U.S. patent application number 12/366860 was filed with the patent office on 2009-06-25 for engine management.
Invention is credited to Brian Gorman Cooper, Richard Charles Elliot Cornwell, Nicola Dilieto, David Greenwood, Andrew David Noble, Anthony Truscott, Edward Colin Winslett.
Application Number | 20090158831 12/366860 |
Document ID | / |
Family ID | 9948616 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090158831 |
Kind Code |
A1 |
Cornwell; Richard Charles Elliot ;
et al. |
June 25, 2009 |
Engine Management
Abstract
An in-cylinder pressure sensor obtains a high resolution
pressure curve for each cylinder cycle allowing the various data to
be derived for improved monitoring and control of operation of the
engine. A more accurate measure of work done by the engine is
obtained allowing more accurate estimation of the vehicle torque
and hence real torque control. In addition, engine losses can be
more accurately calculated and the estimates corrected yet further
by obtaining an accurate top dead centre position for the engine
cylinders.
Inventors: |
Cornwell; Richard Charles
Elliot; (Shoreham-By-Sea, GB) ; Winslett; Edward
Colin; (Grange Close, GB) ; Noble; Andrew David;
(Steyning, GB) ; Cooper; Brian Gorman; (Merstham,
GB) ; Truscott; Anthony; (Worthing, GB) ;
Greenwood; David; (Shoreham-By-Sea, GB) ; Dilieto;
Nicola; (Munichen, DE) |
Correspondence
Address: |
REED SMITH, LLP;ATTN: PATENT RECORDS DEPARTMENT
599 LEXINGTON AVENUE, 29TH FLOOR
NEW YORK
NY
10022-7650
US
|
Family ID: |
9948616 |
Appl. No.: |
12/366860 |
Filed: |
February 6, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10536619 |
Aug 25, 2006 |
7506536 |
|
|
PCT/GB03/04522 |
Oct 20, 2003 |
|
|
|
12366860 |
|
|
|
|
Current U.S.
Class: |
73/114.16 ;
73/114.28 |
Current CPC
Class: |
F02D 41/1497 20130101;
F02D 41/2432 20130101; F02D 2200/1004 20130101; F02D 35/023
20130101; F02B 1/12 20130101; F02D 2200/1006 20130101; F02D 41/009
20130101 |
Class at
Publication: |
73/114.16 ;
73/114.28 |
International
Class: |
G01M 15/00 20060101
G01M015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2002 |
GB |
0227672.3 |
Claims
1. A method of deriving vehicle torque comprising measuring
cylinder pressure during a cylinder cycle; constructing a pressure
variation function; obtaining work done by the engine therefrom and
driving vehicle torque from the work done.
2. A method as claimed in claim 1 further including identifying
vehicle motive efficiency losses and subtracting these from engine
work done to derive vehicle torque.
3. A method as claimed in claim 1 in which the vehicle motive
efficiency loss is derived from a map and/or model.
4. A method as claimed in claim 1 further comprising controlling
vehicle performance by adjusting a performance input variable to
control the derived vehicle torque to a target vehicle torque.
5. A method as claimed in claim 1 further comprising deriving loss
from the difference between the measure of engine shaft output and
the measure of work done on a piston in the cylinder.
6. An engine management system for an internal combustion engine
having at least one cylinder pressure sensor and a data processor
arranged to receive the pressure measurement during a cylinder
cycle from the cylinder pressure sensor and process the measured
pressure according to the method of claim 1.
7. An engine management system for an internal combustion engine
having at least one cylinder pressure sensor and at least one
engine actuator and a data processor arranged to receive pressure
measurements during a cycle from the cylinder pressure sensor and
an actuator controller arranged to control the actuator according
to a performance input variable to carry out a method as claimed in
claim 1.
8. A computer readable medium containing processing instructions to
enable a processor to carry out a method as claimed in claim 1.
9. A method as claimed in claim 2 in which vehicle motive
efficiency loss is measured by skip firing an engine cylinder cycle
and measuring corresponding vehicle deceleration.
