Abstract:
The present invention addresses the problem of being able to increase the effect of preventing an engine from stalling by reducing the engine load attributable to a fixed-capacity hydraulic pump. A working vehicle provided with a fixed-capacity hydraulic pump driven by power from an engine and a working hydraulic actuator driven by working oil pumped from the fixed-capacity hydraulic pump is a rotary working vehicle which is provided with a pressure modifying means for modifying the pressure of working oil from the fixed-capacity hydraulic pump, and the rotary working vehicle is such that if the actual number of revolutions (N) of the engine is reduced by a set number of revolutions (Ns) as the load on the engine increases, then the pressure modifying means operates in accordance with the deviation (e) between the actual number of revolutions (N) of the engine and the specified number of revolutions (Ns), and the pressure of the working oil from the fixed-capacity hydraulic pump is modified.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a working vehicle which can reduce load of an engine caused by a fixed displacement type hydraulic pump. 
       BACKGROUND ART 
       [0002]    Conventionally, a working vehicle such as an excavating working machine is known in which a working hydraulic actuator is driven by hydraulic oil sent from a fixed displacement type hydraulic pump. For example, the Patent Literature 1 describes an excavating working machine in which a first hydraulic pump, a second hydraulic pump, a third hydraulic pump and a fourth hydraulic pump are provided in series on an output shaft of an engine. According to the excavating working machine, the third hydraulic pump is a fixed displacement type hydraulic pump, and hydraulic oil is sent from the fixed displacement type hydraulic pump to working hydraulic actuators such as a turning motor, an arm cylinder, an offset cylinder, a boom cylinder and a bucket cylinder so as to drive them. 
       PRIOR ART REFERENCE 
     Patent Literature 
       [0003]    Patent Literature 1: the Japanese Patent Laid Open Gazette 2000-319942 
       DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
       [0004]    According to the excavating working machine described in the Patent Literature 1, when load on the engine is increased at high-load work with the working hydraulic actuators, engine stall may occur because the load of the engine caused by the fixed displacement type hydraulic pump cannot be reduced. 
         [0005]    The present invention is provided in consideration of the above problem, and the purpose of the present invention is to provide a working vehicle which can reduce load of an engine caused by a fixed displacement type hydraulic pump so as to improve effect of preventing engine stall. 
       Means for Solving the Problems 
       [0006]    Preferably, a working vehicle of the present invention having a fixed displacement type hydraulic pump driven by power from an engine and a working hydraulic actuator driven by hydraulic oil sent from the fixed displacement type hydraulic pump, includes a pressure change means changing a pressure of the hydraulic oil from the fixed displacement type hydraulic pump, a control means controlling the pressure change means, and an actual rotation speed detection means detecting an actual rotation speed of the engine. When load of the engine is increased and the actual rotational speed of the engine becomes lower than a set rotation speed, the pressure of the hydraulic oil from the fixed displacement type hydraulic pump is changed with the pressure change means corresponding to a deviation between the actual rotational speed of the engine and the set rotation speed. 
         [0007]    The working vehicle of the present invention has a variable displacement type hydraulic pump driven by the power from the engine and driving the working hydraulic actuator by sending hydraulic oil, and a swash plate angle change means changing a swash plate angle of the variable displacement type hydraulic pump. The control means controls the swash plate angle change means so that when the load of the engine is increased and the actual rotational speed of the engine becomes lower than the set rotation speed, the swash plate angle change means is operated corresponding to the deviation between the actual rotational speed of the engine and the set rotation speed so as to change the swash plate angle of the variable displacement type hydraulic pump, and when the swash plate angle becomes a limiting angle, the pressure change means is operated corresponding to the deviation so as to change the pressure of the hydraulic oil from the fixed displacement type hydraulic pump. 
         [0008]    The working vehicle of the present invention has an air conditioning device driven by the power from the engine. The pressure change means is operated following on-off operation of the air conditioning device so as to change the pressure of the hydraulic oil from the fixed displacement type hydraulic pump. 
         [0009]    The working vehicle of the present invention has an air conditioning device driven by the power from the engine, and a clutch cutting off and connecting power transmission from the engine to the air conditioning device. 
         [0010]    wherein the control means controls the clutch cutting off and connection of the clutch so that when the load of the engine is increased and the actual rotational speed of the engine becomes lower than the set rotation speed, the pressure of the hydraulic oil from the fixed displacement type hydraulic pump is changed with the pressure change means corresponding to the deviation between the actual rotational speed of the engine and the set rotation speed, and when the actual rotational speed of the engine becomes lower than the set rotation speed though the pressure of the hydraulic oil from the fixed displacement type hydraulic pump is changed, the clutch is disengaged. 
       Effect of the Invention 
       [0011]    According to the working vehicle of the present invention, the load of the engine caused by the fixed displacement type hydraulic pump can be reduced so as to improve the effect of preventing the engine stall 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a side view of an entire configuration of a turning working vehicle. 
           [0013]      FIG. 2  is a hydraulic circuit diagram of a hydraulic device. 
           [0014]      FIG. 3  is a diagram of a control configuration of a turning working vehicle according to a first embodiment. 
           [0015]      FIG. 4  is a flow chart of the control configuration of the turning working vehicle according to the first embodiment. 
           [0016]      FIG. 5  is a diagram of a control configuration of a turning working vehicle according to a second embodiment. 
           [0017]      FIG. 6  is a flow chart of the control configuration of the turning working vehicle according to the second embodiment. 
           [0018]      FIG. 7  is a flow chart of another control configuration of the turning working vehicle according to the second embodiment. 
           [0019]      FIG. 8  is a flow chart of another control configuration of the turning working vehicle according to the second embodiment. 
           [0020]      FIG. 9  is a diagram of a control configuration of a turning working vehicle according to a third embodiment. 
