JP2540574Y2 - Hydraulic drive traveling device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive device applied to a construction machine such as an excavator.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional example of a hydraulically driven traveling device used for an excavator in a construction machine, for example, a hydraulic shovel.
This will be described with reference to FIG. The main hydraulic pumps 2 and 2 a and the pilot hydraulic pump 4 are provided so as to be driven by the engine 6. The main hydraulic pumps 2 and 2a are variable displacement hydraulic pumps, and are provided with swash plate control devices 3 and 3a, which are variable displacement mechanisms, respectively. The pressure oil discharged from the main hydraulic pump 2 is supplied to a hydraulic motor 10 via a pressure oil supply oil passage 8. The pressure oil discharged from the main hydraulic pump 2a is supplied to the hydraulic motor 10 via the pressure oil supply oil passage 8a.
a. The hydraulic motor 10 drives one of the hydraulic excavators (not shown), for example, the left traveling device, and the hydraulic motor 10a drives the other, for example, the right traveling device. Each of the left and right traveling devices has substantially the same configuration except for parts common to the traveling devices. Therefore, only the left traveling device will be described below unless necessary. Regarding the traveling device on the right side, the portions corresponding to the traveling device on the left side are indicated by the same numbers with the alphabetical letter a.

The pressure oil supply oil passage 8 is provided with a direction control valve 12 and a counter balance valve 14. The counter balance valve 14 is driven by the pressure oil discharged from the main hydraulic pump 2. The hydraulic motor 10 is a variable displacement hydraulic motor, and includes a variable displacement mechanism (not shown) including a high-speed piston 16 and a low-speed piston 18. Hydraulic motor 1
The zero discharge oil passage 20 is connected to the oil tank 22 through the counter balance valve 14 and the direction control valve 12. Shuttle valve 24 and overload relief valve 26 are provided in oil passages provided in parallel to connect between hydraulic oil supply oil passage 8 to hydraulic motor 10 and discharge oil passage 20 of hydraulic motor 10, respectively. Have been. An output-side oil passage 28 of the shuttle valve 24 is connected to the pistons 16 and 18 of the hydraulic motor 10 via a capacity switching valve 30. The capacity switching valve 30 is for controlling switching of the capacity of the hydraulic motor 10. When the displacement switching valve 30 is positioned at the low speed traveling position of the chamber A, the discharge pressure oil of the main hydraulic pump 2 is supplied to the low speed piston 18 via the shuttle valve 24, and the high speed piston 16 is returned to the return oil passage 32. Is connected to the oil tank 22. Also, the capacity switching valve 30
Is located at the high-speed traveling position of the chamber B, the discharge pressure oil of the main hydraulic pump 2 is supplied to the high-speed piston 16 through the shuttle valve 24, and the low-speed piston 18 is returned through the return oil passage 32. Connected to oil tank 22. Reference numeral 34 in the drawing indicates a main relief valve.

[0004] The capacity switching valve 30 is controlled by the pilot pressure of the pilot hydraulic pump 4. That is, the pilot hydraulic pump 4 and the pilot port of the capacity switching valve 30 are connected via the pilot oil passage 36. The pilot oil passage 36 is provided with an electromagnetic switching valve 38 and an automatic second-speed switching valve 40 that constitute second-speed switching valve means.
The electromagnetic switching valve 38 is normally positioned at the low-speed traveling position in the room A, but is switched to the high-speed traveling position in the room B by turning on a switch provided in the driver's seat. When the switch is turned off, it is automatically returned to the position of the room A. When the electromagnetic switching valve 38 is positioned at the low-speed traveling position of the chamber A, the pilot oil passage 36 is connected to the oil tank 22. When the electromagnetic switching valve 38 is positioned at the high-speed traveling position of the chamber B, the pilot oil passage 3
6 communicates and is supplied with pilot pressure.

