U.S. patent application number 11/297430 was filed with the patent office on 2006-10-05 for pump device.
Invention is credited to Tomoyuki Fujita, Masamichi Sugihara, Yoshinobu Yasue.
Application Number | 20060222519 11/297430 |
Document ID | / |
Family ID | 36096147 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060222519 |
Kind Code |
A1 |
Fujita; Tomoyuki ; et
al. |
October 5, 2006 |
Pump device
Abstract
A fixed capacity pump (P) sucks working oil from a reservoir (R)
through a conduit (Rp) and a suction passage (1), and discharges
the pressurized working oil into a discharge passage (2) connected
to an actuator (A). A choke (21) is disposed in the discharge
passage (2), and a flow control valve (F) recirculates a part of
the working oil in the discharge passage (2) upstream of the choke
(21) to the suction passage (1) according to a pressure loss
generated by the choke (21). The characteristic of the choke (21)
which significantly increases the flow resistance in a low
temperature state makes the flow rate of the recirculated working
oil increase, thereby preventing cavitation/noise from occurring in
the pump (P) when operated at high speed and in a low temperature
state.
Inventors: |
Fujita; Tomoyuki; (Tokyo,
JP) ; Sugihara; Masamichi; (Tokyo, JP) ;
Yasue; Yoshinobu; (Tokyo, JP) |
Correspondence
Address: |
RABIN & Berdo, PC
1101 14TH STREET, NW
SUITE 500
WASHINGTON
DC
20005
US
|
Family ID: |
36096147 |
Appl. No.: |
11/297430 |
Filed: |
December 9, 2005 |
Current U.S.
Class: |
417/310 |
Current CPC
Class: |
F04C 2270/52 20130101;
F04C 2270/701 20130101; F04C 2270/50 20130101; F04C 14/26
20130101 |
Class at
Publication: |
417/310 |
International
Class: |
F04B 49/00 20060101
F04B049/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2004 |
JP |
2004-370463 |
Claims
1. A pump device for supplying oil to an actuator, comprising: a
fixed capacity pump; a choke through which working oil discharged
by the pump flows; and a flow control valve which recirculates a
part of the working oil discharged by the pump to a suction side of
the pump, according to a pressure loss generated by the choke.
2. The pump device as defined in claim 1, further comprising a
casing in which the pump, the choke and the flow control valve are
enclosed.
3. The pump device as defined in claim 2, further comprising a
suction passage which supplies working oil to the suction side of
the pump, a discharge passage which supplies a part of the working
oil discharged by the pump to the actuator, the choke being
disposed in the discharge passage, and a recirculation passage
which supplies the working oil recirculated by the flow control
valve to the suction passage.
4. The pump device as defined in claim 3, wherein the flow control
valve comprises a spool which regulates a flow rate of the working
oil recirculated by the flow control valve according to a
difference in pressure between an upstream side of the choke and a
downstream side of the choke.
5. The pump device as defined in claim 1, wherein a diameter of the
choke is set within a range of two to eight millimeters, and a
ratio of the diameter to a length of the choke is set to be equal
to or less than unity.
Description
FIELD OF THE INVENTION
[0001] This invention relates to flow control of a fixed capacity
pump used for example in the power steering of a vehicle.
BACKGROUND OF THE INVENTION
[0002] JPH09-170569A published by the Japan Patent Office in 1997
discloses a flow control valve for a fixed capacity pump that can
be used in the power steering of a vehicle.
[0003] The flow control valve supplies working oil discharged from
the fixed capacity pump to an actuator via a variable orifice. The
flow control valve is provided with a spool that displaces in
response to a pressure loss in the orifice and, according to its
displaced position, causes a part of the discharged working oil to
flow into a recirculation passage. Working oil that is sucked by
the pump is supplied from a reservoir via a suction passage. The
recirculation passage recirculates working oil into the suction
passage.
