DE10309443A1 - Method of operating direct start motor vehicle internal combustion engine has gaseous fuel injected into combustion chambers prior to direct starting - Google Patents

Abstract

The method of operating a multi-cylinder four stroke internal combustion engine (10) for a vehicle involves injecting liquid (41) fuel directly into the combustion chambers (14) of the engine while at rest. The combustion chamber charge is then ignited for starting. A gaseous fuel (45) is also injected into the combustion chamber for a direct start.

Description

State of technology

The invention initially relates to a Method for operating a multi-cylinder four-stroke internal combustion engine, in particular for driving a motor vehicle.

The invention further relates to a Four-stroke internal combustion engine with several cylinders, each with a combustion chamber, and with each a fuel injection device assigned to a combustion chamber for direct injection of at least liquid fuel.

A method and an internal combustion engine of the type mentioned are from the DE 100 20 104 A1 known. Then, with a stationary internal combustion engine, an amount of fuel necessary for combustion is injected and ignited into the combustion chamber of a cylinder, the piston of which is in a position that corresponds to one working cycle. Thereafter, fuel is injected into the combustion chamber of the cylinder or cylinders, the pistons of which carry out the next work cycle, at a suitable time. This is ignited as soon as the pistons in question have reached the respective working position. In this way, the internal combustion engine can be designed without an electric starter and the components necessarily connected to it. This process is also called "direct start".

Prerequisite for performing this procedure is an internal combustion engine in which each combustion chamber has its own Fuel injector is associated with the fuel fed directly to the combustion chamber. This process is also referred to as "direct fuel injection". Direct fuel injection is with petrol and Diesel internal combustion engines known, direct start so far only with gasoline internal combustion engines.

The present invention has the Task, a method and an internal combustion engine of the beginning mentioned type so that the engine is inexpensive built and reliable can be started.

This task is done in a process of the type mentioned in that the internal combustion engine can be started without the help of a starter, that when the internal combustion engine is at a standstill, fuel directly in a combustion chamber is injected and ignited (direct start) and that when you start directly instead of liquid fuel automatically a gaseous Fuel can be supplied.

In an internal combustion engine the type mentioned is achieved in that it has a valve device by means of which the fuel injection devices optionally gaseous or more fluid Fuel can be supplied and that it has a control and / or regulating device, which is the valve device for a direct start of the internal combustion engine with a supply gaseous Can switch fuel.

Advantages of invention

According to the invention, it was recognized that it stationary engine can give operating states in which a liquid fuel injected into a combustion chamber is not or evaporates only so little that there is no ignitable fuel-air mixture in the combustion chamber results. Under such operating conditions the internal combustion engine is thus a direct start, i.e. starting the internal combustion engine without the help of, for example, an electric starter motor, impossible. This problem is addressed in the present invention by that the internal combustion engine for a direct start with gaseous Fuel can be operated.

This ensures that in any case, even with the internal combustion engine stopped, in those combustion chambers the internal combustion engine in which combustion takes place and Work is to be done, an ignitable gas mixture is available is. In this way, a direct start is possible even with very unfavorable ones Operating parameters or operating conditions of the internal combustion engine possible.

Advantageous further developments of the inventive method and the internal combustion engine according to the invention are in subclaims specified.

A first development of the method according to the invention provides before that performing a Direct starts with smooth Fuel from a current operating parameter, in particular a temperature the internal combustion engine, preferably a cylinder head temperature and / or a catalyst temperature. In this way the direct start behavior improved the internal combustion engine when the internal combustion engine is cold. Due to the use of a gaseous fuel, none falls the wall of the combustion chamber and the gas present in the combustion chamber cooling evaporative heat. hereby become relatively high combustion temperatures even with a cold internal combustion engine reached in the combustion chamber, which leads to a higher burning rate and thus to a lower condensate formation, and thus to a more complete combustion to lead. Ultimately, this process also results in emission behavior the internal combustion engine improved during a cold start.

Because of the higher temperatures, any catalyst that is present more quickly reaches the temperature at which it has a good conversion rate. This also leads to an improvement in the emissions of the internal combustion engine operated according to the invention. It goes without saying that the method according to the invention is not can only be used for the very first injections and ignitions with a direct start, but also during a warm-up phase of the internal combustion engine until a desired temperature is reached. In this case, it would only be switched back to operation with liquid fuel when the temperature had been reached.

