FR2835285A1 - METHOD FOR STARTING A HEAT ENGINE - Google Patents

Abstract

Method for starting a heat engine comprising a shaft (6) and means (1, 2, 5) for driving it in rotation from the combustion of a flammable mixture in at least one combustion (7) of the engine, the method comprising the steps of putting the engine in a starting configuration, of rotating the shaft of the engine simultaneously with at least one attempt to initiate combustion of the mixture in the chamber to bring the combustion engine from a stopped state to an autonomous operating state, monitoring at least one characteristic of the mixture in the combustion chamber and modifying at least one parameter of the starting configuration to make it correspond to an autonomous operating configuration when the monitored characteristic is representative of at least one combustion actually started.

Description

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 The present invention relates to a method for starting a heat engine such as an internal combustion engine of a motor vehicle.

 A heat engine generally comprises a shaft and means for driving it in rotation from the combustion of a flammable mixture in at least one combustion chamber of the engine.

 In petrol engines conventionally used on motor vehicles, the combustion chamber is delimited by a cylinder, a cylinder head and the front face of a piston mounted to slide in the cylinder and connected via a connecting rod and a crankpin to the shaft. of the engine (or crankshaft). The rotational drive energy of the shaft is provided by the combustion of the previously compressed flammable mixture. The combustion is initiated by a spark provided by a spark plug opening into the cylinder. The combustion of the mixture pushes back the piston, thus initiating the reciprocating movement of the latter which ensures the exhaust of the burnt gases resulting from the combustion of the mixture, the admission of flammable mixture into the cylinder and the compression of the mixture before a spark produces a new explosion maintaining the movement of the shaft (the engine is then in autonomous operation).

 Current starting methods consist in putting the engine in a starting configuration and in rotating the engine shaft simultaneously with at least one attempt to initiate combustion of the mixture in the chamber to bring the heat engine from a stopped state. to an autonomous operating state.

 In the starting configuration, the motor shaft is rotated by means of a starter.

The starter is an electric motor connected to the vehicle battery and actuated directly by the driver of the vehicle who acts on the ignition key or a push button

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 command as long as he considers that the engine does not operate independently. In some cases, the driver operates the starter too briefly to allow the engine to operate independently. The driver must then repeat the operation.

These repeated attempts result in wear of the starter and a significant consumption of the energy supplied by the battery. In other cases, the driver continues to operate the starter while the engine is already operating autonomously. This notably results in overheating of the starter detrimental to its lifespan and unnecessary consumption of the energy supplied by the battery.

 It is known to stop the starter after a predetermined activation time. However, this duration may vary depending on the starting conditions. Thus, a hot start generally requires a shorter starter activation time than that required for a cold start. It is therefore necessary to provide a means of measuring the temperature of the motor to modify the duration of activation as a function thereof. It is also known to stop the starter when the engine is running at a determined speed greater than that of the starter or from the characteristics of the energy consumed by the starter. These methods do not always make it possible to have an optimal duration of actuation of the starter.

 Often, setting in the start-up configuration also includes the step of enriching the mixture with fuel to facilitate ignition of the mixture and produce the first combustions. The amount of unburnt is then important. The start-up mode is therefore very polluting, especially since the catalyst - which equips most modern motor vehicles - has not reached its operating temperature and

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 therefore only performs its function of processing exhaust gases imperfectly.

 An object of the invention is to propose a starting process which is reliable and simple to implement, and which makes it possible to optimize the duration of the starting phase.

 For this purpose, provision is made, according to the invention, for a method of starting a thermal engine comprising the steps of putting the engine in a starting configuration and of rotating the shaft of the engine simultaneously with at least one attempt. initiate combustion of the mixture in the chamber to bring the engine from a stopped state to an autonomous operating state, monitor at least one characteristic of the mixture in the combustion chamber and modify at least one parameter of the configuration starting point to make it correspond to an autonomous operating configuration when the characteristic monitored is representative of at least one combustion actually started.

 Thus, when there is at least one combustion actually started, the engine is capable of operating autonomously. It is then possible to modify the parameter of the starting configuration to correspond to the configuration of autonomous operation, that is to say for example a configuration in which the starter is deactivated and / or in which the enrichment of the mixture and / or the ignition advance under starter is interrupted. The use of a characteristic of the mixture in the combustion chamber makes it possible to have a significant reactivity which allows a rapid passage from the starting configuration to that of autonomous operation as soon as the maintenance of the heat engine in the starting configuration does not is no longer necessary. The duration of the start-up phase is therefore

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 optimized whatever the starting conditions.

