U.S. patent application number 13/009610 was filed with the patent office on 2011-07-28 for method for controlling the feed rate of a feed pump.
Invention is credited to Josef Frank, Alexander Fuchs, Klaus Ortner.
Application Number | 20110182752 13/009610 |
Document ID | / |
Family ID | 44294973 |
Filed Date | 2011-07-28 |
United States Patent
Application |
20110182752 |
Kind Code |
A1 |
Frank; Josef ; et
al. |
July 28, 2011 |
METHOD FOR CONTROLLING THE FEED RATE OF A FEED PUMP
Abstract
A method for controlling the feed rate of a feed pump, including
a drive part having a drive motor and a hydraulic part having an
intake opening, a discharge opening and a feed mechanism situated
in between, a setpoint feed rate being predefined and the feed pump
being triggered based on the setpoint feed rate, the temperature of
the fluid and a pressure difference between the intake opening and
the discharge opening of the hydraulic part of the feed pump.
Inventors: |
Frank; Josef; (Koloman,
AT) ; Fuchs; Alexander; (Adnet, AT) ; Ortner;
Klaus; (Salzburg, AT) |
Family ID: |
44294973 |
Appl. No.: |
13/009610 |
Filed: |
January 19, 2011 |
Current U.S.
Class: |
417/32 ;
417/53 |
Current CPC
Class: |
F04B 49/065 20130101;
F04B 2203/0209 20130101; F04D 15/0066 20130101; F04B 2205/07
20130101; F04B 2205/11 20130101; F04B 17/03 20130101; F04B 49/103
20130101; F04B 49/106 20130101; F04B 49/08 20130101; F04B 2201/1201
20130101; F04B 49/20 20130101 |
Class at
Publication: |
417/32 ;
417/53 |
International
Class: |
F04B 49/06 20060101
F04B049/06; F04B 49/10 20060101 F04B049/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 22, 2010 |
DE |
10 2010 001 150.9 |
Claims
1. A method for controlling a feed rate of a feed pump, including a
drive part having a drive motor and a hydraulic part having an
intake opening, a discharge opening and a feed mechanism situated
in between, comprising: specifying a setpoint feed rate; and
triggering the feed pump based on the setpoint feed rate, a
temperature of the fluid, and a pressure difference between the
intake opening and the discharge opening of the hydraulic part of
the feed pump.
2. The method according to claim 1, further comprising determining
the pressure difference based on a drive torque of the drive
motor.
3. The method according to claim 2, further comprising determining
the drive torque based on a motor current flowing through the drive
motor.
4. The method according to claim 3, further comprising determining
at least one of (a) an actual feed rate and (b) a setpoint
rotational speed using characteristic map based on the temperature
and the motor current.
5. The method according to claim 1, further comprising determining
the pressure difference based on a viscosity and the temperature of
the fluid.
6. The method according to claim 1, further comprising determining
the pressure difference taking into account a temperature-dependent
leakage.
7. The method according to claim 1, further comprising triggering a
setpoint rotational speed of the drive motor.
8. The method according to claim 1, wherein the feed pump is
arranged as a pump of an integrated configuration, in which the
drive part and the hydraulic part form an inseparable unit.
9. The method according to claim 8, further comprising determining
the temperature by measuring in an electronic part of the feed
pump.
10. The method according to claim 9, further comprising determining
a motor current in a power module of the electronic part.
11. A computation unit configured to perform a method for
controlling a feed rate of a feed pump, including a drive part
having a drive motor and a hydraulic part having an intake opening,
a discharge opening and a feed mechanism situated in between, the
method including: specifying a setpoint feed rate; and triggering
the feed pump based on the setpoint feed rate, a temperature of the
fluid, and a pressure difference between the intake opening and the
discharge opening of the hydraulic part of the feed pump.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to Application No.
10 2010 001 150.9, filed in the Federal Republic of Germany on Jan.
