Method and apparatus for controlling the starting of a variable valve timing mechanism of an internal combustion engine.

Abstract

If the intake valve closing timing during cranking is constant, it can easily lead to starting problems under low-temperature conditions, and conversely, knocking under high-temperature conditions. [Solution] The internal combustion engine is equipped with an electrically operated variable valve timing mechanism that changes the phase of the camshaft and the crankshaft that open and close the intake valves within a predetermined angular range. In its default state, the variable valve timing mechanism is set to a late closing setting where the intake valve closing timing IVC is relatively far behind bottom dead center BDC. During cranking, the target conversion angle of the variable valve timing mechanism is controlled according to the coolant temperature, such that the lower the coolant temperature, the closer the intake valve closing timing IVC is to bottom dead center BDC, increasing the amount of intake air in the cylinder.

Description

Technical Field

[0001] This invention relates to the control at the start of an electric variable valve timing mechanism that changes the valve timing of an intake valve of an internal combustion engine.

Background Art

[0002] For example, regarding a camshaft that drives an intake valve to open and close, an electric variable valve timing mechanism is known that retards the phase of the camshaft within a predetermined angle range with respect to the phase of the crankshaft by an electric actuator.

[0003] Patent Document 1 discloses control in an internal combustion engine provided with a variable compression ratio mechanism and a variable valve timing mechanism, in which during normal operation, the intake valve closing timing is variably controlled according to the load, and during cranking at the start, the intake valve closing timing is kept constant while changing the target compression ratio to keep the intake air amount constant.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The start of an internal combustion engine includes so - called cold start and warm - up restart, and the temperature conditions of the internal combustion engine during cranking are various. In Patent Document 1, such temperature conditions of the internal combustion engine are not considered, and the intake valve closing timing is made constant regardless of the temperature during cranking. Therefore, starting failure is likely to occur under low - temperature conditions, and knocking is likely to occur under high - temperature conditions.

Means for Solving the Problems

[0006] The starting control method for a variable valve timing mechanism of an internal combustion engine according to this invention relates to an internal combustion engine equipped with an electrically operated variable valve timing mechanism that changes the phase of a camshaft that opens and closes the intake valves of the internal combustion engine and the phase of a crankshaft that rotates the camshaft within a predetermined angular range, The target shift angle of the variable valve timing mechanism during cranking for starting the internal combustion engine is set according to the temperature such that the amount of intake air in the cylinder increases as the temperature of the internal combustion engine decreases.

[0007] For example, when the intake valve closing timing is far from bottom dead center, the amount of intake air into the cylinder is small, and as the intake valve closing timing approaches bottom dead center, the amount of intake air increases. In this invention, the variable valve timing mechanism is controlled according to the temperature of the internal combustion engine, such that the amount of intake air into the cylinder increases as the temperature of the internal combustion engine decreases. [Effects of the Invention]

[0008] According to this invention, the timing of opening and closing of the intake valve is controlled in a manner that takes into account the temperature of the internal combustion engine during cranking for starting, thereby improving starting performance under low-temperature conditions and preventing knocking under high-temperature conditions. [Brief explanation of the drawing]

[0009] [Figure 1] A diagram illustrating the configuration of an internal combustion engine according to this invention. [Figure 2] A valve timing chart showing an example of valve timing based on coolant temperature during cranking. [Figure 3] A time chart showing an example of operation in the second embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, an embodiment of this invention will be described in detail with reference to the drawings. Figure 1 shows a schematic of an internal combustion engine 1 in an embodiment to which this invention is applied. The internal combustion engine 1 is the driving source for the vehicle and drives the vehicle's drive wheels via a transmission (not shown).

[0011] In one embodiment, the internal combustion engine 1 is a four-stroke cycle spark-ignition internal combustion engine, also known as a gasoline engine. The internal combustion engine 1 is controlled by an engine controller 2. The engine controller 2 receives detection signals from various sensors, either directly or via other controllers, including a crank angle sensor 11 for detecting engine rotational speed, an air flow meter 12 for detecting intake air volume corresponding to the load, a water temperature sensor 13 for detecting coolant temperature representative of the temperature of the internal combustion engine 1, an accelerator position sensor 14 for detecting the opening degree (pressure amount) of the accelerator pedal operated by the driver, an air-fuel ratio sensor 15 for detecting the exhaust air-fuel ratio, a vehicle speed sensor 16 for detecting vehicle speed, a cam angle sensor 17 for detecting the angular position of the intake camshaft (described later), and a brake sensor 18 for detecting the pressure applied to the brake pedal. Based on these detection signals, the engine controller 2 optimally controls the fuel injection amount and timing by the fuel injector, the ignition timing by the spark plug, the throttle valve opening, etc.

