Variable valve timing mechanism

Abstract

To provide a variable valve timing mechanism which can prevent an operation failure by contamination or sludge in oil.SOLUTION: A variable valve timing mechanism 27 includes: a housing 271 that rotates in cooperation with a crank shaft 10a; a rotor 273 that is provided so as to be relatively rotatable to the housing 271 and rotates in cooperation with an exhaust gas cam shaft 29; an advanced angle oil chamber 274 in which oil for rotating the rotor 273 in an advanced angle side enters and a retard angle oil chamber 275 in which oil for rotating the rotor 273 to a retard angle side enters, the chambers being defined by the housing 271 and the rotor 273; and a discharge oil path 278 that is formed on the rotor 273 and communicates the advanced angle oil chamber 274 with outside in a state where the rotor 273 is positioned at the most advanced angle end outside a normal control range. When a predefined cleaning control execution condition is established, an ECU 50 drives the rotor 273 to the most advanced angle end beyond the normal control range.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a hydraulic vane type variable valve timing mechanism. [Background technology]

[0002] Conventionally, a variable valve timing mechanism (AVCS (Active Valve Control System)) has been used to continuously change the timing of opening and closing the intake and exhaust valves of an engine by advancing or retarding the camshaft relative to the crankshaft according to the operating state of the engine (for example, the rotation speed, the load, etc.) and thereby improve the intake and exhaust efficiency over the entire range of engine rotation speeds, thereby improving power output, fuel efficiency, and reducing exhaust gas emissions (see, for example, Patent Document 1).

[0003] A known example of a variable valve timing mechanism is one that has a housing that rotates in conjunction with the engine crankshaft, and a rotor that is rotatable relative to the housing and rotates in conjunction with the camshaft; oil is moved between the advance oil chamber and the retard oil chamber defined by the housing and rotor (vane) (i.e., from the retard oil chamber to the advance oil chamber when advancing, and from the advance oil chamber to the retard oil chamber when retarding), and the amount of oil in the advance oil chamber and the amount of oil in the retard oil chamber are relatively varied, thereby rotating and adjusting the phase difference between the housing and the rotor to vary the valve timing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-77434 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in a configuration in which the valve timing is varied by moving oil between the advance oil chamber and the retard oil chamber and varying the amount of oil in the advance oil chamber relative to the amount of oil in the retard oil chamber (a configuration in which only oil leakage is compensated for by the oil pump), contamination or sludge that has entered or is generated inside the variable valve timing mechanism may continue to remain (circulate) in the oil within the mechanism, and may, for example, clog the hydraulic piping (oil passage) or become caught in the sliding parts of the valve, causing malfunction.

[0006] The present invention has been made to solve the above problems, and has an object to provide a variable valve timing mechanism that can prevent malfunctions caused by contamination or sludge in the oil. [Means for solving the problem]

[0007] A variable valve timing mechanism according to one aspect of the present invention comprises a housing that rotates in conjunction with an engine crankshaft, a rotor that is coaxial with the housing and rotatable relative to the housing and rotates in conjunction with a camshaft, and an advance oil chamber defined by the housing and the rotor, which receives oil to rotate the rotor toward the advance side, and a retard oil chamber which receives oil to rotate the rotor toward the retard side. The variable valve timing mechanism controls the supply and discharge of oil to the advance oil chamber and the retard oil chamber according to the operating state of the engine, thereby adjusting the phase difference between the housing and the rotor, thereby varying the valve timing. The variable valve timing mechanism further comprises: a drain oil passage formed in the rotor that connects the advance oil chamber or the retard oil chamber to the outside when the rotor is positioned at the most advance end or the most retard end outside the normal control range; and a control unit that controls the supply and discharge of oil to the advance oil chamber and the retard oil chamber, and the control unit drives the rotor to the most advance end or the most retard end beyond the normal control range when a predetermined cleaning control execution condition is met.

