Patent Description:
Patent Document <NUM> describes an electric valve timing adjuster for adjusting the valve timing of an engine by using the running torque of a motor. In Patent Document <NUM>, the phase of a camshaft (camshaft phase) relative to an actual crankshaft is calculated based on a camshaft angle, a crankshaft angle, the temperature of lubricating oil, a coolant temperature, and the turning angle of a motor shaft, and a target camshaft phase is calculated according to engine operating conditions. The camshaft phase is calculated in synchronization with the rotation angle of the engine, thereby delaying updates during low revolutions. Thus, the turning angle of the motor shaft is detected using a motor rotation angle sensor, and the phase angle of a variable valve timing control (VTC) mechanism is interpolated.

Patent Document <NUM> discloses a control device and control method for an internal combustion engine. ECM calculates a detected value of a rotating phase on the basis of a crank angle signal and a cam angle signal and transmits the detected value and a calculation timing information of the detected value to an electric VTC driver through a communication circuit. The electric VTC driver inputs a motor angle signal and the crank angle signal, calculates a varying amount of a rotating phase on the basis of a motor angle signal, modifies the varying amount on the basis of the calculation timing information and the crank angle signal and interpolates the detected value on the basis of the after its modification.

Patent Document <NUM>: <CIT>; Patent Document <NUM>: <CIT>.

To reduce the cost of a VTC system, the removal of a motor rotation angle sensor has been examined. For this purpose, phase angle interpolation may be performed according to a motor current by using, for example, the torque-current (T-I) characteristics and the torque-rotating speed (T-N) characteristics of a DC motor.

Unfortunately, phase angle interpolation according to a motor current based on T-I characteristics and T-N characteristics may have low accuracy. A first factor in reducing accuracy is that the T-I characteristics and T-N characteristics are stationary characteristics, whereas VTC repeats a phase advance angle-retard angle by the forward/backward rotations of the motor, leading to a rapid change of a phase angle depending upon a change of a motor current. A second factor is that the T-I characteristics and T-N characteristics are the characteristics of the motor alone, whereas VTC is affected by various factors other than a motor torque, causing a change of a phase angle to exceed an actual change.

The present invention has been devised in view of these circumstances. An object of the present invention is to provide a control device and a control method for a variable valve timing mechanism so as to improve the accuracy of cam phase angle interpolation without using a motor rotation angle sensor.

The aforementioned object is achieved by the subject matter of the independent claims. A control device for a variable valve timing mechanism is a control device for a variable valve timing mechanism configured to detect the phase angle of a cam based on a cam signal and control the phase angle of the cam by using an electric motor, the control device including a controller configured to calculate a motor torque from a motor current based on motor characteristics, calculate a motor rotation angle at least based on the motor torque and an engine operating state, and interpolate the cam phase angle of the variable valve timing mechanism from the motor rotation angle, wherein the controller calculates the motor rotation angle by using an engine speed, an engine rotation angle, and an engine oil temperature in the calculation of the motor rotation angle.

A control method for a variable valve timing mechanism is a control method for a variable valve timing mechanism configured to detect the phase angle of a cam based on a cam signal and control the phase angle of the cam by using an electric motor, the control method including: calculating a motor torque from a motor current based on motor characteristics, calculating a motor rotation angle at least based on the motor torque and an engine operating state, interpolating the cam phase angle of the variable valve timing mechanism from the motor rotation angle, and correcting the calculation of the motor rotation angle by using an engine speed, an engine rotation angle, and an engine oil temperature.

According to the present invention, in interpolation between phase angle detections based on a cam signal, a motor torque is estimated from a motor current based on motor characteristics, and then a motor rotation angle is estimated to perform interpolation based on an equation of motion using the motor torque and an engine operating state. This can achieve cam phase angle interpolation with high accuracy without using a motor rotation angle sensor. Cam phase angle interpolation can be performed without using a motor rotation angle sensor, achieving cost reduction for a VTC system.

<FIG> is a system block diagram of an internal combustion engine to which a control device for a variable valve timing mechanism is applied according to the embodiments of the present invention.

An internal combustion engine (engine) <NUM> is installed in a vehicle and is used as a power source. Internal combustion engine <NUM> illustrated as an in-line engine can be designed in various forms including a V-engine or a horizontally opposed engine.

An air intake duct <NUM> for internal combustion engine <NUM> has an intake air flow sensor <NUM> for detecting an intake air flow QA of internal combustion engine <NUM>.

An air intake valve <NUM> opens and closes the inlet of a combustion chamber <NUM> of each cylinder. An air intake port 102a upstream of air intake valve <NUM> has a fuel injection valve <NUM> placed for each cylinder. In this example, fuel injection valve <NUM> injects fuel into air intake duct <NUM>. The internal combustion engine may be a cylinder direct-injection combustion engine that directly injects fuel into the combustion chamber <NUM>.

Fuel injected from fuel injection valve <NUM> is sucked with air into combustion chamber <NUM> through air intake valve <NUM> and is ignited and burned by spark ignition of an ignition plug <NUM>, and a pressure by the combustion presses down a piston <NUM> toward a crankshaft <NUM>, thereby rotating crankshaft <NUM>.

An exhaust valve <NUM> opens and closes the outlet of combustion chamber <NUM>. The opening of exhaust valve <NUM> ejects exhaust gas in combustion chamber <NUM> into an exhaust pipe <NUM>.

Exhaust pipe <NUM> has a catalyst converter <NUM> containing a three-way catalyst or the like. Catalyst converter <NUM> purifies exhaust gas.

Air intake valve <NUM> opens in response to the rotation of an air intake camshaft 115a rotated by crankshaft <NUM>. Exhaust valve <NUM> opens in response to the rotation of an exhaust camshaft 115b rotated by crankshaft <NUM>.

