Patent Application
20200232325
The present invention relates generally to a variable operation system for an internal combustion engine, and particularly to a variable operation system for an internal combustion engine provided with at least a variable valve mechanism for controlling valve timing of an exhaust valve set and an intake valve set, and a control device for the internal combustion engine variable operation system.
For modern internal combustion engines, it has been proposed to improve performance of an internal combustion engine by a combination of a variable compression ratio mechanism and a variable valve mechanism, wherein the variable compression ratio mechanism controls variably a geometric compression ratio and a geometric expansion ratio of the internal combustion engine, namely, a mechanical compression ratio and a mechanical expansion ratio of the internal combustion engine, and wherein the variable valve mechanism controls variably valve timing (opening and closing timings) of an intake valve and an exhaust valve, on which an actual compression ratio (effective compression ratio) of the internal combustion engine depends. JP 2002-276446 A (patent document 1) discloses such a known variable compression ratio mechanism.
A document “CO2-Potential of a Two-Stage VCR System in Combination with Future Gasoline Powertrains” (non-patent document 1) shows in
According to non-patent document 1, at cold start of the internal combustion engine, the mechanical compression ratio is set to the maximum mechanical compression ratio point, and the mechanical expansion ratio is also set to the maximum mechanical expansion ratio point. This causes a phenomenon that the temperature of exhaust gas of the internal combustion engine falls. This suppresses an exhaust gas purifying catalyst, which is provided in an exhaust pipe, from being warmed up, and thereby causes a decrease in conversion ratio in the exhaust gas purification catalyst for adverse components of exhaust gas. This causes a problematic increase in quantity of adverse components of exhaust gas that is exhausted through a tail pipe to the atmosphere after passing through the exhaust gas purifying catalyst. Similar problems have arisen also with internal combustion engines provided with no variable compression ratio mechanism, because the mechanical expansion ratio εE (=mechanical compression ratio εC) tends to be increased for satisfying a demand for suppressing fuel consumption.
It is an object of the present invention to provide a new variable operation system for an internal combustion engine, and a control device for the variable operation system, which are capable of promoting the progress of warming-up of an exhaust gas purifying catalyst by raising the temperature of exhaust gas at cold start of the internal combustion engine.
An embodiment of the present invention includes: an intake-side variable valve mechanism structured to control a phase of opening and closing timings of an intake valve; and an exhaust-side variable valve mechanism structured to control a phase of opening and closing timings of an exhaust valve; wherein at an engine cold start, the exhaust-side variable valve mechanism sets the opening timing of the exhaust valve advanced at or close to a midpoint between top dead center and bottom dead center, and sets the closing timing of the exhaust valve advanced at a preset point before top dead center, and the intake-side variable valve mechanism sets the opening timing of the intake valve retarded at a preset point after top dead center.
According to a preferable embodiment of the present invention, even when the mechanical expansion ratio of the internal combustion engine is set to a high mechanical expansion ratio point, it is possible to increase the temperature of exhaust gas exiting from a combustion chamber by a sufficient advance of the opening timing of the exhaust valve at engine start, and thereby quickly warm up and increase the conversion ratio of an exhaust gas purifying catalyst arranged downstream of the combustion chamber.
Specifically, the operation of opening the exhaust valve when the temperature of combustion gas is still high after combustion, serves to exhaust hot exhaust gas and particularly exhaust hot exhaust gas swiftly under high pressure because the exhaust valve is opened under a condition that the in-cylinder pressure is high, and thereby further enhance the activity of the exhaust gas purification catalyst, and significantly reduce the adverse components of exhaust gas when the internal combustion engine is in cold state.
The following describes embodiments of the present invention in detail with reference to the drawings. However, the present invention is not limited to the embodiments, but contains in its scope various modifications and applications based on a technical concept of the present invention.
The following describes a variable operation system of an internal combustion engine according to a first embodiment of the present invention.
First, the following describes basic configuration of the variable operation system of the internal combustion engine with reference to
Piston 01 is linked to a crankshaft 02 via a connecting rod mechanism 03, and includes a crown face defining a combustion chamber 04 between the crown face and a lower face of cylinder head SH, wherein connecting rod mechanism 03 includes a lower link 42 and an upper link 43 described below. At a substantially central portion of cylinder head SH, an ignition plug 05 is provided.
Intake port IP is connected to an air cleaner not shown, and is supplied with intake air through an electrically controlled throttle valve 72. Electrically controlled throttle valve 72 is controlled by a controller 22, wherein the opening of electronic throttle valve 72 is controlled basically in accordance with an amount of depression of an accelerator pedal. Exhaust port EP releases exhaust gas through an exhaust gas purification catalyst 74 and through a tail pipe to the atmosphere.
