U.S. patent application number 10/500341 was filed with the patent office on 2005-06-30 for device for pressure regulation of hydraulic pumps.
Invention is credited to Voigt, Dieter.
Application Number | 20050142006 10/500341 |
Document ID | / |
Family ID | 27438038 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050142006 |
Kind Code |
A1 |
Voigt, Dieter |
June 30, 2005 |
Device for pressure regulation of hydraulic pumps
Abstract
Device for pressure regulation of a hydraulic pump for pumping a
hydraulic medium under pressure, comprising delivery-quantity
regulation; a piston unit including first biasing element; a piston
member; a first surface on the piston member to be biased by a
first biasing force of the hydraulic medium in a first direction; a
second surface on the piston member engaged by the first biasing
element to be biased by a second biasing force in a second
direction, opposite to the first direction; second biasing element
to bias the piston member in addition to the hydraulic medium and
the first biasing element, thus influencing the pressure of the
hydraulic medium.
Inventors: |
Voigt, Dieter;
(Braunschweig, DE) |
Correspondence
Address: |
Martin A Farber
Suite 473
866 United Nations Plaza
New York
NY
10017
US
|
Family ID: |
27438038 |
Appl. No.: |
10/500341 |
Filed: |
February 17, 2005 |
PCT Filed: |
December 9, 2002 |
PCT NO: |
PCT/IB02/05187 |
Current U.S.
Class: |
417/410.4 ;
417/440 |
Current CPC
Class: |
F01M 1/20 20130101; F04C
2270/052 20130101; F04C 14/185 20130101; F01M 1/16 20130101 |
Class at
Publication: |
417/410.4 ;
417/440 |
International
Class: |
F04B 017/00; F04B
035/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 12, 2002 |
DE |
102 00 977.5 |
May 28, 2002 |
DE |
102 23 659.3 |
Jul 4, 2002 |
DE |
102 30 040.2 |
Aug 17, 2002 |
DE |
102 37 801.0 |
Claims
1-9. (canceled)
10. A device for pressure regulation of a hydraulic pump for
pumping a hydraulic medium under pressure, comprising
delivery-quantity regulating means; a piston unit including first
biasing means; a piston member; a first surface on said piston
member to be biased by a first biasing force of said hydraulic
medium in a first direction; a second surface on said piston member
engaged by said first biasing means to be biased by a second
biasing force in a second direction, opposite to said first
direction; second biasing means to bias said piston member in
addition to said hydraulic medium and said first biasing means,
thus influencing the pressure of said hydraulic medium.
11. Device as claimed in claim 10, wherein said hydraulic medium is
lubricating oil, and said hydraulic pump supplies said lubricating
oil to an internal combustion engine.
12. Device as claimed in claim 10, wherein said first biasing means
comprise spring means.
13. Device as claimed in claim 10, wherein said second biasing
means comprise magnetic coil means and armature means acting onto
said piston member.
14. Device as claimed in claim 10, wherein said second biasing
means comprise motor means for adjusting said second biasing force
of said first biasing means.
15. Device as claimed in claim 14, wherein said motor means
comprise a stepping motor.
16. Device as claimed in claim 10, further comprising a first path
of hydraulic medium including means to provide an elevated pressure
of hydraulic medium, and a second path of hydraulic medium
including means to provide a lower pressure of said hydraulic
medium as compared with said elevated pressure, and switch means
for opening at least one of said paths.
17. Device as claimed in claim 16, wherein said second biasing
means comprise electric means to be supplied with electric current,
the device further comprising means for urging said switch means to
open said first path and to provide said elevated pressure when
said supply of electric current fails.
18. Device as claimed in claim 10, wherein said second biasing
means comprise centrifugal valve means, drive means for rotating
said centrifugal valve means to exert a speed-dependent influence
onto the pressure of said lubricating oil.
