Patent Publication Number: US-2010115938-A1

Title: Speed control device for hydraulic actuator

Description:
FIELD OF THE INVENTION 
     This invention relates to speed control of a hydraulic actuator when working oil discharged from a hydraulic pump is distributed to a plurality of hydraulic actuators. 
     BACKGROUND OF THE INVENTION 
     A construction equipment such as a hydraulic shovel operates a plurality of hydraulic actuators for driving a boom, an arm, a bucket, and so on. These hydraulic actuators are operated at an operating speed corresponding to an operating amount of an operating lever by an operator. To achieve this, the operating speed of each hydraulic actuator must be calculated, and an amount of working oil supplied to each hydraulic actuator must be controlled in accordance with the calculated operating speed. 
     JPH09-095980A, published by the Japan Patent Office in 1997, proposes throttling the amount of working oil supplied to a hydraulic actuator in the vicinity of a stroke end to alleviate shock generated when the hydraulic actuator reaches the stroke end. 
     SUMMARY OF THE INVENTION 
     When the plurality of hydraulic actuators are operated simultaneously at high speed in this type of construction equipment, a working oil supply ability of a hydraulic pump may reach a limit. As a result, the operating speeds of the boom, arm, bucket, and so on fall below expected speeds. 
     Under these conditions, when a certain hydraulic actuator reaches the stroke end or receives a large resistance to the stroke due to a load increase, a backlog occurs in the supply of working oil to the hydraulic actuator. However, in a conventional construction equipment in such a case, the working oil supply amount to the other hydraulic actuators is not immediately increased. 
     It is therefore an object of this invention to provide a speed control device for a hydraulic actuator with which, when one of a plurality of hydraulic actuators stops operating, a working oil supply amount to another hydraulic actuator can be increased instantaneously. 
     To achieve the object described above, this invention provides a speed control device for hydraulic actuators, which controls operating speeds of the hydraulic actuators operated by a working oil discharged from a hydraulic pump. The speed control device comprises control valves that control a supply flow rate of the working oil supplied to the respective hydraulic actuators in accordance with target operating speeds, a sensor that detects a state in which one of the hydraulic actuators has substantially stopped operating, and a programmable controller. 
     The controller is programmed to set the target operating speeds of the respective hydraulic actuators, reset the target operating speed of the hydraulic actuator that has substantially stopped operating to a smaller value, calculate a required flow rate to be supplied by the hydraulic pump on the basis of the reset target operating speed, calculate a flow distribution factor from a possible supply flow rate of the hydraulic pump and the required flow rate, and correct the target operating speeds of the respective hydraulic actuators in accordance with the flow distribution factor. 
     This invention also provides a speed control method for the hydraulic actuator described above. The method comprises setting the target operating speeds of the respective hydraulic actuators, controlling a supply flow rate of the working oil supplied to the respective hydraulic actuators in accordance with the target operating speeds, detecting a state in which one of the hydraulic actuators has substantially stopped operating, resetting the target operating speed of the hydraulic actuator that has substantially stopped operating to a smaller value, calculating a required flow rate to be supplied by the hydraulic pump on the basis of the reset target operating speed, calculating a flow distribution factor from a possible supply flow rate of the hydraulic pump and the required flow rate, and correcting the target operating speeds of the respective hydraulic actuators in accordance with the flow distribution factor. 
     The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a hydraulic circuit diagram of a hydraulic shovel to which this invention is applied. 
         FIG. 2  is a hydraulic circuit diagram of a plurality of hydraulic actuators provided in the hydraulic shovel. 
         FIG. 3  is a flowchart illustrating an operating speed control routine executed on the hydraulic actuators by a controller according to this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1  of the drawings, a hydraulic shovel  1  includes a crawler type traveling mechanism  6 , a vehicle body  2  provided on an upper portion of the traveling mechanism  6  to be capable of revolving, and an articulated front attachment  20  provided on the vehicle body  2 . 