A VTC mechanism <NUM> is an electric VTC mechanism that changes the relative rotational phase angle of air intake camshaft 115a relative to crankshaft <NUM> by means of an electric motor (brushed DC motor) acting as an actuator, thereby successively changing the phase of the valve operating angle of air intake valve <NUM>, that is, the valve timing of air intake valve <NUM> in the advance angle direction and the retard angle direction.

Moreover, ignition plug <NUM> provided for each cylinder has an ignition module <NUM> for supplying ignition energy to ignition plug <NUM>, ignition module <NUM> being directly mounted on ignition plug <NUM>. Ignition module <NUM> includes a power transistor for controlling an ignition coil and energization to the ignition coil.

A control device (electronic control unit) <NUM> includes an electric VTC controller 201a for controlling the driving of VTC mechanism <NUM> and an engine control module (hereinafter, will be referred to as ECM) 201b for controlling, for example, fuel injection valve <NUM> and ignition module <NUM>. Electric VTC controller 201a and ECM 201b are each provided with a microcomputer including, for example, a CPU, RAM, and ROM. The manipulated variables of various devices are calculated by performing arithmetic processing according to programs stored in advance in memory, e.g., ROM, and then the manipulated variables are output. Moreover, electric VTC controller 201a includes a driving circuit, e.g., an inverter for driving the motor of VTC mechanism <NUM>.

Electric VTC controller 201a and ECM 201b are configured so as to transfer data to each other via a CAN (Controller Area Network) 201c.

In addition to electric VTC controller 201a and ECM 201b, an AT controller or the like for controlling, for example, an automatic transmission combined with an internal combustion engine is connected to CAN 201c that serves as a communication network.

Control device <NUM> receives, in addition to intake air flow QA output from intake air flow sensor <NUM>, output signals from a crank angle sensor <NUM> for outputting a turning angle signal POS of crankshaft <NUM>, an acceleration position sensor <NUM> for detecting the amount of pedaling of an accelerator pedal <NUM>, that is, an accelerator position ACC, a cam angle sensor <NUM> for outputting a turning angle signal CAM of air intake camshaft 115a, a water temperature sensor <NUM> for detecting a temperature TW of coolant of internal combustion engine <NUM>, an air-fuel ratio sensor <NUM> that is installed on exhaust pipe <NUM> upstream of catalyst converter <NUM> and detects an air-fuel ratio AF based on an oxygen concentration in exhaust gas, and an oil temperature sensor <NUM> for detecting an oil temperature TO of engine oil in an oil pan (or the circulation path of engine oil). Control device <NUM> further receives a signal IGNSW from an ignition switch (engine switch) <NUM> serving as a main switch for operating and stopping internal combustion engine <NUM>.

Turning angle signal POS output by crank angle sensor <NUM> is a pulse signal for each unit crank angle (e.g., <NUM> degrees CA) and is constructed to have at least one missing pulse for each crank angle (a crank angle of <NUM> degrees in a four-cylinder engine) corresponding to a stroke phase difference between cylinders (ignition interval).

Crank angle sensor <NUM> can be configured to output turning angle signal POS (unit crank angle signal) for each unit crank angle and a reference crank angle signal for each crank angle corresponding to a stroke phase difference between cylinders (ignition interval). In this case, the output position of a missing portion of turning angle signal POS for each unit crank angle or the reference crank angle signal indicates a reference piston position for each cylinder.

Cam angle sensor <NUM> outputs turning angle signal CAM at each crank angle corresponding to a stroke phase difference between cylinders (ignition interval).

In this case, air intake camshaft 115a rotates at a half speed of the rotation speed of the crankshaft <NUM>. Thus, if internal combustion engine <NUM> is a four-cylinder engine and a crank angle corresponding to a stroke phase difference between cylinders (ignition interval) is <NUM> degrees CA, the crank angle of <NUM> degrees CA corresponds to a turning angle of <NUM> degrees of the air intake camshaft 115a. In other words, each time the air intake camshaft 115a is rotated <NUM> degrees, cam angle sensor <NUM> outputs turning angle signal CAM.

Turning angle signal CAM is a signal (cylinder identification signal) for identifying a cylinder located at the reference piston position. Turning angle signal CAM is output as a pulse having the property of indicating a cylinder number for each crank angle corresponding to a stroke phase difference between cylinders (ignition interval).

For example, in the case of a four-cylinder engine in which a first cylinder, a third cylinder, a fourth cylinder, and a second cylinder are sequentially ignited, cam angle sensor <NUM> outputs a single pulse signal, three pulse signals, four pulse signals, and two pulse signals at respective crank angles of <NUM> degrees, thereby identifying the cylinder located at the reference piston position based on a pulse number. Alternatively, turning angle signal CAM can indicate the cylinder number based on a pulse width or an amplitude instead of a pulse number.

<FIG> each illustrate an example of the structure of VTC mechanism <NUM> in <FIG>.

The structure of VTC mechanism <NUM> is not limited to those illustrated in <FIG>, provided that a voltage is applied to a brushed DC motor only during phase conversion so as to rotate a motor shaft part relative to a sprocket part and convert the phase of a cam shaft part.

As illustrated in <FIG>, VTC mechanism <NUM> includes a timing sprocket (cam sprocket)<NUM> serving as a driving rotor rotated by the crankshaft <NUM> of internal combustion engine <NUM>, air intake camshaft 115a that is rotatably supported on a cylinder head with a bearing <NUM> interposed therebetween and is rotated by a torque transmitted from timing sprocket <NUM>, a cover member <NUM> that is disposed at the front of timing sprocket <NUM> and is fixed to a chain cover <NUM> with a bolt, and a phase changing mechanism <NUM> that is disposed between timing sprocket <NUM> and air intake camshaft 115a and changes the relative rotational phase angle of air intake camshaft 115a relative to timing sprocket <NUM>.

Timing sprocket <NUM> includes a sprocket body 1a and a gear part 1b that is integrated with the outer surface of sprocket body 1a and receives a torque from crankshaft <NUM> via a wound timing chain <NUM>.

