U.S. patent application number 14/633410 was filed with the patent office on 2015-08-27 for method for conveying hydraulic fluid, and electrohydraulic motor-pump unit therefor.
This patent application is currently assigned to Rausch & Pausch GmbH. The applicant listed for this patent is Rausch & Pausch GmbH. Invention is credited to Rocco KEMNITZ.
Application Number | 20150240812 14/633410 |
Document ID | / |
Family ID | 52462141 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150240812 |
Kind Code |
A1 |
KEMNITZ; Rocco |
August 27, 2015 |
METHOD FOR CONVEYING HYDRAULIC FLUID, AND ELECTROHYDRAULIC
MOTOR-PUMP UNIT THEREFOR
Abstract
An electrohydraulic motor-pump unit comprises an unsteadily
conveying displacement pump for conveying hydraulic fluid in a
hydraulic system, an electric motor coupled with the displacement
pump for driving the displacement pump, and an electrical control
device coupled with the electric motor for controlling the electric
motor. By way of a detector there is captured a pulsation
parameter, which originates from a pulsation arising due to
unsteady conveyance of hydraulic fluid in the hydraulic system, and
by way of a modulator as part of the electrical control device the
drive torque or the rotating speed of the electric motor for
driving the displacement pump is modulated on the basis of the
captured pulsation parameter. As a result the drive torque or the
rotating speed of the electric motor is modulated in accordance
with the conveying frequency of the displacement pump.
Inventors: |
KEMNITZ; Rocco;
(Bobenneukirchen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rausch & Pausch GmbH |
Selb |
|
DE |
|
|
Assignee: |
Rausch & Pausch GmbH
Selb
DE
|
Family ID: |
52462141 |
Appl. No.: |
14/633410 |
Filed: |
February 27, 2015 |
Current U.S.
Class: |
417/53 ;
417/410.1 |
Current CPC
Class: |
F04B 49/065 20130101;
F04B 2203/0207 20130101; F04C 2270/035 20130101; F04B 17/03
20130101; F04C 15/0049 20130101; F04C 14/08 20130101; F04B 11/0041
20130101; F04B 3/00 20130101; F04B 15/02 20130101; F04C 2/08
20130101; F04B 11/00 20130101; F04C 2270/0525 20130101; F04C 15/008
20130101; F04C 13/002 20130101; F04C 11/008 20130101 |
International
Class: |
F04C 14/08 20060101
F04C014/08; F04C 13/00 20060101 F04C013/00; F04B 3/00 20060101
F04B003/00; F04B 11/00 20060101 F04B011/00; F04B 15/02 20060101
F04B015/02; F04B 17/03 20060101 F04B017/03; F04C 2/08 20060101
F04C002/08; F04C 15/00 20060101 F04C015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2014 |
DE |
10 2014 102 591.1 |
Claims
1. An electrohydraulic motor-pump unit, comprising: an unsteadily
conveying displacement pump which is arranged for conveying
hydraulic fluid in a hydraulic system, an electric motor coupled
with the displacement pump and arranged for driving the
displacement pump, and an electrical control device coupled with
the electric motor and arranged for controlling the electric motor,
further comprising a modulator as part of the electrical control
device, which is arranged for modulating a drive torque or a
rotating speed of the electric motor for driving the displacement
pump in accordance with a conveying frequency of the displacement
pump.
2. The motor-pump unit according to claim 1, wherein the
displacement pump, the electric motor and the electrical control
device are housed in a common housing block having hydraulic
connections which are arranged for coupling the motor-pump unit to
a hydraulic system, wherein the housing block preferably further
comprises a hydraulic fluid tank for hydraulic fluid.
3. The motor-pump unit according to claim 1, comprising a detector
which is arranged for capturing a pulsation parameter which
originates from a pulsation arising due to unsteady conveyance of
hydraulic fluid in a hydraulic system, wherein the modulator is
arranged for modulating the drive torque or a rotational speed of
the electric motor on the basis of the captured pulsation
parameter.
4. The motor-pump unit according to claim 3, further comprising, as
a detector, a pressure sensor which is arranged for capturing as
the pulsation parameter a hydraulic pressure.