SUMMARY OF THE INVENTION
[0004] The orifice has a feature whereby the flow characteristic is
constant irrespective of the temperature of the working oil that
passes therethrough. For example, when the viscosity of the working
oil is high due to low temperature, the pressure loss in the
working oil passing through the orifice does not become very large
with respect to the flow rate. On the other hand, when the
viscosity of the working oil increases, frictional resistance in
the suction passage inevitably increases, and the suction
resistance of the pump increases.
[0005] The working oil recirculated from the recirculation passage
is under a pushing force originating in the discharge pressure of
the pump, and therefore the suction resistance of the pump when it
sucks the recirculated working oil is small. On the other hand,
when the pump suctions working oil from the reservoir via the
suction passage, it suffers a large suction resistance. The entire
suction resistance of the pump therefore depends on the ratio of
the flow rate of the recirculated working oil to the flow rate of
the working oil supplied from the reservoir.
[0006] When the pump rotation speed rises in a low temperature
state and flow control is performed depending on the pressure loss
in the orifice, flow rate increase in the recirculation passage is
small with respect to the increase in the discharge flow rate of
the pump. As a result, the flow rate of working oil supplied from
the reservoir to the pump increases. In this state, the frictional
resistance in the suction passage is high due to the high viscosity
of the working oil, and hence the suction resistance of the suction
passage is large.
[0007] Thus, in a low temperature state, it is possible that the
working oil supply flow rate of the suction passage becomes
insufficient with respect to the flow rate of the working oil that
the pump requires according to its rotation speed. When the pump
suffers a shortage of working oil for suction, a negative pressure
is generated in the pump, which results in cavitation or noise
generation. Such an inconvenience is apt to occur when the rotation
speed of the fixed capacity pump increases after being started in a
low temperature state.
[0008] It is therefore an object of this invention to prevent an
insufficient working oil supply in a low temperature state for a
fixed capacity pump that is combined with a recirculation
circuit.
[0009] In order to achieve the above object, this invention
provides a pump device for supplying working oil to an actuator,
comprising a fixed capacity pump, a choke through which working oil
discharged by the pump flows, and a flow control valve which
recirculates a part of the working oil discharged by the pump to a
suction side of the pump, according to a pressure loss generated by
the choke.
[0010] The details as well as other features and advantages of this
invention are set forth in the remainder of the specification and
are shown in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a hydraulic circuit diagram of a pump device
according to this invention.
[0012] FIG. 2 is a longitudinal sectional view of a vane pump as a
component of the pump device.
[0013] FIG. 3 is a longitudinal sectional view of a flow control
valve according to this invention.
[0014] FIG. 4 is a diagram showing a result of an experiment
performed by the inventors to test the effect of the working oil
temperature on the flow characteristics of an orifice and a
choke.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Referring to FIG. 1 of the drawings, a pump device according
to this invention comprises a fixed capacity pump P and a flow
control valve F enclosed in a casing C shown by a single dotted
line.
[0016] The fixed capacity pump P is connected to a motive power
source such as an internal combustion engine and, when driven by
the motive power source, sucks work oil through a suction passage 1
formed in the casing C. The suction passage 1 is connected, via an
external conduit Rp, to a reservoir R disposed outside the casing
C. The fixed capacity pump P discharges pressurized work oil to a
discharge passage 2 that is also formed in the casing C.
[0017] The discharge passage 2 is connected to an actuator A
located outside the casing C. A choke 21 is disposed in the
discharge passage 2. A branch passage 2b branches off from the
discharge passage 2 at a position upstream of the choke 21. The
branch passage 2b is connected to an inlet port 4 of the flow
control valve F. In other words, the discharge passage 2 downstream
of the choke 21 communicates with the actuator A and the discharge
passage 2 upstream of the choke 21 communicates with the inlet port
4 of the flow control valve F via the branch passage 2b.
[0018] The flow control valve F comprises a spool 5, a control
pressure chamber 6 and a spring chamber 7. The control pressure
chamber 6 and the spiring chamber 7 are separated by the spool 5.
The control pressure chamber 6 communicates with the branch passage
2b via the inlet port 4. The spring chamber 7 communicates with the
discharge passage 2 downstream of the choke 21 via a pilot passage
9. A spring 8 is enclosed in the spring chamber 7.
[0019] The flow control valve F comprises a recirculation port 10.