[0012] The internal combustion engine 1 has an intake camshaft 3 that drives the intake valves of each cylinder to open and close, and an exhaust camshaft 4 that drives the exhaust valves to open and close. These camshafts 3 and 4 are rotationally driven by the crankshaft 5 via a winding transmission mechanism 6 using a cog belt or chain, in synchronization with the crankshaft 5. The intake camshaft 3 is equipped with an electrically operated variable valve timing mechanism 7 that changes the phase of the intake camshaft 3 and the phase of the crankshaft 5 within a predetermined angular range. The electrically operated variable valve timing mechanism 7 may be of any form, but for example, it is configured to include an outer annular member 7a that rotates in mesh with the cog belt or chain, and an electric actuator 7b that displaces the annular member 7a and the central camshaft 3 relative to each other in the rotational direction. The electric actuator 7b includes, for example, a motor and a reduction mechanism, and is configured to operate in both forward and reverse directions by a control signal output by the engine controller 2 to change the phase of the camshaft 3 relative to the annular member 7a. The rotational position of the intake camshaft 3 is detected by the cam angle sensor 17, and during operation of the internal combustion engine 1, the electric actuator 7b is feedback-controlled to achieve a target conversion angle corresponding to the operating conditions. The conversion angle is defined as the phase change of the camshaft 3 toward the advance side, relative to the crankshaft 5, and is expressed as the crank angle.

[0013] Furthermore, the internal combustion engine 1 has a starter motor 8, which performs cranking during startup. The starter motor 8 is driven via a switching module (not shown) based on a control signal from the engine controller 2. Power supply to the electric variable valve timing mechanism 7 begins with startup. In other words, the electric variable valve timing mechanism 7 becomes operational substantially simultaneously with the start of cranking.

[0014] Figure 2(a) shows the valve timing of the intake and exhaust valves in the default state of the variable valve timing mechanism 7 (i.e., when the conversion angle is 0). In the default state, the intake valve opening time (IVO) is after top dead center (TDC), and the closing time (IVC) is relatively far behind bottom dead center (BDC). In other words, it is set to a so-called delayed closing setting, which reduces the amount of intake air in the cylinder.

[0015] The diagram shows examples of the exhaust valve opening time (EVO) and closing time (EVC), with the closing time (EVC) being before top dead center (TDC). However, the opening and closing timing of the exhaust valve is not limited to this and can be set appropriately.

[0016] During the starting of the internal combustion engine 1, i.e., during cranking, the intake volume in the cylinder is insufficient with the default settings shown in Figure 2(a), and the compression end temperature cannot be sufficiently maintained. Therefore, the variable valve timing mechanism 7 is controlled to advance the timing. In particular, depending on the coolant temperature at startup, a larger target conversion angle is given so that the intake volume in the cylinder increases as the coolant temperature decreases.

[0017] Figure 2(b) shows the valve timing chart when the conversion angle of the variable valve timing mechanism 7 is 10°CA, where the intake valve opening time (IVO) and closing time (IVC) are both advanced by 10°CA. Similarly, Figure 2(c) shows the valve timing chart when the conversion angle is 20°CA, (d) shows the valve timing chart when the conversion angle is 30°CA, and (e) shows the valve timing chart when the conversion angle is 40°CA. As shown in these figures, until the closing time (IVC) reaches bottom dead center (BDC), the larger the conversion angle, the closer the closing time (IVC) gets to bottom dead center (BDC), and the greater the intake air volume in the cylinder (in other words, the volumetric efficiency).

[0018] In one embodiment, for example, when the cooling water temperature is -30°C, the target conversion angle is 40°CA; when it is between 0°C and 10°C, it is 30°CA; when it is 20°C, it is 20°CA; and when it is between 40°C and 80°C, it is 10°CA. That is, at the start of the chiller, the lower the cooling water temperature, the larger the target conversion angle, and in the warm-up restart with a high cooling water temperature, the target conversion angle is small.

[0019] Therefore, when the cooling water temperature is low, the intake air volume in the cylinder increases, so that the compression end temperature becomes sufficiently high and good starting performance can be obtained. On the other hand, during the warm-up restart with a high cooling water temperature, the intake air volume in the cylinder becomes relatively small, and knocking due to an excessive compression end temperature can be avoided.

[0020] In a preferred embodiment, the characteristics of the target conversion angle with respect to the cooling water temperature are determined so that the calculated compression end temperature is substantially constant regardless of the high or low cooling water temperature.

[0021] Next, referring to FIG. 3, a second embodiment will be described in which the target conversion angle is gradually increased when the engine is in a long cranking state where it does not shift to self-sustaining operation within a predetermined time after the start of cranking.

[0022] FIG. 3 is a time chart showing an example of changes in (a) the rotational speed of the internal combustion engine 1, (b) the cranking determination flag indicating that it is during cranking (in other words, before the transition to self-sustaining operation), (c) the conversion angle of the variable valve timing mechanism 7, and (d) the compression end temperature when starting the chiller with a relatively low cooling water temperature.

[0023] In the illustrated example, at time t0, cranking by the starter motor 8 starts, and at time t1 slightly later than this, the electric variable valve timing mechanism 7 operates and the conversion angle increases by one step from 0. The conversion angle for this one step is set to a larger value as the cooling water temperature at the start is lower. Also at time t1, the cranking determination flag is turned on. The cranking determination flag is turned off when the transition to self-sustaining operation occurs.

