Oil condition estimation device and oil condition estimation method

Abstract

To easily and inexpensively estimate the density of oil.SOLUTION: The oil condition estimation device 30 includes the first acquisition section 321 that acquires the pressure P of the oil E stored in the oil pan 10 from the pressure sensor 12 provided on the bottom surface B of the oil pan 10 of the internal combustion engine, the second acquisition section 322 that acquires the distance H between the bottom surface B and the liquid surface T of the oil E from the level sensor 13 provided in the oil pan 10, and the calculation section 324 that calculates the density ρ of the oil E based on the pressure P and the distance H.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an oil state estimating device and an oil state estimating method. [Background technology]

[0002] The oil tester of Patent Document 1 determines that the oil has deteriorated when the propagation rate of ultrasonic waves propagated through oil poured into a measurement oil tank is low. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-127067 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when measuring the density of oil using the oil tester of Patent Document 1, it is necessary to measure the ultrasonic wave propagation rate after transferring the oil from an engine or other device to a measurement oil tank, which is time-consuming. Furthermore, the oscillator for generating ultrasonic waves is expensive, which increases the cost of the measurement.

[0005] The present invention has been made in consideration of these points, and has as its object to estimate the density of oil simply and inexpensively. [Means for solving the problem]

[0006] An oil state estimating device according to a first aspect of the present invention includes a first acquisition unit that acquires the pressure of oil stored in an oil pan of an internal combustion engine from a pressure sensor provided on the bottom surface of the oil pan, a second acquisition unit that acquires the distance between the bottom surface and the oil liquid level from a level sensor provided on the oil pan, and a calculation unit that calculates the density of the oil based on the pressure and the distance.

[0007] The device may further include an estimation unit that estimates that the oil condition is abnormal if a density difference indicating the difference between a first density calculated by the calculation unit at a first time and a second density calculated by the calculation unit at a second time after the first time is equal to or greater than a threshold value.

[0008] The estimation unit may estimate that the oil has deteriorated when the density difference is equal to or greater than the threshold value and the first density is smaller than the second density.

[0009] The estimation unit may estimate that the oil has been diluted by fuel injected into the internal combustion engine when the density difference is equal to or greater than the threshold value and the first density is greater than the second density.

[0010] The estimation unit may set the threshold value to be smaller as the distance traveled by a mobile body including the internal combustion engine after the oil stored in the oil pan has been changed increases.

[0011] The calculation unit may calculate the first density when a change of the oil stored in the oil pan is detected.

[0012] The calculation unit may calculate, as the second density, a statistical quantity of the second densities calculated for each second period that is longer than a predetermined first period.

[0013] The calculation unit may calculate at least one of the first density and the second density during a period from a timing at which an operation to start the internal combustion engine is received to a timing immediately before the internal combustion engine begins to start.

[0014] The internal combustion engine may further include a notification unit that notifies a user of the internal combustion engine that the estimation unit has estimated that the state of the oil is abnormal.

[0015] The calculation unit may further include an estimation unit that calculates the weight of the oil based on the pressure of the oil and the cross-sectional area of ​​the oil pan corresponding to the position of the oil level, and estimates that a malfunction has occurred in the internal combustion engine if a subtraction value obtained by subtracting a second weight of the oil calculated by the calculation unit at a second time after the first time from a first weight of the oil calculated by the calculation unit at a first time is equal to or greater than a threshold value.

[0016] The calculation unit may calculate the weight of the oil during a period from a timing when a predetermined time has elapsed since the internal combustion engine stopped to a timing immediately before the internal combustion engine starts to start.

[0017] The engine may further include a notification unit that notifies a user of the internal combustion engine that the estimation unit has estimated that a failure has occurred in the internal combustion engine.