[0008] According to one aspect of the present invention, a variable valve timing mechanism includes a rotor, and a drain oil passage that connects the advance oil chamber or the retard oil chamber to the outside when the rotor is positioned at the most advanced or most retarded end outside the normal control range. When a predetermined cleaning control execution condition is met, the rotor is driven to the most advanced or most retarded end beyond the normal control range. Therefore, when the predetermined cleaning control execution condition is met, contamination and sludge are discharged to the outside along with the oil through the drain oil passage. As a result, malfunctions caused by contamination and sludge in the oil can be prevented. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent malfunctions caused by contamination or sludge in the oil. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing the configuration of an engine to which a variable valve timing mechanism according to an embodiment is applied; [Figure 2] 1 is a diagram showing the configuration of a variable valve timing mechanism according to an embodiment (when the rotor is at the most advanced end, that is, when cleaning control is being performed). FIG. [Figure 3] 1 is a diagram showing the configuration of a variable valve timing mechanism according to an embodiment (when the rotor is at the most retarded end); [Figure 4] 5 is a flowchart showing a procedure for cleaning control by a variable valve timing mechanism according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be designated by the same reference numerals. In addition, the same elements will be designated by the same reference numerals in each drawing, and redundant explanations will be omitted.

[0012] First, the configuration of a variable valve timing mechanism 27 according to this embodiment will be described with reference to Figures 1 to 3. Figure 1 is a diagram showing the configuration of a direct injection engine (hereinafter also simply referred to as "engine") 10 to which a variable valve timing mechanism 27 according to this embodiment is applied. Figure 2 is a diagram showing the configuration of the variable valve timing mechanism 27 (in a state where the rotor 273 is positioned at the most advanced end, i.e., a state where cleaning control is being executed). Also, Figure 3 is a diagram showing the configuration of the variable valve timing mechanism 27 (in a state where the rotor 273 is positioned at the most retarded end).

[0013] The engine 10 is, for example, a horizontally opposed four-cylinder gasoline engine. The engine 10 is a direct-injection engine that directly injects fuel into the cylinders. In the engine 10, air is drawn in through an air cleaner 16, throttled by an electronically controlled throttle valve (hereinafter simply referred to as a "throttle valve") 13 provided in an intake pipe 15, and then passes through an intake manifold 11 and is drawn into each cylinder formed in the engine 10. The amount of air drawn in through the air cleaner 16 (the amount of air drawn into the engine 10) is detected by an air flow meter 14 disposed between the air cleaner 16 and the throttle valve 13. A vacuum sensor 30 that detects the pressure inside the intake manifold 11 is disposed inside a collector (surge tank) that constitutes the intake manifold 11. A throttle position sensor 31 that detects the opening of the throttle valve 13 is disposed in the throttle valve 13.

[0014] The cylinder head is formed with an intake port 22 and an exhaust port 23 for each cylinder (only one bank is shown in Figure 1). Each intake port 22 and exhaust port 23 is provided with an intake valve 24 and an exhaust valve 25 that open and close the intake port 22 and exhaust port 23, respectively.

[0015] A variable valve timing mechanism 26 is disposed between the intake cam pulley and an intake camshaft 28 that drives the intake valve 24. The variable valve timing mechanism 26 rotates the intake cam pulley and the intake camshaft 28 relative to each other to continuously change the rotational phase (displacement angle) of the intake camshaft 28 relative to the crankshaft 10a, thereby advancing or retarding the valve timing (opening / closing timing) of the intake valve 24. The variable valve timing mechanism 26 variably sets the opening / closing timing of the intake valve 24 depending on the operating state of the engine 10.

[0016] Similarly, a variable valve timing mechanism 27 is disposed between the exhaust camshaft 29 and the exhaust cam pulley (chain sprocket 272) to rotate the exhaust cam pulley (chain sprocket 272) and the exhaust camshaft 29 relative to each other, continuously changing the rotational phase (displacement angle) of the exhaust camshaft 29 relative to the crankshaft 10a, thereby advancing or retarding the valve timing (opening / closing timing) of the exhaust valve 25. The variable valve timing mechanism 27 variably sets the opening / closing timing of the exhaust valve 25 in accordance with the operating state of the engine 10.

[0017] Here, since the configuration of the variable valve timing mechanism 26 provided on the intake valve 24 side and the configuration of the variable valve timing mechanism 27 provided on the exhaust valve 25 side are the same or similar, the following explanation will mainly be given using the variable valve timing mechanism 27 provided on the exhaust valve 25 side as an example.

