FR2888891A1 - Internal combustion engine e.g. diesel engine, starting method, involves heating gas present in combustion chambers so as to keep gas at preset minimum temperature when pistons are in maximum compression position or near to position - Google Patents

Abstract

The method involves heating gas present in combustion chambers so as to keep the gas at a minimum temperature of approximately 415 degree Celsius in the whole of volume defined by the chambers when pistons are in maximum compression position or near to the position. The gas is intended to participate at the combustion and is heated by heating preheating an inlet air (A) using a preheating unit (30) that comprises an electrical resistor (R). An independent claim is also included for a device for starting an internal combustion engine.

Description

2888891 1

  The invention relates to the field of internal combustion engines, in particular diesel engines of motor vehicles.

  It relates more particularly to a method and a starting device of an internal combustion engine, comprising cylinders and pistons defining combustion chambers inside which are admitted gases intended to participate in the combustion.

  It is known that internal combustion engines are operated by an electric starter comprising a pinion capable of coming into mesh with a ring gear integral with rotation of the crankshaft, that is to say of the motor shaft.

  Starting devices of this type pose a number of problems when it comes to starting an engine, especially a diesel engine, in cold weather, especially when the temperature is of the order of -25 C.

  It is known to ensure preheating by several glow plugs (one in each combustion chamber) fixed at the engine cylinder head. These candles generate a hot spot in the combustion chamber, which allows the combustion of injected diesel, even at very low temperatures.

  2888891 2 However, the glow preheating system is localized and leads to overconsumption of fuel at startup, therefore more emissions. In addition, the implantation of the candles in the cylinder head makes it more complex.

  In addition, after a cold start with glow plugs, the internal combustion engine is very unstable during the idling phase and regularly stalling, which causes a number of defects such as vibration, noise, etc. The object of the invention is in particular to overcome the aforementioned drawbacks.

  It aims in particular to provide a method and a starting device of an internal combustion engine that are likely to start this engine in cold weather, especially at temperatures of the order of -25 C.

  It is another object of the invention to provide such a method and starting device which do not require glow plugs in the combustion chambers.

  Another object of the invention is to provide such a method and starting device which are particularly suitable for diesel engines, particularly for motor vehicles.

  To this end, the invention proposes a process of the type defined in the introduction, in which a strategy is adopted according to which the gases present in the chambers are heated so as to bring them to a minimum temperature, in particular of about 415.degree. the entire volume defined by the chambers when the pistons are in the maximum compression position or in the vicinity thereof, including more or less 10.

  It has been found that it is by obtaining a certain level of temperature, such as that defined above, substantially throughout the chamber, that reliable start is allowed, even in difficult conditions.

  According to a first embodiment, an electric machine, in particular an electric starter, is coupled to the crankshaft of the motor in order to drive it in rotation at a chosen rotational speed, greater than a normal rotational speed obtained with said electric machine, so as to to increase the amount of air admitted into the engine cylinders and, consequently, the temperature in the cylinders.

  While the average rotational speed of a crankshaft actuated by electric starter is generally 110 rpm at -25 C, the invention proposes to operate the electric starter at a higher rotational speed. This results in favorable operating conditions for starting in cold weather, in any case up to temperatures of the order of -25 C, because the amount of air admitted into the cylinders of the engine is increased, favoring There is even an increase in the temperature in the cylinders. Indeed, the increase in the rotational speed of the electric starter, therefore the crankshaft, results in an increase in the linear speed of the pistons in the respective cylinders, leading to a reduction in leaks between the pistons and the cylinders and to a decrease in heat loss to the wall.

  The rotational speed chosen is advantageously greater than 200 rpm and more preferably greater than 300 rpm.

  According to another embodiment, the chambers being supplied with gas intended to participate in the combustion by a common conduit, said gases are preheated during their circulation in said conduit.

  According to this embodiment, it is possible to preheat said gases and simultaneously adjust their flow rate.

  By combining the two previous embodiments, it is possible to preheat the gases intended to participate in the combustion and to actuate said electric machine at said chosen rotational speed, in coordination.

  More particularly, it will be possible to preheat said gases before operating said electric machine at said selected speed of rotation.

