JP2002130473A - Hydraulic closed circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic closed circuit capable of lessening clog with rubbish in a flow resisting means. SOLUTION: The hydraulic closed circuit is equipped with a hydraulic pump 3 of variable displacement type, a running motor 4 to be put in closed circuit connection with the pump 3 through a pair of main lines, and a back pressure holding valve 5 including a selector valve 9 installed between the pump 3 and running motor 4 and taking two positions, the drive position (a) to put in continuity the main line side including the outlet side line of the running motor 4 and the neutral position (c), wherein the back pressure holding valve 5 includes check valves 6A and 6B, which admit flow of the pressure oil from the pump 3 to the motor 4 and check the flow in the opposite direction, and the arrangement further includes a communication passage 20 to put the pumping lines 7A and 7B in mutual communication, and the communication passage 20 is furnished with a throttle 20a to put the line 20 in communication in the condition that the pumping lines 7A and 7B have approximately an equal pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable displacement hydraulic pump which is provided in a working machine such as a crawler truck, an agricultural machine, a construction machine and the like, and is connected in a closed circuit through a pair of main pipelines. The present invention relates to a hydraulic closed circuit having a motor and a back pressure holding valve between the hydraulic pump and the hydraulic motor.

[0002]

2. Description of the Related Art A conventional hydraulic closed circuit having a back pressure holding valve is disclosed, for example, in Japanese Patent Application Laid-Open No. 7-227015. This prior art includes a variable displacement type hydraulic pump, a hydraulic motor or traveling motor connected to the hydraulic pump through a pair of main pipes in a closed circuit, and a back pressure holding valve disposed between the hydraulic pump and the traveling motor. And
The back pressure holding valve is a switching position in which the hydraulic pump performs a pumping operation, and a driving position that is a switching position for conducting a main conduit side including the outlet-side conduit of the traveling motor of the pair of main conduits when the traveling motor performs the motor operation, A switching valve having a neutral position and a check valve. The check valve allows the flow of pressure oil from the hydraulic pump side to the traveling motor side and prevents the flow of pressure oil from the traveling motor side to the hydraulic pump side.

Further, this prior art is provided with a relief valve for setting the pressure of the low-pressure side line of the main lines to a predetermined pressure, and between each of the main lines and the tank as a flow resistance means. A switching valve having a throttle is provided.

When the corresponding main line forms the low-pressure side line, these two switching valves communicate the corresponding main line with the tank via the throttle, and the corresponding main line forms the high-pressure side line. When doing so, shut off between the relevant main pipeline and the tank.

[0005] In the prior art constructed as described above, the brake pressure is generated in the main line forming the outflow side of the traveling motor by operating the back pressure holding valve particularly during a downhill, and the brake pressure Excessive rotation exceeding the specified rotation of the traveling motor, the hydraulic pump, and the prime mover that drives the hydraulic pump is prevented, and the work machine provided with the hydraulic closed circuit is prevented from running away. In addition, the two main valves are connected to the tank when the work machine is stopped by two switching valves having throttles, thereby preventing unintended running operation during stop.

[0006]

Generally, in a hydraulic closed circuit having a back pressure holding valve, the rotation of a hydraulic motor, that is, a traveling motor is stopped when a working machine or the like is stopped, that is, the back pressure holding valve is held at a neutral position. Ideally, the flow rate discharged from the hydraulic pump should be zero. However, it is actually difficult to make it completely zero, and a fixed amount of oil is discharged from the hydraulic pump. Even if a fixed amount of oil is discharged from the hydraulic pump in this way, leakage occurs from gaps between components constituting the hydraulic pump, the back pressure holding valve, and the like. As a result, the pressure of the oil discharged from the hydraulic pump is limited to a finite value determined by the discharge amount and the leakage amount from the gap, and this pressure changes the back pressure holding valve to a non-neutral position ("" PC "), the back pressure holding valve is held at the neutral position.

By the way, in the above-mentioned prior art,
By connecting the pair of main lines and the tank via two switching valves each having a throttle, it is intended to achieve the holding of the neutral position of the back pressure holding valve during stoppage. At this time, even if the discharge flow rate of the stopped hydraulic pump is zero, which is the ideal state, the respective pressures in the main pipeline reach the above-described set pressure of the relief valve (referred to as “P1”). A relatively large pressure difference (P1-PT), which is the difference between the set pressure (P1) of the relief valve and the tank pressure (referred to as "PT"), acts on the throttle of the switching valve. Here, since the tank pressure PT is generally zero, the pressure difference acting on the throttle corresponds to P1.

