Internal combustion engine system and control method of internal combustion engine system

Under the condition that a catalyst temperature Tc of a purification catalyst reaches or exceeds a preset reference temperature Tcref, when a cooling water temperature Tw of an engine is not lower than a preset reference temperature Twref, the internal combustion engine system of the invention sets a target exhaust recirculation rate EGR* based on a given rotation speed Ne of the engine and a given load factor KL and performs exhaust recirculation control to open an EGR valve at a specific angle or opening corresponding to the set target exhaust recirculation rate EGR*. When the cooling water temperature Tw is lower than the preset reference temperature Twref, on the other hand, the internal combustion engine system of the invention sets a fuel increment amount α based on the given rotation speed Ne of the engine and the given load factor KL and performs fuel increment control to increase the specific amount of fuel, which is set relative to the amount of intake air to attain the stoichiometric air-fuel ratio as a value to be injected from a fuel injection valve, by the set fuel increment amount α. This arrangement effectively prevents overheat of the purification catalyst while minimizing the deterioration of fuel consumption.

BACKGROUND ART

1. Technical Field

The present invention relates to an internal combustion engine system including an internal combustion engine with a purification catalyst provided in an exhaust line thereof, a fuel injection module configured to inject a fuel into the internal combustion engine, an exhaust recirculation module arranged to recirculate part of exhaust of the internal combustion engine into a gas intake line of the internal combustion engine, and a temperature-reflecting physical quantity detector constructed to measure a temperature-reflecting physical quantity representing temperature of the internal combustion engine, and a control method of the internal combustion engine system.

2. Related Art

One proposed structure of an internal combustion engine system is equipped with an EGR (exhaust gas recirculation) device designed to recirculate the exhaust gas into a gas intake line (see, for example, Patent Document 1). The EGR device mounted on the internal combustion engine system sets an EGR rate according to the engine water temperature and controls on and off an EGR valve to recirculate the exhaust gas into the gas intake line at the set EGR rate. Such controlled recirculation of the exhaust gas aims to lower the temperature of the exhaust gas and thereby prevent an excessive increase of the engine temperature.

SUMMARY OF THE INVENTION

The EGR device is not restrictively used to prevent the excessive increase of the engine temperature (engine water temperature), but is also applicable to lower the temperature of the exhaust gas and thereby prevent a temperature increase of a purification catalyst provided in an exhaust line of the engine. The low engine temperature condition generally worsens the combustion state in the engine and interferes with the EGR operation. The driver's heavy depression of an accelerator pedal to a significant depth immediately after a start of the engine in the cold state triggers an abrupt increase of the catalyst temperature and causes the state of low engine water temperature but high catalyst temperature. In this state, the EGR operation is not allowable, so that the catalyst temperature increases to an undesirably high level. One proposed measure for preventing the increase of the catalyst temperature consistently performs fuel amount increase control, in place of the EGR control, in the condition of the high catalyst temperature. The fuel amount increase control increases the amount of fuel to be injected from a fuel injection valve and utilizes the latent heat of vaporization in the increased amount of the fuel to cool down the purification catalyst. The increased amount of fuel injection, however, undesirably worsens the fuel consumption.

An object of the present invention is to provide an internal combustion engine system and the control method of the internal combustion engine system that prevent overheat of a purification catalyst while minimizing the deterioration of fuel consumption.

In order to achieve at least part of the above-mentioned and other related objects, the internal combustion engine system and the control method of the internal combustion engine system of the present invention is constructed as follows.

One aspect of the invention pertains to an internal combustion engine system including an internal combustion engine with a purification catalyst provided in an exhaust line thereof. In the internal combustion engine system of this aspect of the invention, a fuel injection module is configured to inject a fuel into the internal combustion engine. An exhaust recirculation module is arranged to recirculate part of exhaust of the internal combustion engine into a gas intake line of the internal combustion engine. A temperature-reflecting physical quantity detector is constructed to measure a temperature-reflecting physical quantity representing temperature of the internal combustion engine. A temperature increase controller is configured to, upon satisfaction of a preset condition for preventing a temperature increase of the purification catalyst, when the temperature of the internal combustion engine represented by the temperature-reflecting physical quantity measured by the temperature-reflecting physical quantity detector is not lower than a preset reference temperature, perform a first control of controlling the exhaust recirculation module to recirculate the part of the exhaust of the internal combustion engine into the gas intake line and thereby prevent the temperature increase of the purification catalyst, and when the temperature of the internal combustion engine represented by the temperature-reflecting physical quantity measured by the temperature-reflecting physical quantity detector is lower than the preset reference temperature, perform a second control of controlling the fuel injection module to increment an amount of the fuel to be injected into the internal combustion engine and thereby prevent the temperature increase of the purification catalyst.