The recirculation port 10 communicates with the control pressure
chamber 6 according to displacement of the spool 5 toward the right
hand side of the figure. The recirculation port 10 communicates
with the suction passage 1 via a recirculation passage 11 formed
within the casing C.
[0020] When the recirculation port 10 communicates with the control
pressure chamber 6 as a result of the displacement of the spool 5,
the working oil that has flown into the control pressure chamber 6
from the inlet port 4 recirculates to the suction passage 1 via the
recirculation port 10 and recirculation passage 11, and is sucked
again by the fixed capacity pump P. It can be said that the oil
that has flown into the recirculation port 10 recirculates in the
casing C.
[0021] When the fixed capacity pump P operates, working oil in the
reservoir R is sucked into the pump P via the conduit Rp located
outside the casing C and the suction passage 1 formed within the
casing C. The fixed capacity pump P pressurizes the sucked working
oil and discharges it into the discharge passage 2. The working oil
discharged into the discharge passage 2 is supplied to the actuator
A via the choke 21.
[0022] When working oil flows through the choke 21, it incurs a
pressure loss and a difference in pressure upstream and downstream
of the choke 21 arises. The pressure in the discharge passage 2
upstream of the choke 21 is led to the control pressure chamber 6
of the flow control valve F via the branch passage 2b and the inlet
port 4, and the pressure in the discharge passage 2 downstream of
the choke 21 is led to the spring chamber 7 of the flow control
valve F via the pilot passage 9.
[0023] The working oil pressure in the control pressure chamber 6
acts on the spool 5 as a thrust force from the left hand side of
the figure. The working oil pressure in the spring chamber 7 and
the pressure of the spring 8 act on the spool 5 as a thrust force
from the right hand side of the figure. Accordingly, the spool 5
displaces to a position where these two forces balance. The opening
of the recirculation port 10 depends on the balanced position of
the spool 5.
[0024] When the opening of the recirculation port 10 varies, the
flow rate of working oil that recirculates from the recirculation
port 10 to the suction passage 1 via the recirculation passage 11
also varies. This variation results in a change in the ratio of the
flow rate of the working oil that flows into the actuator A to the
flow rate of the working oil that is recirculated to the suction
passage 1.
[0025] When the pressure upstream of the choke 21 greatly rises
with respect to the pressure downstream of the choke 21 and the
thrust force generated by the control pressure chamber 6 becomes
larger than that generated by the spring chamber 7, the spool 5
displaces towards an opening increase direction of the
recirculation port 10, i.e., towards the right hand side in the
figure. Conversely, when the pressure upstream of the choke 21
approaches the pressure downstream of the choke 21 and the thrust
force generated by the spring chamber 7 becomes larger than that
generated by the control pressure chamber 6, the spool 5 displaces
towards an opening decrease direction of the recirculation port 10,
i.e., towards the left hand side in the figure. In the
recirculation passage 11, as the opening of the recirculation port
10 increases, the recirculation flow rate increases, and as the
opening of the recirculation port 10 decreases, the recirculation
flow rate decreases.
[0026] Providing that the discharge flow rate of the fixed capacity
pump P is Q1, the flowrate of the working oil supplied to the
actuator A is Q2, the flow rate of the working oil that is
recirculated to the suction passage 1 from the recirculation port
10 via the recirculation passage 11 is Q3, and the flow rate of the
working oil supplied to the fixed capacity pump P from the
reservoir R is Q4, the following relations (1) and (2) hold.
Q1=Q3+Q4 Q2=Q1-Q3
[0027] The flow rate Q4 of the oil that is sucked by the pump P
from the reservoir R outside the casing C is represented by the
following relation (3). Q4=Q1-Q3
[0028] From the relations (2) and (3), it is apparent that when the
flow rate Q2 of the oil supplied to the actuator A decreases, the
flow rate Q4 of the oil supplied from the reservoir R also
decreases.
