JP5964188B2 - Hydraulic circuit for construction machinery - Google Patents

Description

  The present invention relates to a hydraulic circuit of a construction machine using a split pump of variable displacement type 1 cylinder 2 port discharge.

  An example of this type of hydraulic circuit is described in Patent Document 1. In the hydraulic circuit described in, for example, FIG. 9 of Patent Document 1, for example, with respect to the first unload valve (2), an amount of oil corresponding to the pressure difference between the first negative control pressure and the second negative control pressure is stored in the tank (54 ) And the valve position for releasing oil to the tank (54) when the direction switching valve is not operated were the same communication position (2a).

International Publication WO 2009/123407 (FIG. 9)

  Here, the degree of opening of the communication position (2a) of the first unload valve (2) may be limited in order to control the pressure of oil supplied to and discharged from the actuator. When the opening degree of the communication position (2a) is limited, a sufficient opening degree cannot be obtained when oil is allowed to escape to the tank (54) when the direction switching valve is not operated, resulting in pressure loss. Thus, the hydraulic circuit described in Patent Document 1 leaves room for reducing pressure loss.

  This invention is made | formed in view of the said situation, The objective is to provide the hydraulic circuit of the construction machine which can reduce a pressure loss conventionally.

Means and effects for solving the problems

  To achieve the above object, the present invention provides a first unload passage connected to one discharge port of a split pump with a regulator for controlling a discharge flow rate, and a first system connected to the first unload passage. A first directional control valve, a second unload passage connected to the other discharge port of the split pump, a second directional control valve of the second system connected to the second unload passage, A tank communicating with the first unload passage and the second unload passage, a first throttle provided in the first unload passage between the first direction switching valve and the tank, and the second direction. A second throttle provided in the second unload passage between the switching valve and the tank, a first negative control pressure which is an oil pressure upstream of the first throttle, and an oil pressure upstream of the second throttle. A second negative control pressure A low-pressure selection valve that outputs the lower hydraulic pressure as the third negative control pressure, and when the first negative control pressure is higher than the second negative control pressure, the pressure difference between the first negative control pressure and the second negative control pressure A communication position for releasing a corresponding amount of oil from the first unload passage on the upstream side of the first directional switching valve to the tank, and the first unload passage and the tank on the upstream side of the first directional switching valve And a first unloading valve having a blocking position for blocking between the first directional switching valve and at least when the first directional switching valve is not operated at least upstream of the first directional switching valve An unloading position for allowing oil to escape from the first unload passage to the tank is further provided in the first unload valve. A hydraulic circuit for a construction machine is provided.

  According to this configuration, in addition to the communication position in which the amount of oil corresponding to the pressure difference between the first negative control pressure and the second negative control pressure is released to the tank, the oil is released to the tank when the direction switching valve is not operated. By providing the load position in the first unload valve, the passage opening at the unload position can be enlarged, and the pressure loss due to excess oil flowing through the first unload valve can be reduced as compared with the prior art. As a result, it is possible to provide a hydraulic circuit for a construction machine that can reduce pressure loss as compared with the prior art.

  In the present invention, a first unload flow control valve having a shut-off position and a communication position is disposed between the first unload valve and the tank, and the first unload valve is in the unload position. Sometimes, it is preferable to hold the first unload flow control valve in the communication position.

  According to this configuration, the pressure loss due to excess oil flowing through the first unload flow control valve can also be reduced as compared with the conventional case.

  Further, in the present invention, one pressure chamber and the other pressure chamber of the first unload flow control valve are connected to the first unload passage on the upstream side of the first unload valve via the first unload valve. The first unload valve is connected to the first unload passage on the upstream side of the first unload valve and one pressure chamber of the first unload flow control valve when in the unload position. The first unload valve by communicating between the first unload passage on the upstream side of the first unload valve and the other pressure chamber of the first unload flow control valve. It is preferable that the first unload flow control valve is held in the communication position when is in the unload position.

