Hydraulic circuit

Abstract

The hydraulic circuit of the present application preferentially supplies pressure oil to an actuator connected to an upstream-side hydraulic circuit. The hydraulic circuit includes an upstream-side hydraulic circuit and a downstream-side hydraulic circuit. The upstream-side hydraulic circuit has an upstream-side series circuit supplied with pressure oil from a hydraulic pump and an upstream-side parallel circuit, an upstream-side switching valve connected in series to the upstream-side series circuit and in parallel to the upstream-side parallel circuit, and an upstream-side unloading valve connected to the upstream-side parallel circuit. The downstream-side hydraulic circuit has a downstream-side series circuit connected to the upstream-side parallel circuit via the upstream-side unloading valve of the upstream-side hydraulic circuit, a downstream-side parallel circuit connected to the upstream-side series circuit of the upstream-side hydraulic circuit, a downstream-side switching valve connected in series to the downstream-side series circuit and in parallel to the downstream-side parallel circuit, and a downstream-side unloading valve between the downstream-side parallel circuit and a tank circuit.

Description

TECHNICAL FIELD

[0001] The present application relates to a hydraulic circuit for controlling supply of pressure oil to a plurality of actuators. BACKGROUND

[0002] A hydraulic circuit is known in which pressure oil ejected from a variable capacity pump is supplied to a plurality of actuators via switching valves. For example, Patent Document 1 discloses a hydraulic circuit that is provided with a plurality of closed-center type switching valves connected in parallel to a pressure oil supply line of a variable capacity pump. The plurality of switching valves respectively supply pressure oil to corresponding actuators in correspondence with the opening degree of a throttle provided on an actuator line of the switching valve.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Publication No. H9-79212 SUMMARY

[0006] Problem to be Solved by the Invention

[0007] In construction machines such as excavators and cranes, for safety reasons, there are cases in which a hydraulic circuit is sought to be configured in such a manner that a plurality of actuators used in the construction machine are not affected by each other.

[0008] An object of the present application is to provide a hydraulic circuit that can effectively solve such a problem.

[0009] Means for Solving the Problem

[0010] The hydraulic circuit of the present application includes:

[0011] an upstream side hydraulic circuit having an upstream side series line and an upstream side parallel line to which pressure oil is supplied from a hydraulic pump, an upstream side switching valve connected in series to the upstream side series line and in parallel to the upstream side parallel line, and an upstream side unloading valve connected to the upstream side parallel line; and

[0012] a downstream side hydraulic circuit having a downstream side series line connected to the upstream side parallel line via the upstream side unloading valve of the upstream side hydraulic circuit, a downstream side parallel line connected to the upstream side series line of the upstream side hydraulic circuit, a downstream side switching valve connected in series to the downstream side series line and in parallel to the downstream side parallel line, and a downstream side unloading valve between the downstream side parallel line and a tank line.

[0013] The hydraulic circuit of the present application can also be such that the upstream-side switching valve has a bypass line connected to the upstream-side series line and an actuator line connected to the upstream-side parallel line through which pressure oil supplied to the corresponding actuator passes.

[0014] The hydraulic circuit of the present application can also be such that the downstream-side switching valve has a bypass line connected to the downstream-side series line and an actuator line connected to the downstream-side parallel line through which pressure oil supplied to the corresponding actuator passes.

[0015] The hydraulic circuit of the present application can also be such that the upstream-side hydraulic circuit has an upstream-side maximum pressure detection line connected in parallel to the actuator line of the upstream-side switching valve by means of a check valve and connected to the upstream-side unloading valve in a manner such that it acts in the closing direction of the upstream-side unloading valve.

[0016] The hydraulic circuit of the present application can also be such that the upstream-side maximum pressure detection line is connected to a pressure compensator by means of the check valve in a manner such that it acts in the closing direction of the pressure compensator connected in series to the actuator line of the upstream-side switching valve of the upstream-side hydraulic circuit.

[0017] The hydraulic circuit of the present application can also be such that the downstream-side hydraulic circuit has a downstream-side maximum pressure detection line connected in parallel to the actuator line of the downstream-side switching valve by means of a check valve and connected to the downstream-side unloading valve in a manner such that it acts in the closing direction of the downstream-side unloading valve.

[0018] The hydraulic circuit of the present application can also be such that the downstream-side maximum pressure detection line is connected to a pressure compensator by means of the check valve in a manner such that it acts in the closing direction of the pressure compensator connected in series to the actuator line of the downstream-side switching valve of the downstream-side hydraulic circuit.