Moreover, timing sprocket <NUM> is rotatably supported on air intake camshaft 115a by a third ball bearing <NUM> that is interposed between a circular groove 1c formed on the inner surface of sprocket body 1a and the outer surface of a flange part 2a integrated with the front end of air intake camshaft 115a.

On the outer edge of the front end of sprocket body 1a, an annular protrusion 1e is integrally formed.

At the front end of sprocket body 1a, an annular member <NUM> and a ring-shaped plate <NUM> are both fastened and fixed with bolts <NUM> in the axial direction, annular member <NUM> being coaxially positioned on the inner surface of annular protrusion 1e with internal teeth 19a provided as wavy engaged portions on the inner surface of annular member <NUM>.

As illustrated in <FIG>, a stopper convex portion 1d provided as an arc-shaped engaging portion is formed on a part of the inner surface of sprocket body 1a so as to circumferentially extend over the range of a predetermined length.

On the outer surface of the front end of plate <NUM>, a cylindrical housing <NUM> protruding forward is fixed with a bolt <NUM> so as to cover the components of a speed reducer <NUM> and an electric motor <NUM>, which will be described later, for phase changing mechanism <NUM>.

Housing <NUM> made of iron metals acts as a yoke and includes a holding part 5a shaped like an annular plate integrated with the front end of housing <NUM>. The outer surface of housing <NUM> along with holding part 5a is entirely covered with cover member <NUM> with a predetermined clearance formed therebetween.

Air intake camshaft 115a has a driving cam (not illustrated) provided on the outer surface of air intake camshaft 115a so as to open air intake valve <NUM> and a driven member <NUM> joined as a driven rotor to the front end of air intake camshaft 115a with a cam bolt <NUM> in the axial direction.

Moreover, as illustrated in <FIG>, flange part 2a of air intake camshaft 115a has a stopper concave groove 2b circumferentially formed as a locking part that receives engaged stopper convex portion 1d of sprocket body 1a.

Stopper concave groove 2b is formed into an arc with a predetermined length in the circumferential direction. Both edges of stopper convex portion 1d rotating in the range of the length come into contact with circumferentially facing edges 2c and 2d, respectively, thereby regulating the relative rotation position of air intake camshaft 115a relative to timing sprocket <NUM> on the maximum advance-angle side and the maximum retard-angle side.

In other words, the range of angle for moving stopper convex portion 1d in stopper concave groove 2b is the variable range of the relative rotational phase angle of air intake camshaft 115a relative to crankshaft <NUM>, that is, the variable range of valve timing.

A bearing surface portion 10c like a flange is integrally formed on an edge near a shaft portion 10b of a head portion 10a of cam bolt <NUM>. The outer surface of shaft portion 10b has an external thread portion screwed into an internal thread portion that is internally formed from the end of air intake camshaft 115a in the axial direction.

Driven member <NUM> is made of iron metals and includes, as illustrated in <FIG>, a disk portion 9a formed at the front end of driven member <NUM> and a cylindrical portion 9b integrally formed at the rear end of driven member <NUM>.

An annular step protrusion 9c is integrally provided substantially at the central position of the rear end of disk portion 9a in the radial direction, annular step protrusion 9c having substantially the same outside diameter as flange part 2a of air intake camshaft 115a.

Moreover, the outer surface of annular step protrusion 9c and the outer surface of flange part 2a are inserted into an inner ring 43a of third ball bearing <NUM>. Third ball bearing <NUM> has an outer ring 43b that is press-fitted and fixed to the inner surface of circular groove 1c of sprocket body 1a.

On the outer surface of disk portion 9a, a holder <NUM> for holding a plurality of rollers <NUM> is integrally provided.

Holder <NUM> is formed so as to protrude from the outer surface of disk portion 9a in the same direction as cylindrical portion 9b and includes a plurality of long slender protrusions 41a circumferentially placed with predetermined clearances at substantially regular intervals.

Cylindrical portion 9b has an insertion hole 9d that penetrates at the center so as to receive inserted shaft portion 10b of cam bolt <NUM>. The outer surface of cylindrical portion 9b has a first needle bearing <NUM>.

Cover member <NUM> is made of a synthetic resin material and includes a cover body 3a expanded like a cup and a bracket 3b integrated with the outer surface of the rear end of cover body 3a.

Cover body 3a is disposed to substantially cover the rear end of housing <NUM> from the front end of phase changing mechanism <NUM>, that is, a holding part 5b of housing <NUM> in the axial direction with a predetermined clearance formed between cover body 3a and housing <NUM>. Bracket 3b is substantially ring-shaped and has bolt insertion holes 3f penetrating respective six bosses.

In cover member <NUM>, bracket 3b is fixed to chain cover <NUM> via a plurality of bolts <NUM>, and two inner and outer slip rings 48a and 48b are embedded and fixed into the inner surface of a front end 3c of cover body 3a such that the inner end faces of slip rings 48a and 48b are exposed.

Furthermore, the upper end of cover member <NUM> has a connector part <NUM> containing a connector terminal 49a fixed while being connected to slip rings 48a and 48b via a conductive member.

Connector terminal 49a receives power supply from a battery power supply, which is not illustrated, via control device <NUM>.

Between the inner surface of the rear end of cover body 3a and the outer surface of housing <NUM>, a first oil seal <NUM> having a large diameter is disposed as a seal member.

First oil seal <NUM> is substantially channel-shaped in cross section and includes a cored bar embedded in a substrate made of synthetic rubber. Annular base portion 50a is fit and fixed into a circular groove 3d formed on the inner surface of the rear end of cover body 3a.

Moreover, on the inner surface of annular base portion 50a of first oil seal <NUM>, a seal surface 50b is integrally formed in contact with the outer surface of housing <NUM>.

