WO2006027315A1

WO2006027315A1 - Method for controlling the compression ratio of a spark-ignition internal combustion engine having discretely adjustable compression ratios

Info

Publication number: WO2006027315A1
Application number: PCT/EP2005/054123
Authority: WO
Inventors: Hong Zhang; Frédéric Galtier
Original assignee: Siemens Aktiengesellschaft; Siemens Vdo Automotive S.A.S
Priority date: 2004-09-08
Filing date: 2005-08-23
Publication date: 2006-03-16
Also published as: DE102004043527A1

Abstract

The invention relates to a method for regulating the compression ratio of a spark-ignition internal combustion engine having discretely adjustable compression ratios. According to the invention, a current global combustion degree of efficiency is determined from the degree of efficiency for the current compression ratio and the degree of efficiency for the current ignition angle and said global combustion degree of efficiency is compared to the alternative global combustion degree of efficiency for the other possible compression ratios with a respective optimal ignition angle, in order to determine the maximum global combustion degree of efficiency in the related operational conditions.

Description

description

Method for controlling the compression ratio of a spark-ignited internal combustion engine with discretely adjustable compression ratios

Internal combustion engines, in particular reciprocating engines, with variable compression ratio have been known for some time. Changes in the compression ratio, which is the ratio between the volumes of the combustion chamber at the top and bottom dead center of the piston, can be e.g. achieve by changing the piston stroke. Internal combustion engines with a continuously variable compression ratio and internal combustion engines with a discretely variable compression ratio are known. The method according to the present invention relates to internal combustion engines with discretely adjustable compression ratios.

In such internal combustion engines, the compression ratio is changed in order to adapt it to operating conditions of the internal combustion engine. A change in the compression ratio of the internal combustion engine is known to influence the course of the combustion pressure via its effect on the mixture ignition (ignition delay and combustion speed). The pressure in the combustion chamber before combustion is naturally also influenced by the compression ratio. Since the knocking behavior of an internal combustion engine is directly linked to the pressure in the combustion chamber, a change in the compression ratio also has an influence on the knocking behavior.

On the other hand, for each value of the compression ratio, there is one op-position (dependent on further operating parameters). optimal ignition timing for the best possible Gemischverbren¬ tion. However, this optimum ignition point (ignition angle) usually lies in the potential knock region, so that it is generally not possible to operate the internal combustion engine with the optimum ignition angle. The ignition point must therefore be shifted in the direction of a later ignition to the so-called knock limit, in order to protect the engine against a knocking combustion.

The knock limit, in turn, depends on the operating point and the compression ratio of the internal combustion engine: the higher the compression ratio, the better the operating behavior of the internal combustion engine, but the greater the risk of knocking. The lower the compression ratio, the lower the risk of knocking, but the poorer the performance of the internal combustion engine.

In internal combustion engines with a variable compression ratio, the compression ratio is normally selected for all operating points of the internal combustion engine with regard to the best possible efficiency and the lowest possible fuel consumption of the internal combustion engine. In principle, the procedure here is that at low load of the internal combustion engine (in which the volumetric efficiency is low and the knock limit is far from the optimum ignition time point), a comparatively high compression ratio is selected in order to achieve the total efficiency of the internal combustion engine to improve. On the other hand, at high load (in which the volumetric efficiency of Hau¬ se is large and the knocking limit is close to the optimum ignition timing or even behind it) becomes a comparatively low value of the compression ratio selected to protect the engine against knocking.

As is clear from the above considerations, both the compression ratio as well as the ignition point have an effect on the efficiency as well as the Klopfverhal¬ th the internal combustion engine. It would be desirable to operate the internal combustion engine with the highest possible compression ratio and an optimal ignition angle. However, there is the risk that knocking of the internal combustion engine will occur, which may reduce the efficiency of combustion and, in particular, damage the internal combustion engine. A compromise in the choice of Verdichtungsverhältnis¬ ses and the ignition timing is therefore inevitable.