Upon satisfaction of the preset condition for preventing the temperature increase of the purification catalyst, when the temperature of the internal combustion engine is not lower than the preset reference temperature, the internal combustion engine system of this aspect of the invention performs the first control of controlling the exhaust recirculation module to recirculate the part of the exhaust of the internal combustion engine into the gas intake line and thereby prevent the temperature increase of the purification catalyst. When the temperature of the internal combustion engine is lower than the preset reference temperature, on the other hand, the internal combustion engine system performs the second control of controlling the fuel injection module to increment the amount of the fuel to be injected into the internal combustion engine and thereby prevent the temperature increase of the purification catalyst. This arrangement effectively prevents overheat of the purification catalyst while minimizing the fuel consumption for controlling the temperature increase of the purification catalyst.

In the internal combustion engine system of the invention, the temperature increase controller may continue the second control without abruptly stopping even when the temperature of the internal combustion engine represented by the measured temperature-reflecting physical quantity increases from a level of lower than the preset reference temperature to a level of not lower than the preset reference temperature during execution of the second control. This arrangement effectively prevents the state of the engine from becoming unstable by an abrupt switchover between the first and the second control.

In the internal combustion engine system of the invention, the temperature increase controller may perform the second control irrespective of the temperature of the internal combustion engine represented by the measured temperature-reflecting physical quantity, in the event of any abnormality arising in the exhaust recirculation module. This arrangement ensures the temperature control of the catalyst even in the case of any abnormality arising in the fuel injection module.

In the internal combustion engine system of the invention, the temperature increase controller may assume satisfaction of the preset condition when the internal combustion engine is driven in a specific high load area, or when temperature of the purification catalyst is not lower than a preset reference catalyst temperature.

In the internal combustion engine system of the invention, the temperature-reflecting physical quantity detector may measure temperature of cooling water in the internal combustion engine.

The internal combustion engine system of the invention may be incorporated in a power output apparatus configured to output power to a driveshaft. The power output apparatus may have: an electric power-mechanical power input output assembly connected with the driveshaft and with an output shaft of the internal combustion engine in a rotatable manner independently of the driveshaft and configured to output a torque to the driveshaft and to the output shaft through input and output of electric power and mechanical power; and a motor designed to input and output power from and to the driveshaft. In this case, the electric power-mechanical power input output assembly may have: a generator designed to input and output power; and a three shaft-type power input output structure connected to three shafts, the driveshaft, the output shaft of the internal combustion engine, and a rotating shaft of the generator, and designed to input and output power to a residual shaft based on powers input from and output to any two shafts among the three shafts.

Another aspect of the invention pertains to control method of an internal combustion engine system including: an internal combustion engine with a purification catalyst provided in an exhaust line thereof; a fuel injection module configured to inject a fuel into the internal combustion engine; an exhaust recirculation module arranged to recirculate part of exhaust of the internal combustion engine into a gas intake line of the internal combustion engine; and a temperature-reflecting physical quantity detector constructed to measure a temperature-reflecting physical quantity representing temperature of the internal combustion engine. The control method including the step of: upon satisfaction of a preset condition for preventing a temperature increase of the purification catalyst, when the temperature of the internal combustion engine represented by the temperature-reflecting physical quantity measured by the temperature-reflecting physical quantity detector is not lower than a preset reference temperature, performing a first control of controlling the exhaust recirculation module to recirculate the part of the exhaust of the internal combustion engine into the gas intake line and thereby prevent the temperature increase of the purification catalyst, and when the temperature of the internal combustion engine represented by the temperature-reflecting physical quantity measured by the temperature-reflecting physical quantity detector is lower than the preset reference temperature, performing a second control of controlling the fuel injection module to increment an amount of the fuel to be injected into the internal combustion engine and thereby prevent the temperature increase of the purification catalyst.

Upon satisfaction of the preset condition for preventing the temperature increase of the purification catalyst, when the temperature of the internal combustion engine is not lower than the preset reference temperature, the control method of this aspect of the invention performs the first control of controlling the exhaust recirculation module to recirculate the part of the exhaust of the internal combustion engine into the gas intake line and thereby prevent the temperature increase of the purification catalyst. When the temperature of the internal combustion engine is lower than the preset reference temperature, on the other hand, the control method performs the second control of controlling the fuel injection module to increment the amount of the fuel to be injected into the internal combustion engine and thereby prevent the temperature increase of the purification catalyst. This arrangement effectively prevents overheat of the purification catalyst while minimizing the fuel consumption for controlling the temperature increase of the purification catalyst.

In the control method of the invention, the step may continue the second control without abruptly stopping even when the temperature of the internal combustion engine represented by the measured temperature-reflecting physical quantity increases from a level of lower than the preset reference temperature to a level of not lower than the preset reference temperature during execution of the second control. This arrangement effectively prevents the state of the engine from becoming unstable by an abrupt switchover between the first and the second control.

In the control method of the invention, the step may perform the second control irrespective of the temperature of the internal combustion engine represented by the measured temperature-reflecting physical quantity, in the event of any abnormality arising in the exhaust recirculation module. This arrangement ensures the temperature control of the catalyst even in the case of any abnormality arising in the fuel injection module.