Phase changing mechanism <NUM> includes electric motor <NUM> that is substantially coaxially disposed at the front end of air intake camshaft 115a and speed reducer <NUM> that reduces the rotation speed of electric motor <NUM> and transmits the rotation speed to air intake camshaft 115a.

Electric motor <NUM> is a brushed DC motor including housing <NUM> serving as a yoke rotating integrally with timing sprocket <NUM>, a motor shaft <NUM> serving as an output shaft rotatably provided in housing <NUM>, a pair of semicircular permanent magnets <NUM> and <NUM> fixed to the inner surface of housing <NUM>, and a stator <NUM> fixed to the inner bottom of holding part 5a.

Motor shaft <NUM> is cylindrical and acts as an armature. An iron-core rotor <NUM> having a plurality of poles is circumferentially fixed substantially at the central position of motor shaft <NUM> in the axial direction, and a magnetic coil <NUM> is circumferentially wound around iron-core rotor <NUM>.

Furthermore, a commutator <NUM> is press-fit and fixed to the outer surface of the front end of motor shaft <NUM>. For commutator <NUM>, magnetic coil <NUM> is connected to separate segments as many as the number of poles of iron-core rotor <NUM>.

Motor shaft <NUM> is rotatably supported on the outer surface of shaft portion 10b near head portion 10a of cam bolt <NUM> via needle bearing <NUM> serving as a first bearing and a fourth ball bearing <NUM> disposed on one side of needle bearing <NUM> in the axial direction.

At the rear end of motor shaft <NUM> near air intake camshaft 115a, a cylindrical eccentric shaft portion <NUM> is integrally provided to constitute a part of speed reducer <NUM>.

Moreover, between the outer surface of motor shaft <NUM> and the inner surface of plate <NUM>, a second oil seal <NUM> is provided as a friction member for preventing leakage of lubricating oil from the inside of speed reducer <NUM> to the inside of electric motor <NUM>.

The inner circumstance of second oil seal <NUM> is elastically in contact with the outer surface of motor shaft <NUM>, thereby providing a friction resistance for the rotation of motor shaft <NUM>.

Speed reducer <NUM> is mainly composed of eccentric shaft portion <NUM> for making an eccentric rotational motion, a second ball bearing <NUM> serving as a second bearing circumferentially provided around eccentric shaft portion <NUM>, rollers <NUM> circumferentially provided around second ball bearing <NUM>, holder <NUM> that accepts a radial motion while holding rollers <NUM> in the rolling direction, and driven member <NUM> integrated with holder <NUM>.

The axis of a cam face formed on the outer surface of eccentric shaft portion <NUM> is slightly misaligned from axis X of motor shaft <NUM> in the radial direction. Second ball bearing <NUM> and rollers <NUM> or the like are configured as a planetary engagement part.

Second ball bearing <NUM> has a large diameter and substantially entirely overlaps at the radial position of first needle bearing <NUM>. Second ball bearing <NUM> has an inner ring 33a that is press-fit and fixed to the outer surface of eccentric shaft portion <NUM>, and rollers <NUM> are always in contact with the outer surface of an outer ring 33b of second ball bearing <NUM>.

Furthermore, an annular clearance C is formed around the outer ring 33b. Clearance C allows the overall second ball bearing <NUM> to radially move according to the eccentric rotation of eccentric shaft portion <NUM>, that is, make an eccentric motion.

Rollers <NUM> are fit into internal teeth 19a of annular member <NUM> while radially moving according to the eccentric motion of second ball bearing <NUM>, and rollers <NUM> are caused to radially make oscillatory movements while being guided by protrusions 41a of holder <NUM> in the circumferential direction.

Lubricating oil is supplied into speed reducer <NUM> from a lubricating oil supply mechanism.

The lubricating oil supply mechanism includes an oil supply line 44a that is formed in bearing <NUM> of the cylinder head and receives lubricating oil supplied from a main oil gallery, which is not illustrated, an oil supply orifice <NUM> that is formed in air intake camshaft 115a in the axial direction and communicates with oil supply line 44a via a groove, a small-diameter oil supply orifice <NUM> that is formed to penetrate driven member <NUM> in the axial direction and has one end opened to oil supply orifice <NUM> and the other end opened near first needle bearing <NUM> and second ball bearing <NUM>, and three large-diameter oil drain holes (not illustrated) that are similarly formed to penetrate driven member <NUM>.

The operations of VTC mechanism <NUM> will be described below.

First, timing sprocket <NUM> is rotated via timing chain <NUM> in response to the rotation of crankshaft <NUM> of internal combustion engine <NUM>, and then a torque from timing sprocket <NUM> causes a synchronous rotation of electric motor <NUM> via housing <NUM>, annular member <NUM>, and plate <NUM>.

The torque of annular member <NUM> is transmitted from rollers <NUM> to air intake camshaft 115a via holder <NUM> and driven member <NUM>. Thus, the cam of air intake camshaft 115a opens and closes air intake valve <NUM>.

When VTC mechanism <NUM> changes the relative rotational phase angle of air intake camshaft 115a relative to crankshaft <NUM>, that is, the valve timing of air intake valve <NUM>, control device <NUM> energizes magnetic coil <NUM> of electric motor <NUM> and drives electric motor <NUM>. In response to a rotation of electric motor <NUM>, the torque of the motor is transmitted to air intake camshaft 115a via speed reducer <NUM>.

Specifically, when eccentric shaft portion <NUM> makes an eccentric rotation in response to a rotation of motor shaft <NUM>, each roller <NUM> rolls from an internal tooth 19a of annular member <NUM> into an adjacent internal tooth 19a while being guided by protrusions 41a of holder <NUM> in the radial direction in each rotation of motor shaft <NUM>. Rollers <NUM> come into rolling contact in the circumferential direction while sequentially repeating this process.

