WO1996000347A1

WO1996000347A1 - Method of controlling the fuel supply to an internal-combustion engine with a selective cylinder cut-off capability

Info

Publication number: WO1996000347A1
Application number: PCT/EP1995/002428
Authority: WO
Inventors: Bernhard Bauer; Johann FRÖHLICH
Original assignee: Siemens Aktiengesellschaft
Priority date: 1994-06-24
Filing date: 1995-06-22
Publication date: 1996-01-04
Also published as: DE59503364D1; EP0766783B1; EP0766783A1

Abstract

In order to avoid the fuel mixture becoming too lean after cutting off the supply to an individual cylinder to reduce torque (traction control), the invention calls for the enrichment requirement for each cylinder when the cut-off cylinder is connected in again to be determined as a function of the point on the engine operating cycle, the coolant temperature and the number of consecutive fuel cut-offs and injections.

Description

description

Method for controlling the fuel supply for an internal combustion engine that can be operated with selective cylinder deactivation

The invention relates to a method for controlling the fuel supply for an internal combustion engine that can be operated with selective cylinder deactivation according to the preamble of claim 1.

To reduce the torque given off by the internal combustion engine when using traction control (ASR), it is known to switch off the fuel supply to one or more cylinders according to a defined pattern for a certain number of cycles (work cycles) of the internal combustion engine (SAE Paper 920641 "Traction Control ( ASR) Using Fuel Injection Supression - A Cost Effective Method of Engine Torque Control ").

Characteristic of such switch-off patterns for the cylinders, hereinafter referred to briefly as blanking patterns, is the blanking of at least one cylinder, i.e. the switching off or on of the fuel supply (injection) to this cylinder taking place according to a defined pattern.

Switching the fuel supply to selected cylinders off and then on again brings with it certain problems.

When the injection is switched off, the equilibrium of the wall film built up during stationary operation of the internal combustion engine, ie the amount of fuel adhering to the inner surfaces of the cylinder and the intake paths, is disturbed. The amount of wall film extracted during each suction process is no longer supplied due to the fuel supply being switched off. When the injection is reinserted, the amount of fuel required for the reconstruction of the wall film is derived from the amount of fuel to be injected calculated for the current load condition. pulled and is therefore not available for combustion in the cylinder. As a result, a mixture which is too lean in relation to the desired state occurs in the combustion chamber of the cylinder in question. The amount of wall film removed is greater the longer the fuel supply to the corresponding cylinder is switched off.

In addition, during stationary operation of the internal combustion engine, the fresh gas filling of a cylinder always contains a certain proportion of exhaust gas due to internal exhaust gas recirculation due to valve overlap (residual gas proportion). When the fuel supply to a cylinder is switched off, this amount of residual gas is flushed out and leads to an increased proportion of oxygen in the combustion mixture in the cylinder.

When the injection is reinserted, this cylinder then has an increased filling, at least for one work cycle, which the load-sensing system (air mass meter or intake manifold pressure sensor) of an engine control for the internal combustion engine can hardly or not at all take into account. This effect is particularly noticeable when a cylinder is operated alternately, since after each combustion there is a purging phase that removes the residual gas.

Alternating operation of a cylinder denotes the operating state of the internal combustion engine in which the fuel supply to this cylinder is interrupted during one working game (corresponding to two revolutions of the crankshaft) of the internal combustion engine and released again during the next working game, etc.

The same problems also occur when the fuel supply to all or individual cylinders is switched off or at least reduced in overrun mode.

In the fuel metering system described in DE-A-27 27 804, it is therefore proposed that after the overrun operation enrich the stationary fuel quantity metered by the metering device in accordance with the operating point of the internal combustion engine by a predetermined additional fuel quantity. The amount added can be constant over a certain number of ignition pulses and the associated metering pulses for the fuel, or can be varied with each metering pulse. A rapid build-up of the fuel wall film is thereby achieved without impairing the quantity balance of the fuel to be metered, but even with a variation in the metering tightness with each metering pulse, the total metered fuel additive amount can be made due to the complex relationships between the required additional wall film amount and the associated company collective history always an inadequate compromise. The amount added may be too large or too small, which has different effects.