[0029] Next, referring to FIG. 2 and FIG. 3, the actual
construction of the pump device will be described.
[0030] The casing C comprises a body 12 and a cover 14 that closes
a bore 13 formed in the body 12.
[0031] In the bore 13, a side plate 15 and a cam ring 16 are
enclosed in this order from the bottom. The cam ring 16
accommodates a rotor 17 which is fixed to a rotation shaft 20. The
rotor 17 comprises plural vane grooves 18 formed in radial
directions at equal angular intervals. In each vane groove 18, a
vane 19 is accommodated so as to be free to protrude radially
therefrom.
[0032] When the rotor 17 undergoes rotation, vanes 19 protrude from
the vane grooves 18 as a result of centrifugal force and their
protruding tips contact the inner circumference of the cam ring 16.
By means of the contact between the protruding tips of the vanes 19
and the inner circumference of the cam ring 16, oil chambers are
formed between adjacent vanes 19.
[0033] The rotation shaft 20 penetrates through the body 12 and
connects to the motive power source such as an internal combustion
engine outside the casing C.
[0034] As the rotor 17 rotates in the cam ring 16, the vanes that
are in contact with the inner circumference of the cam ring 16 move
forward and backward, and accordingly the oil chambers formed by
the vanes and the inner circumference of the cam ring 16 expand and
shrink. The expansion and shrinkage of oil chambers take place
simultaneously. More precisely, some oil chambers expand while
others shrink.
[0035] The suction passage 1 is formed in the cover 14. The suction
passage 1 communicates with the expanding oil chambers and the
discharge passage 2 communicates with the shrinking oil chambers
through one or both of two side faces of the cam ring 16.
[0036] Each of the oil chambers sucks working oil from the suction
passage 1 when it expands, or in other words, when it is in a
suction stroke. When the suction passage 1 shrinks, or in other
words when it is in a discharge stroke, it pressurizes the sucked
working oil and discharges it to the discharge passage 2.
[0037] Referring back to FIG. 1, the branch passage 2b branches off
from the discharge passage 2 as the discharge passage 2 extends
toward the choke 21. The branch passage 2b communicates with the
control pressure chamber 6 via the inlet port 4. However, this
configuration in the circuit diagram has been drawn for the purpose
of explanation. The real construction is somewhat different as
shown in FIG. 3. Specifically, the branch passage 2b shown in FIG.
1 is imaginary and in reality the discharge passage 2 directly
communicates with the control pressure chamber 6 as shown in FIG.
3. The working oil in the control pressure chamber 6 is separated
into two oil streams by the spool 5, i.e., a stream to the actuator
A via the choke 21, and a stream to the suction passage 1 via the
recirculation port 10. The branch passage 2b and the inlet port 4
are therefore not shown in FIG. 2 and FIG. 3.
[0038] Next, the differences between this invention and the
aforesaid prior art will be explained.
[0039] This invention provides the choke 21 instead of an orifice
in the discharge passage 2. Pressure loss caused by an orifice is
not affected by the temperature of the working oil, or the
viscosity thereof.
[0040] FIG. 4 shows an experimental result obtained by the
inventors with respect to the effect of the temperature of working
oil on the flow characteristics of an orifice and a choke. In the
experiment, the orifice and choke have a same diameter D and the
flow path length L of the choke is set at 1.33 times of the
diameter D.
[0041] As can be understood from this diagram, in the case of the
orifice, the relation between the oil temperature and the flow rate
is almost linear as shown by the broken line in the diagram. In
other words, the flow rate of the orifice is hardly affected by the
oil temperature and the differential pressure upstream and
downstream of the orifice does not increase significantly in a low
temperature state.
[0042] In contrast, in the case of the choke, the flow rate
significantly decreases in a low temperature state as shown by the
solid line in the diagram. In other words, the flow rate of the
choke is highly affected by the temperature or the viscosity of the
working oil and the differential pressure between the upstream and
downstream sides of the choke significantly increases in a low
temperature state at an identical flow rate. In the descriptions
below, a differential pressure between the upstream and downstream
sides of an orifice is explained as a differential pressure of an
orifice, and a differential pressure between the upstream and
downstream sides of a choke is explained as a differential pressure
of a choke.
