Construction machine

In a construction machine of a small rotational inertia such as an intrawidth swing machine or a small-sized excavator, a rotative operability varies depending on the posture of a working attachment, and in a reduced state of reach, a change in rotating force is oversensitive to the operation of a working lever, so operation is difficult. To cope with this point, means for detecting the operation of a rotating direction control valve is provided, and an outlet of a center bypassing oil path in the rotating direction control valve and an oil tank are brought into communication with each other through a cut-off valve used for controlling the bleed-off thereof. Further, a pilot port of the cut-off valve and a source of a pilot oil pressure are brought into communication with each other through an electromagnetic proportional pressure reducing valve, and an operation command signal is issued from a controller to the electromagnetic proportional pressure control valve to control the acceleration of rotation and the maximum rotating speed.

BACKGROUND OF THE INVENTION 
1. (Field of the Invention) 
The present invention relates mainly to a construction machine having an 
upper rotating structure. Particularly, the invention is concerned with a 
control circuit in a hydraulic excavator. 
2. (Description of the Related Art) 
FIG. 10 is a circuit diagram of a rotating motor described in Japanese 
Utility Model Laid Open No. 41203/91. 
In the rotating circuit of the prior art shown in FIG. 10, when a rotating 
hydraulic remote control valve 2 for starting the operation of a rotating 
motor 1 is operated, a secondary pilot pressure derived from the valve 2 
acts on pressure increasing ports 4L and 4R of relief valves 3L and 3R, 
respectively, whereby the relief valves 3L and 3R are set at a high relief 
pressure. As a result, the starting torque of the rotating motor 1 is 
increased and a satisfactory accelerating performance can be exhibited at 
the time of start-up of rotation. 
For stopping the rotation of an upper rotating structure, the rotating 
hydraulic remote control valve 2 is returned to its neutral position, 
whereby the secondary pilot pressure is no longer exerted on the pressure 
increasing ports 4L and 4R, so that the set pressure for the relief valves 
3L and 3R shifts to a lower pressure side. Thus, a braking force working 
on the rotating motor 1 does not act abruptly. In other words, since the 
braking force for the motor 1 copes flexibly with the force of inertia of 
the upper rotating structure, there is performed a smooth stop of the 
upper rotating structure. 
FIG. 11 is a side view showing the posture of a working attachment 7 
attached to an upper rotating structure 6 of an hydraulic excavator 5. 
The working attachment 7 comprises a boom 8, an arm 9, and a bucket 10 as a 
working tool, which are connected successively with one another. As shown 
in phantom in FIG. 11, when the boom 8 is brought down and the arm 9 
extended, a working radius R from a rotation center O--O of the upper 
rotating structure 6 to the front end portion of the arm 9 is long. In 
this state, an inertial mass of the upper rotating structure 6 is large. A 
rotation starting force of a rotating motor 11 is set so as to permit 
start-up of rotation even in the case of a large inertial mass. On the 
other hand, when the boom 8 is raised and the arm 9 retracted, as 
indicated with solid line in FIG. 11, a working radius, r, from the 
rotation center O--O of the upper rotating structure 6 to the front end 
portion of the arm 9 is short, and the inertial mass of the upper rotating 
structure 6 is small. Particularly, in the case of a construction machine 
with a small rotational inertia such as, for example, an intra-width swing 
machine or a small-size excavator, the operability for rotation varies 
markedly according to the posture of the working attachment. In a reduced 
state of the working radius of the working attachment, a change in 
rotational force, which occurs in response to the operation of a lever for 
actuating a hydraulic cylinder for the boom or for the arm, is 
oversensitive and therefore operation is difficult. This problem occurs 
also in a rotating operation with a small working load imposed on the boom 
or in a combined operation for both traveling and rotation. Anyhow, it 
cannot be said that the operator is given a comfortable feeling in the 
rotating operation. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a control circuit 
capable of sensing a boom angle, or both boom angle and arm angle, and the 
state of a working load, thereby reading the posture of a working 
attachment, and restricting the acceleration of rotation and the maximum 
speed. 
