WO2008059337A2

WO2008059337A2 - Fuel property estimation device for hybrid vehicle, and hybrid vehicle

Info

Publication number: WO2008059337A2
Application number: PCT/IB2007/003442
Authority: WO
Inventors: Yasuyuki Irisawa
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-11-13
Filing date: 2007-11-12
Publication date: 2008-05-22
Also published as: WO2008059337A3; JP2008120266A

Abstract

A fuel property estimation device (100) for a hybrid vehicle (10) is provided. The hybrid vehicle includes a supply device that supplies fuel, an internal combustion engine (200) that outputs power to a drive shaft (205), a motor (MG2) that outputs power to the drive shaft, a generator (MG1) that generates electricity using the power output from the internal combustion engine, and a battery (500) charged by the electric power generated by the generator. The fuel property estimation device includes a determining unit that determines a difference between an actual output power of the internal combustion engine and a required power; a first controller that controls the motor and the generator in accordance with the determined difference, such that the required power is output to the drive shaft; and an estimation unit that estimates a fuel property of the fuel in accordance with the determined difference.

Description

FUEL PROPERTY ESTIMATION DEVICE FOR HYBRID VEHICLE,

AND HYBRID VEHICLE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] This invention relates to a fuel property estimation device that estimates a fuel property for a hybrid vehicle having, for example, an electric motor and an internal combustion engine as power sources, and to a hybrid vehicle having such a fuel property estimation device.

2. Description of the Related Art

[0002] The fuel property influences the output power of the internal combustion engine. Under the condition in which the actual output power does not meet the required output power due to the change in fuel property, i.e., the abnormality occurs in the output power of the internal combustion engine, drivability may be extremely degraded.. Therefore, when the change in the fuel property occurs, the change must be detected immediately.

[0003] Japanese Patent Application Publication No. 2002-201997 (JP-A-2002-201997) describes, for example, a device that determines a fuel cetane number to detect the fuel property. The fuel property determining device for an internal combustion engine described in JP-A-2002-201997 detects the length of time required for the complete fuel combustion and the temperature of the coolant at the time of start-up when the internal combustion engine is started with the cranking engine speed remaining constant, and determines the fuel cetane number accurately with reference to a map prepared in advance.

[0004] Further, Japanese Patent Application Publication No. 9-140006 describes that, for example, the degradation of drivability due to the change in the fuel property is prevented by controlling an assist force of the electric motor in accordance with the result of knocking detection.

[0005] In the technology described in JP-A-2002-201997, because the fuel property is determined only at the engine start-up, it is difficult to detect the change in the fuel property over time. Further, due to the influences from frictions and influences from battery voltages, it is difficult to maintain the cranking engine speed constant. Thus, practically, the opportunities to determine the fuel property are likely to be extremely restricted. Further, if the cranking engine speed is not maintained constant, the accuracy of the detection is consequently reduced. In other words, it may be practically difficult for the technology described in JP-A-2002-201997 to detect the fuel property rapidly and accurately. Further, the above-described degradation of drivability occurs even during the process to detect the fuel property, it is difficult for the technology described in JP-A-2002-201997 to avoid such degradation of drivability. Such phenomenon may occur similarly in the hybrid vehicle having an electric motor as a power source in addition to an internal combustion engine.

SUMMARY OF THE INVENTION

[0006] The present invention provides a fuel property estimation device for a hybrid vehicle that estimates a fuel property rapidly and accurately, while the degradation of the drivability is minimized. A hybrid having such a fuel property estimation device is also provided.

[0007] An aspect of the present invention provides a fuel property estimation device for a hybrid vehicle. The hybrid vehicle is provided with a supply device that supplies fuel, an internal combustion engine that outputs power to a drive shaft connecting to an axle, a motor that outputs power to the drive shaft, a generator that generates electricity by using the power output from the internal combustion engine, and a battery that is charged by electric power obtained by the electricity generated by the generator. The fuel property estimation device includes a determining unit that determines a difference between actual output power of the internal combustion engine and required output power (i.e., excess or deficiency of the actual output power from the required output power). The fuel property estimation device further includes a first controller that controls the motor and the generator in accordance with the difference determined by the determining unit, such that the required output power is output to the drive shaft; and an estimation unit that estimates a fuel property of the fuel in accordance with the difference determined by the determining unit.

[0008] The internal combustion engine of the hybrid vehicle may be provided with an engine having, for example, multiple cylinders, and supply means, such as electrically controlled injectors, that supply fuel, such as gasoline, light oil, or alcohol, to the combustion chambers in respective cylinders. The internal combustion engine may output the combustion power generated by the combustion of fuel as power such as torque via the mechanical transmission path, such as a piston or a connecting rod, and a crankshaft. Thus, the internal combustion engine may include, for example, a 2-cycle or 4-cycle reciprocating engine. Such an internal combustion engine directly or indirectly outputs power, such as torque, to the drive shaft connecting to the axle.

[0009] The hybrid vehicle may be further provided with a motor as a power source, in addition to the internal combustion engine. The motor also outputs power, such as torque, to the drive shaft. There is no limitation in determining in what ratio the output power to the axle is supplied by the internal combustion engine and the motor. For example, the internal combustion engine may be used as a main power source, and the power of the motor may assist the power of the internal combustion engine as appropriate. Alternatively, for example, the motor may be used as a main power source, and the power of the engine may assist the power of the motor as appropriate. Further alternatively, the distribution ratio between the power of the internal combustion engine and the power of the motor may be determined mutually cooperatively in each case, such that the operation efficiency of the internal combustion engine or of the entire hybrid system is optimized.

[0010] The hybrid vehicle is also provided with the generator that is driven by a portion of power from the internal combustion engine to generate electricity. The battery is charged with the electric power obtained by the electric generation by the generator. [0011] The stoichiometric air fuel ratio changes depending on the fuel property of the fuel supplied to combust in the internal combustion engine. For example, if fuel having a high alcohol content ratio (i.e., the stoichiometric air fuel ratio < 14.6) is supplied under the condition that the stoichiometric air fuel ratio (about 14.6) of gasoline is used as a standard, the amount of supplied fuel becomes insufficient, thereby reducing the output power of the internal combustion engine. On the other hand, if a fuel having a stoichiometric air fuel ratio greater than 14.6 is supplied, the amount of supplied fuel becomes excessive, thereby increasing the output power of the internal combustion engine. In other words, difference occurs between the actual output power of the internal combustion engine and the required output power depending upon the fuel property. When the actual output power of the internal combustion engine continues to be different from the required output power, drivability may be degraded.

[0012] Therefore, in the fuel property estimation device for the hybrid vehicle according to the first aspect of the present invention, when the device is operating, the determining unit determines the difference between the actual output power and the required output power. The determining unit may be implemented by various processing units, such as ECUs (Electronic Control Units), various computer systems, such as various controllers or microcomputer devices, or the like.

