Patent Publication Number: US-2016238041-A1

Title: Hydraulic Pressure Circuit and Working Machine

Description:
TECHNICAL FIELD 
     The present invention relates to a hydraulic pressure circuit including an accumulator and to a working machine provided with the hydraulic pressure circuit. 
     BACKGROUND ART 
     In working machines, pressure oil discharged from a boom hydraulic cylinder when a boom is lowered is accumulated in an accumulator, and pressure oil relieved from a swinging hydraulic motor when swinging is accelerated or decelerated is also accumulated in the accumulator (see Patent Document 1, for example). 
     [Patent Document 1] Japanese Patent Application Laid-open No. 2010-84888 
     While the pressure oil discharged from the boom hydraulic cylinder is being accumulated in the accumulator, the pressure oil discharged from the boom hydraulic cylinder cannot be recovered to the boom hydraulic cylinder. Thus, the required pump flow amount might be failed to be secured and an operation of the boom hydraulic 
     DISCLOSURE OF THE INVENTION 
     The present invention is made in view of such a point, and an object of the present invention is to provide a hydraulic pressure circuit and a working machine that can secure a required pump flow amount even when hydraulic oil is being accumulated in an accumulator. 
     An invention according to claim  1  is a hydraulic pressure circuit including: a plurality of fluid pressure cylinders performing the same operation at the same time by a hydraulic fluid pressurized and supplied from a pump; an accumulator in which the hydraulic fluid is accumulated; an accumulating circuit for accumulating, in the accumulator, the hydraulic fluid pushed out of one fluid pressure cylinder among the plurality of fluid pressure cylinders; and a recovering circuit that recovers the hydraulic fluid pushed out of another fluid pressure cylinder that is different from the one fluid pressure cylinder, among the plurality of fluid pressure cylinders, to the other fluid pressure cylinder. 
     An invention according to claim  2  is the hydraulic pressure circuit according to claim  1  further including a combination valve formed of a single block incorporating a plurality of circuit functions that switch among the accumulating circuit, the recovering circuit, and a circuit that guides the hydraulic fluid pressurized and supplied from the pump to the plurality of fluid pressure cylinders. 
     An invention according to claim  3  is a working machine including: a vehicle body; a working apparatus mounted on the vehicle body; and the hydraulic pressure circuit according to claim  1  or  2  provided for a plurality of fluid pressure cylinders that raise and lower the working apparatus. 
     In the invention according to claim  1 , the accumulating circuit and the recovering circuit are separated from each other and the hydraulic fluid pushed out of the one fluid pressure cylinder is accumulated in the accumulator. At the same time, the hydraulic fluid pushed out of the other fluid pressure cylinder is recovered. Thus, even during the accumulation of the accumulator, the pump flow amount can be saved by an amount corresponding to the recovered flow amount, whereby the required pump flow amount can be easily secured, and the pump can be downsized. A load is not distributed to all of the plurality of fluid pressure cylinders and is concentrated to a smaller number of fluid pressure cylinders. Thus, pressure produced from the fluid pressure cylinder can be raised to increase energy accumulated in the accumulator, whereby the accumulator can be downsized. 
     In the invention according to claim  2 , the combination valve is formed of a single block incorporating the plurality of circuit functions that switch among the accumulating circuit, the recovering circuit, and the circuit that guides the hydraulic fluid pressurized and supplied from the pump to the plurality of fluid pressure cylinders. Thus, a simple layout can be achieved and the cost can be reduced. 
     In the invention according to claim  3 , even during the accumulation operation of the accumulator when the working apparatus of the working machine is lowered, the pump flow amount can be saved by an amount corresponding to the recovered flow amount, whereby the required pump flow amount can be easily secured, and the pump can be downsized. The load is not distributed to all of the plurality of fluid pressure cylinders and is concentrated to a smaller number of fluid pressure cylinders. Thus, pressure produced from the fluid pressure cylinder can be raised to increase energy accumulated in the accumulator, whereby the accumulator can be downsized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram showing an embodiment of a hydraulic pressure circuit according to the present invention. 
         FIG. 2  is a circuit diagram showing a switched state of the circuit. 
