JP7124610B2 - Hydraulic system for construction machinery - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic system for construction machinery, such as a mobile crane, having a hydraulic motor for traveling and a hydraulic motor for driving a hoisting device.

Conventionally, in this type of construction machine, a hydraulic circuit (including a directional switching valve for controlling the operation of the traveling motor) that supplies hydraulic oil from a hydraulic pump to a hydraulic motor for traveling (hereinafter sometimes simply referred to as a traveling motor) has been provided. Hydraulic circuit (hydraulic circuit including a directional switching valve for controlling the operation of the hoisting motor) that supplies hydraulic oil to the hydraulic motor for driving the hoisting device (hereinafter sometimes simply referred to as the hoisting motor) on the downstream side of the circuit) are connected in series and each hydraulic motor is operated so that the travel motor and the hoisting motor are operated at the same time, the hydraulic oil after passing through the travel motor from the hydraulic pump (this A hydraulic system is known that is configured to supply hydraulic oil discharged from a travel motor to a hoisting motor (see, for example, Patent Document 1).

JP-A-2002-46978

In the hydraulic system as described above, since the directional switching valve for the traveling motor can be arranged on the most upstream side, it is easy to form an oil passage that connects the directional switching valve to the traveling motor via a swivel joint or the like. Although there are advantages such as the ability to omit a dedicated oil passage for supplying hydraulic oil from the hydraulic pump to the directional switching valve for the hoisting motor (which in turn reduces the cost and size of the valve unit), the following The inventors of the present application have found that there is a possibility of causing such an inconvenience.

That is, the load on the hoisting motor is often large when, for example, lifting a heavy object is performed. In such a situation where the load on the hoisting motor is large, when the hydraulic oil is supplied to the traveling motor in order to operate the traveling motor, the hydraulic oil inlet side and outlet side of the traveling motor are displaced. Both pressures become high pressure. As a result, there is a risk of malfunction of the travel motor or damage to components such as a cylinder block of the travel motor.

SUMMARY OF THE INVENTION The present invention has been made in view of such a background. An object of the present invention is to provide a hydraulic device capable of preventing pressures on both the inlet side and the outlet side of hydraulic oil from becoming high.

A traveling motor that is a hydraulic motor for traveling, a hoisting motor that is a hydraulic motor for driving a hoisting device, a hydraulic pump that discharges hydraulic oil, and a traveling switching valve that is a directional switching valve connected to the traveling motor. and a hoisting switching valve, which is a directional switching valve connected to the hoisting motor, and the traveling switching valve is arranged so that the hydraulic oil discharged from the hydraulic pump flows upstream of the hoisting switching valve. The hoist switching valve is connected to the hydraulic pump, and the hydraulic oil discharged from the hydraulic pump flows in via the travel switching valve when the travel motor stops operating, and the travel motor is connected to the travel switching valve so as to flow in through the travel switching valve and the travel motor, wherein
Two travel motor oil passages are connected between the travel switching valve and the travel motor, and the two travel motor oil passages are communicated with each other in a first state and the communication is cut off. and a switching valve that is operable in the second state, and the switching valve switches to the above-described second state when the pressure of hydraulic oil supplied from the hoisting switching valve to the hoisting motor reaches a high pressure equal to or higher than a predetermined value. It is characterized in that it is configured to operate according to the pressure so as to switch from the second state to the first state (first invention).

In the present invention, the "two travel motor oil passages" refer to one travel motor oil passage through which hydraulic oil supplied from the travel switching valve to the travel motor flows when the travel motors are in operation, and the other travel motor oil passage. The travel motor oil passage means two oil passages that flow hydraulic oil discharged from the travel motor to the travel switching valve.

According to the first aspect, when the pressure of the hydraulic fluid supplied to the hoisting motor reaches a predetermined value or higher, the state is switched from the second state to the first state. oil passages communicate with each other. Therefore, when the traveling motor and the hoisting motor are operated simultaneously and the pressure of the hydraulic oil supplied to the hoisting motor becomes high, the hydraulic oil discharged from the hydraulic pump does not pass through the traveling motor. is supplied to the hoist motor. As a result, it is possible to prevent the pressure on both the inlet side and the outlet side of the hydraulic oil of the travel motor from becoming high.

In the first aspect of the invention, the switching valve operates between the hoisting switching valve and the hoisting motor so that the pressure of hydraulic fluid supplied from the hoisting switching valve to the hoisting motor is applied as pilot pressure. It is preferable that the switching valve is a pilot-driven switching valve connected via pilot oil passages to two hoisting motor oil passages through which oil flows (second invention).

