Material or article handling – Elevator or hoist and loading or unloading means therefor – Elevator wherein means comprises guide mounted for relative...
Reexamination Certificate
2001-02-26
2004-02-24
Bratlie, Steven A. (Department: 3652)
Material or article handling
Elevator or hoist and loading or unloading means therefor
Elevator wherein means comprises guide mounted for relative...
Reexamination Certificate
active
06695567
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to hydraulic devices for industrial vehicles, and, more particularly, to hydraulic devices preferably used in battery type forklifts.
Generally, a battery type forklift has a motor for driving wheels. The forklift further includes a power steering device and a carriage device that are operated through hydraulic pressure. In other words, the power steering device and the carriage device are supplied with hydraulic fluid from a hydraulic pump. The hydraulic pump is activated by a motor. The motor for driving the wheels and the motor for activating the hydraulic pump are powered by a battery, which is installed in the interior of a body frame of the forklift.
FIG. 7
shows a hydraulic device for a battery type forklift that is described in Japanese Unexamined Utility Model Publication No. 56-84600. The hydraulic device has a pair of hydraulic pumps
81
,
82
that supply hydraulic fluid to a cylinder
80
of a carriage device. The hydraulic pump
81
is activated by a motor
83
, and the hydraulic pump
82
is activated by a motor
84
. When only the pump
81
is activated, the cylinder
80
is operated at a relatively low speed. When both pumps
81
,
82
are activated, the cylinder
80
is operated at a relatively high speed.
In addition to the cylinder
80
, the hydraulic pumps
81
,
82
supply hydraulic fluid to a power steering device (not shown) through a throttle valve
95
. If the power steering device is operated together with the cylinder
80
, the hydraulic pump
81
must constantly supply hydraulic fluid to the power steering device and the cylinder
80
, regardless of the speed at which the cylinder
80
is operated. The displacement of the pump
81
must thus be relatively large. Also, the motor
83
, which activates the pump
81
, is formed relatively large to increase the output of the motor
83
. The motor
83
thus consumes a relatively large power supplied from a battery. Further, even when only the power steering device is operated, the motor
83
consumes the battery power by driving the pump
81
. This shortens durability of the battery.
FIG. 8
shows a hydraulic device described in Japanese Unexamined Patent Publication No. 56-23200. The hydraulic device has a tandem pump that includes a carriage pump
85
and a power steering pump
86
. The carriage pump
85
and the power steering pump
86
are driven by a motor
87
. The motor
87
is controlled by a controller
88
.
A pair of tilt cylinders
90
and a lift cylinder
89
actuate a carriage device. The tilt cylinders
90
are connected to the carriage pump
85
through a tilt valve
97
. The lift cylinder
89
is connected to the carriage pump
85
through a lift valve
98
. A power steering cylinder
91
is connected to the power steering pump
86
through a steering control valve
99
.
Since the motor
87
must drive the carriage pump
85
and the power steering pump
86
, the motor
87
is formed relatively large to increase the output of the motor
87
. This increases power consumption of the motor
87
.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide a hydraulic device for industrial vehicles that lowers power consumption while improving carriage performance.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, the invention provides a hydraulic device for an industrial vehicle that operates a carriage device and a traveling device by supplying the carriage device and the traveling device with hydraulic fluid discharged by a hydraulic pump driven by a motor.
The hydraulic device includes a first hydraulic pump for supplying the hydraulic fluid to the traveling device, a second hydraulic pump for supplying the hydraulic fluid to the carriage device, wherein the second hydraulic pump and the first hydraulic pump together form a tandem pump, a first motor for driving the first hydraulic pump and the second hydraulic pump, a third hydraulic pump for supplying the hydraulic fluid to the carriage device, wherein the third hydraulic pump is operated in accordance with an operation amount of the carriage device, and a second motor for driving the third hydraulic pump.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
REFERENCES:
patent: 3583585 (1971-06-01), Joyce
patent: 4076302 (1978-02-01), Sable
patent: 4164121 (1979-08-01), Houseman
patent: 5201629 (1993-04-01), Simpson et al.
patent: 5370494 (1994-12-01), Holmes et al.
patent: 5357624 (1978-05-01), None
patent: 56-84600 (1979-12-01), None
patent: 56-23200 (1981-03-01), None
patent: 8-301595 (1996-11-01), None
patent: 9110397 (1997-04-01), None
Nagata Hisao
Nakashima Seiji
Bratlie Steven A.
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Morgan & Finnegan , LLP
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