As shown in
The intake side is provided with intake-side variable valve mechanism (henceforth referred to as intake-side VTC mechanism) 1A as a “phase angle varying mechanism” structured to control a center phase angle of valve lifting of intake valves 4, whereas the exhaust side is provided with exhaust-side variable valve mechanism (henceforth referred to as exhaust-side VTC mechanism) 1B as a “phase angle varying mechanism” structured to control a center phase angle of valve lifting of exhaust valves 5. Furthermore, variable compression ratio mechanism (henceforth referred to as VCR mechanism) 3 is provided as a “variable piston stroke mechanism” structured to control the mechanical compression ratio εC and mechanical expansion ratio εE of the cylinder. In this example, VCR mechanism 3 is structured to set the mechanical compression ratio εC and mechanical expansion ratio εE equal to each other.
Each of intake-side VTC mechanism 1A and exhaust-side VTC mechanism 1B includes a phase control hydraulic actuator 2A, 2B, and is structured to hydraulically control the opening and closing timings of intake valves 4 or exhaust valves 5. Hydraulic pressure supply to phase control hydraulic actuator 2A, 2B is controlled by a hydraulic control unit not shown based on control signals from controller 22. By the hydraulic control of phase control hydraulic actuator 2A, 2B, the center phase θ of the lift curve is controlled to be advanced and retarded.
In this way, the lift curve has a constant shape, but is moved as a whole in an advance direction and a retard direction. This movement is carried out continuously. Each of intake-side VTC mechanism 1A and exhaust-side VTC mechanism 1B is not limited to the hydraulic type, but may be variously implemented, for example, by employing an electric motor or an electromagnetic actuator.
Controller 22 identifies a current state of the internal combustion engine, based on an output signal from a crank angle sensor for measuring a current rotation speed Ne [rpm] of the internal combustion engine from crank angle information, and various information signals such as an intake air quantity (i.e. load) from an air flow meter, an accelerator opening sensor, a vehicle speed sensor, a gear position sensor, an engine coolant temperature sensor 31 for sensing a temperature of an engine body, and an atmospheric humidity sensor for sensing humidity in an intake pipe. Controller 22 then outputs at least an intake VTC control signal to intake-side VTC mechanism 1A and an exhaust VTC control signal to exhaust-side VTC mechanism 1B.
The following describes VCR mechanism 3 with reference to
VCR mechanism 3 has a cycle of crank angle of 360°, so that the piston position at compression top dead center is theoretically identical to the piston position at exhaust top dead center. Similarly, the piston position at intake bottom dead center is identical to the piston position at expansion bottom dead center. This means that the compression stroke from the piston position at intake bottom dead center to the piston position at compression top dead center is constantly equal to the expansion stroke from the piston position at compression top dead center to the piston position at expansion bottom dead center, regardless of the position control. Accordingly, the mechanical compression ratio εC and mechanical expansion ratio εE are constantly equal to each other theoretically (εC=εE), regardless of the position control.
VCR mechanism 3 is configured as disclosed in patent document 1 described above as conventional. The following describes its structure briefly. Crankshaft 02 includes journal parts 40 and crank pin parts 41, wherein journal parts 40 are rotatably supported by a main bearing of cylinder block SB. Each crank pin part 41 is eccentric from journal parts 40 by a predetermined distance, wherein lower link 42 as a second link is rotatably connected to crank pin part 41. Lower link 42 is composed of two parts that can be separated laterally, and includes a connection hole substantially at its center where crank pin part 41 is fitted.
Upper link 43 as a first link includes a lower end pivotably connected to a first end of lower link 42 by a connecting pin 44, and an upper end pivotally connected to piston 01 by a piston pin 45. As a third link, a control link 46 includes an upper end pivotally connected to a second end of lower link 42 by a connecting pin 47, and a lower end pivotally connected via a control shaft 48 to a lower part of cylinder block SB that is a part of the engine body.
Control shaft 48 is rotatably supported with respect to the engine body, and includes an eccentric cam part 48a that is eccentric from a rotation center of control shaft 48, wherein a lower end portion of control link 46 is rotatably fitted with eccentric cam part 48a. The rotational position of control shaft 48 is controlled by a compression ratio control actuator 49 employing an electric motor, based on a control signal from controller 22.
In VCR mechanism 3 based on the multi-link piston-crank mechanism as described above, rotation of control shaft 48 caused by compression ratio control actuator 49 causes a change in the center position of eccentric cam part 48a with respect to the engine body. This causes a change in the position where the lower end of control link 46 is pivotally supported. This change causes an upward or downward movement of the position of piston 01 at top dead center, and also causes a change in the stroke of piston 01 as indicated by S1 and S2 in
The mechanical compression ratio (εC) is a compression ratio geometrically determined only by a change in volume of the combustion chamber caused by the stroke of piston 01, and is specifically a ratio of the in-cylinder volume at bottom dead center of piston 01 on the intake stroke with respect to the cylinder volume at top dead center of piston 01 on the compression stroke.