  That being so, it will be possible to detect start conditions and derive information relating to a "cold start" or a "normal start" and adopt said strategy according to said start conditions.

  More particularly, the electric machine can be operated at the chosen speed or at the normal speed, in the case of "cold start" or "normal start" conditions respectively.

  The starting conditions are related, for example, to a temperature difference (DT = TE - TH) between the engine cooling water temperature (TE) and the engine lubricating oil temperature (TH). and define the "cold start" condition or the "normal start" condition according to whether this temperature difference (DT) is respectively less than or greater than a given threshold value (S), especially 5C.

  The invention also relates to a starting device of the type defined in the introduction, comprising means for heating the gases present in the chambers so as to bring them to a minimum temperature throughout the volume of the chambers when the pistons are in position. maximum compression or in the vicinity thereof, including more or less 10.

  According to a first embodiment, said preheating means consist of an electric machine capable of driving the crankshaft of the engine at a chosen rotation speed, greater than a normal rotational speed obtained with said electric machine, so as to increase the quantity air admitted into the engine cylinders and, consequently, the temperature in the cylinders.

  The invention particularly envisages using a conventional electric starter, that is to say a starter capable of operating at a given electrical voltage, for example 12 volts.

  2888891 6 It is then expected to connect the electric starter to an electric circuit capable of supplying the starter from a boosted voltage, that is to say greater than the given voltage constituting the usual operating voltage of the starter.

  Advantageously, the electrical circuit comprises a primary voltage source capable of delivering a nominal voltage of chosen value and a source of boosted voltage capable of delivering a voltage greater than the nominal voltage of the primary voltage source.

  According to a first variant embodiment, the voltage source that is boosted is a battery. In an exemplary embodiment, the primary voltage source is a first battery clean to deliver a nominal voltage of 12 volts, while the boosted voltage source is a second battery clean to deliver a nominal voltage of 24 volts.

  According to a second variant, the boosted voltage source is a supercapacitor, that is to say a double-layer capacitor. In an exemplary embodiment, the primary voltage source is a first battery clean to deliver a nominal voltage of 12 volts, while the supercapacitor is able to deliver a voltage greater than 12 volts.

  According to another characteristic of the invention, the electrical circuit comprises a DC-DC converter for recharging the voltage source 2888891 7, which is boosted from the primary voltage source. This converter can be reversible or not.

  The electrical circuit may also include an electrical relay capable of controlling the starter from the boosted voltage source.

  According to a variant, said circuit comprises a first voltage source, for delivering said nominal voltage, and a second voltage source as well as switching means for associating said voltage sources to obtain said boosted voltage.

  It will thus be possible to use two batteries, for example of the same voltage, and a toggle system making it possible to place said batteries in series or in parallel or to solicit either the two batteries, or only one, as needed.

  Such a configuration is particularly suitable in case of identification of start conditions by comparing TE and TH, as mentioned above.

  It will still be possible to use a battery and a supercapacitor which can be placed in series with the battery.

  The circuit may further comprise a single battery to obtain said nominal voltage and a DC-DC converter, in particular an electronic chopper device provided between the battery and the starter, to obtain said boosted voltage.

  In a different embodiment, the starting device further comprises or alternatively preheating means adapted to preheat the intake air and therefore the gases intended for combustion, said preheating means being provided in the system of preheating. admission of the engine at a duct simultaneously supplying all the combustion chambers.

  According to this embodiment, the preheating means comprise, for example, at least one electrical resistance (R) which can be integrated in a gas flow control valve intended to participate in the combustion, said valve being provided at the level of said leads.

  It is then possible to provide control means for actuating the preheating means and the electric starter in coordination. Preferably, these control means are able to actuate the preheating means before the electric starter.

  In one embodiment, the starting device comprises detection means able to detect start conditions and derive information relating to a "cold start" or "normal start" and selection means connected to the means of detection to actuate the electric starter respectively at the chosen speed or at the normal speed.

  In other words, depending on the start conditions detected, the device of the invention makes it possible to start the engine according to two different modes of operation.

