HYDRAULIC SHOVEL

Abstract

 An object of this invention is to provide a hydraulic excavator equipped with a blade (3), which upon performing digging work by its working equipment (4), allows the working equipment (4) to be heightened in performance to such an extent as permitting full exhibition of mechanical ability with which the working equipment (4) is inherently provided as to the cutting depth.
Described specifically, owing to such an interference-preventing function of a controller (40) that, when a pivoted angle of the first boom (5) takes a value in a predetermined pivoted angle range before a critical angle upon conducting civil engineering works by the working equipment (4) with a truck frame (1) being directed forward, a control signal is outputted to increase a restriction of a solenoid-operated proportional pressure-reducing valve (17) as a first boom (5) approaches closer to a hazardous zone, the first boom (5) is surely prevented from being lowered excessively and interfering with the blade (3). When further digging work is required to dig deeper after digging is effected close to a maximum cutting depth Hd1 by the working equipment (4), a revolving superstructure 2 is caused to revolve over approximately 180° and a change-over switch (37) is pressed. This makes it possible to cancel the interference-preventing function, thereby permitting continuation of subsequent digging work to a maximum cutting depth Hd2.

Description

Technical Field

[0001] This invention relates to a hydraulic excavator, which is provided with a blade mounted on a truck frame at one of opposite ends thereof as viewed in a traveling direction thereof and also with a working equipment supported pivotally in a vertical direction on a front part of a revolving superstructure.

Background Art

[0002] For civil engineering works to lay drain pipes under roads or to dig drain ditches, hydraulic excavators are used primarily. Recently, there is an increasing tendency to bury lifeline pipes and cables, such as water lines, gas lines and power and communication lines, in an overcrowded state in the ground. Upon newly burying a pipe in the ground or replacing an old pipe with a new pipe, the work must thus be conducted carefully to avoid breaking or cutting of the pipes and cables already buried and laid there. It is therefore necessary to place a watchman and to carefully conduct the work while paying attention to signals from the watchman. The efficiency of the work is significantly reduced.

[0003] Japanese Patent Application Laid-Open (Kokai) No. HEI 6-81376 therefore discloses an invention on a working depth limiting system equipped with a controller. When digging work is performed at a level lower than a superstructure, a hazardous zone is set in a height range above a depth level at which already buried and laid pipes and cables are estimated to exist; a quasihazardous zone in a predetermined height range above the hazardous zone; and a safe zone above the quasi-hazardous zone. Based on information on pivotal movements of respective pivotable elements of a working equipment, such as a boom, an arm and a bucket, as detected by angle detection devices for detecting pivoted positions of the respective pivotable elements, depth levels of predetermined points on the respective pivotable elements are computed. The controller outputs a control signal such that the lowering operation of the working equipment is slowed down when the lowest one of the predetermined points is detected to be moving from the safe zone to the quasi-hazardous zone but is stopped when the lowest predetermined point is detected to be moving from the quasi-hazardous zone to the hazardous zone.

[0004] Upon performing digging work at a rather narrow work site, there is an increasing tendency to use a small versatile hydraulic excavator equipped with a blade or the like and having a revolving superstructure the revolving radius of which is set approximately equal to the width of a truck frame. Upon setting a hazardous zone below a predetermined depth level, use of the above-mentioned working depth limiting system for such a hydraulic excavator requires to set the hazardous zone in a range where no interference takes place with the blade. As a consequence, it becomes no longer necessary to worry about any possible interference of the working equipment with the already laid and buried pipes or cables or with the blade. The operator can therefore concentrate upon digging work by the working equipment, thereby making it possible to improve the efficiency of the work.

[0005] Incidentally, upon burying and laying a lifeline pipe, cable or the like such as a water line, a gas line or a power or communication line, it is desired to bury and lay it at a predetermined depth. When such a pipe or cable is dug out or when a new pipe or the like is laid in a neighborhood of a pipe or the like already laid there, a hydraulic excavator of ability that its attainable maximum cutting depth slightly exceeds the buried and laid depth is selected and sent to the work site. However, at a work site where pipes, cables and the like are buried and laid in an overcrowded state in the group as mentioned above, it is not unusual that they are not always buried and laid at recommended depths. Pipes and the like are generally buried and laid at deeper positions in such a case, so that the intended digging-out or laying work may be accomplished by the hydraulic excavator. If this is the case, the hydraulic excavator must be replaced by a greater hydraulic excavator the attainable maximum cutting depth of which is greater. Depending on the work site, however, it may be difficult to conduct work by such a large hydraulic excavator.