[0013] Here, "determining" is a broad concept including the following. That is, the "determining" may be accomplished, for example, by obtaining, directly or indirectly through some detecting means, a target object itself, or a physical quantity or physical state correlating with the target object, as an electric signal. The "determining" may also be accomplished by selecting an appropriate value from a map that is stored in advance in an appropriate storage means based on the directly or indirectly detected physical quantity or physical state correlating with the target object. The "determining" may further be accomplished by performing calculation or estimation from the obtained or selected physical quantity or physical state correlating with the target object, in accordance with a preset algorithm, computation expression, or the like.

[0014] When the determining unit determines the difference between the actual output power and the required output power, the required output power is determined as a result of calculation or by selecting an appropriate value from an appropriate map, based on, for example, an amount of depression of an acceleration pedal (sometimes referred to as an "accelerator angle," hereinafter) and a vehicle speed. Meanwhile, the actual output power is determined as a result of calculation or by selecting an appropriate value from an appropriate map, based on, for example, reaction torque corresponding to torque of the internal combustion engine detected by the generator or the motor, and the engine speed of the internal combustion engine.

[0015] The difference between the actual output power and the required output power is thus determined, and the first controller then controls the motor and the generator in accordance with the determined difference between the actual output power and the required output power, such that the required output power is output to the drive shaft. Here, the first controller may be implemented by various processing units, such as ECUs, various computer systems, such as various controllers or microcomputer devices, or the like. When the motor outputs power to the drive shaft, the total power output to the drive shaft increases. Thus, the shortage of the output power of the internal combustion engine is compensated for. Further, when a portion of the output power of the internal combustion engine is used to generate electricity, the total power output to the drive shaft decreases. Thus, the excess of the output power of the internal combustion engine is compensated for.

[0016] By controlling the motor and the generator as described above, although the abnormality in the output power of the internal combustion engine actually occurs (i.e., the actual output power of the internal combustion engine is different from the required output power) due to the change in the fuel property, the required output power is output to the drive shaft. Accordingly, the degradation of drivability due to the abnormality in the output power of the internal combustion engine is prevented, or the time period in which the degradation of the drivability occurs is shortened to the extent that the degradation is not practically apparent.

[0017] At this time, even if the abnormality in the output power of the internal combustion engine is corrected as describe above (i.e., by the motor and the generator), the abnormality in the output power may continue, because the change in the fuel property is not reflected in the amount of fuel supplied to the internal combustion engine. Therefore, the fuel property must be estimated accurately to fundamentally remove such abnormality. Accordingly, in the fuel property estimation device for the hybrid vehicle, when the determining unit determines the difference between the actual output power and the required output power, the estimation unit estimates the fuel property in accordance with the determined difference (excess or deficiency), in addition to the above-described control of the motor and the generator to compensate for the abnormality in the output power of the internal combustion engine. The estimation unit may be implemented by, for example, various processing units, such as ECUs, various computer systems, such as various controllers or microcomputer devices, or the like.

[0018] As described above, because the fuel property is correlated with the excess/deficiency amount of the actual output power of the internal combustion engine, the fuel property may be estimated in the following manner. For example, if a correspondence relationship between an index value that defines the fuel property (e.g. a stoichiometric air fuel ratio of actual fuel, or a component ratio of the fuel) and the excess/deficiency amount is known in advance experimentally, empirically, theoretically, or based on the simulation, or the like, or can be predicted, such a correspondence relationship may be stored in a map. The fuel property may be estimated by selecting an appropriate index value, or an appropriate component ratio from the map. Alternatively, the fuel property may be estimated as a result of a numeric operation based on the correspondence relationship.

[0019] The method of the estimation by the estimation unit is not limited to the above, as long as it estimates the fuel property. For example, the estimation may be qualitative estimation to determine whether the fuel has a relatively low calorific value or a relatively high calorific value. Alternatively, the estimation may be quantitative estimation to obtain the more specific stoichiometric air fuel ratio or calorific value per unit quantity. Further alternatively, an index value that defines a basic fuel property that is set in advance or a correction amount to correct the index value that is currently used in the fuel supply control may be estimated.

[0020] As described above, by controlling the motor and the generator mounted on the hybrid vehicle, the degradation of drivability due to the excess or deficiency of the actual output power caused by the change in the fuel property (e.g. when the fuel property of 100% gasoline fuel is set as a reference, the change from the reference value) is prevented or reduced. In addition thereto, the fuel property is estimated rapidly and accurately based on the excess/deficiency amount of the actual output power or, in other words, the controlled variables of the motor and the generator.

[0021] The hybrid vehicle may include a power distribution mechanism that distributes the actual output power of the internal combustion engine to the input shaft and the drive shaft in predetermined proportions. A portion of the actual output power of the internal combustion engine distributed to the input shaft by the power distribution mechanism may be input to the generator via the input shaft. The motor may be driven by power supplied from the battery or electric power obtained from the electricity generated by the generator. The determining unit may determine the difference between the actual output power and the require output power in accordance with the portion of the actual output power distributed to the input shaft and is input to the generator via the input shaft.

[0022] Thus, the hybrid vehicle is provided with the power distribution mechanism, such as a planetary gear unit. The power distribution mechanism distributes the power of the internal combustion engine to the input shaft and the drive shaft in predetermined proportions. The input shaft is connected to the generator and a portion of the power of the internal combustion engine is input to the generator via the input shaft. Further, the motor connected to the drive shaft is driven by the electric power supplied from the battery or the electric power generated by the generator.

[0023] According to the above, a portion of the power of the internal combustion engine is used to generate electricity, and the generated electric power drives the motor. As a result, for example, the internal combustion engine always operates at the operation point with the most appropriate fuel consumption rate (hereinafter, sometimes referred to as "fuel mileage"). In other words, the power distribution among the internal combustion engine, the motor and the generator is optimized, thereby optimizing the operation efficiency of the hybrid vehicle.

[0024] In the above, the determining unit determines the above-described excess/deficiency amount based on the power of internal combustion engine input to the generator. At this time, for example, the torque of the internal combustion engine may be detected based on the reaction torque corresponding to the portion of the torque of the internal combustion engine input to the generator, and the detected torque of internal combustion engine is used to determine the actual output power of the internal combustion engine. In other words, because the generator may function as a torque sensor, the accuracy of determination of the actual output power of the internal combustion engine improves, thereby eventually improving the accuracy of determination of the excess/deficiency amount.

[0025] In the fuel estimation device for the hybrid vehicle, the first controller may control the motor to output the power to the drive shaft when the actual output power is lower than the required output power, and the first controller may further control the generator to use the portion of the actual output power of the internal combustion engine to generate electricity when the actual output power is higher than the required output power.

[0026] Thus, when the actual output power is lower than the required output power, the motor is controlled to output the power to the drive shaft. On the other hand, when the actual output power is higher than the required output power, the excessive power is used to generate electricity. Accordingly, even in the period when the fuel property is being estimated, the degradation of drivability of the hybrid vehicle due to the abnormality in the output power of the internal combustion engine is minimized.

[0027] The internal combustion engine may be provided with a booster that is driven by exhaust pressure to boost the pressure of air supplied to the engine, and a boost pressure regulator that regulates a boost pressure of the booster. The first controller may control the boost pressure regulator in accordance with the difference between the actual output power and the required output power such that the required output power is output to the drive shaft.

