Patent Publication Number: US-2011061628-A1

Title: Internal combustion engine and starting method thereof

Description:
RELATED APPLICATION 
     The disclosures of Japanese Patent Application No. 2004-380654, filed Dec. 28, 2004, including the specification, claims and drawings, are incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Disclosed herein is an internal combustion engine constructed to be operated according to an improved starting method, particularly without cranking; that is, starting without rotating the crankshaft. 
     BACKGROUND 
     A starting method and apparatus for an internal combustion engine are disclosed, for example, in Laid-open Japanese Patent Application No. H2-271073. Using this apparatus, a cylinder is identified in which the corresponding piston stops after reaching top dead center and before the exhaust stroke takes place. By injecting fuel into the cylinder so identified, and igniting the fuel, the direct-injection internal combustion engine starts without using an additional cranking means (simply referred to hereinafter as a “starter”) such as a cell motor or a recoil starter. 
     SUMMARY OF THE INVENTION 
     The present internal combustion engine is intended to prevent failure of ignition so as to achieve reliable starting without the use of a starter (i.e., without cranking). 
     The present internal combustion engine comprises a fuel injector for injecting fuel into a combustion chamber to produce an air-fuel mixture in the combustion chamber, an ignition plug for igniting the air-fuel mixture to effect combustion in the combustion chamber, and a controller for controlling combustion to provide torque for starting the engine after the engine has been stopped, wherein the controller adjusts a time interval between the fuel injection and the ignition based on an amount of air in the combustion chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present engine and method will be apparent from the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic view of the present internal combustion engine according to an embodiment thereof; 
         FIG. 2  is a chart showing an example of an output signal from a piston sensor; 
         FIG. 3  is a diagram illustrating a range of air-fuel ratios (mixture ratios) in a combustion chamber for enabling starting without cranking; 
         FIG. 4  is a flowchart illustrating idle-stop control (shutdown and restarting of the engine) according to a first embodiment; 
         FIG. 5  is a continuation of the flowchart of  FIG. 4 ; 
         FIG. 6  is an example of a chart for establishing basic fuel injection quantity and basic ignition delay time; 
         FIG. 7  is an example of a chart for establishing a first correction coefficient Kf 1  for fuel injection quantity; 
         FIG. 8  is an example of a chart for setting a second correction coefficient Kf 2  for fuel injection quantity; 
         FIG. 9  is an example of a chart for setting a first correction coefficient Kt 1  for ignition delay time; 
         FIG. 10  is an example of a chart for setting a second correction coefficient Kt 2  for ignition delay time; 
         FIG. 11  is a flowchart illustrating idle-stop control (shutdown and restart of the engine) according to a second embodiment; and 
         FIG. 12  is a continuation of the flowchart of  FIG. 11 . 
     
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     As shown in  FIG. 1 , a combustion chamber  2  of an engine  1  is formed by a cylinder head  3 , a cylinder block  4 , and a piston  5  fitted in the cylinder bore of the cylinder block  4 . The cylinder head  3  has an intake passage or inlet port  6  and an exhaust passage or exhaust port  7  formed therein, both opening into the combustion chamber  2 . An inlet valve  8  and an exhaust valve  9 , which open and close ports  6  and  7 , are driven by an inlet valve cam and exhaust valve cam (not shown). Meanwhile, a variable valve mechanism (not shown) having a known structure is disposed close to the inlet valve  8  to control the opening and closing times of the inlet valve  8 . Alternatively, the variable valve mechanism may be disposed close to the exhaust valve  9 . 
     Disposed in the cylinder head  3  are a fuel injection valve  10  for directly injecting fuel into the combustion chamber  2  and an ignition plug  11  for spark-igniting an air-fuel mixture in the combustion chamber  2 , both facing into the combustion chamber  2 . 
     The inlet port  6  is connected with an inlet manifold  12 , the inlet manifold  12  being, in turn, connected with an inlet duct  14  upstream thereof, and an inlet collector  13  being interposed therebetween. The inlet duct  14  is provided with an air cleaner  15  for removing dust and so forth from intake air, an airflow meter  16  for detecting the quantity of intake air, and a throttle valve  17  controlling the quantity of intake air, disposed in that order from upstream of the air inlet. A bypass passage  18  extending from the inlet duct  14  upstream of the throttle valve  17  of the inlet duct  14 , bypasses the throttle valve  17 , and is connected to the inlet collector  13 . An idle control valve  19  is disposed in the bypass passage  18  for controlling the quantity of bypassed air. 