When the pump discharge amount is increased for the purpose of running operation, the back pressure holding valve is set to be switched when the pump discharge flow rate reaches Q. The pump discharge pressure when the valve is switched is
P1 + PC, and accordingly, the pressure difference acting on the throttle of each switching valve becomes P1 + PC, and the flow rate passing through the throttle becomes Q.

As described above, in the prior art, since the pressure difference acting on the throttle included in the switching valve is relatively large as P1 + PC, the aperture area of the throttle is set small to realize the throttle effect. I have to do it. However, when the opening area of the aperture is reduced in this way, dust contained in oil tends to be clogged at the aperture. Also,
The flow of the oil passing through the throttle is limited to one direction from the main pipeline to the tank, and it is difficult to remove dust clogged in the throttle. As described above, in the related art, there is a great concern that dust may be clogged in the throttle serving as the flow resistance means included in the switching valve, and when dust is clogged in such a manner, the back pressure is maintained despite the stoppage. A situation in which the valve cannot be held in the neutral position is likely to occur, which may cause unnecessary movement of the traveling motor.

In the prior art, since two switching valves having a throttle are required, the whole structure is complicated and tends to be large, so that a large mounting space is required and the production cost is high. There is a problem.

The present invention has been made in view of the above-described prior art, and has as its object the purpose of ensuring the function of preventing excessive rotation and escape from the back pressure holding valve and reducing the clogging of the flow resistance means. It is an object of the present invention to provide a hydraulic closed circuit that can perform the operation.

[0012]

In order to achieve the above object, the invention according to claim 1 of the present application is directed to a variable displacement type hydraulic pump, which is connected to the hydraulic pump through a closed circuit via a pair of main pipelines. Hydraulic motor, and the hydraulic pump is disposed between the hydraulic pump and the hydraulic motor.
When the hydraulic motor performs a motor operation, the hydraulic motor includes a switching position having a driving position that is a switching position for conducting a main conduit side including the outlet conduit of the hydraulic motor among the pair of main conduits, and a neutral position. A back pressure holding valve, the back pressure holding valve includes a check valve, and the check valve allows a flow of pressure oil from the hydraulic pump side to the hydraulic motor side; In the hydraulic closed circuit for preventing the flow of the pressure oil to the hydraulic pump side, a communication path is provided for enabling communication between a main pipeline portion of the pair of main pipelines located between the hydraulic pump and the check valve. The communication passage is provided with a flow resistance means for communicating the communication passage with the pair of main conduits having substantially the same pressure.

According to the first aspect of the present invention, since each of the main pipelines has the same pressure when the hydraulic motor is stopped, the same pressure acts on the flow resistance means via the communication passage, and No pressure difference occurs in the resistance means.

If the pump discharge flow rate is increased to operate the hydraulic motor, and the pump discharge flow rate reaches, for example, the aforementioned Q, the back pressure holding valve is set to be switched. The pressure difference acting on the flow resistance means when the holding valve is switched is only the switching differential pressure of the back pressure holding valve, and is the aforementioned PC (<P1 + PC). At this time, the flow rate passing through the flow resistance means via the communication path is Q.

Therefore, according to the first aspect of the present invention, since the pressure difference acting on the flow resistance means is small, the opening area of the flow resistance means can be set to be relatively large. Clogging of garbage can be suppressed. Also, by changing the discharge direction of the hydraulic pump, the direction of the oil flowing through the communication passage can be changed. Therefore, even if dust is almost clogged in the flow resistance means, by changing the flow direction of the oil, The clogged trash can be removed. Thus, dust clogging in the flow resistance means can be reduced, and the back pressure holding valve can be reliably held neutral while the hydraulic motor is stopped.

Further, a brake pressure is generated in the main pipeline forming the outflow side of the hydraulic motor by the function of the back pressure holding valve, and the function of preventing over-rotation and run-out can be ensured by the brake pressure.

According to a second aspect of the present invention, in the first aspect of the present invention, one flow resistance means is provided.

As described above, when only one flow resistance means is provided, the number of parts is reduced, the whole configuration is simple, and the size can be reduced.

According to a third aspect of the present invention, in the first aspect of the present invention, there is further provided a shut-off means for shutting off the communication path.