The rolling contact of rollers <NUM> transmits a torque to driven member <NUM> while reducing the rotation speed of motor shaft <NUM>. A reduction ratio upon the transmission of the rotation of motor shaft <NUM> to driven member <NUM> can be optionally set according to, for example, the number of rollers <NUM>.

This allows air intake camshaft 115a to rotate forward and backward relative to timing sprocket <NUM> so as to change the relative rotational phase angle, thereby changing the opening/closing timing of air intake valve <NUM> to the advance angle side or the retard angle side.

In this case, the forward and backward rotation of air intake camshaft 115a relative to timing sprocket <NUM> is regulated by bringing each side of stopper convex portion 1d into contact with one of facing edges 2c and 2d of stopper concave groove 2b.

In other words, driven member <NUM> rotates in the same direction as the rotation direction of timing sprocket <NUM> according to an eccentric rotation of eccentric shaft portion <NUM>, allowing one side of stopper convex portion 1d to come into contact with facing edge 2c on one side of stopper concave groove 2b so as to regulate a further rotation in the same direction. Thus, the relative rotational phase angle of air intake camshaft 115a relative to timing sprocket <NUM> is changed to the maximum on the advance angle side.

Driven member <NUM> rotates in the reverse direction from the rotation direction of timing sprocket <NUM>, allowing the other side of stopper convex portion 1d to come into contact with facing edge 2d of stopper concave groove 2b so as to regulate a further rotation in the same direction. Thus, the relative rotational phase angle of air intake camshaft 115a relative to timing sprocket <NUM> is changed to the maximum on the retard angle side.

In this way, control device <NUM> performs variable control on the relative rotational phase angle of air intake camshaft 115a relative to crankshaft <NUM>, that is, the valve timing of air intake valve <NUM> by controlling the energization of electric motor <NUM> of VTC mechanism <NUM>.

Control device <NUM> calculates a target phase angle (in other words, a target advance angle, target valve timing, or a target conversion angle) based on the operating states of internal combustion engine <NUM>, for example, an engine load, an engine speed, an engine temperature, and a starting condition; meanwhile, control device <NUM> detects the actual relative rotational phase angle of air intake camshaft 115a relative to crankshaft <NUM>.

Furthermore, control device <NUM> performs feedback control on a rotational phase such that the manipulated variable of electric motor <NUM> is calculated and output to bring the actual relative rotational phase angle to the target phase angle. In the feedback control, control device <NUM> calculates the manipulated variable of electric motor <NUM> by, for example, proportional-plus-integral control based on a deviation of the actual relative rotational phase angle from the target phase angle.

<FIG> illustrates an extracted principal part for the control of VTC mechanism <NUM> in control device <NUM> illustrated in <FIG>. Signal IGNSW from ignition switch <NUM> connected to a battery VBAT is input to ECM 201b and electric VTC controller 201a and starts ECM 201b and electric VTC controller 201a by turning on the ignition. ECM 201b includes an input circuit <NUM> and a CPU <NUM>. Turning angle signal CAM from cam angle sensor <NUM> and turning angle signal POS from crank angle sensor <NUM> are input to input circuit <NUM> and CPU <NUM>. ECM 201b controls fuel injection valve <NUM> and ignition module <NUM> based on these signals.

CPU <NUM> calculates, for example, a target value (target phase angle) TGVTC (degrees CA) of a rotational phase adjusted by VTC mechanism <NUM> based on the engine operating state and calculates a rotational phase ANG_CAMec (degrees CA) based on turning angle signal POS from crank angle sensor <NUM> and turning angle signal CAM of air intake camshaft 115a. CPU <NUM> further has the function of transmitting, for example, calculated target value TGVTC and calculated rotational phase ANG_CAMec to electric VTC controller 201a through CAN communications.

Electric VTC controller 201a includes a CPU <NUM>, driving circuits 214a and 214b, an internal power supply circuit <NUM>, an input circuit <NUM>, and a CAN driver circuit <NUM>. The supply terminal and the ground (GND) terminal of electric VTC controller 201a are connected to battery VBAT. This supplies power to driving circuits 214a and 214b and internal power supply circuit <NUM> via a fusible link <NUM>. Internal power supply circuit <NUM> reduces the voltage of battery VBAT, generates an internal power supply voltage of, for example, <NUM> V, and supplies the voltage to circuits in electric VTC controller 201a including CPU <NUM>.

Input circuit <NUM> receives turning angle signal CAM from cam angle sensor <NUM> and turning angle signal POS from crank angle sensor <NUM> via input circuit <NUM> of ECM 201b, and inputs turning angle signals CAM and POS to CPU <NUM>.

CAN driver circuit <NUM> is provided for performing CAN communications between electric VTC controller 201a and ECM 201b. Transmission information CAN_TX from CPU <NUM> is transmitted to ECM 201b, and reception information CAN_RX from ECM 201b is received by CPU <NUM>.

Driving circuits 214a and 214b control energization to electric motor <NUM> of VTC mechanism <NUM> based on PWM (Pulse Width Modulation) signals PWM-P and PWP-N output from CPU <NUM>. Driving circuits 214a and 214b include current sensors 218a and 218b, respectively. Driving circuits 214a and 214b each detect a current passing through the winding of electric motor <NUM> and input the current to CPU <NUM>.

Referring to the functional block diagram of <FIG>, the outline of the present invention will be described below. Electric VTC controller 201a has the function of estimating a motor torque (motor torque estimation unit <NUM>), the function of estimating a motor rotation angle (motor rotation-angle estimation unit <NUM>), the function of calculating a VTC conversion angle (conversion unit <NUM>), and the function of feedback control (feedback control unit <NUM>). In interpolation between phase angle detections based on a cam signal, a motor torque is estimated from a motor current based on motor characteristics, and then a motor rotation angle is estimated to perform interpolation based on an equation of motion using the motor torque and an engine operating state.

