Method and device for estimating the wear rate of a spark plug electrode

Abstract

A method for estimating a wear rate of a spark plug electrode for a spark plug (20) in which a spark discharge takes place between two electrodes by applying a voltage generated by an ignition coil (11), wherein at least one of the two electrodes is a second electrode (27) containing Pt as a main component, the method comprising a second wear rate estimation step of estimating a wear rate of the second electrode (27) in a spark discharge based on a spark discharge voltage and supply power from the ignition coil (11).

Description

FIELD OF THE INVENTIONThe present invention relates to a method and an apparatus for estimating the wear rate of a spark plug electrode.PRIOR ARTAs a technique for estimating an electrode wear rate in the spark discharge of a spark plug, JP 2014-17 153 A discloses a technique for generating a spark discharge between electrodes in atmospheric gas, decomposing light emitted by the spark discharge for each wavelength, calculating an emission intensity based on the result of a captured image, and estimating an electrode wear rate according to the correlation between emission intensities and electrode wear rates obtained in advance. DE 10 2006 011 886 A1 discloses an apparatus and a method for determining the wear of a spark plug of an internal combustion engine. JP 2009-180 157 A discloses an apparatus for estimating a length of an ignition gap of a spark plugHowever, in the above-described technique, a correlation between an emission intensity and an electrode wear rate is obtained in argon gas, so that an emission wavelength range of an electrode and an emission wavelength range of atmospheric gas do not overlap each other. Nevertheless, an electrode is subject to wear in a combustible air-fuel mixture in practice. Therefore, there is a problem in the accuracy of an estimation result based on the correlation obtained in another kind of atmospheric gas.The present invention is intended to solve the above problem, and an object of the present invention is to provide a method and an apparatus for estimating a wear rate of a spark plug electrode, which can improve the accuracy of an estimation result.SUMMARY OF THE INVENTIONTo achieve the object, a method for estimating a wear rate of a spark plug electrode according to claim 1 of the present invention includes a second wear rate estimating step of estimating a wear rate of a second electrode in one, such as a single, spark discharge based on a spark discharge voltage and supply energy from the ignition coil. The second electrode contains Pt as a main component.An apparatus for estimating a wear rate of a spark plug electrode according to claim 4 of the present invention comprises: an obtaining unit configured to obtain information on a spark discharge voltage and supply energy from the ignition coil; and a wear rate estimating unit configured to estimate a wear rate of the second electrode at a spark discharge such as a single spark discharge based on the information.According to an embodiment, a single spark discharge is meant when referring to a spark discharge.EFFECTS OF THE INVENTIONIn the method for estimating a wear rate of a spark plug electrode according to a first aspect of claim 1, a wear rate of a second electrode in a spark discharge is estimated based on a spark discharge voltage and supply energy from the ignition coil. The second electrode containing Pt as a main component is less likely to be subjected to high-temperature oxidation. Therefore, a wear rate of the second electrode is estimated based on the spark discharge voltage and supply energy from the ignition coil, thereby improving the accuracy of the estimation result.In the method for estimating the wear rate of a spark plug according to a second aspect, two electrodes are provided, and one of the two electrodes contains, as a main constituent, one of Ir, Ru, W, and Ni as a main constituent. A wear rate of this electrode upon spark discharge is estimated based on the spark discharge voltage and supply energy from the ignition coil. Therefore, each of the electrode wear rates of the first electrode and the second electrode, which are each made of different materials, can be accurately estimated in addition to the obtained effect of the first aspect.In the method for estimating the wear rate of an electrode of a spark plug according to a third aspect, an increase amount of a spark gap between the two electrodes is estimated based on the results obtained after the wear rates of the first electrode and the second electrode are estimated. An amount of increase of a spark gap length based on the wear of the first electrode and an amount of increase of a spark gap length based on the wear of a second electrode may be estimated, respectively. Therefore, an increase amount of a spark gap between the two