DE102007059877B3 - Delivered torque limiting method for spark-ignited internal-combustion engine of motor vehicle, involves adjusting ignition angle to operating point with delivered torque behind efficiency-optimized reference ignition angle - Google Patents

Abstract

The invention relates to a method for limiting the output torque of a spark-ignited internal combustion engine, wherein at least one ignition angle is set in time before the efficiency-optimized reference ignition angle. Furthermore, the invention relates to an engine control unit for controlling and / or regulating a spark-ignited internal combustion engine, which includes a device for limiting the output torque of the internal combustion engine to a predetermined target value to adjust at least one ignition timing before the efficiency optimized reference ignition angle.

Description

The The invention relates to a method for limiting the output torque a spark ignited Internal combustion engine.

Further The invention relates to a motor control device for control and / or regulation a spark ignited Internal combustion engine and a motor vehicle with an engine control unit. A such limitation of the delivered power can be different establish be necessary, for example, to prevent wheel slip, from tax or model policy reasons or classification in a cheaper To reach insurance class. Furthermore, a power limitation may be required be adapted to the exhaust gas temperature to one for downstream components Value down.

Out The prior art is known that the exhaust gas temperature a spark-ignited internal combustion engine changes both with the speed and with the air / fuel ratio λ. Provided the fuel / air ratio is adjusted so that there is a fuel surplus, the Exhaust gas temperature lower. This depends together with it that the combustion runs off more slowly and the energy needed to vaporize the excess fuel is removed from the combustion process. At high speed is the Exhaust temperature and through the exhaust gas in downstream assemblies registered heat bigger than at lower speed.

Out The prior art is further known that the output torque a spark ignited Internal combustion engine limited by spark ignition can be. Under a late ignition will understood in this context that the ignition point in the direction of top dead center or even over shifted the top dead center to the end of the combustion cycle becomes. This reduces the efficiency of the internal combustion engine and the Exhaust gas temperature rises.

Out establish of the component protection, the exhaust gas temperature may have a certain limit do not exceed. Most of this limit temperature is due to the catalytic converter, the Lambda probe for measurement the fuel / air ratio or an exhaust gas turbocharger determined. If the internal combustion engine via a longer Period high torque is required, the exhaust gas temperature over the increase critical temperature. To the exhaust gas temperature again Lower is known by injecting excess fuel, the exhaust gas temperature to lower. As a result, the exhaust gas temperature can be reliably reduced become. A disadvantage of this method, however, is an increase in Emissions of unburned hydrocarbons and an increase in Fuel consumption. Both can increase by 30% in the worst case.

The DE 10 2006 025 891 B3 describes a method for speed limitation and torque reduction in an internal combustion engine. In this case, in order to decelerate a crankshaft of the internal combustion engine as quickly as possible, a pressure maximum of a gas pressure of combustion gases in at least one cylinder of the internal combustion engine moved early, preferably to the top dead center of the piston in the at least one cylinder or beyond.

The DE 100 39 784 A1 describes a method and a device for operating an internal combustion engine, in which an enrichment of the air / fuel mixture takes place in the sense of a richer mixture composition in the region of high loads and / or component protection reasons. Depending on the switching state of a switch which can be actuated by the driver and / or the gear position, the default value controlling the power of the internal combustion engine is limited in such a way that no mixture enrichment takes place.

The post-published DE 10 2006 053 807 A1 describes a method for operating an internal combustion engine, in which an actual torque output by the internal combustion engine is determined from an exhaust gas temperature of the internal combustion engine.

outgoing From this prior art, the invention is based on the object the exhaust gas temperature and / or the output torque of a spark-ignited internal combustion engine to limit without an excessively increased fuel consumption or increased Pollutant emissions occur.

The The object is achieved by a method for limiting the output torque of a spark ignition Internal combustion engine, in which at least one ignition angle in time before the efficiency-optimized firing angle is adjusted according to claim 1.

Farther is the solution the task in an engine control unit for control and / or regulation a spark ignited Internal combustion engine, in which for limiting the output torque a device is provided to a predefinable setpoint, at least one ignition angle in time before the efficiency-optimized reference ignition angle to adjust, according to claim 9.

