Abstract:
The present invention is a control circuit for a construction machine for using a control lever for revolving and boom swing in common and switching pilot pressure via a switching valve, comprising: a switch for supplying a switching signal to the switching valve; a pressure switch for detecting whether the pilot pressure is output from a remote control valve or not; a switching control circuit for switching a position of switch to a position for a boom swing cylinder when the switching signal is output from the switch and holding the position of switch at the position for the boom swing cylinder when the pilot pressure is detected by the pressure switch, to thereby prevent wrong operation in switching.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a control circuit for a construction machine for switching a plurality of actuators.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventionally, a hydraulicexcavator equipped with a boom swing apparatus is known, for excavating a small place at the corner by swinging a boom left and right around a vertical axis. As an operating means for operating a boom swing cylinder, there is an operating means in which a foot pedal is used. Such an equipment with the foot pedal limits space in foot side. Also, equipment with a nibbler or a breaker as an option increases the number of pedals and makes operations thereof complex.  
           [0005]    For this reason, an operation lever can be used, which performs together operation of the boom swing cylinder and operation of an actuator, for example a revolving motor that is not operated in combination of boom swing.  
           [0006]    In this case, when after switching from revolving to boom swing, if the switching operation is not recognized, there is a problem that mis-operation can occur that the revolving is derived from the operation carried out for a boom swing purpose.  
         SUMMARY OF THE INVENTION  
         [0007]    An object of the present invention is to provide a control circuit for a construction machine capable of certainly preventing wrong operation in a case that a plurality of actuators are operated by means of only one control lever.  
           [0008]    The control circuit for a construction machine according to the present invention has following constitution.  
           [0009]    The present invention comprises: a control lever for carrying out operations of a first actuator and a second actuator in common; a switching valve or a selector valve for supplying pilot pressure output from a remote control valve by means of operation of the control lever to a control port in any one of the first and the second actuators; a control member for supplying a switching signal to the switching valve; a detector for detecting whether the pilot pressure is output from the remote control valve or not; and a switching controller for switching a change-over position in the switching valve from the first actuator to the second actuator when the switching signal is output from the control member and holding the position at the second actuator when output of the pilot pressure is detected by the detector.  
           [0010]    According to the present invention, if the control member is operated, the switching valve switches a pilot pressure supply place to which the pilot pressure is output from the remote control valve of the control lever, from the first actuator to the second actuator, and then the detector detects the pilot pressure if the pilot pressure appears in a pilot line by means of operation of the control lever. The switching control means holds the switching valve at the second actuator when the switching signal is output from the control member and when output of the pilot pressure is detected by the detector. Thereby, switching from the first actuator to the second actuator does not occur as long as the control member is not operated. Also, when the control lever is operated in a state that the control member is operated to switch the position of switch to the second actuator, the position cannot be switched to the first actuator even if the control member is off, as long as the control lever is not restored in neutral position. Therefore, wrong operation can be prevented in switching. Also, even if a finger is taken off the control member during operation, a bad situation that the position of switch is switched to other actuator can be prevented. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a diagram showing a control circuit for a construction machine according to one embodiment of the present invention;  
         [0012]    [0012]FIG. 2 a  is a plan view of the construction machine for explaining boom swing operation and FIG. 2 b  is a side view thereof;  
         [0013]    [0013]FIG. 3 is a circuit diagram showing constitution of a switching control circuit shown in FIG. 1; and  
         [0014]    [0014]FIG. 4 is a schematic view showing operations of a control lever. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Now, the present invention will be explained on the basis of embodiments shown in the drawings. These embodiments are only preferred embodiments of the present invention and the present invention is not limited to them.  
         [0016]    [0016]FIG. 1 shows one embodiment of a control circuit for a construction machine according to the present invention.  
         [0017]    In FIG. 1, a variable capacity type of hydraulic pump  2  and a pilot pump  3  are operated, respectively, by means of driving of an engine  1  equipped in an upper rotating body of the construction machine.  
         [0018]    Hydraulic oil discharged from the hydraulic pump  2  is supplied to a right traveling control valve  4 , a boom control valve  5 , a bucket control valve  6 , a boom swing control valve  7  and a control valve  8  for a crusher/breaker as an option apparatus, arranged in a center bypass line LC on the left of FIG. 1. The hydraulic oil is also supplied to a left traveling control valve  9 , a revolving control valve  10  and an arm control valve  11 , arranged in a center bypass line RC on the right of FIG. 1. The hydraulic oil discharged from the pilot pump  3  is used as a pressure source for various controllers.  
