JP2023096005A - Valve spring failure diagnosis device - Google Patents

Abstract

To provide a valve spring failure determination device capable of detecting failure of a valve spring with a simple structure.SOLUTION: A valve spring failure diagnosis device for detecting failure of a valve spring 170 that biases an exhaust valve 150 for opening and closing an exhaust port 130 of an engine 1 to a valve closing side, is configured to comprise an air-fuel ratio sensor 65 that detects an air-fuel ratio based on an amount of oxygen in exhaust gas of the engine, and a failure determination unit 90 that determines failure of the valve spring when the air-fuel ratio is richer than a determination value set based on an operating state of the engine.SELECTED DRAWING: Figure 4

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for diagnosing failure of a valve spring that biases an intake valve or an exhaust valve of an engine in a valve closing direction.

In a 4-stroke reciprocating engine, the intake port that introduces fresh air (combustion air) into the combustion chamber and the exhaust port that discharges exhaust gas (burned gas) from the combustion chamber are rotated by 1/2 of the crankshaft. The intake valves and exhaust valves driven by the camshaft rotating at high speed are opened and closed at a predetermined valve timing.
The intake and exhaust valves are urged in the valve closing direction by a valve spring, which is a compression coil spring provided around the valve stem, and shuts off gas flow between each port and the combustion chamber except when the valve is open. It is designed to
If the valve spring fails and the force that urges the valve in the valve closing direction weakens, the valve sealing performance deteriorates and the combustion state becomes unstable. In addition, there is concern about the occurrence of failures such as backfiring, falling off of parts around the valve such as rocker arms, and getting caught in the dropped parts.

As a conventional technology related to failure detection of intake and exhaust valves and their peripheral parts, for example, Patent Document 1 discloses that the gas component in the cylinder of a diesel engine has less CO ₂ and more O ₂ at the beginning of combustion, and CO ₂ at the end of combustion. Focusing on the phenomenon that the amount of O2 is large and _O2 is small, exhaust gas is collected from the sampling valve provided at the cylinder outlet during the compression stroke and from the end of combustion until the exhaust valve opens, and each sample is analyzed with an analyzer. It is described that the failure determination of the exhaust valve is performed using the analysis value obtained by the above.
In Patent Document 2, in a gas engine failure prediction diagnosis device used in a gas cogeneration system, the exhaust pressure from a plurality of cylinders measured by an exhaust pressure sensor is sampled at a predetermined cycle, and the exhaust pressure of each cylinder is measured. It is described that an engine failure such as an intake valve blow-by or an exhaust valve blow-by is determined based on the variation of the air pressure representative value.

Japanese Patent Application Laid-Open No. 1-299436 JP-A-7-293311

In the technique described in Patent Document 1, it is necessary to provide the exhaust system of the engine with a sampling valve, a component analyzer, a computer for processing analysis results, and the like, and the configuration of the system is complicated. Moreover, the principle of diagnosis is difficult to apply to a premixed spark ignition engine such as a general gasoline engine.
Also in the technique described in Patent Document 2, it is necessary to sample the exhaust pressure at a predetermined cycle and perform arithmetic processing, which also complicates the configuration of the apparatus.
Therefore, there is a demand for a technique for appropriately detecting valve spring failures without complicating the configuration of the device, using the output of a sensor that is normally provided in an existing general engine.
SUMMARY OF THE INVENTION In view of the problems described above, an object of the present invention is to provide a valve spring failure determination device capable of detecting failure of a valve spring with a simple configuration.

The present invention solves the problems described above by means of the following solutions.
The invention according to claim 1 is a valve spring failure diagnosis device for detecting a failure of a valve spring that biases an exhaust valve that opens and closes an exhaust port of an engine to the valve closing side, wherein the amount of oxygen in the exhaust gas of the engine is and an air-fuel ratio sensor that detects an air-fuel ratio based on the engine operating conditions, and a failure determination unit that determines failure of the valve spring when the air-fuel ratio is richer than a determination value set based on the operating state of the engine. It is a valve spring failure determination device characterized by comprising.

