WO2014030043A2

WO2014030043A2 - Controller and control method for internal combustion engine

Info

Publication number: WO2014030043A2
Application number: PCT/IB2013/001775
Authority: WO
Inventors: Mitsuhiro Nomura
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2012-08-24
Filing date: 2013-08-14
Publication date: 2014-02-27
Also published as: WO2014030043A3; JP2014043771A

Abstract

A controller for an internal combustion engine apparatus equipped with a variable valve timing system being configured to change an operation timing of at least one of an intake valve and an exhaust valve. The controller includes an electronic control unit. The electronic control unit is configured to control an electric motor and drive the variable valve timing system within a stop period from after the internal combustion engine is stopped till the engine is started after the stop. The electronic control unit is configured to be maintained at power-on state when a temperature of at least one component of the electric motor and the drive circuit thereof is higher than a predetermined temperature even if the electronic control unit is required to be power-off state.

Description

CONTROLLER AND CONTROL METHOD FOR INTERNAL COMBUSTION

ENGINE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a controller for an internal combustion engine installed on a vehicle or the like, and more particularly to controlling an electric variable valve timing (abbreviated hereinbelow as VVT) system.

2. Description of Related Art

[0002] VVT systems in which the operation timing of an intake valve or an exhaust valve in an internal combustion engine (referred to hereinbelow also as "engine") installed, for example, on a vehicle have recently received wide acceptance. Comparatively inexpensive hydraulically actuated VVT systems are mainly used, but the usage of electric VVT systems is also being expanding. The electric VVT system can be operated even in the engine stop period in which the hydraulic pump is stopped.

[0003] For example, in the VVT system described in Japanese Patent Application Publication No. 2008-057351 (JP 2008-057351 A), the supply of fuel to the engine and the ignition are stopped in response to a stop command, the electric VVT system is thereafter operated within a period before the crankshaft rotation by inertia is stopped (complete stop), and valve timing is changed to a value suitable for subsequent engine start. Where the valve timing cannot be changed prior to the complete stop, the VVT system is also operated when the engine is started.

[0004] For example, where foreign matter penetrates to mechanical components such as meshing components of gears in the above-described electric VVT system, the increase in load may cause overheating of coils of the electric motor. Further, in a state in which the electric motor is not rotated (motor lock) and only the energization is performed, the electronic components such as the IC of the drive circuit for drive controlling the electric motor may be also overheated.

[0005] Where the electric VVT system such as described in JP 2008-057351 A is operated within a period after the engine has been stopped and before it is subsequently started (engine stop period), the electric motor or electronic components may be overheated during such operation. Thus, where the VVT system is operated immediately after the main relay has been switched off in a state in which the temperature of the electric motor or electronic components is comparatively high when the engine is stopped, an overheated state may be attained within a short period of time if the electric motor is energized in a motor lock state. This overheating may adversely affect the durability reliability of the electric motor and electronic components.

SUMMARY OF THE INVENTION

[0006] The invention provides a controller and a control method for an internal combustion engine equipped with an electric VVT system that suppress the electric motor or electronic components of the drive circuit thereof from overheating and increase the durability reliability thereof.

[0007] According to a first aspect of the invention, a controller for an internal combustion engine equipped with a VVT system that is configured to change an operation timing of at least either one of an intake valve and an exhaust valve, the controller includes an electronic control unit (ECU). The ECU is configured to control an electric motor and drive the VVT system within a stop period from after the internal combustion engine is stopped till the engine is stalled after the stop. The ECU is configured to be maintained at power-on state when a temperature of at least one component of the electric motor or a drive circuit thereof is higher than a predetermined temperature even if the electronic control unit is required to be power-off state.

[0008] With the above-described configuration, for example, when the ignition is switched off and the internal combustion engine is stopped, the ECU is maintained at the power-on state when the temperature of at least one component of the electric motor of the VVT system and drive circuit thereof becomes equal to or lower than the predetermined temperature even if the ECU is required to be power-off state. The ECU is required to be power-off state when the temperature of the component is confirmed to reduce sufficiently.

[0009] Further, with the above-described configuration, where the VVT system is operated immediately after the ECU is required to be power-off state, the component that has cooled to a temperature equal to or lower than the predetennined temperature does not immediately attain an overheated state even when the energization is perfoirned in a motor lock state. Therefore, the component of the electric motor or drive circuit of a variable valve device can be suppressed from overheating and endurance reliability thereof can be increased.

[0010] In the controller, the ECU may limits an energization amount of the electric motor when the temperature of the component is equal to or higher than a first temperature.

[0011] With such a configuration, the amount of heat generated due to the energization is decreased. Therefore, the increase in temperature of the component of the electric motor or drive circuit and overheating thereof can be suppressed.

[0012] In the controller, the ECU may prohibit energization of the electric motor when the temperature of the component is equal to or higher than a second temperature that is higher than the first temperature.

[0013] With such a configuration, the overheating of the component can be suppressed more reliably.

[0014] In the controller, the ECU may prohibit failure diagnosis of the VVT system, the electric motor and the drive circuit thereof when the temperature of the component is equal to or higher than the second temperature and the energization of the electric motor is prohibited.

[0015] With such a configuration, a diagnostic error in failure diagnosis of the electric motor and the drive circuit thereof can be suppressed.

[0016] The controller may be such that the ECU does not determine whether the ECU is required to be power-off state when the electric motor is controlled in the stop period. [0017] With such a configuration, while the VVT system is operated when the operation of the internal combustion engine is stopped, the presence/absence of the power supply OFF request is not determined and the power supply ON state is naturally maintained.

[0018] In the controller, the ECU may prohibit energization of the electric motor from when the ECU is required to be power-off state till the temperature of the component becomes equal to or lower than a temperature.

[0019] With such a configuration, the temperature of the component of the electric motor or the drive circuit thereof can be rapidly reduced and the power supply can be switched off.

[0020] In the controller, the ECU may estimate the temperature of the component on the basis of at least an energization state and a rotation state of the electric motor.

