Control device for variable valve timing device

Abstract

The technical problem of the present invention is to obtain a control device for a variable valve timing device, which can control the phase to an arbitrary fixed valve timing before the internal combustion engine is about to stop and after the internal combustion engine stops. The control device for the variable valve timing device of the present invention is characterized in that, during the engine stop processing of the internal combustion engine, the following control is performed: normal control, when the rotation speed of the crankshaft is above the first threshold, the relative rotation phase of the camshaft is changed to the most advanced angle position or the most retarded angle position; and low rotation control, from the time when the rotation speed of the crankshaft is lower than the first threshold to the time when it becomes zero rotation, the current or voltage supplied to the motor is fixed to a constant value, and the relative rotation phase of the camshaft is maintained at the most advanced angle position or the most retarded angle position.

Description

Technical Field

[0001] The present invention relates to a control device for a variable valve timing device that changes the valve timing (opening and closing timing) of an intake valve or an exhaust valve driven by an electric motor. Background Art

[0002] In the past, for the crankshaft as the output shaft of the internal combustion engine, there were timing pulleys, sprockets or gears as driving force transmission mechanisms for synchronously rotating the camshaft for the intake valve and the camshaft for the exhaust valve, and a variable valve timing device assembled in them to adjust the valve timing of the intake valve according to the operating state of the internal combustion engine was known. In recent years, the hydraulic variable valve timing device has gradually been replaced by an electric variable valve timing device, and its controllable temperature and controllable engine speed have a tendency to expand. However, in the existing electric variable valve timing device, control is particularly difficult at low engine speeds, and it is difficult to control the valve timing of the intake valve at an arbitrary timing when the engine of the car is stopped. In fact, the method that has been adopted is to control the so-called default position of the variable valve timing device and the mechanical position, waiting for the next engine start.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-197591

[0006] Patent Document 2: Japanese Patent Application Publication No. 2019-157750

[0007] Patent Document 3: Japanese Patent Application Publication No. 2018-131985 Summary of the invention

[0008] Technical problem to be solved by the invention

[0009] The electric variable valve timing device includes a mechanism for changing the phase of the camshaft that drives the intake valve or the exhaust valve. In this mechanism, the output from the electric motor is amplified by the reducer and transmitted to the camshaft. If you want to start from any valve timing when the internal combustion engine is started next time, it is difficult to change the phase of the camshaft even if the electric motor is energized during the stop process, so it is best to change the phase of the camshaft just before the internal combustion engine is about to stop. The phase of the camshaft during the operation of the internal combustion engine is calculated based on the relative values ​​of the cam angle sensor and the crank angle sensor, but before the internal combustion engine is about to stop, as the speed decreases, the detection cycle becomes rough, and the signals obtained by the cam angle sensor and the crank angle sensor become extremely rough, so there is a problem of difficulty in controlling the valve timing at the correct phase.

[0010] To address this problem, in a currently known control method for a variable valve timing device, such as the control method disclosed in Japanese Patent Gazette No. 2009-197591 (Patent Document 1), the duty cycle of the power supply to the electric motor is controlled so that it gradually approaches the target advance angle position to prevent overshoot at the target phase.

[0011] Furthermore, in the control method of Japanese Patent Gazette No. 2019-157750 (Patent Document 2), in the hydraulic variable valve timing device, the valve timing of the intake valve in the crank start state of the engine driven by the main motor is delayed, thereby reducing the actual compression ratio and reducing the energy required during crank start.

[0012] In the above-mentioned Patent Document 1, control near the target phase for the purpose of preventing overshoot in a variable valve timing device is described, but the operation when the engine is stopped is not described, so it is difficult to restart the engine from an arbitrary phase. In the above-mentioned Patent Document 2, a hydraulic variable valve timing device is used to control the intake valve at an arbitrary position when the engine is restarted, but there are still the following problems: it cannot be developed in an electric variable valve timing device, and application to a fast-closing Miller cycle engine is not considered.

[0013] The present invention takes into account the problem of such an internal combustion engine at low rotation speed, and its purpose is to provide a control device for a variable valve timing device, in which the phase can be controlled to an arbitrary fixed valve timing before the internal combustion engine is about to stop to after the internal combustion engine stops.

[0014] Technical solutions to technical problems

[0015] In order to achieve the above-mentioned purpose, the control device of the variable valve timing device of the present invention is suitable for an internal combustion engine equipped with a variable valve timing device that changes the relative rotational phase of the camshaft relative to the crankshaft of the internal combustion engine by adjusting the motor speed of the motor connected to the camshaft, and has a control unit for controlling the variable valve timing device, characterized in that the control unit performs the following control during the engine stop processing of the internal combustion engine: normal control, when the rotational speed of the crankshaft is above a first threshold, the current or voltage supplied to the motor is adjusted according to the rotational speed of the crankshaft so that the relative rotational phase of the camshaft changes to the most advanced angle position or the most retarded angle position; and low rotation control, during the period from the rotational speed of the crankshaft being lower than the first threshold to the time when it becomes zero rotation, the current or voltage supplied to the motor is fixed to a constant level, so that the relative rotational phase of the camshaft is maintained at the most advanced angle position or the most retarded angle position.

[0016] Effects of the Invention

[0017] According to the present invention, the phase of the valve timing of the intake valve can be controlled at the most advanced angle position or the most retarded angle position until the rotation speed of the crankshaft is reduced to an arbitrary rotation speed and the internal combustion engine is completely stopped. Other features related to the present invention will become apparent from the description of this specification and the accompanying drawings. In addition, the problems, structures and effects other than those mentioned above are clarified by the description of the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 1 is a configuration diagram of an engine system according to the present embodiment to which the control device for the variable valve timing device of the present invention is applied.

[0019] Figure 2 It is a diagram showing the overall structure of the variable valve timing device according to the present embodiment.

[0020] Figure 3 It is a cross-sectional view of a speed reducer in the variable valve timing device of the present embodiment.

[0021] Figure 4 This is a control block diagram of the control device of the variable valve timing device according to the present embodiment.

[0022] Figure 5 This is a diagram showing the distribution of intake / exhaust camshaft positions when the intake camshaft angle is most advanced when an early-closing Miller cycle engine is installed (Example 1).

[0023] Figure 6 This is a diagram showing the distribution of intake / exhaust camshafts at the most retarded angle when an early-closing Miller cycle engine is installed (Example 1).

