Compression ignition engine
In a compression ignition engine employing a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of an intake valve lift and an intake valve closure timing, a control system operates to temporarily lower an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation. At a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise, the effective compression ratio is risen by controlling the intake valve characteristic. After combustion of the engine has been stabilized, the intake valve characteristic is brought closer to a desired value determined based on engine operating conditions by way of closed-loop control.
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The present invention relates to a compression ignition engine employing a variable valve operating system for at least one of intake and exhaust valves, and specifically to the improvement of a compression ignition engine control technology suited to compression ignition engines such as a four-stroke-cycle Diesel engine, a two-stroke-cycle Diesel engine, a premix compression ignition engine, and the like.
BACKGROUND ARTIn recent years, there have been proposed and developed various engine control technologies for compression ignition engines with variable valve operating systems. Generally, a variable valve operating system, capable of variably adjusting a valve lift and valve timing of at least one of intake and exhaust valves of a reciprocating internal combustion engine depending on engine operating conditions, is widely utilized for controlling a charging efficiency, an effective compression ratio, and an amount of residual gas of the engine, thereby enhancing the engine power performance and exhaust emission control performance. In Diesel engines or premix compression ignition engines, air alone is compressed during the compression stroke, and then fuel, which is sprayed or injected into the cylinder, is self-ignited due to a temperature rise of the compressed air (heat produced by compressing the incoming air). That is, such self-ignition of the sprayed fuel can be performed under a high-temperature high-pressure condition where the pressure and temperature of the compressed air are high enough to ignite spontaneously the sprayed fuel. The spontaneous ignition temperature and spontaneous ignition pressure needed for self-ignition both change depending on sorts of fuel that is sprayed into the compressed air. Generally, unless the temperature of the compressed air is more than 1000 degrees K (Kelvin temperature) and the pressure of the compressed air is more than 1 MPa (mega Pascal), it does not result in spontaneous ignition of the sprayed fuel.
For the reasons discussed above, the compression ratio of the engine has to be set to a high ratio of 15:1 or more, so that the in-cylinder pressure and in-cylinder temperature become high enough to spontaneously ignite the sprayed fuel and to achieve the combustion of the sprayed fuel, for instance, even when the engine cylinder wall temperature is still low during cold starting and thus heat of the compressed air is taken by the cylinder wall. However, such a high compression ratio causes excessively high pressures acting on the piston after the engine warm-up has been completed, thus resulting in the increased mechanical friction loss and reduced engine power performance. To avoid this (for avoidance of undesirable mechanical friction loss), it is effective to reduce the compression ratio to 15:1 or less after completion of the engine warm-up, in other words, after the engine starting operation has been completed, thereby enhancing the engine performance. After completion of the starting operation, the cylinder wall temperature becomes high, and thus the heat produced by compressing the air is hard to be taken by the cylinder wall even at a comparatively low compression ratio. As a result, the temperature and pressure of the compressed air easily become high during the compression stroke, thus ensuring self-ignition of the sprayed fuel. As is generally known, the variable compression ratio adjustment can be achieved by mechanically varying the clearance volume, that is, the air volume with the piston at top dead center (TDC). Alternatively, the variable compression ratio adjustment can be achieved by mechanically varying the piston stroke characteristic. However, such variable compression ratio devices, for example, a multi-link variable compression ratio device and the like, capable of mechanically varying the clearance volume or mechanically varying the piston stroke characteristic, have complicated mechanical configuration and structure. In lieu thereof, it is possible to variably adjust the mass of air entering the engine cylinder at the beginning of the compression stroke by retarding or advancing the intake-valve closure timing, denoted by “IVC” and expressed in terms of crank angle. In such a case, it is possible to retard a rise in in-cylinder pressure and a rise in in-cylinder temperature with respect to a predetermined crank angle. In other words, it is possible to lower the effective compression ratio by retarding an in-cylinder pressure rise and/or an in-cylinder temperature rise by way of variable adjustment of intake valve closure timing IVC. One such IVC adjustment type variable compression ratio device for a compression ignition engine has been disclosed in Japanese Patent Provisional Publication No. 1-315631 (hereinafter is referred to as “JP1-315631”). In the case of JP1-315631, the IVC adjustment type variable compression ratio device is exemplified in a two-stroke-cycle Diesel engine. Concretely, when it is determined that the current operating condition of the two-stroke-cycle Diesel engine corresponds to an engine starting period, intake valve closure timing IVC is phase-advanced towards a timing value near bottom dead center (BDC) by means of an electric-motor driven variable valve operating device (or a motor-driven variable valve timing control (VTC) system), thereby increasing an effective compression ratio and consequently enhancing the self-ignitability during the starting period. In contrast, during engine normal operation, intake valve closure timing IVC is phase-retarded to decrease the effective compression ratio and consequently to reduce a fuel