Abstract:
A device ( 1 ) for determining the position of an internal combustion engine, includes an incremental-type sensor ( 2 ) having a rotary part ( 8 ) which is connected to the rotary body, and a fixed part ( 6 ) which is provided with first elements for detecting the rotation of an increment between the mobile part ( 8 ) and the fixed part ( 6 ), second elements for detecting the direction of rotation between the mobile part ( 8 ) and the fixed part ( 6 ), and analysis elements which are connected to the first elements and the second elements and are used to determine the angular position of the rotary body in relation to the reference position. The device also includes engine controlling elements ( 4 ) which are connected to the analysis elements ( 12 ) of the sensor ( 2 ), and the sensor ( 2 ) is permanently electrically ( 34 ) fed in the device.

Description:
FIELD OF THE INVENTION 
   The invention relates to a device for determining the position of an internal combustion engine comprising a rotary member. 
   More precisely, the invention aims to improve the starting of multi-cylinder internal combustion engines in order to reduce the starting time of such engines, and even allow the engine to be started directly without a starter, as a result of better knowledge of the position of each piston in order to select the cylinders to be supplied with fuel. 
   DESCRIPTION OF THE RELATED ART 
   In multi-cylinder internal combustion engines whose injection and ignition are regulated electronically, engine control means calculate the amount of fuel to be injected, the time at which it must be injected into each cylinder, and the time at which ignition must be effected. In order to do this, the position of the engine must be determined accurately. 
   EP-A-0 017 933 describes a device comprising incremental-type contactless sensors which are mounted on a crankshaft and on a camshaft of an internal combustion engine. The sensors each comprise a plate whose surface exhibits regularly disposed marks (offset angularly by an increment) and reference marks. Probes detect the passage of the successive marks relating to a rotation of the crankshaft and of the camshaft by one increment, and the passage of the reference marks. However, after the engine has been switched off, the position of the engine is no longer known, so that it is necessary to carry out a synchronisation procedure which comprises at least one rotation of the engine crankshaft. 
   Moreover, devices are known which comprise a contactless sensor of the absolute type. Such a device allows the position of the rotary member to be known at any time every 360°, without the need to run the engine, in so far as the signals emitted by the probes are a direct function of the position of the engine. DE-A-197 22 016 describes a device which comprises a sensor of that type comprising a Hall-effect probe and a probe of the magneto-resistive type which are arranged at the end of the camshaft and are subjected to a magnetic field which rotates with the camshaft. 
   However, a device of that type does not allow the position of the crankshaft to be known accurately in so far as on the one hand there is a degree of a play in the mechanism connecting the camshaft and the crankshaft and on the other hand the camshaft and the crankshaft can be offset angularly relative to one another in the case of engines equipped with a device for varying the opening time and amplitude of the valves. 
   SUMMARY OF THE INVENTION 
   The object of the invention is, therefore, to propose a device which is of moderate cost and solves the above-mentioned problems and which, in particular, allows the position of the crankshaft to be known accurately at any time, including after prolonged stoppage of the engine. To that end, according to the invention, the device comprises:
         an incremental-type sensor comprising a rotary part connected to the rotary member and a fixed part comprising:
           first means for detecting a reference position of the rotary member and detecting the relative rotation of the movable part and the fixed part by an increment, said first means generating a first signal,   second means for detecting the relative direction of rotation of the movable part and the fixed part, generating a second signal,   analysis means connected to the first means and to the second means, for determining the angular position of the rotary member relative to the reference position, on the basis of the first signal and the second signal, and generating a third signal as a function of said angular position of the rotary member,   
           engine control means connected to the analysis means of the sensor, said engine control means having a rest state in which they are not supplied with power and a live operating state during which they generate actions on operating members of the engine, such as fuel injectors or spark plugs, as a function of the third signal, in which device the sensor is supplied with power permanently, including when the control means are in the rest state.       

   An incremental-type device can more easily be fitted to the crankshaft than a device of the absolute type, which can only be positioned at the end of the crankshaft. By keeping the analysis means of the sensor supplied with power independently of the engine control means, the change in the position of the engine continues to be followed permanently, including when the fuel supply to the engine has been stopped, without consuming excessive amounts of electrical energy. 
   In order to reduce still further the consumption of electrical energy between two operating periods of the engine, in accordance with an advantageous feature of the invention the sensor has:
         an economic operating mode which comprises, in succession and at regular intervals, a phase of activity during which the first means and the second means are supplied with power, and a phase of inactivity during which the first means and the second means are not supplied with power, and   a normal operating mode, during which the first means and the second means are supplied with power continuously.       