[0018] As shown in Figures 2 and 3, the variable valve timing mechanism 27 provided on the exhaust valve 25 side has a housing 271 that rotates in conjunction with the crankshaft 10a of the engine 10, and a rotor 273 that is coaxial with the housing 271 and is rotatable relative to the housing 271, and that rotates in conjunction with the exhaust camshaft 29.

[0019] More specifically, a chain sprocket 272 having a plurality of external teeth formed on the outer periphery in the radial direction is fixed to the housing 271, and the power of the crankshaft 10a is transmitted through the chain sprocket 272. The housing 271 rotates at half the rotational speed of the crankshaft 10a.

[0020] Furthermore, an accommodation space is formed inside the housing 271 to accommodate the rotor 273. The accommodation space is made up of a circular space and a plurality of (for example, three) fan-shaped spaces cut out radially outward from the circular space. The rotor 273 is accommodated in the accommodation space provided in the housing 271, and is connected to an end of the exhaust camshaft 29. The rotor 273 has a plurality of (three in this embodiment) vanes 273a formed on its outer surface, which protrude radially outward and are accommodated in the fan-shaped spaces. The rotor 273 can rotate relative to the housing 271 within a range in which the vanes 273a can move within the fan-shaped spaces.

[0021] In variable valve timing mechanism 27, housing 271 and rotor 273 (vane 273a) define an advance oil chamber (hydraulic chamber) 274 that receives oil (hydraulic pressure) to rotate rotor 273 toward the advance side, and a retard oil chamber (hydraulic chamber) 275 that receives oil (hydraulic pressure) to rotate rotor 273 toward the retard side. More specifically, vane 273a is formed so that its width in the rotational direction is narrower than the fan-shaped space, dividing the fan-shaped space into advance oil chamber 274 (hydraulic chamber that operates rotor 273 in the advance direction) and retard oil chamber 275 (hydraulic chamber that operates rotor 273 in the retard direction). Here, the advance direction is the right direction in FIGS. 2 and 3, and the retard direction is the left direction in FIGS. 2 and 3.

[0022] The supply and discharge of oil to and from the advance oil chamber 274 and the retard oil chamber 275, that is, the adjustment of the oil amount (valve timing), is controlled by an engine control unit (hereinafter referred to as “ECU”) 50, a linear solenoid 51, and an oil control valve 52.

[0023] The oil control valve 52 is configured by accommodating a spool 522 slidably in the axial direction inside a sleeve 521 having a plurality of ports formed therein. Each port of the sleeve 521 is connected to a first oil supply passage 61 that supplies oil into the sleeve 521 by an oil pump 60, a second oil supply passage 62 that supplies oil to the advance oil chamber 274 or the retard oil chamber 275, a first oil drain passage 63 that discharges oil from the advance oil chamber 274, and a second oil drain passage 64 that discharges oil from the retard oil chamber 275. The oil pump 60 pressurizes and discharges oil stored in an oil pan.

[0024] Furthermore, a spring 523 is disposed at one end of the spool 522, and a linear solenoid 51 is disposed at the other end. The combined force of the driving force of the linear solenoid 51 and the biasing force of the spring 523 drives the spool 522 in the axial direction, thereby controlling the supply and discharge (movement) of oil.

[0025] The linear solenoid 51 is connected to the ECU 50, and its operation is controlled by the ECU 50. The linear solenoid 51 displaces its shaft in the axial direction in accordance with the value of the current applied from the ECU 50, thereby driving the spool 522 in the axial direction (left and right direction in FIGS. 2 and 3). More specifically, when the current supplied to the linear solenoid 51 is reduced below a predetermined value, i.e., when the operation of the linear solenoid 51 is stopped, the spool 522 moves to the left side of the drawing due to the biasing force of the spring 523. On the other hand, when the current supplied to the linear solenoid 51 is increased above a predetermined value, i.e., when the linear solenoid 51 is operated, the spool 522 moves to the right side of the drawing. Note that the linear solenoid 51 may be replaced with, for example, a duty solenoid.

[0026] The ECU 50 is configured to include a microprocessor that performs calculations, an EEPROM that stores programs and the like for causing the microprocessor to execute various processes, a RAM that stores various data such as calculation results, a backup RAM in which the stored contents are maintained by a battery, an input / output I / F, etc. The ECU 50 also includes an injector driver that drives the injector 12, an output circuit that outputs an ignition signal, and a motor driver that drives the electric motor 13a that opens and closes the electronically controlled throttle valve 13. The ECU 50 also includes a driver that drives the linear solenoid 51 that constitutes the variable valve timing mechanism 27.