consumption rate. The motor-driven VTC system of JP1-315631 uses a rotary-to-linear motion converter, such as a ball-bearing screw mechanism, for changing relative phase of an intake-valve camshaft to an engine crankshaft. The rotary-to-linear motion converter (the ball-bearing screw mechanism) of JP1-315631 is comprised of a warm shaft (i.e., a ball bearing shaft with helical grooves) driven by a step motor, an inner slider (i.e., a recirculating ball nut), recirculating balls provided in the helical grooves, and an outer slider axially movable together with the inner slider and rotatable relative to the inner slider. The other types of variable valve operating devices have been disclosed in (i) Japanese document “JSAE Journal Vol. 59, No. 2, 2005” published by Society of Automotive Engineers of Japan, Inc. and titled “Gasoline Engine: Recent Trends in Variable Valve Actuation Technologies to Reduce the Emission and Improve the Fuel Economy” and written by two authors Yuuzou Akasaka and Hajime Miura, and (ii) Japanese document “Proceedings JSAE 9833467, May, 1998” published by Society of Automotive Engineers of Japan, Inc. and titled “Reduction of the engine starting vibration for the Parallel Hybrid System” and written by four authors Hiroshi Kanai, Katsuhiko Hirose, Tatehito Ueda, and Katsuhiko Yamaguchi. The Japanese document “JSAE Journal Vol. 59, No. 2, 2005” discloses various types of variable valve operating systems, such as a helical gear piston type two-stepped phase control system, a rotary vane type continuously variable valve timing control (VTC) system, a swing-arm type stepped valve lift and working angle variator, a continuously variable valve event and lift (VEL) control system, and the like. The VTC and VEL control systems are operated by means of respective actuators for example electric motors or electromagnets, each of which is directly driven in response to a control signal (a drive signal) from an electronic control unit (ECU). Alternatively, the VTC and VEL control systems are often operated indirectly by means of a hydraulically-operated device, which is controllable electronically or electromagnetically. On the other hand, the Japanese document “Proceedings JSAE 9833467, May, 1998” teaches the use of a variable valve timing control system installed on the intake valve side of an engine of a hybrid vehicle employing a parallel hybrid system, for prevention of rapid engine torque fluctuations, which may occur during engine stop and start operation.
SUMMARY OF THE INVENTIONIn the case of the compression ignition engine with the variable valve operating device, as disclosed in JP1-315631, the effective compression ratio is controlled to a relatively high ratio by means of the variable valve operating device during the engine starting period. After the starting operation has been completed, the effective compression ratio is controlled to a relatively low ratio by means of the variable valve operating device. In such an engine control system, there is an increased tendency for the work of compression to increase during the engine starting period. The increased work of compression leads to a drop in cranking speed, thereby resulting in an increased heat loss of the compressed air (compressed gas). As a result of this, a compression temperature, i.e., a temperature of the compressed gas, tends to drop, thus deteriorating the engine startability. According to the engine control system as disclosed in JP1-315631, the effective compression ratio is lowered and decreasingly compensated for, just after the starting operation has been completed. That is to say, the effective compression ratio is controlled to a relatively low ratio, though there is a possibility that the combustion stability is still insufficient just after completion of the starting operation. This leads to the problem of deteriorated combustion stability. Additionally, in order to increase cranking speed, the compression ignition engine as disclosed in JP1-315631 often uses an engine starter of a high torque capacity (a motor generator of a high torque capacity in case of a hybrid vehicle). This leads to another problem of increased manufacturing costs and increased weight. Instead of using an engine starter of a high torque capacity, a so-called decompression device can be used to increase cranking speed. The decompression device is often used for an engine for a two-wheeled vehicle, so as to constantly open an exhaust valve during cranking, thus reducing the work of compression and consequently increasing the cranking speed. However, the decompression device itself does not have an effective-compression-ratio reducing function that reduces the effective compression ratio after completion of the starting operation. Thus, it is difficult to realize the improved fuel economy (i.e., the reduced fuel consumption rate) during normal engine operation, by the use of the decompression device.
In more detail, in the VTC system disclosed in JP1-315631, when there is no application of electric current to the step motor of the VTC system and thus the step motor is de-energized (OFF), intake valve closure timing IVC is automatically controlled to a timing value near bottom dead center (BDC), for example, 20 degrees of crank angle after BDC, under an unfailed condition of the VTC system. Conversely when the step motor is energized (ON), intake valve closure timing IVC is controlled to a timing value retarded from the piston BDC position, for example, 60 degrees of crank angle after BDC. JP1-315631 teaches the phase-advance of intake valve closure timing IVC to a timing value near BDC during the engine starting period, and also teaches the phase-retard of intake valve closure timing IVC after completion of the starting operation. However, according to the system of JP1-315631, the effective compression ratio remains high during cranking, thus resulting in an undesirable drop in cranking speed.
In the case of the system as disclosed in the Japanese document “JSAE Journal Vol. 59, No. 2, 2005”, intake valve closure timing IVC is not phase-retarded from BDC during cranking and cold starting with a starter energized. The effective compression ratio remains high during the cranking and starting period. This also leads to the problem of reduced cranking speed.