           [0021]      FIG. 10  is a flow chart of the control configuration of the turning working vehicle according to the third embodiment. 
           [0022]      FIG. 11  is a diagram of a control configuration of a turning working vehicle according to a fourth embodiment. 
           [0023]      FIG. 12  is a flow chart of the control configuration of the turning working vehicle according to the fourth embodiment. 
           [0024]      FIG. 13  is a schematic drawing of a stepped control pin of the turning working vehicle according to the fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Firstly, an explanation will be given on an entire configuration of a turning working vehicle  1  referring to  FIG. 1 . In this embodiment, the turning working vehicle  1  is explained as an embodiment of a working vehicle. However, the working vehicle is not limited thereto and may alternatively be a vehicle with a hydraulic device, such as an agricultural vehicle, a construction vehicle and an industrial vehicle. 
         [0026]    As shown in  FIG. 1 , the turning working vehicle  1  has a traveling device  2 , a turning device  3  and a working device  4 . 
         [0027]    The traveling device  2  has a pair of left and right crawlers  5 , a left traveling hydraulic motor  5 L and a right traveling hydraulic motor  5 R. The left traveling hydraulic motor  5 L drives the left crawler  5  and the right traveling hydraulic motor  5 R drives the right crawler  5 , whereby the traveling device  2  can make the turning working vehicle  1  travel forward and backward and turn. A blade  17  for leveling work accompanying excavating work is provided in the traveling device  2 . The blade  17  is supported at one of front and rear sides of the traveling device  2  so as to be rotatable vertically, and is moved vertically by a blade cylinder  18  which is driven telescopically. 
         [0028]    The turning device  3  has a turning base  6 , a turning motor  7 , an operation part  8  and an engine  9 . The turning base  6  is arranged above the traveling device  2  and supported rotatably by the traveling device  2 . By driving the turning motor  7 , the turning device  3  can make the turning base  6  turn concerning the traveling device  2 . On the turning base  6 , the operation part  8  having various operation tools, the engine  9  which is a power source, and the like are arranged. 
         [0029]    The engine  9  has a droop characteristic with which engine rotation speed is decreased or increased gradually following variation of load. Namely, when the load on the engine  9  is increased, output of the engine  9  is increased and the rotation speed of the engine  9  is decreased according to the droop characteristic. When increase of the load is continued, the load is over the maximum output of the engine and engine stall is caused. Then, the engine stall is prevented by later-discussed control. 
         [0030]    The working device  4  has a boom  10 , an arm  11 , a bucket  12 , a boom cylinder  13 , an arm cylinder  14 , a bucket cylinder  15  and a swing cylinder  16 . 
         [0031]    One of ends of the boom  10  is supported by a front portion of the turning base  6  so as to be rotatable longitudinally, and the boom  10  is rotated by the boom cylinder  13  which is driven telescopically. Furthermore, the end of the boom  10  is supported via a boom bracket as to be rotatable laterally, and is rotated by the swing cylinder  16  which is driven telescopically. 
         [0032]    One of ends of the arm  11  is pivoted on the other end of the boom  10 , and the arm  11  is rotated by the arm cylinder  14  which is driven telescopically. 
         [0033]    One of ends of the bucket  12  is supported by the other end of the arm  11 , and the bucket  12  is rotated by the bucket cylinder  15  which is driven telescopically. 
         [0034]    Accordingly, in the working device  4 , a multi-articulated structure is configured which excavates earth, sand and the like with the bucket  12 . 
         [0035]    Though a working device provided in the turning working vehicle  1  according to this embodiment is the working device  4  which performs the excavating work with the bucket  12 , the working device is not limited thereto and may alternatively be a similar hydraulic device, such as a working device which has a hydraulic breaker and performs the excavating work. 
         [0036]    Next, an explanation will be given on a hydraulic circuit  20  of the hydraulic device in the turning working vehicle  1  referring to  FIG. 2 . 
         [0037]    The hydraulic circuit  20  has four hydraulic pumps  21 ,  22 ,  23  and  24 , and hydraulic oil is sent from the pumps via a control valve  30  to traveling hydraulic actuators (the traveling hydraulic motors  5 L and  5 R) and working hydraulic actuators (the turning motor  7  and the cylinders  13 ,  14 ,  15 ,  16  and  18 ). 
         [0038]    The hydraulic pumps  21 ,  22 ,  23  and  24  are driven by power from the engine  9  so as to discharge the hydraulic oil. The hydraulic pumps  21  and  22  are variable displacement type hydraulic pumps, and the third pump  23  and the pilot pump  24  are fixed displacement type hydraulic pumps. 
         [0039]    The hydraulic oil sent from the first pump  21 , the second pump  22  and the third pump  23  is supplied to the hydraulic actuators and then returned to a hydraulic oil tank  19  through a return oil passage  19   a.    
         [0040]    The hydraulic oil discharged from the first pump  21  is sent from an oil passage  21   a  via switching valves  31 ,  33  and  38  constituting the control valve  30  to the boom cylinder  13 , the bucket cylinder  15  and the right traveling hydraulic motor  5 R respectively. 
         [0041]    The hydraulic oil discharged from the second pump  22  is sent from an oil passage  22   a  via switching valves  32 ,  34 ,  35 ,  36  and  37  constituting the control valve  30  to the arm cylinder  14 , the swing cylinder  16 , the blade cylinder  18 , the turning motor  7  and the left traveling hydraulic motor  5 L respectively. 
         [0042]    The hydraulic oil discharged from the third pump  23  is sent from an oil passage  23   a  via switching valves  31 ,  32 ,  33 ,  35  and  36  constituting the control valve  30  to the turning motor  7 , the boom cylinder  13 , the arm cylinder  14 , the bucket cylinder  15  and the blade cylinder  18  respectively. 
