Abstract:
An interlock circuit for a working vehicle having a vehicle body, a working implement attached to the vehicle body, a clutch mechanism for connecting and disconnecting power to the working implement, and a shifting device for determining a traveling direction of the vehicle body. The interlock circuit has a check function to check a backward operational run in which the vehicle body travels backward with the clutch mechanism engaged, and a release function to permit a backward operational run by canceling the check function. The check function checks the backward operational run based on a signal indicating an on/off state of the clutch mechanism and a signal indicating a traveling direction of the vehicle body determined by the shifting device. The release function maintains the check function off continuously by operating a release switch when the clutch mechanism is engaged, and the signal indicating a traveling direction of the vehicle body indicates forward or neutral.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an interlock circuit for a working vehicle having a vehicle body, a working implement attached to the vehicle body, a clutch mechanism switchable between an engaged state for transmitting power to the working implement and a disengaged state for breaking power transmission to the working implement, and a shifting device for determining a traveling direction of the vehicle body. More particularly, the invention relates to an interlock circuit having a check function to check a backward operational run in which the vehicle body travels backward with the clutch mechanism engaged, and a release function to permit a backward operational run by canceling the check function. 
     2. Description of the Related Art 
     An interlock circuit for a working vehicle having the above construction is shown in U.S. Pat. No. 5,994,857, for example. This prior art construction, basically, checks a PTO (power takeoff) operation when the vehicle travels backward. Particularly when, with the PTO operated, a switch is moved to a momentary on position before the vehicle travels backward, the vehicle is allowed to travel backward (release state). Even when the switch is moved from the momentary on position, the PTO operation is continued as long as the vehicle travels backward. The release state is canceled to stop the PTO operation when the PTO is turned off or the vehicle is reversed to travel forward. 
     In the above prior art construction, the vehicle is allowed to travel backward with the PTO operated only when the vehicle is caused to travel backward by consciously operating switches in a state of operating the PTO. A backward run with the PTO operated is prevented when the operator makes an operational error or fails to pay good attention, to call for a careful operation. Take an operation with a mower unit for example. When cutting grass around trees or adjacent a fence having a complicated shape, the grass may be cut efficiently by reversing the vehicle back and forth repeatedly with the mower unit operated. In carrying out an operation in such a mode, the mower unit needs to be operated continuously. With the above prior construction, a switch must be operated before driving the vehicle backward, and besides, the PTO operation is stopped when the vehicle is driven forward. Where an operation is performed by driving the vehicle back and forth repeatedly, the switch must be operated each time the vehicle is placed in reverse, which is troublesome. From this viewpoint, the above prior construction has room for improvement. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide an interlock circuit for a working vehicle, which allows an operation to be carried out by backing the vehicle as necessary, without imposing a troublesome task on the operator. 
     The above object is fulfilled, according to this invention, by an interlock circuit comprising a check function circuit for performing a check function, the check function circuit being formed of a circuit portion for checking a backward operational run based on a signal indicating a state of the clutch mechanism and a signal indicating a traveling direction of the vehicle body determined by the shifting device; and a release function circuit for performing a release function, the a release function circuit being formed of a circuit portion having a release switch operable to cancel the check function continuously when the signal indicating a state of the clutch mechanism indicates that the clutch mechanism is engaged, and the signal indicating a traveling direction of the vehicle body indicates forward or neutral. 
     With this construction, when the operator attempts a backward operation run by driving the vehicle body backward with the clutch mechanism engaged, the check function circuit checks the backward operational run based on the signal indicating the state of the clutch mechanism and the signal indicating the traveling direction of the vehicle body. The check function of the check function circuit is canceled only by operating the release switch with the clutch mechanism engaged, and the traveling direction of the vehicle body set to forward or neutral. When the check function of the check function circuit is canceled as above, the check function remains off. Thus, the working implement may be driven continuously when an operation is carried out by reversing the vehicle body backward and forward repeatedly. It is no longer necessary to operate the switch prior to each backward operational run as in the prior art. That is, the interlock circuit according to this invention allows a backward operational run to be performed easily and simply by operating the release switch. 