     A first blow-by passage  20  upstream of the throttle valve  17  interconnects the inlet duct  14  and a crankcase in the cylinder block  4  to each other, and a second blow-by passage  21  interconnects a rocker chamber in the head cover of the cylinder head  3  and the inlet collector  13 . By means of these blow-by passages  20  and  21 , blow-by gas generated in the engine  1  is ventilated by intake air introduced by the inlet duct  14  to the inlet collector  13 . Disposed in the second blow-by passage  21  is a pressure control valve (PCV)  22  for controlling the pressure of the blow-by gas and a blow-by control valve  23  controlling the flow rate of the blow-by gas. 
     The engine  1  is provided with a cranking means or support device such as a starter motor  24  arranged at the lower part thereof, for initiating rotation of the crankshaft. 
     Transmitted to a control unit or controller (C/U)  30  are signals from a variety of sensors, such as a throttle-valve opening sensor  31  detecting the throttle valve opening (TVO), a crank angle sensor  32 , a cam angle sensor  33 , a water (coolant) temperature sensor  34 , a vehicle speed sensor  35 , a gear position sensor  36  detecting the gear position of a transmission, and a brake sensor  37  detecting operation (ON/OFF) of a brake. 
     On the basis of the detection signals it receives, the C/U  30  controls the variable valve mechanism, the fuel injection valve  10 , the ignition plug  11 , the throttle valve  17 , the idle control valve  19 , the blow-by control valve  23 , the starter motor  24 , and so forth. 
     The C/U  30  is capable of determining the number Ne of revolutions of the engine on the basis of the detection signal from the crank angle sensor  32  and can also identifying a cylinder on a specified stroke on the basis of the detection signals of the crank angle sensor  32  and the cam angle sensor  33 , in addition to determining a stop position of the piston  5 . In concrete terms, the stop position of the piston is detected as explained below. 
     A crank pulley has protrusions (or depressions) disposed every 30 degrees (not shown) and two piston position sensors  38  are arranged in a phase shift of 15 degrees on the periphery thereof (as shown in the figure, the crank angle sensor  32  may be used as either of the piston sensors). The piston position sensors  38  generate ON or OFF signals when protrusions (or depressions) pass therethrough. Then, by sequentially managing rise and fall of the ON or OFF signals of the two piston position sensors  38 , a counting operation is conducted. When the order of the ON or OFF signals from the two piston position sensors  38  is reversed (see  FIG. 2 ), a counting-down operation is conducted so that the stop position of the piston  5  is detected on the basis of the count value. Since this serves as only one example of such a method, it will be understood that the stop position of the piston  5  may be obtained different methods. 
     When predetermined idle-stop conditions are satisfied (for example, when the gear of the transmission is set in the D-range, the brake is in an activated or ON condition, and vehicle speed is zero), the C/U  30  executes idle-stop for automatically shutting down the engine  1 . When predetermined idle-stop releasing conditions are satisfied during idle-stop (for example, when the brake is in a deactivated or OFF condition after the idle-stop conditions are satisfied and a driving-off operation is performed by the driver), idle-stop control for releasing the idle-stop and automatically restarting the engine  1  is conducted. 
     By injecting fuel into a cylinder on an expansion stroke and igniting it, the engine  1  according to the present embodiment restarts without use of a starter (i.e., without cranking). In order to obtain torque (combustion pressure) sufficient to enable starting as shown in  FIG. 3 , it is necessary to have a mixture ratio (an air-fuel ratio) lying within a predetermined range upon ignition in the combustion chamber  2 . Accordingly, in order to more reliably achieve starting without cranking, the following steps are required: (1) accurately determining the quantity of air in the combustion chamber and injecting an appropriate quantity of fuel, and (2), taking account into a vaporization (atomization) characteristic of the injected fuel, whereby ignition may be performed in the most appropriate condition of air-fuel ratio in the combustion chamber. Hence, in the present embodiment, taking account that combustion-chamber pressure (cylinder pressure) will decline due to leaking during shutdown or stopping of the engine, fuel injection quantity and time of ignition for starting are determined. 
       FIGS. 4 and 5  comprise a flowchart illustrating the idle-stop control (shut-down and restart of the engine) executed every predetermined time by the C/U  30 . 
     At step S 1 , it is determined whether idle-stop conditions are satisfied. If idle-stop conditions are satisfied, the process moves to step S 2 . If the conditions are not satisfied, the process ends. As described above, while the idle-stop conditions in the present embodiment are satisfied (1) when the gear is set in the D-range, (2) when the car speed is zero (or nearly zero), and (3) when the brake is activated (is ON), the conditions not being limited to these. 
     At step S 2 , an instruction to shut down the engine is generated, whereupon the supply of fuel to the respective cylinders is suspended and the engine is shut down. 
