Method for cold starting a spark-ignition internal combustion engine operating with a fuel comprising ethanol

Abstract

Method for cold starting an internal combustion engine operating with an ethanol fuel, with ignition controlled by a control unit including a basic ignition advance map determined for a given engine, includes the following steps applied to at least one combustion chamber in contact with a piston connected to a drive shaft: determining the engine temperature; rotating the drive shaft; phasing the engine; ensuring the fuel pressure exceeds a determined threshold for injection; injecting fuel for a first operational engine cycle after phasing; below a determined engine temperature, increasing, in the first operational cycle, the advance of the first ignition point before the compression top dead center for gases in the cylinder, with respect to the advance map, by a value between 21 and 50; controlling a first ignition point according to advance map based on the cycle following the first cycle.

Claims

1. A method for cold starting an internal combustion engine operating with a fuel comprising ethanol, the method comprising: cold starting the internal combustion engine with the fuel comprising ethanol using an ignition controlled by an engine control unit comprising a basic ignition advance map determined for a given engine operating point under standard pressure and atmospheric temperature and engine temperature conditions, the engine having at least one combustion chamber in contact with a piston connected to a drive shaft, said cold starting using the fuel comprising ethanol comprising the following steps applied to the at least one combustion chamber in contact with the piston connected to the drive shaft during a cold start phase of the operating with the fuel comprising ethanol: determining the temperature of the engine coolant, the determined temperature of the engine coolant being the engine temperature, rotating the drive shaft using a starter, proceeding to phasing of the engine by means of the engine control unit, checking that a pressure of the fuel exceeds a determined threshold for a purpose of injection, then injecting the fuel for a first operational cycle of the engine following said phasing, below a determined engine temperature, increasing, in said first operational cycle of the engine, the advance of the first ignition point before the compression top dead center for gases present in the combustion chamber, with respect to said basic ignition advance map recorded in the engine control unit, by a value between 21 and 50 so as to produce a temperature rise in the chamber with a minimum engine torque, and while rotating the drive shaft using a starter, controlling a first ignition point according to said basic ignition advance map, based on the operational cycle of the engine in said at least one combustion chamber, following said first operational cycle of the engine, for which an acceleration or a speed of the drive shaft beyond a determined threshold is exceeded, or for which a determined number of combustion top dead centers is reached, wherein, before the step consisting of controlling a first ignition point according to said basic ignition advance map, when an acceleration of the drive shaft beyond a determined threshold is exceeded or when a determined number of combustion top dead centers is reached, the method additionally consists of increasing the advance of the first ignition point before the compression top dead center for the gases present in the cylinder with respect to said basic advance ignition map recorded in the engine control unit, in a second operational cycle of the engine following said first cycle, by a value between 21 and 50, which is lower than the ignition advance before the compression top dead center of the first ignition point of said first cycle.

2. The method according to claim 1, wherein, before the step consisting of controlling a first ignition point according to said basic ignition advance map, when an acceleration of the drive shaft beyond a determined threshold is exceeded or when a determined number of combustion top dead centers is reached, the method consists of controlling a first ignition point of which the advance before the compression top dead center is degressive, specifically from one operational cycle of the engine to the other and from said first operational cycle of the engine, until the engine is started.

3. The method according to claim 1, wherein each of a plurality of ignition points are controlled in at least one same operational cycle of the engine, such that each of said plurality of ignition points are distributed successively in accordance with a phase advance having a value between 21 and 50 with respect to said basic ignition advance map recorded in the engine control unit.

4. The method according to claim 1, wherein the phase advance of said first ignition point, for said first operational cycle of the engine at least, before the compression top dead center, is approximately 52 before the compression top dead center for an engine temperature of approximately 5 C. for a fuel E100.

5. The method according to claim 1, wherein the method is applied to all combustion chambers of the engine.

6. An electronic engine control device comprising an engine control unit enabling implementation of a method according to claim 1.

