Fluid handling – Speed responsive valve control – With other condition responsive valve control
Reexamination Certificate
2001-06-18
2003-03-11
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Speed responsive valve control
With other condition responsive valve control
C137S102000
Reexamination Certificate
active
06530390
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure reducing valve. In particular, the present invention relates to a pressure reducing valve changing an output pressure in correspondence to an engine speed.
2. Description of the Related Art
The following means has been employed in a conventional construction vehicle such as a wheel loader, a bulldozer or the like.
A delivery flow amount of a pump is changed in correspondence to an operation amount of a pilot operating valve. The pilot operating valve reduces a pressure of a supplied pressurized oil in accordance with the operation amount and outputs the oil. In the case that it is intended to change the pump discharge flow amount in correspondence to the engine speed, the pressure of the pressurized oil supplied to the pilot operating valve is changed.
A hydraulic circuit mentioned above is shown, for example, in Japanese Laid-Open Patent Publication Nos. 49-71353 and 10-122363.
FIG. 5
shows an embodiment of a hydraulic circuit having the same function as that of a hydraulic circuit changing the supplied pressure to the pilot operating valve in correspondence to the engine speed, which is disclosed in the publication mentioned above. A variable displacement type pump
1
′ is connected to various kinds of actuators, for example, a traction motor of a vehicle, a cylinder and the like which are not illustrated. A displacement controller
4
′ of the variable displacement type pump
1
′ is connected to an output side of an output circuit
6
′ in an operating apparatus
5
′. A fixed orifice
8
′ is provided in a delivery pipe passage of a fixed displacement type pump
2
′. An upstream pressure of the fixed orifice
8
′ is increased in correspondence to the engine speed.
Accordingly, a differential pressure between front and rear of the fixed orifice
8
′ becomes larger in correspondence to the engine speed.
In this case, the pressure reducing valve inherently has a function of making an output pressure uniform. In the normal pressure reducing valve, the output pressure of the pressure reducing valve is made uniform due to a balance between an output side pressure P
1
′ and a spring
9
a
′ provided in the pressure reducing valve. When the balance of the force is changed, the output pressure is also changed. In this case, the pressure reducing valve can not, of course, output a pressure more than the supplied pressure.
The pressure reducing valve
7
′ shown in
FIG. 5
applies the differential pressure between front and rear of the fixed orifice
8
′ so as to change the output pressure, in addition to the balance. That is, an upstream pressure P
2
′ of the fixed orifice
8
′ is applied in a direction of a position (A)′ in
FIG. 5
so as to change the balance in such a manner as to increase the output pressure of the pressure reducing valve. A downstream pressure P
3
′ of the fixed orifice
8
′ is applied in a direction of a position (B)′ so as to change the balance in such a manner as to reduce the output pressure of the pressure reducing valve. The differential pressure between front and rear of the fixed orifice
8
′ is changed on the basis of the engine speed. That is, the force applied in the direction of the position (A)′ is increased in accordance with an increase of the engine speed, and the output pressure of the pressure reducing valve
7
′ becomes large.
In the hydraulic pressure shown in
FIG. 5
, when the engine speed is increased, the pressure P
1
′ supplied to the operating valves
6
a
′,
6
b
′ is increased. Accordingly, when the engine speed is increased, the maximum pressure output by the operating apparatus
6
′ is increased.
The output circuit of the operating apparatus
6
′ has a pair of pilot operating valves
6
a
′ and
6
b
′. Each of the pilot operating valves
6
a
′ and
6
b
′ is a pressure reducing valve, and changes the output pressure in correspondence to an amount of incline of the operating lever
5
a
′. The output pressure is zero at an illustrated neutral position. When the operating lever
5
a
′ is tilted in a direction of a, the pressure in correspondence to the amount of incline of the operating lever
5
a
′ is output via the pilot operating valve
6
a
′. At this time, in another pilot operating valve
6
b
′, the output pressure keeps zero.
The displacement controller
4
′ changes the displacement of the variable displacement type pump
1
′ in correspondence to the output pressure of the operating apparatus
6
′. In the hydraulic circuit shown in
FIG. 5
, it is designed such that the displacement of the variable displacement type pump
1
′ becomes maximum at the maximum output pressure of the operating apparatus
6
′ in a certain great area or more of the engine speed. Accordingly, when the engine speed is increased, the maximum displacement that the variable displacement type pump
1
′ can operate is increased.
FIG. 6
shows a change of the output pressure of the pressure reducing valve
7
′ in correspondence to the engine speed.
However, in the reducing control valve mentioned above, since the pressure supplied to the operating apparatus
6
′ is small in a low rotational speed area of the engine, the pressure P
5
′ output to the displacement controller
4
′ is also small even when the operating lever is largely operated. Accordingly, the displacement of the variable displacement type pump
1
′ is small and there is generated a case that the displacement is less than a necessary flow amount in the actuator.
An example is shown here. In the construction vehicle such as the wheel loader, the bulldozer or the like mentioned above, a plurality of working machines or traveling apparatuses are operated by the operating apparatus
6
′. When the engine speed is reduced for achieving a low speed travel, and the pressure P
1
′ supplied to the operating apparatus
6
′ is reduced in correspondence thereto so as to reduce the displacement of the variable displacement type pump
1
′, there may be a case that a flow amount of the traveling apparatus which does not require a large flow amount due to a low speed travel is sufficient but a flow amount applied to the working machine performing a work without relation to the traveling speed is insufficient.
Further, although an illustration is omitted, there is a requirement that a command pressure applied to the traveling apparatus of the vehicle is intended to be sufficiently secured for securing a vehicle speed and a traction force even in the case that the engine speed is reduced when the output pressure of the operating apparatus
6
′ shown in
FIG. 5
is used as the command pressure applied to the traveling apparatus of the vehicle. At this time, there may be a case that the command pressure can not be sufficiently secured in the hydraulic circuit employing the pressure reducing valve
7
′ shown in FIG.
5
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a pressure reducing valve which can reduce an engine speed and secure a minimum pressure.
In accordance with a main aspect of the invention, there is provided a pressure reducing valve consisting of a pressure reducing valve portion whose output pressure is uniform and a differential pressure responding portion comprising springs changing the output pressure of the reducing valve portion. Spring forces of the springs are adjusted by differential pressure between front and rear of a fixed orifice provided at a delivery pipe passage of a fixed displacement pump whose rotational speed is in correspondence to an engine speed. In this pressure reducing valve, the output pressure of the pressure reducing valve portion is changed in correspondence to an engine speed by the spring forces of the springs applied to a side in the pressur
Hori Shuuji
Nagura Shinobu
Bell Boyd & Lloyd LLC
Hepperle Stephen M.
Komatsu Limited
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