[0005] The pilot port of the automatic two-speed switching valve 40 is connected to an output-side oil passage 44 of a shuttle valve 42 provided between the left and right pressure oil supply oil passages 8 and 8a. Automatic 2
The speed switching valve 40 is normally located at the high-speed traveling position of the room A. When the load on the traveling device increases and the oil pressure in the discharge oil passages of the main hydraulic pumps 2 and 2a rises above a predetermined level, the oil pressure acts on the pilot port of the automatic two-speed switching valve 40, and the automatic two-speed switching valve 40 Is automatically shifted to the low-speed traveling position of the room B. Also, from this state, when the load on the traveling device decreases and the oil pressure in the discharge oil passages of the main hydraulic pumps 2 and 2a decreases to a predetermined value, the room A is automatically returned to the high-speed traveling position in the room A. When the automatic second-speed switching valve 40 is positioned at the high-speed traveling position in the chamber A, the pilot oil passage 36 is connected, and the pilot pressure is supplied. When the automatic second speed switching valve 40 is positioned at the low speed traveling position of the chamber B, the pilot oil passage 36 is connected to the oil tank 22. As is clear from the above description, when the pilot pressure is supplied to the pilot oil passage 36, the capacity switching valve 30 is positioned at the high-speed traveling position of the chamber B.
When the pilot oil passage 36 is connected to the oil tank 22, the capacity switching valve 30 is positioned at the low-speed traveling position of the chamber A. Reference numeral 46 in the drawing indicates a pilot relief valve.

Next, the operation of the conventional hydraulically driven traveling apparatus having the above-described structure will be described. As described above, only the operation of the left traveling device will be described. When the direction control valve 12 is switched from the neutral position in the drawing to the chamber A or the chamber B, the pressure oil discharged from the main hydraulic pump 2 is supplied to the hydraulic motor 10 via the counter balance valve 14. Thereby, the hydraulic motor 10 is driven. When the electromagnetic switching valve 38 is located at the low-speed traveling position of the chamber A, the pilot pressure does not act on the pilot port of the capacity switching valve 30, so that the capacity switching valve 30 is located at the low-speed traveling position of the chamber A. The pressure oil discharged from the main hydraulic pump 2 is supplied to the low-speed piston 18 via the shuttle valve 24. Therefore, the hydraulic motor 10 is driven in the low speed mode, and the traveling device travels at a low speed.

When the electromagnetic switching valve 38 is positioned at the high-speed traveling position of the chamber B, the pilot pressure acts on the pilot port of the capacity switching valve 30, and the capacity switching valve 30 is moved to the high-speed traveling position of the chamber B. Will be shifted. The discharge pressure oil of the main hydraulic pump 2 is supplied to the high-speed piston 16 via the shuttle valve 24. Therefore, the hydraulic motor 10 is driven in the high-speed mode, and the traveling device travels at a high speed. In this high-speed traveling state, when the load of the traveling device increases as the hydraulic excavator starts to climb the slope from the flat road, the discharge pressure of the main hydraulic pump 2 increases. This high discharge pressure acts on the pilot port of the automatic 2-speed switching valve 40 via the shuttle valve 42, and the automatic 2-speed switching valve 40 is automatically shifted to the low-speed traveling position of the chamber B. The pilot pressure acting on the pilot port of the capacity switching valve 30 becomes zero, and the capacity switching valve 30 is shifted to the low-speed traveling position of the chamber B. Accordingly, the hydraulic motor 10 is switched from the high-speed mode to the low-speed mode, and the traveling device travels uphill at a low speed.

[0008]

As described above, when the hydraulic excavator is traveling in the high-speed mode, the excavator may come down on a slope. In this case, the operator needs to shift the electromagnetic switching valve 38 to the low-speed traveling position in the room A by turning on the switch in the driver's seat. If the operator inadvertently goes downhill in the high-speed mode, there is a danger that the hydraulic shovel will run away. That is, when the hydraulic motor 10 is driven from the traveling device side during a downhill in the high-speed mode,
Since it does not have a sufficient braking function, runaway cannot be prevented unless the operator performs the switching operation to the low speed mode as described above. Particularly on a steep downhill or a gentle but long downhill, the danger is extremely high due to the carelessness of the operator.

Accordingly, an object of the present invention is to provide an improved hydraulically driven traveling device which can surely eliminate the danger of runaway when the construction machine is going downhill, and can always ensure safe traveling. is there.

[0010]