[0021] When the VVT system operates and the electric motor normally operates during the operation of the internal combustion engine, the temperature of the coils of the electric motor or electronic components of the control circuit (components) is generally maintained at a constant designed level. Where the energization is thereafter performed in a locked state, the temperature rises correspondingly to the energization time and energization amount. With the above-described configuration, the temperature of the components can be estimated on the basis of those relationships. Further, the temperature of the cooling water or lubricating oil in the internal combustion engine may be also taken into account in such estimation.

[0022] In the controller, the ECU may store the temperature of the component and a temperature state amount affecting the temperature of the component when the temperature of the component is equal to or lower than the predetermined temperature and the ECU is to be power-off state.

[0023] In addition to the external air temperature and the temperature state of the engine before the internal combustion engine is started, the temperature state at the time the internal combustion engine has heretofore been stopped may also affect the temperature of the component. With the above-described configuration, the temperature state amount that may affect the temperature of the component, that is, the cooling water temperature, lubricating oil temperature, and intake temperature, can be stored.

[0024] In the controller, the ECU may be maintained at power-on state till the temperature of the component of the electric motor and the drive circuit thereof becomes equal to or lower than the predetermined temperature.

[0025] According to a second aspect of the invention, a control method for an internal combustion engine equipped with a VVT system that is configured to change an operation timing of at least one of an intake valve and an exhaust valve, the method includes: controlling an electric motor and driving the VVT system within a stop period from after the internal combustion engine is stopped till the engine is started after the stop; and being maintained at power-on state when a temperature of at least one component of the electric motor or a drive circuit is higher than a predetermined temperature even if the ECU is required to be power-on state.

[0026] With such a configuration, the overheating of the electric motor and the drive circuit is suppressed and the durability reliability thereof is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is. a schematic configuration diagram illustrating an example of an internal combustion engine of an embodiment of the invention;

FIG. 2 is a cross-sectional view illustrating the structure of an electric VVT system of the embodiment;

FIG. 3 is a cross-sectional view taken along the III-III line in FIG. 2, this view illustrating the structure of an electric motor of the embodiment;

FIG. 4 is a cross-sectional view taken along the IV-IV line in FIG. 2, this view illustrating the structure of a phase changing mechanism of the embodiment;

FIG. 5 is a circuit diagram illustrating the configuration of a drive circuit of the electric motor of the VVT system of the embodiment;

FIG. 6 is a block diagram illustrating the configuration of an engine control system of the embodiment;

FIG. 7 is a flowchart illustrating an example of control sequence in a stop period operation mode of the VVT system of the embodiment;

FIG. 8 is a timing chart illustrating an example of operation state, temperature state, and power supply ON/OFF state after IG-OFF of the embodiment; and

FIG. 9 is a view corresponding to FIG. 8 and relating to the case in which lock energization has occurred prior to engine start in the embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0028] The embodiments of the invention will be explained below with reference to the drawings.

[0029] An internal combustion engine (referred to hereinbelow as "engine") of an embodiment of the invention will be described below with reference to FIG. 1. An engine 1 of the present embodiment is a four-cylinder gasoline engine to be installed on a vehicle. A cylinder block l a of the engine 1 is provided with four cylinders (only one cylinder is shown in FIG. 1 ). A piston l c moving reciprocatingly in the vertical direction inside the cylinder is accommodated inside each cylinder. A water jacket is disposed at a position surrounding the four cylinders in the cylinder block l a. A water temperature sensor 32 that detects the temperature of engine cooling water is disposed at the water jacket.

[0030] The reciprocating movement of the pistons l c in the four cylinders is converted by a connecting rod 16 into a rotational movement of a crankshaft 1 5. The crankshaft 15 is connected by a torque converter (or a clutch) to a transmission (not shown in the figure). As a result, the output of the engine 1 is transmitted by the transmission to the drive wheels of the vehicle. The transmission may be a multistep automatic transmission using a friction engaging element, for example, a clutch or a brake, and a planetary gear mechanism, or a belt-type continuously variable transmission.

[0031] A starter motor 10 is disposed to be connectable to the crankshaft 1 5. The starter motor 10 is actuated when the engine 1 is started and forcibly rotate (cranking) the crankshaft 15. A signal rotor 17 is mounted on the crankshaft 15. A plurality of teeth (protrusions) 17a is provided with an equal angular spacing at the outer circumferential surface of the signal rotor 17, and a gear-free section 17b where two gears 1 7a are missing is also provided therein.

[0032] A crank position sensor 3 1 is disposed in the vicinity of the plurality of gears (protrusions) 17a in the signal rotor 17. The crank position sensor 31 is, for example, an electromagnetic pickup. The crank position sensor 3 1 generates a pulse signal corresponding to the gears 17a of the signal rotor 17 when the crankshaft 15 rotates. The engine revolution speed is calculated from the output signal of the crank position sensor 3 1 .

[0033) An oil pan 18 is provided in the lower section of the cylinder block l a so as to cover the crankshaft 15. Lubricating oil (engine oil) is retained in the oil pan 18. The lubricating oil retained in the oil pan 18 is sucked up by an oil pump (not shown in the figure) when the engine 1 operates and then supplied to lubricate and cool engine components such as the piston l c, crankshaft 15, and connecting rod 16. An oil temperature sensor 30 is installed in the oil pan 18 so as to detect the temperature of the lubricating oil.

[0034] A cylinder head l b is fastened to the upper end of the cylinder block l a. The space in each cylinder that is closed at the upper end with the cylinder head 1 b forms a combustion chamber I d. The volume of the combustion chamber I d is changed by the reciprocating movement of the piston l c. A spark plug 3 is disposed in the cylinder head l b at a position facing the combustion chamber I d of each cylinder. The spark timing of the spark plug 3 of each cylinder is adjusted by an igniter 4. The igniter 4 is controlled by an electronic control unit (ECU) 200.

[0035] An intake passage 1 1 and an exhaust passage 12 communicate with the combustion chamber I d of each cylinder. The intake passage 1 1 and the exhaust passage 12 serve to take new air into the combustion chamber I d and discharge combustion gas therefrom. The downstream side (downstream side of intake flow) of the intake passage 1 1 is constituted by an intake port 1 1a and an intake manifold l i b. A surge tank 1 1 c is installed upstream of those intake port 1 la and intake manifold l i b. An air cleaner 7, an air flowmeter 33 of a hot wire system, an intake temperature sensor 34, and a throttle valve 5 are disposed in the intake passage 1 1. The air cleaner 7 filters the intake air. The intake air temperature sensor 34 may be accommodated, for example, in the air flowmeter 33. The throttle valve 5 adjusts the intake air amount of the engine 1.