In the case of the system as disclosed in the Japanese document “Proceedings JSAE 9833467, May, 1998”, intake valve closure timing IVC of the starting period is phase-retarded to reduce the quantity of air charged in the engine, thus preventing a rapid rise in torque generated by the engine. However, even after cranking operation, intake valve closure timing IVC remains retarded, thus deteriorating the engine startability or self-ignitability during start operation.
It is, therefore, in view of the previously-described disadvantages of the prior art, an object of the invention to provide a compression ignition engine, capable of avoiding the aforementioned problem that spontaneous ignition of fuel does not take place owing to a drop in cranking speed during a starting period.
In order to accomplish the aforementioned and other objects of the present invention, a compression ignition engine comprises sensors that detect engine operating conditions, a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator, and a control unit configured to be electrically connected to the sensors and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensors, the control unit comprising a processor programmed to perform the following, temporarily lowering an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation, rising the effective compression ratio by controlling the intake valve characteristic at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise, and bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
According to another aspect of the invention, a compression ignition engine comprises sensors that detect engine operating conditions, a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator, a decompression device provided to operate an exhaust valve in a decompression mode corresponding to a constantly-opened valve operating state during a cranking period of cold starting operation, and a control unit configured to be electrically connected to the sensors and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensors, the control unit also configured to be electrically connected to the decompression device for switching the exhaust valve to the decompression mode during the cranking period, and the control unit comprising a processor programmed to perform the following, temporarily lowering an effective compression ratio of the engine by maintaining the exhaust valve in the decompression mode corresponding to the constantly-opened valve operating state during the cranking period, inhibiting the decompression mode and returning the exhaust valve to a normal operating state at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise, rising the effective compression ratio by controlling the intake valve characteristic substantially at the point of time when the predetermined cranking speed threshold value has been reached owing to the cranking speed rise, and bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
According to a further aspect of the invention, a method for controlling a compression ignition engine employing a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve, the method comprises temporarily lowering an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation, rising the effective compression ratio by controlling the intake valve characteristic at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise, and bringing the intake valve characteristic closer to a desired value determined based on engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
According to a still further aspect of the invention, a method for controlling a compression ignition engine employing a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and a decompression device provided to operate an exhaust valve in a decompression mode corresponding to a constantly-opened valve operating state during a cranking period of cold starting operation, the method comprises temporarily lowering an effective compression ratio of the engine by maintaining the exhaust valve in the decompression mode corresponding to the constantly-opened valve operating state during the cranking period, inhibiting the decompression mode and returning the exhaust valve to a normal operating state at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise, rising the effective compression ratio by controlling the intake valve characteristic substantially at the point of time when the predetermined cranking speed threshold value has been reached owing to the cranking speed rise, and bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings, particularly to
In the case of usual diesel combustion, diesel fuel (fuel oil) is sprayed or injected via a fuel injection valve 4 into the cylinder during the compression stroke. Then, the sprayed fuel is self-ignited and combusted due to the high-temperature high-pressure compressed gas (heat produced by compressing the incoming air). On the other hand, in the case of premix compression ignition, fuel is sprayed or injected via fuel injection valve 4 into the cylinder during the intake stroke so that the sprayed fuel is sufficiently premixed with air charged in the cylinder. Residual gas is set to a comparatively large amount for a temperature rise in air-fuel mixture. When piston 3 moves up, a temperature rise and a pressure rise in premixed air-fuel mixture occur, thereby resulting in spontaneous ignition of the air-fuel mixture so that the mixture is combusted. A fuel injection amount and injection timing of fuel injection valve 4 included in the electronic injection control system are both controlled, responsively to a sensor signal from a crank angle sensor 5, by means of an electronic control unit (ECU) 6. The purpose of crank angle sensor 5 is to inform the ECU 6 of engine speed Ne as well as the relative position of crankshaft 2.
During start operation, an engine starter 7 is operated to crank the engine 1 or to turn the crankshaft 2. In the case of a hybrid-vehicle engine, rather than using starter 7, engine 1 is rotated by means of a motor generator. Additionally, during the starting period, an electric current is applied to a glow plug 8 for a temperature rise in glow plug 8 and for promotion of vaporization of fuel, thus supporting or assisting spontaneous ignition. Harmful exhaust emission gases such as carbon monoxide (CO), hydrocarbons (HCs), soot (particulate matter), nitrogen oxides (NOx), and the like, are filtered out and purified by means of a catalytic converter 301.