According to a fourth aspect of the present invention, in the third aspect of the present invention, when the hydraulic oil is discharged from the hydraulic pump, the shutoff means is operated to shut off the communication passage.

The invention according to claim 5 is characterized in that, in the invention according to claim 3 or 4, the flow resistance means is provided in a pilot switching valve that can be switched by a pilot pressure.

The invention according to claim 6 is the invention according to claims 3 to
In the invention according to any one of the fifth to fifth aspects, the flow resistance means is provided at a neutral position of the switching valve included in the back pressure holding valve.

Further, the invention according to claim 7 is the invention according to claims 3 to
In the invention according to any one of the fifth to fifth aspects, the low-pressure selection valve, which is a switching valve having a low-pressure selection position that is a switching position that selects and takes out the pressure of the low-pressure side pipeline of the pair of main pipelines, and a neutral position, A flushing mechanism including the flow resistance means provided at a neutral position of the low pressure selection valve.

According to an eighth aspect of the present invention, in the invention according to the seventh aspect, the flushing mechanism is provided between the auxiliary hydraulic power source and each of the auxiliary hydraulic power source and each of the main pipelines. A check valve that permits the flow of pressure oil from the hydraulic pressure source side to the main pipeline side and prevents the flow of pressure oil from the main pipeline side to the sub hydraulic pressure source side; And pressure setting means for setting the pressure.

According to a ninth aspect of the present invention, in the eighth aspect of the present invention, the pressure setting means comprises one of a low pressure relief valve and a flow resistance means.

The invention according to claim 10 is the invention according to claim 5.
In the invention according to the fifth aspect, pilot pressure guiding means for guiding the pressure in the main pipeline portion as a pilot pressure for switching the pilot switching valve is provided.

The invention according to claim 11 is the first invention.
In the invention according to any one of the above (10) to (10), the hydraulic motor comprises a traveling motor.

The invention according to claim 12 is the first invention.
In the invention according to the first aspect, the traveling motor, the back pressure holding valve, the communication path, and a flow resistance unit provided in the communication path are integrally provided.

With this configuration, the number of parts is small, the overall configuration is simple, and the size can be reduced.

[0030] The invention according to claim 13 is based on claim 1.
The invention according to any one of the first to twelfth aspects, is provided in the work machine.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic closed circuit according to the present invention will be described below with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram showing a first embodiment of the present invention.

The hydraulic closed circuit shown in FIG. 1 is a traveling hydraulic circuit provided in a working machine such as a crawler type transport vehicle.
A prime mover 1, a variable displacement hydraulic pump 3 connected to the output shaft 2 of the prime mover 1 and driven by the prime mover 1, and a hydraulic motor connected to the hydraulic pump 3 through a pair of main pipelines in a closed circuit; In addition to a traveling motor 4, a back pressure holding valve 5 is provided in a main pipeline located between the hydraulic pump 1 and the traveling motor 4.

The back pressure holding valve 5 includes check valves 6A and 6B provided in parallel with each other, and a switching valve 9.

The check valves 6A and 6B are provided in each of the above-mentioned pair of main conduits, and allow the flow of the pressure oil from the hydraulic pump 3 side to the traveling motor 4 side. Block the flow of pressure oil to the side.

It should be noted that, of the pair of main pipes, the main pipes located between the hydraulic pump 3 and the back pressure holding valve 5 form motor pipes 8A and 8B. Further, for example, the pump line 7A and the motor line 8A form an inflow-side line for guiding the hydraulic oil discharged from the hydraulic pump 3 to the traveling motor 4, and the motor line 8B and the pump line 7B are An outflow side conduit for guiding the pressure oil flowing out of the traveling motor 4 to the hydraulic pump 3 is formed.

The switching valve 9 is provided with a pair of pump lines 7
This is a three-position pilot switching valve that uses the differential pressure between A and 7B as a pilot pressure. The pilot line 10A (10B) and the throttle 11A (11
When the force due to the pilot pressure applied via B) becomes greater than the force of the spring 12B (12A), the position is switched to the drive position (a) or (c), and the pump line 7 is switched.
When the force due to the differential pressure between A and 7B becomes smaller than the force due to the springs 12A and 12B, the neutral position (b) is maintained.

The drive position (a) of the switching valve 9 is a switching position when the working machine provided with the hydraulic circuit travels on level ground or the like. The hydraulic pump 3 performs a pumping operation and the traveling motor 4 performs a motor operation. In the situation this position (a)
Is switched to.

