U.S. patent number 3,890,883 [Application Number 05/332,749] was granted by the patent office on 1975-06-24 for flow control arrangement for an axial piston pump.
This patent grant is currently assigned to Robert Bosch G.m.b.H.. Invention is credited to Paul Bosch, Gerhard Lutz, Eckehart Reichel, Walter Robeller, Werner Rometsch, Gerd Vohringer.
United States Patent |
3,890,883 |
Rometsch , et al. |
June 24, 1975 |
Flow control arrangement for an axial piston pump
Abstract
An axial piston pump has stationary and rotary control faces
formed with inlet and outlet ports, and with cylinder ports,
respectively, and a swash plate determining retracted and advanced
dead center positions of the pistons in an axial plane. The inlet
port has one end located closer to the plane in the region of the
retracted dead center position than half the circumferential
extension of each cylinder port so that each cylinder port
communicates with the inlet port also after the respective piston
has passed through the retracted dead center position and begins to
move toward the advanced dead center position. In this manner, the
respective cylinder is completely filled while the center of the
respective cylinder port moves an angle between 5.degree. and
20.degree. beyond the plane of the dead centers. The other end of
the inlet port may also be closer spaced from the plane of the dead
center positions than half the circumferential extension of each
cylinder port.
Inventors: |
Rometsch; Werner (Gerlingen,
DT), Robeller; Walter (Boblingen, DT),
Lutz; Gerhard (Faurndau, DT), Reichel; Eckehart
(Aschaffenburg-Schweinheim, DT), Bosch; Paul
(Ludwigsburg, DT), Vohringer; Gerd (Schwieberdingen,
DT) |
Assignee: |
Robert Bosch G.m.b.H.
(Stuttgart, DT)
|
Family
ID: |
5837041 |
Appl.
No.: |
05/332,749 |
Filed: |
February 15, 1973 |
Foreign Application Priority Data
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Feb 25, 1972 [DT] |
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2208890 |
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Current U.S.
Class: |
91/499 |
Current CPC
Class: |
F04B
1/2021 (20130101) |
Current International
Class: |
F04B
1/20 (20060101); F04b 013/04 () |
Field of
Search: |
;91/475,6.5,487,499
;417/269 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Freeh; William L.
Attorney, Agent or Firm: Striker; Michael S.
Claims
We claim:
1. Flow control arrangement for an axial piston pump, comprising
cylinder body means having an axis, cylinders arranged in a circle
about said axis, and pistons in said cylinders; housing means
including a swash plate engaged by said pistons, one of said means
being rotatable relative to the other means about said axis so that
each piston is axially advanced and retracted by said swash plate
between advanced and retracted dead center positions located in an
axial plane; said cylinder body means having a first control face
formed with a circular row of cylinder ports communicating with
said cylinders, respectively, and said housing means having a
second control face formed with a part-circular continuous inlet
port and a part-circular continuous outlet port, respectively
located on opposite sides of said plane, said inlet and said outlet
port being the only ports formed in said second control face, said
first and said second control faces cooperating during rotation so
that said inlet and outlet ports are swept by said cylinder ports,
said inlet port being longer than said outlet port and having one
end located closer to said plane in the region of said retracted
dead center position than half of the circumferential extension of
each cylinder port so that each cylinder port communicates with
said one end of said inlet port also after the respective piston
has passed through said retracted dead center position and begins
to move towards said advanced dead center position whereby the
respective cylinder is completely filled while the center of the
respective cylinder port moves a predetermined angle beyond said
plane.
2. Flow control arrangement as claimed in claim 1 wherein said
predetermined angle is between 5.degree. and 20.degree..
3. Flow control arrangement as claimed in claim 1 wherein said
inlet port has the same radius and radial width as said cylinder
ports; wherein said inlet port has at said one end a control edge
extending across the full radial width of said one end of said
inlet port; wherein each cylinder port has a trailing control edge
substantially coinciding with said control edge over the radial
width of said one end of said inlet port when the respective
cylinder port has moved through said predetermined angle and
separates from said inlet port.
4. Flow control arrangement as claimed in claim 3 wherein said
control edge at said one end of said inlet port is convex, and said
trailing control edges of said cylinder ports are concave and
coincide with said control edge of said inlet port when the
respective cylinder port separates from said inlet port.
5. Flow control arrangement as claimed in claim 3 wherein said
predetermined angle is between 5.degree. and 20.degree..