In the control method of the invention, the step may assume satisfaction of the preset condition when the internal combustion engine is driven in a specific high load area, or when temperature of the purification catalyst is not lower than a preset reference catalyst temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1schematically illustrates the configuration of a hybrid vehicle20equipped with an internal combustion engine system incorporated in a power output apparatus in one embodiment of the invention.FIG. 2is a schematic view showing the structure of an engine22. As illustrated, the hybrid vehicle20of the embodiment includes the engine22, a three shaft-type power distribution integration mechanism30connected via a damper28to a crankshaft26or an output shaft of the engine22, a motor MG1connected to the power distribution integration mechanism30and designed to have power generation capability, a reduction gear35attached to a ring gear shaft32aor a driveshaft linked with the power distribution integration mechanism30, a motor MG2connected to the reduction gear35, and a hybrid electronic control unit70configured to control the operations of the whole hybrid vehicle20. The engine22and an engine electronic control unit24configured to control the operations of the engine22constitute the internal combustion engine system of this embodiment.

The engine22is constructed as a six-cylinder internal combustion engine designed to consume a hydrocarbon fuel, such as gasoline or light oil, and thereby generate power. As shown inFIG. 2, the air cleaned by an air cleaner122and taken in via a throttle valve124is mixed with the atomized fuel injected from a fuel injection valve126to the air-fuel mixture. The air-fuel mixture is introduced into a combustion chamber by means of an intake valve128. The introduced air-fuel mixture is ignited with spark made by a spark plug130to be explosively combusted. The reciprocating motions of a piston132pressed down by the combustion energy are converted into rotational motions of the crankshaft26. The exhaust from the engine22goes through a catalytic converter (three-way catalyst)134designed to convert toxic components included in the exhaust, that is, carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), into harmless components and is discharged to the outside air. An EGR tube152is located after the catalytic converter134to recirculate the purified exhaust to the gas intake line. The engine22is thus designed to supply the purified exhaust as an uncombusted gas to the gas intake line and introduce the mixture of the air, the purified exhaust, and the fuel into the combustion chamber.

The engine22is under control of an engine electronic control unit (hereafter referred to as engine ECU)24. The engine ECU24is constructed as a microprocessor including a CPU24a, a ROM24bconfigured to store processing programs, a RAM24cconfigured to temporarily store data, input and output ports (not shown), and a communication port (not shown). The engine ECU24receives, via its input port, signals from various sensors designed to measure and detect the operating conditions of the engine22. The signals input into the engine ECU24include a crank position from a crank position sensor140detected as the rotational position of the crankshaft26, a cooling water temperature Tw from a water temperature sensor142measured as the temperature of cooling water in the engine22, cam positions from a cam position sensor144detected as the rotational positions of camshafts driven to open and close the intake valve128and an exhaust valve for gas intake and exhaust into and from the combustion chamber, a throttle position from a throttle valve position sensor146detected as the position of the throttle valve124, an air flow meter signal AF from an air flow meter148located in an air intake conduit, an intake air temperature from a temperature sensor149located in the air intake conduit, an air-fuel ratio from an air fuel ratio sensor135a, an oxygen signal from an oxygen sensor135b, and a catalyst temperature Tc from a catalyst temperature sensor135cattached to the catalytic converter134. The engine ECU24outputs, via its output port, diverse control signals and driving signals to drive and control the engine22. The signals output from the engine ECU24include driving signals to the fuel injection valve126, driving signals to a throttle valve motor136driven to regulate the position of the throttle valve124, control signals to an ignition coil138integrated with an igniter, control signals to a variable valve timing mechanism150to vary the open and close timings of the intake valve128, and driving signals to an EGR valve154to regulate the flow of the purified exhaust recirculated to the gas intake line. The engine ECU24establishes communication with the hybrid electronic control unit70to drive and control the engine22in response to control signals received from the hybrid electronic control unit70and to output data regarding the operating conditions of the engine22to the hybrid electronic control unit70according to the requirements. The engine ECU24also performs various arithmetic operations to compute a rotation speed of the crankshaft26or a rotation speed Ne of the engine22from the crank position input from the crank position sensor140and to compute a load factor KL representing a ratio of the amount of intake air specified by the air flow meter signal AF input from the air flow meter148to a maximum possible amount of intake air.

The power distribution and integration mechanism30has a sun gear31that is an external gear, a ring gear32that is an internal gear and is arranged concentrically with the sun gear31, multiple pinion gears33that engage with the sun gear31and with the ring gear32, and a carrier34that holds the multiple pinion gears33in such a manner as to allow free revolution thereof and free rotation thereof on the respective axes. Namely the power distribution and integration mechanism30is constructed as a planetary gear mechanism that allows for differential motions of the sun gear31, the ring gear32, and the carrier34as rotational elements. The carrier34, the sun gear31, and the ring gear32in the power distribution and integration mechanism30are respectively coupled with the crankshaft26of the engine22, the motor MG1, and the reduction gear35via ring gear shaft32a. While the motor MG1functions as a generator, the power output from the engine22and input through the carrier34is distributed into the sun gear31and the ring gear32according to the gear ratio. While the motor MG1functions as a motor, on the other hand, the power output from the engine22and input through the carrier34is combined with the power output from the motor MG1and input through the sun gear31and the composite power is output to the ring gear32. The power output to the ring gear32is thus finally transmitted to the driving wheels63aand63bvia the gear mechanism60, and the differential gear62from ring gear shaft32a.