[0018] An oil state estimation method according to a second aspect of the present invention includes a first acquisition step executed by a processor to acquire the pressure of oil stored in an oil pan of an internal combustion engine from a pressure sensor provided on the bottom surface of the oil pan, a second acquisition step to acquire the distance between the bottom surface and the oil liquid level from a level sensor provided on the oil pan, and a calculation step to calculate the density of the oil based on the pressure and the distance. [Effects of the Invention]

[0019] The present invention provides the advantage of being able to estimate the density of oil simply and inexpensively. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing an overview of an oil state estimation system S according to an embodiment of the present invention. [Figure 2] 10 is a diagram illustrating an operation for estimating an abnormality in the state of oil E. FIG. [Figure 3] FIG. 10 is a diagram illustrating an operation of estimating a fault in an internal combustion engine. DETAILED DESCRIPTION OF THE INVENTION

[0021] <Outline of Oil Condition Estimation System S> FIG. 1 is a diagram showing an overview of an oil state estimation system S according to this embodiment. The oil state estimation system S shown in FIG. 1 includes an oil pan 10, a strainer 11, a pressure sensor 12, a level sensor 13, a control device 20, a display device 21, a sound output device 22, and an oil state estimation device 30. The oil state estimation system S has a function of estimating whether or not the state of oil E in an internal combustion engine is abnormal based on the density ρ of the oil E, and notifying the user of the internal combustion engine if an abnormality is estimated. Abnormalities in the state of oil E include, for example, deterioration of the oil E and dilution of the oil E by fuel. The user is, for example, the driver of a moving object when the internal combustion engine is mounted on the moving object such as a vehicle.

[0022] The oil pan 10 is a tank provided below the internal combustion engine that stores the oil E circulating within the engine. The strainer 11 is a filter provided at the tip of the suction port of an oil pump (not shown) that sucks the oil E stored in the oil pan 10 and supplies it to the internal combustion engine, and serves as a filter for filtering the oil E. The pressure sensor 12 is provided on the bottom surface B of the oil pan 10 and is a sensor that detects the pressure of the oil E stored in the oil pan 10. The level sensor 13 is provided inside the oil pan 10 and is a sensor that detects the distance H between the bottom surface B of the oil pan 10 and the liquid level T of the oil E.

[0023] The control device 20 is a device including a processor such as a CPU (Central Processing Unit) or an ECU (Electronic Control Unit), and is a device that controls the operation of the internal combustion engine. The control device 20 starts or stops the internal combustion engine, for example, by accepting an operation from a user. The display device 21 is, for example, a display. The sound output device 22 is, for example, a speaker.

[0024] The oil state estimation device 30 calculates the density ρ of the oil E based on the pressure P of the oil E detected by the pressure sensor 12 and the distance H detected by the level sensor 13. By operating in this manner, the oil state estimation device 30 can easily calculate the density ρ without transferring the oil E to a container outside the oil pan 10. Furthermore, because the oil state estimation device 30 calculates the density ρ without using ultrasonic waves generated by the vibrator, it can calculate the density ρ inexpensively. Then, the oil state estimation device 30 estimates whether the state of the oil E is abnormal based on the calculated density ρ, and if it estimates that the oil E is abnormal, it notifies the user.

[0025] <Configuration of the oil state estimating device 30> 1, the oil state estimating device 30 has a memory unit 31 and a control unit 32. The control unit 32 has a first acquisition unit 321, a second acquisition unit 322, a third acquisition unit 323, a calculation unit 324, an estimation unit 325, and a notification unit 326.

[0026] The storage unit 31 has a storage medium such as a read-only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), or a solid state drive (SSD). The storage unit 31 stores a program executed by the control unit 32 and various information used by the oil condition estimating device 30 to estimate the condition of the oil E.

[0027] The control unit 32 is a processor such as a CPU or an ECU. The control unit 32 executes a program stored in the storage unit 31 to function as a first acquisition unit 321, a second acquisition unit 322, a third acquisition unit 323, a calculation unit 324, an estimation unit 325, and a notification unit 326. The control unit 32 may be configured with one processor, or may be configured with multiple processors or a combination of one or more processors and an electronic circuit.