The "two hoisting motor oil passages" are defined as one of the hoisting motor oil passages through which the operating oil supplied from the hoisting switching valve to the hoisting motor flows when the hoisting motors are operating, and the other of the hoisting motor oil passages. The oil passage means two oil passages that flow hydraulic oil discharged from the hoisting motor to the hoisting switching valve.

According to the second aspect of the invention, the configuration for operating the switching valve can be configured simply and inexpensively.

In the second aspect of the invention, the pilot oil passage is provided with a check valve and a throttle portion which are connected in parallel, and the check valve extends from the hoisting motor oil passage to the switching valve. It is preferable that it is constructed so as to block the flow of hydraulic oil in the direction opposite to the direction in which it is directed (the third invention).

According to this, when the switching valve returns from the first state to the second state in response to a decrease in the pressure of the hydraulic oil supplied to the hoisting motor, the pilot pressure applied to the switching valve gradually increases. Since the pressure decreases, the communication between the two travel motor oil passages is gradually cut off. Therefore, when the switching valve returns from the first state to the second state, even if the travel switching valve is driven so as to operate the travel motor, the travel motor is suddenly supplied with hydraulic oil. You can prevent it from becoming available. As a result, it is possible to prevent the traveling motor from suddenly starting to operate.

1 is a diagram showing a schematic configuration of a construction machine (mobile crane) to which an embodiment of the invention is applied; FIG. The figure which shows the hydraulic-circuit structure of the hydraulic system of embodiment.

An embodiment of the invention is described below with reference to FIGS. 1 and 2. FIG. Referring to FIG. 1, a construction machine 50 equipped with a hydraulic system 1 (shown in FIG. 2) of this embodiment is, for example, a mobile crane. This construction machine 50 includes a lower traveling body 51 having a pair of left and right crawlers 51 a , an upper rotating body 52 rotatably mounted on the lower traveling body 51 , and swinging parts from the upper rotating body 52 via boom foot pins 53 . A boom 54 extending movably (up and down), a hydraulic cylinder 55 for raising and lowering the boom 54, a hoisting device 56 (winch) mounted on the upper rotating body 52 on the rear side of the boom 54, A wire 58 connected from a hoisting device 56 to a hook 59 below the point jave 57 (pulley mechanism) attached to the upper end of the boom 54 and a wire 58 mounted on the upper revolving body 52 . and a driver's cab 60 .

In such a construction machine 50, the wire 58 is run by the hoisting device 56, or the boom 54 is raised and lowered by the hydraulic cylinder 55, or a revolving machine (not shown) is operated while the load is suspended from the hook 59. By causing the upper swing body 52 to swing with the hydraulic motor, it is possible to move the object to be transported.

The hydraulic system 1 of the present embodiment is mounted on such a construction machine 50. As shown in FIG. Specifically, a hoisting motor 3 (hydraulic motor for rotating the drum of the hoisting device 56), a hydraulic pump 4, a traveling switching valve 5 that is a directional switching valve for controlling the operation of the traveling motor 2, and the hoisting motor 3. A hoisting switching valve 6 that is a directional switching valve for operation control is provided.

The construction machine 50 has two traveling motors for separately driving the left and right crawlers 51a constituting the lower traveling body 51, respectively. The traveling motor 2 shown in FIG. 2 is one of the two traveling motors.

The hydraulic pump 4 is driven by an engine (not shown), and in its driving state draws hydraulic oil from a hydraulic oil tank 7 and discharges the hydraulic oil from a discharge port. A center bypass oil passage 10 is connected to the discharge port of the hydraulic pump 4 so as to flow back from the discharge port to the hydraulic oil tank 7 via the traveling switching valve 5 and the hoisting switching valve 6 in that order. there is

The traveling switching valve 5 interposed on the upstream side of the center bypass oil passage 10 is a pilot-driven directional switching valve having a spool valve, and has two pilot ports 5a and 5b. The operating position of the travel switching valve 5 is the A0 position which is a neutral position, the Aa position which is an operating position when a pilot pressure equal to or higher than a predetermined value is applied to the pilot port 5a, and the Aa position which is the operating position when the pilot pressure of the pilot port 5a or more is applied to the pilot port 5b. Ab position, which is an operating position when the above pilot pressure is applied.

The travel switching valve 5 is connected to two inlet/outlet ports 2a and 2b of the travel motor 2 (serving as an inlet or an outlet for hydraulic oil) through two oil passages 11a and 11b as travel motor oil passages in the present invention. two ports), and is connected to the hydraulic oil tank 7 via the oil passage 12 . In this embodiment, a counterbalance valve 30 is interposed in the oil passages 11a and 11b, which will be described later.