[0028] Thus, the internal combustion engine includes a booster, such as a turbocharger. Therefore, the pressure of air supplied to the engine is boosted in accordance with the pressure of exhaust gas (hereinafter, referred to as "exhaust pressure"). Further, the internal combustion engine is provided with the boost pressure regulator, such as a wastegate valve (hereinafter, sometimes referred to as "WGB") or a variable convergent nozzle (hereinafter, sometimes referred to as "VN"). For example, the boost pressure is adjusted or regulated by creating a bypass that conducts exhaust gas to the exhaust system, such as a rear pipe, or by restricting the exhaust gas to flow in the turbine of the booster.

[0029] Because the state of charge (SOC) of the battery constantly changes, the power assist and power absorption by the motor and the generator may be difficult depending on the battery SOC. For example, when the SOC of the battery is relatively low, power assist by the motor is difficult. On the other hand, when the SOC of the battery is at nearly full charge, power absorption by generating electricity is difficult. Therefore, in some cases, the degradation of drivability due to the change in the fuel property may become apparent.

[0030] However, if the booster and the boost pressure regulator are provided, the output power of the internal combustion engine may be adjusted by changing the boost pressure, thereby correcting the abnormality in the output power of the internal combustion engine. In other words, the fuel property may be estimated rapidly and accurately while the abnormality in the output power is corrected regardless of the battery state.

[0031] The boost pressure regulator may include an open-close valve that regulates an amount of the exhaust gas flowing into the booster in accordance with an open-close state of the open-close valve.

[0032] The physical, mechanical or electrical construction of the boost pressure regulator is not limited to the above, as long as it regulates the boost pressure. However, it is effective and efficient if the open-close valve, such as the above-described WGV or VN, is included.

[0033] In the case where the hybrid vehicle includes the booster, after the first controller controls the boost pressure regulator in accordance with the difference between the actual output power of the internal combustion engine and the required output power, the first controller may control the motor and the generator such that the required output power is output to the drive shaft.

[0034] The accuracy of the correction of the output power (torque) of the internal combustion engine by the boost pressure regulator is likely to be lower, as compared with the accuracy of the correction of output power (torque) of the internal combustion engine by the motor and the generator. Therefore, it may sometimes be practically difficult to output the power corresponding to the required output power to the drive shaft by the control of the boost pressure regulator alone. Meanwhile, the motor and the generator are capable of controlling torque with relatively high accuracy, as well as controlling the rotation thereof with relatively high accuracy. Therefore, by correcting the abnormality in the output power by the motor and generator after eliminating a part of the abnormality in the output power by regulating the boost pressure, the abnormality in the output power of the internal combustion engine is compensated for while the load applied to the motor and the generator is reduced. This is practically highly beneficial.

[0035] The estimation unit may estimate the fuel property at least one of when the difference between the actual output power and the required output power is no less than a predetermined upper limit and when the difference is lower than a predetermined lower limit.

[0036] The change in the actual output power of the internal combustion engine is not always influenced only by the fuel property. For example, the actual output power of the internal combustion engine may change due to the influences of various factors, such as intake/exhaust valve timing, ignition timing of ignition devices, conditions in the combustion chambers, combustion state of air-fuel mixture, exhaust pressure, coolant temperature, ambient temperature or humidity. Of course, when the actual output power is different from the required output power, the correction of the output power by controlling the motor and the generator is effective. However, feedback of all the changes in the output power caused by the various factors to estimate the fuel property may result in an erroneous learning of the fuel property. Thus, the accuracy of the estimation of the fuel property may be degraded.

[0037] Here, for example, the upper limit and the lower limit that define the range of change in the output power that could occur in a normal operation of the internal combustion engine without the change in the fuel property (i.e., not abnormal) are set in advance experimentally, empirically, theoretically or based on simulations or the like. Then, at least one of when the determined excess/deficiency amount is no less than the upper limit and when the excess/deficiency amount is smaller than the lower limit (preferably both), the fuel property is estimated. By doing this, the change in the output power of the internal combustion engine that is not caused by the change in the fuel property is prevented from being used in the estimation of the fuel property, thereby maintaining the accuracy of estimation of the fuel property. In this case, it does not matter whether the motor and the generator compensate for the change in the output power of the internal combustion engine or not.

[0038] The fuel property estimation device may includes a correction unit that corrects an amount of the fuel supplied from the supply device in accordance with the fuel property estimated by the estimation unit, and a second controller that controls the supply device to supply the corrected amount of the fuel.

[0039] In this case, the correction unit may be implemented by, for example, various processing units, such as an ECU, various computer systems, such as various controllers or microprocessor devices, or the like. The correction unit corrects the supply amount of the fuel based on the fuel property estimated by the estimation unit. Further, the

VJ second controller may be implemented by, for example, various processing units, such as an ECU, various computer systems, such as various controllers or microprocessor devices, or the like. The second controller controls the supply device to supply the corrected supply amount of the fuel.

[0040] Accordingly, the estimation result of the fuel property is reflected in the actual supply amount of the fuel, thereby the abnormality in the output power of the internal combustion engine is fundamentally removed. In this case, the estimation unit estimates the fuel property rapidly and accurately. Therefore, the time period in which the abnormality in the output power of the internal combustion engine continues (the time period in which the correction has been made and a regular power corresponding to the required output power is being output to the drive shaft) is sufficiently short. In other words, the correction unit and the second controller swiftly shorten the period in which the performance of the internal combustion engine is degraded. Accordingly, the opportunities in which the motor, the generator, or the boost pressure regulator are used to correct the output power of the internal combustion engine are reduced, thereby reducing the physical, mechanical or electrical load.

[0041] Another aspect of the invention provides a hybrid vehicle that includes a supply device that supplies fuel; an internal combustion engine that outputs an actual output power to a drive shaft connecting to an axle; a motor that outputs power to the drive shaft; a generator that generates electricity by using a portion of the actual power output from the internal combustion engine; a battery that is charged by the power obtained by the electricity generated by the generator; a determining unit that determines a difference between the actual output power of the internal combustion engine and a required output power; a first controller that controls the motor and the generator in accordance with the difference determined by the determining unit, such that the required output power is output to the drive shaft; an estimation unit that estimates a fuel property of the fuel supplied by the supply device in accordance with the difference determined by the determining unit; a correction unit that corrects an amount of the fuel supplied from the supply device in accordance with the fuel property estimated by the estimation unit; and a second controller that controls the supply device to supply the corrected amount of the fuel.

[0042] According to this aspect of the present invention, because the fuel property is estimated rapidly and accurately and the estimated fuel property is used to adjust the amount of the fuel to be supplied, the degradation of drivability of the hybrid vehicle is effectively reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG 1 is a block diagram illustrating a hybrid vehicle according to a first embodiment of the present invention;

FIG 2 is a schematic view illustrating a power distribution mechanism of the hybrid vehicle shown in FIG 1 and its relationship with its peripheral portions; FIG 3 is a schematic view illustrating an engine of the hybrid vehicle shown in FIG 1; FIG 4 is a schematic view of a map illustrating an engine operation region; FIG 5 is a flowchart illustrating an injection amount control process performed by an ECU;

FIG 6 is a schematic view illustrating an engine according to a second embodiment of the present invention;

FIG 7 is a flowchart illustrating an injection amount control process performed by the ECU in the hybrid vehicle having the engine shown in FIG 6.