[0036] In the present embodiment, the throttle valve 5 is provided upstream of the surge tank 1 1 c and driven by a throttle motor 6. The opening degree of the throttle valve 5 is detected by a throttle opening degree sensor 35 and feedback controlled by the ECU 200 so as to obtain the optimum intake air amount corresponding to the operation state of the engine 1.

[0037] Further, an injector 2 is disposed in the intake port 1 1 a of each cylinder. The injectors 2 are connected by a common delivery pipe 21 to a fuel supply system 20. For example, the fuel supply system 20 is provided with a fuel supply pipe 22 connected to the delivery pipe 21 , a fuel pump 23, and a fuel tank 24. The injector 2 is controlled by the ECU 200 and injects the fuel into each cylinder at a predetermined timing.

[0038] The fuel injected from the injector 2 into the intake port 1 l a is mixed with intake air to form a fuel/air mixture. The fuel/air mixture is introduced into the combustion chamber I d in the intake stroke of each cylinder as the intake valve 13 is opened. The fuel/air mixture is ignited by the spark plug 3 at the end of the compression stroke of the cylinder, causing burning and combustion. The high-temperature and high-pressure combustion gas pushes the piston l c down and is then discharged into the exhaust passage 12 as the exhaust valve 14 is opened.

[0039] The upstream side (upstream side of the exhaust gas flow) of the exhaust passage 12 is constituted by an exhaust port 12a and an exhaust manifold 12b. A three-way catalyst 8 is disposed on the downstream side. The three-way catalyst 8 purifies the exhaust gas discharged into the exhaust passage 12. Thus, CO and HC contained in the exhaust gas are oxidized, and, NOx is reduced, thereby generating harmless C0₂, H₂0, and N₂. [0040] A front air-fuel ratio sensor 37, for example having a linear characteristic with respect to the air-fuel ratio, is disposed in the exhaust passage 12 on the upstream side of the three-way catalyst 8. A rear O? sensor 38, for example constituted by a lambda sensor, is disposed in the exhaust passages 12 on the downstream side for the three-way catalyst 8. The output signals of the front air-fuel ratio sensor 37 and the rear 0₂ sensor 38 are returned by feedback to the ECU 200 to control the air-fuel ratio.

[0041] The intake and exhaust in the combustion chamber Id such as described hereinabove are performed by opening and closing the intake valve 13 and the exhaust valve 14. Thus, the intake valve 13 is provided between the intake port 1 1a and the combustion chamber Id, and the exhaust valve 14 is provided between the exhaust port 12a and the combustion chamber I d. The intake valve 13 and the exhaust valve 14 are opened and closed by intake and exhaust camshafts 25, 26 at respective predetermined timings. The intake and exhaust camshafts 25, 26 are rotated by the crankshaft 15 through a timing chain or the like.

[0042] More specifically, the intake and exhaust camshafts 25, 26 are rotated at a revolution speed which is half that of the crankshaft 15 and perform one revolution every two strokes of the piston lc. In other words, each camshaft 25, 26 performs one revolution, opens the intake valve 13 in the intake stroke of each cylinder, and opens the exhaust vale 14 in the exhaust stroke of each cylinder as the crankshaft 15 performs two revolutions (rotates through 720°) and the piston l c performs the intake, compression, expansion, and exhaust strokes.

[0043] A cam position sensor 39 is provided in the vicinity of the intake camshaft 25 rotating in the above-described manner. The cam position sensor 39 generates a pulse signal when the piston l c of a specific cylinder (for example, the first cylinder) reaches the compression top dead center (TDC). Similarly to the aforementioned crank position sensor 31 , the cam position sensor 39 is constituted by an electromagnetic pickup and outputs a pulse signal when one tooth (not shown in the figure) on the outer circumference of the rotor of the intake camshaft 25 passes thereby.

[0044] Further, in the present embodiment, a below-described electric VVT system 40 is mounted on the intake camshaft 25 (not shown in FIG. 1 ). The VVT system 40 continuously varies the rotation phase of the intake camshaft 25 with reference to the rotation of the crankshaft 15, thereby continuously changing the opening/closing timing of the intake valve 13 to advance or retard the timing. For example, in the partial load operation range, the VVT system 40 retards the closing timing of the intake valve 13. As a result of such retard of the closing timing of the intake valve, pumping losses can be reduced.

[0045] As shown in FIGS. 2 to 4, in the present embodiment, the VVT system 40 is installed at the end section of the intake camshaft 25. FIG 2 is a cross-sectional view illustrating the internal structure of the VVT system 40. FIGS. 3 and 4 are cross-sectional views taken along the III-III line and IV-IV line, respectively, in FIG. 2. A similar VVT system may be also installed at the exhaust camshaft 26.

[0046] In the present embodiment, the VVT system 40 adjusts the operation timing of the intake valve 13 of the engine 1 , that is, the intake valve timing, by using the running torque of an electric motor (referred to hereinbelow simply as "motor") 42 controlled by the ECU 200. Thus, the VVT system 40 of the present embodiment is configured as the so called motor drive-VVT (MD-VVT) system.

[0047] As shown in FIGS. 2 and 3, the motor 42 is a three-phase motor constituted by a motor shaft 44, bearings 46, a revolution speed sensor 47, and a stator 50. The motor shaft 44 is supported by two bearings 46 and rotates about an axial line O. The axial line O is a rotating shaft of the motor shaft 44. A disk-shaped rotor 45 protruding diametrically outward is fixed to the motor shaft 44. A plurality of magnets 45a is embedded in the outer circumferential wall of the rotor 45.

[0048] The revolution speed sensor 47 is installed in the vicinity of the rotor 45. The revolution speed sensor 47 is constituted, for example, by a Hall element and detects the revolution speed of the rotor 45, that is, the revolution speed of the motor shaft 44 (also referred to hereinbelow as "motor revolution speed"), by detecting the intensity of the magnetic field formed by the magnets 45a.