The travel switching valve 5 is urged to be held at the neutral position A0 when pilot pressure is not applied to both of its pilot ports 5a and 5b. At the A0 position, the travel switching valve 5 opens the upstream center bypass oil passage 10 to the downstream center bypass oil passage 10, 11a is closed and the oil passage 11b is opened to the hydraulic oil tank 7 via the oil passage 12. As shown in FIG.

Therefore, in the A0 position (neutral position) of the travel switching valve 5 , hydraulic oil flowing from the hydraulic pump 4 through the center bypass oil passage 10 on the upstream side into the travel switching valve 5 is not supplied to the travel motor 2. , flows into the center bypass oil passage 10 on the downstream side of the travel switching valve 5 .

Further, when a pilot pressure of a predetermined value or more is applied to the pilot port 5a, the travel switching valve 5 is displaced from the A0 position (neutral position) to the Aa position as the pilot pressure increases. At the Aa position, the travel switching valve 5 closes the center bypass oil passage 10 on the upstream side with respect to the center bypass oil passage 10 on the downstream side, and opens the oil passage 11a on the travel motor 2 side. , the oil passage 11b on the traveling motor 2 side is opened to the center bypass oil passage 10 on the downstream side.

Further, in the process of moving the travel switching valve 5 from the A0 position to the Aa position, the oil passage (bleed-off oil passage) between the upstream center bypass oil passage 10 and the downstream center bypass oil passage 10 is opened. gradually decreases as the pilot pressure applied to the pilot port 5a increases, or the opening of the oil passage (meter-in oil passage) between the center bypass oil passage 10 and the oil passage 11a on the upstream side It is configured to gradually increase as the pilot pressure applied to the port 5a increases.

Therefore, when the travel switching valve 5 is moved to the Aa position, hydraulic oil flowing from the hydraulic pump 4 through the center bypass oil passage 10 on the upstream side into the travel switching valve 5 flows from the travel switching valve 5 through the oil passage 11a. Hydraulic oil is supplied to the inlet/outlet port 2a of the travel motor 2 via the travel motor 2 and discharged from the other inlet/outlet port 2b of the travel motor 2 via the oil passage 11b and the travel switching valve 5 on the Aa position side. , the center bypass oil passage 10 on the downstream side. Furthermore, as the pilot pressure applied to the pilot port 5a increases, the flow rate of the hydraulic oil supplied to the input/output port 2a of the travel motor 2 increases.

Further, when a pilot pressure of a predetermined value or more is applied to the pilot port 5b, the traveling switching valve 5 is displaced from the A0 position (neutral position) to the Ab position as the pilot pressure increases. At the Ab position, the travel switching valve 5 closes the upstream center bypass oil passage 10 with respect to the downstream center bypass oil passage 10, and opens the oil passage 11b on the travel motor 2 side. , the oil passage 11a on the traveling motor 2 side is opened to the center bypass oil passage 10 on the downstream side.

Further, in the process of moving the travel switching valve 5 from the A0 position to the Ab position, the oil passage (bleed-off oil passage) between the upstream center bypass oil passage 10 and the downstream center bypass oil passage 10 is opened. , gradually decreases as the pilot pressure applied to the pilot port 5b increases, or the opening of the oil passage (meter-in oil passage) between the center bypass oil passage 10 and the oil passage 11b on the upstream side It is configured to gradually increase as the pilot pressure applied to the port 5b increases.

Therefore, when the travel switching valve 5 is moved to the Ab position, hydraulic oil flowing from the hydraulic pump 4 through the center bypass oil passage 10 on the upstream side into the travel switching valve 5 flows from the travel switching valve 5 through the oil passage 11b. Hydraulic oil supplied to the inlet/outlet port 2b of the travel motor 2 via the travel motor 2 and discharged from the other inlet/outlet port 2a of the travel motor 2 passes through the oil passage 11a and the travel switching valve 5 at the Ab position, It circulates in the center bypass oil passage 10 on the downstream side. Furthermore, as the pilot pressure applied to the pilot port 5b increases, the flow rate of the hydraulic oil supplied to the input/output port 2b of the travel motor 2 increases.

The pilot ports 5a and 5b of the travel switching valve 5 are connected to an operation device 13 provided with an operation lever 13a (or an operation pedal) for operating the travel motor 2 via pilot oil passages 14a and 14b, respectively. It is

The operation device 13 generates a pilot pressure (secondary pressure) according to the operation of the operation lever 13a by a pressure reducing valve or the like from the primary pressure pilot hydraulic oil supplied from a pilot pump (not shown). Of the pilot ports 5a and 5b, the signal is output to the pilot port 5a or 5b, which is specified according to the operating direction of the operating lever 13a.

