Method for measuring a compression ratio of an engine cylinder of a vehicle and for applying a correction to a combustion process

Abstract

The invention relates to a method (100) which comprises the steps that consist in: - determining (105) an intake pressure in an intake of a combustion chamber; - determining (106), as a function of the intake pressure, a value representative of a nominal compression torque (CPTnom); - determining (107, 108) instantaneous rotational speeds of a crankshaft near a bottom dead centre of an intake phase and a combustion top dead centre; - determining (109) a value representative of an actual compression torque (CPTréel) as a function of the instantaneous rotational speeds; - determining (110) a ratio (R) equal to the value representative of the actual compression torque (CPTréel) / value representative of the nominal compression torque (CPTnom); and - if the ratio (R) is outside a range, applying (111) a correction to the combustion process.

Description

DESCRIPTION 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 heavily on the compression ratio of each cylinder in the engine. The compression ratio of a cylinder is the ratio between the cylinder volume when the piston is at bottom dead center in the intake phase (bottom dead center, which occurs 180° before top dead center), and the cylinder volume when the piston is at top dead center. The higher the compression ratio, the higher the thermodynamic efficiency of the engine.

[0003] The position of the top dead center of combustion as well as the position of the bottom dead center of an intake phase, 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 components that make up an engine cylinder, it is difficult to obtain a stable and relatively undispersed compression ratio across a plurality of engine cylinders.

[0005] In 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 the 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 a compression ratio of a cylinder of a vehicle engine 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, as a function of said determined intake pressure, a value representative of a nominal compression torque; Determine an instantaneous rotation speed of a crankshaft of said cylinder close to a bottom dead center of an intake phase; Determine an instantaneous rotation speed of said crankshaft close to a top dead center of combustion; Determine, as a function of said instantaneous rotation speeds of said crankshaft close to the top dead center of combustion and close to the bottom dead center of a given intake phase, a value representative of an actual compression torque; Determine a ratio equal to said representative value of the actual compression torque / representative value of the nominal compression torque If said ratio is outside an interval delimited by 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 apply a correction to the combustion process that occurs in the cylinder, for example by applying a lag when firing 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 additional 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 representative value of the nominal compression torque; The second threshold is between 105% and 115% of the representative value of the nominal compression torque.

[0011] According to a non-limiting implementation of the invention, the representative value of an actual compression torque is equal to the sum of the instantaneous rotation speeds of the crankshaft close to the top dead center of combustion and close to the bottom dead center of an intake phase, to which sum is multiplied the subtraction of the instantaneous rotation speed of the crankshaft close to the top dead center of combustion from the instantaneous rotation speed of the crankshaft close to the bottom dead center of an intake phase.

[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 the bottom dead center of an intake phase is determined when the position crankshaft angular displacement is between 100° and 140° before top dead center of combustion; The instantaneous crankshaft rotational speed near top dead center is determined when the angular position of the crankshaft is between 0° and 15° before top dead center.

[0016] According to a non-limiting implementation of the invention, the method comprises a step consisting 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 consisting 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 consisting 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 consisting of determining a complementary parasitic couple, 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 couple is present.

[0020] This complementary parasitic torque can for example be generated by: How an air conditioning system works; A current value of a current draw 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 by reading the following description and examining the accompanying figure.

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

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

[0024] Figure 1 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.

[0025] The compression ratio is the ratio between the cylinder volume when the piston is at bottom dead center of the intake phase (bottom dead center which occurs 180° before top dead center of combustion), and the cylinder volume when the piston is at top dead center of combustion. In a four-stroke cycle, the crankshaft makes two revolutions to complete the cycle. Each half-turn of the engine corresponds to a phase, respectively intake, compression, combustion (or expansion) and exhaust. The cycle thus described begins when the piston is at top dead center 'crossover'.

[0026] It should be noted that when the vehicle has several cylinders, the method 100 applies to each of the cylinders. Steps 101 to 111 of the method 100 according to the invention are for example executed by an engine computer.

[0027] 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; Determining 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 call generated by a alternator above a threshold current value, and / or the operation of power steering.

[0028] 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 The power steering is off.

[0029] The method 100 comprises a step of determining 105 an intake pressure in an intake of a combustion chamber of the cylinder.

[0030] It is worth remembering 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 pressure at the combustion chamber intake and then transmit this measurement to the engine control unit. The engine control unit then determines the intake pressure in the combustion chamber.

[0031] The method 100 further comprises a step consisting of determining 106, via a map, as a function of the determined intake pressure, a value representative of a nominal compression torque CPTnom. This map can be formed by a table which establishes the correspondence between intake pressure values ​​which have been determined and values ​​representative of a nominal compression torque CPTnom. This map can be recorded in the engine computer.

[0032] The representative value of a nominal compression torque CPTnom corresponds to the real compression torque value CPT that can be measured when the measured engine has a nominal compression ratio.

[0033] 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 of an intake phase. According to a non-limiting embodiment, the instantaneous rotational speed of the crankshaft close to the bottom dead center of an intake phase is determined when the angular position of the crankshaft is between 100° and 140° before the top dead center of combustion.