An intake valve 9 and an exhaust valve 10 are installed in the upper part of engine 1. Intake valve 9 is driven by an intake cam 11, whereas exhaust valve 10 is driven by an exhaust cam 12. Intake cam 11 is mechanically linked via a variable valve actuation mechanism (or a variable valve characteristic adjustment mechanism) 13 to a camshaft timing pulley 14. In the embodiment shown in
A sensor signal from an engine temperature sensor (a water temperature sensor or an engine coolant temperature sensor) 15, which detects engine temperature Te, is input into ECU 6. A sensor signal from a camshaft sensor 16 of the VTC system is also input into ECU 6. Camshaft sensor 16 is located near the intake camshaft associated with intake cam 11. Camshaft timing pulley 14 is driven by the engine crankshaft at ½ the revolution speed of crankshaft 2. In the variable valve operating system of
During rotation of camshaft timing pulley 14, exhaust cam 12 linked to camshaft timing pulley 14 is also driven. The valve-opening action of exhaust valve 12 is performed once for each two revolutions of crankshaft 2, for exhausting burned gas from the engine cylinder. As can be seen from the left-hand side of
Variable valve actuation mechanism 13 (or the hydraulically-operated rotary vane type VTC mechanism in the engine control system of the compression ignition engine of the embodiment shown in
As shown in
Referring now to
In the engine control system of the compression ignition engine of the embodiment, it is necessary to control relative phase of camshaft 310 to camshaft timing pulley 14 by means of the VTC mechanism during the cranking period. Therefore, even at very low engine speeds, substantially corresponding to zero, the engine control system uses information concerning the actual relative phase of the VTC mechanism. For the reasons discussed above, the engine control system of the compression ignition engine of the embodiment uses the high-precision camshaft sensor 16 having a high detection accuracy at which camshaft sensor 16 is able to detect the angular phase of camshaft 310 (in other words, the operating state of intake valve 9) even at very low engine speeds, substantially corresponding to zero.
Referring to
Referring to
Referring to
In the case that the engine control system of the compression ignition engine of the embodiment uses camshaft sensor 16, which is comprised of the toothed portion 330, the bridge circuit having magnetic resistance elements 331, and magnet 332 and shown in
Referring now to
Referring now to
Referring to
Returning to
Hereupon, it is necessary to care the fact that the quantity of air charged into the cylinder of engine 1 changes depending on intake valve closure timing IVC. When intake valve closure timing IVC is retarded, the quantity of air charged into engine 1 becomes small. Therefore, it is desirable to properly control the fuel-injection amount, fully taking into account the intake valve closure timing IVC. For this reason, the fuel-injection amount is compensated for responsively to at least sensor signals from camshaft sensor 16 and air flow sensor 17 in addition to engine speed Ne and engine load (e.g., the amount APS of depression of the accelerator pedal), thereby preventing or suppressing the generation of soot.
Thereafter, as can be seen from the A characteristic curve (indicated by the solid line in
Referring now to
After an ignition switch (an engine key switch) is turned ON at step 360, a check or a determination for the current VTC phase is made through step 361. Actually, at step 362 just after step 361, the processor of ECU 6 executes a comparative check for the current VTC phase (that is, the current intake valve closure timing IVC) with respect to a first predetermined phase angle. More concretely, when step 362 determines that the current VTC (i.e., the latest up-to-date informational data of intake valve closure timing IVC) is phase-retarded with respect to the first predetermined phase angle, the routine proceeds to step 363. Conversely when step 362 determines that the current intake valve closure timing IVC is not phase-retarded with respect to the first predetermined phase angle, the routine proceeds to step 364.
At step 363, starter 7 becomes energized (ON).
At step 364, starter 7 becomes energized (ON).
Subsequently to step 364, step 365 occurs to initiate VTC phase-retard control for variable valve actuation mechanism 13 (the VTC mechanism). In the control routine of
At step 367, a comparative check similar to step 362 is made again to determine whether the current VTC phase (that is, the current intake valve closure timing IVC) is phase-retarded with respect to the first predetermined phase angle. When the answer to step 367 is affirmative (YES), that is, when the current intake valve closure timing IVC has been phase-retarded with respect to the first predetermined phase angle, the routine proceeds to step 368. Conversely when the answer to step 367 is negative (NO), the routine returns to step 365. The return from step 367 to step 365 is repeatedly executed until the actual intake valve closure timing IVC has been retarded with respect to the first predetermined phase angle. In other words, after a specified time period has expired from the initial execution of step 367, the routine shifts from step 367 to step 368. The current timing value of intake valve closure timing IVC, needed for the comparative check of step 367, is detected or determined based on the sensor signal from camshaft sensor 16.
At step 368, a check is made to determine whether the latest up-to-date informational data of engine speed Ne, determined based on the sensor signal from crank angle sensor 5, is greater than or equal to a first predetermined speed value such as 400 revolutions per minute. When the answer to step 368 is affirmative (YES), that is, when the current engine speed is greater than or equal to the first predetermined speed value (e.g., 400 rpm), the routine proceeds from step 368 to step 369. Conversely when the answer to step 368 is negative (NO), step 368 is repeatedly executed, until the current engine speed exceeds the first predetermined speed value owing to a rise in cranking speed.
At step 369, VTC phase-advance control for variable valve actuation mechanism 13 (the VTC mechanism) is executed. After step 369, step 370 occurs.
At step 370, a comparative check is made to determine whether the current VTC phase (that is, the current intake valve closure timing IVC) is phase-advanced with respect to a second predetermined phase angle. When the answer to step 370 is affirmative (YES), that is, when the current intake valve closure timing IVC has been phase-advanced with respect to the second predetermined phase angle, the routine proceeds to step 371. Conversely when the answer to step 370 is negative (NO), step 370 is repeatedly executed, until the current intake valve closure timing IVC has been phase-advanced with respect to the second predetermined phase angle by way of the VTC phase-advance control.