When the pressure in the motor line 8A, which is the inflow side line, becomes larger than the set pressure, a relief valve 13A which releases the pressure to the motor line 8B, which is the outflow side line,
A relief valve 13B is provided to release the pressure of the motor line 8A, which is the outflow side line, to the motor line 8A, which is the inflow side line, when the pressure of the motor line 8A becomes larger than the set pressure.

The sub hydraulic pressure source 16 and the sub hydraulic pressure source 16
Valves 17A and 17B capable of supplying the pressure oil of each of the pump lines 7A and 7B to the auxiliary hydraulic source 16 and the check valve 17
A relief valve 19 is provided to release the pressure to the tank 14 when the pressure of the sub-hydraulic power supply line 18 located between A and 17B becomes larger than the set pressure.

The above-described check valves 17A and 17B allow the flow of pressure oil from the auxiliary hydraulic source 16 to the main pipeline side including the pump pipelines 7A and 7B, and the pressure from the main pipeline side to the auxiliary hydraulic source 16 side. Blocks oil flow.

The above-mentioned auxiliary hydraulic pressure source 16, relief valve 19,
The pump lines 7A, 7 are operated by the check valves 17A, 17B.
The pressure of B does not fall below the pressure set by the relief valve 19.

Further, when the pressure in the pump lines 7A, 7B becomes larger than the set pressure, relief valves 15A, 15B for releasing the pressure to the auxiliary hydraulic power source line 18 are provided.

Then, the hydraulic pump 3 of the pair of main lines and the pump lines 7A and 7B, which are the main line portions located between the check valves 6A and 6B of the back pressure holding valve 5, can communicate with each other. A passage 20 is provided, and the pressure of the pump lines 7A and 7B is substantially the same in the communication passage 20 so that the communication passage 2
Flow resistance means for communicating 0, for example, a throttle 20a is provided.

The communication passage 20 and the throttle 20a
, The back pressure holding valve 5 and the relief valves 13A and 13B are provided integrally with the traveling motor 4 and constitute one motor assembly 21.

The operation of the first embodiment configured as described above is as follows.

While the work machine is stopped, the hydraulic pump 3 is controlled so as not to discharge the pressure oil to either of the pump lines 7A and 7B. However, it is impossible to completely reduce the discharge amount to zero. It is impossible and a small amount of pressure oil will be discharged. It is now assumed that a small amount of pressure oil is discharged to the pump line 7A.

When a small amount of pressure oil is discharged from the hydraulic pump 3 to the pump line 7A side, the pump line 7A depends on the discharge flow rate and the amount of leakage from a gap inside the hydraulic pump 3 or the like.
Pressure is determined. When the pressure is lower than the set pressure (= P1) of the relief valve 19, the pressure of the pump line 7A becomes equal to the set pressure of the relief valve 19. The pressure in the other pump line 7 </ b> B is equal to the set pressure of the relief valve 19. Therefore, in this case, the pump lines 7A, 7B
Are equalized, and the switching valve 9 of the back pressure holding valve 5 holds neutral. At this time, the aperture 20a does not function for neutral holding.

Further, even if the working machine is stopped,
When the discharge flow rate from the hydraulic pump 3 to the pump line 7A is relatively large and the pressure in the pump line 7A is higher than the set pressure (= P1) of the relief valve 19 (= P2), the other is used. Since the pressure of the pump line 7B is equal to the set pressure of the relief valve 19, the pressure difference P2−P1 between the pump lines 7A and 7B acts on the switching valve 9 of the back pressure holding valve 5.
This value changes the switching valve 9 from the neutral position (b) to the driving position (a).
When the pressure difference (PC) becomes larger than the pressure difference (PC), the switching valve 9 is switched, and the traveling motor 4 is driven to drive the work machine against the intention of the worker. Become.

What prevents such a situation is the communication passage 20 and the throttle 20a. In the case described above, the pressure difference between the pump lines 7A and 7B is reduced through the communication path 20.
Acts on a. At this time, from the hydraulic pump 3 to the pump line 7
A part of the oil discharged to A is connected to the communication passage 20 and the throttle 20a.
Flows out to the pump line 7B side through the valve, and reduces the pressure of the pump line 7A. Therefore, the switching valve 5 can be held at the neutral position (b).