         [0043]    When the switching valves  31 ,  32 ,  33 ,  34 ,  35 ,  36 ,  37  and  38  are switched respectively, the boom cylinder  13 , the arm cylinder  14 , the bucket cylinder  15 , the swing cylinder  16 , the blade cylinder  18 , the turning motor  7 , the right traveling hydraulic motor  5 R and the left traveling hydraulic motor  5 L are driven respectively. 
         [0044]    The oil passage  23   a  at a discharge side of the third pump  23  is branched and connected to an electromagnetic proportional relief valve  43 , and the electromagnetic proportional relief valve  43  is controlled so that a relief pressure is reduced when load of the engine  9  is not less than a predetermined value. 
       Embodiment 1 
       [0045]    An explanation will be given on a control configuration and a control mode of the turning working vehicle  1  according to a first embodiment of the present invention referring to  FIGS. 3 and 4 . 
         [0046]    An engine rotation speed detection means  41  detects an actual rotational speed N of the engine  9 . The engine rotation speed detection means  41  includes a sensor such as an electromagnetic pickup or a rotary encoder and is provided near an output shaft of the engine  9 . The engine rotation speed detection means  41  is connected to a controller  40  and transmits a detection signal to the controller  40 . 
         [0047]    The rotation speed of the engine is set by rotating an accelerator lever, and a set rotation speed Ns is detected by a rotation angle detection means  42 . The rotation angle detection means  42  includes an angle sensor for example, and is provided in a rotation base part of the accelerator lever (not shown). The rotation angle detection means  42  is connected to a controller  40  and transmits a detection signal to the controller  40 . 
         [0048]    The electromagnetic proportional relief valve  43  is a pressure change means which changes a pressure of hydraulic oil from the third pump  23 . A primary side of the electromagnetic proportional relief valve  43  is connected to the oil passage  23   a  and a secondary side of the electromagnetic proportional relief valve  43  is connected to the hydraulic oil tank  19 . The electromagnetic proportional relief valve  43  is configured so that a relief pressure (relief amount) of the hydraulic oil is changed by changing current supplied to a solenoid. The solenoid of the electromagnetic proportional relief valve  43  is connected to the controller  40 , and the relief pressure is changed by a control signal from the controller  40 . 
         [0049]    In the controller  40  of this embodiment, governor control is performed when the load of the engine  9  is less than a predetermined value, and the relief pressure is controlled corresponding to the magnitude of the load when the load is not less than the predetermined value. The said load is found from a map with a difference between the set rotation speed Ns and the actual rotational speed N of the engine  9 , and the relief pressure of the electromagnetic proportional relief valve  43  is changed corresponding to the load. Concretely, a flow shown in  FIG. 4  is performed. 
         [0050]    At a step S 11 , the controller  40  obtains the set rotation speed Ns and the actual rotational speed N of the engine  9 . Then, the control is shifted to a step S 12 . 
         [0051]    At the step S 12 , the controller  40  judges whether the actual rotational speed N of the engine  9  is lower than the set rotation speed Ns or not. When the actual rotational speed N is lower, the control is shifted to a step S 13 . When not lower, the control is shifted to a step S 15 . 
         [0052]    At the step S 13 , the controller  40  calculates a deviation e between the set rotation speed Ns and the actual rotational speed N of the engine  9 . Then, the control is shifted to a step S 14 . 
         [0053]    At the step S 14 , the controller  40  changes the relief pressure of the electromagnetic proportional relief valve  43  into a relief pressure Xe corresponding to the calculated deviation e. Namely, the controller  40  calculates the load from the deviation e and the actual rotational speed N, and when the load is not less than the predetermined value, the controller  40  calculates the relief pressure Xe corresponding to the deviation e and transmits a control signal to the solenoid of the electromagnetic proportional relief valve  43  so as to change the relief pressure into Xe. Then, the pressure of the hydraulic oil from the third pump  23  is changed into the relief pressure Xe from a relief pressure Xa of the case in which the load is less than the predetermined value, and the hydraulic oil excessing the relief pressure Xe is returned to the hydraulic oil tank  19 . Accordingly, the load of the engine  9  caused by the third pump  23  corresponding to energy of the difference of Xa and Xe can be reduced. Then, the control is shifted to RETURN and the flow is repeated. 
         [0054]    The larger the load is, the lower the relief pressure Xe is set so as to prevent the engine stall. 
         [0055]    At the step S 15 , the controller  40  changes the relief pressure of the electromagnetic proportional relief valve  43  into the relief pressure Xa. Namely, the controller  40  transmits a current command corresponding to the relief pressure Xa to the electromagnetic proportional relief valve  43 . Accordingly, the pressure of the hydraulic oil from the third pump  23  is changed into the relief pressure Xa, and the hydraulic oil excessing the relief pressure Xa is returned to the hydraulic oil tank  19 . Then, the control is shifted to RETURN and the flow is repeated. 
         [0056]    As the above, in the turning working vehicle  1  according to the first embodiment of the present invention, when the load of the engine  9  is increased and the actual rotational speed N of the engine  9  becomes lower than the set rotation speed Ns, the electromagnetic proportional relief valve  43  which is the pressure change means is operated corresponding to the deviation e between the actual rotational speed N and the set rotation speed Ns so that the pressure of the hydraulic oil from the third pump  23  is changed. In more detail, the relief pressure of the electromagnetic proportional relief valve  43  is changed from the relief pressure Xa into the relief pressure Xe lower than the relief pressure Xa, whereby the pressure of the hydraulic oil from the third pump  23  is reduced. Accordingly, the load of the engine  9  caused by the third pump  23  which is the fixed displacement type hydraulic pump can be reduced so as to improve the effect of preventing the engine stall. Furthermore, the load of the engine  9  caused by the third pump  23  can be reduced by not changing the third pump  23  from the fixed displacement type hydraulic pump to the variable displacement type hydraulic pump but providing the pressure change means, whereby cost is reduced. 