5. The motor-pump unit according to claim 3, further comprising, as
a detector, a pressure sensor on one of the hydraulic connections,
which is arranged for capturing as the pulsation parameter a
hydraulic pressure present on the hydraulic connection.
6. The motor-pump unit according to claim 3, further comprising, as
a detector, an evaluation circuit which is arranged for capturing
as the pulsation parameter the drive torque of the electric motor,
wherein the evaluation circuit is implemented in the electrical
control device.
7. The motor-pump unit according to claim 1, wherein the modulator
comprises a circuit with an FPGA (field programmable gate
array).
8. A hydraulic system, comprising hydraulic lines and a motor-pump
unit according to claim 1 connected to said hydraulic lines.
9. A method for conveying hydraulic fluid in a hydraulic system by
an electrically driven, unsteadily conveying displacement pump,
comprising: smoothing a pulsation of the hydraulic fluid in the
hydraulic system, arising on due to the unsteady conveyance, by
modulating a drive torque or a rotating speed of the electrical
drive in accordance with a conveying frequency of the displacement
pump.
10. The method according to claim 9, wherein smoothing comprises a
pulsation parameter wherein the pulsation is captured and the drive
torque or the rotational speed of the electrical drive is modulated
on the basis of the captured pulsation parameter.
11. The method according to claim 10, wherein the drive torque or
the rotational speed of the electrical drive is modulated on the
basis of a pressure pulsation measured in the hydraulic fluid.
12. The method according to claim 10, wherein the drive torque of
the electrical drive is modulated on the basis of a torque
pulsation measured on the electrical drive.
13. The method according to claim 10, wherein the modulating of the
drive torque or of the rotational speed of the electrical drive is
effected via a circuit with an FPGA (field programmable gate
array).
14. The method according to claim 9, further comprising employing a
motor-pump unit.
Description
[0001] The present invention relates to a method for conveying
hydraulic fluid in a hydraulic system by means of an electrically
driven, unsteadily conveying displacement pump or, more precisely,
a method for smoothing a pulsation of the hydraulic fluid arising
in the hydraulic system due to the unsteady conveyance. The
invention relates furthermore to an electrohydraulic motor-pump
unit for employment in the method according to the invention.
[0002] The term "electrohydraulic motor-pump unit" refers to a
system consisting of a hydraulic displacement unit, an electric
motor and an appurtenant electrical control device. Such motor-pump
units are frequently designated "power packs" colloquially. They
serve for converting electrical energy to hydraulic energy and find
use in numerous areas of application, such as the automobile
sector, in mobile work machines or also quite generally in the
industrial sector.
[0003] Different hydraulic displacement units, electric motors and
electrical controls for the electric motors are known in connection
with such motor-pump units. A great variety of principles of
displacement are used here, such as for example internal gear
pumps, external gear pumps, piston pumps, and the like. All these
principles of displacement have in common that the displacement
pumps are characterized by an unsteady conveyance of the hydraulic
fluid, in spite of a steady drive by means of the electric motor,
which results in a more or less pronounced pulsation of the
pressure in the hydraulic connections, both on the suction side
and--in particular--on the pressure side.
[0004] The unsteadiness of the hydraulic fluid conveyance is due to
the fact that, depending on their design, the displacement pumps
have one or more pump chambers which successively first draw in
hydraulic fluid from the suction side and subsequently discharge it
on the pressure side. Thus, for example in piston pumps, a pressure
pulse is generated in the hydraulic system with every stroke. In
the case of gear pumps, a number of pressure pulses corresponding
to the number of pump gear teeth is generated in the hydraulic
system with every rotation of the pump gear. The pulsation
frequency thus depends on the speed at which the displacement pump
is operated, that is, on its "conveying frequency", i.e. the
frequency per time unit at which the displacement pump draws in and
discharges hydraulic fluid by means of its pump chamber or pump
chambers. The conveying frequency is generally regular, but this is
by no means necessary.
[0005] The pressure pulsation occurring in the hydraulic fluid as a
result of the unsteady conveying volume leads to disadvantageous
phenomena in the hydraulic system, in particular frequently
bothersome noise as a result of excited vibrations.
[0006] To avoid the pressure pulsation being transferred to the
hydraulic system, secondary measures are taken in known hydraulic
systems, with for example hydraulic accumulators, so-called
pulsation dampeners, or also baffles being integrated in the lines,
or the lines being formed at least partly by hoses with defined
resilience, so-called extension hoses.