When the pump is started for the purpose of running on level ground or the like, the discharge flow rate of the hydraulic pump 3 is gradually increased.
Is set to switch from the neutral position (b) to the driving position (a), the pressure of the pump line 7B on the outflow side when the switching valve 9 is switched is P
1 and the pressure difference for switching the switching valve 9 from the neutral position (b) to the drive position (a) is PC, the pressure of the inflow-side pump line 7A is P1 + PC, and the throttle 2
The pressure difference acting on Oa is PC (<P1 + PC).
At this time, the flow rate passing through the throttle 20a is Q.

When the switching valve 9 is switched to the drive position (a), the motor line 8B on the outflow side communicates with the pump line 7B, and the opening thereof is kept at the maximum. Thereby, the pressure oil discharged from the hydraulic pump 3 flows into the traveling motor 4 through the pump line 7A, the check valve 6A, and the motor line 8A, and the pressure oil discharged from the traveling motor 4 is supplied to the motor line. 8
B, the drive position (a) of the switching valve 9 and the hydraulic pump 3 through the pump line 7B, whereby the traveling motor 4
Is driven to rotate, and flatland traveling and the like are performed.

Also, unlike the above-described flat-land running, when the vehicle is going downhill, an external force is applied along the rotation direction of the running motor 4, so that the running motor 4 performs the pump action and the hydraulic pump 3 performs the motor action. I will do it. At this time, the pressure in the pump line 7A drops, becomes substantially the same as the pressure in the pump line 7B, the force of the spring 12B overcomes, and the switching valve 9 returns to the neutral position (b). In this state, the motor line 8B which is the outlet side line of the traveling motor 4 is closed at the neutral position (b) of the switching valve 9, so that the motor line 8B
Brake pressure is generated. The brake pressure prevents the rotation of the traveling motor 4, the hydraulic pump 3, and the prime mover 1 from exceeding the specified rotation, and prevents the work machine from running away.

When the above-mentioned brake pressure exceeds the set pressure of the relief valve 13B, the pressure of the motor line 8B becomes
It is released to the motor pipeline 8A via 3B. As a result, protection of the hydraulic circuit is achieved.

In the first embodiment configured as described above, the pressure difference acting on the throttle 20a is the switching differential pressure PC (<P1 + PC) of the back pressure holding valve 5 as described above, and is relatively small. For this reason, the aperture area of the stop 20a can be set larger than in the above-described related art. Thereby, clogging of dust in the oil in the throttle 20a can be suppressed. Further, by changing the discharge direction of the hydraulic pump 3 by repeatedly moving the working machine forward and backward, the direction of the oil flowing through the communication passage 20 can be changed. Also, by changing the flow direction of the oil as described above, the clogged dust can be removed. Accordingly, dust clogging in the throttle 20a can be reduced, and the back pressure holding valve 5 can be reliably held neutral while the traveling motor 4 is stopped. Therefore, unnecessary movement of the traveling motor 4 can be prevented, and excellent safety can be secured.

Further, since only one stop 20a is provided, the whole structure is simple and the size can be reduced.
Along with this, a relatively small installation space is required,
Production costs can be reduced.

Further, since the communication passage 20 and the throttle 20a, the back pressure holding valve 5, the relief valves 13A and 13B, and the traveling motor 4 are integrated into one motor assembly 21, another motor assembly 21 is provided. From the viewpoint, the overall configuration is simple, the size can be reduced, the mounting space can be reduced, and the manufacturing cost can be reduced.

FIG. 2 is a hydraulic circuit diagram showing a second embodiment of the present invention.

In the second embodiment, the pump lines 7A,
A pilot-type switching valve 22 that is switched by a pilot pressure is provided in a communication path 20 that can communicate with the communication path 7B, and the communication path is provided at a neutral position of the switching valve 22 when the pressures of the pipelines 7A and 7B are substantially the same. A flow resistance means, for example, a restrictor 23, for communicating the flow path 20 is provided. The switching valve 22 includes driving positions (a) and (c), which are switching positions forming a blocking means capable of blocking the communication passage 20. That is, the switching valve 22 shuts off the communication passage 20 when the hydraulic pump 3 is switched from the neutral position (b) to the drive position (a) or (c) when the hydraulic oil is discharged.

Further, pilot lines 22a and 22b are provided for communicating the communication passage 20 and each of the control chambers of the switching valve 22. These pilot lines 22a, 22b
Constitutes pilot pressure inducing means for guiding the pressure in the pump lines 7A and 7B as pilot pressure for switching the switching valve 22.

