Abstract:
In a method for starting an internal combustion engine having at least one cylinder, an inlet and an outlet valve, and having a piston interacting with a crankshaft, and the crankshaft moving in a predetermined rotational direction during normal operation of the internal combustion engine, the piston is located in an initial position, the piston is moved into a defined starting position against a normal rotational direction of the crankshaft by means of a drive, fuel is injected, and the fuel is ignited.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/EP2008/064527 filed Oct. 27, 2008, which designates the United States of America, and claims priority to German Application No. 10 2008 003 540.8 filed Jan. 8, 2008, the contents of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The invention relates to a method of starting an internal combustion engine according to claim  1 , a device for starting an internal combustion engine. 
     BACKGROUND 
     It is known to start an internal combustion engine without the use of a starter by injecting fuel into a cylinder, the piston of which is in a power phase, and by igniting the injected fuel. 
     The igniting of an internal combustion engine without the use of a starter is necessary in particular to set an engine, which is being operated with many stop phases, running again without high electrical energy. For example, in the case of fuel-economy engines, the engines are stopped during stop phases, for example at traffic lights or upon other interruptions to travel, and the internal combustion engine is restarted by actuation, for example of the clutch. 
     From DE 199 55 857 A1 and from DE 100 20 325 A1 corresponding methods of starting an internal combustion engine are known. Here an internal combustion engine, in particular for a motor vehicle, is described, which is provided with pistons that are movable [in] a cylinder and act upon a crankshaft. During operation of the internal combustion engine the piston runs through an induction phase, a compression phase, a power phase and an exhaust phase. A controller is further provided, by means of which fuel is injected in a first operating mode during a compression phase or in a second operating mode during an induction phase directly into a combustion chamber delimited by the cylinder and the piston. The controller is designed in such a way that in order to start the internal combustion engine in the stationary state of the crankshaft fuel is injected into the cylinder, the piston of which is in the compression phase, and ignited so that the crankshaft moves backwards. In this case, it may be disadvantageous that a cylinder can no longer be used for compression and ignition because combustion residues of a not yet exhausted combustion pre-gas are present, with the result that a combustible mixture does not exist. 
     It could moreover be disadvantageous if the engine is stationary for an extended period because then the pressure in the compression cylinder has dropped to such an extent that reliable ignition cannot occur. As with direct starting, the starting capability depends upon the filling volume, the state of the piston and also upon the length of time between stop and start. The pressure in the cylinder to be ignited lasts for a short time only. After a longer pause between stop and start the pressure adjusts itself to the ambient pressure. The residual volume may then have a lower oxygen content. A further drawback is that parasitic residual gases further impair the ignitability. 
     SUMMARY 
     According to various embodiments, an improved method and an improved device for starting an internal combustion engine with a low consumption of electrical energy can be provided. 
     According to an embodiment, in a method of starting an internal combustion engine having at least one cylinder, an inlet- and an exhaust valve and having a piston that interacts with a crankshaft and moves the crankshaft during normal operation of the internal combustion engine in a defined direction of rotation, wherein the piston is situated in a first or initial position, the piston is moved with the aid of a drive counter to the normal direction of rotation of the crankshaft into a defined start position, fuel is injected into the cylinder and the fuel is ignited. 
     According to a further embodiment, upon a cutting-out of the internal combustion engine an ignition provided for the cylinder is not carried out. According to a further embodiment, the first or initial position may lie in the power stroke of the piston, and the piston may be moved back in the direction of the top dead centre. According to a further embodiment, the piston is not moved back over the top dead centre. According to a further embodiment, before reaching the start position fuel may be injected into the cylinder and then the fuel may be ignited. According to a further embodiment, fuel can be injected into the first cylinder before reaching the start point and the fuel can be ignited at the start point. According to a further embodiment, the internal combustion engine may comprise at least a second cylinder having a second inlet valve, having a second exhaust valve and having a second piston that interacts with the crankshaft, wherein, as the first piston moves into the start position, the second piston is moved into a third position, during which the inlet valve of the second cylinder is opened. According to a further embodiment, the movement of the first piston upon cutting-out of the internal combustion engine can be braked in movement and may come to a standstill in a defined position. According to a further embodiment, the first piston can be moved into a region after the top dead centre but without opening of the exhaust valve. According to a further embodiment, the first piston can be moved from the first or initial position further in the normal direction of rotation of the crankshaft until the exhaust valve of the first cylinder opens, that the first piston is then moved counter to the normal direction of rotation of the crankshaft into the start position. 
