shown in  FIG. 7 , a rotation sensor  37  is provided in a lower part of the vehicle body  2 . The rotation sensor  37  detects whether the front working machine (the snowplow  29 ) is connected to the mid PTO shaft  22  or not. The rotation sensor  37  is arranged so as to be positioned near the shaft  36  when the snowplow  29  is connected via the shaft  36  to the mid PTO shaft  22 . The rotation sensor  37  detects a rotation pulse of the shaft  36  so as to detect rotation of the shaft  36 . The rotation sensor  37  is connected electrically to the control device  40  (see  FIG. 2 ). 
         [0081]    The boss PTO switch  26  is an operation means for selecting artificially states of the mid PTO clutch  24  and the rear PTO clutch to the transmission state or the interruption state. The boss PTO switch  26  is connected electrically to the control device  40 . An ON state of the boss PTO switch  26  corresponds to the transmission state (“engagement”) of the mid PTO clutch  24  and the rear PTO clutch, and an OFF state thereof corresponds to the interruption state (“disengagement”) of the mid PTO clutch  24  and the rear PTO clutch. 
         [0082]    The control device  40  judges whether the front working machine (the snowplow  29 ) is connected to the mid PTO shaft  22  or not based on detection results of the rotation sensor  37 . In detail, in the case in which information that a rotation speed of the shaft  36  is within a predetermined range is received from the rotation sensor  37  for a predetermined period, the control device  40  judges that the front working machine is connected to the mid PTO shaft  22 , and in the other case, the control device  40  judges that the front working machine is not connected to the mid PTO shaft  22 . The predetermined range and the predetermined period are determined suitably in consideration of the minimum rotation speed and the maximum rotation speed of the mid PTO shaft  22  and the like. 
         [0083]    Accordingly, in the tractor  1 , requirements for the control device  40  to judge whether the front working machine is connected to the mid PTO shaft  22  or not are made strict, whereby the control device  40  can judge accurately whether the front working machine is connected to the mid PTO shaft  22  or not. 
         [0084]    The control device  40  judges whether the vehicle operation instrument  15  is operated to the forward traveling side, the rearward traveling side or the neutral position based on detection results of the potentiometer  38 . It may alternatively be configured that a known back switch is provided in the vehicle operation instrument  15  and the control device  40  judges whether the vehicle operation instrument  15  is operated to the rearward traveling side or not based on detection results of the back switch. 
         [0085]    A control flow  200  executed by the control device  40  is explained referring to  FIG. 8 . As shown in  FIG. 8 , the control flow  200  is configured by steps S 201  to S 208 . 
         [0086]    When the power switch  11  is turned ON and the engine  5  is started, the control device  40  starts the control flow  200  (START). 
         [0087]    The control device  40  judges whether the vehicle operation instrument  15  is operated to the rearward traveling side or not (step S 201 ). 
         [0088]    When the vehicle operation instrument  15  is judged to be operated to the rearward traveling side (a signal for making the vehicle body  2  travel rearward (rearward traveling signal of the vehicle body  2 ) is received) (step S 201 , Yes), the control device  40  judges subsequently whether the mid PTO switch  12  is turned ON or not (step S 202 ). 
         [0089]    When the mid PTO switch  12  is turned OFF (step S 202 , No), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 205 ). Namely, when the rearward operation of the vehicle operation instrument  15  is detected (the rearward traveling signal of the vehicle body  2  is received), in principle, the mid PTO clutch  24  is shifted to “disengagement” while the engine  5  is not stopped so as to prevent drive of the mid PTO shaft  22  at the time of rearward traveling. 
         [0090]    When the mid PTO switch  12  is turned ON (step S 202 , Yes), the control device  40  judges whether the front working machine (the snowplow  29 ) is connected to the mid PTO shaft  22  or not (step S 203 ). In detail, the control device  40  judges whether information that the rotation speed of the shaft  36  is within the predetermined range is received from the rotation sensor  37  for the predetermined period or not. 
         [0091]    When the front working machine is judged to be connected to the mid PTO shaft  22  (step S 203 , Yes), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the transmission state (step S 206 ). In this case, regardless of whether the overriding switch  14  is turned ON or OFF, the control device  40  holds the engine  5  at the drive state and holds the mid PTO clutch  24  at the transmission state. Namely, it is judged that a user desires to drive the mid PTO shaft  22  at the time of rearward traveling of the vehicle body  2 , and the drive state of the engine  5  is held and the mid PTO clutch  24  is shifted to “engagement” so as to drive exceptionally the mid PTO shaft  22  at the time of rearward traveling. 