If the valve spring of the exhaust valve fails and the valve sealing performance deteriorates, exhaust gas will flow back from the exhaust passage to the combustion chamber during the intake stroke, reducing the amount of oxygen in the combustion chamber during combustion. For example, when fuel is injected based on the detected value of the air flow meter, etc., the detected value of the air-fuel ratio sensor shifts to the rich side.
According to the present invention, by judging failure of a valve spring when the air-fuel ratio is on the richer side than a judgment value set based on the operating state of the engine, the air-fuel ratio provided in a general engine A failure of the valve spring of the exhaust valve can be appropriately detected with a simple configuration that uses sensors and does not require the addition of new sensors.

The invention according to claim 2 is provided with a speed detection section for detecting a crankshaft rotation speed of the engine, and the failure determination section determines that the air-fuel ratio is richer than the determination value and that the crankshaft rotation speed is higher than the determination value. 2. The valve spring failure determination device according to claim 1, wherein failure of the valve spring is determined only when the variation is equal to or greater than a predetermined value.
When exhaust gas backflow occurs due to failure of the valve spring of the exhaust valve, the amount of fresh air that contributes to combustion in the cylinder decreases, and the torque of the engine during the combustion stroke decreases compared to the combustion stroke of other cylinders. will do.
According to the present invention, in addition to enriching the air-fuel ratio as described above, the determination accuracy is improved by determining failure of the valve spring of the exhaust valve only when the crankshaft rotation speed fluctuation is equal to or greater than a predetermined value. be able to.

In the invention according to claim 3, the engine has a plurality of cylinders, and the failure determination unit detects the cylinder in which the valve spring has failed based on the timing at which the air-fuel ratio periodically transitions to the rich side. The valve spring failure diagnostic device according to claim 1 or 2, characterized in that:
In the invention according to claim 4, the engine has a plurality of cylinders, and the failure determination unit detects the cylinder in which the valve spring has failed based on the timing at which the crankshaft rotational speed periodically decreases. The valve spring failure diagnostic device according to claim 1 or 2, characterized in that:

The enrichment of the air-fuel ratio mentioned above mainly occurs periodically when a cylinder with a failed valve spring of the exhaust valve reaches the exhaust stroke, and the fluctuation (decrease) of the crankshaft rotation speed mainly affects the valve of the exhaust valve. Occurs periodically when a cylinder with a failed spring goes through the combustion stroke.
According to each of these inventions, the cylinder in which the valve spring of the exhaust valve has failed is appropriately selected based on the timing at which the air-fuel ratio periodically transitions to the rich side or the timing at which the crankshaft rotation speed periodically decreases. can be detected.

As described above, according to the present invention, it is possible to provide a valve spring failure determination device capable of detecting a valve spring failure with a simple configuration.

1 is a diagram schematically showing the configuration of an engine provided with an embodiment of a valve spring failure diagnosis device of the present invention; FIG. FIG. 2 is a schematic cross-sectional view of a cylinder head of the engine of FIG. 1; 4 is a flow chart showing the operation of the valve spring failure diagnosis device of the embodiment when diagnosing a valve spring failure of an intake valve. 4 is a flow chart showing the operation of the valve spring failure diagnosis device of the embodiment when diagnosing a valve spring failure of an exhaust valve.

An embodiment of a valve spring failure diagnosis device to which the present invention is applied will be described below.
The valve spring failure diagnosis device of the embodiment has a function of determining a failure of a valve spring that biases an intake valve and an exhaust valve of an engine mounted as a driving power source in an automobile such as a passenger car in the valve closing direction. .
FIG. 1 is a diagram schematically showing the configuration of an engine provided with a valve spring failure determination device according to an embodiment.
The engine 1 is a 4-stroke horizontally opposed 4-cylinder direct injection (in-cylinder injection) gasoline engine mounted as a driving power source in an automobile such as a passenger car.
The output of the engine 1 is transmitted to drive wheels of the vehicle via a power transmission mechanism, which will be described later.

