Abstract:
A method of controlling the startup of an engine using a sensor having a reference index, commanding the rotation of the crankshaft, detecting the rotation of the crankshaft, selecting a group of cylinders for which the reference index is detected less than a half-turn of the crankshaft before the piston reaches the top dead center, before the inlet valves of the selected group of cylinders closes, commanding the injectors of the selected group of cylinders, detecting the reference index, and commanding the ignition element.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a method of controlling the start-up of an indirect injection internal combustion engine. 
   The invention is more particularly intended for vehicles fitted with such an engine and will be described more precisely with reference to this application. 
   When the engine is stopped, the position of the engine and more precisely of the crankshaft is not generally known, at least with accuracy. It is however necessary to know this position in order to make the engine function correctly. In order to know this position, various methods have already been proposed, essentially consisting in rotating the crankshaft, injecting fuel at various times, reading various parameters by means of sensors and deducing the position of the engine from them. 
   SUMMARY OF THE INVENTION 
   The invention aims to reduce the time necessary to know the position of the engine and to make the engine function in a satisfactory manner, without generating pollution. 
   In order to do this, according to the invention, the following steps are carried out:
         an engine is used comprising:
           a plurality of cylinders in each of which a piston slides between a bottom dead center and a top dead center,   a crankshaft whose rotational movement is linked with the sliding of the pistons,   inlet valves and exhaust valves moving between an open position and a closed position, each of the inlet valves and exhaust valves being associated with a cylinder,   inlet manifolds each associated with a cylinder with which they are connected by the intermediary of an inlet valve associated with said cylinder, and   injectors each associated with a cylinder for injecting fuel into the inlet manifold associated with said cylinder,   ignition means each associated with a cylinder for igniting the fuel contained in said cylinder,   
           there is used a sensor comprising a fixed part and a target linked with the crankshaft, said target comprising a reference index detectable by the fixed part,   a group of cylinders is selected for each of which cylinders the reference index is detected less than a half-turn of the crankshaft before the piston associated with it reaches the top dead center,   the rotation of the crankshaft is commanded starting from a starting position of the engine,   the rotation of the crankshaft is detected,   before at least one of the inlet valves associated with the cylinders of the selected group of cylinders changes from the open position to the closed position, the injectors associated with the cylinders of the selected group of cylinders are commanded such that they inject fuel into the inlet manifolds associated with the cylinders of the selected group of cylinders,   the reference index is detected,   the ignition means associated with the cylinders of the selected group of cylinders are commanded at a time determined as a function of the detection of the reference index and substantially corresponding to the arrival at the top dead center of the pistons associated with the cylinders of the selected group of cylinders.       

   Thus, fuel is injected into the cylinders of the selected group before the inlet valves close for the first time. Consequently, the fuel is injected into the cylinders as early as possible. By injecting fuel only into these cylinders, knowledge of the position of the crankshaft is assured (possibly with an uncertainty of one turn of the crankshaft in the operating cycle), before having to ignite that fuel and consequently the obtaining of satisfactory combustion is ensured. The start-up time of the engine is therefore reduced without increasing pollution. 
   It is known by construction which are the cylinders for which the reference index is detected less than one half-turn of the crankshaft before the piston associated with it arrives at the top dead center. Consequently, the selected group of cylinders in which the first injection of fuel will be carried out will generally always be the same throughout the life of the engine. 
   According to one feature of the invention, advantageously in the case where an engine comprising four cylinders is used, commanding the injectors associated with the selected group of cylinders is stopped before the crankshaft has turned through 75 degrees with respect to the starting position of the engine. 
   It is known that the engine stops substantially in the middle, between two consecutive top dead centers, that a top dead center is reached every 180 degrees of rotation of the crankshaft in an engine with four cylinders and that for each of the cylinders the closing of the inlet valve occurs a little less than 180 degrees before the top dead center. Consequently, taking account of the uncertainty of the stopped position of the engine, the fuel injection is thus stopped before the inlet valve which was open in the starting position is closed again. 
   According to another feature of the invention, the target of the sensor is provided with a plurality of marks detectable by the fixed part and the rotation of the engine is detected by the detection of a certain number of marks consecutively. 
   In this way it is detected that the rotation of the engine is effective, unlike a sensor placed on the starter control button, and there is also assurance that it is not simply a jolt of the engine. 
   According to a complementary feature of the invention, the target of the sensor is provided with at least thirty marks detectable by the fixed part and the rotation of the engine is detected by the detection of 3 to 10 marks consecutively. 
   Thirty marks constitutes a minimum for detecting the rotation of the crankshaft sufficiently quickly. The detection of at least three marks is necessary to be sure that the rotation of the engine is destined to make it start up. Above ten marks, there is no longer any doubt in this matter. 
   According to another feature of the invention, the command for the injection of fuel into the inlet manifolds associated with the cylinders of the selected group of cylinders is stopped before at least one of the inlet valves associated with the cylinders of the selected group of cylinders changes from the closed position to the open position. 