[0006] In the case of a small versatile hydraulic excavator equipped with a blade and the above-mentioned working depth limiting system, the attainable maximum cutting depth of a working equipment is a depth which is determined by an interference-preventing function for avoiding an interference with the blade and which is shallower than a depth attainable by the inherent mechanical ability of the working equipment. Namely, as the hydraulic excavator is provided with the blade, the attainable depth of the working equipment is limited to a depth shallower than an attainable maximum cutting depth which is determined by the inherent mechanical ability of the working equipment, that is, an extended or retracted length of a boom cylinder, said length being set to avoid an interference of the boom with a vehicle frame.

[0007] The present invention has been completed in view of the above-described current situation of the conventional art, and has as an object thereof the provision of a hydraulic excavator provided with a blade, which upon performing digging work by its working equipment, allows the working equipment to be heightened in performance to such an extent as permitting full exhibition of mechanical ability with which the working equipment is inherently provided as to the cutting depth.

Disclosure of the Invention

[0008] To achieve the above-described object, the present invention sets a hazardous zone in a vicinity of a blade mounted on a truck frame at one of opposite ends as viewed in a traveling direction, including at least a zone above the blade, and controls operation of a working equipment such that a control means prohibits a predetermined part of the working equipment from entering the hazardous zone and, when a canceling means is operated by an operator at a revolved position of a revolving superstructure where the working equipment remains out of contact with the blade even when pivotally operated downward, the prohibition of entry of the predetermined part of the working equipment into the hazardous zone is canceled; or arranges a revolved-angle detecting device for detecting a revolved angle of the revolving superstructure and controls operation of a working equipment such that, when the revolved angle of the revolving superstructure detected by the revolved-angle detecting means indicates that the pivoted position of the working equipment and the mounted position of the blade are located on substantially opposite sides with the center of revolution interposed therebetween, the prohibition of entry of the predetermined part of the working equipment into the hazardous zone is canceled.

[0009] Since the present invention is constituted as described above, the control means exhibits an interference-preventing function to prohibit entry of the predetermined part of the working equipment into the hazardous zone by performing forward digging work with the revolved position of the revolving superstructure being set such that said working equipment is located in front of the truck frame. The operator can therefore concentrate upon digging work without becoming apprehensive of an interference of the working equipment with the blade. If a need arises to dig down to a position deeper than a usual cutting depth, on the other hand, the prohibition of entry of the predetermined part of the working equipment into the hazardous zone is canceled by causing the revolving superstructure to revolve to a position where the working equipment remains out of contact with the blade even when pivotally operated downward, in other words, where the pivoted position of the working equipment and the mounted position of the blade are located on substantially opposite sides with the center of revolution interposed therebetween, followed by an operation of the canceling means by the operator or by control of the control unit. It is therefore possible to increase the maximum cutting depth of the working equipment to a possible maximum extent by simple operations without any substantial increase in cost.

Brief Description of the Drawings

[0010] FIG. 1 is a hydraulic circuit diagram of a hydraulic excavator according to an embodiment of the present invention, FIG. 2 is a block diagram showing the construction of a controller in this embodiment, FIG. 3 is a sketch of an interior of a cab of the hydraulic excavator as viewed from above, FIG. 4 is a flow diagram showing interference-preventing processing by the controller in this embodiment, FIG. 5(a) is a side view illustrating a digging operation with a revolving superstructure directed forward and FIG. 5(b) is a side view depicting a digging operation with the revolving superstructure directed rearward, FIG. 6 is a fragmentary control circuit diagram of a modification of this embodiment, FIG. 7 is a hydraulic circuit diagram of a hydraulic excavator according to another embodiment, and FIG. 8 is a flow diagram illustrating interference-preventing processing by a controller in this another embodiment.