         FIG. 3  is a circuit diagram showing another switched state of the circuit. 
         FIG. 4  is a perspective view of an embodiment of a working machine according to the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The present invention will be described in detail below based on an embodiment shown in  FIGS. 1 to 4 . 
     As shown in  FIG. 4 , a hydraulic shovel HE as a working machine has a vehicle body  1  formed of a lower traveling body  2  and an upper swinging body  3  disposed on the lower traveling body  2  to be capable of being swung by a swinging motor  3   m.  A machine chamber  4 , a cab  5 , and a working apparatus  6  are mounted on the upper swinging body  3 . An engine and a pump are mounted in the machine chamber  4 . The cab  5  protects an operator. 
     The working apparatus  6  has the following configuration. Specifically, a base end of a boom  7  is pivotally supported by the upper swinging body  3 . The boom  7  is rotated in an up and down direction by two boom cylinders  7   c   1  and  7   c   2  which are fluid pressure cylinders arranged in parallel. A stick  8  is pivotally supported by a distal end of the boom  7 . The stick  8  is rotated in a front and rear direction by a stick cylinder  8   c.  A bucket  9  is pivotally supported by a distal end of the stick  8 . The bucket  9  is rotated by a bucket cylinder  9   c.  The two boom cylinders  7   c   1  and  7   c   2  are arranged in parallel for the common boom  7 , and perform the same operation at the same time. 
       FIG. 1  shows an engine power assist system. The engine power assist system makes potential energy of the working apparatus  6  and kinetic energy of the upper swinging body  3  accumulated into an accumulator, respectively through the boom cylinder  7   c   1  and the swinging motor  3   m.  The energy thus accumulated is used for assisting engine power. 
     Next, a circuit configuration of this system will be described. 
     An assist pump motor  15  is coupled, directly or through a gear, to a main pump shaft  14  of main pumps  12  and  13  which are pumps driven by a mounted engine  11  in the machine chamber  4 . The main pumps  12  and  13  and the assist pump motor  15  each includes a swash plate. A pump/motor capacity (piston stroke) can be variably adjusted with an angle of the swash plate. The swash plate angles (tilt angles) are controlled by regulators  16 ,  17 , and  18  and are detected by swash plate angle sensors  16 φ,  17 φ, and  18 φ. The regulators  16 ,  17 , and  18  are controlled by a solenoid valve. For example, the regulators  16  and  17  of the respective main pumps  12  and  13  can be automatically controlled by a negative flow control pressure (what is known as negative control pressure) guided through a negative flow control path  19   nc . The regulators  16  and  17  may also be controlled by a signal other than the negative control pressure, by electromagnetic switching valves  19   a  and  19   b  of a negative flow control valve  19 . 
     The main pumps  12  and  13  discharge hydraulic oil, which is a hydraulic fluid sucked from a tank  21 , respectively to paths  22  and  23 . Pressure sensors  24  and  25  detect the discharge pressure of the pumps. Output paths  27  and  29  are connected to a boom energy recovery valve  31  that is a combination valve, through a path  30 . The output paths  27  and  29  respectively extend from main and sub boom control valves  26  and  28  for controlling the boom cylinders  7   c   1  and  7   c   2 . The main and sub boom control valves  26  and  28  are pilot operated control valves that are connected to the main pumps  12  and  13  and control the direction and the flow amount. 
     The boom energy recovery valve  31  is a combination valve formed of a single block incorporating a plurality of circuit functions for switching among an accumulating circuit A and a recovering circuit B shown in  FIG. 1  and a circuit shown in  FIG. 2 . The circuit shown in  FIG. 2  guides the hydraulic oil pressurized and supplied from the main pumps  12  and  13 , during the boom raising operation, to head sides of the two boom cylinders  7   c   1  and  7   c   2 . 