     In one preferred embodiment of this invention, the release function circuit is constructed to cancel the release function in favor of the check function when the clutch mechanism is disengaged while the release function is in operation. With this construction, the check function of the check function circuit is reinstated by disengaging the clutch mechanism while the check function is continuously released. Thereafter, the vehicle body cannot be driven backward with the working implement in operation. That is, the check function of the check function circuit is reinstated by a deliberate operation to disengage the clutch mechanism while the check function is canceled. This is rational from the operational point of view. 
     In another preferred embodiment of this invention, the interlock circuit further comprises an indicator lamp unit tuned off when the check function is in operation, and lit or blinked when the check function is canceled by the release function circuit. In this construction, the indicator lamp is lit or blinked only when the check function is off. The operator can readily recognize that a backward operational run is possible. 
     As further preferred embodiment, the interlock circuit may further comprise a prohibition circuit unit for prohibiting the release function circuit from canceling the check function. Since the cancellation of the check function by the release function circuit can be prohibited, as necessary, the release switch may be made ineffective to permit a backward operational run. 
     Other features and advantages of this invention will be apparent from the following description of the embodiment to be taken with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation of a lawn tractor; 
     FIG. 2 is a plan view showing an outline of the lawn tractor; 
     FIG. 3 a plan view showing a control panel; 
     FIG. 4 is a plan view showing a key switch; 
     FIG. 5A is a schematic side view of a shift pedal set to a neutral position; 
     FIG. 5B is a schematic side view of the shift pedal set to a forward drive region; 
     FIG. 5C is a schematic side view of the shift pedal set to a backward drive region; 
     FIG. 6 is an electric circuit diagram; 
     FIG. 7 is an electric circuit diagram showing a state to cancel a check function; 
     FIG. 8 is a hydraulic circuit diagram showing a different embodiment; and 
     FIG. 9 is a hydraulic circuit diagram with a hydraulic cylinder in operation in a further embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of this invention will be described hereinafter with reference to the drawings. 
     As shown in FIGS. 1 and 2, a lawn tractor acting as a working vehicle includes dirigible front wheels  1  of the non-driven type and rear drive wheels  2  supporting a vehicle body  3  having a driver&#39;s seat  4  and a steering wheel  5  arranged thereon. A mower unit  6  is vertically movably suspended from the vehicle body  3  between the front and rear wheels  1  and  2 . A diesel engine  7  is mounted on a front portion of vehicle body  3 . Power is transmitted from the engine  7  through a transmission shaft  8  to a hydrostatic stepless transmission  9 . The stepless transmission  9  and a transmission case  10 , the latter transmitting power from the stepless transmission  9  to the right and left rear wheels  2 , are arranged in a rearward portion of vehicle body  3 . Power is also transmitted from the engine  7  to the mower unit  6  through a belt tension type clutch mechanism  11  and an intermediate transmission shaft  12 . Grass clippings are transmitted from the mower unit  6  through a duct  13  to a grass catcher  14  connected to the rear end of vehicle body  3 . 
     The mower unit  6  includes a housing  15  containing three blades  16  rotatable about vertical axes. The mower unit  6  further includes a gear case  17  and a belt transmission mechanism  18  arranged above the upper surface of housing  15  for transmitting power from the intermediate transmission shaft  12  to the respective blades  16 . A Lift lever  19  is disposed to the right of driver&#39;s seat  4  for vertically moving the mower unit  6 . A clutch lever  20  is disposed to the left of driver&#39;s seat  4  for manually operating the clutch mechanism  11 . The grass catcher  14  is supported to be pivotable about a support shaft  28  extending transversely at the rear end of vehicle body  3  to be switchable to have the rear end of grass catcher  14  set to a raised position shown in phantom lines in FIG. 1 to discharge grass clippings from the grass catcher  14 . 