[0028] The first acquisition unit 321 acquires the pressure P of the oil E stored in the oil pan 10 from a pressure sensor 12 provided on the bottom surface B of the oil pan 10 of the internal combustion engine. The second acquisition unit 322 acquires the distance H between the bottom surface B and the liquid surface T of the oil E (the position of the liquid surface T) from a level sensor 13 provided on the oil pan 10.

[0029] The third acquisition unit 323 acquires various information from the control device 20. For example, the third acquisition unit 323 acquires from the control device 20 replacement information indicating that the oil E has been replaced with new oil E. By acquiring the replacement information, the calculation unit 324 can calculate the density ρ of the oil E immediately after the oil E is replaced with new oil E. If the internal combustion engine is mounted on a mobile object such as a vehicle, the third acquisition unit 323 may acquire distance information indicating the travel distance of the mobile object or time information indicating the travel time of the mobile object, instead of the replacement information. By acquiring the distance information or time information, the calculation unit 324 can estimate the timing of the replacement with new oil E based on the travel distance or travel time of the mobile object, and calculate the density ρ at that timing.

[0030] The third acquisition unit 323 acquires, for example, timing information indicating the start timing for starting the internal combustion engine or the stop timing for stopping the internal combustion engine from the control device 20. The start timing is, for example, the timing at which an operation to start the internal combustion engine is received from a user of the internal combustion engine, and the stop timing is, for example, the timing immediately after the piston stops. By acquiring the timing information, the calculation unit 324 can calculate the density ρ at an appropriate timing.

[0031] The calculation unit 324 calculates the density ρ of the oil E based on the pressure P acquired by the first acquisition unit 321 and the distance H acquired by the second acquisition unit 322. The density ρ can be expressed as in equation (1) using the pressure P and the distance H. The constant g is the gravitational acceleration (9.80665 m / s 2 ) is shown.

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[0032] The calculation unit 324 calculates a first density of the oil E (hereinafter referred to as "density ρ1") when a change of the oil E stored in the oil pan 10 is detected. For example, the calculation unit 324 detects a change of the oil E when the third acquisition unit 323 acquires change information, and calculates the density ρ1. The calculation unit 324 may calculate the density ρ1 when a difference between a travel distance included in distance information acquired by the third acquisition unit at the current time and a travel distance included in distance information acquired when the density ρ1 was calculated before the current time is equal to or greater than a predetermined distance. The calculation unit 324 may calculate the density ρ1 when a difference between a travel time included in time information acquired by the third acquisition unit at the current time and a travel time included in time information acquired when the density ρ1 was calculated before the current time is equal to or greater than a predetermined time.

[0033] The calculation unit 324 calculates a second density of the oil E (hereinafter referred to as "density ρ2") in a predetermined first period from the timing at which the density ρ1 is calculated. The predetermined first period is, for example, one day. The calculation unit 324 may calculate, as the density ρ2, a statistical amount of multiple densities ρ2 calculated for each first period in a second period that is longer than the predetermined first period. When the first period is one day, the second period is, for example, one week. The statistical amount is, for example, an average value or a median value. By operating in this manner, the calculation unit 324 can improve the accuracy of calculating the density ρ2.

[0034] If the internal combustion engine is mounted on a moving body such as a vehicle, when the moving body is traveling on a rough road or when the moving body is suddenly accelerated or decelerated, the height and gradient of the oil liquid surface T change, which may reduce the accuracy of calculating the density ρ of the oil E. Therefore, the calculation unit 324 may calculate at least one of the density ρ1 and the density ρ2 during the period from the timing when an operation to start the internal combustion engine is received to the timing immediately before the internal combustion engine begins to start.