Best Modes for Carrying Out the Invention

[0011] Referring first to FIG. 1 through FIG. 5, a description will be made in detail about the embodiment of the present invention. In these drawings (see FIG. 5 in particular), there are shown a truck frame 1 movable by driving a pair of crawler treads arranged for endless rotation at laterally opposite end portions, respectively, the revolving superstructure 2 supported for revolution on a top part of the truck frame 1, a blade 3 pivotally mounted on a front part of the truck frame 1, and a working equipment 4 attached to a front part of a below-described cab of the revolving superstructure 2 pivotally as a whole in a vertical direction such that it can be articulate at parts thereof. Numerals 5-7,41 designate individual constituents of the working equipment 4, respectively, in which numeral 5 indicates a first boom attached pivotally in the vertical direction to the revolving superstructure 2, numeral 6 indicates a second boom maintained in parallel with the first boom 5 via a link mechanism which is attached to a free end portion of the first boom 5 pivotally in a horizontal direction by an offset cylinder to be described subsequently herein, numeral 70 indicates an arm attached to a free end portion of the second boom 6 pivotally in the vertical direction, and numeral 41 indicates a bucket attached to a free end portion of the arm 7 pivotally in the vertical direction.

[0012] Referring next to the hydraulic circuit shown in FIG. 1, there are illustrated hydraulic actuators 8-11,18-20 for driving the truck frame 1, the revolving superstructure 2 and the working equipment 4, respectively; a boom cylinder 8, offset cylinder 9, arm cylinder 10 and bucket cylinder 11 extendible and retractable for pivoting the first boom 5, second boom 6, arm 7 and bucket 41, respectively; a revolving motor 18, right drive motor 19 and left drive motor 20 for driving the revolving superstructure 2 and the left and right crawler treads of the truck frame 1, respectively. Designated at numerals 23-26, 34-36 are directional control valves for changing over directions and flow rates of pressure fluid to be supplied from a below-described driving hydraulic pump to the respective hydraulic actuators. Numerals 23, 24, 25, 26 indicate a directional control valve for the boom, a directional control valve for the bucket, an offsetting directional control valve, and a directional control valve for the arm, respectively. Numerals 34,35,36 designate a directional control valve for the revolving superstructure, a directional control valve for the right crawler tread, and a directional control valve for the left crawler tread.

[0013] Designated at numerals 12-16 are control levers or control pedals (control devices) arranged in the cab of the hydraulic excavator (see FIG. 3) and adapted to change over the respective directional control valves 23-26,34-36, in which numerals 12,13 indicate right and left control levers, numerals 14,15 designate left and right drive levers, and numeral 16 designates an offset pedal. Designated at numerals 27-33 are pilot valves for outputting, to the corresponding directional control valves 23-26,34-36, pilot fluid pressures corresponding to change-over operations of the control devices 12-16 by the operator, in which numerals 27,28,29,30,31,32,33 indicate a boom control pilot valve, an arm control pilot valve, a bucket control pilot valve, an offset-cylinder control pilot valve, a revolving-superstructure control pilot valve, and left and right drive control pilot valves. Designated at numerals 21, 22 are a hydraulic drive pump and hydraulic pilot pump, which are driven by an unillustrated engine and supply pressure fluids for driving and controlling the actuators, respectively.

[0014] There are also shown a grip portion 12a of the right control lever 12; a change-over switch 37 arranged on the grip portion 12a of the right control lever 12; a boom angle sensor 38 arranged on a portion of the first boom 5, at which the first boom is articulated on the revolving superstructure 2, to detect a pivoted angle of the first boom 5 about the revolving superstructure 2; a solenoid-operated proportional pressure-reducing valve 17 inserted in a pilot line extending to one of two pressure-receiving compartments of the directional control valve 23 for the boom cylinder 8, in which the two compartments receive pilot hydraulic pressure outputted from the boom control pilot valve 27 and the one compartment serves to change over the directional control valve 23 in the direction that the boom cylinder 8 is caused to retract; a controller 40 for controlling an on/off operation of the solenoid-operated proportional pressure-reducing valve 17 on the basis of a control signal from the change-over switch 37 and a detection signal from the boom angle sensor 38; and the cab 42 arranged on a top part of the revolving superstructure 2.

[0015] Signs 40a-40c shown in FIG. 2 indicate constituents of the controller 40, in which sign 40a designates an input unit to which a control signal from the change-over switch 37 and a detection signal from the boom angle sensor 38 are inputted, sign 40b designates a computing unit for ascertaining a pivoted angle of the first boom 5 about the revolving superstructure 2 on the basis of the detection signal from the boom angle sensor 38 and also for computing an angle difference from an upper boundary of a hazardous zone set above the blade 3, and sign 40c designates an output unit for outputting to the solenoid-operated proportional pressure-reducing valve 17 a control signal which corresponds to the result of the computation at the computing unit 40b.

