JP3885522B2 - Control device for variable valve timing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a friction material durability improving technique for a variable valve timing device that variably controls a valve timing by changing a rotational phase of a camshaft with respect to a crankshaft by friction braking by an electromagnetic brake.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is known a variable valve timing device for an engine having a configuration in which a rotational phase of a camshaft with respect to a crankshaft (hereinafter simply referred to as a rotational phase) is changed by friction braking by an electromagnetic brake (see JP-A-10-153105). ).
[0003]
[Problems to be solved by the invention]
In this type of variable valve timing device, if friction braking force is applied by a large electromagnetic brake for a long period of time, such as when the engine is heavily loaded, the friction coefficient of the clutch surface of the electromagnetic brake will decrease. Will also be shorter.
The present invention has been made paying attention to such a conventional problem, and in a variable valve timing device of an electromagnetic brake type, the friction braking force is appropriately adjusted to reduce the friction coefficient of the clutch surface and the durability life. It aims at suppressing.
[0004]
[Means for Solving the Problems]
For this reason, the invention according to claim 1
In a variable valve timing device for an internal combustion engine that variably controls the valve timing by changing the rotational phase of the camshaft relative to the crankshaft by friction braking by an electromagnetic brake,
By correcting the valve timing control amount so as to reduce the friction braking force of the electromagnetic brake when the temperature of the electromagnetic brake is higher than a predetermined temperature, the temperature increase of the electromagnetic brake is suppressed and the friction of the clutch surface of the electromagnetic brake is reduced. It is characterized in that a decrease in coefficient due to temperature rise is suppressed .
[0005]
According to the invention of claim 1,
By correcting the valve timing control amount so as to decrease the friction braking force of the electromagnetic brake when the temperature of the electromagnetic brake is higher than a predetermined temperature, an excessive increase in the electromagnetic brake temperature can be suppressed, and thus the electromagnetic brake A reduction in the friction coefficient of the clutch surface that generates the friction braking force can be suppressed, and the durability of the electromagnetic brake can be improved.
[0006]
Specifically, the amount of conversion from the initial position of the valve timing when the electromagnetic brake is not operating (generally, the advance amount for the intake valve and the retard amount for the exhaust valve) is reduced and corrected. The amount of heat generated by friction braking on the clutch surface of the brake can be reduced to suppress an increase in temperature.
According to a second aspect of the present invention, there is provided a variable valve timing device for an internal combustion engine that variably controls the valve timing by changing the rotational phase of the camshaft relative to the crankshaft by friction braking by an electromagnetic brake.
When the temperature of the electromagnetic brake is higher than a predetermined value, the valve timing control amount is corrected so as to decrease the friction braking force of the electromagnetic brake, and when the required engine torque is higher than the predetermined value, the friction braking force of the electromagnetic brake is reduced. The correction of the valve timing control amount to be decreased is prohibited.
According to the second aspect of the invention, the control can be simplified by switching the durability of the electromagnetic brake and emphasizing the torque by switching.
[0007]
The invention according to claim 3
In a variable valve timing device for an internal combustion engine that variably controls the valve timing by changing the rotational phase of the camshaft relative to the crankshaft by friction braking by an electromagnetic brake,
Correcting the valve timing control amount so as to reduce the friction braking force of the electromagnetic brake when the temperature of the electromagnetic brake is higher than a predetermined value, and variably setting the predetermined temperature according to the degree of deterioration of the engine oil. Features.
As engine oil elapses in use time, the copper material used as the oil seal material melts into the oil. This component causes a chemical reaction with the material of the clutch on the clutch surface of the electromagnetic brake, thereby reducing the friction braking force. This chemical reaction occurs more intensely at higher temperatures.
Therefore, according to the invention according to claim 3, when the degree of deterioration of the engine oil is large, the predetermined temperature for reducing the friction braking force of the electromagnetic brake is set to a lower temperature side so that the chemical reaction does not easily proceed. Thus, deterioration of the friction material can be effectively prevented.