electrodes can be accurately estimated in addition to the effect of the obtained second aspect.The electrode wear rate estimating device according to a fourth aspect or claim 4 and the electrode wear rate estimating device according to a fifth aspect or claim 5 exhibit the same effects as the effects of the first aspect or the second aspect.BRIEF DESCRIPTION OF THE DRAWINGSBoth embodiments of the invention and advantages thereof will be described below with reference to the drawings, without being limited thereto. FIG. 1 shows a schematic view of an ignition system. FIG. 2 is a view showing a waveform of an operation of the ignition system. FIG. 3 is a block diagram illustrating an apparatus for estimating an electrode wear rate according to an embodiment. FIG. 4 is a flowchart showing an estimation process of a spark gap length.EMBODIMENTS OF THE INVENTIONHereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic view of an ignition system 10, and the ignition system 10 is an apparatus for igniting a combustible air-fuel mixture in an engine (not shown), and mainly includes an ignition coil 11, a power switch 16, and a spark plug 20.The ignition coil 11 includes a primary winding 13 and a secondary winding 14 wound around a core 12. A DC power supply 15 is connected to a power receiving side of the primary winding 13, and a ground side of the primary winding 13 is grounded via the power switch 16. The secondary winding 14 is connected to a metal terminal 21 of the spark plug 20. The ECU engine control unit (ECU) 30 is connected to the power switch 16 via an output circuit (not illustrated) or the like. The ECU 30 controls a time at which the ignition coil 11 applies a voltage to the spark plug 20 and controls emission and performance of the engine.The spark plug 20 includes: a center electrode 22 electrically connected to the metal terminal 21; an insulator 24 for holding the metal terminal 21 and the center electrode 22; a metal case 25 holding the insulator 24 and grounded; and a ground electrode 26 connected to the metal case 25. In the present embodiment, a first electrode 23 (tip) is joined to the center electrode 22 containing Ni as a main component, and a second electrode 27 (tip) is joined to the ground electrode 26 containing Ni as a main component. Between the first electrode 23 and the second electrode 27 an ignition gap 28 is formed. The first electrode 23 contains one of Ir, Ru, W, and Ni as a main component. The second electrode 27 contains Pt as a main component. The main component is a component occupying 50 mass percent or more of all the components of each of the first electrode 23 and the second electrode 27.The tips joined to the center electrode 22 and the ground electrode 26 need not necessarily be provided. The spark gap 28 may be formed between the center electrode 22 and the ground electrode 26 without joining the tips thereto. In a case where no tips are attached thereto, at least a portion of the center electrode 22 and / or the ground electrode 26 where the spark discharge is caused may contain one of Ir, Ru, W, Ni, and Pt as a main component. In this case, the first electrode is formed as a portion containing one of Ir, Ru, W, and Ni as a main component, and the second electrode is formed as a portion containing Pt as a main component.In the ignition system 10, when an ignition switch 17 is turned "on" by a driver and an electric current flows through the primary winding 13 side in the ignition coil 11, the magnetic energy storage core 12 is magnetized and a magnetic field is generated around the core 12. When the primary current is interrupted by switching the power switch 16, a high voltage (for example, 10 to 30 kV) is generated in the secondary winding 14, sharing a magnetic circuit and magnetic flux with the primary winding 13.FIG. 2 illustrates a waveform of operation of the ignition system 10. when an ignition signal generated by the ECU 30 is set to "on", the power switch 16 becomes conductive and electric current flows through the primary winding 13 and magnetic energy is stored. After elapse of a charging time T 1, when the ECU 30 sets the ignition signal to "off", a high voltage is generated in the secondary winding 14, and a breakdown of the spark plug 20 occurs, and a spark discharge is generated between the first electrode 23 and the second electrode 27 due to the magnetic energy emitted by the ignition coil 11 during a time T 2 (for example, 0.5 to 2.5 ms).As described above, the ignition coil 11 supplies the magnetic energy according to an ignition signal from the ECU 30 to the ignition plug 20, and energy (supply energy) supplied from the ignition coil 11 to the ignition plug 20 in a spark discharge when the ECU 30 sets the ignition signal to "off" can be calculated according to the voltage and current (secondary voltage and secondary current) of the secondary winding 14 for the time