The motors MG1and MG2are constructed as known synchronous motor generators to enable operations as both a generator and a motor. The motors MG1and MG2transmit electric power to and from a battery50via inverters41and42. Power lines54connecting the battery50with the inverters41and42are structured as common positive bus and negative bus shared by the inverters41and42. Such connection enables electric power generated by one of the motors MG1and MG2to be consumed by the other motor MG2or MG1. The battery50may thus be charged with surplus electric power generated by either of the motors MG1and MG2, while being discharged to supplement insufficient electric power. The battery50is neither charged nor discharged upon the balance of the input and output of electric powers between the motors MG1and MG2. Both the motors MG1and MG2are driven and controlled by a motor electronic control unit (hereafter referred to as motor ECU)40. The motor ECU40inputs various signals required for driving and controlling the motors MG1and MG2, for example, signals representing rotational positions of rotors in the motors MG1and MG2from rotational position detection sensors43and44and signals representing phase currents to be applied to the motors MG1and MG2from current sensors (not shown). The motor ECU40outputs switching control signals to the inverters41and42. The motor ECU40establishes communication with the hybrid electronic control unit70to drive and control the motors MG1and MG2in response to control signals received from the hybrid electronic control unit70and to output data regarding the operating conditions of the motors MG1and MG2to the hybrid electronic control unit70according to the requirements. The motor ECU40also performs arithmetic operations to compute rotation speeds Nm1and Nm2of the motors MG1and MG2from the output signals of the rotational position detection sensors43and44.

The battery50is under control of a battery electronic control unit (hereafter referred to as battery ECU)52. The battery ECU52receives diverse signals required for control of the battery50, for example, an inter-terminal voltage measured by a voltage sensor (not shown) disposed between terminals of the battery50, a charge-discharge current measured by a current sensor (not shown) attached to the power line54connected with the output terminal of the battery50, and a battery temperature Tb measured by a temperature sensor (not shown) attached to the battery50. The battery ECU52outputs data relating to the state of the battery50to the hybrid electronic control unit70via communication according to the requirements.

The hybrid electronic control unit70is constructed as a microprocessor and includes a CPU72, a ROM74that stores processing programs, a RAM76that temporarily stores data, an input-output port (not shown), and a communication port (not shown). The hybrid electronic control unit70receives various data and signals via the input port. The input data and signals include an ignition signal from an ignition switch80, a gearshift position SP from a gearshift position sensor82that detects the current position of a gearshift lever81, an accelerator opening Acc from an accelerator pedal position sensor84that detects the step-on amount of an accelerator pedal83, a brake pedal position BP from a brake pedal position sensor86that detects the step-on amount of a brake pedal85, and a vehicle speed V from a vehicle speed sensor88. The hybrid electronic control unit70is connected with the engine ECU24, the motor ECU40, and the battery ECU52via the communication port as discussed above and transmits various control signals and data to and from the engine ECU24, the motor ECU40, and the battery ECU52.

The hybrid vehicle20of the embodiment constructed as described above sets a torque demand Tr*, which is to be output to the ring gear shaft32aor the driveshaft, based on the vehicle speed V and the accelerator opening Acc determined by the driver's depression amount of the accelerator pedal83, and controls the operations of the engine22and the motors MG1and MG2to ensure output of a power demand equivalent to the preset torque demand Tr* to the ring gear shaft32a. There are several drive control modes of the engine22and the motors MG1and MG2. In a torque conversion drive mode, while the engine22is driven and controlled to output a required level of power corresponding to the power demand, the motors MG1and MG2are driven and controlled to enable all the output power of the engine22to be subjected to torque conversion by the power distribution integration mechanism30and the motors MG1and MG2and to be output to the ring gear shaft32a. In a charge-discharge drive mode, the engine22is driven and controlled to output a required level of power corresponding to the sum of the power demand and electric power used to charge the battery50or discharged from the battery50. The motors MG1and MG2are driven and controlled to enable all or part of the output power of the engine22, which is equivalent to the power demand with charge or discharge of the battery50, to be subjected to torque conversion by the power distribution integration mechanism30and the motors MG1and MG2and to be output to the ring gear shaft32a. In a motor drive mode, the motor MG2is driven and controlled to ensure output of a required level of power corresponding to the power demand to the ring gear shaft32a, while the engine22stops its operation.