  According to this configuration, the first unload flow control valve is in the communication position in conjunction with the first unload valve. That is, the pressure due to excess oil flowing through the first unload flow control valve without adding a new valve or the like for holding the first unload flow control valve in the communication position when the first unload valve is in the unload position. Loss can be reduced as compared with the prior art.

  Furthermore, in the present invention, the first unloading valve has a blocking position disposed at a neutral position, a communication position disposed at one of the blocking positions, and an unloading position disposed at the other of the blocking positions. The first negative control pressure is input to the pressure chamber on the side, and the higher hydraulic pressure of the output of the low pressure selection valve and the hydraulic signal of the non-operation signal generation valve is input to the pressure chamber on the unload position side. In addition, it is preferable to have a neutral spring that holds the first unload valve in the shut-off position when the pressure chamber on the communication position side and the pressure chamber on the unload position side have the same pressure.

  According to this configuration, since it is only necessary to provide one pressure chamber at each end of the first unload valve, a configuration in which a total of three pressure chambers are provided at both ends of the conventional unload valve (for example, international publication) The configuration can be simpler than the first unloading valve (2) described in WO2009 / 123047 (FIG. 9).

It is a circuit diagram showing a hydraulic circuit concerning one embodiment of the present invention. It is the A section enlarged view of FIG. It is a graph which shows the discharge flow rate characteristic of a split pump, and the opening characteristic of an unload valve.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. An embodiment as a hydraulic circuit of a hydraulic excavator is shown below. FIG. 1 is a circuit diagram showing a hydraulic circuit 1 according to an embodiment of the present invention, and FIG. 2 is an enlarged view of a portion A in FIG. The hydraulic circuit 1 according to the present embodiment can also be applied to construction machines other than hydraulic excavators.

  As shown in FIG. 1, a hydraulic excavator to which the hydraulic circuit 1 is applied includes a split pump 51 with a regulator 52 that controls the discharge flow of pressure oil, a pump 53, a pilot pump 54, a tank 55, and a bucket hydraulic cylinder 56. A boom hydraulic cylinder 57, an arm hydraulic cylinder 58, a dozer hydraulic cylinder 60, a traveling hydraulic motor (not shown), and the like. The hydraulic circuit 1 is assembled with respect to these hydraulic cylinders (56 to 58, 60), actuators such as a traveling hydraulic motor, pumps (51, 53, 54), and a regulator 52.

  The split pump 51 is a variable-capacity one-cylinder two-port discharge pump, and discharges the same amount of pressure oil from the two discharge ports 51a and 51b. The split pump 51 is driven by an engine (not shown).

(Configuration of hydraulic circuit)
(Unload passage)
As shown in FIGS. 1 and 2, the hydraulic circuit 1 includes a first unload passage 12 connected to one discharge port 51 a of the split pump 51 and a second unload passage 51 b connected to the other discharge port 51 b of the split pump 51. And an unload passage 13. The first unload passage 12 and the second unload passage 13 merge at the downstream side and communicate with the tank 55. The first unload passage 12 is a first system unload passage, and the second unload passage 13 is a second system unload passage. The hydraulic circuit 1 also includes a third unload passage 29 of a third system connected to the pump 53. The third unload passage 29 also communicates with the tank 55.

(Direction switching valve)
The hydraulic circuit 1 includes three first direction switching valves 4x to 4z in the first system connected in series to the first unload passage 12, and three second systems in the second system connected in series to the second unload passage 13. Two-way switching valves 5x to 5z are provided. The first direction switching valves 4x to 4z and the second direction switching valves 5x to 5z are all center bypass type and hydraulic pilot type direction switching valves. The hydraulic circuit 1 also includes three third direction switching valves 6x to 6z of the third system connected in series to the third unload passage 29.

