DE102010041773A1 - Method for operating internal combustion engine, involves using pressure accumulator or rails with direct injection, with which signal of lambda probe is evaluated - Google Patents

Abstract

The method involves using pressure accumulator or rails (12) with a direct injection, with which an output signal (26) of lambda probe (20) is evaluated. The lambda probe signal monitors engine speed to detect a malfunction. An independent claim is also included for an arrangement for recognizing a malfunction in an internal combustion engine with direct injection.

Description

The invention relates to a method for operating an internal combustion engine and to an arrangement for carrying out the method.

State of the art

In motor vehicles, direct injection engines are used. Direct injection refers to a method for fuel injection for diesel engines and gasoline engines, in which the fuel is injected by means of a pressure accumulator or rail directly into the combustion chamber. The air-fuel mixture is formed directly in the combustion chamber. In direct injection, the fuel is injected with special injectors under high pressure directly into the combustion chamber. The exact dosing, preparation and distribution of air and fuel for each combustion cycle enable the economical consumption and the low emissions of the system.

In direct injection engines, so-called lambda sensors are used. A lambda probe is a sensor that measures the respective residual oxygen content in a combustion exhaust gas. From this, the ratio of combustion air to fuel is determined in order to be able to regulate the further combustion. This is to ensure that neither fuel nor air surplus occurs. In particular, the lambda probe is used as a sensor in the control loop of the lambda control for catalytic exhaust gas purification. The ratio air: fuel is also referred to as lambda ratio. The correct lambda ratio, usually 1: 1, is an important parameter for controlling combustion and enabling exhaust gas purification through the three-way catalyst.

In direct petrol injection (BDE), the high-pressure circuit is fed by the high-pressure pump, which brings the fuel pressure in the fuel rail to the required high level. In addition, a prefeed pump is provided in the low-pressure circuit. The pre-feed pump and the high-pressure pump together provide the required pressure. The high-pressure injection valves mounted on the fuel feeder meter and atomise the fuel in a very short time at high pressure for the best possible mixture preparation directly in the combustion chamber.

It should be noted that no more high pressure is generated by an error in the high-pressure pump or in the pressure control device, whereby the pressure in the pressure accumulator or rail falls to the level of Vorförderpumpe. As a result, the engine has misfires on all cylinders.

It should be noted that only a pressure of about 5 bar is provided by the pre-supply pump. In order to achieve the required pressure in the rail, which is typically about 50 bar, the high-pressure pump is necessary. If the high-pressure pump fails, too little gas is injected at the set injection time, the air / gasoline mixture becomes too lean and the engine stops.

Although it is known a method for Laufunruheerkennung. However, this does not recognize when all cylinders simultaneously suspend, which is the case with too lean a mixture due to a failure of the high pressure pump.

Previous systems with gasoline direct injection have a pressure sensor in the high pressure range and can directly measure a failure of the high pressure generation. If this pressure sensor is defective, the failure can not be detected. In contrast, in mechanically controlled PDA systems, no pressure sensor should be provided any longer. Therefore, a new method is needed to detect the pressure drop in the rail can.

In particular, the method should be used to detect a pressure drop caused by failure of the high pressure pump or the high pressure control.

Disclosure of the invention

Against this background, a method for operating a gasoline direct injection with the features of claim 1 and an arrangement for carrying out the method according to claim 9 are presented. Further embodiments of the invention will become apparent from the dependent claims, the description and the drawings.

Thus, a signal associated with a lambda probe and the gradient of the engine speed are evaluated to detect a malfunction that may be an error in the high pressure pump or in the pressure control. This may possibly even a suspension of the engine can be prevented. In an embodiment, the method can also be used to precisely determine when a malfunction occurs.

The lambda probe is the sensor which measures the residual oxygen content in the exhaust gas of the internal combustion engine in order to be able to regulate the ratio of combustion air to fuel for further combustion in such a way that neither a fuel nor an air excess occurs. For the method, a signal associated with the lambda probe is evaluated. This may be an output signal of the lambda probe or an output signal of the regulator which is assigned to the lambda probe.

Basically, a ratio of air: fuel of 1: 1 is desired. At this ratio, the operability of the engine and in particular the catalyst is ensured. If now the high-pressure pump fails, this has the consequence that too little fuel is injected at the set injection time. The result is too lean a mixture. The caused by the failure of the high-pressure pump or the high pressure control pressure drop is detected by the presented method.

Due to the presented detection of the pressure drop, the vehicle can be driven in emergency operation or it can be prevented that large quantities of gasoline are released.