The communication passage 20 and the switching valve 22, the back pressure holding valve 5, the relief valves 13A and 13B, and the traveling motor 4 are integrally provided, and one motor assembly 2 is provided.
4.

The other structure is the same as that of the first embodiment except that the aperture 20a is omitted.

Even in the second embodiment configured as described above, while the work machine is stopped, the throttle valve 2 of the switching valve 22
3, and the pump conduits 7A and 7B communicate with each other via the communication passage 20, and the same operation and effect as in the first embodiment described above can be obtained.

In particular, in the second embodiment, when the pressure of the pump line 7A on the inflow side becomes high, such as when traveling on level ground, the switching valve 22 is switched to the drive position (a), and the pump line is switched. The connection between 7A and 7B is shut off. Thus, it is possible to effectively use the power of the prime mover 1 and suppress a rise in the temperature of the circuit without causing unnecessary flow of oil in the circuit.

Also in the second embodiment, the first
As in the embodiment, the communication passage 20 and the switching valve 2
2, back pressure holding valve 5, relief valves 13A and 13B,
One motor assembly 2 in which the traveling motor 4 is integrated
4, the overall structure is simple, the size can be reduced, the mounting space can be reduced, and the manufacturing cost can be reduced.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

In the third embodiment, the throttle 27 constituting the flow resistance means is provided at a neutral position of a switching valve 26 which is a pilot switching valve provided in the back pressure holding valve 25.

A back pressure holding valve 25 including the switching valve 26;
The relief valves 13A and 13B and the traveling motor 4 are provided integrally, and constitute one motor assembly 28.

The other structure is the same as the structure of the first embodiment except that the stop 20a is omitted.

Even in the third embodiment configured as described above, while the work machine is stopped, the throttle valve 2 of the switching valve 26
7, and the pump pipelines 7A and 7B communicate with each other via the communication passage 20, and the same operation and effect as those in the first embodiment described above can be obtained.

Also, as in the second embodiment, when the pressure in the inflow side pump line 7A is high, such as when traveling on level ground, the switching valve 26 is switched to the driving position (a), and the pump line 7A, 7B is shut off. Thereby, it is possible to realize the effective use of the power of the prime mover 1 and the suppression of the temperature rise of the circuit without causing unnecessary flow of the oil in the circuit.

Further, a throttle 27 is provided at a neutral position of the switching valve 26, and a back pressure holding valve 25 including the switching valve 26 is provided.
And one motor assembly 28 in which the relief valves 13A and 13B and the traveling motor 4 are integrated, so that the overall configuration is simple, the size can be reduced, and the mounting space can be reduced. Production costs can be reduced.

FIG. 4 is a hydraulic circuit diagram showing a fourth embodiment of the present invention.

In the fourth embodiment, a low-pressure selection position (a) is a switching position for selecting and extracting the pressure of the low-pressure side line of the pair of main lines, that is, the pump lines 7A and 7B.
(C) and a low-pressure selection valve 29 which is a switching valve having a neutral position (b), and is provided between the low-pressure selection valve 29 and the tank 14 to reduce the pressure of the low-pressure side pipe to a predetermined pressure. A pressure setting means for setting, for example, a low pressure relief valve 30 is provided.

The fourth embodiment also has pump lines 7A and 7
B, and the passages 29 a and 29 b formed at the neutral position (b) of the low-pressure selection valve 29 are connected to the communication passage 2.
It is possible to communicate with 0. The above-mentioned passages 29a, 29
b, flow resistance means, for example, throttles 34A,
34B is provided.

The low pressure selection valve 29 described above is connected to the pump line 7
This is a three-position pilot-type switching valve capable of switching the differential pressure between A and 7B as a pilot pressure, and a pilot line 31A (31B) and a throttle 3 serving as pilot pressure inducing means.
When the force due to the pilot pressure applied via 2A (32B) becomes larger than the force of the spring 33B (33A), the position is switched to the low-pressure selection position (a), and the low-pressure side pump line 7B (7A) is switched. It is conducted to the tank 14 through the low pressure relief valve 30. When the force due to the differential pressure between the pump lines 7A and 7B is smaller than the force due to the springs 31A and 31B, the pump line 7A becomes the neutral position (b) and the pump line 7
A and 7B are conducted through the throttles 34A and 34B, and are communicated with the tank 14 through the low-pressure relief valve 30.

The low-pressure selection position (a) of the low-pressure selection valve 29 is a switching position when the working machine provided with the hydraulic circuit is traveling on level ground, and the hydraulic pump 3 operates as a pump and the traveling motor 4 operates as a motor. In the situation where the operation is performed, the position is switched to the position (a) described above.