  In the description which follows, given by way of example only, reference is made to the accompanying drawings, in which: FIG. 1 schematically represents an internal combustion engine with part of its usual equipment, the engine being equipped with a starter device according to the invention; FIG. 2 represents the electrical diagram of an electrical circuit for actuating the electric starter in a first variant; FIG. 3 is a view similar to FIG. 2 in a second variant of the electric circuit; - Figure 4 is a view similar to Figure 1 in another embodiment; and FIG. 5 is a flowchart of the control means of the starting device in the case of the embodiment of FIG. 4.

  Referring first to Figure 1 which shows an internal combustion engine 10, for example a motor vehicle diesel engine, having an intake manifold 12 adapted to admit a flow of intake air A in the chambers combustion engine (not shown) of the engine, from an intake duct 14. The manifold 12 and the duct 14 together constitute the engine intake system.

  The engine 10 is cooled by a coolant circulating in a cooling radiator 16. The engine 10 comprises a crankshaft 18 (or motor shaft) on which is wedged a ring gear 20. The engine is started by the engine. intermediate of an electric starter 22 comprising a DC motor driving a pinion gear 24 engageable with the ring gear 20 by an axial displacement of the pinion, in a manner known per se. The electric starter 22 is a conventional starter which, in the example, is designed to be driven by a usual voltage source, such as a battery delivering a 12 volts DC rated voltage.

  According to the invention, the electric starter 22 is actuated, by means which will be described later, to drive the crankshaft 18 to a chosen rotational speed, greater than its normal rotational speed. This rotational speed chosen is in the example greater than 200 rpm, and preferably greater than 300 rpm, while the normal rotational speed with starter is usually 110 rpm in cold weather.

  For this purpose, control means 26 (shown schematically) make it possible to actuate the electric starter 22 at this chosen speed of rotation, through an electric circuit 28, which will be described later.

  As indicated above, the fact of driving the crankshaft 18 to a higher rotational speed makes it possible to increase the quantity of air admitted into the engine cylinders and, consequently, the temperature in the cylinders, which favors the cold weather engine start.

  To promote this starting, it is also advantageous or alternatively to provide, as shown in Figure 1, preheating means 30 adapted to preheat the intake air A. These preheating means advantageously comprise at least one electrical resistance R. They are here arranged upstream of the intake manifold 12 of the engine, that is to say here on the intake duct 14. Other locations are possible, for example at the inlet of the intake manifold of the engine. engine.

  The control means 26 make it possible to actuate the preheating means 30 and the electric starter 22 in coordination. The actuation of these means 26 and 30 can be done simultaneously, but preferably with a time shift. It is advantageous in fact that the control means actuate the preheating means 30 before the electric starter 22, for example on the occasion of an unlocking order of the vehicle doors provided with the engine to be started.

  As a result, the conventional preheating glow plug system in the cylinder combustion chambers can be eliminated. This results in a simplification of the engine cylinder head. In addition, it should be noted that the preheating system 30 is not more demanding in electrical power than a conventional glow plug system.

  Referring now to Figure 2 which shows an embodiment of an electric circuit associated with the electric starter, according to the invention. The electric starter 22, shown here schematically by a dashed rectangle, comprises, in a manner known per se, a DC motor 32, a contactor 34, a call coil 36 and a holding coil 38. The coil of FIG. Call 36 serves to stick the contactor 34 while the hold coil 38 serves to maintain the contactor in the closed state.

  The electric starter 22 is connected to the electrical circuit 28 mentioned above, which comprises a wiring 40 integrating a primary voltage source 42 and a boosted voltage source 44. In the example shown, the source 42 is a first battery clean to deliver a rated DC voltage of 12 volts, while the boosted voltage source 44 is a second battery which is capable of delivering a nominal DC voltage of 24 volts.

  The circuit 28 comprises a start switch 46 adapted to be actuated by a ignition key or a contact card for starting the engine. The contactor 46 is powered by the source 42, so by a voltage of 12 volts in the example. An electrical relay 48 is included in the circuit 28 following the switch 46 to allow the starter to be controlled from the boosted voltage source 44, that is to say here at 24 volts.