     According to another embodiment, a device for starting an internal combustion engine may comprise a controller and a drive that is connected to a crankshaft of the internal combustion engine, wherein the controller is designed to control the drive in accordance with a method as described above. 
     According to yet another embodiment, a controller can be designed to carry out a method as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       There now follows a detailed description of the invention with reference to the figures. These show in 
         FIG. 1  a diagrammatic representation of an internal combustion having four cylinders, 
         FIG. 2  a diagrammatic representation of one of the cylinders and a controller, 
         FIG. 3  a first program run, 
         FIG. 4  a diagrammatic representation of part of the power strokes of the first and third cylinder, and 
         FIG. 5  a second program run. 
     
    
    
     DETAILED DESCRIPTION 
     An advantage of the method according to various embodiments is that the piston of the cylinder to be ignited is moved into a defined start position. For this purpose a drive is provided, which is workingly connected to the piston. 
     In a further form of implementation, upon cutting-out of the internal combustion engine an ignition provided for the cylinder is not carried out. Thus, no exhaust gases are contained in the cylinder. Furthermore, the oxygen content of the filling of the cylinder is higher than after an ignition. 
     In a further form of implementation the piston is moved from a power stroke back in the direction of the top dead centre. In this case, the piston is preferably not moved back over the top dead centre. This saves current because a high compression energy to a point over the dead centre is not necessary. The lower energy consumption of the starter motor has the added result that a starting-voltage dip as a result of the starter is lower. This allows the electronic equipment in the motor vehicle to be of a simpler design. 
     In a further form of implementation the first piston of the first cylinder is coupled to a second piston of a second cylinder and the first piston is moved back until an inlet valve of the second piston opens and lets ambient air into the second piston. This ensures that the second piston is filled with fresh air, i.e. with air containing unburnt oxygen. 
     In a further form of implementation, after cutting-out of the internal combustion engine the movement of the first piston is braked and hence the first piston is brought to a halt in a desired starting position. In this way the starting position of the first piston may be selected in a defined manner. 
     In a further form of implementation the first piston in the first cylinder is moved back in the direction of the top dead centre, without however opening the exhaust valve of the first cylinder. This ensures that the gas filling in the first cylinder is compressed. 
     In a further form of implementation, upon cutting-out of the internal combustion engine the first piston is braked into a starting position that lies in the power stroke or in the exhaust stroke. 
     In a further form of implementation, the first piston, if it is situated at a standstill in the power stroke, is moved further in the direction of rotation of the engine until the exhaust valve opens. The first piston is then moved counter to the direction of rotation of the engine into the start position. The effect thereby achieved is that the first cylinder is filled with gas through an exhaust channel. 
       FIG. 1  shows in a diagrammatic representation of an internal combustion engine  1  having four cylinders  2 ,  3 ,  4 ,  5 , which are workingly connected to a crankshaft  6 . The crankshaft  6  is connected by a non-illustrated clutch and by a non-illustrated transmission to a non-illustrated drive train, for example of a motor vehicle.  FIG. 1  shows an internal combustion engine that operates according to a four-stroke principle. To control the gas exchange a camshaft rotating at twice the engine speed is used, which is driven by the crankshaft. The camshaft opens the gas exchange valves, which are designed separately to push out the waste gases and take in the fresh gases, counter to the action of the valve springs. Shortly before the bottom dead centre the exhaust valve opens and, given a supercritical pressure ratio, during this preliminary exhaust ca. 50% of the combustion gases leave the combustion chamber. During the exhaust stroke the upward-moving piston ensures an almost complete removal of the combustion gases from the combustion chamber. Shortly before the top dead centre of the piston the inlet valve opens while the exhaust valve is still open. To distinguish it from the ignition TDC, at which combustion occurs, this position of the crankshaft is known as the gas exchange TDC because in this region the otherwise strictly separate intake- and exhaust processes overlap. Shortly before the gas exchange TDC the exhaust valve closes and, while the inlet valve is open, the downward-moving piston may take in fresh air. This second stroke of the gas exchange, the induction stroke, lasts until shortly after the bottom dead centre. During the following upward movement of the piston a compression process is carried out. Then, at the ignition TDC the igniting of the injected fuel occurs. During the following power stroke the combustion occurs and the piston is moved back down. Instead of a camshaft, an electric drive may be provided for opening and closing the inlet- and exhaust valves. A piston therefore executes the induction stroke, the compression stroke, the power stroke and the exhaust stroke, i.e. 4 strokes. In the case of a four-cylinder engine, for example the first and second cylinder are in phase and the third and fourth cylinder are out of phase by one stroke. 
