U.S. patent application number 13/109160 was filed with the patent office on 2012-01-12 for method and control device for determining a characteristic viscosity variable of an oil.
This patent application is currently assigned to SCHAEFFLER TECHNOLOGIES GMBH & CO. KG. Invention is credited to Marco DI PACE, Andreas PETZ, Ilia TARASSOV, Piergiacomo TRAVERSA.
Application Number | 20120006289 13/109160 |
Document ID | / |
Family ID | 44276378 |
Filed Date | 2012-01-12 |
United States Patent
Application |
20120006289 |
Kind Code |
A1 |
PETZ; Andreas ; et
al. |
January 12, 2012 |
METHOD AND CONTROL DEVICE FOR DETERMINING A CHARACTERISTIC
VISCOSITY VARIABLE OF AN OIL
Abstract
In order for the viscosity of the engine oil to be determined as
directly as possible, particularly in the case of a motor vehicle
with hydraulic control of the gas exchange valves, provision is
made for a time period which a hydraulic component, in particular a
solenoid valve, requires to move from a first position to a second
position to be used as a measure of the viscosity. In particular,
an electrical control signal for the solenoid valve is evaluated in
the process. An additional sensor arrangement is not required. The
determined viscosity is preferably actively used for controlling
the gas exchange valves.
Inventors: |
PETZ; Andreas; (INGOLSTADT,
DE) ; TRAVERSA; Piergiacomo; (NUERNBERG, DE) ;
DI PACE; Marco; (HERZOGENAURACH, DE) ; TARASSOV;
Ilia; (NUERNBERG, DE) |
Assignee: |
SCHAEFFLER TECHNOLOGIES GMBH &
CO. KG
Herzogenaurach
DE
|
Family ID: |
44276378 |
Appl. No.: |
13/109160 |
Filed: |
May 17, 2011 |
Current U.S.
Class: |
123/90.12 |
Current CPC
Class: |
F02D 2041/2055 20130101;
F01M 1/18 20130101; F01L 9/14 20210101; F02D 2041/001 20130101;
G01N 33/2888 20130101; F02D 41/0002 20130101; F16N 2250/36
20130101; G01N 11/00 20130101; F02D 2041/2058 20130101; Y02T 10/40
20130101 |
Class at
Publication: |
123/90.12 |
International
Class: |
F01L 9/02 20060101
F01L009/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 17, 2010 |
DE |
10 2010 020 754.3 |
Claims
1-13. (canceled)
14. A method for determining a characteristic viscosity variable of
a hydraulic liquid in a motor vehicle having gas exchange valves
and a hydraulic control system with a hydraulic component for
hydraulically controlling the gas exchange valves, the method
comprising the steps of: adjusting the hydraulic component from a
first position to a second position by means of a control signal;
determining a time period which the hydraulic component requires
for changeover from the first position to the second position; and
using the determined time period determined to measure the
characteristic viscosity variable
15. The method according to claim 14, wherein the hydraulic liquid
is engine oil.
16. The method according to claim 14, wherein the hydraulic
component is an electrically controllable switching valve.
17. The method according to claim 6, wherein the electrically
controllable switching valve is a solenoid valve.
18. The method according to claim 16, wherein the switching valve
is supplied with a control signal and the control signal is
evaluated to determine the time period.
19. The method according to claim 18, wherein the control signal is
a switching valve.
20. The method according to claim 19, wherein a switching time of
the switching valve between the control signal and an end position
of the switching valve is used as the time period.
21. The method according to claim 14, wherein there is a linear
correlation between the viscosity of the hydraulic liquid and the
time period.
22. The method according to claim 21, wherein the time period is
linked directly to the viscosity such that the time period and the
viscosity have a linear relationship and individual measurement
points of the time period and viscosity with respect to each other
can be connected by a regression line, which is determined by means
of linear regression.
23. The method according to claim 14, wherein the time period is
repeatedly determined at a specific temperature of the hydraulic
liquid and a check for a change is made.
24. The method according to claim 23, wherein a conclusion can be
drawn about aging of the hydraulic component and/or about aging of
the hydraulic liquid at a specific operating point based on the
time period.