     The front attachment  20  includes a boom  3  connected to the vehicle body  2  so as to be free to rotate, a left/right pair of hydraulic actuators  7  for driving the boom  3 , an arm  4  connected to a tip end of the boom  3  so as to be free to rotate, a single hydraulic actuator  8  for driving the arm  4 , a bucket  5  connected to a tip end of the arm  4  so as to be free to rotate, and a single hydraulic actuator  9  for driving the bucket  5 . The hydraulic actuators  7 - 9  are all constituted by linear actuators employing a hydraulic cylinder. 
     An oil pressure supply unit  21  is installed in the vehicle body  2 . The oil pressure supply unit  21  includes a hydraulic pump  22  that is driven by an internal combustion engine  17  shown in  FIG. 2 . By causing the hydraulic actuators  7 - 9  to expand and contract in accordance with a supply of pressurized working oil from the oil pressure supply unit  21 , the hydraulic shovel  1  rotates the boom  3 , arm  4 , and bucket  5  respectively to perform operations such as excavating the ground and moving earth. Instead of the bucket  5  for excavating the ground and moving earth, an attachment that performs another operation may be attached to the tip end of the arm  4 . 
     The pair of hydraulic actuators  7  that drive the boom  3  are disposed so as to sandwich the boom  3  from the left and right. In each hydraulic actuator  7 , oil pressure received by a piston accommodated in a cylinder tube  11  causes a piston rod  12  joined to the piston to expand and contract relative to the cylinder tube  11 . A base end portion of each cylinder tube  11  is connected to the vehicle body  2  so as to be free to rotate via a shared support shaft  13 , while a tip end portion of each piston rod  12  is connected to the boom  3  so as to be free to rotate via a shared support shaft  14 . Working oil supply to the pair of hydraulic actuators  7  and working oil discharge from the pair of hydraulic actuators  7  are performed via a shared control valve  15 . Thus, the pair of hydraulic actuators  7  are operated synchronously to rotate the boom  3  in a vertical direction. 
     The hydraulic actuator  8  that drives the arm  4  is installed in a back surface of the boom  3 . In the hydraulic actuator  8 , oil pressure received by a piston accommodated in a cylinder tube  31  causes a piston rod  32  joined to the piston to expand and contract relative to the cylinder tube  31 . A base end portion of the cylinder tube  31  is connected to the boom  3  so as to be free to rotate via a support shaft  33 , while a tip end portion of the piston rod  32  is connected to the arm  4  so as to be free to rotate via a support shaft  34 . Working oil supply to the hydraulic actuator  8  and working oil discharge from the hydraulic actuator  8  are performed via a control valve  35 . Thus, the hydraulic actuator  8  expands and contracts to rotate the arm  4  in a vertical direction. 
     The hydraulic actuator  9  that drives the bucket  5  is installed in a back surface of the arm  4 . In the hydraulic actuator  9 , oil pressure received by a piston accommodated in a cylinder tube  41  causes a piston rod  42  joined to the piston to expand and contract relative to the cylinder tube  41 . A base end portion of the cylinder tube  41  is connected to the arm  4  so as to be free to rotate via a support shaft  43 , while a tip end portion of the piston rod  42  is connected to the bucket  5  so as to be free to rotate via a support shaft  44 . Working oil supply to the hydraulic actuator  9  and working oil discharge from the hydraulic actuator  9  are performed via a control valve  45 . Thus, the hydraulic actuator  9  expands and contracts to rotate the bucket  5  in a vertical direction. 
     Referring to  FIG. 2 , the constitution of the oil pressure supply unit  21  that drives the hydraulic actuators  7 - 9  will be described. 
     As shown in  FIG. 2 , the oil pressure supply unit  21  includes the hydraulic pump  22  driven by the internal combustion engine  17 . A drive circuit  57  for the pair of hydraulic actuators  7 , a drive circuit  58  for the hydraulic actuator  8 , and a drive circuit  59  for the hydraulic actuator  9  are connected to the hydraulic pump  22  in series. 
     The drive circuits  57 - 59  are constituted identically, and therefore the drive circuit  59  for the hydraulic actuator  9  will be described as an example. 
