Pumps – Diverse pumps
Reexamination Certificate
2000-08-24
2001-04-17
Freay, Charles G. (Department: 3746)
Pumps
Diverse pumps
C417S269000, C092S071000
Reexamination Certificate
active
06217289
ABSTRACT:
This invention relates to axial piston pumps and more particularly to the combination of an axial piston pump with an auxiliary pump mounted thereto.
INCORPORATION BY REFERENCE
The parent patent application Ser. No. 09/553,285 is hereby incorporated by reference in its entirety both for the description of the axial piston pump disclosed therein, specifically the valving employed therein, and to which this invention is an improvement thereof and for the HEUI pump application disclosed therein because this invention has particular application for use in an HEUI system.
BACKGROUND
Conventional axial piston pumps (i.e., “Thoma” pump) are often used in high pressure applications. For example, in a hydraulically actuated electronically controlled united injector (HEUI) fuel control system, a high pressure, axial piston oil pump typically supplies the diesel injectors with 3,000-4,000 psi engine oil for hydraulic operation. This high pressure oil pump is charged with low pressurized fluid from another pump, typically the engine's oil pump. Conventionally, an auxiliary pump, the engine's fuel pump, is driven by the HEUI pump. The fuel pump transfers fluid from the fuel tank to the injectors for consumption by the engine and typically pumps at approximately 20-50 psi.
In many of these applications, the high pressure pump also drives a low pressure pump. A typical arrangement is illustrated in prior art
FIG. 1
in which an input shaft
10
is splined to a rotatable cylinder
12
having circumferentially spaced bores containing pistons
13
. One end of each piston is ball shaped and received in a socket receptacle formed as a slipper
14
which, in turn, contacts an end face of a stationary swash plate
15
. Rotation of Input shaft
10
rotates cylinder
12
to cause pistons
13
to axially reciprocate in their bores by slipper contact with swash plate
15
while fluid intake and exhaust of pressurized fluid is through conventional kidney shaped intake/outtake ports
16
. Press fitted onto the tail end of input shaft
10
is a cam
18
which acts as an eccentric to drive a prime mover
19
of an auxiliary pump
20
.
In vehicular applications, space is at a premium and is often a determining factor in the OEM's selection process, especially for mature technologies such as that embodied in an axial piston pump. In the arrangement illustrated in
FIG. 1
, the addition of auxiliary pump
20
onto the tail end of input shaft
10
increases the length of the pump assembly. A more subtle point is that an eccentric lift is provided at a tail extension of the input shaft which requires that the input shaft be soundly journaled so as not only to unduly transmit loads to the high pressure pump but also to insure against any axial run out of the shaft which could potentially adversely affect the smoothness of the lift motion of prime mover
19
, especially if cam
18
wears. In the prior art pump of
FIG. 1
, front and rear ball bearings
21
journal input shaft
10
and internal and external retainer rings
22
,
23
(lubricated) prevent shaft run out. The
FIG. 1
arrangement has proven to be durable and commercially acceptable. Its length, however, is increased by auxiliary pump
20
and its cost must reflect the bearing arrangement.
In SAE Technical Paper 2000-01-0687, entitled “Development of a Variable-Displacement, Rail-Pressure Supply Pump for a Dimethyl Ether” by James C. McCandless, Ho Teng and Jeffrey B. Schneyer presented Mar. 6-9 2000, an axial piston pump is disclosed in which, like the parent application, a rotating swash plate/stationary cylinder is disclosed. In the pump disclosed in the SAE paper, the circumferential edge of the swash plate is used to control valving to the axial piston pump. Like
FIG. 1
, the input shaft of the SAE disclosed pump is journaled in ball bearings. Additionally, springs in the piston bores are used to maintain slippers in contact with the swash plate.
SUMMARY OF THE INVENTION
Accordingly, it is a principal object of the present invention to provided an axial piston pump configuration which allows for inclusion of an auxiliary pump without increasing axial pump length while minimizing cost of the pump.
This object along with other features of the invention is achieved in a pump assembly which includes an axial piston pump having a swash plate rotatable by an input shaft and a non-rotatable cylinder containing a plurality of axially movable pistons having spherical ends extending through the cylinder journaled in slipper assemblies that are in contact with the swash plate. A retainer plate in contact with the slipper assemblies is spring biased to urge the slippers against the swash plate to maintain the swash plate in fixed axial position and permit smooth swash plate rotation not withstanding varying force pulsations attributed to fluid pressure in the piston bores during pump operation. The swash plate has a cam shaped circumferential edge surface. An auxiliary pump having a prime mover in contact with the cam shaped edge of the swash plate is mounted between the axial ends of the piston pump whereby the length of the piston pump assembly is maintained constant.
In accordance with another aspect of the invention, the swash plate has one axial end generally perpendicular to the longitudinal centerline of the input shaft and an opposite swash end inclined at an angle to the longitudinal centerline with the cam edge extending between the swash plate ends. The piston pump has a housing containing a cylindrical shaft inlet passage at one axial end terminating in an intermediate or swash plate chamber containing the swash plate. The intersection of the intermediate chamber and the inlet passage defines an annular seat surface and a Teflon coated thrust plate between the annular seat surface and the axial end of the swash plate functions as a thrust bearing allowing swash plate rotation without grapping or seizing resulting in smooth operation of the secondary pump. The input shaft is only journaled within a similar, Teflon coated sleeve bearing pressed into the cylindrical shaft inlet passage thus eliminating bearing assemblies and retainer rings and the like.
It is thus an object of the present invention to provide an axial piston pump capable of driving an auxiliary pump without increasing the axial length of the pump.
It is another object of the invention to provide an axial piston pump which journals the input shaft and swash plate without the need for bearing assemblies, bearing races, retainer rings and the like.
It is another object of the invention to provide the combination of a high pressure axial piston pump and a low pressure pump ideally suited for HEUI and like applications.
It is yet another object of the invention to provide a low cost axial piston pump especially suited for driving an auxiliary pump.
These and other features, objects and advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the Detailed Description of the Invention set forth below.
REFERENCES:
patent: 3450058 (1969-06-01), Stein
patent: 5191867 (1993-03-01), Glassey
patent: 5515829 (1996-05-01), Wear et al.
patent: 5784949 (1998-07-01), Ryken et al.
patent: 5788469 (1998-08-01), Novacek et al.
patent: 5862704 (1999-01-01), Seljestad
patent: 5957111 (1999-09-01), Rodier
patent: 6092998 (2000-07-01), Dexter et al.
SAE Technical Paper 2000-01-0687, entitled “Development of a Variable-Desplacement, Rail-Pressure Supply Pump for a Dimethyl Ether” by James C. McCandless, Ho Teng and Jeffrey B. Schneyer presented Mar. 6-9, 2000.
Freay Charles G.
Nawalanic Frank J.
The Rexroth Corporation
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