[0016] When the operator holds, for example, the right control lever 12, which is shown in FIG. 3, in his right hand and operates it in a forward or rearward direction as desired, a pilot pressure signal corresponding to the direction and amount of the operation is applied from the boom control pilot valve 27 to the corresponding pilot-pressure receiving compartment of the directional control valve 23 for the boom, so that the directional control valve 23 for the boom is changed over rightward or leftward. As a consequence, the boom cylinder 8 is caused to extend or retract so that the first boom 5 is pivoted upward or downward. When the operator holds the right drive lever 12 in his right hand and operates it in a lateral direction as desired, a pilot pressure signal corresponding to the direction and amount of the operation is applied from the bucket-control pilot valve 29 to the corresponding pilot-pressure receiving compartment of the directional control valve 24 for the bucket, so that the directional control valve 24 for the bucket is changed over rightward or leftward. As a consequence, the bucket cylinder 11 is caused to extend or retract so that the bucket 41 is pivoted upward or downward.

[0017] Further, when the operator holds the left control lever 13 in his left hand and operates it in a forward or rearward direction as desired, a pilot pressure signal corresponding to the direction and amount of the operation is applied from the revolving-superstructure control pilot valve 31 to the corresponding pilot-pressure receiving compartment of the directional control valve 34 for the revolving superstructure, so that the directional control valve 34 for the revolving superstructure is changed over rightward or leftward. As a consequence, the revolving motor 18 is caused to rotate clockwise or counterclockwise so that the revolved position of the revolving superstructure 2 is changed. When the operator holds the left drive lever 13 in his left hand and operates it in a lateral direction as desired, a pilot pressure signal corresponding to the direction and amount of the operation is applied from the arm-control pilot valve 28 to the corresponding pilot-pressure receiving compartment of the directional control valve 26 for the arm, so that the directional control valve 26 for the arm is changed over rightward or leftward. As a consequence, the arm cylinder 10 is caused to extend or retract so that the arm 7 is pivoted in the vertical direction.

[0018] When the left and/or right drive levers 14, 15 are (is) held in his right or left hand and are (is) operated in a forward or rearward direction as desired, pilot pressure signal(s) corresponding to the direction and amount of the operation is (are) applied from the left and/or right drive-control pilot valves 32,33 to the corresponding pilot-pressure receiving compartment(s) of the directional control valve(s) 35,36 for the right and/or left crawler treads, so that the directional control valve(s) 35,36 for the right and/or left crawler treads is (are) changed over rightward or leftward. As a consequence, the right and/or left drive motors 19,20 are (is) caused to rotate clockwise or counterclockwise so that the left and/or right of the truck frame 1 are (is) caused to move forward or rearward. When the operator depresses the offset pedal 16 as desired, a pilot pressure signal corresponding to the direction and amount of the depression is applied from the offset-cylinder control pilot valve 30 to the corresponding pilot-pressure receiving compartment of the directional control valve 25 for the offset cylinder, so that the directional control valve 25 for the offset cylinder is changed over rightward or leftward. As a consequence, the offset cylinder 9 is caused to extend or retract so that the pivoted position of the second boom 6 is shifted leftward or rightward.

[0019] By operating the individual control means (12,13,16) as mentioned above, the operator actuates the working equipment 4 to perform civil engineering works such as digging, loading and the like of earth or sand. The controller 40 monitors movements of the working equipment 4, and controls change-over operations of the directional control valve 23 for the boom such that the working equipment 4 does not interfere with the blade 3 in the course of the civil engineering works. With reference to the flow diagram depicted in FIG. 4, a description will be made of operations of on/off control of the solenoid-operated proportional pressure-reducing valve by the controller 40.

[0020] A boom angle signal detected by the boom angle sensor 38 is inputted to the input unit 40a of the controller 40, and at the computing unit 40b, is converted into its corresponding boom angle data and is then compared with a critical angle indicative of a limit beyond which the first boom 5 reaches the upper boundary of the hazardous zone. It is then determined whether or not the first boom 5 has approached toward the hazardous zone and is located within a predetermined pivoted angle range before the upper boundary of the hazardous zone (S1). If the result of the determination is affirmative, the change-over switch 37 is turned on by the operator, and a determination is then made as to whether or not an "on" signal from the change-over switch 37 has been inputted to the input unit 40a (S2). If the result of the determination is negative, a control signal is outputted from the output unit 40c such that the restriction of the solenoid-operated proportional pressure-reducing valve 17 becomes greater as the angle difference between the boom angle and the above-described critical angle becomes smaller (S3). If the result of the determination in step S1 is negative or if the result of the determination in step S2 is affirmative, a control signal is outputted from the output unit 40c such that the solenoid-operated proportional pressure-reducing valve 17 is fully opened (S4).