The control procedure of the engine22sets a target exhaust recirculation rate EGR* as an object ratio of the amount of the purified exhaust as the uncombusted gas recirculated to the gas intake line to the amount of intake air, based on the torque demand Tr* and the vehicle speed V. The EGR valve154is driven and controlled to open at a specific angle or opening corresponding to the set target exhaust recirculation rate EGR*. The variable valve timing mechanism150is controlled to have the open and close timings of the intake valve128according to the accelerator opening Acc and the torque demand Tr*, while the throttle valve124is controlled to have a throttle opening according to a target torque Te* to be output from the engine22and the target exhaust recirculation rate EGR*. The fuel injection valve126is controlled to inject a specific amount of fuel at an adequate timing. The specific amount of fuel is set relative to the amount of intake air to attain the stoichiometric air-fuel ratio as a value to be injected from the fuel injection valve126. When the cooling water temperature Tw of the engine22does not reach a preset reference temperature Twref, recirculation of the purified exhaust to the gas intake line undesirably worsens the combustion state. In this state, the target exhaust recirculation rate EGR* is accordingly set equal to 0, which represents no recirculation of the purified exhaust to the gas intake line.

The description regards the operations of the internal combustion engine system incorporated in the power output apparatus mounted on the hybrid vehicle20having the configuration discussed above, especially a series of operation control to regulate the catalyst temperature Tc of the catalytic converter134.FIG. 3is a flowchart showing a catalyst temperature control routine executed by the engine ECU24. This catalyst temperature control routine is repeatedly performed at preset time intervals, for example, at every several ten msec.

On the start of the catalyst temperature control routine, the CPU24aof the engine ECU24first inputs various data required for control, the rotation speed Ne of the engine22, the load factor KL, the cooling water temperature Tw from the water temperature sensor142, and the catalyst temperature Tc from the catalyst temperature sensor135c(step S100). The input rotation speed Ne of the engine22is computed from the crank position of the crankshaft26detected by the crank position sensor140. The input load factor KL of the engine22is computed from the air flow meter signal AF of the air flow meter148.

After the data input, it is determined whether the input catalyst temperature Tc reaches or exceeds a preset reference temperature Tcref (step S110). The reference temperature Tcref is set to be slightly lower than an upper limit of an adequate temperature range of the catalyst in the catalytic converter134, for example, 850° C., 900° C., or 950°. When the catalyst temperature Tc is lower than the preset reference temperature Tcref (step S110: no), the catalyst in the catalytic converter134is expected to have the temperature in the adequate temperature range. The CPU24athen resets a fuel increment flag F to 0 (step S120) and exits from the catalyst temperature control routine ofFIG. 3.

When the catalyst temperature Tc is not lower than the preset reference temperature Tcref (step S110: yes), on the other hand, it is required to prevent a further increase in temperature of the catalyst in the catalytic converter134. The CPU24athen sequentially determines whether the input cooling water temperature Tw of the engine22is equal to or higher than the preset reference temperature Twref (step S130), whether the EGR valve154normally functions (step S140), and whether the fuel increment flag F is equal to 0 (step S150). When it is determined that the cooling water temperature Tw of the engine22is not lower than the preset reference temperature Twref, the EGR valve154normally functions, and the fuel increment flag F is equal to 0 (all steps S130, S140, S150: yes), the target exhaust recirculation rate EGR* is set based on the input rotation speed Ne of the engine22and the input load factor KL (step S160). The CPU24athen controls the EGR valve154to open at a specific angle or opening corresponding to the set target exhaust recirculation rate EGR* (step S170) and exits from the catalyst temperature control routine. A concrete procedure of setting the target exhaust recirculation rate EGR* in this embodiment provides and stores in advance variations in target exhaust recirculation rate EGR* against the rotation speed Ne of the engine22with regard to multiple settings of the load factor KL as an exhaust recirculation rate setting map in the ROM24band reads the target exhaust recirculation rate EGR* according to the given rotation speed Ne and the given load factor KL from the exhaust recirculation rate setting map. One example of the exhaust recirculation rate setting map is shown inFIG. 4. As shown inFIG. 4, the exhaust recirculation rate setting map is designed to increase the target exhaust recirculation rate EGR* with an increase in rotation speed Ne and with an increase in load factor KL. This is because the exhaust of the engine22tends to have high temperature and increase the temperature of the catalyst in the catalytic converter134during operation of the engine22in a high load drive area of the high rotation speed Ne and the high load factor KL. The exhaust recirculation control of recirculating part of the exhaust (uncombusted gas) of the engine22to the gas intake line effectively increases the heat capacity and lowers the temperature of the exhaust of the engine22, thus controlling the temperature increase of the catalyst in the catalytic converter134.

