EP1300519A9

EP1300519A9 - Hydraulic circuit and attachment emergency drive method for construction machinery

Info

Publication number: EP1300519A9
Application number: EP01934472A
Authority: EP
Inventors: Hiroshi Onoue; Yasushi Tanaka
Original assignee: Hitachi Construction Machinery Co Ltd
Current assignee: Hitachi Construction Machinery Co Ltd
Priority date: 2000-05-31
Filing date: 2001-05-31
Publication date: 2003-08-06
Anticipated expiration: 2021-05-31
Also published as: DE60143698D1; EP1300519A4; EP1300519B1; EP1300519A1; JP2001336177A; WO2001092651A1

Abstract

A hydraulic circuit includes a hydraulic pilot-operated control valve that controls an actuator for driving a front attachment. A pressure oil injection port that can be connected with a manual hydraulic pump is provided at a pilot line through which a pilot oil pressure is guided to the control valve. Pressure oil is supplied to the pilot line from the port with the manual hydraulic pump to switch the control valve, thus enabling emergency drive of the front attachment. The structure can be achieved through a fairly simple modification, without having to provide a bypass line, a switching valve and the like.

Description

TECHNICAL BACKGROUND

The present invention relates to a hydraulic circuit of a construction machine that drives an actuator for front attachment drive by using a hydraulic pilot control valve and it also relates to an attachment emergency drive method.

BACKGROUND ART

In a construction machine that engages its front attachment in operation by driving a hydraulic cylinder with oil discharged from a hydraulic pump, a failure in the engine or the like that drives the hydraulic pump may result in the front attachment becoming disabled while suspended in the air. Since it is not desirable to leave the attachment suspended above the ground for safety reasons, the attachment must somehow be lowered to the ground.
A construction machine hydraulic circuit which addresses the problem discussed above is disclosed in Japanese Laid-Open Utility Model Publication No. S 59-76659. This hydraulic circuit (first related art example) drives a boom cylinder by employing a hydraulic pilot control valve. It includes a bypass line which is capable of communicating between the cylinder chamber of the boom cylinder and a hydraulic pilot line, with a manual switching valve provided in the bypass line. By manually operating the switching valve when the front attachment, which includes the boom, becomes suspended above the ground, the pressure in the cylinder chamber of the boom cylinder (the pressure attributable to the dead weight of the attachment) is guided to the pilot line via the bypass line. Then, the pressure is applied to the pilot port of the control valve to switch the control valve to the boom-down position. As a result, the cylinder chamber comes into communication with the reservoir via the control valve and the boom is caused to descend by its dead weight.
In addition, there is another hydraulic circuit in the known art, having an accumulator provided at an outlet line extending from the pilot hydraulic source (a second related art example). In this hydraulic circuit, the control valve is switched by the pressure accumulated at the accumulator when the engine is stopped.
However, the hydraulic circuit disclosed in the publication mentioned above (the first related art example) requires additional components such as the bypass line and the manual switching valve. In addition, the hydraulic circuit in the second related art, which must be provided with the accumulator, is bound to be costly due to the inevitable increase in the number of components.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a hydraulic circuit of a construction machine that is capable of driving a front attachment in an emergency with a high degree of safety while assuming a fairly simple structure.
The present invention is adopted in a construction machine hydraulic circuits comprising a hydraulic pump that is driven by an engine, an actuator that is driven with the oil discharged from the hydraulic pump and drives a front attachment and a hydraulic pilot control valve that is switched by a pilot oil pressure to control the inflow/outflow of pressure oil to/from the actuator. The object described above is achieved by providing a pressure oil injection port that can be connected with a manual hydraulic pump (hydraulic source) at a pilot line through which the pilot oil pressure is guided to the control valve and by supplying the pressure oil to the pilot line from the port via the manual hydraulic pump to enable switching of the control valve.
It is desirable that the front attachment include a boom with the pressure oil injection port provided at the pilot line on the boom-down side.
It is also desirable that the pressure oil injection port is provided at a position which is off the travelling locus of the front attachment.
The manual hydraulic pump (hydraulic source) may be constituted by using a grease gun, which is a standard maintenance/inspection tool provided with a construction machine.
In addition, the present invention is adopted in a method of driving an attachment of a construction machine in an emergency. An emergency pilot oil pressure is generated by using a manual grease gun or the like at a pilot line through which a pilot oil pressure is guided to a control valve, and an actuator is engaged in operation by switching the control valve with the pressure oil to drive the attachment.
According to the present invention, in which the pressure oil is supplied to the pilot line from a pressure oil injection port provided at the pilot line with a manual hydraulic pump (e.g., a grease gun) to switch the control valve, emergency drive of the front attachment is achieved through a fairly simple modification. In addition, since it is not necessary to provide a bypass line, a switching valve, an accumulator or the like as required in the related art, a reduction in the production costs is achieved. In particular, by providing the pressure oil injection port at a position which is off the traveling locus of the front attachment, the pressure oil supply can be carried out while assuring safety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a hydraulic excavator mounted with the hydraulic circuit achieved in a first embodiment of the present invention;
FIG. 2 presents a circuit diagram of the hydraulic circuit used to drive a boom provided in the hydraulic excavator;
FIG. 3 shows the structure of a grease gun;
FIG. 4 is a perspective of the hydraulic excavator achieved in a second embodiment;
FIG. 5 is a plan view of the hydraulic excavator shown in FIG. 4;
FIG. 6 presents a circuit diagram of the hydraulic circuit used to drive a boom provided in the hydraulic excavator in FIG. 4; and
FIG. 7 shows the traveling locus of the front attachment of the hydraulic excavator in FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

