Expansible chamber devices – Relatively movable working members – Interconnected with common rotatable shaft
Reexamination Certificate
2001-06-11
2003-10-28
Look, Edward K. (Department: 3745)
Expansible chamber devices
Relatively movable working members
Interconnected with common rotatable shaft
C091S491000
Reexamination Certificate
active
06637313
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a rotary hydraulic device. In particular, the present invention relates to a hydraulic pump or motor including a rotor carrying a number of piston elements around its periphery, and a cam ring enclosing the rotor for causing the piston elements to move along a stroke length as the rotor rotates.
BACKGROUND OF THE INVENTION
Many industrial and automotive devices require a continuous supply of fluid, such as oil, fuel or hydraulic fluid, for proper operation. However, it is also desirable to be able to maintain or vary the delivery rate of the fluid as the application demands. To meet this need, two approaches have been taken:
1. a constant-capacity pump is driven by a prime mover, and the flow rate of the pump is varied by returning a portion of fluid from the output port of the pump back to the input port
2. a variable-capacity pump, including a fluid delivery piston, is driven by a prime mover, and the flow rate of the pump is altered by altering the stroke of the piston
The former approach makes inefficient use of the energy used to drive the pump since a portion of pressurized fluid is returned to the reservoir instead of performing useful work. On the other hand, the latter approach has been favoured because (1) variable-capacity pumps make more efficient use of energy, (2) the speed of the prime mover can vary without impacting on the flow rate of the variable-capacity pump, and (3) variable capacity pumps can alter their output flow rate more rapidly, in response to changes in operating conditions, than constant-capacity pumps.
The conventional variable-flow rotary pump comprises a hollow casing; a cam ring provided within the casing; and a rotor provided within the cam ring and being rotatably mounted about a fixed axis. The rotor includes a series of radial angularly-spaced fluid chambers disposed about its circumference, and a roller provided within each slot. The casing includes a fluid inlet port for delivering fluid to the fluid chambers, and a fluid outlet port for receiving pressurized fluid from the fluid chambers. Generally, the centre axis of the cam ring is displaced a distance from the fixed axis of the rotor. Consequently, as the rotor rotates, the volume of each fluid chamber will vary between minimum and maximum values as the respective roller moves between its innermost position and its outermost position. Further, the cam ring includes means for varying the position of the cam ring relative to the rotor. In one position, the centre of the cam ring is displaced a maximum distance from the fixed axis of the rotor, causing the communication time a fluid chamber of increasing volume is in communication with the inlet port to be maximized. In another position, the centre of the cam ring is displaced a minimum distance from the fixed axis of the rotor, causing the communication time a fluid chamber of increasing volume is in communication with the inlet port to be minimized. Consequently, the output flow rate of the pump can be varied between a maximum and a minimum value without varying the rotational speed of the rotor.
Numerous variations on the conventional variable-flow rotary pump have been developed. For instance, Wilcox (U.S. Pat. No. 3,381,622) teaches a variable-flow rotary pump having a constant output pressure. As shown in
FIG. 1
of the patent, the pump comprises a mounting plate
20
; a cavity body
30
mounted to the mounting plate
20
; a cavity ring
31
provided within the cavity body
30
; and a rotor
32
rotatably mounted about a fixed axis within the cavity ring
31
. The rotor
32
includes a series of radial angularly-spaced slots
33
, each including a pump roller
34
. The mounting plate
20
includes an arcuate fluid inlet port
62
and an arcuate fluid outlet port
63
aligned with the root circle of the roller slots
33
for respectively delivering fluid to and removing fluid from each slot
33
as the rotor
32
rotates. The pump also includes a leaf spring
110
, and a pressure conduit
91
coupled between the cavity ring
31
and the leaf spring
110
for reducing the eccentricity of the cavity ring (and hence the output pressure) as output pressure increases.
Bristow (U.S. Pat. No. 4,679,995) teaches avariable-flow rotary pump which is substantially similar to the variable-flow rotary pump taught by Wilcox, except that the cam ring
10
(equivalent to the cavity ring
31
) is rotatably coupled at one end and to a transversely-extending spring
23
at the opposite end for urging the cam ring
10
into a maximum pump flow position. At the same time, a portion of the pressurized output fluid exerts a force opposite to the force exerted by the spring
23
so as to reduce the output flow of the pump when the output pressure increases.
Maistreli (U.S. Pat. No. 3,642,388) teaches a variable-capacity vane pump whose output flow is continuously variable. As shown in
FIG. 2
of the patent, the vane pump comprises a hollow casing
1
including an inlet port
24
and an outlet port
25
; a cam ring
9
provided within the casing
1
; and a rotor
2
rotatably mounted about a fixed axis within the cam ring
9
. The rotor
2
includes a series of radial angularly-spaced notches
6
each including a cylindrical roller. The cam ring
9
is rotatably coupled to a roller
41
at one end, and to a hydraulically-operated piston
11
at the opposite end for urging the ring
9
between a maximum pump flow position and a minimum pump flow position in response to changes in hydraulic fluid pressure delivered to the piston
11
.
Hutson (U.S. Pat. No. 4,578,948) teaches a reversible-flow vane pump. As shown in FIGS.
3
,
4
and
5
of the patent, the pump comprises a pump case (not shown) including a first
76
and a second
78
; an annular cam ring
40
provided within the pump case and being pivotable about a pin
44
; and a rotor
20
rotatably mounted about a fixed axis within the cam ring
40
. The rotor
20
includes a series of equally-spaced circumferential outwardly-opening slots
32
, each including a roller vane
34
which engages the inner cam surface of the annular cam ring
40
.
In the operating mode shown in
FIG. 4
of the patent, the cam ring
40
is pivoted about pin
44
so as to increase the communication time a fluid chamber of increasing volume is in communication with the first port
76
and thereby cause a forward pump flow between ports
76
and
78
, whereas in the operating mode shown in
FIG. 5
, the cam ring
40
is pivoted in an opposite direction about pin
44
so as to increase the communication time a fluid chamber of increasing volume is in communication with the s econd port
78
and thereby cause a reverse flow between ports
76
and
78
without reversing the direction of rotation of the rotor
20
. In the operating mode shown in
FIG. 3
, the cam ring
40
is positioned so that the communication times of the fluid chambers in communication with the first port
76
is equal to the communication times of fluid chambers in communication with the second port
78
. Consequently, in this latter position, there is no net fluid flow between the ports
76
,
78
.
Delegard (U.S. Pat. No. 2,612,110) describes a variable flow rotary pump which comprises an oval cam ring, a rotor disposed within the cam ring and having a number of pockets each retaining a piston therein, and end plates having fluid inlet and outlet ports in communication with the outermost portion of the pockets.
Grupen (U.S. Pat. No. 2,880,677) describes a variable volume vane pump which includes a stator provided with a symmetric oval through-bore, diametrically-opposed inlet ports and diametrically-opposed outlet ports opening into the bore via the radially outermost portion of the bore, and a set of uniformly-spaced slots opening into the periphery of the rotor each carrying a sliding vane which projects into the bore.
Each of the foregoing variations has addressed deficiencies of the conventional variable-flow rotary pump. However, in each variation, differences in the fluid pressures of the fluid
Clark Hill PLC
Ker-Train Holdings Ltd.
Leslie Michael
Look Edward K.
LandOfFree
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