Where VO represents the in-cylinder volume at piston compression top dead center, and V represents the displacement volume, the in-cylinder volume at piston bottom dead center is equal to “VO+V”, so that the mechanical compression ratio (εC) is expressed as “εC=(VO+V)/VO=V/VO+1”. Based on this formula, the minimum mechanical compression ratio point (εC min=minimum mechanical expansion ratio point εE min) shown in
As discussed in the section “Problem(s) to be Solved by the Invention”, according to non-patent document 1, at cold start of the internal combustion engine, the mechanical compression ratio (εC) is set to the maximum mechanical compression ratio point, and the mechanical expansion ratio (εE) is also set to the maximum mechanical expansion ratio point. This causes a phenomenon that the temperature of exhaust gas of the internal combustion engine falls. This suppresses an exhaust gas purifying catalyst, which is provided in an exhaust pipe, from being warmed up, and thereby causes a decrease in conversion ratio in the exhaust gas purification catalyst for adverse components of exhaust gas. This causes a problematic increase in quantity of adverse components of exhaust gas that is exhausted through a tail pipe to the atmosphere after passing through the exhaust gas purifying catalyst.
For solving the problem described above, the present embodiment is configured such that at a cold start of the internal combustion engine, the exhaust-side VTC mechanism sets the opening timing of the exhaust valve advanced at or close to a “midpoint angular position” between top dead center and bottom dead center, and sets the closing timing of the exhaust valve advanced at a preset point before top dead center, and the intake-side VTC mechanism sets the opening timing of the intake valve retarded at a preset point after top dead center. The exhaust-side VTC mechanism and the intake-side VTC mechanism are controlled as follows.
First, the intake-side VTC mechanism 1A of the present embodiment is structured to be mechanically controlled to be stably at or close to the “midpoint angular position” as a default position, when hydraulic pressure is supplied from a hydraulic pump, and also when no hydraulic pressure is supplied from the hydraulic pump. The default position is a position where intake-side VTC mechanism 1A is mechanically stable.
Phase control hydraulic actuator 2A employs a bias spring that biases vanes in the advance direction. Its biasing force is small so that the vanes are mechanically pushed back to vicinity of the “midpoint angular position” due a valve operating reaction force. As the engine speed falls with this phase, the hydraulic pressure gradually decreases, and the phase in the vicinity of “midpoint angular position” is pin-locked. Namely, the default position is at or close to the “midpoint angular position” between a “most retarded position” and a “most advanced position”.
This produces a mechanical fail-safe function for a situation of disconnection failure or the like in an electric system. As described below, when the internal combustion engine is at rest, intake valve 4 is set in the vicinity of “midpoint angular position”.
Then, exhaust-side VTC mechanism 1B of the present embodiment is structured to be mechanically controlled to be stably at or close to a “most advanced position” as a default position, when hydraulic pressure is supplied from the hydraulic pump, and also when no hydraulic pressure is supplied from the hydraulic pump.
Phase control hydraulic actuator 2B employs a bias spring that biases vanes in the advance direction. When no hydraulic pressure is applied to the vanes, the vanes are maintained stably in vicinity of the “most advanced position”. As the engine speed falls with this phase, the hydraulic pressure gradually decreases, and the phase in the vicinity of the “most advanced position” is pin-locked. Namely, the “most advanced position” is the default position.
This produces a mechanical fail-safe function for a situation of disconnection failure or the like in an electric system. As described below, when the internal combustion engine is at rest, exhaust valve 5 is set in the vicinity of “most advanced position”.
Further description of intake-side VTC mechanism 1A and exhaust-side VTC mechanism 1B is omitted, because JP 2011-220349 A and JP 2013-170498 A, which were made by the present applicant, disclose in detail basic configurations of intake-side VTC mechanism 1A and exhaust-side VTC mechanism 1B. The present embodiment employs the intake-side VTC mechanism and exhaust-side variable valve mechanism described in JP-2011-220349 A, while setting the default positions as described above.
The following describes valve timings of intake valve 4 and exhaust valve 5 during a cold operation including a cold start.
Incidentally, increasing the temperature at compression top dead center by increasing the mechanical compression ratio (=mechanical expansion ratio) during cold operation as described above, serves to improve combustion during cold operation, and thereby achieve preferable start and operation. Therefore, for an internal combustion engine that is set to a high mechanical expansion ratio, and set to the valve timings shown
There is a possibility that the increased mechanical compression ratio causes an increase in compression, and thereby causes an increase in load applied to a starter motor. However, the setting of retarding the closing timing of intake valve 4 from the closing timing point IVC1 to a closing timing point IVC2 away from bottom dead center serves to maintain the degree of compression as for the normal mechanical compression ratio.
However, since the PVO period is maintained unchanged substantially, the operating angles (valve opening periods) of exhaust valve 5 and intake valve 4 are expanded depending on the setting. This may increase mechanical friction of a valve operating system, and thereby adversely affect the fuel efficiency and increase the adverse components of exhaust gas.