When the cooling water temperature Tw of the engine22is lower than the preset reference temperature Twref (step S130: no), the CPU24asets the fuel increment flag F to 1 (step S180) and sets a fuel increment amount a based on the input rotation speed Ne of the engine22and the input load factor KL (step S190). The catalyst temperature control routine is then terminated. The fuel increment amount a represents an amount of fuel to be increased from the specific amount of fuel, which is set relative to the amount of intake air to attain the stoichiometric air-fuel ratio as a value to be injected from the fuel injection valve126. A concrete procedure of setting the fuel increment amount a in this embodiment provides and stores in advance variations in fuel increment amount a against the rotation speed Ne of the engine22with regard to multiple settings of the load factor KL as a fuel increment amount setting map in the ROM24band reads the fuel increment amount a according to the given rotation speed Ne and the given load factor KL from the fuel increment amount setting map. One example of the fuel increment amount setting map is shown inFIG. 5. As shown inFIG. 5, the fuel increment amount setting map is designed to increase the fuel increment amount a with an increase in rotation speed Ne and with an increase in load factor KL. This is because the exhaust tends to have high temperature and increase the temperature of the catalyst in the catalytic converter134during operation of the engine22in the high load drive area of the high rotation speed Ne and the high load factor KL. The fuel increment control of increasing the specific amount of fuel, which is set relative to the amount of intake air to attain the stoichiometric air-fuel ratio as a value to be injected from the fuel injection valve126, by the fuel increment amount a effectively utilizes the latent heat of vaporization in the increased amount of fuel to exert the cooling effect, thus controlling the temperature increase of the catalyst in the catalytic converter134.

It is here assumed that the driver presses down the accelerator pedal83to a significantly large depth immediately after a start of the engine22in the cold state. In this case, the engine22is driven in a high load area of the relatively high rotation speed and the high torque. The exhaust accordingly tends to have high temperature and abruptly increases the temperature of the catalyst in the catalytic converter134. In some conditions, the catalyst temperature Tc of the catalytic converter134reaches or exceeds the preset reference temperature Tcref, before the cooling water temperature Tw becomes equal to or higher than the preset reference temperature Twref. At the cooling water temperature Tw of lower than the preset reference temperature Twref, the combustion state in the engine22is rather unstable, so that the exhaust recirculation control of recirculating part of the exhaust to the gas intake line is not allowable. When the cooling water temperature Tw is lower than the preset reference temperature Twref (step S130: no), the catalyst temperature control routine performs the fuel increment control (step S190) to increase the specific amount of fuel, which is set relative to the amount of intake air to attain the stoichiometric air-fuel ratio as a value to be injected from the fuel injection valve126, by the fuel increment amount α. Even in the state of not allowing the exhaust recirculation control, the fuel increment control is performed to effectively control the temperature increase of the catalyst in the catalytic converter134. The fuel increment control causes the fuel injection valve126to inject the increased amount of fuel corresponding to the fuel increment amount α. Injection of the increased amount of fuel naturally worsens the fuel consumption. The fuel increment control is, however, performed only when the cooling water temperature Tw is lower than the preset reference temperature Twref. This arrangement desirably minimizes the potential deterioration of fuel consumption.

In the event of detection of any abnormality in the EGR valve154(step S140: no), the exhaust recirculation control is not allowable even at the cooling water temperature Tw of not lower than the preset reference temperature Twref (step S130: yes). The CPU24athen sets the fuel increment flag F to 1 (step S180) and specifies the fuel increment amount a (step S190) to perform the fuel increment control. Namely in the event of some abnormality arising in the EGR valve154, the fuel increment control is performed, irrespective of the level of the cooling water temperature Tw. The fuel increment flag F1set to 1 implies execution of the fuel increment control. In response to detection of the fuel increment flag F1set to 1 (step S150: no), the catalyst temperature control routine does not perform the exhaust recirculation control (steps S160and S170) but continues the fuel increment control (step S190) even at the cooling water temperature Tw of not lower than the preset reference temperature Twref (step S130: yes) with no abnormality arising in the EGR valve154(step S140: yes). This arrangement effectively prevents the state of the engine22from becoming unstable by an abrupt switchover of the control from the fuel increment control to the exhaust recirculation control.

As described above, under the condition that the catalyst temperature Tc reaches or exceeds the preset reference temperature Tcref, when the cooling water temperature Tw is not lower than the preset reference temperature Twref, the internal combustion engine system of the embodiment sets the target exhaust recirculation rate EGR* based on the rotation speed Ne of the engine22and the load factor KL and performs the exhaust recirculation control to open the EGR valve154at a specific angle or opening corresponding to the set target exhaust recirculation rate EGR*. When the cooling water temperature Tw is lower than the preset reference temperature Twref, on the other hand, the internal combustion engine system of the embodiment sets the fuel increment amount a based on the rotation speed Ne of the engine22and the load factor KL and performs the fuel increment control to increase the specific amount of fuel, which is set relative to the amount of intake air to attain the stoichiometric air-fuel ratio as a value to be injected from the fuel injection valve126, by the set fuel increment amount α. This arrangement effectively controls the temperature increase of the catalyst in the catalytic converter134even in the state of not allowing the exhaust recirculation control where the cooling water temperature Tw is lower than the preset reference temperature Twref. This arrangement desirably minimizes the deterioration of fuel consumption, compared with the conventional fuel increment control performed consistently to control the temperature increase of the catalyst. The fuel increment control does not abruptly stop but continues even when the cooling water temperature Tw becomes equal to or higher than the preset reference temperature Twref during execution of the fuel increment control. This arrangement effectively prevents the state of the engine22from becoming unstable by an abrupt switchover of the control from the fuel increment control to the exhaust recirculation control. In the event of some abnormality arising in the EGR valve154, the fuel increment control is performed, irrespective of the level of the cooling water temperature Tw. The catalyst temperature control of this embodiment thus ensures the temperature control of the catalyst even in the case of any abnormality arising in the EGR valve154.

