U.S. patent application number 11/412510 was filed with the patent office on 2007-11-01 for pump with variable stroke piston.
This patent application is currently assigned to Campbell Hausfeld/Scott Fetzer Company. Invention is credited to Brian D. Holt.
Application Number | 20070253849 11/412510 |
Document ID | / |
Family ID | 38621113 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070253849 |
Kind Code |
A1 |
Holt; Brian D. |
November 1, 2007 |
Pump with variable stroke piston
Abstract
A pump apparatus includes a housing located on an axis. The
housing has a chamber, an inlet valve and an outlet valve. A piston
driver is configured to axially reciprocate. A piston is a piston
configured to reciprocate in the chamber to draw liquid into the
chamber through the inlet valve during an intake stroke and to
discharge the liquid out of the chamber through the outlet valve
during a delivery stroke. A spring axially biases the piston to a
base position relative to the driver, so that the driver, when
reciprocating, will drive the piston to reciprocate. A preload
structure preloads the spring to enable pressure of the liquid in
the chamber to displace the piston away from the base position
against the spring bias after the pressure exceeds a threshold
level.
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: |
38621113 |
Appl. No.: |
11/412510 |
Filed: |
April 27, 2006 |
Current U.S.
Class: |
417/470 |
Current CPC
Class: |
F04B 49/121
20130101 |
Class at
Publication: |
417/470 |
International
Class: |
F04B 19/00 20060101
F04B019/00 |
Claims
1. A pump apparatus comprising: a housing located on an axis and
having a chamber, an inlet valve and an outlet valve; a piston
driver configured to axially reciprocate; a piston configured to
reciprocate in the chamber to draw liquid into the chamber through
the inlet valve during an intake stroke and to discharge the liquid
out of the chamber through the outlet valve during a delivery
stroke; a spring that axially biases the piston to a base position
relative to the driver, so that the driver, when reciprocating,
will drive the piston to axially reciprocate; and a preload
structure that preloads the spring to enable pressure of the liquid
in the chamber to displace the piston away from the base position
against the spring bias after the pressure exceeds a threshold
level.
2. The apparatus of claim 1 wherein the spring has a spring
constant that increases with increasing compression of the
spring.
3. The apparatus of claim 1 wherein the spring is configured to
render the volume of liquid delivered during each delivery stroke
inversely related to output pressure of the pump.
4. The apparatus of claim 3 wherein the spring is configured to
render the volume of liquid delivered during each delivery stroke
inversely proportional to the output pressure.
5. The apparatus of claim 1 wherein the preload is manually
adjustable.
6. The apparatus of claim 5 wherein manual adjustment of the
preload adjusts the depth of the piston in the chamber.
7. The apparatus of claim 1 wherein the spring is a bias spring,
and the apparatus further comprises a return spring having a lower
spring constant than the bias spring urging the piston out of the
chamber.
8. The apparatus of claim 1 wherein the preload structure includes
a protrusion on the piston that is located in the driver and is
axially urged by the spring against a stop surface of the
driver.
9. The apparatus of claim 8 wherein the stop surface is between the
rod protrusion and the spring.
10. The apparatus of claim 1 wherein the spring is configured to
absorb the entire reciprocation stroke of the driver in a case
where liquid is blocked from exiting the outlet valve piston while
the driver continues to reciprocate.
11. The apparatus of claim 1 further comprising an inlet hose
connected to a water source.
12. A pump apparatus comprising: a housing located on an axis and
having a chamber, an inlet valve and an outlet valve; a piston
driver configured to axially reciprocate; a piston configured to
reciprocate in the chamber to draw liquid into the chamber through
the inlet valve during an intake stroke and to discharge the liquid
out of the chamber through the outlet valve during a delivery
stroke; and a spring that axially biases the piston to a base
position relative to the driver, so that the driver, when
reciprocating, will drive the piston to axially reciprocate while
enabling pressure of the liquid in the chamber to displace the
piston away from the base position against the spring bias, the
spring having a spring constant that increases with increasing
compression of the spring.
13. The apparatus of claim 12 wherein the spring includes coil
springs with different spring constants.