     A piston  46  is accommodated in the cylinder tube  41  of the hydraulic actuator  9  for the bucket  5 . The piston rod  42  joined to the piston  46  projects from the cylinder tube  41  in an axial direction. A rod side oil chamber  48  and an anti-rod side oil chamber  47  are defined inside the cylinder tube  41  by the piston  46 . Pressurized working oil is supplied selectively to the anti-rod side oil chamber  47  and the rod side oil chamber  48  from the hydraulic pump  22  via the control valve  45 . Working oil discharge from the anti-rod side oil chamber  47  and the rod side oil chamber  48  is also performed via the control valve  45 . The hydraulic actuator  9  is caused to expand and contract by the pressurized working oil supplied to one of the anti-rod side oil chamber  47  and the rod side oil chamber  48  via the control valve  45 , and as a result, the bucket  5  is rotated thereby. 
     The control valve  45  is constituted by four solenoid valves V 1 -V 4  forming a bridge circuit. 
     A high pressure passage  25  is connected to a discharge port of the hydraulic pump  22 . The supply passage  25  bifurcates into branch passages  26  and  27  in the control valve  45 . 
     A meter-in solenoid valve V 1  that controls the flow of working oil supplied to the anti-rod side oil chamber  47  of the hydraulic actuator  9  and a meter-out solenoid valve V 2  that controls the flow of working oil discharged from the anti-rod side oil chamber  47  of the hydraulic actuator  9  are provided in series in the branch passage  26 . A meter-in solenoid valve V 3  that controls the flow of working oil supplied to the rod side oil chamber  48  and a meter-out solenoid valve V 4  that controls the flow of working oil discharged from the rod side oil chamber  48  are provided in series in the branch passage  27 . The branch passage  26  passing through the solenoid valves V 1  and V 2  and the branch passage  27  passing through the solenoid valves V 3  and V 4  are connected to a low pressure passage  23  that extends to a suction port of the hydraulic pump  22 . 
     A first passage  28  is connected to the branch passage  26  between the meter-in solenoid valve V 1  and the meter-out solenoid valve V 2 . The first passage  28  is connected to the anti-rod side oil chamber  47  of the hydraulic actuator  9 . A second passage  29  is connected to the branch passage  27  between the meter-in solenoid valve V 3  and the meter-out solenoid valve V 4 . The second passage  29  is connected to the rod side oil chamber  48  of the hydraulic actuator  9 . 
     The meter-in solenoid valve V 1 , meter-out solenoid valve V 2 , meter-in solenoid valve V 3  and meter-out solenoid valve V 4  are all constituted by solenoid flow control valves. Each solenoid valve V 1 -V 4  is operated individually by a current signal output from a controller  50 . An opening area of the valve is adjusted in accordance with the current, whereby the flow of the working oil passing through each solenoid valve V 1 -V 4  is controlled to a value corresponding to the current signal. 
     Detected pressures from a pressure sensor  18  that detects a pressure of the first passage  28  and a pressure sensor  19  that detects a pressure of the second passage  29  are respectively input into the controller  50  as signals. 
     The controller  50  is constituted by a microcomputer including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input/output interface (I/O interface). The controller may be constituted by a plurality of microcomputers. 
     The control valve  15  and the control valve  35  shown in  FIG. 1  are constituted similarly to the control valve  45 . The control valves  15 ,  35 ,  45  are disposed discretely in the vicinity of the respective hydraulic actuators  7 ,  8 ,  9 . 
     By operating the control valves  15 ,  35 ,  45 , the controller  50  switches the direction in which the working oil is supplied to the hydraulic actuators  7 ,  8 ,  9  and controls the supply flow of the working oil. The controller  50  thus drives the articulated front attachment  20  constituted by the boom  3 , arm  4 , and bucket  5  in order to use the bucket  5  connected to the tip end of the arm  4  to excavate the ground and move earth. 
     The controller  50  calculates target operating speeds C 7 , C 8 , C 9  relating to operations of the respective hydraulic actuators  7 ,  8 ,  9  in accordance with an operating amount of an operating lever  51  by an operator. The controller  50  then adjusts respective openings of the control valves  15 ,  35 ,  45  in accordance with the target operating speeds C 7 , C 8 , C 9 . As a result of this operation, expansion/contraction speeds of the respective hydraulic actuators  7 ,  8 ,  9  are caused to correspond to the operating amount of the operating lever  51 . 
     When the boom  3 , the arm  4 , and the bucket  5  are operated simultaneously at high speed, the flow of the working oil discharged from the hydraulic pump  22  may become insufficient. 