The present invention relates to a construction machine having a lower 
carriage, an upper rotating structure mounted rotatably on the lower 
carriage, and a working attachment attached rotatably to the upper 
rotating structure. The construction machine of the present invention 
further includes working radius detecting means for detecting a working 
radius on the basis of the state of the working attachment, rotative 
acceleration suppressing means for suppressing the acceleration of 
rotation of the upper rotating structure when it is detected by the 
working radius detecting means that the working radius is small, and 
maximum rotating speed suppressing means for suppressing a maximum 
rotating speed of the upper rotating structure when it is detected by the 
working radius detecting means that the working radius is small. 
The rotative acceleration suppressing means and the maximum rotating speed 
suppressing means both used in the present invention may each be 
constituted by an unloading valve, which controls the bleed-off of a 
rotating direction control valve in accordance with the working radius. As 
the said unloading valve there may be used a cut-off valve which controls 
the bleed-off by on-off operation. 
In this case, control may be made in such a manner that, when the working 
radius is reduced, the bleed-off of the cut-off valve is controlled to 
permit opening in response to the operation of the rotating direction 
control valve to suppress the acceleration of rotation of the upper 
rotating structure and that the bleed-off of the cut-off valve is 
controlled so as not to be fully closed, thereby suppressing the maximum 
rotating speed of the upper rotating structure. 
An outlet of a center bypassing oil path for the return of main pressure 
oil, which extends through a neutral position of the rotating direction 
control valve, and an oil tank may be brought into communication with each 
other through the above cut-off valve. Using an electromagnetic 
proportional pressure reducing valve, the cut-off valve may be controlled 
in accordance with the working radius. 
The unloading valve may be connected to three valves, the rotating 
direction control valve, a boom (or arm) direction control valve, and a 
traveling direction control valve. In this case, it is preferable that 
priority be set to the operation of the rotating direction control valve. 
Further, the unloading valve may be operated in accordance with a detected 
load pressure of a hydraulic cylinder for rotating a boom. In this case, 
control may be made in such a manner that, with a decrease of the load 
pressure, the bleed-off of the cut-off valve is controlled to permit 
opening in response to the operation of the rotating direction control 
valve to suppress the rotative acceleration of the upper rotating 
structure and that the bleed-off of the cut-off valve is controlled so as 
not to be fully closed, thereby suppressing the maximum rotating speed. 
In the construction machine of the present invention, both rotative 
acceleration and maximum rotating speed of the upper rotating structure 
can be suppressed. Accordingly, it is possible to improve both operability 
and safety.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described in detail 
hereinunder with reference to the accompanying drawings. 
FIG. 1 is a side view of a hydraulic excavator provided with a control 
circuit according to the present invention. In the same figure, the 
reference numeral 12 denotes a lower carriage of the hydraulic excavator. 
Numerals 13L and 13R denote a pair of left and right traveling motors for 
driving the lower carriage 12. The right-hand traveling motor 13R is not 
visible because it is on the opposite side of the left-hand traveling 
motor 13L. Numeral 14 denotes an upper rotating structure connected to the 
upper portion of the lower carriage 12. Numeral 15 denotes a rotating 
motor mounted in the interior of the upper rotating structure 14. Numeral 
16 denotes a controller. Numeral 17 denotes a working attachment attached 
to the upper rotating structure 14. Numerals 18, 19 and 20 denote a boom, 
an arm, and a bucket as a working tool, respectively. Numerals 21, 22 and 
23 denote a boom cylinder, an arm cylinder, and a bucket cylinder, 
respectively. Numeral 24 denotes a pin connection for connection between a 
base end portion of the boom 18 and a boom mounting bracket (not shown) of 
the upper rotating structure 14. Numeral 25 denotes a pin connection for 
connection between a front end portion of the boom 18 and a base end 
portion of the arm 19. Numeral 26 denotes a pin connection for connection 
between a front end portion of the arm 19 and a base portion of the bucket 
20. Numeral 27 denotes a potentiometer attached to the pin connection 24 
to detect the posture of the boom 18. Numeral 28 denotes a potentiometer 
attached to the pin connection 25 to detect the posture of the arm 19. The 
reference mark .theta. denotes a boom angle between a straight line 
joining the pin connections 24 and 25 and a horizontal line (H.L.). The 
mark a denotes an arm angle between a straight line joining the pin 
connections 24 and 25 and a straight line joining the pin connections 25 
and 26. The distance R' is equal to the working radius (the so-called 
reach of the working attachment) from a rotational center O'--O' of the 
upper rotating structure 14 to the front end portion of the arm 19. 