6. Flow control arrangement as claimed in claim 3 wherein said
control edge at said one end of said inlet port is straight and
extends in radial direction.
7. Flow control arrangement as claimed in claim 4 wherein said
trailing control edges of said cylinder ports are straight and
extend in radial direction.
8. Flow control arrangement as claimed in claim 1 wherein said
inlet port has an other end located closer to said plane in the
region of said advanced dead center position than half the
circumferential extension of each cylinder port so that each
cylinder port communicates with said other end of said inlet port
while moving an other predetermined angle before the respective
piston passes through said advanced dead center position.
9. Flow control arrangement as claimed in claim 8 wherein said
other predetermined angle is between 5.degree. and 10.degree..
10. Flow control arrangement as claimed in claim 9 wherein said
predetermined angle in the region of said retracted dead center
position is between 5.degree. and 20.degree..
Description
BACKGROUND OF THE INVENTION
The present invention relates to axial piston pumps of the type
provided with a rotary cylinder body in which pistons are mounted
for axial reciprocation under the control of a swash plate. In
axial piston machines of this type, a stationary control face with
part-circular inlet and outlet ports, cooperates with a rotary
control face provided with cylinder ports which sweep the
part-circular inlet and outlet ports to fill the cylinders with
fluid, and to discharge the fluid again from the filled
cylinders.
An axial piston pump of this type is disclosed in the U.S. Pat. No.
2,299,933. In this pump, the control ports are asymmetrically
arranged to an axial plane passing through the dead center
positions of the pistons. The cylinder ports are connected with the
low pressure port only when the advanced dead center position has
been passed by the cylinder ports, and the piston has begun to move
toward the retracted dead center position. The moment at which the
cylinder ports are provided with fluid from the inlet port, is
delayed relative to the moment at which the respective piston is in
its advanced dead center position. The separation of a cylinder
port from the inlet port takes place exactly in the retracted dead
center position.
The arrangement serves the purpose of preventing pressure
oscillation and mechanical oscillations in the pump by permitting
afterexpansion and precompression of the cylinders before the
cylinder ports are provided with fluid. However, it has been found
that at very high rotary speeds, using small flow cross-section, it
is not possible to fill a cylinder in the available time during
which each of the cylinder ports communicates with the low pressure
inlet port. When the cylinders are then filled with high pressure
fluid, the efficiency is reduced, noise is produced, and cavitation
takes place at the control faces.
SUMMARY OF THE INVENTION
It is one object of the invention to provide an axial piston pump
in which even at very high rotary speed, the cylinders are well
filled due to the construction of the control faces so that upon
connection of the high pressure port, the backflow into the
cylinder is limited to the volume required for compressing the
fluid in the cylinders to the desired pumping pressure. This result
is obtained by the invention by providing an opening angle in which
each of the cylinder ports which communicate with the low pressure
control port, extends at least 5.degree. beyond the angular
position determined by the retracted dead center position.
This has the advantage that the cylinder chamber is already reduced
before the disconnection of the low pressure control port from the
already advancing piston, so that all cylinder spaces which are
still empty, are filled. Furthermore, the increased opening angle
has the result that an equalizing flow can take place which obtains
a better filling of the cylinder space by using the kinetic energy
of the fluid medium entering the cylinder chamber.
In a preferred embodiment, the radial control edges of the cylinder
ports and of the low pressure port, coincide at the moment of
separation, and extend over the full radial width of the respective
ports in the moment of separation. This has the result that the
greatest possible flow cross-section is available until the
respective cylinder port separates from the low pressure inlet
port.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims. The
invention itself, however, both as to its construction and its
method of operation, together with additional objects and
advantages thereof, will be best understood from the following
description of specific embodiments when read in connection with
the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a longitudinal axial sectional view illustrating an axial
piston pump;
FIG. 2 is a cross-sectional view taken along line II--II in FIG.
1;
FIG. 3 is a fragmentary end view illustrating a modified
construction of the control ports;
FIG. 4 is a fragmentary end view illustrating another modified
construction of the control ports; and
FIG. 5 is an end view illustrating a control face according to FIG.
2, but modified.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, an axial piston pump has a pot-shaped
housing 1 with an interior 2 closed by a cover 3 at one end while
the other end is closed by the bottom wall of the pot-shaped
housing 1. Bearings 4 and 5 are mounted in the interior 2 of the
housing, bearing 4 being located in the bottom region, and bearing
5 mounted in the cover 3. A shaft 6 is mounted in the bearings 4
and 5 and has one end projecting through cover 3 to the outside for
connection with a drive motor, if the machine is the operated as a
pump. The interior of housing 1 is sealed by sealing means 7.