[0021] As mentioned above, the computing unit 40b converts a boom angle signal, which has been detected by the boom angle sensor 38 and has been inputted to the input unit 40a, into its corresponding boom angle data (computing means) and compares it with the critical angle indicative of the limit beyond which the first boom 5 reaches the upper boundary of the preset hazardous zone, whereby the computing unit determines whether or not the first boom 5 has approached toward the hazardous zone and is located within the predetermined pivoted angle range before the upper boundary of the hazardous zone. If the pivoted angle of the first boom 5 is of a value not reaching the predetermined pivoted angle range smaller than the critical angle beyond which the first boom reaches the upper boundary of the hazardous zone, the solenoid-operated proportional pressure-reducing valve 17 is fully opened. The working equipment 4 therefore performs operations in accordance with operation states of the control means (12,13,16) as desired by the operator.

[0022] Upon performing civil engineering works with the working equipment 1 directed toward the front part of the truck frame 1, the operator does not turn on the change-over switch 37. When the first boom 5 approaches toward the hazardous zone and is located within the predetermined pivoted angle range before the upper boundary of the hazardous zone and the pivoted angle of the first boom 5 takes a value in the predetermined pivoted angle range before the critical angle, there is accordingly a potential problem that the first boom 5 may interfere with the blade 3 if the first boom 5 continues to descend in the hazardous zone. A control signal is therefore outputted from the output unit 40c such that the restriction of the solenoid-operated proportional pressure-reducing valve 17 becomes greater as the angle difference between the boom angle and the above-described critical angle becomes smaller, in other words, the first boom 5 approaches closer to the hazardous zone, so that the descending movement of the first boom 5 is slowed down to prevent an interference with the blade 3 (hazardous zone entry prohibition control means). In this case, the working equipment 4 stops at a maximum cutting depth Hd1 shown in FIG. 5(a), which the working equipment can attain. Even if the operator operates the right control lever 12 in the direction that the first boom 5 would be lowered further, the first boom 5 cannot descend any further.

[0023] When the working equipment 4 is directed toward the front part of the truck frame 1, said front part carrying the blade 3 mounted thereon, the interference-preventing function of the controller 40 makes it possible, as described above, to surely prevent the first boom 5 from excessively descending and hence interfering with the blade 3 as a result of an operation of the right control lever 12 by the operator. However, when the revolving superstructure 2 is directed rearward, that is, when the working equipment 4 is directed toward a rear part of the truck frame 1 where the blade 3 is not mounted as shown in FIG. 5(b), there is inherently no potential problem that the first boom 5 would interfere with the blade 3 even when as a result of an operation by the operator, the first boom 5 descends to a position where an interference with the blade 3 would otherwise take place. Nonetheless, any further descending movement is slowed down by the interference-preventing function of the controller 40.

[0024] According to this embodiment, the interference-preventing function of the controller 40 is therefore canceled by the operator's change-over operation of the change-over switch 37 when the working equipment 4 is directed toward the rear part of the truck frame 1. This allows the working equipment 4 (first boom 5) to descend to its mechanical limit of descending movement beyond the critical angle. A maximum cutting depth attainable at this time is expressed by Hd2, which is obviously deeper than Hd1. Further, the following inequality is established: L1 > L2, where L1: a fully-retracted length of the first boom cylinder 5 when the change-over switch 37 is not pressed, and L2: a fully-retracted length of the first boom cylinder 5 when the change-over switch 37 is pressed. As a consequence, the working equipment 4 is allowed to dig to a cutting depth greater than a cutting depth which was initially estimated for the working equipment. Intended civil engineering works such as replacement of pipes can therefore be accomplished even if the pipes are found to be buried at a depth greater than an estimated depth.