T 2.FIG. 3 is a block diagram illustrating an apparatus for estimating an electrode wear rate. The ECU 30 is an apparatus for controlling an operating state of the engine (not shown), and is mounted on an automobile. In the present embodiment, the ECU 30 provides the functionality of the electrode wear rate estimating device. The ECU 30 includes a CPU 31, a ROM 32, and a RAM 38 connected to an input / output port 41. Various devices such as the power switch 16 are connected to the input / output terminal 41.The CPU 31 is an arithmetic operation unit for controlling each component. The ROM 32 is a non-rewritable nonvolatile memory for storing a control program (for example, a program for a flowchart illustrated in FIG. 4 ) executed by the CPU 31, various threshold values, and the like. A spark discharge voltage map 33, a supply energy map 34, an electrode temperature map 35, a first calculation equation 36, and a second calculation equation 37 are stored in the ROM 32.In the spark discharge voltage map 33, spark discharge voltages required for the spark discharge of the spark plug 20 are stored. The spark discharge voltage is different for each configuration of the spark plug 20. The spark discharge voltage is lowered when a rotation speed of the motor is low and the load of the motor is low. The spark discharge voltage is increased when there is a high speed of the motor and a high load of the motor. A spark discharge voltage is measured for each of the types of the spark plug 20 and the engine under various conditions by an experiment or the like. The spark discharge voltages are stored in advance in the spark discharge voltage map 33 to be associated with the rotational speeds of the motors and their loads. The spark discharge voltage is calculated by measuring a waveform (see FIG. 2 ) of an operation of the ignition system 10.In the supply energy map 34, supply energy from the ignition coil 11 to the spark plugs 20 is stored. The supply energy is different for each design of the spark plug 11. When the charging time T 1 (see FIG. 2 ) is extended, the supply power is increased. When the charging time T1 is shortened, the power supply is decreased. Therefore, the supply energy of the ignition coil 11 for each of the types of the spark plug 11 and the engine under various conditions is measured by an experiment or the like. The supply energy is stored in advance in the supply energy map 34 to be assigned to the rotational speeds of the motors and their loads. The supply energy is obtained by measuring a waveform (see FIG. 2 ) of an operation of the ignition system 10.In the electrode temperature map 35, temperatures (electrode temperatures) of the first electrode 23 are stored. The electrode temperature is different for each specification of the spark plug 20. When a rotation speed of the motor is low and a load on the motor is low, the electrode temperature is lowered. When a rotation speed of the motor is high and a load on the motor is high, the electrode temperature is increased. An electrode temperature is measured under various conditions for each of the types of the spark plug 20 and the engine through an experiment or the like. The electrode temperatures are stored in advance in the electrode temperature map 35 to be associated with the rotational speeds of the motors and their loads.The electrode temperature may be measured by a thermocouple embedded in the spark plug 20. For example, a hole is formed in the spark plug 20 to reach the first electrode 23, and a temperature measurement point of the thermocouple may be disposed in the first electrode 23. In addition, a hole is formed in the spark plug 20 to reach a portion near the first electrode 23, and the temperature measurement site of the thermocouple may be disposed at the tip end of the center electrode 22 near the first electrode 23. The temperature measurement site of the thermocouple may be disposed at a portion of the center electrode 22 to which the first electrode 23 is to be joined without providing the first electrode 23. An electrode temperature may be obtained such that the spark plug 20 is disposed in the engine having an observation window, an image of the first electrode 23 is taken through the observation window using an infrared camera, and a temperature distribution is measured to obtain the electrode temperature, instead of measuring an electrode temperature using a thermocouple.The first calculation equation 36 is a calculation equation for calculating a wear rate of the first electrode 23 in a spark discharge such as a single spark discharge. The first calculation equation 36 is an equation using at least three parameters that are a temperature (electrode temperature) of the first electrode 23, spark discharge voltage, and supply energy from the ignition coil 11. The first calculation equation 36 is given by an experiment or the like for each