Shaft 6 has near bearing 5, a flange projection with peripheral
grooves and recesses 9 engaging corresponding grooves and recesses
in a collar portion 12 of the rotary cylinder body 10, so that
cylinder body 10 is connected for rotation with shaft 6.
Cylinder body 10 has a central bore 11 in which the drive shaft 6
is located. The rotary cylinder body 10 and shaft 6 rotate about an
axis to which a circular row of cylinders 14 is concentric. Each
cylinder has a port 31 opening on the rotary control face 26 of the
cylinder body 10, as best seen in FIG. 2.
A piston 15 is guided in each cylinder 14 for reciprocating
movement, and the ends of each piston 14 are provided with a ball
head 16 mounted in a spherical seat 17 of a slide shoe 18 at whose
end face, a hydrostatic bearing 19 is provided which receives
pressure fluid through a passage 16a in the head 16. The slide
shoes 18 slidingly engage on rotation of the cylinder body, a swash
plate 20 which is fixedly mounted in the housing and has a central
opening through which the drive shaft 6 passes. A holding ring 21,
holds the slide shoes 18 in sliding contact with the surface of the
swash plate 20.
A pressure ring 22 which has a part-spherical outer surface engages
with the same an inner part-spherical surface of the holding ring
21. Pressure ring 22 has a planar surface confronting the cylinder
body 10, and abutting an axial face on the collar 12 of the
cylinder body 10. A spring 23 is mounted in an annular chamber
formed by bore 11 and shaft 6, and abuts by means of rings 24, 25
on the flange 8 of shaft 6, and on a surface of the cylinder body
10, respectively.
The rotary control face 26 of cylinder body 10 is provided at the
end of the cylinder body 10 remote from the swash plate 20, and
slidingly abuts a control face 27 of a valve plate 28 which is
secured to the bottom wall of housing 1, and may be integral with
the same. The control valve plate 28 and its control face 27 is
provided with part-circular diametrically arranged inlet and outlet
ports 29 and 30 which are connected with the inlet 129 and outlet
130, respectively.
During rotation of the rotary cylinder body 10, the fluid medium
enters some of the cylinders 14 through the inlet port 29 and
cylinder ports 31, and is discharged through other cylinder ports
31 and outlet port 30.
As best seen in FIG. 2, the cylinder ports 31 have the same radial
width as the low pressure inlet port 29, and the high pressure
outlet port 30, and are spaced the same radial distances from the
axis of shaft 6. It is apparent that the cylinder port 31, shown in
chain lines in FIG. 2, will, during rotation of the cylinder body
10, first sweep the end 29b and latter the end 29a of the inlet
port 29. Each cylinder port 31 has inner and outer edges forming
part of circles whose center is located in the axis of shaft 6, and
circumferential ends 32 and 33 which are small circles having a
diameter corresponding to the radial width of the control ports 29
and 30.
As shown in FIG. 2, the inlet port 29 and the outlet port 30 are
diametrically arranged, but not symmetrical to the axial plane 34
in which the retracted dead center position 34a and the advanced
dead center position 34b are located. The angular region in which
each of the cylinder ports 31 is connected with the low pressure
port 29, is displaced between 5.degree. and 20.degree. beyond the
retracted dead center position 34a. The cylinder port 31 is shown
in chain lines in FIG. 2 in the position in which the communication
between the cylinder port and the low pressure inlet port 29 is
interrupted. In this position, the center of the cylinder port 33
is not located in the plane 34, but angularly spaced therefrom, and
when the cylinder port 33 was located with a center in the plane
34, the control edges 32 and 29a overlapped to establish
communication which is maintained until the position shown in FIG.
2 is reached during further clockwise rotation.
The end and control edge 29a is located closer to the plane 34 in
the region of the retracted dead center position 34a than half the
circumferential extension of each cylinder port 31, so that each
cylinder port 31 communicates with the end 29a of the inlet port 29
also after the respective piston has passed through the retracted
dead center position 34a and begins to move toward the advanced
dead center position 34b. In this manner, the respective cylinder
15 is completely filled while the center of the respective cylinder
port 34 moves a predetermined angle A beyond the plane 34.