The low-pressure selection valve 29, the auxiliary hydraulic power source 16,
The check valves 17A and 17B constitute a flushing mechanism for purifying the pressure oil flowing in the hydraulic circuit and adjusting the temperature by replacing the pressure oil corresponding to the discharge flow rate of the sub-hydraulic power source 16.

Further, the above-described low pressure selection valve 29, low pressure relief valve 30, back pressure holding valve 5, relief valves 13A and 13B
Are provided integrally with the traveling motor 4 to form one motor assembly 35.

Even in the fourth embodiment constructed as described above, while the work machine is stopped, the throttles 34A, 34B provided at the neutral position (b) of the low-pressure selection valve 29 constituting the flushing mechanism are provided. And the pump line 7 through the communication passage 20
A and 7B communicate with each other, and the same operation and effect as those of the first embodiment can be obtained.

As in the second and third embodiments, when the pressure of the pump line 7A on the inflow side is high, such as when traveling on level ground, the low pressure selection valve 29 is moved to the low pressure selection position (a). The switching is performed, and the pump lines 7A and 7B are shut off. Thereby, it is possible to realize the effective use of the power of the prime mover 1 and the suppression of the temperature rise of the circuit without causing unnecessary flow of the oil in the circuit.

Further, a low pressure selection valve 29 having throttles 34A and 34B and constituting a flushing mechanism, a low pressure relief valve 30, a back pressure holding valve 5, and relief valves 13A and 13B.
And a single motor assembly 28 in which the traveling motor 4 is integrated, so that the hydraulic circuit including the back pressure holding valve 5 and the flushing mechanism can simplify the entire configuration and reduce the size. Can be realized, the mounting space can be reduced, and the manufacturing cost can be reduced.

In the above description, the low-pressure relief valve 30 is provided between the low-pressure selection valve 29 and the tank 14 for setting the pressure, and the low-pressure relief valve 30 is provided. You may make it the structure which provides a flow resistance means.

In each of the above embodiments, the throttles 20a, 23, 27, and 27 are used as flow resistance means for communicating the communication path 20 with the pump pipes 7A and 7B at substantially the same pressure.
Although 34A and 34B are provided, an orifice may be provided in place of them.

[0085]

According to the invention of each claim of the present application, it is possible to ensure the function of preventing over-rotation and run-out by the back pressure holding valve and to reduce the clogging of dust in the flow resistance means as compared with the prior art. This makes it possible to reliably hold the back pressure holding valve neutral while the hydraulic motor is stopped, thereby preventing unnecessary movement of the hydraulic motor while the hydraulic motor is stopped, and ensuring excellent safety.

According to the second aspect of the present invention,
Since only one flow resistance means is provided, the overall structure is simple and the size can be reduced, so that a relatively small mounting space is required and the manufacturing cost can be reduced.

According to the third aspect of the invention, it is possible to prevent unnecessary oil flow in the circuit due to the oil flowing through the communication passage, to effectively use the power of the prime mover, and to suppress a rise in the temperature of the circuit. And can be realized.

Further, according to the invention of claim 6, since the flow resistance means is included in the back pressure holding valve, the whole structure can be simplified and the size can be reduced. A small installation space is required, and the manufacturing cost can be reduced.

According to the seventh aspect of the present invention, since the flow resistance means is included in the low pressure selection valve of the flushing mechanism, the flow resistance means is provided with the flushing mechanism together with the back pressure holding valve. The overall structure is simple, the size can be reduced, a relatively small mounting space is required, and the manufacturing cost can be reduced.

Further, according to the twelfth aspect of the present invention, the structure is simpler than that of the related art, and the size can be reduced, so that a relatively small mounting space is required and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing a first embodiment of a hydraulic closed circuit of the present invention.