         [0057]    The pressure change means of this embodiment is configured by the electromagnetic proportional relief valve  43 , thereby being matched easily with the controller  40 . 
       Embodiment 2 
       [0058]    An explanation will be given on a control configuration and a control mode of the turning working vehicle  1  according to a second embodiment of the present invention referring to  FIGS. 5 to 8 . Points different from the first embodiment are mainly explained. 
         [0059]    In the second embodiment, in addition to the control of the first embodiment in which the pressure of the hydraulic oil from the third pump  23  is changed, control in which a flow rate of hydraulic oil discharged from the hydraulic pumps  21  and  22  is changed, that is, control in which a swash plate angle R of a movable swash plate in each of the hydraulic pumps  21  and  22  is changed is performed. 
         [0060]    An explanation will be given on the control in which the swash plate angle of the movable swash plate in each of the hydraulic pumps  21  and  22  is changed. As shown in  FIG. 5 , the swash plate of the first pump  21  is interlockingly connected to the swash plate of the second pump  22 , and the swash plate angle R of the swash plate of the first pump  21  can be changed by a swash plate angle change means  51 . 
         [0061]    In this embodiment, the swash plate angle change means  51  includes a hydraulic cylinder ( FIG. 2 ). The swash plate angle change means  51  is connected to the swash plate of the first pump  21  and is actuated by operating an electromagnetic proportional control valve  52 . 
         [0062]    The electromagnetic proportional control valve  52  includes an electromagnetic valve having three parts and two positions (see  FIG. 2 ) which supplies hydraulic oil from the pilot pump  24  to the swash plate angle change means  51  and discharges the hydraulic oil from the swash plate angle change means  51 . The electromagnetic proportional control valve  52  is provided between the pilot pump  24  and the swash plate angle change means  51 . The electromagnetic proportional control valve  52  is configured so that by changing a current flowing in a solenoid, a flow rate of the hydraulic oil flowing in the electromagnetic proportional control valve  52  is changed proportionally to the current. The electromagnetic proportional control valve  52  is connected to the controller  40 , and the flow rate is changed corresponding to a signal from the controller  40  (current command). 
         [0063]    A swash plate angle detection means  53  detects the swash plate angle R of the swash plate of the hydraulic pumps  21  and  22 . The swash plate angle detection means  53  includes a position sensor for example, and is provided in the swash plate angle change means  51 . The swash plate angle detection means  53  is connected to the controller  40  and transmits a detection signal to the controller  40 . 
         [0064]    In the controller  40  of this embodiment, when the load of the engine  9  is less than the predetermined value, governor control is performed, and when the load is not less than the predetermined value, the relief pressure of the electromagnetic proportional relief valve  43  and the swash plate angle of the swash plate of the hydraulic pumps  21  and  22  are controlled corresponding to the magnitude of the load. The load is found from the difference between the set rotation speed Ns and the actual rotational speed N of the engine  9  with the map, and the relief pressure of the electromagnetic proportional relief valve  43  and the swash plate angle of the swash plate of the hydraulic pumps  21  and  22  are changed corresponding to the load. Concretely, a flow shown in  FIG. 6  is performed. 
         [0065]    At a step S 21 , the controller  40  obtains the set rotation speed Ns and the actual rotational speed N of the engine  9  and the swash plate angle R of the swash plate of the hydraulic pumps  21  and  22 . Then, the control is shifted to a step S 22 . 
         [0066]    The step S 22  is similar to the step S 12  of the first embodiment. When the actual rotational speed N of the engine  9  is lower than the set rotation speed Ns, the control is shifted to a step S 23 . When not lower, the control is shifted to a step S 27 . 
         [0067]    The step S 23  is similar to the step S 13  of the first embodiment. Then, the control is shifted to a step S 24 . 
         [0068]    At the step S 24 , the controller  40  judges whether the swash plate angle R of the swash plate of the hydraulic pumps  21  and  22  is a limiting angle Rm or not. The limiting angle Rm is a limiting angle of the swash plate at which the discharge amount of the hydraulic oil from the hydraulic pumps  21  and  22  is the minimum. When the swash plate angle R is the limiting angle Rm, the control is shifted to a step S 25 . When the swash plate angle R is not the limiting angle Rm, the control is shifted to a step S 26 . 
         [0069]    At the step S 25 , the controller  40  changes the swash plate angle R of the swash plate of the hydraulic pumps  21  and  22  into a swash plate angle Re corresponding to the deviation e. Namely, the controller  40  operates the electromagnetic proportional control valve  52  so that the hydraulic oil discharged from the pilot pump  24  is supplied to and discharged from the swash plate angle change means  51 , whereby the swash plate angle is changed into the swash plate angle Re and the discharge amount of the hydraulic oil from the hydraulic pumps  21  and  22  is changed to a discharge amount corresponding to the swash plate angle Re. Then, the control is shifted to RETURN and the flow is repeated. 
         [0070]    At the step S 26 , the controller  40  acts similarly to the step S 14  of the first embodiment. Then, the control is shifted to RETURN and the flow is repeated. 
         [0071]    At the step S 27 , the controller  40  stops the control of the swash plate angle R of the swash plate of the hydraulic pumps  21  and  22  with the swash plate angle change means  51  and the electromagnetic proportional control valve  52 , and changes the relief pressure of the electromagnetic proportional relief valve  43  into Xa. Then, the control is shifted to RETURN and the flow is repeated. 