Specifically, in response to the input of a motor current [A] to motor torque estimation unit <NUM>, a motor torque Tmot[N·m] is calculated based on the T-I characteristics of a DC motor and is input to motor rotation-angle estimation unit <NUM>. In motor rotation-angle estimation unit <NUM>, the motor torque Tmot and influencing factors are input to the equation of motion of a motor rotation, and a motor rotation angle [deg] is calculated. Motor torque Tmot is expressed by the sum of the inertia of a VTC actuator, an influencing factor for the VTC actuator, and an influencing factor for a cam as below: <MAT> where J is a moment of inertia [kg·m2], D is a friction coefficient [N·m·sec/deg], and θ is a motor rotation angle [degrees CA].

Motor rotation angle θ is estimated based on the equation of motion of a motor rotation, and then motor rotation angle θ is converted into a VTC conversion angle [degrees CA] by conversion unit <NUM>. In conversion unit <NUM>, motor rotation angle θ calculated by motor rotation-angle estimation unit <NUM> is converted into a VTC conversion angle based on, for example, the reduction ratio of speed reducer <NUM>. The VTC conversion angle is input to feedback control unit <NUM>, and then phase angle values detected by the cam are interpolated by feedback control. Subsequently, a VTC phase angle [degrees CA] is output from feedback control unit <NUM>.

When a phase angle is detected by the cam, the detected value is selected, and then a VTC phase angle [degrees CA] based on the phase angle detected value is output from feedback control unit <NUM>.

The function of estimating a torque, the function of estimating a motor rotation angle, and the function of calculating a VTC conversion angle in electric VTC controller 201a are implemented by CPU <NUM>. A PWM signal for the VTC phase angle [degrees CA] is output to control electric motor <NUM> of VTC mechanism <NUM>.

<FIG>to <FIG> are characteristic diagrams in which a motor current, a phase angle, and a phase-angle calibration amount are compared with those of the related art while the phase angle interpolation of the present invention is applied to a VTC-phase step response. <FIG> is a characteristic diagram indicating an enlarged area ΔA in a change of the phase-angle calibration amount with time in <FIG>.

In a schematic flow of control according to the related art, a target angle (indicated by a thin broken line L1 in <FIG>) is first calculated by ECM 201b and is transmitted to electric VTC controller 201a. Electric VTC controller 201a calculates the manipulated variable of electric motor <NUM> (indicated by a thick broken line L3) based on a deviation of the received target angle from a VTC phase angle (a stepwise cam detection angle indicated by a thin solid line L2). A motor current (<FIG>) changes with the manipulated variable (driving voltage), and a VTC phase angle changes with the motor current.

In the present invention, the inertia of the VTC actuator (motor + speed reducer) is taken into consideration, thereby reproducing a VTC phase angle with a smooth transient as indicated by a thick solid line L4 in <FIG> without using a motor rotation angle sensor. Since the influencing factors are taken into consideration, a change (slope) closer to an actual change can be reproduced.

Thus, as indicated in <FIG>, the phase-angle calibration amount can be smaller than that of the related art. As indicated in <FIG>, the phase-angle calibration amount is sufficiently small as in the use of a motor rotation angle sensor (solid line MAS).

<FIG> is an explanatory drawing of a control device and a control method for a variable valve timing mechanism according to a first embodiment of the present invention. <FIG> illustrates a more detailed configuration example of the functional block for interpolation between phase angle detections in <FIG>. Electric VTC controller 201a includes motor torque estimation unit <NUM>, motor rotation-angle estimation unit <NUM>, conversion unit <NUM>, and feedback control unit <NUM>.

Motor torque estimation unit <NUM> receives a power supply voltage [V], a driving duty [%], and a motor temperature [°C], which are influencing factors to be considered for an actuator, in addition to a motor current [A] and estimates a motor torque according to at least one of the motor current, the power supply voltage, the driving duty, and the motor temperature based on the characteristics of a DC motor. The motor torque is estimated by, for example, a calculation according to a polynomial expression, reference to a table, or reference to a map.

Motor rotation-angle estimation unit <NUM> receives the estimated motor torque [N·m] and influencing factors for an engine, for example, an oil temperature [°C], an engine rotation angle [degrees CA], and an engine speed [r/min]. A motor rotation angle [degrees] is estimated by using the motor torque, the engine speed, the engine rotation angle, and the oil temperature based on the equation of motion of a motor rotation.

Subsequently, the estimated motor rotation angle is input to conversion unit <NUM>, the unit of the motor rotation angle is converted to a VTC conversion angle, and VTC phase angles are interpolated.

The VTC conversion angle [degrees CA] obtained by the unit conversion and the cam signal are input to feedback control unit <NUM>, and a VTC phase angle is detected by the cam signal. At this point, a phase angle interpolated value is calibrated to a detected value. The VTC conversion angle [degrees CA] is then output from feedback control unit <NUM>.

In this way, phase angle interpolation is performed based on the equation of motion in consideration of the influencing factors of VTC phase conversion, thereby improving the accuracy of phase angle interpolation according to a motor current.

<FIG> is a flowchart for explaining a control device and a control method for a variable valve timing mechanism according to a second embodiment of the present invention. In the second embodiment, phase angle interpolation is performed at the transient of phase angle control, whereas phase angle interpolation is not performed in a steady state. Specifically, whether phase angle control is in a transient state or not is first determined (step S1). If it is determined that phase angle control is in a transient state in which a phase angle is changed, VTC phase angle interpolation is performed (step S2). Whether phase angle control is in a transient state or not is determined according to a difference between a current phase angle and a target phase angle and/or the degree of change of the current phase angle. In step S2, an interpolated value is input as a phase angle or a detected value is input as a phase angle when the cam signal is input.

If it is determined in step S1 that phase angle control is not in a transient state, a phase angle is used as a detected value (rotating speed) without VTC phase angle interpolation (step S3). Subsequently, feedback (F/B) control is performed on the phase angle (step S4).