25. The method according to claim 24, wherein the aging of the
hydraulic component is taken into consideration when determining
the characteristic viscosity variable.
26. The method according to claim 15, wherein the aging of the
hydraulic component is derived from the time period at a high
temperature of the oil at a temperature of greater than 80.degree.
C.
27. The method according to claim 24, wherein an association
between the time period and the viscosity of the hydraulic liquid
is made by a regression line, which is determined by means of
linear regression, and a shift in the regression line in relation
to an unaged state of the hydraulic liquid is used as a measure of
aging.
28. The method according to claim 14, wherein the determined
characteristic viscosity variable is evaluated and used selectively
or in combination for: determining a measure of an oil quality;
identifying impermissible engine oils; establishing an oil change
interval; diagnosing the hydraulic component; and valve
control.
29. A control device for determining a characteristic viscosity
variable of an engine oil in a motor vehicle having a gas exchange
valves with the gas exchange valves being hydraulic controlled by a
hydraulic component being adjusted from a first position to a
second position with by means of a control signal, wherien the
hydraulic component requires a measurement of a time period for
changeover from the first position to the second position and the
time period is used as a measure of the characteristic viscosity
variable.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of DE 10 2010 020 754.3
filed May 17, 2010, which is incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The invention relates to a method and to a control device
for determining a characteristic viscosity variable of an oil in a
machine with hydraulic control, in particular of an engine oil in a
motor vehicle preferably with hydraulic control of the gas exchange
valves, with a hydraulic component being adjusted from a first
position to a second position with the aid of a control signal.
BACKGROUND OF THE INVENTION
[0003] In modern motor vehicles, the so-called gas exchange valves,
that is to say the inlet and/or outlet valves for the motor vehicle
engine, are nowadays controlled in a load-dependent manner for the
purposes of minimizing pollutants and reducing consumption. Various
systems are used in the process. All systems share the common
feature that the closing and/or opening times of the gas exchange
valves are changed in a load-dependent manner in relation to the
crankshaft position (rotational angle). Hydraulic control systems
in which a change in the closing and/or opening times of the gas
exchange valve is induced with the aid of a hydraulic fluid,
specifically the engine oil, are also used here.
[0004] EP 1 544 419 A1, for example, discloses a first hydraulic
control system, specifically a hydraulic camshaft adjuster. In a
system of this kind, the phase angle between the crankshaft and the
camshaft of a motor vehicle engine is changed with the aid of the
hydraulic fluid. This is achieved by variably filling pressure
chambers of an adjusting apparatus. Control valves, which are in
the form of solenoid valves in particular, are usually provided for
actuating and filling and emptying the pressure chambers.
[0005] The article "Elektrohydraulische Ventilsteuerung mit dem
"MultiAir"-Verfahren [Electrohydraulic valve control using the
"MultiAir" method]" in the German automotive engineering journal
MTZ, December 2009, discloses an alternative hydraulic control
system for actuating the gas exchange valves. In the case of this
electrohydraulic valve control arrangement, provision is made for
the movement of the camshaft to be transmitted to a respective gas
exchange valve via the hydraulic liquid. A control or switching
valve, which is in the form of a solenoid valve in particular, is
provided for control purposes. In the closed state, the camshaft is
connected to the respective gas exchange valve via a so-called
hydraulic linkage, and therefore the gas exchange valve necessarily
follows a cam of the camshaft. By also partially opening the
switching valve, the hydraulic fluid can pass into a compensation
or pressure chamber, and therefore the gas exchange valve is
decoupled from the movement of the cam. As a result, it is possible
to vary the opening time point, the closing time point and the
stroke of the gas exchange valve within an envelope curve which is
predefined by the movement of the cam. This variation can he
performed in a cylinder-selective manner.
