Exhaust purification device for internal combustion engine

Claim 2

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst; a first air-fuel ratio sensor installed in said first exhaust passage; and a second air-fuel ratio sensor installed in said second exhaust passage, wherein said first air-fuel ratio controller computes a first feedback correction coefficient based on the output of said first air-fuel ratio sensor, corrects a fuel amount supplied to said first cylinder group using this first feedback correction coefficient, and thereby feedback controls the air-fuel ratio of exhaust led to said first front three-way catalyst, and wherein said second air-fuel ratio controller computes a second feedback correction coefficient based on the output of said second air-fuel ratio sensor, corrects a fuel amount supplied to said second cylinder group using this second feedback correction coefficient, and thereby feedback controls the air-fuel ratio of exhaust led to said second front three-way catalyst, wherein said first and second sensors are so designed that their outputs vary sharply around the stoichiometric air-fuel ratio relative to variation of the air-fuel ratio of the exhaust gas, wherein said first air-fuel ratio controller computes a first feedback correction coefficient by subtracting a first lean shift proportional part when the output of said first air-fuel ratio sensor changes from lean to rich, and adding a first rich shift proportional part when it changes from rich to lean, wherein said second air-fuel ratio controller computes a second feedback correction coefficient by subtracting a second lean shift proportional part when the output of said second air-fuel ratio sensor changes from lean to rich, and adding a second rich shift proportional part when it changes from rich to lean, and wherein said microprocessor is further programmed to set a control midpoint value of the air-fuel ratio of exhaust gas controlled by said first and second air-fuel ratio controllers, to a predetermined air-fuel ratio by setting said first lean shift proportional part, said rich shift proportional part, said second lean shift proportional part and said second rich shift proportional part respectively to predetermined values.

Claim 3

An exhaust purification device for an internal combustion engine as defined in claim 1 , further comprising a rear air-fuel ratio sensor installed in said exhaust passage, and a rear air-fuel ratio controller for correcting the setting of the air-fuel ratio by said microprocessor based on the output of said rear air-fuel ratio sensor, and controlling the air-fuel ratio of the exhaust led to said rear three-way catalyst to a predetermined air-fuel ratio.

Claim 4

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear thruway catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst; a first air-fuel ratio sensor installed in said first exhaust passage; and a second air-fuel ratio sensor installed in said second exhaust passage, wherein said first air-fuel ratio controller computes a first feedback correction coefficient based on the output of said first air-fuel ratio sensor, corrects a fuel amount supplied to said first cylinder group using this first feedback correction coefficient, and thereby feedback controls the air-fuel ratio of exhaust led to said first front three-way catalyst, and wherein said second air-fuel ratio controller computes a second feedback correction coefficient based on the output of said second air-fuel ratio sensor, corrects a fuel amount supplied to said second cylinder group using this second feedback correction coefficient, and thereby feedback controls the air-fuel ratio of exhaust led to said second front three-way catalyst, wherein said first and second sensors are so designed that their outputs vary sharply around the stoichiometric air-fuel ratio relative to variation of the air-fuel ratio of the exhaust gas, wherein said first air-fuel ratio controller computes a first feedback correction coefficient by subtracting a first lean shift proportional part after a first lean shift delay time from when the output of said first air-fuel ratio sensor changes from lean to rich, and adding a first rich shift proportional part after a first rich shift delay time from when it changes from rich to lean, wherein said second air-fuel ratio controller computes a second feedback correction coefficient by likewise subtracting a second lean shift proportional part after a second lean shift delay time from when the output of said second air-fuel ratio sensor changes from lean to rich, and adding a second rich shift proportional part after a second rich shift delay time from when it changes from rich to lean, and wherein said microprocessor is further programmed to set a control midpoint of the air-fuel ratio of the exhaust gas controlled by said first and second air-fuel ratio controllers, to a predetermined air-fuel ratio by setting said first lean shift delay time, said first rich shift delay time, said second lean shift delay time and said second rich shift delay time respectively to predetermined values.

