WO2003040532A1

WO2003040532A1 - Diesel engine and a method and apparatus for fuel injection control in a diesel engine

Info

Publication number: WO2003040532A1
Application number: PCT/SE2002/002012
Authority: WO
Inventors: Roger HÄLLEBERG; Magnus Pettersson
Original assignee: Scania Cv Ab (Publ)
Priority date: 2001-11-07
Filing date: 2002-11-06
Publication date: 2003-05-15
Also published as: SE523734C2; SE0103697L; BR0213295A; SE0103697D0; DE10297412T5; DE10297412B4

Abstract

A method and an arrangement (5) for regulation of fuel injection in a multicylinder piston engine (4) with diesel operation are distinguished in that the fuel injection is controlled (23) individually for at least one cylinder on the basis of measurement or estimation of the at least one cylinder's individual efficiency at the time.

Description

DIESEL ENGINE AND A METHOD AND APPARATUS FOR FUEL INJECTION CONTROL IN A DIESEL ENGINE

FIELD OF THE INVENTION The present invention relates to a method and an arrangement for regulation of fuel injection in a multi-cylinder piston engine with diesel operation in accordance with the preambles of claims 1 and 7 respectively. The invention also relates to a diesel engine incorporating such an arrangement.

STATE OF THE ART

Known diesel engines are generally provided with facilities which make it possible not only to regulate the amount of fuel injected in the engine but also to control injection timing relative to piston position or crankshaft angle position. Such control is effected in response to power mobilisation requirements and to operating parameters such as engine speed etc.

The increasingly stringent emission requirements set recently for diesel engines have resulted in modification of injection with a view to helping to reduce NO_x and particle emissions. The contents of undesirable substances measured in the exhaust system thus provide a basis for modifying the time when injection takes place in diesel engine cylinders relative to crankshaft position.

The principle applied has been found to work well in relation to current requirements, but it has been found difficult to achieve emission reductions which will meet the expected increasingly stringent future requirements while at the same time maintaining good running of engines.

OBJECTS AND MOST IMPORTANT CHARACTERISTICS OF THE INVENTION

One object of the present invention is to improve on the state of the art and, in particular, to indicate a method and an arrangement which make substantially reduced emissions possible while at the same time maintaining at least substantially optimised operation, such as unimpaired power etc.

This object is achieved according to the invention by means of the features in the characterising parts of claims 1 and 7 respectively.

Fuel injection is thus adapted individually to each cylinder on the basis of the particular conditions affecting the respective cylinder.

The invention caters for the fact that the various cylinders are often affected by a variety of different factors due, for example, to the geometry of the intake system and the geometry of the exhaust system. Geometrical factors in the inlet duct may thus cause disparate supply of induction air to the various cylinders of an engine.

Moreover, the geometry of the exhaust manifold and the firing sequence as between adjacent cylinders may cause a particular cylinder to be subject to a higher exhaust pressure resulting in a disproportionately large volume of residual gases remaining in, or even being fed into, that cylinder. The capacity of cylinders is also affected by, for example, the geometry of the EGR system.

Parameters such as those described above which affect the various cylinders in this way are here referred to collectively as the "individual efficiency" of the cylinder concerned. Another way of expressing this individual efficiency is to try to derive a value of the ratio between the actual amount of air intake and the theoretical maximum amount of air intake to a specific cylinder.

According to the invention, fuel injection is thus controlled individually for at least one cylinders on the basis of measurement or estimation of the at least one cylinder's individual efficiency at the time. This means that the values representing, for example, combustion air supply, exhaust pressure etc. for an individual cylinder are used for controlling the amount and timing of injection to that cylinder.

Under one method according to the invention, the individual efficiency of an engine's cylinders is measured or estimated. This can be done by means of measurements and/or simulations for different types of engine.

The invention affords many advantages. If a particular cylinder produces substantially higher NO_x emissions than the other cylinders, that cylinder accounts for a disproportionately large share of the engine's total emissions of harmful substances.

In such situations, previous methods for reducing emissions would entail taking some form of action affecting all the cylinders, e.g. by altering the time of injection, what is known as offsetting the injection angle. However, this would merely result in higher fuel consumption and a risk of causing other operating problems, e.g. problems due to soot in the engine oil.

The invention provides instead the possibility of influencing the injection in each cylinder individually, thereby affording great advantages in that each cylinder is enabled to operate in an optimum manner according to its conditions.

Emission problems vary with the type of operation, so according to the invention the forms of action applicable to the respective cylinders are also adapted to their behaviour in corresponding different forms of operation. Thus during transients, e.g. rapid operating changes, there may be expected to be a particularly great risk of more particle emissions. In such situations it is advantageous that deviating cylinders be corrected in this respect as regards not only the amount of fuel injected but also the injection timing or injection angle, so as to optimise the respective cylinder's operation towards the best possible moment/particle emission ratio.

During steady operation, e.g. substantially uniform operation at approximately constant speed, NO_x emissions may be expected to be the predominant problem, and in such situations it is appropriate for a deviating cylinder to be subjected to injection timing correction in order to optimise the operation of that cylinder, and hence the whole engine, towards the best possible emission consumption ratio.

Further advantages with the invention are achieved by the features according to the other dependent claims.

The invention will now be described in more detail on the basis of embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

Of the drawings:

Fig. 1 depicts a general graph showing both NO_x emission and consumption as a function of crankshaft angle α,

Fig. 2 depicts a graph of injection as a function of time during a transient process, Fig. 3 depicts a block diagram of a method sequence according to the invention, and

Fig. 4 depicts schematically an arrangement according to the invention.