     At step S 3 , engine shutdown is confirmed, and the process moves to step S 4 . 
     At step S 4 , a cylinder in an expansion stroke and the stop position of its piston (crank stop angle) are detected. 
     At step S 5 , the counting operation of a stop timer is started. A count value TC 1  of the count timer corresponds to the time elapsed from shutdown of the engine (i.e., from the beginning of the stopping of the engine). 
     At step S 6 , it is determined whether idle-stop releasing conditions (in other words, restart conditions) are satisfied. If idle-stop releasing conditions are satisfied, the process moves to step S 8 , and if not satisfied, the shutdown condition of the engine is maintained without any change. As described above, while the idle-stop releasing conditions are satisfied in the present embodiment, (1) when the brake is OFF, and (2) a driving-off operation (depressing the accelerator for example) is carried out by a driver, the conditions are not limited to these. 
     At step S 7 , it is determined whether the count value TC 1  of the count timer is equal to or smaller than a predetermined value Tst. If TC 1 ≦Tst; that is, if the elapsed time from shutdown of the engine is within a predetermined range, the process moves to step S 8 . If TC 1 &gt;Tst; that is, if the elapsed time from shutdown of the engine exceeds the predetermined range, the process moves to step S 19 , while presuming that the cylinder pressure has fallen below a predetermined value. Meanwhile, the predetermined value Tst may be constant or set so as to vary, in response, for example, to an operating condition of the engine before the idle-stop conditions were satisfied. Thus, at step S 19 , initiation of combustion is effected by rotating (cranking) the crankshaft by driving the starter motor  24  and, at the same time, by injecting a predetermined quantity of fuel and performing ignition. In other words, if the time elapsed from shutdown has exceeded the predetermined value, restarting is carried out in the conventional manner. 
     At step S 8 , on the basis of the stop position of the piston detected at step S 4 , there are established a basic fuel injection quantity f 0  and a basic value (a basic ignition delay time) t 0  of a time period (time interval) from fuel injection to ignition of a cylinder on an expansion stroke, according to curves such as those shown in  FIG. 6 . Combustion chamber volume can be derived from the piston stop position, and, with combustion chamber volume determined, air quantity Q in the combustion chamber can be estimated. Accordingly, by detecting the piston stop position, fuel injection quantity and an ignition-delaying period of time can be set (as reference conditions) for achieving a predetermined target mixture ratio (a target air-fuel ratio upon starting; see  FIG. 3 ). The chart shown in  FIG. 6  has been prepared from such considerations. 
     At step S 9 , on the basis of the count value TC 1  of the count timer (i.e., the elapsed time from shutdown of the engine), a first correction coefficient Kf 1  for correcting the basic fuel injection quantity f 0  is computed as in the chart shown in  FIG. 7 . After shutdown of the engine, gas leakage through a piston ring or the like causes a decline in combustion chamber pressure and also the corresponding air density (i.e., air quantity); hence, it is necessary to reduce the fuel injection quantity. The chart shown in  FIG. 7  has been prepared from such a consideration. More particularly, the first correction coefficient Kf 1  serves for estimating the time-lapse change in cylinder pressure (and the accompanying change in the air quantity) during shutdown of the engine and for correcting the basic fuel injection quantity f 0  on the basis of the estimated values. The longer the elapsed time from shutdown of the engine, the greater will be the time-lapse change in the cylinder pressure, and thus the less the fuel injection quantity need be (reduction correction). A fuel pressure sensor may be provided to take fuel pressure into account when establishing the first correction coefficient Kf 1 . 
     At step S 10 , a water or coolant temperature (corresponding to engine temperature) is detected by the water temperature sensor  34 , and, on the basis of the detected water temperature, a second correction coefficient Kf 2  for correcting the basic fuel injection quantity f 0  is computed, as represented in the chart shown in  FIG. 8 . When the engine temperature is low, there is a risk that injected fuel will not be quickly vaporized and will accrete to the cylinder wall or the like, and the proportion of the vaporized fuel will be low in comparison to that at high temperature. Accordingly, in order to achieve the target air-fuel ratio upon starting, the lower the engine temperature as compared to a predetermined temperature or temperature threshold typically existing at the time of engine shutdown, the greater the fuel injection quantity required. The chart shown in  FIG. 8  represents this condition. With the second correction coefficient Kf 2 , the higher the temperature of the engine as compared to the predetermined threshold, the less the fuel injection quantity is corrected (reduction correction). 