Claim 5

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear thruway catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst; a first air-fuel ratio sensor installed in said first exhaust passage; and a second air-fuel ratio sensor installed in said second exhaust passage, wherein said first air-fuel ratio controller computes a first feedback correction coefficient based on the output of said first air-fuel ratio sensor, corrects a fuel amount supplied to said first cylinder group using this first feedback correction coefficient, and thereby feedback controls the air-fuel ratio of exhaust led to said first front three-way catalyst, and wherein said second air-fuel ratio controller computes a second feedback correction coefficient based on the output of said second air-fuel ratio sensor, corrects a fuel amount supplied to said second cylinder group using this second feedback correction coefficient, and thereby feedback controls the air-fuel ratio of exhaust led to said second front three-way catalyst, wherein said first and second sensors are so designed that their outputs vary sharply around the stoichiometric air-fuel ratio relative to variation of the air-fuel ratio of the exhaust gas, wherein said first air-fuel ratio controller computes a first feedback correction coefficient by subtracting a first lean shift proportional part after a first lean shift delay time from when the output of said first air-fuel ratio sensor changes from lean to rich, and adding a first rich shift proportional part after a first rich shift delay time from when it changes from rich to lean, wherein said second air-fuel ratio controller computes a second feedback correction coefficient by likewise subtracting a second lean shift proportional part after a second lean shift delay time from when the output of said second air-fuel ratio sensor changes from lean to rich, and adding a second rich shift proportional part after a second rich shift delay time from when it changes from rich to lean, and wherein said microprocessor is further programmed to set a control midpoint of the air-fuel ratio of the exhaust gas controlled by said first and second air-fuel ratio controllers, to a predetermined air-fuel ratio by setting said first lean shift delay time, said first rich shift delay time, said second lean shift delay time and said second rich shift delay time respectively to predetermined values.

Claim 6

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; and a microprocessor programmed to: determine the conditions under which the temperature of the rear thruway catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, wherein said microprocessor is further programmed to alternate between a first setting mode wherein the air-fuel ratio of the exhaust controlled by said first air-fuel ratio controller is set leaner than the stoichiometric air-fuel ratio and the air-fuel ratio of the exhaust controlled by said second air-fuel ratio controller is set richer than the stoichiometric air-fuel ratio, and a second setting mode wherein the air-fuel ratio of the exhaust controlled by said first air-fuel ratio controller is set richer than the stoichiometric air-fuel ratio and the air-fuel ratio of the exhaust controlled by said second air-fuel ratio controller is set leaner than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of the rear three-way catalyst, and wherein said microprocessor is further programmed to alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time.

Claim 7

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; and a microprocessor programmed to: determine the conditions under which the temperature of the rear thruway catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, wherein said microprocessor is further programmed to alternate between a first setting mode wherein the air-fuel ratio of the exhaust controlled by said first air-fuel ratio controller is set leaner than the stoichiometric air-fuel ratio and the air-fuel ratio of the exhaust controlled by said second air-fuel ratio controller is set richer than the stoichiometric air-fuel ratio, and a second setting mode wherein the air-fuel ratio of the exhaust controlled by said first air-fuel ratio controller is set richer than the stoichiometric air-fuel ratio and the air-fuel ratio of the exhaust controlled by said second air-fuel ratio controller is set leaner than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of the rear three-way catalyst, and wherein said microprocessor is further programmed to alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time.

Claim 8

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a startup detecting sensor for detecting startup of said internal combustion engine, wherein said microprocessor is further programmed to determine that the conditions hold for discharging SOx which has been absorbed and deposited on said rear three-way catalyst when startup of said engine is detected.

Claim 9

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a startup detecting sensor for detecting startup of said internal combustion engine, wherein said microprocessor is further programmed to determine that the conditions hold for discharging SOx which has been absorbed and deposited on said rear three-way catalyst when startup of said engine is detected.

Claim 10

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; and a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and estimate an SOx amount which has been absorbed and deposited on said rear three-way catalyst, and determine conditions for discharging SOx deposited on said rear three-way catalyst based on said estimated SOx deposit amount.

Claim 11

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; and a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and estimate an SOx amount which has been absorbed and deposited on said rear three-way catalyst, and determine conditions for discharging SOx deposited on said rear three-way catalyst based on said estimated SOx deposit amount.