[0006] Exact actuation of the gas exchange valves is of critical
importance with regard to the high level of efficiency together
with low emission of pollutants as is required in modern internal
combustion engines. In hydraulic systems, the type of hydraulic
liquid used, that is to say, in particular, the quality of the
engine oil used, has a significant effect on operation. In
particular, the effectiveness of the hydraulic control means is
sensitive to fluctuations in the viscosity of the oil used. Such
fluctuations occur for operational reasons due to different oil
temperatures. As disclosed in the article "Elektrohydraulisehe
Ventilsteuerung mit dem "MultiAir"-Verfahren [Electrohydraulic
valve control using the "MultiAir" method]," the
temperature-dependent fluctuations in oil viscosity have to date
been taken into consideration in a model-based control algorithm
which takes into consideration the measurement values from an oil
temperature sensor.
[0007] This temperature-dependent and therefore indirect
determination operation has disadvantages and does not take into
consideration, for example, aging of the engine oil or wear of the
hydraulic components.
[0008] Proceeding from this, the invention is based on the problem
of specifying an improved method and an improved control device for
directly determining a characteristic viscosity variable for an
oil, it being possible, in particular, to take aging and wear
effects into consideration too.
SUMMARY OF THE INVENTION
[0009] According to the invention, the problem is solved by a
method and a control device for determining a characteristic
viscosity variable of an oil in a machine with hydraulic control,
with a hydraulic component being adjusted from a first position to
a second position with the aid of a control signal which is usually
electrical. The time period which the component requires for the
changeover from the first position to the second position is used
as a measure of the characteristic viscosity variable.
[0010] This refinement is based on the basic consideration that the
movement sequence of a hydraulic component of the hydraulic system
in the event of an adjusting movement of the hydraulic component
from a first position to a second position is critically dependent
on the quality of the oil used and, in particular, on the
viscosity. A frictional force which counteracts the movement of the
hydraulic component is, as it were, exerted by means of the
viscosity, and therefore the time period for the adjusting movement
of the hydraulic component allows a conclusion to be drawn about
the viscosity.
[0011] In this case, the hydraulic component is, in particular, a
component which changes over from the first position to the second
position in a force-controlled manner, but not in a mechanically
positively controlled manner, in such a way that different
frictional resistances lead to different time periods for the
adjusting movement. This free, unforced movement is also called a
ballistic movement. In this case, the force is applied, for
example, by a spring. On account of the counteracting
viscosity-induced frictional force of the oil (possibly
additionally against the oil pressure-induced force), the time
period of the actuating movements varies as a function of the
viscosities.
[0012] The oil is preferably an engine oil in a motor vehicle which
is equipped, in particular, with hydraulic control of the gas
exchange valves, for example with a hydraulic camshaft adjuster
and, in particular, with an electrohydraulic valve control means,
as disclosed, for example, in EP 1 544 419 A1 or the article
"Elektrohydraulische Ventilsteuerung mit dem "MultiAir"-Verfahren
[Electrohydraulic valve control using the "MultiAir" method]."
[0013] A characteristic viscosity variable is understood to mean a
characteristic variable which is directly correlated with the
viscosity. In this case, the characteristic viscosity variable is,
in particular, the viscosity itself, in particular the so-called
kinematic viscosity, or a viscosity indicator, for example the
change in the viscosity, a relative viscosity etc., which is
derived from the viscosity.
[0014] The particular advantage of evaluating the time period of
the adjusting movement of the hydraulic component during the
ballistic movement is that of--in contrast to computer
determination from the oil temperature--the actual system behavior,
which is induced by the viscosity, being evaluated and therefore a
direct characteristic variable for the current viscosity being
obtained. A more definite and reliable conclusion about the actual
value of the viscosity can be drawn solely from detecting the time
period. In comparison to only indirect determination by means of
the temperature of the engine oil, the properties of the oil are
directly detected by means of the movement sequence of the
component in this method, and therefore aging effects of the engine
oil can also be detected.
[0015] According to an expedient refinement, the hydraulic
component is an electrically controllable control or switching
valve, in particular a solenoid valve. Valves of this kind are
used, for example, for controlling the gas exchange valves in order
to switch and control the oil. The valve itself moves, particularly
in the case of ballistic movement, between a closed position and an
open position, these positions therefore forming the first and
second positions of the switching valve. Since a closure element of
the switching valve, for example a valve disk, is guided within the
flow path of the oil, the actuating movement of the closure element
is influenced by the properties of the oil. In the case of a
solenoid valve, the valve usually moves into one position,
preferably into the closed position, in a magnetic-force-operated
manner, and the valve moves back into the second position, in
particular into the open position, in a spring-force-operated
manner after the magnetic force is discontinued.