DETAILED DESCRIPTION OF EMBODIMENTS [0044] The embodiments of the present invention are explained in detail with reference to the drawings. First, a hybrid vehicle 10 of the first embodiment of the present invention is explained with reference to FIG 1. FIG 1 is a block diagram illustrating the hybrid vehicle 10.

[0045] In Fig. 1, the hybrid vehicle 10 includes an axle 11, wheels 12, an ECU

(Electronic Control Unit) 100, an engine 200, a motor generator MGl, a motor generator MG2, a power distribution mechanism 300, an inverter 400, a battery 500, an SOC sensor 600, a vehicle speed sensor 700 and an accelerator position sensor 800.

[0046] The axle 11 is a shaft that transmits power output from the engine 200 and the motor generator MG2 to the wheels. The wheels 12 further transmit the power transmitted from the axle 11 to a road surface. FIG 1 only shows a single right wheel and a single left wheel; however, the hybrid vehicle 10 actually has totally four wheels, i.e., front-right, front-left, rear-right and rear-left wheels.

[0047] The ECU (Electronic Control Unit) 100 has a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and controls the entire action of the hybrid vehicle 10. The ECU 100 may be regarded as an example of the fuel property estimation device for the hybrid vehicle of the present invention. The ECU 100 performs an injection amount control process in accordance with a control program stored in the ROM as described below.

[0048] The engine 200 is a gasoline engine, which is an example of an internal combustion engine, and functions as a main power source of the hybrid vehicle 10. The construction of the engine 200 is described in detail later.

[0049] The motor generator MGl functions as an electric generator that charges the battery 500 and supplies electric power to the motor generator MG2. The motor generator MGl also functions as an electric motor that assists drive power of the engine 200. The motor generator MGl may be regarded as an example of the generator of the present invention.

[0050] The motor generator MG2 functions as an electric motor that assists the drive power of the engine 200, and also functions as an electric generator that charges the battery 500. The motor generator MG2 may be regarded as an example of the motor of the present invention.

[0051] The motor generator MGl and the motor generator MG2 may be synchronous motor generators, each of which includes a rotor having multiple permanent magnets on its outer peripheral surface, and a stator around which a three-phase coil is wound to create a rotating magnetic field. However, the other type of motor generator may be used as well.

[0052] The power distribution mechanism 300 includes a planetary gear mechanism that distributes the output of the engine 200 to the motor generator MGl and the axle 11.

[0053] The construction of the power distribution mechanism 300 is described in detail with reference to FIG 2. FIG 2 is a schematic view illustrating the power distribution mechanism 300 and the relationship with its peripheral parts. In FIG. 2, the portions same as those in FIG 1 are denoted by the same reference numerals and the explanation of these portions will be omitted as appropriate.

[0054] In FIG 2, the power distribution mechanism 300 includes a sun gear 303 provided at the center, a ring gear 301 provided on the outer circumference of and concentric with the sun gear 303, and multiple pinion gears 305 provided between the sun gear 303 and the ring gear 301. Each of the pinion gears 305 rotates on its axis and move around the sun gear 303. The power distribution mechanism 300 further includes a planetary carrier 304 that is connected to an end of a crankshaft 205 and supports the rotation axis of each pinion gear. The crankshaft 205 is an example of an input/output shaft and will be described later.

[0055] Further, the sun gear 303 is connected to the rotor (no reference numeral) of the motor generator MGl via the sun gear shaft 304, which may be an example of an input shaft of the present invention. The ring gear 301 is connected to the rotor (not shown) of the motor generator MG2 via the ring gear shaft 302, which may be regarded as an example of a drive shaft of the present invention. The ring gear shaft 302 is connected to the axle 11. The power generated by the motor generator MG2 is transmitted to the axle 11 via the ring gear shaft 302. Further, the rotational force of the wheels 12 transmitted via the axle 11 is input to the motor generator MG2 via the ring gear shaft 302.

[0056] With the construction as described above, the power distribution mechanism 300 distributes the power generated by the engine 200 to the sun gear 303 and the ring gear 301 in specific proportions through the planetary carrier 306 and the pinion gears 305. Thus, the power distribution mechanism 300 splits the power generated by the engine 200 into two portions, which respectively directed to two systems.

[0057] With reference to FIG. 1 again, the inverter 400 converts the direct current power drawn from the battery 500 into alternate current power, and supplies the alternate current power to the motor generator MGl and the motor generator MG2. The inverter 400 further converts the alternate current power generated by the motor generator MGl and the motor generator MG2 into direct current power and supplies the direct current power to the battery 500. The inverter 400 may be formed as a part of a PCU (Power Control Unit).

[0058] The battery 500 is a rechargeable secondary battery that functions as a power supply source of electric power to drive the motor generator MGl and the motor generator MG2.

[0059] The SOC sensor 600 detects a remaining battery level (or a state of charge: SOC) of the battery 500. The SOC sensor 600 is electrically connected to the ECU 100, and the ECU 100 constantly obtains the SOC of the battery 500 detected by the SOC sensor 600.

[0060] The vehicle speed sensor 700 detects the vehicle speed of the hybrid vehicle 10. The vehicle speed sensor 700 is electrically connected to the ECU 100, and the ECU 100 constantly obtains the detected vehicle speed.

[0061] The accelerator position sensor 800 detects an accelerator angle with respect to an accelerator pedal (not shown). The accelerator position sensor 800 is electrically connected to the ECU 100, and the ECU 100 constantly obtains the detected accelerator angle.

[0062] Next, the main portions of the engine 200 and a part of the operation of the engine 200 are described with reference to FIG 3. FIG 3 is a schematic view illustrating the engine 200. In FIG 3, the portions same as those in FIG 1 are denoted by the same reference numerals and the explanation thereof will be omitted as appropriate.

[0063] The engine 200 includes an ignition device 202 having an ignition plug (no reference numeral), a part of which is exposed in a combustion chamber of a cylinder 201. The engine 200 combusts the air-fuel mixture through the ignition operation of the ignition device 202. The engine 200 further converts the reciprocating motion of the piston 203 generated by the combustion force into a rotational motion of the crankshaft 205 via a connecting rod 204. Further, a crank position sensor 206 is provided in the neighbor of the crankshaft 205. The crank position sensor 206 detects the rotational position (crank angle) of the crankshaft 205. The crank position sensor 206 is electrically connected to the ECU 100. The ECU 100 controls the ignition timing, etc., of the ignition device 202 based on the crank angle detected by the crank position sensor 206. The ECU 100 further calculates an engine speed NE of the engine 200 based on the rotational position of the crankshaft 205.

