DE102010030873A1 - Method for cooling cylinder of internal combustion engine with direct injection, involves taking place fuel injection in combustion chamber of cylinder after stop request and before shutdown of internal combustion engine - Google Patents

Abstract

The method involves taking place a fuel injection in a combustion chamber (4) of a cylinder (3) after a stop request and before a shutdown of an internal combustion engine (1) or immediately after the shutdown of the internal combustion engine, so that the air present in the combustion chamber is cooled. The fuel injection takes place in closed discharge valve (5b) of the cylinder. An independent claim is also included for a processing unit for executing a cooling method.

Description

The present invention relates to a method for cooling at least one cylinder of a direct injection internal combustion engine.

State of the art

Internal combustion engines are conventionally tempered by means of the so-called starter or starter. However, so-called start / stop modes are known in which the engine is parked in certain situations and should be restarted relatively soon. For example, it is known to stop the engine when the vehicle is at a standstill, for example at a traffic light, and to start it again when the clutch or accelerator pedal is actuated. It is desirable to perform this Wiederanlassvorgang without the involvement of a starter to protect it and avoid the associated noise (so-called. Direct start). However, this is difficult for direct injection engines because the engine is not necessarily in a restorable state before being restarted. In particular, there is often not enough oxygen available for direct cylinder restart.

The amount of oxygen present in the cylinder depends on several parameters, in particular the temperature of the air. At high temperature, on the one hand, the oxygen content in the air decreases, on the other hand, the pressure in the cylinder increases, so that air escapes from the cylinder during the stop phase. Both of these factors mean that there is little oxygen available for a subsequent start, that combustion produces little momentum, and that the likelihood of success decreases. In order to guarantee a safe sequential start, starters or starters are also used in the start / stop mode in the prior art.

It is desirable to develop a way to assist the re-starting of a direct injection internal combustion engine by cooling the cylinder, so that a sequential start is quick and reliable.

Disclosure of the invention

According to the invention, a method for cooling at least one cylinder of a direct injection internal combustion engine having the features of patent claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

The invention makes use of the knowledge that at low temperatures of the cylinder or the air therein, the oxygen content in the air increases and at the same time the pressure decreases, whereby less gas mixture or air escapes. A cooling of the cylinder or the air is achieved by injection of fuel before and / or immediately after stopping the engine. Conveniently, only the cylinders are cooled, which have at least one closed outlet valve. The injection leads to a cooling and thus to a lower pressure of the gas trapped in the combustion chamber, so that less air escapes. As a result, more oxygen is available for restarting.

If the engine control is able to predetermine which cylinders are to be used for the next start (discharge prediction), fuel can still be injected into these cylinders immediately before the engine is stopped. If this happens with the intake valve open, cooling of the fresh air is achieved so that more oxygen can flow into the cylinder. If this happens with closed gas exchange valves, the pressure in the enclosed gas decreases and less fresh air escapes through leaks. In both cases, there is more fresh air and thus more momentum available for the next start. Furthermore, a pre-homogenization of the fuel / air mixture takes place during the stop phase. This promotes the ignitability of the mixture at the next start. Alternatively or additionally, an injection can also be carried out during engine standstill, in particular if the engine control system is unable to predict the cylinder to be used for the following start sufficiently early.

The exact timing of the injection is between the stop and the subsequent start request, which range may be divided into two preferred sections, a first section extending from the stop request to the engine stop, and a second section other than the engine stall extends to the start request (restart).

An injection process within the first section preferably takes place, inter alia, in the last intake phase before the engine is stopped. An injection with an open inlet valve cools the intake air so that the air in the combustion chamber is enriched with more oxygen than usual. In particular, injection takes place during the first section into a cylinder whose exhaust valve is closed and remains closed until the engine is stopped. In this case, an engine control which is assigned to the engine preferably calculates an outlet prediction of the individual cylinders and thus can predetermine in which position the valves of the cylinders will be at standstill of the engine.

An injection process within the second section is expediently carried out in a cylinder which is in a compression phase or a working phase. These are phases that are in principle suitable for a direct restart. An injection process within the second section is preferably within 1 sec, preferably 0.5 sec, and more preferably 0.2 sec after the engine is stopped in a cylinder located at a crankshaft position of -90 ° to + 90 ° crankshaft angle relative to ZOT (top dead center ignition).

An arithmetic unit according to the invention, for. As a control device of a motor vehicle is, in particular programmatically, adapted to perform a method according to the invention.

With the invention, a simple and quick restart of an internal combustion engine with direct injection is possible. In particular, this simplifies the use of such internal combustion engines in a start / stop mode. The starter or starter can be made weaker performance, since it would be less or not charged in the start / stop mode The disturbing noises associated with the usual starting process can be avoided when restarting. At the same time, the starter and battery life is increased during start / stop operation.

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 particular combination given, but also with other combinations or in isolation, without departing from the scope of the present invention.

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

Brief description of the drawings

1 shows a schematic representation of an internal combustion engine, as can be based on the present invention.

2 shows a preferred embodiment of the invention with reference to a flow chart.

Embodiment (s) of the invention

In 1 is an internal combustion engine 1 illustrated how they may underlie the present invention. The internal combustion engine 1 includes a piston 2 in a cylinder 3 is movable up and down. The cylinder 3 includes a combustion chamber 4 which has an inlet 5a and an exhaust valve 5b an intake pipe 6 or an exhaust pipe 7 are connected. Furthermore, with the combustion chamber 4 a controllable with a signal ZW spark plug 9 connected. A typical internal combustion engine has other, not described here sensors and actuators, such as. Air mass sensor, lambda sensor, throttle etc. The internal combustion engine is one with direct injection, so that a controllable via a signal TI injector 8th on the cylinder 3 is arranged.