     A shift pedal  21  for shifting the stepless transmission  9 , and a brake pedal  22 , are arranged on a right portion of a foot-rest forwardly of driver&#39;s seat  4 , The shift pedal  21 , when not operated, is maintained in a neutral position as shown in FIG. 5A to stop the vehicle body  3 . The vehicle body  3  is driven forward when the shift pedal  21  is depressed forward from the neutral position as shown in FIG.  5 B. The vehicle body  3  is driven backward when the shift pedal  21  is depressed backward from the neutral position as shown in FIG.  5 C. The shift pedal  21  is linked to the stepless transmission  9  to produce the above states. The brake pedal  22  is linked to brakes mounted in the transmission case  10 . When depressed, the brake pedal  22  causes a braking force to be applied to the rear wheels  2 . As shown in FIG. 3, a panel  23  disposed forwardly of driver&#39;s seat  4  includes various indicators  24  arranged transversely, such as a lamp lit when a remaining amount of fuel decreases and a lamp lit when oil pressure decreases, a key switch  25 , and a release switch  27  with a built-in lamp  26 . The release switch  27  is the momentary type that is turned on only when pressed, and has a transparent or semitransparent operation surface, with the lamp  26  mounted inwardly of the operation surface. The release switch  27 , when not operated, prevents the vehicle body  3  from moving backward with the mower unit  6  in operation. When the operator consciously operates the release switch  27 , the vehicle body  3  is allowed to move backward with the mower unit  6  in operation. 
     As shown in FIG. 1, the vehicle body  3  has, arranged in various positions thereof, a seat switch  31  for determining presence of the operator on the driver&#39;s seat  4  from the weight of the operator, a clutch switch  32  for determining a state of clutch mechanism  11 , a shift switch  33  for determining a traveling direction from a direction in which the shift pedal  21  is depressed, and a brake switch  34  for determining whether the brake pedal  22  is depressed to apply the brakes. 
     As shown in FIG. 4, the key switch  25 , with a key inserted therein, is operable to an off position OFF for supplying no electric power to any electric devices, a glow position G for supplying electric power to a glow plug (not shown) of engine  7 , an on position ON for supplying electric power to the electric devices, and a start position ST for starting the engine  7  while continuing to supply electric power to the electric devices. When the operator maintains the key switch  25  in the start position ST, electric power continues to be supplied to a starter motor  36  (FIG.  6 ). When released, the key switch  25  is returned to the on position ON by a biasing force of a spring, for example. 
     FIG. 6 shows one embodiment of interlock circuit according to this invention. This interlock circuit includes a check function circuit portion for prohibiting backing of vehicle body  3  with the mower unit  6  in operation, and a release function circuit portion for canceling the check function when the operator consciously operates the release switch  27 . 
     The key switch  25  has a terminal “on” for supplying electric power when the key switch  25  is operated to the on position ON, and a terminal “st” for supplying electric power when the key switch  25  is operated to the start position ST (no description being made for the glow position G). A first energizing line  51  is formed for supplying a current from terminal “on” to a fuel cutting solenoid  35 . To the first energizing line  51 , the shift switch  33  and seat switch  31  are connected in series. The fuel cutting solenoid  35 , when energized, supplies fuel to the engine  7 , and when de-energized, stops the fuel supply. The shift switch  33  is turned on when the shift pedal  21  is in the neutral position or forward region, and turned off when the shift pedal  21  is in the backward region. The seat switch  31  is turned on when the operator is seated on the driver&#39;s seat  4 , and is turned off when the operator is absent from the driver&#39;s seat  4 . 
     The clutch switch  32  and brake switch  34  are the type for opening and closing the two contacts simultaneously. The clutch switch  32  has the two contacts turned off when the clutch mechanism  11  is engaged, and turned on when the clutch mechanism  11  is disengaged. The brake switch  34  has the two contacts turned on when the brake pedal  22  is depressed, and turned off when the brake pedal  22  is released. A second energizing line  52  is formed for supplying electric power from terminal “st” to the starter motor  36  of engine  7 . To the second energizing line  52 , one of the contacts of clutch switch  32  and one of the contacts of brake switch  34  are connected in series. The starter motor  36  is operable by the electric power supplied. 