         [0092]    Accordingly, in the tractor  1 , in the case in which the mower working machine  23  is not connected to the mid PTO shaft  22  and the snowplow  29  is connected thereto, when an user operates the vehicle operation instrument  15  to the rearward traveling side while forgetting to turn the overriding switch  14  ON, the engine  5  can be prevented from being stopped and the transmission state of the mid PTO clutch  24  can be maintained. Accordingly, workability can be improved. 
         [0093]    When the front working machine is judged not to be connected to the mid PTO shaft  22  (step S 203 , No), the control device  40  judges whether the overriding switch  14  is turned ON or not (step S 204 ). 
         [0094]    When the overriding switch  14  is turned ON (step S 204 , Yes), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the transmission state (step S 207 ). Namely, it is judged that a user desires to drive the mid PTO shaft  22  at the time of rearward traveling of the vehicle body  2 , and the drive state of the engine  5  is held and the mid PTO clutch  24  is shifted to “engagement” so as to drive exceptionally the mid PTO shaft  22  at the time of rearward traveling and the overriding lamp  18  is switched on. 
         [0095]    When the overriding switch  14  is turned OFF (step S 204 , No), the control device  40  controls the engine starting/stopping means  7  so as to stop the engine  5  and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 208 ). In this case, the control device  40  may alternatively control the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and control the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state. 
         [0096]    In the case in which the vehicle operation instrument  15  is operated to the rearward traveling side of the vehicle body  2  while the engine  5  is driven and the boss PTO switch  26  is turned ON (the mid PTO clutch  24  and the rear PTO clutch are at the transmission state), when the front working machine is judged to be connected to the mid PTO shaft  22  based on the detection results of the rotation sensor  37 , the control device  40  may maintain the drive of the engine  5  and the transmission state of the mid PTO clutch  24  and the rear PTO clutch. 
         [0097]    In the case in which the vehicle operation instrument  15  is operated to the rearward traveling side of the vehicle body  2  while the engine  5  is driven and the boss PTO switch  26  is turned ON (the mid PTO clutch  24  and the rear PTO clutch are at the transmission state), when the front working machine is judged not to be connected to the mid PTO shaft  22  based on the detection results of the rotation sensor  37  and the overriding switch  14  is turned ON, the control device  40  may maintain the drive of the engine  5  and the transmission state of the mid PTO clutch  24  and the rear PTO clutch, and when the overriding switch  14  is turned OFF, the control device  40  may shift the mid PTO clutch  24  and the rear PTO clutch to the interruption state. 
         [0098]    Though the “working vehicle” is the agricultural tractor  1  in this embodiment, the present invention is not limited thereto and another working vehicle which can be equipped with a working machine such as a construction tractor may alternatively be used. 
         [0099]    As the above, the tractor  1  has the mid PTO shaft  22  which can be connected alternatively to the front working machine or the mid working machine, the rotation sensor  37  detecting whether the front working machine is connected to the mid PTO shaft  22  or not, and the control device  40  maintaining the drive of the engine  5  and the transmission state of the mid PTO clutch  24  when the front working machine is judged not to be connected to the mid PTO shaft  22  based on the detection results of the rotation sensor  37  in the case in which the rearward traveling signal of the vehicle body  2  is received (the vehicle operation instrument  15  is operated to the rearward traveling side of the vehicle body  2 ) while the engine  5  is driven and the mid PTO clutch  24  of the mid PTO shaft  22  is at the transmission state. 
         [0100]    Accordingly, when the mid working machine is not connected to the mid PTO shaft  22  and the front working machine is connected thereto, when an user operates the vehicle operation instrument  15  to the rearward traveling side while forgetting to turn the overriding switch  14  ON, the engine  5  can be prevented from being stopped and the transmission state of the mid PTO clutch  24  can be maintained. Accordingly, workability can be improved. 
         [0101]    In the tractor  1 , the front working machine can be connected via the shaft  36  to the mid PTO shaft  22 , the rotation sensor  37  detects the rotation of the shaft  36  connected to the mid PTO shaft  22 , and in the case in which information that the rotation speed of the shaft  36  is within the predetermined range is received from the rotation sensor  37  for the predetermined period, the control device  40  judges that the front working machine is connected to the mid PTO shaft  22 , and in the other case, the control device  40  judges that the front working machine is not connected to the mid PTO shaft  22 . 