The engine 1 has a first cylinder 10 and a second cylinder 20 arranged in order from the front end side of a crankshaft (not shown), which is the output shaft (the side opposite to the transmission, the front side when mounted vertically, the upper side in FIG. 1). , a third cylinder 30 and a fourth cylinder 40 .
The engine 1 has, for example, a crankshaft arranged vertically along the longitudinal direction of the vehicle.
The first cylinder 10 and the third cylinder 30 are provided in the right cylinder block RB arranged on the right side in the vehicle width direction, and the second cylinder 20 and the fourth cylinder 40 are provided in the left cylinder block LB arranged on the left side in the vehicle width direction. ing.
A right cylinder head RH and a left cylinder head LH are provided at end portions of the right cylinder block RB and the left cylinder block LB on the outside in the vehicle width direction (the side opposite to the crankshaft side), respectively.

The first cylinder 10 and the second cylinder 20, and the third cylinder 30 and the fourth cylinder 40 are arranged to face each other across the crankshaft while being shifted by the crankpin offset amount of each cylinder.
The ignition order (explosion order) in the engine 1 is set in order of the first cylinder 10, the third cylinder 30, the second cylinder 20, and the fourth cylinder 40, and ignition (combustion) takes place at regular intervals of 180° in the crank angle. It's like

The first cylinder 10, the second cylinder 20, the third cylinder 30, and the fourth cylinder 40 are cylinders, pistons, combustion chambers, intake/exhaust ports, intake/exhaust valves, valve drive mechanisms, etc., and also injectors 11, 21, . 31, 41, spark plugs 12, 22, 32, 42 and the like.
The injectors 11, 21, 31, 41 are injection devices that directly inject atomized gasoline into the combustion chamber of each cylinder.
The fuel injection amount and fuel injection timing of the injectors 11 , 21 , 31 , 41 are controlled by the engine control unit 90 according to the operating state of the engine 1 .
The injectors 11 , 21 , 31 , 41 receive and accumulate fuel pressurized by a fuel pump (not shown), and open according to an injection signal given from the engine control unit 90 to inject the fuel.

The spark plugs 12, 22, 32, 42 ignite the air-fuel mixture formed in each cylinder by an electric spark.
The ignition timing of spark plugs 12 , 22 , 32 , 42 is controlled by engine control unit 90 .

The engine 1 also has an intake system 50, an exhaust system 60, a variable valve timing system (not shown), a cooling system, a lubricating system, an EGR system, and the like.
The intake device 50 introduces combustion air into each cylinder.
The intake device 50 includes an intake duct (not shown) for introducing outside air (atmosphere) as combustion air, an air cleaner (not shown) for filtering foreign matter such as dust, a throttle valve 51, an intake manifold 52, an intake pressure sensor 53, and the like.

The throttle valve 51 controls the air flow rate to adjust the output of the engine 1 .
The throttle valve 51 is an electric throttle having a butterfly valve (throttle valve) that is opened and closed by an electric actuator. .
The intake manifold 52 is a branch pipe that introduces the air that has passed through the throttle valve 51 into the intake port of each cylinder.
The intake pressure sensor 53 is a pressure sensor that detects the pressure in the intake manifold 52 (intake pipe negative pressure).
The output of the intake pressure sensor 53 is sequentially transmitted to the engine control unit 90 .

The exhaust system 60 discharges exhaust gas (burned gas) from the combustion chambers of the cylinders 10, 20, 30, 40 via exhaust ports.
The exhaust system 60 includes an exhaust manifold 61, an exhaust pipe 62, a catalytic converter 63, a silencer 64, an air-fuel ratio sensor 65, a rear _O2 sensor 66, and the like.

The exhaust manifold 61 is a collecting pipe that collects the exhaust gases emitted from the exhaust ports of the cylinders 10, 20, 30, 40. As shown in FIG.
The exhaust pipe 62 is a conduit that discharges the exhaust gas collected in the exhaust manifold 61 to the outside.