-First Embodiment-

The first embodiment of the present invention is now explained in reference to FIGS. 1 ^~ 3.
FIG. 1 shows the hydraulic excavator achieved in the embodiment. A front attachment FA which is linked to an upper swiveling body is constituted of a boom 2 driven by a boom cylinder 1, an arm 4 driven by an arm cylinder 3 and a bucket 6 driven by a bucket cylinder 5.
FIG. 2 illustrates the boom drive hydraulic circuit of the hydraulic excavator. A hydraulic pilot-operated control valve 12 is provided between a hydraulic pump 11 which is driven by an engine (not shown) and the boom cylinder 1. The flow rate and the direction of the pressure oil flowing into and out from the boom cylinder 1 are controlled by switching the control valve 12. The control valve 12 is switched by the pilot oil pressure at a pilot hydraulic circuit 20. The pilot hydraulic circuit 20 includes a pilot hydraulic pump 21, pilot valves (pressure reducing valves) 22a and 22b that reduce the discharged pressure at the pilot hydraulic pump 21 and pilot lines 23a and 23b that guide the secondary pressures from the pilot valves 22a and 22b to pilot ports 12a and 12b of the control valve 12. The pilot valves 22a and 22b are operated through an operating lever 22c provided at the driver's cab.
At one of the pilot lines 23a and 23b, i.e., the line 23b on the boom-down side, a stop valve 24 (opening/closing valve) is mounted. The line, which is located on the upstream side relative to the stop valve 24, is referred to as a line 23bU and the line located on the downstream side is referred to as a line 23bL. At a pressure oil injection port 25 provided at the line 23bL on the downstream side relative to the stop valve 24, a hydraulic coupling 26 is mounted. The pressure oil injection port 25 is provided at a position (e.g., at a lower portion of the cabin) that facilitates the pressure oil injection process and is also off the traveling locus of the front attachment FA in consideration of the safety factor. Under normal circumstances, the stop valve 24 is in an open state and the pressure oil injection port 25 is closed by the hydraulic coupling 26 and, as a result, the secondary pressure from the pilot valve 22b is applied to the pilot port 12b without hindrance. In an emergency, however, the pressure oil is supplied manually to the pilot line 23bU from the injection port 25. This manual process is implemented by using a grease gun 30 such as that shown in FIG. 3. The grease gun 30 is provided as standard equipment with the hydraulic excavator to be utilized when replenishing grease at the joints and the like of the front attachment FA. According to the present invention, it is used as a manual hydraulic pump (hydraulic source) for pressure oil supply. The procedure and effect of utilizing the grease gun 30 as a manual hydraulic pump are to be detailed later.
When a boom-up operation is performed through the operating lever 22c in the structure described above, the discharged pressure from the pilot hydraulic pump 21 is reduced at the pilot valve 22a, and the secondary pressure (the pilot oil pressure) resulting from the pressure reduction is applied to the pilot port 12a of the control valve 12 via the pilot line 23a. This switches the control valve 12 to the left side position in the figure, causes the oil discharged from the hydraulic pump 11 to be guided to a bottom chamber 1a of the boom cylinder 1 via the control valve 12. In addition, a rod chamber 1b comes into communication with a reservoir 13 and the boom cylinder 1 becomes expanded to raise the boom 2. If, on the other hand, a boom-down operation is performed through the operating lever 22c, the secondary pressure at the pilot valve 22b is applied to the pilot port 12b of the control valve 12 via the pilot line 23b as described earlier, to switch the control valve 12 to the right side position in the figure. As a result, the oil discharged from the hydraulic pump 11 is guided to the rod chamber 1b of the boom cylinder 1 via the control valve 12. At this time, the bottom chamber 1a comes into communication with the reservoir 13, causing the boom cylinder 1 to contract to lower the boom 2.
If the engine comes to an emergency stop while the boom 2 is raised and the bucket 6 is in midair resulting in a disabled operation, the operator brings down the bucket 6 to the ground through the following procedure.
First, the operator tightens the stop valve 24 located at the boom-down side pilot line 23b to prevent the pressure oil from flowing into the line 23bU located toward the pilot valve 22b. Next, he injects the pressure oil from the injection port 25 with the grease gun 30. He loads a cartridge filled with hydraulic fluid in place of a cartridge filled with grease, and connects a hydraulic coupling 32 provided at the front tip of a hose 31 (see FIG. 3) of the grease gun 30 to the hydraulic coupling 26 of the injection port 25.
The operator uses the grease gun 30 in this state to inject the hydraulic fluid into the pilot line 23bL to be used as pressure oil (emergency pilot oil pressure). Since the stop valve 24 is closed, the injected pressure oil is guided to the pilot port 12b of the control valve 12 to switch the control valve 12 to the right side position in the figure. Since this allows the bottom chamber 1a of the boom cylinder 1 to come into communication with the reservoir 13 via the control valve 12, the boom 2 is caused to descend by its own weight, until it stops once the bucket 6 is lowered to the ground.
As described above, by supplying the pressure oil to the pilot line 23bL with the grease gun 30, the control valve 12 is switched to lower the boom 2 in the embodiment. Consequently, since the only modification that is required is to provide the pressure oil injection port 25 at the pilot line 23bL, a reduction in the production cost is achieved over the related art methods. In addition, the extent to which the control valve 12 is switched can be adjusted by varying the degree of pressure oil injection, and thus, the speed with which the boom descends can be controlled freely. Furthermore, the pressure oil injection port 25 is provided at a position that is off the traveling locus of the front attachment FA, assuring a high degree of safety.