Over-greasing of the mixture leads to carbon monoxide exhaust gas peaks, remaining emaciation of the mixture to hydrocarbon emission peaks.

The invention is therefore based on the object of specifying a method for controlling the fuel supply for an internal combustion engine of the type mentioned at the outset, which individually ensures the additional fuel requirement when the fuel supply of a previously blanked cylinder is switched on, depending on its blanking duration.

This object is achieved by a method according to claim 1.

The subclaims are directed to expedient further developments of the inventions.

An embodiment of the invention is shown in the drawing and is explained in more detail with reference to the following description. Show it: 1 shows a simplified block diagram of an internal combustion engine with an electronic control device,. in which the method according to the invention is applied and

Figure 2 in the form of two diagrams (2a, 2b), the relationships between the content of a memory cell and the number of blankings (blanking duration) for a cylinder.

In the case of a control for a motor vehicle, which can be seen in FIG. 1, only the components required to explain the invention are shown as a simplified block diagram. An internal combustion engine 10 has four cylinders Z1, ... Z4. An injection valve EV1, ... EV4 is assigned to each of these cylinders, which injects fuel in a predetermined sequence into the intake pipe of the respective cylinder (sequential fuel injection). The injection valves are components of a fuel circuit, not shown, which in a manner known per se consists of a fuel tank, a pressure regulator, a fuel pump, a fuel filter and corresponding lines.

The internal combustion engine 10 receives the necessary combustion air via an air filter 11, an intake duct 12 and a throttle valve block 13. The throttle valve block 13 contains in a known manner a throttle valve, a throttle valve switch and / or a throttle valve opening angle sensor. To determine the intake air mass LM, an air mass meter 14 is provided in the intake duct 12, which can be implemented either as a hot-film air mass meter or as a hot-wire air mass meter. A three-way catalytic converter 16 is provided in an exhaust gas duct 15 for converting the harmful exhaust gas components HC, CO and NO _x contained in the exhaust gases. To record the oxygen concentration in the exhaust gas, a lambda probe 17 is inserted in the exhaust gas duct 15 upstream of the three-way catalytic converter 16. A speed sensor 18 is used to detect the

Speed N and a sensor 19 for detecting the coolant temperature TKW of the internal combustion engine. The from the probes or Sensors 13 to 19 emitted signals throttle valve opening angle DKW, air mass LM, signal from the lambda probe Uλ, speed N and coolant temperature TKW are transmitted to an electronic engine controller 20 and evaluated by the latter.

Such electronic control devices for internal combustion engines, which in addition to fuel injection can also take on a multitude of other tasks (e.g. ignition control), are known per se, so that only the structure and its mode of operation which are related to the present invention are dealt with below. The motor controller 20 contains a microcomputer (μp) 22, a read-only memory (ROM) 23, a read-write memory (RAM) 24 and other known components, not shown here. According to a program executed by the microcomputer 22, the engine control 20 controls all functions of the internal combustion engine 10. With the aid of the signals supplied by the sensors (air mass meter 14, speed sensor 18) and processed in corresponding circuits, a basic injection time or basic injection time is calculated and dependent Corrections of this basic injection time are carried out by further operating parameters in such a way that a fuel-air mixture which corresponds to the stoichiometric ratio (λ = 1) is generally achieved by using the lambda control.

Control signals are also transmitted via a line 34 from the engine control unit 20 to an ignition control unit 36, which then generates ignition sparks 37 in the combustion chambers of the individual cylinders ZI,... Z4.

A traction control 26 receives and processes the signals from wheel speed sensors 28, one of which is assigned to the front right wheel VR, the front left wheel VL, the rear right wheel HR and the rear left wheel HL. The traction control 26 receives a load signal from the motor control 20 via a line 30 and a motor speed signal via a line 31. The traction control system 26 processes these two signals and the wheel speed signals and generates an intervention signal which is transmitted to the engine control 20 via a line 32. The traction control 26 can be combined with a known anti-lock braking system (ABS), which evaluates the signals from the same wheel speed sensors 28 and prevents the wheels from locking when braking.

If the traction control system 26 recognizes on the basis of the wheel speed signals that one or more driven wheels of the motor vehicle are spinning, it sends an intervention signal to the motor control 20, which brings about a reduction in the motor torque. In order to reduce the engine torque or engine torque, in multi-cylinder engines (generally engines with four or more cylinders) the fuel supply to one or more cylinders is switched off according to a so-called skip pattern.