The catalytic converter 63 is an exhaust gas post-treatment device provided in the intermediate portion of the exhaust pipe 62 .
The catalytic converter 63 is, for example, a three-way catalyst in which a carrier such as alumina carries a noble metal such as platinum, rhodium, or palladium.
The catalytic converter 63 has a function of reducing HC, CO, and _NOX in the exhaust gas in a predetermined active region where the air-fuel ratio of the engine 1 is close to stoichiometric.

The silencer 64 is a silencer that is provided on the downstream side (outlet side) of the catalytic converter 63 in the exhaust pipe 62 and reduces acoustic energy.

The air-fuel ratio sensor 65 is provided near the inlet of the catalytic converter 63 and generates different output voltages according to the air-fuel ratio in the engine 1 .
The engine control unit 90 performs air-fuel ratio feedback control for setting the fuel injection amount so that the air-fuel ratio in the engine 1 is within the active range of the three-way catalyst according to the output of the air-fuel ratio sensor 65 .

The rear _O2 sensor 66 is provided near the outlet of the catalytic converter 63 and generates different output voltages according to the _O2 concentration in the exhaust gas.
The output of rear _O2 sensor 66 is communicated to engine control unit 90 .

The engine 1 further has a crank angle sensor 70, a water temperature sensor 80 and the like.
The crank angle sensor 70 is a magnetic angle sensor that detects the angular position (crank angle·CA) of a crankshaft (not shown) that is the output shaft of the engine 1 .
The crank angle sensor 70 includes a sensor plate 71, a position sensor 72, and the like.

The sensor plate 71 is a disc-shaped member fixed to the rear end of the crankshaft, and has a sprocket-like shape with a plurality of vanes (teeth) protruding radially at predetermined angular intervals on the outer peripheral edge. It has a shape.
The position sensor 72 is a magnetic pickup arranged to face the outer peripheral edge of the sensor plate 71, and has a magnet, core, coil, terminal, and the like.
The position sensor 72 outputs a predetermined pulse signal when the vane of the sensor plate 71 passes in front of it.
The engine control unit 90 can calculate the rotation speed (crankshaft rotation speed) of the engine 1 and the crank angle based on the output of the crank angle sensor 70 .
The engine control unit 90 functions as a speed detector that detects the crankshaft rotation speed of the engine 1 .

The water temperature sensor 80 detects the temperature of cooling water (coolant) flowing in a water jacket, which is a cooling water flow path formed in the cylinder head and cylinder.
Outputs of the crank angle sensor 70 and the water temperature sensor 80 are transmitted to the engine control unit 90 .

An engine control unit (ECU) 90 comprehensively controls the engine 1 and its accessories.
The engine control unit 90 includes, for example, an information processing device such as a CPU, a storage device such as a RAM and a ROM, an input/output interface, and a bus connecting them.
The engine control unit 90 controls the opening of a throttle valve (not shown), fuel injection amount, It controls fuel injection timing, ignition timing, valve timing, etc.
In addition, the engine control unit 90 executes fuel cut to temporarily stop fuel injection when the running state of the vehicle satisfies a predetermined fuel cut condition.
The engine control unit 90 also functions as a failure determination section of a valve spring failure diagnostic device that detects deterioration due to a decrease in spring constant of the intake valve spring 160 and the exhaust valve spring 170, and damage such as breakage.
This point will be explained in detail later.

2 is a schematic cross-sectional view of a cylinder head of the engine of FIG. 1. FIG.
FIG. 2 shows a cross-section taken along a plane including the valve stem axes of the intake valve and exhaust valve of the first cylinder 10 in the cylinder head, but the other cylinders have the same configuration.
The cylinder head 100 includes a combustion chamber 110, an intake port 120, an exhaust port 130, an intake valve 140, an exhaust valve 150, an intake valve spring 160, an exhaust valve spring 170, an intake camshaft 180, an exhaust camshaft 190, and the like. It is

The combustion chamber 110 is a part that forms a space in which the air-fuel mixture is ignited and burned in cooperation with the crown surface of the piston (not shown) and the inner peripheral surface of the cylinder sleeve.
The combustion chamber 110 is, for example, a pent-roof type that is formed as a recessed portion formed by recessing a surface portion inside the cylinder of the cylinder head.