-Second Embodiment-

An embodiment in which the present invention is adopted in a hydraulic excavator conforming to offset specifications is now explained in reference to FIGS. 4 ^~ 7. It is to be noted that members fulfilling functions similar to those in the first embodiment are assigned with reference numerals in the hundreds, with each of these reference numerals sharing the same last two digits with the corresponding member in the first embodiment.
In FIG. 4, a cabin 51, an engine 52, a hydraulic pump 111, a control valve unit VU and the like are mounted at the upper swiveling body of the hydraulic excavator. A front attachment FA' is connected to the right of the upper swiveling body in the figure. The front attachment FA' is constituted of a boom 102 driven by a boom cylinder 101, an arm 104 driven by an arm cylinder 103, a bucket 106 driven by a bucket cylinder 105 and the like.
The boom 102 is constituted of a base end portion 102A and a front end portion 102B, and its front end portion 102B is caused to rotate relative to the bottom end portion 102A as shown in FIG. 5 as an offset cylinder 61 expands/contracts. A cylinder stay 62 rotatably linked to the front end portion 102B travels to the left and to the right while remaining parallels to the bottom end portion 102A as the front end portion 102B rotates, which causes the arm 104 and the bucket 106 connected to its front end to become offset to the left or the right as one. As a result, the hydraulic excavator is enabled to excavate sideways to dig a trench in the ground at its side.
FIG. 6 shows the boom drive hydraulic circuit in the hydraulic excavator achieved in the second embodiment. It differs from the hydraulic circuit shown in FIG. 2 in that its pilot lines 123a and 123b are respectively connected to pilot ports 112a and 112b of a control valve 112 via a solenoid valve unit 70. The solenoid valve unit 70 is provided near the bottom of the cabin 51, as shown in FIG. 4.
Although not shown, the pilot lines for enabling drive of the individual actuators, such as the offset cylinder 61, the arm cylinder 103, the bucket cylinder 105 and the like, as well as the boom cylinder 101, are connected via the solenoid valve unit 70 to the pilot ports of the control valve corresponding to the individual actuators. Thus, the solenoid valve unit 70 includes a plurality of ports (input and output ports) to which the individual lines are connected. By changing the ports to which the individual lines are connected, different pilot lines can be selected for driving the individual actuators. This configuration is widely adopted in order to support the driving operation characteristics of a given operator when a plurality of actuators are operated through a single operating valve. In the embodiment, a coupling or the like is provided at a port of the solenoid valve unit 70 so as to allow the grease gun mentioned earlier to be connected to the port, and the port is utilized as an emergency pressure oil injection port.
The operator performs a manual boom-down operation if the engine 52 comes to an emergency stop while the boom 102 is raised and the bucket 106 is suspended above the ground as described earlier and the attitude of the front attachment FA' determines whether the boom 102 is to be lowered to the front or to the rear. If the position of the center of gravity of the front attachment FA' is further frontward relative to the boom rotational axis, the boom 102 is lowered to the front, whereas if the position of the center of gravity is further rearward, the boom is lowered to the rear.
When the boom is to be lowered to the front, the line 123b is disengaged from a port 70b (see FIG. 6) to which the boom-down side pilot line 123b is connected among the input ports of the solenoid valve unit 70. In place of the line 123b, the hose of the grease gun 30 is connected to the port 70b. As explained earlier, a cartridge filled with hydraulic fluid is loaded in advance at the grease gun 30. The disengaged line 123b should be plugged (not shown) so as to ensure that no hydraulic fluid spills out. The operator operates the grease gun 30 to inject the hydraulic fluid into the pilot line 123b to be used as pressure oil, thereby switching the control valve 112 to the right side position. As a result, the bottom chamber 101a of the boom cylinder 101 comes into communication with the reservoir 113 and the boom 102 is caused to descend to the front by its own weight.
When lowering the boom 102 to the rear, on the other hand, pressure oil is injected with the grease gun 30 into a port 70a to which the boom-up side pilot line 123a is connected. The control valve 112 is switched to the left side position and the bottom chamber 101b of the boom cylinder 101 comes into communication with the reservoir 113. As a result, the boom 102 is caused to descend to the rear by its own weight.
While the boom 102 rotates within the angular range shown in FIG. 7, the left side portion of the cabin 51 where the solenoid valve unit 70 is provided is completely off the traveling locus of the front attachment FA'. For this reason, the attachment FA' never passes near the solenoid valve unit 70, regardless of the offset state of the attachment FA' or the rotating angles of the boom 102 and the arm 104. Thus, the boom-down operation utilizing the solenoid valve unit 70 can be performed while assuring the safety.
It is to be noted that a boom-down operation may be also achieved by releasing the pressure oil from an overload relief valve (not shown) provided at an intake/outlet line of the boom cylinder 101, for instance. However, since the overload relief valve is normally formed as an integrated part of the control valve 112 constituting the control valve unit VU, the pressure oil must be drawn out from the control valve unit VU. As shown in FIG. 4, the control valve unit VU is provided on the right side of the cabin 51 and thus, when the front attachment FA' is offset to the right, as shown in FIG. 5, the vicinity of the control valve unit VU falls within the traveling locus of the front attachment FA'. For this reason, a safety concern arises with regard to the boom-down operation implemented at the control valve unit VU.
It is to be noted that the attachment to be manually driven is not limited to the boom and the present invention may be adopted in conjunction with any other attachment that needs to be moved in an emergency. In addition, the construction machine does not need to be a hydraulic excavator. While pressure oil is injected with a grease gun, another manual hydraulic pump may be used in place of the grease gun.