[0008]
The invention according to claim 4
The temperature of the electromagnetic brake is estimated based on at least the engine temperature.
According to the invention of claim 4,
Since the heat transfer from the engine temperature (oil temperature or water temperature) greatly contributes to the temperature of the electromagnetic brake, the temperature of the electromagnetic brake can be estimated based on at least the engine temperature. The accuracy is further improved by estimating the valve timing control amount in combination.
[0009]
The invention according to claim 5
The temperature of the electromagnetic brake is estimated based on at least the engine speed.
According to the invention of claim 5,
The temperature of the electromagnetic brake also contributes to the engine rotation speed (if the camshaft rotation speed increases as the engine rotation speed increases, the amount of relative rotation slip on the clutch surface per unit time increases and heat is generated. Therefore, the temperature of the electromagnetic brake can be estimated based on at least the engine speed.
The invention according to claim 6
The temperature of the electromagnetic brake is estimated based on a valve timing control amount.
[0010]
According to the invention of claim 6,
Since the temperature increase due to the friction of the electromagnetic brake can be estimated based on the valve timing control amount that determines the friction braking force, the electromagnetic brake is also based on the valve timing control amount in combination with the engine temperature and the engine speed. The accuracy is further improved by estimating the temperature.
The invention according to claim 7
The correction amount of the valve timing control amount for reducing the friction braking force of the electromagnetic brake is set according to the required engine torque.
According to the invention of claim 7 ,
When the required engine torque is large, torque such as acceleration is required while securing the durability of the electromagnetic brake by setting the correction amount of the valve timing control amount to reduce the friction braking force of the electromagnetic brake, etc. In such a case, the torque can be set so as to satisfy the torque.
[0012]
The invention according to claim 8 is
The required engine torque is calculated from an accelerator opening.
According to the invention of claim 8,
The required engine torque can be calculated easily.
[0014]
The invention according to claim 9 is
The predetermined temperature in claim 3 is set to a lower temperature as the degree of deterioration of the engine oil is larger.
[0015]
According to the invention of claim 9 ,
By setting the progress of the above chemical reaction to a lower temperature as the degree of deterioration of the engine oil is greater, the reduction control of the friction braking force of the electromagnetic brake is controlled as necessary and sufficiently, and the deterioration of the friction material is ensured while ensuring engine performance. Can be effectively prevented.
The invention according to claim 10 is
The degree of deterioration of the engine oil is estimated according to a travel distance from when the engine oil is changed.
[0016]
Deterioration of engine oil (melting of the copper material described above) increases according to the increase in usage time from a new article, that is, the distance traveled from the time of engine oil replacement. The degree of engine oil deterioration can be estimated.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 1 shows a cross section and a control system of a variable valve timing device using an electromagnetic brake in the embodiment, and FIG. 2 shows a schematic configuration in which functions of respective parts of the device are clarified. Here, what controls variable control of the valve timing of the intake valve will be described. The structurally the same is also applied to the one that variably controls the valve timing of the exhaust valve, but the control direction of the advance / retard angle when the friction braking force of the electromagnetic brake is applied is opposite.
[0018]
In the figure, on the extension line of the end 1a of the camshaft 1 that is rotatably supported with respect to a cylinder head (not shown), the cylindrical transmission member 2 is engaged with the engagement pin 3 to be prevented from rotating. The bolts 4 are connected and fixed.
A sprocket 5 is rotatably supported on the circumference of the transmission member 2. The sprocket 5 is supported so as to be rotatable relative to the camshaft 1, and rotates synchronously with the rotation of the crankshaft of the engine via a timing chain.
[0019]
The rotation of the sprocket 5 is transmitted to the transmission member 2 through a transmission mechanism described below.