Farther the object can be achieved with a motor vehicle according to claim 12.

at an ignition point from about 25 ° to about 50 ° before the top dead center results in a maximum of the delivered torque. The associated to this maximum firing angle is referred to as the efficiency-optimized reference ignition angle. According to the invention will now proposed to reduce the torque output the firing angle not known from the reference ignition angle as known in the art after late to adjust, d. H. in the direction of top dead center, but exactly opposite. This pre-ignition shifts the maximum Combustion pressure at a time at which the associated piston the upward movement not yet complete has finished. Therefore leads the combustion pressure in a portion of the power stroke to a deceleration of the piston and thus desirably to a reduction of output torque and the output power. An intervention in the air-fuel ratio and a consequent increase in consumption and / or The emissions are therefore no longer necessary.

The proposed pre-ignition will at least made in one stroke. In a multi-cylinder engine will the sparkle at least made on a cylinder, but preferably on all cylinders.

By the pre-ignition proposed according to the invention decreases also the exhaust gas temperature. This is essentially due to that the period from the ignition of the mixture until the expulsion of the Exhaust gas extended into the exhaust system is, so that the combustion gases their thermal energy to the other engine components can give.

Provided the inventive method is used, the exhaust gas temperature at high load of the internal combustion engine Lowering below a predefinable limit is also the case associated with a reduction in efficiency. This goes hand in hand at the same torque output increased consumption. surprisingly However, it has been shown that this reduction in efficiency and the increase Fuel consumption are lower than that of the previously used Mixture greasing resulting fuel consumption.

The sought according to the invention Benefits arise in particular when the ignition angle a flow of about 5 ° to about 20 ° opposite the Referenzzündwinkel having. The skilled person will the lower limit of 5 ° in particular so choose, that the desired Effect on the output torque and / or the exhaust gas temperature established. The upper limit of 20 ° can be given for example by the knock limit, which by Combustion chamber geometry, residual gas content, fuel quality, temperature and wear state of Internal combustion engine is affected.

In a preferred embodiment is at least the upper limit of the Zündwinkelverstellung by the Knock limit of the internal combustion engine determined during operation. In a Further development of the invention may also be the lower limit of the ignition angle adjustment by the knock limit of the internal combustion engine during operation of the machine be determined. Under knocking combustion one understands thereby the simultaneously occurring at different points in the combustion chamber, uncontrolled combustion. It is caused by the pressure increase, which by the alien ignited Combustion is not caused by the flame front collected mixture compressed and thereby to the autoignition temperature heated becomes. Due to the simultaneous combustion in different places then the peak pressure in the cylinder increases sharply, causing a knocking noise arises. In severe cases can the pressure increase for destruction lead the engine.

Around To prevent knocking, the pressure increase due to late ignition can be so far in the range of the downward movement of the piston are shifted, that the peak pressure is lowered. The influence on the exhaust gas temperature and the torque output reduced by ignition angle adjustment accordingly. As the knocking tendency of an internal combustion engine among other things, the state of wear and the fuel quality depend on which can change during operation of the internal combustion engine, the upper limit the ignition timing from the engine control unit dynamically during of the establishment. For example, the ignition can far to early be adjusted until a built-in knock sensor in the engine Knock registered. Starting from this value, the ignition is then again slight after late adjusted and this value is stored as the upper limit in the engine control unit. A recalibration of the upper limit can either be specified Time intervals, by service personnel or by a recognized disturbance variable be triggered. As a disturbance change can For example, a refueling of the vehicle or a change the compression can be viewed.

Furthermore, the upper limit of the possible ignition adjustment is determined by the residual gas ratio, which in turn can be adjusted by valve lift and timing of the intake and exhaust valves and / or an external exhaust gas recirculation valve. In a preferred embodiment tion form of the invention is determined, for example in driving tests, a residual gas ratio, which has a favorable effect on the tendency to knock of the engine in the respective operating state. This residual gas ratio is then set by the control unit with advance adjustment of the ignition to limit the torque and / or the exhaust gas temperature. Of course, the expert can also provide for the residual gas ratio to adjust this value dynamically in operation, as shown above for the upper limit of Zündwinkelverstellung.

Farther A mixture with a smaller fuel / air ratio λ tends to increase Beat. A small fuel / air ratio should be understood to mean a value λ <1, ie a mixture with excess fuel. Furthermore, in this context, a mixture with λ = 1 denotes stoichiometric Mixture. A big Air / fuel ratio, ie λ> 1, indicates a lean mixture with excess air. Because a mixture with λ <1 is more likely to knock is proposed in a development of the invention, simultaneously with the advance adjustment the ignition timing also the fuel-air ratio to λ> 1. Especially preferred is a relationship from about 1.05 to about 1.15. This also results in another Torque reduction.