14. A pump apparatus comprising: a housing located on an axis and
having a chamber, an inlet valve and an outlet valve; a piston
driver configured to axially reciprocate; a piston configured to
reciprocate in the chamber to draw liquid into the chamber through
the inlet valve during an intake stroke and to discharge the liquid
out of the chamber through the outlet valve during a delivery
stroke; a spring that axially biases the piston to a base position
relative to the driver, so that the driver, when reciprocating,
will drive the piston to axially reciprocate while enabling
pressure of the liquid in the chamber to displace the piston away
from the base position against the spring bias; and an inlet hose
connected to the inlet valve and configured to be connected to a
liquid source.
15. The apparatus of claim 14 wherein the inlet hose has a threaded
end configured to be screwed onto a water faucet.
16. A pump apparatus comprising: a housing located on an axis and
having a chamber, an inlet valve and an outlet valve; a piston
driver configured to axially reciprocate; a piston configured to
reciprocate in the chamber to draw liquid into the chamber through
the inlet valve during an intake stroke and to discharge the liquid
out of the chamber through the outlet valve during a delivery
stroke; and a spring that axially biases the piston to a base
position relative to the driver, so that the driver, when
reciprocating, will drive the piston to axially reciprocate while
enabling pressure of the liquid in the chamber to displace the
piston away from the base position against the spring bias, the
spring being configured render the volume of liquid delivered
during each delivery stroke inversely related to output pressure of
the pump.
17. The apparatus of claim 16 wherein the delivery stroke volume is
approximately inversely proportional to output pressure of the
pump.
18. A pump apparatus comprising: a housing located on an axis and
having a chamber, an inlet valve and an outlet valve; a piston
driver configured to axially reciprocate; a piston configured to
reciprocate in the chamber to draw liquid into the chamber through
the inlet valve during an intake stroke and to discharge the liquid
out of the chamber through the outlet valve during a delivery
stroke; and a spring that axially biases the piston to a base
position relative to the driver, so that the driver, when
reciprocating, will drive the piston to axially reciprocate while
enabling pressure of the liquid in the chamber to displace the
piston away from the base position against the spring bias, the
spring being configured to absorb the entire reciprocation stroke
of the driver in a situation where the liquid is blocked from
exiting the outlet valve while the driver continues to reciprocate.
Description
TECHNICAL FIELD
[0001] This application relates to liquid pumps.
BACKGROUND
[0002] A liquid pump includes a piston that reciprocates in a
cylindrical chamber. The piston draws liquid through an inlet valve
into the chamber during an intake stroke and forces the liquid out
of the chamber through an outlet valve during a delivery
stroke.
SUMMARY
[0003] A pump apparatus includes a housing located on an axis. The
housing has a chamber, an inlet valve and an outlet valve. A piston
driver is configured to axially reciprocate. A piston is a piston
configured to reciprocate in the chamber to draw liquid into the
chamber through the inlet valve during an intake stroke and to
discharge the liquid out of the chamber through the outlet valve
during a delivery stroke. A spring axially biases the piston to a
base position relative to the driver, so that the driver, when
reciprocating, will drive the piston to reciprocate. A preload
structure preloads the spring to enable pressure of the liquid in
the chamber to displace the piston away from the base position
against the spring bias after the pressure exceeds a threshold
level.
[0004] Preferably, the spring has a spring constant that increases
with increasing compression of the spring. The spring is configured
to render the volume of liquid delivered during each delivery
stroke inversely related to output pressure of the pump. The
preload is manually adjustable. The preload structure includes a
protrusion on the piston within the driver, and further includes a
stop surface in the driver that blocks the protrusion from exiting
the driver and against which the protrusion is biased by the
spring. The spring is configured to absorb the entire reciprocation
of the driver in a situation where liquid is blocked from exiting
the outlet valve piston while the driver continues to
reciprocate.
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 schematic sectional views of the pump at
different stages during its operation; and
[0007] FIG. 5 is a schematic view of a spring of the pump.
DESCRIPTION
[0008] 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.
[0009] 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 with a threaded end 22
configured to be screwed onto a water faucet. The outlet line 14
has an outlet hose 24 connected to a spray nozzle 26. The pump 10
draws water from the inlet line 12 and forces it out the nozzle 26
in the form of a pressurized spray.