In a refinement, a malfunction is thus detected by evaluation of the signal of the steady-state lambda probe or evaluation of the regulator output of, for example, 2-point lambda control and simultaneous monitoring or observation of the gradient of the engine speed or the misfire detection. Upon detection of a malfunction, an emergency measure is usually initiated, in which, for example, the modeled pressure in the rail is set to the nominal pressure of the prefeed pump. The engine then runs again or can be restarted.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or alone, without departing from the scope of the present invention.

Short description of the drawing

1 shows an embodiment of the presented arrangement in a schematic representation.

Embodiment of the invention

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described below in detail with reference to the drawings.

The illustration shows an internal combustion engine 10 with a pressure accumulator or a rail 12 in which fuel by means of a high-pressure pump 14 is introduced and held therein to be injected directly into the combustion chamber (not shown). The pressure in the rail 12 is by means of a pressure regulator 16 set. Furthermore, the illustration shows a prefeed pump 18 and a lambda probe 20 with a regulator 22 ,

Is it now an error in the high-pressure pump 14 or the pressure regulator 16 , the pressure falls in the rail 12 , Since no pressure sensor is provided, this is not noticed immediately. Since the selected injection time is set to the pressure of the pre-feed pump 18 and the high pressure pump 14 This results in too little gasoline being injected and the lambda ratio becoming too lean, ie the proportion of air is too high. This in turn leads to dropouts on all cylinders of the engine.

There are a device for detecting a malfunction 24 to evaluate a signal 26 , that of the lambda sensor 20 is assigned, and a device 28 for monitoring the rotational speed of the internal combustion engine to be operated 10 intended. The device 24 Thus, an output signal of the lambda probe and / or an output signal 30 of the regulator 22 the lambda probe 20 evaluate.

In the illustration are the two facilities 24 and 28 shown as separate components. Of course it is possible the two facilities 24 and 28 in one unit (dashed line 32 ) to integrate. These may be provided, for example, in a control unit of the motor vehicle.

When implementing the described method, the result of the evaluation of the signal 26 the lambda probe and the monitoring of the engine speed, if necessary, after appropriate processing, eg. In a computing unit, passed on to a control unit to initiate any necessary steps can.

In one embodiment of the method is now in the event that there is a constant or increasing moment request of the driver, ie the driver is unabated or even increasingly gas, monitors the speed. If this decreases, which is reflected in a negative gradient, the signal becomes additional 26 monitored, which is associated with the lambda probe. This can be the output or measurement signal of the lambda probe or the output signal 30 of the regulator 22 the lambda probe 20 be.

In this way, it is detected whether a too lean air-fuel mixture in the rail 12 is present. In this case, ratios of, for example, up to 5: 1 can be achieved. At a ratio of 2: 1, one speaks already of a very lean mixture. If, in the event of a negative gradient of the engine speed, a mixture that is too lean is detected, it is assumed that the high-pressure pump 14 has failed and emergency measures can be taken.

It may, for example, the injection time the nominal pressure of the pre-feed pump 18 be adjusted. This means that the injection time is increased. Does this cause the signal 26 , that of the lambda sensor 20 can be inferred, again pointing to a correct air-fuel ratio, that in fact the high-pressure pump 14 or the high-pressure control device ( 16 ) has failed.

In this way it is possible to determine exactly which component is defective in order to be able to indicate this exactly (pin pointing).

Claims (10)

Method for operating an internal combustion engine ( 10 ) with direct injection by means of a pressure accumulator or Rails ( 12 ), where a signal ( 26 ), which is a lambda probe ( 20 ) is evaluated, and the gradient of the engine speed is monitored to detect a malfunction. Method according to Claim 1, in which an output signal of the lambda probe ( 20 ) is evaluated. Method according to Claim 1 or 2, in which an output signal ( 30 ) of a controller ( 22 ) the lambda probe ( 20 ) is evaluated. The method of claim 1 or 2, which is performed when a constant or increasing torque request of the driver is given. Method according to one of claims 1 to 3, wherein when a malfunction is detected an emergency operation is taken. Method according to Claim 4, in which the modeled pressure in the rail ( 12 ) to the nominal pressure of a prefeed pump ( 18 ) is set. Method according to Claim 6, in which an injection time is equal to the nominal pressure of the prefeed pump ( 18 ) is adjusted. The method of claim 7, wherein an injection time is adjusted by means of a control. Arrangement for detecting a malfunction in an internal combustion engine ( 10 ) with direct injection, in particular for carrying out a method according to one of claims 1 to 8, with a device ( 24 ) for evaluating a signal ( 26 ), which is a lambda probe ( 20 ) and a device ( 28 ) for monitoring the gradient of the engine speed. Arrangement according to Claim 9, in which a regulator ( 22 ) for the lambda probe ( 20 ) and the facility ( 24 ) for evaluating the signal ( 26 ), the lambda probe ( 20 ) for evaluating an output signal ( 30 ) of the controller ( 22 ) is trained.

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