FIG. 2 is a control circuit diagram in the first embodiment of the present 
invention. 
In FIG. 2, the numeral 29 denotes a rotating direction control valve for 
controlling the rotating motor 15. Numerals 30L and 30R denote left and 
right pilot ports of the rotating direction control valve 29. Numeral 31 
denotes a main pump, numeral 32 denotes an oil tank, numeral 33 denotes a 
cut-off valve used as an unloading valve, and numeral 34 denotes a pilot 
port of the cut-off valve 33. Further, numeral 35 denotes an 
electromagnetic proportional pressure reducing valve, and numeral 36 
denotes a solenoid of the valve 35. Numeral 37 denotes a pilot pump as an 
oil pressure source in a pilot circuit. Numeral 38 denotes a hydraulic 
remote control valve for work. Numeral 39 denotes an operating lever for 
the hydraulic remote control valve 38. Numerals 40, 40',41 and 41' denote 
pilot valves each of which produces a secondary pilot pressure upon 
tilting of the operating lever 39. The marks X and Y represent connections 
of pilot lines. 
FIG. 3 shows a relation between a pilot pressure Pi for rotation (the 
secondary pilot pressure derived from the pilot valve 40 or 40') acting on 
the pilot ports 30L and 30R of the rotating direction control valve 29 and 
an operation command pilot pressure Pc derived from the electromagnetic 
proportional pressure reducing valve 35. As shown in FIG. 3, the larger 
the working radius, the larger the inclination of a straight line which 
indicates the relation between the pilot pressure Pi for rotation and the 
operation command pilot pressure Pc. 
The control circuit in the first embodiment of the present invention will 
now be described with reference to FIGS. 1 to 3. As means for detecting 
the posture of the working attachment 17, potentiometers 27 and 28 are 
provided for the boom 18 and arm 19, respectively. Further, as means for 
detecting the operation of the rotating direction control valve 29, 
pressure sensors 42L and 42R (both shown in FIG. 2) are provided for the 
pilot ports 30L and 30R, respectively. An outlet of a center bypassing oil 
path 43 for the return of a main pressure oil, which oil path extends 
through a neutral position of the rotating direction control valve 29, and 
the oil tank 32 are in communication with each other through the cut-off 
valve 33 which performs opening and closing motions selectively to control 
the bleed-off thereof The pilot port 34 of the cut-off valve 33 and the 
pilot pump 37 are in communication with each other through the 
electromagnetic proportional pressure reducing valve 35. The controller 16 
forms a judgment on detection signals provided from the potentiometers 27, 
28 and the pressure sensors 42L, 42R and then provides an operation 
command signal to the solenoid 36 of the pressure reducing valve 35, which 
in turn exerts an operation command pilot pressure Pc to the pilot port 34 
of the cut-off valve 33. 
The following description is now provided about the operation of the 
control circuit in the first embodiment. While the hydraulic excavator is 
performing a work under rotation thereof, a boom angle .theta. detection 
signal and an arm angle a detection signal are fed to the controller 16 
from the potentiometers 27 and 28, respectively. Further, rotating 
operation detection signals are fed to the controller 16 from the pressure 
sensors 42L and 42R. The controller 16 forms a judgment on the basis of 
those detection signals and then outputs a command signal to the solenoid 
36 of the electromagnetic proportional pressure reducing valve 35. The 
valve 35 then operates and generates an operation command pilot pressure 
Pc, which operates on the pilot port 34 of the cut-off valve 33. 