10. A method as claimed in claim 3 in which the derived vehicle
motive efficiency loss is correlated against the measured vehicle
motive efficiency loss to refine the map or model.
11. A method as claimed in claim 5 further comprising adjusting a
performance input variable to control the measure of engine shaft
output to a target value or range to obtain a target measure of
engine shaft output.
12. A method as claimed in claim 11 further comprising monitoring
vehicle performance by obtaining separately a measure of engine
shaft output and/or engine friction losses estimate and comparing
the or each estimate against the respective derived value to
correct the estimate.
13. A method as claimed in claim 12 further comprising controlling
vehicle performance by adjusting a performance input variable to
control the derived measure of engine shaft output to a target
measure of engine shaft output.
14. A method of obtaining the indicated mean effective pressure
IMEP for a vehicle engine cylinder comprising measuring the
cylinder pressure during a cylinder cycle, obtaining corresponding
values of cylinder volume during the cycle, deriving top dead
centre during the cycle, correcting the volume values based on the
derived value of top dead centre, and integrating pressure against
volume to obtain the IMEP.
15. A method as claimed in claim 14 in which top dead centre is
derived at a maximum pressure point of the motoring pressure
curve.
16. A method as claimed in claim 14 further comprising controlling
vehicle performance deriving a vehicle performance output valve
from the IMEP and adjusting a vehicle performance input variable to
control the derived vehicle performance output value to a target
vehicle performance output value.
17. A method of diagnosing engine conditions in an engine with two
or more cylinders comprising the steps of skip firing individual
cylinders, deriving a measure of engine friction loss and comparing
the derived loss to diagnose a respective cylinder condition.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
10/536,619, filed Aug. 25, 2006, the entire disclosure of which is
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The invention relates to a system and method providing
improved engine management and in particular using real time
cylinder pressure data. The aspects discussed herein are an
extension of the concepts disclosed in International patent
application no. PCT/GB02/02385 entitled "Improved Engine
Management" commonly assigned herewith and incorporated herein by
reference.
[0003] Known engine management systems (EMS) monitor and control
the running of an engine in order to meet certain pre-set or design
criteria. Typically these are good drivability coupled with high
fuel efficiency and low emissions. One such known system is shown
schematically in FIG. 1. An internal combustion engine 10 is
controlled by an engine control unit 12 which receives sensor
signals from a sensor group designated generally 14 and issues
control signals to an actuator group designated generally 16. The
engine control unit 12 also receives external inputs from external
input block 18 as discussed in more detail below.
[0004] Based on the engine performance data derived from the sensor
input from the sensor block 14 and any external input from the
external input block 18 the engine control unit (ECU) optimizes
engine performance by varying the relevant performance input
variable within the specified criteria.
[0005] Typically the sensor block 14 may include sensors including
mass airflow sensors, inlet temperature sensors. knock detection
sensors, cam sensor. air/fuel ratio (AFR) or lambda (.lamda.)
sensors, and engine speed sensors. The external input block 18
typically includes throttle or accelerator sensors, ambient
pressure sensors and engine coolant temperature sensors. In a
spark-ignition engine the actuator block 16 typically comprises a
fuel injector control and spark plug operation control. In a
compression ignition engine the actuator block typically comprises
a fuel injector.
[0006] As a result, for example in spark ignition engines, under
variable load conditions induced by the throttle under driver
control, the sensors and actuators enable effective control of the
amount of fuel entering the combustion chamber in order to achieve
stoichiometric AFR, and of the timing of combustion itself.
[0007] Known engine management systems suffer from various
problems. EMS technology remains restricted to parameter based
systems. These systems incorporate various look-up tables which
provide output values based on control parameters such as
set-points, boundaries, control gains, and dynamic compensation
factors, over a range of ambient and engine operating conditions.