[0064] During the combustion of the fuel in the cylinder 201, the air inhaled from the outside passes though an intake pipe 207 and is mixed with the fuel injected from the injector 214 at an intake port 213 to form the air-fuel mixture. The fuel is stored in the fuel tank 215, and is pressurized and supplied by a low-pressure pump 217 to the injector 214 through a delivery pipe 216. The injector 214 is electrically connected to the ECU 100. The injector 214 injects the supplied fuel into the intake port 213 according to the control of the ECU 100. Note that, the injection means that injects the fuel may not be the intake port injector as shown in FIG 3. Alternatively, a direct injection injector, or the like may be used in which a high pressure pump further increases the pressure of the fuel pressurized by the low-pressure pump, and the fuel is directly injected into the high-temperature, high-pressure cylinder 201.

[0065] The engine 200 of this embodiment may use alcohol-blended fuel, which is a mixture of gasoline and alcohol. The engine 200 is operable, even if the alcohol content ratio of the fuel changes between 0 to 100 percent. In other words, the hybrid vehicle 10 is an example of a FFV (Flexible Fuel Vehicle).

[0066] The communication condition between the interior of the cylinder 201 and the intake pipe 207 is controlled by opening and closing the intake valve 218. The air-fuel mixture combusted in the cylinder 201 becomes exhaust gas, which is guided to an exhaust pipe 221 through the exhaust port 220 when an exhaust valve 219 opens. The exhaust valve 219 opens and closes in synchronous with the opening and closing of the intake valve 218.

[0067] A cleaner 208 is provided in the intake pipe 207 and purifies the air inhaled from the outside. Further, an airflow meter 209 is provided in the intake pipe 207 on the downstream side (cylinder side) of the cleaner 208. The airflow meter 209 is a hot-wire airflow meter that directly detects the mass flow rate of the intake air. The airflow meter 209 is electrically connected to the ECU 100, and the ECU 100 constantly obtains the detected mass flow rate of the inhaled air.

[0068] A throttle valve 210 is provided in the intake pipe 207 on the downstream side of the airflow meter 209. The throttle valve 210 regulates the intake air amount of air flowing into the cylinder 201. The throttle valve 210 is electrically connected to a throttle position sensor 212 that detects the throttle opening amount, which indicates opening/closing state of the throttle valve 210.

[0069] A throttle valve motor 211 is electrically connected to the ECU 100 and drives the throttle valve 210. The ECU 100 controls the driving state of the throttle valve motor 211 based on the accelerator angle detected by the above-described accelerator position sensor 800, and thus controls the opening and closing state (i.e. the throttle opening amount) of the throttle valve 210.

[0070] The throttle valve 210 is an electronically controlled throttle valve as described above. The ECU 100 may control the throttle opening amount irrespective of the driver's intention.

[0071] A three-way catalyst 223 is provided in the exhaust pipe 221. The three-way catalyst 223 purifies CO (carbon monoxide), HC (hydrocarbon), and NOx (nitrogen oxide) discharged from the engine 200. An air-fuel ratio sensor 222 is provided in the exhaust pipe 221 on the upstream side of the three-way catalyst 223. The air-fuel ratio sensor 222 detects the air-fuel ratio in the engine 200 from the exhaust gas discharged through the exhaust port 220. The air-fuel ratio sensor 222 is electrically connected to the ECU 100, and the ECU 100 constantly obtains the detected air-fuel ratio.

[0072] A temperature sensor 224 is provided in a water jacket, which is provided in the cylinder block that accommodates the cylinder 201. The temperature sensor 224 detects the temperature of the coolant that cools the engine 200. The temperature sensor 224 is electrically connected to the ECU 100, and the ECU 100 constantly obtains the detected temperature of the coolant.

[0073] In the hybrid vehicle 10 as shown in FIGl, the ECU 100 and the power distribution mechanism 300 control the power distribution among the motor generator MGl, which mainly functions as an electric generator, the motor generator MG2, which mainly functions as an electric motor, and an engine 200. The ECU 100 and the power distribution mechanism 300 thus control the running condition of the hybrid vehicle 10. The operations of the hybrid vehicle 10 under several conditions will be explained, hereinafter.

[0074] For example, at the time of start-up of the hybrid vehicle 10, the motor generator MGl, which is driven by the electric energy of the battery 500, functions as an electric motor. The engine 200 is cranked by the power from the motor generator MGl, and starts.

[0075] When the vehicle starts moving, two situations may occur depending on the state of charge of the battery 500, which is detected based on the output signal from the SOC sensor 600. For example, when the vehicle starts under the normal condition (i.e., the battery SOC is good), the motor generator MGl does not need to charge the battery 500. Therefore, the engine 200 starts only to warm up, and the hybrid vehicle 10 starts moving with the power generated by the motor generator MG2. On the other hand, when the state of charge of the battery is not good (i.e., the battery SOC is low), the motor generator MGl functions as an electric generator to charge the battery 500 with the power generated by the engine 200.

[0076] For example, when the vehicle runs at low speeds or descends a slope, the engine 200 operates at a relatively low efficiency. Therefore, the engine is stopped by stopping the fuel injection from the injector 214, and the hybrid vehicle 10 runs only with the power generated by the motor generator MG2. If the battery SOC is low at this time, the engine 200 starts to drive the motor generator MGl, and the motor generator MGl charges the battery 500.

[0077] In the operation region where the engine operates at a relatively high efficiency (e.g., combustion efficiency, etc. is high), the hybrid vehicle 10 runs mainly with the power generated by the engine 200. In this case, the power distribution mechanism 300 divides the power generated by the engine 200 into two portions. One portion is transmitted to the wheels 12 via the axle 11. The other portion drives the motor generator MGl to generate electricity (electric power). Further, the motor generator MG2 is driven by the electric power generated by the motor generator MGl to assist the power of the engine 200. If the battery SOC is low at this time, the output power of the engine is increased, and the battery 500 is charged with a portion of the electric power generated by the motor generator MGl.

[0078] When the hybrid vehicle 10 decelerates, the motor generator MG2 is rotated by the power transmitted from the wheels 12 via the axle 11. Thus, the motor generator MG2 operates as an electric generator. As a result, the motion energy of the wheels 12 is converted into electric energy, and the battery 500 is charged with the electric energy. This is known as "regeneration".

[0079] Next, a basic control operation of the engine 200 will be described. The ECU 100 repeatedly calculates, at constant intervals of time, required engine output power, which is output power that the engine is required to generate. At this time, the ECU 100 calculates or retrieves from a map previously stored in the ROM an output shaft torque (torque that will be output to the axle 11) corresponding to the current accelerator angle detected by the accelerator position sensor 800 and the current vehicle speed detected by the vehicle speed sensor 700.

[0080] The ECU 100 further obtains a required power generation amount based on the output signal from the SOC sensor 600. The ECU 100 then calculates the required engine output power by correcting the output shaft torque with reference to the obtained required power generation amount and the amount of power required by some accessories or auxiliary devices, such as an air conditioner, a power steering, and the like. The method for calculating the required engine output power may be the one used in the known hybrid vehicle, but the details thereof may be modified appropriately.

