Abstract:
An engine control system for an engine equipped with a catalyst that purifies exhaust gas includes: a catalyst temperature acquisition section that acquires the temperature of the catalyst; and a control section that controls an engine such that a rate of increase in engine output speed is changed in accordance with the temperature of the catalyst.

Description:
INCORPORATION BY REFERENCE 
       [0001]    The disclosure of Japanese Patent Application No. 2009-009915 filed on Jan. 20, 2009 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an engine control system and an engine control method. Particularly, relates to a technology to control an engine that is equipped with a catalyst to purify exhaust gas. 
         [0004]    2. Description of the Related Art 
         [0005]    A hybrid vehicle equipped with a motor as a drive source in addition to an engine is generally known. In the hybrid vehicle, the engine load may be reduced with the assistance of the motor. 
         [0006]    As with a non-hybrid vehicle that is equipped with only an engine as the drive source, the engine of the hybrid vehicle also discharges exhaust gas. Thus, it is desirable to operate the engine such that an amount of the exhaust gas is not excessive. 
         [0007]    Japanese Patent Application Publication 2001-37008 (JP-A-2001-37008) describes that, when electricity is generated to obtain desired electric energy, the engine operation range is determined based on a discharge amount limit of exhaust emissions such as nitrogen oxide and smoke or based on a parameter that significantly affects exhaust performance. Then, the engine speed is corrected to operate the engine within the above range, and electricity is generated. 
         [0008]    According to the technology described in JP-A-2001-37008, the increase of the exhaust emissions is reduced to a minimum level when electricity is generated. Further, the electricity generated is utilized to compensate for output when the output is required such that the discharge amount limit of the exhaust emissions may exceed. Accordingly, it is possible to reduce the amount of the exhaust gas and to improve fuel economy under various driving conditions. 
         [0009]    The exhaust gas discharged from the engine is purified by a catalyst. The purification efficiency of the catalyst may vary in accordance with the temperature of the catalyst. For example, the catalyst cannot purify the exhaust gas until the temperature of the catalyst is equal to or above a prescribed temperature. However, if the temperature of the catalyst becomes too high, the purification efficiency of the catalyst deteriorates. Thus, as in the technology that is described in JP-A-2001-37008, even if the engine operation range is determined based on the discharge amount limit of the exhaust emissions or based on a parameter that significantly affects the exhaust performance, and even if the engine speed is corrected to operate the engine within the above range to generate electricity, the catalyst temperature may be too high to allow effective purification of the exhaust gas by the catalyst. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides an engine control system and an engine control method that restricts a temperature increase of a catalyst. 
         [0011]    The engine control system according to a first aspect of the present invention is an engine control system that includes a catalyst to purify exhaust gas. The engine control system includes a catalyst temperature acquisition section that acquires the temperature of the catalyst and a control section that controls an engine such that the rate of increase in engine output speed is changed in accordance with the temperature of the catalyst. 
         [0012]    According to the above aspect, the rate of increase in engine output speed is changed in accordance with the temperature of the catalyst that purifies the exhaust gas. Accordingly, the rate at which the delivery of exhaust gas to the catalyst is increase may be changed in accordance with the temperature of the catalyst. Thus, in comparison to a case where the catalyst is at low temperature, the rate of increase in delivering the exhaust gas to the catalyst may be decreased when the catalyst is at high temperature. As a result, it is possible to provide the engine control system that restricts the temperature increase of the catalyst. 
         [0013]    The control method of an engine according to a second aspect of the present invention is a control method of an engine that includes a catalyst to purify exhaust gas. The control method of an engine includes: acquiring the temperature of the catalyst; and controlling the engine such that a rate of increase in engine output speed is changed in accordance with the acquired temperature of the catalyst. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The foregoing and/or further objects, features and advantages of the invention will become more apparent from the following description of example embodiments with reference to the accompanying drawings, in which like numerals are used to represent like elements and wherein: 
           [0015]      FIG. 1  shows general configuration of a hybrid vehicle according to an embodiment of the present invention; 
           [0016]      FIG. 2  shows collinearity of a power division mechanism according to the embodiment of the present invention; 
           [0017]      FIG. 3  shows an engine according to the embodiment of the present invention; 
           [0018]      FIG. 4  shows an electric system of the hybrid vehicle according to the embodiment of the present invention; 
           [0019]      FIG. 5  is a function block diagram of a powertrain mechanism-electric control unit (PM-ECU) according to the embodiment of the present invention; and 
           [0020]      FIG. 6  is a flowchart that shows control structure of a program to be executed by the PM-ECU according to the embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0021]    Embodiments of the present invention will hereinafter be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, the description of the same components will not be repeated. 