For example in spark ignition engines spark timing is
conventionally mapped against engine speed and engine load and
requires compensation for cold starting. In compression ignition
engines fuel injection timing is mapped in a similar manner. As
well as introducing a high data storage demand, therefore, known
systems require significant initial calibration. This calibration
is typically carried out on a test bed where an engine is driven
through the full range of conditions mapped into the look-up
tables. As a result the systems do not compensate for factors such
as variations between engine builds let alone individual cylinders,
and in-service wear. Accordingly the look-up tables may be
inaccurate ab initio for an individual engine, and will become less
accurate still with time.
[0008] In one aspect known systems control vehicle performance
based on a consideration of engine conditions together with
mappings. These mappings are derived during vehicle calibration and
can include physical parameters related to engine geometry.
Generally much of the engine performance data is very indirect and
is based on multiple inferences from sensors together with the
mapped or modeled data which can give rise to inaccuracies arising
from the inferences made or from differences between vehicles based
on production tolerances or indeed differences between conditions
in individual cylinders within an engine. The latter is mainly due
to differences in air and inert gas paths, temperatures of the
cylinder walls and production tolerances of valvetrain and
piston/crankshaft geometry. Furthermore such approaches do not
compensate for changes in performance arising from in-service
wear.
[0009] One known system comprises adjusting performance input
variables to the engine to control engine torque to a target. A
problem with this is that the engine torque is in fact inferred
from easily measurable variables such that airflow in a gasoline
engine or fuel flow in a diesel engine. Accordingly the value for
torque that is derived is indirect and inaccurate, suffering from
the disadvantages set out above. Although torque sensors are known,
these are costly and are not robust. Known systems also derive a
measure of engine frictional losses represented by the friction
mean effective pressure (FMEP). However in known systems these
values are currently mapped or modeled at the engine manufacture
stage and hence suffer from the problems set out above.
[0010] The invention is set out in the claims.
BRIEF DESCRIPTION OF THE FIGURES
[0011] Embodiments of the invention will now be described by way of
example with reference to the drawings, of which:
[0012] FIG. 1 is a block diagram representing a prior art EMS;
[0013] FIG. 2 is a schematic diagram representing an EMS according
to the present invention;
[0014] FIG. 3 is a schematic view of a single cylinder in cross
section according to the present invention;
[0015] FIG. 4 is a trace of pressure against crank angle for a
cylinder cycle of a four stroke engine;
[0016] FIG. 5 is a trace showing IMEP for a cylinder cycle;
[0017] FIG. 6 is a plot of pressure against crank angle .theta.
showing pressure variation of a motoring pressure curve to
demonstrate top dead centre;
[0018] FIG. 7 is a block diagram showing control modules in an
engine according to the present invention;
[0019] FIG. 8 is a block diagram showing the components of an EMS
according to the present invention;
[0020] FIG. 9 is a block diagram showing individual cylinder
control in an EMS according to the present invention; and
[0021] FIG. 10 shows the pressure cycle for the selected cylinder
in a six-cylinder engine.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The following discussion of an embodiment of the invention
relates to its implementation in relation to a four stroke
combustion ignition engine comprising a diesel engine. However it
will be appreciated that the invention can be applied equally to
other stroke cycles and types of internal combustion engines
including spark-ignition engines, with appropriate changes to the
model parameters. Those changes will be apparent to the skilled
person and only the best mode presently contemplated is described
in detail below. Like reference numerals refer to like parts
throughout the description.
[0023] FIG. 2 is a schematic view showing the relevant parts of an
engine management system according to the present invention in
conjunction with a six cylinder engine. An engine control unit is
designated generally 20 and controls an engine designated generally
22. The engine includes six cylinders designated generally 24. Each
cylinder includes a pressure sensor 26 which connects to the ECU
via a line 28. In addition the ECU provides electronic control to
each of the cylinder injectors (not shown). The ECU 20 can also
receive additional controls and actuator inputs 32 as discussed in
more detail below. The engine management system monitors the
pressure in each cylinder through each complete engine cycle.
namely 720.sup.0 rotation of the crankshaft in a four-stroke
engine. Based on this data the injection timing for each. cylinder
24 is varied by varying the timing of each injector via control
lines 30.
