METHOD FOR MEASURING A COMPRESSION RATIO OF A VEHICLE ENGINE CYLINDER AND APPLYING A CORRECTION TO A COMBUSTION PROCESS

Abstract

The invention relates to a method 100 for measuring a compression ratio of an engine cylinder and applying a correction to a combustion process comprising the steps of: Determining 105 an intake pressure in an intake of a combustion chamber; Determining 106 as a function of said intake pressure and a nominal compression ratio, a nominal compression value; Determining 107, 108 instantaneous rotational speeds of a crankshaft of said cylinder close to a bottom dead center and a top dead center; Determining 109 an actual compression ratio as a function of said instantaneous rotational speeds; Determining 110 a ratio of said actual compression ratio and said nominal compression value; If said ratio is between a first and a second threshold, applying 111 a correction to the combustion process. Figure to be published with the abstract: Single figure.

Description

Title of the invention: METHOD FOR MEASURING A COMPRESSION RATIO OF A VEHICLE ENGINE CYLINDER AND APPLYING A CORRECTION TO A COMBUSTION PROCESS TECHNICAL FIELD OF THE INVENTION

[0001] The field of the invention is that of measuring a compression ratio of an engine cylinder of a vehicle and applying a correction to a combustion process which occurs in said engine cylinder. The invention applies more particularly to internal combustion engines comprising one or more cylinders. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] The thermodynamic efficiency of an engine depends strongly on the compression ratio of each cylinder of said engine. The compression ratio of a cylinder is formed by the ratio between the volume of the combustion chamber when the piston is at top dead center and the volume of the combustion chamber when the piston is at bottom dead center. The higher the compression ratio, the higher the thermodynamic efficiency of the engine.

[0003] The position of the top dead center as well as the position of the bottom dead center, in other words the compression ratio, depend on manufacturing constraints, in particular the precision of compliance with the manufacturing dimensions of the cylinder head and the cylinder piston.

[0004] Given the precision of the elements constituting an engine cylinder, it is difficult to obtain a stable and little dispersed compression ratio on a plurality of engine cylinders.

[0005] On gasoline engines, when the manufacturing dimensions are not respected and the compression ratio is too high, a self-combustion phenomenon occurs during the expansion phase. This self-combustion phenomenon generates explosive combustion inside the cylinder, leading to premature aging of said engine cylinder. Summary of the invention

[0006] An objective of the invention is to propose a solution for applying a correction to a combustion process of an engine cylinder when the compression ratio of said cylinder is imperfect.

[0007] To this end, the invention thus relates, in its broadest acceptance, to a method for measuring a compression ratio of a cylinder of an engine of a vehicle and applying a correction to a combustion process, the method comprising the steps, executed by an engine computer of said vehicle, consisting of: • Determine an intake pressure in an intake of a combustion chamber of said cylinder; • Determine, via mapping, based on said determined intake pressure and a nominal compression ratio, a nominal compression value; • Determine an instantaneous rotation speed of a crankshaft of said cylinder close to a bottom dead center; • Determine an instantaneous rotation speed of said crankshaft close to top dead center; • Determine an actual compression ratio based on said instantaneous rotation speeds of said crankshaft near bottom dead center and near top dead center determined; • Determine a ratio of said actual compression ratio and said nominal compression value; • If said ratio is between a first threshold and a second threshold higher than said first threshold, apply a correction to the combustion process which occurs in said cylinder.

[0008] Thanks to the invention, if the manufacturing dimensions of the elements constituting the engine cylinder generate a compression ratio that is too high, the method according to the invention is able to detect it, then to apply a correction to the combustion process which occurs in the cylinder, for example by applying an offset during ignition of the cylinder.

[0009] In addition to the characteristics which have just been mentioned in the preceding paragraph, the method according to the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations.

[0010] According to a non-limiting implementation of the invention: • The first threshold is between 85% and 95% of the nominal compression value; • The second threshold is between 105% and 115% of the nominal compression value.

[0011] According to a non-limiting implementation of the invention, the actual compression ratio is representative of the sum of the instantaneous rotation speeds of the crankshaft close to top dead center and close to bottom dead center, a sum to which we multiply subtracting the instantaneous rotational speed of the crankshaft near top dead center from the instantaneous rotational speed of the crankshaft near bottom dead center.

[0012] According to a non-limiting implementation of the invention, the correction is applied by applying an offset when the cylinder is ignited.

[0013] According to a non-limiting implementation of the invention, the correction is applied by applying an offset during the injection of fuel into the cylinder.

[0014] According to a non-limiting implementation of the invention, when the ratio is lower than the first threshold or higher than the second threshold, the method comprises a step, executed by display means of the vehicle, of displaying information reflecting a critical compression ratio.

[0015] According to a non-limiting implementation of the invention: • The instantaneous rotational speed of the crankshaft near bottom dead center is determined when the angular position of the crankshaft is between 100° and 140°; • The instantaneous rotational speed of the crankshaft near top dead center is determined when the angular position of the crankshaft is between 0° and 15°.