19. Device as claimed in claim 18, wherein said centrifugal valve
means comprise a first path for lubricating oil to said first
surface of said piston member, at least one second path for
allowing partial draining of said lubricating oil, switching piston
means movable in an at least partially radial direction for
alternatively opening one of said first and second paths, and third
biasing means for biasing said switching piston towards said first
path.
20. Device as claimed in claim 19, wherein said third biasing means
comprise spring means.
21. Device as claimed in claim 19, wherein said switching piston
means are positioned inclined to said radial direction.
22. Device as claimed in claim 19, wherein said drive means
comprise shaft means and pumping gear means, said switching piston
means and said third biasing means being located within said
pumping gear means.
23. Device as claimed in claim 19, wherein said switching piston
means comprises projection means extending in said at least
partially radial direction, said projection means being engaged by
said third biasing means.
24. Device as claimed in claim 10, wherein said second biasing
means comprise electro-valve means.
25. Device as claimed in claim 10, wherein said second biasing
means comprise conveying means for said hydraulic medium for
conveing it into a certain direction, thus altering the pressure of
said hydraulic medium.
26. Device as claimed in claim 25, wherein said conveying means
comprise rotating shaft means and a helical groove in said shaft
means.
27. Device as claimed in claim 10, wherein said piston member
comprises further at least a third surface to be biased by said
hydraulic medium in said first direction, and switching means for
allowing hydraulic medium to pass to at least one of said first and
said at least third surfaces.
28. Device as claimed in claim 10, further comprising hydraulic
filter means arranged in series with said first surface of said
piston member.
29. Device as claimed in claim 10, further comprising housing means
for receiving said hydraulic medium in at least one cavity, said
second biasing means comprising at least one electrical component
which is mounted outside said housing means and at least one
hydraulic conduit means for communication of said cavity and said
electrical component.
30. Device as claimed in claim 10, further comprising housing means
for receiving said piston member, said second biasing means
comprising at least one electrical component attached to said
housing means.
Description
FIELD OF THE INVENTION
[0001] The invention relates to devices for pressure regulation of
hydraulic pumps, in particular for oil pumps, having a
delivery-quantity-regulating device for supplying lubricating oil
to internal combustion engines, having a regulating piston and a
regulating spring for controlling the delivery-quantity-regulating
device, and having an activating device for the regulating piston.
Regulating devices of this type have the object of adapting the
delivery capacity of the hydraulic pump, and in particular of an
oil pump, to changing requirements, for example of the lubricating
system of an internal combustion engine with respect to oil
pressure and oil quantity. This avoids unnecessarily high oil
pressures, and also enables the driving power of the
lubricating-oil pump to be kept low for good efficiency of the
internal combustion engine.
BACKGROUND OF THE INVENTION
[0002] Known oil pumps having delivery-quantity regulation, in
which the oil delivery quantity is matched in accordance with the
configuration of the oil pumps to the requirements of the internal
combustion engine to be supplied, have a lower oil-pump-driving
power than oil pumps having short-circuit regulation. The delivery
quantities are regulated essentially by the oil pressure, with
corresponding delivery-quantity reductions taking place in
particular at higher engine speeds and also at low operating
temperatures.
[0003] In simple oil-pump constructions having delivery-quantity
regulation, the oil pressure is determined directly by a regulating
spring. However, this embodiment has the disadvantage that the
spring has to be configured in accordance with the maximum
oil-pressure requirement at the maximum engine speed of the
internal combustion engine, this then having the consequence of
unnecessarily high oil pressures with correspondingly high driving
powers in the lower speed range. Furthermore, a delivery-quantity
regulation exclusively by means of a regulating spring, as
proposed, for example, in DE 3028573 and DE 3528651, results,
because of the rising spring force of the regulating spring as its
travel increases, in an additional increase in oil pressure, and so
the driving-power advantage which is sought by reducing the
delivery quantity is at least partially offset again as a
consequence of the unnecessary rise in oil pressure.