[0081] In the hybrid vehicle 10, the fuel property (for example, alcohol content ratio, etc.) of the fuel used in the engine 200 changes. If the fuel property changes, the stoichiometric air-fuel ratio also changes. More specifically, the stoichiometric air-fuel ratio decreases as the alcohol content ratio is higher; and the stoichiometric air-fuel ratio increases as the alcohol content ratio is lower. In other words, if the fuel has a relatively low calorific value, the output power of the engine 200 relatively decreases; and if the fuel has a relatively high calorific value, the output power of the engine 200 relatively increases.

[0082] Meanwhile, the fuel injection amount from the injector 214 is basically calculated on the basis that the alcohol content ratio in the fuel is 0%, i.e., hundred percent gasoline fuel is used in the engine 200. Therefore, when the fuel property changes, difference occurs between the actual output power of the engine 200 and the required engine output power. For example, if the alcohol content ratio increases, a smaller amount of fuel is injected relative to the intake air amount detected by the airflow meter 209. Therefore, the actual output power is lower than the required engine output power. Moreover, because the alcohol has a smaller calorific value, as compared with gasoline, alcohol must be injected more than gasoline to obtain the same level of output power as gasoline. Thus, in this embodiment, the engine 200 is operable with alcohol blended fuel, and the alcohol content ratio in the fuel is described as an example of the fuel property. However, the fuel property may change in a gasoline engine. Therefore, the same phenomenon may occur in gasoline engines, or the like, as well.

[0083] The change in the actual output power of engine 200 due to the fuel property will be described hereinafter with reference to FIG 4. FIG 4 is a schematic view of a map showing an engine operation region of engine 200.

[0084] In FIG 4, the vertical line indicates engine torque TR, and the horizontal line indicates engine speed NE. In this two-dimensional coordinate system, the engine 200 basically operates at the operation point on the operation line R. The operation line R is formed, for example, by connecting operation points, at each of which the fuel consumption is the lowest to obtain a specific amount of actual output power. Once the required engine output power is calculated, a unique operation point is determined basically. For example, for a certain required engine output power PwI, the operation point is the coordinate point Rl, which corresponds to the intersection between the shown equivalent output line EQPwI and the operation line R. The ECU 100 controls the operation states of the motor generator MGl and the motor generator MG2 such that the engine 200 operates at the operation point.

[0085] When the fuel property changes, for example, when fuel having a relatively high calorific value is supplied to the engine 200, the engine 200 generates the actual output power Pw2 (Pw2 > PwI). Thus, the actual output power exceeds the required output power, and the operation point of the engine 200 is the coordinate point R2 on the shown equivalent output line EQPw2. On the other hand, when fuel having a relatively low calorific value is supplied to the engine 200, the engine 200 generates the actual output power Pw3 (Pw3<Pwl). Thus, the actual output falls below the required output power, and the operation point of the engine 200 is the coordinate point R3 on the shown equivalent output line EQPw3.

[0086] As described above, the change in the fuel property gives a large impact on the actual output power of the engine 200, and the driver's intention may not be reflected on the engine output power. Thus, drivability may be degraded. Therefore, the change in the fuel property must be detected quickly and accurately. Moreover, the change in the actual output power occurs in real time with the change in the fuel property. In other words, the change in the actual output power or an abnormality in the output power of the engine 200 continues while the change in the fuel property is detected and is fed back to the actual fuel injection amount. Therefore, it is desired that the abnormal output of the engine 200 is corrected simultaneously with the detection of the change in the fuel property. In the hybrid vehicle 10, the ECU 100 performs the injection mount control as described below, thereby detects the change in the fuel property rapidly and accurately, and compensates for the abnormality in the actual output power of the engine 200 appropriately. [0087] Hereinafter, the fuel injection amount control process is described in detail with reference to FIG 5. FIG 5 is a flowchart illustrating the fuel injection amount control process.

[0088] In FIG 5, the ECU 100 calculates the required output power Pwn, which is the output power that the engine 200 is required to output (step AlO). The required output power Pwn is calculated based on the accelerator angle detected by the accelerator position sensor 800 and the vehicle speed detected by the vehicle speed sensor 700, as described above.

[0089] Next, the ECU 100 calculates the actual output power Pwr of the engine 200 (step All). The actual output power Pwr of the engine 200 is calculated based on the reaction torque of the engine 200 detected by the motor generator MGl. In other words, the power distribution mechanism 300 distributes the torque (i.e., power) output from the engine 200 to the crankshaft 205 to the sun gear shaft 304 in a specific proportion determined by the number of teeth of the sun gear 303, the number of teeth of the ring gear 301, and the like. The motor generator MGl detects the torque distributed to the sun gear shaft 304 as the reaction torque. In other words, the motor generator MGl functions as a kind of torque sensor. The ECU 100 is capable of accurately calculating the torque actually output from the engine 200 based on the reaction torque detected by the motor generator MGl.

[0090] The engine speed NE of the engine 200 is constantly calculated based on the signals output from the crank position sensor 206. Thus, in the process of step All, the ECU 100 accurately calculates the actual output power Pwr based on the calculated engine torque and engine speed.

[0091] After the actual output power Pwr is calculated, the ECU 100 calculates an excess/deficiency output power amount ΔPw (ΔPw = Pwn - Pwr), which is the difference between the actual output power and the required output power (step A12). After the excess/deficiency output power amount ΔPw is calculated, the ECU 100 determines whether the calculated excess/deficiency output power amount ΔPw is smaller than the upper limit value ΔPwH and is equal to or greater than the lower limit ΔPwL (step A13). In other words, it is determined whether the excess/deficiency output power amount ΔPw is within the predetermined range. Here, the .upper limit ΔPwH and the lower limit ΔPwL define the range of change in the output power, in which no significant degradation of drivability is apparent. In other words, when the excess/deficiency output power amount ΔPw is within the predetermined range, it is not practically necessary to feed back the change in the fuel property to the fuel injection amount. Alternatively, the upper limit and the lower limit may define the range of change in the output power that occurs without the change in the fuel property. In this case, it is prevented from erroneously estimating that the fuel property changes.

[0092] Accordingly, if the calculated excess/deficiency output power amount ΔPw is within the predetermined range (step A13: YES), the ECU 100 continues the normal running control, without estimating the fuel property and without compensating for the abnormality in the output power of the engine 200 (step A14). The ECU 100 then returns the process to step AlO and repeats the process of calculating the required output power Pwr.

[0093] Meanwhile, if the excess/deficiency output power amount ΔPw is not within the predetermined range (step A13: NO), the ECU 100 determines whether the excess/deficiency output power amount ΔPw is equal to or greater than the upper limit ΔPwH (step S 15). If the excess/deficiency output power amount ΔPw is equal to or greater than the upper limit ΔPwH (step A15:YES), in other words, if the actual output power Pwr of the engine 200 is lower than the required output power Pwn, the ECU 100 estimates the fuel property indicating that the current fuel in the engine 200 has a relatively low calorific value (step A16).