In this way, interpolation is stopped when phase angle interpolation is not necessary, thereby reducing a computational load.

<FIG> is a flowchart for explaining a modification of the second embodiment according to the present invention. In the present modification, whether an engine speed is at most a predetermined value or not is determined in addition to whether phase angle control is in a transient state or not. When the engine speed is at most the predetermined value, phase angle interpolation is performed. Otherwise phase angle interpolation is not performed. In other words, whether phase angle control is in a transient state or not is first determined (step S11). If it is determined that phase angle control is in a transient state, whether the engine has at most a predetermined rotating speed or not is determined (step S12). Whether phase angle control is in a transient state or not is determined according to a difference between a current phase angle and a target phase angle and/or the degree of change of the current phase angle.

If it is determined that the engine speed is at most the predetermined rotating speed, VTC phase angle interpolation is performed (step S13). In step S13, an interpolated value is input as a phase angle or a detected value is input as a phase angle when the cam signal is input.

If it is determined in step S11 that phase angle control is not in a transient state and if it is determined in step S12 that the engine speed does not have at most the predetermined rotating speed, a phase angle is used as a detected value (rotating speed) without VTC phase angle interpolation (step S14). Subsequently, feedback (F/B) control is performed on the phase angle (step S15).

The engine rotations are taken into consideration because cam detection frequency increases as the engine speed increases and a cam detection period becomes shorter than a VTC control period when the engine speed exceeds a predetermined value. This eliminates the need for phase angle interpolation. Thus, a computational load can be reduced by stopping interpolation when phase angle interpolation is not necessary.

<FIG> are waveform charts for explaining a control device and a control method for a variable valve timing mechanism according to a third embodiment of the present invention. In the third embodiment, the characteristics of an output (motor torque, motor rotation angle) relative to an input (motor current) are learned. The learning is performed, for example, before factory shipment, in a specific engine operating state (a certain engine speed or a certain oil temperature), or upon a learning request from a check tool.

In the flow of learning, a predetermined motor current is first supplied as indicated by a solid line L5 (see time t0 in <FIG>), and then the change characteristics of a VTC phase angle (= the change characteristics of a motor rotation angle) are learned. As indicated by a broken line L6, the change characteristics of a VTC phase angle are plotted like a straight line connecting the corners of a cam detection angle that changes like steps (see <FIG>).

In this way, DC motor characteristics (the slope of a solid line L7 in the T-I characteristics of <FIG>) and the coefficients of the equation of motion (a moment of inertia J, a friction coefficient D) are corrected such that the change characteristics of a motor rotation angle relative to a motor current match an actual device.

<FIG> are waveform charts for explaining a control device and a control method for a variable valve timing mechanism according to a fourth embodiment of the present invention. In the fourth embodiment, a VTC manipulated variable (corresponding to the manipulated variable of electric motor <NUM>) is learned. In this case, the manipulated variable is an amount for controlling a motor to bring a phase angle close to a target angle. The manipulated variable can be expressed by any one of a driving voltage, a duty, and a motor current. A sensor detected value can be used as the motor current. The motor current can be also estimated from a driving voltage according to the relationship "driving voltage = power supply voltage × duty. " The learning is performed, for example, before factory shipment, in a specific engine operating state (a certain engine speed or a certain oil temperature), or upon a learning request from a check tool.

In the flow of learning, a predetermined VTC manipulated variable (a driving voltage [V] and a duty[%]) is first provided as indicated by a solid line L8 (see time t1 to time t2 in <FIG>), and then the detection characteristics of a motor current indicated by a solid line L9 are learned (see time t1 to time t2 in <FIG>).

Thereafter, as indicated in <FIG>, a gain and an offset amount are calculated from the detected values and theoretical values of a motor current at two points as indicated by a solid line L10. The detected values are corrected by using the gain and the offset amount.

In this way, a VTC manipulated variable is learned so as to address variations among current sensors and changes with time, thereby improving the accuracy of phase angle interpolation.

<FIG> is a waveform chart for explaining a control device and a control method for a variable valve timing mechanism according to a fifth embodiment of the present invention. In the first to fourth embodiments, a phase angle is determined in consideration of the predetermined influencing factors for motor characteristics. In the fifth embodiment, a slope is corrected according to a deviation of an interpolated value from a detected value of a cam. In other words, the calculation of a motor torque and/or a motor rotation angle is corrected according to a difference between an interpolated value and a detected value in the calibration of a phase angle.

In the flow of correction, an interpolated value is first calibrated when a cam detection angle is updated. Subsequently, DC motor characteristics and the coefficients and constants of the equation of motion are corrected according to a difference between the interpolated value and the detected value during calibration.

If the DC motor characteristics (T-I characteristics) are corrected, the gain of the T-I characteristics is corrected so as to reduce a motor torque (motor rotation angle). Specifically, as indicated in <FIG>, a broken line represents a base state before correction while a solid line represents a corrected state.

In this way, the slope is corrected so as to bring interpolation close to a detected value, thereby improving the accuracy of phase angle interpolation. In the correction of <FIG>, the slope of motor characteristics is corrected to a smaller slope. The slope may be corrected to a steeper slope depending upon a difference between the interpolated value and the detected value.

<FIG> is a list of torques for the phase conversion of electric VTC and the influencing factors of the torques. The torques include a motor torque, an inertia torque (VTC actuator), a friction torque (VTC actuator), a cam torque, an inertia torque (engine), and a friction torque (engine). Phase angle interpolation is performed in consideration of various factors (a first order factor, a second order factor).

<FIG> is an explanatory drawing of an actuator-side torque and an engine-side torque that are relevant to the phase conversion of electric VTC in <FIG>. The VTC actuator has (A) motor torque, (B) inertia torque, and (C) friction torque, whereas the engine has (D) cam torque, inertia torque, and (F) friction torque.

The influencing factors of the torques will be specifically described below.

