U.S. patent application number 11/356157 was filed with the patent office on 2007-08-16 for liquid pump.
This patent application is currently assigned to Campbell Hausfeld/Scott Fetzer Company. Invention is credited to Brian D. Holt.
Application Number | 20070189911 11/356157 |
Document ID | / |
Family ID | 38368698 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070189911 |
Kind Code |
A1 |
Holt; Brian D. |
August 16, 2007 |
Liquid pump
Abstract
A housing of a pump apparatus includes an undivided cavity, an
inlet valve through which liquid can enter the cavity, and an
outlet valve through which the liquid can exit the cavity. A
primary piston is configured to reciprocate in the cavity to draw
the liquid into the cavity through the inlet valve during an intake
stroke of the piston and discharge the liquid out of the cavity
through the outlet valve during a delivery stroke. A reservoir
structure is configured to add, to the total volume of the cavity,
an extra volume that is a smooth positive function of liquid
pressure in the cavity.
Inventors: |
Holt; Brian D.; (Mount
Juliet, TN) |
Correspondence
Address: |
PATENT GROUP 2N;JONES DAY
NORTH POINT, 901 LAKESIDE AVENUE
CLEVELAND
OH
44114
US
|
Assignee: |
Campbell Hausfeld/Scott Fetzer
Company
|
Family ID: |
38368698 |
Appl. No.: |
11/356157 |
Filed: |
February 16, 2006 |
Current U.S.
Class: |
417/543 |
Current CPC
Class: |
F04B 49/16 20130101;
F04B 49/121 20130101 |
Class at
Publication: |
417/543 |
International
Class: |
F04B 11/00 20060101
F04B011/00 |
Claims
1. A pump apparatus comprising: a housing having a cavity, an inlet
valve through which liquid can enter the cavity, and an outlet
valve through which the liquid can exit the cavity; a primary
piston configured to reciprocate in the cavity to draw tie liquid
into the cavity through the inlet valve during an intake stroke of
the piston and discharge the liquid out of the cavity through the
outlet valve during a delivery stroke of the piston; and a
reservoir structure configured to add, to the total volume of the
cavity, an extra volume that is a smooth positive function of
liquid pressure in the cavity.
2. The apparatus of claim 1 wherein the reservoir structure
includes a secondary piston configured to retract by a displacement
distance that is a smooth positive function of the liquid
pressure.
3. The apparatus of claim 2 wherein the extra volume equals the
displacement distance times a cross-sectional area of the
piston.
4. The apparatus of claim 2 wherein the retraction of the secondary
piston is along an axis perpendicular to the direction of the
reciprocation of the primary piston.
5. The apparatus of claim 4 wherein the axis extends through the
primary piston at some point during the reciprocation.
6. The apparatus of claim 4 wherein the primary piston extends over
and beyond the secondary piston at some point during the
reciprocation.
7. The apparatus of claim 2 further comprising a spring structure
against which the liquid pressure acts to retract the secondary
piston, with a spring constant that increases with increasing
retraction of the secondary piston.
8. The apparatus of claim 1 wherein the reservoir structure is
configured for all the liquid accumulated in the extra volume
during the delivery stroke to be returned to the cavity during the
following intake stroke.
9. The apparatus of claim 1 wherein the extra volume is located in
the primary piston.
10. The apparatus of claim 1 wherein the reservoir structure is
configured for the amount of the liquid discharged during the
delivery stroke to be less than if the extra volume did not
exist.
11. The apparatus of claim 10 wherein the reservoir structure is
configured to render a liquid delivery rate that is inversely
related to output pressure of the pump.
12. The apparatus of claim 11 wherein the delivery rate is
approximately inversely proportional to the output pressure.
13. The apparatus of claim 1 further comprising a source of the
liquid connected to the inlet valve, and a liquid spray nozzle
connected to the outlet valve.