[0094] If the excess/deficiency output power amount ΔPw is neither equal to nor greater than the upper limit ΔPwH (step A15: NO), in other words, if the excess/deficiency output power amount ΔPw is lower than the lower limit ΔPwL, the ECU 100 estimates the fuel property indicating that the fuel has a relatively high calorific value (step A19), because the actual output power Pwr of engine 200 is in excess of the required output power Pwn. [0095] If it is estimated in the process of step A16 that the fuel has a low calorific value, the ECU 100 controls the motor generator MG2 to assist the power insufficient for the required output power Pwn by the torque of the motor generator MG2 (step A17). As a result, in the entire hybrid vehicle 10, the power corresponding to the required output power Pwn is output to the ring gear shaft 302, the abnormality in the output power of the engine 200 is compensated for, and the degradation of drivability is swiftly improved.

[0096] If it is estimated in the process of step A19 that the fuel has a high calorific value, the ECU 100 controls the motor generator MGl such that the motor generator MGl absorbs the power exceeding the required output power to generate electricity (step A20). As a result, in the entire hybrid vehicle 10, the power corresponding to the required output power Pwn is output to the ring gear shaft 302, the abnormality in the output power of the engine 200 is compensated for, and the degradation of drivability is rapidly improved.

[0097] After performing the process from step A17 to step A20, the ECU 100 reflects the excess/deficiency output power amount ΔPw obtained in the process of step Al 2 in the actual fuel injection amount (step A18). In the ROM of the ECU 100, a map showing a correspondence relationship between the excess/deficiency output power amount and the fuel property is stored in advance. The ECU 100 selects from the map an appropriate numeric value to obtain an index value, such as a correction amount to correct the gasoline injection amount by a numeric calculation, the ratio of components in the fuel, or the calorific value obtained per unit quantity of the fuel. The ECU 100 corrects the fuel injection amount by the numeric calculation based on the obtained index value. As a result, the fuel injection amount accurately reflects the current fuel property. The difference between the actual output power Pwr of the engine 200 and the required output Pwn is at least reduced, and may become zero or an ignorable small value. After the process of step A18, the process returns to step AlO, and the series of process will be repeated.

[0098] At this time, the correction value, or the like, regarding correction of the fuel injection amount may be updatably stored in the RAM, for example. Accordingly, for example, even if the fuel property changes over time, the fuel injection amount follows the change in the fuel property, and thus, the most appropriate amount of fuel is constantly injected.

[0099] As described above, according to the hybrid vehicle 10 of the embodiment, the torque absorption by the motor generator MGl and the torque assist by the motor generator MG2 compensate for the excess/deficiency amount of the actual power output Pwr from the required output power Pwn. Accordingly, even if the fuel property changes, the likelihood that abnormality in the output power of the engine 200 causes the degradation of drivability is relatively low. Further, the fuel property is rapidly and accurately estimated based on the excess/deficiency amount. In other words, the time period is minimized in which the change in the fuel property causes abnormality in the output power of the engine 200.

[0100] In the first embodiment, the torque absorption by the motor generator MGl and the torque assist by the motor generator MG2 compensate for the excess/deficiency amount of the actual output power Pwr from the requested output power Pwn. As a result, the deterioration of drivability is reduced in the estimation period of the fuel property. However, for example, when the battery is in an overcharge state, in which the SOC of the battery 500 exceeds a predetermined upper limit, torque absorption by the motor generator may be practically difficult. Further, when the battery is in the electricity power shortage state, in which' the battery SOC is lower than a predetermined lower limit, the torque assist by the motor generator MG2 may be practically difficult. In this case, even if the ECU 100 estimates the fuel property based on the excess/deficiency output power amount ΔPw and the time period required to reflect the estimated fuel property in the actual fuel injection amount is relatively short, the abnormality in the output power of the engine 200 may still cause the degradation of drivability.

[0101] With reference to FIG 6, a second embodiment of the present invention, which may be used in the above-described case, is described. FIG 6 is a schematic view illustrating an engine 900 according to the second embodiment. In FIG 6, the portions same as those in FIG 3 are denoted by the same reference numerals and the explanation of these portions will be omitted as appropriate.

[0102] In FIG 6, the main difference between the engine 900 and the engine 200 of the first embodiment is that the engine 900 includes a turbocharger, which may be regarded as an example of a booster of the present invention. The turbocharger has a turbine 225 and a compressor 226.

[0103] In other words, in engine 900, a portion of the exhaust gas discharged to the exhaust pipe 221 flows into the turbine 225 and causes the turbine 225 to rotate in accordance with the pressure thereof. The rotating axis of turbine 225 is the same as that of the compressor 226 that is located to face the turbine 225. The rotation of the turbine 225 by the exhaust gas rotates the compressor 226 to boost intake pressure of the air supplied to the engine. Further, an intercooler 227 is provided in the intake pipe 207, to thereby improve the boost efficiency of the compressor 226.

[0104] The exhaust pipe 221 is provided with an exhaust bypass pipe (no reference numeral) to bypass the turbine 225. A wastegate valve 228 (sometimes referred to as "WGV" hereinafter) is provided in the exhaust bypass pipe. The WGV 228 is electrically connected to the ECU 100, and is an electro-magnetic open/close valve that opens and closes under the control of ECU 100. The WGV 228 discharges an amount of exhaust gas, which is determined by the valve opening amount or valve opening time, through the exhaust bypass pipe without passing through the turbine 225. In the engine 900, the boost pressure is regulated in accordance with the open/close state of the WGV 228. Thus, the WGV 228 may be regarded as an example of the boost pressure regulator of this invention. The engine 900 may be provided with, as the boost pressure regulator, an exhaust throttle valve or a variable throttle nozzle as an alternative to or together with the WGV 228. In this case, for example, the amount of exhaust gas flowing into the turbine 225 is reduced by narrowing the valve opening, or the amount of exhaust gas flowing into the turbine 225 is increased by opening the valve. The boost pressure is thus regulated. [0105] Next, with reference to FIG 7, a fuel injection amount control process in the hybrid vehicle having the engine 900 is described in detail. FIG 7 is a flowchart illustrating the fuel injection amount control process according to the second embodiment of the present invention. In FIG 7, the portions same as those in FIG 5 are denoted by the same reference numerals and the explanation of these portions will be omitted as appropriate.

[0106] In FIG 7, if it is estimated that the fuel has a low calorific value (step A16), the ECU 100 increases the target boost pressure Pa of the turbocharger to thereby increase the boost pressure in the engine 900 (step BlO). At this time, the ECU 100 regulates the opening amount of the WGV 228 such that the boost pressure detected by a boost pressure sensor (not shown) meets the increased target boost pressure Pa. As a result, the actual output power Pwr of the engine 900 increases.

[0107] However, because the control of the actual output power Pwr by the turbocharger is less accurate, as compared with the control of the torque by the motor generators MGl and MG2, it may be practically difficult to fully compensate for the excess/deficiency output power amount ΔPw by the boost pressure control. Therefore, after the actual output power Pwr of the engine 900 is increased by the process of step BlO, the ECU 100 may compensate for, by the torque assist of the motor generator MG2, the torque corresponding to the excess/deficiency output power amount that is not compensated by the boost pressure control (step BIl). In this case, in the process of step BlO, the opening amount of the WGV 228 may be controlled to compensate for only a part of the excess/deficiency output power amount ΔPw calculated in step Al 2, or to assist only a part of insufficient torque.

