JP4521866B2 - Hydraulic control equipment for construction machinery - Google Patents

Description

  The present invention relates to a hydraulic control device for a construction machine in which load sensing control is performed in which a differential pressure between a discharge pressure of a hydraulic pump and a load pressure of a hydraulic actuator is held at a set value.

  FIG. 2 is a perspective view showing a peripheral portion of a blade provided at the front portion of the vehicle body of the bulldozer.

  In the bulldozer, work is performed such as excavating and carrying soil and leveling the ground after excavation by means of a blade 3 (earthwork plate) attached to the front of the vehicle body.

  A pair of left and right tilt cylinders 4 and 5 are provided between the blade 3 and the vehicle body.

  When both tilt cylinders 4 and 5 are simultaneously driven to extend and contract in the same direction, the blade 3 is placed in a pitch dump posture (forward tilt posture) or pitch back (back tilt posture).

  When one tilt cylinder is stopped and the other tilt cylinder is driven to extend and contract, the right end or left end of the blade 3 is tilted downward (right tilt position or left tilt position). This is called a single tilt operation.

  Further, when one tilt cylinder is driven to extend and at the same time the other tilt cylinder is driven to retract, the operating speed of the tilting operation of the blade 3 is increased. This is called a dual tilt operation. The point of performing the dual tilt operation is described in Patent Document 1 below.

  A load sensing control device is incorporated in the hydraulic circuit for driving and controlling the blade 3.

  Here, the load sensing control means that the differential pressure ΔP (= Pp−PL) between the discharge pressure Pp of the hydraulic pump and the load pressure PL of the tilt cylinders 4 and 5 is maintained at the set value ΔPLS. This is control for changing the capacity (cc / rev), specifically, the tilt position of the swash plate.

  The load sensing control device includes a variable displacement hydraulic pump, a directional flow control valve that controls the flow and flow rate of pressure oil supplied from the hydraulic pump to the tilt cylinder, and a pump discharged from the hydraulic pump per rotation. A capacity control means for controlling the discharge amount (cc / rev). As the capacity control means, a drive cylinder device for driving a swash plate of a hydraulic pump, and a load sensing control valve for controlling the drive of the drive cylinder device ( LS valve) and a hydraulic circuit configuration. Here, the load sensing control valve has a pair of drive parts facing each other, and the discharge pressure Pp of the hydraulic pump and the load pressure PL of the hydraulic actuator are led to these drive parts, respectively. In the drive unit to be applied, a spring having a spring force corresponding to the constant differential pressure ΔPLS is arranged.

  In such a hydraulic circuit configuration, when pressure oil is discharged from the hydraulic pump, the pressure oil is supplied to the tilt cylinders 4 and 5 via the directional flow control valve, the tilt cylinders 4 and 5 are driven, and the blade 3 Actuated. During the operation of the blade 3, the load sensing control valve operates in response to a differential pressure ΔP between the discharge pressure Pp of the hydraulic pump and the load pressure PL (maximum load pressure) of the tilt cylinders 4 and 5, and the drive cylinder device is operated. To drive. As a result, the capacity of the hydraulic pump (swash plate tilt position) is changed so that the differential pressure ΔP is held at a constant differential pressure ΔPLS set by a spring.

  When the opening area of the spool of the directional flow control valve is A and the resistance coefficient is c, the discharge flow rate Q (l / min) of the hydraulic pump is expressed by the following equation (1).

Q = c · A · √ (ΔP) (1)
Since the differential pressure ΔP is made constant (ΔPLS) by the load sensing control valve, the discharge flow rate Q of the hydraulic pump changes only by the opening area A of the spool of the directional flow control valve.

  When the operation lever for tilting is operated from the neutral position, the opening area A of the spool of the directional flow control valve increases according to the operation amount, and the pump flow rate Q increases as the opening area A increases. At this time, the pump flow rate Q is determined only by the operation amount of the tilt operation lever without being affected by the load of the tilt cylinder. By providing the load sensing valve in this way, the pump flow rate Q changes according to the operator's intention (according to the operation position of the operation lever) without increasing or decreasing depending on the load, and fine control, that is, operation in the intermediate operation region. Improves.

  A load sensing control device is also incorporated in the hydraulic excavator. Some hydraulic excavators incorporate a control device that changes the magnitude of a constant differential pressure ΔPLS determined by a spring of a load sensing control valve in accordance with a work type (work mode).

Also, bulldozers have a standard blade specification and a large blade specification.
JP 2002-275931 A

  Unlike the hydraulic excavator, the bulldozer does not require any change according to the work mode. Therefore, the difference in which the differential pressure ΔP between the discharge pressure Pp of the hydraulic pump and the load pressure PL of the tilt cylinders 4 and 5 is made constant. The pressure set value ΔPLS (LS differential pressure) is normally fixed at a constant value (LS set pressure) corresponding to the urging force of a spring attached to the load sensing control valve.

  However, as described above, when the dual tilt operation in which the pair of tilt cylinders 4 and 5 are simultaneously driven is performed and in the case of the single tilt operation in which only one tilt cylinder is driven, the blade 3 Tilt operation speed is different. For this reason, when the operator operates the operation lever during the operation and switches from the dual tilt operation to the single operation (or vice versa), the operator feels uncomfortable with the difference in the operation speed of the blade 3. There is a problem that the operability is affected by feeling and adjusting the operation of the operation lever.

  In order to produce bulldozer standard blade specification models and large blade specification models, a tilt cylinder of a size corresponding to the standard blade specification and a tilt cylinder of a size corresponding to the large blade specification are prepared. It is necessary to incorporate tilt cylinders of different sizes for each. However, there is a request to use other common parts as much as possible.

  However, when the LS set pressure ΔPLS is fixed to a constant value, the discharge flow rate Q of the hydraulic pump is determined by the opening area A of the spool of the directional flow control valve, as shown in the above equation (1). In order to supply a flow rate corresponding to the cylinder size to the tilt cylinder, a directional flow control valve is prepared and installed for each specification, and the opening area A of the spool is set to a size corresponding to each specification. There must be.

  Thus, if a directional flow control valve is prepared for each specification and a directional flow control valve that is different for each model is incorporated, the problem of high production costs is unavoidable. This is the same problem not only in the bulldozer but also in each construction machine such as a hydraulic excavator.

  The present invention has been made in view of such problems, and an optimal pump flow rate can be obtained in each of the dual tilt operation and the single tilt operation without complicating the apparatus configuration and at low cost. Thus, the problem to be solved is to improve the operability by eliminating the uncomfortable feeling caused by the difference in operation speed when switching between the dual tilt operation and the single tilt operation.

  Moreover, this invention makes it a solution subject to implement | achieve common use of a directional flow control valve with each specification from which cylinder sizes differ, and to reduce production cost drastically.

The first invention is
A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
Of the pair of tilt hydraulic actuators, there is a single tilt operation oil path to which pressure oil is supplied to one tilt hydraulic actuator, and a dual tilt operation oil path to which pressure oil is supplied to both tilt hydraulic actuators. Switching means for switching, and
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
An instruction means that is selected according to the single tilt operation, the dual tilt operation, and instructs to change the set value of the differential pressure;
Differential pressure setting value changing means for changing the set value of the differential pressure in accordance with the instruction content of the instruction means.

The second invention is
A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
A single tilt operation oil passage through which pressure oil is supplied to one tilt hydraulic actuator of the pair of tilt hydraulic actuators, and a dual tilt operation oil passage through which pressure oil is supplied to both tilt hydraulic actuators Switching means for performing switching,
Operating means for performing a switching operation of the switching means;
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
Differential pressure set value changing means for changing the set value of the differential pressure in conjunction with a switching operation by the operating means.

The third invention is
A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
An instruction means that is selected in accordance with a change in the size of the hydraulic actuator for tilting and instructs to change a set value of the differential pressure;
Differential pressure set value changing means for changing the set value of the differential pressure in accordance with the content of the instruction.