[0024] In FIG. 3 there is shown schematically a more detailed view
of a single cylinder 24 of the engine. The in-cylinder pressure
sensor 26 comprises a piezoresistive combustion pressure sensor
with a chip made of silicon on insulator (SOI) available from
Kistler Instrumente AG, Winterthur, Switzerland as transducer
Z17619, cable 4767 A2/5/10 and amplifier Z18150. It will be
appreciated that any appropriate in-cylinder pressure sensor can be
used, however. For example the sensor can be of the type described
in co-pending application number DE 100 34 390.2. The pressure
sensor 26 takes continuous readings through the four strokes of the
piston 40. The readings are crank-synchronous and triggered by
crank teeth 42a of the crank 42, detected by a crank tooth sensor
44 which sends an appropriate signal via line 46 to the ECD 20. In
the preferred embodiment readings are taken every 2.degree. of
crankshaft rotation although any desired resolution can be adopted,
the limiting factors being processing power and crank angle sensing
resolution. For each cylinder the readings are taken across a cycle
window of width 7200. As discussed in more detail below with
reference to FIG. 16, the window is selected to run from a point
substantially before engine top dead centre (TDC) for each
cylinder.
[0025] The data obtained from the in-cylinder sensor 26 is
processed as discussed in more detail below and a high resolution
plot of pressure versus crank angle (which can be simply converted
to time if the engine speed is known) is obtained for each cylinder
and each cycle. From this information, monitoring and control of
engine performance is greatly enhanced.
[0026] In overview, in the first aspect the invention makes use of
the possibility of deriving the work done by each cylinder piston
in the engine from in-cylinder measurements of the cylinder
pressure. In particular the indicated mean effective pressure
(IMEP) is derived from the pressure information combined with the
corresponding cylinder volume at each cycle. The brake mean
effective pressure (BMEP), which is a measure of engine output
torque, at any point from and including the crankshaft to the
transmission system, can then be derived from the IMEP and the
losses represented by the FMEP which are calibrated or modeled. As
a result mapped measurements are restricted to the FMEP
calculations rendering the determination of the output torque more
accurate. This is then used to adjust the performance input
parameters to control the output torque to a target desired output
torque providing torque based control.
[0027] In a second aspect an estimate or sensed value for the BMEP
is obtained and, using the measured value of IMEP the FMEP is
derived, again more accurately because of the direct measurement of
IMEP. In this case the relevant information which relates to losses
in the vehicle can be used for on-board diagnostics (OBD) systems.
The derivations of BMEP and FMEP in the respective aspects can be
cross-correlated with their respective estimated values in the
alternative aspect allowing the mappings or models to be refined
based on real vehicle performance and accounting for
variations/deterioration with time.
[0028] Although the following discussion relates principally to
IMEP, it applies equally to equivalent measures of engine output
such as torque or power, and appropriate units and conversions
should be inferred as appropriate. For example as regards engine
shaft output, a measure of this can be expressed as the brake mean
effective pressure BMEP as discussed in more detail below, engine
output torque, engine output power and so forth. A measure of
engine frictional losses may be expressed as the FMEP, as friction
torque or as friction power and a measure of work done on the
piston of a cylinder can be expressed as the IMEP, indicated torque
or indicated power. In each case yet further expressions may be
used as appropriate.
[0029] In either case IMEP must be calculated which requires a
correlation of the measured pressure in the cylinder with the
corresponding cylinder volume at any time. The cylinder volume at
any time is known from the crank angle which is directly related to
the piston position. However because of mechanical tolerances and
variations between engines and individual cylinders, the
relationship between volume and crank angle may differ slightly
between engines and individual cylinders, sufficient to affect the
IMEP calculation. Accordingly the invention further extends to
obtaining a more accurate measurement of piston top dead centre
(TDC) each cylinder and each cycle allowing a correspondingly more
accurate measurement of IMEP.
[0030] The pressure data derived is shown in FIG. 4 which shows the
cylinder pressure variation against crank angle for one full cycle
between -360.degree. and +360.degree.. As is well known the engine
cycle is divided into four regions, induction from -360.degree. to
-180.degree., compression from -180.degree. to 0.degree. (TDC),
expansion from 0.degree. to +180.degree. and exhaust from
+180.degree. to 360.degree., defining a full 720.degree. cycle.