[0016] According to a preferred development, the time or adjustment
period is determined from a control signal of the switching valve,
in particular from the field current of said switching valve.
Therefore, no additional measuring devices, such as position
sensors, are required according to this preferred refinement. The
time period and therefore the viscosity are therefore determined
solely by evaluation (using software), without additional hardware
components being required. As a result, the costs of a system of
this kind are kept low.
[0017] A switch-off time of the valve is preferably used to
determine the time period. In this case, a switch-off time is
understood to mean the time between a switch-off signal, in
particular switch off of the field current of the solenoid valve,
and an, in particular spring-force-operated, end position (closed
position) being reached.
[0018] This evaluation is based on the consideration that, after
the field current is switched off, the closure element moves from
the first position to the second position and, as a result, in
particular on account of the resulting accelerations, produces an
inductive response signal which can be detected. Since this
response signal is correlated with the movement, evaluation of this
response signal (current signal) can define an end position and
determine said end position in a reproducible manner. In principle,
a voltage signal can be evaluated instead of the field current. The
switch-off time of the switching valve is established and
evaluated, for example, in accordance with the method as described
in EP 1 533 506 A2.
[0019] A direct conclusion is preferably drawn about the viscosity
of the oil on the basis of a known association using the determined
time period. To this end, an association between the values for the
time period and the values for the characteristic viscosity
variable, in particular for the absolute viscosities, is preferably
stored in an evaluation unit. The current value of the viscosity is
therefore determined, in particular, by a simple comparison. In
this case, the association can be made, for example, in a table, a
mathematical function or a characteristic diagram. In this case,
different associations are preferably stored for different types of
oil.
[0020] In an expedient refinement, this association is determined
in test runs in the new state of the system as a function of a very
wide variety of operating parameters and operating points, and the
results obtained in this way are stored in the evaluation unit. In
this case, extensive families of characteristic curves can be
provided, these representing, for example, the effect of different
types of oil, the influence of the temperature etc. on the
respective viscosity.
[0021] The association between the time period and the viscosity is
preferably made by means of linear regression. Experiments have
shown that there is a simple linear relationship between the time
period and the absolute value of the viscosity according to the
following equation:
.eta.=mt+b, where
.eta. is the viscosity of the oil, for example in [m.sup.2/s], t is
the determined time period (switch-off time) and m, b are constants
which characterize the system, in particular the solenoid
valve.
[0022] In a preferred development, provision is made for the time
period to be repeatedly determined during operation and for a check
for a change to be made. Since the time period depends to a great
extent on the operating conditions, in particular temperature of
the oil, only the time periods of a specific operating point, in
particular the time periods at the same oil temperature, are
compared with one another for this purpose. Therefore, a change in
the characteristic viscosity variable is determined by this
comparison. In this case, "during operation" is to be understood to
mean normal operation of the machine as intended. In the case of a
motor vehicle, this is normal driving over days, weeks, months and
years. Therefore, the time period is preferably continuously
detected over the entire service life. In this case, the time
period is preferably detected at periodic intervals, triggered, for
example, by specific events, for example starting of the engine.
However, in addition, evaluation can also take place at shorter,
regular time intervals, for example as a function of the
revolutions of the engine.
[0023] In an expedient development, a conclusion can be drawn about
aging of the engine oil and/or of the hydraulic component, that is
to say the switching valve, on the basis of this change. In an
alternative refinement, a conclusion is drawn about the aging
solely on the basis of the determined time period. Therefore, aging
of the engine oil generally leads, for example, to an increase in
the viscosity and therefore to an increase in the time period at
the same temperature. Therefore, different curves can, in
principle, be stored for different aging states, and therefore a
conclusion can be drawn about the state of the engine oil in terms
of an increase in the viscosity solely on the basis of the
measurement of the time period (given a defined temperature).