     Head side ends of the one boom cylinder  7   c   1  and the other boom cylinder  7   c   2  are connected to the boom energy recovery valve  31  respectively through paths  32  and  33 . The other output path  34 , extending from the main boom control valve  26 , is connected to a rod side end of the one boom cylinder  7   c   1 . A pressure sensor  35  that detects boom cylinder rod side pressure is disposed on the rod side end. The rod side ends of the two boom cylinders  7   c   1  and  7   c   2 , which are arranged in parallel, can communicate with each other through a bypass path  36 . An electromagnetic separation valve  37  provided in the bypass path  36  can block the communication from the rod side of the boom cylinder  7   c   1  to the rod side of the boom cylinder  7   c   2 . The rod side of the boom cylinder  7   c   2  is connected to the boom energy recovery valve  31  through a path  38 . 
     The one output path  27  extending from the main boom control valve  26  can communicate with the other output path  34  through an electromagnetic switching valve  39  and a check valve  40 . A pressure sensor  41  is disposed on a discharge side of the assist pump motor  15 , and detects the discharge pressure. A discharge path  42  of the assist pump motor  15  is provided with an electromagnetic switching valve  43 . A path  45  passing through a check valve  44  is connected to the output path  34 . 
     The discharge path  42  of the assist pump motor  15  is branched into three paths  46 ,  47 , and  48 . The path  46  is connected to an electromagnetic unload valve  49 . The electromagnetic unload valve  49  is connected to the tank  21  through tank paths  50  and  51  as well as a spring equipped check valve  52  and an oil cooler  53  or a spring equipped check valve  54 . The path  47  is connected to the tank path  50  through a relief valve  55 . 
     The path  48  is connected to an accumulator path  62  provided with a plurality of first accumulators  61  through an electromagnetic switching valve  57 , a check valve  58 , and a path  59 . A pressure sensor  63  that detects the pressure accumulated in the first accumulator  61  is connected to the accumulator path  62 . The accumulator path  62  is connected to a path  66  passing through an electromagnetic recovery valve  64  and a check valve  65 . The path  66  is connected to an intake side path  68  extending from the tank  21  and connected to an intake port of the assist pump motor  15  through a check valve  67 . A pressure sensor  69  that detects the assist pump motor intake side pressure is disposed on the intake side path  68 . 
     The assist pump motor  15  has the following functions. Specifically, when the pressure accumulated in the first accumulator  61  increases and the accumulator pressure reaches a predetermined value, the electromagnetic recovery valve  64  is switched to a communication position, and thus the hydraulic oil is sucked from the first accumulator  61 , whereby pressure rise in the first accumulator  61  can be prevented. At the same time, the hydraulic oil thus sucked is pressurized and supplied to the rod side of the boom cylinder  7   c   1 . 
     The boom energy recovery valve  31  includes a pilot operated main switching valve  71 . The main switching valve  71  controls the supply and discharge of pilot pressure with an electromagnetic switching valve  72  to switch the relationship among paths  73 ,  74 ,  75 , and  76 . 
     The path  73  is connected to one port of one drift reducing valve  77 . The outer path  32 , extending from the head side end of the one boom cylinder  7   c   1 , is connected to the other port of the drift reducing valve  77  through an inner path  78 . The drift reducing valve  77  controls the pilot pressure in a spring chamber with a pilot valve  79 , to control the opening/closing and an opening amount between the ports. A path  81 , branched off from the path  30 , is connected to the path  73  through a check valve  82 . 
     The path  74  is connected to the path  30 , and is further connected to one port of the other drift reducing valve  83 . The outer path  33 , extending from the head side end of the other boom cylinder  7   c   2 , is connected to the other port of the drift reducing valve  83  through an inner path  84 . The drift reducing valve  83  controls the pilot pressure in the spring chamber with a pilot valve  85  to control the opening/closing and an opening amount between the ports. 
     The spring chambers of the drift reducing valves  77  and  83  are in communication with the paths  78  and  84 , or with the path  86  to the tank  21  through the pilot valve  79  or  85 . 
     The path  75  is branched into paths to a check valve  87 , to a spring equipped check valve  88 , and to a variable throttle valve  89 . The path passing through the check valve  87  is connected to the outer path  38  and an inner path  90 . A relief valve  91  and a check valve  92  are disposed between the path  90  and the path  78 . A relief valve  93  and a check valve  94  are disposed between the path  90  and the path  84 . A pressure sensor  95  and a regulating valve  96  are disposed between the paths  78  and the path  84 . A pressure sensor  97  and a regulating valve  98  are disposed between the path  84  and the path  90 . The spring equipped check valve  88  and the variable throttle valve  89  are connected to the tank path  50  through a path  99 . 