In order to solve the problems described above, as shown in
The opening timing point EVOc of exhaust valve 5 is set at or close to a midpoint between top dead center and bottom dead center. Preferably, the opening timing point EVOc is set in a range of 90°±20°˜30° or so in the advance direction (counterclockwise direction) from expansion bottom dead center as shown in
The advanced EVCc and the retarded IVOc described above cause a “negative valve overlap” between exhaust valve set 5 and intake valve 4 (henceforth referred to as NVO period). This serves to reduce the operating angles (valve opening periods) of exhaust valve set 5 and intake valve 4, and thereby suppress the mechanical friction of the valve operating system from being increased. Furthermore, the employment of the valve timings shown in
<1> Even during cold operation at high mechanical expansion ratio, by sufficiently advancing the opening timing EVO of exhaust valve 5, it is possible to increase the combustion gas temperature at the opening timing of the exhaust valve, i.e. increase the exhaust temperature, and thereby early warm-up and enhance the conversion ratio of the exhaust gas purification catalyst. Namely, it is possible not only to exhaust hot combustion gas (exhaust gas) by opening the exhaust valve 5 while the combustion temperature is high after combustion, but also to exhaust hot combustion gas swiftly under high pressure by opening the exhaust valve 5 while the in-cylinder pressure is high. This serves to further enhance the activity of the catalyst, and effectively reduce the adverse components of exhaust gas during cold operation.
<2> Furthermore, by enclosing and pressing by the piston the hot combustion gas in the cylinder during the NVO period defined by the closing timing point EVCc of exhaust valve 5 and the opening timing point IVOc of intake valve 4, it is possible to heat the in-cylinder gas and the engine body, and thereby significantly improve combustion during cold operation, and reduce the fuel consumption and adverse components of exhaust gas, and increase the engine warm-up performance (the rate of increase of the engine temperature), and thereby further enhance the warm-up rate of the catalyst. This is accompanied by a rise in oil temperature, which serves to reduce the mechanical friction of the internal combustion engine correspondingly, thereby also reducing fuel consumption when the internal combustion engine is in cold state.
<3> In addition, although the closing timing point IVCc of intake valve 4 is identical to the closing timing IVC2 shown in
In this way, according to the valve timing of the present embodiment shown in
The further feature that the exhaust gas can be exhausted under high pressure, serves to promote the warm-up and activation of the exhaust gas purifying catalyst, and further enhance the conversion ratio of the catalyst, and thereby reduce the adverse components of exhaust gas that is finally exhausted to the atmosphere. Moreover, the feature that the valve timing shown in
Although combustion gas can be introduced into the cylinder also with the PVO period, this case includes a process where the combustion gas is swept into the intake system, and thereafter introduced again into the cylinder during the subsequent intake stroke, so that the combustion gas the temperature is theoretically lower than the gas temperature during the NVO period according to the present embodiment. Furthermore, this setting requires the opening periods (working angles) of intake valve 4 and exhaust valve 5 to be also set large, and thereby causes an adverse effect due to the increase in mechanical friction of the valve operating system, and fails to produce the action and effect according to this embodiment described above.
The following describes a control operation of the valve timing and mechanical expansion ratio (mechanical compression ratio) corresponding to changes in operating state with reference to
<From Engine Stop to Engine Start> As shown in
In the present embodiment, during cold start, the mechanical expansion ratio is controlled to a high mechanical expansion ratio point (for example, maximum mechanical expansion ratio point εE max) greater than the minimum mechanical expansion ratio point (εE min) by VCR mechanism 3. Since the exhaust gas temperature decreases to be lower because of high thermal efficiency, there is a possibility that the adverse components of exhaust gas when the internal combustion engine is in cold state are increased by a relative decrease in the catalyst conversion ratio. Even in such a situation, the setting of the opening timing of exhaust valve set 5 (EVO) at the advanced opening timing point (EVOc), serves to suppress the exhaust gas temperature from dropping, and maintaining the catalyst conversion ratio high, and enhance the effect of reducing the adverse components of exhaust gas.
<Immediately Before Completion of Warm-Up Operation After Start of Warm-Up> As shown in
In addition, since the opening timing EVO of exhaust valve 5 gradually shifts in the retard direction, the closing timing EVC of exhaust valve set 5 also shifts to a closing timing point EVCw in the retard direction as the temperature of the internal combustion engine rises. This causes a decrease in quantity of hot EGR gas enclosed in the cylinder, and suppresses an excessive temperature rise more than required for the internal combustion engine and the catalyst, and causes a decrease in the quantity of exhaust gas in the cylinder (EGR gas quantity), and thereby improves the combustion stability during transient operation, and produces a preferable acceleration response to a rapid acceleration request or the like.
When the internal combustion engine reaches a predetermined temperature T0, the warm-up operation is completed. Immediately before the completion, the valve timing is set as shown in
<Low Load After Warm-Up> As shown in
This setting serves to increase the expansion work by retarding the opening timing of exhaust valve 5 to the opening timing point EVOl, and reduce the pumping loss by a so-called intake valve delayed closing Atkinson cycle effect by retarding the closing timing of intake valve 4 to the closing time point IVCl, and further reduce a pumping loss in an initial stage of the intake stroke that can occur in the vicinity of TDC, by no formation of NVO period, and thereby reduce the total pumping loss, and improve the fuel efficiency.
<High Load After Warm-Up> As shown in
This setting serves to improve the charging efficiency by advancing the closing timing of intake valve 4 to the closing timing point IVCh toward bottom dead center, and further enhance a so-called scavenging function (i.e. a method of directing fresh air into the cylinder by synchronization between a negative pressure wave of exhaust pulsation and the PVO period by delaying the occurrence of the negative pressure wave) by forming the large PVO period and retarding the opening timing of exhaust valve 5 to the opening timing point EVOh, and thereby sufficiently enhance the engine torque. Furthermore, since the mechanical compression ratio is controlled to the minimum mechanical compression ratio point εC min (=about 8), it is possible to improve knock resistance and further enhance the engine torque.
In the present embodiment, the employment of VCR mechanism 3 produces actions and effects as follows. For example, by controlling the mechanical expansion ratio to a high mechanical expansion ratio point by the VCR mechanism in a low speed and low load region, it is possible to further enhance the effect of improving the fuel efficiency in the low speed and low load region. Furthermore, by controlling the mechanical compression ratio to a low mechanical compression ratio by the VCR mechanism in a low speed and high load region, it is possible to prevent knocking and further improve the engine torque in the low speed and high load region.
The following briefly describes a control flow for performing a control about the valve timings shown in
<Step S10> First, at Step S10, it reads engine stop information for stopping the internal combustion engine, and operation condition information about the internal combustion engine. The engine stop information for stopping the internal combustion engine is typically a condition that idling stop requirements are satisfied, or may be a key-off signal depending on driver's intention. There are many signals indicating the operating condition information about the internal combustion engine. In the present embodiment, the signals include rotational speed information, intake air quantity information, water temperature information, requested load information (accelerator opening), and others as to the internal combustion engine, and actual position information regarding the intake-side VTC mechanism 1A and exhaust-side VTC mechanism 1B. After reading the various pieces of information at Step S10, the process proceeds to Step S11.
<Step S11> At Step S11, it determines whether or not an engine stop transition condition is satisfied, or whether or not key-off operation occurs. Determination whether or not key-off operation occurs may be implemented, for example, by monitoring a key-off signal. When the key-off signal is not inputted, the process then proceeds to an end, and awaits a next activation timing. On the other hand, when the key-off signal is inputted, or when the engine stop transition condition is satisfied, the process then proceeds to Step S12.
<Step S12> At Step S12, it outputs shift control signals to phase control hydraulic actuator 2A of intake-side VTC mechanism 1A, phase control hydraulic actuator 2B of exhaust-side VTC mechanism 1B, and compression ratio control actuator 49 of VCR mechanism 3, so as to cause intake-side VTC mechanism 1A, exhaust-side VTC mechanism 1B, and VCR mechanism 3 to shift to their default positions. Namely, in order to prepare for a next start-up, a control is performed to achieve valve opening and closing timing characteristics and piston position characteristics shown as “engine at rest->engine at cold start” in
In this way, as shown in
Furthermore, the mechanical expansion ratio (εE) set by VCR mechanism 3 is set to a high mechanical expansion ratio point (=high mechanical compression ratio point), and in this example, is set to the maximum mechanical expansion ratio point (εE max). When the output of setting of intake-side VTC mechanism 1A, exhaust-side VTC mechanism 1B, and VCR mechanism 3 to the default positions is completed, the process then proceeds to Step S13.
<Step S13> At Step S13, it monitors a state of control by determining an actual position of each of phase control hydraulic actuator 2A of intake-side VTC mechanism 1A, phase control hydraulic actuator 2B of exhaust-side VTC mechanism 1B, and compression ratio control actuator 49 of VCR mechanism 3. When the determination of each actual position is completed, the process then proceeds to Step S14.
<Step S14> At Step S14, it determines based on each actual position whether or not intake valve 4 is set in the vicinity of the opening timing point IVOo and in the vicinity of the closing timing point IVCo, and exhaust valve 5 is set in the vicinity of the opening timing point EVOo and in the vicinity of the closing timing point EVCo, and the mechanical expansion ratio (εE) is set to the maximum mechanical expansion ratio point εE max. When this condition is not satisfied, the process then returns to Step S13 where the same control is executed.
On the other hand, when it is determined based on each actual position that intake valve 4 is set in the vicinity of the opening timing point IVOo and in the vicinity of the closing timing point IVCo, and exhaust valve 5 is set in the vicinity of the opening timing point EVOo and in the vicinity of the closing timing point EVCo, and the mechanical expansion ratio (εE) is set to the maximum mechanical expansion ratio point εE max, the process then proceeds to Step S15.
<Step S15> At Step S15, it sends a fuel cut signal to the fuel injection valve so as to stop the internal combustion engine, and also sends an ignition cut signal to the ignition device. This causes a decrease in rotation speed Ne of the internal combustion engine, and thereby stops the internal combustion engine. In this way, the setting of intake-side VTC mechanism 1A, exhaust-side VTC mechanism 1B, and VCR mechanism 3 to the default positions is completed actually, and the internal combustion engine starts to stop, and the process proceeds to the end, and awaits a next start-up of the internal combustion.
The following describes a control flow for restarting operation of the internal combustion engine from this state with reference to
<Step S20> At Step S20, it determines whether or not an engine starting condition is satisfied. This determination may be implemented, for example, by monitoring a key-on signal or a starter activation signal. When the key-on start signal is not inputted, the process then proceeds to the end, and waits for a next activation timing. On the other hand, when the key-on start signal is inputted, it determines that the engine starting condition is satisfied, and the process then proceeds to Step S21.
<Step S21> At Step S21, it outputs shift control signals to phase control hydraulic actuator 2A of intake-side VTC mechanism 1A and phase control hydraulic actuator 2B of exhaust-side VTC mechanism 1B so as to shift the intake-side VTC mechanism 1A and exhaust-side VTC mechanism 1B to their start positions (which are the default positions in this example). It further outputs a shift control signal to compression ratio control actuator 49 of VCR mechanism 3. Namely, in order to prepare for start-up, a control is performed to achieve characteristics of the valve opening and closing timings and piston position as shown as “engine at cold start” in
Thus, as shown in
Under this condition, the opening and closing timings of exhaust valve 5 and intake valve 4 at cold start are set to the default opening and closing timing points as for the stop condition, and the mechanical expansion ratio is set to maximum mechanical expansion ratio point (εE max) as for the stop condition. This serves to achieve a smooth start without requiring a substantive shift operation. In addition, this produces a mechanical fail-safe effect.
After outputting the shift control signals to phase control hydraulic actuator 2A of intake-side VTC mechanism 1A, phase control hydraulic actuator 2B of exhaust-side variable valve mechanism 1B, and compression ratio control actuator 49 of VCR mechanism 3, the process proceeds to Steps S22 and S23.
<Step S22, Step S23> At Step S22, it starts cranking by the starter motor, and subsequently at Step S23, it determines whether or not the rotational speed Ne has reached a predetermined cranking speed. When the rotation speed Ne has not reached the predetermined cranking rotational speed, it then repeats this determination. Then, when the rotation speed Ne reaches the predetermined cranking rotation, the process then proceeds to Step S24.
<Step S24> At Step S24, it supplies driving signals to the fuel injection valve and the ignition device for starting the internal combustion engine in accordance with rotation of the starter motor. After supplying the driving signals to the fuel injection valve and ignition device, the process proceeds to Step S25.
<Step S25> At Step S25, it determines whether or not a predetermined time has elapsed since the cranking. When the predetermined time has not elapsed, it then repeats this determination. When the predetermined time has elapsed, the process then proceeds to Step 26 and Step 27.
<Step S26, Step S27> At Step S26, it senses the engine temperature T (coolant temperature) of the internal combustion engine, and subsequently at Step S27, it performs based on the engine temperature a control by exhaust-side VTC mechanism 1B to retard the opening timing (EVO) of exhaust valve 5 from the opening timing point EVOc to the opening timing point EVOw, and also retard the closing timing (EVC) of exhaust valve 5 from the closing timing point EVCc to the closing timing point EVCw, as shown in
In this state, the opening timing (IVO) and closing timing (IVC) of intake valve 4 are maintained at the same points as at the time of engine stop, namely, as IVOc=IVOw and IVCc=IVCw. The closing timing of exhaust valve 5 changes to the closing timing point EVCw substantially identical to the opening timing of intake valve 4 set to the opening timing point IVOw, wherein the NVO period is substantially eliminated to significantly reduce the internal EGR quantity. Then, while the retard control of exhaust-side VTC mechanism 1B is being performed, it performs the following steps.
<Step S28> At Step S28, it determines whether or not the sensed engine temperature (coolant temperature) of the internal combustion engine has reached a predetermined temperature To. When the sensed engine temperature (coolant temperature) of the internal combustion engine has not reached the predetermined temperature To, it determines that the engine is in cold state, and executes Steps S26 and S27 again. Until the sensed engine temperature (coolant temperature) of the internal combustion engine reaches the predetermined temperature To, it continues the control process of Steps S26 and S27. Immediately before completion of the warm-up, exhaust valve 5 is set to the opening timing point EVOw and the closing timing point EVCw, and intake valve 4 is set to the opening timing point IVOw and the closing timing point IVCw. Then, when the warm-up of the internal combustion engine proceeds, and the predetermined temperature To is reached, it then determines that the warm-up from cold state is completed, and proceeds to Step S29.
<Step S29> At Step S29, it senses the engine operation state (especially, load state), and then perform a control step described below for controlling the opening timing (EVO) and closing timing (EVC) of exhaust valve 5, and the opening timing (IVO) and closing timing (IVC) of intake valve 4, and the mechanical expansion ratio (εE). The load state is identified by using a load map that has a horizontal axis representing the rotational speed and a vertical axis representing the intake air quantity, for example. After sensing the load state, the process proceeds to Step S30.
<Step S30> At Step S30, it determines whether or not the current engine operating state is in a low load region. When determining that the current engine operating state is in the low load region, it then proceeds to Step S31. When determining that the current engine operating state is in a region of higher load than the low-load state, the process then proceeds to Step S32.
<Step S31> At Step S31, it outputs shift control signals for the low load region to phase control hydraulic actuator 2A of intake-side VTC mechanism 1A, and phase control hydraulic actuator 2B of exhaust-side variable valve mechanism 1B. It also outputs a shift control signal to compression ratio control actuator 49 of VCR mechanism 3.
Accordingly, the opening timing (IVO) of intake valve 4 is set to the opening timing point IVOl, and the closing timing (IVC) of intake valve 4 is set to the closing timing point IVCl, and the closing timing (EVC) of exhaust valve 5 is set to the closing timing point EVCl. Furthermore, the mechanical expansion ratio (εE) is set to the high mechanical expansion ratio (εE max).
The closing timing point EVCl of exhaust valve 5 and the opening timing point IVOl of intake valve 4 are substantially equal to each other, so that the internal EGR quantity is significantly reduced. Then, it outputs shift control signals to phase control hydraulic actuator 2A of intake-side VTC mechanism 1A, and phase control hydraulic actuator 2B of exhaust-side VTC mechanism 1B, and compression ratio control actuator 49 of VCR mechanism 3, and proceeds to the end and waits for a next activation timing.
<Step S32> When the load of the internal combustion engine is determined at Step S30 as being above the low load region after the warm-up, it then executes Step S32. At Step S32, it determines whether or not the current engine operating state is in a high load region. When determining that the current engine operating state is in a region of lower load than the high load region (so-called load map region), it then proceeds to Step S33. When the current engine operating state is in the high load region, the process then proceeds to Step S34.
<Step S33> When determining at Step S32 that the load of the internal combustion engine has not reached the predetermined high-load region after the warm-up, it then executes Step S33. At Step S33, it outputs shift control signals based on the load map to phase control hydraulic actuator 2A of intake-side VTC mechanism 1A, and phase control hydraulic actuator 2B of exhaust-side VTC mechanism 1B. It also outputs a shift control signal to compression ratio control actuator 49 of VCR mechanism 3.
For example, it performs a control by intake-side VTC mechanism 1A to advance the opening timing (IVO) of intake valve 4 from the opening timing point IVOl to the opening timing point IVOh, and the closing timing (IVC) of intake valve 4 from the closing timing point IVCl to the closing timing point IVCh. Under this condition, changes of the opening timing (EVO) and closing timing (EVC) of exhaust valve 5 are suppressed as “EVOl≈EVOh” and “EVCl≈EVCh”, although the opening and closing timings change within a range of EVOl to EVOh and a range of EVCl to EVCh, respectively.
The mechanical expansion ratio (εE) is controlled by compression ratio control actuator 49 of VCR mechanism 3 to decrease from the high mechanical expansion ratio point (εE max) to the low mechanical expansion ratio point (εE min). This sets the mechanical compression ratio to the low mechanical compression ratio point (εC min), and thereby prevents knocking.
Then, it outputs shift control signals to phase control hydraulic actuator 2A of intake-side VTC mechanism 1A, and phase control hydraulic actuator 2B of exhaust-side VTC mechanism 1B, and compression ratio control actuator 49 of VCR mechanism 3, and proceeds to the end and waits for a next activation timing.
<Step S34> When determining at Step S32 that the load of the internal combustion engine has reached the predetermined high load region after the warm-up, it then executes Step S34. At Step S34, it outputs shift control signals for the high load region to phase control hydraulic actuator 2A of intake-side VTC mechanism 1A, and phase control hydraulic actuator 2B of exhaust-side variable valve mechanism 1B. It also outputs a shift control signal to compression ratio control actuator 49 of VCR mechanism 3.
In the high load after warming-up, the opening timing (IVO) of intake valve 4 is set to the opening timing point IVOh, and the closing timing (IVC) of intake valve 4 is set to the closing timing point IVCh, and the opening timing (EVO) of exhaust valve 5 is set to the closing timing point EVOh, and the closing timing (EVC) of exhaust valve 5 is set to the closing timing point EVCh. Furthermore, the mechanical expansion ratio (εE) is set to the low mechanical expansion ratio (εE min).
