Variable displacement pump

Details Variable displacement pump Variable displacement pump

1999-12-06

2001-04-17

Walberg, Teresa (Department: 3742)

Pumps

With condition responsive pumped fluid control

Pressure responsive relief or bypass valve

C418S026000, C417S220000

Reexamination Certificate

active

06217296

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a variable displacement pump used in, e.g., a pressure fluid utilizing device such as a power steering device for decreasing the force required to operate the steering wheel of a vehicle.
As a pump for a power steering device of this type, a displacement vane pump directly driven to rotate by a vehicle engine is used. In this displacement pump, the discharge flow rate increases or decreases in accordance with the rotational speed of the engine. A power steering device requires an auxiliary steering force which increases while the vehicle is stopped or is traveling at a low speed and decreases while the vehicle is traveling at a high speed. The characteristics of the displacement pump must be contradictory to this auxiliary steering force. Accordingly, a displacement pump having a large volume must be used so that it can maintain a discharge flow rate necessary to produce a required auxiliary steering force even during low-speed driving with a low rotational speed. For high-speed driving with a high rotational speed, a flow control valve that controls the discharge flow rate to a redetermined value or less is indispensable. For these reasons, the number of constituent components relatively increases, and the structure and path arrangement are complicated, inevitably leading to an increase in entire size and cost.
In order to solve these inconveniences, variable displacement vane pumps each capable of decreasing the discharge flow rate per revolution (cc/rev) in proportion to an increase in rotational speed are proposed in, e.g., Japanese Patent Laid-Open Nos. 56-143383 and 58-93978, U.S. Pat. Nos. 5,538,400, 5,518,380, and 5,562,432, and the like. According to these variable displacement pumps, a flow control valve provided to the displacement pump is unnecessary. The driving power can be decreased to provide an excellent energy efficiency.
An example of such a variable displacement vane pump will be described briefly with reference to
FIG. 16
showing the pump structure in, e.g., U.S. Pat. No. 5,562,432 or the like. Referring to
FIG. 16
, reference numeral
1
denotes a pump body;
1
a,
an adapter ring; and
2
, a cam ring. The cam ring
2
is free to swing in an elliptic space
1
b,
formed in the adapter ring
1
a
of the pump body
1
, through a swing fulcrum pin
2
a
serving as a support shaft. A spring means (compression coil spring
2
b
) biases the cam ring
2
to the left in FIG.
16
.
A rotor
3
is accommodated in the cam ring
2
to be eccentric on one side to form a pump chamber
4
on the other side. When the rotor
3
is rotatably driven by an external drive source, vanes
3
a
held to be movable forward/backward in the radial direction are projected and retracted. Reference numeral
3
b
denotes a driving shaft of the rotor
3
. The rotor
3
is driven by the rotating shaft
3
b
to rotate in a direction indicated by an arrow in FIG.
16
. In the following description, the pump chamber
4
is a space formed in the cam ring
2
on one side of the rotor
3
to have an almost crescent-like shape, and extends from a suction opening
7
(to be described later) to a discharge opening
8
.
First and second fluid pressure chambers
5
and
6
are formed on two sides around the cam ring
2
in the elliptic space
1
b
of the adapter ring
1
a
set in the pump body
1
, and serve as high- and low-pressure chambers, respectively. Paths
5
a
and
6
a
are open to the chambers
5
and
6
, respectively, through a spool type control valve
10
(to be described later), to guide as the control pressure for swinging the cam ring
2
the fluid pressures obtained upstream and downstream of a metering restrictor formed in a pump discharge path
11
.
In this example, a variable metering restrictor
12
is formed of a hole
12
a
formed in the side wall surface of the pump body
1
that forms the second fluid pressure chamber
6
, and a side edge
12
b
of the cam ring
2
that moves to change the opening area by selectively covering the hole
12
a.
For this reason, the second fluid pressure chamber
6
is under the fluid pressure obtained downstream of the variable metering restrictor
12
. This fluid pressure is guided to the low-pressure chamber of the control valve
10
through the path
6
a.
Reference numeral
13
denotes a pump discharge path formed downstream of the variable metering restrictor
12
.
In
FIG. 16
, a pump suction opening (suction port)
7
is formed to oppose a pump suction region
4
A of the pump chamber
4
. A pump discharge opening (discharge port)
8
is formed to oppose a pump discharge region
4
B of the pump chamber
4
. These openings
7
and
8
are formed in at least corresponding ones of a pressure plate and a side plate (not shown) serving as stationary wall portions for holding pump constituent elements composed of the rotor
3
and cam ring
2
by sandwiching them from two sides.
The cam ring
2
is biased by the compression coil spring
2
b
from the fluid pressure chamber
6
and is urged in a direction to keep the volume (pump volume) in the pump chamber
4
maximum. A seal member
2
c
is placed in the outer surface portion of the cam ring
2
to define the fluid pressure chambers
5
and
6
, together with the swing fulcrum pin
2
a,
on the right and left sides.
The spool type control valve
10
is actuated by differential pressures P
1
and P
2
obtained upstream and downstream of the variable metering restrictor
12
serving as a metering orifice and formed between the pump discharge paths
11
and
13
. The control valve
10
introduces a fluid pressure P
3
corresponding to the magnitude of the pump discharge flow rate to the high-pressure fluid pressure chamber
5
outside the cam ring
2
, to maintain a sufficiently large flow rate even immediately after the pump is started.
More specifically, as described above, when the fluid pressures obtained upstream and downstream of the variable metering restrictor
12
between the pump discharge paths
11
and
13
are controlled by the control valve
10
and guided into the fluid pressure chambers
5
and
6
on two sides of the cam ring
2
, the cam ring
2
is swung in a required direction, as indicated by a solid arrow or a white arrow in
FIG. 16
, to change the volume of the pump chamber
4
, so that the discharge flow rate can be controlled to match the pump discharge flow rate, as shown by the flow rate curve of FIG.
17
. Also, flow rate control can be performed as follows. As the rotational speed of the pump increases, the discharge flow rate can be raised to a predetermined value, and this state is maintained. When the rotational speed of the pump is in a high speed range, the flow rate is decreased.
FIG. 16
described above shows a state that takes place from region A to B in FIG.
17
. When the rotational speed of the pump reaches a predetermined value or more, the difference between the fluid pressures obtained upstream and downstream of the variable metering restrictor
12
increases. As a result, the cam ring
2
swings to the right (a direction indicated by a solid arrow) in
FIG. 16
to restrict the variable metering restrictor
12
. The discharge flow rate of the pump decreases in accordance with the restriction amount. When the variable metering restrictor
12
is restricted to the minimum position, the pump discharge flow rate is maintained at the predetermined value, as indicated in a region C.
While the pressure fluid utilizing device (for example, the power cylinder of the power steering device and indicated by PS in
FIG. 16
) is actuated to apply a load, when the differential pressures obtained upstream and downstream of the variable metering restrictor
12
become equal to or higher than a predetermined value, the control valve
10
introduces the fluid pressure P
1
obtained upstream of the variable metering restrictor
12
as a control pressure to the high-pressure fluid pressure chamber
5
outside the cam ring
2
, to prevent swing of the cam ring
2
.
The pump body
1
is formed with a pump suct

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