[0007] Depending on the respective smoothing measures, they involve
effort and/or costs in selection, coordination, arrangement and/or
assembly.
[0008] The object of the present invention is to provide an
alternative for smoothing the pressure pulsation in a hydraulic
system that occurs due to the unsteady conveyance by means of
displacement pumps. In this connection it is a further object of
the present invention to propose an electrohydraulic motor-pump
unit suitable therefor.
[0009] Accordingly, a method according to the invention for
conveying hydraulic fluid in a hydraulic system by means of an
electrically driven, unsteadily conveying displacement pump
provides for smoothing the pulsation of the hydraulic fluid arising
in the hydraulic system due to the unsteady conveyance by suitably
modulating the drive torque or the rotating speed of the electrical
drive in accordance with the conveying frequency of the
displacement pump.
[0010] Since the pulsation in the hydraulic system depends directly
on the conveying frequency of the displacement pump, there can
advantageously be captured and utilized for the purposes of said
modulation a pulsation parameter characterizing the pulsation, for
example i.e. the pressure pulsation in the hydraulic system, and
the drive torque of the electrical drive for driving the
displacement pump can be modulated in accordance with said captured
pulsation parameter.
[0011] For the pulsation in the hydraulic system caused by the pump
chambers of the displacement pump generates an associated torque
pulsation on the drive shaft of the displacement pump. Via the
corresponding modulation of the drive torque of the electrical
drive on the basis of the captured pulsation parameter, i.e. for
example on the basis of the pressure pulsation captured in the
hydraulic system, it is possible to compensate the torque
unsteadiness on the drive shaft of the displacement pump and thus
already smooth, that is, eliminate or at least minimize, the
pulsation on the hydraulic connections.
[0012] Instead of modulating the drive torque of the electrical
drive, it is alternatively also possible to directly modulate the
rotating speed of the electrical drive. For the modulation of the
drive torque also ultimately leads to nothing other than a
corresponding change, i.e. modulation, of the rotating speed and
hence as a result respectively to a temporal modulation of the
conveyance through the displacement pump.
[0013] If the pressure pulsation in the hydraulic system is used as
a hydraulic parameter, it is advantageous to capture the pressure
on one or more of the hydraulic connections of the motor-pump unit
for example by means of a pressure sensor, preferably on the
pressure side. Alternatively, instead of the pressure, there can
also be captured the pulsation of the volume flow, preferably again
directly on one or more of the hydraulic connections of the
motor-pump unit, and preferably again on the pressure side.
[0014] The captured pulsation parameter, whether it be the
pulsation of the hydraulic pressure or the pulsation of the
conveyed volume flow, then serves as the input variable for the
control device of the electric motor for balancing out the
pulsation, after the captured pulsation parameter has been resolved
into a signal processable by the control device. Since said input
variable reacts upon the input variable again via the control
device of the electric motor and via the displacement pump driven
by means of the electric motor, the overall result is a feedback
control system.
[0015] According to a preferred embodiment variant, there is used
as a pulsation parameter, instead of the pressure pulsation or the
volume flow pulsation, a pulsation or vibration of the drive torque
of the electric motor itself. For, as mentioned hereinabove, the
pulsation caused by the unsteadily conveying displacement pump
generates an associated torque pulsation on the drive shaft of the
displacement pump. Through a circuit, implemented in the electrical
control device, for establishing the torque of the electric motor,
said torque pulsation of the drive shaft can be captured and used
for modulating the drive torque of the electric motor for driving
the displacement pump.
[0016] For the necessary modulation of the drive torque on the
basis of such a pulsation parameter, an accordingly fast-reacting
electrical control device of the electric motor is required.
Suitable for such extremely fast cycle times in electronics are for
example circuits with so-called field programmable gate arrays
(FPGAs). Further, when selecting the electric motor one should make
sure the model has sufficient dynamics.