         [0019]    A straight traveling valve  12  provided upstream in the traveling control valve  4 ,  9  has positions of switch comprised of a, b and is normally held at the position a.  
         [0020]    At the position a, the hydraulic oil from the hydraulic pump  2  is independently supplied to the left center bypass line LC and the right center bypass line RC. If, in a state that the right and left traveling levers are operated to the same position, for example the boom or the arm is operated, then the straight traveling valve  12  is switched from the position a to the position b. Accordingly, the hydraulic oil from the hydraulic pump  2  flows in parallel to the left center bypass line LC and the right center bypass line RC. At that time, even if a combined operation is carried out such that the boom is risen and fallen while a traveling motor  16  is driven, the hydraulic oil from the hydraulic pump  2  is supplied equally to the left and the right traveling motors. By means of this, the straight traveling can be kept. Also, in the drawing,  13  is a conflux valve for increasing the boom-up speed and  14  is a cut valve for making the hydraulic oil flow in the left center bypass line LC.  
         [0021]    Next, switching operation of the control lever will be explained with reference to FIG. 4. As shown in FIG. 4, by operating a switch  51  provided at upper grip part of a left control lever sq, revolving of an upper rotating body and boom swing are switched. That is, by means of revolving operation, the operation in {circle over (1)} direction becomes right revolving and the operation in {circle over (2)} direction becomes left revolving. When the switch  51  is pushed, the operation in {circle over (1)} direction makes boom right swing and the operation in {circle over (2)} direction makes boom left swing. For reference, operations of lever for arm releasing and excavating, boom rising and falling, or bucket excavating and releasing are exemplified in FIG. 4. That is, in the left control lever, {circle over (1)} indicates right revolving, {circle over (2)} indicates left revolving, {circle over (3)} indicates arm releasing and {circle over (4)} indicates arm excavating. Also, in the right control lever, {circle over (5)} indicates boom falling, {circle over (6)} indicates boom rising, {circle over (7)} indicates bucket excavating and {circle over (8)} indicates bucket releasing.  
         [0022]    Also, in a case that the switch  51  is a toggle switch, a tumbler switch or the like, the switch is fixed to either the boom swing or the revolving whenever the switch  51  is operated. Also, in a case that the switch  51  is an automatic restoring type of push button switch, it is switched to the boom swing only when pushed with fingers. Here, the present invention is not limited to the switching mode of the control lever as described above.  
         [0023]    Now, a switching operational circuit of the revolving motor (as first actuator) and the boom swing cylinder (as second actuator) related to the present invention will be explained. Explanation for operation of actuators except for them will be omitted for simplification.  
         [0024]    The boom swing cylinder  15  is connected to the boom control valve  7 . If the control valve is switched from the neutral position to the position c, the hydraulic oil is supplied to a head side of the boom swing cylinder  15 . At that time, as shown in FIGS. 2 a  and  2   b , the boom  30  can be swung, for example, right (e direction in the drawing) around the vertical axis VA. If the control valve is switched to the position d, the hydraulic oil is supplied to rod side of the boom swing cylinder  15 . At that time, the boom  30  can be swung left (f direction in the drawing) around the vertical axis VA.  
         [0025]    The revolving motor  16  is connected to the revolving control valve  10 . If switched from the neutral position to the position e, the revolving motor  16  is rotated in g direction to rotate the upper rotating body  31 (see FIG. 2 b ), for example, right. Also, if switched to the position f, the upper rotating body can be rotated left.  
         [0026]    The pilot line of the boom control valve  7  and the pilot line of the revolving control valve  10  are connected to the outlet port of the switching valve  17 , respectively.  
         [0027]    This switching valve  17  is normally positioned at the position i, and is connected to the control port of the revolving control valve  10 . If switching signals is received from the switching control circuit  18  as a switching controller, the switching valve  17  is switched to the position j by means of hydraulic signal sent via the electromagnetic valve  17   a . Accordingly, the pilot pressure is supplied to the control port of the boom swing cylinder  15 .  
         [0028]    The inlet port of the switching valve  17  is connected to the remote control valve  19  of the left control lever  50  (see FIG. 4). If the left control lever  50  is shifted in {circle over (1)} direction, the pilot pressure is derived from the remote control valve  19   a . Also, if the lever is shifted in {circle over (2)} direction, the pilot pressure is derived from the remote control valve  19   b . These pilot pressures flow through the respective pilot lines  20   a  and  20   b  to the inlet port of the switching valve  17 .  