14. A pump apparatus comprising: a housing having a cavity, an
inlet valve through which liquid can enter the cavity, and an
outlet valve through which the liquid can exit the cavity; a
primary piston configured to reciprocate in the cavity to draw the
liquid into the cavity through the inlet valve and discharge the
liquid out from the cavity through the outlet valve; and a
cylindrical chamber defined by the housing and communicating with
the cavity; a secondary piston configured to retract within the
chamber in response to an increase in liquid pressure in the cavity
so as to add an extra volume that, throughout the entire range of
retraction of the secondary piston, is limited to the space vacated
by the secondary piston as the secondary piston retracts.
15. The apparatus of claim 14 configured for all the liquid
accumulated in the extra volume during the delivery stroke to be
returned to the cavity during the following intake stroke.
16. The apparatus of claim 14 wherein the retraction of the
secondary piston is along an axis perpendicular to the direction of
the reciprocation of the primary piston.
17. A pump apparatus comprising: a housing having a primary
chamber, an inlet valve through which liquid can enter the primary
chamber, and an outlet valve through which the liquid can exit the
primary chamber; a primary piston configured to reciprocate in the
primary chamber to draw the liquid into the primary chamber through
the inlet valve during an intake stroke of the piston and discharge
the liquid out of the primary chamber through the outlet valve
during a delivery stroke of the piston; and a reservoir volume
consisting of a single variable-volume space that is continuously
open to the primary chamber and configured to increase in response
to an increase in liquid pressure in the primary chamber.
18. The pump of claim 17 further comprising a secondary piston
configured to vary the volume of the space by retracting in
response to the increase in the liquid pressure.
19. A pump apparatus comprising: a housing having a cavity, an
inlet valve through which liquid can enter the cavity, and an
outlet valve through which the liquid can exit the cavity; a
primary piston configured to reciprocate in the cavity to draw the
liquid into the cavity through the inlet valve during an intake
stroke of the piston and discharge the liquid out of the cavity
through the outlet valve during a delivery stroke of the piston;
and a reservoir structure configured to receive a portion of the
liquid from the cavity during the delivery stroke and to return the
entire received portion back to the cavity during the following
intake stroke.
20. The apparatus of claim 19 wherein the reservoir structure is
configured to yield a liquid delivery rate that is inversely
related to output pressure of the pump.
Description
TECHNICAL FIELD
[0001] This application relates to liquid pumps.
BACKGROUND
[0002] A liquid pump includes a piston that reciprocates in a
cylindrical cavity. The piston draws liquid through an inlet valve
into the cavity during an intake stroke and forces the liquid out
of the cavity through an outlet valve during a delivery stroke.
SUMMARY
[0003] A housing of a pump apparatus includes an undivided cavity,
an inlet valve through which liquid can enter the cavity, and an
outlet valve through which the liquid can exit the cavity. A
primary piston is configured to reciprocate in the cavity to draw
the liquid into the cavity through the inlet valve during an intake
stroke of the piston and discharge the liquid out of the cavity
through the outlet valve during a delivery stroke. A reservoir
structure is configured to add, to the total volume of the cavity,
an extra volume that is a smooth positive function of liquid
pressure in the cavity.
[0004] Preferably, the reservoir structure includes a secondary
piston configured to retract by a displacement distance that is a
smooth positive function of the liquid pressure. The extra volume
equals the displacement distance times a cross-sectional area of
the piston. The retraction of the secondary piston is along an axis
that is perpendicular to the direction of the reciprocation of the
primary piston.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a schematic view of a pressure washer that
includes a pump;
[0006] FIGS. 2-4 are partially-schematic sectional views of the
pump at different times during its operation;
[0007] FIG. 5 is an expanded sectional view of a portion of the
pump, showing additional parts; and
[0008] FIG. 6 is a partially-schematic sectional view of another
pump with parts similar to those in FIG. 2.
DESCRIPTION
[0009] The apparatus 1 shown in FIG. 1 has parts that are examples
of the elements recited in the claims. The apparatus thus includes
examples of how a person of ordinary skill in the art can make and
use the claimed invention. It is described here to meet the
requirements of enablement and best mode without imposing
limitations that are not recited in the claims.
[0010] The apparatus 1 is a pressure washer. It includes a pump 10
for pumping a liquid from a supply line 12 to an outlet line 14.
