Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~099~L87
B~CKGROUND OF T~E INVENTION
Cross Reference to Related Applications
~ he valve disclosed hexe.in may he used in co~junction
with a ~ariable displacement pi5ton pump ~uc]-l as descri~ed
and claimed in commonly assignea coperldil-ly Canadian
Application Serial No. 300,010, filed by Frank Woodruff
on March 30, 1977.
Field of ~he Inven-tion
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This inventi.on relates generally ~o pump pressure
control valves and, paxticularly, to a valve which controls
A
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the discharge manifold pressure of the pump to provide a
pressure for regulating the stroke of the pump pistons.
Description of the Prior Art
The aforenoted copending Canadian ~pplicatlon Serial
No. 300,010 describes a variable displacement piston
pump including a shaft having a driven end and an
opposite end arranged for supporting a swash plate to pivot
about an axis displaced from the center line of the shaft
and preferably, but not necessarily, normal thereto. A
plurality of pistons having hollow cylinders extending
therethrough are arranged with corresponding check valves
in a pump block. During the "delivery" stroke of the
pistons the pressure in the cylinders becomes sufficient
to actuate the check valves whereby fluid is delivered to
a common discharge manifold.
When the manifold pressure approaches a predetermined
value, a force is created which is transmitted to the swash
plate and pivots the plate away from a maximum flow
position. The pistons are arranged with the swash plate so
that when the swash plate pivots r the stroke of the pistons
is decreased to reduce fluid flow and pressure. Equili-
brium is thus established and a reduced fluid flow at a
predetermined substantially constant pressure is maintained.
The valve of the present invention is used in conjunction
with a pump of the type described to control the pump
manifold pressure Eor providing a pressure which creates
the force transmitted to the swash plate. The valve herein
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described features a novel arrangemen-t including an elonyated
spool section responsive to pump discharge manifold pressure
for varying the area of a pair of orifices arranyed in series
relation to provide a pressure which is transmitted to the
pump chamber for regula-ting the stroke of the pump pistons.
According to the present inven-tion there is provided
a pressure control valve having a valve cylinder including a
bore extendiny therethrough with a pressure inlet port extending
externally to the valve and communicating with the valve
cylinder bore so that an inlet pressure is received by the
valve. A spring loaded valve spool is disposed within the
valve cylinder bore and is responsive to the inlet pressure
for being displaced against the spring load. First and second
orifices communicate with the valve cylinder bore and are
arranged with the valve spool so that displacement of the spool
increases the area of one of the first and second orifices and
decreases the area of the other of the orifices to create a control
pressure. A pressure outlet port extends external to the valve
and means communicates the first and second orifices and the
pressure outlet port with the control pressure transmitted
through the means to the pressure outlet port and therefrom
external to the valve.
In a specific embodiment of the invention, the spool
includes an elongated section which varies the area of the pair
of orifices arranged in series relation and used for inlet and
exhaust of a control pressure generated by the valve. The
orifices are of different diameters to permit tailoring of the
control pressure in relation -to spool stroke for obtaining
reasonably balanced slew rates toward or away from full pump
flow. Means are provided for accommodating less than perfect
spring force alignment along the spool axis.
One object of this invention is to provide a pressure
control valve for a variable displacement piston type pump,
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whereby the pump is supplied with a pressure which crea-tes
a force for regulating -the stro]ce of the pump pi.s-tons to
provide a variable fluid flow at a substan-tially constant
pressure.
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~ Another object of this invention is to provide
a valve of the type described which includes an elongated
spool section responsive to pump discharge manifold
pressure for varying the area of control pressure inlet
and outlet orifices.
Another object of this invention is to provide
the orifices of different diameters, with the area of
the orifices being varied by the elongated spool section,
whereby the control pressure in relation to the spool
stroke can be tailored for reasonably balanced slew rates
toward and away rom full pump flow.
Another object of this invention is to actuate
the valve spool against a spring force and to accommodate
misalignment of the spring force along the spool axis.
The foregoing and other objects and advantages
of the invention will appear more fully hereinafter from
a consideration of the detailed description which follows
taken together with the accompanying drawings wherein
one embodiment of the invention is illustrated by way of
example. It is to be expressly understood, however, that
the drawings are for illustration purposes only and are
not to be construed as defining the limits of the invention.
Description of the Drawings
Figure 1 is a partially sectioned front plan view
showing in substantial detail a pump pressure control
valve according to the invention.
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Figure 2 is a schematic diagram illustrating the
operation of the valve shown in detail in Figure 1.
Description of the Invention
With reference first to Fi.gure 1, a pump pressure
control valve designated by the ntlmeral 1 includes an
inlet port 2! an outlet port 4 and an outlet port 6.
Inlet port 2 is connected to a pump discharge mani~old
port whereby the pump discharge manifold pressure is
transmitted to valve 1. Outlet port 4 i5 connected to a
pump pressure control port whereby a control pressure is
transmitted to the pump for creating a force or regulating
the stro~e of the pump's pistons. The operation of the.
pump in this regard is described in the aforenoted copending
Cdn. Application Serial No. 300,010. Outlet port 6
of valve 1 is connected to a pump inlet port for purposes
to be hereinafter described.
