Vehicle and control method thereof

Abstract

When a vehicle speed V is greater than a threshold value Vref when an engine speed difference ΔN between an engine speed Ne and a target engine speed Ne* is greater than a threshold value Nref and a catalyst degradation flag Fc is 1, that engine speed Ne is brought to the target engine speed Ne* while the engine is kept firing. However, when the vehicle speed V is less than the threshold value Vref, a fuel cut is executed even if the engine speed difference ΔN is greater than the threshold value Nref and the catalyst degradation flag Fc is 1. The threshold value Vref is set based on a catalyst bed temperature CT so control to suppress catalyst degradation can be continued for longer the more the operating state is such that the catalyst bed temperature CT is high and degradation of the catalyst is promoted.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 is a block diagram schematically showing the structure of a hybrid vehicle according to one example embodiment of the invention;

FIG. 2 is a block diagram schematically showing the structure of an engine in the hybrid vehicle shown in FIG. 1;

FIGS. 3A, 3B are flowcharts illustrating one example of a control routine during braking;

FIG. 4 is a view illustrating one example of a map used for setting required braking torque;

FIG. 5 is a view illustrating one example of a map used for setting a threshold;

FIG. 6 is a view of one example of an alignment graph showing the mechanical relationship between torque and rotation speed of rotating elements of a power split device;

FIG. 7 is a view of another example of an alignment graph showing the mechanical relationship between torque and rotation speed of rotating elements of the power split device;

FIG. 8 is a view illustrating another example of a map used for setting a threshold;

FIG. 9 is a view illustrating yet another example of a map used for setting a threshold;

FIG. 10 is a graph showing one example of the relationship between battery temperature Tb and an output limit Wout;

FIG. 11 is a block diagram schematically showing the structure of a hybrid vehicle according to a modified example of the example embodiment; and

FIG. 12 is a block diagram schematically showing the structure of a hybrid vehicle according to another modified example of the example embodiment.

Claims

1. A vehicle comprising: a vehicle speed detecting device that detects a vehicle speed;an automatic shutoff apparatus that shuts off an internal combustion engine when the vehicle speed is in a first low vehicle speed region;an exhaust gas control catalyst that purifies exhaust gas discharged from the internal combustion engine;a fuel injection apparatus that injects fuel into the internal combustion engine; anda control apparatus which, i) when a predetermined catalyst degradation condition is satisfied when a predetermined fuel cut condition is satisfied, executes control to suppress catalyst degradation that keeps the internal combustion engine firing without the fuel injection apparatus cutting off the injection of fuel when the vehicle speed detected by the vehicle speed detecting device is outside of a second low vehicle speed region set based on an operating state of the vehicle, and ii) executes fuel cut control that stops the internal combustion engine from firing by the fuel injection apparatus cutting off the injection of fuel when the vehicle speed detected by the vehicle speed detecting apparatus is in the second low vehicle speed region while the control to suppress catalyst degradation is being executed.

2. The vehicle according to claim 1, wherein a parameter relating to the operating state of the vehicle includes a temperature of the exhaust gas control catalyst.

3. The vehicle according to claim 2, wherein the control apparatus sets the second low vehicle speed region such that an upper limit value thereof decreases the higher the temperature of the exhaust gas control catalyst.

4. The vehicle according to claim 1, further comprising: an electric power/power input/output apparatus which is connected to a driveshaft and an output shaft of the internal combustion engine, and outputs at least some power from the internal combustion engine to the driveshaft with the input/output of power and electric power;an electric motor that selectively inputs and outputs power to and from the driveshaft; anda power storing device that selectively supplies and receives electric power to and from the electric power/power input/output apparatus and the electric motor,wherein a parameter relating to the operating state of the vehicle includes a state of the power storing device.

5. The vehicle according to claim 4, wherein the state of the power storing device is a state-of-charge of the power storing device, and the control apparatus sets the second low vehicle speed region such that an upper limit value thereof decreases the lower the state-of-charge of the power storing device.

6. The vehicle according to claim 4, wherein the state of the power storing device is a temperature of the power storing device, and the control apparatus sets the second low vehicle speed region such that an upper limit value thereof decreases the more limited an electric power supply amount from the power storing device which is set according to the temperature of the power storing device.

7. The vehicle according to claim 4, wherein the electric power/power input/output apparatus includes i) a three-shaft power input/output apparatus which is connected to three shafts, one of which is a rotating shaft, another of which is the driveshaft, and yet another of which is an output shaft of the internal combustion engine, and, based on the power input/output to/from any two shafts of the three shafts, selectively inputs and outputs power to and from the remaining shaft; and ii) an electric motor that selectively inputs and outputs power to and from the rotating shaft.

8. A control method of a vehicle including an internal combustion engine, an exhaust gas control catalyst that purifies exhaust gas discharged from the internal combustion engine, fuel injecting means for injecting fuel into the internal combustion engine, vehicle speed detecting means for detecting a vehicle speed, and automatic shutting off means for shutting off the internal combustion engine when the vehicle speed detected by the vehicle speed detecting means is in a first low vehicle speed region, the control method comprising the steps of:i) when a predetermined catalyst degradation condition is satisfied when a predetermined fuel cut condition is satisfied, executing control to suppress catalyst, degradation that keeps the internal combustion engine firing without cutting off the injection of fuel by the fuel injecting means when the vehicle speed detected by the vehicle speed detecting means is outside of a second low vehicle speed region set based on an operating state of the vehicle; andii) executing fuel cut control that stops the internal combustion engine from firing by cutting off the injection of fuel by the fuel injecting means when the vehicle speed detected by the vehicle speed detecting means is in the second low vehicle speed region while the control to suppress catalyst degradation is being executed.