[0019] Effects of the Invention

[0020] According to the present application, pressure oil can be preferentially supplied to an actuator connected to an upstream-side hydraulic circuit. BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a view showing a hydraulic circuit of an embodiment.

[0022] FIG. 2 is a view showing an upstream-side hydraulic circuit of the hydraulic circuit of FIG. 1 in an enlarged manner.

[0023] FIG. 3 is a view showing a downstream-side hydraulic circuit of the hydraulic circuit of FIG. 1FIG. 1 is a diagram of a hydraulic circuit of a hydraulic excavator.

[0024] Explanation of Reference Numerals

[0025] 1 hydraulic circuit, 2 hydraulic pump, 3 high pressure line, 5 tank, 6 tank line, 11 first actuator, 12 second actuator, 13 third actuator, 14 fourth actuator, 20 upstream hydraulic circuit, 21 upstream tandem line, 22 upstream parallel line, 23 upstream unloading valve, 24 upstream maximum-pressure-detecting line, 25 throttle, 30 upstream switching valve, 31 pressure-compensating valve, 32 maximum-pressure-detecting check valve, 33 load-holding check valve, 35 upstream switching valve, 36 pressure-compensating valve, 37 maximum-pressure-detecting check valve, 38 load-holding check valve, 40 downstream hydraulic circuit, 41 downstream tandem line, 42 downstream parallel line, 43 downstream unloading valve, 44 downstream maximum-pressure-detecting line, 45 throttle50, downstream switching valve; 51, pressure-compensating valve; 52, maximum-pressure-detecting check valve; 53, load-holding check valve; 55, downstream switching valve; 56, pressure-compensating valve; 57, maximum-pressure-detecting check valve; 58, load-holding check valve. DETAILED DESCRIPTION

[0026] First, the problem to be solved by the hydraulic circuit 1 of the embodiment of the present application will be described.

[0027] For safety, construction machines such as excavators and cranes are sometimes required to be provided with an interlock function that the machine cannot be operated simultaneously, and independent circuits in which a plurality of actuators are not affected by each other. For example, in a small excavating machine used in cities, in order to prevent a collision accident during a swing, it is preferable that a circuit for supplying pressure oil to an actuator for swing drive is independent with respect to other circuits. Further, in a case where a generator is driven by a hydraulic motor, in order to stabilize the electric performance of the generator, it is preferable that a circuit for supplying pressure oil to the hydraulic motor is constructed independently with respect to other circuits, and the variation in the rotation speed of the hydraulic motor is prevented. On the other hand, the conventional load sensing hydraulic control valve supplies hydraulic pressure to an actuator in accordance with the opening degree of the valve spool. Therefore, in a case where a plurality of control valves are provided in parallel in a pressure oil supply line of a variable capacity pump, a plurality of actuators are affected by each other in the variation in pressure and flow rate.

[0028] To solve such a problem, in the present embodiment, proposed is a configuration in which the hydraulic circuit 1 includes an upstream-side hydraulic circuit 20 having a series circuit of open-center type and a parallel circuit of closed-center type, and a downstream-side hydraulic circuit 40. Specifically, proposed is a configuration in which the hydraulic circuit 1 is configured in such a manner that the series circuit of the upstream-side hydraulic circuit 20 is connected to the parallel circuit of the downstream-side hydraulic circuit 40, and the parallel circuit of the upstream-side hydraulic circuit 20 is connected to the series circuit of the downstream-side hydraulic circuit 40. In this case, when the upstream-side switching valve of the upstream-side hydraulic circuit 20 is operated, the series circuit of the upstream-side hydraulic circuit 20 is blocked, and thus the pressure oil is not supplied to the downstream-side hydraulic circuit 40. Thus, it is possible to prevent the actuator connected to the upstream-side hydraulic circuit 20 from being affected by the change in pressure and flow rate of the actuator connected to the downstream-side hydraulic circuit 40.

[0029] Hereinafter, the hydraulic circuit 1 of the embodiment of the present application will be described in detail with reference to the drawings. In addition, the embodiments shown below are examples of the embodiments of the present application, and the present application is not to be construed limitatively by these embodiments. Further, in the drawings referred to in the present embodiment, the same reference numerals or similar reference numerals are sometimes attached to the same parts or parts having the same function, and the repeated description thereof is omitted. Further, the size ratio of the drawings is sometimes different from the actual ratio for the convenience of description, and further, a part of the structure is sometimes omitted from the drawings.