[0025] In this embodiment, a consideration has been taken to avoid occurrence of a hydraulic shock on the first boom 5 or the hydraulic line extending to it by inserting the solenoid-operated proportional pressure-reducing valve 17 in the pilot line extending to one of the pressure-receiving compartments of the directional control valve 23 for the boom, said compartments serving to receive hydraulic pilot pressure outputted from the boom-control pilot valve 27, and, when the pivoted angle of the first boom 5 has taken a value in the predetermined pivoted angle range before the critical angle, by performing control such that the restriction of the solenoid-operated proportional pressure-reducing valve 17 becomes greater as the first boom 5 approaches closer to the hazardous zone. When the inertia of the working equipment 4 is not substantial, it is possible to ignore this hydraulic shock and to use a less costly solenoid-operated on/off valve instead of the solenoid-operated proportional pressure-reducing valve 17.

[0026] With reference to FIG. 6 which shows a fragmentary control circuit diagram, a description will hereinafter be made about a modification of this embodiment, in which a hydraulic pilot pressure for effecting a change-over of the directional control valve 23 for the boom is controlled by a solenoid-operated on/off valve. A boom angle signal detected by the boom angle sensor 38 is inputted to the controller 40, along with a control signal from the change-over switch 37. The controller 40 successively computes boom angles on the basis of boom angle signals from the boom angle sensor 38 and compares the boom angles with the critical angle. When the first boom 5 is remote from the hazardous zone and the boom angle has not reached the critical angle, an open signal (O) is outputted from the controller 40 to a solenoid-operated on/off valve 17'. As a consequence, a hydraulic pilot pressure outputted from the boom-control pilot valve 27 reaches one of the pressure-receiving compartments of the directional control valve 23 for the boom without being blocked by the solenoid-operated on/off valve 17', so that the directional control valve for the boom is changed over to the position in the boom-lowering direction. In this case, the operator can operate the working equipment 4 as desired by operating a control lever such as the right control lever 12.

[0027] When the boom angle has exceeded the critical angle, in other words, the first boom 5 has descended and reached the hazardous zone, on the other hand, the controller 40 outputs a close signal (C) to the solenoid-operated on/off valve 17'. When the close signal (C) is outputted to the solenoid-operated on/off valve 17', the solenoid-operated on/off valve 17' is changed over to the left position shown in FIG. 6. Accordingly, hydraulic pilot pressure outputted in a boom-lowering direction from the pilot-operated valve 27 is blocked by the solenoid-operated on/off valve 17', and does not reach the one pressure-receiving compartment of the directional control valve 23 for the boom. This one pilot-pressure-receiving compartment is communicated to a reservoir, and the directional control valve 23 for the boom is changed over to the neutral position. The first boom 5 therefore stops at that position, namely, at the boundary of the hazardous zone. As a consequence, the first boom 5 is prevented from being brought into contact at a lower extremity thereof with an upper edge portion of the blade 3.

[0028] Next, assume that the operator wishes to dig further after he has performed digging close to the maximum cutting depth Hd1 by the working equipment 4 directed toward the front part of the truck frame 1. In this case, he can continue the subsequent digging work to the maximum cutting depth Hd2 by holding the left control lever 13 in his left hand, operating it in the forward or rearward direction as desired to make the revolving superstructure 2 rotate over approximately 180° and then pressing the change-over switch 37. Namely, when an "on" signal is inputted from the change-over switch 37 to the controller 40, the controller 40 does not output any close signal (C) to the solenoid-operated open/close valve 17' even when the boom angle has exceeded the critical angle.

[0029] Even when digging work to a greater cutting depth is required and the operator operates the right control lever 12 to have the first boom 5 reached the hazardous zone, the controller 40 is prevented from outputting a close signal (C) to the solenoid-operated on/off valve 17' so that hydraulic pilot pressure outputted from the boom-control pilot valve 27 can be supplied, as is, to one of the pilot-pressure-receiving compartments of the directional control valve 23 for the boom. It is therefore possible to lower the first boom 5 to a maximum limit of descending movement designed to avoid any contact with the truck frame 1 even when the first boom 5 is lowered to a maximum.

[0030] When digging work to a cutting depth greater than an initially planned cutting depth is required, this embodiment makes it possible to lower the working equipment 4 further and to conduct digging work to the greater maximum cutting depth Hd2 by simply rotating the revolving superstructure 2 over approximately 180° to have the working equipment 4 directed toward the rear part of the truck frame 1, where the blade 3 does not exist, and then pressing the change-over switch 37 as described above.