[0049] The stator 50 is installed at the outer circumferential side of the motor shaft 44 and provided with a plurality of coils arranged equidistantly around the axial line O of the motor shaft 44. In the coil, a winding 52 is wound on a core 51. As will be explained hereinbelow with reference to FIG. 5, three windings 52 make a set and are star-connected on one end sides, and the terminals at the other than star-connected sides are connected to a motor drive circuit 100. Where an electric current flows from the motor drive circuit 100 to the windings 52, a rotating magnetic field is formed on the outer circumferential side of the motor shaft 44 and a running torque is generated.

[0050] Under the control of the motor drive circuit 100, the plurality of coils of the stator 50 forms a rotating magnetic field rotating clockwise or counterclockwise about the axial line O of the motor shaft 44 as a center, when viewed from the direction shown in FIG. 3. The rotating magnetic field is formed on the outer circumferential side of the motor shaft 44. Where a clockwise rotating magnetic field is formed, the magnets 45a of the rotor 45 successively receive an attraction force and a repulsion force, and a clockwise running torque is applied to the motor shaft 44. Conversely, where the counterclockwise (as shown in FIG. 3) rotating magnetic field is formed, a counterclockwise running torque is applied to the motor shaft 44.

[0051] As shown in FIGS. 2 and 4, the VVT system 40 is provided with a phase changing mechanism 60. The phase changing mechanism 60 is provided with a sprocket 62, a ring gear 63, an eccentric shaft 64. a planetary gear 65, and an output shaft 66. The sprocket 62 is installed coaxially with the output shaft 66 on the outer circumferential side of the output shaft 66. The sprocket 62 can rotate relative to the output shaft 66 about the axial line O which is identical to the motor shaft 44.

[0052] The rotation of the crankshaft 1 5 is transmitted by a chain or the like to the sprocket 62. The sprocket 62 rotates clockwise, as shown in FIG. 4. about the axial line O, while maintaining the rotation phase with respect to the crankshaft 1 5. The ring gear 63 is constituted by an inner gear and fixed coaxially to the inner circumferential wall of the sprocket 62. Therefore, the ring gear 63 rotates integrally with the sprocket 62.

[0053] The eccentric shaft 64 is provided eccentrically with respect to the axial line O of the motor shaft 44. The eccentric shaft 64 is connected and fixed to the motor shaft 44 and rotates integrally with the motor shaft 44. The planetary gear 65 is an external gear, engaged with the ring gear 63, and provided to be capable of performing planetary movement on the inner circumferential side thereof. The planetary gear 65 is supported coaxially with the eccentric shaft 64 on the outer circumference of the eccentric shaft 64. The planetary gear 65 can rotate about an eccentric axial line P of the eccentric shaft 64.

[0054] The output shaft 66 is installed coaxially with the intake camshaft 25 and fixed with bolts to the intake camshaft 25. The output shaft 66 rotates integrally with the intake camshaft 25 about the axial line O same as that of the motor shaft 44. An annular plate-shaped engagement section 67 centered on the axial line O is formed at the output shaft 66. A plurality of engagement holes 68 is provided in the engagement section 67 equidistantly around the axial line O. A plurality of engagement protrusions 69 is provided in the planetary gear 65 equidistantly about the eccentric axial line P. The plurality of engagement protrusions 69 is disposed at positions facing the plurality of engagement holes 68. The engagement protrusions 69 protrude to the output shaft 66 side and enter the corresponding engagement holes 68.

[0055] In the VVT system 40 of such a structure, when the motor shaft 44 does not rotate relative to the sprocket 62, the planetary gear 65 rotates clockwise, as shown in FIG. 4, following the rotation of the crankshaft 15 and integrally with the sprocket 62, while maintaining the meshing position with the ring gear 63. In this case, the engagement protrusions 69 push the inner circumferential walls of the engagement holes 68 in the rotation direction. Therefore, the output shaft 66 rotates in the aforementioned clockwise direction without rotating relative to the sprocket 62. As a result, the rotation phase of the intake camshaft 25 with respect to the crankshaft 15 is maintained.

[0056] Meanwhile, where the motor shaft 44 rotates counterclockwise (as shown in FIG. 4) with respect to the sprocket 62, the planetary gear 65, due to the planetary movement thereof, changes the meshing position with the ring gear 63 while rotating clockwise relative to the eccentric shaft 64. In this case, the force by which the engagement protrusions 69 push the engagement holes 68 in the rotation direction increases and, therefore, the rotation of the output shaft 66 is advanced with respect to that of the sprocket 62. As a result, the rotation phase of the intake camshaft 25 is changed to the advance.

[0057] Conversely, where the motor shaft 44 rotates clockwise (as shown in FIG. 4) with respect to the sprocket 62, the planetary gear 65, due to the planetary movement thereof, changes the meshing position with the ring gear 63 while rotating counterclockwise relative to the eccentric shaft 64. In this case, the engagement protrusions 69 push the engagement holes 68 in the direction of reverse rotation and, therefore, the rotation of the output shaft 66 is retarded with respect to that of the sprocket 62. As a result, the rotation phase of the intake camshaft 25 is changed to the retard.

[0058] FIG. 5 shows the configuration of the motor drive circuit 100 that performs drive control of the motor 42 of the VVT system 40. The motor drive circuit 100 operates upon receiving a control signal from the ECU 200. In FIG. 5, the motor drive circuit 100 is shown to be positioned outside the motor 42, but in the present embodiment, the motor drive circuit 100 is disposed inside the case of the motor 42. Therefore, the motor drive circuit 100 is affected by the temperature of the cylinder head lb of the engine 1. The temperature, for example, is the engine water temperature or lubricating oil temperature.

[0059] The motor drive circuit 100 shown in the figure has, for example, an energization control unit 102 and a detection unit 104. The energization control unit 102 has a bridge circuit 106 in which other than the star-connected terminals of the motor 42 are connected to three arms 105. In the bridge circuit 106, one end of each arm 105 is connected to a power supply line 132 from a battery 120, and the other end of each arm 105 is grounded. In each arm 105, a switching element 108 constituted by a metal oxide semiconductor (MOS) transistor or the like is provided at each side from a connection point 107 in which the terminal of the motor 42 is connected to the arm . Thus, a total of six switching elements are provided.