   It is known that, for each of the cylinders, the exhaust valve is closed shortly after the opening of the inlet valve. Thus, fuel is prevented from being injected by an injector associated with a cylinder whose exhaust and inlet valves are both open. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will appear even more clearly in the following description, given with reference to the appended drawings in which: 
       FIG. 1  is a diagrammatic representation of a device for implementing the method according to the invention, 
       FIGS. 2A ,  2 B,  2 C and  2 D represent a method according to the invention starting from four different starting points; and 
       FIG. 3  illustrates a group of cylinders. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a device  1  essentially comprising an engine  28 , a sensor  2  and a control unit  22 . 
   The engine  28  here comprises four cylinders  12  (only one of which has been shown). For each of the cylinders  12 , the engine comprises a piston  14 , an inlet valve  16 , an exhaust valve  18 , an inlet manifold  20 , an exhaust manifold  38 , a sparking plug  24 , an injector  26  and a combustion chamber  40 . 
   Each piston  14  slides between a bottom dead center  30  and a top dead center  32 , each shown in dotted line in the cylinder  12  to which it corresponds. 
   Each exhaust valve  18  moves between a closed position and an open position. In the closed position, the exhaust valve is bearing on its seat  36  and prevents any connection between the combustion chamber  40  and the exhaust manifold  38 . On the other hand, when it is in the open position, the exhaust valve  18  is separated from its seat  36  and the combustion chamber  40  is then connected with the exhaust manifold  38 . 
   Similarly, each inlet valve  16  moves between a closed position and an open position. In the closed position, the inlet valve is bearing on its seat  34  and prevents any connection between the combustion chamber  40  and the inlet manifold  20 . On the other hand, when it is in the open position, the inlet valve  16  is separated from its seat  34  and the inlet manifold  20  is then connected with the combustion chamber  40 . 
   Each one of the sparking plugs  24  is placed in the combustion chamber  40  of the corresponding cylinder and each injector  26  is placed in the inlet manifold  20  of the corresponding cylinder. The engine is thus of the “indirect” injection type because the injection does not take place directly into the combustion chamber. The sparking plugs  24  and the injectors  26  are controlled by the control unit  22 . 
   The sensor  2  comprises a target  6  having 60 regularly distributed teeth  8  integral with the crankshaft and a fixed part  4  detecting the teeth  8  of the target  6 . The teeth  8  constitute marks disposed every 6 degrees and separated by indentations. The target  6  more precisely comprises 58 teeth; two consecutive teeth have in fact been eliminated in order to constitute a reference index  10  making it possible to know the position of the crankshaft. 
   The fixed part  4  of the sensor  2  is connected to the control unit  22  which counts the number of teeth  8  detected by the sensor  2 . 
     FIGS. 2A ,  2 B,  2 C and  2 D illustrate the teeth  8  detected by the sensor  2  during the rotation of the engine, above which is indicated the number of teeth  8  counted by the control unit  22 . In these figures there is also marked, by a thick continuous line, for one of the cylinders  12 , the period during which the injectors  26  are injecting fuel into the inlet manifold  20 , the period during which the exhaust valve  18  is open and the period during which the inlet valve  16  is open and, by lightning flash, the time when the sparking plug  24  is energized. 
   As the engine has four cylinders, it substantially comprises four starting positions P 1 , P 2 , P 3  and P 4 , each one positioned in the middle between a bottom dead center and the following top dead center, and vice-versa. These starting positions are those in which the engine naturally has a tendency to stop. There is an uncertainty of a few teeth about these starting positions. 
   Starting from the staring position P 1 , the engine is driven in rotation by a starter (not shown). After the detection of five teeth  8  consecutively, in other words within a relatively short time such as 100 milliseconds, the control unit  22  considers that the engine is rotating for the purpose of its start-up. The engine control unit  22  therefore commands the injector  26  corresponding to the cylinder  12  considered in  FIG. 2A . The sensor  2  detects six teeth  8  between the start  26   a  and the end  26   b  of fuel injection. 
   The fuel injection stops after a rotation of 66 degrees of the crankshaft starting from the starting position P 1  and generally before the opening  16   a  of the inlet valve  16 , despite the uncertainty of the starting position. In this case, the opening  16   a  of the inlet valve  16  takes place after the detection by the sensor  2  of two other teeth  8 , that is to say 78 degrees starting from the starting position P 1 . After that the fuel injected into the inlet manifold  20  enters into the combustion chamber  40 . 
   The piston  14  reaches the top dead center  32  after rotation of the crankshaft by two other teeth  8 , that is to say 12 degrees. Then, after rotation of the crankshaft by another two teeth  8 , the closing  18   b  of the exhaust valve  18  takes place. 
   No reference index  10  having yet been detected, the position of the crankshaft is not yet known by the control unit  22 . 
   The crankshaft continues to rotate, the piston  14  reaches the bottom dead center  30  and then, after detection of three teeth  8 , the reference index  10  is detected by the sensor  2 . The engine control unit  22  then knows the position of the crankshaft and can command the energizing of the sparking plug  24  after the detection of twenty four teeth  8  by the sensor  2 , Meanwhile (three teeth  8  after the arrival of the piston  14  at the bottom dead center  30 ), the closing  16   b  of the inlet valve  16  takes place. 