  Thus, during a start request, closing the start contactor 46 controls the relay 48 which drives the starter control from the source of the boosted voltage 44, so 24 volts. The circuit 28 thus makes it possible to supply the electric starter 22 with a voltage higher than the usual voltage, which enables it to have a higher rotational speed, as already indicated.

  The boosted voltage source 44 may be replaced by means other than a 24-volt battery, provided that it can deliver a voltage greater than the nominal voltage of the primary source 42. Thus, in an alternative embodiment, it is possible to use a supercapacitor, ie a double-layer capacitor. It is known that these capacitors have a much higher active surface than traditional capacitors, which results in very high capacitance values. These supercapacitors also have the advantage of recharging much faster than usual batteries and provide a very high power current.

  Referring now to Figure 3 which shows an alternative embodiment of the circuit of Figure 2. The difference here lies in the fact that the electric circuit 40 further comprises a converter 50 of the DC-DC type to recharge the source voltage converter 44 from the primary voltage source 42. This converter 50 is interposed between two branches of the wiring 40 which respectively contain the voltage sources 42 and 44. This applies regardless of the type of the voltage source boosted 44 (battery, supercapacitor, or other).

  FIG. 4, to which reference is now made, shows an alternative embodiment of the motor and its environment 2888891 14 according to FIG. 1. The main difference here lies in the fact that the control means 26 are connected to detection means to detect startup conditions. More particularly, these detection means comprise a temperature sensor 52 able to detect the temperature of the engine cooling water (TE) and another temperature sensor 54 capable of detecting the temperature of the engine lubricating oil ( TH). Indeed, as will be seen below, depending on the difference between the values TE and TH thus measured, it is possible to define different start conditions, namely a "cold start" condition and a condition of "normal start".

  Referring now to Figure 5 which shows an operating flow chart in the case of the embodiment of Figure 4. The sensors 52 and 54 are connected to a computer 56 which calculates the temperature difference DT = TE-TH. This calculator is connected to a comparator 58 which compares the value DT with a threshold value S for example of 5 C. Two cases can then arise: if the value DT is lower than the threshold value S, it can be deduced that these are cold start conditions. On the other hand, if the value DT is greater than the threshold value S, it is deduced that these are normal start conditions.

  The comparator 58 thus constitutes selection means which, as a function of the value of DT with respect to s, is a cold start or a special start 60, or a normal start 62. In the case of the cold start 60, the control means actuate the electric starter 22 through the electric circuit 28 and the heating means 3088, and this in coordination as described above.

  In the case of normal start 62, the control means 26 actuate the electric starter 22 under usual conditions, that is to say that it is powered by the nominal voltage of the primary voltage source 42. In other words, in the latter case, the drive speed of the crankshaft corresponds to the usual conditions.

  The starting device of the invention has the following main advantages: - reduction of polluting emissions because less fuel is used, - reduction of start-up (and preheating) time, - reduction of combustion failures, - reduction of instability after starting and noise generated accordingly, simplification of the engine cylinder head, and - application to engines with low compression ratio.

  In addition, as already indicated above, the intake air preheating means do not require more electrical power than a system by glow plugs.

  The invention finds general application to internal combustion engines, and particularly to diesel engines of motor vehicles.

Claims (25)