[0035] For example, when the third acquisition unit 323 acquires timing information indicating the start timing, the calculation unit 324 causes the first acquisition unit 321 to acquire the pressure P of the oil E and the second acquisition unit 322 to acquire the distance H. The calculation unit 324 then calculates the density ρ of the oil E based on the acquired pressure P and distance H. Because an internal combustion engine is started using a starter motor after receiving a start operation, by operating as described above, the calculation unit 324 can calculate the density ρ while the starter motor is operating (i.e., before the internal combustion engine starts). As a result, the calculation unit 324 can improve the accuracy with which it calculates the density ρ.

[0036] The calculation unit 324 may calculate the weight W of the oil E stored in the oil pan 10, in addition to the density ρ of the oil E. The calculation unit 324 calculates the weight W of the oil E, for example, based on the pressure P of the oil E and the cross-sectional area A of the oil pan 10 corresponding to the position of the liquid level T of the oil E. The cross-sectional area A is stored in the memory unit 31. The weight W can be expressed as in equation (2) using the distance H, the cross-sectional area A, and the density ρ. Then, the weight W can be expressed as in equation (3) using equations (1) and (2).

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[0037] Because oil E circulates within the internal combustion engine while the internal combustion engine is running, the weight W of oil E stored in the oil pan 10 is smaller than when the internal combustion engine is stopped. Furthermore, immediately after the internal combustion engine is stopped, some of the oil E adheres to various parts of the internal combustion engine, making it impossible to calculate the weight W correctly. Therefore, the calculation unit 324 may calculate the weight W of oil E from the timing when a predetermined time has elapsed since the internal combustion engine was stopped to the timing immediately before the internal combustion engine begins to start. The predetermined time is, for example, three hours.

[0038] For example, the calculation unit 324 detects that a predetermined time has elapsed since the third acquisition unit 323 acquired timing information indicating the stop timing, and that the third acquisition unit 323 has not acquired timing information indicating the start timing. At the time of this detection, the calculation unit 324 causes the first acquisition unit 321 to acquire the pressure P, and calculates the weight W using the pressure P. By operating in the above manner, the calculation unit 324 can improve the accuracy of calculating the weight W of the oil E.

[0039] The cross-sectional area A of the oil pan 10 may vary depending on the distance from the bottom surface B. Therefore, the calculation unit 324 may identify the cross-sectional area A corresponding to the distance H detected by the second acquisition unit 322 and calculate the weight W based on the cross-sectional area A and the pressure P. The calculation unit 324 identifies the cross-sectional area A corresponding to the distance H and calculates the weight W by, for example, referring to a cross-sectional area table stored in the storage unit 31. The cross-sectional area A included in the cross-sectional area table stored in the storage unit 31 is, for example, a division value obtained by dividing each volume of the oil pan 10 corresponding to each distance in the height direction from the bottom surface B by the respective distance. By operating in the above manner, the calculation unit 324 can calculate the weight W of the oil E with high accuracy regardless of the shape of the oil pan 10.

[0040] The estimation unit 325 estimates that the state of the oil E is abnormal when a density difference indicating the difference between the density ρ1 calculated by the calculation unit 324 at a first time and the density ρ2 calculated by the calculation unit 324 at a second time after the first time is equal to or greater than a first threshold. The first time is the timing at which a change of the oil E stored in the oil pan 10 is detected, and the second time is a time at a predetermined cycle from the timing at which the density ρ1 is calculated. The first threshold may be a fixed value stored in the storage unit 31, or may be a predetermined percentage of the density ρ1 (for example, 10%).

[0041] For example, if the density difference is equal to or greater than the first threshold value and the density ρ1 is smaller than the density ρ2, the estimation unit 325 estimates that the oil E has deteriorated due to the evaporation of substances contained in the oil E or the oxidation of the oil E. For example, if the density difference is equal to or greater than the first threshold value and the density ρ1 is larger than the density ρ2, the estimation unit 325 estimates that the oil E has been diluted by the fuel injected into the internal combustion engine. By operating as described above, the estimation unit 325 can estimate the type of abnormality in the state of the oil E.