         [0022]    Referring to  FIG. 1 , a hybrid vehicle equipped with a control system according to an embodiment of the present invention will be described. The vehicle includes an engine  100 , a first motor generator (MG)  110 , a second MG  120 , a power split mechanism  130 , a speed reducer  140 , and a battery  150 . 
         [0023]    This vehicle is driven by the drive force from at least one of the engine  100  and the second MG  120 . For example, the engine  100  and the second MG  120  are controlled such that the engine  100  and the second MG  120  contribute the output power to reach a target output power of the vehicle, which is set based on an accelerator operation amount the vehicle speed, and the like. The target output power of the vehicle is divided into the output power of the engine  100  and the output power of the second MG  120  at an appropriate ratio. The ratio is determined in consideration of various parameters such as fuel economy and an output power limit of the vehicle. 
         [0024]    The engine  100 , the first MG  110 , and the second MG  120  are connected through the power split mechanism  130 . The power generated by the engine  100  is split along two paths by the power split mechanism  130 . One of the paths, which is divided by the power division mechanism  130 , sends power to the front wheel  160  through the speed reducer  140 . The other path, sends power to drive the first MG  110  to generate electricity. 
         [0025]    The first MG  110  is a three-phase alternate-current (AC) rotating generator that includes a U-phase coil, a V-phase coil, and a W-phase coil. The first MG  110  generates electricity using power from the engine  100  diverted to the first MG via the power split mechanism  130 . The electricity generated by the first MG  110  is utilized in accordance with the driving state of the vehicle or the state of charge (SOC) of the battery  150 . For example, the electricity generated by the first MG  110  is utilized to drive the second MG  120  during normal driving. Meanwhile, if the SOC of the battery  150  is below prescribed value, the electricity generated by the first MG  110  is converted from AC to direct current (DC) by an inverter, described below. Then, the voltage of the electricity is adjusted by a converter, which will be described below, and stored in the battery  150 . 
         [0026]    When the first MG  110  operates as an electric generator, the first MG  110  generates negative torque. Negative torque is torque that becomes a load on the engine  100 . When the first MG  110  receives electricity to act as a motor, the first MG  110  generates positive torque. Positive torque is torque that does not become a load on the engine  100 . In other words, positive torque assists the rotation of the engine  100 . The above configuration also applies to the second MG  120 . 
         [0027]    The second MG  120  is a three-phase AC rotating generator that includes a U-phase coil, a V-phase coil, and a W-phase coil. The second MG  120  is driven by at least one of the electricity that is stored in the battery  150  and the electricity that is generated by the first MG  110 . 
         [0028]    The drive force of the second MG  120  is directed to the front wheel  160  through the speed reducer  140 . Accordingly, the second MG  120  assists the engine  100  and supplements the drive force applied to the vehicle. The second MG  120  may drive a rear wheel instead of the front wheel  160  or in addition to the front wheel  160 . 
         [0029]    During regenerative braking of the hybrid vehicle, the second MG  120  is driven by the front wheel  160  through the speed reducer  140  and operates as the electric generator. Thus, the second MG  120  operates as a regenerative brake that converts braking energy to electricity. The electricity that is generated by the second MG  120  is stored in the battery  150 . 
         [0030]    The power split mechanism  130  is a planetary gear train that includes a sun gear, a pinion gear, a carrier, and a ring gear. The pinion gear is engaged with the sun gear and the ring gear. The pinion gear is rotatably supported by the carrier. The sun gear is connected to a rotating shaft of the first MG  110 . The carrier is connected to a crankshaft of the engine  100 . The ring gear is connected to a rotating shaft of the second MG  120  and the speed reducer  140 . 
         [0031]    The engine  100 , the first MG  110 , and the second MG  120  are connected through the power division mechanism  130 , which is the planetary gear train. Thus, the rotational speeds of the engine  100 , the first MG  110 , and the second MG  120  create a collinear relationship as shown in  FIG. 2 . 