[0024] In addition to aging of the oil, aging of the switching
valve also has an influence on the time periods. Therefore,
according to a preferred refinement, provision is made for aging of
the hydraulic component to be determined when determining the
characteristic viscosity variable. In this case, empirically
determined aging can, in principle, he determined, for example as a
function of the length of operation, and taken into
consideration.
[0025] However, provision is preferably made for aging of the
hydraulic component to also be derived from the determined time
period at a defined operating point. The defined operating point
is, in particular, a high engine oil temperature, preferably a
temperature of >80.degree. C. and, in particular,
>100.degree. C. On account of a measure of the aging being
derived from the time period, the actual behavior of the system and
not, for example, only a postulated behavior of the system is
evaluated--as is already the case when establishing the
characteristic viscosity variable for the oil. Therefore, the
direct evaluation understood in this sense is more accurate and
more reliable. The preferred evaluation at a high engine oil
temperature is based on the consideration that, at these high
temperatures, the influence of the viscosity of the oil on the time
period is at least negligible on account of the very low viscosity,
which tends toward zero, at high temperatures. At these high
temperatures, the time period is therefore established solely by
the configuration of the switching valve.
[0026] Aging of the component can also be established from the time
period without establishing the characteristic viscosity variable,
and this forms a separate, independent inventive aspect.
[0027] Therefore, a measure of the aging state can he derived on
the basis of the determined time period. This is again possible
both in absolute terms when an association between the respective
time period and the aging state of the switching valve is stored in
corresponding association tables. As an alternative, a relative
aging state can also be determined by comparison with time periods
which were detected previously during operation.
[0028] A shift in a regression line, which shift is produced on
account of the linear regression for the association between the
time period and the viscosity, is preferably used as a measure of
aging, in particular in accordance with the following formula:
.eta.=m(t+t.sub.old)+b, where
t.sub.old is the additional time period caused by aging.
[0029] The determined characteristic viscosity variable, in
particular also the determined change in the characteristic
variable, preferably the absolute viscosity, is expediently used
selectively or in combination for different derived measures.
According to a preferred first alternative, the quantity of oil
used is established and derived therefrom. The oil can be very
readily characterized overall by measurements, for example, at
different operating points (temperatures). It is possible, in
particular, to create an association to a respective oil quality on
the basis of the measured time periods, in particular in
combination with storage of a large number of families of
characteristic curves for different types of oil and qualities of
oil. In addition, impermissible oil qualities are preferably
identified, and, if required, a warning signal is output, for
example to request a change in engine oil.
[0030] Furthermore, the oil change interval or the next time point
at which an oil change is due is preferably established. It is
therefore possible, on account of the actual state of the oil being
detected, to reliably detect in very good time whether the oil
still meets the requirements, and therefore a time point for the
next oil change can be reliably established. Therefore, it is
generally also possible to establish the oil change interval by
identifying the engine oil quality.
[0031] Furthermore, diagnosis of the hydraulic component, that is
to say in particular the solenoid valve, is preferably performed,
and a check is made, for example, as to whether replacement is
required, a reference preferably also being made to this within the
scope of the evaluation and diagnosis.
[0032] Finally, in a particularly expedient refinement, valve
control is influenced on the basis of the determined variables.
Firstly, for example when aging of the engine oil is detected, that
is to say when an increase in the viscosity is detected, the time
points for actuating the switching valve are varied and matched to
the new conditions in order to maintain gas valve control as
exactly as possible in accordance with the respective requirements.
Furthermore, in a preferred alternative, the entire hydraulic
control operation is performed on the basis of the determined
characteristic variable for the viscosity, and no longer on the
basis of the current oil temperature as was previously customary.
The entire control operation therefore takes into consideration the
actual state of the oil.
[0033] According to a preferred refinement, provision is also made
for a warning signal to be output when the determined oil viscosity
does not permit disturbance-free operation of the engine.
