Canadian Patents Database / Patent 2558203 Summary

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(12) Patent Application: (11) CA 2558203
(54) English Title: PUMP WITH VARIABLE STROKE PISTON
(54) French Title: POMPE AVEC PISTON A COURSE VARIABLE
(51) International Patent Classification (IPC):
  • F04B 49/12 (2006.01)
(72) Inventors :
  • HOLT, BRIAN D. (United States of America)
(73) Owners :
  • CAMPBELL HAUSFELD/SCOTT FETZER COMPANY (United States of America)
(71) Applicants :
  • CAMPBELL HAUSFELD/SCOTT FETZER COMPANY (United States of America)
(74) Agent: FETHERSTONHAUGH & CO.
(74) Associate agent:
(45) Issued:
(22) Filed Date: 2006-08-30
(41) Open to Public Inspection: 2007-10-27
Examination requested: 2006-08-30
(30) Availability of licence: N/A
(30) Language of filing: English

(30) Application Priority Data:
Application No. Country/Territory Date
11/412,510 United States of America 2006-04-27

English 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.


Note: Claims are shown in the official language in which they were submitted.


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.

6


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
7


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.

8

Note: Descriptions are shown in the official language in which they were submitted.


CA 02558203 2006-08-30

EV520395059US
PUMP WITH VARIABLE STROKE PISTON

TECHNICAL FIELD
This application relates to liquid pumps.
BACKGROUND
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
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.
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
FIG. 1 is a schematic view of a pressure washer that includes a pump;
FIGS. 2-4 are schematic sectional views of the pump at different stages during
its operation;
and
FIG. 5 is a schematic view of a spring of the pump.
1


CA 02558203 2006-08-30
~ = ~ I

DESCRIPTION
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 sldll
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.
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.
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.
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.
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.
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 '0.

2


CA 02558203 2006-08-30

. ~ = ~ ~

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.
The delivery stroke starts with the piston 50 fully retracted as shown in Fig.
2, and pressure
P~a,, in the cavity 58 equaling supply line pressure P;, plus crack pressure
P,~.ck 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 Pca, starts to
exceed Poõc+P,,,,,k, 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,a,, remains constant at
Poõc+P.k. This continues until the piston 50 reaches a fully forward position
shown in Fig. 4, the
outlet valve 44 closes, and cavity pressure P., remains at Poõt+Pmck.
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 PCB,, gradually
decreases. When Pc.õ recedes
below P;n-Pmck, 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
Pc$,, remains constant at P;n-Pc,.a,_k. The intake stroke ends as shown in
Fig. 2 with the piston 50 fully
retracted.
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,,.õ 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 Pca,, 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 DP of the piston 50 is shorter than the displacement distance DD of
the driver 72 by the
separation distance OD of the nut 60 from the stop surface 78.
3


CA 02558203 2006-08-30
. . i ~-

If the output pressure Poõt remains below a threshold level sufficient to
overcome the spring
preload, AD will be zero. Above that threshold, over a range of output
pressures Pot for which the
pump 10 is designed, AD is a smooth positive function of output pressure Poõt.
The function is
"positive" in that AD increases with increasing Poõt throughout the pressure
range, and "smooth" in
that the second derivative of AD verses Poõt is finite over the operating
range. Due to the density and
incompressibility of the liquid filling the cavity 58, AD is substantially
unaffected by inertia of the
piston head 52.
The delivery stroke volume, i.e., the volume of liquid delivered during each
delivery stroke,
is proportional to the displacement Dp of the piston 50, which equals
displacement DD of the driver
72 minus AD. Therefore, when Pout is above the threshold pressure, the
delivery stroke volume is
smoothly and inversely related to Poõt. When Põt is below the threshold
pressure, the delivery stroke
volume is unaffected by varying Poõt.
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
Poõt, because the liquid is incompressible.
Power input by the pump 10 from the motor 102 is typically proportional to
motor speed,
delivery stroke volume and outlet pressure Poõt. Since the delivery stroke
volume of this pump 10
decreases with increasing Po,,t, the required power will tend to vary less
with Poõt than without the
reduction AD in stroke displacement.
Preferably, the bias spring 80 is selected to yield a delivery stroke volume
that is
approximately inversely proportional to Po,t, i.e., proportional to 1/Poõt.
That renders the input
power approximately invariant with Put, 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. Altematively, a smoothly increasing spring constant can be achieved
by the bias spring
80 comprising a single coil spring of smoothly varying wire thickness.

4


CA 02558203 2006-08-30

~ =

The spring constant and the preload for the bias spring 80 are preferably
higher thanfor 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.
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.

5

A single figure which represents the drawing illustrating the invention.

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Admin Status

Title Date
Forecasted Issue Date Unavailable
(22) Filed 2006-08-30
Examination Requested 2006-08-30
(41) Open to Public Inspection 2007-10-27
Dead Application 2009-08-31

Abandonment History

Abandonment Date Reason Reinstatement Date
2008-09-02 FAILURE TO PAY APPLICATION MAINTENANCE FEE

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Request for Examination $800.00 2006-08-30
Registration of Documents $100.00 2006-08-30
Filing $400.00 2006-08-30
Current owners on record shown in alphabetical order.
Current Owners on Record
CAMPBELL HAUSFELD/SCOTT FETZER COMPANY
Past owners on record shown in alphabetical order.
Past Owners on Record
HOLT, BRIAN D.
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.

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Abstract 2006-08-30 1 20
Description 2006-08-30 5 276
Claims 2006-08-30 3 142
Drawings 2006-08-30 3 123
Representative Drawing 2007-10-02 1 10
Cover Page 2007-10-16 1 40
Assignment 2006-08-30 5 199