This ensures that when again such operating parameters or operating conditions are present, which allow the liquid fuel to evaporate, back to using liquid Fuel can be switched. This takes into account that the operating conditions of the internal combustion engine vary according to their Change start can. Ultimately, this means that only small amounts of gaseous fuel to operate the internal combustion engine must be stored. The inventive method and the internal combustion engine according to the invention can can therefore be used in motor vehicles without space problems there arise.

The method according to the invention is particularly suitable for use in a diesel internal combustion engine, the gaseous fuel from an ignition device spark ignition becomes. In this way, a diesel engine that can be started directly becomes the first time created which beyond can be started safely even in cold temperatures and thereby has good emission behavior.

Natural gas is preferred as the gaseous fuel or hydrogen gas is used. Both types of fuel can do well are stored and are also in conventional internal combustion engines Can be used without costly modifications.

Particularly advantageous is the embodiment of the method according to the invention in which it is detected which cylinder has to perform the first compression work when starting and in which a closing angle of an intake valve of at least this cylinder is adjusted late for a limited period of time. In this way, the air filling in the cylinder which has to do the compression work at the start is reduced. This in turn leads to a decrease in the compression resistance during the starting process, which in turn leads to a crankshaft of the internal combustion engine being set into a rotational movement much more easily by the first combustion at the beginning of the starting process according to the invention, and the internal combustion engine can thus be started. In detail, this is based on the DE 100 20 104 A1 and the DE 100 24 438 A1 referenced, the disclosure of which is expressly made the subject of the present statements.

In further training, it is proposed that it is determined which cylinder is the second to start compression work must afford and that a closing angle of an intake valve at least this cylinder for a late period is adjusted. This will also be the rotation of the crankshaft braking compression torque of the second compressing cylinder reduced, which makes starting the internal combustion engine even easier. If necessary, you can such late adjustments also with subsequent compressing cylinders be made.

It turned out to be particularly cheap if the closing angle at about 80 ° to 100 ° NUT, preferably around 90 ° NUT, adjusted becomes. At these closing angles (° nUT = angle after bottom dead center) there is another one for the subsequent combustion sufficient air filling reached, but at the same time the compression or Gas spring torque clearly due to the air trapped in the combustion chamber reduced.

Training is proposed this also includes the closing angle of a cylinder, which used to be has to do a compression work, adjusted more late is called the closing angle of a Cylinder, which later has to do a compression work. This means that the late adjustment the closing angle of the intake valves with high-revving internal combustion engine successively is reduced. This makes a particularly favorable starting characteristic and a rapid cranking of the engine crankshaft allows.

A further development of the internal combustion engine according to the invention provides that they have intake valves with a variable closing angle has, the closing angle at least to start late except for approximately 80 ° to 100 ° NUT, preferably around 90 ° NUT, can be adjusted.

drawing

The following are particularly preferred exemplary embodiments of the present invention with reference to the accompanying Drawing explained in detail. The drawing shows:

1 a schematic representation of a diesel internal combustion engine for driving a motor vehicle;

2 a flowchart of a method for direct start of the internal combustion engine of 1 ;

3 a diagram in which an air charge and gas spring torques over a closing angle of an intake valve of the internal combustion engine of 1 are applied;

4 a flowchart similar 2 a method for the direct start of a gasoline engine; and

5 a diagram in which a late adjustment of a closing angle of intake valves of another alternative embodiment of an internal combustion engine is plotted against the number of revolutions of a crankshaft after starting.

description of the embodiments

An internal combustion engine carries in 1 overall the reference symbol 10 , It is used to drive a motor vehicle, which in 1 is not shown.

The internal combustion engine 10 in the present exemplary embodiment comprises a total of four cylinders, of which in 1 however only one with the reference symbol 12 is shown. It includes a combustion chamber 14 , the air from an inlet duct 16 via an inlet valve 18 is fed. The combustion exhaust gases are via an exhaust valve 20 an exhaust duct 22 fed. Fuel gets into the combustion chamber 14 via an injector 24 , An ignition device 26 can one in the combustion chamber 14 Ignite the existing fuel-air mixture.