     In response to this problem, the controller  50  calculates a possible supply flow rate Qa relating to the hydraulic circuits  57 ,  58 ,  59  of the oil pressure supply unit  21  on the basis of a horse power of the internal combustion engine  17  that drives the hydraulic pump  22  and load information relating to the respective hydraulic actuators  7 ,  8 ,  9 . The controller  50  also calculates a required supply flow rate Qb relating to the respective hydraulic actuators  7 ,  8 ,  9  on the basis of the respective target operating speeds C 7 , C 8 , C 9  of the hydraulic actuators  7 ,  8 ,  9 . 
     The controller  50  then determines a flow distribution factor Qr by dividing the possible supply flow rate Qa by the required supply flow rate Qb. The respective target operating speeds C 7 , C 8 , C 9  of the respective hydraulic actuators  7 ,  8 ,  9  are then corrected by multiplying the flow distribution factor Qr by the target operating speeds C 7 , C 8 , C 9 . Through this correction processing, when the possible supply flow rate Qa of the oil pressure supply unit  21  is smaller than the flow rate Qb required to operate the front attachment  20 , the operating speeds of the operative hydraulic actuators  7 ,  8 ,  9  are uniformly reduced. As a result, a situation in which the operating speed of one specific hydraulic actuator decreases dramatically, greatly impairing the operability of the front attachment  20 , is prevented. 
     When one of the hydraulic actuators  7 - 9  substantially stops operating due to a load increase or one of the hydraulic actuators  7 - 9  substantially stops operating after reaching a stroke end, a deficiency in the supply flow rate of the oil pressure supply unit  21  is eliminated by halting the supply of working oil to the hydraulic actuator that has substantially stopped operating. 
     In this case, when the controller  50  continues to output a command relating to the correction processing described above, the flow rate of the working oil supplied to the operative hydraulic actuator falls below the capacity of the oil pressure supply unit  21 , and as a result, the operating speeds of the operative hydraulic actuators remain low. 
     The controller  50  according to this invention detects a state in which one of the respective hydraulic actuators  7 ,  8 ,  9  has substantially stopped operating, and corrects the target operating speed output to the drive circuit of the hydraulic actuator that has substantially stopped operating in a speed reduction direction. Here, the term “substantially stopped operating” indicates a state in which the operating speed of the hydraulic actuator  7 ,  8 ,  9  is zero or a very low speed at or below a predetermined speed set close to zero. 
     For example, when the hydraulic actuator  7  substantially stops operating, the controller  50  corrects the target operating speed C 7  output to the drive circuit  57  of the hydraulic actuator  7  in the speed reduction direction. A target operating speed C 7 L relating to the hydraulic actuator  7  that has substantially stopped operating is preferably set at a very small value larger than 0. 
     After setting the corrected target operating speed C 7 L at this value, the controller  50  calculates the required flow rate Qb on the basis of the target operating speeds C 7 L, C 8 , C 9 , and therefore the calculated required flow rate Qb takes a smaller value than the value obtained when the required flow rate Qb is calculated on the basis of the previous target operating speeds C 7 , C 8 , C 9 . As a result, the flow distribution factor Qr determined by dividing the possible supply flow rate Qa by the required flow rate Qb increases, leading to an increase in the supply flow rate of the working oil supplied to the drive circuits  58  and  59  of the operative hydraulic actuators  8  and  9 . In other words, when the boom  3 , arm  4 , and bucket  5  are operated simultaneously and the boom  3  substantially stops operating, the operating speeds of the arm  4  and the bucket  5  are increased immediately. In so doing, the overall operating speed of the front attachment  20  can be increased. 
     Likewise, when the hydraulic actuator  8  or  9  substantially stops operating, the controller  50  increases the operating speeds of the operative actuators by correcting the target operating speed C 8  or C 9  in the speed reduction direction. 
     The controller  50  detects the state in which the hydraulic actuator  7  has substantially stopped operating in the following manner. On the basis of input signals from the pressure sensors  18  and  19 , the controller  50  determines that a heavy load state in which a working oil pressure supplied to the hydraulic actuator  7 , or in other words a load pressure, has risen beyond a predetermined pressure corresponds to a state in which the hydraulic actuator  7  has substantially stopped operating. 