[0004] The external-gear oil pump which is proposed in DE 10043842
A1 and has axial displacement of the gearwheel largely avoids the
undesirable rise in oil pressure upon reduction of the delivery
quantity by means of a throttle regulation which stabilizes the
oil-pressure level. However, its oil pressure pulsates during the
regulating mode because of a slight, constant variation, caused by
the regulation, in the axial engagement overlap of the two delivery
gearwheels. Frictional forces opposing the axial displacement of
the gearwheels reinforces this effect. To further minimize the
delivery quantity and oil pressure, in particular in accordance
with the lower oil-pressure requirement at low engine speeds, this
throttle regulation additionally requires electric control
components.
[0005] DE 19915737 A1 discloses a method for regulating the
lubrication of an internal combustion engine, in which the
regulation of the oil pump is controlled via a characteristic
diagram as a function of the operating state of the internal
combustion engine, the characteristic variables being taken from
the engine controller. An actuator (not described specifically) of
the oil pump converts the electric activations into changes in the
delivery capacity of the oil pump.
[0006] DE-C-753580 describes an oil pump having a speed-variable
delivery quantity, in which the centrifugal regulator of an
injection pump changes the delivery quantity of the oil pump via a
mechanical coupling. Other configurations of oil pumps which can be
regulated are to be found in DE-A-37 26 800 and U.S. Pat. No.
4,828,462.
SUMMARY OF THE INVENTION
[0007] Starting from this prior art, it is the object of the
invention to provide a regulating device for oil pumps having a
delivery-quantity-regulating device which, as a function of
predefined operating values, for example the operating speed of an
internal combustion engine, reliably minimizes the oil pressure and
also the oil-delivery quantity largely in accordance with the
hydraulic supply requirements, and therefore reduces the driving
power of the oil pump.
[0008] To achieve this object, a device for pressure regulation of
hydraulic pumps having the features mentioned at the beginning is
proposed, the device being distinguished by the fact that the
regulating piston has an active surface for oil pressure which is
always produced, and furthermore can be subjected to an additional
force by the activating device. This has the effect that the oil
pressure is set at least in two regulating-pressure stages. For
this purpose, the regulating piston, which can be subjected to a
variable force by an activating device, brings about the associated
setting of the delivery-quantity-regulating device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention will be explained in greater detail with
respect to function and variant possibilities with reference to the
following drawings:
[0010] FIG. 1 shows an external gear pump which can be regulated in
its delivery quantity with an electromagnetically variable action
of force upon its regulating piston;
[0011] FIG. 2 shows an external gear pump which can be regulated in
its delivery quantity with variable action of force upon its
regulating piston by means of a stepping motor;
[0012] FIG. 3 shows an external gear pump which can be regulated in
its delivery quantity with variable, hydraulic action of force upon
a stepped regulating piston by means of a centrifugally actuated
switching piston;
[0013] FIG. 4 shows an external gear pump which can be regulated in
its delivery quantity with variable action of force upon its
regulating piston by means of an electrovalve and/or by means of a
speed-dependent action upon the oil pressure;
[0014] FIG. 5 shows a further exemplary embodiment, as a variant
for FIG. 3;
[0015] FIG. 6 shows an alternative to FIG. 2; and
[0016] FIG. 7 shows a preferred exemplary embodiment of a
regulating unit.
DETAILED DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a first exemplary embodiment of the
pressure-regulating device according to the invention for an
external-gear oil pump with delivery-quantity regulation. This oil
pump comprises an oil-pump housing 1 in which a driving gearwheel
3, which is fixed on a drive shaft 2, is arranged. The drive shaft
2 is mounted in a cover piston 5 belonging to a closure cover 4.
During a regulation of the delivery quantity, a displacement
gearwheel 6 which is in meshing engagement with the driving
gearwheel 3 is displaced axially in a known manner relative to said
driving gearwheel 3, so that then the oil-delivery quantity is
correspondingly changed by the changed width of engagement of the
teeth.