In the classic knock control, a knock correction is performed by means of a Zündwinkelkorrektur. More precisely, knock detection signals are generated with the aid of knock sensors, with which the ignition angle is then adjusted so that knocking is just avoided. The ignition angle is thus to some extent moved to the knock limit (see, for example, US Pat. No. 4,884,206, US Pat. No. 6,317,681 B2, EP 1 092 087 B1). As already mentioned, however, this usually leads to a reduction in the efficiency of the mixture combustion and thus of the achievable torque. In order nevertheless to produce the required torque, it is therefore sometimes necessary to increase the amount of fuel injected, which has an unfavorable effect on fuel consumption and pollutant emissions. In addition, it is sometimes necessary for strong knocking phenomena and thus very large ignition angle adjustments to enrich the fuel mixture in order to avoid excessive operating temperatures of the internal combustion engine or exhaust gas temperatures. The conventional knock control is therefore to avoid knocking. extremely effective, but has some disadvantages in terms of the performance and fuel consumption of the internal combustion engine.

DE 199 50 682 A1 discloses a method for regulating the compression ratio of an internal combustion engine, in which a compression ratio which is too high is determined by means of a knock sensor in order then to reduce the compression ratio below the knock limit and then to increase it again.

From DE 102 20 596 B3 a method for controlling the compression ratio of an internal combustion engine is known, in which the compression ratio in response to a knock detection information in a closed Regel¬ loop is controlled so that knocking is just avoided.

Basically, it is desirable that the internal combustion engine at each operating point with its best possible ignition angle

(Combustion efficiency and performance) and its best possible compression ratio (performance while avoiding knocking) is operated.

The present invention has for its object to provide a method for controlling the compression ratio of a spark-ignited internal combustion engine with discretely adjustable compression ratios, which allows in relatively simple way to operate the engine in each operating point with the best possible ignition angle and the best possible compression ratio , The method according to the present invention is defined in An¬ claim 1.

In an internal combustion engine with an electronic engine control based on torque, the efficiencies of the operating parameters, in particular the ignition angle, the air mass flow, the air / fuel ratio λ and, if appropriate, a factor for switching off one or more cylinders are the usual variables for determining of the current torque of the internal combustion engine. In the case of a variable compression ratio internal combustion engine, a corresponding degree of efficiency for the compression ratio can also be defined, specifically in the form of the ratio of the instantaneous torque which the internal combustion engine generates at the current compression ratio to the maximum torque attainable , which results when all operating parameters of the internal combustion engine have their best¬ possible values.

The present invention is based on the recognition that a global combustion efficiency can be determined with the aid of the ignition angle efficiency and the compression ratio efficiency, with the aid of which the compression ratio which is optimal for a specific operating point can then be selected.

More specifically, in the method of the invention during operation of the internal combustion engine with discretely adjustable compression ratios

a current global combustion efficiency η _actua i for a current compression ratio σ _act uai and a current ignition angle IGA _actU ai calculated using the following formula: ⁷ JaCtUaI - ⁷ I _ ^£ actual ^'7 I _ ^{I GA} actual (D

wherein η_ ε is the degree of efficiency dependent on the compression ratio ε and 77_IGA is the degree of efficiency dependent on the ignition angle,

alternative global combustion efficiencies η _x for the other possible compression ratios ε _x at an optimal ignition angle IGA _bes tx for the relevant compression ratio ε _{x is} calculated with the following formula:

η _x = η_ ε _κ - ^ IGAbest x (2;

the current global combustion efficiency η _actua i is compared with the alternative global combustion efficiencies η _{x in} order to determine the highest possible global combustion efficiency,

and then continued the operation of the internal combustion engine with the Verdich¬ tion ratio for the highest possible Verbrennungswirkungs¬ degree.

The variables r \ _ε and η_IGA used can be determined in the simplest case as follows:

r] _ε = TQ (σ) / TQ _ref η_IGA = TQ (IGA) / TQ _ref

wherein

TQ (ε) = torque as a function of the compression ratio ε TQ (IGA) = torque dependent on the ignition angle IGA TQref = maximum achievable torque with optimally set operating parameters of the internal combustion engine.

If the above comparison shows that the current compression ratio gives the best results, the operation of the internal combustion engine is continued with the previous compression ratio. On the other hand, if the comparison shows that one of the other compression ratios not set leads to better efficiency, the operation of the internal combustion engine is switched to this other compression ratio, the compression ratio being higher or else lower depending on the result of the comparison can be changed.