     In  FIG. 2 , the drive circuits  57 - 59  have equivalent constitutions. Hence, the controller  50  determines a state in which the hydraulic actuator  8  or  9  has substantially stopped operating in a similar manner, i.e. on the basis of the input signals from the pressure sensors  18  and  19  provided in the respective drive circuits  58  and  59 . 
     Referring to  FIG. 3 , an oil pressure control routine executed by the controller  50  to achieve the above control will now be described. The controller  50  executes this routine at fixed intervals, for example every ten milliseconds, while the front attachment  20  is working. 
     First, in a step S 1 , the controller  50  reads the load information relating to the hydraulic actuators  7 ,  8 ,  9  detected by the pressure sensors  18  and  19  of the drive circuits  57 - 59 . 
     In a step S 2 , the controller  50  sets a discharge pressure of the hydraulic pump  22  from the load information by referring to a map stored in the ROM in advance. 
     In a step S 3 , the controller  50  reads the horse power of the internal combustion engine  17  that drives the hydraulic pump  22 . 
     In a step S 4 , the controller  50  calculates the possible supply flow rate Qa of the hydraulic pump  22  on the basis of the discharge pressure of the hydraulic pump  22  and the horse power of the internal combustion engine  17 . 
     In a step S 5 , the controller  50  calculates the target operating speed C 7  of the hydraulic actuators  7  for the boom  3  in accordance with the operating amount of the operating lever  51  by the operator. By varying the opening of the control valve  15  in accordance with the target operating speed C 7 , the operating speed of the boom  3  required by the operator is obtained. 
     In a step S 6 , the controller  50  determines whether or not a state in which the hydraulic actuators  7  have substantially stopped operating has been established. When it is determined that a state in which the hydraulic actuators  7  have substantially stopped operating has been established, the controller  50  corrects the target operating speed C 7  to the smaller value C 7 L in a step S 7 . When it is determined in the step S 6  that a state in which the hydraulic actuator  7  has substantially stopped operating has not been established, the controller  50  does not correct the target operating speed C 7  of the hydraulic actuator  7 . 
     In a step S 8 , the controller  50  calculates the target operating speed C 8  of the hydraulic actuator  8  for the arm  4  in accordance with the operating amount of the operating lever  51  by the operator. By varying the opening of the control valve  35  in accordance with the target operating speed C 8 , the operating speed of the arm  4  required by the operator is obtained. 
     In a step S 9 , the controller  50  determines whether or not a state in which the hydraulic actuator  8  has substantially stopped operating has been established. When it is determined that a state in which the hydraulic actuator  8  has substantially stopped operating has been established, the controller  50  corrects the target operating speed C 8  to a smaller value C 8 L in a step S 10 . When it is determined in the step S 9  that a state in which the hydraulic actuator  8  has substantially stopped operating has not been established, the controller  50  does not correct the target operating speed C 8  of the hydraulic actuator  8 . 
     In a step S 11 , the controller  50  calculates the target operating speed C 9  of the hydraulic actuator  9  for the bucket  5  in accordance with the operating amount of the operating lever  51  by the operator. By varying the opening of the control valve  45  in accordance with the target operating speed C 9 , the operating speed of the bucket  5  required by the operator is obtained. 
     In a step S 12 , the controller  50  determines whether or not a state in which the hydraulic actuator  9  has substantially stopped operating has been established. When it is determined that a state in which the hydraulic actuator  9  has substantially stopped operating has been established, the controller  50  corrects the target operating speed C 9  to a smaller value C 9 L in a step S 13 . When it is determined in the step S 12  that a state in which the hydraulic actuator  9  has substantially stopped operating has not been established, the controller  50  does not reset the target operating speed C 9  of the hydraulic actuator  9 . 
     After calculating the target operating speeds C 7  (C 7 L), C 8  (C 8 L), C 9  (C 9 L) of the hydraulic actuators  7 ,  8 ,  9  in this manner, the controller  50  calculates the required flow rate Qb on the basis of the target operating speeds C 7  (C 7 L), C 8  (C 8 L), C 9  (C 9 L) in a step S 14 . 