Valve 1 includes a cylinder 8 having a bore 9
: extending therethrough, and havfng control pressure inlet
orifices 10 and.control pressure outlet orifices 12 which
.~0 are in communication with a channel 14. Channel 14 is
in turn in communication with valve outlet port 4. Valve
1 further includes an orifice 16 which is in communication
with valve outlet port 6. In this connection it is noted
that orifices 10 and 12 are provided on both sides of
2~ cylinder ~ to preclude a side load on the spool. As a
design matter, more than one pair of orifices may be used
.as may be desired.
A valve spool 18 is axially disposed within bore
9 and includes end sections 20 and 22 of a predetermined
diameter and an elongated section 24 intermediate end
sections 20 and 22. Section 24 is of a substantially
larger diameter than sections 20 and 22. Section 24
is arranged with orifices 10 and 12 so as to vary the
area of the orifices and to thereby provide a control
pressure at valve outlet port 4 as will be hereinafter
described.
Cylinder 8 terminates in an enlarged section 26
which is held in.place by a valve housing 28. A spring
30 is disposed within valve housing 28 intermediate a
spring follower 32 disposed near section 26 and an
oppositely dispo~ed.spring follower 34. Spring follower
~5 34 includes an axially extending portion 41 having a
purpose which will be hereinafter described.
A free floating pin designated by the numeral 36
is disposed within bore 9 adjacent the end of spool
`se~,tion 22 and intermediate said.end and spring follower
'0 32. Pin 36 is designed to have sufficient strength and
surface area to carry any sideload resulting from less
than perfect alignment of the force of spring 30 along
the common axis of pin 36 and spool 18. Bore 9 may or
may not be enlarged in the area containing pin 36, as
'5 dictated by.the proper design of the pin. As a design
matter, diametral.clearance between pin 36 and bore 9
need not be closely held, since the clearance does not
,affect fluid leakage, and only nominal concentricity
relative to spool 18 is required.
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;~
A rod 40 extends through valve housing 38 and
is adjustable through a thread and nut arrangement 42
for displacing spring follower 34 to adjust the tension
on spring 30. Axially extending portion 41 of spring
follower 34 which is arranged for sufficient clearance
with spring fol10wer 32 so that compression of spring
30 beyond spool stroke requirements is precluded.
This is an optional design feature to protect the spring
from over-stress and possible permanent deformation.
Operation of the Invention
With the specific structural details of valve 1
illustrated and described with reference to Figure l!
the operation of the valve will next be described with
i reference to the schematic diagram of Figure 2.
Thus, the pump discharge manifold pressure
received by valve 1 through port 2, and which pressure
may be for purposes of illustration 6,000 psi, forces
spool 18 in bore 9 upward against the downward force
extended by spring 30, relative to the illustration of
Figure 2. This increases the area of orifices 10 which
may have a diameter of .040 inches and decreases the
area of orifices 12 which may have a diameter of .090
inches. Oriices 10 and 12, of different diameters and
in the series arrangement as shown, create an intermediate
control pressure in channel 14, which may be 500 psi,
for transmission to the pump pressure control port via
valve outlet port 4. With the arrangement shown, the
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pressure at valve outlet port 6 which is transmitted to the
pump inlet port is substantially zero. The pressure at
port ~ actuates a mechanism and c:auses the pump to de-stroke
as described in the aforenoted Cdn- Application Serial
No. 300,010.
With further reference to Figure 1, it will be seen
that fluid leakage to vent must either go through the
control pressure route or alon~ elongated section 24 of
spool 18. The relatively long enlarged diameter of spool
section 24 facilitates the use of separate orifices 10 and
12 which, in turn, facilita*e obtaining desired rates of
change in the area of the orifices in relation to the
stroke of spool 18. Elongated spool section 24 also
permits a desired low fluid leakage with a practical
diametral clearance with bore 8, the same being
advantageous from a manufacturing standpoint.
The ratio of the diameters of orifices 10 and 12,
orifices 10 being of the smaller diameter and orifices 12
being of the larger diameter, provides considerable
flexibility in tailoring the control pressure in relation
to the stroke of spool 18 to obtain both reasonably
balanced slew rates toward or away from full pump flow
and desired rates of change of the areas of the orifices.
This results in a desired change of control pressure in
relation to spool stroke.
It is understood that the recited pressures and
orifice diameters are for illustration purposes only and
,may be varied depending upon the size of the pump, the
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amount of fluid to be pumped, and the several other
parameters which may be taken into account, the same
being a matter of design.
It will now be seen from the aforegoing
description of the invention that a fuel pump pressure
control valve has been described which controls the
pressure from the pump discharge manifold to proviae
a pressure for regulating the stroke of the pump
pistons. The valve as described minimizes ~luid
leakage without extremely severe diameter tolerances
and minimizes spring side loading. The spool diameter
is chosen to:
a. provide sufficent force for an allowed
change in pump discharge pressure to
obtain a practical spool stroke with
a spring rate-to-inertia ratio which
puts the spring-mass resonance above
the pump piston frequency for maY~imum
pump speed;
b. minimize leakage by using minimum spool
diameters; and
c. allow sufficient area around spool
portion 22 so as not to restrict flow
through orifice 12.
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. Although but a single embodiment of the invention
has been illustrated and described in detail, it is to be
expressly understood that the invention is not limited
thereto. Various changes may also be made in the design
and arrangement of the parts without departing from the
spirit and scope of the invention as the same will now
be understood by those skilled in the art.
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