Intake port 120 is a flow path that is connected to intake manifold 52 and introduces fresh air (air) into combustion chamber 110 .
The exhaust port 130 is a passage for discharging exhaust gas (burnt gas) from the combustion chamber 110 to the exhaust manifold 61 .
The intake port 120 and the exhaust port 130 are bifurcated, for example, and two intake valves 140 and two exhaust valves 150 are provided for each cylinder.

The intake valve 140 opens and closes the intake port 120 at a predetermined valve timing.
Intake valve 140 is normally opened from the end of the exhaust stroke, through the intake stroke, to the beginning of the compression stroke.
The intake valve 140 has a valve head 141 and a valve stem 142 .
The valve head 141 is a disk-shaped portion provided at the end of the intake valve 140 on the combustion chamber 110 side.
The valve head 141 functions as a valve element that closes the end of the intake port 120 on the combustion chamber 110 side when the intake valve 140 is closed.
The valve stem 142 is a cylindrical portion that protrudes from the surface of the valve head 141 on the side opposite to the combustion chamber 110 side.
The valve stem 142 is inserted into a cylindrical stem guide provided in the cylinder head 100 and is slidably supported on the cylinder head 100 along its longitudinal direction.

The exhaust valve 150 opens and closes the exhaust port 130 at a predetermined valve timing.
The exhaust valve 150 is normally opened from the end of the combustion stroke, through the exhaust stroke, to the beginning of the intake stroke.
The exhaust valve 150 has a valve head 151 and a valve stem 152 .
The valve head 151 is a disc-shaped portion provided at the end of the exhaust valve 150 on the combustion chamber 110 side.
The valve head 151 functions as a valve body that closes the end of the exhaust port 130 on the combustion chamber 110 side when the exhaust valve 150 is closed.
The valve stem 152 is a cylindrical portion that protrudes from the surface of the valve head 151 on the side opposite to the combustion chamber 110 side.
The valve stem 152 is inserted into a cylindrical stem guide provided in the cylinder head 100 and is slidably supported on the cylinder head 100 along its longitudinal direction.

The intake valve spring 160 is a spring element that biases the intake valve 140 toward the closing side.
The exhaust valve spring 170 is a spring element that biases the exhaust valve 150 toward the closing side.
The intake valve spring 160 and the exhaust valve spring 170 are, for example, compression coil springs, and the longitudinal camshaft side portions of the valve stems 142 and 152 of the respective valves are inserted into the inner diameter sides thereof.
End portions of the intake valve spring 160 and the exhaust valve spring 170 on the side of the combustion chamber 110 are in contact with a seat formed in the cylinder head 100 .
The ends of the intake valve spring 160 and the exhaust valve spring 170 on the camshaft side are in contact with spring seats 161 and 171 projecting radially outward from the ends of the valve stems 142 and 152 .

The intake camshaft 180 and the exhaust camshaft 190 are shaft-shaped members that rotate at half the rotation speed of the crankshaft of the engine 1 .
The intake camshaft 180 and the exhaust camshaft 190 are attached to the cylinder head 100 so as to be rotatable around a rotation axis parallel to the crankshaft.
The intake camshaft 180 and the exhaust camshaft 190 have cam portions that open the intake valve 140 and the exhaust valve 150 at predetermined valve timings, respectively.
Cam sprockets (not shown) are provided at the ends of the intake camshaft 180 and the exhaust camshaft 190 .
The cam sprocket is rotationally driven in conjunction with the crankshaft through a cranksprocket and a timing chain (not shown) provided on the crankshaft.
The cam sprocket is provided with a variable valve timing mechanism that changes the phases of the intake camshaft 180 and the exhaust camshaft 190 with respect to the cam sprocket according to the operating state of the engine 1 to change the valve timing.
The variable valve timing mechanism is controlled by engine control unit 90 .