         [0032]    Referring back to the  FIG. 1 , the battery  150  is an assembled battery in which plural battery modules are connected in series. Each of the battery modules includes integrated battery cells. The voltage of the battery  150  is approximately 200 V, for example. 
         [0033]    According to the embodiment, the engine  100  is controlled by a powertrain manager-electronic control unit (PM-ECU)  170 . The first MG  110  and the second MG  120  are controlled by an MG-ECU  172 . The PM-ECU  170  and the MG-ECU  172  are communicatively connected in both directions. The PM-ECU  170  outputs commands to the MG-ECU  172  on the supply of the generated electricity of the first MG  110  and the driving electricity of the second MG  120 . 
         [0034]    The engine  100  will be further described with reference to  FIG. 3 . The engine  100  is an internal combustion engine in which air-fuel mixture is ignited by a spark plug  1006  and combusted in a combustion chamber. The air-fuel mixture is mixture of air that is drawn from an air cleaner  1002  and fuel that is injected by an injector  1004 . The ignition timing is advanced minimally for best torque (MBT) at which the output torque reaches a maximum value. However, the ignition timing is delayed or advanced in accordance with the operational state of the engine  100 , such as occurrence of knock. 
         [0035]    When the air-fuel mixture is combusted, a piston  1008  is pushed down by combustion pressure, causing a crankshaft  1010  to rotate. The combusted air-fuel mixture (exhaust gas) is purified by a three-way catalyst  1012 , which is provided in the engine  100 , before being discharged from the vehicle. The three-way catalyst  1012  promotes its purification effect by being heated to a particular temperature. The amount of the air that is drawn to the engine  100  is regulated by a throttle valve  1014 . 
         [0036]    The PM-ECU  170  that controls the engine  100  is connected to a knock sensor  300 , a coolant temperature sensor  302 , a crank position sensor  306  that is provided opposite a timing rotor  304 , a throttle opening sensor  308 , an airflow meter  310 , an accelerator operation amount sensor  312 , and a vehicle speed sensor  314 . 
         [0037]    The knock sensor  300  is provided in a cylinder block of the engine  100 . The knock sensor  300  includes a piezoelectric element. The knock sensor  300  generates voltage by the vibration of the engine  100 . The magnitude of the voltage corresponds to the degree of the vibration. The knock sensor  300  transmits a signal that indicates the magnitude of the generated voltage to the PM-ECU  170 . 
         [0038]    The coolant temperature sensor  302  detects the temperature of coolant in a water jacket of the engine  100  and transmits a signal that indicates the detected coolant temperature to the PM-ECU  170 . 
         [0039]    The timing rotor  304  is provided on and rotates with the crankshaft  1010 . A plurality of projections are formed along the outer circumference of the timing rotor  304  at specified intervals. The crank position sensor  306  is provided opposite to and facing the projections of the timing rotor  304 . A gap distance between the projections of the timing rotor  304  and the crank position sensor  306  changes as the timing rotor  304  rotates. Thus, a magnetic flux that passes through the coil of the crank position sensor  306  fluctuates, and thereby, an electromotive force is generated in the coil. The crank position sensor  306  transmits a signal that indicates the detected electromotive force to the PM-ECU  170 . Based on the signal that is transmitted from the crank position sensor  306 , the PM-ECU  170  determines the crank angle and engine speed NE (i.e., the rotational speed of the crankshaft  1010 ). 
         [0040]    The throttle-opening sensor  308  detects throttle opening amount and transmits a signal that indicates the detected opening amount to the PM-ECU  170 . 
         [0041]    The airflow meter  310  detects the amount of the air that is drawn to the engine  100  and transmits a signal that indicates the detected amount of airflow to the PM-ECU  170 . 
         [0042]    The accelerator operation amount sensor  312  detects the operation amount of an accelerator pedal and transmits a signal that indicates the detected operation amount to the PM-ECU  170 . The vehicle speed sensor  314  detects the vehicle speed and transmits a signal that indicates the detected vehicle speed to the PM-ECU  170 . 
         [0043]    An electrical system of the hybrid vehicle will be further described with reference to  FIG. 4 . The hybrid vehicle includes a converter  200 , a first inverter  210 , a second inverter  220 , and a system main relay (SMR)  230 . 
         [0044]    The converter  200  includes a reactor, two NPN transistors, and two diodes. One end of the reactor is connected to the cathode of the battery  150 , and the other end of the reactor is connected to a connecting point of the two NPN transistors. 
         [0045]    The two NPN transistors are connected in series. The NPN transistors are controlled by the MG-ECU  172 . Each of the diodes is connected between a corrector and an emitter of the corresponding NPN transistor so that electricity flows from the emitter side to the corrector side. 
         [0046]    An insulated gate bipolar transistor (IGBT) may be employed as the NPN transistor, for example. Instead of the NPN transistor, a power switching element such as a power metal oxide semiconductor field-effect transistor (power MOSFET) can be utilized. 
         [0047]    When the electricity that is discharged from the battery  150  is supplied to the first MG  110  or the second MG  120 , the voltage is increased by the converter  200 . On the other hand, when the electricity that is generated by the first MG  110  or the second MG  120  is used to charge the battery  150 , the voltage is reduced by the converter  200 . 
         [0048]    A system voltage VH between the converter  200  and the first inverter  210  and between the converter  200  and the second inverter  220  is detected by a voltage sensor  180 . The voltage detected by the voltage sensor  180  is transmitted to the MG-ECU  172 . 
         [0049]    The first inverter  210  includes a U-phase arm, a V-phase arm, and a W-phase arm. The U-phase arm, the V-phase arm, and the W-phase arm are connected in parallel. Each of the U-phase arm, the V-phase arm, and the W-phase arm includes two NPN transistors that are connected in series. Each diode is connected between the corrector and the emitter of the corresponding NPN transistor so that electricity flows from the emitter to the corrector. A connecting point between the NPN transistors of each arm is connected to one end of each coil of the first MG  110  that differs from a neutral point  112  of each coil. 
         [0050]    The first inverter  210  converts direct current that is supplied from the battery  150  to alternating current, and supplies the alternating current to the first MG  110 . The first inverter  210  also converts the alternating current that is generated by the first MG  110  to direct current. 
         [0051]    The second inverter  220  includes the U-phase arm, the V-phase arm, and the W-phase arm. The U-phase arm, the V-phase arm, and the W-phase arm are connected in parallel. Each of the U-phase arm, the V-phase arm, and the W-phase arm includes the two NPN transistors that are connected in series. Each diode is connected between the corrector and the emitter of the corresponding NPN transistor so that electricity flows from the emitter to the corrector. The connecting point between the NPN transistors of each arm is connected to one end of each coil of the second MG  120  that differs from a neutral point  122  of each coil. 
         [0052]    The second inverter  220  converts the direct current that is supplied from the battery  150  to the alternating current, and supplies the alternating current to the second MG  120 . The second inverter  220  also converts the alternating current that is generated by the second MG  120  to the direct current. 
         [0053]    The converter  200 , the first inverter  210 , and the second inverter  220  are controlled by the MG-ECU  172 . The MG-ECU  172  has a function to control the converter  200 , the first inverter  210 , and the second inverter  220 , and also has a function to detect failure (abnormality) of the converter  200 , the first inverter  210 , and the second inverter  220 . 
         [0054]    For example, the MG-ECU  172  detects failure when the system voltage VH that is detected by the voltage sensor  180 , input or output current that is detected by a current sensor (not shown), the temperature of the converter  200 , the first inverter  210 , or the second inverter  220  that is detected by a temperature sensor (not shown), or the like is equal to or higher than a threshold value. When the MG-ECU  172  detects the failure, a signal that represents the failure is transmitted from the MG-ECU  172  to the PM-ECU  170 . 
         [0055]    The SMR  230  is provided between the battery  150  and the converter  200 . The SMR  230  is a relay that switches between a state in which the battery  150  and the electric system are connected and a state in which the battery  150  and the electric system are disconnected. When the SMR  230  is open, the battery  150  is disconnected from the electric system. When the SMR  230  is closed, the battery  150  is connected with the electric system. 
         [0056]    More specifically, when the SMR  230  is open, the battery  150  is electrically disconnected from the converter  200  and the like. When the SMR  230  is closed, the battery  150  is electrically connected with the converter  200  and the like. 