For example, when the operating lever 13a is operated in the direction to operate the traveling motor 2 in the normal direction, the operating device 13 outputs a pilot pressure to the pilot port 5a according to the amount of operation of the operating lever 13a. . Further, when the operating lever 13a is operated in the direction to operate the traveling motor 2 in the reverse direction, the operating device 13 outputs a pilot pressure corresponding to the amount of operation of the operating lever 13a to the pilot port 5b.

The hoist switching valve 6, which is interposed on the downstream side of the center bypass oil passage 10, is a directional switching valve of a pilot drive type like the travel switching valve 5, and has two pilot ports 6a and 6b. The operating positions of the hoist switching valve 6 are the B0 position, which is a neutral position, the Ba position, which is an operating position when a pilot pressure equal to or higher than a predetermined value is applied to the pilot port 6a, and the predetermined pressure at the pilot port 6b. and a Bb position, which is an operating position when the above pilot pressure is applied.

The hoisting switching valve 6 is connected to the two inlet/outlet ports 3a, 3b of the hoisting motor 3 (operating oil inlet or outlet) through two oil passages 21a, 21b as hoisting motor oil passages in the present invention. ), and is connected to the hydraulic oil tank 7 via the oil passage 22 .

The hoist switching valve 6 is biased so as to be held at the B0 position, which is the neutral position, when pilot pressure is not applied to both of its pilot ports 6a and 6b. At the B0 position, the hoisting switching valve 6 opens the center bypass oil passage 10 on the upstream side to the center bypass oil passage 10 on the downstream side, and closes both the oil passages 21a and 21b on the hoisting motor 3 side. is configured to

Therefore, in the B0 position (neutral position) of the hoisting switching valve 6, the hydraulic oil flowing into the hoisting switching valve 6 from the center bypass oil passage 10 on the upstream side of the hoisting switching valve 6 is supplied to the hoisting motor 3. Instead, it flows into the center bypass oil passage 10 on the downstream side of the hoisting switching valve 6 .

When a pilot pressure equal to or higher than a predetermined value is applied to the pilot port 6a of the hoisting switching valve 6, the hoisting switching valve 6 is displaced from the B0 position (neutral position) to the Ba position as the pilot pressure increases. At the Ba position, the hoist switching valve 6 closes the center bypass oil passage 10 on the upstream side with respect to the center bypass oil passage 10 on the downstream side, and opens the oil passage 21a on the hoist motor 3 side. , the oil passage 21b on the hoisting motor 3 side is opened to the center bypass oil passage 10 on the downstream side.

Further, in the process of displacing the hoist switching valve 6 from the B0 position to the Ba position, the oil passage (bleed-off oil passage) between the upstream center bypass oil passage 10 and the downstream center bypass oil passage 10 is opened. , gradually decreases as the pilot pressure applied to the pilot port 6a increases, or the opening of the oil passage (meter-in oil passage) between the center bypass oil passage 10 and the oil passage 21a on the upstream side It is configured to gradually increase as the pilot pressure applied to the port 6a increases.

Therefore, when the hoisting switching valve 6 is operated to the Ba position, the hydraulic oil flowing into the hoisting switching valve 6 from the center bypass oil passage 10 on the upstream side of the hoisting switching valve 6 flows from the hoisting switching valve 6 to the oil passage 21a. Hydraulic oil is supplied to the inlet/outlet port 3a of the hoisting motor 3 via and discharged from the other inlet/outlet port 3b of the hoisting motor 3 through the oil passage 21b and the hoisting switching valve 6 at the Ba position. , to the center bypass oil passage 10 on the downstream side. Furthermore, as the pilot pressure applied to the pilot port 6a increases, the flow rate of hydraulic oil supplied to the inlet/outlet port 3a of the hoist motor 3 increases.

When a pilot pressure of a predetermined value or more is applied to the pilot port 6b of the hoisting switching valve 6, the hoisting switching valve 6 is displaced from the B0 position (neutral position) to the Bb position as the pilot pressure increases. At the Bb position, the hoisting switching valve 6 closes the center bypass oil passage 10 on the upstream side with respect to the center bypass oil passage 10 on the downstream side, and opens the oil passage 21b on the hoisting motor 3 side. , the oil passage 21a on the hoisting motor 3 side is opened to the center bypass oil passage 10 on the downstream side.