A cylindrical drum 6 having a flange 6 a is provided coaxially with the camshaft 1, and a direction in which the rotational phase of the drum 6 is advanced between this drum 6 and the sprocket 5 (retarded for exhaust valves). A coil spring 7 is interposed as a return spring biasing in the direction). That is, a case member 8 is fixed to the sprocket 5, one end portion (right end portion in the drawing) of the coil spring 7 is fixed to the case member 8, and the other end portion of the coil spring 7 is fixed to the flange 6 a of the drum 6. Has been.
[0020]
At opposite ends of the drum 6 and the case member 8, stoppers 6b and 8a for restricting the relative rotation amounts are provided (see FIG. 3 for the case member 8).
The gear 2a formed on the outer peripheral surface of the transmission member 2 and the gear 9a formed on the inner periphery of the cylindrical piston member 9 are engaged with each other by a helical mechanism using a helical gear.
[0021]
On the other hand, a male screw 9b is formed on the outer peripheral surface of the left end portion of the piston member 9 and a female screw 6c is formed on the inner peripheral surface of the drum 6 by about three threads, both of which are engaged by a screw action. The gear 9c formed on the outer peripheral surface of the right end portion of the piston member 9 and the gear 8b formed on the inner peripheral surface of the case member 8 are engaged with each other by a helical mechanism using a helical gear.
[0022]
The drum bearing member 10 is interposed between the outer peripheral surface of the transmission member 2 and the inner peripheral surface of the drum 6, and supports the relative rotation between the two. The outer peripheral portion of the drum bearing member 10 is engaged with an annular claw member 11 fitted to the drum 6 and a nut 12 screwed to the outer peripheral surface of the end portion of the transmission member 2 to move in the axial direction. Is regulated.
In addition, an electromagnetic brake 13 is fixedly disposed on the engine body at the outside (left side in the figure) of the drum 6. The electromagnetic brake 13 has a clutch member 13b with a friction member 13a attached to the surface of the drum 6 facing the flange 6a. When energized, the clutch member 13b extends in the direction of the flange 6a and is attached to the end surface of the flange 6a. It can be pressed.
[0023]
The basic operation of such a variable valve timing device will be described.
When the electromagnetic brake 13 is not energized (control current = 0), the drum 6 is held at a position regulated by one of the stoppers 6b and 8a by the biasing force of the coil spring 7. The camshaft 1 is held at a position most retarded with respect to the crankshaft.
[0024]
When the camshaft 1 is controlled to the target valve timing by advancing the target angle with the most retarded position as a reference, the electromagnetic brake 13 is energized and the clutch member 13b is pressed against the flange surface 6a of the drum 6 to cause friction. Apply braking. As a result, the drum 6 is delayed with respect to the rotation of the sprocket 5 synchronized with the crankshaft. As a result, the piston member 9 engaged with the male screw 9b and the female screw 6c moves in the axial direction of the camshaft 1 (shown in the figure). Move from left to right)
[0025]
The piston member 9 is meshed with the case member 8 and the transmission member 2 by the helical mechanism cut at opposite angles, and when the piston member 9 moves in the axial direction, the piston member 9 is cut at the opposite angle. The transmission member 2 rotates relative to the case member 8 in the advance direction along the helical tooth stripe, and the cam shaft 1 moves in the advance direction relative to the crankshaft that rotates synchronously with the sprocket 5. Relative rotation. Here, among the two helical mechanisms provided on the outer peripheral side and the inner peripheral side, one can be configured with a straight spline mechanism, but by providing two helical mechanisms cut at opposite angles, It can be advanced more greatly.
[0026]
As the current value to the electromagnetic brake 13 is increased and the braking force (sliding friction) against the urging force of the coil spring 7 is increased, the rotational phase of the camshaft 1 is advanced (or retarded for exhaust valves). Will be changed.