[0024] Figure 7 is to use Figure 5 Schematic diagram showing the intake air distribution within the engine cylinder during the engine cycle.

[0025] Figure 8 This is a diagram showing changes in the engine speed during the engine stop process.

[0026] Fig. 9 The graph is a diagram for explaining the relationship between the engine speed, the phase of the intake valve, and the indicated duty ratio when the engine is restarted from a stop.

[0027] Fig.10 This is a diagram for explaining the relationship between the engine speed, the phase of the intake valve, and the load current to the circuit when the engine is stopped and restarted.

[0028] Fig.11 This is a flowchart for explaining the phase control of the intake valve when the engine is stopped.

[0029] Fig.12This is a diagram showing the relationship between the engine speed and the PWM signal during normal control when the engine is stopped.

[0030] Fig.13 This is a diagram showing the relationship between the engine speed and the PWM signal during low-speed control when the engine is stopped.

[0031] Fig.14 FIG. 1 is a diagram showing a flowchart for explaining the phase control of the intake valve when the engine is stopped.

[0032] Fig.15 This is a diagram showing the relationship between the engine speed and the PWM signal during normal control at the time of engine startup.

[0033] Fig.16 This is a diagram showing the relationship between the engine speed and the PWM signal during low-speed control at engine startup.

[0034] Fig.17 This is a diagram showing the distribution of intake / exhaust camshaft positions when the intake camshaft angle is most advanced when a late-closing Miller cycle engine is installed (Example 2).

[0035] Fig.18 This is a diagram showing the distribution of intake / exhaust camshaft positions when the intake camshaft angle is most retarded when the engine is equipped with a late-closing Miller cycle (Example 2). DETAILED DESCRIPTION

[0036] Hereinafter, specific embodiments of the variable valve timing device of the present invention will be described using the accompanying drawings. In addition, in each figure, the parts given the same reference numerals represent the same or corresponding parts.

[0037] [Example 1]

[0038] <Engine structure>

[0039] Figure 1 1 is a configuration diagram of an engine system according to the present embodiment to which the variable valve timing device of the present invention is applied.

[0040] The engine system of this embodiment is a system of a series hybrid vehicle equipped with a traction motor for running and an engine dedicated to power generation. In the series hybrid vehicle, when the battery charge capacity is lower than a certain threshold, the engine is operated to generate electricity, and when the battery charge capacity is higher than a certain threshold, the engine is controlled to stop.

[0041] The engine is an internal combustion engine consisting of a four-cycle engine, and a combustion chamber is formed by a cylinder head 1, a cylinder block 2, and a piston 3 inserted into the cylinder block 2. The piston 3 is connected to a crankshaft 5 via a connecting rod 4, and a crank angle sensor 6 can detect the rotation speed of the crankshaft, that is, the engine speed.

[0042] An intake pipe 7 and an exhaust pipe 8 are connected to the combustion chamber. The intake pipe 7 and the exhaust pipe 8 are connected by branching into two for each cylinder, and two intake valves 9 and exhaust valves 10 are provided to open and close the openings to the combustion chamber. An intake cam 11 and an exhaust cam 12 are provided on the upper parts of the intake valve 9 and the exhaust valve 10, respectively, and the intake valve 9 and the exhaust valve 10 are opened and closed by the rotation of these cams 11 and 12. An intake cam pulley connected to the intake cam, an exhaust cam pulley connected to the exhaust cam, and a crankshaft pulley connected to the crankshaft 5 are provided on the side of the engine (not shown), and they are connected by a timing belt. As a result, when the engine is operated, the crankshaft 5 rotates, and the intake cam 11 and the exhaust cam 12 rotate. The size of the crank pulley and the cam pulley is set so that the intake cam 11 and the exhaust cam 12 rotate once when the crankshaft 5 rotates twice. The camshaft of the intake cam 11 is provided with a variable valve timing device 27 capable of changing the phase (relative rotation phase) relative to the crankshaft 5. The variable valve timing device 27 has a structure that changes the phase of the camshaft of the intake cam 11 relative to the crankshaft 5 by adjusting the motor speed of the motor (VTC motor) connected to the camshaft. The crankshaft 5 is connected with an electric generator, which is used as a generator when generating electricity and as a motor when the engine is started or stopped. The intake cam 11 is provided with an intake cam angle sensor 13 to detect the rotation speed of the cam.

[0043] An injector 14 is provided on the intake side of the combustion chamber, and a spark plug 15 and an ignition coil 16 are provided on the upper part of the combustion chamber. The fuel is stored in a fuel tank 17 and is sent to a high-pressure fuel pump 19 through a fuel pipe by a feed pump 18. The high-pressure fuel pump 19 is driven by the exhaust cam 12, and the boosted fuel is sent to a common rail 20. A fuel pressure sensor 21 is provided on the common rail 20 to detect the fuel pressure. The common rail 20 and the injector 14 provided in each cylinder are connected through a fuel pipe.

[0044] The three-way catalyst 22 is provided at the front end of the exhaust pipe 8, and the oxygen sensor 23 is provided downstream thereof. The temperature sensor 24 is provided in the three-way catalyst 22 to detect the temperature of the three-way catalyst 22. The cylinder block 2 is provided with a water temperature sensor 25 for measuring the temperature of water flowing through the cylinder block 2.

[0045] The signals of the water temperature and the engine speed are input to the engine control unit (ECU) 26, and based on these information, the on / off of the fuel injection and the phase of the variable valve timing device 27 are controlled. In other words, the ECU 26 constitutes a control device for the variable valve timing device 27. The ECU 26 has a CPU and a memory, and the CPU constitutes a control unit of the control device for the variable valve timing device 27.

[0046] <Overall structure and driving principle of the electric variable valve timing device>

[0047] The relative phase difference between the crankshaft 5 and the camshaft is calculated by inputting the rotation speed signals of the crankshaft 5, the intake cam 11, and the exhaust cam 12 detected by the crank angle sensor 6 and the cam angle sensor 13 into the ECU 26. In the present engine structure, the crank angle is obtained at every 6 degrees CA, and the cam angle is obtained at every 180 degrees CA. The variable valve timing device 27 provided in the intake cam 11 is set to an electric type, and its structure is as follows: Figure 2 and Figure 3 shown.