         [0057]    The SMR  230  is controlled by the PM-ECU  170 . For example, when the PM-ECU  170  is activated, the SMR  203  is closed. When the PM-ECU  170  is deactivated, the SMR  230  is opened. 
         [0058]    The function of the PM-ECU  170  will be further described with reference to  FIG. 5 . It should be noted that the function described below may be implemented by software or hardware. 
         [0059]    The PM-ECU  170  includes an estimating section  400 , a first control section  411 , and a second control section  412 . The estimating section  400  estimates the temperature of the three-way catalyst  1012 . For example, the temperature of the three-way catalyst  1012  may be estimated based on parameters such as the engine speed (output speed of the engine  100 ) NE, the load that is calculated from a intake air amount (load rate), or the time period that has elapsed since the activation of the engine  100 . 
         [0060]    Through an experiment and a simulation that are conducted during a development stage of the engine  100 , a map depicting the relationship between the temperature of the three-way catalyst  1012  and the parameters such as the engine speed NE, the load, and the time period that elapsed since the activation of the engine  100  may be created and stored in memory. The PM-ECU  170  then estimates the temperature of the three-way catalyst  1012  using the map. 
         [0061]    A conventional method may also be utilized as a method to estimate the temperature of the three-way catalyst  1012 . Thus, the method will not be described in detail repeatedly. Instead of estimating the temperature of the three-way catalyst  1012 , the temperature of the three-way catalyst  1012  may directly be detected by utilizing a temperature sensor or the like. 
         [0062]    The first control section  411  controls the engine  100  so that the rate of increasing the engine speed NE changes in accordance with the temperature of the three-way catalyst  1012 . More specifically, when the SOC of the battery  150  is equal to or above a threshold SOC, the engine  100  is controlled so that the rate of increase in the engine speed NE is decreased inversely with increases in the temperature of the three-way catalyst  1012 . In other words, if the motor can sufficiently assist the engine, the engine is controlled such that the rate of increase in engine speed is decreased inversely with increases in the temperature of the three-way catalyst  1012 . Accordingly, the temperature increase of the catalyst is restricted without degrading the acceleration of the vehicle. 
         [0063]    The second control section  412  controls the engine  100  such that the load on the engine  100  is reduced inversely with increases in the temperature of the three-way catalyst  1012 . Thus, compared to a case when the catalyst temperature is low, the amount of the exhaust gas that is delivered to the catalyst may be reduced when the catalyst is at high temperature. Therefore, the temperature increase of the catalyst can be restricted. 
         [0064]    Next, the control structure of a program to be executed by the PM-ECU  170  will be described with reference to  FIG. 6 . 
         [0065]    In step (hereinafter abbreviated as “S”)  100 , the PM-ECU  170  detects the accelerator operation amount. The accelerator operation amount may be detected by utilizing a conventional technology, such as an accelerator operation amount sensor. Thus, a detection method of the accelerator operation amount will not be described in detail. 
         [0066]    In  5102 , the PM-ECU  170  detects the vehicle speed and calculates the SOC of the battery  150 . The SOC of the battery  150  may be calculated by utilizing a conventional technology. For example, the SOC of the battery  150  can be calculated from the voltage of the battery  150  or integrated from of the input and output currents of the battery  150 . Thus, a calculation method of the SOC will not be described in detail. 
         [0067]    In S 104 , the PM-ECU  170  estimates the temperature of the three-way catalyst  1012 . In S 106 , the PM-ECU  170  determines an operating point of the engine  100  in accordance with the accelerator operation amount, the vehicle speed, the SOC of the battery  150 , the temperature of the three-way catalyst  1012 , and the like. In the embodiment, the operating point of the engine indicates a target output power of the engine  100 . The output power of the engine  100  is expressed by a product of the engine speed NE and the output torque of the engine  100 . Thus, upon determination of the operating point of the engine  100 , the target output speed, the target output torque, and the like of the engine  100  may be determined. 
         [0068]    In the embodiment, the operating point of the engine  100  is determined such that the load on the engine  100  is reduced inversely with increases in temperature of the three-way catalyst  1012 . However, the operating point of the engine  100  may be determined without consideration of the temperature of the three-way catalyst  1012 . 