22, 2010, which is expressly incorporated herein in its entirety by
reference thereto.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for controlling
the feed rate, i.e., the feed volume per unit of time, of a feed
pump.
BACKGROUND INFORMATION
[0003] Feed pumps for fluids are widely used. In the automotive
field, for example, feed pumps are used for feeding fuel to the
engine. These feed pumps are usually designed as vane pumps or
rotary vane pumps. In internal combustion engines in particular, it
is important to accurately preselect the feed rate in order to
obtain the desired injection pressure, the desired combustion
performance and also low-emissions combustion. It is therefore
conventional to regulate the feed rate, i.e., the setpoint feed
rate is to be compared with the actual feed rate, and the feed pump
is to be controlled according to a control deviation. This requires
actual feed rate sensors, which makes regulation of feed rate
relatively complex.
[0004] German Published Patent Application No. 10 2008 043 127
describes the regulation of the pump pressure. It is unnecessary to
provide a pressure sensor if the actual pressure is ascertained by
a so-called control observer. The feed pressure is determined on
the basis of the motor current and the motor speed. No feed rate is
determined.
[0005] It is therefore desirable to regulate the feed rate of a
feed pump without measuring the actual feed rate.
SUMMARY
[0006] Example embodiments of the present invention include the
provision of not measuring the actual feed rate of a feed pump but
instead determining it based on the temperature of the fluid and
the pressure difference of the intake opening and the discharge
opening of the pump part or hydraulic part of the feed pump.
Complex additional cost-intensive sensors may be omitted in this
manner. The determination may be performed in practice on the basis
of a characteristic map, for example, which extends over the
temperature and pressure difference. The pressure difference to be
taken into account includes the counter-pressure minus the inlet
pressure.
[0007] For ascertaining the pressure difference, a drive torque of
the drive motor, which is proportional to the pressure difference,
may be used. A viscosity and temperature of the fluid are
expediently also taken into account as these also have an influence
on the pressure difference.
[0008] A relationship between drive torque M.sub.ZP and pressure
difference .DELTA..sub.p may be written, for example, as:
M ZP = V theo .DELTA. p 2 .pi. .eta. ZP ##EQU00001##
[0009] where:
[0010] V.sub.theo represents the theoretical feed volume per
revolution;
[0011] .eta..sub.ZP represents the overall efficiency of the
pump.
[0012] The drive torque may in turn be determined relatively easily
based on known or easily determinable variables. The drive torque
may be derived from the motor current, for example, if an engine
characteristic map is known. This current measurement may be
implemented inexpensively in the power electronics equipment.
[0013] A highly accurate quantitative regulation may be achieved
even without performing a flow measurement by taking into account
the pump geometry, for example, by performing a single measurement
and storing additional measured values to correct the
characteristic map.
[0014] Conventional feed pumps include a hydraulic part and a drive
part flange-connected to the former. In addition, there are certain
variants in which an internally or externally geared pump axially
flange-connected to a motor shaft. The drive motors are arranged as
DC variants as well as brushless DC variants. All these electric
feed pumps are always arranged such that the feed part and the
drive part are separate units. However, example embodiments of the
present invention provide for the use of a pump of an integrated
configuration, i.e., when the drive part and the hydraulic part
form an inseparable unit. Examples of such a pump are described in
U.S. Pat. No. 2,761,078 and European Published Patent Application
No. 1 803 938. The use of such integrated pumps offers the
advantage of a close spatial contact between the fluid and the
electronics, so that a temperature sensor may be installed easily
and without complex cabling, for example. If the control
electronics or power electronics are connected directly to the feed
medium, a temperature measurement cell may be accommodated here
inexpensively and used for the regulation described herein.
[0015] In determining the pressure difference, a
temperature-dependent leakage is expediently taken into account.