The method according to the invention offers a simple possibility

to determine the timing for switching the compression ratio,

to ensure the best possible ignition angle under the given operating conditions

to ensure an optimal overall efficiency of the internal combustion engine with optimal control of the compression ratio and ignition angle during the entire service life,

- Ensure a smooth transition in the operating behavior of Brennkraft¬ machine when switching the compression ratio si¬. The use of the above formulas in a more detailed and refined process analysis can help to control the correct time for switching the compression ratio as well as the timing of the switching of the ignition angle in order to ensure torque-neutral switching of the internal combustion engine.

A simple improvement of the above-defined process according to the invention is that the formulas (1) and (2) are modified as follows:

Hactual ⁼ r | _ E actual 'Η _IGA _actU al - 77 _Pactual (1')

wherein η_P is the efficiency of another operating parameter or the product of the efficiencies of further operating parameters of the internal combustion engine.

The efficiency of a further operating parameter can be considered in particular as the λ efficiency, so that when the global combustion efficiency is calculated, a possibly envisaged enrichment of the combustion efficiency

Air / fuel mixture is taken into account. Also, an efficiency for a possible shutdown of one or more cylinders can be considered.

With reference to the drawings, further details of the inventive method will be explained. It shows:

FIG. 1 shows a flow diagram of an exemplary embodiment of a method according to the invention; Figure 2 is a map of the maximum achievable torque TQref;

FIG. 3 shows the relationship between the ignition angle efficiency and the ignition angle.

It is based on a spark-ignited Brennkraftmaschi¬ ne, with a motor control based on torque. Since such engine control systems (EMS = Engine Management System) is today common prior art, this will not be discussed further. The internal combustion engine is further provided with a device for the discrete adjustment of the compression ratio. For example, this device can set three or four different compression ratios.

It is assumed that the internal combustion engine is in operation with a set actual compression ratio ε _actua i and a current ignition angle η_IGA _actU ai (block 1 in FIG. 1). With the method to be described now, it is checked during operation of the internal combustion engine whether another compression ratio ε x which can be set in the internal combustion engine leads to a better combustion efficiency.

For this purpose, after the start of the process (block 2), the current global combustion efficiency η actuai is determined by means of the formula (1) given above (block 3). In a torque-based motor control, the efficiencies τ \ _ε and η_IGA required for this purpose are readily available.

The efficiency τ \ _ε is defined by

η ε = TQU) / TQ _ref Here, TQ (^) can be determined:

TQ (ε) = η_IGA -η_X → _7- SCC -TQ _ref

Herein mean η_IGA the firing angle, η_λ the λ efficiency and η_SCC a factor (between 0 and 1), which takes into account the Abschal¬ tion of one or more of the cylinder.

TQ _ref is the maximum possible torque that can be achieved with optimal adjustment of all operating parameters of the internal combustion engine. It is usually stored in a map that is plotted against the rotational speed N and the load L; an example of this is shown in FIG. 2.

The ignition angle efficiency η_IGA is determined in the simplest case

η_IGA = TQ (IGA) / TQ _ref

however, there are also more complex ways of determining η_IGA.

The efficiency η_IGA is usually stored in a map, which is also spanned over the speed N and the load L. An example of the relationship between the ignition angle efficiency η_IGA and the ignition angle IGA is shown in FIG.

In a next step (block 4), the global combustion efficiency η _x for the other settable compression ratios with the formula (2) given above is determined. It should be noted that the formula (2) in each case the ignition angle efficiency η_IGA _{best x used} for the best possible Zündwin¬ angle at the respective compression ratio. The actual ignition angle IGA _actU ai _{/ used} in the determination of Zünd¬ angle efficiency in the formula (1) may not be identical to the best Zündwink¬ angle for the current compression ratio; For example, the current ignition point may be set back from the best possible ignition point in order to avoid knocking of the internal combustion engine.

The current global combustion efficiency η _actua i is now compared with each of the global combustion efficiencies η _x for the other possible compression ratios (block 5). This process is carried out in an iteration loop, as indicated schematically in the flowchart of FIG. 1.