     At step S 11 , fuel injection quantity F is established by multiplying the basic fuel injection quantity f 0  by the first correction coefficient Kf 1  and the second correction coefficient Kf 2 , (F=f 0 ×Kf 1 ×Kf 2 ). 
     At step S 12 , on the basis of the count value TC 1  of the stop timer (the elapsed time from shutdown of the engine) a first correction coefficient Kt 1  for correcting the basic ignition delay time t 0  is computed as represented in the chart shown in  FIG. 9 . As described above, since gas leakage through a piston ring or the like causes a decline in cylinder pressure to reduce after shutdown of the engine, the difference in cylinder pressure causes the vaporization (atomization) characteristic of the injected fuel to vary, resulting in changes in vaporization-stabilizing time and the like (in general, the higher the cylinder pressure as compared to a predetermined pressure or pressure threshold typically existing at the time of engine shutdown, the longer the vaporization-stabilizing time). Accordingly, in order to perform ignition at the most appropriate time, it is necessary to establish an ignition delay time while taking account into the vaporization characteristic (the vaporization-stabilizing time). The chart shown in  FIG. 9  has been prepared accordingly. In other words, the first correction coefficient Kt 1  serves for estimating a time-lapse change in the cylinder pressure during shutdown of the engine on the basis of the elapsed time from shutdown and for correcting the basic ignition delay time t 0  on the basis of the change. For longer elapsed time from shutdown of the engine (i.e., for lower cylinder pressure as compared to the predetermined threshold), the ignition delay time is corrected for further delay (delay correction). Meanwhile, the above-mentioned fuel pressure sensor may be provided to take account fuel pressure when establishing the first correction coefficient Kt 1 . 
     At step S 13 , on the basis of the water temperature (i.e., the engine temperature), a second correction coefficient Kt 2  for correcting the basic ignition delay time t 0  is computed as represented in the chart shown in  FIG. 10 . Since the vaporization characteristic of the injected fuel varies with variations in the combustion chamber temperature, this correction is intended to provide ignition at the most appropriate time while taking account this temperature variation. The chart of  FIG. 10  shows that in accordance with this second correction coefficient Kt 2 , that when the temperature of the engine is relatively high, the ignition delay time is corrected for further delay (delay correction). 
     At step S 14 , an ignition delay time Twait is established by multiplying the basic ignition delay time t 0  by the first correction coefficient Kt 1  and the second correction coefficient Kt 2 , (Twait=t 0 ×Kt 1 ×Kt 2 ). In the normal temperature condition under the combustion chamber volume at an ideal piston stop position, 150 msec can be adopted as the ignition delay time Twait when the elapsed time corresponds to the condition in which the cylinder pressure is 200 Kpa. In the same condition, 100 msec can be adopted as the ignition delay time Twait when the elapsed time corresponds to the condition in which the cylinder pressure is 100 Kpa. The tardiness until start of the engine can be made a minimum by making the delay time a minimum requirement. 
     At step S 15 , a fuel injection command to inject the established fuel injection quantity F is issued to the fuel injection valve  10  of a cylinder on an expansion stroke. Also, an injection timer begins counting. A count value TC 2  of the injection timer corresponds to the time elapsed from (completion of) fuel injection. 
     At step S 16 , it is determined whether the elapsed time from fuel injection has reached the ignition delay time Twait (that is, TC 2 ≧Twait is satisfied). If TC 2 ≧Twait is satisfied, the process moves to step S 17 , and an ignition command is issued to the ignition plug  11  of the cylinder on the expansion stroke to effect ignition. 
     At step S 18 , the count values of the stop timer and the injection timer are cleared. 
     According to the first embodiment, at the time of restart after idle-stop, a time-lapse change in the cylinder pressure during shutdown of the engine is estimated on the basis of elapsed time after shutdown, and control parameters; i.e., fuel injection quantity and ignition delay time are corrected on the basis of the estimated time-lapse change in the cylinder pressure, thereby achieving the most appropriate condition of combustion-chamber air-fuel mixture ratio at the time of ignition for restarting. The control unit  30  adjusts a time interval between the fuel injection and the ignition based on an amount of air in the combustion chamber. Accordingly, reliable ignition can be achieved and starting without cranking can be improved. 
     Also, when it is determined that the elapsed time from shutdown of the engine has exceeded the predetermined time and the cylinder pressure falls below the predetermined value, starting is performed by an assisting means such as a starter motor (combustion starting is assisted, see explanation of step S 19  above), whereby reliable starting can be achieved even when the torque necessary for starting can no longer be obtained from combustion-starting alone, due to reduction in the cylinder pressure below a predetermined value. 