[0060] The switching elements 108 of the energization control unit 102 are ON/OFF switched upon receiving a control signal from the ECU 200. As a result, the energization of the motor 42 by the battery 120 is controlled, and the running torque or the revolution speed of the motor 42 is controlled. Thus, as will be described hereinbelow, the control signal of the VVT system 40 generated in the ECU 200 coiTespondingly to the operation state of the engine 1 is inputted to the energization control unit 102. In response to the control signal, the energization control unit 102 performs, for example, duty control of the motor 42.

[0061] In each ami 105 of the bridge circuit 106 shown in FIG. 5, a load resistance element 1 12 is provided between a connection point 1 1 1 to which the power supply line 132 is connected and the switching element 108 close thereto. The detection unit 104 connected to both ends of each load resistance element 1 12 detects the current value of each load resistance element 1 12 that represent the energization amount of the motor 42. The detection unit 104 is connected to the ECU 200 and transmits a signal representing the aforementioned current value, that is, the energization amount of the motor 42.

[0062] In FIG. 5, the reference numerals 130, 140 stand for main relays that are provided to connect or disconnect (ON/OFF) the supply of power from the battery 120 to the motor drive circuit 100 and the main control unit of the ECU 200, respectively. Those main relays 130, 140 receive a control signal from the power supply control unit of the ECU 200 and are switched interlockingly to an ON or OFF state.

[0063] FIG. 6 shows the configuration of the ECU 200. The main control unit that performs operation control of the engine 1 is shown in FIG. 6 and the power supply control unit is not shown. As shown in the figure, the ECU 200 is provided with a central processing unit (CPU) 201 , read only memory (ROM) 202, random access memory (RAM) 203, and a backup RAM 204.

[0064] The ROM 202 stores various control programs and maps that are referred to when the control programs are executed. The CPU 201 executes a variety of computational processing operations on the basis of the control programs and maps stored in the ROM 202. The RAM 203 is a memory that temporarily stores the computation results obtained in the CPU 201 or data inputted from the sensors. The backup RAM 204 is a nonvolatile memory that stores, for example, data on the engine 1 that should be saved when the engine is stopped.

[0065] The CPU 201 , ROM 202, RAM 203, and backup RAM 204 are connected to each other by a bus 207 and also connected to an input interface 205 and an output interface 206.

[0066] Various sensors such as the oil temperature sensor 30, the crank positions sensor 3 1 , a water temperature sensor 32, the air flowmeter 33, the intake temperature sensor 34, the throttle opening degree sensor 35, an accelerator depression amount sensor 36, the front air-fuel sensor 37, the rear 0₂ sensor 38, and the cam position sensor 39 are connected to the input interface 205. The accelerator depression amount sensor 36 outputs a detection signal corresponding to the depression amount of the accelerator pedal.

[0067] The revolution speed sensor (VVT revolution speed sensor) 47 of the VVT system 40, an ignition switch 48, a starter switch 49, and the detection unit 104 of the motor drive circuit 100 of the VVT system 40 are connected to the input interface 205. The ignition switch 48 performs ON/OFF switching of the main power source of the vehicle. The starter switch 49 is operated by the driver of the vehicle to start the engine 1 .

[0068] For example, the injector 2 of each cylinder, the igniter 4 of each cylinder, and also the tluottle motor 6, starter motor 10, and motor drive circuit 100 of the VVT system 40 are connected to the output interface 206.

[0069] The ECU 200 executes various types of control of the engine 1 on the basis of signals from the aforementioned sensors and switches. For example, those types of control of the engine 1 include drive control of the injectors 2 (control of fuel injection amount and injection timing), control of ignition timing by the spark plug 3, drive control of the throttle motor 6 (control of the throttle opening degree), and operation control of the VVT system 40 (phase control of the intake valve 13).

[0070] For example, as the operation control of the VVT system 40, the ECU 200 determines whether to hold or change the valve timing on the basis of the signals from the crank position sensor 3 1 and the cam position sensor 39. This determination is performed by comparing the target rotation phase that has been set on the basis of the detected values such as the throttle opening degree, lubricating oil temperature, and crank revolution speed or the engine operation state such as the cam revolution speed with the actual rotation phase derived from the detected value of the crank revolution speed and cam revolution speed.

[0071] Thus, when the valve timing is held, the ECU 200 assumes that the target variation amount of the revolution speed of the motor 42 of the VVT system 40 (corresponds to the variation rate of the phase necessary to match the actual rotation phase with the target rotation phase) is substantially zero. Meanwhile, when the valve timing is changed, a phase difference is calculated by comparing the target rotation phase with the actual rotation phase of the intake camshaft 25 and setting the target variation amount of the motor revolution speed from the calculated phase difference.

[0072] For example, the ECU 200 stores the correlation (table) between the phase difference between the target rotation phase and the actual rotation phase of the intake camshaft 25 and the target variation amount of the motor revolution speed correspondingly to the operation state of the engine 1 , this correlation being determined by tests in advance. The ECU 200 can determine the target variation amount according to this correlation. A control signal corresponding to the target variation amount that has thus been set is transmitted from the ECU 200 to the motor drive circuit 100.

[0073] The motor drive circuit 100, which has received the control signal, controls power supply to the motor 42 in the above-described manner. The running torque or revolution velocity of the motor 42 is controlled and the revolution speed of the motor 42 is changed by controlling the supply of power to the motor 42. As a result, the actual rotation phase of the intake camshaft 25 is brought close to the target rotation phase. The valve timing of the intake valve 13 is thus advantageously controlled according to the operation state of the engine 1 .

[0074] In addition to the above-described VVT control performed during the operation of the engine 1 , the ECU 200 of the present embodiment controls the operation of the VVT system 40 also within a period from after the engine 1 is stopped to the subsequent start thereof (period in which the engine is stopped) in the below described manner (stop period operation mode).