  Here, for example, the first direction switching valve 4x and the second direction switching valve 5x are valves that control the supply of pressure oil to a traveling hydraulic motor (not shown). The first direction switching valve 4y is a valve that controls the supply of pressure oil to the boom hydraulic cylinder 57 that operates the boom, and the first direction switching valve 4z is the pressure applied to the bucket hydraulic cylinder 56 that operates the bucket. This valve controls the supply of oil. The second direction switching valve 5z is a valve that controls the supply of pressure oil to the arm hydraulic cylinder 58 that operates the arm, and the third direction switching valve 6y is the pressure oil to the dozer hydraulic cylinder 60. This valve controls the supply.

  Here, of the first direction switching valves 4x to 4z, the first throttle 10 of the first system is provided in the first unload passage 12 between the first direction switching valve 4z on the most downstream side and the tank 55. It has been. Similarly, the second throttle 11 of the second system is provided in the second unload passage 13 between the second direction switching valve 5z on the most downstream side of the second direction switching valves 5x to 5z and the tank 55. It has been.

  In addition, sub-valves 17x-17z, 18x-18z, 28x-28z are integrally provided for all the directional control valves 4x-4z, 5x-5z, 6x-6z of the first to third systems, respectively. . The sub valves 17x to 17z, 18x to 18z, and 28x to 28z are all center bypass type valves. A pilot passage 20 that branches into the first pilot passage 26 and the second pilot passage 27 on the downstream side is connected to the pilot pump 54. All the sub valves 17x to 17z, 18x to 18z, and 28x to 28z of the first to third systems are connected in series to the first pilot passage 26. The first system sub-valve 17 x and the second system sub-valve 18 x are also connected in series to the second pilot passage 27. The sub valves 17x to 17z, 18x to 18z, 28x to 28z are in communication positions (first pilot passages) when the corresponding directional control valves 4x to 4z, 5x to 5z, and 6x to 6z are in the neutral position (when not operated). 26 communication position), and when the direction switching valves 4x to 4z, 5x to 5z, and 6x to 6z are in the switching position (operated), they are formed to be in the cutoff position (first pilot passage 26 cutoff position). ing.

  A first pilot line throttle 16 is provided in the first pilot passage 26 upstream of the sub valve 28z, and a second pilot line throttle 30 is provided in the second pilot passage 27 upstream of the sub valve 18x. Both the first pilot passage 26 and the second pilot passage 27 communicate with the tank 55 when the sub valve is in the communication position.

(Low pressure selection valve)
Further, the hydraulic circuit 1 uses the lower one of the first negative control pressure, which is the upstream hydraulic pressure of the first throttle 10, and the second negative control pressure, which is the upstream hydraulic pressure of the second throttle 11, as the third negative control pressure. As a low-pressure selection valve 9 for output. Here, the first negative control pressure, which is the hydraulic pressure of the first unload passage 12 between the first direction switching valve 4z and the first throttle 10, is input to one pressure chamber 91 of the low pressure selection valve 8. The second negative control pressure that is the hydraulic pressure of the second unload passage 13 between the second direction switching valve 5z and the second throttle 11 is input to the other pressure chamber 92 of the low pressure selection valve 9.

  Further, a regulator pilot passage 15 that connects the low-pressure selection valve 9 and the regulator 52 is provided. The third negative control pressure output from the low pressure selection valve 9 is input to the regulator 52 through the regulator pilot passage 15.

(Unload valve)
Further, the hydraulic circuit 1 includes a first unload valve 2 including a cutoff position 2a, a communication position 2b, and an unload position 2c. The first unload valve 2 is disposed in the first unload passage 12 between the discharge port 51a of the split pump 51 and the first direction switching valve 4x.

  The shutoff position 2a of the first unload valve 2 is a position that shuts off the first unload passage 12 and the tank 55 upstream of the first direction switching valve 4x on the most upstream side. Further, the communication position 2b of the first unloading valve 2 has an amount of oil corresponding to the pressure difference between the first negative control pressure and the second negative control pressure when the first negative control pressure is higher than the second negative control pressure. Is released to the tank 55 from the first unload passage 12 on the upstream side of the first direction switching valve 4x on the most upstream side. In addition, the unloading position 2c of the first unloading valve 2 is the first upstream of the first direction switching valve 4x on the upstream side when at least all of the first direction switching valves 4x to 4z are not operated. 1 is a position for oil to escape from the unload passage 12 to the tank 55. The first unload passage 12 on the upstream side of the first unload valve 2 and the first unload valve 2 on the downstream side of the first unload valve 2 at any of the blocking position 2a, the communication position 2b, and the unload position 2c. The first unload passage 12 communicates with the first unload passage 12.