[0048] The electric variable valve timing device 27 includes, from the intake cam 11 side, a speed reducer 27 a having a sprocket 27 d , an intake cam driving motor 27 b , and a control unit 27 c . Figure 3 2 shows a cross-sectional view of the speed reducer 27a. In addition, for the structure of the mechanical structure of the electric variable valve timing device 27, for example, the structure shown in Patent Document 3 can be applied. Inside the control unit 27c, there are a general IC 27c-a and a motor driver 27c-b as a calculation unit for driving the motor. Figure 4 A control block diagram of this embodiment based on these is shown.

[0049] Next, the acquisition path until the ECU 26 of the valve timing device in this embodiment acquires information on the actual rotation speed and rotation direction of the intake cam drive motor 27b will be described. First, the rotation of the intake cam drive motor 27b is detected by the Hall IC provided in the control unit 27c, and the generated voltage is acquired by the general IC 27c-a provided in the circuit within the control unit. Inside the general IC 27c-a, the input voltage is converted into the rotation speed and rotation direction of the intake cam drive motor 27b, and output to the ECU 26, so that the ECU 26 acquires information on the motor rotation speed and rotation direction.

[0050] In addition, the phase of the variable valve timing device 27 is calculated and controlled to be in an appropriate phase. Therefore, the ECU 26 calculates the appropriate valve timing according to the required engine speed and the required engine torque based on the calculation result of the actual phase. The calculated appropriate valve timing is converted into the target rotation direction and target speed of the intake cam driving motor 27b of the variable valve timing device 27 in the ECU 26, and is sent to the control unit 27c of the valve timing device as a PWM signal of duty ratio control.

[0051] In the control unit 27c, the indication of the motor target speed and the motor target rotation direction is received by the general IC 27c-a via the target motor speed receiving unit. In the general IC 27c-a, the actual speed and actual rotation direction of the intake cam driving motor 27b of the above-mentioned variable valve timing device 27 are obtained, and feedback control is applied according to the signal of the motor target rotation direction and the motor target speed, and then the signal is sent to the motor driver 27c-b to obtain the appropriate motor speed. The motor driver 27c-b converts it into a three-phase AC signal of UVW, and outputs it as a UVW drive signal to the intake cam driving motor 27b, thereby driving the intake cam driving motor 27b. The intake cam driving motor 27b is driven by the current and voltage provided from the motor driver 27c-b as the UVW drive signal.

[0052] In the universal IC 27c-a of this embodiment, the signal receiving the rotation direction and speed command of the intake cam driving motor 27b from the ECU 26 has the following specifications. The rotation in the same direction as the rotation direction of the camshaft is assumed to be positive rotation, and the rotation in the opposite direction is assumed to be reverse rotation. The positive rotation / reverse rotation is distinguished by the frequency of the input PWM. The positive rotation is 100 Hz, and the reverse rotation is 200 Hz.

[0053] Normally, the rotation speed of the crankshaft 5: the rotation speed of the intake cam 11 is 2:1, but in order to use the variable valve timing device 27 to switch the phase of the crankshaft 5 and the intake cam 11, the rotation speed of the intake cam 11 needs to be controlled to be higher or lower than 1 / 2 times the rotation speed of the crankshaft 5. Instantly increasing the rotation speed of the camshaft to control the phase of the intake valve or the exhaust valve 10 in the engine cycle toward early opening and early closing is called advance angle control, while on the other hand, instantaneously controlling the rotation speed to be lower to control the phase of the intake valve or the exhaust valve 10 in the engine cycle toward late opening and late closing is called retard angle control.

[0054] Here, for the type of engine that performs the Miller cycle by installing a variable valve timing device 27, there are a late closing Miller cycle and an early closing Miller cycle. In this embodiment, it is assumed that the variable valve timing device 27 is installed on the intake cam 11, and the engine is of the type that can perform the early closing Miller cycle. The early closing Miller cycle refers to an engine stroke in which the intake valve 9 is closed before the piston 3 reaches the bottom dead center during the intake stroke of the four-cycle engine. The engine cited in this embodiment has a structure that enables the above-mentioned early closing Miller cycle to be established by performing a phase shift of the intake cam 11 to the advance angle side through the installed electric variable valve timing device 27.

[0055] Here, a phase conversion method of the intake cam 11 and the crankshaft 5 of the electric variable valve timing device 27 will be described. Figure 3(1) is a diagram showing a state where the speed reducer 27a is at the most advanced angle. Figure 3 (2) is a diagram showing the state where the speed reducer 27a is at the most retarded angle. Figure 3 As shown, the reducer 27a of the above-mentioned electric variable valve timing device 27 includes a driving rotating body 27e having a recessed portion 27j and a driven rotating body 27h having a convex portion 27i in the internal structure. The reducer 27a has a shape in which the recessed portion 27j of the driving rotating body 27e is fitted into the convex portion 27i of the driven rotating body 27h. The convex portion 27i reciprocates in the recessed portion 27j along the rotation direction of the camshaft of the intake cam 11, and abuts against the most advanced angle stopper 27f on one side of the recessed portion 27j or the most retarded angle stopper 27g on the other side, thereby becoming a mechanism for physically determining the most advanced angle position and the most retarded angle position for the phase of the above-mentioned intake cam 11, and can perform phase conversion within the range of the most advanced angle position and the most retarded angle position. The intake cam 11 connected to the driving rotor 27e and the crankshaft 5 connected to the driven rotor 27h via the timing belt are configured to shift the phases of the intake cam 11 connected to the driving rotor 27e and the crankshaft 5 connected to the driven rotor 27h via the timing belt.

[0056] <Purpose and operating principle of variable valve timing device at low engine speed>

[0057] Next, the action sequence during the engine stop process is shown based on the phase conversion driving principle of the variable valve timing device 27. The required action of the variable valve timing device 27 during the engine stop process is to control the phase of the intake cam 11 through the control device of the variable valve timing device 27 so that it is in the most advanced angle position before the engine stops, and to completely stop the engine (zero rotation) while maintaining the above phase.