[0017] An electrohydraulic motor-pump unit suitable for the
hereinabove described method accordingly comprises an unsteadily
conveying displacement pump for conveying hydraulic fluid in a
hydraulic system, an electric motor coupled with the displacement
pump for driving the displacement pump, and an electrical control
device coupled with the electric motor for controlling the electric
motor, wherein the displacement pump, the electric motor and the
control device are preferably housed in a common housing block
having hydraulic connections which are arranged for coupling the
motor-pump unit to a hydraulic system. The housing block can
furthermore advantageously comprise a hydraulic fluid tank for the
hydraulic system. In any case the electrohydraulic motor-pump unit
additionally has, as part of the electrical control device, a
modulator for modulating the drive torque of the electric motor in
accordance with the conveying frequency of the displacement pump,
wherein preferably furthermore a detector for capturing one of the
hereinabove described pulsation parameters is provided and the
modulator is arranged for modulating the drive torque of the
electric motor on the basis of the captured pulsation
parameter.
[0018] However, the capturing of a pulsation parameter and
modulating of the drive torque on the basis of the captured
pulsation parameter, that is, the setup of a complete feedback
control system, is by no means necessary for smoothing the
pulsation. A smoothing is already obtained when the modulation of
the drive torque in accordance with the conveying frequency of the
displacement pump is firmly preset on the basis of values derived
from experience. It is true that the pulsation also depends on
properties of the hydraulic system, in particular the elasticity of
the hydraulic system, so that a completely feedback-controlled
system with consideration of current pulsation parameters is
advantageous. But a firm presetting of a drive-torque modulation
dependent on the conveying frequency of the displacement pump can
already lead to satisfactory results. For purposes of optimization
it is also possible to adapt said firm presetting later, or to only
set it when the motor-pump unit is connected to the hydraulic
system for which it is intended.
[0019] The advantages achieved with the invention consist in that
the pressure pulsation on the hydraulic connections can be
minimized or almost completely eliminated. Secondary measures for
pulsation reduction in the hydraulic system can thereby be omitted,
where applicable, so that for example assembly effort and/or costs
can be reduced.
[0020] Hereinafter the invention will be described by way of
example with reference to the accompanying drawings. Therein are
shown:
[0021] FIG. 1 a realistic representation of an electrohydraulic
motor-pump unit according to a first exemplary embodiment of the
invention on a 1:1 scale,
[0022] FIG. 2 a schematic and idealized representation of the time
course of the hydraulic pressure of the drive torque and of the
motor speed in a hydraulic system with and without pulsation
compensation,
[0023] FIG. 3 a realistic representation of an electrohydraulic
motor-pump unit according to a second exemplary embodiment of the
invention on a 1:1 scale, and
[0024] FIG. 4 a realistic representation of an electrohydraulic
motor-pump unit with an integrated hydraulic tank on a 1:2
scale.
[0025] FIG. 1 shows a first exemplary embodiment of an
electrohydraulic motor-pump unit, wherein a displacement pump 1, an
electric motor 2 and an electrical control device 3 are housed in a
common housing block. The displacement pump 1 possesses two
hydraulic connections 4 for connecting the motor-pump unit to the
suction side and the pressure side of a hydraulic system. Further
hydraulic connections can be provided.
[0026] As displacement pumps there come into consideration a great
variety of unsteadily conveying hydraulic displacement units, such
as for example the hereinabove mentioned internal gear pumps,
external gear pumps, piston pumps or other pumps with successively
conveying pump chambers. The nature of the electric motor is
substantially uncritical for the invention. What is crucial is that
the drive torque for the electric motor 1 supplied by the electric
motor and the rotating speed of the electric motor 1 are
adjustable, for drive torque and rotating speed are directly
related to each other. For adjusting or modulating the drive torque
or the rotating speed of the electric motor 2 there is used the
electrical control device 3.
[0027] A pressure sensor 5 is so disposed on the hydraulic pump 1
that the pressure on the pressure-side hydraulic connection 4 can
be measured therewith. In reversible motor-pump units it may be
expedient to provide a further pressure sensor on the second
hydraulic connection 4 in a corresponding manner. Via a return line
6 the sensor signal supplied by the pressure sensor 5 is fed to the
electronic control device 3. The sensor signal is processed in the
electronic control device 3 and employed for modulating the drive
torque of the electric motor in accordance with the conveying
frequency of the displacement pump such that it is constant if
possible. As a result this also leads to the rotating speed of the
electric motor being modulated. Through suitable modulation of the
drive torque or of the rotating speed of the electric motor the
pressure relations in the hydraulic system can be changed, and
through suitable change pressure fluctuations can be compensated.