  Here, the first unloading valve 2 has a blocking position 2a at a neutral position, and a communication position 2b and an unloading position 2c on both sides of the blocking position 2a. The first negative control pressure is input to the pressure chamber 22 on the communication position 2b side, and the pressure chamber 21 on the unload position 2c side includes the output of the low pressure selection valve 9 and the hydraulic signal of the non-operation signal generation valve 19 described later. The higher hydraulic pressure is input. Specifically, the passage 36 branched from the regulator pilot passage 15 and the passage 37 from the non-operation signal generation valve 19 are merged and then connected to the pressure chamber 21, whereby the low pressure selection valve 9. The higher hydraulic pressure of the output and the hydraulic pressure signal of the non-operation signal generating valve 19 described later is input to the pressure chamber 21. Further, when the pressure chamber 22 on the communication position 2b side and the pressure chamber 21 on the unload position 2c side have the same pressure, neutral springs 24 and 23 (biasing means) that hold the first unload valve 2 at the shut-off position 2a. ) Are disposed in the pressure chambers 22 and 21, respectively.

  Further, when the first unload valve 2 is in the communication position 2b, a passage in the first unload valve 2 that connects the first unload passage 12 upstream of the first unload valve 2 and the tank 55 is provided. Is provided with a diaphragm 25. The passage opening connected to the tank 55 in the first unloading valve 2 when the first unloading valve 2 is in the unloading position 2c is the passage opening connected to the tank 55 in the first unloading valve 2 when the first unloading valve 2 is in the communication position 2b. Bigger than.

  Similarly, the hydraulic circuit 1 includes a second unload valve 3 including a cutoff position 3a, a communication position 3b, and an unload position 3c. The second unload valve 3 is disposed in the second unload passage 13 between the discharge port 51b of the split pump 51 and the second direction switching valve 5x. The configuration of the first unload valve 2 described above and the configuration of the second unload valve 3 are the same except that the systems are different from each other.

(Unload flow control valve)
The hydraulic circuit 1 also includes a first unload flow control valve 31 provided in the downstream passage 38 of the first unload valve 2 between the first unload valve 2 and the tank 55. The first unload flow control valve 31 includes a blocking position 31a and a communication position 31b.

  One pressure chamber 33 and the other pressure chamber 34 of the first unload flow control valve 31 are connected to the first unload passage 12 upstream of the first unload valve 2 via the first unload valve 2. ing. A spring 35 (biasing means) is disposed in the other pressure chamber 34 of the first unload flow control valve 31. Here, when the first unload valve 2 is at the unload position 2 c, the first unload passage 12 on the upstream side of the first unload valve 2 and the one pressure chamber 33 of the first unload flow control valve 31 The circuit is configured so that the first unload passage 12 on the upstream side of the first unload valve 2 and the other pressure chamber 34 of the first unload flow control valve 31 communicate with each other. Yes. Thus, when the first unload valve 2 is at the unload position 2c, the first unload flow control valve 31 is held at the communication position 31b.

  Similarly, the hydraulic circuit 1 includes a second unload flow control valve 32 provided in a downstream passage 39 of the second unload valve 3 between the second unload valve 3 and the tank 55. The second unload flow control valve 32 includes a blocking position 32a and a communication position 32b. The configuration of the first unload flow control valve 31 and the configuration of the second unload flow control valve 32 are the same except that the systems are different from each other.

  The unload flow control valves 31 and 32 allow the excess flow of oil corresponding to the operation amount of the direction switching valve to escape to the tank 55 regardless of the load pressure of the actuator, thereby further suppressing deterioration of the operability of the actuator. It is a valve.