[0058] If the phase control during the above-mentioned engine stop processing can keep the phase of the intake cam 11 at the most advanced angle position even when the engine is completely stopped, the phase of the intake cam 11 can be restarted from the most advanced angle position even when the engine is restarted next time. As an effect of restarting the engine with the valve timing of the intake valve 9 controlled at the most advanced angle position, the intake flow rate into the engine cylinder decreases during the operation of the motor that increases the rotation by the generator before the initial explosion. When the engine is started, the intake flow rate into the engine cylinder decreases, thereby reducing the air flow rate in the engine compression stroke, thereby reducing pumping losses. Suppressing the pumping losses during the operation of the motor reduces the load applied to the up and down movement of the piston 3 and suppresses the speed fluctuation when the engine speed increases. Finally, by suppressing the engine speed fluctuation in this way, the vibration when the engine is restarted can be reduced. Therefore, it is a requirement in this embodiment to set the phase of the intake cam 11 at the most advanced angle position when the engine is restarted.

[0059] Figure 5 shows the distribution of the intake valve 9 at the most advanced angle in this embodiment, Figure 6 The distribution at the most retarded angle is shown. In addition, Figure 5 and Figure 6 The distribution of the intake valve 9 in the reducer 27a is represented by 9a (most advanced angle distribution) and 9b (most retarded angle distribution), and the distribution of the exhaust valve 10 is represented by 10a. The engine cycle action at the physical most advanced angle position in the reducer 27a is the most advanced angle distribution 9a of the intake valve 9. That is, in this embodiment, Figure 5 The purpose is to restart the engine in a state where the valve timing of the intake valve 9 is advanced to the most advanced angle position.

[0060] In this embodiment, the operating angle of the intake cam 11 and the exhaust cam 12 is 180 degrees CA. When the intake cam 11 is set to the most advanced phase, the phase of the intake cam 11 is advanced to IVC140 degrees CA_ABDC (the valve timing at which the intake valve closes after the crankshaft 5 rotates 140 degrees after the intake bottom dead center). Therefore, Figure 7 The state of the engine cylinder in each scene of the engine cycle when the intake cam 11 is controlled to the most advanced angle position is shown. By controlling the phase of the intake cam 11 in this structure to IVC 140deg.CA_ABDC to start the engine, the compression load applied to the piston 3 during the compression stroke is reduced to about 1 / 3 compared with the previous engine start (IVC60deg.CA_ABDC).

[0061] As described above, by feedback controlling the rotation speed of the intake cam driving motor 27b in the variable valve timing device 27 with respect to the rotation speed of the crank angle sensor 6 and the intake cam angle sensor 13 obtained by the ECU 26, the ECU 26 calculates the phase of the intake cam 11 with respect to the rotation of the crankshaft 5 of the engine equipped with the variable valve timing device 27. When the engine speed is above a constant value, the phase of the intake cam 11 can be calculated without any problem by the above method. However, in the low engine speed region where the engine speed is lower than the constant value, such as just before the engine stops or just after the engine restarts, it is difficult to calculate using the above method. As a reason for this, in the crank angle sensor 6 that detects the rotation speed of the crankshaft 5 every 6 degrees, in the low engine speed region, the interval between the signals input to the crank angle sensor 6 becomes rough with respect to time, and the detection cycle becomes rough.

[0062] Therefore, in this embodiment, in the low engine speed range, the phase of the intake cam 11 is guaranteed by switching from normal control to special control. The action name of each time sequence in the engine stop sequence from the low engine speed to the engine stop is defined as follows: Figure 8 shown.

[0063] The period from when the engine stop request from the ECU 26 is received and the fuel injection of the fuel injection device is stopped until the engine speed reaches zero revolutions is called coasting, which is defined as the period "during the engine stop process". The period after the engine speed reaches zero revolutions during the period of the engine stop process is defined as "after the engine stop". Fig. 9 A series of sequences of engine speed, phase of intake cam 11, and indicated duty ratio from the engine operation process to the engine stop process, after the engine stop, and the next time the engine is restarted are shown. In addition, the history of the current value flowing from the battery into the power supply line in a series of sequences is shown as follows: Fig.10 The duty cycle indicated here refers to the Figure 4 The PWM signal from the ECU 26 to the control unit 27 c of the variable valve timing device 27 is indicative of the motor speed and the rotation direction of the motor.

[0064] <Definition of Application Timing of This Embodiment>

[0065] Next, the control flow of this embodiment is described. In this embodiment, when the fuel cut signal of the ECU 26 is turned on, the engine speed of 200 rpm is defined as the control switching condition (first threshold value), the area where the engine speed is above 200 rpm is defined as the normal control area, and the area where the engine speed is less than 200 rpm is defined as the low rotation control area.

[0066] A flow chart showing a method for determining normal control and low rotation control at engine speed is shown in FIG. Fig.11 In addition, the schematic diagram of duty cycle control when the engine is stopped is shown in Fig.12 and Fig.13 shown. Fig.12 This shows the situation where the duty cycle is switched in proportion to the engine speed as normal control. Fig.13 The following shows a case where a command is issued at a constant duty ratio, which is not proportional to the engine speed, as a low rotation control. Fig.11 The flowchart shown is explained step by step. In this flowchart, the start condition is the engine operation process, and the end condition is the engine stop.

[0067] 《Step S01》

[0068] The control of the variable valve timing device 27 during engine operation is as described above. As normal control, a PWM signal having a duty ratio proportional to the engine speed calculated by the ECU 26 based on the signal from the crank angle sensor 6 is output to the control unit 27c.

[0069] 《Step S02》

[0070] The ECU 26 determines whether the engine stop flag is satisfied. For example, the battery charge capacity is checked. At this time, the state in which the battery charge capacity reaches the upper limit value is set as the engine stop preparation completion. In the state in which the battery charge capacity does not reach the upper limit value, as long as the key is not turned off, the engine will not be turned off even if the vehicle stops due to a traffic signal or congestion.

[0071] 《Step S03》

[0072] Before the engine stops, it goes through a process of transitioning to a fuel cut operation in which fuel injection is stopped. At this time, since the engine torque is not required, the engine enters a fuel cut operation mode, disconnects the fuel injection signal from the ECU 26 to the injector 14, and stops the fuel supply to the combustion chamber. During the fuel cut operation period after the fuel is cut, the engine rotates due to inertia, and the engine speed eventually reaches zero. Therefore, confirmation of the stop of fuel injection is used as one of the signs for transitioning to the engine low speed control.