[0016] According to a non-limiting implementation of the invention, the method comprises a step of determining an engine speed, the steps of the method according to any one of the aforementioned aspects of the invention being executed if and only if said engine speed is lower than a threshold engine speed, formed by an idle speed.

[0017] According to a non-limiting implementation of the invention, the method comprises a step of determining a temperature of the engine, the steps of the method according to any one of the aforementioned aspects of the invention being executed if and only if said temperature of the engine is greater than a threshold temperature.

[0018] According to a non-limiting implementation of the invention, the method comprises a step of determining an operating state of a transmission system of the vehicle, the steps of the method according to any one of the aforementioned aspects of the invention being executed if and only if said transmission system is mechanically disconnected from the engine.

[0019] According to a non-limiting implementation of the invention, the method comprises a step of determining a complementary parasitic torque, the steps of the method according to any one of the aforementioned aspects of the invention being executed if and only if no complementary parasitic torque is present.

[0020] This complementary parasitic torque can for example be generated by: • The operation of an air conditioning system; • A current value of a current call generated by an alternator greater than a threshold current value; and / or • How power steering works.

[0021] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figure.

[0022] [Fig-1] illustrates, schematically, a method according to a non-implementation limiting of the invention.

[0023] The figure is presented for information purposes only and in no way limits the invention.

[0024] [Fig.l] illustrates the steps of a method 100 for measuring a compression ratio of a cylinder of an engine of a vehicle, in particular a motor vehicle, and for applying a correction to a combustion process which occurs in said cylinder. It should be noted that when the vehicle has several cylinders, the method 100 applies to each of the cylinders.

[0025] Steps 101 to 111 of the method 100 according to the invention are for example executed by an engine computer.

[0026] According to a non-limiting exemplary embodiment, the method 100 comprises the steps consisting of: • Determine 101 an engine speed; • Determine 102 an engine temperature; • Determine 103 an operating state of a vehicle transmission system, the operating state of the transmission system being defined by the mechanical connection or disconnection of the transmission system with the engine; • Determine 104 an additional parasitic torque, the additional parasitic torque being able to be formed by the operation of the air conditioning system, a current value of a current draw generated by an alternator greater than a threshold current value, and / or the operation of a power steering.

[0027] According to this non-limiting embodiment, steps 105 to 112 of the method 100 which follow are executed if and only if: • The engine speed is below a threshold engine speed corresponding to engine idling, for example between 600 and 1500 rpm; • The engine temperature is above a threshold temperature, for example above 70°C; • The transmission system is mechanically disconnected from the engine; • The air conditioning system is turned off; • The current value is less than a threshold current value, for example 5A; and • Power steering is off.

[0028] The method 100 comprises a step of determining 105 an intake pressure in an intake of a combustion chamber of the cylinder.

[0029] It should be remembered that the pressure in the cylinder before the intake valves close is close to the pressure upstream of the valves. Thus, a vehicle pressure sensor is capable of measuring the pressure at the intake of the combustion chamber, then transmitting this measurement to the engine computer. The engine computer then determines the intake pressure in the combustion chamber.

[0030] The method 100 further comprises a step consisting of determining 106, via a map, as a function of the determined intake pressure and a nominal compression ratio, a nominal compression value. This map can be recorded in the engine computer.

[0031] The method 100 also comprises a step of determining 107 an instantaneous rotational speed of a crankshaft of the cylinder close to a bottom dead center. According to a non-limiting embodiment, the instantaneous rotational speed of the crankshaft close to the bottom dead center is determined when the angular position of the crankshaft is between 100° and 140°.

[0032] According to a non-limiting embodiment, a target position sensor can be used to measure the instantaneous rotational speed of the crankshaft. The target can be integral in rotation with the crankshaft and comprise teeth. Thus, for example at 110°, the position sensor determines the time required for two adjacent teeth to pass in front of this angle. Depending on this time, the position sensor is able to deduce the instantaneous rotational speed of the crankshaft close to the bottom dead center and then transmit it to the engine computer. The engine computer then determines the instantaneous rotational speed of the crankshaft close to the bottom dead center.

[0033] The method 100 also comprises a step consisting of determining 108, an instantaneous rotational speed of the crankshaft of the cylinder close to a top dead center.

[0034] According to a non-limiting embodiment, the instantaneous rotation speed of the crankshaft close to top dead center is determined when the angular position of the crankshaft is between 0° and 15°.

[0035] Thus, for example, at 10°, the position sensor determines the time required for two adjacent teeth to pass in front of this angle. Based on this time, the position sensor is able to deduce the instantaneous rotational speed of the crankshaft close to top dead center and then transmit it to the engine computer. The engine computer then determines the instantaneous rotational speed of the crankshaft close to top dead center.