The fourth invention is
A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
A single tilt operation oil passage through which pressure oil is supplied to one tilt hydraulic actuator of the pair of tilt hydraulic actuators, and a dual tilt operation oil passage through which pressure oil is supplied to both tilt hydraulic actuators Switching means for performing switching,
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
A first instruction means that is selected according to the single tilt operation and the dual tilt operation and instructs to change a set value of the differential pressure;
Second instruction means selected according to a change in the size of the tilting hydraulic actuator and instructing a change in a set value of the differential pressure;
Differential pressure set value changing means for changing the set value of the differential pressure in accordance with the instruction contents of the first and second instruction means.

The fifth invention
A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
A single tilt operation oil passage through which pressure oil is supplied to one tilt hydraulic actuator of the pair of tilt hydraulic actuators, and a dual tilt operation oil passage through which pressure oil is supplied to both tilt hydraulic actuators Switching means for performing switching,
Operating means for performing a switching operation of the switching means;
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
An instruction means that is selected in accordance with a change in the size of the hydraulic actuator for tilting and instructs to change a set value of the differential pressure;
Differential pressure set value changing means for changing the set value of the differential pressure in conjunction with a switching operation by the operating means so that a single tilt operation or a dual tilt operation corresponding to the size instructed by the indicating means is performed. It is characterized by having and.

The sixth invention
A variable displacement hydraulic pump that supplies pressure oil to the working hydraulic actuator of the construction machine;
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the working hydraulic actuator is maintained at a set value;
A first instruction means selected in accordance with the work content and instructing a change in the set value of the differential pressure;
Second instruction means selected according to a change in the size of the working hydraulic actuator and instructing a change in a set value of the differential pressure;
Differential pressure set value changing means for changing the set value of the differential pressure in accordance with the instruction contents of the first and second instruction means.

  In the first invention, as shown in FIGS. 1 and 6A, when the dual tilt operation is desired, the switch 141b is selected, and the load sensing set pressure switching valve 39 is greatly opened according to the selection result. The As a result, a relatively large pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  When it is desired to perform a single tilt operation, the switch 141a is selected and the load sensing set pressure switching valve 39 is opened small according to the selection result. As a result, a relatively small pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  As a result, at the time of the dual tilt operation, the value of the differential pressure setting value ΔPLS becomes small, and a relatively small flow rate is supplied from the hydraulic pump 7 to the left and right tilt cylinders 4 and 5. For this reason, the expansion / contraction speed of the left and right tilt cylinders 4 and 5 is reduced.

  On the other hand, during the single tilt operation, the value of the differential pressure set value ΔPLS increases, and a relatively large flow rate is supplied from the hydraulic pump 7 to the left tilt cylinder 4. For this reason, the expansion / contraction speed of the left tilt cylinder 4 increases.

  In this way, the operation speed of the blade 3 is originally low (half the operation speed of the dual tilt operation), the expansion / contraction speed of the left tilt cylinder 4 during the single tilt operation is increased, and the operation speed of the blade 3 is originally high (dual As a result of lowering the expansion / contraction speeds of the two tilt cylinders 4 and 5 in the dual tilt operation, the tilt operation speed of the blade 3 in the dual tilt operation and the blade 3 in the single tilt operation are reduced. The tilt operation speed can be made the same size. As a result, when the dual tilt operation is switched to the single tilt operation (or vice versa), the operation speed of the blade 3 does not change, and the uncomfortable feeling associated with the change of the operation speed at the time of switching is eliminated. be able to. For this reason, the operability during the operation of the bulldozer is dramatically improved.

  In the second invention, as shown in FIG. 3, when neither of the switches 23a and 23b is pressed (during a single tilt operation) or when the switch 23b is pressed (during a dual tilt operation). Electric signals of different magnitudes are generated by the controller 42, and electric signals of different magnitudes are applied to the load sensing set pressure switching valve 39 from the controller 42 during the single operation and during the dual tilt operation. The opening area of the load sensing set pressure switching valve 39 is made different depending on the tilt.

  That is, when a dual tilt operation is desired, an operation is performed in which the dual tilt switch 23b of the operation lever 23 is pressed. In conjunction with this operation, the load sensing set pressure switching valve 39 is greatly opened. As a result, a relatively large pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  When a single tilt operation is desired, an operation (operation off) is performed in which neither the pitch dump / pitch back switch 23a or the dual tilt switch 23b of the operation lever 23 is pressed. In conjunction with this operation, the load sensing set pressure switching valve 39 is opened small. As a result, a relatively small pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  As a result, at the time of the dual tilt operation, the value of the differential pressure setting value ΔPLS becomes small, and a relatively small flow rate is supplied from the hydraulic pump 7 to the left and right tilt cylinders 4 and 5. For this reason, the expansion / contraction speed of the left and right tilt cylinders 4 and 5 is reduced.

  On the other hand, during the single tilt operation, the value of the differential pressure set value ΔPLS increases, and a relatively large flow rate is supplied from the hydraulic pump 7 to the left tilt cylinder 4. For this reason, the expansion / contraction speed of the left tilt cylinder 4 increases. As a result, the tilt operation speed of the blade 3 during the dual tilt operation and the tilt operation speed of the blade 3 during the single tilt operation can be made the same magnitude. When the operation is switched (or vice versa), the tilt operation speed of the blade 3 does not change, and the uncomfortable feeling can be eliminated. For this reason, the operability during the operation of the bulldozer is dramatically improved.

  Furthermore, according to the second aspect of the invention, since the blade tilt operation speed is automatically controlled in conjunction with the operation of the switches 23a and 23b provided on the operation lever 23, the instruction operation by the instruction device 41 becomes unnecessary. In addition to reducing the burden on the operator, it is possible to eliminate mistakes in instruction operation, forgetting instruction operation, and the like.

  Specifically, the third invention has a configuration in which an indicating device 241 shown in FIG. 6B is provided instead of the indicating device 41 in the hydraulic circuit of FIG.

  That is, when the cylinder size is small, the switch 241b is selected, and the load sensing set pressure switching valve 39 is greatly opened according to the selection result. As a result, a relatively large pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  When the cylinder size is large, the switch 241a is selected and the load sensing set pressure switching valve 39 is opened small according to the selection result. As a result, a relatively small pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  As a result, when the cylinder size is small, the value of the differential pressure set value ΔPLS becomes small, and a relatively small flow rate Q is left and right from the hydraulic pump 7 according to the above equation (1) (Q = cA√ (ΔP)). This is supplied to the tilt cylinders 4 and 5. For this reason, the left and right tilt cylinders 4 and 5 operate at an expansion / contraction speed suitable for a small cylinder size.

  On the other hand, when the cylinder size is large, the value of the differential pressure set value ΔPLS increases, and a relatively large flow rate Q is supplied from the hydraulic pump 7 to the left and right tilt cylinders 4, 5. For this reason, the left and right tilt cylinders 4 and 5 operate at an expansion / contraction speed suitable for a large cylinder size.

  As described above, according to the third invention, the directional flow control valves 9 and 16 may remain common when producing a bulldozer standard blade specification model or a large blade specification model, and only the instruction operation by the instruction device 241 is performed. Thus, a flow rate suitable for the cylinder size of each specification can be supplied to the tilt cylinder.

  For this reason, the production cost when producing each model of the bulldozer can be suppressed. Alternatively, the number of modification man-hours between different specifications can be reduced.

  In the fourth invention, as shown in FIG. 5, when the dual tilt operation is desired, the switch 141b is selected and operated. When it is desired to perform a single tilt operation, the switch 141a is selected and operated.

  When the cylinder size of the tilt cylinders 4 and 5 is small, the switch 241b is selected and operated. When the cylinder size of the tilt cylinders 4 and 5 is large, the switch 241a is selected and operated.

  Therefore, according to the fourth aspect of the present invention, an effect obtained by combining the first and third aspects of the invention can be obtained.

  Specifically, as shown in FIG. 4, the fifth invention has a configuration in which an instruction device 241 shown in FIG. 6B is provided in place of the instruction device 41.

