Power output apparatus, vehicle equipped with power output apparatus, and control method of power output apparatus

#1. Technical Field

#The present invention relates to a power output apparatus that outputs power to a driveshaft, a vehicle equipped with the power output apparatus, and a control method of the power output apparatus.

#2. Description of the Related Art

#FIG. 1 schematically illustrates the configuration of a hybrid vehicle equipped with a power output apparatus in one embodiment of the invention;

#FIG. 2 schematically illustrates the structure of an engine mounted on the hybrid vehicle of the embodiment;

#FIG. 3 is a flowchart showing an air-fuel ratio sensor failure detection routine;

#One mode of carrying out the invention is discussed below as a preferred embodiment. FIG. 1 schematically illustrates the construction of a hybrid vehicle 20 with a power output apparatus mounted thereon in one embodiment of the invention, and FIG. 2 schematically illustrates the structure of an engine mounted on the hybrid vehicle of the embodiment. As illustrated, the hybrid vehicle 20 of the embodiment includes an engine 22, a three shaft-type power distribution integration mechanism 30 that is linked with a crankshaft 26 functioning as an output shaft of the engine 22 via a damper 28, a motor MG1 that is linked with the power distribution integration mechanism 30 and is capable of generating electric power, a reduction gear 35 that is attached to a ring gear shaft 32a functioning as a drive shaft connected with the power distribution integration mechanism 30, another motor MG2 that is linked with the reduction gear 35, and a hybrid electronic control unit 70 that controls the whole power output apparatus.

#The engine 22 is an internal combustion engine that consumes a hydrocarbon fuel, such as gasoline or light oil, to output power. As shown in FIG. 2, the air cleaned by an air cleaner 122 and taken in via a throttle valve 124 is mixed with the atomized fuel injected by a fuel injection valve 126 to the air-fuel mixture. The air-fuel mixture is introduced into a combustion chamber via an intake valve 128. The introduced air-fuel mixture is ignited with spark made by a spark plug 130 to be explosively combusted. The reciprocating motions of a piston 132 by the combustion energy are converted into rotational motions of a crankshaft 26. The exhaust from the engine 22 goes through a catalytic conversion unit 134 (filled with three-way catalyst) to convert toxic components included in the exhaust, that is, carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), into harmless components, and is discharged to the outside air.

#The engine 22 is under control of an engine electronic control unit 24 (hereafter referred to as engine ECU). The engine ECU 24 is constructed as a microprocessor including a CPU 24a, a ROM 24b that stores processing programs, a RAM 24c that temporarily stores data, input and output ports (not shown), and a communication port (not shown). The engine ECU 24 receives, via its input port, diverse signals from various sensors that measure and detect the operating conditions of the engine 22. The signals input into the engine ECU 24 include a crank position from a crank position sensor 140 detected as the rotational position of the crankshaft 26, a cooling water temperature from a water temperature sensor 142 measured as the temperature of cooling water in the engine 22, a cam position from a cam position sensor 144 detected as the rotational position of a camshaft driven to open and close the intake valve 128 and an exhaust valve for gas intake and exhaust into and from the combustion chamber, a throttle valve position from a throttle valve position sensor 146 detected as the opening or position of the throttle valve 124, an air flow meter signal from an air flow meter 148 located in an air intake conduit, an intake air temperature from a temperature sensor 149 located in the air intake conduit, an air-fuel ratio AF from an air-fuel ratio sensor 135a located upstream the catalytic conversion unit 134 in an exhaust conduit, and an oxygen concentration from an oxygen sensor 135b located downstream the catalytic conversion unit 134 in the exhaust conduit. The air-fuel ratio sensor 135a is a known limiting current sensor designed to detect the air-fuel ratio. Although not being specifically illustrated, the air-fuel ratio sensor 135a has two electrodes placed on respective faces of a solid electrolyte. One electrode is exposed to the exhaust, and the other electrode is exposed to the atmospheric air. Under application of a preset voltage between the two electrodes, the amount of oxygen ion shifting through the solid electrolyte is measured as electric current corresponding to the concentration of oxygen reaching the electrode exposed to the exhaust. The air-fuel ratio is computed from the measured electric current. The engine ECU 24 outputs, via its output port, diverse control signals and driving signals to drive and control the engine 22. The signals output from the engine ECU 24 include driving signals to the fuel injection valve 126, driving signals to a throttle valve motor 136 for regulating the position of the throttle valve 124, control signals to an ignition coil 138 integrated with an igniter, and control signals to a variable valve timing mechanism 150 to vary the open and close timings of the intake valve 128. The engine ECU 24 establishes communication with the hybrid electronic control unit 70 to drive and control the engine 22 in response to control signals received from the hybrid electronic control unit 70 and to output data regarding the operating conditions of the engine 22 to the hybrid electronic control unit 70 according to the requirements.