         [0102]    Accordingly, the control device  40  can judge accurately whether the front working machine is connected to the mid PTO shaft  22  or not. 
         [0103]    The tractor  1  has the overriding switch  14 , and in the case in which the front working machine is judged not to be connected to the mid PTO shaft  22  based on the detection results of the rotation sensor  37  at the state at which the rearward traveling signal of the vehicle body  2  is received (the vehicle operation instrument  15  is operated to the rearward traveling side of the vehicle body  2 ) while the engine  5  is driven and the mid PTO clutch  24  is at the transmission state, when the overriding switch  14  is turned ON, the control device  40  maintains the drive of the engine  5  and the transmission state of the mid PTO clutch  24 , and when the overriding switch  14  is turned OFF, the control device  40  shifts the mid PTO clutch  24  to the interruption state. 
         [0104]    Accordingly, by turning ON the overriding switch  14 , the vehicle body  2  can travel rearward while the mid working machine is driven. 
         [0105]    Next, a third embodiment of the agricultural tractor  1  which is the example of the working vehicle is explained. 
         [0106]    As shown in  FIG. 1 , the front wheels  3  and the rear wheels  4  are arranged respectively at the front and rear parts of the vehicle body  2  of the tractor  1 . In the front part of the vehicle body  2 , the engine (diesel engine)  5  which is the power source of the tractor  1  is mounted, and the engine  5  is covered by the bonnet  6 . 
         [0107]    As shown in  FIG. 2 , the engine starting/stopping means  7  includes a supply means  39  having a fuel supply valve, a solenoid and an injector. In the supply means  39 , by opening and closing the fuel supply valve, which is provided in the fuel supply passage, by the solenoid, supply (injection) and stop of the supply of fuel from the injector to cylinders of the engine  5  is performed. 
         [0108]    The control device  40  judges whether the vehicle operation instrument  15  is operated to the forward traveling side, the rearward traveling side or the neutral position based on detection results of the potentiometer  38 . It may alternatively be configured that a known back switch is provided in the vehicle operation instrument  15  and the control device  40  judges whether the vehicle operation instrument  15  is operated to the rearward traveling side or not based on detection results of the back switch. 
         [0109]    A control flow  300  executed by the control device  40  is explained referring to  FIG. 9 . As shown in  FIG. 9 , the control flow  300  is configured by steps S 301  to S 308 . 
         [0110]    When the power switch  11  is turned ON and the engine  5  is started, the control device  40  starts the control flow  300  (START). 
         [0111]    The control device  40  judges whether the vehicle operation instrument  15  is operated to the rearward traveling side or not (step S 301 ). 
         [0112]    When the vehicle operation instrument  15  is judged to be operated to the rearward traveling side (a signal for making the vehicle body  2  travel rearward (rearward traveling signal of the vehicle body  2 ) is received) (step S 301 , Yes), the control device  40  judges subsequently whether the mid PTO switch  12  is turned ON or not (step S 302 ). 
         [0113]    When the mid PTO switch  12  is turned OFF (step S 302 , No), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 304 ). Namely, when the rearward operation of the vehicle operation instrument  15  is detected (the rearward traveling signal of the vehicle body  2  is received), in principle, the mid PTO clutch  24  is shifted to “disengagement” while the engine  5  is not stopped so as to prevent drive of the mid PTO shaft  22  at the time of rearward traveling. 
         [0114]    When the mid PTO switch  12  is turned ON (step S 302 , Yes), the control device  40  judges subsequently whether the overriding switch  14  is turned ON or not (S 303 ). 
         [0115]    When the overriding switch  14  is turned ON (step S 303 , Yes), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the transmission state (step S 305 ). Namely, it is judged that a user desires to drive the mid PTO shaft  22  at the time of rearward traveling of the vehicle body  2 , and the drive state of the engine  5  is held and the mid PTO clutch  24  is shifted to “engagement” so as to drive exceptionally the mid PTO shaft  22  at the time of rearward traveling and the overriding lamp  18  is switched on. 