Due to the angular displacement of the low pressure inlet port 29
relative to the plane of symmetry 34, the cylinder space 14 is
connected by cylinder port 31 so long with the low pressure side of
the pump until piston 15 has moved beyond the retracted dead center
position an angle between 5.degree. and 20.degree., and has started
its discharging motion. The result is that unsufficiently filled
empty spaces in cylinder 14 are filled by fluid medium displaced by
the pistons after moving through plane 34. Furthermore, a time
period remains in which the kinetic energy of the fluid flowing
from the low pressure inlet port into the pump can be used for
better filling the cylinders.
The arrangement according to the invention described above
considerably improves the suction efficiency of the pump, assures
an extension of the span of life of the machine by avoiding
cavitational damage, and has a favorable influence on the
suppression of noise.
In accordance with the further improvement of the invention shown
in FIG. 3, the cylinder ports 31' have control edges 32' which
coincide with the control edge 29a' of the control port 29' along
the entire radial width of the control ports 29' and 31'. The
control edge 32' is part circular and inward concave, and the
control edge 29a' of the low pressure port 29' is convex, and has
the same curvature so that when cylinder port 31' turns farther to
the right during rotation in clockwise direction, the control edges
32' and 29a' fully coincide, and then sudden separation of the
communication between the cylinder port 31' and the low pressure
port 29' takes place. Shortly before the interruption of the flow
through control ports 29', 31', the entire cross section of low
pressure control port 29' is available, contrary to the arrangement
shown in FIG. 2 in which the flow cross section of both control
ports 31 and 29 are reduced before separation takes place
communication between control ports 29 and 31 is cut off.
The large flow cross section until the moment of separation takes
place, is favorable for the filling of the cylinders, since it has
been found that irrespective of low piston speeds, the flow speed
and thereby also the suction resistance are great in the
construction of the control port 31, 29 shown in FIG. 2.
FIG. 4 illustrates another modification in which the cylinder port
31" has a straight radially extending control edge 32", cooperating
with a straight radially extending control edge 29a" of the low
pressure port 29". The control edges 29a" and 32" coincide at the
moment of separation of cylinder port 31" from low pressure port
29", so that the complete flow cross section is available for
communication before this moment.
FIG. 5 shows a modification of FIG. 2, the cooperation between the
cylinder ports 31 and the low pressure port 29 being the same as in
FIG. 2. It will be noted that the end 49a of the inlet port 49 is
more closely adjacent the plane 34 in the region of the retracted
dead center position than half the circumferential width of the
cylinder port 31, not shown in FIG. 5 at the end 49a. The ends 50a
and 50b of the high pressure ports 50 are spaced the same
circumferential distances from the plane 34, but the end 49b of the
inlet port 49 is located closer to the plane 34 in the region of
the advanced dead center position 34b. The angle in which the
cylinder port 31 communicates with the low pressure port 49 is
increased, and the moment of communication between the cylinder
port 31 and the end 49b of the low pressure port 49 starts about
5.degree. earlier. The end 50b of the high pressure port 50 is
correspondingly shortened. Due to the extension of the end 49b
toward the plane 34, the angular region in which the cylinder ports
communicate with the low pressure port is substantially increased
as compared with the arrangement of FIG. 2. The extension of the
end 49b toward the plane 34 in the region of the advanced dead
center position obtains at the low inlet pressures in the region of
high rotary speeds, good filling of the cylinders 14, although the
acceleration rate cannot be fully obtained in the region of the
highest piston speed.
Evidently, the constructions of the control edges shown in FIG. 3
and FIG. 4 can be applied to the arrangement of FIG. 5.
It will be understood that each of the elements described above, or
two or more together, may also find a useful application in other
types of flow control arrangement for an axial piston pump
differing from the types described above.
While the invention has been illustrated and described as embodied
in an arrangement in which the low pressure inlet port of an axial
piston machine is extended toward the plane in which the dead
center positions of the pistons are located in order to obtain
better filling of the cylinder chambers, it is not intended to be
limited to the details shown, since various modifications and
structural changes may be made without departing in any way from
the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can by applying current
knowledge readily adapt it for various applications without
omitting features that, from the standpoint of prior art, fairly
constitute essential characteristics of the generic or specific
aspects of this invention and, therefore, such adaptations should
and are intended to be comprehended within the meaning and range of
equivalence of the following claims.
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims.
* * * * *