At step 371, fuel injection starts. At this time, the fuel-injection amount is compensated for responsively to at least the sensor signal from camshaft sensor 16 and the sensor signal (representative of the quantity of air charged into the cylinder) from air flow sensor 17 in addition to engine speed Ne and engine load (e.g., accelerator-pedal depression amount APS). After step 371, step 372 occurs.
At step 372, a check is made to determine whether the latest up-to-date informational data of engine speed Ne (i.e., the current engine speed) is greater than or equal to a second predetermined speed value such as 500 revolutions per minute. When the answer to step 372 is affirmative (YES), that is, when the current engine speed is greater than or equal to the second predetermined speed value (e.g., 500 rpm), the routine proceeds from step 372 to step 373. Conversely when the answer to step 372 is negative (NO), step 372 is repeatedly executed, until the current engine speed exceeds the second predetermined speed value.
At step 373 a check is made to determine whether the latest up-to-date informational data of engine temperature, determined based on the sensor signal from engine temperature sensor 15, is greater than or equal to a predetermined temperature value (a temperature threshold) such as 60° C. When the answer to step 373 is affirmative (YES), that is, when the current engine temperature is greater than or equal to the predetermined temperature value (,e.g., 60° C.), the routine proceeds from step 373 to step 374. Conversely when the answer to step 373 is negative (NO), step 373 is repeatedly executed, until the current engine temperature exceeds the predetermined temperature value owing to an engine temperature rise after the fuel injection operation.
At step 374, VTC phase-retard control for variable valve actuation mechanism 13 (the VTC mechanism) is executed so that the actual VTC phase (that is, the actual intake valve closure timing IVC) is retarded towards a phase suited to the normal engine operation of engine 1. After step 374, step 375 occurs.
At step 375, a check is made to determine whether the current VTC phase (i.e., the actual intake valve closure timing IVC) is brought closer to the desired phase (the desired timing) suited for the normal engine operation and determined based on the up-to-date informational data of engine speed Ne and engine load APS, by way of closed-loop control for the VTC phase. In this manner, through step 375, the intermediate VTC phase control suited for the normal engine operation is executed within an intermediate phase-angle range phase-advanced from the maximum phase-retarded VTC phase and retarded from the maximum phase-advanced VTC phase.
According to the control routine of
In the engine stopped state, as can be supposed, there are two cases, namely one being a case that intake valve closure timing IVC (VTC phase) has already been set to the maximum phase-retard timing under the engine stopped state, and the other being a case that intake valve closure timing IVC (VTC phase) is controlled to the maximum phase-retard timing simultaneously with the turned-ON operation of the ignition switch. Therefore, in the case that intake valve closure timing IVC (VTC phase) has to be controlled to the maximum phase-retard timing simultaneously with the ignition switch turned-ON operation, through steps 365 and 367 the current intake valve closure timing IVC (or the actual IVC) is detected or determined based on the sensor signal from camshaft sensor 16, and then a phase-angle difference (a deviation or an error signal) between the detected actual intake valve closure timing IVC and the desired value (e.g., the maximum phase-retard timing) is determined. In order to adjust the phase-angle difference to zero, VTC phase control (IVC control) is performed. On the contrary, in the case that intake valve closure timing IVC (VTC phase) has already been set to the maximum phase-retard timing under the engine stopped state, the routine of
In the starting-period VTC control system of
In the case that intake valve closure timing IVC is not set to the maximum phase-retard timing in the engine stopped state, through step 365 of the control routine of
Instead of executing (i) a check for the necessity for VTC phase retard and (ii) VTC phase-retard control (see the flow from step 361 via steps 362 and 364 to step 365 in
The combustion stability of engine 1 is affected by various control parameters, namely, engine temperature, fuel property (for example, cetane value), intake air temperature (charge air temperature), residual gas ratio, EGR rate, boost pressure, and the like. In the engine control system of the compression ignition engine of the embodiment, it is preferable that a plurality of control parameters, directly participating in combustion stability, are detected and intake valve closure timing IVC is controlled, fully taking into account the detected control parameters. As the control parameters, directly participating in combustion stability, the following parameters are exemplified.
- (1) In-cylinder pressure;
- (2) Vibrations of cylinder head, caused by gas vibrations of controlled or uncontrolled burning
- (3) Rotational-speed fluctuations in crankshaft
- (4) Ionic current arising from combustion
- (5) Emission intensity of flame
A threshold value for each of the above-mentioned control parameters, suited for engine speed and engine load after engine warm-up, is experimentally measured and determined beforehand. Thus, it is possible to determine, based on the comparison result of the detected value of the control parameter and its threshold value, whether or not a stable combustion state has been reached. Based on such a decision result concerning a stable/unstable combustion state, it is possible to prevent forcible phase-advance of intake valve closure timing IVC during the starting period, thus enabling intake valve closure timing IVC to timely control in the phase-retard direction. At this time, it is necessary to experimentally measure and determine the threshold value of each of the control parameters in the VTC phase-advance state with a target engine, beforehand. The threshold values for these control parameters can be used for fuel-injection amount control and fuel-injection timing control in real time.