  That is, when it is desired to perform a dual tilt operation, an operation is performed in which the dual tilt switch 23b of the operation lever 23 is pressed, and this operation content is input to the controller 42 as an electrical signal. When a single tilt operation is desired, an operation (operation off) is performed in which neither of the pitch dump / pitch back switch 23a and the dual tilt switch 23b of the operation lever 23 is pressed, and this operation content is transmitted as an electrical signal to the controller. 42.

  When the cylinder size of the tilt cylinders 4 and 5 is small, the switch 241b is selected and operated. When the cylinder size of the tilt cylinders 4 and 5 is large, the switch 241a is selected and operated.

  For this reason, according to the fifth aspect of the present invention, an effect obtained by combining the second and third aspects of the invention can be obtained.

  In the sixth invention, specifically, as shown in FIG. 7, an instruction device 341 is provided instead of the instruction device 41 shown in FIG.

  When it is desired to perform “operation 2”, the switch 341b is selected and operated. Further, when it is desired to perform “operation 1”, the switch 341a is selected and operated.

  When the cylinder size of the working machine cylinder is small, the switch 241b is selected and operated. In addition, when the cylinder size of the working machine cylinder is large, the switch 241a is selected and operated.

  Therefore, according to the sixth aspect of the invention, the differential pressure set value can be changed according to the work mode to improve the work efficiency, and the directional flow control valve is not changed when changing the cylinder size. Therefore, it is possible to cope with it, and it is possible to suppress the production cost, the modification of the apparatus, and the repair cost.

  Embodiments of a hydraulic control device for a construction machine according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a first embodiment of the present invention. FIG. 1 is a hydraulic circuit diagram showing a bulldozer hydraulic control device. FIG. 2 is a perspective view showing a configuration of a peripheral portion of the bulldozer blade.

  As shown in FIG. 2, a blade 3 is provided at the front of the vehicle main body (not shown). That is, one end of a pair of left and right straight frames 1 and 2 is supported on the left and right outer sides of a track frame (not shown) with a trunnion as a fulcrum. The front ends of the straight frames 1 and 2 are pivotally supported on the left and right of the back surface of the blade 3, respectively.

  Between the blade 3 and the straight arms 1 and 2, a pair of left and right tilt cylinders (tilting hydraulic actuators) 4 and 5 for tilting the blade 3 left and right are provided. The rods of the tilt cylinders 4 and 5 are connected to the left and right of the back surface of the blade 3, and the cylinder bodies of the tilt cylinders 4 and 5 are connected to the straight frames 1 and 2. Although omitted in FIG. 2, the bulldozer is provided with a pair of left and right lift cylinders that raise and lower the blade 3.

  As shown in FIG. 1, pressure oil is supplied from a variable displacement hydraulic pump 7 to the left tilt cylinder 4 and the right tilt cylinder 5, respectively. The capacity (cc / rev) of the variable displacement hydraulic pump 7 is changed by changing the tilt position of the swash plate 6.

  The discharge port of the hydraulic pump 7 communicates with the discharge oil passage 8. The discharge oil passage 8 communicates with the pump port 10 of the directional flow control valve 9 for the left tilt cylinder 4. A tank port 11 of the directional flow control valve 9 communicates with a tank 12.

  The cylinder ports 13 and 14 of the directional flow control valve 9 communicate with the bottom oil chamber 4a and the head oil chamber 4b of the left tilt cylinder 4, respectively.

  The directional flow control valve 9 has a valve position A for connecting the pump port 10 to the cylinder port 14 and a tank port 11 for communication with the cylinder port 13, a neutral position, and a pump port 10 for communication with the cylinder port 13 for connecting the tank port 11 to the cylinder port. 14 has a valve position B that communicates with the valve 14.

  The directional flow control valve 9 is provided with pilot ports 9a and 9b. When pilot pressure oil is supplied to the pilot port 9a, the directional flow control valve 9 operates to the valve position A side. When pilot pressure oil is supplied to the pilot port 9b, the directional flow control valve 9 operates to the valve position B side.

  On the other hand, the discharge oil passage 8 branches into a branch oil passage 15, and the branch oil passage 15 communicates with the pump port 17 of the directional flow control valve 16 for the right tilt cylinder 5. A tank port 18 of the directional flow control valve 16 communicates with a tank 19.

  The cylinder ports 20 and 21 of the directional flow control valve 16 communicate with the bottom oil chamber 5a and the head oil chamber 5b of the right tilt cylinder 5, respectively.

  The directional flow control valve 16 has a valve position A, a neutral position, which connects the pump port 17 to the cylinder port 21 and a tank port 18 to the cylinder port 20, and a pump port 17 which communicates with the cylinder port 20, and the tank port 18 to the cylinder port. 21 has a valve position B that communicates with the valve 21.

  The directional flow control valve 16 is provided with pilot ports 16a and 16b. When pilot pressure oil is supplied to the pilot port 16a, the directional flow control valve 16 operates to the valve position A side. Further, when pilot pressure oil is supplied to the pilot port 16b, the directional flow control valve 9 operates to the valve position B side.

  Pilot pressure oil is supplied to the pilot ports 9a, 9b, 16a, 16b of the directional flow control valves 9, 16 through a pilot pressure signal circuit 22 using a pilot pump (not shown) as a drive source.

  The bulldozer driver's seat is provided with a tilt operation lever 23 that can be operated in the left-right direction. A pilot valve 23 d is attached to the operation lever 23, and the pilot valve 23 d is operated according to the operation of the operation lever 23. The operation lever 23 is provided with a pitch dump / pitch back switch 23a and a dual tilt switch 23b.

  In addition, a pilot switching valve 24 is inserted in the pilot signal circuit 22 and the pilot oil passages 22a to 22f are arranged. .

  Pilot pressure oil is supplied from the pilot pump to the inlet port of the pilot valve 23 d attached to the operation lever 23. The outlet port of the pilot valve 23 communicates with the pilot oil passage 22a or 22b according to the operation direction of the operation lever 23. The pilot oil passage 22 a communicates with the pilot port 9 a of the directional flow control valve 9, and the pilot oil passage 22 b communicates with the pilot port 9 b of the directional flow control valve 9. The pilot oil passage 22a communicates with the pilot oil passage 22c, and the pilot oil passage 22b communicates with the pilot oil passage 22d. The pilot oil passages 22c and 22d communicate with the inlet ports 24a and 24b of the pilot switching valve 24, respectively.

  The outlet ports 24c and 24d of the pilot switching valve 24 communicate with the pilot ports 16a and 16b of the directional flow control valve 16 through pilot oil passages 22e and 22f, respectively.

  The pilot switching valve 24 has a valve position A, a neutral position, which allows the inlet port 24a to communicate with the outlet port 24c and the inlet port 24b to communicate with the outlet port 24d, and the inlet port 24b communicates with the outlet port 24d. Has a valve position B to be communicated with. The pilot switching valve 24 is provided with an electromagnetic solenoid 24e, and the pilot switching valve 24 is operated and the valve position is switched in accordance with an electric signal applied to the electromagnetic solenoid 24e. An electric signal corresponding to the operating state of the switches 23a and 23b is applied to the electromagnetic solenoid 24e of the pilot switching valve 24.

  As will be described later, depending on the operating direction of the operating lever 23 and the operating states of the switches 23a and 23b, the pitch dumping operation (forward tilting operation) of the blade 3 by driving both the tilt cylinders 4 and 5 and the both tilt cylinders 4 and 5 are driven. The operation is switched to a pitch back operation (backward tilting operation) of the blade 3 by driving, a single tilt operation of the blade 3 by driving only the left tilt cylinder 4, and a dual tilt operation of the blade 3 by driving both tilt cylinders 4 and 5. It is done.

  A load sensing control device is incorporated in the hydraulic circuit shown in FIG.