As described above, the rotational phase of the camshaft 1 changes with respect to the sprocket 5 (crankshaft) according to the rotational delay amount of the drum 6 determined according to the braking force by the electromagnetic brake 13, and the braking force by the electromagnetic brake 13 is increased. Can continuously control the amount of change in rotational phase (advance amount, retard amount for exhaust valves) by, for example, duty-controlling the control current supplied to the electromagnetic brake 13.
[0027]
Further, a number of protrusions (detected portions) 1b corresponding to the number of engine cylinders are formed at equal intervals in the rotational direction of the cam shaft 1 or the rotating member connected to the cam shaft 1. For example, in the case of a V-type 6-cylinder engine, three protrusions 1b are formed at intervals of 120 ° on the two left and right camshafts 1 corresponding to the left and right banks. A cam sensor 21 for detecting the protrusion 1b is provided in the vicinity of the outer periphery of the cam shaft 1.
[0028]
In addition to the cam sensor 21, an air flow meter 23 for detecting the intake air amount of the engine is included in a control unit 22 incorporating a microcomputer that controls energization to the electromagnetic brake 13 to control the valve timing of the intake and exhaust valves. Detection signals from a crank angle sensor 24 that detects crank rotation, a water temperature sensor 25 that detects engine coolant temperature, an accelerator opening sensor 26 that detects an accelerator opening, and the like are input.
[0029]
The control unit 22 sets the target valve timing of the intake / exhaust valves based on the engine operating state (rotation speed, load, water temperature, etc.) detected based on the detection signals from the sensors, In order to obtain the target rotational phase of the camshaft corresponding to the target valve timing, the rotational phase is detected on the basis of the signal from the crank angle sensor 24 and the signal from the cam sensor 21, and matches the target rotational phase. Thus, the control current of the electromagnetic brake 13 is controlled.
[0030]
As a configuration according to the present invention, VTC control is performed to appropriately adjust the friction braking force that suppresses the decrease in the friction coefficient and the durability life of the electromagnetic brake clutch surface. In the following, the detected relative rotation position (rotation phase) between the camshaft 1 and the sprocket 5 is the actual angle (conversion angle with respect to the initial value) of the variable valve timing control device (VTC), and the target value is the target of the VTC. This will be described as an angle.
[0031]
FIG. 4 shows a flowchart of the VTC control including the correction control based on the clutch surface temperature according to the present invention, but for easy understanding, the clutch surface temperature estimation calculation necessary for the correction control is performed prior to the description of the VTC control. This will be described with reference to the flowchart of FIG.
In step 21, it is determined whether the VTC target angle VTCRG is not 0 (when VTC is not operating). Since the temperature of the clutch surface of the clutch member 13b differs between when the VTC is activated (when the electromagnetic brake is on) and when it is not activated (when the electromagnetic brake is off), the determination is made.
[0032]
When the VTC target angle VTCTRG is not 0, that is, when it is determined that the VTC is operating, the routine proceeds to step 22 and subsequent steps to perform the clutch surface temperature estimation calculation.
In step 22, an oil temperature sensitivity parameter GOIL that is a gain corresponding to the clutch surface temperature oil temperature element that contributes to the clutch surface temperature is used as a clutch temperature calculation oil temperature that is an oil temperature (engine oil temperature) necessary for calculating the clutch temperature. According to the deviation between VTTOIL and the oil temperature offset (reference oil temperature) OFSTOIL #, the following equation is calculated.
[0033]
GOIL = DGDT # × (VTTOIL−OFSTOIL #) + OFSGRAD #
DGDT #: Temperature-intercept conversion coefficient OFSGRAD #: Intercept offset (sensitivity at reference oil temperature OFSTOIL #)
In step 23, the clutch surface temperature oil temperature component FSKOIL that contributes to the clutch surface temperature is calculated as follows.