     A third energizing line  53  branches from the first energizing line  51  which supplies current from the terminal “on”. The third energizing line  53  supplies electric power to the fuel cutting solenoid  35  through a first diode  37  (bypassing the shift switch  33  and seat switch  31 ). To the third energizing line  53 , the other contact of clutch switch  32  and the other contact of brake switch  34  are connected in series. Further, a fourth energizing line  54  is formed for supplying the current having passed through the clutch switch  32 , through a second diode  38  to the first energizing line  51  between the shift switch  33  and seat switch  32 . 
     As shown in FIG. 6, the electric circuit includes a self-hold circuit portion  40 . The self-hold circuit portion  40  has a signal line for receiving a signal from the release switch  27 , a line for supplying electric power to the lamp  26 , a first relay  41  and a second relay  42 . That is, the self-hold circuit portion  40  has a main line  55  for supplying a current from terminal “st” (i.e. from the second energizing line  52 ) to the lamp  26  through a third diode  43 , and a line for supplying a current from the fourth energizing line  54  to a solenoid of first relay  41 . Further, the self-hold circuit portion  40  has a line for transmitting a current from terminal “on” (i.e. from the first energizing line  51 ) through a fuse  44  to a contact opened and closed by the first relay  41 , and from this contact to the main line  55  through a contact opened and closed by the second relay  42 . The main line  55  has a line for transmitting a current from the main line  55  to the solenoid of second relay  42 . A line is provided to transmit a current from the fourth energizing line  54  to the main line  55  through a fourth diode  45  and release switch  27 . A fifth diode  46  leads a current to the fourth energizing line  54  upon an increase in the potential of main line  55 . 
     The electric circuit system having the above construction functions as follows. When the operator seated on the driver&#39;s seat  4  sets the shift pedal  21  to the neutral position and operates the key switch  25  to the on position ON, the fuel cutting solenoid  35  is maintained in a fuel supply state. Further, when the operator turns the key switch  25  to the start position ST with the clutch mechanism  11  disengaged and the brake pedal  22  depressed, the lamp  26  is lit (or may be blinked depending on a circuit construction) and at the same time electric power is supplied to the starter motor  36  to start the engine  7 . When, subsequently, the key switch  25  returns from the start position ST to the on position, the lamp  26  is turned off, but the current supplied through the first energizing line  51  maintains the fuel cutting solenoid  35  in the state for supplying fuel to keep the engine  7  running. After the engine  7  is started in this way, the clutch switch  32  remains on as long as the clutch mechanism  11  is disengaged. Consequently, the current continues to be supplied from the third energizing line  53  to the fourth energizing line  54  to allow the vehicle body  3  to travel backward by operation of the shift pedal  21 . When the shift pedal  21  is depressed backward with the clutch mechanism  11  engaged (with the mower unit  6  in operation and the clutch switch  32  turned off), the shift switch  33  is turned off. This stops the current from the first energizing line  51  and the current from the fourth energizing line  54 , and stops the fuel supply from the fuel cutting solenoid  35  to the engine  7 , thereby stopping the engine  7 . This is the check function, and the circuit portion providing this function is called the check function circuit portion. This construction is provided by a combination of shift switch  33  and clutch switch  32  for stopping the engine  7  when the clutch mechanism  11  is engaged to drive the vehicle body  3  backward. 