  That is, the tilt position of the swash plate 6 of the hydraulic pump 7 is controlled by the capacity control device 25. This capacity control device 25 changes a tilting position of the swash plate 6 of the hydraulic pump 7 in accordance with the position of the piston 28 to change the capacity (cc / rev), and a hydraulic pump. The drive of the piston 28 of the drive cylinder device 26 is controlled so that the differential pressure ΔP between the discharge pressure Pp of 7 and the load pressure PL of the tilt cylinders 4 and 5 is maintained at the set value ΔPLS, and the swash plate of the hydraulic pump 7 6 and a load sensing control valve 27 for controlling the tilting position 6.

  The drive cylinder device 26 includes a piston 28 having a large diameter pressure receiving portion 28a and a small diameter pressure receiving portion 28b at both ends, and a first cylinder 29 and a second cylinder 29 into which the pressure receiving portions 28a and 28b of the piston 28 are inserted. And a cylinder 30. The first cylinder 29 is connected to the load sensing control valve 27 via the oil passage 31. The second cylinder 30 is connected to the discharge oil passage 8 of the hydraulic pump 7 through the oil passage 32. The piston 28 is connected to the swash plate 6 of the hydraulic pump 7. When the piston 28 is driven leftward in the figure, the tilting position of the swash plate 6 of the hydraulic pump 7 increases and the capacity increases. When the piston 26 is driven rightward in the figure, the tilting position 6 of the swash plate 6 of the hydraulic pump 7 becomes smaller and the capacity is reduced.

  The load sensing control valve 27 includes a first drive unit (pilot port) 34 into which the discharge pressure Pp of the hydraulic pump 7 is introduced via an oil passage 32 and a pilot oil passage 33 communicating with the oil passage 32, the tilt cylinder 4, 5 has a second drive part (pilot port) 36 into which a load pressure PL of 5 (maximum load pressure of both tilt cylinders 4 and 5) is introduced through the pilot oil passage 35, and the second drive part A spring 37 having a spring force corresponding to a set differential pressure ΔPLS of a differential pressure ΔP between the discharge pressure Pp of the hydraulic pump 7 and the load pressure PL of the tilt cylinders 4, 5. ing.

  When the load sensing control valve 27 is in the A position (shown position), the cylinder chamber of the first cylinder 29 is communicated with the tank 38 via the oil passage 31, and the cylinder chamber of the first cylinder 29 becomes the tank pressure. . When the load sensing control valve 27 is in the B position, the cylinder chamber of the first cylinder 29 is communicated with the discharge oil passage 8 of the hydraulic pump 7 via the oil passage 31 and the oil passage 32, and The cylinder chamber serves as the discharge pressure Pp of the hydraulic pump 7. Further, when the load sensing control valve 27 is at an intermediate position between the A position and the B position, the cylinder chamber of the first cylinder 29 communicates with both the tank 38 and the discharge oil passage 8 in a communication state corresponding to the position. The cylinder chamber of the first cylinder 29 becomes an intermediate pressure between the tank pressure and the discharge pressure Pp of the hydraulic pump 7.

  The magnitude of the differential pressure set value ΔPLS is switched by the load sensing set pressure switching valve 39. The inlet port of the load sensing set pressure switching valve 39 is in communication with a pilot pump (not shown). The outlet port of the load sensing set pressure switching valve 39 communicates with the first drive unit 34 of the load sensing control valve 27 via the pilot oil passage 40. The load sensing set pressure switching valve 39 has an electromagnetic solenoid 39a. The valve position changes according to an electric signal applied to the electromagnetic solenoid 39a, the opening area changes, the pilot pump changes to the switching valve 39, the pilot oil. The magnitude of the pilot pressure applied to the first drive unit 34 of the load sensing control valve 27 via the path 40 is changed. When the magnitude of the pilot pressure applied to the first drive unit 34 is changed, the magnitude of the differential pressure set value ΔPLS is changed. Since the first drive unit 34 is provided facing the spring 37 (set differential pressure ΔPLS), the magnitude of the differential pressure set value ΔPLS is determined by the biasing force (spring force) of the spring 37 and the pilot oil. It is determined by the difference value from the pilot pressure introduced into the first drive unit 34 via the path 40. When the pilot pressure applied to the first drive unit 34 increases, the differential pressure set value ΔPLS decreases, and when the pilot pressure applied to the first drive unit 34 decreases, the differential pressure set value ΔPLS increases.

  An electric signal corresponding to the content instructed by the indicating device 41 is applied to the electromagnetic solenoid 39a of the load sensing set pressure switching valve 39.

  That is, the instruction device 41 is provided in the driver's seat. As shown in FIG. 6A, the pointing device 41 includes a switch 141a selected during the “single tilt” operation and a switch 141b selected during the “dual tilt” operation, and is selectively operated by an operator. The instruction device 41 is connected to the controller 42 via an electric signal line. The controller 42 is connected to an electromagnetic solenoid 39a of the load sensing set pressure switching valve 39 via an electric signal line.

  When one of the switches 141a and 141b of the indicating device 41 is selected, an electrical signal corresponding to the selected content is generated by the controller 42, and the electrical signal corresponding to the selected content is output from the controller 42 to the load sensing set pressure switching valve. 39 electromagnetic solenoids 39a. The load sensing set pressure switching valve 39 is switched to a valve position corresponding to the content selected and instructed by the indicating device 41, whereby the opening area changes, and the pilot pressure of the magnitude corresponding to the selected and instructed content is It is added to the first drive unit 34 of the load sensing control valve 27.

  Hereinafter, the operation of the hydraulic circuit described above will be described.

  When it is desired to perform the pitch dump operation, the operator performs an operation of tilting the operation lever 23 in the “right direction” while pressing the pitch dump / pitch back switch 23 a of the operation lever 23.

  When the operation lever 23 is operated to the right, the pilot pressure discharged from the outlet port of the pilot valve 23d is supplied to the pilot oil passage 22b, and the pilot port 9b of the directional flow control valve 9 is passed through the pilot oil passage 22b. Act on.

  Further, when the switch 23a is pressed, the pilot switching valve 24 is switched to the A position. Therefore, the pilot pressure discharged from the outlet port of the pilot valve 23d acts on the pilot port 16b of the directional flow control valve 16 via the pilot oil passage 22b, the pilot oil passage 22d, the pilot switching valve 24, and the pilot port 22f.

  Thereby, the directional flow control valve 9 is switched to the B position, and the directional flow control valve 16 is also switched to the B position. As a result, the pressure oil discharged from the hydraulic pump 7 is supplied to the bottom side oil chamber 4a of the left tilt cylinder 4 through the pump port 10 and the cylinder port 13 of the directional flow control valve 9, and the left tilt cylinder 4 Actuated in the extending direction. The return pressure oil from the head side oil chamber 4 b of the left tilt cylinder 4 is collected in the tank 12 through the cylinder port 14 and the tank port 11 of the directional flow control valve 9.

  At the same time, the pressure oil discharged from the hydraulic pump 7 is supplied to the bottom oil chamber 5a of the right tilt cylinder 5 through the pump port 17 and the cylinder port 20 of the directional flow control valve 16, and the right tilt cylinder 5 is Actuated in the extending direction. The return pressure oil from the head side oil chamber 5 b of the right tilt cylinder 5 is collected in the tank 19 through the cylinder port 21 and the tank port 18 of the directional flow control valve 16. As described above, the left and right tilt cylinders 4 and 5 are simultaneously extended at a constant speed, and the blade 3 performs a pitch dump (forward tilt) operation.

  To perform the pitch back operation, the operator performs an operation of tilting the operation lever 23 in the “left direction” while pressing the pitch dump / pitch back switch 23 a of the operation lever 23.

  When the operating lever 23 is operated in the left direction, the pilot pressure discharged from the outlet port of the pilot valve 23d is supplied to the pilot oil passage 22a, and the pilot port 9a of the directional flow control valve 9 is passed through the pilot oil passage 22a. Act on.

  Further, when the switch 23a is pressed, the pilot switching valve 24 is switched to the A position. Therefore, the pilot pressure discharged from the outlet port of the pilot valve 23d acts on the pilot port 16a of the directional flow control valve 16 via the pilot oil passage 22a, the pilot oil passage 22c, the pilot switching valve 24, and the pilot port 22e.