The internal combustion engine system of the embodiment does not abruptly stop but continues the fuel increment control even when the cooling water temperature Tw becomes equal to or higher than the preset reference temperature Twref during execution of the fuel increment control. One modification may switch over the control from the fuel increment control to the exhaust recirculation control upon satisfaction of a predetermined condition.

The internal combustion engine system of the embodiment determines whether the EGR valve154normally functions and, in the event of detection of any abnormality in the EGR valve154, performs the fuel increment control. One modification of the catalyst temperature control routine may omit such detection for any abnormality of the EGR valve154from the catalyst temperature control routine when not required.

The internal combustion engine system of the embodiment specifies the requirement for preventing the temperature increase of the catalyst in the catalytic converter134according to the catalyst temperature Tc measured by the catalyst temperature sensor135c. One modification may determine whether the engine22is driven in the high load area of the high rotation speed and the high torque based on the rotation speed Ne of the engine22and the load factor KL and may specify the requirement for preventing the temperature increase of the catalyst in the catalytic converter134according to the result of such determination. Another modification may specify the requirement for preventing the temperature increase of the catalyst in the catalytic converter134according to another parameter.

In the hybrid vehicle20of the embodiment, the power of the motor MG2is subjected to speed change by the reduction gear35and is output to the ring gear shaft32a. The technique of the invention is, however, not restricted to this configuration but is also applicable to a hybrid vehicle120of one modified structure shown inFIG. 6. In the hybrid vehicle120ofFIG. 6, the power of the motor MG2is output to another axle (axle linked with wheels64aand64b) that is different from the axle connecting with the ring gear shaft32a(axle linked with the drive wheels63aand63b). In the hybrid vehicle20of the embodiment, the power of the engine22is transmitted via the power distribution integration mechanism30to the ring gear shaft32aas the driveshaft linked with the drive wheels63aand63b. The technique of the invention is, however, not restricted to this configuration but is also applicable to a hybrid vehicle220of another modified structure shown inFIG. 7. The hybrid vehicle220ofFIG. 7is equipped with a pair-rotor motor230. The pair-rotor motor230includes an inner rotor232connected to the crankshaft26of the engine22and an outer rotor234connected to the drive shaft arranged to output power to the drive wheels63aand63b. The pair-rotor motor230transmits part of the output power of the engine22to the driveshaft, while converting the residual engine output power into electric power. The technique of the invention is also applicable to an automobile320of a conventional structure driven with the power of the engine22that is subjected to speed change by an automatic transmission330and is output to the drive wheels63aand63bas shown inFIG. 8.

The embodiment regards the internal combustion engine system incorporated in the power output apparatus mounted on the hybrid vehicle20. The principle of the invention is also attainable as an internal combustion engine system incorporated in a power output apparatus mounted on any of various vehicles other than the hybrid vehicles as well as any of various other moving bodies including ships and boats and aircraft. The principle of the invention is further attainable as an internal combustion engine system incorporated in a power output apparatus built in diversity of stationary equipment, such as construction machinery. The internal combustion engine system may be not part of such a power output apparatus but may be constructed separately from the power output apparatus. Another application of the invention is a control method of the internal combustion engine system.