   The combustion of the fuel in the combustion chamber  40  therefore starts one tooth  8  (6 degrees) before the arrival of the piston  32  at the top dead center  32  and about 1¼ turn of the crankshaft after the starting position P 1 . 
     FIG. 2B  illustrates the start-up of the engine starting from the starting position P 2 , offset by one half-turn of the crankshaft with respect to the starting position P 1 . 
   As described above, starting from the starting position P 2 , the engine is driven in rotation by a starter. After the detection of five teeth  8 , the engine control unit  22  commands the injector  26  corresponding to the cylinder  12  considered in  FIGS. 2A ,  2 B,  2 C and  2 D. 
   The injection  26  of fuel into the inlet manifold  20  takes place whilst the crankshaft is rotating by six teeth  8 . 
   In this case, the injection  26  of fuel occurs entirely whilst the exhaust valve  18  is closed and the inlet valve  16  is open. The injected fuel therefore enters directly into the combustion chamber  40 . 
   Shortly after (about four teeth  8 , that is to say 24 degrees of rotation of the crankshaft) the end  26   b  of fuel injection  26 , the piston  14  reaches the bottom dead center  30 . Then, as mentioned before, the reference index  10  is detected, the inlet valve  16  is closed and then the control unit  22  commands the sparking plug  24 . 
   The energizing of the sparking plug  24  and the combustion of the fuel in the combustion chamber  40  which follows therefore takes place substantially three quarters of a turn after the starting position P 2 . 
     FIG. 2C  illustrates the start-up of the engine starting from the starting position P 3 , offset by one turn of the crankshaft with respect to the starting position P 1 . 
   After the detection of five teeth  8 , starting from the starting position P 3 , the engine control unit  22  commands the injector  26  corresponding to the cylinder  12  considered in  FIGS. 2A ,  2 B,  2 C and  2 D. 
   The injection  26  of fuel into the inlet manifold  20  takes place whilst the crankshaft is rotating by six teeth  8 . 
   In this case, the injection  26  of fuel takes place entirely whilst the exhaust valve  18  and the inlet valve  16  are closed. 
   Then, the piston  14  reaches the top dead center  32 , the opening  18   a  of the exhaust valve  18  occurs, the piston  14  reaches the bottom dead center  30 , the reference index  10  is detected, the opening  16   a  of the inlet valve  16  occurs and the fuel enters the combustion chamber  40 , the piston  14  teaches the top dead center  32 , the closing  18   b  of the exhaust valve  18  takes place, the piston reaches the bottom dead center  30 , the reference index  10  is detected a second time (after detection of fifty eight teeth  8 ), the closing  16   b  of the inlet valve  16  takes place and finally the energizing of the sparking plug  24  is commanded by the control unit  22 . 
   The combustion of the fuel in the combustion chamber  40  therefore takes place substantially 2¼ turns of the crankshaft after the starting position P 3 . 
     FIG. 2D  illustrates the start-up of the engine starting from the starting position P 4 , offset by one turn of the crankshaft with respect to the starting position P 2 . 
   After detection of five teeth  8 , starting from the starting point P 4 , the engine control unit  22  commands the injector  26  corresponding to the cylinder  12  considered in  FIGS. 2A ,  2 B,  2 C and  2 D. 
   The injection  26  of fuel takes place entirely whilst the inlet valve  16  is closed and the combustion of the fuel in the combustion chamber  40  occurs substantially 1¾ turns of the crankshaft after the starting position P 4 . 
   In order to start-up the engine faster, before the first combustion, it is possible to inject fuel simultaneously for all of the cylinders for which the reference index  10  is detected less than one half-turn of the crankshaft before the position  14  associated with it reaches the top dead center  32 , in other words, in half of the cylinders. 
   In the present case, the fuel is injected simultaneously into another cylinder, which is offset by one turn of the crankshaft with respect to the cylinder considered in  FIGS. 2A ,  2 B,  2 C and  2 D. 
   Thus, less than a quarter of a turn of the crankshaft after the starting position, fuel is injected simultaneously into the inlet manifold of a cylinder whose starting position is the position P 1  and into the inlet manifold of a cylinder whose starting position is the position P 3 , or into the inlet manifold of a cylinder whose starting position is the position P 2  and into the inlet manifold of a cylinder whose starting position is the position P 4 . The fuel injections into the inlet manifolds of the other two cylinders can be offset by one half-turn of the crankshaft in order to ensure combustion in each engine cycle. 
   The first combustion therefore takes place either three quarters of a turn of the crankshaft after the starting position, that is to say 1¼ turns of the crankshaft after the starting position. 
   The invention is of course in no way limited to the embodiment which has just been described as a non-limiting example. Thus, other means could be provided for detecting the rotation of the engine, for example by analysing the magnitude of the current flowing through the starter.