[0027] The ECU 50 identifies the cylinder from the output of the cam angle sensor 32 and determines the engine speed from the output of the crank angle sensor 33. The ECU 50 also acquires various information such as the intake air amount, intake pipe negative pressure, accelerator pedal operation amount, air-fuel ratio of the mixture, intake air temperature, and water temperature and oil temperature of the engine 10 based on detection signals input from various sensors. The ECU 50 then comprehensively controls the engine 10 by controlling the fuel injection amount, fuel injection timing, ignition timing, and various devices such as the throttle valve 13 based on the acquired information.

[0028] Furthermore, ECU 50 controls the supply and discharge (oil amount) of oil to and from advance oil chamber 274 and retard oil chamber 275 of variable valve timing mechanism 27 in accordance with the operating state of engine 10 (for example, rotation speed, load, etc.), and varies the valve timing by rotating and adjusting the phase difference between housing 271 and rotor 273. In other words, ECU 50 functions as a control unit recited in the claims.

[0029] More specifically, the ECU 50 drives the linear solenoid 51 to move the spool 522 to the right in the drawing, thereby discharging oil from the retard oil chamber 275 and supplying (moving) oil to the advance oil chamber 274 (i.e., driving the variable valve timing mechanism 27 to the advance side). On the other hand, the ECU 50 stops driving the linear solenoid 51 and moves the spool 522 to the left in the drawing, thereby discharging oil from the advance oil chamber 274 and supplying (moving) oil to the retard oil chamber 275 (i.e., driving the variable valve timing mechanism 27 to the retard side).

[0030] At this time, the ECU 50 operates the linear solenoid 51 (spool 522) so that the target angle of the rotor 273 (vane 273a) matches the actual angle (sensor value). Cam torque is used as the driving force to move the oil. Cam torque is input in both directions, but when reverse torque occurs, the advance side check valve 276 or the retard side check valve 277 closes to maintain the state.

[0031] In particular, the variable valve timing mechanism 27 has a function of preventing malfunctions caused by contamination or sludge in the oil.

[0032] Therefore, the variable valve timing mechanism 27 is provided with a discharge oil passage (drain circuit) 278 formed in the rotor 273, which connects the advance oil chamber 274 to the outside (i.e., discharges oil to the outside) when the rotor 273 (vane 273a) is positioned at the most advance end outside the normal control range.

[0033] For example, if the normal control range of variable valve timing mechanism 27 is up to 35 degrees CA and the most advanced end (mechanical limit of movement) is 39 degrees CA, then oil discharge passage 278 is formed to open (communicate) between 37 and 39 degrees CA. In the example shown in FIG. 2, oil discharge passage 278 is open when positioned at the most advanced end (only within this range), connecting advance oil chamber 274 to the outside. Therefore, oil discharge passage 278 is closed during normal control.

[0034] More specifically, the drain oil passage (drain circuit) 278 opens to the oil chamber defining surface of the rotor 273 and passes through the inside of the rotor 273 to communicate with the outside. The oil discharged to the outside (oil containing contamination and sludge) is returned to the oil pan that stores the oil. The contamination and sludge in the oil are then captured by a strainer, oil filter, etc.

[0035] A plurality of (for example, three) advance oil chambers 274 (and retard oil chambers 275) are defined along the circumferential direction of the housing 271 and rotor 273, and a discharge oil passage (drain circuit) 278 is provided for each of the plurality of advance oil chambers 274. Since the rotor 273 is rotationally symmetric, only one configuration is shown in Figures 2 and 3.

[0036] When a predetermined cleaning (flushing) control execution condition is met, ECU 50 drives rotor 273 (vanes 273a) beyond the normal control range to the most advanced end. As described above, for example, if the normal control range of variable valve timing mechanism 27 is up to 35 degrees CA and the most advanced end (mechanical movement limit) is 39 degrees CA, ECU 50 drives rotor 273 to the range of 37 to 39 degrees CA (most advanced end) when executing cleaning control, and opens discharge oil passage 278 (i.e., communicates with the outside).