claims   1. A method of starting an internal combustion engine comprising cylinders and pistons defining combustion chambers inside which gases are admitted for participating in the combustion, a method in which a strategy is adopted according to which one warms the gases present in the chambers so as to bring them to a minimum temperature throughout the volume defined by the chambers when the pistons are in the maximum compression position or in the vicinity thereof.   2. The process of claim 1 wherein said minimum temperature is about 415 C.   3. Method according to claim 1 or 2 wherein, said motor comprising a crankshaft (18), an electric machine (22) is coupled to the crankshaft to drive it in rotation at a chosen speed of rotation, greater than a rotational speed. normal obtained with said electric machine, so as to increase the amount of air present in the engine cylinders and, therefore, the temperature in the cylinders.   4. The method of claim 3 wherein the rotational speed chosen is greater than 200 rpm.   5. The method of claim 4 wherein the selected rotational speed is greater than 300 rpm.   6. Method according to any one of the preceding claims wherein, the chambers being fed with gases intended to participate in the combustion by a common conduit, said gases are preheated during their circulation in said conduit.   7. The method of claim 6 wherein, said gas is preheated and their flow rate is adjusted simultaneously.   8. A method according to claim 3 and one of claims 6 or 7 wherein the gas intended to participate in the combustion is preheated and said electric machine (22) is actuated at said selected rotational speed, in coordination.   9. The method of claim 8 wherein said gas is preheated before operating said electric machine at said selected rotational speed.   10. A method according to any one of the preceding claims in which startup conditions are detected and inferred information relating to a "cold start" or a "normal start" and adopted said strategy according to said start conditions.   11. The method of claims 3 and 10 wherein the electric machine (22) is actuated at the selected speed or at the normal speed, in the case, respectively, of conditions of "cold start" or "normal start".   12 Method according to one of claims 10 or 11 wherein the start conditions are relative to a temperature difference (DT = TE - TH) between the 2888891 18 temperature of the engine cooling water (TE) and the temperature the engine lubrication oil (TH) and define the "cold start" condition or the "normal start" condition depending on whether this temperature difference (DT) is respectively less than or greater than a threshold value ( S) given.   13. Starting method according to claim 12, characterized in that the threshold value (S) is 5 C. 14. Starting device of an internal combustion engine comprising cylinders and pistons defining combustion chambers inside which gases are admitted to participate in the combustion, said device comprising means for heating the gases present in the chambers so as to bring them to a minimum temperature in the entire volume of the chambers when the pistons are in the maximum compression position or in the vicinity thereof.   15. Device according to claim 14 comprising an electric machine (22) adapted to be coupled to the crankshaft (18) of the motor to drive it in rotation, at a chosen rotational speed, greater than a normal rotational speed obtained with said machine electric, so as to increase the amount of air admitted into the engine cylinders and, therefore, the temperature in the cylinders.   16. Device according to claim 15, wherein said electric machine (22) is an electric starter, adapted to operate under at least one given voltage, said starter being connected to an electrical circuit 2888891 19 (28) adapted to power the starter from a boosted electrical voltage, higher than the given voltage.   17. Device according to claim 16, wherein the electric circuit (28) comprises a primary voltage source (42) adapted to deliver a nominal voltage of selected value and a voltage source boosted (44) adapted to deliver a voltage greater than the nominal voltage of the primary voltage source (42).   The apparatus of claim 17, wherein the boosted voltage source (44) is a battery.   The device of claim 18, wherein the primary voltage source (42) is a battery capable of delivering a nominal voltage of 12 volts, while the boosted voltage source (44) is a battery capable of delivering a nominal voltage. 24 volts.   The apparatus of claim 17, wherein the boosted voltage source (44) is a supercapacitor.   The device of claim 20, wherein the primary voltage source (42) is a battery capable of delivering a nominal voltage of 12 volts, while the boosted voltage source (44) is a supercapacitor capable of delivering a higher voltage. at 12 volts.   22. Device according to one of claims 17 to 21, wherein the electric circuit (28) comprises a converter (50) DC direct current for 2888891 20: recharge the boosted voltage source (44) from the source of primary voltage (42).   23. Device according to one of claims 17 to 22, wherein the electric circuit (28) comprises an electrical relay (48) adapted to control the electric starter (22) from the boosted voltage source (44).   24. The device according to claim 16, wherein said circuit comprises a first voltage source for delivering said given voltage and a second voltage source as well as switching means for associating said voltage sources to obtain said boosted voltage.   25. The device according to claim 16, wherein said circuit comprises a single battery for obtaining said given voltage and a DC-DC converter for obtaining said boosted voltage.   26. Device according to one of claims 14 to 25, said device comprising preheating means (30) adapted to preheat the gas intended for combustion, said intake air (A), said preheating means being provided at the a duct simultaneously supplying all the combustion chambers.   2'7. Apparatus according to claim 26, wherein the preheating means (30) comprises at least one electrical resistance (R).   28. Device according to claim 27, wherein said electrical resistance (R) is integrated in a gas flow control valve intended to participate in the combustion, said valve being provided at said duct.