Theoretically, for instantaneous combustion occurring over an
infinitely small period of time the optimum point for combustion is
at 0.degree. TDC, but in practice injection timing can vary by
several degrees from TDC.
[0031] The pressure curve obtained is then processed to provide
additional engine performance data allowing enhanced control.
[0032] In the first aspect, the pressure curve is used to obtain a
measure of mean engine torque in the form of the BMEP at the engine
output based on the direct relationship between BMEP and torque. In
particular it can be shown that for a four stroke engine:
B M E P V S N 2 = .tau. N 2 .pi. ##EQU00001##
[0033] Where V.sub.S=swept volume of all cylinders.
[0034] N=number of revolutions and .tau.=torque.
[0035] This can be simplified to
[0036] As a result it can be seen that tracking the BMEP allows
tracking of the vehicle torque.
[0037] Now BMEP is given by the difference between the work done by
the engine and the subsequent losses, i.e:
BMEP=IMEP-FMEP
[0038] where the FMEP represents the losses between the net work
done by the gases in the cylinders and the point in the engine
where BMEP is referenced. These losses are due to crankshaft and
piston friction, valvetrain losses, air conditioning, power
steering, side mounted electrical machine losses and so forth.
[0039] The FMEP can be derived in various manners. In one approach
it can be mapped or modeled based on detected engine conditions
with a map or model constructed during engine prototyping.
Alternatively the FMEP can be derived by monitoring deceleration
(in conjunction with the vehicle road information) during skip
firing in an overrun or cranking configuration. Here as the
cylinder is not being fired. the deceleration is caused because of
the losses in the vehicle including deceleration owing to gravity
when the vehicle is on a slope, aerodynamic losses and mechanical
losses in the powertrain which in turn are made up of the losses
between the wheels and the point where BMEP is referenced (rolling
resistance, transmission and differential losses and so forth), and
FMEP. Appropriate sensors models or maps can be used to obtain the
value of the relevant losses. At low speeds aerodynamic losses can
be ignored and the effect of gravity cancelled out if the road
gradient is known (by an inclination sensor, for example). As a
result only the mechanical losses need to be estimated to obtain
FMEP. Furthermore, when skip-firing individual cylinders, a
comparison can be made of their respective FMEPs. This is useful
for detecting failures such as piston ring deterioration.
[0040] Yet a further approach is to apply the "morse test" which is
known to the skilled reader as described in Introduction to
Internal Combustion Engines, Richard Stone, Second Edition,
Macmillan, 1992, pp 476-477 in which individual cylinders are
sequentially skip fired and the RPM loss summed to obtain a measure
of the FMEP.
[0041] The work done by the gases on the piston for each engine
cycle can be represented by the IMEP over the engine cycle as
represented in FIG. 5 which shows a plot of cylinder pressure, P
against volume V over a single four-stroke cycle. The area shown
shaded is the gross IMEP relating to the work done during the
compression and expansion strokes while the area enclosed by the
entirety of the plot is the net IMEP relating to the work done over
the whole cycle, including work done on the gases by the piston
during the induction and exhaust strokes. The gross IMEP region is
also shown on the pressure versus crank angle plot of FIG. 4.
[0042] Because the samples taken are sufficient to plot the
Pressure/Volume curve the IMEP for a single cylinder can be
obtained empirically by applying trapezoidal integration yielding,
for the net IMEP:
I M E P net = 1 V cs l = 1 m - 1 P l + P i + 1 2 ( V i + 1 - V l )
m = 720 .theta. res ##EQU00002##
[0043] where V.sub.cs is the swept volume of one cylinder. This net
IMEP will be referred to here onwards as `IMEP`.