     When the operator desires to carry out an operation by driving the vehicle body  3  backward while driving the mower unit  6 , the operator may press the release switch  27  after engaging the clutch mechanism  11  and setting the shift pedal  21  to the neutral position or forward region. Then, the current is supplied from the first energizing line  51  through the fuse  44 , first relay  41  and second relay  42  to the main line  55 . As a result, as described hereinafter (see FIG.  7 ), the self-hold circuit portion  40  reaches a self-hold state to light the lamp  26   a  of indicator lamp unit  26 . The lamp  26   a  may be blinked by providing a blinking control function circuit portion having a capacitor or the like for the indicator lamp unit  26 . With the lighting or blinking of lamp  26   a , the current continues to be supplied from the main line  55  to the fourth energizing line  54 . Subsequently, the current continues to be supplied to the fuel cutting solenoid  35  to keep the engine  7  running even when the shift pedal  21  is depressed backward, as long as the operator remains seated on the driver&#39;s seat  4 . Thus, a grass cutting operation may be continued while moving the vehicle body  3  back and forth. This is the release function, and the circuit portion for providing this function is called the release function circuit portion which mainly comprises the self-hold circuit portion  40  to be described in detail hereinafter. 
     The self-hold circuit portion  40  will be described with reference to FIG.  7 . The first relay  41  has the contact switchable to position “b” when the clutch mechanism  11  is disengaged (with the current supplied to the fourth energizing line  54  through the clutch switch  32 ), and to position “a” when the clutch mechanism  11  is engaged (with the current from the clutch switch  32  stopped). As noted hereinbefore, when the release switch  27  is pressed with the clutch mechanism  11  engaged and the shift pedal  21  set to the neutral position or forward region, the current from the first energizing line  51  flows to the main line  55  through the fourth diode  45  (at this time, the current from the first energizing line  51  flows through part of the fourth energizing line  54 ). The solenoid of the second relay  42  is energized by this current, whereby the contact is switched from position “b” to position “a”, and the current from the contact (in position “a”) of first relay  41  flows to the main line  55  through the contact of second relay  42 . As a result, the solenoid of second relay  42  remains energized. As indicated by arrows in FIG. 7, the current is continuously supplied from the first energizing circuit  51  (upstream of shift switch  33  with respect to the direction of current flow), which receives the current from the key switch  25 , to the main line  55  through the fuse  44  and the contacts of first relay  41  and second relay  42 . While lighting the lamp  26  connected to the main line  55 , the current of main line  55  is supplied through the fifth diode  46  to the first energizing line  51  downstream of shift switch  33 . The fuse  44  may act as a prohibition circuit unit for prohibiting the release function circuit portion from canceling the check function. Of course, the prohibition circuit unit may be given improved operability by employing a switch or the like. 
     When the clutch mechanism  11  is disengaged with the self-hold circuit portion  40  in the self-hold state as above, the clutch switch  32  is turned on to energize the solenoid of first relay  41  to switch the contact to position “b”. As a result, the contact of second relay  42  is de-electrified to stop the current supply to the main line  55 . The self-hold state is thereby terminated to stop the current supply from the self-hold circuit portion  40  to the first energizing line  51 . When, in this state, the vehicle body  3  is driven backward with the clutch mechanism  11  remaining engaged, the engine  7  is stopped forcibly. Whether the self-hold circuit portion  40  is in the self-hold state or not, the engine  7  is stopped forcibly when the operator leaves the driver&#39;s seat  4 . 
     Thus, in this invention, in time of starting the engine  7 , fuel supply to the engine  7  is enabled by the operator seated on the driver&#39;s seat  4  and the shift pedal  21  set to the neutral position (or to the forward region as far as the interlock circuit is concerned). In this state, the engine is allowed to start, with the clutch mechanism  11  disengaged, the brake pedal  22  depressed, and the key switch  25  operated to the start position ST, that is to say the load on the engine  7  reduced and the vehicle stopped. The lamp  26  is lit at this starting time, to allow detection of any disconnection of lamp  26  with ease. After the engine  7  is started by the above operation, the vehicle may be driven in any selected direction by operating the shift pedal  21  in the forward region and backward region as long as the clutch mechanism  11  is disengaged. In addition, only when the clutch mechanism  11  is engaged to drive the mower unit  6  and the operator consciously operates the release switch  27 , the self-hold circuit portion  40  reaches the self-hold state to allow the vehicle body  3  to travel backward with the clutch mechanism  11  remaining engaged to keep driving the mower unit  6 . Even when the vehicle body  3  is driven forward after being driven backward, the self-hold circuit portion  40  is maintained in the self-hold state. Thus, when cutting grass around trees or adjacent a fence having a complicated shape, for example, the operation may be carried out by frequently reversing the vehicle body  3  back and forth, without imposing a troublesome task on the operator. 