(Non-operation signal generation valve)
Further, the hydraulic circuit 1 includes a non-operation signal generation valve 19. Connected to one pressure chamber 41 of the non-operation signal generating valve 19 is a passage 40 branched from the first pilot passage 26 downstream of the third system sub-valve 28x and upstream of the second system sub-valve 18x. Has been. Further, a spring 42 (biasing means) is disposed in the pressure chamber 11. Further, the pressure of the pilot passage 20 on the upstream side of the first pilot line throttle 16 and the second pilot line throttle 30 is input to the other pressure chamber 43 of the non-operation signal generating valve 19.

  This non-operation signal generation valve 19 is provided for the first unload valve 2 when all the sub valves 17x to 17z and 18x to 18z of the first system and the second system are in the communication position (the first pilot passage 26 communication position). The pressure of the pilot passage 20 is introduced into the pressure chamber 21 on the unload position 2c side and the pressure chamber on the unload position 3c side of the second unload valve 3, and at least one of the sub valves 17x to 17z and 18x to 18z Is formed so as to block the introduction of the pilot passage 20 pressure into the pressure chambers of the unload valves 2 and 3 when the valve is in the cutoff position (the first pilot passage 26 cutoff position).

(Hydraulic excavator operation)
Here, the characteristics of the split pump 51 and the unload valves 2 and 3 will be described first. FIG. 3A is a graph showing the discharge flow rate characteristics of the split pump 51. FIG. 3B is a graph showing the opening characteristics of the passage in the valve connected to the tank 55 (provided with the throttle 25) when the unload valves 2 and 3 are switched to the communication positions 2b and 3b. FIG. 3C is a graph showing the opening characteristics of the in-valve passage leading to the tank 55 when the unload valves 2 and 3 are switched to the unload positions 2c and 3c.

  As shown in FIG. 3 (a), the discharge flow rate characteristic of the split pump 51 is adjusted by the regulator 52 so that the maximum flow rate Qmax is obtained when the negative control pressure (third negative control pressure) is 0 to Pf. When the negative control pressure is Pf to Ps, the pressure decreases in proportion to the increase of the negative control pressure, and when the negative control pressure is Ps or more, the minimum flow rate Qmin is obtained. Note that Pf <Ps. Pf is the maximum negative control pressure when the discharge flow rate of the split pump 51 is maximum (Qmax), and Ps is the minimum negative control pressure when the discharge flow rate of the split pump 51 is minimum (Qmin). is there. The discharge flow rate of the split pump 51 refers to the discharge flow rate discharged from one of the two discharge ports 51a and 51b.

  In FIG. 3B, the valve opening characteristics when the unload valves 2 and 3 are switched to the communication positions 2b and 3b are connected to the tank 55 of the unload valves 2 and 3 (throttle 25 is connected). The opening area of the passage in the valve) is 0 (blocking position 2a, 3a) when the negative control differential pressure (the absolute value of the difference between the first negative control pressure and the second negative control pressure) is zero, and the negative control differential pressure is When it is 0 to (Ps-Pf), it increases in proportion to the increase in negative control differential pressure (unload valve stroke intermediate position), and when the negative control differential pressure is Ps-Pf or more, the maximum opening area (maximum unload valve stroke position) It becomes. Note that the amount of oil flowing through the unload valves 2 and 3 increases as the opening area of the unload valves 2 and 3 increases.

  In the example shown in FIG. 3 (b), the opening characteristics of the unload valves 2 and 3 when switching to the communication positions 2b and 3b are linear. The opening characteristics of the unload valves 2 and 3 may be non-linear depending on convenience and operator preference. For example, as shown by the alternate long and short dash line in FIG. 3 (b), by making the opening characteristic concave, the supply flow rate at the time of the composite operation can be increased, and the pressure can be increased only at the time of the additional composite operation. The power of operation increases. Further, as indicated by a two-dot chain line in FIG. 3B, the soft feeling of the operation is increased by making the opening characteristic convex.

  On the other hand, as shown in FIG. 3 (c), the valve opening characteristics when the unload valves 2 and 3 are switched to the unload positions 2c and 3c are indicated by solid lines. The maximum opening area of the in-valve passage connected to the tank 55 in the unload valves 2 and 3 when 3c is the maximum opening of the in-valve passage connected to the tank 55 when the unload valves 2 and 3 are in the communication positions 2b and 3b. It is larger than the area (see FIG. 3B). In addition, the linear inclination of the opening characteristic when switching to the unload positions 2c and 3c is larger than the linear inclination of the opening characteristic when switching to the communication positions 2b and 3b. The opening characteristics when switching to the unload positions 2c and 3c may be nonlinear.

  Next, the operation of the hydraulic excavator (operation of the hydraulic circuit 1) will be described with reference to FIGS. First, it is assumed that all the direction switching valves 4x to 4z, 5x to 5z, and 6x to 6z of the first to third systems are not operated. At this time, all the sub valves 17x to 17z, 18x to 18z, and 28x to 28z are in communication positions, and the first pilot passage 26 is in communication with the tank 55. Therefore, the pressure in the passage 40 branched from the first pilot passage 26 is low. On the other hand, the pressure of the pilot passage 20 (pressure oil from the pilot pump 54) is input to the pressure chamber 43 of the non-operation signal generation valve 19. Therefore, the non-operation signal generation valve 19 is in the position 19b. As a result, the passage 37 is connected to the pilot pump 54.

  Here, the discharge pressure of the pilot pump 54 is higher than the discharge pressure of the split pump 51. That is, the discharge pressure of the pilot pump 54 is higher than the first negative control pressure and the second negative control pressure. Therefore, high pressure oil from the pilot pump 54 is input to the pressure chamber 21 of the first unload valve 2 via the passage 37, and the first unload valve 2 is switched from the shut-off position 2a to the unload position 2c. (The same applies to the second unload valve 3). In general, the negative control pressure is set to a pressure lower than 3 MPa, and the pressure of the pilot pump 54 is set to 3 MPa or more.

  When the first unload valve 2 is switched to the unload position 2c, the first unload passage 12 on the upstream side of the first unload valve 2 is disconnected from the pressure chamber 33 of the first unload flow control valve 31. In addition, the first unload passage 12 on the upstream side of the first unload valve 2 and the pressure chamber 34 of the first unload flow control valve 31 communicate with each other. Accordingly, the first unload flow control valve 31 is held at the communication position 31b (the same applies to the second unload flow control valve 32).

  As a result, oil escapes from the first unload passage 12 on the upstream side of the first unload valve 2 (upstream side of the first direction switching valve 4x) to the tank 55 via the first unload flow control valve 31 ( The same applies to the second unload valve 3). At this time, the high pressure oil from the pilot pump 54 is input to the regulator 52 via the passage 37, the passage 36, and the regulator pilot passage 15, so that the discharge flow rate of the split pump 51 is the minimum flow rate (Qmin (See FIG. 3A). As a result, the first negative control pressure and the second negative control pressure are the same low pressure.

  In this state, for example, if the arm hydraulic cylinder 58 is operated by operating the second direction switching valve 5z, the sub valve 18z is moved to the shut-off position in conjunction with the second direction switching valve 5z. When the sub valve 18z is in the cutoff position, the pressures before and after the first pilot line throttle 16 (upstream and downstream) become substantially equal, and the pressure in the passage 40 increases. As a result, the non-operation signal generating valve 19 is switched from the position 19b to the position 19a. When the non-operation signal generating valve 19 is switched to the position 19a, the discharge pressure of the pilot pump 54 does not act on the passage 37. On the other hand, as described above, the first negative control pressure and the second negative control pressure are the same low pressure. When the discharge pressure of the pilot pump 54 does not act on the passage 37, the pressure chamber 21 of the first unload valve 2 (the same applies to the second unload valve 3) and the regulator 52 are connected to the third pressure from the low pressure selection valve 9. Negative control pressure is input. The third negative control pressure is equal to the first negative control pressure and the second negative control pressure, which are the same pressures. Further, the first negative control pressure is input to the pressure chamber 22 of the first unload valve 2 (the same applies to the second unload valve 3). As a result, the unload valves 2 and 3 return from the unload positions 2c and 3c to the cutoff positions 2a and 3a, the discharge flow rate of the split pump 51 increases, and the first negative control pressure and the second negative control pressure increase. .

  On the other hand, when the second direction switching valve 5z is operated, pressure oil is supplied from the second unload passage 13 to the arm hydraulic cylinder 58, so that the second negative control pressure is lower than the first negative control pressure. When the second negative control pressure is lowered, the second negative control pressure is selected by the low pressure selection valve 9 and is output as the third negative control pressure and is input to the regulator 52 via the regulator pilot passage 15. As a result, the discharge flow rate from the discharge port 51a and the discharge port 51b of the split pump 51 both increases to the required flow rate of the second system.

  Further, the second negative control pressure is input from the low pressure selection valve 9 to the pressure chamber 21 of the first unload valve 2. Since the first negative control pressure higher than the second negative control pressure is inputted to the pressure chamber 22 on the opposite side of the first unloading valve 2, the first unloading valve 2 has a stroke amount corresponding to the negative control differential pressure. Only the switching position 2a is changed (moved) from the shut-off position 2a to the unloading valve opening area corresponding to the negative control differential pressure, and the excess oil in the first system (the amount of oil corresponding to the negative control differential pressure) Escapes to tank 55.

(effect)
As described above, according to the hydraulic circuit 1, the directional control valve is operated separately from the communication position 2b in which an amount of oil corresponding to the pressure difference between the first negative control pressure and the second negative control pressure is released to the tank. By providing the first unloading valve 2 with the unloading position 2c for allowing oil to escape to the tank when there is not, the passage opening communicating with the tank 55 at the unloading position 2c is connected to the tank opening at the communication position 2b. The pressure loss due to surplus oil flowing through the first unload valve 2 when the direction switching valve is not operated can be reduced as compared with the prior art. As a result, the pressure loss of the oil flowing through the hydraulic circuit 1 can be reduced as compared with the prior art, and the fuel consumption of the engine of the construction machine can be further suppressed. It is also an effective effect that it is not necessary to separately provide a valve having the function of the unloading position 2c.

  Further, according to the hydraulic circuit 1, when the first unload valve 2 is at the unload position 2c, the first unload flow control valve 31 is held at the communication position 31b, so that surplus flows through the first unload flow control valve 31. Pressure loss due to oil can also be reduced as compared with the prior art. The pressure chamber 33 of the first unload flow control valve 31 is placed in the tank 55 at the unload position 2c, instead of blocking the hydraulic pressure introduction passage at the unload position 2c to the pressure chamber 33 of the first unload flow control valve 31. The circuit may be configured to be connected.

  Further, according to the hydraulic circuit 1, the first unload flow control valve 31 is in the communication position 31 b in conjunction with the first unload valve 2. That is, without adding a new valve or the like for holding the first unload flow control valve 31 at the communication position 31b when the first unload valve 2 is at the unload position 2c, the first unload flow control valve 31 is The pressure loss due to the surplus oil flowing can be reduced as compared with the prior art.

  Furthermore, the first unload valve 2 constituting the hydraulic circuit 1 is only provided with pressure chambers 21 and 22 respectively at both ends thereof. On the other hand, for example, the first unload valve (2) described in International Publication WO2009 / 123047 (FIG. 9) is provided with a total of three pressure chambers at both ends thereof. That is, in the present embodiment, the configuration of the first unload valve 2 can be simplified.

  The effects described above are related to the first unload valve 2 of the first system, but the same applies to the second unload valve 3 of the second system.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. .

