Control device for hybrid vehicle

Assumed torque Tb is calculated based on an operation state of an engine when there is no abnormality in sensors, the engine is in a warm-up completion state, and a travel mode is a series mode, and actual torque Ta is calculated and friction torque Tf is calculated based on information on an actual amount of electric power generation of a generator. When the friction torque Tf is larger than an upper limit clip value, the upper limit clip value is the friction torque Tf, and when the friction torque Tf is smaller than the lower limit clip value, the lower limit clip value is the friction torque Tf, correction torque Tc is calculated, and an operation of an electronic control instrument of the engine is controlled so as to set the assumed torque Tb to the correction torque Tc.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control device for a hybrid vehicle, and more particularly to friction learning of an internal combustion engine.

2. Description of the Related Art

In recent years, a hybrid vehicle has been developed that includes both an internal combustion engine (engine) and an electric motor, and has a parallel mode in which the vehicle travels using the engine and the electric motor as a power source, and a series mode in which a power generator is driven by power of the engine to generate electric power, which is used to drive the electric motor or charge a secondary battery. The engine provided in the hybrid vehicle has variations in parts that constitute the engine. The variations in the parts that constitute the engine cause variations in output torque of the engine.

The variations in the output torque of the engine causes variations in an amount of electric power generation of the power generator driven by the engine. For example, the variations in the output torque of the engine on an increase side of the amount of electric power generation of the power generator cause an excessive terminal voltage of the secondary battery, leading to a fault of a hybrid system. Also, the variations in the output torque of the engine on a decrease side of the amount of electric power generation of the power generator cause a constantly insufficient amount of electric power generation of the power generator, thereby reducing a state of charge (hereinafter referred to as SOC) of the secondary battery, which may disable the vehicle for traveling.

As an example of a method for estimating variations in output torque of an engine and correcting the output torque of the engine, a technique described in Japanese Patent Laid-Open No. 2009-97347 has a friction torque map for previously calculating friction torque of an engine depending on a temperature of engine cooling water, and corrects the friction torque of the engine calculated from the friction torque map based on a rotational speed difference between an assumed engine rotational speed and an actual engine rotational speed at start of the engine. Then, the output torque of the engine is adjusted based on the corrected friction torque of the engine.

A control device for an internal combustion engine described in Japanese Patent Laid-Open No. 2009-97347 corrects the friction torque of the engine based on the rotational speed difference between the assumed engine rotational speed and the actual engine rotational speed at start of the engine, and adjusts the output torque of the engine based on the corrected friction torque of the engine.

For example, it is considered that the technique described in Japanese Patent Laid-Open No. 2009-97347 is applied to correction of the output torque of the engine of the hybrid vehicle described above.

However, the hybrid vehicle drives the power generator or drive wheels immediately after start of the engine, and a load applied to the engine at start of the engine changes depending on the amount of electric power generation of the power generator or a traveling state of the vehicle such as a vehicle speed.

Thus, if the technique described in Japanese Patent Laid-Open No. 2009-97347 is applied to the hybrid vehicle, the amount of electric power generation of the power generator or the traveling state of the vehicle changes at each start of the engine, the load applied to the engine at start of the engine changes, and an actual engine rotational speed also changes. Thus, it is difficult to correct the friction torque of the engine depending on the rotational speed difference between the assumed engine rotational speed and the actual engine rotational speed.

SUMMARY OF THE INVENTION

The present invention is achieved to solve such a problem, and has an object to provide a control device for a hybrid vehicle that can accurately calculate friction torque of an internal combustion engine.

To achieve the object, the present invention provides a control device for a hybrid vehicle comprising: a mode switching unit for switching a travel mode of the vehicle, between a series mode in which drive wheels are driven by power of an electric motor driven by electric power generated by a power generator driven by power of an internal combustion engine, and a parallel mode in which the drive wheels are driven by power of the internal combustion engine and power of the electric motor driven by electric power supplied from a secondary battery; an operation state detection unit for detecting an operation state of the internal combustion engine; an assumed output value calculation unit for calculating an assumed output value of the internal combustion engine assumed based on the operation state of the internal combustion engine; an actual output value calculation unit for calculating an actual output value of the internal combustion engine based on an amount of electric power generation of the power generator; and a friction torque calculation unit for subtracting the actual output value from the assumed output value to calculate friction torque when the travel mode is the series mode.

Thus, when the travel mode is the series mode, the power generator is driven by power of the internal combustion engine to generate electric power, thereby allowing calculation of an actual output value of the internal combustion engine from the amount of electric power generation of the power generator in the series mode.