     The path  76  is connected to the path  59  through a path  105  passing through a check valve  104 . A pressure sensor  106  detects the pressure in the path  105 . A path branched off from the path  105  is connected to the tank path  50  through a relief valve  107 , a path  108 , and the path  99 . The path  108  is in communication with the path  105  through the check valve  109 . The path  105  is connected to the path  108  through an electromagnetic switching valve  110 . 
     As shown in  FIG. 1 , the accumulating circuit A is a circuit leading to the first accumulator  61  through the path  32  extending from the head side end of the one boom cylinder  7   c   1 , and through the path  78 , the drift reducing valve  77 , the path  73 , the main switching valve  71 , the check valve  104 , and the path  105  that are in the boom energy recovery valve  31 . The accumulating circuit A has a function of accumulating the oil pushed out of the head side of the boom cylinder  7   c   1  into the first accumulator  61 . 
     As shown in  FIG. 1 , the recovering circuit B is a circuit leading to the rod side end of the other boom cylinder  7   c   2  through the path  33  extending from the head side end of the other boom cylinder  7   c   2  and through the path  84 , the drift reducing valve  83 , the path  74 , the main switching valve  71 , the path  75 , the check valve  87 , and the path  38  that are in the boom energy recovery valve  31 . The recovering circuit B has a function of recovering the oil pushed out of the head side of the boom cylinder  7   c   2  to the rod side of the boom cylinder  7   c   2 . 
     Relief valves  114  and  115  oriented in opposite directions as well as check valves  117  and  118  oriented in opposite directions are disposed between paths  112  and  113  of a motor driving circuit C that connect the swinging motor  3   m  and a swing control valve  111  for controlling the direction and the speed of the swinging of the swinging motor  3   m.  A makeup path  116  is connected between the relief valves  114  and  115 , and the check valves  117  and  118 . The makeup path  116  has a tank path function of returning the oil discharged from the motor driving circuit C to the tank  21 . The makeup path  116  also has a makeup function with which the hydraulic oil can be supplied to the motor driving circuit C. The hydraulic oil is supplied to the path  112  or  113 , on aside where vacuum might be produced, from the makeup path  116  through the check valve  117  or  118 , at the pressure not exceeding the spring biasing pressure of the spring equipped check valve  52 . 
     The paths  112  and  113  of the motor driving circuit C are in communication with a path  121  for recovering swinging energy, through the check valves  119  and  120 . The path  121  is connected to a path  123  through a sequence valve  122 . The source pressure on the input side of the sequence valve  122  is less likely to change due to the back pressure on the output side. The path  121  is further connected to a second accumulator  125  through a path  124 . A pressure sensor  126  detects the pressure related to the second accumulator  125 . The path  123  is connected to the accumulator path  62  of the first accumulator  61  through a path  129  passing through an electromagnetic switching valve  127  and a check valve  128 . The path  129  is connected to the tank path  50  through a relief valve  130 . The second accumulator  125  is connected to the tank path  51  through a relief valve  131 . 
     When the swinging by the swinging motor  3   m  is accelerated and stopped, the driving energy and the braking energy relieved through the relief valves  114  and  115  are converted into the pressure to be accumulated in the second accumulator  125  before the relief valves  114  and  115  operate. Thus, the relieved swinging energy is recovered. In an assist mode, the electromagnetic switching valve  127  and the electromagnetic recovery valve  64  are switched to the communication position. Thus, the pressure oil discharged from the second accumulator  125  is pressurized and supplied to the assist pump motor  15 , through the accumulator path  62  and the electromagnetic recovery valve  64  on the side of the first accumulator  61 . The assist pump motor  15  is driven as a hydraulic motor to assist hydraulic outputs from the main pumps  12  and  13 , thereby reducing an engine load. 