element (Ir, Ru, W, Ni, Pt) that is a main component of the first electrode 23. In the first calculation equation 36, another parameter by which the electrode wear is influenced can be set, of course, in addition to these three parameters. For example, an electrostatic capacity between the metal terminal 21 and the metal shell 25 of the spark plug 20, a flow rate in a combustion chamber of the engine, and an oxygen concentration of a combustible air-fuel mixture may be regarded as the other parameter.The second calculation equation 37 is a calculation equation for calculating a wear rate of the second electrode 27 in spark discharge. The second calculation equation 37 is an equation using at least two parameters that are a spark discharge voltage and supply energy from the ignition coil 11. The second calculation equation 37 is given by an experiment or the like. In the second calculation equation 37, of course, in addition to these two parameters, another parameter can be set by which the electrode wear is influenced. For example, an electrostatic capacity between the metal terminal 21 and the metal shell 25 of the spark plug 20, a flow rate in a combustion chamber of the engine, and an oxygen concentration of a combustible air-fuel mixture may be regarded as the other parameter. Similarly to the first calculation equation 36, a temperature of the second electrode 27 may be set as one of the parameters for the second calculation equation 37.The RAM 38 is a rewritable memory for storing various data. A first variable 39 to which a wear rate of the first electrode 23 is added in a spark discharge and a second variable 40 to which a wear rate of the second electrode 27 is added in a spark discharge are set in the RAM 38. The first variable 39 and the second variable 40 are not reset and stored in the RAM 38 until the spark plug 20 is replaced with a new one.A crank angle sensor 42 detects a rotational speed of the engine. A throttle sensor 43 detects a throttle angle of a throttle. The crank angle sensor 42 and the throttle sensor 43 each include an output circuit for outputting a detection result to the ECU 30. A load on the engine can be estimated according to a throttle angle of the throttle detected by the throttle sensor 43. A warning lamp 44 is disposed at a location where the warning lamp 44 can be seen by a driver of the motor vehicle.Examples of another input / output device 45 include an accelerator operation detection sensor for detecting an operation amount of an accelerator pedal, a cylinder pressure sensor for detecting a pressure in the combustion chamber of the engine, a water temperature sensor for detecting a temperature of cooling water in the engine, an oil temperature sensor for detecting a temperature of an engine oil, an air amount sensor for detecting an inflow amount of air into the engine, an oxygen sensor for detecting an oxygen concentration of the exhaust gas, and a vehicle speed sensor for detecting a speed of a motor vehicle. The ECU 30 may estimate, for example, a load on the engine, an amount of air in the combustion chamber, and an oxygen concentration (atmosphere) in the combustion chamber by using the detection results from the sensors.FIG. 4 is a flowchart illustrating an estimation process of a spark gap length. The spark gap length estimation process is a process for estimating an amount of increase of the spark gap 28 between the first electrode 23 and the second electrode 27. the CPU 31 repeatedly performs (for example, at intervals of 0.2 seconds) the spark gap length estimation process while the power supply to the ECU 30 is "on".In the spark gap length estimating process, the CPU 31 obtains a rotational speed of the engine according to the detection result of the crank angle sensor 42 and obtains information on a load on the engine according to the detection result from the throttle sensor 43 (S1). Subsequently, the CPU 31 obtains a spark discharge voltage using the spark discharge voltage map 33 based on the rotation speed of the motor and its load (S 2). The CPU 31 obtains supply energy from the ignition coil 11 to the spark plug 20 using the supply energy map 34 based on the rotational speed of the engine and its load (S3). The CPU 31 obtains a temperature of the first electrode 23 using the electrode temperature map 35 based on the rotation speed of the motor and its load (S 4).The CPU 31 substitutes the temperature of the first electrode 23, the supply energy, and the spark discharge voltage into the first calculation equation 36, and calculates a wear rate of the first electrode 23 upon spark discharge (S 5). Next, the CPU 31 estimates the number of discharges in a cycle time (from the start via S 1 to S 9 to a time point at which the operations return to S 1) at which the spark gap length estimation operation is performed once, based on the rotation speed of the motor, multiplies