The supply line 12 has an inlet hose 20 connectable to a water
spigot. The outlet line 14 has an outlet hose 22 connected to a
spray nozzle 24. The pump 10 draws water from the inlet line 12 and
forces it out the nozzle 24 in the form of a pressurized spray.
[0011] As shown in FIG. 2, the pump 10 includes a housing 30
defining a cylindrical primary chamber 32 centered on a primary
axis Al. Liquid from the inlet line 12 enters the chamber 32
through an inlet check valve 34. The liquid exits the chamber 32
through an outlet check valve 36 to enter the outlet line 14.
[0012] The housing 30 has a cylindrical piston-bearing surface 40
defining an opening 42. A cylindrical primary piston 50 extends
through the opening 42 into the chamber 32. The bearing surface 40
slidingly supports the piston 50 and forms with the piston 50 a
liquid-tight seal that surrounds the piston 50. A coil spring 52 is
wrapped about the piston 50. It is compressed between a
spring-support flange 54 of the piston 50 and the housing 30 to
bias the piston 50 axially outward.
[0013] An outlet shaft 60 of a motor 62 extends parallel to the
primary axis Al. The shaft 60 is attached to a wobble plate 64 that
has a slide surface 66 that pushes the piston 50 axially inward
against the spring bias. The slide surface 66 is inclined relative
to shaft 60, for the piston 50 to axially reciprocate as the wobble
plate 64 rotates with the shaft 60.
[0014] The housing 30 further has a cylindrical secondary surface
70 defining a secondary chamber 72 adjoining the primary chamber
32. The secondary chamber 72 is centered on a secondary axis A2
perpendicular to the primary axis A1.
[0015] A secondary piston 80 is slidingly supported by the
cylindrical secondary surface 70 and forms, with the secondary
surface 70, a seal that surrounds the piston 80 continually as the
piston 80 moves axially through the secondary chamber 72. A
secondary spring 84 is compressed by and between the secondary
piston 80 and the housing 30. The spring 84 biases the secondary
piston 80 toward the primary axis A1, to a fully extended position
into abutment with a shoulder 86 of the housing 30.
[0016] Liquid-filled portions of the first and second chambers 32
and 72 are parts of an undivided cavity 90 that is bounded by the
housing 30 and the primary and secondary pistons 50 and 80. The
cavity 90 has a total volume that varies gradually with movement of
the pistons 50 and 80, being a smooth function of the pistons'
displacements D.sub.1 and D.sub.2. The function is "smooth" in that
there is no sudden increase or decrease in volume with change in
D.sub.1 and D.sub.2.
[0017] Reciprocation of the primary piston 50 is defined by an
intake stroke and a delivery stroke, while the cavity 90 is
continuously filled with the liquid. Due to the density and
incompressibility of the liquid in the cavity 90, movement of the
secondary piston 80 is dependent on liquid pressure P.sub.cav in
the cavity 90 and substantially independent of the secondary
piston's own inertia.
[0018] The delivery stroke starts with the primary piston 50 fully
retracted as shown in FIG. 2, and cavity pressure P.sub.cav
equaling supply line pressure P.sub.in plus inlet valve crack
pressure P.sub.crack. The secondary piston 80 is fully extended,
because the cavity pressure P.sub.cav urging it to retract is too
weak to overcome the spring bias pressing the secondary piston 80
against the shoulder 86.
[0019] Thereafter during the delivery stroke, the primary piston 50
moves axially inward (arrow 95) as shown in FIG. 3. When the cavity
pressure P.sub.cav exceeds outlet line pressure P.sub.out plus
crack pressure P.sub.crack, the outlet valve 36 opens to let the
liquid into the outlet line 14.