[0073] 《Steps S04, S05》

[0074] At the same time as the fuel cut is started, the ECU 26 performs control so that the phase of the intake cam 11 is advanced relative to the variable valve timing device 27. The target phase of the intake cam 11 after the fuel cut is set to the most advanced angle position ( Figure 5The most advanced angle distribution of the intake cam 9a), and the completion of the phase conversion to the most advanced angle position is used as one of the signs for transferring to the low rotation control of the engine.

[0075] 《Steps S06, S07》

[0076] As a condition for switching between normal control and low rotation control, as described above, the engine speed (= crankshaft speed) is used as a threshold for switching. In this embodiment, the first threshold is set to 200 rpm for explanation. That is, as described above, the condition for entering low rotation control is the AND logic condition that the engine speed is less than 200 rpm, the fuel is cut, and the intake cam 11 is phase-controlled to the most advanced angle position.

[0077] 《Step S08》

[0078] As mentioned above, in the fuel cut state, when the engine speed drops below 200 rpm, Fig.12 Normal control switches shown Fig.13 The low rotation control shown in FIG. 2 is performed, and the duty ratio of the PWM signal output from the ECU 26 to the control unit 27c of the variable valve timing device 27 is fixed to a predetermined value of 10%. When the ECU 26 issues a command to the control unit 27c with a duty ratio of 10%, it originally becomes a command corresponding to a motor speed of 100 rpm (the engine speed is converted to 200 rpm).

[0079] However, since the phase of the intake cam 11 has been controlled by the variable valve timing device 27 at the most advanced angle position physically, the intake cam drive motor 27b can only generate a motor speed corresponding to the actual engine speed at which it is timed. For example, the speed of the intake cam drive motor 27b becomes 50rpm at an engine speed of 100rpm. That is, until the engine stops completely, the excessive motor torque continues to be generated in the most advanced angle position further in the advanced angle direction, that is, in the direction in which the convex portion 27i of the driven rotor 27h presses against the most advanced angle stopper 27f of the driving rotor 27e. Therefore, the intake cam 11 can maintain the state of phase control at the most advanced angle position until the engine stops completely.

[0080] Furthermore, by fixing the duty ratio at low rotation control to 10%, it is possible to reduce the current or voltage applied to the circuit and each circuit component in the control unit 27c of the variable valve timing device 27. Here, when the duty ratio of the PWM output from the ECU 26 is not fixed to 10% and a rotation speed instruction is issued to the control unit 27c, the intake cam drive motor 27b of the variable valve timing device 27 may generate excessive motor torque, which may cause a malfunction caused by heating of the intake cam drive motor 27b or a malfunction caused by heating of circuit components.

[0081] On the other hand, if the duty ratio instruction provided from the ECU 26 to the control unit 27c is too small, the motor torque of the intake cam driving motor 27b is too small, and the convex portion 27i of the driven rotating body 27h may be separated from the most advanced angle stopper 27f of the concave portion 27j of the driving rotating body 27e by the influence of the cam reaction force in the rotation of the intake cam 11 linked to the rotation of the crankshaft 5, so that the phase of the intake cam 11 is shifted from the most advanced angle position to the retarded angle side. Therefore, the speed indication generated by the fixed duty ratio switched at the low engine speed needs to be switched to an optimal value according to the type of engine mounted, the cam width and the cam lift amount. In this embodiment, the set current and the set voltage provided from the motor driver 27c-b to the intake cam driving motor 27b are set to be 3% or more and 20% or less of the rated current of the intake cam driving motor 27b and the circuit.

[0082] 《Steps S09, S10》

[0083] When no signal is input from the crank angle sensor 6 to the ECU 26 for a certain fixed period, the engine is judged to be stopped, and the output of the PWM signal with a fixed duty ratio of 10% from the ECU 26 to the control unit 27c stops, entering the standby state.

[0084] <Application Effect of This Embodiment>

[0085] By setting the configuration to switch the duty ratio of the PWM output from the above-mentioned ECU 26, the phase of the intake cam 11 can be controlled to the most advanced angle position when the engine is stopped by the variable valve timing device 27, and the phase of the intake cam 11 can be started from the most advanced angle position when the engine is restarted next time.

[0086] As described above, during the pre-ignition period when the engine is restarted, i.e., the period when the motor is running, the phase of the intake cam 11 is controlled to the most advanced angle position, thereby setting the distribution of the valve timing of the intake valve 9 to the most advanced angle distribution 9a, in an effort to achieve a reduction in engine speed fluctuation and NVH (Noise, Vibration, Harshness) when the engine is restarted. For this purpose, Fig. 9 As shown in FIG. 1 , similarly to the engine stop process, even when the engine is restarted, the engine speed needs to be increased while the phase of the intake cam 11 is controlled at the most advanced angle position. Therefore, when the engine is restarted, the control at the low engine speed and the normal control after the engine speed is increased are also switched between.

[0087] Fig.14 A flowchart based on low rotation control when the engine is restarted is shown. In addition, a schematic diagram of duty ratio control when the engine is started is shown in FIG. Fig.15 and Fig.16 shown. Fig.15 This shows the situation where the duty cycle is switched in proportion to the engine speed as normal control. Fig.16 The following shows a case where a command is issued at a constant duty ratio regardless of the engine speed as a low rotation control. Fig.14 The flowchart shown is explained step by step. In this flowchart, the start condition is the engine stop process, and the end condition is the switch to normal control after the engine restarts.

[0088] 《Steps S11, S12》

[0089] The period from the last engine stop to the next engine restart is regarded as a standby state, and preparations of each device are performed.

[0090] <Step S13>

[0091] After all the start condition flags of the devices are turned on, when the engine start determination flag from the ECU 26 turns on, a rotation command is issued to the control unit 27c of the variable valve timing device 27 to start energizing the intake cam drive motor 27b.

[0092] 《Steps S14, S15》

[0093] A rotation command for pressing in the direction of the most advanced angle stopper 27f is provided to the variable valve timing device 27. The rotation command at this time is the same as that in the engine stop processing, and a fixed value of a duty ratio of 10% is provided as a rotation command in the same direction as the rotation direction of the camshaft as a low rotation control. The ECU 26 receives a signal from the crank angle sensor 6 and calculates the rotation speed of the crankshaft 5. When the rotation speed of the crankshaft 5 exceeds the stage of 200rpm as the second threshold value, the low rotation control is terminated and the process is transferred to step S16.