Then, it outputs shift control signals to phase control hydraulic actuator 2A of intake-side VTC mechanism 1A, and phase control hydraulic actuator 2B of exhaust-side VTC mechanism 1B, and compression ratio control actuator 49 of VCR mechanism 3, and proceeds to the end and waits for a next activation timing.
In the present embodiment, a configuration is proposed which includes: an intake-side VTC mechanism structured to control a phase of opening and closing timings of an intake valve of an internal combustion engine; and an exhaust-side VTC mechanism structured to control a phase of opening and closing timings of an exhaust valve of the internal combustion engine; wherein at a cold start of the internal combustion engine, the exhaust-side VTC mechanism sets the opening timing of the exhaust valve advanced at or close to a midpoint between top dead center and bottom dead center, and sets the closing timing of the exhaust valve advanced at a preset point before top dead center; and the intake-side VTC mechanism sets the opening timing of the intake valve retarded at a preset point after top dead center.
Even when the mechanical expansion ratio is set to the high mechanical expansion ratio point, this configuration serves to enhance the temperature of exhaust gas exhausted from the combustion chamber by sufficiently advancing the opening timing of the exhaust valve at engine start, and thereby early warm up and increase the conversion ratio of the exhaust gas purifying catalyst on the downstream side, as specifically described above.
The following describes a second embodiment of the present invention. In the first embodiment, each of the intake-side VTC mechanism and the exhaust-side VTC mechanism employs a valve operating mechanism where the operating angle (valve opening period) is constant. In contrast, the second embodiment is provided with a variable operating angle mechanism (henceforth referred to as VEL) capable of adjusting the operating angle, in addition to the intake-side VTC mechanism and the exhaust-side VTC mechanism. This serves to produce actions and effects exceeding those of the first embodiment. Specifically, the intake-side variable valve mechanism of the second embodiment includes the intake-side VTC mechanism of the first embodiment and an intake-side VEL, and the exhaust variable valve mechanism of the second embodiment includes the exhaust-side VTC mechanism of the first embodiment and an exhaust-side VEL. The intake-side and exhaust-side VELs are as described in JP 2016-003649 A. Therefore, description of the principle of variation of the operating angle is omitted. This system is also applicable to variable operating angle mechanisms other than VEL.
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As can be understood from the above description, the intake-side VTC mechanism and exhaust-side VTC mechanism of the present invention may be a hydraulic variable phase type or an electric variable phase type, or may be provided with a mechanism structured to control the lift. The VCR mechanism is of the type controlling the mechanical compression ratio and the mechanical expansion ratio to a common value, but may be modified as being of a type capable of controlling the mechanical compression ratio and mechanical expansion ratio differently as disclosed in JP 2016-017489 A. As appropriate, the VCR mechanism may be omitted. With the type capable of controlling the mechanical compression ratio and mechanical expansion ratio differently, in the high load after the warm-up corresponding to
As described above, the present invention is characterized by including: an intake-side variable valve mechanism structured to control a phase of opening and closing timings of an intake valve of an internal combustion engine; and an exhaust-side variable valve mechanism structured to control a phase of opening and closing timings of an exhaust valve of the internal combustion engine; wherein at a cold start of the internal combustion engine, the exhaust-side variable valve mechanism sets the opening timing of the exhaust valve advanced at or close to a midpoint between top dead center and bottom dead center, and sets the closing timing of the exhaust valve advanced at a preset point before top dead center; and the intake-side variable valve mechanism sets the opening timing of the intake valve retarded at a preset point after top dead center.
Even when the mechanical expansion ratio is set to the high mechanical expansion ratio point, this configuration serves to enhance the temperature of exhaust gas exhausted from the combustion chamber by sufficiently advancing the opening timing of the exhaust valve at engine start, and thereby early warm up and increase the conversion ratio of the exhaust gas purifying catalyst on the downstream side.
The present invention is not limited to the embodiments described above, but contains various modifications. For example, although the embodiments are detailed in order to better describe the invention, the invention is not limited to those having all of the features described above. Furthermore, a part of the features of one of the embodiments may be replaced with features of another one of the embodiments. Moreover, features of one of the embodiments may be added to the features of another one of the embodiments. A part of the features of each embodiment may be modified by addition of other features, or deleted, or replaced with other features.
01 . . . Piston; 02 . . . Crankshaft; 03 . . . Connecting Rod Mechanism; 04 . . . Combustion Chamber; 05 . . . Ignition Plug; 1A . . . Intake-Side Variable Valve Mechanism; 1B . . . Exhaust-Side Variable Valve Mechanism; 2A, 2B . . . Phase Control Hydraulic Actuator; 3 . . . Variable Compression Ratio Mechanism; 4 . . . Intake Valve; 5 . . . Exhaust Valve; 2 . . . Controller; 49 . . . Compression Ratio Control Actuator; 72 . . . Throttle Valve.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-156335 | Aug 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/027210 | 7/20/2018 | WO | 00 |