This may be accomplished in particular from the following
standpoints:
[0016] Based on a leakage cross section, such that positions 1 and
2 having pressures p.sub.1 and p.sub.2 are adjacent in the
direction of the backpressure, and positions 3 and 4 having
pressures p.sub.3 and p.sub.4 are adjacent in the intake pressure
direction, it holds that:
[0017] p.sub.1.apprxeq.p.sub.2 pump backpressure
[0018] p.sub.4.apprxeq.p.sub.3 pump intake pressure
[0019] Since fluids are usually incompressible media, density
.rho..sub.1 is the same in positions i=1 through 4:
.rho..sub.1=.rho..sub.2=.rho..sub.3=.rho..sub.4=.rho.
[0020] Using a Bernoulli equation with a loss term, the influence
of .beta..sub.p on the leakage flow is estimated as follows:
v 2 2 2 + p 1 .rho. = v 3 2 2 + p 4 .rho. + .DELTA. p v .rho. +
.rho. .intg. s 1 s 2 .differential. v .differential. t s assuming
.differential. v .differential. t = 0 and v 2 = v 3 , it follows
that ( 1 ) p 1 .rho. = p 4 .rho. + .DELTA. p v .rho. or ( 2 )
.DELTA. p v .rho. = p 1 .rho. - p 4 .rho. or .DELTA. p v = p 1 - p
4 ( 3 ) ##EQU00002##
[0021] The loss term for a constant cross section is
.DELTA. p v = .lamda. l d .rho. v 2 2 ( 4 ) ##EQU00003##
[0022] It thus follows that:
v = 2 .rho. .DELTA. p d .lamda. l where ( 5 ) .lamda. = .rho. 64 Re
= .rho. 64 v d .gamma. ( 6 ) ##EQU00004##
[0023] A friction moment estimate M.sub.Reib of a radial friction
bearing is given, for example, as:
M Reib = .mu. F Lager ##EQU00005## where ##EQU00005.2## .mu. = .mu.
0 ( - a h min Rq ) ##EQU00005.3##
where
[0024] a represents a constant; and
[0025] Rq represents a standard deviation of roughness Rq for
contact pairing;
where:
h min .apprxeq. B F Lager .eta. D 3 C .pi. n 60 ( 1 + 2 ( 1 -
.gamma. 2 ) F B E h min ) 2 / 3 ##EQU00006##
where
[0026] B represents a supporting width;
[0027] .eta. represents a dynamic viscosity;
[0028] E represents a modulus of elasticity;
[0029] .gamma. represents a transverse contraction number;
[0030] D represents a diameter;
[0031] n represents a rotational speed [1/min]
[0032] Thus a loss term which depends on rotational speed may be
given.
[0033] Frictional resistance M of the rotor is formulated in a
manner similar to that of a rotating disk:
M = 2 .intg. r F r = 2 .intg. rc F .rho. v 2 2 A = .intg. 0 d / 2
rc F .rho. .omega. 2 r 2 2 .pi. r r = 4 .pi. c F 5 C M .rho.
.omega. 2 2 ( d 2 ) 5 ##EQU00007##
where for laminar flow and Re<310.sup.4 it holds that:
C M = 2 .pi. d s Re ##EQU00008##
where s represents an axial distance between the rotor and the
housing;
[0034] A loss term as a function of rotational speed may in turn be
given using .omega.=2.pi.n.
[0035] The frictional resistance on the outer cylindrical surface
is already taken into account in the bearing calculation.
[0036] Thus to determine the feed rate, a characteristic map as a
function of temperature and motor current may be used. This is
particularly simple because these parameters may be determined
relatively accurately but nevertheless inexpensively and with
little effort. A preferred relationship is obtained as follows:
V . = n ( V theo K 1 ) - V . Temp - V . .DELTA. .rho. + n 2 K 10 +
n 1 / 2 K 11 + K 12 drehzahlabh a .. ngige Verluste
##EQU00009##
[0037] where drehzahlabhangige Verluste refers to rpm-dependent
losses;
where
{dot over
(V)}.sub.Temp=T.sup.2-K.sub.2+TK.sub.3+T.sup.1/2K.sub.4+K.sub.5
and
{dot over
(V)}.sub..DELTA..rho.=I.sub.Motor.sup.2K.sub.6+I.sub.MotorK.sub.7+I.sub.M-
otor.sup.1/2K.sub.8+K.sub.9
where V.sub.theo denotes the theoretical feed volume per revolution
of the pump.