[0018] The displacement gearwheel 6 is mounted on a nonrotating
bolt 7 which bears a displacement piston 8 on the right-hand side
and a spring piston 9 on the left-hand side. This composite which
is formed is referred to as the displacement unit 10. The
displacement unit 10 is continuously subjected to oil pressure on
its displacement piston 8 while, in a manner opposed to this on the
spring piston 9, a piston spring 11 and also a control pressure
which can be regulated and acts in the spring chamber 12 undertake
the regulation of the delivery quantity.
[0019] The regulation of the control pressure acting in the spring
chamber 12 is undertaken via a control bore 13 by a regulating
piston 14 which is subjected continuously to oil pressure on its
active surface 15 via a connection 16. As a counterforce to this, a
regulating spring 17 acts on the left-hand side of the regulating
piston 14. In the shown regulating position of the regulating
piston 14, its regulating pin 18 is situated lying directly
opposite the control bore 13. The regulating pin 18 is bounded on
the left-hand side by a pressure groove 19 and on the right-hand
side by a relief groove 20.
[0020] Since the regulating pin 18 is slightly narrower than the
diameter of the control bore 13, in the regulating position which
is shown a control pressure is set in the spring chamber 12, it
being possible for the control pressure to lie between the oil
pressure produced in the pressure groove 19 via a further
connection 21 and a complete relief from pressure, which can be fed
in via the relief groove 20. The relief groove 20 is connected to
the surroundings via a diagonal bore 22 in the regulating piston
14.
[0021] As soon as the oil pressure produced at the active surface
15 exceeds the level of the maximum operating oil pressure required
of, for example, 5 bar for the associated internal combustion
engine, the regulating piston 14 is displaced counter to the force
of the regulating spring 17 with the effect of reducing the control
pressure in the spring chamber 12. By this means, the displacement
unit 10 is displaced, for the purpose of reducing the delivery
quantity, to the left until the oil pressure reaches the desired
value of, for example, 5 bar. Conversely, a dropping of the
pressure below the desired oil pressure of 5 bar leads to a
displacement of the regulating piston 14 by the regulating spring
17 to the right, this triggering, by means of an increase in the
control pressure in the spring chamber 12, a corresponding increase
in the delivery quantity with a resultant rise in the oil
pressure.
[0022] The activating device of the regulating piston 14, which
device is required for the reduction according to the invention of
the oil pressure, comprises a magnet coil 23 which, upon
appropriate activation by means of a controller of the internal
combustion engine, exerts via its armature 24 a magnetic additional
force on the regulating piston 14. A change in the magnetic
positional force can be undertaken by the controller either
continuously or in a stepwise manner orientated to requirements,
which has a corresponding effect on the regulation of the oil
pressure and delivery quantity of the oil pump.
[0023] The hydraulic connections 16, 21 and 26 to the displacement
piston 8 and the regulating piston 14, which connections do not
branch off until behind the oil filter 25, have two advantages.
Firstly, the oil pressure behind the oil filter 25 is set to the
desired pressure level by the pressure regulation of the oil pump,
so that a reliable oil pressure for the lubrication of the internal
combustion engine is ensured irrespective of variable pressure
losses from the oil filter 25 caused by soiling. Secondly, all of
the parts of the regulating device and also all bearings of the oil
pump, for example the mounting of the drive shaft 2 in the cover
piston 5, are supplied with filtered oil from displacement chamber
28 via an oil bore 27, so that the operational reliability and also
the service life of the oil pump are increased.