  As a result, the directional flow control valve 9 is switched to the A position, and the directional flow control valve 16 is also switched to the A position.

  As a result, the pressure oil discharged from the hydraulic pump 7 is supplied to the head side oil chamber 4b of the left tilt cylinder 4 through the pump port 10 and the cylinder port 14 of the directional flow control valve 9, and the left tilt cylinder 4 Operated in the degenerate direction. The return pressure oil from the bottom side oil chamber 4 a of the left tilt cylinder 4 is collected in the tank 12 through the cylinder port 13 and the tank port 11 of the directional flow control valve 9.

  At the same time, the pressure oil discharged from the hydraulic pump 7 is supplied to the head side oil chamber 5b of the right tilt cylinder 5 through the pump port 17 and the cylinder port 21 of the directional flow control valve 16, and the right tilt cylinder 5 is Operated in the degenerate direction. The return pressure oil from the bottom side oil chamber 5 a of the right tilt cylinder 5 is collected in the tank 19 through the cylinder port 20 and the tank port 18 of the directional flow control valve 16. Thus, the left and right tilt cylinders 4 and 5 are simultaneously retracted at a constant speed, and the blade 3 performs a pitch back (backward tilt) operation.

  To perform the right dual tilt operation, the operator performs an operation of tilting the operation lever 23 in the “right direction” while pressing the dual tilt switch 23 b of the operation lever 23.

  When the operation lever 23 is operated to the right, the pilot pressure discharged from the outlet port of the pilot valve 23d is supplied to the pilot oil passage 22b, and the pilot port 9b of the directional flow control valve 9 is passed through the pilot oil passage 22b. Act on.

  Further, when the switch 23b is pressed, the pilot switching valve 24 is switched to the B position. Therefore, the pilot pressure discharged from the outlet port of the pilot valve 23d acts on the pilot port 16a of the directional flow control valve 16 via the pilot oil passage 22b, the pilot oil passage 22d, the pilot switching valve 24, and the pilot port 22e.

  As a result, the directional flow control valve 9 is switched to the B position, and the directional flow control valve 16 is switched to the A position.

  As a result, the pressure oil discharged from the hydraulic pump 7 is supplied to the bottom side oil chamber 4a of the left tilt cylinder 4 through the pump port 10 and the cylinder port 13 of the directional flow control valve 9, and the left tilt cylinder 4 Actuated in the extending direction. The return pressure oil from the head side oil chamber 4 b of the left tilt cylinder 4 is collected in the tank 12 through the cylinder port 14 and the tank port 11 of the directional flow control valve 9.

  At the same time, the pressure oil discharged from the hydraulic pump 7 is supplied to the head side oil chamber 5 b of the right tilt cylinder 5 through the pump port 17 and the cylinder port 21 of the directional flow control valve 16, and the right tilt cylinder 5. Is actuated in the degenerate direction. The return pressure oil from the bottom side oil chamber 5 a of the right tilt cylinder 5 is collected in the tank 19 through the cylinder port 20 and the tank port 18 of the right direction control valve 16.

  Thus, the extension operation of the left tilt cylinder 4 and the contraction operation of the right tilt cylinder 5 are performed simultaneously, and the blade 3 performs the right dual tilt operation at high speed (almost twice as fast as the single tilt operation).

  To perform the left dual tilt operation, the operator performs an operation of tilting the operation lever 23 in the “left direction” while pressing the dual tilt switch 23 b of the operation lever 23.

  When the operating lever 23 is operated in the left direction, the pilot pressure discharged from the outlet port of the pilot valve 23d is supplied to the pilot oil passage 22a, and the pilot port 9a of the directional flow control valve 9 is passed through the pilot oil passage 22a. Act on.

  Further, when the switch 23b is pressed, the pilot switching valve 24 is switched to the B position. Therefore, the pilot pressure discharged from the outlet port of the pilot valve 23d acts on the pilot port 16b of the directional flow control valve 16 via the pilot oil passage 22a, the pilot oil passage 22c, the pilot switching valve 24, and the pilot port 22f.

  As a result, the directional flow control valve 9 is switched to the A position, and the directional flow control valve 16 is switched to the B position.

  As a result, the pressure oil discharged from the hydraulic pump 7 is supplied to the head side oil chamber 4b of the left tilt cylinder 4 through the pump port 10 and the cylinder port 14 of the directional flow control valve 9, and the left tilt cylinder 4 Operated in the degenerate direction. The return pressure oil from the bottom side oil chamber 4 a of the left tilt cylinder 4 is collected in the tank 12 through the cylinder port 13 and the tank port 11 of the directional flow control valve 9.

  At the same time, the pressure oil discharged from the hydraulic pump 7 is supplied to the bottom oil chamber 5a of the right tilt cylinder 5 through the pump port 17 and the cylinder port 20 of the directional flow control valve 16, and the right tilt cylinder 5 is Actuated in the extending direction. The return pressure oil from the head side oil chamber 5 b of the right tilt cylinder 5 is collected in the tank 19 through the cylinder port 21 and the tank port 18 of the directional flow control valve 16.

  In this way, the retracting operation of the left tilt cylinder 4 and the extending operation of the right tilt cylinder 5 are performed at the same time, and the blade 3 performs the left dual tilt operation at high speed (almost double the single tilt operation).

  When it is desired to perform the right single tilt operation, the operation lever 23 is tilted in the “right direction” without pressing any of the pitch dump / pitch back switch 23a and the dual tilt switch 23b of the operation lever 23.

  When the operation lever 23 is operated to the right, the pilot pressure discharged from the outlet port of the pilot valve 23d is supplied to the pilot oil passage 22b, and the pilot port 9b of the directional flow control valve 9 is passed through the pilot oil passage 22b. Act on.

  Further, since the switches 23a and 23b are not pushed, the pilot switching valve 24 is held in the neutral position. Therefore, pilot pressure is not supplied to the pilot ports 16a and 16b of the directional flow control valve 16.

  As a result, the directional flow control valve 9 is switched to the B position, and the directional flow control valve 16 holds the neutral position.

  As a result, the pressure oil discharged from the hydraulic pump 7 is supplied to the bottom side oil chamber 4a of the left tilt cylinder 4 through the pump port 10 and the cylinder port 13 of the directional flow control valve 9, and the left tilt cylinder 4 Actuated in the extending direction. The return pressure oil from the head side oil chamber 4 b of the left tilt cylinder 4 is collected in the tank 12 through the cylinder port 14 and the tank port 11 of the left direction control valve 9.

  On the other hand, since the directional flow control valve 16 is in the neutral position, no pressure oil is supplied to the right tilt cylinder 5 and the operation of the right tilt cylinder 5 is stopped.

  Thus, with the right tilt cylinder 5 stopped, only the extension operation of the left tilt cylinder 4 is performed, and the blade 3 performs the right single tilt operation at the normal speed (low speed).

  When it is desired to perform the left single tilt operation, the operation lever 23 is tilted “leftward” without pressing any of the pitch dump / pitch back switch 23a and the dual tilt switch 23b of the operation lever 23.

  When the operating lever 23 is operated in the left direction, the pilot pressure discharged from the outlet port of the pilot valve 23d is supplied to the pilot oil passage 22a, and the pilot port 9a of the directional flow control valve 9 is passed through the pilot oil passage 22a. Act on.

  Further, since the switches 23a and 23b are not pushed, the pilot switching valve 24 is held in the neutral position. Therefore, pilot pressure is not supplied to the pilot ports 16a and 16b of the directional flow control valve 16.

  As a result, the directional flow control valve 9 is switched to the A position, and the directional flow control valve 16 maintains the neutral position.

  As a result, the pressure oil discharged from the hydraulic pump 7 is supplied to the head side oil chamber 4b of the left tilt cylinder 4 through the pump port 10 and the cylinder port 14 of the directional flow control valve 9, and the left tilt cylinder 4 Operated in the degenerate direction. The return pressure oil from the bottom side oil chamber 4 a of the left tilt cylinder 4 is collected in the tank 12 through the cylinder port 13 and the tank port 11 of the left direction control valve 9.