Furthermore, provision is made for even starting of the engine to
be suppressed, in order, for example, to prevent damage to the
engine on account of excessively high viscosity and the associated
lack of lubrication of the engine. This is advantageous, for
example, in winter when the initial viscosity during cold-starting
is too high on account of the external temperatures. Therefore, a
minimum external temperature which must not be undershot can be
established on the basis of the oil state determined in a preceding
operating cycle.
BRIEF DESCRIPTION OF THE DRAWING
[0034] An exemplary embodiment of the invention will be explained
in greater detail below with reference to the drawing, in
which:
[0035] FIG. 1 shows, in a schematic and highly simplified
illustration of a detail, the basic manner of operation of an
electrohydraulic control means of a gas valve in a motor vehicle
engine,
[0036] FIG. 2 shows a schematic, highly simplified illustration of
the profile of a control or field current for a switching valve
which is in the form of a solenoid valve,
[0037] FIG. 3 shows a graph in which the kinematic viscosity of an
oil is plotted against the switch-off time of a solenoid valve for
a system in the new state (new oil and new switching valve),
[0038] FIG. 4 shows a graph which is comparable to FIG. 3, with an
additional regression line for a system with an aged switching
valve being added,
[0039] FIG. 5 shows a schematic, highly simplified graph in which
the time period and viscosity are plotted against the oil
temperature for two different types of oil or oil qualities,
and
[0040] FIG. 6 shows a schematic graph, in which the time period and
viscosity are plotted against the oil temperature for an oil in the
new state and in the aged state.
[0041] Identically acting parts are provided with the same
reference symbols in the figures.
DETAILED DESCRIPTION OF THE INVENTION
[0042] An electrohydraulic control system for hydraulically
controlling a gas exchange valve 2 in a motor vehicle 4 which is
indicated by a dashed border in FIG. 1 comprises a hydraulic system
which transmits a movement of a cam 6 of a camshaft 7 to a
respective gas exchange valve 2 by means of a hydraulic liquid,
specifically the engine oil. The electrohydraulic valve control
means is known per se. An essential feature is a switching valve
which, in particular, is in the form of a solenoid valve 8 and is
connected in a hydraulic line 10. The hydraulic line 10 is
connected firstly to the cam 6 and secondly to the gas exchange
valve 2 via a hydraulic cylinder 12. The hydraulic line 10 to a
compensation or pressure chamber 14 can be blocked by means of the
solenoid valve 8. Pistons 18 are mounted within the hydraulic
cylinder 12, for example such that they can be moved against the
force of a spring 16. In the event of rotation of the cam 6, the
piston 18 of the associated hydraulic cylinder 12 follows the
movement of the cam. When the solenoid valve 8 is closed, the
hydraulic system acts in the manner of a hydraulic linkage, and
therefore the piston 18 in the hydraulic cylinder 12 which is
associated with the gas exchange valve 2 directly follows the
movement of the cam 6.
[0043] The oil can pass into the pressure chamber 14 by opening of
the solenoid valve 8, and therefore the movement of the gas
exchange valve 2 is decoupled from the movement of the cam 6.
[0044] The solenoid valve 8 is connected to a control or evaluation
unit 20. The control unit 20 is integrated, for example, in the
engine control means. The solenoid valve is supplied with a control
signal by means of the control unit 20. In the exemplary
embodiment, this control signal is a field current I for a magnet
coil of the solenoid valve 8.
[0045] The solenoid valve 8 is usually open in the inactivated
state, and therefore the hydraulic line 10 is free in the direction
of the pressure chamber 14. In the activated state, that is to say
when the solenoid valve 8 is supplied with an adequate field
current 1, the solenoid valve 8 is in its closed position. In this
case, the solenoid valve 8 has a design which is known per se and
is typical of a solenoid valve. An armature is operated by the
magnet, which is formed by an electrical coil, in the closing and
opening directions. A closure element for closing the hydraulic
line 10 is arranged on this armature. The magnetic force usually
acts against a spring force of a spring which is mounted in the
solenoid valve 8 and pushes the solenoid valve 8 into its starting
position, in particular its open position, in the inactive
state.