Claims

A hydraulic circuit of a construction machine, comprising;

a hydraulic pump that is driven by an engine; an actuator that is driven by oil discharged from said hydraulic pump and drives a front attachment;

a hydraulic pilot-operated control valve that is switched by a pilot oil pressure to control inflow/outflow of pressure oil to/from said actuator; and

a pressure oil injection port provided at a pilot line through which the pilot oil pressure is guided to said control valve and is capable of being connected with a hydraulic source other than a hydraulic source from which the pilot oil pressure originates.
A hydraulic circuit of a construction machine according to claim 1, wherein:

said front attachment includes a boom capable of rotating along an upward/downward direction relative to a main body of said construction machine and said pressure oil injection port is provided at the pilot line located on a boom-down side.
A hydraulic circuit of a construction machine according to claim 1 or claim 2, wherein:

said pressure oil injection port is provided at a position that is off a traveling locus of said front attachment.
A hydraulic circuit of a construction machine according to any one of claims 1 through 3, wherein:

said manual hydraulic pump is a grease gun.
A hydraulic circuit of a construction machine according to any one of claims 1 through 4, further comprising;

an opening/closing valve provided between said pressure oil injection port and said hydraulic source from which the pilot oil pressure originates.
A hydraulic circuit of a construction machine, comprising;

a hydraulic pump that is driven by an engine;

an actuator that is driven by oil discharged from said hydraulic pump and drives a front attachment;

a hydraulic pilot-operated control valve that is switched by a pilot oil pressure to control inflow/outflow of pressure oil to/from said actuator;

a grease gun that supplies pressure oil to a pilot line through which the pilot oil pressure is guided to said control valve; and

a pressure oil injection port provided at said pilot line and is to be connected with said grease gun.
An attachment emergency drive method for driving a front attachment of a construction machine by controlling oil discharged from a hydraulic pump driven by an engine through a control valve that is switched by a pilot oil pressure comprising:

generating emergency pilot oil pressure at a hydraulic source other than a hydraulic source from which the pilot oil pressure originates; and

driving said front attachment by applying the emergency pressure oil to said control valve.
An attachment emergency drive method according to claim 7, wherein:

the emergency pilot oil pressure is generated by a grease gun which is different from the hydraulic source from which the pilot oil pressure originates.