[0030] Hydraulic Circuit

[0031] FIG. 1 is a view showing the hydraulic circuit 1 of the present embodiment. The hydraulic circuit 1 includes a hydraulic pump 2, a high-pressure line 3, an upstream-side hydraulic circuit 20, a downstream-side hydraulic circuit 40, a tank line 6, and a tank 5. In the present embodiment, a case in which the hydraulic pump 2 is a single pump having one discharge port is described. The hydraulic pump 2 is connected to the upstream-side hydraulic circuit 20 via the high-pressure line 3. The pressure oil supplied from the hydraulic pump 2 to the upstream-side hydraulic circuit 20 via the high-pressure line 3 is supplied to the downstream-side hydraulic circuit 40 after passing through the upstream-side hydraulic circuit 20. The pressure oil supplied to the upstream-side hydraulic circuit 20 and the downstream-side hydraulic circuit 40 is returned to the tank 5 via the tank line 6. In addition, as the hydraulic pump 2, various pumps other than the single pump can be used.

[0032] Upstream Side Hydraulic Circuit

[0033] The upstream-side hydraulic circuit 20 has at least an upstream-side series circuit 21, an upstream-side parallel circuit 22, a plurality of upstream-side switching valves 30, 35, an upstream-side unloading valve 23, an upstream-side maximum pressure detection circuit 24, and a restriction 25. Pressure oil is supplied from the hydraulic pump 2 to the upstream-side series circuit 21 and the upstream-side parallel circuit 22 via the high-pressure circuit 3. The upstream-side series circuit 21 and the upstream-side parallel circuit 22 are connected to the upstream-side switching valves 30, 35, respectively. The upstream-side switching valves 30, 35 supply pressure oil to the corresponding actuators 11, 12, respectively. The actuators 11, 12 are not particularly limited and are, for example, hydraulic motors.

[0034] FIG. 2 FIG. 2 is a diagram that schematically shows the upstream-side hydraulic circuit 20. The upstream-side switching valves 30, 35 of the upstream-side hydraulic circuit 20 can take a neutral position 30x, 35x, a first working position 30y, 35y, or a second working position 30z, 35z by moving a valve spool, not shown. In the first working position 30y, 35y, pressure oil from the upstream-side switching valves 30, 35 is supplied to a first port 11a, 12a of the actuators 11, 12, after which the pressure oil is discharged from a second port 11b, 12b and returned to the tank 5 via the tank circuit 6. In the second working position 30z, 35z, pressure oil from the upstream-side switching valves 30, 35 is supplied to the second port 11b, 12b of the actuators 11, 12, after which the pressure oil is discharged from the first port 11a, 12a and returned to the tank 5 via the tank circuit 6. In the following description, the first working position 30y, 35y and the second working position 30z, 35z are sometimes collectively referred to as working positions.

[0035] The upstream-side switching valves 30, 35 include at least a bypass circuit 30a, 35a and an actuator circuit 30b, 35b. The bypass circuits 30a, 35a are connected in series to the upstream-side series circuit 21. The bypass circuit 30a of the upstream-side switching valve 30 is located at a position more upstream than the bypass circuit 35a of the upstream-side switching valve 35.

[0036] The upstream-side switching valves 30, 35 are so-called open-center types. Thus, in the case where the upstream-side switching valves 30, 35 are in the neutral position 30x, 35x, pressure oil of the upstream-side series circuit 21 can pass through the bypass circuit 30a of the upstream-side switching valve 30 and the bypass circuit 35a of the upstream-side switching valve 35 in that order.

[0037] The actuator circuits 30b, 35b are connected in parallel to the upstream-side parallel circuit 22, respectively.

[0038] In the case where the upstream side switching valves 30, 35 are in the 1st working positions 30y, 35y, the pressure oil from the upstream side parallel line 22 to the upstream side switching valves 30, 35 is supplied to the 1st ports 11a, 12a of the actuators 11, 12 after passing through the actuator lines 30b, 35b. Thereafter, the pressure oil is returned to the tank 5 via the tank line 6 after being discharged from the 2nd ports 1 lb, 12b, passing through the actuator lines 30b, 35b of the upstream side switching valves 30, 35.

[0039] In the case where the upstream side switching valves 30, 35 are in the 2nd working positions 30z, 35z, the pressure oil from the upstream side parallel line 22 to the upstream side switching valves 30, 35 is supplied to the 2nd ports 1 lb, 12b of the actuators 11, 12 after passing through the actuator lines 30b, 35b. Thereafter, the pressure oil is returned to the tank 5 via the tank line 6 after being discharged from the 1st ports 11a, 12a, passing through the actuator lines 30b, 35b of the upstream side switching valves 30, 35.