the wear rate of the first electrode 23 in a spark discharge by the number of discharges, and estimates a wear rate of the first electrode 23 in the cycle time at which the spark gap length estimation operation is performed once, and adds the estimated wear rate to the first variable 39 (S 6).Similarly, the CPU 31 substitutes the supply power and the spark discharge voltage into the second calculation equation 37, and calculates a wear rate of the second electrode 27 upon spark discharge (S 7). Next, the CPU 31 multiplies a wear rate of the second electrode 27 in a spark discharge by the number of discharges estimated from the rotational speed of the motor in the cycle time in which the spark gap length estimation process is performed once, estimates a wear rate of the second electrode 27 in the cycle time in which the spark gap length estimation process is performed once, and adds the estimated wear rate to the second variable 40 (S 8).Next, the CPU 31 converts each of the first variable 39 and the second variable 40 into a spark gap length (S 9). In the process step of S 9, spark gap lengths that increase due to the wear of the first electrode 23 and the second electrode 27 are individually estimated using estimation results of the wear rates of the first electrode 23 and the second electrode 27 because the cross-sectional areas of the first electrode 23 and the second electrode 27 are known.The CPU 31 adds an amount of increase of a spark gap length based on the wear of the first electrode 23 and an amount of increase of a spark gap length based on the wear of the second electrode 27 to each other (S 10), and determines whether or not a sum of the two spark gap lengths (amounts of increase) is larger than a threshold (S 11). The threshold is set as a spark gap length (increase amount) at which, for example, the desired emission and performance of the engine is not achieved, the engine start by the spark plug 20 is difficult, or misfire is likely when the vehicle is running.When the sum of the two spark gap lengths is larger than the threshold value as a result of the processing step of S 11 (S 11: YES), the CPU 31 turns on the warning lamp 44 to promote replacement of the spark plug 20 (S 12). Thus, it can be prevented that the desired emission and performance of the engine is not obtained, that starting of the engine becomes difficult, or that misfire easily occurs when the vehicle is running. When the spark plug 20 has been replaced with a new one, the first variable 39 and the second variable 40 are reset. When the sum of the two spark gap lengths is less than or equal to the threshold (S 11: NO), the CPU 31 returns to S 1.In the spark gap length estimation process, a wear rate of the first electrode 23 in a spark discharge is estimated using the first calculation equation 36 based on a temperature of the first electrode 23 and spark discharge voltage and supply energy from the ignition coil 11. In the first electrode 23 containing any one of Ir, Ru, W, and Ni as a main component, the electrode wear is affected by high-temperature oxidation. Therefore, by estimating a wear rate based on a temperature of the first electrode 23 and a spark discharge voltage and supply energy from the ignition coil 11, the accuracy for the result of estimating a wear rate of the first electrode 23 can be improved.A wear rate of the second electrode 27 in a spark discharge is estimated using the second calculation equation 37 based on the spark discharge voltage and supply energy from the ignition coil 11. The second electrode 27 containing Pt as a main component is less likely to be subjected to high-temperature oxidation. Therefore, a wear rate is estimated based on a spark discharge voltage and supply energy from the ignition coil 11, whereby the accuracy for the result of estimating a wear rate of the second electrode 27 can be improved. In addition, by utilizing the fact that the second electrode 27 containing Pt as a main component is less likely to be subjected to high-temperature oxidation, the temperature of the second electrode 27 is removed from the parameters for the second calculation equation 37, whereby a computational load on, for example, the CPU 31 using the second calculation equation 37 can be reduced.A wear rate of the first electrode 23 is calculated according to the first calculation equation 36. A wear rate of the second electrode 27 is calculated according to the second calculation equation 37. Therefore, each of the electrode wear rates of the first electrode 23 and the second electrode 27 each made of different materials can be accurately estimated.After the wear rates of the first electrode 23 and the second electrode 27 are individually estimated, an amount of increase of the spark gap 28 between the first electrode 23 and the second electrode 27 is estimated according to the result of the estimation of the