[0075] The control of the VVT system 40 executed within the period in which the engine is stopped is explained below. With this control, for example, the VVT system 40 is operated to change the intake valve timing to that suitable to start the engine within several revolutions of the crankshaft 15 by inertia after the supply of fuel to the engine 1 and the ignition have been stopped in response to the OFF operation of the ignition switch 48. Alternatively, the VVT system 40 can be operated in response to the ON operation of the ignition switch 48.

[0076] In the case in which the VVT system 40 is thus operated in response to the ON operation of the ignition switch 48, the temperature of the motor 42 or the motor drive circuit 100 can be already high when such operation is initiated. In such a case, where the energization or the like occurs in the motor lock period, the coils of the motor 42 or the switching elements 108 of the drive circuit 100 can be overheated and endurance reliability may be lost.

[0077] Thus, during the operation of the engine 1 , the VVT system 40 is operated by the motor 42 to obtain the intake valve timing conforming to this operation state. Therefore, the motor 42 is in the energized state almost at all times. For this reason, during the operation of the engine 1 , the coils of the motor 42 and the switching elements 108 of the drive circuit 100 are maintained at a constant designed temperature (for example, about 100°C to 120°C).

[0078] In this state, where the operation of the engine 1 is stopped in response to the OFF operation of the ignition switch 48, and the main relays 130. 140 are directly switched OFF, the energization of the motor 42 is stopped. After the energization of the motor 42 has been stopped, the temperature of the coils and the switching elements 108 decreases gradually from the aforementioned constant temperature. In some cases, the ignition switch 48 that has been switched off is immediately switched on.

[0079] The VVT system 40 may be also operated when the ignition switch 48 is thus immediately switched on. In such a case, where a large load is applied to the motor 42, for example, due to the penetration of foreign matter into the phase changing mechanism 60, heat generation in the coils (windings 52) increases and an overheated state may be attained within a short period of time. The overheated state may be also attained in a state in which the motor 42 does not rotate (motor lock), since the temperature of the two switching elements 108 that are single-phase energized rapidly increases.

[0080] In the present embodiment, the temperature state of the motor 42 or the motor drive circuit 100 is estimated when the engine 1 is stopped and the ON state of the main relays 130, 140 is maintained till the estimated temperature drops to a value equal to or lower than the allowed temperature. Further, when the VVT system 40 is operated in the stop period operation mode, the energization of the motor 42 is limited and, if necessary, inhibited in response to the increase in the estimated temperature. As a result, the aforementioned overheating of the motor 42 or switching elements 108 can be suppressed.

[0081] The control sequence of the VVT system 40 executed within the period in which the engine is stopped is explained below in greater detail with reference to the flowchart shown in FIG. 7. This processing flow is repeatedly executed by the ECU 200 with predetermined periodicity when the ignition switch 48 is in the ON state.

[0082] First, in step S 1 after the start, the ECU 200 determines whether or not a VVT system actuation request is present. This determination is made on the basis of the target variation amount of the motor revolution speed of the VVT system 40. Where the target variation amount is not zero (YES in step S I ), the processing flow advances to the below-described step S6. Meanwhile, where the target variation amount is zero (NO in step S I ), the processing flow advances to step S2. In step S2, it is determined whether or not the ignition switch 48 has been switched off (is there an IG-OFF request?).

[0083] Thus, the determination as to whether the IG-OFF request is present is not performed when the VVT system actuation request is present. Therefore, when the VVT system 40 operates, even if the ignition switch 48 is switched off. the determination as to whether the IG-OFF request is present is not performed and the main relays 130, 140 are maintained in the ON state.

[0084] In the case in which there is no IG-OFF request in step S2 (NO), it is determined that there is no power supply OFF request for the ECU 200, and the present control returns. Meanwhile, when the IG-OFF request is present (YES in step S2), it is determined that the power supply OFF request for the ECU 200 is present, and the processing flow advances to step S3. In step S3, it is determined whether or not the estimated temperature T of components, such as the coils (windings 52) of the electric motor 42 or the switching elements 108 of the motor drive circuit 100, is higher than an allowed temperature Ta. The allowed temperature Ta is set to a temperature (for example, 30°C to 40°C) that is sufficiently lower than the designed constant temperature during the usual operation of the motor 42.

[0085] During the usual operation of the motor 42, the temperature of the aforementioned components (windings 52 or switching elements 108) is apparently the designed constant temperature. Therefore, the temperature of the components can be estimated with consideration for the increase in temperature caused by single-phase energization during motor lock by assuming that, for example, when the motor 42 does not rotate despite the energized state, the temperature rises proportionally to the energization amount and energization time.

[0086] When the energization of the motor 42 is stopped in response to the affirmative determination of the IG-OFF request, the estimated temperature T of the components decreases gradually from the designed constant temperature with the passage of time. Since the VVT system 40 is installed at the cylinder head I d and the motor drive circuit 100 is disposed inside the case of the motor 42, it is preferred that the effect of engine water temperature and lubricating oil temperature be also taken into account when estimating the estimated temperature T.

[0087] When the temperature (estimated temperature T) of the components that has thus been estimated is higher than the allowed temperature Ta (YES in step S3), the processing flow advances to step S4. In step S4, a main relay ON request is issued, the main relays 130, 140 are maintained in the ON state, and the processing flow returns. In other words, when the IG-OFF request is received and the operation of the engine 1 is stopped, the supply of power to the motor drive circuit 100 and the main control unit of the ECU 200 is continued till the estimated temperature T of the components of the VVT system 40 or the motor drive circuit 100 decreases sufficiently.

[0088] Where the estimated temperature T then becomes equal to or lower than the allowed temperature Ta with the passage of time, as described hereinabove (NO in step S3), the processing flow advances to step S5. In step S5, the estimated temperature T at this point of time and the engine water temperature, lubricating oil temperature, external air temperature (temperature state amounts) that can affect the temperature of the components are stored in the backup RAM 204 of the ECU 200, and the processing flow returns to the start.

[0089] The ON/OFF switching of the main relays 130, 140 is performed by the power supply control unit of the ECU 200 that receives the supply of power at all times from the battery 120. A main relay ON request from a routine other than the VVT control, for example, a throttle control routine, can be sometimes also inputted to the power supply control unit. Therefore, when the main relay ON request of the VVT control routine is not issued, as in the above-described step S5, the main relays 130, 140 are switched OFF, unless the main relay ON request is issued from a control routine other than the aforementioned control routine.