[0040] The upstream side unloading valve 23 is connected to the upstream side parallel line 22 at an upstream side port and to the downstream side series line 41 at a downstream side port. The upstream side unloading valve 23 takes a blocking position 23x in an interval where the pressure of the hydraulic pressure of the upstream side parallel line 22 is below an upstream side threshold value and takes an unloading position 23y when the pressure of the hydraulic pressure of the upstream side parallel line 22 is greater than the upstream side threshold value. The upstream side threshold value of the upstream side unloading valve 23 is the sum of the pressure from a spring 23a provided to the upstream side unloading valve 23 and the pressure from the upstream side highest pressure detection line 24 connected to the upstream side unloading valve 23.

[0041] The upstream side highest pressure detection line 24 is connected in parallel to the actuator lines 30b, 35b of the upstream side switching valves 30, 35 via highest pressure detection check valves 32, 37, respectively. The upstream side highest pressure detection line 24 is connected to the tank line 6 via a restrictor 25. The pressure of the upstream side highest pressure detection line 24 is equal to the highest pressure of the actuator lines 30b, 35b. Further, the upstream side highest pressure detection line 24 is connected to the upstream side unloading valve 23 in a manner to act in the closing position direction of the upstream side unloading valve 23. By providing such an upstream side highest pressure detection line 24, it is possible to raise the hydraulic pressure of the upstream side parallel line 22 to the sum of the highest pressure of the actuator lines 30b, 35b and the pressure of the spring 23a when the upstream side switching valves 30, 35 are in the working positions.

[0042] The upstream-side hydraulic circuit 20 can also have pressure compensating valves 31, 36 connected in series to the actuator lines 30b, 35b of the upstream-side switching valves 30, 35, respectively, by means of load-holding check valves 33, 38. The aforementioned upstream-side maximum pressure detection line 24 is connected to each of the pressure compensating valves 31, 36 by means of check valves 32, 37 in a manner that acts in the closing direction at each of the pressure compensating valves 31, 36. Thus, it is possible to equalize the pressure of the pressure oil supplied to each of the actuators 11, 12. For example, in the case where the pressure of the first actuator 11 is higher than that of the second actuator 12, at the pressure compensating valve 36, the pressure of the first actuator 11 acts in the closing direction as the pressure of the upstream-side maximum pressure detection line 24. Thus, at the pressure compensating valve 36, the pressure of the actuator line 35b increases. Thereby, it is possible to equally divide the pressure oil to the first actuator 11 and the second actuator 12.

[0043] Downstream Side Hydraulic Circuit

[0044] The downstream-side hydraulic circuit 40 has at least a downstream-side series line 41, a downstream-side parallel line 42, a plurality of downstream-side switching valves 50, 55, a downstream-side unloading valve 43, a downstream-side maximum pressure detection line 44, and a restriction 45. The downstream-side series line 41 is connected to the upstream-side parallel line 22 of the upstream-side hydraulic circuit 20 by means of the upstream-side unloading valve 23. The downstream-side parallel line 42 is connected to the upstream-side series line 21 of the upstream-side hydraulic circuit 20. The downstream-side series line 41 and the downstream-side parallel line 42 are connected to the downstream-side switching valves 50, 55, respectively. The downstream-side switching valves 50, 55 supply pressure oil to corresponding actuators 13, 14, respectively. The actuators 13, 14 are not particularly limited and are, for example, hydraulic cylinders.

[0045] FIG. 3 is a diagram that enlargedly shows the downstream-side hydraulic circuit 40. The downstream-side switching valves 50, 55 of the downstream-side hydraulic circuit 40 can likewise attain the neutral position 50x, 55x, the first working position 50y, 55y, or the second working position 50z, 55z by moving a valve spool not shown. At the first working position 50y, 55y, pressure oil from the downstream-side switching valves 50, 55 is supplied to the first port 13a, 14a of the actuators 13, 14, after which the pressure oil is discharged from the second port 13b, 13b and returned to the tank 5 via the tank line 6. At the second working position 50z, 55z, pressure oil from the downstream-side switching valves 50, 55 is supplied to the second port 13b, 14b of the actuators 13, 14, after which the pressure oil is discharged from the first port 13a, 14a and returned to the tank 5 via the tank line 6.

[0046] The downstream side switching valves 50, 55 are open center type switching valves including at least a bypass line 50a, 55a and an actuator line 50b, 55b. The bypass lines 50a, 55a are connected in series to the downstream side series line 41. The bypass line 50a of the downstream side switching valve 50 is located at a position more upstream than the bypass line 55a of the downstream side switching valve 55. The actuator lines 50b, 55b are connected in parallel to the downstream side parallel line 42, respectively. Since the structure and function of the downstream side switching valves 50, 55 are the same as those of the upstream side switching valves 30, 35, detailed description is omitted.

[0047] The downstream side unloading valve 43 is connected to the downstream side parallel line 42 at an upstream side port and to the tank line 6 at a downstream side port. The downstream side unloading valve 43 takes a blocking position 43x in an interval where the pressure of the hydraulic fluid of the downstream side parallel line 42 is below a downstream side threshold value and takes an unloading position 43y when the pressure of the hydraulic fluid of the downstream side parallel line 42 is greater than the downstream side threshold value. The downstream side threshold value of the downstream side unloading valve 43 is the sum of the pressure from a spring 43a provided to the downstream side unloading valve 43 and the pressure from the downstream side highest pressure detection line 44 connected to the downstream side unloading valve 43.

[0048] The downstream side highest pressure detection line 44 is connected in parallel to the actuator lines 50b, 55b of the downstream side switching valves 50, 55 via highest pressure detection check valves 52, 57, respectively. The downstream side highest pressure detection line 44 is connected to the tank line 6 via a restrictor 45. The pressure of the downstream side highest pressure detection line 44 is equal to the highest pressure of the actuator lines 50b, 55b. Further, the downstream side highest pressure detection line 44 is connected to the downstream side unloading valve 43 in a manner to act on the downstream side unloading valve 43 in the direction of the closed position. By providing such a downstream side highest pressure detection line 44, it is possible to raise the hydraulic pressure of the downstream side parallel line 42 to the sum of the highest pressure of the actuator lines 50b, 55b and the pressure of the spring 43a when the downstream side switching valves 50, 55 are in the working position.

[0049] The downstream side hydraulic circuit 40 can also have pressure compensation valves 51, 56 connected in series to the actuator lines 50b, 55b of the downstream side switching valves 50, 55 via load holding check valves 53, 58, respectively. The above-described downstream side highest pressure detection line 44 is connected to each of the pressure compensation valves 51, 56 via check valves 52, 57 in a manner to act on each of the pressure compensation valves 51, 56 in the direction of the closed position. Thus, it is possible to equalize the pressure of the pressure oil supplied to each of the actuators 13, 14. Thereby, it is possible to equally divide the pressure oil to the 3rd actuator 13 and the 4th actuator 14.

[0050] Next, the action and effect of the present embodiment configured by such a structure will be described. Here, the operation of the hydraulic circuit 1 will be described.

[0051] (Case where each switching valve is in neutral position)

[0052] First, the case where each upstream-side switching valve 30, 35, 50, 55 is in the neutral position 30x, 35x, 50x, 55x will be described. In this case, the pressure oil supplied from the hydraulic pump 2 and the high-pressure line 3 to the upstream-side series line 21 of the upstream-side hydraulic circuit 20 passes through the bypass lines 30a, 35a of the upstream-side switching valves 30, 35 and the downstream-side parallel line 42 of the downstream-side hydraulic circuit 40 to reach the downstream-side unloading valve 43. Since no pressure oil is supplied to the actuator lines 50b, 55b, the pressure of the downstream-side maximum pressure detection line 44 is substantially equal to the pressure of the tank line 6 connected by means of the throttle 45. Therefore, the downstream-side unloading valve 43 takes the unloading position 43y under the pressure of the downstream-side parallel line 42, and the pressure oil reaching the downstream-side unloading valve 43 is drained to the tank line 6.

[0053] On the other hand, the pressure oil supplied from the hydraulic pump 2 and the high-pressure line 3 to the upstream-side parallel line 22 of the upstream-side hydraulic circuit 20 reaches the upstream-side unloading valve 23. Since no pressure oil is supplied to the actuator lines 30b, 35b, the pressure of the upstream-side maximum pressure detection line 24 is substantially equal to the pressure of the tank line 6 connected by means of the throttle 25. Therefore, the upstream-side unloading valve 23 takes the unloading position 23y under the pressure of the upstream-side parallel line 22, and the pressure oil reaching the upstream-side unloading valve 23 is drained to the tank line 6 through the downstream-side series line 41 of the downstream-side hydraulic circuit 40 and the bypass lines 50a, 55a of the downstream-side switching valves 50, 55.