[0108] The ECU 100 may perform different control processes depending upon the current SOC of the battery 500. That is, when the current SOC of the battery 500 is good, the ECU may perform the above-described control process. On the other hand, when the battery SOC is not good, the ECU 100 may cause the engine 900 to generate the output power more than the excess/deficiency output power amount ΔPw by the boost pressure control of the WGV 228. The ECU 100 then may supply the excessive portion of the power to the motor generator MGl to generate electricity for the restoration of the battery SOC. Further, after performing the process of step BlO, the ECU 100 may return the process to step All for the calculation of the actual output power Pwr, the calculation of the excess/deficiency output power amount ΔPw, and the comparison and determination with respect to the excess/deficiency output power amount ΔPw in this order.

[0109] If it is determined in the process of step Al 9 that the fuel has a high calorific value, the ECU 100 reduces the target boost pressure Pa of the turbocharger to thereby reduce the boost pressure in the engine 900 (step B12). At this time, the ECU 100 regulates the opening amount of the WGV 228 such that the boost pressure detected by a boost pressure sensor (not shown) meets the reduced target boost pressure Pa. As a result, the actual output power Pwr of the engine 900 decreases.

[0110] However, because the control of the actual output power Pwr by the turbocharger is less accurate, as compared with the control of the torque by the motor generators MGl and MG2, it may be practically difficult to fully compensate for the excess/deficiency output power amount ΔPw by the boost pressure control. Therefore, after the actual output power Pwr of the engine 900 is reduced by the process of step B 12, the ECU 100 compensates for, by the torque absorption of the motor generator MGl, the torque corresponding to the excess/deficiency output power amount that is not compensated by the boost pressure control (step B13). In this case, in the process of step B 12, the opening amount of the WGV 228 may be controlled to compensate for only a part of the excess/deficiency output power amount ΔPw calculated in step A12, or to reduce only a part of excessive torque.

[0111] The ECU 100 may perform different control processes depending upon the current SOC of the battery 500. That is, when the current SOC of the battery 500 is low, the ECU 100 may perform the above-described control process. On the other hand, when the battery SOC is good, the ECU 100 may cause the engine 900 to reduce the output power more than the excess/deficiency output power amount ΔPw by the boost pressure control of the WGV 228. The ECU 100 then may cause the motor generator MG2 to generate torque to assist the insufficient power. Further, after performing the process of step B 12, the ECU 100 may return the process to step All for the calculation of the actual output power Pwr, the calculation of the excess/deficiency output power amount ΔPw, and the comparison and determination with respect to the excess/deficiency output power amount in this order.

[0112] As described above, in the fuel injection amount control process according to the second embodiment, the boost pressure control by the WGV 228 may compensate for the abnormality in the output power of the engine 900 due to the change in the fuel property without considering the SOC of the battery 500. Further, the torque absorption of the motor generator MGl and the torque assist of the motor generator MG2 compensate for the minute output power that exceeds the accuracy limit of the boost pressure control. In other words, the degradation of drivability caused by the change in the fuel property is reduced more efficiently and effectively.

[0113] While some embodiments of the invention have been illustrated above, it is to be understood that the invention is not limited to details of the illustrated embodiments, but may be embodied with various changes, modifications or improvements, which may occur to those skilled in the art, without departing from the spirit and scope of the invention.

Claims

1. A fuel property estimation device for a hybrid vehicle that is provided with a supply device that supplies fuel, an internal combustion engine that outputs power to a drive shaft connecting to an axle, a motor that outputs power to the drive shaft, a generator that generates electricity by using power output from the internal combustion engine, and a battery that is charged by electric power obtained by the electricity generated by the generator, the fuel property estimation device comprising: a determining unit that determines a difference between actual output power of the internal combustion engine and a required output power; a first controller that controls the motor and the generator in accordance with the difference determined by the determining unit, such that the required output power is output to the drive shaft; and an estimation unit that estimates a fuel property of the fuel in accordance with the difference determined by the determining unit.

2. The fuel property estimation device according to claim 1, wherein the hybrid vehicle is further provided with a power distribution mechanism that distributes the actual output power of the internal combustion engine to an input shaft and the drive shaft in predetermined proportions, a portion of the actual output power of the internal combustion engine distributed to the input shaft by the power distribution mechanism is input to the generator via the input shaft, the motor is driven by power supplied from the battery or electric power obtained from the electricity generated by the generator, and the determining unit determines the difference in accordance with the portion of the actual output power distributed to the input shaft.

3. The fuel property estimation device according to claim 1 or 2, wherein the first controller controls the motor to output the power to the drive shaft when the actual output power is lower than the required output power, and the first controller further controls the generator to use the portion of the actual output power of the internal combustion engine to generate electricity when the actual output power is higher than the required output power.

4. The fuel property estimation device according to any one of claims 1 to 3, wherein the internal combustion engine is further provided with a booster that is driven by exhaust pressure to boost the pressure of air supplied to the engine, and a boost pressure regulator that regulates a boost pressure of the booster, the first controller controls the boost pressure regulator in accordance with the difference between the actual output power and the required output power such that the required output power is output to the drive shaft.

5. The fuel property estimation device according to claim 4, wherein the boost pressure regulator includes an open-close valve that regulates an amount of the exhaust gas flowing into the booster in accordance with an open-close state of the open-close valve.

6. The fuel property estimation device according to claim 4 or 5, wherein after the first controller controls the boost pressure regulator in accordance with the difference between the actual output power and the required output power, the first controller then controls the motor and the generator such that the required output power is output to the drive shaft.

7. The fuel property estimation device according to any one of claims 1 to 6, wherein the estimation unit estimates the fuel property at least one of when the difference between the actual output power and the required output power is no less than a predetermined upper limit and when the difference is lower than a predetermined lower limit.

8. The property estimation device according to any one of claims 1 to 7, further comprising: a correction unit that corrects an amount of the fuel supplied from the supply device in accordance with the fuel property estimated by the estimation unit; and a second controller that controls the supply device to supply the corrected amount of the fuel.

9. A hybrid vehicle comprising: a supply device that supplies fuel; an internal combustion engine that outputs an actual output power to a drive shaft connecting to an axle; a motor that outputs power to the drive shaft; a generator that generates electricity by using a portion of the actual power output from the internal combustion engine; a battery that is charged by the power obtained by the electricity generated by the generator; a determining unit that determines a difference between the actual output power of the internal combustion engine and a required output power; a first controller that controls the motor and the generator in accordance with the difference determined by the determining unit, such that the required output power is output to the drive shaft; an estimation unit that estimates a fuel property of the fuel supplied by the supply device in accordance with the difference determined by the determining unit; a correction unit that corrects an amount of the fuel supplied from the supply device in accordance with the fuel property estimated by the estimation unit; and a second controller that controls the supply device to supply the corrected amount of the fuel.