During operation of the internal combustion engine, fuel from the injection nozzle 8th in the combustion chamber 4 directly injected and with the air in the combustion chamber 4 mixed. Thereafter, the fuel-air mixture is compressed during the compression phase, and then from the spark plug 9 to be detonated. Due to the expansion of the ignited fuel (working phase), the piston 2 driven. In operation, the driven piston becomes a crankshaft 14 offset in a rotational movement over which ultimately the wheels of the motor vehicle are driven. On the crankshaft 14 is an example of a tachometer wheel 13 arranged, whose teeth from an associated speed sensor 15 be scanned. The speed sensor 15 generates a signal indicative of the rotational speed N and the crankshaft angle φ of the crankshaft 14 be determined.

It is understood that an internal combustion engine may have more than one cylinder, which are assigned to the same crankshaft and the same exhaust pipe and form an exhaust bank.

A control unit (ECU) 16 is acted upon by input signals representing operating variables of the internal combustion engine measured by means of sensors. For example, the controller 16 the speed sensor 15 connected. The control unit 16 generates output signals with which the behavior of the internal combustion engine via actuators 1 can be influenced according to the desired control and / or regulation. For example, the controller 16 with the injector 8th and the spark plug 9 connected and generates the signals required for their control TI or ZW. For this purpose, the control unit 16 provided with a microprocessor which has stored in a storage medium, in particular in a read only memory (ROM) a program which is suitable for the entire control and / or regulation of the internal combustion engine 1 perform. The control unit 16 is set up to carry out a method according to the invention.

The following is with reference to 2 the sequence of a preferred embodiment of the invention with reference to a flowchart 200 explained. This embodiment may be an internal combustion engine according to 1 underlying with any number of cylinders.

The process begins with a step 201 which is preceded by a stop request and in which the engine is thus in coasting. In a subsequent step 202 a check is made as to whether the engine is still in motion, ie in coasting, or is already stationary.

Is the engine during the step 202 still in coasting, an injection takes place before the engine stops, thus in the first section of the area between stop and start request. This is done first in the subsequent step 203a Checks whether the exhaust valves of a cylinder are in an open position at the time of engine standstill. If the exhaust valve will be open at the time of engine shutdown, that cylinder will not be used for the next start and a next cylinder will be on a path 204a checked. If, on the other hand, it is determined that the exhaust valves will be closed by the time the engine is stopped, it will start in one step 205a Fuel injected into the cylinder concerned for cooling. In the case of a z. B. electromagnetic operation of the valves can also be ensured with the valve actuator that the valve remains closed.

Will in step 202 found that the engine is stylish, with step 203b continued. In step 203b it is checked whether a cylinder is in the compression phase, that is, whether the piston is in a crankshaft position from -90 ° to 0 ° crankshaft angle relative to ZOT. If this is the case, then in the next step 205b Fuel injected into the cylinder concerned. If the cylinder is not in the compression phase, it will have a path 204b the step 206b initiated.

In step 206b It is checked whether the cylinder is in the working phase. In the working phase, the piston is at a crankshaft position of 0 ° to + 90 ° crankshaft angle relative to ZOT. If the cylinder is in the working phase, it will be in one step 208b Fuel injected into the cylinder. If the cylinder is not in the working phase, then follows a path 207b a step 209b ,

In step 209b is waiting for the start request.

The right branch of the 2 , which describes the injection after the engine stoppage and is indicated by the suffix "b", is suitably run through for each cylinder. The injection takes place here in the cylinder, in which both the inlet and the exhaust valve (compression and working phase) are present in the closed position. The injection is expediently carried out immediately after the engine has stopped, preferably within 1 sec.

It is usually sufficient to have the same cylinder in either the left or the right branch of the diagram 200 according to 2 to use. If a cylinder has already cooled down in the engine outlet, it is not necessary - but possible - to cool it down again when the engine is at a standstill.

Claims (8)

Method for cooling at least one cylinder ( 4 ) an internal combustion engine ( 1 ) with direct injection, wherein after a stop request and before a stoppage of the internal combustion engine ( 1 ) and / or immediately after the stoppage of the internal combustion engine ( 1 ) an injection ( 205a . 205b . 208b ) of fuel into the combustion chamber ( 4 ) of the at least one cylinder ( 3 ), so that one in the combustion chamber ( 4 ) existing air is cooled. Method according to claim 1, wherein the injection ( 205a . 205b . 208b ) with the exhaust valve closed ( 5b ) of the at least one cylinder ( 4 ) he follows. Method according to claim 1 or 2, wherein the injection ( 205b . 208b within a 1 sec., preferably 0.5 sec. after, and more preferably 0.2 sec., after the stoppage of the internal combustion engine ( 1 ) he follows. Method according to claim 1, 2 or 3, wherein the injection ( 205b . 208b ) occurs at a crankshaft position of -90 ° to + 90 ° crankshaft angle relative to ZOT. Method according to claim 2, wherein the injection ( 205a ) takes place in the last intake phase before the engine is stopped. Method according to claim 2 or 5, wherein the injection ( 205a ) before the stoppage of the internal combustion engine ( 1 ) into the cylinders ( 4 ), in which the exhaust valve ( 5b ) to standstill of the internal combustion engine ( 1 ) remains closed. Method according to one of the preceding claims, wherein at least in the cylinder ( 3 ) ( 205a . 205b . 208b ), which is to restart the internal combustion engine ( 1 ) are provided. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims.

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