[0024] FIG. 2 shows a further exemplary embodiment of the invention
with continuously variable regulation of the oil pressure. For the
reduction according to the invention of the oil pressure, instead
of the magnet coil 23 from FIG. 1, here a stepping motor 29 having
an adjustable spring system 30 for the regulating spring 17 of the
regulating piston 14 (now illustrated without being cut away) is
used. The basic position of the spring system 30 of regulating
spring 17, which is set automatically without electric activation
of the stepping motor 29, ensures the maximum operating oil
pressure required of, for example, 5 bar, by the appropriate
prestressing of the regulating spring 17. A correspondingly
programmed controller of the internal combustion engine enables the
oil pressure to be reduced in a manner matching requirements or, in
special applications, even to be increased further.
[0025] FIG. 3 shows a preferred exemplary embodiment of the
oil-pressure and delivery-quantity regulation according to the
invention using the example of an external-gear oil pump, in which
the activating device of the regulating piston takes place
exclusively as a function of centrifugal force in two
speed-regulating-pressure stages. The regulating piston, which is
now formed as a step piston 51, is derived from the regulating
piston 14 of FIGS. 1 and 2. It has a regulating spring 52 on the
left-hand side and, on the right-hand side, a first active surfaces
53 which is continuously subjected to oil pressure. At low
operating speeds of the internal combustion engine, a second active
surface 54 on the right-hand side of the step piston 51 is likewise
subjected to oil pressure, so that an oil-pressure regulation at,
for example, 2.5 bar of the first regulating-pressure stage takes
place by the action of the oil pressure on the two active surfaces
53 and 54 and on the correspondingly configured regulating spring
52. The increase in oil pressure, which is required by the engine
at high speeds, to an oil-pressure level of, for example, 5 bar of
the second regulating-pressure stage requires a complete relieving
of the second active surface 54 from pressure for the corresponding
regulating function of the step piston 51. In this exemplary
embodiment, the activating device for changing between the two
regulating-pressure stages by the action of oil pressure on the
second active surface 54 of the step piston 51 or relief thereof
from pressure comprises a centrifugal valve which is arranged in
the driving gearwheel 55 and acts as a function of the speed.
[0026] FIG. 4, which belongs to FIG. 3, shows the compact
centrifugal valve on an enlarged scale. It comprises a switching
piston 56 and a switching-piston spring 57. For spatial reasons,
the switching piston 56 is orientated obliquely with respect to the
radial direction of centrifugal force, but could, in certain cases,
also be orientated radially, i.e. its orientation has to have at
least one radial component. The stepped receiving bore of the
switching piston 56 and switching-piston spring 57 may even, for
space reasons, protrude partially into a tooth of the driving
gearwheel 55. The position which is shown for the switching piston
56 with relaxed switching-piston spring 57 corresponds to low
operation speeds with little centrifugal-force action. A guide pin
59 situated on the switching piston 56 ensures the radial guidance
of the switching-piston spring 57 and prevents deflections thereof
caused by centrifugal force.
[0027] The oil pressure produced on the switching piston 56 via the
oil bore 27 and the associated circumferential bevel of the cover
piston 5 also acts continuously via its central bore 60 in the
chamber of the switching-piston spring 57. At low operating speeds,
the oil pressure is conducted, as a consequence of the position of
the switching piston 56 that is shown in FIG. 4, via an oblique
bore 61 of the driving gearwheel 55 and via a connecting bore 62 of
the oil-pump housing 63 onto the second active surface 54 of the
step piston 51 in order thereby to activate the first
regulating-pressure stage with oil pressure, for example of 2.5
bar.
[0028] After the changeover speed for activating the second
regulation-pressure stage is exceeded, for example at 2500/min, the
switching piston 58 is caused by centrifugal force to be displaced
counter to the switching-piston spring 57 into its outer end
position. By this means, in order to raise the oil pressure to the
second regulating-pressure stage of 5 bar, the step piston 51 is
relieved from pressure on its second active surface 54 by a
connection being produced via the oblique bore 61 and a
circumferential groove 64 of the switching piston 56 and via
further cross sections to the central bore 65 of the drive shaft
58, which is open at the right-hand end.