wear rates. Since an amount of increase of a spark gap length based on wear of the first electrode 23 and an amount of increase of a spark gap length based on wear of the second electrode 27 can be respectively estimated, an amount of increase of the spark gap 28 can be accurately estimated by adding the amounts of increase of the spark gap lengths.In the flow chart of the spark gap length estimating process illustrated in FIG. 4, the process steps S1, S2, S3, and S4 correspond to a first obtaining unit recited in the claims, and the process steps S1, S2, and S3 correspond to a second obtaining unit recited in the claims. The operation step S 5 corresponds to a first wear rate estimation unit recited in the claims, and the operation step S 7 corresponds to a second wear rate estimation unit. When the first calculation equation 36 uses a parameter other than the three parameters of the temperature of the first electrode 23, spark discharge voltage, and power supply from the ignition coil 11, or when the second calculation equation 37 uses a parameter other than the two parameters of spark discharge voltage and power supply from the ignition coil 11, the ECU 30 acquires, from various input devices, information on the parameters required for the calculations.As described above, although the present invention has been described with reference to the embodiments, it is not limited to the above-described embodiments. It is readily understood that various modifications may be made without departing from the spirit of the present invention.In the present embodiment, information on a temperature of the first electrode 23 and spark discharge voltage and supply energy from the ignition coil 11 is obtained according to the detection results from the crank angle sensor 42 and the throttle sensor 43. However, the present invention is not necessarily limited thereto. Information on a temperature of the first electrode 23 and spark discharge voltage and supply energy from the ignition coil 11 can be obtained, of course, by using a sensor other than the crank angle sensor 42 and the throttle sensor 43. Examples of the other sensor include an accelerator operation detection sensor for detecting an operation amount of an accelerator pedal and a vehicle speed sensor.In the present embodiment, the ECU 30 mounted on a vehicle has a function of the electrode wear rate estimating device, and estimates wear rates of the first electrode 23 and the second electrode 27 of the spark plug 20 mounted on the engine. However, the present invention is not necessarily limited thereto. Of course, the wear rates of the first electrode 23 and the second electrode 27 can be estimated according to the method described in the embodiments when the spark plug 20 is designed, and the required sizes of the first electrode 23 and the second electrode 27 can be estimated.In this case, first, a travel distance of a vehicle to be ensured by the spark plug 20 is set, and it is estimated how the vehicle is used on the travel distance. At this time, the number of hours of each operating state of the engine in the total of an operating time of the travel route is estimated appropriately accurately. The number of hours can be estimated with improved accuracy by indicating a type of the vehicle and using an empirical rule or the like. Next, the frequency of discharge of the spark plug 20 during a time is estimated for each operating state of the engine, and further, the temperature of the first electrode 23 as well as the spark discharge voltage and the supply energy from the ignition coil 11 are estimated in each operating state.Next, the temperature of the first electrode 23 and the spark discharge voltage and the supply energy from the ignition coil 11 are substituted into the first calculation equation 36, and a wear rate of the first electrode 23 upon spark discharge is estimated, and the estimated wear rate is multiplied by the number of discharges, thereby estimating a wear rate of the first electrode 23 in time for each operation state. A wear rate of the first electrode 23 on the travel path of the vehicle to be ensured by the spark plug 20 is estimated according to the sum of the wear rates.Also, the spark discharge voltage and the supply energy from the ignition coil 11 are substituted into the second calculation equation 37, and a wear rate of the second electrode 27 at a spark discharge is estimated, and the estimated wear rate is multiplied by the number of discharges, thereby estimating a wear rate of the second electrode 27 in a time for each operation state. A wear rate of the second electrode 27 on the travel path of the vehicle to be ensured by the spark plug 20 is estimated according to the sum of the wear rates.When the spark plug 20 is designed using the wear rates of the first electrode 23 and the second electrode 27 thus estimated, the required sizes of the