[0020] Further extension of the primary piston 50 delivers liquid
to the outlet line 14, while P.sub.cav remains constant at
P.sub.out+P.sub.crack. Concurrently, the secondary piston 80 is
displaced from its fully extended position by distance D.sub.2,
which is a smooth positive function of cavity pressure P.sub.cav
and therefore also a smooth function of the primary piston's
displacement distance D.sub.1. Extension of the primary piston 50
subtracts a displacement volume V.sub.1, proportional to D.sub.1,
from the total cavity volume V.sub.cav. This is partially offset by
retraction of the secondary piston 80, which adds to the total
volume a displacement volume V.sub.2 that is, advantageously,
smoothly related to D.sub.2 and equals D.sub.2 times the
cross-sectional area of the chamber 72 and piston 80. The delivery
stroke ends with the primary piston 50 fully extended as shown in
FIG. 4, with cavity pressure P.sub.cav equaling
P.sub.out+P.sub.crack.
[0021] The intake stroke starts with the primary piston 50 fully
extended as shown in FIG. 4. As the primary piston 50 retracts,
spring bias gradually returns the secondary piston 80 to its fully
extended position as cavity pressure P.sub.cav gradually decreases.
When P.sub.cav reaches P.sub.in+P.sub.crack, the inlet valve 34
opens to let liquid from the supply line 12 into the cavity 90.
Further retraction of the primary piston 50 draws liquid through
the inlet valve 34 into the cavity 90, while P.sub.cav remains
constant at P.sub.in+P.sub.crack and the secondary piston 80
remains fully extended. The intake stroke ends as shown in FIG. 2,
with the primary piston 50 fully retracted and the secondary piston
80 fully extended.
[0022] The secondary piston 80 thus functions as a reservoir.
During the delivery stroke, the secondary piston 80 accumulates a
displacement volume V.sub.2 of liquid that would otherwise be
delivered to the outlet line 14, and completely returns that volume
V.sub.2 to the cavity 90 during the intake stroke. The pump's
overall delivery rate, in cubic foot per minute, is thus reduced by
an amount proportional to V.sub.2, which is a smooth positive
function of and preferably proportional to the secondary
displacement distance D.sub.2, which is itself a smooth positive
function of outlet pressure P.sub.out. Therefore, the overall
delivery rate is a smooth inverse function of P.sub.out.
[0023] Power that is input from the motor 62 to drive the pump 10
is typically proportional to delivery rate times outlet pressure.
Since the delivery rate of this pump 10 is configured to decrease
with increasing outlet pressure, the required power will tend to
vary less with P.sub.out than if the second piston 80 were absent
and the delivery rate were independent of P.sub.out.
[0024] Preferably, the secondary spring 84 is selected to yield a
delivery rate that is approximately inversely proportional to
P.sub.out, i.e., proportional to I/P.sub.out. That would cause the
input power to be approximately invariant with P.sub.out, so that a
motor optimized for one power level at one outlet pressure would be
optimal for other pressures too. This can be achieved by replacing
the secondary spring 84 with a spring structure 100 having a spring
constant that increases with increasing piston displacement
D.sub.2. A step-wise-increasing spring bias can be achieved using
two or more concentric springs 101, 102 and 103 of different
lengths as shown in FIG. 6.
[0025] Isolating the secondary piston 72 from the motion of the
primary piston 50 is facilitated by the piston axes A1 and A2 being
perpendicular, and also by the primary piston 50 extending over the
secondary piston 80 and its axis A2 during reciprocation. To avoid
the primary piston 50 blocking the secondary chamber 72, the
primary piston 50 is spaced from the cavity wall 110. The extra
cavity volume due to this clearance does not decrease the
achievable output pressure, because the liquid is
incompressible.
[0026] FIG. 7 shows another pump 10'. It has parts that correspond
to those of FIG. 2 and that function in the same way as those in
FIG. 2 and are denoted with primed reference numbers matching the
reference numerals of corresponding parts in FIG. 2. The pump 10 of
FIG. 7 differs from the pump 10 of FIG. 2 in that its secondary
chamber 72', its secondary piston 80' and the displacement volume
it provides are all located within the primary piston 50', and the
primary and secondary pistons 50' and 80' reciprocate along the
same axis A1'.
[0027] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to make and use the invention. The patentable
scope of the invention is defined by the claims, and may include
other examples that occur to those skilled in the art. Such other
examples are intended to be within the scope of the claims if they
have elements that do not differ from the literal language of the
claims, or if they include equivalent structural elements with
insubstantial differences from the literal language of the
claims.
* * * * *