[0029] With reference to FIG. 3, FIG. 5 shows an exemplary
embodiment in which the step piston 51 can be subjected to oil
pressure on its second active surface 54 by two further,
independent activating devices (illustrated in FIG. 5). The two
activating devices may, as shown in FIG. 5, enter into operation in
combination with each other, but may also each operate
independently with the other activating device being omitted.
[0030] The first activating device, has, on the drive shaft 74, a
spiral groove 73 which is bounded on both sides by the
circumferential grooves 75 and 76. It has a relatively small groove
depth and, during rotation of the drive shaft 74, produces a
speed-dependent drop of pressure over its length by means of
oil-shearing forces which occur. The circumferential groove 75 on
the left-hand side is subjected to oil pressure via the oil bore
27. The direction of inclination of the spiral groove 73 is
selected in such a manner that, when the drive shaft 74 rotates,
the drop in pressure acting in the spiral groove 73 causes a
reduction in pressure in the circumferential groove 76 on the
right-hand side. The speed-variable pressure in the circumferential
groove 76 is conducted via a longitudinal bore in the drive shaft
74 and via a connecting bore 79, which is situated in the housing
78, onto the second active surface 54 of the step piston 51.
[0031] At maximum speed, the oil pressure of, for example, 5 bar
which is produced in the circumferential groove 75 is reduced by a
relatively high drop in pressure produced by the spiral groove 73
to virtually 0 bar in the circumferential groove 76, so that the
second active surface 54 of the step piston 51 is effectively
relieved from pressure at 5 bar for the desired pressure regulation
of the oil pressure. With decreasing speed, the drop in pressure in
the spiral groove 73 is reduced continuously, so that pressure on
the second active surface 54 of the step piston 51 correspondingly
rises and the oil pressure is regulated at a pressure level which
can vary as a function of speed.
[0032] The second activating device for the step piston 51, which
device can be fitted on its own or together with the first
activating device, comprises an electrovalve 71 which, upon
electrical activation, switches the oil pressure onto the second
active surface 54 of the step piston in order to reduce the oil
pressure of the oil pump. Both active surfaces 53 and 54 are
therefore loaded by oil pressure, so that the step piston 51, even
at an oil pressure of, for example, 2.5 bar for the first
regulating-pressure stage, exerts its regulating function counter
to the force of the regulating spring 52 and provides the
corresponding control pressure for regulating the delivery
quantity.
[0033] When the electrovalve 71 is not energized, the supply of oil
pressure is interrupted and a pressure relief or loading of the
second active surface 54 is caused via a relief connector 72 on the
electrovalve 71. The oil pressure, which is now only produced on
the first active surface 53 of the step piston 51, then shifts the
start of the regulating operation to a higher value, for example 5
bar, of the second regulating-pressure stage. The second
regulating-pressure stage is ensured as a safety oil pressure for
all operating conditions of the internal combustion engine if there
is an interruption, caused by a defect, in the electrical
connections of the electrovalve 71.
[0034] In the combined function (for example) of the two activating
devices that are shown in FIG. 5, a continuously speed-variable
regulation of the oil pressure can be carried out by the spiral
groove 73 when the internal combustion engine is operationally
warm, but the electrovalve 71 then has to keep its connection to
the step piston 51 closed by means of an additional function. The
electrovalve 71 then enters into operation during cold operation
when the spiral groove 73 is effectively unusable because of
viscous oil. Its two-stage oil-pressure regulation by means of
pressurization or pressure release of the second active surface 54
of the step piston 51 then takes place in a known manner.
[0035] In principle, the regulation of the oil pressure that is
undertaken by the step piston 51 can also be carried out in a
number of stages with a correspondingly formed step piston. In this
case, its partial active surfaces would then have to be subjected
to oil pressure in a speed-offset manner, for example, by an
activating device formed with multiple stages.