According to the present invention, in order to achieve the above main object, the hydraulic pump is provided in a hydraulic oil supply passage from a hydraulic pump to a hydraulic motor having a variable displacement mechanism. A counterbalance valve driven by pressure oil, a capacity switching valve for switching and controlling the capacity of the hydraulic motor, and a pilot port of the capacity switching valve via a second speed switching valve means for discharging pressure oil from a pilot hydraulic pump. And a shuttle valve provided in an oil passage connecting the pressure oil supply oil passage and the discharge oil passage of the hydraulic motor, and an output-side oil passage of the shuttle valve has the capacity. In the hydraulic drive traveling device configured to be connected to the variable displacement mechanism via a switching valve, a pilot switching valve is provided in the pilot oil passage, and one pilot port of the pilot switching valve is The other pilot port is connected to the pressure oil supply oil passage, and the other pilot port is connected to the output oil passage of the shuttle valve, and only when the oil pressure of the output oil passage is higher than the oil pressure of the pressure oil supply oil passage, A hydraulically driven traveling device is provided, wherein the pilot switching valve is configured such that the pilot oil passage is connected to an oil tank so that the displacement switching valve can be switched to a low-speed traveling position.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a hydraulically driven traveling device improved in accordance with the present invention; In FIG. 1, the same parts as those in FIG. 2, which is a conventional apparatus, are denoted by the same reference numerals, and description thereof will be omitted. As in the description of the conventional device, only the configuration of the traveling device on the left side will be described, and the method of attaching reference numerals on the right side will be described with reference to FIG.
Same as A pilot switching valve 48 is provided downstream of the automatic second speed switching valve 40 in the pilot oil passage 36. One pilot port of the pilot switching valve 48 is connected to the pressure oil supply oil passage 8 of the main hydraulic pump 2. That is, in this example, the counter balance valve 1
4, a pressure detection port 50 connected to the pressure oil supply oil passage 8 is provided. The pressure detection port 50 is connected to the pressure oil supply oil passage 8 when the counter balance valve 14 switches to a position other than the neutral position of the chamber A or the chamber B. The one pilot port of the pilot switching valve 48 is connected to the pressure detection port 50. The other pilot port of the pilot switching valve 48 is connected to the output-side oil passage 28 of the shuttle valve 24. When pilot switching valve 48 is located in chamber B, pilot oil passage 36 and oil tank 22 are connected via return oil passage 52. When the oil pressure of the pressure oil supply oil passage 8 is substantially equal to or higher than the oil pressure of the output oil passage 28 of the shuttle valve 24,
The pilot switching valve 48 is positioned in the chamber A, and opens the pilot oil passage 36 so that pilot pressure can be supplied to the pilot port of the capacity switching valve 30. The pilot switching valve 48 is positioned in the chamber B only when the oil pressure in the output oil passage 28 of the shuttle valve 24 is higher than the oil pressure in the pressure oil supply oil passage 8. Thereby, the pilot oil passage 36 returns to the oil tank 22 and is connected via the oil passage 52, and the capacity switching valve 30 is switched to the low-speed traveling position of the chamber A.

Next, the operation of the hydraulically driven traveling device according to the present invention configured as described above will be described. Note that, similarly to the conventional device, only the operation of the left traveling device will be described. When the hydraulic motor 10 is driven in the low-speed mode and the traveling device is traveling at a low speed, the oil pressure of the pressure oil supply oil passage 8 and the oil pressure of the output oil passage 28 of the shuttle valve 24 are substantially equal. The pilot switching valve 48 is positioned in the chamber A by the action of a spring force, and the pilot oil passage 36 is in a communicating state. However, since the electromagnetic switching valve 38 upstream of the pilot oil passage 36 is positioned at the low-speed traveling position of the chamber A, the pilot oil passage 36 is connected to the oil tank 22. As a result, since the pilot pressure is not supplied to the pilot port of the capacity switching valve 30, the capacity switching valve 30 is positioned at the low-speed traveling position of the chamber A.

The hydraulic motor 10 is driven in a high speed mode,
When the traveling device is traveling at a high speed, the hydraulic pressure of the pressure oil supply oil passage 8 and the hydraulic pressure of the output side oil passage 28 of the shuttle valve 24 are substantially equal. And the pilot oil passage 36 is in a communicating state. On the other hand, since the electromagnetic switching valve 38 is positioned at the high-speed traveling position of the chamber B, the pilot oil passage 36 is connected to the pilot hydraulic pump 4. As a result, the pilot pressure is supplied to the pilot port of the capacity switching valve 30, so that the capacity switching valve 30 is positioned at the high-speed traveling position of the chamber B.

In this high-speed running state, when the vehicle travels down a hill, the load on the traveling device decreases, so that the discharge pressure of the main hydraulic pump 2, that is, the hydraulic pressure of the pressure oil supply oil passage 8 decreases.
As a result, the pressure detection port 5 of the counterbalance valve 14
The oil pressure of 0 drops. On the other hand, due to a decrease in the discharge pressure of the main hydraulic pump 2, the counterbalance valve 14 moves in a direction of returning from the position of the chamber A or B to the neutral position. Due to this movement, a hydraulic pressure is generated in the discharge oil passage 20 of the hydraulic motor 10. As a result, the output side oil passage 28 of the shuttle valve 24
Is higher than the oil pressure at the pressure detection port 50, the pilot switching valve 48 is shifted to the chamber B. Thereby, the pilot oil passage 36 is connected to the oil tank 22, and the capacity switching valve 30 is switched to the low-speed traveling position of the chamber A. The pressure oil in the output-side oil passage 28 of the shuttle valve 24 is supplied to the low-speed piston 16, the hydraulic motor 10 automatically enters the low-speed mode, and the traveling device travels downhill safely at low speed.

