Hybrid vehicle and method for controlling hybrid vehicle

Abstract

In a hybrid vehicle, when the shift position SP is set to the S position at which a driver is allowed to select any one of the shift positions SP1 to SP6, and it is determined that warm-up of a purifying device has not been completed, the target air-fuel ratio AF* is set based on the S position / low coolant temperature-time target air-fuel ratio setting map. The air-fuel ratio AF* set based on the S position / low coolant temperature-time target air-fuel ratio setting map tends to be richer than the target air-fuel ratio AF* set based on any one of the normal-time target air-fuel ratio setting map and the D position / low coolant temperature-time target air-fuel ratio setting map that are used when the D position is selected.

Description

INCORPORATION BY REFERENCE[0001]The disclosure of Japanese Patent Application No. 2006-006237 filed on Jan. 13, 2006 including the specification, drawings and abstract is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to a hybrid vehicle and a method for controlling a hybrid vehicle.[0004]2. Description of the Related Art[0005]Japanese Patent Application Publication No. 11-280457 (JP-A-11-280457) describes a technology for a vehicle that uses only an internal combustion engine as a drive power source for the vehicle. According to the technology, the amount of oxygen stored in a three-way catalyst during fuel supply cutoff period is calculated. When the fuel-supply cutoff is cancelled to restart fuel supply, the air-fuel ratio is made richer by an amount based on the calculated amount of oxygen stored in the three-way catalyst. Japanese Patent Application Publication No. 2000-161098 (JP-A-2000-161...

AI Technical Summary

Benefits of technology

[0007]The invention provides a hybrid vehicle in which reduction of the NOx purification efficiency of an exhaust gas purification catalyst is suppressed when selection of one of the operation modes which define respective different ranges, where a required drive power required to cause the vehicle to run can be set, is allowed, and a method for controlling such hybrid vehicle. The invention also provides a hybrid vehicle in which reduction of the NOx purification efficiency of an exhaust gas purification catalyst is suppressed to purify the exhaust gas more effectively, and a method for controlling such hybrid vehicle.

[0010]In the hybrid vehicle according to the first aspect of the invention, the execution operation mode is set to one of the multiple operation modes which define respective different ranges where a required drive power required to cause the vehicle to run. The multiple operation modes include the predetermined operation mode at which the driver is allowed to select any one of the operation modes included in the predetermined operation mode. When the driver is not allowed to select any one of the operation modes included in the predetermined operation mode, the target air-fuel ratio for the internal combustion engine is set under the first constraint. On the other hand, when the driver is allowed to select any one of the operation modes included in the predetermined operation mode, the target air-fuel ratio is set under the second constraint. Under the second constraint, the target air-fuel ratio is set to a value richer than the target air-fuel ratio set under the first constraint. The internal combustion engine, the electric power / power reception / output device, and the electric motor are controlled so that the air-fuel ratio in the internal combustion engine becomes equal to the set target air-fuel ratio, and the drive power corresponding to the required drive power set according to the set execution operation mode is output. Namely, when the driver is allowed to select any one of the operation modes, it is assumed that fuel-supply cutoff in response to an instruction to decelerate the vehicle will be performed relatively frequently. If no measures are taken in such a case, the NOx purification efficiency may be reduced, because a great amount of air is supplied to the exhaust gas purification catalyst due to fuel-supply cutoff and, therefore, oxygen adheres to the exhaust gas purification catalyst. To avoid such inconvenience, when the driver is allowed to select any one of the operation modes included in the predetermined operation mode, the target air-fuel ratio is set to a value richer than the target air-fuel ratio set when the driver is not allowed to select any one of the operation modes included in the predetermined operation mode. Thus, the amount of oxygen supplied to the purifying device can be reduced before fuel-supply is cut off or when fuel-supply is restarted after fuel-supply is cut off. As a result, even if a relatively great amount of air is supplied to the purifying device when fuel-supply is cut off, reduction in the NOx purification efficiency of the catalyst is suppressed, and, consequently, exhaust gas is purified more effectively.

[0011]The hybrid vehicle according to the first aspect of the invention may further include a catalyst warm-up determination device that determines whether warm-up of the purifying device has been completed. The target air-fuel ratio setting device may set the target air-fuel ratio under the second constraint, when the driver is allowed to select any one of the operation modes included in the predetermined operation mode and it is determined that warm-up of the purifying device has not been completed. Generally, if a great amount of air is supplied to the exhaust gas purification catalyst due to fuel-supply cutoff while the purifying device has not been warmed sufficiently, the NOx purification efficiency of the catalyst may be reduced significantly. Accordingly, when the driver is allowed to select any one of the operation modes and it is determined that warm-up of the purifying device has not been completed, the target air-fuel ratio is set to a richer value. As a result; it is possible to suppress reduction in both fuel efficiency and NOx purification efficiency of the catalyst.

[0016]As in the hybrid vehicle to which the method is applied, when the driver is allowed to select any one of the operation modes included in the predetermined operation modes, it is assumed that fuel-supply cutoff in response to an instruction to decelerate the vehicle will be performed relatively frequently. In such a case, the NOx purification efficiency may be reduced, because a great amount of air is supplied to the exhaust gas purification catalyst due to fuel-supply cutoff and, therefore, oxygen adheres to the exhaust gas purification catalyst. To avoid such inconvenience, when the driver is allowed to select any one of the operation modes included in the predetermined operation mode, the target air-fuel ratio is set to a value richer than the target air-fuel ratio set when the driver is not allowed to select any one of the operation modes included in the predetermined operation mode. Thus, the amount of oxygen supplied to the purifying device can be reduced before fuel-supply is cut off or when fuel-supply is restarted after fuel-supply is cut off. As a result, even if a relatively great amount of air is supplied to the purifying device when fuel-supply is cut off, reduction in the NOx purification efficiency of the catalyst is suppressed, and, consequently, exhaust gas is purified more effectively.

Problems solved by technology

However, when a driver is allowed to select any one of the shift positions (operation modes), fuel-supply may be frequently cut off in response to instructions for deceleration.

If fuel-supply is frequently cut off, a great amount of air is supplied to an exhaust gas purification catalyst, which causes adhesion of oxygen to the catalyst.

As a result, the NOx purification efficiency of the catalyst may be reduced.

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