[0036] The method 100 also comprises a step of determining 109 an actual compression ratio as a function of the instantaneous rotational speed of the crankshaft close to the bottom dead center determined and the instantaneous rotational speed of the crankshaft close to the top dead center determined.

[0037] According to a non-limiting embodiment, the actual compression ratio is representative of: (instantaneous rotation speed of the crankshaft close to the determined top dead center + instantaneous rotation speed of the crankshaft close to the determined bottom dead center) * (instantaneous rotation speed of the crankshaft close to the determined bottom dead center - instantaneous rotation speed of the crankshaft close to the determined top dead center).

[0038] The method 100 also comprises a step of determining 110 a ratio of the actual compression ratio and the nominal compression value. Stated another way, the ratio = actual compression ratio / the nominal compression value.

[0039] If the determined ratio is between a first threshold and a second threshold greater than said first threshold, the method 100 comprises a step consisting of applying 111 a correction to the combustion process of the cylinder.

[0040] According to a non-limiting implementation of the invention: • The first threshold is between 85% and 95% of the nominal compression value; • The second threshold is between 105% and 115% of the nominal compression value.

[0041] According to a non-limiting embodiment, for a gasoline engine, the correction is applied to the combustion process of the cylinder by applying an offset during ignition of the cylinder.

[0042] According to a different non-limiting embodiment, for a diesel engine, the correction is applied to the combustion process of the cylinder by applying an offset during the injection of fuel into the cylinder.

[0043] According to a non-limiting embodiment, when the ratio is lower than the first threshold or higher than the second threshold, the method 100 comprises a step, executed by display means of the vehicle, consisting of displaying 112 information reflecting a critical compression ratio. Thus, the driver can bring his vehicle to the after-sales service in order to carry out a check of the compression ratio.

Claims

Claims

1. Method (100) for measuring a compression ratio of a cylinder of an engine of a vehicle and applying a correction to a combustion process, said method (100) comprising the steps, executed by an engine computer of said vehicle, consisting of: - Determining (105) an intake pressure in an intake of a combustion chamber of said cylinder; - Determining (106), via a map, as a function of said determined intake pressure and a nominal compression ratio, a nominal compression value; - Determining (107) an instantaneous rotational speed of a crankshaft of said cylinder close to a bottom dead center; - Determining (108) an instantaneous rotational speed of said crankshaft close to a top dead center;- Determine (109) an actual compression ratio as a function of said instantaneous rotational speeds of said crankshaft near top dead center and near bottom dead center determined; - Determine (110) a ratio of said actual compression ratio and said nominal compression value; - If said ratio is between a first threshold and a second threshold greater than said first threshold, apply (111) a correction to the combustion process which occurs in said cylinder.;

2. Method (100) according to the preceding claim, characterized in that: - The first threshold is between 85% and 95% of the nominal compression value; - The second threshold is between 105% and 115% of the nominal compression value.

3. Method (100) according to any one of the preceding claims, characterized in that the actual compression ratio is representative of the sum of the instantaneous rotational speeds of the crankshaft near top dead center and near bottom dead center, sum to which is multiplied the subtraction of the rotational speed instantaneous rotational speed of the crankshaft near top dead center to the instantaneous rotational speed of the crankshaft near bottom dead center.

4. Method (100) according to any one of the preceding claims, characterized in that the correction is applied by applying: - An offset when the cylinder is ignited; - Or an offset when fuel is injected into the cylinder.

5. Method (100) according to any one of the preceding claims, characterized in that when the ratio is lower than the first threshold or higher than the second threshold, the method (100) comprises a step, executed by display means of the vehicle, consisting of displaying (112) information reflecting a critical compression ratio.

6. Method (100) according to any one of the preceding claims, characterized in that: - The instantaneous rotational speed of the crankshaft close to the bottom dead center is determined when the angular position of the crankshaft is between 100° and 140°; - The instantaneous rotational speed of the crankshaft close to the top dead center is determined when the angular position of the crankshaft is between 0° and 15°.

7. Method (100) according to any one of the preceding claims, characterized in that the method (100) comprises a step of determining (101) an engine speed, the steps of the method (100) according to any one of claims 1 to 6 being executed if and only if said engine speed is lower than a threshold engine speed.

8. Method (100) according to any one of the preceding claims, characterized in that the method (100) comprises a step of determining (102) a temperature of the engine, the steps of the method (100) according to any one of claims 1 to 6 being executed if and only if said temperature of the engine is greater than a threshold temperature.

9. Method (100) according to any one of the preceding claims, characterized in that the method (100) comprises a step of determining (103) an operating state of a transmission system of the vehicle, the steps of the method according to any one of claims 1 to 6 being carried out if and only if said transmission system is mechanically disconnected from the engine.

10. Method (100) according to any one of the preceding claims, characterized in that the method (100) comprises a step of determining (104) a complementary parasitic torque, the steps of the method (100) according to any one of claims 1 to 6 being executed if and only if no complementary parasitic torque is present.

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