[0042] The estimation unit 325 may set the first threshold value smaller the longer the distance traveled by the mobile body equipped with an internal combustion engine after changing the oil E stored in the oil pan 10. The estimation unit 325 may set the first threshold value smaller the longer the time that has elapsed since the oil E stored in the oil pan 10 was changed. By operating in this manner, the estimation unit 325 becomes more likely to estimate that the state of the oil E is abnormal the longer the distance traveled or the time that has elapsed since detecting the change of the oil E, and therefore, it is possible to more easily prompt the driver to change the oil E.

[0043] The estimation unit 325 may estimate that a malfunction has occurred in the internal combustion engine when a subtraction value obtained by subtracting a second weight of oil calculated by the calculation unit 324 at a second time after the first time from a first weight of oil E calculated by the calculation unit 324 at a first time is equal to or greater than a second threshold value. The second threshold value may be a fixed value stored in the memory unit 31, or may be a predetermined percentage (e.g., 10%) of the first weight. By operating in this manner, the estimation unit 325 can estimate whether or not a malfunction of the internal combustion engine is causing consumption of oil E. In the following description, the first weight will be referred to as "weight W1" and the second weight will be referred to as "weight W2."

[0044] The notification unit 326 notifies the driver of the estimation result estimated by the estimation unit 325 by displaying a warning image corresponding to the estimation result on the display device 21 or by emitting a warning sound corresponding to the estimation result from the sound output device 22. The notification unit 326 notifies the user of the internal combustion engine that the estimation unit 325 has estimated that the state of the oil E is abnormal, for example, because the density difference is equal to or greater than a first threshold. The notification unit 326 may display a first warning image on the display device 21 when the estimation unit 325 estimates that the oil E has deteriorated, or may display a second warning image on the display device when the estimation unit 325 estimates that the oil E has been diluted.

[0045] The notification unit 326 notifies the user of the internal combustion engine that the estimation unit 325 has estimated that a malfunction has occurred in the internal combustion engine, for example, based on the weight of the oil E. In this case, the notification unit 326 causes, for example, the display device 21 to display a third warning image corresponding to the malfunction of the internal combustion engine. By operating the notification unit 326 as described above, the user of the internal combustion engine can easily know the state of the oil E and the state of the internal combustion engine.

[0046] <Processing sequence in the oil state estimation device 30> 2 and 3 are diagrams showing an example of a processing sequence in the oil state estimating device 30. Fig. 2 is a diagram showing the operation of estimating an abnormality in the state of oil E, and Fig. 3 is a diagram showing the operation of estimating a malfunction of the internal combustion engine.

[0047] First, the operation of estimating an abnormality in the state of oil E will be described. As shown in Fig. 2, the calculation unit 324 detects whether or not the oil E has been changed based on whether or not the third acquisition unit 323 has acquired change information (S11). If the calculation unit 324 does not detect an oil change (NO in S11), it repeats the processing of step S11. If the calculation unit 324 detects an oil change (YES in S11), it determines whether or not the user of the internal combustion engine has performed an operation to start the internal combustion engine based on the timing information acquired by the third acquisition unit 323 (S12).

[0048] If the third acquisition unit 323 has not acquired timing information indicating the start timing (NO in S12), the calculation unit 324 repeats the process of step S12. If the third acquisition unit 323 has acquired the timing information (YES in S12), the calculation unit 324 calculates the density ρ1 (S13). If a predetermined period has not elapsed since calculating the density ρ1 (NO in S14), the calculation unit 324 detects whether the oil E has been changed again (S15). If an oil change has been detected (YES in S15), the calculation unit 324 returns to the process of step S12, and if an oil change has not been detected (NO in S15), the calculation unit 324 returns to the process of step S14.

[0049] If a predetermined period has elapsed since the density ρ1 was calculated (YES in S14), the calculation unit 324 determines whether or not the user has performed an operation to start the internal combustion engine (S16). If the third acquisition unit 323 has not acquired timing information indicating the start timing (NO in S16), the calculation unit 324 repeats the process of step S16. If the third acquisition unit 323 has acquired the timing information (YES in S16), the calculation unit 324 calculates the density ρ2 (S17), and the estimation unit 325 calculates the absolute value D of the difference between the density ρ1 and the density ρ2 (S18).