         [0072]    The swash plate angle R of the swash plate of the hydraulic pumps  21  and  22  can be changed with not only the swash plate angle change means  51  but also three swash plate angle change means  54 ,  55  and  56  (see  FIG. 2 ) which are operated corresponding to the flow rate of the hydraulic oil discharged from the hydraulic pumps  21 ,  22  and  23 . Accordingly, when the control is stopped at the step, the swash plate angle R is changed corresponding to the discharge amount of the hydraulic oil discharged from the hydraulic pumps  21 ,  22  and  23 . 
         [0073]    As the above, in the turning working vehicle  1  according to the second embodiment of the present invention, when the load of the engine  9  is increased and the actual rotational speed N of the engine  9  becomes lower than the set rotation speed Ns, the swash plate angle change means  51  is operated corresponding to the deviation e between the actual rotational speed N and the set rotation speed Ns so that the swash plate angle R of the swash plate of the hydraulic pumps  21  and  22  is changed into the swash plate angle Re, and when the swash plate angle Re is the limiting angle Rm, the electromagnetic proportional relief valve  43  which is the pressure change means is operated corresponding to the deviation e so that the pressure of the hydraulic oil from the third pump  23  is changed. In more detail, the relief pressure of the electromagnetic proportional relief valve  43  is changed from the relief pressure Xa into the relief pressure Xe lower than the relief pressure Xa, whereby the pressure of the hydraulic oil from the third pump  23  is reduced. Accordingly, the load of the engine  9  caused by the third pump  23  and the load of the engine  9  caused by the first pump  21  and the second pump  22  can be reduced. Therefore, the effect of preventing the engine stall is improved further. In comparison with the first embodiment, the pressure of the hydraulic oil from the third pump  23  is not reduced excessively, whereby balance of the work is not lost and working ability is not reduced. 
         [0074]    As shown in a flow in  FIG. 7 , in the controller  40 , when the load of the engine  9  is increased and the actual rotational speed N of the engine  9  becomes lower than the set rotation speed Ns, the relief pressure of the electromagnetic proportional relief valve  43  is changed corresponding to the deviation e between the actual rotational speed N and the set rotation speed Ns, and when the relief pressure X becomes a limiting pressure Xm (a limiting pressure at which the pressure of the hydraulic oil from the third pump  23  is the minimum), the swash plate angle R of the swash plate of the hydraulic pumps  21  and  22  can be changed so as to change the discharge amount of the hydraulic pumps  21  and  22 . 
         [0075]    Furthermore, as shown in a flow in  FIG. 8 , in the controller  40 , when the load of the engine  9  is increased and the actual rotational speed N of the engine  9  becomes lower than the set rotation speed Ns, the relief pressure of the electromagnetic proportional relief valve  43  and the swash plate angle of the swash plate of the hydraulic pumps  21  and  22  can be changed simultaneously corresponding to the deviation e between the actual rotational speed N and the set rotation speed Ns so as to change the pressure of the hydraulic oil from the third pump  23  and the discharge amount of the hydraulic pumps  21  and  22  simultaneously. In this case, the load of the engine  9  caused by the hydraulic pumps  21 ,  22  and  23  is dispersed, whereby the balance of the work is not lost and the working ability is not reduced. 
       Embodiment 3 
       [0076]    An explanation will be given on a control configuration and a control mode of the turning working vehicle  1  according to a third embodiment of the present invention referring to  FIGS. 9 and 10 . Points different from the first and second embodiments are mainly explained. 
         [0077]    Different from the turning working vehicle  1  of the first and second embodiments configured so that the load of the engine  9  is detected and the pressure of the hydraulic oil from the third pump  23  is changed, the turning working vehicle  1  according to the third embodiment is configured so that application of the load on the engine  9  is predicted beforehand and the pressure of the hydraulic oil from the third pump  23  is changed. According to this embodiment, the pressure change means changing the pressure of the hydraulic oil from the third pump  23  includes a low pressure side relief valve  61 , a high pressure side relief valve  62  and a switching valve  63 . 
         [0078]    The low pressure side relief valve  61  reduces the pressure of the hydraulic oil from the third pump  23 . A suction port of the low pressure side relief valve  61  is connected via the switching valve  63  to a discharge port of the third pump  23 . A discharge port of the low pressure side relief valve  61  is connected to the hydraulic oil tank  19 . A relief pressure of the low pressure side relief valve  61  is set to Xl of the low pressure side. 
         [0079]    The high pressure side relief valve  62  increases the pressure of the hydraulic oil from the third pump  23 . A suction port of the high pressure side relief valve  62  is connected via the switching valve  63  to a discharge port of the third pump  23 . A discharge port of the high pressure side relief valve  62  is connected to the hydraulic oil tank  19 . A relief pressure of the high pressure side relief valve  62  is set to Xh of the high pressure side. 
         [0080]    The switching valve  63  switches an oil passage which guides the hydraulic oil discharged from the third pump  23  to the low pressure side relief valve  61  and an oil passage which guides the hydraulic oil discharged from the third pump  23  to the high pressure side relief valve  62 . The switching valve  63  is provided between the third pump  23  and the low pressure side relief valve  61  and the high pressure side relief valve  62 . The switching valve  63  is an electromagnetic switching valve and is connected to the controller  40  and switches the oil passages following a signal from the controller  40 . 
         [0081]    An air conditioning device  64  conditions air in a cabin covering the operation part  8 . The air conditioning device  64  includes a compressor  64   a , a receiver dryer, an expansion valve, an evaporator and the like. The compressor  64   a  of the air conditioning device  64  is provided on the output shaft of the engine  9  and is driven by power from the engine  9 . 
         [0082]    An air conditioning operation tool  65  is a means for operating the air conditioning device  64 . The air conditioning operation tool  65  is provided in the operation part  8 . The air conditioning operation tool  65  includes an ON-OFF switch, a temperature control lever, an airflow control knob and the like. The ON-OFF switch of the air conditioning operation tool  65  is connected to the controller  40  and transmits a detection signal (ON-OFF signal) to the controller  40 . Instead of the ON-OFF switch of the air conditioning operation tool  65 , a detection means detecting operation of the compressor  64   a  may alternatively be provided and connected to the controller  40 . 