[0038] A computation unit, for example, a control unit of a motor
vehicle, is equipped, in particular as far as programming is
concerned, to perform a method described herein.
[0039] It should be understood that the features mentioned above
and those yet to be explained below may be used not only in the
particular combination given but also in other combinations or
alone.
[0040] Example embodiments of the present invention are illustrated
schematically in the Figures and are described below in more detail
with reference to the Figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 schematically shows a feed pump, which is suitable in
particular for performing a method according to an example
embodiment of the present invention.
[0042] FIG. 2 shows in a diagram the relationship between feed rate
and rotational speed as a function of the pressure difference at a
constant fluid temperature.
[0043] FIG. 3 shows in a diagram the relationship between feed rate
and rotational speed as a function of the inlet pressure at a
constant pressure difference and a constant fluid temperature.
[0044] FIG. 4 shows in a diagram the relationship between feed rate
and rotational speed as a function of the fluid temperature at a
constant pressure difference.
DETAILED DESCRIPTION
[0045] FIG. 1 shows an electric feed pump of an integrated
configuration, in which the drive part and the hydraulic part or
feed part form an inseparable unit 120, which is diagramed
schematically and labeled as 100 as a whole. In the present
example, the integrated configuration is achievable by the fact
that the rotor of the drive motor at the same time also forms the
moving pump element of the hydraulic part, as described in European
Published Patent Application No. 1 803 938, for example, which is
expressly incorporated herein in its entirety by reference thereto.
Hydraulic part 120 thus includes drive motor 121, which also acts
as feed mechanism 121, drawing in a fluid, fuel in particular,
through an intake opening 122 and discharging it through a
discharge opening 123. There is therefore a pressure difference
.DELTA..sub.p between intake opening 122 and discharge opening
123.
[0046] The pump also includes an electronic part 110. A regulating
module 111 and a power module 112 are provided in electronic part
110. Regulating module 111 receives a setpoint feed rate {dot over
(V)}.sub.setpoint from a motor control unit 150 and determines
therefrom a setpoint rotational speed n.sub.setpoint for the drive
motor, which is transmitted to power module 112. Power module 112
may have, for example, an inverter for operation of the drive
motor. Motor current I.sub.motor is determined in power module 112
and transmitted to regulating module 111.
[0047] Based on the integrated configuration of pump 100, there is
a close spatial contact between electronic part 110 and drive and
hydraulic part 120, so that fluid temperature T.sub.actual-fluid is
easily measurable by a measurement performed by a sensor 113
provided within electronic part 110.
[0048] The feed rate of feed pump 110 may be controlled on the
basis of measured motor current I.sub.motor and measured fluid
temperature T.sub.actual-fluid. A characteristic map as a function
of temperature T.sub.actual-fluid and motor current I.sub.motor is
used in regulating module 111 according to the equation:
V . Soll = n Soll ( V theo K 1 ) -- ( T 1 st - Fluid 2 K 2 + T 1 st
- Fluid K 3 + T 1 st - Fluid 1 2 K 4 + K 5 ) -- ( I Motor 2 K 6 + I
Motor K 7 + I Motor 1 2 K 8 + K 9 ) ++ n Soll 2 K 10 + n Soll 1 2 K
11 + K 12 ##EQU00010##
where
[0049] Soll denotes a setpoint, Ist denotes actual; and
[0050] V.sub.theo denotes the theoretical feed volume per
revolution of the pump and is usually given on the data sheet.
Characteristic map constants K.sub.1-K.sub.12 are ascertained
empirically. To do so, a sufficient number of measured points [{dot
over (V)}, n, T, I] is preferably measured and evaluated using
known fitting methods (e.g., least squares fitting).