[0094] <Step S16>

[0095] In step S16, the low rotation control is switched to the normal control. Here, the phase of the intake cam 11 is kept controlled at the most advanced angle by the normal control which makes the engine speed proportional to the duty ratio of the PWM output from the ECU 26 to the control unit 27c.

[0096] 《Step S17》

[0097] In order to reduce the NVH when the engine is restarted, in this embodiment, the engine speed of 1000 rpm is set as the third threshold, and the phase of the intake cam 11 is kept controlled at the most advanced angle position until the engine speed reaches 1000 rpm. That is, in step S17, the engine speed after switching from low speed control to normal control is monitored, which has the function of triggering switching between the phase for reducing NVH and the phase for initial explosion.

[0098] <Steps S18, S19, S20>

[0099] As shown in step S17, when the engine speed exceeds the third threshold value of 1000 rpm, the control of maintaining the intake cam 11 at the most advanced angle position is terminated, and the phase conversion of the intake cam 11 is started. The reason for the phase conversion is that since the phase of the intake cam 11 exists in the position (valve profile 9a) that abuts against the most advanced angle stopper 27f, the intake compression amount is insufficient, and thus ignition cannot be performed. Therefore, from the stage exceeding the third threshold value of 1000 rpm, the valve timing of the intake valve needs to be converted to an arbitrary pre-set initial explosion valve timing position (step S19). The ECU 26 confirms that the valve timing of the initial explosion has been reached, and toward the initial explosion, the fuel injection signal from the ECU 26 to the injector 14 is turned on, and the fuel supply to the combustion chamber is started.

[0100] <Step S21>

[0101] Thereafter, the control switches to normal control in which the variable valve timing device 27 is driven in proportion to the engine speed and the duty ratio until the next time the engine is stopped.

[0102] Through the above control, it is possible to reduce the fluctuation in engine speed and the vehicle body vibration (NVH) associated with engine stop and engine restart.

[0103] [Example 2]

[0104] <Applicable engine structure>

[0105] In this embodiment, the basic structure of the engine and its peripheral equipment is the same as that of embodiment 1. Figure 1 The engine of this embodiment is an engine using a late closing Miller cycle. The distribution of the intake valve 9 and the exhaust valve 10 of the late closing Miller cycle is shown in FIG. Fig.17 and Fig.18 shown. Fig.17 1 shows the distribution when the phase of the intake cam 11 is set to the most advanced angle position in the late-closing Miller cycle engine. Fig.18 The distribution is shown when the phase of the intake cam 11 is set to the most retarded angle position in the late Miller cycle engine. In an engine having a late Miller cycle function, the cam width and the cam lift amount as cam profiles tend to be larger than those of an engine having an early Miller cycle function.

[0106] <Control Method of Variable Valve Timing Device 27>

[0107] In the late closing Miller cycle, it is expected that the engine will be restarted with the phase of the intake cam 11 controlled at the most retarded angle position when the engine is restarted. In an engine equipped with a late closing Miller cycle, in contrast to the early closing Miller cycle, there is a mechanism that opens the intake valve 9 in the middle of the intake stroke in the stroke of a four-cycle engine, and can be set to a phase that closes the intake valve 9 after entering the compression stroke. Therefore, by controlling the phase of the intake cam 11 at the most retarded angle position when the engine is restarted, the air flow in the engine cylinder of the compression stroke can be reduced, and the speed fluctuation when the crankshaft 5 rotates upward when the engine is restarted can be reduced, and the vehicle body vibration (NVH) can be suppressed when the engine is restarted. In the present embodiment, this action is achieved by phase conversion of the valve timing device mounted on the intake camshaft.

[0108] In this embodiment, by switching the control according to the engine speed, the phase of the intake cam 11 can be controlled to the most retarded angle position when the engine is restarted. In the late-closing Miller cycle engine, in order to press the convex portion 27i of the driven rotating body 27h to the most retarded angle stopper 27g when the engine is controlled at a low speed, it is necessary to control the rotation speed of the intake cam drive motor 27b to the reverse rotation direction of the camshaft or zero rotation.

[0109] In the engine low rotation control of the present embodiment, as a rotation speed command in the direction opposite to the rotation of the camshaft, a PWM output of 200 Hz and a duty ratio of 10% is provided from the ECU 26 to the control unit 27c of the variable valve timing device 27. As a result, the current or voltage supplied to the motor is fixed at a current or voltage that changes the relative rotation phase of the camshaft in the retarded angle direction at the most retarded angle position. Then, the convex portion 27i of the driven rotating body 27h can be brought into contact with the most retarded angle stopper 27g in the concave portion 27j and pressed in the direction of the most retarded angle stopper, and the phase of the intake cam 11 from the engine low rotation region when the engine is stopped to the engine stop can be controlled at the most retarded angle position while maintaining this state.

[0110] In this embodiment, when the fuel cut-off signal of the ECU 26 is turned on, the engine speed of 200 rpm is defined as the switching condition of the control (the first threshold value), the area where the engine speed is above 200 rpm is defined as the normal control area, and the area where the engine speed is less than 200 rpm is defined as the low rotation control area. After the ECU 26 determines that the engine is stopped and the injector 14 stops supplying fuel to the cylinder, the engine speed is switched to rotation based on inertia, so the engine speed, that is, the speed of the crankshaft 5 gradually decreases. The ECU 26 calculates the signal of the crank angle sensor 6 as the speed of the crankshaft 5. As described above, at the stage where the speed is lower than 200 rpm, the control of the valve timing device is switched from normal control to low rotation control (200 Hz, the duty ratio is fixed to 10%). By controlling in this way, the phase of the intake cam 11 can be controlled at the most retarded angle position until the engine stops.

[0111] <Application Effect of This Embodiment>

[0112] On the other hand, by the above-mentioned method, the phase of the intake cam 11 can be kept controlled at the most retarded angle position when the engine is stopped. Then, when the phase of the intake cam 11 can be controlled at the most retarded angle position when the engine is stopped, the engine can be started from the most retarded angle position even when the engine is restarted next time. The control switching when the engine is restarted is also based on the engine speed of 200 rpm as the threshold. During the period before the initial explosion when the engine is restarted, the ECU 26 obtains the signal from the crank angle sensor 6, calculates the engine speed, and switches from the low rotation control to the normal control at the stage where the speed of 200 rpm or more is detected. After that, the duty ratio following the engine speed is output as a PWM signal from the ECU 26 to the control unit 27c of the variable valve timing device 27.