In the above case, as shown in FIG. 3, the pilot pressure Pi for rotation 
derived from the pilot valve 40 or 40' of the hydraulic remote control 
valve 38 in a rotating operation and the operation command pilot pressure 
Pc of a value corresponding to the working radius R' up to the front end 
portion of the working attachment 17 are outputted to the pilot port 34 of 
the cut-off valve 33 in accordance with the judgment made by the 
controller 16. Therefore, when the working radius R' of the working 
attachment 17 is reduced, if the bleed-off of the cut-off valve 33 is 
controlled in a rather opening direction in response to the operation of 
the rotating direction control valve 29, it becomes possible to suppress 
the rotative acceleration of the upper rotating structure 14. Further, by 
controlling the bleed-off of the cut-off valve 33 so as not to be fully 
closed, it is made possible to suppress the maximum rotating speed. To be 
more specific, a low maximum rotating speed results in the braking inertia 
being also small, and it is possible to improve the operability and safety 
at a small reach and at a total of acceleration and deceleration. 
Although in this embodiment the pilot pressure Pi for rotation and a 
command value of the operation command pilot pressure Pc derived in 
accordance with the working radius R' are set so as to change linearly, as 
shown in FIG. 3, there is made no limitation to such a linear change. The 
change in question may be non-linear insofar as there is attained 
operability which matches the construction machine. 
FIG. 4 is a control circuit diagram according to the second embodiment of 
the present invention. In FIG. 4, the same components as in the control 
circuit of the first embodiment shown in FIGS. 1 and 2 are indicated by 
the same reference numerals. 
Numeral 44 denotes an arm direction control valve for controlling the arm 
cylinder 22. Numerals 45L and 45R denote pilot ports of the arm direction 
control valve 44. Numeral 46 denotes a traveling direction control valve 
for controlling the (left) traveling motor 13L. Numerals 47L and 47R 
denote pilot ports of the traveling direction control valve 46. Numeral 
16a denotes a controller. 
FIG. 5 is a graph showing a relation between a pilot pressure Pi for the 
arm which pressure works on the pilot ports 45L and 45R of the arm 
direction control valve 44 and an operation command pilot pressure Pca 
derived from an electromagnetic proportional pressure reducing valve 35. 
FIG. 6 is a graph showing a relation between a traveling pilot pressure Pib 
acting on the pilot ports 47L and 47R of the traveling direction control 
valve 46 and an operation command pilot pressure Pcb derived from the 
electromagnetic proportional pressure reducing valve 35. A pilot valve for 
outputting the traveling pilot pressure Pib is not shown. 
Also in this second embodiment the relation between a rotating pilot 
pressure Pi acting on pilot ports 30L and 30R of a rotating direction 
control valve 29 and an operation command pilot pressure derived from the 
electromagnetic proportional pressure reducing valve 35 is the same as the 
relation shown in FIG. 3. Although the traveling direction control valve 
46' used in the first embodiment is a push-pull type, the traveling 
direction control valve 46 used in the control circuit of this second 
embodiment is a hydraulic remote control type. 
The construction of the control circuit in the second embodiment will now 
be described with reference to FIGS. 4 to 6. As means for detecting the 
posture of the working attachment 17 there are provided the potentiometers 
27 and 28 for boom 18 and arm 19. Further, as means for detecting the 
operation of the rotating direction control valve 29 there are provided 
the pressure sensors 42L and 42R for the pilot ports 30L and 30R. As means 
for detecting the operation of the arm cylinder 22 there are provided 
pressure sensors 48L and 48R for the pilot ports 45L and 45R of the arm 
direction control valve 44. As means for detecting the operation of the 
traveling motor 13L there are provided pressure sensors 49L and 49R for 
the pilot ports 47L and 47R of the traveling direction control valve 46. 
The output of a center bypassing oil path 43 for the return of a main 
pressure oil, which oil path extends through neutral positions of the 
direction control valves 46, 44 and 29 for traveling, for arm and for 
rotation, respectively, and the oil tank 32 are in communication with each 
other through the cut-off valve 33 which is adapted for opening and 
closing motion to control the bleed-off thereof. The pilot port 34 of the 
cut-off valve 33 and the pilot pump 37 are in communication with each 
other through the electromagnetic proportional pressure reducing valve 35. 