The additional amount of fuel that must be provided when the fuel supply of a previously hidden cylinder is reinserted depends on several factors.

If a cylinder is operated alternately, ie the fuel supply is interrupted for one work cycle and released again for the next work cycle, the additional mixing requirement depends on the engine load, the engine speed and the coolant temperature. The value range of the additional mixture requirement is between 10% and 50% of the injection quantity required under steady-state conditions. Comprehensive test bench measurements also show that a single enrichment is sufficient for this type of operation, that is to say during the transition from "alternating operation" to "normal operation", the fuel-air mixture for the cylinder concerned has to be enriched only once after its last suppression. For the alternating operation, a fade-out period = 1 is characteristic. If the same cylinder is hidden for a long time, the measurements show the following results:

The mixture requirement increases with an increasing number of hidden work cycles (cycles) and then remains approximately constant. The additional mixture requirement when the injection is successful decreases faster than it increases, i.e. the additional mixture requirement after eight cycles of blanking one and the same cylinder is e.g. after four cycles of injection = 0, i.e. after four cycles, the fuel-air mixture no longer needs to be enriched.

The first injection after longer blanking has the highest need for enrichment, while the next enrichments decrease sharply. This decrease in the need for enrichment can take place according to a selectable function (e.g. linear or exponential).

Since each individual cylinder can be masked out independently of the other cylinders according to the known masking patterns, the additional mixture requirement for each cylinder when the fuel supply is re-used must be determined individually. For this reason, a separate memory cell is defined for each cylinder of the internal combustion engine, which contains the current need for enrichment as a numerical value. With a four-cylinder engine, four memory cells AX (X = 1, ... 4) are defined. A computer program of the microcomputer 22 of the electronic engine control 20 then, depending on the number of the next cylinder Z1,... Z4, which is to be supplied with fuel again, accesses one of these memory cells AX and fetches the necessary enrichment for this cylinder from. In order to fill the memory cells AX with the correct values for the enrichment requirement, information is required about the number of blankings and about the number of injections after blanking, individually for each cylinder. With an increasing number of hidden cycles of one and the same cylinder, the need for enrichment rises slowly when re-injected, and with ongoing re-injection, the need for enrichment decreases significantly faster from this variable starting value. For this reason, further memory cells BX are defined. The content of each of these cells BX (X = 1, ... 4 for a four-cylinder engine) is incremented by a value BINC as soon as a blanking takes place. The incrementation takes place up to a value range end of the memory cell (with 8-bit cell: 255 values) or up to a definable limit value BMAX. With further fades out, ie more than 255 fades out with an 8-bit cell or more than BMAX fades out with a defined limit value BMAX, the content of the memory cell remains unchanged. In the case of a subsequent re-injection of the same cylinder, the content of the cell is decremented by BDEC, namely up to the value 0 of the memory cell BX.

The content of the memory cell BX serves as an input variable for calculating the actual enrichment requirement for the cylinders which are switched on again, depending on their respective fade-out times.

In FIG. 2, the content of a memory cell BX is given in the form of two diagrams, once when a cylinder is hidden for a longer time (FIG. 2a) and once when a cylinder is alternately hidden (FIG. 2b). In both diagrams of FIG. 2, an injection in the respective cylinder is identified on the abscissa with a filled circle, and an empty circle characterizes a blanking. The distance between two successive circles corresponds to the duration of one work cycle of the internal combustion engine. The contents of the memory cell BX are indicated on the ordinate. It is assumed that the maximum value of the memory cell BMAX = 8 is selected. In the diagram according to FIG. 2a), after three injections, the cylinder is first masked out and the content of the memory cell BX is increased by BINC = 1. During the next working cycle, this cylinder remains hidden and the content of the memory cell BX is incremented again by 1. This is repeated until the maximum value BMAX = 8 of the memory cell BX is reached after a total of 8 blankings. Although this cylinder is hidden for a further five working cycles, the content of the memory cell BX remains unchanged at the BMAX value. Only after a total of 13 blankings is this cylinder supplied with fuel again, ie the injection is released and the content of the cell is decremented by the value BDEC = 2. Since this cylinder remains switched on during the next working cycle of the internal combustion engine, a further incrementation by the value BDEC takes place. The same applies to the next working game. After these three successive injections for this cylinder, the latter is hidden again and the content of the memory cell BX, which previously had the value 2, is incremented by 1 again. The same thing is repeated for the next work cycle. After these two fades out of this cylinder, two injections follow again, whereby the value of the memory cell BX is decremented twice by the value BDEC. The content of this memory cell has now reached the value 0 after two consecutive injections. Since, as mentioned at the beginning, the need for enrichment when the blanking increases more slowly than the need for enrichment during re-injection from this variable start value (here in this example the start value is 8 and therefore equal to the maximum value BMAX) decreases again significantly faster, the values for BINC and BDEC are chosen differently in such a way that BDEC is larger. In the example according to FIG. 2, the value BDEC is selected twice as large as the value BINC.