The assumed output value of the internal combustion engine is an output value in a standard state of the internal combustion engine previously determined by a test or the like and stored for each operation state of the internal combustion engine depending on a throttle valve opening, a fuel injection amount or the like in a case of no variations in parts that constitute the internal combustion engine, that is, in a case of the internal combustion engine in the standard state.

Thus, the actual output value is subtracted from the assumed output value as an output value of the internal combustion engine in the standard state, thereby allowing accurate calculation of friction torque due to variations in parts that constitute the internal combustion engine.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic diagram of a vehicle including a control device for a hybrid vehicle according to the present invention. Now, a configuration of the control device for a hybrid vehicle will be described.

As shown inFIG. 1, the control device for a hybrid vehicle according to the present invention includes an engine (internal combustion engine)4, a high voltage battery (secondary battery)5, a generator (power generator)6, a front inverter8, a front motor (electric motor)9, a rear inverter10, a rear motor (electric motor)11, a reducer12including a clutch12atherein, a hybrid control unit (an actual output value calculation unit)20, and an engine control unit (an operation state detection unit, an assumed output value calculation unit, a friction torque calculation unit, an operation control unit, an operation control correction unit)40provided in the vehicle (hybrid vehicle)1.

The vehicle1that uses the control device for a hybrid vehicle according to the present invention is a hybrid vehicle including, as traveling devices for the vehicle1, the engine4, the front motor9, and the rear motor11, wherein a charge cable extending from an external power supply is connected to a charging inlet lid (not shown), and the high voltage battery5can be charged by a charger.

The engine4includes a plurality of electronic control instruments (an operation state detection unit, an operation control unit) such as an electronic control throttle valve that controls a flow rate of air flowing into a combustion chamber (not shown) in the engine4or a fuel injection valve that supplies fuel into an intake passage (not shown). The engine4also includes a plurality of sensors (an operation state detection unit) such as a crank angle sensor that detects a rotational speed of the engine4, a throttle opening sensor that detects a throttle opening of the electronic control throttle valve, and a water temperature sensor that detects a temperature of cooling water of the engine4The engine4is controlled by the engine control unit40based on a control signal such as requested output torque supplied from the hybrid control unit20to the engine control unit40, and generates power using fuel supplied from a fuel tank2via a fuel pipe3. The power generated by the engine4is transmitted to the generator6via the reducer12with a fixed change gear ratio, and the drive axle15that drives the drive wheels16via the clutch12aincluded in the reducer12.

The high voltage battery5includes a secondary battery such as a lithium-ion battery. The high voltage battery5also includes a battery module including a plurality of modules, each module including a plurality of battery cells having a cell monitoring unit that monitors the battery cells, and a battery monitoring unit that monitors a temperature and a state of charge (hereinafter referred to as SOC) of the battery module based on an output signal from the cell monitoring unit.

The generator6is driven by the engine4to generate electric power, and supplies the electric power to the high voltage battery5, the front motor9, and the rear motor11via the front inverter8. The operation of the generator6is controlled by the front inverter8.

The front inverter8includes a front motor control unit and a generator control unit, and controls an amount of electric power generation of the generator6and an output of the front motor9based on the control signal from the hybrid control unit20. The generator control unit supplies information on an actual amount of electric power generation of the generator6to the hybrid control unit20.

The front motor9is provided in a front part of the vehicle1. The front motor9is driven by electric power of a high voltage generated by the generator6or electric power of a high voltage stored in the high voltage battery5, which is supplied via a high voltage circuit7. An operation of the front motor9is controlled by the front inverter8, and the front motor9drives the drive wheels16via the reducer12and the drive axle15.

The rear inverter10includes a rear motor control unit, and controls an output of the rear motor11based on the control signal from the hybrid control unit20.

The rear motor11is provided in a rear part of the vehicle1. The rear motor11is driven by electric power of a high voltage generated by the generator6or electric power of a high voltage stored in the high voltage battery5, which is supplied via the high voltage circuit7. An operation of the rear motor11is controlled by the rear inverter10, and the rear motor11drives drive wheels19via a reducer17and a drive axle18.

The reducer12includes the clutch12atherein. The clutch12ais mounted between the engine4and the drive axle15, and connects/disconnects transmission of power of the engine4to the drive axle15based on the control signal from the hybrid control unit20.

The hybrid control unit20is a control device for generally controlling the vehicle1, and includes an input/output device, a storage device (ROM, RAM, nonvolatile RAM, or the like), a central processing unit (CPU), a timer, or the like.