[0037] In addition, in order to make up for the discharged oil and replace it with new oil, the ECU 50 supplies oil discharged from the oil pump 60 to the advance oil chamber 274 while cleaning (flushing) control is being performed, i.e., when oil is being discharged from the advance oil chamber 274 through the discharge oil passage 278.

[0038] That is, the ECU 50 discharges contamination and sludge together with the oil to the outside through the discharge oil passage 278, while supplying the discharged oil from the oil pump 60, thereby replacing the oil in the advance oil chamber 274 with new oil (free from contamination and sludge).

[0039] Here, in order to execute cleaning (flushing) control in an operating state that does not affect the combustion of the engine 10, the ECU 50 determines that a predetermined cleaning control execution condition is met, for example, when the engine is in an engine braking state and a fuel cut state, and executes cleaning control.

[0040] The ECU 50 executes engine brake control when predetermined engine braking conditions are met (for example, the accelerator is off, the brake is off, and the vehicle speed is 20 km / h or more and the lock-up clutch is engaged). Furthermore, when predetermined fuel injection stop conditions are met, such as during deceleration, the ECU 50 stops the drive of the injector 12 to stop the fuel supply to the engine 10 (i.e., fuel cut). More specifically, the ECU 50 executes fuel cut when the following fuel cut conditions are met, i.e., when the accelerator pedal is fully closed, the engine speed Ne is 1000 (rpm), and the vehicle speed v is 10 (km / h).

[0041] Furthermore, to prevent oil shortage (decrease in oil pressure), the ECU 50 determines that a predetermined cleaning control execution condition is met when the oil temperature is equal to or lower than a predetermined temperature, and executes cleaning control. More specifically, the ECU 50 permits execution of cleaning control until the engine is fully warmed up (oil temperature of approximately 80 to 90°C), and prohibits (stops) cleaning control when the oil temperature rises further and exceeds, for example, 100°C.

[0042] Next, the operation of the variable valve timing mechanism 27 will be described with reference to Fig. 4. Fig. 4 is a flowchart showing the procedure of cleaning control by the variable valve timing mechanism 27 (ECU 50). This process is repeatedly executed by the ECU 50 at predetermined intervals.

[0043] First, in step S100, it is determined whether the oil temperature is equal to or lower than a predetermined temperature. If the oil temperature is higher than the predetermined temperature, the process is temporarily terminated. On the other hand, if the oil temperature is equal to or lower than the predetermined temperature, the process proceeds to step S102.

[0044] In step S102, it is determined whether the vehicle is in the engine braking state and the fuel cut state. If the vehicle is not in the engine braking state and the fuel cut state, the process temporarily ends. On the other hand, if the vehicle is in the engine braking state and the fuel cut state, the process proceeds to step S104.

[0045] In step S104, rotor 273 (vanes 273a) is driven to the most advanced position beyond the normal control range. Contamination and sludge are then discharged to the outside along with the oil through discharge oil passage 278, while the discharged oil is supplied from oil pump 60, and the oil in advance oil chamber 274 is replaced with new oil (free of contamination and sludge).

[0046] As described above in detail, according to this embodiment, when the rotor 273 (vanes 273a) is positioned at the most advanced angle end outside the normal control range, a drain oil passage (drain circuit) 278 that connects the advance oil chamber 274 to the outside is formed in the rotor 273, and when a predetermined cleaning (flushing) control execution condition is met, the rotor 273 is driven to the most advanced angle end beyond the normal control range. Therefore, when the predetermined cleaning control execution condition is met, contamination and sludge are discharged to the outside along with the oil through the drain oil passage 278. As a result, it is possible to prevent malfunctions caused by contamination and sludge in the oil.

[0047] According to this embodiment, the discharge oil passage (drain circuit) 278 opens to the oil chamber defining surface of the rotor 273 and passes through the inside of the rotor 273 to communicate with the outside, so that oil containing contamination and sludge can be discharged to the outside through the inside of the rotor 273.

[0048] According to this embodiment, while cleaning control is being performed, that is, while oil is being discharged from the advance oil chamber 274 through the discharge oil passage 278, oil discharged from the oil pump 60 is supplied to the advance oil chamber 274. Therefore, the oil discharged can be compensated for by the oil pump 60 and replaced with new oil.