         [0069]    In S 108 , the PM-ECU  170  determines whether the SOC of the battery  150  is equal to or above the threshold SOC. In other words, it is determined whether the SOC of the battery  150  is sufficient. If the SOC of the battery  150  is equal to or above the threshold SOC (YES in S 108 ), the process proceeds to S 110 . If not (NO in S 108 ), the process proceeds to S 114 . 
         [0070]    In S 110 , the PM-ECU  170  sets the increase rate of the engine speed NE to be decreased inversely with increases in the temperature of the three-way catalyst  1012 . The rate of increase in engine speed NE may be determined in consideration of the accelerator operation amount, the vehicle speed, and the like, in addition to the temperature of the three-way catalyst  1012 . 
         [0071]    In S 112 , the PM-ECU  170  controls the engine  100  such that the engine speed NE is increased at the set rate of increase until the actual operating point of the engine  100  reaches the determined operating point. 
         [0072]    In S 114 , the PM-ECU  170  controls the engine  100  such that the engine speed NE is increased at a rate of increase that is higher than that utilized when the SOC of the battery  150  is equal to or higher than the threshold SOC, until the actual operating point of the engine  100  reaches the determined operating point. The rate of increase for the engine speed NE may be determined in consideration of the accelerator operation amount, the vehicle speed, and the like. 
         [0073]    The operation of the engine  100  that is based on the above structure and the above flowchart is described below. 
         [0074]    During running of the vehicle, the accelerator operation amount is detected (S 100 ). In addition, the vehicle speed is detected, and the SOC of the battery  150  is calculated (S 102 ). Further, the temperature of the three-way catalyst  1012  is estimated (S 104 ). 
         [0075]    The operating point of the engine  100  is determined in accordance with the accelerator operation amount, the vehicle speed, the SOC of the battery  150 , the temperature of the three-way catalyst  1012 , and the like (S 106 ). In the embodiment, the operating point of the engine  100  is determined such that the load of the engine  100  is reduced inversely with increases in the temperature of the three-way catalyst  1012 , and eventually, the engine  100  is controlled so that the actual operating point of the engine  100  reaches the determined operating point (S 112 , S 114 ). Thus, compared to a when the temperature of the three-way catalyst  1012  is low, it is possible to reduce the amount of the exhaust gas that is delivered to the three-way catalyst  1012  when the temperature of the three-way catalyst  1012  is high. Therefore, the temperature increase of the three-way catalyst  1012  may be restricted. 
         [0076]    However, if the SOC of the battery  150  is equal to or above the threshold SOC (YES in S 108 ), that is, if the SOC of the battery  150  is sufficient, even if the output power of the engine  100  is gently increased, an acceleration request by a driver is met by supplementing the output power with the output power of the second MG  120 . 
         [0077]    Accordingly, if the SOC of the battery  150  is equal to or above the threshold SOC (YES in S 108 ), the rate of increase in the engine speed NE is set to be decreased inversely with increases in the temperature of the three-way catalyst  1012  (S 110 ). Subsequently, the engine  100  is controlled such that the engine speed NE is increased at the set rate of increase until the actual operating point of the engine  100  reaches the determined operating point. 
         [0078]    Thus, compared to the case where the temperature of the three-way catalyst  1012  is low, it is possible to reduce the amount of the exhaust gas that is delivered to the three-way catalyst  1012  when the temperature of the three-way catalyst  1012  is high. Therefore, the temperature increase of the three-way catalyst  1012  may be restricted. 
         [0079]    On the other hand, if the SOC of the battery  150  is below the threshold SOC (NO in S 108 ), that is, if the SOC of the battery  150  is insufficient, an assisted amount of the engine  100  with the second MG  120  is restricted. Thus, the acceleration request by the driver cannot be met unless the output power of the engine  100  is immediately increased. 
         [0080]    Considering the above, if the SOC of the battery  150  is below the threshold value (NO in S 108 ), the engine  100  may be controlled so that the engine speed NE is increased at a rate higher than the increasing rate used when the SOC of the battery  150  is equal to or exceeds the threshold value, until the actual operating point of the engine  100  reaches the determined operating point (S 114 ). 
         [0081]    While the invention has been described with reference to example embodiments thereof, it should be understood that the invention is not limited to the example embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.