         [0116]    When the overriding switch  14  is turned OFF (step S 303 , No), the control device  40  controls the engine starting/stopping means  7  so as to stop the engine  5 . Namely, the control device  40  operates the solenoid so as to stop supply of fuel to the engine  5  by the supply means  39 . Furthermore, the control device  40  controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the interruption state (step S 306 ). Accordingly, the mid PTO clutch  24  is shifted to the interruption state while the mid PTO switch  12  is turned ON. 
         [0117]    The control device  40  judges whether the vehicle operation instrument  15  is operated to a position other than the rearward traveling side (the neutral position or the forward traveling side) after the stop of supply of fuel to the engine  5  by the supply means  39  (step S 306 ) for a predetermined time T (step S 307 ). 
         [0118]    The predetermined time T is a period in which after the stop of supply of fuel to the engine  5 , the fuel is supplied to the engine  5  driven inertially (the engine  5  not stopped completely) so as to return the engine  5  to the drive state, that is, to restart inhalation, compression, combustion and exhaust processes, and is determined suitably by an experiment or the like. 
         [0119]    When the vehicle operation instrument  15  is operated to the neutral position or the forward traveling side until the predetermined time T (step S 307 , Yes), the control device  40  restarts the supply of fuel to the engine  5  by the supply means  39  until the predetermined time T (step S 308 ). In detail, the fuel supply valve is opened by the solenoid and the supply of fuel from the injector to the cylinders of the engine  5  is restarted. As a result, the engine  5  is returned to the drive state by only the operation of the vehicle operation instrument  15  without the operation of the power switch  11 . 
         [0120]    Accordingly, even if a user makes the vehicle body  2  travel rearward by wrong operation while the mid PTO switch  12  is turned ON and the overriding switch  14  is turned OFF, by operating the vehicle operation instrument  15  so as to shift the vehicle body  2  to the state other than the rearward traveling until the predetermined time T, the engine  5  can be prevented from being stopped so as to continue the work. Accordingly, operability can be improved. 
         [0121]    When the vehicle operation instrument  15  is operated to the neutral position or the forward traveling side until the predetermined time T, that is, the operation of the vehicle operation instrument  15  to the rearward traveling side is continued (step S 307 , No), the control device  40  does not restart the supply of fuel to the engine  5  by the supply means  39 . As a result, the engine  5  is stopped completely (step S 309 ). 
         [0122]    At the step S 306 , when the mid PTO switch  12  is turned ON and the mid PTO clutch  24  is shifted to the interruption state and then a user turns the mid PTO switch  12  OFF and ON in this order, the control device  40  shifts the mid PTO clutch  24  to the transmission state. Until the operation of the mid PTO switch  12  (OFF to ON) is performed, the control device  40  maintains the interruption state of the mid PTO clutch  24 . 
         [0123]    Accordingly, in the tractor  1 , by requiring operation for shifting the mid PTO clutch  24  to the transmission state of a user, wrong operation of the mid working machine by the user can be suppressed. 
         [0124]    A control flow  400  executed by the control device  40  is explained referring to  FIG. 10 . As shown in  FIG. 10 , the control flow  400  is configured by steps S 401  to S 404 . 
         [0125]    When the power switch  11  is turned ON and the engine  5  is started, the mid PTO switch  12  is turned OFF (the mid PTO clutch  24  is shifted to the interruption state), and the vehicle operation instrument  15  is operated to the rearward traveling side (the rearward traveling signal of the vehicle body  2  is received), the control device  40  starts the control flow  400  (START). 
         [0126]    The control device  40  judges whether the mid PTO switch  12  is turned ON or not (step S 401 ). 
         [0127]    When the mid PTO switch  12  is turned ON (step S 401 , Yes), the control device  40  judges whether the overriding switch  14  is turned ON or not (step S 402 ). 
         [0128]    When the overriding switch  14  is turned ON (step S 402 , Yes), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state and controls the PTO solenoid  25  so as to shift the mid PTO clutch  24  to the transmission state (step S 403 ). Namely, it is judged that a user desires to drive the mid PTO shaft  22  at the time of rearward traveling of the vehicle body  2 , and the drive state of the engine  5  is held and the mid PTO clutch  24  is shifted to “engagement” so as to drive exceptionally the mid PTO shaft  22  at the time of rearward traveling and the overriding lamp  18  is switched on. 