[0051] Based on the characteristic map, setpoint rotational speed
n.sub.setpoint is determined and transmitted to power module 112.
To regulate the feed rate, actual rotational speed n.sub.actual of
drive motor 121 is regulated at setpoint rotational speed
n.sub.setpoint. A known rotational speed regulation may be used to
do so.
[0052] Alternatively it is possible to use actual rotational speed
n.sub.actual together with measured motor current I.sub.motor and
measured fluid temperature T.sub.actual-fluid to determine the
actual feed rate via the characteristic map and to regulate the
actual feed rate at the setpoint feed rate, again with the setpoint
rotational speed being regulated.
[0053] Various relationships are explained purely qualitatively
below with reference to FIGS. 2 to 4 merely for the purpose of
illustration.
[0054] FIG. 2 shows a diagram 200, illustrating the relationship
between feed rate {dot over (V)} on the ordinate as a function of
rotational speed n on the abscissa at a constant temperature. Three
feed rate curves 210, 220 and 230 are shown in diagram 200, each
curve being characterized by a different pressure difference
.DELTA.p between the intake opening and the discharge opening. Thus
a first pressure difference .DELTA.p.sub.1 is assigned to feed rate
curve 210, a second pressure difference .DELTA.p.sub.2 is assigned
to feed rate curve 200, and a third pressure difference
.DELTA.p.sub.3 is assigned to feed rate curve 230, the pressure
difference increasing, so that it holds that:
.DELTA.p.sub.1<.DELTA.p.sub.2<.DELTA.p.sub.3. The feed
volume/rotational speed characteristic curve is shifted to the
right with an increase in pressure difference .DELTA.p because
internal leakage increases. In other words, a higher rotational
speed is also necessary to supply a certain feed rate at a higher
pressure difference.
[0055] Each of the three feed rate curves includes a first
essentially linearly increasing range A and a following curved
range B. The slope in range A is constant and depends essentially
only on the geometric displacement volume of the pump. The feed
volume curve flattens out in range B due in particular to partial
cavitation phenomena on the intake end, caused in particular by
high local flow velocities.
[0056] FIG. 3 shows in a diagram 300 the influence of pressure at
the intake opening, i.e., inlet pressure p.sub.inlet on the feed
volume/rotational speed characteristic curve. Diagram 300 shows
three characteristic curves 310, 320 and 330 at a constant pressure
difference .DELTA.p, these characteristics differing in their inlet
pressure. Characteristic curve 310 is defined by inlet pressure
p.sub.inlet1 characteristic curve 320 is defined by inlet pressure
p.sub.inlet2 and characteristic curve 330 is defined by
p.sub.inlet3 where the following holds:
p.sub.inlet1>p.sub.inlet2>p.sub.inlet3.
[0057] A variation in the inlet pressure produces a shift in ranges
A and B such that the stable, i.e., linear operating range A
becomes smaller with a drop in inlet pressure. In other words, the
stable range is smaller the higher the inlet pressure p.sub.inlet.
It is thus advisable to provide a limit in the pump specification
to avoid operating in range B.
[0058] FIG. 4 shows the influence of the fluid temperature on the
feed volume/rotational speed characteristic curve in a diagram 400.
Three characteristic curves 410, 420 and 430 are shown in diagram
400, a different fluid temperature T.sub.1, T.sub.2 and T.sub.3
being assigned to each diagram, where it holds that
T.sub.1<T.sub.2<T.sub.3. The characteristic curves are
shifted to the right with an increase in fluid temperature because
the temperature influences the viscosity of the fluid and thus
affects the leakage. Furthermore, the pump components expand, so
that different materials are usually used for different components
and thus there is different thermal expansion. For example, the
housing is often made of aluminum, whereas the feed mechanism often
has steel elements, which thus have a lower thermal expansion than
the housing. As a result, the leakage increases with an increase in
temperature. On the whole, it is apparent that a higher rotational
speed is also needed at a higher fluid temperature to supply a
certain feed rate.
* * * * *