[0043] Due to the above difference in the flow rate
characteristics, in the hydraulic circuit shown in FIG. 1, if an
orifice were used instead of the choke 21, the balanced position of
the spool 5 in a low temperature state would move towards the left
hand side with respect to the case where the choke 21 is used, and
therefore a smaller flow rate of working oil that flows into the
recirculation passage 11 through the recirculation port 10 would be
the result.
[0044] The discharge flow rate Q1 of the fixed capacity pump P is
obtained as a product of a unit discharge volume and a rotation
speed of the pump P. The rotation speed of the fixed capacity pump
P depends on the rotation speed of the motive power source such as
an internal combustion engine. When the rotation speed of the
motive power source increases, the discharge flow rate Q1 of the
fixed capacity pump P increases accordingly, even in a low
temperature state. If the differential pressure of the orifice were
large in this situation, the recirculation flow rate Q3 via the
recirculation port 10 would increase, so the suction flow rate of
the fixed capacity pump P would not suffer a shortage. However, in
reality, the differential pressure of the orifice is small even in
a low temperature state, and so the flow rate Q2 of working oil
supplied to the actuator A increases and the recirculation flow
rate Q3 decreases relatively.
[0045] When the recirculation flow rate Q3 decreases, in order to
maintain the suction flow rate of the fixed capacity pump P that is
required according to the pump rotation speed, the flow rate Q4 of
the working oil supplied from the reservoir R increases. As a
result, the suction resistance of the fixed capacity pump P
varies.
[0046] With respect to the working oil that is recirculated through
the recirculation passage 11, the suction resistance by the pump P
is small, because the recirculated working oil is under the
influence of a pushing force originating from the discharge
pressure of the fixed capacity pump P. With respect to the fresh
working oil that is supplied from the reservoir R through the
conduit Rp and the suction passage 1, since there is no pushing
force applied to the fresh working oil supplied from the reservoir
R, all the frictional resistance in the conduit Rp and the suction
passage 1 acts as suction resistance of the fixed capacity pump P.
Accordingly, the suction resistance of the fresh working oil
supplied from the reservoir R is larger than the suction resistance
of the recirculated working oil. As a result, as the ratio of the
flow rate Q4 to the flow rate Q3 increases, the suction resistance
by the pump P increases.
[0047] If the fixed capacity pump P tends to suck a large amount of
working oil from the reservoir R when the oil temperature is low
and the oil viscosity is large, the suction flow rate of the fixed
capacity pump P may not match the discharge flow rate thereof due
to an excessively large suction resistance. This situation
generates a negative pressure in the pump P which causes cavitation
and generates noise.
[0048] This invention focuses attention on the temperature
characteristics of an orifice and choke as shown in FIG. 4, and by
the use of the choke 21 that generates a large differential
pressure under low temperature, achieves a relative increase in the
recirculation flow rate Q3 with respect to the flow rate Q4 of the
working oil supplied from the reservoir R in a low temperature
state.
[0049] This invention defines the term "choke" as follows. Both the
choke and orifice generate pressure loss due to restriction of the
flow area. In general, the choke denotes a narrow flow area with a
long flow path length L, while the orifice denotes a narrow flow
area that has a short flow path length L. According to this
invention it should be understood that the choke indicates a narrow
flow path in which the pressure loss decreases as the working oil
temperature increases and takes a constant value when the working
oil temperature is above a predetermined temperature.
[0050] In FIG. 4, it can be seen that, when the oil temperature is
lower than twenty degrees Centigrade, especially when it is lower
than zero degrees Centigrade, the pressure loss of the choke is
extremely large. In this temperature range, the flow rate of the
working oil passing through the choke is small.
