METHOD FOR MEASURING THE 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 the compression ratio of an engine cylinder and applying a correction to a combustion process, comprising the steps of: Determining 105 an intake pressure in the 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 near bottom dead center and 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 to 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 abbreviation: Single Figure.

Description

Title of the invention: METHOD FOR MEASURING THE 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 the compression ratio of a vehicle engine cylinder and applying a correction to a combustion process occurring in said engine cylinder. The invention is particularly applicable 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 greater the thermodynamic efficiency of the engine.

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

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

[0005] In gasoline engines, when manufacturing specifications are not met and the compression ratio is too high, auto-ignition occurs during the expansion phase. This auto-ignition 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 sense, to a method for measuring the compression ratio of a cylinder of an engine of a vehicle and application of a correction to a combustion process, the process comprising the steps, executed by an engine control unit of said vehicle, consisting of: • Determine an intake pressure in an intake of a combustion chamber of said cylinder; • Determine, via mapping, based on the said determined intake pressure and a nominal compression ratio, a nominal compression value; • Determine an instantaneous rotational speed of a crankshaft of said cylinder close to bottom dead center; • Determine an instantaneous rotational speed of said crankshaft close to top dead center; • Determine an actual compression ratio as a function of the said instantaneous rotational 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 constituent elements of the engine cylinder generate a compression ratio that is too high, the method according to the invention is able to detect it, and then apply a correction to the combustion process that occurs in the cylinder, for example by applying an offset when the cylinder is fired.

[0009] In addition to the characteristics mentioned in the preceding paragraph, the process according to the invention may have one or more additional characteristics from among the following, considered individually or according to all technically possible combinations.

[0010] According to a non-limiting embodiment 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 embodiment of the invention, 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, to which is multiplied the subtraction of 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 during the ignition of the cylinder.

[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 less than the first threshold or greater than the second threshold, the method includes a step, executed by vehicle display means, 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 embodiment of the invention, the method includes a step of determining an engine speed, the steps of the method according to any of the aforementioned aspects of the invention being executed if and only if said engine speed is less than a threshold engine speed, formed by an idle speed.

[0017] According to a non-limiting embodiment of the invention, the method includes a step of determining an engine temperature, the steps of the method according to any of the aforementioned aspects of the invention being carried out if and only if said engine temperature is above a threshold temperature.

[0018] According to a non-limiting embodiment of the invention, the method comprises a step of determining an operating state of a vehicle transmission system, the steps of the method according to any 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 includes a step of determining a complementary parasitic torque, the steps of the method according to any of the aforementioned aspects of the invention being carried out if and only if no complementary parasitic torque is present.

[0020] This complementary parasitic couple can, for example, be generated by: • The operation of an air conditioning system; • A current value from a current surge generated by an alternator that exceeds a threshold current value; and / or • The operation of power steering.

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

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

[0023] The figure is presented for illustrative purposes only and is in no way limiting of the invention.

[0024] Figure 1 illustrates the steps of a method 100 for measuring the compression ratio of a cylinder in a vehicle engine, particularly a motor vehicle, and for applying a correction to a combustion process occurring in said cylinder. It should be noted that when the vehicle has several cylinders, the method 100 is applied to each of the cylinders.

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

[0026] According to a non-limiting embodiment, process 100 comprises the steps of: • Determine 101 an engine speed; • Determine 102, a temperature of the engine; • 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 a complementary parasitic torque, the complementary parasitic torque being able to be formed by the operation of the air conditioning system, a current value of a current inrush generated by an alternator greater than a threshold current value, and / or the operation of a power steering system.

[0027] According to this non-limiting embodiment, steps 105 to 112 of the following process 100 are performed if and only if: • The engine speed is below a threshold engine speed corresponding to an engine idle, 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 off; • The current value is less than a threshold current value, for example 5A; and • The power steering is off.

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

[0029] It should be noted 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 able to measure the intake pressure of the combustion chamber and then transmit this measurement to the engine control unit. The engine control unit then determines the intake pressure in the combustion chamber.

[0030] The method 100 further includes a step of determining 106, via a map, based on the determined intake pressure and a nominal compression ratio, a nominal compression value. This map can be stored in the engine control unit.

[0031] The method 100 also includes a step of determining 107, an instantaneous rotational speed of a crankshaft of the cylinder near bottom dead center. According to a non-limiting embodiment, 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°.

[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 fixed to the crankshaft and have teeth. Thus, for example, at 110°, the position sensor determines the time required for two adjacent teeth to pass this angle. Based on this time, the position sensor can deduce the instantaneous rotational speed of the crankshaft near bottom dead center and then transmit it to the engine control unit. The engine control unit then determines the instantaneous rotational speed of the crankshaft near bottom dead center.

[0033] The method 100 also includes a step 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 rotational speed of the crankshaft near 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 this angle. Based on this time, the position sensor can deduce the instantaneous rotational speed of the crankshaft near top dead center and then transmit it to the engine control unit. The engine control unit then determines the instantaneous rotational speed of the crankshaft near top dead center.

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

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

[0038] The process 100 also includes a step of determining 110 a ratio of the actual compression ratio and the nominal compression value. In other words, the ratio = actual compression ratio / nominal compression value.

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

[0040] According to a non-limiting embodiment 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 a shift during the 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 when injecting fuel into the cylinder.

[0043] According to a non-limiting embodiment, when the ratio is below the first threshold or above the second threshold, the method 100 includes a step, performed by vehicle display means, of displaying 112 information reflecting a critical compression ratio. Thus, the driver can take their vehicle to the service center to have the compression ratio checked.

Claims

Demands

1. A method (100) for measuring the compression ratio of a cylinder of a vehicle engine and applying a correction to a combustion process, said method (100) comprising the steps, executed by an engine control unit of said vehicle, of: - Determining (105) an intake pressure in an intake of a combustion chamber of said cylinder; - Determining (106), via mapping, 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 near bottom dead center; - Determining (108) an instantaneous rotational speed of said crankshaft near 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 higher 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. A 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, to which is multiplied the subtraction of the rotational speed instantaneous crankshaft speed near top dead center to the instantaneous crankshaft rotation speed near bottom dead center.

4. A method (100) according to any one of the preceding claims, characterized in that the correction is applied by applying: - A delay when the cylinder is fired; - Or a delay when fuel is injected into the cylinder.

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

6. A method (100) according to any one of the preceding claims, characterized in that: - 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°.

7. A 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 carried out if and only if said engine speed is less than a threshold engine speed.

8. A method (100) according to any one of the preceding claims, characterized in that the method (100) comprises a step of determining (102) a motor temperature, the steps of the method (100) according to any one of claims 1 to 6 being carried out if and only if said motor temperature is above a threshold temperature.

9. A 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 vehicle transmission system, 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. A 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 carried out if and only if no complementary parasitic torque is present.