     In a step S 15 , the controller  50  determines whether or not the possible supply flow rate Qa is equal to or greater than the required flow rate Qb. When the possible supply flow rate Qa is equal to or greater than the required flow rate Qb, all of the hydraulic actuators  7 - 9  can be operated at the speeds desired by the operator. When the possible supply flow rate Qa is smaller than the required flow rate Qb, the supply flow rate is insufficient, and therefore all of the hydraulic actuators  7 - 9  cannot be operated at the speeds desired by the operator. 
     When the possible supply flow rate Qa is equal to or greater than the required flow rate Qb, the controller  50  sets the flow distribution factor Qr at 1.0 in a step S 16 . 
     When the possible supply flow rate Qa is smaller than the required flow rate Qb, the controller  50  calculates the flow distribution factor Qr using the equation Qr=Qa/Qb in a step S 17 . In this case, the flow distribution factor Qr takes a smaller value than 1.0. 
     In a step S 18 , the controller  50  calculates corrected target operating speeds C 7 A, C 8 A, C 9 A by multiplying the flow distribution factor Qr by the target operating speeds C 7  (C 7 L), C 8  (C 8 L), C 9  (C 9 L) of the respective hydraulic actuators  7 ,  8 ,  9 . The controller  50  then outputs the calculated corrected target operating speeds C 7 A, C 8 A, C 9 A to the solenoid valves V 1 -V 4  of the respective drive circuits  57 - 59 . 
     By executing the routine described above, when one of the hydraulic actuators  7 - 9  is subjected to a large load and substantially stops operating or one of the hydraulic actuators  7 - 9  reaches the stroke end and substantially stops operating, the target operating speed of the corresponding hydraulic actuator is reset at a smaller value, leading to a reduction in the required flow rate Qb, which is calculated on the basis of the target operating speeds. As a result, a situation in which the required flow rate Qb is calculated to exceed the flow rate actually required by the hydraulic actuators  7 - 9  can be avoided, and the flow distribution factor Qr can be calculated appropriately at all times. Therefore, when one of the hydraulic actuators  7 - 9  substantially stops operating, the operating speeds of the other hydraulic actuators are raised quickly. As a result, favorable operating efficiency is maintained in the articulated front attachment  20 . 
     When one of the hydraulic actuators  7 - 9  substantially stops operating, the target operating speed C 7 L, C 8 L or C 9 L of the hydraulic actuator is set at a very small value larger than 0, and therefore newly usable working oil can be supplied to the operative hydraulic actuators quickly. 
     In this speed control device, the load pressure of the hydraulic actuator  7 - 9  is detected by the pressure sensors  18  and  19 , and the state in which the hydraulic actuator  7 - 9  has substantially stopped operating is determined on the basis of the detected load pressure. Hence, there is no need to provide a sensor for detecting the operating speed of the hydraulic actuator  7 - 9 , and as a result, speed control of the hydraulic actuator  7 - 9  can be realized with a simple constitution. 
     With regard to the above description, the contents of Tokugan 2007-109417, with a filing date of Apr. 18, 2007 in Japan, are herein incorporated by reference. 
     Although the invention has been described above with reference to certain embodiments, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, within the scope of the claims. 
     For example, a stroke position of the hydraulic actuator  7 - 9  may be detected by a stroke sensor, a determination as to whether or not the hydraulic actuator  7 - 9  has reached a stroke end region may be made on the basis of the stroke position, and when the hydraulic actuator  7 - 9  has reached the stroke end region, the state in which the hydraulic actuator  7 - 9  has substantially stopped operating may be considered to be established. 
     Further, the hydraulic actuator is not limited to a hydraulic cylinder, and may be a hydraulic motor, for example. 
     In the above embodiment, the parameters required for control are detected using sensors, but this invention can be applied to any device which can perform the claimed control using the claimed parameters regardless of how the parameters are acquired. 
     INDUSTRIAL FIELD OF APPLICATION 
     As described above, with this invention, operating characteristics of a plurality of hydraulic actuators driven using oil pressure from a single oil pressure source can be improved. Accordingly, this invention exhibits particularly favorable effects in improving the operating efficiency of an articulated construction equipment. 
     The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: