Patent Publication Number: US-11378054-B2

Title: Driving source control apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2020-189068 filed on Nov. 13, 2020, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a driving source control apparatus and, more specifically, to a driving source control apparatus that controls a driving source. 
     2. Description of Related Art 
     A driving source control apparatus is proposed as one of driving source control apparatuses of this type (see, for example, Japanese Unexamined Patent Application Publication No. 2014-080919 (JP 2014-080919 A)). The driving source control apparatus is used for a driving apparatus (vehicle) including a driving source (engine) connected to a drive-train and controls the driving source such that the driving source is driven at a target torque. The apparatus calculates a rate of change in difference between the rotation speed of the engine and an average rotation speed that is an average of the rotation speed of the engine by using the rotation speed (actual rotation speed) of the engine, and corrects the target torque based on the rate of change in difference such that longitudinal vibrations in the driving apparatus due to torsional fluctuations (torsional resonance) of the drive-train are reduced. With this configuration, the vibrations of the driving apparatus can be reduced. 
     SUMMARY 
     However, the driving source control apparatus may not be able to properly reduce vibrations. The rotation speed of the engine also fluctuates due to vibrations input from a road surface via the drive-train in addition to torsional vibrations. The driving source control apparatus corrects a target torque based on a rate of change in difference between the rotation speed of the engine and an average rotation speed regardless of whether fluctuations in the rotation speed of the engine are due to torsional fluctuations, so the driving source control apparatus may not be able to properly reduce the vibrations of the driving apparatus. 
     The present disclosure provides a driving source control apparatus that further properly reduces the vibrations of a driving apparatus. 
     Some aspects of the driving source control apparatus of the present disclosure are configured as follows. 
     An aspect of the present disclosure relates to a driving source control apparatus. The driving source control apparatus is used for a driving apparatus including a driving source. The driving source is connected to a drive-train including a drive shaft. The driving source control apparatus is configured to control the driving source such that the driving source is driven at a torque based on a target torque. The driving source control apparatus includes an electronic control unit. The electronic control unit is configured to repeatedly compute a period and amplitude of torsional fluctuations of the drive-train to be obtained by applying a phase-lead process, which is a process of advancing a phase by a predetermined amount, to a difference between a rotation speed of the driving source and a rotation speed of the driving source, computed from a rotation speed of the drive shaft, and, when the computed amplitude of the torsional fluctuations in a predetermined period becomes greater than or equal to a predetermined amplitude at least two times consecutively, execute predetermined control in which the driving source is controlled so as to be driven at a torque obtained by adding a correction torque opposite in phase to the torsional fluctuations to the target torque. 
     In the driving source control apparatus according to the aspect of the present disclosure, a period and amplitude of torsional fluctuations of the drive-train to be obtained by applying a phase-lead process, which is a process of advancing a phase by a predetermined amount, to a difference between a rotation speed of the driving source and a rotation speed of the driving source, computed from a rotation speed of the drive shaft, are repeatedly computed. When the computed amplitude of the torsional fluctuations in a predetermined period becomes greater than or equal to a predetermined amplitude at least two times consecutively, execute predetermined control in which the driving source is controlled so as to be driven at a torque obtained by adding a correction torque opposite in phase to the torsional fluctuations to the target torque. When the computed amplitude of the torsional fluctuations in the predetermined period becomes greater than or equal to the predetermined amplitude at least two times, it is estimated that torsional resonance of the drive-train is occurring. Therefore, when the computed amplitude of the torsional fluctuations in the predetermined period becomes greater than or equal to the predetermined amplitude at least two times, the vibrations of the driving apparatus are properly reduced by executing the predetermined control. Here, the predetermined amount may be, for example, a value determined by experiment, analysis, or the like in advance as a lag amount of the computed torsional fluctuations of the drive-train from actual torsional fluctuations of the drive-train. The predetermined period may be, for example, a half period or one period. The predetermined amplitude may be, for example, a threshold for determining whether a user feels deterioration of drivability. 
     In the driving source control apparatus according to the above aspect, the electronic control unit may be configured to, when the computed amplitude of the torsional fluctuations in the predetermined period becomes greater than or equal to the predetermined amplitude a first number of times that is at least two times consecutively, execute the predetermined control, and the electronic control unit may be configured to, during execution of the predetermined control, when the computed amplitude of the torsional fluctuations in the predetermined period becomes greater than or equal to the predetermined amplitude a second number of times greater than the first number of times, stop execution of the predetermined control and control the driving source such that the driving source is driven at the target torque. When the computed amplitude of the torsional fluctuations in the predetermined period becomes greater than or equal to the predetermined amplitude the second number of times, it is estimated that vibrations are amplified by execution of the predetermined control because of an abnormality in the driving apparatus. Therefore, an increase in vibrations is suppressed by stopping execution of the predetermined control and controlling the driving source such that the driving source is driven at the target torque. 
     In the driving source control apparatus according to the above aspect, the driving source may be an internal combustion engine, in the predetermined control, target ignition timing may be computed such that the torque obtained by adding the correction torque to the target torque is output, a control signal is output to the internal combustion engine such that ignition takes place at the target ignition timing, and the internal combustion engine is controlled by using the control signal, and the predetermined amount may be the sum of a first lag amount corresponding to a time required to compute the target ignition timing, a second lag amount corresponding to a time from when the control signal is output to when ignition takes place in the internal combustion engine, and a third lag amount corresponding to a time from when ignition takes place in the internal combustion engine to when the torque is output from the internal combustion engine. With this configuration, when the driving source is an internal combustion engine, a lag of computed torsional fluctuations of the drive-train from actual torsional fluctuations of the drive-train is properly compensated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG. 1  is a configuration diagram schematically showing the configuration of a vehicle on which a driving source control apparatus that is one embodiment of the present disclosure is mounted; 
         FIG. 2  is a configuration diagram schematically showing the configuration of an engine; 
         FIG. 3  is a flowchart showing an example of an engine ignition control routine to be executed by an ECU; 
         FIG. 4  is a graph illustrating an example of the relationship between the frequency of vibrations of a drive-train excited by torsion, and transmission sensitivity; 
         FIG. 5  is a graph illustrating an example of a time change in processed rotation speed difference and a time change in torsional fluctuation component; 
         FIG. 6  is a graph illustrating an example of a time change in torsional fluctuation component when an amplitude becomes greater than or equal to a threshold consecutively because of an abnormality; 
         FIG. 7  is a timing chart illustrating an example of a time change in torsional fluctuation component, a time change in the number of times of consecutive determination, and a time change in control execution flag; and 
         FIG. 8  is a graph illustrating an example of a time change in torsional fluctuation component when large torsional fluctuations that do not occur during normal times are occurring. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present disclosure will be described. 
       FIG. 1  is a configuration diagram schematically showing the configuration of a vehicle  20  on which a driving source control apparatus that is one embodiment of the present disclosure is mounted. As shown in the drawing, the vehicle  20  of the embodiment includes an engine  22 , a torque converter  28 , an automatic transmission  30 , and an electronic control unit (hereinafter, referred to as ECU)  50 . 
     The engine  22  is an internal combustion engine that outputs power by using gasoline, light oil, or the like as fuel.  FIG. 2  is a configuration diagram schematically showing the configuration of the engine  22 . As shown in the drawing, the engine  22  takes air, cleaned by an air cleaner  122 , into an intake pipe  123  and passes the air through a throttle valve  124 , mixes air and fuel by injecting fuel from a fuel injection valve  126 , and takes the air-fuel mixture into a combustion chamber  129  via an intake valve  128 . The engine  22  burns the intake air-fuel mixture with electric spark by using an ignition plug  130  and converts the reciprocating motion of a piston  132  pushed downward by the energy to the rotating motion of a crankshaft  26 . Exhaust gas discharged from the combustion chamber  129  to an exhaust pipe  133  via an exhaust valve  131  is emitted to the outside air via exhaust gas control devices  134 ,  136 . Each of the exhaust gas control devices  134 ,  136  has an associated one of catalysts (three-way catalysts)  134   a ,  136   a  that reduce toxic substances such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) in exhaust gas. 
     The torque converter  28  is configured as a general fluid transmission device. The torque converter  28  transmits the power of the crankshaft  26  of the engine  22  to an input shaft  32  of the automatic transmission  30  while amplifying torque or directly transmits the power without amplifying torque. The torque converter  28  includes a pump impeller, a turbine runner, a stator, a one-way clutch, and a hydraulically-driven lockup clutch  28   a . The pump impeller is connected to the crankshaft  26  of the engine  22 . The turbine runner is connected to the input shaft  32 . The stator aligns the flow of hydraulic fluid from the turbine runner to the pump impeller. The one-way clutch restricts the rotation direction of the stator to one direction. The lockup clutch couples the pump impeller and the turbine runner. The drive of the lockup clutch  28   a  is controlled by the ECU  50 . 
     The automatic transmission  30  is connected to the input shaft  32  and is connected to a drive shaft  37 . The drive shaft  37  is connected via a differential gear to axles respectively coupled to drive wheels (front wheels)  36   a ,  36   b . The automatic transmission  30  includes a plurality of planetary gears and a plurality of hydraulically-driven friction engagement elements (clutches and brakes). The automatic transmission  30  shifts into any one of first to fourth forward gears and a reverse gear through engagement and release of the plurality of friction engagement elements to transmit power between the input shaft  32  and the drive shaft  37  or shifts into a neutral state to cancel transmission of power between the input shaft  32  and the drive shaft  37 . The drive of the automatic transmission  30  is controlled by the ECU  50 . The automatic transmission  30  is not limited to the one of which the highest gear is fourth gear and may be the one of which the highest gear is lower than or equal to third gear or higher than or equal to fifth gear. In the embodiment, the drive shaft  37  and the components closer to the drive wheels  36   a ,  36   b  than the drive shaft  37 , that is, the torque converter  28 , the input shaft  32 , and the automatic transmission  30 , may be referred to as drive-train. 
     Although not shown in the drawing, the ECU  50  is configured as a microprocessor that mainly includes a CPU and that, in addition to the CPU, further includes a ROM that stores process programs, a RAM that temporarily stores data, input and output ports, and a communication port. 
     Signals required to control the operation of the engine  22  and to control the lockup clutch  28   a  and the automatic transmission  30  are input from various sensors to the ECU  50  via the input port. Examples of the signals to be input to the ECU  50  include a crank angle θcr from a crank position sensor  140 , and a coolant temperature Tw from a coolant temperature sensor  142 . The crank position sensor  140  detects the rotation position of the crankshaft  26  of the engine  22 . The coolant temperature sensor  142  detects the temperature of coolant of the engine  22 . Examples of the signals to be input to the ECU  50  also include cam angles θci, θco from a cam position sensor  144 . The cam position sensor  144  detects the rotation position of an intake camshaft that opens and closes the intake valve  128  and the rotation position of an exhaust camshaft that opens and closes the exhaust valve  131 . Examples of the signals to be input to the ECU  50  also include a throttle opening degree TH from a throttle position sensor  124   a , an intake air volume Qa from an air flow meter  148 , and an intake air temperature Ta from a temperature sensor  149 . The throttle position sensor  124   a  detects the position of the throttle valve  124 . The air flow meter  148  is attached to the intake pipe  123 . The temperature sensor  149  is attached to the intake pipe  123 . Examples of the signals to be input to the ECU  50  also include an air-fuel ratio AF 1  from an air-fuel ratio sensor  135   a , and an air-fuel ratio AF 2  from an air-fuel ratio sensor  135   b . The air-fuel ratio sensor  135   a  is attached to the exhaust pipe  133  upstream of the exhaust gas control device  134 . The air-fuel ratio sensor  135   b  is attached to the exhaust pipe  133  between the exhaust gas control device  134  and the exhaust gas control device  136 . For example, a rotation speed Ni of the input shaft  32  from a rotation speed sensor attached to the input shaft  32  is input via the input port. Examples of the signals to be input to the ECU  50  also include an ignition signal from an ignition switch  60 , and a shift position SP from a shift position sensor  62 . The shift position sensor  62  detects the operating position of a shift lever  61 . Examples of the signals to be input to the ECU  50  include an accelerator operation amount Acc from an accelerator pedal position sensor  64 , a brake pedal position BP from a brake pedal position sensor  66 , a vehicle speed V from a vehicle speed sensor  68 , and wheel speeds Vwa, Vwb that are the rotation speeds of the drive wheels  36   a ,  36   b  from wheel speed sensors  70   a ,  70   b . The accelerator pedal position sensor  64  detects the depression amount of an accelerator pedal  63 . The brake pedal position sensor  66  detects the depression amount of a brake pedal  65 . The wheel speed sensors  70   a ,  70   b  are respectively attached to the drive wheels  36   a ,  36   b.    
     Various control signals required to control the operation of the engine  22  and to control the lockup clutch  28   a  and the automatic transmission  30  are output from the ECU  50  via the output port. Examples of the various control signals include a control signal to a throttle motor  124   b , a control signal to the fuel injection valve  126 , and a control signal to the ignition plug  130 . The throttle motor  124   b  adjusts the position of the throttle valve  124 . Examples of the various control signals also include a control signal to the lockup clutch  28   a  of the torque converter  28 , and a control signal to a hydraulic circuit of the automatic transmission  30 . 
     The ECU  50  computes the rotation speed Ne of the engine  22  based on the crank angle θcr from the crank position sensor  22   a  or computes the rotation speed Nds of the drive shaft  37  by using an average of the wheel speeds Vwa, Vwb of the drive wheels  36   a ,  36   b  from the wheel speed sensors  70   a ,  70   b.    
     In the vehicle  20  of the thus configured embodiment, the ECU  50  executes the following travel control. In travel control, the ECU  50  sets a required drive torque Tdrv* required to run based on an accelerator operation amount Acc and a vehicle speed V. The ECU  50  sets a target gear ratio Gr* of the automatic transmission  30  based on the required drive torque Tdrv* and controls the hydraulic circuit of the automatic transmission  30  such that the gear ratio Gr of the automatic transmission  30  becomes a target gear ratio Gr*. The ECU  50  sets a required torque Tin* of the input shaft  32  of the automatic transmission  30  based on the required drive torque Tdrv* and the gear ratio Gr of the automatic transmission  30  and sets a target torque Te* of the engine  22  such that the required torque Tin* is output to the input shaft  32  of the automatic transmission  30 . The ECU  50  executes intake air volume control, fuel injection control, ignition control, and the like over the engine  22  based on the target torque Te*. Intake air volume control is executed by controlling the opening degree of the throttle valve  124 . Fuel injection control is executed by controlling the fuel injection amount from the fuel injection valve  126 . Ignition control is executed by controlling the ignition timing of the ignition plug  130 . 
     Next, the operation of the vehicle  20  of the thus configured embodiment, particularly, the operation at the time of reducing vibrations, will be described.  FIG. 3  is a flowchart showing an example of an engine ignition control routine to be executed by the ECU  50 . This routine is repeatedly executed when execution of vibration reduction control for reducing the vibrations of the engine  22  is requested. Execution of vibration reduction control is requested when all the five conditions, that is, a first condition, a second condition, a third condition, a fourth condition, and a fifth condition. In the first condition, there is no abnormality in the sensors such as the air-fuel ratio sensors  135   a ,  135   b  and the air flow meter  148  used to control the engine  22 . In the second condition, the automatic transmission  30  is not in a neutral state. In the third condition, the lockup clutch  28   a  is engaged. In the fourth condition, the difference between the rotation speed Ne of the engine  22 , computed based on the crank angle θcr from the crank position sensor  22   a , and the rotation speed of the turbine runner falls with a predetermined range. In the fifth condition, a plurality of the friction engagement elements of the automatic transmission  30  is engaged. 
     When the routine is executed, the ECU  50  executes a process of inputting the rotation speed Ne of the engine  22  and the wheel speeds Vwa, Vwb (step S 100 ). The rotation speed Ne to be input is computed based on the crank angle θcr from the crank position sensor  22   a . The wheel speeds Vwa, Vwb to be input are respectively detected by the wheel speed sensors  70   a ,  70   b.    
     Subsequently, the ECU  50  computes a wheel rotation speed Nec as the rotation speed of the engine  22  with the following expression 1 by using the wheel speeds Vwa, Vwb, a wheel radius Wr of the drive wheel  36   a , a gear ratio G 1  of the automatic transmission  30 , and a gear ratio G 2  of the differential gear (step S 110 ). The rotation speed Nrc of the drive shaft  37  can be computed with the following expression 2 by using the wheel speeds Vwa, Vwb, the wheel radius Wr of the drive wheel  36   a , and the gear ratio G 2  of the differential gear. Therefore, the wheel rotation speed Nec is obtained by multiplying the rotation speed Nrc of the drive shaft  37  by the gear ratio G 2  and is the rotation speed of the engine  22 , computed from the rotation speed Nrc of the drive shaft  37 . 
     
       
         
           
             
               
                 
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     Subsequently, the ECU  50  computes a rotation speed difference DNe by subtracting the wheel rotation speed Nec from the rotation speed Ne (step S 120 ). Here, the reason why the rotation speed difference DNe is computed will be described. 
     When the rotation speed Ne of the engine  22  is equal to the wheel rotation speed Nec that is the rotation speed of the engine  22 , computed from the wheel speeds Vwa, Vwb (the rotation speed Nrc of the drive shaft  37 ), that is, when the rotation speed difference DNe is zero, the engine  22  is rotating at the rotation speed corresponding to the wheel speeds Vwa, Vwb. At this time, torsion of the drive-train closer to the drive wheels  36   a ,  36   b  than the crankshaft  26  (the torque converter  28 , the input shaft  32 , the automatic transmission  30 , and the drive shaft  37 ) is not occurring. When the rotation speed Ne of the engine  22  is not equal to the wheel rotation speed Nec, that is, when the rotation speed difference DNe is a positive value or a negative value, the engine  22  is not rotating at the rotation speed corresponding to the rotation speeds of the drive wheels  36   a ,  36   b . At this time, torsion occurs in the drive-train closer to the drive wheels  36   a ,  36   b  than the crankshaft  26 . Therefore, the rotation speed difference DNe is a parameter that reflects torsion of the drive-train closer to the drive wheels  36   a ,  36   b  than the crankshaft  26 . For such a reason, the ECU  50  computes the rotation speed difference DNe. 
     Subsequently, the ECU  50  computes a torsional fluctuation component Vt obtained by applying a phase-lead process, which is a process of advancing a phase by a predetermined amount θref, to a processed rotation speed difference DNeref obtained by filtering the rotation speed difference DNe (step S 130 ). 
     Filtering is a process of extracting a signal in a resonant frequency band (a band higher than or equal to a frequency fl (for example, 2 Hz, 3 Hz, 4 Hz, or the like) and lower than or equal to a frequency fh (for example, 8 Hz, 10 Hz, 12 Hz, or the like) corresponding to resonance of the drive-train from the rotation speed difference DNe.  FIG. 4  is a graph illustrating an example of the relationship between the frequency of vibrations of the drive-train excited by torsion, and transmission sensitivity. In the graph, the continuous line, the dashed line, and the alternate long and short dashed line respectively illustrate cases where the gears of the automatic transmission  30  are different. As shown in the graph, the transmission sensitivity increases in the frequency band corresponding to primary resonance, so, in the embodiment, a frequency band including the primary resonance in each gear is defined as resonant frequency band. Through such filtering, a signal (noise) in a frequency band different from the resonant frequency band included in the rotation speed difference DNe is removed. 
     The phase-lead process is a process of advancing the phase of the processed rotation speed difference DNeref by the predetermined amount θref. The predetermined amount θref is a phase corresponding to a time required for the process of step S 100 , step S 110 , step S 120 , step S 130 , step S 140 , step S 150 , step S 160 , step S 170 , step S 180 , step S 190 , step S 200 , step S 210 , and step S 220  (described later) and is computed as the sum of a first lag amount θref 1 , a second lag amount θref 2 , and a third lag amount θref 3 . The first lag amount θref 1  is a time determined in advance as a lag amount corresponding to a time taken until target ignition timing tf* is computed in step S 100 , step S 110 , step S 120 , step S 130 , step S 140 , step S 150 , step S 160 , step S 170 , step S 180 , step S 190 , step S 200 , step S 210 , and step S 220  (described later). The second lag amount θref 2  is a lag amount corresponding to an average of a time from when the ECU  50  outputs an ignition control signal in step S 220  (described later) to when ignition actually takes place and is set based on the number of cylinders of the engine  22  and the rotation speed Ne. The second lag amount θref 2  is set so as to increase when the number of cylinders of the engine  22  is small as compared when the number of cylinders of the engine  22  is large (increase as the number of cylinders of the engine  22  reduces) and increase when the rotation speed Ne of the engine  22  is low as compared to when the rotation speed Ne of the engine  22  is high (increase as the rotation speed Ne of the engine  22  decreases). The third lag amount θref 3  is a value determined by experiment, analysis, or the like in advance as a lag amount corresponding to a time from when ignition takes place in the engine  22  to when a torque is actually output from the engine  22 .  FIG. 5  shows an example of a time change in processed rotation speed difference DNeref and a time change in torsional fluctuation component Vt. In the graph, the dashed line represents processed rotation speed difference DNeref, and the continuous line represents torsional fluctuation component Vt. 
     Subsequently, the ECU  50  sets an amplitude Am of the torsional fluctuation component Vt in a predetermined period (step S 140 ). The predetermined period is defined as a half period that is a period from when the torsional fluctuation component Vt crosses a value of zero and then crosses a value of zero next time. The amplitude Am is set as an amplitude in a period from the timing at which the torsional fluctuation component Vt crossed a value of zero immediately before to the timing at which the torsional fluctuation component Vt crossed a value of zero before that. Therefore, when step S 140  is executed at time t 0  in  FIG. 5 , the amplitude in the period from time t 1  (timing at which the torsional fluctuation component Vt crossed a value of zero immediately before) to time t 2  (the torsional fluctuation component Vt crossed a value of zero before that) is set for the amplitude Am. 
     Subsequently, it is determined whether the amplitude Am is greater than or equal to a threshold Amref (step S 150 ). The threshold Amref is a value determined in advance as a threshold for determining whether a user feels deterioration of drivability. Therefore, step S 150  is a process of determining whether such vibrations that a user feels deterioration of drivability are occurring. 
     When the amplitude Am is greater than or equal to the threshold Amref in step S 150 , the ECU  50  determines that such vibrations that a user feels deterioration of drivability are occurring, and sets the number of times of consecutive determination Nji (step S 160 ). The number of times of consecutive determination Nji is the number of times the ECU  50  consecutively determines in step S 150  that the amplitude Am is greater than or equal to the threshold Amref. The number of times of consecutive determination Nji is set to a value obtained by adding a value of 1 to the number of times of consecutive determination Nji (last Nji) set in the last step S 160 . The last Nji is set to a value of zero as an initial value. 
     Subsequently, the ECU  50  compares the number of times of consecutive determination Nji with the thresholds Nref 1 , Nref 2  (step S 170 ). The threshold Nref 1  is a threshold of the number of times for determining whether torsional resonance due to torsion of the drive-train is occurring. The threshold Nref 1  is set to two or more, for example, two, three, four, or the like. The threshold Nref 2  is a threshold for determining whether any abnormality, such as an abnormality of a control signal to be output from the ECU  50  to the engine  22 , is occurring. The threshold Nref 2  is greater than the threshold Nref 1  and is set to, for example, nine, ten, eleven, or the like.  FIG. 6  is a graph illustrating an example of a time change in torsional fluctuation component Vt when the amplitude Am becomes greater than or equal to the threshold Amref consecutively because of an abnormality. As shown in the graph, when an abnormality occurs, the torsional fluctuation component Vt can continuously increase. A process of comparing the number of times of consecutive determination Nji with the threshold Nref 2  is a process of determining whether such an abnormality is occurring. 
     When the number of times of consecutive determination Nji is less than the threshold Nref 1  in step S 170 , the ECU  50  ends the routine. In this case, the ECU  50  sets a target torque Te* of the engine  22  such that the required torque Tin* is output to the input shaft  32  of the automatic transmission  30  and executes ignition control over the engine  22  such that ignition takes place at normal ignition timing based on the target torque Te*. The normal ignition timing is optimal ignition timing set in consideration of efficiency or timing earlier than (advanced from) the optimal ignition timing to such an extent that vibrations do not become too large. 
     When the number of times of consecutive determination Nji is greater than or equal to the threshold Nref 1  and less than the threshold Nref 2  in step S 170 , the ECU  50  determines that torsional resonance is occurring, and determines whether a control duration tc that is a time during which the process of step S 190 , step S 200 , step S 210 , and step S 220  (described later) is being continuously executed is shorter than a threshold tcref (step S 180 ). The threshold tcref is a threshold for determining whether to stop the process of step S 190 , step S 200 , step S 210 , and step S 220  (described later) and is set to, for example, 2.5 seconds, 3.0 seconds, 3.5 seconds, or the like. 
     When the control duration tc is shorter than the threshold tcref in step S 180 , the ECU  50  determines that the process of step S 190 , step S 200 , step S 210 , and step S 220  can be continuously executed. Then, the ECU  50  sets a control execution flag F 1  to a value of 1 (step S 190 ), and sets a correction torque ΔTe to a larger one of a minimum torque ΔTemin and a smaller one of a value of zero and a value obtained by multiplying the torsional fluctuation component Vt by a conversion factor kp and a value of (−1) (step S 200 ). The conversion factor kp of step S 200  is a positive value determined in advance as a factor for converting the torsional fluctuation component Vt to torque fluctuations of the engine  22 . The minimum torque ΔTemin is a negative value determined in advance as a minimum value of the correction torque ΔTe. Therefore, the correction torque ΔTe is set to a value opposite in phase to the torsional fluctuation component Vt within the range greater than or equal to the minimum torque Temin and less than or equal to a value of zero. The reason why the correction torque ΔTe is set within the range greater than or equal to the minimum torque Temin and less than or equal to a value of zero will be described later. 
     When the ECU  50  sets the correction torque ΔTe in this way, the ECU  50  sets a control torque Tes* to a value obtained by adding the correction torque ΔTe to the target torque Te* (step S 210 ), executes ignition control over the engine  22  such that the correction torque Tes* is output from the engine  22  (step S 220 ), and ends the routine. Since the correction torque ΔTe is set within the range less than or equal to a value of zero, the control torque Tes* is set to less than or equal to the target torque Te*, and the ignition timing is set to the normal ignition timing or timing later than (retarded from) the normal ignition timing. Since the correction torque ΔTe is set to a torque opposite in phase to the torsional fluctuation component Vt within the range less than or equal to a value of zero and greater than or equal to the minimum torque ΔTemin, torsion of the drive-train is reduced and torsional resonance is suppressed by executing ignition control over the engine  22  at the control torque Tes* obtained by adding the correction torque ΔTe to the target torque Te*. With this configuration, the vibrations of the vehicle  20  are properly reduced. 
     Here, the reason why the ECU  50  sets the correction torque ΔTe within the range greater than or equal to the minimum torque Temin and less than or equal to a value of zero in step S 200  will be described. In the embodiment, the normal ignition timing is set to optimal ignition timing or timing earlier than (advanced from) the optimal ignition timing to such an extent that vibrations do not become too large. Therefore, setting the ignition timing earlier than (advanced from) the normal ignition timing is not desirable from the viewpoint of reducing vibrations. When the correction torque ΔTe becomes a positive value, the control torque Tes* is set so as to be greater than the target torque Te* in step S 210 , with the result that the ignition timing is made earlier than (advanced from) the normal ignition timing. In the embodiment, the ignition timing is restrained from being earlier than (advanced from) the normal ignition timing by setting the correction torque ΔTe to less than or equal to a value of zero. Setting the correction torque ΔTe to greater than or equal to the minimum torque Temin is to suppress a misfire of the engine  22  and an excessive increase in temperature due to excessively delayed (excessively retarded) ignition timing. In this way, by setting the ignition timing, occurrence of vibrations, a misfire of the engine  22 , and an excessive increase in temperature are suppressed. 
     When the number of times of consecutive determination Nji is greater than or equal to the threshold Nref 2  in step S 170  or when the control duration tc is longer than or equal to the threshold tcref in step S 180  even when the number of times of consecutive determination Nji is greater than or equal to the threshold Nref 1  and less than the threshold Nref 2  in step S 170 , the ECU  50  determines that vibrations are not reduced through control over the engine  22  by setting the correction torque ΔTe to a torque opposite in phase to the torsional fluctuation component Vt within the range less than or equal to a value of zero and greater than or equal to the minimum torque ΔTemin, and sets the number of times of non-reduction determination Njt (step S 230 ). The number of times of non-reduction determination Njt is the number of times the ECU  50  determines that vibrations are not reduced even when the engine  22  is controlled by setting the correction torque ΔTe to a torque opposite in phase to the torsional fluctuation component Vt within the range less than or equal to a value of zero and greater than or equal to the minimum torque ΔTemin in the current trip (a period from when the system of the vehicle  20  is started up by turning on the ignition switch  60  to when the system of the vehicle  20  is stopped by turning off the ignition switch  60 ). The number of times of non-reduction determination Njt is set to a value obtained by adding a value of 1 to the number of times of non-reduction determination Njt (last Njt) set at the time when the last step S 230  is executed. The last Njt is set to a value of zero as an initial value and is reset to a value of zero when the ignition switch  60  is turned off to end the trip. 
     Subsequently, the ECU  50  determines whether the number of times of non-reduction determination Njt is greater than or equal to a threshold Njtref (step S 240 ). The threshold Njtref is a threshold for determining whether vibrations are not reduced due to an abnormality even when the engine  22  is controlled by setting the correction torque ΔTe to a torque opposite in phase to the torsional fluctuation component Vt within the range less than or equal to a value of zero and greater than or equal to the minimum torque ΔTemin. 
     When the number of times of non-reduction determination Njt is less than the threshold Njtref in step S 240 , the ECU  50  executes a control stop process (step S 270 ), resets the control execution flag F 1  and the number of times of consecutive determination Nji to a value of zero (step S 280 ), and ends the routine. 
     In the control stop process of step S 270 , while the ECU  50  gradually increases the correction torque ΔTe (last ΔTe) set during execution of the last routine toward a value of zero, the ECU  50  sets a value obtained by adding the correction torque ΔTe to the target torque Te* for the control torque Tes*, and executes ignition control over the engine  22  such that the control torque Tes* is output from the engine  22 . Since the correction torque ΔTe is gradually increased toward a value of zero, the control torque Tes* gradually approaches the target torque Te*. Through such a control stop process, a shock due to a sudden change in the control torque Tes* is reduced. 
     When the number of times of non-reduction determination Njt is greater than or equal to the threshold Njtref in step S 240 , the ECU  50  sets a control prohibition flag F 2  to a value of 1 (step S 250 ), executes the control stop process (step S 270 ), resets the control execution flag F 1  and the number of times of consecutive determination Nji to a value of zero (step S 280 ), and ends the routine. When the number of times of non-reduction determination Njt is greater than or equal to the threshold Njtref, it is presumable that torsional fluctuations due to resonance cannot be reduced because of an abnormality even when the correction torque ΔTe is set to a torque opposite in phase to the torsional fluctuation component Vt within the range less than or equal to a value of zero and greater than or equal to the minimum torque ΔTemin. Therefore, in this case, the ECU  50  sets the control prohibition flag F 2  to a value of 1. When the control prohibition flag F 2  is a value of 1, the correction torque ΔTe becomes a value of zero in step S 270 , and the ECU  50  prohibits execution of control of the routine in the current trip after execution of step S 280 . With this configuration, it is possible to reduce execution of the routine although vibrations cannot be reduced. 
     When the amplitude Am is less than the threshold Amref in step S 150 , the ECU  50  determines whether the control execution flag F 1  is a value of 1 (step S 260 ). When the control execution flag F 1  is a value of zero, the ECU  50  ends the routine. In this case, the ECU  50  sets a target torque Te* of the engine  22  such that the required torque Tin* is output to the input shaft  32  of the automatic transmission  30  and executes ignition control over the engine  22  such that ignition takes place at the normal ignition timing based on the target torque Te*. 
     When the control execution flag F 1  is a value of zero in step S 260 , the ECU  50  executes the control stop process (step S 270 ), resets the control execution flag F 1  and the number of times of consecutive determination Nji to a value of zero (step S 280 ), and ends the routine. With this configuration, when the amplitude Am is reduced, control can be properly completed. 
       FIG. 7  is a timing chart illustrating an example of a time change in torsional fluctuation component Vt, a time change in number of times of consecutive determination Nji, and a time change in control execution flag F 1 . When the amplitude Am becomes greater than or equal to the threshold Amref, the number of times of consecutive determination Nji increments by a value of 1 (step S 160 , time t 01 ). When the number of times of consecutive determination Nji becomes greater than or equal to the threshold Njiref 1  (step S 170 , time t 02 ), while the control duration tc is shorter than the threshold tcref, the control execution flag F 1  is set to a value of 1 (step S 190 ), and step S 200 , step S 210 , and step S 220  are executed. Through execution of step S 200 , step S 210 , and step S 220 , torsion of the drive-train is reduced, and torsional resonance is suppressed. When the amplitude Am becomes less than the threshold Amref before the number of times of consecutive determination Nji becomes greater than or equal to the threshold Njiref 2  (step S 150 , step S 260 , time t 04 ), the control stop process is executed (step S 270 ), and the control execution flag F 1  and the number of times of consecutive determination Nj are reset to a value of zero (step S 280 ). In this way, by executing step S 200 , step S 210 , and step S 220  when the number of times of consecutive determination Nji becomes greater than or equal to the threshold Njiref 1 , torsion of the drive-train is reduced, and torsional resonance is suppressed. With this configuration, vibrations are further properly reduced. 
     When the number of times of consecutive determination Nji becomes greater than or equal to the threshold Njiref 2  (step S 160 ), the ECU  50  executes the control stop process (step S 270 ), and controls the engine  22  such that the engine  22  is driven at the target torque Te*. Therefore, an increase in vibrations is suppressed. 
     With the vehicle  20  equipped with the driving source control apparatus of the above-described embodiment, the period and amplitude of the torsional fluctuation component Vt to be obtained by applying the phase-lead process, which is a process of advancing the phase by the predetermined amount θref, to the difference between the rotation speed Ne of the engine  22  and the wheel rotation speed Nec computed from the rotation speed of the drive shaft  37  are repeatedly computed, and, when the number of times of consecutive determination Nji becomes greater than or equal to the threshold Nref 1 , the engine  22  is controlled so as to be driven at a torque obtained by adding the correction torque ΔTe opposite in phase to the torsional fluctuation component Vt to the target torque Te*. As a result, vibrations of the vehicle  20  are further properly reduced. 
     When the number of times of consecutive determination Nji becomes greater than or equal to the threshold Njiref 2 , the control stop process is executed, and the engine  22  is controlled so as to be driven at the target torque Te*. Therefore, an increase in vibrations is further suppressed. 
     When the predetermined amount θref is set to the sum of the first lag amount θref 1  corresponding to a time to compute the target ignition timing tf*, the second lag amount θref 2  corresponding to a time from when the ignition control signal is output to when ignition actually takes place in the engine  22 , and the third lag amount θref 3  corresponding to a time from when ignition takes place in the engine  22  to when a torque is actually output from the engine  22 , a lag of the computed torsional fluctuation component Vt of the drive-train from actual torsional fluctuations of the drive-train can be properly compensated. 
     In the vehicle  20  equipped with the driving source control apparatus of the embodiment, the predetermined amount θref is set to the sum of the first lag amount θref 1 , the second lag amount θref 2 , and the third lag amount θref 3  in the phase-lead process. Alternatively, the predetermined amount θref may be an invariable predetermined value determined in advance by experiment, analysis, or the like. 
     In the vehicle  20  equipped with the driving source control apparatus of the embodiment, in step S 200 , the correction torque ΔTe is set to a larger one of the minimum torque ΔTemin and a smaller one of a value of zero and a value obtained by multiplying the torsional fluctuation component Vt by the conversion factor kp and a value of −1. Alternatively, a value obtained by multiplying the torsional fluctuation component Vt by the conversion factor kp and a value of −1 may be set for the correction torque ΔTe. 
     In the vehicle  20  equipped with the driving source control apparatus of the embodiment, when the number of times of consecutive determination Nji is greater than or equal to the threshold Nref 2  in step S 170  or when the control duration tc is longer than or equal to the threshold tcref in step S 180  even when the number of times of consecutive determination Nji is greater than or equal to the threshold Nref 1  and less than the threshold Nref 2  in step S 170 , the ECU  50  executes step S 230 , step S 240 , and step S 250 , and then executes the control stop process (step S 270 ). However, in addition to step S 170  and step S 180 , the ECU  50  may determine whether the amplitude Am is greater than or equal to a threshold Amrefmax greater than the threshold Amref. The threshold Amrefmax is a threshold for determining whether large torsional fluctuations that do not occur during normal times are occurring and is set to, for example, 25 rpm, 30 rpm, 35 rpm, or the like.  FIG. 8  is a graph illustrating an example of a time change in torsional fluctuation component Vt when large torsional fluctuations that do not occur during normal times are occurring. Such large torsional fluctuations presumably occur due to a misfire or abnormal fuel injection of the engine  22 . Therefore, when the amplitude Am is greater than or equal to the threshold Amrefmax, the ECU  50  executes step S 230 , step S 240 , and step S 250 , and then executes the control stop process (step S 270 ). Thus, when a misfire or abnormal fuel injection is occurring in the engine  22 , further execution of control different from normal control is suppressed. 
     In the vehicle  20  equipped with the driving source control apparatus of the embodiment, the ECU  50  executes the control stop process in step S 270  to gradually bring the control torque Tes* close to the target torque Te*, thus suppressing a sudden change in torque. However, when a sudden change in torque is permitted, the control torque Tes* may be immediately set to the target torque Te* in step S 270 . 
     In the vehicle  20  equipped with the driving source control apparatus of the embodiment, in control over the engine  22 , the normal ignition timing is optimal ignition timing set in consideration of efficiency or the like or timing earlier than (advanced from) the optimal ignition timing to such an extent that vibrations do not become too large. Alternatively, the normal ignition timing may be set to timing later than the optimal ignition timing. 
     In the embodiment, the present disclosure is applied to the vehicle  20  including the engine  22 , the torque converter  28 , and the automatic transmission  30 . Alternatively, a manual transmission may be used instead of the torque converter  28  and the automatic transmission  30 . 
     The present disclosure may be applied to a vehicle in which a crankshaft of an engine and a rotary shaft of a motor are connected via a clutch and the rotary shaft of the motor is connected to a drive shaft coupled to axles via an automatic or manual transmission. In this case, the period and amplitude of the torsional fluctuation component Vt to be obtained by applying the phase-lead process, which is the process of advancing the phase by the predetermined amount θref, to the difference between the rotation speed of the engine or the motor and the wheel rotation speed Nec computed from the rotation speed of the drive shaft just need to be repeatedly computed, and, when the number of times of consecutive determination Nji becomes greater than or equal to the threshold Nref 1 , the engine or the motor just needs to be controlled so as to be driven at a torque obtained by adding the correction torque ΔTe opposite in phase to the torsional fluctuation component Vt to the target torque Te*. 
     The present disclosure may be applied to a vehicle in which a motor is connected via a transmission or without intervening a transmission to a drive shaft coupled to axles. In this case, the period and amplitude of the torsional fluctuation component Vt to be obtained by applying the phase-lead process, which is the process of advancing the phase by the predetermined amount θref, to the difference between the rotation speed of the motor and the wheel rotation speed Nec computed from the rotation speed of the drive shaft just need to be repeatedly computed, and, when the number of times of consecutive determination Nji becomes greater than or equal to the threshold Nref 1 , the motor just needs to be controlled so as to be driven at a torque obtained by adding the correction torque ΔTe opposite in phase to the torsional fluctuation component Vt to the target torque Te*. The present disclosure may be implemented as a driving apparatus including the engine  22 , the torque converter  28 , and the automatic transmission  30  or may be implemented as a driving source control apparatus that controls the engine  22 . 
     The correspondence relation between major elements of the embodiment and major elements of the present disclosure described in Summary will be described. In the embodiment, the engine  22  may be regarded as the driving source, and the ECU  50  may be regarded as the electronic control unit of the driving source control apparatus. 
     The correspondence relation between major elements of the embodiment and major elements of the present disclosure described in Summary does not limit the elements of the present disclosure described in the Summary since the embodiment is an example for specifically describing the aspect of the present disclosure described in the Summary. In other words, the present disclosure described in the Summary should be interpreted based on the description therein, and the embodiment is only a specific example of the present disclosure described in the Summary. 
     The embodiment of the present disclosure is described above; however, the applicable embodiment is not limited to the embodiment and may be, of course, modified into various forms without departing from the scope of the present disclosure. 
     The present disclosure is usable in the industry of manufacturing driving source control apparatuses.