         [0083]    The controller  40  operates the switching valve  63  following on-off operation of the air conditioning device  64  (operation of the ON-OFF switch of the air conditioning operation tool  65 ). Concretely, a flow shown in  FIG. 10  is performed. 
         [0084]    At a step S 31 , the controller  40  judges whether the air conditioning device  64  is turned on or not, that is, whether the ON-OFF switch of the air conditioning operation tool  65  is ON or not. When the ON-OFF switch is ON, the control is shifted to a step S 32 . When the ON-OFF switch is not ON, the control is shifted to a step S 33 . 
         [0085]    At the step S 32 , the controller  40  changes the relief pressure X into Xl. Namely, the switching valve  63  is switched and the hydraulic oil discharged from the third pump  23  is supplied to the low pressure side relief valve  61 . Accordingly, the pressure of the hydraulic oil from the third pump  23  is changed into the relief pressure Xl. Therefore, the hydraulic oil excessing the relief pressure Xl is returned to the hydraulic oil tank  19 . Then, the control is shifted to RETURN and the flow is repeated. 
         [0086]    At the step S 33 , the controller  40  changes the relief pressure X into Xh. Namely, the switching valve  63  is switched and the hydraulic oil discharged from the third pump  23  is supplied to the high pressure side relief valve  62 . Accordingly, the pressure of the hydraulic oil from the third pump  23  is changed into the relief pressure Xh. Therefore, the hydraulic oil excessing the relief pressure Xh is returned to the hydraulic oil tank  19 . Then, the control is shifted to RETURN and the flow is repeated. 
         [0087]    Accordingly, when the air conditioning device  64  is turned on, the pressure of the hydraulic oil from the third pump  23  is changed from the relief pressure Xh of the high pressure side into the relief pressure Xl of the low pressure side, whereby the load of the engine  9  caused by the third pump  23  can be reduced for a difference between Xh and Xl. Therefore, when the compressor  64   a  of the air conditioning device  64  is driven, the engine stall can be prevented. 
         [0088]    The pressure change means may alternatively be the electromagnetic proportional relief valve shown in the first embodiment so as to change the relief pressure continuously corresponding to a set temperature of the air conditioning device  64  or the like. 
         [0089]    As the above, in the turning working vehicle  1  according to the third embodiment of the present invention, the pressure change means is operated following on-off operation of the air conditioning device  64  (operation of the ON-OFF switch of the air conditioning operation tool  65 ) so as to change the pressure of the hydraulic oil from the third pump  23 . In detail, interlocking with the turning-on operation of the air conditioning device  64 , the switching valve  63  is operated so as to make the hydraulic oil from the third pump  23  flow to the low pressure side relief valve  61 , whereby the pressure of the hydraulic oil from the third pump  23  is reduced, and interlocking with the turning-off operation of the air conditioning device  64 , the switching valve  63  is operated so as to make the hydraulic oil from the third pump  23  flow to the high pressure side relief valve  62 , whereby the pressure of the hydraulic oil from the third pump  23  is increased. Accordingly, by reducing the pressure of the hydraulic oil from the third pump  23  by the turning-on operation of the air conditioning device  64 , the load of the engine  9  caused by the third pump  23  can be reduced, whereby the effect of preventing the engine stall is improved. 
       Embodiment 4 
       [0090]    An explanation will be given on a circumference configuration of an engine  110  according to a fourth embodiment of the present invention referring to  FIG. 11 . 
         [0091]    In  FIG. 11 , in a hydraulic drive system  130 , thick lines show a main circuit and thin lines show a pilot circuit. In  FIG. 11 , in an air conditioning system  120 , thick lines show a coolant circuit. In  FIG. 11 , dotted lines show electric signal lines. 
         [0092]    The engine  110  and the hydraulic drive system  130  of this embodiment are different from those of the first to third embodiments. 
         [0093]    In the circumference of the engine  110 , a first pump  131  as a hydraulic pump, a second pump  132  as a hydraulic pump, a third pump  133  as a hydraulic pump, a compressor  121 , a controller  150  as a control means, a rack actuator  153  as a rotation speed change means, and an accelerator lever  155  as a target rotation speed set means are provided. 
         [0094]    An explanation will be given on a configuration of the engine  110 . 
         [0095]    An output shaft of the engine  110  is connected to an input shaft of the first pump  131 , an input shaft of the second pump  132  and an input shaft of the third pump  133  (in this embodiment, the input shaft of the first pump  131 , the input shaft of the second pump  132  and the input shaft of the third pump  133  are configured by one shaft, and the shaft is an input shaft  201  in  FIG. 12  discussed later), and the first pump  131 , the second pump  132  and the third pump  133  are driven by the engine. Furthermore, the output shaft of the engine  110  is connected via a clutch  152  to an input shaft of the compressor  121 . 
         [0096]    An engine rotation speed sensor  151  as an actual rotation speed detection means is arranged near a crankshaft of the engine  110 . The engine rotation speed sensor  151  detects an actual rotation speed Ne of the engine  110 . The engine rotation speed sensor  151  is connected to the controller  150 . 
         [0097]    The engine  110  is controlled so as to realize a target rotation speed, set by the accelerator lever  155 , with an electronic governor. In more detail, for realizing the target rotation speed set by the accelerator lever  155 , a fuel injection amount is changed and controlled by operation of the rack actuator  153  which is the rotation speed change means. The rack actuator  153  is connected to the controller  150 . 
         [0098]    An explanation will be given on a configuration of the hydraulic pumps. 