     The vacuum might be produced on the upstream side of the swinging motor  3   m,  when the swing stop energy is supplied to the second accumulator  125 . Thus, the electromagnetic unload valve  49  is opened when the swinging operation starts, and the swash plate angle of the assist pump motor  15  is controlled in accordance with the amount and the speed of the swinging operation lever operation. Thus, the hydraulic oil is supplied to a path in which the vacuum is likely to be produced in the motor driving circuit C, from the assist pump motor  15  through the electromagnetic unload valve  49 , the tank paths  50  and  51 , and the makeup path  116 , by a flow amount corresponding to the amount and the speed of the swinging operation lever operation. 
     In the circuit configuration described above, the swash plate angle sensors  16 φ,  17 φ, and  18 φ as well as the pressure sensors  24 ,  25 ,  35 ,  41 ,  63 ,  69 ,  95 ,  97 ,  106 , and  126  input the detected swash plate angle signals and the pressure signals to an on-board controller (not shown). The electromagnetic switching valves  39 ,  43 ,  57 ,  72 ,  110 , and  127  as well as the electromagnetic unload valve  49  and the electromagnetic recovery valve  64  perform an ON/OFF operation in accordance with a driving signal output from the on-board controller (not shown) or are switched through a proportional action corresponding to the driving signal. A pilot operation is performed on the boom control valves  26  and  28 , the swing control valve  111 , and other unillustrated hydraulic actuator control valves (for the drive motor, the stick cylinder, the bucket cylinder, and the like), through a manual operation valve, known as a remote control valve, operated by an operator in the cab  5  through a lever or a pedal. The pilot operation on the drift reducing valves  77  and  83  as well as the pilot valves  79  and  85  is performed in conjunction with the pilot operation. 
     The control performed by the on-board controller is described below as a function. 
     (Engine Power Assist Function) 
     An engine power assist function in the hydraulic pressure circuit having the configuration described above will be described. 
       FIG. 1  shows a circuit state at the time of boom lowering operation for lowering the boom  7 . The hydraulic oil, pushed out of the head side of the one boom cylinder  7   c   1  to the paths  32  and  78  by the load of the working apparatus  6  and the like, passes through the drift reducing valve  77  of the boom energy recovery valve  31  and then has the direction controlled by the main switching valve  71  to move from the path  73  to the path  76 . Then, the hydraulic oil passes through the paths  105  and  59  to be accumulated in the first accumulator  61 . 
     At the same time, the hydraulic oil pushed out of the head side of the other boom cylinder  7   c   2  to the paths  33  and  84  passes through the drift reducing valve  83  of the boom energy recovery valve  31  and then has the direction controlled by the main switching valve  71  to move from the path  74  to the path  75 . Then, the hydraulic oil passes through the check valve  87  and the path  38  to be recovered to the rod side of the other boom cylinder  7   c   2 . Depending on the rod side pressure balance between the one and the other boom cylinders  7   c   1  and  7   c   2 , the hydraulic oil is also recovered to the rod side of the one boom cylinder  7   c   1  through the check valve in the electromagnetic separation valve  37 . 
     As described above, when the boom is lowered, the boom energy recovery valve  31  performs the accumulation into the first accumulator  61  and the recovering to the rod sides of the boom cylinders  7   c   1  and  7   c   2  through the main switching valve  71  and the drift reducing valves  77  and  83 . 
       FIG. 2  shows a circuit state at the time of boom raising operation for raising the boom  7 . At the time of boom raising operation, the boom energy recovery valve  31  stops the pressure accumulation into the first accumulator  61  and the recovering to the rod sides of the boom cylinders  7   c   1  and  7   c   2 . The hydraulic oil, supplied to the path  30  through the boom control valves  26  and  28  from the main pumps  12  and  13 , has the direction controlled by the main switching valve  71  subjected to the switching operation to move from the path  74  to the path  73 . Thus, the hydraulic oil is guided to the head sides of both of the boom cylinders  7   c   1  and  7   c   2  from the paths  73  and  30  through the drift reducing valves  77  and  83 . 
     Here, the assist pump motor  15 , which has pump and motor functions and is coupled to the main pump shaft  14  directly or through a gear, functions as a hydraulic motor as shown in  FIG. 2  through the following operation. Specifically, the electromagnetic unload valve  49  and the electromagnetic recovery valve  64  are switched to the communication position. The assist pump motor  15  is rotated by the energy accumulated in the first accumulator  61 . Thus, the hydraulic outputs of the main pumps  12  and  13  are assisted, whereby the engine load is reduced. 