first electrode 23 and the second electrode 27 can be estimated by multiplying the wear rates by a safety factor, respectively. Thus, it is not necessary that the spark plug 20 ensuring the travel distance of a vehicle have the first electrode 23 and the second electrode 27 that are excessively large. Accordingly, with secured quality of the spark plug 20, the material of the first electrode 23 and the second electrode 27 can be reduced, which contributes to resource saving.In the present embodiment, the first electrode 23 containing one of Ir, Ru, W, or Ni as a main component is disposed on the center electrode 22 side of the spark plug 20, and the second electrode 27 containing Pt as a main component is disposed on the ground electrode 26 side of the spark plug. However, the present invention is not necessarily limited thereto. The second electrode 27 containing Pt as a main component may be naturally disposed on the center electrode 22 side of the spark plug 20, and the first electrode 23 containing one of Ir, Ru, W, and Ni as a main component may be disposed on the ground electrode 26 side of the spark plug.In the present embodiment, in a spark plug 20, both the first electrode 23 containing one of Ir, Ru, W, or Ni as a main component and the second electrode 27 containing Pt as a main component are arranged. However, the present invention is not necessarily limited thereto. As described in the embodiments, even if any one of the first electrode 23 and the second electrode 27 is disposed in the spark plug 20, the same effect can be obtained because a wear rate of the first electrode 23 and a wear rate of the second electrode 27 can be individually estimated.In the present embodiment, the ECU 30 estimates both a wear rate of the first electrode 23 and a wear rate of the second electrode 27. Of course, even if the spark plug 20 is designed, only a wear rate of the first electrode 23 or only a wear rate of the second electrode 27 can be estimated.DESCRIPTION OF THE REFERENCE NUMERALS11 Ignition coil 20 Ignition plug 23 First electrode (electrode) 27 Second electrode (electrode) 28 Spark gap 30 ECU (electrode wear rate estimating device)

Claims

A method for estimating a wear rate of a spark plug electrode for a spark plug (20) in which spark discharge occurs between two electrodes by applying a voltage generated by an ignition coil (11), at least one of the two electrodes being a second electrode (27) containing Pt as a main component, the method comprising a second wear rate estimating step of estimating a wear rate of the second electrode (27) in spark discharge based on a spark discharge voltage and supply energy from the ignition coil (11).The method for estimating a wear rate of a spark plug electrode for a spark plug (20) according to claim 1, wherein the other of the two electrodes is a first electrode (23) containing one of Ir, Ru, W and Ni as a main component, the method comprising a first wear rate estimating step of estimating a wear rate of the first electrode (23) in a spark discharge based on a temperature of the first electrode (23) and spark discharge voltage and supply energy from the ignition coil (11).The method for estimating the wear rate of a spark plug electrode according to claim 2, further comprising: a spark gap length estimating step for estimating an amount of increase of a spark gap (28) between the two electrodes based on results obtained after the wear rates of the first electrode (23) and the second electrode (27) are estimated in the first wear rate estimating step and the second wear rate estimating step.An apparatus (30) for estimating a wear rate of a spark plug electrode for a spark plug (20) in which spark discharge occurs between two electrodes by applying a voltage generated by an ignition coil (11), the apparatus comprising: a second electrode (27) which is at least one of the two electrodes and which contains Pt as a main component; a second obtaining unit (S1 to S3) configured to obtain information on a spark discharge voltage and supply energy from the ignition coil (11); and a second wear rate estimating unit (S7) configured to estimate a wear rate of the second electrode (27) in spark discharge based on the information.The apparatus (30) for estimating a wear rate of a spark plug electrode for a spark plug (20) according to claim 4, the apparatus further comprising: a first electrode (23) which is the other of the two electrodes and which contains one of Ir, Ru, W, and Ni as a main component; a first obtaining unit (S1 to S4) configured to obtain information on a temperature of the first electrode (23) and spark discharge voltage and supply energy from the ignition coil (11); and a first wear rate estimating unit (S5) configured to estimate a wear rate of the first electrode (23) at a spark discharge based on the information.

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