Measuring and testing – Simulating operating condition – Marine
Reexamination Certificate
1999-05-27
2001-01-23
McCall, Eric S. (Department: 2855)
Measuring and testing
Simulating operating condition
Marine
C060S431000, C123S319000
Reexamination Certificate
active
06176126
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
This invention relates to an engine speed control system for a construction machine such as a hydraulic excavator, which is suitable for arrangement in the construction machine and, when directional control valves for controlling drive of actuators are all held in center valve positions thereof, can perform automatic idling control such that the speed of an engine is maintained at an idling speed of a predetermined low rpm.
b) Description of the Related Art
As prior art of this type, there is one disclosed in Japanese Utility Model Publication (Kokoku) No. HEI 3-52284.
FIG. 3
is a hydraulic circuit diagram illustrating this conventional engine speed control system as arranged in a construction machine.
The conventional engine speed control system is arranged in association with a hydraulic circuit of the construction machine. The hydraulic circuit is provided with an engine
40
, plural main hydraulic pumps driven by the engine
40
, specifically a first main pump
41
and a second main pump
42
, plural actuators driven by pressure fluid supplied from these first main pump
41
and second main pump
42
, respectively, specifically hydraulic system actuators
55
-
58
,
62
,
63
, directional control valves connected with the first main pump
41
to control flows of pressure fluid to be supplied to their corresponding hydraulic system actuators
55
-
58
from the first main pump
41
, specifically change-over control valves
51
-
54
, directional control valves connected with the second main pump
42
to control flows of pressure fluid to be supplied to the corresponding hydraulic system actuators
62
,
63
,
58
from the second main pump
42
, specifically change-over control valves
59
-
61
, and a reservoir
77
.
Of the above-mentioned hydraulic system actuators
55
-
58
,
62
,
63
, the hydraulic system actuator
55
constitutes one of a pair of travel motors, the hydraulic system actuator
62
constitutes the other travel motor, and the hydraulic system actuators
56
,
57
,
58
,
63
constitute actuators other than those mentioned above.
As has been mentioned above, the hydraulic actuator
55
which constitutes the one travel motor is connected with the first main pump
41
, while the hydraulic actuator
62
which constitutes the other travel motor is connected with the second main pump
42
.
The conventional engine speed control system arranged in association with the hydraulic circuit as described above is provided with an engine control mechanism, which performs automatic idling control to set the speed of the engine
40
at an idling speed of a predetermined low rpm and can also perform control to cancel the above-mentioned automatic idling control. This engine control mechanism comprises, for example, a speed governor
67
which in turn, is equipped inter alia with a governor lever
69
for controlling a quantity of fuel to be injected and a spring
68
by which the governor lever
69
is biased.
The conventional engine speed control system is also provided with a pilot pump
64
capable of supplying a pilot pressure, a pilot line
65
for guiding the pilot pressure supplied from the pilot pump
64
, pilot valves
70
-
76
arranged independently in the pilot line
65
in association with the above-mentioned change-over control valves
51
-
54
,
59
-
61
, respectively, such that the pilot valves are operated in association with their corresponding change-over control valves, and a pressure detection device for detecting a pressure developed in the pilot line
65
upon change-over of at least one of these pilot valves
70
-
76
and then outputting it as a detection signal to the above-mentioned speed governor
67
, for example, a line
78
.
When the change-over control valves
51
-
54
,
59
-
61
are all held in their center positions, for example, as shown in
FIG. 3
, the pilot line
65
is in communication with the reservoir
77
so that the pilot line
65
has the reservoir pressure. This reservoir pressure is supplied to the speed governor
67
via the line
78
. By the force of the spring
68
which is greater than the force of the reservoir pressure, the governor lever
69
assumes a position “a” in FIG.
3
. As a consequence, the speed of the ending
40
is maintained at an idling speed of a predetermined low rpm, thereby realizing a reduction in fuel consumption.
Let's assume that, to drive one of the hydraulic system actuators
55
-
58
,
62
,
63
, for example, the corresponding one of the change-over control valves
51
-
54
,
59
-
61
is operated. One of the pilot valves
70
-
76
, said one pilot valve corresponding to the operated change-over control valve, is changed over concurrently and as a consequence, a pressure is developed in the pilot line
65
at a part between the change-over control valve
74
, which is arranged on a most upstream side in the pilot line
65
, and the pilot pump
64
. This pressure is supplied to the governor
67
via the line
78
, so that the spring
68
is compressed and the governor lever
69
assumes a position “b” in FIG.
3
. Accordingly, control is performed to cancel the control that the engine speed be maintained at the idling speed as mentioned above, namely, the automatic idling control. As a result, the engine
40
can be driven at a desired rpm, for example, a rated rpm or the like.
In the above-described conventional art, the change-over control valve
51
for controlling drive of the hydraulic actuator
55
, which constitutes the one travel motor, and the change-over control valves
52
-
54
for controlling drive of the hydraulic system actuators
56
-
58
, which constitute the plural other actuators, are connected to the first main pump
41
, whereas the change-over control valve
59
for controlling drive of the hydraulic system actuator
62
, which constitutes the other travel motor, and the change-over control valves
60
,
61
for controlling drive of the hydraulic system actuators
63
,
58
, which constitute the other actuators, are connected to the second main pump
42
.
Accordingly, upon single operation of travelling, the pressure fluid delivered from the first main pump
41
is supplied to the change-over control valve
51
for the hydraulic system actuator
55
and the pressure fluid delivered from the second main pump
42
is supplied to the change-over control valve
59
for the hydraulic system actuator
62
, so that the single operation of travelling can be performed as desired.
However, when it is desired to perform, for example, a combined operation of travelling and another operation, which is to be performed by driving the hydraulic system actuator
56
, from the state of such a single operation of travelling, the pressure fluid delivered from the first main pump
41
is supplied to both of the change-over control valve
51
for the hydraulic system actuator
55
, which constitutes the one travel motor, and the change-over control valve
52
for the hydraulic system actuator
56
, while the pressure fluid delivered from the second main pump
42
is supplied only to the change-over control valve
59
for the hydraulic system actuator
62
which constitutes the other travel motor. During such a combined operation of travelling and another operation by another actuator, it is therefore impossible to assure independence for the travelling, leading to a potential problem that the construction machine may be caused to travel in a zigzag.
SUMMARY OF THE INVENTION
With the foregoing problem of the conventional art in view, the present invention has as an object thereof the provision of an engine speed control system for a construction machine, which makes it possible to assure independence of travelling while enabling to achieve automatic idling control to automatically set an engine speed at a predetermined low rpm and cancellation of the automatic idling control.
To attain the above-described object, the present invention provides, in a first aspect thereof, an engine speed control system for a construction machine, said system being for arrangemen
Kanai Takashi
Kawamoto Junya
Nakatani Kenichiro
Tsuruga Yasutaka
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Hitachi Construction Machinery Co. Ltd.
McCall Eric S.
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