The intake camshaft 180 and the exhaust camshaft 190 support the end portions of the valve stems 142 and 152 of the intake valve 140 and the exhaust valve 150 via rocker arms 181 and 191 that swing around a support shaft provided in the cylinder head 100. By pressing, the intake valve 140 and the exhaust valve 150 are opened.
The rocker arms 181, 191 are provided with hydraulic lash adjusters 182, 192 for automatically adjusting the valve clearance.

The operation of the valve spring failure diagnosis device of the embodiment will be described below.
FIG. 3 is a flow chart showing the operation of the valve spring failure diagnosis system of the embodiment when diagnosing a valve spring failure of an intake valve.
Each step will be described in order below.

<Step S01: Judgment during execution of fuel cut>
The engine control unit 90 determines whether fuel cut, which temporarily stops the fuel injection of the engine 1, is being executed.
If the fuel cut is being executed, the process proceeds to step S02; otherwise, the series of processes is terminated (returned).

<Step S02: Engine operating state detection>
The engine control unit 90 detects parameters indicating the current operating state of the engine 1 .
For example, the rotation speed of the crankshaft (so-called engine speed) detected by the crank angle sensor 70, the opening of the throttle valve 51, the fresh air flow rate in the intake device 50 detected by an air flow meter (not shown), the valve timing, and the EGR rate. , to get information about atmospheric pressure, etc.
After that, the process proceeds to step S03.

<Step S03: Acquisition of Intake Manifold Internal Pressure History>
The engine control unit 90 acquires the internal pressure (intake pipe pressure) of the intake manifold 52 detected by the intake pressure sensor 53, and records and accumulates the history over a predetermined period.
After that, the process proceeds to step S04.

<Step S04: Valve Spring Failure Judgment Value Setting>
The engine control unit 90 sets a valve spring failure determination value (for determination based on the intake pipe pressure) based on the operating state of the engine 1 acquired in step S02.
The valve spring failure determination value is set, for example, based on the intake pipe pressure normally possible in the current operating state of the engine 1 when the intake valve spring 160 is normal.
After that, the process proceeds to step S05.

<Step S05: Valve Spring Failure Determination Using Intake Manifold Internal Pressure>
The engine control unit 90 compares the internal pressure of the intake manifold 52 acquired in step S03 with the valve spring failure determination value set in step S04.
For the internal pressure used here, in order to eliminate a peak value instantaneously generated due to intake pulsation or the like, for example, an average value for a predetermined period or a value obtained by removing a high frequency range using a predetermined low-pass filter can be used.
If the internal pressure of the intake manifold 52 is equal to or higher than the valve spring failure determination value, the process proceeds to step S06; otherwise, the series of processes is terminated (returned).

<Step S06: Establishment of Valve Spring Failure Determination>
The engine control unit 90 establishes the failure determination of the intake valve spring 160 .
After that, the process proceeds to step S07.

<Step S07: Identification of failed cylinder>
The engine control unit 90 identifies the cylinder in which the intake valve spring 160 has failed based on the history of the internal pressure of the intake manifold 52 acquired in step S03.
For example, it can be determined that the intake valve spring 160 has failed in the cylinder that is in the compression stroke when the internal pressure of the intake manifold 52 periodically increases.
After that, the process proceeds to step S08.

<Step S08: Engine control safe mode/warning output>
In order to prevent damage to the engine 1 from progressing, the engine control unit 90 switches to safe mode engine control that limits the output torque and rotation speed (crankshaft rotation speed) of the engine 1 to a predetermined upper limit value or less.
Also, the engine control unit 90 outputs a warning indicating that a valve spring failure has occurred using a warning light or an image display device provided on an instrument panel (not shown).
After that, the series of processing ends.

FIG. 4 is a flow chart showing the operation of the valve spring failure diagnosis device of the embodiment when diagnosing a valve spring failure of an exhaust valve.
Each step will be described in order below.

<Step S11: Judgment during execution of fuel cut>
The engine control unit 90 determines whether fuel cut, which temporarily stops the fuel injection of the engine 1, is being executed.
If the fuel cut is being executed, the series of processes is terminated (returned), otherwise the process proceeds to step S12.