7. The method according to claim 1, further comprising controlling a plurality of ignition points in at least one same operational cycle of the engine, said ignition points being distributed successively in accordance with a phase advance having a value between 21 and 50 with respect to said basic ignition advance map recorded in the engine control unit.

8. The method according to claim 2, wherein the phase advance of said first ignition point, for said first operational cycle of the engine at least, before the compression top dead center, is approximately 52 before the compression top dead center for an engine temperature of approximately 5 C. for a fuel E100.

9. The method according to claim 2, wherein the method is applied to all combustion chambers of the engine.

10. An electronic engine control device comprising an engine control unit enabling implementation of a method according to claim 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and features will become clear upon reading hereinafter an exemplary embodiment of a method according to the invention accompanied by annexed drawings, given by way of non-limiting example.

(2) The sole FIGURE shows a schematic graph of the development of three parameters during an exemplary starting of a vehicle having an internal combustion engine, comparing a starting method according to the prior art and a starting method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) The starting method shown by way of example in the sole FIGURE is a method for cold starting an internal combustion engine with direct injection into the combustion chambers, operating with a fuel comprising ethanol, in the example the fuel E100. The engine in the example is a spark-ignition engine of which the ignition is controlled by an engine control unit comprising, in a known manner, a basic ignition advance map determined for a given engine operating point under standard pressure and atmospheric temperature and engine temperature conditions.

(4) The temperature of the engine coolant at the moment of starting is 5 C. This temperature is measured at the probe for measuring the temperature of the coolant and fitted on an engine in a known manner.

(5) The starting method according to the invention is illustrated in the sole FIGURE by means of three curves 1, 2 and 3 in a solid line for the starting in accordance with the exemplary embodiment according to the invention, and by means of three curves 1, 2, 3 in dashed lines for the comparative example of starting in accordance with the prior art, all curves being illustrated synchronously with respect to the time t in seconds corresponding to the abscissa, over which the successive engine cycles progress. The ordinate axis in fact shows three different axes, allocated to the curves 1 and 1 (ordinate 4), 2 and 2 (ordinate 5), 3 and 3 (ordinate 6). These different ordinate axes correspond to the following parameters: curve 1 and 1: speed of rotation of the drive shaft in revolutions per minute (rpm), measured, in the known manner, on the basis of the position sensor of the drive shaft fitted on an internal combustion engine and calculated by means of the ECU of the vehicle, curve 2 and 2: advance of the first ignition point in the engine cycle(s), in a combustion chamber, in degrees of advance with respect to the compression top dead centre ( A/TDC), controlled and applied by the ECU, curve 3 and 3: quantity of fuel consumed during the starting procedure, in milligrams per compression top dead centre (mg/TDC).

(6) The illustrated method comprises the following steps, applied to at least one combustion chamber in contact with a piston connected to a drive shaft: determining the temperature of the engine coolant, also known as the engine temperature, rotating the drive shaft by means of a starter, for example the electric starter associated with the engine, proceeding to the phasing of the engine by means of the engine control unit, checking that the pressure of the fuel exceeds a determined threshold for the purpose of injection, then injecting fuel into the combustion chamber for a first operational cycle of the engine following the phasing, following an angular condition or time window determined in a known manner in the case of direct injection, such that the quantity of injected fuel remains in the combustion chamber; it should be noted that, in the case of indirect injection, the fuel is injected into the intake manifold in accordance with any known method.

(7) In accordance with the invention, the method then additionally comprises the following steps: below a determined engine temperature, for example 5 C. for a fuel E100, increasing, in the first operational cycle of the engine, the advance of the first ignition point before the compression top dead centre for the gases present in the combustion chamber or the cylinder with respect to the conventional basic ignition advance map recorded in the engine control unit, by a value of approximately 40. This early advance in accordance with the invention, in the example, brings the first ignition point in the first operation cycle of the engine to an absolute advance of approximately 52 before the compression top dead centre as illustrated on the curve 2. In the present example, an absolute advance up to 60 before the compression top dead centre can be envisaged. Generally, for a fuel E100, an absolute advance between 40 and 65 before the compression top dead centre, in accordance with the basic map and the engine temperature at the moment of starting, can be applied for the first operational cycle of the engine. A lesser absolute advance, before the compression top dead centre, preferably between 10 and 40, can be applied for a fuel having a weaker ethanol content.