[0034]
FSKOIL = VTTOIL + (FSSTT # −OILSTTT #) × GOIL
FSTTT #: Reference clutch surface temperature OILTT #: Reference oil temperature Step 24 calculates the VTC angle parameter GNOW, which is a gain for the VTC angle element contributing to the clutch surface temperature. Since the gain corresponding to the VTC angle element varies depending on the engine speed, it is calculated as follows according to the deviation between the actual engine speed HNRPM and the engine speed offset (reference engine speed) OFSNE #.
[0035]
GNOW = DTTDNE # × (HNRPM−OFSNE #) + OFSDT #
DTDNE #: Engine rotation speed-temperature increase rate conversion coefficient OFSDT: Temperature conversion rate offset (temperature conversion rate at the reference engine rotation speed)
In step 25, the VTC angle element component FSKNOW that contributes to the clutch surface temperature is calculated as follows.
[0036]
FSKNOW = (VTCNOW−NOWST #) × GNOW
VTCNOW: VTC actual angle NOWST #: VTC reference angle In step 26, the engine rotational speed component FSKNE that contributes to the clutch surface temperature is calculated as follows.
[0037]
FSKNE = (HNRPM−NEST #) × GNE #
NEST #: Reference engine rotational speed GNE #: Engine rotational speed sensitivity parameter Step 27 adds the oil temperature component FSKKOIL, VTC angle component FSKNOW, and engine rotational speed component FSLNE to obtain the VTC clutch surface equilibrium temperature FSEQT. calculate.
[0038]
FSEQT = FSKOIL + FSKNOW + FSKNE
Further, when the VTC target angle VTCTRG is 0 in step 21, that is, when the VTC is not operating, no heat is generated due to clutch sliding, so the clutch surface temperature is equal to the oil temperature. In step 28, the clutch temperature calculation oil temperature VTTOIL Is set as the clutch surface equilibrium temperature FSEQT.
[0039]
In step 29, since the clutch surface temperature change can be treated as a temporary delay, a temporary delay process is performed on the clutch surface equilibrium temperature FSEQ to calculate the estimated clutch surface temperature FSEST.
FSEST = (1-TCFS #) × FSESTz + TCFS # FSEQUT
In the previous step 30 of TCFS #: clutch surface temperature rise time constant FSESTz: FSEST, the clutch surface temperature is determined using the clutch surface estimated temperature FSEST calculated as described above. That is, it is determined whether or not the clutch surface estimated temperature FSEST is equal to or higher than the predetermined temperature HITTS #.
[0040]
Then, if the condition of FSEST ≧ HIFTTS # is satisfied in step 30, and if FSEST ≧ HIFTTS # −10 ° C. with hysteresis is satisfied after the condition is satisfied, the process proceeds to step 31. Clutch surface high temperature determination flag #HIFST is set to 1.
If the condition of FSEST ≧ HIFTTS # is not satisfied in Step 30, or if the condition is satisfied and FSEST <HIFTTS # −10 ° C. with hysteresis is satisfied, the clutch surface temperature is not high. The process proceeds to step 33, and the clutch surface high temperature determination flag #HIFST is reset to zero.
[0041]
Next, VTC control will be described with reference to the flowchart of FIG.
In step 1, it is determined whether the clutch surface high temperature determination flag #HIFST set as described above is 1, that is, whether the clutch surface is in a high temperature state equal to or higher than a predetermined temperature.
When # HIFST = 1 (high temperature), the process proceeds to step 2 to determine whether the high load determination flag FFULAPO is 0 or not. The high load determination flag FFULAP0 is set to 1 when it is detected that the accelerator opening detected by the accelerator opening sensor 26 is not less than a predetermined opening close to full open, for example, during acceleration. It has become.
[0042]
When the high load determination flag FFULAPO is determined to be 0, the process proceeds to step 3 and subsequent steps in order to execute the friction braking force decrease correction control.
In step 3, a clutch temperature deviation amount FSTHT (= FSEST-HIFTTS #) of the clutch surface estimated temperature FSEST calculated in a clutch surface temperature calculation routine described later with respect to the clutch surface high temperature determination temperature HITTS # is calculated.