   The rotation of the engine is supposed to be reduced when the sensor is in economic operating mode as compared with when the sensor is in normal operating mode, the engine control means additionally advantageously not being supplied with power when the sensor is in economic operating mode. The first means and the second means can consequently operate intermittently in order to consume less electricity, but without missing any displacement of the engine. 
   Preferably, when the sensor is in economic operating mode, he duration of the phases of inactivity is at least 10 times longer than the duration of the phases of activity, and the duration of a phase of activity added to that of a consecutive phase of inactivity is less than 1 second. 
   Advantageously, the analysis means do not generate the third signal until they have received a fourth signal emitted by the engine control means. 
   In that manner, the work of the analysis means and their power consumption are reduced to a minimum. 
   In addition, the analysis means transmit to the engine control means a signal corresponding to the first signal. 
   In that manner, the engine control means are able to know the displacement of the engine relative to the position transmitted by the third signal and thus deduce therefrom the position of the engine in real time. 
   According to an advantageous embodiment in accordance with the invention, the device has the following features:
         the first signal comprises at least two levels,   the sensor further comprises a counter which is increased or decreased by an increment at each change in level of the first signal according to the direction of rotation detected by the second means, and   the counter is reset to zero after detection by the first means of the reference position of the rotary member.       

   That solution is simple, reliable and inexpensive. 
   Advantageously, in addition,
         the internal combustion engine comprises a crankshaft,   the rotary member is constituted by the crankshaft of the engine,   the counter is reset to zero only one time out of two after detection by the first means of the reference position of the rotary member.       

   Accordingly, the position of the crankshaft is known every 720°, and consequently the position of the engine is known perfectly. 
   According to an alternative that is likewise in accordance with the invention, although less advantageous a priori, the device has the following features:
         the internal combustion engine comprises a crankshaft and a camshaft,   the rotary member is constituted by the crankshaft of the engine,   the device further comprises an angular position sensor which is located on the camshaft and generates a binary signal.       