Claim 12

An exhaust purification device for an internal combustion engine as defined in claim 6 , wherein said microprocessor is further programmed to determine that the conditions hold for discharging SOx deposited on said rear three-way catalyst when said estimated SOx deposition amount is equal to or greater than a first predetermined amount, and determine that SOx discharge conditions no longer hold when said estimated SOx deposition amount has fallen to or below a second predetermined amount less than said first predetermined amount.

Claim 13

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and an NOx concentration sensor for detecting the NOx concentration of the exhaust flowing from said rear three-way catalyst, and wherein said microprocessor is further programmed to estimate an NOx amount absorbed on said rear three-way catalyst, and determine that conditions hold for discharging the SOx deposited on said rear three-way catalyst based on said detected NOx concentration and said estimated NOx absorption amount.

Claim 14

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and an NOx concentration sensor for detecting the NOx concentration of the exhaust flowing from said rear three-way catalyst, and wherein said microprocessor is further programmed to estimate an NOx amount absorbed on said rear three-way catalyst, and determine that conditions hold for discharging the SOx deposited on said rear three-way catalyst based on said detected NOx concentration and said estimated NOx absorption amount.

Claim 15

An exhaust purification device for an internal combustion engine as defined in claim 8 , wherein said microprocessor is further programmed to determine that the conditions hold for discharging deposited SOx when the NOx concentration, detected at a time when the NOx amount absorbed on said rear three-way catalyst is equal to or greater than a predetermined amount, is greater than a predetermined permitted value.

Claim 16

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a running condition detecting sensor for detecting running conditions, wherein said microprocessor is further programmed to determine that the conditions do not hold for increasing the temperature of said rear three-way catalyst when the detected running conditions are outside a predetermined SOx discharge running region, regardless of whether or not the conditions hold for discharging SOx deposited on said rear three-way catalyst.

Claim 17

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a running condition detecting sensor for detecting running conditions, wherein said microprocessor is further programmed to determine that the conditions do not hold for increasing the temperature of said rear three-way catalyst when the detected running conditions are outside a predetermined SOx discharge running region, regardless of whether or not the conditions hold for discharging SOx deposited on said rear three-way catalyst.

Claim 18

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a temperature measuring sensor for detecting a temperature of said rear three-way catalyst, wherein said microprocessor is further programmed to determine that the conditions do not hold for increasing the temperature of said rear three-way catalyst when the temperature of said three-way catalyst exceeds a permitted temperature even when the temperature of said rear three-way catalyst is equal to or greater than a predetermined SOx discharge temperature, regardless of whether or not the conditions hold for discharging SOx deposited on said rear three-way catalyst.

Claim 19

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a temperature measuring sensor for detecting a temperature of said rear three-way catalyst, wherein said microprocessor is further programmed to determine that the conditions do not hold for increasing the temperature of said rear three-way catalyst when the temperature of said three-way catalyst exceeds a permitted temperature even when the temperature of said rear three-way catalyst is equal to or greater than a predetermined SOx discharge temperature, regardless of whether or not the conditions hold for discharging SOx deposited on said rear three-way catalyst.

Claim 20

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a temperature measuring sensor for detecting a temperature of said rear three-way catalyst, wherein said microprocessor is further programmed to set the air-fuel ratios of the exhaust controlled by said first and second air-fuel ratio controllers such that the air-fuel ratio of the exhaust led to said rear three-way catalyst is richer than the stoichiometric air-fuel ratio when the conditions hold for discharging SOx deposited on said rear three-way catalyst, and the temperature of said rear three-way catalyst is equal to or greater than an SOx discharge temperature, and wherein said microprocessor is further programmed to set the degree of richness of the air-fuel ratio to be greater the larger the SOx amount deposited on said rear three-way catalyst.

Claim 21

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a temperature measuring sensor for detecting a temperature of said rear three-way catalyst, wherein said microprocessor is further programmed to set the air-fuel ratios of the exhaust controlled by said first and second air-fuel ratio controllers such that the air-fuel ratio of the exhaust led to said rear three-way catalyst is richer than the stoichiometric air-fuel ratio when the conditions hold for discharging SOx deposited on said rear three-way catalyst, and the temperature of said rear three-way catalyst is equal to or greater than an SOx discharge temperature, and wherein said microprocessor is further programmed to set the degree of richness of the air-fuel ratio to be greater the larger the SOx amount deposited on said rear three-way catalyst.