Detection signals provided from the potentiometers 27, 28 and the pressure 
sensors 42L, 42R, 48L, 48R, 49L and 49R are subjected to judgment by the 
controller 16a, which in turn outputs an operation command signal to the 
solenoid 36 of the electromagnetic proportional pressure reducing valve 
35, whereby the operation command pilot pressure Pc, Pca, or Pcb, is 
exerted on the pilot port 34 of the cut-off valve 33 from the valve 35. 
Detection signals provided from the pressure sensors 42L and 42R as means 
for detecting the operation of the rotating direction control valve 29 are 
subjected to the judgment in preference to detection signals provided from 
the pressure sensors 48L, 48R, 49L and 49R as means for detecting the 
operation of the traveling direction control valves 44 and 46. 
Although a control valve for boom is not described in FIG. 4 which 
illustrates the second embodiment, it also may be used. 
Description is now directed to the operation of the control circuit 
according to the second embodiment. When the hydraulic excavator is 
performing a work without rotation, boom angle .theta. detection signal 
and arm angle .alpha. detection signal from the potentiometers 27 and 28, 
arm cylinder operation detection signals from the pressure sensors 48L and 
48R, and traveling motor operation detection signals from the pressure 
sensors 49L and 49R, are fed to the controlled 16a. The controller 16a 
forms a judgment on the basis of those detection signals and outputs a 
command signal to the solenoid 36 of the electromagnetic proportional 
pressure reducing valve 35. As a result, the valve 35 operates and 
operation command pilot pressures Pca and Pcb of such values as shown in 
FIGS. 5 and 6 are outputted to the pilot port 34 of the cut-off valve 33. 
In this way it is possible to perform the ordinary operation of the arm 
and traveling in a rotation-free condition. However, when the hydraulic 
excavator is performing a rotating operation, boom angle .theta. and arm 
angle .alpha. detection signals from the potentiometers 27 and 28, as well 
as rotating motor operation detection signals from the pressure sensors 
42L and 42R, are fed to the controller 16a. In the controller 16a, 
detection signals provided from the pressure sensors 42L and 42R as means 
for detecting the operation of the rotating direction control valve 29 are 
subjected to judgment in preference to detection signals provided from the 
pressure sensors 48L, 48R, 49L and 49R as means for detecting the 
operation of the traveling direction control valves 44 and 46. Thus, it is 
possible to prevent the occurrence of pressure interference at the time of 
change-over of spool (not shown) in the arm direction control valve 44 and 
traveling direction control valve 46 which valves share the main pump 31 
with each other. Accordingly, unlike the prior art, there is no fear that 
the change-over of spool in the arm direction control valve during 
rotation may result in dosing of bleed-off of the same valve and increase 
of rotation in decelerative control. As mentioned above, bleed-off of the 
arm direction control valve 44 and that of the traveling direction control 
valve 46, which share the main pump 31 with each other, are controlled by 
the cut-off valve 33. More specifically, if the arm is operated or 
operation for traveling is performed, other than rotation, in a rotation 
decelerating control, the control for the cut-off valve sets priority to a 
pilot pressure command for rotation, so the cut-off valve does not dose 
and hence a stable operability for rotation can be attained. 
FIG. 7 is a control circuit diagram according to the third embodiment of 
the present invention. In the same figure, the same components as in the 
control circuit of the first embodiment shown in FIGS. 1 and 2 are 
indicated by the same reference numerals as in FIGS. 1 and 2. 
The numeral 50 denotes a boom direction control valve for controlling a 
boom cylinder 21. The boom cylinder sometimes comprises two cylinders, so 
in FIG. 7 there are illustrated two cylinders. Numerals 51L and 51R denote 
pilot ports of the boom direction control valve 50. Numeral 16b denotes a 
controller. Numeral 52B denotes a pressure sensor for detecting the 
pressure of a bottom-side oil chamber 53 of the boom cylinder 21. Numeral 
52R denotes a pressure sensor for detecting the pressure of a rod-side oil 
chamber 54 of the boom cylinder 21. 