[0113] The control device of the variable valve timing device in the above-mentioned embodiment is capable of controlling the valve timing phase during the engine stop process and the fuel cut-off process when the engine is restarted to the most advanced angle stop position or the most retarded angle stop position. In the low rotation area where the engine speed is difficult to obtain, the control device continues to provide instructions to the intake cam drive motor in the direction of the stop fixed to a low duty cycle. In the area where the correct engine speed can be obtained, a variable duty cycle instruction proportional to the engine speed is sent to the motor, and the control is switched according to the engine speed, so that the valve timing can be controlled at an arbitrary value when the engine speed is low.

[0114] According to the present invention, by stopping the engine while controlling the phase of the intake cam 11 at an arbitrary position when the engine is rotating at a low speed, the intake cam 11 can be started from an arbitrary phase when the engine is restarted next time, thereby reducing the amount of intake air into the engine cylinder, reducing engine speed fluctuations and vehicle NVH when the engine is restarted.

[0115] The present invention 1 is a control device, which is suitable for an internal combustion engine having a variable valve timing device that changes the relative rotational phase of the camshaft with respect to the crankshaft of the internal combustion engine by adjusting the motor speed of the motor connected to the camshaft, and has a control unit that controls the variable valve timing device, characterized in that the control unit performs the following control during the engine stop processing of the internal combustion engine: normal control, when the rotational speed of the crankshaft is above a first threshold value, the current or voltage supplied to the motor is adjusted according to the rotational speed of the crankshaft so that the relative rotational phase of the camshaft changes to the most advanced angle position or the most retarded angle position; and low rotation control, during the period from the rotational speed of the crankshaft being lower than the first threshold value to the time when it becomes zero rotation, the current or voltage supplied to the motor is fixed to a constant level so that the relative rotational phase of the camshaft is maintained at the most advanced angle position or the most retarded angle position.

[0116] According to the first embodiment of the present invention, the relative rotation phase of the camshaft can be maintained at the most advanced angle position or the most retarded angle position until the rotation speed of the crankshaft is reduced to an arbitrary rotation speed and the internal combustion engine is completely stopped. Therefore, it can be applied to an early-closing Miller cycle engine. In particular, when the engine rotation is unstable before the engine is about to stop, the relative rotation phase of the camshaft can be prevented from returning from the most advanced angle position to the retarded angle side, or from the most retarded angle position to the advanced angle side due to the friction of the cam ridge or the reaction force of the valve spring.

[0117] Invention 2 is a control device described in invention 1, characterized in that the control unit, during the low rotation control, controls the current or voltage supplied to the motor to be fixed to a current or voltage that causes the relative rotation phase of the camshaft to change in the advance angle direction at the most advanced angle position, or to a current or voltage that causes the relative rotation phase of the camshaft to change in the retarded angle direction at the most retarded angle position.

[0118] According to the second embodiment of the present invention, the camshaft can be forced in the advanced angle direction at the most advanced angle position, and can be forced in the retarded angle direction at the most retarded angle position. Therefore, the relative rotation phase of the camshaft can be maintained at the most advanced angle position or the most retarded angle position until the rotation of the crankshaft stops completely.

[0119] Invention 3 is a control device described in Invention 2, characterized in that the control unit sets the current or voltage of the motor fixed in the low rotation control to the same value as the current or voltage of the motor set according to the first threshold in the normal control.

[0120] According to the third embodiment of the present invention, since the rotation speed of the crankshaft is gradually reduced due to the engine stop process, the camshaft rotates in conjunction with the crankshaft, and its rotation speed is gradually reduced. On the other hand, in the low rotation control, the current or voltage set according to the first threshold value is supplied to the motor. Therefore, the camshaft is forced in the advance angle direction at the most advanced angle position, and is forced in the retarded angle direction at the most retarded angle position. Therefore, the relative rotation phase of the camshaft can be maintained at the most advanced angle position or the most retarded angle position.

[0121] Invention 4 is a control device described in Invention 1, characterized in that the control unit switches the normal control to the low rotation control under the conditions that the fuel supply to the internal combustion engine is stopped, the rotation speed of the crankshaft is less than the first threshold, and the relative rotation phase of the camshaft is controlled at the most advanced angle position or the most retarded angle position.

[0122] According to the present invention 4, before the internal combustion engine is about to stop, as the speed decreases, the detection cycle will become rough, and the signal obtained by the cam angle sensor or the crank angle sensor will become extremely rough, but it can be switched to low rotation control at an appropriate timing, and the valve timing can be controlled to the correct phase.

[0123] Invention 5 is a control device described in invention 1, characterized in that the variable valve timing device includes a motor driver, which provides current or voltage to the motor to drive the motor based on a PWM signal with an indication pulse, and the control unit outputs a PWM signal with a duty cycle proportional to the rotational speed of the crankshaft to the motor driver in the normal control, and outputs a PWM signal with a fixed duty cycle fixed to a constant value to the motor driver in the low rotation control.

[0124] According to the fifth embodiment of the present invention, when the rotation speed of the crankshaft is greater than or equal to the first threshold value, the motor driver drives the motor based on a PWM signal having a duty ratio proportional to the rotation speed of the crankshaft, and when the rotation speed of the crankshaft is less than the first threshold value, the motor driver drives the motor using a fixed duty ratio fixed to a constant value. Therefore, by controlling the motor using the PWM signal, the relative rotation phase of the camshaft can be changed to the most advanced angle position or the most retarded angle position and maintained at the most advanced angle position or the most retarded angle position.

[0125] Invention 6 is a control device described in invention 5, characterized in that when the PWM signal with a fixed duty cycle fixed to a constant value is input from the control unit, the motor driver provides the motor with a current below a set current value or a voltage below a set voltage value.

[0126] According to the sixth aspect of the present invention, the electric motor can be controlled to be maintained at the most advanced angle position or the most retarded angle position during the low rotation control.