The primary elements in the embodiment and its modified examples are mapped to the primary constituents in the claims of the invention as described below. The engine22of the embodiment is equivalent to the ‘internal combustion engine’ of the invention. The combination of the fuel injection valve126with the engine ECU24configured to control the fuel injection valve126corresponds to the ‘fuel injection module’ of the invention. The combination of the EGR pipe152and the EGR valve154with the engine ECU24configured to control the EGR valve154corresponds to the ‘exhaust recirculation module’ of the invention. The water temperature sensor142is equivalent to the ‘temperature-reflecting physical quantity detector’ of the invention. The engine ECU24configured to perform the catalyst temperature control routine ofFIG. 3is equivalent to the ‘temperature increase controller’ of the invention. Under the condition that the catalyst temperature Tc reaches or exceeds the preset reference temperature Tcref, when the cooling water temperature Tw is not lower than the preset reference temperature Twref, the catalyst temperature control routine ofFIG. 3sets the target exhaust recirculation rate EGR* based on the rotation speed Ne of the engine22and the load factor KL and performs the exhaust recirculation control to open the EGR valve154at a specific angle or opening corresponding to the set target exhaust recirculation rate EGR*. When the cooling water temperature Tw is lower than the preset reference temperature Twref, on the other hand, the catalyst temperature control routine ofFIG. 3sets the fuel increment amount a based on the rotation speed Ne of the engine22and the load factor KL and performs the fuel increment control to increase the specific amount of fuel, which is set relative to the amount of intake air to attain the stoichiometric air-fuel ratio as a value to be injected from the fuel injection valve126, by the fuel increment amount α. The combination of the power distribution integration mechanism30with the motor MG1in the embodiment or the pair-rotor motor230in the modified example corresponds to the ‘electric power-mechanical power input output assembly’ of the invention. The motor MG2, the motor MG1, and the power distribution integration mechanism30are respectively equivalent to the ‘motor’, the ‘generator’, and the ‘three shaft-type power input output structure’ of the invention. The ‘internal combustion engine’ is not restricted to the engine22designed to consume a hydrocarbon fuel, such as gasoline or light oil, and thereby output power, but may be an internal combustion engine of any other design, for example, a hydrogen engine. The ‘fuel injection module’ is not restricted to the combination of the fuel injection valve126with the engine ECU24configured to control the fuel injection valve126but may be any configuration of enabling injection of the fuel into the internal combustion engine. The ‘exhaust recirculation module’ is not restricted to the combination of the EGR pipe152and the EGR valve154with the engine ECU24configured to control the EGR valve154but may be any configuration of regulating the exhaust recirculation rate as the ratio of the amount of exhaust recirculated to the gas intake line of the internal combustion engine to the amount of intake air and recirculating the exhaust to the gas intake line at the regulated exhaust recirculation rate. The ‘temperature increase controller’ is not restricted to the engine ECU24configured to perform the catalyst temperature control routine ofFIG. 3that, under the condition of the catalyst temperature Tc of not lower than the preset reference temperature Tcref, at the cooling water temperature Tw of not lower than the preset reference temperature Twref, sets the target exhaust recirculation rate EGR* based on the rotation speed Ne of the engine22and the load factor KL and performs the exhaust recirculation control to open the EGR valve154at a specific angle or opening corresponding to the set target exhaust recirculation rate EGR*, while at the cooling water temperature Tw of lower than the preset reference temperature Twref, setting the fuel increment amount a based on the rotation speed Ne of the engine22and the load factor KL and performing the fuel increment control to increase the specific amount of fuel, which is set relative to the amount of intake air to attain the stoichiometric air-fuel ratio as a value to be injected from the fuel injection valve126, by the fuel increment amount α. The ‘temperature increase controller’ may be any configuration that, upon satisfaction of a preset condition for preventing a temperature increase of the purification catalyst, when the temperature of the internal combustion engine represented by the temperature-reflecting physical quantity measured by the temperature-reflecting physical quantity detector is not lower than the preset reference temperature, performs the first control of controlling the exhaust recirculation module to recirculate part of the exhaust of the internal combustion engine into the gas intake line and thereby prevent the temperature increase of the purification catalyst, and when the temperature of the internal combustion engine represented by the temperature-reflecting physical quantity measured by the temperature-reflecting physical quantity detector is lower than the preset reference temperature, performs the second control of controlling the fuel injection module to increment the amount of the fuel to be injected into the internal combustion engine and thereby prevent the temperature increase of the purification catalyst. The ‘electric power-mechanical power input output assembly’ is not restricted to the combination of the power distribution integration mechanism30with the motor MG2or to the pair-rotor motor230but may be any structure connected with the driveshaft and with the output shaft of the internal combustion engine in a rotatable manner independently of the driveshaft and configured to output the torque to the driveshaft and to the output shaft through input and output of electric power and mechanical power. The ‘motor’ is not restricted to the motor MG2constructed as a synchronous motor generator but may be any type of motor designed to input and output power from and to the driveshaft, for example, an induction motor. The ‘generator’ is not restricted to the motor MG1constructed as a synchronous motor generator but may be any type of generator designed to input and output power, for example, an induction motor generator. The ‘three shaft-type power input output structure’ is not restricted to the power distribution integration mechanism30but may be any structure connected to three shafts, the driveshaft, the output shaft of the internal combustion engine, and the rotating shaft of the generator, and designed to input and output power to a residual shaft based on powers input from and output to any two shafts among the three shafts, for example, a structure adopting a double pinion-type planetary gear mechanism, a structure connected to four or a greater number of shafts by combination of multiple planetary gear mechanisms, or a structure adopting a differential gear or another differential motion mechanism other than the planetary gear mechanism. The above mapping of the primary elements in the embodiment and its modified examples to the primary constituents in the claims of the invention is not restrictive in any sense but is only illustrative for concretely describing the modes of carrying out the invention. Namely the embodiment and its modified examples discussed above are to be considered in all aspects as illustrative and not restrictive.

The embodiment discussed above is to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention.

The present invention claims priority from Japanese Patent Application No. 2007-110844 filed on Apr. 19, 2007, the entire contents of which are incorporated herein by reference.