If it is determined in this process that the current global combustion efficiency η _ac tuai is the best possible efficiency, the internal combustion engine continues to operate with the current compression ratio _{a a} ctuai and the current ignition angle IGAactuai. However, if it is found out in the comparison that an η _x for another compression ratio leads to a higher global combustion efficiency, then the operation of the internal combustion engine with the compression ratio ε _x and ignition angle I _{x x is} switched over for this optimum combustion efficiency (block 6). The internal combustion engine then runs with the newly set compression ratio and ignition angle (block 7).

The method for controlling the compression ratio may then begin again (block 2). As already explained at the outset, the described method can be refined in such a way that, when calculating the global combustion efficiency (blocks 3 and 4), efficiencies of further operating parameters are taken into account. In question is primarily the λ efficiency η_λ, by which a possibly envisaged enrichment of the air fuel mixture is taken into account.

The method described provides a simple and efficient way of controlling the operating parameters and the

Changeover time and direction of the compression ratio of an internal combustion engine with discretely adjustable compression ratios. The internal combustion engine can therefore be operated at any time with the best possible global combustion efficiency by adjusting the compression ratio taking into account the influence of the other relevant combustion parameters, which has correspondingly positive effects on the combustion, the operating behavior of the internal combustion engine as well as the fuel consumption.

Claims

claims

A method for controlling the compression ratio of a spark-ignited internal combustion engine with discretely adjustable compression ratios, which includes a torque-based engine control, in which method during operation of the internal combustion engine

a current global combustion efficiency η _ac tuai for a current compression ratio ε _actua i and a current ignition angle IGA _{actual is} calculated using the following formula:

* 1 actuai = η _ ^ε ac _t uar η _ IGA _actU al (D

wherein η_ ε is the degree of efficiency dependent on the compression ratio ε and 7_IGA is the degree of efficiency dependent on the ignition angle,

alternative global combustion efficiencies η _x for the other possible compression ratios ε _x at optimal

Ignition angle IGA _bes tx for the relevant compression ratio ε _{x is} calculated with the following formula:

η _x = η_ ε _x -η_IGΑ _{best x} (2)

the current global combustion efficiency η _ac tuai is compared with the alternative global combustion efficiencies η _{x in} order to determine the highest possible global combustion efficiency,

and then the operation of the internal combustion engine is continued with the compression ratio for the greatest possible degree of combustion efficiency.

2. The method according to claim 1, characterized in that the dependent of the compression ratio efficiency τ \ _ε and the ignition angle dependent efficiency η_IGA will be determined as follows:

τ \ _ε = ΥQ (ε) / TQ _ref η_IGA = TQ (IGA) / TQ _ref ,

wherein

TQ (ε) = torque dependent on the compression ratio ε

TQ (IGA) = torque dependent on the ignition angle IGA TQ _ref = maximum achievable torque with optimally set operating parameters of the internal combustion engine.

3. The method of claim 1 or 2, characterized in that the dependent of the ignition angle IGA efficiency η_IGA ei¬ nem spanned over speed and load map is taken.

4. The method according to claim 2 or 3, characterized in that the maximum achievable torque TQ _{ref is taken} over a Dreh¬ number and load spanned map.

5. The method according to any one of claims 2 to 4, characterized ge indicates that the dependent of the compression ratio ε torque TQ (^) is determined as follows:

TQU) = η_IGA-η_X - ^ _ SCC -TQ _ref (3) wherein η_λ the efficiency taken for a map of the air / fuel ratio λ in a mixture enrichment and η_SCC is a measure of a reduction in torque at Ab¬ circuit of one or more cylinders.

6. The method according to any one of the preceding claims, characterized in that the formulas (1) and (2) are modified as follows:

Hactual ⁼ r | _ E actual 'Η _IGA _actU al - 77 _Pactual (1') η _x = η_ ε _x -η_IGΑ _{best x} -η_P _x (2 ')

wherein η_P is the efficiency of another operating parameter or the product of the efficiencies of other operating parameters of the internal combustion engine.

7. The method according to claim 5, characterized in that η_P the dependent on the air / fuel ratio λ Wirkungs¬ degree η_λ in a Gemischanfettung.

8. The method according to claim 5 or 6, characterized in that the efficiency η_P comprises the efficiency η_SCC, which is a measure of the torque reduction due to the Abschal¬ tion of one or more cylinders.