To an input side of the hybrid control unit20, the battery monitoring unit of the high voltage battery5, the front motor control unit and the generator control unit of the front inverter8, the rear motor control unit of the rear inverter10, an accelerator position sensor that detects an accelerator opening and a sensor that detects a vehicle state such as a vehicle speed sensor (not shown), and the engine control unit40are connected, and detection information from these instruments are input.

On the other hand, to an output side of the hybrid control unit20, the front motor control unit and the generator control unit of the front inverter8, the rear motor control unit of the rear inverter10, the reducer12, and the engine control unit40are connected. The hybrid control unit20and the engine control unit40are connected by a controller area network in which the control units are connected to each other to allow high speed transfer of control information.

The hybrid control unit20supplies a control signal to the reducer12, the engine control unit40, the front motor control unit, the generator control unit, and the rear motor control unit based on detection information of the battery monitoring unit of the high voltage battery5, the front motor control unit and the generator control unit of the front inverter8, the rear motor control unit of the rear inverter10, the accelerator position sensor and the sensor that detects a vehicle state such as a vehicle speed sensor, to control switching of the travel mode, outputs of the engine4, the front motor9, and the rear motor11, and the amount of electric power generation of the generator6.

Specifically, the travel mode includes an electric vehicle mode (hereinafter referred to as EV mode), a series mode, and a parallel mode. The hybrid control unit20switches the travel mode to the electric vehicle mode (hereinafter referred to as EV mode) with a sufficient SOC of the high voltage battery5and a low vehicle speed and a low load. Also, the hybrid control unit20switches the travel mode to the series mode when the SOC of the high voltage battery5is insufficient for the EV mode or when high electric power is required in acceleration or the like. The hybrid control unit20switches the travel mode to the parallel mode in traveling in a high speed region with high efficiency of the engine4, that is, high fuel efficiency of the engine4. The hybrid control unit20supplies a request signal to the engine control unit40so as to provide output of the engine4depending on the amount of electric power generation of the generator6, the vehicle speed, and the load in the series mode and the parallel mode.

The EV mode is a series mode described later in which the operation of the engine4is stopped, the clutch12ain the reducer12is disconnected, the front motor9and the rear motor11are driven by electric power stored in the high voltage battery5, and the drive wheels16and19are driven by power of the front motor9and the rear motor11to cause the vehicle1to travel, that is, the engine4is not operated.

In the series mode, the clutch12ain the reducer12is disconnected, the operation of the engine4is controlled, the generator6is driven by the engine4and, while the high voltage battery5is charged with electric power generated by the generator6so as to prevent the SOC of the high voltage battery5from being less than a predetermined value, the front motor9and the rear motor11are driven by electric power generated by the generator6and electric power stored in the high voltage battery5, and the drive wheels16and19are driven by power of the front motor9and the rear motor11to cause the vehicle1to travel. Specifically, the series mode is a mode in which the vehicle1is not caused to travel by power of the engine4.

In the parallel mode, the operation of the engine4is controlled, the generator6is driven by the engine4, the front motor9and the rear motor11are driven by electric power generated by the generator6and electric power stored in the high voltage battery5, the drive wheels16and19are driven by power of the front motor9and the rear motor11, further, the clutch12ain the reducer12is connected, the operation of the engine4is controlled, and the drive wheels16are driven by power of the engine4via the reducer12to cause the vehicle1to travel. Specifically, the parallel mode is a travel mode in which the vehicle1is caused to travel by power of the front motor9, the rear motor11, and the engine4.

The hybrid control unit20calculates actual torque (actual output value) Ta of the engine4actually output by the engine4based on information on the actual amount of electric power generation supplied from the generator control unit of the front inverter8. The information on the actual torque Ta is then supplied to the engine control unit40.

The engine control unit40is a control device for generally controlling the engine4, and includes an input/output device, a storage device (ROM, RAM, nonvolatile RAM, or the like), a central processing unit (CPU), a timer, or the like.

To an input side of the engine control unit40, a plurality of electronic control instruments such as the electronic control throttle valve or the fuel injection valve provided in the engine4, a plurality of sensors such as the crank angle sensor, the throttle opening sensor, an intake pressure sensor, and an air-fuel sensor provided in the engine4, and the hybrid control unit20are connected, and detection information from these instruments and sensors are input.

On the other hand, to an output side of the engine control unit40, the plurality of electronic control instruments provided in the engine4and the hybrid control unit20are connected.