         [0099]    The first pump  131 , the second pump  132  and the third pump  133  are included in the hydraulic drive system  130 . The hydraulic drive system  130  has the left traveling hydraulic motor  5 L, the right traveling hydraulic motor  5 R, the blade cylinder  18 , the boom cylinder  13 , the arm cylinder  14 , the bucket cylinder  15 , and the swing cylinder  16 , which are mentioned above, as hydraulic actuators. In the hydraulic drive system  130 , the hydraulic pumps suck hydraulic oil stored in a hydraulic oil tank and apply pressure on the hydraulic oil, and then send the hydraulic oil to the hydraulic actuators. 
         [0100]    The first pump  131  and the second pump  132  are variable displacement type hydraulic pumps whose discharge amounts of the hydraulic oil can be changed by changing tilt angles of a movable swash plate  141  and a movable swash plate  142 . The movable swash plate  141  and the movable swash plate  142  are configured integrally. Namely, the first pump  131  and the second pump  132  are configured so that a plurality of plungers are arranged in one cylinder block so as to be movable reciprocally, one suction port and two discharge ports are formed, the plungers contact with one swash plate, and the discharge amounts are changed simultaneously. The third pump  133  is a fixed displacement type hydraulic pump which is configured by a trochoid type or gear type pump whose discharge amount is fixed. 
         [0101]    The tilt angle of the movable swash plate  141  is limited (controlled) by a spring mechanism  147 , a first damper mechanism  161  and a rotation deviation damper mechanism  165 . The spring mechanism  147  biases the movable swash plate  141  so as to make the discharge amounts of the first pump  131  and the second pump  132  the maximum discharge amount, that is, to tilt the movable swash plate  141  at a predetermined tilt angle. The first damper mechanism  161  biases the movable swash plate  141  so as to control the discharge amounts of the first pump  131  and the second pump  132  corresponding to the discharge amount of the first pump  131 , that is, to control the tilt angle of the movable swash plate  141 . 
         [0102]    The tilt angle of the movable swash plate  142  is limited by a second damper mechanism  162  and a third damper mechanism  163 . The second damper mechanism  162  biases the movable swash plate  142  so as to control the discharge amounts of the first pump  131  and the second pump  132  corresponding to the discharge amount of the second pump  132 , that is, to control the tilt angle of the movable swash plate  142 . The third damper mechanism  163  biases the movable swash plate  142  so as to control the discharge amounts of the first pump  131  and the second pump  132  corresponding to the discharge amount of the third pump  133 , that is, to control the tilt angle of the movable swash plate  142 . 
         [0103]    An electromagnetic proportional control valve  169  controls a pilot pressure from a pilot pump (not shown) to the rotation deviation damper mechanism  165 . A solenoid which is a switching operation part of the electromagnetic proportional control valve  169  is connected to the controller  150 . 
         [0104]    An explanation will be given on a configuration of the compressor  121 . 
         [0105]    The compressor  121  is included in the air conditioning system  120 . The air conditioning system  120  has an outdoor heat exchanger, an expansion valve and an indoor heat exchanger (not shown). The air conditioning system  120  circulates a coolant with the compressor  121  so as to condition air in the operation part  8 . 
         [0106]    The clutch  152  is interposed between the output shaft of the engine  110  and the input shaft of the compressor  121 , and the clutch  152  switches ON (connection) and OFF (disconnection). The clutch  152  includes an electromagnetic clutch and is connected to the controller  150 . 
         [0107]    The accelerator lever  155  is a means for setting the target rotation speed mNe of the engine  110 . The accelerator lever  155  is arranged in the operation part  8 . An operation amount (rotation angle) of the accelerator lever  155  is detected by an angle sensor which is an operation amount detection means, and the angle sensor is connected to the controller  150 . 
         [0108]    The controller  150  controls totally the engine  110 , the air conditioning system  120  and the hydraulic drive system  130 . The controller  150  is connected to the engine rotation speed sensor  151 , the clutch  152 , the accelerator lever  155  and the electromagnetic proportional control valve  169 . 
         [0109]    An explanation will be given on a flow of engine stall avoidance control S 100  referring to  FIG. 12 . 
         [0110]    Steps S 120  to S 130  show steps of speed sensing control. 
         [0111]    In the engine  110 , for example, when the load of the hydraulic pump is increased, the actual rotation speed Ne of the engine is reduced and the reduction of the actual rotation speed is suppressed to a predetermined amount by the electronic governor until the load reaches a first set value A1 discussed later. When the engine load A is increased further from the first set value A1, until the load reaches a second set value A2, the electromagnetic proportional control valve  169  is operated and the tilt of the movable swash plate  142  is changed so as to reduce the discharge amount of the hydraulic oil of the first pump  131  and the second pump  132 . Furthermore, when the engine load excesses the second set value A2, the engine  110  is stalled. Therefore, in the engine stall avoidance control S 100 , when the engine load A excesses the second set value A2, the clutch  152  has been turned OFF for a predetermined time so as to cut off power transmission to the compressor  121 , whereby the engine  110  is prevented from being stalled. 
         [0112]    In this embodiment, the engine load is calculated based on the difference between the target rotation speed mNe and the actual rotation speed Ne. However, the detection of the load is not limited to this embodiment, and the load may alternatively be found based on a difference between a target rack position and an actual rack position which change the fuel injection amount, a difference between a target angle and an actual angle of the movable swash plate, or the pressure of the hydraulic oil, for example. 
         [0113]    At a step S 110 , the controller  150  calculates a rotation speed deviation dNe by deducting the actual rotation speed Ne detected by the engine rotation speed sensor  151  from the target rotation speed mNe set with the accelerator lever  155 , and calculates the engine load A based on the rotation speed deviation dNe. 