     The self-hold state of self-hold circuit portion  40  is canceled when the clutch mechanism  11  is disengaged after an operation carried out by operating the release switch  27  to allow the vehicle body  3  to travel backward as described above. Further, with the self-hold state of self-hold circuit portion  40  canceled, the self-hold circuit portion  40  may be set to the self-hold state again by turning on the release switch  27 . Where there is no need to engage in a grass cutting operation by driving the vehicle body  3  backward, the fuse  44  may be removed to avoid an inconvenience of canceling the checking state due to a mis-operation of the release switch  27 . 
     Apart from the above embodiment, this invention may be implemented in other forms as described below (like reference numerals being used to identify like parts in the foregoing embodiment). 
     (1) As shown in FIG. 8, the stepless transmission  9  includes a variable displacement pump  61  and a charge pump  62  driven by the engine  7 , and a hydraulic motor  64  for receiving pressure oil from the hydraulic pump  61  and draining the pressure oil through a pair of oil lines  63 . Pressure oil from the charge pump  62  is supplied to a hydraulic device  65  mounted on the vehicle body, and then to the oil lines  63  to compensate for any leakage. It is assumed in this embodiment that, when driving the vehicle body  3  forward, a higher pressure occurs in the upper oil line  63  in FIG. 8 and a lower pressure in the lower oil line  63 , and when driving the vehicle body  3  backward, a lower pressure occurs in the upper oil line  63  and a higher pressure in the lower oil line  63 . The illustrated circuit includes a double-acting hydraulic cylinder  66  operable by a pressure difference between these oil lines  63 , and an electromagnetic selector valve  67  for stopping oil flows to and from the hydraulic cylinder  66 . The hydraulic cylinder  66  and clutch lever  20  are linked to each other through a plate  68  defining a slot to operate the clutch lever  20  forcibly to a declutching position for disengaging the clutch mechanism  11 . 
     The selector valve  67  is operable by a controller  69 . The controller  69  receives signals from the clutch switch  32  which detects the clutch lever  20  in the engaging position, the seat switch  31  which detects the operator seated on the driver&#39;s seat  4 , and the release switch  27 . The controller  69  outputs a signal to supply a current to the lamp  26 . A control device in the form of software, for example, is set to the controller  69  to light the lamp  26  and operate the selector valve  67  to a stop position only when the operator consciously operates the release switch  27  with the clutch mechanism  11  engaged to drive the working implement  6 . When the vehicle body  3  is driven backward in a normal operation (with the release switch  27  turned off) and the clutch lever  20  in the engaging position, as shown in FIG. 9, the piston rod of hydraulic cylinder  66  is extended to operate the clutch lever  20  forcibly to the declutching position to disengage the clutch mechanism  11 . When the vehicle body  3  is driven backward after turning on the release switch  27 , with the clutch lever  20  in the engaging position, the clutch mechanism  11  is maintained engaged to allow the vehicle body  3  to travel backward while continuing to drive the working implement  6 . 
     That is, in these two embodiments, the interlock circuit is provided, in respect of both hardware and software, by the controller  69  having a microcomputer unit as the central element. 
     (2) The clutch mechanism  11  may be the electromagnetic type for transmitting power and disconnecting power transmission to a working implement such as the mower unit  6 . 
     The interlock circuit can be constructed to cancel the checking state by pressing the release switch  27  once, and reinstate the checking state by pressing the release switch  27  a second time. It will be advantageous in this case that the interlock circuit is provided in software form by using a microcomputer unit such as the above controller  69 .