DESCRIPTION OF EMBODIMENTS

In Fig. 1, the curve marked 1 represents the relative NO_x value per km, and curve 2 the relative fuel consumption per km as a function of α, which is the crankshaft angle with respect to the top dead centre point in a cylinder of a diesel engine for a heavy vehicle. Both NO_x emissions and fuel consumption are moderate within a preferred operating range marked A.

Fig. 2 shows the injection quantity M as a function of time t during a transient process, and curve 3 represents the application of an average real injection increase which would cause a process significantly deviating from a stepped process such as represented by a square curve 7. Curve 3 in Fig. 2 refers instead to the process of an injection increase taking into account the amount of air available in practice to the particular cylinder. The closer the injection process 3 comes to the square curve 7, the more smoke will be generated during operation.

In the case of cylinders which differ in their level of air supply, the optimum practice is to design the injection process individually according to different curves of type 3 for the different cylinders. In other words, less air means a flatter curve, more air means a steeper curve. The broken lines 8', 8" in Fig. 3 indicate the boundaries of a realistic range of curves 3 for the individual cylinders of a conventional diesel engine for a heavy vehicle. According to the invention, injection is compensated within the scope of what is permissible for the engine concerned, taking care also to ensure that no imbalance occurs in the engine. Substantially disparate power output in the engine's various cylinders might otherwise cause risk of such imbalance.

Typically, compensation of plus or minus about 10% for the individual cylinders can be applied without risk of any appreciable imbalance, as indicated by the broken curves 8', 8" in Fig. 2. In certain circumstances, however, compensation of up to plus or minus 20% may nevertheless apply.

Fig. 3 is intended to illustrate a sequence according to the invention, in which position 20 denotes the start of the sequence.

Position 21 denotes the input or gathering of operating data such as engine speed, power mobilisation, vehicle speed, acceleration etc.

Position 22 denotes the retrieving from a memory of information concerning the engine's various cylinders regarding the operating data of position 21.

Position 23 denotes the system sending signals to the respective injection pumps regarding the times or crankshaft angles for activating the respective injectors and the amount of fuel to be injected individually into each cylinder.

Position 24 denotes the end of the sequence, after which the sequence may be repeated.

Fig.4 depicts very schematically an engine 4 which has an output shaft 10 and is controlled by a control unit 5. This control unit is connected to a memory 6 in which information relating to the individual efficiency of each cylinder in different operating situations is stored. This information therefore refers to the time or crankshaft angle for activation of the respective injector and the amount of fuel to be injected individually into each cylinder. Ref. 9 denotes a number of injection pumps which corresponds to the number of cylinders incorporated in the engine 4.

The invention indicates an effective way of bringing about reduced emissions of a diesel engine in practical operation. Diesel engine emissions which may be mentioned in this context in addition to the previously mentioned NO_x and particles (or smoke) are CO and HC (HC substantially comprising unburnt fuel).

In practical operation, it is precisely the NO_x and particle emissions which are the real problem, so this description concentrates on discussing such emissions.

The basis for a method according to the invention therefore involves accurate mapping of the engine's geometry, as discussed above. Achieving the best possible results entails thorough mapping of an engine with regard to "individual efficiency" with respect to all permissible operating situations such as steady operation, transient operation, low power, high power etc. There are several possible ways of carrying out such mapping. One way is to do the mapping on a test engine whereby sensors may be arranged in various parts of the engine and be associated with the various cylinders in order to provide information on such aspects as combustion air supply, exhaust pressure in the exhaust manifold, residual gases retained by each of the cylinders etc. etc. It should be noted that the mapping of a test engine can provide the basis for estimating the individual efficiency of similar engines, i.e. not necessarily identical engines. It is also within the scope of the invention to carry out said mapping by doing corresponding simulations in a computer.

Thereafter, the results of the mappings are stored in a memory (the memory 6 in Fig.4) connected to the vehicle's control unit (ref. 5 in Fig. 4) in the form of discrete values in tabular form or in the form of functions which in such cases make it possible to derive continuously variable values from the memory.

The possibility of control being based on signals obtained from direct measurements taken in a specific engine during the latter' s operation is not excluded.

Claims

1. A method for regulation of fuel injection in a multi-cylinder piston engine (4) with diesel operation, characterised in that the fuel injection is controlled individually (23) for at least one cylinder on the basis of measurement or estimation (22) of the at least one cylinder's individual efficiency at the time.

2. A method according to claim 1, characterised in that the amount of fuel intended for injection is controlled.

3. A method according to claim 1 or 2, characterised in that the time of injection is controlled relative to crankshaft position.

4. A method according to claim 2 or 3, characterised in that the amount of fuel intended for injection is controlled to deviate by up to about 20% from a standard value.

5. A method according to any one of the foregoing claims, characterised in that the injection is effected by means of individually controllable injectors or injection pumps.

6. A method according to any one of the foregoing claims, characterised in that the fuel injection is controlled for optimisation of the operation of the at least one cylinder in a variety of different operating situations.

7. An arrangement for regulation of fuel injection in a multi-cylinder piston engine (4) with diesel operation, characterised by means (5) for controlling the fuel injection individually (23) for at least one cylinder on the basis of measurement or estimation of the at least one cylinder's individual efficiency at the time.

8. An arrangement according to claim 7, characterised in that said means (5) is designed to control the amount of fuel intended for injection.

9. An arrangement according to claims 7 or 8, characterised in that said means (5) is designed to control the timing of injection relative to crankshaft position.

10. An arrangement according to any one of claims 7-9, characterised by individually controllable injectors or injection pumps by which the injection is intended to be effected.

11. An arrangement according to any one of claims 7-10, characterised by means for optimisation of fuel injection for the operation of the at least one cylinder in a variety of different operating situations.

12. A diesel engine incorporating an arrangement according to any one of claims 7-11.