<Step S12: Engine operating state detection>
The engine control unit 90 detects parameters indicating the current operating state of the engine 1 .
After that, the process proceeds to step S13.

<Step S13: Air-fuel ratio sensor output history acquisition>
The engine control unit 90 acquires the detected value of the air-fuel ratio detected by the air-fuel ratio sensor 65, and records and accumulates the history over a predetermined period.
After that, the process proceeds to step S14.

<Step S14: Crank Angle Sensor Output History Acquisition>
The engine control unit 90 acquires the angular position of the crankshaft detected by the crank angle sensor 70, and records and accumulates the history over a predetermined period.
After that, the process proceeds to step S15.

<Step S15: Air-fuel ratio determination value setting>
The engine control unit 90 sets a valve spring failure determination value (for determination based on the air-fuel ratio) based on the operating state of the engine 1 acquired in step S12.
The valve spring failure determination value is set, for example, based on an air-fuel ratio that can normally be obtained in the current operating state of the engine 1 when the exhaust valve spring 170 is normal.
After that, the process proceeds to step S16.

<Step S16: Rotation fluctuation determination value setting>
The engine control unit 90 sets a valve spring failure determination value (for determination based on rotation fluctuation) based on the operating state of the engine 1 acquired in step S12.
The valve spring failure determination value is, for example, a rotation fluctuation that can normally occur in the current operating state of the engine 1 when the exhaust valve spring 170 is normal (for example, a crank angle of 180 degrees corresponding to the combustion stroke of each cylinder). It is set based on the difference between the maximum value and the minimum value of the average rotation speed for each cylinder in the range).
After that, the process proceeds to step S17.

<Step S17: Determination of valve spring failure using air-fuel ratio>
The engine control unit 90 compares the detection value of the air-fuel ratio sensor 65 acquired in step S13 with the valve spring failure determination value set in step S15.
If the air-fuel ratio detected by the air-fuel ratio sensor 65 is on the rich side of the valve spring failure determination value, the process proceeds to step S18, otherwise the series of processes is terminated (returned).

<Step S18: Determination of Valve Spring Failure Using Rotational Fluctuation>
The engine control unit 90 compares the variation in the rotational speed of the crankshaft acquired in step S14 with the valve spring failure determination value set in step S16.
If the absolute value of the rotation speed fluctuation detected by the crank angle sensor 70 is equal to or greater than the valve spring failure determination value, the process proceeds to step S19, otherwise the series of processes is terminated (returned).

<Step S19: Establishment of Valve Spring Failure Determination>
The engine control unit 90 establishes the failure determination of the exhaust valve spring 170 .
After that, the process proceeds to step S20.

<Step S20: Identification of failed cylinder>
The engine control unit 90 identifies the cylinder in which the exhaust valve spring 170 has failed based on the air-fuel ratio history acquired in step S13.
For example, it can be determined that the exhaust valve spring 170 has failed in the cylinder that is in the exhaust stroke when the air-fuel ratio periodically becomes rich.
After that, the process proceeds to step S21.

<Step S21: Engine Control Safe Mode/Warning Output>
In order to prevent damage to the engine 1 from progressing, the engine control unit 90 switches to safe mode engine control that limits the output torque and rotation speed (crankshaft rotation speed) of the engine 1 to a predetermined upper limit value or less.
Also, the engine control unit 90 outputs a warning indicating that a valve spring failure has occurred using a warning light or an image display device provided on an instrument panel (not shown).
After that, the series of processing ends.