[0090] When the VVT actuation request is present in the aforementioned step S 1 (YES ), the processing flow advances to step S6. In step S6, it is determined whether or not the estimated temperature T of the components is equal to or less than a first temperature Tb. For example, when the ignition switch 48 is switched on after the operation of the engine 1 has been stopped, as described hereinabove, the VVT system 40 is operated, unless the target variation amount of the motor revolution speed of the VVT system 40 is zero. Thus, in this case, the temperature state of the motor 42 and the motor drive circuit 100 is also estimated.

[0091 ] In this case, an initial value can be set for the temperature of the components (windings 52 and switching elements 108) and the estimated temperature T can be determined on the basis of the subsequent energization and operation state of the motor 42. The initial value of the temperature of the components is set on the basis of the estimated temperature T at the engine stopping time that has been saved in the backup RAM 204 in step S5, data on the engine water temperature, lubricating oil temperature, and external air temperature, and also data on the temperature detected by the oil temperature sensor 30, water temperature sensor 32, and intake temperature sensor 34 at the present point of time.

[0092] Where the estimated temperature T is equal to or less than the first temperature Tb (YES in step S6), the usual energization control of the motor 42 is performed (step S7) and the operation of the VVT system 40 is advanced or retarded so that the target variation amount approaches zero. In other words, where the temperature of the components is less than the first temperature Tb, the control of the VVT system 40 is executed as usual within the period in which the engine is stopped.

[0093] By contrast, where the estimated temperature T is higher than the first temperature Tb (NO in step S6), the processing flow advances to step S8. . In step S8, it is determined whether or not the estimated temperature T is equal to or lower than a second temperature Tc which is higher than the first temperature Tb. Where it is determined in step S8 that the estimated temperature T is equal to or lower than the second temperature Tc (YES), the operation of the VVT system 40 is advanced or retarded, while inhibiting the generation of heat in the motor 42 by restricting the energization amount thereof (in step S9).

[0094] Meanwhile, where the estimated temperature T is higher than the second temperature Tc (YES in step S8). overheating may occur, and therefore the energization of the motor 42 is prohibited (in step S 10) and subsequent increase in temperature is suppressed. Further, failure diagnosis of the VVT system 40, motor 42, and motor drive circuit 100 is prohibited" (in step S l l ) to suppress such prohibition of energization of the motor 42 from causing a diagnostic error, and the processing flow returns.

[0095] The operation of the VVT system 40 and the motor 42 performed when the operation of the engine 1 is stopped and the engine is thereafter started by the above-described control of the VVT system 40, and variations in temperature of the components such as the coils (windings 52) or switching elements 108 of the motor drive circuit 100 will be explained below with reference to FIGS. 8 and 9.

[0096] As shown in FIG. 8, when the engine 1 is stopped at a timing tl , the ignition switch 48 (IG) is switched off. When the target variation amount of the motor revolution speed of the VVT system 40 does not become zero even after the ECU 200 has stopped the supply of fuel to the engine 1 and the ignition at the timing t l , the operation of the VVT system 40 is continued. Therefore, the determination of the IG-OFF request is not perfonned, the energization of the motor 42 is continued, and the pulse signal (motor pulse) from the revolution speed sensor 47 of the VVT system 40 is inputted following this rotation. The estimated temperature T is generally maintained at a constant designed value.

[0097] Where the VVT system 40 operates, the intake valve timing is changed, and the target variation amount of the motor 42 becomes zero, the energization of the motor 42 is stopped (timing t2), and the rotation of the motor 42 is also stopped. The estimated temperature T decreases gradually after the energization has been stopped. However, while the estimated temperature T is still higher than the allowed temperature Ta, the main relays 130, 140 are held in the ON state and the energization of the motor 42 is continued.

[0098] Where the estimated temperature T becomes equal to or lower than the allowed temperature Ta at a timing t3, the main relays 130, 140 are interlockingly switched off, and the supply of power to the motor drive circuit 100 and the ECU 200 (main control unit) is stopped. In other words, the power supply of the ECU 200 is switched off after the temperature of the motor 42 of the VVT system 40 and the motor drive circuit 100 has sufficiently decreased. The temperature data such as the estimated temperature T are stored in the ECU 200 before the power supply is thus switched off.

[0099] Meanwhile, when the engine is started, as shown in FIG. 9, where the ignition switch 48 is switched on and the main relays 1 30, 140 are interlockingly switched on (timing t4) by the power supply control unit of the ECU 200, the supply of power is started to the ECU 200 (main control unit) and the motor drive circuit 100 of the VVT system 40. In this case, where the target variation amount of the motor 42 of the VVT system 40 is not zero, the VVT control in the stop period operation mode is started, the energization of the motor 42 is started, and a pulse signal (motor pulse) is inputted, following the rotation of the motor 42, from the revolution speed sensor 47 of the VVT system 40. Further, the estimated temperature T starts increasing following the energization start of the motor 42.

[0100] When the operation control of the VVT system 40 is thus started, for example, where foreign matter has penetrated into the phase changing mechanism 60 and an excessive load is applied to the motor 42, the generation of heat in the coils (windings 52) may increase. Where the rotation of the motor 42 is then stopped (timing t5), the temperature of the two switching elements 108 that are in a single-phase energization state in the motor drive circuit 100 rises rapidly.

[0101] Where the rotation of the motor 42 is thus stopped, the estimated temperature T also rises rapidly due to a loss of motor pulses. Where the estimated temperature exceeds the first temperature Tb (timing t6), the energization amount of the motor 42 is limited. As a result, heat generation in the coils (windings 52) or the switching elements 108 of the motor drive circuit 100 is inhibited and the increase in temperature is slowed down. Therefore, those components are suppressed from overheating.

[0102] In the example shown in FIG. 9, the increase in temperature of the coils (windings 52) or switching elements 108 is not checked even by the above-described restriction of the energization amount. In this case, the estimated temperature T also further increases and exceeds the second temperature Tc (timing t7). The energization of the motor 42 is prohibited in response to this increase in the estimated temperature T, and then the temperature of the coils (windings 52) and switching elements 108 starts decreasing. In other words, the overheating of the components can be suppressed more reliably.