         [0029]    These pilot lines  20   a  and  20   b  are provided with pressure switches  21   a  and  21   b  as detector, respectively. If any one of the pilot lines  20   a  and  20   b  detects the pilot pressure, the signal is output to the switching control circuit  18 .  
         [0030]    Therefore, in the present invention, the detector is comprised of pressure switches provided in the pilot lines passing from the remote control valve to the switching valve. In this case, because the detector is constructed with the conventional pressure switch for detecting operational pressure from the remote control valve, the control circuit of the present invention can be embodied without new sensor required.  
         [0031]    Next, construction of the switching control circuit  18  will be explained with reference to FIG. 3.  
         [0032]    First, if the push-button switch (control member)  51  provided in grip of the left control lever  50  is pushed, an electromagnetic coil R 3  of the relay  180  is excited. As a result, the contact point R 3-a  is closed. Thereby, the solenoid of the electromagnetic valve  17   a  is turned on and the electromagnetic valve  17   a  is switched from the intercepting position k to turn-on position or conducting position  1 .  
         [0033]    If the hydraulic signal is applied to the control port of the switching valve  17  via the electromagnetic valve  17   a , the switching valve  17  is switched to the position j. As a result, the pilot lines  20   a  and  20   b  are connected to the control port of the boom swing control valve  7 . Accordingly, {circle over (1)} and {circle over (2)} operations by the left control lever  50  function as the boom swing operations.  
         [0034]    If the contact point R 3-a  is closed, current flows through the signal line  180   a  to the relay  181 . As a result, the electromagnetic coil R 2  is excited and the contact point R 2-a  is closed. In this state, if the left control lever  50  is shifted in any of {circle over (1)} direction and {circle over (2)} direction, the pressure switch  21   a  or  21   b  is closed to turn on electricity and to make current flow. This current flows via the contact point R 2-a  and diode  182  to the electromagnetic coil R 3 . As a result, the relay  180  is self-held. That is, even when fingers are taken off the switch  51 , the switching valve  17  is held at the position j. Accordingly, the boom swing operation is continued.  
         [0035]    Also, if the revolving operation is carried out when the switch  51  is not pushed, the electromagnetic coil R 1  of the relay  183  is excited to open the contact point R 1-a . As a result, even when the switch  51  is pushed, the relay  180  and  181  do not function and the switching valve  17  is never switched to the boom swing control valve  7 . That is, when the switch  51  is not pushed, the operation mode is always fixed to the revolving operation. Only when the switch  51  is pushed, the operation mode is switched to the boom swing operation.  
         [0036]    In the present invention, a relay is provided between the control member and the switching valve, the relay being constructed to be self-held with signal output from the detector. In this case, the control circuit of the present invention can be embodied with a simple construction such that a relay circuit is added.  
         [0037]    As described above, in the control circuit of the present embodiment, the operation mode is not switched to the boom swing operation as long as the switch  51  is not pushed. Moreover, after the operation mode is switched to the boom swing operation, the boom swing operation is continued as long as the left control lever  50  is not restored to the neutral position. As a result, the revolving operation and the boom swing operation can be switched surely and safely. Also, even when fingers are taken off the switch  51  during the boom swing operation, the operation mode is never switched to the revolving operation.  
         [0038]    Moreover, although the relay is used to control in sequence in the above embodiment, the switching control means of the present invention is not limited to it and a microcomputer may be used to control in software.  
         [0039]    Also, the first actuator and the second actuator in the present invention are comprised of a revolving motor for revolving the upper rotating body and a boom swing cylinder for swinging the boom left and right around the vertical axis, respectively, in the above embodiment. In addition, the first actuator may be the revolving motor and the second actuator may be an offset cylinder for offsetting the boom in machine-width direction.  
         [0040]    In this case, when the revolving operation and the boom swing operation are carried out by means of only one control lever, the revolving operation of the upper rotating body can be carried out during the control member is not operated. Also, only when operation of the control member is carried out, the boom swing operation can be carried out. Even when operation of the control member is released during the boom swing operation, the boom swing operation can be continued as long as the control lever is not restored to the neutral position. As a result, a trouble that the upper rotating body is revolved rapidly by means of wrong operation can be prevented.  
         [0041]    In brief, if it is combination of actuators without combined operation, for example, any lever operation in standard operating mode prescribed with ISO and lever operation of option apparatus can be combined.  
         [0042]    As described above, although one embodiment of the present invention is disclosed, the scope of the protection of the present invention is not limited to it.