[0046] The field current I usually exhibits a typical profile, as
illustrated in FIG. 2. The coil is usually initially supplied with
a switch-on current I.sub.1 at a time t.sub.1. This switch-on
current h leads only to pre-magnetization, but not to a movement of
the closure element. For the purpose of activating, that is to say
closing, the valve 8, said valve is supplied with a closing current
I.sub.2 which is established at time point t.sub.2. At this time
point, the closure element moves to its closed position. On account
of an inductive response, the closing current drops to a certain
extent. After the closing operation, the current is reduced to a
holding current I.sub.3, usually at a time t.sub.3.
[0047] In order to open the valve, the power supply is switched off
at a time point t.sub.4. On account of the spring, the closure
element shifts in the direction of the open position. In this case,
an inductive response is again generated, which is reflected after
time point t.sub.4 in a current pulse, as can be seen in FIG. 2.
The profile of this current pulse is correlated with the movement
of the closure element of the solenoid valve 8. A defined position
of the closure element, in particular its open position, can he
unambiguously derived from the profile of the current pulse. This
is reached at time point t.sub.5 in the exemplary embodiment.
[0048] Time points t.sub.4 and t.sub.5 correspond to a first
position and a second position of the solenoid valve 8. The time
period .DELTA.t between t.sub.4 and t.sub.5 represents the
switch-off time for the switching process and therefore the
adjustment process of the solenoid valve. The time period .DELTA.t
is linked directly to the viscosity .eta. of the oil used.
Experiments have shown that, in this case, there is a linear
relationship between the time period .DELTA.t and the kinematic
viscosity .eta., as illustrated in FIG. 3 by way of example. Each
time period .DELTA.t is unambiguously assigned a specific value for
the viscosity .eta.. The individual measurement points indicated by
dots can be connected by a regression line. This can be established
in general in accordance with the equation:
.eta.=m .DELTA.t+b
where: [0049] .eta. is the kinematic viscosity, [0050] .DELTA.t is
the time period or switch-off time of the solenoid valve 8, [0051]
m, b are solenoid-valve-specific constants which characterize the
solenoid valve.
[0052] As illustrated in the graph according to FIG. 3, the
individual measurement points correspond to specific temperatures
of the oil when using the same oil. In this case, the individual
temperature values define a specific operating point of the motor
vehicle engine.
[0053] The linear relationship between viscosity .eta. and time
period .DELTA.t is independent of the choice of engine oil and also
the aging state of said engine oil. Different engine oils or
different aging states of an oil are reflected in the switching
times .DELTA.t and, in association, the viscosities .eta. being
different at a defined operating point, that is to say at a defined
temperature. This will be explained further below in conjunction
with FIGS. 5 and 6.
[0054] In the graph according to FIG. 4, aging of the solenoid
valve 8 is taken into consideration. Experiments have shown that
this is reflected in a shift in the regression line. The relevant
regression line in the case of an aged solenoid valve 8 can be
expressed by the following equation:
.eta.=m(.DELTA.t+.DELTA.t.sub.old)+b,
where: [0055] .DELTA.t.sub.old is a change in the time period
.DELTA.t on account of aging of the solenoid valve 8.
[0056] In this case, the value of .DELTA.t.sub.old is detected at
high oil temperatures >80.degree. C., for example
.gtoreq.100.degree. C. At these temperatures, the time period
.DELTA.t is established solely by the properties of the solenoid
valve 8 on account of the low viscosity of the oil, which virtually
reaches zero here. Therefore, in the graph in FIG. 3, the line on
the left indicates the regression line with a new solenoid valve 8,
and the regression line which has shifted to the right indicates
the regression line with an aged solenoid valve 8.
[0057] As soon as a shift of this kind on account of aging of the
solenoid valve 8 is observed, the shifted regression line is used
for the association between the time period .DELTA.t and the
viscosity .eta..
[0058] FIG. 5 illustrates a highly simplified graph in which the
temperature is plotted against the time period .DELTA.t and,
corresponding to this, .eta.. The same applies for the graph
according to FIG. 6.
[0059] FIG. 5 shows two curves A, B for two different types of
engine oil or engine oil qualities.