FIG. 2 is a hydraulic circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a hydraulic circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a hydraulic circuit diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 motor 2 output shaft 3 hydraulic pump 4 traveling motor (hydraulic motor) 5 back pressure holding valve 6A check valve 6B check valve 7A pump line 7B pump line 8A motor line 8B motor line 9 switching valve 10A pilot tube Road (pilot pressure guiding means) 10B Pilot pipeline (pilot pressure guiding means) 11A Restrictor (pilot pressure guiding means) 11B Restrictor (pilot pressure guiding means) 12A Spring 12B Spring 13A Relief valve 13B Relief valve 14 Tank 15A Relief valve 15B Relief valve Valve 16 Auxiliary hydraulic source 17A Check valve 17B Check valve 18 Auxiliary hydraulic source line 19 Relief valve 20 Communication path 20a Restrictor (flow resistance means) 21 Motor assembly 22 Switching valve 22a Pilot line (pilot pressure induction means) 22b Pilot Pipe line (pilot pressure guiding means) 2 Throttle (flow resistance means) 24 motor assembly 25 back pressure holding valve 26 switching valve 27 throttle (flow resistance means) 28 motor assembly 29 low pressure selection valve 29a passage 29b passage 30 low pressure relief valve (pressure setting means) 31A pilot line (pilot) 31B Pilot line (pilot pressure inducing means) 32A Restrictor (pilot pressure inducing means) 32B Restrictor (pilot pressure inducing means) 33A Spring 33B Spring 34A Restrictor (flow resistance means) 34B Restrictor (flow resistance means) 35 Motor Assen

Continuation of the front page F term (reference) 3H089 AA86 BB06 BB23 BB27 CC09 DA03 DA13 DB03 DB13 DB33 DB46 DB49 GG02 JJ01 JJ17 3J053 AA01 AB14 AB17 EA07 FB01 FB03

Claims (13)

[Claims] 1. A variable displacement hydraulic pump, a hydraulic motor connected to the hydraulic pump via a pair of main lines in a closed circuit, and the hydraulic pump is disposed between the hydraulic pump and the hydraulic motor. Has a pump position, a drive position which is a switching position for conducting a main line side including an outlet side line of the hydraulic motor among the pair of main lines when the hydraulic motor performs a motor operation, and a neutral position. A back pressure holding valve including a switching valve, the back pressure holding valve including a check valve, the check valve allowing a flow of pressure oil from the hydraulic pump side to the hydraulic motor side; In a hydraulic closed circuit for preventing a flow of hydraulic oil from a motor side to the hydraulic pump side, a hydraulic circuit that enables communication between a main pipe portion of the pair of main pipelines located between the hydraulic pump and the check valve. With a passage, A hydraulic closed circuit, characterized in that the communication passage is provided with flow resistance means for communicating the communication passage with the pair of main conduits having substantially the same pressure. 2. The hydraulic closed circuit according to claim 1, wherein one flow resistance means is provided. 3. The hydraulic closed circuit according to claim 1, further comprising a shut-off means for shutting off the communication passage. 4. The hydraulic closed circuit according to claim 3, wherein the shut-off means is operated when the hydraulic oil is discharged from the hydraulic pump to shut off the communication path. 5. The hydraulic closed circuit according to claim 3, wherein said flow resistance means is provided in a pilot switching valve which is switched by a pilot pressure. 6. The hydraulic closed circuit according to claim 3, wherein the flow resistance means is provided at a neutral position of the switching valve included in the back pressure holding valve. 7. A flushing mechanism including a low-pressure selection valve, which is a switching valve having a low-pressure selection position that is a switching position for selecting and extracting a pressure of a low-pressure side pipeline of the pair of main pipelines and a neutral position. The hydraulic closed circuit according to any one of claims 3 to 5, wherein the flow resistance means is provided at a neutral position of the low pressure selection valve. 8. The flushing mechanism is provided between a sub-hydraulic power source and each of the sub-hydraulic power source and the main pipeline, and allows a flow of pressure oil from the sub-hydraulic power source side to the main pipeline side. A check valve for preventing flow of pressure oil from the main pipeline to the auxiliary hydraulic power source; and pressure setting means for setting a pressure of the low-pressure pipeline to a predetermined pressure. 7. The hydraulic closed circuit according to 7. 9. The hydraulic closed circuit according to claim 8, wherein said pressure setting means is one of a low pressure relief valve and a flow resistance means. 10. The hydraulic closed circuit according to claim 5, further comprising a pilot pressure guiding means for guiding the pressure of the main pipeline as a pilot pressure for switching the pilot switching valve. 11. The closed hydraulic circuit according to claim 1, wherein the hydraulic motor is a traveling motor. 12. The hydraulic closed circuit according to claim 11, wherein said traveling motor, said back pressure holding valve, said communication path, and flow resistance means provided in said communication path are integrally provided. 13. The closed hydraulic circuit according to claim 1, wherein the closed hydraulic circuit is provided in a work machine.