 Advantageously, the drive means operating from a series of combustions, the parameter is modified when the monitored characteristic is representative of a predetermined number of combustions actually started and preferably the predetermined number of combustions actually started is order of one to two combustions per cylinder of the heat engine.

 After several combustions, the risk of the engine stalling is low so that the reliability and efficiency of the starting process are increased.

 According to a particular embodiment, the characteristic monitored corresponds to an ionization of at least part of the mixture. Optionally, the engine comprising at least one spark plug having two electrodes opening into the combustion chamber, the monitoring step preferably comprises the phases of applying a potential difference to the electrodes and of detecting a current flowing between the electrodes , and the modification of the parameter includes a phase of comparing an intensity of the detected current with a predetermined threshold.

 During combustion, a flame front consisting of ionizing species (free radicals) propagates in the combustion chamber. It is known to use means for detecting an ionization of the mixture in the combustion chamber in order to verify on the one hand the presence or absence of combustion and to control the heat engine in particular in order to avoid misfire and on the other hand the appearance of rattling for example.

In this embodiment of the invention, these existing means provide an additional function for managing the starting of the heat engine.

 Other features and benefits of

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 the invention will emerge on reading the following description of a particular non-limiting embodiment of the invention.

 Reference will be made to the appended single figure schematically representing in a partial view a heat engine arranged for the implementation of the method according to the invention.

 Referring to the figure, the method according to the invention is intended to start a heat engine, here an internal combustion petrol engine of the 4-stroke type.

 The engine conventionally comprises an engine block delimiting cylinders 1 (only one of which is visible here) in which slide pistons 2 which have a front face 3 opposite a cylinder head 4 closing the cylinders and which are connected to the opposite the front face 3 by a connecting rod 5 to a crankshaft 6 constituting the engine shaft. Each cylinder 1, the front face 3 of each piston 2 and the cylinder head 4 delimit a combustion chamber 7 into which open two electrodes 8, 9 of a spark plug 10 and intake and exhaust ducts to allow intake of a mixture of air and fuel, the ignition of this mixture and the evacuation of the burnt gases resulting from the combustion of the mixture. An engine control module 11 manages the current operation of the engine (and in particular the ignition, the amount of air, fuel or mixture admitted into each cylinder, cooling, etc.). A starter 12, known in itself, is connected to the crankshaft 6 to drive the latter in rotation when the engine is stopped in order to start the engine and start its autonomous operation. The electrical supply of the electrical components of the heat engine is provided by a battery and an alternator not shown. Engine architecture and day-to-day operation

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 these are known in themselves and will not be described here in more detail.

 The engine further comprises means for detecting ionization of the mixture in the combustion chamber 7. These means, known in themselves, comprise an ionization circuit 13 connected to the spark plug 10 and to the engine control module 11 and arranged for, on the one hand, apply a potential difference (a few hundred volts approximately) between the electrodes 8 and 9 so as to polarize them and, on the other hand, detect a so-called ionization current between the electrodes 8 and 9 , the ions present in the mixture during combustion closing the circuit between the electrodes 8, 9 and allowing the passage of this current.

 The engine control module 11 is also connected to a control circuit 14 of the starter 12.

 The driver of the vehicle who wants to start the engine controls the start of the starting process either by actuating the ignition key or by pressing a button provided for this purpose. Starting is then taken over by the engine control module 11.

 The engine control module 11 puts the heat engine in a determined starting configuration to bring the heat engine from a stopped state to an autonomous operating state. To do this, the engine control module 11 notably controls the injection to enrich the mixture, the starter 12 via the control circuit 14 to rotate the engine shaft and simultaneously controls the ignition of the spark plug 10 to ignite combustion of the mixture contained in chamber 7 with a predetermined advance to facilitate ignition of the mixture.

 At the same time, the engine control module 11 monitors the ionization of the mixture in the

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 combustion 7 via the ionization circuit 13. The ionization circuit 13 applies a potential difference between the electrodes 8 and 9, detects the current between the electrodes 8 and 9, amplifies it and sends a signal corresponding to the control module engine 11. The detections are carried out at regular intervals at a sufficient frequency determined to allow the subsequent processing of the signal by the engine control module 11 (for example at each engine cycle of a cylinder).