[0044] Equation (4) is preferably calculated based on the raw
pressure data as the effects of noise are reduced because the IMEP
is effectively obtained by integration. Similarly any pressure
off-set correction required for medium to long-term sensor drift,
is irrelevant to the IMEP calculation since it is a cycle integral
of the area enclosed the PV diagram of FIG. 7 and so it is
independent of absolute pressure values.
[0045] Once the IMEP and FMEP is obtained then the BMEP can be
similarly obtained by the above equation. It will be noted that if
FMEP is indirectly measured using a skip firing or similar
technique then this can be correlated against the mapped or modeled
FMEP to refine the map or model appropriately.
[0046] As a result, real torque control is obtained where a more
accurate model of the engine torque is derived. The engine
performance input variables can then be adjusted to track BMEP to a
target value demanded by the driver or EMS. This can be done either
to optimize vehicle torque or to maintain it stable dependent on
the driving mode required. Stability is particularly attractive if
the engine is switching between operating modes (for example in
order to regenerate exhaust after treatment systems).
[0047] Because the model is based on a restricted set of
assumptions it is correspondingly enhanced and hence compensates
for variations between engines and cylinders. The real torque based
control system hence provides the possibility of improved idle
speed control improved transmission control and improved torque
based control during engine mode switching such as switching of
air/fuel ratios between stoichiometric lean and rich mixtures
switches between compression ignition modes such as homogeneous and
stratified modes. variations in compression ratio switches between
compression ignition and spark ignition cylinder de-activation and
switches between two stroke and four stroke operation. Yet further
the invention provides improved torque control for hybrid engines
for example electric/fuel or bi-fuel hybrids.
[0048] In a second aspect a similar approach to that identified
above is adopted but to obtain a measure of the losses in the
vehicle in the form of the FMEP. FMEP can be obtained by
rearranging equation (3) to obtain:
FMEP=IMEP-BMEP
[0049] As discussed above IMEP can be derived from direct
in-cylinder pressure measurements during each cylinder cycle.
[0050] BMEP can be obtained in a known manner for example by
estimation from a vehicle model or from a torque sensor in
conjunction where appropriate with factors such as the vehicle
weight and road inclination. In that case the estimation of FMEP is
enhanced as it is based on reduced assumptions. The FMBP can be
used to allow feedback to torque control or can be used in
conjunction with the first aspect to allow respective refinement of
the BMEP and FMEP values as the values calculated for each by
respective equations (3) and (5) can be correlated against the
derived values from the model or map.
[0051] In one embodiment estimation of FMEP is scheduled at
predetermined intervals, for example, a predetermined driven
distance allowing vehicle losses to be determined at various
intervals and operation according to the first aspect to continue
the rest of the time.
[0052] As a result the second aspect allows fault or wear diagnosis
to be performed by monitoring vehicle losses in the form of FMEP
and/or allows enhancement of real torque based control.
[0053] It will be seen that both firsts and second aspects of the
invention, i.e. calculation of the BMEP or FMEP rely on an accurate
derivation of the engine IMEP. Referring to the equation set out
above and FIG. 5, IMEP is obtained by the integration of PdV,
requiring V.sub.i, the cylinder or volume at a given reading
instant i to be known in conjunction with P.sub.i. The cylinder
volume depends on the piston position which is known from the crank
angle. In the preferred embodiment, however, TDC is measured from
the pressure data itself allowing the cylinder volume to be more
accurately synchronized with the cylinder pressure.
[0054] Referring to FIG. 6, the specific TDC required is the
mechanical TDC 50, that is, the point in time at which the cylinder
volume is at a minimum. This differs from the thermodynamic TDC 52
at which the motored cylinder pressure is at a maximum simply
because of the thermodynamics of the gas. In particular the
thermodynamic TDC 52 will lag the mechanical TDC 50 by a
thermodynamic loss angle TLA 54. This lag can be mapped during
engine prototyping or modeled, as will be apparent to the skilled
reader, from heat release analysis. The engine speed of course
needs to be taken into account as this will affect the offset,
again as known to the skilled reader. For the purposes of
calculated IMEP the mechanical IDC is required as this relates to
the actual volume in the cylinder.