  For example, in the above-described embodiment, the circuit configuration is such that the first unload valve 2 is switched to the unload position 2c when all the direction switching valves of the first system and the second system are not operated. Regardless of whether or not the direction switching valves of the system (second direction switching valves 5x to 5z) are operated, the first direction switching valve (first direction switching valves 4x to 4z) is not operated. A circuit configuration in which the 1 unload valve 2 is switched to the unload position 2c may be used (the same applies to the second system unload valve (second unload valve 3)).

  In the above-described embodiment, the unload flow control valves 31 and 32 are disposed between the unload valves 2 and 3 and the tank 55, but the unload flow control valves 31 and 32 are not necessarily required. That is, the unload flow control valves 31 and 32 may not be arranged.

1: Hydraulic circuit 2: First unloading valve 3: Second unloading valve 4x, 4y, 4z: First direction switching valve 5x, 5y, 5z: Second direction switching valve 6x, 6y, 6z: Third direction switching Valve 9: Low pressure selection valve 10: First throttle 11: Second throttle 12: First unload passage 13: Second unload passage 51: Split pump 52: Regulator 54: Pilot pump 55: Tank

Claims (4)

A first unload passage connected to one discharge port of a split pump with a regulator for controlling the discharge flow rate;
A first direction switching valve of a first system connected to the first unload passage;
A second unload passage connected to the other outlet of the split pump;
A second directional valve of the second system connected to the second unload passage;
A tank communicating with the first unload passage and the second unload passage;
A first throttle provided in the first unload passage between the first directional control valve and the tank;
A second throttle provided in the second unload passage between the second direction switching valve and the tank;
A low pressure selection valve that outputs a lower one of the first negative control pressure that is the hydraulic pressure upstream of the first throttle and the second negative control pressure that is the hydraulic pressure upstream of the second throttle as the third negative control pressure; ,
When the first negative control pressure is higher than the second negative control pressure, an amount of oil corresponding to the pressure difference between the first negative control pressure and the second negative control pressure is upstream of the first directional control valve. A first unloading valve having a communication position for allowing the tank to escape from one unloading passage, and a blocking position for blocking between the first unloading passage on the upstream side of the first directional control valve and the tank;
In the hydraulic circuit of a construction machine comprising
At least when the first directional switching valve is not operated, the first unloading valve further has an unloading position for releasing oil from the first unloading passage upstream of the first directional switching valve to the tank. A hydraulic circuit for a construction machine, characterized by being provided. In the hydraulic circuit of the construction machine according to claim 1,
A first unload flow control valve having a shut-off position and a communication position is disposed between the first unload valve and the tank,
A hydraulic circuit for a construction machine, wherein the first unload flow control valve is held in a communication position when the first unload valve is in an unload position. In the hydraulic circuit of the construction machine according to claim 2,
One pressure chamber and the other pressure chamber of the first unload flow control valve are connected to the first unload passage on the upstream side of the first unload valve via the first unload valve,
When the first unload valve is in the unload position, the first unload valve shuts off the first unload passage on the upstream side of the first unload valve and one pressure chamber of the first unload flow control valve. The first unload valve is placed in the unload position by communicating between the first unload passage on the upstream side of the first unload valve and the other pressure chamber of the first unload flow control valve. Sometimes, the hydraulic circuit of the construction machine, wherein the first unload flow control valve is held in a communication position. In the hydraulic circuit of the construction machine according to any one of claims 1 to 3,
The first unload valve is
The blocking position is arranged at the neutral position, the communication position is arranged at one of the blocking positions, and the unloading position is arranged at the other of the blocking positions,
The first negative control pressure is input to the pressure chamber on the communication position side, and the higher hydraulic pressure of the output of the low pressure selection valve and the hydraulic signal of the non-operation signal generation valve is input to the pressure chamber on the unload position side. Has been
A hydraulic circuit for a construction machine, comprising: a neutral spring that holds the first unload valve in a shut-off position when the pressure chamber on the communication position side and the pressure chamber on the unload position side have the same pressure.