[0043]
In step 4, it is determined whether the VTC angle sensitivity parameter GNOW representing the clutch surface temperature change amount per unit VTC angle (conversion angle) is not zero.
When the VTC angle parameter GNOW is not 0, the routine proceeds to step 5 where the clutch protection retardation amount VTTH is calculated by dividing the clutch temperature deviation amount FSTHT by the VTC angle sensitivity parameter GNOW as in the following equation.
[0044]
VTTH (degCA) = FSTHT (° C) / GNOW (° C / degCA)
In step 6, the clutch protection retardation amount VTTH calculated as described above is multiplied by a P-component gain KPFTVT # to calculate a P-component control amount VTTP of the clutch protection retardation amount.
VTTP = VTFTH × KPFTVT #
In step 7, an I-part control amount VTTI of the clutch protection retardation amount VTTH is calculated as follows using the clutch protection retardation amount VTTH and the I gain KIFTVT #.
[0045]
VTTI = VTFTH × KIFTVT # + VTTIz
In the previous value step 8 of VTTIz: VTTI, the P-part control amount VTTP and the I-part control amount VTTI are added to calculate the feedback control amount VTFFTH of the clutch protection retardation amount VTTH.
[0046]
VTFFTH = VTTP + VTFTI
In step 9, a lower limiter process is performed so that the feedback control amount VTFFTH is maintained at 0 or more.
In step 10, the feedback control amount VTFFTH subjected to the lower limiter process is subtracted and corrected from the VTC basic target angle BASTRG to calculate a VTC corrected basic target angle BSTRG.
[0047]
BSTRG = BASTRG-VTFFTH
In step 11, a lower limiter process is performed so that the VTC-corrected basic target angle BSTRG subjected to the subtraction correction does not become smaller than the most retarded angle position regulated by the stopper.
Further, when the VTC angle sensitivity parameter GNOW is 0 in step 4, in order to avoid the division by GNOW = 0 in step 5, the routine proceeds to step 12 and the feedback control amount VTFFTH of the clutch surface protection retardation amount is set to the upper limit value. (When the control amount is 1 byte [FF]).
[0048]
On the other hand, when #HIFST is 0 in step 1, it is determined that the current clutch surface temperature is low and does not increase so as to affect the friction coefficient. In step 2, the high load determination flag FFULAP0 is determined to be 1. In such a case, it is determined that the required engine torque is so high that the friction braking force decrease correction control must be prohibited, such as during sudden acceleration, and both control is not performed based on the clutch surface temperature. The basic target angle BASTRG is set to the VTC corrected basic target angle BSTRG.
[0049]
In this way, only when the output demand of the engine is extremely high, while ensuring normal VTC control to satisfy the demand (even if the clutch surface becomes hot), otherwise, By performing feedback control so that the clutch surface temperature is maintained below the reference temperature while estimating the clutch surface temperature, it is possible to suppress a decrease in the friction coefficient of the clutch surface and enhance the durability of the clutch.
[0050]
6 and 7 show changes in various states when the VTC correction control based on the clutch surface temperature according to the above embodiment is performed. When the clutch surface estimated temperature FSEST becomes equal to or higher than the predetermined temperature HITTS #, correction control is started, and control is performed to maintain the VTC basic target angle BASTRG in the vicinity of the predetermined temperature HITTS # while switching to the VTC corrected basic target angle BSTRG.
[0051]
Further, as shown in FIG. 7, even when the clutch surface estimated temperature FSEST is equal to or higher than the predetermined temperature HITFT #, the correction control is prohibited and the VTC basic is disabled at a high load higher than a predetermined level such that the high load determination flag FFULAPO is set. The engine output is ensured by giving priority to the control for maintaining the target angle BASTRG.
In the embodiment described above, the correction control is prohibited when the required engine torque is greater than a predetermined value. However, the correction control amount may be variably set according to the magnitude of the required engine torque.