[0049] According to this embodiment, when the engine is in the engine braking state and the fuel is cut, it is determined that the predetermined cleaning control execution condition is met, so that cleaning (flushing) control can be executed in an operating state that does not affect combustion. Also, according to this embodiment, when the oil temperature is equal to or lower than a predetermined temperature, it is determined that the predetermined cleaning control execution condition is met, so that oil shortage (decrease in oil pressure) can be prevented.

[0050] According to this embodiment, a plurality of advance oil chambers 274 (and retard oil chambers 275) are defined along the circumferential direction of the housing 271 and the rotor 273, and a discharge oil passage (drain circuit) 278 is provided for each of the plurality (three in the above embodiment) advance oil chambers 274. Therefore, the oil in all of the advance oil chambers 274 can be replaced.

[0051] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the discharge oil passage 278 is provided in the advance oil chamber 274, and the rotor 273 is driven to the most advance end during cleaning control. However, the discharge oil passage 278 may be provided in the retard oil chamber 275, and the rotor 273 may be driven to the most retard end during cleaning control. Furthermore, the discharge oil passage 278 may be provided in both the advance oil chamber 274 and the retard oil chamber 275.

[0052] Furthermore, the piping shape and diameter of the discharge oil passage (drain circuit) 278 are not limited to those in the above embodiment, and can be set arbitrarily according to requirements and the like.

[0053] Furthermore, the conditions for executing cleaning (flushing) control are not limited to those in the above embodiment, but can be set arbitrarily according to requirements, etc. For example, the cleaning (flushing) control may be executed when a malfunction of the variable valve timing mechanism 27 occurs. [Explanation of symbols]

[0054] 10 Engine 10a crankshaft 24 intake valve 25 Exhaust valve 26,27 Variable valve timing mechanism 271 Housing 272 chain sprocket 273 Rotor 273a Vane 274 Advance oil chamber 275 Retard oil chamber 276 Advance side check valve 277 Retard side check valve 278 Discharge oil passage (drain circuit) 28 Intake camshaft 29 Exhaust camshaft 50 ECU (control unit) 51 Linear solenoid 52 Oil control valve 521 Sleeve 522 spool 523 Spring 60 Oil pump 61 First oil supply line 62 Second oil supply line 63 First drain oil passage 64 Second drain oil passage

Claims

1. a variable valve timing mechanism comprising: a housing that rotates in conjunction with an engine crankshaft; a rotor that is coaxial with the housing and rotatable relative to the housing, and that rotates in conjunction with a camshaft; an advance oil chamber that is defined by the housing and the rotor and receives oil for rotating the rotor to the advance side, and a retard oil chamber that receives oil for rotating the rotor to the retard side; and a variable valve timing mechanism that controls the supply and discharge of oil to the advance oil chamber and the retard oil chamber in accordance with an operating state of the engine, thereby adjusting the phase difference between the housing and the rotor by rotation, a discharge oil passage formed in the rotor, the discharge oil passage connecting the advance oil chamber or the retard oil chamber to the outside when the rotor is positioned at the most advance end or the most retard end outside a normal control range; a control unit that controls the supply and discharge of oil to the advance oil chamber and the retard oil chamber, The control unit drives the rotor beyond a normal control range to the most advanced end or the most retarded end when a predetermined cleaning control execution condition is met.

2. 2. The variable valve timing mechanism according to claim 1, wherein the oil discharge passage opens to a surface of the rotor that defines an oil chamber, and passes through the interior of the rotor to communicate with the outside.

3. An oil pump is provided to pressurize and discharge oil.

3. The variable valve timing mechanism according to claim 2, wherein the control unit supplies oil discharged from the oil pump to the advance oil chamber or the retard oil chamber when oil is being discharged from the advance oil chamber or the retard oil chamber through the discharge oil passage during execution of the cleaning control.

4. 4. The variable valve timing mechanism according to claim 3, wherein the control unit determines that the predetermined cleaning control execution condition is met when the engine is in an engine braking state and a fuel cut state.

5. 5. The variable valve timing mechanism according to claim 4, wherein the control unit determines that the predetermined cleaning control execution condition is met when the oil temperature is equal to or lower than a predetermined temperature.

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