When the vehicle returns to a flat road from the high speed / downhill traveling state described above, the load on the traveling device increases, so that the discharge pressure of the main hydraulic pump 2 also increases. Since the oil pressure at the pressure detection port 50 of the counterbalance valve 14 is higher than the oil pressure at the output oil passage 28 of the shuttle valve 24, the pilot switching valve 4
8 is automatically switched to chamber A, and pilot oil passage 3
6 becomes a communication state. As a result, the pilot pressure is supplied to the pilot port of the capacity switching valve 30, so that the capacity switching valve 30 is switched to the high-speed traveling position of the chamber B.

Although the present invention has been described in detail based on the embodiments, the present invention is not limited to the above-described embodiments, but can be variously modified or modified within the scope of the present invention. . For example, in this embodiment, the counterbalance valve 14 is provided with a pressure detection port 50 connected to the pressure oil supply oil passage 8, and one pilot port of the pilot switching valve 48 is connected to the pressure detection port 50. It is configured to be. The following configuration is considered as another example of the pressure detection port 50.
That is, the counterbalance valve 14 having the configuration shown in FIG. 2 is provided instead of the counterbalance valve 14 provided in the circuit of FIG. Furthermore, a communication oil path is provided between the upstream position of the counterbalance valve 14 in the pressure oil supply oil path 8 and the downstream position of the counterbalance valve 14 in the discharge oil path 20, and a shuttle valve is provided in the communication oil path. . The output side oil passage of this shuttle valve is connected to the pilot switching valve 48.
To one of the pilot ports. It will be apparent that the output side oil passage of the shuttle valve has the same function as the pressure detection port 50.

[0017]

According to the invention described above based on one embodiment, the following effects can be achieved. (1) Since the hydraulically driven traveling device according to the present invention is configured to automatically switch to the low speed mode regardless of the operator's intention when traveling downhill during traveling in the high speed mode, the downhill of the construction machine is used. The danger of runaway at times can be reliably removed, and safe driving is always guaranteed. (2) Since the present invention is configured by providing a pilot switching valve in a pilot oil passage of a hydraulic circuit in a conventional hydraulic drive traveling device, it can be put into practical use very easily and at low cost.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a hydraulically driven traveling device improved according to the present invention.

FIG. 2 is a hydraulic circuit diagram showing a conventional hydraulic drive device.

[Explanation of symbols]

 2 Main hydraulic pump 4 Pilot hydraulic pump 8 Pressure oil supply oil passage 10 Hydraulic motor 12 Directional control valve 14 Counter balance valve 16 Low speed piston 18 High speed piston 20 Discharge oil passage 24 Shuttle valve 28 Shuttle valve output oil passage 30 Capacity Switching valve 36 Pilot oil passage 38 Electromagnetic switching valve 40 Automatic 2-speed switching valve 48 Pilot switching valve 50 Pressure detection port

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-203434 (JP, A) JP-A-2-134302 (JP, U) JP-A-3-279 (JP, U)

Claims (1)

(57) [Scope of request for utility model registration] 1. A counterbalance valve provided from a hydraulic pump to a hydraulic oil supply oil path to a hydraulic motor having a variable displacement mechanism and driven by the hydraulic oil of the hydraulic pump, the capacity of the hydraulic motor being adjusted. A displacement switching valve for switching control, a pilot oil passage for supplying discharge pressure oil from a pilot hydraulic pump to a pilot port of the displacement switching valve via a two-speed switching valve means, the pressure oil supply oil passage, and the hydraulic motor And a shuttle valve provided in an oil passage connecting the discharge oil passage to the hydraulic pump, wherein an output oil passage of the shuttle valve is connected to the variable displacement mechanism via the displacement switching valve. In the drive traveling device, a pilot switching valve is provided in the pilot oil passage, one pilot port of the pilot switching valve is connected to the pressure oil supply oil passage, and the other pilot port is The pilot switching valve connects the pilot oil passage to an oil tank only when the oil pressure of the output oil passage is higher than the oil pressure of the pressure oil supply oil passage. A hydraulically driven traveling device characterized in that the displacement switching valve can be switched to a low-speed traveling position.