Referring now to
As clearly shown in
Phase-advance hydraulic line 32 and phase-retard hydraulic line 33 are formed or defined in intake camshaft 200 shown in
As shown in
As shown in
As shown in
As set forth above, by way of the axial position control for spool 41, in other words, by way of applied current control for solenoid 40, as can be seen from the phase-change characteristic curves of
Additionally, during the cranking period, intake valve closure timing IVC is considerably phase-retarded from BDC, and as a result the work of compression is effectively reduced and a cranking speed increase occurs, thus ensuring enhanced startability. After completion of engine warm-up, the effective compression ratio is lowered by slightly retarding intake valve closure timing IVC from BDC, thus effectively reducing a fuel consumption rate after engine starting. Additionally, owing to the lowered effective compression ratio, an excessive rise in combustion temperature will be effectively suppressed, thus reducing NOx (nitrogen oxides) emissions.
Returning to
As best seen from
As shown in
In
Referring to
On the contrary, when hydraulic pressure in phase-retard hydraulic chamber 31 is higher than that in phase-advance hydraulic chamber 30, phase-retard hydraulic chamber 31 is filled with working fluid. Under these conditions, vane body 22 is conditioned in its maximum phase-retard state (the maximum phase-retard angular position) shown in
As set forth above, by means of springs 25 disposed in respective phase-advance chambers 30, it is possible to automatically set intake valve closure timing IVC to the maximum phase-advance timing (i.e., IVC≈BDC) shown in
In the case of the motor-driven spiral disk type VTC mechanism shown in
According to the VTC phase control shown in
As another method of reducing the work of compression during cranking, a starting-period decompression device may be combined with phase change means or phase control means, such as the VTC mechanism, the VVL mechanism, the VEL mechanism or the like. The decompression device is provided to constantly open exhaust valve 10 during a cranking period, thereby permitting a reduction in the work of compression even when intake valve closure timing IVC of intake valve 9 has been phase-advanced to a timing value substantially corresponding to a phase-advance state. For instance, by pushing exhaust valve 10 downwards by means of an electromagnet, it is possible to slightly open exhaust valve 10, thus realizing a decompressing function.
Returning to
On automotive vehicles, owing to a rapid engine torque rise, the vehicle body tends to vibrate undesirably. To avoid this, as can be seen from the phase-control characteristic of
On hybrid vehicles employing an automatic engine stop-restart system capable of temporarily automatically stopping an internal combustion engine under a specified condition where a selector lever of an automatic transmission is kept in its neutral position, the vehicle speed is zero, the engine speed is an idle speed, and the brake pedal is depressed, and automatically restarting the engine from the vehicle standstill state, the engine stop and restart operation is frequently executed even after completion of engine warm-up. In the case of engine restart operation, engine 1 has already been warmed up and thus engine 1 is in the stable combustion state without executing phase-advance control for the IVC phase. Therefore, it is possible to omit the phase-advancing process of the VTC phase to a phase corresponding to a phase-advance state (=BDC) from the time tb in
The effective compression ratio can be controlled by means of either one of the VTC mechanism, the VVL mechanism, and the VEL mechanism.
On compression ignition engines, glow plug (a small electric heater) 8 shown in
Returning to
By way of execution of the glow-plug/electric-heater control routine shown in
As will be appreciated from the above, according to the compression ignition engine of the embodiment, employing a variable valve operating system being responsive to a control signal from an electronic control unit for variably adjusting or bringing an intake valve characteristic including at least one of an intake valve lift and an intake valve closure timing IVC closer to a desired value (a desired valve characteristic value determined based on engine operating conditions) via an actuator (electrically-controlled actuator means), during a cranking period of cold starting operation with a starter energized (ON), an effective compression ratio of an engine is temporarily decreased or lowered by controlling the intake valve characteristic. At a point of time when a predetermined cranking speed threshold value (e.g., 400 revolutions per minute) has been reached owing to a cranking speed rise, the effective compression ratio is increased or risen by controlling the intake valve characteristic. After combustion of the engine has been stabilized, the intake valve characteristic is brought closer to the desired value (the desired valve characteristic value) determined based on the engine operating conditions by way of closed-loop control. Thus, it is possible to reconcile the enhanced engine startability during cranking and cold starting operation and improved fuel economy during normal engine operation (after engine warm-up). Suppose that the compression ignition engine of the embodiment, capable of properly controlling the effective compression ratio by varying the intake valve characteristic depending on engine operating conditions, such as during a cranking period of cold starting operation, during an engine warm-up period, and after engine warm-up, is combined with an engine starter of a low torque capacity (or a motor generator of a low torque capacity) and a fixed compression-ratio compression-ignition internal combustion engine of a low geometrical compression ratio. This contributes to the reduced engine gross weight. Thus, the compression ignition engine of the embodiment is suitable for the engine for hybrid vehicles.