An example of the memory cell BX and its content is given in the diagram according to FIG. 2b) when a cylinder is faded out alternately (fade-out duration = 1). After three injections, there is a blanking for one working cycle. The content of the memory cell BX for this cylinder is increased by the value BINC = 1 and remains at this value until the next work cycle. During the next work cycle, the fuel supply to this cylinder is released again and the in- The memory cell BX stops at 0. When a cylinder is operated alternately, this change in the content of the memory cell BX is repeated with each working cycle.

The need for enrichment when reinstalling after differently long blanking times is therefore taken into account by a first enrichment factor FBX. This factor is calculated in a characteristic curve, the input variable being the content of the memory cell BX of the cylinder to be supplied in each case. The following table shows the assignment of the contents of the memory cell BX and the factor FBX, a value of BMAX = 8 being used as a basis.

Table 1

BX 0 1 2 4 6 8

FBX 0 1 1, 05 1, 1 1, 2 1, 4

alternating operation

BX = 0 means no blanking, BX = 1 denotes alternating operation with a blanking duration equal to 1. In this operating state, the factor FBX = 1. This table also shows that the need for enrichment after the first injection after eight hidden cycles (BX = 8) is 1.4 times higher than with alternating operation.

In addition to the first enrichment factor FBX, which takes into account the differently long blanking times, a basic enrichment value must also be taken into account. This basic enrichment value FNML represents the different enrichment requirements at different engine speeds N and engine loads ML. The engine load can be detected, for example, via the air mass flow, the intake manifold pressure or via the throttle valve position. The basic enrichment value FNML can be displayed either additively (with the unit [ms]) for the injection duration or multiplicatively (factor> 1). The factor FNML is calculated in a two-dimensional map with the input variables speed N and engine load ML.

N 1500 3000 4500 6000 V L // miAnJ ML

25% 1.10 1.15 1.20 1.30

50% 1.15 1.15 1.20 1.35

75% 1.15 1.20 1.35 1.40

100% 1.20 1.20 1.35 1.40

From this table it can be seen that the enrichment requirement for alternating operation (FBX = 1) and small loads (ML <25%) is around 15%, for high loads around 30 to 40%.

Another factor that has to be taken into account when switching on a previously hidden cylinder is the temperature of the internal combustion engine. The temperature can be detected directly with the aid of a temperature sensor on the internal combustion engine itself or indirectly via the temperature of the coolant with the aid of the coolant temperature sensor 19. This factor HFC reflects the different enrichment requirements at different engine temperatures. This factor is calculated in a characteristic curve, the input variable of this characteristic curve being the engine temperature or the coolant temperature TKW. Table 3

TKW - 20 - 10 0 20 40 80 [° C]

FTKW 1, 8 1, 4 1, 2 1, 1 1, 05 1, 0 [ ^o / o]

From Table 3 it can be seen that the enrichment requirement increases with decreasing coolant temperature. In the case of a cold internal combustion engine, the factor FTKW is high, which in turn means that more must be added. In the case of a warm internal combustion engine (TKW> 80 ° C), the factor FTKW has a value of = 1 and is not included in the calculation of the enrichment requirement.

The enrichment for the individual cylinders which are switched on again after a blanking therefore consists of three components, namely the first enrichment factor FBX, the basic enrichment value FNML and the second enrichment factor FTKW. These individual factors multiply into an overall factor

ANX = FNML • FBX • FTKW

linked, which takes into account the need for enrichment when reinstalling previously hidden cylinders.