[0036] When electric components are used for the oil-pressure
regulation of an internal combustion engine, an arrangement of the
electric parts outside the crank space accommodating the oil pump
is advantageous. While, on the one hand, the loading of
temperature- and/or oil-sensitive electric parts is reduced as a
result, the electric connections to the crank space are also
omitted, on the other hand, with the accessibility to the electric
parts, for example for repair purposes, being improved. The
electric valve 71 which is shown in FIG. 5 may be fitted, for
example, on the outside of the crank case. The electrically
switchable action of oil pressure on the second active surface 54
of the step piston 51 can then take place via oil bores through the
flange face of the oil-pump fastening on the crank case. However,
with the electrically produced action of an additional force on the
regulating piston 14 according to FIGS. 1 and 2, an arrangement of
the magnet coil 23 or stepping motor 29 external to the crank space
also requires the regulating piston 14 to be shifted.
[0037] The exemplary embodiment in FIG. 6 shows, as an alternative
to FIG. 2, an arrangement in which the stepping motor 29 is
combined with the regulating piston 80 in a common housing 81 to
form a regulating unit 82. The regulating unit 82, which is fitted
to the outside of the crank case 84, ensures a reliable pressure
regulation of the oil pump by means of an electric connection 83,
which is now problem-free, and via a control bore 87, which passes
through the flange face 85, to the spring chamber 12 of the oil
pump 86.
[0038] To further increase the operational reliability, the
regulating unit 82 is fed from an adjacent crank case main oil bore
88 with pressure oil cleaned in an oil filter 89. This pressure oil
acts continuously, in the manner relevant for regulation via
corresponding connecting cross sections of the regulating unit 82,
on the end side on the active surface 90 of the regulating piston
80 and also via a line 91 in the displacement chamber 28 of the oil
pump 86. The necessary pressure relief of the spring side of the
regulating piston 80 and also the conducting of oil out of the
spring chamber 12 when reducing the delivery quantity takes place
via corresponding connecting cross sections of the regulating unit
82 into the relief duct 92 which is open to the interior of the
crank case 84.
[0039] FIG. 7 illustrates an electrically activated regulating unit
100 which operates in two regulator stages, with an arrangement on
the crank case. It comprises the step piston 51, which has already
been described with reference to FIG. 5, an associated housing 101
and an electrovalve 102. As in the embodiment according to FIG. 6,
in this two-stage pressure regulation too, the oil pump 103 is
pressure-regulated only via the connecting control bore 87. By this
means, and also by means of an oil-pump-internal pressurization of
the displacement chamber 28 with the delivery-oil pressure
(omission of the line 91 from FIG. 6), an advantageous
simplification of the oil pump is also possible in a two-stage
pressure regulation. Without an electric activation of the
electrovalve 102, the second active surface 54 of the step piston
51 is relieved from pressure via the relief duct 92, which is on
the left in FIG. 7, so that the step piston 51, which is acted upon
by oil pressure only via the first active surface 53, then carries
out with its regulating spring 52 the pressure regulation of the
oil pump at a higher pressure-regulating level. By contrast, with
the electric activation of the electrovalve 102, the second active
surface 54 of the step piston 51 is additionally also acted upon by
the oil pressure, so that then the pressure regulation of the oil
pump 103 takes place at a reduced pressure-regulating level.
[0040] The regulation according to the invention of the oil
pressure is largely independent of the temperature-dependent
viscosity of the delivery oil. Therefore, by means of the proposed
pressure regulation for oil pumps of motor-vehicle internal
combustion engines, effectively reduced fuel consumption by means
of oil-pump driving powers which are not inconsiderably reduced can
be obtained not only when the engine is operationally warm, but
also, in particular, even in the daily cold operation with oil
temperatures which are still low after the engine is started.
[0041] Numerous modifications are conceivable within the context of
the invention; for example, individual features from various
embodiments of the one described above can be combined with one
another and/or with the prior art. It is also possible for, for
example, the activating device to have a plurality of the
above-mentioned components.
* * * * *