[0054] (Case where upstream-side switching valve 30 is in working position)

[0055] Next, the case where the upstream-side switching valve 30 is switched to the working position from the state where each switching valve 30, 35, 50, 55 is in the neutral position 30x, 35x, 50x, 55x will be described. When the upstream-side switching valve 30 is switched to the working position, the upstream-side series line 21 of the upstream-side hydraulic circuit 20 is blocked, and thus the supply of pressure oil to the downstream-side parallel line 42 of the downstream-side hydraulic circuit 40 is stopped.

[0056] The pressure oil of the upstream-side parallel line 22 of the upstream-side hydraulic circuit 20 reaches the pressure compensating valve 31 through the actuator line 30b of the upstream-side switching valve 30. The pressure compensating valve 31 takes the open position under the pressure of the actuator line 30b on the upstream side of the pressure compensating valve 31. The pressure oil that has passed through the pressure compensating valve 31 is supplied to the 1st actuator 11 via the load holding one-way valve 33.

[0057] Further, the pressure oil of the actuator line 30b is supplied to the upstream side maximum pressure detection line 24 via the maximum pressure detection check valve 32. The pressure of the upstream side maximum pressure detection line 24 acts in the closing direction of the upstream side unloading valve 23 together with the spring 23a. Therefore, the pressure of the upstream side parallel line 22 connected to the upstream side port of the upstream side unloading valve 23 rises to the pressure obtained by adding the pressure from the upstream side maximum pressure detection line 24 and the pressure from the spring 23a.

[0058] (The case where the upstream side switching valve 35 is in the working position)

[0059] In the case where each of the switching valves 30, 50, 55 is in the neutral position 35x, 50x, 55x and the upstream side switching valve 35 is in the working position, as in the above case where the upstream side switching valve 30 is in the working position, the pressure oil is not supplied to the downstream side parallel line 42 of the downstream side hydraulic circuit 40. Further, the pressure oil of the upstream side parallel line 22 is supplied to the second actuator 12 via the pressure compensator valve 36 and the load holding check valve 38. The pressure of the upstream side parallel line 22 rises to the pressure obtained by adding the pressure from the upstream side maximum pressure detection line 24 and the pressure from the spring 23a.

[0060] (The case where the upstream side switching valves 30, 35 are in the working position)

[0061] Next, the case where both of the upstream side switching valves 30, 35 are in the working position will be described. In this case, since the upstream side series line 21 of the upstream side hydraulic circuit 20 is blocked, the pressure oil is not supplied to the downstream side parallel line 42 of the downstream side hydraulic circuit 40. The pressure oil of the upstream side parallel line 22 is supplied to the actuators 11, 12 via the actuator lines 30b, 35b, the pressure compensator valves 31, 36 and the load holding check valves 33, 38.

[0062] Further, the pressure oil of the actuator lines 30b, 35b is supplied to the upstream-side maximum pressure detection line 24 via the maximum pressure detection check valves 32, 37, respectively. In this case, the higher pressure of the first actuator 11 and the second actuator 12 acts on the upstream-side maximum pressure detection line 24. The pressure of the upstream-side parallel line 22 rises to the pressure obtained by adding the pressure from the upstream-side maximum pressure detection line 24 and the pressure from the spring 23a. Further, the pressure of the upstream-side maximum pressure detection line 24 acts on the pressure compensating valves 31, 36 in the closing direction. Therefore, for example, in the case where the pressure of the first actuator 11 is higher than the pressure of the second actuator 12, at the pressure compensating valve 36, the pressure of the first actuator 11 acts as the upstream-side maximum pressure detection line 24 in the closing direction. As a result, at the pressure compensating valve 36, the pressure of the actuator line 35b increases. Thus, the pressure of the first actuator 11 and the pressure of the second actuator 12 become equal, and the pressure oil can be equally branched to the first actuator 11 and the second actuator 12.

[0063] Thus, according to the present embodiment, as in the case of the conventional load sensing hydraulic control valve, the load of each actuator 11, 12 connected to the upstream-side hydraulic circuit 20 can be adjusted, and the pressure oil can be supplied in accordance with the opening degree of each upstream-side switching valve 30, 35.

[0064] (Case where the downstream-side switching valve 50 is in the working position)

[0065] Next, a case where the upstream-side switching valves 30, 35 of the upstream-side hydraulic circuit 20 and the downstream-side switching valve 55 of the downstream-side hydraulic circuit 40 are in the neutral position and the downstream-side switching valve 50 of the downstream-side hydraulic circuit 40 is in the working position will be described. In this case, since the downstream-side series line 41 of the downstream-side hydraulic circuit 40 is blocked, the pressure oil does not flow from the upstream-side parallel line 22 of the upstream-side hydraulic circuit 20 to the downstream-side series line 41.