Furthermore, according to the compression ignition engine of the embodiment, the variable valve operating system is comprised of a variable valve actuation mechanism capable of varying the intake valve characteristic including at least one of the intake valve lift and intake valve closure timing IVC, before the start of cranking operation or simultaneously with cranking operation, and an engine sensor (concretely, a camshaft sensor) that is able to detect information regarding an intake valve operating state (i.e., the actual intake valve lift and the actual intake valve closure timing) from a substantially zero engine speed value. Thus, even when a temporary drop in battery voltage is occurring during operation of the engine starter, it is possible to satisfactorily adjust (phase-advance or phase-retard) or bring the actual intake valve characteristic, in particular, intake valve closure timing IVC, closer to the desired value, according to various situations, that is, during cranking and starting operation and after warm-up (in a stable combusting state).
Additionally, according to the compression ignition engine of the embodiment, by means of the electronic control unit, at least one of a fuel injection amount and a fuel injection timing, both determined based on engine speed and engine load (e.g., an accelerator-pedal depression amount), can be compensated for based on at least one of information regarding a quantity of air charged into an engine cylinder and information regarding an intake valve operating state (i.e., the actual intake valve lift and the actual intake valve closure timing). Thus, it is possible to compensate for at least one of the fuel injection amount and fuel injection timing in real time responsively to a change in the intake valve operating state, and whereby the generation of soot and unstable combustion can be prevented beforehand.
Additionally, according to the compression ignition engine of the embodiment, when restarting the engine by either one of a starter and a motor generator, an intake valve operating state including at least an actual intake valve closure timing, is gradually shifted or controlled from a phase-retard state to a normal intake valve operating state with the lapse of time. This results in a compression pressure fall of the engine during cranking. Thus, it is possible to reduce the electric power consumption during the cranking period of engine restarting operation, and also to avoid a rapid engine torque rise and uncomfortable noise and vibrations of the vehicle during the restarting operation.
Preferably, during an engine stopping period, the electronic control unit generates a control command signal to the electrically-controlled actuator means for controlling at least the intake valve closure timing IVC to a desired standby timing spaced apart from BDC, and thereafter generates an engine stop signal. During the next starting operation, (i) a check for a current phase of the variable valve actuation mechanism and (ii) phase-retard control of the variable valve actuation mechanism can be eliminated, thereby shortening the engine starting time.
More preferably, during the cranking period of cold starting operation, the electronic control unit operates to temporarily shut off (disable) or reduce electric power supply to either one of glow plug 8 and an electric heater. The temporary shut-off/reduction operation of electric power supply to glow plug 8 or the electric heater, contributes to the increased certainty in sufficient electric power supply to the starter, thereby ensuring the enhanced engine startability.
Moreover, in the case of a starting-period decompression device is combined with the variable valve actuation mechanism, during a cranking period of cold starting operation an exhaust valve is maintained in a constantly-opened valve operating state (i.e., in a decompression mode) to decrease an effective compression ratio by way of decompression for in-cylinder pressure during the cranking period for a smooth cranking speed rise. At a point of time when a predetermined cranking speed threshold value (e.g., 400 revolutions per minute) has been reached owing to the smooth cranking speed rise, the decompression mode is inhibited and the exhaust valve is returned to a normal valve operating state. Additionally, substantially at the point of time when the predetermined cranking speed threshold value (400 rpm) has been reached owing to the smooth cranking speed rise, the effective compression ratio is increased or risen by controlling an intake valve characteristic including at least one of an intake valve lift and intake valve closure timing IVC, for enhancing the self-ignitability of fuel, which is injected after the predetermined cranking speed threshold value (e.g., 400 rpm) has been reached. After combustion of the engine has been stabilized, the intake valve characteristic is brought closer to a desired value (a desired valve characteristic value) determined based on engine operating conditions by way of closed-loop control. By such a combination of the decompression device and the variable valve actuation mechanism, the control system for the variable valve actuation mechanism employed in the variable valve operating system can be simplified, thus ensuring the reduced control system cost. Additionally, by way of an adequate decompressing function of the decompression device, the work of compression can be remarkably reduced, thus enabling a smooth cranking speed rise, that is, a shortened engine starting time.
The entire contents of Japanese Patent Application No. 2005-166538 (filed Jun. 7, 2005) are incorporated herein by reference.
While the foregoing is a description of the preferred embodiments carried out the invention, it will be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the scope or spirit of this invention as defined by the following claims.
Claims
1. A compression ignition-engine comprising:
- sensors that detect engine operating conditions;
- a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator; and
- a control unit configured to be electrically connected to the sensors and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensors; said control unit comprising a processor programmed to perform the following, (a) temporarily lowering an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation; (b) rising the effective compression ratio by controlling the intake valve characteristic at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise; and (c) bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
2. The compression ignition engine as claimed in claim 1, wherein:
- the variable valve actuation mechanism of the variable valve operating system is able to vary the intake valve characteristic, before cranking operation of the engine is started or simultaneously with the engine cranking operation; and
- the variable valve operating system further comprises a sensor that is able to detect information regarding an operating state of the intake valve from a substantially zero engine speed value.