FIG. 8 is a graph showing a relation between a pilot pressure Pic for the 
boom acting on the pilot ports 51L and 51R of the boom direction control 
valve 50 and an operation command pilot pressure P.sub.CC derived from an 
electromagnetic proportional pressure reducing valve 35. Given that the 
internal pressure of the bottom-side oil chamber 53 in the boom cylinder 
21 is P.sub.B, the internal pressure of the rod-side oil chamber 54 is 
P.sub.R, a bottom-side pressure receiving area of a piston 55 in the boom 
cylinder 21 is A.sub.B, and a rod-side pressure receiving area of the same 
piston is A.sub.R, a boom load pressure, W, acting on the boom cylinder 21 
during work is calculated by the controller 16b in accordance with the 
following formula: 
EQU W =P.sub.B *A.sub.B -P.sub.R *A.sub.R 
Description is now directed to the construction of the control circuit 
according to the third embodiment with reference to FIGS. 7 and 8. As 
means for detecting the operation of a rotating direction control valve 29 
there are provided the pressure sensors 42L and 42R for pilot ports 30L 
and 30R, respectively. As means for detecting a boom load pressure in the 
boom cylinder 21 there are provided pressure sensors 52B and 52R for the 
bottom-side oil chamber 53 and the rod-side oil chamber 54, respectively, 
in the boom cylinder 21. An outlet of a center bypassing oil path 43 for 
the return of a main pressure oil which oil path extends through a neutral 
position of the rotating direction control valve 29, and the cut-off valve 
33 adapted for opening and dosing motions to control the bleed-off 
thereof. A pilot port 34 of the cut-off valve 33 and the pilot pump 37 are 
in communication with each other through the electromagnetic proportional 
pressure reducing valve 35. The controller 16b forms a judgment on 
detection signals provided from the pressure sensors 42L, 42R, 52B and 52R 
and outputs an operation command signal to a solenoid 36 of the 
electromagnetic proportional pressure reducing valve 35, thereby causing 
an operation command pilot pressure P.sub.CC to be exerted on the pilot 
port 34 of the cut-off valve 33 from the valve 35. 
The operation of the control circuit according to the third embodiment will 
now be described. When a working load is imposed on the boom under 
rotation of the hydraulic excavator, rotating operation detecting signals 
from the pressure sensors 42L and 42R, as well as boom load pressure 
detection signals from the pressure sensors 52B and 52R, are fed to the 
controller 16b. The controller 16bperforms an arithmetic processing on the 
basis of those detection signals and outputs a command signal to the 
solenoid of the electromagnetic proportional pressure reducing valve 35, 
which in turn operates and outputs an operation command pilot pressure 
P.sub.CC of such a value as shown in FIG. 8 to the pilot port 34 of the 
cut-off valve 33. When the boom load pressure is small, therefore, by 
controlling the bleed-off of the cut-off valve 33 in a rather opening 
direction in response to the operation of the rotating direction control 
valve 29, it is possible to suppress the rotative acceleration of the 
upper rotating structure 14. Further, by controlling the bleed-off of the 
cut-off valve 33 so as not to fully close, it is possible to suppress the 
maximum rotating speed. Thus, a small boom load pressure results in the 
braking inertia being also small and it is possible to improve both 
operability and safety at a small boom load pressure and at a total of 
acceleration and deceleration. 
FIG. 9 is a control circuit diagram according to the fourth embodiment of 
the present invention. In FIG. 9 the same components as in the control 
circuit of the first embodiment shown in FIGS. 1 and 2 are indicated by 
the same reference numerals as in FIGS. 1 and 2. 
In the fourth embodiment, instead of the cut-off valve 33 connected in 
serial between the rotating direction control valve 29 and the oil tank 32 
as shown in FIG. 2, another cut-off valve 71 is connected in parallel 
between the main pump 31 and the traveling direction control valve 46'. A 
pilot port 75 of the cut-off valve 71 is connected to a directional 
control valve 72. A pilot port 74 of the directional control valve 72 is 
electrically connected to a controller 16'. A pilot pump 73 and the 
hydraulic remote control valve 38 are connected to a port of the 
directional control valve 72. In the fourth embodiment shown in FIG. 9, 
the cut-off valve 71 controls the bleed-off amount from the main pump 31.