[0066] On the other hand, the pressure oil supplied from the hydraulic pump 2 and the high-pressure line 3 to the upstream-side series line 21 of the upstream-side hydraulic circuit 20 is supplied to the downstream-side parallel line 42 of the downstream-side hydraulic circuit 40 through the bypass lines 30a, 35a of the upstream-side switching valves 30, 35. The pressure oil of the downstream-side parallel line 42 reaches the pressure compensating valve 51 through the actuator line 50b of the downstream-side switching valve 50. The pressure compensating valve 51 takes the open position under the action of the pressure of the actuator line 50b on the upstream side of the pressure compensating valve 51. The pressure oil that has passed through the pressure compensating valve 51 is supplied to the third actuator 13 via the load holding check valve 53.

[0067] Further, the pressure oil of the actuator line 50b is communicated to the downstream side maximum pressure detection line 44 via the maximum pressure detection check valve 52. The pressure of the downstream side maximum pressure detection line 44 acts in the closing direction of the downstream side unloading valve 43 together with the spring 43a. Therefore, the pressure of the downstream side parallel line 42 connected to the upstream side port of the downstream side unloading valve 43 rises to the pressure obtained by adding the pressure from the downstream side maximum pressure detection line 44 and the pressure from the spring 43a.

[0068] (When the downstream side switching valve 55 is in the working position)

[0069] When the upstream side switching valves 30, 35 of the upstream side hydraulic circuit 20 and the downstream side switching valve 50 of the downstream side hydraulic circuit 40 are in the neutral positions and the downstream side switching valve 55 of the downstream side hydraulic circuit 40 is in the working position, as in the above case where the downstream side switching valve 50 is in the working position, the pressure oil does not flow from the upstream side parallel line 22 of the upstream side hydraulic circuit 20 to the downstream side series line 41. Further, the pressure oil of the upstream side series line 21 is supplied to the 4th actuator 14 via the bypass lines 30a, 35a of the upstream side switching valves 30, 35, the downstream side parallel line 42 of the downstream side hydraulic circuit 40, the pressure compensator 56, and the load holding check valve 58. The pressure of the downstream side parallel line 42 rises to the pressure obtained by adding the pressure from the downstream side maximum pressure detection line 44 and the pressure from the spring 43a.

[0070] (When the downstream side switching valves 50, 55 are in the working position)

[0071] Next, a case where the upstream side switching valves 30, 35 of the upstream side hydraulic circuit 20 are in the neutral positions and the downstream side switching valves 50, 55 of the downstream side hydraulic circuit 40 are in the working positions will be described. In this case, the pressure oil does not flow from the upstream side parallel line 22 of the upstream side hydraulic circuit 20 to the downstream side series line 41. The pressure oil supplied from the upstream side series line 21 to the downstream side parallel line 42 is supplied to the actuators 13, 14 via the actuator lines 50b, 55b, the pressure compensators 51, 56, and the load holding check valves 53, 58.

[0072] Further, the pressure oil of the actuator lines 50b, 55b is supplied to the downstream-side maximum pressure detection line 44 via the maximum pressure detection check valves 52, 57, respectively. In this case, the higher pressure of the 3rd actuator 13 and the 4th actuator 14 acts on the downstream-side maximum pressure detection line 44. The pressure of the downstream-side parallel line 42 rises to the pressure obtained by adding the pressure from the downstream-side maximum pressure detection line 44 and the pressure from the spring 43a. Further, the pressure of the downstream-side maximum pressure detection line 44 acts on the pressure compensating valves 51, 56 in the closing direction. Therefore, for example, in the case where the pressure of the 3rd actuator 13 is higher than the pressure of the 4th actuator 14, at the pressure compensating valve 56, the pressure of the 3rd actuator 13 acts as the downstream-side maximum pressure detection line 44 in the closing direction. As a result, at the pressure compensating valve 56, the pressure of the actuator line 55b increases. Thus, the pressure of the 3rd actuator 13 and the pressure of the 4th actuator 14 become equal, and the pressure oil can be equally branched to the 3rd actuator 13 and the 4th actuator 14.

[0073] Thus, according to the present embodiment, as in the upstream-side hydraulic circuit 20, at the downstream-side hydraulic circuit 40 as well, the load of each actuator 13, 14 connected to the downstream-side hydraulic circuit 40 can be adjusted, and the pressure oil can be supplied in accordance with the opening degree of each downstream-side switching valve 50, 55.