[0060] In particular, the following procedure is followed in order
to determine the engine oil quality used or to determine the type
of oil used:
[0061] the time periods .DELTA.t for different oil temperatures T
are detected. A curve of best fit is, for example, created by the
measurement points determined in this way. The measured association
between the temperature and time period .DELTA.t is compared with
known associations, for example families of characteristic curves,
which are stored in the control unit 20. On the basis of
correspondence upon comparison with a known family of
characteristic curves, the currently used oil is then associated
with a known oil of a specific quality. However, in principle, it
is also possible to establish the quality solely on the basis of
the measurement values, without comparison with the stored families
of characteristic curves.
[0062] The graph according to FIG. 6 shows, in a schematic and
highly simplified manner, the effect of aging of the engine oil.
The two curves C, D represent firstly the temperature dependence
for a new oil (curve C) and secondly for the same, aged oil (curve
D). Aging of the oil is reflected in an increase in the viscosity
.eta. and therefore the time period .DELTA.t at the same
temperature T.
[0063] FIG. 6 shows, by way of example, a maximum permissible value
max for the time period .DELTA.t and for the viscosity .eta..
Different minimum temperatures T minC, minD are assigned to this
maximum value for the two curves. As can be read from the graph, a
lower minimum temperature minC is permissible with the new oil than
with the aged oil (minD).
[0064] This is used, for example, in order to output a warning
signal when the minimum permissible temperature minC, minD is
undershot or, in extreme cases, to suppress starting of the
engine.
[0065] The aged curve D is determined in a similar way to that
described in FIG. 5 by the time periods .DELTA.t being determined
at different temperatures T. The increasing aging is detected by
continuous or periodic measurement during operation. A change in
engine oil is detected by an abrupt change in the curve
profile.
[0066] The method described here is distinguished in that the time
period .DELTA.t is detected and evaluated as a characteristic
variable for the current viscosity r.eta. of the engine oil.
Therefore, the actual state of the hydraulic system is
determined.
[0067] It is also of particular importance that the time period for
the actuating movement of the solenoid valve is evaluated in order
to determine the time period .DELTA.t. and that this is done, in
particular, by evaluating the control signal I for the solenoid
valve 8.
[0068] A further essential consideration is that aging of the
switching valve 8 is taken into consideration. It is again of
particular importance here that aging of the switching signal is
also obtained by evaluating the time period .DELTA.t.
[0069] Therefore, in general, the link or relationship between the
electrical actuation of the hydraulic component (solenoid valve 8)
and the hydraulic action (closing/opening) triggered by said
hydraulic component is evaluated and the viscosity .eta. is
derived. Independently of the electrical actuation of the solenoid
valve, this correlation, which is reflected in the reaction time
and therefore the time period .DELTA.t, is established by a change
in the functioning of the solenoid valve 8 (aging, mechanical wear)
and by a change in the viscosity .eta. of the hydraulic liquid. In
this case, the change in viscosity is caused by wear and/or aging
of the oil and/or by the current temperature of the hydraulic
liquid.
[0070] The particular advantage of determining the actual viscosity
.eta. is, particularly in the case of a time-critical and
emissions-relevant system, such as in an electrohydraulic valve
control means, that a hydraulic control system of this kind for
actuating the gas exchange valves can be operated independently of
aging of the oil without adversely affecting the functioning and
the exhaust gas values.
[0071] To this end, control of the gas exchange valves is
expediently actively influenced on the basis of the information
obtained. The entire control operation of the gas exchange valves
is preferably carried out with the aid of the present method based
on the actually existing viscosity .eta. (and not indirectly by
means of the temperature as was the case previously). The control
parameter is therefore the actual viscosity determined over the
time period .DELTA.t.
LIST OF REFERENCE NUMERALS
[0072] 2 Gas Exchange Valve [0073] 4 Motor Vehicle [0074] 6 Cam
[0075] 7 Camshaft [0076] 8 Solenoid Valve [0077] 10 Hydraulic Line
[0078] 12 Hydraulic Cylinder [0079] 14 Pressure Chamber [0080] 16
Spring [0081] 18 Piston [0082] 20 Control Unit
* * * * *