Provided is detected by the knock detection of the internal combustion engine, that the operation of the internal combustion engine with a firing angle before the efficiency-optimized reference ignition angle no longer upright can be obtained, this operating state is preferred by finished that ignition angle behind the efficiency-optimized reference ignition angle to an operating point retracted with the same torque. As a result, the switching from an operating state designed torque neutral in the other operating state, d. H. for the driver imperceptibly.

For this is proposed in a development of the invention, always in the engine control unit a reserve ignition angle ready to hold, which in terms of time to the efficiency-optimized Referenzzündwinkel lies, thus represents a late ignition, and to provide an operating state with the same output torque can. The determination of this reserve ignition angle can either by Calculation done or by a numeric map matrix. occasionally, can neural networks are also used. Since the reserve ignition angle at early adjustment the ignition angle always in the engine control unit is kept ready, the controller can if a detected error this reserve ignition angle set as soon as possible, before it damages comes from engine components.

Provided a cylinder-selective knock control is provided, the torque-neutral Reservezündwinkel also be used to single cylinders of a multi-cylinder internal combustion engine with Pre-ignition and single cylinders with delayed ignition too operate and so the advantages of the invention despite a recognized Error at least in a limited way Scope to realize.

Provided the early adjustment the ignition timing has been done to reduce the exhaust gas temperature, the mixture is after Changeover to the reserve ignition angle again set to values λ <1 to to limit the exhaust gas temperature.

following the invention is based on figures and an embodiment without restriction of the general inventive concept will be explained in more detail.

1 shows the relationship between the output engine torque and the ignition timing, expressed as the ignition angle relative to the top dead center OT.

2 shows the relationship between the exhaust gas temperature and the ignition timing, again expressed as the ignition angle relative to top dead center.

1 schematically shows the output torque of a single-cylinder internal combustion engine as a function of the ignition timing. Since the ignition occurs cyclically every second crankshaft revolution of a four-stroke engine, the ignition timing is indicated as the ignition angle relative to the top dead center of the piston. For a multi-cylinder engine, the facts apply 1 mutatis mutandis for each cylinder with a corresponding phase shift. Ignition timing and torque development can usually be controlled individually for each cylinder. The total torque of a Mehrzylin dermaschine results from in-phase summation of the torques of the individual cylinders.

1 shows that the output torque is very dependent on the ignition angle. The maximum torque is obtained when the fuel-air mixture is ignited before reaching the top dead center of the piston. In this case, the time to reach top dead center is available to form the flame front in the cylinder. After the piston has exceeded the top dead center, the pressure in the cylinder reaches its maximum and thus generates the greatest possible torque. The firing angle at which the maximum possible rotation moment is reached, is in 1 referred to as the reference ignition angle.

From the prior art is known to lower the torque to the ignition timing in the direction of top dead center. In this case, a shift over the top dead center can be done occasionally, for example, to point 1 in 1 , An advantage of this type of torque influencing is in particular that the intervention can be done very quickly, for example, to prevent detected slip on the Antriebrädern. In some cases, the vehicle speed can be limited in this way, or the maximum power of the internal combustion engine, for example, for model policy reasons.

According to the invention, it is now proposed to shift the firing angle from the reference firing angle to the left in order to limit the delivered torque, ie from a position before the top dead center to a position which is still further ahead of the top dead center. The schematic torque curve in 1 shows that the output torque falls off on both sides of the reference ignition angle. According to the invention, it has been recognized that an influencing of the internal combustion engine can thus also take place in that the ignition angle is shifted from the reference ignition angle to "early", for example to point 2 , This is the point 2 between the reference ignition angle and the knock limit of the internal combustion engine.

The Knocking limit of the internal combustion engine depends on a variety of Parameters, for example the combustion chamber geometry, the residual gas content, the fuel quality, the temperature or the state of wear of the internal combustion engine. Some of these parameters, such as wear, temperature and fuel quality, change during operation of the internal combustion engine. Therefore, the invention proposes to monitor the knock limit dynamically by the engine control unit and the respectively valid Value in the control unit save. Thus, always an optimal operating condition with reduced torque to be approached, either by early or late adjustment the ignition timing.

Provided an operating point with reduced torque and / or reduced Exhaust gas temperature must be approached, the ignition angle preferably moved to "early" decreases the output torque and the exhaust gas temperature. Provided required, the fuel / air ratio and / or the residual gas content be set to avoid knocking combustion.

