Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Reexamination Certificate
2001-12-28
2003-12-23
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
C060S414000
Reexamination Certificate
active
06666022
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a drive apparatus of working machine such as an excavator, a crane and the like that uses an engine such as a diesel engine and the like as a power source, and in particular to a drive apparatus of working machine, in which an electric motor concurrently serving as a generator and a battery, which are connected to one end of an output of engine, supplement the output of the engine.
BACKGROUND OF THE INVENTION
Conventionally, a working machine such as an excavator, a crane and the like is generally provided with an engine such as a diesel engine and the like in order to obtain a power for self-traveling, by which a hydraulic pump is driven, and the rotation of crawlers or tires for traveling and the movement of each working part such as a boom, an arm, a bucket and the like are performed by supplying hydraulic oil discharged from the hydraulic pump to a hydraulic actuator such as a hydraulic pump, a hydraulic cylinder and the like.
FIG. 13
is a view showing a general construction of a self-traveled excavator,
FIG. 14
is a graph showing a relationship between discharge flow rate and discharge pressure of a hydraulic pump, and
FIG. 15
a graph showing a relationship between the number of revolutions and output torque of an engine.
In
FIG. 18
, the self-traveled excavator comprises traveling crawlers
102
having left and right travel-driving hydraulic motors
101
, and an upper rotating body
103
is provided on the traveling crawlers
102
to be rotatable about a vertical axis. The upper rotating body
103
is provided with an engine
105
, a hydraulic pump
106
, a hydraulic oil tank
107
, a fuel tank
108
, a rotation-driving hydraulic motor
109
, a rotation-driving decelerator
110
and the like as well as a cab
104
. In the front part of the upper rotating body
103
, a boom
111
, an arm
112
, and a bucket
113
are provided as working members for performing the working, which are connected to be actuated by a boom cylinder
114
, an arm cylinder
115
, and a bucket cylinder
116
, respectively. The hydraulic pump
106
is rotated by using the output of the engine
105
as a power source and the travel-driving hydraulic motor
101
, the rotation driving hydraulic motor
109
, the boom cylinder
114
, the arm cylinder
115
, and the bucket cylinder
116
, which actuate respective working members, are driven by using hydraulic oil discharged from the hydraulic pump
106
.
For the hydraulic pump
106
, e.g. a variable discharge pump may be used, and its output is controlled to have a constant power (discharge pressure x discharge flow rate) characteristic in relation to discharge pressure and discharge flow rate, thereby to be set to a value near a rated output of engine so that its output shall not exceed the nominal power of engine. By this, it is envisaged that the power of engine can be utilized at its most while preventing the absorbed horse power of the hydraulic pump from exceeding the nominal power of engine to cause an engine stall (ENST).
As shown in
FIG. 14
, the constant power characteristic of a variable discharge pump is indicated as a hyperbola on the plane of discharge pressure-discharge flow rate, and the input of pump (B) is set to a value near the rated output (A) of the engine, so that the rated output of the engine can be utilized as much as possible.
In addition, as shown in
FIG. 15
, the engine
105
has a torque rising characteristic in the range below the rated number of revolutions, while it has a characteristic that both of its output and torque are reduced, in the range from the rated number of revolutions to the number of high idle revolutions.
In order to efficiently use the power of engine, the engine
105
reaches to the maximum (rated) number of revolutions when the input of hydraulic pump
106
is at the maximum, and is operated near the rated number of revolutions. Therefore, if the input of hydraulic pump becomes smaller, the number of revolutions of engine shifts toward the number of high idle revolutions and is operated in the number of revolutions higher than the rated number of revolutions. The number of high idle revolutions is higher than the rated number of revolutions up to about 10%.
Further, in a transition state where the input of hydraulic pump
106
is temporarily increased larger than the output of the engine
105
, the number of revolutions of engine is decreased lower than the rated number of revolutions due to a delay in control of the variable discharge pump and the like, whereas the output torque of the engine is increased and the engine stall is prohibited due to the torque rising characteristic of engine. In this way, engine is operated between the rated number of revolutions and the number of high idle revolutions in the normal state except the transition state.
Like this, the reason why the power by hydraulic pressure is used as a drive apparatus is that it has some merits as compared to electric power in that (1) because driving machinery and tools are light and compact, they are suitable to be mounted in a working machine to meet its self-traveling movement, and (2) it is easy to obtain a large reciprocating thrust if a hydraulic cylinder is used. However, power by hydraulic pressure has a problem in that energy efficiency for working is poor as compared to electric power. In a hydraulic circuit, by performing the control of directions, pressure and flow rate for hydraulic fluid discharged from the hydraulic pump using a control valve, actuating direction, actuating force and actuating velocity of a hydraulic actuator are controlled. In this case, if the proportion of hydraulic energy bled and wasted by the control valve for performing the control of pressure and flow rate of hydraulic oil is large, and when the energy supplied from the power source is used for working, the loss of energy is large.
Furthermore, the energy needed by a working machine to perform a work is varied with the lapse of time in accordance with the content of work to be formed; there were problems in that an engine which is a power source should have a capacity that can provide a maximum input energy required by a hydraulic pump, and the utilization efficiency of engine power is low.
Therefore in recent years, in order to overcome the lowering of utilization efficiency of the engine power and the deterioration of utilization efficiency of hydraulic power, the following techniques have been proposed, from the view of saving energy.
Firstly, an internal combustion engine for a hydraulic excavator has been proposed, wherein an inductor is provided in a power line of engine and the combustion engine comprises a battery for accumulating electric energy regenerated by the inductor, an inverter circuit for converting electric energy accumulated in the battery into AC electric power and supplying it to said inductor as well as for converting AC electric power regenerated by the inductor into DC electric power and supplying it to said battery, and a switching means for switching and controlling the actions of said inverter circuit (Japanese Utility Model Unexamined Publication No. Hei 5-48501:first prior art).
This is to operate the inductor as a regenerative generator to charge the battery with electricity via the inverter circuit when the work performed by the working machine is a low load one in which the engine power has a margin, and to operate the inductor as an electric motor using the electric power accumulated in the battery via the inverter circuit to assist the engine when the work performed by the working machine is a high load work in which a power larger than the engine power is required.
By this, it becomes possible to cope with all kinds of works using an engine, the capacity of which is smaller than a maximum working energy required by the hydraulic pump (rated power of engine in FIG.
14
(C)), whereby it is envisaged that the engine can be miniaturized to efficiently utilize the power of engine.
Next, it has been also proposed to provide a rotating hydraulic
Hideura Masami
Imanishi Etsujiro
Yoshimatsu Hideaki
Kobelco Construction Machinery Co., Ltd.
Leslie Michael
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