[0055] Accordingly to obtain TDC, the thermodynamic TDC is first
obtained from the motoring curve 56. The motoring curve is the
pressure curve that would be obtained if combustion did not take
place in the cylinder, representing purely the varying pressure
resulting from the compression stroke in the cylinder.
[0056] The motoring curve 56 can be derived in various ways known
to the skilled person. For example it can be calibrated or obtained
by "skip firing" in which at certain intervals fuel is not injected
into the cylinder for one cycle (e.g. during cranking or overrun)
and the resultant pressure curve obtained.
[0057] Once the motoring curve is derived, then to obtain the
thermodynamic IDC the maximum pressure P.sub.max 58 is obtained. It
will be seen that the value is easily derivable simply by selecting
the maximum on the curve as shown in FIG. 6. The relevant point can
be identified in any appropriate way, for example by
differentiating the curve and identifying the crossover point
between positive and negative gradient. Depending on the resolution
of the measured data, the maximum can be interpolated between
adjacent data points, for example by using polynomial curve fitting
techniques as will be well known to the skilled reader.
[0058] The mechanical TDC 50 can then be obtained by subtracting
the TLA 54, corrected for engine speed, from the thermodynamic TDC.
This can then "be used to correct the value of V in equation (4).
For example the difference between the measured mechanical mc and
the assumed mechanical TDC can be applied as a correction for each
value of V.sub.i.
[0059] As a result a more accurate IMEP value is obtained.
[0060] It will be noted that the thermodynamic mc 52 can also be
used directly for example for governing combustion events such as
spark time or injection timing control.
[0061] As a result the preferred approach compensates for
mechanical tolerances as well as in-service wear allowing improved
IMEP estimation. TDC can be derived for each cycle or can be
measured at predetermined intervals to ensure that the true TDC and
assumed TDC remain equivalent.
[0062] Any appropriate control mechanism and strategy can be
adopted to implement the various enhancements discussed above, as
will be apparent to the skilled person. One appropriate system is
discussed in overview with reference to FIG. 7 and includes a
controller 100, one or more actuators 102, cylinder 104, processor
106 and a module 108 supporting a model or map correlating
predetermined values. The measured pressure from the cylinder
together with the corresponding crank angle .theta..sub.a are fed
to the processor 106 which derives a pressure curve and/or pressure
value and from those performance output variables such as
temperature, heat release, AFR and so forth as discussed above.
These parameters are output to a controller 100 together with other
necessary sensor inputs from a sensor or sensors 110.
[0063] Where necessary the controller takes these inputs and feeds
them to the model or mapping module 108 in order to obtain the
desired adjusted performance input variables. The module 108 can be
calibrated during engine prototyping on the test-bed, for example,
to provide mappings between performance output values such as BMEP
and desired performance input variables such as fuel injection
timing and quantity.
[0064] The adjusted performance input variables are then fed to the
relevant actuators 102 which control conditions in the cylinder
104. As a result a feedback loop is provided in which the, measured
pressure value provides a performance output value which is either
controlled to track a target performance output value, or which can
be used as a check or correlation against values obtained from the
module 108.
[0065] It will be appreciated that, where appropriate, instead of
closed loop control the pressure value can simply be fed through
the processor to obtain a calibrated performance input value at
pre-determined intervals or otherwise. It will be further
appreciated that the module 108 can be formed at various levels of
sophistication, for example providing multiple dimensional mapping
tables allowing trade-offs between a plurality of desired
performance output values.
[0066] A platform for an engine management system according to the
present invention is described in more detail with reference to
FIGS. 8 to 10 for a system monitoring the pressures in all six
cylinders of an engine and providing information concerning fuel
quantity and injection, 1 timing which override the corresponding
outputs of a production engine control unit 170.
[0067] Cylinder pressure sensors 172 are digitised by processing
means comprising in the preferred embodiment an EMEK II intelligent
data acquisition system 174. The data acquisition system also
receives signals from sensors 176 which may include, for example, a
mass air flow sensor, inlet temperature sensor, cam sensor,
air/fuel ratio or lambda sensor or any other appropriate sensors of
known type. As can be seen from FIG. 10 the data acquisition system
174 yet further receives a crank tooth signal providing a value of
the crank angle (CA).