Further, in the process of moving the hoisting switching valve 6 from the B0 position to the Bb position, the oil passage (bleed-off oil passage) between the upstream center bypass oil passage 10 and the downstream center bypass oil passage 10 is opened. , gradually decreases as the pilot pressure applied to the pilot port 6b increases, or the opening of the oil passage (meter-in oil passage) between the center bypass oil passage 10 and the oil passage 21b on the upstream side It is configured to gradually increase as the pilot pressure applied to the port 6b increases.

Therefore, when the hoisting switching valve 6 is operated to the Bb position, the hydraulic oil flowing into the hoisting switching valve 6 from the center bypass oil passage 10 on the upstream side of the hoisting switching valve 6 flows from the hoisting switching valve 6 to the oil passage 21b. Hydraulic oil is supplied to the inlet/outlet port 3b of the hoisting motor 3 via and discharged from the other inlet/outlet port 3a of the hoisting motor 3 through the oil passage 21a and the hoisting switching valve 6 at the Bb position. , to the center bypass oil passage 10 on the downstream side. Furthermore, as the pilot pressure applied to the pilot port 6b increases, the flow rate of hydraulic oil supplied to the inlet/outlet port 3b of the hoisting motor 3 increases.

The pilot ports 6a and 6b of the hoisting switching valve 6 are connected to an operating device 23 provided with an operating lever 23a for operating the hoisting motor 3 through pilot oil passages 24a and 24b, respectively.

Similar to the operating device 13 for the traveling motor 2, the operating device 23 generates a pilot pressure according to the operation of the operating lever 23a from the primary pressure pilot hydraulic oil supplied from a pilot pump (not shown). Of the pilot ports 6a and 6b, the pressure is output to the pilot port 6a or 6b, which is specified according to the operating direction of the operating lever 23a.

For example, when the operating lever 23a is operated in the direction to operate the hoisting motor 3 in the normal direction, the operating device 23 outputs a pilot pressure corresponding to the amount of operation of the operating lever 23a to the pilot port 6a. . Further, when the operating lever 23a is operated in the direction to operate the hoisting motor 3 in the reverse direction, the operating device 23 outputs a pilot pressure corresponding to the amount of operation of the operating lever 23a to the pilot port 6b.

The hydraulic system 1 of this embodiment further includes a counterbalance valve 30 interposed in oil passages 11a and 11b between the travel switching valve 5 and the travel motor 2, and a counterbalance valve 30 between the counterbalance valve 30 and the travel motor 2. Two relief valves 33a, 33b respectively interposed in two oil passages 32a, 32b connecting the oil passages 11a, 11b , and connected to the oil passages 11a, 11b between the counterbalance valve 30 and the traveling switching valve 5 , and a switching valve 35 .

The counterbalance valve 30 is a pilot-driven switching valve and has two pilot ports 30a and 30b. The counterbalance valve 30 has operating positions C0, which is a neutral position, Ca, which is an operating position when a pilot pressure equal to or higher than a predetermined value is applied to the pilot port 30a, and a predetermined pressure at the pilot port 30b. and a Cb position, which is an operating position when the above pilot pressure is applied.

The pilot ports 30a, 30b of the counterbalance valve 30 are respectively connected to the oil passages 11a, 11b via the pilot oil passages 31a, 31b. Accordingly, pilot pressure is applied to the pilot ports 30 a and 30 b of the counterbalance valve 30 basically according to the operating state of the travel switching valve 5 .

Specifically, when the travel switching valve 5 is held at the A0 position (neutral position), the pilot ports 30a and 30b of the counterbalance valve 30 are not applied with pilot pressure. In this state, the counterbalance valve 30 is biased to be held at the neutral position C0. At the C0 position, the counterbalance valve 30 functions as a check valve for both oil passages 11a and 11b, and operates in the direction from the travel switching valve 5 toward the travel motor 2 in both oil passages 11a and 11b. It is configured to allow the flow of oil while blocking the flow of hydraulic oil in the opposite direction.

Therefore, at the C0 position, the hydraulic oil is prevented from flowing through the travel motor 2, and the travel motor 2 is thus held in a stopped state.

Further, when the travel switching valve 5 is moved from the A0 position (neutral position) to the Aa position, the pressure in the oil passage 11a to which hydraulic oil is supplied from the hydraulic pump 4 becomes higher than the pressure in the oil passage 11b. A higher pilot pressure is applied to the pilot port 30a of the valve 30 than to the pilot port 30b. In this state, the counterbalance valve 30 operates to the Ca position. At the Ca position, the counterbalance valve 30 is configured to open the oil passage 11b and to function as a check valve for the oil passage 11a in the same manner as at the C0 position (neutral position). It is configured.