As described above, according to this embodiment, the following effects can be obtained.
(1) When the internal pressure of the intake manifold 52 is higher than a judgment value set based on the operating state of the engine 1 (when it is abnormally higher than the normal intake pipe pressure), the failure of the intake valve spring 160 is detected. By making this determination, it is possible to appropriately detect the failure of the intake valve spring 160 by using the intake pressure sensor 53 provided in a general engine and with a simple configuration that does not require the addition of new sensors. can.
(2) By detecting the cylinder in which the intake valve spring 160 has failed based on the timing at which the internal pressure of the intake manifold 52 periodically rises, it is possible to appropriately identify the failed cylinder with a simple configuration.
(3) Failure of the exhaust valve spring 170 when the air-fuel ratio is on the richer side than the judgment value set based on the operating state of the engine 1 (when the air-fuel ratio is abnormally rich with respect to the normal air-fuel ratio). By determining the air-fuel ratio sensor 65 provided in a general engine, the failure of the exhaust valve spring 170 can be appropriately detected with a simple configuration that does not require the addition of new sensors. can be done.
(4) In addition to enriching the air-fuel ratio, it is possible to improve the determination accuracy by determining failure of the exhaust valve spring 170 only when the rotational speed fluctuation (rotational fluctuation) of the crankshaft exceeds a predetermined value. can.
(5) By detecting the cylinder in which the exhaust valve spring 170 has failed based on the timing at which the air-fuel ratio periodically transitions to the rich side, it is possible to appropriately identify the failed cylinder with a simple configuration.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, which are also within the technical scope of the present invention.
(1) The configurations of the valve spring failure diagnosis device and the engine are not limited to the above-described embodiments, and can be changed as appropriate.
For example, the cylinder layout of the engine, the number of cylinders, the fuel injection method, the presence or absence of a supercharger, etc. are not limited to the configuration of the above-described embodiment, and can be changed as appropriate.
(2) In the embodiment, the exhaust valve spring failure diagnosis is performed by comparing the air-fuel ratio and the crankshaft rotation fluctuation with respective set valve spring failure determination values. Failure determination may be established by
(3) In the embodiment, the cylinder in which the exhaust valve spring has failed is specified by using the fluctuation of the air-fuel ratio. may be specified. For example, a cylinder that is in a combustion process during a period when the rotation speed is periodically reduced may be identified as a failure-occurring cylinder.

1 engine 10 first cylinder 11 injector 12 spark plug 20 second cylinder 21 injector 22 spark plug 30 third cylinder 31 injector 32 spark plug 40 fourth cylinder 41 injector 42 spark plug 50 intake device 51 throttle valve 52 intake manifold 53 intake pressure Sensor 60 exhaust system 61 exhaust manifold 62 exhaust pipe 63 catalytic converter 64 silencer 65 air-fuel ratio sensor 66 rear _O2 sensor 70 crank angle sensor 71 sensor plate 72 position sensor 80 water temperature sensor 90 engine control unit (ECU)
100 cylinder head 110 combustion chamber 120 intake port 130 exhaust port 140 intake valve 141 valve head 142 valve stem 150 exhaust valve 151 valve head 152 valve stem 160 intake valve spring 161 spring seat 170 exhaust valve spring 171 spring seat 180 intake camshaft 181 rocker Arm 182 Hydraulic lash adjuster 190 Exhaust camshaft 191 Rocker arm 192 Hydraulic lash adjuster

Claims (4)

A valve spring failure diagnosis device for detecting a failure of a valve spring that biases an exhaust valve that opens and closes an exhaust port of an engine to the valve closing side,
an air-fuel ratio sensor that detects an air-fuel ratio based on the amount of oxygen in the exhaust gas of the engine;
A valve spring failure determination device, comprising: a failure determination unit that determines failure of the valve spring when the air-fuel ratio is richer than a determination value set based on the operating state of the engine. A speed detection unit that detects the crankshaft rotation speed of the engine,
The failure determination unit determines failure of the valve spring only when the air-fuel ratio is on the richer side than the determination value and the fluctuation of the crankshaft rotational speed is equal to or greater than a predetermined value. Item 2. A valve spring failure determination device according to Item 1. The engine has a plurality of cylinders,
3. The valve spring according to claim 1, wherein the failure determination unit detects a cylinder in which the valve spring has failed based on the timing at which the air-fuel ratio periodically transitions to the rich side. Fault diagnosis device. The engine has a plurality of cylinders,
3. The valve spring failure according to claim 1, wherein the failure determination unit detects a cylinder in which the valve spring has failed, based on a timing at which the crankshaft rotation speed periodically decreases. diagnostic equipment.

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