  On the other hand, since the directional flow control valve 16 is in the neutral position, no pressure oil is supplied to the right tilt cylinder 5 and the operation of the right tilt cylinder 5 is stopped.

  In this way, with the right tilt cylinder 5 stopped, only the retracting operation of the left tilt cylinder 4 is performed, and the blade 3 performs the left single tilt operation at the normal speed (low speed).

  Incidentally, an unload valve (not shown) is provided in an oil passage connecting the discharge oil passage 8 of the hydraulic pump 7 and the load pressure introduction oil passage 35 of the tilt cylinders 4 and 5.

  When the directional flow control valves 9 and 16 are in the neutral position, the unload valve causes the discharge pressure (minimum discharge pressure) of the hydraulic pump 7 when the swash plate 6 of the hydraulic pump 7 is in the minimum tilt position to It is set to be the specified pressure for the unload valve.

  The minimum discharge pressure of the hydraulic pump 7 is guided to the second cylinder 30 of the drive cylinder device 26 and to the first drive unit 34 of the load sensing control valve 27. For this reason, the load sensing control valve 27 is driven to the B position against the urging force of the spring 37. As a result, the minimum discharge pressure is also guided to the first cylinder 29 of the drive cylinder device 26 via the oil passage 31, and the piston 28 is driven rightward in the figure due to the area difference between the pressure receiving portions 28 a and 28 b, and the hydraulic pump 7 The minimum tilt position of the swash plate 6 is maintained.

  It is assumed that the directional flow control valves 9 and 16 are switched from the neutral position to the A position or the B position from this state. Then, the tilt cylinders 4 and 5 are driven by the pressure oil discharged from the hydraulic pump 7 as described above. When the tilt cylinders 4 and 5 are driven, a load pressure PL is generated in the tilt cylinders 4 and 5. The load pressure PL is introduced into the second drive unit 36 of the load sensing control valve 27 through the oil passage 35. As a result, the load sensing control valve 27 is moved to the A position side. When the load sensing control valve 27 moves to the A position side, the cylinder chamber of the first cylinder 29 is communicated with the tank 38, the piston 28 is driven leftward in the figure, and the tilt angle of the swash plate 6 of the hydraulic pump 6 is increased. Increases, and the capacity of the hydraulic pump 7 increases. As a result of the increase in the capacity of the hydraulic pump 7, the flow rate supplied to the discharge oil passage 8 increases. The increase in the discharge flow rate is caused by the fact that the differential pressure ΔP between the discharge pressure Pp of the hydraulic pump 7 and the load pressure PL of the tilt cylinders 4 and 5 is generated via the biasing force of the spring 37 and the pilot oil passage 40. Is continued until a differential pressure set value ΔPLS determined by a differential value with respect to the pilot pressure introduced in is balanced. In other words, the capacity of the hydraulic pump 7 is maintained so that the differential pressure ΔP is maintained according to the differential pressure set value ΔPLS determined by the differential value between the biasing force of the spring 37 and the pilot pressure introduced into the first drive unit 34. Is controlled.

  In the first embodiment, by selecting and operating the switches 141a and 141b provided in the pointing device 41 shown in FIG. 6A, electric signals having different magnitudes during the single tilt operation and during the dual tilt operation. Is added to the load sensing set pressure switching valve 39 via the controller 42, and the opening area of the load sensing set pressure switching valve 39 is made different between the single tilt operation and the dual tilt operation.

  That is, when it is desired to perform the dual tilt operation, the switch 141b is selected and the load sensing set pressure switching valve 39 is greatly opened according to the selection result. As a result, a relatively large pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  When it is desired to perform a single tilt operation, the switch 141a is selected and the load sensing set pressure switching valve 39 is opened small according to the selection result. As a result, a relatively small pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  As a result, at the time of the dual tilt operation, the value of the differential pressure setting value ΔPLS becomes small, and a relatively small flow rate is supplied from the hydraulic pump 7 to the left and right tilt cylinders 4 and 5. For this reason, the expansion / contraction speed of the left and right tilt cylinders 4 and 5 is reduced.

  On the other hand, during the single tilt operation, the value of the differential pressure set value ΔPLS increases, and a relatively large flow rate is supplied from the hydraulic pump 7 to the left tilt cylinder 4. For this reason, the expansion / contraction speed of the left tilt cylinder 4 increases.

  In this way, the operation speed of the blade 3 is originally low (half the operation speed of the dual tilt operation), the expansion / contraction speed of the left tilt cylinder 4 during the single tilt operation is increased, and the operation speed of the blade 3 is originally high (dual As a result of lowering the expansion / contraction speeds of the two tilt cylinders 4 and 5 in the dual tilt operation, the tilt operation speed of the blade 3 in the dual tilt operation and the blade 3 in the single tilt operation are reduced. The tilt operation speed can be made the same size. As a result, when the dual tilt operation is switched to the single tilt operation (or vice versa), the operation speed of the blade 3 does not change, and the uncomfortable feeling associated with the change of the operation speed at the time of switching is eliminated. be able to. For this reason, the operability during the operation of the bulldozer is dramatically improved.

  In the first embodiment, an electric signal having a different magnitude is applied to the load sensing set pressure switching valve 39 during the single tilt operation and during the dual tilt operation, but the single tilt operation is performed by operating the switch 141a. When selected, an electric signal is not supplied to the load sensing set pressure switching valve 39, and the load sensing set pressure switching valve 39 is kept closed, and the difference is determined only by the urging force of the spring 37. The pressure set value ΔPLS may be determined. When the dual tilt operation is selected by operating the switch 141b, an electric signal is supplied to the load sensing setting switching valve 39, and the differential pressure setting value ΔPLS is set to the biasing force of the spring 37 and the first driving unit. 34 is set according to the pilot pressure applied to 34.

  Note that FIG. 6A is illustrated for convenience of description, and the switch arrangement and switch type in the pointing device 41 are arbitrary.

  In the first embodiment, the spring 37 is arranged on the second drive unit 36 side, and the pilot pressure is supplied to the first drive unit 34 side opposite to the spring 37. The first drive unit 34 may be arranged on the arranged side, and the pilot pressure may be supplied from the load sensing set pressure switching valve 39 to the first drive unit 34.

  Next, a second embodiment will be described.

  In the first embodiment described above, the switch for selecting whether the operation is the single tilt operation or the dual tilt operation is performed using the control levers 23b and 23a (the switch 23b is on and the dual tilt operation is on, the switch 23b is off and the switch is off). The indicator device 41 (switches 141a, 141b) is provided separately from the single tilt operation when the switch 23b is off, but the arrangement of the indicator device 41 is omitted and the switches 23b, 23a of the operation lever 23 are omitted. In conjunction with the operation, the differential pressure set value ΔPLS can be changed in the same manner as in the first embodiment.

  FIG. 3 is a hydraulic circuit diagram of the second embodiment.

  In FIG. 3, the arrangement of the pointing device 41 is omitted, and an electrical signal indicating the operation contents of the pitch dump / pitch back switch 23a and the dual tilt switch 23b is applied to the controller 42 via an electrical signal line. In the controller 42, an electrical signal is generated according to the operation content of the switches 23a and 23b.

  In the second embodiment, the electric power of different magnitude is different when neither of the switches 23a and 23b is pressed (during a single tilt operation) and when the switch 23b is pressed (during a dual tilt operation). A signal is generated by the controller 42, and an electric signal having a magnitude different between the single operation and the dual tilt operation is applied from the controller 42 to the load sensing set pressure switching valve 39, and at the time of the single tilt and the dual tilt, The opening area of the load sensing set pressure switching valve 39 is set to a different size.