[0034] 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° before the top dead center of combustion, 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 of an intake phase 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 of an intake phase.

[0035] The method OO also includes a step of determining 108, an instantaneous rotational speed of the crankshaft of the cylinder close to a top dead center of combustion.

[0036] According to a non-limiting embodiment, the instantaneous rotational speed of the crankshaft close to the combustion top dead center is determined when the angular position of the crankshaft is between 0° and 15° before the combustion top dead center. Thus, for example at 10° before the combustion top dead center, 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 the combustion 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 the combustion top dead center.

[0037] The method OO also comprises a step consisting of determining 109, as a function of the instantaneous rotation speed of the crankshaft close to the bottom dead center of a determined intake phase and the instantaneous rotation speed of the crankshaft close to the determined top dead center of combustion, a value representative of an actual compression torque CPTreal.

[0038] According to a non-limiting embodiment, the representative value of an actual compression torque CPTreal = (instantaneous rotation speed of the crankshaft close to the determined top dead center of combustion + instantaneous rotation speed of the crankshaft close to the bottom dead center of a determined intake phase) * (instantaneous rotation speed of the crankshaft close to the bottom dead center of a determined intake phase - instantaneous rotation speed of the crankshaft close to the determined top dead center of combustion).

[0039] The method 100 also comprises a step consisting of determining 110 a ratio R equal to the representative value of the actual compression torque CPTreal / representative value of the nominal compression torque CPTnom.

[0040] If the determined ratio R is outside an interval delimited by a first threshold and a second threshold higher than said first threshold, the method 100 comprises a step consisting of applying 111 a correction to the combustion process of the cylinder.

[0041] According to a non-limiting implementation of the invention, The first threshold is between 85% and 95% of the representative value of the nominal compression torque CPTnom; The second threshold is between 105% and 115% of the representative value of the nominal compression torque CPTnom.

[0042] In other words, in the invention, we seek a value representative of the nominal compression torque CPTnom and a value representative of the actual compression torque CPTréel to deduce a ratio R. More particularly, the ratio R is equal to the value representative of the actual compression torque CPTréel / value representative of the nominal compression torque CPTnom. This ratio R is also equal to an actual compression ratio / a nominal compression ratio of the cylinder. Depending on the value of this ratio R, we are able to apply, or not, a correction to the combustion process that occurs in the cylinder.

[0043] In other words, thanks to the method according to the invention, a correction is applied if it is detected that the ratio R is outside the interval between the first threshold and the second threshold, without it being necessary to directly determine the actual compression ratio, a value which is almost impossible to determine. This is made possible by the fact that the ratio CTPréel / CPTnom is equal to the actual compression ratio / nominal compression ratio.

[0044] 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.

[0045] 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.

[0046] According to a non-limiting embodiment, when the ratio R 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. A method (100) of 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, performed by an engine computer of said vehicle, consisting of: - Determine (105) an intake pressure in an intake of a combustion chamber of said cylinder; - Determine (106), via a map, as a function of said determined intake pressure, a value representative of a nominal compression torque (CPTnom); - Determine (107) an instantaneous rotation speed of a crankshaft of said cylinder close to a bottom dead center of an intake phase; - Determine (108) an instantaneous rotation speed of said crankshaft close to a top dead center of combustion; - Determine (109), as a function of said instantaneous rotation speeds of said crankshaft close to the top dead center of combustion and close to the bottom dead center of a determined intake phase, a value representative of an actual compression torque (CPTreal); - Determine (110) a ratio (R) equal to said representative value of the actual compression torque (CPTreal) / representative value of the nominal compression torque (CPTnom); - If said ratio (R) is outside an interval delimited by 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 representative value of the nominal compression torque (CPTnom); The second threshold is between 105% and 115% of the representative value of the nominal compression torque (CPTnom). [Claim s] Method (100) according to any one of the preceding claims, characterized in that the representative value of an actual compression torque (CPTreal) is equal to the sum of the instantaneous rotation speeds of the crankshaft close to the top dead center of combustion and close to the bottom dead center of an intake phase to which sum is multiplied the subtraction of the instantaneous rotation speed of the crankshaft close to the top dead center of combustion from the instantaneous rotation speed of the crankshaft close to the bottom dead center of an intake phase.

4. Method (100) according to any one of the preceding claims, characterized in that the correction is applied by applying: - A lag when igniting the cylinder; - A lag when injecting fuel into the cylinder. [Claim s] Method (100) according to any one of the preceding claims, characterized in that when the ratio (R) 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. [Claim s] Method (100) according to any one of the preceding claims, characterized in that: - The instantaneous rotation speed of the crankshaft near the bottom dead center of an intake phase is determined when the angular position of the crankshaft is between 100° and 140° before the top dead center of combustion; - The instantaneous rotational speed of the crankshaft near the top dead center of combustion is determined when the angular position of the crankshaft is between 0° and 15° before top dead center of combustion.

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. [Claim s] 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 executed 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.

Images