[0050] If the absolute value D is less than the first threshold value (NO in S19), the calculation unit 324 returns to the process of step S14. If the absolute value D is equal to or greater than the first threshold value (YES in S19) and the density ρ1 is greater than the density ρ2 (YES in S20), the estimation unit 325 estimates that the oil E has been diluted with fuel (S21). Then, the notification unit 326 notifies the user that the estimation unit 325 has estimated that the oil E has been diluted with fuel (S23).

[0051] If the absolute value is equal to or greater than the first threshold value (YES in S19) and the density ρ1 is smaller than the density ρ2 (NO in S20), the estimation unit 325 estimates that the oil E has deteriorated (S22). Then, the notification unit 326 notifies the user that the estimation unit 325 has estimated that the oil E has deteriorated (S23). If an instruction to stop the processing has not been received (NO in S24), the oil state estimation device 30 returns to the processing of step S11. If an instruction to stop the processing has been received (YES in S24), the oil state estimation device 30 ends the processing.

[0052] Next, the operation of estimating a malfunction of the internal combustion engine will be described. As shown in Fig. 3, the calculation unit 324 determines whether or not the user has performed an operation to stop the internal combustion engine based on the timing information acquired by the third acquisition unit 323 (S31). If the third acquisition unit 323 has not acquired timing information indicating the stop timing (NO in S31), the calculation unit 324 repeats the process of S31. If the third acquisition unit 323 has acquired the timing information (YES in S31), the calculation unit 324 determines whether or not a predetermined time has elapsed (S32).

[0053] If the predetermined time has not elapsed (NO in S32), the calculation unit 324 repeats the process of step S32. If the predetermined time has elapsed (YES in S32), the calculation unit 324 determines whether the current time is before or after the timing of the operation to start the internal combustion engine, based on the timing information acquired by the third acquisition unit 323 (S33). If the third acquisition unit 323 has acquired timing information indicating the start timing, the calculation unit 324 determines that the current time is after the timing of the operation to start the internal combustion engine (NO in S33), and returns to the process of step S31. If the third acquisition unit 323 has not acquired the timing information, the calculation unit 324 determines that the current time is before the timing of the operation to start the internal combustion engine (YES in S33), and calculates the weight W2 of oil E (S34).

[0054] The estimation unit 325 references the storage unit 31 to obtain the weight W1 of oil E calculated by the calculation unit 324 at a previous time (for example, the time when the calculation unit 324 detected an oil change) (S35), and calculates a subtraction value V by subtracting the weight W2 from the weight W1 (S36). If the subtraction value V is less than the second threshold value (NO in S37), the estimation unit 325 estimates that no malfunction has occurred in the internal combustion engine (S39), and the process returns to step S31. If the subtraction value V is equal to or greater than the second threshold value (YES in S37), the estimation unit 325 estimates that a malfunction has occurred in the internal combustion engine (S38). Then, the notification unit 326 notifies the user that a malfunction has occurred in the internal combustion engine (S40).

[0055] <Effects of the oil state estimation device 30> As described above, the oil state estimation device 30 has a first acquisition unit 321 that acquires the pressure P of the oil E stored in the oil pan 10 from the pressure sensor 12 provided on the bottom surface B of the oil pan 10 of the internal combustion engine, a second acquisition unit 322 that acquires the distance H between the bottom surface B and the liquid level T of the oil E from the level sensor 13 provided in the oil pan 10, and a calculation unit 324 that calculates the density ρ of the oil E based on the pressure P and the distance H.