     In  FIG. 1  a controller  7  and a drive  8 , in particular an electric motor and/or a motor/generator unit are further provided. The drive  8  is connected to the crankshaft  6 . The four cylinders  2 ,  3 ,  4 ,  5  are substantially identical in construction and are now described with reference to the first cylinder  2 . 
       FIG. 2  shows the first cylinder  2  having a first piston  9 , which is connected by a connecting rod  10  to the crankshaft  6 . On the first cylinder  2  an inlet valve  11  and an exhaust valve  12  are provided. The inlet valve  11  and the exhaust valve  12  are actuated by a non-illustrated camshaft. The inlet valve  11  is disposed in an intake channel, through which fresh air is sucked into the first cylinder  2 . The exhaust valve  12  is disposed in an exhaust channel, through which burnt exhaust gases may be discharged into the exhaust channel  14 . An ignition device  15  is further provided, which projects into the first cylinder  2  and by means of which a fuel-air mixture may be ignited. An injection valve  16  is moreover provided, which injects fuel into the first cylinder  2 . 
     Further represented is the drive  8 , which is connected to the controller  7 . By means of the drive  8  the position of the pistons may be adjusted via the crankshaft. The controller  7  is connected to a plurality of sensors  17 , which acquire various operating parameters of the internal combustion engine and/or of the motor vehicle, in particular a crankshaft angle of the crankshaft  6 . In the data/program memory  18  values and programs are filed, which the controller  7  uses to control the internal combustion engine  1 . For example, in the data/program memory  18  values, at which the inlet- and/or exhaust valve  11 ,  12  are opened and/or closed, are filed. Further filed in the data/program memory  18  are data that determine the instant, at which an ignition by means of the ignition device  15  occurs in the cylinder. The controller  7  is moreover connected to a start/stop switch  19 . The start/stop switch  19  is used to communicate to the controller  7  whether the internal combustion engine is to be started or cut out. The start/stop switch may be designed in the form of an ignition switch or an on/off switch. 
       FIG. 3  shows a form of implementation for carrying out a method of starting an internal combustion engine  1 . In this case, the internal combustion engine  1  in a first program point  100  is in a stationary state, i.e. no injection and no ignition is being carried out and the pistons of the cylinders are not moving. Then, in program point  110  the information that the internal combustion engine  1  is to be started is passed to the controller  7 . This may be realized for example by means of the start/stop switch  19  or by actuation of another switch, for example by detection of the actuation of the clutch pedal. The controller  7 , which acquires the position of the individual pistons of the cylinders by means of the sensors  17 , selects the cylinder that is situated in the power stroke. This is carried out in program point  120 . 
     In the following program point  130  the controller  7  controls the drive  8  in such a way that the selected cylinder is moved counter to the direction of motion during normal operation of the internal combustion engine back in the direction of the top dead centre. In this case, the gas in the first cylinder  2  is compressed. 
     This situation is represented in  FIG. 4 . In the inoperative state of the internal combustion engine the first cylinder is situated in a first position P 1  shortly before opening of the exhaust valve. The first piston is then moved by the drive  8  back in the direction of a second position P 2  until shortly before the top dead centre. Assuming that the internal combustion engine  1  has a plurality of cylinders, in particular four cylinders  2 ,  3 ,  4 ,  5 , then for example the third cylinder is situated in the compression stroke in a third position P 3  in the inoperative state of the internal combustion engine. As the first piston is moved back into the second position P 2 , a third piston of the third cylinder is moved back in the fourth position P 4 . In the fourth position P 4  the inlet valve of the third cylinder is open, so that fresh air may flow into the third cylinder. Through the use of the drive  8  the instant and the position of the pistons during backward motion may be selected freely within specific limits. For example, the first piston of the first cylinder is reversed in the direction of the top dead centre but not beyond the top dead centre. In the second position P 2  of the first piston, in a program point  140  fuel is injected into the first cylinder and then the fuel is ignited by means of the ignition device  15 . 