Since the pressure sensor 5 captures pressure fluctuations directly
on the hydraulic connection 4 and since the pressure fluctuations
occurring on the hydraulic connection originate substantially
solely from the unsteady conveyance of the hydraulic fluid by means
of the displacement pump, the described setup of the motor-pump
unit according to FIG. 1 enables pressure pulsations in the
hydraulic system to be smoothed through suitable modulation of the
drive torque or of the rotating speed of the electric motor.
[0028] FIG. 2 shows schematically over the time t the course of the
pressure p in the hydraulic system and the course of the drive
torque M on the drive shaft of the electrical drive in comparison
to the course of the rotating speed (U/min, or rpm) of the
electrical drive. The course without pressure compensation control
is represented therein in dash lines with p.sub.0, M.sub.0 and
U.sub.0/min, while the course with compensation control is
respectively represented as a continuous line. In this idealized
representation it is recognizable that upon operation without
compensation control the pressure p.sub.0 in the hydraulic system
and the drive torque of the electrical drive respectively fluctuate
around an average p.sub.M and M.sub.M, while the motor speed
remains constant at an average rotational speed U.sub.M/min. In
reality, said value U.sub.M/min actually also fluctuates around the
average U.sub.M/min, but only slightly, because the motor conveys
alternately against slightly higher and lower pressures in the
hydraulic system due to the unsteady conveyance and the resulting
volume flow pulsation.
[0029] By the drive torque M.sub.0 of the electrical drive now
being modulated in accordance with the hydraulic pressure measured
on the hydraulic connection 4, a change of the rotating speed
p.sub.0 of the electric motor is obtained, the result being that
the time course of the hydraulic fluid volume conveyed by the
displacement pump undergoes a corresponding change, so that
ultimately the hydraulic pressure p present in the hydraulic system
and on the hydraulic connections 4 and the drive torque M present
on the electric motor also change accordingly. The modulation of
the drive torque of the electric motor or of the rotating speed of
the electric motor is in so doing adjusted such that the pressure
pulsation on the hydraulic connection 4 is ideally compensated
completely. That is to say, in an idealized view, at times when the
pressure p.sub.0 in the system sinks due to the pressure pulsation,
the drive torque M or the rotating speed of the electric motor is
so modulated that the electric motor conveys more volume per time
unit in order to raise the lower system pressure p.sub.0 to the
average pressure p.sub.M, and at a higher system pressure p.sub.0
vice versa.
[0030] FIG. 3 shows a second exemplary embodiment of an
electrohydraulic motor-pump unit. In this exemplary embodiment, a
different pulsation parameter is used for modulating the drive
torque or the rotating speed of the electric motor 2, i.e. the
drive torque M.sub.0 of the electric motor 2 is utilized as a basis
for the modulation instead of the hydraulic pressure p.sub.0 in the
hydraulic system. That is to say, by means of an evaluation circuit
of the electrical control device 3 it is monitored to what extent
the drive torque M.sub.0 of the electric motor 2 pulsates due to
the unsteadily conveying displacement pump 1, and this pulsation
parameter serves in the electrical control device 3 for regulating
the drive torque or the rotating speed of the electric motor 2 such
that all drive torque fluctuations are compensated if possible.
This technical solution is the least elaborate constructively and
leads to a smoothing of the pressure pulsation in the hydraulic
system in a simple manner, because all pressure pulsation in the
hydraulic system reacts upon the torque Mo present on the electric
motor 2.
[0031] FIG. 4 shows a motor-pump unit, having a hydraulic
displacement unit 1, an electric motor 2 and an integrated
hydraulic tank 7, as is preferably employed in a hydraulic system.
The hydraulic lines are marked as 8. The electrical control device
3 is not clearly recognizable here, but is part of the electric
motor 2.
[0032] In the above-described pulsation compensation circuits an
accordingly fast electrical control of the electric motor 1 is
required due to the extremely fast cycle times. Circuits with field
programmable gate arrays (FPGAs) are advantageously suited
therefor, whereby when selecting the electric motor 1 one should of
course also make sure the model has sufficient dynamics.
* * * * *