[0051] When the oil temperature is low, the viscosity of the oil is
large and the pressure loss of the choke 21 in FIG. 1 is large. In
other words, the differential pressure of the choke 21 is large
when the oil temperature is low. As a result, the difference in
pressure in the control pressure chamber 6 and spring chamber 7
increases beyond the difference in pressure at a normal working oil
temperature, and the spool 5 displaces towards the spring chamber 7
so as to increase the opening of the recirculation port 10 at the
same discharge flow rate Q1 of the fixed capacity pump P as in the
case where the working oil temperature is high. Accordingly, the
flowrate Q2 of the working oil supplied to the actuator A decreases
and the recirculation flow rate Q3 of the working oil recirculated
from the recirculation port 10 to the fixed capacity pump P via the
recirculation passage 11 increases.
[0052] Decrease in the flow rate Q2 of the working oil supplied to
the actuator A and increase in the flow rate Q3 of the recirculated
working oil leads to a decrease in the flow rate Q4 of the working
oil supplied from the reservoir R. When the flow rate Q4 of the
working oil sucked from the reservoir R decreases, the pressure
loss generated in the working oil passing through the conduit Rp
decreases. Therefore, cavitation or noise generation in the fixed
capacity pump P does not occur even at a high rotation speed in a
low temperature state.
[0053] As a result, the fixed capacity pump P does not suffer from
a shortage of work oil for suction, while the flow rate Q4 of the
working oil sucked through the conduit Rp remains small.
[0054] Further, the flow rate Q3 represents the flow rate of the
working oil that recirculates through the recirculation passage 11
formed internally in the casing C, and so the pressure loss due to
recirculation is small.
[0055] Referring again to FIG. 4, when the oil temperature rises
above twenty degrees Centigrade, the flow characteristic of the
choke is no longer affected by the viscosity of the oil. In this
situation, the choke 21 functions in the same way as an orifice.
Moreover, when the working oil temperature is high, the suction
resistance due to friction in the conduit Rp does not become very
large. The fixed capacity pump P can therefore suck an adequate
amount of working oil without suffering a large suction resistance,
and the working oil is supplied to the actuator A at a constant
flow rate defined depending on the flow diameter D and flow path
length L of the choke 21.
[0056] As described above, according to this invention, the fixed
capacity pump does not suffer from an insufficient suction flow
rate, and therefore cavitation or generation of noise is prevented
from occurring even when the rotation speed of the motive power
source increases in a low temperature state.
[0057] According to the experiment by the inventors, when the
diameter D of the flow area is set within a range of two to eight
millimeters, by setting the flow path length L to a value that
makes L/D larger than unity, a preferable cavitation/noise
prevention effect is obtained.
[0058] The contents of Tokugan 2004-370463, with a filing date of
Dec. 22, 2004 in Japan, are hereby incorporated by reference.
[0059] Although the invention has been described above by reference
to certain embodiments of the invention, the invention is not
limited to the embodiments described above. Modifications and
variations of the embodiments described above will occur to those
skilled in the art, within the scope of the claims.
[0060] For example, in the above embodiment, this invention is
applied to a pump device wherein the fixed capacity pump P is
connected to the reservoir R via the conduit Rp, but this invention
may also be applied to a pump device wherein the fixed capacity
pump is directly connected to the reservoir, not via a conduit.
[0061] By directly connecting the pump with the reservoir, it is
possible to reduce the suction resistance of the pump, but even in
this case the suction resistance of the working oil supplied from
the reservoir is larger than the suction resistance of the working
oil recirculated through the recirculation passage 11, because the
working oil in the recirculation passage 11 is under the influence
of the pushing force originating from discharge pressure of the
pump.
[0062] Therefore, by applying this invention to a pump device where
the fixed capacity pump is directly connected to the reservoir, a
preferable effect is obtained in preventing an insufficient working
oil supply in a low temperature state for the fixed capacity
pump.
[0063] The opening of the choke 21 is not limited to a circular
shape. When the shape of the opening is polygonal, the diameter D
of a circular opening that has the same cross-sectional area should
be used to determine the flow path length L of the choke 21.
[0064] The embodiments of this invention in which an exclusive
property or privilege is claimed are defined as follows:
* * * * *