     As described above, the engine power assist function is as follows. Specifically, the assist pump motor  15  is rotated as the hydraulic motor by the energy that is accumulated in the first accumulator  61  from the head side of the one boom cylinder  7   c   1 . Thus, the assist pump motor  15  reduces the load on the mounted engine  11  coupled through the main pump shaft  14 . 
       FIG. 3  shows a circuit state in a case where the engine load is small. The electromagnetic switching valve  57  is switched to the communication position, whereby the assist pump motor  15  functions as the hydraulic pump. Thus, the hydraulic oil pumped up from the tank  21  is supplied to and thus accumulated in the first accumulator  61 . 
     An effect of the engine power assist function is described. 
     Head side oil of the boom cylinder  7   c   1  on one side is accumulated in the first accumulator  61 . Thus, the load of the working apparatus  6  is concentrated to one boom cylinder  7   c   1  instead of being distributed to the two boom cylinders  7   c   1  and  7   c   2 . Thus, the energy density can be increased, whereby the pressure produced from the boom cylinder  7   c   1  is raised to increase the energy accumulated in the first accumulator  61 . In other words, the components such as the first accumulator  61  and the assist pump motor  15  can be downsized, whereby the cost reduction and a simple layout can be achieved. 
     When the boom cylinders  7   c   1  and  7   c   2  and the other hydraulic actuator (such as the swinging motor  3   m,  the stick cylinder  8   c , and the bucket cylinder  9   c ) are operated in conjunction with each other, the hydraulic oil pushed out of the head side of the boom cylinder  7   c   2  on one side is recovered to the rod sides of the boom cylinders  7   c   1  and  7   c   2 . Thus, the recovered amount of hydraulic oil can be provided to the other hydraulic actuators from the main pumps  12  and  13 . Thus, the speed drop in the conjunctive operation can be prevented, whereby the conjunctive operation can be facilitated. 
     When the accumulation circuit A and the recovering circuit B are separated from each other and the working apparatus  6  of the hydraulic shovel HE is lowered, the hydraulic oil pushed out of the head side of the one boom cylinder  7   c   1  is accumulated in the first accumulator  61 . At the same time, the hydraulic oil pushed out of the head side of the other boom cylinder  7   c   2  is recovered to the rod sides of the boom cylinders  7   c   1  and  7   c   2 . Thus, even during the accumulation operation for the first accumulator  61 , the main pump flow amount can be saved by an amount corresponding to the recovered flow amount. As a result, the required pump flow amount including the main pump flow amount required in the other hydraulic actuators can be readily secured, and the pumps  12  and  13  can be downsized. 
     The boom energy recovery valve  31  is formed of a single block incorporating a plurality of circuit functions in a concentrated manner, whereby a simple layout can be achieved and the cost can be reduced with a smaller number of assembly steps. 
     The assist pump motor  15  selectively uses the pump or the motor function in accordance with the engine load. Thus, the engine load can be balanced, and the energy can be stored in the first accumulator  61  from the mounted engine  11  which has energy to spare, to be used for assisting the engine load when required. Thus, an exhaust gas post-processing apparatus for reducing the exhaust gas of the mounted engine  11  can be downsized. The load is concentrated to the one boom cylinder  7   c   1 , whereby the energy accumulated in the first accumulator  61  can be increased. Thus, high level assisting can be achieved with a small accumulator, whereby the cost can be reduced and a compact vehicle body layout can be achieved. 
     INDUSTRIAL APPLICABILITY 
     The present invention has industrial applicability for companies involved in manufacturing, selling, and the like of hydraulic pressure circuits or working machines. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
         A accumulating circuit 
         B recovering circuit 
         HE hydraulic shovel as working machine 
           1  vehicle body 
           6  working apparatus 
           7   c   1 ,  7   c   2  boom cylinder as fluid pressure cylinder 
           12 ,  13  main pump as pump 
           31  boom energy recovery valve as combination valve 
           61  accumulator