The engine control unit40calculates output torque that can be generated in a standard state of the engine4without considering variations or the like in parts that constitute the engine4, that is, assumed torque (assumed output value) Tb based on operation states of the plurality of electronic control instruments and detection results of the plurality of sensors. The assumed torque Tb is previously determined by a test, an analysis or the like, mapped, and stored as an assumed torque map in the engine control unit40.

The engine control unit40controls the operation of the plurality of electronic control instruments to control a fuel injection amount, an intake air amount or the like so as to provide the actual torque Ta requested by the hybrid control unit20based on a request signal of the output of the engine4supplied from the hybrid control unit20and the assumed torque map.

The engine control unit40calculates friction torque Tf generated due to variations or the like in the parts that constitute the engine4based on the actual Ta supplied from the hybrid control unit20and the assumed torque Tb. Then, the engine control unit40calculates correction torque (correction output value) Tc for controlling the operation of the electronic control instrument of the engine4so that the actual torque Ta of the engine4is the output of the engine requested by the hybrid control unit20based on the friction torque Tf. Specifically, the correction torque Tc is a target value of the assumed torque Tb for the actual torque Ta of the engine4to be the output of the engine requested by the hybrid control unit20.

Now, correction control of the engine output torque performed by the control device for a hybrid vehicle according to the present invention thus configured will be described.

FIG. 2is a flowchart showing a control routine for the correction control of the engine output torque by the control device for a hybrid vehicle according to the present invention.

As shown inFIG. 2, in Step S10, it is determined whether or not there is an abnormality in a sensor. Specifically, it is determined whether or not there is an abnormality in any of the plurality of sensors such as the crank angle sensor, the throttle opening sensor, and the water temperature sensor provided in the engine4. When the determination result is true (Yes), and there is an abnormality in any of the plurality of sensors, the routine is returned. When the determination result is false (No), and there is no abnormality in any of the plurality of sensors, the process proceeds to Step S12.

In Step S12, it is determined whether or not the engine4is in a warm-up completion state. Specifically, it is determined whether or not the engine4is in the warm-up completion state from detection results of the water temperature sensor provided in the engine4, a temperature sensor that detects a temperature of an exhaust gas purification catalyst for purifying exhaust gas, or the like. When the determination result is Yes, and the engine4is in the warm-up completion state, the process proceeds to Step S14. When the determination result is No, and the engine4is not in the warm-up completion state, the routine is returned.

In Step S14, it is determined whether or not the travel mode is the series mode. When the determination result is true (Yes), and the travel mode is the series mode, the process proceeds to Step S16. When the determination result is false (No), and the travel mode is not the series mode, the routine is returned.

In Step S16, the assumed torque Tb is calculated. Specifically, the assumed torque Tb is calculated based on the operation state of the engine4determined from the operation states of the plurality of electronic control instruments and the detection results of the plurality of sensors. Then, the process proceeds to Step S18. The assumed torque Tb is an output value of the engine4in the standard state of the engine4previously determined by a test or the like for each operation state of the engine4depending on the throttle valve opening, the fuel injection amount or the like in a case of no variations in the parts that constitute the engine4, that is, in a case of the engine4in the standard state. The assumed torque Tb is calculated by the mapped assumed torque map.

In Step S18, the actual torque Ta is calculated. Specifically, the hybrid control unit20calculates the actual torque Ta of the engine4based on information on the actual amount of electric power generation of the generator6supplied from the generator control unit of the front inverter8. Then, the process proceeds to Step S20.

In Step S20, the friction torque Tf is calculated. Specifically, the actual torque Ta is subtracted from the assumed torque Tb to calculate the friction torque Tf. Then, the process proceeds to Step S22.

In Step S22, it is determined whether or not the friction torque Tf is an upper limit clip value or less. When the determination result is true (Yes), and the friction torque Tf is the upper limit clip value or less, the process proceeds to Step S24. When the determination result is false (No), and the friction torque Tf is not the upper limit clip value or less, the process proceeds to Step S26.

In Step S24, it is determined whether or not the friction torque Tf is a lower limit clip value or more. When the determination result is true (Yes), and the friction torque Tf is the lower limit clip value or more, the process proceeds to Step S30. When the determination result is false (No), and the friction torque Tf is not the lower limit clip value or more, the process proceeds to Step S28.

In Step S26, the friction torque Tf is set to the upper limit clip value. Then, the process proceeds to Step S30.

In Step S28, the friction torque Tf is set to the lower limit clip value. Then, the process proceeds to Step S30.

In Step S30, the correction torque Tc is calculated. Specifically, the friction torque Tf is added to the assumed torque Tb to calculate the correction torque Tc. Then, the process proceeds to Step S32.