[0052]
In addition, as described above, when engine oil deteriorates, the copper content in the oil increases, and the copper component causes a chemical reaction with the material of the clutch surface to advance the deterioration of the clutch surface. Therefore, the predetermined temperature HITTS # prohibiting the correction control in the embodiment may be set so as to be corrected to a lower temperature side as the degree of deterioration of the engine oil is larger. In that case, if the degree of deterioration of the engine oil is estimated according to the distance traveled since the engine oil was changed, it can be estimated easily and accurately.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view and a partial side view of a variable valve timing device according to an embodiment.
FIG. 2 is a sectional view showing a schematic configuration in which the function of the variable valve timing device is clarified.
FIG. 3 is a perspective view showing a stopper forming portion of the variable valve timing device.
FIG. 4 is a flowchart showing a main routine of valve timing control in the embodiment.
FIG. 5 is a flowchart showing a clutch surface temperature estimation routine in the embodiment.
FIG. 6 is a time chart showing a first pattern in the embodiment.
FIG. 7 is a time chart showing a second pattern in the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Cam shaft 13 ... Electromagnetic brake 21 ... Cam sensor 22 ... Control unit 24 ... Crank angle sensor 26 ... Accelerator opening sensor

Claims (10)

In a variable valve timing device for an internal combustion engine that variably controls the valve timing by changing the rotational phase of the camshaft relative to the crankshaft by friction braking by an electromagnetic brake,
By correcting the valve timing control amount so as to reduce the friction braking force of the electromagnetic brake when the temperature of the electromagnetic brake is higher than a predetermined temperature, the temperature increase of the electromagnetic brake is suppressed and the friction of the clutch surface of the electromagnetic brake is reduced. A control device for a variable valve timing device, characterized in that a decrease in coefficient due to a temperature rise is suppressed . In a variable valve timing device for an internal combustion engine that variably controls the valve timing by changing the rotational phase of the camshaft relative to the crankshaft by friction braking by an electromagnetic brake,
When the temperature of the electromagnetic brake is higher than a predetermined value, the valve timing control amount is corrected so as to decrease the friction braking force of the electromagnetic brake, and when the required engine torque is higher than the predetermined value, the friction braking force of the electromagnetic brake is reduced. A control device for a variable valve timing device, which prohibits correction of a valve timing control amount to be decreased. In a variable valve timing device for an internal combustion engine that variably controls the valve timing by changing the rotational phase of the camshaft relative to the crankshaft by friction braking by an electromagnetic brake,
Correcting the valve timing control amount so as to reduce the friction braking force of the electromagnetic brake when the temperature of the electromagnetic brake is higher than a predetermined temperature, and variably setting the predetermined temperature according to the degree of deterioration of the engine oil. A control device for a variable valve timing device.   4. The control device for a variable valve timing device according to claim 1, wherein the temperature of the electromagnetic brake is estimated based on at least an engine temperature. 5.   The control device for a variable valve timing device according to any one of claims 1 to 4, wherein the temperature of the electromagnetic brake is estimated based on at least an engine rotational speed. 6. The control device for a variable valve timing device according to claim 4 , wherein the temperature of the electromagnetic brake is estimated based on a valve timing control amount . The variable valve timing according to any one of claims 1 to 6 , wherein a correction amount of a valve timing control amount for reducing the friction braking force of the electromagnetic brake is set according to a required engine torque. Control device for the device.   8. The control device for a variable valve timing device according to claim 7, wherein the required engine torque is calculated from an accelerator opening. 4. The control device for a variable valve timing device according to claim 3 , wherein the predetermined temperature is set to a lower temperature as the degree of deterioration of the engine oil is larger. 10. The control device for a variable valve timing device according to claim 3, wherein the deterioration degree of the engine oil is estimated according to a travel distance from when the engine oil is changed.

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