A motor torque is calculated from a motor current based on T-I characteristics. In the relationship between a motor torque and a motor rotation speed, the motor rotation speed decreases with an increase in motor torque as indicated by a solid line L11 in <FIG>. At this point, if a high voltage is applied, the relationship between a motor torque and a motor rotation speed is determined as indicated by a broken line L12. If a low voltage is applied, the relationship between a motor torque and a motor rotation speed is determined as indicated by a broken line L13. In this way, the T-N characteristics change according to fluctuations in applied voltage.

In the relationship between a motor current and a motor torque, a motor torque increases with a motor current as indicated by a solid line L14 in <FIG>. At this point, the relationship between a motor current and a motor torque is determined as indicated by a broken line L15 at a low motor temperature. At a high motor temperature, the relationship between a motor current and a motor torque is determined as indicated by a broken line L16. In this way, the T-I characteristics change according to fluctuations in motor temperature.

If a motor rotation angle is estimated and interpolated based on T-I characteristics and T-N characteristics (no inertia torque), the estimated value of a phase angle is obtained as indicated in <FIG> when a motor current changes as indicated in <FIG>. A thick broken line L17 indicates an estimated value without calibration while a thick solid line L18 indicates an interpolated value with calibration. A thin broken line L19 indicates a target angle while a thin solid line L20 rising like steps indicates a cam detection angle.

If an estimated value and an interpolated value are calculated in consideration of an inertia torque, an estimated value without calibration changes with a gentle slope as indicated by a thick broken line L21 in <FIG> while an interpolated value with calibration is smoothed as indicated by a thick solid line L22.

In this way, the inertia torque is taken into consideration, thereby reproducing a transient motion including the start and convergence of a smooth change of a phase angle.

As indicated in <FIG>, a friction torque is applied in proportion to a motor rotation speed. A friction torque increases with a motor rotation speed. <FIG> indicates the relationship between an oil temperature and a kinematic viscosity (friction coefficient). A kinematic viscosity tends to increase with falling oil temperature depending upon the viscosity. In other words, the friction coefficient changes according to an oil temperature. A low friction coefficient causes a small change of the friction torque, whereas a high friction coefficient causes a large change of the friction torque.

In this way, the friction torque changes according to a motor rotation speed and a friction coefficient.

When a motor current changes as indicated in <FIG>, an estimated value and an interpolated value are calculated only in consideration of an inertia torque as indicated in <FIG>. A thick broken line L25 indicates an estimated value without calibration while a thick solid line L26 indicates an interpolated value with calibration. A thin solid line L27 rising like steps indicates a cam detection angle.

The calculation of an estimated value and an interpolated value in consideration of both of an inertia torque and a friction torque reduces a change (slope) of a phase angle as indicated by a thick broken line L28 (an estimated value without calibration) and a thick solid line L29 (an interpolated value with calibration) in <FIG>.

In this way, a friction coefficient changes according to an oil temperature while the friction torque changes according to a motor rotation speed and the friction coefficient. Thus, phase angle interpolation is performed in consideration of the inertia torque and the friction torque, thereby improving the accuracy of phase angle interpolation. For example, in <FIG>, a change (slope) of a phase angle decreases, thereby improving the accuracy of phase angle interpolation.

As indicated in <FIG>, a cam torque is alternately applied according to an engine rotation angle. As indicated in <FIG>, the maximum value and the minimum value of an alternating torque change according to an engine speed.

In this way, a torque is alternately applied in VTC advance angle/retard angle directions according to the engine rotation angle, thereby affecting phase angle interpolation.

When a motor current changes as indicated in <FIG>, an estimated value and an interpolated value are calculated only in consideration of an inertia torque. An estimated value without calibration (broken line L25), an interpolated value with calibration (thick solid line L26), and a cam detection angle (thin solid line L27) are determined as indicated in <FIG>.

The calculation of an estimated value and an interpolated value in consideration of both of an inertia torque and a cam torque reduces a change (slope) of a phase angle as indicated in <FIG>. A thick broken line L30 indicates an estimated value without calibration while a thick solid line L31 indicates an interpolated value with calibration. A thin solid line L27 rising like steps indicates a cam detection angle.

In this way, a cam torque is alternately applied in VTC advance angle/retard angle directions according to the engine rotation angle and an engine speed. Thus, phase angle interpolation is performed in consideration of the inertia torque and the cam torque, thereby improving the accuracy of phase angle interpolation. For example, in <FIG>, a change (slope) of a phase angle decreases, thereby improving the accuracy of phase angle interpolation.

When an engine speed is raised, a torque is applied to the motor shaft opposite to the direction of engine rotation (traveling direction) by inertia.

In this way, a torque is applied in VTC advance angle/retard angle directions when the engine speed is raised, thereby affecting phase angle interpolation. The influence of a torque on phase conversion is taken into consideration, the torque being applied according to the acceleration and deceleration of the engine rotation. This can improve the accuracy of phase angle interpolation.

A friction torque applied around the cam shaft serves as a resistance of a phase angle change. The friction torque (around the cam shaft) changes according to the engine speed. Moreover, the friction torque (around the cam shaft) changes according to fluctuations in kinematic viscosity (friction coefficient). The kinematic viscosity changes according to an oil temperature.

Thus, the accuracy of phase angle interpolation can be improved by taking the influence of a friction torque into consideration.

Claim 1:
A control device (<NUM>) for a variable valve timing mechanism configured to detect a phase angle of a cam based on a cam signal and control the phase angle of the cam by using an electric motor (<NUM>),
the control device (<NUM>) comprising a controller (201a) configured to calculate a motor torque from a motor current based on motor characteristics, calculate a motor rotation angle (θ), and interpolate a cam phase angle of the variable valve timing mechanism from the motor rotation angle (θ),
wherein the controller (201a) is configured to estimate the motor rotation angle (θ) by using the motor torque, an engine speed, an engine rotation angle, and an engine oil temperature.