Therefore, when the travel switching valve 5 moves from the A0 position to the Aa position, the counterbalance valve 30 moves from the C0 position to the Ca position in conjunction with this. As a result, the traveling motor 2 operates while the hydraulic oil is supplied to the inlet/outlet port 2a of the traveling motor 2 and the hydraulic oil is discharged from the inlet/outlet port 2b.

Further, when the travel switching valve 5 is moved from the A0 position (neutral position) to the Ab position, the pressure in the oil passage 11b to which the hydraulic oil is supplied from the hydraulic pump 4 becomes higher than the pressure in the oil passage 11a. A pilot pressure higher than that of the pilot port 30a is applied to the pilot port 30b of the valve 30 . In this state, the counterbalance valve 30 operates to the Cb position. At the Cb position, the counterbalance valve 30 is configured to open the oil passage 11a and to function as a check valve for the oil passage 11b as at the C0 position (neutral position). It is configured.

Therefore, when the travel switching valve 5 moves from the A0 position to the Ab position side, the counterbalance valve 30 moves from the C0 position to the Cb position in conjunction therewith. As a result, the traveling motor 2 operates while the hydraulic oil is supplied to the inlet/outlet port 2b of the traveling motor 2 and the hydraulic oil is discharged from the inlet/outlet port 2a.

The relief valves 33a and 33b are for generating brake pressure when the operation of the travel motor 2 is released (when the traveling drive of the crawler 51a of the lower travel body 51 by the travel motor 2 is released). In this case, the relief valve 33b is opened when the counterbalance valve 30 returns from the Ca position to the C0 position as the operating position of the travel switching valve 5 returns from the Aa position to the A0 position. When the pressure of the hydraulic oil on the 2b side (the hydraulic oil discharged from the traveling motor 2) becomes higher than the pressure of the hydraulic oil on the inlet/outlet port 2a side by a predetermined set pressure or higher, the oil passage 32b is opened ( Hydraulic oil is recirculated from the inlet/outlet port 2b of the traveling motor 2 to the inlet/outlet port 2a through the oil passage 32b).

In addition, the relief valve 33a is opened when the counterbalance valve 30 returns from the Cb position to the C0 position as the operating position of the travel switching valve 5 returns from the Ab position to the A0 position. When the pressure of the hydraulic oil on the side (the hydraulic oil discharged from the traveling motor 2) becomes higher than the pressure of the hydraulic oil on the inlet/outlet port 2b side by a predetermined set pressure or more, the oil passage 32a is opened (and eventually , the working oil is circulated from the inlet/outlet port 2a of the travel motor 2 to the inlet/outlet port 2b through the oil passage 32a).

The switching valve 35 is a pilot-driven switching valve interposed in an oil passage 36 whose both ends are connected to the oil passages 11a and 11b (two travel motor oil passages). 35b. The switching valve 35 has three operating positions: D0, which is a neutral position; Da, which is an operating position when a pilot pressure equal to or greater than a predetermined value is applied to the pilot port 35a; and a Db position, which is an operating position when a pilot pressure of . The D0 position (neutral position) is an operating position that closes the oil passage 36 through which hydraulic oil can flow from one of the oil passages 11a and 11b to the other through the switching valve 35, and is the second state of the present invention. corresponds to Both the Da position and the Db position are operating positions for opening the oil passage 36, and correspond to the first state in the present invention.

In the process of shifting from the D0 position to the Da position or Db position, the switching valve 35 gradually enlarges the opening of the oil passage 36 as the pilot pressure applied to the pilot port 35a or 35b increases. It is configured.

A pilot port 35a of the switching valve 35 has a passage portion in which a check valve 37a and a throttle portion 38a are connected in parallel to an oil passage 21a connected to one inlet/outlet port 3a of the hoisting motor 3. They are connected via passage 39a. In this case, the check valve 37a is configured to allow the pilot hydraulic fluid to flow in the direction from the oil passage 21a to the pilot port 35a and prevent the pilot hydraulic fluid to flow in the opposite direction.

A pilot port 35b of the switching valve 35 has a passage portion in which a check valve 37b and a throttle portion 38b are connected in parallel to an oil passage 21b connected to the other input/output port 3b of the hoisting motor 3. They are connected via passage 39b. In this case, the check valve 37b is configured to allow the pilot hydraulic fluid to flow in the direction from the oil passage 21b to the pilot port 35b and prevent the pilot hydraulic fluid to flow in the opposite direction.