  That is, when a dual tilt operation is desired, an operation is performed in which the dual tilt switch 23b of the operation lever 23 is pressed. In conjunction with this operation, the load sensing set pressure switching valve 39 is greatly opened. As a result, a relatively large pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  When a single tilt operation is desired, an operation (operation off) is performed in which neither the pitch dump / pitch back switch 23a or the dual tilt switch 23b of the operation lever 23 is pressed. In conjunction with this operation, the load sensing set pressure switching valve 39 is opened small. As a result, a relatively small pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  As a result, at the time of the dual tilt operation, the value of the differential pressure setting value ΔPLS becomes small, and a relatively small flow rate is supplied from the hydraulic pump 7 to the left and right tilt cylinders 4 and 5. For this reason, the expansion / contraction speed of the left and right tilt cylinders 4 and 5 is reduced.

  On the other hand, during the single tilt operation, the value of the differential pressure set value ΔPLS increases, and a relatively large flow rate is supplied from the hydraulic pump 7 to the left tilt cylinder 4. For this reason, the expansion / contraction speed of the left tilt cylinder 4 increases. Thereby, the tilt operation speed of the blade 3 at the time of the dual tilt operation and the tilt operation speed of the blade 3 at the time of the single tilt operation can be made the same size, and the dual tilt operation can be performed as in the first embodiment. When switching to the single tilt operation (or vice versa), the tilt operation speed of the blade 3 does not change, and the uncomfortable feeling can be eliminated. For this reason, the operability during the operation of the bulldozer is dramatically improved.

  Further, according to the second embodiment, since the blade tilt operation speed is automatically controlled in conjunction with the operation of the switches 23a and 23b provided on the operation lever 23, the instruction operation by the instruction device 41 is not performed. This eliminates the need for the operator, reduces the burden on the operator, and eliminates mistakes in the instruction operation and forgetting the instruction operation.

  Next, a description will be given of a third embodiment suitable for the case where the left and right tilt cylinders 4 and 5 having different cylinder sizes are incorporated into the hydraulic circuit between the standard blade specification model and the large blade specification model.

  The hydraulic circuit of the third embodiment has a configuration in which an indicating device 241 shown in FIG. 6B is provided instead of the indicating device 41 in the hydraulic circuit of FIG.

  As shown in FIG. 6B, the indicating device 241 is selected when the switch 241a is selected when the tilt cylinders 4 and 5 are “large in cylinder size” and when the tilt cylinders 4 and 5 are “small in cylinder size”. Switch 241b, which is selectively operated by an operator. The instruction device 241 is connected to the controller 42 via an electric signal line. The controller 42 is connected to an electromagnetic solenoid 39a of the load sensing set pressure switching valve 39 via an electric signal line.

  When one of the switches 241a and 241b of the indicating device 241 is selected, an electrical signal corresponding to the selected content is generated by the controller 42, and the electrical signal corresponding to the selected content is output from the controller 42 to the load sensing set pressure switching valve. 39 electromagnetic solenoids 39a. The load sensing set pressure switching valve 39 is switched to a valve position corresponding to the content selected and instructed by the indicating device 241, thereby changing the opening area, and a pilot pressure having a magnitude corresponding to the selected and instructed content is obtained. It is added to the first drive unit 34 of the load sensing control valve 27.

  When the cylinder size is small, the switch 241b is selected and the load sensing set pressure switching valve 39 is greatly opened according to the selection result. As a result, a relatively large pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  When the cylinder size is large, the switch 241a is selected and the load sensing set pressure switching valve 39 is opened small according to the selection result. As a result, a relatively small pilot pressure is introduced into the first drive unit 34 via the oil passage 40.

  As a result, when the cylinder size is small, the value of the differential pressure set value ΔPLS becomes small, and a relatively small flow rate Q is left and right from the hydraulic pump 7 according to the above equation (1) (Q = cA√ (ΔP)). This is supplied to the tilt cylinders 4 and 5. For this reason, the left and right tilt cylinders 4 and 5 operate at an expansion / contraction speed suitable for a small cylinder size.

  On the other hand, when the cylinder size is large, the value of the differential pressure set value ΔPLS increases, and a relatively large flow rate Q is supplied from the hydraulic pump 7 to the left and right tilt cylinders 4, 5. For this reason, the left and right tilt cylinders 4 and 5 operate at an expansion / contraction speed suitable for a large cylinder size.

  As described above, according to the third embodiment, the directional flow control valves 9 and 16 may remain the same when producing the bulldozer standard blade specification model and the large blade specification model. A flow rate suitable for the cylinder size of each specification can be supplied to the tilt cylinder only by operation.

  For this reason, the production cost when producing each model of the bulldozer can be suppressed. Alternatively, the number of modification man-hours between different specifications can be reduced.

  In the third embodiment, the tilt cylinder has been described. However, not only the tilt cylinder but also other hydraulic actuators such as a lift cylinder that lifts the blade 3 are similarly operated by an instruction operation by the instruction device 241. A flow rate suitable for the cylinder size may be supplied.

  Further, the third embodiment can be similarly applied not only to a bulldozer but also to other construction machines such as a hydraulic excavator. Note that the pointing device 241 shown in FIG. 6B can be disposed as a hidden switch in a place where it cannot be easily operated so that only a specific person can operate it.

Next, a fourth embodiment that combines the first embodiment and the third embodiment will be described. FIG. 5 shows pointing devices 41 and 241 provided in the fourth embodiment. The pointing device 41 is the same as the pointing device 41 of FIG. The other configuration is the same as that of the hydraulic circuit of FIG. 1, and illustration and description thereof are omitted. To perform a dual tilt operation, the switch 141b is selected and operated. When it is desired to perform a single tilt operation, the switch 141a is selected and operated.

  When the cylinder size of the tilt cylinders 4 and 5 is small, the switch 241b is selected and operated. When the cylinder size of the tilt cylinders 4 and 5 is large, the switch 241a is selected and operated.

The controller 42 generates an electrical signal to be applied to the load sensing set pressure switching valve 39 based on the switch selection operation result. That is,
(A) When “single tilt” is selected and “small cylinder size” is selected, and when “single tilt” is selected and “large cylinder size” is selected, “ When “single tilt” is selected and “large cylinder size” is selected, an electric signal is generated so that the differential pressure setting value ΔPLS is increased.

(B) When “dual tilt” is selected and “small cylinder size” is selected, and “dual tilt” is selected and “large cylinder size” is selected, When “dual tilt” is selected and “large cylinder size” is selected, an electric signal is generated so that the differential pressure setting value ΔPLS is increased.

 (C) When “single tilt” is selected and “small cylinder size” is selected, and “dual tilt” is selected and “small cylinder size” is selected, When “single tilt” is selected and “small cylinder size” is selected, an electrical signal is generated so that the differential pressure setting value ΔPLS becomes larger.

(D) When “single tilt” is selected and “large cylinder size” is selected, and “dual tilt” is selected and “cylinder size is large” is selected, When “single tilt” is selected and “large cylinder size” is selected, an electric signal is generated so that the differential pressure setting value ΔPLS is increased.

  Therefore, according to the fourth embodiment, an effect obtained by combining the first embodiment and the third embodiment can be obtained.

  Further, the second embodiment and the third embodiment may be combined.

  As shown in FIG. 4, the fifth embodiment has a configuration in which an instruction device 241 shown in FIG. 6B is provided instead of the instruction device 41.

  That is, when it is desired to perform a dual tilt operation, an operation is performed in which the dual tilt switch 23b of the operation lever 23 is pressed, and this operation content is input to the controller 42 as an electrical signal. When a single tilt operation is desired, an operation (operation off) is performed in which neither of the pitch dump / pitch back switch 23a and the dual tilt switch 23b of the operation lever 23 is pressed, and this operation content is transmitted as an electrical signal to the controller. 42.

  When the cylinder size of the tilt cylinders 4 and 5 is small, the switch 241b is selected and operated. When the cylinder size of the tilt cylinders 4 and 5 is large, the switch 241a is selected and operated.

The controller 42 generates an electrical signal to be applied to the load sensing set pressure switching valve 39 based on the switch selection operation result. That is,
(A) When “single tilt” is selected and “small cylinder size” is selected, and when “single tilt” is selected and “large cylinder size” is selected, “ When “single tilt” is selected and “large cylinder size” is selected, an electric signal is generated so that the differential pressure setting value ΔPLS is increased.