Provided in such an operating condition the knock limit changes unexpectedly, for example by too high engine temperature or lubricant entry, it can nevertheless in this operating state to a knocking combustion come. For reasons the driving comfort and the component protection must be this operating condition to be ended. This can be done, for example, by a slight delay shift the ignition angle done so that this is still between knock limit and reference ignition angle is, but closer to the reference ignition angle draws near. Such an adjustment leads that the output torque increases slightly.

In order to prevent this increase in the torque, the operating state near or beyond the knock limit may be preferably changed by the ignition angle from the operating point 2 to the operating point 1 is withdrawn. Both operating points show the same torque output. This avoids an unexpected acceleration of the vehicle or an erroneous engine operation. At the same time, by retarding the firing angle past the reference firing angle, the uncontrolled pressure increase is shifted so far into the region of downward movement of the piston that the peak pressure in the cylinder is squeezed far enough to prevent knocking.

2 shows the influence of the ignition angle on the exhaust gas temperature. 2 represents a merely schematic representation. The actual course of the exhaust gas temperature may also be different depending on the engine type.

Out 2 It can be seen that by adjusting the ignition angle of the reference ignition angle in the direction of the operating point 2 the exhaust gas temperature is lowered. As a result, the adjustment of the ignition timing according to the invention is also particularly suitable for keeping the exhaust gas temperature below a predefinable value at full load or near the full load of the internal combustion engine. This lowering of the exhaust gas temperature avoids damage to components in the exhaust gas system, for example the lambda probe, the catalytic converter or the turbocharger. An operating state with a high load is understood to be an operating state in which between 60% and 100% of the maximum torque required at the respective rotational speed is requested.

To In the prior art, the exhaust gas temperature is limited by that extra fuel is injected. The fuel / air ratio λ is thus smaller than 1. By this measure can the heat of evaporation of the fuel for cooling be used. This increases consumption and hydrocarbon emissions at.

According to the invention, it is now proposed to lower the exhaust gas temperature the operating point 2 to approach, in which the ignition timing is in front of the reference ignition angle. How out 2 As can be seen, this reduces the exhaust gas temperature. Furthermore, the engine power decreases and the fuel consumption increases, but to a much lesser degree than by the injection of additional fuel. The operating mode according to the invention offers an advantage over component protection by additional fuel injection, since the overall efficiency is less deteriorated as a result of the pre-ignition proposed according to the invention.

If the internal combustion engine can not be operated reliably, in particular if knocking combustion occurs, the ignition angle is preferably drawn back to an operating point with the same torque. This is the operating point 1 in 2 , If the increase in the exhaust gas temperature caused thereby exceeds a predefinable exhaust gas temperature, it is possible to counteract a value λ <1 by changing the fuel / air ratio.

Claims (12)

Method for limiting the output torque of a spark-ignition internal combustion engine, characterized in that at least one ignition angle is set in time before the efficiency-optimized reference ignition angle, and that the ignition angle is set behind the efficiency-optimized reference ignition angle to an operating point with the same torque, if detected an error during operation of the internal combustion engine becomes. Method according to claim 1, characterized in that that the firing angle to limit the torque output by a flow of about 5 ° to about 20 ° before set the reference ignition angle becomes. Method according to claim 2, characterized in that that the flow determined by the knock limit of the internal combustion engine becomes. Method according to one of claims 1 to 3, characterized that the firing angle in front of the reference ignition angle is set if the exhaust gas temperature exceeds a predefinable limit. Method according to one of claims 1 to 4, characterized that the air-fuel ratio is enlarged. Method according to one of claims 1 to 5, characterized that a specifiable residual gas ratio on the Control times of the valves and / or an exhaust gas recirculation valve is set. Method according to one of claims 1 to 6, characterized that with the retreat the ignition angle behind the reference ignition angle the Air-fuel ratio is reduced. Method according to one of claims 1 to 7 for power limitation an internal combustion engine in a motor vehicle. Engine control unit for controlling and / or regulating a spark-ignited internal combustion engine, characterized characterized in that for limiting the torque output the internal combustion engine provided to a predetermined setpoint means is at least one ignition angle in time before the efficiency-optimized reference ignition angle and that means are provided with which a firing angle behind the efficiency-optimized reference ignition angle at one operating point can be provided with the same torque. Engine control unit according to claim 9, characterized in that the ignition angle around a flow of about 5 ° to about 20 ° before the reference ignition angle is adjustable. Engine control unit according to claim 10, characterized in that a device intended to determine the knock limit. Motor vehicle with an engine control unit after a the claims 9 to 11.