Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Reexamination Certificate
2000-03-07
2002-04-30
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
Reexamination Certificate
active
06378303
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic control device of controlling an actuator provided on a working machine such as a hydraulic excavator, and particularly to a hydraulic control device of a working machine suitable for controlling a swinging operation.
2. Description of the Related Art
Conventionally, in the hydraulic excavator as the working machine, when attachments such as a swing motor, a travel motor, a boom cylinder, an arm cylinder, a bucket cylinder and so on are operated, an operating lever is operated to a full lever at a stretch, a lever operating amount is held constant, or the operating amount is somewhat changed while operating the actuator in a constant amount.
When the response of the actuator to the lever operation is excessively sensitive, there involves inconveniences such that when in operation, the actuator is actuated with the shock; it is difficult to hold the lever operating amount constant; or when the lever operation is changed in slight amount, the actuator sensitively reacts therewith to bring forth hunting. It is difficult for an unskilled operator to handle such a sensitively operating actuator as described. Then, an attempt has been made wherein a bleed-off passage of a control valve designed so that when the full lever operation is made, it is normally fully closed is made in a slightly open state even at the full lever operation, thereby improving the operativeness.
For example, in Japanese Patent Application Laid-Open No. 9-165791 Publication, there is shown a constitution in which in the full lever operation, a predetermined flow rate is discharged to a tank from a hydraulic pump, as shown in FIG.
10
. In
FIG. 10
, reference numeral
60
designates an engine;
61
and
62
a first hydraulic pump and a second hydraulic pump driven by the engine
60
;
63
a cylinder for an earth-discharge plate;
64
a swing motor;
65
an arm cylinder;
66
a left travel motor;
67
a bucket cylinder;
68
a swing cylinder;
69
a boom cylinder; and
70
a right travel motor. Direction control valves are disposed on a center bypass line
71
connected to the first hydraulic pump
61
, and a direction control valve
73
for an arm is connected in tandem at the downstream side of a direction control valve
72
for swing. The direction control valve
72
for swing is provided with a throttle
72
a
forming a bleed-off opening.
According to this constitution, in the full lever operation, the direction control valve
72
for swing bleeds off a part of pressure oil, and where single driving of the swing motor
64
is switched to composite driving of the swing motor
64
and the arm cylinder
65
, the flow rate discharged from the throttle
72
a
is supplied to the arm cylinder
65
through a direction control valve
73
for an arm positioned at the downstream of the direction control valve
72
for swing. At this time, the flow rate substantially equal to that at the swing single driving is supplied to the swing motor
64
. Accordingly, it is possible to prevent rapid swing operation in the swing single driving, and in the composite driving, it is possible to prevent the swing speed from being lowered rapidly.
However, since in the aforementioned conventional hydraulic circuit, the bleed-off passage (the throttle
72
a
) is in a normally open state, when the engine is increased in rotation to discharge a predetermined flow rate of pressure oil from the first hydraulic pump
61
, no problem occurs, but since a predetermined flow rate of pressure oil is subject to the bleeding-off, when the rotational frequency of the engine lowers, the flow rate flowing into the swing motor
64
reduces, so that the swing speed lowers.
The concrete work is taken as an example and explained. Where the swing work is carried out on the inclined ground and where an upper swing body is swung toward the upper side of the inclined surface, load applied to the swing motor
54
increases. When the bleed-off passage (the throttle
72
a
) is opened, the bleed-off flow rate discharged from the bleed-off passage naturally increases, so that the swing speed lowers. Moreover, normally, in the inclined ground, an operator lowers the rotational frequency of the engine for operation in consideration of the stability of the hydraulic excavator. Accordingly, under the conditions as described, it is sometimes that pressure oil necessary for swinging is not sufficiently supplied to the swing motor
64
to stop the swing operation.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a hydraulic control device of a hydraulic working machine, in which for example, in a swing operation, even if full lever operation is carried out, no shock caused by rapid swinging occurs, and a second object thereof is to provide said device, in which for example, in a swing operation, even if the rotational frequency of the engine is lowered, the flow rate necessary for swinging can be supplied to a swing motor to carry out a stable swing operation.
The present invention relates to a hydraulic control device of a working machine having a hydraulic pump driven by a power source, an actuator operated by pressure oil discharged from the hydraulic pump, a control valve for controlling a flow rate and a direction of the pressure oil discharged from the hydraulic pump, and an operating member for switching and operating the control valve, said hydraulic control device of a working machine comprising a bleed-off oil path for bleeding off a part of pressure oil supplied to a specific actuator out of the actuator, a bleed-off amount adjusting means for adjusting a bleed-off amount provided in the bleed-off oil path, an operating amount detecting means for detecting an operating amount of the operating member, and a control means for setting a bleed-off amount according to the operating amount detected by the operating amount detecting means and controlling the bleed-off amount set.
The bleed-off oil path can be constituted by a bypass oil path for communication between an upstream side of the oil path and a downstream side of the oil path of the control valve connected to the specific actuator.
Further, the control valve connected to the specific actuator can be formed with a meter-in passage, a meter-out passage, and said bleed-off oil path as a third passage.
Further, the bleed-off oil path can be constituted by a branch path branched from an oil path which connects the hydraulic pump and the control valve connected the specific actuator.
Further, the bleed-of amount adjusting means can be constituted specifically by a pilot switching valve for opening and closing the bleed-off oil path, and a solenoid proportional valve for exerting a pilot pressure according to the set bleed-off amount on the pilot switching valve.
The control means according to the present invention is possible to control the bleed-off amount adjusting means so that the bleed-off oil path is closed according to the operating amount of the operating member, and when the operating amount reaches a full stroke, the bleed-off oil path is not fully closed.
In the present invention provided with the bypass oil path, if the control valve connected to the specific actuator is designed to intercept the center bypass at the time of switching operation, the control means can be constituted such that the bypass oil path is switched from a full open position to a full closed position with delay for a predetermined time when switching operation is carried out. Further, the control means can be designed so that when the operating amount of the operating member exceeds a first set operating amount, the bypass oil path is gradually closed with delay of time, and when the operating amount of the operating member lowers than a second set operating amount, the closed bypass oil path is released.
In the present invention, where the rotational frequency detecting means for detecting rotational frequency of the power source is present, the control means is possible to control so that when th
Higuchi Fumikazu
Tajima Kazuharu
Tohji Yutaka
(Kobe Steel, Ltd.)
Lopez F. Daniel
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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