(B) When “dual tilt” is selected and “small cylinder size” is selected, and “dual tilt” is selected and “large cylinder size” is selected, When “dual tilt” is selected and “large cylinder size” is selected, an electric signal is generated so that the differential pressure setting value ΔPLS is increased.

 (C) When “single tilt” is selected and “small cylinder size” is selected, and “dual tilt” is selected and “small cylinder size” is selected, When “single tilt” is selected and “small cylinder size” is selected, an electrical signal is generated so that the differential pressure setting value ΔPLS becomes larger.

(D) When “single tilt” is selected and “large cylinder size” is selected, and “dual tilt” is selected and “large cylinder size” is selected, When “single tilt” is selected and “large cylinder size” is selected, an electrical signal is generated so that the differential pressure setting value ΔPLS is increased.

  Therefore, according to the fifth embodiment, an effect obtained by combining the second embodiment and the third embodiment can be obtained.

  Some construction machines include a control device that performs control to change the value of the differential pressure set value ΔPLS in accordance with various types of work (work modes).

  In this sixth embodiment, the magnitude of the differential pressure setting value is changed according to the work mode as described above, and the change in the cylinder size can be dealt with without replacing the directional flow control valve. is there.

  The configuration of the sixth embodiment applied in such a case is shown in FIG.

  As shown in FIG. 7, an instruction device 341 is provided instead of the instruction device 41 shown in FIG. The instruction device 341 includes a switch 341a that selects one of the work types “work 1” (for example, heavy excavation) and a switch 341b that selects “work 2” (for example, a fine operation) that is one of the work types. , Selectively operated by an operator. The instruction device 341 is connected to the controller 42 via an electric signal line. “Work 1” is a work performed by supplying a relatively large flow rate to the working machine cylinder, and “Work 2” is a work performed by supplying a relatively small flow rate to the work machine cylinder.

  When it is desired to perform “operation 2”, the switch 341b is selected and operated. Further, when it is desired to perform “operation 1”, the switch 341a is selected and operated.

  When the cylinder size of the working machine cylinder is small, the switch 241b is selected and operated. In addition, when the cylinder size of the working machine cylinder is large, the switch 241a is selected and operated.

The controller 42 generates an electrical signal to be applied to the load sensing set pressure switching valve 39 based on the switch selection operation result. That is,
(A) When “Work 1” is selected and “Cylinder size is small” is selected, “Work 1” is selected, and “Cylinder size is large” is selected. When “Work 1” is selected and “Cylinder size is large” is selected, an electrical signal is generated so that the differential pressure setting value ΔPLS is increased.

(B) When “work 2” is selected and “small cylinder size” is selected, and when “work 2” is selected and “large cylinder size” is selected, “ When “operation 2” is selected and “large cylinder size” is selected, an electric signal is generated so that the differential pressure setting value ΔPLS becomes larger.

 (C) When “Work 1” is selected and “Cylinder size is small” is selected and “Work 2” is selected and “Cylinder size is small” is selected, When “operation 1” is selected and “small cylinder size” is selected, an electric signal is generated so that the differential pressure setting value ΔPLS is increased.

(D) When “Work 1” is selected and “Cylinder size is large” is selected, and “Work 2” is selected and “Cylinder size is large” is selected, When “Work 1” is selected and “Cylinder size is large” is selected, an electric signal is generated so that the differential pressure setting value ΔPLS becomes larger.

  For this reason, according to the sixth embodiment, it is possible to improve the working efficiency by changing the magnitude of the differential pressure setting value according to the working mode, and also to change the cylinder size, the directional flow control valve It is possible to cope without replacement, and it is possible to suppress production costs, device modifications, and repair costs.

FIG. 1 is a hydraulic circuit diagram of a hydraulic control device for a bulldozer according to a first embodiment of the present invention. FIG. 2 is a perspective view of the peripheral portion of the blade of the bulldozer in the present embodiment. FIG. 3 is a hydraulic circuit diagram showing a second embodiment as a modification of the first embodiment. FIG. 4 is a hydraulic circuit diagram showing a fifth embodiment. FIG. 5 is a diagram for explaining the fourth embodiment. 6A and 6B are diagrams illustrating the pointing device. FIG. 7 is a diagram for explaining the sixth embodiment.

Explanation of symbols

3 Blade 4, 5 Tilt cylinder 7 Hydraulic pump 9, 16 Directional control valve 25 Discharge control device 26 Drive cylinder device 27 Load sensing control valve 28 Piston 39 Load sensing set pressure switching valve 41, 241, 341 Indicator device 42 Controller

Claims (6)

A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
Of the pair of tilt hydraulic actuators, there is a single tilt operation oil path to which pressure oil is supplied to one tilt hydraulic actuator, and a dual tilt operation oil path to which pressure oil is supplied to both tilt hydraulic actuators. Switching means for switching, and
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
An instruction means that is selected according to the single tilt operation, the dual tilt operation, and instructs to change the set value of the differential pressure;
A hydraulic pressure control device for a construction machine, comprising: a differential pressure setting value changing unit that changes a set value of the differential pressure in accordance with an instruction content of the instruction unit. A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
A single tilt operation oil passage through which pressure oil is supplied to one tilt hydraulic actuator of the pair of tilt hydraulic actuators, and a dual tilt operation oil passage through which pressure oil is supplied to both tilt hydraulic actuators Switching means for performing switching,
Operating means for performing a switching operation of the switching means;
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
A hydraulic control device for a construction machine, comprising: differential pressure setting value changing means for changing the set value of the differential pressure in conjunction with a switching operation by the operating means. A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
An instruction means that is selected in accordance with a change in the size of the hydraulic actuator for tilting and instructs to change a set value of the differential pressure;
A hydraulic control device for a construction machine, comprising: a differential pressure set value changing unit that changes the set value of the differential pressure in accordance with the content of the instruction. A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
A single tilt operation oil passage through which pressure oil is supplied to one tilt hydraulic actuator of the pair of tilt hydraulic actuators, and a dual tilt operation oil passage through which pressure oil is supplied to both tilt hydraulic actuators Switching means for performing switching,
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
A first instruction means that is selected according to the single tilt operation and the dual tilt operation and instructs to change a set value of the differential pressure;
Second instruction means selected according to a change in the size of the tilting hydraulic actuator and instructing a change in a set value of the differential pressure;
A hydraulic control apparatus for a construction machine, comprising: differential pressure setting value changing means for changing the set value of the differential pressure in accordance with the instruction contents of the first and second instruction means. A blade attached to the vehicle body so as to be tiltable;
A pair of tilting hydraulic actuators attached to the left and right of the blade;
A variable displacement hydraulic pump for supplying pressure oil to the tilt hydraulic actuator;
A single tilt operation oil passage through which pressure oil is supplied to one tilt hydraulic actuator of the pair of tilt hydraulic actuators, and a dual tilt operation oil passage through which pressure oil is supplied to both tilt hydraulic actuators Switching means for performing switching,
Operating means for performing a switching operation of the switching means;
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the tilt hydraulic actuator is maintained at a set value;
An instruction means that is selected in accordance with a change in the size of the hydraulic actuator for tilting and instructs to change a set value of the differential pressure;
Differential pressure set value changing means for changing the set value of the differential pressure in conjunction with a switching operation by the operating means so that a single tilt operation or a dual tilt operation corresponding to the size instructed by the indicating means is performed. And a hydraulic control device for a construction machine. A variable displacement hydraulic pump that supplies pressure oil to the working hydraulic actuator of the construction machine;
Capacity control means for controlling the capacity of the hydraulic pump so that the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the working hydraulic actuator is maintained at a set value;
A first instruction means selected in accordance with the work content and instructing a change in the set value of the differential pressure;
Second instruction means selected according to a change in the size of the working hydraulic actuator and instructing a change in a set value of the differential pressure;
A hydraulic control apparatus for a construction machine, comprising: differential pressure setting value changing means for changing the set value of the differential pressure in accordance with the instruction contents of the first and second instruction means.

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