[0056] By configuring the oil state estimation device 30 in this manner, the oil state estimation device 30 can estimate the density of the oil E with high accuracy without transferring the oil E from the oil pan 10 to an external container. Furthermore, the oil state estimation device 30 can estimate the density of the oil E with high accuracy without using an oil sensor equipped with a vibrator. As a result, the oil state estimation device 30 can estimate the density of the oil E with high accuracy simply and inexpensively.

[0057] The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by functionally or physically distributing or integrating any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination also have the effects of the original embodiments. [Explanation of symbols]

[0058] S Oil condition estimation system 10 Oil pan 11 Strainer 12 Pressure Sensor 13 Level Sensor 20 Control device 21 Display device 22 Sound output device 30 Oil condition estimation device 31 Storage section 32 Control section 321 First acquisition part 322 Second Acquisition Department 323 Third Acquisition Department 324 Calculation Unit 325 Estimation Department 326 Information Department

Claims

1. a first acquisition unit that acquires a pressure of oil stored in an oil pan from a pressure sensor provided on a bottom surface of the oil pan of the internal combustion engine; a second acquisition unit that acquires the distance between the bottom surface and the oil level from a level sensor provided in the oil pan; a calculation unit that calculates the density of the oil based on the pressure and the distance; An oil condition estimation device having:

2. The oil condition monitoring system further includes an estimation unit that estimates that the oil state is abnormal when a density difference indicating a difference between a first density calculated by the calculation unit at a first time and a second density calculated by the calculation unit at a second time after the first time is equal to or greater than a threshold value. The oil condition estimating device according to claim 1 .

3. the estimation unit estimates that the oil has deteriorated when the density difference is equal to or greater than the threshold value and the first density is smaller than the second density. The oil state estimating device according to claim 2 .

4. the estimation unit estimates that the oil has been diluted by fuel injected into the internal combustion engine when the density difference is equal to or greater than the threshold value and the first density is greater than the second density. The oil state estimating device according to claim 2 .

5. the estimation unit reduces the threshold value as the distance traveled by the mobile body including the internal combustion engine after the oil stored in the oil pan is increased after the oil has been replaced; The oil state estimating device according to claim 2 .

6. the calculation unit calculates the first density when a change of the oil stored in the oil pan is detected. The oil state estimating device according to claim 2 .

7. the calculation unit calculates, as the second density, statistics of the second densities calculated for each first period in a second period that is longer than a predetermined first period; The oil state estimating device according to claim 2 .

8. the calculation unit calculates at least one of the first density and the second density during a period from a timing at which an operation to start the internal combustion engine is received to a timing immediately before the internal combustion engine starts to start. The oil state estimating device according to claim 2 .

9. The internal combustion engine further includes a notification unit that notifies a user of the internal combustion engine that the estimation unit has estimated that the state of the oil is abnormal. The oil state estimating device according to claim 2 .

10. the calculation unit calculates the weight of the oil based on the pressure of the oil and a cross-sectional area of ​​the oil pan corresponding to the position of the oil level; an estimation unit that estimates that a failure has occurred in the internal combustion engine when a subtraction value obtained by subtracting a second weight of the oil calculated by the calculation unit at a second time after the first time from a first weight of the oil calculated by the calculation unit at the first time is equal to or greater than a threshold value; The oil condition estimating device according to claim 1 .

11. the calculation unit calculates the weight of the oil during a period from a timing when a predetermined time has elapsed since the internal combustion engine stopped to a timing immediately before the internal combustion engine starts to start. The oil state estimating device according to claim 10.

12. The apparatus further includes a notification unit that notifies a user of the internal combustion engine that the estimation unit has estimated that a failure has occurred in the internal combustion engine. The oil state estimating device according to claim 10.

13. The processor executes a first acquisition step of acquiring a pressure of oil stored in an oil pan of an internal combustion engine from a pressure sensor provided on a bottom surface of the oil pan; a second acquiring step of acquiring a distance between the bottom surface and the oil level from a level sensor provided in the oil pan; a calculation step of calculating the density of the oil based on the pressure and the distance; The oil condition estimation method has the following steps.

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