(8) In the case of another example, that is to say 0 C. engine temperature before starting for the same fuel E100, an absolute advance of 50 before the compression top dead centre can be applied advantageously for the first ignition point.

(9) In the example described on the basis of a direct injection engine, it should be noted that the step of injection of the fuel into the combustion chamber must be performed before the first early ignition point according to the invention. The result may thus be that the entire quantity of fuel provided by the calculator cannot be injected taking into account the provided early advance. In this case, the injection train provided by the engine control unit should be shifted, such that the last programmed injection is performed before the first early ignition point in accordance with the invention, taking into account the required angular margin where applicable.

(10) The method according to the invention advantageously also consists in increasing the advance of the first ignition point before the compression top dead centre for the gases present in the cylinder with respect to the basic ignition advance map recorded in the engine control unit, in a second operational cycle of the engine successive to said first cycle, by a value between 21 and 50, which is lower than the ignition advance before the compression top dead centre of the first ignition point of said first cycle, for example 5 to 6 lower. In the example, this would give an absolute advance of 47 before the top dead centre for an advance decrease of 5. This is true to the extent that an acceleration or a speed of the drive shaft has not exceeded said determined threshold after the first operational cycle of the engine.

(11) The method according to the invention preferably additionally consists of controlling a first ignition point, of which the advance before the compression top dead centre is degressive, specifically from one operational cycle of the engine to the other and from the first operational cycle of the engine until the engine is started, that is to say until the crankshaft is driven in rotation by the energy of the combustions.

(12) The method according to the invention may consist in controlling a plurality of ignition points in the same first operational cycle of the engine, the ignition points being distributed successively in accordance with a phase advance having a value between 21 and 50 with respect to or additionally to the basic ignition advance map recorded in the engine control unit, that is to say for example four ignition points (not shown) in the same first engine cycle.

(13) The method illustrated in the sole FIGURE then consists of controlling a first ignition point according to the basic ignition advance map based on the operational cycle of the engine in the combustion chamber in question following the first operational cycle of the engine, for which an acceleration of the drive shaft beyond a determined threshold is exceeded, or for which an engine speed threshold is exceeded, or for which a determined number of combustion top dead centers is reached. This threshold corresponds to the driving of the crankshaft by the energy of the combustions. In accordance with the curve 2 in the sole FIGURE, the anticipated advance according to the invention disappears when the engine has started, which would occur approximately at the time t=1.6 seconds.

(14) It can be seen on the basis of the sole FIGURE and of the compared curves 1 and 1 that the engine starting with the method according to the invention described above is obtained approximately two seconds before the starting in accordance with the shown example of the prior art method, in which the engine starts approximately at the time t=2.6 seconds. As soon as the starting has been implemented in accordance with the curve 1, it can be seen that the ignition advance curve 2 falls below the ignition advance curve 2 according to the prior art, the basic ignition advance map implemented in the engine control unit taking over (see the significant difference along the abscissa of the two curves 2 and 2 by a value corresponding substantially to the time gained during the starting process).

(15) The compared curves 3 and 3 of consumed quantities of fuel logically show a saving of fuel achieved with the described method corresponding to the time gained when starting of the engine.

(16) The method described with the aid of the sole FIGURE is preferably (not illustrated) applied to all the combustion chambers of an engine when an ignition process has to be performed in a chamber before the starting of the engine or more specifically for example before an acceleration threshold of the drive shaft is exceeded.

(17) The method according to the invention can be implemented in an engine control unit of the known type already having a basic ignition map by means of an additional software.