[0031] Referring next to FIG. 7 and FIG. 8, a description will be made of another embodiment of the present invention, in which instead of canceling the interference-preventing function by the operator's pressing of the change-over switch, the interference-preventing function is automatically canceled when the working equipment is located on the side of the rear part of the truck frame. In FIG. 7, numeral 39 indicates a revolved angle sensor arranged on a rotatably-connecting part between the truck frame 1 and the revolving top superstructure 2. A signal corresponding to a revolved angle of the revolving superstructure 2 as detected by the revolved angle sensor 39 is inputted to the input unit 40a of the controller 40, along with a boom angle signal detected by the boom angle sensor 38.

[0032] As is illustrated in FIG. 8, at the computing unit 40b, the boom angle signal detected by the boom angle sensor 38 is converted into its corresponding boom angle data and then compared with the critical angle indicative of a limit beyond which the first boom 5 reaches the upper boundary of the hazardous zone. It is then determined whether or not the first boom 5 has approached toward the hazardous zone and is located within the predetermined pivoted angle range before the upper boundary of the hazardous zone (S11). If the result of the determination is affirmative, a revolved angle of the revolving superstructure 2 as detected by the revolved angle sensor 39 is compared with an angle range of (180° ± α) (α: a predetermined angle which is not large) to determine whether or not it is within the angle range (S12) (entry determination means). If the result of the determination is negative, a control signal is outputted from the output unit 40c such that the restriction of the solenoid-operated proportional pressure-reducing valve 17 becomes greater as the angle difference between the boom angle and the above-described critical angle becomes smaller (S13). If the result of the determination in step S11 is negative or if the result of the determination in step S12 is affirmative, a control signal is outputted from the output unit 40c such that the solenoid-operated proportional pressure-reducing valve 17 is fully opened (S14).

[0033] As has been described above, it is designed in this embodiment to automatically determine, based on a revolved angle signal of the revolving superstructure 2 as detected by the revolved angle sensor 39, whether or not the interference-preventing function should be canceled. When digging work to a cutting depth greater than an initially planned cutting depth is required, it is therefore possible, while surely preventing any interference between the first boom 5 and the blade 3, to perform digging work to Hd2 deeper than the maximum cutting depth Hd1, which has been regulated by the interference-preventing control, by simply causing the revolving superstructure 2 to rotate over approximately 180° and then operating the control means (12,13,16) in the usual manner to actuate the working equipment 4. By the way, the working equipment 4 in this embodiment was designed to be of the type that includes the second boom 6 maintained in parallel with the first boom 5 via the link mechanism attached pivotally leftward and rightward by the offset cylinder 9 to the free end portion of the first boom 5. Needless to say, the present invention is not limited to a working equipment of such a type, but is also applicable likewise to a hydraulic excavator provided with a working equipment comprising a pivotal arm simply attached to a free end portion of a boom.

Claims

1. A hydraulic excavator provided with a truck frame (1), a revolving superstructure (2) arranged on a top part of said truck frame (1), a working equipment (4) attached to a front part of said revolving super-structure (2) pivotally in a vertical direction about a horizontal fulcrum, an angle-detecting means (38) for detecting a pivoted angle of said working equipment (4), a computing means for computing a lowered position of a predetermined part of said working equipment (4) on a basis of a detection signal outputted from said angle-detecting means (38), a control means (40) for controlling operation of said working equipment (4) in accordance with a lowered position signal outputted from said computing means, a control device (12-16) for outputting control information corresponding to an amount of an operation thereof, a hydraulic pressure control means (23-26,34-36) for controlling a flow rate and direction of pressure fluid to be supplied to a hydraulic actuator (8-11,18-20) for driving said working equipment (4) in accordance with said operation information outputted from said control device (12-16) and control information outputted from said control means (40), and a blade (3) mounted on said truck frame (1) at one of opposite ends thereof as viewed in a travelling direction thereof for gouging out earth or sand by traveling of said truck frame (1), comprising a hazardous zone entry prohibition control means for outputting entry-prohibiting information which prohibits entry of said predetermined part of said working equipment (4) into a hazardous zone preset in a vicinity of said blade (3) and including at least a zone above said blade (3), and a canceling means (37) for canceling said prohibition of entry of said predetermined part of said working equipment (4) into said hazardous zone by said hazardous zone entry prohibition control means, wherein said control unit (40) controls operation of said working equipment (4) such that, when said canceling means (37) is operated by an operator at a revolved position of said revolving superstructure (2) where said working equipment (4) remains out of contact with said blade (3) even when pivotally operated downward, said prohibition of entry of said predetermined part of said working equipment (4) into said hazardous zone is canceled.