[0010] As shown in FIG. 2, the pump 10 includes a housing 30
located on a central axis A. The housing 30 has axially front and
rear ends 32 and 34 and a cylindrical piston-bearing surface 36
defining a cylindrical chamber 38. The chamber 38 is centered on
the axis A and extends forward from a rear opening 40 of the
housing 30. Liquid enters the chamber 38 from the supply line 12
through an inlet check valve 42. The liquid exits the chamber 38
into the outlet line 14 through an outlet check valve 44.
[0011] A piston 50 includes piston head 52 rigidly fixed to a
piston rod 54. A threaded front end 56 of the rod 54 is screwed
into a threaded bore 57 of the head 52. The length L of the piston
50 depends on the depth to which the rod 54 is screwed into the
head 52. The head 52 extends from the rod 54 into the chamber 38.
It forms an annular liquid-tight seal with, and is axially slidable
against, the piston-bearing surface 36. The head 52 and the housing
30 together enclose a compression cavity 58, which is a closed
section of the chamber 38 that has a volume that varies as the head
52 reciprocates. A nut 60 is screwed onto the rear end 62 of the
rod 54 and protrudes radially outward from the rod 54.
[0012] The rear end 62 of the rod 54 is captured in a bore 70 of a
piston driver 72. A threaded ring 74 surrounding the rod 54 is
screwed into a threaded front end 76 of the bore 54. A
rearward-facing stop surface 78 of the ring 74 blocks the nut 60
from exiting the bore 70.
[0013] A bias spring 80 is wrapped about the rod 54 and compressed
between respective spring bearing surfaces 82 and 84 of the head 52
and the driver 72. The spring 80 biases the rod 54 into a base
position relative to the driver 72, as shown in FIG. 2, in which
the nut 60 abuts the stop surface 78. The nut 60 and the stop
surface 78 thus together preload the spring 80. The stop surface 78
is axially between the nut 60 and the bias spring 80.
[0014] A return spring 90 is wrapped about the piston head 54 and
compressed between respective spring bearing surfaces 92 and 94 of
the housing 30 and the head 52. The return spring 90 keeps the
driver 72 in contact with a front wobble surface 96 of a wobble
plate 98. The plate 98 is attached to an axially-extending output
shaft 100 of a motor 102. The wobble surface 96 is inclined with
respect to the axis A so that it reciprocatingly pushes the driver
72 forward against the bias of the return spring 90 as the plate 98
rotates. The piston 50 is driven by the driver 72 to reciprocate,
with a series of intake and delivery strokes in phase with forward
and rearward strokes of the driver 72.
[0015] The delivery stroke starts with the piston 50 fully
retracted as shown in FIG. 2, and pressure P.sub.cav in the cavity
58 equaling supply line pressure P.sub.in plus crack pressure
P.sub.crack of the inlet valve 42. Thereafter during the delivery
stroke, the piston 50 advances, causing the pressure in the cavity
58 to increase. At some point, as in FIG. 3, when the cavity
pressure P.sub.cav starts to exceed P.sub.out+P.sub.crack, the
outlet valve 44 starts to open to let the liquid into the outlet
line 14. From then on, further advancement of the piston 50
delivers liquid into the outlet line 14 while P.sub.cav remains
constant at P.sub.out+P.sub.crack. This continues until the piston
50 reaches a fully forward position shown in FIG. 4, the outlet
valve 44 closes, and cavity pressure P.sub.cav remains at
P.sub.out+.sub.crack.
[0016] The intake stroke starts with the piston 50 fully extended
as shown in FIG. 4. As the return spring 90 pushes the piston 50
rearward, cavity pressure P.sub.cav gradually decreases. When
P.sub.cav recedes below P.sub.in-P.sub.crack, the inlet valve 42
opens to let liquid from the supply line 12 into the cavity 58.
Further retraction of the piston 50 draws liquid through the inlet
valve 42 into the cavity 58, while P.sub.cav remains constant at
P.sub.in-P.sub.crack. The intake stroke ends as shown in FIG. 2
with the piston 50 fully retracted.