[0127] Invention 7 is a control device described in invention 1, characterized in that the control unit performs the following control during the operation of the motor when the engine of the internal combustion engine is restarted: low rotation control, during the period when the rotation speed of the crankshaft increases from zero rotation to the second threshold, the current or voltage supplied to the motor is fixed to a constant level, and the relative rotation phase of the camshaft is maintained at the most advanced angle position or the most retarded angle position; and normal control, under the condition that the rotation speed of the crankshaft exceeds the second threshold, the current or voltage supplied to the motor is adjusted according to the rotation speed of the crankshaft, so that the relative rotation phase of the camshaft changes toward the most advanced angle position or the most retarded angle position.

[0128] According to the seventh aspect of the present invention, during the period of motor operation when the engine is restarted, the relative rotational phase of the camshaft can be maintained at the most advanced angle position or the most retarded angle position until the rotational speed of the crankshaft increases from zero to the second threshold value.

[0129] The eighth aspect of the present invention is the control device according to the seventh aspect of the present invention, wherein the control unit performs control to convert the relative rotation phase of the camshaft to the initial explosion valve timing position on the condition that the rotation speed of the crankshaft exceeds a third threshold value that is larger than the second threshold value.

[0130] According to the eighth aspect of the present invention, the relative rotation phase of the camshaft can be converted into the initial explosion valve timing position and the intake air compression amount can be ensured to ignite the mixed gas in the engine cylinder.

[0131] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments, and various design changes can be made without departing from the spirit of the present invention as described in the claims. For example, the above embodiments are described in detail to facilitate understanding of the present invention, and are not limited to having all the structures described. In addition, a part of the structure of a certain embodiment can be replaced with the structure of other embodiments, and the structure of other embodiments can also be added to the structure of a certain embodiment. In addition, for a part of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0132] Description of symbols

[0133] 1…cylinder head, 2…cylinder block, 3…piston, 4…connecting rod, 5…crankshaft, 6…crank angle sensor, 7…intake pipe, 8…exhaust pipe, 9…intake valve, 10…exhaust valve, 11…intake cam, 12…exhaust cam, 13…intake cam angle sensor, 14…injector, 15…spark plug, 16…ignition coil, 17…fuel tank, 18…feed pump, 19…high-pressure fuel pump; 20…common rail, 21…fuel pressure sensor; 22…three-way catalyst, 23…oxygen sensor, 24…temperature sensor, 25…water temperature sensor, 26…ECU (control unit), 27…variable valve timing device, 27a…reducer, 27b…intake cam drive motor, 27c…control unit, 27d…camshaft sprocket, 27e…driving rotor, 27j…driving rotor recess, 27f…driving rotor recess most advanced angle stopper, 27g…driving rotor recess most retarded angle stopper, 27h…driven rotor, 27i…driven rotor convex part, 27c-a…universal IC, 27c-b…motor driver, 9a…early closing Miller cycle most advanced angle intake valve distribution, 9b…early closing Miller cycle most retarded angle intake valve distribution, 10a…early closing Miller cycle exhaust valve distribution, 9c…late closing Miller cycle most advanced angle intake valve distribution, 9d…late closing Miller cycle most retarded angle intake valve distribution, 10c…late closing Miller cycle exhaust valve distribution.

Claims

1. A control device for a variable valve timing device, the control device being suitable for an internal combustion engine having a variable valve timing device for changing the relative rotational phase of the camshaft with respect to the crankshaft of the internal combustion engine by adjusting the motor speed of a motor connected to the camshaft, and comprising a control unit for controlling the variable valve timing device, characterized in that: The control unit performs the following control during the engine stop processing of the internal combustion engine: normal control, when the rotation speed of the crankshaft is above a first threshold, adjusting the current or voltage supplied to the motor according to the rotation speed of the crankshaft so that the relative rotation phase of the camshaft changes to the most advanced angle position or the most retarded angle position; and low rotation control, during the period from when the rotation speed of the crankshaft is lower than the first threshold to when it becomes zero rotation, fixing the current or voltage supplied to the motor to be constant so that the relative rotation phase of the camshaft is maintained at the most advanced angle position or the most retarded angle position, The variable valve timing device includes a motor driver that supplies the current or voltage to the motor based on a PWM signal having an instruction pulse to drive the motor. The control unit outputs a PWM signal having a duty ratio proportional to the rotation speed of the crankshaft to the motor driver in the normal control, and outputs a PWM signal having a fixed duty ratio fixed to a constant value to the motor driver in the low rotation control.

2. The control device of the variable valve timing device according to claim 1, characterized in that: During the low rotation control, the control unit controls the current or voltage supplied to the motor to be fixed to a current or voltage that causes the relative rotation phase of the camshaft to change in the advance angle direction at the most advanced angle position, or to a current or voltage that causes the relative rotation phase of the camshaft to change in the retarded angle direction at the most retarded angle position.

3. The control device of the variable valve timing device according to claim 2, characterized in that: The control unit sets the current or voltage of the electric motor fixed in the low rotation speed control to the same value as the current or voltage of the electric motor set based on the first threshold value in the normal control.

4. The control device for the variable valve timing device according to claim 1, characterized in that: The control unit switches the normal control to the low rotation control under the condition that fuel supply to the internal combustion engine is stopped, the rotation speed of the crankshaft is less than the first threshold, and the relative rotation phase of the camshaft is controlled to the most advanced angle position or the most retarded angle position.

5. The control device for the variable valve timing device according to claim 1, characterized in that: When the PWM signal having a fixed duty ratio fixed to a constant value is input from the control unit, the motor driver supplies a current equal to or less than a set current value or a voltage equal to or less than a set voltage value to the motor.

6. The control device for the variable valve timing device according to claim 1, characterized in that: The control unit performs the following control during the motor operation period when the engine of the internal combustion engine is restarted: low rotation control, during the period when the rotation speed of the crankshaft increases from zero rotation to a second threshold value, the current or voltage supplied to the motor is fixed to a constant level, and the relative rotation phase of the camshaft is maintained at a most advanced angle position or a most retarded angle position; And normal control, under the condition that the rotation speed of the crankshaft exceeds the second threshold, the current or voltage supplied to the motor is adjusted according to the rotation speed of the crankshaft, so that the relative rotation phase of the camshaft changes to the most advanced angle position or the most retarded angle position.

7. The control device for the variable valve timing device according to claim 6, characterized in that: The control unit performs control to switch the relative rotation phase of the camshaft to a first explosion valve timing position under the condition that the rotation speed of the crankshaft exceeds a third threshold value that is larger than a second threshold value.

Images