         [0114]    At a step S 120 , in the controller  150 , when the rotation speed deviation dNe is increased and the engine load A is larger than the first set value A1, the control is shifted to a step S 130 . On the other hand, when the engine load A is not larger than the first set value A1, the control is shifted to a step S 200 , and the rotation speed deviation dNe is controlled toward 0 with governor control. 
         [0115]    At the step S 130 , the controller  150  changes the tilt of the movable swash plate  142  by controlling the pilot pressure with the electromagnetic proportional control valve  169  so as to reduce the discharge amount of the hydraulic oil of the first pump  131  and the second pump  132 , that is, to reduce a load torque of the first pump  131  and the second pump  132 . The steps S 120  to S 130  show the steps of the speed sensing control. 
         [0116]    At a step S 140 , the controller  150  judges whether the rotation speed deviation dNe is increased and the engine load A is larger than the second set value A2 after the speed sensing control is performed or not. When the engine load A is larger than the second set value A2, the control is shifted to a step S 150 . 
         [0117]    At the step S 150 , the controller  150  turns OFF the clutch  152 , and the control is shifted to a step S 160 . At this time, the connection of the engine  110  and the compressor  121  is cut off, whereby the engine load A is reduced. 
         [0118]    At the step S 160 , whether a set time t1 passes after the clutch  152  is turned OFF or not is judged. When the set time t1 passes, the control is shifted to a step S 170  and the clutch  152  is turned ON. 
         [0119]    An explanation will be given on effect of the engine stall avoidance control S 100 . 
         [0120]    According to the engine stall avoidance control S 100 , the engine stall can be avoided. Namely, when the rotation speed deviation dNe is increased and the load A is increased after the speed sensing control is performed, the connection of the engine  110  and the compressor  121  is cut off, whereby the load of the engine  110  is reduced and engine output is reduced so as to avoid the engine stall. 
         [0121]    An explanation will be given on a left stepped pin  210  and a right stepped pin  220  referring to  FIG. 13 . 
         [0122]      FIG. 13(A)  is a schematic side view partially in section of a pump unit  200 . 
         [0123]      FIG. 13(B)  is a schematic plan view partially in section of the pump unit  200 . In  FIG. 13 , for make the explanation plain, the first pump  131  and the second pump  132  are not shown. 
         [0124]    The pump unit  200  is configured by integrating the first pump  131 , the second pump  132  and the third pump  133  in one casing  300 . 
         [0125]    The pump unit  200  has the casing  300 , the input shaft  201 , plungers of the first pump  131  and the second pump  132  (not shown), the third pump  133 , the left stepped pin  210 , the right stepped pin  220 , a spring mechanism  230  and a swash plate  240 . 
         [0126]    The swash plate  240  corresponds to the movable swash plate  141  and the movable swash plate  142  in  FIG. 11 . The spring mechanism  230  corresponds to the spring mechanism  147  in  FIG. 11 . 
         [0127]    The left stepped pin  210  corresponds to the first damper mechanism  161  and the second damper mechanism  162  in  FIG. 11 . The left stepped pin  210  has a first diameter part (small diameter part)  211  and a second diameter part (large diameter part)  212 . The first diameter part  211  is formed at one of ends of the left stepped pin  210 . The second diameter part  212  is formed at the other end of the left stepped pin  210 , and the other end contacts with the swash plate  240 . The second diameter part  212  has larger diameter than the first diameter part  211 . 
         [0128]    In the casing  300 , spaces in which the left stepped pin  210  is housed are formed. In a first space  311 , the first diameter part  211  of the left stepped pin  210  is housed. In a second space  312 , the second diameter part  212  of the left stepped pin  210  is housed. A first oil passage  411  is communicated with one of ends of the first diameter part  211 . The first oil passage  411  is communicated with a discharge pipe of the first pump  131 . A second oil passage  412  is communicated with one of ends of the second diameter part  212 . The second oil passage  412  is communicated with a discharge pipe of the second pump  132 . A ratio of a pressure receiving area of the first diameter part  211  and a pressure receiving area of the second diameter part  212  is proportional to a ratio of a discharge capacity of the first pump  131  and a discharge capacity of the second pump  132 . 
         [0129]    According to the configuration, the left stepped pin  210  is biased toward the swash plate  240  corresponding to the discharge amount of the first pump  131  or the discharge amount of the second pump  132 . Namely, a tilt angle of the swash plate  240  is changed with the left stepped pin  210 . 
         [0130]    The right stepped pin  220  corresponds to the third damper mechanism  163  and the rotation deviation damper mechanism  165  in  FIG. 11 . The right stepped pin  220  has a third diameter part (small diameter part)  223  and a fourth diameter part (large diameter part)  224 . The third diameter part  223  is formed at one of ends of the right stepped pin  220 . The fourth diameter part  224  is formed at the other end of the right stepped pin  220 , and the other end contacts with the swash plate  240 . The fourth diameter part  224  has larger diameter than the third diameter part  223 . 
         [0131]    In the casing  300 , spaces in which the right stepped pin  220  is housed are formed. In a third space  323 , the third diameter part  223  of the right stepped pin  220  is housed. In a fourth space  324 , the fourth diameter part  224  of the right stepped pin  220  is housed. A third oil passage  423  is communicated with one of ends of the third diameter part  223 . The third oil passage  423  is communicated with a discharge pipe of the third pump  133 . A fourth oil passage  424  is communicated with one of ends of the fourth diameter part  224 . The fourth oil passage  424  is communicated with a pilot pipe of the electromagnetic proportional control valve  169 . 
         [0132]    According to the configuration, the right stepped pin  220  is biased toward the swash plate  240  corresponding to the discharge amount of the third pump  133  or the pilot pressure controlled with the electromagnetic proportional control valve  169 . Namely, the tilt angle of the swash plate  240  is changed with the right stepped pin  220 . 
       INDUSTRIAL APPLICABILITY 
       [0133]    The present invention can be used for a working vehicle.