2. A hydraulic excavator according to claim 1, wherein said working equipment (4) comprises a boom (5,6) attached to said front part of said revolving superstructure (2) pivotally in said vertical direction, an arm (7) attached to a free end portion of said boom (5,6) pivotally in said vertical direction, and a bucket (41) attached to a free end portion of said arm (7) pivotally in said vertical direction.

3. A hydraulic excavator according to claim 2, wherein said angle-detecting means (38) is an angle sensor (38) secured on an articulate part of said boom (5).

4. A hydraulic excavator according to claim 2, wherein said hydraulic pressure control means (23-26, 34-36) is a directional control valve (23-26,34-36) which is changed over by a pilot hydraulic pressure.

5. A hydraulic excavator according to claim 4, wherein said control means (40) controls operation of said working equipment (4) by controlling an on/off state of a solenoid-operated valve (17) arranged in a pilot line extending to a pilot port through which a directional control valve (23) for said boom is changed over into a boom-lowering direction.

6. A hydraulic excavator according to claim 5, wherein said solenoid-operated valve (17) is a proportional pressure-reducing valve (17).

7. A hydraulic excavator according to claim 5, wherein said solenoid-operated valve (17) is an on/off valve (17') which is changed over into one of "open" and "closed" positions.

8. A hydraulic excavator according to claim 1, wherein said blade (3) is mounted on a front part of said truck frame (1).

9. A hydraulic excavator provided with a truck frame (1), a revolving superstructure (2) arranged on a top part of said truck frame (1), a working equipment (4) attached to a front part of said revolving super-structure (2) pivotally in a vertical direction about a horizontal fulcrum, an angle-detecting means (38) for detecting a pivoted angle of said working equipment (4), a computing means for computing a lowered position of a predetermined part of said working equipment (4) on a basis of a detection signal outputted from said angle-detecting means (38), a control means (40) for controlling operation of said working equipment (4) in accordance with a lowered position signal outputted from said computing means, a control device (12-16) for outputting control information corresponding to an amount of an operation thereof, a hydraulic pressure control means (23-26,34-36) for controlling a flow rate and direction of pressure fluid to be supplied to a hydraulic actuator (8-11,18-20) for driving said working equipment (4) in accordance with said operation information outputted from said control device (12-16) and control information outputted from said control means (40), a revolved-angle detecting means (39) for detecting a revolved angle of said revolving super-structure (2), and a blade (3) mounted on said truck frame (1) at one of opposite ends thereof as viewed in a travelling direction thereof for gouging out earth or sand by traveling of said truck frame (1), comprising a hazardous zone entry prohibition control means for outputting entry-prohibiting information which prohibits entry of said predetermined part of said working equipment (4) into a hazardous zone preset in a vicinity of said blade (3) and including at least a zone above said blade (3), wherein said control means (40) controls operation of said working equipment (4) such that, when said revolved angle of said revolving superstructure (2) detected by said revolved-angle detecting means (39) does not indicate that a pivoted position of said working equipment (4) and a mounted position of said blade (3) are located on substantially opposite sides with a center of revolution interposed therebetween, entry of said predetermined part of said working equipment (4) into said hazardous zone is prohibited in accordance with said entry-prohibiting information outputted from said hazardous zone entry prohibition control means and, when said revolved angle of said revolving superstructure (2) detected by said revolved-angle detecting means (39) indicates that said pivoted position of said working equipment (4) and said mounted position of said blade (3) are located on substantially opposite sides with said center of revolution interposed therebetween, said prohibition of entry of said predetermined part of said working equipment (4) into said hazardous zone by said hazardous zone entry prohibition control means is canceled.

10. A hydraulic excavator according to claim 1 or 9, wherein said hazardous zone entry prohibition control means has an entry determination means for determining whether or not said predetermined part of said working equipment (4) has entered said hazardous zone by checking a relation between said lowered position of said working equipment (4) and said hazardous zone preset in the vicinity of said blade (3) and including at least said zone above said blade in accordance with said lowered position signal outputted from said computing means and, when said entry determination means determines affirmatively, prohibits entry of said predetermined part of said working equipment (4) into said hazardous zone.

Drawing