[0074] (Situation where the switching valves 30, 50 are in the working position)

[0075] Next, the situation where the upstream-side switching valve 30 of the upstream-side hydraulic circuit 20 and the downstream-side switching valve 50 of the downstream-side hydraulic circuit 40 are in the working position will be described. In this case, since the upstream-side series line 21 of the upstream-side hydraulic circuit 20 is blocked, the pressure oil is not supplied to the downstream-side parallel line 42 of the downstream-side hydraulic circuit 40. Therefore, the pressure oil is not supplied to the 3rd actuator 13 connected to the actuator line 50b of the downstream-side switching valve 50. The pressure oil of the upstream-side parallel line 22 is supplied to the 2nd actuator 12 via the pressure compensating valve 36 and the load holding check valve 38.

[0076] Thus, according to the present embodiment, in the case where the upstream-side switching valve of the upstream-side hydraulic circuit 20 and the downstream-side switching valve of the downstream-side hydraulic circuit 40 are in the working position at the same time, the hydraulic circuit 1 can be caused to operate in a manner where the pressure oil is supplied to only the actuators connected to the upstream-side hydraulic circuit 20 and not to the actuators connected to the downstream-side hydraulic circuit 40. That is, the priority function of causing the actuators connected to the upstream-side hydraulic circuit 20 to operate preferentially can be achieved. Further, the mechanical interlock function of intentionally preventing the actuators on the upstream-side hydraulic circuit 20 side and the actuators on the downstream-side hydraulic circuit 40 side from operating at the same time can be achieved.

[0077] According to the present embodiment, as described above, at the upstream-side hydraulic circuit 20 and the downstream-side hydraulic circuit 40, the load of each actuator can be adjusted, and pressure oil is supplied in correspondence with the opening degree of each switching valve. Further, the priority function, the interlock function of the machine can be implemented. Therefore, a hydraulic device excellent in safety and practicality can be provided.

Claims

1. A hydraulic circuit, wherein the hydraulic circuit includes: an upstream side hydraulic circuit having an upstream side series circuit to which pressure oil is supplied from a hydraulic pump and an upstream side parallel circuit, an upstream side switching valve connected in series to the upstream side series circuit and in parallel to the upstream side parallel circuit, and an upstream side unloading valve connected to the upstream side parallel circuit; and a downstream side hydraulic circuit having a downstream side series circuit connected to the upstream side parallel circuit via the upstream side unloading valve of the upstream side hydraulic circuit, a downstream side parallel circuit connected to the upstream side series circuit of the upstream side hydraulic circuit, a downstream side switching valve connected in series to the downstream side series circuit and in parallel to the downstream side parallel circuit, and a downstream side unloading valve between the downstream side parallel circuit and a tank circuit.

2. The hydraulic circuit according to claim 1, wherein the upstream side switching valve has a bypass circuit connected to the upstream side series circuit and an actuator circuit connected to the upstream side parallel circuit through which pressure oil is supplied to a corresponding actuator.

3. The hydraulic circuit according to claim 1, wherein the downstream side switching valve has a bypass circuit connected to the downstream side series circuit and an actuator circuit connected to the downstream side parallel circuit through which pressure oil is supplied to a corresponding actuator.

4. The hydraulic circuit according to claim 2, wherein the upstream side hydraulic circuit has an upstream side maximum pressure detection circuit connected in parallel to the actuator circuit of the upstream side switching valve via a check valve, the upstream side maximum pressure detection circuit being connected to the upstream side unloading valve in a manner to act in a closing direction of the upstream side unloading valve.

5. The hydraulic circuit according to claim 4, wherein the upstream side maximum pressure detection circuit is connected to a pressure compensating valve via the check valve in a manner to act in a closing direction of the pressure compensating valve connected in series to the actuator circuit of the upstream side switching valve of the upstream side hydraulic circuit.

6. The hydraulic circuit according to claim 3, wherein the downstream side hydraulic circuit has a downstream side maximum pressure detection circuit connected in parallel to the actuator circuit of the downstream side switching valve via a check valve, the downstream side maximum pressure detection circuit being connected to the downstream side unloading valve in a manner to act in a closing direction of the downstream side unloading valve.

7. The hydraulic circuit according to claim 6, wherein the downstream side maximum pressure detection circuit is connected to a pressure compensating valve via the check valve in a manner to act in a closing direction of the pressure compensating valve connected in series to the actuator circuit of the downstream side switching valve of the downstream side hydraulic circuit.

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