The total injection period TIA then results in

TIA = TI + ANX [ms],

if the enrichment factor ANX is additively linked to the basic injection duration TI. The enrichment factor ANX can also be linked multiplicatively with the injection duration.

Tables 1-3 show that with alternating operation (FBX = 1) and warm engine (FTKW = 1) the value for the Enrichment is only determined by the basic enrichment value FNML.

In order to be able to fine-tune the different course of the enrichment requirement at different engine temperatures, the values BINC, BDEC and BMAX can also be determined depending on the engine temperature. This gives an even more precise value for the enrichment requirement.

Claims

claims

1. Method for controlling the fuel supply for an internal combustion engine (10) which can be operated with selective cylinder deactivation and which has an engine control (20) and a plurality of cylinders

(Z1, ... Z4) and successive fuel injections into these cylinders (Z1, ... Z4) in a predetermined order, the cylinder deactivation by suppressing fuel injection pulses according to a predetermined switch-off pattern (masking pattern) for at least a work cycle takes place and when the fuel injection pulses of the previously deactivated cylinders (Z1,... Z4) are re-enriched, the fuel / air mixture takes place, characterized in that

that the enrichment requirement (ANX) depends on

a) the operating point (N, ML) of the internal combustion engine (10) when the previously deactivated cylinders (Z1, ... Z4) are switched on again (basic enrichment value FNML) and / or

b) the number of work cycles for which the respective cylinder (Z1, ... Z4) is switched off (first enrichment factor FBX) and / or

c) the internal combustion engine temperature or a variable derived from it (TKW) (second enrichment factor FTKW) is determined,

- That the enrichment requirement (ANX) is stored individually for each cylinder (Z1, ... Z4) in memory cells (AX) of a memory (RAM 24) of the engine control (20) and

- That when the fuel injection pulses for individual cylinders (Z1, ... Z4) are released again, the enrichment requirement (ANX) is taken into account when determining the cylinder-specific injection quantity.

2. The method according to claim 1, characterized in that the second enrichment factor (FTKW) with decreasing Brenn¬ engine temperature or the size derived therefrom (TKW) is selected higher.

3. The method according to claim 1, characterized in that when a limit value for the internal combustion engine temperature or for the size derived therefrom (TKW), the second enrichment factor (FTKW) is not taken into account when determining the enrichment requirement (ANX).

4. The method according to claim 1, characterized in that at the transition from alternating operation of a cylinder

(Z1, ... Z4) in an operation with continuous injection. a one-time enrichment takes place within the following work cycle.

5. The method according to claim 1, characterized in that with increasing number of successive work cycles, during which a cylinder (Z1, ... Z4) is hidden, the enrichment requirement (ANX) gradually increases and then approximately maintains a constant value.

6. The method according to claim 1, characterized in that the enrichment requirement (ANX) decreases when the injection is repeated, starting from a maximum value (BMAX) determined by the number of hidden working cycles, as it increases.

7. The method according to claim 6, characterized in that. the enrichment requirement (ANX) has the greatest value for the first repeated injection and decreases for the next injections after a selectable function.

8. The method according to claim 1, characterized in that the first enrichment factor (FBX) is determined depending on the content of a memory cell (BX) of a memory (RAM) and the Content of the memory cell (BX) is incremented by a value (BINC) as soon as a cylinder (Z1, ... Z4) is hidden and decremented by a value (BDEC) when the injection is released again.

9. The method according to claim 8, characterized in that the incrementation of the content of the memory cell (BX) takes place up to a definable maximum value (BMAX) and the content of the memory cell (BX) remains unchanged in the event of fading-outs which persist even further.

10. The method according to claim 8, characterized in that the increment value (BINC) and the decrement value (BDEC) are selected different from one another.

11. The method according to claim 8 or 10, characterized gekennzeich¬ net that the decrement value (BDEC) is a multiple of the increment value (BINC).

12. The method according to claim 8, 10 or 11, characterized gekenn¬ characterized in that the values (BINC, BDEC, BMAX) are determined depending on the engine temperature or a variable derived therefrom (TKW).