[0017] During the delivery and intake strokes, the bias spring 80
functions as follows: At the start of the delivery stroke,
portrayed in FIG. 2, the cavity pressure P.sub.cav is too weak to
overcome the preload of the bias spring 80 urging the nut 60
against the stop surface 78. At some point during the delivery
stroke, if and when the cavity pressure P.sub.cav increases
sufficiently to overcome the preload, the nut 60 will start to
separate from the stop surface 78. For comparison purposes, FIG. 4
shows the positions of the driver 72 and the piston 50 at the start
of the delivery stroke in dashed lines and their positions at the
end of the delivery stroke in solid lines. By the end of the
delivery stroke, the displacement distance D.sub.p of the piston 50
is shorter than the displacement distance D.sub.D of the driver 72
by the separation distance AD of the nut 60 from the stop surface
78.
[0018] If the output pressure P.sub.out remains below a threshold
level sufficient to overcome the spring preload, .DELTA.D will be
zero. Above that threshold, over a range of output pressures
P.sub.out for which the pump 10 is designed, .DELTA.D is a smooth
positive function of output pressure P.sub.out. The function is
"positive" in that .DELTA.D increases with increasing P.sub.out
throughout the pressure range, and "smooth" in that the second
derivative of .DELTA.D verses P.sub.out is finite over the
operating range. Due to the density and incompressibility of the
liquid filling the cavity 58, .DELTA.D is substantially unaffected
by inertia of the piston head 52.
[0019] The delivery stroke volume, i.e., the volume of liquid
delivered during each delivery stroke, is proportional to the
displacement D.sub.P of the piston 50, which equals displacement
D.sub.D of the driver 72 minus .DELTA.D. Therefore, when P.sub.out
is above the threshold pressure, the delivery stroke volume is
smoothly and inversely related to P.sub.out. When P.sub.out is
below the threshold pressure, the delivery stroke volume is
unaffected by varying P.sub.out.
[0020] The threshold can be manually increased by increasing the
preload on the bias spring 80. This can be done by screwing the rod
54 deeper into the head 52 or screwing the ring 74 deeper into the
driver 72. Either of these steps decreases the depth of the head 52
in the chamber 38. The resulting increase in initial volume of the
cavity 58 does not affect the achievable output pressure Pout,
because the liquid is incompressible.
[0021] Power input by the pump 10 from the motor 102 is typically
proportional to motor speed, delivery stroke volume and outlet
pressure P.sub.out. Since the delivery stroke volume of this pump
10 decreases with increasing P.sub.out, the required power will
tend to vary less with P.sub.out than without the reduction
.DELTA.D in stroke displacement.
[0022] Preferably, the bias spring 80 is selected to yield a
delivery stroke volume that is approximately inversely proportional
to P.sub.out, i.e., proportional to 1/P.sub.out. That renders the
input power approximately invariant with P.sub.out, so that a motor
102 optimized for one power level at one outlet pressure would be
optimal for other pressures too. This can be achieved by the bias
spring 80 having a spring constant that increases with increasing
spring compression. A step-wise increasing spring constant can be
achieved by the bias spring 80 comprising coil springs 111 and 112
differing in spring constant. In the example shown in FIG. 5, the
springs 111 and 112 are arranged in parallel, more specifically
concentric, with successively shorter springs having successively
higher spring constants. Alternatively, a smoothly increasing
spring constant can be achieved by the bias spring 80 comprising a
single coil spring of smoothly varying wire thickness.
[0023] The spring constant and the preload for the bias spring 80
are preferably higher than for the return spring 90. This ensures
that most of the driver reciprocation will be passed to the piston
50 and absorbed by the return spring 90 and not absorbed by the
bias spring 80. On the other hand, the bias spring's spring
constant and preload are preferably sufficiently low, and its
initial length sufficiently high, to enable the bias spring 80 to
absorb the entire reciprocation stroke of the driver 72 in a
situation where the piston 50 is jammed in its fully retracted
position. Such a situation can occur if a clog in the outlet line
14 totally prevents the liquid from exiting the outlet valve
44.
[0024] 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.
* * * * *