Claim 22

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a temperature measuring sensor for detecting a temperature of said rear three-way catalyst, wherein said microprocessor is further programmed to set the air-fuel ratios of the exhaust controlled by said first and second air-fuel ratio controllers such that the air-fuel ratio of the exhaust led to said rear three-way catalyst is richer than the stoichiometric air-fuel ratio when the conditions hold for discharging SOx deposited on said rear three-way catalyst, and the temperature of said rear three-way catalyst is equal to or greater than an SOx discharge temperature, and wherein said microprocessor is further programmed to set the degree of richness of the air-fuel ratio to be smaller the longer the elapsed time from when air-fuel ratio rich shift control starts.

Claim 23

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, alternate between said first setting mode and said second setting mode whenever a running time in one of these setting modes reaches a predetermined time, and determine conditions under which Sox deposited on said rear three-way catalyst should be discharged, and determine that the conditions hold for increasing the temperature of said rear three-way catalyst when the conditions hold for discharging Sox which has been absorbed and deposited on said rear three-way catalyst, and a temperature measuring sensor for detecting a temperature of said rear three-way catalyst, wherein said microprocessor is further programmed to set the air-fuel ratios of the exhaust controlled by said first and second air-fuel ratio controllers such that the air-fuel ratio of the exhaust led to said rear three-way catalyst is richer than the stoichiometric air-fuel ratio when the conditions hold for discharging SOx deposited on said rear three-way catalyst, and the temperature of said rear three-way catalyst is equal to or greater than an SOx discharge temperature, and wherein said microprocessor is further programmed to set the degree of richness of the air-fuel ratio to be smaller the longer the elapsed time from when air-fuel ratio rich shift control starts.

Claim 24

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, and an exhaust valve opening timing control device for applying an advance correction to an opening timing of an exhaust valve which is preset according to running conditions when the conditions hold for increasing the temperature of said rear three-way catalyst.

Claim 25

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, and an exhaust valve opening timing control device for applying an advance correction to an opening timing of an exhaust valve which is preset according to running conditions when the conditions hold for increasing the temperature of said rear three-way catalyst.

Claim 26

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, and an exhaust gas recirculation control device for applying a reduction correction to an exhaust gas recirculation amount which is preset according to running conditions when the conditions hold for increasing the temperature of said rear three-way catalyst.

Claim 27

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, and an exhaust gas recirculation control device for applying a reduction correction to an exhaust gas recirculation amount which is preset according to running conditions when the conditions hold for increasing the temperature of said rear three-way catalyst.

Claim 28

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, and an ignition timing control device for applying a delay correction to an ignition timing which is preset according to running conditions when the conditions hold for increasing the temperature of said rear three-way catalyst.

Claim 29

An exhaust purification device for an internal combustion engine comprising: a first front three-way catalyst installed in a first exhaust passage connected to a first cylinder group; a second front three-way catalyst installed in a second exhaust passage connected to a second cylinder group; a rear three-way catalyst installed in an exhaust gas passage which combines the exhaust of said first and second exhaust passages; a first air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said first front three-way catalyst to a predetermined air-fuel ratio; a second air-fuel ratio controller for controlling the air-fuel ratio of the exhaust led to said second front three-way catalyst to a predetermined air-fuel ratio; a microprocessor programmed to: determine the conditions under which the temperature of the rear three-way catalyst should be increased, and set the air-fuel ratio of the exhaust controlled by one of said air-fuel ratio controllers to a richer air-fuel ratio than the stoichiometric air-fuel ratio, and set the air-fuel ratio of the exhaust controlled by the other of said air-fuel ratio controllers to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, when the conditions hold for increasing the temperature of said rear three-way catalyst, and an ignition timing control device for applying a delay correction to an ignition timing which is preset according to running conditions when the conditions hold for increasing the temperature of said rear three-way catalyst.