The injector 24 is with a valve device 28 connected. Through this, the injection device 24 optionally with a fuel system 30 for liquid fuel or with a fuel system 32 for gaseous fuel. The fuel system 30 for liquid fuel includes a fuel rail 34 , which is also called "Rail". This is where the fuel is stored under very high pressure, and they are also attached to it 1 Valve devices and injection devices (not shown) of the other cylinders of the internal combustion engine 10 connected.

The liquid fuel is from a high pressure fuel pump 36 into the fuel rail 34 promoted, in turn, by an electric fuel pump 38 is fed, which in turn from a fuel tank 40 for liquid fuel 41 promotes. In the present exemplary embodiment of an internal combustion engine 10 is in the fuel tank 40 Diesel fuel 41 stored. The fuel system 30 for liquid fuel includes a pressure line 42 which between the valve device 28 and a storage container 44 is arranged for the gaseous fuel. In the storage container 44 is natural gas in the present exemplary embodiment 45 saved.

When operating the internal combustion engine 10 becomes a crankshaft 46 set in rotation. Their position is determined by a rotation angle sensor 48 detected. The temperature of a cylinder head (not shown) of the internal combustion engine 10 is from a temperature sensor 50 detected. Both sensors 48 and 50 deliver signals to a control and regulating device 52 , On an electronic store 54 of the control and regulating device 52 A computer program is stored, which according to a method for operating and in particular for starting the internal combustion engine 10 is programmed. Such a method for starting the internal combustion engine 10 will now be described with reference to the 2 and 3 explained in detail:
After a starting block 56 is in a block 58 detects whether starting the engine 10 is requested by a user of the motor vehicle. The answer is in block 58 "yes" are in one block 60 based on the signals from the rotation angle sensor 48 those two cylinders C1 and C2 are determined, which after the crankshaft has started to rotate 46 be the first to perform a compression stroke. In the present exemplary embodiment, it is assumed that the in 1 cylinder shown 12 is the cylinder C1 which will be the first to perform a compression stroke after a start.

In one block 62 becomes one in 1 Device not shown controlled so that the closing angle of the two intake valves of the cylinders C1 and C2, that is also the intake valve 18 of the cylinder 12 , at 90 ° NUT (after bottom dead center) of this cylinder 12 assigned piston (in 1 not shown).

How out 3 can be seen, the air charge in the combustion chamber is at such a closing angle 14 still 60% of the maximum possible air filling, that when compressing the in the combustion chamber 14 trapped air generated and the rotation of the crankshaft 46 counteracting gas spring torque is only about two thirds of the maximum gas spring torque. The corresponding gas spring energy is even less than half the maximum gas spring energy with a closing angle of the inlet valve 18 of 50 ° NUT and thus corresponds to the gas spring energy customary in gasoline internal combustion engines. By this measure the crankshaft starts rotating 46 compression work to be performed is significantly reduced.

In the block 62 it is also stipulated that this late adjustment of the closing angle of the intake valves, including the intake valve 18 , only during the first crank revolution of the crankshaft 46 , so only during the first two compression cycles of the internal combustion engine 10 after starting, applies.

In one block 64 it is checked whether the temperature sensor 50 determined temperature TB is less than a limit value TG and whether the speed NKW of the crankshaft 46 is less than a limit value NKW1. The answer is in the block 64 "yes", it means that a cold start of the engine 10 is present. In this case, the block 66 the valve device 28 controlled so that the injectors of the internal combustion engine 10 , including the injector 24 of the cylinder 12 , from the fuel system 32 for gaseous fuel 45 be supplied. Furthermore, the external ignition device 26 activated.

In the block 68 is then in that cylinder of the internal combustion engine 10 , the piston of which is in a position which corresponds to one work cycle, gaseous fuel is introduced, and the gas-air mixture created thereby is released by the ignition device 26 inflamed. As a result, the piston of the corresponding cylinder is moved towards the bottom dead center and the crankshaft 46 set in rotation. Due to the reduced compression work that has to be done during the first crankshaft revolution, the rotational speed of the crankshaft increases 46 comparatively quickly. After the first crankshaft revolution, the late adjustment of the closing angle of the intake valves of cylinders C1 and C2 is canceled.