         [0129]    When the overriding switch  14  is turned OFF (step S 402 , No), the control device  40  controls the engine starting/stopping means  7  so as to hold the engine  5  at the drive state (continues the supply of fuel to the engine  5 ) and cancels the turning ON operation of the mid PTO switch  12  so as to continue the interruption state of the mid PTO clutch  24  (step S 404 ). Namely, it is judged that a user does not desire to stop the engine  5 , and the mid PTO clutch  24  is shifted to “disengagement” while the drive state of the engine  5  is held. Accordingly, the mid PTO clutch  24  is shifted to “disengagement” while the mid PTO switch  12  is turned ON. 
         [0130]    Accordingly, when the mid PTO switch  12  is turned ON, the overriding switch  14  is turned OFF and the vehicle body  2  travels rearward, even if a user turns the mid PTO switch  12  ON by wrong operation, the engine  5  can be prevented from being stopped so as to continue the work. Accordingly, operability can be improved. 
         [0131]    At the step  404 , in the case in which the mid PTO switch  12  is turned ON and the interruption state of the mid PTO clutch  24 , when a user operates the vehicle operation instrument  15  to the neutral position or the forward traveling side and turns the mid PTO switch  12  OFF and ON in this order, the control device  40  shifts the mid PTO clutch  24  to the transmission state. At this state, by turning the overriding switch  14  ON, the user can make the vehicle body  2  travel rearward while maintaining the transmission state of the mid PTO clutch  24  (while driving the mower working machine  23 ). 
         [0132]    Though the “working vehicle” is the agricultural tractor  1  in this embodiment, the present invention is not limited thereto and another working vehicle which can be equipped with a working machine such as a construction tractor may alternatively be used. 
         [0133]    As the above, the tractor  1  has the mid PTO switch  12  which is turned ON so as to shift the mid PTO clutch  24  to the transmission state and turned OFF so as to shift the mid PTO clutch  24  to the interruption state, the supply means  39  supplying fuel to the engine  5 , the overriding switch  14 , and the control device  40  stopping the supply of fuel to the engine  5  by the supply means  39  when the rearward traveling signal of the vehicle body  2  is received (the vehicle operation instrument  15  is operated so as to make the vehicle body  2  travel rearward) in the case in which the engine  5  is driven, the mid PTO switch  12  is turned ON and the overriding switch  14  is turned OFF and subsequently restarting the supply of fuel to the engine  5  by the supply means  39  when the rearward traveling signal is stopped (the vehicle operation instrument  15  is operated so as to shift the vehicle body  2  from the rearward traveling state to the other state) until the predetermined time T. 
         [0134]    Accordingly, in the case in which the mid PTO switch  12  is turned ON and the overriding switch  14  is turned OFF, when a user makes the vehicle body  2  travel rearward by wrong operation, by operating the vehicle operation instrument  15  so as to shift the vehicle body  2  to the state other than the rearward traveling state until the predetermined time T, the engine  5  can be prevented from being stopped so as to continue the work. Accordingly, operability can be improved. 
         [0135]    In the tractor  1 , in the case in which the engine  5  is driven, the mid PTO switch  12  is turned ON and the overriding switch  14  is turned OFF, when the rearward traveling signal is received (the vehicle operation instrument  15  is operated so as to make the vehicle body  2  travel rearward), the control device  40  shifts the mid PTO clutch  24  to the interruption state while turning the mid PTO switch  12  ON and maintains the interruption state of the mid PTO clutch  24  until the mid PTO switch  12  is turned OFF and ON. 
         [0136]    Accordingly, wrong operation of the mid working machine by the user can be suppressed. 
         [0137]    In the tractor  1 , in the case in which the engine  5  is driven, the mid PTO switch  12  is turned OFF and the overriding switch  14  is turned OFF, when the rearward traveling signal is received (the vehicle operation instrument  15  is operated so as to make the vehicle body  2  travel rearward) and the mid PTO switch  12  is turned ON, the control device  40  maintains the drive of the engine  5  and the interruption state of the mid PTO clutch  24 . 
         [0138]    Accordingly, when the mid PTO switch  12  is turned ON, the overriding switch  14  is turned OFF and the vehicle body  2  travels rearward, even if a user turns the mid PTO switch  12  ON by wrong operation, the engine  5  can be prevented from being stopped so as to continue the work. Accordingly, operability can be improved. 
       INDUSTRIAL APPLICABILITY 
       [0139]    The present invention can be used for a working vehicle such as a tractor.