[0103] Therefore, with the engine controller of the present embodiment, the temperature of the components that may be overheated, such as the motor 42 of the electric VVT system 40 or the switching elements 108 of the motor drive circuit 100 is estimated, and after the estimated temperature T has been confirmed to decrease to a value equal to or lower than the allowed temperature Ta when the operation of the engine 1 is stopped, the power supply is switched off. As a result, even if the lock energization is generated in the stop period operation mode in which the VVT system 40 is operated before the engine is started after the aforementioned stop, the motor 42 and the motor drive circuit 100 are suppressed from immediately attaining the overheated state, and the durability reliability thereof can be increased.

[0104] Further, when the motor 42 of the VVT system 40 is controlled in the stop period operation mode, where the estimated temperature T of the components is equal to or higher than the first temperature Tb, the energization amount of the motor 42 is restricted. As a result, the increase in temperature of the motor 42 and the motor drive circuit 100 is restricted and overheating thereof can be suppressed.

[0105] Where the estimated temperature T then becomes equal to or higher than the second temperature Tc, which is higher than the first temperature Tb, the motor 42 and the motor drive circuit 100 can suppressed from overheating by prohibiting the energization of the motor 42. In this case, the occurrence of a diagnostic error can be suppressed by also prohibiting failure diagnosis of the VVT system 40. motor 42, and motor drive circuit 100.

[0106] In the above-described embodiment, as shown in the flowchart in FIG. 7, whether or not an IG-OFF request is present is determined when the VVT actuation request is absent, and even if the ignition switch 48 is switched off during the operation of the VVT system 40, it is not immediately determined that an IG-OFF request is present. The embodiments of the invention are not limited to the above-described configuration, and whether or not the IG-OFF request is present may be determined during the operation of the VVT system 40.

[0107] Whether or not the power supply OFF request to the ECU 200 is present may be determined on the basis of not only the signal from the ignition switch 48, but also the signals from other switches or sensors.

[0108] Where it is determined that the IG-OFF request is present, the energization of the motor 42 of the VVT system 40 may be stopped immediately. As a result, the temperature of the components such as the coils (windings 52) of the motor 42 and the switching elements 108 of the motor drive circuit 100 can be rapidly decreased and the main relays 130, 140 can be switched off.

[0109] In the present embodiment, the estimation of the temperature of the components of the motor 42 and the motor drive circuit 100 is mainly focused on the increase in temperature caused by motor lock, and the temperature is estimated by the energization amount of the motor 42 and the rotation state thereof. The embodiments of the invention are not limited to this configuration, and the temperature of the aforementioned components may be detected by temperature sensors or the like.

[0110] In the above-described embodiment, an example is explained in which the invention is applied to the VVT system 40 of the engine 1 of a port injection system. The invention is not limited to this configuration and can be also applied to an engine of a cylinder injection system and also to an engine provided with fuel injection valves for port injection and also for cylinder injection. Further, the embodiment of the invention can be also applied to the case in which the engine 1 is installed on the so-called hybrid vehicle.

[0111 ] According to the invention, the electric motor and the drive circuit thereof that operate the VVT system of the internal combustion engine are suppressed from overheating and durability reliability thereof can be increased. The invention is particularly effective when applied to passenger cars that have a comparatively high operation and stop frequency.

Claims

CLAIMS:

1. A controller for an internal combustion engine equipped with a variable valve timing system being configured to change an operation timing of at least one of an intake valve and an exhaust valve, the controller comprising:

an electronic control unit configured to control an electric motor and drive the variable valve timing system within a stop period from after the internal combustion engine is stopped till the engine is started after the stop, and

the electronic control unit being configured to be maintained at power-on state when a temperature of at least one component of the electric motor and a drive circuit thereof is higher than a predetermined temperature even if the electronic control unit is required to be power-off state.

2. The controller for an internal combustion engine according to claim 1 , wherein the electronic control unit limits an energization amount of the electric motor when the temperature of the component is equal to or higher than a first temperature.

3. The controller for an internal combustion engine according to claim 2, wherein the electronic control unit prohibits energization of the electric motor when the temperature of the component is equal to or higher than a second temperature that is higher than the first temperature.

4. The controller for an internal combustion engine according to claim 3, wherein the electronic control unit prohibits failure diagnosis of the variable valve timing system, the electric motor and the drive circuit thereof when the temperature of the component is equal to or higher than the second temperature and the energization of the electric motor is prohibited.

5. The controller for an internal combustion engine according to any one of claims 1 to 4, wherein

the electronic control unit does not determine whether the electronic control unit is required to be power-off state when the electric motor is controlled in the stop period.

6. The controller for an internal combustion engine according to any one of claims 1 to 5. wherein

the electronic control unit prohibits energization of the electric motor from when the electronic control unit is required to be power-off state till the temperature of the component becomes equal to or lower than a set temperature.

7. The controller for an internal combustion engine according to any one of claims 1 to 6, wherein

the electronic control unit estimates the temperature of the component on the basis of at least an energization state and a rotation state of the electric motor.

8. The controller for an internal combustion engine according to any one of claims 1 to 7, wherein

the electronic control unit stores the temperature of the component and a temperature state amount affecting the temperature of the component when the temperature of the component is equal to or lower than the predetermined temperature and the electronic control unit is to be power-off state.

9. The controller for an internal combustion engine according to claim 1 , wherein the electronic control unit is maintained at power-on state till the temperature of the component of the electric motor and the drive circuit thereof becomes equal to or lower than the predetermined temperature.

10. A control method for an internal combustion engine equipped with a variable valve timing system being configured to change an operation timing of at least one of an intake valve and an exhaust valve can be changed, the control method comprising:

controlling an electric motor and driving the variable valve timing system within a stop, period from after the internal combustion engine is stopped till the engine is started after the stop; and

being maintained at power-on state of the electronic control unit when a temperature of at least one component of the electric motor and a drive circuit thereof is higher than a predetermihed temperature even if the electronic control unit is required to be power-off state.