In Step S32, the actual torque Ta is corrected. Specifically, the operation of the electronic control instrument of the engine4is controlled so as to set the assumed torque Tb of the engine4to the correction torque Tc, so that the actual torque Ta is the output of the engine requested by the hybrid control unit20. Then, the routine is returned.

As such, the control device for a hybrid vehicle according to the present invention calculates the assumed torque Tb based on the operation state of the engine4determined from the operation states of the plurality of electronic control instruments and the detection results of the plurality of sensors when there is no abnormality in the sensors provided in the engine4, the engine4is in the warm-up completion state, and the travel mode is the series mode. The hybrid control unit20calculates the actual torque Ta of the engine4based on information on the actual amount of electric power generation of the generator6supplied from the generator control unit of the front inverter8. Then, the actual torque Ta is subtracted from the assumed torque Tb to calculate the friction torque Tf. When the friction torque Tf is larger than the upper limit clip value, the upper limit clip value is the friction torque Tf, and when the friction torque Tf is smaller than the lower limit clip value, the lower limit clip value is the friction torque Tf. Then, the friction torque Tf is added to the assumed torque Tb to calculate the correction torque Tc. Then, the operation of the electronic control instrument of the engine4is controlled to set the assumed torque Tb to the correction torque Tc, so that the actual torque Ta of the engine4is the output of the engine requested by the hybrid control unit20.

As such, when the travel mode is the series mode, the actual torque Ta of the engine4calculated based on the information on the actual amount of electric power generation of the generator6is subtracted from the assumed torque Tb of the engine4calculated based on the operation state of the engine4to calculate the friction torque Tf.

When the travel mode is the series mode, the generator6is driven by power of the engine4to generate electric power, thereby allowing calculation of the actual torque Ta generated by the engine4from the amount of electric power generation of the generator6in the series mode.

The assumed torque Tb of the engine4is the output value of the engine4in the standard state previously determined by a test or the like and stored for each operation state of the engine4depending on the throttle valve opening, the fuel injection amount or the like in a case of no variations in the parts that constitute the engine4, that is, in a case of the engine4in the standard state.

Thus, the actual torque Ta is subtracted from the assumed torque Tb as the output value of the engine4in the standard state, thereby allowing accurate calculation of the friction torque Tf due to variations in the parts that constitute the engine4. For the friction torque Tf, the actual torque Ta of the engine4is sometimes larger than the assumed torque Tb depending on variations in the parts that constitute the engine4.

Also, the friction torque Tf is calculated when the engine4is in the warm-up completion state. This allows accurate calculation of the friction torque Tf due to variations in the parts that constitute the engine4because, for example, there is no influence of an increase in the friction torque Tf due to an increase in viscosity of a lubricant caused by a low temperature of the lubricant, or a reduction in the actual torque Ta of the engine4due to poor combustion caused by a low temperature of the cooling water of the engine4.

When the calculated friction torque Tf is larger than the upper limit clip value, the friction torque Tf is set to the upper limit clip value, and when the calculated friction torque Tf is smaller than the lower limit clip value, the friction torque Tf is set to the lower limit clip value. This can prevent the friction torque Tf from being a positively or negatively excessive abnormal value, resulting from the fact that the assumed torque Tb is excessively larger or smaller than the actual torque Ta due to, for example, false calculation of the assumed torque Tb caused by false detection of the operation state of the engine4, or false calculation of the actual torque Ta caused by some trouble.

Thus, when the actual torque Ta of the engine4is corrected considering the friction torque Tf, excessive correction of the actual torque Ta of the engine4can be prevented when the friction torque Tf is larger than the upper limit clip value or smaller than the lower limit clip value.

Also, the friction torque Tf is added to the assumed torque Tb of the engine4to calculate the correction torque Tc, and the operation of the electronic control instrument of the engine4is controlled so as to set the assumed torque Tb to the correction torque Tc.

Thus, the operation of the engine4is controlled so as to set the assumed torque Tb of the engine4to the correction torque Tc considering the friction torque Tf. This can prevent a fault of the hybrid system which may be caused by the fact that variations in the actual torque Ta of the engine4on an increase side increase the amount of electric power generation of the generator6and causes an excessive terminal voltage of the high voltage battery5and a reduction in SOC of the high voltage battery5due to a constantly insufficient amount of electric power generation of the generator6caused by the fact that variations in the actual torque Ta of the engine4on a decrease side reduce the amount of electric power generation of the generator6, under the influence of the friction torque Tf.