Therefore, when the hoisting motor 3 is in operation (when hydraulic oil is supplied to the inlet/outlet port 3a or 3b of the hoisting motor 3), if the pressure of the hydraulic oil flowing into the inlet/outlet port 3a or 3b of the hoisting motor 3 becomes greater than or equal to a predetermined value, of the oil passages 21a and 21b connected to the hoisting motor 3, from the oil passage 21a or 21b on the side supplying the operating oil to the hoisting motor 3, through the pilot oil passage 39a or 39b to the pilot port 35a or 35b. A pilot pressure greater than or equal to the value is applied. As a result, the switching valve 35 is operated from the D0 position (neutral position) to the Da position side or the Db position side, and the oil passages 11a and 11b are operated to the Da position side or the Db position side. 36.

Since the hydraulic device 1 of this embodiment is configured as described above, the following effects can be obtained. For example, in order to move an object suspended on the hook 59, the operating lever 23a of the operating device 23 is operated to operate the hoist switching valve 6 to the Ba position side or the Bb position side, and the hydraulic pump 4 to the center bypass oil passage is opened. 10 and the hoisting switching valve 6 to the hoisting motor 3, in order to operate the traveling motor 2, the operating lever 13a of the operating device 13 is operated to set the traveling switching valve 5 to the A0 position (neutral). position) to the Aa position side or the Ab position side.

In this case, the counterbalance valve 30 moves from the C0 position to the Ca position side or the Cb position side in conjunction with the operation of the travel switching valve 5, thereby connecting the hydraulic pump 4 to the travel switching valve 5 and the oil passages 11a and 11b. Hydraulic oil is supplied to the traveling motor 2 through one of the hydraulic fluid passages 11a and 11b, and the hydraulic fluid discharged from the traveling motor 2 is supplied to the other of the oil passages 11a and 11b, the traveling switching valve 5, and the downstream side of the oil passages 11a and 11b. The oil is supplied to the hoisting motor 3 through the center bypass oil passage 10 and the hoisting switching valve 6 .

Here, since the objects to be transported suspended from the hook 59 are often heavy objects, the load on the hoisting motor 3 is often quite large. In such a case, of the oil passages 11a and 11b, the oil passage 11a or 11b on the discharge side (return side of hydraulic oil) of the traveling motor 2 may 21b, if the switching valve 35 and the oil passage 36 were not provided, the pressure in the oil passage 11a or 11b on the discharge side of the travel motor 2 would rise to a large pressure, and the pressure on the supply side of the travel motor 2 would increase. The pressure in the oil passage 11b or 11a on the discharge side rises to a pressure equal to or higher than the pressure in the oil passage 11a or 11b on the discharge side.

As a result, high pressure is applied to both the inlet/outlet ports 2a and 2b of the travel motor 2, which may cause problems such as damage to the cylinder block of the travel motor 2.

However, in this embodiment, when the pressure in the oil passage 21a or 21b on the supply side of the hydraulic oil of the hoisting motor 3 becomes greater than a predetermined value, the oil passage 21a or 21b on the supply side will flow to the pilot oil passage 39a or 39b. The pilot pressure applied to the pilot port 35a or 35b of the switching valve 35 via , actuates the switching valve 35 to the Da position side or the Da position side.

As a result, the oil passages 11 a and 11 b between the travel switching valve 5 and the counterbalance valve 30 communicate with each other via the oil passage 36 and the switching valve 35 . Therefore, the hydraulic oil supplied from the hydraulic pump 4 to the oil passage 11a or 11b via the travel switching valve 5 is not supplied to the travel motor 2, but is supplied from the oil passage 11a or 11b to the oil passage 36, The oil is supplied to the hoisting motor 3 through the return side oil passage 11b or 11a, the traveling switching valve 5, the center bypass oil passage 10 on the downstream side thereof, and the hoisting switching valve 6.

As a result, high pressure is prevented from acting on both the input/output ports 2a and 2b of the travel motor 2, thereby preventing problems such as damage to the travel motor 2. FIG. In this case, the oil passages 11a and 11b between the travel switching valve 5 and the counterbalance valve 30 communicate with each other via the oil passage 36 and the switching valve 35, thereby eliminating the pressure difference between the oil passages 11a and 11b. Therefore, the counterbalance valve 30 automatically returns to the C0 position (neutral position). Therefore, the traveling motor 2 is held in a stopped state. Therefore, when the load on the hoisting motor 3 is large, the operation of the traveling motor 2 is substantially prohibited.