 The engine control module 11 then processes this signal to calculate the intensity of the current (for example by integrating the signal on a predetermined acquisition window) and compares it to a predetermined threshold. The intensity of the current is representative of the number of ions present in the mixture. These ions being produced during the combustion of the mixture, the intensity of the current is therefore an indicator of combustion. The predetermined threshold is equal to the intensity of the current carried between the electrodes by the ions generated during combustion.

 As long as the current intensity is below this threshold, there is no combustion, or this is not sufficient to start the engine and initiate its autonomous operating cycle. The engine is then kept in the starting configuration.

 When the intensity of the current becomes equal to or greater than this threshold, there is combustion actually started, sufficient to start the engine and start the autonomous operating cycle thereof.

 When, for example, four exceedances of this threshold have been detected corresponding to a combustion in four cylinders ignited successively according to the engine ignition order (or to four combustions in the same cylinder for example in the case of a single-cylinder engine ), the engine control module 11 modifies

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 the parameters concerned by the start-up configuration to make them correspond to an autonomous operating configuration. The engine control module 11 thus controls in particular the injection to deplete the mixture, the ignition to increase the ignition advance and the control circuit 14 of the starter 12 to deactivate the latter.

 Of course, the invention is not limited to the embodiment described but also encompasses the variants coming within the scope of the claims.

 In particular, the invention is not limited to internal combustion petrol engines with reciprocating pistons (whatever the number of cylinders thereof) but is also applicable to rotary piston engines, to diesel engines, to engines external combustion, injection or carburetor engines, continuous combustion engines ...

 The ionization detection means may comprise a dedicated sensor comprising for example two electrodes associated with an ionization circuit (in particular for engines without a spark plug such as diesel engines).

 In addition, parameters of the mixture other than ionization can be used to implement the process of the invention and, in particular, the pressure of the mixture in the combustion chamber, the temperature of the mixture in the combustion chamber, the natural frequency of the molecules of the mixture ... and more generally any characteristic of the mixture which appears or undergoes a detectable variation during the combustion of the mixture in the combustion chamber.

 The number of exceedances of the threshold used to pass from the starting configuration to that of autonomous operation is preferably configurable in the engine control module 11 and can be lower or

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 greater than four.

 The engine control module 11 can be provided for the implementation of several starting configurations: for example depending on whether the engine is cold or hot, depending on the humidity of the air ... Similarly, the engine control module 11 may be provided for the implementation of several autonomous operating configurations which may be implemented successively, for example a first configuration for heating the engine and a second when the engine is hot, or alternatively.

 The start-up configuration can relate to a single operating parameter or to several, and in particular more than three.

Claims (8)

1. A method of starting a heat engine comprising a shaft (6) and means (1, 2.5) for driving it in rotation from the combustion of a flammable mixture in at least one engine combustion chamber (7), the method comprising the steps of placing the engine in a starting configuration and rotating the engine shaft simultaneously with at least one attempt to initiate combustion of the mixture in the chamber for bringing the heat engine from a stopped state to an autonomous operating state, characterized in that it comprises the steps of monitoring at least one characteristic of the mixture in the combustion chamber and of modifying at least one parameter of the configuration of starting to make it correspond to an autonomous operating configuration when the monitored characteristic is representative of at least one combustion actually started.  2. Method according to claim 1, in which, the drive means (1, 2.5) operating from a sequence of combustions, the parameter is modified when the monitored characteristic is representative of a predetermined number of combustions actually started.  3. Method according to claim 1 or claim 2, wherein the predetermined number of actually initiated combustions is of the order of one to two combustions per cylinder of the engine.  4. Method according to any one of claims 1 to 3, wherein the characteristic monitored corresponds to an ionization of at least part of the mixture.  5. Method according to claim 4, in the- <Desc / Clms Page number 11>  which, the engine comprising at least one spark plug (10) having two electrodes (8,9) opening into the combustion chamber (7), the monitoring step comprises the phases of applying a potential difference to the electrodes and detecting a current flowing between the electrodes, and the modification of the parameter comprises a phase of comparing an intensity of the detected current with a predetermined threshold.  6. Method according to any one of the preceding claims, characterized in that the shaft (6) of the motor is rotated by means of a starter (12) in the starting configuration, and in that the starter is disabled in the stand-alone operation configuration.  7. Method according to any one of the preceding claims, in which the parameter of the starting configuration which is modified relates to the enrichment of the fuel mixture.  8. Method according to any one of the preceding claims, in which the parameter of the starting configuration which is modified relates to the ignition advance.