     As a result of the combustion in the first cylinder  1  and the kinetic energy thus produced, the first piston is moved in the normal direction of motion of the internal combustion engine, wherein the air in the third cylinder is compressed. Upon reaching an optimum instant in the region of the top dead centre, in a following program point  150  fuel is injected into the third cylinder and the fuel-gas mixture is ignited. In this way it is possible for the third cylinder, directly after the first cylinder, also to execute a full power stroke. By means of these two power strokes it is possible to start the engine, without starting of the internal combustion engine with the aid of a starter being required. Compared to a starter the drive  8  may be of a markedly weaker design, as the drive has to reverse a piston of a cylinder only in the direction of the top dead centre, without having to compress air with the piston beyond the top dead centre. Thus, no compression over the top dead centre is required, nor is there any need to have to reach a minimum engine speed or carry out a plurality of ignition attempts. The drive  8  may therefore be of a markedly lighter and more economical construction than a normal starter-generator. 
     The first point P 1  is situated for example at a crankshaft angle of 1° to 10° before opening of the exhaust valve. The second position P 2  is situated for example at a crankshaft angle of 1° to 10° after the top dead centre for the ignition. 
       FIG. 5  shows a further variant of a program run for carrying out a method of starting an internal combustion engine. In this case, the internal combustion engine in a program point  200  is operating normally, i.e. fuel is being injected into the cylinders and ignited. In a following program point  210  the controller  7  receives the information that the internal combustion engine  1  is to be cut out. The controller  7 , which acquires the positions of the individual pistons of the cylinders, selects a suitable piston. For this purpose the controller  7  uses the information of a crankshaft sensor and the information of a camshaft sensor for the corresponding pistons. This is carried out in program point  220 . In a following program point  230  the controller  7  for example with the aid of the drive  8  brakes the selected piston, in the present example the first piston  9  of the first cylinder  2 , in such a way that the first piston  9  after the top dead centre stops in the power stroke, i.e. in the first position P 1 . The first position P 1  is preferably selected in such a way that the first cylinder  2  has as large an air filling as possible, i.e. that the first piston  1  is situated in a position just before opening of the exhaust valve of the first cylinder  2 . In this case, the power stroke is no longer executed, i.e. preferably no more fuel is injected and no ignition occurs. 
     The internal combustion engine then remains in this position until a start request occurs. The start request occurs in program point  240 . Then, in program point  250  the first piston  9  is moved counter to the normal engine running direction from the first position P 1  back in the direction of the top dead centre OT. In this case, both the inlet valve and the exhaust valve of the first cylinder are closed. Before reaching the second position P 2 , which represents the end value of the reversed piston with maximally compressed air, fuel is injected. By means of the further compression stroke a swirling of the air-fuel mixture is achieved. On reaching the second position P 2  the air-fuel mixture is ignited. The second position P 2 , as in the above example, is after the top dead centre OT, since energy to overcome the top dead centre is to be saved. The engine is moreover to start up in the direction of rotation. The fuel is injected for example at a crankshaft angle of 10° before reaching the second position P 2 . 
     Depending on the selected form of implementation, the second position P 2  may be selected in such a way that the inlet valve of a further cylinder, in the present example the third cylinder, is opened and the third cylinder is supplied with fresh air. Depending on the selected form of implementation, the braking of the internal combustion engine may be carried out with the aid of a starter-generator for energy recovery, for example to recover electrical energy. 
     In a further form of implementation, during starting the piston of the selected cylinder that is ignited first is moved further by the drive  8  initially in the normal direction of motion until fresh air flows through the exhaust channel  14  into the selected cylinder. Only then is the piston of the selected cylinder moved counter to the direction of rotation of the engine back in the direction of the top dead centre, in the manner described above. As a rule, all of the pistons are connected to the crankshaft, so that all of the pistons are simultaneously moved. 
     In a further form of implementation, moreover, the piston of the selected cylinder during braking is braked in such a way that the exhaust valve of the selected cylinder is already open. Furthermore, in a further form of implementation the controller  7  may select a cylinder, the exhaust valve of which shortly after the power stroke is just open. 
     In a further form of implementation, an eddy-current brake  20  is used to brake the engine in order to recover electrical energy, which is fed into a battery.