   Accordingly, by combining the position of the crankshaft every 360° as determined by the incremental-type sensor and the binary signal generated by the angular position sensor mounted on the camshaft, the position of the engine can be known every 720° of the crankshaft. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention will become more apparent from the following description, which makes reference to the accompanying drawings, in which: 
       FIG. 1  is a diagrammatic representation of a device according to the invention, comprising especially a sensor and an engine control unit, 
       FIG. 2  is a detailed view of the fixed part of the sensor belonging to the device shown in  FIG. 1 , 
       FIG. 3  shows the current consumption of the sensor, 
       FIG. 4  shows signals transmitted by the sensor to the engine control unit, 
       FIG. 5  shows a variant of the device of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a device  1  which essentially comprises a sensor  2  and an engine control unit  4 . The sensor  2  is connected to the engine control unit  4  by a single wire  48 . The engine control unit  4  is connected to operating members of the engine, such as the spark plugs  50  and the injectors  52 . 
   The sensor  2  comprises a rotary part  8 , which is integral with an engine crankshaft, and a fixed part  6  which is to detect displacements of the rotary part  8  and is shown in greater detail in  FIG. 2 . The rotary part is constituted by a plate  8  formed by a succession of 60 teeth and 60 spaces distributed uniformly, so that the teeth (and the spaces) are arranged on the periphery of the plate every 6 degrees, which corresponds to one displacement increment of the crankshaft. Two teeth have in fact been removed from the plate  8  in order to mark a reference position  24  of the crankshaft. 
   The fixed part  6  comprises an assembly  10  for detecting the displacement of the rotary part  8 , an analysis unit  12  and a memory  14 . The analysis unit  12  combines analogue signal processing means, a microprocessor, an analysis programme, an internal counter and a clock. 
   The assembly  10  for detecting the displacement of the rotary part  8  comprises a magnet  16 , three probes  18 ,  20 ,  22  and a signal processing circuit  26 . The magnet  16  generates a magnetic field, which is modified by the presence of the teeth of the plate  8 , so that the voltage detected by the probes  18 ,  20 ,  22 , which are here of the Hall-effect type, is a function of the presence or absence of a tooth opposite the probe. The probes  18  and  20  are offset by a distance less than the width of one tooth. The voltages emitted by the probes  18  and  20  are input into a first part of the signal processing circuit  26 , which transmits to the analysis unit  12  a first signal  28  which has a first value when the probes  18 ,  20  are opposite a tooth and a second value when the probes  18 ,  20  are opposite a space. 
   The analogue signal processing means, the microprocessor and the analysis programme of the analysis unit  12  process the signal  28  and detect the passage of the signal  28  from the first value to the second value, which corresponds to a rotation of the crankshaft by one increment. Furthermore, processing of the first signal  28  by the analysis unit  12  allows the reference position  24  to be detected. 
   The probe  22  is offset relative to the probe  20  by a distance less than the width of one tooth. The voltages emitted by the probes  20  and  22  are input into a second part of the signal processing circuit  26 , which transmits to the analysis unit  12  a second signal  30  which has a first value when the probes  20 ,  22  are opposite a tooth and a second value when the probes  20 ,  22  are opposite a space. The analysis programme and the processor of the analysis unit  12  process the signals  28 ,  30  and determine the direction of rotation of the crankshaft. 
   As a function of the determined direction of rotation, the analysis unit  12  increases or decreases the internal counter by an increment in accordance with the displacement of the crankshaft by an increment. When the internal counter reaches a value that corresponds substantially to two turns of the crankshaft, the internal counter is reset to a given initial value (advantageously zero) when the reference position  24  is detected. In that manner, if an error occurs during counting, it is corrected by the detection of the reference position  24  and does not affect the following counting operation. 
   As shown in  FIG. 1 , the power supply to the engine control unit  4  is cut off when the user of the vehicle on which the device is mounted breaks the contact  32 ; the sensor  2 , on the other hand, is permanently supplied with power from the vehicle battery  34 . More precisely, the analysis unit  12  is permanently supplied with power by the vehicle battery and manages the power supply  36 ,  37  of the assembly  10  for detecting the displacement of the rotary part  8  and of the memory  14 . 
   When the engine is running, the engine control unit  4  is supplied with power, as are the assembly  10  for detecting the displacement of the rotary part  8  and the memory  14 . By contrast, when the engine control unit  4  is no longer being supplied with power, the engine stops and, after a given period of time during which no rotation of the engine is detected on the basis of the signal  28 , the analysis unit  12  stores the value of the internal counter in the memory  14  and then puts the sensor in economic operating mode  38 . 
   As shown in  FIG. 3 , when the sensor  2  is in economic operating mode  38 , the assembly  10  for detecting the displacement of the rotary part  8  is periodically supplied with power for a time t, which here is advantageously approximately 100 μs, and then is not supplied for a time T which here is advantageously approximately 10 ms. If the analysis unit  12  does not detect rotation of the crankshaft on the basis of the first signal  28 , economic operating mode continues. If, on the other hand, a displacement of the crankshaft is detected, the analysis unit  12  puts the sensor  2  in normal operating mode  40 , the assembly  10  for detecting the displacement of the rotary part  8  and the memory  14  then being permanently supplied with power, and the value of the memory  14  is read off, modified as a function of the detected displacement and transmitted to the internal counter. The analysis unit puts the sensor  2  in economic operating mode again after the given period of time during which no rotation of the crankshaft is detected on the basis of the first signal  28 . 
   When the analysis unit  12  receives a given signal from the engine control unit  4 , advantageously just before the engine is started, the analysis unit  12  transmits to the engine control unit  4 , for a short period of time  42 , the value  46  of the internal counter, which value is here framed by two parity bits. In order to count the 116 positions of the plates (58 teeth over two turns), the counter here comprises 7 bits. 
   During operation  44  of the internal combustion engine, the analysis unit  12  transmits to the engine control unit  4  a rectangular pulse  54  (having two values alternately) which corresponds substantially to the signal  28  or to the signal  30  received from the signal processing circuit  26 , each descending front of the rectangular pulse  54  representing one displacement increment of the crankshaft detected by the assembly  10  for detecting the displacement of the rotary part  8 . The engine control unit  4  accordingly always knows the precise position of the engine before it acts on the operating members of said engine. 
   If the analysis unit  12  detects a break in the power supply, when it receives the given signal from the unit  4 , instead of transmitting the value to the counter it transmits a defined signal to that effect (for example the value  116  or the value  117  in binary) to the engine control unit  4  in order to carry out a prior initialisation procedure. 
   Advantageously, the memory  14  is of the read-only type, so that it does not consume current when the sensor is in economic operating mode. However, it would likewise be possible to provide a memory of the low-consumption read-write type, which would be supplied with power permanently. 
     FIG. 5  shows a device  101 . The device  101  differs from the device  1  shown in  FIGS. 1 to 4  in that it further comprises an angular position sensor  156  having a movable part  158 , which is connected to the camshaft of the engine, and a fixed part  160 , such as a Hall-effect probe, which is arranged opposite the movable part. Because the other elements are unchanged, their reference numerals have been retained. 
   The angular position sensor  156  is connected to the engine control unit  4 . Because the movable part  158  is half-moon shaped, the angular position sensor  156  generates a binary signal  162  which has a first value when the camshaft occupies a position between 0° and 180° and a second value when the camshaft occupies a position between 180° and 360°. 
   In that manner, by combining the position of the crankshaft every 360° as determined by the incremental-type sensor  2  and the binary value  162  generated by the angular position sensor  156  mounted on the camshaft, the engine control unit  4  knows the position of the engine every 720° of the cam-shaft. The internal counter is therefore re-initialised (for example reset to zero) each time the crankshaft passes the reference position.