3. The compression ignition engine as claimed in claim 1, further comprising:
- a sensor that is able to detect information regarding an operating state of the intake valve from a substantially zero engine speed value; and
- a sensor that detects information regarding a quantity of air charged into an engine cylinder,
- wherein the processor is further programmed for: (d) compensating for, based on at least one of the information regarding the intake valve operating state and the information regarding the quantity of air charged into the cylinder, at least one of a fuel injection amount and a fuel injection timing, both determined based on the engine operating conditions including engine speed and engine load.
4. The compression ignition engine as claimed in claim 1, further comprising:
- a sensor that is able to detect information regarding an operating state of the intake valve from a substantially zero engine speed value,
- wherein the processor is further programmed for: (e) gradually controlling the intake valve operating state including at least an actual intake valve closure timing, to a normal intake valve operating state, when restarting the engine by either one of a starter and a motor generator.
5. The compression ignition engine as claimed in claim 1, wherein the processor is further programmed for:
- (f) generating a control command signal to the actuator for controlling at least the intake valve closure timing to a desired standby timing spaced apart from a piston bottom dead center position during a stopping period of the engine; and
- (g) generating an engine stop signal after generating the control command signal.
6. The compression ignition engine as claimed in claim 1, wherein the processor is further programmed for:
- (h) temporarily shutting off or reducing electric power supply to either one of a glow plug and an electric heater, during the cranking period of cold starting operation.
7. A compression ignition engine (1) comprising:
- sensors that detect engine operating conditions;
- a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator;
- a decompression device provided to operate an exhaust valve in a decompression mode corresponding to a constantly-opened valve operating state during a cranking period of cold starting operation; and
- a control unit configured to be electrically connected to the sensors and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensors; said control unit also configured to be electrically connected to the decompression device for switching the exhaust valve to the decompression mode during the cranking period; and said control unit comprising a processor programmed to perform the following, (a) temporarily lowering an effective compression ratio of the engine by maintaining the exhaust valve in the decompression mode corresponding to the constantly-opened valve operating state during the cranking period; (b) inhibiting the decompression mode and returning the exhaust valve to a normal operating state at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise; (c) rising the effective compression ratio by controlling the intake valve characteristic substantially at the point of time when the predetermined cranking speed threshold value has been reached owing to the cranking speed rise; and (d) bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
8. A compression ignition engine comprising:
- sensor means for detecting engine operating conditions;
- a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator; and
- a control unit configured to be electrically connected to the sensor means and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensor means; said control unit comprising (a) means for temporarily lowering an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation; (b) means for rising the effective compression ratio by controlling the intake valve characteristic at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise; and (c) means for bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
9. A compression ignition engine comprising:
- sensor means for detecting engine operating conditions;
- a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator;
- a decompression device provided to operate an exhaust valve in a decompression mode corresponding to a constantly-opened valve operating state during a cranking period of cold starting operation; and
- a control unit configured to be electrically connected to the sensor means and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensor means; said control unit also configured to be electrically connected to the decompression device for switching the exhaust valve to the decompression mode during the cranking period; and said control unit comprising (a) means for temporarily lowering an effective compression ratio of the engine by maintaining the exhaust valve in the decompression mode corresponding to the constantly-opened valve operating state during the cranking period; (b) means for inhibiting the decompression mode and returning the exhaust valve to a normal operating state at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise; (c) means for rising the effective compression ratio by controlling the intake valve characteristic substantially at the point of time when the predetermined cranking speed threshold value has been reached owing to the cranking speed rise; and (d) means for bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
10. A method for controlling a compression ignition engine employing a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve, the method comprising:
- (a) temporarily lowering an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation;
- (b) rising the effective compression ratio by controlling the intake valve characteristic at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise; and
- (c) bringing the intake valve characteristic closer to a desired value determined based on engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
11. A method for controlling a compression ignition engine employing a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and a decompression device provided to operate an exhaust valve in a decompression mode corresponding to a constantly-opened valve operating state during a cranking period of cold starting operation, the method comprising:
- (a) temporarily lowering an effective compression ratio of the engine by maintaining the exhaust valve in the decompression mode corresponding to the constantly-opened valve operating state during the cranking period;
- (b) inhibiting the decompression mode and returning the exhaust valve to a normal operating state at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise;
- (c) rising the effective compression ratio by controlling the intake valve characteristic substantially at the point of time when the predetermined cranking speed threshold value has been reached owing to the cranking speed rise; and
- (d) bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.
Type: Application
Filed: Jun 6, 2006
Publication Date: Dec 7, 2006
Applicant:
Inventors: Seinosuke Hara (Kanagawa), Tomio Hokari (Kanagawa), Seiji Suga (Kanagawa), Makoto Nakamura (Kanagawa), Masahiko Watanabe (Yokohama)
Application Number: 11/447,249
International Classification: F01L 13/08 (20060101);