[0024] In this manner, when the electric variable valve timing mechanism 7 is advanced by one step and the starter motor 8 cranks the engine, the internal combustion engine 1 transitions to autonomous operation. Once the engine starts, the start of the internal combustion engine 1 is complete, and the conversion angle of the electric variable valve timing mechanism 7 becomes the target conversion angle for normal operation.

[0025] On the other hand, if a predetermined time ΔT has elapsed without transitioning to autonomous operation, it is considered to be in a long-cranking state, and the conversion angle increases by another step. In other words, at time t2, when the predetermined time ΔT has elapsed, the conversion angle increases by one step. This increase in the conversion angle leads to a rise in the compression end temperature.

[0026] In the illustrated example, the long cranking state continues, so at time t3, after a predetermined time ΔT has elapsed from time t2, the conversion angle increases by another step. Since the engine does not transition to autonomous operation at this stage either, at time t4, after a predetermined time ΔT has elapsed from time t3, the conversion angle increases by another step. Subsequently, at time t5, the internal combustion engine 1 transitions to autonomous operation, and the cranking determination flag is turned off.

[0027] As described above, in the embodiment, when a long cranking state occurs, the conversion angle of the variable valve timing mechanism 7 increases by one step every predetermined time ΔT, and the compression end temperature is gradually increased. Here, the amount of increase in the conversion angle for one step is the same as the magnitude of the conversion angle for the first step, and is set to a larger value as the coolant temperature decreases. Therefore, the lower the coolant temperature, the faster the rate of increase in the conversion angle. As a result, the continuation of an excessively long long cranking state is reliably avoided.

[0028] Furthermore, according to this second embodiment, since the conversion angle gradually increases, the initial conversion angle in the first step can be set relatively small, preventing the compression end temperature from becoming unnecessarily high. Note that the increase in the conversion angle at predetermined time intervals ΔT is limited when the intake valve closing timing (IVC) approaches bottom dead center (BDC) (see Figure 2).

[0029] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, coolant temperature is used as a parameter representing the temperature of the internal combustion engine, but other parameters such as intake air temperature or lubricating oil temperature may be used as the temperature of the internal combustion engine. Furthermore, in the variable valve timing mechanism of the above embodiment, the intake valve closing timing (IVC) is set to be relatively delayed compared to bottom dead center (BDC) in the default position, but the present invention can also be applied to a setting that closes earlier than bottom dead center (BDC), a so-called early closing setting. In this case, the valve timing will be changed to the retarded side during cranking.

[0030] Furthermore, although the above embodiment was described assuming that a variable valve timing mechanism is not provided on the exhaust valve side, the present invention can also be applied when a variable valve timing mechanism is provided on the exhaust valve side. [Explanation of symbols]

[0031] 1…Internal combustion engine 2…Engine controller 3…Intake camshaft 5…Crankshaft 7. Electrically operated variable valve timing mechanism 8... Starter motor 13…Water temperature sensor

Claims

1. In an internal combustion engine equipped with an electrically operated variable valve timing mechanism that changes the phase of the camshaft that opens and closes the intake valves of the internal combustion engine, and the phase of the crankshaft that rotates the camshaft, within a predetermined angular range, The target shift angle of the variable valve timing mechanism during cranking for starting the internal combustion engine is set according to the temperature such that the amount of intake air in the cylinder increases as the temperature of the internal combustion engine decreases. A method for controlling the variable valve timing mechanism of an internal combustion engine during startup.

2. When the target shift angle of the above variable valve timing mechanism is 0, the intake valve closing timing is set to a delayed closing setting, which is later than the bottom dead center. During the cranking described above, the target conversion angle increases as the temperature decreases, so that the intake valve closing timing approaches bottom dead center. A method for controlling the variable valve timing mechanism of an internal combustion engine during startup, as described in claim 1.

3. The characteristics of the target conversion angle with respect to the above temperature are defined such that the calculated compression end temperature remains approximately constant regardless of the above temperature. A method for controlling the variable valve timing mechanism of an internal combustion engine during startup, as described in claim 1.

4. After cranking begins, it is determined whether or not the system is in a long-cranking state where it does not transition to autonomous operation within a predetermined time. When a long cranking state is detected, the target conversion angle is corrected in a direction that further increases the intake air volume in the cylinder. A method for controlling the variable valve timing mechanism of an internal combustion engine during startup, as described in claim 1.

5. While the long cranking state continues, the target conversion angle is gradually corrected in a direction that further increases the intake volume in the cylinder, The rate of change of this target conversion angle is increased as the temperature decreases. A method for controlling the variable valve timing mechanism of an internal combustion engine during startup, as described in claim 4.

6. An electrically operated variable valve timing mechanism that changes the phase of the camshaft that opens and closes the intake valve of an internal combustion engine, and the phase of the crankshaft that rotates this camshaft, within a predetermined angular range. A controller that controls the conversion angle of this variable valve timing mechanism, Equipped with, The above controller is The target shift angle of the variable valve timing mechanism during cranking for starting the internal combustion engine is set according to the temperature such that the amount of intake air in the cylinder increases as the temperature of the internal combustion engine decreases. A control device for starting a variable valve timing mechanism in an internal combustion engine.

Images