Also, when the load on the hoisting motor 3 is reduced by releasing the load on the hook 59 or the like, the switching valve 35 returns to the D0 position (neutral position). In this return operation, hydraulic oil is discharged through the throttle portion 38a or 38b from the pilot port 35a or 35b of the switching valve 35 to which the high-pressure pilot pressure is applied, so that the pilot pressure gradually decreases. . As a result, the switching valve 35 gradually returns from the Da position or the Db position to the D0 position (neutral position).

Therefore, when the load on the hoisting motor 3 becomes small, even if the operation lever 13a of the operation device 13 is operated to operate the travel switching valve 5 to the Aa position or the Ab position, the travel motor 2 is not operated. A sudden increase in the supply amount of hydraulic oil (and thus a sudden start of operation of the travel motor 2) is prevented.

It should be noted that the present invention is not limited to the embodiments described above, and other embodiments can be employed. Some other embodiments are described below.

In the above embodiment, the switch valve 35 between the oil passages 11a and 11b has three operating positions D0, Da and Db. and a set of pilot ports 35b (a switching valve having two operating positions) can be used instead of the switching valve 35. FIG. In this case, the pilot pressure may be applied from the oil passages 21a and 21b to the pilot port for moving the switching valve from the neutral position (valve closed position) to the valve open position via the shuttle valve.

Further, instead of using the pressure in the oil passages 21a and 21b as pilot pressure to operate the switching valve 35, for example, a pressure sensor for detecting the pressure in the oil passages 21a and 21b is provided, It is also possible to actuate the switching valve 35 via a proportional valve or the like.

In the above embodiment, the check valves 37a, 37b and throttle portions 38a, 38b connected in parallel are interposed in the pilot oil passages 39a, 39b for the switching valve 35, respectively. 37a, 37b and throttle portions 38a, 38b may be omitted.

In the above-described embodiment, the hoisting device 56 is a device for moving the hook 59 via the wire 58, but the hoisting device in the present invention, for example, raises and lowers the boom 54 (jib) via the wire. It may be a device that allows

Further, the hydraulic system 1 of the above embodiment has the counterbalance valve 30 and the relief valves 33a and 33b in the hydraulic circuit for the travel motor 2, but the hydraulic system of the present invention includes the counterbalance valve 30 and the relief valves One or both of the valves 33a and 33b may be omitted.

The construction machine 50 of the above embodiment is a mobile crane having the structure shown in FIG. may have been Also, the construction machine may be a construction machine other than a mobile crane.

DESCRIPTION OF SYMBOLS 1... Hydraulic system 2... Traveling motor 3... Hoisting motor 4... Hydraulic pump 5... Traveling switching valve 6... Hoisting switching valve 11a, 11b... Oil passage (oil passage for traveling motor) 21a, 21b... Oil passage (oil passage for hoisting motor) 35...Switching valve 37a, 37b...Check valve 38a, 38b...Throttle portion 39a, 39b...Pilot oil passage.

Claims (3)

A traveling motor that is a hydraulic motor for traveling, a hoisting motor that is a hydraulic motor for driving a hoisting device, a hydraulic pump that discharges hydraulic oil, and a traveling switching valve that is a directional switching valve connected to the traveling motor. and a hoisting switching valve, which is a directional switching valve connected to the hoisting motor, and the traveling switching valve is arranged so that the hydraulic oil discharged from the hydraulic pump flows upstream of the hoisting switching valve. The hoist switching valve is connected to the hydraulic pump, and the hydraulic oil discharged from the hydraulic pump flows in via the travel switching valve when the travel motor stops operating, and the travel motor is connected to the travel switching valve so as to flow in through the travel switching valve and the travel motor, wherein
Two travel motor oil passages are connected between the travel switching valve and the travel motor, and the two travel motor oil passages are communicated with each other in a first state and the communication is cut off. and a switching valve that is operable in the second state, and the switching valve switches to the above-described second state when the pressure of hydraulic oil supplied from the hoisting switching valve to the hoisting motor reaches a high pressure equal to or higher than a predetermined value. A hydraulic system for a construction machine, characterized in that it operates according to the pressure so as to switch from the second state to the first state. In the hydraulic system for construction machinery according to claim 1,
The switching valve has two hoists that flow hydraulic fluid between the hoisting switching valve and the hoisting motor so that the pressure of hydraulic fluid supplied from the hoisting switching valve to the hoisting motor is applied as pilot pressure. 1. A hydraulic system for construction machinery, comprising: a pilot-driven switching valve connected to a motor oil passage through a pilot oil passage. In the hydraulic system for construction machinery according to claim 2,
The pilot oil passage is provided with a check valve and a throttle portion which are connected in parallel with each other. A hydraulic system for a construction machine, characterized in that it is configured to block the flow of hydraulic oil.

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