     The second embodiment differs from the first embodiment in that a cylinder pressure sensor (not shown) is provided, and fuel injection quantity and ignition delay time are corrected on the basis of the cylinder pressure so detected and the stop position of the piston  5  is corrected to a position appropriate for combustion starting. 
       FIGS. 11 and 12  show a flowchart illustrating idle-stop control (shutdown and restart of the engine) according to the second embodiment, executed each predetermined time. 
     Steps S 21  through S 24  are the same as steps S 1  through S 4  shown in  FIG. 4 . At step S 25 , in the same fashion as in step S 6  shown in  FIG. 4 , it is determined whether idle-stop releasing conditions (in other words, restart conditions) are satisfied. If the idle-stop releasing conditions are satisfied, the process moves to step S 26 . If not, the shutdown condition of the engine is maintained without any change. 
     At step S 26 , cylinder pressure (combustion chamber pressure) Pc is detected by a cylinder pressure sensor. 
     At step S 27 , it is determined whether the detected cylinder pressure Pc is equal to or higher than a predetermined value Ps (Pc≧Ps). If Pc≧Ps, the process moves to step S 28 . On the other hand, if Pc&lt;Ps, the process moves to step S 28  via steps S 39  and S 40 . 
     At step S 39 , it is determined whether the piston stop position detected in step S 24  coincides with a predetermined position (within a predetermined range). Meanwhile, the predetermined position (range) is established to obtain torque sufficient for starting by fuel injection and ignition and is presumed as, for example, about ATDC 60 degrees with respect to a six-cylinder engine (about ATDC 90 degrees with respect to a four-cylinder engine). If the piston stop position coincides with the predetermined position, the process moves to step S 41 , and if not, the process moves to step S 40 . 
     At step S 40 , the piston stop position is corrected to the predetermined position. While this correction can be performed with, for example, the starter motor  24 , the correction is not limited to this and may be performed in any suitable manner. The process moves to step S 28  after correcting the piston stop position. 
     Steps S 28  through S 38  are the same as steps S 8  through S 18  shown in  FIGS. 4 and 5 . 
     In the same fashion as in the first embodiment, at the time of restart after idle-stop, a time-lapse change in the cylinder pressure during shutdown of the engine is estimated on the basis of an elapsed time after shutdown, and control parameters; i.e., fuel injection quantity and ignition time (ignition delay time), are corrected on the basis of the estimated time-lapse change in the cylinder pressure, thereby achieving the most appropriate condition of combustion-chamber mixture ratio at the time of ignition for restart. With this, reliable ignition can be achieved and starting without cranking can be improved. 
     In particular, when the cylinder pressure falls below the predetermined value, the piston stop position (i.e., the combustion chamber volume) is corrected to an appropriate position, and, at the same time, the control parameters; i.e., the fuel injection quantity and the ignition time (the ignition delay time) for combustion starting are corrected on the basis of the detected cylinder pressure, thereby providing the torque necessary for starting and reliably effecting starting without cranking. 
     While, in the first and second embodiments, both the fuel ignition quantity and the ignition-delay time are corrected with respect to a direct-injection internal combustion engine, the present engine is not so limited. For example, a typical internal combustion engine may be so operated that fuel will remain in a cylinder or that only either one of the fuel ignition quantity and the ignition-delay time need be corrected. 
     Also, while the basic fuel injection quantity f 0  is established and corrected, it may be arranged to correct the air quantity Q in the combustion chamber and to establish the fuel injection quantity required for achieving a target air-fuel ratio based on the corrected air quantity. 
     Also, while the first and second embodiments are intended for restart in the idle-stop control, they can be applied to starting in general at any time by modifying the foregoing flowcharts as follows. Briefly, in step S 1  (or step S 21 ), it is first determined whether an ignition switch is turned off, and if turned off, the process moves to step S 2  (or step S 22 ). Then, in step S 6  (or step S 25 ), it is determined whether the ignition switch is turned on, and if so, the process moves to step S 7  (or step S 26 ). With this modification, starting without cranking is reliably achieved at any time. 
     In addition, control in the first and second embodiments can be partially exchanged between embodiments. For example, steps S 5  and S 7  (determination based on the elapsed time from shutdown of the engine) in the first embodiment may be replaced with step S 26  (determination based on the detected cylinder pressure) in the second embodiment, or steps S 39  and S 40  (correction of the piston stop position) in the second embodiment may be added before step S 19  (crank starting) in the first embodiment. Thus, even when cylinder pressure is relatively low, quick and reliable starting can be achieved. 
     While the present engine and method have been described in connection with certain specific embodiments thereof, this is by way of illustration and not of limitation, and the appended claims should be construed as broadly as the prior art will permit.