[0068] The digitised signals from the data acquisition system 174
are transmitted to a control and diagnostics unit 178 which may
comprise a C40/C167 prototyping unit developed by Hema Elektronik
GmbH of Germany. The control and diagnostics unit 178 further
receives data including production sensor data from production
engine control unit 170 and all input data is received in external
input block 180. The control and diagnostics algorithms are
configured in the preferred embodiment, in MatrixXlSystemBuild, a
high level simulation and algorithm development tool, and
downloaded as compiled code to a digital signal processing (DSP)
board generally designated 182. The processed control data is
transmitted from an external output block 184 of the control and
diagnostics unit 178 to the modified production engine control unit
170 which controls the production actuators including, for example
fuel injectors according to their control systems and algorithms
discussed above.
[0069] It will be seen that the control and diagnostics unit 178
further includes a calibration block 188 which interfaces with an
external calibration system 190 connected, for example, to a host
PC 192. The calibration system 190 can carry out various
calibration steps. For example the performance input variables for
obtaining a performance output variable such as a desired BMEP. It
will be appreciated that any other appropriate calibration steps
can equally be performed, or a model derived equivalently.
[0070] The DSP shown generally at block 182 runs separate cylinder
pressure based EMS algorithms to implement the control strategies
outlined above.
[0071] The plot in FIG. 10 is of cylinder pressure against crank
angle and it will be seen that, for each cylinder, the cycle window
200 runs over a full 7200 cycle from a crank angle significantly
before TDC to a crank: angle shortly after TDC. This is followed by
a data acquisition period 202 allowing the finite processing time
required which runs up to a first "TN interrupt" 204. A second
interrupt 206 occurs 1200 later for a six cylinder engine. Crank
synchronization timing and fuel quantity commands derived from the
data acquired in the previous cycle window are applied at the
second interrupt 206 as a result of which signal processing 208
must take place within the interval between the first and second
interrupts. It will be noted that as the engine speed increases,
although the crank angle interval between the first and second
interrupts remains the same, in the time domain the interval
decreases accordingly such that the signal processing step 208 must
be implemented efficiently so as not to overlap the second TN
interrupt. For example referring to the second plot of FIG. 10, in
cylinder 4, it will be seen that the signal processing step 208 is
carried out at a higher engine speed and hence falls closer to the
second IN interrupt.
[0072] The ordering of the cylinders in FIG. 11 is 1, 4, 3, 6, 2,
5.
[0073] In the preferred embodiment the timing commands generated in
control and diagnostics unit 178 are transmitted via the control
area network (CAN) bus 194 to the production ECU 170 where they
bypass the normal commands generated by the production control
algorithms. As a result the system can be "bolted on" in a
preferred embodiment to an existing production ECU 170 with the
logic appropriately modified to allow priority to the modified
system in controlling production actuators.
[0074] It will be appreciated that the various embodiments
discussed can be combined or interchanged and components therefrom
combined or interchanged in any appropriate manner. In particular
multiple control regimes can be combined and traded off against one
another so as to achieve a compromise mode of operation meeting
more than one target output performance value. The approach can be
applied in engine types of different configurations, stroke cycles
and cylinder numbers and to different fuel type or combustion type
internal combustion engines including natural gas engines and spark
or compression ignition type engines and to different injection
processes such as port-injection, direct injection, Late
Compression Ignition (LCI), Homogeneous Charge Compression Ignition
(RCCI) etc. a combination of both, multi-injection and
multi-injector engines in which case the in-cylinder pressure data
can be processed generally as discussed above but modified
appropriately to obtain data on the equivalent parameters, which
data can then be applied to appropriate actuation points dependent
upon the engine type. Although the discussion above is principally
applied to taking readings and applying on a cylinder-by-cylinder
and cycle-by-cycle basis. averaging techniques can be applied over
multiple cylinders or cycles as appropriate.
* * * * *