In the block 64 is the temperature TB of the cylinder head of the internal combustion engine 10 supervised. Only when the temperature TB has at least reached the limit value TG is in the block 70 the valve device 28 set so that the injectors 24 from the fuel system 30 for liquid fuel, i.e. for diesel fuel. At the same time, the ignition device 26 switched off. So this means that the internal combustion engine 10 after a warm-up phase in which it is operated with gaseous fuel, it is switched to normal diesel operation. The corresponding injections of the diesel fuel into the combustion chambers of the internal combustion engine 10 be in the block 72 causes. This in 2 The direct start procedure shown ends in the block 74 ,

In the previous embodiment was the use of gaseous Fuel for made the direct start dependent on the cylinder head temperature TB. However, a direct start is always a must, especially with diesel engines with gaseous To carry fuel.

In 4 A direct start method of an alternative embodiment of an internal combustion engine is shown. Function blocks with an equivalent function have the same reference symbols. The internal combustion engine 10 , in which the in 4 method is used, is different from that in 1 shown internal combustion engine not operated with diesel but with gasoline. This in 4 method shown differs from that in 2 Therefore, the method described in particular in that in block 66 is only switched to gas operation, whereas the ignition device 26 in the block 66 does not have to be activated separately (however, the ignition angle may be adjusted). Furthermore, it goes without saying that even in petrol mode, which is in the block 70 is initiated, corresponding ignitions must take place, according to the block 72 ,

How out 5 can be seen, a closing angle of the intake valves of the internal combustion engine can also be adjusted late over a longer period after the start of the crankshaft rotation. A corresponding dependency of the late adjustment SV of the closing angle of the injection valves on the number N of revolutions of the crankshaft since the start of rotation is off 5 seen. It follows from this that the retardation is gradually reduced while the internal combustion engine is starting up.

Claims (10)

Method for operating a multi-cylinder four-stroke internal combustion engine ( 10 ), in particular for driving a motor vehicle, characterized in that the internal combustion engine ( 10 ) can be started without the help of a starter by having the internal combustion engine at a standstill ( 10 ) Fuel is injected and ignited directly into a combustion chamber (direct start), and that the combustion chamber ( 14 ) instead of liquid fuel ( 41 ) automatically a gaseous fuel ( 45 ) can be fed ( 66 ). A method according to claim 1, characterized in that performing a direct start with liquid Fuel from a current operating parameter, especially one Temperature of the internal combustion engine, preferably a cylinder head temperature (TB) and / or a catalyst temperature. Method according to one of the preceding claims, characterized in that in a diesel internal combustion engine ( 10 ) is applied and that the gaseous fuel ( 45 ) from an ignition device ( 26 ) is ignited ( 68 ). Method according to one of the preceding claims, characterized in that natural gas ( 45 ) or hydrogen gas is used. Method according to one of the preceding claims, characterized in that it is determined which cylinder ( 12 ) be the first to do a compression job at start-up, and that an intake valve closing angle ( 18 ) at least this cylinder ( 12 ) is delayed for a limited period ( 62 ). A method according to claim 5, characterized in that it is determined which cylinder has to perform a second compression work at the start, and that a closing angle of an intake valve of at least this cylinder is adjusted late for a limited period ( 62 ). Method according to one of claims 5 or 6, characterized in that the closing angle is adjusted to approximately 80 ° to 100 ° NUT, preferably to approximately 90 ° NUT ( 62 ). Method according to one of claims 6 or 7, characterized in that that the closing angle of a cylinder, which used to be has to do a compression work, adjusted more late is called the closing angle of a cylinder, which later Compression work. Four-stroke internal combustion engine ( 10 ) with several cylinders ( 12 ) with one combustion chamber each ( 14 ), and each with a combustion chamber ( 14 ) associated fuel injection device ( 24 ) for direct injection of at least liquid fuel ( 41 ), characterized in that it has a valve device ( 28 ), by means of which the fuel injection devices optionally with a fuel system ( 32 ) to supply gaseous fuel ( 45 ) or with a fuel system ( 30 ) for the supply of liquid fuel ( 41 ) can be connected and that they are a control and / or regulating device ( 52 ) which the valve device ( 28 ) for a direct start on a supply of gaseous fuel ( 45 ) can switch. Internal combustion engine ( 10 ) according to claim 9, characterized in that they have inlet valves ( 18 ) with variable closing angle, the closing angle being able to be set at least for starting late to approximately 80 ° to 100 ° NUT, preferably to approximately 90 ° NUT ( 62 ).